JPH09314739A - Polyethylene-coated steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve low temperature impact resistance by laminating an epoxy primer layer of a reaction curing type epoxy resin, a fiber reinforced modified polyethylene layer in which modified polyethylene layers are laminated previously on both sides of a fiber cloth, and an low density polyethylene layer in sequence on the surface of surface-treated steel. SOLUTION: On the surface of steel 1 which is surface-treated with a chromate coat 2, an epoxy primer layer 3 of a reaction curing type epoxy resin, a fiber reinforced modified polyethylene layer 4 in which modified polyethylene layers 6 are laminated previously on both sides of a fiber cloth 7, and a low density polyethylene layer 5 in sequence to make a polyethylene-coated steel 8. By forming the fiber reinforced modified polyethylene layer 4, a crack propagation preventive function is given to improve impact resistance under cryogenic environment, e.g. at -60 deg.C.

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 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 then laminating a modified polyethylene layer and a polyethylene layer in this 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, as shown in FIG. 2, the modified polyethylene layer 6 was formed into the fiber-reinforced modified polyethylene layer 4 laminated on both sides of the fiber cloth 7, and the crack propagation preventing function was imparted to the modified polyethylene layer 6 in an extremely low temperature environment such as −60 ° C. The inventors have found that the impact resistance of the present invention is greatly improved and have reached the present invention. That is, according to the present invention, as shown in FIGS. 1 and 2, an epoxy primer layer 3 made of a reaction-curable epoxy is laminated on the surface of a steel material 1 that has been subjected to a base 2 treatment, and a fiber is formed on the epoxy primer layer 3. Laminating the fiber-reinforced modified polyethylene layer 4 in which the modified polyethylene layer 6 is previously laminated on both front and back surfaces of the cloth 7, and laminating the low-density polyethylene layer 5 on the fiber-reinforced modified polyethylene layer 4, or the fiber-reinforced modified layer The polyethylene layer 4 includes a modified polyethylene layer 6, a fiber cloth 7 and a modified polyethylene layer 6 on the epoxy primer layer 3.
Is sequentially laminated and formed directly on the steel material, and is a polyethylene-coated steel material having excellent corrosion resistance and low-temperature impact resistance. 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 epoxy primer layer 3 is a chromate film 2 on the surface of the steel material 1.
An epoxy primer composed of a mixture of an epoxy, a curing agent and a pigment is applied onto the above by a method such as spray painting or ironing, and is heated and cured to form. The epoxy is preferably a diglycidyl ether of bisphenol A or bisphenol F, or a mixture thereof. As the curing agent, 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. Good results are obtained when the epoxy primer layer has a thickness of 0.01 mm to 0.2 mm. If it is less than 0.01 mm, the corrosion resistance is insufficient, and if it exceeds 0.2 mm, the impact resistance is lowered.

The fiber-reinforced modified polyethylene layer 4 is a laminate in which the modified polyethylene 6 is laminated on both sides of the fiber cloth 7. The fiber-reinforced modified polyethylene layer 4 is formed by sequentially laminating modified polyethylene, fiber cloth, and modified polyethylene at the time of producing a polyethylene-coated steel material, and then pressure-bonding with a roller or the like, or a laminated body of modified polyethylene, fiber cloth, and modified polyethylene in advance. It is formed into a sheet by hot pressing or the like, and is formed on the epoxy primer by means such as heating, remelting, and coating when producing a polyethylene-coated steel material.

The modified polyethylene 6 used in the fiber-reinforced modified polyethylene layer 4 may be any one as long as it has excellent adhesiveness with the epoxy primer 3 and the fiber cloth 7 and fusion bond with the low density polyethylene layer 5. Maleic anhydride is added to ethylene homopolymer or ethylene-α-olefin copolymer obtained by copolymerizing ethylene and α-olefin such as 1-butene, propylene, 1-hexene or 1-octene, or a mixture thereof. It is preferable to use graft-polymerized maleic anhydride-modified polyethylene because it has excellent adhesion to steel materials. The thickness of the modified polyethylene layer is 0.02 on both sides of the fiber cloth.
Good results are obtained with a thickness of 1.0 mm. 0.0
Epoxy primer layer 3 and fiber cloth 7 for 2 mm or less
Adhesive strength with is insufficient. Further, if it exceeds 1.0 mm, it is not preferable from the economical viewpoint.

The fiber cloth 7 used in the fiber-reinforced modified polyethylene layer 4 may be an inorganic fiber (including a metal) or an organic fiber, but may be glass fiber, carbon fiber, boron fiber, alumina fiber, nylon fiber, and By using a fiber cloth made of one or more kinds of aramid fibers or the like, the fiber-reinforced modified polyethylene layer 4 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 is not preferable from the economical viewpoint. In addition, in order to improve the adhesiveness between the fiber cloth and the modified polyethylene, a conventionally known surface treatment agent may be applied to the fiber cloth and used.

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, etc. 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 /
If it exceeds cm 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 intended use, and the effect of the present invention will not be affected. . Hereinafter, the present invention will be described in detail with reference to examples in which a steel pipe is used as a steel material.

[0014]

[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. The steel pipe was heated by high frequency induction heating so that the surface temperature became 200 ° C. to cure the epoxy primer layer. The thickness of the epoxy primer layer is 0.0
It was 5 mm. A modified polyethylene (a modified polyethylene obtained by modifying an ethylene homopolymer with maleic anhydride, and the addition amount of maleic anhydride to 1 g of modified polyethylene was 1 × 10 ⁻⁵ mol) was extrusion-coated on the surface with a T-die.
The modified polyethylene had a thickness of 0.15 mm. A fiber cloth having a width of 150 mm was spirally coated thereon. As the fiber cloth, the fiber cloths shown in Tables 1a to 1c were used. Then, the modified polyethylene and the low-density polyethylene were extrusion-coated from the T-die on the fiber cloth as a single layer in two layers. The modified polyethylene had a thickness of 0.15 mm and the polyethylene had a thickness of 2.0 mm. The polyethylene-coated steel pipe according to the present invention was manufactured by pressing with a rubber roll and cooling.

In order to evaluate the low temperature impact resistance of the coated steel pipe of the present invention, an impact test was conducted at -60 ° C. using an impact test apparatus 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, instead of the fiber-reinforced modified polyethylene, a coated steel pipe using ordinary modified polyethylene was prepared and the same impact test was conducted.

The results are collectively shown in Table 2. From Table 2,
An epoxy primer layer is provided on the surface of the steel material subjected to the base treatment, and a fiber-reinforced modified polyethylene layer in which modified polyethylene is laminated on both surfaces of the fiber cloth and a low-density polyethylene layer are sequentially laminated to obtain -60 ° C.
The low temperature impact resistance can be improved.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

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 pipe of the present invention.

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

[Explanation of symbols]

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

Claims (2)

[Claims] 1. A fiber in which an epoxy primer layer made of a reaction-curable epoxy is laminated on the surface of a steel material that has been subjected to a base treatment, and modified polyethylene layers are previously laminated on both front and back surfaces of a fiber cloth on the epoxy primer layer. A polyethylene-coated steel material having excellent low-temperature impact resistance, comprising a laminated layer of reinforced modified polyethylene, and a layer of low-density polyethylene laminated on the fiber-reinforced modified polyethylene layer. 2. The fiber-reinforced modified polyethylene layer comprises a modified polyethylene layer on the epoxy primer layer,
The polyethylene-coated steel material according to claim 1, wherein the fiber cloth and the modified polyethylene layer are sequentially laminated and directly formed on the steel material.