JP4301467B2 - Polystyrene resin multilayer foam and container comprising the multilayer foam - Google Patents
Polystyrene resin multilayer foam and container comprising the multilayer foam Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、熱成形時に発泡体表面に部分的な溶融等が発生する虞れのないポリスチレン系樹脂多層発泡体及びその多層発泡体を熱成形してなる外観、剛性に優れた容器に関する。
【０００２】
【従来の技術】
従来、シート状又は板状のポリスチレン系樹脂発泡体（以下、単に発泡体とも言う）は、熱成形されてトレイ、弁当箱、丼、カップ等の各種容器として広く使用されている。これらの発泡体を製造する場合、基材樹脂であるポリスチレン系樹脂、発泡剤および各種添加剤を、押出機により溶融混練し、この発泡性溶融樹脂を押出機先端に取付けられた環状のダイスから低圧域に筒状に押出して発泡させる方法（所謂、押出発泡法）が採用されている。押出発泡された筒状の発泡体は、マンドレルと呼ばれる円柱形状の冷却装置上を通過させて冷却した後、切開いてシート状発泡体としたり、マンドレルによる冷却を行うことなく筒状発泡体を挟圧ロール間を通過させ発泡体内面を融着させて板状発泡体としている。しかしながら、このようにして得られる発泡体は熱成形すると、その表面が部分的にケロイド状に溶融したり、クラック（裂け）が発生したりするという問題があった。また、発泡体の片面にポリスチレン系樹脂シートを積層した積層体の場合でも、熱成形すると、積層体の発泡体側表面又は該樹脂シート積層面側の樹脂シート下層の発泡体表面において同様の現象が発生することがあった。
【０００３】
【発明が解決しようとする課題】
本発明は、従来のポリスチレン系樹脂発泡体に見られた、熱成形によって発泡体表面にケロイド状の溶融やクラックが部分的に発生する現象を解消したポリスチレン系樹脂多層発泡体及びその多層発泡体を熱成形してなる外観、剛性の優れた容器を提供することを目的とする。
【０００４】
本発明者らは、前記課題を解決すべく種々検討した結果、押出発泡法によってポリスチレン系樹脂発泡体を製造する方法において、発泡性溶融樹脂をダイスより押出す際に、ダイスよりスチレン二量体及びスチレン三量体（以下、これを「揮発性低分子量成分」と呼称することがある。）が同時に放出され、このスチレン二量体及びスチレン三量体が冷却用のマンドレルの表面等に凝縮して再度発泡体表面に付着し、発泡体を汚染することが前記した問題を生じる原因ではないかと考えた。本発明者等は更に鋭意研究を続けた結果、ポリスチレン系樹脂発泡体中に含まれるスチレン二量体及びスチレン三量体量を一定値以下とすることにより、前記したような発泡体を熱成形する際の問題が激減することがことを見出し、本発明を完成するに至った。
【０００５】
【課題を解決するための手段】
即ち、本発明のポリスチレン系樹脂多層発泡体は、複数のポリスチレン系樹脂発泡体の層を有するシート状又は板状のポリスチレン系樹脂多層発泡体であって、該多層発泡体の少なくとも一方の表面側が、スチレン二量体及びスチレン三量体の合計含有率２０００重量ｐｐｍ以下のポリスチレン系樹脂発泡体の層で構成されていることを特徴とする。
【０００６】
本発明のポリスチレン系樹脂多層発泡体は、スチレン二量体及びスチレン三量体の合計含有率が２０００重量ｐｐｍ以下のポリスチレン系樹脂発泡体の層と、スチレン二量体及びスチレン三量体の合計含有率が２０００重量ｐｐｍを超えるポリスチレン系樹脂多層発泡体の層とが積層されたものであっても良い。本発明多層発泡体において、スチレン二量体及びスチレン三量体の合計含有率が２０００重量ｐｐｍ以下のポリスチレン系樹脂発泡体の層は、密度０．０５〜０．７ｇ／ｃｍ３、厚み０．３〜４ｍｍ、平均気泡径０．０２〜０．４５ｍｍであることが好ましい。また、多層発泡体の一方の表面側がスチレン二量体及びスチレン三量体の合計含有率が２０００重量ｐｐｍ以下のポリスチレン系樹脂発泡体の層で構成され、他方の表面側がスチレン二量体及びスチレン三量体の合計含有率が２０００重量ｐｐｍを超えるポリスチレン系樹脂多層発泡体の層で構成されているものが好ましい。更に本発明の多層発泡体は、各ポリスチレン系樹脂発泡体の層が共押出により積層されていることが好ましい。
【０００７】
本発明の容器は、上記多層発泡体を熱成形してなるものであり、一方の面がスチレン二量体及びスチレン三量体の合計含有率が２０００重量ｐｐｍ以下のポリスチレン系樹脂発泡体層で構成され、他方の面がスチレン二量体及びスチレン三量体の合計含有率が２０００重量ｐｐｍを超えるポリスチレン系樹脂多層発泡体層で構成されている多層発泡体を熱成形してなる容器の場合、容器外面側がスチレン二量体及びスチレン三量体の合計含有率が２０００重量ｐｐｍを超えるポリスチレン系樹脂多層発泡体層で構成されていることが好ましい。
【０００８】
【発明の実施の形態】
本明細書においてポリスチレン系樹脂とは、スチレン単独重合体やスチレン系共重合体、或いはこれらと他の樹脂の混合物が包含される。スチレン系共重合体や混合物の場合、スチレン系モノマー単位の含有率は少なくとも２５重量％以上、好ましくは５０重量％以上のものが用いられる。ポリスチレン系樹脂の具体例としては、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挙げられる。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素添加物を混合したものや、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４０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。更にビカット軟化点が１１０℃以上のポリスチレン系樹脂を使用することにより、該ポリスチレン系樹脂より得られる発泡体の耐熱性を向上させることができる。上記ポリスチレン系樹脂には、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。
【０００９】
尚、本明細書において、上記ビカット軟化点とは、ＪＩＳ Ｋ７２０６（試験荷重はＡ法、伝熱媒体の昇温速度は５０℃／時の条件）にて求められる値である。
【００１０】
本発明の多層発泡体を製造する代表的な方法としては、▲１▼目的とする多層発泡体の層の数に相当する各発泡体を押出発泡法により製造し、それらの各発泡体を熱ロール、熱風等により加熱して積層接着する方法、▲２▼目的とする多層発泡体の層の数に相当する複数の押出機を使用し発泡性溶融樹脂を各々の押出機から一つの合流ダイスに供給し、合流ダイスの内部又はダイス出口付近の外部にてそれらの樹脂を多層発泡体となるように積層して多層発泡体得る方法（所謂、共押出発泡法）に大別される。
【００１１】
上記▲２▼の共押出発泡法によって製造する場合、各発泡性溶融樹脂の押出発泡温度は、１４０〜１６５℃であることが望ましい。押出発泡温度が高すぎると発泡体中の揮発性低分子量成分含有量が高くなる虞れがある。また、多層発泡体を構成する各発泡体の溶融粘度は特に限定されるものではないが、共押出発泡法を考慮した場合、各発泡体の溶融粘度は、おおむね１９０℃、剪断速度１００ｓｅｃ-1の条件下で２００〜１０００００ｐｏｉｓｅで相互に近い値であることが望ましく、各発泡体を構成しているポリスチレン系樹脂の溶融粘度（ｐｏｉｓｅ）の算術平均値の４分の１以上、４倍未満の値の範囲であることが好ましい。上記▲２▼の方法は、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好ましい製造方法である。
【００１２】
押出発泡によって発泡体を製造するには、例えば、ポリスチレン系樹脂と気泡調整剤、必要によりその他の添加剤とを押出機にて溶融混練し、その溶融樹脂を押出機に圧入された発泡剤と混合して発泡性溶融樹脂とし、押出機先端に取付けられた環状のダイスから発泡性溶融樹脂を低圧域に筒状に押出発泡する方法が採用される。押出発泡された筒状発泡体は、マンドレルと呼ばれる円柱形状の冷却装置上に引き取って冷却した後、切開いてシート状発泡体としたり、押出された筒状の発泡体をマンドレル上を通過させることなく筒状の発泡体の内部が融着可能なうちに挟圧ロール間を通して筒状発泡体を押しつぶして発泡体の内面を融着させることで板状発泡体とすることができる。
【００１３】
ポリスチレン系樹脂発泡体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。また、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の分解型発泡剤も用いることができる。更に、二酸化炭素等の無機ガスや水も発泡剤として使用できる。これらの発泡剤は適宜混合して用いることができる。このなかでも環境への負荷低減、取扱い性の良さ、低コスト等の面で二酸化炭素、水、脂肪族炭化水素等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当たり、０．０１〜０．１モルの範囲で、目標とする発泡体密度に応じて適宜選択することができる。
【００１４】
気泡調整剤としてはタルク、カオリン、マイカ、シリカ、炭酸カルシウム、硫酸バリウム、酸化チタン、クレー、酸化アルミニウム、ベントナイト、ケイソウ土等の無機物粉末又は重炭酸ナトリウム、クエン酸モノナトリウム塩等が例示される。これらの気泡調整剤は、通常は単独で使用されるが２種以上組み合わせて用いてもよい。気泡調整剤として用いる無機物粉末は、粒子径が小さいほど少量の使用でも発泡体の気泡径を小さくする効果が高い。そのような観点から無機物粉末の平均粒子径（遠心沈降法）は３０μｍ以下であることが好ましく、２０μｍ以下であることがより好ましく、１５μｍ以下であることが更に好ましい。ただし、あまりにも平均粒子径が小さいとその加工のために無機物粉末の価格が高くなるので０．１μｍを下限とすることが好ましい。上記無機物粉末の中でも特にタルクが有効であると共に安価であるので最も好ましい。
【００１５】
上記方法等により製造される発泡体には、通常、スチレン二量体やスチレン三量体等の揮発性低分子量成分が２０００重量ｐｐｍを超える割合で含有されている（以下、揮発性低分子量成分含有率が２０００重量ｐｐｍを超えるポリスチレン系樹脂発泡体を、便宜上、“通常のポリスチレン系樹脂発泡体”と言うことがある。）。このような“通常のポリスチレン系樹脂発泡体”は、その製造工程においてダイスより発泡性溶融樹脂を押出す際に、揮発性低分子量成分を同時に放出し、放出された揮発性低分子量成分は冷却用のマンドレルの表面、挟圧ロール表面等に凝縮し、これが押出発泡された発泡体表面に部分的に再付着する虞れがある。そして、揮発性低分子量成分の凝縮物が付着している“通常のポリスチレン系樹脂発泡体”を熱成形すると、発泡体表面が部分的にケロイド状に溶融したり、クラックが発生したりする虞れがある。
【００１６】
本発明のポリスチレン系樹脂多層発泡体は、複数のポリスチレン系樹脂発泡体の層を有するシート状又は板状の多層発泡体において、少なくとも一方の表面側が、揮発性低分子量成分の含有率が２０００重量ｐｐｍ以下のポリスチレン系樹脂発泡体（以下、この発泡体を便宜上“低揮発性成分含有ポリスチレン系樹脂発泡体”と呼ぶことがある。）の層で構成されていることにより、上記した“通常のポリスチレン系樹脂発泡体”の有する問題を解決し得たものである。
【００１７】
“低揮発性成分含有ポリスチレン系樹脂発泡体”は、該発泡体を押出発泡する際に放出される揮発性低分子量成分の量も少なく、放出された揮発性低分子量成分の凝縮物の発泡体表面への再付着に起因すると考えられる、発泡体を熱成形する際等の、発泡体表面が部分的にケロイド状に溶融したり、クラックが発生したりする現象（以下、単に表面焼け現象とも言う）の発生を防ぐことができるものと考えられる。
【００１８】
本発明において、上記ポリスチレン系樹脂発泡体中の揮発性低分子量成分含有量とは、以下のようにして測定した値であり、実質的にはスチレン二量体とスチレン三量体の合計量である。
【００１９】
▲１▼試料の調整及び測定法
１．ポリスチレン系樹脂発泡体約０．２ｇを正確に秤量し、ビーカー中の約１５ｍｌのテトラヒドロフランに溶解させる。
２．ポリスチレン系樹脂発泡体がテトラヒドロフランに完全に溶解したことを確認した後、その約１５ｍｌのポリスチレン系樹脂テトラヒドロフラン溶液を、約２５０ｍｌのｎ−ペンタン中に滴下してポリスチレン樹脂を析出させる。更に、ビーカー中に約５ｍｌのテトラヒドロフランを入れ、ビーカー中を洗浄し、洗浄に使用した約５ｍｌのテトラヒドロフランを更に、前記ｎ−ペンタン中に滴下する操作を２回行う。
３．ｎ−ペンタンに中に析出したポリスチレン系樹脂を、Ｎｏ.５Ｂのろ紙を使用してろ別する。尚、ろ過の際は吸引ろ過を行なわず自然ろ過とする。
４．ろ液の入ったビーカーを１５℃の水浴にて保温しつつコンプレッサーエアーをろ液に吹きかけながら６〜８時間かけて、ろ液を約１００ｍｌに濃縮する。
５．約１００ｍｌに濃縮されたろ液に約４０ｍｌのアセトニトリルを加え、更に１５℃の水浴にて保温しつつコンプレッサーエアーをろ液に吹きかけながら２〜３時間かけてろ液を約６〜９ｍｌに濃縮する。
６．約６〜９ｍｌに濃縮されたろ液をアセトニトリルで全量が１０ｍｌとなるように希釈したものを測定用試料とする。
７．測定用試料を高速液体クロマトグラフに注入して測定を行う。
【００２０】
▲２▼測定装置（高速液体クロマトグラフ）
液送ポンプＬＣ−６Ａ（２台）、自動試料注入装置ＳＩＬ−６Ａ、紫外分光光度計検出器ＳＰＤ−６Ａ、カラムオーブンＣＴＯ−６Ａ、システムコントローラＳＣＬ−６Ａ、データ処理装置Ｃ−Ｒ３Ａ、全て（株）島津製作所製
【００２１】
▲３▼測定条件
カラム：ＵＬＴＲＯＮ ＶＸ−ＯＤＳ（充填材ＯＤＳシリカ、内径４．６ｍｍ.長さ２５０ｍｍ、粒径５μｍ）、信和化工（株）製
カラム温度：５０℃
移動相：アセトニトリル：水（体積比６：４）を初期濃度とし、測定試料注入直後から１３分間のリニアグラジエントによりアセトニトリルのみとした後、更に２２分間溶出。
流速：１．５ｍｌ／ｍｉｎ．
検出波長：２２５ｎｍ
注入量：５〜１００μｌの範囲で適宜調節
検量線：スチレン二量体及びスチレン三量体の標準試料（関東化学（株）製）を使用し、絶対検量線法により定量する。
【００２２】
“低揮発性成分含有ポリスチレン系樹脂発泡体”を得るためには、一つには原料ポリスチレン系樹脂として揮発性低分子量成分の含有量が２０００重量ｐｐｍ以下のものを選択して使用すること、より好ましくは１０００重量ｐｐｍ以下のものを選択して使用することである。特にポリスチレン系樹脂を重合する際、重合時の熱履歴において熱的処理時間が短いもの、重合時に重合系内に存在する酸素量を少なくしたものや、脱揮時の真空度を高くしたもの等が好適である。ポリスチレン系樹脂は、懸濁重合、塊状重合、溶液重合、乳化重合等の重合法によるもののうち、特に懸濁重合によるものが好ましい。また、押出発泡工程においては押出機内でのポリスチレン系樹脂の溶融混練時に、不必要な剪断力が樹脂に働かないようなスクリューを備えた押出機を選択すること、ベント押出機を使用し揮発性低分子量成分をベント口より排出させて押出発泡させる方法等を採用することも、“低揮発性成分含有ポリスチレン系樹脂発泡体”を得るために好適な方法である。
【００２３】
本発明のポリスチレン系樹脂多層発泡体は、上記した“低揮発性成分含有ポリスチレン系樹脂発泡体”の層のみが、２層以上積層された構成を有していても、少なくとも一方の面が“低揮発性成分含有ポリスチレン系樹脂発泡体”で構成され、且つ“低揮発性成分含有ポリスチレン系樹脂発泡体”と“通常のポリスチレン系樹脂発泡体”の層とが２層以上積層された構成を有していても良い。本発明の多層発泡体の全体としての密度は、０．０５〜０．７ｇ／ｃｍ3が好ましく、更に好ましくは０．１〜０．５ｇ／ｃｍ3である。密度が０．０５ｇ／ｃｍ3未満の場合、多層発泡体を成形して得た容器の強度が不足することがあるばかりでなく、加熱成形するときに伸びが不足して容器に穴が開く場合がある。一方、密度が０．７ｇ／ｃｍ3を超えると軽量性、経済性が問題となるとともに、容器の断熱性が低下し容器に食品を入れて加熱すると、手で持てないくらいに熱くなり、発泡体製容器の特徴である断熱性が不十分なことがある。また、多層発泡体の厚みは、好ましくは０．７〜７ｍｍ、更に好ましくは０．７〜３ｍｍである。厚みが０．７ｍｍ未満では強度や断熱性の点で実用に耐え得ない虞れがある。厚みが７ｍｍを超えると、加熱成形の際に発泡体の内部と外部との間の加熱ムラが起こりやすく、精密な温度制御が必要となる。
【００２４】
また、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層のみが２層以上積層された構成の多層発泡体の場合、各“低揮発性成分含有ポリスチレン系樹脂発泡体”の層は、平均気泡径が０．０２〜０．４５ｍｍであることが好ましく、更に好ましくは０．０３〜０．３ｍｍである。外観、印刷適性が良好なものとするうえでは上記平均気泡径は細かいものが好ましいが、あまり細かすぎると発泡体の成形性、剛性の面において不十分なものとなってしまう。一方、平均気泡径が大きすぎると外観、印刷適性において良好なものが得られなくなる。更に、各“低揮発性成分含有ポリスチレン系樹脂発泡体”の層は、連続気泡率が４０％以下であることが好ましく、更に好ましくは２５％以下である。連続気泡率が高いものは熱成形等の際に発泡体の二次発泡性が低下するため、発泡体の金型再現性の悪化（金型形状通りの成型体が得られ難くなる。）、成形体の肉厚不足の発生等、熱成形性の低下が見られる。また、得られる成形体の強度も同じ密度では弱くなる。しかし、吸水性素材等の用途に使用する場合は、連続気泡率は必ずしも低いものでなくても良く、５０％以上のものであっても良い。
尚、本発明において発泡体の連続気泡率はＡＳＴＭ Ｄ２８５６、手順Ｃによって求められる値である。
【００２５】
“低揮発性成分含有ポリスチレン系樹脂発泡体”の層と、“通常のポリスチレン系樹脂発泡体”の層とが積層された構成の多層発泡体の場合、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層の厚みを０．３〜４ｍｍとすることが、製造コスト等の面から好ましい。尚、揮発性低分子量成分２０００重量ｐｐｍ以下のポリスチレン系樹脂発泡体層の厚みが薄い多層発泡体を得る場合、具体的には０．７ｍｍ未満の“低揮発性成分含有ポリスチレン系樹脂発泡体”の層を有するものの場合には、特に共押出発泡法により多層発泡体を得るのが好適である。またこの多層発泡体の場合も、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層は、密度０．０５〜０．７ｇ／ｃｍ3、平均気泡径０．０２〜０．４５ｍｍであることが好ましく、より好ましくは密度０．１〜０．５ｇ／ｃｍ3、平均気泡径０．１５〜０．４５ｍｍ、連続気泡率４０％以下である。更に、低揮発性成分含有ポリスチレン系樹脂発泡体”の層は、連続気泡率４０％以下であることが好ましく、より好ましくは連続気泡率２５％以上である。尚、吸水性素材等の用途によっては、連続気泡率は５０％以上であって良い。
【００２６】
一方、多層発泡体を構成する“通常のポリスチレン系樹脂発泡体”の層は、従来のポリスチレン系樹脂発泡体により構成すれば良く、その密度は、好ましくは０．０５〜０．７ｇ／ｃｍ3、更に好ましくは０．１〜０．５ｇ／ｃｍ3である。“通常のポリスチレン系樹脂発泡体”の層の密度が０．０５ｇ／ｃｍ3未満では、成形性、成形体の強度において不十分となる虞れがある。一方、０．７ｇ／ｃｍ3を超えると軽量性、断熱性が不十分となることがある。また、“通常のポリスチレン系樹脂発泡体”の層の厚みは０．５〜５ｍｍであることが成形性、成形体の強度等の面から好ましく、更に好ましくは０．９〜４ｍｍである。また、“通常のポリスチレン系樹脂発泡体”の層の平均気泡径は、好ましくは０．０２〜０．４５ｍｍ、更に好ましくは０．０２〜０．４ｍｍである。上記平均気泡径が細かすぎると発泡体の成形性、剛性の面において不十分なものとなってしまい、平均気泡径が大きすぎると外観、印刷適性において良好なものが得られなくなる。また、“通常のポリスチレン系樹脂発泡体”の層の連続気泡率は、好ましくは４０％以下、更に好ましくは２５％以下である。連続気泡率が高い多層発泡体は、熱成形等の際に発泡体の二次発泡性が低下するために発泡体の金型再現性悪化、成形体の厚み厚薄の発生等の熱成形性の低下が見られる。
【００２７】
本発明の多層発泡体は、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層と、“通常のポリスチレン系樹脂発泡体”の層とが、各々１層づつ積層された２層構成のものに限定されるものではなく、“通常のポリスチレン系樹脂発泡体”の層を芯層とし、その両面に“低揮発性成分含有ポリスチレン系樹脂発泡体”の層が積層された構成のもの、“通常のポリスチレン系樹脂発泡体”の層同士が積層されたものに、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層が積層された構成のもの、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層と、“通常のポリスチレン系樹脂発泡体”の層とを、非発泡ポリスチレン系樹脂を介して積層したもの等、複数の発泡体の層が積層されたものであっても、積層されている各発泡体の層間に、非発泡樹脂からなる層を有するものであってもよく、少なくとも“低揮発性成分含有ポリスチレン系樹脂発泡体”の層が、多層発泡体の一方の表面側に形成されているものであればよい。
【００２８】
本発明の多層発泡体は、その少なくとも一方の表面側が、上記した“低揮発性成分含有ポリスチレン系樹脂発泡体”の層で形成されていることにより、発泡体の片面を加熱板に接触させて軟化させた後、金型にて成形する所謂熱板成形等の如き、発泡体の片側から加熱して成形を行なう場合において、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層側を加熱するようにすれば、発泡体の表面焼け現象発生を防ぐことができる。また、多層発泡体の両面側が、前記“低揮発性低成分含有ポリスチレン系樹脂発泡体”の層で形成されている場合には、どちらの面から加熱を行っても多層発泡体の表面焼け現象の発生を防止できる。
【００２９】
また、▲１▼一方の表面側が“低揮発性成分含有ポリスチレン系樹脂発泡体”の層により構成され、他方の表面側が“通常のポリスチレン系樹脂発泡体”の層で構成される多層発泡体（２層構成に限らず、３層以上の構成の場合も含む）を、前記した環状ダイスを用いた共押出発泡法によって製造し、且つ押出発泡された筒状の多層発泡体をマンドレルで冷却した後、切り開いてシート状発泡体を得る場合、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層が、筒状の多層発泡体の内面側（即ちマンドレルと接する側）に形成されるようにして押出発泡することが好ましい。
【００３０】
また、▲２▼共押出発泡された筒状の多層発泡体を、マンドレルで冷却することなく挟圧ロールによって押しつぶして内面側を融着させることにより板状発泡体とする場合、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層が、筒状多層発泡体の外面側（挟圧ロールと接する側）に形成されるようにして押出発泡することが好ましい。
【００３１】
上記、▲１▼、▲２▼の方法により得られた多層発泡体は、どちらの面から加熱を行っても多層発泡体の表面焼け現象の発生を防止できる。
【００３２】
“低揮発性成分含有ポリスチレン系樹脂発泡体”は、“通常のポリスチレン系樹脂発泡体”に比べ、剛性に優れる反面、成形時の伸びや柔軟性の面で多少改善の余地がある。その為、上記したように多層発泡体の片面を“低揮発性成分含有ポリスチレン系樹脂発泡体”の層にて形成し、他方の片面を“通常のポリスチレン系樹脂発泡体”の層にて形成することにより、多層発泡体の熱成形時の伸び、脆性が改善され、深絞り等の熱成形性、抜き加工性に優れたものとなる。
【００３３】
また、本発明の多層発泡体の印刷適性及び成形性をより向上させるために、一方の表面側の発泡体の層の平均気泡径を２０〜１４０μｍとし、他方の表面側の発泡体の層の平均気泡径を１５０〜４５０μｍとするが好ましい。この場合、平均気泡径が１５０〜４５０μｍの発泡体の層を“低揮発性成分含有ポリスチレン系樹脂発泡体”で構成し、平均気泡径を２０〜１４０μｍの発泡体の層を“通常のポリスチレン系樹脂発泡体”で構成すると成形性の面で特に好ましい。また本発明の多層発泡体は、用途に応じて連続気泡率や厚みが異なる各発泡体の層を積層接着することができる。
【００３４】
また本発明の“低揮発性成分含有ポリスチレン系樹脂発泡体”の層を有する多層発泡体は、無発泡の熱可塑性樹脂の層が積層された構造のものであっても構わない。無発泡の熱可塑性樹脂の層を構成する熱可塑性樹脂としては、ハインパクトポリスチレン等のポリスチレン系樹脂、高密度ポリエチレン、ポリプロピレン系樹脂等のポリオレフィン系樹脂、ポリエチレンテレフタレート、ポリエチレンナレフタレート等のポリエステル系樹脂等が挙げられる。
【００３５】
無発泡の熱可塑性樹脂の層を有する多層発泡体の代表的な製造方法としては、▲１▼前記した押出発泡法により多層発泡体を製造し、その後、この発泡体に対して、製造ライン上または別ラインで、シート状熱可塑性樹脂を熱ロール等を通して積層接着する方法、▲２▼各発泡体の層と熱可塑性樹脂の層とを共押出法によって積層接着する方法、▲３▼押出機により多層発泡体を製造し、その後、この発泡体に対して、製造ライン上または別ラインで、別の押出機より押出された熱可塑性樹脂を積層接着する方法、▲４▼押出発泡法により各発泡体を製造し、これらの発泡体に対して、製造ライン上または別ラインでシート状熱可塑性樹脂を積層し、熱風又は熱ロール等で各発泡体及びシート状熱可塑性樹脂を積層接着する方法等がある。また、無発泡のシート状熱可塑性樹脂の厚みは０．０１〜０．５ｍｍが好ましく、特に０．０２〜０．２ｍｍが好ましい。０．０１ｍｍ未満では熱成形する際に伸ばされて更に薄くなるために破れやピンホールが生じやすい。厚みが０．５ｍｍを超える場合は発泡体との接着が難しくなり、コスト高となってしまう。無発泡の熱可塑性樹脂層中には、必要に応じて各種の添加剤、例えば酸化防止剤、熱安定剤、帯電防止剤、導電性付与剤、紫外線防止剤、着色剤、難燃剤、無機充填剤等を添加することができる。
【００３６】
本発明の容器は、前述した多層発泡体を熱成形してなる容器である。多層発泡体の熱成形方法としては、これらを加熱軟化させ、金型を使用した真空成形法及び／又は圧空成形法、更にはそれらを応用したマッチドモールド成形法、プラグアシスト成形法等の成形法が挙げられ、主にトレイ、カップ、丼、弁当箱等の容器に成形される。尚、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層が片面側のみに設けられている多層発泡体の場合、容器の内側側に“低揮発性成分含有ポリスチレン系樹脂発泡体”の層が位置するように多層発泡体を熱成形することが熱成形の面で好ましい。本発明容器は外観、剛性において優れたものであり、特に“低揮発性成分含有ポリスチレン系樹脂発泡体”の層が容器内面側に位置し、“通常のポリスチレン系樹脂発泡体”の層が容器外面側に位置している容器は、更に脆性も改善され、柔軟性、外観、剛性に優れ、丼、カップ等の深絞り容器や剛性を必要とする積み重ね高さの低いロースタックトレイに好適なものである。
【００３７】
【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。
【００３８】
実施例１
ポリスチレン樹脂Ａ（電気化学工業（株）製のポリスチレン樹脂、商品名『ＧＸ-0196』）を９５．５重量部、気泡調整剤としてタルクを１重量部の割合で６０ｍｍ径の押出機に投入して加熱した後、イソブタン６５重量％とノルマルブタン３５重量％からなる混合ブタン発泡剤３．５重量部を押出機内の溶融ポリスチレン樹脂Ａに圧入して約２００℃で溶融混練した。次いで上記押出機と接続された９０ｍｍ径の押出機内に、上記溶融混練物を押出して該押出機内で冷却して約１５７℃の発泡性溶融樹脂を得た。一方、ポリスチレン樹脂Ｂ（出光石油化学（株）製のポリスチレン樹脂、商品名『ＨＨ３２』）を９５．５重量部、気泡調整剤としてタルクを１重量部の割合で、他の６０ｍｍ径の押出機に投入して加熱した後、イソブタン６５重量％とノルマルブタン３５重量％からなる混合ブタン発泡剤３．５重量部を押出機内の溶融ポリスチレン樹脂Ｂに圧入して約２００℃で溶融混練した後、上記押出機と接続された９０ｍｍ径の押出機内に押出して冷却し、約１５７℃の発泡性溶融樹脂を得た。各押出機内の発泡性溶融樹脂を合流環状ダイスで合流させて積層した後、約１５７℃で該ダイスから共押出ししてポリスチレン樹脂Ａからなる発泡体の層が内面側となるように、筒状に発泡させると共にその直径を拡大させつつ表面を冷却し、更に筒状発泡体の内側をマンドレルに接するようにして移送しながら更に冷却させ、マンドレル下流側に固定された1つのカッターナイフにより押出方向に沿って筒状発泡体を切開いた。次いでその切断部から押し広げることによりシート状にして連続的にロール状に巻取った。尚、得られた多層発泡シートは、幅が１０４０ｍｍ、厚みが２．５ｍｍ、密度が０．１１ｇ／ｃｍ3であった。
【００３９】
参考例１
ポリスチレン樹脂Ａを９５．５重量部、気泡調整剤としてタルクを１重量部の割合で６０ｍｍ径の押出機に投入して加熱した後、イソブタン６５重量％とノルマルブタン３５重量％からなる混合ブタン発泡剤３．５重量部を押出機内の溶融ポリスチレン樹脂Ａに圧入して約２００℃で溶融混練した。次いで上記押出機と接続された９０ｍｍ径の押出機内に上記溶融混練物を押出し、該押出機内で約１５７℃まで冷却した後、同温度で環状ダイスから押出して筒状に発泡させると共に、その直径を拡大させつつ表面を冷却し、更に筒状発泡体の内側をマンドレルに接するようにして移送しながら更に冷却させ、マンドレル下流側に固定された1つのカッターナイフにより押出方向に沿って筒状発泡体を切開いた。次いでその切断部から押し広げることによりシート状にして連続的にロール状に巻取った。尚、得られた発泡シートは幅が１０４０ｍｍ、厚みが２．３ｍｍ、密度が０．１１ｇ／ｃｍ3であった。
【００４０】
参考例２
ポリスチレン樹脂Ａ、タルク及びイソブタン６５重量％とノルマルブタン３５重量％からなる混合ブタン発泡剤とを約２５０℃で溶融混練した以外は、参考例１と同様にしてシート状のポリスチレン系樹脂発泡体を得た。
【００４１】
比較例１
ポリスチレン樹脂Ａのかわりにポリスチレン樹脂Ｂを用いた以外は参考例１と同様にして、シート状のポリスチレン系樹脂発泡体を得た。
【００４２】
上記各実施例、参考例及び比較例にて得られた多層発泡体又は発泡体について、揮発性低分子量成分の含有率等の諸物性を測定した結果を表１に示す。また、該多層発泡体又は発泡体について熱成形を行なった結果も併せて表１に示す。表１の物性及び評価については以下の通り行なった。尚、揮発性低分子量成分含有率、連続気泡率は前記した方法により測定した。
【００４３】
発泡体の密度
単層の発泡体については、縦２ｃｍ×横２ｃｍ×発泡体厚み（ｃｍ）の試験片を切り出し、試験片の重量（ｇ）を測定し、該重量を縦２ｃｍ×横２ｃｍ×発泡体厚み（ｃｍ）より求められる試験片体積（ｃｍ3）で割ることにより求めた。また、多層発泡体の場合は、積層されている各々の発泡体において、縦２ｃｍ×横２ｃｍ×任意の発泡体厚み（ｃｍ）の試験片を切り出し、試験片の重量（ｇ）を測定し、該重量を縦２ｃｍ×横２ｃｍ×発泡体厚み（ｃｍ）より求められる試験片体積（ｃｍ3）で割ることにより求める。但し、試験片の厚みについては出来るだけ厚く設定した。尚、各発泡体の層のうち、いずれか一つの発泡体が薄い場合は、その層の発泡体の密度を、他の層の発泡体の密度と多層発泡体全体の密度より逆算して求めても良い。
【００４４】
発泡体の厚み
発泡体の厚み方向垂直断面の任意の２０カ所の厚みを測定し、それらの値の算術平均値を採用した。
【００４５】
平均気泡径
発泡体の全厚み（ｍｍ）（多層発泡体の場合は、各発泡体層の全厚み（ｍｍ））に亘って発泡体厚み方向に直線を引き、該直線の長さ（ｍｍ）を直線上の気泡数にて割ることにより求めた。
【００４６】
成形性
実施例、参考例及び比較例にて得られた多層発泡体又は発泡体を、単発成形機にて開口部形状が直径１５０ｍｍ、底面部直径１２０ｍｍ、深さ６０ｍｍ又は３０ｍｍの円錐台形状の容器成形用の金型を使用して真空成形によりカップを成形した時の成形性を以下の基準で評価した。尚、実施例１の多層発泡体については“低揮発性成分含有ポリスチレン系樹脂発泡体”の層が、カップ内面側となるように成形を行なった。
◎：深さ６０ｍｍの金型を使用して成形された容器の金型再現性が良好である。
○：深さ３０ｍｍの金型を使用して成形された容器の金型再現性が良好であり、深さ６０ｍｍの金型を使用して成形された容器の金型再現性が多少劣る。
×：深さ３０ｍｍの金型を使用して成形された容器の金型再現性が劣る。
【００４７】
外観
上記、深さ３０ｍｍの金型を使用して成形された、５０００個の容器の外観を観察し以下の基準にて評価を行なった。
○：容器の表面にケロイド状の溶融又はクラックの発生が見られるものが一つもない。
×：容器の表面にケロイド状の溶融及び／又はクラックの発生が見られるものがある。
【００４８】
剛性
上記、深さ３０ｍｍの金型を使用して成形された容器を、開口面が鉛直方向となるようにリップ強度測定装置に装着し、開口面を形成しているリップ部を鉛直方向に１０ｍｍ圧縮した時の応力をリップ強度（ｇｆ）とし、以下の基準で評価を行った。
○：リップ強度が５００ｇｆ以上である。
△：リップ強度が５００ｇｆ未満である。
【００４９】
【表１】
【発明の効果】
本発明のポリスチレン系樹脂多層発泡体は、熱成形時に発泡体表面において、ケロイド状の溶融やクラックが部分的に発生する等の虞れがなく、外観良好で剛性に優れた成形体を得ることできる。また、発泡体を数日間連続的に製造する場合、従来のように生産を一時停止させてマンドレルや挟圧ロール等の表面の清掃を行う等の必要が殆どなく、生産性が良好なものである。更に、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層と“通常のポリスチレン系樹脂発泡体”の層とが積層されている多層発泡体の場合、上記の効果に加え、熱成形時の伸び、脆性が改善され深絞り等の熱成形性、抜き加工性に優れたものとなり、特に一方の表面側を“低揮発性成分含有ポリスチレン系樹脂発泡体”の層で構成され、他方の表面側を“通常のポリスチレン系樹脂発泡体”の層で構成されているものは更に、これらの効果に優れるものとなる。また、“低揮発性成分含有ポリスチレン系樹脂発泡体”の層と、“通常のポリスチレン系樹脂発泡体”の層とを積層してなる多層発泡体は、“通常のポリスチレン系樹脂発泡体”を構成する樹脂に比して生産性の低い“低揮発性成分含有ポリスチレン系樹脂発泡体”を構成する樹脂の絶対量を少なくすることができるため、生産コストをおさえることが出来る。
【００５１】
また、本発明の容器は外観、剛性において優れたものであり、特に“低揮発性成分含有ポリスチレン系樹脂発泡体”の層が容器内側に位置し、“通常のポリスチレン系樹脂発泡体”の層が容器外面に位置している容器は、更に脆性も改善され、柔軟性、外観、剛性に優れ、丼、カップ等の深絞り容器や、ロースタックトレイに好適なものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polystyrene resin multilayer foam in which there is no possibility of partial melting or the like occurring on the foam surface during thermoforming, and a container having excellent appearance and rigidity formed by thermoforming the multilayer foam.
[0002]
[Prior art]
Conventionally, a sheet-like or plate-like polystyrene-based resin foam (hereinafter, also simply referred to as a foam) is thermoformed and widely used as various containers such as trays, lunch boxes, bowls, cups and the like. When manufacturing these foams, the base resin polystyrene-based resin, foaming agent and various additives are melt-kneaded by an extruder, and this foamable molten resin is removed from an annular die attached to the tip of the extruder. A method (so-called extrusion foaming method) in which the foam is extruded into a low pressure region and foamed is employed. The extruded and foamed cylindrical foam is cooled by passing it over a cylindrical cooling device called a mandrel, and then cut into a sheet-like foam or sandwiched without being cooled by the mandrel. A plate-like foam is obtained by passing between pressure rolls and fusing the inner surface of the foam. However, when the foam obtained in this way is thermoformed, there is a problem that the surface thereof is partially melted in a keloid form or cracks are generated. Further, even in the case of a laminate in which a polystyrene resin sheet is laminated on one side of a foam, when thermoformed, the same phenomenon occurs on the foam side surface of the laminate or the foam surface of the resin sheet lower layer on the resin sheet laminate side. It sometimes occurred.
[0003]
[Problems to be solved by the invention]
The present invention relates to a polystyrene resin multilayer foam that eliminates the phenomenon of partial keloid-like melting and cracking on the foam surface caused by thermoforming, as found in conventional polystyrene resin foam, and the multilayer foam An object of the present invention is to provide a container having excellent appearance and rigidity formed by thermoforming.
[0004]
As a result of various studies to solve the above problems, the inventors of the present invention produced a polystyrene resin foam by an extrusion foaming method. When extruding a foamable molten resin from a die, Styrene dimer and styrene trimer (hereinafter sometimes referred to as “volatile low molecular weight components”) Are released at the same time Styrene dimer and styrene trimer It was thought that the above-mentioned problems may be caused by condensation on the surface of the cooling mandrel and the like, and re-adhering to the surface of the foam to contaminate the foam. As a result of further intensive studies, the present inventors have been included in a polystyrene resin foam. Styrene dimer and styrene trimer content It has been found that the problem of thermoforming a foam as described above can be drastically reduced by keeping the value below a certain value, and the present invention has been completed.
[0005]
[Means for Solving the Problems]
That is, the polystyrene resin multilayer foam of the present invention is a sheet-like or plate-like polystyrene resin multilayer foam having a plurality of polystyrene resin foam layers, and at least one surface side of the multilayer foam is , Total of styrene dimer and styrene trimer It is characterized by comprising a layer of polystyrene resin foam having a content of 2000 ppm by weight or less.
[0006]
The polystyrene resin multilayer foam of the present invention is Total of styrene dimer and styrene trimer A layer of polystyrene resin foam having a content of 2000 ppm by weight or less, Total of styrene dimer and styrene trimer A layer of a polystyrene resin multilayer foam having a content rate exceeding 2000 ppm by weight may be laminated. In the multilayer foam of the present invention, Total of styrene dimer and styrene trimer The layer of polystyrene resin foam having a content of 2000 ppm by weight or less has a density of 0.05 to 0.7 g / cm. 3 The thickness is preferably 0.3 to 4 mm and the average cell diameter is 0.02 to 0.45 mm. Also, one surface side of the multilayer foam is Total of styrene dimer and styrene trimer It is composed of a layer of polystyrene resin foam with a content of 2000 ppm by weight or less, and the other surface side is Total of styrene dimer and styrene trimer What is comprised by the layer of the polystyrene-type resin multilayer foamed body whose content rate exceeds 2000 weight ppm is preferable. Further, in the multilayer foam of the present invention, it is preferable that layers of each polystyrene resin foam are laminated by coextrusion.
[0007]
The container of the present invention is formed by thermoforming the above-mentioned multilayer foam, and one surface is Total of styrene dimer and styrene trimer It is composed of a polystyrene resin foam layer with a content of 2000 ppm by weight or less, and the other surface is Total of styrene dimer and styrene trimer In the case of a container formed by thermoforming a multi-layer foam composed of a polystyrene resin multi-layer foam layer having a content rate exceeding 2000 ppm by weight, the container outer surface side is Total of styrene dimer and styrene trimer Consists of polystyrene resin multilayer foam layer with content over 2000 ppm by weight Have It is preferable.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In this specification, the polystyrene resin includes a styrene homopolymer, a styrene copolymer, or a mixture of these and other resins. In the case of a styrene copolymer or a mixture, the content of styrene monomer units is at least 25% by weight, preferably 50% by weight or more. Specific 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, styrene-methacrylic acid. Acid methyl copolymer, styrene-ethyl methacrylate copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-maleic anhydride copolymer, polystyrene-polyphenylene ether copolymer, Examples thereof include a mixture of polystyrene and polyphenylene ether. These resins are blended with styrene-conjugated diene block copolymers and their hydrogenated products for the purpose of improving brittleness, and polyolefin resins such as polypropylene resins and high density polyethylene in consideration of mixing of recycled resins. Can be used in a ratio of 40% by weight or less. Further, by using a polystyrene resin having a Vicat softening point of 110 ° C. or higher, the heat resistance of the foam obtained from the polystyrene resin can be improved. Antioxidants, heat stabilizers, antistatic agents, conductivity-imparting agents, weathering agents, ultraviolet absorbers, colorants, flame retardants, inorganic fillers, and the like can be added to the polystyrene resin.
[0009]
In the present specification, the Vicat softening point is a value determined according to JIS K7206 (test load is method A, heating rate of heat transfer medium is 50 ° C./hour).
[0010]
As a typical method for producing the multilayer foam of the present invention, (1) each foam corresponding to the number of layers of the target multilayer foam is produced by an extrusion foaming method, and each foam is heated. A method of laminating and bonding by heating with a roll, hot air, etc. (2) Using a plurality of extruders corresponding to the number of layers of the target multi-layer foam, a foamable molten resin is fed from each extruder into one joining die And a method of so-called coextrusion foaming to obtain a multilayer foam by laminating these resins inside the junction die or outside the vicinity of the die outlet to form a multilayer foam.
[0011]
When producing by the coextrusion foaming method of (2) above, the extrusion foaming temperature of each foamable molten resin is preferably 140 to 165 ° C. If the extrusion foaming temperature is too high, the content of volatile low molecular weight components in the foam may be increased. In addition, the melt viscosity of each foam constituting the multilayer foam is not particularly limited. However, when the coextrusion foaming method is considered, the melt viscosity of each foam is approximately 190 ° C. and the shear rate is 100 sec. -1 It is desirable that the values are close to each other at 200 to 100,000 poise under the conditions of the above, and are not less than one quarter and less than four times the arithmetic average value of the melt viscosity (poise) of the polystyrene resin constituting each foam. A range of values is preferred. The method (2) is a preferable production method because the process is simple and the cost can be reduced compared to other methods.
[0012]
In order to produce a foam by extrusion foaming, for example, a polystyrene resin and a foam adjusting agent, and if necessary, other additives are melt-kneaded in an extruder, and the molten resin is press-fitted into the extruder. A method is adopted in which foamable molten resin is mixed to form a foamable molten resin, and the foamable molten resin is extruded into a cylindrical shape in a low pressure region from an annular die attached to the tip of the extruder. The extruded foam is taken up on a cylindrical cooling device called a mandrel and cooled, and then cut into a sheet foam, or the extruded tubular foam is passed over the mandrel. In addition, while the inside of the cylindrical foam can be fused, a plate-like foam can be obtained by crushing the cylindrical foam through the sandwiching rolls and fusing the inner surface of the foam.
[0013]
Examples of the foaming agent used in the production of the polystyrene resin foam include propane, n-butane, i-butane, a mixture of n-butane and i-butane, aliphatic hydrocarbons such as pentane and hexane, cyclobutane, cyclohexane Cycloaliphatic hydrocarbons such as pentane, trichlorofluoromethane, dichlorodifluoromethane, 1,1-difluoroethane, 1,1-difluoro-1-chloroethane, 1,1,1,2-tetrafluoroethane, methyl chloride, Examples thereof include halogenated hydrocarbons such as ethyl chloride and methylene chloride, and mixtures thereof. Decomposable foaming agents such as azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile and sodium bicarbonate can also be used. Furthermore, inorganic gas such as carbon dioxide and water can be used as a foaming agent. These foaming agents can be appropriately mixed and used. Among these, it is preferable to use carbon dioxide, water, aliphatic hydrocarbons, etc. from the viewpoints of reducing environmental burden, ease of handling, and low cost. Although the usage-amount of a foaming agent is not specifically limited, It can select suitably according to the target foam density in the range of 0.01-0.1 mol in general per 100g of resin.
[0014]
Examples of the air conditioner include inorganic powders such as talc, kaolin, mica, silica, calcium carbonate, barium sulfate, titanium oxide, clay, aluminum oxide, bentonite, diatomaceous earth, sodium bicarbonate, monosodium citrate, etc. . These bubble regulators are usually used alone, but may be used in combination of two or more. As the particle size of the inorganic powder used as the bubble adjusting agent is smaller, the effect of reducing the bubble size of the foam is higher even when used in a smaller amount. From such a viewpoint, the average particle diameter (centrifugal sedimentation method) of the inorganic powder is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. However, if the average particle size is too small, the price of the inorganic powder is increased due to the processing, so 0.1 μm is preferable as the lower limit. Among the inorganic powders, talc is particularly preferable because it is effective and inexpensive.
[0015]
The foam produced by the above method usually contains a volatile low molecular weight component such as styrene dimer or styrene trimer in a proportion exceeding 2000 ppm by weight (hereinafter referred to as volatile low molecular weight component). For the sake of convenience, a polystyrene resin foam having a content of more than 2000 ppm by weight may be referred to as a “normal polystyrene resin foam”. Such “ordinary polystyrene resin foams” simultaneously release volatile low molecular weight components when the foamable molten resin is extruded from a die in the production process, and the released volatile low molecular weight components are cooled. There is a possibility that it will condense on the surface of the mandrel for use, the surface of the pinching roll, etc., and this may partially reattach to the extruded foam surface. And, if "normal polystyrene resin foam" to which condensate of volatile low molecular weight components is attached is thermoformed, the foam surface may partially melt into keloid or cracks may occur. There is.
[0016]
The polystyrene resin multilayer foam of the present invention is a sheet-like or plate-like multilayer foam having a plurality of polystyrene resin foam layers, and at least one surface side has a volatile low molecular weight component content of 2000 weight. It is composed of a layer of a polystyrene resin foam of ppm or less (hereinafter, this foam may be referred to as “low-volatile component-containing polystyrene resin foam” for convenience), The problem of “polystyrene resin foam” could be solved.
[0017]
“Polystyrene resin foam containing a low volatile component” is a foam of a condensate of a released volatile low molecular weight component with a small amount of volatile low molecular weight component released when the foam is extruded and foamed. Phenomenon that the foam surface is partially melted into a keloid or cracks, such as when thermoforming the foam, which is thought to be caused by re-adhesion to the surface (hereinafter, simply referred to as surface burn phenomenon) It is thought that it can prevent the occurrence of
[0018]
In the present invention, the volatile low molecular weight component content in the polystyrene resin foam is a value measured as follows, and is substantially the total amount of a styrene dimer and a styrene trimer. is there.
[0019]
(1) Sample preparation and measurement method
1. About 0.2 g of polystyrene resin foam is accurately weighed and dissolved in about 15 ml of tetrahydrofuran in a beaker.
2. After confirming that the polystyrene resin foam was completely dissolved in tetrahydrofuran, about 15 ml of the polystyrene resin tetrahydrofuran solution was dropped into about 250 ml of n-pentane to precipitate the polystyrene resin. Further, about 5 ml of tetrahydrofuran is placed in a beaker, the inside of the beaker is washed, and about 5 ml of tetrahydrofuran used for washing is further dropped into the n-pentane twice.
3. The polystyrene resin precipitated in n-pentane is filtered off using No. 5B filter paper. In the filtration, suction filtration is not performed and natural filtration is performed.
4). While keeping the beaker containing the filtrate in a 15 ° C. water bath, the filtrate is concentrated to about 100 ml over 6 to 8 hours while blowing the compressor air to the filtrate.
5. About 40 ml of acetonitrile is added to the filtrate concentrated to about 100 ml, and the filtrate is concentrated to about 6 to 9 ml over 2 to 3 hours while blowing compressor air to the filtrate while keeping the temperature in a water bath at 15 ° C.
6). A measurement sample is prepared by diluting the filtrate concentrated to about 6 to 9 ml with acetonitrile so that the total amount becomes 10 ml.
7). Measurement is performed by injecting a measurement sample into a high performance liquid chromatograph.
[0020]
(2) Measuring device (high performance liquid chromatograph)
Liquid feed pump LC-6A (2 units), automatic sample injection device SIL-6A, ultraviolet spectrophotometer detector SPD-6A, column oven CTO-6A, system controller SCL-6A, data processing device C-R3A, all ( Made by Shimadzu Corporation
[0021]
(3) Measurement conditions
Column: ULTRON VX-ODS (filler ODS silica, inner diameter 4.6 mm, length 250 mm, particle size 5 μm), manufactured by Shinwa Kako Co., Ltd.
Column temperature: 50 ° C
Mobile phase: Acetonitrile: water (volume ratio 6: 4) was used as the initial concentration, and acetonitrile was used alone for 13 minutes from the immediately after injection of the measurement sample, followed by further elution for 22 minutes.
Flow rate: 1.5 ml / min.
Detection wavelength: 225 nm
Injection volume: Adjust appropriately within the range of 5-100 μl
Calibration curve: A standard sample of styrene dimer and styrene trimer (manufactured by Kanto Chemical Co., Ltd.) is used and quantified by the absolute calibration curve method.
[0022]
In order to obtain a “low volatile component-containing polystyrene resin foam”, one of the raw material polystyrene resin having a content of volatile low molecular weight components of 2000 ppm by weight or less is used. More preferably, one having a weight of 1000 ppm by weight or less is selected and used. Especially when polymerizing polystyrene resins, those with short heat treatment time in polymerization history, those with less oxygen present in the polymerization system during polymerization, and those with higher vacuum during devolatilization, etc. Is preferred. Of the polystyrene resins, those by suspension polymerization are preferred among those by polymerization methods such as suspension polymerization, bulk polymerization, solution polymerization, and emulsion polymerization. In addition, in the extrusion foaming process, when melt-kneading polystyrene resin in the extruder, select an extruder equipped with a screw that prevents unnecessary shearing force from acting on the resin, and use a vent extruder to make it volatile. It is also a suitable method for obtaining a “low-volatile component-containing polystyrene resin foam” by adopting a method in which a low molecular weight component is discharged from a vent port and subjected to extrusion foaming.
[0023]
Even if the polystyrene-based resin multilayer foam of the present invention has a configuration in which only two layers of the above-mentioned “low-volatile component-containing polystyrene-based resin foam” are laminated, at least one surface is “ Consists of a low-volatile component-containing polystyrene resin foam and a laminate of two or more layers of low-volatile component-containing polystyrene resin foam and normal polystyrene resin foam. You may have. The overall density of the multilayer foam of the present invention is 0.05 to 0.7 g / cm. Three Is more preferable, and 0.1 to 0.5 g / cm is more preferable. Three It is. Density is 0.05g / cm Three If the ratio is less than 1, not only the strength of the container obtained by molding the multilayer foam may be insufficient, but there may be a case where the container is not sufficiently stretched to form a hole in the container. On the other hand, the density is 0.7 g / cm Three Exceeding this will cause problems such as lightness and economy, and the heat insulation of the container will decrease, and if food is put in the container and heated, it will become too hot to hold by hand, and the heat insulation characteristic of the foam container will be It may be insufficient. The thickness of the multilayer foam is preferably 0.7 to 7 mm, and more preferably 0.7 to 3 mm. If the thickness is less than 0.7 mm, there is a possibility that it cannot be practically used in terms of strength and heat insulation. If the thickness exceeds 7 mm, uneven heating between the inside and the outside of the foam tends to occur during thermoforming, and precise temperature control is required.
[0024]
In addition, in the case of a multilayer foam in which only two layers of “low volatile component-containing polystyrene resin foam” are laminated, each “low volatile component-containing polystyrene resin foam” layer has an average It is preferable that a bubble diameter is 0.02-0.45 mm, More preferably, it is 0.03-0.3 mm. In order to make the appearance and printability good, the average cell diameter is preferably fine, but if it is too fine, the foam is insufficient in moldability and rigidity. On the other hand, if the average cell diameter is too large, a good appearance and printability cannot be obtained. Furthermore, each “low volatile component-containing polystyrene resin foam” layer preferably has an open cell ratio of 40% or less, more preferably 25% or less. When the open cell ratio is high, the secondary foamability of the foam is reduced during thermoforming and the like, so that the mold reproducibility of the foam deteriorates (it is difficult to obtain a molded body according to the shape of the mold). Deterioration of thermoformability such as occurrence of insufficient thickness of the molded body is observed. Further, the strength of the obtained molded body is weak at the same density. However, when used for applications such as a water-absorbing material, the open cell ratio is not necessarily low, and may be 50% or more.
In the present invention, the open cell ratio of the foam is a value determined by ASTM D2856, Procedure C.
[0025]
In the case of a multi-layer foam composed of a layer of “low-volatile component-containing polystyrene resin foam” and “ordinary polystyrene-based resin foam”, “low-volatile component-containing polystyrene resin foam” The thickness of the “body” layer is preferably 0.3 to 4 mm from the viewpoint of production cost and the like. In addition, when obtaining the multilayer foam in which the thickness of the polystyrene resin foam layer having a volatile low molecular weight component of 2000 ppm by weight or less is thin, specifically, “low volatile component-containing polystyrene resin foam” of less than 0.7 mm. In the case of those having the above layer, it is particularly preferable to obtain a multilayer foam by a coextrusion foaming method. Also in the case of this multilayer foam, the layer of “low-volatile component-containing polystyrene resin foam” has a density of 0.05 to 0.7 g / cm. Three The average cell diameter is preferably 0.02 to 0.45 mm, more preferably 0.1 to 0.5 g / cm. Three The average cell diameter is 0.15 to 0.45 mm, and the open cell rate is 40% or less. Furthermore, the layer of the low volatile component-containing polystyrene resin foam is preferably 40% or less of open cell ratio, more preferably 25% or more of open cell ratio. The open cell ratio may be 50% or more.
[0026]
On the other hand, the layer of “ordinary polystyrene resin foam” constituting the multilayer foam may be composed of a conventional polystyrene resin foam, and its density is preferably 0.05 to 0.7 g / cm. Three More preferably, 0.1 to 0.5 g / cm Three It is. “Normal polystyrene resin foam” layer density is 0.05 g / cm Three If it is less than the range, the moldability and the strength of the molded product may be insufficient. On the other hand, 0.7 g / cm Three If it exceeds 1, the lightness and heat insulating properties may be insufficient. In addition, the thickness of the “normal polystyrene-based resin foam” layer is preferably 0.5 to 5 mm from the viewpoints of moldability and the strength of the molded body, and more preferably 0.9 to 4 mm. Moreover, the average cell diameter of the layer of “ordinary polystyrene resin foam” is preferably 0.02 to 0.45 mm, more preferably 0.02 to 0.4 mm. If the average cell diameter is too small, the foam is insufficient in moldability and rigidity, and if the average cell size is too large, good appearance and printability cannot be obtained. Further, the open cell ratio of the layer of “ordinary polystyrene resin foam” is preferably 40% or less, more preferably 25% or less. Multi-layer foams with a high open-cell ratio have low thermofoaming properties such as deterioration of mold reproducibility of foams and occurrence of thicknesses and thinnesses of molded products because the secondary foamability of foams is reduced during thermoforming. There is a decline.
[0027]
The multilayer foam of the present invention has a two-layer structure in which a layer of “low-volatile component-containing polystyrene resin foam” and a layer of “ordinary polystyrene resin foam” are laminated one by one. It is not limited to the above, and a structure in which a layer of “ordinary polystyrene resin foam” is used as a core layer, and layers of “low-volatile component-containing polystyrene resin foam” are laminated on both sides, A structure in which a layer of “low-volatile component-containing polystyrene-based resin foam” is laminated on a layer in which layers of ordinary polystyrene-based resin foam are laminated, “low-volatile component-containing polystyrene-based resin foam” Even if a plurality of foam layers are laminated, such as those obtained by laminating a layer of “body” and a layer of “ordinary polystyrene resin foam” via a non-foamed polystyrene resin Between each foam layer, May be one having a layer made of a foamed resin, a layer of at least "low volatility component containing polystyrene resin foam" is, as long as it is formed on one surface side of the multilayer foamed body.
[0028]
In the multilayer foam of the present invention, at least one surface side is formed of the above-mentioned “low volatile component-containing polystyrene resin foam” layer, so that one surface of the foam is brought into contact with the heating plate. When softening and then molding from one side of the foam, such as so-called hot plate molding, which is molded with a mold, the layer side of the “low-volatile component-containing polystyrene resin foam” is heated. By doing so, it is possible to prevent the occurrence of a surface burn phenomenon of the foam. In addition, when both sides of the multilayer foam are formed of the above-mentioned “low volatility low component-containing polystyrene resin foam” layer, the surface of the multilayer foam is burned regardless of which side is heated. Can be prevented.
[0029]
In addition, (1) a multilayer foam in which one surface side is composed of a “low volatile component-containing polystyrene resin foam” layer and the other surface side is composed of a “normal polystyrene resin foam” layer ( (Including not only a two-layer structure but also a structure of three or more layers) was manufactured by the coextrusion foaming method using the annular die described above, and the extruded and foamed cylindrical multilayer foam was cooled with a mandrel. Thereafter, when a sheet-like foam is obtained by cutting open, a layer of “low-volatile component-containing polystyrene resin foam” is formed on the inner surface side of the cylindrical multilayer foam (that is, the side in contact with the mandrel). It is preferable to perform extrusion foaming.
[0030]
(2) When a co-extrusion-formed cylindrical multilayer foam is made into a plate-like foam by crushing with a pinching roll without being cooled by a mandrel and fusing the inner surface side, The component-containing polystyrene-based resin foam "is preferably extruded and foamed so as to be formed on the outer surface side (side in contact with the pinching roll) of the cylindrical multilayer foam.
[0031]
The multilayer foam obtained by the above methods (1) and (2) can prevent the occurrence of the surface burn phenomenon of the multilayer foam, regardless of which surface is heated.
[0032]
The “low-volatile component-containing polystyrene resin foam” is superior in rigidity to the “normal polystyrene resin foam”, but has some room for improvement in terms of elongation and flexibility during molding. Therefore, as described above, one side of the multilayer foam is formed with a layer of “low-volatile component-containing polystyrene resin foam” and the other side is formed with a layer of “ordinary polystyrene resin foam” By doing so, the elongation and brittleness of the multilayer foam during thermoforming are improved, and it becomes excellent in thermoformability such as deep drawing and punchability.
[0033]
Further, in order to further improve the printability and moldability of the multilayer foam of the present invention, the average cell diameter of the foam layer on one surface side is set to 20 to 140 μm, and the foam layer on the other surface side is formed. The average cell diameter is preferably 150 to 450 μm. In this case, a foam layer having an average cell diameter of 150 to 450 μm is composed of a “low-volatile component-containing polystyrene resin foam”, and a foam layer having an average cell diameter of 20 to 140 μm is “normal polystyrene system”. It is particularly preferable from the viewpoint of moldability that the resin foam is used. Moreover, the multilayer foam of this invention can carry out the lamination | stacking adhesion | attachment of the layer of each foam from which an open cell rate and thickness differ according to a use.
[0034]
The multilayer foam having the “low-volatile component-containing polystyrene resin foam” layer of the present invention may have a structure in which layers of non-foamed thermoplastic resins are laminated. Examples of the thermoplastic resin constituting the non-foamed thermoplastic resin layer include polystyrene resins such as high impact polystyrene, polyolefin resins such as high density polyethylene and polypropylene resins, and polyester resins such as polyethylene terephthalate and polyethylene naphthalate. Etc.
[0035]
As a typical method for producing a multilayer foam having a non-foamed thermoplastic resin layer, (1) a multilayer foam is produced by the extrusion foaming method described above, and then this foam is subjected to the production line. Or a method of laminating and adhering a sheet-like thermoplastic resin through a hot roll or the like in a separate line, (2) a method of laminating and adhering each foam layer and the thermoplastic resin layer by coextrusion, and (3) an extruder. A multilayer foam is manufactured by the following, and then, a thermoplastic resin extruded from another extruder is laminated and bonded to the foam on a production line or in another line, and (4) each by an extrusion foaming method. Method for producing foams, laminating sheet-like thermoplastic resins on the production line or on another line, and laminating and adhering each foam and sheet-like thermoplastic resin with hot air or hot roll Etc. The thickness of the non-foamed sheet-like thermoplastic resin is preferably 0.01 to 0.5 mm, and particularly preferably 0.02 to 0.2 mm. If it is less than 0.01 mm, it is stretched and further thinned during thermoforming, so that tears and pinholes are likely to occur. When the thickness exceeds 0.5 mm, adhesion to the foam becomes difficult, resulting in high cost. In the non-foamed thermoplastic resin layer, various additives such as an antioxidant, a heat stabilizer, an antistatic agent, a conductivity imparting agent, an ultraviolet ray inhibitor, a colorant, a flame retardant, and an inorganic filler are added as necessary. An agent or the like can be added.
[0036]
The container of this invention is a container formed by thermoforming the multilayer foam mentioned above. As thermoforming methods for multilayer foams, these are heat-softened, vacuum forming method and / or pressure forming method using a die, and further, forming methods such as matched mold forming method and plug assist forming method using them And are mainly molded into containers such as trays, cups, bowls, lunch boxes and the like. In addition, in the case of a multilayer foam in which the layer of “low volatile component-containing polystyrene resin foam” is provided only on one side, the layer of “low volatile component-containing polystyrene resin foam” on the inner side of the container From the viewpoint of thermoforming, it is preferable to thermoform the multilayer foam so that is located. The container of the present invention is excellent in appearance and rigidity. In particular, the layer of “low-volatile component-containing polystyrene resin foam” is located on the inner surface of the container, and the “ordinary polystyrene resin foam” layer is the container. Containers located on the outer surface side are further improved in brittleness and are excellent in flexibility, appearance and rigidity, and suitable for deep-drawn containers such as bottles and cups and low stack trays with low stacking height that require rigidity. Is.
[0037]
【Example】
Next, the present invention will be described in more detail with reference to examples.
[0038]
Example 1
95.5 parts by weight of polystyrene resin A (polystyrene resin manufactured by Denki Kagaku Kogyo Co., Ltd., trade name “GX-0196”) and 1 part by weight of talc as an air conditioner were put into a 60 mm diameter extruder. After heating, 3.5 parts by weight of a mixed butane blowing agent consisting of 65% by weight of isobutane and 35% by weight of normal butane was pressed into the molten polystyrene resin A in the extruder and melt-kneaded at about 200 ° C. Next, the melt-kneaded product was extruded into a 90 mm diameter extruder connected to the extruder and cooled in the extruder to obtain a foamable molten resin having a temperature of about 157 ° C. On the other hand, polystyrene resin B (polystyrene resin manufactured by Idemitsu Petrochemical Co., Ltd., trade name “HH32”) is 95.5 parts by weight, talc is 1 part by weight as an air conditioner, and another 60 mm diameter extruder. And heated to about 200 ° C. after being injected into the molten polystyrene resin B in the extruder with 3.5 parts by weight of a mixed butane blowing agent consisting of 65% by weight of isobutane and 35% by weight of normal butane. It extruded and cooled in the 90 mm diameter extruder connected with the said extruder, and about 157 degreeC foamable molten resin was obtained. After the foamable molten resin in each extruder is merged with a confluent annular die and laminated, it is co-extruded from the die at about 157 ° C. so that the foam layer made of polystyrene resin A is on the inner surface side. The surface is cooled while expanding the diameter and further cooled while being transferred so that the inside of the cylindrical foam is in contact with the mandrel, and the extrusion direction is performed by one cutter knife fixed on the downstream side of the mandrel. A cylindrical foam was incised along the line. Subsequently, it was rolled out from the cut portion to form a sheet and continuously wound into a roll. The obtained multilayer foam sheet has a width of 1040 mm, a thickness of 2.5 mm, and a density of 0.11 g / cm. Three Met.
[0039]
Reference example 1
Polystyrene resin A is 95.5 parts by weight, and talc is used as a foam control agent in a ratio of 1 part by weight into an extruder having a diameter of 60 mm and heated, and then mixed butane foamed from 65% by weight isobutane and 35% by weight normal butane. 3.5 parts by weight of the agent was press-fitted into the molten polystyrene resin A in the extruder and melt-kneaded at about 200 ° C. Next, the melt-kneaded product is extruded into a 90 mm diameter extruder connected to the extruder, cooled to about 157 ° C. in the extruder, then extruded from an annular die at the same temperature and foamed into a cylindrical shape, and the diameter The surface is cooled while enlarging, and further cooled while being transferred so that the inside of the cylindrical foam is in contact with the mandrel, and the cylindrical foam is formed along the extrusion direction by one cutter knife fixed to the mandrel downstream side. The body was incised. Subsequently, it was rolled out from the cut portion to form a sheet and continuously wound into a roll. The obtained foamed sheet had a width of 1040 mm, a thickness of 2.3 mm, and a density of 0.11 g / cm. Three Met.
[0040]
Reference example 2
A sheet-like polystyrene resin foam was prepared in the same manner as in Reference Example 1 except that a mixed butane foaming agent composed of 65% by weight of polystyrene resin A, talc and isobutane and 35% by weight of normal butane was melt-kneaded at about 250 ° C. Obtained.
[0041]
Comparative Example 1
A sheet-like polystyrene resin foam was obtained in the same manner as in Reference Example 1 except that polystyrene resin B was used in place of polystyrene resin A.
[0042]
Table 1 shows the results of measurements of various physical properties such as the content of volatile low molecular weight components for the multilayer foams or foams obtained in the above Examples, Reference Examples and Comparative Examples. Table 1 also shows the results of thermoforming the multilayer foam or foam. The physical properties and evaluation in Table 1 were performed as follows. The volatile low molecular weight component content and the open cell ratio were measured by the methods described above.
[0043]
Foam density
For a single-layer foam, a test piece of 2 cm long × 2 cm wide × foam thickness (cm) was cut out, the weight (g) of the test piece was measured, and the weight was 2 cm long × 2 cm wide × foam thickness ( Test piece volume (cm) Three ). Moreover, in the case of a multilayer foam, in each foam laminated | stacked, cut out the test piece of 2 cm long x 2 cm wide x arbitrary foam thickness (cm), and measure the weight (g) of a test piece, Specimen volume (cm) obtained by calculating the weight from 2 cm long × 2 cm wide × foam thickness (cm) Three ) Divided by However, the thickness of the test piece was set as thick as possible. If any one of the foam layers is thin, the density of the foam in that layer is calculated by calculating back from the density of the foam in the other layer and the density of the entire multilayer foam. May be.
[0044]
Foam thickness
The thicknesses at 20 arbitrary positions in the vertical cross section in the thickness direction of the foam were measured, and the arithmetic average value of these values was adopted.
[0045]
Average bubble diameter
A straight line is drawn in the foam thickness direction over the entire thickness (mm) of the foam (in the case of multilayer foam, the total thickness (mm) of each foam layer), and the length (mm) of the straight line is linear. It was obtained by dividing by the number of bubbles.
[0046]
Formability
The multilayer foams or foams obtained in the examples, reference examples and comparative examples are formed into a truncated cone-shaped container having an opening shape of 150 mm diameter, a bottom surface diameter of 120 mm, a depth of 60 mm or 30 mm by a single molding machine. The moldability was evaluated according to the following criteria when a cup was molded by vacuum molding using a metal mold. In addition, about the multilayer foam of Example 1, it shape | molded so that the layer of a "low volatile component containing polystyrene resin foam" might become the cup inner surface side.
(Double-circle): The mold reproducibility of the container shape | molded using the 60 mm deep metal mold | die is favorable.
○: The mold reproducibility of a container molded using a mold having a depth of 30 mm is good, and the mold reproducibility of a container molded using a mold having a depth of 60 mm is somewhat inferior.
X: The mold reproducibility of a container molded using a mold having a depth of 30 mm is inferior.
[0047]
appearance
The appearance of 5000 containers formed using the above-described mold having a depth of 30 mm was observed and evaluated according to the following criteria.
○: None of the surface of the container shows keloid-like melting or cracking.
X: Some of the surface of the container shows keloid-like melting and / or cracking.
[0048]
rigidity
The container formed using the above-mentioned 30 mm deep mold is mounted on the lip strength measuring device so that the opening surface is in the vertical direction, and the lip portion forming the opening surface is compressed by 10 mm in the vertical direction. The stress at this time was defined as lip strength (gf), and evaluation was performed according to the following criteria.
○: Lip strength is 500 gf or more.
Δ: Lip strength is less than 500 gf.
[0049]
[Table 1]
【The invention's effect】
The polystyrene-based resin multi-layer foam of the present invention is capable of obtaining a molded body having a good appearance and excellent rigidity without the risk of partial occurrence of keloid-like melting or cracks on the foam surface during thermoforming. it can. In addition, when producing foam continuously for several days, there is almost no need to temporarily stop production and clean the surface of mandrels, pinching rolls, etc. as in the past, and productivity is good. is there. Furthermore, in the case of a multilayer foam in which a layer of “low-volatile component-containing polystyrene resin foam” and a “normal polystyrene resin foam” layer are laminated, in addition to the above effects, Elongation and brittleness are improved and it becomes excellent in thermoformability such as deep drawing and punching workability. Especially, one surface side is composed of a layer of “low-volatile component-containing polystyrene resin foam” and the other surface Those composed of a layer of “normal polystyrene resin foam” on the side are further excellent in these effects. In addition, a multilayer foam formed by laminating a layer of “low-volatile component-containing polystyrene resin foam” and a layer of “normal polystyrene resin foam” is called “normal polystyrene resin foam”. Since the absolute amount of the resin constituting the “low volatility component-containing polystyrene resin foam”, which is less productive than the constituent resin, can be reduced, the production cost can be reduced.
[0051]
The container of the present invention is excellent in appearance and rigidity. In particular, the layer of “low-volatile component-containing polystyrene resin foam” is located inside the container, and the “ordinary polystyrene resin foam” layer The container located on the outer surface of the container is further improved in brittleness and excellent in flexibility, appearance, and rigidity, and is suitable for deep-drawn containers such as bottles and cups and low stack trays.
Claims (7)
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| Application Number | Priority Date | Filing Date | Title |
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| JP15434299A JP4301467B2 (en) | 1999-06-01 | 1999-06-01 | Polystyrene resin multilayer foam and container comprising the multilayer foam |
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| Application Number | Priority Date | Filing Date | Title |
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| JP15434299A JP4301467B2 (en) | 1999-06-01 | 1999-06-01 | Polystyrene resin multilayer foam and container comprising the multilayer foam |
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| JP4301467B2 true JP4301467B2 (en) | 2009-07-22 |
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| GB2474431B (en) | 2009-10-13 | 2012-10-31 | Gurit Uk Ltd | Production of extruded foam |
| MX2014014206A (en) | 2012-05-22 | 2015-06-04 | Owens Corning Intellectual Cap | Laminated foam product and methods for making laminated foam products. |
| JP2015066917A (en) * | 2013-09-30 | 2015-04-13 | 積水化成品工業株式会社 | Laminated foam sheet and sheet molding |
| JP6588855B2 (en) * | 2016-03-30 | 2019-10-09 | 積水化成品工業株式会社 | Polystyrene resin foam sheet, laminated sheet, container and lid |
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