Anti-fouling coating and method for preparing an Anti-fouling coating

Abstract

The invention relates self-polishing anti-fouling coating composition comprising a) a self-polishing binder, b) particles of a copper compound and / or a zinc compound; c) optionally a biocide, wherein the mean particle diameter of the copper compound and zinc compound is in the range of from 2 to 100 nm, preferably 5 to 50 nm such as in the range of from 8 to 40 nm, preferably in the range of from 10 - 30 nm, 12 - 25 nm, 14 - 20 nm, or 16 - 18 nm; and a coating made thereof.

Description

[0001] Anti-fouling coating and method for preparing an anti-fouling coating

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a self-polishing anti-fouling coating composition, a method for preparing a self-polishing anti-fouling coating on a substrate and a cured self-polishing anti-fouling coating. The present invention also relates to an underwater vehicle or an underwater static structure having at least parts of the surface coated with the self-polishing anti-fouling coating composition or having at least parts of the surface covered by the cured self-polishing anti-fouling coating according to the invention as well as the use of a cured self-polishing anti-fouling coating of the present invention and the use of the self-polishing anti-fouling coating composition of the present invention. The present invention also relates to an article or substrate having at least a part of the surface coated with the cured selfpolishing anti-fouling coating of the invention.

[0004] BACKGROUND OF THE INVENTION

[0005] Water vehicles and in particular Unmanned Underwater Vehicles (UUVs) and Autonomous Underwater Vehicles (AUVs) have become increasingly prevalent in various operations such as oceanographic research, mine countermeasures, and inspections. The propulsion system and onboard sensors and cameras are typically powered by batteries, which, in turn, are charged by solar panels that convert sunlight into electricity. This allows for long mission times with little, or no, need for a support vessel to refuel the underwater vehicle.

[0006] However, over time biofouling accumulation on the vehicle surfaces can significantly reduce the optical clarity of transparent materials and lower the electrical efficiency of solar cells for power generation. Moreover, due to the high fouling rate at static conditions, the biological growth affects subsequent hydrodynamic performance and maneuverability of the vehicle.

[0007] To prevent this, coatings that are transparent and yet maintain adequate antifouling efficiency become a pre-requisite. Over extended time periods immersed underwater vehicles often stay immobile and subsequent removal of settled organisms require an external force or grooming (i.e. mechanical cleaning).

[0008] Although most silicon binder systems used in the prevailing silicon-based fouling release coatings (FRCs) domain are transparent, static exposure calls for either mechanical or hydrodynamic cleaning, which limits their efficiency (Noguera, A.C., Olsen, S.M., Hvilsted, S., Kiil, S., (2017) Field study of the long-term release of block copolymers from fouling-release coatings, Progress in Organic Coatings, 112, 101-108). Similarly, due to the high absorption value in the visible spectrum of biocidal Cu?O pigment and the pigment-leached layer forming at the coating surface during seawater exposure, present self-polishing antifouling coatings are fouling-resistant, but not transparent.

[0009] Known investigations cover the use of silicone- and silane-based fouling release coatings (FRCs). In addition to conventional hydrophobic FRCs, transparent hydrogel-based fouling release coatings, utilizing a unique blend of silicone polymers that maintain a hydrophilic surface, are a recent development, which distinctly delay diatomic slime settlement and, therefore, subsequent biofouling as mentioned by Noguera et al. Although there are studies on transparent hydrogels that exhibit decent antifouling efficiency and self-cleaning abilities, none of them contain detailed data on the performance under natural seawater exposure.

[0010] The problem underlying the present invention is that over time biofouling accumulation on water vehicle surfaces can significantly reduce the optical clarity of transparent materials and lower the electrical efficiency of solar cells for power generation. Moreover, due to the high fouling rate in particular at static conditions, the biological growth affects subsequent hydrodynamic performance and manoeuvrability of the vehicle.

[0011] Hence, there is a need for transparent fouling control coatings that, in the absence of human intervention, maintain high UV and visible light transmission levels over an extended time period. Besides, it is important to maintain adequate antifouling efficiency.

[0012] It is therefore the object of the present invention to provide an antifouling coating which provides sufficient transparency and also has good anti-fouling properties.

[0013] The problem of the invention has been solved by the subject-matter as defined in the independent claims.

[0014] DESCRIPTION OF THE INVENTION

[0015] In a first aspect the present invention relates to a self-polishing anti-fouling coating composition comprising, preferably consisting of, a) a self-polishing binder, b) particles of a copper compound, wherein the copper compound is preferably a copper salt, a copper oxide or a copper organic compound, and / or a zinc compound, wherein the zinc compound is preferably a zinc salt, a zinc oxide or a zinc organic compound, c) optionally a biocide, wherein the mean particle diameter of the copper compound and zinc compound is in the range of from 2 to 100 nm, preferably 5 to 50 nm such as in the range of from 8 to 40 nm, preferably in the range of from 10 - 30 nm, 12 - 25 nm, 14 - 20 nm, or 16 - 18 nm, and wherein the pigment volume concentration of the particles of copper compound and / or zinc compound is less than 1 %, preferably is 0.01 - 0.2 %, more preferably 0.02 - 0.15 %, and more preferably 0.03 - 0.12%.

[0016] There are two ways that an anti-fouling coating composition can be designed to prevent the adhesion and build-up of fouling agents on a surface. Firstly, the anti-fouling coating can contain a compound which serves to poison the organisms attached to the surface, thus causing the organism to die and fall off the surface. Such compounds are also referred to as biocide compound or biocide. This mode of adhesion prevention is often referred to as “antifouling” and such coatings regularly referred to as anti-fouling coatings.

[0017] Alternatively or in addition to that, coatings may be designed to slowly polish over time. Besides, the polishing supports the release of biocides. The degradation is often caused by a slow hydrolyzation of the coating (usually the binder within the coating). This mode of adhesion prevention is often referred to as "self-polishing" and such coatings are often referred to as self-polishing coatings. Binders having the property of “self-polishing” are referred to as self-polishing binders.

[0018] In order to obtain an effective and efficient removal of organisms from surfaces it is common practice to produce coating compositions that both contain a compound providing biocidal properties and which slowly degrade over time. Such dual functional coatings are often referred to as self-polishing anti-fouling coatings.

[0019] In the present invention to ensure adequate polishing and leaching rates a self-polishing binder is applied. Besides, by adding particles of a copper compound and / or a zinc compound having a mean particle diameter in the range of from 2 to 100 nm strong biofouling protection, as well as low degrees of scattering, and reflection of visible light, were obtained. However, the nano-particle size of Cu?O also leads to strong absorption of the light, and for that reason ultra-low pigment volume concentrations are required in the coating.

[0020] With the inventive composition dry films with a thickness of e.g. 100 pm can be prepared which remain essentially free of biofouling for several weeks, or even months, after which “polish through” appears. Notably, to stay fouling-free under static conditions, a coating prepared from the composition coating does not require intermittent cleaning or additional maintenance.The mean particle diameter may be referred to as the arithmetic mean diameter, which is determined by averaging the diameters of all particles in a sample.

[0021] For an antifouling coating to be transparent, certain conditions are required. These relate to absorption, scattering and reflection. As some of these requirements are contradictory and to formulate a workable coating, which limits absorption, scattering, and reflection, the present invention applies nano-sized particles of copper or zinc compounds. Such nano-sized particles of copper or zinc compounds are applied in a pigment volume concentration (PVC) of less than 1 %, preferably 0.01-0.2%, more preferably 0.02-0.15% and more preferably 0.03-012%. A PVC of as described in the present invention provides the advantage of obtaining the best possible transmission of light, such as visible light, ultraviolet and infrared light, and thereby is the foundation of the best absorption properties of the surface the coating according to the present invention is applied to or on. For example, the self-polishing anti-fouling coating may be applied on any device such as a sensor, where the sensor may be a sonar, acoustic, magnetic, or light sensor. It may be applied on a camera lens, radar devices, Light Detection and Ranging (LiDAR), and solar panels. These rather low pigment volume concentrations are advantageous for the absorption properties. If the PVC is too high the transmission gets too low.

[0022] As mentioned before, binder affect the polishing rates or anti-fouling properties of an antifouling coating. According to the invention, any binder that reacts with a saline solution so polishing takes place is referred to as “self-polishing” binder. A saline solution in the context of the present invention is to be understood as to be sea water as such and any water solution having a salinity ranging from brackish to highly concentrated water. Brackish water is defined as water having a salinity of 0.5 to 30 grams of sodium chloride per litre (g / L). Highly concentrated water is defined as water having a salinity of 300-350 grams of sodium chloride per litre. Water of any salinity between brackish and highly concentrated water is encompassed by the present invention.

[0023] Known self-polishing binders according to the invention include acrylic polymers and copolymers, vinyl copolymers, metal acrylates, in particular zinc, silyl and copper acrylates, rosin, gum-rosin, hydrogenated rosin, thermocatalytically treated rosin, polymerized rosin, rosin metal carboxylates (resinates) such as fused resinates or precipitated resinates, rosin polycarboxylates, rosin amines, rosin esters of mono- and polyhydric alcohols, and mixtures thereof.

[0024] In an embodiment, the self-polishing binder is selected from the group consisting of triyalkylsilylbase (meth) acrylate, Cu-based acrylate, Zn-based acrylate, rosin, hydrogenated rosin, thermocatalytically treated rosin, polymerized rosin, rosin metal carboxylates (resinates) such as fused resinates or precipitated resinates, rosin polycarboxylates, rosin amines, rosin esters of mono- and polyhydric alcohols, and nanocapsule acrylate particles.

[0025] Fused resinates are prepared from resinic acid and metal oxide such as ZnO. Precipitated resinates are sodium soap and metal in aqueous solution, whereby the metal can for example be zinc or calcium.

[0026] It is preferred that the self-polishing binder is selected from the group consisting of Zn-based acrylate, Cu-based acrylate or silyl-acrylate, and preferably is a silyl-acrylate.

[0027] In an embodiment the binder is a transparent binder. A transparent binder is defined as a binder or coating which shows minimal absorption, scattering or reflection of electromagnetic radiation, such as visible light, ultraviolet light, or infrared radiation. At least 60% of the incident radiation will be allowed to pass. An example of a binder is a Nano Acrylate Technology (NAD) binder.

[0028] The particle size of the copper and zinc compound is i.e., relevant for transparency properties of the final coating.

[0029] In another embodiment the coating composition comprises a second self-polishing binder.

[0030] It is preferred that the second self-polishing binder is selected from the group consisting of triyalkylsilylbase (meth) acrylate, Cu-based acrylate, Zn-based acrylate, rosin, hydrogenated rosin, thermocatalytically treated rosin, polymerized rosin, rosin metal carboxylates (resinates) such as fused resinates or precipitated resinates, rosin polycarboxylates, rosin amines, rosin esters of mono- and polyhydric alcohols, and nanocapsule acrylate particles, preferably the second binder is selected from the group consisting of rosin, gum-rosin, hydrogenated rosin, thermocatalytically treated rosin, polymerized rosin, rosin metal carboxylate (resinate) such as a fused resinate or a precipitated resinate, rosin polycarboxylate, rosin amine, rosin esters of mono- and polyhydric alcohols, and more preferably is a gum-rosin.

[0031] When rosin is added to e.g., silyl acrylate, the polishing rate increases, which leads to less biofouling and thereby maintenance of the transparency.

[0032] In one embodiment the second binder has a polishing rate different from the first binder.

[0033] In another embodiment the weight ratio of first binder to second binder is from 90:10 to 40:60, preferably 80:20 to 50:50 and more preferably 70:30 to 60:40 in the coating composition. In one embodiment, the second binding is a rosin binder, gum-rosin binder, hydrogenated rosin binder, thermocatalytically treated rosin binder, polymerized rosin binder, rosin metal carboxylate (resinate) binder sch as a fused resinate or a precipitated resinate, rosin polycarbozylate binder, rosin amie binder, rosin esters of mono- and polyhydric alcohols binder, preferably a gum-rosin binder; and / or wherein the second binder has a polishing rate different from the first binder; and / or wherein the weight ratio of first binder to second binder is from 90:10 to 40:60, preferably 80:20 to 50:50 and more preferably 70:30 to 60:40.

[0034] In one embodiment, the second binding is a rosin binder, gum-rosin binder, hydrogenated rosin binder, thermocatalytically treated rosin binder, polymerized rosin binder, rosin metal carboxylate (resinate) binder sch as a fused resinate or a precipitated resinate, rosin polycarbozylate binder, rosin amie binder, rosin esters of mono- and polyhydric alcohols binder, preferably a gum-rosin binder; and wherein the second binder has a polishing rate different from the first binder; and wherein the weight ratio of first binder to second binder is from 90:10 to 40:60, preferably 80:20 to 50:50 and more preferably 70:30 to 60:40.

[0035] In an embodiment, the copper compound is a copper salt, a copper oxide or a copper organic compound. The copper salt comprises inorganic and organic copper salts such as copper chloride or copper acetate. The copper organic compound comprises organometallic compounds such as copper pyrithione.

[0036] In one embodiment the particles of copper compound and / or zinc compound are water- soluble, soluble in saline water such as seawater having a salinity of 0.5-30 gram sodium chloride per litre water to 300-350 gram sodium chloride per litre water.

[0037] In one embodiment each binder is transparent.

[0038] In a particular embodiment, the particles of copper compound and zinc compound are water- soluble, soluble in saline water such as seawater having a salinity of 0.5-30 gram sodium chloride per litre water to 300-350 gram sodium chloride per litre water, and wherein each binder is transparent.

[0039] The copper oxide may be selected from the group consisting of CU2O, CuO, CuO?, CU2O3 and combinations thereof, and preferably the copper salt is CU2O.

[0040] In a preferred embodiment the copper compound is copper oxide selected from the group consisting of CU2O, CuO, CUO2, CU2O3 and combinations thereof, and preferably the copper oxide is CU2O.

[0041] In an embodiment the particles of copper compound are water soluble, preferably soluble in saline water such as seawater having a salinity of 0.5-30 gram sodium chloride per litre water to 300-350 gram sodium chloride per litre water. In one embodiment, the zinc compound is a zinc salt, a zinc oxide or a zinc organic compound. The zinc salt comprises inorganic and organic zinc salts such as zinc chloride or zinc acetate. The zinc organic compound comprises organometallic compounds such as zinc pyrithione.

[0042] The zinc oxide may be ZnO and preferably the zinc salt is ZnO.

[0043] In a preferred embodiment the zinc compound is ZnO.

[0044] In an embodiment the particles of Zinc compound are water soluble, preferably soluble in saline water such as seawater having a salinity of 0.5-30 gram sodium chloride per litre water to 300-350 gram sodium chloride per litre water.

[0045] In a particular embodiment, the copper compound is selected from the group consisting of CU2O, CuO, CuO?, Cu2Os and combinations thereof, and preferably the copper compound is CU2O; and wherein the zinc compound is ZnO.

[0046] In an embodiment the composition comprises a biocide. It is preferred that the biocide is selected from the group consisting of copper bis(1 ,hydroxy-2(1 H)-pyridinethionato-O,S)- (capsaicin), 2,4,5,6-tetrachloroisophthalonitrile, powderous copper, copper naphthalene-2- carboxylate, copper (II) acetate, cuprous thiocyanate, N-[dichloro(fluoro)methyl]sulfanyl-N- (dimethylsulfamoyl)aniline, 3-(3,4-Dichlorophenyl)-1 ,1 -dimethylurea (Diuron), 2-Methylthio-4- tert-butylamino-6-cyclopropylamino-s-triazine, Manganese(2+) N -[2- (sulfidocarbothioylamino)ethyl]carbamodithioate, 5-[1-(2,3-Dimethylphenyl)ethyl]-1 H- imidazole (Medetomidine), 1-(2,4,6-Trichlorophenyl)pyrrole-2,5-dione, N-Ethyl-2- methylbenzenesulfonamide, Methanesulfenamide, 1 ,1-Dichloro-N-((dimethylamino) sulfonyl)-

[0047] 1-fluoro-N-(4-methylphenyl), Dimethylcarbamothioylsulfanyl N,N dimethylcarbamodithioate (Thiram), 2-N-tert-butyl-4-N-ethyl-6-methylsulfanyl-1 ,3,5-triazine-2,4-diamine, 2- (Thiocyanomethylthio)benzothiazole, 2,3,5,6-Tetrachloro-4-(methylsulphonyl)pyridine, 4,5- Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT; Sea-Nine 211), Pyridine; triphenylborane, 4- Bromo-2-(4-chlorophenyl)-5-(trifluoromethyl)-1 H-pyrrole-3-carbonitrile (T ralopyril), Tributylstannyl 2-methylprop-2-enoate, Tributyl(tributylstannyloxy)stannane, Zinc ethylenebis (dithiocarbamate), copper bis(1 ,hydroxy-2(1 H)-pyridinethionato-O,S)- (copper pyrithione) and / or zinc-2-pyridinethiol-1 -oxide (zinc pyrithione), Ziram, preferably 4, 5-Dichloro-2-n-octyl- 4-isothiazolin-3-one (Sea-Nine 211 ), Copper pyrithione and / or Zinc pyrithione, and more preferably is 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one (Sea-Nine 211).

[0048] In a preferred embodiment, the biocide is selected from the group consisting of 4,5-dichloro-

[0049] 2-n-octyl-4-isothiazolin-3-one (Sea-Nine 211 ), copper pyrithione and / or zinc pyrithione, and preferably is 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (Sea-Nine 211 ). The biocide provides anti-fouling properties.

[0050] According to another embodiment the biocide is transparent.

[0051] According to another embodiment the biocide is not transparent.

[0052] In a further embodiment the biocide is a liquid biocide.

[0053] In another embodiment the amount of biocide is 15 wt.% or less, preferably 10 wt.% or less, more preferably 5 wt.% or less, and even more preferably 4 wt.% or less of the overall composition. The amount of the biocide may be in the range of from 0.1 to 15 wt.%, preferably 0.5 to 10 wt.%, and more preferably 1 .0 to 5 wt.% of the overall composition.

[0054] In a particular embodiment, the the biocide is selected from the group consisting of 4,5- dichloro-2-n-octyl-4-isothiazolin-3-one (Sea-Nine 211 ), copper pyrithione and / or zinc pyrithione, and preferably is 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (Sea-Nine 211 ); and wherein the biocide is transparent; and wherein the amount of biocide is 15 wt.% or less, preferably 10 wt.% or less, more preferably 5 wt.% or less, and even more preferably 4 wt.% or less of the overall composition.

[0055] In another embodiment the composition comprises a solvent, preferably an organic solvent such as xylene.

[0056] According to another embodiment, the composition comprises additives such as surface modifiers, dispersing agents, stabilizers, antioxidants, and combinations thereof.

[0057] In a second aspect the present invention relates to a method for preparing a self-polishing anti-fouling coating on a substrate comprising, preferably consisting of, the steps of dispersing particular compounds, preferably dispersing using an ultrasonicator, a highspeed disk disperser, a ball mill or a pearl mill, and homogenizing, a) a self-polishing binder, and b) particles of a copper compound, wherein the copper compound is preferably a copper salt, a copper oxide, or copper organic compound, and / or a zinc compound, wherein the zinc compound is preferably a zinc salt, a zinc oxide or a zinc organic compound, and c) optionally a biocide, wherein the mean particle diameter of the copper compound and zinc compound is in the range of from 2 to 100 nm, preferably 5 to 50 nm such as in the range of from 8 to 40 nm, e.g. in the range 10 to 30 nm, 12 to 25 nm, 14 to 20 nm, or 16 to 18 nm, and wherein the pigment volume concentration of the particles of copper compound and / or zinc compound is less than 1 %, preferably is 0.01 - 0.2 %, more preferably 0.02 - 0.15 %, and more preferably 0.03 - 0.12%. thereby obtaining a homogenized mixture; applying the homogenized mixture on a substrate; and curing the homogenized mixture on the substrate, preferably at a temperature in the range of from 1 - 200 °C, and more preferably of from 5 - 150 °C.

[0058] It should be understood that any feature and / or aspect discussed above in connections with the composition according to the invention apply by analogy to the method described herein.

[0059] By dispersing the particular compounds, i.e. particles, agglomeration, i.e. clusters of particles, are avoided. By dispersing the particular compounds, i.e., particles, agglomeration / aggregation (clusters of particles) are avoided. Optimal properties, herein included transparency in particular, are secured and a homogeneous, well-performing coating is obtained. When properly dispersed, other coating properties, such as flowability, biofouling protection, and polishing and leaching rates, become optimal.

[0060] According to an embodiment the homogenized mixture is applied on the substrate by draw down, brush, roller or spray.

[0061] In one embodiment the homogenized mixture is cured on the substrate at a temperature in the range of from 10 - 120 °C.

[0062] In another embodiment the homogenized mixture is cured on the substrate at a temperature in the range of from 5 - 50 °C, and preferably at a temperature in the range of from 10 - 40 °C.

[0063] In another embodiment the homogenized mixture is cured on the substrate at a temperature in the range of from 55 - 150°C, preferably in the range of from 60 - 125°C.

[0064] Additionally, the homogenized mixture is cured on the substrate for 8 days or less, preferably 7 days or less, more preferably 5 days or less. The homogenized mixture is at least cured for 1 h. In some instances, some residual solvent may be present in the coating after the curing step. This needs to be removed. A heating step will accelerate the diffusion of solvent out of the coating. Hence, the heat treatment removes residual solvent. Through the heat treatment at different temperatures, the transparency of the final coating can be controlled. Curing at elevated temperatures for at least several hours up to three days increases the stability of the coating with respect to transparency significantly. This is in particular for sensor or camera applications advantageous.

[0065] Treating at lower temperatures is less costly. Besides, it regularly still provides a transparency which is satisfactory, and which is sufficient for solar panel applications.

[0066] In a third aspect the invention relates to a cured self-polishing anti-fouling coating, wherein the cured coating is prepared from the coating composition according to the invention.

[0067] It should be understood that any feature and / or aspect discussed above in connections with the composition or method according to the invention apply by analogy to the coating described herein.

[0068] According to an embodiment the coating has a dry film thickness of at least 10 pm, preferably at least 25 pm, more preferably at least 50 pm, even more preferably at least 100 pm such as 100 pm, 150 pm, 200 pm, 250 pm, 300 pm, or 400 pm.

[0069] In an embodiment the coating has a dry film thickness in the range of from 10 pm - 500pm, preferably in the range of from 25 pm - 400 pm, and more preferably in the range of from 50 pm - 250 pm.

[0070] In another embodiment the pigment volume concentration (PVC) of the particles of copper compound and / or zinc compound is less than 0.7%, preferably is in the range of from 0.001 - 0.3 %, more preferably 0.005 - 0.2 %, and even more preferably 0.01 - 0.15 % in the coating.

[0071] In another embodiment the amount of biocide is 15 wt.% or less, preferably 10 wt.% or less, more preferably 5 wt.% or less, and even more preferably 4 wt.% or less of the coating. The amount of the biocide may be in the range of from 0.1 to 15 wt.%, preferably 0.5 to 10 wt.%, and more preferably 1 .0 to 5 wt.%.

[0072] In another embodiment the weight ratio of first binder to second binder is from 90:10 to 40:60, preferably 80:20 to 50:50 and more preferably 70:30 to 60:40 in the coating.

[0073] According to another embodiment, the coating is transparent.

[0074] In an embodiment the coating is UV and optically transparent. It is within the knowledge of the skilled person to measure optical transparency, but for completeness, UV / visible spectroscopy can be used to measure transparency of electromagnetic radiation.

[0075] Optical transparency according to this invention means that the coating is transparent for electromagnetic radiation in the range of from 400 nm to 800 nm.

[0076] UV transparency according to this invention means that the coating is transparent for electromagnetic radiation in the range of from 50 nm to 400 nm. It is preferred that the coating is at least optically transparent. The coating of the present invention is particularly beneficial to use on any device which rely on optical clarity for accurate measurements. Such devices may be an optical sensor, camera, lasers, sonars, submersible lights, sonar domes, underwater scientific instruments (like spectrometers and fluorometers). Any optical instrument / device for e.g., surveillance or exploration purposes require optical transparency.

[0077] In one embodiment the coating has a transparency of greater than 60 %, preferably greater than 70%, and more preferably greater than 80% relative to an uncoated substrate, for at least 2 weeks, preferably at least 6 weeks and more preferably at least 10 weeks. It is important to note that the transparency relative to an uncoated substrate can be in a range above 60% for more than a year. This means that the transparency lasts for at least a year before the coating according to the invention may be applied again.

[0078] In a particular embodiment, the coating has a dry film thickness of at least 10 pm, preferably at least 25 pm, more preferably at least 50 pm, and even more preferably at least 100 pm; and wherein the coating is transparent, preferably optically transparent; and wherein the coating has a transparency of greater than 60 %, preferably greater than 70 %, relative to an uncoated substrate, for at least 2 weeks, preferably at least 6 weeks and more preferably at least 10 weeks.

[0079] The transparency is determined according to the method described in the example section below.

[0080] Higher transparency is important for applications such as sensors or cameras.

[0081] According to another embodiment the coating has a transparency of greater than 20 %, preferably greater than 30% relative to an uncoated substrate, for at least 2 weeks, at least 6 weeks and more preferably at least 10 weeks. It is important to note that the transparency relative to an uncoated substrate can be in a range above 20% for more than a year and up to 5 years.

[0082] Solar panel applications tolerate lower transparencies for still satisfying operation.

[0083] The transparency is determined according to the method described in the example section below.

[0084] According to a further embodiment the coating has a refractive index in the range of from

[0085] 1 .20 - 1 .60, and preferably 1.30 - 1.50. The closer the refractive index is to the surrounding water, in particular sea water, the less reflection occurs at the interface. In another embodiment the coating according to the invention has a ECHA fouling resistance rating after 6 weeks of at least 50, preferably at least 60.

[0086] In another embodiment the coating according to the invention has a ECHA fouling resistance rating after 10 weeks of at least 50, preferably at least 60.

[0087] The ECHA fouling resistance rating is determined according to the method described under ECHA rating described below. In particular, the ECHA is determined according to the Guidance on the Biocidal Products Regulation: Volume II: Efficacy-Part A: Information Requirements. Helsinki: European Chemicals Agency.). The ECHA Fouling Resistance Rating (FRR) is a standardized method developed by the European Chemicals Agency to evaluate the effectiveness of fouling control coatings (FCC). The rating system assesses the degree of biofouling on surfaces submerged in seawater, such as ship hulls, by categorizing and quantifying the coverage of different types of biofouling organisms.

[0088] The FRR is determined based on the percentage coverage of various biofouling categories, including light and dense slime, macroalgae, and animals.

[0089] In a fourth aspect the invention relates to a cured self-polishing anti-fouling coating obtainable by the method for preparing a self-polishing anti-fouling coating on a substrate.

[0090] It should be understood that any feature and / or aspect discussed above in connection with the composition, the method or the coating according to the invention apply by analogy to the coating described herein.

[0091] In a fifth aspect the invention relates to an underwater vehicle or an underwater static structure having at least parts of the surface coated with the self-polishing anti-fouling coating composition according to the invention or having at least parts of the surface covered by the cured self-polishing anti-fouling coating according to the invention.

[0092] It should be understood that any feature and / or aspect discussed above in connection with the composition, the method or the coating according to the invention apply by analogy to the underwater vehicle and the underwater static structure described herein.

[0093] In an embodiment the underwater vehicle is an unmanned underwater vehicle (UUV) or a solar powered autonomous underwater vehicle (AUV). Those vehicles are regularly used in oceanographic research, mine countermeasures, and inspections, but are not limited to such vehicles. In a sixth aspect the invention relates to the use of a cured self-polishing anti-fouling coating according to the invention for covering at least parts of the surface of an underwater static structure, preferably an underwater solar cell, an underwater window, an underwater camera, an underwater sensor, an underwater communication device, an underwater research facility, and / or underwater communication network, or an underwater vehicle, preferably a low-activity underwater vehicle, more preferably an unmanned underwater vehicle or autonomous underwater vehicle.

[0094] It should be understood that any feature and / or aspect discussed above in connection with the composition, the method, underwater vehicle and the underwater static structure or the coating according to the invention apply by analogy to the use of a cured self-polishing anti-fouling coating according to the invention described herein.

[0095] Underwater is to be understood as being at least part time under water. Underwater further includes that the vehicle may be placed or operated in what is known as the splash zone. A splash zone is an area which is at the surface of water, close to water such as a pier, steel racks, rocks or stones creating a fence preventing water to overflow land, and at the feet of offshore wind turbines, where water may splash onto the vehicle due to storms and waves. A floating solar cell I floating solar panel is understood to be within the meaning and purpose of splash zone. In particular, splash zones may be solar cells connected to an underwater device, wherein such connection may be achieved by means of connections such as an adjustable cord or cable.

[0096] An underwater vehicle can be equipped with different underwater devices, preferably underwater solar cells, underwater windows, underwater cameras and / or underwater sensors. It is to be understood that the cured self-polishing anti-fouling coating according to the invention is also used for covering at least parts of the surface these underwater devices.

[0097] In a seventh aspect the invention relates to the use of a self-polishing anti-fouling coating composition according to the invention for preparing a coating on at least parts of the surface of an underwater static structure, preferably underwater solar cell, an underwater window, an underwater camera, an underwater sensor, an underwater communication device, an underwater research facility, and / or underwater communication network, or an underwater vehicle, preferably a low-activity underwater vehicle, more preferably an unmanned underwater vehicle or autonomous underwater vehicle.

[0098] It should be understood that any feature and / or aspect discussed above in connections with the composition, the method, underwater vehicle and the underwater static structure or the coating according to the invention apply by analogy to the use of a cured self-polishing antifouling coating composition according to the invention described herein.

[0099] Underwater is to be understood as being at least part time under water and as described elsewhere herein.

[0100] An underwater vehicle can be equipped with different underwater devices, preferably underwater solar cells, underwater windows, underwater cameras and / or underwater sensors. It is to be understood that the cured self-polishing anti-fouling coating composition according to the invention is also used for covering at least parts of the surface these underwater devices.

[0101] In an eight aspect the present invention relates to an article or substrate having at least a part of the surface coated with the cured self-polishing anti-fouling coating according to the present invention.

[0102] It should be understood that any feature and / or aspect discussed above in connection with the composition, the method, underwater vehicle and the underwater static structure, and the uses of the coating and the composition or the coating according to the invention apply by analogy to the article or substrate described herein.

[0103] In an embodiment the article or substrate is a solar panel, a sensor, a camera, a lens, a glass cover, a polymer cover, a glass plate, a window, a communication device, and / or polymer plates.

[0104] For example, can the article be a cover of a solar panel.

[0105] In an embodiment the article or the substrate is replaceable. This is particularly useful as it allows the fast change of components, which become covered by biofouling after the coating has polished through (i.e. completely reacted and dissolved in seawater). The article may be a replaceable coated panel.

[0106] The following figures and examples are provided below to illustrate the present invention. They are intended to be illustrative and are not to be construed as limiting in any way.

[0107] BRIEF DESCRIPTION OF FIGURES

[0108] Fig. 1. Photos taken at regular intervals of the transparent binder systems (SA (BS1 ) and SA-R (BS2)) with no biocides, exposed for 10 weeks at static seawater conditions. Visual resolving power, before and after seawater exposure, was used to qualitatively evaluate both transparency and antifouling efficiency.

[0109] Fig. 2. UV-Vis spectra of the transparent coatings showing transparencies above 80% in the visible spectrum with SA (BS1 ) as the binder system and different biocidal components incorporated individually (SA-NC, SA-NZ, SA-SN) and in combination (SA-NC-NZ-SN) at a DFT of 100 pm. Notice that the substrate absorb all UV light (200-400 nm).

[0110] Fig. 3. The UV-Vis spectra of the coating formulations (at 100 pm DFT on polycarbonate substrates) based on the SA-R (BS2) binder system with biocides incorporated separately and in a combination. All formulations show visible light transmission above 80%.

[0111] Fig. 4. Evaluation after exposure of the formulation consisting of nano-Cu?© (NC) in the SA (BS1 ) and SA-R (BS2) binder systems.

[0112] Fig. 5. Effect of nano-ZnO (NZ) in SA (BS1 ) and SA-R (BS2) binder systems.

[0113] Fig. 6. The impact of SeaNine-211 (SN) on both the SA (BS1 ) and SA-R (BS2) binder systems after 10 weeks of exposure to static seawater. The development of haziness was observed in both binder systems starting from week 2.

[0114] Fig. 7. Antifouling performance of coatings with the combination of NC, NZ, and SN for both SA (BS1 ) and SA-R (BS2) binder systems. Throughout the exposure time, the fouling resistance of the SA-R (BS2) binder system was excellent. By week 10, the coating was polished through.

[0115] Fig. 8. Antifouling performance of coatings with the combination of the micron-sized pigments (MC, and MZ), and SN for both SA (BS1 ) and SA-R (BS2) binder systems.

[0116] Fig. 9. The efficiency of solar power generation of F4 coating with SA-R (BS2) binder system compared to a blank substrate measured on a weekly basis. It is to be noted that the reported measurements of solar power generation via coating and substrate are based on averages of four replicates, and the associated uncertainty is within 5%.

[0117] Fig. 10 Graphs showing fouling resistance rating of coatings based on (a) SA (BS1 ) binder and (b) SA-R (BS2) binder. Error bars express one standard deviation of panel replicates, performed three times during the summer season from April to August 2022.

[0118] Fig. 11. Close-up photographs of the coating containing a combination of NC, NZ, and SN in an SA-R (BS2) binder after 2 weeks of exposure. Haziness is evident (indicated by circles).

[0119] Fig. 12. UV-Vis spectra of the F4 coating with SA-R (BS2) binder, compared to a blank substrate and measured on a weekly basis. Note that the reported measurements are based on averages of four replicates, and that the associated uncertainty is within 5%.

[0120] EXAMPLES

[0121] Coating materials and application

[0122] All coatings were formulated based on a silyl acrylate (SA) self-polishing binder in xylene (NSP-100X) from Nitto Kasei (Japan), and a solid, fully hydrogenated ForalTM gum-rosin (R) from Eastman, USA. These two binders have different polishing rates in seawater.

[0123] The first series of coatings were formulated with neat (i.e. particle-free) silyl acrylate (SA) and the second with a mixture of silyl acrylate and rosin (SA-R) in weight ratio of 70:30.

[0124] Two particulate biocides, nano-Cu?© (NC) and nano-ZnO (NZ), with particle size of 16 and 18 nm, respectively, were acquired from Nanografi, Germany. SeaNine 211 (SN), an organic liquid biocide, was from Rohm & Haas. The formulation details and the biocide concentrations are provided in Table 1.

[0125] Table 1 Overview of formulations with individual biocides (F1 , F2, and F3) and in combination (F4) for two different binder systems, SA (binder system 1 ; BS1 ) and SA-R (binder system 2, BS2). F5 is a reference formulation that contains micronsized CU2O (average particle size of 3 pm) (MC) and micron-sized ZnO (average particle size of 1 pm) (MZ) for both SA and SA-R binders. (SA: Silyl acrylate, R: Rosin, NC: n-Cu2O, NZ: n-ZnO, SN: SeaNine 211)

[0126] At first, the efficiency of each of the three biocides were examined individually (F1 , F2, F3) under static seawater conditions, and in step two as a combination of all biocides together (F4). Additionally, conventional micron-sized C112O (MC) and ZnO (MZ), with concentrations identical to NC and NZ in F4, respectively, were formulated in a reference coating (F5). Proper dispersion and homogenous distribution of NZ and NC in the binder systems were ensured with an UP400St ultrasonic homogenizer from Hielscher Ultrasound Technology (Germany). For F5, pigment dispersion was done using a high-speed dissolver (Dispermat CV3-Plus) from VMA-GETZMANN GMBH (Germany).

[0127] Coatings were applied on 6 mm thick and smooth transparent polycarbonate substrates of dimensions 200 mm x 100 mm, acquired from the Office of Naval Research, USA. Using a bar applicator (width of 50 mm), the coatings, aiming at a dry film thickness (DFT) of 100 ± 15 pm, were applied to one side of the substrate panels and dried at room temperature for a minimum of 5 days.

[0128] UV-Vis spectroscopy analysis

[0129] To measure UV-Vis spectra, within a wavelength range of 320-875 nm, a Shimadzu UV- 2600i double-beam spectrophotometer equipped with an ISR-2600 integrating sphere accessory from Duisburg, Germany was used. The instrument was set to operate with a slit beam width of 0.2 nm, a scan rate of 90 nm / min, a data interval of 0.1 nm, and a signal averaging time of 0.067 s. Prior to seawater exposure, the level of coating transparency was evaluated. The criterion for acceptable transparency, in the visible spectrum, was defined as greater than 60% (relative to the uncoated substrate panel).

[0130] Seawater exposure (raft experiments)

[0131] At The CoaST Maritime Test Centre, located in Hundested Harbor, Denmark, (55o 57' 57.5" N 11o 50' 33.6" E), static panel exposure was conducted from May to June 2022 and repeated twice from July to August 2022. At a water depth of 0.25-0.75 m, coated polycarbonate panels were vertically immersed in a southern direction. During the summer season, when the fouling intensity was at its highest, each of the coated panels were exposed for two and a half months and inspections performed after 2, 6, and 10 weeks. Despite variations in weather conditions and an average pH of 7.7 ± 0.2, the salinity was relatively constant (15-21 %o which corresponds to 15-21 grams of NaCI per liter water). To avoid disturbance of the biofouling activity, the panels were photographed and re-immersed at the raft in less than 5 minutes. Non-coated polycarbonate panels were used as negative controls (i.e. blanks). Fouling Evaluation

[0132] Visual Resolving Power

[0133] Assessment of the antifouling performance of the coatings was conducted by visual inspection and photos. The optical clarity, also referred to as visual resolving power, on the other hand, was evaluated by placing the panels on a special paper print with a white background and random numbers and markings. Visual resolving power is a measure of the ability of the coating to allow the viewer to distinguish between different numbers or markings placed beneath it. In other words, a coating with a high visual resolving power will appear clear and transparent, enabling the viewer to observe the underlying substrate clearly. Hence, it is a critical factor to consider when designing coatings for applications that require transparency, such as underwater assets and solar panels.

[0134] ECHA Rating

[0135] Subsequently, to assess the antifouling performance of coating samples (Regulation, B. P. (2018). Guidance on the Biocidal Products Regulation: Volume II: Efficacy-Part A: Information Requirements. Helsinki: European Chemicals Agency.), the European Chemicals Agency’s (ECHA) Guidance on Efficacy Assessment for Type 21 antifouling products was used (Table 2).

[0136] Table 2 Evaluation guidelines according to ECHA. (a) the type of fouling is divided into four fouling categories, and each fouling category is given a weighted coverage rating, and (b) the overall efficacy is categorized based on calculated fouling resistance. The guidance, also needed for authorization of an antifouling product in the EU, is based on a simple and effective method that does not overestimate the capabilities of static panel exposure tests, which can be influenced by highly variable field conditions, such as nutrient availability, salinity, temperature, hydrodynamic energy, and light intensity.

[0137] According to procedures, the following is reported; (a) the main categories of fouling (light slime, dense slime, algae, and animals) with a so-called coverage rating (weighted), describing the amount of fouling attached to the surface for each fouling category (Table 2a). (b) To assess the overall antifouling performance of the coatings (Table 2b), a fouling resistance, FR, is expressed as FR = 100 - (LS + DS + MA + A), where LS is defined as light slime, DS as dense slime, MA as microalgae, and A as animals. Slime is a biofilm of bacteria, diatoms, microalgae, and protozoa. Light slime is more easily cleared than dense slime. In practice, this is evaluated by sliding a finger across the coating surface. Macroalgae include red, green and brown algae. Animals are restricted to the main categories, such as barnacles, mussels, tubeworms, hydroids, and bryozoans.

[0138] To avoid the influence of indirect (surrounding) fouling growth, the evaluation was performed in the center area (200 x 100 mm2) of the panel with 2.5 cm to the edges of the panel. The assessment of soft fouling (e.g., algae) was targeted at the area where the algae attached to the surface, as opposed to the area covered by hanging ‘algae leaves’ (i.e. , biofouling attached on top of other fouling organisms, so-called secondary fouling, was excluded from the assessment).

[0139] Coating experiments without copper or zinc compound

[0140] Binder system 1 (BS1) is silyl-acrylate (SA) in xylene.

[0141] Binder system 2 (BS2) is a SA binder system which was modified with addition of rosin (R) as a co-binder in a 70:30 ratio, thereby forming the second binder system, which is termed the silyl acrylate-rosin (SA-R) system.

[0142] Neat SA and SA-R binders were initially exposed to static seawater conditions. In Fig. 1 , the visual resolving power (VRP) shows a significant (though indirect) increase in the polishing rate of the SA-R binder compared to SA, as a result of the higher rate of seawater dissolution of gum rosin. However, due to the absence of biocides, by week 10, both binder systems completely foul. Estimation of the PVC limits

[0143] Using UV-Vis spectroscopy, the maximum allowable concentrations of three copper or zinc compounds with biocidal properties, separately and in combination, in both binder systems (BS1 and BS2), are described.

[0144] In terms of the pigment volume concentration (PVC) of the two copper oxide and zinc oxide nano-pigments, the maximum limit for the coating to maintain a transparency higher than 80% was measured to only 0.04 and 0.08% for NC and NZ, respectively. On the other hand, the further biocide SN, being transparent, showed no significant absorption in the UV Vis spectra and thus the commercially recommended concentration of 3 wt.% (on a dry-coating basis) was incorporated. For reference, formulations containing conventional micron size CU2O (MC) and ZnO (MZ), with PVC values identical to NC and NZ, were also formulated and exposed.

[0145] All formulations (based on SA (BS1 ) or SA-R (BS2) binder systems), as shown in Fig. 2 and 3, show transmission values above 80% in the visible spectrum (400-800 nm). For both figures, the curve named “Substrate - Polycarbonate’’ is the uncoated polycarbonate substrate, which shows a marginal absorbance. The curve named “80% Transmission Limit’’ is the chosen 80% transmission limit, relative to the substrate, and represents the minimum transparency value allowed for the coatings. This curve was obtained simply by multiplying the substrate values by 0.8.

[0146] Effect of copper and zinc compounds on anti-fouling performance

[0147] Exposure of the transparent anti-fouling coatings, under static seawater conditions, was initiated. The coating formulation details and photographic visual observations (dry measurements) of each formulation for 2.5 months (10 weeks) are summarized below.

[0148] In Fig. 4, the fouling efficiency of the coating formulation with NC is evident only for week 2. By week 6 and finally week 10, both SA (BS1 ) and SA-R (BS2) systems show intense fouling, suggesting that NC alone is not sufficient to maintain the fouling resistance at static conditions.

[0149] Fig. 5 is a clear indication that NZ is effective for the early stage of fouling (up to week 2 for the SA (BS1) binder system) but has no significant resistance to later hard fouling organisms. By week 10, both coating systems show intense fouling.

[0150] The biocide SN alone in both SA (BS1) and SA-R (BS2) binder systems show significantly better fouling resistance compared to NC and NZ. As shown in Fig. 6, both binders with SN remained completely fouling free after week 2 and the SA-R binder with SN showed only a thin layer of slime deposition after week 6. However, by week 10, the effectiveness reduced drastically and both binder systems fouled completely. Moreover, after week 2, both binder systems with SN developed haziness.

[0151] The combined effect of the two nano pigments (NC and NZ) along with the biocide (SN) can be seen in Fig. 7. The excellent fouling resistance observed during the 10-week exposure period can be attributed to the combined effect of biocide, their concentration, and the fast polishing rate of the SA-R (BS2) binder. Interestingly, the formulation with combined biocides in the SA-R (BS2) binder (100 pm DFT) completely polished off by week 10, indicating a polishing rate of about 1.4 pm / day, which is substantially higher than ’’conventional” polishing rates of 5-15 pm / month. If needed, an increase in the DFT from 100 to 200 pm (or even higher) could prolong the service life of the transparent anti-fouling coating. NZ acted as a polishing facilitator by increasing both the polishing rate of the binder and the release rate of the biocidal pigments (only indirectly verified via the biofouling growth). Though an improved performance for the neat SA (BS1 ) binder was observed when all biocides were present in combination, the slow polishing rate, by week 6 could not keep the coatings free of fouling.

[0152] Similarly, the effect of micron-sized biocidal pigments MC and MZ when combined with SN in the same concentration as that of NC, NZ, and SN for both SA (BS1) and SA-R (BS2) binder systems were also evaluated under static seawater conditions (see Fig. 8). For the initial 2 weeks of exposure, even the low PVC of the micron sized pigments, surprisingly, showed excellent fouling resistance for the SA-R (BS2) binder. However, the fouling efficiency dropped significantly for week 6 and finally by week 10 the exposed coatings were fouled completely for both SA (BS1) and SA-R (BS2) binders. This observation confirms that micron-sized biocidal pigments can also be used for transparent antifouling coatings.

[0153] However, their efficacy in preventing fouling is significantly lower than for the nano-size pigments.

[0154] An additional static exposure study was conducted on the most effective formulation (F4, featuring an SA-R (BS2) binder) in the tropical region of Florida, USA. Despite harsh and warm seawater conditions, in comparison to the Nordic region, the exposed coating exhibited exceptional resistance to biofouling, remaining very close to fouling-free for a period of 10 weeks. Furthermore, as shown in Fig. 9, measurements of solar power generation through coating and substrate showed an efficiency above 90 % throughout the 10-week exposure period except for a decrease in week 3, which showed a value of 70%. Fouling resistance rating

[0155] The corresponding evaluation of fouling resistance for both SA (BS1) and SA-R (BS2) binder systems, performed according to the ECHA guidance, is expressed in a column plot in Fig. 10a and 10b respectively. Each column represents the average fouling resistance of three replicate panels. The two neat binder systems without copper and zinc compounds and / or biocide, SA (BS1 ) and SA-R (BS2) acting as references, were fouled completely by week 10. Nevertheless, owing to its faster polishing rate, the SA-R (BS2) binder system showed a decent rating of 60 for the initial weeks (till week 2) even without the presence of biocides. According to the ratings, it is clear that all three biocides utilized in this study exhibit decent fouling resistance only for 2 weeks, after which the performance drops significantly. Only SN for the SA-R (BS2) binder system shows a rating of 70 till week 6 and then substantially drops to 20 by week 10.

[0156] However, when all biocides in combination are used, the SA (BS1 ) binder system shows an improved rating of 60 after 10 weeks, and the SA-R (BS2) binder system shows excellent fouling resistance throughout the 10 weeks with the rating not falling below 90. On the other hand, the micron-size pigments MC and MZ combined with SN, which acted as reference coatings showed the lowest rating (below 10) for both binder systems. This emphasizes the role of nano-size pigments in achieving the transparency and yet maintaining excellent antifouling efficiency under static conditions.

[0157] Haziness as a result of exposure

[0158] After two weeks of seawater exposure, the best performing coating (F4 with SA-R (BS2) binder) develop a certain degree of haziness (Fig. 11 ). Despite having a fouling resistance rating above 90 throughout the 10 weeks of static seawater exposure, this phenomenon kept developing until the coating polished through in week 10.

[0159] As shown in Figure 12, the development of haziness in the coating resulted in a decrease in the visible light transmission of the coating. This decline reached a maximum of 50%, compared to the initial measurement, when no biofouling was present. However, it is important to note that despite the compromised optical clarity, the transparent antifouling coatings are still suitable for solar panel applications (as seen in Fig. 9).

[0160] Moreover, the scattering phenomenon, referred to as the edge-of-the-cloud effect, has been found to enhance the efficiency of solar panels by increasing the path length of photons and promoting their absorption by the photovoltaic material. The scattered light is redirected and ’’trapped” within the material, which increases the probability of photon absorption and improves the overall efficiency of the solar panel. Therefore, the haziness observed in the coatings is a desirable property for solar panel applications, as it promotes an increase in energy conversion efficiency.

[0161] A self-polishing anti-fouling coating is presented. The tested self-polishing binder system, consisting of silyl acrylate binder with rosin as a co-binder, with nanoparticles of CU2O and ZnO, as well as the organic biocide SeaNine 211 showed advantageous properties. Surprisingly, only low PVC levels for the nano-particles were required to achieve excellent biofouling resistance. The above tested coatings remained transparent and showed high ECHA fouling resistance ratings for up to 10 weeks of exposure at static seawater conditions.

Claims

CLAIMS1 . A self-polishing anti-fouling coating composition comprising: a) a self-polishing binder, b) particles of a copper compound, wherein the copper compound is preferably a copper salt, a copper oxide, or copper organic compound, and / or a zinc compound, wherein the zinc compound is preferably a zinc salt, a zinc oxide or a zinc organic compound; c) optionally a biocide, wherein the mean particle diameter of the copper compound and zinc compound is in the range of from 2 to 100 nm, preferably 5 to 50 nm such as in the range of from 8 to 40 nm, preferably in the range of from 10 - 30 nm, 12 - 25 nm, 14 - 20 nm, or 16 - 18 nm, and wherein the pigment volume concentration of the particles of copper compound and / or zinc compound is less than 1 %, preferably is 0.01 - 0.2 %, more preferably 0.02 - 0.15 %, and more preferably 0.03 - 0.12%.

2. Self-polishing anti-fouling coating composition according to claim 1 , wherein the self-polishing binder is selected from the group consisting of Zn-based acrylate, Cu-based acrylate or silyl-acrylate, and preferably is a silyl-acrylate.

3. Self-polishing anti-fouling coating composition according to any one of the preceding claims, wherein the coating composition comprises a second self-polishing binder.

4. Self-polishing anti-fouling coating composition according to claim 3, wherein the second binder is a rosin binder, gum-rosin binder, hydrogenated rosin binder, thermocatalytically treated rosin binder, polymerized rosin binder, rosin metal carboxylate (resinate) binder such as a fused resinate or a precipitated resinate, rosin polycarboxylate binder, rosin amine binder, rosin esters of mono- and polyhydric alcohols binder, preferably a gum-rosin binder; and / or wherein the second binder has a polishing rate different from the first binder; and / or wherein the weight ratio of first binder to second binder is from 90:10 to 40:60, preferably 80:20 to 50:50 and more preferably 70:30 to 60:40.

5. Self-polishing anti-fouling coating composition according to any one of the preceding claims, wherein the particles of copper compound and / or zinc compound are water-soluble, soluble in saline water such as seawater having a salinity of 0.5-30 gram sodium chloride per litre water to 300-350 gram sodium chloride per litre water; and / or wherein each binder is transparent.

6. Self-polishing anti-fouling coating composition according to any one of the preceding claims, wherein the copper compound is selected from the group consisting of CU2O, CuO, CuC>2, Cu2Os and combinations thereof, and preferably the copper compound is CU2O; and / or wherein the zinc compound is ZnO.

7. Self-polishing anti-fouling coating composition according to any one of the preceding claims, wherein the biocide is selected from the group consisting of 4,5-dichloro-2-n-octyl-4- isothiazolin-3-one (Sea-Nine 211 ), copper pyrithione and / or zinc pyrithione, and preferably is 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (Sea-Nine 211 ); and / or wherein the biocide is transparent; and / or wherein the amount of biocide is 15 wt.% or less, preferably 10 wt.% or less, more preferably 5 wt.% or less, and even more preferably 4 wt.% or less of the overall composition.

8. A method for preparing a self-polishing anti-fouling coating on a substrate comprising the steps of- dispersing particular compounds, preferably dispersing using an ultrasonicator, a high-speed disk disperser, a ball mill or a pearl mill, and homogenizing, a) a self-polishing binder, and b) particles of a copper compound, wherein the copper compound is preferably a copper salt, a copper oxide, or copper organic compound,and / or a zinc compound, wherein the zinc compound is preferably a zinc salt, a zinc oxide or a zinc organic compound, and c) optionally a biocide, wherein the mean particle diameter of the copper compound and zinc compound is in the range of from 2 to 100 nm, preferably 5 to 50, such as in the range of from 8 to 40 nm, e.g. in the range 10 to 30 nm, 12 to 25 nm, 14 to 20 nm, or 16 to 18 nm, and wherein the pigment volume concentration of the particles of copper compound and / or zinc compound is less than 1 %, preferably is 0.01 - 0.2 %, more preferably 0.02 - 0.15 %, and more preferably 0.03 - 0.12%. thereby obtaining a homogenized mixture;- applying the homogenized mixture on a substrate; and- curing the homogenized mixture on the substrate, preferably at a temperature in the range of from 1 - 200 °C, and more preferably of from 5 - 150 °C.

9. A cured self-polishing anti-fouling coating, wherein the cured coating is prepared from the coating composition according to any one of claims 1 to 8.

10. The cured self-polishing anti-fouling coating according to claim 9, wherein the coating has a dry film thickness of at least 10 pm, preferably at least 25 pm, more preferably at least 50 pm, and even more preferably at least 100 pm; and / or wherein the coating is transparent, preferably optically transparent; and / or wherein the coating has a transparency of greater than 60 %, preferably greater than 70 %, relative to an uncoated substrate, for at least 2 weeks, preferably at least 6 weeks and more preferably at least 10 weeks.

11. The cured self-polishing anti-fouling coating according to any one of claims 9 or 10, wherein the coating has a ECHA fouling resistance rating after 6 weeks of at least 50; and / or wherein the coating has a ECHA fouling resistance rating after 10 weeks of at least 50.

12. An underwater vehicle or an underwater static structure having at least parts of the surface coated with the self-polishing anti-fouling coating composition according to claims 1 - 8 or having at least parts of the surface covered by the cured self-polishing anti-fouling coating according to any one of claims 9 to 11 .

13. Use of a cured self-polishing anti-fouling coating as defined in any one of claims 9 to 11 for covering at least parts of the surface of an underwater static structure, preferably an underwater solar cell, an underwater window, an underwater camera, an underwater sensor, an underwater communication device, an underwater research facility, and / or underwater communication network, or an underwater vehicle, preferably a low-activity underwater vehicle, more preferably an unmanned underwater vehicle or autonomous underwater vehicle.

14. Use of a self-polishing anti-fouling coating composition as defined in any one of claims 1 to 8 for preparing a coating on at least parts of the surface of an underwater static structure, preferably an underwater solar cell, an underwater window, an underwater camera, an underwater sensor, an underwater communication device, an underwater research facility, and / or underwater communication network, or an underwater vehicle, preferably a low-activity underwater vehicle, more preferably an unmanned underwater vehicle or autonomous underwater vehicle.

15. Article or substrate having at least a part of the surface coated with the cured selfpolishing anti-fouling coating according to any one of claims 9 to 11.

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