Antifouling coating compositions

Abstract

The invention is directed to an antifouling self-polishing coating composition comprising a silyl-acrylate copolymer, one or more metal-organic biocides each of which is present at no more than 1 wt%, one or more organic biocides, and a polar organic 5 solvent, where each organic biocide is present at no more than 1 wt%. It is suitable for application to substrates that are intended to be fully or partially immersed in water when in use, for example the immersible surfaces of ships, boats and offshore structures.

Description

[0001] ANTIFOULING COATING COMPOSITIONS

[0002] Technical Field

[0003] The invention relates generally to antifouling self polishing coating compositions, to their use in controlling aquatic fouling, and to substrates coated with such self-polishing coating compositions.

[0004] Background Art

[0005] Fouling of ship hulls and other water-borne objects by aquatic organisms is a continuing problem. Fouling can increase frictional resistance of ships and boats in the water, increasing fuel costs and greenhouse gas emissions for powered vessels and also increase the risk of translocation of invasive species leading to the loss of biodiversity in aquatic environments. On static structures, for example on drilling rigs, it can alter the water flow around the supporting legs, risking unpredictable and increased stresses. Fouling can also make inspections more difficult by obscuring defects and cracks. It can further reduce the cross-sectional area of pipework such as cooling water or ballast tank intakes, leading to reduced flow rates.

[0006] Coatings can be used to reduce fouling. Such coatings can contain a biocide to control the growth of aquatic organisms on the surface. These fall typically into two broad categories, namely “hard” antifouling coatings, where biocide gradually leaches from the coating over time, and “eroding” or “self-polishing” antifouling coatings which commonly comprise a rosin material, a polymer that becomes water-soluble upon reaction with water (sometimes known as a self-polishing copolymer or SPC), or a combination of both. In such coatings, the coating gradually erodes or polishes to release biocide. Examples of antifouling coatings are described in EP2873683, EP3284783, EP3480267, EP3480268, EP3483215 and EP4119620.

[0007] Silyl acrylate copolymers can be used in such antifouling coatings, as described in EP0646630, EP1016681 , EP1323745, EP2128208, EP2161316, EP3299427, EP3354667, EP3540022, EP3805327, GB2560158, GB2576431 , US2016 / 185913, US2021 / 0301153, US11472967, WO2015 / 150249 and WO2019 / 081495. Silyl acrylate copolymers are formed from a mixture of polymerizable monomers where at least one of the monomers is a silyl acrylate ester. The copolymers also tend to include other silyl- free acrylate monomers, and optionally also other non-acrylate monomers. In the examples of the above-mentioned publications, the specifically identified silyl acrylate monomers include monomers that fall within the following general formula: where each R is a C1-C4 alkyl group.

[0008] There remains a need for antifouling coatings with improved properties. In particular, there is a need for antifouling coatings having reduced drying times to help improve operational efficiency of shipyards and dry docks.

[0009] Additionally, there is a need for antifouling coatings with relatively low biocide content in order to meet current and anticipated future regulatory requirements.

[0010] Summary of Invention

[0011] The invention is directed to an antifouling self-polishing coating composition comprising: a silyl-acrylate copolymer one or more metal-organic biocides, each of which is present at no more than 1 wt%; one or more organic biocides, each of which is present at no more than 1 wt% a polar organic solvent.

[0012] The invention is also directed to a method for coating a substrate that is intended to be fully or partially, permanently or intermittently immersed in water, comprising applying such a coating to a surface of the substrate and allowing it to dry. The invention is also directed to a method of protecting a substrate against aquatic biofouling by applying such a coating to the substrate and allowing it to dry.

[0013] The invention is further directed to a substrate coated with such a coating composition.

[0014] The invention is still further directed to the use of such a coating composition for controlling aquatic biofouling on the substrate.

[0015] Terminology

[0016] “Acrylate-based monomer” is a monomer having a moiety in which the carbon atom of a carbonyl moiety in a carboxyl or carboxylate group is directly bound to a carbon atom of a carbon - carbon double bond. Such monomers include, for example, acrylate, methacrylate, maleate, itaconate, citraconate and fumarate monomers.

[0017] ’’Acrylate-based polymer (or co-polymer)” is a polymer or co-polymer obtainable by polymerisation of one or more acrylate-based monomers.

[0018] “Aliphatic hydrocarbyl” groups or substituents include saturated and unsaturated hydrocarbyl groups (e.g. alkyl or alkenyl groups), which can be cyclic, linear or branched. Cyclic hydrocarbyl groups include hydrocarbyl groups that have a mixture of cyclic and non-cyclic portions. Similarly, references to “alkyl” or “alkenyl” groups or substituents includes cyclic, linear or branched groups, where cyclic alkyl or alkenyl groups include groups comprising a mixture of cyclic and non-cyclic portions. Unsaturated groups, for example alkenyl groups, have a minimum of two carbon atoms.

[0019] “Aryl” compounds, groups or substituents comprising one or more aromatic rings that are based on carbon atoms.

[0020] “Atmospheric pressure” is defined as 1.013 bar-a, where bar-a represents bar-absolute as opposed to bar-gauge. “Biocide” means an active ingredient that is intended to prevent, destroy, repel or mitigate against aquatic plants, animal life or virus, bacteria or other microorganisms (biofouling) by chemical or biological means.

[0021] “Haloalkyl” means an alkyl group comprising one or more halide substituents, which will typically be selected from F and Cl.

[0022] “Heteroaryl” compounds, groups or substituents are aryl compounds, groups or substituents that comprise one or more heteroatoms in the aromatic ring in place of a carbon atom, the heteroatoms typically being selected from oxygen, nitrogen and sulfur.

[0023] “Hydrocarbon solvent” means a solvent having only carbon and hydrogen atoms in its molecular formula.

[0024] “Monomer unit” means a constituent monomer of a polymer, i.e. the moiety derived from the monomer after being incorporated into a polymer. The monomer (or monomer unit) content of a polymer or oligomer, expressed in either weight% (wt%) or molar% (mol%), can be calculated from, respectively, the weight fraction or the mole fraction of monomer used to make the polymer or oligomer.

[0025] “Organic” groups, compounds or other moieties means a compound, group or other moiety that comprises at least one carbon-hydrogen covalent bond, carbon-carbon covalent bond or carbon-halogen covalent bond.

[0026] “Polar organic solvent” means an organic solvent having one or more carbon-heteroatom covalent bonds, where the heteroatom is selected from oxygen, nitrogen and sulfur. Heteroatom-containing organic solvents tend to be more polar than hydrocarbon solvents.

[0027] “Saturated carbon atom” means to a carbon atom that has four single covalent bonds to other atoms, and no double or triple covalent bonds to other atoms. ’’Silyl acrylate monomer” is an acrylate-based monomer having a triorganosilyl carboxylate ester moiety that is directly bonded to a carbon atom of a C=C double bond, for example a trialkylsilyl ester of (meth)acrylic acid.

[0028] ’’Silyl acrylate (co)polymer” is a (co)polymer made from a monomer mixture comprising at least one silyl acrylate monomer.

[0029] “Unsaturated carbon atom” means to a carbon atom that has at least one double or triple bond to another atom.

[0030] Description of Embodiments

[0031] [Antifouling self-polishing coating composition]

[0032] An antifouling coating is one that comprises one or more biocides, and a self-polishing coating is one that erodes over time. Thus, an antifouling self-polishing coating enables continuous release of biocide (and any other embedded active ingredients) within the coating itself to maintain antifouling activity. Continuous removal of the outer layer of the coating itself can also prevent adhesion of biological organisms.

[0033] [Silyl acrylate copolymer]

[0034] The antifouling coating composition comprises one or more silyl acrylate copolymers, which are typically self-polishing copolymers made up predominantly of acrylate-based monomers, including one or more silyl acrylate monomers. They are typically thermoplastic polymers. The total amount of silyl acrylate copolymers in the coating composition can be in the range of from 1 to 80 wt%, for example from 2 to 75 wt%, from 5 to 70 wt% or from 10 to 60 wt%.

[0035] In embodiments, the silyl acrylate copolymer comprises at least one silyl acrylate monomer unit of Formula (1):

[0036] Formula (1)

[0037] Each Rais independently selected from C1-10 alkyl, C6-12 aryl, where the C6-12 aryl is optionally substituted with one or more substituents (e.g. from 1 to 4 or from 1 to 2) selected from C1-6 alkyl and C1-6 alkoxy. In embodiments, each Rais independently selected from C1-8 alkyl or from C1-4 alkyl. In current commercially available polymers, all Ratend to be C1-4 alkyl.

[0038] Rbis selected from H and methyl.

[0039] They can be made from polymerisation of one or more silyl acrylate monomers of Formula (2) Formula (2) where Raand Rbare as defined above.

[0040] In embodiments the silyl acrylate monomer is a triorganosilyl ester of acrylic or methacrylic acid, for example a tri(Ci-4 al kyl)silyl ester such as triisopropylsilyl acrylate, triisopropylsilyl methacrylate, tributylsilyl acrylate or tributylsilyl methacrylate.

[0041] The silyl acrylate copolymer can additionally comprise one or more acrylate-based monomer units of Formula (3):

[0042]

[0043] These acrylate-based monomer units can be derived from corresponding monomers of Formula (4), i.e. Formula (4)

[0044] In these two formulae:

[0045] Z is -ORX, NRX2.

[0046] Each Rf, Rgand Rhare independently selected from H, C(O)ORX, optionally substituted C1-20 aliphatic hydrocarbyl, optionally substituted C6-12 aryl, and C6-12 aryl with one or more C1-6 aliphatic hydrocarbyl groups that can optionally have additional substituents. There can be 1 to 4, for example 1 to 2, optional substituents selected from halide (typically selected from F and Cl), -ORXand -C(O)ORX. In the case of aryl groups, optional substituents also include C1-6 aliphatic hydrocarbyl groups.

[0047] Each Rxis independently selected from H and Ry.

[0048] Ryis selected from optionally substituted C1-6 alkyl, where optional substituents are selected from halide and -(OCH2CH2)nORz, where n is in the range of from 0 to 25, and Rzis selected from H and C1-6 alkyl. In embodiments, there can be from 1 to 4, for example from 1 to 2, optional substituents.

[0049] In embodiments, the optionally substituted aliphatic hydrocarbyl groups are selected from C1-10 aliphatic hydrocarbyl groups, such as C1-6 hydrocarbyl groups. In further embodiments, the optionally substituted aliphatic hydrocarbyl groups are optionally substituted alkyl groups.

[0050] In embodiments, there are no optionally substituted aryl groups in Rf, Rgand Rh.

[0051] In embodiments, there are no halide groups or substituents in any of the acrylate-based monomers.

[0052] In embodiments, Rhis selected from H, optionally substituted C1-20 aliphatic hydrocarbyl, and optionally substituted Ce-36 aryl. There can be from 1 to 4, for example from 1 to 2, optional substituents selected from halide (typically selected from F and Cl), -ORXand C(O)ORX.

[0053] In embodiments, only one of Rfand Rgcan comprise a -C(O)ORXmoiety. In further embodiments, only one of Rf, Rgand Rhcan comprise a -C(O)ORXmoiety.

[0054] In embodiments, each Rxis selected from H and C1-6 alkyl, for example from H and C1-4 alkyl.

[0055] In embodiments, Z is ORXand in further embodiments Z is ORy

[0056] In embodiments, all -C(O)ORXin Rf, Rgand Rhare -C(O)ORy.

[0057] In embodiments, each of Rfand Rgare selected from H and C1-6 alkyl, for example H and C1-2 alkyl.

[0058] In embodiments, Rhis selected from H and C1-6 alkyl optionally substituted with -- C(O)ORX, for example H and C1-2 alkyl optionally substituted with -C(O)ORX. In further embodiments, Rhis H or methyl. In embodiments, Rfand Rgare H and Rhis H or methyl. In further embodiments, Z is ORywhere Ryis H or C1-4 alkyl.

[0059] In embodiments, the acrylate-based monomers units of Formula (3) are derived from one or more alkyl esters of acrylic or methacrylic acid such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, ethylhexyl (meth)acrylate.

[0060] In embodiments, the acrylate-based monomer units of Formula (3) are derived from one or more alkyl-ether esters of acrylic or methacrylic acid such as 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxytriethylene glycol (meth)acrylate and polyethylene glycol methyl ether (meth)acrylate.

[0061] Other types of co-monomer (i.e. non acrylate-based monomers) can form part of the silyl acrylate copolymer, including monomers having polymerizable unsaturated carboncarbon bonds.

[0062] In embodiments, these other types of co-monomer are selected from styrenes, olefins, halo-olefins, vinyl ethers and vinyl pyrrolidones.

[0063] In embodiments, other types of co-monomer can be represented by Formula (5):

[0064] CRJ2= CR)RkFormula (5)

[0065] Each Rjis independently selected from H, halide (e.g. selected from F and Cl), and C1-6 alkyl. Rkcan be selected from Rj, C2-6 alkenyl, C6-12 aryl and C6-12 aryl substituted with one or more (e.g. from 1 to 4 or from 1 to 2) C1-6 aliphatic hydrocarbyl groups. In embodiments, only one of Rjand Rkcan be a halide or comprise a halide-containing substituent. In embodiments Rkis C6-12 aryl. In embodiments, the co-monomer can comprise one or more optional substituents, selected from halide, -ORX, -C(O)ORX, - OC(O)ORXand -C(O)NRX2, where Rxis as defined above. In embodiments, the optional substituents are selected from -ORX, and -C(O)ORX. In embodiments the silyl acrylate copolymer is metal free, i.e. it does not comprise any metal cations associated with any anionic groups. For example, in the above definitions, Z = -ORy, any -C(O)ORXgroups are -C(O)ORy, and any -OC(O)ORXgroups are -OC(O)ORy.

[0066] Although metal-containing self-polishing polymer can be present in the antifouling coating composition, their total content is typically no more than 5 wt%, for example no more than 1 wt%. Examples of metal-containing self-polishing polymers include the metal containing hydrolysable resins described in EP0204456. In embodiments, there is no metal-containing self-polishing polymer in the antifouling coating composition.

[0067] In embodiments, the average number of monomer units in the silyl acrylate copolymer can be in the range of from 5 to 1 000, for example from 10 to 500.

[0068] The proportion of silyl acrylate monomer units in the silyl acrylate copolymer can be in the range of from 10 to 90 wt%, for example from 20 to 80 wt%, such as from 30 to 75 wt% or from 40 to 70 wt%. On a molar basis, the proportion of silyl acrylate monomer units in the silyl acrylate copolymer is 5 to 80 mol%, for example 15 to 60 mol% or from 20 to 40 mol%. These quantities can be calculated based on the relative amount of monomers used to make the silyl acrylate copolymer.

[0069] In embodiments, at least 30 wt% of monomer units (including the silyl acrylate monomer units) are acrylate-based monomer units, for example at least 50 wt% or at least 70 wt%. In embodiments, the silyl acrylate copolymer only comprises acrylate-based monomer units.

[0070] The proportion of all acrylate-based monomer units (including the silyl acrylate monomer units) in the silyl acrylate copolymer can be greater than 20 mole%, for example at least 40 mole%, at least 60 mole% or at least 80 mole%. In embodiments, all monomer units are acrylate-based monomer units. Current commercially available silyl acrylate copolymers tend to have at least 95 mole % acrylate-based monomers. [Solvents]

[0071] The antifouling coating composition comprises a polar organic solvent. In embodiments, the antifouling coating composition also comprises a hydrocarbon solvent.

[0072] The hydrocarbon solvent can be aromatic or aliphatic. Mixtures of two or more hydrocarbon solvents can be used. Example solvents include petroleum ether, hexane, isohexane, cyclohexane, octane, isooctane, decane, toluene and xylene, mixed xylenes, ethyl benzene, trimethylenzene, solvent naphtha, isoparaffins, white spirit and kerosene.

[0073] The polar organic solvent can be selected from oxygen-containing organic solvents such as alcohols, ethers, glycol ethers, ketones, esters, and glycolic esters. Specific examples include methanol, ethanol, 1 -propanol, 2-propanol, n-butanol, sec-butanol, iso-butanol, tert-butanol, hexanol, cyclohexanol, methyl acetate, ethyl acetate, n-butyl acetate, diethyl ether, diisopropyl ether, acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), methyl amyl ketone (MAK), methyl isoamylketone (MIAK), diisobutyl ketone, isophorone, cyclohexanone, diacetone alcohol (DAA), ethylene glycol propyl ether (EGPE), ethylene glycol butyl ether (EGBE), ethylene glycol butyl ether acetate (EGBEA), diethylene glycol butyl ether (DEGBE), diethylene glycol butyl ether acetate (DEGBEA), propylene glycol methyl ether (PGME), propylene glycol butyl ether (PGBE), dipropylene glycol methyl ether (DPGME), dipropylene glycol butyl ether (DPGBE), propylene glycol methyl ether acetate (PGMEA).

[0074] In embodiments, the polar organic solvent is an alcohol or ketone or a mixture thereof.

[0075] Hydrocarbon solvents can be present in the antifouling coating composition in amounts of from 0 to 40%, for example from 5 to 40 wt%, from 5 to 30% or from 10 to 25%.

[0076] Polar organic solvents can be present in the antifouling coating composition in amounts of up to 10 wt%, for example up to 8 wt% or up to 5 wt%. In embodiments, the antifouling coating composition comprises at least 0.1 wt% polar organic solvent, for example at least 0.2 wt% polar organic solvent, i.e. it can be present in amounts of from 0.1 to 10 wt%, from 0.1 to 8 wt%, from 0.1 to 5 wt%, from 0.2 to 10 wt%, from 0.2 to 8 wt% or from 0.2 to 5 wt%. [Water]

[0077] In embodiments, the antifouling coating composition is a non-aqueous composition. Therefore, in embodiments, the antifouling coating composition comprises no more than 5 wt%, for example no more than 1 wt% water or no more than 0.5 wt% water.

[0078] [Marine biocides]

[0079] Marine biocides can be classified under three broad categories based on their chemical structure, namely “organic biocides”, “metal-organic biocides” and “inorganic biocides”.

[0080] An “Inorganic biocide” is a biocide having a chemical structure free of organic groups, and covers metals (including alloys), metal oxides and inorganic metal salts.

[0081] An “organic biocide” means a biocide that comprises an organic group and is free of metal atoms or ions.

[0082] A “metal-organic biocide” means a biocide that has a chemical structure comprising one or more metal atoms and one or more organic groups. This includes, for example, metal salts of organic anions and metal-organic complexes.

[0083] The antifouling coating composition comprises one or more organic biocides and one or more metal-organic biocides. The content of each organic biocide is no more than 1 wt% in the antifouling coating composition, for example no more than 0.9 wt%, and is typically at least 0.05 wt%. The content of each metal-organic biocide is also no more than 1 wt%, for example no more than 0.9 wt%, and is typically at least 0.05 wt%.

[0084] In embodiments, the total content of all organic biocide(s) in the antifouling coating composition is no more than 1 wt%, for example no more than 0.9 wt%, with minimum total amounts of 0.05 wt% or more. In embodiments, the total content of metal-organic biocide(s) is also no more than 1 wt%, for example no more than 0.9 wt%, with minimum total amounts of 0.05 wt% or more. Other types of biocides, e.g. inorganic biocides, can also be present in total amounts of up to 60 wt%, for example in the range of from 10 to 60 wt% or 20 to 50 wt%.

[0085] Examples of inorganic biocides include metallic copper and its alloys such as copper bronze and coper nickel alloys, copper compounds such as copper oxide, copper thiocyanate, copper carbonate, copper chloride, and silver salts such as silver chloride or nitrate. In embodiments, the inorganic biocides are selected from copper-containing compounds. In embodiments the antifouling coating composition comprises cuprous oxide, and in further embodiments cuprous oxide is present in amount of at least 20 wt%.

[0086] Metal-organic biocides include zinc pyrithione (the zinc salt of 2-pyridinethiol-1 -oxide), copper pyrithione, bis(N-cyclohexyl-diazeniumdioxy) copper, zinc ethylene- bis(dithiocarbamate) (i.e. zineb), zinc dimethyl dithiocarbamate (ziram), and manganese ethylene-bis(dithiocarbamate) complexed with zinc salt (i.e. mancozeb). In embodiments, the antifouling coating composition comprises at least one of copper pyrithione, zinc pyrithione and zineb (zinc ethylene-bis(dithiocarbamate)).

[0087] Organic biocides include formaldehyde, dodecylguanidine monohydrochloride, thiabendazole, medetomidine, N-trihalomethyl thiophthalimides, trihalomethyl thiosulphamides, N-aryl maleimides such as N-(2,4,6-trichlorophenyl) maleimide, 3-(3,4- dichlorophenyl)-1 ,1 -dimethylurea (diuron), 2,3,5,6-tetrachloro-4-(methylsulphonyl) pyridine, 3-benzo[b]thien-yl-5,6-dihydro-1 ,4,2-oxathiazine 4-oxide, 4,5-dichloro-2-(n- octyl)-3(2H)-isothiazolone, 2,4,5,6-tetrachloroisophthalonitrile, tolylfluanid, dichlofluanid, diiodomethyl-p-tosylsulphone, capsaicin and substituted capsaicins, 3-iodo-2- propynylbutyl carbamate, 1 ,4-dithiaanthraquinone-2,3-dicarbonitrile (dithianon), boranes such as pyridine triphenylborane, 2-trihalogenomethyl-3-halogeno-4-cyano pyrrole derivatives substituted in position 5 and optionally in position 1 , such as 2-(p- chlorophenyl)-3-cyano-4-bromo-5-trifluoromethyl pyrrole (tralopyril), furanones such as 3-butyl-5-(dibromomethylidene)-2(5H)-furanone, butenolide, macrocyclic lactones such as avermectins, for example avermectin B1 , ivermectin, doramectin, abamectin, amamectin and selamectin, and quaternary ammonium salts such as didecyldimethylammonium chloride and an alkyldimethylbenzylammonium chloride. In embodiments, the antifouling coating composition comprises one or more of medetomidine, 4,5-dichloro-2-(n-octyl)-3(2H)-isothiazolone, and 2-(p-chlorophenyl)-3- cyano-4-bromo-5-trifluoromethyl pyrrole (tralopyril).

[0088] The biocide can, in embodiments, be wholly or partially encapsulated, adsorbed, entrapped, supported or bound. Certain biocides are difficult or hazardous to handle and are advantageously used in an encapsulated, entrapped, absorbed, supported, or bound form. Encapsulation, entrapment, absorption, support or binding of the biocide can provide a secondary mechanism for controlling biocide leaching from the coating system in order to achieve an even more gradual release and long-lasting effect. The method of encapsulation, entrapment, adsorption, support or binding of the biocide is not particularly limited. Examples include the use of mono and dual walled aminoformaldehyde or hydrolysed polyvinyl acetate-phenolic resin capsules or microcapsules as described in W02006 / 032019. An example of a suitable encapsulated biocide is encapsulated 4,5-dichloro-2-(n-octyl)-3(2H)-isothiazolone marketed by Dow Microbial Control as Sea-Nine CR2 Marine Antifouling Agent. Examples of ways in which an absorbed or supported or bound biocide may be prepared include the use of host-guest complexes such as clathrates as described in EP0709358, phenolic resins as described in EP0880892, carbon-based adsorbents such as those described in EP1142477, inorganic microporous carriers such as the amorphous silicas, amorphous aluminas, pseudoboehmites or zeolites described in WOOO / 11949, or silica aerogels as described in W02009 / 062975 or W02020 / 002659.

[0089] In embodiments, the antifouling coating composition comprises a metal pyrithione, for example copper pyrithione or zinc pyrithione. In embodiments, the antifouling coating composition comprises cuprous oxide and copper pyrithione. In embodiments, the antifouling coating composition comprises cuprous oxide, copper pyrithione and medetomidine.

[0090] [Pigments and fillers]

[0091] In embodiments, one or more pigments, fillers and / or extenders can be included in the antifouling coating composition. In this context, such pigments, fillers and / or extenders are non-biocidal, in that they do not fall within the definition of biocide provided above. Examples of suitable fillers and extenders include zinc oxide, zinc phosphate, barium sulfate, calcium sulphate, calcium carbonate, silicas or silicates or other minerals (such as talc, wollastonite, dolomite, gypsum, feldspar, and china clay), including pyrogenic silica, bentonite and other clays. Some fillers, such as fumed silica, may have a thixotropic effect on the antifouling coating composition.

[0092] Examples of pigments include colouring pigments such as black iron oxide, red iron oxide, yellow iron oxide, titanium dioxide, carbon black, graphite, red molybdate, yellow molybdate, zinc sulfide, antimony oxide, sodium aluminium sulfosilicates, quinacridones, phthalocyanine blue, phthalocyanine green, indanthrone blue, cobalt aluminium oxide, carbazoledioxazine, chromium oxide, isoindoline orange, bis-acetoaceto-tolidiole, benzimidazolone, quinaphthalone yellow, isoindoline yellow, tetrachloroisoindolinone, quinophthalone yellow, and azo compounds. Pigments can be present in amounts of from 0 to 25 wt%, based on the total weight of the antifouling coating composition.

[0093] In embodiments, where any pigments, fillers or extenders are included, they can constitute in total up to 55 wt% of the antifouling coating composition based on the total weight of the coating composition, for example up to 45 wt%. In embodiments, there is at least 0.1 wt% of these components, for example at least 5 wt%, at least 10 wt%, or at least 20 wt%. Example ranges include from 0.1 to 55 wt%, from 0.1 to 45 wt%, from 5 to 55 wt%, from 5 to 45 wt%, from 10 to 55 wt%, or from 10 to 45 wt%, from 20 to 55 wt% and from 20 to 45 wt%

[0094] [Additional components]

[0095] The antifouling coating composition may optionally also contain other components, for example one or more substances selected from polymers that are free of silyl acrylate monomer units, waxes, rosins, thixotropic agents, dispersing agents, plasticizers, inorganic and organic dehydrators (stabilizers), UV stabilizers, defoamers, reinforcing agents and any combination thereof. These components are well-known to the skilled person. Examples of rosins include gum rosin, wood rosin and tall oil rosin, and also rosin derivatives produced by chemical modification of rosins, for example hydrogenated rosins, partially hydrogenated rosins, disproportionated rosins, polymerised rosins, dimerised rosins, fumarated rosins and maleated rosins. Further examples include metal salts of rosins, such as copper salts, zinc salts, magnesium salts and calcium salts, for example zinc salts and copper salts.

[0096] In embodiments, the antifouling coating composition comprises in total 1 to 45% by weight of rosins.

[0097] In embodiments the weight ratio of silyl acrylate copolymer(s) : rosin(s) in the antifouling coating composition is from 5:95 to 95:5, for example from 20:80 to 80:20 or from 30:70 to 70:30.

[0098] Thixotrope can optionally be present in an amount of up to 5 wt%, for example from 0.1 to 5 wt%, based on the total weight of the antifouling coating composition.

[0099] The total amount of such further optional components can be in the range of from 0 to 30 wt% based on the total content of the antifouling coating composition, typically no more than 10 wt%, or no more than 5 wt%.

[0100] In embodiments, there is no more than 2 wt% of any curable components such as curable resins, crosslinking agents and reactive diluents. In embodiments, there are no more than 1 wt% of such components. In embodiments, the antifouling coating composition is free from such components.

[0101] Further, the antifouling coating composition can optionally comprise non-volatile and non-reactive fluids or oils. They can be selected from polysiloxane oils (for example polydimethyl siloxane, polyphenylmethyl siloxane, and hydrophilic modified polydimethylsiloxane comprising one or more polyethylene glycol, polypropylene glycol or mixed polyethylene / polypropylene glycol groups), fluoropolymers (for example perfluoropolyethers, and hydrocarbon oils, waxes and jellies (for example petrolatum). For example, their content can be 5 wt% or less, such as 3 wt% or less, 1 wt% or less or 0.1 wt% or less. In embodiments there are no such non-volatile and non-reactive fluids or oils

[0102] [Properties of the antifouling coating composition]

[0103] The antifouling coating composition in embodiments has a non-volatile content of 35 wt% or more, based on the entire weight of the coating composition. In further embodiments, the non-volatile content is 50 wt% or more, for example 70 wt% or more. In embodiments the non-volatile content is 85 wt% or less. Non-volatile content can be determined according to ASTM D2697, e.g. D2697-03 (2014).

[0104] In embodiments, the touch dry time of the antifouling coating composition at 23°C is in the range of 52 to 195 minutes

[0105] In embodiments, the hard dry time at 23°C is in the range of 132 to 312 minutes

[0106] [Preparation of the antifouling coating composition]

[0107] The antifouling coating composition may be prepared by any suitable technique, for example by mechanical mixing of the components using conventional equipment including agitation mixers such as anchor, paddle, propellor, turbine and helical mixers, ball mills, bead mills, sand mills and basket mills.

[0108] Typically, the antifouling coating composition is a 1-pack or 1-component (1 K) composition, i.e. the formulation is provided in a single pack, such that no mixing of separate parts is necessary at the point of application.

[0109] [Application of the antifouling coating composition]

[0110] The antifouling coating composition can be applied to a substrate by known methods, for example by conventional air-spraying, or by airless- or airmix-spraying equipment. It can alternatively be applied using brush or roller, for example when applied to smaller vessels including yachts. It can be applied at ambient conditions without pre-heating the coating composition. In spraying applications, conventional pressures such as 3 to 6 bar-a (barabsolute) can be used.

[0111] The antifouling coating composition is typically applied in one or more coats each having a dry film thickness of from 20-500 pm is obtained, such as 30-300 pm or 30-250 pm. The total dry film thickness of the applied antifouling composition is typically 20-1000 pm is obtained, such as 30-800 pm or 40-700 pm. The applied film thickness can be selected depending on the nature of substrate being coated, the speed and activity profile of the substrate, the environment to which it will be exposed and the desired in-service lifetime of the applied coating.

[0112] [Coating systems]

[0113] The antifouling coating composition can be used on its own or can be part of a coating system comprising more than one coating composition. It can be applied directly to a substrate surface or to a previously coated surface. For example, it can be applied on top of a primer, an intermediate coat such as a tie-coat.

[0114] In embodiments, the antifouling coating composition is applied to a previously coated substrate, such that it comprises one or more pre-existing and pre-cured and / or dried coating layers. In embodiments, the antifouling coating composition is applied to an aged coating layer such as an aged antifouling coating. In other embodiments, the antifouling coating composition is applied to a non-aged fouling control composition that is at least partially cured, for example a different antifouling control coating or a foul release coating.

[0115] In embodiments, the antifouling coating composition is applied to a primer layer on the substrate. The origin of the primer layer is not particularly limited, although in embodiments the primer is an epoxy resin-based primer.

[0116] In embodiments, the antifouling coating composition is applied to a tie-coat layer on the substrate, in which the tie-coat layer is optionally on a primer layer on the substrate. In embodiments, the antifouling coating composition forms part of a multi-coat system that additionally comprises a primer and / or a tie-coat.

[0117] In embodiments, a tie-coat layer can be applied on top of the primer layer to assist binding of the antifouling coating composition with the primer layer. In other embodiments, no tie-coat is required.

[0118] [Substrate]

[0119] The substrate to which the coating is applied can be one that is intended to be fully or partially immersed permanently or intermittently in water when in use. Substrates include metal, such as steel or aluminium, concrete, wood or polymeric surfaces.

[0120] Polymeric surfaces include polyvinyl chloride (PVC), or composites of fibre-reinforced resins. They also include flexible polymeric carrier foils, tiles or sheets, e.g. a PVC carrier foil to which the non-coated side is or can be adhered to a different surface.

[0121] In embodiments, the substrate is an immersible surface of a man-made object such as a boat or ship, e.g. selected from one or more of the hull (or at least the draft portion of the hull), the propeller, and the rudder. In embodiments, the immersible surface is part of an offshore structure, for example structures associated with oil and gas exploration and / or production. These can be selected, for example, from oil and / or gas rigs, floating production storage and offloading structures (FPSOs), well heads, pipes and pipelines, offshore wind turbines, tidal energy generators, wave energy generators, and cooling water intakes for power plants.

[0122] Examples

[0123] The invention will now be described with reference to the following, non-limiting examples. [Preparation of antifouling coating compositions]

[0124] Antifouling coating compositions were prepared by mixing the components in the proportions shown (% by weight) in Table 1 using a laboratory high speed disperser (Dispermat).

[0125] Silyl acrylate copolymer, zinc rosinate and polyamide wax were obtained commercially as dispersions in solvents. In Table 1, the wt% values for these components does not include the solvent, the solvents instead being listed separately. The separately quoted solvent values include all sources of the solvent, i.e. specifically added solvent and solvent derived from the dispersions.

[0126] Table 1 - Antifouling Coating Compositions

[0127] 4] Plasticizer

[0128] 2] Colouring pigment

[0129] 3] Filler

[0130] 4] Inorganic biocide

[0131] 5] Metal-organic biocide

[0132] 6] Organic biocide

[0133] 7] Thixotrope [Drying time test]

[0134] Antifouling coating compositions were applied to degreased 1”x12” glass panels using a cube applicator with a 400 pm gap size, and drying time was measured with a mechanical drying time recorder (TQC Sheen Drying Time Recorder) at 23 °C and ambient relative humidity following Test Method A of ASTM D5895-13).

[0135] [Viscosity test]

[0136] The viscosity of the antifouling coating compositions was measured shortly after their preparation using a digital cone and plate viscometer (ViscoMaster CP1 digital cone and plate viscometer, Sheen Instruments) at 25 °C following ASTM D4287-00.

[0137] [Results]

[0138] Results of the drying time and viscosity measurements are shown in Table 2 along with the proportions (% by weight) of total hydrocarbon solvent, total polar solvent, metalorganic biocide and organic biocide in each coating composition.

[0139] Table 2 - Results

[0140] The results show that the drying times for coating compositions with the same polar solvent content are shorter for coating compositions with lower metal-organic biocide content than the corresponding formulations with higher metal-organic biocide content. This is evident when comparing Example 1 with comparative Example 7 (respectively 315 and 530 minutes hard dry time), Example 3 with Comparative Example 6 (respectively 132 and 159 minutes hard dry time), and Example 2 with Comparative Example 5 (respectively 149 minutes and 198 minutes hard dry time).

[0141] Additionally, the results show a benefit of higher amounts of polar organic solvent. The drying times for coating compositions with the same total solvent content tend to be shorter for coating compositions with higher ratios of polar solvent. In addition, the viscosity of coating compositions with the same total solvent content tends to be lower for coating compositions with higher ratios of polar organic solvent.

[0142] Overall, the results show that reducing the level of metal-organic biocide in the antifouling coating composition leads to a significant reduction in drying time, and that drying times can be further reduced by increasing the proportion of polar solvent in the coating composition. Furthermore, the viscosity of the coating compositions can also be reduced by increasing the proportion of polar organic solvent in the coating composition.

[0143] Faster drying times are desirable since they reduce the time taken to complete the coating process, and hence improve throughput. Lower viscosities are also desirable as they can ensure efficient application of the coating, particularly when using spray techniques.

Claims

CLAIMS1. An antifouling self-polishing coating composition comprising: a silyl-acrylate copolymer one or more metal-organic biocides, each of which is present at no more than 1 wt%; one or more organic biocides, each of which is present at no more than 1 wt% a polar organic solvent.

2. The antifouling self-polishing coating composition as claimed in claim 1 , in which the amount of silyl acrylate copolymer is in the range of from 1 to 80 wt%.

3. The antifouling self-polishing coating composition as claimed in claim 1 or claim2, in which the total amount of polar organic solvent in present in an amount of 0.1 to 10 wt%.

4. The antifouling self-polishing coating composition as claimed in any one of claims 1 to 3, additionally comprising a hydrocarbon solvent.

5. The antifouling self-polishing coating composition as claimed in claim 4, in which the total amount of hydrocarbon solvent is in the range of from 5 to 40 wt%.

6. The antifouling self-polishing coating composition as claimed in any one of claims 1 to 5, in which the amount of metal-containing polymers is no more than 5 wt%.

7. The antifouling self-polishing coating composition as claimed in any one of claims 1 to 6, additionally comprising one or more inorganic biocides, their total amount being up to 60 wt%.

8. The antifouling self-polishing coating composition as claimed in any one of claims 1 to 7, additionally comprising one or more rosins, their total amount being in the range of from 1 to 45 wt%.

9. The antifouling self-polishing coating composition as claimed in any one of claims 1 to 8, in which the silyl acrylate copolymer is thermoplastic.

10. The antifouling self-polishing coating composition as claimed in any one of claims 1 to 9, comprising cuprous oxide and copper pyrithione.

11. The antifouling self-polishing coating composition as claimed in any one of claims 1 to 10, in which the silyl acrylate copolymer is metal free.

12. A method of protecting a substrate against aquatic biofouling, where the substrate is intended to be fully or partially immersed in water when in use, the method comprising applying an antifouling self-polishing coating composition as claimed in any one of claims 1 to 11 to the substrate and allowing it to dry.

13. The method as claimed in claim 12, in which the substrate is selected from immersible surfaces of boats, ships, oil and / or gas drilling rigs, floating production storage and offloading structures (FPSOs), well heads, pipes and pipelines, offshore wind turbines, tidal energy generators, wave energy generators, and cooling water intakes for power plants.

14. The method as claimed in claim 12 or claim 13, in which the substrate is precoated with a primer layer and / or a tie-coat layer.

15. The use of an antifouling coating composition as claimed in any one of claims 1 to 11 for protecting a substrate against aquatic biofouling, where the substrate is intended to be fully or partially immersed in water when in use.

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