JP3580357B2 - Polypropylene resin foam sheet - Google Patents

Description

【００２６】
上記歪量γ（ｔ）を一定応力σｃで割って得られた値をクリープコンプライアンスＪ（ｔ）といい、下記（１）式で定義される。
【数１】Ｊ（ｔ）＝γ（ｔ）／σｃ （１）
【００２７】
クリープコンプライアンスＪ（ｔ）は、歪量γ（ｔ）と同様に最初は急激に増加するが経時と共になだらかに増加し、充分な時間が経過すると時間に対して直線的に変化するようになる（図１に示す）。該直線状に変化するようになったクリープコンプライアンスＪ（ｔ）は、下記（２）式で表すことができる。
【数２】Ｊ（ｔ）＝Ｊ_０＋ｔ／η （２）
【００２８】
本明細書における平衡コンプライアンス（Ｊ_０）は、（２）式におけるＪ_０として与えられる。即ちクリープコンプライアンスＪ（ｔ）を縦軸に、時間ｔを横軸にプロットした図において、クリープコンプライアンスＪ（ｔ）の直線部分を時間ｔ＝０に外挿したときの時間ｔ＝０における切片として与えられる。
又、本明細書における溶融粘度（η）は、（２）式におけるクリープコンプライアンスＪ（ｔ）の直線部分の傾きの逆数として与えられる。
【００２９】
本明細書において使用するポリプロピレン系樹脂を主成分とし、特定の平衡コンプライアンス（Ｊ_０）及び溶融粘度（η）を有する基材樹脂としては、例えば、触媒技術によりポリプロピレン樹脂中に超高分子量のポリプロピレンやポリエチレン等のポリオレフィン成分を遍在することなく分散させ、特定の平衡コンプライアンス（Ｊ_０）及び溶融粘度（η）を満足する分子鎖の絡み合いを実現させたもの、ポリプロピレン系樹脂をイソプレンモノマー等により特定の平衡コンプライアンス（Ｊ_０）及び溶融粘度（η）を満足するように改質したもの等を使用することができる。具体的には、チッソ株式会社製のポリプロピレン系樹脂『ＮＥＷＦＯＡＭＥＲ ＦＨ３４００』を選択することができる。
但し、本発明で使用する基材樹脂はポリプロピレン系樹脂を主成分とし、特定の平衡コンプライアンス（Ｊ_０）及び溶融粘度（η）を有するものであれば良く、基材樹脂の合成方法、改質方法、調整方法には限定されない。
【００３０】
本発明の発泡シートは、上記基材樹脂を押出発泡することによって得られる。該押出発泡としては、例えば上記基材樹脂を押出機内で加熱溶融、混練し、更に高温高圧下で発泡剤を注入、混練して発泡性溶融樹脂組成物とした後、押出機先端に設けられた環状ダイを通して大気圧下に押出して筒状に発泡させ、この筒状発泡体を押出方向に沿って切り開いて発泡シートとする等の方法が挙げられる。
【００３１】
上記発泡剤としては、物理発泡剤、化学発泡剤が用いられる。物理発泡剤の中で、無機系のものとしては二酸化炭素、空気、窒素等が挙げられれる。
【００３２】
また物理発泡剤の中で有機系のものとしては、プロパン、ｎ−ブタン、ｉ−ブタン、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、クロロフロロメタン、トリフロロメタン、１，１−ジフロロエタン、１−クロロ−１，１−ジフロロエタン、１，１，１，２−テトラフロロエタン、１−クロロ−１，２，２，２−テトラフロロエタン、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等を用いることができる。また、化学発泡剤としては、アゾジカルボンアミド、ジニトロソペンタメチレンテトラミン、アゾビスイソブチロニトリル、重炭酸ナトリウム等を用いることができる。
【００３３】
これらの発泡剤は適宜混合して用いることができる。発泡剤の使用量は、発泡剤の種類、所望する発泡シートの発泡倍率等によっても異なるが、本発明の発泡シートを得るための発泡剤の使用量の目安は、基材樹脂１００重量部当たり、物理発泡剤の場合、０．５〜２５重量部（ブタン換算）程度である。
【００３４】
本発明の発泡シートの製造においては、基材樹脂中に必要に応じて気泡調整剤を添加することができる。気泡調整剤としては、タルク、シリカ等の無機粉末や多価カルボン酸の酸性塩、多価カルボン酸と炭酸ナトリウム或いは重炭酸ナトリウムとの反応混合物等が挙げられる。気泡調整剤の添加量は基材樹脂１００重量部当たり一般に３重量部程度以下が好ましい。
【００３５】
更に必要に応じて基材樹脂に、帯電防止剤、流動性向上剤等や、所期の目的を妨げない範囲の量の着色剤等の各種添加剤を配合することもできる。更に、タルク、シリカ、炭酸カルシウム、クレー、ゼオライト、アルミナ、硫酸バリウム等を無機充填剤として添加することもできる。これら無機充填剤の添加量は樹脂と他の添加剤等を合計した総重量の４０重量％を上限とすることが好ましい。上記無機粉末や無機充填剤は平均粒径が１〜７０μｍのものが好ましい。無機充填剤を添加すると得られた発泡シートの耐熱性が向上するとともに、発泡シートを焼却する際の燃焼カロリーを低下させることができる。
【００３６】
本発明の発泡シートは、密度が１５０〜４５０ｋｇ／ｍ³である。特に、１８０〜３６０ｋｇ／ｍ ³ であることが好ましい。密度度が１５０ｋｇ／ｍ³未満の場合は、熱成形によって得られる成形品の剛性が弱くなる虞や、成形品の角部や凹凸模様が明瞭に成形すること（以下、「金型再現性」という。）ができない等の熱成形性が悪化する虞がある。一方、密度が４５０ｋｇ／ｍ³を超える場合は、熱成形によって得られる成形品の断熱性や緩衝性が悪くなる虞がある。
【００３７】
本発明の発泡シートは、厚みが０．５〜２．０ｍｍである。特に、０．８〜１．８ｍｍであることが好ましい。
厚みが０．５ｍｍ未満の場合は、断熱性が悪くなる虞があり、２．０ｍｍを超える場合は、熱成形の際の成形サイクルの低下、金型再現性の低下、軽量性の低下等の虞がある。
【００３８】
本発明の発泡シートは、１８０℃の雰囲気下で３分間加熱した場合の寸法変化率が、押出方向において−４０〜−８０％、幅方向において１０〜−２０％である。特に、押出方向において−５０〜−７５％、幅方向において１０〜−１０％が好ましい。
上記寸法変化率が、押出方向において−８０％未満の場合や幅方向において−２０％未満の場合は、熱成形の際に発泡シートの伸びが悪く一部のみが局部的に伸ばされて、均一な厚みの成形品を得ることができない等の虞がある。一方、寸法変化率が、押出方向において−４０％を超える場合や幅方向において１０％を超える場合は、熱成形時のドローダウンが改善されない虞がある。
【００３９】
本明細書における寸法変化率は、タバイ エスペック株式会社製の「パーフェクトオーブンＰＨ２００」を使用して測定した。測定試料は、縦方向を発泡シートの押出方向に一致させ、横方向を発泡シートの押出方向と直交する幅方向に一致させて、発泡シートを１０ｃｍ角に切断したものを使用した。
寸法変化率の測定は、上記測定試料を１８０℃に設定した上記オーブン中に３分間放置し（尚、測定試料はオーブン中にて平らな金属プレート上にタルクを散布し、その上に水平に静置することとする。）、取出して冷却した後の試験片の縦方向、横方向の寸法を測定し、該寸法とオーブンに入れる前の縦方向、横方向の寸法との差から計算によって求めた。具体的には、縦方向の寸法変化率の場合は、冷却後の縦方向の寸法から加熱前の縦方向の寸法を引いて得られた値を、加熱前の縦方向の寸法で割って、１００を掛けることによって求めた。幅方向も同様に求めた。
【００４０】
尚、本発明において上記特定の加熱寸法変化率を示す発泡シートの調整方法は、前述の特定の平衡コンプライアンス（Ｊ_０）及び溶融粘度（η）を有する基材樹脂を使用することが必要条件として挙げられ、更に、押出発泡工程において、例えば、ダイから樹脂を押出し、発泡させつつ、押出方向及び／又は幅方向に延伸する度合を変えることにより調整することができる。
【００４１】
本発明の他の態様のポリプロピレン系樹脂積層発泡シートは、上記基材樹脂を上記発泡シートと同様に、押出発泡することによって得られた密度１５０〜４５０ｋｇ／ｍ^３、厚み０．５〜２．０ｍｍの発泡シートの少なくとも片面にポリプロピレン系樹脂が積層されたポリプロピレン系樹脂積層発泡シート（以下、「積層発泡シート」という。）であって、１８０℃の雰囲気下で３分間加熱した場合の寸法変化率が、上記発泡シートと同様に押出方向において−４０〜−８０％、好ましくは押出方向において−５０〜−７５％、幅方向において１０〜−２０％、好ましくは幅方向において１０〜−１０％である。
【００４２】
積層発泡シートにおける基材樹脂の構成、好ましい平衡コンプライアンス（Ｊ_０）、好ましい溶融粘度（η）、好ましい発泡シートの密度、好ましい厚み、１８０℃の雰囲気下で３分間加熱した場合の積層発泡シートの寸法変化率の測定方法は上記単層の発泡シートと同様である。
【００４３】
上記積層されるポリプロピレン系樹脂は、発泡シートの基材樹脂の主成分を構成するポリプロピレン系樹脂と同様のものを用いることができるが、積層発泡シートの熱成形性の面から平衡コンプライアンス（Ｊ_０）が２．０×１０^−３Ｐａ^−１未満のポリプロピレン系樹脂を使用することが好ましい。
【００４４】
上記積層されるポリプロピレン系樹脂の厚みは、５〜３００μｍが好ましく、２０〜２５０μｍがより好ましい。該厚みが５μｍ未満の場合は、外観向上効果は期待できるが、機械的物性はさほど向上しない。一方、該厚みが３００μｍを超えると、機械的物性は向上するが、熱成形性等の加工性が悪くなる虞があり、また積層発泡シートの重量が増加にも繋がる。
【００４５】
発泡シートとポリプロピレン系樹脂との積層は、予め形成された発泡シートにポリプロピレン系樹脂を接着剤や、加熱融着や、押出ラミネートによって積層する方法が挙げられる。但し、本発明はこれらに限定するものではなく、共押出しによって積層することもできる。
【００４６】
又、積層発泡シートにおける上記特定の加熱寸法変化率を示す積層発泡シートの調整方法は、前述の単層の発泡シートの製造方法について説明した方法と同様の方法が適用される。又、積層されるポリプロピレン系樹脂の厚みによっても積層発泡シートの加熱寸法変化率を調整することができ、更に、予め形成されているフィルムを積層する方法にてポリプロピレン系樹脂を積層する場合は、フィルムの延伸倍率を変えることによっても積層発泡シートの加熱寸法変化率を調整することができる。
【００４７】
本発明の発泡シートに積層されるポリプロピレン系樹脂には、本発明の目的、効果を阻害しない範囲において、その他の熱可塑性樹脂を添加することもできる。又、着色剤、無機充填材、その他の添加剤を適宜配合することもできる。
【００４８】
本発明の発泡シート及び積層発泡シートには、更にポリスチレン系樹脂、ポリエチレン系樹脂、ポリエステル系樹脂等のポリプロピレン系樹脂以外の樹脂層、樹脂発泡層、不織布層、織布層を一層又は二層以上積層することもできる。
【００４９】
【実施例】
以下、実施例を挙げて本発明を更に詳細に説明する。
【００５０】
実施例１〜４においては、基材樹脂を構成するポリプロピレン系樹脂として、チッソ株式会社製ポリプロピレン系樹脂「ＮＥＷＦＯＡＭＥＲ ＦＨ３４００」（以下、「樹脂Ａ」という。）を、比較例１，３においては米国モンテル社製長鎖分岐ポリプロピレン系樹脂「ＰＦ８１４」（以下、「樹脂Ｂ」という。）を、比較例２においては微架橋処理が施されたポリプロピレン系樹脂（以下、「樹脂Ｃ」という。）を使用した。
【００５１】
上記樹脂Ａは直鎖状のホモポリマー、樹脂Ｂは長鎖分岐を有するホモポリマーである。
樹脂Ｃは、出光石油化学株式会社製ポリプロピレン系樹脂「Ｅ２５０Ｇ（プロピレン−エチレンブロックコポリマー）」と日本ポリオレフィン株式会社製ポリプロピレン系樹脂「Ｍ７５００（プロピレン−エチレンブロックコポリマー）」との重量比２：８のブレンド物を、押出機内で加熱溶融、混練し、ストランド状に押出し、切断することによって作製した平均重量２．５ｍｇ／個の樹脂粒子を微架橋したものである。
【００５２】
上記樹脂Ｃの微架橋処理は、次の様におこなった。
まず容積５００リットルのオートクレーブ中に、ドデシルベンゼンスルホン酸ナトリウム０．０１重量部が添加された水２５０重量部と、上記ポリプロピレン系樹脂粒子と、過酸化物と、主鎖切断防止剤とを投入してオートクレーブの蓋を閉じて、オートクレーブ内の上部空間を酸素濃度が０．２体積％以下となるように窒素置換を行なった。次に、オートクレーブ内を攪拌しながら、２℃／分の昇温速度で用いた過酸化物の１０時間半減期温度まで加熱して、その温度で２時間保持し、その後、２℃／分の昇温速度で用いた過酸化物の１分間半減期温度まで加熱して、その温度で２０分間保持した後に冷却した。
【００５３】
尚、上記過酸化物としてはｍ−トルオイル−ベンゾイルパーオキサイド（日本油脂株式会社製ナイパーＢＭＴ−Ｍ４０）を上記樹脂粒子１００重量部に対して０．６２５重量部添加し、主鎖切断防止剤としてジビニルベンゼンを上記樹脂粒子１００重量部に対して０．０５重量部添加した。
【００５４】
樹脂Ａ、樹脂Ｂ、樹脂Ｃの融点、結晶化温度、メルトテンション（ＭＴ）、メルトフローレイト（ＭＦＲ）を表２に、２１０℃の動的粘弾性測定における平衡コンプライアンス（Ｊ_０）、溶融粘度（η）を表３に示す。
【００５５】
【表２】

【００５６】
表２におけるメルトテンション（ＭＴ）は、株式会社東洋精機製作所製のメルトテンションテスターＩＩ型を使用して、ノズル径２．０９５ｍｍ、長さ８ｍｍのノズルを用い、樹脂温度２３０℃、ピストン速度１０ｍｍ／分の押出条件で樹脂を紐状に押出し、捲き取り速度１．５ｍ／ｍｉｎにて測定した。またメルトフローレイト（ＭＦＲ）は、ＪＩＳ Ｋ７２１０の表２の条件１４で測定した。
【００５７】
又、結晶化温度は、ＪＩＳ Ｋ７１２１に準拠して熱流束ＤＳＣにより一定の熱処理を行なった試験片から求められる結晶化ピークの頂点温度とした。尚、二つ以上の結晶化ピークが現れる場合は、ピーク面積の最も大きな主結晶化ピークの頂点温度を結晶化温度とした。
【００５８】
【表３】

【００５９】
実施例１〜４、比較例１〜３
樹脂Ａ，Ｂ，Ｃの各々と、発泡剤としてのブタンと、気泡調整剤（クエン酸モノナトリウム塩）とを表４に示す配合で（表４に示すブタン添加量及び上記気泡調整剤の添加量は、ポリプロピレン系樹脂、ブタン及び気泡調整剤の合計量に対する割合である。）、９０ｍｍφの第一押出機と１２０φの第二押出機を連結したタンデム型の押出機へ供給し、加熱溶融混練した後、押出機先端に取り付けた径１３５ｍｍφ、リップ間隙０．９ｍｍのサーキュラーダイを通して大気中に押出し、発泡させて筒状の発泡体を形成した。
【００６０】
【表４】

【００６１】
次いで、上記筒状の発泡体を切り開いて発泡シートを形成した。更に、実施例３においては得られた発泡シートの片面にポリプロピレン系樹脂として出光石油化学株式会社製プロピレン−エチレンブロック共重合体「Ｊ９５０ＨＰ」にタルクを１５重量％配合したものを押出して厚さ６０μｍのフィルムを積層して積層発泡シートとし、実施例４においては得られた発泡シートの両面に同様の方法で厚さ１１０μｍのフィルムを積層して積層発泡シートとし、比較例３においては得られた発泡シートの両面に同様の方法で厚さ８０μｍのフィルムを積層して積層発泡シートとした。
得られた発泡シートの密度、厚み、寸法変化率を表５に示す。
【００６２】
【表５】

【００６３】
実施例１〜４、比較例１〜３において得られた発泡シート、積層発泡シートについて、焼きそばトレー用金型が取り付けられた単発成形機（三和興業株式会社製の「ＰＬＡＶＡＣ−ＦＥ３６ＨＰ 型」）を用いて熱成形を行なった。得られた成形品について外観及び金型再現性を評価した結果を表６に示す。又、各シートについて測定したドローダウン量や、成形品を脱泡し再ペレット化した原料について測定したメルトテンション（ＭＴ）、メルトフローレート（ＭＦＲ）の測定結果も表６にあわせて示す。
【００６４】
尚、実施例１〜２の発泡シート、実施例３〜４の積層発泡シートは熱成形時のドローダウンが小さく容易に成形できた。これに対し、比較例１の発泡シート、比較例３の積層発泡シートは、熱成形時のドローダウンが激しく、得られた成形品に皺やブリッジが発生することを防ぐことができなかった。又、比較例２で得られた発泡シートは、熱成形時のドローダウンは比較例１，３のものよりは改善されていたが、得られた成形品は外観が劣るものであった。
【００６５】
【表６】

【００６６】
外観は、得られた成形品を目視により以下の基準にて評価した。
○ …… 皺やブリッジが無く良好な成形品が得られた。
△ …… 側面及び／又は底面に皺のある成形品が得られた。
× …… 側面及び／又は底面にブリッジや亀裂のある成形品が得られた。
【００６７】
金型再現性は熱成形を行い、得られた容器を下記の基準にて評価した。
○ …… 金型形状通りに成形されており、凹凸模様も明瞭である。
△ …… 金型形状通りに成形されているが、凹凸模様が不明瞭である。
× …… 金型形状通りに成形されていない。
【００６８】
表６におけるドローダウン量は、加熱時のシートの垂れ下がり量の指標となる数値であって、ドローダウン量が少ないほど熱成形し易いことを意味する。ドローダウン量の測定は、発泡シートや積層発泡シートを縦方向６００ｍｍ、横方向３００ｍｍに切断して試験シートを作製し、次に試験シートの横方向を固定し表面温度が１４５℃になるまで加熱し、その時の試験シートの垂れ下がり距離を測定し、垂れ下がり距離の最大値をドローダウン量とした。
【００６９】
表２〜６から、実施例１〜４の本発明の構成を満たす発泡シートや積層発泡シートは、ドローダウンが小さく成形が容易で、得られた成形品の外観、金型再現性も良好であることが判る。
これに対し、比較例１〜３の発泡シート、積層発泡シートは、成形時のドローダウンが大きいものであった。
【００７０】
比較例１〜３の発泡シートは、該発泡シートを粉砕したものを押出機を用いて、加熱、溶融、混練し、再ペレット化することにより、リサイクル原料としたところ、該原料のメルトテンション（ＭＴ）が表６に示す通り著しく低下しており、発泡シート製造用の原料としては不適当なもの（比較例１，３）、若しくは押出発泡条件の大きな変更を余儀なくされるもの（比較例２）であった。
【００７１】
【発明の効果】
以上説明したように、本発明のポリプロピレン系樹脂発泡シートは、ポリプロピレン系樹脂を主成分とし、２１０℃の動的粘弾性測定における平衡コンプライアンス（Ｊ_０）が５．０×１０^−３〜２０．０×１０^−３Ｐａ^−１、溶融粘度（η）が１．０×１０^３〜９．０×１０^３Ｐａ・ｓである基材樹脂を押出発泡することによって得られた密度１５０〜４５０ｋｇ／ｍ^３、厚み０．５〜２．０ｍｍのポリプロピレン系樹脂発泡シートであって、１８０℃の雰囲気下で３分間加熱した場合の寸法変化率が、押出方向において−４０〜−８０％、幅方向において１０〜−２０％であるという構成を採用している。従って、本発明によれば、熱成形時のドローダウンが小さく、熱成形が容易で不良成形品の発生率が小さく生産性に優れ、得られる成形品の金型再現性及び外観が良好な密度１５０〜４５０ｋｇ／ｍ^３、厚み０．５〜２．０ｍｍのポリプロピレン系樹脂発泡シートを提供することができる。
【００７２】
又、本発明のポリプロピレン系樹脂発泡シートを脱泡、溶融して再ペレット化して得られた樹脂は、メルトテンション（ＭＴ），メルトフローレート（ＭＦＲ）の変化が小さく、再度ポリプロピレン系樹脂発泡シートの基材樹脂として使用できる。
【００７３】
又、本発明の他のポリプロピレン系樹脂積層発泡シートは、ポリプロピレン系樹脂を主成分とし、２１０℃の動的粘弾性測定における平衡コンプライアンス（Ｊ_０）が５．０×１０^−３〜２０．０×１０^−３Ｐａ^−１、溶融粘度（η）が１．０×１０^３〜９．０×１０^３Ｐａ・ｓである基材樹脂を押出発泡することによって得られた密度１５０〜４５０ｋｇ／ｍ^３、厚み０．５〜２．０ｍｍのポリプロピレン系樹脂発泡シートの少なくとも片面にポリプロピレン系樹脂が積層されたポリプロピレン系樹脂積層発泡シートであって、１８０℃の雰囲気下で３分間加熱した場合の寸法変化率が、押出方向において−４０〜−８０％、幅方向において１０〜−２０％であるという構成を採用している。かかる構成のポリプロピレン系樹脂積層発泡シートは、熱成形時のドローダウンが小さく、得られる成形品の金型再現性及び外観が良好で、発泡シート製造用の原料としてリサイクルが可能な上に、ポリプロピレン系樹脂が積層されているので強度に優れ、美麗で滑らかな外観の成形品を提供することができる。
【図面の簡単な説明】
【図１】図１は、クリープコンプライアンスＪ（ｔ）と時間との関係の一例を示すグラフである。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a foamed polypropylene resin sheet having excellent thermoformability.
[0002]
[Prior art]
BACKGROUND ART Foamed sheets made of a polypropylene-based resin are widely used for forming various containers and trays. Also, as a method for producing a polypropylene resin foam sheet, a foamable molten resin mixture obtained by melt-kneading a polypropylene resin and a foaming agent in an extruder is discharged under atmospheric pressure through a die attached to the extruder tip. An extrusion foaming method for foaming is known.
[0003]
However, the polypropylene-based resin has a property that the viscoelasticity in a molten state greatly changes in response to a slight temperature change, and this has been a major problem in the extrusion foaming method. That is, when a small change occurs in the resin temperature when extruding a foamable molten resin mixture containing a polypropylene-based resin as a main component from an extruder, the viscoelasticity of the molten resin mixture greatly changes, so that polypropylene having excellent properties is used. Suitable foaming temperature range in which a resin foam sheet can be obtained is narrow. This has been a major problem in producing a polypropylene resin foam sheet.
[0004]
Specifically, when the temperature of the extruded resin rises slightly, the elasticity of the molten resin mixture containing a polypropylene-based resin as a main component is greatly reduced, and the foam film withstands the escape of the foaming agent in the molten resin mixture. As a result, the resulting foamed sheet has an open-cell structure or has a disadvantage such as a reduction in the expansion ratio. Further, when the temperature of the extruded resin slightly decreases, the elasticity of the molten resin mixture sharply increases. As a result, uniform foaming is hindered, and the surface becomes uneven, so that it is difficult to obtain a foamed sheet having a smooth surface. Had also occurred.
[0005]
Various improvements have been studied in order to improve such defects in extrusion foaming of the polypropylene resin. For example, a polypropylene-based resin having a free-end long-chain branch (hereinafter, referred to as a "long-chain-branched polypropylene-based resin") is known (JP-A-2-69533). The long-chain branched polypropylene-based resin is free-end by irradiating an electron beam to decompose a part thereof to form free radicals, re-bond the free radicals and deactivate the remaining free radicals. It has long chain branches.
[0006]
Since the long-chain branched polypropylene-based resin is excellent in extrusion foaming property, it is possible to obtain an excellent foamed sheet over a wide density range by using the above resin.
[0007]
[Problems to be solved by the invention]
However, the foamed sheet obtained from the long-chain branched polypropylene resin has a property of drooping greatly when heated during thermoforming (hereinafter, this drooping is referred to as “drawdown”). When such a large drawdown occurs, a large wrinkle is generated in the obtained thermoformed product, defects such as overlapping of foam sheets called a bridge occur, and the foam sheet is deteriorated by contact with the heater (burn). Or shrink or puncture).
[0008]
In addition, when the foamed sheet is defoamed and pelletized, the melt chain (MT) due to the decomposition of the molecular chain is sharply reduced and it becomes difficult to use the long-chain branched polypropylene resin as a raw material of the foamed sheet. There was also a problem that it was difficult to do.
[0009]
For the purpose of solving the drawback in the thermoforming of the long-chain branched polypropylene resin, the present applicant finely cross-links the polypropylene resin within a range of about 0 gel fraction to obtain a melt tension (MT), A polypropylene resin having a specific relationship with melt flow rate (MFR) has been proposed (JP-A-11-80262).
[0010]
However, the finely crosslinked polypropylene-based resin is easily extruded and foamed, and the obtained foamed sheet has excellent thermoformability, but has a problem that it is difficult to uniformly perform the finely crosslinked treatment. Was. In addition, although the finely crosslinked polypropylene resin having a high melt tension can be recycled, the problem that the melt tension (MT) is greatly reduced due to the decomposition of the molecular chain has not been solved.
[0011]
The present invention has been made in view of the above-mentioned drawbacks of the conventional polypropylene resin, and has excellent thermoformability, does not cause a large drawdown at the time of thermoforming, and has a melt tension by defoaming and repelletizing ( An object of the present invention is to provide a polypropylene-based resin foam sheet having a small decrease in MT) and good recyclability.
[0012]
[Means for Solving the Problems]
That is, the foamed polypropylene resin sheet of the present invention contains a polypropylene resin as a main component and has an equilibrium compliance (J) in a dynamic viscoelasticity measurement at 210 ° C.₀) Is 5.0 × 10^-3~ 20.0 × 10^-3Pa^-1, Melt viscosity (η) is 1.0 × 10³~ 9.0 × 10³Density 150 to 450 kg / m obtained by extruding and foaming a base resin having Pa · s³And a foamed polypropylene resin sheet having a thickness of 0.5 to 2.0 mm, wherein the dimensional change rate when heated in an atmosphere at 180 ° C. for 3 minutes is −40 to −80% in the extrusion direction and 10% in the width direction. -20%.
[0013]
Further, the polypropylene-based resin laminated foam sheet of the present invention contains a polypropylene-based resin as a main component and has an equilibrium compliance (J in dynamic viscoelasticity measurement at 210 ° C.).₀) Is 5.0 × 10^-3~ 20.0 × 10^-3Pa^-1, Melt viscosity (η) is 1.0 × 10³~ 9.0 × 10³Density 150 to 450 kg / m obtained by extruding and foaming a base resin having Pa · s³A polypropylene-based resin laminated foamed sheet in which a polypropylene-based resin is laminated on at least one surface of a polypropylene-based resin foamed sheet having a thickness of 0.5 to 2.0 mm, and a dimensional change when heated at 180 ° C. for 3 minutes The rate is -40 to -80% in the extrusion direction and 10 to -20% in the width direction.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
The foamed polypropylene resin sheet of the present invention (hereinafter referred to as “foamed sheet”) contains a polypropylene resin as a main component. Examples of the polypropylene resin include a propylene homopolymer and a copolymer of propylene and another monomer component. In the case of a copolymer, any of a block copolymer, a random copolymer, and a graft copolymer can be used, and not only a binary copolymer but also a ternary copolymer can be used. . Among these, as the polypropylene resin used for the foamed sheet of the present invention, a block copolymer having excellent heat resistance and low-temperature impact resistance, particularly a propylene-ethylene block copolymer, is preferable.
[0015]
In the case of the above block copolymer, it is preferable that other monomer components other than propylene are contained in an amount of 20.0% by weight or less, and in the case of a random copolymer, the content is 5.0% by weight or less. Preferably, it is contained. If the amount of other monomer components contained in the copolymer is larger than this, the inherent properties such as rigidity and heat resistance of polypropylene may be impaired.
[0016]
Other monomer components copolymerizable with propylene include ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, and 1-heptene. , 3-methyl-1-hexene and the like.
[0017]
Further, in the foamed sheet of the present invention, the polypropylene-based resin can be used not only alone but also in combination of two or more. Further, the polypropylene-based resin of the present invention includes a high-density polyethylene, a low-density polyethylene, a linear low-density polyethylene within a range (preferably within a range of 30% by weight or less) that does not impair the inherent properties of polypropylene as described above. , Linear ultra-low density polyethylene, ethylene resin such as ethylene-butene copolymer, ethylene-maleic anhydride copolymer, butene resin, polyvinyl chloride, vinyl chloride such as vinyl chloride-vinyl acetate copolymer A system resin, a styrene resin or the like can be mixed.
[0018]
The polypropylene resin preferably has a melt flow rate: MFR (condition 14 in Table 2 of JIS K7210) of 1 to 20 g / 10 minutes. Further, the melting point of the polypropylene resin is preferably 135 ° C. or higher, more preferably 145 ° C. or higher, and particularly preferably 155 ° C. or higher.
[0019]
The melting point of the polypropylene-based resin was determined by heating 3 to 5 mg of the resin from room temperature to 220 ° C. at a rate of 10 ° C./min using a differential scanning calorimeter (heat flux DSC) for the first DSC. Immediately after the curve was obtained, the temperature was lowered to 40 ° C. at a temperature lowering rate of 10 ° C./min, and then the temperature was raised to 220 ° C. again at a temperature increasing rate of 10 ° C./min. Means the temperature of the peak of the peak appearing at
However, when two or more melting peaks appear, the peak temperature of the melting peak having the largest peak area is defined as the melting point.
[0020]
The foamed sheet of the present invention comprises the above polypropylene-based resin as a main component, and has an equilibrium compliance (J₀) Is 5.0 × 10^-3~ 20.0 × 10^-3Pa^-1, Preferably 8.0 × 10^-3~ 15.0 × 10^-3Pa^-1And the melt viscosity (η) is 1.0 × 10³~ 9.0 × 10³Pa · s, preferably 3.0 × 10³~ 8.0 × 10³It is obtained by extrusion-foaming a base resin having Pa · s.
[0021]
Equilibrium compliance of base resin (J₀) Is 5.0 × 10^-3Pa^-1When it is less than 1, a foamed sheet can be obtained, but the foamed sheet has a large drawdown property at the time of thermoforming, and is inferior in thermoformability.
On the other hand, the equilibrium compliance (J₀) Is 20.0 × 10³Pa^-1When the ratio exceeds the above, the thermoformability of the obtained foamed sheet is reduced, and it is particularly difficult to obtain a molded product shape according to a mold.
[0022]
Melt viscosity (η) of base resin is 1.0 × 10³When it is less than Pa · s, it is difficult to obtain a foamed sheet having a low expansion ratio, and even if a foamed sheet can be obtained, the thermoformability is poor, such as a large drawdown.
On the other hand, the melt viscosity (η) is 9.0 × 10³If it exceeds Pa · s, it will be difficult to adjust the cell diameter of the foamed sheet to be obtained, and the thermoformability will deteriorate, leading to a deterioration in appearance.
[0023]
The equilibrium compliance (J₀) And melt viscosity (η) are measured by a dynamic viscoelasticity meter (Dynamic Analyzer SR200 manufactured by Rheometrics Scientific F.E.).
[0024]
Equilibrium compliance (J₀) And the melt viscosity (η) are specifically determined as follows.
First, a disk sample having a diameter of 25 mm is prepared from a sample resin plate for measurement having a thickness of 2 mm obtained by press molding for 5 minutes at a temperature of 260 ° C. and a pressure of 8000 kPa using a heat press. Next, this sample was sandwiched between parallel plates having a diameter of 25 mm of a dynamic viscoelasticity measuring apparatus, heated to 210 ° C., left under a nitrogen atmosphere for about 10 minutes, and then adjusted to 1.4 mm between parallel plates. Then, the molten resin protruding from the parallel plate is removed. Next, the upper parallel plate is rotated so that a constant stress σc of 100 Pa is applied to the sample melted in the nitrogen atmosphere, and the time of the strain amount γ (t) based on the time t = 0 at which the constant stress σc is started to be applied. Measure the change. The amount of strain γ (t) rapidly increases at first but gradually increases with time, and changes linearly with time after a sufficient time has elapsed.
The apparatus settings of the dynamic analyzer SR200 were set as shown in Table 1, and the equilibrium compliance (J₀) And melt viscosity (η) are calculated by an automatic function on the apparatus.
[0025]
[Table 1]

[0026]
The value obtained by dividing the strain amount γ (t) by the constant stress σc is called creep compliance J (t) and is defined by the following equation (1).
J (t) = γ (t) / σc (1)
[0027]
The creep compliance J (t) rapidly increases at the beginning like the strain amount γ (t), but gradually increases with time, and changes linearly with time after sufficient time has passed ( Shown in FIG. 1). The creep compliance J (t) that changes linearly can be expressed by the following equation (2).
## EQU2 ## J (t) = J₀+ T / η (2)
[0028]
The equilibrium compliance (J₀) Is J in equation (2).₀Given as That is, in a diagram in which the creep compliance J (t) is plotted on the vertical axis and the time t is plotted on the horizontal axis, the intercept at the time t = 0 when the linear portion of the creep compliance J (t) is extrapolated to the time t = 0. Given.
The melt viscosity (η) in the present specification is given as the reciprocal of the slope of the linear portion of the creep compliance J (t) in the equation (2).
[0029]
A specific equilibrium compliance (J₀) And a melt viscosity (η), for example, by dispersing a polyolefin component such as ultrahigh molecular weight polypropylene or polyethylene in a polypropylene resin by a catalyst technique without being ubiquitous, and obtaining a specific equilibrium compliance (J₀) And a melt-viscosity (η) that achieves entanglement of molecular chains, and a polypropylene resin is subjected to specific equilibrium compliance (J₀) And those modified to satisfy the melt viscosity (η). Specifically, polypropylene resin "NEWFOAMER FH3400" manufactured by Chisso Corporation can be selected.
However, the base resin used in the present invention is mainly composed of a polypropylene resin and has a specific equilibrium compliance (J₀) And a melt viscosity (η), and are not limited to the method of synthesizing, modifying, or adjusting the base resin.
[0030]
The foamed sheet of the present invention is obtained by extruding and foaming the base resin. As the extrusion foaming, for example, the above-mentioned base resin is heated and melted in an extruder, kneaded, and further, a foaming agent is injected under a high temperature and a high pressure, and kneaded to form a foamable molten resin composition. Extruded under atmospheric pressure through an annular die to foam into a tubular shape, and cut out the tubular foam along the extrusion direction to form a foamed sheet.
[0031]
As the foaming agent, a physical foaming agent and a chemical foaming agent are used. Among the physical foaming agents, examples of the inorganic foaming agents include carbon dioxide, air, and nitrogen.
[0032]
Among the physical foaming agents, organic compounds include aliphatic hydrocarbons such as propane, n-butane, i-butane, pentane and hexane; cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane; and chlorofluoromethane. , Trifluoromethane, 1,1-difluoroethane, 1-chloro-1,1-difluoroethane, 1,1,1,2-tetrafluoroethane, 1-chloro-1,2,2,2-tetrafluoroethane, methyl Halogenated hydrocarbons such as chloride, ethyl chloride and methylene chloride can be used. Further, as the chemical foaming agent, azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate and the like can be used.
[0033]
These foaming agents can be used by being appropriately mixed. The amount of the foaming agent used varies depending on the type of the foaming agent, the desired expansion ratio of the foamed sheet, and the like. However, the guideline of the amount of the foaming agent used to obtain the foamed sheet of the present invention is 100 parts by weight of the base resin. In the case of a physical foaming agent, it is about 0.5 to 25 parts by weight (in terms of butane).
[0034]
In the production of the foamed sheet of the present invention, a cell regulator can be added to the base resin as required. Examples of the foam control agent include inorganic powders such as talc and silica, acid salts of polycarboxylic acids, and reaction mixtures of polycarboxylic acids with sodium carbonate or sodium bicarbonate. In general, it is preferable that the added amount of the bubble adjuster is about 3 parts by weight or less per 100 parts by weight of the base resin.
[0035]
Further, if necessary, various additives such as an antistatic agent, a fluidity improver and the like, and a colorant in an amount which does not disturb the intended purpose can be added to the base resin. Further, talc, silica, calcium carbonate, clay, zeolite, alumina, barium sulfate and the like can be added as an inorganic filler. The upper limit of the amount of the inorganic filler to be added is preferably 40% by weight of the total weight of the resin and other additives. The inorganic powder and the inorganic filler preferably have an average particle size of 1 to 70 μm. The addition of the inorganic filler improves the heat resistance of the obtained foamed sheet and can reduce the calories burned when the foamed sheet is incinerated.
[0036]
The density of the foam sheet of the present invention is 150 to 450 kg / m.^ThreeIt is. In particular, 180-360kg / m ^Three It is preferable that Density is 150kg / m^ThreeIf it is less than 1, the rigidity of the molded product obtained by thermoforming may be weakened, and the corners and the uneven pattern of the molded product cannot be clearly molded (hereinafter, referred to as “mold reproducibility”). There is a possibility that thermoformability may deteriorate. On the other hand, the density is 450 kg / m^ThreeIf the ratio exceeds the above range, the heat insulation and cushioning properties of the molded product obtained by thermoforming may be deteriorated.
[0037]
The foam sheet of the present invention has a thickness of 0.5 to 2.0 mm. In particular, it is preferable that the thickness be 0.8 to 1.8 mm.
When the thickness is less than 0.5 mm, the heat insulating property may be deteriorated. When the thickness is more than 2.0 mm, the molding cycle at the time of thermoforming, the decrease in mold reproducibility, the decrease in lightness, etc. There is a fear.
[0038]
The dimensional change rate of the foamed sheet of the present invention when heated in an atmosphere at 180 ° C. for 3 minutes is −40 to −80% in the extrusion direction and 10 to −20% in the width direction. In particular, it is preferably -50 to -75% in the extrusion direction and 10 to -10% in the width direction.
When the dimensional change rate is less than -80% in the extrusion direction or less than -20% in the width direction, the foamed sheet has poor elongation during thermoforming, and only a part is locally stretched to be uniform. There is a possibility that a molded article having a large thickness cannot be obtained. On the other hand, if the dimensional change exceeds -40% in the extrusion direction or exceeds 10% in the width direction, drawdown during thermoforming may not be improved.
[0039]
The dimensional change rate in this specification was measured using “Perfect Oven PH200” manufactured by Tabai Espec Co., Ltd. As a measurement sample, a foamed sheet cut into a 10 cm square was used, with the longitudinal direction coinciding with the extrusion direction of the foam sheet, and the horizontal direction coincident with the width direction orthogonal to the extrusion direction of the foam sheet.
For the measurement of the dimensional change, the measurement sample was left in the oven set at 180 ° C. for 3 minutes (the measurement sample was sprayed with talc on a flat metal plate in the oven, and then placed horizontally on the plate. After taking out and cooling, measure the vertical and horizontal dimensions of the test specimen, and calculate from the difference between this dimension and the vertical and horizontal dimensions before placing in the oven. I asked. Specifically, in the case of the vertical dimension change rate, the value obtained by subtracting the vertical dimension before heating from the vertical dimension after cooling is divided by the vertical dimension before heating, Determined by multiplying by 100. The width direction was similarly obtained.
[0040]
In the present invention, the method for adjusting the foamed sheet exhibiting the specific heating dimensional change rate is based on the specific equilibrium compliance (J₀) And the use of a base resin having a melt viscosity (η) as a necessary condition. In the extrusion foaming step, for example, the resin is extruded from a die and foamed in the extrusion direction and / or in the width direction. It can be adjusted by changing the degree of stretching.
[0041]
A polypropylene-based resin laminated foam sheet according to another aspect of the present invention has a density of 150 to 450 kg / m obtained by extruding and foaming the base resin in the same manner as the foamed sheet.³A foamed sheet having a thickness of 0.5 to 2.0 mm and a polypropylene-based resin laminated foamed sheet (hereinafter referred to as a “laminated foamed sheet”) in which a polypropylene-based resin is laminated on at least one surface thereof, under an atmosphere of 180 ° C. The dimensional change rate when heated for 3 minutes is -40 to -80% in the extrusion direction, preferably -50 to -75% in the extrusion direction, and 10 to -20%, preferably in the width direction, similarly to the foamed sheet. It is 10 to -10% in the width direction.
[0042]
Composition of base resin in laminated foamed sheet, preferred equilibrium compliance (J₀), The preferred melt viscosity (η), the preferred density of the foamed sheet, the preferred thickness, and the method of measuring the dimensional change of the laminated foamed sheet when heated in an atmosphere at 180 ° C. for 3 minutes are the same as those for the single-layer foamed sheet. is there.
[0043]
As the laminated polypropylene resin, the same polypropylene resin as the main component of the base resin of the foamed sheet can be used. However, from the viewpoint of the thermoformability of the laminated foamed sheet, the equilibrium compliance (J₀) Is 2.0 × 10^-3Pa^-1It is preferable to use less than the polypropylene resin.
[0044]
The thickness of the laminated polypropylene resin is preferably 5 to 300 μm, more preferably 20 to 250 μm. When the thickness is less than 5 μm, the effect of improving appearance can be expected, but the mechanical properties are not significantly improved. On the other hand, when the thickness exceeds 300 μm, mechanical properties are improved, but workability such as thermoformability may be deteriorated, and the weight of the laminated foamed sheet may be increased.
[0045]
The lamination of the foamed sheet and the polypropylene-based resin includes a method of laminating the polypropylene-based resin on a foamed sheet formed in advance by an adhesive, heat fusion, or extrusion lamination. However, the present invention is not limited to these, and can be laminated by co-extrusion.
[0046]
In addition, as a method for adjusting a laminated foamed sheet exhibiting the specific heating dimensional change rate in the laminated foamed sheet, a method similar to the method described for the above-described method for producing a single-layer foamed sheet is applied. In addition, the heating dimensional change rate of the laminated foamed sheet can be adjusted also by the thickness of the laminated polypropylene resin, and when the polypropylene resin is laminated by a method of laminating a film formed in advance, By changing the stretching ratio of the film, the heating dimensional change rate of the laminated foamed sheet can be adjusted.
[0047]
Other thermoplastic resins can be added to the polypropylene resin laminated on the foamed sheet of the present invention as long as the objects and effects of the present invention are not impaired. Further, a coloring agent, an inorganic filler, and other additives can be appropriately compounded.
[0048]
The foamed sheet and the laminated foamed sheet of the present invention further include one or more layers of resin layers other than polypropylene-based resins such as polystyrene-based resins, polyethylene-based resins, and polyester-based resins, resin foamed layers, nonwoven fabric layers, and woven fabric layers. They can also be stacked.
[0049]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[0050]
In Examples 1 to 4, a polypropylene resin “NEWFOAMER FH3400” (hereinafter, referred to as “resin A”) manufactured by Chisso Corporation was used as the polypropylene resin constituting the base resin, and in Comparative Examples 1 and 3, the resin was used in the United States. A long-chain branched polypropylene resin “PF814” (hereinafter, referred to as “resin B”) manufactured by Montell Co., and a polypropylene resin subjected to fine cross-linking treatment (hereinafter, referred to as “resin C”) in Comparative Example 2. used.
[0051]
The resin A is a linear homopolymer, and the resin B is a homopolymer having a long-chain branch.
Resin C has a weight ratio of 2: 8 of a polypropylene resin “E250G (propylene-ethylene block copolymer)” manufactured by Idemitsu Petrochemical Co., Ltd. and a polypropylene resin “M7500 (propylene-ethylene block copolymer)” manufactured by Japan Polyolefin Co., Ltd. The blend is heated and melted in an extruder, kneaded, extruded into strands, and cut to give finely crosslinked resin particles having an average weight of 2.5 mg / piece.
[0052]
The fine crosslinking treatment of the resin C was performed as follows.
First, in a 500-liter autoclave, 250 parts by weight of water to which 0.01 part by weight of sodium dodecylbenzenesulfonate was added, the above polypropylene-based resin particles, peroxide, and a main chain scission inhibitor were charged. Then, the lid of the autoclave was closed, and the upper space in the autoclave was purged with nitrogen so that the oxygen concentration was 0.2% by volume or less. Next, while stirring the inside of the autoclave, the peroxide used was heated to a 10-hour half-life temperature at a heating rate of 2 ° C./min, kept at that temperature for 2 hours, and then kept at 2 ° C./min. The peroxide used was heated to the half-life temperature for 1 minute at the rate of temperature increase, held at that temperature for 20 minutes, and then cooled.
[0053]
As the peroxide, 0.625 parts by weight of m-toluoyl-benzoyl peroxide (Nipper BMT-M40 manufactured by NOF Corporation) was added to 100 parts by weight of the resin particles, and as a main chain breaking inhibitor. 0.05 parts by weight of divinylbenzene was added to 100 parts by weight of the resin particles.
[0054]
The melting point, crystallization temperature, melt tension (MT) and melt flow rate (MFR) of Resin A, Resin B and Resin C are shown in Table 2, and the equilibrium compliance (J₀) And melt viscosity (η) are shown in Table 3.
[0055]
[Table 2]

[0056]
The melt tension (MT) in Table 2 was measured using a melt tension tester type II manufactured by Toyo Seiki Seisaku-sho, Ltd., using a nozzle having a nozzle diameter of 2.095 mm and a length of 8 mm, a resin temperature of 230 ° C. and a piston speed of 10 mm / The resin was extruded in a string shape under the extrusion conditions of 1 minute, and measured at a winding speed of 1.5 m / min. The melt flow rate (MFR) was measured under the conditions 14 in Table 2 of JIS K7210.
[0057]
The crystallization temperature was defined as the peak temperature of the crystallization peak determined from a test piece that had been subjected to a constant heat treatment by heat flux DSC according to JIS K7121. When two or more crystallization peaks appear, the apex temperature of the main crystallization peak having the largest peak area was defined as the crystallization temperature.
[0058]
[Table 3]

[0059]
Examples 1-4, Comparative Examples 1-3
Each of the resins A, B, and C, butane as a foaming agent, and a cell regulator (monosodium citrate) were blended as shown in Table 4 (butane addition amount and addition of the cell regulator shown in Table 4). The amount is a ratio with respect to the total amount of the polypropylene resin, butane, and the cell regulator.), And is supplied to a tandem-type extruder in which a first extruder having a diameter of 90 mm and a second extruder having a diameter of 120 mm are connected, and heated and melt-kneaded. After that, the mixture was extruded into the atmosphere through a circular die having a diameter of 135 mm and a lip gap of 0.9 mm attached to the tip of the extruder, and foamed to form a cylindrical foam.
[0060]
[Table 4]

[0061]
Next, the tubular foam was cut open to form a foam sheet. Further, in Example 3, a foamed sheet obtained by blending 15% by weight of talc with a propylene-ethylene block copolymer “J950HP” manufactured by Idemitsu Petrochemical Co., Ltd. as a polypropylene resin was extruded on one side of the foamed sheet, and the thickness was 60 μm. Are laminated to form a laminated foamed sheet. In Example 4, a film having a thickness of 110 μm is laminated on both sides of the foamed sheet obtained in the same manner to form a laminated foamed sheet. In Comparative Example 3, the laminated foamed sheet is obtained. An 80 μm-thick film was laminated on both sides of the foamed sheet in the same manner to obtain a laminated foamed sheet.
Table 5 shows the density, thickness, and dimensional change of the obtained foamed sheet.
[0062]
[Table 5]

[0063]
For the foamed sheets and laminated foamed sheets obtained in Examples 1 to 4 and Comparative Examples 1 to 3, a single-shot molding machine ("PLAVAC-FE36HP type" manufactured by Sanwa Kogyo Co., Ltd.) equipped with a mold for a fried noodle tray. Was used for thermoforming. Table 6 shows the results of evaluation of the appearance and mold reproducibility of the obtained molded product. Table 6 also shows the drawdown amount measured for each sheet and the measurement results of melt tension (MT) and melt flow rate (MFR) measured for the raw material obtained by defoaming and repelletizing the molded product.
[0064]
Note that the foamed sheets of Examples 1 and 2 and the laminated foamed sheets of Examples 3 and 4 had a small drawdown during thermoforming and could be easily formed. On the other hand, the foamed sheet of Comparative Example 1 and the laminated foamed sheet of Comparative Example 3 suffered severe drawdown during thermoforming, and could not prevent wrinkles and bridges from being generated in the obtained molded product. In the foamed sheet obtained in Comparative Example 2, the drawdown during thermoforming was improved as compared with those of Comparative Examples 1 and 3, but the obtained molded product was inferior in appearance.
[0065]
[Table 6]

[0066]
The appearance was evaluated by visual observation of the obtained molded article according to the following criteria.
: A good molded product without wrinkles or bridges was obtained.
Δ: A molded product having wrinkles on the side surface and / or bottom surface was obtained.
×: A molded product having a bridge or a crack on the side surface and / or the bottom surface was obtained.
[0067]
The mold reproducibility was determined by thermoforming, and the obtained container was evaluated according to the following criteria.
: Molded according to the shape of the mold, and the uneven pattern is clear.
Δ: Molded according to the mold shape, but the uneven pattern is unclear.
×: Not molded according to the mold shape.
[0068]
The drawdown amount in Table 6 is a numerical value that indicates the amount of sag of the sheet during heating, and means that the smaller the drawdown amount, the easier the thermoforming. To measure the drawdown amount, a test sheet is prepared by cutting a foamed sheet or laminated foamed sheet 600 mm in the vertical direction and 300 mm in the horizontal direction, and then the test sheet is fixed in the horizontal direction and heated until the surface temperature reaches 145 ° C. The sagging distance of the test sheet at that time was measured, and the maximum value of the sagging distance was defined as the drawdown amount.
[0069]
From Tables 2 to 6, the foamed sheets and laminated foamed sheets satisfying the constitution of the present invention of Examples 1 to 4 have a small drawdown, are easy to mold, and have good appearance and mold reproducibility of the obtained molded article. It turns out there is.
On the other hand, the foamed sheets and the laminated foamed sheets of Comparative Examples 1 to 3 had a large drawdown during molding.
[0070]
The foamed sheets of Comparative Examples 1 to 3 were obtained by heating, melting, kneading and repelleting the pulverized foamed sheet using an extruder to obtain a recycled material. MT) is remarkably reduced as shown in Table 6, and is unsuitable as a raw material for producing a foamed sheet (Comparative Examples 1 and 3), or one in which a large change in extrusion foaming conditions is required (Comparative Example 2) )Met.
[0071]
【The invention's effect】
As described above, the polypropylene-based resin foamed sheet of the present invention has a polypropylene-based resin as a main component and has an equilibrium compliance (J) in a dynamic viscoelasticity measurement at 210 ° C.₀) Is 5.0 × 10^-3~ 20.0 × 10^-3Pa^-1, Melt viscosity (η) is 1.0 × 10³~ 9.0 × 10³Density 150 to 450 kg / m obtained by extruding and foaming a base resin having Pa · s³And a foamed polypropylene resin sheet having a thickness of 0.5 to 2.0 mm, wherein the dimensional change rate when heated in an atmosphere at 180 ° C. for 3 minutes is −40 to −80% in the extrusion direction and 10% in the width direction. -20% is adopted. Therefore, according to the present invention, the drawdown at the time of thermoforming is small, the thermoforming is easy, the occurrence rate of defective molded products is small, the productivity is excellent, and the mold reproducibility and appearance of the obtained molded product are excellent in density. 150-450 kg / m³And a foamed polypropylene resin sheet having a thickness of 0.5 to 2.0 mm.
[0072]
Further, the resin obtained by defoaming, melting and repelleting the foamed polypropylene resin sheet of the present invention has a small change in melt tension (MT) and melt flow rate (MFR), and the foamed polypropylene resin sheet again. Can be used as a base resin.
[0073]
Further, another polypropylene-based resin laminated foam sheet of the present invention contains a polypropylene-based resin as a main component and has an equilibrium compliance (J in dynamic viscoelasticity measurement at 210 ° C.).₀) Is 5.0 × 10^-3~ 20.0 × 10^-3Pa^-1, Melt viscosity (η) is 1.0 × 10³~ 9.0 × 10³Density 150 to 450 kg / m obtained by extruding and foaming a base resin having Pa · s³A polypropylene-based resin laminated foamed sheet in which a polypropylene-based resin is laminated on at least one surface of a polypropylene-based resin foamed sheet having a thickness of 0.5 to 2.0 mm, and a dimensional change when heated in an atmosphere at 180 ° C. for 3 minutes The ratio is set to -40 to -80% in the extrusion direction and 10 to -20% in the width direction. The polypropylene resin laminated foam sheet having such a structure has a small drawdown during thermoforming, has good mold reproducibility and appearance of a molded product obtained, and can be recycled as a raw material for producing a foamed sheet. Since the base resin is laminated, it is possible to provide a molded article having excellent strength and a beautiful and smooth appearance.
[Brief description of the drawings]
FIG. 1 is a graph showing an example of a relationship between creep compliance J (t) and time.

Claims (2)

Equilibrium compliance (J ₀ ) in dynamic viscoelasticity measurement at 210 ° C. is 5.0 × 10 ^{−3 to} 20.0 × 10 ⁻³ Pa ⁻¹ , and melt viscosity (η) is 1 with a polypropylene-based resin as a main component. Polypropylene resin foam having a density of 150 to 450 kg / m ³ and a thickness of 0.5 to 2.0 mm obtained by extruding and foaming a base resin having a thickness of 0.0 × 10 ^{3 to} 9.0 × 10 ³ Pa · s. A polypropylene resin, wherein the sheet has a dimensional change rate of −40 to −80% in the extrusion direction and 10 to −20% in the width direction when heated in an atmosphere at 180 ° C. for 3 minutes. Foam sheet. Equilibrium compliance (J ₀ ) in dynamic viscoelasticity measurement at 210 ° C. is 5.0 × 10 ^{−3 to} 20.0 × 10 ⁻³ Pa ⁻¹ , and melt viscosity (η) is 1 with a polypropylene-based resin as a main component. Polypropylene resin foam having a density of 150 to 450 kg / m ³ and a thickness of 0.5 to 2.0 mm obtained by extruding and foaming a base resin having a thickness of 0.0 × 10 ^{3 to} 9.0 × 10 ³ Pa · s. A polypropylene-based resin laminated foamed sheet in which a polypropylene-based resin is laminated on at least one surface of a sheet, wherein a dimensional change rate when heated for 3 minutes in an atmosphere of 180 ° C. is −40 to −80% in an extrusion direction, and a width. A polypropylene-based resin laminated foam sheet characterized by being 10-20% in the direction.

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