Anticorrosive primer coating composition

Abstract

The invention relates to an anticorrosive primer coating composition and to a method of coating it onto a metallic surface, the anticorrosive coating composition comprising: from 15 to 45 wt% of bisphenol epoxy resin; from 7 to 25 wt% of curing agent; from 4 to 15 wt% of epoxy reactive diluent from 0.1 to 8 wt% of (alkoxysilyl)alkylamine; and no more than 15 wt% solvent.

Description

[0001]

[0002] ANTICORROSIVE PRIMER COATING COMPOSITION

[0003] Technical Field

[0004] This invention relates to an anticorrosive primer coating composition, in particular a low solvent / high solids anticorrosive primer coating composition. The invention also relates to a method for protecting a metallic substrate against corrosion by applying such a coating to the metallic substrate.

[0005] Background Art

[0006] Epoxy-amine based coatings are essential in the protective and marine coatings industries due to their versatility and their effective corrosion resistance performance. They can be used as intermediate coats over zinc-rich primers or as direct-to-metal primers. However, they often contain organic solvents which can be significant sources of Volatile Organic Compounds (VOCs) which are facing increasing scrutiny.

[0007] Solvent levels in primer compositions can be reduced, and low-VOC and so-called “ultra- high solid” (UHS) coatings have been described, for example in W02018 / 046702 and WO2021 / 110829. However, there remains a need for alternative low solvent anticorrosive primer coating compositions which perform adequately as anticorrosive primers, while still meeting legislative requirements.

[0008] Summary of Invention

[0009] The invention is directed towards an anticorrosive primer coating composition that comprises:

[0010] 15 to 45 wt% of bisphenol epoxy resin;

[0011] 7 to 25 wt% of curing agent;

[0012] 4 to 15 wt% of epoxy reactive diluent

[0013] 0.1 to 8 wt% of (alkoxysilyl)alkylamine; and no more than 15 wt% solvent.

[0014] The invention is also directed towards a method for protecting a metallic substrate against corrosion by applying such an anticorrosive primer coating composition to the substrate and allowing it to cure.

[0015] Description of Embodiments

[0016] [Bisphenol epoxy resin]

[0017] The anticorrosive primer coating composition comprises at least one bisphenol epoxy resin, which can be selected from bisphenol A and bisphenol F epoxy resins.

[0018] In embodiments, the one or more bisphenol epoxy resins are predominantly selected from bisphenol A epoxy resins, with other bisphenol epoxy resins being present in minor amounts. Thus, the amount of bisphenol A epoxy resin based on the total amount of bisphenol epoxy resins is 60 wt% or more, for example 80 wt% or more or 90 wt% or more. In embodiments, the anticorrosive primer coating composition comprises bisphenol A epoxy as the only type of resin.

[0019] The bisphenol epoxy resin is typically liquid under ambient conditions (23 °C, atmospheric pressure, i.e. 1.013 bar-absolute) and has a viscosity in the range of from 1 000 to 25 000 mPas at 25 °C, for example 5 000 to 20 000 mPas or from 8 000 to 17 000 mPas . It also typically has an epoxy equivalent weight (EEW) in the range of from 155 to 265, for example from 160 to 220, or from 170 to 200 g / eq.

[0020] One or more bisphenol epoxy resins can be used. The total amount of bisphenol epoxy resin in the coating composition is in the range of from 15 to 45 wt% based on the total coating composition. In embodiments the amount is in the range of from 20 to 40 wt%, for example from 22 to 34 wt%.

[0021] In embodiments, other resins can be present, for example other types of epoxy resin such as novolac epoxy resins, vinyl resins, alkyd resins or acrylic resins. However, in embodiments, there are no more than 5 wt% of other types of resins in the anticorrosive primer coating composition, for example no more than 1 wt% or no more than 0.5 wt%. In embodiments, there no other resins.

[0022] Resins are generally defined as reactive components that, when cured, are capable of forming a coating film. They are distinct from other reactive components such as coupling agents or reactive diluents, which are not themselves capable of forming a coating film when cured, or at least are not capable of forming a cured film that is sufficiently robust to function as a coating.

[0023] [Curing agent]

[0024] The anticorrosive coating composition comprises one or more curing agents. The curing agents in embodiments are selected from amine curing agents, which comprise one or more -NH bonds that are reactive with an epoxy group to form urethane links. The -NH bonds of the curing agent are present in one or more amine groups selected from primary and secondary amine groups. Typically, the curing agent has a minimum of two such amine groups.

[0025] At least one amine group on the curing agent has at least one active hydrogen (an -NH group), i.e. the curing agent has at least one primary or secondary amine group. In embodiments there are at least two amine groups that are primary or secondary amine groups. In embodiments all the amine groups are primary or secondary amine groups. Typically, the amine curing agent has on average at least two active hydrogens per molecule. Typically, the curing agent does not contain silicon atoms.

[0026] Various types of curing agent can be used, e.g. aliphatic amines, cycloaliphatic amines, Mannich base amines and aromatic amines.

[0027] Examples of aliphatic amines include alkyleneamines, such as those of Formula (1) Formula (1) where each Rdand Rgis independently selected from H and C1-4 alkyl, such as from H and C1-2 alkyl, k is from 1 to 3, such as from 2 to 3, and m is from 1 to 5, for example from 2 to 4.

[0028] At least one and preferably at least two Rdgroups are H. In embodiments, all Rdare selected from H and C1-2 alkyl, and in further embodiments only one Rdgroup is other than H. In embodiments, all Rgare selected from H and C1-2 alkyl.

[0029] Rdand Rgcan optionally be substituted with one or more groups (typically one group) selected from -OR*, -NR*2, and halide (typically Cl or Br). In embodiments, the optional substituents are selected from -OR* or -NR*2. Typically, the optional substituents are selected from -NR*2.

[0030] Each R* is independently selected from H, C1-6 alkyl and C1-6 haloalkyl. In embodiments, R* is selected from H and C1-6 alkyl, for example H and C1-4 alkyl.

[0031] In embodiments, each k is 2, and Rdand Rgare each independently and on each occurrence selected from H and C1-2 alkyl optionally substituted with NR*2. In embodiments, all Rdand Rggroups are hydrogen.

[0032] Examples include ethyleneamines such as ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA) and tetraethylenepentamine (TEPA).

[0033] Cyclic aliphatic amines (cycloaliphatic amines) comprise at least one cyclic aliphatic group bound directly to a primary or secondary amine. The cycloaliphatic amine curing agent can be selected from monomeric, dimeric, oligomeric, or polymeric cycloaliphatic amines, or a mixture of any two or more thereof.

[0034] Examples of monocyclic cycloaliphatic amines include para-aminodicyclohexyl methane (or bis(4-aminocyclohexyl)methane, often abbreviated as PACM), 2,4’- diaminodicyclohexylmethane, 2,2’-diaminodicyclohexylmethane, 3,3’-dimethyl-4,4’- diaminodicyclohexylmethane, bis(4-amino-3-methylcyclohexyl) methane, N-cyclohexyl- 1 ,3-propanediamine, 1 ,2-diaminocyclohexane, N-aminoethyl piperazine, 3-

[0035] (cyclohexylamino) propylamine, piperazine, N-aminopiperazine, 4-methylcyclohexane- 1 ,3-diamine, isophorone diamine, and 1 ,3-bis(aminomethyl)cyclohexane.

[0036] Examples of aliphatic amines also include amines that can comprise an aromatic or heteroaromatic ring, but where the amine groups are bound to an aliphatic carbon and not directly to the (hetero)aromatic ring. Examples of such amines would include m- xylylenediamine (MXDA) and 1 ,4-bis(aminomethyl)benzene.

[0037] Aromatic amines include amine compounds where the amine moiety is bound directly to an aromatic or heteroaromatic ring. They can additionally comprise cyclic or non-cyclic aliphatic components. In embodiments, the aromatic or heteroaromatic ring is a 6- membered ring. In embodiments, the ring is aromatic (not heteroaromatic). Examples of aromatic amines include 1 ,3-diaminobenzene.

[0038] Mannich base amines are based the reaction product of a phenol compound (e.g. phenol, cresol or resorcinol) with an aldehyde or ketone (e.g. formaldehyde or acetone) and an amine (e.g. polyamines such as 1 ,3-diaminobenzene, EDA, DETA, MXDA or 1 ,4- bis(aminomethyl)benzene). Examples of Mannich base amines include those formed from phenol, formaldehyde and a polyamine such as MXDA.

[0039] Examples of Mannich base amines include those of Formula (2):

[0040] Formula (2)

[0041] Rd, Rgand k are as defined above, each f, q and r are independently and on each occurrence selected from whole numbers in the range of from 0 to 3, and w is an integer in the range of from 1 to 3.

[0042] A2is a phenol, i.e. a benzene ring having one or more hydroxy substituents, and one or more further optional substituents selected from C1-30 aliphatic hydrocarbyl (e.g. Ci- alkyl or C2-24 alkenyl), C1-6 alkoxy, C1-6 haloalkyl, C1-6 haloalkoxy, and halide. Where a halogen is present (i.e. as halide, or on a haloalkyl or haloalkoxy group), it is typically selected from F and Cl. In embodiments, no halogen is present.

[0043] Each Ar1is independently selected from aromatic and heteroaromatic groups, e.g. groups with a 5- or 6-membered aromatic or heteroaromatic ring, typically 6-membered (hetero)aromatic rings. Heteroatoms in the heteroaromatic group can be selected from one or more O, S and N atoms, for example from 1 to 3 heteroatoms. In embodiments, Ar1is aromatic (i.e. not heteroaromatic). The aromatic or heteroaromatic group can optionally be substituted with one or more substituents selected from C1-30 aliphatic hydrocarbyl (e.g. Ci- alkyl or C2-24 alkenyl), C1-6 alkoxy, C1-6 haloalkyl, C1-6 haloalkoxy, halide and hydroxy. Where halogen is present (i.e. as halide, or on a haloalkyl or haloalkoxy group), it is typically selected from F and Cl. In embodiments, no halogen is present. In embodiments, the optional substituent is selected from C1-2 alkyl. In embodiments all Ar1groups are the same. In embodiments, Ar1comprises a single benzene ring.

[0044] At least one Rdgroup is H. In embodiments, at least two Rdgroups are H. In embodiments, all Rdand Rggroups are hydrogen.

[0045] In embodiments, Ar2is substituted with one hydroxy group and optionally also a C1-30 aliphatic hydrocarbyl group. In embodiments, Ar2comprises no substituents other than hydroxy and C1-24 aliphatic hydrocarbyl.

[0046] In embodiments, w is 1.

[0047] In embodiments, f is at least 1 , and in further embodiments, f is 1.

[0048] In embodiments, all occurrences of k are independently selected from 1 or 2.

[0049] In embodiments, w is 1 , all Rdand Rgare H, r is from 0 to 3, q is 0, and all occurrences of k are independently selected from 1 to 3.

[0050] The phenol that us used to make a Mannich base curing agent (i.e. Ar2) can be substituted or unsubstituted. In embodiments, the Mannich base curing agent is substituted (in addition to the one or more amine-containing groups) with one or more Ci to C30 aliphatic hydrocarbyl groups, for example Cs-20 or C12-18 aliphatic hydrocarbyl groups. The aliphatic hydrocarbyl group(s) can comprise unsaturated bonds, for example up to 4 carbon-carbon double bonds, for example from 0 to 3 or from 1 to 3 double bonds. The group can be at an ortho, meta or para position to the hydroxy group on the phenol.

[0051] In embodiments there can be more than one aliphatic hydrocarbyl substituent on the phenol, for example from 1 to 3 substituents, although in embodiments there is only one. In further embodiments there is only one aliphatic hydrocarbyl substituent at a metaposition.

[0052] In embodiments, the Mannich base curing agent is selected from phenalkamines, which are derived from natural phenols present in cashew nut shell liquid (CNSL). One example of a phenol that is derived from CNSL is cardanol, which has a C15 unsaturated aliphatic hydrocarbyl chain (with two double bonds) at the meta position.

[0053] In embodiments, the phenalkamine comprises a fully aliphatic amine component, i.e. the curing agent is made from the reaction of cardanol, formaldehyde and an alkyleneamine such as EDA, DETA or TETA. In further embodiments, with reference to Formula (2), q =0, w = 1 , r = 1 or 2, each k is 1 or 2, and all Rdand Rgare H. In embodiments, the phenalkamine is made from cardanol, formaldehyde and EDA.

[0054] Mannich base curing agents (such as phenalkamines) often contain residual amine, i.e. amine that has not reacted during its preparation. In embodiments, the amount of this free amine is no more than 10 wt%, for example no more than 5 wt%, based on the source of Mannich base curing agent (or phenalkamine).

[0055] In embodiments, the one or more curing agents are provided in a solvent-free form, with a viscosity in the range of from 500 to 10000 mPas at 25 °C, for example in the range of from 800 to 5000 mPas or from 1500 to 3000 mPas at 25 °C.

[0056] One or more curing agents can be used in the anticorrosive primer coating composition. The total amount used is in the range of from 7 to 25 wt% based on the total coating composition. In embodiments the amount is in the range of from 10 to 20 wt%, for example from 12 to 18 wt%.

[0057] In embodiments, at least 90 wt% of all curing agents used are Mannich base curing agents, and in other embodiments at least 90 wt% of all curing agents are phenalkamines. In such embodiments, other curing agents constitute no more than 10 wt%, for example no more than 5 wt%. or no more than 2 wt% of all the curing agents.

[0058] [Catalysts / Accelerators]

[0059] One or more catalysts (or accelerators) can be used to speed up the curing reaction. In embodiments they are selected from compounds containing one or more dialkylaminoalkyl- moieties, e.g. of formula -(CH2)eNRe2, where e is from 1 to 4, and Reis selected from C1-4 alkyl. Examples include tertiaryalkylaminophenols, such as tris(dimethylaminomethyl)phenol.

[0060] In embodiments, they can be present in amounts of up to 3 wt%, for example in the range of from 0.1 to 2 wt% or from 0.2 to 1 .5 wt%.

[0061] [Epoxy reactive diluent]

[0062] Epoxy-containing reactive diluents are widely used components of coating compositions. They are reactive species that can participate in the curing reaction. They have lower viscosities than the bisphenol epoxy resins and help to lower viscosity of the coating composition.

[0063] The epoxy reactive diluents can be monofunctional, having one epoxy group per molecule, or they can be polyfunctional, for example having two or more epoxy groups per molecule.

[0064] Examples of epoxy reactive diluents include phenyl glycidyl ether, C1-30 alkyl phenyl glycidyl ethers (e.g. C1-12 or C1-5 alkyl phenyl glycidyl ethers such as methyl phenyl glycidyl ether, ethyl phenyl glycidyl ether, propyl phenyl glycidyl ether and para t-butyl phenyl glycidyl ether), and glycidyl esters of carboxylic acids (e.g. glycidyl esters of fatty acids or versatic acids such as pivalic acid or neodecanoic acid).

[0065] Further examples include alkyl glycidyl ethers, e.g. C1-6 alkyl glycidyl ethers which include glycidyl ethers of di- and polyhydric aliphatic alcohols such as hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, trimethylolpropane triglycidyl ether, glycerol triglycidylether, pentaerythritol tetraglycidyl ether, di pentaerythritol polyglycidyl ethers, butanediol diglycidyl ether, neopentylglycol diglycidyl ether, and sorbitol glycidyl ether.

[0066] Still further examples include glycidyl ethers of an aliphatic ether or polyether, e.g. dipropyleneglycol diglycidyl ether.

[0067] They can also be made by epoxidation of unsaturated fats and oils, for example unsaturated fatty acids, diglycerides or triglycerides having C4-30 fatty acid or fatty acid ester groups, and phenols having C4-30 aliphatic chains. An example is Cardolite™ NC- 513, which is made by reacting epichlorohydrin with cardanol, which can be obtained from the shells of cashew nuts.

[0068] The reactive diluent can also be selected from epoxidized olefins, including dienes and polydienes. They can be C2-30, Ce-28, Ce-is, C14-16 or C6-12 epoxidised olefins.

[0069] In embodiments, the epoxy reactive diluent is a mono- or di-functional reactive diluent, and in further embodiments it is a di-functional reactive diluent derived from an aliphatic diol, which can be selected from a C4-C6 aliphatic diol such as 1 ,4-butanediol or 1 ,6- hexanediol.

[0070] Other types of reactive diluent can be present, although in minor amounts. In embodiments, epoxy reactive diluents make up at least 60 wt% of all reactive diluents in the anticorrosive primer coating composition, and in further embodiments at least 75 wt% or at least 90 wt% of all reactive diluents. In still further embodiments, the only reactive diluents used in the coating composition are epoxy reactive diluents.

[0071] One or more than one epoxy reactive diluent can be used. The total amount of epoxy reactive diluent in the anticorrosive primer coating composition is in the range of from 4 to 15 wt%, for example from 5 to 10 wt%.

[0072] [(Alkoxysilyl)alkylamine]

[0073] The anticorrosive primer coating composition comprises an (alkoxysilyl)alkylamine. This is a type of coupling agent. Coupling agents are generally used to improve adhesion to the substrate. They are often relatively small molecules (compared to resins or reactive diluents) and will generally have two or more reactive groups.

[0074] In embodiments, the (alkoxysilyl)alkylamine is of Formula (3)

[0075] [(RxO)xRySi - (CH2)a]b- N - [(CH2)C- NH]dH Formula (3)

[0076] Each Rxand Ryare independently selected form C1-8 alkyl, for example C1-4 alkyl. In embodiments, they are selected from C1-2 alkyl and jn further embodiments from Ci alkyl. x is an integer in the range of from 1 to 3. y is a whole number in the range of from 3-x. In embodiments, x is 2 or 3, and in further embodiments x is 3. a is an integer in the range of from 1 to 4, for example from 2 to 4. In embodiments a is 3. b is an integer in the range of from 1 to 2. c is an integer in the range of from 1 to 4, for example from 2 to 3. In embodiments, c is 2. d is a whole number in the range of from 0 to 2, for example from 0 to 1.

[0077] In embodiments, x is 3, a is 3, b is 1 or 2, c is 2, d is 0 or 1 and all Rxare methyl.

[0078] In embodiments, x is 3, a is 3, b is 1 , c is 2, d is 0 or 1 and all Rxare methyl.

[0079] In embodiments, x is 3, a is 3, b is 2, d is 0 and all Rxare methyl.

[0080] Specific examples include (trimethoxysilane)propylamine, N-[3- (trimethoxysilyl)propyl]ethylenediamine and bis[(trimethoxysilyl)propyl]amine.

[0081] Other types of coupling agents can be present, for example epoxy-containing coupling agents such as (alkoxysilyl)epoxyalkanes (exemplified by glycidoxypropyltrimethoxysilane). However, these are in the minority. In embodiments, (alkoxysilyl)alkylamines make up at least 60 wt% of all coupling agents in the anticorrosive primer coating composition, for example at least 75 wt% or at least 90 wt% of all coupling agents. In embodiments, all coupling agents used are (alkoxysilyl)alkylamine coupling agents.

[0082] If there are epoxy-containing coupling agents present in the coating composition, their concentration is preferably maintained at no more than 1 .5 wt% based on the coating composition and typically their amount is no more than 1.0 wt%. If they are present, they are in amount of at least 0.1 wt%, for example in the range of from 0.1 to 1 .5 wt% or 0.1 to 1.0 wt%.

[0083] One or more (alkoxysilyl)alkylamines can be used. They are present in the anticorrosive primer coating composition in amounts of from 0.1 to 8 wt%, for example from 0.4 to 8 wt%. In other embodiments, the anticorrosive primer coating composition comprises from 0.1 to 6 wt%, for example from 0.4 to 6 wt% (alkoxysilyl)alkylamine.

[0084] Particularly advantageous (alkoxysilyl)alkylamines are those comprising trimethoxysilylpropyl groups directly attached to the nitrogen of an amine or ethylenediamine group, for example (trimethoxysilane)propylamine, N-[3- (trimethoxysilyl)propyl]ethylenediamine and bis[(trimethoxysilyl)propyl]amine. These materials are less hazardous than many conventional amine- and amide-based curing agents, yet they can be used without sacrificing other requirements of the anticorrosive primer coating composition, in particular drying times, corrosion resistance efficacy and low viscosity.

[0085] [Solvent]

[0086] The anticorrosive primer coating composition can comprise one or more organic solvents in amounts of no more than 15 wt%. When solvent is present, it can be selected from hydrocarbons and oxygen-containing solvents, for example being selected from alkyl aromatic hydrocarbons (such as xylene and toluene), alcohols, ethers, ketones and esters (such as methyl ethyl ketone, methyl isobutyl ketone, methoxypropanol, butyl acetate, benzyl alcohol, octyl phenol, resorcinol, n-butanol, isobutanol and isopropanol). In embodiments, the solvent comprises from 2 to 20 carbon atoms, for example from 3 to 15 carbon atoms.

[0087] In embodiments, the solids volume of the anticorrosive primer coating composition (measured according to ASTM D5201-05) is at least 85%.

[0088] In embodiments, hydrocarbon solvents only are used, and in further embodiments the solvent is xylene.

[0089] The anticorrosive primer coating composition is typically non-aqueous, in that no water is added to the composition. In embodiments, the anticorrosive primer coating composition comprises no more than 1 wt% water, for example no more than 0.5 wt% water or no more than 0.1 wt% water. In embodiments, the anticorrosive primer coating composition comprises no water.

[0090] [Aluminium]

[0091] The anticorrosive primer coating composition typically comprises an aluminium pigment, which in embodiments is present in the coating composition in amounts of at least s wt%, for example in the range of from 3 to 11 wt%, such as from 4 to 11 wt% or from 5 to 10 wt%. It can be provided in metallic form or as part of an alloy. Where provided in alloy form, the wt% values above apply to the weight of the alloy.

[0092] The aluminium can be provided in the form of a paste or slurry, for example as a paste or dispersion in a hydrocarbon solvent.

[0093] [Other Ingredients]

[0094] The coating composition can comprise other components, for example one or more auxiliary anti-corrosion additives, pigments (other than aluminium), fillers and extenders, crosslinking catalysts, thixotropic agents, plasticizers, inorganic and organic dehydrators (stabilizers), UV stabilizers, antifouling agents, defoamers or combinations thereof.

[0095] The total amount of such further optional components can be no more than 65 wt%, for example no more than 50 wt%.

[0096] Fillers and extenders include those with a low oil absorption value, such as barium sulfate (including baryte), glass spheres, feldspar, calcite, silica, aluminum oxide, zirconium oxide, dolomite, kaolin or wollastonite and optionally a laminar type of extender such as mica, talc, aluminum flakes, chlorite and china clay. One or more fillers can be used. In embodiments, the amount of filler in the coating composition can be in the range of from 20.0 to 50.0 wt%.

[0097] Examples of inorganic auxiliary corrosion inhibitors include polyphosphates (for example calcium aluminium polyphosphate and strontium aluminium polyphosphate), silicates (such as potassium silicate and aluminium silicate), hydrogen phosphates (such as calcium hydrogen phosphate, magnesium hydrogen phosphate, and strontium hydrogen phosphate), phosphates (such as zinc phosphate, zinc orthophosphate, zinc orthophosphate hydrate, zinc aluminium orthophosphate, and organically modified basic zinc orthophosphate), phosphosilicates (such as calcium strontium phosphosilicate and strontium zinc phosphosilicate), borophosphates (such as strontium borophosphate), molybdates, tungstates, vanadates, and metals (such as zinc dust, zinc powder, zinc alloy, magnesium, and magnesium alloy).

[0098] Examples of organic auxiliary corrosion inhibitors include azoles, such as imidazoles, thiazoles, tetrazoles, and triazoles, e.g. (substituted) benzotriazole, and 2- mercaptobenzothiazole; amines, such as N-phenyl-1 ,4-phenylenediamine and Schiff bases such as N,N’ o-phenylene-bis(3-methoxysalicylidenimine); amino acids, such as tryptophan thiole group-containing compounds such as DMTD (2-5,dimercapto-1 ,3,4- thiadiazole) and 1 -phenyl-2, 5-dithiohydrazodicarbonamide; phthalazine derivatives, such as 2-[(7-anilino-5-[1 ,2,4]triazolo[3,4-b][1 ,3,4]thiadiazine-3-yl)methyl]phthalazine- 1 (2H)-one; tannins and substituted uracils; phosphonic acid group-containing materials, such as styrenephosphonic acid; succinic acid; (benzothiazol-2-ylthio) succinic acid; fatty acid derivatives such as triethanolamine-linoleic acid and tall oil fatty acid salts; and sulphonates.

[0099] More than one auxiliary corrosion inhibitor can be used, although in embodiments they are present in amounts of no more than 10 wt% based on the total anticorrosion primer coating composition.

[0100] [Preparation of the Coating Composition]

[0101] The coating composition may be prepared by any suitable technique.

[0102] In embodiments, the constituents are mechanically mixed, for example using a highspeed disperser, a ball mill, a pearl mill, a three-roll mill or an inline mixer.

[0103] The compositions may be filtered, for example using bag filters, patron filters, wire gap filters, wedge wire filters, metal edge filters, EGLM tumoclean filters (ex Cuno), DELTA strain filters (ex Cuno), and Jenag Strainer filters (ex Jenag), or by vibration filtration.

[0104] In an embodiment, the anticorrosive primer coating composition can be provided in two or more parts, in which the compounds comprising epoxy groups (e.g. epoxy resin and epoxy reactive diluent) are included in one component (part A) and the curing agents are included in a separate component (part B). Optionally, the (alkoxysilyl)alkylamine can be included in the part B component, or alternatively can form part of a separate component.

[0105] When needed, the different components can be mixed and stirred until homogeneous. The mixture can then be applied to a substrate, optionally after a prior induction time.

[0106] [Application of the Coating Composition]

[0107] The coating composition can be applied to a substrate (for example a steel structure) by known methods, for example by conventional air-spraying, by airless- or airmix-spraying equipment, or by 2K airless spray pumps. It can alternatively be applied using brush or roller, for example when used as a stripe coat. The composition can be applied at ambient conditions without pre-heating the coating composition. In spraying applications, conventional pressures such as 3 to 5 bars can be used.

[0108] The coating is typically applied so that a total dry film thickness of from 100-1000 pm is obtained, such as 100-500 pm or 150-350 pm. The applied film thickness can vary depending on the nature of substrate being coated and the environment to which it will be exposed.

[0109] [Drying and Curing Characteristics]

[0110] The anticorrosive coating composition is typically provided in 2 of more parts (or 2 or more components), where the epoxy-containing components are kept separate from the components with which they react, i.e. any curing agents or amine-containing coupling agents such as the (alkoxysilyl)alkylamines.

[0111] The coating composition is typically self-curing, i.e. is able to self-cure once the curing agent and epoxy resin components are mixed, without the need for any additional initiation process, e.g. heat. Curing can take place at ambient temperature, for example in the range of from -10 to 50 °C or from 0 to 40 °C. Heat can optionally be applied should the rate of curing need to be accelerated for any reason.

[0112] The coating can be applied as a coating layer. In addition, since the VOC and solvent content is low, it also is possible to apply a further coating whilst the first layer is “wet”. This enables rapid build-up of layers to create a thicker coating in a shorter period of time. It is also possible to wait until the first layer is cured before applying subsequent layers.

[0113] It has been found that the use of (alkoxysilyl)alkylamines can be advantageous in increasing storage stability of the coating compositions. This is particularly the case for coating compositions comprising 2 or more-components. It has been found that use of alternative coupling agents, such as epoxy-containing coupling agents, bubbling can occur during storage, particularly in aluminium containing compositions. Use of (alkoxysilyl)alkylamines can avoid this happening, not least because they can be included in the curing component instead of the binder component of the coating composition.

[0114] Another problem associated with alternative coupling agents in 2- or more-component compositions is that, after aging for a period of time, the initial viscosity of the coating composition after mixing the different components can be higher than the initial viscosity of freshly prepared components. The use of the (alkoxysilyl)alkylamines helps to avoid this problem.

[0115] Thus, in embodiments, the anticorrosive coating composition comprises a binder component and a curing component, in which the binder component comprises the epoxy-containing compounds such as the epoxy resin(s) and epoxy reactive diluent(s), the binder component comprises the curing agent(s), and the (alkoxysilyl)alkylamine is provided either with the curing component or as a separate component. Typically, the (alkoxysilyl)alkylamine will form part of the curing component, and in embodiments the viscosity of the curing component is 360 cps or less at 25 °C, for example in the range of from 100 to 360 cps or from 100 to 300 cps at 25 °C. Viscosities can be measured by method ASTM D4287(2019).

[0116] In embodiments, the concentration of epoxy-containing coupling agents (e.g. epoxysilane-based coupling agents such as (alkoxysilyl)epoxyalkanes) in the anticorrosive primer coating composition is no more than 1.5 wt%.

[0117] [Metallic substrate]

[0118] The anticorrosive primer coating composition can be applied to a metallic substrate, for example an iron, steel or aluminium substrate.

[0119] In embodiments, the substrate is part of a structure which is exposed to the elements, such as wind, rain, ice or snow. In further embodiments, the structure can be exposed to sea-water, freshwater or brackish water environments, for example in an off-shore platform, a wind turbine, a ship or other water-borne vehicle. The coating composition is particularly suited to substrates that are submerged for extended periods of time, i.e. ship hulls, ship ballast tanks, ship propellors or sub-surface metallic portions of fixed or floating platforms or shoreside structures.

[0120] The substrate surface to which the coating is applied does not necessarily have to be on the external surface of the structure. For example, the substrate can be the inside surface of a ballast tank or storage tank, such as a potable water tank.

[0121] The anticorrosive primer coating composition forms a layer on the substrate. It can be used on its own, e.g. where is used as a ballast tank coating. In other embodiments, it can form part of a coating system comprising more than one coating composition. For example, it can be used in a coating system in combination with one or more topcoats, which can be selected from cleartop coats and pigmented top coats. Any coating layers can optionally be overcoated, for example to give improved UV radiation or antifouling protection, or to improve colour stability.

[0122] The coating composition can be coated on a pre-treated substrate, for example on top of a previously applied coating layer. In embodiments, the coating composition is a primer composition, on which other coating layers are optionally added. In further embodiments, the coating composition is a universal primer composition.

[0123] [Other considerations]

[0124] In embodiments, the anticorrosive coating composition comprises no more than 5 wt% of components that have a GHS classification [H314] (causes severe burns and eye damage). This rating is commonly associated with many amine or amide curing agents.

[0125] An anticorrosive primer coating composition in which phenalkamines are used as the predominant curing agent and (alkoxysilyl)alkylamines according to Formula (3) are used as the predominant coupling agent can have an improved safety profile compared to conventional primer compositions, while maintaining other important characteristics of the primer composition, in particular viscosity (ensuring it remains low enough to allow application of the composition by spray techniques, particularly airless spray techniques), anticorrosive properties, and drying times.

[0126] By predominant is meant at least 90 wt% of all curing agents (or coupling agents), for example at least 95 wt% or even 100 wt% of all curing agents (or coupling agents).

[0127] In embodiments, this can be achieved by means of an anticorrosive primer coating composition comprising from 15 to 45 wt% of bisphenol epoxy resin; from 7 to 25 wt% of phenalkamine curing agent; from 4 to 15 wt% of epoxy reactive diluent; and from 0.1 to 8 wt% of (alkoxysilyl)alkylamine.

[0128] The (alkoxysilyl)alkylamine is selected from (trimethoxysilane)propylamine, N-[3- (trimethoxysilyl)propyl]ethylenediamine and bis[(trimethoxysilyl)propyl]amine, and the total weight% of all components (including those that are not specified) is 100 wt%.

[0129] In embodiments, the anticorrosive primer coating consists of: from 15 to 45 wt% of bisphenol epoxy resin; from 7 to 25 wt% of phenalkamine curing agent; from 4 to 15 wt% of epoxy reactive diluent; from 0.1 to 8 wt% of (alkoxysilyl)alkylamine; from 5 to 11 wt% of aluminium pigment; no more than 15 wt% solvent; up to 50 wt% one or more other components as described above

[0130] The (alkoxysilyl)alkylamine is selected from (trimethoxysilane)propylamine, N-[3- (trimethoxysilyl)propyl]ethylenediamine and bis[(trimethoxysilyl)propyl]amine, and the total weight% of all components is 100 wt%.

[0131] In embodiments, such anticorrosive primer coating compositions comprise no more than 1.5 wt% of epoxy-containing coupling agents (e.g. (alkoxysilyl)epoxyalkane coupling agents).

[0132] Examples

[0133] The invention will now be described with reference to the following, non-limiting examples. Anticorrosive primer coating compositions were made based on the ingredients and relative amounts set out in Tables 1 and 2 below. The Part A and Part B components were separately prepared. The Part A and Part B components were then mixed together and viscosity measurements were taken immediately. Tables 1 and 2 include the viscosities of these freshly prepared and mixed samples. Also presented are corresponding viscosity values for batches of Part A and Part B that were held for 1 month and 6 months in an oven at 35 °C, and the viscosities of their corresponding mixtures directly after mixing. The viscosity values were measured using a Sheen CP1 cone-and-plate viscometer with a 0-20 poise cone at 750 rpm.

[0134] In the tables:

[0135] Viscosity values are in units of centipoise (cps), measured at 25 °C and at the same shear rate. Note: 1 cps = 1 mPa s.

[0136] * = Comparative example

[0137] [1] = Liquid bisphenol A epoxy resin, EEW = 184-190 g / eq,

[0138] [2] = 1,6-hexanediol diglycidyl ether

[0139] [3] = Glycidoxypropyl trimethoxy silane [4] = Micronised amide modified hydrogenated castor oil rheology modifier

[0140] [5] = Supplied as a 65 wt% paste in hydrocarbon

[0141] [6] = Phenalkamine curing agent with 2 wt% free amine (EDA)

[0142] [7] = Phenalkamine curing agent with 10-15 wt% free amine (MXDA)

[0143] [8] = Polyetheramine - a difunctional primary amine [9] = 3-Aminopropyl triethoxy silane

[0144]

[0010] = 3-Aminopropyl trimethoxy silane

[0145]

[0011] = tris-(dimethylaminomethyl)phenol

[0146]

[0012] = Substances with GHS classification [H314] (causes severe burns and eye damage)

[0147]

[0148] Table 1 - Formulations (wt%) and Properties of Examples 1-5

[0149] Table 2 - Formulations (wt%) and Properties Examples 6-14

[0150] Lower viscosities can be achieved by using (alkoxysilyl)alkylamines. This can be seen when comparing Example 1 (comparative) with Examples 4, 7 and 8. Example 1 comprises no coupling agent and Examples 4, 7 and 8 partly replace the curing agent with (alkoxysilyl)alkylamine. In all cases, the viscosities of the initial and “aged” batches of the Part B and their mixtures with the corresponding Part A are lower for Examples 4, 7 and 8. The benefits of reduced viscosity within increasing amounts of the (alkoxysilyl)alkylamines are also apparent from a comparison of Examples 1 , 4, 6, 7 and 8, and for the aluminium-containing samples of Example 5 and Examples 9, 10, 11 and 14).

[0151] The results further highlight an advantage of using (alkoxysilyl)alkylamines as coupling agents in place of, for example, epoxy-containing coupling agents such as glycidoxypropyl trimethoxysilane (GOPTMS), where reduced degradation over time is observed (reflected in increased viscosities over time). Example 5 can be compared with Examples 9 to 11. As the GOPTMS content increases, the viscosity of the Part A and mixed coating tends to get worse the longer the Part A and Part B are stored. This is mitigated by the use of (alkoxysilyl)alkylamine.

[0152] The results additionally highlight that lower quantities of relatively hazardous components (with a GHS rating of [H314]) can be used while still having viscosities that enable them to be applied using airless spraying techniques. This is clear by the comparable viscosities of Examples 6, 7 and 8 those of Examples 1 and 3.

[0153] The formulations are also able to avoid issues associated with degradation of the Part A component with time that can otherwise arise when using higher quantities of epoxy- containing coupling agents. This is especially so for examples that include metallic pigment such as aluminium. Less bubbling and less increase in viscosity over time is experienced in the compositions having lower amounts of epoxy-containing coupling agents. Table 3 shows results of visual inspection of the Part A components of some of the Examples, highlighting the extent of bubbling observed after 6 months storage at 35 °C. Corresponding viscosity data are also provided (as per Table 2). The results highlight a benefit of reducing the amount of epoxy-containing coupling agents in the coating composition. Table 3 - Properties after 6 months storage

Claims

CLAIMS1. An anticorrosive primer coating composition comprising: from 15 to 45 wt% of bisphenol epoxy resin; from 7 to 25 wt% of curing agent; from 4 to 15 wt% of epoxy reactive diluent from 0.1 to 8 wt% of (alkoxysilyl)alkylamine; and no more than 15 wt% solvent.

2. The anticorrosive primer coating composition as claimed in claim 1, having a solids volume of at least 85% according to ASTM D5201-053. The anticorrosive primer coating composition as claimed in claim 1 or claim 2, in which the curing agent is a Mannich base curing agent.

4. The anticorrosive primer coating composition as claimed in claim 3, in which the curing agent is a phenalkamine.

5. The anticorrosive primer coating composition as claimed in any one of claims 1 to4, in which the bisphenol epoxy resin is a bisphenol A epoxy resin.

6. The anticorrosive primer coating composition as claimed in any one of claims 1 to5, in which the (alkoxysilyl)alkylamine is selected from those of formula:[(RxO)xRySi - (CH2)a]b- N - [(CH2)C- NH]dHH(2-b) where:Rxand Ryare each independently selected from C1-8 alkyl; x is an integer in the range of from 1 to 3; y is a whole number in the range of from 3-x; a is an integer in the range of from 1 to 4;b is an integer in the range of from 1 to 2; c is an integer in the range of from 1 to 4; and d is a whole number in the range of from 0 to 2.

7. The anticorrosive primer coating composition as claimed in claim 6, in which each Rxis methyl, each x is 3, each a is 3, b is 1 or 2, c is 2, and d is 0 or 1.

8. The anticorrosive primer coating composition as claimed in claim 7, in which the (alkoxysilyl)alkylamine is selected from (trimethoxysilane)propylamine, N-[3- (trimethoxysilyl)propyl]ethylenediamine and bis[(trimethoxysilyl)propyl]amine.

9. The anticorrosive primer coating composition as claimed in any one of claims 1 to8, comprising in the range of from 3 to 11 wt% aluminium in metallic or alloy form and / or no more than 1.5 wt% epoxy-containing coupling agents.

10. The anticorrosive primer coating composition as claimed in any one of claims 1 to9, provided in a multicomponent form where the epoxy-containing materials form part of one component and before use are kept separate from the remaining materials that form part of one or more different components.

11. The anticorrosive primer coating composition as claimed in claim 10, provided in a 2- or 3-component form, where the epoxy-containing materials form part of a binder component, the curing agents form part of a curing component, and the (alkoxysilyl)alkylamine is included either as a separate component or is included in the curing component.

12. The anticorrosive primer coating composition as claimed in any one of claims 1 to 11 , comprising or consisting of(a) from 15 to 45 wt% of bisphenol epoxy resin;(b) from 7 to 25 wt% of phenalkamine curing agent;(c) from 4 to 15 wt% of epoxy reactive diluent(d) from 0.1 to 8 wt% of (alkoxysilyl)alkylamine;(e) from 3 to 11 wt% of aluminium pigment;(f) no more than 15 wt% solvent;(g) no more than 1.5 wt% epoxy-containing coupling agents; and(h) up to 50 wt% one or more other components; where the (alkoxysilyl)alkylamine is selected from (trimethoxysilane)propylamine, N-[3-(trimethoxysilyl)propyl]ethylenediamine and bis[(trimethoxysilyl)propyl]amine; and where the phenalkamine curing agent is made from the reaction of cardanol, formaldehyde and ethylene diamine.

13. The anticorrosive primer coating composition as claimed in claim 12, in which the one or more other components are selected from the group consisting of auxiliary anti-corrosion additives, pigments, fillers and extenders, crosslinking catalysts, thixotropic agents, plasticizers, inorganic and organic dehydrators (stabilizers), UV stabilizers, antifouling agents, defoamers and combinations thereof.

14. A method of coating a metallic substrate comprising applying to the substrate an anticorrosive primer coating composition as claimed in any one of claims 1 to 13, and allowing the coating composition to cure.

15. The method as claimed in claim 14, in which the substrate is selected from ship hulls, ship ballast tanks, ship propellors, and sub-surface metallic portions of fixed platforms, floating platforms and shoreside structures.

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