Coating system

Abstract

This coating system comprises: at least one first coating film layer 2 formed on the surface of a metal substrate 1; and a zinc-rich paint coating film layer 3 that is formed on the first coating film layer 2 and contains a zinc-rich paint.

Description

Painting System

[0001] The present disclosure relates to painting systems.

[0002] Paints containing zinc-rich paint are used as anticorrosion paints for outdoor steel structures. Zinc-rich paints contain a large amount of zinc powder (hereinafter referred to as "zinc dust") and are excellent anticorrosion paints that have two anticorrosion properties: a "sacrificial corrosion protection" effect, which takes advantage of the fact that zinc is a less noble metal than the substrate (e.g., steel), even if the paint film is scratched to the metal substrate of the object being coated, and a "protective film" effect, which forms a dense film of zinc corrosive organisms (rust) that inhibits subsequent corrosion.

[0003] Patent No. 6785382 International Publication No. 2022 / 003906

[0004] Matsuda et al. Rust Prevention Management 61 (12), 462-469 Study on the corrosion prevention behavior of inorganic zinc-rich paint by self-repair (2017) Miwa et al. Abstracts of the 69th Materials and Environment Symposium, B-303, Study on high corrosion resistance technology of zinc-rich paint (2022)

[0005] Of the two corrosion protection effects mentioned above, the sacrificial corrosion protection effect cannot be achieved unless the zinc powder contained in the zinc-rich paint is applied directly to the metal substrate and there is electrical continuity between the substrate and the zinc-rich paint. Furthermore, zinc-rich paint is often applied to galvanized steel as a replacement for the zinc plating after the zinc plating has been worn away by corrosion. For these reasons, it is common practice to use zinc-rich paint as the first coating layer applied directly to the substrate.

[0006] However, if the coating is scratched down to the metal substrate, zinc-rich paint will exhibit excellent corrosion protection in the short term, but over the long term, corrosion of the zinc dust near the damaged area of ​​the coating will progress, causing the coating to lose its sacrificial corrosion protection properties and resulting in a coating with many voids, resulting in a decrease in corrosion protection.

[0007] The present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to improve the long-term corrosion resistance of zinc-rich paint, extend the repainting interval of metal substrates, and reduce the maintenance costs of metal substrates.

[0008] To achieve the above object, one aspect of the present disclosure is a coating system comprising at least one first coating layer formed on a surface of a metal substrate, and a zinc-rich paint coating layer containing zinc-rich paint formed on the first coating layer.

[0009] According to the present disclosure, the long-term corrosion resistance of zinc-rich paint can be improved, the interval between repainting of metal substrates can be extended, and the maintenance costs of metal substrates can be reduced.

[0010] Fig. 1 shows an example of a coating structure according to an embodiment. Fig. 2 is a schematic diagram illustrating corrosion of a metal substrate in a conventional coating structure. Fig. 3 is a schematic diagram illustrating corrosion of a metal substrate in a coating structure according to an embodiment. Fig. 4 is a schematic diagram illustrating a damaged portion of a coating film in a sample. Fig. 5 shows an example of a modified coating structure.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0012] An example of a coating system according to this embodiment is shown in Figure 1. The coating system according to this embodiment relates to the order and combination of multiple coating materials that are applied to a metal substrate such as steel and then dried, and is also referred to as a coating structure or coating specification. Hereinafter, the coating system will be referred to as a coating structure.

[0013] The coating structure of this embodiment comprises at least one first coating layer 2 formed on the surface of a metal substrate 1, which is the object to be coated, and a zinc-rich paint coating layer 3 containing zinc-rich paint formed on the first coating layer 2. In other words, the zinc-rich paint coating layer 3 is not applied as a first layer directly to the metal substrate 1, but as a second or subsequent layer that does not directly contact the metal substrate 1. The metal substrate 1 is, for example, steel (Fe) or the like.

[0014] The first coating layer 2 is formed (painted) directly on the surface of the metal substrate 1. A resin coating layer can be used for the first coating layer 2. Specifically, paints using binders such as epoxy resin, modified epoxy resin, acrylic styrene resin, and polyurethane resin are preferably used for the first coating layer 2. These paints have high blocking properties against corrosion-accelerating factors such as oxygen, water, and salt. Paints using other resins can also be used preferably as long as they do not contain zinc dust (zinc powder) and have high blocking properties against corrosion-accelerating factors. The first coating layer 2 may be a single layer or multiple layers.

[0015] The zinc-rich paint coating layer 3 is formed directly on the first coating layer 2 and contains zinc-rich paint. Zinc-rich paint (ZRP) exhibits excellent corrosion resistance even when the coating is scratched to the metal substrate 1 due to its sacrificial anticorrosion properties and protective coating properties, and is therefore used in coating structures that require high corrosion resistance and long life. The zinc-rich paint coating layer 3 may consist of one layer or multiple layers.

[0016] The coating structure of this embodiment may also include at least one second coating layer 4 on the zinc-rich paint coating layer 3. That is, the second coating layer 4 may be formed by applying another paint onto the zinc-rich paint coating layer 3. The paint for the second coating layer 4 may be a highly weather-resistant topcoat paint such as a fluororesin or polyurethane resin.

[0017] When the zinc-rich paint film layer 3 is applied as the final (top) layer of the paint structure, corrosion of the zinc dust always progresses from the surface of the zinc-rich paint film layer 3. For this reason, the progression of zinc dust corrosion can be prevented by applying at least one other paint layer on top of the zinc-rich paint film layer 3. Therefore, the progression of zinc dust corrosion can be limited to cases where the paint film is scratched and the cross section of the zinc-rich paint film layer 3 is exposed.

[0018] The zinc-rich paint coating layer 3 may contain at least one of calcium sulfate and a basic inorganic compound as an additive. That is, it is possible to add a chemical agent to the zinc-rich paint to enhance the protective coating effect.

[0019] For example, the zinc-rich paint coating layer 3 may contain calcium sulfate as an additive (see Patent Document 1). By adding sulfate to the zinc-rich paint, it is possible to increase the proportion of gordaite (NaZn4(SO4)(OH)6Cl.6H2O), which has a higher protective coating effect than other zinc corrosion products.

[0020] The zinc-rich paint coating layer 3 may also contain a basic inorganic compound as an additive. The basic inorganic compound includes an inorganic base or a basic oxide. Examples of the basic inorganic compound include at least one of barium carbonate, barium hydrogen phosphate, beryllium carbonate, calcium carbonate, calcium hydrogen phosphate, calcium phosphate, lithium carbonate, lithium phosphate, magnesium carbonate, basic magnesium carbonate, magnesium hydroxide, magnesium oxide, and magnesium phosphate. Adding a basic inorganic compound to the zinc-rich paint coating layer 3 increases the pH of the aqueous film in which the corrosion reaction progresses, thereby inhibiting corrosion of zinc and steel and increasing the proportion of gordaite (NaZn4(SO4)(OH)6Cl.6H2O), hydrozincite (Zn5(CO3)2(OH)6), etc.

[0021] Among basic inorganic compounds, it is preferable to use basic magnesium carbonate (see Patent Document 2). Basic magnesium carbonate does not increase the pH too much even when added until the solution becomes saturated, does not dissolve zinc powder, which is an amphoteric metal, and has a moderate solubility in pure water (0.025 g / 100 mL at 25° C.). Therefore, basic magnesium carbonate can gradually supply hydroxide ions over a long period of time.

[0022] In Patent Documents 1 and 2, zinc-rich paint containing these additives is applied directly to the metal substrate 1 as the first coating layer. This has the advantage that the additives dissolve in water and supply sulfate ions or hydroxide ions to damaged areas of the coating, further enhancing the protective coating effect of zinc. However, on the other hand, when these additives dissolve in water and gradually decrease, the areas where the additives were present in the zinc-rich paint coating become voids, which reduces the coating's environmental barrier properties (its ability to block water, oxygen, salt, etc.).

[0023] In this embodiment, by forming the zinc-rich paint on a layer other than the first layer that is applied directly to the metal substrate 1, it is possible to reduce the disadvantage of the zinc-rich paint's reduced environmental barrier properties while retaining the advantage of enhancing the protective coating effect of zinc.

[0024] In particular, basic magnesium carbonate dissolves relatively quickly in weakly acidic rainfall, which creates voids where the added basic magnesium carbonate was present, resulting in a significant disadvantage of reducing the environmental barrier properties of the zinc-rich paint. However, in this embodiment, not only is this disadvantage reduced, but the voids created in the areas where the basic magnesium carbonate was present create paths through which water can pass. This significantly increases the contact area between water and the zinc dust and / or calcium sulfate in the zinc-rich paint compared to when basic magnesium carbonate is not added, resulting in the advantage of being able to efficiently supply more active ingredients, such as zinc ions and / or sulfate ions, to damaged areas of the paint film.

[0025] In this embodiment, by applying the zinc-rich paint coating layer 3 to a layer other than the first layer that is applied directly to the metal substrate 1, the disadvantage of the zinc-rich paint coating layer 3 being reduced in its environmental barrier properties is reduced, and the advantage of being able to efficiently supply the active ingredients to damaged areas of the coating is increased.

[0026] Furthermore, when the zinc-rich paint coating layer 3 is formed as the first layer to be applied directly to the metal substrate 1, excessive addition of the above-mentioned additives would hinder electrical conduction between the zinc dust particles themselves and between the zinc dust and the metal substrate 1, thereby preventing the sacrificial corrosion protection effect, and would also result in voids forming in the areas where the additives had been present, so it is not possible to add too much of them. However, in this embodiment, even if large amounts of calcium sulfate and basic magnesium carbonate are added to the zinc-rich paint coating layer 3, there is an effect that such disadvantages are small.

[0027] The zinc-rich paint of this embodiment is preferably an organic zinc-rich paint with an organic binder (e.g., epoxy resin, modified epoxy resin, acrylic styrene resin, polyurethane resin, etc.). The coating film of inorganic zinc-rich paint with an inorganic binder has a certain amount of voids from the beginning, whereas the coating film of organic zinc-rich paint does not have voids from the beginning. Therefore, by using a first coating layer 2 (e.g., a resin coating layer) other than zinc-rich paint as the first layer applied directly to the metal substrate 1, the advantage of the first layer applied directly to the metal substrate 1 not becoming a coating film with many voids even over a long period of time is greater in the case of organic zinc-rich paint.

[0028] In this way, the paint structure of this embodiment uses a combination and order of multiple paints that are applied to a metal substrate 1 such as a steel plate and then dried, and the paints used include zinc-rich paint, which is applied to a layer other than the first layer of paint that is applied directly to the metal substrate 1.

[0029] As shown in Figure 2, it has been common practice to paint a zinc-rich paint coating layer 3 as the first layer applied directly to a metal substrate 1. This is because the sacrificial corrosion protection effect cannot be achieved unless there is electrical continuity between the zinc powder contained in the zinc-rich paint and the metal substrate 1 to be painted, and because zinc-rich paint is often applied as a substitute for zinc plating to galvanized steel, such as steel materials where the zinc plating has been worn away by corrosion or large steel materials where zinc plating cannot be applied.

[0030] When a scratch 80 is developed in the coating films 2-4 that reaches the metal substrate 1, zinc-rich paint exhibits excellent corrosion protection in the short term due to its sacrificial corrosion protection and protective coating properties. However, over a long period of time, such as several years in salt-damaged areas, corrosion of the zinc dust near the damaged area 80 progresses, and the zinc-rich paint 81 near the damaged area 80 in the zinc-rich paint coating layer 3 loses its sacrificial corrosion protection properties, resulting in a coating with many voids. While the corrosion products of the zinc dust fill the voids to some extent, the resulting coating still has many voids, making the metal substrate 1 more susceptible to corrosion and reducing the corrosion protection properties of the zinc-rich paint. In Figure 2, the portion 82 of the metal substrate 1 that is in contact with the zinc-rich paint 81 with many voids near the damaged area 80 is more susceptible to corrosion.

[0031] In particular, it has been reported in Non-Patent Document 1 that the sacrificial corrosion protection effect only works for a very short period of time in the case of inorganic zinc-rich paint (for example, when the binder is inorganic, such as alkyl silicate or alkali silicate).Non-Patent Document 1 also considers that, based on the mechanism, organic zinc-rich paint will also only work for a short period of time.

[0032] As such, it is considered that the sacrificial corrosion protection effect of zinc-rich paint has little benefit in terms of corrosion prevention, so in this embodiment, as shown in Figure 1, the zinc-rich paint coating layer 3 is applied to a layer other than the first layer that is applied directly to the metal substrate 1. By using such a coating structure, the sacrificial corrosion protection effect of the two corrosion protection effects of zinc-rich paint is lost, but the first layer that is applied directly to the metal substrate 1 is made of a paint other than zinc-rich paint (for example, a modified epoxy resin paint). As a result, in this embodiment, the first layer that is applied directly to the metal substrate 1 has the great advantage that "unlike zinc-rich paint, it does not become a coating with many voids even over a long period of time."

[0033] 3, in this embodiment, the zinc-rich paint coating layer 3 is formed in addition to the first layer applied directly to the metal substrate 1. Over the long term, corrosion of the zinc dust in the vicinity of the damaged portion 70 of the zinc-rich paint coating layer 3 progresses, and the zinc-rich paint 71 in the vicinity of the damaged portion 70 loses its sacrificial corrosion protection effect, resulting in a coating with many voids. However, compared to the case where the first layer applied directly to the metal substrate 1 becomes a coating with many voids, even if the zinc-rich paint 71 in the vicinity of the damaged portion 70 of the zinc-rich paint coating layer 3 formed in addition to the first layer becomes a coating with many voids, the decrease in corrosion protection is relatively small.

[0034] As shown in Figure 3, in the first coating layer 2 of the first layer in contact with the metal substrate 1, voids do not increase near the damaged coating portion 70, so the area of ​​the corroded portion 72 where a corrosion reaction of the metal substrate 1 occurs can be kept small.

[0035] Furthermore, when basic magnesium carbonate, which is easily dissolved in weakly acidic rainfall, is added as an additive to the zinc-rich paint coating layer 3, it promotes voids in the zinc-rich paint coating layer 3, but this does not pose a disadvantage in the coating structure of this embodiment. In other words, water can easily penetrate the zinc-rich paint coating layer 3, and the active ingredient (Zn 2+ , Ca 2+ , Mg 2＋ , O.H. - , SO4 2- Therefore, even if the zinc-rich paint 71 near the damaged area 70 becomes a coating with many voids, there is little disadvantage, and there is an advantage in that a large amount of components for forming a protective coating is supplied.

[0036] In the conventional coating structure shown in Figure 2, the addition of basic magnesium carbonate promotes the formation of voids in the zinc-rich paint applied directly to the metal substrate 1, and therefore the corrosion reaction progresses quickly in the portion 82 of the metal substrate 1 that is in contact with the zinc-rich paint 81, which has many voids.

[0037] Thus, in this embodiment, although the sacrificial anticorrosion effect of the zinc-rich paint is lost, if the coating is scratched down to the metal substrate 1, it is possible to prevent the first layer in direct contact with the metal substrate 1 from becoming a coating with many voids. Furthermore, the protective coating effect is exerted by zinc ions supplied by corrosion of the zinc dust of the zinc-rich paint applied to layers other than the first layer in direct contact with the metal substrate 1. This makes it possible to lengthen the repainting interval of metal substrates 1 such as infrastructure steel structures and reduce the maintenance costs of the metal substrate 1.

[0038] <Examples> Next, examples of the coating structure of this embodiment and comparative examples will be described.

[0039] In each example and comparative example, a blast-treated SS400 steel plate measuring 150 × 70 × 3 mm was used as the metal substrate 1, a thick-film modified epoxy resin paint (Lubigol G, manufactured by Kansai Paint Co., Ltd.) was used as the first coating layer 2, an organic zinc-rich paint (SD Zinc Mild 500, manufactured by Kansai Paint Co., Ltd.) was used as the zinc-rich paint coating layer 3, and a topcoat paint (Unitect 30SF, manufactured by Kansai Paint Co., Ltd.) was used as the second coating layer 4.

[0040] In Experimental Examples 1 to 4, a thick-film modified epoxy resin paint was applied to a thickness of 120 μm on an SS400 steel plate as a first layer, a zinc-rich paint was applied to a thickness of 40 μm on top of that as a second layer, and a silicone epoxy resin paint was applied to a thickness of 55 μm on top of that as a topcoat paint as a third layer.

[0041] In Comparative Examples 1 to 4, zinc-rich paint was applied to a thickness of 40 μm on an SS400 steel plate as a first layer, then a thick-film modified epoxy resin paint was applied to a thickness of 120 μm on top of that as a second layer, and then a silicone epoxy resin paint was applied to a thickness of 55 μm as a topcoat paint on top of that as a third layer.

[0042] As shown in Table 1, Experimental Example 1 and Comparative Example 1 are samples with a coating structure in which no additives were added to the zinc-rich paint. Experimental Example 2 and Comparative Example 2 are samples with a coating structure in which 2 wt% of calcium sulfate (dihydrate) was added as an additive. Experimental Example 3 and Comparative Example 3 are samples with a coating structure in which 4 wt% of basic magnesium carbonate was added as an additive. Experimental Example 4 and Comparative Example 4 are samples with a coating structure in which 2 wt% of calcium sulfate (dihydrate) and 4 wt% of basic magnesium carbonate were added as additives.

[0043]

[0044] After the paint on each sample dried, an artificial "X"-shaped scratch was made in the lower half of each sample, reaching down to the SS400 steel plate (metal substrate 1), using a small-bladed utility knife to create a damaged area of ​​the paint film. This was done to evaluate the sacrificial corrosion protection and protective coating effects on the damaged areas of the paint film, as shown in Figure 4. Each sample with damaged areas underwent a combined cycle test, which involved repeated exposure to salt spray, wetting, and drying. The test conditions and test solutions for the combined cycle test were the NTT combined cycle test described in Non-Patent Document 2. This NTT combined cycle test was performed on each sample for 200 to 600 cycles (960 to 2880 hours).

[0045] (Example 1 and Comparative Example 1) First, a comparison will be made between corrosion at the damaged areas of the paint film in Example 1 and Comparative Example 1. At the 200th cycle, red rust was observed in Example 1, whereas no red rust was observed in Comparative Example 1, and the degree of corrosion was milder in Comparative Example 1. However, after 600 cycles, red rust derived from the steel was flowing downward from the damaged areas of the paint film in both Example 1 and Comparative Example 1 (hereinafter referred to as "rust flow"), but the degree of corrosion was clearly milder in Example 1.

[0046] This shows that in the early stages up to 200 cycles, Comparative Example 1, where the zinc-rich paint was in direct contact with the steel, provided better corrosion protection due to the sacrificial corrosion protection effect.However, over the long term, in the zinc-rich paint in direct contact with the steel in Comparative Example 1, the areas where zinc dust was present became voids containing zinc corrosion products, which is thought to have resulted in a disadvantage in that the environmental barrier properties of the zinc-rich paint (its ability to block the penetration of water, oxygen, salt, etc.) were reduced.

[0047] In contrast, in Example 1, the sacrificial corrosion protection effect was not exerted in the early stages, but the zinc-rich paint was not in direct contact with the steel material, so the disadvantage that the areas where zinc dust was present in the zinc-rich paint became voids containing zinc corrosion products was not as great as in Comparative Example 1, and therefore it is thought that Example 1 was superior in long-term corrosion protection.

[0048] (Example 2 and Comparative Example 2) Next, the corrosion at the damaged area of ​​the paint film in Example 2 and Comparative Example 2 will be compared. The zinc-rich paint used in Example 2 and Comparative Example 2 is a zinc-rich paint with improved corrosion resistance due to the addition of calcium sulfate. The amount of calcium sulfate added is 2 wt %.

[0049] At the 400th cycle, red rust was observed in both Example 2 and Comparative Example 2, but the degree of corrosion was milder in Comparative Example 2. However, after 600 cycles, rust flow occurred in Comparative Example 2, while red rust occurred in Example 2, and the degree of corrosion was milder in Example 2. This is because corrosion in the damaged areas of the paint film progressed considerably in Comparative Example 2 between 400 and 600 cycles, whereas corrosion in the damaged areas of the paint film did not progress very much between 400 and 600 cycles in Example 2.

[0050] This is thought to be due to the difference in coating structure between Example 1 and Comparative Example 1, as well as the fact that in the early stages of the test, the proportion of gordaite increased due to sulfate ions leached from calcium sulfate, resulting in an enhanced protective coating effect in Comparative Example 2. On the other hand, in the long term, in Comparative Example 2, the areas where calcium sulfate was present in the zinc-rich paint that was in direct contact with the steel material became voids, which is thought to have resulted in the disadvantage of a decrease in the environmental barrier properties of the coating.

[0051] In contrast, in Example 2, the zinc-rich paint is not in direct contact with the steel material, so the disadvantage of voids forming in the zinc-rich paint where calcium sulfate had been present is not as great as in Comparative Example 2, and it is thought that Example 2 was superior in long-term corrosion prevention.

[0052] (Example 3 and Comparative Example 3) Next, we will compare the corrosion at the damaged areas of the paint film in Example 3 and Comparative Example 3. The zinc-rich paint used in Example 3 and Comparative Example 3 has improved corrosion prevention properties due to the addition of basic magnesium carbonate. The amount of basic magnesium carbonate added is 4 wt %.

[0053] At the 200th cycle, red rust was observed in both Example 3 and Comparative Example 3, but the degree of corrosion was milder in Comparative Example 3. However, after 600 cycles, rust flow was observed in both Example 3 and Comparative Example 3, but the degree of corrosion was milder in Example 3. This is because corrosion in the damaged areas of the paint film progressed considerably between 200 and 600 cycles in Comparative Example 3, whereas corrosion in the damaged areas of the paint film did not progress as much as in Comparative Example 3 between 200 and 600 cycles in Example 3.

[0054] This is thought to be due to the difference in coating structure between Example 1 and Comparative Example 1, as well as the fact that in the early stages of the test, Comparative Example 3 had the effect of reducing the corrosion rate of zinc dust due to an increase in pH caused by hydroxide ions leached from the basic magnesium carbonate, and increasing the proportion of gordaite, thereby enhancing the protective coating effect. On the other hand, in the long term, in Comparative Example 3, the areas where the basic magnesium carbonate was present in the zinc-rich paint that was in direct contact with the steel material became voids, which is thought to have resulted in the disadvantage of reducing the environmental barrier properties of the coating.

[0055] In contrast, in Example 3, the zinc-rich paint is not in direct contact with the steel material, and therefore the disadvantage of voids forming in the zinc-rich paint where basic magnesium carbonate was present is not as great as in Comparative Example 3, and it is thought that Example 3 was superior in long-term corrosion prevention.

[0056] (Example 4 and Comparative Example 4) Next, the corrosion at the damaged areas of the paint film in Example 4 and Comparative Example 4 will be compared. The zinc-rich paint used in Example 4 and Comparative Example 4 contains both calcium sulfate and basic magnesium carbonate added. The amount of calcium sulfate added is 2 wt %, and the amount of basic magnesium carbonate added is 4 wt %.

[0057] At 200 cycles, no red rust had developed in the damaged areas of the paint film in either Example 4 or Comparative Example 4. After 600 cycles, rust flowed in Comparative Example 4, while light spot-like red rust developed in Example 4, and the degree of corrosion was significantly lighter in Example 4. This is because corrosion in the damaged areas of the paint film progressed significantly between 200 and 600 cycles in Comparative Example 4, whereas corrosion in the damaged areas of the paint film did not progress very much between 200 and 600 cycles in Example 4.

[0058] (Examples 1 to 4 and Comparative Examples 1 to 4) In the examples and comparative examples in which the order of application of the zinc-rich paint and the modified epoxy resin paint was reversed, it was found that in the short term, Comparative Examples 1 to 4, in which the zinc-rich paint was in direct contact with the steel material, had better corrosion resistance, but in the long term, Examples 1 to 4, in which the zinc-rich paint was not in direct contact with the steel material, had better corrosion resistance.

[0059] In the early stages, Comparative Examples 1 to 4, where the zinc-rich paint was in direct contact with the steel, provided better corrosion protection due to the sacrificial corrosion protection effect. However, over the long term, the areas where zinc dust was present in the zinc-rich paint that was in direct contact with the steel in Comparative Examples 1 to 4 became voids containing zinc corrosion products, which is thought to have resulted in a disadvantage of a decrease in the environmental barrier properties of the zinc-rich paint.

[0060] In contrast, in Examples 1 to 4, the initial sacrificial corrosion protection effect was not exhibited, but because the zinc-rich paint was not in direct contact with the steel material, the areas in the zinc-rich paint where zinc dust had been present became voids containing zinc corrosion products, a disadvantage that was not as great as in Comparative Examples 1 to 4. For this reason, it is believed that Examples 1 to 4 were superior in long-term corrosion protection.

[0061] Furthermore, it was found that the difference between the examples and the comparative examples became greater when zinc-rich paint containing additives such as calcium sulfate and / or basic magnesium was used. In the case of zinc-rich paint containing additives such as calcium sulfate and / or basic magnesium, the areas where calcium sulfate and / or basic magnesium were present also become voids, and this disadvantage is thought to become greater.

[0062] On the other hand, in Examples 2 to 4, the zinc-rich paint is not in direct contact with the steel, so the disadvantage of the zinc-rich paint forming voids is less significant, and the benefits of adding calcium sulfate and / or basic magnesium are thought to outweigh the benefits. These benefits are due to the fact that the corrosion of zinc and steel can be inhibited by appropriately raising the pH of the water film in which the corrosion reaction progresses, and that the proportion of gordaite (NaZn4(SO4)(OH)6Cl.6H2O) and hydrozincite (Zn5(CO3)2(OH)6, etc.) can be increased.

[0063] <Modifications> In Example 4, calcium sulfate and basic magnesium carbonate were added to the zinc-rich paint coating layer 3, but calcium sulfate and basic magnesium carbonate may also be formed as additives in a layer separate from the zinc-rich paint coating layer 3. If a coating layer containing such additives is damaged and the calcium sulfate and basic magnesium carbonate are eluted and lost from the cross-section of the damaged area due to rainfall or condensation, the coating will become porous. For this reason, it is recommended to avoid using a coating layer containing additives as the first layer to be applied directly to the metal substrate 1.

[0064] 5 is a diagram showing an example of a modified coating structure. The coating structure shown in the figure includes at least one first coating layer 2 (e.g., a resin coating layer containing an epoxy resin) formed on the surface of a metal substrate 1 (object to be coated), a zinc-rich paint coating layer 3 containing zinc-rich paint formed on the first coating layer, a third coating layer 5 containing calcium sulfate and basic magnesium carbonate formed on the zinc-rich paint coating layer 3, and a second coating layer 4 (top coating layer) formed on the third coating layer.

[0065] That is, the modified coating structure includes a third coating layer 5 containing calcium sulfate and basic magnesium carbonate as additives for zinc-rich paint, and the third coating layer 5 is formed on the zinc-rich paint coating layer 3. The third coating layer 5 may be an epoxy resin paint containing calcium sulfate and basic magnesium carbonate.

[0066] The first coating film layer 2 and the second coating film layer 4 are the same as the first coating film layer 2 and the second coating film layer 4 in the embodiment shown in FIG.

[0067] Even in the case of this modified paint structure, if the coating layers 2 to 5 are damaged and rain or condensation occurs, zinc ions eluted from the zinc-rich paint coating layer 3 and sulfate ions and hydroxide ions eluted from the third coating layer 5 containing calcium sulfate and basic magnesium carbonate will merge in the aqueous solution in the damaged area. This increases the proportion of corrosive organisms that form high-quality films, such as gordaite (NaZn4(SO4)(OH)6Cl.6H2O) and hydrozincite (Zn5(CO3)2(OH)6), in the damaged area, just like in this embodiment.

[0068] The difference between this modification and the case where calcium sulfate and basic magnesium carbonate are added to the zinc-rich paint coating layer 3 is that adding calcium sulfate and basic magnesium carbonate to a layer other than the zinc-rich paint coating layer 3 can suppress porosity in the zinc-rich paint coating layer 3 and reduce the wear of zinc in the zinc-rich paint due to corrosion. Therefore, this modification is expected to extend the life of the zinc-rich paint near damaged areas of the coating.

[0069] However, when calcium sulfate and basic magnesium carbonate are added to zinc-rich paint, more zinc ions are eluted in a shorter time, which is thought to allow a sufficient protective film to be formed more quickly. Therefore, although the lifespan is somewhat shorter, when calcium sulfate and basic magnesium carbonate are added to the zinc-rich paint coating layer 3, the corrosion prevention effect is higher.

[0070] As described above, according to this embodiment, the long-term corrosion resistance of zinc-rich paint can be improved, the repainting interval of metal substrates 1 such as infrastructure steel structures can be extended, and the maintenance costs of metal substrates can be reduced.

[0071] The present disclosure is not limited to the above-described embodiments, and various modifications and combinations are possible within the scope of the gist of the present disclosure.

[0072] 1: Metal substrate 2: First coating layer (resin coating layer) 3: Zinc-rich paint coating layer 4: Second coating layer (top coating layer) 5: Third coating layer

Claims

1. A coating system comprising: at least one first coating layer formed on a surface of a metal substrate; and a zinc-rich paint coating layer, comprising a zinc-rich paint, formed on the first coating layer.

2. The coating system according to claim 1, further comprising at least one second coating layer on said zinc-rich paint coating layer.

3. The coating system according to claim 1, wherein the first coating layer is a resin coating layer.

4. The coating system according to claim 1, wherein the zinc-rich paint coating layer contains at least one of calcium sulfate and a basic inorganic compound as an additive.

5. The coating system according to claim 4, wherein the basic inorganic compound includes at least one of barium carbonate, barium hydrogen phosphate, beryllium carbonate, calcium carbonate, calcium hydrogen phosphate, calcium phosphate, lithium carbonate, lithium phosphate, magnesium carbonate, basic magnesium carbonate, magnesium hydroxide, magnesium oxide, and magnesium phosphate.

6. The coating system according to claim 1, further comprising a third coating layer containing calcium sulfate and basic magnesium carbonate as additives to the zinc-rich paint, the third coating layer being formed on the zinc-rich paint coating layer.

7. The coating system according to any one of claims 1 to 6, wherein the zinc-rich paint has an organic binder.

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