JP4338114B2 - Polystyrene resin foam / polyolefin resin multilayer - Google Patents

Description

前記一般式（１）において、Ｒは水素原子またはメチル基を示し、Ｚはハロゲン原子またはメチル基を示し、ｐは０または１〜３の整数である。
前記ポリスチレン系樹脂としては、ポリスチレン、ゴム変性ポリスチレン、スチレン−アクリロニトリル共重合体、スチレン−ブタジエン−アクリロニトリル共重合体、スチレン−アクリル酸共重合体、スチレン−メタクリル酸共重合体、スチレン−メタクリル酸メチル共重合体、スチレン−メタクリル酸エチル共重合体、スチレン−アクリル酸メチル共重合体、スチレン−アクリル酸エチル共重合体、スチレン−無水マレイン酸共重合体、ポリスチレン−ポリフェニレンエーテル共重合体、ポリスチレンとポリフェニレンエーテルとの混合物などが例示される。これらの樹脂に脆性改善等を目的としてスチレン共役ジエンブロック共重合体やその水添物等のエラストマー、エチレン−プロピレン−ジエン共重合体等の弾性成分、リサイクル樹脂の混合等を考慮してポリプロピレン系樹脂や高密度ポリエチレン等のポリオレフィン系樹脂を３０重量％以下の割合で混合したものも使用することができる。なお、ビカット軟化点が１１０℃以上のポリスチレン系樹脂を使用することにより、本発明多層シートの耐熱性を向上させることができる。
【０００９】
次に、本発明の多層シートの層構成について詳述する。
本発明の多層シートは、ポリスチレン系樹脂発泡体層を有する。この発泡体層において、その密度は０．０２〜０．７ｇ／ｃｍ³、好ましくは０．０３〜０．５ｇ／ｃｍ³であり、特に熱成形用のものは０．０４〜０．５ｇ／ｃｍ³のものが好ましい。また、その厚みは０．３〜７ｍｍ、好ましくは０．５〜５ｍｍであり、特に熱成形用のものは０．５〜４ｍｍである。この発泡体層の連続気泡率（ＡＳＴＭ Ｄ２８５６、手順Ｃ）は４０％以下、好ましくは３０％以下、更に好ましくは２０％以下である。その密度が前記範囲より小さくなると、その多層シートを熱成形して得られる成形体の強度が不足するばかりでなく、加熱真空成形するときに伸び不足を生じて成形体に透孔を生じることがある。一方、その密度が前記範囲よりも大きくなると、経済的に不利になる他、低温耐衝撃性が低下するという問題があり、さらに、成形体の断熱性が悪くなるため、容器等の成形体に熱湯を入れたときに、その容器を手で持つことができなくなる。また、前記発泡体層の厚みが余りにも薄くなると、真空成形等により得られる成形体の壁厚が不十分となり、強度や断熱性の点で劣ったものとなり、低温耐衝撃性が低下する。一方、その厚みが大きくなりすぎると、加熱真空成形の際に、シートの内部と外部の加熱ムラが起りやすく、精密な温度制御が必要となる。発泡体層の連続気泡率は熱成形時の二次発泡性や得られる成形体の品質（強度や低温衝撃性等の物性）に影響を与えるので、前記の通りに規定するのがよい。
本明細書において、多層シートの厚みは多層シートの押出方向に対し、垂直な幅方向の断面厚みを顕微鏡により等間隔で１０点撮影する。次いで撮影した写真より多層シートの厚みを測定しその平均値を採用する。
本明細書において、発泡体層の密度は下記に示す方法で行う。予め前記した多層シートの厚みと坪量を測定し、顕微鏡により多層シートの押出方向に対し、垂直な幅方向の多層シートの断面を等間隔で１０点撮影し、撮影した写真より測定された樹脂層の厚みと接着層の厚みの平均値を算出する。前記各層の厚みを多層シートの厚みから引いた値を発泡体層の厚みとした。次いで樹脂層の厚みと接着層の厚みに各層を構成している樹脂密度をかけ単位換算して樹脂層及び接着層の坪量を算出する。前記の最外層と接着層の坪量を多層シートの坪量から引いた値を発泡体層の坪量とする。この発泡体層の坪量を前記した発泡体層の厚みで割った値を単位換算し発泡体層の密度として採用する。
【００１０】
接着層としては、変性ポリオレフィン樹脂、変性エチレン−酢酸ビニル共重合樹脂等の接着性樹脂が用いられ、その他、リサイクル性、コスト面で好ましいポリオレフィン系樹脂とポリスチレン系樹脂との混合物、更に該混合物に相溶化させるため添加剤を添加したものも採用することができる。前記接着層は、ポリスチレン系樹脂８５〜４０重量％、好ましくは８０〜４５重量％、更に好ましくは７５〜５０重量％と、ポリオレフィン系樹脂１５〜６０重量％、好ましくは２０〜５５重量％、更に好ましくは２５〜５０重量％との混合樹脂からなる。但し、ポリスチレン系樹脂とポリオレフィン系樹脂との合計が１００重量％とする。なお、接着層に使用されるポリオレフィン系樹脂としては、接着層の上面に積層されるポリオレフィン系樹脂層に用いられるポリオレフィン系樹脂と同一の樹脂、もしくは熱融着可能な同種のポリオレフィン系樹脂が好ましく用いられる。この接着層において、そのポリスチレン系樹脂の含有率が前記範囲より高くなると、その接着層と発泡体層との間の接着強度は満足するものの、その接着層とポリオレフィン系樹脂層との間の接着強度が不十分になる。一方、そのポリスチレン系樹脂の含有率が前記範囲より低くなると、逆に、その接着層とポリオレフィン系樹脂層との間の接着強度は満足するものの、その発泡体層と接着層との間の接着強度が不十分となる。さらに熱成形する際、多層シートに破れや透孔が発生し、成形性が悪くなる。接着層において、その厚みは０．０１５〜０．２ｍｍ、好ましくは０．０２〜０．１５ｍｍであり、その発泡体層の厚みに対する割合は、３〜５０％、好ましくは５〜４０％である。接着層の厚みが前記範囲よりも小さくなると、接着性が不十分となり、一方、前記範囲を超えると、発泡体層の連続気泡率が高くなる傾向にあり、また、コストアップの原因となる。
【００１１】
本発明の多層シートは、その接着層の上面に形成されたポリオレフィン系樹脂層を有する。このポリオレフィン系樹脂層において、その厚みは０．０１〜０．５ｍｍが好ましく、さらに、熱成形用として０．０１５〜０．４ｍｍが好ましい。特に０．０１５〜０．３ｍｍが好ましい。その発泡体層の厚みに対する割合は３〜５０％、好ましくは５〜４０％である。このポリオレフィン系樹脂層の厚みが前記範囲よりも小さくなると、低温耐衝撃性が低下する。また、熱成形時に多層シートに透孔や破れを生じるので好ましくない。一方、余りにも厚くなりすぎると、コストアップになるばかりか、そのポリオレフィン系樹脂層の加熱成形時間と発泡体層の加熱成形時間との差が開きすぎて、そのポリオレフィン系樹脂層に最適な加熱時間で多層シートを成形すると、その発泡体層が溶融したりする。
【００１２】
本発明の多層シートにおいて、その発泡体層の両面に前記接着層を介してポリオレフィン系樹脂層を積層させることができるが、必ずしもその両面に接着層を介してポリオレフィン系樹脂層を積層させる必要はなく、その発泡体層の一方の片面は、未積層面とすることができ、また、ポリスチレン系樹脂層や接着層等の樹脂層を積層することができる。そのポリスチレン系樹脂層や接着層において、その厚みは０．０１５〜０．３５ｍｍ、好ましくは０．０２〜０．２５ｍｍであり、その発泡体層の厚みに対する割合は３〜５０％、好ましくは５〜４０％である。その発泡体層の片面にポリスチレン系樹脂層が積層されているものは、そのポリスチレン系樹脂層が印刷性、光沢性にすぐれているので、熱成形された成形体の外側の印刷面とすることができる。一方、その発泡体層の片面に接着層として接着層が積層されているものは、その接着層が印刷適性にすぐれ、また光沢性にもすぐれているので、熱成形された成形体の外側の印刷面として有利に用いることができると共に、共押出法により発泡体層の両面に形成する２つの接着層を同じ押出機を使用して同時に積層することができる為、生産性において優れる。
【００１３】
本発明の多層シートにおいて、その接着層としての接着層には、相溶化させるために相溶化成分を添加することができる。この場合の相溶化成分としては、ポリスチレン系樹脂とポリオレフィン系樹脂とを相溶化し得るものであればよく、従来公知の各種のものを用いることができる。このようなものとしては、特にスチレン系熱可塑性エラストマーの使用が好ましい。このスチレン系熱可塑性エラストマーには、ＳＥＢＳ系やＳＥＰＳ系のものや、ＳＢＳ系又はＳｌＳ系のもの等が包含される。ＳＢＳ系又はＳＩＳ系のものは、ハードセグメントとしてポリスチレンの結晶相を有し、ソフトセグメントとしてポリブタジエン又はポリイソプレンがブロック的に共重合された構造を有する。一方、ＳＥＢＳ系やＳＥＰＳ系のものは、前記ＳＢＳ系やＳＩＳ系のものに含まれているポリブタジエン、ポリイソプレンを高度に水素化してその主鎖中の二重結合を飽和させたものである。これらのＳＥＢＳ系や、ＳＥＰＳ系、ＳＢＳ系及びＳＩＳ系等のスチレン系熱可塑性エラストマーについては、「プラスチックエージ」、第１０１頁〜第１０６頁（Ｊｕｎｅ １９８５）に詳述されている。
【００１４】
相溶化成分は、接着層中の接着１００重量部当たり、０．１〜３０重量部、好ましくは０．５〜１０重量部の割合で添加するのが好ましい。特に、スチレン系熱可塑性エラストマーの場合には、２〜１０重量部添加するのが好ましい。この相溶化成分の添加により、発泡体層とポリオレフィン系樹脂層との接着性、多層シートの衝撃強度や脆性がさらに改善される。
本発明の多層シートにおいて、その接着層及び発泡体層には、脆性改善を目的に弾性成分を添加することができる。弾性成分としては、スチレン、α−メチルスチレン、ｐ−メチルスチレン等のスチレン成分とブタジエンやイソプロピレン系ジエン成分からなるランダム共重合体、ブロック共重合体、グラフト共重合体又はこれらの共重合体同士の混合物、或いはこれらの共重合体とこれらの共重合体以外のポリスチレン系樹脂との混合物が挙げられる。
前記弾性成分は、接着層の混合樹脂１００重量部あたり２〜５０重量部、好ましくは、５〜３０重量部添加することが好ましい。
一方、発泡体層への弾性成分は、基材樹脂１００重量部あたり０．５〜３０重量部、好ましくは、１〜２０重量部添加することが好ましい。
よって、スチレン系熱可塑性エラストマーは特定量を樹脂組成物に添加することにより、相溶化成分及び弾性成分として作用させることができるため特に好ましい。
【００１５】
本発明の多層シートにおいて、その発泡体層とポリオレフィン系樹脂層との間の接着強度は、接着層として接着層を用いた場合１００ｇｆ／２５ｍｍ以上、特に好ましくは３００ｇｆ／２５ｍｍ以上、更には５００ｇｆ／２５ｍｍ以上という大きな接着強度を有する。その接着強度の上限値は、通常、２５００ｇｆ／２５ｍｍ程度である。
接着強度が１００ｇｆ／２５ｍｍより小さい場合、多層シートを熱成形した際に発泡体とポリオレフィン系樹脂層が剥離したり、多層シートの低温耐衝撃性が低下する虞がある。
【００１６】
本発明の多層シートは、従来公知の方法で製造することができる。その代表的な方法としては、予め発泡体層を製造し、その後製造ライン上または別ラインでポリオレフィン系樹脂層と接着層を別な押出機より供給して接着する方法、発泡体層を製造し、製造ライン上または別ラインでポリオレフィン系樹脂層としてポリオレフィン系樹脂フィルムを導入し、接着層を別な押出機より供給して接着する方法、多層共押出法によって発泡体層の少なくとも片面に接着層及びポリオレフィン系樹脂層を設けて押出製造する方法等がある。
なかでも多層共押出法によって得られる多層シートは、他の方法に比べて工程がシンプルで低コスト化が可能であり、また発泡体層と接着層、接着層とポリオレフィン系樹脂層との接着強度が高くなるので好ましい。
また、特に片面にハイインパクトポリスチレン（ＨＩＰＳ）等のポリスチレン系樹脂を積層した本発明多層シートを製造する方法としては、前記共押出法等にてポリスチレン系樹脂発泡体層の片面に接着層を介してポリオレフィン系樹脂を積層した多層シートを得て、次にＴダイスを使用してハイインパクトポリスチレン溶融物を該発泡体層のポリオレフィン系樹脂層が積層されていない面側に押出ラミネート法により積層する方法等が採用される。
接着層として用いるポリスチレン系樹脂、ポリオレフィン系樹脂および相溶化成分はペレット状でドライブレンドした後、そのまま押出機の投入口に入れても良く、また予め溶融混練して用いても良い。
【００１７】
ポリスチレン系樹脂発泡体層を製造する場合に用いる発泡剤としては、プロパン、ｎ−ブタン、ｉ−ブタン、ｎ−ブタンとｉ−ブタンとの混合物、ペンタン、ヘキサン等の脂肪族炭化水素、シクロブタン、シクロペンタン等の環式脂肪族炭化水素、トリクロロフロロメタン、ジクロロジフロロメタン、１，１−ジフルオロエタン、１，１−ジフルオロ−１−クロロエタン、１，１，１，２−テトラフルオロエタン、メチルクロライド、エチルクロライド、メチレンクロライド等のハロゲン化炭化水素およびこれらの混合物等が挙げられる。
更に、発泡剤としては、分解型発泡剤を用いることができるが、その具体例としては、アゾジカルボンアミド、ジニトロソペンタメチレンテトラミン、アゾビスイソブチロニトリル、重炭酸ナトリウム等が挙げられる。また、二酸化炭素等の無機ガスや水も挙げられる。これらの発泡剤は適宜混合して用いることができる。
このなかでもハロゲン化水素を含まないオゾン層の破壊等環境への影響の少ないものを使用することが好ましい。
発泡剤の使用量は、特に限定されないが、おおむね樹脂１００ｇあたり０．０１〜０．１モルで目標のシート密度に対し自由に選択することができる。
【００１８】
本発明の多層シートに用いられるポリスチレン系樹脂およびポリオレフィン系樹脂には、本発明の目的を著しく損なわない範囲で、必要に応じて各種の添加剤、例えば、造核剤、酸化防止剤、熱安定剤、帯電防止剤、導電性付与剤、耐候剤、紫外線吸収剤、着色剤、難燃剤、無機充填剤等を添加することができる。
【００１９】
本発明の多層シートは、雄型及び／又は雌型からなる金型を使用して熱成形することができる。熱成形する方法としては、例えば、真空成形、圧空成形や、これらの応用としてフリードローイング成形、プラグ・アンド・リッジ成形、リッジ成形、マッチド・モールド成形、ストレート成形、ドレープ成形、リバースドロー成形、エアスリップ成形、プラグアシスト成形、プラグアシストリバースドロー成形等やこれらを組み合わせた成形方法等が挙げられる。前記のような成形方法を用いて所望の容器等の成形体に成形することができる。また、このように成形体を得る熱成形方法は、短時間に連続して成形体を得ることができるため好ましい。
【００２０】
本発明の多層シートは、浅い形状の成形体から深絞り形状の成形体まで成形できる。具体的に例えば、トレイ、弁当箱、カップ、丼等が挙げられる。
【００２１】
【実施例】
次に本発明を実施例によりさらに詳細に説明する。
【００２２】
実施例１〜５、比較例１〜２
表１に示す構成の多層シートを作製した。また、表２には、この多層シートにおける発泡体層の密度（ｇ／ｃｍ³）、発泡体層の連続気泡率（％）、多層シート厚み（ｍｍ）についても示した。さらに表２には、その多層シートの耐油性、多層シートを熱成形して得られた成形体の耐熱性及び低温耐衝撃性についても示した。
【００２３】
表２に示した多層シートにおいて、ポリオレフィン系樹脂層（Ｚ１）はその表面層を示し、ポリオレフィン系樹脂層（Ｚ２）は裏面層を示した。
【００２４】
多層シートの製法の具体的内容は以下の通りである。
実施例１〜４、比較例１〜２
発泡体層用の押出機として直径６５ｍｍと直径９０ｍｍの２台の押出機を、ポリオレフィン系樹脂層用の押出機としては直径５０ｍｍの押出機を、接着層用としては直径４０ｍｍの押出機を用い、口金（ダイス）としては、直径８４ｍｍ、厚み０．５ｍｍの円筒状細隙を有するものを用いた。
発泡体層は直径６５ｍｍの押出機で原料投入口より所定の量の樹脂および樹脂１００重量部あたりタルク１重量部と表１で示したように樹脂１００重量部あたりの添加剤の量を必要に応じて添加して加熱混練し、約２００℃に調整された樹脂混合物に対して表２に示す発泡剤を表２に示すポリスチレン系樹脂１００重量部あたりの量で圧入し、次いで、直径９０ｍｍの押出機に供給した。一方、ポリオレフィン系樹脂層は直径５０ｍｍの押出機より、接着層は直径４０ｍｍの押出機よりそれぞれポリスチレン系樹脂発泡体層形成用溶融物の片面又は両面に必要に応じて供給し、ダイス内部で発泡体層形成用溶融物と合流させ共押出した。なお、接着層には必要に応じて添加剤を、表１に示したようにポリスチレン系樹脂とポリオレフィン系樹脂との混合樹脂１００重量部あたりの量で添加した。
【００２５】
実施例５
片面に接着層を介してポリオレフィン系樹脂層を形成し、もう一方の面は、接着層のみとした他は実施例１と同様に共押出を行った。
前記実施例１〜５、比較例１〜２にて押出された円筒状積層発泡体を、冷却された円筒に沿わせて引取り、切り開くことにより、多層シートとなし、これを巻き取った。
【００２６】
表１の発泡体層（Ｘ）に関して符号で示したＰＳ樹脂（ポリスチレン系樹脂）の具体的内容は後記に示すものを用いた。また、ＰＳ樹脂に配合したタルクは松村産業（株）製ハイフィラー＃１２を用いた。
【００２７】
表１のＰＯ樹脂（Ｚ）に関して符号で示したＰＯ樹脂の具体的内容は後記において示すものを用いた。
【００２８】
表２に多層シートを構成する発泡体層（Ｘ）、接着層（Ｙ）及びポリオレフィン系樹脂層（Ｚ）の具体的内容について示した。
表２で示した発泡剤の、ブタンはｎ−ブタン７０ｗｔ％とｉｓｏ−ブタン３０ｗｔ％からなるブタン混合物を示した。
表２の接着層（Ｙ１、Ｙ２）に関してＰＯ樹脂（ポリオレフィン系樹脂）及び表１の添加剤の具体的内容は、後記に示すものを用いた。
なお、接着層（Ｙ１）と接着層（Ｙ２）の成分組成は同じものを用いた。
なお、表２のＰＯ層（Ｚ１）とＰＯ層（Ｚ２）の成分組成は同じものを用いた。
【００２９】
前記多層シートに関して表２の耐油性、多層シートを熱成形して得られた成形体の耐熱性及び低温耐衝撃性の評価法は以下の通りで行なった。
（耐油性）
２５ｍｍ×４０ｍｍの多層シートのポリオレフィン系樹脂層側を上にしてその中央に米炊飯調味油（フレッシュロールホワイト、（株）ローリング製）を０．０２５ｍｌ滴下し均一に延ばした後、８０℃で５分間加熱し前後の変化を調べた。
○・・・・変化なし
×・・・シート表面に侵食有り
（耐熱性）
実施例及び比較例で得られた多層シートを単発成形機（三和興業株式会社製のＰＬＡＶＡＣ−ＦＥ３６ＨＰ型）にて開口部形状が直径１５０ｍｍの円形、深さ７０ｍｍの容器（絞り比０．４７）成形用金型を取り付けて真空成形を行った。この容器に水を５００ｍ１入れ、電子レンジ（５００ｗ）にて１０分間加熱を行い、加熱前後の容器の変化を調べた。
○・・・・１０分間加熱しても容器の変化なし
△・・・・５分間加熱しても容器の変形なし
×・・・・５分未満で容器の変化あり
（低温耐衝撃性）
実施例及び比較例で得られた多層シートを単発成形機（三和興業株式会社製のＰＬＡＶＡＣ−ＦＥ３６ＨＰ型〉にて開口部形状が縦１５０ｍｍ、横１２０ｍｍ、深さ３０ｍｍの容器（絞り比０．１９）成形用金型を取り付けて真空成形を行った。この容器に内容物として１５０ｇの米飯を入れ、開口部を蓋材にてシールする。その後−２５℃に２時間保持した後、室温（温度２３℃、湿度５５％）に取り出して２秒以内に高さ１００ｃｍからステンレス盤上に落下させた。この時の容器の破損状況を調べた。
○・・・・変化なしまたは容器にへこみが入るがわれは発生せず。
×・・・・容器に穴が開くまたは容器内側に亀裂が入る。
（接着強度）
表２におけるポリスチレン系樹脂発泡体層（Ｘ）とポリオレフィン系樹脂層（Ｚ）との間の接着強度は多層シートより押出方向に平行な短冊状で幅２５ｍｍの試験片を切り出し、ＪＩＳ Ｚ０２３７に準拠し、剥離速度３００ｍｍ／ｍｉｎの条件にて９０°剥離試験にて測定して求めた値（ｇｆ／２５ｍｍ）を接着強度（ｇｆ／２５ｍｍ）とした。尚、本明細書において接着強度は上記の通り測定すればよいが、幅２５ｍｍの試験片が切り出せない場合は、できるだけ広幅の試験片を切り出し切り出した試験片について上記測定を行ない得られた値（ｇｆ）に（２５／試験片の幅（ｍｍ））を掛け算して接着強度（ｇｆ／２５ｍｍ）とする。
【００３０】
表１において符号で示した樹脂の具体的内容を下記に示した。
（１）樹脂Ａ
出光石油化学（株）製、「３１０Ｅ」（高密度ポリエチレン（ＨＤＰＥ）、溶融粘度ポイズ１６５００、密度０．９６５ｇ／ｃｍ³）
（２）樹脂Ｂ
出光石油化学（株）製、「５２０ＭＢ」（ＨＤＰＥ、溶融粘度ポイズ１９０００、密度０．９６４ｇ／ｃｍ³）
（３）樹脂Ｃ
三井化学（株）製、「５０００Ｓ」 （ＨＤＰＥ、溶融粘度ポイズ２１０００、密度０．９５４ｇ／ｃｍ³）
（４）樹脂Ｄ
日本ポリオレフイン（株）製、「Ａ８２０ＦＳ」（直鎖状低密度ポリエチレン（ＬＬＤＰＥ）、溶融粘度ポイズ１６５０００、密度０．９２９ｇ／ｃｍ³）
（５）樹脂Ｅ
出光石油化学（株）製、「２１０ＪＺ」 （ＨＤＰＥ、溶融粘度８２００ポイズ、密度０．９６８ｇ／ｃｍ³）
（６）樹脂Ｆ
出光石油化学（株）製、「ＭＫ２１１」（プロピレン−エチレンブロック共重合体、溶融粘度８０００ポイズ、密度０．９ｇ／ｃｍ³）
（７）樹脂Ｈ
旭化成工業（株）製、「タフプレン１２５」（スチレンブタジエンスチレンエラストマー、溶融粘度１２１００ポイズ、密度０．９５ｇ／ｃｍ³）
（８）樹脂Ｉ
エー・アンド・エム スチレン（株）、「Ｇ９００１」（スチレン−メタクリル酸共重合体、溶融粘度２６８００ポイズ、密度１．１ｇ／ｃｍ³）
（９）樹脂Ｊ
出光石油化学（株）製、「ＨＨ３２」（ポリスチレン、汎用ポリスチレン（ＧＰＰＳ）、溶融粘度２０４００ポイズ、密度１．０５ｇ／ｃｍ³）
【００３１】
前記樹脂に関して示したその溶融粘度は下記のようにして測定した。
（樹脂の溶融粘度）
剪断速度１００ｓｅｃ^-1の条件下の溶融粘度は、ノズル内径（Ｄ）が１．０ｍｍ、Ｌ／Ｄ＝１０（Ｌはノズル長（ｍｍ））のノズルを用い樹脂温度１９０℃の条件にてチアスト社製レオビス２１００で測定した。
【００３２】
【表１】

【００３３】
【表２】

【００３４】
【発明の効果】
ポリスチレン系樹脂発泡体層（Ｘ）の少なくとも片面に、接着層（Ｙ）を介して−２０℃でのアイゾット衝撃値が１０ＫＪ／ｍ²以上、かつ、ビカット軟化点が１００℃以上のポリオレフィン系樹脂またはポリオレフィン系樹脂組成物からなるポリオレフィン系樹脂層（Ｚ）が積層された多層体であって、該多層体の低温での落錘衝撃試験による５０％破壊エネルギーが０．３Ｊ以上であることを特徴とするポリスチレン系樹脂発泡体／ポリオレフィン系樹脂多層体であることから、低温輸送中の衝撃による割れや冷凍雰囲気中から室温雰囲気中へ取出す際、落としても割れない等の低温耐衝撃性を有し、かつ、電子レンジでの加熱に耐えうる耐熱性や耐油性を有する多層体である。
さらにポリスチレン系樹脂発泡体層（Ｘ）の基材がビカット軟化点１１０℃以上のポリスチレン系樹脂からなることを特徴とするポリスチレン系樹脂発泡体／ポリオレフィン系樹脂多層体であることから、電子レンジの加熱の際、長時間の加熱であっても発泡体層の熱変形がない優れた耐熱性を有する多層体である。[0001]
BACKGROUND OF THE INVENTION
The present invention is a sheet-like or plate-like polystyrene resin foam excellent in low-temperature impact resistance, which is preferably used as a food packaging container material mainly processed into trays, cups, lunch boxes, bowls, etc. Body / polyolefin resin multilayer body (hereinafter also simply referred to as multilayer sheet).
[0002]
[Prior art]
Conventionally, an expanded polystyrene sheet is thermoformed and widely used in various containers such as trays, lunch boxes, bowls, and cups. In particular, with the widespread use of microwave ovens, the demand for frozen food containers is increasing. However, the expanded polystyrene sheet is inferior in heat resistance and oil resistance, and also inferior in low-temperature impact resistance, and it has been difficult to use as a frozen food container.
Therefore, for the purpose of improving the drawbacks of the heat resistance and oil resistance of the expanded polystyrene sheet, a multilayer sheet in which a resin film of polyethylene, polypropylene, polyester or the like is bonded to one side or both sides of the expanded polystyrene sheet has been studied.
In Japanese Utility Model Publication No. 59-17628, a molten mixture of polystyrene resin 40 to 60% by weight and polyolefin resin 60 to 40% by weight is used as an adhesive, and a polyolefin resin film is applied to one or both sides of a polystyrene foam sheet. A multi-layer sheet formed by bonding has been proposed, but no investigation has been made on low-temperature impact resistance.
In addition, Japanese Utility Model Publication No. 7-8409 describes a foamed polystyrene tray that does not crack or have holes due to impact during transportation, and the technology disclosed therein is a foamed polystyrene in which linear low density polyethylene and a gas barrier film are laminated. This is a styrofoam tray formed by molding a sheet so that the depth is 10 mm to 25 mm, and the corners of the bottom and side walls are 15 mm to 50 mm.
This multi-layer sheet is useful for expanded polystyrene trays having a rounded part with a specific depth and specific range, but when a container with a complex shape or a deep-drawn shape is molded, a thin part or tear occurs in the container. It was something to do. Furthermore, no consideration has been given to low temperature impact resistance.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to provide a polystyrene resin foam / polyolefin resin multilayer body having a low temperature impact resistance higher than that of a conventional polystyrene resin foam multilayer body and having excellent heat resistance and oil resistance. .
[0004]
[Means for Solving the Problems]
As a result of various studies to solve the above problems, the present inventors have found that the Izod impact value at −20 ° C. is 10 KJ / m as the polyolefin resin layer in the polystyrene resin foam / polyolefin resin multilayer body. ² Use of the above polyolefin resin or polyolefin resin composition, and the 50% fracture energy by the drop weight impact test at a low temperature of the multilayer body is 0.3 J or more. It is found that a polystyrene resin foam / polyolefin resin multilayer body having low temperature impact resistance, such as no cracking even when dropped from a frozen atmosphere to a room temperature atmosphere, is obtained. Found that a polystyrene resin foam / polyolefin resin multilayer body having heat resistance capable of withstanding heating in a microwave oven can be obtained by using a resin having a Vicat softening point of 100 ° C. or higher. Polystyrene resin foam in resin foam / polyolefin resin multilayer By using a polystyrene resin having a Vicat softening point of 110 ° C. or higher as a base material, a polystyrene resin foam / polyolefin resin multilayer body having heat resistance that can be directly cooked in a microwave oven from a frozen state can be obtained. I found it.
That is, according to the present invention, the Izod impact value at −20 ° C. is 10 KJ / m on at least one surface of the polystyrene resin foam layer (X) via the adhesive layer (Y). ² A multilayer body in which a polyolefin resin layer (Z) made of a polyolefin resin or a polyolefin resin composition having a Vicat softening point of 100 ° C. or higher is laminated, and falling weight impact of the multilayer body at a low temperature A polystyrene-based resin foam / polyolefin-based resin multilayer body having a 50% fracture energy by test of 0.3 J or more is provided.
Moreover, according to the present invention, in the polystyrene resin foam / polyolefin resin multilayer body, the polystyrene resin base material of the polystyrene resin foam layer (X) is made of a polystyrene resin having a Vicat softening point of 110 ° C. or higher. A resin foam / polyolefin-based resin multilayer body is provided.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
The polyolefin resin or polyolefin resin composition constituting the polyolefin resin layer (hereinafter also simply referred to as resin layer) used in the present invention includes an olefin homopolymer, an olefin copolymer (random copolymer, A block copolymer, etc.), a copolymer of an olefin containing 50% by weight or more of an olefin unit component with another monomer (random copolymer, block copolymer, etc.), the homopolymer and the copolymer A mixture of two or more selected mixtures, at least one of the homopolymer and the copolymer, and a thermoplastic resin or a thermoplastic elastomer different from them, and the ratio of the olefin unit component in the mixture is 50 50% by weight or more of the above-mentioned homopolymer, the above-mentioned copolymer, or the above mixture, an antioxidant, a lubricant, External absorber, flame retardant, antistatic agent, and mixtures of more than 50 wt% resin additives such as fillers and the like. In the present invention, in particular, from the viewpoint of impact resistance at low temperatures, the polyolefin resin or polyolefin resin composition constituting the resin layer used in the present invention has an Izod impact value at −20 ° C. of 10 KJ / m. ² From the viewpoint of heat resistance, the Vicat softening point is 100 ° C. or higher, and preferably 112 ° C. or higher. The upper limit of the softening point is not particularly limited, but is about 160 ° C. From the above points, among the polyolefin resins, polyethylene resins satisfying the Izod impact value and the Vicat softening point are preferable, and the use of high-density polyethylene or linear low-density polyethylene is particularly preferable. The Izod impact value at −20 ° C. is 10 KJ / m. ² If it is less than 1, sufficient impact resistance at low temperature of the multilayer sheet cannot be obtained.
In the present specification, the Izod impact value at −20 ° C. of the base resin is determined by sufficiently drying the polyolefin resin or polyolefin resin composition constituting the resin layer (water content is 0.1 wt. %), Then temperature 230 ° C., pressure 490 N / cm ² After being heated and compressed by sandwiching between steel plates for 10 minutes under the above conditions, immediately moved between 30 ° C. cooling presses in a state of being sandwiched between steel plates and sufficiently cooled, a resin plate having a thickness of 2.5 mm was produced. A No. 1 A test piece (provided that the width of the test piece is 2.5 mm) specified in JIS K 7110-1984 is prepared from the resin plate, and measured according to JIS K 7110-1984 using the test piece. Value. The details of the test conditions are as follows.
Test machine: No. manufactured by Toyo Seiki Seisakusho Co., Ltd. 612 Izod Impact Tester (machine number 121903304).
Hammer weight: 784 g.
Distance from the rotation axis center line of the hammer to the center of gravity ... 6.85 cm.
Distance from the rotation axis center line of the hammer to the edge of the impact blade: 30.7 cm.
Capacity: 1J.
Hammer lifting angle: 150 °.
Hammer impact speed: 3.35 m / sec.
Direction of impact: Edgewise impact.
Condition adjustment of the test piece, etc .: The test piece is left for 24 hours at a temperature of −20 ° C., taken out in a room with an air temperature of 23 ° C. and a relative humidity of 50%, and the time taken to give an impact to the test piece is 3.5. Set to ± 0.5 seconds.
Number of specimens ... 5. As the Izod impact value in the present invention, an arithmetic average value based on the measured values of these five test pieces is adopted.
When the test piece is not broken under the above measurement conditions, the Izod impact value is at least 31 kJ / m in the present invention. ² Is considered.
Moreover, in this specification, the Vicat softening point of resin refers to the value calculated | required by JlS K7206 (a test load is A method and the temperature increase rate of a heat-transfer medium is 50 degreeC / hour conditions).
[0006]
The multilayer sheet of the present invention is a multilayer sheet in which the polyolefin resin layers described above are laminated, and the 50% fracture energy in a drop weight impact test at a low temperature is 0.3 J or more. Further, 0.7J or more is preferable from the viewpoint of improving low temperature impact resistance. When the 50% fracture energy is less than 0.3 J, the multilayer sheet has low-temperature impact resistance such as cracking due to impact during low-temperature transport and cracking when dropped from a frozen atmosphere to a room temperature atmosphere.
In order to obtain a multilayer sheet having a 50% fracture energy of 0.3 J or more, the Izod impact value at −20 ° C. is 10 KJ / m. ² Employing a polyolefin resin layer made of the above polyolefin resin or polyolefin resin composition, the thickness of a polyolefin resin layer described later, the thickness of a polystyrene resin foam layer (hereinafter also simply referred to as a foam layer). It can be obtained by adjusting the density of the foam layer, the adhesive strength between the resin layer and the foam layer, and the open cell ratio of the foam layer.
In this specification, the 50% fracture energy in the drop weight impact test at a low temperature of the multilayer sheet is a low temperature of a rectangular multilayer sheet having a size of 150 m in length and 120 mm in width, which is frozen in a low temperature bath of −40 ° C. for 6 hours. The temperature is stored in a chamber at a temperature of 23 ° C. and a humidity of 55%, and the chamber is placed in a constant humidity chamber. A drop weight impact test is performed on 20 test pieces per sample from the polyolefin resin layer side, and the calculation method according to JIS K7211 Ask for. At this time, each test piece is taken out from the low-temperature bath and then measured within 2 seconds. The testing machine is No. manufactured by Toyo Seiki Seisakusho. A 621 falling weight impact tester is used, and the weight used is a spherical weight having a diameter of 36.5 mm and a mass of 198.5 g.
[0007]
In the polystyrene resin used in the present invention, the melt viscosity is 190 ° C. shear rate 100 sec. ^-1 The melt viscosity under the above conditions is 200 poise or more and less than 100,000 poise, preferably 1000 to 50000 poise. If the melt viscosity is smaller than the above range, the molten resin extruded from the die during foam molding may sag, making molding difficult. On the other hand, when the above range is exceeded, the viscosity is too high, the extrusion pressure rises and extrusion molding becomes difficult, and a high-quality polystyrene resin foam layer may not be molded.
[0008]
The polystyrene resin used in the present invention includes styrene homopolymers and copolymers, and the styrene monomer units contained in the polymer are at least 25 wt% or more, preferably 50 wt% or more. A preferred polystyrene-based resin used in the present invention is a resin containing at least 25% by weight of a structural unit represented by the following general formula (1) in the resin.
[Chemical 1]

In the general formula (1), R represents a hydrogen atom or a methyl group, Z represents a halogen atom or a methyl group, and p is 0 or an integer of 1 to 3.
Examples of the polystyrene resin include polystyrene, rubber-modified polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, and styrene-methyl methacrylate. Copolymer, styrene-ethyl methacrylate copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-maleic anhydride copolymer, polystyrene-polyphenylene ether copolymer, polystyrene and Examples thereof include a mixture with polyphenylene ether. For the purpose of improving brittleness etc. for these resins, polypropylene based on styrene conjugated diene block copolymers and elastomers such as hydrogenated products thereof, elastic components such as ethylene-propylene-diene copolymers, mixing of recycled resins, etc. What mixed polyolefin resin, such as resin and high density polyethylene, in the ratio of 30 weight% or less can also be used. In addition, the heat resistance of this invention multilayer sheet can be improved by using the polystyrene-type resin whose Vicat softening point is 110 degreeC or more.
[0009]
Next, the layer structure of the multilayer sheet of the present invention will be described in detail.
The multilayer sheet of the present invention has a polystyrene resin foam layer. In this foam layer, the density is 0.02 to 0.7 g / cm. ^Three , Preferably 0.03 to 0.5 g / cm ^Three In particular, those for thermoforming are 0.04 to 0.5 g / cm. ^Three Are preferred. Moreover, the thickness is 0.3-7 mm, Preferably it is 0.5-5 mm, and especially the thing for thermoforming is 0.5-4 mm. The foam layer has an open cell rate (ASTM D2856, Procedure C) of 40% or less, preferably 30% or less, and more preferably 20% or less. When the density is smaller than the above range, not only the strength of the molded body obtained by thermoforming the multilayer sheet is insufficient, but also the molded body may be insufficiently stretched to form through holes in the molded body. is there. On the other hand, when the density is larger than the above range, there is a problem that the low-temperature impact resistance is lowered in addition to being economically disadvantageous, and furthermore, the heat insulating property of the molded body is deteriorated. When hot water is added, the container cannot be held by hand. On the other hand, if the thickness of the foam layer is too thin, the wall thickness of the molded body obtained by vacuum molding or the like becomes insufficient, resulting in inferior strength and heat insulation, and low temperature impact resistance is lowered. On the other hand, if the thickness is too large, uneven heating inside and outside the sheet is likely to occur during vacuum heating and precise temperature control is required. Since the open cell ratio of the foam layer affects the secondary foamability during thermoforming and the quality of the resulting molded body (physical properties such as strength and low-temperature impact properties), it is preferably specified as described above.
In this specification, the thickness of the multilayer sheet is taken at 10 points at equal intervals with a microscope in the cross-sectional thickness in the width direction perpendicular to the extrusion direction of the multilayer sheet. Next, the thickness of the multilayer sheet is measured from the photograph taken and the average value is adopted.
In this specification, the density of a foam layer is performed by the method shown below. The thickness and basis weight of the multilayer sheet described above were measured in advance, and the cross section of the multilayer sheet in the width direction perpendicular to the extrusion direction of the multilayer sheet was photographed at equal intervals with a microscope, and the resin measured from the photographed photograph The average value of the thickness of the layer and the thickness of the adhesive layer is calculated. The value obtained by subtracting the thickness of each layer from the thickness of the multilayer sheet was taken as the thickness of the foam layer. Next, the basis weight of the resin layer and the adhesive layer is calculated by multiplying the thickness of the resin layer and the thickness of the adhesive layer by the resin density constituting each layer and converting the unit. A value obtained by subtracting the basis weight of the outermost layer and the adhesive layer from the basis weight of the multilayer sheet is defined as the basis weight of the foam layer. A value obtained by dividing the basis weight of the foam layer by the thickness of the foam layer is converted into a unit and adopted as the density of the foam layer.
[0010]
As the adhesive layer, an adhesive resin such as a modified polyolefin resin or a modified ethylene-vinyl acetate copolymer resin is used. In addition, a mixture of a polyolefin resin and a polystyrene resin that are preferable in terms of recyclability and cost, and further to the mixture What added the additive in order to make it compatible can also be employ | adopted. The adhesive layer has a polystyrene resin of 85 to 40% by weight, preferably 80 to 45% by weight, more preferably 75 to 50% by weight, and a polyolefin resin of 15 to 60% by weight, preferably 20 to 55% by weight. Preferably it consists of a mixed resin of 25 to 50% by weight. However, the total of the polystyrene resin and the polyolefin resin is 100% by weight. The polyolefin resin used for the adhesive layer is preferably the same resin as the polyolefin resin used for the polyolefin resin layer laminated on the upper surface of the adhesive layer, or the same kind of polyolefin resin that can be heat-sealed. Used. In this adhesive layer, if the content of the polystyrene resin is higher than the above range, the adhesive strength between the adhesive layer and the foam layer is satisfied, but the adhesion between the adhesive layer and the polyolefin resin layer is satisfied. Insufficient strength. On the other hand, when the content of the polystyrene resin is lower than the above range, on the contrary, the adhesion strength between the adhesive layer and the polyolefin resin layer is satisfied, but the adhesion between the foam layer and the adhesive layer is satisfied. Insufficient strength. Further, when thermoforming, the multilayer sheet is torn and through holes are formed, resulting in poor moldability. In the adhesive layer, the thickness is 0.015 to 0.2 mm, preferably 0.02 to 0.15 mm, and the ratio to the thickness of the foam layer is 3 to 50%, preferably 5 to 40%. . When the thickness of the adhesive layer is smaller than the above range, the adhesiveness is insufficient. On the other hand, when the thickness exceeds the above range, the open cell ratio of the foam layer tends to be high, and the cost is increased.
[0011]
The multilayer sheet of the present invention has a polyolefin resin layer formed on the upper surface of the adhesive layer. In this polyolefin resin layer, the thickness is preferably 0.01 to 0.5 mm, and more preferably 0.015 to 0.4 mm for thermoforming. In particular, 0.015 to 0.3 mm is preferable. The ratio with respect to the thickness of the foam layer is 3 to 50%, preferably 5 to 40%. When the thickness of the polyolefin resin layer is smaller than the above range, the low temperature impact resistance is lowered. Moreover, since a through-hole and a tear are produced in a multilayer sheet at the time of thermoforming, it is not preferable. On the other hand, if the thickness is too thick, not only will the cost increase, but the difference between the heat molding time of the polyolefin resin layer and the heat molding time of the foam layer will be too wide, so that the optimum heating for the polyolefin resin layer will occur. When a multilayer sheet is formed over time, the foam layer is melted.
[0012]
In the multilayer sheet of the present invention, a polyolefin resin layer can be laminated on both surfaces of the foam layer via the adhesive layer, but it is not always necessary to laminate a polyolefin resin layer on both surfaces via the adhesive layer. Instead, one surface of the foam layer can be a non-laminated surface, and a resin layer such as a polystyrene-based resin layer or an adhesive layer can be laminated. In the polystyrene resin layer or adhesive layer, the thickness is 0.015 to 0.35 mm, preferably 0.02 to 0.25 mm, and the ratio to the thickness of the foam layer is 3 to 50%, preferably 5 ~ 40%. When the polystyrene resin layer is laminated on one side of the foam layer, the polystyrene resin layer is excellent in printability and glossiness. Can do. On the other hand, when the adhesive layer is laminated on one side of the foam layer, the adhesive layer is excellent in printability and glossiness. Since it can be advantageously used as a printing surface and two adhesive layers formed on both surfaces of the foam layer by a co-extrusion method can be simultaneously laminated using the same extruder, it is excellent in productivity.
[0013]
In the multilayer sheet of the present invention, a compatibilizing component can be added to the adhesive layer as the adhesive layer for compatibilization. As the compatibilizing component in this case, any compatibilizing component may be used as long as it can compatibilize a polystyrene resin and a polyolefin resin, and various conventionally known components can be used. As such, it is particularly preferable to use a styrene-based thermoplastic elastomer. Examples of the styrene thermoplastic elastomer include SEBS type, SEPS type, SBS type, and SlS type. The SBS-based or SIS-based one has a polystyrene crystal phase as a hard segment, and has a structure in which polybutadiene or polyisoprene is block-copolymerized as a soft segment. On the other hand, in the SEBS and SEPS series, polybutadiene and polyisoprene contained in the SBS and SIS series are highly hydrogenated to saturate double bonds in the main chain. These SEBS type, SEPS type, SBS type, SIS type and other styrenic thermoplastic elastomers are described in detail in “Plastic Age”, pages 101 to 106 (June 1985).
[0014]
The compatibilizing component is preferably added at a ratio of 0.1 to 30 parts by weight, preferably 0.5 to 10 parts by weight per 100 parts by weight of the adhesive in the adhesive layer. In particular, in the case of a styrene thermoplastic elastomer, it is preferable to add 2 to 10 parts by weight. By adding this compatibilizing component, the adhesiveness between the foam layer and the polyolefin resin layer, and the impact strength and brittleness of the multilayer sheet are further improved.
In the multilayer sheet of the present invention, an elastic component can be added to the adhesive layer and the foam layer for the purpose of improving brittleness. As an elastic component, a random copolymer, a block copolymer, a graft copolymer or a copolymer thereof composed of a styrene component such as styrene, α-methylstyrene, and p-methylstyrene and a butadiene or isopropylene-based diene component And a mixture of these copolymers and a polystyrene resin other than these copolymers.
The elastic component is added in an amount of 2 to 50 parts by weight, preferably 5 to 30 parts by weight per 100 parts by weight of the mixed resin of the adhesive layer.
On the other hand, the elastic component to the foam layer is added in an amount of 0.5 to 30 parts by weight, preferably 1 to 20 parts by weight per 100 parts by weight of the base resin.
Therefore, a styrene-based thermoplastic elastomer is particularly preferable because it can act as a compatibilizing component and an elastic component by adding a specific amount to the resin composition.
[0015]
In the multilayer sheet of the present invention, the adhesive strength between the foam layer and the polyolefin resin layer is 100 gf / 25 mm or more, particularly preferably 300 gf / 25 mm or more, more preferably 500 gf / when the adhesive layer is used as the adhesive layer. It has a large adhesive strength of 25 mm or more. The upper limit of the adhesive strength is usually about 2500 gf / 25 mm.
If the adhesive strength is less than 100 gf / 25 mm, the foam and the polyolefin resin layer may be peeled off when the multilayer sheet is thermoformed, or the low temperature impact resistance of the multilayer sheet may be reduced.
[0016]
The multilayer sheet of the present invention can be produced by a conventionally known method. As a typical method, a foam layer is manufactured in advance, and then a polyolefin resin layer and an adhesive layer are supplied from another extruder on a production line or in a separate line and bonded to each other, and a foam layer is manufactured. A method in which a polyolefin resin film is introduced as a polyolefin resin layer on a production line or in a separate line, and an adhesive layer is supplied from another extruder and bonded, or an adhesive layer on at least one surface of a foam layer by a multilayer coextrusion method And a method of extrusion production by providing a polyolefin resin layer.
In particular, the multilayer sheet obtained by the multilayer coextrusion method is simpler and less costly than other methods, and the adhesive strength between the foam layer and the adhesive layer, and between the adhesive layer and the polyolefin resin layer. Is preferable because of high.
Further, as a method for producing the multilayer sheet of the present invention in which a polystyrene resin such as high impact polystyrene (HIPS) is laminated on one side, an adhesive layer is provided on one side of the polystyrene resin foam layer by the coextrusion method or the like. To obtain a multilayer sheet laminated with a polyolefin resin, and then, using a T-die, a high impact polystyrene melt is laminated on the side of the foam layer on which the polyolefin resin layer is not laminated by extrusion lamination. A method or the like is adopted.
The polystyrene resin, polyolefin resin and compatibilizing component used as the adhesive layer may be dry blended in the form of pellets and then directly put into the inlet of the extruder or may be melt kneaded in advance.
[0017]
Examples of the foaming agent used in producing the polystyrene resin foam layer include propane, n-butane, i-butane, a mixture of n-butane and i-butane, aliphatic hydrocarbons such as pentane and hexane, cyclobutane, Cycloaliphatic hydrocarbons such as cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, 1,1-difluoroethane, 1,1-difluoro-1-chloroethane, 1,1,1,2-tetrafluoroethane, methyl chloride Halogenated hydrocarbons such as ethyl chloride and methylene chloride, and mixtures thereof.
Furthermore, a decomposable foaming agent can be used as the foaming agent, and specific examples thereof include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate, and the like. Moreover, inorganic gas and water, such as a carbon dioxide, are also mentioned. These foaming agents can be appropriately mixed and used.
Among these, it is preferable to use a material that has little influence on the environment, such as destruction of an ozone layer that does not contain hydrogen halide.
Although the usage-amount of a foaming agent is not specifically limited, It can be freely selected with respect to a target sheet density in about 0.01-0.1 mol per 100 g of resin.
[0018]
The polystyrene resin and polyolefin resin used in the multilayer sheet of the present invention have various additives as required, for example, nucleating agents, antioxidants, thermal stability, as long as the object of the present invention is not significantly impaired. An agent, an antistatic agent, a conductivity imparting agent, a weathering agent, an ultraviolet absorber, a colorant, a flame retardant, an inorganic filler, and the like can be added.
[0019]
The multilayer sheet of the present invention can be thermoformed using a mold comprising a male mold and / or a female mold. Examples of thermoforming methods include vacuum forming, pressure forming, free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, air Examples thereof include slip molding, plug assist molding, plug assist reverse draw molding, and a molding method combining these. It can shape | mold into molded objects, such as a desired container, using the above shaping | molding methods. Further, the thermoforming method for obtaining a molded body in this way is preferable because the molded body can be obtained continuously in a short time.
[0020]
The multilayer sheet of the present invention can be molded from a shallow shaped article to a deep drawn shaped article. Specific examples include a tray, a lunch box, a cup, and a bowl.
[0021]
【Example】
Next, the present invention will be described in more detail with reference to examples.
[0022]
Examples 1-5, Comparative Examples 1-2
A multilayer sheet having the structure shown in Table 1 was produced. Table 2 also shows the density (g / cm) of the foam layer in this multilayer sheet. ^Three ), The open cell ratio (%) of the foam layer, and the multilayer sheet thickness (mm). Further, Table 2 also shows the oil resistance of the multilayer sheet, the heat resistance and the low temperature impact resistance of a molded product obtained by thermoforming the multilayer sheet.
[0023]
In the multilayer sheet shown in Table 2, the polyolefin resin layer (Z1) showed the surface layer, and the polyolefin resin layer (Z2) showed the back layer.
[0024]
The specific contents of the method for producing the multilayer sheet are as follows.
Examples 1-4, Comparative Examples 1-2
Two extruders with a diameter of 65 mm and a diameter of 90 mm are used as the foam layer extruder, a 50 mm diameter extruder is used as the polyolefin resin layer extruder, and a 40 mm diameter extruder is used as the adhesive layer. As the die, a die having a cylindrical slit having a diameter of 84 mm and a thickness of 0.5 mm was used.
The foam layer is an extruder with a diameter of 65 mm and requires a predetermined amount of resin and 1 part by weight of talc per 100 parts by weight of resin and the amount of additive per 100 parts by weight of resin as shown in Table 1. The foaming agent shown in Table 2 was press-fitted into the resin mixture adjusted to about 200 ° C. in an amount per 100 parts by weight of the polystyrene-based resin shown in Table 2, and then 90 mm in diameter. Feeded to the extruder. On the other hand, the polyolefin resin layer is supplied to one or both sides of the melt for forming the polystyrene resin foam layer from an extruder having a diameter of 50 mm, and the adhesive layer is supplied from an extruder having a diameter of 40 mm, respectively, and foamed inside the die. The melt for body layer formation was merged and coextruded. In addition, as shown in Table 1, an additive was added to the adhesive layer as necessary in an amount per 100 parts by weight of a mixed resin of a polystyrene resin and a polyolefin resin.
[0025]
Example 5
Coextruding was carried out in the same manner as in Example 1 except that a polyolefin resin layer was formed on one side through an adhesive layer and the other side was only the adhesive layer.
The cylindrical laminated foams extruded in Examples 1 to 5 and Comparative Examples 1 and 2 were taken along a cooled cylinder and cut to form a multilayer sheet, which was wound up.
[0026]
The specific contents of the PS resin (polystyrene resin) indicated by reference numerals for the foam layer (X) in Table 1 were those shown below. Moreover, Matsumura Sangyo Co., Ltd. high filler # 12 was used for the talc mix | blended with PS resin.
[0027]
The specific contents of the PO resin indicated by reference numerals with respect to the PO resin (Z) in Table 1 were those shown below.
[0028]
Table 2 shows specific contents of the foam layer (X), the adhesive layer (Y) and the polyolefin resin layer (Z) constituting the multilayer sheet.
Of the blowing agent shown in Table 2, butane was a butane mixture consisting of 70% by weight of n-butane and 30% by weight of iso-butane.
Regarding the adhesive layers (Y1, Y2) in Table 2, the specific contents of the PO resin (polyolefin resin) and the additives in Table 1 were those described below.
The same component composition was used for the adhesive layer (Y1) and the adhesive layer (Y2).
In addition, the same composition was used for the PO layer (Z1) and the PO layer (Z2) in Table 2.
[0029]
With respect to the multilayer sheet, the oil resistance shown in Table 2 and the evaluation methods of the heat resistance and low temperature impact resistance of the molded product obtained by thermoforming the multilayer sheet were as follows.
(Oil resistance)
A 25 mm × 40 mm multilayer sheet with the polyolefin resin layer side up, 0.025 ml of rice cooking seasoning oil (Fresh Roll White, manufactured by Rolling Co., Ltd.) dropped in the center and uniformly spread, then at 80 ° C. 5 It was heated for minutes and examined before and after.
○ ・ ・ ・ ・ No change
× ・ ・ ・ Erosion on the sheet surface
(Heat-resistant)
The multilayer sheets obtained in the examples and comparative examples were subjected to a single-stage molding machine (PLAVAC-FE36HP type manufactured by Sanwa Kogyo Co., Ltd.) with a circular opening having a diameter of 150 mm and a depth of 70 mm (drawing ratio 0.47). ) Vacuum molding was performed with a molding die attached. 500 ml of water was put into this container, and it heated for 10 minutes with the microwave oven (500w), and investigated the change of the container before and behind a heating.
○ ··· No change in container even after heating for 10 minutes
△ ・ ・ ・ ・ No deformation of container even after heating for 5 minutes
× ··· Change in container in less than 5 minutes
(Low temperature impact resistance)
The multilayer sheets obtained in the examples and comparative examples were subjected to a single molding machine (PLAVAC-FE36HP type manufactured by Sanwa Kogyo Co., Ltd.) with an opening of 150 mm in length, 120 mm in width, and 30 mm in depth (drawing ratio 0. 19) Vacuum molding was performed with a molding die attached, 150 g of cooked rice was put into the container, the opening was sealed with a lid, and then kept at −25 ° C. for 2 hours. The temperature was 23 ° C. and the humidity was 55%, and the sample was dropped from a height of 100 cm onto a stainless steel board within 2 seconds.
○ ・ ・ ・ ・ No change or dents in the container.
× ···· A hole is formed in the container or a crack is formed inside the container.
(Adhesive strength)
The adhesive strength between the polystyrene-based resin foam layer (X) and the polyolefin-based resin layer (Z) in Table 2 is a strip shape parallel to the extrusion direction cut out from the multilayer sheet and has a width of 25 mm, and conforms to JIS Z0237. Then, the value (gf / 25 mm) obtained by measurement in a 90 ° peel test under the condition of a peel rate of 300 mm / min was defined as the adhesive strength (gf / 25 mm). In this specification, the adhesive strength may be measured as described above. However, when a test piece having a width of 25 mm cannot be cut out, a value obtained by performing the above measurement on a test piece cut out as wide as possible ( gf) is multiplied by (25 / width of test piece (mm)) to obtain adhesive strength (gf / 25 mm).
[0030]
The specific contents of the resins indicated by symbols in Table 1 are shown below.
(1) Resin A
“310E” (high density polyethylene (HDPE), melt viscosity poise 16500, density 0.965 g / cm, manufactured by Idemitsu Petrochemical Co., Ltd.) ^Three )
(2) Resin B
"520MB" (HDPE, melt viscosity poise 19000, density 0.964 g / cm, manufactured by Idemitsu Petrochemical Co., Ltd. ^Three )
(3) Resin C
“5000S” (HDPE, melt viscosity poise 21000, density 0.954 g / cm, manufactured by Mitsui Chemicals, Inc. ^Three )
(4) Resin D
“A820FS” (linear low density polyethylene (LLDPE), melt viscosity poise 165000, density 0.929 g / cm, manufactured by Nippon Polyolefin Co., Ltd. ^Three )
(5) Resin E
“210JZ” (HDPE, melt viscosity 8200 poise, density 0.968 g / cm, manufactured by Idemitsu Petrochemical Co., Ltd. ^Three )
(6) Resin F
“MK211” (propylene-ethylene block copolymer, melt viscosity 8000 poise, density 0.9 g / cm, manufactured by Idemitsu Petrochemical Co., Ltd. ^Three )
(7) Resin H
“Tufprene 125” (styrene butadiene styrene elastomer, melt viscosity 12100 poise, density 0.95 g / cm, manufactured by Asahi Chemical Industry Co., Ltd. ^Three )
(8) Resin I
A & M Styrene Co., Ltd., "G9001" (styrene-methacrylic acid copolymer, melt viscosity 26800 poise, density 1.1 g / cm ^Three )
(9) Resin J
“HH32” (polystyrene, general-purpose polystyrene (GPPS), melt viscosity 20400 poise, density 1.05 g / cm, manufactured by Idemitsu Petrochemical Co., Ltd. ^Three )
[0031]
The melt viscosity indicated for the resin was measured as follows.
(Melt viscosity of resin)
Shear rate 100sec ^-1 The melt viscosity under the conditions of No. 1 was 1.0 mm and L / D = 10 (L is the nozzle length (mm)), and the resin temperature was 190 ° C. It was measured.
[0032]
[Table 1]

[0033]
[Table 2]

[0034]
【The invention's effect】
An Izod impact value at −20 ° C. of 10 KJ / m is applied to at least one surface of the polystyrene resin foam layer (X) via the adhesive layer (Y). ² A multilayer body in which a polyolefin resin layer (Z) made of a polyolefin resin or a polyolefin resin composition having a Vicat softening point of 100 ° C. or higher is laminated, and falling weight impact of the multilayer body at a low temperature Since it is a polystyrene resin foam / polyolefin resin multilayer body having a 50% fracture energy of 0.3 J or more by a test, it is cracked by impact during low-temperature transport or from a frozen atmosphere to a room temperature atmosphere When taking out, it is a multilayer body having low temperature impact resistance such as not cracking even if dropped and having heat resistance and oil resistance that can withstand heating in a microwave oven.
Furthermore, since the base material of the polystyrene resin foam layer (X) is a polystyrene resin foam / polyolefin resin multilayer body comprising a polystyrene resin having a Vicat softening point of 110 ° C. or higher, In the heating, the multilayer body has excellent heat resistance without thermal deformation of the foam layer even if the heating is performed for a long time.

Claims (2)

Polyolefin resin having an Izod impact value at −20 ° C. of at least 10 KJ / m ² and a Vicat softening point of at least 100 ° C. on at least one surface of the polystyrene resin foam layer (X) via the adhesive layer (Y). Or a multilayer body in which a polyolefin resin layer (Z) made of a polyolefin resin composition is laminated, and the 50% fracture energy of the multilayer body by a falling weight impact test at a low temperature is 0.3 J or more. Polystyrene resin foam / polyolefin resin multilayer body characterized. The polystyrene resin foam / polyolefin resin multilayer body according to claim 1, wherein the base material of the polystyrene resin foam layer (X) is made of a polystyrene resin having a Vicat softening point of 110 ° C or higher.