Method for coating metal substrate

Abstract

The invention relates to a method for coating a substrate, said method comprising the steps of applying a layer of a coating composition to a substrate, said substrate being a metal substrate, and curing said coating composition, said coating composition comprising:-metal particles having an average diameter in the range of 20-120 microns in an amount of 50-95 wt.%, based on the total weight of the coating composition, of 50-95 wt.%, based on the total weight of the coating composition; -a curable resin in an amount of from 5 to 50 wt.%, based on the total weight of the coating composition, where the curable resin is selected from the group consisting of epoxy resins, acrylic resins and polyester resins,-a catalyst adapted to accelerate the curing of the curable resin,-the coating after curing having a total layer thickness of from 50 to 2000 microns. The invention also relates to a substrate provided with a coating. It has been found that if a metal substrate is coated with the above composition, a coating having excellent adhesion properties, wear resistance and corrosion resistance is obtained. In addition, the coating has an attractive appearance. The coating may be readily applied by spray coating and cured under relatively mild conditions.

Description

[0001] The present invention relates to a method for coating a metallic substrate. In particular, the present invention relates to a method for coating a metallic substrate with a coating composition that improves the corrosion resistance of the substrate. The present invention also relates to a metallic substrate provided with a coating.

[0002] Corrosion-resistant coatings for metallic substrates are known in the art. However, there is still a need for corrosion-resistant coatings for metallic substrates. In particular, there is a need for a coating composition that produces a coating having good corrosion-resistant properties, wherein at the same time the coating can be easily applied by spraying and cured under relatively mild conditions.

[0003] The present invention provides a method for coating a substrate, the method comprising the steps of: applying a layer of a coating composition to the substrate, and curing the coating composition, wherein,

[0004] - the substrate is a metallic substrate,

[0005] - the coating composition comprises:

[0006] - metallic particles having an average diameter in the range of 20 - 120 microns, in an amount of 50 - 95 wt.% based on the total weight of the coating composition,

[0007] - a curable resin, in an amount of 5 - 50 wt.% based on the total weight of the coating composition, wherein the curable resin is selected from the group consisting of epoxy resins, acrylic resins, and polyester resins,

[0008] - a catalyst suitable for accelerating the curing of the curable resin,

[0009] - the cured coating has a total layer thickness of 50 - 2000 microns.

[0010] It has been found that if a metallic substrate is coated with the above composition, a coating having excellent adhesion properties, wear-resistant properties, and corrosion-resistant properties is obtained. The coating has a long service life and is relatively flexible. In addition, the coating has an attractive appearance. The coating composition can be easily applied by spraying, painting, or roll coating, and can be cured under relatively mild conditions.

[0011] The present invention and the advantages associated therewith are further explained below.

[0012] The coating composition comprises metallic particles. The metallic particles can be particles of any known metal. Preferably, the metallic particles are selected from the group consisting of aluminum, zinc, tin, magnesium, and combinations thereof and their alloys (if applicable). Particular preference is given to the use of aluminum and / or zinc.

[0013] Particularly preferably, at least 50 wt.% of the total metal particles are aluminum particles, especially at least 70 wt.%, more especially at least 80 wt.%, preferably at least 90 wt.%. In one embodiment, all the metal particles are aluminum particles. Aluminum has a lower density than zinc, and for a given thickness, aluminum results in a coating of lower weight. In addition, compared to a coating containing zinc particles, a coating containing aluminum particles seems to be more easily spray-coated to a thickness of up to 500 microns on a vertical surface without intermediate drying, and the coating does not peel off or sag. The lifespan of a coating containing aluminum particles seems to be longer than that of a coating containing zinc particles. A coating based on aluminum particles is applied in one layer with a wet thickness of 500 microns and a dry thickness of 450 microns, and has a theoretical lifespan of 60 years.

[0014] Another advantage of using aluminum particles is that the coating composition in the can is less prone to sagging than when using zinc particles. This means that the "pot life" of the coating composition is longer. It has also been shown that a coating containing aluminum particles has high flexibility. This not only means that the coating is more resistant to impact, bending, and denting, but also means that the coated sheet can be further processed by bending or even rolling without damaging the coating.

[0015] The metal particles have an average diameter in the range of 20 - 120 microns. The average diameter is D50, that is, the value at which 50% of the particles have a larger diameter and 50% of the particles have a smaller diameter. The particle size distribution can be determined in a conventional manner in the art, for example, by laser diffraction. If the particles are too large, the uniformity of the coating is reduced, thereby reducing the coverage of the substrate. If the particles are too small, it is difficult to obtain a layer with sufficient thickness and uniformity.

[0016] Preferably, the metal particles have an average diameter in the range of 20 - 100 microns, more preferably 30 - 90 microns, even more preferably 40 - 80 microns. Suitable metal particles are commercially available.

[0017] The metal particles are present in the coating composition in an amount of 50 - 95 wt.%, based on the total weight of the coating composition before application to the substrate (i.e., before curing).

[0018] One of the advantages of the present invention is that the coating composition has a relatively high metal content, so the final coating contains a large amount of metal. This contributes to good corrosion resistance results of the composition. Therefore, the composition may preferably contain at least 60 wt.% of metal, preferably at least 65 wt.%, and sometimes even at least 70 wt.%. On the other hand, there must be sufficient space for the resin, catalyst, and any other components. Therefore, the amount of metal particles is at most 95 wt.%, and it may be desirable if the composition contains at most 90 wt.% of metal particles or at most 85 wt.% of metal particles.

[0019] The exact amount of metal particles also depends on the particle size and further properties of the metal particles. In some cases, especially if the metal is aluminum or if particles with an average particle size greater than 55 microns are used, the preferred composition contains 50 - 80 wt.% of metal particles, especially 50 - 70 wt.% of metal particles.

[0020] The composition contains a curable resin selected from the group consisting of epoxy resins, acrylic resins, and polyester resins. Polyester resins are preferred. Thermosetting resins are preferred. It is particularly preferred that the resin is curable at a temperature of at most 100 °C, especially at most 60 °C, more especially at most 45 °C or at most 40 °C. Suitable resin compositions are well-known and do not require further explanation. In addition to the curable resins mentioned, the presence of other curable resins is neither necessary nor desirable. Thus, in one embodiment, the coating composition does not contain more than 10 wt.%, especially not more than 5 wt.%, of curable resins other than those described above.

[0021] Based on the amount of the coating composition, the resin is present in an amount of 5 - 50 wt.%. If less than 5 wt.% of the resin is present, the adhesion is insufficient. If more than 50 wt.% of the resin is present, there is not enough space for the other components of the composition, especially the metal particles. Preferably, the resin is present in an amount of 5 - 40 wt.%, especially 5 - 30 wt.%, even more especially 5 - 25 wt.%, based on the total weight of the composition.

[0022] The composition further contains a catalyst. A catalyst suitable for the resin curing mechanism is selected. Catalysts for thermosettable resins are preferred. Suitable catalysts are known and do not require further explanation. The catalyst is applied in a conventional amount known in the art, usually in the range of 0.001 - 2 wt.%, based on the weight of the coating composition.

[0023] The coating composition may contain an organic diluent, for example, in an amount of 2 - 40 wt% based on the total coating composition. This is generally desirable to impart good processability to the composition, especially a sufficiently low viscosity. Using less than 2 wt% of the diluent generally does not achieve the effect of the diluent. Using more than 40 wt% of the diluent reduces the amount of other components. It may be more desirable to use at least 5 wt% diluent and / or at most 35 wt%, more preferably at most 30 wt%.

[0024] Suitable diluents include, for example, organic diluents such as alcohols having, for example, 2 - 10 carbon atoms (such as ethanol, propanol, butanol, and octanol). Other suitable diluents include alkyl esters and alkyl ethers (such as ethyl acetate, ethyl acetate, methyl ethyl ketone, and methyl isobutyl ketone, as well as alkyl ethers of diols). Aromatic hydrocarbons such as benzene, toluene, and xylene, as well as mixtures of aromatic solvents derived from petroleum, can also be used.

[0025] Preferably, the coating composition contains 5-40 wt.% of a diluent having a boiling point or decomposition point higher than 60 °C, preferably higher than 80 °C. Compared with low-boiling solvents such as ethanol, the advantage is that the diluent can remain in the composition for a long time, thus maintaining good processability. The total amount range of the diluent provided above is also applicable here.

[0026] A particularly preferred class of diluents is synthetic oils and natural oils. Suitable natural oils include vegetable oils such as cottonseed oil, peanut oil, coconut oil, cocoa butter, pumpkin seed oil, linseed oil, corn oil, olive oil, palm kernel oil, palm oil, rapeseed oil, sesame oil, soybean oil, sunflower oil, grape seed oil, walnut oil, and wheat germ oil. Animal oils such as fish oil can also be used, and oils from algae can also be used. Suitable oils also include petroleum products such as petroleum fractions having a boiling point in the range of 50-400 °C, especially 50-250 °C. Suitable petroleum fractions include gasoline, diesel, and kerosene.

[0027] Vegetable oils are preferably used because they are durable and provide good results. Peanut oil, linseed oil, corn oil, olive oil, palm oil, rapeseed oil, sunflower oil, sesame oil, or soybean oil is preferably used.

[0028] Mixtures of different diluents and / or different oils can be used. Preferably, the composition comprises a total of 5-40 wt.% of synthetic oil and / or natural oil, especially vegetable oils as described above. The range of the total amount of the diluent given above is also applicable here.

[0029] It is also preferred that at least 30 wt.% of the total amount of the diluent in the composition is synthetic oil or natural oil, especially vegetable oils as described above, more preferably at least 50 wt.%, even more preferably at least 60 wt.%, or at least 70 wt.%, or at least 80 wt.%.

[0030] Since the metal content of the coating is important for the effect and the inclusion of solid particles other than metal particles may adversely affect the processability and effect of the composition, it is preferred that at least 80 wt.% of the solid particles in the composition consist of metal particles having an average diameter in the range of 20-120 microns, especially at least 90 wt.%, even more especially at least 95 wt.%, or at least 98 wt.%.

[0031] The use of glass particles in coating compositions has been described in the literature. For the compositions according to the invention, their presence is neither necessary nor desirable. The presence of glass particles occupies the volume that would otherwise be occupied by metal particles in the coating compositions according to the invention. Therefore, preferably, the composition contains no more than 7 wt.%, preferably no more than 5 wt.%, more preferably no more than 2 wt.%, especially no more than 1 wt.% of glass particles.

[0032] In one embodiment, the total amount of metal particles, resin, catalyst and diluent forms at least 70 wt.%, especially at least 80 wt.%, more especially at least 90 wt.%, in particular at least 95 wt.% of the coating composition.

[0033] The substrate coated in the method according to the invention is a metal substrate, usually a steel substrate. Since the method according to the invention is especially aimed at providing corrosion resistance, the substrate will generally be used for outdoor applications or applications in high humidity environments. Suitable substrates include substrates on an industrial scale, such as metal structural components selected from machinery and machine parts, for buildings, roads and other infrastructure (including bridges, factories, wind turbines) and other offshore and onshore applications. The substrate may have been provided with a primer, but this is not necessary. In one embodiment, the coating composition is applied directly to the metal substrate without an intermediate layer.

[0034] The coating composition can be applied in a conventional manner, for example by spraying, roll coating, pouring, ironing and dipping. Application by spraying is preferred because it is a rapid and accurate way of applying the coating composition and gives uniform results. Airless spraying is particularly preferred because it is a known method for spraying large areas. It has been found that the compositions according to the invention can be excellently processed by spraying, especially airless spraying.

[0035] The coating composition can be applied in one or more layers, for example two, three, four or five layers. In the present specification, a single layer is a layer applied without intermediate curing. If the composition is applied in multiple layers, the composition must be at least partially cured in between. This can be easily accomplished depending on the curing mechanism. A feature of the present invention is that the coating composition can be applied to a relatively high total layer thickness without intermediate curing. This applies especially to aluminum-based coatings.

[0036] After applying the composition, a curing step is carried out. How this is done depends on the curing mechanism of the resin used. Thermal curing is preferably used. In this case, curing is preferably carried out at a temperature of 5 - 100 °C, particularly 10 - 60 °C, more particularly 15 - 45 °C, for example 20 - 40 °C. The time required depends on the selected temperature (the lower the temperature, the longer the time required). The curing time is generally 1 - 48 hours, more specifically 2 - 36 hours, for example 4 - 30 hours. At lower temperatures, the curing time will be longer than at higher temperatures.

[0037] After curing, the composition has a total layer thickness of 50 - 2000 μm. This is the sum of all the applied layers. At layer thicknesses below 50 μm, the required anti-corrosion effect cannot be achieved. Layer thicknesses above 2000 μm generally do not provide additional benefits. The total layer thickness is preferably at least 75 μm, more preferably at least 100 μm, particularly above 150 μm. The total layer thickness is preferably at most 1500 μm, more preferably at most 1200 μm. The selection of the coating thickness depends on the required lifetime of the coating. In some cases, a layer thickness of at most 1000 μm may be sufficient, or at most 800 μm, or at most 600 μm, or at most 400 μm. It has been found that the coatings according to the invention provide sufficient protection even in relatively thin layers.

[0038] After coating and curing, one or more post-treatment steps can optionally be carried out. Suitable finishing steps include sanding or polishing to obtain a surface with a metallic appearance. If desired, one or more additional coatings can be applied, but this is not necessary. The additional coatings are generally used for decorative purposes, for example to provide the desired color. The coatings obtained according to the invention are directly paintable.

[0039] The invention also relates to a metal substrate provided with a coating comprising metal particles and a resin, wherein the coating is a coating of a coating composition comprising:

[0040] - metal particles with an average diameter in the range of 20 - 120 μm, in an amount of 50 - 95 wt.% based on the total weight of the coating composition,

[0041] - a resin in an amount of 10 - 50 wt.% calculated based on the total weight of the coating composition, the resin being selected from the group consisting of epoxy resins, acrylic resins and polyester resins,

[0042] - a catalyst suitable for accelerating the curing of the resin,

[0043] and the total layer thickness of the coating composition is 50 - 2000 μm.

[0044] The preferred options for the properties of the substrate, coating composition, layer thickness, and other features described above also apply to this embodiment of the present invention. Preferably, the layer of the coating composition has been cured.

[0045] Obviously, unless they are mutually exclusive, the preferred options described for different aspects of the present invention can be combined.

[0046] The present invention is illustrated by the following examples, without being limited thereto or thereby defined.

[0047] Example 1: Compositions Tested

[0048] Coating A: A coating composition containing zinc particles

[0049] A coating composition containing zinc particles was prepared by mixing zinc particles with a curable polyester resin and a diluent. The composition also contained a catalyst. The average particle size of the zinc particles was 45 microns. The coating composition contained 72 wt.% of zinc particles. The diluent was vegetable oil and was applied in an amount of about 7 wt.% based on the total coating composition. This coating composition is also referred to as zinc paint herein.

[0050] Coating B: A coating composition containing aluminum particles

[0051] A coating composition containing aluminum particles was prepared by mixing aluminum particles with a curable polyester coating and a diluent. The composition also contained a catalyst. The average particle size of the aluminum particles was 45 microns. The coating composition contained 55 wt.% of aluminum particles. The diluent was vegetable oil and was applied in an amount of about 11 wt.% based on the total coating composition. This coating composition is also referred to as aluminum-zinc paint herein.

[0052] Example 2: Properties of Coated Metal Substrates and Coatings

[0053] Steel plates were coated with the aluminum paint and zinc paint from Example 1. The paint was applied by airless spraying. The paint was cured at a temperature of 20 °C for about 24 hours.

[0054] For the zinc coating, the layer thickness after curing was about 500 microns. For the aluminum coating, the layer thickness after curing was about 850 microns.

[0055] Example 3: Testing of the Coatings Obtained in Example 2

[0056] Neutral salt spray test according to ISO 12944-6 C5H

[0057] Multiple aluminum-coated and zinc-coated samples were subjected to neutral salt spray testing according to ISO 12944-6C5H. The test lasted approximately 1440 hours. The temperature was 35 ± 2 °C. The salt solution contained 5% NaCl. The pH of the salt solution was 6.5 - 7.2. The amount of liquid was 1 - 2 ml per 80 cm 2 per hour. For 100% zinc coatings, ISO 12944 equates the salt spray test to 15 - 20 years of exposure.

[0058] Pull-off adhesion

[0059] Before and after the salt spray test, the pull-off adhesion of various samples was determined. The average values are as follows:

[0060]

[0061] A value of 5 MPa is sufficient to pass the test according to ISO 12944-6C5H. This indicates that both coatings have excellent pull-off adhesion before and after the salt spray test.

[0062] Wear test

[0063] According to ASTM D4060:2014 (Taber abrasion), the wear of the coatings was studied under a load of 1 kg and using a CS17 abrasion wheel for 1000 cycles. The panel with zinc coating A showed a wear index of 0.10. The panel with aluminum coating B showed a wear index of 0.16.

[0064] Layer thickness

[0065] Sections were made to examine the coating structure. The layer thickness was measured. This was done before and after the salt spray test. In both cases, the thickness was determined at six locations on the panel.

[0066] Coating A: Zinc coating

[0067]

[0068] Coating B: Aluminum coating

[0069]

[0070] For zinc coating A and aluminum coating B, the coating thickness before the salt spray test is greater than that after the salt spray test. For the zinc coating, the thickness reduction is about 150 microns. ISO 12944 sets that the salt spray test of 100% zinc coating is equivalent to 15 - 20 years of exposure. For external coatings in industrial areas with high humidity and corrosive atmosphere, for coastal areas with high salt concentration, and for internal coatings in areas with high condensation and high pollution, a loss of 4.2 - 8.4 microns is allowed. A loss of 150 microns over 20 years is equivalent to a loss of 7.5 microns per year, so it is a good result.

[0071] For the aluminum coating, the thickness reduction is about 160 microns. This is also a good result.

[0072] Example 4: Durability test - Aluminum coating - 6 months

[0073] A carbon steel sheet with primer was partially coated with a coating layer as described for coating B in Example 1 and cured under ambient conditions. The thickness of the cured coating was about 150 microns. The coated sheet was exposed to outdoor weather conditions (Westervoort, Netherlands) for 18 months. After 18 months, the corrosion grade was approximately the same as that of the steel plate just after coating. The adhesion test via X - cut according to ASTM - D3359 - 09 (for coatings with a thickness exceeding 125 microns) resulted in a grade of 4A. This example shows that the coating has excellent durability.

[0074] Example 5: Adhesion to blasted panels

[0075] Generally, metal substrates are blasted before coating to improve adhesion. It is preferred to apply the coating as soon as possible after blasting, usually within 6 hours. This is not always feasible in practice. Therefore, the effect of longer storage times of metal sheets after blasting and before coating on the adhesion of the coating was studied.

[0076] Steel sheets were blasted to SA 2.5 according to ISO 8501 - 1. Then the panels were stored outdoors and, after the times shown in the following table, a coating as described for coating B in Example 1 was applied and then dried under ambient conditions. The coating was applied with a roller. After drying, the adhesion was determined according to ISO 4624:2016. A value of 5 or higher is an acceptable result.

[0077]

[0078] The results of this test show that even if the coating is not applied to the metal sheet immediately after blasting, the coating has good adhesion. This increases the flexibility of application.

[0079] Example 6: Adhesion to other coatings

[0080] The coating according to the invention can be provided with additional coatings, for example to achieve the desired color or surface properties. It is important that any additional coatings exhibit good adhesion to the coating of the invention. Therefore, the adhesion of various commercially available coatings has been investigated.

[0081] After sandblasting to SA 2.5, the steel pipe was coated with the coating composition as described for Coating B in Example 1 by airless spraying, with an average layer thickness of 174 μm, and then air-dried. According to ISO 4624:2016 (2 test blocks), the coating had an adhesion of 10.71 MPa and 13.36 MPa.

[0082] Then, the steel pipe was coated with various commercial coating compounds by airless spraying. The following table shows the results of the adhesion tests according to ISO 4624:2016.

[0083]

[0084] It seems that all the tested compositions have sufficient adhesion.

[0085] Example 7: Influence of rolling on coated sheets

[0086] Four steel plates of 1000×550×8 mm were coated with Coating B from Example 1 and the coating from Example 4 after sandblasting, and after drying, the average layer thickness was 120 μm.

[0087] First, two sheets were rolled on a roller with a diameter of 3 m and then welded together. The other two sheets were first welded together and then rolled on a roller with a diameter of 3 m. In both cases, the bending by rolling did not cause damage to the coating. Welding caused damage to the coating directly below the weld. This damage could be easily removed by grinding.

[0088] Example 8: Application of the coating to large objects

[0089] Coating B of Example 1 was applied to a part of a steel bridge. The total coated area of the bridge part was 88 m 2 . All sides (top, bottom, sides) of the bridge part were coated. It was applied in two layers by airless spraying without intermediate drying. The final coating thickness was 150 μm. It was found that the coating according to the invention was easily applied even on large objects, vertical surfaces, and surfaces to be sprayed facing upwards. The coating was uniform and of good quality.

Claims

1. A method of coating a substrate, the method comprising the steps of: applying a layer of a coating composition to a substrate and curing the coating composition, wherein, - the substrate is a metal substrate, - the coating composition comprises: ﹣ metal particles having an average diameter in the range of 20 - 120 microns, in an amount of 50 - 95 wt.% based on the total weight of the coating composition, ﹣ a curable resin, in an amount of 5 - 50 wt.% based on the total weight of the coating composition, wherein the curable resin is selected from the group consisting of epoxy resins, acrylic resins and polyester resins, ﹣ a catalyst suitable for accelerating the curing of the curable resin, - the cured coating has a total layer thickness of 50 - 2000 microns.

2. The method according to claim 1, wherein the curable resin is an acrylic resin or a polyester resin, particularly a polyester resin.

3. The method according to any one of the preceding claims, wherein the metal particles are selected from the group consisting of aluminum, zinc, tin, magnesium and combinations thereof, and alloys thereof where applicable, and aluminum and / or zinc are particularly preferably used.

4. The method according to claim 3, wherein at least 50 wt.% of the metal particles are aluminum particles, particularly at least 70 wt.%, more particularly at least 80 wt.%, preferably at least 90 wt.%.

5. The method according to any one of the preceding claims, wherein the average diameter of the metal particles is in the range of 20 microns to 100 microns, preferably 30 microns to 90 microns, more preferably 40 microns to 80 microns.

6. The method according to any one of the preceding claims, wherein the coating composition comprises the metal particles in an amount of 60 - 95 wt.%, particularly 65 - 90 wt.%, more particularly 70 - 85 wt.% based on the total weight of the coating composition, or particularly if the metal is aluminum or if particles having an average particle size greater than 55 microns are used, then comprises 50 - 80 wt.%, particularly 50 - 70 wt.% of the metal particles.

7. The method according to claim 6, wherein at least 50 wt.% of the metal particles are aluminum particles, particularly at least 70 wt.%, more particularly at least 80 wt.%, preferably at least 90 wt.%, and the coating composition comprises the metal particles in an amount of 50 - 80 wt.%, particularly 50 - 70 wt.%.

8. The method according to any one of the preceding claims, wherein the resin is a thermally curable resin, particularly a resin curable at a temperature of at most 100°C, particularly at most 60°C, more particularly at most 45°C or at most 40°C.

9. The method according to any one of the preceding claims, wherein the resin is in an amount of 5 - 40 wt.%, particularly 5 - 30 wt.%, even more particularly 5 - 25 wt.% based on the total weight of the composition of the resin polymer.

10. The method according to any one of the preceding claims, wherein the coating composition comprises an organic diluent, for example, the amount of the organic diluent is 2 - 40 wt.%, preferably at least 5 wt.% and / or at most 35 wt.%, more preferably at most 30 wt.%.

11. The method according to claim 7, wherein the diluent is selected from synthetic or natural oils, preferably vegetable oils and / or petroleum fractions, especially vegetable oils.

12. The method according to any one of the preceding claims, wherein the substrate is a metal substrate intended for outdoor applications or applications in high humidity environments, and the substrate is selected from mechanical and machine parts, metal structural parts for buildings, roads and other infrastructures, and the other infrastructures include bridges, factories, windmills.

13. The method according to any one of the preceding claims, wherein the coating composition is applied by spraying, roll coating, pouring, ironing, dipping, especially by spraying, more especially by airless spraying, and the total layer thickness is preferably at least 75 microns, preferably at least 100 microns, especially greater than 150 microns and / or at most 1500 microns, preferably at most 1200 microns, or at most 1000 microns, or at most 800 microns, or at most 600 microns, or at most 400 microns.

14. The method according to any one of the preceding claims, wherein the coating composition is cured at a temperature of 5 - 100 °C, especially 10 - 60 °C, more especially 15 - 45 °C, for example 20 - 40 °C for 1 - 48 hours, especially 2 - 36 hours, for example 4 - 30 hours.

15. A metal substrate provided with a coating comprising metal particles and a resin, wherein the coating is a coating of a coating composition comprising: - Metal particles having an average diameter in the range of 20 - 120 microns, and the amount thereof is 50 - 95 wt.% based on the total weight of the coating composition, - A resin, and the amount thereof is 10 - 50 wt.% based on the total weight of the coating composition, and the resin is selected from the group consisting of epoxy resins, acrylic resins and polyester resins, - A catalyst suitable for accelerating the curing of the resin, and the coating has a total layer thickness of 50 - 2000 microns measured after curing.

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