JPH11254588A - Heavily corrosion-resistant coated sheet pile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the long-term adhesive properties of a coated layer in brine by specifying the density and the residual stress of a corrosion-resistant polyethylene layer to be applied on at least, one of the faces of a primer-coated sheet pile through a modified polyolefin layer. SOLUTION: This heavily corrosion-resistant coated sheet pile comprises a sheet pile 1, a primer-coated layer 2, a modified polyethylene layer 3, a corrosion-resistant polyethylene layer 4 and an end part sealing layer 5. The polyethylene resin of the corrosion-resistant polyethylene layer 4 is a noncrosslinked polyethylene and has 0.940 g/cm<3> or more density. The sheet pile 1 having the corrosion-resistant layer 4 of high-density polyethylene shows at least, 30 kgf/cm<2> or more coating residual stress and, in most of the cases, 40 kgf/cm<2> or more, when coated by a routine coating method. Therefore, it is possible to reduce the residual stress of the coating by setting the Vicat softening point of the modified polyethylene layer 3 as an adhesive layer within the range of for example, 50-90 deg.C. Thus the residual stress of the coating is below 20 kgf/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heavy-duty coated steel sheet pile having a heavy-duty coating formed on the surface of a steel sheet pile by sticking a polyethylene sheet, and more particularly, to a long-term close contact between the sheet and the steel material. The present invention relates to a heavy-duty anticorrosion coated steel sheet pile having excellent resistance.

[0002]

2. Description of the Related Art Steel sheet piles forming quays of oceans, harbors, rivers, etc. are exposed to a severe corrosive environment. Therefore, a sheet made of polyolefin resin such as polyethylene or polypropylene is adhered to the surface of the sheet piles via an adhesive layer. By doing so, so-called heavy-corrosion-coated steel sheet piles that have been subjected to corrosion protection have been increasingly used.

[0003] This heavy duty steel sheet pile is disclosed in
As disclosed in Japanese Patent No. 24717 or Japanese Patent Application Laid-Open No. 60-8058, a base treatment layer consisting of a chemical conversion treatment layer, a primer layer, etc. is formed on a steel sheet pile whose base has been adjusted, and then a modified polyethylene or the like is bonded. A method is known in which an anticorrosion polyethylene layer is formed via an agent layer, and as a production method, a sheet-shaped anticorrosion polyethylene layer is attached to a preheated steel sheet pile to produce the anticorrosion polyethylene layer. When pasting an anticorrosion polyethylene sheet after forming a modified polyethylene layer by a method such as powder coating in advance,
Also, there is known a case where a sheet in which a modified polyethylene layer and an anticorrosion polyethylene layer are integrated is covered. As the anticorrosion polyethylene layer, a crosslinked polyethylene is generally used (JP-A-59-224717).

[0004]

However, the polyethylene-coated steel sheet pile manufactured by sticking the sheet, when exposed to the marine environment for a long time after casting, has a reduced adhesion between the sheet and the steel material, especially in the mid-sea area. In the worst case, the coating may be lifted or turned up.

[0005] In recent years, the design life of harbor facilities and the like has also been prolonged, and in view of the current situation in which it is desired to reduce the maintenance costs during that time, the long-term adhesion of the coating of the heavy corrosion-resistant coated steel sheet pile is further improved. This is a very significant issue that can produce enormous economic effects.

[0006] The cause of the decrease in the adhesion of the heavy-corrosion-coated steel sheet pile in seawater is that the adhesive layer and the ground treatment layer are deteriorated by moisture and oxygen permeating the corrosion-resistant polyethylene layer of the coating because the sheet pile is exposed to seawater for a long time. First, it is conceivable that the adhesion between the coating layer and the steel material is reduced. Furthermore, due to the characteristic that the sheet is attached to one side of a steel sheet pile having a curved surface portion, it is also likely that the adhesive layer and the base treatment layer are liable to be deteriorated due to invasion of environmental substances from the end of the sheet.

In order to prevent deterioration due to moisture or the like penetrating the coating, for example, Japanese Patent Application Laid-Open No. 61-72127 discloses a method in which the relationship between the density and the film thickness of polyethylene falls within a predetermined relational expression. A technique for reducing the moisture permeability of the coating is disclosed.It is said that the higher the density of polyethylene, the lower the moisture permeability.However, in the study of the present inventors, it was sufficient to simply use high-density polyethylene. It was found that long-term adhesion could not be obtained.

The present invention has been made in order to solve the above-mentioned problems, and relates to a heavy-duty corrosion-resistant coated steel sheet pile having a polyethylene sheet adhered to the surface of the steel sheet pile, and has a long-term adhesion of the coating layer in seawater. It is an object of the present invention to provide a heavy corrosion-resistant coated steel sheet pile excellent in quality.

[0009]

Means for Solving the Problems The present inventor has made intensive studies to eliminate the above-mentioned cause of the decrease in adhesion and to develop a heavy duty anticorrosion coated steel sheet pile having excellent long-term adhesion of polyethylene sheet in seawater. went. As a result, heavy-corrosion-coated steel sheet piles that have a specific density and molecular structure as a corrosion-resistant polyethylene layer and that control the residual stress of the coating layer within a specific range are extremely excellent in long-term adhesion in seawater. And finally completed the present invention.

That is, the present invention provides a heavy-duty coated steel sheet pile wherein at least one surface of a steel sheet pile subjected to a ground treatment is coated with a corrosion-resistant polyethylene sheet via a modified polyethylene layer, the corrosion-resistant polyethylene layer has a density of 0.940 g / cm
^The present invention relates to a heavy-duty coated steel sheet pile characterized by having a coating stress of ³ or more and a coating residual stress of 20 kgf / cm ² or less.

[0011] The present invention also relates to a heavy-corrosion-coated steel sheet pile, wherein the polyethylene resin of the corrosion-resistant polyethylene layer is non-crosslinked polyethylene.

In the heavy-corrosion-coated steel sheet pile described above, the corrosion-resistant polyethylene layer is formed of a polyethylene resin having a density of 0.940 g / cm ³ or more. The density is 0.940g / c
m ³ or more polyethylene is generally referred to as high density polyethylene, very density among polyethylene has a high type. These are produced by a medium-to-low pressure polymerization method using a high-performance catalyst such as a Ziegler-based catalyst, and have a structure in which the degree of branching of polyethylene molecules is extremely small and the number of branches is small. Due to the characteristics of this molecular structure, not only are the mechanical strength and impact resistance excellent, but also the permeability of moisture and oxygen due to the high density is extremely low. Originally, polyethylene is a resin with excellent moisture resistance,
The high-density polyethylene has only 1/3 to 1/5 of the low-density polyethylene in terms of the amount of water vapor transmission as a measure of the moisture permeability in the polyethylene. For this reason, when the high-density polyethylene is used as the anticorrosion polyethylene layer, the rate of penetration of moisture into the coating becomes extremely lower than that of the low-density polyethylene. Further, the amount of oxygen permeation becomes extremely small as compared with low density polyethylene. In the case of heavy corrosion-resistant steel sheet piles, the thickness of the corrosion-resistant polyethylene layer is usually 2.0 mm or more, but with such a thickness, the penetration of moisture and oxygen to reach the steel surface is extremely slow, and if Even if it reaches, since the amount is very small, it is considered that it does not reach the point where the adhesive layer and the base treatment layer are deteriorated.

However, the above-mentioned density of 0.940 g / c
be used m ³ or more high-density polyethylene as anticorrosion polyethylene heavy duty coated steel sheet piles, when immersed in a long period of time in sea water, but is not observed decrease in the adhesive strength of the central portion of the covered area, the edge of the cover Peeling from the part and turning up may occur. This is probably because high-density polyethylene has a high modulus of elasticity, so that thermal stress when coating the steel sheet pile with polyethylene becomes extremely large.

On the other hand, the present inventors have found that the density is 0.940 g /
As a result of examining a heavy duty anticorrosion coated steel sheet pile that does not easily peel off or bend from the edge of the coating while taking advantage of the low permeability of water or oxygen of high density polyethylene of ³ cm3 or more, the residual stress of the coating was 20 kgf / It has been found that when it is not more than cm ² , regardless of the production method, it shows high resistance to each of the coating permeation moisture and the permeation moisture from the end, and exhibits extremely excellent long-term adhesion.

When a steel sheet pile having a corrosion-resistant layer made of high-density polyethylene having a density of 0.940 g / cm ³ or more is coated by an ordinary method, the residual stress of the coating is at least 30 kgf / cm 3.
² or more, and in many cases 40 kgf / cm ² or more. Therefore, a special material and manufacturing method are required to reduce the residual stress of the coating to 20 kgf / cm ² or less.

One method is to replace high density polyethylene with non-crosslinked polyethylene. Several cross-linking methods such as electron beam cross-linking, silane cross-linking, and chemical cross-linking are known for polyethylene, and these cross-linked polyethylenes are sometimes used for heavy-duty corrosion-resistant steel sheet piles. It is preferable to use a non-crosslinked polyethylene without using it. This is to promote the displacement between molecules without taking a crosslinked structure between the molecular chains of polyethylene, thereby efficiently relaxing the thermal stress generated in the cooling process after the polyethylene is attached.

Further, it lowers the Vicat softening point of the modified polyethylene layer which is the adhesive layer.
The range of ° C. is also effective for reducing the residual stress of the coating. Furthermore, it is also effective to make the cooling rate on the polyethylene side higher than the cooling rate on the steel material side by taking a specific cooling method in the cooling process after the polyethylene is attached. All of these methods make it possible to reduce the thermal stress generated by lowering the temperature of the anticorrosion polyethylene layer in the solidification stage of the adhesive layer.

As described above, there are several methods for reducing the residual stress of the coating, and these may be appropriately combined. Regardless of the method described above, there is no particular limitation on the method as long as the method can reduce the residual stress of the coating to 20 kgf / cm ² or less.

[0019]

Embodiments of the present invention will be described below in detail. As shown in FIG. 1, the heavy steel sheet pile of the present invention comprises a steel sheet pile 1, a base treatment layer 2, a modified polyethylene layer 3, a corrosion protection polyethylene layer 4, and an end sealing layer 5.

The steel sheet pile used in the present invention includes harbors, rivers,
Used for revetment of landfills, etc.
U-type, Z-type, I-type specified in 5528, and those having a shape conforming thereto can be used. There are no particular restrictions on its dimensions. In the present invention, heavy anticorrosion coating is applied to a portion where anticorrosion needs to be applied. For example, when used for seawall protection in harbors, the coating is often applied mainly to the side facing the sea, but it goes without saying that heavy corrosion protection coating can be applied to both sides of the steel sheet pile. Also used in combination with cathodic protection, heavy anticorrosion coating is L.W.
L. It is usually performed on a limited area of about -1 m.

The steel sheet pile of the present invention is subjected to a known base adjustment such as degreasing, pickling, shot blasting, grit blasting, and sand blasting to remove oil and scale from the surface of the steel material. is necessary. The level of the substrate adjustment is preferably, for example, about Sa2 1/2 or more in the Swedish standard (SIS). If the substrate adjustment is insufficient, the long-term anticorrosion of the heavy duty anticorrosion coating is significantly impaired. Further, it is preferable to perform a known chemical conversion treatment such as a chromate treatment from the viewpoint of long-term adhesion and corrosion resistance.

Further, the primer layer of the steel sheet pile of the present invention comprises:
An epoxy resin-based or urethane resin-based organic resin-based primer having excellent adhesion between the surface of a steel sheet pile subjected to substrate adjustment and chemical conversion treatment and a modified polyethylene layer is used. The primer layer is formed by a known coating method such as air spray, airless spray, brush coating,
If necessary, after coating, heating is performed to obtain a completely cured film. The thickness of the primer layer is 10 to 200 μm,
Particularly, 20 to 100 μm is preferable. If the thickness is less than 10 μm, the adhesion of the polyethylene sheet to the steel material is reduced, so that there is a problem that the polyethylene sheet is peeled off. If the thickness exceeds 200 μm, the residual stress of the primer layer itself increases, Adversely affect the long-term adhesion of

In the heavy-corrosion-coated steel sheet pile of the present invention, the modified polyethylene layer is obtained by modifying a polyethylene resin by a graft reaction of an unsaturated carboxylic acid such as maleic acid, acrylic acid or methacrylic acid or an anhydride thereof. And refers to a resin layer having significantly improved adhesion to other substances as compared to polyethylene alone. Modified polyethylene is known to have various thermal properties depending on the type and amount of the functional group to be grafted, but the Vicat softening point of the modified polyolefin used in the present invention is 50 ° C or more and 90 ° C or more.
The following is preferred. If the softening point is 50 ° C or less, the adhesiveness of the sheet is lowered in the aerial part of the heavy-duty corrosion-resistant steel sheet pile due to a rise in temperature due to sunlight or the like, and the residual stress of the sheet is significantly increased at 90 ° C or more. It is not preferable because the coating length is large, the long-term adhesion of the coating is poor, and the energy cost is increased by increasing the required heating temperature of the steel sheet pile. A more preferred Vicat softening point is 55-70 ° C. Other properties of the modified polyethylene include a melt index of about 0.2 to 10 g / 10 min, preferably about 0.5 to 5 g / 10 min, and a melting point of 60.
A temperature of about 100 to about 100C, preferably about 60 to 80C is suitable. This modified polyethylene layer functions as an adhesive layer for the anticorrosion polyethylene layer, and the layer thickness is 0.1 mm.
About 1 to 1.5 mm, preferably about 0.2 to 1 mm is appropriate.

In the heavy-corrosion-coated steel sheet pile of the present invention, the anticorrosion polyethylene layer has a density of 0.940 g / cm ^3.
This is the so-called high-density polyethylene. Propylene for the purpose of improving environmental stress cracking resistance, impact resistance and toughness,
A copolymer using a polyolefin-based component such as butene-1 or hexene-1 as a copolymerization component may be used. The preferred softening point difference from the modified polyethylene layer is about 10 to 70 ° C. In order to improve long-term properties such as weather resistance, it is preferable to add various additives such as carbon black, color pigments, and antioxidants to the anticorrosion polyethylene layer. The thickness of the anticorrosion polyethylene layer is preferably in the range of about 1 to 6 mm, particularly about 1 to 4 mm, from the viewpoint of long-term adhesion, long-term anticorrosion, and maintenance of the mechanical strength of the coating layer. Incidentally, the standard of the anticorrosion polyethylene of the heavy-corrosion protection steel sheet pile is set to 2.0 mm or more, and generally, the thickness of the anticorrosion polyethylene layer is often 2.0 mm or more.

Also, several cross-linking methods such as electron beam cross-linking, silane cross-linking, and chemical cross-linking are known for polyethylene, and these cross-linked polyethylenes are sometimes used for heavy-duty corrosion-resistant steel sheet piles. These crosslinked polyethylenes are not used, and non-crosslinked polyethylene is used. This is because the effect of relaxing the stress after cooling is not hindered, and since high-density polyethylene is used, it has sufficient mechanical strength, so that it is not necessary to take a crosslinked structure.

Next, a method of manufacturing a heavy-corrosion-coated steel sheet pile according to the present invention will be described. The scale is completely removed by blasting, and a chemical conversion treatment such as a chromate treatment is performed. Further, the primer coating is applied by a spray coating method or another method, and cured by standing or heating to form a primer layer.

The steel sheet pile that has been subjected to the blasting, chemical conversion treatment, and primer treatment such as primer coating is heated by a heating device such as a heating furnace. The heating temperature needs to be a temperature necessary for fusing the polyethylene sheet, and is therefore a temperature higher than or equal to the melting point of the modified polyethylene layer, preferably about 10 to 100 ° C. higher than the melting point, and usually about 80 to 200 ° C. It is.

The heated steel sheet pile is coated with a corrosion-resistant polyethylene sheet via a modified polyethylene layer. As this coating method, it is preferable to prepare a polyethylene sheet formed by integrating a modified polyethylene layer and an anticorrosion polyethylene layer in advance, and supply the integrated sheet to a steel sheet pile so that the modified polyethylene layer side is in contact with the steel sheet pile. However, it is not always necessary to be integrated, and only the modified polyethylene layer is formed in advance on a steel sheet pile that has been subjected to base treatment,
A sheet made of only the anticorrosion polyethylene layer may be attached thereon. In this case, the modified polyethylene layer may be formed by melt extrusion coating, powder coating, fluid immersion, thermal spraying, sheet sticking, or the like. In order to thermally bond the anticorrosion polyethylene sheet, the modified polyethylene layer needs to be at least in a molten state.

The sheet supplied onto the steel sheet pile is adhered by pressing the sheet against the steel sheet pile with a pressing device such as a roll. At that time, it is preferable to sequentially press the steel sheet pile from the central portion to the curved surface portion and then to the peripheral portion in order to prevent air bubbles and the like from being mixed into the sheet and to efficiently attach the sheet.

After the fusion, the excess length of the sheet is trimmed, and the steel sheet pile to which the sheet is adhered is cooled. In the present invention, cooling from the polyethylene side first is preferred from the viewpoint of reducing residual stress. Water is cooled by water cooling, air cooling, or other refrigerants, but the most efficient way is to spray water from the polyethylene side to cool. Further, it is preferable to perform this cooling at least until the modified polyethylene layer as the adhesive layer is solidified from the viewpoint of the residual stress reduction effect. Thereafter, even if cooling is performed from both the polyethylene side and the steel material side, the effect of reducing the residual stress does not change, and the cooling time can be shortened.

After cooling, it is preferable to seal the end of the coating with a sealing material. As shown in FIG. 1, the shape of the end seal is preferably applied so as to fill the gap between the end and the steel material and not to protrude much from the sheet plane.

[0032]

Embodiments of the present invention will be described below. U-shaped steel sheet pile (effective width 500 mm, height 225 mm, thickness 24.
3, the surface of the concave surface having a length of 6 m) is subjected to sand blasting until SIS Sa2 1/2 is reached, and a chromating agent is applied and baked on the surface in contact with the sea at the time of use, and the total chromium adhesion amount is 500 mg / m ^2. Was formed. After curing the unpainted part, an epoxy-based primer was spray-coated on the surface so as to have a thickness of 40 μm, and was cured by heating.

Thereafter, the steel sheet pile was heated to 140 ° C. in a heating furnace to form a sheet in which a modified polyethylene layer having a thickness of 0.5 mm and a corrosion-resistant polyethylene layer having a thickness of 2.0 mm were integrated with the steel sheet pile in a high temperature state. Was placed and pressed to fuse. The modified polyethylene is a maleic anhydride-modified polyethylene. The density of the anticorrosion polyethylene used and the Vicat softening point of the modified polyethylene are shown in Table 1.

The cooling was performed by the method shown in Table 1. Thereafter, the entire side edge of the sheet was sealed with a moisture-curable urethane resin composition to form a heavy duty corrosion-resistant coated steel sheet pile of the present invention. The following evaluation was performed on this steel sheet pile.

(1) Investigation of Residual Stress of Coating After cooling, a part of the coating was peeled off from the steel sheet pile while keeping the coating from being deformed. The residual stress of the coating was calculated from the Young's modulus. (2) Warm salt water immersion test The obtained steel sheet pile was cut into a suitable size, and was cut at 50 ° C and 3%.
Immersion in salt water for a long period of time, the adhesion of the coating after immersion is 90 °
It was evaluated by the peel strength method (JIS G 3469). In addition, the coated end portion of the end seal portion was forcibly peeled off, and deterioration conditions such as rust and exposure of the iron base at the peeled portion were investigated. (3) Salt spray test The obtained steel sheet pile was cut into an appropriate size, and JIS K5
A salt spray test specified in No. 400 was carried out, and the progress of rust from the end was investigated.

[0036]

[Table 1]

[0037]

[Table 2]

According to the result of the accelerated test, 0.940 g /
cm ³ or more high-density polyethylene of the system hardly observed decrease in the peel strength due to moisture coming through the coating,
In addition, heavy corrosion-resistant coated steel sheet piles having a coating residual stress of 20 kgf / cm ² or less, particularly in a test carried out at a temperature close to the environmental temperature such as a salt spray test, are deteriorated at the edge due to penetration of corrosive substances from the edge. Was found to be suppressed. Further, in a system using a high-density polyethylene as a coating material as in the present invention, it is possible to use a modified polyethylene having a low Vicat softening point or to cool from the polyethylene side after application, so that the residual stress of the coating is low. It was effective in obtaining a sheet pile.

In a marine exposure test of steel sheet piles carried out by the group of the present inventors, the steel sheet piles of Example 2 and Comparative Example 4 were tested. In the steel sheet pile having the configuration of Comparative Example 4, the coating had already been peeled around the corners at the ends in the undersea part at the stage of five years. However, Example 2
In the steel sheet pile having the above structure, the end seal completely remained even after 10 years had passed, and no progress of deterioration from the end was observed. Also, the peel strength of the coating was 30 kgf /
cm ² or more, and did not deteriorate at all. this is,
The high-density polyethylene exhibited a high barrier effect against moisture penetration and the residual stress of the coating was 20 kgf / cm.
^It is thought that the penetration of moisture from the end was suppressed, and the peeling and turning-up from the end were effectively suppressed, because the sample was small in No. ² .

As described above, it was found that the heavy-corrosion-coated steel sheet pile of the present invention exhibited extremely excellent adhesion even in various accelerated tests and long-term exposure in the sea.

[0041]

As described above, the heavy-corrosion-coated steel sheet pile of the present invention exhibits extremely excellent long-term adhesion in an acceleration test and an exposure test in a marine environment. As a result, the long-term service life of the coated steel sheet pile can be significantly extended, the maintenance and management costs of the port facility can be reduced, and the loss of repair costs due to peeling can be prevented. Absent.

[Brief description of the drawings]

FIG. 1 is a sectional view (an enlarged view of a side end) of a heavy-corrosion-coated steel sheet pile of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel sheet pile 2 Base treatment layer 3 Modified polyethylene layer 4 Corrosion-proof polyethylene layer 5 Edge sealing layer

Continued on the front page (72) Inventor Yoshiro Saito 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Yoshihiro Okano 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Stock In company

Claims (2)

[Claims] 1. A heavy-duty coated steel sheet pile wherein at least one surface of a steel sheet pile subjected to a base treatment is coated with a corrosion-resistant polyethylene layer via a modified polyethylene layer, the polyethylene resin of the corrosion-resistant polyethylene layer has a density of 0.940 g / c
Heavy duty coated steel sheet pile, characterized in that in m ³ or more, and the residual stress of the coating is 20 kgf / cm ² or less. 2. The anticorrosion polyethylene layer according to claim 1, wherein the polyethylene resin is a non-crosslinked polyethylene.
The heavy duty anticorrosion coated steel sheet pile as described.