JPS60208218A - Corrosion-proof coated steel pipe pile and preparation thereof - Google Patents

Abstract

PURPOSE:To continuously prepare a corrosion-proof steel pipe pile having excellent capacity, by applying a specific polyethylene composition to the periphery of a steel pipe pile by extrusion molding. CONSTITUTION:A corrosion-proof layer having a thickness of 0.5-5mm., which comprises a polyethylene composition compounded with 80wt% or more of high- pressure low density polyethylene of which the melt index (MI) is 0.05-0.5g/ 10min, the density is 0.9-0.930g/cm<3> and the content of a vinyl acetate constitutional unit is 0.5-5%, is formed around a steel pipe pile. By using the above- mentioned specific high-pressure low density polyethylene, a corrosion-proof coated steel pipe pile excellent in chemical resistance, mechanical physical properties and corrosion-proof capacity can be prepared continuously with good reproducibility.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to anti-corrosion steel pipe piles used for civil engineering and construction, and a method for coating steel pipe piles with anti-corrosion coating. A polyethylene composition containing mainly low-density polyethylene is extruded to form an anti-corrosion coating layer around the steel pipe pile, for example,
In particular, it is extruded into a sheet-like body in a molten state using the T-gui extrusion molding method, and the sheet-like body is wrapped around the steel pile to form a corrosion-proofing coating layer, which has excellent corrosion protection properties. This invention relates to a method for continuously manufacturing coated steel pipe piles and anti-corrosion coated steel pipe piles.

(Prior Art) Conventionally, steel pipe piles have been used, for example, for seawalls such as ports, rivers, and rivers, for pier structures, and for pier structures. 1G It was widely used as a type A for various civil engineering and construction works such as rivers, etc., and was cast underground or at the bottom of the water.

However, conventional steel pipe piles, for example, are exposed to direct sunlight [I light, wind and rain,
Steel pipe piles are often installed in places where they are directly exposed to harsh natural environments such as waves, drainage water, seawater, and drifting debris, so they are often subject to severe corrosion, but corrosion prevention measures for steel pipe piles are not always sufficient. Instead, there was a game that could not withstand long-term use, having been left on the edge for about 20 years.

Recently, the surroundings of steel pipe piles have been made using polyolefin thermoplastic (1
1) A method of coating steel pipe piles by die extrusion has been proposed as a fairly preferred coating method, but this method of coating steel pipe piles still does not provide a stable method for producing steel pipe piles with sufficiently satisfactory corrosion resistance. It cannot be manufactured with good reproducibility, and the optimal coating method has not yet been established.

Although the method for coating steel pipe piles described above produces steel pipe piles with a 4JJ oil coating layer that has excellent corrosion resistance, there are still some deficiencies, especially:
When winding a resin notebook extruded from a T-die around the circumferential surface of a steel pipe pile in a II 1M shape, the winding process itself may become impossible due to lack of resin, or the mechanical damage to the coating layer after the coating may become impossible. The physical properties (hardness, low-temperature brittleness, etc.) may not be sufficient, and the overlapping parts of the side edges of the resin sort may shift during coating, resulting in corrosion resistance at the overlapped parts. Furthermore, if the steel pipe pile is installed for a long period of time in a harsh environment, such as an environment exposed to high temperatures, There were problems such as insufficient deterioration resistance and durability of r1il'J.

(Object of the Invention) The present inventors have discovered that in a method of coating the circumferential surface of steel pipe piles used for civil engineering and construction with polyolefin-based thermal IIJ plastic cedar 1 fat (by extrusion molding method), the coating obtained by the coating [ While maintaining the excellent points of !14 'a!Anti' having a coating layer, we are working diligently on a method to solve all the problems of this type of coating method as described in i:j. As a result of research, it was discovered that a method of covering steel pipe piles by extrusion molding using a specific high-pressure low-density polyethylene could extremely effectively solve the various problems mentioned above, and this invention was completed. It is.

(Structure and operation of the invention) That is, the gist of this invention is that the melt index (Ml) is 0.05 to 0.5 g/10 min ζ, and the density is 0.915 to 0.930 g/cal. Moreover, a corrosion-resistant coating layer with a thickness of 0.5 to 5 mm is made of a polyethylene composition containing 80% by weight or more of high-pressure polyethylene having 0.5 to 5% of acid-resistant vinyl constituent units. An anti-corrosion coated steel pipe pile is formed around the pile, and has a melt index (sometimes abbreviated as Ml) of 0.05 to 0.5 g/10 min and a density of 0.915 to 0.915. 0.930 g/CIw
1, and contains 0.5 to 5% of hinyl acetate structural units.
A polyethylene composition containing 80% by weight or more of high-pressure polyethylene having the same composition is extruded into a molten sheet-shaped body or a tubular body by an extrusion molding method to form a molten sheet-shaped body or a tubular body. Forming an anti-corrosion coating layer around the steel pipe pile, in particular, extruding it into a molten sheet-like material using the 1-die extrusion method, and forming the molten sheet-like material in a spiral shape around the steel pipe pile. Makitsu L
The present invention relates to a method for producing an anti-corrosion coated steel pipe pile, which is characterized by forming an anti-corrosion coating layer.

The manufacturing method of the present invention uses the above-mentioned specific high-pressure low-density polyethylene (for example, Ml is 0.05 to 0.5 g ZlO and density is 0.9 to 0.930 g/cJ). This is an industrially excellent manufacturing method that can continuously manufacture corrosion-resistant coated steel pipe piles with a corrosion-resistant fli layer having excellent chemical resistance, mechanical properties, and corrosion-resistant performance with good reproducibility.

In addition, the corrosion-resistant coated steel pipe pile of the present invention produced by the above-mentioned manufacturing method of the present invention, etc., is characterized in that the resin forming the corrosion-resistant coating layer is a specific high-pressure polyethylene (the above-mentioned M1).
value, density, and 0.5 to 5 hinyl acetate structural units.
%), therefore, (al) a corrosion-resistant coating with mechanical properties (protective performance for the surface of steel pipe piles) that can sufficiently withstand various ij+IiI when steel pipe piles are driven underground. It is a steel pipe pile with an excellent coating layer that can withstand a variety of harsh natural environments, especially under relatively high temperatures. The durability of the corrosion-resistant coating layer is extremely high when the product is installed in contact with river water, waste water, seawater, etc. for a long period of time (for example, under high temperature conditions heated by direct sunlight).

Hereinafter, the anti-corrosion coated steel pipe pile of the present invention and its manufacturing method will be explained in more detail with reference to the drawings.

The drawing is a perspective view schematically showing an embodiment of the manufacturing method of the present invention.

For example, as shown in the drawings, the manufacturing method of the present invention includes supplying a polyethylene composition containing the above-mentioned specific high-pressure low-density polyethylene in a specific ratio to a T-die extrusion molding machine (not shown in its entirety). Then, the polyethylene composition is extruded into a sheet from the T-die 1 of the extrusion molding machine, and the molten sheet 2 is immediately heated in a heating furnace 6 or the like and placed on a rotating long steel pipe pile 3. The resin layer is wound spirally around a circular surface, and the resin layer is cooled with an appropriate cooling means (for example, water spray 4, etc.) to form a continuous corrosion-resistant coating layer 5 with excellent corrosion-proofing performance on the circumferential surface of the steel pipe pile 3. It is formed in a specific manner.

The polyethylene composition used for coating steel pipe piles by extrusion molding in the production method of this invention has a melt index (Ml) of 0.05 to 0.5 g/10 min, preferably 0.06 to 0.4 g/10 min. and the density (at room temperature) is 0
．． 915-0.930 g/cTA, preferably 0.9
20 to 0.928 g/- and having vinyl acetate structural units in the main chain of the polymer in a proportion of 0.5 to 5%, preferably 0.8 to 4%, It is a polyethylene composition containing 80% by weight or more, preferably 90% by weight or more.

In this invention, the melt index (Ml) is A
Values are determined according to STM D123B, and density is determined according to AS''rM D1505.

The content of vinyl acetate structural units in the main chain of high-pressure polyethylene is a value calculated from the results of measuring a polyethylene sample by infrared absorption spectroscopy using a suspension method.

In this invention, high-pressure polyethylene refers to a polymerization pressure of 1000 atm or more and a polymerization temperature of 100 to 300'C.
It is a polymer obtained by copolymerizing ethylene with vinyl acetate in the presence of a catalyst that generates free radicals.

In this invention, all or most of the high-pressure low-density polyethylene is replaced with polyethylene obtained by other manufacturing methods such as medium- or low-pressure methods, or with polyethylene having physical properties outside the range of each of the above-mentioned physical properties. If a polyethylene composition is used, it is not possible to form a corrosion-resistant coating layer with excellent corrosion-proofing performance on the circular surface of a steel pipe pile with good reproducibility.

For example, in this invention, Ml of high-pressure polyethylene
If it is smaller than 0.05 g/10 minutes, the sorted material extruded from the die of the extruder, for example, the 'r die, may break during extrusion molding, or the material may not have an appropriate uniform thickness. It is not suitable because continuous extrusion cannot be performed because a sheet-like body of the steel pipe pile is not formed. Also, if the Ml of the polymer is larger than 0.5 g/lo, Since the mechanical strength, especially the hardness, of the corrosion-resistant coating layer that is formed decreases, it may not be able to withstand the impact of driving steel pipe piles and may be susceptible to deformation (formation of dents) or damage. , not appropriate.

In addition, in this invention, it is difficult to obtain polyethylene whose density is lower than 0.915 g/ad by industrially polymerizing such polyethylene by a high-pressure method, and the density of high-pressure polyethylene is lower than 0.915 g/ad. 0.9
If it is larger than 30 g/cJ, for example, when a sheet extruded from a 1-die die is partially overlapped and wound spirally around the steel pipe pile, the seal
The overlapping part (wrap part) of the shaped bodies shifts and the width of the overlap r; Therefore, it is not appropriate, and furthermore, it is not appropriate because uneven thickness of the resin coating layer in the molten state occurs in the welded convex portion (also called bead portion) on the circumferential surface of the steel pipe pile.

Furthermore, in this invention, if the content of vinyl acetate structural units in the high-pressure polyethylene is less than 0.5% or if the high-pressure polyethylene does not have any vinyl acetate structural units, the basic Corrosion resistance, only a corrosion-resistant coating layer with poor durability is formed, such as environmental stress cracking resistance, environmental stress cracking resistance after thermal aging, and additives (e.g. antioxidants) in air or salt water. This is not suitable because the bleed-out resistance inside the pipe pile deteriorates, and if the content of vinyl acetate structural units in high-pressure polyethylene exceeds 5%, corrosion protection formed on the circumferential surface of the steel pipe pile is not suitable. This is not suitable because the hardness of the coating layer becomes small and the corrosion-resistant coating layer becomes easily deformed or damaged during driving of the steel pipe pile.

In addition to the high-pressure low-density polyethylene described above, the polyethylene composition used in this invention includes, for example, ethylene homopolymers and ethylene-vinyl acetate copolymers having physical properties outside the above range or obtained by other manufacturing methods. , ethylene polymers such as ethylene-propylene copolymers,
Alternatively, a thermoplastic synthetic resin such as polypropylene, polyvinyl chloride, polyester, polyamide, etc. may be used in an amount of about 15% by weight or more, especially 1
It may be blended in a small amount at a ratio of 0% by weight or less.

The above polyethylene composition may contain additives such as an ultraviolet inhibitor and an antioxidant. For example, about 0.5 to 10% of carbon black may be added as an ultraviolet inhibitor.
, especially preferably 1 to 5% by weight, and further,
As antioxidants, use phenolic antioxidants, sulfite antioxidants, bosphite antioxidants, etc.
．． It is preferable to blend it in a proportion of 0.01 to 5% by weight, particularly 0.05 to 3% by weight.

The polyethylene composition used in this invention preferably has a melt tension of approximately 3 to 8 g, particularly 4 to 8 g.
It is particularly desirable to prevent uneven thickness of a sheet-like material in a melted and softened state that is wound around the circumferential surface of a steel pipe pile, and to perform coating using a stable T-die extrusion molding method that does not cause resin breakage.

In the manufacturing method of the present invention, the molding conditions for the extrusion molding method, particularly for the 1'' extrusion molding method, are not particularly limited. It is preferable that the degree of

The steel pipe pile used in this invention is preferably a steel pipe pile coated with adhesive in advance, and for example, a sheet of polyethylene composition extruded from a T-die is wrapped around the steel pipe pile. , when coated, about 80~
It is preferable that it is preheated to about 250°C, 110°C and about 90 to 230°C.

Examples of the adhesive include polyethylene, polypropylene, ethylene-vinyl acetate copolymer, and ethylene-vinyl acetate copolymer.
Polyolefin-based q-polymers such as propylene copolymers or modified polyolefin-based polymers, or thermoplastic resins such as polyvinyl chloride, polyester, and polyamide, and various tackifiers are used as main components. A hot melt type having a temperature of about 80 to 250°C is sufficient.

Further, the above-mentioned adhesive can be applied by an extrusion coating method or by spraying a powdered adhesive onto the heated peripheral surface of the steel pipe pile immediately before the step of coating the peripheral surface of the steel pipe pile with the polyethylene composition of the present invention. The surrounding surface of the steel pipe pile may be coated with the above material.

In the manufacturing method of the present invention, the corrosion-resistant coating layer formed on the peripheral surface of the steel pipe pile has a thickness of about 0.5 to 5 mm, especially about 0.5 mm.
The temperature is preferably 8 to 4° C., and the molding conditions (discharge rate, discharge rate, etc.) at the time of discharge of the extrusion molding method, particularly the T-die extrusion molding method, may be determined accordingly.

According to the manufacturing method of this invention, it is possible to coat the circumferential surface of steel pipe piles for civil engineering and construction with an anti-corrosion film that has excellent corrosion resistance. 11! '4ti. r
i. The corrosion-resistant coated steel pipe pile of this invention can form a layer and continuously produce a corrosion-resistant coated steel pipe pile.
It is excellent in the points already explained in detail,
It has an excellent anti-corrosion performance of about 20 years or more.

(Examples and effects) Examples and comparative examples are shown below.

In Examples and Comparative Examples, "thickness unevenness" refers to the thickness a of the corrosion-resistant coating layer on the flat peripheral surface of the corrosion-resistant coated steel pipe pile, and the thickness b of the corrosion-resistant coating layer on the convex strip of the welded part.
and the calculation formula ((a-b)/a)X100 (
%), and "ramp deviation" is the deviation of the overlapping part of the sheet material when wrapping the peripheral surface of the steel pipe pile with a sheet material in the extrusion molding method. The occurrence of the deviation was observed, and the length of the deviation that occurred was measured and shown.

"Heat oxidative deterioration resistance" refers to test pieces obtained from the corrosion-resistant coating layer of corrosion-resistant coated steel pipe piles (1) as is without treatment, (2)
After being left in air at 70°C for 100 hours, or (3) in salt water at 100°C for 100 days,
It indicates the time it takes for the polymer to react with oxygen and begin to deteriorate when left in a furnace heated to 00°C, and the "environmental stress cracking resistance" is the time required for the polymer to react with oxygen and begin to deteriorate. The obtained test piece was (1) left untreated, +
2+ Measured according to ASTM D1693 after being left in an air oven at 150°C for 480 hours, and is expressed as the durability time until 50% cracking occurs in the test piece.

Furthermore, "hardness" is measured by measuring a test piece obtained from the corrosion-resistant coating layer of a corrosion-resistant coated steel pipe pile under a load of 2
A needle of 500 g and a flat needle area of 0.025 C was used, and the measurement temperature was 60° C., and the depth of penetration of the needle was shown after 24 hours.

Example 1 and Comparative Examples 1 to 4 100 parts by weight of high-pressure polyethylene having the melt index (Ml) and density (at normal temperature) shown in Table 1 and the content of vinyl acetate structural units shown in Table 1. ,
A polyethylene composition for coating steel pipe piles was produced by kneading 3 ffii parts of carbon black and 0.2 parts by weight of a thiobisphenol-based antioxidant at 200'C for coating steel pipe piles using a T-die extrusion method. , molded into pellets.

Using pellets of the polyethylene composition prepared as described above, the T-die of the extruder was heated to about 230°C.
extrude a sheet of polyethylene composition at 200°
A long steel pipe pile (length: 12 m, outer diameter: 5 m) heated to C and coated with modified polyolefin adhesive
08 Dragon, the surrounding surface of the steel pipe (thickness: 9.5 + n) is covered with the sheet-like material in a molten and softened state, partially overlapping, wrapped in a spiral shape, and cold water is sprinkled on the coating layer. The mixture was cooled to form a corrosion-resistant coating layer.

The average thickness of the corrosion-resistant coating layer of each of the corrosion-resistant coated steel pipe piles coated as described above was about 3 mm.

Table 1 shows the coating conditions of those steel pipe piles and the various test results of the corrosion-resistant coating layers of the corrosion-resistant coated steel pipe piles obtained as a result.

[Brief explanation of the drawing]

The drawing is a perspective view schematically showing an example of the manufacturing method of the present invention. l; 'r die of extrusion molding machine, 2; sheet-like body, 3; steel pipe pile, 4; water spray, 5; i-layer, 6; heating furnace,
7; Press roll. Patent applicant: Nippon Steel Corporation Ube Industries, Ltd.

Claims (2)

[Claims] (1) Melt index (Ml) is 0.05 to 0°5 g/10 min, and density is 0.915 to 0.930.
g/cIi+ and contains 0 vinyl acetate structural units.
．． A 0.5-thick polyethylene composition containing 80% by weight or more of high-pressure polyethylene containing 5% to 5%.
An anti-corrosion coated steel pipe pile, characterized in that an anti-corrosion coating layer of ~5I11 is formed around the steel pipe pile. (2) Melt index (Ml) is 0.05~0°5g/10min, density is 0.915~0.930g
/ cl, and the vinyl acetate structural unit is 0.5
A polyethylene composition containing 80% by weight or more of high-pressure polyethylene having a content of ~5% is extruded into a molten sheet or sheared body by an extrusion molding method,
A method for producing an anti-corrosion coated steel pipe pile, which comprises forming an anti-corrosion coating layer around the steel pipe pile using the molten sheet or tubular body.