JP3557766B2

JP3557766B2 - Polyolefin-based electron beam crosslinked foam

Info

Publication number: JP3557766B2
Application number: JP02279296A
Authority: JP
Inventors: 成夫上拾石; 幸成中津
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 1995-02-08
Filing date: 1996-02-08
Publication date: 2004-08-25
Anticipated expiration: 2016-02-08
Also published as: JPH08277339A

Description

【０００１】
【産業上の利用分野】
本発明はポリオレフィン系架橋発泡体に関する。さらに詳しくは自動車内装材、緩衝材、建築材、産業資材、家具、家庭用電気器具などに適用できる緩衝性、断熱性、衝撃吸収性、振動吸収性に優れたポリオレフィン系電子線架橋発泡体に関するものである。
【０００２】
【従来の技術】
近年、ポリオレフィン系架橋発泡体は、軽量性、断熱性、遮音性に優れていることや各種の加工法による成形が容易であることから自動車内装用緩衝材や建築用途、産業資材用途、生活用品用途などで広く利用されている。
【０００３】
しかし、従来のポリオレフィン系架橋発泡体は架橋度や発泡倍率、厚みを適時選定することにより耐熱性、緩衝性、衝撃吸収性を変化させて用いられていたが、樹脂の結晶性や樹脂の構造的な特性が障害となり反発弾性が高いため同時に満足することはできず、また、振動吸収性は期待できなかった。一般的傾向として耐熱性を良くする方向は架橋度を高く、衝撃吸収性は発泡倍率を高くする方向、振動吸収性は結晶性を低くし、ブチルゴムのごとき樹脂構造にする方向であるが、これらは、いずれも相反する傾向を示し、また、樹脂の加工性が悪化するため同時に要求を満たすことは難しかった。
【０００４】
【発明が解決しようとする課題】
本発明者らは、ポリオレフィン系電子線架橋発泡体を構成する樹脂の検討を行い、樹脂組成の骨格となるポリオレフィン系樹脂を電子線により架橋性させるとき配合する樹脂の電子線架橋性あるいは架橋助剤を検討し、さらに、動的粘弾性測定で得られるｔａｎδと振動吸収性、樹脂加工性の向上した共役ジエン系樹脂と混合することにより結晶性の影響が軽減され、反発弾性が制御された、広範囲の架橋度で緩衝性、衝撃吸収性、振動吸収性を満足するポリオレフィン系電子線架橋発泡体を見出だし、本発明に至った。
【０００５】
【課題を解決するための手段】本発明の目的は、ポリオレフィン系樹脂に特定の構造、特定特性を有する樹脂を混合し、特に電子線照射により架橋状態を制御して広範囲の架橋度で緩衝性、衝撃吸収性、振動吸収性を満足するポリオレフィン架橋発泡体を提供することにある。かかる本発明の目的は、基本的には下記の構成により達成される。すなわち、「ポリオレフィン系樹脂（Ａ）と動的粘弾性測定で得られるｔａｎδのピ−クが−２０℃から４０℃の温度範囲にある共役ジエン系重合体（Ｂ）からなるポリオレフィン系架橋発泡体であって、該ポリオレフィン系架橋発泡体が電子線架橋発泡体であることを特徴とするポリオレフィン系架橋発泡体。」、「ポリオレフィン系樹脂（Ａ）と動的粘弾性測定で得られるｔａｎδのピ−クが−２０℃から４０℃の温度範囲にある共役ジエン系重合体（Ｂ）からなるポリオレフィン系架橋発泡体であって、該ポリオレフィン系樹脂（Ａ）のポリエチレン系樹脂（ａ）とポリプロピレン系樹脂（ｂ）の重量比（（ａ）／（（ａ）＋（ｂ）））が０．２〜０．８であることを特徴とするポリオレフィン系架橋発泡体。」である。
【０００６】
本発明に用いるポリオレフィン系樹脂（Ａ）とはエチレン、プロピレン、ブテン−１、４メチルペンテン−１などのいわゆるオレフィンモノマ−の単独重合体、或いは、これらのモノマ−を用いたランダム、ブロック共重合体、或いは、ビニルアセテ−ト、アクリル酸（メタ）アルキルアクリレ−ト、無水マレイン酸などとの共重合体などの融点が７０〜１６５℃、ＭＦＲが０．５〜２０ｇ／１０分を満足する公知の製造方法で得られる樹脂でれば良い。ポリオレフィン系樹脂（Ａ）の融点は７０〜１６５℃、好ましくは８０〜１５５℃である。融点が７０℃未満であるとシ−ト製造工程の押出し機での混練りゾ−ンでの剪断発熱による発泡剤の分解を止められる点、製品の柔軟性、衝撃吸収性、振動吸収性の点では好ましいが、融点が低いため製品の腰がなく巻取、後加工時のハンドリング性が悪化したり、製品がブロッキングするなど製造面での安定性にかけるので好ましくない。一方、１６５℃を越えたものは耐熱性の点では好ましいが、前述の様にシ−ト製造工程の押出し機での混練りゾ−ンでの剪断発熱による発泡剤の分解が生じやすくなり、気泡構造の制御された発泡体が得られなくなるので好ましくない。ＭＦＲは０．５〜２０ｇ／１０分、好ましくは１．５〜１０ｇ／１０分である。ＭＦＲが０．５ｇ／１０分では樹脂の溶融後の溶融粘性が高いため、押出しに適した粘度となる様に溶融温度を上げるか、もしくは高剪断下で押出しする必要が生じるが前述の様に発泡剤が分解を生じ、気泡構造の制御された発泡体が得られなくなるので好ましくない。一方、２０ｇ／１０分を越えると剪断発熱による発泡剤の分解の点では好ましいが、溶融後の粘性が低下するため、所望の表面形態、厚みのシ−ト成形が特殊な装置（具体的には急速冷却装置）を備えたシ−ト成形機でないと得られなくなるので好ましくない。
【０００７】
本発明に用いられる動的粘弾性測定で得られるｔａｎδのピ−クが−２０℃から４０℃の温度範囲にある数平均分子量が３００００〜５０００００の共役ジエン系重合体もしくは水添物（Ｂ）とは芳香族ビニルモノマ−、イソプレン、ブタジエンからなる共重合体もしくは、その水添物である。共役ジエン系重合体もしくは水添物中の芳香族ビニルモノマ−の含有量は５〜５０％、好ましくは１０〜３５％である。芳香族ビニルモノマ−の含有量が５０％を越えるとｔａｎδのピ−クの範囲が低温サイドにシフトし、樹脂自体硬くなり、衝撃吸収性が低下すると共に振動吸収性も低下するので好ましくなく、また、５％未満であるとｔａｎδのピ−クの範囲が高温サイドにシフトし、ゴム弾性体として柔軟性が向上し衝撃吸収性が良くなるように見えるが、本発明の場合、高発泡倍率の架橋発泡体とするため過度の柔軟性は、逆に発泡体の過度の変形となり衝撃吸収性が悪化するので好ましくない。本発明に用いられる芳香族ビニルモノマ−としてはスチレン系、ナフタレン系の物が用いられるが、スチレン系のものが生産性、価格の点で好ましい。本発明の共役ジエン系重合体の中のイソプレン、ブタジエンの割合はいずれも５〜９０％の範囲である。また、本樹脂の水添物の水添率は９０％以下に押さえる方が好ましく、より好ましくは８０％以下、さらに好ましくは７０％以下である。これは、電子線により架橋させるが水添率が９０％を越えると共役ジエン系重合体の架橋性が極端に低下し、発泡体としたとき架橋不足の共役ジエン系重合体部分に粗大気泡を生じ、気泡径の制御が難しくなり、結果的に発泡体の衝撃吸収性、振動吸収性が低下するので好ましくない。
【０００８】
また、動的粘弾性測定で得られるｔａｎδのピ−クは−２０℃から４０℃の温度範囲であるが、最も好ましいのは−５℃〜３５℃である。この温度範囲外のものは衝撃吸収性、振動吸収性能に劣るので好ましくない。共役ジエン系重合体の数平均分子量は３００００〜５０００００、好ましくは５００００〜２０００００である必要があるが３００００未満では発泡体としたときの機械的強度が低下したり、粘着性が顕著となり、発泡体としたときブロッキングが発生するので好ましくない。一方、５０００００を越えると樹脂の溶融粘度が高くなり、ポリオレフィン系樹脂と溶融混合したとき粘度差により分散性が悪化し、結果的に発泡体の気泡制御ができなくなるので好ましくない。
【０００９】
本発明に用いられる共役ジエン系重合体の製造方法は特に限定されるものではないが特開平５−３４５８３３号公報に例示されているものも一例である。
【００１０】
本発明に用いるポリオレフィン系樹脂（Ａ）が実質的にエチレンで構成されているものである場合、特に製造方法に限定されるものではないが一般に高圧重合法によって得られる低密度ポリエチレンや中低圧イオン重合法によるエチレンと炭素数が４〜１２のα−オレフィンとの共重合体である直鎖状ポリエチレン、エチレンと酢酸ビニルとの共重合体、エチレンとアクリル酸アルキルエステルとの共重合体、あるいはさらに無水マレイン酸を共重合した３元共重合体などが例示されるが、好ましくは、ジビニルベンゼン等の反応性架橋助剤を加えることなく電子線照射だけにより架橋するものを選定する必要がある。これは、混合する共役ジエン系重合体が骨格内に２重結合をもっており、電子線照射により架橋するが発泡に適した架橋状態を制御するには同一エネルギ−でおのおのの樹脂の架橋度に大幅な差が生じないようにするためである。なお、上述、ポリエチレン系樹脂は単独で用いても、混合して用いても架橋度に大幅な差が生じないものであれば制限されるものではない。
【００１１】
本発明に用いるエチレン系樹脂の融点は７０〜１３５℃、好ましくは８０〜１３０℃である。融点が７０℃未満であると耐熱性の点から用途的に制限が発生するので好ましくなく、１３５℃を越えると融点が高くなり用途的に広範囲をカバ−できる点では好ましいが、実質的に結晶性の高い樹脂となるため剛性が高くなり発泡体としたとき緩衝性が悪化するので好ましくない。
【００１２】
本発明に用いるエチレン系樹脂はＭＦＲが０．５〜１０ｇ／１０分、好ましくは１．０〜８ｇ／１０分である。ＭＦＲが０．５ｇ／１０分未満であると樹脂の溶融粘度が高くなるため発泡用シ−ト製造時剪断発熱により発泡剤の分解が起こりやすくなり粗大気泡を発生しやすくなるので好ましくない。一方、１０ｇ／１０分を越えると溶融粘度が低くなるためシ−ト製造上では好ましいが発泡体の伸びが低下したり、真空成形など加熱成形加工時に形状の保持力が悪化し、良好な成形品が得られにくくなるので好ましくない。
【００１３】
本発明に用いるポリオレフィン系樹脂（Ａ）が実質的にプロピレンで構成されたものの場合、その製造方法は特に限定されるものではないが一般にチ−グラ型触媒によって重合されるプロピレン単独重合体、また、エチレン、もしくは炭素数が４〜１２のα−オレフィンが２〜３５重量％ランダムもしくはブロック共重合された融点が１２５〜１６５℃、ＭＦＲが０．５〜２０ｇ／１０分である。共重合されるエチレン、もしくは炭素数が４〜１２のα−オレフィンの種類には特に制限はないが、エチレン、ブテン、ヘキセン単独、あるいはエチレン・ブテン、エチレン・ヘキセンなどの併用が上げられるが、発泡体の強度を維持するには炭素数が極力大きく、かつ、３元共重合のものが好ましい。共重合されるエチレン、もしくは炭素数が４〜１２のα−オレフィンは２〜３５重量％、好ましくは３〜２０重量％であるが、２重量％未満であるとポリプロピレン単独重合樹脂より融点が低下し、耐熱性が悪化するだけで実質的にはポリプロピレン単独重合樹脂を用いて得た発泡体と衝撃、振動吸収特性と大差なくなるので好ましくない。一方、３５重量％を越えると架橋状態の制御および緩衝性、反発弾性、耐衝撃性の点では好ましいが、融点が低下するため耐熱性が低下するので好ましくない。樹脂の融点は１２５〜１６５℃、好ましくは１３０〜１５５℃であるが、融点が１２５℃未満であると耐熱性の点から用途的に制限が発生するので好ましくなく、１６５℃を越えると融点が高くなり用途的に広範囲をカバ−できる点では好ましいが、発泡用シ−ト製造時剪断発熱により発泡剤の分解が起こりやすくなり粗大気泡を発生しやすくなるので好ましくない。ＭＦＲは０．５〜２０ｇ／１０分、好ましくは１．０〜１０ｇ／１０分である。ＭＦＲが０．５ｇ／１０分未満であると樹脂の溶融粘度が高くなるため発泡用シ−ト製造時剪断発熱により発泡剤の分解が起こりやすくなり粗大気泡を発生しやすくなるので好ましくない。一方、２０ｇ／１０分を越えると溶融粘度が低くなるためシ−ト製造上では好ましいが発泡体の伸びが低下したり、真空成形など加熱成形加工時に形状の保持力が悪化し、良好な成形品が得られにくくなるので好ましくない。
【００１４】
一般にポリプロピレン系樹脂は電子線などの電離性放射線を照射すると、プロピレンの３級炭素部分で主鎖切断を生じ、樹脂劣化するが、本発明の場合、特にプロピレン系樹脂が樹脂全体の５０重量％を越える場合、この現象を防止するためビニル性２重結合を２個以上有する反応性モノマ−、或いはダイマ−を架橋助剤（Ｃ）として添加することが好ましい。かかる架橋助剤（Ｃ）は、樹脂成分１００重量部に対し０．５〜１０重量部添加することが好ましく、０．５〜５重量部添加することがさらに好ましい。この添加量が０．５重量部未満であると発泡剤の分解ガスを保持し発泡体とするに必要な架橋度を共役ジエン系重合体部分のみに頼ることになるが、前述の様にポリプロピレン系樹脂部分の架橋が不足し実質的に広範囲の架橋度を得ることができなくなるので好ましくなく、１０重量部を越えると共役ジエン系重合体の電子線による架橋と反応性モノマ−の電子線による架橋差が過多となり、片方の樹脂成分の架橋が優先し、均一な架橋を得ることができず、従って、均一な気泡構造の架橋発泡体が得られなくなるので好ましくない。本発明に用いるビニル性２重結合を１分子中に２個以上含有する架橋助剤（Ｃ）としての作用を発揮できるものであれば特に限定されるものではないが、ジビニルベンゼン、なかでもパラ体含有率が２５％以上のもの、あるいはトリアリルトリメリテート、ペンタエリスリトールトリアクリレートやビスフェノール系誘導体などが例示できるが、液状物を用いる方が均一分散性に優れるため架橋の制御には好ましい。なお、共役ジエン系重合体（Ｂ）中の２重結合と架橋助剤（Ｃ）の電子線による架橋性差の影響を小さくし発泡に必要な安定した架橋状態を得るために共役ジエン系重合体の水添物を用いるのが更に好ましい。
【００１５】
本発明においてポリオレフィン系樹脂（Ａ）が実質的にエチレンで構成されたポリエチレン系樹脂（ａ）と実質的にポリプロピレンで構成されたポリプロピレン系樹脂（ｂ）とからなり、その配合比（ａ）／（（ａ）＋（ｂ））が０．２〜０．８のものを用いる場合、この目的は柔軟性や耐熱性、振動吸収性、衝撃吸収性を任意の範囲に設定する場合有効で、ポリエチレン系樹脂（ａ）とポリプロピレン系樹脂（ｂ）は前述の範囲の樹脂で良い。その場合、配合比（ａ）／（（ａ）＋（ｂ））は０．２〜０．８であるが、０．２未満であると前述のポリプロピレン系樹脂の範囲、例えば共重合比率などから適時選定可能となるので特に必要では無い。一方、０．８を越えるとポリエチレン系樹脂の範囲、例えば密度、共重合比率などから適時選定可能となるので特に必要では無い。
【００１６】
本発明による発泡体はポリオレフィン系樹脂（Ａ）に共役ジエン系重合体もしくは水添物（Ｂ）の配合比（Ｂ）／（（Ａ）＋（Ｂ））は０．１〜０．５が好ましく、０．２〜０．４がより好ましい。配合比が０．１未満の場合、耐熱性、機械物性の点では好ましいが、結晶性が高くなるため剛性が高くなり硬くなるため衝撃吸収性、振動吸収性、緩衝性が悪化するので好ましくない。一方、０．５を越えると理由は不明であるが衝撃吸収性、振動吸収性、大幅な性能向上は無く、むしろ非晶性成分の増加により耐熱性、強度など機械物性が低下するので好ましくない。
【００１７】
本発明の発泡体の架橋度は好ましくは１５〜８０％、より好ましくは２５〜７０％、さらに好ましくは３０〜６０％である。架橋度が１５％未満であると柔軟性や伸び、成形性の点では好ましいが、架橋度が不足し、発泡時に発泡体表面から発泡ガスが逸散しやすく所定の発泡倍率が得られなかったり、発泡体表面が荒れたり、また、耐熱性が低下するので好ましくない。一方、架橋度が８０％を越えると共役ジエン系重合体のゴム成分としての衝撃吸収性、振動吸収性、機械的強度、耐熱性の点では好ましいが、架橋度過多により任意の発泡倍率のものが得られなく、特に１０倍以上の高発泡倍率の発泡体が得られなくなったり、実質的に架橋点が増加するため伸びが低下し、成形性が悪化するため各種の形状に成形できなくなるので好ましくない。
【００１８】
本発明の発泡倍率は好ましくは２〜４０倍、より好ましくは５〜３０倍であるが、発泡倍率が２倍未満では振動吸収性、機械的強度、成形性の点では好ましいが、硬い発泡体となるため衝撃吸収性、緩衝性が低下するので好ましくなく、一方、４０倍を越えると柔軟性が増し、緩衝性の点では好ましいが、機械的強度、成形性が低下することと、理由は不明であるが振動吸収性が低下するので好ましくない。
【００１９】
本発明の発泡体は、２５℃における衝撃吸収性の反発弾性率が、好ましくは１０〜５０％，より好ましくは１５〜３５％であるが、反発弾性率が１０％未満であると、衝撃吸収性の点では好ましいが発泡体の腰がなくなり成形品など加工後、自己形状を保持する事が困難となるので好ましくなく、一方、５０％を越えると加工後の自己形状保持力は高まり成形性としては好ましいが、衝撃に対し反発する力が増大し衝撃吸収力が低下するので好ましくない。
【００２０】
本発明の発泡体は、２０℃における振動吸収性（Ｃ／Ｃｃ）は０．１％以上であるが、振動吸収性が０．１％未満であると複合品としたとき複合する広範囲の材料に対し、良好な振動吸収性、すなわち制振性を与える事ができなくなるので好ましくない。この場合、振動吸収性は前記衝撃吸収性と同様に発泡体の自己形状保持力の点から１．５％程度が上限である。
【００２１】
本発明の発泡体は前記の架橋度の範囲で成形性（Ｌ／Ｄ）が、０．４以上，好ましくは０．５〜０．９である。成形性（Ｌ／Ｄ）が０．４未満であると複雑な形状の製品を得ることができず成形法や成形のデザインに制限ができるので好ましくなく、一方、Ｌ／Ｄが大きいほど成形法や成形のデザインの自由度の点では好ましいが、一般的には成形品の形態保持性、緩衝性の点から０．９程度が上限と言える。
【００２２】
発明の発泡体の１２０℃下の耐熱性は５％以下であるが、５％を超えると１２０℃以上に加熱すると製品が変形し、形態の保持が困難となり、自動車のエンジンルーム仕切り板など内装材として広範囲に使用できないので好ましくない。
【００２３】
ポリオレフィン系樹脂を３０重量部以下混入してもよい。具体的には低密度ポリエチレン、エチレン−プロピレンゴム（ＥＰＭ）、エチレン−プロピレンゴム−ジエンゴム（ＥＰＤＭ）、高密度ポリエチレン、エチレン−酢酸ビニル共重合体（ＥＶＡ）、エチレン−アクリル酸共重合体、エチレン−（メタ）アルキルアクリレート共重合体あるいはこれらのエチレンとの共重合体に第三成分として無水マレイン酸を共重合した３元共重合体等が例示される。混入量が３０重量部を超えると柔軟性、緩衝性の点では好ましいが、特に反発弾性の高いＥＶＡ、ＥＰＭ、ＥＰＤＭなどは振動吸収性を阻害するので好ましくない。
【００２４】
その他、必要に応じて熱安定剤、耐候剤、難燃剤、難燃助剤、分散剤、顔料、充填剤を添加しても良いが、特に熱安定剤としてはヒンダ−ドフェノ−ル系とチオ系安定剤あるいは金属板との複合を考慮して金属害防止剤の添加は極力添加することが好ましい。振動吸収性を向上させるためにタルク、炭酸カルシウム、マイカ、あるいはカーボン等の微粒子を、発泡体樹脂１００重量部に対して、５〜３０重量部添加することが好ましい。
【００２５】
また、最近の環境問題に鑑みた素材のオレフィン化の進展に伴い使用部位によっては難燃剤、あるいは難燃助剤を添加する必要があるが、架橋発泡体には融点が１８０〜２４０℃の難燃剤、中でもリン・ハロゲン系難燃剤や、芳香族ハロゲン化イミド系の難燃剤を用いる事が望ましい。
【００２６】
本発明において適応できる分解型発泡剤としては有機、無機系の各種があるが、有機系ではアゾジカルボンアミド、Ｎ，Ｎ´−ジニトロソペンタメチレンテトラミン、Ｐ．Ｐ´−オキシベンゼンスルフォニルヒドラジド、トリアゾ−ル系、テトラゾ−ル系の有機塩系のもの単独、或いは混合して用いることが例示され、無機系の場合は炭酸ナトリウム、炭酸アンモニウム、重炭酸アンモニウム、カルシュウムアジド等が上げられる。中でも、アゾジカルボンアミド、Ｎ，Ｎ´−ジニトロソペンタメチレンテトラミンの混合系を用いると発泡温度の低温側でも安定した発泡体が得られるので樹脂劣化を最小限にとどめることができるので好ましい。また、Ｎ，Ｎ´−ジニトロソペンタメチレンテトラミンの代わりにアゾジテトラゾ−ル・グアニジン塩を用いても同様の効果が得られるので好ましい。
【００２７】
本発明においては発泡体の樹脂部分が架橋されていることが必要であるが、本発明の一態様である電子線架橋発泡体の架橋方法としては電離性放射線を照射して行う放射線架橋法が用いられる。化学架橋法の場合は、ジクミルパ−オキサイド、ｔ−ブチルパ−−ベンゾエ−ト、ジタ−シャリ−ブチルパ−オキサイド等の過酸化化合物を樹脂成分に対し０．５〜５重量部添加して架橋させる公知の手法が知られているが、ポリオレフィン系樹脂全体への任意適応性に欠ける。具体的にはポリプロピレン系樹脂を用いた場合、樹脂の劣化を助長し、ビニル系反応性モノマ−を適用しても、その劣化度合いは放射線架橋法よりも大きく、実質的に架橋の制御ができないので好ましくない。
【００２８】
本発明に適用する発泡方法は公知の方法が適用できるが、型内発泡法、押出し発泡法などのバッチ製品や幅・厚さに制限のある方法より、連続シ−ト状として製造できる縦型熱風発泡法、横型熱風発泡法、横型薬液発泡法などの連続シ−ト状として製造できるものが好ましい。
【００２９】
次に本発明によるポリオレフィン系架橋発泡体の製造方法の一態様について、電子線架橋発泡体の例を用いて説明する。
【００３０】
高圧法低密度ポリエチレン（密度：０．９２５ｇ／ｃｍ^３、融点：１１２℃、ＭＦＲ４．８ｇ／１０）（Ａ）５０ｋｇ、ｔａｎδのピ−クが−３℃、数平均分子量が５５０００、スチレン含有量１０％のスチレン−イソプレン−スチレンブロック共重合水添樹脂（Ｂ）３０ｋｇ、熱安定剤としてＩｒｇａｎｏｘ１０１０を０．３ｋｇ、分解型発泡剤としてアゾジカルボンアミド６．５ｋｇを内容積４５０リットルのヘンシェルミキサ−に投入し、第一次混合し、組成物を得た。この混合原料を発泡剤の分解しない温度、具体的には１３０〜１５０℃に加熱したベント付き押出し機に導入して、セットされている口径３ｍｍの口金より水冷槽に押し出し、ストランドガットとして水冷槽から引き出し、圧力空気を吹き付け、水切りしながらペレタイザ−に導入して、直径２ｍｍ，長さ３ｍｍのペレットにして、発泡用シ−ト原料を得た。この原料を１３０〜１５０℃に加熱した押出し機に導入してセットされている口金より押し出し、ロ−ル温度が６５℃のポリシングタイプのシ−ト成形機にかけ空気巻込みによる気泡のない厚さが３．０ｍｍ、幅が５００ｍｍの連続シ−ト状にして巻き取った。
【００３１】
このシ−トに電子線を照射し、発泡に適した架橋、すなわち発泡体としたときに架橋度が１５〜５０％となるように電子線を照射して架橋を付与した。このシ−トを発泡剤の分解温度より３０〜１００℃高い温度に加熱した熱媒浴上に連続的に供給して発泡させた。
【００３２】
このようにして得られた発泡体は厚みが６．１ｍｍ，幅１３００ｍｍ、発泡倍率が２５倍の表面の平滑な発泡体であった。
【００３３】
本発明は上述したように、ポリオレフィン系樹脂に特定の共役ジエン系重合体を配合し架橋発泡体としたことによりポリオレフィン系樹脂の結晶性に起因する反発弾性を軽減し、広範囲の架橋度でポリオレフィン系樹脂の特性を保持しつつ緩性、衝撃吸収性、振動吸収性に優れたものとなった。
【００３４】
本発明の効果の得られることについては定かではないが、本発明者らの経験ではポリエチレン系樹脂にゴム系樹脂を混合する場合、ゴム系樹脂の特性を発揮させるにはゴム系樹脂の配合量がポリオレフィン系樹脂と等量以上配合する必要があり、したがってポリオレフィン系樹脂の特性を保持することは極めて困難であり、一方、ゴム系成分を共重合したポリエチレン系樹脂、例えばＥＶＡ樹脂は少量の成分でさらに結晶性を低下させ、柔軟性を付与できるが衝撃吸収性、振動吸収性を満足する事はできない。本発明では特定の共役ジエン系重合体樹脂、ポリオレフィン系樹脂を配合して架橋発泡体としたことにより樹脂相互間に架橋が発生し、一見、共役ジエン系重合体樹脂とポリオレフィン系樹脂が共重合したごとき状態となるため共役ジエン系重合体樹脂の配合量が少なくてすみ、したがって、ポリオレフィン系樹脂の基本特性の低下をまねくことなく衝撃吸収性、振動吸収性が付与できるものと考える。
本発明による発泡体は，反発弾性が小さくなっているため衝撃吸収能力に優れ、さらに振動吸収性にも優れているため、各種の表皮と張り合わせた自動車内装材として従来の公知品では得られなかった独特のソフト感および衝撃吸収性、微妙な振動を吸収し制振性のある内装材が得られる。また、振動吸収性を生かし鉄板等の不燃材と張り合わせた制振性仕切り板、無機、繊維マットと張合わせた不燃性ボ−ド用裏打ち材等、金属板と粘合わせて折板加工する洗濯機などの外板やプラスチック板と粘合わせて成形加工して洗濯槽蓋など振動を発生する部分の振動を吸収させる制振性複合材や、あるいはゴムやポリ塩化ビニルに金属粉末を配合した制振シ−トと複合した低周波振動吸収制振性複合材、発泡体の少なくとも片面に粘着剤を配し、窓など振動による不快感の除去テ−プまた、合板などとの積層体は制振床材、金属フォイル、フィルム、無機繊維等との複合品で各種の成形分野に適応できる。
【００３５】
本発明における測定法、評価基準は次の通りである。
【００３６】
（１）架橋度
発泡体を細断し、０．２ｇ精秤する。このものを１３０℃のテトラリン中に浸積し、攪拌しながら３時間加熱し溶解部分を溶解せしめ、不溶部分を取り出しアセトンで洗浄してテトラリンを除去後、純水で洗浄しアセトンを除去して１２０℃の熱風乾燥機にて水分を除去して室温になるまで自然冷却する。このものの重量（Ｗ_１）ｇを測定し、次式で架橋度を求める。
【００３７】
架橋度＝（０．２−Ｗ_１／０．２）×１００（％）
（２）発泡倍率
発泡体から１０×１０ｃｍを切り出し、厚みｔ_１（ｃｍ）と重量Ｗ_２（ｇ）を測定し、次式で本発明の発泡倍率を算出する。
【００３８】
発泡倍率＝Ｗ_２／（１０×１０×ｔ_１）（ｇ／ｃｍ^３）
（３）融点
示差走査熱量計（パ−キンエルマ社ＤＳＣ−ＩＩ）で測定した溶融吸熱カ−ブの最も大きなピ−クを融点とする。
【００３９】
（４）ＭＦＲ
ポリエチレン系樹脂はＪＩＳＫ−６７６０に準じる。
【００４０】
（５）ｔａｎδの吸収ピ−ク
レオバイブロン（オリエンテック社製）ＤＤＶ−ＩＩＩの粘弾性スペクトルを測定し、スペクトルカ−ブのピ−ク温度をｔａｎδの吸収ピ−クとする。
【００４１】
（６）衝撃吸収性
リュプケの反発弾性測定装置（測定温度２５℃）で測定した値を用いる。
【００４２】
（７）振動吸収性
複素弾性係数測定装置を用い、鋼板（１ｍｍ厚さ、１５ｍｍ×２５０ｍｍ）だけでの臨界粘性減衰係数Ｃｃと粘性減衰係数Ｃとの比すなわち減衰係数比Ｃ／Ｃｃを測定した後、同サイズの試料を鋼板に貼付け、固定圧縮率７５％（鋼板の厚さを含む全試料厚さに対する圧縮固定）で片持ちばりしＣ／Ｃｃを測定し、試料を鋼板に貼付けたときの値から鋼板だけでの値を差し引いた値を振動吸収性とする。
【００４３】
（８）緩衝性
ＪＩＳＫ６７６７に準じて測定した圧縮硬さを緩衝性とする。緩衝性は０．３０〜１．２ｋｇ／ｃｍ^２の範囲を適性とする。
【００４４】
（９）成形性
直径（Ｄ）に対し深さ（Ｌ）のカップ状の成形金型を備えた真空成形機で成形し、発泡体が破れることなくカップ状に成形されたＬ／Ｄ比を成形性とした。
【００４５】
Ｌ／Ｄが０．４以上を合格とした。
【００４６】
（１０）耐熱性
発泡体から１５×１５ｃｍを切り出し、長さ方向（ＭＤ）、幅方向（ＴＤ）に１０ｃｍ間隔の測定用標線を書き、厚み（Ｔ）を測定する。このサンプルを１２０℃の熱風循環オーブンに入れ２時間加熱後、取出し、室温になるまで自然冷却する。この加熱処理サンプルの各方向の標線間隔（ＭＤｘ、ＴＤｘ）、厚み（Ｔｘ）を測定し、下記の式で寸法変化率を算出し、これを耐熱性とした。ｎ数は５、平均寸法変化率が±５％以内を合格とする。
【００４７】
ＭＤ：［（１５−ＭＤｘ）／１５］×１００（％）
ＴＤ：［（１５−ＴＤｘ）／１５］×１００（％）
厚さ：［（Ｔ−Ｔｘ）／Ｔ］×１００（％）
次に実施例に基づいて本発明の実施態様を説明する。
【００４８】
実施例１
プロピレンにエチレンを４．８重量％ランダム共重合した融点が１３４℃、ＭＦＲ０．８ｇ／１０分のポリプロピレン系樹脂（Ａ）の粉体１００ｋｇ、ｔａｎδのピークが−３℃、数平均分子量が５５０００、スチレン含有量１０％のスチレン−イソプレン−スチレンブロック共重合水添樹脂（Ｂ）５０ｋｇ、熱安定剤として“Ｍａｒｋ”ＡＯ３０を０．５ｋｇ、ＤＳＴＤＰ１．０ｋｇを内容積７５０ｌのヘンシェルミキサーに投入し、第一次混合した。更に架橋助剤（Ｃ）としてｐ体含有率４８％のジビニルベンゼン５ｋｇを投入して十分混合し、ヘンシェルミキサーのモーター負荷が低下した時点で分解型発泡剤としてアゾジカルボンアミド１２ｋｇ投入して混合し、混合原料を発泡剤の分解しない温度、具体的には１５０〜１８０℃に加熱したベント付き押出し機に導入して、セットされているＴダイから押し出し、空気巻込みによる気泡のない厚さが２．０ｍｍ、幅が４５０ｍｍの連続シート状にして巻き取った。
【００４９】
このシートに５．９０Ｍｒａｄの電子線を照射し、架橋せしめた。このシートを２１０℃、２２０℃、２２５℃の順に加熱したシリコーン薬液法の発泡装置に導入し発泡し連続シート状発泡体として巻き取った。
【００５０】
この発泡体は架橋度が３８％、発泡倍率が２０倍で厚みが４．２ｍｍ、幅１１５０ｍｍの製品とした。
【００５１】
この製品の特性を表３に示した。
【００５２】
表の如く本発明範囲内の発泡体であるため成形性、耐熱性、衝撃吸収性、振動吸収性などの品質に優れたポリプロピレン系電子線架橋発泡体である。
【００５３】
実施例２〜実施例５
表１に示したような成分を用い、表２に示したような発泡条件で発泡体とし、得られた発泡体の特性を表３に示した。
【００５４】
【表１】

【表２】

【表３】

実施例６
高圧法低密度ポリエチレン（融点：１１３℃、ＭＦＲ４．３ｇ／１０分）の粉体５０ｋｇ、ｔａｎδのピークが−３℃、数平均分子量が５５０００、スチレン含有量１０％のスチレン−イソプレン−スチレンブロック共重合水添樹脂２５ｋｇ、熱安定剤として“Ｍａｒｋ”ＡＯ３０を０．５ｋｇ、ＤＳＴＤＰ１．０ｋｇ、分解型発泡剤としてアゾジカルボンアミド８ｋｇを内容積４５０ｌのヘンシェルミキサーに投入し、第一次混合した。このものを発泡剤の分解しない温度、具体的には１３０〜１４０℃に加熱したベント付き押出し機に導入して、セットされているＴダイから押し出し、空気巻込みによる気泡のない厚さが２．０ｍｍ、幅が４５０ｍｍの連続シート状にして巻き取った。
【００５５】
このシートに３．５Ｍｒａｄの電子線を照射し、架橋せしめた。このシートを２０５℃、２１５℃、２２０℃の順に加熱したシリコーン薬液法の発泡装置に導入し発泡し連続シート状発泡体として巻き取った。
【００５６】
この発泡体は架橋度が２３％、発泡倍率が２５倍で厚みが４．２ｍｍ、幅１２５０ｍｍの製品とした。
【００５７】
この製品の特性を表６に示した。
【００５８】
表の如く本発明範囲内の発泡体であるため衝撃吸収性、振動吸収性などの品質に優れたポリエチレン系電子線架橋発泡体である。
【００５９】
実施例７〜１０
表４に示したような成分を用い、表５に示したような発泡条件で発泡体とし、得られた発泡体の特性を表６に示した。
【００６０】
【表４】

【表５】

【表６】

実施例１１、１２比較例１〜５
表７、９に示したような成分を用い、表８、１０に示したような発泡条件で発泡体とし、得られた発泡体の特性を表１１に示した。
【００６１】
【表７】

【表８】

【表９】

【表１０】

【表１１】

【００６２】
【発明の効果】
このように、実施例に示した本発明による発泡体はポリオレフィン系樹脂、特定の動的粘弾性を有する共役ジエン系重合体を配合し電子線架橋発泡体としたため、広範囲の架橋度で衝撃吸収性、振動吸収性に優れたポリオレフィン系電子線架橋発泡体が得られた。
【００６３】
一方、比較例に示した従来の公知の方法や本発明以外の範囲によるポリオレフィン系電子線架橋発泡体は樹脂、配合剤が適性でないため、衝撃吸収性、振動吸収性の不足する不満足な発泡体である。[0001]
[Industrial applications]
The present invention relates to a crosslinked polyolefin foam. More specifically, the present invention relates to a polyolefin-based electron beam crosslinked foam excellent in cushioning property, heat insulating property, shock absorbing property and vibration absorbing property applicable to automobile interior materials, cushioning materials, building materials, industrial materials, furniture, household electric appliances and the like. Things.
[0002]
[Prior art]
In recent years, polyolefin-based cross-linked foams are excellent in lightness, heat insulation and sound insulation, and are easy to form by various processing methods. Therefore, cushioning materials for automobile interiors, architectural uses, industrial materials, daily necessities Widely used for applications.
[0003]
However, conventional polyolefin-based cross-linked foams have been used by changing the heat resistance, cushioning properties, and shock absorption properties by appropriately selecting the degree of cross-linking, expansion ratio, and thickness. However, it could not be satisfied at the same time due to the high rebound resilience, and the vibration absorption could not be expected. As a general tendency, the direction to improve heat resistance is to increase the degree of cross-linking, the impact absorption is to increase the expansion ratio, the vibration absorption is to decrease the crystallinity, and to the resin structure such as butyl rubber. All show conflicting tendencies, and it has been difficult to satisfy the requirements at the same time because the processability of the resin deteriorates.
[0004]
[Problems to be solved by the invention]
The present inventors have studied the resin constituting the polyolefin-based electron beam crosslinked foam, and have found that the electron beam crosslinkability or cross-linking aid of the resin blended when the polyolefin resin serving as the skeleton of the resin composition is crosslinked with an electron beam. Investigation of the agent, furthermore, the effect of crystallinity was reduced by mixing with a conjugated diene-based resin with improved tanδ and vibration absorption and resin processability obtained by dynamic viscoelasticity measurement, and the rebound resilience was controlled. The present inventors have found a polyolefin-based electron beam crosslinked foam which satisfies the buffering property, shock absorbing property and vibration absorbing property with a wide range of crosslinking degree, and has reached the present invention.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to mix a polyolefin resin with a resin having a specific structure and specific characteristics, and particularly to control a cross-linking state by electron beam irradiation to provide a wide range of degrees of cross-linking and buffering properties. Another object of the present invention is to provide a crosslinked polyolefin foam which satisfies shock absorption and vibration absorption. The object of the present invention is basically achieved by the following configuration. That is, a polyolefin-based cross-linked foam comprising a polyolefin-based resin (A) and a conjugated diene-based polymer (B) having a peak of tan δ obtained by dynamic viscoelasticity measurement in a temperature range of −20 ° C. to 40 ° C.A crosslinked polyolefin-based foam, wherein the polyolefin-based crosslinked foam is an electron beam crosslinked foam. And "a polyolefin-based crosslinked foam comprising a polyolefin-based resin (A) and a conjugated diene-based polymer (B) having a peak of tan δ obtained by dynamic viscoelasticity measurement in a temperature range of -20 ° C to 40 ° C. Wherein the weight ratio ((a) / ((a) + (b))) of the polyethylene resin (a) and the polypropylene resin (b) of the polyolefin resin (A) is 0.2 to 0.1. 8. A crosslinked polyolefin-based foam characterized by being 8.It is.
[0006]
The polyolefin resin (A) used in the present invention is a homopolymer of a so-called olefin monomer such as ethylene, propylene, butene-1, or 4-methylpentene-1, or a random or block copolymer using these monomers. It has a melting point of 70 to 165 ° C. and an MFR of 0.5 to 20 g / 10 minutes, for example, a copolymer with vinyl acetate, (meth) alkyl acrylate, maleic anhydride or the like. The resin may be any resin obtained by a known production method. The melting point of the polyolefin resin (A) is 70 to 165 ° C, preferably 80 to 155 ° C. If the melting point is less than 70 ° C., the decomposition of the foaming agent due to the heat generated by shearing in the kneading zone in the extruder in the sheet manufacturing process can be stopped, and the flexibility, impact absorption and vibration absorption of the product can be reduced. However, since the melting point is low, the product does not have enough rigidity to be wound, and the handleability during post-processing is deteriorated. On the other hand, a temperature exceeding 165 ° C. is preferable in terms of heat resistance, but as described above, the foaming agent is easily decomposed due to heat generated by shearing in a kneading zone in an extruder in a sheet manufacturing process. It is not preferable because a foam having a controlled cell structure cannot be obtained. The MFR is 0.5 to 20 g / 10 min, preferably 1.5 to 10 g / 10 min. When the MFR is 0.5 g / 10 min, the melt viscosity of the resin after melting is high, so it is necessary to raise the melting temperature so as to obtain a viscosity suitable for extrusion or to extrude under high shear, as described above. It is not preferable because the foaming agent is decomposed and a foam having a controlled cell structure cannot be obtained. On the other hand, if it exceeds 20 g / 10 minutes, it is preferable in terms of decomposition of the foaming agent due to heat generated by shearing. However, since the viscosity after melting is reduced, sheet molding with a desired surface morphology and thickness is performed by a special device (specifically, Is not preferable unless it is a sheet molding machine equipped with a rapid cooling device).
[0007]
The conjugated diene-based polymer or hydrogenated product (B) having a number average molecular weight of 30,000 to 500,000 having a peak of tan δ obtained by dynamic viscoelasticity measurement in the temperature range of -20 ° C to 40 ° C used in the present invention. Is a copolymer of aromatic vinyl monomer, isoprene and butadiene, or a hydrogenated product thereof. The content of the aromatic vinyl monomer in the conjugated diene polymer or hydrogenated product is 5 to 50%, preferably 10 to 35%. If the content of the aromatic vinyl monomer exceeds 50%, the range of the peak of tan δ shifts to the low temperature side, the resin itself becomes hard, and the shock absorption and the vibration absorption are reduced, which is not preferable. If it is less than 5%, the range of the peak of tan δ shifts to the high-temperature side, and it appears that the rubber elastic body has improved flexibility and improved shock absorption, but in the case of the present invention, it has a high expansion ratio. Excessive flexibility for forming a crosslinked foam is not preferable because conversely, the foam is excessively deformed and the shock absorbing property is deteriorated. As the aromatic vinyl monomer used in the present invention, styrene-based and naphthalene-based ones are used, and styrene-based ones are preferred in terms of productivity and cost. The proportion of isoprene and butadiene in the conjugated diene polymer of the present invention is in the range of 5 to 90%. The hydrogenation rate of the hydrogenated product of the present resin is preferably suppressed to 90% or less, more preferably 80% or less, and further preferably 70% or less. The reason for this is that, when the hydrogenation ratio exceeds 90%, the crosslinkability of the conjugated diene-based polymer is extremely reduced, and when the foam is formed, coarse bubbles are formed in the conjugated diene-based polymer portion that is insufficiently crosslinked. As a result, it becomes difficult to control the cell diameter, and as a result, the shock absorption and vibration absorption of the foam are reduced, which is not preferable.
[0008]
The peak of tan δ obtained by the dynamic viscoelasticity measurement is in a temperature range of -20 ° C to 40 ° C, and most preferably -5 ° C to 35 ° C. Those outside this temperature range are not preferred because they are inferior in shock absorption and vibration absorption performance. The number average molecular weight of the conjugated diene-based polymer needs to be 30,000 to 500,000, preferably 50,000 to 200,000, but if it is less than 30,000, the mechanical strength of the foam decreases, and the adhesiveness becomes remarkable, Is not preferable because blocking occurs. On the other hand, if it exceeds 500,000, the melt viscosity of the resin increases, and when melt-mixed with the polyolefin resin, the dispersibility deteriorates due to the difference in viscosity, and as a result, it becomes impossible to control the cells of the foam.
[0009]
The method for producing the conjugated diene polymer used in the present invention is not particularly limited, but one exemplified in JP-A-5-345833 is also an example.
[0010]
When the polyolefin-based resin (A) used in the present invention is substantially composed of ethylene, it is not particularly limited to a production method, but is generally a low-density polyethylene or a medium-low pressure ion obtained by a high-pressure polymerization method. Linear polyethylene, which is a copolymer of ethylene and an α-olefin having 4 to 12 carbon atoms by a polymerization method, a copolymer of ethylene and vinyl acetate, a copolymer of ethylene and an alkyl acrylate, or Further, a terpolymer obtained by copolymerizing maleic anhydride is exemplified, but it is preferable to select one that can be crosslinked only by electron beam irradiation without adding a reactive crosslinking aid such as divinylbenzene. . This is because the conjugated diene-based polymer to be mixed has a double bond in the skeleton and crosslinks by electron beam irradiation. However, to control the crosslinking state suitable for foaming, the degree of crosslinking of each resin is greatly increased with the same energy. This is to prevent a significant difference from occurring. The polyethylene resin is not limited as long as it does not cause a significant difference in the degree of crosslinking even when used alone or in combination.
[0011]
The melting point of the ethylene resin used in the present invention is 70 to 135 ° C, preferably 80 to 130 ° C. If the melting point is less than 70 ° C., it is not preferable because the application is restricted from the viewpoint of heat resistance. If it exceeds 135 ° C., the melting point is high, and it is preferable in that it can cover a wide range of applications. It is not preferable because the resin has high stiffness because the resin has high water resistance and the cushioning property is deteriorated when the foam is used.
[0012]
The ethylene resin used in the present invention has an MFR of 0.5 to 10 g / 10 minutes, preferably 1.0 to 8 g / 10 minutes. If the MFR is less than 0.5 g / 10 minutes, the melt viscosity of the resin becomes high, so that the foaming agent is liable to be decomposed due to the heat generated by shearing during the production of the sheet for foaming, and coarse bubbles are easily generated, which is not preferable. On the other hand, when the melt viscosity exceeds 10 g / 10 minutes, the melt viscosity becomes low, which is preferable in the production of sheets. However, the elongation of the foam is reduced, and the shape holding power is deteriorated at the time of heat forming such as vacuum forming. It is not preferable because it becomes difficult to obtain a product.
[0013]
When the polyolefin resin (A) used in the present invention is substantially composed of propylene, the production method is not particularly limited, but a propylene homopolymer generally polymerized by a Ziegler catalyst, , Ethylene or an α-olefin having 4 to 12 carbon atoms is randomly or block copolymerized by 2 to 35% by weight, the melting point is 125 to 165 ° C, and the MFR is 0.5 to 20 g / 10 min. The type of ethylene to be copolymerized or the α-olefin having 4 to 12 carbon atoms is not particularly limited, but ethylene, butene, hexene alone, or a combination of ethylene and butene, ethylene and hexene can be used. In order to maintain the strength of the foam, those having as large a carbon number as possible and terpolymerization are preferred. The ethylene or α-olefin having 4 to 12 carbon atoms to be copolymerized is 2 to 35% by weight, preferably 3 to 20% by weight, but if less than 2% by weight, the melting point is lower than that of the polypropylene homopolymer resin. However, it is not preferable because the heat and heat resistance deteriorates and the impact and vibration absorption characteristics of the foam obtained by using the polypropylene homopolymer resin are not substantially different. On the other hand, if it exceeds 35% by weight, it is preferable in terms of control of the cross-linking state and cushioning, rebound resilience and impact resistance, but it is not preferable because the melting point is lowered and the heat resistance is lowered. The melting point of the resin is from 125 to 165 ° C, preferably from 130 to 155 ° C. However, if the melting point is less than 125 ° C, there is a restriction in application from the viewpoint of heat resistance. However, it is not preferable in that the foaming agent is likely to be decomposed due to the heat generated by shearing during the production of the sheet for foaming and coarse bubbles are easily generated. The MFR is 0.5 to 20 g / 10 min, preferably 1.0 to 10 g / 10 min. If the MFR is less than 0.5 g / 10 minutes, the melt viscosity of the resin becomes high, so that the foaming agent is liable to be decomposed due to the heat generated by shearing during the production of the sheet for foaming, and coarse bubbles are easily generated, which is not preferable. On the other hand, if the melt viscosity exceeds 20 g / 10 minutes, the melt viscosity is low, which is preferable in sheet production. However, the elongation of the foam is reduced, and the shape holding force is deteriorated at the time of heat forming such as vacuum forming. It is not preferable because it becomes difficult to obtain a product.
[0014]
Generally, when a polypropylene-based resin is irradiated with an ionizing radiation such as an electron beam, the tertiary carbon portion of the propylene causes a main chain scission, and the resin is deteriorated. In order to prevent this phenomenon, it is preferable to add a reactive monomer or dimer having two or more vinylic double bonds as a crosslinking aid (C). Preferably, 0.5 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, of such a crosslinking assistant (C) is added to 100 parts by weight of the resin component. If the addition amount is less than 0.5 parts by weight, the degree of crosslinking required to retain the decomposition gas of the foaming agent and form the foam depends on only the conjugated diene-based polymer portion. When the amount exceeds 10 parts by weight, the crosslinking of the conjugated diene polymer by the electron beam and the electron beam of the reactive monomer are not preferred. The difference in crosslinking is excessive, and the crosslinking of one resin component takes precedence, and uniform crosslinking cannot be obtained. Therefore, a crosslinked foam having a uniform cell structure cannot be obtained, which is not preferable. Although it is not particularly limited as long as it can exhibit the function as a crosslinking aid (C) containing two or more vinylic double bonds in one molecule used in the present invention, divinylbenzene, and especially Examples thereof include those having a body content of 25% or more, triallyl trimellitate, pentaerythritol triacrylate, bisphenol derivatives, and the like, but use of a liquid material is preferable for controlling the crosslinking because of its excellent uniform dispersibility. The conjugated diene-based polymer is used in order to reduce the influence of the cross-linking difference due to the electron beam between the double bond in the conjugated diene-based polymer (B) and the crosslinking aid (C) and to obtain a stable cross-linked state required for foaming. It is more preferable to use a hydrogenated product of
[0015]
In the present invention, the polyolefin-based resin (A) comprises a polyethylene-based resin (a) substantially composed of ethylene and a polypropylene-based resin (b) substantially composed of polypropylene, and the compounding ratio (a) / When ((a) + (b)) is 0.2 to 0.8, the purpose is effective when flexibility, heat resistance, vibration absorption, and shock absorption are set to arbitrary ranges. The polyethylene-based resin (a) and the polypropylene-based resin (b) may be resins in the above-described range. In this case, the compounding ratio (a) / ((a) + (b)) is 0.2 to 0.8, but if it is less than 0.2, the range of the above-mentioned polypropylene resin, for example, the copolymerization ratio, etc. It is not particularly necessary because it can be selected in a timely manner. On the other hand, if it exceeds 0.8, it is not particularly necessary because it can be selected as appropriate from the range of the polyethylene resin, for example, the density, the copolymerization ratio and the like.
[0016]
In the foam according to the present invention, the blend ratio (B) / ((A) + (B)) of the conjugated diene polymer or the hydrogenated product (B) to the polyolefin resin (A) is 0.1 to 0.5. Preferably, 0.2 to 0.4 is more preferable. When the compounding ratio is less than 0.1, it is preferable in terms of heat resistance and mechanical properties, but it is not preferable because the crystallinity is high, the rigidity is high, and the hardness is high, so that shock absorption, vibration absorption, and buffering properties are deteriorated. . On the other hand, if it exceeds 0.5, the reasons are unclear, but there is no significant improvement in shock absorption, vibration absorption, and performance. Rather, mechanical properties such as heat resistance and strength are deteriorated due to an increase in amorphous components, which is not preferable. .
[0017]
The degree of crosslinking of the foam of the present invention is preferably 15 to 80%, more preferably 25 to 70%, and still more preferably 30 to 60%. When the degree of cross-linking is less than 15%, flexibility, elongation, and moldability are preferable. However, the degree of cross-linking is insufficient, and foaming gas easily escapes from the foam surface during foaming, and a predetermined expansion ratio cannot be obtained. This is not preferred because the surface of the foam becomes rough and the heat resistance decreases. On the other hand, if the degree of crosslinking exceeds 80%, it is preferable in terms of shock absorption, vibration absorption, mechanical strength, and heat resistance of the conjugated diene polymer as a rubber component. In particular, it is not possible to obtain a foam having a high expansion ratio of 10 times or more, or the elongation is reduced due to a substantial increase in the number of cross-linking points, and the moldability is deteriorated. Not preferred.
[0018]
The expansion ratio of the present invention is preferably 2 to 40 times, more preferably 5 to 30 times. When the expansion ratio is less than 2 times, vibration absorption, mechanical strength, and moldability are preferable, but hard foams are preferred. It is not preferable because the shock absorbing property and the buffering property are reduced because it becomes less. On the other hand, if it exceeds 40 times, the flexibility increases and the buffering property is preferable, but the mechanical strength and the moldability are reduced. Although unknown, it is not preferable because the vibration absorption is reduced.
[0019]
The foam of the present invention preferably has a rebound resilience of 10 to 50%, more preferably 15 to 35%, at 25 ° C. Although it is preferable in terms of properties, it is not preferable because the rigidity of the foam is lost and it becomes difficult to maintain the self-shape after processing a molded article, etc. On the other hand, if it exceeds 50%, the self-shape holding force after processing is increased and moldability is increased. However, it is not preferable because the repulsive force against the impact increases and the impact absorbing power decreases.
[0020]
The foam of the present invention has a vibration absorption (C / Cc) at 20 ° C. of 0.1% or more, but if the vibration absorption is less than 0.1%, a wide range of materials that are composited when a composite product is obtained. On the other hand, good vibration absorption, that is, vibration damping cannot be provided, which is not preferable. In this case, the upper limit of the vibration absorption is about 1.5% from the viewpoint of the self-shape holding force of the foam, similarly to the shock absorption.
[0021]
The foam of the present invention has a moldability (L / D) of 0.4 or more, preferably 0.5 to 0.9 within the above-mentioned range of the degree of crosslinking. If the moldability (L / D) is less than 0.4, it is not preferable because a product having a complicated shape cannot be obtained and the molding method and the design of the molding can be restricted. Although it is preferable in terms of the degree of freedom of molding and the design of molding, it can be generally said that the upper limit is about 0.9 from the viewpoint of the shape retention and cushioning of the molded article.
[0022]
The heat resistance of the foam of the present invention at 120 ° C. is 5% or less, but if it exceeds 5%, the product will be deformed when heated to 120 ° C. or more, and it will be difficult to maintain its shape. It is not preferable because it cannot be used widely as a material.
[0023]
A polyolefin resin may be mixed in an amount of 30 parts by weight or less. Specifically, low-density polyethylene, ethylene-propylene rubber (EPM), ethylene-propylene rubber-diene rubber (EPDM), high-density polyethylene, ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid copolymer, ethylene Examples thereof include a terpolymer obtained by copolymerizing maleic anhydride as a third component with a (meth) alkyl acrylate copolymer or a copolymer thereof with ethylene. If the amount exceeds 30 parts by weight, it is preferable in terms of flexibility and cushioning. However, EVA, EPM, EPDM, etc., which have high rebound resilience, are not preferable because they hinder vibration absorption.
[0024]
In addition, if necessary, a heat stabilizer, a weathering agent, a flame retardant, a flame retardant aid, a dispersant, a pigment, and a filler may be added. Particularly, as the heat stabilizer, hindered phenol and thiol are used. It is preferable to add the metal harm inhibitor in consideration of the combination with the system stabilizer or the metal plate as much as possible. It is preferable to add 5 to 30 parts by weight of fine particles such as talc, calcium carbonate, mica, or carbon to 100 parts by weight of the foamed resin in order to improve the vibration absorption.
[0025]
In addition, it is necessary to add a flame retardant or a flame retardant auxiliary depending on the use site with the progress of olefination of the material in view of recent environmental problems. However, a crosslinked foam having a melting point of 180 to 240 ° C. It is desirable to use a flame retardant, especially a phosphorus / halogen flame retardant or an aromatic halogenated imide flame retardant.
[0026]
Various types of decomposition type foaming agents applicable to the present invention include organic and inorganic types. Among organic types, azodicarbonamide, N, N'-dinitrosopentamethylenetetramine, P.I. P'-oxybenzenesulfonyl hydrazide, triazole-based, tetrazole-based organic salts may be used alone or in combination. In the case of inorganics, sodium carbonate, ammonium carbonate, ammonium bicarbonate, Calcium azide and the like. Above all, it is preferable to use a mixed system of azodicarbonamide and N, N'-dinitrosopentamethylenetetramine because a stable foam can be obtained even at a low foaming temperature side, so that resin deterioration can be minimized. It is also preferable to use an azoditetrazole guanidine salt instead of N, N'-dinitrosopentamethylenetetramine, since the same effect can be obtained.
[0027]
In the present invention, it is necessary that the resin portion of the foam is cross-linked.Of the electron beam crosslinked foam which is one aspect of the present inventionRadiation cross-linking method using ionizing radiationIs used.In the case of the chemical cross-linking method, a known method in which a peroxide compound such as dicumyl peroxide, t-butyl per-benzoate, and di-tert-butyl peroxide is added to the resin component in an amount of 0.5 to 5 parts by weight to cross-link. Method is known, but lacks optional adaptability to the entire polyolefin resin.You. IngredientPhysically, when a polypropylene-based resin is used, the deterioration of the resin is promoted, and even if a vinyl-based reactive monomer is applied, the degree of the deterioration is larger than that of the radiation crosslinking method, and the crosslinking cannot be substantially controlled. It is not preferable.
[0028]
A known method can be applied to the foaming method applied to the present invention, but a vertical product that can be manufactured as a continuous sheet from a batch product such as an in-mold foaming method or an extrusion foaming method or a method having a limited width and thickness. What can be manufactured as a continuous sheet, such as a hot air foaming method, a horizontal hot air foaming method, and a horizontal chemical liquid foaming method, is preferable.
[0029]
Next, an embodiment of the method for producing a polyolefin-based crosslinked foam according to the present invention will be described using an example of an electron beam crosslinked foam.You.
[0030]
High pressure method low density polyethylene (density: 0.925 g / cm³(A) 50 kg, tan δ peak of -3 ° C., number average molecular weight of 55000, styrene content of 10%, styrene-isoprene-styrene block copolymerized hydrogenated resin. (B) 30 kg, 0.3 kg of Irganox 1010 as a heat stabilizer, and 6.5 kg of azodicarbonamide as a decomposable foaming agent were charged into a Henschel mixer having an internal volume of 450 liters, and first mixed to obtain a composition. . This mixed raw material is introduced into a vented extruder heated to a temperature at which the foaming agent does not decompose, specifically, heated to 130 to 150 ° C., and extruded into a water-cooling tank from a set die having a diameter of 3 mm, and is used as a strand gut. The pellets were blown with compressed air, introduced into a pelletizer while draining water, and formed into pellets having a diameter of 2 mm and a length of 3 mm to obtain a foaming sheet material. This raw material is introduced into an extruder heated to 130 to 150 ° C. and extruded from a set die. The roll is heated to a polishing type sheet molding machine having a roll temperature of 65 ° C. and has a thickness free of air bubbles caused by air entrainment. Was wound into a continuous sheet having a width of 3.0 mm and a width of 500 mm.
[0031]
The sheet was irradiated with an electron beam and cross-linked by applying an electron beam such that the cross-linking suitable for foaming, that is, the degree of cross-linking when the foam was formed was 15 to 50%. The sheet was continuously supplied to a heating medium bath heated to a temperature 30 to 100 ° C. higher than the decomposition temperature of the foaming agent, and foamed.
[0032]
The foam thus obtained was 6.1 mm in thickness, 1300 mm in width, and had a foaming ratio of 25 times and had a smooth surface.
[0033]
As described above, the present invention reduces the rebound resilience due to the crystallinity of the polyolefin-based resin by blending a specific conjugated diene-based polymer with the polyolefin-based resin to form a crosslinked foam. While maintaining the characteristics of the base resin, it became excellent in looseness, shock absorption and vibration absorption.
[0034]
Although it is not clear that the effects of the present invention can be obtained, according to the experience of the present inventors, when mixing a rubber-based resin with a polyethylene-based resin, in order to exhibit the characteristics of the rubber-based resin, the compounding amount of the rubber-based resin is required. Must be mixed with the polyolefin-based resin in an amount equal to or greater than that of the polyolefin-based resin. Therefore, it is extremely difficult to maintain the characteristics of the polyolefin-based resin. However, the crystallinity can be further reduced and flexibility can be imparted, but the shock absorption and vibration absorption cannot be satisfied. In the present invention, a specific conjugated diene-based polymer resin and a polyolefin-based resin are blended to form a crosslinked foam, whereby cross-linking occurs between the resins, and at a glance, the conjugated diene-based polymer resin and the polyolefin-based resin are copolymerized. It is considered that the conjugated diene-based polymer resin can be added in a small amount because of the above-described state, and therefore, shock absorption and vibration absorption can be imparted without lowering the basic characteristics of the polyolefin-based resin.
The foam according to the present invention is excellent in shock absorbing ability due to low rebound resilience and also excellent in vibration absorbing property, so that it cannot be obtained by conventional known products as automobile interior materials bonded to various skins. The interior material has a unique soft feeling, shock absorption, and subtle vibration, and provides vibration damping. In addition, laundry that is laminated with a metal plate, such as a vibration-damping partition plate that is laminated with an incombustible material such as an iron plate and a backing material for noncombustible boards that is laminated with a fiber mat, taking advantage of vibration absorption. Vibration-damping composite material that absorbs vibrations from parts that generate vibrations, such as the lid of a washing tub, or is formed by mixing metal powder with rubber or polyvinyl chloride. A low frequency vibration absorbing and damping composite material combined with a vibration sheet, an adhesive is disposed on at least one surface of the foam, and a tape for removing discomfort due to vibration such as windows, and a laminate with plywood etc. is controlled. It can be applied to various molding fields with composite products with shaking bed materials, metal foils, films, inorganic fibers and the like.
[0035]
The measuring method and evaluation criteria in the present invention are as follows.
[0036]
(1) Degree of crosslinking
The foam is shredded and 0.2 g is precisely weighed. This was immersed in tetralin at 130 ° C. and heated for 3 hours with stirring to dissolve the dissolved portion, the insoluble portion was taken out and washed with acetone to remove tetralin, and then washed with pure water to remove acetone. Moisture is removed by a hot air dryer at 120 ° C., and the mixture is naturally cooled to room temperature. The weight of this product (W₁G) is measured, and the degree of crosslinking is determined by the following equation.
[0037]
Degree of crosslinking = (0.2−W₁/0.2)×100 (%)
(2) Foaming ratio
Cut out 10 × 10cm from the foam, thickness t₁(Cm) and weight W₂(G) is measured, and the expansion ratio of the present invention is calculated by the following equation.
[0038]
Expansion ratio = W₂/ (10 × 10 × t₁) (G / cm³)
(3) Melting point
The maximum peak of the melting endothermic curve measured by a differential scanning calorimeter (Perkin Elmer DSC-II) is defined as the melting point.
[0039]
(4) MFR
The polyethylene resin conforms to JIS K-6760.
[0040]
(5) Tan δ absorption peak
The viscoelastic spectrum of Leovibron (manufactured by Orientec) DDV-III is measured, and the peak temperature of the spectrum curve is taken as the absorption peak of tan δ.
[0041]
(6) shock absorption
The value measured with a Lupke rebound resilience measuring device (measuring temperature 25 ° C) is used.
[0042]
(7) Vibration absorption
After measuring the ratio between the critical viscous damping coefficient Cc and the viscous damping coefficient C of only a steel plate (1 mm thick, 15 mm × 250 mm), that is, the damping coefficient ratio C / Cc, using a complex elastic coefficient measuring device, a sample of the same size is measured. Is attached to a steel plate, and the cantilevered C / Cc is measured at a fixed compression ratio of 75% (compressed and fixed with respect to the total sample thickness including the thickness of the steel plate). The value obtained by subtracting the value of is regarded as the vibration absorption.
[0043]
(8) Buffering
The compression hardness measured according to JIS K6767 is defined as cushioning. The buffering property is 0.30 to 1.2 kg / cm²Range is appropriate.
[0044]
(9) Formability
Molding was performed with a vacuum forming machine equipped with a cup-shaped molding die having a depth (L) with respect to the diameter (D), and the L / D ratio molded into a cup without breaking the foam was defined as moldability.
[0045]
L / D of 0.4 or more was regarded as acceptable.
[0046]
(10) Heat resistance
A 15 × 15 cm piece is cut out from the foam, and a measurement mark is drawn at 10 cm intervals in the length direction (MD) and the width direction (TD), and the thickness (T) is measured. This sample is placed in a hot air circulating oven at 120 ° C., heated for 2 hours, taken out, and naturally cooled to room temperature. The line spacing (MDx, TDx) and thickness (Tx) in each direction of this heat-treated sample were measured, and the dimensional change rate was calculated by the following equation, which was regarded as heat resistance. The number n is 5, and the average dimensional change is within ± 5%.
[0047]
MD: [(15−MDx) / 15] × 100 (%)
TD: [(15−TDx) / 15] × 100 (%)
Thickness: [(T-Tx) / T] × 100 (%)
Next, embodiments of the present invention will be described based on examples.
[0048]
Example 1
Melting point of random copolymerization of ethylene with 4.8% by weight of propylene is 134 ° C., powder of polypropylene resin (A) having MFR of 0.8 g / 10 min. 100 kg, peak of tan δ is −3 ° C., number average molecular weight is 55000, 50 kg of a hydrogenated styrene-isoprene-styrene block copolymer resin (B) having a styrene content of 10%, 0.5 kg of “Mark” AO30 as a heat stabilizer, and 1.0 kg of DSTDP were charged into a Henschel mixer having an inner volume of 750 l. Primary mixing. Further, 5 kg of divinylbenzene having a p-body content of 48% was added as a crosslinking aid (C) and mixed well, and when the motor load of the Henschel mixer was reduced, 12 kg of azodicarbonamide was added as a decomposable foaming agent and mixed. Then, the mixed raw material is introduced into a vented extruder heated to a temperature at which the foaming agent does not decompose, specifically, heated to 150 to 180 ° C., and extruded from a set T-die. The sheet was wound into a continuous sheet having a width of 2.0 mm and a width of 450 mm.
[0049]
This sheet was irradiated with 5.90 Mrad of electron beam to crosslink. This sheet was introduced into a foaming device of the silicone chemical solution method heated in the order of 210 ° C., 220 ° C., 225 ° C., foamed, and wound up as a continuous sheet foam.
[0050]
This foam was a product having a degree of crosslinking of 38%, an expansion ratio of 20 times, a thickness of 4.2 mm and a width of 1150 mm.
[0051]
The properties of this product are shown in Table 3.
[0052]
As shown in the table, since it is a foam within the scope of the present invention, it is a polypropylene-based electron beam crosslinked foam having excellent quality such as moldability, heat resistance, shock absorption and vibration absorption.
[0053]
Example 2 to Example 5
The components shown in Table 1 were used to form a foam under the foaming conditions shown in Table 2, and the properties of the obtained foam were shown in Table 3.
[0054]
[Table 1]

[Table 2]

[Table 3]

Example 6
50 kg of powder of high-pressure low-density polyethylene (melting point: 113 ° C., MFR 4.3 g / 10 min), styrene-isoprene-styrene block having a tan δ peak of −3 ° C., a number average molecular weight of 55000, and a styrene content of 10%. 25 kg of the polymerized hydrogenated resin, 0.5 kg of "Mark" AO30 as a heat stabilizer, 1.0 kg of DSTDP, and 8 kg of azodicarbonamide as a decomposable foaming agent were put into a 450 L Henschel mixer and primary mixed. This is introduced into a vented extruder heated to a temperature at which the foaming agent does not decompose, specifically, heated to 130 to 140 ° C., extruded from a set T-die, and has a thickness of 2 bubbles free from air entrainment. The sheet was wound into a continuous sheet having a width of 0.0 mm and a width of 450 mm.
[0055]
The sheet was irradiated with 3.5 Mrad of electron beam to crosslink. This sheet was introduced into a foaming apparatus of the silicone chemical solution method heated in the order of 205 ° C., 215 ° C., and 220 ° C., foamed, and wound up as a continuous sheet foam.
[0056]
This foam was a product having a degree of crosslinking of 23%, an expansion ratio of 25 times, a thickness of 4.2 mm and a width of 1250 mm.
[0057]
The properties of this product are shown in Table 6.
[0058]
As shown in the table, since it is a foam within the scope of the present invention, it is a polyethylene-based electron beam crosslinked foam excellent in quality such as shock absorption and vibration absorption.
[0059]
Examples 7 to 10
The components shown in Table 4 were used to form a foam under the foaming conditions shown in Table 5, and the properties of the obtained foam were shown in Table 6.
[0060]
[Table 4]

[Table 5]

[Table 6]

Examples 11 and 12 Comparative Examples 1 to 5
Using the components shown in Tables 7 and 9, a foam was obtained under the foaming conditions shown in Tables 8 and 10, and the properties of the obtained foam were shown in Table 11.
[0061]
[Table 7]

[Table 8]

[Table 9]

[Table 10]

[Table 11]

[0062]
【The invention's effect】
As described above, since the foam according to the present invention shown in the examples is made of a polyolefin-based resin and a conjugated diene-based polymer having a specific dynamic viscoelasticity to form an electron beam cross-linked foam, impact absorption can be achieved in a wide range of cross-linking degrees. A polyolefin-based electron beam crosslinked foam having excellent properties and vibration absorption was obtained.
[0063]
On the other hand, the polyolefin-based electron beam cross-linked foam according to the conventional known method and the range other than the present invention shown in the comparative examples is an unsatisfactory foam having insufficient shock absorption and vibration absorption because the resin and the compounding agent are not suitable. It is.

Claims

The polyolefin resin (A) and peak of tanδ obtained by dynamic viscoelasticity measurement - click the conjugated diene polymer in the temperature range of 40 ° C. from -20 ° C. (B) Tona Lupo Li olefin crosslinked foam Wherein the polyolefin-based crosslinked foam is an electron beam crosslinked foam.

A polyolefin-based cross-linked foam comprising a polyolefin-based resin (A) and a conjugated diene-based polymer (B) having a peak of tan δ obtained by dynamic viscoelasticity measurement in a temperature range of -20 ° C to 40 ° C, The weight ratio ((a) / ((a) + (b))) of the polyolefin resin (A) between the polyethylene resin (a) and the polypropylene resin (b) is 0.2 to 0.8. A crosslinked polyolefin-based foam, characterized in that:

Against polyolefin resin (A) 100 parts by weight of a conjugated diene polymer (B) and characterized in that it contains 10 to 100 parts by weight of claim 1 or polyolefin mounting serial two crosslinked foam.

Shock absorption is 10% to 50% at 25 ° C., 20 ° C. vibration absorption in (C / Cc) is characterized in that at least 0.1% claim 1 or polyolefin 2 in serial mounting crosslinked foam .

Polyolefin crosslinked foam of the mounting serial to claim 1 or 2, characterized in that the polyolefin-based resin (A) is a polypropylene resin.

Polyolefin crosslinked foam of the polyolefin resin (A) placing serial to claim 1 or 2, characterized in that a polyethylene resin.

Moldability (L / D) is a polyolefin-based crosslinked foam of the mounting serial to claim 1 or 2, characterized in that at least 0.4.

Degree of crosslinking 15 to 80% claim 1 or polyolefin mounting serial two crosslinked foam, wherein the expansion ratio is 2 to 40 times.

Conjugated diene-based polymer (B) is a styrene - isoprene - styrene block copolymer according to claim 1 or polyolefin mounting serial two crosslinked foam characterized in that it is a.

Impact to the use of polyolefin-based crosslinked foam placing serial to claim 1 or 2, characterized in that used as the buffer material that absorbs vibration.

It is characterized in that a polyolefin resin (A) and a conjugated diene polymer (B) having a peak of tan δ obtained by dynamic viscoelasticity measurement in a temperature range of -20 ° C to 40 ° C are mixed and foamed. process for producing a polyolefin cross-linked foam of the serial placement in claim 1 or 2.