JP4207632B2 - Polyolefin coated steel - Google Patents

Description

【化６】

【０００８】
本発明者らは、上記課題を解決するため鋭意検討した結果、本発明に係わる被覆層を、鋼材表面からクロメート処理層、上記（イ）および（ロ）の成分を含有する熱硬化性樹脂組成物から形成されるプライマー層、変性ポリオレフィン樹脂からなる接着層（これを変性ポリオレフィン接着剤層という）、ポリオレフィン樹脂層の順序で積層させた構成とする。
【０００９】
このような構成かつ順序で積層させた被覆層としたのは、以下の理由による。
先ず、ポリオレフィン樹脂は無極性であるため、直接、鋼材表面と接着しない。
そこで、本発明では、極性基を持ち、接着性を有する変性ポリオレフィン接着剤層を、鋼材とポリオレフィン樹脂層との間に介在させることにより、両者の密着力向上が図れる。
次に変性ポリオレフィン接着剤層と鋼材との間に、クロメート処理層とプライマー層を設けることによりさらに両者の密着力は向上する。つまり、クロメート処理層を形成させることにより、耐陰極剥離性（陰極剥離とは電気防食が施される環境下での過防食電流によって被覆欠陥を起点として容易に被覆樹脂が剥離すること）が向上し、またプライマー層を形成することにより高温接水環境下での長期防食性能がある程度確保できる。
【００１０】
本発明に係わるプライマー層は、主剤として（イ）の成分のエポキシ樹脂と、硬化剤として（ロ）の成分の変性ポリアミンとを配合、硬化させて形成される層である。
ここで、上記（イ）の成分のエポキシ樹脂は、エポキシ当量１５６〜２８０のビスフェノールＡ系エポキシ樹脂、ビスフェノールＦ系エポキシ樹脂の一方または両者の混合物からなるエポキシ樹脂である。
上記（イ）の成分のエポキシ樹脂は、対称性の高い、しかも剛直なビスフェノール骨格を持つため、安定した高温特性（耐温水性）を有する。また骨格中にエーテル結合を有するため適度の可撓性を有する。さらにエポキシ基が反応した結果、水酸基が生成することから接着力が上がる。
【００１１】
同様に、本発明者らは、硬化剤に関しても、耐温水性および可撓性を有する成分を得るべく鋭意検討した。この結果、硬化剤をキシリレンジアミンとするだけでは、高温特性（耐温水性）を有するものの、可撓性を欠く。そこで、さらに鋭意検討した結果、キシリレンジアミンとフェノールをマンニッヒ付加反応して、さらに第三級脂肪酸モノグリシジルエステルをアダクトして得られる変性ポリアミンを硬化剤として用いることにより、高い可撓性を示す硬化物（プライマー層）が得られることがわかった。また、このプライマー層を有する樹脂被覆鋼材は長期間に亘る耐温水性、ヒートショック性に優れたプライマー層が得られることを見いだした。ここで上記反応生成物である変性ポリアミンは、上記化学式（１），（２）に示す子構造を有する材料である。
【００１２】
このような変性ポリアミンを硬化剤とし、前述の特性を有するエポキシ樹脂を主剤とすることにより、８０℃を越える耐温水性、および耐ヒートショック性が良好なプライマー層が形成される。
【００１３】
本発明は、ポリオレフィン被覆鋼材に関するものであり、鋼材表面を上述した構成で被覆し、プライマー層として、上述した熱硬化性樹脂組成物を用いることで、ポリオレフィン樹脂層−鋼材間の密着力が向上し、８０℃を越える高温接水環境下における耐温水性、耐陰極剥離性、耐ヒートショック性が良好な防食性能に優れたポリオレフィン被覆鋼材が得られる。
【００１４】
【発明の実施の形態】
本発明に係わる鋼材は、炭素鋼、低合金鋼等を形鋼、鋼板、棒鋼、鋼管杭、鋼矢板、原油・重質油・天然ガス輸送用の鋼管などに加工したものを対象とし、屋外、地中、海水中等で用いられるものを対象とする。
【００１５】
上記（イ）の成分のエポキシ樹脂には、酸化チタン、シリカ、タルク、白雲母、酸化クロム、リン酸亜鉛等の無機顔料を添加しても良い。また、エポキシ樹脂との接着性を良くするために、無機顔料にシランカップリング処理等の化学処理を施しても良い。
ビスフェノールＡ系エポキシ樹脂としては、エポキシ当量１７０〜２８０のものが使用できるが、取り扱い作業性を考慮すると、好ましくはエポキシ当量が１８４〜１９４の範囲のもの（油化シェルエポキシ（株）製、商品名：エピコート８２８が該当する）が望ましい。
ビスフェノールＦ系エポキシ樹脂としては、エポキシ当量１５６〜２８０のものが使用できるが、取り扱い作業性を考慮すると、好ましくはエポキシ当量が１６０〜１７５の範囲のもの（油化シェルエポキシ（株）製、商品名：エピコート８０７が該当する）が望ましい。
【００１６】
上記（ロ）の成分の変性ポリアミンは、主として上記化学式（１），（２）の分子構造を有するキシリレンジアミンの変性物であるが、この変性物を合成するときに生成する不純物および未反応のキシリレンジアミンが残留していても良い。またキシリレンジアミンは、Ｏ−（オルト−）、ｍ−（メタ−）、Ｐ（パラ−）の異性体の内、どれでも良いが、好ましくは取り扱い作業性、反応性の点からメタキシリレンジアミンが望ましい。
また、（ロ）の成分の変性ポリアミンは、化学式（１），（２）の分子構造を持つ化合物の単独もしくは混合物であれば良い。
【００１７】
また、上記（イ）および（ロ）の成分の配合に関しては、上記（イ）の成分のエポキシ樹脂（主剤）中のエポキシ基のモル数（ａ）と、上記（ロ）の成分の変性ポリアミン（硬化剤）中の活性水素のモル数（ｂ）の比（ｂ／ａ）が、０．７〜１．２の範囲で配合することで優れた耐温水性を有するプライマー層が得られる。
ここで、そのモル数の比（ｂ／ａ）が０．７未満、１．２を越えると、硬化物のガラス転移温度が低下してしまい、耐温水性が低下するので好ましくない。
【００１８】
クロメート処理剤としては、高分子有機質の還元剤で全クロムに対する６価クロムの重量比を、０．３５〜０．６５の範囲になるよう部分還元したクロム酸水溶液にシリカ微粉末を添加したシリカ系クロメート処理剤を用いることができる。
【００１９】
本発明に係わるポリオレフィン樹脂層の材料となるポリオレフィン樹脂とは、低密度ポリエチレン、中密度ポリエチレン、高密度ポリエチレン、直鎖状低密度ポリエチレン、ポリプロピレン等の従来より公知のポリオレフィン等である。
【００２０】
また、変性ポリオレフィン接着剤層の材料となる変性ポリオレフィン樹脂とは、上記のポリオレフィン樹脂をマレイン酸、アクリル酸、メタクリル酸などの不飽和カルボン酸またはその酸無水物で変性したもの、あるいはその変性物をポリオレフィン樹脂で適宜希釈したもの等であり、従来より公知の変性ポリオレフィンである。
【００２１】
次に、本発明に係るポリオレフィン被覆鋼材の一実施形態として、ポリエチレン被覆鋼管の製造方法を説明する。
先ず、錆を除去した鋼管の表面に、クロメート処理剤塗布装置によってクロメート処理剤を塗布し、加熱装置でクロメート処理剤を焼き付けて、クロメート処理層を形成させる。クロメート処理剤塗布装置の出口には、しごき治具を設けてクロメート処理層の表面を均一にさせる。次に、エポキシ樹脂供給容器からは上記（イ）の成分のエポキシ樹脂を、硬化剤供給容器からは上記（ロ）の成分の硬化剤を、それぞれ所定の割合（重量比）で送り出し、エアースプレーのガンの直前で、ミキサーによって混合し、エアースプレーガンでクロメート処理層が形成された鋼管の表面上に吹き付け、塗装されたのち、後加熱装置によって加熱硬化し、プライマー層を形成する。
【００２２】
次に、プライマー層が形成された鋼管の表面上に、丸型ダイス（またはＴ型ダイスでも良い）によって変性ポリエチレン樹脂とポリエチレン樹脂を二層同時に押出し被覆する。この後、冷却装置によって冷却し、ポリエチレン被覆鋼管を得る。この際に、変性ポリエチレン樹脂とポリエチレン樹脂とをそれぞれ単層毎押し出し被覆しても良い。上記製造法の場合、鋼管の表面にクロメート処理剤を塗布し、焼き付けてから後、鋼管が丸型ダイスに達するまでの間に鋼管の表面にプライマー層を形成して十分硬化していればよく、上記エポキシプライマーの塗布方法は、ロール塗布、しごき塗り等の従来公知の方法の中から適宜選択して用いることかできる。また、後加熱装置による鋼管の加熱方法は、高周波誘導加熱、遠赤外線加熱、ガス加熱等の従来公知の方法の中から適宜選択することができる。
【００２３】
以下、本発明の実施の形態について、実施例を用いて具体的に説明する。なお、本発明はその要旨を越えない限り、以下に説明する実施の形態に限定されるものではない。
【００２４】
【実施例】
本発明の効果を確認するため、上述の被覆鋼管製造法によりポリエチレン被覆鋼管を製造し、これより試験片を採取して、防食性能を確性した。
ポリエチレン被覆鋼管の製造は、先ず外径８９．１ｍｍ（８０Ａ）の鋼管表面を、ショットブラストしてスケール等を除去した後、クロメート処理剤を塗布し焼付けた。このクロメート処理層上に、後述する表１、２に示す主剤および硬化剤からなるプライマーを４０〜５０ミクロン厚に塗布し、１３０℃で加熱硬化させて、プライマー層を形成した。
その後、プライマー層上に、無水マレイン酸変性ポリエチレン樹脂層、ポリエチレン樹脂層の順に丸型ダイスを使用して二層同時に溶融押出し、被覆層を形成させた。この際の変性ポリエチレン接着層、ポリエチレン樹脂層の厚みはそれぞれ０．５ｍｍ、３．０ｍｍであった。
なお、表１は、上述した本発明に係るプライマー層の生成に用いたエポキシ樹脂（主剤）および硬化剤の物質と、それらの配合割合を示す。
【００２５】
【表１】

【００２６】
【表２】

【００２７】
製造したポリエチレン被覆鋼管から、所定の大きさの試験片を採取して、温水浸漬試験、陰極剥離試験、熱サイクル試験を行った。なお、各試験法は以下の通りであり、表３に試験結果を示す。
【００２８】
＜温水浸漬試験＞
この試験は、耐温水性を評価するための試験である。
製造したポリエチレン被覆鋼管から幅１０ｍｍ、長さ２００ｍｍの試験片を切出し、サンプルとした。この試験片を試験温度：８５℃の水槽内に、浸漬時間：１００００ｈｒ浸漬した後、被覆樹脂層を引張り試験機で引張り、剥離させた場合の引張強度（これをピール強度という）を測定する。引張試験の測定条件は、温度：室温、剥離角：９０度、剥離速度：１０ｍｍ／ｍｉｎとし、単位はＮ／ｃｍ。ピール強度は、２９．４Ｎ／ｃｍを越えると８０℃を越える耐温水性が良好であると判定する。
【００２９】
＜高温陰極剥離試験＞
この試験は、耐陰極剥離性を評価するための試験である。
試験温度：８５℃、電解液：３％食塩水、印加電圧：−１．５ＶｖｓＡｇ／ＡｇＣｌ、初期ホリデー径：直径９ｍｍ、試験時間：５０日間、試験終了後の被覆樹脂剥離面積を測定する。被覆樹脂剥離面積が８ｃｍ² 以下であると、耐陰極剥離性が良好であると判定する。
【００３０】
＜熱サイクル試験＞
この試験は、耐ヒートショック性を評価するための試験である。
試験条件：−７０℃（８ｈｒ）→２３℃水中（８ｈｒ）→＋４５℃（８ｈｒ）
を１サイクルとし、２５サイクル繰り返した後の試験片の端部剥離の有無を目視観察する。被覆樹脂の端部剥離がないと、耐ヒートショック性が良好であると判定する。
【００３１】
【表３】

【００３２】
実施例１〜６は、エポキシ樹脂（（イ）の成分＝主剤）として、エピコート８２８、エピコート８０７の２種類のものを使用し、キシリレンジアミン変性物（（（ロ）の成分＝硬化剤）として、活性水素当量が７６の化合物を使用した。そして、エポキシ樹脂とキシリレンジアミン変性物を表１、２に示す配合割合で配合し、得られた硬化物をプライマー層とした。
ここで、配合割合とは、エポキシ樹脂（主剤）１００重量部に対して変性ポリアミン（硬化剤）の重量で示したものである。
【００３３】
実施例１〜６に対して温水浸漬試験、陰極剥離試験、熱サイクル試験を行った結果、表３からわかるように、温水浸漬試験後のピール強度は２９．４Ｎ／ｃｍを越え、高温陰極剥離試験による被膜樹脂剥離面積は、８ｃｍ² 以下が得られた。また、熱サイクル試験による被覆樹脂の端部剥離は認められなかった。この結果８０℃を越える耐温水性、耐陰極剥離性、耐ヒートショック性のいずれも良好で、防食性能に優れたポリエチレン被覆鋼管が得られた。
【００３４】
比較例１〜６は、エポキシ樹脂（主剤）としてエピコート８２８を使用し、硬化剤としては（ロ）の成分のもの以外にＢ００２、またはＢ００２とＭＸＤＡの混合物を使用した。
ここで、Ｂ００２は、特開昭５６−１４３２２３号公報に開示されているように、下記化学式（３）の分子構造を有する複素環状ミン２モルに対してブチルグリシジルエーテル１モルを反応させた変性複素環状アミンであり、ＭＸＤＡは下記化学式（４）の分子構造を有するｍ−キシリレンジアミンである。
【化７】

【化８】

【００３５】
比較例１〜６に対して温水浸漬試験、陰極剥離試験、熱サイクル試験を行った結果、表３からわかるように、ピール強度および被覆樹脂剥離面積の値は良好でなく、さらに被覆樹脂の端部剥離も認められた。また、比較例４〜６は、耐ヒートショック性は良好であるが、８０℃を越える耐温水性、耐陰極剥離性は、いずれも良好と判断できず、防食性能に優れたポリエチレン被覆鋼管であると評価できない。
【００３６】
【発明の効果】
以上のように本発明に係るポリオレフィン被覆鋼材は、鋼材表面からクロメート処理層、プライマー層、変性ポリオレフィン接着剤層、ポリオレフィン樹脂層を順次鋼材表面に被覆したポリオレフィン被覆鋼材であって、上記（イ）および（ロ）の成分を含有する熱硬化性樹脂組成物をプライマー層に用いたので、ポリオレフィン樹脂層−鋼材間の密着力が向上し、８０℃を越える耐温水性、耐陰極剥離性、耐ヒートショック性が良好な、防食性能に優れたポリオレフィン被覆鋼材が得られる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyolefin-coated steel material, and more particularly to a polyolefin-coated steel material that can improve the adhesion between the polyolefin resin layer and the steel material and has excellent anticorrosion performance.
[0002]
[Prior art]
Steel materials coated with polyolefin resin on the surface (hereinafter referred to as polyolefin coated steel materials) have excellent long-term anticorrosion performance, so in addition to conventional applications such as steel pipes, steel pipe piles, and steel sheet piles, It has also come to be used as a steel for building materials used in cold regions and the tropics, and as a steel for pipelines that transport crude oil, heavy oil, and natural gas.
Since it has come to be used in a wide range of temperature environments and high-temperature water contact environments, it is required to improve anticorrosion performance, that is, to improve resistance to warm water and heat shock, compared to conventional methods. . In addition, in an environment in which cathodic protection is used in combination, cathode peeling due to over-corrosion current becomes a problem, and therefore, improvement in resistance to cathode peeling is also a problem.
[0003]
As a conventional technique related to a polyolefin-coated steel material, there is a method of applying a chromate treatment layer between a steel material and a modified polyolefin resin adhesive layer (see, for example, Patent Document 1 and Patent Document 2). Further, there is a method of interposing an epoxy primer layer (see, for example, Patent Document 3 and Patent Document 4). Furthermore, there is a method of further improving the anticorrosion performance by interposing an epoxy primer layer on the chromate treatment layer (see, for example, Patent Document 5).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 54-120682 [Patent Document 2]
JP-A-1-280545 [Patent Document 3]
JP 56-143223 A [Patent Document 4]
JP 59-222275 A [Patent Document 5]
JP-A-60-245544
[Problems to be solved by the invention]
However, the methods of performing chromate treatment and the method of interposing an epoxy primer layer disclosed in Patent Documents 1 to 4 can provide satisfactory performance in a wetted environment of 60 ° C. or lower, but exceed 60 ° C. There was a problem that satisfactory performance in hot water resistance and cathodic peel resistance could not be obtained in a wetted environment.
In addition, the method of using the chromate treatment and the primer treatment disclosed in Patent Document 5 can achieve satisfactory performance in a water contact environment of 80 ° C. or lower, but in a water contact environment exceeding 80 ° C., Satisfactory performance in hot water resistance and cathode peel resistance cannot be obtained. In particular, the adhesion between the polyolefin resin layer and the steel material was significantly reduced, and it was difficult to maintain long-term anticorrosion performance.
[0006]
The present invention has been made in order to solve the above-described problems, and has improved adhesion between the polyolefin resin layer and the steel material, and is resistant to warm water and cathodic resistance under high temperature water contact exceeding 80 ° C. An object of the present invention is to provide a polyolefin-coated steel material having excellent peelability and heat shock resistance and excellent anticorrosion performance.
[0007]
[Means for Solving the Problems]
The polyolefin-coated steel material according to the present invention is characterized in that a thermosetting resin composition containing the following components (a) and (b) is used for the primer layer.
(A) an epoxy resin comprising one or a mixture of a bisphenol A type epoxy resin and a bisphenol F type epoxy resin having an epoxy equivalent of 156 to 280,
(B) A modified polyamine comprising a mixture having a structure represented by chemical formulas (1) and (2), which is a modified xylylenediamine.
[Chemical formula 5]

[Chemical 6]

[0008]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have determined that the coating layer according to the present invention comprises a chromate-treated layer, a thermosetting resin composition containing the components (a) and (b) above from the steel surface. It is set as the structure laminated | stacked in order of the primer layer formed from a thing, the contact bonding layer (this is called a modification polyolefin adhesive layer) which consists of modification polyolefin resin, and the polyolefin resin layer.
[0009]
The reason why the coating layer is laminated in this configuration and order is as follows.
First, since polyolefin resin is nonpolar, it does not directly adhere to the steel surface.
Therefore, in the present invention, the adhesive strength between the two can be improved by interposing a modified polyolefin adhesive layer having a polar group and adhesion between the steel material and the polyolefin resin layer.
Next, by providing a chromate treatment layer and a primer layer between the modified polyolefin adhesive layer and the steel material, the adhesion between them is further improved. In other words, by forming a chromate treatment layer, the resistance to cathodic peeling (cathodic peeling is the ability of the coating resin to peel off easily starting from coating defects due to over-corrosion current in an environment where cathodic protection is applied). In addition, by forming the primer layer, long-term anticorrosion performance in a high temperature wetted environment can be secured to some extent.
[0010]
The primer layer according to the present invention is a layer formed by blending and curing an epoxy resin of component (a) as a main agent and a modified polyamine of component (b) as a curing agent.
Here, the epoxy resin of the component (A) is an epoxy resin made of one or a mixture of a bisphenol A epoxy resin and a bisphenol F epoxy resin having an epoxy equivalent of 156 to 280.
The epoxy resin as the component (a) has a high symmetry and a rigid bisphenol skeleton, and therefore has stable high temperature characteristics (warm water resistance). Moreover, since it has an ether bond in the skeleton, it has moderate flexibility. Furthermore, as a result of the reaction of the epoxy group, a hydroxyl group is generated, so that the adhesive force is increased.
[0011]
Similarly, the present inventors have also intensively studied to obtain a component having hot water resistance and flexibility with respect to the curing agent. As a result, merely using xylylenediamine as a curing agent has high temperature characteristics (warm water resistance), but lacks flexibility. Therefore, as a result of further intensive studies, high flexibility is exhibited by using a modified polyamine obtained by subjecting xylylenediamine and phenol to a Mannich addition reaction and further adducting a tertiary fatty acid monoglycidyl ester as a curing agent. It was found that a cured product (primer layer) was obtained. Moreover, it has been found that the resin-coated steel material having this primer layer can provide a primer layer excellent in warm water resistance and heat shock resistance over a long period of time. Here, the modified polyamine which is the reaction product is a material having a child structure represented by the chemical formulas (1) and (2).
[0012]
By using such a modified polyamine as a curing agent and an epoxy resin having the above-mentioned characteristics as a main agent, a primer layer having a warm water resistance exceeding 80 ° C. and a good heat shock resistance can be formed.
[0013]
The present invention relates to a polyolefin-coated steel material, and the adhesion between the polyolefin resin layer and the steel material is improved by coating the steel material surface with the above-described configuration and using the above-described thermosetting resin composition as a primer layer. In addition, a polyolefin-coated steel material excellent in anticorrosion performance having excellent hot water resistance, cathodic peel resistance, and heat shock resistance in a high temperature water contact environment exceeding 80 ° C. can be obtained.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Steel materials according to the present invention are made by processing carbon steel, low alloy steel, etc. into shaped steel, steel plates, steel bars, steel pipe piles, steel sheet piles, steel pipes for transporting crude oil, heavy oil, natural gas, etc. It is intended for use in the ground, seawater, etc.
[0015]
An inorganic pigment such as titanium oxide, silica, talc, muscovite, chromium oxide, or zinc phosphate may be added to the epoxy resin as the component (a). Further, in order to improve the adhesiveness with the epoxy resin, the inorganic pigment may be subjected to chemical treatment such as silane coupling treatment.
As the bisphenol A-based epoxy resin, those having an epoxy equivalent of 170 to 280 can be used. However, in consideration of handling workability, those having an epoxy equivalent of 184 to 194 are preferably (Product made by Yuka Shell Epoxy Co., Ltd. Name: Epicoat 828) is desirable.
As the bisphenol F-based epoxy resin, those having an epoxy equivalent of 156 to 280 can be used. However, in consideration of handling workability, those having an epoxy equivalent of 160 to 175 (product made by Yuka Shell Epoxy Co., Ltd., product) (Name: Epicoat 807 corresponds).
[0016]
The modified polyamine as the component (b) is a modified product of xylylenediamine mainly having the molecular structure of the chemical formulas (1) and (2), and impurities generated when this modified product is synthesized and unreacted Of xylylenediamine may remain. Xylylenediamine may be any of the isomers O- (ortho-), m- (meta-), and P (para-), but is preferably metaxylylene diene in terms of handling workability and reactivity. Amines are desirable.
The modified polyamine as the component (b) may be a single compound or a mixture of compounds having the molecular structures of the chemical formulas (1) and (2).
[0017]
Regarding the blending of the components (a) and (b), the number of moles of epoxy groups (a) in the epoxy resin (main agent) of the component (a) and the modified polyamine of the component (b) A primer layer having excellent hot water resistance can be obtained by blending the ratio (b / a) of the number of moles (b) of active hydrogen in (curing agent) in the range of 0.7 to 1.2.
Here, when the ratio (b / a) of the number of moles is less than 0.7 or more than 1.2, the glass transition temperature of the cured product is lowered and the hot water resistance is lowered, which is not preferable.
[0018]
As a chromate treatment agent, silica obtained by adding silica fine powder to a chromic acid aqueous solution that was partially reduced to a weight ratio of hexavalent chromium to total chromium in the range of 0.35 to 0.65 with a high molecular weight organic reducing agent. A system chromate treating agent can be used.
[0019]
The polyolefin resin used as the material of the polyolefin resin layer according to the present invention is a conventionally known polyolefin such as low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, and polypropylene.
[0020]
Moreover, the modified polyolefin resin used as the material of the modified polyolefin adhesive layer is obtained by modifying the above polyolefin resin with an unsaturated carboxylic acid such as maleic acid, acrylic acid or methacrylic acid, or an acid anhydride thereof, or a modified product thereof. Are appropriately diluted with polyolefin resins, and are conventionally known modified polyolefins.
[0021]
Next, as an embodiment of the polyolefin-coated steel material according to the present invention, a method for producing a polyethylene-coated steel pipe will be described.
First, a chromate treatment agent is applied to the surface of the steel pipe from which rust has been removed by a chromate treatment agent coating device, and the chromate treatment agent is baked by a heating device to form a chromate treatment layer. An ironing jig is provided at the outlet of the chromate treatment agent coating apparatus to make the surface of the chromate treatment layer uniform. Next, the epoxy resin of component (a) is sent out from the epoxy resin supply container, and the curing agent of component (b) is sent out from the curing agent supply container at a predetermined ratio (weight ratio), respectively, and air spray Immediately before the gun, they are mixed by a mixer, sprayed onto the surface of the steel pipe on which the chromate treatment layer is formed by an air spray gun, painted, and then heated and cured by a post-heating device to form a primer layer.
[0022]
Next, two layers of the modified polyethylene resin and the polyethylene resin are simultaneously extruded and coated on the surface of the steel pipe on which the primer layer is formed, using a round die (or a T-type die). Then, it cools with a cooling device and obtains a polyethylene covering steel pipe. At this time, each of the modified polyethylene resin and the polyethylene resin may be extruded and coated in a single layer. In the case of the above manufacturing method, a primer layer is formed on the surface of the steel pipe after the chromate treatment agent is applied to the surface of the steel pipe and baked until the steel pipe reaches the round die. The method of applying the epoxy primer can be appropriately selected from conventionally known methods such as roll coating and ironing. Moreover, the heating method of the steel pipe by the post-heating device can be appropriately selected from conventionally known methods such as high-frequency induction heating, far-infrared heating, and gas heating.
[0023]
Hereinafter, embodiments of the present invention will be specifically described using examples. It should be noted that the present invention is not limited to the embodiment described below unless it exceeds the gist.
[0024]
【Example】
In order to confirm the effect of the present invention, a polyethylene-coated steel pipe was manufactured by the above-described coated steel pipe manufacturing method, and a test piece was collected from the polyethylene-coated steel pipe to ensure the anticorrosion performance.
In the production of a polyethylene-coated steel pipe, first, the surface of a steel pipe having an outer diameter of 89.1 mm (80 A) was shot blasted to remove scales, and then applied with a chromate treatment agent and baked. On this chromate-treated layer, a primer composed of a main agent and a curing agent shown in Tables 1 and 2 described later was applied to a thickness of 40 to 50 microns and cured by heating at 130 ° C. to form a primer layer.
Then, two layers were melt-extruded simultaneously on the primer layer using a circular die in the order of the maleic anhydride-modified polyethylene resin layer and the polyethylene resin layer to form a coating layer. At this time, the thicknesses of the modified polyethylene adhesive layer and the polyethylene resin layer were 0.5 mm and 3.0 mm, respectively.
Table 1 shows the substances of the epoxy resin (main agent) and the curing agent used for generating the primer layer according to the present invention described above, and the blending ratio thereof.
[0025]
[Table 1]

[0026]
[Table 2]

[0027]
A test piece of a predetermined size was collected from the manufactured polyethylene-coated steel pipe and subjected to a hot water immersion test, a cathode peeling test, and a thermal cycle test. Each test method is as follows, and Table 3 shows the test results.
[0028]
<Hot water immersion test>
This test is a test for evaluating hot water resistance.
A test piece having a width of 10 mm and a length of 200 mm was cut out from the manufactured polyethylene-coated steel pipe to prepare a sample. After immersing this test piece in a water bath at a test temperature of 85 ° C., immersion time: 10000 hr, the tensile strength (this is called peel strength) is measured when the coated resin layer is pulled with a tensile tester and peeled off. The measurement conditions of the tensile test are as follows: temperature: room temperature, peel angle: 90 degrees, peel speed: 10 mm / min, and the unit is N / cm. When the peel strength exceeds 29.4 N / cm, it is determined that the warm water resistance exceeding 80 ° C. is good.
[0029]
<High temperature cathode peeling test>
This test is a test for evaluating the cathode peel resistance.
Test temperature: 85 ° C., electrolyte solution: 3% saline, applied voltage: −1.5 V vs Ag / AgCl, initial holiday diameter: diameter 9 mm, test time: 50 days, coating resin peeling area after completion of test is measured. When the coating resin peeling area is 8 cm ² or less, it is determined that the cathode peeling resistance is good.
[0030]
<Thermal cycle test>
This test is a test for evaluating heat shock resistance.
Test conditions: -70 ° C. (8 hr) → 23 ° C. water (8 hr) → + 45 ° C. (8 hr)
1 cycle, and the presence or absence of end peeling of the test piece after repeating 25 cycles is visually observed. If there is no end peeling of the coating resin, it is determined that the heat shock resistance is good.
[0031]
[Table 3]

[0032]
In Examples 1 to 6, two types of Epicoat 828 and Epicoat 807 were used as the epoxy resin (component (b) = main agent), and xylylenediamine modified product (((b) component = curing agent). A compound having an active hydrogen equivalent of 76 was used, and an epoxy resin and a xylylenediamine modified product were blended in the blending ratios shown in Tables 1 and 2, and the resulting cured product was used as a primer layer.
Here, the blending ratio is the weight of the modified polyamine (curing agent) with respect to 100 parts by weight of the epoxy resin (main agent).
[0033]
As a result of performing the hot water immersion test, the cathode peeling test, and the thermal cycle test on Examples 1 to 6, as can be seen from Table 3, the peel strength after the hot water immersion test exceeded 29.4 N / cm, and the high temperature cathode peeling The coating resin peeling area by the test was 8 cm ² or less. Moreover, the edge part peeling of coating resin by a heat cycle test was not recognized. As a result, it was possible to obtain a polyethylene-coated steel pipe excellent in anticorrosion performance, with all of hot water resistance exceeding 80 ° C., cathodic peel resistance, and heat shock resistance.
[0034]
In Comparative Examples 1 to 6, Epicoat 828 was used as the epoxy resin (main agent), and B002 or a mixture of B002 and MXDA was used as the curing agent in addition to the component (b).
Here, as disclosed in JP-A-56-143223, B002 is a modified product obtained by reacting 1 mol of butyl glycidyl ether with 2 mol of a heterocyclic amine having a molecular structure of the following chemical formula (3). It is a heterocyclic amine, and MXDA is m-xylylenediamine having a molecular structure of the following chemical formula (4).
[Chemical 7]

[Chemical 8]

[0035]
As a result of performing a warm water immersion test, a cathode peeling test, and a thermal cycle test on Comparative Examples 1 to 6, as can be seen from Table 3, the peel strength and the coating resin peeling area are not good, and the edge of the coating resin Partial peeling was also observed. Further, Comparative Examples 4 to 6 have good heat shock resistance, but cannot be judged to have good warm water resistance and cathode peel resistance exceeding 80 ° C., and are polyethylene-coated steel pipes excellent in anticorrosion performance. It cannot be evaluated that there is.
[0036]
【The invention's effect】
As described above, the polyolefin-coated steel material according to the present invention is a polyolefin-coated steel material in which the steel material surface is sequentially coated with the chromate-treated layer, the primer layer, the modified polyolefin adhesive layer, and the polyolefin resin layer from the steel material surface. And the thermosetting resin composition containing the component (b) is used for the primer layer, so that the adhesion between the polyolefin resin layer and the steel material is improved, and the hot water resistance exceeding 80 ° C., the cathode peeling resistance, A polyolefin-coated steel material having good heat shock and excellent anticorrosion performance can be obtained.

Claims (2)

A polyolefin-coated steel material comprising a thermosetting resin composition containing the following components (a) and (b) as a primer layer.
(A) an epoxy resin comprising one or a mixture of a bisphenol A type epoxy resin and a bisphenol F type epoxy resin having an epoxy equivalent of 156 to 280,
(B) A modified polyamine comprising a mixture having a structure represented by chemical formulas (1) and (2), which is a modified xylylenediamine.

It is a polyolefin-coated steel material in which a chromate treatment layer, a primer layer, a modified polyolefin adhesive layer, and a polyolefin resin layer are sequentially coated on the steel material surface from the steel material surface,
A polyolefin-coated steel material, wherein a thermosetting resin composition containing the following components (a) and (b) is used for the primer layer.
(A) an epoxy resin comprising one or a mixture of a bisphenol A type epoxy resin and a bisphenol F type epoxy resin having an epoxy equivalent of 156 to 280,
(B) A modified polyamine comprising a mixture having a structure represented by chemical formulas (1) and (2), which is a modified xylylenediamine.