JP2605742B2 - Repair method for damaged part of polyethylene coated steel - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for repairing a damaged portion generated in a coating layer of a polyethylene-coated steel material in which a steel material such as a steel pipe or a steel sheet pile is coated with polyethylene.

[Prior Art] Polyethylene-coated steel materials have been developed for the purpose of maintaining the anti-corrosion properties of anti-corrosion steel pipe piles, anti-corrosion steel sheet piles, etc. used as materials for civil engineering and construction such as offshore structures and seawall protection for a long time. Polyethylene has become the mainstream of anticorrosion coatings in recent years because of its excellent mechanical properties such as hardness and impact strength, weather resistance, water resistance, chemical resistance and the like. Polyethylene coated steel is extruded lining method,
It is manufactured by a sheet lining method, a powder lining method, or the like, and has a mill-coated polyethylene coating layer formed on a steel material surface. The polyethylene-coated steel material may be damaged during storage, transportation, laying, and placing by impact due to contact between the steel materials or jigs and tools. If such a damaged portion is left as it is, it causes rusting and peeling of the coating layer, and an excellent anticorrosion effect cannot be maintained. Therefore, it is necessary to repair the damaged portion.

As a conventional repair technique for a damaged portion of the above-mentioned mill-coated polyethylene coating layer, several methods are known. FIG. 5 is an explanatory view of a repair method disclosed in Japanese Patent Application Laid-Open No. 61-19777. In FIG. 5, reference numeral 1 denotes a steel material 2 which is a mill-coated polyethylene coating layer. The repair method is to apply a urethane-based primer 10 to a damaged portion of the coating layer 2 and its surroundings, and then apply a two-component hardening agent to the damaged portion. A polyurethane-based sealant 11 is filled, and the primer 10
Polyolefin sheet 12 coated with the same primer as
Is repaired by thermocompression bonding.

FIG. 6 is an explanatory diagram of a repair method disclosed in Japanese Patent Application Laid-Open No. Sho 61-170586. In FIG. 6, 1 is a steel material, 2 is a mill-coated polyethylene coating layer, and the repair method is to fill a damaged portion with a sealant 13 and then to a mill-coated polyethylene coating layer 2 on the upper surface of the sealant 13 and its surroundings. A crosslinked polyolefin sheet 15 provided with an adhesive layer 14 having a softening point of 50 ° C. or lower is heat-pressed, and a polyolefin sheet 16 having a softening point of 90 ° C. or higher is continuously coated with the crosslinked polyolefin sheet 15 and the mill-coated polyethylene coating layer 2. Thermocompression bonding.

[Problems to be Solved by the Invention] However, the above-described related art has the following problems. In the method of JP-A-61-197077 shown in FIG. 5, it is necessary to mix two liquids for preparing the sealant, and in addition, it is necessary to proceed to the next step until the curing curing of the primer and the sealant is completed. There is a problem in the workability. Further, the method of JP-A-61-170586 shown in FIG. 6 has the same problems as JP-A-61-197077 due to the use of a two-liquid mixed sealant. In the case of thermocompression bonding to a polyethylene coating layer, since the polyolefin sheet has a high softening point, it is difficult to firmly bond the crosslinked polyolefin sheet and the mill-coated polyethylene coating layer without lowering the performance or causing thermal deformation. As described above, in the prior art, it is necessary to wait for hardening and curing to use a primer or a sealant, or it is said that the adhesion between the reinforcing polyolefin sheet and the steel-coated mill coat polyethylene coating layer is insufficient. There was a problem.

The present invention has been made in order to solve the problems of the prior art as described above, and does not require a waiting time during the repairing process, and also has an adhesive surface between the repairing layer and the steel-coated mill-coated polyethylene coating layer. An object of the present invention is to provide a method for repairing a damaged portion of a polyethylene-coated steel material that can be firmly adhered.

[Means for Solving the Problems] The present invention relates to a method for repairing a damaged portion of a coating layer of a polyethylene-coated steel material, wherein (1) an ethylene-α-olefin copolymer obtained by graft polymerization of an anhydride of an unsaturated carboxylic acid. (2) a step of applying a modified polyethylene sheet having a melting point of 75 ° C to 100 ° C as a component to the damaged portion of the steel-coated polyethylene coating layer and the surface of the mill-coated polyethylene coating layer around the damaged portion by heating and pressing; Heat-pressing and covering a two-layer sheet in which the lower layer is made of the above-mentioned modified polyethylene and the upper layer is coated on the modified polyethylene covering layer formed in the above step, thereby forming a damaged portion of the polyethylene-coated steel material. Repair method.

[Action] As described above, the modified polyethylene of the present invention is obtained by graft-polymerizing an unsaturated carboxylic acid or an anhydride thereof to a copolymer of ethylene-α-olefin, and has an adhesive property and a melting point higher than that of polyethylene. Is also low. For this reason, in the first step, when the modified polyethylene sheet is heat-pressed to the damaged portion and the surrounding mill-coated polyethylene coating layer, the performance of the mill-coated polyethylene coating layer is not reduced, and the modified polyethylene sheet is applied to the mill-coated polyethylene coating layer. And it can be in close contact with the steel surface of the damaged part. In the next step, when a two-layer sheet whose lower layer is made of the above-mentioned modified polyethylene and whose upper layer is made of polyethylene is heat-pressed on the modified polyethylene layer formed in the previous step, this two-layer sheet is formed by the adhesion of the modified polyethylene, Strongly adheres to the modified polyethylene layer. And the polyethylene layer of the two-layer sheet has a function as a reinforcing layer of the repaired part. As described above, the present invention is a repair method for bringing a polyethylene sheet into close contact with a damaged portion via a modified polyethylene sheet.

[Example] Hereinafter, a specific description will be given based on an example.

1a to 1c are explanatory views showing an example of a repair method according to the present invention. The order of repair will be described with reference to FIGS. In FIGS. 1b and 1c, first, the damaged portion 3 of the mill-coated polyethylene coating layer 2 of the steel material 1 and the mill-coated polyethylene coating layer 2 around the damaged portion 3 are heated by an induction heater, or the uncoated steel material surface (back side). Preheat by heating with a burner. Next, a modified polyethylene (hereinafter referred to as a modified polyethylene) having a main component obtained by graft-polymerizing an anhydride of an unsaturated carboxylic acid onto an ethylene-α-olefin copolymer having a size to cover the damaged portion 3 of the mill-coated polyethylene coating layer 2 and its periphery. (It is referred to as a modified polyethylene in the description.) Next, as shown in FIG. 1a, a two-layer sheet 7 made of modified polyethylene 5 and polyethylene 6 as the lower layer cut into a shape corresponding to the concave portion formed in the damaged portion 3 (in the following description, (Abbreviated as polyethylene two-layer sheet) while applying pressure by a roller or the like. At this time, the polyethylene two-layer sheet 7 is pressure-bonded with the lower-layer modified polyethylene facing the steel material 1 side. Thus, the damaged portion 3 and the surrounding mill-coated polyethylene coating layer 2
After the thickness of the sheet is made substantially the same, the polyethylene two-layer sheet 8 is pressed thereon with a roller or the like while being heated to complete the repair.

In addition, when the state of the flaw of the damaged portion 3 does not reach the surface of the steel material 1 or when it is minute, the modified polyethylene sheet 4 is embedded in the flaw as shown in FIGS. Then, the polyethylene two-layer sheet 8 may be heated and pressed on the coating layer.

 Next, the repair process will be described in further detail.

The reason why the steel material 1 is preheated before coating is to effectively press the modified polyethylene sheet 4 against the damaged portion 3. When the modified polyethylene sheet 4 is applied without preheating and heated with a burner from the side of the mill-coated polyethylene coating layer 2, it takes a long time for the exposed surface of the steel material 1 of the damaged portion 3 to reach a temperature at which bonding is possible, and In some cases, thermal degradation, thermal deformation or peeling of the mill-coated polyethylene coating layer 2 around 3 may occur. The preheating temperature of the steel material 1 is preferably set to about 60 to 100 ° C. as a temperature at which preheating hardening is exhibited and an adverse effect on the mill coat polyethylene coating layer 2 can be avoided.

Next, using a modified polyethylene sheet 4 having a thickness of 0.1 mm to 1.0 mm manufactured by extrusion molding, press molding, etc., heating the modified polyethylene sheet and the repaired surface to about 100 ° C., and then applying a roller to the repaired surface of the modified polyethylene sheet. And pressure-coated. Here, the thickness of the modified polyethylene sheet is set to 0.1 mm to 1.0 mm because if it is less than 0.1 mm, the modified polyethylene sheet is easily broken at the time of pressure bonding, and
If the thickness exceeds 1.0 mm, voids are likely to be formed between the modified polyethylene sheet and the repaired surface during pressure bonding.

The area covered with this modified polyethylene sheet 4 is the first
In some cases, as shown in FIG. B, the entire surface of the steel material 1 of the damaged portion 3 is covered. However, when the repaired surface is wide, the case where the steel material 1 is partially covered as shown in FIG. It is possible. As described above, the coverage of the modified polyethylene single sheet 4 is appropriately considered depending on the size of the damaged portion 3.

The modified polyethylene used in the present invention is ethylene and α-
The main component is a composition obtained by graft-polymerizing an anhydride of an unsaturated carboxylic acid to impart an adhesive function to an olefin copolymer, and has a melting point of 75 to 100 ° C. The polyethylene-coated steel material that is the subject of the present invention is exposed to direct sunlight, and the surface temperature can reach as high as 60 to 70 ° C.
Therefore, when modified polyethylene having a melting point of 70 ° C. or less is used, as shown in FIG. 3, the adhesive strength is extremely reduced, and when an external force such as a collision is applied, the repair layer is displaced or peeled off. When a modified polyethylene having a melting point of 100 ° C. or more is used, the mill coat polyethylene coating layer around the damaged portion must be heated to 100 ° C. or more, and the strength of the mill coat polyethylene coating layer decreases, as shown in FIG. Thus, the mill-coated polyethylene coating layer is thermally deformed, and the adhesion between the mill-coated polyethylene coating layer and the steel surface is also reduced. Based on such studies, the melting point of the modified polyethylene was determined.

Next, the purpose of coating the intermediate polyethylene two-layer sheet 7 is not only to reinforce the damaged portion 3 but also to fill the concave portion of the damaged portion 3 to eliminate the step between the mill-coated polyethylene coating layer 2 and the damaged portion 3. Polyethylene two-layer sheet 8 for coating
When crimping is performed, it is also possible to prevent formation of an air pocket and poor adhesion. The polyethylene two-layer sheet 7 for covering the recessed portion of the damaged portion 3 may be covered a plurality of times depending on the depth and size of the flaw. However, depending on the condition and size of the flaw, this intermediate polyethylene 2
In some cases, it is not necessary to cover the layer sheet 7.

The polyethylene two-layer sheet 8 to be coated at the end of the repair is
The coating is performed so as not to exceed the coating area of the modified polyethylene sheet 4 previously coated. This is to ensure that the two-layered polyethylene sheet 8 is in close contact and to prevent the polyethylene two-layered sheet 8 from peeling off from the end. Such a two-layer sheet can be produced by press molding or two-layer extrusion. The thickness of the lower modified polyethylene sheet is 0.1 mm to 1.0 mm for the same reason as the above modified polyethylene sheet, and the thickness of the upper polyethylene sheet is desirably 0.5 mm to 5.0 mm. The reason is that sufficient contact resistance cannot be expected if the thickness is less than 0.5 mm.
If it exceeds m, the resistance at the time of laying or driving is undesirably increased. After heating the polyethylene two-layer sheet to about 100 ° C., a pressure-bonded coating is formed on the repaired surface.

As described above, the feature of the present invention is to adhere the polyethylene sheet through the modified polyethylene sheet. For example, when the polyethylene sheet is covered only with the polyethylene sheet, it is difficult to obtain strong adhesion. Further, when coated with a modified polyethylene sheet alone, the modified polyethylene sheet is not preferable because the mechanical properties such as hardness and impact strength are greatly inferior to those of the mill-coated polyethylene coating layer. For these reasons, there are two types of polyethylene, modified polyethylene for improving adhesion and polyethylene for reinforcement.
Layer sheets are used.

The modified polyethylene used in the present invention may be a modified polyethylene prepared by blending an unmodified ethylene-α-olefin copolymer with the modified polyethylene produced as described above. Further, the modified polyethylene and polyethylene used in the present invention are colored pigments,
It may contain additives such as stabilizers and inorganic fillers.

 Next, examples and comparative examples of the present invention will be described.

(Example) A damaged part reaching a steel surface of 50 mm in diameter is artificially formed on the coating layer of a polyethylene-coated steel pipe in which a high-density polyethylene of about 3 mm is coated on the outer surface of a 36-inch outer diameter steel pipe. After wiping with a thinner, the damaged part and its surroundings were preheated from inside the steel pipe with a propane gas burner.
The preheating was stopped when the steel surface of the damaged portion reached 90 ° C., and 0.5 mm of modified polyethylene made of a maleic anhydride graft-modified ethylene-butene 1 copolymer composition having a melting point of 83 ° C., which had been previously press-molded, was formed. Thick sheet about 120mm in diameter
The milled polyethylene coating layer around the damaged portion and its surroundings was pressed with a roller while heating until the temperature reached 100 ° C. Next, the lower layer is 0.
The modified polyethylene layer formed of the modified polyethylene sheet having a thickness of 5 mm and the upper layer composed of a high-density polyethylene sheet having a melting point of 130 ° C. and having a thickness of 2.5 mm was cut to a diameter of 50 mm and applied to the recessed portion of the damaged portion, and then formed. Face 100
It was pressed with a roller while heating to ℃, so that the coating surface of the damaged portion was almost the same as the thickness of the surrounding mill-coated polyethylene coating layer. Further, the lower layer is a sheet of the modified polyethylene 0.3 mm thick, and the upper layer is a high density polyethylene 0.7 mm.
Polyethylene two-layer sheet consisting of a sheet with a diameter of 11 mm
The sheet was cut to 0 mm, and was applied to the damaged portion as a center.

After the repaired part reached room temperature, loading, transport, and collision tests (collision between 36-inch steel pipes) were performed on the repaired polyethylene-coated steel pipes. As a result of the experiment, no abnormality such as pinholes or peeling was observed in the coating of the repaired part.

When the peel adhesion between the polyethylene layer of the repaired part and the steel pipe surface was measured, the width was 13 kg / 10 mm at 20 ° C and 7 kg /
A value of 10 mm width was obtained, and it was confirmed that the polyethylene layer of the repaired part was firmly adhered to and integrated with the mill coat polyethylene coating layer.

(Comparative Example) Repair was performed under exactly the same conditions as in the experimental example, except that a maleic anhydride graft-modified polyethylene-based composition having a melting point of 122 ° C was used as the modified polyethylene. After the temperature of the repaired part reached room temperature, the repair status was examined, and the polyethylene layer of the repaired part hardly adhered to the steel surface and the mill-coated polyethylene coating layer, and it was easily peeled off when external force was applied. there were.

Next, the temperature was set at 125 ° C. at the time of thermocompression bonding, and repair was performed under the same conditions as above. Under these conditions, thermal deformation of the mill-coated polyethylene coating layer became severe, and repair was extremely difficult.

[Effects of the Invention] The repairing method of the present invention provides a method for repairing an ethylene-α olefin copolymer having a lower melting point than polyethylene and having an adhesive property, by modifying an unsaturated carboxylic acid anhydride by graft polymerization with a modified polyethylene. , Because it is a method of coating polyethylene, without adverse effects such as thermal deformation or thermal degradation on the steel mill coat polyethylene coating layer,
It is possible to form a coating layer firmly adhered to and integrated with the steel surface of the damaged portion and the mill coat polyethylene coating layer around it. Further, since there is no need to use a primer or a sealant which requires a hardening curing time as in the prior art, the repair method is excellent in workability without waiting time occurring during the repair process.

[Brief description of the drawings]

FIGS. 1a to 1c are explanatory views showing an example of the repair method of the present invention.
FIG. 2 is an explanatory view of a modified polyethylene sheet covering area, and FIG.
FIG. 4 is a diagram showing the relationship between the temperature and the adhesion of the modified polyethylene, FIG. 4 is a diagram showing the relationship between the temperature, the adhesion and the thermal deformability of the polyethylene, and FIG. 5 and FIG. is there. 1 ... steel material, 2 ... mill coat polyethylene coating layer, 3
…… Damaged part, 4,5 …… Modified polyethylene sheet, 6 ……
Polyethylene, 7,8: Polyethylene two-layer sheet.

Claims (1)

(57) [Claims] 1. A method for repairing a damaged portion of a coating layer of a polyethylene-coated steel material, comprising: (1) a melting point of from 75 ° C. to 100 ° C., the main component of which is obtained by graft-polymerizing an anhydride of an unsaturated carboxylic acid to an ethylene-α-olefin copolymer. (2) covering the damaged portion of the steel-coated mill-coated polyethylene coating layer and the surface of the mill-coated polyethylene coating layer around the damaged portion by heating and press-fitting the modified polyethylene sheet; Covering the coating layer by heating and pressing a two-layer sheet in which the lower layer is made of the above-mentioned modified polyethylene and the upper layer is made of polyethylene.