JP7572991B2 - Corrosion prevention methods - Google Patents

Description

The present invention relates to a method for preventing corrosion of steel materials, and in particular to a corrosion prevention method suitable for areas where minute repeated deformations occur due to stresses caused by movements or external pressure.

As disclosed in Patent Document 1, conventional corrosion prevention measures for steel materials have often been applied to parts where it is difficult to ensure a sufficient coating thickness, such as the edges of components and bolts, due to factors such as thinness, large curvature, and corners.

The specific method is to apply a base treatment agent (cement-based anticorrosive paint) that forms a passive film to areas that include parts where it is difficult to ensure the thickness of the paint film, and after this base treatment agent has hardened, apply a general paint to an area wider than the base treatment agent. By performing base treatment with cement-based anticorrosive paint, it is possible to ensure the thickness of the paint film even on edges, and it is possible to prevent internal corrosion caused by cracking or peeling of the thin paint film.

In addition, corrosion protection treatment of steel materials generally involves multiple applications of anticorrosive paint, but since it is necessary to wait for the paint to dry (harden) after each application, there is a problem of large process losses. The method disclosed in Patent Document 2 and Non-Patent Document 1 is a technology to eliminate such process losses, and involves attaching a sheet made of a conductive adhesive with sacrificial corrosion protection and a protective layer to a component, and then applying a top coat to this protective layer. With this method, the process of undercoating the component (application of anticorrosive paint, undercoating, and undercoating) can be completed simply by attaching the sheet, making it possible to significantly shorten the painting process to prevent corrosion of the component.

However, the method disclosed in Patent Document 1 may cause cracks in the hardened base treatment agent itself in areas where micro-deformations of components are severe due to stress changes during operation, such as the arms and legs of heavy machinery such as container cranes. In addition, the technology disclosed in Patent Document 2 and Non-Patent Document 1 uses a flexible sheet, which makes it difficult to handle when the coverage area is large. In addition, because the sheet is flexible, the top coat must be applied after the sheet is installed.

JP 2017-101404 A Patent No. 7000604

Dai Nippon Paint Co., Ltd., Sekisui Chemical Co., Ltd., "Metamor Sheet #1 Heavy-duty Anti-corrosion Paint for Partial Repairs" [Searched on March 22, 2022], Internet <URL: https://www.dnt.co.jp/products/structure/list/upload_files/ctl_202.pdf>

The present invention aims to provide a corrosion prevention method that can be applied to areas where components are subject to severe micro-deformation due to stress changes or where the area to be covered is large, and that also allows a topcoat to be applied to the covered areas before construction.

The corrosion prevention method according to the present invention for solving the above problems is a corrosion prevention method using a covering sheet having a protective layer made of resin or metal and covering the surface to be covered, a conductive adhesive layer for sacrificial corrosion protection arranged on the back surface of the protective layer and containing a powder of a metal whose natural electrode potential is lower than that of the metal constituting the surface to be covered, and a release film covering the exposed surface of the conductive adhesive layer, characterized in that it has a base preparation step of cleaning the surface of the surface to be covered, a covering sheet shape formation step of deforming the protective layer to conform to the surface shape of the surface to be covered, and a covering step of peeling off the release film and attaching the covering sheet that has been through the covering sheet shape formation step to the surface to be covered that has been through the base preparation step.

In addition, in the corrosion prevention method having the above characteristics, it is preferable that the covering sheet shape forming process is performed simultaneously with the base material preparation process or before the base material preparation process. By having such a characteristic, it is possible to perform the work in parallel, which makes it possible to shorten the construction period.

In addition, in a corrosion prevention method having the above-mentioned characteristics, a top coat can be applied to the protective layer before the coating process. With such characteristics, it is possible to paint the coating sheet before it is delivered to the site, which can shorten the construction period and improve the coating quality.

Furthermore, the corrosion prevention method having the above-mentioned characteristics may include a duct arrangement step of arranging a drain duct for draining liquid between the surface to be coated and the conductive adhesive layer. By having such a characteristic, liquid pools are prevented from forming in the stepped portion, making it possible to prevent the induction of corrosion.

The corrosion prevention method with the above characteristics can be applied to areas where minute deformations of components caused by stress changes are severe, or when the area to be covered is large. It also makes it possible to apply a top coat of paint to the covered areas before construction on site.

1 is a diagram showing a configuration of a covering sheet applied to a corrosion prevention method according to an embodiment. FIG. 1 is a diagram showing one structure having a surface to be coated to which a corrosion prevention method according to an embodiment is applied; 1A to 1C are diagrams for explaining steps of a corrosion prevention method according to an embodiment. 10A to 10C are diagrams for explaining a procedure for attaching a cover sheet to a convex portion. FIG. 13 is a diagram for explaining the difference in construction period compared to a corrosion prevention method using painting. FIG. 13 is a diagram showing an example of a case where a step formed when a cover sheet is applied becomes a liquid pool. 13 is a diagram showing a configuration in which a drain duct is disposed between the surface to be coated and the conductive adhesive layer. FIG. FIG. 13 is a diagram showing how liquid is drained from a liquid pool through a drain duct.

The corrosion prevention method of the present invention will be described in detail below with reference to the drawings. Note that the embodiments shown below are some of the preferred forms for implementing the present invention, and even if some of the configuration is changed within the scope of the effect, it can be considered as part of the present invention.

[composition]
First, referring to FIG. 1, the configuration of the covering sheet 10 applied to the corrosion prevention method according to the embodiment will be described. The covering sheet 10 applied to this embodiment has at least a protective layer 12, a conductive adhesive layer 14, and a release film 16. The protective layer 12 is an element that plays a role of covering the exterior of the surface to be covered, which is made of a metal member that is relatively easily oxidized, such as iron. In this embodiment, it is preferable to configure the protective layer 12 from a member that is a thin plate of resin or metal and can be plastically deformed by applying an external force. For example, when the protective layer 12 is made of a general metal such as aluminum, iron, copper, or stainless steel, it can be plastically deformed into any shape by simply applying an external force. In addition, when the protective layer 12 is made of a thermoplastic resin or the like, it can be deformed into any shape by heating it to a temperature equal to or higher than the deflection temperature under load and then applying an external force.

The conductive adhesive layer 14 is an element that provides a sacrificial anticorrosive effect to suppress oxidation (corrosion) of the surface to be coated, and is formed by mixing metal powder 14b into adhesive 14a. Here, adhesive 14a can be, for example, various resin-based adhesives such as acrylic adhesives, rubber-based adhesives, urethane-based adhesives, and silicon-based adhesives, and these materials can be selected or used in combination depending on the usage environment of the coated surface. Note that it is desirable for adhesive 14a constituting the conductive adhesive layer 14 in this embodiment to be one that can retain elastic properties for a long period of time.

In order to provide a sacrificial corrosion protection effect, metal powder 14b is used that is made of a metal that has a lower natural electrode potential than the metal that constitutes the surface to be coated. For example, if the metal member that constitutes the surface to be coated is iron, zinc or aluminum can be used for metal powder 14b.

The conductive adhesive layer 14 having such a configuration is provided on the back side of the protective layer 12. Here, the back side of the protective layer 12 is the main surface facing the surface to be coated. In other words, the conductive adhesive layer 14 is provided so that it is located between the surface to be coated and the protective layer 12 when the covering sheet 10 is attached to the surface to be coated.

The release film 16 is an element that plays a role in protecting the conductive adhesive layer 14. The material of the release film 16 according to the embodiment is not particularly limited as long as it has excellent releasability against the adhesive 14a. When ease of handling is taken into consideration, it is advisable to use a thermoplastic resin film such as a polyethylene film, a polypropylene film, a PET film, or an acrylic resin film. A release film 16 configured in this manner is attached to the adhesive surface of the conductive adhesive layer 14, and is peeled off when the conductive adhesive layer 14 is attached to the surface to be coated.

[Object]
The surfaces to be coated to which the corrosion prevention method according to the present embodiment is preferably applied include surfaces located at locations where minute deformation of the member is severe due to stress changes during operation, such as the arms and legs of heavy machinery such as a container crane 50 as shown in Fig. 2, and the edge portion 54 shown as a convex portion in Fig. 3. In locations where minute deformation (elastic deformation) of the member is severe, even if a general paint is applied to protect the surface to be coated, the expansion and contraction of the hardened paint film is less than the deformation amount of the member, and cracks may occur in the paint film or gaps may occur between the paint film and the surface to be coated. For this reason, it is said that repair (corrosion prevention) with a general paint is not suitable for locations where minute deformation of the member is severe due to stress changes during operation.

[Action and Effects]
A corrosion prevention method in which the covering sheet 10 having the above-mentioned configuration is applied to the object as described above will be described with reference to Fig. 3. First, corroded parts 56 such as rust occurring on the edge part 54, which is the surface to be covered, and paint or the like covering the surface to be covered are removed to form a clean surface on the surface to be covered (substrate preparation step: see Fig. 3(A)).

At the same time as or before or after the base material adjustment process, the covering sheet 10 is processed to match the shape of the surface to be covered. The shape of the covering sheet 10 is formed by applying an external force or a combination of heat and external force to the protective layer 12 to cause plastic deformation. The shape may be formed by bending the protective layer 12 to a design angle, or by pressing the covering sheet 10 against the surface to be covered (the edge portion 54, which is a convex portion in the example shown in Figure 3) with the release film 16 attached to the conductive adhesive layer 14. By deforming the protective layer 12 to match the surface to be covered, it becomes possible to confirm the area covered by the covering sheet 10 and improve the adhesion of the covering sheet 10 (covering sheet shape forming process: see Figure 3 (B)).

After the base preparation process and the covering sheet shape formation process are completed, the release film 16 attached to the conductive adhesive layer 14 of the covering sheet 10 is peeled off and attached to the surface to be covered (edge portion 54) after the base preparation. When attaching the covering sheet 10, if the surface to be covered is a convex portion such as the edge portion 54 as shown in FIG. 3, as shown in FIG. 4(A), only the release film 16a at the portion that abuts the tip portion of the surface to be covered, i.e., the concave bottom portion of the covering sheet 10, is peeled off, and the covering sheet 10 is pressed against the surface to be covered as shown in FIG. 4(B).

This is to prevent the conductive adhesive layer 14 from adhering to the side of the convex surface to be coated, which prevents the positioning and smooth application of the coating sheet 10. After the convex portion of the surface to be coated and the concave bottom of the coating sheet are brought into close contact, the release film 16b provided in the coating sheet 10 at a position facing the side of the convex portion of the surface to be coated is peeled off, and the conductive adhesive layer 14 is adhered to the corresponding portion. In this embodiment, when a part of the release film (release film 16b) is peeled off after a part of the coating sheet 10 (concave bottom) is adhered to the surface to be coated, it is preferable to allow the end of the release film 16b to protrude from the conductive adhesive layer 14, as shown in Figures 4(A) and (B). This is because, even when the surface to be coated and the conductive adhesive layer 14 are placed in close contact with each other, it is easy to peel off the release film 16b by allowing a part of the release film 16b to protrude from the close contact surface (coating process: see Figures 3(C) and 4(C)).

According to the corrosion prevention method that involves such steps, a conductive adhesive layer 14 that absorbs minute deformations of the component caused by stress changes is interposed between the surface to be coated and the protective layer 12. As a result, there is no risk of stress affecting the protective layer 12. There is no risk of cracks or breaks caused by deformation of the component in the protective layer itself, or in the coating film formed on the protective layer 12. In addition, since the protective layer 12 is made of a metal or resin that can be plastically deformed, it is easy to handle even when the surface to be coated is large, and there is no risk of the conductive adhesive layers 14 being adhered to each other.

In addition, in the corrosion prevention method described above, the shape of the protective layer 12 is stabilized before the coating process, so the protective layer 12 can be topcoated before the coating process. In this way, according to the corrosion prevention method of this embodiment, after the base preparation process, the surface to be coated can be protected and corrosion-prevented simply by attaching the coating sheet, without going through the priming process (two coats) on the surface to be coated. Therefore, as shown in FIG. 5(A), after the base preparation process, the zinc layer (rust-preventive coating film) formation process, the priming process (twice), the intermediate coating process, and the topcoat process are performed, and in addition, the construction period can be significantly shortened compared to the conventional corrosion prevention method (construction period 5 days) in which drying and curing time is provided between each process (construction period 1 day: see FIG. 5(B)).

In addition to being able to carry out the base material preparation process and the covering sheet shape formation process in parallel, the protective layer 12 overcoat process can be carried out before the covering sheet 10 is attached to the surface to be covered. In other words, it is possible to carry out the protective layer 12 overcoat process during the base material preparation process or in a process separate from the base material preparation process (for example, after the covering sheet shape is formed in the factory and before it is delivered to the site), which further shortens the construction period (see FIG. 5(C)).

[Application form]
In the corrosion prevention method carried out as described above, if a step occurs between the portion to which the covering sheet 10 is attached and the portion to which the covering sheet 10 is not attached as shown in Fig. 6, and a liquid pool 30 due to rain or seawater occurs at this step, a duct arrangement step of arranging a cylindrical drain duct 18 as shown in Fig. 7 along the surface to be covered may be added after the surface preparation step, and a covering step of attaching the covering sheet 10 may be carried out after the duct arrangement step. By arranging the drain duct 18 in this manner, the liquid pooled in the liquid pool 30 is guided to the lower side of the edge portion 54 via the drain duct 18 and discharged as shown in Fig. 8. This makes it difficult for the liquid pool 30 to occur at the step caused by the covering sheet 10, and makes it possible to suppress corrosion of the portion.

In the above embodiment, the covering sheet 10 is applied to the surface to be covered, where small elastic deformation occurs due to the influence of stress. However, the covering sheet 10 shown in the embodiment can also be applied to a general painted surface, etc.

10: Covering sheet, 12: Protective layer, 14: Conductive adhesive layer, 14a: Adhesive, 14b: Metal powder, 16: Release film, 16a: Release film, 16b: Release film, 18: Drain duct, 50: Container crane, 54: Edge portion.

Claims (4)

A corrosion prevention method using a covering sheet having a protective layer made of resin or metal and covering a surface to be covered, a conductive adhesive layer for sacrificial corrosion protection arranged on a back surface of the protective layer and containing a powder of a metal having a natural electrode potential lower than that of the metal constituting the surface to be covered, and a release film for covering an exposed surface of the conductive adhesive layer,
a surface preparation step of cleaning the surface to be coated;
a covering sheet shape forming step of deforming the protective layer to conform to a surface shape of the surface to be covered;
a coating process for peeling off the release film and attaching the coating sheet that has been through the coating sheet shape forming process to the surface to be coated that has been subjected to the base material adjustment process. The corrosion prevention method according to claim 1, characterized in that the covering sheet shape forming process is carried out simultaneously with the base material preparation process or prior to the base material preparation process. The corrosion prevention method according to claim 2, characterized in that a topcoat is applied to the protective layer prior to the coating process. The corrosion prevention method according to any one of claims 1 to 3, characterized in that it includes a duct arrangement step of arranging a drain duct for draining liquid between the surface to be coated and the conductive adhesive layer.

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