JP3597989B2 - Inclined structure foam sheet and manufacturing method thereof - Google Patents

Description

【００１８】
体積平均径の物理的な意味は、単純な個数（算術）平均径に対して体積換算分の重み付けがされたものであることである。
【００１９】
体積平均径を求めるには、例えばシート断面の幅の中間層あるいは表面層に限定された部分の拡大写真を撮り、そこに存在する数十〜数百個の気泡の各方向の長さを測って、上記式［Ｉ］に従って各方向別に径の平均値を算出する。
【００２０】
したがって、上記直径Ｄｚは、上記式［Ｉ］で求められる、発泡シート中の気泡のシート厚み方向（ｚ方向と呼ぶ）の直径であり、上記直径Ｄｘｙは、上記式［ Ｉ］で求められる、発泡シート中の気泡のシート幅および長さ方向（ｘｙ方向と 呼ぶ）の直径である。
【００２１】
上記中間層とは、シート厚み方向の中心部を含み、両表面を含まない層をいい、全シート厚に対して８０％を占める。また、上記表面層とは、シート厚み方向の中心部を含まず、両表面を含む表裏２層をいい、全シート厚に対して合計２０％を占める。
【００２２】
本発明による傾斜構造発泡シートは、厚み方向に圧縮力を受けると、中間層では紡錘形の長軸方向に力がかかることになるので、高い圧縮強度を有する。
【００２３】
本発明において、傾斜構造をもつ発泡シートとは、シート中間層ではアスペクト比（Ｄｚ／Ｄｘｙ）が大きく気泡が紡錘形をなし、表面層ではアスペクト比が小さく気泡が球形に近く、アスペクト比が中間層から表面層へ傾斜状にすなわち徐々に変化しているシートをいう。
【００２４】
このように傾斜構造をもつ発泡シートは、中間層では紡錘形気泡形状の故に剛性をもち、表面層では球状に近い気泡形状の故に発泡体のような弾力性をもつものであり、そのため、全体に紡錘形気泡の発泡シートがもつ、塑性変形を起こし易く、永久歪みが大きくなるという欠点を克服することができる。
【００２５】
本発明による傾斜構造発泡シートにおいて、中間層のアスペクト比（Ｄｚ／Ｄｘｙ）が２．０未満であると、発泡シートは全体として圧縮強度が不足する。中間層のアスペクト比は好ましくは２．５以上である。また、表面層のアスペクト比（Ｄｚ／Ｄｘｙ）が１．５以上であると、表面層のアスペクト比は発泡シートは全体として圧縮永久歪みが大きくなりすぎる。表面層のアスペクト比は好ましくは１．２未満である。
【００２６】
上記構成の傾斜構造発泡シートを製造する１つの方法は、熱分解型化学発泡剤を含む熱可塑性樹脂組成物からなる発泡性シートの少なくとも片面に、面内方向の発泡力を抑制し得る強度を有するシート状物を積層し、得られた積層原反シートをシート厚み方向に加熱発泡させ、得られた溶融状態の発泡シートの厚みを２〜４０％減少させると同時にあるいはその後に同発泡シートを冷却固化させる方法である。
【００２７】
熱可塑性樹脂は前述したものであってよい。熱可塑性樹脂は、また、ポリオレフィン系樹脂と、ジオキシム化合物、ビスマレイミド、ジビニルベンゼン、アリル系多官能モノマーよりなる群から選択される少なくとも１種のモノマーとを溶融混和して得られる変性ポリオレフィンであってもよい。変性ポリオレフィンについては後で更に詳しく説明する。
【００２８】
本発明方法で用いる熱分解型化学発泡剤は、加熱により分解ガスを発生するものであれば特に限定されるものではない。熱分解型化学発泡剤の代表的な例は、アゾジカルボンアミド、ベンゼンスルホニルヒドラジド、ジニトロソペンタメチレンテトラミン、トルエンスルホニルヒドラジド、４，４−オキシビス（ベンゼンスルホニルヒドラジド）である。これらは単独で用いてもまたは２種以上組み合せて用いてもよい。その中でもアゾジカルボンアミドが特に好適に用いられる。
【００２９】
熱分解型化学発泡剤は、熱可塑性樹脂１００重量部に対し、１〜５０重量部、好ましくは２〜３５重量部の範囲で所望の発泡倍率に応じて適宜の量で使用される。
【００３０】
面内方向の発泡力を抑制し得る強度を有するシート状物としては、例えば、発泡倍率が５倍以下の場合は、引っ張り強度が０．４〜０．８ｋｇｆ／ｃｍ、発泡倍率が５〜１０倍の場合には、引っ張り強度が０．８〜１０ｋｇｆ／ｃｍ、発泡倍率が１０倍以上の場合には、引っ張り強度が１０〜１００ｋｇｆ／ｃｍの範囲のものが好ましい。
【００３１】
但し、このシート状物の強度が低すぎると、発泡に際してシート状物が裂けてしまい、発泡性シートの面内方向の発泡を充分に抑制することができないことがあり、逆に強度が高すぎると、得られる発泡体の柔軟性が低下する嫌いがある。またシート状物としては、発泡性シートと積層・一体化させる際に、発泡性シートとの間にある程度の接着性を発現するものが望ましいが、接着性が無いシート状物であっても粘着剤や接着剤を適宜用いることで発泡性シートに接着可能なものであればよい。
【００３２】
ここで、面内方向とは、シート面内のあらゆる方向をいい、シートの長手方向および幅方向を含む２次元の全方向である。
【００３３】
強度、耐久性等から好ましいシート状物としては、ガラスクロス、織布、不織布等が挙げられる。
【００３４】
ガラスクロスとは、ガラス繊維を抄造して得られるサーフェイスマット、ガラスロービングが織られてなるものをいう。また織布、不織布とは、紙、有機繊維・無機繊維等からなるものである。なお、サーフェイスマットについてはガラス短繊維同士を結着するためのバインダーが含まれてもよい。織布、不織布を構成する有機繊維としてはポリエステル繊維、綿、アクリル繊維、ナイロン繊維、炭素繊維、アラミド繊維等が挙げられる。
【００３５】
また、シート状物として、スチール製シート、ステンレススチール製シートまたはアルミニウム製シートからなるものも好ましい。このような金属製のシート状物としては、厚み０．０１ｍｍ〜１０ｍｍの圧延されたスチール、ステンレススチール、アルミニウム製の薄いシートが特に好適に使用される。この場合、これらの金属は任意に有機塗料あるいは無機塗料で塗装されていてもよく、あるいは粘接着剤が塗布されていてもよい。
【００３６】
上記熱可塑性樹脂と熱分解型化学発泡剤を混練してなる発泡性樹脂組成物は、一旦シート形状に賦形され、発泡性シートとなる。賦形の方法としては押出成形の他、プレス成形、ブロー成形、カレンダリング成形、射出成形など、プラスチックの成形加工で一般的に行われる方法が適用可能であるが、スクリュー押出機より吐出する発泡性樹脂組成物を、直接賦形する方法が、生産性の観点から好ましい。
【００３７】
発泡性シートの少なくとも片面にシート状物を積層する方法は特に限定されるものではないが、例えば、（イ）一旦冷却固化した発泡性シートにシート状物を加熱しながら貼付する方法、（ロ）発泡性シートを溶融状態になるまで加熱しておき、これをシート状物に熱融着する方法、（ハ）発泡性シートにシート状物を接着剤で貼り合わせる方法などが挙げられる。
【００３８】
積層原反シートの厚み精度を確保するには方法（イ）が最も好ましい。方法（ロ）の熱融着では、例えば、Ｔダイから押し出された直後の溶融状態の発泡性シートの少なくとも片面に、シート状物を軽く積層した状態で、これらを対向状の冷却ロール間を通過させ、ロールの押圧力で両者を一体化する方法が好ましい。
【００３９】
なお、上記のように発泡性シートとシート状物を積層して一体化するとは、発泡性シートとシート状物とを両者の界面において剥離しようとした場合に、高い割合材料破壊が生じる程度に両者が固着されている状態を意味するものとする。
【００４０】
こうして得られた積層原反シートは、適切な温度条件で加熱することにより、一定圧力下で所望の発泡倍率に発泡させることができる。上記加熱は、通常は熱分解型化学発泡剤の分解温度から、分解温度＋１００℃までの温度範囲で行われる。特に連続式発泡装置としては、加熱炉の出口側で発泡体を引き取りながら発泡させる引き取り式発泡器の他、ベルト式発泡器、縦型または横型発泡炉、熱風恒温槽や、あるいはオイルバス、メタルバス、ソルトバスなどの熱浴が用いられる。
【００４１】
本発明方法では、発泡性シートの少なくとも片面に、発泡時に面内方向の発泡力を抑制しうる強度を有するシート状物が積層されているので、発泡性シートは発泡時に面内の２次元方向には全く発泡せず、厚み方向にのみ発泡することになる。その結果、発泡体の気泡は厚み方向にその長軸を配向した紡錘形となるのである。
【００４２】
ついで、発泡が実質的に完了した後、溶融状態の発泡シートの厚みを減少させると同時に、あるいはその後に、同発泡シートを冷却固化させる。
【００４３】
この時一旦膨らんだシートの厚みをｔ_Ａ 、溶融状態で与える厚みの減少量をｔ_Ｂ とするとき、厚み減少率（ｔ_Ｂ ／ｔ_Ａ ×１００）は２〜４０％、好ましくは３〜１０％である。
【００４４】
なお熱可塑性樹脂が冷却固化する時に体積減少を伴う場合があるが、このとき回収される傾斜構造発泡シートの全厚みｔ_Ｃ は必ずしもｔ_Ａ −ｔ_Ｂ にはならず、ｔ_Ａ −ｔ_Ｂ ＜ｔ_Ｃ となる。
【００４５】
厚み減少率が２％未満であると最終的に得られる傾斜構造発泡シートの表面層のアスペクト比（Ｄｚ／Ｄｘｙ）が１．５未満とならず、４０％を上回ると中間層のアスペクト比（Ｄｚ／Ｄｘｙ）が２．０とならない。
【００４６】
厚み減少の手段は特に限定されないが、操作を連続的に行う場合には、例えばシートを適切な間隙をもつ２本のロールの間を通過させる方法があり、また厚み減少と同時に冷却を行う場合には、同ロールが冷媒を循環させた冷却ロールであればよい。またシートを適切な間隙をもつ２枚のブレードの間を通過させる方法や、シートを適切な間隙をもつ２枚のベルトを通過させる方法もある。
【００４７】
不連続操作を行う場合は、（冷却）プレスを用いる方法が適用できる。
【００４８】
本発明による傾斜構造発泡シートおよびその製造方法において、熱可塑性樹脂は、前述したように、ポリオレフィン系樹脂と、ジオキシム化合物、ビスマレイミド、ジビニルベンゼン、アリル系多官能モノマーよりなる群から選択される少なくとも１種のモノマーとを溶融混和して得られる変性ポリオレフィンであってもよい。
【００４９】
上記ポリオレフィン系樹脂の主体をなすポリオレフィンは、オレフィン性モノマーの単独重合体、または主成分オレフィン性モノマーと他のモノマーとの共重合体であり、特に限定されるものではないが、例えば、低密度ポリエチレン、高密度ポリエチレン、直鎖状低密度ポリエチレン等のポリエチレン、ホモタイプポリプロピレン、ランダムタイプポリプロピレン、ブロックタイプポリプロピレン等のポリプロピレン、ポリブテン、エチレン−プロピレン共重合体、エチレン−プロピレン−ジエン三元共重合体、エチレン−ブテン共重合体、エレチン−酢酸ビニル共重合体、エチレン−アクリル酸エステル共重合体等のエチレンを主成分とする共重合体などが例示され、またこれらの２以上の組合わせであってもよい。
【００５０】
上記ポリオレフィン系樹脂の主体をなすポリオレフィンとしては、上述したポリエチレンやポリプロピレンの１種もしくは２種以上の組み合わせが好ましい。
【００５１】
ポリオレフィン系樹脂とは上記ポリオレフィンの割合が７０〜１００重量％である樹脂組成物を指す。ポリオレフィン系樹脂を構成するポリオレフィン以外の樹脂は限定されないが、例えば、ポリスチレン、スチレン系エラストマーなどが挙げられる。ポリオレフィン系樹脂中のポリオレフィンの割合が７０重量％未満であると、ポリオレフィンの特徴である軽量、耐薬品性、柔軟性、弾性等が発揮できないばかりか、発泡に必要な溶融粘度を確保することが困難となる場合があるので好ましくない。
【００５２】
本発明方法で用いる変性用モノマーのうち、まず、ジオキシム化合物とは、オキシム基またはその水素原子が他の原子団（主に炭化水素基）で置換された構造を分子内に２個有する化合物であり、例えばｐ−キノンジオキシム、ｐ，ｐ−ベンゾイルキノンジオキシムが例示される。ジオキシム化合物は２種以上の組合わせで使用することもできる。
【００５３】
本発明方法で用いるビスマレイミド化合物とは、マレイミド構造を分子内に２個有する化合物であり、例えばＮ，Ｎ’−Ｐ−フェニレンビスマレイミド、Ｎ，Ｎ’−ｍ−フィニレンビスマレイミド、ジフェニルメタンビスマレイミドが例示される。ビスマレイミド化合物は２個以上の組合わせで使用することもできる。
【００５４】
本発明方法で用いるジビニルベンゼンは、２つのビニル基がオルト、メタ、パラのいずれの位置関係にあるものであってもよい。
【００５５】
本発明方法で用いるアリル系多官能モノマーとは、分子内にアリル基を少なくとも２個有する化合物であり、ジアリルフタレート、トリアリルシアヌレート、トリアリルイソシアヌレート、ジアリルクロレンデートが例示される。アリル系多官能モノマーは２種以上の組合わせで使用することもできる。
【００５６】
変性用モノマーの配合量は、同モノマーの種類に応じて適宜選択すればよいが、概ねポリオレフィン系樹脂１００重量部に対して０．０５〜５重量部であり、好ましくは０．２〜２重量部である。変性用モノマーの配合量が０．０５重量部未満であると、発泡に必要な溶融粘度を付与できず、５重量部を越えると、架橋度が上がりすぎ、押出成形性が悪くなる（例えば、高負荷がかかる、メルトフラクチャーが発生する）上に、後で添加する発泡剤を樹脂組成物中に均一に混練できず、不必要にゲル分率が上がりすぎ、リサイクル性を損なう。加えて、同モノマーが製品中に未反応物として残留する割合が多くなり、人体に刺激を及ぼすと共に、原料に対する製品効率が低くなることがある。
【００５７】
本発明方法において、変性用モノマーとしてジビニルベンゼンまたはアリル系多官能モノマーを用いる場合には、これに有機過酸化物を併用することが好ましい。有機過酸化物はポリオレフィンのグラフト反応に一般的に用いられる任意のものであれば良く、例えば、ベンゾイルパーオキサイド、２，４−ジクロロベンゾイルパーオキサイド、ｔ−ブチルパーオキシアセテート、ｔ−ブチルパーオキシベンゾエート、ジクミルパーオキサイド、２，５−ジメチル−２，５−ジ（ｔ−ブチルパーオキシ）ヘキサン、ジ−ｔ−ブチルパーオキサイド、２，５−ジメチル−２，５−ジ（ｔ−ブチルパーオキシ）ヘキシン−３等が挙げられ、これらが単独でまたは２種以上の組合わせで好適に用いられる。
【００５８】
有機過酸化物の使用量は、少なすぎるとグラフト化反応の転化が不十分であり、多すぎるとポリプロピレンのいわゆるβ解裂が顕著に起こり、変性物の分子量が低すぎて物性の低下あるいは粘度低下による発泡不良に至ることがある。これらの点を考慮すると、有機過酸化物の使用量は、ポリオレフィン系樹脂１００重量部に対し、０．００１〜０．５重量部であることが好ましく、０．００５〜０．１５重量部であることがより好ましい。
【００５９】
変性樹脂を得るには、ポリオレフィン系樹脂と変性用モノマーを所定条件で溶融混和する。具体的には、スクリュー押出機やニーダーなどの混練装置に上記両物質を所要量ずつ投入し、溶融混和する。この溶融混和温度は１７０℃以上かつポリオレフィン系樹脂の分解温度以下、好ましくは２００〜２５０℃である。溶融混和温度が１７０℃未満であると変性が不十分で、最終的に得られる発泡体の発泡倍率が十分高くならないことがあり、２５０℃を越えるとポリオレフィン系樹脂が分解し易くなる。
【００６０】
なお、変性ポリオレフィン系樹脂は、後にその流動性を改良する目的で、さらに同種あるいは異種のポリオレフィン系樹脂または他の熱可塑性樹脂と溶融ブレンドされても良い。ブレンド用樹脂の種類および使用量は、得られる積層原反シートの成形性、外観、シート状物との接着性、およびこれらから得られる発泡シートの発泡倍率、機械的物性、熱的物性、セル形状等によって適宜調整される。変性ポリオレフィン系樹脂１００重量部に対して、同種または異種のポリオレフィン系樹脂５０〜２００重量部を溶融ブレンドすることが好ましい。
【００６１】
【作用】
本発明による傾斜構造をもつ発泡シートは、中間層では紡錘形気泡形状の故に厚み方向に圧縮力を受けると高い圧縮強度をもち、表面層では球状に近い気泡形状の故に弾力性をもつものであり、そのため、全体に紡錘形気泡の発泡シートがもつ、塑性変形を起こし易く、永久歪みが大きくなるという欠点を克服することができる。
【００６２】
すなわち、発泡シートの中間層において厚み方向に長軸をもつ紡錘形の気泡は、その方向に強い弾性率を示す。ただし、紡錘形の気泡は一旦変形すると歪みが回復しにくく、弾性率も低下する。しかし、球形に近い気泡がシートの表面層に存在するので、シートの局所的な変形歪みを吸収し、中間層の紡錘形気泡の変形を抑制する。
【００６３】
このような傾斜構造発泡シートは、厚み方向においてサイジングが行われることが多いため、その厚み寸法精度が大幅に向上する。
【００６４】
【発明の実施の形態】
本発明を実施例によってより具体的に説明する。
【００６５】
ｉ）変性ポリオレフィン系樹脂の調製
変性用スクリュー押出機として、ＢＴ４０（プラスチック工学研究所社製）同方向回転２軸スクリュー押出機を用いた。これはセルフワイピング２条スクリューを備え、そのＬ／Ｄは３５、Ｄは３９ｍｍである。シリンダーバレルは押出機の上流から下流側へ第１〜４バレルからなり、ダイは３穴ストランドダイであり、揮発分を回収するため第４バレルに真空ベントが設置されている。
【００６６】
操作条件は下記の通りである。
【００６７】

【００６８】
上記構成の変性用スクリュー押出機に、まず、ポリオレフィン系樹脂およびジオキシム化合物をその後端ホッパーから別々に投入し両者を溶融混和し、変性樹脂を得た。このとき、押出機内で発生した揮発分は真空ベントにより真空引きした。
【００６９】
ポリオレフィン系樹脂はプロピレンのランダム共重合体（三菱化学製「ＥＧ８」、ＭＩ；０．８、密度；０．９ｇ／ｃｍ^３ ）てあり、その供給量は１０ｋｇ／ｈとした。
【００７０】
変性用モノマーはｐ−キノンジオキシム（大内新興化学社製「バルノックＧＭ−Ｐ」）であり、その供給量はポリオレフィン系樹脂１００重量部に対して０．７５重量部とした。
【００７１】
ポリオレフィン系樹脂とジオキシム化合物の溶融混和によって得られた変性樹脂を、ストランドダイから吐出し、水令し、ペレタイザーで切断して、変性樹脂のペレットを得た。
【００７２】
ｉｉ）発泡性シートの調製
発泡剤混練用スクリュー押出機はＴＥＸ−４４型（日本製鋼所社製）同方向回転２軸スクリュー押出機であり、これはセルフワイピング２条スクリューを備え、そのＬ／Ｄは４５．５、Ｄは４７ｍｍである。シリンダーバレルは押出機の上流から下流側へ第１〜１２バレルからなり、成形ダイはＴダイ（幅５００ｍｍ、厚み０．８ｍｍ）である。
【００７３】
温度設定区分は下記の通りである。
【００７４】
第１バレルは常時冷却
第１ゾーン；第２〜４バレル
第２ゾーン；第５〜８バレル
第３ゾーン；第９〜１２バレル
第４ゾーン；ダイ及びアダプター部
【００７５】
発泡剤を供給するために第６バレルにサイドフィーダーが設置され、揮発分を回収するため第１１バレルに真空ベントが設置されている。
【００７６】
操作条件は下記の通りである。
【００７７】

・スクリュー回転数：４０ｒｐｍ
上述のようにして得られた変性樹脂を変性用スクリュー押出機から発泡剤混練用スクリュー押出機に供給した。変性樹脂の供給量は２０ｋｇ／ｈとした。また、同押出機にそのサイブフィーダーから発泡剤を供給し、分散させた。発泡剤は、アゾジカルボンアミド（ＡＤＣＡ）であり、その供給量は１ｋｇ／ｈとした。こうして変性樹脂と発泡剤の混練によって得られた発泡性樹脂組成物を、Ｔダイから吐出し、得られたシート状物を３本ロールで冷却し、厚み０．８ｍｍの連続状の発泡性シートを得た。
【００７８】
ｉｉｉ） 積層原反シートの調製
他方、ポリエチレンテレフタレート製の不織布（東洋紡績社製、「スパンボンド エクーレ ６３０１Ａ」、秤量３０ｇ／ｍ^２ 、引張り強度：縦１．６ｋｇ／ｃｍ、横１．２ｋｇ／ｃｍ）を用意し、これを上記発泡性シートの両面に重ねて全体を６インチ加熱ロール（ロール表面温度１９５℃）に通し、連続融着積層した。得られた積層原反シートの端部をカットし、幅を４００ｍｍとした。
【００７９】
ｉｖ）傾斜構造発泡シートの調製
発泡機は、図１に示すように、予熱ゾーン（１） 、発泡ゾーン（２） 、冷却ゾーン（３） の３ゾーンとベルト式引取り機（６） から主として構成されている。予熱ゾーン（１） および発泡ゾーン（２） はそれぞれ２インチの搬送ロール（４） を備え、両ゾーンの全長は４ｍである。冷却ゾーン（３） は４インチの上下一対の水循環式冷却ロール（５）（５’） を備え、その全長は２ｍである。上下冷却ロール（５）（５’） の間隙は自由に設定できる。発泡ゾーン（２） の出口には光学式すなわち非接触式の厚み測定器（７） が備えられている。
【００８０】
上記構成の発泡機の予熱ゾーン（１） を１９０℃、発泡ゾーン（２） を２３０℃、冷却ロール（５）（５’） の表面温度を２５℃にそれぞれ設定し、積層原反シート（８） を上記発泡機の予熱ゾーン（１） に供給した。シート供給の線速度は０．５ｍ／ｍｉｎ、よって予熱ゾーン（１） 、発泡ゾーン（２） での滞留時間は合計８分、冷却ゾーン（３） のそれは４分であった。
【００８１】
発泡ゾーン（２） 出口付近にあるシート厚み測定器（７） により、幅方向に３ケ所でシート厚みを測定し、それらの平均値を求めたところ、８．７ｍｍであった（表１中ｔ_Ａ ）。
【００８２】
冷却ゾーン（３） の上下冷却ロール（５）（５’） の間隙を８ｍｍ（表１中ｔ_Ｃ ）に設定した。
【００８３】
発泡機出口で引取り機（６） から、図２に示す傾斜構造発泡シート（９） を回収した。この傾斜構造発泡シート（９） は、両面にシート状物（１０）が積層された熱可塑性樹脂発泡シートであって、その中間層（１２）のアスペクト比（Ｄｚ／Ｄｘｙ）が３．５で、両側の表面層（１３）のアスペクト比（Ｄｚ／Ｄｘｙ）が１．４であるものである。図２中、（１１）は中間層（１２）を構成する紡錘形気泡、（１４）は両側の表面層（１３）を構成する球状に近い気泡である。
【００８４】
ｖ）性能評価
得られた発泡シートを下記の項目について性能評価した。
【００８５】
・発泡倍率：
発泡シートからシート状物をカッターで削り取った後、ＪＩＳ Ｋ６７６７に従い発泡体の発泡倍率を測定した。
【００８６】
圧縮強度：
発泡シートを５ｃｍ角にカットし、ＪＩＳ Ｋ６７６７に従い２５％圧縮強度を測定した。
【００８７】
・圧縮永久歪み：
発泡シートを５ｃｍ角にカットし、ＪＩＳ Ｋ６７６７に従い２５％圧縮永久歪みを測定（標準状態温度２０℃で測定）
・セル形状：
発泡シートをカットし、断面の中間層と表面層を光学顕微鏡写真（３０倍）をとり、紡錘形の発泡セル約８０個の長軸長及び短軸長をデジタイザーで計測し、上記式［Ｉ］にしたがってアスペクト比（Ｄｚ／Ｄｘｙ）を算出した。
【００８８】
（実施例２）
変性ポリオレフィンの調製において、変性用モノマーとしてジビニルベンゼン（表１中ＤＶＢ）をポリプロピレン１００重量部に対して０．１重量部、および有機過酸化物としてジ−ｔ−ブチルパーオキサイドをポリプロピレン１００重量部に対して０．０３重量部使用し、また、冷却ゾーン（３） の上下冷却ロール（５）（５’） の間隙を６．０ｍｍとしたこと以外は、実施例１と同様の方法で傾斜構造発泡シートを得た。発泡ゾーン（２） 出口でのシート厚みは９．５ｍｍであった。
【００８９】
（実施例３）
熱可塑性樹脂として三菱化学社製の低密度ポリエチレン（ＹＫ４００、表１中ＬＤＰＥ）を用い、これの１００重量部に、上記発泡剤ＡＤＣＡ５重量部を、１６０℃に設定した上記発泡剤混練用スクリュー押出機にて溶融混練し、ついで実施例１と同様の方法で積層原反シートを成形した。これに５００ｋｅＶで８Ｍｒａｄの電子線を照射した。発泡ゾーン（２） 出口でのシート厚みは９．１ｍｍであった。これ以降は、実施例１と同様の方法で傾斜構造発泡シートを得た。
【００９０】
（比較例１）
発泡性組成物の調製において、冷却ゾーン（３） の上下冷却ロール（５）（５’） の間隙を２０ｍｍとしたこと以外は、実施例１と同様の方法で傾斜構造発泡シートを得た。発泡ゾーン（２） 出口でのシート厚みは８．８ｍｍであった。
【００９１】
（比較例２）
発泡性組成物の調製において、冷却ゾーン（３） の上下冷却ロール（５）（５’） の間隙を４．０ｍｍとしたこと以外は、実施例１と同様の方法で傾斜構造発泡シートを得た。発泡ゾーン（２） 出口でのシート厚みは８．７ｍｍであった。
【００９２】
実施例および比較例で得られた各発泡シートの性能評価結果を表１にまとめて示す。
【００９３】
【表１】

【００９４】
【発明の効果】
本発明による傾斜構造をもつ発泡シートは、中間層では紡錘形気泡形状の故に厚み方向に圧縮力を受けると高い圧縮強度をもち、表面層では球状に近い気泡形状の故に弾力性をもつものであり、そのため、全体に紡錘形気泡の発泡シートがもつ、塑性変形を起こし易く、永久歪みが大きくなるという欠点を克服することができる。
【００９５】
すなわち、発泡シートの中間層において厚み方向に長軸をもつ紡錘形の気泡は、その方向に強い弾性率を示す。ただし、紡錘形の気泡は一旦変形すると歪みが回復しにくく、弾性率も低下する。しかし、球形に近い気泡がシートの表面層に存在するので、シートの局所的な変形歪みを吸収し、中間層の紡錘形気泡の変形を抑制する。
【００９６】
このような傾斜構造発泡シートは、厚み方向においてサイジングが行われることが多いため、その厚み寸法精度が大幅に向上する。
【００９７】
さらに熱可塑性樹脂が変性ポリオレフィンである場合は、特に圧縮強度が高い傾斜構造発泡シートが得られる。
【００９８】
このように、本発明により、圧縮永久歪みが小さく、しかも厚み寸法精度に優れた傾斜構造発泡シートが提供され、例えば建物用の屋上断熱材、床や壁用の複合建材の芯材等に利用することができる。
【図面の簡単な説明】
【図１】図１は連続発泡器の概略図である。
【図２】図２（ａ） は傾斜構造発泡シートの斜視図、図２（ｂ） は図２（ａ） 中のｂ−ｂ線に沿う断面図である。
【符号の説明】
１：予熱ゾーン
２：発泡ゾーン
３：冷却ゾーン
４：搬送ロール
５，５´：冷却ロール
６：引取り機
７：厚み測定器
８：積層原反シート
９：傾斜構造発泡シート
１０：シート状物
１１：紡錘形気泡
１２：中心層
１３：表面層
１４：球状に近い気泡[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a composite foamed sheet mainly composed of a polyolefin-based resin, and more specifically, has a spindle-shaped cell shape in an intermediate layer of the sheet, has a nearly spherical cell shape in a surface layer, and has a cell shape from the intermediate layer to the surface layer. The present invention relates to a foamed sheet having a sloping structure having a sloping shape, that is, gradually changing. The present invention also relates to a method for producing a foamed sheet having such a structure.
[0002]
[Prior art]
BACKGROUND ART Polyolefin resin foams such as polyethylene and polypropylene are widely used as various heat insulating materials, cushioning materials, flotation materials, etc. because of their excellent lightness, heat insulating properties, flexibility and the like. However, polyolefin-based resin foams have lower compressive strength than polystyrene-based resin foams, and therefore cannot be used for applications such as roof insulation of buildings and insulation for floors. Was.
[0003]
In order to solve this problem, Japanese Patent Application Laid-Open No. 9-150431 discloses an in-plane direction (sheet-like foaming) that is generated when at least one side of a polyolefin-based resin sheet containing a thermal decomposition type chemical foaming agent is heated and foamed. A composite thermoplastic resin foam obtained by laminating sheet materials having a strength capable of suppressing the foaming force (in a two-dimensional direction including the longitudinal direction and the width direction of the body) and heating and foaming the laminated sheet is proposed. Have been.
[0004]
In the foamable resin sheet thus obtained, a sheet-like material having a strength capable of suppressing an in-plane foaming force at the time of foaming is laminated on at least one surface. It does not foam, but foams only in the thickness direction. Therefore, the cells of the foam are arranged in a spindle shape having the major axis oriented in the thickness direction, that is, a rugby ball standing upright in the sheet thickness direction. Therefore, when the obtained foam receives a compressive force in the thickness direction of the sheet, a force is applied in the major axis direction of the spindle shape, so that the foam exhibits high strength in the thickness direction.
[0005]
Further, in the composite foam, when a sheet having a particularly high elastic modulus is used as the sheet-like material, the mechanical properties in the in-plane direction are greatly improved, and as a result, the use range is further widened.
[0006]
[Problems to be solved by the invention]
However, the foamed sheet having the spindle-shaped cells has a drawback that plastic deformation is apt to occur particularly with respect to local strain, and permanent deformation is increased.
[0007]
This is because the spindle-shaped bubbles secure rigidity in the bubble shape instead of the original mechanical properties of the resin, so that once the bubbles are deformed, the strength rapidly decreases.
[0008]
Further, in the case of foaming only in the thickness direction, such as the foamed sheet, it is difficult to secure the accuracy of the thickness dimension at the time of manufacturing, and the thickness is generally uneven.
[0009]
The reason is that (thickness variation of the foamed sheet) = (thickness variation of the foamable sheet) × (expansion ratio). For example, the thickness variation of the foamable sheet is ± 0.1%, and the foaming ratio is 20 times. In this case, the thickness variation of the foamed sheet becomes ± 2%.
[0010]
On the other hand, in a foamed sheet having ordinary spherical cells, there is a relation of (variation in thickness of foamed sheet) = (variation in thickness of foamable sheet) × (cubic root of expansion ratio). When the thickness variation is ± 0.1% and the expansion ratio is 20 times, the thickness variation of the foamed sheet is ± 0.27%.
[0011]
An object of the present invention is to solve the above-mentioned problems and to provide a foamed sheet having an inclined structure, which has a small compression set and is excellent in thickness dimensional accuracy, and a method for producing the same.
[0012]
[Means for Solving the Problems]
As shown in FIG. 2, the foamed sheet having the inclined structure according to the present invention is a thermoplastic resin foamed sheet having a sheet-like material laminated on at least one side, and has a diameter Dz in the thickness direction of bubbles of the thickness intermediate layer and an in-plane direction. The ratio Dz / Dxy (hereinafter referred to as the intermediate layer aspect ratio (Dz / Dxy)) of the diameter Dxy of the air bubbles is 2.0 or more on average, and the above ratio Dz of the air bubbles in the surface layer on which the sheet-like material is laminated / Dxy (hereinafter referred to as surface layer aspect ratio (Dz / Dxy)) is less than 1.5 on average.
[0013]
The thermoplastic resin forming the main part of the inclined structure foam sheet according to the present invention is not particularly limited as long as it is a resin that melts when heated to a softening temperature or higher and can be heated and foamed. For example, olefins such as polyethylene and polypropylene Base resin, polyvinyl chloride, chlorinated polyvinyl chloride, ABS resin, polystyrene, polycarbonate, polyamide, polyvinylidene fluoride, polyphenylene sulfide, polysulfone, and polyether ether ketone. These may be used alone or in combination. The above-mentioned polymer also includes a copolymer obtained by copolymerizing the raw material monomer as a main component and another monomer polymerizable with the raw material monomer.
[0014]
The thermoplastic resin is also a modified polyolefin obtained by melt-mixing a polyolefin resin and at least one monomer selected from the group consisting of a dioxime compound, bismaleimide, divinylbenzene, and an allyl-based polyfunctional monomer. You may. The modified polyolefin will be described later in more detail.
[0015]
The sheet-like material laminated on at least one surface of the foamed sheet may be the one described later in the description of the method for producing the inclined structure foamed sheet.
[0016]
The diameter Dz in the thickness direction of the bubbles in the thickness intermediate layer of the foamed sheet and the diameter Dxy of the bubbles in the in-plane direction are both volume average diameters. The volume average diameter is a value represented by the following formula [I], where d is the diameter of an arbitrary bubble in the foam sheet in a specific direction (direction of each coordinate axis), and n is the number of particles.
[0017]
(Equation 1)

[0018]
The physical meaning of the volume average diameter is that a simple number (arithmetic) average diameter is weighted in terms of volume.
[0019]
In order to determine the volume average diameter, for example, take an enlarged photograph of a portion limited to the intermediate layer or the surface layer of the width of the sheet cross section, measure the length of each direction of tens to hundreds of bubbles existing there in each direction. Then, the average value of the diameter for each direction is calculated according to the above formula [I].
[0020]
Accordingly, the diameter Dz is the diameter of the cells in the foamed sheet in the sheet thickness direction (called the z direction), which is obtained by the above equation [I], and the diameter Dxy is obtained by the above equation [I]. This is the diameter of the cells in the foam sheet in the sheet width and length directions (called xy directions).
[0021]
The intermediate layer refers to a layer that includes the central portion in the sheet thickness direction and does not include both surfaces, and occupies 80% of the total sheet thickness. In addition, the above-mentioned surface layer refers to the front and back two layers including both surfaces without including the center in the sheet thickness direction, and occupies a total of 20% of the total sheet thickness.
[0022]
The inclined foamed sheet according to the present invention has a high compressive strength because, when a compressive force is applied in the thickness direction, a force is applied to the intermediate layer in the longitudinal direction of the spindle.
[0023]
In the present invention, a foamed sheet having an inclined structure is defined as a sheet intermediate layer having a large aspect ratio (Dz / Dxy) and bubbles in a spindle shape, a surface layer having a small aspect ratio and bubbles close to a sphere, and an aspect ratio of an intermediate layer. From the surface layer to the surface layer.
[0024]
The foam sheet having the inclined structure as described above has rigidity in the middle layer because of the spindle-shaped cell shape, and has elasticity like a foam in the surface layer because of the nearly spherical cell shape in the surface layer. It is possible to overcome the disadvantages of the foamed sheet of spindle-shaped cells, which are liable to cause plastic deformation and increase permanent set.
[0025]
When the aspect ratio (Dz / Dxy) of the intermediate layer is less than 2.0 in the foamed sheet having the inclined structure according to the present invention, the foamed sheet has insufficient compressive strength as a whole. The aspect ratio of the intermediate layer is preferably 2.5 or more. When the aspect ratio (Dz / Dxy) of the surface layer is 1.5 or more, the aspect ratio of the surface layer is such that the compression set of the foam sheet as a whole becomes too large. The aspect ratio of the surface layer is preferably less than 1.2.
[0026]
One method for producing the inclined structure foam sheet having the above configuration is to provide a foam sheet made of a thermoplastic resin composition containing a pyrolytic chemical foaming agent on at least one side with a strength capable of suppressing in-plane foaming force. The obtained sheet material is laminated, and the obtained laminated raw sheet is heated and foamed in the sheet thickness direction to reduce the thickness of the obtained molten foam sheet by 2 to 40% or at the same time or thereafter. This is a method of cooling and solidifying.
[0027]
The thermoplastic resin may be as described above. The thermoplastic resin is also a modified polyolefin obtained by melt-mixing a polyolefin resin and at least one monomer selected from the group consisting of a dioxime compound, bismaleimide, divinylbenzene, and an allyl-based polyfunctional monomer. You may. The modified polyolefin will be described later in more detail.
[0028]
The thermal decomposition type chemical blowing agent used in the method of the present invention is not particularly limited as long as it generates a decomposition gas by heating. Representative examples of the thermal decomposition type chemical blowing agent are azodicarbonamide, benzenesulfonyl hydrazide, dinitrosopentamethylenetetramine, toluenesulfonyl hydrazide, and 4,4-oxybis (benzenesulfonyl hydrazide). These may be used alone or in combination of two or more. Among them, azodicarbonamide is particularly preferably used.
[0029]
The thermal decomposition type chemical foaming agent is used in an appropriate amount in a range of 1 to 50 parts by weight, preferably 2 to 35 parts by weight, based on 100 parts by weight of the thermoplastic resin according to a desired expansion ratio.
[0030]
As a sheet-like material having a strength capable of suppressing the in-plane foaming force, for example, when the foaming ratio is 5 times or less, the tensile strength is 0.4 to 0.8 kgf / cm, and the foaming ratio is 5 to 10 In the case of double, the tensile strength is preferably in the range of 0.8 to 10 kgf / cm, and when the expansion ratio is 10 or more, the tensile strength is preferably in the range of 10 to 100 kgf / cm.
[0031]
However, if the strength of the sheet-like material is too low, the sheet-like material is torn at the time of foaming, and the foaming in the in-plane direction of the foamable sheet may not be sufficiently suppressed, and conversely, the strength is too high. And there is a dislike that the flexibility of the obtained foam falls. Also, as the sheet-like material, it is desirable that the material exhibit a certain degree of adhesiveness with the foamable sheet when laminated and integrated with the foamable sheet. Any material can be used as long as it can be adhered to the foamable sheet by appropriately using an agent or an adhesive.
[0032]
Here, the in-plane direction refers to any direction in the sheet surface, and is a two-dimensional all direction including the longitudinal direction and the width direction of the sheet.
[0033]
Preferred examples of the sheet-like material from the viewpoint of strength, durability and the like include glass cloth, woven fabric, and nonwoven fabric.
[0034]
The glass cloth refers to a surface mat obtained by forming glass fibers and a glass roving woven. The woven fabric and the non-woven fabric are made of paper, organic fibers, inorganic fibers, and the like. Note that the surface mat may include a binder for binding the short glass fibers to each other. Examples of the organic fiber constituting the woven or nonwoven fabric include polyester fiber, cotton, acrylic fiber, nylon fiber, carbon fiber, and aramid fiber.
[0035]
Further, as the sheet-like material, a sheet made of a steel sheet, a stainless steel sheet, or an aluminum sheet is also preferable. As such a metal sheet, a thin sheet of rolled steel, stainless steel, or aluminum having a thickness of 0.01 mm to 10 mm is particularly preferably used. In this case, these metals may be optionally coated with an organic or inorganic paint, or may be coated with an adhesive.
[0036]
The foamable resin composition obtained by kneading the thermoplastic resin and the thermal decomposition type chemical foaming agent is once shaped into a sheet to form a foamable sheet. As a shaping method, in addition to extrusion molding, a method generally performed in plastic molding such as press molding, blow molding, calendering molding, injection molding, etc. can be applied, but foaming discharged from a screw extruder is applicable. The method of directly shaping the conductive resin composition is preferable from the viewpoint of productivity.
[0037]
The method of laminating the sheet-like material on at least one side of the foamable sheet is not particularly limited. For example, (a) a method of applying the sheet-like material to a foamed sheet once cooled and solidified while heating the sheet-like material, A) a method in which the foamable sheet is heated until it is in a molten state and this is thermally fused to the sheet-like material; and (c) a method in which the sheet-like material is bonded to the foamable sheet with an adhesive.
[0038]
The method (a) is the most preferable for ensuring the thickness accuracy of the laminated raw sheet. In the heat fusion of the method (b), for example, a sheet-like material is lightly laminated on at least one surface of a foamed sheet in a molten state immediately after being extruded from a T-die, and these are placed between opposed cooling rolls. A method is preferable in which the two are passed and the two are integrated by the pressing force of the roll.
[0039]
Note that, as described above, laminating and integrating the foamable sheet and the sheet-like material means that when the foamable sheet and the sheet-like material are to be peeled off at the interface between them, a high rate of material destruction occurs. It means that both are fixed.
[0040]
The thus obtained laminated raw sheet can be foamed to a desired expansion ratio under a constant pressure by heating under appropriate temperature conditions. The heating is usually performed in a temperature range from the decomposition temperature of the thermal decomposition type chemical foaming agent to the decomposition temperature + 100 ° C. In particular, as a continuous foaming apparatus, in addition to a take-up foamer that foams while taking out a foam at an outlet side of a heating furnace, a belt-type foamer, a vertical or horizontal foaming furnace, a hot air thermostat, or an oil bath, a metal bath A hot bath such as a bath or a salt bath is used.
[0041]
In the method of the present invention, a sheet-like material having a strength capable of suppressing an in-plane foaming force at the time of foaming is laminated on at least one surface of the foamable sheet. Does not foam at all, but only in the thickness direction. As a result, the cells of the foam have a spindle shape whose major axis is oriented in the thickness direction.
[0042]
Next, after the foaming is substantially completed, the thickness of the foamed sheet in the molten state is reduced, or at the same time, the foamed sheet is cooled and solidified.
[0043]
At this time, the thickness of the sheet once expanded is t _A , The amount of thickness reduction given in the molten state is t _B , The thickness reduction rate (t _B / T _A × 100) is 2 to 40%, preferably 3 to 10%.
[0044]
When the thermoplastic resin is cooled and solidified, the volume may be reduced, but the total thickness t of the inclined structure foamed sheet recovered at this time is _C Is not necessarily t _A -T _B Does not become t _A -T _B <T _C It becomes.
[0045]
When the thickness reduction rate is less than 2%, the aspect ratio (Dz / Dxy) of the surface layer of the finally obtained gradient structure foam sheet does not become less than 1.5, and when it exceeds 40%, the aspect ratio of the intermediate layer ( Dz / Dxy) does not become 2.0.
[0046]
The means for reducing the thickness is not particularly limited. In the case where the operation is performed continuously, for example, there is a method in which the sheet is passed between two rolls having an appropriate gap. In this case, the roll may be a cooling roll in which a refrigerant is circulated. There are also a method of passing a sheet between two blades having an appropriate gap, and a method of passing a sheet through two belts having an appropriate gap.
[0047]
When performing a discontinuous operation, a method using a (cooling) press can be applied.
[0048]
In the gradient structure foam sheet and the method for producing the same according to the present invention, the thermoplastic resin is, as described above, a polyolefin-based resin, a dioxime compound, bismaleimide, divinylbenzene, and at least one selected from the group consisting of allyl-based polyfunctional monomers. It may be a modified polyolefin obtained by melt-mixing one kind of monomer.
[0049]
The polyolefin as a main component of the polyolefin resin is a homopolymer of an olefinic monomer, or a copolymer of a main component olefinic monomer and another monomer, and is not particularly limited. Polyethylene such as polyethylene, high-density polyethylene, linear low-density polyethylene, polypropylene such as homo-type polypropylene, random-type polypropylene, block-type polypropylene, polybutene, ethylene-propylene copolymer, ethylene-propylene-diene terpolymer And ethylene-butene copolymers, eletin-vinyl acetate copolymers, ethylene-acrylate copolymers, and other copolymers containing ethylene as a main component, and combinations of two or more of these. You may.
[0050]
As the polyolefin as a main component of the polyolefin-based resin, one or a combination of two or more of the above-described polyethylene and polypropylene is preferable.
[0051]
The polyolefin resin refers to a resin composition in which the proportion of the polyolefin is 70 to 100% by weight. The resin other than the polyolefin constituting the polyolefin resin is not limited, and examples thereof include polystyrene and styrene elastomer. When the proportion of the polyolefin in the polyolefin resin is less than 70% by weight, not only the characteristics of polyolefin such as light weight, chemical resistance, flexibility and elasticity cannot be exhibited, but also the melt viscosity required for foaming can be secured. It is not preferable because it may be difficult.
[0052]
Among the modifying monomers used in the method of the present invention, first, a dioxime compound is a compound having two in a molecule a structure in which an oxime group or a hydrogen atom thereof is replaced with another atomic group (mainly a hydrocarbon group). For example, p-quinone dioxime and p, p-benzoylquinone dioxime are exemplified. The dioxime compounds can be used in combination of two or more.
[0053]
The bismaleimide compound used in the method of the present invention is a compound having two maleimide structures in a molecule, for example, N, N′-P-phenylenebismaleimide, N, N′-m-finylenebismaleimide, diphenylmethanebis Maleimide is exemplified. Bismaleimide compounds can be used in combination of two or more.
[0054]
The divinylbenzene used in the method of the present invention may have two vinyl groups in any of ortho, meta and para positions.
[0055]
The allyl-based polyfunctional monomer used in the method of the present invention is a compound having at least two allyl groups in a molecule, and examples thereof include diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, and diallyl chloride. The allylic polyfunctional monomer can be used in combination of two or more.
[0056]
The amount of the modifying monomer may be appropriately selected depending on the type of the monomer, but is generally 0.05 to 5 parts by weight, preferably 0.2 to 2 parts by weight, per 100 parts by weight of the polyolefin resin. Department. If the amount of the modifying monomer is less than 0.05 part by weight, the melt viscosity required for foaming cannot be imparted. If the amount exceeds 5 parts by weight, the degree of crosslinking is too high, and the extrudability is poor (for example, In addition, a high load is applied and melt fracture occurs), and a foaming agent to be added later cannot be uniformly kneaded in the resin composition, so that the gel fraction is unnecessarily increased and the recyclability is impaired. In addition, the proportion of the monomer remaining as an unreacted substance in the product increases, which may irritate the human body and lower the product efficiency with respect to the raw material.
[0057]
In the method of the present invention, when divinylbenzene or an allyl-based polyfunctional monomer is used as the modifying monomer, it is preferable to use an organic peroxide in combination. The organic peroxide may be any organic peroxide generally used for a polyolefin grafting reaction. Examples thereof include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, t-butylperoxyacetate, and t-butylperoxy. Benzoate, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t-butyl Peroxy) hexyne-3 and the like, which are suitably used alone or in combination of two or more.
[0058]
If the amount of the organic peroxide used is too small, the conversion of the grafting reaction is insufficient, and if it is too large, the so-called β-cleavage of polypropylene occurs remarkably, and the molecular weight of the modified product is too low, resulting in a decrease in physical properties or viscosity. Poor foaming may occur due to the decrease. In consideration of these points, the amount of the organic peroxide to be used is preferably 0.001 to 0.5 part by weight, preferably 0.005 to 0.15 part by weight, based on 100 parts by weight of the polyolefin resin. More preferably, there is.
[0059]
In order to obtain a modified resin, a polyolefin resin and a modifying monomer are melt-mixed under predetermined conditions. Specifically, the above-mentioned two substances are charged by a required amount into a kneading device such as a screw extruder or a kneader, and are melt-mixed. The melt mixing temperature is 170 ° C. or higher and the decomposition temperature of the polyolefin resin or lower, preferably 200 to 250 ° C. If the melt mixing temperature is less than 170 ° C., the denaturation is insufficient, and the expansion ratio of the finally obtained foam may not be sufficiently high. If it exceeds 250 ° C., the polyolefin-based resin is easily decomposed.
[0060]
The modified polyolefin resin may be further melt-blended with the same or different polyolefin resin or another thermoplastic resin for the purpose of improving its fluidity later. The type and amount of the resin for blending are determined according to the moldability, appearance, adhesiveness to the sheet-like material, and the expansion ratio, mechanical properties, thermal properties, and cells of the foamed sheet obtained therefrom. It is appropriately adjusted depending on the shape and the like. It is preferred that 50 to 200 parts by weight of the same or different polyolefin-based resin is melt-blended with respect to 100 parts by weight of the modified polyolefin-based resin.
[0061]
[Action]
The foamed sheet having the inclined structure according to the present invention has high compressive strength when subjected to a compressive force in the thickness direction due to the spindle-shaped cell shape in the intermediate layer, and has elasticity due to the nearly spherical cell shape in the surface layer. Therefore, it is possible to overcome the disadvantages of the foamed sheet of the spindle-shaped cells as a whole, which easily cause plastic deformation and increase permanent set.
[0062]
That is, a spindle-shaped bubble having a major axis in the thickness direction in the intermediate layer of the foamed sheet shows a strong elastic modulus in that direction. However, once the spindle-shaped air bubbles are deformed, the distortion is hardly recovered, and the elastic modulus also decreases. However, since near-spherical bubbles exist in the surface layer of the sheet, local deformation distortion of the sheet is absorbed, and deformation of the spindle-shaped bubbles in the intermediate layer is suppressed.
[0063]
Since the sizing is often performed in the thickness direction of such an inclined structure foam sheet, the thickness dimensional accuracy is greatly improved.
[0064]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be described more specifically with reference to examples.
[0065]
i) Preparation of modified polyolefin resin
As a screw extruder for denaturation, a BT40 (made by Plastic Engineering Laboratory) co-rotating twin screw extruder was used. It has a self-wiping double-start screw with an L / D of 35 and a D of 39 mm. The cylinder barrel is composed of first to fourth barrels from upstream to downstream of the extruder. The die is a three-hole strand die, and a vacuum vent is provided in the fourth barrel to collect volatile components.
[0066]
The operating conditions are as follows.
[0067]

[0068]
First, a polyolefin-based resin and a dioxime compound were separately charged from the rear end hopper into the modifying screw extruder having the above-described configuration, and the two were melt-mixed to obtain a modified resin. At this time, volatiles generated in the extruder were evacuated by a vacuum vent.
[0069]
The polyolefin resin is a random copolymer of propylene (“EG8” manufactured by Mitsubishi Chemical Corporation, MI: 0.8, density: 0.9 g / cm) ³ ) And the supply rate was 10 kg / h.
[0070]
The modifying monomer was p-quinone dioxime ("Barnock GM-P" manufactured by Ouchi Shinko Chemical Co., Ltd.), and the supply amount was 0.75 parts by weight based on 100 parts by weight of the polyolefin resin.
[0071]
The modified resin obtained by melt-mixing the polyolefin resin and the dioxime compound was discharged from a strand die, cooled, and cut with a pelletizer to obtain pellets of the modified resin.
[0072]
ii) Preparation of foamable sheet
The screw extruder for kneading the foaming agent is a TEX-44 type (manufactured by Nippon Steel Works) co-rotating twin-screw extruder, which is equipped with a self-wiping double-screw, whose L / D is 45.5, D Is 47 mm. The cylinder barrel comprises first to twelfth barrels from upstream to downstream of the extruder, and the molding die is a T die (width 500 mm, thickness 0.8 mm).
[0073]
The temperature setting categories are as follows.
[0074]
The first barrel is always cooled
1st zone; 2nd to 4th barrel
2nd zone; 5th to 8th barrels
3rd zone; 9th to 12th barrels
4th zone; die and adapter part
[0075]
A side feeder is installed in the sixth barrel to supply the blowing agent, and a vacuum vent is installed in the eleventh barrel to collect volatiles.
[0076]
The operating conditions are as follows.
[0077]

-Screw rotation speed: 40 rpm
The modified resin obtained as described above was supplied from a modifying screw extruder to a blowing agent kneading screw extruder. The supply amount of the modified resin was 20 kg / h. The foaming agent was supplied to the extruder from the sieve feeder and dispersed. The blowing agent was azodicarbonamide (ADCA), and the supply amount was 1 kg / h. The foamable resin composition obtained by kneading the modified resin and the foaming agent in this manner is discharged from a T-die, and the obtained sheet is cooled by three rolls to form a continuous foamable sheet having a thickness of 0.8 mm. Got.
[0078]
iii) Preparation of laminated raw sheet
On the other hand, a non-woven fabric made of polyethylene terephthalate (manufactured by Toyobo Co., Ltd., “Spunbond Ecule 6301A”, weighing 30 g / m) ² , Tensile strength: 1.6 kg / cm in length and 1.2 kg / cm in width), which are piled up on both sides of the foamable sheet, passed through a 6-inch heating roll (roll surface temperature 195 ° C.), and continuously. It was fused and laminated. The end of the obtained laminated raw sheet was cut to have a width of 400 mm.
[0079]
iv) Preparation of inclined foam sheet
As shown in FIG. 1, the foaming machine mainly includes a preheating zone (1), a foaming zone (2), a cooling zone (3), and a belt type take-up machine (6). The preheating zone (1) and the foaming zone (2) each have a 2 inch transport roll (4), the total length of both zones being 4 m. The cooling zone (3) is provided with a pair of upper and lower water-circulating cooling rolls (5) (5 ') of 4 inches, and its total length is 2 m. The gap between the upper and lower cooling rolls (5) (5 ') can be freely set. At the outlet of the foaming zone (2) an optical or non-contact thickness gauge (7) is provided.
[0080]
The preheating zone (1) of the foaming machine having the above configuration was set at 190 ° C., the foaming zone (2) at 230 ° C., and the surface temperatures of the cooling rolls (5) and (5 ′) at 25 ° C., respectively. ) Was supplied to the preheating zone (1) of the foaming machine. The linear speed of sheet feeding was 0.5 m / min, and the residence time in the preheating zone (1) and the foaming zone (2) was 8 minutes in total, and that in the cooling zone (3) was 4 minutes.
[0081]
The sheet thickness was measured at three places in the width direction by a sheet thickness measuring device (7) near the outlet of the foaming zone (2), and the average value thereof was 8.7 mm (t in Table 1). _A ).
[0082]
The gap between the upper and lower cooling rolls (5) and (5 ') in the cooling zone (3) is 8 mm (t in Table 1). _C ).
[0083]
At the outlet of the foaming machine, the inclined foamed sheet (9) shown in FIG. 2 was recovered from the take-up machine (6). This inclined structure foam sheet (9) is a thermoplastic resin foam sheet in which a sheet material (10) is laminated on both sides, and the intermediate layer (12) has an aspect ratio (Dz / Dxy) of 3.5. And the aspect ratio (Dz / Dxy) of the surface layers (13) on both sides is 1.4. In FIG. 2, (11) is a spindle-shaped bubble constituting the intermediate layer (12), and (14) is a nearly spherical bubble constituting the surface layer (13) on both sides.
[0084]
v) Performance evaluation
The performance of the obtained foam sheet was evaluated for the following items.
[0085]
・ Expansion ratio:
After shaving off the sheet from the foamed sheet with a cutter, the expansion ratio of the foam was measured according to JIS K6767.
[0086]
Compressive strength:
The foamed sheet was cut into a 5 cm square, and the 25% compressive strength was measured according to JIS K6767.
[0087]
-Compression set:
Cut the foamed sheet into 5 cm squares and measure 25% compression set in accordance with JIS K6767 (measured at a standard temperature of 20 ° C).
・ Cell shape:
The foamed sheet is cut, and an optical microscope photograph (30 times) of the intermediate layer and the surface layer of the cross section is taken. The major axis length and the minor axis length of about 80 spindle-shaped foaming cells are measured with a digitizer, and the above formula [I] is obtained. The aspect ratio (Dz / Dxy) was calculated according to the following equation.
[0088]
(Example 2)
In the preparation of the modified polyolefin, divinylbenzene (DVB in Table 1) was used as a modifying monomer in an amount of 0.1 part by weight based on 100 parts by weight of polypropylene, and di-t-butyl peroxide was used as an organic peroxide in an amount of 100 parts by weight of polypropylene. 0.03 parts by weight of the cooling zone (3) and the gap between the upper and lower cooling rolls (5) (5 ′) in the cooling zone (3) was 6.0 mm, except that the gap was 6.0 mm. A structural foam sheet was obtained. The sheet thickness at the outlet of the foaming zone (2) was 9.5 mm.
[0089]
(Example 3)
A low-density polyethylene (YK400, LDPE in Table 1) manufactured by Mitsubishi Chemical Corporation was used as the thermoplastic resin. The mixture was melted and kneaded by a machine, and then a laminated raw sheet was formed in the same manner as in Example 1. This was irradiated with an electron beam of 8 Mrad at 500 keV. The sheet thickness at the outlet of the foaming zone (2) was 9.1 mm. After that, a foamed sheet having an inclined structure was obtained in the same manner as in Example 1.
[0090]
(Comparative Example 1)
In the preparation of the foamable composition, an inclined structure foam sheet was obtained in the same manner as in Example 1 except that the gap between the upper and lower cooling rolls (5) and (5 ') in the cooling zone (3) was set to 20 mm. The sheet thickness at the outlet of the foaming zone (2) was 8.8 mm.
[0091]
(Comparative Example 2)
In the preparation of the foamable composition, an inclined foam sheet was obtained in the same manner as in Example 1 except that the gap between the upper and lower cooling rolls (5) and (5 ′) in the cooling zone (3) was 4.0 mm. Was. The sheet thickness at the outlet of the foaming zone (2) was 8.7 mm.
[0092]
Table 1 summarizes the performance evaluation results of the foamed sheets obtained in Examples and Comparative Examples.
[0093]
[Table 1]

[0094]
【The invention's effect】
The foamed sheet having the inclined structure according to the present invention has high compressive strength when subjected to a compressive force in the thickness direction due to the spindle-shaped cell shape in the intermediate layer, and has elasticity due to the nearly spherical cell shape in the surface layer. Therefore, it is possible to overcome the drawbacks that the foamed sheet of the spindle-shaped cells as a whole easily causes plastic deformation and increases permanent distortion.
[0095]
That is, a spindle-shaped bubble having a major axis in the thickness direction in the intermediate layer of the foamed sheet shows a strong elastic modulus in that direction. However, once the spindle-shaped air bubbles are deformed, the distortion is hardly recovered, and the elastic modulus also decreases. However, since bubbles close to a spherical shape exist in the surface layer of the sheet, local deformation distortion of the sheet is absorbed, and deformation of the spindle-shaped bubbles in the intermediate layer is suppressed.
[0096]
Since the sizing is often performed in the thickness direction of such an inclined structure foam sheet, the thickness dimensional accuracy is greatly improved.
[0097]
Furthermore, when the thermoplastic resin is a modified polyolefin, a gradient-structured foam sheet having particularly high compressive strength is obtained.
[0098]
As described above, the present invention provides an inclined foamed sheet having a small compression set and an excellent thickness dimensional accuracy, and is used, for example, as a roof insulation material for buildings and a core material of composite building materials for floors and walls. be able to.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a continuous foaming device.
FIG. 2A is a perspective view of a foamed sheet having an inclined structure, and FIG. 2B is a cross-sectional view taken along line bb in FIG. 2A.
[Explanation of symbols]
1: Preheating zone
2: Foaming zone
3: Cooling zone
4: Conveyance roll
5, 5 ': cooling roll
6: Pick-up machine
7: Thickness measuring device
8: laminated raw sheet
9: Inclined structure foam sheet
10: sheet-like material
11: Spindle-shaped bubble
12: Central layer
13: Surface layer
14: Bubbles that are nearly spherical

Claims (4)

A thermoplastic resin foam sheet in which a sheet material is laminated on at least one side, wherein the ratio Dz / Dxy of the diameter Dz in the thickness direction of the bubbles in the thickness intermediate layer to the diameter Dxy of the bubbles in the in-plane direction is 2.0 or more on average. Wherein the ratio Dz / Dxy of bubbles in the surface layer on which the sheet material is laminated is less than 1.5 on average. A laminated sheet obtained by laminating a sheet having a strength capable of suppressing in-plane foaming force on at least one side of a foamable sheet made of a thermoplastic resin composition containing a thermal decomposition type chemical foaming agent, and obtained. Characterized in that the foamed sheet is heated and foamed in the sheet thickness direction, and the thickness of the obtained foamed sheet in the molten state is reduced by 2 to 40%, or at the same time, the foamed sheet is cooled and solidified, followed by solidifying the foamed sheet. . The thermoplastic resin is a modified polyolefin obtained by melt-mixing a polyolefin-based resin and at least one monomer selected from the group consisting of a dioxime compound, bismaleimide, divinylbenzene, and an allyl-based polyfunctional monomer. The inclined structure foam sheet according to claim 1, characterized in that: The thermoplastic resin is a modified polyolefin obtained by melt-mixing a polyolefin resin and at least one monomer selected from the group consisting of a dioxime compound, bismaleimide, divinylbenzene, and an allyl-based polyfunctional monomer. The method for producing a foamed sheet having a gradient structure according to claim 2.

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