Powder coating composition

Abstract

1. A powder coating composition comprising: an acid-functional polyester resin A formed by reacting one or more polyol components, at least 90 mol % of which are neopentyl glycol, with one or more polyacid components, at least 87 mol % of which are isophthalic acid (IPA); the polyester resin A having an acid number (AN) of between 20 and 90 mg KOH / g; and a hydroxyl number of less than 50, preferably less than 15 mg KOH / g; a glycidyl-functional acrylic resin B having a weight average molecular weight of between 2500 and 7000; a curing catalyst C capable of catalyzing the reaction between the polyester resin A and the acrylic resin B; and optionally a β-hydroxyalkylamide D.

Description

[Technical Field]

[0001] The present invention relates to powder coating compositions, methods for using the powder coating compositions to provide coated substrates with improved edge coverage, methods for making the powder coating compositions, and articles coated with the powder coating compositions.

[0002] Powder coatings are an advanced and fast-growing technology widely recognized for their durability, gloss retention, weatherability, ability to be applied at high thicknesses up to 200 microns, and unlimited range of colors, finishes, glosses, and textures. All this, combined with their ability to prevent corrosion on metal substrates (corrosion is considered to have very high direct costs), makes powder an important technology in the world of coatings.

[0003] Additionally, powder coatings offer a solvent-free finish and a nearly 100% recyclable process for unpainted powder paints, making them an important part of sustainable or green building projects that incorporate low VOC emitting products.

[0004] Even when powder coatings are applied primarily to metal substrates, it is difficult to uniformly coat certain areas, such as corners and edges, through standard coating applications.

[0005] Thin coating thickness at the edges can result in insufficient corrosion protection and remains a common problem with current technology.

[0006] Various solutions have been proposed, for example involving the application of multiple powder coating layers, the first of which has a low flow rate that results in a strong orange peel and good edge coverage, followed by the application of a second coating of better flow rate but with limited thickness and coverage at the edges, which requires at least two applications, resulting in reduced productivity and a higher risk of unevenness.

[0007] There remains a need to find a single coating that combines outstanding edge coverage and protection against corrosion, while at the same time having good flow and all-over coatability. [Background technology]

[0008] Corrosion resistance is a very important feature of coatings for agricultural construction equipment, and powder coating compositions with improved edge coverage have been proposed as a solution to this problem for many years.

[0009] For example, U.S. Pat. No. 10,940,505 (B2) describes a powder coating with improved edge coverage obtained by applying two powder coatings by the dry-on-dry method, the first of which has a strong orange peel with short flat flows and good edge coverage, and a second top coat which has longer flat flows but poor edge coverage, and then curing both coatings together.

[0010] WO 2021 / 174086 A1 describes powder coatings with improved edge coverage obtained by applying a primer containing a catalyst or active ingredient or a rheology modifier for the powder coating, followed by applying a top coating.

[0011] The application of two layers reduces paint line productivity, introduces process inefficiencies and delays, and increases complexity in end-user operations.

[0012] At the same time, the combination of a solid, ultra-weatherable carboxylated polyester combined with a glycidyl methacrylate (GMA) acrylic resin, optionally in the presence of an additional curing agent such as a β-hydroxy-alkylamide, is known, as described, for example, in Japanese Patent No. 6567783, which reports that a GMA-based acrylic resin with a specific weight-average molecular weight and solubility parameter combined with a carboxylic acid group-containing carboxylated polyester with a specific solubility parameter and solubility parameter difference provides a coating exhibiting good overall properties, including scratch resistance. However, these polyesters have a large amount of OH functional groups (high OH value) present that do not participate in the reaction with the GMA-based acrylic resin and β-hydroxy-acrylamide, which may result in reduced chemical resistance due to limited increase in the molecular weight of the resulting coating during curing.

[0013] Another example is European Patent Application Publication No. 0522648 (EP0522648 A1), which discloses that a GMA-based acrylic resin combined with a carboxylated polyester containing at least 15 mol% 1,4-cyclohexanedicarboxylic acid (CHDA) in the polyacid mixture provides good solvent and impact resistance. However, the polyester described in this example has a low Tg of 39 to 44°C due to the presence of a large amount of CHDA. This results in reduced storage stability of the polyester and also reduced storage stability of powder coatings made therewith. Furthermore, the high amount of CHDA reduces the outdoor weatherability of the coating when compared to coatings made with similar polyesters having lower amounts of CHDA. Summary of the Invention [Problem to be solved by the invention]

[0014] It is therefore an object of the present invention to provide a powder coating composition that overcomes the above-mentioned drawbacks. It is a further object of the present invention to provide a powder coating composition that provides a coating that exhibits good edge and corner coverage in a single application and after thermal curing. It is a further object of the present invention that the composition provides a coating that, after curing, has a combination of good smoothness, flexibility (cupping), outdoor weatherability, chemical resistance, and other physical properties, such as corrosion resistance.

[0015] These objects are at least partly achieved by the powder coating composition according to claim 1. [Means for solving the problem]

[0016] Thus, a first aspect of the present invention is: an acid-functional polyester resin A formed by reacting one or more polyol components, at least 90 mol % of which are neopentyl glycol, with one or more polyacid components, at least 87 mol % of which are isophthalic acid (IPA), wherein the polyester resin A has an acid number (AN) between 20 and 90 mg KOH / g; and a hydroxyl number of less than 50, preferably less than 15 mg KOH / g; · a glycidyl-functional acrylic resin B having a weight average molecular weight between 2500 and 7000; a curing catalyst C capable of catalyzing the reaction between a polyester resin A and an acrylic resin B; Optionally, β-hydroxyalkylamide D The present invention relates to a powder coating composition comprising:

[0017] It has been surprisingly found that such powder coating compositions, even after application in just one single layer, can upon curing exhibit an excellent combination of physical properties such as smoothness, flexibility, chemical and corrosion resistance, and above all, outstanding edge coverage when tested by the low voltage wet sponge test method (ASTM D5162) and / or outstanding corner coverage when tested via the Standard Method for Corner Coverage of Powder Coatings (ASTM Method D2967-7).

[0018] In a second aspect, the present invention provides a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: contacting an uncoated metal substrate having a surface and an edge with a single layer of a powder coating composition according to the first aspect; Curing the powder coating composition wherein the powder coating composition exhibits an edge coverage rating of at least 2.0 when tested via the low voltage wet sponge test method (ASTM D5162).

[0019] In a third aspect, the present invention provides a method for producing a medicament for the treatment of a pulmonary arthritis, comprising: preparing an acrylic resin B in a reactor; mixing the acrylic resin B with the catalyst C before or while it leaves the reactor to form a BC mixture; or mixing the acrylic resin B with the catalyst C via extrusion to form a BC mixture; or mixing the acrylic resin B with the catalyst C through dry blending to form a BC mixture; dry blending the BC mixture, polyester resin A, and optionally, β-hydroxyalkylamide D to form a blend; extruding the blend to form a homogenized mixture; Cooling and grinding the homogenized mixture The present invention relates to a method for making a powder coating composition according to the first aspect, comprising:

[0020] In a fourth aspect, the present invention relates to an article, preferably having a metal substrate, partially or totally coated with a powder coating composition according to the first aspect or a powder coating composition made by a method according to the third aspect.

[0021] After application and curing of one layer, the coating composition of the present invention allows for a smooth, high gloss finish to be obtained, providing good solvent resistance, flexibility, corrosion resistance and edge coverage.

[0022] In a fifth aspect, the present invention relates to a metal substrate produced by the method according to the second aspect of the invention.

[0023] In a sixth aspect, the present invention relates to the use of a powder coating composition according to the first aspect or made by the method of the third aspect to provide good edge coverage of a metal substrate in a single layer, whereby the powder coating composition provides an edge coverage of at least 2.0 when tested via the low voltage wet sponge test method (ASTM D5162). [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram of a metal test plate used in ASTM D5162 testing, having a pinhole (1), a substrate 2, four surfaces: a top surface (2), two side surfaces (3), and a bottom surface (4), an edge (5), and four corners (6). [Figure 2] FIG. 1 is a representation of a metal test bar used in ASTM Method D2967-7 testing, with corners (7)—only four shown; and flats (8)—only two shown. DETAILED DESCRIPTION OF THE INVENTION

[0025] "Resin" shall refer to a polymer having functional groups that can be cured or crosslinked through a reaction involving those functional groups, said reaction being induced using heat (for heat-curable compositions) and / or radiation (for radiation-curable compositions) to connect polymer chains together through the formation of permanent covalent (crosslink) bonds, resulting in a cured resin.

[0026] By "functional group" herein is meant a covalently bonded group of atoms within a molecule, such as a carboxylic acid group (-COOH), a hydroxyl group (-OH), or an oxirane (also called glycidyl) group, that is capable of reacting with a functional group of another molecule. For example, a carboxylic acid functional polyester resin contains a carboxylic acid functional group that is capable of reacting with a functional group of another molecule, such as a glycidyl epoxy acrylic resin that contains a glycidyl group.

[0027] The terms "amorphous" and "crystalline" (sometimes including "semi-crystalline") used to characterize resins or thermosetting powder coating compositions are informal terms used in the art to indicate the primary characteristic of the relevant resin or thermosetting powder coating composition with respect to its crystallinity. An amorphous resin does not have a melting temperature (Tm) when melted over a range of temperatures, whereas a crystalline resin typically has a Tm. An amorphous resin is typically defined by its Tg. If a crystalline resin has a Tg, it is lower than its Tm. "Tg" as used herein means glass transition temperature. Tg is measured using differential scanning calorimetry (DSC) as described herein.

[0028] Curing of the thermosetting powder coating compositions of the present invention is accomplished using heat and can be referred to as "thermal curing," for example, using infrared (IR) lamps. For clarity, the term thermal curing does not include radiation curing, such as ultraviolet (UV) or electron beam induced curing.

[0029] Curable thermosetting powder coating compositions are applied onto an object, such as an article, and after thermal curing form a coating or film on the substrate, which can typically be referred to as a paint when the composition contains a pigment or pigments.

[0030] A composition containing functional resins and, if present, a curing catalyst, which can react together to form a cured composition by curing (i.e., by crosslinking), is often referred to as the binder component of the coating composition. Other ingredients, such as pigments, flow additives, etc., can be added to the binder to form the final composition that is applied to an object to form a coating on the object after curing.

[0031] "Edge coated" according to the present invention means that the edges of a metal substrate are covered by applying and curing one layer of a powder coating composition that provides an edge coverage of at least 2.0 when the composition is tested according to the Low Voltage Wet Sponge Test Method (ASTM D5162).

[0032] The "Low-Voltage Wet Sponge Test" according to the present invention is a test described in ASTM D5162, whereby a single layer of powder coating is applied to a metal test panel. The test panel has four corners (6) and edges (5) on four sides: top (2), bottom (4), and two sides (3) of the panel (see Figure 1). The edges are approximately 0.5 mm thick. The metal test panel has holes (1) for hanging and holding the panel. The panel is suspended from a holder via a metal wire perpendicular to the floor of the hood, as per standard procedure. After curing, the powder coating averages 50 to 125 μm thick. A pinhole detector, such as the DeFelsko Posi Test LPD Pinhole Detector, is used to detect discontinuities and pinholes at the edges (5) and corners (6) according to ASTM D5162, modified by using tap water instead of tap water and a low-foaming wetting agent.

[0033] The level of substrate exposure (i.e., discontinuities and pinholes) at edges and corners was assessed as follows (numbers in parentheses refer to numbers in Figure 1): 0.0 No coverage on the bottom (4), edges (5) along the sides (3), and no coverage on the corners (6) (poor edge coverage) 1.0 Some coverage on the edges (5) along the bottom (4) or sides (3) but no coverage on the edges and corners (6) along the top (2) (insufficient edge coverage) 2.0 Complete coverage of the edges (5) along the bottom (4) and some coverage of the edges (5) along the sides (3) but no coverage at the corners (6) (good edge coverage) 3.0 Full edge coverage (5) along all four sides (2, 3, and 4), including all corners (very good edge coverage)

[0034] When the results are better than the lower level but still do not meet the requirements of the subsequent level, intermediate values (1.5, 2.5) can be evaluated.

[0035] The term "corner coverage" as used herein refers to the ratio of the average corner thickness of the coating on the test bar to the average face thickness of the coating on the test bar, as described in ASTM method D2967-7(2013) (Standard Test Method for Corner Coverage of Powder Coatings), modified by spraying the substrate (square test bar) with the powder coating composition instead of immersing the substrate in a fluidized bed. "Corner coverage" is the ratio, expressed as a percentage, of the average corner thickness of the coating on the test bar to the average face thickness of the coating on the test bar, where face coverage refers to the thickness of the coating applied to each of the flat surfaces of the test bar ((8) in Figure 2), and corner thickness refers to the average thickness of the coating at the sharp 90° corners of the steel bar ((7) in Figure 2). Note that this means that the term "corner" as used in "edge covering" (Fig. 1(6)) has a different meaning than when the term is used in "corner covering" (sharp 90° corner of a bar (Fig. 2(7))).

[0036] [Detailed Description of the Invention] Acid-functional polyester resin A The polyester resin A is acid-functional, meaning that the polyester contains terminal carboxylic acid groups. The acid-functional polyester resin A is formed from one or more polyol components, at least 90 mol% of which are neopentyl glycol, and one or more polyacid components, at least 87 mol% of which are isophthalic acid (IPA); the polyester resin A has an acid number (AN) of 20 to 90 mg KOH / g; and a hydroxyl number of less than 50 mg KOH / g, preferably less than 15 mg KOH / g;

[0037] Polyester resin A may also be referred to as an "ultra-weatherable polyester," which is meant to refer herein to a polyester containing at least 87 mole % isophthalic acid by polyacid mole part and at least 90 mole % neopentyl glycol by polyol mole part.

[0038] The carboxylic acid group-containing polyester A of the present invention is a polyester resin that is a carboxylic acid functional polyester. Typically, it can be obtained by a) reacting a polyol with a diacid and / or anhydride thereof to form a hydroxyl functional polyester, followed by reaction with a polycarboxylic acid and / or anhydride thereof, or b) reacting all polyols with all di- and polycarboxylic acids and / or anhydrides thereof in a single step.

[0039] The carboxylic acid functional polyester resin A according to the invention is preferably prepared by reacting all polyols with all di- and poly-carboxylic acids and / or their anhydrides in a single step.

[0040] The carboxylic acid group-containing polyester resin A of the present invention generally has an acid number of at least 20, preferably at least 30, more preferably at least 40 mg KOH / g. The acid number of the polyester resin A is generally at most 90, preferably at most 75, more preferably at most 60 mg KOH / g.

[0041] Polyester resin A has a hydroxyl value of less than 50 mg KOH / g, preferably less than 15 mg KOH / g, and even more preferably less than 10 mg KOH / g.Unexpectedly, it has been found that when polyester resin A has a significantly low viscosity and such a low amount of residual OH functional groups, it is possible to obtain similar or better coating performance and better flow compared with polyesters with higher hydroxyl values and viscosities, which leads to lower flow and poorer appearance, and therefore requires additional coating layers to obtain good appearance.On the other hand, the coating composition of the present invention only requires one coating layer to have both good edge coverage and good appearance.

[0042] The diacid component of Polyester A generally comprises 87 to 100 mole percent isophthalic acid and 0 to 13 mole percent of another diacid component selected from one or more aliphatic, cycloaliphatic, and / or aromatic diacids, such as terephthalic acid, fumaric acid, maleic acid, phthalic anhydride, CHDA, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, succinic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,12-dodecanedioic acid, undodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, eptadecanedioic acid, octadecanedioic acid, or the corresponding anhydrides, and any mixtures thereof. CHDA and adipic acid are most preferred.

[0043] Polybasic organic carboxylic acid refers to an organic compound containing at least three carboxylic acid groups. The polybasic organic acid can be used in the acid form, the anhydride form, or a mixture of the acid and the anhydride. The polybasic organic acid of polyester A is generally present as 0 to 10 mole percent of the total acid and / or anhydride of polyester A. The polybasic organic acid is preferably selected from trimellitic acid, pyromellitic acid, trimellitic anhydride, and pyromellitic anhydride, and any mixture thereof. Trimellitic anhydride is most preferred.

[0044] The polyol component of polyester resin A comprises at least 90 mol% neopentyl glycol. The polyol component in polyester resin A may contain additional polyols having two OH groups, such as glycols, or at least three OH groups, such as trimethylolpropane.

[0045] Such glycols can be from 0 to 10 mole percent of another glycol component selected from one or more aliphatic and / or cycloaliphatic glycols such as: ethylene glycol, diethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, hydrogenated bisphenol A, hydroxypivalate of neopentyl glycol, etc. 1,6-hexanediol is most preferred.

[0046] The polyol component of polyester resin A having at least three OH groups is generally present as 0 to 10 mole percent of the total hydroxyl groups of polyester resin A. The polyol component of polyester A having at least three OH groups is preferably selected from glycerin, trimethylolpropane, tris-hydroxyethyl isocyanate (THEIC), ditrimethylolpropane, and pentaerythritol. Trimethylolpropane is most preferred.

[0047] Advantageously, the carboxylic acid functionality of polyester resin A is higher than 1.2, preferably 1.4, more preferably 1.6.

[0048] Advantageously, the carboxylic acid functionality of polyester A is lower than 2.6, preferably 2.4, more preferably 2.2 (functionality being defined as the average number of acid groups per molecule as "measured Mn" / (56100 / ANV), where ANV is the acid number value).

[0049] The carboxyl-functional polyester resin A of the present invention advantageously has a number average molecular weight (Mn), determined by gel permeation chromatography (GPC), of at least 1000, preferably at least 1500. The Mn of this polyester resin A is preferably at most 3000, more particularly at most 2500, as determined by GPC (using polystyrene standards and tetrahydrofuran as eluent at 35° C.).

[0050] The carboxyl-functional polyester resin A of the present invention advantageously has a weight average molecular weight (Mw), determined by gel permeation chromatography (GPC), of at least 2500, preferably at least 4000. The Mw of this polyester resin A is preferably at most 11000, more particularly at most 8000, as determined by GPC (using polystyrene standards and tetrahydrofuran as eluent at 35° C.).

[0051] Advantageously, the carboxyl functional polyester resin A of the present invention is an amorphous polyester.

[0052] The carboxyl functional polyester resin A of the present invention advantageously has a glass transition temperature measured by differential scanning calorimetry (DSC) according to ASTM D3418 at a heating gradient of 10° C. per minute from 45 to 90° C. Preferably, this polyester resin A has a glass transition temperature below 70° C., more preferably below 63° C.

[0053] The carboxyl functional polyester resin A of the present invention advantageously has a Brookfield cone and plate viscosity according to ASTM D4287-88 measured at 200° C. ranging from 500 to 10,000 mPa·s, preferably between 1,200 and 2,400 mPa·s.

[0054] Polyester resin A according to the present invention may be prepared using conventional esterification techniques well known in the art.

[0055] The polyesters are preferably prepared according to a procedure consisting of one or more reaction steps. In preparing these polyesters, conventional reactors equipped with a stirrer, an inert gas (nitrogen) inlet, a thermocouple, a distillation column connected to a water-cooled condenser, a water separator, and a vacuum connection are used. The esterification conditions used to prepare the polyesters are conventional, i.e., standard esterification catalysts, such as dibutyltin oxide, dibutyltin dilaurate, n-butyltin trioctoate, monobutyltin oxide, tin oxalate, sulfuric acid, or sulfonic acid, can be used in an amount of 0.0 to 0.50% by weight of the reactants, and optionally, color stabilizers, such as phosphonite- and phosphite-type stabilizers, e.g., tributyl phosphite, triphenyl phosphite, etc., can be added in an amount of 0 to 1% by weight of the reactants. Polyesterification is generally carried out at temperatures gradually increasing from 130°C to about 190-250°C, initially at atmospheric pressure or under pressure, and then, if necessary, under reduced pressure at the end of each process step, with these operating conditions maintained until a polyester having the desired hydroxyl and / or acid number is obtained. The degree of esterification is monitored by determining the amount of water formed during the reaction and the properties of the resulting polyester, such as hydroxyl number, acid number, and viscosity. Final additives, including catalysts, can be added to the reactor during release and / or during extrusion or mixing in powder coating preparations.

[0056] Glycidyl-functional acrylic resin B The glycidyl-functional acrylic resin B of the powder composition according to the invention has a weight average molecular weight, as determined by GPC (using polystyrene standards and tetrahydrofuran as eluent at 35° C.), of 2500 to 7000. Preferably, the glycidyl-functional acrylic resin B has a weight average molecular weight (Mw), as determined by gel permeation chromatography (GPC), of at least 2500, preferably at least 4200. Preferably, the Mw of this glycidyl-functional acrylic resin B is at most 7000, more particularly at most 5500, as determined by GPC (using polystyrene standards and tetrahydrofuran as eluent at 35° C.).

[0057] The glycidyl-functional acrylic resin B preferably results from the reaction of glycidyl methacrylate and / or glycidyl acrylate, at least one (meth)acrylic monomer, and optionally an ethylenically monounsaturated monomer different from the glycidyl (meth)acrylate and the (meth)acrylic monomer. The (meth)acrylic monomer is represented by the formula [ka] The alkyl ester of an α,β-ethylenically unsaturated carboxylic acid having the formula:

[0058] In the formula, R1 is a hydrogen atom or a methyl group, and R2 represents an alkyl group containing 1 to 18 carbon atoms, preferably 1 to 6 carbon atoms. Examples of (meth)acrylic monomers include alkyl esters of acrylic or methacrylic acid, such as ethyl acrylate, butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, and lauryl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl methacrylate, and lauryl methacrylate.

[0059] The optionally usable ethylenically monounsaturated monomers are preferably selected, alone or in mixture, from styrene, vinyltoluene, dimethylstyrene, α-methylstyrene, hydroxyethyl acrylate or methacrylate, hydroxypropyl acrylate or methacrylate, acrylonitrile, acrylamide, vinyl acetate, etc. The glycidyl group-containing acrylic copolymer B is preferably obtained from about 27 to 47% by weight of glycidyl methacrylate and / or glycidyl acrylate (preferably glycidyl methacrylate), about 73 to 53% by weight of (meth)acrylic monomers (preferably methyl- and n-butyl-methacrylate), and about 0 to 20% by weight of other ethylenically monounsaturated monomers (preferably styrene), taking into account the total reaction mixture for preparing the glycidyl group-containing acrylic copolymer B. These acrylic copolymers are prepared by known polymerization methods, such as polymerization in bulk, emulsion, or solution in an organic solvent. The monomers are copolymerized in the presence of a free radical initiator such as benzoyl peroxide, t-butyl peroxide, decanoyl peroxide, azo-bisisobutyronitrile, and the like in an amount of 0.1 to 7.0% by weight of the monomers.

[0060] The preferred glycidyl-functional acrylic resins B of the present invention advantageously have a number average molecular weight (Mn), as determined by gel permeation chromatography (GPC), of at least 1000, preferably at least 1500. The Mn of this glycidyl-group-containing acrylic copolymer B is preferably at most 2500, more particularly at most 2000, as determined by GPC (using polystyrene standards and tetrahydrofuran as eluent at 35° C.).

[0061] To achieve better control of the molecular weight and its distribution, a chain transfer agent can be added during the polymerization, preferably one of the mercaptan type, such as n-dodecyl mercaptan, t-dodecanethiol, isooctyl mercaptan, and the like, a halide, such as carbon tetrabromide, a disulfide, or a thioether. The chain transfer agent is used in an amount of 0 to 10% by weight of the monomers used in the copolymerization.

[0062] The glycidyl-functional acrylic resin B of the present invention generally has an epoxy equivalent weight (EEW) of at least 280, preferably at least 320, more preferably at least 360 g / eq (epoxy equivalent weight). The epoxy equivalent weight (EEW) of the glycidyl-group-containing acrylic copolymer B is generally at most 500, preferably at most 450, more preferably at most 400 g / eq (epoxy equivalent weight).

[0063] The glycidyl-functional acrylic resin B of the present invention advantageously has a glass transition temperature, measured by differential scanning calorimetry (DSC) according to ASTM D3418 with a heating ramp of 10° C. per minute, of 35 to 60° C. Preferably, this glycidyl-group-containing acrylic copolymer B has a glass transition temperature higher than 40° C., more preferably higher than 42° C.

[0064] The glycidyl-functional acrylic resin B of the present invention advantageously has a Brookfield cone and plate viscosity according to ASTM D4287-88 measured at 150° C. ranging from 10,000 to 75,000 mPa·s, preferably between 15,000 and 55,000 mPa·s.

[0065] An example of a commercially available glycidyl-functional acrylic resin B is Almatex PD3402 from Anderson Development Company, although many more are available from DIC, Estron, and Allnex, among others.

[0066] Advantageously, the functionality of the glycidyl-functional acrylic resin B is at least 2.5, preferably at least 4, and at most 8.5, preferably at most 7.0 (functionality being defined as the average number of glycidyl groups per molecule, as determined Mn / EEW).

[0067] Catalyst C The curing catalyst C is capable of catalyzing the reaction between the polyester resin A and the acrylic resin B. The curing catalyst C is typically a thermosetting curing catalyst and can be selected from the group consisting of amines, imidazoles, phosphines, ammonium salts, phosphonium salts, blocked amine or phosphine catalysts, encapsulation catalysts, and combinations thereof, preferably a combination of an arylphosphonium halide with an imidazole and a tertiary amine, more preferably a combination of ethyl-triphenylphosphonium bromide (BETP) with 2-methyl-imidazole and tributylamine.

[0068] The total weight percent of curing catalyst C in the powder coating composition is between 0.2 and 1.3 weight percent based on the total weight of the powder coating composition.

[0069] Advantageously, the total % of curing catalyst C is at least 0.2%, preferably at least 0.3%, and at most 1.3, preferably at most 1.2%.

[0070] When a combination of catalysts is used, the ratio between the three catalysts can be between 0 / 0 / 100 to 0 / 100 / 0 and 100 / 0 / 0.

[0071] The catalyst C can be mixed with the polyester resin A or the glycidyl-functional acrylic resin B, but preferably with the glycidyl-group-containing acrylic copolymer B, before or during leaving the reactor of the synthesis, or in a premix or extrusion.

[0072] Any β-hydroxyalkylamide D Optionally, a β-hydroxyalkylamide is added to the powder coating composition. The β-hydroxyalkylamide contains at least one, preferably two, bis-(β-hydroxyalkyl)amide groups. More preferred β-hydroxyalkylamides are those commercially available from EMS under the trade names Primid XL552, Primid QM1260, and Primid SF 4510, and are also described in U.S. Patent No. 4,727,111 (US 4,727,111), U.S. Patent No. 4,788,255 (US 4,788,255), U.S. Patent No. 5,407,6917 (US 5,407,6917), European Patent No. 0,322,834 (EP 0,322,834), and European Patent No. 0,473,380 (EP 0,473,380).

[0073] For Primid XL 552, the typical hydroxylamide number range is 600-725 mg KOH / g, with an equivalent weight range of 94-77 g / hydroxylamide group.

[0074] Advantageously, the ratio between the equivalents of glycidyl-functional acrylic resin B (moles of glycidyl groups in resin B) combined with the moles of hydroxyamide groups of the β-hydroxyalkylamide, if present, and the equivalents of carboxylic acid groups of polyester resin A (moles of carboxylic acid groups in resin A) is between 33 / 67 and 67 / 33, preferably between 45 / 55 and 55 / 45.

[0075] The ratio between the equivalent amount of acrylic resin B glycidyl group-containing acrylic copolymer B (moles of glycidyl groups in acrylic resin B) and the moles of hydroxylamide groups of any, if present, β-hydroxyalkylamide D (moles of hydroxyalkylamide groups in β-hydroxyalkylamide D) is comprised between 100 / 1 and 40 / 60, preferably between 75 / 25 and 50 / 50. The powder coating composition may comprise additional components.

[0076] In addition to the above-mentioned components, compositions within the scope of the present invention can also contain one or more components, such as carboxyl-containing semicrystalline polyesters, as additives, typically in an amount of less than 5% of the powder coating composition. The carboxyl-containing crystalline or semicrystalline polyester resins are based on polycarboxylic acids and polyols. The polycarboxylic acids are, for example, linear, aliphatic dicarboxylic acids having 2 to 22 methylene groups, and / or terephthalic acid / isophthalic acid, in an amount of at least 85 mol % based on the total amount of all polycarboxylic acids used. As polyols, for example, (cyclo)aliphatic alcohols having 2 to 10 C atoms can be used.

[0077] Other ingredients include flow control agents such as ADDITOL® P 896, ADDITOL® P 824, MODAFLOW® P 6000 (ALLNEX), RESIFLOW® P-67, and PV5 (ESTRON), ACRONAL® 4F, ACRONAL® LR8820 (BASF), BYK360, and BYK® 361 (BYK Chemie), degassing agents such as Benzoin (BASF), fillers, UV light absorbers such as TINUVIN® 900 (BASF), hindered amine light stabilizers such as TINUVIN® 144 (BASF), other stabilizers such as TINUVIN® 312 and 1130 (BASF), antioxidants such as IRGANOX® 1010 (BASF), and phosphonite or phosphite type stabilizers such as IRGAFOS® 168 (BASF), ULTRANOX® 626 (SI GROUP), DOVERPHOS® 613 (DOVER), or HOSTANOX® P-EPQ (CLARIANT), pigments, fillers, and dyes.

[0078] Colored and transparent lacquers can be prepared. Various dyes, fillers, and pigments can be utilized in the compositions of the present invention. Examples of useful pigments, fillers, and dyes include metal oxides, such as titanium oxide, iron oxide, zinc oxide, and the like, metal hydroxides, metal powders, sulfides, sulfates, carbonates, silicates such as ammonium silicate, carbon black, talc, china clay, baryte, iron blue, lead blue, organic red, organic maroon, and the like.

[0079] The powder composition typically contains less than 40% by weight of these additional ingredients based on the total powder coating weight.

[0080] Preferably, the powder coating composition has a gel time measured at 200°C of less than 100 seconds, preferably between 20 and 50 seconds.

[0081] The components of the compositions according to the present invention may be mixed by dry blending in a mixer or blender (e.g., a drum mixer). The premix is then homogenized in a single-screw extruder such as a BUSS-Ko-Kneter or a twin-screw extruder such as a PRISM or Werner & Pfleiderer ZSK at temperatures generally ranging from 50 to 120°C. When cooled, the extrudate is ground into a powder with a particle size generally ranging from 10 to 150 μm. The powdered composition may be deposited onto a substrate using a powder gun such as an electrostatic CORONA gun or a triboelectric TRIBO spray gun. Alternatively, well-known methods of powder deposition, such as fluidized bed techniques, can also be used. After deposition, the powder is typically heated by various heating methods, including IR, to a target temperature between 140 and 220°C, preferably about 180 to 200°C, for 10 to 30 minutes to cause the particles to flow and fuse together to form a smooth, uniform, continuous, and pit-free coating on the substrate surface.

[0082] In one embodiment, the powder coating composition provides a good edge coverage rating (2.0) or a very good edge coverage rating (3.0), or any level in between these ratings.

[0083] In yet another embodiment, the powder coating composition provides corner coverage of greater than 10%, preferably greater than 15%, and more preferably greater than 20%.

[0084] The powder compositions according to the invention may provide outstanding flow and make it possible to obtain glossy coatings, excellent edge coverage in a single coat, mechanical properties, and solvent resistance.

[0085] The present invention further provides a method for providing good edge coverage of a metal substrate, comprising: contacting an uncoated metal substrate having a surface and an edge with a single layer of the powder coating composition described above; curing the powder coating composition; Including, The powder coating composition provides an edge coverage rating of at least 2.0 when tested using the low voltage wet sponge test method (ASTM D5162).

[0086] Preferably, curing is carried out at a temperature in the range of from 160 to 210°C, more preferably from 180 to 200°C, for a period of from 10 to 30 minutes, preferably from 10 to 15 minutes.

[0087] In one embodiment, the cured monolayer has a thickness of 50 to 125 μm.

[0088] The invention also relates to metal substrates coated by such methods.

[0089] The present invention provides preparing an acrylic resin B in a reactor; mixing the acrylic resin B with the catalyst C before or during leaving the reactor to form a BC mixture; or mixing the acrylic resin B with the catalyst C via extrusion to form a BC mixture; or · Mixing the acrylic resin B with the catalyst C through dry blending to form a BC mixture; dry blending the BC mixture, polyester resin A, and optionally, β-hydroxyalkylamide D to form a blend; extruding the blend to form a homogenized mixture; Cooling and grinding the homogenized mixture The present invention also relates to a method for making a powder coating composition, comprising:

[0090] The present invention further relates to an article, typically having a metal substrate, partially or totally coated with the powder coating composition described above or with a powder coating composition made by the method described above.

[0091] The present invention further relates to the use of a powder coating composition as described above or made by the method described above to provide good edge coverage of a metal substrate by applying a single layer, whereby the powder coating composition provides an edge coverage of at least 2.0 when tested via the low voltage wet sponge test method (ASTM D5162).

[0092] method 1.Acid value AN The amount of resin is accurately weighed into a 250 ml Erlenmeyer flask. 50-60 ml of tetrahydrofuran is then added. The solution is gently heated until the resin is completely dissolved, ensuring that the solution does not boil. The solution is cooled to room temperature, and then 3 drops of phenolphthalein are added, followed by titration with standard potassium hydroxide until the end point is reached. The acid number is calculated as follows: Acid value (mgKOH / g)=mL×N * 56.1 / g g = mass of resin N = normality of potassium hydroxide solution

[0093] 2.Viscosity Viscosity is measured according to ASTM D 4287 using a Brookfield CAP 2000 viscometer (variable speed) for the determination of viscosity of high viscosity polyesters. The required temperature and speed are selected. A small amount of resin sample is placed on the heated plate so that a small amount of excess spreads around the sides as the cone is lowered. The spindle rotation is started. The sample is thoroughly evacuated by moving the cone up and down several times while the cone rotation button is stopped. Once fully evacuated, the next reading is taken. This process is repeated until a very stable, reproducible reading is obtained.

[0094] 3. Tg by DSC The Tg values reported herein are the midpoint Tg determined at the slope of the DSC curve. The DSC curves were determined using a heating rate of 10°C / min.

[0095] 4. Molecular weight by GPC The weight and number average molecular weights and molecular mass distributions of the polymers were determined by gel permeation chromatography (GPC) on an HPLC Perkin-Elmer equipped with a refractive index (RI) detector using tetrahydrofuran HPLC grade at 35°C as eluent and three PLgel columns 100-1000-10000A (300 x 7.8 mm) 5 microns, Polymer Standard Service (PSS) using polystyrene standards (MW range 162 to 96000 Daltons), and toluene added with each sample as a flow marker peak.

[0096] 5. Sensuality Functionality is defined as the average number of acid or glycidyl groups per molecule, as calculated by Mn / (56100 / AN) or Mn / EEW.

[0097] 6. Epoxy equivalent weight (EEW) The epoxy equivalent weight is the weight of an epoxy compound containing exactly one mole of glycidyl groups, expressed in g / mol.

[0098] An amount of resin equivalent to 0.7-0.8 milliepoxide equivalents was accurately weighed into a 250 ml Erlenmeyer flask. 20 ml of methylene chloride was then added. The solution was gradually heated until the resin was completely dissolved, ensuring that the solution did not boil. The solution was then cooled to room temperature. Approximately 0.5-1 g of tetraethylammonium bromide powder and 4-6 drops of crystal violet indicator (the color will change from blue to green) were then added via a cylinder.

[0099] It is then immediately titrated with 0.1 N perchloric acid solution with magnetic stirring until the end point is reached.

[0100] calculation Epoxide equivalent weight = (P x 1000) / ((V-Vo) x N) g / eq (epoxy equivalent weight) During the ceremony: V = ml of 0.1N perchloric acid solution used to titrate the sample Vo = ml of 0.1N perchloric acid solution used to titrate the blank solution N = normality of perchloric acid P = sample weight in grams

[0101] 7. Hydroxyl Value (OHV) The hydroxyl number (OHV) is defined as the number of mg of KOH equivalent to the amount of acetic acid esterified after acetylation of the hydroxyl groups of 1 g of sample (see method DIN 53240).

[0102] Acetylation mixture: 15 g of acetic anhydride is diluted with analytical grade pyridine in a 250 ml Erlenmeyer flask.

[0103] The determination must be carried out in duplicate and a blank test must be completed at the same time according to the procedure reported here below.

[0104] 20 ml of the acetylation mixture is added to a precisely weighed sample based on the predicted hydroxyl value in a flask. An air condenser is inserted, and the flask is placed in a constant temperature bath at 100°C and refluxed for 1 hour. 30 ml of tetrahydrofuran is then added to thoroughly rinse the air condenser, followed by 10 ml of distilled water. After vigorously stirring, the solution is again placed in the bath for 10 minutes or more. After removing the flask from the bath, 30 ml more tetrahydrofuran is added. The flask is again vigorously shaken, and the solution is allowed to cool.

[0105] Indicator solution: Dissolve 0.80 g of thymol blue and 0.25 g of cresol red in 1 L of methanol.

[0106] OHV is determined by manual titration of prepared cold blank and sample flasks with standardized 0.5N methanolic potassium hydroxide solution using 10 drops of indicator solution. The endpoint is reached when the color changes from yellow to gray to blue, resulting in a blue color that persists for 10 seconds. The hydroxyl number is then calculated as follows: Hydroxyl number = (BS) × N × 56.1 / M + AN During the ceremony: B = ml of KOH used in the blank titration S = ml of KOH used in sample titration N = normality of potassium hydroxide solution M = sample weight (base resin) AN = Acid number of the sample in mgKOH / g

[0107] 8. Gel Time Measurement The time required by the test sample to change its physical state from liquid (molten) to solid-gum (gelled) is measured; this time is called the "gel time". Both the finished coating or the physical blend of resin and appropriate hardener can be tested (DIN 55990 Part 8, ISO 8130-6).

[0108] The tester plate is preheated to the test temperature. A spoonful of the test sample of powder paint, equivalent to approximately 0.9 g, is introduced into one of the gaps (cavities) of the tester plate. A stopwatch is started and immediately the test sample is stirred gently and continuously in a circular motion with a metal pencil until the melt viscosity begins to increase visibly. By raising the metal pencil vertically, gelation of the material is achieved by the easy breaking of the strands: at this point the stopwatch is stopped.

[0109] The total time in seconds to the end of the test (when gelation occurs) at the specified test temperature represents the result of the measurement. [Example]

[0110] Example 1 Polyester A: 425 parts of neopentyl glycol were placed in a conventional four-neck round-bottom flask equipped with a stirrer, a distillation column connected to a water-cooled condenser, a nitrogen inlet, and a thermometer attached to a temperature controller. The contents of the flask were heated under nitrogen with stirring to a temperature of approximately 140°C, at which point 721 parts of isophthalic acid and 1 part of monobutyltin oxide were added. The reaction was continued at 240°C under atmospheric pressure until approximately 95% of the theoretical amount of water had distilled and a clear, carboxyl-functionalized prepolymer was obtained. 0.6 parts of triphenyl phosphite were added to the first-step polyester at 200°C, and a vacuum of 50 mmHg was gradually applied at a temperature of 235°C. Once the target acid number and viscosity were achieved, the polyester was cooled at 200°C and 0.3 parts of BETP were added. After 60 minutes, the following properties were obtained: Acid value: 35mgKOH / g Brfld(cone / plate): 2000 mPa·sec at 200°C Tg(DSC): 61℃ Hydroxyl value OHV: 4.5mgKOH / g Molecular weight distribution: Mn 2363 / Mw 6245 Functionality: 1.5

[0111] Example 2 Glycidyl group-containing acrylic copolymer B: 500 parts of ethyl acetate are introduced into a reactor equipped with a thermocouple, a stirrer, a reflux condenser, and a dropping funnel and heated to reflux temperature. A mixture consisting of 178 parts of glycidyl methacrylate, 173 parts of methyl methacrylate, 70 parts of butyl methacrylate, 47 parts of styrene, 14 parts of n-dodecyl mercaptan, and 17 parts of 2,2-azobis(2-methylpropionitrile) is added through the dropping funnel over a period of 5 hours. Upon completion of the addition, the reaction mixture is boiled under reflux for 1 hour. 10 parts of 2,2-azobis(2-methylpropionitrile) are then added, and the reaction mixture is maintained under reflux for an additional 2 hours. The solvent is distilled off under reduced pressure, and the glycidyl group-containing acrylic copolymer is collected. The acrylic copolymer thus obtained is a solid product that is easily pulverized into a whitish powder. It has the following properties: Epoxy equivalent: 400g / eq (epoxy equivalent): Brfld (cone / plate) 50000 mPa·sec at 150°C Tg(DCC) 51℃ Molecular weight distribution: Mn: 2120 and Mw 5845 Sensuality: 5.3

[0112] As example 3, a glycidyl-containing acrylic resin prepared in a similar manner and based on glycidyl methacrylate, methyl methacrylate, butyl methacrylate, and styrene, commercially designated Almatex PD 3402, is used. Epoxy equivalent: 380g / eq (epoxy equivalent): Brfld (cone / plate) 19000 mPa·sec at 150°C Tg(DSC) 46℃ Molecular weight distribution: Mn: 1732 and Mw 4612, and functionality 4.6

[0113] The polyester and glycidyl-containing acrylic resins shown above were then blended into the powder according to the formulations set forth below. Black paint formulation Binder 100.0 Carbon Black 2.0 Modaflow P 6000 1.8 Benzoin 1.0

[0114] The binder compositions of the various powder blends are shown in the table below.

[0115] Powders were prepared by first dry-blending the various solid components in a bag, then homogenizing them in the melt using a ZSK-30P extruder at an extrusion temperature of approximately 90°C and a speed of 600 rpm. The homogenized mixture was then cooled and pulverized in a Vortisiv. The powder was then sieved to obtain a particle size of less than 200 microns. The resulting powder was deposited onto MDF or Q-Panel CRS panels (0.05 x 7.5 x 12.5 cm) by electrostatic deposition using a GEMA-Optiflex-2 spray gun. At film thicknesses of 50 to 140 microns, the panels were cured in an electrically heated oven, with the curing proceeding for 15 minutes at a target temperature of 180°C unless otherwise reported. The compositions (components and amounts by weight) of the various polyesters are reported in Table 1, while the moles of glycol and acid % are reported in Table 2. [Table 1] [Table 2]

[0116] The powder coating compositions are reported in Table 3 and the single coatings were cured at a target temperature of 200°C for 10 minutes. [Table 3]

[0117] The paint properties of the finishes obtained with binders according to the invention (PC1, PC2) and a reference (CPC1) are shown in Table 4. [Table 4]

[0118] The powders according to the invention (PC1 and PC2) produce single layer coatings with very good edge coverage compared to a reference based on the same resin of Example 1 but in combination with glycidyl-containing acrylic resin B and TGIC (tris-glycidyl-isocyanurate) instead of β-hydroxyalkylamide D.

[0119] To understand the effect of various percentages of curing catalyst on the sponge test results, PC1 and PC2 were prepared with additional amounts of BETP ranging from 0 to 1%, whereby PC3 is PC1 with 0.5% BETP, PC4 is PC1 with 1% BETP instead of 0.75%, PC5 is PC2 with 0.35% BETP, PC6 is PC2 with 0.5% BETP instead of 0.75%, and CPC3 is PC2 without BETP, and the results after curing the objects at 180°C for 15 minutes are reported in Tables 5 and 6. [Table 5] [Table 6]

[0120] Based on the results reported in Tables 5 and 6, it was surprisingly found that powder coatings must contain at least 0.35% BETP to meet the required edge coverage rating, while CPC2 and CPC3, which do not contain BETP, have insufficient edge coverage. [Table 7]

[0121] When tested at various times and temperatures, PC2 demonstrates very good edge coverage between 180°C and 200°C and at 10 and 15 minutes of cure.

[0122] Additional tests were performed to examine the effect of % pigment on the powder coatings in black and white as reported in Table 8. [Table 8]

[0123] This does not affect the outstanding edge coverage rating, as reported in Table 9. This result is combined with the same good flexibility, smoothness, and good chemical resistance. [Table 9]

[0124] From the test results on PC2, the inventors also confirmed that edge coverage as measured by ASTM D5162 represents a good prediction of corner coverage as measured by ASTM D2967-7, recognizing that good corner coverage is achieved when the percent thickness at the corners of the bar is at least 15% of the thickness measured on the flat surface of the bar. Furthermore, after a 500-hour salt spray resistance test based on ASTM B117 evaluated according to Procedure C of ASTM D1654, the creep increase produced at the edges of PC is only 0.5 mm, recognizing that good corrosion resistance is achieved with a creep increase of less than 20 mm and in the best case, an increase of less than 5 mm.

[0125] The polyester of Example 5 from Table 1 was tested in a white powder coating compared to the polyester of Example 4 as well as a powder coating containing the comparative polyester. [Table 10] [Table 11]

[0126] Table 11 shows that even with an increased Tg compared to Example 4, the polyester-based powder coating of Example 5 exhibits outstanding edge coverage.

[0127] Furthermore, Table 11 shows that the edge coverage of the comparative example, with an OH value greater than 50, is very low compared to the other paints. Additionally, the distinctness of image (DOI) is the lowest of all. [Table 12]

[0128] In Tables 12 and 13, a comparison between two different glycidyl-containing acrylic resins is reported, and it can be seen that the powder coating based on the glycidyl-containing acrylic resin of Example 2 can also provide good edge coverage. [Table 13]

[0129] 1507 parts of the GMA acrylic resin of Example 3 are dry blended in a bag with 74 parts of BETP, then homogenized to a melt at an extrusion temperature of about 90° C. and a speed of 600 rpm, then cooled and ground (Example 8). [Table 14] [Table 15]

[0130] Table 15 shows that mixing catalyst C and acrylic resin B in an extruder to form a BC mixture results in a composition with better flow and a coating with better impact resistance compared to mixing polyester A, acrylic resin B, and catalyst C during extrusion.

Claims

1. 1. A powder coating composition comprising: an acid-functional polyester resin A formed by reacting one or more polyol components, at least 90 mol % of which are neopentyl glycol, with one or more polyacid components, at least 87 mol % of which are isophthalic acid (IPA), wherein the polyester resin A has an acid number (AN) between 20 and 90 mg KOH / g and a hydroxyl number of less than 50, preferably less than 15 mg KOH / g; a glycidyl-functional acrylic resin B having a weight average molecular weight of between 2500 and 7000, as determined by gel permeation chromatography (GPC) using polystyrene standards; a curing catalyst C capable of catalyzing the reaction between the polyester resin A and the acrylic resin B, and optionally β-hydroxyalkylamide D A powder coating composition comprising:

2. a. Polyester Resin A is present in an amount of 70 to 98.8 wt %; b. Acrylic Resin B is present in an amount of 1 to 30 wt. %; c. the curing catalyst C is present in an amount of 0.2 to 1.3 wt. %; d. β-hydroxyalkylamide D is present in an amount of 0 and 5 wt. %; The weight percent amounts are based on the total weight of the powder coating composition. The powder coating composition according to claim 1.

3. 3. A powder coating composition according to claim 1 or 2, wherein the ratio of equivalents of glycidyl groups of acrylic resin B (moles of glycidyl groups in resin B) to equivalents of carboxylic acid groups of polyester resin A (moles of carboxylic acid groups in polyester resin A) combined with the moles of hydroxylamide groups of β-hydroxyalkylamide D, if present, is between 33 / 67 and 67 / 33, preferably between 45 / 55 and 55 / 45.

4. 4. Powder coating composition according to any one of claims 1 to 3, wherein the ratio of the equivalents of glycidyl groups of the acrylic resin B (number of moles of glycidyl groups in the acrylic resin B) to the number of moles of hydroxylamide groups of the β-hydroxyalkylamide D, if present, is comprised between 100 / 1 and 40 / 60, preferably between 75 / 25 and 50 / 50.

5. a. 75 to 83 wt. % of Polyester Resin A; b. 12 to 22% by weight of Acrylic Resin B; c. 0.3 to 1.2 wt. % of curing catalyst C; d. 2 to 3.5 wt. % of a β-hydroxyalkylamide wherein the weight percent amounts are based on the total weight of the powder coating composition; A powder coating composition according to any one of claims 1 to 4.

6. The polyester component A has the following characteristics: a. a polyester resin A acid number of at least 20, preferably at least 30, more preferably at least 40 mg KOH / g, and said polyester resin A acid number is at most 90, preferably at most 75, more preferably at most 60 mg KOH / g; b. The hydroxyl number of the polyester resin A is less than 10 mg KOH / g; c. the polyester resin A has a number average molecular weight (Mn) as determined by gel permeation chromatography (GPC) of at least 1000, preferably at least 1500; d. the polyester resin A has a number average molecular weight (Mn) determined by gel permeation chromatography (GPC) of at most 3000, preferably at most 2500; e. the polyester resin A is an amorphous resin, preferably having a glass transition temperature comprised between 30 and 90°C, preferably at least 45°C, as measured by differential scanning calorimetry (DSC) according to ASTM D3418 with a heating ramp of 10°C per minute; f. said polyester resin A has a functionality of at least 1.2, preferably at least 1.4, and more preferably at least 1.6, said functionality being defined as the average number of acid groups per molecule as determined by Mn / (56100 / ANV); g. said polyester resin A has a functionality of at most 2.6, preferably at most 2.4, more preferably at most 2.2, said functionality being defined as the average number of acid groups per molecule as determined by "Measured Mn" / (56100 / ANV); h. the glycol component of the polyester resin A is composed of 90 to 100 mole percent neopentyl glycol and 0 to 10 mole percent other polyols; i. the glycol component of the polyester resin A is composed of 90 to 100 mole percent neopentyl glycol and 0 to 10 mole percent of another glycol component selected from one or more aliphatic and / or cycloaliphatic glycols, such as ethylene glycol, diethylene glycol, 1,3-propanediol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, hydrogenated bisphenol A, and hydroxypivalate of neopentyl glycol, preferably the other glycol component comprising 1,6-hexadiol; j. the diacid component of the polyester resin A is composed of 87 to 100 mole percent isophthalic acid and 0 to 13 mole percent of another diacid component; k. the diacid component of said polyester resin A is generally composed of 87 to 100 mole percent isophthalic acid and 0 to 13 mole percent of another diacid component selected from one or more aliphatic, cycloaliphatic, and / or aromatic diacids, such as terephthalic acid, fumaric acid, maleic acid, phthalic anhydride, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, succinic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,12-dodecanedioic acid, undodecanedioic acid, tridecanedioic acid, tetradecanedioic acid, hexadecanedioic acid, eptadecanedioic acid, octadecanedioic acid, or the corresponding anhydrides and any mixtures thereof, with 1,4-cyclohexanedicarboxylic acid (CHDA) and adipic acid being most preferred; l. the sum of the polyol having at least 3 OH groups and the polybasic organic carboxylic acid component of Polyester A is generally present as 0 to 10 mole percent of the sum of the polyol and carboxylic acid of Polyester Resin A, and is preferably trimethylolpropane and trimellitic anhydride; m. The carboxylic acid functional polyester component A according to the present invention is preferably prepared by reacting all polyols with all di- and poly-carboxylic acids and / or their anhydrides in a single step.

6. The powder coating composition of claim 1, wherein the coating composition has one or more of the following properties:

7. 7. The powder coating composition according to claim 1, wherein the curing catalyst C is selected from the group consisting of ethyl-triphenyl-phosphonium bromide, tributyltin, or 2-methyl-imidazole, or mixtures thereof.

8. The glycidyl-functional acrylic resin B has the following characteristics: a. an epoxy equivalent weight of at least 280, preferably at least 320, more preferably at least 360 g / eq, and at most 500, preferably at most 450, more preferably at most 400 g / eq; b. a number average molecular weight (Mn) as determined by gel permeation chromatography (GPC) of at least 1000, preferably at least 1200; c. a glass transition temperature of 35 to 60°C, as measured by differential scanning calorimetry (DSC) according to ASTM D3418 with a heating ramp of 10°C per minute; d. Brookfield cone and plate viscosity according to ASTM D4287-88 measured at 150°C ranging from 10,000 to 75,000 mPa-sec, preferably between 15,000 and 55,000 mPa-sec; e. Functionality greater than 2.5 and less than 8.5 (functionality defined as the average number of glycidyl groups per molecule, as per "measured Mn" / EEW) The composition of claim 1 , wherein the at least one of

9. The glycidyl-functional acrylic resin B has the following characteristics: a. an epoxy equivalent weight of at least 280, preferably at least 320, more preferably at least 360 g / eq, and at most 500, preferably at most 450, more preferably at most 400 g / eq; b. a number average molecular weight (Mn) as determined by gel permeation chromatography (GPC) of at least 1000, preferably at least 1500, and at most 2500, preferably at most 2000; c. a glass transition temperature of 35 to 50°C, as measured by differential scanning calorimetry (DSC) according to ASTM D3418 with a heating ramp of 10°C per minute; d. Brookfield cone and plate viscosity according to ASTM D4287-88 measured at 150°C ranging from 10,000 to 40,000 mPa·s, preferably between 15,000 and 25,000 mPa·s 9. The powder coating composition of claim 1, wherein

10. 10. The powder coating composition according to any one of claims 1 to 9, wherein the content of the polyester resin A, the acrylic resin B, the catalyst C, and, if present, the β-hydroxyalkylamide D is from 60 to 100% by weight based on the total powder coating composition.

11. 11. A powder coating composition according to any one of claims 1 to 10, wherein the gel time of the composition measured at 200°C is less than 100 seconds, preferably between 20 and 50 seconds.

12. 12. A powder coating composition according to any one of claims 1 to 11, wherein the composition exhibits an edge coverage rating of at least 2.0 when tested using the Low Voltage Wet Sponge Test Method (ASTM D5162), and / or the composition exhibits corner coverage of greater than 10%, preferably greater than 15%, even more preferably greater than 20% according to the Standard Test Method for Corner Coverage of Powder Coatings (ASTM method D2967-7).

13. 1. A method for providing good edge coverage of a metal substrate, comprising: - contacting an uncoated metal substrate having a surface and an edge with a single layer of a powder coating composition according to any one of claims 1 to 12, - curing the powder coating composition Including, the powder coating composition exhibits an edge coverage rating of at least 2.0 when tested using the low voltage wet sponge test method (ASTM D5162); method.

14. 14. The method of claim 13, wherein the curing step is carried out at a temperature in the range of 160 to 210°C, preferably 180 to 200°C, for a period of 10 to 30 minutes, preferably 10 to 15 minutes.

15. 15. The method of claim 13 or 14, wherein the monolayer after curing has a thickness of 50 to 125 μm.

16. - preparing acrylic resin B in a reactor; mixing acrylic resin B with catalyst C before or during leaving the reactor to form a BC mixture; or mixing acrylic resin B with catalyst C through extrusion to form a BC mixture; or - mixing acrylic resin B with catalyst C through dry blending to form a BC mixture; dry blending the BC mixture, polyester resin A, and optionally β-hydroxyalkylamide D to form a blend; - extruding the blend to form a homogenized mixture; cooling and grinding the homogenized mixture 13. A method for making the powder coating composition of any one of claims 1 to 12, comprising:

17. 17. An article, preferably having a metal substrate, partially or totally coated with a powder coating composition according to any one of claims 1 to 12 or with a powder coating composition made by the method according to claim 16.

18. A metal substrate produced by the method of any one of claims 12 to 15.

19. 17. Use of a powder coating composition according to any one of claims 1 to 12 or a powder coating composition made by the method of claim 16 to provide good edge coverage of a metal substrate by applying a single layer, wherein the powder coating composition exhibits an edge coverage of at least 2.0 when tested via the low voltage wet sponge test method (ASTM D5162).

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