CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to European Patent Application No.

19184443.0, filed on July 4, 2019, and Indian Patent Application No. 201911008308, filed March 4, 2019, the entire contents of which are both incorporated by reference herein.

BACKGROUND

[0001] Many surface finishing industries are seeking alternative coatings which have less or no volatile organic compounds (VOC). As an example, steel is used for broad purposes in the engineering industry. Steel, as most of the metals employed in service life, is subject to deterioration either by corrosion at room temperature or by oxidation at high temperature. To prevent oxidation, chemical reaction, and erosion of steel at high temperatures, protective coatings are often applied. Powder coating provides a reliable barrier coating for substrates such as aluminum, steel, and other metal alloys. It also provides UV protection, abrasion resistance, and corrosion resistance.

[0002] Thermosetting epoxy resins exhibit excellent properties of toughness, corrosion resistance, and chemical resistance, as well as low cost. The properties make these resins ideal as coating materials in a variety of applications such as automotive coatings, building materials, and household electronic appliances. Advantageously, the epoxy resins have applicability as environmentally friendly powder coatings because they contain no organic solvents. However, powder coating formulations including conventional epoxy resins often lack high temperature stability, for example at temperatures higher than 160°C.

[0003] Accordingly, there remains a need for thermosetting epoxy powder coating compositions that can provide powder coatings with high temperature stability, good mechanical properties, and improved chemical stability.

BRIEF DESCRIPTION

[0004] According to an aspect, a powder coated substrate comprises a substrate; and a thermosetting epoxy powder coating composition, wherein the thermosetting epoxy powder coating composition is powder coated on the substrate, wherein the thermosetting epoxy powder coating composition comprises: 100 parts by weight of an epoxy resin composition; 30 to 200 parts by weight of an aromatic dianhydride curing agent; optionally a curing catalyst; and optionally an additional curing promoter, wherein an anhydride to epoxy stoichiometric ratio (A/E) is 0.1 : 1 to 1.6: 1, preferably 0.5: 1 to 1.3: 1, more preferably 0.6: 1 to 1.2: 1, as determined by molar ratio of total anhydride functionalities to total epoxy functionalities in the thermosetting epoxy powder coating composition, wherein the amounts are based on the total parts by weight of the epoxy resin composition and the aromatic dianhydride curing agent, and wherein the aromatic dianhydride curing agent is of formula (1)

wherein T is -0-, -S-, -SO2-, -SO-, -C _y H2 _y - wherein y is an integer from 2 to 5 or a halogenated derivative thereof, or -O-Z-O- wherein Z is an aromatic C6-24 monocyclic or polycyclic moiety optionally substituted with 1 to 6 Ci- ₈ alkyl groups, 1 to 8 halogen atoms, or a combination thereof, wherein the thermosetting epoxy powder coating composition after curing has a glass transition temperature of 120 to 320°C, preferably 160 to 320°C, more preferably 180 to 320°C, even more preferably 200 to 320°C, still more preferably 250 to 320°C, as determined by dynamic mechanical analysis, and wherein the thermosetting epoxy powder coating composition after curing has an impact resistance of greater than 2 Newton meters, preferably greater than 3 Newton meters, more preferably greater than 4 Newton meters, when measured according to ASTM D2794.

[0005] Another aspect provides a method of manufacturing the powder coated substrate, the method comprising applying the thermosetting epoxy powder coating composition to at least one surface of the substrate; preferably wherein the applying comprises electrostatically applying the thermosetting epoxy powder coating composition in particulate form.

[0006] The above described and other features are exemplified by the following detailed description.

DETAILED DESCRIPTION

[0007] This disclosure relates to a thermosetting epoxy powder coating composition for forming a powder coating on a substrate. The thermosetting epoxy powder coating composition includes an epoxy resin composition, an aromatic dianhydride curing agent, optionally an additional curing promoter, and optionally a curing catalyst. The inventors have discovered that an aromatic dianhydride, for example bisphenol-A dianhydride (BPA-DA), can be a useful curing agent for making high heat cured epoxy resins. The thermosetting epoxy powder coating composition including the aromatic dianhydride as an epoxy curing agent can provide a cured thermoset product, for example as a powder coating on a substrate, having good high heat resistance properties, such as a glass transition temperature of 230°C or greater.

[0008] Provided herein is a thermosetting epoxy powder coating composition including an epoxy resin composition, an aromatic dianhydride curing agent, optionally an additional curing promoter, and optionally a curing catalyst. The thermosetting epoxy powder coating composition after curing has a glass transition temperature (T _G ) of greater than or equal to 120°C. The thermosetting epoxy powder coating composition after powder coating a substrate and curing has an impact resistance of greater than 2 Newton meters (N m) when measured according to ASTM D2794. In particular aspects, the aromatic dianhydride curing agent is soluble in the epoxy resin composition. In some aspects, the thermosetting epoxy powder coating composition is substantially free of monoanhydride.

[0009] The stoichiometric ratio between the aromatic dianhydride curing agent and the epoxy resin composition is 0.1 : 1 to 2.0: 1 or 0.1 : 1 to 1.6: 1, preferably 0.4: 1 to 1.2: 1 or 0.5: 1 to 1.3: 1, more preferably 0.6: 1 to 1.2: 1 or 0.6: 1 to 1 : 1. The stoichiometric ratio is the molar ratio of total anhydride functionalities to the total epoxy functionalities in the thermosetting epoxy powder coating composition. The stoichiometric ratio is also referred to herein as the anhydride to epoxy (A/E) ratio.

[0010] The thermosetting epoxy powder coating composition includes 100 parts by weight of the epoxy resin composition, based on the total parts by weight of the epoxy resin composition, the aromatic dianhydride curing agent, and optionally the additional curing promoter. The epoxy resin composition can include one or more epoxy resins, such as bisphenol A epoxy resin, a triglycidyl-substituted epoxy resin, a tetraglycidyl-substituted epoxy resin, a bisphenol F epoxy resin, a phenol novolak epoxy resin, a cresol novolak epoxy resin, a cycloaliphatic diglycidyl ester epoxy resin, a cycloaliphatic epoxy resin comprising a ring epoxy group, an epoxy resin containing a spiro-ring, a hydantoin epoxy resin, or a combination thereof. In a particular aspect, the epoxy resin is bisphenol-A diglycidyl ether (BPA-DGE).

[0011] In some aspects, the epoxy resin composition may include one or more“high heat” epoxy compounds of formulas (I) to (IX):

wherein, in Formulas (I) to (IX), R ¹ and R ² at each occurrence are each independently an epoxide-containing functional group; R ^a and R ^b at each occurrence are each independently halogen, Ci-12 alkyl, C2-12 alkenyl, C3-8 cycloalkyl, or Ci-12 alkoxy; p and q at each occurrence are each independently 0 to 4; R ¹³ at each occurrence is independently a halogen or a Ci- ₆ alkyl group; c at each occurrence is independently 0 to 4; R ¹⁴ at each occurrence is independently a Ci - ₆ alkyl, phenyl, or phenyl substituted with up to five halogens or Ci- ₆ alkyl groups; R ^g at each occurrence is independently Ci-12 alkyl or halogen, or two R ^g groups together with the carbon atoms to which they are attached form a four-, five, or six-membered cycloalkyl group; and t is 0 to 10.

[0012] In other aspects, the epoxy resin composition does not include a compound of formulas (I) to (IX). That is, the epoxy resin composition, and by extension the thermosetting epoxy powder coating composition, is free of the high heat epoxy compounds of formulas (I) to (IX).

Preferably, the epoxy resin composition does not include a compound of formulas (I) to (IX).

[0013] The epoxide equivalent weight (EEW) of the epoxy resin composition is generally from 100 to 20,000 grams per equivalent (g/eq), preferably from 100 to 5,000 g/eq, more preferably from 100 to 1,000 pg/eq. As used herein the terms“epoxide equivalent weight” refers to the number average molecular weight of the epoxide moiety divided by the average number of epoxide groups present in the molecule.

[0014] The thermosetting epoxy powder coating composition includes 30 to 200 parts by weight of the aromatic dianhydride curing agent, based on the total parts by weight of the epoxy resin composition, the aromatic dianhydride curing agent, and optionally the additional curing promoter. For example, the thermosetting epoxy powder coating composition can include 50 to 150 parts by weight, preferably 60 to 140 parts by weight, more preferably 80 to 120 parts by weight of the aromatic dianhydride curing agent, based on the total parts by weight of the epoxy resin composition, the aromatic dianhydride curing agent, and optionally the additional curing promoter.

[0015] The aromatic dianhydride curing agent can be of the formula (1)

wherein T is -0-, -S-, -SO2-, -SO-, -CyFEy- wherein y is an integer from 1 to 5 or a halogenated derivative thereof, or -O-Z-O- wherein Z is an aromatic C6-24 monocyclic or polycyclic moiety optionally substituted with 1 to 6 Ci- ₈ alkyl groups, 1 to 8 halogen atoms, or a combination thereof. In some aspects, the R ¹ is a monovalent Ci-13 organic group. In some aspects, T is -O- or a group of the formula -O-Z-O- wherein the divalent bonds of the -O- or the -O-Z-O- group are in the 3,3', 3,4', 4,3', or the 4,4' positions. In particular aspects, T is not -O-, -SO2-, or -SO-.

[0016] Exemplary groups Z include groups of formula (2)

wherein R ^a and R ^b are each independently the same or different, and are a halogen atom or a monovalent Ci- ₆ alkyl group, for example; p and q are each independently integers of 0 to 4; c is 0 to 4; and X ^a is a bridging group connecting the hydroxy-substituted aromatic groups, where the bridging group and the hydroxy substituent of each Ce arylene group are disposed ortho, meta, or para (specifically para) to each other on the Ce arylene group. The bridging group X ^a can be a single bond, -O-, -S-, -S(O)-, -S(0) ₂ -, -C(O)-, or a C1-18 organic bridging group. The C1-18 organic bridging group can be cyclic or acyclic, aromatic or non-aromatic, and can further comprise heteroatoms such as halogens, oxygen, nitrogen, sulfur, silicon, or phosphorous. The Ci-18 organic group can be disposed such that the Ce arylene groups connected thereto are each connected to a common alkylidene carbon or to different carbons of the C1-18 organic bridging group. A specific example of a group Z is a divalent group of the formula (3a) or (3b)

wherein Q is -O-, -S-, -C(O)-, -SO2-, -SO-, -P(R ^a )(=0)- wherein R ^a is a Ci- ₈ alkyl or C6-12 aryl, or -C _y H2 _y - wherein y is an integer from 1 to 5 or a halogenated derivative thereof (including a perfluoroalkylene group). In some aspects, Q is 2,2-isopropylidene. In some aspects, T is -0-Z-0-, preferably wherein Z is derived from bisphenol A (i.e., Z is

2,2-(4-phenylene)isopropylidene).

[0017] Illustrative examples of aromatic dianhydrides include 3,3-bis[4-(3,4- dicarboxyphenoxy)phenyl]propane dianhydride; 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride; 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride; 4,4'-bis(3,4- dicarboxyphenoxy)benzophenone dianhydride; 4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride; 2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride; 4,4'-bis(2,3- dicarboxyphenoxy)diphenyl ether dianhydride; 4,4'-bis(2,3-dicarboxyphenoxy)diphenyl sulfide dianhydride; 4,4'-bis(2,3-dicarboxyphenoxy)benzophenone dianhydride; 4,4'-bis(2,3- dicarboxyphenoxy)di phenyl sulfone dianhydride; 4-(2,3-dicarboxyphenoxy)-4'-(3,4- dicarboxyphenoxy)diphenyl-2, 2-propane dianhydride; 4-(2,3-dicarboxyphenoxy)-4'-(3,4- dicarboxyphenoxy)diphenyl ether dianhydride; 4-(2,3-dicarboxyphenoxy)-4'-(3,4- dicarboxyphenoxy)diphenyl sulfide dianhydride; 4-(2,3-dicarboxyphenoxy)-4'-(3,4- dicarboxyphenoxy)benzophenone dianhydride; and 4-(2,3-dicarboxyphenoxy)-4'-(3,4- dicarboxyphenoxy)diphenyl sulfone dianhydride. In particular aspects, the aromatic dianhydride curing agent is bisphenol-A dianhydride.

[0018] The aromatic dianhydride curing agent can be soluble in the epoxy resin composition. The term“soluble in the epoxy resin composition” means that there is a temperature range where a combination of the aromatic dianhydride curing agent and the epoxy resin composition can be combined to form a homogeneous phase. As used herein, “forming a homogeneous phase” means creating a state where there is no visible separation between the components. The homogeneous phase can be formed in a certain temperature range without regard to any separation that may occur outside of that temperature range, for example, at room temperature. For example, a combination of the aromatic dianhydride curing agent and the epoxy resin composition can be stirred, heated, or heated under stirring to form a

homogeneous phase.

[0019] In some aspects, the aromatic dianhydride curing agent can be soluble in the epoxy resin composition at a temperature from 50 to 200°C. For example, the aromatic dianhydride curing agent can be soluble in the epoxy resin composition from 80 to 200°C, more preferably from 100 to 190°C, even more preferably from 120 to 180°C.

[0020] The aromatic dianhydride curing agent can be soluble in the epoxy resin composition without the inclusion of any additives or solvents to improve the solubility of the dianhydride. In an aspect, the thermosetting epoxy powder coating composition is substantially free of solvent or solvents. In a particular aspect, the thermosetting epoxy powder coating composition is free of solvent. The term“substantially free of solvent” means that the thermosetting epoxy powder coating composition contains less than 500 parts per million (ppm) by weight of solvent. A“solvent free” thermosetting epoxy powder coating composition can have greater than 0 to 450 ppm by weight, preferably greater than 0 to 300 ppm by weight, more preferably greater than 0 to 200 ppm by weight, even more preferably greater than 0 to 100 ppm by weight of solvent, based on the total weight of the thermosetting epoxy powder coating composition.

[0021] The thermosetting epoxy powder coating composition optionally includes an effective amount of curing catalyst. In an aspect, the thermosetting epoxy powder coating composition can include 0.1 to 5 weight percent (wt%) of a curing catalyst, based on the total weight of the composition. For example, the thermosetting epoxy powder coating composition can include 0.4 to 4 wt%, preferably 0.6 to 3 wt%, more preferably 0.7 to 2 wt% of the curing catalyst, based on the total weight of the composition.

[0022] The curing catalyst can be a heterocyclic curing catalyst. Heterocyclic compounds include benzotriazoles; triazines; piperazines such as aminoethylpiperazine, N-(3- aminopropyl)piperazine, or the like; imidazoles such as 1-methylimidazole, 2-methylimidazole, 3-methyl imidazole, 4-methylimidazole, 5-methylimidazole, 1-ethylimidazole, 2-ethylimidazole, 3-ethylimidazole, 4-ethylimidazole, 5-ethylimidazole, 1-n-propylimidazole, 2-n- propylimidazole, 1-isopropylimidazole, 2-isopropylimidazole, 1-n-butylimidazole, 2-n- butylimidazole, 1-isobutylimidazole, 2-isobutylimidazole, 2-undecyl-lH-imidazole, 2- heptadecyl-lH-imidazole, 1,2-dimethylimidazole, 1,3-dimethylimidazole, 2,4- dimethylimidazole, 2-ethyl-4-methylimidazole, 1-phenylimidazole, 2-phenyl-lH-imidazole, 4- methyl-2-phenyl-lH-imidazole, 2-phenyl-4-methylimidazole, 1 -benzyl-2 -methylimidazole, 1- benzyl-2-phenylimidazole, 1 -cyanoethyl-2 -methylimidazole, 1 -cyanoethyl-2-ethyl-4- methylimidazole, 1 -cyanoethyl-2 -undecylimidazole, l-cyanoethyl-2-phenylimidazole, 2-phenyl- 4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1 -cyanoethyl-2 - phenyl-4, 5-di(2-cyanoethoxy)methylimidazole; cyclic amidine such as 4- diazabicyclo(2,2,2)octane, diazabicycloundecene, 2-phenyl imidazoline, or the like; N,N- dimethylaminopyridine; sulfamidate; or a combination thereof. In a particular aspect, the thermosetting epoxy powder coating composition does not include a heterocyclic curing catalyst.

[0023] In some aspects, the thermosetting epoxy powder coating composition can further include an additional curing promoter. The term“additional curing promoter” as used herein encompasses compounds whose roles in curing epoxy resins are variously described as those of a hardener, a hardening accelerator, a curing accelerator, a curing catalyst, and a curing co catalyst, among others. Exemplary additional curing promoters can include, for example, amines, dicyandiamide, polyamides, amidoamines, Mannich bases, anhydrides,

phenol-formaldehyde resins, carboxylic acid functional polyesters, polysulfides,

polymercaptans, isocyanates, cyanate esters, and combinations thereof.

[0024] In some aspects, the additional curing promoter comprises an amine. The amine can be a polyamine, a tertiary amine, an amidine, and combinations thereof. Examples of suitable polyamines include amine hardeners such as isophoronediamine, triethylenetetraamine, diethylenetriamine, aminoethylpiperazine, 1,2- and l,3 diaminopropane,

2.2-dimethylpropylenediamine, 1,4-diaminobutane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,12-diaminododecane, 4-azaheptamethylenediamine, N,N’-bis(3-aminopropyl)butane-l, 4-diamine, cyclohexanediamine, 4,4'-methylenedianiline, diethyltoluenediamine, /«-phenyl enedi amine, //-phenyl enedi amine, tetraethylenepentamine, 3-diethylaminopropylamine, 3,3'-iminobispropylamine, 2,4-bis(p-aminobenzyl)aniline, tetraethylenepentamine, 3-diethylaminopropylamine, 2,2,4- and

2.4.4-trimethylhexamethylenediamine, 1,2- and 1,3-diaminocyclohexane,

1.4-diamino-3,6-diethylcyclohexane, l,2-diamino-4-ethylcyclohexane,

l,4-diamino-3,6-diethylcyclohexane, l-cyclohexyl-3,4-diaminocyclohexane,

4,4'-diaminondicyclohexylmethane, 4,4'-diaminodicyclohexylpropane,

2.2-bis(4-aminocyclohexyl)propane, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane,

3-amino-l-cyclohexaneaminopropane, 1,3- and l,4-bis(aminomethyl)cyclohexane, m- and //-xylylenediamine, diethyl toluene diamines, and combinations thereof. In some aspects, the curing promoter comprises a hardener selected from the group consisting of

/«-phenylenediamine, 4,4’-diaminodiphenylmethane, or a combination thereof.

[0025] Examples of amine compounds further include tertiary amine hardening accelerators such as triethylamine, tributylamine, dimethylaniline, diethylaniline,

benzyldimethylamine, a-methylbenzyldimethylamine, N,N-dimethylaminoethanol, N,N- dimethylaminocresol, tri(N,N-dimethylaminomethyl)phenol, and combinations thereof.

[0026] The additional curing promoter can comprise other amine compounds. Examples of other amine compounds include hardeners such as ketimines, which are the reaction products of ketones and primary aliphatic amines; polyether amines, which are the reaction products of polyols derived from ethylene oxide or propylene oxide with amines; amine-terminated polyamides, prepared by the reaction of dimerized and trimerized vegetable oil fatty acids with polyamines; amidoamines, imidazolines, and combinations thereof, for example the reaction product of diethylene triamine and tail-oil fatty acid.

[0027] The additional curing promoter can comprise an anhydride hardener. Examples of anhydrides include maleic anhydride (MA), phthalic anhydride (PA), hexahydro-o-phthalic anhydride (HEP A), tetrahydrophthalic anhydride (THPA), methyltetrahydrophthalic anhydride (MTHPA), methylhexahydrophthalic anhydride (MHHPA), nadic methyl anhydride (methyl himic anhydride, MHA), benzophenonetetracarboxylic dianhydride (BTDA), tetrachlorophthalic anhydride (TCP A), pyromellitic dianhydride (PMDA), trimellitic anhydride (TMA), or a combination thereof.

[0028] In some aspects, the additional curing promoter can include a liquid

monoanhydride compound. Exemplary liquid monoanhydride curing agents include norbomene dicarboxylic anhydrides (e.g., methyl-5-norbornene-2,3-dicarboxylic anhydride, or the like), hexahydrophthalic anhydrides (e.g., 1,2-cyclohexanedicarboxylic anhydride, 4- methylhexahydrophthalic anhydride, 5-methylhexahydrophthalic anhydride, or the like), tetrahydrophthalic anhydrides (e.g., 1,2,3,6-tetrahydrophthalic anhydride, l,2,3,6-tetrahydro-4- methylphthalic anhydride, or the like), phthalic anhydrides (e.g., 3-fluorophthalic anhydride), maleic anhydrides (e.g., 2-methylmaleic anhydride, dimethylmaleic anhydride, or the like), succinic anhydrides (e.g., dodecenylsuccinic anhydride, hexadecenylsuccinic anhydride, or the like), trimellitic anhydride, perfluoroglutaric anhydride, or the like. As used herein,“liquid monoanhydride” refers to a monoanhydride compound that is a liquid at a temperature from 15 to 45°C, preferably 20 to 40°C, more preferably 20 to 30°C, even more preferably 20 to 25°C at atmospheric pressure.

[0029] The additional curing promoter can comprise a phenol-formaldehyde resin. Exemplary phenol-formaldehyde resins include, for example, novolac type phenol resins, resole type phenol resins, aralkyl type phenol resins, dicyclopentadiene type phenol resins, terpene modified phenol resins, biphenyl type phenol resins, bisphenol type phenol resins,

triphenylmethane type phenol resins, or a combination thereof.

[0030] The additional curing promoter can comprise a Mannich base. Examples of Mannich bases are the reaction products of an amine with phenol and formaldehyde, melamine-formaldehyde resins, urea-formaldehyde resins, or a combination thereof.

[0031] Other exemplary additional curing promoters include substituted ureas, for example 3 -phenyl- 1,1 -dimethyl urea; the reaction product of phenyl isocyanate with

dimethylamine; the reaction product of toluene diisocyanate with dimethylamine; quaternary phosphonium salts, such as tetraalkyl- and alklytriphenylphosphonium halide; or a combination thereof.

[0032] The additional curing promoter can comprise a metal salt, for example a copper (II) or aluminum (III) salt of an aliphatic or aromatic carboxylic acid. Exemplary metal salts include the copper (II), tin (II), and aluminum (III) salts of acetate, stearate, gluconate, citrate, benzoate, and like anions, or a combination thereof. The additional curing promoter can comprise a copper (II) or aluminum (III) b-diketonate. Exemplary metal diketonates include the copper (II) and aluminum (III) salts of acetyl acetonate. The additional curing promoter can comprise a boron trifluoride-trialkylamine complex. An illustrative boron

trifluoride-trialkylamine complex is boron trifluoride-trimethylamine complex.

[0033] The additional curing promoter can comprise a latent cationic cure catalyst.

Latent cationic cure catalysts are used, for example, in UV-cured epoxy resin compositions. Latent cationic cure catalysts include, for example, diaryliodonium salts, phosphonic acid esters, sulfonic acid esters, carboxylic acid esters, phosphonic ylides, triarylsulfonium salts,

benzylsulfonium salts, aryldiazonium salts, benzylpyridinium salts, benzylammonium salts, isoxazolium salts, or a combination thereof. For example, the curing promoter can be a latent cationic cure catalyst comprising a diaryliodonium salt having the structure

[(R ¹⁰ )(R ^U )I] ⁺ X- wherein R ¹⁰ and R ¹¹ are each independently a C6-C14 monovalent aromatic hydrocarbon radical, optionally substituted with from 1 to 4 monovalent radicals selected from C1-C20 alkyl, C1-C20 alkoxy, nitro, and chloro; and wherein X is an anion. In some aspects, the curing promoter is a latent cationic cure catalyst comprising a diaryliodonium salt having the structure

[(R ¹⁰ )(R ^U )I] ⁺ SbF ₆ - wherein R ¹⁰ and R ¹¹ are each independently a C6-C14 monovalent aromatic hydrocarbon radical, optionally substituted with from 1 to 4 monovalent radicals selected from C1-C20 alkyl, C1-C20 alkoxy, nitro, and chloro. In some aspects, the curing promoter is a latent cationic cure catalyst comprising 4-octyloxyphenyl phenyl iodonium hexafluoroantimonate. In particular aspects, the thermosetting epoxy powder coating composition does not include a latent cationic cure catalyst.

[0034] In some aspects, the thermosetting epoxy powder coating composition does not include a dicyandiamide, a polyamide, an amidoamine, a Mannich base, a monoanhydride, a phenol-formaldehyde resin, a carboxylic acid functional polyester, a polysulfide, a

polymercaptan, an isocyanate, and a cyanate ester.

[0035] In some aspects, the thermosetting epoxy powder coating composition does not include benzophenone tetracarboxylic anhydride, a (Ci- ₆ alkyl)styrene-maleic anhydride copolymer, chlorendic anhydride, dodecenyl succinic anhydride, hexahydrophthalic anhydride, hexahydro-4-methylphthalic anhydride, maleic anhydride, methylbutenyl tetrahydrophthalic anhydride, methylcyclohexene dicarboxylic anhydride, methylnadic anhydride,

methyltetrahydrophthalic anhydride, nadic anhydride, phthalic anhydride, pyromellitic anhydride, succinic anhydride, tetrahydrophthalic anhydride, and trimellitic anhydride.

[0036] The amount of additional curing promoter will depend on the type of curing promoter, as well as the identities and amounts of the other components of the composition. For example, the additional curing promoter can be present in an amount of 10 to 100 parts by weight, preferably 20 to 100 parts by weight, more preferably 20 to 80 parts by weight, based on the total parts by weight of the epoxy resin composition, the aromatic dianhydride curing agent, and the additional curing promoter.

[0037] In some aspects, the thermosetting epoxy powder coating composition is substantially free of monoanhydride curing agent and/or monoanhydride. The term

“substantially free of monoanhydride” means that the thermosetting epoxy powder coating composition contains less than 500 ppm by weight of monoanhydride. For example, a“monoanhydride free” thermosetting epoxy powder coating composition can have less than 450 ppm by weight, preferably less than 300 ppm by weight, more preferably less than 200 ppm by weight, even more preferably less than 100 ppm by weight of monoanhydride, based on the total weight of the thermosetting epoxy powder coating composition.

[0038] The thermosetting epoxy powder coating composition can include one or more fillers or reinforcing agents. The fillers and reinforcing agents can be in the form of

nanoparticles, that is, particles with a median particle size (D50) smaller than 100 nanometers (nm) as determined using light scattering methods. Exemplary fillers or reinforcing agents include, for example, silicates and silica powders such as aluminum silicate (mullite), synthetic calcium silicate, zirconium silicate, fused silica, crystalline silica graphite, and natural silica sand; boron powders such as boron-nitride powder, and boron-silicate powders; oxides such as T1O2, aluminum oxide, and magnesium oxide; calcium sulfate (as its anhydride, dihydrate, or trihydrate); calcium carbonates such as chalk, limestone, marble, and synthetic precipitated calcium carbonates; talc, including fibrous, modular, needle shaped, and lamellar talc; wollastonite; surface-treated wollastonite; glass spheres such as hollow and solid glass spheres, silicate spheres, cenospheres, and aluminosilicate spheres (armospheres); kaolin, including hard kaolin, soft kaolin, calcined kaolin, and kaolin comprising various coatings known in the art to facilitate compatibility with the polymeric matrix resin; single crystal fibers or“whiskers” such as silicon carbide, alumina, boron carbide, iron, nickel, and copper whiskers; fibers (including continuous and chopped fibers) such as carbon fibers (including carbon nanofibers), glass fibers (such as E, A, C, ECR, R, S, D, and NE glass fibers), basalt fibers, ceramic fibers, aramid fibers (including poly(p-phenylene terephthalamide) fibers), boron fibers, liquid crystal fibers, and polyethylene fibers; sulfides such as molybdenum sulfide, and zinc sulfide; barium compounds such as barium titanate, barium ferrite, barium sulfate, and heavy spar; metals and metal oxides such as particulate and fibrous aluminum, bronze, zinc, copper, and nickel; flaked fillers such as glass flakes, flaked silicon carbide, aluminum diboride, aluminum flakes, and steel flakes; inorganic fibrous fillers, for example short inorganic fibers such as those derived from blends comprising at least one of aluminum silicates, aluminum oxides, magnesium oxides, and calcium sulfate hemihydrate; natural fillers and reinforcements, such as wood flour obtained by pulverizing wood, fibrous products such as cellulose, cotton, sisal, jute, starch, cork flour, lignin, ground nut shells, com, and rice grain husks;

organic fillers such as polytetrafluoroethylene; reinforcing organic fibrous fillers formed from organic polymers capable of forming fibers such as poly(ether ketone), polyimide,

polybenzoxazole, poly(phenylene sulfide), polyesters, polyethylene, aromatic polyamides, aromatic polyimides, polyetherimides, polytetrafluoroethylene, acrylic resins, and poly(vinyl alcohol); as well as additional fillers and reinforcing agents such as mica, clay, feldspar, flue dust, fly ash, fillite, quartz, quartzite, perlite, tripoli, diatomaceous earth, and carbon black; as well as combinations of the foregoing fillers and reinforcing agents. When present, fillers and reinforcing agents can be present in an amount of 5 to 90 wt%, based on the total weight of the thermosetting epoxy powder coating composition. Within this range, the content of fillers and reinforcing agents can be 10 to 80 wt%, specifically 20 to 80 wt%, more specifically 40 to 80 wt%, even more specifically 50 to 80 wt%.

[0039] In a preferred aspect, the thermosetting epoxy powder coating composition comprises fillers of mica and calcium silicate such as wollastonite. Mica can be given the general chemical formula X ₂ Y _4-6 Z ₈ 0 ₂ o(OHF) ₄ , wherein X is K, Na, or Ca; Y is Al, Mg or Fe; and Z is Si or Al. Calcium silicate is a compound obtained by reacting calcium oxide and silica in different ratios, and can take one of four forms, having the chemical compositions Ca ₃ 0-Si0 ₄ , Ca ₂ Si0 ₄ , Ca ₃ Si ₂ 0 ₇ , or CaSi0 _3.

[0040] The filler or reinforcing agent can include particles having one or more morphologies and physical dimensions. For example, one or more of spherical particles, semi- spherical particles, spheroids, oblates, amorphous particles, hollow spheres, porous materials, rods, whiskers, geometric shapes, tubes, fibers having at least one dimension that is longer than another dimension, or the like. The mean or average dimension distribution can be less than or equal to 75 micrometers (pm), less than or equal to 50 pm, less than or equal to 35 pm, less than or equal to 25 mih, or the dimension can be sub-micrometer. The particles can have a bimodal particle size distribution, a trimodal particle size distribution, or a higher modality particle size distribution. In particular aspects, the particles have a bimodal particle size distribution and substantially all of the particles present are spherical.

[0041] The filler or reinforcing agent can be treated with a silane coupling agent.

Exemplary silane coupling agents include, but are not limited to, aminosilanes, epoxysilanes, mercaptosilanes, styrylsilanes, or a combination thereof. Exemplary aminosilanes include (4- aminobutyl)-dimethylmethoxysilane, N-(2-aminoethyl-3-aminopropyl)-methyldimethoxysilane, N-(2-aminoethyl-3-aminopropyl)trimethoxysilane, (3-aminopropyl)-methyldiethoxysilane, (3- aminopropyl)-tri ethoxy silane, (3 -aminopropyl)-trimethoxy silane, 3-(N-aminophenyl)- propyltrimethoxy silane, or the like. Exemplary epoxy silanes include 2 -(3, 4-epoxy cyclohexyl- ethyl)-trimethoxysilane, (3-glycidoxy propyl)- bis(trimethylsiloxy)-methylsilane, (3- glycidoxypropyl)-diisopropylethoxysilane, (3-glycidoxypropyl)-dimethylethoxysilane, (3- glycidoxypropyl)-methyldiethoxysilane, (3-glycidoxypropyl)-methyldiisopropenoxysilane, (3- glycidoxypropyl)-trimethoxysilane, or the like. Exemplary mercaptosilanes include (3- mercaptopropy-methyldimethoxysilane, (3-mercaptopropyl)-trimethoxysilane,

(mercaptomethyl)-dimethylethoxy silane, (mercaptomethyl)-methyldi ethoxy silane, (3- mercaptopropyl)-triethoxysilane, or the like. Exemplary styrylsilanes include

styrylethyltrimethoxy silane, 3 -(N-styrylmethyl-2-aminoethylamino)-propyltrimethoxy silane, or the like.

[0042] The treatment with the silane coupling agent can increase compatibility of the otherwise hydrophilic filler or reinforcing agent with an at least partially non-polar organic phase matrix. In the case of silica, the treatment can leave residual active termination sites on the silica (e.g., silanol) that can reduce stability. Therefore, a subsequent or second treatment of the silica can be performed with a capping or passivating agent. Exemplary passivating agents include a silazane, such as hexamethyldisilazane. This two-part treatment can remove substantially all of the active termination sites available on the silica that could reduce stability or shelf life, or undesirably increase viscosity or initiate crosslinking over time.

[0043] In some aspects, the thermosetting epoxy powder coating composition includes an additive composition. The additive composition can include an antioxidant, a heat stabilizer, a light stabilizer, a ultraviolet light stabilizer, a ultraviolet light-absorbing compound, a near infrared light-absorbing compound, an infrared light-absorbing compound, a plasticizer, a lubricant, a release agent, an antistatic agent, a surfactant, an anti-fog agent, an antimicrobial agent, colorants such as pigments and dyes, a high temperature pigment, a surface effect additive, a radiation stabilizer, a flame retardant, flame retardant synergists such as antimony pentoxide, an anti-drip agent, a corrosion inhibiting agent, a defoaming or degassing agent, diluents, an adhesion promoter, a flow control agent, a stress-relief additive, a coating additive, a polymer different from the thermoset (epoxy resin) polymer, or a combination thereof. In a preferred aspect, the thermosetting epoxy powder coating composition is substantially free of any polymer other than the thermoset (epoxy resin) polymer. The amount of the optional additives used can range generally from 0 to 99 wt%, preferably 0.001 to 95 wt%, more preferably 0.01 to 10 wt%, and most preferably 0.05 to 5 wt%, based on total weight of the thermosetting epoxy powder coating composition.

[0044] Exemplary corrosion inhibiting agents include calcium nitrite and/or nitrate, sodium nitrite and/or nitrate, sodium benzoate, certain phosphates, fluoroaluminates,

fluorosilicates, amines, esters, molybdates, phosphates, fatty acid esters, and borates (e.g. borax, sodium borate, potassium borate, lithium borate, and mixtures thereof). Such corrosion inhibiting agents can be employed in the amount of 0 to 50 wt%, preferably 0.1 to 30 wt%, based on total weight of the thermosetting epoxy powder coating composition.

[0045] Exemplary pigments include titanium dioxide, zinc oxide, iron oxide, chrome oxide, cobalt sulfide (cobalt black), or alloys thereof; carbon black, phthalocyanine blue, phthalocyanine green, quinacridone red, perylene red, isoindolone yellow, dioxazine violet, scarlet 3B lake, red 188 azo red, azo pigment yellow 83, or the like; other metallic powders, such as metal hydroxides, sulfides, sulfates, or the like; and filler pigments. The thermosetting epoxy powder coating composition preferably comprises a high temperature pigment, for example high temperature resistant cobalt black (such as Cobalt Black Ferro F6331-2, manufactured by Ferro). These can be used in amounts of 0 to 80 wt%, preferably 0.1 to 60 wt%, more preferably 25 to 50 wt%, based on total weight of the thermosetting epoxy powder coating composition.

[0046] Exemplary flow control agents include organic flow control agents such as polyacrylic esters, non-ionic fluorinated alkylester surfactants, non-ionic alkylaryl polyether alcohols, silicones, or the like; and inorganic flow control agents such as fumed silica or fumed alumina, such as ultrafme aluminum oxide (having an average particle diameter of 0.1 pm or less, preferably 0.005 to 0.05 pm). The flow control agents can be used in amounts of 0.5 to 5 wt%, preferably 0.5 to 3 wt%, based on total weight of the thermosetting epoxy powder coating composition.

[0047] Exemplary defoaming and degassing agents include benzoin (which may also function as an additional curing catalyst), bisphenol A, phenyl acetyl salicylate, bisphenoxy propanol, and 1,4 cyclohexane dimethanol dibenzoate. These can be used in amounts of 0.5 to 5 wt%, preferably 0.5 to 3 wt%, based on total weight of the thermosetting epoxy powder coating composition.

[0048] The thermosetting epoxy powder coating composition can be manufactured by combining the epoxy resin composition, the aromatic dianhydride curing agent, the curing catalyst, and optionally the additional curing promoter at a temperature of 100 to 200°C, preferably 120 to 190°C, more preferably 130 to 180°C to provide the thermosetting epoxy powder coating composition.

[0049] In some aspects, the thermosetting epoxy powder coating composition and/or reaction mixture contains no solvent or reactive diluent. In other aspects, the thermosetting epoxy powder coating composition and/or the reaction mixture further includes a solvent with the proviso that the solvent does not render an otherwise insoluble aromatic dianhydride soluble in the epoxy resin composition.

[0050] For example, the solvent can be C _3-8 ketones, C _4-8 A/ZV-dialkylamides, C _4-16 dialkyl ethers, Ce-u aromatic hydrocarbons, C _3-6 alkyl alkanoates, C _2-6 alkyl nitriles, C _2-6 dialkyl sulfoxides, or a combination thereof. Examples of C _3-8 ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, and combinations thereof. Examples of C _4-8 A/ A'-dialkylamides include dimethylformamide, dimethylacetamide, A-m ethyl -2-pyrrol i done, and combinations thereof. Examples of C _4-16 dialkyl ethers include tetrahydrofuran, dioxane, and combinations thereof. The C _4-16 dialkyl ether can optionally further include one or more ether oxygen atoms within the alkyl groups and one or more hydroxy substituents on the alkyl groups, for example the C _4-16 dialkyl ether can be ethylene glycol monomethyl ether. The aromatic hydrocarbon solvent can be an ethylenically unsaturated solvent. Examples of C _6-12 aromatic hydrocarbons include benzene, toluene, xylenes, styrene, divinylbenzenes, and combinations thereof.

Examples of C3-6 alkyl alkanoates include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and combinations thereof. Examples of C2-6 alkyl cyanides include acetonitrile, propionitrile, butyronitrile, and combinations thereof. Examples of C2-6 dialkyl sulfoxides include dimethyl sulfoxide, methyl ethyl sulfoxide, diethyl sulfoxide, and combinations thereof. In some aspects, the solvent comprises acetone, methyl ethyl ketone, /V-methyl-2-pyrrolidone, toluene, or a combination thereof. In still other aspects, the solvent can be a halogenated solvent such as methylene chloride, chloroform, 1,1,1-trichloroethane, chlorobenzene, or the like.

[0051] The thermosetting epoxy powder coating composition can be cured, for example, following powder coating of a substrate. There is no particular limitation on the method by which the composition can be cured, with the proviso that the curing does not damage or adversely affect the underling substrate. The thermosetting epoxy powder coating composition can, for example, be cured thermally or by using irradiation techniques, including UV irradiation and electron beam irradiation. When heat curing is used, the temperature selected can be 80 to 300°C, and preferably 120 to 250°C. The heating period can be 1 minute to 10 hours, though such heating period may advantageously be 1 minute to 6 hours, preferably 2 minutes to 4 hours, more preferably 15 minutes to 4 hours. Such curing may be staged to produce a partially cured and often tack-free resin, which then is fully cured by heating for longer periods or temperatures within the aforementioned ranges.

[0052] The cured product of the thermosetting epoxy powder coating composition after curing has a glass transition temperature (T _g ) of 120 to 320°C, preferably 160 to 320°C, more preferably 180 to 320°C, even more preferably 200 to 320°C, still more preferably 250 to 320°C, as determined by dynamic mechanical analysis (DMA).

[0053] The cured product of the thermosetting epoxy powder coating composition after powder coating a substrate and curing has an impact resistance of greater than 2 N m, preferably greater than 3 N m, more preferably greater than 4 N m, when measured according to ASTM D2794.

[0054] The cured product of the thermosetting epoxy powder coating composition after powder coating a substrate and curing can have a flex strength of from 65 to 200 megapascals (MPa), preferably from 70 MPa to 160 MPa, more preferably from 75 to 150 MPa, as measured according to ASTM D790.

[0055] The cured product of the thermosetting epoxy powder coating composition after powder coating a substrate and curing can have a pencil hardness of 6H to 10H, preferably 7H to 10H, as measured according to ASTM D2794.

[0056] The cured product of the thermosetting epoxy powder coating composition after powder coating a substrate and curing can have a bending resistance of greater than or equal to 4 mm, preferably greater than or equal to 5 mm, more preferably greater than or equal to 6 mm at 23°C.

[0057] The cured product of the thermosetting epoxy powder coating composition after powder coating a substrate and curing can have a solvent resistance of greater than or equal 80 double rubs, preferably greater than or equal to 100 double rubs using methyl ethyl ketone.

[0058] It is to be understood that“curing the thermosetting epoxy powder coating composition” results in“a cured product of the thermosetting epoxy powder coating

composition”. Thus, after curing the thermosetting epoxy powder coating composition, the powder coated substrate includes the cured product of the thermosetting epoxy powder coating composition (i.e., the cured product is disposed on at least one surface of the substrate). [0059] In a particular aspect, the thermosetting epoxy powder coating composition includes 100 parts by weight of the epoxy resin composition, 60 to 185 parts by weight of the aromatic dianhydride curing agent, a flow modifier, a degassing agent, and titanium dioxide, wherein after powder coating a substrate and curing the thermosetting epoxy powder coating composition can have an impact resistance of greater than 4 N m, as measured according to ASTM D2794; and a pencil hardness of 7H to 10H, as measured according to ASTM D2794.

[0060] In a particular aspect, the thermosetting epoxy powder coating composition includes bisphenol A epoxy, bisphenol A dianhydride, a flow modifier, a degassing agent, and titanium dioxide, wherein after powder coating a substrate and curing the thermosetting epoxy powder coating composition can have an impact resistance of greater than 4 N m, as measured according to ASTM D2794; and a pencil hardness of 7H to 10H, as measured according to ASTM D2794.

[0061] In a particular aspect, the thermosetting epoxy powder coating composition includes 100 parts by weight of the epoxy resin composition, 60 to 185 parts by weight of the aromatic dianhydride curing agent, and a heterocyclic curing promoter, wherein the anhydride to epoxy (A/E) ratio is from 0.4 to 1.2, and wherein after curing the thermosetting epoxy powder coating composition can have a T _g of 225 to 270°C, preferably 230 to 265°C.

[0062] In a particular aspect, the thermosetting epoxy powder coating composition includes 100 parts by weight of bisphenol A diglycidyl ether, 60 to 185 parts by weight of bisphenol A dianhydride, and 2-ethyl-4-methylimidazole, wherein the anhydride to epoxy (A/E) ratio is from 0.4 to 1.2, and wherein after curing the thermosetting epoxy powder coating composition can have a T _g of 225 to 270°C, preferably 230 to 265°C.

[0063] Also provided is a method of powder coating a substrate. The thermosetting epoxy powder coating composition is prepared by combining the epoxy resin composition and the aromatic dianhydride curing agent to form a mixture, as described above. For example, the components of the powder coating composition can be pre-blended or ground in a grinder, and the resulting ground powder mixture exiting from the grinder is then fed into an extruder.

[0064] In the extruder, the powder mixture can be heated at low temperature and melted into a semi-liquid form. During this process, the components of the molten mixture are thoroughly and uniformly dispersed. Because of the fast operation of the extruder and the relatively low temperature within the extruder, the components of the powder coating composition do not undergo a significant chemical reaction, such as curing. The resulting molten extrudate of the powder coating composition exiting from the extruder can be passed from the extruder onto a flaker which then feeds the flakes into a mill/classifier to obtain a thermosetting epoxy powder coating composition with a desired particle size. The final powder coating product can be packaged in closed containers, using a packaging unit to avoid moisture ingression into the product.

[0065] The thermosetting epoxy powder coating composition can be applied to a substrate by various methods, such as by electrostatic spraying techniques (See e.g., U.S. Pat.

No. 3,904,346 of Shaw et al. and U.S. Pat. No. 5,178,902 of Wong et ah), or by using a fluidized bed, which can be electrostatic. For example, in one aspect, the thermosetting epoxy powder coating composition can be applied to a substrate by (1) heating the substrate to a suitable curing temperature for the thermosetting epoxy powder coating composition; and (2) applying the thermosetting epoxy powder coating composition by an electrostatic spray or a fluidized bed. In another aspect, the thermosetting epoxy powder coating composition can be applied to a cold substrate by (1) applying the thermosetting epoxy powder coating composition to the substrate (e.g. with an electrostatic application method); and (2) heating the thermosetting epoxy powder coating composition and the substrate to a temperature at which the powder flows and cures. In some aspect, powder coated articles can he formed by applying the thermosetting epoxy powder coating composition to a substrate and then curing the curable thermosetting epoxy powder coating composition

[0066] An exemplary method for making an electrostatically applicable dry powder coating composition comprises the step of blending the epoxy resin composition and the aromatic dianhydride curing agent to form a mixture; passing the mixture through a conventional extruder to obtain a flaked product; and then reducing the mixture into a powder, for example by pulverizing the flaked product. After being ground, milled, or pulverized into a powder, the coating composition can optionally be passed through a sieve to remove particles that are too large or too small. Preferably, a sieve which eliminates particles of maximum dimension greater than 150 micrometers (pm) can be used, more preferably to provide a D50 particle size of 50 pm or less. The size and amount of the particles depend on the nature of the substrate or article being coated.

[0067] The thermosetting epoxy powder coating composition can be used to coat a variety of substrates. Exemplary substrates include steel pipes, steel pipelines, rebar, pipe hangers, valves, pumps, gears, manifolds, ladders, mesh, cable and wire rope, I-beams, girders, panels, column coils, anchor plates, strappings, casings, metal parts, or the like. The substrate materials can include, but are not limited to, metals such as steel, cast iron, aluminum, or the like; concrete, cement, thermoset resins, wood, or a combination thereof.

[0068] The thermosetting epoxy powder coating composition can be applied directly to one or more surfaces of the substrate, although for some end-uses a primer can be used. In some aspects, the thermosetting epoxy powder coating composition can be applied to substantially the entire surface of the substrate, or to the entire exterior surface of the substrate. It is preferable that the surface to be coated be first cleaned, such as, for example, by grinding or grit blasting.

[0069] The thermosetting epoxy powder coating composition can be applied either in one pass or in several passes to provide variable thicknesses, after cure, of 0.1 to 2 mm, preferably 0.2 to 1.5 mm, more preferably 0.2 to 1 mm, depending on the desired end-use of the coated article. Some pipes, for example, which are to be buried underground, require a coating thickness of approximately 0.2 to 0.8 mm.

[0070] The articles coated with the thermosetting epoxy powder coating composition can be used for a variety of applications. Exemplary applications include automotive finishes, industrial finishes such as building and construction applications or farm and agricultural applications. For example, building applications include coating aluminum or steel doors and door frames, window frames and sashes, siding, and garage doors. In the farm and agricultural applications, coating compositions can be used for power equipment (tractors, lawn mowers, power tools), as well as for metal implements, tools, sheds, fenceposts, or the like, that are exposed to outdoor weather. In the automotive area, a variety of parts for cars, buses, trucks, and train cars can be powder coated for anticorrosion protection. The coatings may also be used on indoor metal objects such as office furniture, filing cabinets, or the like. Other industrial applications include pipelines, such as the internal and/or external surfaces of steel pipes, structural steel used in concrete or in marine environments, storage tanks, valves, oil production tubing and casings, or the like.

[0071] This disclosure is further illustrated by the following examples, which are non limiting.

EXAMPLES

[0072] Materials used in the examples are described in Table 1.

Table 1.

[0073] Glass transition temperature (T _g ) was measured on a RDA III dynamic mechanical analyzer from TA Instruments. Samples (40 mm x 4 mm x 3 mm) were heated in the range of -40°C to 300°C at a heating rate of 3°C/min and a frequency of 6.283 radians per second. T _g was determined as the temperature of the tan d maximum.

[0074] Impact resistance for the coatings was measured according to ADTM D2794, which tests for deformation of the coating after impact from a ball or punch at 23°C. Impact resistance is measured using a Gardner Impact Tester and is reported as the impact pressure (in Newton meters, N m) at which deformation is first noted.

[0075] Chemical resistance was tested by methyl ethyl ketone (MEK)“double rub” technique. After curing, the coated substrates were allowed to cool to room temperature and remained under ambient conditions for at least 15 hours before being subjected to the methyl ethyl ketone (MEK) double rub or impact tests. MEK double rub tests (MEK DR) were performed under ambient conditions using a two-pound ballpein hammer as weight. The rounded head of the hammer was wrapped in six-layers of grade 10 cheesecloth and soaked with methyl ethyl ketone. The rounded head of the hammer was then placed on the coating and manually moved back and forth across the coating under its own weight. Each back and forth stroke was counted as 1 double rub. When the substrate became exposed the test was ended and the number of double rubs until substrate exposure was recorded. In cases in which the substrate did not become exposed, the tests were terminated after 100 double rubs. Thus, the actual number of MEK double rubs required to effect exposure of the substrate may be higher than the value of 100 recorded.

[0076] Hardness was tested using a 1 kg load according to ASTM D3363. Five repeated measurements of the pencil hardness test procedure were performed, with the pencil hardness being the hardness of the pencil used for the test when none of the measurements result in scratches or other disturbances to the appearance. Pencil hardness is reported on the scale of 9B (softest), 8B, 7B, 6B, 5B, 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H, and 10H (hardest).

[0077] Bending resistance of the powder coatings was measured by wrapping 1 cm wide strips around mandrels of different diameters under a force of 1 kg for 1 minute until cracks in the film were visibly apparent under a microscope. The resistance to cracking is reported as pass-fail for the appearance of visual cracking at a mandrel diameter of 6.35 millimeters (mm).

Example 1 and Comparative Example 1

[0078] Table 2 shows the components for high heat resistant epoxy powder coating components of Example 1 and Comparative Example 1. The amount of each component is provided in parts by weight (pbw).

Table 2.

[0079] The components as shown in Table 2 were premixed in a Vitamix 3600 blender and then extruded at 500 RPM with heating zones set to 100°C using an APV 19 mm co-rotating twin-screw extruder. The resulting flakes were pulverized in a grinding mill and then sieved through a 140 mesh (106 pm) screen filter. The resulting powders were spray coated electrostatically onto cold-rolled steel test panels (dimensions: 7.62 cm x 15.24 cm) and baked in an electric convection oven at 200°C for 15 minutes.

[0080] The mechanical properties for Example 1 and Comparative Example 1 are provided in Table 3.

Table 3.

[0081] Table 3 shows that BP AD A has improved mechanical properties over PMDA when used as a curing agent for epoxy powder coating formulations. The impact resistance of Example 1 (4.52 N m) was 100% greater than Comparative Example 1 (2.26 N m). Unlike to powder coating of Comparative Example 1, the BP ADA powder coating of Example 1 passed the mandrel bend test at 6.35 mm, although the pencil hardness was slightly lower for Example 1. Both Example 1 and Comparative Example 1 passed the chemical resistance test after 100 doubled rubs.

Examples 2 to 6

[0082] Samples were prepared as follows. BPA-DGE was heated at 160°C and BPADA was added thereto. A homogenous and transparent reaction mixture was afforded. The reaction mixture was cooled to 90°C and 2,4-EMI was added while stirring. The resulting mixture was poured into a preheated mold (130°C) and then cured in the mold at 220°C for 60 minutes to provide a rigid and clear casting.

[0083] Table 4 provides the compositions, anhydride to epoxy (A/E) ratios, and thermal properties of Examples 2 to 6. The amount of each component is provided in parts per hundred resin (phr). Table 4.

[0084] As shown in Table 4, the BP ADA-based epoxy formulations for powder coatings had high heat resistance as demonstrated by T _g of greater than 230°C. The optimum heat resistance was observed at A/E ratio of 0.8, as higher loadings of BP ADA were unexpectedly found to decrease the T _g. The data indicate that BP ADA can be used effectively as a curing or co-curing agent to prepare high heat resin formulations for use in applications such as powder coating.

[0085] This disclosure further encompasses the following aspects.

[0086] Aspect 1. A powder coated substrate comprising: a substrate; and a thermosetting epoxy powder coating composition, wherein the thermosetting epoxy powder coating

composition is powder coated on the substrate, wherein the thermosetting epoxy powder coating composition comprises: 100 parts by weight of an epoxy resin composition; 30 to 200 parts by weight of an aromatic dianhydride curing agent; optionally a curing catalyst; and optionally an additional curing promoter, wherein an anhydride to epoxy stoichiometric ratio (A/E) is 0.1 : 1 to 1.6: 1, preferably 0.5: 1 to 1.3: 1, more preferably 0.6: 1 to 1.2: 1, as determined by molar ratio of total anhydride functionalities to total epoxy functionalities in the thermosetting epoxy powder coating composition, wherein the amounts are based on the total parts by weight of the epoxy resin composition, the aromatic dianhydride curing agent, and optionally the additional curing promoter, and wherein the aromatic dianhydride curing agent is of formula (1) as provided herein, wherein the thermosetting epoxy powder coating composition after curing has a glass transition temperature of 120 to 320°C, preferably 160 to 320°C, more preferably 180 to 320°C, even more preferably 200 to 320°C, still more preferably 250 to 320°C, as determined by dynamic mechanical analysis, and wherein the thermosetting epoxy powder coating composition after powder coating a substrate and curing has an impact resistance of greater than 2 Newton meters, preferably greater than 3 Newton meters, more preferably greater than 4 Newton meters, when measured according to ASTM D2794.

[0087] Aspect la. A powder coated substrate comprising: a substrate; and a

thermosetting epoxy powder coating composition, wherein the thermosetting epoxy powder coating composition is powder coated on the substrate, wherein the thermosetting epoxy powder coating composition comprises: 100 parts by weight of an epoxy resin composition; 30 to 200 parts by weight of an aromatic dianhydride curing agent; optionally a curing catalyst; and optionally an additional curing promoter, wherein an anhydride to epoxy stoichiometric ratio (A/E) is 0.1 : 1 to 1.6: 1, preferably 0.5: 1 to 1.3: 1, more preferably 0.6: 1 to 1.2: 1, as determined by molar ratio of total anhydride functionalities to total epoxy functionalities in the thermosetting epoxy powder coating composition, wherein the amounts are based on the total parts by weight of the epoxy resin composition, the aromatic dianhydride curing agent, and optionally the additional curing promoter, and wherein the aromatic dianhydride curing agent is of formula (1) as provided herein, wherein the thermosetting epoxy powder coating composition after curing has a glass transition temperature of 120 to 320°C, preferably 160 to 320°C, more preferably 180 to 320°C, even more preferably 200 to 320°C, still more preferably 250 to 320°C, as determined by dynamic mechanical analysis, wherein the thermosetting epoxy powder coating composition after powder coating a substrate and curing has an impact resistance of greater than 2 Newton meters, preferably greater than 3 Newton meters, more preferably greater than 4 Newton meters, when measured according to ASTM D2794, and wherein the epoxy resin composition does not include a high heat epoxy compound of formulas (I) to (IX) as provided herein.

[0088] Aspect 2. The powder coated substrate of any one or more of the preceding aspects, wherein the epoxy resin composition comprises an epoxy resin that is a bisphenol A epoxy resin, a triglycidyl-substituted epoxy resin, a tetraglycidyl-substituted epoxy resin, a bisphenol F epoxy resin, a phenol novolak epoxy resin, a cresol novolak epoxy resin, a cycloaliphatic diglycidyl ester epoxy resin, a cycloaliphatic epoxy resin comprising a ring epoxy group, an epoxy resin containing a spiro-ring, a hydantoin epoxy resin, or a combination thereof; preferably wherein the epoxy resin composition comprises bisphenol-A diglycidyl ether.

[0089] Aspect 3. The powder coated substrate of any one or more of the preceding aspects, wherein T is -O- or a group of the formula -O-Z-O- wherein Z is of the formula (2) as provided herein; preferably wherein T is a group of the formula -O-Z-O- wherein Z is a divalent group of formulas (3a) or (3b) as provided herein; more preferably wherein the aromatic dianhydride curing agent comprises bisphenol-A dianhydride.

[0090] Aspect 4. The powder coated substrate of any one or more of the preceding aspects, wherein the thermosetting epoxy powder coating composition further comprises a curing catalyst, preferably wherein the curing catalyst comprises a substituted or unsubstituted C3-6 heterocycle comprising 1 to 4 ring heteroatoms, wherein each heteroatom is independently the same or different, and is nitrogen, oxygen, phosphorus, silicon, or sulfur; more preferably wherein the curing catalyst comprises a C3-4 five-membered ring wherein the ring heteroatoms are one or two nitrogen atoms.

[0091] Aspect 5. The powder coated substrate of any one or more of the preceding aspects, wherein the thermosetting epoxy powder coating composition further comprises: 0.5 to 5 wt%, preferably 0.5 to 3 wt% of a flow control agent, preferably wherein the flow control agent is a poly(meth)acrylic ester, a non-ionic fluorinated alkylester, non-ionic alkylaryl polyether alcohol, fumed silica, fumed alumina, or a combination thereof, more preferably ultrafme aluminum oxide; and 0.1 to 60 wt%, preferably 25 to 50 wt% of a pigment, preferably wherein the pigment is titanium dioxide, zinc oxide, iron oxide, chrome oxide, carbon black, cobalt sulfide, an alloy thereof, or a combination thereof, more preferably cobalt sulfide, wherein the amounts are based on the total weight of the thermosetting epoxy powder coating

composition.

[0092] Aspect 6. The powder coated substrate of any one or more of the preceding claims, wherein the thermosetting epoxy powder coating composition further comprises a filler, preferably wherein the filler is fused silica, fumed silica, colloidal silica, aluminum oxide, boron nitride, titanium dioxide, titanium diboride, talc, fly ash, mica, calcium carbonate, calcium silicate, carbon black, zinc oxide, graphite, or a combination thereof; more preferably wherein the filler is mica, calcium silicate, or a combination thereof.

[0093] Aspect 7. The powder coated substrate of any one or more of the preceding claims, wherein the thermosetting epoxy powder coating composition further comprises an additive; preferably wherein the additive is antioxidant, a heat stabilizer, a light stabilizer, a ultraviolet light stabilizer, a ultraviolet light-absorbing compound, a near infrared light absorbing compound, an infrared light-absorbing compound, a plasticizer, a lubricant, a release agent, an antistatic agent, a surfactant, an anti-fog agent, an antimicrobial agent, a pigments, a surface effect additive, a radiation stabilizer, a flame retardant, a flame retardant synergist, an anti-drip agent, a corrosion inhibiting agent, a defoaming agent, a degassing agent, a diluent, an adhesion promoter, a flow control agent, a stress-relief additive, a coating additive, or a combination thereof.

[0094] Aspect 7a. The powder coated substrate of any one or more of the preceding claims, wherein the thermosetting epoxy powder coating composition comprises 100 parts by weight of an epoxy resin composition; 30 to 200 parts by weight of an aromatic dianhydride curing agent; optionally a curing catalyst; optionally an additional curing promoter; 0.5 to 5 wt% of a flow control agent; and 0.1 to 60 wt% of a pigment, wherein the amounts are based on the total weight of the thermosetting epoxy powder coating composition.

[0095] Aspect 8. The powder coated substrate of any one of the preceding aspects, wherein the thermosetting epoxy powder coating composition is powder coated and cured on the substrate. [0096] Aspect 9. The powder coated substrate of any one of the preceding aspects, wherein the substrate is steel, cast iron, aluminum, concrete, cement, a thermoset resin, wood, or a combination thereof; preferably wherein the substrate comprises steel pipe, steel pipeline, rebar, pipe hanger, valve, pump, gear, manifold, ladder, mesh, cable, wire rope, I-beam, girder, panel, column coil, anchor plate, strapping, casing, or metal part.

[0097] Aspect 10. The powder coated substrate of any one of the preceding aspects, comprising a cured product of the thermosetting epoxy powder coating composition.

[0098] Aspect 11. The powder coated substrate of any one of the preceding aspects, wherein the cured product of the thermosetting epoxy powder coating composition has at least one of: a pencil hardness of 6H to 10H, preferably 7H to 10H, as measured according to ASTM D2794; a bending resistance of greater than or equal to 4 mm, preferably greater than or equal to 5 mm, more preferably greater than or equal to 6 mm at 23°C; or a solvent resistance of greater than or equal 80 double rubs, preferably greater than or equal to 100 double rubs using methyl ethyl ketone.

[0099] Aspect 11a. The powder coated substrate of one or more of the preceding aspects, wherein the thermosetting epoxy powder coating composition includes: the epoxy resin composition comprising bisphenol-A diglycidyl ether; the aromatic dianhydride comprising bisphenol A dianhydride, and 2-ethyl-4-methylimidazole.

[0100] Aspect l ib. The powder coated substrate of one or more of the preceding aspects, wherein the thermosetting epoxy powder coating composition includes: the epoxy resin composition comprising bisphenol-A diglycidyl ether; the aromatic dianhydride comprising bisphenol A dianhydride, and 2-ethyl-4-methylimidazole, wherein the thermosetting epoxy powder coating composition does not comprise a monoanhydride.

[0101] Aspect 11c. The powder coated substrate of one or more of the preceding aspects, wherein the thermosetting epoxy powder coating composition includes the additional curing promoter; preferably wherein the additional curing promoter is an amine, a dicyandiamide, a polyamide, an amidoamine, a Mannich base, an anhydride, a phenol-formaldehyde resin, a carboxylic acid functional polyester, a polysulfide, a polymercaptan, an isocyanate, a cyanate ester, or a combination thereof; preferably wherein the additional curing promoter is

benzophenone tetracarboxylic anhydride, (Ci- ₆ alkyl)styrene-maleic anhydride copolymer, chlorendic anhydride, dodecenyl succinic anhydride, hexahydrophthalic anhydride, hexahydro- 4-methylphthalic anhydride, maleic anhydride, methylbutenyl tetrahydrophthalic anhydride, methylcyclohexene dicarboxylic anhydride, methylnadic anhydride, methyltetrahydrophthalic anhydride, nadic anhydride, phthalic anhydride, pyromellitic anhydride, succinic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, or a combination thereof.

[0102] Aspect 12. A method of manufacturing the powder coated substrate of any one or more of the preceding aspects, the method comprising applying the thermosetting epoxy powder coating composition to at least one surface of the substrate; preferably wherein the applying comprises electrostatically applying the thermosetting epoxy powder coating composition in particulate form.

[0103] Aspect 13. The method of claim 12, further comprising heating the powder coated substrate at a temperature sufficient to cure the thermosetting epoxy powder coating

composition, preferably wherein the curing temperature is 120 to 250°C.

[0104] Aspect 14. The method of claim 12, further comprising preparing the

thermosetting epoxy powder coating composition, the method comprising: combining the epoxy resin composition and the aromatic dianhydride curing agent to form a mixture; processing the mixture to obtain a flaked product; and pulverizing the flaked product.

[0105] Aspect 15. The method of claim 14, wherein the processing comprises melt processing at a temperature less than a curing temperature of the thermosetting epoxy powder coating composition.

[0106] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any appropriate materials, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any materials (or species), steps, or components, that are otherwise not necessary to the achievement of the function or objectives of the compositions, methods, and articles.

[0107] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of“up to 25 wt%, or, more specifically,

5 wt% to 20 wt%”, is inclusive of the endpoints and all intermediate values of the ranges of“5 wt% to 25 wt%,” etc.). Disclosure of a narrower range or more specific group in addition to a broader range is not a disclaimer of the broader range or larger group.

[0108] The singular forms“a”“an,” and“the” include plural referents unless the context clearly dictates otherwise. “Combination” is inclusive of blends, mixtures, alloys, reaction products, and the like. The terms“first,”“second,” and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. “Or” means“and/or” unless clearly stated otherwise. Reference throughout the specification to“an aspect” means that a particular element described in connection with the aspect is included in at least one aspect described herein and may or may not be present in other aspects. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various aspects. A“combination thereof’ is open and includes any combination comprising at least one of the listed components or properties optionally together with a like or equivalent component or property not listed.

[0109] Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears. Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this application belongs. All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0110] Compounds are described using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dash that is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, -CHO is attached through carbon of the carbonyl group.

[0111] The term“hydrocarbyl” refers to a monovalent group containing carbon and hydrogen. Hydrocarbyl can be alkyl, cycloalkyl, alkenyl, cycloalkenyl, aryl, alkylaryl, or arylalkyl as defined below. The term“hydrocarbylene” refers to a divalent group containing carbon and hydrogen. Hydrocarbylene can be alkylene, cycloalkylene, arylene, alkylarylene, or arylalkylene as defined below. The term "alkyl" means a branched or straight chain, unsaturated aliphatic hydrocarbon group, e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl, t-butyl, n- pentyl, s-pentyl, and n- and s-hexyl. “Alkenyl” means a straight or branched chain, monovalent hydrocarbon group having at least one carbon-carbon double bond (e.g., ethenyl (-HC=CH2)). “Alkoxy” means an alkyl group that is linked via an oxygen (i.e., alkyl-O-), for example methoxy, ethoxy, and sec-butyloxy groups. "Alkylene" means a straight or branched chain, saturated, divalent aliphatic hydrocarbon group (e.g., methylene (-CH2-) or, propylene (-(CH2)3- )). “Cycloalkylene” means a divalent cyclic alkylene group, -CiTUn-x, wherein x is the number of hydrogens replaced by cyclization(s). “Cycloalkenyl” means a monovalent group having one or more rings and one or more carbon-carbon double bonds in the ring, wherein all ring members are carbon (e.g., cyclopentyl and cyclohexyl). "Aryl" means an aromatic hydrocarbon group containing the specified number of carbon atoms, such as phenyl, tropone, indanyl, or naphthyl. “Arylene” means a divalent aryl group.“Alkylaryl” means an aryl group substituted with an alkyl group. “Arylalkyl” means an alkyl group substituted with an aryl group (e.g., benzyl). “Aryloxy” means an aryl group with the indicated number of carbon atoms attached through an oxygen bridge (-0-). “Amino” means a monovalent radical of the formula— NRR' wherein R and R' are independently hydrogen or a Ci- ₃₀ hydrocarbyl, for example a Ci- ₂₀ alkyl group or a C _6-30 aryl group.“Halogen” or“halogen atom” means a fluorine, chlorine, bromine, or iodine atom. The prefix "halo" means a group or compound including one more of a fluoro, chloro, bromo, or iodo substituent. A combination of different halo groups (e.g., bromo and fluoro), or only chloro groups can be present. The prefix“hetero” means that the compound or group includes at least one ring member that is a heteroatom (e.g., 1, 2, or 3 heteroatom(s)), wherein the heteroatom(s) is each independently N, O, S, Si, or P.

[0112] Unless substituents are otherwise specifically indicated, each of the foregoing groups can be unsubstituted or substituted, provided that the substitution does not significantly adversely affect synthesis, stability, or use of the compound. “Substituted” means that the compound, group, or atom is substituted with at least one (e.g., 1, 2, 3, or 4) substituents instead of hydrogen, where each substituent is independently nitro (-NO ₂ ), cyano (-CN), hydroxy (-OH), halogen, thiol (-SH), thiocyano (-SCN), Ci- ₆ alkyl, C _2-6 alkenyl, C _2-6 alkynyl, Ci- ₆ haloalkyl, C _1-9 alkoxy, Ci-6 haloalkoxy, C ₃ -12 cycloalkyl, C5-1 ₈ cycloalkenyl, C ₆ -12 aryl, C7-1 ₃ arylalkyl (e.g., benzyl), C _7-12 alkylaryl (e.g., toluyl), C _4-12 heterocycloalkyl, C _3-12 heteroaryl, Ci- ₆ alkyl sulfonyl (-S(=0) ₂ -alkyl), C _6-12 arylsulfonyl (-S(=0) ₂ -aryl), or tosyl (CH ₃ C ₆ H ₄ SO ₂ -), provided that the substituted atom’s normal valence is not exceeded, and that the substitution does not

significantly adversely affect the manufacture, stability, or desired property of the compound. When a compound is substituted, the indicated number of carbon atoms is the total number of carbon atoms in the compound or group, including those of any substituents.

[0113] While particular aspects have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents.