WO2024026334A1

WO2024026334A1 - Thermosetting powder coating compositions

Info

Publication number: WO2024026334A1
Application number: PCT/US2023/070991
Authority: WO
Inventors: John Thorton Maddox; Geoffrey Richard WEBSTER; Stacey James Marsh; Sunil Vilas KULKARNI; Soma Mukherjee; Thauming Kuo
Original assignee: Eastman Chemical Co
Current assignee: Eastman Chemical Co
Priority date: 2022-07-27
Filing date: 2023-07-26
Publication date: 2024-02-01
Anticipated expiration: 2025-01-27
Also published as: EP4562082A1; CN119604569A

Abstract

The invention provides polyester-based powder coating compositions useful in the coating of shaped or formed articles, which exhibit improved properties such as weathering performance and flexibility. In general, the polyesters are comprised of residues of 2,2,4,4-tetramethyl-1,3-cyclobutanedio; a diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6-hexanediol, 1,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof; residues of trimethylolpropane; and residues of hexahydrophthalic anhydride. The polyester component of the compositions is formulated as predominantly carboxyl-functional and have an acid number of about 20 to 90 mg KOH/g of resin, and thus are suitably cross-linked in a thermosetting powder coating composition system with cross-linking compounds known to react with such carboxyl groups.

Description

THERMOSETTING POWDER COATING COMPOSITIONS

Field of the Invention

[0001] The invention relates to powder coating compositions comprising carboxyl- functional polyesters. The polyesters are comprised of 2,2,4,4-tetramethyl-l,3- cyclobutanediol and trimethylolpropane.

Background of the Invention

[0002] There have been increasing demands for powder coatings in the industry due to their good corrosion protection and outdoor durability. Various types of resin technologies are used for powder coatings. These include epoxy, polyester, acrylic, and the hybrids thereof. For outdoor applications, polyester, fluoropolymer, and acrylic resins are commonly used. Polyesters generally provide a good balance of desirable coating properties such as appearance and impact resistance, while acrylic resin and fluoropolymer typically exhibit better weatherability. Thus, it would be highly desirable to develop a polyester-based powder coating composition having good weatherability while also possessing a glass transition temperature (T_g) suitable for powder coating systems.

Summary of the Invention

[0003] In summary, the invention provides polyester-based powder coating compositions useful in the coating of shaped or formed articles, which exhibit improved properties such as weathering performance and flexibility. In one or more embodiments herein, the powder coating composition comprises: A. at least one carboxyl-functional polyester which comprises:!, a polyol component comprising: i. about 50 to about 87 mole percent of 2,2,4,4-tetramethyl-l,3-cyclobutanediol residues, based on the total moles of i., ii., iii. and iv.; ii. about 5 to about 35 mole percent of a diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6-hexanediol, 1,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 8 to about 25 mole percent of trimethylolpropane residues, based on the total moles of i., ii., iii. and iv.; a dicarboxylic acid component comprising: v. about 70 to about 100 mole percent of hexahydrophthalic anhydride residues, based on the total moles of v. and vi.; and vi. 0 to about 30 mole percent of a C6-C12 acyclic diacid residues, based on the total moles of v. and vi.; wherein the polyester has a glass transition temperature of about 45° to 90°C, an acid number of about 20 to about 90 mg KOH/g, a number average molecular weight of about 1,000 to about 10,000 g/mole, and a weight average molecular weight of about 5,000 to about 100,000 g/mole; and B. one or more compounds reactive with the carboxyl-functional polyester.

[0004] In further embodiments herein, the powder coating composition comprises: A. at least one carboxyl-functional polyester, in an amount of about 70 to 95 weight percent, based on the total weight of A. B. and C., which comprises: 1. a polyol component comprising: i. about 60 to about 80 mole percent of 2,2,4,4-tetramethyl-l,3- cyclobutanediol residues, based on the total moles of i., ii., iii. and iv.; ii. 8 to about 28 mole percent of diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6-hexanediol, 1 ,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 12 to about 17 mole percent of trimethylolpropane residues, based on the total moles of i., ii., iii., and iv.; 2. a dicarboxylic acid component comprising: v. about 75 to about 95 mole percent of hexahydrophthalic anhydride residues, based on the total moles of v. and vi.; and vi. about 5 to about 25 mole percent of a C6-C12 acyclic diacid residues, based on the total moles of v. and vi.; wherein the polyester has a glass transition temperature of about 45° to 90°C, an acid number of about 40 to about 60 mg KOH/g, a number average molecular weight of about 1,000 to about 10,000 g/mole, and a weight average molecular weight of about 5,000 to a about 100,000 g/mole; B. a glycidyl functional crosslinker in an amount of about 5 to about 30 weight percent, based on the total weight of A., B., and C.; and C. a P-hydroxy alkyl amide cross-linker in an amount of about 0 to about 5 weight percent, based on the total weight of A., B., and C.

[0005] In even further embodiments herein the powder composition comprises: A. at least one carboxyl-functional polyester, in an amount of about 80 to 90 weight percent, based on the total weight of A. and B., which comprises: 1. a polyol component comprising: i. about 60 to about 80 mole percent of 2,2,4,4-tetramethyl-l,3- cyclobutanediol residues, based on the total moles of i., ii., iii. and iv.; ii. 8 to about 28 mole percent of diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6-hexanediol, 1 ,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 12 to about 17 mole percent of trimethylolpropane residues, based on the total moles of i., ii., iii., and iv.; 2. a dicarboxylic acid component comprising: v. about 80 to about 100 mole percent of hexahydrophthalic anhydride residues, based on the total moles of v. and vi.; and vi. 0 to about 20 mole percent of a C6-C12 acyclic diacid residues, based on the total moles of v. and vi.; wherein the polyester has a glass transition temperature of about 45° to 90°C, an acid number of about 30 to about 80 mg KOH/g, a number average molecular weight of about 1,000 to about 10,000 g/rnole, and a weight average molecular weight of about 5,000 to a about 100,000 g/mole; and B. a P-hydroxy alkyl amide cross-linker in an amount of about 10 to about 20 weight percent, based on the total weight of A. and B.

Detailed Description

[0006] In a first aspect, the invention provides a powder coating composition comprising: A. at least one carboxyl-functional polyester which comprises:!, a polyol component comprising: i. about 50 to about 87 mole percent of 2,2,4,4-tetramethyl-l,3- cyclobutanediol residues, based on the total moles of i., ii., iii. and iv.; ii. about 5 to about 35 mole percent of a diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6-hexanediol, 1 ,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 8 to about 25 mole percent of trimethylolpropane residues, based on the total moles of i., ii., iii. and iv. ; a dicarboxylic acid component comprising: v. about 70 to about 100 mole percent of hexahydrophthalic anhydride residues, based on the total moles of v. and vi.; and vi. 0 to about 30 mole percent of a C6-C12 acyclic diacid residues, based on the total moles of v. and vi.; wherein the polyester has a glass transition temperature of about 45° to 90°C, an acid number of about 20 to about 90 mg KOH/g, a number average molecular weight of about 1,000 to about 10,000 g/mole, and a weight average molecular weight of about 5,000 to about 100,000 g/mole; and B. one or more compounds reactive with the carboxyl-functional polyester.

[0005] It should be understood that the following is not intended to be an exclusive list of defined terms. Other definitions may be provided in the description, such as, for example, when accompanying the use of a defined term in context. As used herein, the terms “a,” “an,” and “the” mean one or more. As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone; B alone; C alone; A and B in combination; A and C in combination, B and C in combination; or A, B, and C in combination.

[0006] The term "polyester", as used herein, is intended to include "copolyesters" and is understood to mean a synthetic polymer prepared by the reaction of one or more difunctional carboxylic acids and/or multifunctional carboxylic acids with one or more difunctional hydroxyl compounds and/or multifunctional hydroxyl compounds, as referred to above as comprised of a dicarboxylic acid component and a polyol component. Typically, the difunctional carboxylic acid can be a dicarboxylic acid and the difunctional hydroxyl compound can be a dihydric alcohol, for example, glycols and diols. The term "polyol " as used herein includes, but is not limited to, diols, glycols, and/or multifunctional hydroxyl compounds. The term "residue", as used herein, means any organic structure incorporated into a polymer through a polycondensation and/or an esterification reaction from the corresponding monomer. The term "repeating unit", as used herein, means an organic structure having a dicarboxylic acid residue and a diol residue bonded through an ester group. Thus, for example, the dicarboxylic acid residues may be derived from a dicarboxylic acid monomer or its associated acid halides, esters, salts, anhydrides, and/or mixtures thereof. Furthermore, as used herein, the term "diacid" includes multifunctional acids. As used herein, therefore, the term "dicarboxylic acid" is intended to include dicarboxylic acids and any derivative of a dicarboxylic acid, including its associated acid halides, esters, half-esters, salts, halfsalts, anhydrides, mixed anhydrides, and/or mixtures thereof, useful in a reaction process with a diol to make a polyester.

[0007] The stoichiometry of the polyol components and dicarboxylic acid components can be adjusted as needed to obtain the desired acid number (and/or hydroxyl number) in the final carboxyl-functional polyester to be utilized in the powder coating composition.

[0008] The polyester portion of the compositions of the invention can be made by processes known in the art, for example, by processes in homogenous solution, by transesterification processes in the melt, and by two phase interfacial processes. Suitable methods include, but are not limited to, the steps of reacting one or more dicarboxylic acids with one or more diols at a temperature of 100°C to 315°C at a pressure of 0.1 to 760 mm Hg for a time sufficient to form a polyester. See U.S. Pat. No. 3,772,405 for methods of producing polyesters, the disclosure regarding such methods is hereby incorporated herein by reference.

[0009] In one embodiment, the carboxyl-functional polyester is comprised of all aliphatic groups or is comprised of substantially no aromatic groups. In another embodiment, the carboxyl-functional polyester comprises not more than about 10 mole percent aromatic diacid residues, such as isophthalic acid and terephthalic acid, based on the total moles of the dicarboxylic acid components.

[0010] In another embodiment, the polyol component comprises about 55 to 85 mole percent of 2,2,4,4-tetramethyl-l,3-cyclobutanediol residues, based on the total moles of

1., ii., iii. and iv.; ii. about 5 to about 30 mole percent of a diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6-hexanediol, 1,4- butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 10 to about 20 mole percent of trimethylolpropane residues, based on the total moles of i.,

11., iii. and iv.; and wherein the dicarboxylic acid component comprises about 75 to about 100 mole percent of hexahydrophthalic anhydride residues; and 0 to about 25 mole percent of a C6-C12 acyclic diacid residues.

[0011] In another embodiment, the polyol component comprises about 60 to 80 mole percent of 2,2,4,4-tetramethyl-l ,3 -cyclobutanediol residues, based on the total moles of

1., ii., iii. and iv.; ii. about 8 to about 28 mole percent of a diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6-hexanediol, 1,4- butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 12 to about 17 mole percent of trimeth ylolpropane residues, based on the total moles of i.,

11., iii. and iv.; and wherein the dicarboxylic acid component comprises about 80 to about 100 mole percent of hexahydrophthalic anhydride residues; and 0 to about 20 mole percent of a C6-C12 acyclic diacid residues.

[0012] Examples of diol residues which is other than (i) and (ii) may include 2-butyl- 2-ethyl-l,3-propanediol (BEPD), ethylene glycol, propylene glycol, 2-methyl-l,3- propanediol (MPDiol), and mixtures thereof. In one embodiment, the diol residues which is other than (i) and (ii) is selected from the group consisting of 2-methyl-l,3- propanediol and 2-butyl-2-ethyl-l,3-propanediol.

[0013] In embodiments herein, the acyclic diacid is a C6-C12 diacid. Exemplary C6- C12 acyclic diacids include adipic acid, sebacic acid, and dodecanedicarboxylic acid. In some embodiments, the C6-C12 acyclic diacid is adipic acid.

[0014] As noted above, the carboxyl-functional polyester has an acid number of about 20 to 90 mg KOH/g resin. In certain embodiments, the polyester has an acid number of about 30 to 80, 35 to 70, or 40 to 60 mg KOH/g.

[0015] In certain embodiments, the carboxyl-functional polyester has a hydroxyl number of 0 to 20, 0 to 15, 0 to 10, or 0 to 5 mg KOH/g resin.

[0016] As noted above, the carboxyl-functional polyesters have a glass transition temperature of about 45° to 90°C. In certain embodiments, the polyester has a T_g of about 50° to about 80°C, or about 55° to about 75°C. [0017] As noted above, the carboxyl-functional polyester will have a number average molecular weight of about 1,000 to about 10,000 g/mole. In certain embodiments, the carboxyl-functional polyester will have a number average molecular weight of about 1,000 to about 9,000, about 1,500 to about 8,000, or about 1,500 to about 6,000 g/mole. As noted above, the carboxyl-functional polyester will have a weight average molecular weight of about 5,000 to about 100,000. In certain embodiments, the carboxyl- functional polyester will have a weight average molecular weight of about 5,000 to about 80,000 or about 5,000 to about 50,000 g/mole.

[0018] In certain embodiments, the compounds reactive with the carboxyl-functional polyester is a cross-linker chosen from P-hydroxyalkylamides and glycidyl -functional compounds. In certain embodiments, the P-hydroxyalkylamide is chosen from bis(N,N'-dihydroxyethyl)adipamide, bis(N,N'-dihydroxypropyl)adipamide, or a mixture thereof. Commercially-available P-hydroxyalkylamides include bis(N,N'- dihydroxyethyl)adipamide (Primid® XL-552), bis(N,N'-dihydroxypropyl)adipamide (Primid® QM-1260), and Primid® SF-4510 available from EMS-GRILTECH. Also commercially available is Megamid XL from MEGARA RESINS-ANASTASIOS FANIS S.A.

[0019] Commercially-available glycidyl functional curing agents include triglycidyl isocyanurate based crosslinkers available from Huntsman as Araldite PT 810, PT910, and PT 912. Also suitable are glycidyl acrylates and glycidyl methacrylates such as those commercially available as GMA 300G, 400G and 500 from Estron Chemical.

[0020] In other embodiments, the compound reactive with the carboxyl-functional polyester is an epoxy resin. Exemplary epoxy resins include those having a molecular weight of about 300 to about 4000, and have approximately 0.05 to about 0.99 epoxy groups per 100 grams of resin (i.e., 100-2000 weight per epoxy (WPE)). Such resins are widely known and commercially available under the EPON® mark (Hexion), ant the Araldite® mark (Huntsman).

[0021] In the coating compositions of the invention, in certain embodiments the polyester is present in an amount of about 70 to about 97 percent, by weight, and either: (a) the one or more compounds reactive with the carboxyl-functional polyester or (b) the cross-linker, is present in an amount of about 3 to about 30 percent, by weight, based on the total amount of polyester and the one or more compounds or cross-linker. In another embodiment, the coating composition of the present invention the carboxyl- functional polyester is present in an amount of about 70 to 95, 75 to 95, or 80 to 90 weight percent and either: (a) the one or more compounds reactive with the carboxyl- functional polyester or (b) the cross-linker, is present in an amount of about 5 to 30, 5 to 25, or 10 to 20 weight percent, based on the total amount of polyester and the one or more compounds or cross-linker.

[0022] In another aspect, the invention provides a powder coating composition comprising: A. at least one carboxyl-functional polyester, in an amount of about 80 to 90 weight percent, based on the total weight of A. and B., which comprises: 1. a polyol component comprising: i. about 60 to about 80 mole percent of 2,2,4,4-tetramethyl-l,3- cyclobutanediol residues, based on the total moles of i., ii., iii. and iv.; ii. 8 to about 28 mole percent of diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6-hexanediol, 1 ,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 12 to about 17 mole percent of trimethylolpropane residues, based on the total moles of i., ii., iii., and iv.; 2. a dicarboxylic acid component comprising: v. about 80 to about 100 mole percent of hexahydrophthalic anhydride residues, based on the total moles of v. and vi.; and vi. 0 to about 20 mole percent of a C6-C12 acyclic diacid residues, based on the total moles of v. and vi.; wherein the polyester has a glass transition temperature of about 45° to 90°C, an acid number of about 30 to about 80 mg KOH/g, a number average molecular weight of about 1,000 to about 10,000 g/mole, and a weight average molecular weight of about 5,000 to a about 100,000 g/mole; and B. a P-hydroxyalkylamide cross-linker in an amount of about 10 to about 20 weight percent, based on the total weight of A. and B.

[0023] In certain embodiments, the P-hydroxyalkylamide cross-linker will be present in an amount of about 3 to about 20 weight percent, based on the total weight of A. and B. [0024] In certain embodiments, the carboxyl-functional polyester of the invention comprises an acyclic diacid to further improve the flexibility in order to meet the need of certain applications such as, for example, automotive wheel powder coating, that require higher flexibility.

[0025] Thus, this invention further provides a powder coating composition comprising: A. at least one carboxyl-functional polyester, in an amount of about 70 to 95 weight percent, based on the total weight of A. B. and C., which comprises: 1. a polyol component comprising: i. about 60 to about 80 mole percent of 2,2,4,4-tetramethyl-l,3- cyclobutanediol residues, based on the total moles of i., ii., iii. and iv.; ii. 8 to about 28 mole percent of diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6-hexanediol, 1 ,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 12 to about 17 mole percent of trimethylolpropane residues, based on the total moles of i., ii., iii., and iv.; 2. a dicarboxylic acid component comprising: v. about 75 to about 95 mole percent of hexahydrophthalic anhydride residues, based on the total moles of v. and vi.; and vi. about 5 to about 25 mole percent of a C6-C12 acyclic diacid residues, based on the total moles of v. and vi.; wherein the polyester has a glass transition temperature of about 45° to 90°C, an acid number of about 40 to about 60 mg KOH/g, a number average molecular weight of about 1,000 to about 10,000 g/mole, and a weight average molecular weight of about 5,000 to a about 100,000 g/mole; B. a glycidyl functional crosslinker in an amount of about 5 to about 30 weight percent, based on the total weight of A., B., and C.; and C. a P-hydroxyalkylamide cross-linker in an amount of about 0 to about 5 weight percent, based on the total weight of A., B., and C

[0026] Examples of said acyclic diacid include C6 to C12 linear diacid such as adipic acid, sebacic acid, and dodecanedicarboxylic acid.

[0027] In other embodiments, the powder coating compositions of the invention may further comprise waxes, pigments, fillers, degassing agents, flow agents, and/or other additives. Examples of pigments include inorganic and organic pigments such as titanium dioxide, iron oxide, chromium oxide, zinc sulfide, zinc phosphate, mica, azo compounds, and the like. Suitable fillers include silicates, sulfates, and carbonates. Examples of additives include degassing agents, antioxidants, and UV stabilizers. Exemplary weathering stabilizers that can be used in these embodiments include are hindered amine light stabilizers and UV absorbers. Examples of degassing agents include cyclohexane dimethanol dibenzoate, benzoin, and benzoin derivatives. Examples of flow control agents include Byk® 361 N (BYK) and Resiflow® PV-5 (Estron). Further examples of typical additives for powder coating compositions can be found in U.S. Patent No. 10,916,539, incorporated herein by reference.

[0028] The powder coating compositions of the invention may be prepared by any methods known in the art. In a typical method, the powders of the carboxyl-functional polyester and the crosslinker are mixed along with any desired additives at room temperature to obtain a premix. The premix is then extruded at an elevated temperature such as, for example, 80° to 130°, 90° to 125°, or 100° to 120 °C, to yield an extrudate, which is then cooled to solidify the mixture. The resulting solid is then made into powder by milling and subsequently sieved to classify the size of the particles. The powder coating of the present invention desirably has particle sizes less than about 120 pm, less than 110 pm, or less than 100 pm.

[0029] The powder coating composition may be applied to an article, such as, a substrate by a common method such as electrostatic spray deposition (ESD) or fluidized bed application at a thickness of about 1 to about 10 mils (1 mil - 25 pm). The coating may be cured at 140° to 230°C, 140° to 200°C, 140° to 180°C, or 140° to 160°C for 10 minutes to one hour, or other suitable conditions, and allowed to cool.

[0030] See also: User’s Guide to Powder Coating, 4^th Ed., Nicholas Liberto, editor, Society of Manufacturing Engineers (2003).

[0031] As noted above, the powder coating compositions of the invention can be applied to a substrate or shaped or formed article. Thus, a further aspect of the present invention is a shaped or formed article, of which at least a portion has been coated with the coating compositions of the present invention. The substrate can be any common substrate such as aluminum, tin, steel or galvanized sheeting, and the like. The coating composition can be coated onto a substrate using techniques known in the art, for example, by electrostatic spray deposition (ESD) or fluidized bed application at a thickness of about 1 to about 10 mils (1 mil = 25 pm). The coating can be cured at a temperature of about 140°C to about 230°C for a time period that ranges from about 10 minutes to about 60 minutes and allowed to cool.

[0032] One mechanical property of the cured (i.e., thermoset) powder coating compositions of the invention can be described by Erichsen cupping test in accordance with ISO-1520. In some embodiments, the cured powder coating compositions of the invention exhibit an Erichsen cupping test rating of 3 mm or more, 3.5 mm or more, 4mm or more, 4.25 mm or more, or 5 mm or more for the onset of cracking, and with no delamination of > 7mm.

[0033] Thus, in certain embodiments, the cured coating compositions on such articles exhibit improved performance characteristics. For example, articles coated with the cured compositions of the invention can exhibit an Erichsen crack rating of 3 mm or more according to the method of ISO-1520.

[0034] The invention can be further illustrated by the following Examples of certain embodiments thereof, although it will be understood that these Examples are included merely for the purposes of illustration and are not intended to limit the scope of the invention unless otherwise specifically indicated.

Examples

[0035] In these Examples, the following abbreviations are used:

TMCD - 2,2,4,4-tetramethyl-l,3-cyclobutanediol - from Eastman Chemical Co.

TMP- trimethylol propane - available from Sigma-Aldrich

NPG= 2,2-dimethyl-l,3-propanediol (neopentyl glycol) - available from Sigma- Aldrich

CHDM - 1 ,4-cyclohexanedimethanol from Eastman Chemical Co.

MP Diol ~ 2-methyl-l,3-propanediol from Eastman Chemical Co.

BEPD = 2-butyl-2-ethyl-l,3-propanediol available from Sigma- Aldrich

HPHP ~ hydroxypivalyl hydroxypivalate from Eastman Chemical Co.

HHPA - hexahydrophthalic anhydride - available from Sigma- Aldrich DDDA - Dodecanedioic acid available from Sigma- Aldrich

Adipic = adipic acid available from Sigma- Aldrich

Succinic = succinic acid available from Sigma-Aldrich

TPP = triphenylphosphite - available from Sigma- Aldrich

Butyl stannoic acid available from Sigma-Aldrich

Al AQT 36 = Aluminum test panel available from Q-Panel Inc.

CRS B1000 - Steel test panel available from ACT Inc.

P EPQ = Hostanox® P-EPQ® powder (Qari ant)

Primid® XL 552 - hydroxyl alkyl amide crosslinker available from Estron Inc.

GMA 300 - glycidyl functional acrylate crosslinker available from Estron Inc.

GMA 500 - glycidyl functional acrylate crosslinker available from Estron Inc.

Resiflow® PL-200 - flow and wetting additive available from Estron Inc.

Benzoin - degassing agent available from Estron Inc.

Irganox® 1076 - an antioxidant available from BASF

Staphyloid AC 4030 - A plasticizer available from Danick Specialties and Support.

Tinuvin® 405 is a UV absorber from BASF

Tinuvin® 144 is a hindered amine light stabilizer from BASF

Example 1. Synthesis of Carboxyl-Functional Polyester Resin (Resin 1)

[0036] The resin was prepared in a two-liter reaction kettle equipped with a heating mantle, mechanical stirrer, thermocouple, nitrogen blanket (1.0 standard cubic feet per hour), oil-heated partial condenser (103 °C - 105°C), condensate trap, and water-cooled total condenser (15°C). The condensate trap, kettle top and adapter from the kettle to the column were wrapped in aluminum foil and fiberglass tape to facilitate water removal. [0037] 786.7 grams HHPA, 186.4 grams adipic acid, 586.4 grams TMCD and 1.7 grams TPP were charged to the reactor. The reactor was then heated from room temperature to 100°C at l°C/minute to obtain a homogeneous melt. Agitation was then started at 300 rpm and the temperature was increased to 165°C at l°C/minute. An exotherm was observed from 140°C to 180°C. After the exotherm, acid number was taken to ensure complete reaction of the TMCD, and the reactor was allowed to cool to 150°C.

[0038] At 150°C and under agitation, 84.7 grams NPG, 72 grams TMP and 1.7 grams butylstannoic acid were added. The temperature was then set to 165 °C. Once the temperature stabilized at 165°C, the temperature was increased to 235°C at 0.1°C/min.

The reaction is held at 235°C until the target acid number, 55 mg KOH/g, was reached.

Example 2. Synthesized Carboxyl-Functional Polyester Resins (Resins 1 to 8)

[0039] Using the same method as Example 1, Resins 1 to 8 were synthesized according to the mole ratios of the components listed in Table 1 and the weights of the components charged as listed in Table 2.

[0040] Table 1. List of Synthesized Polyester Resin Compositions in Mole Ratios

[0041] Table 2. List of Synthesized Polyester Resin Compositions (Weight Charged)

Comparative Example 1. Synthesized Comparative Carboxyl-Functional Polyester Resins (Comparative Resins Cl to C8)

[0042] Using the same method as Example 1, Comparative Resins Cl to C8 were synthesized according to the mole ratios of the components listed in T able 3 and the weights of the components charged as listed in Table 4.

[0043] Table 3. List of Synthesized Comparative Polyester Resin Compositions in Mole Ratios

[0044] Table 4. List of Synthesized Comparative Polyester Resin Compositions

(Weight Charged)

Example 3. Resin Properties of Synthesized Polyester Resins [0045] Glass transition temperature (T_g) was determined using a Q2000 differential scanning calorimeter (DSC) from TA Instruments, New Castle, DE, US, at a scan rate of 20°C/min. Number average molecular weight (M_n) and weight average molecular weight (M_w) were measured by gel permeation chromatography (GPC) using polystyrene equivalent molecular weight. Acid number was measured by using a procedure based on ASTM D7253-1 entitled “Standard Test Method for Polyurethane

Raw Materials: Determination of Acidity as Acid Number for Polyether Polyols,” and hydroxyl number was measured using a procedure based on ASTM E222-1 entitled “Standard Test Methods for Hydroxyl Groups Using Acetic Anhydride.” Viscosity was measured using a CAP 2000 viscometer at 200°C. [0046] Table 5. Resin Properties of Synthesized Polyester Resins 1 to 8

Comparative Example 2. Resin Properties of Synthesized Comparative Polyester

Resins

[0047] Table 6. Resin Properties of Synthesized Comparative Polyester Resins Cl to

C8

Example 4. Preparation of Powder Coating Compositions Pl to P8

[0048] Powder coating compositions (P1 to P8) were prepared respectively by using Resins 1 to 8. Each coating composition was weighed into a container. The compositions were then milled using a Vitamix mill. The resulting milled compositions were extruded on a two-zone twin screw extruder at 320 RPM and 60-70% torque. Zone 1 was heated to 100°C while Zone 2 was at 110°C. The compositions were cooled on a twin roll chiller at 2-5 °C and collected in a plastic bag. The compositions were allowed to fully cool to room temperature overnight. They were then powdered using a Strand mill. The resulting powder compositions were sieved using 106-micron mesh. The sieved powder coating compositions were then considered ready to spray. The compositions are listed in Table 7.

[0049] Table 7. List of Powder Coating Compositions Pl to P8 (in grams)

Comparative Example 3. Preparation of Comparative Powder Coating Compositions CPI to CP8

[0050] Coating formulations were prepared according to the method described in Example 4 by using comparative resins Cl to C8. Their compositions are listed in Table 8.

[0051] Table 8. List of Comparative Powder Coating Compositions CPI to CPS (in grams)

Example 5. Coating Preparation and Testing

[0052] Powder coating compositions P1 to P8 prepared using the procedure from Example 4 were applied to the metal substrate using a Parker Ionics GX700C Powder Gun System electrostatic powder spray apparatus. The composition was applied to AQT-36 aluminum panels purchased from Q-Panel Inc and on Bl 000 pretreated cold rolled steel purchased from ACT inc. The compositions were cured in an oven at 200C for 25 minutes (5 minutes ramp to temp, 20 minutes at metal temperature). The resulting film thickness of the coating was targeted to be between 45-75 microns. The actual range was wider.

Testing

[0053] Coating composition flexibility was tested using an Erichsen indenter following ISO 1520:2006E. Coating thickness was determined using a Fischer Permascope calibrated on ACT B1000. Film build was targeted to be between 50-75 microns. Before Erichson cupping is run, the cured panels are equilibrated at room temperature for 24 hrs.

[0054] The painted panel is placed in the Erichson indenter with the coating facing away from the indenter ball and secured by the retainer ring. The indenter ball is driven into the panel at a rate of 0.1 -0.3 mm/s. The onset of visual cracking is measured in mm of indention.

[0055] The chart below shows the onset of cracking for the coatings:

[0056] Table 9. Erichsen Cupping Results of the Inventive Powder Coatings

[0057] Comparative Example 4. Comparative Coating Preparation and Testing

[0058] Comparative Coatings were prepared by using powder coating compositions CPI to CP8 prepared using the procedure from Comparative Example 3 and tested according to the method described in Example 5. The results are listed in Table 10.

[0059] Table 10. Erichsen Cupping Results of the Comparative Powder Coatings

Example 6. Synthesis of Additional Carboxyl-Functional Polyester Resins (Resins 9 to 18}

[0060] Using the same method as described in Example 1, Resins 9 to 18 were synthesized according to the mole ratios of the components listed in Table 11. Their resin properties are listed in Table 12. [0061] Table 11. List of Synthesized Polyester Resin Compositions in Mole Ratios

[0062] Table 12. Resin Properties of Resins 9 to 18

[0063] Example 7. Preparation of Powder Coating Compositions P9 to Pl 8

[0064] Powder coating compositions were preprepared according to Example 4 by using Resins 9 to 18. The compositions are listed in Table 13. [0065] Table 13. List of Powder Coating Compositions CP9 to CPI 8 (in grams)

[0066] Example 8. Coating Preparation and Testing

[0067] Coatings were prepared by using powder coating compositions P9 to Pl 8 prepared from Example 7 and tested according to the method of ASTM D522. The results are listed in Table 14. As shown by the data, coatings based on resins 10 to 18, which comprise a linear diacid, adipic acid or dodecanedicarboxylic acid (DDDA), in each resin composition, have superior flexibility over the coating based on resin 9 without linear diacid, as tested by the Conical Mandrel method. This property is particularly desirable for automotive wheel powder coating applications. [0068] Table 14. Powder Coating Test Results According to the Rating from 0 to 5 below:

Example 9. Synthesis of Polyester Resins with Various Monomers (Resins 19 to 25) [0069] Additional polyester resins having various monomers were prepared and evaluated according to the methods described previously. Their compositions in mole ratios are listed in Table 15; their weights charged in grams are listed in Table 16; their resin properties are listed in Table 17; their powder coating compositions are listed in Table 18; and their coating test results are listed in Table 19. [0070] Table 15. List of Polyester Resin Compositions in Mole Ratios (Resins 19 to

2-5)

[0071] Table 16. Lisi of Polyester Resin Compositions (Weight Charged) (Resins 19 to 25)

[0072] Table 17. Resin Properties of Synthesized Polyester Resins 19 to 25

[0073] Table 18. List of Powder Coating Compositions P19 to P25 (in grams)

[0074] Table 19. Erichsen Cupping Results of the Powder Coatings P19 to P25

Comparative Example 5. Synthesis of Polyester Resins with Lower TMP Ratio (Resins C9 to C10)

[0075] Comparative polyester resins having a lower ratio (6 mole %) of the branching agent, TMP, were prepared and evaluated according to the methods described previously. Their compositions in mole ratios are listed in Table 20; their weights charged in grams are listed in Table 21; their resin properties are listed in Table 22; their powder coating compositions are listed in Table 23; and their coating test results are listed in Table 24.

[0076] Table 20. List of Polyester Resin Compositions in Mole Ratios (Resins C9 to CIO)

[0077] Table 21. List of Polyester Resin Compositions (Weight Charged) (Resins C9 to CIO)

[0078] Table 22. Resin Properties of Synthesized Polyester Resins C9 to CIO

[0079] Table 23. List of Powder Coating Compositions CP9 to CP10 (in grams)

[0080] Table 24. Erichsen Cupping Results of the Powder Coatings CP9 to CP 10

Claims

1. A powder coating composition comprising:

A. at least one carboxyl-functional polyester which comprises:

1. a polyol component comprising: i. about 50 to about 87 mole percent of 2,2,4,4-tetramethyl- 1,3-cyclobutanediol residues, based on the total moles of i., ii., iii. and iv.; ii. about 5 to about 35 mole percent of a diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1 ,6-hexanediol, 1 ,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 8 to about 25 mole percent of trimethylolpropane residues, based on the total moles of i., ii., iii. and iv.;

2. a dicarboxylic acid component comprising: v. about 70 to about 100 mole percent of hexahydrophthalic anhydride residues, based on the total moles of v. and vi.; and vi. 0 to about 30 mole percent of a C6-C12 acyclic diacid residues, based on the total moles of v. and vi. ; wherein the polyester has a glass transition temperature of about 45° to 90°C, an acid number of about 20 to about 90 mg KOH/g, a number average molecular weight of about 1,000 to about 10,000 g/mole, and a weight average molecular weight of about 5,000 to about 100,000 g/mole; and

B. one or more compounds reactive with the carboxyl-functional polyester.

2 A powder coating composition comprising: A. at least one carboxyl-functional polyester, in an amount of about 70 to 95 weight percent, based on the total weight of A. B. and C., which comprises:

1 . a polyol component comprising: i. about 60 to about 80 mole percent of 2,2,4,4-tetramethyl- 1,3-cyclobutanediol residues, based on the total moles of i., ii., iii. and iv.; ii. 8 to about 28 mole percent of a diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6- hexanediol, 1,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 12 to about 17 mole percent of trimethylolpropane residues, based on the total moles of i., ii., iii., and iv.;

2. a dicarboxylic acid component comprising: v. about 75 to about 95 mole percent of hexahydrophthalic anhydride residues, based on the total moles of v. and vi.; and vi. about 5 to about 25 mole percent of a C6-C12 acyclic diacid residues, based on the total moles of v. and vi.; wherein the polyester has a glass transition temperature of about 45° to 90°C, an acid number of about 40 to about 60 mg KOH/g, a number average molecular weight of about 1,000 to about 10,000 g/mole, and a weight average molecular weight of about 5,000 to a about 100,000 g/mole;

B. a glycidyl functional crosslinker in an amount of about 5 to about 30 weight percent, based on the total weight of A., B., and C.; and

C. a P-hydroxyalkylamide cross-linker in an amount of about 0 to about 5 weight percent, based on the total weight of A., B., and C. A powder coating composition comprising:

A. at least one carboxyl-functional polyester, in an amount of about 80 to weight percent, based on the total weight of A. and B., which comprises:

1. a polyol component comprising: i. about 60 to about 80 mole percent of 2,2,4, 4-tetramethyl- 1 ,3-cyclobutanediol residues, based on the total moles of i., ii., iii. and iv.; ii. 8 to about 28 mole percent of a diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6- hexanediol, 1,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 12 to about 17 mole percent of trimethylolpropane residues, based on the total moles of i., ii., iii., and iv.;

2. a dicarboxylic acid component comprising: v. about 80 to about 100 mole percent of hexahydrophthalic anhydride residues, based on the total moles of v. and vi. ; and vi. 0 to about 20 mole percent of a C6-C12 acyclic diacid residues, based on the total moles of v. and vi. ; wherein the polyester has a glass transition temperature of about 45° to 90°C, an acid number of about 30 to about 80 mg KOH/g, a number average molecular weight of about 1,000 to about 10,000 g/mole, and a weight average molecular weight of about 5,000 to a about 100,000 g/mole; and

B. a P-hydroxyalkylamide cross-linker in an amount of about 10 to about 20 weight percent, based on the total weight of A. and B.

4. The composition of claim 1, wherein the compounds reactive with the carboxyl- functional polyester is a cross-linker chosen from [3-hydroxyalkylamides and glycidyl- functional compounds.

5. The composition of claim 1, wherein the compound reactive with the carboxyl- functional polyester is an epoxy resin.

6. The composition of claim 1, wherein the compounds reactive with the carboxyl- functional polyester is a cross-linker chosen from P-hydroxyalkylamides, and wherein the P-hydroxyalkylamides is selected from the group consisting of bis(N,N'- dihydroxyethyl)adipamide, bis(N,N'-dihydroxypropyl)adipamide, and a mixture thereof.

7. The composition of claim 1, wherein the polyol component comprises about 55 to 85 mole percent of 2,2,4,4-tetramethyl-l,3-cyclobutanediol residues, based on the total moles of i. , ii. , iii. and iv. ; ii. about 5 to about 30 mole percent of a diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6- hexanediol, 1,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 10 to about 20 mole percent of trimethylolpropane residues, based on the total moles of i., ii., iii. and iv.; and wherein the dicarboxylic acid component comprises about 75 to about 100 mole percent of hexahydrophthalic anhydride residues; and 0 to about 25 mole percent of a C6-C12 acyclic diacid residues.

8. The composition of claim 1 , wherein the polyol component comprises about 60 to 80 mole percent of 2,2,4,4-tetramethyl-l,3-cyclobutanediol residues, based on the total moles of i. , ii. , iii. and iv. ; ii. about 8 to about 28 mole percent of a diol residue selected from the group consisting of neopentyl glycol, cyclohexanedimethanol, 1,6- hexanediol, 1,4-butanediol, hydroxypivalyl hydroxypivalate, and combinations thereof, based on the total moles of i., ii., iii., and iv.; iii. 0 to about 20 mole percent of diol residues which is other than (i) and (ii), based on the total moles of i., ii., iii., and iv.; and iv. about 12 to about 17 mole percent of trimethylolpropane residues, based on the total moles of i., ii., iii. and iv.; and wherein the dicarboxylic acid component comprises about 80 to about 100 mole percent of hexahydrophthalic anhydride residues; and 0 to about 20 mole percent of a C6-C12 acyclic diacid residues.

9. The composition of claims 1-8, wherein the diol residues which are other than (i) and (ii) are selected from the group consisting of 2 -methyl- 1,3-propanediol and 2- butyl-2-ethyl- 1 ,3-propanediol.

10. The composition of claims 1 -9, wherein the C6-C12 acyclic diacid is chosen from dodecanedioic acid, adipic acid, and sebacic acid.

11. The composition of claims 1-10, wherein the C6-C12 acyclic diacid is adipic acid.

12. The composition of claims 1-11, wherein the polyester has an acid number of about 40 to about 60 mg KOH/g.

13. The composition of claims 1-12, wherein the polyester has a glass transition temperature of about 55 to about 75°C.

14. The composition of claims 1-13, wherein the polyester is present in an amount of about 70 to about 97 percent, by weight, and either: (a) the one or more compounds reactive with the carboxyl-functional polyester or (b) the cross-linker, is present in an amount of about 3 to about 30 percent, by weight, based on the total amount of polyester and the one or more compounds or cross-linker.

15. An article coated with the coating composition of claims 1-14, wherein the composition is cured.

16. The article of claim 15, wherein the cured coating exhibits an Erichsen crack rating of 3 mm or more according to the method of ISO- 1520.