Filiform corrosion resistant coating composition

Abstract

The present invention relates to a powder coating composition comprising an addition polymer containing epoxy functional groups, a carboxylic acid functional crosslinker, and a blocked isocyanate functional crosslinker. The addition polymer is obtained from a component comprising at least one epoxy-functional ethylenically unsaturated monomer. The component comprises an amount of at least one epoxy-functional ethylenically unsaturated monomer in the range of more than 10% and less than 22% by weight, based on the components forming the addition polymer.

Description

[Technical Field]

[0001] The present invention relates to powder coating compositions. [Background technology]

[0002] Substrates, such as metal substrates, including those used in vehicles, are often provided with coatings to provide corrosion resistance. For example, substrates are coated with corrosion resistant coatings to provide corrosion resistant properties. The substrates can be covered and coated with a coating having corrosion resistant properties to protect the substrate from corrosion over time. Summary of the Invention

[0003] The present invention is directed to a powder coating composition comprising: (a) an addition polymer comprising epoxy functionality, the addition polymer being derived from components comprising (i) at least one epoxy-functional ethylenically unsaturated monomer, the components comprising an amount of (i) the at least one epoxy-functional ethylenically unsaturated monomer in the range of greater than 10% and less than 22% by weight, based on the components forming the addition polymer; (b) a carboxylic acid-functional crosslinker; and (c) a blocked isocyanate-functional crosslinker. Although overlapping with other descriptions, various aspects of the present invention are described below, however, the present invention is not limited to the following. [1] 1. A powder coating composition comprising: (a) an addition polymer containing epoxy functional groups, said addition polymer comprising: an addition polymer obtained from components comprising (i) at least one epoxy-functional ethylenically unsaturated monomer, said components comprising an amount of (i) said at least one epoxy-functional ethylenically unsaturated monomer in the range of greater than 10% and less than 22% by weight, based on the components forming said addition polymer; (b) a carboxylic acid functional crosslinker; and (c) a blocked isocyanate-functional crosslinker. [2] (i) The powder coating composition of [1], wherein the at least one epoxy-functional ethylenically unsaturated monomer comprises an epoxy-functional (meth)acrylate monomer. [3] 3. The powder coating composition of claim 2, wherein the epoxy-functional (meth)acrylate monomer comprises a mono-epoxy-functional (meth)acrylate monomer. [4] The powder coating composition according to any one of [1] to [3], wherein the components forming the addition polymer further comprise (ii) at least one non-functional ethylenically unsaturated monomer. [5] (ii) The powder coating composition of [4], wherein the at least one non-functional ethylenically unsaturated monomer comprises at least two different non-functional ethylenically unsaturated monomers. [6] (ii) The powder coating composition according to [5], wherein the non-functional ethylenically unsaturated monomer comprises an aliphatic non-functional ethylenically unsaturated monomer and an aromatic non-functional ethylenically unsaturated monomer. [7] [4] - [6] The powder coating composition according to any one of [4] to [6], wherein the components comprise at least 50 wt% of (ii) the non-functional ethylenically unsaturated monomer, based on the components forming the addition polymer. [8] [7] The powder coating composition according to any one of [1] to [7], wherein the reaction product of (a) and (b) comprises a hydroxyl functional group, and (c) the blocked isocyanate-functional crosslinker is reactive with the hydroxyl functional group. [9] [8] The powder coating composition according to any one of [1] to [8], wherein the components comprise (i) the at least one epoxy-functional ethylenically unsaturated monomer in an amount ranging from 15% by weight to 20% by weight, based on the components forming the addition polymer.

[10] The powder coating composition according to any one of [1] to [9], wherein the powder coating composition is substantially free of pigment.

[11] The powder coating composition according to any one of [1] to

[10] , wherein the addition polymer has a glass transition temperature of at least 30°C.

[12]

[10] The powder coating composition according to any one of [1] to

[11] , wherein the powder coating composition comprises at least 70 wt. % of (a) the addition polymer, based on the total solids weight of the powder coating composition.

[13] A substrate at least partially coated with a coating formed from the powder coating composition according to any one of [1] to

[12] .

[14] The substrate according to

[13] , wherein the substrate comprises a metal.

[15]

[14] The substrate according to

[14] , wherein the metal comprises aluminum, steel, magnesium, or an alloy thereof.

[16] The substrate according to any one of

[13] to

[15] , wherein the substrate comprises a metal wheel for a vehicle.

[17] The substrate according to any one of

[13] to

[16] , wherein the substrate includes a pretreatment layer that serves as a base for at least a part of the coating.

[18] The substrate according to any one of

[13] to

[16] , wherein the coating covers at least a portion of the substrate to form a monocoat.

[19] 1. A method of making a metal wheel, comprising: A method comprising applying the powder coating composition according to any one of [1] to

[12] to cover at least a portion of the metal wheel.

[20] 19. The method of claim 19, wherein the powder coating composition is applied to form a monocoat over the at least a portion of the metal wheel.

[21] Use of the powder coating composition according to any one of [1] to

[12] for reducing filiform corrosion. DETAILED DESCRIPTION OF THE INVENTION

[0004] For purposes of the following detailed description, it should be understood that the invention may assume various alternative variations and step sequences unless expressly indicated to the contrary. Further, other than in any examples or unless otherwise indicated, all numbers expressing quantities of ingredients used in the specification and claims, for example, should be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and appended claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the reported significant digits and by applying ordinary rounding techniques.

[0005] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible, however, any numerical value inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.

[0006] It should also be understood that any numerical range recited herein is intended to include all subranges subsumed therein. For example, a range of "1 to 10" is intended to include all subranges between (and including) the stated minimum of 1 and the stated maximum of 10, i.e., having minimums equal to or greater than 1 and maximums equal to or less than 10.

[0007] In this application, the use of the singular includes the plural, and the plural encompasses the singular, unless otherwise specified. Additionally, in this application, although "and / or" may be explicitly used in certain instances, the use of "or" means "and / or" unless otherwise specified. Furthermore, in this application, the use of "a" or "an" means "at least one" unless otherwise specified. For example, "a" cross-linker, "a" addition polymer, etc., refers to one or more of any of these items. Also, as used herein, the term "polymer" is meant to refer to prepolymers, oligomers, and both homopolymers and copolymers. The term "resin" is used interchangeably with "polymer."

[0008] As used herein, the transitional phrase "comprising" (and other equivalent terms, e.g., "containing" and "including") is open-ended and not limited to encompassing unspecified items. Although written in terms of "comprising," the terms "consisting essentially of" and "consisting of" are also within the scope of the present invention.

[0009] The present invention is directed to a powder coating composition comprising: (a) an addition polymer comprising epoxy functionality, the addition polymer being derived from components comprising (i) at least one epoxy-functional ethylenically unsaturated monomer, the components comprising an amount of (i) the at least one epoxy-functional ethylenically unsaturated monomer in the range of greater than 10% and less than 22% by weight, based on the components forming the addition polymer; (b) a carboxylic acid-functional crosslinker; and (c) a blocked isocyanate-functional crosslinker.

[0010] The powder coating composition includes an addition polymer, which may be formed from the linkage of monomers without the co-production of other by-products. The components used to form the addition polymer may be solid at ambient temperature (20°C to 25°C). The addition polymer of the powder coating composition may be derived from an ethylenically unsaturated monomer (e.g., by emulsion polymerization). As used herein, "ethylenically unsaturated" refers to a group having at least one carbon-carbon double bond. Non-limiting examples of ethylenically unsaturated groups include, but are not limited to, a (meth)acrylate group, a (meth)acrylamide group, a vinyl group, or a combination thereof. As used herein, the term "(meth)acrylate" refers to both methacrylate and acrylate. Additionally, terms such as "(meth)acrylamide" refer to both acrylamide and methacrylamide.

[0011] The addition polymer is derived from components including at least one epoxy-functional ethylenically unsaturated monomer. The addition polymer may be derived from additional components, such as additional ethylenically unsaturated monomers, which may be different from the epoxy-functional ethylenically unsaturated monomer.

[0012] Non-limiting examples of epoxy-functional ethylenically unsaturated monomers include glycidyl methacrylate, glycidyl acrylate, 3,4-epoxy-1-butene, and (R)-(+)-1,2-epoxy-9-decene. For example, one non-limiting example of an epoxy-functional ethylenically unsaturated monomer is the Epoxy Embedding Medium kit available from SigmaAldrich (St. Louis, MO). Epoxy-functional (meth)acrylate monomers include mono-epoxy-functional (meth)acrylate monomers.

[0013] The components used to form the addition polymer include the epoxy-functional ethylenically unsaturated monomer in an amount greater than 10% and less than 22% by weight, based on the components forming the addition polymer. The components used to form the addition polymer may include the epoxy-functional ethylenically unsaturated monomer in an amount of 15% to 20% by weight, based on the components forming the addition polymer.

[0014] The epoxy-functional ethylenically unsaturated monomer may contain at least one, or at least two, or at least three epoxy functional groups in the epoxy-functional ethylenically unsaturated monomer. The epoxy-functional ethylenically unsaturated monomer may contain exactly one epoxy functional group, such that the epoxy-functional ethylenically unsaturated monomer is a mono-epoxy-functional ethylenically unsaturated monomer. The epoxy-functional ethylenically unsaturated monomer may contain from one to three epoxy functional groups in the epoxy-functional ethylenically unsaturated monomer.

[0015] The addition polymer may contain at least one, at least two, or at least three epoxy functional groups per repeat unit of the addition polymer. The addition polymer may contain exactly one epoxy functional group per repeat unit of the addition polymer. The addition polymer may contain from one to three epoxy functional groups per repeat unit of the addition polymer.

[0016] The additional ethylenically unsaturated monomers may include mono-ethylenically unsaturated monomers, multi-ethylenically unsaturated monomers, or combinations thereof. A mono-ethylenically unsaturated monomer refers to a monomer containing only one ethylenically unsaturated group, and a multi-ethylenically unsaturated monomer refers to a monomer containing two or more ethylenically unsaturated groups.

[0017] Non-limiting examples of ethylenically unsaturated monomers that are different from epoxy-functional ethylenically unsaturated monomers include, but are not limited to, alkyl esters of (meth)acrylic acid, hydroxyalkyl esters of (meth)acrylic acid, acid group containing ethylenically unsaturated monomers, vinyl aromatic monomers, (meth)acrylamide monomers, and combinations thereof.

[0018] Non-limiting examples of alkyl esters of (meth)acrylic acid include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, isobutyl (meth)acrylate, ethylhexyl (meth)acrylate, lauryl (meth)acrylate, octyl (meth)acrylate, isononyl (meth)acrylate, isodecyl (meth)acrylate, vinyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, acetoacetoxypropyl (meth)acrylate, and combinations thereof. Other non-limiting examples include di(meth)acrylate alkyl diesters formed from the condensation of two equivalents of (meth)acrylic acid with, for example, ethylene glycol di(meth)acrylate. C esters such as butanediol and hexanediol are also suitable. 2- C 24 Di(meth)acrylate alkyl diesters formed from diols may also be used.

[0019] Non-limiting examples of hydroxyalkyl esters of (meth)acrylic acid include hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, and combinations thereof.

[0020] Non-limiting examples of acid group containing ethylenically unsaturated monomers include (meth)acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, aspartic acid, malic acid, mercaptosuccinic acid, and combinations thereof.

[0021] Non-limiting examples of vinyl aromatic monomers include styrene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, vinylnaphthalene, vinyltoluene, divinyl aromatic monomers such as divinylbenzene, and combinations thereof.

[0022] Non-limiting examples of (meth)acrylamide monomers include acrylamide, methacrylamide, di-(meth)acrylamide functional monomers such as N,N-dimethylacrylamide, N,N'-methylenebisacrylamide, and combinations thereof.

[0023] The additional ethylenically unsaturated monomer may include a functional ethylenically unsaturated monomer different from the epoxy-functional ethylenically unsaturated monomer. As used herein, the term "functional ethylenically unsaturated monomer" refers to an ethylenically unsaturated monomer that, in addition to an ethylenically unsaturated carbon-carbon double bond, contains a group reactive with the functional group of another component of the coating composition. The functional ethylenically unsaturated monomer may have at least one of a variety of reactive functional groups, including, but not limited to, amine, hydroxyl, thiol, carbamate, amide, urea, carboxyl, aldehyde, ester, ether, carbonyl, and combinations thereof. Non-limiting examples of functional ethylenically unsaturated monomers include esters of acrylic or methacrylic acid and hydroxyl-functional monomers such as hydroxyethyl methacrylate. In one non-limiting example, the functional ethylenically unsaturated monomer may contain an additional group that is reactive with the functional group of another component of the coating composition, but is not reactive with the epoxy functionality of the at least one epoxy-functional ethylenically unsaturated monomer used to obtain the addition polymer.

[0024] The additional ethylenically unsaturated monomer may include a non-functional ethylenically unsaturated monomer. As used herein, the term "non-functional ethylenically unsaturated monomer" refers to an ethylenically unsaturated monomer that does not contain, in addition to an ethylenically unsaturated carbon-carbon double bond, a group that is reactive with the functional group of another component of the coating composition. The non-functional ethylenically unsaturated monomer may include an aliphatic non-functional ethylenically unsaturated monomer and / or an aromatic non-functional ethylenically unsaturated monomer. Non-limiting examples of non-functional ethylenically unsaturated monomers include styrene, methyl methacrylate, and n-butyl methacrylate.

[0025] The additional ethylenically unsaturated monomer may comprise at least one, at least two, at least three, at least four, or more different ethylenically unsaturated monomers. The additional ethylenically unsaturated monomer or monomers may comprise only functional ethylenically unsaturated monomers, only non-functional ethylenically unsaturated monomers, or a combination of both functional and non-functional ethylenically unsaturated monomers. The additional ethylenically unsaturated monomer may comprise multiple different non-functional ethylenically unsaturated monomers. The non-functional ethylenically unsaturated monomers may comprise aliphatic non-functional ethylenically unsaturated monomers and aromatic non-functional ethylenically unsaturated monomers.

[0026] The components used to form the addition polymer may include the additional ethylenically unsaturated monomer in an amount of at least 50%, or at least 55%, or at least 60%, or at least 65% by weight, based on the components forming the addition polymer. The components used to form the addition polymer may include the additional ethylenically unsaturated monomer in an amount of up to 85%, or up to 80%, or up to 75%, or up to 70% by weight, based on the components forming the addition polymer. The components used to form the addition polymer may include the additional ethylenically unsaturated monomer in a range of 50% to 85% by weight, such as 55% to 80%, or 60% to 75%, or 65% to 70% by weight, based on the components forming the addition polymer.

[0027] In one non-limiting embodiment, the components used to form the addition polymer can include epoxy-functional ethylenically unsaturated monomer in the range of 10% to 22% by weight based on the components forming the addition polymer, additional ethylenically unsaturated monomer in an amount in the range of 50% to 85% by weight based on the components forming the addition polymer, with the remainder of the weight balance of the components used to form the addition polymer being additional materials and additives.

[0028] The addition polymer may have a number average molecular weight of at least 1,000 g / mol or at least 2,000 g / mol. The addition polymer may have a number average molecular weight of up to 8,000 g / mol or up to 5,000 g / mol. The addition polymer may have a number average molecular weight in the range of 1,000 g / mol to 8,000 g / mol, such as 2,000 g / mol to 5,000 g / mol.

[0029] The addition polymer may have a weight average molecular weight of at least 2,000 g / mol, or at least 4,000 g / mol, or at least 5,000 g / mol. The addition polymer may have a weight average molecular weight of up to 20,000 g / mol, or up to 16,000 g / mol, or up to 15,000 g / mol, or up to 12,000 g / mol. The addition polymer may have a weight average molecular weight in the range of 2,000 g / mol to 20,000 g / mol, such as 4,000 g / mol to 20,000 g / mol, such as 5,000 g / mol to 20,000 g / mol, such as 2,000 g / mol to 16,000 g / mol, such as 5,000 g / mol to 15,000 g / mol, or 4,000 g / mol to 12,000 g / mol. For example, the addition polymer can have a weight average molecular weight in the range of 7,000 g / mol to 8,000 g / mol.

[0030] Molecular weights (both number and weight average), as used herein, are determined by gel permeation chromatography using polystyrene standards according to ASTM D6579-11 (performed using a Waters 2695 Separation Module equipped with a Waters 2414 Differential Refractometer (RI detector), using tetrahydrofuran (THF) as the eluent at a flow rate of 1 mL / min, and two PLgel Mixed-C (300 x 7.5 mm) columns for separation at room temperature. Weight and number average molecular weights of polymer samples can be measured by gel permeation chromatography relative to linear polystyrene standards of 800-900,000 Da).

[0031] The addition polymer may have a Tg of at least 25°C, or at least 30°C, or at least 40°C, or at least 50°C. The addition polymer may have a Tg of up to 175°C, or up to 150°C, or up to 100°C, or up to 90°C, or up to 80°C, or up to 70°C. The addition polymer may have a Tg in the range of 25°C to 175°C, or 25°C to 150°C, or 25°C to 100°C, or 25°C to 90°C, or 30°C to 90°C, or 40°C to 90°C, or 40°C to 80°C, or 50°C to 80°C, or 50°C to 70°C. As used herein, the term "Tg" refers to the glass transition temperature as measured by differential scanning calorimetry according to ASTM D3418-12, unless otherwise indicated.

[0032] Addition polymers can include thermosetting polymers. Thus, as used herein, a "thermosetting" polymer refers to a resin that is irreversibly hardened upon curing or crosslinking, where the polymer chains of the polymer components are joined together by covalent bonds. Upon curing or crosslinking, a thermosetting polymer does not melt upon application of heat and is insoluble in solvents. Additionally, as used herein, a "thermoplastic" polymer refers to a polymer that includes polymer components that are not covalently bonded, thereby capable of undergoing liquid flow upon heating, and that are soluble in solvents.

[0033] The powder coating composition may comprise the addition polymer in an amount of at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 85% by weight, based on the total solids weight of the powder coating composition. The powder coating composition may comprise the addition polymer in an amount of up to 96%, or up to 95%, or up to 94%, or up to 90% by weight, based on the total solids weight of the powder coating composition. The powder coating composition may comprise the addition polymer in an amount ranging from 50% to 96% by weight, or from 60% to 96% by weight, or from 70% to 96% by weight, or from 70% to 94% by weight, or from 80% to 96% by weight, or from 80% to 95% by weight, or from 80% to 90% by weight, or from 85% to 96% by weight, or from 85% to 95% by weight, or from 85% to 90% by weight, based on the total solids weight of the powder coating composition.

[0034] The powder coating composition includes a carboxylic acid functional crosslinker. As used herein, "crosslinker" refers to a chemical species containing two or more functional groups that are reactive with other functional groups and capable of linking two or more monomer or polymer molecules through covalent bonds. The carboxylic acid functional crosslinker may be reactive with epoxide groups, such as epoxide groups of an addition polymer. The carboxylic acid functional crosslinker may be solid at ambient temperature (20°C to 25°C).

[0035] Carboxylic acid functional crosslinkers can include various types of polyacids. As used herein, "polyacid" refers to a compound containing at least two carboxylic acid functional groups. Carboxylic acid functional crosslinkers include C3-C4 crosslinkers with two or more carboxylic acid functional groups. 30 The carboxylic acid functional crosslinker may comprise an alkyl, alkenyl, or alkynyl compound. HO2C-[(CH2) n ]-CO2H where n is an integer ranging from 1 to 18. Examples of carboxylic acid functional crosslinkers include polycarboxy compounds such as dodecanedioic acid and its derivatives, azelaic acid, terephthalic acid, isophthalic acid, adipic acid, succinic acid, pimelic acid, sebacic acid, maleic acid, citric acid, itaconic acid, aconitic acid, octadecanedioic acid, etc. Further examples of aliphatic dicarboxylic acids include 1,2-, 1,3-, and 1,4-cyclohexanedicarboxylic acid.

[0036] The carboxylic acid functional crosslinker may comprise a carboxylic acid group-containing polymer, examples of which include acrylic polymers, polyester polymers, and polyurethane polymers, where the acrylic polymers, polyester polymers, and / or polyurethane polymers contain two or more carboxylic acid groups.

[0037] The carboxylic acid functional crosslinker may comprise a combination of polyacids. The combination of polyacids may comprise any of the polyacids previously disclosed that are suitable for use in the carboxylic acid functional crosslinker. For example, the carboxylic acid functional crosslinker may comprise a combination of at least two, or at least three, or at least four, or at least five polyacids.

[0038] The powder coating composition may comprise the carboxylic acid functional crosslinker in an amount of at least 3 wt%, or at least 5 wt%, or at least 7 wt%, or at least 7.5 wt%, based on the total solids weight of the powder coating composition. The powder coating composition may comprise the carboxylic acid functional crosslinker in an amount of up to 20 wt%, or up to 18 wt%, or up to 15 wt%, or up to 12 wt%, based on the total solids weight of the powder coating composition. The powder coating composition may comprise the carboxylic acid functional crosslinker in an amount ranging from 3 wt% to 20 wt%, or from 5 wt% to 18 wt%, or from 5 wt% to 15 wt%, or from 5 wt% to 12 wt%, or from 7 wt% to 15 wt%, or from 7.5 wt% to 12 wt%, based on the total solids weight of the powder coating composition.

[0039] The addition polymer and the carboxylic acid functional crosslinker can react to form a reaction product containing at least one hydroxyl group, and at least one acid group of the crosslinker can react with at least one epoxy group of the addition polymer.

[0040] The powder coating composition includes a blocked isocyanate-functional crosslinker. The blocked isocyanate-functional crosslinker (when unblocked) can react with hydroxyl groups, such as the hydroxyl groups of the reaction product of the addition polymer and the carboxylic acid-functional crosslinker. The blocked isocyanate-functional crosslinker can be solid at ambient temperature (20°C to 25°C).

[0041] The blocked isocyanate-functional crosslinker may include a polyisocyanate. As used herein, the term "polyisocyanate" refers to a compound containing two or more isocyanate functional groups. Polyisocyanates that can be used include aliphatic and aromatic diisocyanates, as well as polyisocyanates of higher functionality. Non-limiting examples of suitable polyisocyanates include isophorone diisocyanate (IPDI), dicyclohexylmethane 4,4'-diisocyanate (H12MDI), cyclohexyl diisocyanate (CHDI), m-tetramethylxylylene diisocyanate (m-TMXDI), p-tetramethylxylylene diisocyanate (p-TMXDI), ethylene diisocyanate, 1,2-diisocyanatopropane, 1,3-diisocyanatopropane, 1,6-diisocyanatohexane (hexamethylene diisocyanate or HDI), 1, 4-butylene diisocyanate, lysine diisocyanate, 1,4-methylenebis-(cyclohexyl isocyanate), toluene diisocyanate (TDI), m-xylylene diisocyanate (MXDI) and p-xylylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 1,5-tetrahydro-naphthalene diisocyanate, 4,4'-dibenzyl diisocyanate, and 1,2,4-benzenetricyanate, xylylene diisocyanate (XDI), and mixtures and combinations thereof.

[0042] In some examples, two or more isocyanate-functional crosslinkers may be linked together as dimers and / or trimers to form a polyisocyanate, such as a trimer of IPDI.

[0043] As used herein, the term "blocked isocyanate" refers to a compound having an isocyanate functional group that is internally blocked and / or reacted with an external blocking agent to prevent the isocyanate functional group from reacting until the internal and / or external blocking agent is removed, such as upon exposure to an external stimulus such as heat. Non-limiting examples of external blocking agents include phenols, pyridinols, thiophenols, methyl ethyl ketoxime, amides, caprolactams (e.g., ε-caprolactam), imidazoles, and pyrazoles. Blocked isocyanates can include uretdione isocyanates, such as uretdione internally blocked isocyanate adducts.

[0044] The blocked isocyanate-functional crosslinker may include ε-caprolactam-blocked isophorone diisocyanate. The ε-caprolactam-blocked isophorone diisocyanate may primarily include blocked difunctional monomeric isophorone diisocyanate, such as a mixture of cis and trans isomers of 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate, its blocked difunctional dimer, its blocked trifunctional trimer, or a mixture of monomeric, dimeric, and / or trimeric forms. The blocked isocyanate-functional crosslinker may include a mixture including ε-caprolactam-blocked difunctional monomeric isophorone diisocyanate and ε-caprolactam-blocked trifunctional trimer of isophorone diisocyanate.

[0045] The blocked isocyanate functional crosslinker is a 1,3-diazetidine-2,4-dione dimer of isophorone diisocyanate with the structure: [ka] wherein n is equal to or greater than 1 and R 1 is a divalent 1-methylene-1,3,3-trimethyl-5-cyclohexyl radical, e.g., the structure: [ka] is a radical having the formula R 2 is a divalent aliphatic, alicyclic, araliphatic, or aromatic residue of a diol, and X is a 1,3-diazetidine-2,4-dionediyl radical, for example, a radical having the following structure: [ka] The ratio of NCO to OH groups in the formation of the adduct can be 1:0.5 to 1:0.9. The molar ratio of diazetidinedione to diol can be 2:1 to 10:9. The content of free isocyanate groups in the adduct should not exceed 8 wt. % based on the total weight of the adduct. The adduct can have a weight and / or number average molecular weight of 500 to 4000. The adduct can have a melting point and / or Tg of 40°C to 130°C. As used herein, melting point and / or Tg are measured using differential scanning calorimetry according to ASTM D3418-12 unless otherwise specified.

[0046] Adducts of the 1,3-diazetidine-2,4-dione dimer of isophorone diisocyanate with a diol can be prepared by reacting the diazetidine dimer of isophorone diisocyanate (in some instances, not including the isocyanurate trimer of isophorone diisocyanate) with a diol in a ratio of reactants that provides an isocyanate:hydroxyl ratio of 1:0.5 to 1:0.9, such as 1:0.6 to 1:0.8. The adducts can have weight or number average molecular weights of 1450 to 2800 and melting points of 85°C to 120°C. The diol reactant can include 1,4-butanediol.

[0047] The powder coating composition may comprise an isocyanate-functional crosslinker in an amount of at least 0.1 wt%, or at least 0.5 wt%, or at least 1 wt%, or at least 3 wt%, or at least 5 wt%, based on the total solids weight of the powder coating composition. The powder coating composition may comprise an isocyanate-functional crosslinker in an amount of up to 20 wt%, or up to 15 wt%, or up to 12 wt%, or up to 10 wt%, based on the total solids weight of the powder coating composition. The powder coating composition may comprise an isocyanate-functional crosslinker in an amount ranging from 0.1 wt% to 20 wt%, or from 0.5 wt% to 20 wt%, or from 1 wt% to 20 wt%, or from 2 wt% to 20 wt%, or from 3 wt% to 20 wt%, or from 3 wt% to 15 wt%, or from 3 wt% to 12 wt%, or from 3 wt% to 10 wt%, or from 5 wt% to 10 wt%, based on the total solids weight of the powder coating composition.

[0048] The blocked isocyanate-functional crosslinker can be unblocked when the powder coating composition is heated to a temperature of at least 100°C, or at least 120°C, or at least 150°C, or at least 180°C, allowing the isocyanate groups to react with the hydroxyl groups of the reaction product of the epoxy-functional addition polymer and the carboxylic acid-functional crosslinker. The additional crosslinking provided by the isocyanate-functional crosslinker can provide the resulting coating with improved acid etch resistance.

[0049] The powder coating composition may comprise, based on the total solids weight of the powder coating composition, 50% to 96% by weight of the addition polymer (a), 3% to 20% by weight of the carboxylic acid functional crosslinker (b), and 0.1% to 20% by weight of the blocked isocyanate functional crosslinker (c). The powder coating composition may comprise, based on the total solids weight of the powder coating composition, 70% to 94% by weight of the addition polymer (a), 5% to 18% by weight of the carboxylic acid functional crosslinker (b), and 1% to 20% by weight of the blocked isocyanate functional crosslinker (c). The powder coating composition may comprise, based on the total solids weight of the powder coating composition, 75% to 90% by weight of the addition polymer (a), 5% to 15% by weight of the carboxylic acid functional crosslinker (b), and 3% to 15% by weight of the blocked isocyanate functional crosslinker (c). The powder coating composition may comprise the addition polymer (a) in the range of 80% to 85% by weight, the carboxylic acid functional crosslinker (b) in the range of 5% to 12% by weight, and the blocked isocyanate functional crosslinker (c) in the range of 3% to 10% by weight, based on the total solids weight of the powder coating composition. For example, the powder coating composition may comprise the addition polymer (a) in an amount of 82% by weight, the carboxylic acid functional crosslinker (b) in an amount of 11% by weight, and the blocked isocyanate functional crosslinker (c) in an amount of 7% by weight, based on the total solids weight of the powder coating composition.

[0050] The powder coating composition may contain additional materials. Non-limiting examples of materials that may be included in the powder coating composition include plasticizers, antioxidants, flow agents, surface control agents (e.g., anti-crater additives), thixotropic agents, slip aids, catalysts, gas suppressants such as benzoin, reaction inhibitors (e.g., corrosion inhibitors), texturizers, UV absorbers, thermo-oxidative stabilizers, light stabilizers (e.g., hindered amine light stabilizers (HALS)), and other conventional adjuvants.

[0051] The powder coating composition may include pigment. Alternatively, the powder coating composition may be substantially free, essentially free, or completely free of pigment. The phrase "substantially free of pigment" means that the coating composition contains less than 1000 parts per million (ppm) by weight pigment based on the total solids weight of the powder coating composition, "essentially free of pigment" means that the coating composition contains less than 100 ppm pigment based on the total solids weight of the powder coating composition, and "completely free of pigment" means that the coating composition contains less than 20 parts per billion (ppb) pigment based on the total solids weight of the powder coating composition.

[0052] Exemplary pigments and / or pigment compositions include, but are not limited to, carbazole dioxazine crude pigments, azo, monoazo, diazo, naphthol AS, salt forms (flakes), benzimidazolone, isoindolinone, isoindoline, and polycyclic phthalocyanines, quinacridone, perylene, perinone, diketopyrrolopyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazine, triarylcarbonium, quinophthalone pigments, diketopyrrolopyrrole red ("DPPBO red"), titanium dioxide, carbon black, and mixtures or combinations thereof.

[0053] The present invention also relates to substrates at least partially coated with a coating formed from the powder coating compositions described herein. For example, the powder coating compositions may be applied to vehicle substrates, including automotive substrates, industrial substrates, aerospace substrates, marine substrates, packaging substrates, electronics substrates, building substrates, and the like.

[0054] In this disclosure, the term "vehicle" is used in the broadest sense and includes all types of aircraft, spacecraft, watercraft, and ground vehicles. For example, vehicles can include, but are not limited to, aircraft such as airplanes (e.g., private airplanes and small, medium, or large commercial passenger, cargo, and military airplanes), helicopters (e.g., private, commercial, and military helicopters), and aerospace vehicles (e.g., rockets and other spacecraft). Vehicles can also include ground vehicles such as animal trailers (e.g., horse trailers), cars, trucks, buses, vans, heavy-duty equipment, golf carts, motorcycles, bicycles, trains, and railcars. Vehicles can also include watercraft such as ships, boats, and hovercraft.

[0055] The coating compositions may be applied over industrial substrates, which may include tools, heavy-duty equipment, furniture such as office furniture (e.g., office chairs, desks, filing cabinets, etc.), appliances such as refrigerators, ovens and ranges, dishwashers, microwave ovens, washing machines, dryers, small appliances (e.g., coffee makers, slow cookers, pressure cookers, blenders, etc.), metal hardware, extruded metals such as extruded aluminum used in window frames, other indoor and outdoor metal building materials, and the like.

[0056] Suitable building substrates over which the coating composition can be applied include, but are not limited to, metallic or non-metallic substrates, including concrete, stucco, masonry elements, cement board, MDF (medium density fiberboard) and particle board, gypsum board, wood, stone, metal, plastic (e.g., vinyl siding and recycled plastic), wallpaper, fabric, plaster, fiberglass, ceramic, etc., which can be pre-primed with a water-based or solvent-based primer. The building substrate can be the interior wall (or other interior surface) of a building or home. The building substrate can also be an outdoor substrate exposed to outdoor conditions. The building substrate can be smooth or textured.

[0057] Specific non-limiting substrates include cars, trucks, ships, vessels, onshore and offshore installations, storage tanks, wind turbines, power generation industry substrates such as nuclear power plants, electrical wire, batteries and battery components, bus bars, metal wire, copper or aluminum conductors, wood flooring and furniture, apparel, housings and circuit boards, glass and transparency sheets, sporting goods including golf balls, stadiums, buildings, bridges, and the like.

[0058] The powder coating composition can be applied over at least a portion of a substrate, including a metal wheel, such as a metal wheel included as a vehicle component, such as an automobile metal wheel. The metal wheel can comprise aluminum, steel, magnesium, or an alloy thereof. The powder coating composition can be applied over at least a portion of the metal wheel. The powder coating composition can be applied as a monocoat over the metal wheel or as a coating layer in a multi-layer coating system applied to the metal wheel.

[0059] Substrates can include, for example, metallic or non-metallic substrates. Metallic substrates include, but are not limited to, tin, steel (including electrogalvanized steel, cold-rolled steel, and hot-dip galvanized steel, among others), aluminum, aluminum alloys, zinc-aluminum alloys, zinc-aluminum alloy-coated steel, and aluminized steel. Metallic substrates can include aluminum, steel, magnesium, or alloys thereof. Non-metallic substrates include polymers, plastics, polyesters, polyolefins, polyamides, cellulose, polystyrene, polyacrylics, poly(ethylene naphthalate), polypropylene, polyethylene, nylon, EVOH, polylactic acid, other "eco-friendly" polymer substrates, poly(ethylene terephthalate) (PET), polycarbonate, polycarbonate acrylobutadiene styrene (PC / ABS), polyamides, wood, veneers, wood composites, particleboard, medium-density fiberboard, cement, stone, glass, paper, cardboard, fabrics, and both synthetic and natural leathers.

[0060] The coating composition can be applied to a substrate to form a monocoat. As used herein, "monocoat" refers to a single-layer coating system that does not include an additional coating layer. Thus, the coating composition can be applied directly to a substrate and cured to form a single-layer coating, i.e., a monocoat. A single coating layer can be applied over a pretreatment layer, as defined below, which is not a coating layer. When a curable coating composition is applied to a substrate to form a monocoat, the coating composition can include additional components to provide other desired properties. For example, the curable coating composition can also include an inorganic component that acts as a corrosion inhibitor. As used herein, "corrosion inhibitor" refers to a component, such as a material, substance, compound, or composite, that reduces the rate or severity of corrosion on the surface of a metal or metal alloy substrate. Inorganic components that act as corrosion inhibitors can include, but are not limited to, alkali metal components, alkaline earth metal components, transition metal components, or combinations thereof.

[0061] The term "alkali metal" refers to Group 1 elements of the Periodic Table of Chemical Elements (International Union of Pure and Applied Chemistry (IUPAC)), including, for example, cesium (Cs), francium (Fr), lithium (Li), potassium (K), rubidium (Rb), and sodium (Na). The term "alkaline earth metal" refers to Group 2 elements of the Periodic Table of Chemical Elements (IUPAC), including, for example, barium (Ba), beryllium (Be), calcium (Ca), magnesium (Mg), and strontium (Sr). The term "transition metal" refers to Groups 3-12 elements of the Periodic Table of Chemical Elements (IUPAC), including, for example, titanium (Ti), chromium (Cr), and zinc (Zn), among others.

[0062] Specific non-limiting examples of inorganic components that act as corrosion inhibitors include magnesium oxide, magnesium hydroxide, magnesium carbonate, magnesium phosphate, magnesium silicate, zinc oxide, zinc hydroxide, zinc carbonate, zinc phosphate, zinc silicate, zinc dust, and / or combinations thereof.

[0063] The compositions of the present invention can be used alone or in combination with one or more other compositions, such as in coating systems having two or more coating layers (multi-layer coating systems). For example, the compositions of the present invention, which may or may not contain pigments, can be used as a primer layer, a base coat, and / or a top coat.

[0064] The coating composition can be used to form a primer layer. As used herein, a "primer layer" refers to an undercoating that can be deposited on a substrate to prepare the surface for the application of a protective or decorative coating system.

[0065] The coating composition can be used to form a topcoat layer. The term "topcoat" as used herein refers to a top coating deposited over another coating layer, such as a basecoat, to provide a protective and / or decorative layer. The topcoat layer can be a clearcoat layer. A clearcoat layer is understood to be a coating layer that is substantially transparent or translucent. Thus, the clearcoat layer may have some color, provided that it does not render the clearcoat opaque or significantly affect the ability to reveal the underlying substrate. The clearcoat layer can be used, for example, in combination with a pigmented basecoat. The coating composition can be used as a topcoat layer over a substrate to provide durability to the substrate.

[0066] The coating composition can be used to form a basecoat layer. A multi-layer coating system can have a first basecoat and a second basecoat coated over the first basecoat. The term "basecoat" as used herein refers to a coating that is deposited directly on a primer and / or substrate, and optionally includes components (such as pigments) that affect color and / or provide other visual effects. In a substrate coated with multiple basecoat layers, one or more of the basecoat layers can be formed from the coating composition described herein.

[0067] Compositions such as pigmented basecoats or pigmented monocoats used in conjunction with clearcoats may contain pigments. Such coating layers for providing decorative and / or protective finishes may be used in a variety of industries. For example, such coatings or coating systems may be applied to vehicles, such as vehicle wheels. It will be understood that the portion of a vehicle coated in accordance with the present invention may vary depending on the reason for the coating's use. When used as a pigmented basecoat or monocoat, the coating may be applied to those visible portions of a vehicle, such as the roof, hood, doors, and trunk lid, but may also be applied to other areas, such as the inside of the trunk or inside of the doors, particularly when the composition is formulated as a sealant or adhesive. For example, the composition may be formulated to have a viscosity that provides sound and / or vibration damping to the vehicle. The composition may also be applied to those portions of a vehicle that come into contact with the driver and / or passengers, such as the steering wheel, dashboard, gearshift, controls, and door handles. Clearcoats may be applied to the exterior of a vehicle.

[0068] The substrate may include a pretreatment layer disposed over the substrate and a coating formed from a powder coating composition described herein disposed over at least a portion of the pretreatment layer. As used herein, "pretreatment layer" refers to a layer formed from a composition that reacts with and chemically alters the substrate surface to achieve at least one of the following: 1) forming a protective layer, 2) improving the shape or reactivity of the substrate to enhance coating adhesion, or 3) forming a protective layer with improved coating adhesion compared to a substrate not including the pretreatment. The pretreatment layer may form a discontinuous layer over the surface. Non-limiting examples of pretreatment layer compositions include compositions containing iron phosphate, manganese phosphate, zinc phosphate, rare earth metals, permanganates or manganese, molybdates or molybdenum, zirconium, titanium, hafnium, lanthanides, silanes such as alkoxysilanes, hydrolyzed silanes, and silane oligomers and polymers, metal chelates, trivalent chromium (TCP), silicates, silica, phosphonic acids, chromate coatings, hydrotalcites, layered double hydroxides, metal oxides, other metals such as Group IV metals, or any combination thereof. Non-limiting examples of organic pretreatments include phosphated epoxies, silanated epoxies, and chemically modified resins such as amino-functional resins. Pretreatments can also include anodizing using, for example, sulfuric acid, nitric acid, hydrofluoric acid, tartaric acid, and / or other anodizing methods. Pretreatment layer compositions can be in sol-gel, liquid, or solid form. In some cases, the pretreatment may contain or be sealed using an oligomeric or polymeric solution or suspension. In yet other examples, the pretreatment composition may contain small organic molecules that contain reactive functional groups or that function as corrosion inhibitors.

[0069] The present invention also relates to a method of applying the powder coating composition described herein to a substrate. Once prepared, the powder coating composition can be applied to at least a portion of a substrate and cured to form a coating. The powder coating composition can be applied to a substrate using any suitable technique. Suitable methods for applying the powder coating composition to any of the aforementioned substrates include electrostatic spraying, dipping, and the like. The powder coating composition can be applied in a single pass or multiple passes to provide a film having a cured thickness of 1 to 10 mils, such as 1 to 5 mils. After application, the composition can be cured by heating to a temperature of 120°C to 220°C, such as 140°C to 190°C, or 160°C to 180°C, for a period ranging from 3 to 30 minutes, such as 15 to 25 minutes. Heating by any means known in the art, such as by placing the coated substrate in an oven, can be effective. IR radiation can be used to cure the coated substrate.

[0070] Powder coating compositions can be used to reduce filiform corrosion. As used herein, "filiform corrosion" refers to a type of corrosion that occurs in thin films and coatings, characterized by thread-like, filament-like defects on and / or below the surface of the coating. The powder coating composition can form a coating over at least a portion of a substrate and can reduce the amount of filiform corrosion on the coated substrate compared to an identical substrate that does not include a coating formed from the powder coating composition under the same conditions (i.e., the same environmental conditions). For example, it has been found that coated substrates of the present invention can provide improved filiform corrosion resistance (as tested in accordance with SAE J2635 "Filiform Corrosion Test Procedure for Painted Aluminum Wheels and Painted Aluminum Wheel Trim") compared to an identical coated substrate that does not include a coating formed from the powder coating composition of the present invention. Furthermore, the coating composition of the present invention allows for avoidance of such corrosion without the need to spray a liquid composition before applying the powder coating. [Example]

[0071] The following examples are presented to demonstrate the general principles of the present invention and should not be construed as limited to the specific examples presented.

[0072] Example 1 Synthesis of powdered acrylic polymer A powdered acrylic polymer was prepared from the ingredients in Table 1. [Table 1]

[0073] Charge 1 was added to a four-neck, 3-L round-bottom flask equipped with a thermocouple, reflux condenser, nitrogen inlet port, air motor agitator, and two additional ports and heated to reflux (approximately 280°F (138°C)) under a nitrogen blanket. Once a temperature of approximately 280°F (138°C) was reached, Charges 2 and 4 were added simultaneously, with the addition occurring over 180 minutes. Upon completion of the addition of Charges 2 and 4, Charges 3 and 5, respectively, were used to rinse the addition funnel, and the batch was held at a constant temperature of 280°F (138°C) for 30 minutes. Charge 6 was then introduced over 30 minutes, followed by a rinse with Charge 7, and the batch was then held at a temperature of 280°F (138°C) for 30 minutes. Upon completion of polymerization, solvent was removed from the batch by vacuum distillation while the batch was gradually heated under vacuum to 338°F (170°C) and held at a constant temperature for an additional 60 minutes after distillate collection ceased. The final polymer had a number average molecular weight of 2,569 g / mol, a weight average molecular weight of 7,142 g / mol, a total solids content of 96.8%, and an epoxy equivalent weight of 1,470. As used herein, epoxy equivalent weight is the mass in grams of a sample containing one mole of epoxide functional groups, as determined by potentiometric titration with perchloric acid and quaternary ammonium bromide.

[0074] The powdered acrylic polymer formed in Example 1 from the ingredients in Table 1 corresponds to Resin #1 in Table 2 below. Resins #2-#5 were also formed using the method described in Example 1 and the ingredients in Table 1, except that the amount of each of the ingredients in Charge 2 was adjusted to reflect the weight percentage contained in each resin in Table 2. [Table 2]

[0075] Examples 2 to 13 Preparation of the Curable Coating Composition Twelve (12) curable coating compositions were prepared from the ingredients set forth in Table 3. [Table 3]

[0076] For each of Examples 2-13, each of the components listed in Table 3 was weighed into a container and mixed for 30 seconds in a PRISM high-speed mixer at 22,500 RPM to form a dry, homogenous mixture. The mixture was then melt-mixed in a Werner Pfleiderer 19mm twin-screw extruder with a tight screw configuration and a speed of 500 RPM. The first zone was set at 50°C, and the second, third, and fourth zones were set at 120°C. The feed rate was such that 30% to 45% torque was observed on the equipment. The mixture was dropped onto a set of chill rolls, allowing the mixture to cool and resolidify into solid chips. The chips were milled in a Mikro ACM-11 Air Classifying Mill to obtain an average particle size of 10 microns to 100 microns. The resulting coating compositions for each of Examples 2-13 were free-flowing, solid, particulate powder coating compositions.

[0077] Example 14 Preparation of aluminum test panels and application of powder coating For each of Examples 2-13, A-412 aluminum Q-Panels from ACT (Hillsdale, MI) were cleaned using ULTRAX 14AWS, an alkaline spray cleaner available from PPG Industries, Inc. (Pittsburgh, PA). Each panel was then deoxidized in AMC66AW acid etching solution available from PPG Industries, Inc. (Pittsburgh, PA). Each panel was then pretreated using XBOND 4000 zirconium pretreatment available from PPG Industries, Inc. (Pittsburgh, PA). Examples 2-13 were electrostatically applied to the panels at a film build of 2 mil to 5 mil. The coated panels were baked at a temperature of 171°C or 191°C (as specified in Table 4) for 30 minutes.

[0078] Example 15 Filiform corrosion resistance evaluation Each of the coatings made from the compositions of Examples 2-13 was evaluated for filiform corrosion resistance and final film thickness. Film build was measured with a dry film gauge from Elcometer. Filiform corrosion resistance was determined in accordance with SAE J2635. Panels were indented and placed in a copper-accelerated acetate spray cabinet for one day to initiate filiform corrosion growth. The panels were then placed in a humidity cabinet for 28 days to allow filiform fiber growth. Each panel was then measured for filiform corrosion using the SAE J2635 method, and the magnitude of creep for each filiform indent is provided in Table 4 below. [Table 4]

[0079] As shown in Table 4, coatings containing lower GMA contents are observed to exhibit the lowest filiform corrosion growth. For example, all coatings produced from the compositions of Examples 6-13, which contain less than 22 wt. % GMA, exhibit acceptable filiform corrosion resistance. However, as the GMA content increases to amounts greater than 22 wt. %, as in the coatings produced from the compositions of Examples 2-5, the coatings exhibit filiform corrosion resistance. Therefore, acceptable filiform corrosion resistance is achieved by incorporating less than 22 wt. % of the epoxy-functional ethylenically unsaturated monomer in the reactant mixture used to form the addition polymer. Furthermore, the GMA content that provided the best filiform corrosion resistance was in the range of greater than 10 wt. % and less than 22 wt. %.

[0080] Example 16 Physical property evaluation Each coating formed from the compositions of Examples 2-13 was also tested for physical properties and appearance. Adhesion testing was performed according to ISO 2409. Water immersion testing was performed according to NES M0007.29 (3 days of water immersion at 60°C followed by crosshatch adhesion). 100MEK double rub testing was performed according to ASTM D5402-15 under Appendix X1.2.2. Gasoline resistance was performed according to 4271Z-SNA-A000, where gasoline was applied to the panel at room temperature for 6.18 to 7 hours, and then the panel was checked for changes in appearance or adhesion. Appearance measurements were generated using a gloss meter and a BYK-MAC color reader. The data generated for each example is provided in Table 5 below. [Table 5]

[0081] As shown in Table 5, resins with very low GMA content are observed to produce inferior properties in the coatings in which they are used. For example, coatings produced from the compositions of Examples 2-9, which contain GMA contents greater than 15 wt%, exhibit only slight to moderate scratches from the MEK double rub test, maintain a smooth, glossy appearance after the gasoline resistance test, and exhibit acceptable adhesion to the panel. In contrast, coatings produced from the compositions of Examples 10-13 all exhibit severe scratches after the MEK double rub test, a smooth appearance after the gasoline resistance test, and little or no adhesion to the panel. Therefore, the most robust physical properties are achieved by incorporating at least 15 wt% of an epoxy-functional ethylenically unsaturated monomer into the mixture of reactants used to form the addition polymer.

[0082] By carefully selecting the components of the powder coating composition, specifically the amount of epoxy-functional ethylenically unsaturated monomer in the mixture of reactants used to form the addition polymers discussed herein, it was unexpected and surprising to find that coatings formed from powder coatings including a mixture of reactants containing greater than 10 wt. % and less than 22 wt. % epoxy-functional ethylenically unsaturated monomers had low filiform corrosion, and addition polymers formed from a mixture of reactants containing 15 wt. % to 20 wt. % epoxy-functional ethylenically unsaturated monomers had low filiform corrosion and excellent adhesion, were gasoline resistant, had a smooth, glossy appearance, and exhibited only slight to moderate scratches.

[0083] While particular embodiments of the present invention have been described above for purposes of illustration, it will be apparent to those skilled in the art that numerous changes can be made in the details of the invention without departing from the invention as defined in the appended claims.

Claims

1. 1. A powder coating composition comprising: (a) an addition polymer containing epoxy functional groups, said addition polymer comprising: (i) a component comprising at least one epoxy-functional ethylenically unsaturated monomer, said component comprising an amount of (i) said at least one epoxy-functional ethylenically unsaturated monomer in the range of greater than 10% and less than 22% by weight, based on the components forming said addition polymer; (ii) at least one non-functional ethylenically unsaturated monomer; an addition polymer consisting of (b) a carboxylic acid functional crosslinker; and (c) a blocked isocyanate-functional crosslinker; the powder coating composition comprising at least 70 wt. % of (a) the addition polymer, based on the total solids weight of the powder coating composition; Powder coating compositions.

2. 10. The powder coating composition of claim 1, wherein (i) the at least one epoxy-functional ethylenically unsaturated monomer comprises an epoxy-functional (meth)acrylate monomer.

3. The powder coating composition of claim 2, wherein the epoxy-functional (meth)acrylate monomer comprises a mono-epoxy-functional (meth)acrylate monomer.

4. 10. The powder coating composition of claim 1, wherein (ii) the at least one non-functional ethylenically unsaturated monomer comprises at least two different non-functional ethylenically unsaturated monomers.

5. 5. The powder coating composition of claim 4, wherein (ii) the non-functional ethylenically unsaturated monomers comprise aliphatic non-functional ethylenically unsaturated monomers and aromatic non-functional ethylenically unsaturated monomers.

6. 6. The powder coating composition of claim 4 or 5, wherein said components comprise at least 50% by weight, based on the components forming said addition polymer, of (ii) said non-functional ethylenically unsaturated monomer.

7. 7. The powder coating composition of claim 1, wherein the components comprise (i) the at least one epoxy-functional ethylenically unsaturated monomer in an amount in the range of 15% to 20% by weight, based on the components forming the addition polymer.

8. The powder coating composition of any one of claims 1 to 7, wherein the powder coating composition is substantially free of pigments.

9. The powder coating composition of any one of claims 1 to 8, wherein the addition polymer comprises a glass transition temperature of at least 30°C.

10. A substrate at least partially coated with a coating formed from the powder coating composition of any one of claims 1 to 9.

11. The substrate of claim 10 , wherein the substrate comprises a metal.

12. The substrate of claim 11 , wherein the metal comprises aluminum, steel, magnesium, or an alloy thereof.

13. The substrate according to any one of claims 10 to 12, wherein the substrate comprises a metal wheel for a vehicle.

14. The substrate of any one of claims 10 to 13, wherein the substrate comprises a pretreatment layer that underlies at least a portion of the coating.

15. The substrate of any one of claims 10 to 14, wherein the coating forms a monocoat over at least a portion of the substrate.

16. 1. A method of making a metal wheel, comprising: A method comprising applying the powder coating composition of any one of claims 1 to 9 over at least a portion of the metal wheel.

17. 17. The method of claim 16, wherein the powder coating composition is applied to form a monocoat over the at least a portion of the metal wheel.

18. Use of a powder coating composition according to any one of claims 1 to 9 for reducing filiform corrosion.

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