WO2026010953A1 - Compositions and methods for low temperature powder coating - Google Patents

Abstract

Disclosed herein are low cure powder coating compositions that are curable at a non-limiting temperature of 120 to 125 °C for a non-limiting time period of 5 to 10 minutes. The compositions may include phenolic and/or an amine crosslinking agents having low melting temperatures. The compositions also include low melting epoxy resins.

Description

COMPOSITIONS AND METHODS FOR

LOW TEMPERATURE POWDER COATING

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63/667,088, filed July 2, 2024, which is incorporated by reference herein in its entirety.

BACKGROUND

[0002] Low temperature powder coatings can advantageously be applied to heat-sensitive substrates due to the ability of the coating to cure at low temperatures. For example, low temperature powder coatings can be applied to composites, wood, alloy metals, plastics, and industrial medium density fiberboards (MDFs) without damaging the substrate with high temperature curing conditions. Additionally, low temperature powder coatings offer other advantages such a lower energy consumption, higher coating transfer efficiency, faster cure, and one-coat finish that is smooth, tough, and durable.

SUMMARY

[0003] This summary is provided to introduce a selection of concepts in a simplified form that are further described herein. This summary is not intended to identify key features or essential features of the claimed subject matter. Nor is this summary intended to be used to limit the scope of the claimed subject matter.

[0004] Disclosed herein are low cure powder coating compositions and methods for coating a substrate with the low cure powder compositions. The compositions incorporate an epoxy resin component, a crosslinker, and a catalyst, wherein the crosslinker is selected from the group consisting of a phenolic crosslinker and an amine crosslinker. The components included in the low cure powder compositions provide compositions which are capable of being cured a temperature of about 125 °C or less in a time period of about 10 minutes or less. The low temperature curing properties allow for the powder coating compositions to be applied to materials which are sensitive to high heat, such as medium-density fiberboard (MDF). The cured coatings of the disclosed powder coating compositions exhibit high smoothness. [0005] Both the foregoing summary and the following detailed description provide examples and are explanatory only. Accordingly, the foregoing summary and the following detailed description should not be considered to be restrictive. Further, features or variations may be provided in addition to those set forth herein. For example, certain aspects may be directed to various feature combinations and sub-combinations described in the detailed description.

BRIEF DESCRIPTION OF THE FIGURES

[0006] Non-limiting and non-exhaustive examples are described with reference to the following Figures.

[0007] FIG. 1A Depicts a chemical structure of an exemplary amine crosslinking agent: dihydrazide (VDH).

[0008] FIG. IB: Depicts a chemical structure of an exemplary amine crosslinking agent: 4, 4’- methylenebis(2-chloroaniline) (MOCA).

[0009] FIG. 1C: Depicts a chemical structure of an exemplary amine crosslinking agent: 4,4'- methylenebis(2,6 diethylaniline) (M-CDEA).

[0010] FIG. ID: Depicts a chemical structure of an exemplary amine crosslinking agent: phenolic crosslinkers.

[0011] FIG. 2 depicts overlapped differential scanning calorimetry (DSC) exothermic curves for Samples 1-4 of Example 1.

[0012] FIG. 3 depicts an image of sprayed MDF panels coated by Sample 2 (top) and 3 (bottom) of Example 1.

[0013] FIG. 4 depicts DSC exothermic curves for Sample 5 of Example 2.

[0014] FIG. 5 depicts rheological dynamic mechanical analysis (DMA) profiles for Sample

5 of Example 2.

[0015] FIG. 6 depicts cured film DMA profiles for Sample 5 of Example 2.

[0016] FIG. 7 depicts an image of a sprayed MDF panel coated by Sample 5 of Example 2.

[0017] FIG. 8 depicts overlaid DSC exothermic curves for Samples 6-9 of Example 3.

[0018] FIG. 9 depicts an image of MDF panels coated by a formulation of Example 3.

[0019] FIG. 10 depicts DSC exothermic curves for formulations of Example 4.

[0020] FIG. 11 depicts an image of MDF panels coated by formulations of Example 4.

[0021] FIG. 12 depicts overlaid DSC exothermic curves for Samples 28-30 of Example 6. [0022] FIG. 13 depicts overlaid DSC exothermic curves for Samples 30-32 of Example 6.

[0023] FIG. 14 depicts an image of substrates coated by formulations of Example 6.

DETAILED DESCRIPTION

[0024] In the following detailed description, references are made to the accompanying drawings that form a part hereof, and in which are shown by way of illustrations specific embodiments or examples. These examples may be combined, other examples may be utilized, and structural changes may be made without departing from the present disclosure. Examples may be practiced as methods, systems, or devices. It should be understood that this invention is not limited to the particular methodology, protocols, and reagents, etc., described herein and as such may vary. The terminology used herein is for the purpose of describing particular embodiments only. The following detailed description is therefore not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims and their equivalents.

[0025] To define more clearly the terms used herein, the following definitions are provided. Unless otherwise indicated, the following definitions are applicable to this disclosure. If a term is used in this disclosure but is not specifically defined herein, the definition from the IUPAC Compendium of Chemical Terminology, 2^nd Ed (1997), can be applied, as long as that definition does not conflict with any other disclosure or definition applied herein, or render indefinite or nonenabled any claim to which that definition is applied. To the extent that any definition or usage provided by any document incorporated herein by reference conflicts with the definition or usage provided herein, the definition or usage provided herein controls.

[0026] Herein, features of the subject matter are described such that, within particular aspects, a combination of different features can be envisioned. For each and every aspect and/or feature disclosed herein, all combinations that do not detrimentally affect the compositions and processes described herein are contemplated with or without explicit description of the particular combination. Additionally, unless explicitly recited otherwise, any aspect and/or feature disclosed herein can be combined to describe inventive features consistent with the present disclosure.

[0027] The processes, systems, and compositions of the present disclosure may comprise, consist essentially of, or consist of the components and ingredients of the present disclosure as well as other ingredients described herein. As used herein, “consisting essentially of’ means that the methods and compositions may include additional steps, components or ingredients, but only if the additional steps, components or ingredients do not materially alter the basic and novel characteristics of the claimed processes and compositions.

[0028] As used herein, “weight percent,” “wt%,” “percent by weight,” “% by weight,” and variations thereof refer to the concentration of a substance as the weight of that substance divided by the total weight of the composition and multiplied by 100. It is understood that, as used here, “percent,” “%,” and the like are intended to be synonymous with “weight percent,” “wt%,” etc.

[0029] As used herein, “g” represents gram; “L” represents liter; “mg” represents “milligram (10-3 gram);” “mL” represents milliliter (10-3 liter); “cm” represents centimeter (10-2 meter); micron represents 10-6 meter; “mm” represents millimeter (10-3 meter); “inch” is used as a length unit, and one inch equals to about 2.54 cm; “centipoise” or “cPs” or “cP” is used as a viscosity unit, and 1 cP = 10-3 Pa-s = 1 mPa-s. The temperature unit used herein is degree Celsius (°C).

[0030] The term “about” is used in conjunction with numeric values to include normal variations in measurements, as expected by persons skilled in the art, and is understood to have the same meaning as “approximately” and to cover a typical margin of error, such as ± 10 % of the stated value. The term “about” also encompasses amounts that differ due to different equilibrium conditions for a composition resulting from a particular initial composition. Whether or not modified by the term “about,” the claims include equivalents to the quantities.

[0031] It should be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a composition containing “a compound” includes having two or more compounds that are either the same or different from each other. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise.

[0032] In the interest of brevity and conciseness, any ranges of values set forth in this specification contemplate all values within the range, and are to be construed as support for claims, reciting any sub-ranges having endpoints which are real number values within the specified range in question. By way of a hypothetical illustrative example, a disclosure in this specification of a range of from 1 to 5 shall be considered to support claims to any of the following ranges: 1-5; 1- 4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5.

[0033] The “epoxide equivalent weight” (EEW) refers to the number of grams of epoxy resin required to give 1 mole of epoxide groups. The EEW may be determined by titration. The EEW standard test method for epoxy content of epoxy resins is ASTM 17 DI 652. Weight per Epoxy Equivalent (WPE) may be determined using ASTM DI 652 test method.

[0034] The “NH equivalent weight” or “EW-NH” refers to the number of grams of an amine compound required to give 1 mole of NH. For example, in the case of 4,4’-methylenebis(2- chloroaniline) (MOCA), the MOCA compound has a molecular weight (MW) of 267.15 g/mol and contains four NH groups, see FIG. IB. Therefore, MOCA has an EW-NH of 66.80 g/eq, which is 267.15 g/mol divided by four. A similar concept is applied for the “phenol hydroxyl equivalent weight” or “EW-PhOH” which refers to the number of grams of a phenolic compound required to give 1 mole of PhOH. As used herein, “phenol compound”, or “phenolic compound”, refers to a compound containing a group having a formula of -C6H4OH, abbreviated as PhOH.

[0035] As used herein, the term “low cure” refers to powder coatings having a low application temperature (LAT) of less than or equal to: about 150°C, about 145°C, about 140°C, about 135°C, about 130°C, about 125°C, about 120°C, about 115°C, about 110°C, about 105°C, about 100°C. The temperature may also vary based on the curing time which is from about 1 minute (min) to about 20 mins, or from about 10 mins to about 15 mins.

[0036] The application of many commercially available powder coating compositions to substrates requires high curing temperatures, for example, 200 °C to 250 °C for time periods of up to or longer than 30 minutes. However, this limits the application of such powder coating compositions to substrates which can withstand the high curing temperatures. In addition, many commercially available powder coating compositions include components which require special handling and storage, such as polyesters and peroxides. Therefore, low cure powder coating compositions which do not include sensitive materials are necessary in order to provide coatings on heat sensitive materials such as MDF.

[0037] Thus, one objective of this invention is to develop low temperature powder coatings that are curable at a non-limiting temperature of 120 °C to 125 °C for a non-limiting time period of 5 minutes to 10 minutes. Inclusion of low melting materials such as epoxies and crosslinkers allow for a low cure composition. Thus, the compositions of the present invention can be applied to heat sensitive materials. Also, the compositions of the present invention may reduce environmental impact by requiring less energy input for the curing process.

[0038] When applied to surfaces or substrates, the powder coating compositions of the present invention can form a smooth coating. In some examples, the compositions of the present invention can be applied to any suitable surface or substrate. For instance, the compositions can be applied to medium-density fiberboard (MDF), wood, metal, plastic, or other substrates.

POWDER COATING COMPOSITIONS

[0039] In one example, a powder composition is disclosed herein. The powder composition may comprise an epoxy resin component, a crosslinker, and a catalyst, wherein the crosslinker is selected from the group consisting of a phenolic crosslinker and an amine crosslinker.

[0040] Suitable epoxy resin components that may be used in the compositions disclosed herein include, without limitation, an epoxy resin containing one or more epoxide or glycidyl groups per molecule. Epoxides are three-membered cyclic ethers with an oxygen atom and two carbon atoms. Glycidyl groups are three-membered cyclic ethers with an oxygen atom and two carbon atoms attached to a methylene group. These epoxides and glycidyl groups represent the reactive sites on the epoxy resin component and, due to their reactivity, can undergo polymerization or cross-linking reactions.

[0041] A non-limiting example of a suitable epoxy resin component consistent with examples of this invention, includes but is not limited to, bisphenol A epoxies sold under the Kukdo YD- 012 series. Suitable epoxies also include glycidyl methacrylate (GMA) resins such as the AP and PD series sold by Anderson Development. Suitable epoxy resins include epoxies having an EEW of less than about 800 g/eq, about 775 g/eq, about 750 g/eq, about 725 g/eq, about 700 g/eq, about 675 g/eq, about 650 g/eq, about 625 g/eq, about 600 g/eq, about 575 g/eq, about 550 g/eq, about 525 g/eq, or about 500 g/eq. In general, the epoxies are Type 1.5 to Type 4.0, or Type 2.0.

[0042] The composition of the present invention can contain any suitable amount of the epoxy resin component. Suitable amounts of the epoxy resin component include about 30 wt% to about 80 wt%, about 35 wt% to about 75 wt%, about 40 wt% to about 70 wt%, about 45 wt% to about 65 wt%, about 50 wt% to about 55 wt%, based on a total weight of the composition.

[0043] The composition of the present invention can contain any suitable phenolic crosslinker. A non-limiting example of suitable phenolic crosslinkers consistent with examples of this invention, include but are not limited to, the Kukdo KD series phenol excess type curing agents including Kukdo KD-405 (Ts 73-85 °C), Kukdo KD-427 (T_s 95-100 °C), Kukdo KD-452 (Ts 96- 106 °C), and Kukdo KD-448 (T_s 95-120 °C), having the general structure shown in FIG. ID. Suitable phenolic crosslinkers have a Ph-OH EW of less than about 600 g/eq, about 575 g/eq, about 550 g/eq, about 525 g/eq, about 500 g/eq, about 475 g/eq, about 450 g/eq, about 425 g/eq, about 400 g/eq, about 375 g/eq, about 350 g/eq, about 325 g/eq, about 300 g/eq, about 275 g/eq, about 250 g/eq, about 225 g/eq, or about 200 g/eq. The size of the phenolic crosslinker, among other properties, affects the softening point or melting point of the phenolic crosslinker. Suitable phenolic crosslinkers have a melting temperature of about 110 °C or less, about 105 °C, about 100 °C, about 95 °C, about 90 °C, about 85 °C, about 80 °C, about 75 °C, or about 70 °C.

[0044] The composition of the present invention can contain any suitable amount of the phenolic crosslinker. Suitable amounts of the phenolic crosslinker include about 1 wt% to about 30 wt%, about 5 wt% to about 25 wt%, about 10 wt% to about 20 wt%, or about 15 wt%, based on a total weight of the composition.

[0045] The composition of the present invention can contain any suitable amine crosslinker. An amine crosslinker contains reactive amine (NH2) sites which can undergo crossdinking reactions. A non-limiting example of suitable amine crosslinkers consistent with examples of this invention, include but are not limited to, valine dihydrazide (VDH) (FIG. 1A), 4,4’- methylenebis(2-chloroaniline) (MOCA) (FIG. IB) and 4,4'-methylenebis(2,6 diethylaniline) (M- CDEA) (FIG. 1C). Suitable amine crosslinkers have a NH EW of less than about 100 g/eq, about 75 g/eq, or about 50 g/eq. The size of the amine crosslinker, among other properties, affects the softening point or melting point of the amine crosslinker. Suitable amine crosslinkers have a melting temperature of about 120 °C or less, about 115 °C, about 110 °C, about 105 °C, about 100 °C, about 95 °C, about 90 °C, about 85 °C, about 80 °C, about 75 °C, or about 70 °C. The composition of the present invention can contain both a phenolic crosslinker and an amine crosslinker.

[0046] The composition of the present invention can contain any suitable amount of the amine crosslinker. Suitable amounts of the amine crosslinker include about 1 wt% to about 10 wt%, about 2 wt% to about 8 wt%, or about 4 wt% to about 6 wt%, based on a total weight of the composition. [0047] The composition of the present invention can contain any suitable ratio (by weight) of epoxy resin component to the crosslinker. Suitable weight ratios of the epoxy resin component to the crosslinker include about 20: 1 to about 3: 1, about 19: 1 to about 4: 1, about 18: 1 to about 5: 1, about 17: 1 to about 6: 1, about 16: 1 to about 7: 1, about 15: 1 to about 8: 1, about 14: 1 to about 9: 1, about 13:1 to about 10: 1, about 12: 1 to about 11 :1. [0048] The composition of the present invention can contain any suitable catalyst capable of reacting the epoxy resin component and the crosslinker. A non-limiting example of a suitable catalyst consistent with examples of this invention, includes but is not limited to, an amine adduct, such as the imidazole adduct Epikure™ P-101 catalyst. An amine adduct is a compound formed by the reaction of an amine with another molecule, where the amine acts as a catalyst to facilitate a chemical reaction.

[0049] The composition of the present invention can contain any suitable amount of the catalyst. Suitable amounts of the catalyst include about 0.1 wt% to about 5 wt%, about 0.5 wt% to about 4.5 wt%, about 1.0 wt% to about 4.0 wt%, about 1.5 wt% to about 3.5 wt%, about 2.0 wt% to about 3.0 wt%, or about 2.5 wt%, based on a total weight of the epoxy resin component and the crosslinker.

[0050] In some examples, the composition has a glass transition temperature (T_g) of less than about 115 °C, about 110 °C, about 105 °C, about 100 °C, about 95 °C, about 90 °C, or about 85 °C. In some examples, the composition has a Tpeak of greater than about 125 °C, about 130 °C, about 135 °C, about 140 °C, about 145 °C, or about 150 °C. In some examples, the composition has a Tonset of about 50 °C to about 120 °C, about 55 °C to about 115 °C, about 60 °C to about 110 °C, about 65 °C to about 105 °C, about 70 °C to about 100 °C, about 75 °C to about 95 °C, about 80 °C to about 90 °C, or about 85 °C.

[0051] In some examples, the composition is capable of being cured a temperature of about 125 °C or less, about 120 °C to about 115 °C, or about 110 °C in a time period of about 10 minutes or less, about 9 mins, about 8 mins, about 7 mins, about 6 mins, or about 5 mins. In some examples, the composition has greater than 90%, 95%, 99%, or 100% cure at a temperature of 125 °C or less in a time period of 10 minutes or less.

[0052] In another example, a powder composition is disclosed herein. The powder composition may comprise a resin component and a catalyst, wherein the catalyst comprises an anionic tertiary amine catalyst and a cationic onium salt and wherein the composition does not comprise a crosslinker.

[0053] The resin component may include an epoxy resin. Suitable epoxy resin components that may be used in the compositions disclosed herein include, without limitation, an epoxy resin containing one or more epoxide or glycidyl groups per molecule. Epoxides are three-membered cyclic ethers with an oxygen atom and two carbon atoms. Glycidyl groups are three-membered cyclic ethers with an oxygen atom and two carbon atoms attached to a methylene group. These epoxides and glycidyl groups represent the reactive sites on the epoxy resin component and, due to their reactivity, can undergo polymerization or cross-linking reactions.

[0054] A non-limiting example of a suitable epoxy resin consistent with examples of this invention, includes but is not limited to, bisphenol A epoxies sold under the Kukdo YD-012 series. Suitable epoxies also include glycidyl methacrylate (GMA) resins such as the AP and PD series sold by Anderson Development. Suitable epoxy resins include epoxies having an EEW of less than about 800 g/eq, about 775 g/eq, about 750 g/eq, about 725 g/eq, about 700 g/eq, about 675 g/eq, about 650 g/eq, about 625 g/eq, about 600 g/eq, about 575 g/eq, about 550 g/eq, about 525 g/eq, or about 500 g/eq. In general, the epoxies are Type 1.5 to Type 4.0, or Type 2.0.

[0055] The composition of the present invention can contain any suitable amount of the epoxy resin component. Suitable amounts of the epoxy resin component include about 30 wt% to about 80 wt%, about 35 wt% to about 75 wt%, about 40 wt% to about 70 wt%, about 45 wt% to about 65 wt%, about 50 wt% to about 55 wt%, based on a total weight of the composition.

[0056] The resin component may also include a carboxylated polyester resin. A carboxylated polyester resin is a polyester resin which is functionalized with a carboxylic acid group (COOH). A non-limiting example of a suitable carboxylated polyester resin consistent with examples of this invention, includes but is not limited to, Crylcoat E ® 1551-6 resin. Suitable carboxylated polyester resin include those having an EW-COOH of less than about 800 g/eq, about 775 g/eq, about 750 g/eq, about 725 g/eq, about 700 g/eq, about 675 g/eq, about 650 g/eq, about 625 g/eq, about 600 g/eq, about 575 g/eq, about 550 g/eq, about 525 g/eq, or about 500 g/eq.

[0057] The composition of the present invention can contain any suitable ratio (by weight) of epoxy resin to the carboxylated polyester resin in the resin component. Suitable weight ratios of the epoxy resin to the carboxylated polyester resin include about 1 : 1 to 2: 1, about 1.2: 1, about 1.4:1, about 1.6: 1, or about 1.8: 1.

[0058] The composition of the present invention can contain any suitable catalyst. The catalyst may also include multiple catalysts, for example two catalysts, or more than two catalysts. In some examples, the catalyst includes an anionic tertiary amine catalyst. A non-limiting example of a suitable anionic tertiary amine catalyst consistent with examples of this invention, includes but is not limited to, a 2MI-90 catalyst or 2-methyl imidazole catalyst. In some examples, the catalyst also includes a cationic onium salt catalyst. A non-limiting example of a suitable cationic onium salt catalyst consistent with examples of this invention, includes but is not limited to, an IL 169, or a phosphonium ionic liquid. Other phosphonium or sulfonium salts may also be used. In some examples, the catalyst does not include an amine adduct.

[0059] The composition of the present invention can contain any suitable amount of the catalyst. Suitable amounts of the catalyst include about 0.1 wt% to about 5 wt%, about 0.5 wt% to about 4.5 wt%, about 1.0 wt% to about 4.0 wt%, about 1.5 wt% to about 3.5 wt%, about 2.0 wt% to about 3.0 wt%, or about 2.5 wt%, based on a total weight of the resin component.

[0060] The composition of the present invention can contain any suitable ratio (by weight) of anionic tertiary amine catalyst to the cationic onium salt catalyst. Suitable weight ratios of the anionic tertiary amine catalyst to the cationic onium salt catalyst include about 10: 1 to 2: 1, about 9: 1, about 8:1, about 7: 1, about 6:1, about 5: 1, about 4: 1, about 3: 1, or about 2: 1.

[0061] In some examples, the composition is capable of being cured a temperature of about 130 °C to about 150 °C, about 135 °C to about 145 °C, or about 140 °C in a time period of about 10 minutes (herein also “mins” or “min”) or less, about 9 mins, about 8 mins, about 7 mins, about 6 mins, or about 5 mins.

[0062] The compositions of the present invention may further include additives such as waxes for flow and wetting, flow control agents, degassing additives such as benzoin, adjuvant resins to modify coating properties, antioxidants, fillers, pigments, and the like. These optional additives, when used, can be present in amounts up to 10 wt%, based on total weight of the coating composition, and if used will typically comprise about 1 wt% to 5 wt%.

[0063] In some examples, the powder coating compositions are not UV-curable and do not include photo-initiators or free-radical curing agents, such as peroxides.

[0064] In some examples, the powder coating compositions have average particle sizes from about 15 to about 200 microns, about 50 to about 150 microns, or about 100 microns. In some examples, the powder coatings have powder particle sizes such as D10 = 35 to 40 microns and D90 = 80 to 85 microns.

METHODS OF MAKING A COATED SUBSTRATE

[0065] The powder coating compositions of the present invention can be applied to a substrate. The substrate can be made of any suitable material. Suitable materials include plastics such as thermosets or thermoplastics, cardboard, paper, wood, metal, metal alloys, particleboard and medium density fiberboard (MDF), or mixtures/combinations thereof. Substrates which cannot withstand high temperatures are particularly suited to be coated with the low cure powder coating compositions of the present invention. Substrates coated according to the present methods are also within the scope of the present invention.

[0066] The powder coating compositions of the present invention can be applied to a substrate in any number of ways, such as by electrostatic spraying, for example a spray voltage of about 60 kV. The powder coating can be applied in a single sweep or in several passes to provide a film having a thickness after cure of from about 10 microns to about 500 microns, or about 50 microns to 100 microns. Other standard methods for coating application can also be used, for example, fluidized bed coating. In some examples, only a single coat is applied to the substrate.

[0067] After application, the present compositions may be cured by heating to a temperature of about 125 °C or less, about 120 °C to about 115 °C, or about 110 °C for a time period of about 10 minutes or less, about 9 mins, about 8 mins, about 7 mins, about 6 mins, or about 5 mins. In some examples, the composition is cured a temperature of about 130 °C to about 150 °C, about 135 °C to about 145 °C, or about 140 °C for a time period of about 10 minutes or less, about 9 mins, about 8 mins, about 7 mins, about 6 mins, or about 5 mins. Heat can be applied by any means known in the art, such as by placing the substrate with the applied composition in an oven.

[0068] Accordingly, the present invention is further directed to a method for coating a substrate comprising applying to the substrate one or more of the coating compositions described herein and curing the composition as described herein to form a coated substrate.

[0069] The coated substrate has a PCI smoothness of 5 to 10, or 7 to 10 at between about 4 to 5 mil DFT. The PCI Powder Coating Visual Smoothness Standards are a set of ten panels showing the normal degrees of smoothness achievable with powder coatings.

[0070] The physical advantages of such epoxy formulations include storage and transport at ambient temperature, as opposed to the low storage temperatures necessary for formulations such as unsaturated polyesters and free-radical peroxides.

EXAMPLES

[0071] The invention is further illustrated by the following examples, which are not to be construed in any way as imposing limitations to the scope of this invention. Various other examples, embodiments, modifications, and equivalents thereof which, after reading the description herein, can suggest themselves to one of ordinary skill in the art without departing from the spirit of the present invention or the scope of the appended claims.

[0072] Glass transition temperature T_g was determined experimentally according to DIN51005 Thermal analysis (TA) - terms and DIN 53765 “Thermal analysis dynamic scanning calorimetry (DSC). This involves weighing out a 5- 10g sample into a sample pan and introduce it into a DSC instrument. After cooling to the start temperature, 1^st and 2^nd measurement runs are carried out with inert gas flushing (N2) of 50ml/min with a heating rate of 7 or 20°C/min, with cooling to the start temperature again between the measurement runs. Measurement takes place customarily in the temperature range from about 50 °C lower than the expected glass transition temperature to about 50 °C higher than the glass transition temperature. The T_g for the purposes of the present invention, in accordance with DIN 53765, is that temperature in the 2^nd measurement run at which half of the change in the specific heat capacity (0.5 ACp) is reached. This temperature is determined from the DSC exotherm (plot of the heat flow against the temperature). It is the temperature at the point of intersection of the midline between the extrapolated baselines, before and after glass transition, with the measurement plot (the exothermic curve).

EXAMPLE 1: PHENOLIC CROSSLINKER AND EPOXY COMPOSITION

[0073] Powder coatings of Example 1 were prepared as follows. The components shown in Table 1 were added together in the described amounts. The amount of phenolic crosslinker and epoxy resin were varied for Samples 1-4, however each of Samples 1-4 had the same total parts by weight (ppw) in the total composition of 1441 .96. A Type 2 epoxy resin, that is, Kukdo’s YD- 012Q (T_s 75-85 °C) was used. Micral 1500 is aluminum trihydrate (ATH) with a fine particle size average of 1.5pm incorporated for even cold sprayability on MDF panels, and S-345-N5 is a micronized polyethylene wax with a melting point of 110 °C to address grain raise or puff issues that are specific to wood substrates.

Table 1. Components of Samples 1-4.

[0074] The amounts and type of phenolic crosslinker with different molecular weights and EW-PhOHs are shown in Table 2. Sample 1 included Kukdo KD-405 (EW-PhOH 250, T_s 73-85 °C), Sample 2 included Kukdo KD-427 (EW-PhOH 380, T_s 95-100 °C), Sample 3 included Kukdo KD-452 (EW-PhOH 530, T_s 96-106 °C), and Sample 4 included Kukdo KD-448 (EW-PhOH 700, Ts 95-120 °C). The amounts of epoxy in Samples 1-4 are also shown in Table 2. Each of Samples 1-4 had a formulation index (FI) of 3.50 and a catalyst loading level (phr) of 3.736, based on the amount of epoxy and crosslinker. The powder coatings were cured on MDF substrates at 125°C for 10 minutes. The performance of each of Samples 1-4 was determined based on the measurement of properties shown in Table 2.

Table 2. Properties of Samples 1-4.

[0075] As shown in Table 2, Samples 1-4 included phenolic crosslinkers and a type 2 epoxy catalyzed by an imidazole adduct, which provided sufficient cure (>99%). FIG. 2 shows differential scanning calorimetry (DSC) plots of Samples 1-4. DSC measurements were taken at a heating rate of 7 °C/min and a heating rate of 20 °C/min. The residue AH, T_peak, and Tonset were calculated for each of Samples 1-4 as shown in Table 2 from the DSC plots. These values were not calculated for Samples 1 and 4, however as shown in FIG. 2, the plots for Samples 1 and 4 are similar to that of Samples 2 and 3. Samples 1-4 had a glass transition temperature of about 102 °C. As shown in FIG. 3, cured coatings of Samples 1-4 on MDF substrates at 125°C for 10 minutes produced tough and smooth (PCI 5-7) coatings with excellent edge coverage.

[0076] Sample 3 having phenolic crosslinker Kukdo KD-452 (EW-PhOH 530), performed the best, as it had the shortest gel time and the longest pill flow. While not wishing to be bound by theory, it is thought that Sample 4 including KD-448 had a MW that is too high to be reactively responsive. Smoothness and gloss were consistent with flow data, and edge coverage was the best for Sample 2 at 4-5 mil DFT on MDF and at 12-14 mil DFT on blasted steel substrates, followed by Sample 3.

EXAMPLE 2: AMINE CROSSLINKER AND EPOXY COMPOSITION [0077] Powder coatings of Example 2 were prepared as follows. The components shown in Table 3 were added together in the described amounts to form Sample 5. Sample 5 had a formulation index (FI) of 2.00 and a catalyst loading level (phr) of 3.45, based on the amount of epoxy and crosslinker. A Type 2 epoxy resin, that is, Epo-Thoto YD-012Q was used. A valine dihydrazide (VDH) (MW 314.0, EW-NH 78.5, T_m 120 °C) crosslinker was used. VDH is a commercially accessible dihydrazide having the lowest melting point of all dihydrazides, 120 °C.

Table 3. Components of Sample 5.

[0078] Gel times and pill flows (0.50-gram pills) were measured to be 29.0/6.6 sec and 46.8/53.9 mm at 250/350 °F, respectively.

[0079] FIG. 4 shows DSC plots of Sample 5. DSC measurements were taken at a heating rate of 7 °C/min and a heating rate of 20 °C/min. The normalized enthalpy (J/g), Tpeak, and Tonset were calculated for Sample 5 from the DSC plots. The enthalpy was 115.6 J/g, the Tpeak was 106.9 °C, and the Tonset was 82.6 °C at a heating rate of 7 °C/min. The enthalpy was 109.0 J/g, the T_peak was 126.3 °C, and the Tonset was 101.9 °C at a heating rate of 20 °C/min. The powder had a T_g of 46.1 °C and the cured composition had a T_g of 112.5 °C. [0080] FIG. 5 shows rheological dynamic mechanical analysis (DMA) profiles for Sample 5. FIG. 6 shows DMA profiles for the cured film of Sample 5. Sample 5 included an amine crosslinker and a type 2 epoxy catalyzed by an imidazole adduct, which provided sufficient cure (>95%). Sample 5 had a glass transition temperature of about 109 °C. As shown in FIG. 7, cured coatings of Sample 5 on MDF substrates produced tough and smooth (PCI 5-7) coatings with great edge coverage. However, based on DSC T_peak and Tonset temperatures that exceeded the target cure temperature of 125 °C as well as the resulting gritty finishes on MDF panels, as shown in FIG. 7, the performance was not as high as other compositions. While not wishing to be bound by theory, in general, Tonset should be significantly lower than the underlying cure temperature, which should preferably be greater than Tpeak.

EXAMPLE 3: CROSSLINKER FREE DUAL CATALYST EPOXY COMPOSITION

[0081] Powder coatings of Example 3 were prepared as follows. Components similar to that of Examples 1 and 2 were used except that no crosslinker was added. Instead, a dual catalyst of an anionic tertiary amine, such as 2MI-90, and a cationic onium catalyst, such as IL 169, was used. The type of epoxy from type 1.5-5 were varied for each sample. In general, as the epoxy type increases from 1 to 5, the molecular weight, EEW, softening point, and viscosity increase. The epoxies also included fillers in Samples 11-13.

[0082] The measured properties of Samples 6-13 are shown in Table 4 and the properties of the cured films are shown in Table 5. FIG. 8 depicts overlaid DSC exothermic curves for Samples 6-9 of Example 3. Samples 8 and 9 including type 2 and type 4 epoxies had the shortest gel time, however pill flow began to decrease. Samples 11-13 including fillers did not have high curing performance. In Example 3, for Sample 8, a 75+% cure was achievable, with a T_g of 115°C, which provides a smooth (PCI 5-7) coating, as shown in FIG. 9.

Table 4. Properties of Samples 6-13.

Table 5. Properties of Cured Films of Samples 6-13. [0083] While not wishing to be bound by theory, it is thought that of the disadvantages of using type epoxy 1.5 resins, such as Example 6, is that the cured T_g will likely end up over 120 °C, which is near to the desired curing temperature of 125 °C, causing concerns about harmful vitrification during curing. In another aspect, filler overloading impedes cure completion. For instance, filler loadings in Samples 11-13 reduced cure levels. Therefore, filler loadings should be tuned such that adequate cure (up to 90%) can be achieved on thermally insulating MDF panels. According to historical and statistical data, an undercure (UC) level of up to 5-10% has no or limited effect on physical performance as a whole. In addition, the dual-cure catalyst approach remains effectively applicable and delivers faster and better curing performance than cationic salts alone.

EXAMPLE 4: HYBRID POLYESTER EPOXY COMPOSITION

[0084] Powder coatings of Example 4 were prepared as follows. Components similar to that of Example 3 were used except that a polyester was added. Samples 14-22 were prepared with different amounts of epoxy and carboxylated (COOH functional) polyester. In the hybrid formulations comprising an epoxy and a COOH-functional polyester resin, consideration was also taken in the use of an appropriate resin and catalyst package. Each of Samples 14-22 included a Type 1.9-2.0 epoxy resin. Lower-type epoxy resins were used due to their lower molecular weights and thus faster cure response and better flowability at the desired sure temperature. The coupled polyester resin should compatibly render great flow and leveling in order to achieve a high level of smoothness. For hybrid formulations, epoxy resins were used so that their pbw addition levels are greater than those of the polyester resins in order to improve flow and leveling.

[0085] Samples 14-17 included both a loncryl (JC) 848 resin and a Crylcoat E 1551-6 resin, which is a carboxylated polyester (EW-COOH 790 g/eq). Sample 18 did not include JC 848 resin and Sample 19 included only JC 848. Samples 20-22 included Crylcoat E 1551-6 resin. Table 6 provides the molar ratio of epoxies to polyesters (PE) (FI), in terms of capable cure schedules at 125 °C for Samples 14-22.

Table 6. Properties of Samples 14-22.

Table 7. Properties of Cured Films of Samples 14-22.

[0086] The measured properties of Samples 14-22 are shown in Table 6 and the properties of the cured films are shown in Table 7. As opposed to the dual-cure crosslinker-free formulations of Example 3, highly catalyzed hybrids exhibited noticeable advantages, such as lower T_peak below 120 °C and Tonset and T_g lower than 85 °C, all in favor of faster cure completion at the underlying 125 °C. FIG. 10 shows a comparison between the hybrid formulation having a Type 2.0 epoxy resin and a Type 1.5 epoxy resin formulation of Example 3.

[0087] Sample 14 produced a smooth gloss coated on steel and MDF. It was necessary to reduce fdler loading levels for hybrids to produce MDF panels with a sufficiently smooth PCI finish of 5-7 at 4-5 mils, as shown in FIG. 11. Unfortunately, hybrids on MDFs that were subjected to an oven post-cure setting of 125 °C for 10 min were severely under-cured, that is, 69.1% cured against 76.0% cured for the dual-cure crosslinker-free formulations. Otherwise, the hybrid coating’s mechanical and physical properties were observably compromised by under-cure. The optimal cure temperature range for these hybrid systems was found to be between 130 °C and 150 °C. The hybrid provided 65+% cure, a T_g 83.4°C, and PCI 5-7 if unfilled or slightly filled.

EXAMPLE 5: CROSSLINKER AND GMA COMPOSITION

[0088] Powder coatings of Example 5 were prepared as follows. Table 8 shows the components of Samples 23-27. In Samples 25-27, a GMA resin was used instead of an epoxy resin.

Table 8. Components of Samples 23-27

Table 9. Properties of Samples 23-27.

EXAMPLE 6: AMINE CROSSLINKER AND EPOXY COMPOSITION

[0089] Powder coatings of Example 6 were prepared as follows. Table 10 shows the components of Samples 28-34. In Samples 28-34, the amine crosslinker and amount of amine crosslinker were varies between VDH (MW 314.0, EW-NH 78.5, T_m 120 °C), MOCA (MW 67.15 g/mol, EW-NH 66.80 g/eq, T_m about 106.5 °C), and M-CDEA (MW 379.37, EW-NH 4.84, Tm 88-90 °C) and combinations thereof.

Table 10. Components of Samples 28-34.

[0090] Sample 31 performed the best as a compounded formulation in terms of ultra-low cure capacity, suitability to MDFs (matteness, smoothness, edge coverage, grain raise control).

[0091] FIG. 12 shows DSC plots of Samples 28-30. DSC measurements were taken at a heating rate of 7 °C/min and a heating rate of 20 °C/min. The normalized enthalpy (J/g), Tpeak, and Tonset were calculated from the DSC plots and are shown in Table 11. The lower Tpeak and Tonset of Sample 30 determined that VDH performs best in terms of ultra-low cure.

[0092] FIG. 13 shows DSC plots of Samples 30-32. DSC measurements were taken at a heating rate of 7 °C/min and a heating rate of 20 °C/min. The normalized enthalpy (J/g), Tpeak, and Tonset were calculated from the DSC plots and are shown in Table 11. The Tpeak, T_g, and Tonset decreased as the amount of catalyst increased across Samples 30-32. Coatings of Samples 30 (labeled “#16”), 31 (labeled “#17”), and 33 (labeled “#15”) are shown in FIG. 14.

Table 11. Properties of Samples 28-34.

[0093] While particular uses of the technology have been illustrated and discussed above, the disclosed technology can be used with a variety of environments in accordance with many examples of the technology. The above discussion is not meant to suggest that the disclosed technology is only suitable for implementation within the environments shown and described above. As should be appreciated, the various aspects described with respect to the figures herein are not intended to limit the technology to the particular aspects described. Accordingly, additional configurations can be used to practice the technology herein and/or some aspects described can be excluded without departing from the methods and systems disclosed herein.

[0094] This disclosure described some aspects of the present technology with reference to the accompanying drawings, in which only some of the possible aspects were shown. Other aspects can, however, be embodied in many different forms and should not be construed as limited to the aspects set forth herein. Rather, these aspects were provided so that this disclosure was thorough and complete and fully conveyed the scope of the possible aspects to those skilled in the art.

[0095] Similarly, where operations of a process are disclosed, those operations are described for purposes of illustrating the present technology and are not intended to limit the disclosure to a particular sequence of operations. For example, the operations can be performed in differing order, two or more operations can be performed concurrently, additional operations can be performed, and disclosed operations can be excluded without departing from the present disclosure. Further, each operation can be accomplished via one or more sub-operations. The disclosed processes can be repeated.

[0096] Although specific aspects were described herein, the scope of the technology is not limited to those specific aspects. One skilled in the art will recognize other aspects or improvements that are within the scope of the present technology. Therefore, the specific structure, acts, or operations are disclosed only as illustrative aspects. The scope of the technology is defined by the following claims and any equivalents therein. Examples of the disclosure may be described according to the following aspects.

[0097] Aspect 1. A powder coating composition, comprising: an epoxy resin component; a crosslinker; and a catalyst, wherein the crosslinker is selected from the group consisting of a phenolic crosslinker and an amine crosslinker, wherein the phenolic crosslinker has a melting temperature of about 110 °C or less, wherein the amine crosslinker has a melting temperature of about 120 °C or less, and wherein the composition is capable of being cured a temperature of about 125 °C or less in a time period of about 10 minutes or less.

[0098] Aspect 2. The composition of aspect 1, wherein the epoxy resin component comprises an epoxy resin having an epoxy equivalent weight (EEW) molecular weight of less than about 800 g/eq.

[0099] Aspect 3. The composition of any of aspects 1-2, wherein the epoxy resin component is present in an amount of about 30 wt% to about 80 wt%, based on a total weight of the composition.

[00100] Aspect 4. The composition of any of aspects 1-3, wherein the catalyst comprises an amine adduct.

[00101] Aspect 5. The composition of any of aspects 1-4, wherein the catalyst is present in an amount of about 1 wt% to about 5 wt%, based on a total weight of the epoxy resin component and the crosslinker.

[00102] Aspect 6. The composition of any of aspects 1-5, wherein the crosslinker is a phenolic crosslinker and has a Ph-OH equivalent weight (EW) of less than about 600 g/eq.

[00103] Aspect 7. The composition of any of aspects 1-6, wherein the crosslinker is a phenolic crosslinker is present in an amount of about 1 wt% to about 30 wt%, based on a total weight of the composition. [00104] Aspect 8. The composition of any of aspects 1-5, wherein the crosslinker is an amine crosslinker and has a NH equivalent weight (EW) of less than about 100 g/eq.

[00105] Aspect 9. The composition of any of aspects 1-6, wherein the crosslinker is an amine crosslinker is present in an amount of about 1 wt% to about 10 wt%, based on a total weight of the composition.

[00106] Aspect 10. The composition of any of aspects 1-9, wherein the composition comprises a weight ratio of epoxy resin component to crosslinker of about 20: 1 to about 3: 1.

[00107] Aspect 11. The composition of any of aspects 1-10, wherein the composition has a glass transition temperature (T_g) of less than about 115 °C, a Tpeak of greater than about 125 °C, and a Tonset of about 50 °C to 120 °C.

[00108] Aspect 12. The composition of any of aspects 1-11, wherein the composition has greater than about 90% cure at a temperature of about 125 °C or less in a time period of about 10 minutes or less.

[00109] Aspect 13. A powder coating composition, comprising: a resin component; and a catalyst, wherein the resin component comprises an epoxy resin and optionally a carboxylated polyester resin, wherein the catalyst comprises an anionic tertiary amine catalyst and a cationic onium salt, wherein the catalyst does not comprise an amine adduct, wherein the composition does not comprise a crosslinker, and wherein the composition is capable of being cured a temperature of about 130 °C to about 150 °C in a time period of about 10 minutes or less.

[00110] Aspect 14. The composition of aspect 13, wherein a weight ratio of the anionic tertiary amine catalyst to the cationic onium salt catalyst is about 10:1 to about 2:1.

[00111] Aspect 15. The composition of any of aspects 13-14, wherein the catalyst is present in an amount of about 1 wt% to about 5 wt%, based on a total weight of the resin component.

[00112] Aspect 16. The composition of any one of aspects 13-15, wherein the resin component comprises an epoxy resin and a carboxylated polyester resin in a weight ratio of epoxy resin to carboxylated polyester resin of about 1 : 1 to about 2: 1.

[00113] Aspect 17. The composition of any one of aspects 13-16, wherein the epoxy resin has an epoxy equivalent weight (EEW) molecular weight of less than about 800 g/eq.

[00114] Aspect 18. A method of coating a substrate, comprising: applying the composition of any one of aspects 1-17 to a surface of the substrate; and curing the composition to form a coated substrate. [00115] Aspect 19. The method of aspect 18, wherein the substrate is made of at least one material selected from the group consisting of particleboard, medium density fiberboard (MDF), wood, plastic, metal, and metal alloys.

[00116] Aspect 20. A coated substrate made by the method of any one of aspects 18-19.

Claims

What is claimed is:

1. A powder coating composition, comprising: an epoxy resin component; a crosslinker; and a catalyst, wherein the crosslinker is selected from the group consisting of a phenolic crosslinker and an amine crosslinker, wherein the phenolic crosslinker has a melting temperature of about 110 °C or less, wherein the amine crosslinker has a melting temperature of about 120 °C or less, and wherein the composition is capable of being cured a temperature of about 125 °C or less in a time period of about 10 minutes or less.

2. The composition of claim 1, wherein the epoxy resin component comprises an epoxy resin having an epoxy equivalent weight (EEW) molecular weight of less than about 800 g/eq.

3. The composition of any of claims 1-2, wherein the epoxy resin component is present in an amount of about 30 wt% to about 80 wt%, based on a total weight of the composition.

4. The composition of any of claims 1-3, wherein the catalyst comprises an amine adduct.

5. The composition of any of claims 1 -4, wherein the catalyst is present in an amount of about 1 wt% to about 5 wt%, based on a total weight of the epoxy resin component and the crosslinker.

6. The composition of any of claims 1-5, wherein the crosslinker is a phenolic crosslinker and has a Ph-OH equivalent weight (EW) of less than about 600 g/eq.

7. The composition of any of claims 1-6, wherein the crosslinker is a phenolic crosslinker is present in an amount of about 1 wt% to about 30 wt%, based on a total weight of the composition.

8. The composition of any of claims 1-5, wherein the crosslinker is an amine crosslinker and has a NH equivalent weight (EW) of less than about 100 g/eq.

9. The composition of any of claims 1-6, wherein the crosslinker is an amine crosslinker is present in an amount of about 1 wt% to about 10 wt%, based on a total weight of the composition.

10. The composition of any of claims 1-9, wherein the composition comprises a weight ratio of epoxy resin component to crosslinker of about 20: 1 to about 3: 1.

11. The composition of any of claims 1-10, wherein the composition has a glass transition temperature (T_g) of less than about 115 °C, a T_peak of greater than about 125 °C, and a Tonset of about 50 °C to 120 °C.

12. The composition of any of claims 1-11, wherein the composition has greater than about 90% cure at a temperature of about 125 °C or less in a time period of about 10 minutes or less.

13. A powder coating composition, comprising: a resin component; and a catalyst, wherein the resin component comprises an epoxy resin and optionally a carboxylated polyester resin, wherein the catalyst comprises an anionic tertiary amine catalyst and a cationic onium salt, wherein the catalyst does not comprise an amine adduct, wherein the composition does not comprise a crosslinker, and wherein the composition is capable of being cured a temperature of about 130 °C to about 150 °C in a time period of about 10 minutes or less.

14. The composition of claim 13, wherein a weight ratio of the anionic tertiary amine catalyst to the cationic onium salt catalyst is about 10: 1 to about 2: 1.

15. The composition of any of claims 13-14, wherein the catalyst is present in an amount of about 1 wt% to about 5 wt%, based on a total weight of the resin component.

16. The composition of any one of claims 13-15, wherein the resin component comprises an epoxy resin and a carboxylated polyester resin in a weight ratio of epoxy resin to carboxylated polyester resin of about 1 : 1 to about 2: 1.

17. The composition of any one of claims 13-16, wherein the epoxy resin has an epoxy equivalent weight (EEW) molecular weight of less than about 800 g/eq.

18. A method of coating a substrate, comprising: applying the composition of any one of claims 1-17 to a surface of the substrate; and curing the composition to form a coated substrate.

19. The method of claim 18, wherein the substrate is made of at least one material selected from the group consisting of particleboard, medium density fiberboard (MDF), wood, plastic, metal, and metal alloys.

20. A coated substrate made by the method of any one of claims 18-19.