A moisture-curable, solvent-based coating composition curable at ambient temperature

Abstract

A moisture-curable, solvent-based coating composition curable at ambient temperature comprising: - an alkoxysilyl-functional resin; and - a catalyst obtainable by dissolving an acid and a hydroxide salt in a liquid carrier, wherein the equivalent ratio of acidic protons in the acid and hydroxide ions in the hydroxide salt is from 3:1 to 1.5:1, the acid is selected from the group consisting of benzoic acid, neopentanoic acid, 2-ethyl hexanoic acid, and neodecanoic acid, halogenated carboxylic acids, alkyl esters of phosphoric acid, and mixtures thereof, and the coating composition is essentially free of an amine and is essentially free of tin. A substrate coated with a coating layer deposited from such coating composition, a multilayer coating system comprising a primer layer, optionally a basecoat layer, and a topcoat layer deposited from such coating composition, and a process for coating a substrate with a coating layer deposited from such coating composition.

Description

[0001] P81961067W001

[0002] A MOISTURE -CURABLE, SOLVENT-BASED COATING COMPOSITION CURABLE AT AMBIENT TEMPERATURE

[0003] Field of the Invention

[0004] The present invention relates to a moisture-curable, solvent-based coating composition that is curable at ambient temperature comprising an alkoxysilyl-functional resin and a catalyst, to a substrate coated with a coating layer deposited from such coating composition, to a multilayer coating system comprising a primer layer, optionally a basecoat layer, and a topcoat layer deposited from such coating composition, and to a process for coating a substrate with a coating layer deposited from such coating composition. of the Invention

[0005] Moisture-curable coating compositions comprising a resin with alkoxysilyl functional groups that can cure at ambient temperature are known in the art. The resin cures through hydrolysis of the alkoxysilyl functional groups into silanol groups, followed by condensation of the silanol groups. In order to achieve an acceptable cure rate at ambient temperatures, the rate of the hydrolysis and condensation is typically increased by using a catalyst. Well-known catalysts for this reaction are tin-based catalysts, typically organotin compounds such as tin carboxylates. The use of tin is, however, undesirable in view of its toxicity.

[0006] In US2006 / 128919 is disclosed a one-part curable composition of high viscosity (kneadable) for providing cured articles. The curable composition comprises an organic polymer having one or more silicon-containing functional groups capable of cross-linking by forming siloxane bonds, and a component selected from the groups consisting of a silicate, a tin carboxylate, an organotin catalyst, a non-tin catalyst, and a microballoon. Several non-tin catalysts are mentioned in US2006 / 128919, including carboxylic acids, carboxylic acid salts other than tin carboxylate, organic sulfonic acid, acidic phosphate ester, and organotitanate compounds. In all examples, the curable composition comprises a tin carboxylate or an organotin catalyst, often together with an amine compound.

[0007] In WO2023 / 059477 is disclosed a one-component solvent borne curable coating composition comprising an organic polymer having silicon-containing group(s) which can be crosslinked by the formation of a siloxane bond and a catalyst that may be either a sterically hindered primary P81961067W001 hydroxylamine or a combination of a sterically hindered primary hydroxylamine and an organic acid.

[0008] The use of amines is, however, not desirable in coating compositions since it generally results in poor weatherability. Moreover, many amines cause in-can yellowing of the coating composition and / or yellowing of the resulting coating.

[0009] In W02020 / 040886 is disclosed a method for condensation polymerization of hydroxyl-terminated polydiorganosiloxanes at a temperature of 50 °C to 150 °C and employing a catalyst that minimizes production of cyclic polydiorganosiloxane by-products. The catalyst includes a saltanion complex and a free acid, wherein the free acid is a fluorinated carboxylic acid or a sulphonic acid and wherein the salt-anion complex is a complex of a specific cation and a fluorinated carboxylate or a sulphonate as anion.

[0010] In US2013 / 164539 is disclosed a polycarbonate substrate for automotive glazing, provided with a primer layer and a laminate of two silicone hard layers. The primer layer is prepared from a coating composition containing a vinyl copolymer having an alkoxysilyl group and a UV-absorbing group and containing fine particle silicon oxide and not containing any curing catalyst. The two silicone hard layers are each prepared from a coating composition containing a polysiloxane that is solid at a temperature up to 40 °C, a co- hydro lysate of an organo-silane and a UV-absorbing silane, fine particles of silicon oxide, and an alkaline curing catalyst. The alkaline curing catalyst promotes the formation of bonds between alkoxysilyl groups in the silanes and the silanol groups in the fine particles of silicon oxide at high crosslinking density. The primer layer and the two silicone hard layers are heat-cured at 120 °C, 120 °C, and 100 °C, respectively.

[0011] In WO2016 / 137881 is disclosed a tin-free curable coating composition comprising a polymer having a reactive silicon-containing group and a silanol condensation catalyst composition consisting of a combination of one or more metal amidine complexes and one or more amine carboxylate salts.

[0012] In the field of automotive coating compositions, condensation polymers are often used as topcoats in multilayer coating systems on exterior parts. These systems typically comprise a primer layer directly on a substrate that is optionally pretreated, a basecoat layer to impart color and / or effect to the coating (such as metallic appearance), and a topcoat over the basecoat layer (or over the primer layer if no basecoat layer is present) to protect the coating system. The topcoat is usually a clear coat. Coating compositions comprising moisture-curable alkoxysilyl-functional resins could P81961067W001 suitably be used as topcoat in such multilayer coating systems, provided these coating compositions show an acceptable cure rate at ambient temperature, do not discolor, and result in cured coatings with good chemical resistance.

[0013] There is a need for tin-free and amine-free curing catalysts for coating compositions comprising moisture-curable alkoxysilyl-functional resins, in particular for topcoats on exterior parts of automotive vehicles, that result in an acceptable cure rate of the applied coating composition at ambient temperature, avoid discoloration of the coating composition and the coating, and result in cured coatings with good chemical resistance.

[0014] Summary of the invention

[0015] It has been found that a catalyst obtainable by dissolving an acid as specified in the claims and a hydroxide salt in a liquid carrier in an equivalent ratio of acidic protons in the acid and hydroxide ions in the hydroxide salt in the range of from 3:1 to 1 .5:1 , results in a catalyst that quickly cures an alkoxysilyl-functional resin at ambient temperature to provide a coating with good chemical resistance. The curing rate is improved compared to coating compositions with a catalyst prepared from equivalent amounts of acid groups and hydroxide salt, such as potassium neodecanoate.

[0016] Accordingly, the invention provides in a first aspect a moisture-curable, solvent-based coating composition that is curable at ambient temperature comprising: an alkoxysilyl-functional resin; and a catalyst obtainable by dissolving an acid and a hydroxide salt in a liquid carrier, wherein the equivalent ratio of acidic protons in the acid and hydroxide ions in the hydroxide salt is in the range of from 3:1 to 1.5:1 , wherein the acid is an aliphatic or aromatic carboxylic acid selected from the group consisting of benzoic acid, neopentanoic acid, 2-ethyl hexanoic acid, and neodecanoic acid, a halogenated carboxylic acid, an alkyl ester of phosphoric acid, or a mixture of two or more thereof, and wherein the coating composition is essentially free of an amine and is essentially free of tin.

[0017] A further advantage of the coating composition according to the invention is that it does not result in yellowing of the coating composition when it is stored in a container (so-called ‘in-can yellowing’), even if the catalyst would already be present in the coating composition in the container. P81961067W001

[0018] It has been found that the coating composition according to the invention not only can be cured at an acceptable curing rate at ambient temperature, i.e. without any external heat applied - typically in the range of from 15 °C to 40 °C, but even at temperatures below typical room temperature, such as in the range of from 5 °C to 15 °C. The coating composition will also cure at higher temperatures, but such higher temperature is not needed for an acceptable cure rate.

[0019] The properties found make the coating composition according to the invention particularly suitable as topcoat, more particular a clearcoat, in a multilayer coating system as used on exterior parts of automotive or aerospace vehicles. The coating composition combines quick drying at low temperature with good chemical resistance and non-yellowing.

[0020] Accordingly, in a second aspect, the invention provides a substrate coated with a coating layer deposited from the coating composition according to the first aspect of the invention.

[0021] In a third aspect, the invention provides a multilayer coating system comprising a primer layer, optionally a basecoat layer, and a topcoat layer applied on the primer layer or the basecoat layer, wherein the topcoat layer is deposited from the coating composition according to the first aspect of the invention.

[0022] In a final aspect, the invention provides a process for coating a substrate with a coating layer deposited from the coating composition according to the first aspect of the invention, comprising applying the coating composition on the substrate and allowing the applied coating composition to cure at a temperature in the range of from 5 °C to 60 °C, preferably of from 15 °C to 40 °C.

[0023] Detailed Description of the Invention

[0024] The coating composition according to the present invention is a moisture-curable, solvent-based coating composition comprising an alkoxysilyl-functional resin that cures by hydrolysis of the alkoxysilyl functional groups and subsequent condensation of the thus-formed silanol groups.

[0025] The coating composition is curable at ambient temperature, i.e. at a temperature in the range of from 15 °C to 40 °C, and therefore comprises a catalyst. The catalyst is a catalyst obtainable by dissolving an acid and a hydroxide salt in a liquid carrier, wherein the equivalent ratio of acidic protons in the acid and hydroxide ions in the hydroxide salt is in the range of from 3:1 to 1.5:1.

[0026] The liquid carrier for dissolving the acid and the hydroxide salt may be any suitable liquid carrier. Suitable carriers are carriers wherein the hydroxide salt and the acid dissolve and that are miscible with the alkoxysilyl-functional resin. Polar organic solvents, optionally mixed with P81961067W001 water, can suitably be used as liquid carrier for dissolving the acid and hydroxide. Suitable polar organic solvents include alcohols, ketones, esters, acetonitrile, and mixtures thereof. Alcohols are preferred polar organic solvents, more preferably alcohols with 1 to 12 carbon atoms, such as ethanol, n-butanol, hexanol, and decanol. A particularly preferred organic solvent is n- butanol.

[0027] The acid and hydroxide salt may be dissolved in the liquid carrier in any suitable way, for example by directly dissolving the (solid or liquid) acid and the hydroxide salt in the liquid carrier or, alternatively, by first dissolving the acid and hydroxide salt in water and then adding the solution to an organic solvent to obtain a liquid carrier that comprises both water and organic solvent.

[0028] Preferably, the liquid carrier for dissolving the acid and the hydroxide salt comprises less than 20 vol.% water, more preferably less than 10 vol.%, even more preferably less than 1 vol.%.

[0029] The amount of liquid carrier in which the acid and hydroxide salt are dissolved is not critical. The amount is preferably chosen such that the viscosity of the catalyst (acid and hydroxide salt in liquid carrier) is such that it can be mixed with the resin.

[0030] The acid is an aliphatic or aromatic carboxylic acid selected from the group consisting of benzoic acid, neopentanoic acid, 2-ethyl hexanoic acid, and neodecanoic acid, a halogenated carboxylic acid, an alkyl ester of phosphoric acid, or a mixture of two or more thereof. The acid may be a monoprotic or polyprotic acid, preferably a monoprotic acid. It has been found that the use of these acids in the catalyst provides a coating composition with an acceptable cure rate when moisture-cured at ambient temperature. Reference herein to moisture curing is to a process wherein a coating composition cures by reacting with moisture in the surrounding air.

[0031] The acid may be a mixture of two or more acids. If a mixture of a monoprotic acid and a polyprotic acid, the acid is considered a polyprotic acid. Preferably all acids in the mixture are monoprotic acids.

[0032] In preferred embodiments, the acid is an alkyl monocarboxylic acid comprising a branched alkyl group. Neopentanoic acid, 2-ethyl hexanoic acid, and neodecanoic acid are particularly preferred acids, more in particular neodecanoic acid.

[0033] Reference herein to halogenated carboxylic acids is to carboxylic acids of general formula

[0034] R(COOH)m, wherein R is an aliphatic or aromatic residue wherein one or more hydrogen atoms P81961067W001 are substituted by a halogen atom and wherein m is an integer. Residue R preferably has 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms. The number of acid groups (m) is preferably at most 3, more preferably is 1 (monocarboxylic acid).

[0035] Preferably, the halogenated carboxylic acid is a saturated halogenated carboxylic acid, more preferably a chlorinated or fluorinated saturated carboxylic acid, even more preferably one of more of trichloroacetic acid, dichloroacetic acid, trifluoro acetic acid, and difluoro acetic acid, still more preferably trichloroacetic acid or dichloroacetic acid.

[0036] Reference herein to an alkyl ester of phosphoric acid is to a compound of general formula (R)n(H)3-nPO4wherein n is 1 or 2. Preferably n is 2 (a monoprotic acid). Each residue R preferably has, independently, 1 to 20 carbon atoms, more preferably 1 to 12 carbon atoms. Preferably, at least one of the alkyl groups in the alkyl ester of phosphoric acid is a branched alkyl group, more preferably all alkyl groups in the alkyl ester of phosphoric acid are branched alkyl group. A particularly preferred alkyl ester of phosphoric acid is di(2-ethylhexyl)phosphoric acid (monoprotic and comprising two branched alkyl groups).

[0037] Preferably, the acid is an alkyl carboxylic acid selected from the group consisting of neopentanoic acid, 2-ethyl hexanoic acid, and neodecanoic acid, or an alkyl ester of phosphoric acid. Preferably, an alkyl carboxylic acid selected from the group consisting of neopentanoic acid, 2-ethyl hexanoic acid, and neodecanoic acid, or an alkyl ester of phosphoric acid comprising a branched alkyl group.

[0038] The hydroxide salt may be any hydroxide salt soluble in the liquid carrier. Preferred hydroxide salts are potassium hydroxide and alkyl ammonium hydroxide. Particularly preferred alkyl ammonium hydroxides are tetra-alkylammonium hydroxide, more in particular tetrabutylammonium hydroxide.

[0039] The catalyst is obtainable by dissolving the acid and the hydroxide salt in the liquid carrier in such amounts that the equivalent ratio of acidic protons in the acid and hydroxide ions in the hydroxide salt is in the range of from 3:1 to 1.5:1 , preferably of from 2.5:1 to 1.7:1 , more preferably of from 2.3:1 to 1.8:1 , even more preferably of from 2.1 :1 to 1.9:1. A ratio of 2.0:1 is particularly preferred.

[0040] Without wishing to be bound to any theory it is believed that at this ratio, a complex conjugated base is formed of two equivalents of acid that share one proton and the cation of the hydroxide P81961067W001 salt. The thus-formed conjugated base acts as a catalyst for both hydrolysis of alkoxysilyl groups and condensation of thus-formed silanol groups.

[0041] The coating composition, and thus also the catalyst, is essentially free of an amine. Reference herein to an amine is to a compound that contains a basic nitrogen atom with a lone pair. A lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bond and is sometimes called an unshared pair or non-bonding pair. A quaternary ammonium compound is not considered an amine.

[0042] The coating composition, and thus also the catalyst, is essentially free of tin.

[0043] Reference herein to essential free of a compound is to a composition to which such compound is not intentionally added. Trace amounts of such compound that are unintentionally added with other ingredients may be present, for example in an amount up to 0.05 wt.%, preferably up to 0.01 wt.%.

[0044] Reference herein to an alkoxysilyl-functional resin is to a film-forming polymer with alkoxysilyl functional groups. The alkoxysilyl-functional resin may be any film-forming polymer with alkoxysilyl functional groups that cures by forming siloxane crosslinks by the above-described hydrolysis and subsequent condensation of silanol groups and that is able to cure at ambient temperature (15°C - 40 °C). The resin preferably has a polymer backbone of polyacrylate, polyester, polyurethane, or polyether. The alkoxysilyl-functional resin may be a single alkoxysilyl-functional resin or a mixture of two or more different alkoxysilyl-functional resins, preferably is a single alkoxysilyl-functional resin.

[0045] More preferably, the resin is a resin obtainable by radical polymerization of a mixture of ethylenically unsaturated monomers, wherein the mixture comprises an alkoxysilane-functional ethylenically unsaturated monomer. The mixture of ethylenically unsaturated monomers preferably comprises the alkoxysilane-functional ethylenically unsaturated monomer and one or more ethylenically unsaturated monomers without alkoxysilane-functionality. Examples of such ethylenically unsaturated monomers without alkoxysilane-functionality are (meth)acrylate esters, OH- or glycidyl-functional (meth)acrylate esters, (meth)acrylic acid, styrene, alkylated styrene, other vinyl-functional monomers, and combinations thereof.

[0046] The mixture of ethylenically unsaturated monomers preferably comprises the alkoxysilane- functional ethylenically unsaturated monomer in an amount in the range of from 10 wt.% to 60 P81961067W001 wt.%, based on the total weight of ethylenically unsaturated monomers, more preferably of from 15 wt.% to 50 wt.%, even more preferably of from 20 wt.% to 40 wt.%.

[0047] The alkoxysilyl-functional ethylenically unsaturated monomer may be any suitable alkoxysilyl- functional ethylenically unsaturated monomer. Preferably, the alkoxysilyl-functional ethylenically unsaturated monomers include one or more of 3-(trimethoxysilyl)propyl (meth)acrylate, 3- (triethoxysilyl)propyl (meth)acrylate, 3-(trimethoxysilyl)methyl (meth)acrylate, 3- (triethoxysilyl)methyl (meth)acrylate, 3-[diethoxy(methyl)silyl]propyl (meth)acrylate, 3- [diethoxy(methyl)silyl]methyl (meth)acrylate, 3-[ethoxy(dimethyl)silyl]propyl (meth)acrylate, 3- [ethoxy(dimethyl)silyl]methyl (meth)acrylate, vinyltrimethoxysilane, and vinyltriethoxysilane. More preferably the alkoxysilyl-functional ethylenically unsaturated monomers include one or more of 3-(trimethoxysilyl)propyl (meth)acrylate, 3-(triethoxysilyl)propy I (meth)acrylate, 3- (trimethoxysilyl)methyl (meth)acrylate, and 3-(triethoxysilyl)methyl (meth)acrylate. More preferably, the alkoxysilyl-functional ethylenically unsaturated monomer is selected from the group consisting of 3-(trimethoxysilyl)propyl (meth)acrylate, 3-(triethoxysilyl)propyl (meth)acrylate, 3-(trimethoxysilyl)methyl (meth)acrylate, 3-(triethoxysilyl)methyl (meth)acrylate, vinyltrimethoxysilane, vinyltriethoxysilane, and mixtures thereof. Preferably, the alkoxysilyl- functional ethylenically unsaturated monomers do not include UV-absorbing alkoxysilyl- functional ethylenically unsaturated monomers that are a benzophenone derivative. The coating composition may comprise a further film-forming resin that is not an alkoxysilyl-functional resin. If such further film-forming resin is comprised in the coating composition, the amount of further film-forming resin is preferably at most 50 wt.% based on the total weight of film-forming resin (including the alkoxysilyl-functional resin), more preferably at most 30 wt.%, even more preferably at most 10 wt.%. In a preferred embodiment, the coating composition does not comprise a film-forming resin that is not an alkoxysilyl-functional resin.

[0048] The solvent-based coating composition may be a one-component coating composition or a multi-component composition comprising two or more components.

[0049] In one embodiment, the coating composition is a one-component coating composition wherein the alkoxysilyl-functional resin and the catalyst are present in the same component and are thus both comprised in a coating container prior to application of the coating composition on a substrate. It has been found that the coating composition of the invention does not show unacceptable yellowing of the coating composition in the container, even not if provided as a one-component composition. P81961067W001

[0050] In another embodiment, the coating composition is a multi-component coating composition comprising a resin component comprising the alkoxysilyl-functional resin as first component and a catalyst component comprising the catalyst as second component. Such composition may comprise one or more further components, for example a thinner component.

[0051] The catalyst may be used in any suitable amount. Preferably the combined amount of acid and hydroxide salt is in the range of from 0.5 wt.% to 10 wt.% based on the solid weight of alkoxysilyl-functional resin, more preferably of from 1 wt.% to 5 wt.%.

[0052] The coating composition is a solvent-based composition. Reference herein to a solvent-based coating composition is to a composition comprising a liquid carrier for the resin comprising at least 50 wt.% organic solvent, preferably at least 70 wt.%. In case of a one-component coating composition, the liquid carrier includes the liquid carrier in which the acid and hydroxide salt of the catalyst are dissolved. The organic solvent may be any suitable organic solvent or mixture of organic solvents.

[0053] Preferably, the coating composition comprises less than 1 wt.% water, more preferably is essentially free of water.

[0054] Preferably, the coating composition comprises in the range of from 10 wt.% to 90 wt.% filmforming resin solids, more preferably of from 30 wt.% to 85 wt.%, even more preferably of from 50 wt.% to 80 wt.%.

[0055] The coating composition may further comprise compounds that are typically used in coating compositions, such as for example color pigments, extender pigments, and additives.

[0056] Commonly used additives that can suitably be comprised in the coating composition include but are not limited to flow control agents, anti-foam agents, light stabilizers, moisture scavengers, dispersants, and crosslinking agents. Preferably, the coating composition does not comprise silicon oxide particles as crosslinking agent. If silicon oxide particles are present as additive, e.g. as rheology modifier or matting agent, the amount of silicon oxide particles is preferably less than 5 wt.% based on the solids weight of the alkoxysilyl-functional resin, more preferably less than 1 wt.%.

[0057] The coating composition may have any suitable viscosity, i.e. , a viscosity such that it can be applied as a thin layer on a substrate to form a coating film. P81961067W001

[0058] The coating composition may be used for any type of coating layer, such as a primer coating layer, a topcoat layer, or a basecoat layer. The coating composition is particularly suitable for a clearcoat that is used as a topcoat, for example on top of a primer coating layer or a basecoat layer in a multilayer coating system for exterior parts of automotive vehicles.

[0059] The invention further relates to a substrate coated with a coating layer deposited from the coating composition according to the first aspect of the invention.

[0060] The substrate may be any suitable substrate, including substrates already coated with one or more coating layers. The substrate may be a metal, wood (including solid wood and engineered wood), plastic, composite (fiber-reinforced plastic), or ceramic substrate. If the coating composition is used as a topcoat in the automotive industry, the substrate typically will be a metal, plastic, or composite substrate that is already provided with a primer layer and / or basecoat layer.

[0061] The coating layer deposited from the coating composition of the invention is preferably deposited as a toplayer on a substrate already provided with a primer layer and preferably also a basecoat layer. The coating layer deposited from the coating composition preferably has a dry film thickness in the range of from 30 pm to 300 pm, more preferably of from 50 to 200 pm.

[0062] The invention further relates to a multilayer coating system comprising a primer layer, optionally a basecoat layer, and a topcoat layer applied on the primer layer or the basecoat layer, wherein the topcoat layer is deposited from the coating composition according to the first aspect of the invention. Such multilayer coating system can suitably be used on exterior parts of automotive vehicles such as cars, trucks or airplanes.

[0063] Preferably, the topcoat layer has a dry film thickness in the range of from 30 pm to 300 pm, more preferably of from 50 pm to 200 pm.

[0064] The invention further relates to a process for coating a substrate with a coating layer deposited from the coating composition according to the first aspect of the invention, comprising applying the coating composition on the substrate and allowing the applied coating composition to cure, at a temperature in the range of from 5 °C to 60 °C, preferably of from 15 °C to 40 °C. The coating composition is preferably allowed to cure by moisture cure, i.e. by reacting the alkoxyfunctional resin with moisture in surrounding air. This requires curing in a system open to the surrounding air (in contrast to thermal curing in a closed system such as in an oven or autoclave). P81961067W001

[0065] Preferably, the substrate already comprising a primer layer and optionally a basecoat layer, and the coating layer deposited from the coating composition according to the first aspect of the invention is deposited on the primer layer or, if present, the basecoat layer as a topcoat. Preferably, the coating layer deposited from the coating composition according to the first aspect of the invention is applied at a dry film thickness in the range of from 30 pm to 300 pm, more preferably of from 50 pm to 200 pm.

[0066] The present invention will further be illustrated by means of the following non-limiting examples.

[0067] Examples

[0068] EXAMPLE 1 - preparation of coating compositions

[0069] Resin preparation

[0070] An alkoxysilyl-functional resin was prepared by a charging a reactor of 1 liter with 100 grams n- butyl acetate, 16.2 grams methyl trimethoxysilane, and 16.2 grams n-butanol, under continuous stirring. For 30 minutes, the reactor content was gradually heated to 170 °C. A homogenized mixture of monomers (262.5 grams n-butyl acrylate, 214.8 grams methyl methacrylate, and 162.9 grams 3-(trimethoxysilyl) propyl methacrylate) and initiator (9.8 grams Trigonox B) was then gradually added during 4 hours at a rate of 2.83 g / minute via an inlet tube. The inlet tube was then rinsed with n-butyl acetate (10 grams) and added to the reactor. The reactor was kept at 170 °C for another 30 minutes and then cooled to 126 °C. Further initiator (2.0 Trigonox 42S in 10 grams n-butyl acetate) was added, and the inlet tubes were rinsed with another 10 grams of butyl acetate. The reactor was kept at 126 °C for another 2.5 hours. After one hour, further initiator (2.0 Trigonox 42S in 10 grams n-butyl acetate followed by rinsing of the inlet tubes with 10 grams of n-butyl acetate) was added.

[0071] The reactor was then quickly cooled using pressurized air to a temperature below 80 °C to stop the radical polymerization reaction. After further cooling to 23 °C, 12.8 grams of vinyl trimethoxysilane was added as moisture scavenger. The resulting resin composition was stored at 4 °C under atmospheric pressure until it was applied on a substrate.

[0072] The resulting resin composition comprised 75.3 wt.% resin solids (based on total weight of the composition) and had a viscosity of 580 mPa.s as determined according to ISO 2884-1 using a Brookfield CAP2000+ cone-and-plate viscometer at a shear rate of 10,000 s-1and at a P81961067W001 temperature of 23 °C The resin had a number average molecular weight of 2,188 g / mol and a weight average molecular weight of 5,522 g / mol.

[0073] Catalyst compositions

[0074] The following catalyst compositions were used:

[0075] 1. K-Kat 670: commercially available catalyst (ex. King Industries, Inc.); zinc complex catalyst for polysiloxane 1 K moisture cure coatings.

[0076] 2. Borchers ® Deca Potassium 12: commercially available catalyst (ex. Borchers): potassium neodecanoate dissolved in diethylene glycol (potassium content is 12 wt%).

[0077] 3. Dibutyltin dilaurate (DBTL): commercially available catalyst (ex. Merck): 95 wt% dibutyltin dilaurate in organic solvent.

[0078] 4. Di(2-ethylhexyl) phosphoric acid (DEHPA) - 100%

[0079] 5. Dichloro acetic acid (DCAA) - 100%

[0080] 6. Versatic™ Acid 10 (ex. Hexion): neodecanoic acid (NDA) - 100 %

[0081] Catalyst compositions 7 to 20 (all 20 wt% acid plus base in 80 wt% alcohol) were prepared as follows:

[0082] (catalyst compositions 7, 12, 16 and 20) mixing a solution of 1 M tetrabutylammonium hydroxide (TBAH) in methanol with 3 grams of n-butanol and adding acid to obtain 1 gram acid and TBAH in 4 grams methanol / n-butanol; or

[0083] (catalyst compositions 8-11 , 13-15, and 17-19) dissolving acid and a base (potassium hydroxide (KOH) or 2-amino-2-methyl-1 -propanol (AMP)), in 4 grams of butanol. The amount of acid plus base was 1 gram for all compositions. For catalyst composition 9, first half of the acid (0.43 grams) and all of the potassium hydroxide was dissolved in 4 grams butanol and then the other half of acid (0.43 grams) was added.

[0084] The amounts of acid, potassium hydroxide, 2-amino-2-methyl-1 -propanol (AMP), or TBAH solution used are given in Table 1 . P81961067W001

[0085] Table 1 Catalyst compositions 7 to 20 - amounts of acid and base in grams aNDA: neodecanoic acid (Versatic™ Acid 10; ex. Hexion)bDEPHA: Di(2-ethylhexyl) phosphoric acidcDCAA: dichloro acetic aciddTCAA: trichloro acetic acideAA: acetic acid

[0086] Coating compositions

[0087] Twenty coating compositions were prepared. For each coating composition, n-butanol and one of the catalyst compositions were added to 20 grams of the resin composition prepared as described in EXAMPLE 1. For coating compositions 1 to 6 (with catalyst compositions 1 to 6): 2.0 grams n- butanol and 0.3 grams of the catalyst composition; for coating compositions 7 to 20 (with catalyst compositions 7 to 20): the total amount of alcohol (n-butanol and methanol) was 2.0 grams (total of amount of n-butanol plus any alcohol in catalyst composition) and the amount of acid plus any base was 0.3 grams. P81961067W001

[0088] EXAMPLE 2 - Testing of coating compositions

[0089] Yellowing

[0090] Three days after adding the catalyst composition to the resin composition, it was visually inspected whether the coating composition had yellowed (y: yellowing; n: no yellowing).

[0091] Chemical resistance (MEK double rub test)

[0092] The twenty coating compositions of EXAMPLE 1 were applied at a dry film thickness of 60 pm on a tin panel of 250 x 150 mm. The chemical resistance of the cured coatings was determined as follows.

[0093] After allowing the applied coating to dry for 7 days at ambient conditions (23 °C, 50% relative humidity), the chemical resistance of the cured coating was determined as follows. A cotton ball with a diameter of approximately 1.0 cm was soaked in methyl ethyl ketone (MEK) and then rubbed back and forth along a 5 cm section of the coating, at a rate of two rubs (one double rub) per second. The test was performed until 200 double rubs (dr) were reached or until coating failure. During the rubs, no pressure was applied. The number of double rubs until failure is shown in Table 2 (MEKdr). No failure after200 double rubs is considered good chemical resistance. Failure before 200 double rubs is considered insufficient chemical resistance.

[0094] Drying performance

[0095] Drying performance was determined according to ASTM D1640-95. The twenty coating compositions of EXAMPLE 1 were applied at a wet film thickness of 150 pm on a tin panel of 250 x 150 mm and allowed to dry at 23 °C and 50% relative humidity. Dust-Free Times were determined according to the Cotton Fiber Test Method of ASTM D1640-95; Dry-To-Touch Times were determined according to ASTM D1640-95 (section 7.5.1).

[0096] All test results are shown in Table 2. As can be seen from the results in Table 2, the coating compositions according to the invention, i.e. with a catalyst obtained as specified in claim 1 , do not yellow after adding the catalyst to the resin component, show good drying properties, and result in coatings with good chemical resistance (no coating failure after 200 double rubs with a cotton ball soaked in methyl ethyl ketone). The performance of the coating compositions P81961067W001 according to the invention is comparable or even better than the performance of a coating composition comprising a conventional tin-comprising catalyst such as DBTL.

[0097] Table 2 - Properties of coating compositions 1 to 20 comparison experiment n.d.: not determined

Claims

1. P81961067W001CLAIMS1 . A moisture-curable, solvent-based coating composition that is curable at ambient temperature comprising: an alkoxysilyl-functional resin; and a catalyst obtainable by dissolving an acid and a hydroxide salt in a liquid carrier, wherein the equivalent ratio of acidic protons in the acid and hydroxide ions in the hydroxide salt is in the range of from 3:1 to 1.5:1 , wherein the acid is an aliphatic or aromatic carboxylic acid selected from the group consisting of benzoic acid, neopentanoic acid, 2-ethyl hexanoic acid, and neodecanoic acid, a halogenated carboxylic acid, an alkyl ester of phosphoric acid, or a mixture of two or more thereof, and wherein the coating composition is essentially free of an amine and is essentially free of tin.

2. A coating composition according to claim 1 , wherein the equivalent ratio of acid groups in the acid and hydroxide ions in the hydroxide salt is in the range of from 2.5:1 to 1.8:1 , preferably is 2.0:1.

3. A coating composition according to claim 1 or 2, wherein the hydroxide salt is potassium hydroxide or a tetra-alkylammonium hydroxide, preferably is potassium hydroxide or tetrabutylammonium hydroxide, more preferably is potassium hydroxide.

4. A coating composition according to any one of the preceding claims, wherein the acid is a monoprotic acid.

5. A coating composition according to any one of the preceding claims, wherein the acid is an alkyl carboxylic acid selected from the group consisting of neopentanoic acid, 2-ethyl hexanoic acid, and neodecanoic acid, or an alkyl ester of phosphoric acid.

6. A coating composition according to claim 5, wherein the acid comprises one or more branched alkyl group.

7. A coating composition according to claim 6, wherein the acid is neodecanoic acid.P81961067W0018. A coating composition according to any one of claims 1 to 6, wherein the acid is a dialkyl ester of phosphoric acid, preferably is di(2-ethylhexyl)phosphoric acid.

9. A coating composition according to any one of the preceding claims, wherein the alkoxysilyl-functional resin is obtainable by radical polymerization of a mixture of ethylenically unsaturated monomers comprising an alkoxysilyl-functional ethylenically unsaturated monomer.

10. A coating composition according to claim 9, wherein the alkoxysilyl-functional ethylenically unsaturated monomer is selected from the group consisting of 3- (trimethoxysilyl)propyl (meth)acrylate, 3-(triethoxysilyl)propyl (meth)acrylate, 3- (trimethoxysilyl)methyl (meth)acrylate, 3-(triethoxysilyl)methyl (meth)acrylate, vinyltrimethoxysilane, vinyltriethoxysilane, and mixtures thereof.

11. A coating composition according to claim 9 or 10, wherein the mixture of ethylenically unsaturated monomers comprises the alkoxysilane-functional ethylenically unsaturated monomer in an amount in the range of from 10 wt.% to 60 wt.%, based on the total weight of ethylenically unsaturated monomers, preferably of from 15 wt.% to 50 wt.%.

12. A substrate coated with a coating layer deposited from the coating composition according to any one of the preceding claims, preferably at a dry film thickness in the range of from 30 pm to 300 pm, more preferably of from 50 pm to 200 pm.

13. A multilayer coating system comprising a primer layer, optionally a basecoat layer, and a topcoat layer applied on the primer layer or the basecoat layer, wherein the topcoat layer is deposited from the coating composition according to any one of claims 1 to 11 .

14. A multilayer coating system according to claim 13, wherein the topcoat layer has a dry film thickness in the range of from 30 pm to 300 pm, preferably of from 50 pm to 200 pm.

15. A process for coating a substrate with a coating layer deposited from the coating composition according to any one of claims 1 to 11 , comprising applying the coating composition on the substrate and allowing the applied coating composition to cure at a temperature in the range of from 5 °C to 60 °C, preferably of from 15 °C to 40 °C.

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