JPH09314741A - Polyethylene-coated steel material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a low-temperature impact resistance by laminating a fiber-reinforced epoxy primer layer wherein both front and rear faces of a fiber cloth are impregnated in advance with a reactive cure type epoxy, a modified polyethylene layer, and a low-density polyethylene layer in order named on the surface of a steel material subjected to undercoating treatment. SOLUTION: A polyethylene-coated steel material 8 is formed by successively laminating a fiber-reinforced epoxy primer layer 3 wherein both front and rear faces of a fiber cloth 6 are impregnated in advance with reactive cure type epoxys 7, 7, a modified polyethylene layer 4, and a low-density polyethylene layer 5 in order named on the surface of a steel material 1 subjected to undercoating treatment with a chromate coating 2. In this case, the fiber- reinforced epoxy primer layer 3 is directly formed on the steel material 1 by successively laminating the reactive cure type epoxy 7, the fiber cloth 6, and the reactive cure type epoxy 7 in order named during the manufacture of the polyethylene-coated steel material 8. Accordingly, since a crack transmissionpreventing function is imparted to the fiber-reinforced epoxy primer layer 3, an impact resistance under the condition of environment at an ultra-low temperature such as, for example, -60 deg.C is greatly improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyethylene-coated steel material, and more particularly to a polyethylene-coated steel material having excellent corrosion resistance and low-temperature impact resistance.

[0002]

2. Description of the Related Art Polyethylene-coated steel materials having an outer surface coated with polyethylene are often used in construction materials for civil engineering such as line pipes for oil and natural gas and steel sheet piles and steel pipe piles. Since polyethylene is chemically stable, a polyethylene coating layer on steel allows long-term corrosion protection of steel. However, due to its chemical stability, polyethylene has poor adhesion to steel. Therefore, the polyethylene-coated steel material prevents the polyethylene layer from peeling off from the steel material by interposing an adhesive layer between the steel material and the polyethylene layer.

[0003] A general polyethylene-coated steel material is prepared by forming an epoxy primer layer on the surface of a steel material that has been subjected to a rust-removing treatment and a chromate treatment as a base treatment, and laminating a modified polyethylene layer and a polyethylene layer in that order to form polyethylene. Prevents peeling of the layer from the steel material.
In recent years, energy development in polar regions has progressed, and -30 to -45
Civil engineering work such as pipeline laying work has come to be performed in a low temperature environment such as ℃. Even in such a low temperature environment, polyethylene-coated steel shows excellent corrosion resistance,
The polyethylene coating layer may be cracked due to the impact of the contact between the coated steel material and the heavy machine at the time of construction or the collision between the coated steel materials, and the polyethylene layer may be separated from the steel material to impair the corrosion resistance. Therefore, the polyethylene-coated steel material used in cold regions is coated with low-density polyethylene, which has excellent embrittlement resistance at low temperatures, to prevent coating cracking due to impact.

[0004]

With a polyethylene-coated steel material coated with low density polyethylene, it is possible to prevent coating cracking due to impact up to -45 ° C. However, in the future, further energy development in the polar regions
When civil engineering work is carried out in an extremely low temperature environment of 60 ° C., the impact resistance of the current polyethylene-coated steel material is insufficient, and the impact causes the coating layer to crack. Therefore, it is desired to improve the low temperature impact resistance of the polyethylene coating layer.

[0005]

Means for Solving the Problems The inventors of the present invention have made extensive studies in order to solve the above-mentioned problems. As a result, by adding a crack propagation prevention function to the epoxy primer layer,
The inventors have found that the impact resistance in an extremely low temperature environment such as −60 ° C. is greatly improved, and have reached the present invention. That is, according to the present invention, as shown in FIGS. 1 and 2, a fiber-reinforced epoxy primer layer 3 obtained by preliminarily impregnating the front and back surfaces of a fiber cloth 6 with a reaction-curable epoxy 7 on the surface of a steel material 1 that has been subjected to a base 2 treatment. And a modified polyethylene layer 4 and a low-density polyethylene layer 5 are sequentially laminated on the fiber-reinforced epoxy primer layer 3, or the fiber-reinforced epoxy primer layer 3 is a steel material that has been subjected to a base 2 treatment. On the surface of 1,
Reaction-curable epoxy 7 and fiber cloth 6 are sequentially laminated,
Reaction curing type epoxy 7 from the lower surface to the upper surface of the fiber cloth 6
It is a polyethylene-coated steel material having excellent anticorrosion properties and low-temperature impact resistance, which is obtained by directly impregnating the front and back surfaces with a reaction hardening type epoxy 7 and directly forming on the steel material 1. The base 2 is a chromate film for further improving the anticorrosion property.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The steel material 1 used in the present invention is a steel sheet such as a cold rolled steel sheet, a hot rolled steel sheet, a thick steel sheet, a shaped steel such as an H-shaped steel, an I-shaped steel, an L-shaped steel, or a steel sheet pile. , Steel bar, steel wire, cast iron pipe,
Examples include steel pipes and steel pipe sheet piles. Further, as the steel material used in the present invention, a clad steel material obtained by laminating a metal such as stainless steel, titanium, aluminum, nickel, copper or an alloy steel thereof on the surface of these steel materials can be used. Further, a plated steel material in which the surface of the steel material is plated can also be used.

The steel material 1 is preferably subjected to rust removal treatment such as blast treatment, degreasing and pickling treatment. Further, it is preferable to apply a chromate treatment agent to the surface of the steel material 1 with a roll, a brush or the like and heat / bak it to form the chromate film 2 because the anticorrosion property can be further improved. The chromate treating agent is, for example, an organic reducing agent added to an aqueous solution of chromic anhydride and heated to obtain 6
A mixture or the like in which fine particles of silica are added and dispersed in a reducing aqueous solution in which a part of valent chromium is partially reduced to trivalent chromium is used.

Good results are obtained when the chromate film has a thickness of ²⁰ mg to 1000 mg / m ^{2 in} terms of the total amount of chromium deposited after heating and baking. If it is less than 20 mg / m ² , the corrosion resistance is insufficient, and if it exceeds 1000 mg / m ² , the adhesion between the steel material and the epoxy primer layer decreases. The fiber-reinforced epoxy primer layer 3 is a laminate in which the reaction-curable epoxy 7 and the fiber cloth 6 are sequentially laminated, and the reaction-curable epoxy 7 is transmitted from the lower surface to the upper surface of the fiber cloth 6. The fiber-reinforced epoxy primer layer 3 can be directly formed on the steel material by sequentially laminating the reaction-curable epoxy 7 and the fiber cloth 6 when manufacturing the polyethylene-coated steel material. Alternatively, the fiber-reinforced epoxy primer layer 3 manufactured in advance can be laminated on the steel material. Reaction curable epoxies are mixtures of liquid epoxies, hardeners and pigments. The liquid epoxy is preferably a diglycidyl ether of bisphenol A or bisphenol F, or a mixture thereof. As a curing agent, an alicyclic amine,
Aliphatic amine, dicyandiamide, modified imidazole and the like are used. As the pigment, an inorganic pigment such as silica or alumina is used. The fibers used for the fiber cloth 6 may be inorganic fibers (including metals) or organic fibers, but one or two of glass fibers, carbon fibers, boron fibers, alumina fibers, nylon fibers, aramid fibers, etc. When a fiber cloth made of at least one kind is used, the fiber-reinforced epoxy primer layer 3 can be provided with an excellent crack propagation preventing function. In particular, glass fiber cloth is preferable from the viewpoint of economy and easy availability. Although the thickness of the fiber and the woven structure of the fiber cloth are not limited, good results are obtained when the weight of the fiber cloth is 10 to 800 g / m ² .
If it is less than 10 g / m ² , the crack propagation preventing effect is not sufficient, and if it exceeds 800 g / m ² , it becomes difficult to sufficiently impregnate the fiber cloth with the reaction-curable epoxy, and it is difficult to impregnate the fiber cloth with the epoxy cured product. Since there is a gap, the anticorrosion performance becomes insufficient. In addition, in order to improve the adhesiveness between the fiber cloth and the reaction-curable epoxy, a conventionally known surface treatment agent may be applied to the fiber cloth and used. Although the thickness of the fiber reinforced epoxy primer layer 3 varies depending on the thickness of the fiber cloth used, good results can be obtained if the thickness is 0.01 mm to 0.2 mm thicker than the original thickness of the fiber cloth.
If it is less than 0.01 mm, the impregnation of the fiber cloth with the epoxy primer is insufficient, and if it exceeds 0.2 mm, the impact resistance is lowered.

The modified polyethylene layer 4 may be any as long as it has excellent adhesiveness to the fiber-reinforced epoxy primer layer 3 and fusion property to the low-density polyethylene layer 5, but is not limited to ethylene homopolymer or ethylene. And an ethylene-α-olefin copolymer obtained by copolymerizing α-olefin such as 1-butene, propylene, 1-hexene or 1-octene, or a maleic anhydride obtained by graft-polymerizing maleic anhydride to a mixture thereof. The use of modified polyethylene is preferable because it has excellent adhesiveness to steel materials. Good results are obtained when the modified polyethylene layer 4 has a thickness of 0.02 to 1.0 mm. If it is less than 0.02 mm, the adhesive strength with the steel material is insufficient. Further, if it exceeds 1.0 mm, it is not preferable from the economical viewpoint.

Low density polyethylene layer 5 used in the present invention
Is a low-density polyethylene obtained by homopolymerizing ethylene by a high-pressure method, or a linear low-density polyethylene obtained by copolymerizing ethylene and an α-olefin such as 1-butene, propylene, 1-hexene or 1-octene by a medium-low pressure method. It is a composition comprising one or more of the above polyethylenes. The density of the composition is preferably 0.935 g / cm ³ or less. The composition has a density of 0.935 g / cm
^If it exceeds ³ , the low temperature toughness becomes insufficient, so cracking may occur due to low temperature impact. It is preferable that the low density polyethylene layer 5 has a thickness of 0.5 mm or more because sufficient corrosion resistance can be obtained.

The low-density polyethylene layer 5 may be mixed with a color pigment, an antioxidant, an ultraviolet absorber, a flame retardant, an antistatic agent, etc., depending on the application, and the effect of the present invention may be obtained. . Hereinafter, the present invention will be described in detail with reference to examples in which a steel pipe is used as a steel material.

[0012]

[Example] Steel pipe (SGP200A x 5500 mm length x
The outer surface of 5.8 mm thickness is rust-treated by blasting, and the chromate treatment agent (weight ratio of trivalent chromium to total chromium in the aqueous solution is 0.4, weight ratio of silica is 2.0, and weight of phosphoric acid) A ratio of 1.0) was applied with a brush and dried. The total amount of chromium deposited on the chromate film was 550 mg / m ² . An epoxy primer (Epicoat 828: 10 manufactured by Yuka Shell Epoxy Co., Ltd.) was formed on the outer surface of the chromated steel pipe.
0 parts by weight, Epomate B-00 manufactured by Yuka Shell Epoxy Co., Ltd.
A mixture of 2:50 parts by weight and fine particle silica: 3 parts by weight) was spray-coated, and a fiber cloth having a width of 150 mm was spirally coated on the outer surface of the steel pipe. The fiber cloths are ac in Table 1
The fiber cloth shown in was used. After the epoxy cloth was sufficiently impregnated with the epoxy primer by roll-pressing, the steel pipe was heated by high-frequency induction heating so that the surface temperature became 200 ° C. to cure the epoxy primer layer. Two layers of low-density polyethylene and modified polyethylene (modified polyethylene obtained by modifying an ethylene homopolymer with maleic anhydride; the addition amount of maleic anhydride is 1 x 10 ^-5 mol per 1 g of modified polyethylene) and low-density polyethylene Extrusion coated from a T-die. Modified polyethylene thickness is 0.25mm
The thickness of polyethylene was 2.0 mm. After cooling, a polyethylene-coated steel pipe according to the present invention was manufactured.

In order to evaluate the low temperature impact resistance of the coated steel pipe of the present invention, an impact test was carried out at -60 ° C using an impact test device shown in ASTM G14. A 20-point impact test was conducted with the impact energy kept constant at 70 J, and it was observed whether or not coating cracking occurred due to impact. For comparison, a polyethylene-coated steel pipe in which the thickness of the epoxy primer layer was changed using a normal epoxy primer and a polyethylene-coated steel pipe having no epoxy primer layer were prepared, and the same impact test was performed.

The results are collectively shown in Table 2. From Table 2,
A fiber-reinforced epoxy primer layer consisting of a reaction-curing epoxy and a fiber cloth impregnated with a reaction-curing epoxy is provided on the surface of a steel material that has been subjected to a base treatment, and a modified polyethylene layer and a low-density polyethylene layer are sequentially laminated on it. By doing so, the low temperature impact resistance at −60 ° C. can be improved.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

As is apparent from the examples, the polyethylene-coated steel material of the present invention is superior to the conventional polyethylene-coated steel material in low-temperature impact resistance in an extremely low temperature environment of -60 ° C. Therefore, when it is used for line pipes, steel sheet piles, steel pipe piles, etc., it is possible to prevent coating cracking due to impact even during civil engineering work in a cryogenic environment, and to exhibit unprecedented excellent corrosion resistance.

[Brief description of drawings]

FIG. 1 is a view showing a partial cross section of a polyethylene-coated steel material of the present invention.

FIG. 2 is a cross-sectional view of a fiber-reinforced epoxy primer layer used in the polyethylene-coated steel material of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Steel material 2 ... Chromate film 3 ... Fiber reinforced epoxy primer layer 4 ... Modified polyethylene layer 5 ... Low density polyethylene layer 6 ... Fiber cloth 7 ... Reaction hardening type epoxy 8 ... Polyethylene coated steel material

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Claims (2)

[Claims] 1. A surface of a steel material that has been subjected to a base treatment is laminated with a fiber-reinforced epoxy primer layer in which both sides of a fiber cloth are impregnated with a reaction-curable epoxy in advance, and on the fiber-reinforced epoxy primer layer, A polyethylene-coated steel material having excellent low-temperature impact resistance, which is obtained by sequentially laminating a modified polyethylene layer and a low-density polyethylene layer. 2. The fiber-reinforced epoxy primer layer comprises:
A reaction-curable epoxy and a fiber cloth are sequentially laminated on the surface of the steel material subjected to the base treatment, the reaction-curable epoxy is allowed to permeate from the lower surface to the upper surface of the fiber cloth, and the reaction-curable epoxy is provided on both front and back surfaces. The polyethylene-coated steel material according to claim 1, wherein the polyethylene-coated steel material is impregnated with, and is directly formed on the steel material.