JPH04108572A - Corrosion-resistant multilayer-coated square steel pipe pile and its production - Google Patents

Abstract

PURPOSE:To make high waterproof adhesion strength between a colored coating film and a polyolefine layer by successively laminating colored coating films on the outer surface of an outside polyolefine-coated square steel pipe pile having a flame-treated polyolefine layer. CONSTITUTION:While an outside polyolefine-coated square steel pipe pile 9 having an outer-most layer of polyolefine containing 0.05-5.0wt.% antioxidant is rotated and transfered by a roller conveyer 8 which is moved and rotated, flame treatment is carried out using a burner to give >=36dyn/cm surface tension of the outer-most surface and then an urethane primer or a modified polyolefine primer 6 is applied to the outer surface and coloring paint 7 such as various kinds of fluoro-based, acrylic-silicone-based, acrylic-urethane-based acrylic- urethane-based coating materials, etc., is applied to give a corrosion-resistant multilayer-coated square steel pipe pile. The layers 2, 3, and 4 are a chromate- treated layer, an epoxy primer layer, and a modified polyolefine adhesive layer, respectively.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to heavy corrosion-proof coated square steel pipe piles used for steel structures such as foundation piles used in oceans, rivers, ports, etc., and a method for manufacturing the same. is a heavy-duty anti-corrosion coated square steel pipe pile which has a colored coating film in various colors with excellent weather resistance on the outer surface of the heavy-duty anti-corrosion coating, which has an excellent appearance, and which has excellent water-resistant adhesion between the colored coating film and the heavy-duty anti-corrosion coating. and its manufacturing method.

(Prior Art) Conventional polyolefin-coated steel materials, such as polyolefin-coated square steel pipe piles, are coated with black polyethylene, which has excellent corrosion resistance. However, due to the recent increase in market needs for beautiful landscapes of steel structures such as urban landscapes, rivers, and ports, steel structures are being made into square shapes and colored in various colors to harmonize with the environment and have excellent weather resistance. The development of square steel pipe piles with heavy corrosion protection coating is desired. To meet such needs, for example, as shown in FIG. 3, a polyolefin-coated steel material having a flame-treated polyolefin coating layer 15 on its outer surface is coated with a urethane primer layer 16 and a colored fluorine-based paint coating 17. There is a heavy corrosion-resistant coated steel material that is laminated in sequence. In the figure, 1 is a square steel pipe pile, 12 is a chromate treatment agent layer, 13 is an epoxy primer layer, and 14 is a modified polyolefin adhesive layer.

(Problem to be solved by the invention) However, with such conventional heavy corrosion-resistant coated steel materials,
In the marine practical test, the adhesion between the flame-treated polyolefin coating layer 15 and the colored fluorine-based paint coating 17 gradually decreased, and blisters tended to occur in the fluorine-based paint coating, resulting in water resistance. Further improvement of adhesion is required.

(Means for Solving the Problems) As a result of intensive studies to solve the above-mentioned problems, the present inventors added 0.05 to 5% of an antioxidant to the outermost layer of the outer surface of a square steel pipe.
．． 0% by weight, and the outer surface has a surface tension of 36
After applying a urethane primer or a modified polyolefin primer to the outer surface of an outer polyolefin-coated square steel pipe pile that has been flame-treated to a temperature of dyn/cm or more,
The inventors have discovered that the above-mentioned problems can be solved by laminating colored paint films such as fluorine-based paints, acrylic silicone-based FFI materials, and acrylic urethane-based paints in various colors, leading to the present invention.

That is, the present invention, as shown in FIG. 1, contains 0.05 to 5.0% by weight of an antioxidant in the outermost layer of the outer surface of the square steel pipe 1,
And on the outer surface of the polyolefin coated square steel pipe pile having polyolefin 5 which has been flame-treated so that the outer surface has a surface tension of 366 yn/cm or more, urethane primer or modified polyolefin primer 6, fluorine-based paint in various colors, A square steel pipe pile with a heavy anti-corrosion coating characterized by sequentially laminating colored paint type 1i7 such as acrylic silicone paint and acrylic urethane paint, and as shown in Figure 's2, an antioxidant is applied to the outermost layer of the outer surface of the square steel pipe. 0.05
The outer surface of a polyolefin-coated steel pipe pile 9 having a polyolefin content of ~5.0% by weight was rotated and transferred on a six-moving roller cart 8, while the outer surface was heated with a slit burner 10 to a surface tension of 36 dyn/cta.
After flame treatment as described above, the outer surface is coated with a urethane primer or a modified polyolefin primer, and colored paints such as fluorine-based paints, acrylic silicone-based paints, acrylic urethane-based paints, etc. are applied in various colors. This is a manufacturing method for heavy-duty anti-corrosion coated square steel pipe piles. In the figure, 2 is a chromate treatment layer, 3 is an epoxy primer layer,
4 indicates a modified polyolefin adhesive layer.

Hereinafter, the present invention will be explained in detail.

The square steel pipe used in the present invention is a square steel pipe made of alloy steel such as carbon steel and stainless steel. In addition, in order to improve the corrosion resistance of steel pipes, the outer and inner surfaces of square steel pipes are plated with zinc, aluminum, nickel, etc., alloy plating such as zinc-iron, zinc-aluminum, zinc-cobalt-nickel, etc. Dispersion plating in which inorganic fine particles such as silica and titanium oxide are dispersed can also be used.

For square steel pipe piles coated with external polyolefin, the outside surface of the square steel pipe is blasted using grid blasting, sandblasting, etc. to remove rust, then subjected to chromate treatment and base treatment with epoxy primer, and then modified polyolefin modified with maleic anhydride, etc. It is possible to use polyolefin-coated rectangular steel pipe piles whose outer surfaces are coated with polyolefin after being coated with an adhesive, but from the point of view of the present invention, it is sufficient that the outermost layer of the coated rectangular steel pipe piles has polyolefin, and conventional ground preparation is required. It is also possible to use square steel pipe piles coated with polyolefin on the outside that have been subjected to known chromate treatment, epoxy brimer phosphate treatment, silane coupling treatment, etc. alone, or a combination of these surface treatments.

The polyolefin coated on the outermost layer of the square steel pipe pile covered with external polyolefin contains an antioxidant of 0.05 to 5.0.
Polyethylene, polypropylene, polybutene, or ethylene and propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-
Copolymers with α-olefins such as octene can be used. If the antioxidant content of the polyolefin coating is less than 0.05% by weight or more than 5.0% by weight, the polyolefin coating may be coated with fluorine-based, acrylic-silicon-based, or acrylic-urethane-based paint in various colors after an actual marine use test. The adhesion between the paint and the paint film decreases, and blisters occur in the paint film.

Next, the flame treatment applied to the polyolefin-coated outer surface of the polyolefin-coated square steel pipe pile will be described. For flame treatment, it is sufficient to apply colored paints of various colors to the surface of the polyolefin coating without any problems after flame treatment, and to cure them to form a coating film.The key is to apply flame treatment uniformly to the outer surface of the polyolefin coating. is necessary. For this purpose, a method using a slit burner as shown in FIG. 2 can be used. If the outer surface of the polyolefin coating is not flame-treated uniformly, the adhesion between the polyolefin coating and the colored paint film of various colors will decrease after the marine practical test, and blisters will occur on the paint film. . Regarding the degree of flame treatment, for example, in the case of low-density polyethylene, high-density polyethylene, and ethylene-propylene block copolymers, the "wetting test method for polyethylene and polypropylene" specified in JIS K6768 specifies " It is desirable to perform flame treatment so that the "wetting index (surface tension)" is 36 dyn/cm or more.
If the "surface tension" is less than 36 dyn/cm, the adhesion between the polyolefin coating and the colored paint film of various colors will decrease after the marine practical use test, and blisters will occur in the colored paint film. do.

Next, the urethane primer and modified polyolefin primer to be laminated and applied to the surface of the flame-treated polyolefin coating will be explained.

The urethane primer used in the present invention has the following characteristics in terms of water resistance:
A urethane prepolymer containing a terminal isocyanate group obtained by reacting a polyol compound having a molecular weight of 400 to 2000 and having two or more hydroxyl groups in the molecule with a polyisocyanate compound having an isocyanate group in the molecule is desirable. In addition, from the viewpoint of water resistance, the modified polyolefin primer is preferably a liquid primer made by diluting with a solvent a modified polyolefin whose main component is a polyolefin modified with an acid anhydride such as ethylene-vinyl acetate copolymer or maleic anhydride. As a commercially available product, for example, Thermotac E200 manufactured by Chugoku Paint Co., Ltd. Thermotac E300, Thermotac E500, etc. can be used.

Next, the colored paint used in the present invention will be explained. From the viewpoint of weather resistance, the paints include NY Porin in various colors manufactured by Shinto Paint Co., Ltd. and ■Top # in various colors manufactured by Dai Nippon Toyo Co., Ltd.
General commercially available acrylic-urethane paints such as 100, Silica Lac in various colors manufactured by Chugoku Paint Co., Ltd., general commercially available acrylic-silicon paints such as Ceraforte in various colors manufactured by Shinto Paint Co., Ltd., and Nippon Paint Co., Ltd. Duflon in various colors,
It is preferable to use commercially available fluorine-based paints such as Synthoflon in various colors manufactured by Shinto Yoyo Co., Ltd. and ■Freon in various colors manufactured by Dainippon Toyo Co., Ltd.

Next, a method for manufacturing a square steel pipe pile with heavy corrosion protection coating according to the present invention will be explained.

As shown in FIG. 2, while the outer polyolefin-coated square steel pipe pile 9 containing 0.05 to 5.0% by weight of an antioxidant in the outermost layer of the outer surface of the square steel pipe is being conveyed on the table roller 8, the outer surface of the square steel pipe pile 9 is The surface tension of each of the four faces is 36 dy
After flame treatment with a slit burner 10 so that the temperature is n/c+a or more, a urethane primer or modified polyolefin in primer is applied to the outer surface, and colored paints such as fluorine-based paints, acrylic silicone-based paints, acrylic urethane-based paints, etc. of various colors are applied. is coated to obtain a heavy anti-corrosion coated square steel pipe pile according to the present invention. Regarding the degree of flame treatment of the polyolefin-coated surface, for example, for low-density polyethylene, high-density polyethylene, and ethylene-propylene block copolymers, flame treatment is performed using the "Wetting test method for polyethylene and polypropylene films" specified in JIS 6768. Flame treatment is performed so that the subsequent "wetting index (surface tension)" becomes 36 dyn/cm or more.

In Figure 2, one slit burner is placed on each of the four sides of the square steel pipe pile, but if it is difficult to achieve uniform flame treatment due to the transportation speed of the square steel pipe pile, a slit burner is placed on each of the four sides. By arranging two or more, we can measure the wettability index (surface tension).
” is 36 dyn/cm or more. A slit burner is effective in making the flame treatment uniform.

(Function of the Invention) As shown in FIG. 1, the heavy corrosion-proof coated square steel pipe pile of the present invention has an antioxidant added to the outermost layer of the outer surface of the square steel pipe pile 1 in an amount of 0.05 to 5.
A urethane primer or modified polyolefin primer 6, fluorine-based, acrylic-silicon-based, acrylic-urethane-based in various colors is applied to the outer surface of the square steel pipe pile coated with external polyolefin, which has polyolefin 5 containing 0% by weight and whose surface has been flame-treated. This is a square steel pipe pile with a heavy anti-corrosion coating in which colored paint coatings 7 such as paint are sequentially laminated. Furthermore, as shown in FIG. 2, the manufacturing method of the heavy corrosion-proof coated square steel pipe pile of the present invention is as follows: As shown in FIG. While the coated square steel pipe pile 9 is transferred and conveyed on the table roller 8, each of the four outer surfaces has a surface tension of 366 yn/c.
After flame treatment to a temperature of at least m, a urethane primer or modified polyolefin primer is applied to the outer surface, and colored paints such as fluorine-based paints, acrylic silicone-based paints, acrylic urethane-based paints, etc. are applied in various colors. do.

In addition, the polyolefin 5 in the figure has a thickness of 1 to 10+ nm,
The urethane primer or modified polyolefin primer 6 has a film thickness of 5 to 10 μm, and the colored paint film of various colors such as fluorine-based, acrylic-silicon-based, and acrylic-urethane paints has a film thickness of 10 to 100 μm. and good results are obtained.

(Example) Example-1 Four sides are 200 mm square x length 5500 mm x thickness 5.0 m
While running a square steel pipe of 500 m in diameter on a table roller, each of its four sides was subjected to grid blasting to remove rust, and a chromate treatment agent was applied to the total chromium coating amount of 350 mg/+'' and baked, followed by epoxy primer. The film thickness is 5
It was spray coated to a film thickness of 0 μm and cured, and then a modified polyolefin mainly composed of an ethylene-1-butene copolymer modified with maleic anhydride was extruded from a square die to a film thickness of 200 μm. The surface was extruded and coated with low-density polyethylene from a square die, and the pile was cooled to produce a square steel pipe pile whose outer surface was coated with polyethylene. The content of antioxidant in the low density polyethylene coating was 0.3% by weight, and the film thickness of the low density polyethylene was 2.5 mm. The external polyethylene-coated square steel pipe pile manufactured as described above was
As shown in FIG. 2, the surface of the polyethylene coating was flame-treated by arranging one slit burner on each of the four sides while being transferred and conveyed on a table roller. % by weight, toluene 50% by weight), and then sprayed a fluorine-based paint (Duflon manufactured by Nippon Paint Co., Ltd., color Marcel value: IOB 5/10 (blue)) to a film thickness of 30 μm. A heavily anti-corrosion coated square steel pipe pile 1 according to the present invention was manufactured by painting. The "wetting index (surface tension)" of the low-density polyethylene coated surface after flame treatment is 54
It was dyn/cm.

As a comparison material, each of the four outer surfaces of the external low-density polyethylene-coated square steel pipe pile obtained as described above was heated with a hunt burner for 5 minutes to raise the surface temperature to 70 to 80°C, and urethane was applied to the surface. Apply 5 to 10μ of primer, then spray paint fluorine-based paint (Duflon manufactured by Nippon Paint Co., Ltd., color tone Marcel value: IOB 5/10 (blue)) to a film thickness of 30μ and compare the weight. An anti-corrosion coated square steel pipe pile 1 was manufactured. The "wetting index (surface tension)" of the low-density polyethylene coated surface after flame treatment with a hand burner was 31 to 54 dyn/cm, with large variations depending on the measurement position.

The heavy-duty anti-corrosion coated rectangular steel pipe pile 1 according to the present invention obtained as described above and the comparative heavy-duty anti-corrosion coated square steel pipe pile 1 were subjected to a three-year marine practical test, and after the test, blisters of the fluorine-based paint coating were observed. In addition to observing the presence or absence of went. The results are shown in Table 1.

As is clear from the results in Table 1, the heavy corrosion-resistant coated rectangular steel pipe pile according to the present invention has a higher resistance to fluorine-based paint than the conventional heavy-duty anti-corrosion coated square steel pipe pile even after three years of marine practical use tests. There is no occurrence of blisters in the paint film, and the adhesion between the fluorine-based paint film and the low-density polyethylene coating is sufficiently high, and the water-resistant adhesion between the colored paint film and the polyolefin coating is excellent.

Example-2 The antioxidant content in the low-density polyethylene coating of the external low-density polyethylene-coated square steel pipe pile used for manufacturing the heavy corrosion-proof coated square steel pipe pile of the present invention in Example 1 was set to 0.05 to 5.0. Heavy-duty anti-corrosion coated square steel pipe piles 2 to 4 according to the present invention were manufactured in the same manner as in Example 1 by changing the weight % range. As a comparative example, the same method as in Example 1 was carried out, but the content of the antioxidant was 0.
A comparative heavy corrosion protection coated rectangular steel pipe pile 2 having an antioxidant content of 0.01% by weight and a comparative heavy corrosion protection coated square steel pipe pile 3 having an antioxidant content of 6% by weight were manufactured. Comparison of the heavy anti-corrosion coated rectangular steel pipe pile obtained as described above The heavy anti-corrosion coated rectangular steel pipe pile was subjected to the same marine practical test as in Example 1, and after the test was completed, the presence or absence of blisters in the fluorine-based paint coating was determined. At the same time, an adhesion test between the fluorine-based paint film and the low-density polyethylene coating was carried out according to JIS K5400.
Displayed with a score of 0 (out of 10). Results first
Shown in the table.

As is clear from the results in Table 1, if the antioxidant content in the polyolefin coating of the heavy corrosion protection coated square steel pipe pile according to the present invention is in the range of 0.05 to 5.0% by weight, the Even after the actual marine use test, there was no occurrence of blisters in the fluorine-based paint film, and the adhesion between the fluorine-based paint film and the low-density polyethylene coating was sufficiently high. However, when the antioxidant content is 0.01% by weight and 6% by weight, blistering occurs in the fluorine-based paint film, and the fluorine-based paint film and low-density polyethylene coating The adhesive strength between them also decreases.

Example 3 In the same manner as in Example 1, the degree of flame treatment applied to the outer low-density polyethylene coating was varied from 36 to 70 dyn/cm in terms of "wetting index (surface tension)" to obtain heavy corrosion protection according to the present invention. Covered square steel pipe piles 5 and 6 were manufactured. As a comparative example, a comparative heavy anti-corrosion coated square steel pipe pile 4 was manufactured in the same manner as in Example 1, with the degree of flame treatment being 34 dyn/cm in terms of [wetting index (surface tension)]. Comparison of the heavy anti-corrosion coated square steel pipe piles obtained as described above The heavy anti-corrosion coated square steel pipe piles were subjected to the same three-year marine practical test as in Example 1, and after the test, blister coated with fluorine-based paint was applied. In addition to observing the presence or absence of occurrence, an adhesion test between the fluorine-based paint film and the low-density polyethylene coating was conducted using the "base test: JIS K54".
According to 0G, the adhesive strength was evaluated on a scale of 0 to 10 (out of 10 points). The results are shown in Table 1.

As is clear from the results in Table 1, the degree of flame treatment used in the present invention is 36 in terms of "wetting index (surface tension)".
At ~70 dyn/cm, no blisters were generated in the fluorine-based paint film even after three years of actual marine use tests, and the adhesion between the fluorine-based paint film and the low-density polyethylene coating was sufficiently high. However, the "wetting index (surface tension)"
At 34 dyn/cm, blistering of the fluorine-based paint film occurs and the adhesion between the fluorine-based paint film and the low-density polyethylene coating also decreases.

Example 4 In the same manner as in Example 1, the square steel pipe piles coated with low-density polyethylene on the outside were replaced with square steel pipe piles coated with high-density polyethylene on the outside, and square steel pipe piles coated with ethylene-propylene block copolymer on the outside to produce square steel pipe piles according to the present invention. Heavy anti-corrosion coated square steel pipe piles 7 and 8 were manufactured. Comparison of the heavy corrosion-resistant coated square steel pipe pile obtained as described above The heavy-duty corrosion-proof coated square steel pipe pile was subjected to the same 3-year marine practical test as in Example 1, and after the test, blisters of the fluorine-based paint coating occurred. In addition to observing the presence or absence of
Display the results on a scale of 10 (out of 10)
Shown in the table. As is clear from the results in Table 1, the heavy corrosion-resistant coated rectangular steel pipe piles according to the present invention can be used even after three years of marine practical use tests, regardless of the type of polyolefin used in the outer polyolefin-coated square steel pipe piles used for manufacturing them. There is no occurrence of blisters in the fluorine-based paint film, and the adhesive strength between the fluorine-based paint film and the polyolefin coating is sufficiently high.

Example-5 A fluorine-based paint (Duflon manufactured by Nippon Paint Co., Ltd., Marcel value of color tone: IOB 5/1) was applied in the same manner as in Example 1.
0 (blue)) was replaced with the acrylic-silicon and acrylic-urethane colored paints shown in Table 2, heavy anti-corrosion coated square steel pipe piles 9 to 13 according to the present invention were manufactured. The heavy corrosion-proof coated square steel pipe pile obtained as described above was
It was subjected to a yearlong marine practical use test, and after the test was completed, the presence or absence of blisters on the fluorine paint film was observed, and an adhesion test between the colored paint film and the low-density polyethylene coating was conducted (baseline test: JIS K5400). Accordingly, the adhesive strength was expressed as a rating from 0 to 1o (out of 10), and the results are shown in Table 1. As is clear from the results in Table 1,
Even when acrylic-silicon-based or acrylic-urethane-based colored paints were used, there was no blister formation in the colored paint film even after 3 years of marine practical use tests, and fluorine-based paint films had a low density. The adhesive strength between the polyethylene coating and the polyethylene coating is also sufficiently high.

Example 6 In the same manner as in Example 1, the urethane primer was replaced with a modified polyolefin primer (“Thermotac E500J,” “Thermotac E300J, or “Thermotac E200J” manufactured by China Paint Co., Ltd.) to produce heavy-duty anti-corrosion coated square steel pipes according to the present invention. Piles 14 to 16 were manufactured.The heavy anti-corrosion coated rectangular steel pipe piles obtained as described above were subjected to the same 3-year marine practical test as in Example 1, and after the test, the occurrence of pristal of the fluorine-based paint film was observed. At the same time, an adhesion test was conducted between these colored paint films and the low-density polyethylene coating. The results are shown in Table 1. As is clear from the results in Table 1, even when a modified polyolefin primer was used instead of a urethane primer, no blisters occurred in the colored paint film even after three years of actual marine use tests. The adhesion between the fluorine paint coating and the low density polyethylene coating is also sufficiently high.

(Effects of the Invention) As is clear from the above examples, the outermost layer of the outer surface of the square steel pipe contains 0.05 to 5.0% by weight of an antioxidant, and the surface has a surface tension of 36 dyn/cm. The outer surface of the polyolefin-coated square steel pipe pile, which has flame-treated polyolefin as described above, is coated with colored paint such as urethane primer or modified polyolefin primer, fluorine-based paint in various colors, acrylic silicone-based paint, acrylic urethane-based paint, etc. The heavy-duty anti-corrosion coated rectangular steel pipe pile of the present invention obtained by sequentially laminating films can be coated with fluorine-based paints, acrylic-silicon-based paints, and acrylic-urethane-based paints in various colors, compared to conventional heavy-duty anti-corrosion coated square steel pipe piles. It has a remarkable effect of excellent water-resistant adhesion between the colored paint film and the polyolefin coating.

[Brief explanation of drawings]

Fig. 1 is a partial cross-sectional view of a square steel pipe pile with heavy corrosion protection coating according to the present invention, Fig. 2 is an explanatory diagram showing an example of the manufacturing method of a square steel pipe pile with heavy corrosion protection coating according to the present invention, and Fig. 3 is a conventional heavy corrosion protection coated square steel pipe pile. A partial cross-sectional view of a covered square steel pipe pile is shown. In the figure, 1 is a square steel pipe pile, 2 is a chromate treatment agent layer, 3 is an epoxy primer layer, 4 is a modified polyolefin adhesive layer,
5 is a polyolefin layer containing 0.05 to 50% by weight of an antioxidant and flame-treated to have a surface tension of 36 dyn/cm or more; 6 is a urethane primer or modified polyolefin primer layer; 7 is a polyolefin layer of various colors. Colored paint film such as fluorine paint, acrylic-silicon paint, acrylic-urethane paint, 8 is a roller truck that runs while rotating, and 9 is an antioxidant before flame treatment of 0.05 to 5. 10 is a slit burner; 11 is a polyolefin-coated square steel pipe pile containing 0.05 to 5.0% by weight of antioxidant after flame treatment; 12 is a chromate treatment agent layer; 13 is a polyolefin-coated square steel pipe pile containing 0% by weight; 14 is a modified polyolefin adhesive layer, 15 is a polyolefin layer, 16 is a urethane primer layer, and 17 is a fluorine-based paint coating. Figure 1 1: Square steel pipe pile 2: Chromate treatment agent layer 3: Epoxy primer layer 4: Modified polyolefin adhesive layer 5 Contains 0.05 to 5.0% by weight of antioxidant, and has a surface tension of 36 dyn/ Polyolefin layer 6 flame-treated to a thickness of cm or more: Urethane primer or modified polyolefin primer layer 7, colored paint coatings such as fluorine paints of various colors, acrylic-silicon paints, acrylic-urethane paints, etc., and 4 others.

Claims (1)

[Claims] 1. An antioxidant of 0.05 to 5.0 is added to the outermost layer of the outer surface of the steel pipe.
% by weight, and the surface tension of the outer surface is 36 dyn/c.
Colored paints such as urethane primer or modified polyolefin primer, fluorine-based paints of various colors, acrylic silicone-based paints, acrylic urethane-based paints, etc. are applied to the outer surface of square steel pipe piles coated with external polyolefin, which have polyolefin that has been flame-treated to a thickness of 50 m or more. A heavy corrosion-resistant coated square steel pipe pile characterized by sequentially laminated coating films. 2 Add 0.05 to 5.0 of antioxidant to the outermost layer of the outer surface of the steel pipe.
A rectangular steel pipe pile coated with polyolefin on the outer surface having a polyolefin content of % by weight was transferred and conveyed on a rotating and moving table roller, and each of the four sides of the outer surface was flame treated so that the surface tension thereof became 36 dyn/cm or more. A heavy anti-corrosion coated square steel pipe pile characterized in that the outer surface is then coated with a urethane primer or a modified polyolefin primer, and colored paints such as fluorine-based paints, acrylic silicone-based paints, acrylic urethane-based paints, etc. in various colors are applied. manufacturing method.