Powder coating composition for preparing dielectric coating

Abstract

The present disclosure relates to a powder coating composition for preparing a dielectric coating, the powder coating composition comprising: a) an epoxy functional polymer; the invention relates to a coating composition comprising a) an epoxy-functional polymer, b) a polycarboxylic acid-functional polyester polymer reactive with the epoxy-functional polymer, and c) optionally a colorant, where (i) the coating composition further comprises an isocyanate-functional crosslinker, the isocyanate functional crosslinking agent is reactive 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 wherein 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 of making the dielectric coatings. Background Art

[0002] Substrates such as metal substrates including metal electrical components are often protected with high dielectric strength materials to provide insulating properties. For example, components have been coated with dielectric coatings to provide insulating properties. Although dielectric coatings can provide insulating properties, it is difficult to obtain good insulating properties at low film thicknesses. Therefore, it is desirable to develop improved dielectric coatings that provide good electrical insulation at low film thicknesses. Summary of the invention

[0003] The present disclosure relates to a powder coating composition for preparing a dielectric coating, the powder coating composition comprising: a) 15 wt % 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 reactive with the epoxy-functional polymer and having an acid value of less than 100 mg KOH / g, and c) 0 wt % 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 reactive with a hydroxy-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 greater than 2.5 kV at a dry film thickness of less than 8 mils, wherein 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, the powder coating composition comprising: a) 15 wt % 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 reactive with the epoxy-functional polymer and having an acid value of less than 100 mg KOH / g, and c) 0 wt % 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 reactive with a hydroxy-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 greater than 2.5 kV at a dry film thickness of less than 8 mils, wherein the epoxy-functional polymer comprises a novolac epoxy resin. DETAILED DESCRIPTION

[0005] For the purpose of the following detailed description, it should be understood that the present disclosure may take various alternative changes and step sequences, unless explicitly stated to the contrary. In addition, except in any operating examples or where otherwise indicated, all numerals representing the amount of ingredients used in the specification and claims, for example, should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise indicated, the numerical parameters set forth in the following specification and the attached claims are approximate values ​​that can be changed according to the desired properties to be obtained by the present disclosure. At least, and not attempting to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be interpreted in accordance with the number of reported significant digits and by applying the usual rounding techniques.

[0006]

[0013] While the numerical ranges and parameters setting forth the broad scope of the present disclosure are 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 deviation found in their respective testing measurements.

[0007] Furthermore, it should be understood that any numerical range described 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 ratios of) the recited minimum value of 1 and the recited maximum value of 10, i.e., having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10.

[0008] In this application, unless otherwise specifically stated, the use of the singular includes the plural, and the plural encompasses the singular. In addition, in this application, unless otherwise specifically stated, the use of "or" means "and / or", even though "and / or" may be explicitly used in some cases. In addition, in this application, unless otherwise specifically stated, the use of "a / an" means "at least one". For example, "a" epoxy-functional polymer, "a" polycarboxylic acid-functional polyester polymer, "a" colorant, "a" isocyanate-functional crosslinking agent, "a" powder coating composition, etc. refer to one or more items in 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 that is embodied in a solid particulate form rather than a liquid form. Thus, the components described herein can be combined to form a curable solid particulate powder coating composition. For example, the components forming the coating composition described herein can be combined into 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 aggregation between individual particles.

[0010] Furthermore, a "dielectric coating" refers to an electrically insulating coating. As will be described in further detail herein, the dielectric coatings disclosed herein can provide a dielectric strength greater than 2.5 kV as measured by a Sefelec dielectric meter RMG12 AC-DC and according to the ASTM D149-09 Hipot test.

[0011] According to the present disclosure, a powder coating composition for preparing a dielectric coating includes: an epoxy-functional polymer; a polycarboxylic acid-functional polyester polymer reactive with the epoxy-functional polymer and having an acid value of less than 100 mg KOH / g; and a polycarboxylic acid-functional (meth)acrylate polymer optionally reactive with the epoxy-functional polymer. It should be 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 grafted polymers. The term "resin" can be used interchangeably with "polymer." In addition, the term "crosslinker" refers to a molecule that contains two or more functional groups that are reactive with other functional groups and is capable of connecting two or more monomer or polymer molecules by chemical bonds.

[0013] As previously described, the powder coating composition of the present disclosure may comprise 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 may comprise a single polycarboxylic acid functional polymer. For example, the powder coating composition may comprise an epoxy functional polymer and a polycarboxylic acid functional polyester polymer. The powder coating composition may be substantially free of or free of a polycarboxylic acid functional (meth) acrylate polymer, which may correspond to less than 0.05 wt % or 0 wt % based on the total solids weight of the powder coating composition.

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

[0016] The polycarboxylic acid functional polyester polymer may 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 may comprise up to 80 wt %, or up to 70 wt %, or up to 60 wt %, or up to 50 wt %, based on the total resin solids weight of the powder coating composition. The amount of the polycarboxylic acid functional polyester polymer may also comprise from 20 wt % to 80 wt %, such as from 20 wt % to 50 wt %, from 30 wt % to 50 wt %, from 50 wt % to 80 wt %, or from 50 wt % to 70 wt %, 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 include polycarboxylic acid functional (meth) acrylate polymer.As used herein, "(meth) acrylate" and similar terms refer to both acrylate and corresponding methacrylate.Based on the total resin solids weight of the powder coating composition, the polycarboxylic acid functional (meth) acrylate polymer can account for 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 polycarboxylic acid functional (meth) acrylate polymer can account for at most 10 weight %, at most 5 weight % or at most 3 weight % of the powder coating composition.Based on the total resin solids weight of the powder coating composition, the amount of the polycarboxylic acid functional (meth) acrylate polymer can also account for 0.05 weight % to 10 weight % or 0.1 weight % to 5 weight % or 1 weight % to 3 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 the powder coating composition to provide a desired weight ratio. For example, the polycarboxylic acid functional polyester polymer and the polycarboxylic acid functional (meth) acrylate polymer can be combined in the powder coating composition to provide 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 composition can also include other 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. In addition, any previously described carboxylic acid functional polymers can have any of a variety of other functional groups, including but not limited to amine, hydroxyl, thiol, carbamate, amide, urea and combinations thereof. Alternatively, the powder coating composition described herein can be free of such other polycarboxylic acid functional polymers.

[0020] Based on the total solid weight of the powder coating composition, the total amount of carboxylic acid functional polymers can account for at least 20 weight %, at least 30 weight % or at least 40 weight % of the powder coating composition. Based on the total solid weight of the powder coating composition, the total amount of carboxylic acid functional polymers can account for up to 70 weight %, up to 60 weight % or up to 50 weight % of the powder coating composition. Based on the total solid weight of the powder coating composition, the total amount of carboxylic acid functional polymers can also account for 20 weight % to 70 weight % or 30 weight % to 60 weight % or 40 weight % to 50 weight % of the powder coating composition.

[0021] The total amount of carboxylic acid functional polymers may account for 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 total amount of carboxylic acid functional polymers may account for 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 total amount of carboxylic acid functional polymers may also account for 20 wt % to 70 wt %, 30 wt % to 60 wt %, or 40 wt % to 50 wt % 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 composition described herein can include a polycarboxylic 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 polycarboxylic acid functional polyester is recycled poly(ethylene terephthalate).

[0023] As previously described, the powder coating compositions described herein may also include an epoxy-functional polymer reactive at least with a polycarboxylic acid functional polyester polymer and a polycarboxylic acid functional (meth) acrylate polymer. It should be understood that the epoxy-functional polymer comprises two or more epoxy functional groups and acts as a crosslinking agent when reacting with a 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 polyols, polyglycidyl esters of polycarboxylic acids, and combinations thereof. Non-limiting examples of suitable epoxy resins may also be obtained from NanYa Plastics under the trade name NPES-903 and from Hexion under the trade name EPON TM 2002 and EPON 2004 TM Commercially available. Non-limiting examples of other suitable epoxy-functional polymers include novolac epoxy resins.

[0024] The equivalent weight of epoxy functional polymers such as diglycidyl ethers of bisphenol A, polyglycidyl ethers of polyols, polyglycidyl esters of polycarboxylic acids may be at least 500 or at least 700. The equivalent weight of epoxy functional polymers such as diglycidyl ethers of bisphenol A, polyglycidyl ethers of polyols, polyglycidyl esters of polycarboxylic acids may also be up to 1000 or up to 5100. The equivalent weight of epoxy functional polymers such as diglycidyl ethers of bisphenol A, polyglycidyl ethers of polyols, polyglycidyl esters of polycarboxylic acids may be from 500 to 5100 or from 700 to 1000. The equivalent weight of epoxy functional polymers such as novolac epoxy resins may be in any of the previously mentioned ranges, or the equivalent weight may be from 125 to 500, such as from 125 to 300 or from 150 to 250. The equivalent weight of epoxy functional polymers such as novolac epoxy resins may be at least 125, such as at least 150. The equivalent weight of epoxy functional polymers such as novolac epoxy resins can be 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 the resin divided by the number of functional groups. Therefore, 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 epoxy groups and any other optional functional groups that are not epoxides. In addition, the average weight molecular weight is determined by gel permeation chromatography relative to a linear polystyrene standard of 800 to 900,000 Daltons, as measured using a Waters 2695 separation module with a Waters 410 differential refractometer (RI detector). Tetrahydrofuran (THF) is used as the eluent (flow rate is 1 ml min-1), and two PLgel Mixed-C (300×7.5 mm) columns are used for separation.

[0025] It should be understood that the epoxy-functional polymer can include one or more types of epoxy-functional polymers. When using a variety of epoxy-functional polymers, the multiple epoxy-functional polymers can have the same or different equivalents. For example, the equivalent of the first epoxy-functional polymer can be greater than the equivalent of the second epoxy-functional polymer. The epoxy-functional polymer can also include other functional groups except the epoxy-functional group, including but not limited to any previously described functional groups. Alternatively, the epoxy-functional polymer can be free of any or all previously described functional groups except the epoxy-functional group.

[0026] Based on the total solid weight of the powder coating composition, the epoxy-functional polymer may comprise at least 15% by weight of the powder coating composition, such as at least 20% by weight, at least 30% by weight, or at least 40% by weight. Based on the total solid weight of the coating composition, the epoxy-functional polymer may comprise up to 60% by weight or up to 50% by weight of the powder coating composition. Based on the total solid weight of the powder coating composition, the amount of the epoxy-functional polymer may also comprise from 15% to 60% by weight, from 30% to 50% by weight, or from 40% to 50% by weight of the powder coating composition.

[0027] The epoxy-functional polymer may comprise at least 15% by weight of the powder coating composition, such as at least 20% by weight, at least 30% by weight, or at least 40% by weight, based on the total resin solids weight of the powder coating composition. The epoxy-functional polymer may comprise up to 60% by weight, or up to 50% by weight, based on the total resin solids weight of the coating composition. The amount of the epoxy-functional polymer may also comprise from 15% to 60% by weight, or from 30% to 50% by weight, or from 40% to 50% by weight, 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 the polycarboxylic acid functional polyester polymer to the epoxy functional polymer of 85:15 to 15:85, such as 80:20 to 20:80, 70:30 to 30:70, 60:40 to 40:60, or 50:50.

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

[0030] The powder coating compositions described herein may also include an isocyanate functional crosslinker that is reactive with the previously described reaction products containing hydroxyl functional groups. Isocyanate crosslinkers may provide additional properties, including, for example, higher crosslink density to increase chemical and wear resistance.

[0031] Isocyanate functional crosslinking agents can include various types of polyisocyanates. Useful polyisocyanates include aliphatic and aromatic diisocyanates and polyisocyanates of higher functionality. Non-limiting examples of suitable polyisocyanates include isophorone diisocyanate (IPDI), dicyclohexylmethane 4,4'-diisocyanate (H12MDI), cyclohexane diisocyanate (CHDI), m-tetramethylxylene diisocyanate (m-TMXDI), p-tetramethylxylene diisocyanate (p-TMXDI), ethylene diisocyanate, 1,2-diisocyanatopropane, 1,3-diisocyanatopropane, 1,6-diisocyanatohexane (hexylene diisocyanate). methyl diisocyanate or HDI), 1,4-butylene diisocyanate, lysine diisocyanate, 1,4-diisocyanate dicyclohexylmethane, toluene diisocyanate (TDI), meta-xylylene diisocyanate (MXDI) and para-xylylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 1,5-tetrahydronaphthalene diisocyanate, 4,4'-dibenzyl diisocyanate and 1,2,4-phenylene triisocyanate, xylylene diisocyanate (XDI) and mixtures or combinations thereof.

[0032] Isocyanate crosslinking agent can comprise blocked isocyanate functional crosslinking agent." blocked isocyanate " refers to the compound with isocyanate functional group, and the isocyanate functional group has reacted with blocking agent and prevents the isocyanate functional group from reacting until the blocking agent is removed when exposed to external stimulation such as heat. The limiting examples of blocking agent include phenol, pyridinol, thiophenol, methyl ethyl ketone oxime, amides, caprolactam, imidazoles and pyrazoles. Isocyanate can also include uretdione isocyanate, such as the isocyanate adduct of uretdione internal blocking.

[0033] The isocyanate functional crosslinking agent may comprise at least 0.1 wt %, at least 1 wt %, or at least 3 wt % of the powder coating composition, based on the total solid weight of the powder coating composition. The isocyanate functional crosslinking agent may comprise up to 10 wt %, up to 8 wt %, or up to 5 wt % of the powder coating composition, based on the total solid weight of the powder coating composition. The amount of the isocyanate functional crosslinking agent may also comprise from 0.1 wt % to 10 wt %, from 1 wt % to 8 wt %, or from 3 wt % to 5 wt % of the powder coating composition, based on the total solid weight of the powder coating composition.

[0034] The isocyanate functional crosslinking agent may 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 crosslinking agent may 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 amount of the isocyanate functional crosslinking agent may also comprise from 0.1 wt % to 10 wt %, from 1 wt % to 8 wt %, or from 3 wt % to 5 wt % of the powder coating composition, based on the total resin solids weight of the powder coating composition.

[0035] The coating composition may optionally include an additional film-forming resin, such as any of the previously described resins, which does not contain a carboxylic acid group, and which includes a different functional group, such as any of the other previously described functional groups. In addition, the coating composition may also optionally include an additional cross-linking agent that is reactive with any of the previously described resins (including the optional additional film-forming resin). Non-limiting examples of additional cross-linking agents that may be optionally used with the compositions described herein include carbodiimides, polyhydrazides, aziridines, alkylated urethane 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 can be used with the powder coating composition described herein include plasticizers, antioxidants, flow and surface control agents (such as waxes (e.g., amide waxes)), thixotropic agents, slip agents, catalysts (such as metal catalysts (e.g., tin catalysts)), anti-gassing agents (such as benzoin), reaction inhibitors, conditioning agents, and other commonly used adjuvants.

[0037] The powder coating composition may be substantially free, substantially free, or completely free of triglycidyl isocyanurate. As used herein, a powder coating composition is substantially free or substantially free of triglycidyl isocyanurate if triglycidyl isocyanurate is present in an amount of less than wt. % or less than 0.1 wt. %, respectively, based on the total solid 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, substantially free, or completely free of a glycidyl-containing acrylic copolymer. As used herein, the powder coating composition is substantially free or substantially free of a glycidyl-containing acrylic copolymer if the glycidyl-containing acrylic copolymer is present in an amount of less than 5 wt % or less than 1 wt %, respectively, based on the total solid weight of the powder coating composition. As used herein, the powder coating composition is completely free of a glycidyl-containing acrylic copolymer if the glycidyl-containing acrylic copolymer is not present in the powder coating composition.

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

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

[0041] The coating compositions described herein may also be free of colorants or 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] Example colorants include pigments (organic or inorganic), dyes and colorants, such as those used in the paint industry and / or listed in the Dry Color Manufacturers Association (DCMA), and special effect compositions. Colorants can 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] Example pigments and / or pigment compositions include, but are not limited to, carbazole dioxazine crude pigments, azo, monoazo, diazo, naphthol AS, salt types (flakes), benzimidazolone, isoindolinone, isoindolinone and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolopyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavonanthrone, pyranthrone, anthraquinone, dioxazines, triarylcarbonium, quinophthalone pigments, diketopyrrolopyrrole red ("DPPBO red"), titanium dioxide, carbon black, and mixtures or combinations thereof. The terms "pigment" and "colored filler" may be used interchangeably.

[0044] Exemplary dyes include, but are not limited to, solvent-based and / or water-based dyes such as phthalocyanine green or blue, iron oxide, bismuth vanadate, and mixtures or combinations thereof.

[0045] Example colorants 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 the Accurate Dispersions Division of Eastman Chemical, Inc.

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

[0047] In addition, the coating composition may be substantially free, substantially free, or completely free of colorants, such as pigments. The term "substantially free of colorants" means that the coating composition contains less than 1000 parts by weight (ppm) of colorants based on the total solid weight of the composition, "substantially free of colorants" means that the coating composition contains less than 100 ppm of colorants based on the total solid weight of the composition, and "completely free of colorants" means that the coating composition contains less than 20 parts by weight (ppb) of colorants based on the total solid weight of the composition.

[0048] The coating composition can be prepared by mixing the previously described polycarboxylic acid functional polyester polymer, optional polycarboxylic acid functional (meth) acrylate polymer, epoxy functional polymer, optional isocyanate functional crosslinking agent and other optional additional components. The components are mixed so as to form a uniform mixture. These components can be mixed using techniques and equipment recognized in the art, such as using a prism high-speed mixer. When a solid coating composition is formed, the uniform mixture is then melted and further mixed. The mixture can be melted using a twin-screw extruder or similar equipment known in the art. During the melting process, the temperature will be selected to melt-mix the solid uniform mixture without solidifying the mixture. The uniform mixture can be melt-mixed in a twin-screw extruder having a temperature zone set to 75°C to 125°C, such as 85°C to 115°C or 100°C.

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

[0050] The coating compositions described herein can be applied to various substrates known in the coating industry. For example, the coating compositions described herein can be applied to automotive substrates, industrial substrates, aircraft and aircraft components, marine substrates and components, packaging substrates, electronic equipment, architectural substrates, etc.

[0051] Specific non-limiting substrates include automobiles, trucks, ships, boats, onshore and offshore facilities, storage tanks, windmills, power industry substrates (such as nuclear power plants), wires, batteries and battery components, bus bars, metal wires, copper or aluminum conductors, wood floors and furniture, clothing, housings and circuit boards, glass and transparencies, sporting equipment (including golf balls), stadiums, buildings, bridges, etc.

[0052] For example, the substrate can be a metal or non-metal substrate that requires electrical insulation properties. Metal substrates include, but are not limited to, tin, steel (including electrogalvanized steel, cold-rolled steel, hot-dip galvanized steel, etc.), aluminum, aluminum alloys, zinc-aluminum alloys, steel coated with zinc-aluminum alloys, and aluminized steel. Non-metal substrates include polymers, plastics, polyesters, polyolefins, polyamides, cellulose, polystyrene, polyacrylic acid, poly(ethylene naphthalate), polypropylene, polyethylene, nylon, EVOH, polylactic acid, other "green" polymer substrates, poly(ethylene terephthalate) (PET), polycarbonate, polycarbonate propylene butadiene styrene (PC / ABS), polyamide, wood, thin board, wood composite, particle board, medium density fiberboard, cement, stone, glass, paper, cardboard, textiles, synthetic and natural leather, etc.

[0053] The coating compositions described herein are particularly beneficial when applied directly to a metal substrate or a pre-treated metal substrate to form a dielectric coating that provides insulating properties.

[0054] The coating compositions described herein can be applied by any standard method in the art, such as spraying, electrostatic spraying, fluidized bed processes, etc. After the coating composition is applied to the substrate, the composition can be cured or at least partially cured, such as by heat or by other means such as actinic radiation, to form a coating. As used herein, the terms "curable", "curing", etc. mean that at least a portion of the resin material in the composition is cross-linked or cross-linkable. The term "actinic radiation" refers to electromagnetic radiation that can initiate a chemical reaction. Actinic radiation includes, but is not limited to, visible light, ultraviolet (UV) rays, and infrared radiation (IR).

[0055] In some examples, the powder coating compositions described herein are cured by 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 compositions described herein can also be cured by infrared radiation, where the peak metal temperature can reach 400°F to 500°F within 10 seconds. The elevated heat ramp achieved by infrared radiation allows for fast curing times. In some examples, the powder coating compositions described herein are cured by infrared radiation to heat the composition from 300°F to 550°F for 1 to 20 minutes, or from 350°F to 525°F for 2 to 10 minutes, or from 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 with various types of heat sources such as 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 over the substrate. For example, a first powder coating composition according to the present disclosure can be applied over at least a portion of the substrate. A second powder coating composition according to the present disclosure can be applied over at least a portion of the first coating composition. Before applying the second powder coating composition, the first powder coating composition can be optionally cured or at least partially cured. Alternatively, the second powder coating composition can be applied over at least a portion of the first coating composition. The first coating composition and the second coating composition can then be cured together simultaneously. The powder coating composition can be cured by any of the methods previously described.

[0058] A coating 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 should be understood that when multiple powder coating compositions are applied, each composition can be applied individually to provide any of the previously described dry film thicknesses. For example, when two separate powder coating compositions described herein are applied, each separate powder coating composition can be applied at any of the previously described dry film thicknesses.

[0059] It has been found that the dielectric coating described herein can provide good dielectric strength above the substrate. For example, as measured by Sefelec dielectric meter RMG12AC-DC and according to ASTM D149-09 Hipot test, the dielectric coating described herein can provide a dielectric strength greater than 2.5kV with a film thickness less than 8 mils. As measured by Sefelec dielectric meter RMG12AC-DC and according to ASTM D149-09 Hipot test, the dielectric coating described herein can also provide a dielectric strength greater than 4.0kV with a dry film thickness less than 5 mils or less than 4 mils or less than 2 mils. As measured by Sefelec dielectric meter RMG12AC-DC and according to ASTM D149-09 Hipot test, the dielectric coating described herein can also provide a dielectric strength of at least 6.0kV with a dry film thickness of 3 mils or less. 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 dielectric meter RMG12 AC-DC and according to ASTM D149-09 Hipot test.

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

[0061] The present disclosure also relates to a method for preparing a dielectric coating. The method comprises 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 may include any of the coating compositions previously described. The method for applying the coating composition may also include applying the coating composition according to the present disclosure multiple times over the substrate.

[0062] The curing of the coating composition may also include any of the curing steps described previously. For example, the coating composition may be cured to form a dielectric coating by infrared radiation, convection heating, or a combination thereof. In addition, when applying a plurality of coating compositions according to the present disclosure, each coating composition may be independently partially or fully cured before applying the next coating composition. Alternatively, a plurality of coating compositions may be cured together simultaneously.

[0063] The following examples are presented to illustrate the general principles of the present disclosure. The present disclosure should not be considered limited to the specific examples presented. Unless otherwise indicated, all parts and percentages in the examples are by weight.

[0064] Examples 1-6

[0065] Preparation of powder coating compositions

[0066] The curable powder coating compositions were prepared from the components listed in Table 1.

[0067] Table 1

[0068] 1 A carboxyl functional polyester having an acid value of 69 mg KOH / g.

[0069] 2 A carboxyl functional polyester having an acid number of 70 mg KOH / g was prepared from recycled poly(ethylene terephthalate).

[0070] 3 NPES-903, commercially available from Nan Ya Plastics Corp.

[0071] 4 819, a carboxyl functional solid grade acrylic resin, is commercially available from BASF.

[0072] 5 Butaflow BT-71, commercially available from Estron Chemical.

[0073] 6 Acrylic / silica flow and leveling control agents, commercially available from Estron Chemical Inc.

[0074] 7 Micromide 520L, a fine micronized EBS wax, is commercially available from Micro Powders, Inc.

[0075] 8 Benzoin is commercially available from Mitsubishi Chemical Corporation.

[0076] 9 BF 1540, an internally blocked polyisocyanate adduct, is commercially available from Evonik. 10 White pigment.

[0077] Each of the components listed in Table 1 was weighed in a container and mixed at 3500 RPM for 30 seconds in a prismatic high speed mixer to form a dry homogenous mixture. The mixture was then melt mixed in a Werner Pfleiderer 19 mm twin screw extruder with an active 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 mixture was dripped onto a set of cooling rolls to cool the mixture and to resolidify the mixture into solid chips. The chips were placed on a Mikro -1 air classifying grinder to obtain a particle size of 5 to 150 microns, wherein most of the particles are 20 to 40 microns. The resulting coating composition is a free-flowing solid particulate powder coating composition.

[0078] Example 7

[0079] Application and evaluation of powder coatings

[0080] The curable powder coating compositions prepared in Examples 1-6 were applied to aluminum substrates (Q-PANEL aluminum panels with a size of 4 inches x 12 inches and a thickness of 0.64 mm or 0.81 mm) by electrostatic spraying. During application, a first layer of 4-7 mils was applied and then gelled using a conventional oven at 350°F for 2 minutes. Then, a second layer of 4-7 mils was applied and then fully baked using a conventional oven at 350°F for 30 minutes.

[0081] The dielectric strength of each of the coatings prepared from the composition was evaluated as measured by a Sefelec dielectric meter RMG12AC-DC and according to ASTM D149-09 Hipot test. The parameters of the test were as follows: voltage limit: 12 kVDC, I max Limits: 4.0 mA, 3 seconds ramp, 1 second dwell, 2 seconds fall. The results of the Hipot test are shown in Table 2.

[0082] Table 2

[0083]

[0084] 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.

[0085] Example 8

[0086] Application and evaluation of powder coatings

[0087] The curable powder coating composition prepared in Example 1 was applied to an aluminum substrate (Q-PANEL aluminum panel with a size of 4 inches x 12 inches and a thickness of 0.64 mm or 0.81 mm) by electrostatic spraying. During application, a first layer of 5 mils was applied and then gelled using a short wave IR oven at 315°F-345°F for 2 minutes. Then, a second layer of 5 mils was applied and then fully baked in a short wave IR oven at 415°F-515°F for 5 minutes.

[0088] The dielectric strength of the coatings prepared from the compositions was evaluated as measured by a Sefelec dielectric meter RMG12AC-DC and according to ASTM D149-09 Hipot test. The parameters of the test were as follows: Voltage limit: 12 kV DC, I max Limits: 4.0 mA, 3 seconds ramp, 1 second dwell, 2 seconds fall. The results of the Hipot test are shown in Table 3.

[0089] Table 3

[0090] nature Example 1 Film Thickness(mil) 10 Dielectric strength(kV) 10.8

[0091] As shown in Table 3, the coating formed from the powder coating composition of Example 1 using IR curing also exhibited good dielectric strength.

[0092] Example 9-19

[0093] Preparation and testing of powder coatings

[0094] Each component of the components of each example in the examples 9-19 listed in Table 4-5 is weighed in a container and mixed at 1500RPM for 30 seconds to 120 seconds to form a dry homogeneous mixture in a Henschel high speed mixer. Then, the mixture is melt mixed at a speed of 350-425RPM in a Werner and Pfleiderer 30mm twin screw extruder. The extruder zone is set at 90°F to 115°F. The feed rate is such that a torque of 20% to 25% is observed on the equipment. The mixture is added dropwise to a set of cooling rollers to cool the mixture and to resolidify the mixture into solid fragments. The fragments are ground in a Strand grinder to obtain a particle size of significantly 5 microns to 100 microns, wherein the volume of most of the particles is 20 microns to 60 microns. The resulting coating composition of each example in the examples 9-19 is a free-flowing solid particulate powder coating composition.

[0095] Table 4

[0096]

[0097] 11 An O-cresol novolac epoxy resin commercially available from TedaGolone Chemical (Tianjin, China)

[0098] 12 Solid bisphenol-A / epichlorohydrin epoxy resin from Hexion (Columbus, Ohio) 13 Imidohydroxyurethane resin powder

[0099] Table 5

[0100]

[0101] 14 URALAC P 6040, a polyester commercially available from DSM

[0102] 15 URALAC P 2450, a polyester commercially available from DSM Coating Resins, LLC (Zwolle, The Netherlands)

[0103] Each of the solid particulate powder coating compositions of Examples 9-19 was electrostatically sprayed onto an aluminum substrate (a Q-PANEL aluminum panel having a size of 4 inches x 12 inches and a thickness of 0.64 mm or 0.81 mm) using a Nordson hand spray gun at an a voltage of 45 kV to 90 kV with a vibrating feed dispenser and flowing air at 20 psi. During application, a layer of 2.0 mil to 4.0 mil was applied and then gel cured at 375° F. using a conventional oven for 5 minutes. Then, another layer of 2.0-4.0 mils was applied and fully cured at 375° F. using a conventional oven for 20-30 minutes.

[0104] The dielectric strength of each of the coatings prepared from the compositions of Examples 9-19 was evaluated as measured by a Sefelec dielectric strength tester RMG12AC-DC and in accordance with ASTM D149-09 dielectric breakdown voltage and dielectric strength test. The parameters of the test were as follows: voltage limit 12.0 kV DC, I max Limits: 0.5 mA, 20 seconds ramp, 20 seconds dwell and 2 seconds ramp. The dielectric strength test results are reported in Tables 4-5.

[0105] Each of the coatings in Examples 9-19 had good dielectric strength at low film thicknesses.

[0106] While specific embodiments of the present disclosure have been described above for purposes of illustration, it will be apparent to those skilled in the art that numerous changes in detail may be made thereto without departing from the present disclosure as defined in the appended claims.

Claims

1. A powder coating composition for preparing a dielectric coating, the powder coating composition 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 reactive with the epoxy functional polymer and having an acid value of less than 100 mg KOH / g; and c) from 0% to 35% by weight of a colorant, based on the total solids weight of the coating composition, wherein (i) the coating composition further comprises an isocyanate functional crosslinker reactive 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 greater than 2.5 kV at a dry film thickness of less than 8 mils, The powder coating composition is substantially free of or free of polycarboxylic acid functional (meth)acrylate polymers.

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

3. A powder coating composition according to claim 1 or 2, wherein the epoxy-functional polymer comprises two or more epoxy functional groups.

4. The powder coating composition according to any one of claims 1 to 3, wherein the epoxy-functional polymer comprises at least one of the following: a diglycidyl ether of bisphenol A, a polyglycidyl ether of a polyol, a polyglycidyl ester of a polycarboxylic acid, and / or a combination thereof.

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

6. A powder coating composition according to any one of claims 1 to 5, wherein the equivalent weight of the epoxy functional polymer is 500 to 5100.

7. A powder coating composition according to claim 5 or 6, wherein the equivalent weight of the epoxy functional polymer is from 125 to 500.

8. The powder coating composition according to any one of claims 1 to 7, wherein the powder coating composition comprises the isocyanate functional crosslinking agent.

9. The powder coating composition according to claim 8, wherein the isocyanate functional crosslinking agent is a blocked isocyanate functional crosslinking agent.

10. A powder coating composition according to claim 8 or 9, wherein the isocyanate functional crosslinking agent is a uretdione isocyanate.

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

12. The powder coating composition according to any one of claims 1 to 11, wherein the acid value of the polycarboxylic acid functional polyester polymer is from 20 mg KOH / g to 100 mg KOH / g.

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 greater than 2.5 kV at a dry film thickness of less than 8 mils.

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

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 a powder coating composition according to any one of claims 1 to 12.

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

18. A powder coating composition for preparing a dielectric coating, the powder coating composition 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 reactive with the epoxy functional polymer and having an acid value of less than 100 mg KOH / g; and c) 0% to 35% by weight of a colorant, based on the total solid weight of the coating composition, wherein (i) the coating composition further comprises an isocyanate functional crosslinker reactive 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 greater than 2.5 kV at a dry film thickness of less than 8 mils, wherein the epoxy-functional polymer comprises a novolac epoxy resin.

19. The powder coating composition of claim 18, further comprising c) a polycarboxylic acid functional (meth)acrylate polymer reactive with the epoxy functional polymer.

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

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