FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to coating compositions, dielectric coatings formed from the coating compositions, and methods of preparing the dielectric coatings.

BACKGROUND

[0002] Substrates, such as metal substrates including metal electrical components, are often protected with a high dielectric strength material to provide insulating properties. For example, components have been coated with a dielectric coating to provide insulating properties. While dielectric coatings can provide insulating properties, it is difficult to obtain good insulating properties at low film thicknesses. Thus, it is desirable to develop improved dielectric coatings that provide good electrical insulation at low film thicknesses.

SUMMARY

[0003] The present disclosure relates to a powder coating composition for preparing a dielectric coating including: a) 15 to 60 weight % of an epoxy functional polymer, based on the total resin solids weight of the powder coating composition; b) a poly-carboxylic acid functional polyester polymer reactive with the epoxy functional polymer and which includes an acid value of less than 100 mg KOH/g, and c) 0 to 35 weight % of a colorant, based on the total solids weight of the coating composition, where (i) the coating composition further includes an isocyanate functional crosslinker reactive with a hydroxyl functional reaction product obtained from the epoxy functional polymer and the poly-carboxylic acid functional polyester polymer and/or (ii) a coating formed from the powder coating composition has a dielectric strength of greater than 2.5 kV at a dry film thickness of less than 8 mils, where the powder coating composition is substantially free of a poly-carboxylic acid functional (meth)acrylate polymer.

[0004] The present disclosure also relates to a powder coating composition for preparing a dielectric coating including: a) 15 to 60 weight % of an epoxy functional polymer, based on the total resin solids weight of the powder coating composition; b) a poly-carboxylic acid functional polyester polymer reactive with the epoxy functional polymer and which includes an acid value of less than 100 mg KOH/g, and c) 0 to 35 weight % of a colorant, based on the total solids weight of the coating composition, wherein (i) the coating composition further includes an isocyanate functional crosslinker reactive with a hydroxyl functional reaction product obtained from the epoxy functional polymer and the poly-carboxylic acid functional polyester polymer and/or (ii) a coating formed from the powder coating composition has a dielectric strength of greater than 2.5 kV at a dry film thickness of less than 8 mils, where the epoxy functional polymer includes a Novolac epoxy.

DETAILED DESCRIPTION

[0005] For purposes of the following detailed description, it is to be understood that the disclosure may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to 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 attached claims are approximations that may vary depending upon the desired properties to be obtained by the present disclosure. 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 number of reported significant digits and by applying ordinary rounding techniques.

[0006] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the disclosure arc approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.

[0007] Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

[0008] In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of “or” means “and/or” unless specifically stated otherwise, even though “and/or” may be explicitly used in certain instances. Further, in this application, the use of “a” or “an” means “at least one” unless specifically stated otherwise. For example, “an” epoxy functional polymer, “a” poly-carboxylic acid functional polyester polymer, “a” colorant, “an” isocyanate functional crosslinker, “a” powder coating composition, and the like refer to one or more of any of these items.

[0009] As indicated, the present disclosure relates to a powder coating composition for preparing a high dielectric strength coating. As used herein, a “powder coating composition” refers to a coating composition embodied in solid particulate form as opposed to liquid form. Thus, the components described herein can be combined to form a curable solid particulate powder coating composition. For instance, the components described herein that form the coating composition can be combined as a curable solid particulate powder coating composition that is free flowing. As used herein, the term “free flowing” with regard to curable solid particulate powder coating compositions refers to a solid particulate powder composition having a minimum of clumping or aggregation between individual particles.

[0010] Further, a “dielectric coating” refers to a coating that is electrically insulating. As will be described in further detail herein, the dielectric coating disclosed herein can provide a dielectric strength of greater than 2.5 kV as measured by a Sefelec Dielectrimeter RMG12AC-DC and in accordance with ASTM D 149-09 Hipot test.

[0011] In accordance with the present disclosure, the powder coating composition for preparing the dielectric coating can include: an epoxy functional polymer; a poly-carboxylic acid functional polyester polymer reactive with the epoxy functional polymer and which comprises an acid value of less than 100 mg KOH/g; and optionally a poly-carboxylic acid functional (meth)acrylate polymer reactive with the epoxy functional polymer. It is appreciated that the epoxy functional polymer, poly-carboxylic acid functional polyester polymer, and poly-carboxylic acid functional (meth)acrylate polymer can react to form a hydroxyl functional reaction product.

[0012] As used herein, the term “polymer” refers to oligomers, homopolymers (e.g., prepared from a single monomer species), copolymers (e.g., prepared from at least two monomer species), and graft polymers. The term “resin” is used interchangeably with “polymer.” Further, the term “crosslinker” refers to a molecule comprising two or more functional groups that are reactive with other functional groups and which is capable of linking two or more monomers or polymer molecules through chemical bonds.

[0013] As previously described, the powder coating composition of the present disclosure can comprise at least two different poly-carboxylic acid functional polymers: (i) a poly-carboxylic acid functional polyester polymer; and (ii) a poly-carboxylic acid functional (meth)acrylate polymer. As used herein, a “poly-carboxylic acid functional polymer” refers to a polymer having two or more carboxylic acid functional groups.

[0014] The powder coating composition can comprise a single poly-carboxylic acid functional polymer. For example, the powder coating composition can comprise the epoxy functional polymer and the poly-carboxylic acid functional polyester polymer. The powder coating composition can be substantially free or free of the poly-carboxylic acid functional (meth)acrylate polymer, which can correspond to less than 0.05 weight % or 0 weight %, based on the total solids weight of the powder coating composition.

[0015] The poly-carboxylic acid functional polyester polymer used in the powder coating composition described herein can have an acid value of less than 100 mg KOH/g or less than 80 mg KOH/g. The poly-carboxylic acid functional polyester polymer can further have an acid value of at least 20 mg KOH/g, such as at least 40 mg KOH/g, such as at least 60 mg KOH/g. The polycarboxylic acid functional polyester polymer can also have, for example, an acid value of from 20 mg KOH/g to 100 mg KOH/g, such as from 20 mg KOH/g to 80 mg KOH/g, from 40 mg KOH/g to 100 mg KOH/g, from 40 mg KOH/g to 80 mg KOH/g, from 60 mg KOH/g to 100 mg KOH/g, or from 60 mg KOH/g to 80 mg KOH/g. The poly-carboxylic acid functional polyester polymer can be formed from various materials such as poly(ethylene terephthalate) for example.

[0016] The poly-carboxylic acid functional polyester polymer can comprise at least 20 weight %, at least 25 weight %, at least 30 weight %, at least 35 weight %, at least 40 weight %, or at least 50 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition. The poly-carboxylic acid functional polyester polymer can comprise up to 80 weight % or up to 70 weight % or up to 60 weight % or up to 50 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition. The poly-carboxylic acid functional polyester polymer can also comprise an amount of from 20 to 80 weight %, such as from 20 to 50 weight %, from 30 to 50 weight %, from 50 to 80 weight %, or from 50 to 70 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition.

[0017] As indicated, the powder coating composition can also comprise a poly-carboxylic acid functional (meth)acrylate polymer. As used herein, “(meth)acrylate” and like terms refers both to the acrylate and the corresponding methacrylate. The poly-carboxylic acid functional (meth)acrylate polymer can comprise at least 0.05 weight %, at least 0.1 weight %, at least 0.5 weight %, at least 1 weight %, or at least 2 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition. The poly-carboxylic acid functional (meth)acrylate polymer can comprise up to 10 weight %, up to 5 weight %, or up to 3 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition. The poly-carboxylic acid functional (meth)acrylate polymer can also comprise an amount of from 0.05 to 10 weight %, or from 0.1 to 5 weight %, or from 1 to 3 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition.

[0018] The poly-carboxylic acid functional polyester polymer and the poly-carboxylic acid functional (meth) acrylate polymer can be combined in the powder coating composition to provide a desired weight ratio. For example, the poly-carboxylic acid functional polyester polymer and the poly-carboxylic acid functional (meth)acrylate polymer can be combined in the powder coating composition to provide a weight ratio of the poly-carboxylic acid functional polyester polymer to the poly-carboxylic acid functional (meth) aery late polymer of 1: 1 or greater, or 5: 1 or greater, or 10: 1 or greater, or 15: 1 or greater, or 20: 1 or greater.

[0019] The powder coating composition can also include additional carboxylic acid functional polymers including, but not limited to, carboxylic acid functional polyurethane polymers, polyamide polymers, polyether polymers, polysiloxane polymers, vinyl resins, copolymers thereof, and combinations thereof. Further, any of the previously described carboxylic acid functional polymers can have any of a variety of additional functional groups including, but not limited to, amine groups, hydroxyl groups, thiol groups, carbamate groups, amide groups, urea groups, and combinations thereof. Alternatively, the powder coating composition described herein can be free of such additional poly-carboxylic acid functional polymers.

[0020] The total amount of carboxylic acid functional polymers can comprise at least 20 weight %, at least 30 weight %, or at least 40 weight % of the powder coating composition, based on the total solids weight of the powder coating composition. The total amount of carboxylic acid functional polymers can comprise up to 70 weight %, up to 60 weight %, or up to 50 weight % of the powder coating composition, based on the total solids weight of the powder coating composition. The total amount of carboxylic acid functional polymers can also comprise an amount of from 20 to 70 weight %, or from 30 to 60 weight %, or from 40 to 50 weight % of the powder coating composition, based on the total solids weight of the powder coating composition. [0021] The total amount of carboxylic acid functional polymers can comprise at least 20 weight %, at least 30 weight %, or at least 40 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition. The total amount of carboxylic acid functional polymers can comprise up to 70 weight %, up to 60 weight %, or up to 50 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition. The total amount of carboxylic acid functional polymers can also comprise an amount of from 20 to 70 weight %, or from 30 to 60 weight %, or from 40 to 50 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition.

[0022] The carboxylic acid functional polymers can also be formed from recycled materials. For example, the powder coating composition described herein can comprise a poly-carboxylic acid functional polyester prepared from at least one recycled material. A non-limiting example of a recycled material that can be used to form the poly-carboxylic acid functional polyester is recycled poly (ethylene terephthalate).

[0023] As previously described, the powder coating composition described herein can also comprise an epoxy functional polymer that is reactive with at least the poly-carboxylic acid functional polyester polymer and the poly-carboxylic acid functional (meth)acrylate polymer. It is appreciated that the epoxy functional polymer comprises two or more epoxy functional groups and acts as a crosslinker when reacted with the carboxylic acid functional polymers. Non-limiting examples of suitable epoxy functional polymers include, but are not limited to, diglycidyl ethers of bisphenol A, polyglycidyl ethers of polyhydric alcohols, polyglycidyl esters of polycarboxylic acids, and combinations thereof. Non-limiting examples of suitable epoxy resins are also commercially available from NanYa Plastics under the trade name NPES-903, and from Hexion under the trade names EPON™ 2002 and EPON 2004™. Other non-limiting examples of suitable epoxy functional polymers include Novolac epoxies.

[0024] The epoxy functional polymer, such as the diglycidyl ethers of bisphenol A, polyglycidyl ethers of polyhydric alcohols, polyglycidyl esters of polycarboxylic acids, can have an equivalent weight of at least 500 or at least 700. The epoxy functional polymer, such as the diglycidyl ethers of bisphenol A, polyglycidyl ethers of polyhydric alcohols, polyglycidyl esters of polycarboxylic acids, can also comprise an equivalent weight of up to 1000 or up to 5100. The epoxy functional polymer, such as the diglycidyl ethers of bisphenol A, polyglycidyl ethers of polyhydric alcohols. polyglycidyl esters of polycarboxylic acids, can comprise an equivalent weight of from 500 to 5100 or from 700 to 1000. The epoxy functional polymer, such as the Novolac cpoxics, can comprise an equivalent weight of any of the previously recited ranges or can comprise an equivalent weight of from 125 to 500, such as from 125 to 300, or from 150 to 250. The epoxy functional polymer, such as the Novolac epoxies, can comprise an equivalent weight of at least 125, such as at least 150. The epoxy functional polymer, such as the Novolac epoxies, can comprise an equivalent weight of up to 500, such as up to 300, or up to 250. As used herein, “equivalent weight” refers to the average weight molecular weight of a resin divided by the number of functional groups. As such, the equivalent weight of the epoxy functional polymer is determined by dividing the average weight molecular weight of the epoxy resin by the total number of epoxide groups and any other optional functional groups that are not an epoxide. Further, the average weight molecular weight is determined by gel permeation chromatography relative to linear polystyrene standards of 800 to 900,000 Daltons as measured with a Waters 2695 separation module with a Waters 410 differential refractometer (RI detector). Tetrahydrofuran (THF) is used as the eluent at a flow rate of 1 ml min-1, and two PLgel Mixed-C (300x7.5 mm) columns is used for separation.

[0025] It is appreciated that the epoxy functional polymer can comprise one or multiple types of epoxy functional polymers. When multiple epoxy functional polymers are used, the multiple epoxy functional polymers can have the same or different equivalent weights. For instance, a first epoxy functional polymer can have an equivalent weight that is greater than an equivalent weight of a second epoxy functional polymer. The epoxy functional polymers can also include additional functional groups besides the epoxy functional groups including, but not limited to, any of the previously described functional groups. Alternatively, the epoxy functional polymer can be free of any one, or all, of the previously described functional groups besides the epoxy functional groups.

[0026] The epoxy functional polymer can comprise at least 15 weight %, such as at least 20 weight %, at least 30 weight %, or at least 40 weight % of the powder coating composition, based on the total solids weight of the powder coating composition. The epoxy functional polymer can comprise up to 60 weight % or up to 50 weight % of the powder coating composition, based on the total solids weight of the coating composition. The epoxy functional polymer can also comprise an amount of from 15 to 60 weight %, or from 30 to 50 weight %, or from 40 to 50 weight % of the powder coating composition, based on the total solids weight of the powder coating composition.

[0027] The epoxy functional polymer can comprise at least 15 weight %, such as at least 20 weight %, at least 30 weight %, or at least 40 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition. The epoxy functional polymer can comprise up to 60 weight % or up to 50 weight % of the powder coating composition, based on the total resin solids weight of the coating composition. The epoxy functional polymer can also comprise an amount of from 15 to 60 weight %, or from 30 to 50 weight %, or from 40 to 50 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition.

[0028] The poly-carboxylic acid functional polyester polymer and the epoxy functional polymer can also be combined in the powder coating composition to provide a desired weight ratio. For example, the poly-carboxylic acid functional polyester polymer and the epoxy functional polymer can be combined in the powder coating composition to provide a weight ratio of the polycarboxylic acid functional polyester polymer to the epoxy functional polymer of from 85: 15 to 15:85, such as from 80:20 to 20:80, from 70:30 to 30:70, from 60:40 to 40:60, or 50:50.

[0029] The carboxylic acid functional polymer(s) and the epoxy functional polymer of the powder coating composition may be reacted to form a reaction product comprising hydroxyl functional groups. The reaction product can comprise one or multiple hydroxyl groups. For example, the reaction product can comprise multiple pendant hydroxyl groups and, optionally, terminal hydroxyl groups.

[0030] The powder coating composition described herein can also comprise an isocyanate functional crosslinker that is reactive with the previously described reaction product comprising hydroxyl functional groups. The isocyanate crosslinker can provide additional properties including, for example, a higher crosslink density for increased chemical and abrasion resistance. [0031] The isocyanate functional crosslinker can include various types of polyisocyanates. Polyisocyanates that can be used include aliphatic and aromatic diisocyanates as well as higher functional polyisocyanates. 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 diisocyanatc, lysine diisocyanatc, 1,4-mcthylcnc bis-(cyclohcxyl isocyanate), toluene diisocyanatc (TDI), m-xylylenediisocyanate (MXDI) and p-xylylenediisocyanate, 4-chloro-l,3-phenylene diisocyanate, 1,5-tetrahydro-naphthalene diisocyanate, 4,4'-dibenzyl diisocyanate, and 1,2,4- benzene triisocyanate, xylylene diisocyanate (XDI), and mixtures or combinations thereof.

[0032] The isocyanate crosslinker can comprise a blocked isocyanate functional crosslinker. A “blocked isocyanate” refers to a compound with isocyanate functional groups that have been reacted with a blocking agent and which prevents the isocyanate functionality from reacting until the blocking agent is removed upon exposure to an external stimulus such as heat. Non-limiting examples of blocking agents include phenols, pyridinols, thiophenols, methylethylketoxime, amides, caprolactam, imidazoles, and pyrazoles. The isocyanate can also include a uretdione isocyanate such as a uretdione internally blocked isocyanate adduct.

[0033] The isocyanate functional crosslinker can comprise at least 0.1 weight %, at least 1 weight %, or at least 3 weight % of the powder coating composition, based on the total solids weight of the powder coating composition. The isocyanate functional crosslinker can comprise up to 10 weight %, up to 8 weight %, or up to 5 weight % of the powder coating composition, based on the total solids weight of the powder coating composition. The isocyanate functional crosslinker can also comprise an amount of from 0.1 to 10 weight %, or from 1 to 8 weight %, or from 3 to 5 weight % of the powder coating composition, based on the total solids weight of the powder coating composition.

[0034] The isocyanate functional crosslinker can comprise at least 0.1 weight %, at least 1 weight %, or at least 3 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition. The isocyanate functional crosslinker can comprise up to 10 weight %, up to 8 weight %, or up to 5 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition. The isocyanate functional crosslinker can also comprise an amount of from 0.1 to 10 weight %, or from 1 to 8 weight %, or from 3 to 5 weight % of the powder coating composition, based on the total resin solids weight of the powder coating composition.

[0035] The coating composition can optionally include additional film-forming resins, such as any of the previously described resins, that are free of carboxylic acid groups, and which include different functional groups such any of the other previously described functional groups. Further, the coating composition can also optionally include additional crosslinkers that are reactive with any of the previously described resins including the optional additional film-forming resins. Nonlimiting examples of additional crosslinkers that can optionally be used with the compositions described herein include carbodiimides, polyhydrazides, aziridines, alkylated carbamate resins, polyamines, polyamides, aminoplasts, melamines, hydroxyalkyl ureas, hydroxyalkyl amides, and any combination thereof.

[0036] The powder coating composition can also include additional materials. Non-limiting examples of materials that can be used with the powder coating compositions described herein include plasticizers, anti-oxidants, flow and surface control agents as such waxes (e.g., amide waxes), thixotropic agents, slip aids, catalysts such as metal catalysts (e.g., tin catalysts), antigassing agents such as benzoin, reaction inhibitors, texturizers, and other customary auxiliaries.

[0037] The powder coating composition may be substantially free, essentially free, or completely free of triglycidyl isocyanurate. As used herein, a powder coating composition is substantially free or essentially free of triglycidyl isocyanurate if triglycidyl isocyanurate is present in an amount of less than % by weight or less than less than 0.1% by weight, respectively, based upon the total solids weight of the powder coating composition. As used herein, a powder coating composition is completely free of triglycidyl isocyanurate if triglycidyl isocyanurate is not present in the powder coating composition.

[0038] The powder coating composition may be substantially free, essentially free, or completely free of glycidyl group containing acrylic copolymer. As used herein, a powder coating composition is substantially free or essentially free of glycidyl group containing acrylic copolymer if glycidyl group containing acrylic copolymer is present in an amount of less than 5% by weight or less than less than 1% by weight, respectively, based upon the total solids weight of the powder coating composition. As used herein, a powder coating composition is completely free of glycidyl group containing acrylic copolymer if glycidyl group containing acrylic copolymer is not present in the powder coating composition.

[0039] The powder coating composition may be substantially free, essentially free, or completely free of ammonium salt, phosphonium salt, and imidazole curing catalysts. As used herein, a powder coating composition is substantially free or essentially free of ammonium salt, phosphonium salt, and imidazole curing catalysts if ammonium salt, phosphonium salt, and imidazole curing catalysts are present in an amount of less than 0.1% by weight or less than less than 0.01 % by weight, respectively, based upon the total solids weight of the powder coating composition. As used herein, a powder coating composition is completely free of ammonium salt, phosphonium salt, and imidazole curing catalysts if ammonium salt, phosphonium salt, and imidazole curing catalysts are not present in the powder coating composition.

[0040] The powder coating composition may be substantially free, essentially free, or completely free of tetrabutyl ammonium bromide curing catalyst. As used herein, a powder coating composition is substantially free or essentially free of tetrabutyl ammonium bromide curing catalyst if the tetrabutyl ammonium bromide curing catalyst is present in an amount of less than 0.1% by weight or less than less than 0.01% by weight, respectively, based upon the total solids weight of the powder coating composition. As used herein, a powder coating composition is completely free of tetrabutyl ammonium bromide curing catalyst if the tetrabutyl ammonium bromide curing catalyst is not present in the powder coating composition.

[0041] The coating composition described herein may also be free of colorants or contain a controlled amount of colorants, which has been found to improve dielectric strength of the final coating. As used herein, a “colorant” refers to any substance that imparts color and/or other opacity and/or other visual effect to the composition. Colorants are typically used in a variety of forms, such as discrete particles, dispersions, solutions, and/or flakes.

[0042] Example colorants include pigments (organic or inorganic), dyes, and tints, such as those used in the paint industry and/or listed in the Dry Color Manufacturers Association (DCMA), as well as special effect compositions. A colorant may include, for example, a finely divided solid powder that is insoluble, but wettable, under the conditions of use. A colorant can be organic or inorganic and can be agglomerated or non-agglomerated.

[0043] Example pigments and/or pigment compositions include, but are not limited to, carbazole dioxazine crude pigment, azo, monoazo, diazo, naphthol AS, salt type (flakes), benzimidazolone, isoindolinone, isoindoline and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolo pyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazine, triarylcarbonium, quinophthalone pigments, diketo pyrrolo pyrrole red (“DPPBO red”), titanium dioxide, carbon black, and mixtures or combinations thereof. The terms “pigment” and “colored filler” can be used interchangeably. [0044] Example dyes include, but are not limited to, those that are solvent and/or aqueous based such as phthalo green or blue, iron oxide, bismuth vanadate, and mixtures or combinations thereof. [0045] Example tints include, but are not limited to, pigments dispersed in water-based or water- miscible carriers such as AQUA-CHEM 896 commercially available from Degussa, Inc., CHARISMA COLORANTS and MAXITONER INDUSTRIAL COLORANTS commercially available from Accurate Dispersions Division of Eastman Chemical, Inc.

[0046] The powder coating composition described herein can comprise 35 weight % or less, or 30 weight % or less, or 25 weight % or less, or 20 weight % or less, or 15 weight % or less, or 10 weight % or less, or 5 weight % or less, or 1 weight % or less, or 0.1 weight % or less, of a colorant such as a pigment, based on the total solids weight of the powder coating composition. The powder coating composition can also contain less than 0.05 weight % or less than 0.01 weight % of a colorant such as a pigment, based on the total solids weight of the powder coating composition.

[0047] Further, the coating composition can be substantially free, essentially free, or completely free of a colorant such as a pigment. The term “substantially free of a colorant” means that the coating composition contains less than 1000 parts per million by weight (ppm) of a colorant based on the total solids weight of the composition, “essentially free of a colorant” means that the coating composition contains less than 100 ppm of a colorant based on the total solids weight of the composition, and “completely free of a colorant” means that the coating composition contains less than 20 pails per billion by weight (ppb) of a colorant based on the total solids weight of the composition.

[0048] The coating composition can be prepared by mixing the previously described polycarboxylic acid functional polyester polymer, optionally the poly-carboxylic acid functional (meth)acrylate polymer, the epoxy functional polymer, optionally the isocyanate functional crosslinker, and other optional additional components. The components are mixed such that a homogenous mixture is formed. The components can be mixed using art-recognized techniques and equipment such as with a Prism high speed mixer for example. When a solid coating composition is formed, the homogenous mixture is next melted and further mixed. The mixture can be melted with a twin screw extruder or a similar apparatus known in the art. During the melting process, the temperatures will be chosen to melt mix the solid homogenous mixture without curing the mixture. The homogenous mixture can be melt mixed in a twin screw extruder with zones set to a temperature of 75°C to 125°C, such as from 85°C to 115°C or at 100°C. [0049] After melt mixing, the mixture is cooled and re-solidified. The re-solidified mixture is then ground such as in a milling process to form a solid particulate curable powder coating composition. The re-solidified mixture can be ground to any desired particle size. For example, in an electrostatic coating application, the re-solidified mixture can be ground to an average particle size of at least 10 microns or at least 20 microns and up to 100 microns as determined with a Beckman-Coulter LS™ 13 320 Laser Diffraction Particle Size Analyzer following the instructions described in the Beckman-Coulter LS™ 13 320 manual. Further, the particle size range of the total amount of particles in a sample used to determine the average particle size can comprise a range of from 1 micron to 200 microns, or from 5 microns to 180 microns, or from 10 microns to 150 microns, which is also determined with a Beckman-Coulter LS™ 13 320 Laser Diffraction Particle Size Analyzer following the instructions described in the Beckman-Coulter LS™ 13 320 manual.

[0050] The coating composition described herein can be applied to a wide range of substrates known in the coatings industry. For example, the coating compositions described herein can be applied to automotive substrates, industrial substrates, aerocraft and aerocraft components, marine substrates and components, packaging substrates, electronics, architectural substrates, and the like. [0051] Specific non-limiting substrates include cars, trucks, ships, vessels, on-shore and offshore installations, storage tanks, windmills, power industry substrates such as nuclear plants, power wires, batteries and battery components, bus bars, metal wires, copper or aluminum conductors, wood flooring and furniture, apparel, housings and circuit boards, glass and transparencies, sports equipment, including golf balls, stadiums, buildings, bridges, and the like. [0052] The substrates can be, for example, metallic or non-metallic substrates that require electrical insulating properties. Metallic substrates include, but are not limited to, tin, steel (including electrogalvanized steel, cold rolled steel, hot-dipped galvanized steel, among others), aluminum, aluminum alloys, zinc-aluminum alloys, steel coated with a zinc-aluminum alloy, and aluminum plated steel. Non-metallic substrates include polymeric, plastic, polyester, polyolefin, polyamide, cellulosic, polystyrene, polyacrylic, poly(ethylene naphthalate), polypropylene, polyethylene, nylon, EVOH, polylactic acid, other “green” polymeric substrates, poly(ethyleneterephthalate) (PET), polycarbonate, polycarbonate acrylobutadiene styrene (PC/ABS), polyamide, wood, veneer, wood composite, particle board, medium density fiberboard, cement, stone, glass, paper, cardboard, textiles, leather both synthetic and natural, and the like. [0053] The coating compositions described herein are particularly beneficial when applied directly to a metallic substrate or a pretreated metallic substrate to form dielectric coatings that provide insulating properties.

[0054] The coating compositions described herein can be applied by any means standard in the art, such as spraying, electrostatic spraying, a fluidized bed process, and the like. After the coating compositions are applied to a substrate, the compositions can be cured or at least partially cured such as with heat, or with other means such as actinic radiation to form a coating. As used herein, the terms “curable”, “cure”, and the like mean that at least a portion of the resinous materials in a composition is crosslinked or crosslinkable. The term “actinic radiation” refers to electromagnetic radiation that can initiate chemical reactions. Actinic radiation includes, but is not limited to, visible light, ultraviolet (UV) light, and infrared radiation (IR).

[0055] In some examples, the powder coating composition described herein is cured with heat, such as convection heating from 250°F to 500°F for 2 to 40 minutes, or from 250°F to 400°F for 10 to 30 minutes, or from 300°F to 400°F for 10 to 30 minutes. The coating composition described herein can also be cured with infrared radiation in which peak metal temperatures can reach 400°F to 500°F in 10 seconds. The elevated heat ramping with infrared radiation allows for fast cure times. In some examples, the powder coating composition described herein is cured with infrared radiation to heat the composition from 300°F to 55O°F for 1 to 20 minutes, or from 35O°F to 525°F for 2 to 10 minutes, or from 370°F to 515°F for 5 to 8 minutes.

[0056] It is appreciated that the powder coating composition described herein can be cured with multiple types of heat sources such as both convection heating and infrared radiation. For example, the powder coating composition described herein can be partially cured with convection heating or infrared radiation, and then completely cured with a different heat source chosen from convection heating and infrared radiation.

[0057] The powder coating compositions described herein can also be applied in multiple applications over a substrate. For instance, a first powder coating composition according to the present disclosure can be applied over at least a portion of a substrate. A second powder coating composition according to the present disclosure can be applied over at least a portion of the first coating composition. The first powder coating composition can optionally be cured or at least partially cured before applying the second powder coating composition. Alternatively, the second powder coating composition can be applied over at least a portion of the first coating composition. The first and second coating composition can then be cured together at the same time. The powder coating compositions can be cured with any of the methods previously described.

[0058] Coatings formed from a single powder coating composition according to the present disclosure can be applied to a dry film thickness of less than 12 mils, less than 10 mils, less than 8 mils, or less than 6 mils, or less 5 mils, or less than 4 mils, or less than 3 mils, or less than 2 mils. It is appreciated that, when multiple powder coating compositions are applied, each composition can be applied to separately provide any of the previously described dry film thicknesses. For instance, when two separate powder coating compositions described herein are applied, each individual powder coating composition can be applied at any of the previously described dry film thicknesses.

[0059] It has been found that the dielectric coatings described herein can provide good dielectric strength over substrates. For example, the dielectric coating described herein can provide a dielectric strength of greater than 2.5 kV at a film thickness of less 8 mils as measured by a Sefelec Dielectrimeter RMG12AC-DC and in accordance ASTM D149-09 Hipot test. The dielectric coating described herein can also provide a dielectric strength of greater than 4.0 kV at a dry film thickness of less than 5 mils, or less than 4 mils, or less than 2 mils, as measured by a Sefelec Dielectrimeter RMG12AC-DC and in accordance ASTM D149-09 Hipot test. The dielectric coating described herein can also provide a dielectric strength of at least 6.0 kV at a dry film thickness of 3 mils or less, as measured by a Sefelec Dielectrimeter RMG12AC-DC and in accordance ASTM D 149-09 Hipot test. The dielectric coating described herein can also provide a dielectric strength of at least 8.0 kV, or at least lOkV, at a dry film thickness of 12 mils or less, or 10 mils or less, as measured by a Sefelec Dielectrimeter RMG12AC-DC and in accordance ASTM D 149-09 Hipot test.

[0060] The dielectric coatings described herein also provide additional properties including, but not limited to, good adhesive properties. For instance, the dielectric coating described herein can exhibit an adhesive strength of 5B when applied to a substrate as determined in accordance with ASTM D3359-17.

[0061] The present disclosure is also directed to a method of preparing a dielectric coating. The method comprises applying the coating composition described herein over at least a portion of a substrate, and curing the coating composition to form a coating. The coating composition can include any of the previously described coating compositions. The method of applying the coating composition can also include applying multiple applications of the coating composition according to the present disclosure over the substrate.

[0062] The curing of the coating composition can also include any of the previously described curing steps. For example, the coating composition can be cured with infrared radiation, convection heating, or a combination thereof to form the dielectric coating. Further, when multiple coating compositions according to the present disclosure are applied, each coating composition can be independently partially or completely cured before applying the next coating composition. Alternatively, the multiple coating compositions can be cured together at the same time.

[0063] The following examples are presented to demonstrate the general principles of the disclosure. The disclosure should not be considered as limited to the specific examples presented. All parts and percentages in the examples are by weight unless otherwise indicated.

EXAMPLES 1-6

Preparation of a powder coating composition

[0064] Curable powder coating compositions were prepared from the components listed in Table 1.

Table 1

¹ Carboxyl-functional polyester with acid value of 69 mg KOH/g.

² Carboxyl-functional polyester with acid value of 70 mg KOH/g prepared with recycled poly(ethylene terephthalate).

³ NPES-903, commercially available from Nan Ya Plastics Corp. ⁴ Joncryl® 819. carboxyl functional solid grade acrylic resin, commercially available from BASF.

⁵ Butaflow BT-71, commercially available from Estron Chemical.

⁶ Acrylic/silica flow and leveling control agent, commercially available from Estron Chemical Inc.

⁷ Micromide 520L, finely micronized EBS wax, commercially available from Micro Powders, Inc.

⁸ Benzoin, commercially available from Mitsubishi Chemical Corporation.

⁹ VESTAGON® BE 1540, internally blocked polyisocyanate adduct, commercially available from Evonik.

¹⁰ White pigment.

[00651 Each of the components listed in Table 1 were weighed in a container and mixed in a prism high speed mixer for 30 seconds at 3500 RPM to form dry homogeneous mixtures. The mixtures were then melt mixed in a Werner Pfleiderer 19 mm twin screw extruder with an aggressive 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 110°C. The feed rate was such that a torque of 50-60% was observed on the equipment. The mixtures were dropped onto a set of chill rolls to cool and re-solidify the mixtures into solid chips. The chips were ground in a Mikro ACMO-1 Air Classifying Mill to obtain a particle size of 5 to 150 microns with a majority of the particles being from 20 to 40 microns. The resulting coating compositions were solid particulate powder coating compositions that were free flowing.

EXAMPLE 7

Application and evaluation of powder coatings

[0066] The curable powder coating compositions prepared in Examples 1-6 were applied by electrostatic spray onto aluminum substrates (Q-PANEL aluminum panels having a size of 4 inches by 12 inches with a thickness of 0.64 mm or 0.81 mm). During application, a first layer of 4-7 mils was applied and then gelled with a conventional oven at 35O°F for 2 minutes. A second layer of 4-7 mils was then applied and then a full bake was done with a conventional oven at 35O°F for 30 minutes.

[0067] Each of the coatings prepared from the compositions were evaluated for dielectric strength, as measured by a Sefelec Dielectrimeter RMG12AC-DC and in accordance with ASTM D 149-09 Hipot test. The parameters of the testing were as follows: Voltage limit: 12 kV DC, I _m ax Limit: 4.0 mA. 3 seconds ramp, 1 second dwell, 2 second fall. The results of the Hipot test are shown in Table 2. Table 2

[0068] As shown in Table 2, the coatings formed from the powder coating compositions of Examples 1 and 3-6 exhibited improved dielectric strength as compared to the coating of Comparative Example 2.

EXAMPLE 8

Application and evaluation of powder coatings

[0069] A curable powder coating composition prepared in Example 1 was applied by electrostatic spray onto aluminum substrates (Q-PANEL aluminum panels having a size of 4 inches by 12 inches with a thickness of 0.64 mm or 0.81 mm). During application, a first layer of 5 mils was applied and then gelled with a shortwave IR oven at 315°F-345°F for 2 minutes. A second layer of 5 mils was then applied and then a full bake with a shortwave IR oven at 415°F- 515°F for 5 minutes.

[0070] The coating prepared from the composition was evaluated for dielectric strength, as measured by a Sefelec Dielectrimeter RMG12AC-DC and in accordance with ASTM D149-09 Hipot test. The parameters of the testing were as follows: Voltage limit: 12 kV DC, I _m x Limit: 4.0 mA, 3 seconds ramp, 1 second dwell, 2 second fall. The results of the Hipot test are shown in Table 3.

Table 3

[0071] As shown in Table 3, the coating formed from the powder coating composition of Example 1 using IR for curing also exhibited good dielectric strength. EXAMPLES 9-19

Preparation and testing of powder coatings

[0072] Each of the components listed in Tables 4-5 for each of Examples 9-19 were weighed in a container and mixed in a Henschel high speed mixer for 30 to 120 seconds at 1500 RPM to form a dry homogeneous mixture. The mixture was then melt mixed in a Wemer & Pfleiderer 30mm twin screw extruder with a speed of 350-425 RPM. The extruder zones were set at 90 to 115°F. The feed rate was such that a torque of 20 to 25% was observed on the equipment. The mixtures were dropped onto a set of chill rolls to cool and re-solidify the mixtures into solid chips. The chips were milled in a Strand mill to obtain a particle size of predominantly 5 to 100 microns with a majority of the particles being from 20 to 60 microns by volume. The resulting coating compositions for each of Examples 9-19 were solid particulate powder coating compositions that were free flowing.

Table 4 1 An O-cresol Novolac type epoxy resin, available from Teda Golone Chemical (Tianjin, China)

A solid bisphenol-A/epichlorohydrin epoxy resin from Hexion (Columbus, OH)

Imide hydroxyl urethane resin powder

Table 5 URALAC P 6040, polyester commercially available from DSM URALAC P 2450, polyester commercially available from DSM Coating Resins, LLC (Zwolle, Netherlands) [0073] Each of the solid particulate powder coating compositions of Examples 9-19 were electrostatically sprayed with a Nordson manual spray gun at a voltage of 45 kV to 90 kV with a vibratory feed dispenser with 20 psi flow air onto aluminum substrates (Q-PANEL aluminum panels having a size of 4 inches by 12 inches with a thickness of 0.64 mm or 0.81 mm). During application, a layer of 2.0 to 4.0 mils was applied and then gel cured with a conventional oven at 375°F for 5 minutes. An additional layer of 2.0-4.0 mils was then applied and fully cured with a conventional oven at 375 °F for 20-30 minutes.

[0074] Each of the coatings prepared from the compositions of Examples 9-19 were evaluated for dielectric strength, as measured by a Sefelec Dielectric Strength Tester RMG12AC-DC and in accordance with ASTM D 149-09 Dielectric Breakdown Voltage and Dielectric Strength test. The parameters of the testing were as follows: Voltage limit 12.0 kV DC, I _m ax Limit: 0.5 mA, 20 second ramp, 20 second dwell, and 2 second fall. The results of the dielectric strength test are reported in Tables 4-5.

[0075] Each of the coatings in Examples 9-19 had a good dielectric strength at a low film thickness.

[0076] Whereas particular embodiments of this disclosure have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present disclosure may be made without departing from the disclosure as defined in the appended claims.