Powder coating composition for preparing a dielectric coating

Abstract

The present disclosure relates to a powder coating composition for preparing a dielectric coating, comprising: a) an epoxy-functional polymer; b) a polycarboxylic acid-functional polyester polymer capable of reacting with the epoxy-functional polymer; and c) optionally a colorant; wherein (i) the coating composition further comprises an isocyanate-functional crosslinker capable of reacting with a hydroxyl-functional reaction product obtained from the epoxy-functional polymer and the polycarboxylic acid-functional polyester polymer; and / or (ii) a film formed from the powder coating composition has a dielectric strength greater than 2.5 kV at a dry film thickness of less than 8 mils; and the powder coating composition is substantially free of polycarboxylic acid-functional (meth)acrylate polymers.

Description

[Technical Field]

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

[0002] Substrates, such as metal substrates containing metallic electrical components, are often protected with materials that have high dielectric strength to provide electrical insulation. For example, dielectric coatings are applied to the components to provide insulation. While dielectric coatings can provide insulation, it is difficult to obtain good insulation at thin thicknesses. Therefore, there is a need for improved dielectric coatings that provide good electrical insulation at thin thicknesses. Summary of the Invention

[0003] The present disclosure relates to a powder coating composition for preparing a dielectric coating, comprising: a) 15 to 60 weight percent, based on the total resin solids weight of the powder coating composition, of an epoxy-functional polymer; b) a polycarboxylic acid-functional polyester polymer capable of reacting with the epoxy-functional polymer, the polycarboxylic acid-functional polyester polymer having an acid number of less than 100 mg KOH / g; and c) 0 to 35 weight percent, based on the total solids weight of the coating composition, of a colorant; (i) the coating composition further comprises an isocyanate-functional crosslinker capable of reacting with a hydroxyl-functional reaction product obtained from the epoxy-functional polymer and the polycarboxylic 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, and the powder coating composition is substantially free of polycarboxylic acid-functional (meth)acrylate polymers.

[0004] The present disclosure also relates to a powder coating composition for preparing a dielectric coating, comprising: a) 15 to 60 wt % of an epoxy-functional polymer, based on the total resin solids weight of the powder coating composition; b) a polycarboxylic acid-functional polyester polymer capable of reacting with the epoxy-functional polymer, the polycarboxylic acid-functional polyester polymer having an acid number of less than 100 mg KOH / g; and c) 0 to 35 wt % of a colorant, based on the total solids weight of the coating composition; wherein (i) the coating composition further comprises an isocyanate-functional crosslinker capable of reacting with the hydroxyl-functional reaction product obtained from the epoxy-functional polymer and the polycarboxylic acid-functional polyester polymer; and / or (ii) a film 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, and the epoxy-functional polymer comprises a novolac-type epoxy. DETAILED DESCRIPTION OF THE INVENTION

[0005] For purposes of the following detailed description, it should be understood that the disclosure may contemplate various alternative variations and step sequences unless expressly stated to the contrary. Furthermore, other than in any examples or unless otherwise indicated, all numerical values ​​expressing quantities of ingredients used in the specification and claims, for example, should be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and appended claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, the application of the doctrine of equivalents is not intended to limit the scope of the claims, and each numerical parameter should be construed in light of at least 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 are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. However, any numerical value inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0007] It should also be understood that any numerical range recited herein is intended to include all subranges subsumed therein. For example, a range of "1 to 10" is intended to include all subranges between (and including) the recited minimum of 1 and the recited maximum of 10, i.e., minimums of 1 or greater and maximums of 10 or less.

[0008] In this application, the use of the singular includes the plural, and the plural encompasses the singular, unless expressly stated otherwise. Additionally, in this application, the use of "or" means "and / or" unless expressly stated otherwise, even though "and / or" may be expressly used in certain instances. Furthermore, in this application, the use of "a" or "an" means "at least one" unless expressly stated otherwise. For example, "an" epoxy-functional polymer, "a" polycarboxylic acid-functional polyester polymer, "a" colorant, "a" isocyanate-functional crosslinker, and "a" powder coating composition, etc., refer to one or more of any of these items.

[0009] As indicated, the present disclosure relates to powder coating compositions for preparing high dielectric coatings. As used herein, "powder coating composition" refers to a coating composition embodied in a solid particulate form, as opposed to a liquid form. Thus, the components described herein can be combined to form a curable solid particulate powder coating composition. For example, the components described herein that form the coating composition can be combined as a free-flowing curable solid particulate powder coating composition. As used herein, the term "free-flowing" with respect to a curable solid particulate powder coating composition refers to a solid particulate powder composition with minimal agglomeration or clumping between individual particles.

[0010] Furthermore, the term "dielectric coating" refers to an electrically insulating coating. As described in further detail herein, the dielectric coatings disclosed herein can provide a dielectric strength of greater than 2.5 kV as measured by a Sefelec RMG12AC-DC dielectric meter in accordance with the ASTM D149-09 hipot test.

[0011] In accordance with the present disclosure, a powder coating composition for preparing a dielectric coating can include an epoxy-functional polymer, a polycarboxylic acid-functional polyester polymer capable of reacting with the epoxy-functional polymer and having an acid number of less than 100 mg KOH / g, and, optionally, a polycarboxylic acid-functional (meth)acrylate polymer capable of reacting with the epoxy-functional polymer. It is understood that the epoxy-functional polymer, the polycarboxylic acid-functional polyester polymer, and the polycarboxylic 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 synonymously with "polymer." Additionally, the term "crosslinker" refers to a molecule that contains two or more functional groups capable of reacting with other functional groups and can link two or more monomer or polymer molecules through chemical bonds.

[0013] As previously mentioned, the powder coating compositions of the present disclosure can include at least two different polycarboxylic acid functional polymers: (i) a polycarboxylic acid functional polyester polymer, and (ii) a polycarboxylic acid functional (meth)acrylate polymer. As used herein, "polycarboxylic acid functional polymer" refers to a polymer having two or more carboxylic acid functional groups.

[0014] The powder coating composition can include a single polycarboxylic acid functional polymer. For example, the powder coating composition can include an epoxy functional polymer and a polycarboxylic acid functional polyester polymer. The powder coating composition can be substantially free of, or completely free of, polycarboxylic acid functional (meth)acrylate polymer, which can represent less than 0.05 wt. % or 0 wt. % based on the total solids weight of the powder coating composition.

[0015] The polycarboxylic acid functional polyester polymers used in the powder coating compositions described herein can have an acid number of less than 100 mgKOH / g or less than 80 mgKOH / g. The polycarboxylic acid functional polyester polymers can further have an acid number of at least 20 mgKOH / g, e.g., at least 40 mgKOH / g, e.g., at least 60 mgKOH / g. The polycarboxylic acid functional polyester polymers can also have an acid number of, for example, 20 mgKOH / g to 100 mgKOH / g, e.g., 20 mgKOH / g to 80 mgKOH / g, 40 mgKOH / g to 100 mgKOH / g, 40 mgKOH / g to 80 mgKOH / g, 60 mgKOH / g to 100 mgKOH / g, or 60 mgKOH / g to 80 mgKOH / g. The polycarboxylic acid functional polyester polymers can be formed from a variety of materials, such as, for example, poly(ethylene terephthalate).

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

[0017] As indicated, the powder coating composition can also include a polycarboxylic acid-functional (meth)acrylate polymer. As used herein, terms such as "(meth)acrylate" refer to both the acrylate and the corresponding methacrylate. The polycarboxylic acid-functional (meth)acrylate polymer can comprise at least 0.05 wt%, at least 0.1 wt%, at least 0.5 wt%, at least 1 wt%, or at least 2 wt% of the powder coating composition, based on the total resin solids weight of the powder coating composition. The polycarboxylic acid-functional (meth)acrylate polymer can comprise up to 10 wt%, up to 5 wt%, or up to 3 wt% of the powder coating composition, based on the total resin solids weight of the powder coating composition. The polycarboxylic acid-functional (meth)acrylate polymer can also comprise an amount of 0.05 to 10 wt%, or 0.1 to 5 wt%, or 1 to 3 wt%, of the powder coating composition, based on the total resin solids weight of the powder coating composition.

[0018] The polycarboxylic acid functional polyester polymer and the polycarboxylic acid functional (meth)acrylate polymer can be combined in a powder coating composition in any desired weight ratio. For example, the polycarboxylic acid functional polyester polymer and the polycarboxylic acid functional (meth)acrylate polymer can be combined in a powder coating composition in a weight ratio of polycarboxylic acid functional polyester polymer to polycarboxylic acid functional (meth)acrylate 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 compositions may 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. Furthermore, any of the foregoing carboxylic acid functional polymers may 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 compositions described herein may not include any such additional polycarboxylic acid functional polymers.

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

[0022] The carboxylic acid functional polymer can also be formed from recycled materials. For example, the powder coating compositions described herein can include a polycarboxylic acid functional polyester prepared from at least one recycled material. Non-limiting examples of recycled materials that can be used to form the polycarboxylic acid functional polyester include recycled poly(ethylene terephthalate).

[0023] As previously mentioned, the powder coating compositions described herein can also include an epoxy-functional polymer capable of reacting with at least the polycarboxylic acid-functional polyester polymer and the polycarboxylic acid-functional (meth)acrylate polymer. It is understood that the epoxy-functional polymer contains two or more epoxy functional groups and acts as a crosslinker when reacted with the carboxylic acid-functional polymer. 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 include those commercially available from NanYa Plastics under the tradename NPES-903 and from Hexion under the tradenames EPON™ 2002 and EPON™ 2004. Other non-limiting examples of suitable epoxy-functional polymers include novolac-type epoxies.

[0024] Epoxy-functional polymers such as diglycidyl ethers of bisphenol A, polyglycidyl ethers of polyhydric alcohols, and polyglycidyl esters of polycarboxylic acids can have an equivalent weight of at least 500 or at least 700. Epoxy-functional polymers such as diglycidyl ethers of bisphenol A, polyglycidyl ethers of polyhydric alcohols, and polyglycidyl esters of polycarboxylic acids can also contain an equivalent weight of up to 1000 or up to 5100. Epoxy-functional polymers such as diglycidyl ethers of bisphenol A, polyglycidyl ethers of polyhydric alcohols, and polyglycidyl esters of polycarboxylic acids can contain an equivalent weight of 500 to 5100 or 700 to 1000. Epoxy-functional polymers such as novolac-type epoxies can contain an equivalent weight in any of the aforementioned ranges or can contain an equivalent weight of 125 to 500, e.g., 125 to 300, or 150 to 250. Epoxy-functional polymers, such as novolac-type epoxies, can have an equivalent weight of at least 125, e.g., at least 150. Epoxy-functional polymers, such as novolac-type epoxies, can have an equivalent weight of up to 500, e.g., up to 300, or even up to 250. As used herein, "equivalent weight" refers to the average weight molecular weight of the resin divided by the number of functional groups. Thus, the equivalent weight of an epoxy-functional polymer is determined by dividing the average weight molecular weight of the epoxy resin by the total number of epoxide groups and optional other non-epoxide functional groups. Furthermore, the average weight molecular weight is determined by gel permeation chromatography against linear polystyrene standards of 800-900,000 daltons measured on a Waters 2695 Separation Module equipped with a Waters 410 Differential Refractometer (RI detector). Tetrahydrofuran (THF) was used as the eluent at a flow rate of 1 ml / min, and two PLgel Mixed-C (300 x 7.5 mm) columns were used for the separation.

[0025] It will be understood that the epoxy-functional polymer can include one or more 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 example, a first epoxy-functional polymer can have an equivalent weight greater than that of a second epoxy-functional polymer. The epoxy-functional polymer can also include additional functional groups other than the epoxy functionality, including, but not limited to, any of the functional groups described above. Alternatively, the epoxy-functional polymer can be free of any one or all of the functional groups described above other than the epoxy functionality.

[0026] The epoxy-functional polymer can comprise at least 15 wt. % of the powder coating composition, e.g., at least 20 wt. %, at least 30 wt. %, or at least 40 wt. % 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 wt. % or up to 50 wt. % 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 15-60 wt. %, or 30-50 wt. %, or 40-50 wt. % 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 wt. % of the powder coating composition, e.g., at least 20 wt. %, at least 30 wt. %, or at least 40 wt. % 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 wt. % or up to 50 wt. % 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 15-60 wt. %, or 30-50 wt. %, or 40-50 wt. % of the powder coating composition, based on the total resin solids weight of the powder coating composition.

[0028] The polycarboxylic 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 polycarboxylic acid functional polyester polymer and the epoxy functional polymer can be combined in the powder coating composition to provide a weight ratio of polycarboxylic acid functional polyester polymer to epoxy functional polymer of 85:15 to 15:85, for example, 80:20 to 20:80, 70:30 to 30:70, 60:40 to 40:60, or 50:50.

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

[0030] The powder coating compositions described herein can also include an isocyanate-functional crosslinker capable of reacting with the aforementioned reaction products containing hydroxyl functionality. The isocyanate crosslinker can provide additional properties, including, for example, high crosslink density for improved chemical resistance and abrasion resistance.

[0031] The isocyanate-functional crosslinker can include various types of polyisocyanates. Usable polyisocyanates 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, and 1,6-diisocyanatohexane (hexamethylene diisocyanate or HDI). , 1,4-butylene diisocyanate, lysine diisocyanate, 1,4-methylenebis-(cyclohexyl isocyanate), toluene diisocyanate (TDI), m-xylylene diisocyanate (MXDI) and p-xylylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, 4,4′-dibenzyl diisocyanate and 1,2,4-benzene triisocyanate, xylylene diisocyanate (XDI), and mixtures or combinations thereof.

[0032] The isocyanate crosslinker can include a blocked isocyanate-functional crosslinker. A "blocked isocyanate" refers to a compound having an isocyanate functional group that, when reacted with a blocking agent, prevents the isocyanate functional group from reacting until exposed to an external stimulus, such as heat, which removes the blocking agent. Non-limiting examples of blocking agents include phenol, pyridinol, thiophenol, methyl ethyl ketoxime, amide, caprolactam, imidazole, and pyrazole. The isocyanate can also include uretidione isocyanates, such as uredione internally blocked isocyanate adducts.

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

[0035] The coating composition can optionally further comprise a film-forming resin, such as any of the resins described above, that does not comprise a carboxylic acid group but comprises a different functional group, such as one of the other aforementioned functional groups. Furthermore, the coating composition can optionally also comprise an additional crosslinking agent capable of reacting with any of the aforementioned resins, including the optional additional film-forming resin. Non-limiting examples of additional crosslinking agents 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 may also include additional materials. Non-limiting examples of materials that may be used with the powder coating compositions described herein include plasticizers, antioxidants, flow and surface control agents such as waxes (e.g., amide waxes), thixotropic agents, lubricants, catalysts such as metal catalysts (e.g., tin catalysts), degassing agents such as benzoin, reaction inhibitors, texture modifiers, and other common adjuvants.

[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 when triglycidyl isocyanurate is present in an amount of less than 0.1 wt.% or less than 1 wt.%, respectively, based on the total solids weight of the powder coating composition. As used herein, a powder coating composition is completely free of triglycidyl isocyanurate when 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 copolymers. As used herein, a powder coating composition is substantially free or essentially free of glycidyl group-containing acrylic copolymers when the glycidyl group-containing acrylic copolymers are present in an amount of less than 5 wt.% or less than 1 wt.%, respectively, based on the total solids weight of the powder coating composition. As used herein, a powder coating composition is completely free of glycidyl group-containing acrylic copolymers when no glycidyl group-containing acrylic copolymers are present in the powder coating composition.

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

[0040] The powder coating composition may be substantially free, essentially free, or completely free of tetrabutylammonium bromide cure catalyst. As used herein, a powder coating composition is substantially free or essentially free of tetrabutylammonium bromide cure catalyst when the tetrabutylammonium bromide cure catalyst is present in an amount of less than 0.1 wt.% or less than 0.01 wt.%, respectively, based on the total solids weight of the powder coating composition. As used herein, a powder coating composition is completely free of tetrabutylammonium bromide cure catalyst when the tetrabutylammonium bromide cure catalyst is not present in the powder coating composition.

[0041] The coating compositions described herein may be free of colorants or may contain controlled amounts of colorants, which have been shown to improve the dielectric strength of the final coating. As used herein, "colorant" refers to any substance that imparts color and / or other opacity and / or other visual effects to the composition. Colorants are typically used in various forms, such as discrete particles, dispersions, solutions, and / or flakes.

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

[0043] Examples of pigments and / or pigment compositions include, but are not limited to, carbazole dioxazine crude pigments, azo, monoazo, diazo, naphthol AS, salt type (flake), benzimidazolone, isoindolinone, isoindoline and polycyclic phthalocyanines, quinacridone, perylene, perinone, diketopyrrolopyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazine, triallyl carbonium, quinophthalone pigments, diketopyrrolopyrrole red ("DPPBO red"), titanium dioxide, carbon black, and mixtures or combinations thereof. The terms "pigment" and "colored filler" can be used interchangeably.

[0044] Examples of dyes include, but are not limited to, solvent and / or aqueous based dyes such as phthalo green or phthalo blue, iron oxide, bismuth vanadate, and mixtures or combinations thereof.

[0045] Examples of tints include pigments dispersed in a water-based or water-miscible carrier, including, but not limited to, AQUA-CHEM 896 available from Degussa, Inc., CHARISMA COLORANTS and MAXITONER INDUSTRIAL COLORANTS available from the Accurate Dispersions Division of Eastman Chemical, Inc.

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

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

[0048] The coating composition can be prepared by mixing the aforementioned polycarboxylic acid-functional polyester polymer, optionally a polycarboxylic acid-functional (meth)acrylate polymer, an epoxy-functional polymer, optionally an isocyanate-functional crosslinker, and other optional additional components. These components are mixed to form a homogeneous mixture. These components can be mixed using art-recognized techniques and equipment, such as, for example, a prism high-speed mixer. Once the solid coating composition is formed, the homogeneous mixture is then melted and further mixed. This mixture can be melted in a twin-screw extruder or similar equipment known in the art. In this melting process, a temperature is selected to melt-mix a solid homogeneous mixture without curing the mixture. This homogeneous mixture can be melt-mixed in a twin-screw extruder with a temperature of 75°C to 125°C, for example, a zone set at 85°C to 115°C or 100°C.

[0049] After melt mixing, the mixture is cooled and re-solidified. The re-solidified mixture is then pulverized, such as by a grinding process, to form a solid particulate curable powder coating composition. The re-solidified mixture can be pulverized to any desired particle size. For example, for electrostatic coating applications, the re-solidified mixture can be pulverized to an average particle size of at least 10 microns, or at least 20 microns and up to 100 microns, as determined using a Beckman-Coulter LS™ 13 320 Laser Diffraction Particle Size Analyzer according to the instructions in the Beckman-Coulter LS™ 13 320 manual. Additionally, the particle size range of the total amount of particles in a sample used to determine the average particle size can include ranges of 1 micron to 200 microns, or 5 microns to 180 microns, or 10 microns to 150 microns, also determined using a Beckman-Coulter LS™ 13 320 Laser Diffraction Particle Size Analyzer according to the instructions provided in the Beckman-Coulter LS™ 13 320 manual.

[0050] The coating compositions described herein can be applied to a wide variety of substrates known in the coatings industry, such as automotive substrates, industrial substrates, aircraft and aircraft parts, marine substrates and parts, packaging substrates, electronics, and architectural substrates.

[0051] Specific non-limiting substrates include automobiles, trucks, boats, ships, onshore and offshore equipment, storage tanks, wind turbines, power industry substrates such as nuclear power plants, power lines, batteries and battery components, bus bars, metal wire, copper or aluminum conductors, wood flooring and furniture, apparel, housings and circuit boards, glass and transparent materials, sporting goods including golf balls, stadiums, buildings, and bridges.

[0052] The substrate can be, for example, a metallic substrate requiring electrical insulation or a non-metallic substrate. Metallic substrates include, but are not limited to, tin, steel (including electrogalvanized steel, cold-rolled steel, and hot-dip galvanized steel, among others), aluminum, aluminum alloys, zinc-aluminum alloys, zinc-aluminum alloy-coated steel, and aluminized steel. Non-metallic substrates include polymeric compounds, plastics, polyesters, polyolefins, polyamides, cellulosics, polystyrene, polyacrylics, poly(ethylene naphthalate), polypropylene, polyethylene, nylon, EVOH, polylactic acid, other "green" polymeric substrates, poly(ethylene terephthalate) ("PET"), polycarbonate, polycarbonate acrylobutadiene styrene ("PC / ABS"), polyamides, wood, veneers, wood composites, particleboard, medium-density fiberboard, cement, stone, glass, paper, cardboard, textiles, and both synthetic and natural leathers.

[0053] The coating compositions described herein are particularly useful when applied directly to metal substrates or pre-treated metal substrates 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, or fluidized bed processes. After the coating composition is applied to a substrate, the composition can be cured or at least partially cured by heat or 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 resin material in the composition has been crosslinked or is capable of being crosslinked. The term "actinic radiation" refers to electromagnetic radiation capable of causing a chemical reaction. Actinic radiation includes, but is not limited to, visible light, ultraviolet (UV), and infrared (IR) radiation.

[0055] In some examples, the powder coating compositions described herein are cured by heat, such as convection heating at 250°F to 500°F for 2 to 40 minutes, or at 250°F to 400°F for 10 to 30 minutes, or at 300°F to 400°F for 10 to 30 minutes. The coating compositions described herein can also be cured by infrared radiation, in which case the peak temperature of the metal can reach 400°F to 500°F in 10 seconds. The rapid temperature rise to high temperatures achieved by infrared radiation allows for faster cure times. In some examples, the powder coating compositions described herein are cured by infrared radiation to heat the composition to 300°F to 550°F for 1 to 20 minutes, or to 350°F to 525°F for 2 to 10 minutes, or to 370°F to 515°F for 5 to 8 minutes.

[0056] It should be understood that the powder coating compositions described herein can be cured using multiple types of heat sources, such as both convection heating and infrared radiation. For example, the powder coating compositions described herein can be partially cured with convection heating or infrared radiation, and then fully cured with a different heat source selected from convection heating and infrared radiation.

[0057] The powder coating compositions described herein can also be applied multiple times to cover a substrate. For example, a first powder coating composition according to the present disclosure can be applied to cover at least a portion of a substrate. A second powder coating composition according to the present disclosure can be applied to cover 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 to cover at least a portion of the first coating composition. The first and second coating compositions can then be cured simultaneously. These powder coating compositions can be cured by 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 than 5 mils, or less than 4 mils, or less than 3 mils, or less than 2 mils. It is understood that when multiple powder coating compositions are applied, each composition can be applied individually to provide any of the aforementioned dry film thicknesses. For example, when two separate powder coating compositions described herein are applied, each individual powder coating composition can be applied to any of the aforementioned dry film thicknesses.

[0059] The dielectric coatings described herein have been found to provide good dielectric strength across a substrate. For example, the dielectric coatings described herein can provide a dielectric strength of greater than 2.5 kV at a film thickness of less than 8 mils, as measured by a Sefelec RMG12AC-DC Dielectric Meter in accordance with the ASTM D149-09 Hipot Test. The dielectric coatings described herein can also provide a dielectric strength of greater than 4.0 kV at a dry film thickness of less than 5 mils, less than 4 mils, or less than 2 mils, as measured by a Sefelec RMG12AC-DC Dielectric Meter in accordance with the ASTM D149-09 Hipot Test. The dielectric coatings 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 RMG12AC-DC Dielectric Meter in accordance with the ASTM D149-09 Hipot Test. The dielectric coatings described herein may also provide a dielectric strength of at least 8.0 kV, or at least 10 kV, at a dry film thickness of 12 mils or less, or 10 mils or less, as measured by a Sefelec Dielectrimeter RMG12AC-DC in accordance with the ASTM D149-09 Hipot Test.

[0060] The dielectric coatings described herein also provide additional properties, including, but not limited to, good adhesion. For example, the dielectric coatings described herein can exhibit a 5B adhesion strength when applied to a substrate, as determined and measured according to ASTM D3359-17.

[0061] The present disclosure is also directed to a method for preparing a dielectric coating. The method includes applying a 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 coating compositions described above. The method for applying the coating composition can also include applying multiple applications of a coating composition according to the present disclosure over the substrate.

[0062] Curing the coating composition can include any of the curing steps previously described. For example, the coating composition can be cured by infrared radiation, convection heating, or a combination thereof to form a dielectric coating. Furthermore, when multiple coating compositions according to the present disclosure are applied, each coating composition can be independently partially or fully cured before applying the next coating composition. Alternatively, multiple coating compositions can be cured together simultaneously.

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

[0064] Examples 1 to 6 Preparation of Powder Coating Compositions Curable powder coating compositions were prepared from the ingredients shown in Table 1. [Table 1]

[0065] The components listed in Table 1 were weighed into a container and mixed in a Prism high-speed mixer at 3500 RPM for 30 seconds to form a dry, homogeneous mixture. This mixture was then melt-mixed in a Werner Pfleiderer 19mm twin-screw extruder at 500 RPM using the positive screw configuration. 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 50-60% torque was observed on the equipment. The mixture was dropped onto a set of chill rolls, and the mixture was allowed to cool and resolidify into solid chips. The chips were milled in a Mikro ACM®-1 Air Classifying Mill to obtain particle sizes ranging from 5 to 150 microns, with the majority of particles ranging from 20 to 40 microns. The resulting coating composition was a free-flowing, solid, particulate powder coating composition.

[0066] Example 7 Powder coating application and evaluation The curable powder coating compositions prepared in Examples 1-6 were applied by electrostatic spraying onto aluminum substrates (Q-PANEL aluminum panels measuring 4 inches by 12 inches and having a thickness of 0.64 mm or 0.81 mm). During application, a first layer of 4-7 mils was applied and then allowed to gel in a conventional oven at 350°F for 2 minutes. Thereafter, a second layer of 4-7 mils was applied and then fully baked in a conventional oven at 350°F for 30 minutes.

[0067] The dielectric strength of each coating prepared from these compositions was evaluated using a Sefelec Dielectric Meter RMG12AC-DC in accordance with the hipot test of ASTM D149-09. The test parameters were as follows: voltage limit: 12 kV DC, maximum current (I max ): 4.0 mA, Ramp: 3 seconds, Dwell: 1 second, Fall: 2 seconds. 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 compared to the coating of Comparative Example 2.

[0069] Example 8 Powder coating application and evaluation The curable powder coating composition prepared in Example 1 was applied by electrostatic spraying onto aluminum substrates (Q-PANEL aluminum panels measuring 4 inches by 12 inches and having a thickness of 0.64 mm or 0.81 mm). During application, a first layer of 5 mils was applied and then gelled in a shortwave IR oven at 315°F to 345°F for 2 minutes. Thereafter, a second layer of 5 mils was applied and then fully baked in a shortwave IR oven at 415°F to 515°F for 5 minutes.

[0070] The coatings prepared from these compositions were evaluated for dielectric strength as measured by a Sefelec Dielectric Meter RMG12AC-DC according to the ASTM D149-09 Hipot test. The test parameters were as follows: voltage limit: 12 kV DC, maximum current (I max ): 4.0 mA, Ramp: 3 seconds, Dwell: 1 second, Fall: 2 seconds. 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.

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

[0073] The solid particulate powder coating compositions of Examples 9-19 were electrostatically sprayed onto aluminum substrates (4" x 12" Q-PANEL aluminum panels with thicknesses of 0.64 mm or 0.81 mm) using a Nordson manual spray gun at voltages of 45 kV to 90 kV and an air flow rate of 20 psi using a vibratory feed dispenser. During application, a 2.0-4.0 mil layer was applied and gel cured in a conventional oven at 375°F for 5 minutes. An additional 2.0-4.0 mil layer was then applied and fully cured in a conventional oven at 375°F for 20-30 minutes.

[0074] The coatings prepared from the compositions of Examples 9-19 were evaluated for dielectric strength as measured in accordance with the ASTM D149-09 Dielectric Breakdown Voltage and Dielectric Strength Test using a Sefelec RMG12AC-DC dielectric strength tester. The test parameters were as follows: voltage limit 12.0 kV DC, maximum current (I max ): 0.5 mA, Ramp: 20 seconds, Dwell: 20 seconds, Fall: 2 seconds. The results of the dielectric strength test are shown in Tables 4 and 5.

[0075] Each of the coatings of Examples 9 to 19 exhibited good dielectric strength despite its thin thickness.

[0076] While particular embodiments of the present disclosure have been described above for purposes of illustration, it will be apparent to those skilled in the art that many changes can be made in the details of the present disclosure without departing from the disclosure as defined by the appended claims.

Claims

1. 1. A powder coating composition for preparing a dielectric coating, comprising: a) 15 to 60 weight percent, based on the total resin solids weight of the powder coating composition, of an epoxy-functional polymer; b) a polycarboxylic acid functional polyester polymer capable of reacting with the epoxy functional polymer and having an acid number of less than 100 mg KOH / g; c) 0 to 35 wt. % of a colorant present based on the total solids weight of the coating composition; (i) the coating composition further comprises an isocyanate-functional crosslinker capable of reacting with the hydroxyl-functional reaction product obtained from the epoxy-functional polymer and the polycarboxylic 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; A powder coating composition, wherein the powder coating composition is substantially free of, or completely free of, polycarboxylic acid functional (meth)acrylate polymers.

2. 10. The powder coating composition of claim 1, wherein the powder coating composition comprises 20 to 80 weight percent of the polycarboxylic acid functional polyester polymer, based on the total resin solids weight of the powder coating composition.

3. 3. The powder coating composition of claim 1, wherein the epoxy-functional polymer comprises two or more epoxy functional groups.

4. 4. The powder coating composition of claim 1, wherein the epoxy-functional polymer comprises at least one of a diglycidyl ether of bisphenol A, a polyglycidyl ether of a polyhydric alcohol, a polyglycidyl ester of a polycarboxylic acid, and / or combinations thereof.

5. The powder coating composition of any one of claims 1 to 4, wherein the epoxy-functional polymer comprises a novolac-type epoxy.

6. The powder coating composition of any of claims 1 to 5, wherein the epoxy functional polymer comprises an equivalent weight of 500 to 5100.

7. 7. The powder coating composition of claim 5 or 6, wherein the epoxy functional polymer comprises an equivalent weight of 125 to 500.

8. The powder coating composition of any of claims 1 to 7, wherein the powder coating composition comprises the isocyanate-functional crosslinker.

9. 9. The powder coating composition of claim 8, wherein the isocyanate-functional crosslinker is a blocked isocyanate-functional crosslinker.

10. 10. The powder coating composition of claim 8 or 9, wherein the isocyanate-functional crosslinker is uretidione isocyanate.

11. 11. The powder coating composition of any of claims 1 to 10, wherein the powder coating composition is substantially free of colorants, based on the total solids weight of the coating composition.

12. 12. The powder coating composition of any of claims 1 to 11, wherein the polycarboxylic acid functional polyester polymer has an acid number of from 20 mg KOH / g to 100 mg KOH / g.

13. 13. A substrate at least partially coated with a coating formed from the powder coating composition of any one of claims 1 to 12, wherein the coating has a dielectric strength of greater than 2.5 kV at a dry film thickness of less than 8 mils.

14. 14. The coated substrate of claim 13, wherein the coating has a dielectric strength greater than 4.0 kV at a dry film thickness of less than 5 mils.

15. 15. The coated substrate of claim 13 or 14, wherein the substrate comprises a metal.

16. A battery or battery component at least partially coated with a coating formed from the powder coating composition of any one of claims 1 to 12.

17. A metal wire at least partially coated with a coating formed from the powder coating composition of any one of claims 1 to 12.

18. 1. A powder coating composition for preparing a dielectric coating, comprising: a) 15 to 60 weight percent, based on the total resin solids weight of the powder coating composition, of an epoxy-functional polymer; b) a polycarboxylic acid functional polyester polymer capable of reacting with the epoxy functional polymer and having an acid number of less than 100 mg KOH / g; c) 0 to 35 wt. % of a colorant, based on the total solids weight of the coating composition; (i) the coating composition further comprises an isocyanate-functional crosslinker capable of reacting with the hydroxyl-functional reaction product obtained from the epoxy-functional polymer and the polycarboxylic 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; A powder coating composition wherein the epoxy-functional polymer comprises a novolac-type epoxy.

19. 20. The powder coating composition of claim 18, further comprising: c) a polycarboxylic acid functional (meth)acrylate polymer capable of reacting with said epoxy functional polymer.

20. 20. The powder coating composition of claim 19, wherein the weight ratio of said polycarboxylic acid functional polyester to said polycarboxylic acid functional (meth)acrylate polymer is 1:1 or greater.

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