JP4028649B2 - Multilayer pipe manufacturing method - Google Patents

Description

で表される膨張率（ｅ）が５％以上である超高分子量ポリエチレン樹脂パイプを内層パイプとして外層パイプ内に遊嵌したのち、前記超高分子量ポリエチレン樹脂パイプを加熱して膨張させて前記超高分子量ポリエチレン樹脂パイプの外周面を外層パイプの内周面に圧接させる工程を備えている構成とした。
【００１０】
本発明の請求項２に記載の発明にかかる複層パイプの製造方法（請求項２の製造方法）は、請求項１の製造方法において、金型が、溶融樹脂を押出機のシリンダ内径より縮径した状態に賦形する断面縮小部を備え、この断面縮小部が、入口側樹脂流路の断面積（Ｓ１）と出口側樹脂流路の断面積（Ｓ２）との比（Ｓ１／Ｓ２）が１．０より大きく、入口側樹脂流路の外径Ｄ₀ １と、出口側樹脂流路の外径Ｄ₀ ２の比（Ｄ₀ １／Ｄ₀ ２）が１．０５よりも大きくなるように形成されている構成とした。
【００１１】
また、本発明において、外層パイプとしては、内層パイプの膨張・圧接のための加熱温度に耐える耐熱性や、膨張・圧接の圧力に耐える剛性を備えているものであれば、特に限定されないが、例えば、金属製のもの、繊維強化プラスチック（ＦＲＰ）製のもの等が挙げられる。
また、外層パイプとして使用できる金属材料としては、特に限定されないが、例えば、炭素鋼，鋳鋼等の汎用鋼、ステンレス鋼，クロム鋼等の特殊鋼、銅合金，アルミニウム等の軽合金が挙げられる。
【００１２】
繊維強化プラスチックとしては、特に限定されないが、例えば、ガラス繊維や炭素繊維等の補強繊維に熱硬化性樹脂等を含浸したものが挙げられる。
熱硬化性樹脂としては、特に限定されないが、例えば、エポキシ樹脂、フェノール樹脂、不飽和ポリエステル樹脂等が使用できる。
【００１３】
内層パイプは、上記式（１）で規定される膨張率（ｅ）が５％以上の超高分子量ポリエチレン樹脂パイプに限られるが、５％以上１００％以下のものがより好ましい。
すなわち、膨張率（ｅ）が１００％を越えると、被覆時に長手方向（管軸方向）の収縮が大きくなり、被覆効率が悪くなる恐れがある。また、５％未満では、被覆される外層パイプに対する被覆応力が小さくなり、外層パイプとの密着性が低下する。
【００１４】
加熱膨張前の超高分子量ポリエチレン樹脂パイプの径や肉厚は、特に限定されないが、外径（Ｄ）が１０mm以上、肉厚（ｔ）が０．１mm以上とすることが好ましく、高生産性かつ経済的に成形できる範囲として、さらに好ましくは、外径（Ｄ）が１５mm以上３００mm以下、肉厚（ｔ）が０．３mm以上０．８mm以下である。また、外径（Ｄ）／肉厚（ｔ）の比は、１０以上３００以下が好ましく、剛性が良好なパイプが得られる点で、外径（Ｄ）／肉厚（ｔ）の比が１５以上２００以下とすることがより好ましい。
【００１５】
超高分子量ポリエチレン樹脂パイプを形成する超高分子量ポリエチレン樹脂としては、特に限定されないが、粘度平均分子量が３０万以上のものが好ましく、１００万以上１０００万以下のものがより好ましい。
すなわち、分子量が大きい程、耐磨耗性，耐薬品性などの性質がより向上するが、１０００万を越えると、成形が非常に困難となってくる。なお、本発明の目的を達成できるのであれば、粘度平均分子量が３０万未満のものが混合されていても構わない。
【００１６】
また、本発明において、超高分子量ポリエチレン樹脂とは、エチレンを主成分とするものであり、例えば、エチレンの単独重合体、エチレンを主成分とし、エチレンと、このエチレンに共重合可能な単量体との共重合体などが挙げられる。
【００１７】
エチレンに共重合可能な単量体としては、特に限定されないが、例えば、プロピレン、１−ブテン、１−ペンテン、４−メチル−１−ペンテン、１−ヘキセン、１−ヘプテン、１−オクテン等のモノオレフィン；１，３−ブタジエン、２−メチル−２，４−ペンタジエン、２，３−ジメチル−１，３−ブタジエン、２，４−ヘキサジエン、３−メチル−２，４−ヘキサジエン、１，３−ペンタジエン、２−メチル−１，３−ブタジエン等の共役ジエン系炭化水素化合物；１，４−ペタンジエン、１，５−ヘキサジエン、１，６−ヘプタジエン、１，７−オクタジエン、２，５−ジメチル−１，５−ヘキサジエン、４−メチル−１，４−ヘキサジエン、５−メチル−１，４−ヘキサジエン、４−エチル−１，４−オクタジエン、４−ｎ−プロピル−１，４−デカジエン等の非共役ジエン系炭化水素化合物；１，３，５−ヘキサトリエン、１，３，５，７−オクタテトラエン、２−ビニル−１，３−ブタジエン等の共役ポリオレフィン系炭化水素化合物；スクアレン等の非共役ポリオレフィン系炭化水素化合物；その他ジビニルベンゼン、ビニルノルボルネン等の分子内に少なくとも２個の不飽和結合、好ましくは二重結合を有する炭化水素化合物等が挙げられる。
【００１８】
さらに、超高分子量ポリエチレン樹脂には、本発明の目的を達成できる範囲で、必要に応じて他の合成樹脂や天然樹脂、可塑剤、耐熱安定剤、耐候安定剤、滑剤、アンチブロッキング剤、スリップ剤、顔料、染料、充填剤等を配合するようにしても構わない。
【００１９】
本発明において、遊嵌とは、超高分子量ポリエチレン樹脂パイプの外径が外層パイプの内径より小さく、挿入時に、超高分子量ポリエチレン樹脂パイプが外層パイプの軸方向に自由にスライドできる状態を意味する。
具体的には、超高分子量ポリエチレン樹脂パイプの外径は、外層パイプの内径より１％以上３０％以下小さいものが好ましい。すなわち、１％未満の場合には、外層パイプへの挿入が困難になる恐れがあり、３０％を越えると外層パイプへの被覆応力が小さくなり、外層パイプとの密着性が低下する恐れがあるとともに、加熱膨張機の長手方向（管軸方向）の収縮が大きく、被覆効率が悪くなる恐れがある。
【００２０】
本発明において、圧接させるとは、上記で規定した膨張率（ｅ）の温度を実際の加熱温度に置き換えた測定方法により、その加熱温度での超高分子量ポリエチレン樹脂パイプを外層パイプに遊嵌した後、超高分子量ポリエチレン樹脂パイプの実質膨張率（ｅ₁)が、同じく加熱により熱膨張した外層パイプとの隙間も塞ぐのに必要な膨張率よりも大きくなる条件で、外層パイプに内面被覆している状態をいう。
すなわち、この圧接では、超高分子量ポリエチレン樹脂パイプ内部に外層パイプを拡径する方向に残留応力が発生し、膨張した超高分子量ポリエチレン樹脂パイプと外層パイプとが強固に密着する。これらの条件は、超高分子量ポリエチレン樹脂パイプ製造時の金型流路形状や温度条件を調節することにより達成可能である。
【００２１】
また、超高分子量ポリエチレン樹脂パイプと外層パイプとの間には、超高分子量ポリエチレン樹脂パイプと外層パイプとの密着性を強固にするため、接着剤を介在させるようにしても構わない。
接着剤としては、超高分子量ポリエチレン樹脂パイプと外層パイプとを接着できるものであれば、特に限定されないが、例えば、マレイン酸, メタクリル酸, アクリル酸, メタクロリロニトリル酸等の不飽和カルボン酸、またはそれらの無水物で変性したポリエチレンやシラン変性したポリエチレン等が挙げられ, 、これらをホットメルトタイプの接着剤として使用できる。
【００２２】
接着剤は、超高分子量ポリエチレン樹脂パイプの外周面と、外層パイプの内周面との両方に均一に塗布しておくことが好ましい。
膨張させる場合の加熱方法としては、特に限定されず、例えば、エアーオーブン等の熱風による加熱、電熱ヒータによる加熱、液体熱媒槽による加熱、火炎等による加熱等の方法にて行うことができる。
【００２３】
膨張させる場合の加熱温度は、接着剤の使用有無により若干異なり、接着剤を使用しない場合、１００℃以上１６０℃以下が好ましく、１２０℃以上１４０℃以下がより好ましい。一方、接着剤を使用する場合、接着剤の融点＋１０℃以上１６０℃以下が好ましい、接着剤として前記の不飽和カルボン酸またはその無水物で変性したポリエチレンを用いる場合には、１４０℃以上１６０℃以下が好ましい。
【００２４】
請求項１の製造方法において、非反応性ガスとは、常温・常圧で気体状態の有機または無機物質であって、超高分子量ポリエチレン樹脂と反応を起こさず、さらにこの樹脂を劣化させるなどの悪影響を樹脂に与えないガスを意味する。
このようなガスとてしは、上記の条件を満たせば特に限定されず、例えば、二酸化炭素、窒素、アルゴン、ネオン、ヘリウム、酸素などの無機ガス、フロン、低分子量の炭化水素などの有機ガスなどが挙げられ、これらガスのうち、環境に与える悪影響が低く、そしてガスの回収を必要としない点で無機ガスが好ましく、超高分子量ポリエチレン樹脂に対する溶解度が高く、樹脂の可塑化効果が大きく、そして直接大気中に放出してもほとんど害がないという観点から、二酸化炭素が好ましい。なお、このような非反応性ガスは、単独で用いられてもよく、あるいは２種類以上併用してもよい。
【００２５】
超高分子量ポリエチレン樹脂に非反応性ガスを高圧下で溶解させる方法としては、非反応性ガスを溶融状態の樹脂に溶解させる方法、および固体状態の樹脂に溶解させる方法が挙げられ、どちらの手段を用いてもよく、両者を併用してもよい。
【００２６】
非反応性ガスを溶融状態の超高分子量ポリエチレン樹脂に溶解させる方法としては、例えば、ベントタイプスクリュー押出機を用いて、樹脂が充填されたシリンダーの途中からベント部分に非反応性ガスを混入する方法、タンデム押出機を用いて、第１押出機内部または第２押出機への樹脂流入部付近においてガスを圧入して第２押出機内部で十分樹脂中にガスを溶解・混練する方法などが挙げられる。
【００２７】
固体状態の樹脂に溶解させる方法としては、例えば、（１）予め高圧容器などでペレットまたはパウダー状の固体状態にある樹脂に非反応性ガスを溶解させておく方法、および（２）成形装置の耐圧ホッパ内および／または押出機の固体輸送部において非反応性ガスを固体状態にある樹脂中に溶解させる方法などが挙げられる。
【００２８】
上記（１）の方法の場合、非反応性ガスを溶解させた樹脂を押出機に供給する際には、樹脂に溶解した非反応性ガスが拡散によって樹脂の外へ抜けてしまうことを抑制するために、できるだけ速やかに供給を行うことが好ましい。一方、上記（２）の手段の場合には、非反応性ガスが押出機の外部に揮散しないように、スクリュー駆動軸およびホッパを耐圧シール構造とすることが好ましい。
【００２９】
非反応性ガスはガスボンベから押出機に直接供給してもよく、プランジャーポンプなどを用いて加圧供給しても良い。
超高分子量ポリエチレン樹脂に対する非反応性ガスの溶解量は、溶解によって樹脂の溶解粘度が成形に適した粘度になれば、特に限定されず、樹脂の分子量、非反応性ガスの種類によって適宜選択できる。
【００３０】
因みに、非反応性ガスとして二酸化炭素を用いる場合には、超高分子量ポリエチレン樹脂に対する二酸化炭素の溶解量を、１重量％以上３０重量％以下とすることが好ましく、３重量％以上２０重量％以下とすることがより好ましい。
【００３１】
すなわち、超高分子量ポリエチレン樹脂に対する二酸化炭素の溶解量が１重量％未満である場合には、超高分子量ポリエチレン樹脂の粘度が充分に低下せず、流動性に欠け押出が困難になる恐れがあり、超高分子量ポリエチレン樹脂に対する二酸化炭素の溶解量が３０重量％を超える量にしようとする場合、大がかりな設備を用いて溶解時の圧力を極端に高くする必要がある場合があり、生産効率上好ましくない。
【００３２】
非反応性ガスとして二酸化炭素が用いられる場合には、超高分子量ポリエチレン樹脂に対する二酸化炭素の溶解量を上記の１重量％以上３０重量％以下の範囲内とするためには、二酸化炭素の圧力を約０．２ＭＰａ以上約５０ＭＰａ以下とすることが好ましく、約０．６ＭＰａ以上約３５ＭＰａ以下とすることがより好ましい。
【００３３】
請求項１の製造方法において、超高分子量ポリエチレン樹脂パイプは、溶融混練によって得られた溶融樹脂を押出機の排出側に設けられた金型内で超高分子量ポリエチレン樹脂の（降温時の結晶化ピーク温度−２０℃）〜（融点＋２０℃）の温度に保ちながら、押出機のシリンダ内径より縮径した状態に賦形したのち、この賦形物を超高分子量ポリエチレン樹脂の降温時の結晶化ピーク温度以下の温度にして金型の排出口から押し出すことによって得られるが、請求項２の製造方法のように、入口側樹脂流路の断面積（Ｓ１）と出口側樹脂流路の断面積（Ｓ２）との比（Ｓ１／Ｓ２）が１．０（より好ましくは、１．５〜６０）より大きく、入口側樹脂流路の外径Ｄ₀ １と、出口側樹脂流路の外径Ｄ₀ ２の比（Ｄ₀ １／Ｄ₀ ２）が１．０５（より好ましくは１．１〜３．０）よりも大きい断面縮小部を有する金型を用いることが好ましい。
【００３４】
すなわち、上記（１）式に規定される膨張率（ｅ）は、比（Ｓ１／Ｓ２）、比（Ｄ₀ １／Ｄ₀ ２）および樹脂温度に大きく影響され、比（Ｓ１／Ｓ２）が１．０より小さい場合、発泡しやすく、賦形が困難になる恐れがあり、比（Ｓ１／Ｓ２）が大きすぎると、圧力が高くなりすぎて、押出が困難になる恐れがある。一方、比（Ｄ₀ １／Ｄ₀ ２）が１．０５より小さい場合、膨張率が小さく、外層パイプに対する被覆応力が小さくなる恐れがあり、大きすぎると、圧力が高くなるすぎて、押出が困難となったり、長手方向（管軸方向）の収縮が大きく、被覆効率が悪くなり好ましくない。
【００３５】
また、溶融状態の超高分子量ポリエチレン樹脂を断面縮小部に通過させた後の断面縮小部出口における樹脂の温度が融点を超える場合には、得られるパイプの機械強度を高くする効果が小さいという不都合が生じる恐れがある。
【００３６】
したがって、樹脂が金型内部の断面縮小部を通過する際の温度は、（降温時の結晶化ピーク温度−２０℃）以上（融点＋２０℃）の範囲が好ましく、（降温時の結晶化ピーク温度）以上（融点＋１０℃）以下の範囲がより好ましい。そして、断面縮小部の出口を通過する際は、融点以下の温度とすることが好ましい。
すなわち、（降温時の結晶化ピーク温度−２０℃）未満の場合には、樹脂はかなり硬化している状態になっているため、樹脂が断面縮小部を通過する際に必要な押出圧力が高くなり、樹脂を押し出すことができなくなる場合がある。一方、（融点＋２０℃）を越えた場合には、断面縮小部での樹脂の冷却が不十分であり、融点以下で樹脂を断面縮小部の出口から押し出すことができなくなる場合がある。
【００３７】
また、膨張率（ｅ）は、断面縮小部を通過している樹脂が、融点以下になる位置および出口断面での樹脂温度により調節することが可能であり、例えば、融点以下になる位置が入口側に近づくほど、また出口側での樹脂温度が低いほど膨張率（ｅ）が大きくなる。
さらに、樹脂の（降温時の結晶化ピーク温度）以下の条件で脱圧して押出成形すると、樹脂中に溶解しているガスの発泡を抑制することができ、内部に欠陥となる気泡が存在しないパイプを製造できる。一方、結晶化ピーク温度以上の条件で脱圧して押出成形すると、樹脂中に溶解しているガスが発泡して発泡体となり、押出後の加熱による膨張率が小さくなる。
【００３８】
この場合、脱圧は断面縮小部と流路が連続している金型内でガスを溶解している樹脂を冷却した後、その金型先端から押出すると同時に行うことができる。また、断面縮小部を有する金型から直ちに高圧賦形装置にガスを溶解している樹脂を導入し、この装置内で冷却しながら装置出口から押出すると同時に脱圧することも可能である。ここで、高圧の発生・保持は、液体、例えば、グリセリン等を密閉し、加圧する方法や樹脂を塑性変形させることで生じる圧力を利用する方法等を行うことができる。また、脱圧後に引取りを行うことでより安定して成形することができる。
【００３９】
なお、本発明において、「降温時の結晶化ピーク温度」とは、溶融状態の樹脂が冷却されて結晶化する際の結晶化ピーク温度を意味し、より詳細には、このような冷却の際に、樹脂が発熱する熱量が最大となる温度を意味する。「降温時の結晶化ピーク温度」は、大気圧下で示差走査型熱量計（ＤＳＣ）により測定され、ＪＩＳ Ｋ ７１２１の９．２にその求め方と共に詳細に記載されている。
金型は、その内面およびインナーダイの表面が、フッ素樹脂によって被覆されていることが好ましい。
【００４０】
本発明の製造方法において得られる複合パイプの形状は、円筒形だけでなく、金型の形状を適宜選択することによって、用途に合わせて異形パイプとすることができる。例えば、金型流路を断面角形や断面楕円形等にすれば、これに対応した外形を有する異形の超高分子量ポリエチレン樹脂パイプを得ることができる。
【００４１】
【発明の実施の形態】
以下、本発明の実施の形態を図面と共に詳細に説明する。
図１は本発明にかかる複合パイプの製造方法に内層パイプとして用いられる超高分子量ポリエチレン樹脂パイプの成形装置の１例をあらわしている。
【００４２】
本発明に係る複層パイプの製造方法は、図１に示すように、まず、耐圧構造になったホッパ（１６）から超高分子量ポリエチレン樹脂を押出機（１）内に供給する。
【００４３】
そして、押出機（１）に供給された超高分子量ポリエチレン樹脂を、押出機（１）のシリンダ（１９）内に備えられたスクリュー（２）によって固体輸送部（３）中を、図面右方向に向かって送ると同時に、押出機（１）に設けられた加熱手段（図示せず）により加熱して溶融状態とする。また、ガスボンベ（１０）から供給される二酸化炭素を加圧ポンプ（１２）を用いて加圧し、次いでこの高圧状態の二酸化炭素を、固体輸送部（３）に設けられたガス供給口（１４）より押出機（１）内に供給し、溶融状態の樹脂を非反応性ガスに曝して、樹脂中に非反応性ガスを溶解させ、樹脂の粘度を低くする。
【００４４】
さらに樹脂をスクリュー（２）によって液状物輸送部（４）に送り、この液状物輸送部（４）で加熱手段によってさらに加熱するとともに、ガスボンベ（１１）から供給され加圧ポンプ（１３）を用いて加圧された高圧状態の非反応性ガスを、液状物輸送部（４）に設けられたガス供給口（１５）より押出機（１）内に供給する。
【００４５】
すなわち、ガス供給口（１５）からの非反応性ガスの供給によって、溶融した樹脂中に非反応性ガスがさらに溶解し、樹脂の粘度がさらに低くなり、易成形状態の溶融超高分子量ポリエチレン樹脂となる。なお、樹脂に対するガスの溶解量によって、上記のようにガス供給口（１４）（１５）を２つ用いてもよく、またはいずれか１つのガス供給口のみを用いても良い。
【００４６】
つぎに、上記のようにして易成形状態になった溶融超高分子量ポリエチレン樹脂を図１〜図３に示すように、入口側樹脂流路（６１）の断面積（Ｓ１）と出口側樹脂流路（６２）の断面積（Ｓ２）との比（Ｓ１／Ｓ２）が１．０より大きく、入口側樹脂流路（６１）の外径Ｄ₀ １と、出口側樹脂流路（６２）の外径Ｄ₀ ２の比（Ｄ₀ １／Ｄ₀ ２）が１．０５よりも大きい断面縮小部（６）を有する押出機（１）の排出口に設けられた金型（５）に連続的に供給する。
【００４７】
そして、断面縮小部（６）を通過させながら、溶融超高分子量ポリエチレン樹脂を超高分子量ポリエチレン樹脂の（降温時の結晶化ピーク温度−２０℃）〜（融点＋２０℃）の温度に保ちながら、押出機（１）のシリンダ（１９）内径より縮径した状態、すなわち、出口側樹脂流路（６２）の断面形状に賦形したのち、この賦形物を金型の排出口から超高分子量ポリエチレン樹脂の融点以下の温度にして押し出して膨張率（ｅ）が５％以上の図４に示すような円筒形の超高分子量ポリエチレン樹脂パイプＰ１を得る。
【００４８】
つぎに、図４（ａ）に示すように、この超高分子量ポリエチレン樹脂パイプＰ１を、その内径（ｄ）が超高分子量ポリエチレン樹脂パイプＰ１の外径（Ｄ）より大きい外層パイプＰ２内に遊嵌したのち、この状態で熱風加熱炉中に投入し、超高分子量ポリエチレン樹脂パイプＰ１を膨張させて、図４（ｂ）および図５に示すように、外層パイプＰ２の内周面に膨張した超高分子量ポリエチレン樹脂パイプＰ１´の外周面が圧接し、外層パイプＰ２の内側に超高分子量ポリエチレン樹脂パイプＰ１´が固定された複層パイプＰを得るようになっている。
【００４９】
この製造方法によれば、加熱して超高分子量ポリエチレン樹脂パイプＰ１を膨張させるだけで複層パイプを得ることができるため、製造設備が小規模なものですみ、設備コストがかからない。
さらに、内層パイプとして、超高分子量ポリエチレン樹脂パイプＰ１を用いたので、耐磨耗性、非粘着性、自己潤滑性、耐薬品性に優れており、鉱石，石炭，穀物等の粉粒体、岩石を含む泥水、生コンクリートの如きスラリー、あるいは、液体食品等の輸送管として好適に使用できる複層パイプを得ることができる。
【００５０】
一方、超高分子量ポリエチレン樹脂パイプＰ１を製造する際に、樹脂中に非反応性ガスを溶解させることにより樹脂が可塑化するようにしたので、容易に成形が可能になる。
しかも、超高分子量ポリエチレン樹脂に非反応性ガスを溶解した状態で金型（５）に溶融樹脂が導入され、金型（５）の断面縮小部（６）で縮径されながら融点以下まで冷却されるため、縮径前の形状を記憶した状態で固化する。したがって、再加熱により形状記憶効果があらわれて、５％以上の膨張率（ｅ）となる。
【００５１】
また、降温時の結晶化ピーク温度以下の温度まで冷却した後、押し出して脱圧するので、超高分子量ポリエチレン樹脂中に溶解している非反応性ガスによる発泡を抑制することができ、内部に欠陥となる気泡を含まない超高分子量ポリエチレン樹脂パイプＰ１を得ることができる。
【００５２】
【実施例】
以下、実施例により本発明を具体的に説明するが、以下の実施例は例示の目的にのみ用いられ、限定の目的に用いられてはならない。
【００５３】
（実施例１）
超高分子量ポリエチレン（三井石油化学工業株式会社製「ハイゼックス・ミリオン２４０Ｍ」、粘度平均分子量２３０万、融点１３６℃、降温時の結晶化ピーク温度１１８℃）を図１に示す成形装置の耐圧ホッパ（１６）から単軸押出機（１、スクリュー径４０ｍｍ、Ｌ／Ｄ＝３０）に供給した。非反応性ガスとして二酸化炭素を用い、これをガス供給口（１４）（１５）から押出機（１）の固体輸送部（３）および液状物輸送部（４）に１５ＭＰａの圧力で圧入した。この圧力下における超高分子量ポリエチレンに対する二酸化炭素の溶解量は約１０重量％であった。なお、この時、押出機（１）はスクリュー駆動軸の高圧軸シール機構、耐圧ホッパ構造、および押出機近傍の溶融状態の超高分子量ポリエチレンにより、押出機（１）内の二酸化炭素を高圧状態に保持した。次いで、押出機（１）に供給された樹脂は、その内部で、押出量５kg／ｈ、スクリュー回転数１０ｒｐｍ、バレル設定温度２００℃の条件下で充分に溶融混練した。
【００５４】
続いて、この溶融混練した樹脂をバイプ用の金型（５）に通過させてパイプ状に押し出し、外径５２．２mm、内径４７．８mmの超高分子量ポリエチレン樹脂パイプを得た。得られた超高分子量ポリエチレン樹脂パイプは、上記式（１）の計算式で得られた膨張率（ｅ）が２０％であった。
【００５５】
なお、金型（５）は、断面縮小部（６）の入口側樹脂流路（６１）の断面（外径７０mm、内径６５mm）、出口側樹脂流路（６２）の断面（外径５２mm、内径４８mm）、Ｓ１／Ｓ２＝１．７、Ｄ₀ １／Ｄ₀ ２＝１．３で、金型出口側（外径５２mm、内径４８mm）であって、断面縮小部（６）が１２０℃、金型出口が１０５℃を保持した。また、断面縮小部（６）を通過する樹脂の温度は、断面縮小部（６）の入口側樹脂流路（６１）で１４０℃、出口側樹脂流路（６２）で１２０℃、金型出口で１０５℃であった。
【００５６】
このようにして得られた５．７ｍの超高分子量ポリエチレン樹脂パイプを、内径５４mm、長さ５．５ｍの外層パイプとなる配管用炭素鋼管に挿入し、この挿入状態を保ち水平移動しながら、上下方向から熱風の吹き出す熱風加熱装置内を往復動させ管中央から管両端にかけて１３０℃で１時間加熱した。その後、室温で４０分間冷却して図 に示すように、鋼管の内周面に沿って膨張した超高分子量ポリエチレン樹脂パイプからなるライニング層が形成された複層パイプを得た。得られた複層パイプは、超高分子量ポリエチレン樹脂パイプが膨張してその外周面が鋼管の内周面に密着した状態で圧接されていた。
【００５７】
（比較例１）
二酸化炭素を超高分子量ポリエチレン樹脂に溶解させなかった以外は、実施例１と同様にして超高分子量ポリエチレン樹脂パイプを押出成形しようとしたが、圧力が押出機の耐圧（１００ＭＰａ）を越えてしまい、押出不能になってしまった。
【００５８】
（比較例２）
金型（５）の断面縮小部（６）の加熱温度を１４０℃とし、断面縮小部（６）を通過する樹脂の温度を、入口側樹脂流路（６１）で１６５℃、出口側樹脂流路（６２）で１４０℃とした以外は、実施例１と同様にして外径５２．２mm、内径４７．８mmの超高分子量ポリエチレン樹脂パイプを得た。得られた超高分子量ポリエチレン樹脂パイプは、膨張率が２％であった。
【００５９】
このようにして得られた５．７ｍの超高分子量ポリエチレン樹脂パイプを、内径５３mm、長さ５．５ｍの外層パイプとなる配管用炭素鋼管に挿入し、実施例１と同様にして複層パイプを得ようとしたが、超高分子量ポリエチレン樹脂パイプの膨張が不十分で膨張した超高分子量ポリエチレン樹脂パイプの外周面が鋼管の内周面に密着した状態にならなかった。
【００６０】
（比較例３）
金型（５）の出口温度を１２５℃に保ち、金型（５）から押し出される樹脂の温度１２５℃とした以外は、実施例１と同様にして超高分子量ポリエチレン樹脂パイプを押出成形した。得られた超高分子量ポリエチレン樹脂パイプは、外径が５４mm、内径が４６mmで発泡しており、膨張率は０．５％であった。
【００６１】
（比較例４）
二酸化炭素を超高分子量ポリエチレン樹脂に溶解させないで、金型（５）の断面縮小部（６）の加熱温度を１４０℃とし、断面縮小部（６）を通過する樹脂の温度を、入口側樹脂流路（６１）で１６５℃、出口側樹脂流路（６２）で１４０℃とした以外は、実施例１と同様にして外径５２．２mm、内径４７．８mmの超高分子量ポリエチレン樹脂パイプを得た。得られた超高分子量ポリエチレン樹脂パイプは、膨張率が３％であった。
【００６２】
このようにして得られた５．７ｍの超高分子量ポリエチレン樹脂パイプを、内径５３mm、長さ５．５ｍの外層パイプとなる配管用炭素鋼管に挿入し、実施例１と同様にして複層パイプを得ようとしたが、超高分子量ポリエチレン樹脂パイプの膨張が不十分で膨張した超高分子量ポリエチレン樹脂パイプの外周面が鋼管の内周面に密着した状態にならなかった。
【００６３】
（比較例５）
断面縮小部（６）の入口側樹脂流路（６１）の断面（外径５４mm、内径４８mm）、出口側樹脂流路（６２）の断面（外径５２mm、内径４８mm）、Ｓ１／Ｓ２＝１．５、Ｄ₀ １／Ｄ₀ ２＝１．０４とした以外は、実施例１と同様にして外径５２．２mm、内径４７．８mmの超高分子量ポリエチレン樹脂パイプを得た。得られた超高分子量ポリエチレン樹脂パイプは、膨張率が０．８％であった。
【００６４】
（比較例６）
断面縮小部（６）の入口側樹脂流路（６１）の断面（外径７０mm、内径６７．５mm）、出口側樹脂流路（６２）の断面（外径５２mm、内径４８mm）、Ｓ１／Ｓ２＝０．９、Ｄ₀ １／Ｄ₀ ２＝１．３とした以外は、実施例１と同様にして押出成形を行ったが、発泡が激しく起こり、押出困難となった。
【００６５】
【発明の効果】
本発明にかかる複層パイプの製造方法は、以上のように構成されているので、耐磨耗性、非粘着性、自己潤滑性、耐薬品性に優れており、鉱石，石炭，穀物等の粉粒体、岩石を含む泥水、生コンクリートの如きスラリー、あるいは、液体食品等の輸送管として好適に使用できる複層パイプを、製造設備が小規模で、設備コストをかけずに製造することができる。
【００６６】
また、加熱により自然に膨張する超高分子量ポリエチレン樹脂パイプを効率よく、かつ容易に製造することができる。
【図面の簡単な説明】
【図１】本発明にかかる複層パイプの製造方法に用いられる超高分子量ポリエチレン樹脂パイプの成形装置の１例をあらわす概略図である。
【図２】図１のＸ−Ｘ線断面図である。
【図３】図１のＹ−Ｙ線断面図である。
【図４】複層パイプの超高分子量ポリエチレン樹脂パイプと外層パイプの固定方法を説明する断面図である。
【図５】本発明にかかる複層パイプの製造方法で得られる複層パイプの斜視図である。
【符号の説明】
１ 押出機
１９ シリンダ
５ 金型
６ 断面縮小部
６１ 入口側樹脂流路
６２ 出口側樹脂流路
Ｐ 複層パイプ
Ｐ１ 超高分子量ポリエチレン樹脂パイプ
Ｐ１´ 膨張した超高分子量ポリエチレン樹脂パイプ
Ｐ２ 外層パイプ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a multi-layer pipe, and more particularly to a method for producing a multi-layer pipe that is excellent in wear resistance, non-adhesiveness, self-lubrication, and chemical resistance and can be suitably used for various applications. .
[0002]
[Prior art]
Conventionally, pipes used for underground underground pipes for water and sewage, building pipes, hot water pipes, gas pipes, chemical pipes, etc., are resin lining with a galvanized layer or vinyl chloride resin or polyethylene resin on the inner surface of metal pipes. A multi-layer pipe is used in which the corrosion resistance of the pipe inner surface is improved by forming a layer.
However, in the case of the above conventional multi-layer pipe, when used as a transport pipe for powders such as ores, coal, grains, etc., mud containing rocks, slurries such as ready-mixed concrete, or liquid food, transport goods and pipes Friction with the inner wall causes a large wear loss, and there is a problem in terms of durability. In addition, zinc powder and resin powder scraped by friction are mixed in the transported goods, and the transported goods are contaminated. In particular, when the transported product is a liquid food or the like, there is a problem of toxicity.
[0003]
Therefore, a multi-layer pipe using an ultrahigh molecular weight polyethylene resin excellent in abrasion resistance, non-adhesiveness, self-lubricating property, and chemical resistance as a lining layer has already been proposed (see JP-A-5-24153). ).
[0004]
In this multilayer pipe, an ultra-high molecular weight polyethylene resin pipe having an outer diameter smaller than the inner diameter of the steel pipe and having a thin wall is loosely fitted inside the steel pipe to be an outer layer pipe, and the ultra-high molecular weight polyethylene resin pipe is heated. Applying pressure from the inside to the ultra high molecular weight polyethylene resin pipe to expand the diameter of the ultra high molecular weight polyethylene resin pipe and applying the adhesive to the outer peripheral surface of the ultra high molecular weight polyethylene resin pipe and / or the inner peripheral surface of the steel pipe in advance It is manufactured by bonding and fixing a steel pipe and an expanded ultra-high molecular weight polyethylene resin pipe via a pipe.
[0005]
However, in the case of the above multi-layer pipe, in order to expand the diameter of the ultra high molecular weight polyethylene resin pipe, it is necessary to send pressurized air into the ultra high molecular weight polyethylene resin pipe. Therefore, there is a problem that the equipment cost is too high.
[0006]
[Problems to be solved by the invention]
In view of the circumstances as described above, the present invention provides a method for producing a multi-layer pipe that does not need to keep the inside of an ultra-high molecular weight polyethylene resin pipe airtight, requires only a small-scale production facility, and does not require equipment costs. The purpose is to do.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the manufacturing method of the multilayer pipe according to the first aspect of the present invention (the manufacturing method of the first aspect) includes an inner layer pipe made of synthetic resin in the outer layer pipe. In a method for producing a multi-layer pipe fixed in an interpolated state, an ultrahigh molecular weight polyethylene resin made into an easily molded state by dissolving a non-reactive gas in a gaseous state at normal temperature and normal pressure under high pressure is used in an extruder. In the mold provided on the discharge side of the extruder, the melted resin obtained by melt kneading is melted and kneaded with ultrahigh molecular weight polyethylene resin (crystallization peak temperature at the time of cooling-20 ° C) to (melting point + 20 ° C). ) While maintaining the temperature of the extruder, the shape is reduced to a diameter smaller than the cylinder inner diameter of the extruder, and then this shaped product is set to a temperature equal to or lower than the crystallization peak temperature when the ultrahigh molecular weight polyethylene resin is cooled. Extruded from the exit and down (1)
[0008]
[Expression 2]

so expressed After the ultrahigh molecular weight polyethylene resin pipe having an expansion coefficient (e) of 5% or more is loosely fitted in the outer layer pipe as an inner layer pipe, the ultrahigh molecular weight polyethylene resin pipe is heated and expanded to expand the ultrahigh molecular weight polyethylene resin. It was set as the structure provided with the process of press-contacting the outer peripheral surface of a pipe to the inner peripheral surface of an outer-layer pipe.
[0010]
Claims of the invention 2 A method for producing a multilayer pipe according to the invention described in claim 1 2 Manufacturing method) 1 In this manufacturing method, the mold includes a cross-sectional reduced portion that shapes the molten resin into a state in which the molten resin is reduced in diameter from the cylinder inner diameter of the extruder, and the cross-sectional reduced portion has a cross-sectional area (S1) of the inlet-side resin flow path. The ratio (S1 / S2) to the sectional area (S2) of the outlet side resin flow path is larger than 1.0, and the outer diameter D of the inlet side resin flow path ₀ 1 and the outer diameter D of the outlet side resin flow path ₀ Ratio of 2 (D ₀ 1 / D ₀ 2) was configured to be larger than 1.05.
[0011]
Further, in the present invention, the outer layer pipe is not particularly limited as long as it has heat resistance that can withstand the heating temperature for expansion and pressure welding of the inner layer pipe and rigidity that can withstand the pressure of expansion and pressure welding, For example, the thing made from a metal, the thing made from fiber reinforced plastics (FRP), etc. are mentioned.
Moreover, it does not specifically limit as a metal material which can be used as an outer layer pipe, For example, light alloys, such as general-purpose steel, such as carbon steel and cast steel, special steel, such as stainless steel and chromium steel, copper alloy, and aluminum.
[0012]
Although it does not specifically limit as fiber reinforced plastic, For example, what impregnated reinforcement fibers, such as glass fiber and carbon fiber, with thermosetting resin etc. is mentioned.
Although it does not specifically limit as a thermosetting resin, For example, an epoxy resin, a phenol resin, unsaturated polyester resin etc. can be used.
[0013]
The inner layer pipe is limited to an ultrahigh molecular weight polyethylene resin pipe having an expansion coefficient (e) defined by the above formula (1) of 5% or more, but is preferably 5% or more and 100% or less.
That is, if the expansion coefficient (e) exceeds 100%, the contraction in the longitudinal direction (in the tube axis direction) increases during coating, and the coating efficiency may deteriorate. If it is less than 5%, the coating stress on the outer layer pipe to be coated becomes small, and the adhesion to the outer layer pipe is lowered.
[0014]
The diameter and wall thickness of the ultrahigh molecular weight polyethylene resin pipe before heating and expansion are not particularly limited, but the outer diameter (D) is preferably 10 mm or more and the wall thickness (t) is preferably 0.1 mm or more. Further, as an economically moldable range, the outer diameter (D) is more preferably 15 mm or more and 300 mm or less, and the wall thickness (t) is 0.3 mm or more and 0.8 mm or less. The ratio of outer diameter (D) / thickness (t) is preferably 10 or more and 300 or less, and the ratio of outer diameter (D) / thickness (t) is 15 in that a pipe having good rigidity can be obtained. More preferably, it is 200 or less.
[0015]
The ultrahigh molecular weight polyethylene resin forming the ultrahigh molecular weight polyethylene resin pipe is not particularly limited, but preferably has a viscosity average molecular weight of 300,000 or more, more preferably 1,000,000 to 10,000,000.
That is, as the molecular weight increases, properties such as wear resistance and chemical resistance are further improved. However, if the molecular weight exceeds 10 million, molding becomes very difficult. As long as the object of the present invention can be achieved, those having a viscosity average molecular weight of less than 300,000 may be mixed.
[0016]
In the present invention, the ultra-high molecular weight polyethylene resin is mainly composed of ethylene, for example, a homopolymer of ethylene, a main component of ethylene, and a single amount copolymerizable with ethylene. And a copolymer with the body.
[0017]
The monomer copolymerizable with ethylene is not particularly limited, and examples thereof include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Monoolefin; 1,3-butadiene, 2-methyl-2,4-pentadiene, 2,3-dimethyl-1,3-butadiene, 2,4-hexadiene, 3-methyl-2,4-hexadiene, 1,3 -Conjugated diene hydrocarbon compounds such as pentadiene and 2-methyl-1,3-butadiene; 1,4-petanediene, 1,5-hexadiene, 1,6-heptadiene, 1,7-octadiene, 2,5-dimethyl -1,5-hexadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4-hexadiene, 4-ethyl-1,4-octadiene, 4-n-propiene Non-conjugated diene hydrocarbon compounds such as 1,4-decadiene; conjugated polyolefins such as 1,3,5-hexatriene, 1,3,5,7-octatetraene and 2-vinyl-1,3-butadiene Non-conjugated polyolefin hydrocarbon compounds such as squalene; other hydrocarbon compounds having at least two unsaturated bonds, preferably double bonds in the molecule, such as divinylbenzene and vinylnorbornene.
[0018]
Furthermore, in the ultra high molecular weight polyethylene resin, other synthetic resins and natural resins, plasticizers, heat stabilizers, weathering stabilizers, lubricants, antiblocking agents, slips can be used as long as the object of the present invention can be achieved. You may make it mix | blend an agent, a pigment, dye, a filler, etc.
[0019]
In the present invention, loose fitting means that the outer diameter of the ultrahigh molecular weight polyethylene resin pipe is smaller than the inner diameter of the outer layer pipe, and the ultrahigh molecular weight polyethylene resin pipe can slide freely in the axial direction of the outer layer pipe when inserted. .
Specifically, the outer diameter of the ultrahigh molecular weight polyethylene resin pipe is preferably 1% or more and 30% or less smaller than the inner diameter of the outer layer pipe. That is, if it is less than 1%, it may be difficult to insert into the outer layer pipe, and if it exceeds 30%, the covering stress on the outer layer pipe may be reduced, and the adhesion to the outer layer pipe may be reduced. At the same time, the shrinkage in the longitudinal direction (tube axis direction) of the heating expander is large, and the coating efficiency may be deteriorated.
[0020]
In the present invention, the pressure contact means that an ultrahigh molecular weight polyethylene resin pipe at the heating temperature is loosely fitted to the outer pipe by a measurement method in which the temperature of the expansion coefficient (e) defined above is replaced with an actual heating temperature. Thereafter, the actual expansion coefficient of the ultrahigh molecular weight polyethylene resin pipe (e ₁ ) Is a state in which the outer layer pipe is coated on the inner surface under the condition that the coefficient of expansion is larger than that necessary for closing the gap with the outer layer pipe that is also thermally expanded by heating.
That is, in this pressure welding, residual stress is generated in the direction of expanding the outer layer pipe inside the ultra high molecular weight polyethylene resin pipe, and the expanded ultra high molecular weight polyethylene resin pipe and the outer layer pipe are firmly adhered. These conditions can be achieved by adjusting the mold channel shape and temperature conditions during the production of the ultrahigh molecular weight polyethylene resin pipe.
[0021]
Further, an adhesive may be interposed between the ultrahigh molecular weight polyethylene resin pipe and the outer layer pipe in order to strengthen the adhesion between the ultrahigh molecular weight polyethylene resin pipe and the outer layer pipe.
The adhesive is not particularly limited as long as it can bond the ultrahigh molecular weight polyethylene resin pipe and the outer layer pipe. For example, unsaturated carboxylic acid such as maleic acid, methacrylic acid, acrylic acid, methacrylonitrile acid, Examples thereof include polyethylene modified with anhydrides thereof and polyethylene modified with silane, and these can be used as hot melt type adhesives.
[0022]
The adhesive is preferably applied uniformly to both the outer peripheral surface of the ultrahigh molecular weight polyethylene resin pipe and the inner peripheral surface of the outer layer pipe.
The heating method in the case of expansion is not particularly limited, and for example, heating by hot air such as an air oven, heating by an electric heater, heating by a liquid heat medium tank, heating by a flame or the like can be performed.
[0023]
The heating temperature in the case of expansion varies slightly depending on whether or not an adhesive is used. When no adhesive is used, it is preferably 100 ° C. or higher and 160 ° C. or lower, and more preferably 120 ° C. or higher and 140 ° C. or lower. On the other hand, when an adhesive is used, the melting point of the adhesive is preferably + 10 ° C. or more and 160 ° C. or less. When the polyethylene modified with the unsaturated carboxylic acid or its anhydride is used as the adhesive, 140 ° C. or more and 160 ° C. The following is preferred.
[0024]
Claim 1 In this manufacturing method, the non-reactive gas is an organic or inorganic substance in a gaseous state at normal temperature and normal pressure, and does not react with the ultrahigh molecular weight polyethylene resin, and further has an adverse effect such as deteriorating the resin. Means no gas to give to.
Such a gas is not particularly limited as long as the above conditions are satisfied. For example, an inorganic gas such as carbon dioxide, nitrogen, argon, neon, helium, oxygen, or an organic gas such as chlorofluorocarbon or low molecular weight hydrocarbon. Among these gases, inorganic gas is preferable in that the adverse effect on the environment is low, and recovery of the gas is not required, the solubility in the ultrahigh molecular weight polyethylene resin is high, and the plasticizing effect of the resin is large. Carbon dioxide is preferred from the standpoint that there is almost no harm when released directly into the atmosphere. Such non-reactive gases may be used alone or in combination of two or more.
[0025]
Examples of the method for dissolving the non-reactive gas in the ultrahigh molecular weight polyethylene resin under high pressure include a method in which the non-reactive gas is dissolved in the molten resin and a method in which the non-reactive gas is dissolved in the solid resin. May be used, or both may be used in combination.
[0026]
As a method for dissolving the non-reactive gas in the melted ultra high molecular weight polyethylene resin, for example, using a vent type screw extruder, the non-reactive gas is mixed into the vent portion from the middle of the cylinder filled with the resin. And a method of using a tandem extruder to press-fit a gas in the first extruder or in the vicinity of the resin inflow portion to the second extruder and sufficiently dissolve and knead the gas in the resin in the second extruder. Can be mentioned.
[0027]
Examples of the method for dissolving in a solid state resin include (1) a method in which a non-reactive gas is dissolved in a pellet or powdery resin in advance in a high-pressure vessel or the like, and (2) a molding apparatus. Examples include a method in which a non-reactive gas is dissolved in a resin in a solid state in a pressure hopper and / or in a solid transport part of an extruder.
[0028]
In the case of the above method (1), when the resin in which the non-reactive gas is dissolved is supplied to the extruder, the non-reactive gas dissolved in the resin is prevented from escaping out of the resin due to diffusion. Therefore, it is preferable to supply as soon as possible. On the other hand, in the case of the above means (2), it is preferable that the screw drive shaft and the hopper have a pressure-resistant seal structure so that the non-reactive gas does not volatilize outside the extruder.
[0029]
The non-reactive gas may be supplied directly from the gas cylinder to the extruder, or may be supplied under pressure using a plunger pump or the like.
The amount of the non-reactive gas dissolved in the ultra-high molecular weight polyethylene resin is not particularly limited as long as the resin has a viscosity suitable for molding by dissolution, and can be appropriately selected depending on the molecular weight of the resin and the type of the non-reactive gas. .
[0030]
Incidentally, when carbon dioxide is used as the non-reactive gas, the amount of carbon dioxide dissolved in the ultrahigh molecular weight polyethylene resin is preferably 1% by weight to 30% by weight, and preferably 3% by weight to 20% by weight. More preferably.
[0031]
That is, when the amount of carbon dioxide dissolved in the ultrahigh molecular weight polyethylene resin is less than 1% by weight, the viscosity of the ultrahigh molecular weight polyethylene resin is not sufficiently lowered, and there is a possibility that extrusion is difficult due to lack of fluidity. If the amount of carbon dioxide dissolved in the ultra-high molecular weight polyethylene resin exceeds 30% by weight, it may be necessary to increase the pressure during dissolution using a large-scale facility, which increases production efficiency. It is not preferable.
[0032]
When carbon dioxide is used as the non-reactive gas, the carbon dioxide pressure should be adjusted so that the amount of carbon dioxide dissolved in the ultrahigh molecular weight polyethylene resin is within the range of 1 wt% to 30 wt%. The pressure is preferably about 0.2 MPa to about 50 MPa, more preferably about 0.6 MPa to about 35 MPa.
[0033]
Claim 1 In the production method of the above, the ultrahigh molecular weight polyethylene resin pipe is obtained by melting the melted resin obtained by melt kneading in the mold provided on the discharge side of the extruder (crystallization peak temperature at the time of cooling- 20 ° C.) to (melting point + 20 ° C.) while maintaining a temperature reduced from the cylinder inner diameter of the extruder, this shaped product is below the crystallization peak temperature when the ultra high molecular weight polyethylene resin is cooled. Can be obtained by extruding from a mold outlet at a temperature of 2 The ratio (S1 / S2) of the cross-sectional area (S1) of the inlet-side resin flow path to the cross-sectional area (S2) of the outlet-side resin flow path is 1.0 (more preferably 1.5). ~ 60) larger than the outer diameter D of the inlet side resin flow path ₀ 1 and the outer diameter D of the outlet side resin flow path ₀ Ratio of 2 (D ₀ 1 / D ₀ It is preferable to use a mold having a cross-sectional reduced portion where 2) is larger than 1.05 (more preferably 1.1 to 3.0).
[0034]
That is, the expansion coefficient (e) defined in the above equation (1) is the ratio (S1 / S2), the ratio (D ₀ 1 / D ₀ 2) If the ratio (S1 / S2) is less than 1.0, the ratio is greatly affected by the resin temperature, and foaming tends to be difficult and shaping may be difficult. If the ratio (S1 / S2) is too large, the pressure May become too high and extrusion may be difficult. On the other hand, the ratio (D ₀ 1 / D ₀ If 2) is smaller than 1.05, the expansion coefficient is small and the coating stress on the outer layer pipe may be small. If it is too large, the pressure becomes too high and extrusion becomes difficult, or the longitudinal direction (tube axis) (Direction) is large and the coating efficiency is unfavorable.
[0035]
In addition, when the temperature of the resin at the exit of the cross-sectional reduced portion after passing the melted ultrahigh molecular weight polyethylene resin through the cross-sectional reduced portion exceeds the melting point, there is a disadvantage that the effect of increasing the mechanical strength of the obtained pipe is small. May occur.
[0036]
Therefore, the temperature at which the resin passes through the reduced cross-section inside the mold is preferably (crystallization peak temperature at the time of cooling-20 ° C) or more (melting point + 20 ° C), and (crystallization peak temperature at the time of cooling) ) Or more (melting point + 10 ° C.) or less. And when passing the exit of a cross-sectional reduction part, it is preferable to set it as the temperature below melting | fusing point.
That is, when the temperature is lower than (crystallization peak temperature at lower temperature −20 ° C.), the resin is in a considerably hardened state, and therefore the extrusion pressure required when the resin passes through the cross-section reduced portion is high. Therefore, the resin may not be extruded. On the other hand, when the temperature exceeds (melting point + 20 ° C.), the resin is not sufficiently cooled at the cross-sectional reduced portion, and the resin may not be pushed out from the outlet of the cross-sectional reduced portion below the melting point.
[0037]
In addition, the expansion coefficient (e) can be adjusted by the position where the resin passing through the cross-sectionally reduced portion is equal to or lower than the melting point and the resin temperature at the outlet cross section. The closer to the side, the lower the resin temperature on the outlet side, the greater the expansion coefficient (e).
Furthermore, if the resin is depressurized and extruded under the conditions below the crystallization peak temperature when the resin is cooled, foaming of the gas dissolved in the resin can be suppressed, and there are no defective bubbles inside. Can produce pipes. On the other hand, when depressurization and extrusion molding are performed at a temperature equal to or higher than the crystallization peak temperature, the gas dissolved in the resin is foamed to form a foam, and the expansion coefficient due to heating after extrusion becomes small.
[0038]
In this case, the depressurization can be performed simultaneously with the extrusion from the tip of the mold after cooling the resin dissolving the gas in the mold in which the cross-section reduced portion and the flow path are continuous. It is also possible to introduce a resin in which a gas is dissolved into a high-pressure shaping device immediately from a mold having a cross-sectionally reduced portion, and while extruding from the device outlet while cooling in this device, it is possible to release the pressure at the same time. Here, the generation and maintenance of the high pressure can be performed by a method of sealing and pressurizing a liquid, for example, glycerin or the like, a method of using a pressure generated by plastic deformation of a resin, or the like. Moreover, it can shape | mold more stably by taking out after depressurization.
[0039]
In the present invention, the “crystallization peak temperature during cooling” means the crystallization peak temperature when the molten resin is cooled and crystallized, and more specifically, during such cooling. In addition, it means a temperature at which the amount of heat generated by the resin is maximized. The “crystallization crystallization peak temperature at the time of temperature drop” is measured by a differential scanning calorimeter (DSC) under atmospheric pressure, and is described in detail in 9.2 of JIS K 7121 together with the method for obtaining it.
The inner surface of the mold and the surface of the inner die are preferably coated with a fluororesin.
[0040]
The shape of the composite pipe obtained in the production method of the present invention is not limited to a cylindrical shape, but can be a deformed pipe according to the application by appropriately selecting the shape of the mold. For example, if the mold channel has a square cross section, an elliptical cross section, or the like, an unusually shaped ultrahigh molecular weight polyethylene resin pipe having an outer shape corresponding to this can be obtained.
[0041]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows an example of an apparatus for forming an ultrahigh molecular weight polyethylene resin pipe used as an inner layer pipe in the method for producing a composite pipe according to the present invention.
[0042]
In the method for producing a multilayer pipe according to the present invention, as shown in FIG. 1, first, an ultrahigh molecular weight polyethylene resin is supplied into an extruder (1) from a hopper (16) having a pressure resistant structure.
[0043]
Then, the ultrahigh molecular weight polyethylene resin supplied to the extruder (1) is passed through the solid transport section (3) by the screw (2) provided in the cylinder (19) of the extruder (1), and rightward in the drawing. Simultaneously, it is heated by a heating means (not shown) provided in the extruder (1) to be in a molten state. Further, the carbon dioxide supplied from the gas cylinder (10) is pressurized using the pressure pump (12), and then the high-pressure carbon dioxide is supplied to the gas supply port (14) provided in the solid transport section (3). Further, the resin is supplied into the extruder (1), and the molten resin is exposed to a non-reactive gas, so that the non-reactive gas is dissolved in the resin and the viscosity of the resin is lowered.
[0044]
Further, the resin is sent to the liquid material transport section (4) by the screw (2), and further heated by the heating means in the liquid material transport section (4), and supplied from the gas cylinder (11) using the pressure pump (13). The high-pressure nonreactive gas thus pressurized is supplied into the extruder (1) from the gas supply port (15) provided in the liquid material transport section (4).
[0045]
That is, by supplying the non-reactive gas from the gas supply port (15), the non-reactive gas is further dissolved in the melted resin, and the viscosity of the resin is further reduced. It becomes. Depending on the amount of gas dissolved in the resin, two gas supply ports (14) and (15) may be used as described above, or only one gas supply port may be used.
[0046]
Next, as shown in FIGS. 1 to 3, the melted ultra-high molecular weight polyethylene resin that has been easily molded as described above has a cross-sectional area (S1) of the inlet-side resin flow path (61) and the outlet-side resin flow. The ratio (S1 / S2) to the cross-sectional area (S2) of the channel (62) is greater than 1.0, and the outer diameter D of the inlet side resin channel (61) ₀ 1 and the outer diameter D of the outlet side resin flow path (62) ₀ Ratio of 2 (D ₀ 1 / D ₀ 2) is continuously fed to the mold (5) provided at the discharge port of the extruder (1) having the cross-sectional reduction part (6) larger than 1.05.
[0047]
And while maintaining the temperature of the ultrahigh molecular weight polyethylene resin (crystallization peak temperature at the time of cooling-20 ° C) to (melting point + 20 ° C) of the ultrahigh molecular weight polyethylene resin while passing through the cross-sectionally reduced portion (6), After forming into a reduced diameter from the inner diameter of the cylinder (19) of the extruder (1), that is, after forming into a cross-sectional shape of the outlet side resin flow path (62), the shaped product is discharged from the outlet of the mold. Extruding at a temperature below the melting point of the polyethylene resin to obtain a cylindrical ultrahigh molecular weight polyethylene resin pipe P1 having an expansion coefficient (e) of 5% or more as shown in FIG.
[0048]
Next, as shown in FIG. 4 (a), the ultrahigh molecular weight polyethylene resin pipe P1 is allowed to enter the outer layer pipe P2 whose inner diameter (d) is larger than the outer diameter (D) of the ultrahigh molecular weight polyethylene resin pipe P1. After fitting, it was put into a hot-air heating furnace in this state, and the ultrahigh molecular weight polyethylene resin pipe P1 was expanded to expand to the inner peripheral surface of the outer layer pipe P2, as shown in FIGS. 4 (b) and 5. The outer peripheral surface of the ultrahigh molecular weight polyethylene resin pipe P1 ′ is in pressure contact, and a multilayer pipe P in which the ultrahigh molecular weight polyethylene resin pipe P1 ′ is fixed inside the outer layer pipe P2 is obtained.
[0049]
According to this manufacturing method, a multilayer pipe can be obtained simply by expanding the ultrahigh molecular weight polyethylene resin pipe P1 by heating, so that the manufacturing equipment is small and the equipment cost is not required.
Furthermore, since the ultra-high molecular weight polyethylene resin pipe P1 is used as the inner layer pipe, it is excellent in wear resistance, non-adhesiveness, self-lubricating property and chemical resistance. It is possible to obtain a multilayer pipe that can be suitably used as a transport pipe for muddy water containing rocks, slurry such as ready-mixed concrete, or liquid food.
[0050]
On the other hand, when the ultra high molecular weight polyethylene resin pipe P1 is manufactured, since the resin is plasticized by dissolving the non-reactive gas in the resin, it can be easily molded.
Moreover, the molten resin is introduced into the mold (5) in a state in which the non-reactive gas is dissolved in the ultrahigh molecular weight polyethylene resin, and cooled to below the melting point while being reduced in diameter by the cross-sectionally reduced portion (6) of the mold (5). Therefore, it solidifies in a state where the shape before the diameter reduction is stored. Therefore, the shape memory effect appears by reheating, and the expansion rate (e) becomes 5% or more.
[0051]
In addition, after cooling to a temperature below the crystallization peak temperature at the time of temperature drop, it is extruded and depressurized, so it is possible to suppress foaming due to non-reactive gas dissolved in the ultrahigh molecular weight polyethylene resin, and internal defects An ultra-high molecular weight polyethylene resin pipe P1 that does not contain bubbles can be obtained.
[0052]
【Example】
Hereinafter, the present invention will be described specifically by way of examples. However, the following examples are used only for the purpose of illustration and should not be used for the purpose of limitation.
[0053]
Example 1
Ultrahigh molecular weight polyethylene ("Hi-Zex Million 240M" manufactured by Mitsui Petrochemical Co., Ltd., viscosity average molecular weight 2,300,000, melting point 136 ° C, crystallization peak temperature 118 ° C during cooling) is a pressure-resistant hopper ( 16) to a single screw extruder (1, screw diameter 40 mm, L / D = 30). Carbon dioxide was used as the non-reactive gas, and this was press-fitted at a pressure of 15 MPa from the gas supply ports (14) and (15) into the solid transport section (3) and the liquid transport section (4) of the extruder (1). The amount of carbon dioxide dissolved in ultrahigh molecular weight polyethylene under this pressure was about 10% by weight. At this time, the extruder (1) uses a high-pressure shaft sealing mechanism for the screw drive shaft, a pressure-resistant hopper structure, and a molten ultra-high molecular weight polyethylene in the vicinity of the extruder to bring carbon dioxide in the extruder (1) into a high-pressure state. Held on. Next, the resin supplied to the extruder (1) was sufficiently melt-kneaded inside under the conditions of an extrusion rate of 5 kg / h, a screw rotation speed of 10 rpm, and a barrel set temperature of 200 ° C.
[0054]
Subsequently, this melt-kneaded resin was passed through a die (5) for viping and extruded into a pipe shape to obtain an ultrahigh molecular weight polyethylene resin pipe having an outer diameter of 52.2 mm and an inner diameter of 47.8 mm. The obtained ultrahigh molecular weight polyethylene resin pipe had an expansion coefficient (e) of 20% obtained by the calculation formula of the above formula (1).
[0055]
The mold (5) includes a cross-section (outer diameter 70 mm, inner diameter 65 mm) of the inlet-side resin flow path (61) of the cross-sectional reduction portion (6), and a cross-section of the outlet-side resin flow path (62) (outer diameter 52 mm, 48mm inner diameter), S1 / S2 = 1.7, D ₀ 1 / D ₀ At 2 = 1.3, on the mold exit side (outer diameter 52 mm, inner diameter 48 mm), the cross-sectionally reduced portion (6) maintained 120 ° C. and the mold exit maintained 105 ° C. The temperature of the resin passing through the cross-sectional reduced portion (6) is 140 ° C. in the inlet-side resin flow path (61) of the cross-sectional reduced portion (6), and 120 ° C. in the outlet-side resin flow path (62). It was 105 ° C.
[0056]
The 5.7 m ultrahigh molecular weight polyethylene resin pipe obtained in this way was inserted into a carbon steel pipe for piping to be an outer layer pipe having an inner diameter of 54 mm and a length of 5.5 m, while maintaining this insertion state and horizontally moving, The inside of the hot air heating apparatus in which hot air blows from the vertical direction was reciprocated and heated at 130 ° C. for 1 hour from the center of the tube to both ends of the tube. Then, it cooled at room temperature for 40 minutes, and obtained the multilayer pipe in which the lining layer which consists of the ultra high molecular weight polyethylene resin pipe expanded along the inner peripheral surface of the steel pipe was formed as shown in the figure. The obtained multilayer pipe was press-contacted in a state where the ultrahigh molecular weight polyethylene resin pipe expanded and its outer peripheral surface was in close contact with the inner peripheral surface of the steel pipe.
[0057]
(Comparative Example 1)
An attempt was made to extrude an ultrahigh molecular weight polyethylene resin pipe in the same manner as in Example 1 except that carbon dioxide was not dissolved in the ultrahigh molecular weight polyethylene resin, but the pressure exceeded the pressure resistance (100 MPa) of the extruder. It became impossible to extrude.
[0058]
(Comparative Example 2)
The heating temperature of the cross section reduced portion (6) of the mold (5) is 140 ° C., and the temperature of the resin passing through the cross section reduced portion (6) is 165 ° C. in the inlet side resin flow path (61). An ultrahigh molecular weight polyethylene resin pipe having an outer diameter of 52.2 mm and an inner diameter of 47.8 mm was obtained in the same manner as in Example 1 except that the temperature was 140 ° C. in the path (62). The obtained ultrahigh molecular weight polyethylene resin pipe had an expansion rate of 2%.
[0059]
The 5.7 m ultrahigh molecular weight polyethylene resin pipe obtained in this way was inserted into a carbon steel pipe for piping to be an outer layer pipe having an inner diameter of 53 mm and a length of 5.5 m. However, the expansion of the ultrahigh molecular weight polyethylene resin pipe was insufficient and the outer peripheral surface of the expanded ultrahigh molecular weight polyethylene resin pipe did not come into close contact with the inner peripheral surface of the steel pipe.
[0060]
(Comparative Example 3)
An ultrahigh molecular weight polyethylene resin pipe was extruded in the same manner as in Example 1 except that the outlet temperature of the mold (5) was kept at 125 ° C. and the temperature of the resin extruded from the mold (5) was 125 ° C. The obtained ultrahigh molecular weight polyethylene resin pipe was foamed with an outer diameter of 54 mm and an inner diameter of 46 mm, and the expansion coefficient was 0.5%.
[0061]
(Comparative Example 4)
Without dissolving carbon dioxide in the ultrahigh molecular weight polyethylene resin, the heating temperature of the cross-sectionally reduced portion (6) of the mold (5) is set to 140 ° C., and the temperature of the resin passing through the cross-sectionally reduced portion (6) is set to the inlet side resin. An ultra high molecular weight polyethylene resin pipe having an outer diameter of 52.2 mm and an inner diameter of 47.8 mm was obtained in the same manner as in Example 1 except that the flow path (61) was 165 ° C. and the outlet side resin flow path (62) was 140 ° C. Obtained. The obtained ultrahigh molecular weight polyethylene resin pipe had an expansion rate of 3%.
[0062]
The 5.7 m ultrahigh molecular weight polyethylene resin pipe obtained in this way was inserted into a carbon steel pipe for piping to be an outer layer pipe having an inner diameter of 53 mm and a length of 5.5 m. However, the expansion of the ultrahigh molecular weight polyethylene resin pipe was insufficient and the outer peripheral surface of the expanded ultrahigh molecular weight polyethylene resin pipe did not come into close contact with the inner peripheral surface of the steel pipe.
[0063]
(Comparative Example 5)
Cross section (outer diameter 54 mm, inner diameter 48 mm) of the inlet side resin flow path (61) of the reduced section (6), cross section of the outlet side resin flow path (62) (outer diameter 52 mm, inner diameter 48 mm), S1 / S2 = 1 .5, D ₀ 1 / D ₀ An ultrahigh molecular weight polyethylene resin pipe having an outer diameter of 52.2 mm and an inner diameter of 47.8 mm was obtained in the same manner as in Example 1 except that 2 = 1.04. The obtained ultrahigh molecular weight polyethylene resin pipe had an expansion rate of 0.8%.
[0064]
(Comparative Example 6)
Cross section (outer diameter 70 mm, inner diameter 67.5 mm) of the inlet side resin flow path (61) of the reduced section (6), cross section of the outlet side resin flow path (62) (outer diameter 52 mm, inner diameter 48 mm), S1 / S2 = 0.9, D ₀ 1 / D ₀ Except that 2 = 1.3, extrusion was carried out in the same manner as in Example 1, but foaming occurred vigorously, making extrusion difficult.
[0065]
【The invention's effect】
Since the method for producing a multilayer pipe according to the present invention is configured as described above, it is excellent in wear resistance, non-adhesiveness, self-lubricating property and chemical resistance, such as ore, coal, and grain. It is possible to manufacture multi-layer pipes that can be suitably used as powder, muddy water containing rocks, slurries such as ready-mixed concrete, or transport pipes for liquid foods, etc., with small manufacturing equipment and without any equipment costs. it can.
[0066]
Also , An ultra-high molecular weight polyethylene resin pipe that expands naturally by heat can be produced efficiently and easily.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an apparatus for forming an ultrahigh molecular weight polyethylene resin pipe used in a method for producing a multilayer pipe according to the present invention.
2 is a cross-sectional view taken along line XX of FIG.
3 is a cross-sectional view taken along line YY in FIG.
FIG. 4 is a cross-sectional view illustrating a method for fixing an ultrahigh molecular weight polyethylene resin pipe and an outer layer pipe of a multilayer pipe.
FIG. 5 is a perspective view of a multilayer pipe obtained by the multilayer pipe manufacturing method according to the present invention.
[Explanation of symbols]
1 Extruder
19 cylinders
5 Mold
6 Cross section reduction part
61 Inlet side resin flow path
62 Outlet side resin flow path
P Multi-layer pipe
P1 Ultra high molecular weight polyethylene resin pipe
P1 'expanded ultra high molecular weight polyethylene resin pipe
P2 outer pipe

Claims (2)

In a multi-layer pipe manufacturing method in which an inner-layer pipe made of synthetic resin is fixed in an outer-layer pipe, it is easily molded by dissolving a non-reactive gas in a gaseous state at normal temperature and pressure under high pressure. The ultra-high molecular weight polyethylene resin in the state is melt-kneaded in the extruder, and the molten resin obtained by melt-kneading is crystallized in the mold provided on the discharge side of the extruder (crystallization at the time of cooling) While maintaining the temperature between the peak temperature of −20 ° C. and the melting point of + 20 ° C., the molded product was shaped into a diameter smaller than the cylinder inner diameter of the extruder, and this shaped product was crystallized when the ultrahigh molecular weight polyethylene resin was cooled. Extruded from the mold outlet at a temperature below the peak temperature, the following formula (1)

A step of obtaining an ultrahigh molecular weight polyethylene resin pipe having an expansion coefficient (e) represented by
The obtained ultrahigh molecular weight polyethylene resin pipe is loosely fitted into the outer layer pipe as an inner layer pipe, and then the ultrahigh molecular weight polyethylene resin pipe is heated and expanded so that the outer peripheral surface of the ultrahigh molecular weight polyethylene resin pipe becomes the outer layer pipe. The manufacturing method of the multilayer pipe characterized by providing the process of press-contacting to an internal peripheral surface. The mold includes a cross-sectional reduced portion that shapes the molten resin in a state where the molten resin is reduced in diameter from the cylinder inner diameter of the extruder, and the cross-sectional reduced portion includes the cross-sectional area (S1) of the inlet-side resin flow path and the outlet-side resin flow path. large ratio of the cross-sectional area (S2) (S1 / S2) is from 1.0, the outer diameter D ₀ 1 inlet side resin passage, the outer diameter D ₀ 2 ratio of the outlet-side resin channel (D ₀ The method for manufacturing a multilayer pipe according to claim 1 , wherein 1 / D ₀ 2) is formed to be larger than 1.05.

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