JP4042894B2 - Production method of polystyrene resin foam sheet for thermoforming and polystyrene resin foam sheet - Google Patents

Description

上記一般式（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。
【００２８】
上記スチレンの単独重合体や共重合体は、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。
【００２９】
上記ポリスチレン系樹脂は、ビカット軟化点が１００℃以上のものを使用することが、発泡シートの耐熱性を向上させることができるので好ましい。ビカット軟化点の上限は、特に制限はないが通常は１３０℃である。
尚、該ビカット軟化点はＪＩＳＫ７２０６（１９９１）（試験荷重はＡ法、液体加熱法の昇温速度は５０℃／時）にて求められる。
【００３０】
前記ポリスチレン系樹脂として、脆性改善等が要求される場合は、耐衝撃性ポリスチレン、スチレン−共役ジエンブロック共重合体や、該共重合体の水添物を用いることが好ましい。
【００３１】
又、前記ポリスチレン系樹脂には、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、難燃剤、無機充填剤、化学発泡剤等を添加することができ、又その他の熱可塑性樹脂を混合することもできる。
【００３２】
本発明方法においては、通常、前記ポリスチレン系樹脂に気泡調整剤を添加することにより、得られる発泡シートの気泡径の調整が行われる。該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種以上組合せて用いてもよい。
【００３３】
気泡調整剤として用いる無機物粉末は、粒子系が小さいほど発泡シートの気泡径を小さくする効果が大きいので、使用量が少なくても気泡径を小さくすることができる。かかる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。但し、平均粒子径が小さくなるほど加工に費用がかかり、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、タルクが気泡径を小さくする効果が大きいと共に安価なので最も好ましい。
【００３４】
本発明方法において用いられる前記物理発泡剤としては、（ｉ）イソブタン、ノルマルペンタン、イソペンタンの中から選択される１種以上の発泡剤が合計５０〜９５モル％、（ii）炭酸ガス、水、沸点１４０℃以下のエーテル、沸点１４０℃以下のジアルキルカーボネートの中から選択される１種以上の発泡剤が合計５〜５０モル％、これら（ｉ）の発泡剤と（ii）の発泡剤との混合物理発泡剤（但し、混合物理発泡剤に含まれる（ｉ）の発泡剤と（ii）の発泡剤との発泡剤量の合計は１００モル％である。）を主成分とするものが使用される。
【００３５】
また、好ましくは前記物理発泡剤として、（iii）イソブタン５０〜９５モル％、（iv）炭酸ガス、水、沸点１４０℃以下のエーテルの中から選択される１種以上の発泡剤が合計５〜５０モル％、これら（iii）の発泡剤と（iv）の発泡剤との混合物理発泡剤（但し、混合物理発泡剤に含まれる（iii）の発泡剤と（iv）の発泡剤との発泡剤量の合計は１００モル％である。）を主成分とするものが使用される。
【００３６】
尚、本発明において混合物理発泡剤を物理発泡剤の主成分とするとは、本発明の目的、効果を阻害しない範囲でその他の物理発泡剤を併用することができることを意味するものであり、前記混合物理発泡剤は物理発泡剤に対して概ね８０モル％以上、好ましくは８５モル％以上、更に好ましくは９０モル％以上含有される。上記その他の物理発泡剤としては、例えば、プロパン、ノルマルブタン等が挙げられる。但し、ノルマルブタンのような、ポリスチレン系樹脂に対する透過速度が空気の約１／８の発泡剤の含有量は少ないほど好ましく、具体的には、押出発泡に使用される物理発泡剤１００重量部に対して０〜１０重量部の範囲内とすることが好ましい。
【００３７】
上記の通り特定される物理発泡剤を用いると、驚くべきことに冬季であっても夏季よりも速い熟成期間（例えば２週間以下）で熱成形が可能になると共に、短い熟成期間であっても、ロール状に巻いた発泡シートの巻き方向及び幅方向における熱成形性が安定し、一定の二次厚みの成形品を得ることができ、しかもシートライフが長い発泡シートを製造することができる。
【００３８】
前記混合物理発泡剤は、５０〜９５モル％のイソブタン、ノルマルペンタン、イソペンタンの中から選択される１種以上の発泡剤（以下、残留発泡剤ともいう。）を含有する。残留発泡剤の含有量が５０％未満の場合は、得られる発泡シートの二次発泡厚が小さなものとなる。シートライフが長く、製造後４０日経過後でも十分な二次発泡厚を得ることができるという点からは、混合物理発泡剤が残留発泡剤、特にイソブタンを７０〜９５モル％含むことが好ましい。
【００３９】
一方、混合物理発泡剤が残留発泡剤を９５モル％超含む場合は、残留発泡剤の可塑化効果により発泡シートの熱成形可能な加熱温度や加熱時間の範囲が狭くなる虞がある。即ち、わずかでも加熱しすぎると発泡シートの表面荒れが発生するのに対し、加熱しすぎを警戒して加熱時間を短めにすると加熱不足になり、発泡シートが破れたり、金型形状通りの成形品を得ることができなくなるという不都合が発生しやすくなる。かかる不都合を回避するためには、混合物理発泡剤に含まれる残留発泡剤が９０モル％以下であることが好ましい。
【００４０】
尚、前記の残留発泡剤の効果は、残留発泡剤のポリスチレン系樹脂に対する透過速度が極めて遅い（空気のポリスチレン系樹脂に対する透過速度の（１／１０）以下である。）ことに起因するものである。
【００４１】
従って、本発明の技術に基づいて、残留発泡剤の代わりにポリスチレン系樹脂に対する透過速度が極めて遅い発泡剤を用いることができることが想起され、前記のもの以外にも存在してくることが予想される。よって、本発明の技術によれば、ポリスチレン系樹脂に対する透過速度が空気に対して極めて遅いものであって、ポリスチレン系樹脂と共に押出機にて加熱、混練して発泡性溶融樹脂とし、該発泡性溶融樹脂を押出発泡すことさえできれば、残留発泡剤の代わりに、いかなる発泡剤であっても使用することができるといえる。
【００４２】
本発明方法で用いる混合物理発泡剤は、炭酸ガス、水、沸点１４０℃以下のエーテル、沸点１４０℃以下のジアルキルカーボネートの中から選択される１種以上からなる発泡剤（以下、早期逸散発泡剤という。）を５〜５０モル％含む。これらの発泡剤のポリスチレン系樹脂に対する透過速度は極めて速く、ポリスチレン系樹脂に対する空気の透過速度よりも数倍速い（空気のポリスチレン系樹脂に対する透過速度の５倍を超える）ので、大部分が発泡シート製造直後に発泡シートから逸散し、たとえ該発泡剤が多少発泡シート中に残ったとしても製造後極めて早期に発泡シートから逸散する。従って、ノルマルブタンのように、熟成期間中徐々に発泡シート外へ散逸することにより、ロール状の外側と内部で発泡剤量が大きく異なるということがないので、ロール状の巻き方向及び幅方向における発泡剤量が均一なものとなる。
【００４３】
又、多少の早期逸散発泡剤が発泡シート中に残ったとしても早期逸散発泡剤はポリスチレン系樹脂に対する透過速度が空気より速いため、空気が気泡内に入ってくるより早期逸散発泡剤が気泡から出て行く速度が速いので、発泡シートの気泡内部の圧力が大きく高まることはない。従って、従来のロール状に巻かれた発泡シートのように、養生初期において発泡シートどうしが互いにきつく締め付けあって、ロール状に巻かれた発泡シート内からの物理発泡剤の流出、発泡シート外からの空気の流入を妨げるような状態になることがない。むしろ、従来のロール巻きの締付け状態と比較すると、発泡シートどうしの締付け状態が多少緩めになるので、発泡シートどうしの間を通って空気が効率よく流通することとなるものと考えられる。
【００４４】
また、熟成期間中に発泡シート内部への空気透過により気泡内圧が上昇し、ロール巻きされた発泡シートどうしの締め付けがきつくなるという現象が、冬季においては発泡体の剛性の増加により抑制されるため、更に空気が効率よく流通することが期待される。
【００４５】
前記沸点１４０℃以下のエーテルとして、沸点が−３０〜１００℃のエーテルを用いることが好ましく、沸点が−３０〜４０℃のエーテルを用いることがより好ましく、エチルメチルエーテル、ジメチルエーテル、ジエチルエーテルを用いることが更に好ましい。
【００４６】
前記沸点１４０℃以下のジアルキルカーボネートとして、沸点が−１０〜１３０℃のジアルキルカーボネートを用いることが好ましく、ジメチルカーボネート、ジエチルカーボネート、ジイソプロピルカーボネートを用いることが更に好ましい。
【００４７】
尚、前記早期逸散発泡剤は、安全性の点からは水、炭酸ガスを用いて構成されていることが好ましい。
【００４８】
本発明の混合物理発泡剤は、前記早期逸散発泡剤を５〜５０モル％含み、好ましくは７〜４０モル％、より好ましくは１０〜２５モル％含むものである。該早期逸散発泡剤の含有量が５モル％未満の場合は、得られる発泡シートの熱成形性が低下する。一方、早期逸散発泡剤の含有量が５０モル％を超えると、得られる発泡シートの二次発泡厚が小さなものとなる。
【００４９】
本発明方法においては、前記混合物理発泡剤を主成分とする物理発泡剤を使用して発泡シートを製造するので、従来技術において多量に併用していたノルマルブタンが発泡シートから徐々に逸散するのとは異なり、押出発泡後急速に早期逸散発泡剤が逸散する。従って、製造後短期間で気泡内部の発泡剤或いは発泡シートを構成するポリスチレン系樹脂に溶け込んでいる発泡剤の大部分が残留発泡剤となる。従って、その後の熟成工程において空気が気泡内部に取り込まれるだけで、充分且つ均一な二次発泡性を示す発泡シートとなる。
【００５０】
本発明方法により得られた発泡シートは、イソブタンを多量に使用する公知技術によって得られる発泡シートの抱えていた二つの問題、熱成形時に表面が荒れやすくなる、熟成期間が長くなるという問題を、残留発泡剤と早期逸散発泡剤とが特定範囲内で配合された混合物理発泡剤を用いて解決したものである。即ち、必要以上のイソブタンが発泡シート中に含まれないようにすることにより、熱成形時の表面荒れを防ぎ、熟成工程においては空気が気泡中に取り込まれるだけで熱成形が可能になる。更に、ロール巻きにされた内側の発泡シートの内部にも容易に空気が取り込まれるようになっていると考えられ、そのことによっても熟成工程の短縮化が図られていると思われる。しかも、発泡シート中に含まれるガスが残留発泡剤と空気のみになので、シートライフが長い発泡シートとなる。
【００５１】
本発明方法により得られた発泡シートは、以上説明したように、気泡内に残留発泡剤と空気を含有するので長期間に亘り良好な二次発泡性を示すのでシートライフが長くなる。また、早期逸散発泡剤が製造後直ちに逸散するので、該早期逸散発泡剤の使用量に対応してロール状に巻かれた発泡シートどうしの締付けが抑制されていると考えられ、結果として空気がロール巻きにされた内側の発泡シートの内部にも早期に取り込まれることとなり、熟成期間が短縮される。
【００５２】
尚、本発明方法の技術に基づいて用いることができる早期逸散発泡剤は前記のもの以外にも存在してくることが予想される。従って、ポリスチレン系樹脂に対する透過速度が空気に対して数倍速いものであって、ポリスチレン系樹脂と共に押出機にて加熱、混練して発泡性溶融樹脂とし、該発泡性溶融樹脂を押出機内の高圧域から低圧域に押出すことさえできれば、いかなる発泡剤であっても使用することができる。
参考として、空気のポリスチレン系樹脂に対する透過速度を１００とした場合の各種発泡剤の透過速度を表１に示す。
【００５３】
【表１】

【００５４】
本発明方法においては、下記（１）式を満足する量の物理発泡剤を押出機内に圧入することが好ましい。
【００５５】
【数３】
５０（モル／ｍ^３）≦α・ｄ≦９０（モル／ｍ^３）……（１）
【００５６】
但し、αは押出発泡に使用するポリスチレン系樹脂１ｋｇに対する物理発泡剤の合計モル数（モル／ｋｇ）、ｄは押出発泡にて得られる発泡シートの見かけ密度（ｋｇ／ｍ^３）である。
【００５７】
α・ｄが５０（モル／ｍ^３）未満の場合は、目的とする見かけ密度の発泡シートを得ても、熱成形時における十分な二次発泡厚が得られないものとなる虞がある。一方、９０（モル／ｍ^３）を超える場合は、目的とする見かけ密度の発泡シートを得ても、熱成形性に劣るものとなる虞がある。
【００５８】
本発明方法によって得られる発泡シートの見かけ密度は、好ましくは７０〜３００（ｋｇ／ｍ^３）であり、更に好ましくは７０〜１５０（ｋｇ／ｍ^３）であり、特に好ましくは９０〜１５０（ｋｇ／ｍ^３）である。見かけ密度が小さすぎる場合は、熱成形性が悪くなり、金型通りの形状の成形品を得ることができなくなる虞がある上に、得られる成形品の強度も低下する虞がある。一方、見かけ密度が大きすぎる場合は、軽量性、断熱性、緩衝性等の発泡体の特徴が失われる虞がある。
【００５９】
本明細書における発泡シートの見かけ密度は、発泡シートの単位面積あたりの重量を、発泡シートの厚みにより除した値を単位換算することにより求められる。
【００６０】
熱成形用ポリスチレン系樹脂発泡シートは前述した本発明方法により製造することができる。該発泡シートの厚みは、０．５〜５ｍｍであり、好ましくは０．５〜３．５ｍｍであり、より好ましくは０．７〜３ｍｍである。厚みが薄すぎる場合は、熱成形によって得られる成形品の強度が低下しすぎる虞があり、厚みが厚すぎる場合は、熱成形性が悪くなり、成形品に厚みむらが発生する虞がある。
【００６１】
本明細書における発泡シートの厚みの測定は、発泡シートの全幅に沿って等間隔に１０個所厚みを測定し、求められた各測定値の算術平均値を発泡シートの厚みとする。
【００６２】
本発明により得られる発泡シートの見かけ密度が特に７０〜１５０（ｋｇ／ｍ^３）である場合は、熱成形性に優れると共に、軽量性、断熱性、緩衝性が特に優れたものとなる。
【００６３】
本発明により得られる発泡シートにおいては、有機系物理発泡剤の合計残存量が発泡シート１ｋｇに対して０．４５〜０．７０モル、更に０．６０〜０．７０モルであることが好ましい。該合計残存量が少なすぎる場合は、熟成工程において大気と等しい圧力の空気が発泡シートに取り込まれても、二次発泡厚が不十分な発泡シートになる。一方、多すぎる場合は、熱成形時に発泡シートの表面荒れが発生する等の熱成形性が劣るものとなる。
【００６４】
本発明により得られる発泡シートにおいては、前記有機系物理発泡剤の合計残存量の条件に加えて、イソブタン、ノルマルペンタン、イソペンタンから選択される残留発泡剤の合計残存量が有機系物理発泡剤の合計残存量に対して９０〜１００モル％であることが好ましい。該残留発泡剤の合計残存量が少なすぎる場合は、熟成工程に要する時間の短縮、発泡シートのロングライフ化、発泡シートの巻き方向及び幅方向における熱成形性が安定するという効果を同時に達成できない虞がある。
【００６５】
本明細書における有機物理発泡剤の残存量の測定は、発泡シートから採取した測定試料を、トルエンを入れた蓋付の試料ビンの中に入れ、撹拌して発泡シート中の発泡剤をトルエンに溶解させた後、発泡剤を溶解したトルエンをマイクロシリンジで採取してガスクロマトグラフィー分析にかけて、内部標準法により求めることができる。
【００６６】
本発明により得られる発泡シートはその連続気泡率が０〜１５％、更に０〜１０％であることが、熱成形時の二次発泡性に優れたものとなり、得られる成形品の機械的強度、厚みの均一性において特に良好なものとなる点から好ましい。
【００６７】
本明細書における連続気泡率の測定は、ＡＳＴＭ Ｄ−２８５６−７０(手順Ｃ)に準じて次の様に行なわれる。
エアピクノメーターを使用して測定試料の真の体積Ｖｘ（ｃｍ³）を求め、測定試料の外寸から見掛けの体積Ｖａ（ｃｍ³）を求め、下記（２）式により連続気泡率（％）を計算する。尚、真の体積Ｖｘとは、測定試料中の樹脂の体積と独立気泡部分の体積との和である。
【００６８】
【数４】
連続気泡率（％）＝｛（Ｖａ−Ｖｘ）／（Ｖａ−Ｗ／ρ）｝×１００ ……（２）
【００６９】
（２）式において、Ｗは測定試料の重量（ｇ）、ρは発泡シートを構成する基材樹脂の密度（ｇ／ｃｍ³）である。
【００７０】
連続気泡率の測定における測定試料の寸法は縦２５ｍｍ、横２５ｍｍ、厚み４０ｍｍである。本発明においては、１枚のサンプルでは上記測定試料の寸法に適合した寸法のものが得られないので、複数のサンプルを重ね合わせて１つの測定試料を調製する。
【００７１】
上記測定試料のサンプリング箇所は複数とし（１０箇所以上が好ましい）、得られた複数の測定試料についてそれぞれ連続気泡率を求めると共にそれらの算術平均値を算出し、その値をもって本発明発泡シートの連続気泡率とする。
【００７２】
本発明により得られる発泡シートにおいては、スキン層を含む表層部分の密度が０．０８〜０．３５ｇ／ｃｍ³、更に０．１２〜０．２８ｇ／ｃｍ³、特に０．１４〜０．２５ｇ／ｃｍ³であること好ましい。かかる発泡シートは、前記本発明の方法による特定混合比の発泡剤を使用すると共に、発泡シート押出直後に冷却エアー等を用いて発泡シート表面を冷却することにより調整できる。また、発泡シートの表層部分の密度を調整することにより発泡シート自体の見かけ密度の調整も可能となる。上記範囲の表層部分の密度を有する発泡シートは成形性が良好で、得られた成形品は機械的物性及び印刷適性に優れたものとなるので好ましい。
【００７３】
また、上記の通り表層部分の密度を調整することは、発泡シートの見かけ密度を調整（単に周知の発泡剤量による調整方法だけによることなく上記方法にて微調整できる）することに繋がる。そしてこのことは、本発明の方法による特定混合比の発泡剤の使用量を、得られる発泡シートの見かけ密度に大きく制約されることなく、発泡シートの早期熟成完了を考慮した設計に合わせて、発泡シート製造直後における発泡シート中の残留発泡剤の残存量を容易に変更できる素晴らしい効果をもたらす。
【００７４】
前記発泡シートのスキン層を含む表層部分の密度の測定は、次のように行う。
まず発泡シートから縦２０ｍｍ、横５ｍｍ、厚みが発泡シート厚みの短冊状の発泡体を切り出す。次に該発泡体の表面から深さ２００μｍまでの部分をスライスして、縦２０ｍｍ、横５ｍｍ、厚み２００μｍのスキン層を含む表層部分の試験片を得る。この操作によって測定しようとする発泡シートの表面及び裏面において各々１０個、合計２０個の試験片を得る。得られた２０個の試験片について、各々重量（ｇ）を読み取り、重量を測定した試験片の外形寸法（ｃｍ）から算出される体積（ｃｍ^３）にて割り算することにより、各試験片の表層部分の密度を算出する。そして、２０個の試験片の表層部分の密度の算術平均値をもって、発泡シートのスキン層を含む表層部分の密度とする。
【００７５】
本発明により得られる発泡シートにおいては、発泡シートの厚み方向の平均気泡径：Ｘ、発泡シートの押出方向（ＭＤ）の平均気泡径：Ｙ、発泡シートの幅方向の平均気泡径：Ｚとの間に、下記（ａ）〜（ｃ）式で現される関系が成り立つものが好ましい。
【００７６】
【数５】
０．４≦Ｘ／Ｚ≦０．９ ……（ａ）
【００７７】
【数６】
０．４≦Ｘ／Ｙ≦０．９ ……（ｂ）
【００７８】
【数７】
１５０μｍ≦（Ｘ＋Ｙ＋Ｚ）／３≦２７０μｍ ……（ｃ）
【００７９】
発泡シートの厚み方向の平均気泡径：Ｘと押出方向の平均気泡径の比：Ｘ／Ｙ、厚み方向の平均気泡径：Ｘと幅方向の平均気泡径：Ｚの比Ｘ／Ｚは、各々０．５〜０．８であることがより好ましい。
【００８０】
Ｘ／Ｙ、Ｘ／Ｚの一方又は両方が０．４未満の場合は、扁平な形状の気泡となるため、発泡シートを熱成形して得られる成形品の機械的強度が低下する虞がある。一方、Ｘ／Ｙ、Ｘ／Ｚが０．９を超える発泡シートは、熱成形時のシートのドローダウンが大きなものとなる虞がある。したがって、Ｘ／Ｙ、Ｘ／Ｚの値が上記範囲を満足するような形状の気泡を有する発泡シートは、熱成形性、得られる成形品の機械的強度において優れたものとなる。
【００８１】
前記厚み方向の平均気泡径：Ｘ、押出方向の平均気泡径：Ｙ、幅方向の平均気泡径：Ｚは、発泡シートの押出方向の垂直断面及び、幅方向の垂直断面を顕微鏡で観察して求めることができる。具体的には、次のようにして行う。
【００８２】
押出方向の平均気泡径：Ｙは、発泡シートの押出方向に沿った垂直断面を顕微鏡等で拡大撮影し、得られた垂直断面拡大図中において、発泡シート表面付近、中央部及び裏面付近に、それぞれ、拡大前の長さが５０００μｍに相当する水平な線を引く。次に、各線分と交差する気泡の数ｎ（ｎは、該線分上に気泡の一部が交差するものも含む。）を求め、計算式：［５０００／（ｎ−１）］により各線分上の気泡１個あたりの平均気泡径を、表面付近、厚み方向中央部、裏面付近に引いた計３本の線分の各々から求め、求められた気泡１個当たりの各平均気泡径の算術平均値をもってＹ（μｍ）とする。
【００８３】
前記Ｚについては、発泡シートの幅方向に沿った垂直断面を顕微鏡等で拡大撮影し、得られた幅方向垂直断面拡大図中に、発泡シート表面付近、中央部及び、裏面付近に、拡大前の長さが５０００μｍに相当する水平な線を引き、Ｙを求める操作と同様の操作により求められる値をＺ（μｍ）とする。
【００８４】
前記Ｘについては、押出方向垂直断面拡大図によって求める。まず測定用試料の押出方向垂直断面拡大図中に、発泡シートの全厚みに亘って垂直な直線を引き、該直線と交差する気泡の数ｎ_２を求め、計算式：［発泡シートの厚み（μｍ）／ｎ_２］により求められる値をＸ（μｍ）とする。
【００８５】
本発明により得られる発泡シートは、その片面又は両面に非発泡のシートやフィルムを積層することにより、熱成形性、剛性、引裂き強度等が改良された積層発泡シートとして構成することが好ましい。上記シート、フィルムを構成する熱可塑性樹脂としては、高密度ポリエチレン、低密度ポリエチレン、直鎖状低密度ポリエチレン、エチレン−酢酸ビニル共重合体等のポリエチレン系樹脂、ポリスチレン、耐衝撃性ポリスチレン等のポリスチレン系樹脂、ポリプロピレン系樹脂、ポリエステル系樹脂等が挙げられる。これらの熱可塑性樹脂のうち、接着層を設けなくても積層可能なポリスチレン系樹脂が好ましい。
【００８６】
前記積層されるシートやフィルムの厚みに制限はないが、通常０．０１〜０．３ｍｍである。該厚みが薄すぎる場合は、非発泡のシートやフィルムを積層することによるシート物性等の向上効果が不十分となる虞があり、厚すぎると軽量性が低下し、経済性が悪くなる虞がある。
【００８７】
前記シートやフィルムの積層は、発泡シートのみを製造した後、別工程で製造されたフィルムやシートを熱又は接着剤にて積層する方法、押出発泡した発泡シートに他の押出機からフィルムやシートを押出して積層するエクストルージョンラミネート法、発泡性溶融樹脂と非発泡性熱可塑性溶融樹脂とを共押出する共押出法により行なうことができる。
【００８８】
本発明により得られる発泡シートは、雄型及び／又は雌型からなる金型を用いて熱成形することができる。該熱成形法としては、真空成形や圧空成形、更に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。これらの熱成形法は、短時間に連続して容器を得ることができるので、好ましい方法である。
【００８９】
本発明の発泡シートから熱成形によって得られた成形品は、トレイ、丼、弁当箱、カップ等の用途に好適に用いられる。
【００９０】
【実施例】
以下、実施例、比較例を挙げて本発明を更に説明する。
【００９１】
実施例１
出光石油化学株式会社製スチレン系樹脂：ＨＨ３２（ＭＩ：１．６ｇ/１０分（２００℃、４９．０３Ｎ））１００重量部と、タルク１重量部とを直径９０ｍｍの第一押出機に投入して加熱溶融混練した後、表２に示した物理発泡剤を第一押出機内に圧入して混練した。次いで第一押出機と接続された直径１２０ｍｍの第二押出機内で上記溶融混練物を冷却し、表２に示す樹脂温度で直径９０ｍｍの環状ダイから押出して円筒状に発泡させた。次いでこの円筒状の発泡体を直径３３３ｍｍの冷却された円柱状の冷却装置の側面に沿わせて引き取り、押出方向に切り開いて発泡シートを得た。
【００９２】
実施例２〜４、比較例１〜５
表２又は表３に示した発泡剤を押出機内に圧入して溶融混練したこと、第二押出機内で溶融混練物を表２又は表３に示す樹脂温度まで冷却したこと以外は、実施例１と同様に発泡シートを得た。
【００９３】
実施例１〜４、及び比較例１〜５において得られた発泡シートの厚み（ｍｍ）、坪量（ｇ/ｍ^２）、見かけ密度（ｇ/ｃｍ^３）、有機系物理発泡剤の全残存量、イソブタンの残存量、二次発泡倍率Ａ、二次発泡倍率Ｂ、熱成形時の発泡シートの表面荒れ、熱成形時の発泡シート品質安定性Ｑ及びＱ'、α・ｄ（モル／ｍ^３）等を表２又は３に併せて示す。
【００９４】
（表２）

【００９５】
【表３】

【００９６】
有機系物理発泡剤の残存量の測定
発泡シートの有機系物理発泡剤の残存発泡剤量は、発泡シート製造後３０分間経過後に発泡シートから切り出したサンプルをトルエンの入った蓋付きの試料ビンの中に入れ、内部標準としてシクロペンタンを加え、蓋を閉めた後十分に攪拌して発泡シート中の有機系物理発泡剤をトルエンに溶解させ、ガスクロマトグラフィー分析を行なうことより求めた。
【００９７】
ガスクロマトグラフィー分析により得られたガスクロマトグラムのピーク面積から下記（３）式を用いて試料中における各物理発泡剤の濃度（重量％）を計算し、単位換算して有機系物理発泡剤の残存発泡剤量（モル／ｋｇ）を求めた。
【００９８】
【数８】
ｘ_ｉ＝（Ｆ_ｉ×Ａ_ｉ×Ｗ_ｓ×１００）÷（Ａ_ｓ×Ｗ_ｓｍ）……（３）
【００９９】
ｘ_ｉ：試料中における各有機系物理発泡剤の重量％濃度
Ｆ_ｉ：補正係数
Ａ_ｓ：標準物質のピーク面積
Ａ_ｉ：発泡剤のピーク面積
Ｗ_ｓ：標準物質の重量
Ｗ_ｓｍ：試料重量
【０１００】
測定機は（株）島津製作所製GC-14Bを用い、次の条件で測定した。
カラム：（株）島津製作所製カラムSilicone DC 550 20% on Chromosorb W AW-DMCS 60/80mesh 4.1m×3.2mm
カラム温度：40℃
検出器温度：180℃
注入口温度：180℃
検出器：FID
キャリアガス：窒素140ml/min
試料量：2μl
【０１０１】
二次発泡倍率の測定
長さ２００ｍの発泡シートをロールに巻いた状態で温度２３℃、相対湿度５０％の雰囲気下で、製造直後から１０日間熟成した。熟成終了後、ロール巻の最外周部から２６０ｍｍ×２６０ｍｍの試験片を切り出し、厚みを測定した。次に、タバイエスペック（株）製恒温器：パーフェクトオーブンオリジナルＰＨ−２００を用い、上記試験片の周囲を内寸が縦２００ｍｍ、横２００ｍｍの木枠に固定した状態で、１４５℃で２７秒間加熱し、室温まで冷却してから厚みを測定した。加熱後の試験片の厚みを加熱前の試験片の厚みで除した値を、二次発泡倍率Ａとした。
【０１０２】
また、ロール巻の中間部（長さ２００ｍの発泡シートをロールの巻外から発泡シート長さ１２０ｍの部分）の発泡シート幅方向中央部から２６０ｍｍ×２６０ｍｍの試験片を切り出し、該試験片について二次発泡倍率Ａの測定と同様にして二次発泡倍率Ｂを求めた。
また、ロール巻の中間部の発泡シート幅方向端部から２６０ｍｍ×２６０ｍｍの試験片を切り出し、該試験片について二次発泡倍率Ａの測定と同様にして二次発泡倍率Ｃを求めた。
【０１０３】
品質安定性Ｑ及びＱ’
ロール巻の最外周部の二次発泡倍率Ａとロール巻の中間部の二次発泡倍率Ｂとの差「Ａ−Ｂ」を求め、下記（４）式により発泡シートをロールに巻いた状態での品質安定性Ｑを求めた。
また、ロール巻の中間部の幅方向端部の二次発泡倍率Ｃとロール巻の中間部の幅方向中央部の二次発泡倍率Ｂとの差「Ｃ−Ｂ」を求め、下記（５）式により発泡シートをロールに巻いた状態での品質安定性Ｑ’を求めた。
尚、品質安定性Ｑ及びＱ’は絶対値が小さいほど、二次発泡倍率の差が小さく品質が安定していることを意味する。
【０１０４】
【数９】
品質安定性Ｑ＝（（Ａ−Ｂ）／Ａ）×１００ ……（４）
【０１０５】
【数１０】
品質安定性Ｑ’＝（（Ｃ−Ｂ）／Ｃ）×１００ ……（５）
【０１０６】
熱成形時の発泡シートの表面荒れ
発泡シートを温度２３℃、相対湿度５０％の雰囲気下に置き、製造から７日間熟成後、前記二次発泡倍率の測定と同様の条件で二次発泡させた後、試験片表面を観察し、表面荒れのないものを○、表面荒れのあるものを×として評価した。
【０１０７】
【発明の効果】
本発明の熱成形用ポリスチレン系樹脂発泡シートの製造方法においては、発泡剤としてポリスチレン系樹脂に対する透過速度が空気よりも極めて遅い特定量の発泡剤と、ポリスチレン系樹脂に対する透過速度が空気よりも数倍速い特定量の発泡剤とからなる混合物理発泡剤とを用いているので、本発明方法によって得られる発泡シートは、熟成期間が短縮され冬季であっても２週間程度の熟成期間で熱成形が可能になる。しかも、２週間程度の熟成期間であっても、ロール状に巻いた発泡シートの巻き方向及び幅方向における熱成形性が安定し、一定の品質の成形品を得ることができ、しかもシートライフが長い。
【０１０８】
本願発明で得られる熱成形用ポリスチレン系樹脂発泡シートは、特定範囲の厚み、特定範囲の見掛け密度、特定範囲の物理発泡剤の合計残存量、特定範囲のイソブタンの残存量を有している。従って、本発明の発泡シートはシートライフが長い上に、ロール状に巻かれた発泡シート全体において、熱成形時の発泡シートの浪打を抑制することができると共に、熱成形時の発泡シートの表面荒れがなく、良好な二次発泡性を示す一定の品質の容器などの成形品を得ることができる。[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a method for producing a polystyrene resin foam sheet for thermoforming.About.
[0002]
[Prior art]
Polystyrene resin foam sheets have excellent thermoformability, the appearance of the resulting molded products are beautiful, light weight and excellent heat insulation, etc., so they have been used in large quantities as thermoforming foam sheets for food containers in recent years. Has been.
[0003]
Such a polystyrene resin foam sheet is obtained by heating and melting a polystyrene resin in an extruder, adding a foam control agent such as a foaming agent and talc to this, kneading with the molten resin, and then bringing the extruder into atmospheric pressure. It is manufactured by a method such as extrusion and foaming.
[0004]
As the foaming agent, industrial butane has been widely used because it is inexpensive and has excellent secondary formability when a foamed sheet is thermoformed.
[0005]
However, in the case of a polystyrene resin foam sheet using industrial butane as a foaming agent, the normal butane dissipation rate in the foaming agent in the foamed sheet is high, so the residual amount of foaming agent in the foamed sheet is short. There was a drawback of being too low. That is, if the residual amount of the foaming agent in the foamed sheet is too low, the expansion of the thickness due to heating during thermoforming of the foamed sheet is reduced, and the desired thickness (hereinafter referred to as expansion of the foamed sheet due to heating during thermoforming is “ There was a phenomenon in which it was called “secondary foaming”, and the thickness after expansion of the foamed sheet was called “secondary foaming thickness”).
[0006]
For this reason, there has been a problem that the thermoforming suitability period (hereinafter referred to as sheet life) in which a molded product having a desired thickness can be obtained when the foamed sheet is thermoformed. Japanese Patent Publication No. 5-42977 discloses a method for solving such a problem and producing a foamed sheet having a long sheet life. The method extends the sheet life of the foamed sheet by using a mixed foaming agent composed of 70 to 100% by weight of isobutane that is slowly dissipated from the foamed sheet and 0 to 30% by weight of normal butane that is quickly dissipated. It is to plan.
[0007]
However, the foamed sheet produced by the method of Japanese Patent Publication No. 5-42977 has a drawback that the aging period from the production to the time when heat molding becomes possible becomes too long. As a result, there is a new problem that profitability deteriorates because it must be stocked for a long time.
[0008]
That is, since the foamed sheet produced by the method of Japanese Patent Publication No. 5-42977 is produced using a large amount of isobutane, the period during which the content of isobutane decreases until thermoforming becomes possible becomes long. When thermoforming is performed, there is a drawback that surface roughness occurs in a molded product obtained by thermoforming a foam sheet due to the plasticizing effect of isobutane. As a result, the foam sheet has to be stored in a warehouse until the surface roughness during thermoforming does not occur, and the cost for storage has been great.
[0009]
In addition, the molded product in which the surface roughness occurred was not acceptable as a product because the appearance was impaired and the printability on the surface of the molded product was also lowered.
[0010]
In order to solve these problems and satisfy both the securing of a sufficient life cycle and the shortening of the ripening period at the same time, a method disclosed in JP-A-7-165969 is disclosed.
[0011]
In the method of JP-A-7-165969, the content of isobutane in the foaming agent is 50 to 70% by weight, the content of normal butane is 30 to 50% by weight, and the surface layer density is set to the total density of the foamed sheet. By performing extrusion foaming while controlling within a specific range, thermoforming can be performed in a aging period of about 2 weeks after production, and a sufficient sheet life can be secured.
[0012]
In the method of JP-A-7-165969, the normal butane content relative to isobutane was increased from the method described in Japanese Patent Publication No. 5-42977 because the permeation rate of polystyrene resin was higher than that of isobutane. This is because the reduction of the foaming agent in the foam sheet is promoted by increasing the amount. The reason why the surface layer density is controlled within a specific range with respect to the entire density of the foam sheet is to prevent the surface roughness of the foam sheet during thermoforming by relatively increasing the surface layer density.
[0013]
However, the method disclosed in Japanese Patent Laid-Open No. 7-165969 is not sufficient, and the following two problems remain.
The first problem is that in the winter season, a ripening period of about 2 weeks is insufficient and 3 to 4 weeks are required. This problem is due to the fact that normal butane has a faster permeation rate to polystyrene resins than isobutane, but is about 1/8 faster than the permeation rate of air to polystyrene resins. It is. As a result, it decreased to the range where thermoforming was possible in the aging period of about 2 weeks in summer, but it took 3 to 4 weeks to decrease to the range where thermoforming was possible in winter.
[0014]
The second problem is that the secondary thickness and molding conditions change greatly in the winding direction and width direction of the foamed sheet wound in a roll shape for aging for about two weeks, and the stability of thermoforming is lacking. The resulting molded product has a different secondary thickness and lacks quality stability.
[0015]
The second problem is that the remaining amount of the foaming agent is reduced in the outer portion of the foam sheet wound in a roll shape, whereas the remaining amount of the foaming agent is in the portion wound inside the roll. It is thought that there are many. Moreover, while the residual amount of the foaming agent at the width direction edge part of the foam sheet is decreasing, it is also considered that the residual amount of the foaming agent is large in the center part in the width direction.
[0016]
That is, isobutane has a very low permeation rate with respect to polystyrene-based resin, so it hardly dissipates outside the foamed sheet even during the aging period, whereas normal butane gradually grows during the aging period. In order to dissipate to the outside, there is a large difference in the remaining amount of foaming agent between the outside wound in a roll shape (in contact with outside air) and the inside portion wound in a roll shape. This is considered to be the cause of the difference in secondary thickness.
[0017]
Also, since the permeation rate of normal butane to polystyrene-based resin is about 1/8 of air, the rate at which air penetrates into the foam sheet is faster than the rate at which normal butane in the foam sheet decreases. It is considered that the internal pressure in the bubbles is equal to or higher than atmospheric pressure, which is a cause of changes in secondary thickness and thermoformability between the outside and inside of the foam sheet wound in a roll shape.
[0018]
That is, when the internal pressure in the bubbles on the outer side in the width direction of the foamed sheet wound in a roll shape becomes equal to or higher than the atmospheric pressure, the foamed sheets adjacent to each other are in a state of being tightened and sealed with each other, and the gas flows between the foamed sheets. It becomes difficult to circulate through the space. As a result, normal butane inside the roll is less likely to dissipate between the foam sheets, making it difficult for air to enter the interior from between the outside of the rolls and between the foam sheets. It is considered that the normal butane content and the air content are greatly different between the outer side and the inner side of the sheet.
[0019]
[Problems to be solved by the invention]
  The present invention enables thermoforming in a ripening period of about 2 weeks even in winter, stabilizes thermoformability in the winding direction and width direction of a foam sheet wound in a roll, and has a constant secondary thickness. An object of the present invention is to provide a method for producing a polystyrene resin foam sheet for thermoforming that has a long sheet life..
[0020]
[Means for solving the problems]
  The present invention
(1) A polystyrene resin and a physical foaming agent are heated and kneaded in an extruder to form a foamable molten resin. The foamable molten resin is extruded and foamed into a cylindrical shape, and then the cylindrical foam is extruded. In the method of obtaining a foamed sheet by slitting, the physical foaming agent is 75 to 95 mol% in total of at least one foaming agent selected from isobutane, normal pentane, and isopentane, and carbon dioxide gas, water, boiling point 140 Mixed physical foaming agent comprising at least one foaming agent selected from ethers having a boiling point of not more than ℃ and dialkyl carbonate having a boiling point of not more than 140 ° C in a total amount of 5 to 25 mol% (however, a mixed physical blowing agent comprising the blowing agent) The total amount of foaming agent contained in is 100 mol%.)It consists of 90-100 mol% and other physical foaming agents 0-10 mol%.Is a thing,The thickness of the foam sheet is 0.5 to 5 mm, and the apparent density of the foam sheet is 70 to 150 kg / m.³A method for producing a polystyrene-based resin foam sheet for thermoforming, characterized in that
(2) Mixed physics in which physical foaming agent is 75 to 95 mol% of isobutane, and one or more blowing agents selected from carbon dioxide, water, and ether having a boiling point of 140 ° C. or less are 5 to 25 mol% in total. Foaming agent (however, the total amount of foaming agent contained in the mixed physical foaming agent comprising the foaming agent is 100 mol%)It consists of 90-100 mol% and other physical foaming agents 0-10 mol%The method for producing a polystyrene-based resin foam sheet for thermoforming as described in (1) above, wherein
(3) Production of polystyrene-based resin foam sheet for thermoforming as described in (1) or (2) above, wherein the mixed physical foaming agent contains at least 75 to 95 mol% of isobutane and 5 to 25 mol% of water. Method,
(4) The polystyrene-based resin foam sheet for thermoforming according to any one of (1) to (3), wherein an amount of a physical foaming agent that satisfies the following formula (1) is pressed into an extruder: Production method,
[0021]
[Expression 2]
50 (mol / m³) ≦ α · d ≦ 90 (mol / m³) …… (1)
[0022]
Where α is the total number of moles of physical foaming agent per mole of polystyrene resin (mol / kg), and d is the apparent density of the polystyrene resin foam sheet (kg / m).³).
[0023]
(5) The foamable molten resin is extruded and foamed so that the total remaining amount of the organic physical foaming agent is 0.45 to 0.70 mol with respect to 1 kg of the obtained polystyrene resin foam sheet. The manufacturing method of the polystyrene-type resin foam sheet for thermoforming as described in any one of (1) to (4),
Is the gist.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
In the method for producing a polystyrene resin foam sheet for thermoforming according to the present invention, a polystyrene resin is heated, melted and kneaded in an extruder, and a physical foaming agent is press-fitted into the extruder and kneaded to obtain a foamable molten resin. Then, the foamable molten resin is extruded from a high pressure region to a low pressure region in the extruder to form a thermosetting polystyrene resin foam sheet (hereinafter simply referred to as a foam sheet).
[0025]
The foamable molten resin is extruded from a high pressure region to a low pressure region in an extruder through an annular die attached to the tip of the extruder and foamed into a cylindrical shape, and then the cylindrical foam is cut in the extrusion direction to form a sheet. It is preferable that the foamed sheet can be efficiently manufactured.
However, in the present invention, the foamable molten resin may be extruded and foamed through a T die attached to the tip of the extruder.
[0026]
The polystyrene resin used in the method of the present invention includes a homopolymer and a copolymer of styrene. The copolymer preferably contains a styrene monomer represented by the following general formula (1) as a copolymerization component, and the content of monomer units of the copolymerization component is preferably 25% by weight or more, 50% by weight or more is more preferable, and 75% by weight or more is particularly preferable.
[0027]
[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.
[0028]
The styrene homopolymer and copolymer are polystyrene, rubber-modified polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, Styrene-methyl methacrylate 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 polymer, a mixture of polystyrene and polyphenylene ether, and the like.
[0029]
It is preferable to use a polystyrene-based resin having a Vicat softening point of 100 ° C. or higher because the heat resistance of the foamed sheet can be improved. The upper limit of the Vicat softening point is not particularly limited, but is usually 130 ° C.
The Vicat softening point is determined according to JISK7206 (1991) (the test load is the method A, and the heating rate of the liquid heating method is 50 ° C./hour).
[0030]
When brittleness improvement or the like is required as the polystyrene resin, it is preferable to use impact-resistant polystyrene, a styrene-conjugated diene block copolymer, or a hydrogenated product of the copolymer.
[0031]
In addition, the polystyrene-based resin has various additives as necessary, for example, a nucleating agent, an antioxidant, a heat stabilizer, an antistatic agent, and conductivity, as long as the object of the present invention is not significantly impaired. Agents, weathering agents, ultraviolet absorbers, flame retardants, inorganic fillers, chemical foaming agents, and the like can be added, and other thermoplastic resins can also be mixed.
[0032]
In the method of the present invention, the cell diameter of the obtained foamed sheet is usually adjusted by adding a cell regulator to the polystyrene resin. Examples of the air conditioner include talc, kaolin, mica, silica, calcium carbonate, barium sulfate, titanium oxide, clay, aluminum oxide, bentonite, diatomaceous earth and the like, or sodium bicarbonate, monosodium citrate, and the like. Illustrated. These bubble regulators are usually used alone, but may be used in combination of two or more.
[0033]
Since the inorganic powder used as the bubble adjusting agent has a larger effect of reducing the bubble diameter of the foam sheet as the particle system is smaller, the bubble diameter can be reduced even if the amount used is small. From this 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 further preferably 15 μm or less. However, the smaller the average particle size, the higher the processing cost and the higher the price of the inorganic powder, so 0.1 μm is preferable as the lower limit. Among the inorganic powders, talc is most preferable because it has a large effect of reducing the bubble diameter and is inexpensive.
[0034]
As the physical blowing agent used in the method of the present invention, (i) one or more blowing agents selected from isobutane, normal pentane, and isopentane total 50 to 95 mol%, (ii) carbon dioxide gas, water, One or more blowing agents selected from ethers having a boiling point of 140 ° C. or lower and dialkyl carbonates having a boiling point of 140 ° C. or lower are 5 to 50 mol% in total, and the blowing agent of (i) and the blowing agent of (ii) The main component is a mixed physical foaming agent (however, the total amount of the foaming agent of (i) and (ii) contained in the mixed physical foaming agent is 100 mol%). Is done.
[0035]
Preferably, as the physical blowing agent, a total of 5 or more of one or more blowing agents selected from (iii) isobutane 50 to 95 mol%, (iv) carbon dioxide gas, water, and ether having a boiling point of 140 ° C. or less are used. 50 mol%, mixed foaming agent of foaming agent of (iii) and foaming agent of (iv) (however, foaming of foaming agent of (iii) and foaming agent of (iv) contained in mixed physical foaming agent) The total amount is 100 mol%).
[0036]
  Incidentally, the mixed physical foaming agent as a main component of the physical foaming agent in the present invention means that other physical foaming agents can be used in combination as long as the purpose and effect of the present invention are not impaired. The mixed physical foaming agent is contained in an amount of generally about 80 mol% or more, preferably 85 mol% or more, more preferably 90 mol% or more based on the physical foaming agent. Examples of the other physical foaming agents include propane and normal butane.Etc.Can be mentioned. However, the content of the blowing agent having a permeation rate of about 1/8 of polystyrene, such as normal butane, is preferably as low as possible. Specifically, the amount of the physical blowing agent used for extrusion foaming is 100 parts by weight. On the other hand, it is preferably within the range of 0 to 10 parts by weight.
[0037]
When the physical blowing agent specified as described above is used, it is surprisingly possible to perform thermoforming in a ripening period (for example, 2 weeks or less) faster than in summer even in winter, and even in a short ripening period. Moreover, the thermoformability in the winding direction and the width direction of the foamed sheet wound in a roll shape can be stabilized, a molded product having a constant secondary thickness can be obtained, and a foamed sheet having a long sheet life can be produced.
[0038]
The mixed physical foaming agent contains one or more foaming agents (hereinafter also referred to as residual foaming agents) selected from 50 to 95 mol% of isobutane, normal pentane, and isopentane. When the content of the residual foaming agent is less than 50%, the resulting foamed sheet has a small secondary foam thickness. From the standpoint that the sheet life is long and a sufficient secondary foaming thickness can be obtained even after 40 days have elapsed after production, the mixed physical foaming agent preferably contains 70 to 95 mol% of a residual foaming agent, particularly isobutane.
[0039]
On the other hand, when the mixed physical foaming agent contains the residual foaming agent in excess of 95 mol%, there is a possibility that the range of heating temperature and heating time at which the foamed sheet can be thermoformed becomes narrow due to the plasticizing effect of the residual foaming agent. In other words, the surface of the foamed sheet may be roughened if it is heated too much, but if the heating time is shortened by virtue of being overheated, the heating will be insufficient and the foamed sheet will be torn or molded in accordance with the mold shape. The inconvenience that the product cannot be obtained is likely to occur. In order to avoid such inconvenience, the residual foaming agent contained in the mixed physical foaming agent is preferably 90 mol% or less.
[0040]
The effect of the residual foaming agent is due to the extremely low permeation rate of the residual foaming agent with respect to the polystyrene resin (which is (1/10) or less of the permeation rate of air with respect to the polystyrene resin). is there.
[0041]
Therefore, based on the technology of the present invention, it is recalled that a foaming agent having a very low permeation rate with respect to polystyrene resin can be used instead of the residual foaming agent, and it is expected that other foaming agents may exist. The Therefore, according to the technique of the present invention, the permeation rate with respect to the polystyrene resin is extremely slow with respect to the air, and is heated and kneaded in an extruder together with the polystyrene resin to obtain a foamable molten resin. As long as the molten resin can be extruded and foamed, any foaming agent can be used instead of the residual foaming agent.
[0042]
The mixed physical foaming agent used in the method of the present invention is a foaming agent comprising at least one selected from carbon dioxide gas, water, ether having a boiling point of 140 ° C. or lower, and dialkyl carbonate having a boiling point of 140 ° C. or lower (hereinafter referred to as early escape foaming). 5 to 50 mol%). The permeation rate of these foaming agents to polystyrene resins is extremely fast, and is several times faster than the permeation rate of air to polystyrene resins (more than 5 times the permeation rate of air to polystyrene resins), so most of them are foam sheets. It dissipates from the foam sheet immediately after production, and even if the foaming agent remains in the foam sheet, it dissipates from the foam sheet very early after production. Therefore, like normal butane, the amount of foaming agent does not differ greatly between the outside and inside of the roll by gradually dissipating out of the foam sheet during the aging period, so in the roll winding direction and width direction The amount of foaming agent is uniform.
[0043]
Also, even if some early-dissipating foaming agent remains in the foam sheet, the early-dissipating foaming agent has a faster permeation rate to the polystyrene resin than air, so that the early dissipating foaming agent is faster than air entering the bubbles. Since the speed at which the bubbles exit from the bubbles is high, the pressure inside the bubbles of the foam sheet does not increase greatly. Therefore, like a conventional foam sheet wound in a roll shape, the foam sheets are tightly tightened with each other in the initial stage of curing, so that the physical foaming agent flows out of the foam sheet wound in a roll shape, and from the outside of the foam sheet. It will not be in a state that prevents the inflow of air. On the contrary, it is considered that the air is efficiently circulated between the foam sheets because the tightening state of the foam sheets is somewhat loosened as compared with the tightening state of the conventional roll winding.
[0044]
In addition, the phenomenon that the internal pressure of bubbles rises due to air permeation into the foam sheet during the aging period and the tightness of the roll-wrapped foam sheets becomes tight is suppressed by the increase in foam rigidity in winter. Furthermore, it is expected that air will circulate efficiently.
[0045]
As the ether having a boiling point of 140 ° C. or lower, it is preferable to use an ether having a boiling point of −30 to 100 ° C., more preferably an ether having a boiling point of −30 to 40 ° C., and ethyl methyl ether, dimethyl ether or diethyl ether is used. More preferably.
[0046]
As the dialkyl carbonate having a boiling point of 140 ° C. or lower, a dialkyl carbonate having a boiling point of −10 to 130 ° C. is preferably used, and dimethyl carbonate, diethyl carbonate, or diisopropyl carbonate is more preferably used.
[0047]
In addition, it is preferable that the said early escape foaming agent is comprised using water and a carbon dioxide gas from the point of safety.
[0048]
The mixed physical foaming agent of the present invention contains 5 to 50 mol%, preferably 7 to 40 mol%, more preferably 10 to 25 mol% of the early escape foaming agent. When the content of the early-dissipating foaming agent is less than 5 mol%, the thermoformability of the resulting foamed sheet is lowered. On the other hand, if the content of the early-dissipating foaming agent exceeds 50 mol%, the secondary foam thickness of the resulting foamed sheet will be small.
[0049]
In the method of the present invention, a foamed sheet is produced using a physical foaming agent containing the mixed physical foaming agent as a main component, so that normal butane used in a large amount in the prior art gradually dissipates from the foamed sheet. Unlike the above, the early escape foaming agent dissipates rapidly after extrusion foaming. Therefore, most of the foaming agent dissolved in the polystyrene resin constituting the foaming agent inside the foam or the foamed sheet in a short period after production becomes the residual foaming agent. Therefore, it becomes a foamed sheet exhibiting sufficient and uniform secondary foaming property only by the air being taken into the bubbles in the subsequent aging step.
[0050]
The foamed sheet obtained by the method of the present invention has two problems that the foamed sheet obtained by a known technique using a large amount of isobutane, the problem that the surface is easily roughened during thermoforming, and the aging period is prolonged. This is achieved by using a mixed physical foaming agent in which a residual foaming agent and an early escape foaming agent are blended within a specific range. That is, by preventing excessive isobutane from being contained in the foamed sheet, surface roughening at the time of thermoforming is prevented, and in the aging process, thermoforming becomes possible only by taking air into the bubbles. Furthermore, it is considered that air is easily taken into the inside of the foamed inner foam sheet, and it is considered that the aging process is shortened. And since the gas contained in a foam sheet is only a residual foaming agent and air, it becomes a foam sheet with a long sheet life.
[0051]
As described above, the foamed sheet obtained by the method of the present invention contains a residual foaming agent and air in the bubbles, and therefore exhibits a good secondary foaming property over a long period of time, so that the sheet life is prolonged. In addition, since the early dissipative foaming agent dissipates immediately after production, it is considered that the tightening of the foam sheets wound in a roll shape corresponding to the usage amount of the early dissipative foaming agent is suppressed. As a result, air is also taken into the inside of the inner foam sheet wound in a roll, and the aging period is shortened.
[0052]
In addition, it is anticipated that the early-dissipating foaming agent that can be used based on the technique of the present invention will be present in addition to the above. Therefore, the permeation rate of polystyrene resin is several times faster than air, and is heated and kneaded with an extruder together with a polystyrene resin to form a foamable molten resin. Any blowing agent can be used as long as it can be extruded from the region to the low pressure region.
As a reference, Table 1 shows the permeation rates of various foaming agents when the permeation rate of air to polystyrene resin is 100.
[0053]
[Table 1]

[0054]
In the method of the present invention, it is preferable to press-fit an amount of a physical foaming agent that satisfies the following formula (1) into the extruder.
[0055]
[Equation 3]
50 (mol / m³) ≦ α · d ≦ 90 (mol / m³) …… (1)
[0056]
Where α is the total number of moles of physical foaming agent (mol / kg) with respect to 1 kg of polystyrene resin used for extrusion foaming, and d is the apparent density (kg / m) of the foamed sheet obtained by extrusion foaming.³).
[0057]
α · d is 50 (mol / m³If it is less than), even if a foam sheet having the desired apparent density is obtained, there is a possibility that a sufficient secondary foam thickness during thermoforming cannot be obtained. On the other hand, 90 (mol / m³) Exceeding (), even if a foam sheet having an intended apparent density is obtained, the thermoformability may be inferior.
[0058]
The apparent density of the foamed sheet obtained by the method of the present invention is preferably 70 to 300 (kg / m³More preferably 70 to 150 (kg / m³), Particularly preferably 90 to 150 (kg / m)³). When the apparent density is too small, the thermoformability is deteriorated, there is a possibility that a molded product having a shape as in a mold cannot be obtained, and the strength of the obtained molded product may be lowered. On the other hand, when the apparent density is too high, there is a possibility that the characteristics of the foam such as lightness, heat insulation, and buffering properties may be lost.
[0059]
The apparent density of the foam sheet in the present specification is determined by converting the value obtained by dividing the weight per unit area of the foam sheet by the thickness of the foam sheet.
[0060]
Polystyrene resin foam sheet for thermoformingIt can be produced by the method of the present invention described above. The thickness of the foamed sheet is 0.5 to 5 mm, preferably 0.5 to 3.5 mm, and more preferably 0.7 to 3 mm. If the thickness is too thin, the strength of the molded product obtained by thermoforming may be too low, and if the thickness is too thick, the thermoformability may be deteriorated and uneven thickness may occur in the molded product.
[0061]
In the measurement of the thickness of the foamed sheet in this specification, the thickness is measured at 10 locations at regular intervals along the entire width of the foamed sheet, and the arithmetic average value of each measured value is used as the thickness of the foamed sheet.
[0062]
  The present inventionObtained byThe apparent density of the foam sheet is particularly 70 to 150 (kg / m³), The thermoformability is excellent, and the lightness, heat insulation, and buffering properties are particularly excellent.
[0063]
  The present inventionObtained byIn the foamed sheet, the total remaining amount of the organic physical foaming agent is preferably 0.45 to 0.70 mole, more preferably 0.60 to 0.70 mole relative to 1 kg of the foamed sheet. When the total remaining amount is too small, even if air having a pressure equal to the atmosphere is taken into the foam sheet in the aging process, the foam sheet has an insufficient secondary foam thickness. On the other hand, when it is too much, the thermoformability is inferior, for example, the surface of the foam sheet is roughened during thermoforming.
[0064]
  The present inventionObtained byIn the foam sheet, in addition to the condition of the total residual amount of the organic physical foaming agent, the total residual amount of the residual foaming agent selected from isobutane, normal pentane, and isopentane is based on the total residual amount of the organic physical foaming agent. It is preferably 90 to 100 mol%. When the total residual amount of the residual foaming agent is too small, the effects of shortening the time required for the aging process, extending the life of the foamed sheet, and stabilizing the thermoformability in the winding direction and the width direction of the foamed sheet cannot be achieved at the same time. There is a fear.
[0065]
In this specification, the remaining amount of the organic physical foaming agent is measured by placing a measurement sample collected from the foam sheet in a sample bottle with a lid containing toluene and stirring the foaming agent in the foam sheet into toluene. After being dissolved, toluene in which the blowing agent is dissolved can be collected by a microsyringe and subjected to gas chromatography analysis, which can be determined by an internal standard method.
[0066]
  The present inventionObtained byThe foamed sheet has an open cell ratio of 0 to 15%, more preferably 0 to 10%, which is excellent in secondary foaming properties during thermoforming, and mechanical strength and thickness uniformity of the resulting molded product. Is preferable because it is particularly good.
[0067]
The measurement of the open cell rate in this specification is performed as follows according to ASTM D-2856-70 (procedure C).
Use the air pycnometer to measure the true volume of the sample Vx (cm^Three) And the apparent volume Va (cm^Three) And the open cell ratio (%) is calculated by the following equation (2). The true volume Vx is the sum of the volume of the resin in the measurement sample and the volume of the closed cell portion.
[0068]
[Expression 4]
Open cell ratio (%) = {(Va−Vx) / (Va−W / ρ)} × 100 (2)
[0069]
In the formula (2), W is the weight (g) of the measurement sample, and ρ is the density of the base resin constituting the foamed sheet (g / cm).^Three).
[0070]
The dimensions of the measurement sample in the measurement of the open cell ratio are 25 mm in length, 25 mm in width, and 40 mm in thickness. In the present invention, since one sample cannot have a size that matches the size of the measurement sample, a plurality of samples are overlapped to prepare one measurement sample.
[0071]
The measurement sample has a plurality of sampling locations (preferably 10 locations or more), the open cell ratio is calculated for each of the obtained measurement samples, and the arithmetic average value thereof is calculated. Let the bubble rate.
[0072]
  The present inventionObtained byIn the foam sheet, the density of the surface layer portion including the skin layer is 0.08 to 0.35 g / cm.^ThreeFurthermore, 0.12-0.28 g / cm^Three, Especially 0.14-0.25g / cm^ThreePreferably it is. Such a foam sheet can be adjusted by using a foaming agent having a specific mixing ratio according to the method of the present invention and cooling the foam sheet surface using cooling air or the like immediately after the foam sheet is extruded. Further, the apparent density of the foam sheet itself can be adjusted by adjusting the density of the surface layer portion of the foam sheet. The foamed sheet having the density of the surface layer in the above range is preferable because the moldability is good, and the obtained molded product is excellent in mechanical properties and printability.
[0073]
Moreover, adjusting the density of the surface layer portion as described above leads to adjusting the apparent density of the foamed sheet (which can be finely adjusted by the above method without using only the adjustment method using a known amount of foaming agent). And this is based on the design considering the early aging completion of the foam sheet, without greatly restricting the use amount of the foaming agent of a specific mixing ratio according to the method of the present invention, to the apparent density of the foam sheet obtained, This brings about a wonderful effect that the residual amount of the residual foaming agent in the foamed sheet immediately after the foamed sheet is produced can be easily changed.
[0074]
The density of the surface layer portion including the skin layer of the foamed sheet is measured as follows.
First, a strip-shaped foam having a length of 20 mm, a width of 5 mm, and a thickness of the foam sheet is cut out from the foam sheet. Next, a portion from the surface of the foam to a depth of 200 μm is sliced to obtain a test piece of a surface layer portion including a skin layer having a length of 20 mm, a width of 5 mm, and a thickness of 200 μm. A total of 20 test pieces are obtained, 10 on each of the front and back surfaces of the foam sheet to be measured by this operation. For the 20 test pieces obtained, the weight (g) was read, and the volume (cm) calculated from the outer dimensions (cm) of the test pieces whose weights were measured.³) To calculate the density of the surface layer portion of each test piece. And let the arithmetic mean value of the density of the surface layer part of 20 test pieces be the density of the surface layer part including the skin layer of a foamed sheet.
[0075]
  The present inventionObtained byIn the foam sheet, the average cell diameter in the thickness direction of the foam sheet: X, the average cell diameter in the extrusion direction (MD) of the foam sheet: Y, and the average cell diameter in the width direction of the foam sheet: Z Those satisfying the relation expressed by the formulas (a) to (c) are preferable.
[0076]
[Equation 5]
0.4 ≦ X / Z ≦ 0.9 (a)
[0077]
[Formula 6]
0.4 ≦ X / Y ≦ 0.9 (b)
[0078]
[Expression 7]
150 μm ≦ (X + Y + Z) / 3 ≦ 270 μm (c)
[0079]
Average cell diameter in the thickness direction of the foamed sheet: ratio of X and average cell size in the extrusion direction: X / Y, average cell size in the thickness direction: X and average cell size in the width direction: Z ratio X / Z is respectively More preferably, it is 0.5 to 0.8.
[0080]
When one or both of X / Y and X / Z is less than 0.4, flat bubbles are formed, which may reduce the mechanical strength of a molded product obtained by thermoforming the foam sheet. . On the other hand, foamed sheets having X / Y and X / Z exceeding 0.9 may cause a large drawdown of the sheet during thermoforming. Therefore, a foamed sheet having bubbles in such a shape that the values of X / Y and X / Z satisfy the above ranges is excellent in thermoformability and mechanical strength of the obtained molded product.
[0081]
The average cell diameter in the thickness direction: X, the average cell diameter in the extrusion direction: Y, and the average cell diameter in the width direction: Z are obtained by observing the vertical section in the extrusion direction and the vertical section in the width direction of the foam sheet with a microscope. Can be sought. Specifically, this is performed as follows.
[0082]
Average bubble diameter in the extrusion direction: Y is an enlarged photograph of a vertical section along the extrusion direction of the foam sheet with a microscope or the like, and in the obtained enlarged vertical section, in the vicinity of the foam sheet surface, the central portion and the back surface, Each draws a horizontal line corresponding to a length of 5000 μm before enlargement. Next, the number n of bubbles intersecting with each line segment (n includes those in which a part of the bubbles intersects with the line segment) is obtained, and each line is calculated according to the calculation formula: [5000 / (n-1)]. The average bubble diameter per bubble in the minute is obtained from each of the three line segments drawn near the surface, in the center in the thickness direction, and near the back surface, and the average bubble diameter of each obtained bubble is calculated. Let the arithmetic mean value be Y (μm).
[0083]
For Z, a vertical section along the width direction of the foam sheet was magnified and photographed with a microscope or the like, and in the obtained width direction vertical section enlarged view, in the vicinity of the foam sheet surface, near the center, and near the back surface, before magnification A horizontal line corresponding to a length of 5000 μm is drawn, and a value obtained by the same operation as that for obtaining Y is Z (μm).
[0084]
About said X, it calculates | requires by an extrusion direction vertical cross-section enlarged view. First, in a vertical cross-sectional enlarged view of the measurement sample in the extrusion direction, a vertical straight line is drawn over the entire thickness of the foam sheet, and the number of bubbles intersecting the straight line is n.₂The calculation formula: [foamed sheet thickness (μm) / n₂] Is X (μm).
[0085]
  The present inventionObtained byThe foam sheet is preferably configured as a laminated foam sheet having improved thermoformability, rigidity, tear strength, and the like by laminating a non-foamed sheet or film on one or both sides. Examples of the thermoplastic resin constituting the sheet and film include high-density polyethylene, low-density polyethylene, linear low-density polyethylene, polyethylene-based resins such as ethylene-vinyl acetate copolymer, polystyrene such as polystyrene and impact-resistant polystyrene. Resin, polypropylene resin, polyester resin and the like. Of these thermoplastic resins, polystyrene resins that can be laminated without providing an adhesive layer are preferred.
[0086]
Although there is no restriction | limiting in the thickness of the sheet | seat and film which are laminated | stacked, Usually, it is 0.01-0.3 mm. If the thickness is too thin, the effect of improving the physical properties of the sheet by laminating a non-foamed sheet or film may be insufficient, and if it is too thick, the lightness may be reduced and the economy may be deteriorated. is there.
[0087]
Lamination of the sheet or film is a method in which only a foamed sheet is produced, and then the film or sheet produced in a separate process is laminated with heat or an adhesive. The extrusion laminating method of extruding and laminating and the coextrusion method of coextruding a foamable molten resin and a non-foamable thermoplastic molten resin can be used.
[0088]
  The present inventionObtained byThe foamed sheet can be thermoformed using a mold comprising a male mold and / or a female mold. The thermoforming methods include vacuum forming, pressure forming, and free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, and air slip forming. , Plug assist molding, plug assist reverse draw molding, etc., and a molding method combining these. These thermoforming methods are preferable because the container can be obtained continuously in a short time.
[0089]
The molded product obtained by thermoforming from the foamed sheet of the present invention is suitably used for applications such as trays, baskets, lunch boxes and cups.
[0090]
【Example】
Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples.
[0091]
Example 1
Idemitsu Petrochemical Co., Ltd. styrene resin: 100 parts by weight of HH32 (MI: 1.6 g / 10 min (200 ° C., 49.03 N)) and 1 part by weight of talc were charged into a first extruder having a diameter of 90 mm. After heating and melt-kneading, the physical foaming agent shown in Table 2 was pressed into the first extruder and kneaded. Next, the melt-kneaded product was cooled in a second extruder having a diameter of 120 mm connected to the first extruder, extruded from an annular die having a diameter of 90 mm at the resin temperature shown in Table 2, and foamed into a cylindrical shape. Next, this cylindrical foam was taken along the side of a cooled columnar cooling device having a diameter of 333 mm, and cut in the extrusion direction to obtain a foamed sheet.
[0092]
Example 2~ 4Comparative Examples 1-5
  Example 1 except that the foaming agent shown in Table 2 or 3 was injected into the extruder and melt-kneaded, and the melt-kneaded product was cooled to the resin temperature shown in Table 2 or Table 3 in the second extruder. A foamed sheet was obtained in the same manner as above.
[0093]
  Example 1~ 4, And the thickness (mm) and basis weight (g / m) of the foamed sheet obtained in Comparative Examples 1 to 5²), Apparent density (g / cm³), The total remaining amount of the organic physical foaming agent, the remaining amount of isobutane, the secondary foaming ratio A, the secondary foaming ratio B, the surface roughness of the foamed sheet during thermoforming, the foam sheet quality stability Q during thermoforming, and Q ′, α · d (mol / m³) Etc. are also shown in Table 2 or 3.
[0094]
(Table 2)

[0095]
[Table 3]

[0096]
Measurement of residual amount of organic physical foaming agent
The amount of remaining foaming agent in the organic physical foaming agent of the foamed sheet was determined by placing a sample cut from the foamed sheet 30 minutes after the foamed sheet was produced and placing it in a sample bottle with a lid containing toluene, and using cyclopentane as an internal standard. In addition, after the lid was closed, the mixture was sufficiently stirred to dissolve the organic physical foaming agent in the foamed sheet in toluene, and the gas chromatographic analysis was performed.
[0097]
The concentration (wt%) of each physical foaming agent in the sample is calculated from the peak area of the gas chromatogram obtained by gas chromatographic analysis using the following formula (3), and the remaining organic physical foaming agent is converted into units. The amount of blowing agent (mol / kg) was determined.
[0098]
[Equation 8]
x_i= (F_i× A_i× W_s× 100) ÷ (A_s× W_sm) …… (3)
[0099]
x_i: Weight% concentration of each organic physical foaming agent in the sample
F_i: Correction coefficient
A_s: Peak area of reference material
A_i: Peak area of foaming agent
W_s: Weight of reference material
W_sm: Sample weight
[0100]
The measuring instrument was GC-14B manufactured by Shimadzu Corporation and measured under the following conditions.
Column: Shimadzu Corporation Column Silicone DC 550 20% on Chromosorb W AW-DMCS 60 / 80mesh 4.1m x 3.2mm
Column temperature: 40 ° C
Detector temperature: 180 ° C
Inlet temperature: 180 ° C
Detector: FID
Carrier gas: nitrogen 140ml / min
Sample volume: 2μl
[0101]
Measurement of secondary expansion ratio
A foam sheet having a length of 200 m was wound on a roll and aged for 10 days immediately after production in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50%. After completion of aging, a 260 mm × 260 mm test piece was cut out from the outermost periphery of the roll and the thickness was measured. Next, using a thermostat manufactured by Tabai Espec Co., Ltd .: Perfect Oven Original PH-200, the periphery of the test piece was heated at 145 ° C. for 27 seconds with the inner dimensions fixed to a wooden frame of 200 mm length and 200 mm width. Then, after cooling to room temperature, the thickness was measured. A value obtained by dividing the thickness of the test piece after heating by the thickness of the test piece before heating was defined as a secondary foaming ratio A.
[0102]
In addition, a 260 mm × 260 mm test piece was cut out from the center part in the width direction of the foam sheet in the middle part of the roll (a foam sheet having a length of 200 m and a part having a length of 120 m from the outside of the roll). The secondary expansion ratio B was determined in the same manner as the measurement of the secondary expansion ratio A.
In addition, a 260 mm × 260 mm test piece was cut out from the end portion in the width direction of the foamed sheet at the middle part of the roll, and the secondary foaming ratio C was determined for the test piece in the same manner as the measurement of the secondary foaming ratio A.
[0103]
Quality stability Q and Q '
The difference “A−B” between the secondary foaming magnification A at the outermost peripheral part of the roll winding and the secondary foaming magnification B at the middle part of the roll winding is obtained, and the foamed sheet is wound around the roll by the following formula (4) The quality stability Q was determined.
In addition, the difference “C−B” between the secondary foaming ratio C at the widthwise end of the middle part of the roll and the secondary foaming ratio B at the center in the widthwise direction of the middle part of the roll is obtained, and the following (5) The quality stability Q ′ in a state where the foamed sheet was wound on a roll was determined by the formula.
In addition, quality stability Q and Q 'means that the smaller the absolute value, the smaller the difference in secondary foaming ratio and the more stable the quality.
[0104]
[Equation 9]
Quality stability Q = ((A−B) / A) × 100 (4)
[0105]
[Expression 10]
Quality stability Q ′ = ((C−B) / C) × 100 (5)
[0106]
Surface roughness of foam sheet during thermoforming
Place the foamed sheet in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50%, and after aging for 7 days from production, after secondary foaming under the same conditions as the measurement of the secondary foaming ratio, observe the surface of the test piece, Evaluation was made with ○ having no surface roughness and × with surface roughness.
[0107]
【The invention's effect】
In the method for producing a polystyrene-based resin foam sheet for thermoforming according to the present invention, as a foaming agent, a specific amount of foaming agent whose permeation rate with respect to the polystyrene-based resin is extremely slower than air, and the permeation rate with respect to the polystyrene-based resin is several times that of air. Since a mixed physical foaming agent composed of a specific amount of foaming agent twice as fast is used, the foamed sheet obtained by the method of the present invention has a shortened aging period and is thermoformed in an aging period of about 2 weeks even in winter. Is possible. Moreover, even in the aging period of about 2 weeks, the thermoformability in the winding direction and width direction of the foamed sheet wound in a roll shape is stable, and a molded product of a certain quality can be obtained, and the sheet life is increased. long.
[0108]
  Invention of the present applicationObtained inThe polystyrene-based resin foam sheet for thermoforming has a specific range of thickness, a specific range of apparent density, a specific range of physical foaming agent total residual amount, and a specific range of isobutane residual amount. Therefore, the foam sheet of the present invention has a long sheet life, and in the entire foam sheet wound in a roll shape, the foam sheet can be prevented from being struck during thermoforming and the surface of the foam sheet during thermoforming. There can be obtained a molded article such as a container of a certain quality which is not rough and exhibits a good secondary foaming property.

Claims (5)

A polystyrene resin and a physical foaming agent are heated and kneaded in an extruder to form a foamable molten resin. After the foamable molten resin is extruded and foamed into a cylindrical shape, the cylindrical foam is cut in the extrusion direction. In the method for obtaining a foamed sheet, the physical foaming agent is a total of 75 to 95 mol% of at least one foaming agent selected from isobutane, normal pentane, and isopentane, carbon dioxide gas, water, and a boiling point of 140 ° C. or lower. One or more foaming agents selected from ether and dialkyl carbonate having a boiling point of 140 ° C. or lower are mixed physical foaming agents composed of a total of 5 to 25 mol% (however, included in the mixed physical foaming agent composed of the foaming agent) total blowing agent amount is 100 mol%.) and made of 90 to 100 mol% and other physical blowing agents 0 to 10 mol%, the thickness of the foamed sheet 0.5~5mm And the apparent density of the foamed sheet is 70 to 150 kg / m ^{3. A} method for producing a polystyrene-based resin foamed sheet for thermoforming, characterized in that: A physical foaming agent is a mixed physical foaming agent comprising 75 to 95 mol% of isobutane and at least one foaming agent selected from carbon dioxide, water, and an ether having a boiling point of 140 ° C. or less and a total of 5 to 25 mol%. However, the total amount of the foaming agent contained in the mixed physical foaming agent composed of the foaming agent is 100 mol%.) It is composed of 90 to 100 mol% and other physical foaming agents 0 to 10 mol%. The manufacturing method of the polystyrene-type resin foam sheet for thermoforming of Claim 1 characterized by the above-mentioned.   The method for producing a polystyrene-based resin foam sheet for thermoforming according to claim 1 or 2, wherein the mixed physical foaming agent contains at least 75 to 95 mol% of isobutane and 5 to 25 mol% of water. The method for producing a thermoforming polystyrene resin foam sheet according to any one of claims 1 to 3, wherein an amount of a physical foaming agent satisfying the following formula (1) is press-fitted into an extruder.
(Equation 1) 50 (mol / m ³ ) ≦ α · d ≦ 90 (mol / m ³ ) (1)
Where α is the total number of moles of the physical foaming agent per mole of polystyrene resin (mol / kg), and d is the apparent density (kg / m ³ ) of the polystyrene resin foam sheet.   The foamable molten resin is extruded and foamed so that the total remaining amount of the organic physical foaming agent is 0.45 to 0.70 mol with respect to 1 kg of the obtained polystyrene resin foam sheet. The manufacturing method of the polystyrene-type resin foam sheet for thermoforming in any one of 1-4.