Patent Description:
Powder coating compositions are applied to substrates to provide numerous properties including protective properties and decorative properties. For instance, fluoropolymer based powder coating compositions are commonly applied to substrates, such as metal substrates, to provide good weather resistance. While fluoropolymer based powder coating compositions provide good weather resistance, these compositions typically require large amounts of the fluoropolymer component. As a result, these compositions are typically expensive due to the high cost of fluoropolymer raw materials. As such, it is desirable to provide fluoropolymer based powder coating compositions that utilize other components to reduce the amount of fluoropolymer and which still provide good physical properties such as good weather and corrosion resistance.

<CIT> discloses powder coating compositions that comprise an acid-functional polyester and a FEVE in a weight ratio of about <NUM>:<NUM>, β-hydroxyalkylamide as a curing agent for the polyester and an isocyanate curing agent for the fluoropolymer.

The present invention is directed to a powder coating composition that includes: a polyester polymer having carboxylic acid functional groups and having an acid value of at least <NUM> KOH/g; a first crosslinker reactive with the carboxylic acid functional groups of the polyester polymer; and a fluoropolymer unreactive with the polyester polymer and first crosslinker, wherein the fluoropolymer comprises a fluoroethylene vinyl ether copolymer, a polyvinylidene fluoride polymer, or a combination thereof, and the weight ratio of the polyester polymer to the fluoropolymer in the powder coating composition is from <NUM>:<NUM> to <NUM>:<NUM>. When cured, the powder coating composition forms a single coating layer including the polyester polymer and the fluoropolymer.

For purposes of the following detailed description, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

In this application, the use of the singular includes the plural and plural encompasses singular, unless specifically stated otherwise. In addition, in this application, the use of "or" means "and/or" unless specifically stated otherwise, even though "and/or" may be explicitly used in certain instances. Further, in this application, the use of "a" or "an" means "at least one" unless specifically stated otherwise. For example, "a" fluoropolymer, "a" polyester polymer, "a" crosslinker, and the like refer to one or more of any of these items.

As indicated, the present invention is directed to a powder coating composition that includes a polyester polymer having carboxylic acid functional groups, a first crosslinker reactive with the carboxylic acid functional groups of the polyester polymer, and a fluoropolymer unreactive with the polyester polymer and first crosslinker, where a weight ratio of the polyester polymer to the fluoropolymer is from <NUM>:<NUM> to <NUM>:<NUM>, and where when cured, the powder coating composition forms a single coating layer including the polyester polymer and the fluoropolymer
As used herein, a "powder coating composition" refers to a coating composition embodied in solid particulate form as opposed to liquid form. Thus, the components that form the powder coating composition can be combined to form a curable solid particulate powder coating composition. For instance, the polyester polymer, fluoropolymer, first crosslinker, and optional additional components can be combined to form a curable solid particulate powder coating composition that is free flowing. As used herein, the term "free flowing" with regard to curable solid particulate powder coating compositions of the present invention, refers to a curable solid particulate powder composition having a minimum of clumping or aggregation between individual particles. The spraying suitability factor R of a powder coating may be measured with a Sames AS <NUM> Fluidity Indicator according to Test method ISO/DIS <NUM>-<NUM> or the AS <NUM> Fluidity User Manual. The powder coating composition of the present invention may have a spraying suitability factor R of greater than <NUM> (Very Good rating), or greater than <NUM> (Good rating).

As indicated, the powder coating composition of the present invention comprises a polyester polymer. As used herein, a "polyester polymer" refers to a polymer that includes one or more ester functional groups to link monomer units. As used herein, the term "polymer" refers to oligomers and homopolymers (e.g., prepared from a single monomer species), copolymers (e.g., prepared from at least two monomer species), and graft polymers. The term "resin" is used interchangeably with "polymer.

Non-limiting examples of suitable polyester polymers that can be used in the powder coating compositions of the present invention include polyester polymers based on a condensation reaction of aliphatic polyols, including cycloaliphatic polyols, with aliphatic and/or aromatic polycarboxylic acids and anhydrides. The term "aliphatic" refers to non-aromatic straight, branched, or cyclic hydrocarbon structures that contain saturated carbon bonds. The saturated carbon chain or chains of the aliphatic structures can also comprise and be interrupted by other elements including, but not limited to, oxygen, nitrogen, carbonyl groups, and combinations thereof. Thus, the saturated carbon chain of the aliphatic structures can comprise, but is not limited to, ether groups, ester groups, and combinations thereof. Further, the term "aromatic" refers to a cyclically conjugated hydrocarbon with a stability (due to electron delocalization) that is significantly greater than that of a hypothetical localized structure.

As used herein, a "polyol" refers to a compound comprising two or more hydroxyl groups. Aliphatic polyols that can be used to prepare polyester polymers useful in the powder coating compositions of the present invention can for example comprise from <NUM> to <NUM> carbon atoms. Non-limiting examples of suitable aliphatic polyols include <NUM>,<NUM>-ethanediol, <NUM>,<NUM>-propanediol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-hexanediol, neopentyl glycol, cyclohexane dimethanol and trimethylol propane.

A "polycarboxylic acid" refers to an organic compound with two or more carboxylic acid groups, or an anhydride of the acid. The polycarboxylic acid or anhydride may be an aromatic and/or cyclic polycarboxylic acid or anhydride thereof. As used herein, a "cyclic polycarboxylic acid" refers to a component comprising at least one closed ring structure, such as a carbocycle, for example an aromatic ring structure, with two or more carboxylic acid groups or the anhydride of the acid. The cyclic polycarboxylic acid, typically a cyclic diacid, can include aromatic cyclic polycarboxylic acids, aliphatic cyclic polycarboxylic acids, and combinations thereof. Non-limiting examples of aromatic cyclic polycarboxylic acids, or the anhydride thereof, include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic anhydride, trimellitic acid, trimellitic anhydride, and combinations thereof. Non-limiting examples of aliphatic non-aromatic cyclic polycarboxylic acids, or the anhydride thereof, include <NUM>,<NUM>-cyclohexanedicarboxylic acid, <NUM>,<NUM>-cyclohexanedicarboxylic acid, decahydronaphthalene dicarboxylic acid, <NUM>,<NUM>-cyclopentanedicarboxylic acid, <NUM>,<NUM>-cyclopropanedicarboxylic acid, tetrahydrophthalic acid, hexahydrophthalic acid, hexahydrophthalic anhydride, and combinations thereof. Other suitable polycarboxylic acids and anhydrides include linear aliphatic polycarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, and anhydrides of such acids. The polyol and the polycarboxylic acid may be reacted with a molar excess of the polycarboxylic acid over polyol so as to form a polyester with carboxylic acid functionality. Suitable polyester polymers are also commercially available from Arkema under the trade name REAFREE® and from Royal DSM under the trade name URALAC®.

The polyester polymer used with the powder coating composition is a thermoset polymer. By "thermoset polymer" it is meant a polymer having functional groups that are reactive with themselves and/or a crosslinking agent, and upon such reaction (referred to as curing), the polymer forms irreversible covalent bonds. Once cured or crosslinked, a thermoset polymer will not melt upon the application of heat and is insoluble in solvents.

The terms "curable", "cure", and the like, as used in connection with a coating composition, means that at least a portion of the components that make up the coating composition are polymerizable and/or crosslinkable. The coating composition of the present invention can be cured at ambient conditions, with heat, or with other means such as actinic radiation. The term "actinic radiation" refers to electromagnetic radiation that can initiate chemical reactions. Actinic radiation includes, but is not limited to, visible light, ultraviolet (UV) light, X-ray, and gamma radiation. Further, "ambient conditions" refers to the conditions of the surrounding environment (e.g., the temperature, humidity, and pressure of the room or outdoor environment in which the substrate is located such as, for example, at a temperature of <NUM> and at a relative humidity in the air of <NUM>% to <NUM>%).

The polyester polymers used with the powder coating composition of the present invention comprise carboxylic acid functional groups that are reactive with the first crosslinker, which is described in further detail herein. The polyester polymers used with the powder coating compositions of the present invention can also include additional functional groups such as, for example, epoxide groups, hydroxyl groups, amine groups, alkoxy groups, thiol groups, carbamate groups, amide groups, urea groups, and combinations thereof. The polyester polymers used with the present invention can also be free of any one of the previously described additional functional groups.

The polyester polymer used with the powder coating compositions of the present invention can comprise at least <NUM> weight %, at least <NUM> weight %, at least <NUM> weight %, at least <NUM> weight %, <NUM> weight %, at least <NUM> weight %, at least <NUM> weight %, at least <NUM> weight %, or at least <NUM> weight %, based on the total solids weight of the powder coating composition. The polyester polymers used with the coating compositions of the present invention can comprise up to <NUM> weight %, or up to <NUM> weight %, based on the total solids weight of the coating composition. The polyester polymers can also comprise a range such as from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, or from <NUM> to <NUM> weight %, based on the total solids weight of the coating composition.

The polyester polymers can have an acid value of at least <NUM> KOH/g, at least <NUM> KOH/g, or at least <NUM> KOH/g. The polyester can have an acid value of up to <NUM> KOH/g, up to <NUM> KOH/g, or up to <NUM> KOH/g. The polyester can have an acid value in the range such as from <NUM> to <NUM> KOH/g, from <NUM> to <NUM> KOH/g, or from <NUM> to <NUM> KOH/g. The acid value is expressed on solids.

The acid value of the polyester polymers may be measured by any suitable method. Methods to measure acid value will be well known to a person skilled in the art. Suitably, the acid value is determined by titration with <NUM> methanolic potassium hydroxide (KOH) solution. A sample of solid polyester (typically, <NUM> to <NUM>) is weighed accurately into a conical flask and is dissolved, using light heating and stirring as appropriate, in <NUM> of dimethyl formamide containing phenolphthalein indicator. The solution is then cooled to room temperature and titrated with the <NUM> methanolic potassium hydroxide solution. The resulting acid number is expressed in units of mg KOH/g and is calculated using the following equation: <MAT>.

The polyester polymers used with the powder coating compositions of the present invention can have a hydroxyl value of less than <NUM> KOH/g, less than <NUM> KOH/g, less than <NUM> KOH/g, less than <NUM> KOH/g, or less than <NUM> KOH/g. The polyester polymers can have a hydroxyl value within a range of from <NUM> to <NUM> KOH/g, from <NUM> to <NUM> KOH/g, from <NUM> to <NUM> KOH/g, from <NUM> to <NUM> KOH/g, from <NUM> to <NUM> KOH/g, or from <NUM> to <NUM> KOH/g.

The polyester polymers used according to the present invention can have a glass transition temperature ("Tg") of at least <NUM>, at least <NUM>, or at least <NUM>. The polyester polymers can have a Tg of up to <NUM>, up to <NUM>, or up to <NUM>. The polyester polymers can have a Tg in a range such as from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>. Glass transition temperature ("Tg"), as reported herein, was measured by differential scanning calorimetry according to ASTM D3418-<NUM> unless otherwise indicated.

The polyester polymers can have a melt viscosity at <NUM> of at least <NUM> Pa·s, at least <NUM> Pa·s, or at least <NUM> Pa·s. The polyester polymers can have a melt viscosity at <NUM> of up to <NUM> Pa·s, up to <NUM> Pa·s, or up to <NUM> Pa·s. The polyester polymers can have a melt viscosity at <NUM> within a range such as from <NUM> to <NUM> Pa·s, from <NUM> to <NUM> Pa·s, or from <NUM> to <NUM> Pa·s. As used herein, the melt viscosity is measured by a Cone and Plate Viscometer made by Research Equipment (London) Ltd. Reference may be made to ASTM D <NUM>.

The polyester polymers can have a weight average molecular weight (Mw) of at least <NUM>,<NUM>/mol, at least <NUM>,<NUM>/mol, or at least <NUM>,<NUM>/mol. The polyester polymers can have a Mw of up to <NUM>,<NUM>/mol, up to <NUM>,<NUM>/mol, up to <NUM>,<NUM>/mol, or up to <NUM>,<NUM>/mol. The polyester polymers can have a Mw within a range such as from <NUM>,<NUM> to <NUM>,<NUM>/mol, from <NUM>,<NUM> to <NUM>,<NUM>/mol, from <NUM>,<NUM> to <NUM>,<NUM>/mol, or from <NUM>,<NUM> to <NUM>,<NUM>/mol. As used herein, the Mw is measured by gel permeation chromatography using a polystyrene standard according to ASTM D6579-<NUM> (performed using a Waters <NUM> separation module with a Waters <NUM> differential refractometer (RI detector); tetrahydrofuran (THF) was used as the eluent at a flow rate of <NUM>/min, and two PLgel Mixed-C (<NUM>×<NUM>) columns were used for separation at the room temperature; weight and number average molecular weight of polymeric samples can be measured by gel permeation chromatography relative to linear polystyrene standards of <NUM> to <NUM>,<NUM> Da) unless otherwise indicated.

The powder coating composition of the present invention also includes a fluoropolymer. The fluoropolymer may be a thermoplastic polymer. A "thermoplastic polymer" refers to a polymer that can be heated to become pliable or moldable and re-solidify upon cooling. It is appreciated that the fluoropolymer does not react with the polyester polymer or first crosslinker. Further, the fluoropolymer may not react with any other optional component in the powder coating composition so that the fluoropolymer does not chemically bond with such components. As such, the fluoropolymer may be an inert component.

In one non-limiting embodiment of the powder coating composition of the present invention, the fluoropolymer may react with a second crosslinker such that the fluoropolymer is at least partially crosslinked.

As used herein, a "fluoropolymer" refers to a polymer derived from one or more monomers with at least one of the monomers having at least one pendant fluorine substituent. For example, the fluoropolymer can include a polymer that has one or more monomeric repeat unit(s) selected from chlorotrifluoroethylene, tetrafluoroethylene, perfluoro(methyl vinyl ether), perfluoro(propyl vinyl ether), perfluoro(ethyl vinyl ether), vinylidene fluoride, hexafluoropropylene, and combinations thereof. The fluoropolymer can also include a polymer that has a monomeric repeat unit selected from tetrafluoroethylene oxide, hexafluoropropylene oxide, and combinations thereof.

Non-limiting examples of suitable fluoropolymers that can be used with the coating compositions of the present invention include a fluoropolyether, a perfluoropolyether, a chlorotrifluoroethylene polymer, a polyvinylidene fluoride polymer, a tetrafluoroethylene polymer, polyhexafluoropropylene, polytetrafluoroethylene, and copolymers and/or combinations thereof. Suitable fluoropolyether polymers include, but are not limited to, fluoroethylene vinyl ether copolymers. Suitable fluoropolymers are also commercially available from Asahi Glass Co. under the trade name LUMIFLON® and from Arkema under the trade name KYNAR®.

Further, as previously mentioned, the fluoropolymer is unreactive with the polyester polymer and first crosslinker. As such, the fluoropolymer does not comprise functional groups that are reactive with and which can chemically bond to the functional groups of the polyester polymer or first crosslinker. It is appreciated that the fluoropolymer may have reactive functional groups, provided that the reactive functional groups do not react and bond with the polyester polymer or first crosslinker. The fluoropolymer may comprise functional groups that are reactive with a second crosslinker, wherein the second crosslinker is different from the first crosslinker. Non-limiting examples of reactive functional groups include hydroxyl groups, thiol groups, (meth)acrylate groups, amine groups, carbamate groups, amide groups, urea groups, and combinations thereof. As used herein, the term "(meth)acrylate" refers to both the methacrylate and the acrylate. The fluoropolymer may also be free of any one of the previously described reactive functional groups.

The fluoropolymer used with the coating compositions of the present invention can comprise at least <NUM> weight %, at least <NUM> weight %, at least <NUM> weight %, at least <NUM> weight %, at least <NUM> weight %, or at least <NUM> weight %, based on the total solids weight of the powder coating composition. The fluoropolymer used with the coating compositions of the present invention can comprise up to <NUM> weight %, or up to <NUM> weight %, based on the total solids weight of the coating composition. The fluoropolymer can also comprise a range such as from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, or from <NUM> to <NUM> weight %, based on the total solids weight of the coating composition.

The fluoropolymer can have a glass transition temperature (Tg) of at least <NUM>, at least <NUM>, or at least <NUM>. The fluoropolymer can have a Tg of up to <NUM>, up to <NUM>, or up to <NUM>. The fluoropolymer can have a Tg in a range such as from <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>.

The fluoropolymer can have a weight average molecular weight (Mw) of at least <NUM>,<NUM>/mol, at least <NUM>,<NUM>/mol, or at least <NUM>,<NUM>/mol. The fluoropolymer can have a Mw of up to <NUM>,<NUM>/mol, up to <NUM>,<NUM>/mol, up to <NUM>,<NUM>/mol. The fluoropolymer can have a Mw within a range such as from <NUM>,<NUM> to <NUM>,<NUM>/mol, from <NUM>,<NUM> to <NUM>,<NUM>/mol, or from <NUM>,<NUM> to <NUM>,<NUM>/mol.

The amount of polyester polymer in the powder coating composition is greater than the amount of fluoropolymer, based on the total resin solids weight of the powder coating composition. The powder coating composition may have a weight ratio of the polyester polymer to the fluoropolymer of from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>.

It has been found that the powder coating composition of the present invention, when cured to form a coating, may form a single coating layer comprising the polyester polymer and the fluoropolymer. The fluoropolymer and the polyester polymer are dispersed throughout the single layer coating such that separate layers do not form, as observed by Scanning Electron Microscopy. The single coating layer comprising the polyester polymer and the fluoropolymer may include phase separation, provided that the phase comprising the fluoropolymer and the phase comprising the polyester polymer are distributed throughout the single layer. For example, the single coating layer may include pockets of the phase comprising the fluoropolymer dispersed throughout the phase comprising the polyester polymer. The single coating layer may be a non-homogenous coating layer. The powder coating composition of the present invention may be applied to a substrate such that, when cured, both the polyester polymer and the fluoropolymer are in direct contact with the substrate. The powder coating composition of the present invention may be applied to a substrate such that it is not layer-separated when cured and does not provide a cured film having a bilayer structure.

As indicated, the coating composition also comprises a first crosslinker that is reactive with the carboxylic acid functional groups of the polyester polymer. As used herein, a "crosslinker" refers to a molecule comprising two or more functional groups that are reactive with other functional groups and which is capable of linking two or more monomers or polymer molecules through chemical bonds. It will be appreciated that the polyester polymer of the present invention can cure through the reaction between the carboxylic acid functional groups of the polyester polymer, and the functional groups of the first crosslinker.

Non-limiting examples of suitable first crosslinkers include phenolic compounds, epoxy compounds, triglycidyl isocyanurate (TGIC), (meth)acrylic compounds, hydroxyalkyl amide compounds, alkylated carbamate resins, polyacids, anhydrides, organometallic acid-functional materials, polyamines, polyamides, aminoplasts, and mixtures thereof. As such, the first crosslinker can comprise, but is not limited to, compounds comprising epoxide groups, acids groups, anhydride groups, hydroxyl groups, amino groups such as primary and secondary amino groups, amide groups, aminoplast based compounds, and combinations thereof.

Non-limiting examples of (meth)acrylic crosslinkers include epoxy functional (meth)acrylic compounds, such as glycidyl functional (meth)acrylic compounds, or other (meth)acrylic compounds having a functional group reactive with the carboxylic acid of the polyester polymer. As used herein, the term "(meth)acrylic" refers to both methacrylic and acrylic. An example of a suitable epoxy functional (meth)acrylic compound is ISOCRYL EP-<NUM>® which is commercially available from Estron Chemical.

Non-limiting examples of hydroxylalkyl amide crosslinkers include beta-hydroxylalkylamide compounds such as beta-hydroxyethylamide compounds. An example of a suitable hydroxylalkylamide compound is LUNAMER <NUM>® which is commercially available from DKSH.

The first crosslinker may comprise only one crosslinker, two crosslinkers, or more than two crosslinkers that are reactive with the carboxylic acid groups of the polyester polymer. For example the powder coating composition according to the present invention may comprise a hydroxylalkyl amide compound, an epoxy functional compound, such as an epoxy functional (meth)acrylic compound, or a combination thereof. For example, the powder coating composition may include both a hydroxylalkyl amide compound and a functional (meth)acrylic compound, such as an epoxy functional (meth)acrylic compound, as first crosslinkers. The amount of the functional (meth)acrylic compound in the powder coating composition may be greater than the amount of the hydroxylalkyl amide compound, based on the total solids weight of the powder coating composition. The ratio of hydroxylalkyl amide crosslinker to functional (meth)acrylic crosslinker in the powder coating composition may be from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>. The functional (meth)acrylic crosslinker may be used with the powder coating composition both as a crosslinker and as a matting agent to reduce the gloss of the resulting coating.

The first crosslinker(s) can comprise at least <NUM> weight %, at least <NUM> weight %, or at least <NUM> weight % of the powder coating composition, based on the total solids weight of the coating composition. The first crosslinker(s) can comprise up to <NUM> weight %, up to <NUM> weight %, or up to <NUM> weight %, up to <NUM> weight %, or up to <NUM> weight % of the coating composition, based on the total solids weight of the coating composition. The first crosslinker(s) can also comprise an amount within a range such as from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, or from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, or from <NUM> to <NUM> weight % of the coating composition, based on the total solids weight of the coating composition.

Further, the first crosslinker can also be added to the coating composition such that an equivalent ratio of the reactive functional groups on the first crosslinker to reactive functional groups on the polyester polymer is from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>. For example, the first crosslinker can comprise hydroxyl groups and the polyester polymer can comprise carboxylic acid groups such that a ratio of total hydroxyl equivalents to total carboxylic acid equivalents is from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>.

The powder coating composition of the present invention may further comprise a second crosslinker that is reactive with the fluoropolymer. The use of a second crosslinker may result in a powder coating composition exhibiting enhanced solvent resistance. The second crosslinker may be an isocyanate functional crosslinker, such as a blocked isocyanate. The isocyanate functional crosslinker can comprise at least <NUM> weight %, at least <NUM> weight %, at least <NUM> weight %, or at least <NUM> weight % of the powder coating composition, based on the total solids weights of the coating composition. The isocyanate functional crosslinker can comprise up to <NUM> weight %, up to <NUM> weight %, or up to <NUM> weight % of the coating composition, based on the total solids weight of the coating composition. The isocyanate functional crosslinker can comprise an amount within a range such as from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, or from <NUM> to <NUM> weight % of the coating composition, based on the total solids weight of the coating composition.

The optional second crosslinker may be reactive with the fluoropolymer through the reaction between the functional groups of the fluoropolymer, such as hydroxyl groups, and the functional groups of the second crosslinker. In one non-limiting embodiment of the powder coating composition of the present invention, the second crosslinker may react with only a portion of the functional groups of the fluoropolymer such that the fluoropolymer is not fully crosslinked, as determined by the stoichiometry of the functional groups of the fluoropolymer and the second crosslinker. The second crosslinker can be added to the coating composition such that an equivalent ratio of the reactive functional groups on the second crosslinker to reactive functional groups on the fluoropolymer is less than <NUM>:<NUM>, less than <NUM>:<NUM>, less than <NUM>:<NUM>, less than <NUM>:<NUM>, less than <NUM>:<NUM>, less than <NUM>:<NUM>, less than <NUM>:<NUM>, less than <NUM>:<NUM>, or less than <NUM>:<NUM>. The second crosslinker can be added to the coating composition such that an equivalent ratio of the reactive functional groups on the second crosslinker to reactive functional groups on the fluoropolymer is at least <NUM>:<NUM>, at least <NUM>:<NUM>, at least <NUM>:<NUM>, at least <NUM>:<NUM>, at least <NUM>:<NUM>, or at least <NUM>:<NUM>. For example, the second crosslinker can comprise isocyanate groups and the fluoropolymer can comprise hydroxyl groups such that a ratio of total isocyanate equivalents to total hydroxyl group equivalents is from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>.

The powder coating composition may be free of a second crosslinker. The powder coating composition of the present invention may be substantially free, essentially free, or completely free of an isocyanate functional crosslinker. The term "substantially free" as used in this context means the powder coating composition contains less than <NUM> parts per million (ppm) of an isocyanate functional crosslinker based on the total solids weight of the coating composition, "essentially free" means less than <NUM> ppm of an isocyanate functional crosslinker based on the total solids weight of the coating composition, and "completely free" means less than <NUM> parts per billion (ppb) of an isocyanate functional crosslinker based on the total solids weight of the coating composition.

The coating composition of the present invention can also include a matting agent. As used herein, the term "matting agent" refers to a material added to a coating composition to reduce the gloss of a coating formed from the composition. The term "matting agent" is interchangeable with the term "flatting agent". The matting agent can also provide other properties in the final coating. For instance, the matting agent can also improve abrasion, rub, and/or scratch resistance; control viscosity; and/or enhance soft touch properties in the final coating. Non-limiting examples of suitable matting agents include metal hydroxides, metal oxides, silicas, pyrogenic silica, wax-treated silica, micronized wax, polyether condensate, polyamide microbeads, polyurethane microbeads, silicone microbeads, (meth)acrylic compounds, and mixtures thereof.

The first crosslinker used with the present invention may also function as a matting agent. For instance, the coating composition may utilize a functional (meth)acrylic compound, such as an epoxy functional (meth)acrylic compound, that also functions as a matting agent. It has been found that functional (meth)acrylic compounds provide better performance as matting agents, including but not limited to weatherability performance, as compared to other matting agents that do not crosslink or react with the carboxylic acid groups of the polyester polymer.

The coating compositions of the present invention can also include other optional materials. For example, the coating compositions can also comprise a colorant. As used herein, "colorant" refers to any substance that imparts color and/or other opacity and/or other visual effect to the composition. The colorant can be added to the coating in any suitable form, such as discrete particles, dispersions, solutions, and/or flakes. A single colorant or a mixture of two or more colorants can be used in the coatings of the present invention.

Example colorants include pigments (organic or inorganic), dyes and tints, such as those used in the paint industry and/or listed in the Dry Color Manufacturers Association (DCMA), as well as special effect compositions. A colorant may include, for example, a finely divided solid powder that is insoluble, but wettable, under the conditions of use. A colorant can be organic or inorganic and can be agglomerated or non-agglomerated. Colorants can be incorporated into the coatings by use of a grind vehicle, such as an acrylic grind vehicle, the use of which will be familiar to one skilled in the art.

Example pigments and/or pigment compositions include, but are not limited to, carbazole dioxazine crude pigment, azo, monoazo, diazo, naphthol AS, salt type (flakes), benzimidazolone, isoindolinone, isoindoline and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolo pyrrole, thioindigo, anthraquinone, indanthrone, anthrapyrimidine, flavanthrone, pyranthrone, anthanthrone, dioxazine, triarylcarbonium, quinophthalone pigments, diketo pyrrolo pyrrole red ("DPPBO red"), titanium dioxide, carbon black, and mixtures thereof. The terms "pigment" and "colored filler" can be used interchangeably.

Other examples of pigments include, but are not limited to, those that are solvent and/or aqueous based such as phthalo green or blue, iron oxide, bismuth vanadate, anthraquinone, and perylene and quinacridone.

Example tints include, but are not limited to, pigments dispersed in water-based or water miscible carriers such as AQUA-CHEM <NUM> commercially available from Degussa, Inc. , CHARISMA COLORANTS and MAXITONER INDUSTRIAL COLORANTS commercially available from Accurate Dispersions Division of Eastman Chemical, Inc.

It is appreciated that the colorants used with the powder coating composition can be selected for use with certain substrates in certain areas. For example, the colorants can be selected, as determined by one skilled in the art, for use with architectural base substrates. Non-limiting examples of colorants that may be used in the architectural industry include carbon black, C. Pigment Black <NUM>, C. Pigment Red <NUM>, C. Pigment Brown <NUM>, titanium dioxide, mica-based pigments, barium sulfate, or combinations thereof.

The colorant(s) can comprise at least <NUM> weight %, at least <NUM> weight %, or at least <NUM> weight % of the powder coating composition, based on the total solids weight of the coating composition. The colorant(s) can comprise up to <NUM> weight %, up to <NUM> weight %, or up to <NUM> weight % of the coating composition, based on the total solids weight of the coating composition. The colorant(s) can also comprise an amount within a range such as from <NUM> to <NUM> weight %, from <NUM> to <NUM> weight %, or from <NUM> to <NUM> weight % of the coating composition, based on the total solids weight of the coating composition.

The powder coating composition may include various other additives. Non-limiting examples of materials that can be used with the powder coating compositions of the present invention include plasticizers, anti-oxidants, flow and surface control agents such as waxes (e.g., amide waxes), flow and leveling control agents such as acrylic and/or silica agents, thixotropic agents, slip aids, catalysts such as metal catalysts (e.g., tin catalysts), anti-gassing agents such as benzoin, reaction inhibitors, texturizers, and other customary auxiliaries.

The powder coating composition and/or the coating system according to the present invention may also be substantially free, may be essentially free or may be completely free of triglycidyl isocyanurate (TGIC). The term "substantially free" as used in this context means the powder coating composition contains less than <NUM> parts per million (ppm) of a component based on the total solids weight of the coating composition, "essentially free" means less than <NUM> ppm of a component based on the total solids weight of the coating composition, and "completely free" means less than <NUM> parts per billion (ppb) of a component based on the total solids weight of the coating composition. Further, the powder coating composition may be substantially free, may be essentially free or may be completely free of epsilon-caprolactam. Further still, the powder coating composition may be substantially free, may be essentially free, or may be completely free (as defined above) of an organic ultraviolet absorber. An "ultraviolet absorber", as used herein, refers to a compound that absorbs ultraviolet radiation to reduce the ultraviolet degradation of a material. Non-limiting examples of organic ultraviolet absorbers include a salicylate, a benzotriazole, a benzophenone, or a cyanoacrylate compound. The powder coating composition may be substantially free, may be essentially free, or may be completely free (as defined above) of an inorganic ultraviolet absorber. Non-limiting examples of inorganic ultraviolet absorbers include cerium oxide and zinc oxide. The powder coating composition may be substantially free, may be essentially free, or may be completely free (as defined above) of a hindered amine light stabilizer.

The powder coating composition of the present invention can be prepared by mixing the previously described polyester polymer, fluoropolymer, first crosslinker, and optional additional components, if used. The components can be mixed using art-recognized techniques and equipment such as with a Prism high speed mixer for example. When a solid coating composition is formed, the mixture is next melted and further mixed. The mixture can be melted with a twin screw extruder or a similar apparatus known in the art. During the melting process, the temperatures will be chosen to melt mix the solid mixture without curing the mixture. The mixture can be melt mixed in a twin screw extruder with zones set to a temperature of <NUM> to <NUM>, such as from <NUM> to <NUM> or at about <NUM>. After melt mixing, the mixture is cooled and re-solidified. The re-solidified mixture is then ground such as in a milling process to form a solid particulate curable powder coating composition.

The re-solidified mixture can be ground to any desired particle size. For example, the re-solidified mixture can be ground to an average particle size of at least <NUM> (microns) or at least <NUM> (microns) and up to <NUM> (microns) as determined with a Malvern Mastersizer <NUM> Laser Diffraction Particle Size Analyzer following the instructions described in the Malvern Mastersizer <NUM> manual. The powder may have an average particle size from <NUM> to <NUM> (microns), such as from <NUM>-<NUM> (microns), from <NUM>-<NUM> (microns), from <NUM>-<NUM> (microns), from <NUM>-<NUM> (microns), or from <NUM>-<NUM> (microns). Further, the particle size range of the total amount of particles in a sample used to determine the average particle size can comprise a range of from <NUM> (micron) to <NUM> (microns), or from <NUM> (microns) to <NUM> (microns), or from <NUM> (microns) to <NUM> (microns), which is also determined with a Malvern Mastersizer <NUM> Laser Diffraction Particle Size Analyzer following the instructions described in the Malvern Mastersizer <NUM> manual.

After forming the coating composition of the present invention, the composition can be applied to a wide range of substrates known in the coatings industry. For example, the coating composition of the present invention can be applied to automotive substrates and components (e.g. automotive vehicles including, but not limited to, cars, buses, trucks and trailers), industrial substrates, aircraft and aircraft components, marine substrates and components such as ships, vessels, and on-shore and off-shore installations, storage tanks, windmills, nuclear plants, heavy equipment (e.g. heavy machines, heavy trucks, construction equipment, heavy vehicles, heavy hydraulics), packaging substrates, wood flooring and furniture, apparel, electronics, including housings and circuit boards, glass and transparencies, sports equipment, including golf balls, stadiums, buildings and bridges. These substrates can be, for example, metallic or non-metallic.

Metallic substrates include, but are not limited to, tin, steel (including electrogalvanized steel, cold rolled steel, hot-dipped galvanized steel, steel alloys, or blasted/profiled steel, among others), aluminum, aluminum alloys, zinc-aluminum alloys, steel coated with a zinc-aluminum alloy, and aluminum plated steel. As used herein, blasted or profiled steel refers to steel that has been subjected to abrasive blasting and which involves mechanical cleaning by continuously impacting the steel substrate with abrasive particles at high velocities using compressed air or by centrifugal impellers. The abrasives are typically recycled/reused materials and the process can efficiently remove mill scale and rust. The standard grades of cleanliness for abrasive blast cleaning is conducted in accordance with BS EN ISO <NUM>-<NUM>.

Further, non-metallic substrates include polymeric and plastic substrates including polyester, polyolefin, polyamide, cellulosic, polystyrene, polyacrylic, poly(ethylene naphthalate), polypropylene, polyethylene, nylon, EVOH, polylactic acid, other "green" polymeric substrates, poly(ethylene terephthalate) (PET), polycarbonate, polycarbonate acrylobutadiene styrene (PC/ABS), polyamide, wood, veneer, wood composite, particle board, medium density fiberboard, cement, stone, glass, paper, cardboard, textiles and leather, both synthetic and natural. It is appreciated that the coating compositions can be applied to various areas of any of the previously described substrates to form a continuous solid coating such as over the body and edges of a substrate and which provides the superior properties described herein.

The coatings of the present invention are particularly useful when applied in architectural applications. For example, the coatings of the present invention can be applied to substrates such as windows, roofing, siding, door frames and railings.

The coating compositions of the present invention can be applied by any means standard in the art, such as spraying and electrostatic spraying. After the coating compositions are applied to a substrate, the compositions can be cured at ambient conditions, with heat, or with other means such as actinic radiation to form a coating, such as a single coating layer.

The coatings formed from the coating compositions of the present invention can be applied to a dry film thickness of less than <NUM> (<NUM> mils), less than <NUM> (<NUM> mils), less than <NUM> (<NUM> mils), less than <NUM> (<NUM> mils), or less than <NUM> (<NUM> mils), such as <NUM> (<NUM> mils).

The coating composition can be applied to a substrate to form a monocoat. As used herein, a "monocoat" refers to a single layer coating system that is free of additional coating layers. Thus, the coating composition can be applied directly to a substrate without any intermediate coating layer and cured to form a single layer coating, i.e. a monocoat.

Alternatively, the coating composition can be applied to a substrate as a first coating layer along with additional coating layers, such as a second coating layer, to form a multi-layer coating system. It is appreciated that the multi-layer coating can comprise multiple coating layers such as three or more, or four or more, or five or more, coating layers. For example, the previously described coating composition of the present invention can be applied to a substrate as a primer layer and second and third coating layers, and, optionally, additional coatings layers, can be applied over the primer layer as basecoats and/or topcoats. As used herein, a "primer" refers to a coating composition from which an undercoating may be deposited onto a substrate in order to prepare the surface for application of a protective or decorative coating system. A "basecoat" refers to a coating composition from which a coating is deposited onto a primer and/or directly onto a substrate, optionally, including components (such as pigments) that impact the color and/or provide other visual impact, and which may be overcoated with a protective and decorative topcoat. Alternatively, the coating composition of the present invention may be applied as a basecoat and/or a topcoat over a primer layer. The coating composition of the present invention may be applied over another coating system, which may enhance the weatherability of the coating system.

The powder coating compositions of the present invention can be applied to a substrate and cured to have coatings which have a broad gloss range available. For example, coatings formed from the powder coating compositions described herein can exhibit a low <NUM> Degree Gloss, such as less than <NUM>, less than <NUM>, less than <NUM>, or less than <NUM>, as measured by ASTM D523-<NUM> test method using a BYK Gardner micro-TRI-gloss meter. However, coatings formed from the powder coating compositions described herein may also exhibit a high <NUM> Degree Gloss, such as at least <NUM>, or at least <NUM>. The coating compositions of the present invention are formulated to maintain good durability with and without the presence of matting agents to allow for a broad variety of gloss in the cured coatings.

The powder coating compositions of the present invention can be applied to a substrate to provide durable coatings as exhibited by good adhesion, impact resistance, corrosion resistance, and humidity resistance. For example, coatings formed from the powder coating compositions described herein have been found to exhibit one or more than one, or all of the following: less than <NUM>% area removed in Dry Adhesion tests, such as <NUM>% area removed, as measured by ASTM D3359-<NUM> test method B; less than <NUM>% area removed in Boiling Adhesion tests, such as less than <NUM>% area removed, such as <NUM>% area removed, as measured by ASTM AAMA <NUM>-17A Section <NUM>. <NUM> and ASTM D3359-<NUM> test method B; a Pass in Forward Impact Resistance test, as measured by AAMA <NUM>-17A Section <NUM>; less than <NUM>% area removed in Reverse Impact Tests, such as less than <NUM>% area removed, as measured by AAMA <NUM>-17A Section <NUM> when the impact is applied to the opposite side of the coating and <NUM>. 025x3x6 inch (<NUM>. 0635x7.62x15. <NUM>) aluminum panels with no pretreatment are used; less than <NUM> average scribe creepage in Cyclic Corrosion Resistance tests, such as less than <NUM>, as measured by AAMA <NUM>-17A Section <NUM>. <NUM> and ASTM G85, Annex A5 and ASTM D <NUM>; less than <NUM> average scribe creepage in <NUM> hr. Copper Accelerated Acetic-Acid Salt Spray corrosion tests, such as less than <NUM>, as measured by ASTM B368 and ASTM D <NUM>; and the observation of no blisters in Humidity Resistance tests as measured by AAMA <NUM>-17A Section <NUM>. <NUM> and ASTM D4585-<NUM>.

Thus, the powder coating compositions described herein can be applied to a substrate to form coatings with good weatherability and corrosion resistance, and other properties desired in a coating. Moreover, the coating compositions utilize polyester polymers to form the crosslinked coating, thereby lowering the amount of fluoropolymer required in the coating composition and reducing the cost of the required raw materials.

The following examples are presented to demonstrate the general principles of the invention. The invention should not be considered as limited to the specific examples presented. All parts and percentages in the examples are by weight unless otherwise indicated.

Seven (<NUM>) curable coating compositions were prepared from the components listed in Table <NUM>. Example <NUM> is not according to the invention.

For Examples <NUM>-<NUM> and <NUM>, each of the components listed in Table <NUM> were weighed in a plastic bag and mixed by shaking vigorously in the bag for <NUM> seconds to form a dry homogeneous mixture. For Example <NUM>, the first eleven ingredients listed in Table <NUM> were used to form an intermediate solid particulate powder coating composition. This intermediate solid particulate powder coating composition was weighed in a plastic bag along with the final two ingredients in Table <NUM> and mixed by shaking vigorously in the bag for <NUM> seconds to yield a final solid particulate powder coating composition that is free flowing.

Each mixture was melt mixed in a Theysohn <NUM> twin screw extruder with a moderately aggressive screw configuration and a speed of <NUM> RPM. The first extruder zone was set at <NUM>, and the second zone was set to <NUM>. The feed rate was such that a torque of <NUM>-<NUM>% was observed on the equipment. The mixtures were dropped onto a set of chill rolls to cool and re-solidify the mixtures into solid chips. The chips were milled using a coffee grinder and sieved through a <NUM> (micron) screen to obtain a mass median diameter particle size of <NUM>-<NUM> (microns). The resulting coating compositions for each of Examples <NUM>-<NUM> were solid particulate powder coating compositions that were free flowing.

All powder coating compositions from Examples <NUM>-<NUM> were applied over several chromate pretreated <NUM> (<NUM> inch) by <NUM> (<NUM> inch) by <NUM> (<NUM> inch) aluminum panels at film thicknesses shown in Table <NUM> and heated for <NUM> minutes at <NUM> (<NUM>°F). Various properties of the cured coatings, determined by tests performed on these coated panels, are shown in Table <NUM>.

As shown in Table <NUM>, the coatings prepared from the coating compositions of Examples <NUM> -<NUM> of the present invention exhibit a broad gloss range, good adhesion, impact resistance, corrosion resistance, and humidity resistance.

<FIG> and <FIG> show Scanning Electron Microscopy (SEM) images for the cured coatings of Examples <NUM> and <NUM>, respectively. As shown in the images, the cured coatings form a single coating layer comprising the polyester polymer and the fluoropolymer. The single coating layer is non-homogenous with phase separation.

Two <NUM> x <NUM> (<NUM>"x1") square sections were cut out and removed from the coated panels. Sections were prepared for top-down SEM/Energy-dispersive X-ray spectroscopy (EDX) analysis by placing the samples onto SEM stubs with carbon tape and sputter coating with Au/Pd for approximately <NUM> seconds. Sections were also prepared for cross-sectional SEM/EDX analysis by mounting the samples in epoxy to cure overnight, sanding and polishing the mounted samples, and sputter-coating with Au/Pd for approximately <NUM> seconds.

<FIG> and <FIG> show the cross-sectional SEM/EDX images for the coating compositions of Examples <NUM> and <NUM>, respectively. Elemental mapping is shown for carbon (C), oxygen (O), fluorine (F), aluminum (Al), silicon (Si), chlorine (Cl), titanium (Ti), and manganese (Mn). Aluminum and manganese are contributions from the substrate. Fluorine and chlorine can be found in pockets, indicating that there is phase separation between the fluoropolymer and the polyester polymer. The elemental mapping shows that the darker colored phases in <FIG> and <FIG> contain the fluoropolymer and the lighter colored phases contain the polyester polymer. The pockets containing the fluoropolymer are dispersed throughout the phase containing the polyester polymer to form a single coating layer and do not result in layer separation. Both the fluoropolymer and the polyester polymer are in direct contact with the substrate.

Four (<NUM>) curable coating compositions were prepared from the components listed in Table <NUM>. Example <NUM> is not according to the invention.

Each of the components listed in Table <NUM> for Examples <NUM>-<NUM> were weighed in a plastic bag and mixed by shaking vigorously in the bag for <NUM> seconds to form a dry homogeneous mixture. The mixture was melt mixed in a Werner & Pfleiderer <NUM> twin screw extruder with a moderately aggressive screw configuration and a speed of <NUM> RPM. The first extruder zone was set at <NUM>, and the second zone was set to <NUM>. The feed rate was such that a torque of <NUM>-<NUM>% was observed on the equipment. The mixtures were dropped onto a set of chill rolls to cool and re-solidify the mixtures into solid chips. The chips were milled using a coffee grinder and sieved through a <NUM> (micron) screen to obtain a mass median diameter particle size of <NUM>-<NUM> (microns). The resulting coating compositions for each of Examples <NUM>-<NUM> were solid particulate powder coating compositions that were free flowing.

Each powder coating composition from Examples <NUM>-<NUM> were applied over several chromate pretreated <NUM> (<NUM> inch) by <NUM> (<NUM> inch) by <NUM> (<NUM> inch) aluminum panels at film thicknesses shown in Table <NUM> and heated for <NUM> minutes at <NUM>'°C (<NUM>°F). Various properties of the cured coatings, determined by tests performed on these coated panels, are shown in Table <NUM>.

As shown in Table <NUM>, the coatings formed from the compositions of Examples <NUM>-<NUM> all exhibited good adhesion, impact resistance, corrosion resistance, and humidity resistance.

Claim 1:
A powder coating composition comprising:
a polyester polymer comprising carboxylic acid functional groups and having an acid value of at least <NUM> KOH/g;
a first crosslinker reactive with the carboxylic acid functional groups of the polyester polymer; and
a fluoropolymer unreactive with the polyester polymer and first crosslinker, wherein the fluoropolymer comprises a fluoroethylene vinyl ether copolymer, a polyvinylidene fluoride polymer, or a combination thereof,
wherein the weight ratio of the polyester polymer to the fluoropolymer is from <NUM>:<NUM> to <NUM>:<NUM>, and
wherein when cured, the powder coating composition forms a single coating layer comprising the polyester polymer and the fluoropolymer.