JP3943003B2

JP3943003B2 - Manufacturing method of multi-layer coated metal curved pipe

Info

Publication number: JP3943003B2
Application number: JP2002297615A
Authority: JP
Inventors: 厚生平山; 良治小林; 千浩検見崎; 易之谷口
Original assignee: Dai Ichi High Frequency Co Ltd
Current assignee: Dai Ichi High Frequency Co Ltd
Priority date: 2002-10-10
Filing date: 2002-10-10
Publication date: 2007-07-11
Anticipated expiration: 2022-10-10
Also published as: JP2004130669A

Description

【０００１】
【発明の属する技術分野】
本発明は、外周面にポリオレフィン樹脂被覆を形成した金属曲管の製造方法に関する。
【０００２】
【従来の技術】
【特許文献１】
特開昭５９−６２３７３号公報
【非特許文献１】
雑誌「防錆管理」 '８３−１０号第２０〜２７行
「ポリエチレン被覆重防食鋼管杭」
従来より、海域で使用する鋼構造物に用いる鋼管、あるいは、寒冷地などの過酷な環境下に敷設するパイプラインに用いる鋼管として、外周面にポリエチレン樹脂などのポリオレフィン樹脂を被覆した樹脂被覆鋼管が使用されている。これらのポリオレフィン樹脂被覆鋼管には、ポリオレフィン樹脂の単層被覆を施したものと、鋼管表面にエポキシ樹脂などのプライマーを塗布し、その上に変性ポリオレフィン等の熱融接着剤を介して防食用の非極性ポリオレフィンを接着した３層構造の被覆を施したものがあり、後者が被覆の傷口起点剥離耐久性に優れているので、推奨されている。この傷口起点剥離の代表的なものとして陰極剥離現象がある。これは、敷設管には被覆傷入リスク対策として傷部の管体腐食を防ぐための電気防食（陰極防食）が適用されるが、これによって生じる卑電位が、露呈している被覆・管体界面（被覆端面）に作用して、傷口を起点とする接着の喪失が進行して行くという現象である。この陰極剥離に対する耐久性は、電気防食の適用されていないケースでの傷口起点剥離耐久性の指標ともなる。
【０００３】
上記の非特許文献１には、鋼管に対して３層構造の樹脂被覆を施す方法が記載されている。この非特許文献１に記載の方法は、鋼管を予熱し、その鋼管にプライマーを塗布した後、その鋼管を長手方向に移動させながら、微粉末状態の接着剤を静電塗装法によって塗布し、その後、その上に押出機から丸ダイ或いはＴダイを介して溶融ポリオレフィン樹脂を押し出して被覆し、冷却するというものである。また、上記の特許文献１にも、鋼管或いは鋼板等の金属表面へ３層被覆を施す方法が記載されている。すなわち、この特許文献１には、金属表面にプライマーを塗布した後、その上に、変性ポリオレフィンと未変性ポリオレフィンの共押出シートを押出ラミネートする方法、金属表面にプライマーを塗布した後、その上に、変性ポリオレフィンと未変性ポリオレフィンの積層シートを乗せ、加熱ロールまたは加熱プレスを用いて圧着させる方法、金属表面にプライマーを塗布した後、その上に、変性ポリオレフィンを粉末塗装し、更にその上に未変性ポリオレフィンを粉末塗装する方法などが記載されている。
【０００４】
【発明が解決しようとする課題】
ところで、パイプラインには曲げ部分があり、その部分には鋼製の金属曲管が使用されている。従って、この金属曲管にも外周面に３層のポリオレフィン樹脂被覆を施すことが望まれる。しかしながら、金属曲管の外周面は、直管や平板に比べて形状が複雑であるため、上記したような、ポリオレフィン樹脂を押出ラミネートする方法、或いは、ポリオレフィンシートを加熱ロールまたは加熱プレスを用いて圧着させる方法等を採用することができず、現在のところ、適切な被覆方法が開発されていない。なお、粉末塗装を用いて３層被覆を施すことは理論的には可能であるが、実際には実用化がきわめて困難である。すなわち、ポリオレフィン樹脂の粉末塗装には、金属曲管を３００°Ｃ前後に加熱することが望ましいが、エポキシ樹脂プライマーの耐熱性はせいぜい２００°Ｃ程度であるため、金属曲管に予めエポキシプライマーを塗布し、その金属曲管をポリオレフィン樹脂の粉末塗装に必要な温度（３００°Ｃ前後）に炉加熱することはできない。そのため、金属曲管を２００°Ｃ程度に加熱しておき、その後、エポキシプライマーを塗布し、それに続いて、接着剤の粉末塗装及びポリオレフィン樹脂の粉末塗装を行うという工程を採らざるを得ないが、この方法では、エポキシプライマーを敏速に塗布しないと、硬化が進んでしまって変性ポリオレフィン等の接着剤に対する被接着性を十分に確保できず、また、金属曲管の加熱温度が２００°Ｃ程度と低いので、ポリオレフィン樹脂の塗布膜厚を十分に確保できないといった問題があり、実用化が容易でない。そこで、従来は、ポリオレフィン樹脂のみを粉末塗装し、単層の樹脂被覆を施しているが、単層のポリオレフィン樹脂被覆では、３層被覆に比べて傷口起点剥離耐久性が低い。また、直管に適用している押出しライニングでは高密度ポリエチレンを使用できるが、粉末塗装では低密度又は中密度ポリエチレンしか使用できず、このため硬さに劣るといった問題もあった。
【０００５】
本発明はかかる問題点に鑑みてなされたもので、金属曲管の外周面に、少なくともエポキシ樹脂のプライマー層と熱融接着剤の薄膜層とポリオレフィンの厚膜層とを備えた複層被覆を施した構成の複層樹脂被覆金属曲管を製造する方法を提供することを課題とする。
【０００６】
【課題を解決するための手段】
本願における第一の解決手段は、金属曲管の外周面に全長に亘って、少なくともエポキシ樹脂プライマー層、熱融接着剤の薄膜層及びポリオレフィンの厚膜層の３層を備えた複層被覆を施すために、金属曲管の外周面に全長に亘って、まず、反応硬化性エポキシ樹脂の、ゲル化率が３０〜９０％の不完全硬化定着層を形成し、次いで、この定着層のゲル化率を９０％以下に保っている間に該定着層の上に、熱融接着剤の薄膜層及びポリオレフィンの厚膜層を接触した状態に配置して該定着層を有する前記金属曲管の外周面に接触して配置された仮組み複層被覆を形成し、その後、この被覆の下の金属曲管を誘導加熱することにより、該金属曲管からの伝熱で前記不完全硬化定着層の完全硬化と、前記熱融接着剤薄膜層の溶融による、該薄膜層の前記不完全硬化状態で供されているエポキシ樹脂プライマー層への接着を含む層間接合とを同時進行させて、前記仮組み複層被覆を、一体化複層被覆に完成させるという構成としたものである。ここで形成する仮組み複層被覆は、前記した定着層、薄膜層及び厚膜層が、金属曲管からの伝熱によって必要な温度に加熱されるよう、互いに接触した状態に維持されたものであればよく、定着層と薄膜層の間、及び／又は、薄膜層と厚膜層の間は、非融着状態であってもよい。このように本発明では、金属曲管の外周面に反応硬化性エポキシ樹脂の不完全硬化定着層を形成し、次いで、この定着層の上に、熱融接着剤の薄膜層及びポリオレフィンの厚膜層を接触した状態に配置した仮組み複層被覆を形成する方法を採用したことで、困難な作業を要することなく、仮組み複層被覆を形成することができ、しかも、ポリオレフィン厚膜層を所望厚さにすることができると共に高密度ポリエチレン等の所望材料も使用することができる。そして、その後、複層被覆の下の金属曲管を誘導加熱して、該金属曲管からの伝熱で前記不完全硬化定着層の完全硬化と前記熱融接着剤薄膜層の溶融による層間接合とを同時進行させて、前記仮組み複層被覆を一体化複層被覆に完成させる構成としたことで、ポリオレフィン厚膜層を金属曲管の外周面に全長に亘って強固に接合することができ、耐久性に優れた複層樹脂被覆金属曲管を製造できる。
【０００７】
本願における第二の解決手段は、金属曲管の外周面に全長に亘って複層被覆を施すために、金属曲管の外周面に全長に亘って、まず、反応硬化性エポキシ樹脂の、ゲル化率が３０〜９０％の不完全硬化定着層を形成し、次いで、この定着層のゲル化率を９０％以下に保っている間に該定着層の上に、熱融接着剤の薄膜層及び熱収縮性のポリオレフィンの厚膜層を配置して該定着層を有する前記金属曲管の外周面に接触して配置された仮組み複層被覆を形成し、その後、外面側からポリオレフィンの厚膜層を加熱して収縮させ、且つこの被覆の下の金属曲管を誘導加熱することにより、該金属曲管からの伝熱で前記不完全硬化定着層の完全硬化と、前記熱融接着剤薄膜層の溶融による、該薄膜層の前記不完全硬化状態で供されているエポキシ樹脂プライマー層への接着を含む層間接合とを同時進行させて、前記仮組み複層被覆を一体化複層被覆に完成させるという構成としたものである。このように、この解決手段では仮組み複層被覆に熱収縮性のポリオレフィンの厚膜層を用いたことで、ポリオレフィンの厚膜層を最初からその下の層に接触した状態に配置する必要がなくなり、仮組み複層被覆の形成が一層容易となる。そして、仮組み複層被覆を形成した後、外面側からポリオレフィンの厚膜層を加熱して収縮させ、且つこの被覆の下の金属曲管を誘導加熱する構成としたことで、ポリオレフィンの厚膜層を収縮させてその下の熱融接着剤の薄膜層に接触させることができると共に金属曲管からの伝熱で前記不完全硬化定着層の完全硬化と前記熱融接着剤の溶融による層間接合とを同時進行させて、前記仮組み複層被覆を一体化複層被覆に完成させることができ、耐久性に優れた複層樹脂被覆金属曲管を製造できる。
【０００８】
本願における第三の解決手段は、金属曲管の外周面に全長に亘って複層被覆を施すために、金属曲管の外周面に全長に亘って、まず、反応硬化性エポキシ樹脂の、ゲル化率が３０〜９０％の不完全硬化定着層を形成し、次いで、この定着層のゲル化率を９０％以下に保っている間に該定着層の上に、熱融接着剤の薄膜層及びポリオレフィンの多孔質構造の厚膜層を配置して該定着層を有する前記金属曲管の外周面に接触して配置された仮組み複層被覆を形成し、その後、この被覆の下の金属曲管を誘導加熱することにより、該金属曲管からの伝熱で前記不完全硬化定着層の完全硬化と、前記熱融接着剤薄膜層の溶融による、該薄膜層の前記不完全硬化状態で供されているエポキシ樹脂プライマー層への接着を含む層間接合と、前記厚膜層の溶融緻密化を同時進行させて、前記仮組み複層被覆を一体化複層被覆に完成させるという構成としたものである。このように、この解決手段では仮組み複層被覆にポリオレフィンの多孔質構造の厚膜層を用いたことで、その厚膜層の形成が容易となる。すなわち、その厚膜層の形成には、ポリオレフィンの多孔質構造のシートを用いることができ、そのシートは適度な柔軟性を備えているため、金属曲管の外周面に押し当てて配置することで、容易に金属曲管の外周面にフィットさせることができ、厚膜層を容易に形成できる。そして、仮組み複層被覆を形成した後、この被覆の下の金属曲管を誘導加熱することで、該金属曲管からの伝熱で前記不完全硬化定着層の完全硬化と前記熱融接着剤の溶融による層間接合と前記厚膜層の溶融緻密化を同時進行させて、前記仮組み複層被覆を一体化複層被覆に完成させることができ、耐久性に優れた複層樹脂被覆金属曲管を製造できる。
【０００９】
【発明の実施の形態】
本発明に使用する被覆対象の金属曲管は、限定されるものではないが、多くの場合、パイプラインやプラント配管に使用する鋼管である。金属曲管の形状は湾曲した部分を備えたものであれば任意であり、代表例として、図１（ａ）に示すように、全体が一定半径Ｒの金属曲管１、及び図１（ｂ）に示すように、一定半径Ｒの曲管部１ａの両端に直管部１ｂ，１ｂを備えた金属曲管１Ａを挙げることができる。金属曲管の直径Ｄ、曲げ半径Ｒ、曲げ角度θ、直管部長さＬ等も限定されるものではないが、代表例として、直径Ｄが４００〜１２００ｍｍ、曲げ半径Ｒが３Ｄ〜８Ｄ、曲げ角度θが１０〜９０°、直管部長さＬが１Ｄ〜３Ｄを挙げることができる。
【００１０】
以下、金属曲管１を例にとって、本発明を適用して複層樹脂被覆を施す方法を説明する。図２（ａ）〜（ｄ）は金属曲管１の表面に対する被覆の手順の一例を示す概略断面図である。まず、金属曲管１の外周面に前処理を施し、被覆に適した状態に調整する。例えば、金属曲管１の表面の水分を除去し、ショットブラストによりスケールや錆びを除去する。また、必要に応じ、クロメート処理等の表面処理を施してもよい。
【００１１】
次に、金属曲管１の外周面に、反応硬化性エポキシ樹脂（プライマー）を一様に塗布し、半硬化させて反応硬化性エポキシ樹脂の不完全硬化定着層２を形成する。不完全硬化定着層２の厚さは、５０〜５００μｍ程度が好ましく、更には、１００〜３００μｍが一層好ましい。ここで使用する反応硬化性エポキシ樹脂は、金属面の防食のために従来より用いられているものを適宜使用できる。その反応硬化性エポキシ樹脂の形態は、１液型あるいは２液型の液状樹脂でもよいし、粉末形態としたものでもよいが、塗布の容易さからは２液型の液状樹脂を用いることが好ましい。反応硬化性エポキシ樹脂の塗布方法は、液状樹脂を用いる場合には、スプレー、刷毛を用いる方法とすることができ、また、粉末形態のものを用いる場合には、静電塗装が好ましい。塗布した反応硬化性エポキシ樹脂を半硬化させるには、塗布前に金属曲管１をエポキシ樹脂の半硬化に適した温度に加熱しておく方法、塗布後に加熱する方法のいずれを採用してもよいが、塗布前に金属曲管１を加熱しておく方法を採用することが、反応硬化性エポキシ樹脂の半硬化作業を敏速に行うことができるので好ましい。
【００１２】
形成した不完全硬化定着層２におけるエポキシ樹脂の硬化の程度は、少なくとも、形成した不完全硬化定着層の上に、熱融接着剤の薄膜層及びポリオレフィンの厚膜層を形成する作業を支障なく行うことができるように（例えば、作業時に、定着層が剥がれたり、流れ落ちたりすることがないように）、適度に乾燥し且つ金属曲管の外周面に完全ではない接着力を以て付着した状態を確保できるように定めるものであり、具体的には、反応硬化性エポキシ樹脂の組成にもよるが、おおよその目安としては、ゲル化率が３０％程度以上とするのが好ましい。また、あまり硬化が進んでしまうと、後工程で、その上に熱融接着剤の薄膜層及びポリオレフィンの厚膜層を密着配置し、加熱溶融して接合した際に十分な接合強度を確保できなくなるので、あまり硬化が進まない状態とする。具体的には、反応硬化性エポキシ樹脂の組成にもよるが、おおよその目安としては、ゲル化率９０％程度以下とするのが好ましい。なお、塗布した反応硬化性エポキシ樹脂を半硬化させ、エポキシ樹脂の不完全硬化定着層２を形成した後は、金属曲管を強制冷却してエポキシ樹脂の硬化の進行を止めてもよいし、金属曲管を強制冷却せず、単に放冷しておき、エポキシ樹脂の硬化がゆるやかに進行するままとしておいてもよい。後者の場合には、後工程で、不完全硬化定着層２の上に熱融接着剤の薄膜層及びポリオレフィンの厚膜層を密着配置し、加熱溶融を開始する時点においても、定着層２のエポキシ樹脂が、例えば、ゲル化率が９０％程度以下の不完全硬化の状態に保持されるようにしておけばよい。
【００１３】
次に、反応硬化性エポキシ樹脂の不完全硬化定着層２の上に、熱融接着剤の薄膜層３及びポリオレフィンの厚膜層４を接触した状態に配置した仮組み複層被覆５を形成する。この仮組み複層被覆５は、定着層２、薄膜層３及び厚膜層４が、金属曲管１からの伝熱によって必要な温度に加熱されるよう、互いに接触した状態に維持されたものであればよく、定着層２と薄膜層３の間、及び／又は、薄膜層３と厚膜層４の間は、単に接触させただけの非融着状態であってもよいし、適度に融着した状態でもよい。なお、定着層２、薄膜層３及び厚膜層４の各層間の接触状態は、伝熱効率を高め且つ各層間の融着の際の気泡の抱き込みを少なくするため、なるべく密とする（各層間の接触圧力を大きくする）ことが好ましい。
仮組み複層被覆５に用いる熱融接着剤は、エポキシ樹脂の定着層とポリオレフィンの厚膜層のいずれにも良好に接合可能な特性のものであり、主として、マレイン酸変性などの各種の変性ポリオレフィンが使用されるが、これに限らず、他の材料、例えば、ＥＶＡ，ＥＡＡ，ＥＭＡＡ等を使用してもよい。熱融接着剤の薄膜層３の厚さは１００〜３００μｍ程度でよい。ポリオレフィンの厚膜層４は、耐食性、耐候性、耐衝撃性などの所望の保護特性を備えたものであり、具体的には、高密度ポリエチレン、中密度ポリエチレン、低密度ポリエチレン、ポリプロピレン、ポリプロピレンとポリエチレンの共重合体、ポリブテン等を用いることができる。また、その厚さも所望の保護特性に応じて定めるものであり、具体的には２〜５ｍｍ程度に選定される。
【００１４】
この仮組み複層被覆５を形成するには、図２に示すように、まず、熱融接着剤の薄膜層３を形成し、その上にポリオレフィンの厚膜層４を形成する方法、熱融接着剤の薄膜層３とポリオレフィンの厚膜層４を同時に形成する方法のいずれを採用してもよい。また、熱融接着剤の薄膜層３の形成、ポリオレフィンの厚膜層４を形成には、種々の方法を採り得る。以下、その代表的なものを説明する。
【００１５】
熱融接着剤の薄膜層３を金属曲管外周面のエポキシ樹脂不完全硬化定着層２の上に形成する一つの方法は、薄膜の熱融接着剤のテープを金属曲管に包帯巻きする方法である。すなわち、図３に示すように、金属曲管１の外周面に薄膜の熱融接着剤のテープ７を、その側縁が重なるように巻き付けてゆくことで、熱融接着剤の薄膜層３を形成することができる。この際、テープ７は金属曲管１の外周面（厳密には定着層２の上）に密に接するように巻き付けることが、後工程で加熱、融着させる際の気泡の抱き込みを小さくする上から好ましく、このため、テープ７に適度な張力を付与した状態で巻き付けることが好ましい。また、テープ７を溶融温度を越えない範囲で適当に加熱して膨張させ、その状態で金属曲管に巻付け、その後の放冷、或いは強制的な冷却によって収縮させ、金属曲管に密着させる方法を採っても良い。使用するテープ７の厚さは、１重に巻き付けることで所望厚さの薄膜層３を形成できるように、薄膜層３の厚さに等しいものとしてもよいし、２重，３重に重ね巻きすることで所望厚さの薄膜層３を形成できるように、薄いものとしてもよい。
【００１６】
熱融接着剤の薄膜層３を金属曲管外周面のエポキシ樹脂不完全硬化定着層２の上に形成する他の方法は、熱融接着剤の溶射によるものである。この方法では、溶射によって熱融接着剤をエポキシ樹脂不完全硬化定着層の上に不完全な形態ではあるが融着し、熱融接着剤の薄膜層３を形成できる。
【００１７】
ポリオレフィンの厚膜層４を金属曲管外周面の熱融接着剤の薄膜層３の上に形成する一つの方法は、厚膜のポリオレフィンのテープを、前記金属曲管に包帯巻きする方法である。すなわち、図４に示すように、金属曲管１外周面の薄膜層３（なお、図面ではテープ７を包帯巻きして形成したものを示している）の上に厚膜のポリオレフィンのテープ９を、その側縁が重なるように巻き付けてゆくことで、ポリオレフィンの厚膜層４を形成することができる。この際にも、テープ９は金属曲管１の外周面（厳密には薄肉層３上）に密に接触するように巻き付けることが、後工程で加熱、融着させる際の気泡の抱き込みを小さくする上から好ましく、このため、テープ９に適度な張力を付与した状態で巻き付けることが好ましい。テープ９に付与する張力としては、テープ９に１〜５％の弾性伸び歪が生じる張力とすることが好ましい。また、テープ９の巻付けの際に、そのテープ９を溶融温度を越えない範囲で加熱し、柔らかくして巻き付けることが、巻付け作業を容易とできるので好ましい。テープ９を加熱して巻き付ける際には、テープ９に付与する張力は小さくて良い。すなわち、テープ９を加熱して巻き付けた場合には、その後の放冷、或いは強制的な冷却によってテープ９が収縮し、金属曲管に密着するので、巻付け時のテープ９の張力は小さくてよい。使用するテープ９の厚さは、１重に巻き付けることで所望厚さの厚膜層４を形成できるように、厚膜層４の厚さに等しいものとする。
【００１８】
図５（ａ）に拡大して示すように、テープ９を包帯巻きすると、テープ９とテープ９の側縁が重なった状態となる。この重なった部分の接触面１０は、非接着の状態でもよいが、必要に応じ、テープ９の外面側から遠赤外線ヒータ、バーナー、ローラー鏝等で加熱して融着しておいてもよい。厚膜層４の形成に用いるテープ９は、全幅に亘って一定厚さのものとするが、場合によっては、図５に示すテープ９Ａのように、側縁部分の厚さを、側縁に向かうにつれて徐々に薄くなるようにしたものを用いても良い。このテープ９Ａを用いると、テープ９Ａの重なり部分の厚さが小さくなり、接触面１０Ａを、外側から加熱して融着させる際、あるいは、金属曲管表面からの伝熱によって融着させる際の加熱時間を短縮できる利点が得られる。
【００１９】
ポリオレフィンの厚膜層４を金属曲管外周面の熱融接着剤の薄膜層３の上に形成する他の方法は、ポリオレフィンの溶射によるものである。この方法では、溶射によってポリオレフィンが熱融接着剤の薄膜層３の上に不完全な形態ではあるが融着し、密着したポリオレフィンの厚膜層４を形成できる。
【００２０】
前記ポリオレフィンの厚膜層を金属曲管外周面の熱融接着剤の薄膜層の上に形成する更に他の方法は、予め、金属曲管の外周面上に定着層２及び熱融接着剤の薄膜層３を介して密に嵌合可能な形状のポリオレフィン製の複数の短管を用いる方法である。すなわち、あらかじめ図６に示す短管１２を複数個作成しておき、これらを金属曲管１に次々と嵌合していって厚膜層４を形成する方法である。ここで使用する短管１２は、金属曲管１の外周面上に定着層及び熱融接着剤の薄膜層３を介して密に嵌合可能なよう、その内径ｄを、金属曲管１の外周面上に配置している熱融接着剤の薄膜層３の外径Ｄ₂（テープ７を包帯巻きして薄膜層３を形成した場合には、テープ７の重なりの無い部分の外径）よりも若干小さく、例えば、１〜５％程度小さくなるように、定めている。また、短管１２の肉厚は、形成すべき厚膜層４に要求される肉厚に等しく選定されている。短管１２の形状は、金属曲管１の湾曲に適合するよう湾曲した形状としてもよいし、単に直管状としてもよい。直管状の短管１２を用いる場合には、短管１２の長さを短く選定することにより、湾曲した金属曲管１に支障無く嵌合させて取り付けることができ、また、図１（ｂ）に示す直管部付の金属曲管１Ａに対しても支障なく嵌合させて取り付けることができる。直管状の短管１２は、図７に示すポリオレフィン製の直管１３を、交互に傾斜した切断線１４に沿って切断することで製造でき、低コストで製造できる。なお、湾曲した短管を用いる場合には、短管を長くしても、全体が一定の半径で湾曲している金属曲管１に対しては支障なく取り付けることができるが、一方、製造コストは高くなる。そこで、短管の取付作業性や製造コスト等を考慮して短管長さを選定すればよい。また、湾曲した短管を、直管部付の金属曲管１Ａに対して用いる場合には、あまり長くすると、直管部を通り抜けることが困難となるので、短めに設定することが望ましい。
【００２１】
図６において、短管１２を金属曲管１に嵌合させるには、短管１２を一時的に拡径させた状態で遊嵌し、その後、元の径へ復元させる操作を行う。ここで、短管１２の一時的な拡径は、該短管１２を溶融温度未満の温度に加熱することにより、容易に行うことができ、また、遊嵌後、冷却することで元の径へ復元させることができる。なお、短管１２の一時的な拡径は、加熱に限らず、機械的手段によって行っても良い。短管１２を金属曲管１に次々と嵌合させてゆくが、その際、先に嵌合した短管１２と後続の短管１２とは図８（ａ）に示すように、単に突き合わせ状態とし、その突き合わせ部分を樹脂１５によって溶接接合する。以上のようにして複数の短管１２を金属曲管１に次々と嵌合し、且つ隣接した短管同志の接合部を溶接接合することで、金属曲管１の外周面に、一体化したポリオレフィンの厚膜層４を形成できる。なお、短管１２を加熱して金属曲管１に嵌合する場合において、短管同志の溶接接合は短管１２が冷却される前に行っても良いし、冷却した後に行っても良い。
【００２２】
上記の実施形態では、隣接した短管同志を溶接接合しているが、この構造に限らず、図８（ｂ）に示すように、短管１２の後端と次の短管１２の先端とを嵌合させる構成としても良い。この場合、嵌合した短管１２、１２の接触面１６は、非接着の状態でもよいが、必要に応じ、短管１２の外面側から遠赤外線ヒータ、バーナー、ローラー鏝等で加熱して融着しておいてもよい。また、短管同志を嵌合させる場合、図８（ｃ）に示す短管１２Ａのように、嵌合させる領域の厚さを、端面に向かうにつれて徐々に薄くなるようにしたものを用いても良い。この短管１２Ａを用いると、短管同志の重なり部分の厚さが小さくなり、接触面１６Ａを、外側から加熱して融着させる際、あるいは、金属曲管表面からの伝熱によって融着させる際の加熱時間を短縮できる利点が得られる。
【００２３】
ポリオレフィンの厚膜層４を金属曲管外周面の熱融接着剤の薄膜層３の上に形成する更に他の方法は、予め、金属曲管の外周面上に定着層２及び熱融接着剤の薄膜層３を介して密に嵌合可能な形状のポリオレフィン製の曲管状成形体を用いる方法である。すなわち、予め、図９に示すポリオレフィン製の曲管状成形体１８を作成しておき、これを金属曲管１に嵌合する方法である。この曲管状成形体１８は、金属曲管１の外周面上に定着層及び熱融接着剤の薄膜層３を介して密に嵌合可能なよう、その内径ｄを、金属曲管１の外周面上に配置している熱融接着剤の薄膜層３の外径Ｄ₂（テープ７を包帯巻きして薄膜層３を形成した場合には、テープ７の重なりの無い部分の外径）よりも若干小さく、例えば、１〜５％程度小さくなるように、定めている。また、曲管状成形体１０の肉厚は、形成すべき厚膜層４に要求される肉厚に等しく選定されている。この曲管状成形体１８を金属曲管１に嵌合させるには、曲管状成形体１８を一時的に拡径させた状態で遊嵌し、その後、元の径へ復元させる操作を行う。ここで、曲管状成形体１８の一時的な拡径は、該曲管状成形体を溶融温度未満の温度に加熱することにより、容易に行うことができ、遊嵌後、冷却することで元の径へ復元させることができる。なお、曲管状成形体１８の一時的な拡径は、加熱に限らず、機械的手段によって行っても良い。以上のように、曲管状成形体１８を金属曲管１に嵌合させることで、金属曲管１の外周面にポリオレフィンの厚膜層を形成できる。
【００２４】
上記の実施形態では、曲管状成形体１８として、全長に亘って筒状に成形したものを用いている。しかしこの構造では、例えば、図１（ｂ）に示すように、直管部１ｂを有する金属曲管１Ａに対しては嵌合作業が困難となる場合がある。そこで、そのような場合には、嵌合作業を容易にするため、曲管状成形体の管周の内径側に、管周方向に延びる複数のスリットを形成するとか、曲管状成形体に、長手方向に延びるスリットを形成しておいてもよい。このようなスリットを形成しておくと、曲管状成形体を、加熱等によって一時的に拡径させ、その状態で金属曲管１Ａに遊嵌する際に、そのスリットを利用して曲管状成形体を変形させることができ、遊嵌作業を容易とすることができる。なお、曲管状成形体を金属曲管の所定位置に遊嵌した後は、スリットを溶接接合して一体化しておけばよい。
【００２５】
図９に示す実施形態では、ポリオレフィンの厚膜層の形成のために全体が一体となった曲管状成形体１８を用いたが、この構造に限らず、これを長手方向に切断して複数のセグメントに分割した形態の成形体を用いても良い。図１０はその形態のポリオレフィン製の成形体１８Ａを示すものである。この成形体１０Ａは、図１（ｂ）に示す金属曲管１Ａの外周面上に定着層及び熱融接着剤の薄膜層を介して密に嵌合可能な形状のポリオレフィン製の曲管状成形体がその円周方向に２個の曲管状成形体セグメント１８Ａａ，１８Ａｂに分割された形態のものである。この成形体１８Ａを金属曲管に取り付けるには、先ず、加熱等によって一時的に拡径させ、その状態で金属曲管にかぶせ、隣接したセグメント１８Ａａ，１８Ａｂの端縁同志を突き合わせて溶接接合し、一体化する。その後、元の径への復元によって金属曲管外面に密に接触した状態となる。以上により、金属曲管の外周面にポリオレフィンの厚膜層を形成できる。
【００２６】
以上の実施形態は、ポリオレフィンの厚膜層４を金属曲管外面上に密に接触するように配置するために、テープを張力を付与した状態で巻き付けるとか、密着嵌合可能なサイズの短管，成形体等を用いているが、これに代えて、熱収縮性のポリオレフィン樹脂を使用することも可能である。その場合には、熱収縮性のポリオレフィンのテープをゆるく巻き付けるとか、金属曲管よりもかなり大径の短管、成形体等を取り付けて厚膜層を形成し、その後、その厚膜層を外面側から加熱することで、金属曲管外周面に密に接触させて配置することができる。
【００２７】
以上のようにして、図２（ｄ）に示すように、金属曲管１の外周面上に、エポキシ樹脂不完全硬化定着層２、熱融接着剤の薄膜層３及びポリオレフィンの厚膜層４を有する仮組み複層被覆５を形成した後は、この被覆の下の金属曲管１を誘導加熱することにより、該金属曲管１からの伝熱で前記不完全硬化定着層２の完全硬化と前記熱融接着剤の溶融による層間接合とを同時進行させて、前記仮組み複層被覆５を、一体化複層被覆に完成させる。このように、金属曲管の誘導加熱を利用したことで、ポリオレフィン厚膜層の外側から加熱して不完全硬化定着層の完全硬化と前記熱融接着剤の溶融を行う場合に比べて、はるかに敏速に且つ厚膜層を熱で損傷させることなく、不完全硬化定着層及び熱融接着剤の薄膜層の加熱を行うことができる。なお、必要に応じ、金属曲管の誘導加熱に並行して、ポリオレフィンの厚膜層の外側から、遠赤外線ヒータ、バーナー等で加熱してもよい。また、ポリオレフィンの厚膜層４を、図４，図５に示すようにポリオレフィンのテープ９，９Ａを部分的に重ね合わせて形成した場合、或いは図６，図８に示すようにポリオレフィンの短管１２，１２Ａを部分的に重ね合わせて形成した場合であって、且つ接触面１０，１０Ａ，１６，１６Ａを十分には融着していない場合には、加熱時間を長くしてこの接触面１０，１０Ａ，１６，１６Ａの融着も行う。また、加熱中に、融着がスムーズに進行するように外側からローラー等を用いて機械的な圧縮力を加えても良い。
【００２８】
金属曲管の誘導加熱は、金属曲管の全長に亘って同時に加熱する一発式で行っても良いし、金属曲管の長手方向の小区間を誘導加熱し、その加熱部位を長手方向に移動させてゆく連続的で行っても良い。金属曲管の誘導加熱を行うための誘導コイルは、金属曲管の外面側、内面側のいずれに配置してもよいが、作業性からは外面側に配置することが好ましい。図１１、図１２は移動式で金属曲管１を誘導加熱する１例を示すものである。外周面に仮組み複層被覆５を施した金属曲管１の外周側に誘導コイル２５を配し、その誘導コイル２５で、金属曲管１の対向した領域を誘導加熱しながら、誘導コイル２５を金属曲管１に沿って相対的に移動させてゆく。これにより、金属曲管１の表層部分が誘導加熱されて昇温し、その昇温部分からの伝熱によって不完全硬化定着層２、熱融接着剤の薄膜層３及びポリオレフィンの厚膜層４が加熱され、不完全硬化定着層２の完全硬化と熱融接着剤の溶融が同時に進行し、ポリオレフィンの厚膜層４が金属曲管１の外周面に強固に接着される。そして、この加熱部位が金属曲管１に沿って移動することで、熱融接着剤が溶融してゆく部分も移動し、その際、層間にあった空気が押し出されて行くこととなり、気泡の抱き込みのきわめて少ない被覆層が形成される。金属曲管１を誘導加熱する際、必要ならば、ポリオレフィンの厚膜層の外側から、遠赤外線ヒータ、バーナー等で加熱してもよい。外側からの加熱を併用することで、加熱時間を短縮でき、また、ポリオレフィンの厚膜層がテープの包帯巻きによって形成されていた場合などには、重なり合ったテープ同志の接触面の接着を一層確実とできる。また、前述のようにローラー等を用いて圧縮力を加えても良いし、あらかじめ外側に熱収縮性のラッピングテープ等を巻いておけば、均一に圧縮力がかけられる。
【００２９】
以上のようにして、金属曲管の外周面に、エポキシ樹脂、熱融接着剤の薄膜層及びポリオレフィンの厚膜層を一体化した複層被覆を形成し、複層樹脂被覆金属曲管を製造することができる。また、エポキシ樹脂の完全硬化と熱融接着剤の溶融とを同時に進行させているため、得られた複層樹脂被覆金属曲管では、ポリオレフィン厚膜層の金属曲管外周面に対する接合強度が大きくなっており、耐久性に優れた複層被覆を形成できる。
【００３０】
なお、上記実施形態はいずれも、仮組み複層被覆５の形成に際して、熱融接着剤の薄膜層３の形成とポリオレフィンの厚膜層４の形成とを別工程で行っているが、本発明はこれに限らず、熱融接着剤の薄膜層の形成と、ポリオレフィンの厚膜層の形成とを同時に行うことも可能である。以下、その場合の実施形態を説明する。
【００３１】
一つの実施形態では、図４に示す実施形態で用いたポリオレフィンテープ９の片面にあらかじめ、熱融接着剤の薄膜層を形成しておき、そのポリオレフィンテープを、前記薄膜層を内側にして、外周面にエポキシ樹脂不完全硬化定着層を形成した金属曲管に、図４に示す実施形態と同様にして、包帯巻きする。これにより、エポキシ樹脂不完全硬化定着層の上に熱融接着剤の薄膜層とポリオレフィンの厚膜層とを密に接触した状態に配置した構成の仮組み複層被覆を形成できる。
なお、ポリオレフィンテープ９に予め熱融接着剤の薄膜層を形成しておくと、図５に示すようにポリオレフィンテープ９を重ね合わせた部分において接触面１０に熱融接着剤の薄膜層が存在することとなり、重なったポリオレフィンテープ９，９同志を、ポリオレフィン同志を直接接合する場合に比べて低温で確実に接着できる利点が得られる。
【００３２】
他の実施形態では、図６に示す実施形態で用いた短管１２の内面にあらかじめ熱融接着剤の薄膜層を形成しておく。そして、その短管を外周面にエポキシ樹脂不完全硬化定着層を形成した金属曲管に、図６に示す実施形態と同様にして嵌合させてゆく。これにより、エポキシ樹脂不完全硬化定着層の上に熱融接着剤の薄膜層とポリオレフィンの厚膜層とを密に接触した状態に配置した構成の仮組み複層被覆を形成できる。
【００３３】
更に他の実施形態では、図９，図１０に示す実施形態で用いた成形体１８，１８Ａの内面にあらかじめ熱融接着剤の薄膜層を形成しておく。そして、その成形体を、外周面にエポキシ樹脂不完全硬化定着層を形成した金属曲管に、図９，図１０に示す実施形態と同様にして取り付ける。これにより、エポキシ樹脂不完全硬化定着層の上に熱融接着剤の薄膜層とポリオレフィンの厚膜層とを密に接触した状態に配置した構成の仮組み複層被覆を形成できる。
【００３４】
更に他の実施形態では、ポリオレフィンの厚膜層を熱収縮性のポリオレフィンによって形成する構成とし、且つその際用いるポリオレフィンのテープ、短管、成形体等の内面にあらかじめ熱融接着剤の薄膜層を形成しておく。そして、そのテープ、短管、成形体等を、外周面にエポキシ樹脂不完全硬化定着層を形成した金属曲管に取り付け、その後、加熱して収縮させることにより、エポキシ樹脂不完全硬化定着層の上に熱融接着剤の薄膜層とポリオレフィンの厚膜層とを密に接触した状態に配置した構成の仮組み複層被覆を形成できる。
【００３５】
なお、熱収縮性のポリオレフィンを用いる場合には、熱収縮性のポリオレフィンの厚膜層を形成した後、熱収縮させる操作と、不完全硬化定着層の完全硬化及び熱融接着剤の溶融のための金属曲管の誘導加熱とを同時に行っても良い。すなわち、金属曲管表面に形成した反応硬化性エポキシ樹脂の不完全硬化定着層の上に、熱融接着剤の薄膜層及び熱収縮性のポリオレフィンの厚膜層を配置した仮組み複層被覆を形成し、その後、外面側からポリオレフィンの厚膜層を加熱して収縮させ、且つこの被覆の下の金属曲管を誘導加熱することにより、該金属曲管からの伝熱で前記不完全硬化定着層の完全硬化と前記熱融接着剤の溶融による層間接合とを同時進行させて、前記仮組み複層被覆を一体化複層被覆に完成させることができる。
【００３６】
以上に説明した実施形態はいずれも、ポリオレフィンの厚膜層を、中実形態のポリオレフィンのテープ、短管、成形体等を用いて形成しており、従って、ポリオレフィンの厚膜層が中実形態となっているが、これに代えて、多孔質構造を用いることも可能である。すなわち、金属曲管表面に形成した反応硬化性エポキシ樹脂の不完全硬化定着層の上に、熱融接着剤の薄膜層及びポリオレフィンの多孔質構造の厚膜層を接触した状態に配置した仮組み複層被覆を形成し、その後、この被覆の下の金属曲管を誘導加熱することにより、該金属曲管からの伝熱で前記不完全硬化定着層の完全硬化と前記熱融接着剤の溶融による層間接合と前記厚膜層の溶融緻密化を同時進行させて、前記仮組み複層被覆を一体化複層被覆に完成させることができ、この方法によっても、金属曲管の外周面上に３層構造の複層被覆を施すことができる。
【００３７】
前記のポリオレフィンの多孔質構造の厚膜層を形成するには、上記した実施形態に用いているポリオレフィン製のテープ、短管、成形体等に代えて、多孔質構造のテープ、短管、成形体等を用いてもよいが、単に平坦な多孔質構造のシートを用いることが、製造コストが低く且つ取り扱いが容易であるので、推奨される。多孔質構造のテープ、短管、成形体、シート等としては、ポリオレフィンの粉体樹脂を、未溶融又は一部溶融した状態で所望の形状に成形したもの、例えば、特公平５−１９８９４号公報に記載のものを用いることができる。
【００３８】
多孔質構造のシートを用いて、金属曲管外周面に厚膜層を形成する具体的な方法としては、図１３（ａ），（ｂ）に示すように、金属曲管１の外周面に形成している熱融接着剤の薄膜層３の上に、適当なサイズのシート２７を次々と一部が重なる状態で配置して行く方法を挙げることができる。この際、多孔質構造のシート２７は或る程度の柔軟性を有しているので、容易に金属曲管１の外周面に倣った形状に変形させることができ、金属曲管１外周面の薄膜層３にフィットした状態に配置することができる。配置したシート２７を薄膜層３に接触した状態に維持するには、シート２７を適当な粘着剤を用いて貼り付ける方法、金属曲管１外周面上に配置したシート２７の外側に、適当なラッピングテープ、好ましくは熱収縮性のラッピングテープを巻き付ける方法などを挙げることができる。このようにして多数のシート２７を金属曲管１の外周面に配置して厚膜層４Ａを形成した後は、上記したように、金属曲管１を誘導加熱することにより、金属曲管１からの伝熱で不完全硬化定着層２の完全硬化と熱融接着剤の溶融による層間接合と厚膜層４Ａの溶融緻密化を同時進行させて、仮組み複層被覆を一体化複層被覆に完成させる。この際、多孔質構造のシート２７を完全に溶融させて緻密化するので、シート２７，２７の重なり合った部分も確実に溶融させて緻密化できると共に一体化できる。かくして、金属曲管１の外周面を確実に覆った被覆層を形成できる。なお、この場合にも、金属曲管１を誘導加熱する際に、並行して外面側から、遠赤外線ヒータ、バーナー等で加熱してもよいし、ローラー等を用いて圧縮力を加えても良い。また、あらかじめ外側に熱収縮性のラッピングテープを巻いていた場合には、そのラッピングテープの収縮によって均一に圧縮力がかけられる。
【００３９】
なお、上記した実施形態はいずれも、金属曲管外周面の樹脂被覆を施すべき領域全体を覆う仮組み複層被覆を形成した後、金属曲管を誘導加熱して仮組み複層被覆を一体化複層被覆に完成させているが、本発明はこの構成に限らず、金属曲管外周面の一部領域に仮組み複層被覆を形成し、その領域の金属曲管を誘導加熱して仮組み複層被覆を一体化複層被覆に完成させ、次いで、隣接した領域に仮組み複層被覆を形成し、その領域の金属曲管を誘導加熱して仮組み複層被覆を一体化複層被覆に完成させるというように、小領域ずつ逐次被覆を形成してゆく方法を採っても良い。
【００４０】
【実施例】
［実施例１］
図１（ａ）に示す金属曲管１を用意した。この金属曲管１の仕様は、外径Ｄ＝４０６．４ｍｍ（２４インチ）、曲げ半径Ｒ＝２０３２ｍｍ、曲げ角度θ＝９０°、材質＝ＡＰＩ５ＬＸ６５である。
この金属曲管１を、誘導加熱によって６０°Ｃに予熱し、その外周面に２液型のエポキシ樹脂（商品名「エポサーム」、大日本色材工業株式会社製）を刷毛により塗布し、９分間放置することにより、ゲル化率５０％程度に硬化した不完全硬化定着層が形成された。そこで、この上に、接着性ポリエチレンのテープ（厚さ１００μｍ、幅２００ｍｍ、商品名「アドマーＮＥ０９０」、三井化学株式会社製）をほぼハーフラップで包帯巻きして、厚さ２００μｍの薄膜層を形成した。
【００４１】
その後、その上に、高密度ポリエチレンのテープ（厚さ２．５ｍｍ、幅２００ｍｍ、商品名「ハイゼックス５０００Ｈ」、三井化学株式会社製）を、２％伸びを生じさせる張力を付与した状態で包帯巻きし、且つ外面側から遠赤外線加熱を行って、テープの重なり合った部分の融着及びテープの下地へのフィットを行った。
その後、図１１に示すように、加熱幅５０ｍｍの誘導コイル２５を金属曲管１の外周に配置し、金属曲管１の表層部分を誘導加熱しながら、移動速度５０ｍｍ／分で連続的に移動させ、金属曲管１の全長を誘導加熱した。この時、誘導加熱された金属曲管１の表面温度は、約２５０°Ｃに昇温していた。金属曲管１を誘導加熱した後、約３０分間放置し、金属曲管１からの伝熱により、不完全硬化定着層の完全硬化と熱融接着剤の溶融による層間接合とを同時進行させた。その後、外面側から冷却水を吹き付けて冷却し、溶融部分を硬化させた。以上により、完全に一体化した３層構造のポリエチレン被覆の金属曲管を得た。
【００４２】
得られた被覆について、ＡＳＴＭＧ１４規格に示された陰極剥離試験を行ったところ、２０°Ｃ×３０日で剥離径は３．５ｍｍであり、十分な傷口起点剥離耐久性を示していた。また、被覆の表面硬さは７８ＨＤＤ、接着力は２０Ｎ／ｃｍであり、十分な硬さ及び接着力を示していた。従って、傷口起点剥離耐久性などの長期耐久性に優れ、且つ耐衝撃性に優れたポリエチレン被覆が得られた。
【００４３】
［実施例２］
実施例１と同一仕様の金属曲管１を用意し、実施例１と同様にして、不完全硬化定着層及び接着性ポリエチレンの薄膜層を形成した。
その上に、予め作成したポリエチレン製の短管１２（図６参照）（内径４０３．０ｍｍ、肉厚３．０ｍｍ、中央部の長さ２００ｍｍ）を約１００°Ｃに加熱し、内径を約１０ｍｍ拡径させた状態で次々と遊嵌し、突き合わせ端部を溶接接合した後、冷却水を吹き付けて冷却し、金属曲管に密に嵌合させた。
【００４４】
その後、図１１に示すように、加熱幅５０ｍｍの誘導コイル２５を金属曲管１の外周に配置し、金属曲管１の表層部分を誘導加熱しながら、移動速度５０ｍｍ／分で連続的に移動させ、金属曲管１の全長を誘導加熱した。この時、誘導加熱された金属曲管１の表面温度は、約２５０°Ｃに昇温していた。金属曲管１を誘導加熱した後、約３０分間放置し、金属曲管１からの伝熱により、不完全硬化定着層の完全硬化と熱融接着剤の溶融による層間接合とを同時進行させた。その後、外面側から冷却水を吹き付けて冷却し、溶融部分を硬化させた。以上により、完全に一体化した３層構造のポリエチレン被覆の金属曲管を得た。
【００４５】
得られた被覆について、実施例１と同様にして、陰極剥離試験を行ったところ、２０°Ｃ×３０日で剥離径は３．２ｍｍであり、十分な傷口起点剥離耐久性を示していた。また、被覆の表面硬さは７８ＨＤＤ、接着力は１９Ｎ／ｃｍであり、十分な硬さ及び接着力を示していた。従って、傷口起点剥離耐久性などの長期耐久性に優れ、且つ耐衝撃性に優れたポリエチレン被覆が得られた。
【００４６】
［実施例３］
実施例１と同一仕様の金属曲管１を用意し、実施例１と同様にして、不完全硬化定着層を形成した。
その上に、熱融接着剤付ポリエチレンシュリンクテープ（ポリエチレン厚さ１．５ｍｍ、接着剤厚さ１．５ｍｍ、幅２００ｍｍ、商品名「ＷＰＣ１００Ｍ」、米国レイケム社製）を、ゆるくフィットする程度のテンションで包帯巻きし、その後、外面側から遠赤外線加熱を行って、テープの収縮及び重なり合った部分の融着を行った。
【００４７】
その後、図１１に示すように、加熱幅５０ｍｍの誘導コイル２５を金属曲管１の外周に配置し、金属曲管１の表層部分を誘導加熱しながら、移動速度５０ｍｍ／分で連続的に移動させ、金属曲管１の全長を誘導加熱した。この時、誘導加熱された金属曲管１の表面温度は、約２５０°Ｃに昇温していた。金属曲管１を誘導加熱した後、約３０分間放置し、金属曲管１からの伝熱により、不完全硬化定着層の完全硬化と熱融接着剤の溶融による層間接合とを同時進行させた。その後、外面側から冷却水を吹き付けて冷却し、溶融部分を硬化させた。以上により、完全に一体化した３層構造のポリエチレン被覆の金属曲管を得た。
【００４８】
得られた被覆について、実施例１と同様にして、陰極剥離試験を行ったところ、２０°Ｃ×３０日で剥離径は３．９ｍｍであり、十分な傷口起点剥離耐久性を示していた。また、被覆の表面硬さは６５ＨＤＤ、接着力は１５Ｎ／ｃｍであり、十分な硬さ及び接着力を示していた。従って、傷口起点剥離耐久性などの長期耐久性に優れ、且つ耐衝撃性に優れたポリエチレン被覆が得られた。
【００４９】
【発明の効果】
以上のように、本発明によれば、金属曲管の外周面にポリオレフィン厚膜層を反応硬化性エポキシ樹脂及び熱融接着剤を介して強固に接合した複層樹脂被覆を備えた複層樹脂被覆金属曲管を製造することができ、得られた複層樹脂被覆金属曲管は優れた耐久性を備えており、土中や海域などの過酷な環境下に設置されるパイプラインに好適に使用できるといった効果を有している。
【図面の簡単な説明】
【図１】（ａ），（ｂ）はそれぞれ本発明に使用する金属曲管の例を示す概略平面図
【図２】（ａ），（ｂ），（ｃ），（ｄ）は、金属曲管の外周面に仮組み複層被覆を形成する手順の１例を示す概略断面図
【図３】金属曲管外周面に熱融接着剤のテープを包帯巻きする状態を示す概略平面図
【図４】金属曲管外周面にポリオレフィンのテープを包帯巻きする状態を示す概略平面図
【図５】（ａ），（ｂ）はそれぞれ、金属曲管外周面に巻いたポリオレフィンテープの重なり部分を拡大して示す概略断面図
【図６】金属曲管外周面にポリオレフィンの短管を嵌合する状態を示す概略平面図
【図７】図６の実施形態に用いる短管を製造する工程を説明する概略断面図
【図８】（ａ），（ｂ），（ｃ）はそれぞれ、金属曲管外周面に嵌合した短管の接合部分を拡大して示す概略断面図
【図９】外周面に熱融接着剤の薄膜層を形成した金属曲管とそれに嵌合する曲管状成形体を示す概略平面図及び断面図
【図１０】（ａ）は成形体１８Ａのセグメント１８Ａａの概略平面図
（ｂ）は成形体１８Ａの概略正面図
【図１１】外周面に仮組み複層被覆を形成した金属曲管を誘導加熱する状態を示す概略平面図
【図１２】外周面に仮組み複層被覆を形成した金属曲管を誘導加熱する状態を示す概略断面図
【図１３】（ａ）金属曲管外周面にポリオレフィンの多孔質構造のシートを配置する状態を示す概略平面図
（ｂ）金属曲管外周面に配置したシート同志の重なり部分を拡大して示す概略断面図
【符号の説明】
１，１Ａ金属曲管
２エポキシ樹脂不完全硬化定着層
３熱融接着剤の薄膜層
４ポリオレフィンの厚膜層
５仮組み複層被覆
７熱融接着剤のテープ
９ポリオレフィンのテープ
１２ポリオレフィンの短管
１８ポリオレフィンの曲管状成形体
１８Ａポリオレフィンの成形体
１８Ａａ，１８Ａｂ曲管状成形体セグメント
２５誘導コイル
２７ポリオレフィンの多孔質構造のシート[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a bent metal pipe having a polyolefin resin coating formed on an outer peripheral surface thereof.
[0002]
[Prior art]
[Patent Document 1]
JP 59-62373 A
[Non-Patent Document 1]
Magazine "Rust Control"'83 -10 No. 20-27
"Polyethylene-coated heavy-duty-proof steel pipe pile"
Conventionally, as steel pipes used in steel structures used in the sea area, or steel pipes used in pipelines laid in harsh environments such as cold regions, resin-coated steel pipes whose outer peripheral surfaces are coated with a polyolefin resin such as polyethylene resin have been used. in use. These polyolefin resin-coated steel pipes are coated with a single layer of polyolefin resin, and a primer such as an epoxy resin is applied to the surface of the steel pipe, and a heat-resistant adhesive such as a modified polyolefin is applied thereon for anticorrosion. Some are coated with a three-layer structure to which a non-polar polyolefin is bonded, and the latter is recommended because it is excellent in the scratch starting point peeling durability of the coating. As a typical example of the wound origin peeling, there is a cathode peeling phenomenon. This is because the laid pipe is applied with anticorrosion (cathodic protection) to prevent tube corrosion of the wound as a countermeasure against the risk of damage to the coating, but the underlying potential caused by this is exposed This is a phenomenon that acts on the interface (coating end face) and the loss of adhesion starts from the wound. This durability against cathodic peeling also serves as an index of the scratch starting point peeling durability in a case where cathodic protection is not applied.
[0003]
Non-Patent Document 1 describes a method of applying a three-layer resin coating to a steel pipe. The method described in Non-Patent Document 1 preheats a steel pipe, applies a primer to the steel pipe, and then applies an adhesive in a fine powder state by electrostatic coating while moving the steel pipe in the longitudinal direction. Thereafter, a molten polyolefin resin is extruded from the extruder through a round die or a T die, coated, and cooled. Also, Patent Document 1 described above describes a method of applying a three-layer coating to a metal surface such as a steel pipe or a steel plate. That is, in Patent Document 1, after a primer is applied to a metal surface, a coextruded sheet of a modified polyolefin and an unmodified polyolefin is extrusion laminated thereon, and after the primer is applied to the metal surface, A method in which a laminated sheet of a modified polyolefin and an unmodified polyolefin is placed and pressure-bonded by using a heating roll or a heating press. After a primer is applied to a metal surface, the modified polyolefin is powder-coated thereon, and further, an unmodified polyolefin is coated thereon. A method for powder-coating modified polyolefin is described.
[0004]
[Problems to be solved by the invention]
By the way, the pipeline has a bent part, and a metal bent pipe made of steel is used for the part. Therefore, it is desired that this metal curved pipe is also provided with a three-layer polyolefin resin coating on the outer peripheral surface. However, since the shape of the outer peripheral surface of the metal bent pipe is more complicated than that of a straight pipe or a flat plate, the method for extruding and laminating a polyolefin resin as described above, or using a heating roll or a heating press for a polyolefin sheet. The method of crimping cannot be adopted, and an appropriate coating method has not been developed at present. Although it is theoretically possible to apply a three-layer coating using powder coating, practical application is extremely difficult. That is, for polyolefin resin powder coating, it is desirable to heat the metal bent tube to around 300 ° C. However, since the heat resistance of the epoxy resin primer is at most about 200 ° C, an epoxy primer is previously applied to the metal bent tube. Once applied, the metal bend cannot be furnace heated to the temperature required for powder coating of polyolefin resin (around 300 ° C.). For this reason, the metal bent tube is heated to about 200 ° C., and then an epoxy primer is applied, followed by powder coating with an adhesive and powder coating with a polyolefin resin. In this method, unless the epoxy primer is applied promptly, curing proceeds and sufficient adhesion to an adhesive such as modified polyolefin cannot be secured, and the heating temperature of the metal bent tube is about 200 ° C. Therefore, there is a problem that a sufficient coating thickness of the polyolefin resin cannot be secured, and it is not easy to put it to practical use. Therefore, conventionally, only a polyolefin resin is powder-coated and a single-layer resin coating is applied. However, a single-layer polyolefin resin coating has a lower scratch origin separation durability than a three-layer coating. In addition, high-density polyethylene can be used in extrusion lining applied to straight pipes, but only low-density or medium-density polyethylene can be used in powder coating, which causes a problem of poor hardness.
[0005]
The present invention has been made in view of such problems, and a multilayer coating comprising at least an epoxy resin primer layer, a heat-melt adhesive thin film layer, and a polyolefin thick film layer is provided on the outer peripheral surface of the metal bent pipe. It is an object of the present invention to provide a method for producing a multi-layer resin-coated metal bent tube having a given configuration.
[0006]
[Means for Solving the Problems]
The first solution in the present application is the outer peripheral surface of the metal bent pipe. Over the whole length In order to apply a multi-layer coating comprising at least three layers of an epoxy resin primer layer, a heat-melt adhesive thin film layer and a polyolefin thick film layer, Over the whole length First of all, reaction curable epoxy resin The gelation rate is 30-90% Forming an incompletely cured fixing layer and then fixing layer The fixing layer while maintaining the gelation rate of 90% or less A thin film layer of heat-melt adhesive and a thick film layer of polyolefin in contact with each other. In contact with the outer peripheral surface of the metal bent pipe having the fixing layer. Then, a temporary assembly multilayer coating is formed, and then the metal curved tube under the coating is induction-heated, whereby the incompletely cured fixing layer is completely cured by heat transfer from the metal curved tube, and the thermal fusion is performed. adhesive Thin film layer By melting , Including adhesion of the thin film layer to the epoxy resin primer layer provided in the incompletely cured state The temporary bonding multilayer coating is completed into an integrated multilayer coating by simultaneously proceeding with interlayer bonding. The temporarily assembled multilayer coating formed here is such that the fixing layer, the thin film layer, and the thick film layer are maintained in contact with each other so as to be heated to a necessary temperature by heat transfer from the metal bent tube. The fixing layer and the thin film layer and / or the thin film layer and the thick film layer may be in a non-fused state. As described above, in the present invention, an incompletely cured fixing layer of a reaction curable epoxy resin is formed on the outer peripheral surface of a metal bent tube, and then a thin film layer of a heat-melt adhesive and a thick film of polyolefin are formed on the fixing layer. By adopting a method of forming a temporarily assembled multilayer coating in which the layers are in contact with each other, it is possible to form a temporarily assembled multilayer coating without requiring a difficult operation, and the polyolefin thick film layer The desired thickness can be achieved and a desired material such as high density polyethylene can also be used. And after that, the metal bent tube under the multi-layer coating is induction-heated, and heat transfer from the metal bent tube completely cures the incompletely cured fixing layer and the heat-melt adhesive. Thin film layer The multilayer thick film layer is formed on the outer peripheral surface of the metal bent pipe by simultaneously proceeding with the interlayer bonding by melting of the metal layer and completing the temporary assembly multilayer coating into an integral multilayer coating. Over the whole length A multi-layer resin-coated metal bent tube that can be firmly bonded and has excellent durability can be manufactured.
[0007]
The second solution in the present application is the outer peripheral surface of the metal bent pipe. Over the whole length In order to apply a multi-layer coating, Over the whole length First of all, reaction curable epoxy resin The gelation rate is 30-90% Forming an incompletely cured fixing layer and then fixing layer The fixing layer while maintaining the gelation rate of 90% or less A thin film layer of heat-melt adhesive and a thick film layer of heat-shrinkable polyolefin. In contact with the outer peripheral surface of the metal bent pipe having the fixing layer. Then, a thick film layer of polyolefin is heated and contracted from the outer surface side, and the metal bending tube under the coating is induction-heated to thereby transfer the metal coating from the metal bending tube. Complete curing of the incompletely cured fixing layer with heat, and the heat-melt adhesive Thin film layer By melting , Including adhesion of the thin film layer to the epoxy resin primer layer provided in the incompletely cured state The interlaminar bonding is simultaneously advanced to complete the temporary assembly multilayer coating into an integrated multilayer coating. Thus, in this solution, it is necessary to arrange the polyolefin thick film layer in contact with the underlying layer from the beginning by using a heat-shrinkable polyolefin thick film layer for the temporarily assembled multilayer coating. The provisionally assembled multilayer coating becomes easier to form. Then, after forming the temporarily assembled multilayer coating, the polyolefin thick film layer is heated and contracted from the outer surface side, and the metal bent pipe under the coating is induction-heated. The layer can be shrunk and brought into contact with the underlying thin film layer of the heat-melting adhesive, and the heat-transfer from the metal bent tube completely cures the incompletely-cured fixing layer and melts the heat-melting adhesive. The temporary assembly multilayer coating can be completed into an integral multilayer coating, and a multilayer resin-coated metal bent tube having excellent durability can be manufactured.
[0008]
The third solution in the present application is the outer peripheral surface of the metal bent pipe. Over the whole length In order to apply a multi-layer coating, Over the whole length First of all, reaction curable epoxy resin The gelation rate is 30-90% Forming an incompletely cured fixing layer and then fixing layer The fixing layer while maintaining the gelation rate of 90% or less A thin film layer of heat-melt adhesive and a thick film layer of porous structure of polyolefin In contact with the outer peripheral surface of the metal bent pipe having the fixing layer. Then, a temporary assembly multilayer coating is formed, and then the metal curved tube under the coating is induction-heated, whereby the incompletely cured fixing layer is completely cured by heat transfer from the metal curved tube, and the thermal fusion is performed. adhesive Thin film layer By melting , Including adhesion of the thin film layer to the epoxy resin primer layer provided in the incompletely cured state Interlayer bonding and melt densification of the thick film layer are simultaneously performed to complete the temporarily assembled multilayer coating into an integrated multilayer coating. Thus, in this solution, the thick film layer can be easily formed by using the thick film layer having a porous structure of polyolefin for the temporarily assembled multilayer coating. That is, for the formation of the thick film layer, a sheet having a porous structure of polyolefin can be used, and since the sheet has appropriate flexibility, the sheet is pressed against the outer peripheral surface of the metal bent tube. Thus, it is possible to easily fit the outer peripheral surface of the metal bent tube, and it is possible to easily form a thick film layer. Then, after forming the temporarily assembled multi-layer coating, the metal curved tube under the coating is induction-heated, so that the incompletely cured fixing layer is completely cured and the heat fusion bonding is performed by heat transfer from the metal curved tube. Multi-layer resin-coated metal with excellent durability, which can complete the temporary assembly multi-layer coating into an integrated multi-layer coating by simultaneously proceeding with interlayer bonding by melting of the agent and melt densification of the thick film layer Can produce curved pipes.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The metal bent pipe to be coated used in the present invention is not limited, but in many cases, is a steel pipe used for pipelines and plant piping. The shape of the metal bent tube is arbitrary as long as it has a curved portion. As a typical example, as shown in FIG. 1A, the metal bent tube 1 having a constant radius R as a whole, and FIG. As shown in FIG. 4A, there can be mentioned a metal bent tube 1A having straight tube portions 1b and 1b at both ends of a bent tube portion 1a having a constant radius R. The diameter D, the bending radius R, the bending angle θ, the straight pipe portion length L, etc. of the metal bent pipe are not limited, but as a typical example, the diameter D is 400 to 1200 mm, the bending radius R is 3D to 8D, the bending The angle θ is 10 to 90 °, and the straight pipe portion length L is 1D to 3D.
[0010]
Hereinafter, a method for applying a multilayer resin coating by applying the present invention will be described taking the metal bent tube 1 as an example. 2A to 2D are schematic cross-sectional views showing an example of a procedure for covering the surface of the metal bent tube 1. First, pretreatment is performed on the outer peripheral surface of the metal bent tube 1 to adjust it to a state suitable for coating. For example, moisture on the surface of the metal bent tube 1 is removed, and scale and rust are removed by shot blasting. Moreover, you may perform surface treatments, such as a chromate process, as needed.
[0011]
Next, a reaction curable epoxy resin (primer) is uniformly applied to the outer peripheral surface of the metal bent tube 1 and semi-cured to form an incompletely cured fixing layer 2 of the reaction curable epoxy resin. The thickness of the incompletely cured fixing layer 2 is preferably about 50 to 500 μm, and more preferably 100 to 300 μm. As the reaction-curable epoxy resin used here, those conventionally used for corrosion protection of metal surfaces can be appropriately used. The form of the reaction curable epoxy resin may be a one-component or two-component liquid resin, or may be a powder form, but it is preferable to use a two-component liquid resin for ease of application. . The application method of the reaction curable epoxy resin can be a method using a spray or a brush when using a liquid resin, and electrostatic coating is preferable when using a powder form. In order to semi-cure the applied reaction-curable epoxy resin, either a method of heating the metal bent tube 1 to a temperature suitable for semi-curing of the epoxy resin before application or a method of heating after application is adopted. Although it is good, it is preferable to employ a method in which the metal bent tube 1 is heated before coating because the semi-curing operation of the reaction-curable epoxy resin can be performed quickly.
[0012]
The degree of curing of the epoxy resin in the formed incompletely cured fixing layer 2 is at least as long as the operation of forming the thin film layer of the heat-melt adhesive and the thick film layer of polyolefin on the formed incompletely cured fixing layer. A state where it is properly dried and attached to the outer peripheral surface of the metal bent pipe with an incomplete adhesive force so that it can be performed (for example, the fixing layer does not peel off or flow down during operation). Specifically, although it depends on the composition of the reaction-curable epoxy resin, it is preferable that the gelation rate is about 30% or more as a rough guide. Also, if the curing progresses too much, it is possible to secure sufficient bonding strength when a heat-melt adhesive thin film layer and a polyolefin thick film layer are placed in close contact with each other and heated and melted in a subsequent process. Since it will disappear, it will be in a state where curing does not proceed much. Specifically, although it depends on the composition of the reaction curable epoxy resin, it is preferable that the gelation rate is about 90% or less as a rough standard. In addition, after semi-curing the applied reaction curable epoxy resin and forming the incompletely cured fixing layer 2 of the epoxy resin, the metal bent tube may be forcibly cooled to stop the progress of curing of the epoxy resin, The bent metal pipe may not be forcibly cooled, but may be simply allowed to cool, so that the curing of the epoxy resin proceeds slowly. In the latter case, in the subsequent step, the thin film layer of the heat-melt adhesive and the thick film layer of polyolefin are closely arranged on the incompletely cured fixing layer 2, and the fixing layer 2 is also heated at the time of starting the heat melting. For example, the epoxy resin may be maintained in an incompletely cured state with a gelation rate of about 90% or less.
[0013]
Next, the temporarily assembled multilayer coating 5 is formed on the incompletely cured fixing layer 2 of the reaction curable epoxy resin, in which the thin film layer 3 of the heat-melt adhesive and the thick film layer 4 of the polyolefin are in contact with each other. . The temporarily assembled multilayer coating 5 is such that the fixing layer 2, the thin film layer 3, and the thick film layer 4 are maintained in contact with each other so that the heat transfer from the metal bent tube 1 is heated to a necessary temperature. The fixing layer 2 and the thin film layer 3 and / or the thin film layer 3 and the thick film layer 4 may be in a non-fused state simply in contact with each other. It may be in a fused state. The contact state between the fixing layer 2, the thin film layer 3, and the thick film layer 4 is as dense as possible in order to increase heat transfer efficiency and reduce the entrapment of bubbles during fusion between the layers (each It is preferable to increase the contact pressure between the layers.
The heat-melt adhesive used for the temporary multi-layer coating 5 has a characteristic that it can be satisfactorily bonded to both the epoxy resin fixing layer and the polyolefin thick film layer, and mainly various modifications such as maleic acid modification. Polyolefin is used, but not limited to this, other materials such as EVA, EAA, EMAA, etc. may be used. The thickness of the thin film layer 3 of the hot-melt adhesive may be about 100 to 300 μm. The polyolefin thick film layer 4 is provided with desired protective properties such as corrosion resistance, weather resistance, impact resistance, and specifically, high density polyethylene, medium density polyethylene, low density polyethylene, polypropylene, and polypropylene. Polyethylene copolymer, polybutene, and the like can be used. The thickness is also determined according to the desired protective properties, and is specifically selected to be about 2 to 5 mm.
[0014]
In order to form this temporarily assembled multilayer coating 5, as shown in FIG. 2, first, a method of forming a thin film layer 3 of a heat-melting adhesive and then forming a thick film layer 4 of polyolefin thereon, heat melting Any method of simultaneously forming the adhesive thin film layer 3 and the polyolefin thick film layer 4 may be employed. Various methods can be used for forming the thin film layer 3 of the heat-melt adhesive and the thick film layer 4 of the polyolefin. Hereinafter, typical ones will be described.
[0015]
One method of forming the heat-melt adhesive thin film layer 3 on the epoxy resin incompletely cured fixing layer 2 on the outer peripheral surface of the metal bent tube is to bandage the thin film heat-melt adhesive tape around the metal bent tube. It is. That is, as shown in FIG. 3, the thin film layer 3 of the heat-melting adhesive is wound by winding the thin-film heat-melting adhesive tape 7 on the outer peripheral surface of the metal bent tube 1 so that the side edges thereof overlap. Can be formed. At this time, the tape 7 is wound so as to be in close contact with the outer peripheral surface of the metal bent tube 1 (strictly, on the fixing layer 2), thereby reducing the entrapment of bubbles when heated and fused in a subsequent process. For this reason, it is preferable to wind the tape 7 in a state where an appropriate tension is applied. In addition, the tape 7 is appropriately heated and expanded within a range not exceeding the melting temperature, wound around the metal bent tube in that state, and then contracted by being allowed to cool or forcibly cooled to be in close contact with the metal bent tube. You may take the method. The thickness of the tape 7 to be used may be equal to the thickness of the thin film layer 3 so that the thin film layer 3 having a desired thickness can be formed by winding it in a single layer, or two or three layers can be wound in layers. By doing so, it is good also as a thin thing so that the thin film layer 3 of desired thickness can be formed.
[0016]
Another method for forming the thin film layer 3 of the heat-melt adhesive on the epoxy resin incompletely cured fixing layer 2 on the outer peripheral surface of the metal bent tube is by thermal spraying of the heat-melt adhesive. In this method, the heat-melt adhesive is fused on the incompletely cured fixing layer of the epoxy resin by thermal spraying, but the thin film layer 3 of the heat-melt adhesive can be formed.
[0017]
One method for forming the thick film layer 4 of polyolefin on the thin film layer 3 of the hot-melt adhesive on the outer peripheral surface of the metal bent tube is a method in which a thick polyolefin tape is bandaged around the metal bent tube. . That is, as shown in FIG. 4, a thick-film polyolefin tape 9 is formed on the thin film layer 3 (shown by bandaging the tape 7 in the drawing) on the outer peripheral surface of the metal bent tube 1. The thick film layer 4 of polyolefin can be formed by wrapping so that the side edges overlap. Also at this time, the tape 9 is wound so as to be in intimate contact with the outer peripheral surface of the metal bent tube 1 (strictly, on the thin layer 3). For this reason, it is preferable to wind the tape 9 in a state where an appropriate tension is applied. The tension applied to the tape 9 is preferably a tension that causes an elastic elongation strain of 1 to 5% on the tape 9. Further, when the tape 9 is wound, it is preferable to heat the tape 9 within a range not exceeding the melting temperature and to soften the tape 9 because the winding operation can be facilitated. When the tape 9 is heated and wound, the tension applied to the tape 9 may be small. That is, when the tape 9 is heated and wound, the tape 9 contracts due to subsequent cooling or forced cooling, and the tape 9 is in close contact with the metal bent tube. Therefore, the tension of the tape 9 during winding is small. Good. The thickness of the tape 9 to be used is assumed to be equal to the thickness of the thick film layer 4 so that the thick film layer 4 having a desired thickness can be formed by winding the tape 9 in a single layer.
[0018]
As shown in an enlarged view in FIG. 5A, when the tape 9 is bandage-wrapped, the side edges of the tape 9 and the tape 9 are overlapped. The overlapping contact surface 10 may be in an unbonded state, but may be fused by heating from the outer surface side of the tape 9 with a far-infrared heater, a burner, a roller rod or the like, if necessary. The tape 9 used for forming the thick film layer 4 has a constant thickness over the entire width, but in some cases, as in the tape 9A shown in FIG. You may use what was made to become thin gradually as it goes. When this tape 9A is used, the thickness of the overlapping portion of the tape 9A becomes small, and when the contact surface 10A is heated and fused from the outside, or when fused by heat transfer from the surface of the metal bent tube. The advantage of shortening the heating time can be obtained.
[0019]
Another method of forming the thick film layer 4 of polyolefin on the thin film layer 3 of the hot-melt adhesive on the outer peripheral surface of the metal bent pipe is by thermal spraying of polyolefin. In this method, the polyolefin is fused by heat spraying onto the thin film layer 3 of the heat-melt adhesive, although it is in an incomplete form, and the thick film layer 4 of the adhered polyolefin can be formed.
[0020]
Still another method of forming the thick film layer of polyolefin on the thin film layer of the heat-fusing adhesive on the outer peripheral surface of the metal bent tube is to previously apply the fixing layer 2 and the heat-melting adhesive on the outer peripheral surface of the metal bent tube. This is a method using a plurality of polyolefin short tubes that can be closely fitted via the thin film layer 3. That is, this is a method in which a plurality of short pipes 12 shown in FIG. 6 are prepared in advance, and these are successively fitted to the metal bent pipe 1 to form the thick film layer 4. The short tube 12 used here has an inner diameter d of the metal bent tube 1 so that the short tube 12 can be closely fitted on the outer peripheral surface of the metal bent tube 1 via the fixing layer and the thin film layer 3 of the hot-melt adhesive. Outer diameter D of the thin film layer 3 of the hot-melt adhesive disposed on the outer peripheral surface ₂ (When the thin film layer 3 is formed by bandaging the tape 7, the outer diameter of the portion where the tape 7 does not overlap is slightly smaller, for example, about 1 to 5%. The thickness of the short tube 12 is selected to be equal to the thickness required for the thick film layer 4 to be formed. The shape of the short tube 12 may be a curved shape so as to match the curve of the metal bent tube 1 or may be a straight tube. When the straight tube 12 is used, the length of the tube 12 can be selected to be short so that it can be fitted and attached to the curved metal bent tube 1 without any trouble. FIG. It can be fitted and attached to the metal bent pipe 1A with a straight pipe portion shown in FIG. The straight short tube 12 can be manufactured by cutting the polyolefin straight tube 13 shown in FIG. 7 along the alternately inclined cutting lines 14 and can be manufactured at low cost. In the case of using a curved short pipe, even if the short pipe is lengthened, it can be attached to the metal curved pipe 1 which is curved with a constant radius without any trouble. Becomes higher. Therefore, the short pipe length may be selected in consideration of short pipe mounting workability, manufacturing cost, and the like. Further, when a curved short pipe is used for the metal bent pipe 1A with a straight pipe portion, if it is made too long, it becomes difficult to pass through the straight pipe portion, so it is desirable to set it to be short.
[0021]
In FIG. 6, in order to fit the short pipe 12 to the metal curved pipe 1, the short pipe 12 is loosely fitted in a state where the diameter is temporarily expanded, and then an operation for restoring the original diameter is performed. Here, the temporary expansion of the short tube 12 can be easily performed by heating the short tube 12 to a temperature lower than the melting temperature, and the original diameter can be reduced by cooling after loose fitting. Can be restored. The temporary diameter expansion of the short tube 12 is not limited to heating, and may be performed by mechanical means. The short pipes 12 are successively fitted to the bent metal pipe 1, and at this time, the short pipe 12 fitted first and the subsequent short pipe 12 are simply in a butted state as shown in FIG. The butted portion is welded and joined with the resin 15. As described above, the plurality of short pipes 12 are successively fitted to the metal bent pipe 1 and the adjacent short pipes are joined to the outer peripheral surface of the metal bent pipe 1 by welding. A thick film layer 4 of polyolefin can be formed. In the case where the short pipe 12 is heated and fitted to the bent metal pipe 1, the welding of the short pipes may be performed before the short pipe 12 is cooled or after the short pipe 12 is cooled.
[0022]
In the above embodiment, adjacent short pipes are welded together, but not limited to this structure, as shown in FIG. 8B, the rear end of the short pipe 12 and the front end of the next short pipe 12 It is good also as a structure which fits. In this case, the contact surface 16 of the fitted short tubes 12 and 12 may be in an unbonded state, but if necessary, heat is melted by heating from the outer surface side of the short tube 12 with a far-infrared heater, burner, roller rod or the like. You may wear it. Further, when the short pipes are fitted together, as in the short pipe 12A shown in FIG. 8 (c), the thickness of the fitted area may be gradually reduced toward the end face. good. When the short pipe 12A is used, the thickness of the overlapping portion between the short pipes is reduced, and the contact surface 16A is fused by heating from the outside or by heat transfer from the metal curved pipe surface. The advantage of shortening the heating time can be obtained.
[0023]
Still another method of forming the thick film layer 4 of polyolefin on the thin film layer 3 of the hot-melt adhesive on the outer peripheral surface of the metal bent tube is to previously fix the fixing layer 2 and the hot-melt adhesive on the outer peripheral surface of the metal bent tube. This is a method of using a bent tubular molded body made of polyolefin having a shape that can be closely fitted through the thin film layer 3. That is, this is a method in which a polyolefin bent tubular body 18 shown in FIG. 9 is prepared in advance and is fitted to the metal bent tube 1. The bent tubular molded body 18 has an inner diameter d of the outer periphery of the metal bent tube 1 so that it can be closely fitted onto the outer peripheral surface of the metal bent tube 1 via the fixing layer and the thin film layer 3 of the hot-melt adhesive. Outer diameter D of thin film layer 3 of hot-melt adhesive disposed on the surface ₂ (When the thin film layer 3 is formed by bandaging the tape 7, the outer diameter of the portion where the tape 7 does not overlap is slightly smaller, for example, about 1 to 5%. Further, the thickness of the curved tubular molded body 10 is selected to be equal to the thickness required for the thick film layer 4 to be formed. In order to fit the curved tubular molded body 18 to the metal curved pipe 1, an operation of loosely fitting the curved tubular molded body 18 in a state where the diameter is temporarily expanded and then restoring the original diameter is performed. Here, the temporary diameter expansion of the curved tubular molded body 18 can be easily performed by heating the curved tubular molded body to a temperature lower than the melting temperature. It can be restored to the diameter. The temporary diameter expansion of the curved tubular molded body 18 is not limited to heating, and may be performed by mechanical means. As described above, a thick film layer of polyolefin can be formed on the outer peripheral surface of the metal curved tube 1 by fitting the curved tubular molded body 18 to the metal curved tube 1.
[0024]
In said embodiment, what was shape | molded in the cylinder shape over the full length is used as the curved tubular molded object 18. FIG. However, in this structure, for example, as shown in FIG. 1B, it may be difficult to fit the metal bent tube 1A having the straight pipe portion 1b. Therefore, in such a case, in order to facilitate the fitting work, a plurality of slits extending in the pipe circumferential direction are formed on the inner diameter side of the tube circumference of the curved tubular molded body, or the longitudinal direction is formed in the curved tubular molded body. A slit extending in the direction may be formed. When such a slit is formed, the curved tubular molded body is temporarily expanded in diameter by heating or the like, and when it is loosely fitted to the metal curved pipe 1A in this state, the curved tubular molded body is utilized using the slit. The body can be deformed, and the loose fitting work can be facilitated. In addition, after loosely fitting the curved tubular molded body at a predetermined position of the metal curved pipe, the slits may be integrated by welding.
[0025]
In the embodiment shown in FIG. 9, the curved tubular molded body 18 which is integrated as a whole for the formation of the thick film layer of polyolefin is used. However, the present invention is not limited to this structure. You may use the molded object of the form divided | segmented into the segment. FIG. 10 shows a molded product 18A made of polyolefin in that form. This molded body 10A is a polyolefin curved tubular molded body having a shape that can be tightly fitted onto the outer peripheral surface of the metal curved pipe 1A shown in FIG. 1B via a fixing layer and a thin film layer of a hot-melt adhesive. Is divided into two curved tubular molded body segments 18Aa and 18Ab in the circumferential direction. In order to attach this molded body 18A to a bent metal pipe, first, the diameter is temporarily expanded by heating or the like, and then covered with the bent metal pipe in that state, and the edges of adjacent segments 18Aa and 18Ab are butted together and welded together. Integrate. Then, it will be in the state which contacted the metal curved pipe outer surface closely by restoration to the original diameter. As described above, a thick film layer of polyolefin can be formed on the outer peripheral surface of the metal bent pipe.
[0026]
In the above embodiment, in order to arrange the thick film layer 4 of polyolefin so as to be in close contact with the outer surface of the bent metal tube, a short tube having a size capable of being tightly fitted or wound with a tape is applied. However, instead of this, a heat-shrinkable polyolefin resin can also be used. In that case, a thick film layer is formed by loosely wrapping a heat-shrinkable polyolefin tape, or by attaching a short pipe or molded body having a diameter much larger than that of a metal bent pipe, and then forming the thick film layer on the outer surface. By heating from the side, the metal curved pipe can be placed in close contact with the outer peripheral surface.
[0027]
As described above, as shown in FIG. 2 (d), the epoxy resin incompletely cured fixing layer 2, the heat-melt adhesive thin film layer 3, and the polyolefin thick film layer 4 are formed on the outer peripheral surface of the metal bent tube 1. After forming the temporarily assembled multilayer coating 5 having the above, the incompletely cured fixing layer 2 is completely cured by heat transfer from the metal curved tube 1 by induction heating of the metal curved tube 1 under the coating. And the interlaminar bonding by melting the hot-melt adhesive are simultaneously performed to complete the temporarily assembled multilayer coating 5 into an integrated multilayer coating. Thus, by using induction heating of the metal curved pipe, compared with the case of heating from the outside of the polyolefin thick film layer to completely cure the incompletely cured fixing layer and melt the hot-melt adhesive. It is possible to heat the incompletely cured fixing layer and the thin film layer of the hot-melt adhesive agent quickly and without damaging the thick film layer with heat. In addition, you may heat with a far-infrared heater, a burner, etc. from the outer side of the thick film layer of polyolefin in parallel with the induction heating of a metal curved pipe as needed. When the polyolefin thick film layer 4 is formed by partially overlapping the polyolefin tapes 9 and 9A as shown in FIGS. 4 and 5, or as shown in FIGS. In the case where the contact surfaces 10, 12A are partially overlapped and the contact surfaces 10, 10A, 16, 16A are not sufficiently fused, the contact time 10 is increased by increasing the heating time. , 10A, 16, 16A. Further, during heating, a mechanical compression force may be applied from the outside using a roller or the like so that the fusion proceeds smoothly.
[0028]
The induction heating of the metal curved pipe may be performed by a single-shot method that simultaneously heats the entire length of the metal curved pipe, or induction heating is performed on a small section in the longitudinal direction of the metal curved pipe, and the heating portion is set in the longitudinal direction. It may be performed continuously by moving. The induction coil for performing induction heating of the metal bent tube may be arranged on either the outer surface side or the inner surface side of the metal bent tube, but is preferably arranged on the outer surface side from the viewpoint of workability. 11 and 12 show an example in which the metal bent tube 1 is induction-heated in a movable manner. An induction coil 25 is arranged on the outer peripheral side of the bent metal tube 1 with the temporarily assembled multilayer coating 5 on the outer peripheral surface, and the induction coil 25 is induction-heated while induction heating the opposed region of the bent metal tube 1 with the induction coil 25. Is relatively moved along the metal bent tube 1. As a result, the surface layer portion of the metal bent tube 1 is heated by induction heating, and the incompletely cured fixing layer 2, the thin film layer 3 of the heat-melting adhesive, and the thick film layer 4 of the polyolefin by heat transfer from the temperature rising portion. Is heated, and the complete curing of the incompletely cured fixing layer 2 and the melting of the hot-melt adhesive proceed simultaneously, and the thick film layer 4 of polyolefin is firmly bonded to the outer peripheral surface of the metal bent tube 1. Then, the heated part moves along the curved metal pipe 1, so that the part where the hot-melt adhesive is melted also moves. At that time, the air between the layers is pushed out, and the bubbles are held. A coating layer with very little embedding is formed. When the metal bent tube 1 is induction-heated, if necessary, it may be heated from the outside of the polyolefin thick film layer by a far-infrared heater, a burner or the like. Combined with heating from the outside, the heating time can be shortened, and when the thick film layer of polyolefin is formed by tape bandage, adhesion of the contact surfaces of the overlapping tapes is more reliable And can. In addition, as described above, a compressive force may be applied using a roller or the like, or if a heat-shrinkable wrapping tape or the like is previously wound around the outside, the compressive force can be applied uniformly.
[0029]
As described above, a multi-layer coating in which an epoxy resin, a thin film layer of a hot-melt adhesive, and a thick film layer of polyolefin are integrated is formed on the outer peripheral surface of the metal bent tube, and a multi-layer resin-coated metal bent tube is manufactured. can do. In addition, since the complete curing of the epoxy resin and the melting of the hot-melt adhesive are simultaneously performed, the obtained multilayer resin-coated metal curved pipe has a large bonding strength with respect to the outer circumferential surface of the polyolefin thick film layer. Thus, a multi-layer coating excellent in durability can be formed.
[0030]
In any of the above embodiments, the formation of the heat-bonding adhesive thin film layer 3 and the formation of the polyolefin thick film layer 4 are performed in separate steps when the temporarily assembled multilayer coating 5 is formed. However, the present invention is not limited to this, and it is also possible to simultaneously form the thin film layer of the hot-melt adhesive and the thick film layer of the polyolefin. Hereinafter, an embodiment in that case will be described.
[0031]
In one embodiment, a thin film layer of a hot-melt adhesive is previously formed on one side of the polyolefin tape 9 used in the embodiment shown in FIG. 4, and the polyolefin tape is placed on the outer periphery with the thin film layer inside. Bandages are wound on a metal bent tube having an epoxy resin incompletely cured fixing layer on the surface in the same manner as in the embodiment shown in FIG. Thereby, the temporary assembly multilayer coating of the structure which has arrange | positioned the thin film layer of a heat-melt-adhesive agent and the thick film layer of polyolefin in the state which contacted closely on the epoxy resin incomplete hardening fixed layer can be formed.
If a thin film layer of a heat-melt adhesive is previously formed on the polyolefin tape 9, a thin film layer of the heat-melt adhesive exists on the contact surface 10 at the portion where the polyolefin tape 9 is overlaid as shown in FIG. In other words, there is an advantage that the overlapping polyolefin tapes 9 and 9 can be securely bonded at a low temperature as compared with the case where the polyolefin tapes are directly bonded.
[0032]
In another embodiment, a thin film layer of a hot-melt adhesive is previously formed on the inner surface of the short tube 12 used in the embodiment shown in FIG. Then, the short tube is fitted into a metal bent tube having an epoxy resin incompletely cured fixing layer formed on the outer peripheral surface in the same manner as in the embodiment shown in FIG. Thereby, the temporary assembly multilayer coating of the structure which has arrange | positioned the thin film layer of a heat-melt-adhesive agent and the thick film layer of polyolefin in the state which contacted closely on the epoxy resin incomplete hardening fixed layer can be formed.
[0033]
In still another embodiment, a thin film layer of a hot-melt adhesive is previously formed on the inner surfaces of the molded bodies 18 and 18A used in the embodiments shown in FIGS. Then, the molded body is attached to a metal curved pipe having an epoxy resin incompletely cured fixing layer formed on the outer peripheral surface in the same manner as the embodiment shown in FIGS. Thereby, the temporary assembly multilayer coating of the structure which has arrange | positioned the thin film layer of a heat-melt-adhesive agent and the thick film layer of polyolefin in the state which contacted closely on the epoxy resin incomplete hardening fixed layer can be formed.
[0034]
In still another embodiment, the polyolefin thick film layer is formed of a heat-shrinkable polyolefin, and a thin film layer of a heat-melt adhesive is previously formed on the inner surface of the polyolefin tape, short tube, molded article or the like used in that case. Form it. Then, the tape, short tube, molded body, etc. are attached to a metal bent tube having an epoxy resin incompletely cured fixing layer formed on the outer peripheral surface, and then heated to shrink to thereby form an epoxy resin incompletely cured fixing layer. A temporarily assembled multi-layer coating having a structure in which a thin film layer of a heat-melt adhesive and a thick film layer of polyolefin are arranged in close contact with each other can be formed.
[0035]
When heat-shrinkable polyolefin is used, the heat-shrinkable polyolefin thick film layer is formed, followed by heat-shrinking operation, complete curing of the incompletely cured fixing layer, and melting of the hot-melt adhesive. The induction heating of the metal bent tube may be performed simultaneously. In other words, a temporarily assembled multilayer coating in which a thin film layer of heat-melt adhesive and a thick film layer of heat-shrinkable polyolefin are arranged on an incompletely cured fixing layer of a reactive curable epoxy resin formed on the surface of a metal curved pipe. Forming and then shrinking the thick film layer of polyolefin from the outer surface side, and inductively heating the metal bent tube under the coating, thereby incompletely fixing the heat by heat transfer from the metal bent tube The temporary assembly multi-layer coating can be completed into an integrated multi-layer coating by simultaneously proceeding with complete curing of the layer and interlayer bonding by melting the hot-melt adhesive.
[0036]
In any of the embodiments described above, the polyolefin thick film layer is formed using a solid polyolefin tape, a short tube, a molded body, and the like. Therefore, the polyolefin thick film layer is solid. However, instead of this, it is also possible to use a porous structure. In other words, a temporary assembly in which a thin film layer of a heat-melt adhesive and a thick film layer of a porous structure of polyolefin are placed in contact with an incompletely cured fixing layer of a reactive curable epoxy resin formed on the surface of a metal curved pipe. A multi-layer coating is formed, and then the metal bent tube under the coating is induction-heated, whereby the incompletely cured fixing layer is completely cured and the hot-melt adhesive is melted by heat transfer from the metal bent tube. The temporary joining multilayer coating can be completed into an integrated multilayer coating by simultaneously proceeding with interlayer bonding by melting and melting and densification of the thick film layer, and also by this method on the outer peripheral surface of the metal curved pipe A multi-layer coating with a three-layer structure can be applied.
[0037]
In order to form the above-mentioned polyolefin porous structure thick film layer, the porous tape, short tube, molded article, etc., instead of the polyolefin tape, short tube, molded product, etc. used in the above-described embodiment. Although a body or the like may be used, it is recommended to simply use a sheet having a flat porous structure because the manufacturing cost is low and the handling is easy. As a tape, a short tube, a molded body, a sheet or the like having a porous structure, a polyolefin powder resin molded into a desired shape in an unmelted or partially melted state, for example, Japanese Patent Publication No. 5-19894 Can be used.
[0038]
As a specific method for forming a thick film layer on the outer peripheral surface of the metal curved pipe using a porous sheet, as shown in FIGS. 13 (a) and 13 (b), the outer peripheral surface of the metal curved pipe 1 is formed. An example is a method in which a sheet 27 having an appropriate size is sequentially disposed on the thin film layer 3 of the heat-melting adhesive so as to partially overlap each other. At this time, since the porous sheet 27 has a certain degree of flexibility, it can be easily deformed into a shape that follows the outer peripheral surface of the metal bent tube 1. It can arrange | position in the state fitted to the thin film layer 3. FIG. In order to keep the arranged sheet 27 in contact with the thin film layer 3, a method of attaching the sheet 27 using an appropriate pressure-sensitive adhesive, an appropriate outside of the sheet 27 arranged on the outer peripheral surface of the metal curved pipe 1 is used. Examples thereof include a method of winding a wrapping tape, preferably a heat-shrinkable wrapping tape. After a large number of sheets 27 are thus arranged on the outer peripheral surface of the metal bent tube 1 to form the thick film layer 4A, the metal bent tube 1 is heated by induction heating as described above. Heat transfer from the incompletely cured fixing layer 2, interlayer bonding by melting of the hot-melt adhesive, and melt densification of the thick film layer 4A are simultaneously advanced to integrate the temporarily assembled multilayer coating. To complete. At this time, since the porous sheet 27 is completely melted and densified, the overlapping portions of the sheets 27 and 27 can be melted and densified and integrated together. Thus, a coating layer that reliably covers the outer peripheral surface of the metal bent tube 1 can be formed. Also in this case, when the metal bending tube 1 is induction-heated, it may be heated from the outer surface side in parallel with a far-infrared heater, a burner or the like, or a compression force may be applied using a roller or the like. good. In addition, when a heat-shrinkable wrapping tape is wound on the outside in advance, a compressive force is uniformly applied by the shrinkage of the wrapping tape.
[0039]
In any of the above-described embodiments, after forming the temporarily assembled multilayer coating covering the entire region to be coated with the resin on the outer peripheral surface of the metal curved pipe, the metal curved pipe is induction-heated to integrate the temporarily assembled multilayer coating. However, the present invention is not limited to this configuration, and a temporarily assembled multilayer coating is formed in a partial region of the outer peripheral surface of the metal bent tube, and the metal bent tube in that region is induction-heated. The temporary assembly multi-layer coating is completed into an integrated multi-layer coating, and then a temporary assembly multi-layer coating is formed in an adjacent region, and the metal curved pipe in that region is induction-heated to integrate the temporary assembly multi-layer coating. A method of sequentially forming the coating for each small region, such as completing the layer coating, may be adopted.
[0040]
【Example】
[Example 1]
A metal bent tube 1 shown in FIG. The specifications of the metal bent tube 1 are: an outer diameter D = 406.4 mm (24 inches), a bending radius R = 2032 mm, a bending angle θ = 90 °, and a material = API 5LX65.
The metal bent tube 1 is preheated to 60 ° C. by induction heating, and a two-pack type epoxy resin (trade name “Epotherm”, manufactured by Dainippon Color Material Co., Ltd.) is applied to the outer peripheral surface with a brush. By standing for a minute, an incompletely cured fixing layer cured to a gelation rate of about 50% was formed. Therefore, an adhesive polyethylene tape (thickness: 100 μm, width: 200 mm, trade name “Admer NE090”, manufactured by Mitsui Chemicals, Inc.) is bandaged with a half wrap to form a thin film layer having a thickness of 200 μm. did.
[0041]
Thereafter, a high-density polyethylene tape (thickness 2.5 mm, width 200 mm, trade name “Hi-Zex 5000H”, manufactured by Mitsui Chemicals, Inc.) is wound on the bandage with a tension that gives 2% elongation applied thereto. In addition, far-infrared heating was performed from the outer surface side, and the overlapping portions of the tape were fused and fitted to the base of the tape.
After that, as shown in FIG. 11, an induction coil 25 having a heating width of 50 mm is arranged on the outer periphery of the metal bent tube 1 and continuously moves at a moving speed of 50 mm / min while induction heating the surface layer portion of the metal bent tube 1. The entire length of the metal bent tube 1 was induction-heated. At this time, the surface temperature of the metal bent tube 1 heated by induction was raised to about 250 ° C. After induction heating of the metal bent tube 1, the metal bent tube 1 was allowed to stand for about 30 minutes, and heat transfer from the metal bent tube 1 caused the complete curing of the incompletely cured fixing layer and the interlayer bonding by melting of the hot-melt adhesive simultaneously. . Thereafter, cooling water was sprayed from the outer surface side to cool the cured portion. In this way, a completely integrated three-layer polyethylene-coated metal bent tube was obtained.
[0042]
The obtained coating was subjected to a cathode peeling test shown in the ASTM G14 standard. As a result, the peeling diameter was 3.5 mm at 20 ° C. for 30 days, and the wound starting point peeling durability was sufficient. Moreover, the surface hardness of the coating was 78 HDD, and the adhesive strength was 20 N / cm, indicating sufficient hardness and adhesive strength. Accordingly, a polyethylene coating having excellent long-term durability such as scratch origin separation durability and excellent impact resistance was obtained.
[0043]
[Example 2]
A metal bent tube 1 having the same specifications as in Example 1 was prepared, and an incompletely cured fixing layer and an adhesive polyethylene thin film layer were formed in the same manner as in Example 1.
On top of that, a pre-made polyethylene short tube 12 (see FIG. 6) (inner diameter 403.0 mm, wall thickness 3.0 mm, center length 200 mm) is heated to about 100 ° C., and the inner diameter is about 10 mm. In the state where the diameter was expanded, the mats were loosely fitted one after another, and the butted ends were welded and joined, then cooled by blowing cooling water, and closely fitted to the metal curved pipe.
[0044]
After that, as shown in FIG. 11, an induction coil 25 having a heating width of 50 mm is arranged on the outer periphery of the metal bent tube 1 and continuously moves at a moving speed of 50 mm / min while induction heating the surface layer portion of the metal bent tube 1. The entire length of the metal bent tube 1 was induction-heated. At this time, the surface temperature of the metal bent tube 1 heated by induction was raised to about 250 ° C. After induction heating of the metal bent tube 1, the metal bent tube 1 was allowed to stand for about 30 minutes, and heat transfer from the metal bent tube 1 caused the complete curing of the incompletely cured fixing layer and the interlayer bonding by melting of the hot-melt adhesive simultaneously. . Thereafter, cooling water was sprayed from the outer surface side to cool the cured portion. In this way, a completely integrated three-layer polyethylene-coated metal bent tube was obtained.
[0045]
The obtained coating was subjected to a cathode peeling test in the same manner as in Example 1. As a result, the peeling diameter was 3.2 mm at 20 ° C. × 30 days, and sufficient wound-point peeling durability was exhibited. Moreover, the surface hardness of the coating was 78 HDD, and the adhesive strength was 19 N / cm, indicating sufficient hardness and adhesive strength. Accordingly, a polyethylene coating having excellent long-term durability such as scratch origin separation durability and excellent impact resistance was obtained.
[0046]
[Example 3]
A bent metal tube 1 having the same specifications as in Example 1 was prepared, and an incompletely cured fixing layer was formed in the same manner as in Example 1.
On top of that, a polyethylene shrink tape with a heat-melt adhesive (polyethylene thickness 1.5 mm, adhesive thickness 1.5 mm, width 200 mm, trade name “WPC100M”, manufactured by Raychem, USA) is a tension that allows a loose fit. After that, bandage winding was performed, and then far-infrared heating was performed from the outer surface side to shrink the tape and fuse the overlapping portions.
[0047]
After that, as shown in FIG. 11, an induction coil 25 having a heating width of 50 mm is arranged on the outer periphery of the metal bent tube 1 and continuously moves at a moving speed of 50 mm / min while induction heating the surface layer portion of the metal bent tube 1. The entire length of the metal bent tube 1 was induction-heated. At this time, the surface temperature of the metal bent tube 1 heated by induction was raised to about 250 ° C. After induction heating of the metal bent tube 1, the metal bent tube 1 was allowed to stand for about 30 minutes, and heat transfer from the metal bent tube 1 caused the complete curing of the incompletely cured fixing layer and the interlayer bonding by melting of the hot-melt adhesive simultaneously. . Thereafter, cooling water was sprayed from the outer surface side to cool the cured portion. In this way, a completely integrated three-layer polyethylene-coated metal bent tube was obtained.
[0048]
The obtained coating was subjected to a cathode peeling test in the same manner as in Example 1. As a result, the peeling diameter was 3.9 mm at 20 ° C. for 30 days, and sufficient scratch starting point peeling durability was exhibited. Moreover, the surface hardness of the coating was 65 HDD, and the adhesive strength was 15 N / cm, indicating sufficient hardness and adhesive strength. Accordingly, a polyethylene coating having excellent long-term durability such as scratch origin separation durability and excellent impact resistance was obtained.
[0049]
【The invention's effect】
As described above, according to the present invention, the multilayer resin comprising the multilayer resin coating in which the polyolefin thick film layer is firmly bonded to the outer peripheral surface of the metal bent pipe through the reaction curable epoxy resin and the hot-melt adhesive. Coated metal bent pipes can be manufactured, and the obtained multilayer resin-coated metal bent pipes have excellent durability, and are suitable for pipelines installed in harsh environments such as soil and sea It has the effect that it can be used.
[Brief description of the drawings]
1A and 1B are schematic plan views showing examples of metal bent pipes used in the present invention, respectively.
FIGS. 2A, 2B, 2C, and 2D are schematic cross-sectional views showing an example of a procedure for forming a temporarily assembled multilayer coating on the outer peripheral surface of a metal bent pipe;
FIG. 3 is a schematic plan view showing a state where a hot-melt adhesive tape is bandage-wrapped on the outer peripheral surface of a metal bent pipe
FIG. 4 is a schematic plan view showing a state where a polyolefin tape is bandage-wrapped on the outer peripheral surface of a metal bent pipe
FIGS. 5A and 5B are schematic cross-sectional views showing, on an enlarged scale, an overlapping portion of a polyolefin tape wound around an outer peripheral surface of a metal bent pipe.
FIG. 6 is a schematic plan view showing a state where a polyolefin short pipe is fitted to the outer peripheral surface of a metal bent pipe.
7 is a schematic cross-sectional view illustrating a process for manufacturing a short tube used in the embodiment of FIG.
8 (a), (b), and (c) are schematic cross-sectional views showing an enlarged joint portion of a short pipe fitted to the outer peripheral surface of a metal bent pipe, respectively.
FIGS. 9A and 9B are a schematic plan view and a cross-sectional view showing a metal bent tube having a thin film layer of a hot-melt adhesive on the outer peripheral surface and a bent tubular molded body fitted to the metal bent tube.
10A is a schematic plan view of a segment 18Aa of a molded body 18A. FIG.
(B) is a schematic front view of the molded body 18A.
FIG. 11 is a schematic plan view showing a state where induction bending is performed on a metal bent pipe having a temporarily assembled multilayer coating formed on the outer peripheral surface thereof.
FIG. 12 is a schematic cross-sectional view showing a state in which a metal bent tube having a temporarily assembled multilayer coating formed on the outer peripheral surface is inductively heated.
FIG. 13A is a schematic plan view showing a state in which a polyolefin porous structure sheet is disposed on the outer peripheral surface of a metal curved pipe.
(B) Schematic cross-sectional view showing, in an enlarged manner, overlapping portions of sheets arranged on the outer peripheral surface of the metal curved pipe
[Explanation of symbols]
1,1A metal curved pipe
2 Epoxy resin incompletely cured fixing layer
3 Thin film layer of hot-melt adhesive
4 Thick film layer of polyolefin
5 Temporary assembly multilayer coating
7 Hot-melt adhesive tape
9 Polyolefin tape
12 Polyolefin short tube
18 Curved tubular molded body of polyolefin
18A Polyolefin molded body
18Aa, 18Ab Curved tubular body segment
25 induction coil
27 Sheet of polyolefin porous structure

Claims

A method of manufacturing a metal bend tube in which a three-layer structure coating including an epoxy resin primer layer is applied over the entire length of the outer peripheral surface of the metal bend tube. Forming an incompletely cured fixing layer of a curable epoxy resin having a gelation rate of 30 to 90% , and then, on the fixing layer while maintaining the gelation rate of the fixing layer at 90% or less , A thin film layer of heat-melting adhesive and a thick film layer of polyolefin are disposed in contact with each other to form a temporarily assembled multi-layer coating disposed in contact with the outer peripheral surface of the metal bending tube having the fixing layer ; , by induction heating the metal bends under this coating, the complete curing of the incompletely cured fixing layer in the heat transfer from the metal bent pipe, due to melting of the thermal fusion adhesive film layer, the thin film layer Adhesion to the epoxy resin primer layer provided in the incompletely cured state of And no interlayer bonding by simultaneously producing method of multilayered coated metal bent tube, characterized in that to complete the pre-assembled multilayer coating integral multilayer coating.

The method for producing a multilayer coated metal bent tube according to claim 1, wherein the thick film layer of the temporarily assembled multilayer coated polyolefin is formed by an operation of bandaging a thick film polyolefin tape around the metal curved tube.

The method for producing a multi-layer coated metal bent tube according to claim 2, wherein the bandaging is performed while applying a tension at which an elastic elongation strain of 1 to 5% is applied to the polyolefin tape.

The method for producing a multilayer coated metal bent tube according to claim 2 or 3, wherein the bandaging is performed in a state where the polyolefin tape is heated to a temperature lower than a melting temperature.

The method for producing a multilayer coated metal bent tube according to claim 1, wherein the polyolefin thick film layer of the temporarily assembled multilayer coating is formed by thermal spraying of polyolefin.

A plurality of polyolefin-made thick film layers of the temporarily assembled multilayer coating can be fitted onto the outer peripheral surface of the bent metal pipe through the fixing layer and the thin film layer of the heat-melt adhesive. The method for producing a multi-layer coated metal bent pipe according to claim 1, wherein the short pipe is formed by an operation of loosely fitting in a state where the diameter is temporarily expanded and closely fitting by restoring the original diameter.

The method for producing a multilayer coated metal bent tube according to claim 6, wherein the short pipe is temporarily expanded by heating the short pipe to a temperature lower than a melting temperature.

A polyolefin curved tube having a shape capable of closely fitting the thick film layer of polyolefin of the temporarily assembled multilayer coating on the outer peripheral surface of the metal bent tube via the fixing layer and a thin film layer of a hot-melt adhesive. The method for producing a multi-layer coated metal bent tube according to claim 1, wherein the formed body is formed by an operation of loosely fitting in a state where the diameter is temporarily expanded and closely fitting by restoring the original diameter.

A polyolefin curved tube having a shape capable of closely fitting the thick film layer of polyolefin of the temporarily assembled multilayer coating on the outer peripheral surface of the metal bent tube via the fixing layer and a thin film layer of a hot-melt adhesive. A polyolefin bent tubular molded segment in which the molded body is divided into a plurality of segments in the circumferential direction is disposed on the outer peripheral surface of the metal bent tube, and the end portions of adjacent segments are welded together to be integrated. The method for producing a multilayer coated metal bent tube according to claim 1, wherein the multilayer coated metal bent tube is formed by an operation of converting into a multilayered metal.

The thin film layer of the hot-melt adhesive of the temporarily assembled multilayer coating is formed by an operation of bandaging a thin-film hot-melt adhesive tape around the metal bent tube. A method for producing a multilayer coated metal curved pipe.

The method for producing a multilayer coated metal bent tube according to any one of claims 1 to 9, wherein the thin film layer of the hot-melt adhesive of the temporarily assembled multilayer coating is formed by thermal spraying of the hot-melt adhesive.

A thin film layer of a hot-melt adhesive is formed in advance on one side of the polyolefin tape, and the polyolefin tape is bandage-wrapped around the metal bent tube with the thin film layer inside, so that the temporarily assembled multilayer coating is formed. The method for producing a multilayer coated metal bent tube according to claim 2, 3 or 4, wherein the thin film layer of the hot-melt adhesive and the thick film layer of the polyolefin are formed simultaneously.

A thin film layer of a hot-melt adhesive is formed on the inner surface of the polyolefin short pipe in advance, and the short pipe is attached to the bent metal pipe to thereby form a thin film layer of the hot-melt adhesive of the temporarily assembled multilayer coating. The method for producing a multilayer coated metal bent tube according to claim 6 or 7, wherein a thick film layer of polyolefin and a polyolefin film are simultaneously formed.

A thin film layer of a heat-melt adhesive is formed in advance on the inner surface of the polyolefin curved tubular molded body, and the curved tubular molded body is attached to the metal curved pipe to thereby heat-bond the temporary assembly multilayer coating. The method for producing a multilayer coated metal bent tube according to claim 8, wherein the thin film layer of the agent and the thick film layer of the polyolefin are formed simultaneously.

A heat-melt adhesive thin film layer is formed in advance on the inner surface of the polyolefin curved tubular segment, and the curved tubular segment is attached to the metal curved tube to heat the temporarily assembled multilayer coating. The method for producing a multilayer coated metal bent tube according to claim 9, wherein the thin film layer of the melt adhesive and the thick film layer of the polyolefin are formed simultaneously.

A method of manufacturing a metal bend tube in which a three-layer structure coating including an epoxy resin primer layer is applied over the entire length of the outer peripheral surface of the metal bend tube. Forming an incompletely cured fixing layer of a curable epoxy resin having a gelation rate of 30 to 90% , and then, on the fixing layer while maintaining the gelation rate of the fixing layer at 90% or less , A thin film layer of heat-melting adhesive and a thick film layer of heat-shrinkable polyolefin are disposed to form a temporarily assembled multilayer coating disposed in contact with the outer peripheral surface of the metal curved pipe having the fixing layer , and thereafter The polyolefin thick film layer is heated and contracted from the outer surface side, and the metal curved tube under the coating is induction-heated to completely cure the incompletely cured fixing layer by heat transfer from the metal curved tube. When, due to melting of the thermal fusion adhesive film layer, the incomplete curing of the thin film layer An interlayer bonding, including adhesion to epoxy resin primer layer is provided by state by simultaneously, multilayer coated metal bent tube, characterized in that to complete the pre-assembled multilayer coating integral multilayer coating Manufacturing method.

A method of manufacturing a metal bend tube in which a three-layer structure coating including an epoxy resin primer layer is applied over the entire length of the outer peripheral surface of the metal bend tube. Forming an incompletely cured fixing layer of a curable epoxy resin having a gelation rate of 30 to 90% , and then, on the fixing layer while maintaining the gelation rate of the fixing layer at 90% or less , A temporarily assembled multi-layer coating disposed in contact with the outer peripheral surface of the metal curved pipe having the fixing layer by arranging the thin film layer of the heat-melt adhesive and the thick film layer of the porous structure of polyolefin in contact with each other. Then, by inductively heating the metal bent tube under the coating, heat transfer from the metal bent tube causes complete curing of the incompletely cured fixing layer and melting of the hot-melt adhesive thin film layer . An epoxy resin primer provided in the incompletely cured state of the thin film layer An interlayer bonding, including adhesion to and co allowed to proceed melt densification of the thick film layer, a multilayer coated metal bent tube, characterized in that to complete the pre-assembled multilayer coating integral multilayer coating Production method.

The method for producing a multilayer coated metal bent tube according to any one of claims 1 to 17, wherein the reaction-curable epoxy resin is a two-component liquid resin.