JP4109377B2 - Method for producing polyolefin resin foam - Google Patents

Description

【００１９】
【化２】

【００２０】
【化３】

【００２１】
【化４】

【００２２】
第一工程で用いる変性用モノマーのうち、下記一般式で示されるようなマレイミド構造（化学式V ）を分子内に２個有するビスマレイミド化合物としては、例えば、Ｎ，Ｎ’−ｐ−フェニレンビスマレイミド（化学式VI）、Ｎ，Ｎ’−ｍ−フェニレンビスマレイミド（化学式VII ）、ジフェニルメタンビスマレイミド（化学式VIII）が例示される。ビスマレイミド化合物は２種以上の組合わせで使用することもできる。又、マレイミド構造が分子内に２個以上有するポリマレイミド（化学式IX）も、同じ効果を奏するのでビスマレイミド化合物の範疇に含まれる。
【００２３】
【化５】

【００２４】
【化６】

【００２５】
【化７】

【００２６】
【化８】

【００２７】
【化９】

【００２８】
第一工程で用いる変性用モノマーのうち、分子内にビニル基を２個有する化合物、即ち、ジビニル化合物は、例えば下記化学式で示されるジビニルベンゼン（化合物X ）であり、２つのビニル基はオルト、メタ、パラのいずれの位置関係にあってもよい。
【００２９】
【化１０】

【００３０】
第一工程で用いる変性用モノマーのうち、分子内にアリル基を２個以上有する化合物、即ち、アリル系多官能モノマーとしては、例えば下記化学式で示されるジアリルフタレート（化学式XI）、トリアリルシアヌレート（化学式XII ）、トリアリルイソシアヌレート（化学式XIII）、ジアリルクロレンデート（化学式XIV ）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。
【００３１】
【化１１】

【００３２】
【化１２】

【００３３】
【化１３】

【００３４】
【化１４】

【００３５】
第一工程で用いる変性用モノマーのうち、分子内に（メタ）アクリル基を２個以上有する化合物、即ち、（メタ）アクリル系多官能モノマーとしては、（メタ）アクリロイルオキシ基を２〜４個有する化合物が挙げられる。
【００３６】
（メタ）アクリロイルオキシ基を２個有する（メタ）アクリル系２官能モノマーとしては、アルカンジオールジ（メタ）アクリレート、エチレングリコールジ（メタ）アクリレート、プロピレングリコールジ（メタ）アクリレート、ポリエチレングリコールジ（メタ）アクリレート、ポリプロピレングリコールジ（メタ）アクリレート、ネオペンチルグリコールジ（メタ）アクリレート、ジメチロールトリシクロデカンジ（メタ）アクリレート、ビスフェノールＡのエチレングリコール付加物ジ（メタ）アクリレート、ビスフェノールＡのプロピレングリコール付加物ジ（メタ）アクリレートが例示される。
【００３７】
（メタ）アクリロイルオキシ基を３個有する（メタ）アクリル系３官能モノマーとしては、トリメチロールプロパントリ（メタ）アクリレート、ペンタエリスリトールトリ（メタ）アクリレート、トリメチロールプロパンエチレンオキサイド付加トリ（メタ）アクリレート、グリセリンプロピレンオキサイド付加トリ（メタ）アクリレート、トリス（メタ）アクリロイルオキシエチルフォスフェートが例示される。
【００３８】
（メタ）アクリロイルオキシ基を４個有する（メタ）アクリル系４官能モノマーとしては、ペンタエリスリトールテトラ（メタ）アクリレート、ジトリメチロールプロパンテトラ（メタ）アクリレートが例示される。
【００３９】
第一工程で用いる変性用モノマーのうち、分子内に２個以上のケトン基を有する環状化合物の代表例はキノン化合物であり、キノン化合物としてはヒドロキノン、ｐ−ベンゾキノン、テトラクロロ−ｐ−ベンゾキノンが例示される。
【００４０】
変性用モノマーの配合量は、該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が得られ難い。配合量が５重量部を超えると、架橋度が上がり過ぎ、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過ぎ、リサイクル性を損なうことがある。加えて、後に加熱発泡時の発泡圧力が高くなり過ぎ、面内方向の発泡を抑制するためのシート状物として引張強さの小さいものが使用できなくなることがある。
【００４１】
本発明方法においては、変性用モノマーと共に有機過酸化物を併用してもよい。特に、変性用モノマーとしてジビニルベンゼン又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、これらが単独で又は２種以上の組合わせで好適に用いられる。
【００４２】
特に、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等のうちの１種もしくは２種以上がより好適に用いられる。
【００４３】
有機過酸化物の使用量は、少な過ぎるとグラフト化反応の転化が不十分であり、多過ぎるとポリプロピレンの所謂β解裂が顕著に起こり、変性物の分子量が低過ぎて物性の低下或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。
【００４４】
変性樹脂を得るには、スクリュー押出機やニーダー等の混練装置を用い、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し、反応させる。このときの反応温度は、１７０℃以上且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℃を下回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℃を超えるとポリオレフィン系樹脂が分解し易くなる。
【００４５】
上記変成反応に用いる装置は、スクリュー押出機の他、一般的にプラスチック成形加工で使用され得る溶融混練装置であればよく、例えば、ニーダー、ローター、連続混練機等が例示される。このうち連続運転が行えるスクリュー押出機が好ましく、１軸スクリュー押出機、２軸スクリュー押出機、３本以上のスクリューを備えた多軸スクリュー押出機等がいずれも好適に用いられる。１軸スクリュー押出機としては、一般的なフルフライト型スクリューに加え、不連続フライト型スクリュー、ピンバレル、ミキシングヘッド等を有する押出機等も用いられる。又、上記２軸スクリュー押出機としては、噛合い同方向回転型押出機、噛合い異方向回転型押出機、非噛合い異方向回転型押出機等が好適に使用し得る。尚、押出機の後段に真空ベントを設けることは、樹脂組成物中に揮発物が残存するのを防ぐのに効果的である。
【００４６】
スクリュー押出機を用いる場合、ポリオレフィン系樹脂は通常はホッパーから押出機へ投入されるが、定量性を増すため、スクリュー式フィーダー、重量管理式フィーダー等を用いることも好ましい。
【００４７】
変性用モノマーは、ポリオレフィン系樹脂と同時にホッパーから押出機へ投入してもよいが、特にジビニルベンゼンやアリル系多官能モノマーの幾つかは常温常圧で液体であるので、押出機にてポリオレフィン系樹脂が溶融する位置より後流部に設けられた液体注入孔から供給する方が、これを溶融樹脂中に均一に分散できるので好ましい。このとき液体モノマーは、プランジャーポンプ等の圧送式のポンプで送液することが望ましい。
【００４８】
変性用モノマーに有機過酸化物を併用する場合は、有機過酸化物を同モノマーと予め混合してこれらを同時に投入する方法、或いはモノマー投入と前後して有機過酸化物を別投入する方法等が適用できる。
【００４９】
得られた変性樹脂は、第二工程において熱分解型化学発泡剤を加えて混練され、発泡性樹脂組成物が調製される。
変性樹脂は、単独で用いられてもよいが、同種或いは異種の未変性ポリオレフィン系樹脂と溶融ブレンドされたものでも良い。このような変性樹脂と未変性樹脂とのブレンドを用いることにより、得られる発泡性樹脂組成物の流動性が改善され、これによって、極めて薄い発泡性原反が成形可能となり、その結果、薄いシート状複合発泡体の製造が可能となる。その上、発泡性樹脂組成物の流動性の改善が紡錘形の気泡を形成するのに好適に働き、その結果として、より高圧縮強度の発泡体を得ることも可能となる。
【００５０】
未変性ポリオレフィン系樹脂は、変性樹脂の変性前のポリオレフィン系樹脂の定義で先に説明したものであって良い。
【００５１】
未変性ポリオレフィン系樹脂の種類は、得られる発泡性複合シートの成形性、外観、シート状物との接着性、及びこれから得られる複合発泡体の発泡倍率、機械的物性、熱的物性、セル形状等によって適宜選ばれる。例えば、発泡体原反の流れ性を良くしたければ、未変性ポリオレフィン系樹脂として粘度の低い樹脂を用いる。柔らかい発泡体を得たければ、未変性樹脂として密度の低いポリオレフィンを用いる。
【００５２】
変性樹脂と未変性ポリオレフィン系樹脂の割合は、変性樹脂１００重量部に対して、未変性樹脂を好ましくは５０〜２００重量部、より好ましくは７０〜１３０重量部ブレンドする。未変性ポリオレフィン系樹脂の割合が大き過ぎると、発泡に必要な溶融張力が保持できないため、発泡倍率の低下を引き起こし、良好な発泡体が得られないことがある。
【００５３】
本発明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又は２種以上組み合わせて用いてもよい。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。
【００５４】
熱分解型化学発泡剤は、変性樹脂１００重量部に対して、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量が使用される。熱分解型化学発泡剤が分解する温度は、発泡剤の種類、粒径等で異なるが、粒径１８μｍのアゾジカルボアミドを例にとると、およそ２００℃である。
【００５５】
このようにして、ポリオレフィン系樹脂と変性用モノマーから得られた変性樹脂に熱分解型化学発泡剤を混練して発泡性樹脂組成物を得るには、上述した反応用の溶融混練装置と、これとは別の発泡剤混和用の溶融混練装置（構造は反応用の溶融混練装置のそれと同じであってもよい）とを用いて、該発泡剤が実質的に分解しない最高温度以下で両者を混合する。この溶融混練の態様としては以下に示すものがある。
【００５６】
(a) 反応用の回分式或いは連続式の溶融混練装置において、ポリオレフィン系樹脂を変性用モノマーと溶融混和して反応させ、得られた変性樹脂を該溶融混練装置から取り出して固化、造粒等を行った後、該樹脂組成物を発泡剤混和用の回分式或いは連続式の混練装置に移し、これに発泡剤を投入し両者を溶融混練し、発泡性樹脂組成物を得る。
【００５７】
(b) 反応用の回分式の溶融混練装置において、ポリオレフィン系樹脂を変性用モノマーと溶融混和して反応させ、得られた変性樹脂を該混練装置内で、発泡剤が実質上分解しない温度もしくは多量には分解しない温度まで冷却しておき、次いで、これに発泡剤を投入し両者を溶融混練し、発泡性樹脂組成物を得る。
【００５８】
(c) 反応用のスクリュー押出機（連続式の溶融混練装置）において、ポリオレフィン系樹脂を変性用モノマーと１７０℃以上の温度で溶融混和して反応させ、得られた変性樹脂を発泡剤が実質上分解しない温度もしくは多量には分解しない温度まで降温させておき、更に該スクリュー押出機の途中に設けた供給口より発泡剤を投入し、両者を溶融混練し、発泡性樹脂組成物を得る。
【００５９】
(d) 連続操作のもう一つの形態では、２台のスクリュー押出機等を連結して、１台目でポリオレフィン系樹脂を変性用モノマーと溶融混和して反応させ、得られた変性樹脂を上記と同様に降温させた後、同樹脂組成物を２台目に移し、これに発泡剤を投入し、両者を溶融混練し、発泡性樹脂組成物を得る。
【００６０】
混合物に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、第三工程においてシート状に賦形される。賦形の方法は押出成形の他、プレス成形、ブロー成形、カレンダリング成形、射出成形等、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。
【００６１】
特に、上記(a)(b)の方法に従って得られる発泡性樹脂組成物を、回分式の発泡剤混和用混練装置より取り出し、これをスクリュー押出機に投入して連続的にシート形状に賦形する方法、或いは、上記(a)(c)(d) の方法に従って、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、生産性の観点より好ましい。
【００６２】
本発明方法の第四工程で用いるシート状物を構成する材料は、紙、布、木材、鉄等の金属、非鉄金属、プラスチック、ガラス、無機物等自由に選べ、特に限定されるものではない。又、シート状物は発泡性シートと積層・一体化させる場合には、発泡性シートとの間に或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。
【００６３】
シート状物とは、発泡性シートを加熱発泡させる際の面内方向への発泡を抑制し得る強度を有するものである。シート状物の強度が低過ぎると、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る。従って、面内発泡を抑制するためのシート状物としては、例えば、発泡倍率が１０である場合は、引張り強度０．１ｋｇｆ／ｃｍ以上のものが好ましい。
【００６４】
本発明方法の第四工程で好適に用いられるシート状物としては、ガラスクロス、寒冷紗、織布又は不織布、紙等が挙げられる。上記ガラスクロスには、ガラス繊維を織成してなるものの他、抄造して得られるガラスマットをも包含するものとする。又、寒冷紗、不織布は、主にポリエステルやナイロン等の合成繊維からなるものである。織布は一般的な天然繊維や合成繊維からなるものであって良い。尚、抄造して得られるガラスクロスに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。該バインダーとしては、シート状物の引張強度が上記範囲を満たすものであれば特に限定されず、例えば、ポリビニルアルコール、飽和ポリエステル、アクリル系樹脂等の熱可塑性樹脂や、エポキシ樹脂、不飽和ポリエステル等の熱硬化性樹脂が挙げられる。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。これらのシート状物を使用することによって、軽量で高圧縮強度を有するポリオレフィン系樹脂複合発泡体を得ることができる。又、適切な強度のシート状物を用いることによって、同発泡体をポリオレフィン系樹脂の融点以上の温度に再加熱することで二次賦形が可能となる。よって、得られた複合発泡体は自動車用の成型天井材や内装パネル等の芯材等に好適に使用することができる。
【００６５】
又、第四工程で用いるシート状物は、金属製シート、例えば、鉄製シート、又はアルミニウム、チタン、銅等の非鉄金属製シートからなるものであっても良い。鉄製シートには、溶融亜鉛鋼板や溶融亜鉛アルミニウム合金鋼板、ステンレス鋼板等が含まれる。このような金属製のシート状物としては、厚み０．０１ｍｍ〜２ｍｍの圧延された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メッキされていてもよいし、有機塗料或いは無機塗料で塗装されていてもよく、或いは粘接着剤が塗布されていてもよい。これらの金属製シート状物を使用する場合、得られるポリオレフィン系樹脂複合発泡体は軽量の金属複合板となり得る。これは、厚さ１〜５ｍｍの金属板や、中間層としてポリエチレン層等を配した金属複合板と比較して、実用上極端な強度不足を来たさずに、更に軽量化と低コスト化が図れるメリットを有する。又、この複合発泡体は発泡性複合シートを発泡させて製造されるため、発泡体に後から金属シート状物を貼付した金属複合板と比較して、表面平滑性が極めて優れたものになる。
【００６６】
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等が挙げられる。
【００６７】
発泡性複合シートの厚み精度を確保するには方法（イ）又は（ハ）が好ましい。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。
【００６８】
尚、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、高い割合で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。
【００６９】
本発明のポリオレフィン系樹脂発泡体の製造方法において、発泡性ポリオレフィン系樹脂組成物をシート状に賦形する第三工程と、発泡性ポリオレフィン系樹脂シートを加熱発泡させる際の面内方向への発泡を抑制し得る強度を有するシート状物を積層して発泡性複合シートとする第四工程を経て、発泡性複合シートを熱分解型化学発泡剤の分解温度以上の温度に加熱する第五工程との間で、第三工程で得られた発泡性シートもしくは第四工程で得られた発泡性複合シートを平板間で（形状変更をさせず）、前記変性樹脂の融点以上、熱分解型化学発泡剤の分解温度未満の温度において加熱焼鈍される。
【００７０】
即ち、第三工程後、発泡性シート単体の状態で加熱焼鈍され、然る後、発泡性シートを加熱発泡させる際の面内方向への発泡を抑制し得る強度を有するシート状物を積層してもよく、発泡性シートに上記シート状物が積層された発泡性複合シートの状態で加熱焼鈍されてもよいのであるが、積層時の成形歪を考慮すれば、後者がより大きい加熱焼鈍効果を得られるものとして好ましいものである。
【００７１】
発泡性シートもしくは発泡性複合シートの形状を変形させないように加熱焼鈍する手段はとして、特に限定されるものではないが、これらの被加熱焼鈍体の両面を平板間に挟持させて加熱焼鈍することが好ましい。
上記加熱焼鈍が行われる平板間とは、２枚の剛性の大きな板の間のみを意味するものではなく、背中合わせに互いに反対方向に回転する一対の、例えば、スチールベルトのような無端ベルトであってもよく、更に、上記無端ベルトが対向して平坦な板状空間を形成している位置において両ベルトの対向する面に直交する方向に負荷を加え、両ベルト間を搬送される発泡性シートもしくは発泡性複合シートを挟圧する装置が付設されたものであってもよく、更には、引抜き金型、例えば、被加熱焼鈍体の厚さと幅に略等しい厚さと幅のスリット孔を有する加熱焼鈍用金型等であってもよく、これらの２枚の平板間を適宜面圧を受けて通過するのと同じ作用及び効果を有するものを包括して指すものである。
上記加熱焼鈍を連続的に実施する手段としては、例えば、以下に示すような方法が挙げられる。
【００７２】
１）被加熱焼鈍体である発泡性シートもしくは発泡性複合シートの厚さに略等しい厚さの加熱焼鈍空間を背中合わせに互いに反対方向に回転する無端ベルト（以下、ダブルベルトと略称する）によって被加熱焼鈍体を挟持して搬送し、無端ベルトを加熱して加熱焼鈍する方法。
上記ダブルベルトによって搬送される被加熱焼鈍体に加わるダブルベルトの負荷は、余り小さいと被加熱焼鈍体が加熱焼鈍時に自由変形し、余り大き大きいと加重によって変形するおそれがあるので、好ましくは５〜３００ｇ／ｃｍ² 程度、より好ましくは２０〜１００ｇ／ｃｍ² 程度である。
尚、無端ベルトの加熱手段は、無端ベルトが適宜加熱手段によって直接加熱されるものであってもよく、上記加熱焼鈍が同温度の加熱雰囲気中で行われてもよい。
【００７３】
２）被加熱焼鈍体の厚さと幅に略等しい厚さと幅のスリット孔を有する加熱焼鈍用金型のスリット孔内壁に被加熱焼鈍体を接触させて引き抜くことにより加熱焼鈍する方法。
【００７４】
図１〜図３に、第四工程と第五工程の間に加熱焼鈍工程を付加した本発明のポリオレフィン系樹脂発泡体の製造方法の幾つかの実施例を示す。
図１は、ダブルベルト１、１によって発泡性複合シート２をベルトの駆動によって搬送し、ベルトの内側に対向する加熱板３、３をダブルベルト１、１を介して発泡性複合シート２を挟圧するように設置し、発泡性複合シート２を加熱焼鈍すると共に前記する荷重が負荷されて発泡性複合シート２の変形が抑制される加熱焼鈍工程４である。
【００７５】
図２は、図１に示された加熱板３、３に替えて、ダブルベルト１、１の内側にその進行方向に複数の加熱ロール３１、３１、・・・をその中心軸が直交し、且つ、ダブルベルト１、１との接触部が、発泡性複合シート２の加熱焼鈍工程のためにダブルベルト１、１が形成する平面と略同じ平面を形成するように密に並列して配置され、発泡性複合シート２を加熱焼鈍すると共に前記する荷重が負荷されて発泡性複合シート２の変形が抑制される加熱焼鈍工程４である。
【００７６】
又、図３は、図１及び図２に示された加熱及び変形防止手段に替えて、発泡性複合シート２の厚さと幅に略等しい高さと幅のスリット孔３２を有する加熱焼鈍用金型３３を用いる方法であり、加熱された加熱焼鈍用金型３３のスリット孔３２内面に接触させて引き抜くことにより、発泡性複合シート２を変形を防止して加熱焼鈍する加熱焼鈍工程４である。
尚、図１〜図３に示された本加熱焼鈍工程４に連なる次工程は、いずれも発泡の第五工程５である。
【００７７】
図４は、第三工程と第四工程の間に加熱焼鈍工程を付加した本発明のポリオレフィン系樹脂発泡体の製造方法の実施例を示す。
図４において、４１は、図２において示した加熱焼鈍工程４を発泡の第五工程５と分離したものに相当し、前記複数の加熱ロール３１、３１、・・・とダブルベルト１、１が図２におけると同様に組み合わされて用いられている。
【００７８】
第四工程において、加熱焼鈍された発泡性シート２１は、その両面からこれを挟圧するラミネートロール４２、４２によって、シート状物２２、２２が両面に積層される。
このようにシート状物２２を積層された発泡性複合シート２は、無端ベルト５２上を引取ロール５３、５３、・・・によって搬送され、図示されていない加熱装置によって熱分解型化学発泡剤の分解温度以上に加熱され、これを発泡させる第五工程５１に連なっている。
【００７９】
加熱焼鈍の温度は、被加熱焼鈍体の変性ポリオレフィン系樹脂の融点以上、熱分解型化学発泡剤の分解温度未満の温度である。変性ポリオレフィン系樹脂の融点未満では、被加熱焼鈍体内の成形歪が十分に緩和されず、発泡剤の分解温度以上では発泡が開始され、被加熱焼鈍体の内圧が上昇し、被加熱焼鈍体の幅方向に変形が起こり、所望の発泡体を得ることができない。
【００８０】
加熱焼鈍の加熱時間は、被加熱焼鈍体の内部まで上記加熱焼鈍温度に達するに必要な時間であって、変性ポリオレフィン系樹脂の種類、厚さ及び加熱手段等によって定まるものであって、特に限定されるものではないが、例えば、厚さ０．５〜１０ｍｍのホモタイプのポリプロピレンシートの場合、好ましくは３０〜１０００秒程度である。
加熱焼鈍の加熱時間が３０秒未満では、被加熱焼鈍体内の成形歪が十分に緩和されず、１０００秒を超えて必要以上加熱しても加熱焼鈍効果は飽和してしまうばかりか、生産性を低下するばかりか、加熱焼鈍装置が長大なものとなって作業性等を煩瑣なものとする。
【００８１】
こうして得られた発泡性複合シートは、適切な温度条件で加熱することにより、常圧下或いは一定加圧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取式発泡器の他、ベルト式発泡器、縦型又は横型発泡炉、熱風恒温槽や、或いはオイルバス、メタルバス、ソルトバス等の熱浴が用いられる。
【００８２】
得られたポリオレフィン系樹脂発泡性複合シートを加熱発泡させる際、シート状物が面内方向の発泡を抑制しつつ、積極的に厚み方向に発泡を導くには、発泡性シートを構成する樹脂は流動性を有する必要がある。本発明方法によれば、ポリオレフィン系樹脂と特定の変性用モノマーを混和して得られた変性樹脂は、この厚み方向への発泡の他、変性樹脂と発泡剤との混練、シートへの賦形が充分可能な溶融流動性を維持しつつ、同時に発泡が可能な程度の融体強度を持たせることができる。
【００８３】
そして、発泡時に面内方向の発泡を抑制しうる強度を有するシート状物が発泡性シートの少なくとも片面に積層されているため、発泡時、面内の二次元方向には殆ど発泡せず、厚み方向にのみ発泡する。従って、同発泡性複合シートの加熱発泡によって得られた複合発泡体の気泡は、厚み方向にその長軸を配向した紡錘形、即ちシート厚み方向に直立したラグビーボール状になって並ぶ。そのため、得られた発泡体は、シート厚み方向に圧縮力を受けると、紡錘形の長軸方向に力がかかることになるので、その方向に高い強度を示す。
【００８４】
従来技術に従って架橋材料シラン変性ポリオレフィンを使用して得られた発泡性シートと比較して、本発明における発泡性シートは、発泡圧が低くなるため、０．３ｋｇ／ｃｍという極端に低い強度を有するシート状物を用いても、破損することなく面内方向の発泡を抑制することができる。この結果、この発泡性シートを加熱発泡することによって、厚み方向にのみ発泡させ、厚み方向に長軸を有する紡錘形のセルからなる発泡体を得ることができる。
【００８５】
又、変性樹脂に未変性のポリオレフィン系樹脂又は他の熱可塑性樹脂がブレンドされることによって、更に流動性が向上するため発泡圧は一層低下すると同時に、球形と比べて変形歪みが伴う紡錘形の気泡が形成され易くなる。
【００８６】
尚、本発明方法においては、長い反応時間を要する水架橋を利用しないので、生産性が高い。又、発泡性樹脂複合シート及びこれから得られた発泡体は、溶融流動性を有するので実質的にリサイクル可能である。
【００８７】
【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。
【００８８】
（実施例１）
ｉ）発泡性樹脂組成物の製造
(1) 変性ポリオレフィン系樹脂の調製（第一工程）
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。
【００８９】
上記変性用スクリュー押出機のシリンダーバレル設定温度は、第１バレル；１８０℃、第２バレル；２２０℃、第３バレル；２２０℃、第４バレル；２２０℃及びダイ；２２０℃とし、スクリュー回転数は、１５０ｒｐｍに設定した。
変性用スクリュー押出機に、先ず、ポリオレフィン系樹脂及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。
【００９０】
ポリオレフィン系樹脂はポリプロピレンランダム共重合体（三菱化学製、商品名「ＥＧ８」、ＭＩ；０．８ｇ／１０分、密度；０．９ｇ／ｃｍ³ ）であり、その供給量は１０ｋｇ／ｈとした。
【００９１】
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、商品名「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。
【００９２】
ポリオレフィン系樹脂とジオキシム化合部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、水冷し、ペレタイザーで切断して、変性樹脂のペレットを得た。
【００９３】
(2) 発泡性樹脂組成物の調製（第二工程）
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７穴ストランドダイである。
【００９４】
発泡剤混練用スクリュー押出機の温度設定区分は、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バレル及び第４ゾーン；ダイおよびアダプター部である。
【００９５】
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。
【００９６】
発泡剤混練用スクリュー押出機のシリンダーバレル設定温度は、第１バレル；１５０℃、第２バレル；１７０℃、第３バレル；１８０℃、第４バレル；１６０℃とし、スクリュー回転数は、４０ｒｐｍに設定した。
【００９７】
上述のようにして得られた変性樹脂を反応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。又、同押出機にそのサイド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。
【００９８】
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、ストランドダイから吐出し、水冷し、ペレタイザーで切断して、同組成物のペレットを得た。
【００９９】
(3) 発泡性シートの調製（第三工程）
上記のようにして得られた発泡性樹脂組成物を、Ｔダイ法によって、成形温度１８０℃にて幅５００ｍｍ、厚み１．３ｍｍの発泡性シートを調製した。
【０１００】
(4) シート状物の積層（第四工程）
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、商品名「スパンボンド エクーレ ６３０１Ａ」、秤量３０ｇ／ｍ² 、引張強さ：縦１．６ｋｇ／ｃｍ、横１．２ｋｇ／ｃｍ）を用意し、上記Ｔダイ法の押出成形に際して、クリアランス１．５ｍｍに設定された一対の冷却ロールの両側から未だ溶融状態にある発泡性シートをサンドイッチ状に包み込むように供給して幅５００ｍｍ、厚み１．５ｍｍの長尺発泡性複合シートを調製した。
【０１０１】
(5) 加熱焼鈍の実施
得られた発泡性複合シートは、外側がダブルベルト加熱板である予熱炉内をダブルベルトに挟持されて、移動速度０．５ｍ／分で移送され、１８０℃で３分間加熱焼鈍された。
尚、上記加熱焼鈍は、発泡性複合シートに４０ｇ／ｃｍ² の負荷となるようにダブルベルトに挟圧が負荷された。
【０１０２】
(6) 加熱発泡（第五工程）
次いで、加熱焼鈍された発泡性複合シートを、熱風循環型発泡炉で、２３０℃で４分間加熱し発泡させ、発泡終了後、冷却して幅５００ｍｍ、厚み１５ｍｍの発泡体を作製した。
【０１０３】
得られた発泡性積層シートから縁部を取り除き、一辺３００ｍｍの正方形サンプルを得た。
【０１０４】
(4) 発泡
タルクを敷き付けたステンレススチール製バットを熱風オープン内に置き、上記発泡性シートサンプルをタルク上に置き、同サンプルを２３０℃で約４分間加熱発泡させ、複合発泡体を得た。
【０１０５】
（実施例２）
実施例１において第四工程終了後に実施した発泡性複合シートの加熱焼鈍工程を、第三工程が終了した後、実施例１における発泡性複合シートの加熱焼鈍条件と同一条件で、得られた発泡性シート単体で加熱焼鈍し、然る後、実施例１の第四工程におけると同様にシート状物を積層する工程として、加熱焼鈍の工程を一工程前にずらしたこと以外、実施例１と同様にして複合発泡体を得た。
【０１０６】
（比較例１）
実施例１の加熱焼鈍工程において、ダブルベルトに挟圧することなく、発泡性複合シートをオープンスペースで実施例１と同じ温度及び時間で加熱焼鈍したこと以外、実施例１と同様にして複合発泡体を得た。
【０１０７】
（性能評価）
実施例１、２及び比較例で得られた複合発泡体を下記の項目について性能評価した。
【０１０８】
１．発泡倍率：
複合発泡体より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。
【０１０９】
２．表面平滑性：
目視にて発泡体の幅方向の凹凸の状態を、○：表面平滑で幅方向の凹凸が認められないもの、×：表面の幅方向に凹凸が認められるもの、の２段階で評価した。
【０１１０】
実施例１、２及び比較例の発泡体の評価結果を表１に示す。
【０１１１】
【表１】

【０１１２】
【発明の効果】
本発明のポリオレフィン系樹脂発泡体の製造方法は、叙上のように構成されているので、得られる複合発泡体は、高い圧縮強度を有し、軽量性、断熱性、柔軟性等に優れる上、変形等のない表面平滑性の極めて優れたものとなる。
そのため、これを各種断熱材、緩衝材、浮揚材等に幅広く用いることができる上に、建物の屋上断熱材や床用断熱材等の用途にも美麗な仕上がりで使用することができる。
【図面の簡単な説明】
【図１】本発明のポリオレフィン系樹脂発泡体の製造方法の第四工程と第五工程の間に付加される加熱焼鈍工程の一例を前後の工程と共に示す概略説明図である。
【図２】本発明のポリオレフィン系樹脂発泡体の製造方法の第四工程と第五工程の間に付加される加熱焼鈍工程の他の例を前後の工程と共に示す概略説明図である。
【図３】本発明のポリオレフィン系樹脂発泡体の製造方法の第四工程と第五工程の間に付加される加熱焼鈍工程の他の例を前後の工程と共に示す概略説明図である。
【図４】本発明のポリオレフィン系樹脂発泡体の製造方法の第三工程と第四工程の間に付加される加熱焼鈍工程の一例を前後の工程と共に示す概略説明図である。
【符合の説明】
１ ダブルベルト
２ 発泡性複合シート
２１ 発泡性シート
２２ シート状物
３ 加熱板
３１ 加熱ロール
３２ スリット孔
３３ 加熱焼鈍用金型
４、４１ 加熱焼鈍工程
４２ ラミネートロール
５、５１ 発泡工程
５２ 無端ベルト
５３ 引取ロール[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a polyolefin resin foam.
[0002]
[Prior art]
Polyolefin resin foams such as polyethylene and polypropylene are excellent in light weight, heat insulation, flexibility, and the like, and thus are widely used for various heat insulating materials, buffer materials, levitation materials, and the like. However, the polyolefin resin foam has a lower compressive strength than the polystyrene resin foam, so it cannot be used, for example, for applications such as building roof insulation or floor insulation. It was.
[0003]
In order to solve this problem, for example, Japanese Patent Application Laid-Open No. 9-150431 discloses that the foaming force in the in-plane direction generated when a foamable polyolefin resin sheet containing a pyrolytic foaming agent is heated and foamed is suppressed. There has been proposed a composite foam in which sheet-like materials having sufficient strength are laminated on at least one side.
[0004]
In order to produce this composite foam, specifically, a polyolefin resin and a silane-modified polyolefin that is incompatible with this are blended, and a thermal decomposition type chemical foaming agent is added to the blend and kneaded. The foamable resin composition was shaped into a sheet and simultaneously laminated on both sides of the obtained foamable sheet was a sheet of a polyethylene terephthalate nonwoven fabric, and the silane-modified polyolefin in the resulting foamable composite sheet was mixed with water. After cross-linking, it is heated and foamed.
[0005]
The foamable resin sheet thus obtained has a sheet-like material having a strength capable of suppressing the foaming force in the in-plane direction at the time of foaming and is laminated on at least one side. It does not foam and foams only in the thickness direction. Therefore, the bubbles of the foam are arranged in a spindle shape in which the major axis is oriented in the thickness direction, that is, in a rugby ball shape standing upright in the thickness direction of the sheet (see FIG. 1). Therefore, when the obtained foam is subjected to a compressive force in the thickness direction of the sheet, a force is applied in the long axis direction of the spindle shape, and thus exhibits high strength in the thickness direction.
[0006]
However, in the above prior art, on the other hand, silane-modified polyolefin is expensive, or the crosslinking reaction takes a long time (usually 1 hour or more). In order to solve these problems, the present inventors have disclosed a polyolefin resin foamable composite sheet in Japanese Patent Application No. 10-219136 as a method for solving these problems. With respect to the production method and the composite foam, at least one selected from the group consisting of polyolefin resins and dioxime compounds, bismaleimide compounds, divinyl compounds, allyl polyfunctional monomers, (meth) acrylic polyfunctional monomers, and quinone compounds. It was proposed to use a polyolefin-based resin modified by reacting with a modifying monomer composed of a compound.
[0007]
[Problems to be solved by the invention]
The invention of the above Japanese Patent Application No. 10-219136 is intended to solve the above-mentioned problems of the prior art and to provide a composite foam having a high compressive strength and excellent in lightness, heat insulation, flexibility and the like. However, when the foamable modified polyolefin resin composition is molded into a sheet, a bank generated when the foamable modified polyolefin resin composition extruded into a sheet form from a mold is sandwiched between cooling rolls ( bank) is crushed by the cooling roll and stored as a molding strain in the original fabric before foaming, and when this is heated and foamed, it may be deformed and a smooth board-like foam may not be obtained. found.
[0008]
The present invention has been made in view of the above-mentioned facts, and its purpose is to produce a polyolefin resin foam having excellent appearance performance and high compressive strength by reducing molding distortion of the raw material before foaming. It is to provide a method.
[0009]
[Means for Solving the Problems]
The method for producing a polyolefin-based resin foam according to the first aspect of the present invention includes a first step of modifying a polyolefin-based resin by reacting the polyolefin-based resin with a modifying monomer; The second step of adding a foaming agent and kneading to form a foamable resin composition, the third step of shaping the obtained foamable resin composition into a sheet to form a foamable sheet, and the obtained foamable sheet The fourth step and the foamable composite sheet are heated by laminating a sheet-like material having a strength capable of suppressing foaming in the in-plane direction when the foamable sheet is heated and foamed on at least one side. In the method for producing a polyolefin resin foam comprising the fifth step of foaming by heating to a temperature equal to or higher than the decomposition temperature of the decomposable chemical foaming agent, the third step is obtained between the third step and the fourth step. Effervescent foam Preparative the modified resin above the melting point in between the plates, characterized by adding the step of heating annealing at a temperature lower than the decomposition temperature of the thermally decomposable chemical foaming agent. Here, the step of heat annealing means a so-called annealing step. same as below.
[0010]
The method for producing a polyolefin resin foam of the invention according to claim 2 comprises: A first step of modifying a polyolefin resin by reacting a polyolefin resin with a modifying monomer, a second step of adding a pyrolytic chemical foaming agent to the resulting modified resin and kneading to obtain a foamable resin composition A third step of shaping the obtained foamable resin composition into a sheet shape to obtain a foamable sheet, an in-plane direction when the foamable sheet is heated and foamed on at least one side of the obtained foamable sheet The fourth step to form a foamable composite sheet by laminating sheet-like materials having a strength capable of suppressing foaming into the foam and the foamable composite sheet is heated to a temperature equal to or higher than the decomposition temperature of the pyrolytic chemical foaming agent to be foamed In the manufacturing method of polyolefin resin foam consisting of the fifth step In addition, between the fourth step and the fifth step, a step of heating and annealing the obtained foamable composite sheet between the flat plates at a temperature above the melting point of the modified resin and below the decomposition temperature of the pyrolytic chemical foaming agent is added. It is characterized by doing.
[0011]
The method for producing a polyolefin resin foam of the invention according to claim 3 is the method according to claim 1. Or 2 In the method for producing a polyolefin resin foam according to the described invention, the modifying monomer is selected from the group consisting of a dioxime compound, a bismaleimide compound, a divinyl compound, an allyl polyfunctional monomer, a (meth) acrylic polyfunctional monomer, and a quinone compound. One or more selected compounds.
[0012]
Throughout this specification, the “in-plane direction” means any direction in the sheet surface of the foamable sheet, and includes a length direction and a width direction. In addition, the “sheet” does not mean a form in a strict sense based on the thickness, but includes a relatively thin material usually called a film to a relatively thick material usually called a plate material.
[0013]
The polyolefin constituting the main component of the polyolefin resin in the method of the present invention is a homopolymer of an olefin monomer, or a copolymer of a main component olefin monomer and another monomer, and is not particularly limited. For example, polyethylene such as low density polyethylene, high density polyethylene and linear low density polyethylene, polypropylene such as homotype polypropylene, random type polypropylene, block type polypropylene, polybutene, ethylene-propylene copolymer, ethylene-propylene-diene Examples of such copolymers include ethylene-based copolymers, ethylene-butene copolymers, ethylene-vinyl acetate copolymers, ethylene- (meth) acrylic acid ester copolymers, and the like. Or a combination of two or more of
[0014]
As the polyolefin which is the main component of the polyolefin resin in the method of the present invention, one or a combination of two or more of the above-described polyethylene and polypropylene is preferable.
[0015]
The polyolefin resin refers to a resin composition in which the ratio of the polyolefin is 70 to 100% by weight. Resins other than the polyolefin constituting the polyolefin resin are not limited, and examples thereof include polystyrene and styrene elastomer. If the proportion of 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, but also it is difficult to secure the melt viscosity necessary for foaming. This is not preferable.
[0016]
The modifying monomer used in the first step of the method of the present invention is a compound having two or more functional groups capable of radical reaction in the molecule. Examples of the functional group include an oxime group, a maleimide group, a vinyl group, an allyl group, and a (meth) acryl group. The modifying monomer is preferably a dioxime compound, a bismaleimide compound, divinylbenzene, an allyl polyfunctional monomer, or a (meth) acrylic polyfunctional monomer. The modifying monomer may be a cyclic compound having two or more ketone groups in the molecule, such as a quinone compound.
[0017]
Among the modifying monomers used in the first step, a compound having two oxime groups in the molecule, that is, a dioxime compound, has an oxime group (chemical formula I) or a hydrogen atom thereof as represented by the following general formula. A compound having in its molecule two structures (chemical formula II) substituted with other atomic groups (mainly hydrocarbon groups), for example, p-quinonedioxime (chemical formula III), p, p-dibenzoylquinonedi An oxime (Chemical Formula IV) is exemplified. Dioxime compounds can also be used in combinations of two or more.
[0018]
[Chemical 1]

[0019]
[Chemical formula 2]

[0020]
[Chemical 3]

[0021]
[Formula 4]

[0022]
Among the modifying monomers used in the first step, as a bismaleimide compound having two maleimide structures (chemical formula V) represented by the following general formula in the molecule, for example, N, N′-p-phenylenebismaleimide (Chemical Formula VI), N, N′-m-phenylenebismaleimide (Chemical Formula VII), and diphenylmethane bismaleimide (Chemical Formula VIII) are exemplified. A bismaleimide compound can also be used in combination of 2 or more types. In addition, polymaleimide (chemical formula IX) having two or more maleimide structures in the molecule also has the same effect and is included in the category of bismaleimide compounds.
[0023]
[Chemical formula 5]

[0024]
[Chemical 6]

[0025]
[Chemical 7]

[0026]
[Chemical 8]

[0027]
[Chemical 9]

[0028]
Among the modifying monomers used in the first step, a compound having two vinyl groups in the molecule, that is, a divinyl compound is, for example, divinylbenzene (compound X) represented by the following chemical formula, and the two vinyl groups are ortho, The positional relationship may be either meta or para.
[0029]
[Chemical Formula 10]

[0030]
Among the modifying monomers used in the first step, compounds having two or more allyl groups in the molecule, ie, allylic polyfunctional monomers include, for example, diallyl phthalate (chemical formula XI) represented by the following chemical formula, triallyl cyanurate (Chemical Formula XII), triallyl isocyanurate (Chemical Formula XIII), diallyl chlorendate (Chemical Formula XIV). The allylic polyfunctional monomer can also be used in a combination of two or more.
[0031]
Embedded image

[0032]
Embedded image

[0033]
Embedded image

[0034]
Embedded image

[0035]
Among the modifying monomers used in the first step, a compound having two or more (meth) acrylic groups in the molecule, that is, (meth) acrylic polyfunctional monomer has 2 to 4 (meth) acryloyloxy groups. The compound which has is mentioned.
[0036]
Examples of the (meth) acrylic bifunctional monomer having two (meth) acryloyloxy groups include alkanediol di (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polyethylene glycol di (meth) ) Acrylate, polypropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, dimethylol tricyclodecane di (meth) acrylate, ethylene glycol adduct of bisphenol A di (meth) acrylate, propylene glycol addition of bisphenol A An example is di (meth) acrylate.
[0037]
Examples of the (meth) acrylic trifunctional monomer having three (meth) acryloyloxy groups include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, trimethylolpropane ethylene oxide-added tri (meth) acrylate, Examples thereof include glycerin propylene oxide-added tri (meth) acrylate and tris (meth) acryloyloxyethyl phosphate.
[0038]
Examples of the (meth) acrylic tetrafunctional monomer having four (meth) acryloyloxy groups include pentaerythritol tetra (meth) acrylate and ditrimethylolpropane tetra (meth) acrylate.
[0039]
Among the modifying monomers used in the first step, a typical example of a cyclic compound having two or more ketone groups in the molecule is a quinone compound, and examples of the quinone compound include hydroquinone, p-benzoquinone, and tetrachloro-p-benzoquinone. Illustrated.
[0040]
The blending amount of the modifying monomer may be appropriately selected according to the type of the monomer, but is generally 0.05 to 5 parts by weight, preferably 0.2 to 2 parts by weight with respect to 100 parts by weight of the polyolefin resin. Part. When the blending amount of the modifying monomer is less than 0.05 parts by weight, it is difficult to obtain the melt viscosity necessary for foaming. When the blending amount exceeds 5 parts by weight, the degree of crosslinking is excessively increased, the extrusion moldability is deteriorated (for example, a high load is applied, a melt fracture occurs), and a foaming agent to be added later is added to the resin composition. Cannot be kneaded uniformly, and the gel fraction is unnecessarily increased, which may impair the recyclability. In addition, the foaming pressure at the time of heating and foaming becomes too high later, and a sheet-like material for suppressing foaming in the in-plane direction may not be able to be used.
[0041]
In the method of the present invention, an organic peroxide may be used in combination with the modifying monomer. In particular, when divinylbenzene or an allylic polyfunctional monomer is used as the modifying monomer, it is preferable to use an organic peroxide in combination. The organic peroxide is not particularly limited as long as it is generally used in the grafting reaction of polyolefin. For example, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, t-butyl peroxyacetate, t-butyl peroxy 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, and these are preferably used alone or in combination of two or more.
[0042]
In particular, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, di-t-butyl peroxide, 2,5-dimethyl-2,5-di (t-butyl) One or more of peroxy) hexyne-3 and the like are more preferably used.
[0043]
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, so-called β-cleavage of polypropylene occurs significantly, and the molecular weight of the modified product is too low, resulting in a decrease in physical properties or viscosity. It may lead to poor foaming due to lowering. Considering these points, the amount of the organic peroxide used is preferably 0.001 to 0.5 parts by weight with respect to 100 parts by weight of the polyolefin resin, and 0.005 to 0.15 parts by weight. More preferably.
[0044]
In order to obtain the modified resin, a kneading apparatus such as a screw extruder or a kneader is used, and the polyolefin resin and the modifying monomer are melted and mixed under a predetermined condition and reacted. The reaction temperature at this time is 170 degreeC or more and below the decomposition temperature of polyolefin resin, Preferably it is 200 to 250 degreeC. If the melt blending temperature is lower than 170 ° C., the modification is insufficient, and the foaming factor of the finally obtained foam may not be sufficiently high, and if it exceeds 250 ° C., the polyolefin resin is easily decomposed.
[0045]
The apparatus used for the above-mentioned modification reaction may be a melt kneader that can be generally used in plastic molding in addition to a screw extruder, and examples thereof include a kneader, a rotor, and a continuous kneader. Among these, a screw extruder capable of continuous operation is preferable, and a single screw extruder, a twin screw extruder, a multi-screw extruder equipped with three or more screws, and the like are all suitably used. As the single screw extruder, in addition to a general full flight type screw, an extruder having a discontinuous flight type screw, a pin barrel, a mixing head, and the like are also used. Further, as the above-described twin screw extruder, a meshing co-rotating extruder, a meshing counter-rotating extruder, a non-meshing counter-rotating extruder, and the like can be suitably used. It should be noted that providing a vacuum vent at the subsequent stage of the extruder is effective in preventing volatiles from remaining in the resin composition.
[0046]
When a screw extruder is used, the polyolefin resin is usually charged from the hopper into the extruder, but it is also preferable to use a screw type feeder, a weight control type feeder or the like in order to increase quantitativeness.
[0047]
The modifying monomer may be fed into the extruder from the hopper simultaneously with the polyolefin resin. In particular, some divinylbenzene and allyl polyfunctional monomers are liquid at room temperature and normal pressure. It is preferable to supply from the liquid injection hole provided in the downstream portion from the position where the resin is melted, because this can be uniformly dispersed in the molten resin. At this time, it is desirable that the liquid monomer is fed by a pressure-feed pump such as a plunger pump.
[0048]
When using an organic peroxide in combination with the modifying monomer, a method of mixing the organic peroxide with the same monomer in advance and simultaneously adding them, or a method of adding the organic peroxide separately before and after the monomer charging, etc. Is applicable.
[0049]
The obtained modified resin is kneaded by adding a pyrolytic chemical foaming agent in the second step to prepare a foamable resin composition.
The modified resin may be used alone or may be melt blended with the same or different unmodified polyolefin resin. By using such a blend of a modified resin and an unmodified resin, the flowability of the resulting foamable resin composition is improved, and as a result, an extremely thin foamable raw fabric can be formed. It becomes possible to produce a composite foam. In addition, the improvement in the fluidity of the foamable resin composition works favorably for forming spindle-shaped bubbles, and as a result, a foam with higher compressive strength can be obtained.
[0050]
The unmodified polyolefin resin may be the one described above in the definition of the polyolefin resin before modification of the modified resin.
[0051]
The types of unmodified polyolefin resin are: moldability of the foamable composite sheet, appearance, adhesion to the sheet-like material, and foaming ratio, mechanical properties, thermal properties, cell shape of the composite foam obtained therefrom It is appropriately selected depending on the like. For example, in order to improve the flowability of the foam original fabric, a low-viscosity resin is used as the unmodified polyolefin resin. To obtain a soft foam, a low-density polyolefin is used as the unmodified resin.
[0052]
The ratio of the modified resin to the unmodified polyolefin-based resin is preferably 50 to 200 parts by weight, more preferably 70 to 130 parts by weight of the unmodified resin with respect to 100 parts by weight of the modified resin. If the proportion of the unmodified polyolefin-based resin is too large, the melt tension necessary for foaming cannot be maintained, so that the foaming ratio is lowered and a good foam may not be obtained.
[0053]
The pyrolytic chemical foaming agent used in the present invention is not particularly limited as long as it generates a decomposition gas by heating. Typical examples of the thermal decomposition type chemical blowing agent are azodicarbonamide, benzenesulfonylhydrazide, dinitrosopentamethylenetetramine, toluenesulfonylhydrazide, and 4,4-oxybis (benzenesulfonylhydrazide). These may be used alone or in combination of two or more. Of these, azodicarbonamide is particularly preferably used.
[0054]
The pyrolytic chemical foaming agent is used in an amount of 1 to 50 parts by weight, preferably 2 to 35 parts by weight, depending on the desired foaming ratio, with respect to 100 parts by weight of the modified resin. The temperature at which the thermally decomposable chemical foaming agent decomposes varies depending on the type of foaming agent, the particle size, etc., but is approximately 200 ° C. when azodicarboxamide having a particle size of 18 μm is taken as an example.
[0055]
Thus, in order to obtain a foamable resin composition by kneading a pyrolytic chemical foaming agent into a modified resin obtained from a polyolefin-based resin and a modifying monomer, the above-described reaction melt-kneading apparatus, Using a melt-kneader for mixing a foaming agent (the structure may be the same as that of a melt-kneader for reaction), and at a temperature below the maximum temperature at which the foaming agent is not substantially decomposed. Mix. Examples of this melt kneading include the following.
[0056]
(a) In a batch or continuous melt kneader for reaction, the polyolefin resin is melted and mixed with a modifying monomer and reacted, and the resulting modified resin is taken out of the melt kneader and solidified, granulated, etc. Then, the resin composition is transferred to a batch type or continuous type kneading apparatus for mixing a foaming agent, and the foaming agent is added thereto, and both are melt-kneaded to obtain a foamable resin composition.
[0057]
(b) In a batch-type melt-kneading apparatus for reaction, the polyolefin resin is melt-mixed with the modifying monomer and reacted, and the resulting modified resin is heated to a temperature at which the foaming agent is not substantially decomposed in the kneading apparatus. It is cooled to a temperature at which it does not decompose in a large amount, and then a foaming agent is added thereto, and both are melt-kneaded to obtain a foamable resin composition.
[0058]
(c) In a reaction screw extruder (continuous melt kneader), the polyolefin resin is melted and reacted with the modifying monomer at a temperature of 170 ° C. or higher. The temperature is lowered to a temperature at which no decomposition occurs or a temperature at which decomposition does not occur in a large amount, and a foaming agent is introduced from a supply port provided in the middle of the screw extruder, and both are melt-kneaded to obtain a foamable resin composition.
[0059]
(d) In another form of continuous operation, two screw extruders or the like are connected, and the polyolefin resin is melt-blended with the modifying monomer and reacted in the first unit, and the resulting modified resin is treated as described above. After the temperature is lowered in the same manner as described above, the resin composition is transferred to a second unit, a foaming agent is added thereto, and both are melt-kneaded to obtain a foamable resin composition.
[0060]
A foamable resin composition obtained by kneading a pyrolytic chemical foaming agent into a mixture is shaped into a sheet in the third step. As a shaping method, a method generally used in plastic molding, such as press molding, blow molding, calendering molding, injection molding, and the like, can be applied in addition to extrusion molding.
[0061]
In particular, the foamable resin composition obtained according to the above methods (a) and (b) is taken out from a batch-type foaming agent kneading apparatus, and this is put into a screw extruder and continuously shaped into a sheet shape. From the viewpoint of productivity, it is preferable that the foaming resin composition discharged from the screw extruder is directly shaped according to the method of (a), (c) and (d).
[0062]
The material constituting the sheet-like material used in the fourth step of the method of the present invention can be freely selected from metals such as paper, cloth, wood and iron, non-ferrous metals, plastics, glass and inorganic materials, and is not particularly limited. In addition, when the sheet-like material is laminated and integrated with the foamable sheet, it is desirable that it exhibits a certain degree of adhesiveness with the foamable sheet. Also, any adhesive that can be adhered to the foamable sheet by appropriately using an adhesive or an adhesive may be used.
[0063]
The sheet-like material has a strength capable of suppressing foaming in the in-plane direction when the foamable sheet is heated and foamed. If the strength of the sheet-like material is too low, the sheet-like material may tear during foaming, and foaming in the in-plane direction of the foamable sheet may not be sufficiently suppressed. Therefore, as the sheet-like material for suppressing in-plane foaming, for example, when the foaming ratio is 10, a sheet having a tensile strength of 0.1 kgf / cm or more is preferable.
[0064]
Examples of the sheet-like material suitably used in the fourth step of the method of the present invention include glass cloth, cold chill, woven or non-woven fabric, and paper. The glass cloth includes a glass mat obtained by weaving as well as a glass fiber woven material. In addition, the cold and non-woven fabrics are mainly composed of synthetic fibers such as polyester and nylon. The woven fabric may be made of general natural fibers or synthetic fibers. The glass cloth obtained by papermaking may contain a binder for binding short glass fibers. The binder is not particularly limited as long as the tensile strength of the sheet material satisfies the above range. For example, thermoplastic resins such as polyvinyl alcohol, saturated polyester, acrylic resin, epoxy resin, unsaturated polyester, etc. These thermosetting resins can be mentioned. Examples of the organic fiber constituting the woven fabric and the nonwoven fabric include polyester fiber, cotton, acrylic fiber, nylon fiber, carbon fiber, and aramid fiber. By using these sheet-like materials, it is possible to obtain a polyolefin resin composite foam that is lightweight and has high compressive strength. Further, by using a sheet-like material having an appropriate strength, secondary shaping can be performed by reheating the foam to a temperature not lower than the melting point of the polyolefin resin. Therefore, the obtained composite foam can be used suitably for core materials such as molded ceiling materials for automobiles and interior panels.
[0065]
The sheet-like material used in the fourth step may be a metal sheet, for example, an iron sheet or a non-ferrous metal sheet such as aluminum, titanium, or copper. The iron sheet includes a molten zinc steel sheet, a molten zinc aluminum alloy steel sheet, a stainless steel sheet, and the like. As such a metal sheet, a thin rolled sheet having a thickness of 0.01 mm to 2 mm is particularly preferably used. In this case, these metals may be arbitrarily plated, may be coated with an organic paint or an inorganic paint, or may be coated with an adhesive. When these metal sheets are used, the resulting polyolefin resin composite foam can be a lightweight metal composite plate. Compared to a metal plate with a thickness of 1 to 5 mm and a metal composite plate with a polyethylene layer as an intermediate layer, it is lighter and less costly without causing a practically extreme lack of strength. Has the merit that can be achieved. In addition, since this composite foam is produced by foaming a foamable composite sheet, the surface smoothness is extremely excellent compared to a metal composite plate in which a metal sheet-like material is pasted on the foam. .
[0066]
The method for laminating the sheet-like material on at least one side of the foamable sheet is not particularly limited. For example, (a) a method in which the sheet-like material is applied to a foamed sheet that has been cooled and solidified while being heated; Examples thereof include a method in which the foamable sheet is heated until it is in a molten state and this is heat-sealed to a sheet-like material, and (c) a method in which the sheet-like material is bonded to the foamable sheet with an adhesive.
[0067]
In order to ensure the thickness accuracy of the foamable composite sheet, the method (A) or (C) is preferable. In the thermal fusion of the method (b), for example, in a state where a sheet-like material is lightly laminated on at least one surface of a molten foam sheet immediately after being extruded from a T die, these are placed between opposing cooling rolls. A method in which both are integrated by the pressing force of the roll is preferable.
[0068]
In addition, when the foamable sheet and the sheet-like material are laminated and integrated as described above, when an attempt is made to peel off the foamable sheet and the sheet-like material at the interface between them, a material breakage occurs at a high rate. It is assumed that both are fixed to each other.
[0069]
In the method for producing a polyolefin resin foam of the present invention, a third step of shaping the foamable polyolefin resin composition into a sheet shape, and foaming in the in-plane direction when the foamable polyolefin resin sheet is heated and foamed A fifth step of heating the foamable composite sheet to a temperature equal to or higher than the decomposition temperature of the thermally decomposable chemical foaming agent through the fourth step of laminating sheet-like materials having a strength capable of suppressing the foaming to form a foamable composite sheet; Between the flat plate of the foamable sheet obtained in the third step or the foamable composite sheet obtained in the fourth step (without changing the shape), the melting point of the modified resin is higher than the thermal decomposition type chemical foaming Heat annealing is performed at a temperature lower than the decomposition temperature of the agent.
[0070]
That is, after the third step, the sheet is heated and annealed in the state of a foamable sheet alone, and thereafter, a sheet-like material having a strength capable of suppressing foaming in the in-plane direction when the foamable sheet is heated and foamed is laminated. It may be heat-annealed in the state of a foamable composite sheet in which the above sheet-like material is laminated on a foamable sheet, but the latter has a larger heat-annealing effect in consideration of molding distortion during lamination. Is preferable.
[0071]
The means for heat annealing so as not to deform the shape of the foamable sheet or the foamable composite sheet is not particularly limited, but it is possible to heat-anneal by sandwiching both surfaces of these heat-treated annealing bodies between flat plates. Is preferred.
The space between the flat plates on which the heat annealing is performed does not mean only between the two large rigid plates, but may be a pair of endless belts, for example, steel belts, rotating in opposite directions back to back. Well, further, a load is applied in a direction perpendicular to the opposed surfaces of both belts at a position where the endless belts are opposed to form a flat plate-like space, and a foamable sheet or foam is conveyed between the belts. It may be provided with a device for sandwiching the porous composite sheet, and furthermore, a drawing die, for example, a heat annealing metal having a slit hole having a thickness and width substantially equal to the thickness and width of the object to be heated. It may be a mold or the like, and collectively refers to those having the same action and effect as passing between these two flat plates under appropriate surface pressure.
Examples of means for continuously performing the heat annealing include the following methods.
[0072]
1) A heated annealing space having a thickness substantially equal to the thickness of the foamable sheet or foamable composite sheet, which is an object to be heated, is covered by an endless belt (hereinafter abbreviated as a double belt) rotating in opposite directions. A method in which a heat-annealed body is sandwiched and conveyed, and an endless belt is heated and heat-annealed.
If the load of the double belt applied to the heated annealing body conveyed by the double belt is too small, the heated annealing body may be freely deformed during heating annealing, and if it is too large, the load may be deformed by load. ~ 300g / cm ² Degree, more preferably 20-100 g / cm ² Degree.
The heating means for the endless belt may be one in which the endless belt is directly heated by a heating means as appropriate, and the heating annealing may be performed in a heating atmosphere at the same temperature.
[0073]
2) A method of performing heat annealing by bringing a heated annealing body into contact with an inner wall of a slit hole of a mold for heating annealing having a slit hole having a thickness and a width approximately equal to the thickness and width of the heated annealing body and pulling out.
[0074]
1 to 3 show some examples of the method for producing a polyolefin resin foam of the present invention in which a heat annealing step is added between the fourth step and the fifth step.
In FIG. 1, the foamable composite sheet 2 is conveyed by driving the belt by the double belts 1, 1, and the heating plates 3, 3 facing the inside of the belt are sandwiched between the double belts 1, 1. This is a heat annealing step 4 in which the foamable composite sheet 2 is heat-annealed while being heat-annealed and the load described above is applied to suppress deformation of the foamable composite sheet 2.
[0075]
2, instead of the heating plates 3 and 3 shown in FIG. 1, a plurality of heating rolls 31, 31,... In addition, the contact portions with the double belts 1 and 1 are arranged closely in parallel so as to form a plane substantially the same as the plane formed by the double belts 1 and 1 for the heat annealing process of the foamable composite sheet 2. This is a heat annealing step 4 in which the foamable composite sheet 2 is heat-annealed and the above-described load is applied to suppress deformation of the foamable composite sheet 2.
[0076]
FIG. 3 shows a heating annealing mold having slit holes 32 having a height and a width substantially equal to the thickness and width of the foamable composite sheet 2 in place of the heating and deformation preventing means shown in FIGS. This is a heating annealing step 4 in which the foamable composite sheet 2 is heated and annealed while preventing deformation by bringing it into contact with the inner surface of the slit hole 32 of the heated heating annealing mold 33.
In addition, all the next processes following the main heat annealing process 4 shown in FIGS. 1 to 3 are the fifth process 5 of foaming.
[0077]
FIG. 4 shows an embodiment of the method for producing a polyolefin resin foam of the present invention in which a heat annealing step is added between the third step and the fourth step.
4, 41 is equivalent to what the heating annealing process 4 shown in FIG. 2 separated from the 5th process 5 of foaming, The said several heating rolls 31, 31, ... and the double belts 1, 1 are They are used in combination as in FIG.
[0078]
In the fourth step, the heat-annealed foamable sheet 21 is laminated on both surfaces by laminating rolls 42 and 42 that sandwich the sheet from both sides.
The foamable composite sheet 2 on which the sheet-like material 22 is laminated in this way is conveyed on the endless belt 52 by take-up rolls 53, 53,..., And is formed of a pyrolytic chemical foaming agent by a heating device (not shown). It is heated to the decomposition temperature or higher and is connected to a fifth step 51 for foaming it.
[0079]
The temperature of the heat annealing is a temperature that is equal to or higher than the melting point of the modified polyolefin resin of the object to be heated and lower than the decomposition temperature of the pyrolytic chemical foaming agent. Below the melting point of the modified polyolefin-based resin, the molding strain in the heated annealing body is not sufficiently relaxed, and foaming is started above the decomposition temperature of the foaming agent, the internal pressure of the heated annealing body increases, Deformation occurs in the width direction, and a desired foam cannot be obtained.
[0080]
The heating time of heat annealing is the time required to reach the heat annealing temperature up to the inside of the object to be heated, and is determined by the type, thickness, heating means, etc. of the modified polyolefin resin, and is particularly limited. For example, in the case of a homo-type polypropylene sheet having a thickness of 0.5 to 10 mm, it is preferably about 30 to 1000 seconds.
If the heating time of the heat annealing is less than 30 seconds, the molding strain in the heated annealing body is not sufficiently relaxed, and the heating annealing effect is saturated not only when it is heated more than necessary for more than 1000 seconds, but also the productivity is reduced. In addition to the decrease, the heat annealing apparatus becomes long and the workability and the like become troublesome.
[0081]
The foamable composite sheet thus obtained can be foamed to a desired foaming ratio under normal pressure or constant pressure by heating at an appropriate temperature condition. The heating is usually performed in a temperature range from the decomposition temperature of the pyrolytic chemical foaming agent to the decomposition temperature + 100 ° C. In particular, as continuous foaming equipment, in addition to a take-up foamer that foams while taking out foam on the outlet side of the heating furnace, a belt-type foamer, a vertical or horizontal foaming furnace, a hot air thermostat, or an oil bath, metal Hot baths such as baths and salt baths are used.
[0082]
When the obtained polyolefin resin foamable composite sheet is heated and foamed, in order to positively guide foaming in the thickness direction while the sheet-like material suppresses foaming in the in-plane direction, the resin constituting the foamable sheet is It must have fluidity. According to the method of the present invention, a modified resin obtained by mixing a polyolefin-based resin and a specific modifying monomer is not only foamed in the thickness direction but also kneaded with a modified resin and a foaming agent, and shaped into a sheet. However, it is possible to provide a melt strength that allows foaming while maintaining a sufficiently high melt fluidity.
[0083]
And since the sheet-like material which has the intensity | strength which can suppress foaming of an in-plane direction at the time of foaming is laminated | stacked on the at least single side | surface of a foamable sheet, at the time of foaming, it hardly foams in the in-plane two-dimensional direction, thickness Foam only in the direction. Accordingly, the bubbles of the composite foam obtained by heating and foaming the foamable composite sheet are arranged in a spindle shape in which the major axis is oriented in the thickness direction, that is, in a rugby ball shape standing upright in the sheet thickness direction. Therefore, when the obtained foam is subjected to a compressive force in the sheet thickness direction, a force is applied in the spindle major axis direction, and thus shows high strength in that direction.
[0084]
Compared with the foamable sheet obtained by using the cross-linking material silane-modified polyolefin according to the prior art, the foamable sheet in the present invention has an extremely low strength of 0.3 kg / cm because the foaming pressure is low. Even if a sheet-like material is used, foaming in the in-plane direction can be suppressed without being damaged. As a result, by heating and foaming the foamable sheet, it is possible to obtain a foamed body made of spindle-shaped cells having foamed only in the thickness direction and having a major axis in the thickness direction.
[0085]
Also, by blending the unmodified polyolefin resin or other thermoplastic resin with the modified resin, the flowability is further improved and the foaming pressure is further reduced, and at the same time, spindle-shaped bubbles with deformation strain compared to the spherical shape. Is easily formed.
[0086]
In the method of the present invention, since water crosslinking that requires a long reaction time is not used, productivity is high. Moreover, since the foamable resin composite sheet and the foam obtained therefrom have melt fluidity, they can be substantially recycled.
[0087]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described more specifically with reference to examples.
[0088]
(Example 1)
i) Production of foamable resin composition
(1) Preparation of modified polyolefin resin (first step)
As a screw extruder for modification, BT40 (Plastics Engineering Laboratory Co., Ltd.) same direction rotating twin screw extruder was used. This is equipped with a self-wiping double thread, L / D is 35 and D is 39 mm. The cylinder barrel is composed of first to fourth barrels from the upstream side to the downstream side of the extruder, the die is a three-hole strand die, and a vacuum vent is installed in the fourth barrel to collect volatile components.
[0089]
The cylinder barrel set temperature of the modification screw extruder is as follows: first barrel; 180 ° C., second barrel; 220 ° C., third barrel; 220 ° C., fourth barrel; 220 ° C. and die; Was set to 150 rpm.
First, a polyolefin resin and a dioxime compound were separately charged from the rear end hopper into a modification screw extruder, and both were melted and mixed to obtain a modified resin. At this time, the volatile matter generated in the extruder was evacuated by a vacuum vent.
[0090]
Polyolefin-based resin is a polypropylene random copolymer (Mitsubishi Chemical, trade name “EG8”, MI: 0.8 g / 10 min, density: 0.9 g / cm ^Three The supply amount was 10 kg / h.
[0091]
The modifying monomer was p-quinonedioxime (trade name “Varnock GM-P” manufactured by Ouchi Shinsei Chemical Co., Ltd.), and the supply amount was 0.75 part by weight with respect to 100 parts by weight of the polyolefin resin.
[0092]
The modified resin obtained by melt blending the polyolefin resin and the dioxime compound was discharged from a strand die, cooled with water, and cut with a pelletizer to obtain modified resin pellets.
[0093]
(2) Preparation of foamable resin composition (second step)
The blowing agent kneading screw extruder is a TEX-44 type (manufactured by Nippon Steel Works) co-rotating twin screw extruder, which is equipped with a self-wiping twin screw, whose L / D is 45.5, D Is 47 mm. The cylinder barrel is composed of 1st to 12th barrels from the upstream side to the downstream side of the extruder, and the forming die is a 7-hole strand die.
[0094]
The temperature setting section of the screw extruder for kneading the foaming agent is as follows. The first barrel is always cooled, the first zone; the second to fourth barrel, the second zone; the fifth to eighth barrel, the third zone; Fourth zone: die and adapter part.
[0095]
A side feeder is installed in the sixth barrel for supplying the foaming agent, and a vacuum vent is installed in the eleventh barrel for recovering volatile components.
[0096]
The cylinder barrel set temperature of the screw extruder for kneading the foaming agent is as follows: first barrel: 150 ° C., second barrel: 170 ° C., third barrel: 180 ° C., fourth barrel: 160 ° C., screw rotation speed is 40 rpm Set.
[0097]
The modified resin obtained as described above was supplied from the reaction screw extruder to the blowing agent kneading screw extruder. The supply amount of the modified resin was 20 kg / h. Moreover, the foaming agent was supplied to the extruder from the side feeder and dispersed. The blowing agent was azodicarbonamide (ADCA), and the supply amount was 1 kg / h.
[0098]
The foamable resin composition thus obtained by kneading the modified resin and the foaming agent was discharged from a strand die, cooled with water, and cut with a pelletizer to obtain pellets of the same composition.
[0099]
(3) Preparation of foamable sheet (third process)
From the foamable resin composition obtained as described above, a foamable sheet having a width of 500 mm and a thickness of 1.3 mm was prepared at a molding temperature of 180 ° C. by a T-die method.
[0100]
(4) Laminating sheets (fourth process)
On the other hand, a non-woven fabric made of polyethylene terephthalate (manufactured by Toyobo Co., Ltd., trade name “Spunbond Ecule 6301A”, weighing 30 g / m ² , Tensile strength: 1.6 kg / cm in length, 1.2 kg / cm in width), and melted from both sides of a pair of cooling rolls set at a clearance of 1.5 mm during the extrusion molding by the T-die method. The long foamable composite sheet having a width of 500 mm and a thickness of 1.5 mm was prepared.
[0101]
(5) Implementation of heat annealing
The obtained foamable composite sheet was sandwiched by a double belt inside a preheating furnace having a double belt heating plate on the outside, transferred at a moving speed of 0.5 m / min, and heated and annealed at 180 ° C. for 3 minutes.
In addition, the said heat annealing is 40 g / cm on a foamable composite sheet. ² Clamping pressure was applied to the double belt so that
[0102]
(6) Heating foaming (5th process)
Subsequently, the heat-expandable foamable composite sheet was heated and foamed at 230 ° C. for 4 minutes in a hot air circulation type foaming furnace, and after foaming, the foamed composite sheet was cooled to produce a foam having a width of 500 mm and a thickness of 15 mm.
[0103]
Edge portions were removed from the obtained foamable laminated sheet to obtain a square sample having a side of 300 mm.
[0104]
(4) Foam
A stainless steel bat laid with talc was placed in a hot air open, the foamable sheet sample was placed on talc, and the sample was heated and foamed at 230 ° C. for about 4 minutes to obtain a composite foam.
[0105]
(Example 2)
Foaming obtained in Example 1 after the fourth step was completed, after the third step, after the third step, in the same conditions as the heating annealing conditions for the foamable composite sheet in Example 1 Example 1 with the exception that the step of heat annealing was shifted one step earlier as a step of laminating sheet-like materials as in the fourth step of Example 1, after heat annealing with a single sheet. A composite foam was obtained in the same manner.
[0106]
(Comparative Example 1)
In the heat annealing step of Example 1, a composite foam was obtained in the same manner as in Example 1 except that the foamable composite sheet was heat-annealed at the same temperature and time as Example 1 in an open space without being sandwiched between double belts. Got.
[0107]
(Performance evaluation)
The composite foams obtained in Examples 1 and 2 and Comparative Example were evaluated for the following items.
[0108]
1. Foaming ratio:
After the sheet-like material was scraped off from the composite foam with a cutter, the foaming ratio of the foam was measured according to JIS K6767.
[0109]
2. Surface smoothness:
The state of unevenness in the width direction of the foam was visually evaluated in two stages: ○: smooth surface with no unevenness in the width direction, and x: unevenness in the width direction of the surface.
[0110]
Table 1 shows the evaluation results of the foams of Examples 1 and 2 and the comparative example.
[0111]
[Table 1]

[0112]
【The invention's effect】
Since the method for producing a polyolefin resin foam of the present invention is configured as described above, the resulting composite foam has high compressive strength and is excellent in lightness, heat insulation, flexibility, and the like. The surface smoothness without deformation is extremely excellent.
Therefore, it can be widely used for various heat insulating materials, cushioning materials, levitation materials, and the like, and can also be used with a beautiful finish for applications such as building roof heat insulating materials and floor heat insulating materials.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view showing an example of a heat annealing step added between the fourth step and the fifth step of a method for producing a polyolefin resin foam of the present invention, together with the preceding and following steps.
FIG. 2 is a schematic explanatory view showing another example of the heat annealing step added between the fourth step and the fifth step of the method for producing a polyolefin resin foam of the present invention, together with the preceding and following steps.
FIG. 3 is a schematic explanatory view showing another example of the heat annealing step added between the fourth step and the fifth step of the method for producing a polyolefin resin foam of the present invention, together with the preceding and following steps.
FIG. 4 is a schematic explanatory view showing an example of a heat annealing step added between the third step and the fourth step of the method for producing a polyolefin resin foam of the present invention, together with the preceding and following steps.
[Explanation of sign]
1 Double belt
2 Foamable composite sheet
21 Foamable sheet
22 Sheet
3 heating plate
31 Heating roll
32 slit holes
33 Heat annealing mold
4, 41 Heat annealing process
42 Laminate roll
5, 51 Foaming process
52 Endless belt
53 Take-up roll

Claims (3)

  A first step of modifying a polyolefin resin by reacting a polyolefin resin with a modifying monomer, a second step of adding a pyrolytic chemical foaming agent to the resulting modified resin and kneading to obtain a foamable resin composition A third step of shaping the obtained foamable resin composition into a sheet shape to obtain a foamable sheet, an in-plane direction when the foamable sheet is heated and foamed on at least one side of the obtained foamable sheet The fourth step to form a foamable composite sheet by laminating sheet-like materials having a strength capable of suppressing foaming into the foam and the foamable composite sheet is heated to a temperature equal to or higher than the decomposition temperature of the pyrolyzable chemical foaming agent and foamed. In the method for producing a polyolefin resin foam comprising the fifth step, between the third step and the fourth step, the foamable sheet obtained in the third step is thermally decomposed above the melting point of the modified resin between the flat plates. Type chemical foaming agent Process for producing a polyolefin resin foam, which comprises adding the step of heating annealing at a temperature below the temperature. A first step of modifying a polyolefin resin by reacting a polyolefin resin with a modifying monomer, a second step of adding a pyrolytic chemical foaming agent to the resulting modified resin and kneading to obtain a foamable resin composition A third step of shaping the obtained foamable resin composition into a sheet shape to obtain a foamable sheet, an in-plane direction when the foamable sheet is heated and foamed on at least one side of the obtained foamable sheet The fourth step to form a foamable composite sheet by laminating sheet-like materials having a strength capable of suppressing foaming into the foam and the foamable composite sheet is heated to a temperature equal to or higher than the decomposition temperature of the pyrolyzable chemical foaming agent and foamed. In the method for producing a polyolefin resin foam consisting of the fifth step, between the fourth step and the fifth step, the obtained foamable composite sheet has a thermal decomposition-type chemical foaming that is equal to or higher than the melting point of the modified resin between the flat plates. Decomposition temperature not yet Process for producing a polyolefin resin foam, which comprises adding the step of heating annealing at a temperature.   The modifying monomer is at least one compound selected from the group consisting of dioxime compounds, bismaleimide compounds, divinyl compounds, allyl polyfunctional monomers, (meth) acrylic polyfunctional monomers, and quinone compounds. 3. A method for producing a polyolefin resin foam according to 2.

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