JP3692178B2

JP3692178B2 - Method for producing open-cell polyolefin foam for insulation material around hot water piping or for sealing water

Info

Publication number: JP3692178B2
Application number: JP10320196A
Authority: JP
Inventors: 達雄松原
Original assignee: Inoac Corp
Current assignee: Inoac Corp
Priority date: 1996-03-29
Filing date: 1996-03-29
Publication date: 2005-09-07
Anticipated expiration: 2016-03-29
Also published as: JPH09267349A

Description

【０００１】
【発明の属する技術分野】
本発明は、連泡性が高く、耐薬品性、耐水性等に優れ、且つ耐熱性が良好であって、熱収縮率の小さい温水配管まわりの断熱材用又は止水用のパッキン材用連泡性ポリオレフィン発泡体の製造方法に関する。本発明の温水配管まわりの断熱材用又は止水用のパッキン材用連泡性ポリオレフィン発泡体は、温水配管まわりの断熱材、止水用のパッキン材等として利用することができる。
【０００２】
【従来の技術】
耐薬品性、耐水性等、優れた特性を有する連泡性ポリオレフィン発泡体は、従来より、ポリウレタンスポンジの代替品として幅広く使用されている。その製法としては、下記の方法が一般的である。先ず、ポリオレフィン樹脂、発泡剤、架橋剤等からなる樹脂組成物を、１次型内において高圧下に加熱する。これによって、ゆるやかな架橋構造を形成するとともに、発泡剤の一部を分解して核気泡を形成し、その後、除圧し、１次膨張させて１次発泡体を得る。次いで、この１次発泡体を常圧下に加熱することにより、上記のゆるやかな架橋状態を維持しつつ、残余の発泡剤を分解して２次膨張させる。そして、得られた２次発泡体を機械的に圧縮し、独立気泡を破泡し、連通化させて連泡性ポリオレフィン発泡体とする（特開昭５６−１２１７３９号公報、特開昭５７−１９１０２７号公報、特公平５−１１１３９号公報等）。
【０００３】
上記の「ゆるやかな架橋」とは、発泡剤が分解して発生したガスが、そのまま樹脂組成物中に保持されてしまう架橋状態であって、且つ最終工程で気泡を圧縮し、破泡する際、容易に破泡することができる架橋状態をいう。このような微妙な架橋状態とするためためには、樹脂としては、一般に、エチレンと酢酸ビニルとの共重合体（以下、ＥＶＡということもある。）が使用されている。即ち、ＥＶＡは、その分子内にアセテート基を数多く持っているため、低い活性化エネルギーで容易に架橋反応が誘起される。従って、低温において架橋を開始することができ、それによって架橋剤の分解が緩やかとなり、上述の如き微妙なゆるやかな架橋状態を容易に実現することができる。
【０００４】
【発明が解決しようとする課題】
しかし、ＥＶＡは、例えばポリエチレンに比べて耐熱性が低く、ＥＶＡからなる連泡性の発泡体は、加熱時の熱収縮率が大きいという問題がある。連泡性の発泡体の用途である温水配管まわりの断熱材、又は止水用のパッキン材等では、一般に、１００℃で１０％以下、好ましくは５％以下の熱収縮率であることが要求されている。しかし、ＥＶＡからなる連泡性の発泡体の熱収縮率は、酢酸ビニルの含有量にもよるが、一般的に、１００℃で２０〜３０％にもなり、上記の断熱材、止水材等として使用することができない。また、この点を改良するため、ＥＶＡより耐熱性の高いポリエチレンをブレンドする方法が提案されているが、連泡性と耐熱性とが同時に満足された発泡体はいまだ得られていない。
【０００５】
本発明は、上記の問題を解決するものであり、特定のＥＶＡと、特定の軟化点を有するポリオレフィン系樹脂とをブレンドして使用し、１次型での加熱温度を特定することにより、連泡性が高く、且つ耐熱性に優れ、熱収縮率の小さい温水配管まわりの断熱材用又は止水用のパッキン材用連泡性ポリオレフィン発泡体を製造する方法を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明の温水配管まわりの断熱材用又は止水用のパッキン材用連泡性ポリオレフィン発泡体の製造方法は、連泡率が８８％〜９９％又は熱収縮率が４．８％〜９．３％の温水配管まわりの断熱材用又は止水用のパッキン材用連泡性ポリオレフィン発泡体の製造方法であって、エチレン−酢酸ビニル共重合体、ポリオレフィン系樹脂、架橋剤及び発泡剤を含む樹脂組成物を１次型に充填し、加圧下、所定温度に加熱した後、除圧し、１次膨張させ、生成した１次発泡体を上記１次型から取り出す工程、該１次発泡体を２次型内に配置し、常圧下、加熱し、２次膨張させて、生成した２次発泡体を上記２次型から取り出す工程、該２次発泡体を圧縮し、連泡化する工程、からなる連泡性ポリオレフィン発泡体の製造方法において、上記所定温度は、上記架橋剤の１分間半減期温度より３５〜５０℃低い温度範囲であり、上記エチレン−酢酸ビニル共重合体の酢酸ビニル含有量は２０重量％以下であって、且つ上記エチレン−酢酸ビニル共重合体と上記ポリオレフィン系樹脂との合計量を１００重量％とした場合に、その中の酢酸ビニルの含有量は８重量％以上であり、さらに上記エチレン−酢酸ビニル共重合体は６０〜７５重量％、上記ポリオレフィン系樹脂は２５〜４０重量％であって、該ポリオレフィン系樹脂の軟化点は、上記連泡性ポリオレフィン発泡体の使用時の最高雰囲気温度以上であることを特徴とする。
また、他の本発明の温水配管まわりの断熱材用又は止水用のパッキン材用連泡性ポリオレフィン発泡体の製造方法は、エチレン−酢酸ビニル共重合体、ポリオレフィン系樹脂、架橋剤及び発泡剤を含む樹脂組成物を１次型に充填し、加圧下、所定温度に加熱した後、除圧し、１次膨張させ、生成した１次発泡体を上記１次型から取り出す工程、該１次発泡体を２次型内に配置し、常圧下、加熱し、２次膨張させて、生成した２次発泡体を上記２次型から取り出す工程、該２次発泡体を圧縮し、連泡化する工程、からなる温水配管まわりの断熱材用又は止水用のパッキン材用連泡性ポリオレフィン発泡体の製造方法において、上記所定温度は、上記架橋剤の１分間半減期温度より４０〜５０℃低い温度範囲であり、上記エチレン−酢酸ビニル共重合体の酢酸ビニル含有量は２０重量％以下であって、且つ上記エチレン−酢酸ビニル共重合体と上記ポリオレフィン系樹脂との合計量を１００重量％とした場合に、その中の酢酸ビニルの含有量は８重量％以上であり、さらに上記エチレン−酢酸ビニル共重合体は６０〜７５重量％、上記ポリオレフィン系樹脂は２５〜４０重量％であって、該ポリオレフィン系樹脂の軟化点は、上記連泡性ポリオレフィン発泡体の使用時の最高雰囲気温度以上であることを特徴とする。
本発明の上記連泡率及び上記熱収縮率は、発明の実施の形態の項に記載した方法により求められる値である。
【０００７】
上記「所定温度」が、「架橋剤の１分間半減期温度」より「３５℃低い温度」を越えて高い場合は、架橋剤の分解が急激に誘起されて、ゆるやかな架橋状態とすることが困難となる。そのため、架橋が過度に進んで、気泡壁は強靱になり、２次発泡体を圧縮しても十分に破泡することができなくなる。また、所定温度が、架橋剤の１分間半減期温度より５０℃を超えて低い場合は、架橋が不充分となり、発泡剤の分解したガスが樹脂組成物から抜け去る、所謂、「ガス抜け」を生じ、所要の発泡体を製造することができない。
【０００８】
上記「エチレン−酢酸ビニル共重合体」の酢酸ビニル含有量が２０重量％を越える場合は、併用するポリオレフィン系樹脂との架橋性能の差が大きくなりすぎる。そのため、ＥＶＡの架橋性能に適した架橋条件とした場合は、ポリオレフィン系樹脂の架橋が不足となり、ガス抜けを生ずる。一方、ポリオレフィン系樹脂の架橋性能に適した架橋条件とした場合は、ＥＶＡの架橋が過度となり、気泡壁が強靱となって破泡、連泡化が難しくなる。
【０００９】
ＥＶＡとポリオレフィン系樹脂との合計量を１００重量％とした場合に、ポリオレフィン系樹脂が２５重量％未満では、併用の効果が十分に発揮されず、得られる連泡性ポリオレフィン発泡体の耐熱性の改善が不十分となる。また、この配合量が４０重量％を超えると、架橋し易いＥＶＡの特性が抑えられてしまい、必要とされるゆるやかな架橋状態とすることが極めて困難になり、ガス抜けを生ずる。従って、このポリオレフィン系樹脂の配合量は、２５〜４０重量％の範囲内とすることが必要で、特に３０〜３５重量％の範囲とすることが好ましい。
【００１０】
更に、ブレンドした後の合計樹脂量に対する酢酸ビニル含有量が８重量％未満である場合、１次加熱温度が低めの場合は、架橋し易いというＥＶＡの特性が失われ、ガス抜けを生ずる。一方、１次加熱温度が高めである場合は、ＥＶＡの架橋が過度となり、破泡して、連泡化することが難しくなる。このように、合計樹脂量に対する酢酸ビニル含有量が少ない場合は、成形条件の僅かな違いが、結果に大きく影響を及ぼすことが予想される。そのため、この酢酸ビニル含有量は、特に１０重量％以上であることが好ましく、そのようにすれば、より安定な成形が可能となる。
【００１１】
上記「ポリオレフィン系樹脂」としては、低密度ポリエチレン、高密度ポリエチレン、ポリプロピレン等の他、エチレンを主成分とする各種共重合体を使用することができる。そのような共重合体としては、エチレン−プロピレン共重合体、エチレン−ブテン共重合体、エチレンとメチル、エチル、プロピル若しくはブチルの各アクリル酸アルキルエステルとの共重合体等が挙げられる。これらは２種以上を併用することもできる。上記の各種の樹脂の中では、耐熱性に優れ、且つ比較的容易に架橋することができる低密度ポリエチレンが特に好ましい。
【００１２】
また、ポリオレフィン系樹脂の「軟化点」が、最終製品使用時の最高雰囲気温度未満である場合、ポリオレフィン系樹脂の配合量を上限値、或いはそれ以上の量としても、得られる発泡体の耐熱性は十分に改良されず、熱収縮率の大きい発泡体となってしまう。この軟化点は、当該温度より２℃以上、特に５℃以上高いことが好ましく、そのようなポリオレフィン系樹脂を使用すれば、耐熱性に優れ、熱収縮率の小さい発泡体を得ることができる。
【００１３】
上記「架橋剤」としては、ジクミルパーオキサイドの他、２，５−ジメチル−２，５−ジターシャリーブチルパーオキシヘキサン、２，３，５−ジメチル−２，５−ジターシャリーブチルパーオキシヘキサン、α，α−ジターシャリーブチルパーオキシジイソプロピルベンゼン等を使用することができる。また、架橋状態は、架橋剤の添加量によっても調整することができるが、これはポリオレフィン系樹脂の種類によって微妙に変化するため、それぞれの樹脂について、適宜、添加量を設定する必要がある。
【００１４】
上記「発泡剤」としては、上記ポリオレフィン系樹脂の流動開始温度以上の分解温度を有するものを使用することができる。例えば、アゾジカルボンアミド、ジニトロソペンタメチレンテトラミン等が挙げられる。また、本発明においては、発泡状態をコントロールするために、尿素を主成分とする化合物、酸化亜鉛、酸化鉛等の金属酸化物、低級若しくは高級脂肪酸又は低級若しくは高級脂肪酸の金属塩等の発泡助剤などを添加することもできる。更に、物性改善のためにカーボンブラック、酸化チタン等の他、この種の発泡性組成物に常用される各種の配合剤を適宜添加してもよい。
【００１５】
上記「１次型」としては、通常の密閉型の金型を使用することができる。この１次型内の圧力は、５０〜１５０ｋｇ／ｃｍ²程度とすることが好ましい。この１次型内の圧力が５０ｋｇ／ｃｍ²未満では、１次膨張が過大となり、１次発泡体の発泡倍率が高くなりすぎることがある。それにより膨張時に１次型より樹脂組成物の洩れが生じ、１次発泡体の変形原因になり、更にこれが製品化率の低下を招くことになるため好ましくない。
【００１６】
一方、圧力が１５０ｋｇ／ｃｍ²を越える場合は、発泡剤の分解により発生するガスの分散速度が遅く、形成される核気泡の数密度が低くなりすぎる。そのため、気泡壁が過大に厚くなり、所定発泡倍率の発泡体が得られず、また、圧縮により破泡し、連泡化することが難しくなる。尚、ここでいう圧力とは閉止された１次型の内表面全面に負荷される圧力のことである。
【００１７】
また、１次発泡体を得る工程において、発泡剤は、生成する核気泡が隣接する気泡と合一化して集合し、容易に成長することができる程度に分解させることが好ましい。この発泡剤の分解率が高すぎる場合、１次発泡体の膨張率が過大となり、変形、ワレ等の不良を招来して２段発泡本来の目的が損なわれる。この発泡剤の分解率は、これらを勘案し、その種類、１次型の圧力、或いは本発明において特定された範囲の温度等、適宜設定して調整することができる。尚、発泡剤の分解率は、金属酸化物、尿素系助剤などの発泡助剤の添加量等によって調整することもできる。
【００１８】
更に、本発明において使用する「２次型」は、１次型として用いる密閉型であって加圧して使用するものとは異なり、非密閉の内部空間を有するものであればよい。そして、この内部空間内において１次発泡体が２次膨張する際、内部空間内に残存する空気を発泡体の膨張圧により外部へ排除しうる構造を有し、通常、２次型の適宜な型面に上記内部空間と外部雰囲気とを連通させる小孔が、各面に１〜２個設けられている。
【００１９】
【発明の実施の形態】
表１及び表２に示す酢酸ビニル含有量の異なるＥＶＡ及びビカット軟化点の異なる低密度ポリエチレンを、表１及び表２の割合でブレンドした混合物１００重量部に、架橋剤として、１分間半減期温度が１７０℃のジクミルパーオキサイド（濃度；４０重量％）を２重量部、発泡剤としてアゾジカーボンアミドを２０重量部、及びその他の助剤を適宜配合した樹脂組成物を調製した。この樹脂組成物を、１次型である金型（１００×１００×１０ｍｍ）内に充填し、６０ｋｇ／ｃｍ²の加圧下、表１及び表２に示す各温度で加熱した後、除圧して１次発泡体を得た。尚、表１及び表２において、ＶＡは酢酸ビニルの、またＬＤＰＥは低密度ポリエチレンの、それぞれ略称である。
【００２０】
この１次発泡体を２次型である金型（３００×３００×３０ｍｍ）に配置し、常圧下、１７０℃で更に５０分間加熱し、２次膨張させて２次発泡体を得た。この２次発泡体を、常温で、間隔３ｍｍの２本のロール間を通過させ、破泡し、連通化させ、最終的に密度０．０３８／ｃｍ³程度の連泡性の発泡体を得た。それらの発泡体について成形性、連泡性及び１００℃における熱収縮率を評価した。その結果を表１及び表２に併記する。
【００２１】
尚、成形性、連泡性及び熱収縮率は、以下の方法によって評価した。
成形性：２次発泡体におけるガス抜けによる収縮の有無によって判定した。評価の基準は、○；ガス抜け無し、×；ガス抜け有り、とする。
連泡性：ＡＳＴＭＤ２８５６（エアーピクノメータ法）に準拠して製品の連泡率を測定した。評価の基準は、○；連泡率が８０％以上で、連泡性良好、×；連泡率が８０％未満で、連泡性不良、とする。
【００２２】
熱収縮率：製品を、１００℃の空気雰囲気下、２２時間放置した後、下式によりその値を算出した。
熱収縮率＝〔（Ｌ₀−Ｌ₁）／Ｌ₀〕×１００（％）
（尚、Ｌ₀＝熱処理前のサンプル長、Ｌ₁＝熱処理後のサンプル長である。）
【００２３】
【発明の効果】
本発明によれば、連泡性を低下させることなく、耐薬品性、耐水性等に優れ、且つ耐熱性が良好であって、例えば、１００℃に加熱した場合の熱収縮率の小さい温水配管まわりの断熱材用又は止水用のパッキン材用連泡性ポリオレフィン発泡体を得ることができる。
【００２４】
【表２】

【００２５】
表１の結果によれば、実施例３では、酢酸ビニル含有量が多めであるため、ＥＶＡの架橋が過度に進んで、破泡し難くなり、それぞれ連泡性がやや低くなっている。更に、実施例４では、低密度ポリエチレンの配合量が少なめであるため、熱収縮率がやや大きくなっている。しかし、いずれも各比較例の性能を十分に上回るものであり、成形性、連泡性及び熱収縮率のいずれも優れている実施例１、２の場合も含め、優れた性能の連泡性ポリオレフィン発泡体が得られていることが分かる。
【００２６】
一方、表２の結果によれば、１次加熱温度の低い比較例１及び低密度ポリエチレンの量比が高すぎる比較例３では、架橋が不十分となって、ガス抜けを生じ、発泡体の成形が難しい。また、１次加熱温度が高すぎる比較例２では、ＥＶＡの架橋が進みすぎ、非常に連泡性の低い発泡体となっていることが分かる。更に、低密度ポリエチレンの量比が低い比較例４では、ＥＶＡのみの場合に類似し、連泡性はよくなるものの、耐熱性が十分に向上せず、熱収縮率が大きくなることが分かる。また、樹脂混合物中の酢酸ビニル含有量が低い場合、１次加熱温度の違いによって結果はまったく異なり、比較例５では、ガス抜けを生じてしまうが、温度が５℃高い比較例６では、発泡体は生成するものの、連泡性が大きく低下することが分かる。
【００２７】
更に、ビカット軟化点の低い低密度ポリエチレンを使用した比較例７では、その量比を上限にまで高めても、耐熱性を十分に向上させることができず、熱収縮率の大きい発泡体となってしまう。また、ＥＶＡの酢酸ビニル含有量が上限を越えている比較例８では、ガス抜けを生じ、低密度ポリエチレンをまったく使用していない比較例９では、連泡性は非常に良好であるが、熱収縮率の大きい、耐熱性の低い発泡体しか得られないことが分かる。
【００２８】
【発明の効果】
本発明によれば、連泡性を低下させることなく、耐薬品性、耐水性等に優れ、且つ耐熱性が良好であって、例えば、１００℃に加熱した場合の熱収縮率の小さい連泡性ポリオレフィン発泡体を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention has high foamability, excellent chemical resistance, water resistance, etc., and good heat resistance, and is used for a heat insulating material or a sealing material for a water stop around a hot water pipe having a small heat shrinkage rate. The present invention relates to a method for producing a foamable polyolefin foam. The open-cell polyolefin foam for a heat insulating material around a hot water pipe or a packing material for water stop according to the present invention can be used as a heat insulating material around a hot water pipe, a packing material for water stop, or the like.
[0002]
[Prior art]
Open-cell polyolefin foams having excellent properties such as chemical resistance and water resistance have been widely used as substitutes for polyurethane sponges. As its production method, the following methods are common. First, a resin composition composed of a polyolefin resin, a foaming agent, a crosslinking agent and the like is heated under high pressure in the primary mold. As a result, a gently cross-linked structure is formed, and a part of the foaming agent is decomposed to form a nuclear bubble, and then the pressure is released and primary expansion is performed to obtain a primary foam. Next, by heating the primary foam under normal pressure, the remaining foaming agent is decomposed and subjected to secondary expansion while maintaining the above-mentioned gentle crosslinking state. Then, the obtained secondary foam is mechanically compressed, the closed cells are broken and connected to form a continuous foam polyolefin foam (Japanese Patent Laid-Open Nos. 56-121739 and 57-57). No. 191027 and Japanese Patent Publication No. 5-11139).
[0003]
The above-mentioned “gradual crosslinking” is a crosslinked state in which the gas generated by the decomposition of the foaming agent is retained in the resin composition as it is, and when the bubbles are compressed and broken in the final step It refers to a cross-linked state that can be easily broken. In order to achieve such a delicate cross-linked state, a copolymer of ethylene and vinyl acetate (hereinafter sometimes referred to as EVA) is generally used as the resin. That is, since EVA has many acetate groups in its molecule, a crosslinking reaction is easily induced with a low activation energy. Accordingly, the crosslinking can be started at a low temperature, whereby the decomposition of the crosslinking agent becomes gradual, and the above-described delicate and gentle crosslinking state can be easily realized.
[0004]
[Problems to be solved by the invention]
However, EVA has a problem that heat resistance is lower than that of polyethylene, for example, and an open-cell foam made of EVA has a large heat shrinkage rate upon heating. In the heat insulating material around the hot water pipe, which is a use of open-cell foam, or a packing material for water stopping, it is generally required that the heat shrinkage is 10% or less, preferably 5% or less at 100 ° C. Has been. However, the heat shrinkage ratio of the open cell foam made of EVA is generally 20 to 30% at 100 ° C., although it depends on the content of vinyl acetate. Cannot be used as etc. Further, in order to improve this point, a method of blending polyethylene having higher heat resistance than EVA has been proposed, but a foam satisfying both open cell resistance and heat resistance has not been obtained yet.
[0005]
The present invention solves the above-mentioned problem. By blending a specific EVA and a polyolefin resin having a specific softening point and specifying the heating temperature in the primary mold, It is an object of the present invention to provide a method for producing an open-cell polyolefin foam for a heat insulating material or a water-proof packing material around a hot water pipe having high foamability, excellent heat resistance, and low thermal shrinkage.
[0006]
[Means for Solving the Problems]
In the method for producing a continuous foamed polyolefin foam for a heat insulating material or a waterproofing material around a hot water pipe of the present invention, the open cell rate is 88% to 99% or the thermal shrinkage rate is 4.8% to 9. A method for producing an open-cell polyolefin foam for a heat insulating material or a water sealing material around a 3% hot water pipe , comprising an ethylene-vinyl acetate copolymer, a polyolefin resin, a crosslinking agent and a foaming agent Filling a resin composition into a primary mold, heating to a predetermined temperature under pressure, then depressurizing and primary expansion, and removing the generated primary foam from the primary mold; Placing in the secondary mold, heating under normal pressure, secondary expansion, and taking out the produced secondary foam from the secondary mold, compressing the secondary foam and making it open-celled; In the method for producing an open-cell polyolefin foam comprising: The temperature range is 35 to 50 ° C. lower than the one minute half-life temperature of the cross-linking agent, the vinyl acetate content of the ethylene-vinyl acetate copolymer is 20% by weight or less, and the ethylene-vinyl acetate copolymer weight When the total amount of the coalesced and the polyolefin resin is 100% by weight, the vinyl acetate content therein is 8% by weight or more, and the ethylene-vinyl acetate copolymer is 60 to 75% by weight. The polyolefin-based resin is 25 to 40% by weight, and the softening point of the polyolefin-based resin is equal to or higher than the maximum ambient temperature when the open-cell polyolefin foam is used.
In addition, another method for producing a foamed polyolefin foam for a heat insulating material or a waterproofing packing material around a hot water pipe according to the present invention includes an ethylene-vinyl acetate copolymer, a polyolefin resin, a crosslinking agent, and a foaming agent. Filling a primary mold with a resin composition containing heat, heating to a predetermined temperature under pressure, removing the pressure and performing primary expansion, and removing the generated primary foam from the primary mold, the primary foaming The body is placed in the secondary mold, heated under normal pressure, and subjected to secondary expansion, and the resulting secondary foam is taken out of the secondary mold, and the secondary foam is compressed and made open-celled. In the method for producing an open-cell polyolefin foam for a heat insulating material or a water-stopping packing material around a hot water pipe comprising a step, the predetermined temperature is 40 to 50 ° C. lower than the 1-minute half-life temperature of the cross-linking agent. Temperature range, the ethylene-vinyl acetate The vinyl acetate content of the coalescence is 20% by weight or less, and when the total amount of the ethylene-vinyl acetate copolymer and the polyolefin resin is 100% by weight, the content of vinyl acetate therein The ethylene-vinyl acetate copolymer is 60 to 75% by weight, the polyolefin resin is 25 to 40% by weight, and the softening point of the polyolefin resin is the above-mentioned open cell foam. It is characterized by being at or above the maximum ambient temperature when using the conductive polyolefin foam.
The said open-cell rate and the said heat shrinkage rate of this invention are the values calculated | required by the method described in the term of embodiment of invention.
[0007]
When the “predetermined temperature” is higher than “temperature lower by 35 ° C.” than the “one minute half-life temperature of the crosslinking agent”, decomposition of the crosslinking agent is abruptly induced to form a loosely crosslinked state. It becomes difficult. For this reason, the crosslinking proceeds excessively, the cell walls become tough, and even if the secondary foam is compressed, the bubbles cannot be sufficiently broken. Further, when the predetermined temperature is lower than the one minute half-life temperature of the crosslinking agent by more than 50 ° C., the crosslinking is insufficient and the gas decomposed by the foaming agent escapes from the resin composition. And the required foam cannot be produced.
[0008]
When the vinyl acetate content of the “ethylene-vinyl acetate copolymer” exceeds 20% by weight, the difference in crosslinking performance with the polyolefin resin used in combination is too large. For this reason, when the crosslinking conditions are suitable for the EVA crosslinking performance, the polyolefin resin is insufficiently crosslinked, resulting in outgassing. On the other hand, when the cross-linking conditions are suitable for the cross-linking performance of the polyolefin resin, EVA cross-linking becomes excessive, the cell walls become tough, and it becomes difficult to break and foam.
[0009]
When the total amount of EVA and polyolefin resin is 100% by weight, if the polyolefin resin is less than 25% by weight, the combined effect is not sufficiently exhibited, and the heat resistance of the resulting open-cell polyolefin foam is not sufficient. Improvement is insufficient. On the other hand, when the blending amount exceeds 40% by weight, the characteristics of EVA that is easily crosslinked are suppressed, and it becomes extremely difficult to obtain a required loosely crosslinked state, resulting in outgassing. Therefore, the blending amount of the polyolefin resin is required to be in the range of 25 to 40% by weight, and particularly preferably in the range of 30 to 35% by weight.
[0010]
Furthermore, when the vinyl acetate content is less than 8% by weight with respect to the total resin amount after blending, when the primary heating temperature is low, the EVA characteristic that it is easy to crosslink is lost, resulting in outgassing. On the other hand, when the primary heating temperature is high, EVA cross-linking becomes excessive and bubbles are broken, making it difficult to form a continuous bubble. As described above, when the vinyl acetate content is small relative to the total resin amount, a slight difference in molding conditions is expected to greatly affect the results. Therefore, the vinyl acetate content is particularly preferably 10% by weight or more, and by doing so, more stable molding becomes possible.
[0011]
As the above-mentioned “polyolefin resin”, low-density polyethylene, high-density polyethylene, polypropylene and the like, as well as various copolymers mainly composed of ethylene can be used. Examples of such a copolymer include an ethylene-propylene copolymer, an ethylene-butene copolymer, and a copolymer of ethylene and each alkyl acrylate ester of methyl, ethyl, propyl, or butyl. Two or more of these may be used in combination. Among the above-mentioned various resins, low density polyethylene that is excellent in heat resistance and that can be crosslinked relatively easily is particularly preferable.
[0012]
In addition, when the “softening point” of the polyolefin resin is lower than the maximum ambient temperature when the final product is used, the heat resistance of the resulting foam can be obtained even if the blending amount of the polyolefin resin is the upper limit value or more. Is not sufficiently improved, resulting in a foam having a large heat shrinkage rate. This softening point is preferably 2 ° C. or more, particularly 5 ° C. or more higher than the temperature. When such a polyolefin resin is used, a foam having excellent heat resistance and a small heat shrinkage rate can be obtained.
[0013]
Examples of the “crosslinking agent” include dicumyl peroxide, 2,5-dimethyl-2,5-ditertiary butyl peroxyhexane, 2,3,5-dimethyl-2,5-ditertiary butyl peroxyhexane. , Α, α-ditertiary butyl peroxydiisopropylbenzene and the like can be used. The crosslinking state can also be adjusted by the addition amount of the crosslinking agent. However, since this slightly changes depending on the type of polyolefin resin, it is necessary to appropriately set the addition amount for each resin.
[0014]
As said "foaming agent", what has a decomposition temperature more than the flow start temperature of the said polyolefin resin can be used. For example, azodicarbonamide, dinitrosopentamethylenetetramine and the like can be mentioned. In the present invention, in order to control the foaming state, foaming aids such as compounds mainly composed of urea, metal oxides such as zinc oxide and lead oxide, lower or higher fatty acids or metal salts of lower or higher fatty acids, etc. An agent or the like can also be added. Furthermore, in order to improve the physical properties, various compounding agents commonly used in this type of foamable composition may be added as appropriate in addition to carbon black and titanium oxide.
[0015]
As the “primary mold”, a normal hermetic mold can be used. The pressure in the primary mold is preferably about 50 to 150 kg / cm ² . If the pressure in the primary mold is less than 50 kg / cm ² , the primary expansion becomes excessive, and the expansion ratio of the primary foam may become too high. As a result, the resin composition leaks from the primary mold during expansion, which causes deformation of the primary foam, which further decreases the productization rate, which is not preferable.
[0016]
On the other hand, when the pressure exceeds 150 kg / cm ² , the dispersion speed of the gas generated by the decomposition of the foaming agent is slow, and the number density of the formed nuclear bubbles becomes too low. For this reason, the bubble wall becomes excessively thick, a foam having a predetermined foaming ratio cannot be obtained, and it is difficult to break up bubbles by compression and to form a continuous bubble. The pressure referred to here is the pressure applied to the entire inner surface of the closed primary mold.
[0017]
In the step of obtaining the primary foam, it is preferable that the foaming agent is decomposed to such an extent that the generated nuclear bubbles are united with the adjacent bubbles and can be easily grown. When the decomposition rate of the foaming agent is too high, the expansion rate of the primary foam becomes excessive, leading to defects such as deformation and cracking, and the original purpose of the two-stage foaming is impaired. The decomposition rate of the foaming agent can be adjusted by appropriately setting the type, the primary pressure, the temperature within the range specified in the present invention, etc. in consideration of these factors. The decomposition rate of the foaming agent can be adjusted by the amount of foaming aid added such as a metal oxide or urea-based aid.
[0018]
Furthermore, the “secondary type” used in the present invention is a sealed type used as a primary type and may be any type having a non-sealed internal space, unlike a type used under pressure. And, when the primary foam secondarily expands in this internal space, it has a structure that can eliminate the air remaining in the internal space to the outside by the expansion pressure of the foam. One or two small holes are provided on each surface for communicating the internal space with the external atmosphere on the mold surface.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
1 minute half-life temperature as a cross-linking agent in 100 parts by weight of a mixture obtained by blending EVA having different vinyl acetate contents and low density polyethylene having different Vicat softening points shown in Tables 1 and 2 in proportions shown in Tables 1 and 2. Prepared a resin composition in which 2 parts by weight of dicumyl peroxide (concentration: 40% by weight) at 170 ° C., 20 parts by weight of azodicarbonamide as a foaming agent, and other auxiliaries were appropriately blended. The resin composition was filled in a primary mold (100 × 100 × 10 mm), heated at 60 kg / cm ² under the temperature shown in Tables 1 and 2, and then depressurized. A primary foam was obtained. In Tables 1 and 2, VA is an abbreviation for vinyl acetate and LDPE is an abbreviation for low-density polyethylene.
[0020]
This primary foam was placed in a secondary mold (300 × 300 × 30 mm), heated at 170 ° C. for 50 minutes under normal pressure, and subjected to secondary expansion to obtain a secondary foam. This secondary foam is passed through two rolls with an interval of 3 mm at room temperature, bubble-breaked and connected, and finally an open-cell foam having a density of about 0.038 / cm ³ is obtained. It was. These foams were evaluated for moldability, open cell foam, and heat shrinkage at 100 ° C. The results are also shown in Tables 1 and 2.
[0021]
In addition, the moldability, the open cell property, and the heat shrinkage rate were evaluated by the following methods.
Moldability: Determined by the presence or absence of shrinkage due to outgassing in the secondary foam. The evaluation criteria are as follows: ◯: no outgassing, x: outgassing.
Open cell property: The open cell rate of the product was measured according to ASTM D2856 (air pycnometer method). The standard of evaluation is as follows: ◯: The open cell rate is 80% or more and the open cell property is good, and X: The open cell rate is less than 80% and the open cell property is poor.
[0022]
Thermal contraction rate: The product was allowed to stand in an air atmosphere at 100 ° C. for 22 hours, and the value was calculated by the following formula.
Thermal contraction rate = [(L ₀ −L ₁ ) / L ₀ ] × 100 (%)
(L ₀ = sample length before heat treatment, L ₁ = sample length after heat treatment)
[0023]
【The invention's effect】
According to the present invention, hot water piping that has excellent chemical resistance, water resistance, etc., and good heat resistance without lowering the foamability, for example, has a low heat shrinkage when heated to 100 ° C. An open- cell polyolefin foam for a surrounding heat insulating material or a water-proof packing material can be obtained.
[0024]
[Table 2]

[0025]
According to the result of Table 1, in Example 3, since vinyl acetate content is rather large, the bridge | crosslinking of EVA progresses too much, it becomes difficult to break a bubble, and each foamability is a little low. Furthermore, in Example 4 , since the blending amount of the low density polyethylene is small, the heat shrinkage rate is slightly increased. However, all of the comparative examples sufficiently exceed the performance of each comparative example, including the cases of Examples 1 and 2 in which all of the moldability, the foamability, and the heat shrinkage ratio are excellent. It can be seen that a polyolefin foam is obtained.
[0026]
On the other hand, according to the results in Table 2, in Comparative Example 1 where the primary heating temperature is low and Comparative Example 3 where the amount ratio of the low density polyethylene is too high, the crosslinking is insufficient, causing outgassing, Molding is difficult. Moreover, in the comparative example 2 whose primary heating temperature is too high, it turns out that the bridge | crosslinking of EVA progresses too much and it has become a foam with very low foamability. Furthermore, in Comparative Example 4 in which the amount ratio of the low density polyethylene is low, it is similar to the case of EVA alone, and although the foamability is improved, it is understood that the heat resistance is not sufficiently improved and the heat shrinkage rate is increased. In addition, when the vinyl acetate content in the resin mixture is low, the results are completely different depending on the difference in the primary heating temperature. In Comparative Example 5, gas escape occurs, but in Comparative Example 6 where the temperature is higher by 5 ° C., foaming occurs. Although the body is produced, it can be seen that the foamability is greatly reduced.
[0027]
Furthermore, in Comparative Example 7 using low density polyethylene having a low Vicat softening point, even when the amount ratio is increased to the upper limit, the heat resistance cannot be sufficiently improved, and a foam having a large heat shrinkage rate is obtained. End up. Further, in Comparative Example 8 where the vinyl acetate content of EVA exceeds the upper limit, outgassing occurred, and in Comparative Example 9 in which no low-density polyethylene was used, the foamability was very good. It can be seen that only a foam having a large shrinkage rate and low heat resistance can be obtained.
[0028]
【The invention's effect】
According to the present invention, open bubbles having excellent chemical resistance, water resistance, etc., and good heat resistance without lowering open cells, for example, having a low thermal shrinkage when heated to 100 ° C. Can be obtained.

Claims

This is a method for producing an open-cell polyolefin foam for a heat insulating material or a water- proof packing material around a hot water pipe having an open cell rate of 88% to 99% or a thermal shrinkage rate of 4.8% to 9.3%. hand,
A resin composition containing an ethylene-vinyl acetate copolymer, a polyolefin-based resin, a crosslinking agent and a foaming agent is filled in a primary mold, heated to a predetermined temperature under pressure, then depressurized and primarily expanded to produce. The step of taking out the primary foam from the primary mold, placing the primary foam in the secondary mold, heating under normal pressure, and secondary expansion, and producing the secondary foam produced by the secondary mold In the method for producing an open-cell polyolefin foam comprising the step of removing from the above, and the step of compressing and forming the secondary foam, the predetermined temperature is 35 to 50 from the 1-minute half-life temperature of the cross-linking agent. The ethylene-vinyl acetate copolymer has a vinyl acetate content of 20% by weight or less, and the total amount of the ethylene-vinyl acetate copolymer and the polyolefin resin is 100% by weight. % The content of vinyl acetate is 8% by weight or more, the ethylene-vinyl acetate copolymer is 60 to 75% by weight, the polyolefin resin is 25 to 40% by weight, and the polyolefin resin is softened. The point is a method for producing an open-cell polyolefin foam for a heat insulating material or a packing material for water-stopping around a hot water pipe , characterized in that the temperature is equal to or higher than the maximum ambient temperature when the open-cell polyolefin foam is used.

A resin composition containing an ethylene-vinyl acetate copolymer, a polyolefin-based resin, a crosslinking agent and a foaming agent is filled in a primary mold, heated to a predetermined temperature under pressure, then depressurized and primarily expanded to produce. The step of taking out the primary foam from the primary mold, placing the primary foam in the secondary mold, heating under normal pressure, and secondary expansion, and producing the secondary foam produced by the secondary mold In the method for producing a foamed polyolefin foam for a heat insulating material or a packing material for water-stopping around a hot water pipe , comprising the step of removing from the step, compressing the secondary foam and forming a continuous foam. Is a temperature range 40-50 ° C. lower than the 1 minute half-life temperature of the cross-linking agent, the vinyl acetate content of the ethylene-vinyl acetate copolymer is 20% by weight or less, and the ethylene-vinyl acetate Copolymer and the above polyolefin When the total amount with the resin is 100% by weight, the vinyl acetate content in the resin is 8% by weight or more, and the ethylene-vinyl acetate copolymer is 60 to 75% by weight. is a 25 to 40 wt%, the softening point of the polyolefin resin, for a thermal insulator or stop around hot water pipes, characterized in that at the connecting foam polyolefin foam maximum ambient temperature or when using the A process for producing an open-cell polyolefin foam for a packing material for water .