MXPA01002809A - Powder coatings based on branched oligoesters and triazole blocked polyisocyanates - Google Patents

Abstract

The present invention relates to powder coating compositions which can be cured at low temperatures. The powder coating compositions of the invention include a unique combination of a branched oligoester polyol and triazole blocked isocyanate cross-linking agent which when cured results in a coating binder with desirable hardness, flexibility, solvent resistance, corrosion resistance, weatherability and gloss.

Description

POWDER COATINGS BASED ON OLIGOESTERS AND POLYISOCIANATOS BLOCKED WITH TRIAZOLA The present invention relates to powder coating compositions that can be cured at low temperatures with or without the use of a catalyst. More particularly, the present invention relates to branched, terminated hydroxyl oligoesters which, when crosslinked, provide improved performance properties at low curing temperatures, even without catalyst. BACKGROUND OF THE INVENTION Thermoplastic powder coating compositions are well known in the art, and are widely used as coatings for electrical appliances, bicycles, garden furniture, accessories for the automotive industry, metal parts in general, and the like. Thermosetting powders consist of a mixture of a primary resin and one or more crosslinkers, often referred to as hardeners or curing agents. The general approach associated with powder coating technology is to formulate a coating from solid components, mix them, disperse pigments (and other insoluble components) in a matrix of the main binder components, and spray the formulation into a powder. As far as possible, each particle contains all the ingredients of the formulation. The powder is applied to the substrate, normally, but not limited to, a metal, and melted to a continuous film by baking. One problem with powder coating compositions is that they often have low glass transition temperatures (Tg) which will lead to agglomeration or sintering of the powder coating particles when stored at elevated temperatures for a prolonged time. The agglomerated powder coating can cause problems during application, and may require a regrind, which in itself can cause additional problems, for example, by adversely affecting the particle size distribution of the re-milled powder coating. Frequently, powder coating compositions that are formulated to avoid problems with agglomeration and sintering do not provide optimal coating properties. It is an object of the invention to provide a powder coating composition having a relatively high glass transition temperature, which resists agglomeration during storage, and whose composition cures without a catalyst at a relatively low temperature. It is an object of the invention to provide a powder coating composition that maximizes film properties, such as hardness, flexibility, solvent resistance, corrosion resistance, weather resistance and gloss, and yet also provide a coating composition with a relatively high glass transition temperature, and which cures without a catalyst at relatively low temperatures. It is another object of the invention to provide a powder coating composition that can be cured at temperatures as low as about 150 ° C, without the use of an effective amount of catalyst. It is another object of the invention to provide a powder coating composition with a desirable melt viscosity. Other objects, advantages, features and characteristics of the present invention will become clearer after a consideration of the following description and the appended claims. SUMMARY OF THE INVENTION The present invention provides a powder coating composition that will not readily agglomerate during storage, and that can be cured at temperatures as low as about 140 ° C, with the use of a urethane catalyst, and of 145 ° C at about 155 ° C without the use of a catalyst. The powder coating composition of the invention comprises a unique combination of a branched oligoester polyol and a crosslinking agent which, when cured, it results in a coating with desirable hardness, flexibility, solvent resistance, corrosion resistance, weather resistance and brightness. The branched oligoester polyol has a unique combination of branched structure, number average molecular weight, hydroxyl number, and acid number, which provides a relatively high glass transition temperature and, consequently, agglomeration resistance. When this latter branched oligoester polyol is cured with an isocyanate blocked with triazole, the combination of the branched oligomer and the isocyanate provides a coating binder with good performance characteristics, even without catalysts. The invention provides a reactivity and high curing speed at lower temperatures without sacrificing storage stability towards agglomeration or sintering. The branched oligoester polyol has a Tg of at least about 40 ° C to about 80 ° C, a number average molecular weight of about 1,000 to about 7,500 Daltons, a hydroxyl functionality of about 1.5 to about 5.0, a hydroxyl number from about 15 to about 250, and an acid number from about 1 to about 25, and in a very important aspect, an acid number from about 5 to about 7. In another important aspect, the branched oligoester will have a viscosity of about 20 to about 90 poise, at approximately 200 ° C. The powder coating composition of the invention comprises the branched oligoester polyol and the crosslinking agent of the isocyanate powder coating blocked with triazole, each in relative amounts which are effective to provide crosslinked coating compositions with a pencil hardness of when less about H, a direct impact resistance of at least about 14,288 kg / cm, and a reverse impact resistance of at least about 14,288 kg / cm, in a binder thickness of about 20.32 microns to about 63.5 microns, when the Curing is conducted on milled steel panels of a thickness of 812.8 microns, at temperatures as low as about 140 ° C, preferably from about 145 ° C to about 155 ° C. The powder coating composition of the invention, which comprises the branched oligoester polyol and the blocked isocyanate with triazole has a Tg of from about 40 ° C to about 70 ° C. In an important aspect, the powder coating composition comprises from about 18 to about 97 weight percent of the branched hydroxyl terminated oligoester, based on the weight of the branched oligoester polyol and the crosslinking agent. The branched oligosterol polyol can be synthesized by the formation of a generally linear hydroxyl-terminated oligoester diol, by the reaction of a diol and a diacid, and then the reaction of the resulting hydroxyl-terminated oligoester diol with less than a stoichiometric amount (in relation to the hydroxyls on the oligoester) of a polyacid having a carboxyl functionality of at least about 3. This amount less than the stoichiometric provides some carboxyl groups to the oligomer, but its most important purpose is to provide in general a complex branching of the oligoster polyol, in such a way that the chains of the oligomer extend in some cases, from all the carboxyl functionality of the polyacid, and some of the polyacids are interconnected by oligomeric chains. In an important aspect, the carboxyl functionality from the polyacid which reacted with the oligoester, is not greater than about 15 percent of the equivalents of the stoichiometric amount of the carboxyl equivalent necessary to react with all the hydroxyl groups of the oligoester. In an important aspect, the proportion of the hydroxyl-terminated oligoester diol to the triacid is from about 9.0: 1 to about 30: 1, preferably from about 10: 1 to about 20: 1. In an important aspect of the invention, the hydroxyl-terminated diol is the reaction product of an aliphatic diol (open chain or cycloaliphatic) and an aromatic diacid, diacid halide, or diacid anhydride, such as terephthalic acid, which provides a hydroxyl-terminated oligoester diol having aromatic groups. Alternatively in this aspect, the acid may be a straight chain or a cycloaliphatic diacid, diacid anhydride, or diacid halide, and the diol may be hydroquinone, to provide the oligoester, aromatic monomers along its main chain . In another important aspect, the diol used for the oligoester diol is a straight chain or cycloaliphatic aliphatic diol, and the diacid is a cycloaliphatic diacid, diacid anhydride, or diacid halide, whose monomers provide an oligoester diol having cycloaliphatics. In still another aspect, if the diacid, diacid anhydride or halide, and diol used to make the oligoester diol are both straight chain, an aromatic monomer having hydroxyl and carboxyl functionality can be used to improve the properties of the diol. the final coating composition. These aromatic monomers having hydroxyl and carboxyl functionality include ortho-, meta-, and para-hydroxybenzoic acid. Although it is not intended to be bound by any theory, it appears that the combination of straight ring and chain, or aromatic sky-aromatic combination provides desired film properties. The hydroxyl-terminated oligoester diol is the reaction product of excess diol with a diacid. The diol can be one or more diols selected from the group consisting of neopentyl glycol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, diethylene glycol, 1,3- propanediol, hydrogenated bisphenol A, 2, 3, 4, 4-tetramethyl-l, 3-cyclobutanediol, ethylene glycol, propylene glycol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2-ethyl-2-isobutyl- 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, thiodiethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-xylylenediol, ethoxylated bisphenol A, ester diol 204 (Union Carbide), 3-hydroxy-2, 2-dimethyl propionate, 1-oxo-6-diol, methylpropanediol, 2-methyl-1,3-propanediol, hydroxypivalyl hydroxypivalate (HPHP), vinyl-cyclohexanediol, dipropylene glycol, ester diols, dimethylol propionic acid (DMPA), and mixtures thereof. The acids / anhydrides / aromatic acid halides used in the invention are selected from the group consisting of terephthalic acid, phthalic acid, phthalic anhydride, dimethyl terephthalic acid, naphthalene dicarboxylate, tetrachlorophthalic acid, bis-glycol ester of terephthalic acid, isophthalic, tertiary butyl isophthalic acid, and mixtures thereof. The acids / anhydrides / aliphatic acid halides useful in the present invention are selected from the group consisting of fumaric acid, adipic acid, azelaic acid, sebacic acid, dodecanoic acid, glutaric acid, succinic acid, oxalic acid, itaconic acid, dimeric fatty acids, maleic anhydride, succinic anhydride, chlordenedic acid, diglycolic acid, nadic acid, and mixtures thereof. The acids / anhydrides / cycloaliphatic acid halides used in the invention may include acids / anhydrides, such as 1,4-cyclohexane diacid, 1,3-cyclohexanedicarboxylic acid, hexahydrophthalic anhydride, dimethylcyclohexane dicarboxylate, and mixtures thereof. the same. Mixtures of these compounds can also be used for the preparation of the ester diols. Aromatic diols or dihydroxy-phenolic compounds that can be used to make the oligoester diol include hydroquinone, catechol, resorcinol, p, p'-dihydroxydi-phenylmethane, bisphenol A, p, p'-dihydroxydiphenylketone, p, p'-dihydroxydiphenyl, and mixtures thereof. Normally, when these phenolic-type dihydroxy compounds are used to make the oligoester diols, a base catalyst is usually required. The reaction forming the hydroxyl-terminated oligoester diol is conducted for a time and at an effective temperature to provide an oligoester diol having a number average molecular weight in the range of about 400 to about 1,500 Daltons, and then the reaction is it slows down by cooling from about 170 ° C to about 200 ° C, to provide the last diol of oligoester. In general, the reaction that provides the oligoester diol is conducted at a temperature of about 140 ° C, for about 4 to about 15 hours before the reaction cools. This hydroxyl-terminated oligoester diol of a relatively low molecular weight is reacted with the polyacid / anhydride / polyols, or mixtures thereof, selected from citric acid, pyromellitic anhydride, trimellitic anhydride, trimethylolpropane, trimethylolethane, pentaerythritol and ditrimethylolpropane . In an important aspect of the invention, the polyacid or triacid that is reacted with the hydroxyl-terminated oligoester diol is an aromatic acid. The branching reaction is conducted for a time and at a temperature effective to provide the branched oligoester polyol described herein. The reaction forming the branched oligoester polyol is conducted at a temperature from about 180 ° C to about 240 ° C, for about 4 to about 15 hours. The isocyanate blocked with triazole, which is a reaction product of a triazole substituted or unsubstituted with an isocyanate compound, is an important crosslinking agent in the present invention. The amount of crosslinking agent in the composition is effective to provide an equivalent ratio of isocyanate groups to hydroxyl groups of about 0.5: 1.0 to about 1.8: 1.0. In an important aspect of the invention, the isocyanate blocked with triazole is a pre-polymer of isophorone diisocyanate blocked with triazole, or likewise a mixture of isophorone diisocyanate trimer, isophorone diisocyanate monomer, and other homologs of isophorone diisocyanate, all blocked with triazole. In the aspect of the invention using the pre-polymer, the pre-polymer is the reaction product of isophorone diisocyanate and trimethylolpropane. The pre-polymer is blocked with a triazole blocking agent to provide a pre-polymer having less than 1 percent free isocyanate. In an important aspect, when the isocyanate blocked with triazole is used as the crosslinking agent in the composition, the composition contains from about 3 to about 82 weight percent of isocyanate-blocked isocyanate crosslinking agent with triazole, based on in the weight of the branched hydroxyl terminated oligoester and the crosslinking agent. In another important aspect, the present invention further provides a process for the preparation of powder coating compositions, wherein the branched hydroxyl-terminated oligoester prepared as described herein, is mixed with an isocyanate powder coating crosslinking agent. blocked with triazole, and optionally with auxiliary substances conventionally used in the manufacture of powder coatings. Detailed Description of the Invention Definitions As used herein, "coating binder" is the polymer portion of a coating film after baking and after crosslinking. "Polymeric vehicle" means all polymeric and resinous components in the formulated coating; that is, before the formation of the film. Pigments and additives can be mixed with the polymer vehicle to provide a foated powder coating composition. "Diol" is a compound with two hydroxyl groups. "Polyol" is a compound with two or more hydroxyl groups. "Diácido" is a compound with two carboxyl groups. "Polyacid" is a compound with two or more carboxyl groups, and may be an acid or an acid anhydride. A "film" is formed by applying the powder coating composition to a base or substrate, and then crosslinking the powder coating composition. "Sintering" means the loss of the particulate characteristics of the powder during storage, which results in lumps and agglomeration, or in extreme cases, a solid mass. In the composition of the present invention, amounts of material are used that are effective to provide a powder coating that is substantially not sintered. "Substantially non-sintered" means that, after exposing a powder coating to a given set of conditions that are hotter than those normally recommended for storage of the powder coating, and then cooled to room temperature, the powder coating retains its particulate characteristics with only a few lumps that can break easily with moderate pressure. "Polyester" means a polymer that has bonds II -CO- in the polymer backbone. "Oligomer" means a compound that has in general repeating monomer units, and is similar to a polymer, but has a number average weight no greater than about 7,500 Daltons with or without repeating monomer units. A "polymer" will have a number average molecular weight of more than about 7,500 Daltons. "Acid number" or "acid value" means the number of milligrams of potassium hydroxide required for the neutralization of free acids present in one gram of resin. "Hydroxyl number" or "hydroxyl value", which is also called the "acetyl value", is a number that indicates the degree to which a substance can be acetylated; is the number of milligrams of potassium hydroxide required for the neutralization of the acetic acid released after the saponification of 1 gram of the acetylated sample. "Catalyst" means a material that, under a given set of conditions, speeds up a chemical reaction. In general, less than about 0.02 weight percent urethane catalyst, based on the weight of the powder coating composition, is not effective for urethane catalysis, and does not increase the reaction rates. Oli Resin Oester Branched Finished in Hydroxyl Both the Tg and the viscosity of the resin melt are largely influenced by the choice of monomers. In an important aspect of the invention, the hydroxyl-terminated branched oligoester resin is made by a two-step process. In step one, a hydroxyl-terminated oligoester diol is prepared, and in step two a hydroxyl-terminated branched oligoester polyol is formed. Step one: In step one, a hydroxyl-terminated oligoester diol is formed through the esterification or the condensation reaction of a stoichiometric molar excess of a diol (relative to the acid carboxyls) with a dicarboxylic acid, a dicarboxylic acid anhydride, or a dicarboxylic acid halide, such as an acid chloride. (1) The diols which can be used in the reaction can be selected from the group consisting of neopentyl glycol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, diethylene glycol, 1,3-propanediol, hydrogenated bisphenol A, 2, 3,4,4-tetramethyl-l, 3-cyclobutanediol, ethylene glycol, propylene glycol, 2,4-dimethyl-2-ethylhexane-1, 3-diol, 2- ethyl-2-isobutyl-l, 3-propanediol, 1,3-butanediol, 1,4-butane-diol, 1,5-pentanediol, thiodiethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1, 4-xylynediol, ethoxylated bisphenol A, 204-diol ester (Union Carbide), 3-hydroxy-2, 2-dimethyl propionate, 1-oxo-6-diol, methylpropanediol, 2-methyl-1,3-propanediol, hydroxypivalyl hydroxypivalate (HPHP), vinyl-cyclohexa-nodiol, dipropylene glycol, ester-diols, dimethylol-propionic acid (DMPA), and mixtures thereof. Aromatic diols, such as hydroquinone, catechol, resorcinol, p, p'-dihydroxydiphenylmethane, bisphenol A, p, p'-dihydroxydiphenyl ketone, p, p'-dihydroxydiphenyl, and mixtures thereof, can also be reacted with diacids of Straight chain or cycloaliphatics. (2) Aromatic diacids, aliphatic diacids and / or diacids or cycloaliphatic anhydrides, or acid halides, can be used to make the hydroxyl-terminated diols. In an important aspect, the acid / anhydride / aromatic acid halide is selected from the group consisting of terephthalic acid, phthalic acid, phthalic anhydride, dimethylterephthalic acid, naphthalene dicarboxylate, tetraclo-rophthalic acid, bis-glycol ester of terephthalic acid, isoftáli-co, tertiary butyl isophthalic acid, and mixtures thereof, or acid halides thereof. The acids / anhydrides / aliphatic acid halides that can be used in the invention include fumaric acid, adipic acid, azelaic acid, sebacic acid, dodecanoic acid, glutaric acid, succinic acid, oxalic acid, itaconic acid, dimeric fatty acids, maleic anhydride, succinic anhydride, chlordenedic acid, diglycolic acid, nadic acid, and mixtures thereof. The acids / anhydrides / cycloaliphatic acid halides which can be used in the invention include acids / anhydrides, such as 1,4-diacid hexane, 1,3-cyclohexanedicarboxylic acid, hexahydrophthalic anhydride, dimethylcyclohexane dicarboxylate, and mixtures of the same. Mixtures of these compounds can also be used for the preparation of the ester diols as mixed functional intermediates. The ester diols are those prepared in a known manner from lactones and dihydric alcohols as starting molecules through a ring opening reaction. The preparation of the ester diols may include lactones, such as β-propiolactone, β-butyrolactone, β- and d-valerolactone, e-caprolactone, 3,5,5- and 3, 3, 5-trimethylcaprolactone, or mixtures thereof. Suitable starting molecules include the listed dihydric alcohols described. In a very important aspect of the invention, the aromatic acid is one or more aromatic acids selected from the group consisting of terephthalic acid (TPA), isophthalic acid (IPA), and tertiary butyl isophthalic acid. These are reacted with an aliphatic or cycloaliphatic diol, such as neopentyl glycol, 1,6-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, and 1,4-cyclohexanedimethanol. The diol component and the diacid component are each present in effective amounts to provide the coating composition, and the subsequent coating with the properties described. In an important aspect of the invention, the combination of neopentyl glycol and 1,6-hexanediol in a molar ratio of about 4.0: 1 to about 7.0: 1, preferably of about 5.6: 1, is reacted with TPA, IPA or acid isophthalic butyl tertiary, and provides a coating composition with an acceptable Tg. The reaction to obtain the hydroxyl-terminated oligoester diol can be conducted at about 240 ° C for about 4 to about 15 hours, and then cooled to obtain the generally linear product having the Mn from about 400 to about 1,500 Daltons. If an aliphatic acid is reacted with an aromatic dihydroxy lo compound, such as hydroquinone, catechol, resorcinol, p-p'-dihydroxydiphenylmethane, bisphenol A, p, p'-dihydroxydiphenyl ketone, p, p'-dihydroxydiphenyl, and mixtures thereof of them, the use of base catalysts is normally required. Step Two: In step two, the hydroxyl-terminated oligoester diol prepared in step one is reacted to form a branched hydroxyl-terminated oligoester polyol. In an important aspect of the invention, the hydroxyl-terminated oligoester prepared in Step 1 is reacted with a polyacid / anhydride, or with a mixture of polyacids / anhydrides that are at least one triacid. The triacid, or triacid mixture, is selected from the group consisting of trimellitic anhydride (TMA) and citric acid. In a very important aspect, the triacid is an aromatic acid, such as trimellitic anhydride. In an important aspect of the invention, the resulting branched hydroxyl terminated oligoester has a hydroxyl functionality of about 1.5 to about 5.0, a hydroxyl number of about 15 to about 250, an acid value of about 1 to about 25, and a number average molecular weight in the range of about 1,000 to about 7,500 Daltons. The branched hydroxyl-terminated oligoester has a Tg of at least about 40 ° C, and in an important aspect, from about 40 ° C to about 80 ° C. In a very important aspect, the proportion of the hydroxyl-terminated oligoester to the polyacid is from about 9.0: 1 to about 30: 1. Crosslinking Agents Isocyanate Crosslinkers Blocked with Triazole: In an important aspect of the invention, the crosslinking agent is a polyisocyanate compound blocked with triazole, which is the reaction product of a substituted or unsubstituted triazole, with an isocyanate compound. The polyisocyanates known as the isocyanate compounds can be used as starting materials for the production of the blocked polyisocyanates according to the present invention. These known polyisocyanates generally contain from about 2 to about 4 isocyanate groups, and have a molecular weight of from about 100 to about 10,000, preferably from about 150 to about 3,000. Polyisocyanates suitable for use in the present invention include simple polyisocyanates, such as hexamethylene di-isocyanate, 2,4-diisocyanato toluene, 2,6-diisocyanato toluene, 3-isocyanato-3. , 5-trimethyl-5-isocyanatomethyl-cyclohexane, 4,4-di-isocyanatodiphenyl-methane, 2,4'-di-isocyanatodiphenyl-methane, or derivatives of these diisocyanates containing biuret or urethane groups. Isocyanate compounds that can be reacted with a triazole-blocking group also include derivatives containing biuret groups, and include polyisocyanates of the type described in U.S. Patent No. 3,124,605, ie, mixtures of homologs consisting of tris- (isocyanatohexyl) biuret, and the higher homologs of this polyisocyanate, of the type obtained in the biuretization of hexamethylene diisocyanate. These biuret polyisocyanates also have an NCO-average functionality of 2 to 4, and an average molecular weight of less than 10,000, preferably from about 150 to about 3,000. The suitable urethane derivatives or "pre-polymers" of the diisocyanates exemplified above, can be used as isocyanate compounds, which are reacted with triazole. These urethane derivatives or prepolymers can include the above polyisocyanates as reaction products with minor amounts to the equivalents of aliphatic diols or triols having molecular weights of about 62 to about 200, such as ethylene glycol, 1,2- or 1 , 3-propanediol, 1,2-butanediol, tetramethylene- or hexamethylene glycol, diethylene glycol, trimethylolpropane, trimethyl-letan or glycerol. In the production of these urethane-modified derivatives of the aforementioned diisocyanates, the diisocyanates are reacted with the polyhydric alcohols exemplified in proportions corresponding to an equivalent ratio of NCO / OH of at least about 2: 1, preference of approximately 2: 1 approximately 20: 1. The urethane-modified polyisocyanates obtainable in this manner also have NCO functionalities from about 2 to about 4, preferably from about 2 to about 3, and molecular weights (average) of less than about 10,000, preferably about 150. to approximately 3,000. In an important aspect, the blocked polyisocyanate compounds according to the present invention can be represented by the general formulas: Y where R is an isocyanate compound as described above, R1 is H or thiol, R2 is H or pyridine, and x is 2 a. In this aspect of the invention, each isocyanate group on the isocyanate may be blocked with a triazole. In a very important aspect of the invention, the triazole blocking agent may include 1 H-1,2,4-triazole, 1 H-1,2,3-triazole, 1 H-1,2,4-triazole-3-thiol, and 1H-1, 2, 3-triazole [4, 5-b] pyridine. The reaction of the starting polyisocyanate compounds with the blocking agent can be carried out in the presence of aprotic solvents which are inert to the isocyanate groups, or in the melt. Suitable solvents are, for example, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran or dioxane. The blocking reaction is generally carried out at temperatures from about 40 ° C to about 160 ° C, preferably from about 60 ° C to about 130 ° C. At reaction temperatures greater than about 60 ° C, the reaction can be carried out in the absence of catalysts, and in most cases, it is finished after only 30 to 60 minutes. The blocking agent is preferably used in an amount at least equivalent. In many cases, it is advisable to use a slight excess in order to obtain a more complete blockage of the free isocyanate groups. The content of free NCO is usually less than about 1 percent. In cases where the exemplified urethane-modified polyisocyanates are used as starting material, the production and blocking thereof can be carried out in a single-stage or multi-stage reaction, or in a continuous process, such as it is described in U.S. Patent No. 4,997,900, wherein the di-isocyanate not modified with urethane is reacted with the blocking agent and one or more of the exemplified polyols. Preparation and Application of the Third-Purposeable Powder For the preparation of the thermosettable powder compositions, the hydroxyl-terminated branched oligoester resin, the crosslinking agent, and various auxiliary substances conventionally used for the manufacture of powder coatings, are mixed in a homogeneous manner . This homogenization is carried out, for example, by melting the oligoester, the crosslinking agent, and the various auxiliary substances at a temperature in the range of about 50 ° C to about 150 ° C, preferably in an extruder, for example, a Buss extruder. -Ko-Kneader, or a twin-screw extruder of the Werner-Pfleiderer or Baker Perkins type. The extrudate is then allowed to cool, grind and sieved to obtain a powder suitable for electrostatic or fluidized bed application. Another factor that affects viscosity and flow is the level of pigmentation and fillers in the system. High levels of pigmentation and / or fillers impair the flow of the system, increasing the viscosity of the fusion. Organic pigments of a fine particle size, such as carbon black, phthalocyanine blue, and quinacridones, also cause a significant increase in melt viscosity, even at low levels.

Auxiliary substances that can be added to the thermosetting compositions according to the invention include ultraviolet light absorbing compounds, such as Tinuvin 900 (from CIBA-GEIGY Corp.), light stabilizers based on sterically hindered amines (eg, Tinuvin). 144 of CIBA-GEIGY Corp.), phenolic antioxidants (for example, Irganox 1010 and Irgafos 168 of CIBA-GEIGY Corp.), and stabilizers of the phosphonite or phosphite type. A variety of pigments can also be added to the thermosettable compositions according to the invention. Examples of the pigments that can be used in the invention are metal oxides, such as titanium dioxide, iron oxide, zinc oxide, and the like, metal hydroxides, metal powders, sulfides, sulfates, carbonates, carbon black, iron blues, organic reds, organic yellows, organic browns, and the like. Examples of the fillers that may be used are aluminum silicate, talc, barytes, fixed white, calcium carbonate and magnesium carbonate. Auxiliary substances can also include flow control agents, such as Resiflow PV5 (from WORLEE), Modaflow 3 and 2000 (from MONSANTO), Acronal 4F (from BASF), Resiflo P-67 (from Estron), plasticizers, such as dicyclohexyl phthalate, triphenyl phosphate, grinding aids, degassing agents, such as benzoin, and catalysts, such as stannous octoate, dibutyl tin dilaurate, and zinc, manganese, iron, aluminum and magnesium acetylacetonates. These auxiliary substances are added in conventional amounts, it being understood that, if the thermosettable compositions of the invention are used as transparent coatings, the opacifying auxiliary substances should be omitted. In addition, urethane catalysts can also be mixed with the thermoforming composition of the invention. Catalysts useful in the present invention include 1,4-diazobicyclo (4.3.0) non-5-ene, 1,8-diazabicyclo (5.4.0) undec-7-ene, dibutyl tin dilaurate, butane-stanoic acid, dibutyl tin oxide, stannous octoate, and others known in the art. The powder coating compositions which are the subject matter of the present invention, are suitable for being applied to articles to be coated by, but not limited to, conventional techniques, for example, by application by means of an electrostatic spray gun or tribostatic, or by fluidized bed techniques, or by powder nebulization technology (Material Sciences Corporation). After being applied to the article in question, the deposited coatings are cured by heating in an oven. In an important aspect, curing is carried out at a temperature as low as about 145 ° C for about 45 minutes, or at 155 ° C for about 30 minutes, in order to obtain sufficient cross-linking with the non-catalyzed compositions, to provide the described properties of the coating. Alternatively, desirable coating properties can be obtained by curing at a temperature of about 190 ° C for about 7 minutes, heating at about 205 ° C for about 5 minutes, and for end uses of roll coating by heating at about 400 ° C for about 20 seconds. Infrared (IR) curing is also applicable. The following examples illustrate the methods for carrying out the invention, and it should be understood that they are illustrative of, but not limited to, the scope of the invention, which is defined in the appended claims. EXAMPLES EXAMPLE 1 Stage 1 Preparation of the Reactive Hydroxylated Oligomer Weight Neopentyl glycol (Eastman) 805 grams 1, 6-hexanediol (UBE) 161 grams Terephthalic acid (Amoco) 1145 grams Butylchloro-butyl dihydroxide (Elf-Atochem) 2.1 grams Antioxidant (eston 618-General Electric) 4.6 grams The mixture was gradually heated to 205 ° C, and then processed at 240 ° C to an acid value of 4 to 7 milligrams of KOH / gram of resin, with an ICI cone and plate viscosity of 10-14 poise at 125 ° C. It was found that the hydroxyl number of this oligomer was about 130-140 milligrams of KOH / gram of resin. Step 2 Preparation of Branched Oligoester Finished in Hydroxyl The above oligomer was cooled to 180 ° C, and 153.5 grams of trimellitic anhydride were added. The temperature was raised to 210-215 ° C, and a vacuum was slowly applied for a period of 50 minutes, until a vacuum of 58-61 centimeters of mercury was obtained. The reaction was monitored by regularly taking a sample, and determining the acid number and ICI cone and plate viscosity at approximately 200 ° C. When an ICI cone and plate viscosity of 50-60 poise, and an acid value of 4 to 10 milligrams of KOH / gram of resin were obtained, the melt was cooled to 195 ° C, and discharged from the flask. The color of the resin was from almost colorless / clear to a light yellow color. EXAMPLE 2 Stage 1 Preparation of Reactive Hydroxylated Oligomer Weight Neopentyl glycol (Eastman) 1396.99 grams 1,6-hexanediol (UBE) 279.93 grams Terephthalic acid (Amoco) 2048.14 grams Butylchloro-butyl dihydroxide 4.00 grams (Elf-Atochem) Antioxidant (Weston 618- General Electric) 8.00 grams The mixture was gradually heated to 205 ° C, and then processed at 240 ° C to an acid value of 4 to 7 milligrams of KOH / gram of resin, with an ICI cone and plate viscosity of 10-14 poise at 125 ° C. It was found that the hydroxyl number of this oligomer was from about 130 to 140 milligrams of KOH / gram of resin. Step 2 Preparation of the Branched Oligoester Finished in Hydroxyl The above oligomer was cooled to 180 ° C, and 277.86 grams of trimellitic anhydride were added. The temperature was raised to 210-215 ° C, and a vacuum was slowly applied for a period of 50 minutes, until a vacuum of 58-61 centimeters of mercury was obtained. The reaction was monitored by regularly taking a sample, and determining the acid number and ICI cone and plate viscosity at approximately 200 ° C. When an ICI cone and plate viscosity of 50-60 poise, and an acid value of 4 to 10 milligrams of KOH / gram of resin were obtained, the melt was cooled to 195 ° C, and discharged from the flask. The color of the resin was from almost colorless / clear to a light yellow color. EXAMPLES 3-6 Preparation of Powder Coatings All oligoesters were made in a high gloss white powder coating prepared as follows: fifteen twenty All the above ingredients were initially mixed in a high speed mill, such as a mixer, Welex, where a homogeneous mixture was obtained. The resulting mixture was processed through a Buss PR-46 single screw extruder at 200 rpm, with zone 1 at 92 ° C, and zone 2 at 140 ° C. The resulting melt was discharged onto a pair of water-cooled tightening rollers, from which the cooled sheet emerging before being pulverized in a Brinkmann grinder or a coffee grinder was crushed and sieved through a 140 mesh. Powder coatings were sprayed electrostatically onto milled steel panels (Type S-39, The Q-Panel Company). The physical properties of the formulated powder coatings were determined after the curing programs and cured film thicknesses mentioned. The test results for these powder coatings are given in Table 1.

Table 1 fifteen twenty Explanation of the References in Table 1: Reference 1: Essentially, the Recommended Procedure by the Powder Coating Institute # 8. Evaluations: 1 = There is no discernible loss in brightness. 2 = Loss barely discernible in the brightness from the peaks in the film. 3 = Slight loss in brightness from the peaks in the film. 4 = Loss of brightness on the rubbed area, but many areas of high brightness in the valleys between the peaks in the film. 4 = Loss of brightness on the rubbed area, but a few high brightness areas in the valleys between the peaks of the film. There was no significant removal of the coating. 15 Reference 2: Powder Softness Standards of the Powder Coating Institute. Standard panels to compare the smoothness, with 1 = the roughest, and 10 = the softest.

The inventors are expected to devise numerous modifications and variations in the practice of the invention, after a consideration of the above detailed description of the invention. Accordingly, it is intended that these modifications and variations be included within the scope of the following claims.

Claims (45)

1. CLAIMS 1. A powder coating composition, comprising: a branched, hydroxyl-terminated polyol oligoester, which has a hydroxyl value in the range of about 15 to about 250, an acid number of about 1 to about 25, and a number average molecular weight in the range of about 1,000 to about 7,500 Daltons, where the hydroxyl-terminated, branched polyol oligoester is the reaction product of a hydroxyl-terminated oligoester diol and a polyacid or anhydride having a functionality carboxyl of at least about 3; and a triazole-blocked polyisocyanate crosslinking agent, the branched hydroxyl-terminated polyol oligoester and the crosslinking agent each being in effective relative amounts to cure the powder coating composition at a temperature as low as about 140 * C. with the use of an effective amount of urethane catalyst and as low as about 145"C without the use of an effective amount of urethane catalyst to provide a cured coating binder having a pencil hardness of at least about H, a direct impact resistance of at least about 80 in Ib and an inverted impact resistance of at least about 80 in Ib to a cured film thickness of about 0.8 to 2.5 thousandths of an inch, the coating composition having a Tg of at least about 40 * C 2. A powder coating composition, as defined in claim 1, wherein the oligoest ratio The hydroxyl-terminated diol to polyacid is about 9: 1 to about 30: 1. 3. A powder coating composition, as defined in claim 2, wherein the hydroxyl-terminated diol oligoester is the reaction product of a diol and a diacid reactant selected from the group consisting of an open chain aliphatic dicarboxylic acid, a cycloaliphatic dicarboxylic acid, an aromatic dicarboxylic acid, an open chain aliphatic dicarboxylic acid anhydride, a cycloaliphatic dicarboxylic acid anhydride, an aromatic dicarboxylic acid anhydride, an open-chain dicarboxylic acid halide, a cycloaliphatic dicarboxylic acid halide, an aromatic dicarboxylic acid halide, and mixtures thereof, the reaction of the diol and the diacid at an effective time and temperature to provide the hydroxyl terminated oligoester diol having a molecular weight in the range of about 400 to about 1,500 Daltons. 4. A powder coating composition, as defined in claim 1, wherein the polyisocyanate blocked with triazole is the reaction product of a triazole selected from the group consisting of 1H-1,2,4-triazole, 1H-1 , 2,3-triazole, 1H-1, 2,4-triazole-3-thiol and 1H-1,2,3-triazolo [4, 5-b] pyridine, and mixtures thereof, and an isocyanate compound. 5. A powder coating composition, as defined in claim 4, wherein the polyisocyanate blocked with triazole has the general formula Y where R is an isocyanate compound, R1 is H or thiol, R2 is H or pyridine, and x is 2 to 4. 6. A powder coating composition, as defined in claim 3, wherein the diol is selected from the group consists of neopentyl glycol, 1,6-hexane diol, 2-butyl-2-ethyl-l, 3-propane diol, 1,4-diclohexanedimethanol, diethylene glycol, 1,3-propanediol, hydrogenated bisphenol A, dimethylol propionic acid, 2 , 3,4,4-tetramethyl-1,3-cyclobutanediol, ethylene glycol, propylene glycol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2-ethyl-2-isobutyl-1,3-propanediol, , 3-butanediol, 1,4-butanediol, 1,5-pentanediol, thiodiethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-xylylenediphenol, ethoxylated bisphenol A, 3-hydroxy-2, 2 -dimethylpropionate, methyl propanediol, 2-methyl-1,3-propanediol, hydroxypivalyl hydroxypivalate, vinyl cyclohexanediol, dipropylene glycol, dimethylol propionic acid, aromatic diol compounds, and mixtures thereof. A powder coating composition, as defined in claim 6, wherein the diacid reagent includes an aromatic diacid reactant wherein the aromatic diacid reactant is aromatic acid, acid anhydride, or acid halide of terephthalic acid, phthalic acid, anhydride phthalic, dimethyl terephthalic acid, naphthalene dicarboxylate, tetrachlorophthalic acid, bis-glycol ester of terephthalic acid, isophthalic acid, t-butyl isophthalic acid, and mixtures thereof. A powder coating composition, as defined in claim 6, wherein the diacid reactant includes an open chain aliphatic diacid reactant, wherein the open chain aliphatic diacid reactant is aliphatic acid, acid anhydride or acid acid halide of open chains of fumaric acid, adipic acid, azelaic acid, sebacic acid, dodecanoic acid, glutaric acid, succinic acid, oxalic acid, itaconic acid, dimeric fatty acids, maleic anhydride, succinic anhydride, chlordenedic acid, diglycolic acid, nadic acid, and mixtures thereof . 9. A powder coating composition, as defined in claim 6, wherein the diacid reagent includes a cycloaliphatic diacid reactant, wherein the cycloaliphatic diacid reactant is cycloaliphatic acid, cycloaliphatic anhydride or cycloaliphatic acid halide of 1,4-cydohexane acid dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, hexahydrophthalic acid, dimethyl cyclohexane dicarboxylic acid, and mixtures thereof. 10. A powder coating composition, as defined in claim 7, wherein the diol is selected from the group consisting of neopentyl glycol, 1,6-hexane diol, 2-butyl-2-ethyl-l, 3-propanediol, 1,4-cyclohexanedimethanol and its mixtures. 11. A powder coating composition, as defined in claim 10, wherein the diacid reagent is an acid, anhydride or aromatic acid halide of an aromatic acid selected from the group consisting of terephthalic acid, isophthalic acid, t-butyl acid isophthalic, and its mixtures. 12. A powder coating composition, as defined in claim 1, wherein the oligoester diol is the reaction product of a lactone selected from the group consisting of β-propiolactone, β-butyrolactone, α- and β-valerolac- tone, e-caprolactone, 3,5,5- and 3, 3, 5-trimethylcaprolactone, and mixtures thereof, and a dihydric compound. 13. A powder coating composition, as defined in claims 1, 2, 7, 10 or 11, wherein the polyacid is at least one triacid. 14. A powder coating composition, as defined in claim 13, wherein the triacid is selected from the group consisting of trimellitic anhydride, citric acid, and mixtures thereof. 15. A powder coating composition, as defined in claim 14, wherein the triacid is trimellitic anhydride. 16. A powder coating composition, as defined in claim 1, wherein the hydroxyl-terminated, branched polyol oligoester has a hydroxyl functionality of about 1.5 to about 5.0. 17. A powder coating composition, as defined in claims 1 or 2, wherein the powder coating composition has from about 18 to about 97% by weight of hydroxyl-terminated, branched polyol oligoester based on the weight of the hydroxyl-terminated, branched, polyol oligoester and the crosslinking agent. 18. A powder coating composition, as defined in claims 1 or 2, wherein the powder coating composition has from about 3 to about 82% polyisocyanate crosslinking agent blocked with triazole, based on the weight of the hydroxyl-terminated, branched polyol oligoester, and the crosslinking agent. 19. A process for preparing a powder coating composition which, when applied to a substrate, is effective to provide a coating having a Tg of at least about 40"C, a pencil hardness of at least about H , a direct impact resistance of at least about 80 in Ib and an inverted impact resistance of at least about 80 in Ib at a film thickness of about 0.8 to about 2.5 mils, the process comprising: mixing physically a branched, hydroxyl-terminated polyol oligoester with an isocyanate crosslinking agent blocked with triazole, to provide the powder coating composition, wherein the branched, hydroxyl-terminated polyol oligoester has a hydroxyl value in the range of about 15 to about 250, an acid number of about 1 to about 25, and a number average molecular weight in the range of about 1,000 to about and 7,500 Daltons, and wherein the branched, hydroxyl-terminated polyol oligoester is the reaction product of a hydroxyl-terminated oligoester diol and a polyacid / anhydride having a carboxyl functionality of at least about 3; where the isocyanate cross-linking agent blocked with triazole is effective to provide an equivalent ratio of isocyanate groups to hydroxyl groups of about 0.5: 1.0 to about 1.8: 1.0, and the polyisocyanate crosslinking agent blocked with triazole is present in an amount effective to cure the powder coating composition at temperatures as low as about 140"C with the use of an effective amount of urethane catalyst and as low as about 145 ° C without the use of an effective amount of urethane catalyst 20. A process for preparing a powder coating composition, as defined in claim 19, wherein the ratio of hydroxyl terminated oligoester to polyacid is from about 9: 1 to about 30: 1 21. A process for preparing a powder coating composition, as defined in claim 20, wherein the hydroxyl-terminated oligoester diol is the reaction product of a diol and a diacid reactant selected from the group consisting of an open chain aliphatic dicarboxylic acid, a cycloaliphatic dicarboxylic acid, a dicarboxylic acid aromatic, an open chain aliphatic dicarboxylic acid anhydride, a cycloaliphatic dicarboxylic acid anhydride, an aromatic dicarboxylic acid anhydride, an open chain dicarboxylic acid halide, a cycloaliphatic dicarboxylic acid halide, an aromatic dicarboxylic acid halide, and its mixtures, the reaction of the diol and the diacid at an effective time and temperature to provide the hydroxyl terminated oligoester diol having a molecular weight in the range of about 400 to about 1,500 Daltons. 22. A process for preparing a powder coating composition, as defined in claim 21, wherein the diacid reagent includes an aromatic diacid reactant wherein the aromatic diacid reactant is aromatic acid, acid anhydride, or acid halide of terephthalic acid, phthalic acid , phthalic anhydride, dimethyl terephthalic acid, naphthalene dicarboxylate, tetrachlorophthalic acid, bis-glycol ester of terephthalic acid, isophthalic acid, t-butyl isophthalic acid, and mixtures thereof. 23. A process for preparing a powder coating composition, as defined in claim 21, wherein the diacid reactant includes a cycloaliphatic diacid reactant, wherein the cycloaliphatic diacid reactant is cycloaliphatic acid, cycloaliphatic anhydride or cycloaliphatic acid halide. 1,4-cyclohexane dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, hexahydrophthalic acid, dimethyl cyclohexane dicarboxylic acid, and mixtures thereof. 24. A process for preparing a powder coating composition, as defined in claim 21, wherein the diol is selected from the group consisting of neopentyl glycol, 1,6-hexane diol, 2-butyl-2-ethyl- 1,3-propanediol, 1,4-cyclohexanedimethanol, and mixtures thereof, the diacid reactant is selected from the group consisting of an aromatic diacid reactant, a cycloaliphatic diacid reactant, and mixtures thereof, and wherein the aromatic diacid reactant is the acid, acid anhydride or aromatic acid halide of terephthalic acid, phthalic acid, phthalic anhydride, dimethyl terephthalic acid, naphthalene dicarboxylate, tetrachlorophthalic acid, bis-glycol ester of terephthalic acid, isophthalic acid, t-butyl isophthalic acid, and mixtures thereof, and where the reactant cycloaliphatic is the cycloaliphatic acid, the cycloaliphatic anhydride or the halide cycloaliphatic acid of 1,4-cydohexane dicarboxylic acid, 1,3-cyclohexa-no-dicarboxylic acid, acid hexahydrophthalic acid, dimethyl cydohexane dicarboxylic acid, and mixtures thereof. 25. A process for preparing a powder coating composition, as defined in claim 24, wherein the polyacid is at least one triacid. 26. A process for preparing a powder coating composition, as defined in claim 25, wherein the branched, hydroxyl-terminated polyol oligoester has a hydroxyl functionality of about 1.5 to about 5.0. 27. A process for preparing a powder coating composition, as defined in claim 25, wherein the reaction forming the hydroxyl-terminated oligoester diol is cooled to about 170 to about 200 * C to provide the oligoester diol with the molecular weight of around 400 to about 1,500 Daltons. 28. A process for preparing a powder coating composition, as defined in claims 19 or 20, wherein the powder coating composition has from about 18 to about 97% by weight of branched, hydroxyl-terminated, polyol oligoester. based on the weight of the hydroxyl-terminated, branched polyol oligoester and the crosslinking agent. 29. A process for preparing a powder coating composition, as defined in claims 19 or 20, wherein the powder coating composition has from about 3 to about 82% by weight of crosslinking agent blocked with triazole, with base on the weight of the hydroxyl-terminated, branched polyol oligoester and the crosslinking agent. 30. A process for preparing a powder coating composition, as defined in claim 19, wherein the polyisocyanate blocked with triazole is the reaction product of a triazole selected from the group consisting of lH-1, 2,4-triazole , 1H-1, 2, 3-triazole, 1H-1, 2,4-triazole-3-thiol and 1H-1, 2, 3-triazolo [4, 5-b] pyridine, and mixtures thereof, and an isocyanate . 31. A powder coating composition, comprising: a branched, hydroxyl-terminated polyol oligoester having a hydroxyl value in the range of about 15 to about 250, an acid number of about 1 to about 25, and a number average molecular weight in the range of about 1,000 to about 7,500 Daltons, where the branched, hydroxyl-terminated, polyol oligoester is the reaction product of a hydroxyl-terminated oligoester diol and a polyacid or anhydride having a carboxyl functionality of at least about 3; and a triazole-blocked polyisocyanate crosslinking agent, the branched, hydroxyl-terminated oligoester polyol, and the crosslinking agent each being in effective relative amounts to cure the powder coating composition at a temperature as low as about 100%. 140"C with the use of an effective amount of urethane catalyst and as low as about 145 'C without the use of an effective amount of urethane catalyst, to provide a cured coating binder having a pencil hardness of at least around H, a direct impact resistance of at least about 80 in. lbs. at a cured film thickness of about 0.8 to about 2.5 mils, the coating composition having a Tg of at least about 40 * C wherein the polyisocyanate blocked with triazole is the reaction product of a triazole selected from the group consisting of 1H-1,2,4-triazole, 1H-1, 2, 3-triazole, 1H-1,2,4-triazole-3-thiol and 1H-1,2,3-triazolo [4, 5-b] pyridine, and mixtures thereof, and an isocyanate compound. 32. A powder coating composition, as defined in claim 31, wherein the polyisocyanate blocked with triazole has the general formula Y where R is an isocyanate compound, R1 is H or thiol, R2 is H or pyridine, and x is 2 to 4. 33. A powder coating composition, as defined in claim 31, wherein the ratio of oligoester diol terminated in hydroxyl to polyacid is around 9: 1 to about 30: 1. 34. A powder coating composition, as defined in claim 33, wherein the hydroxyl-terminated diol oligoester is the reaction product of a diol and a diacid reactant selected from the group consisting of an open chain aliphatic dicarboxylic acid, a cycloaliphatic dicarboxylic acid, an aromatic dicarboxylic acid, an open chain aliphatic dicarboxylic acid anhydride, a cycloaliphatic dicarboxylic acid anhydride, an aromatic dicarboxylic acid anhydride, an open-chain dicarboxylic acid halide, a cycloaliphatic dicarboxylic acid halide, an aromatic dicarboxylic acid halide, and mixtures thereof, the reaction of the diol and the diacid at an effective time and temperature to provide the hydroxyl terminated oligoester diol having a molecular weight in the range of about 400 to about 1,500 Daltons. 35. A powder coating composition, as defined in claim 33, wherein the diol is selected from the group consisting of neopentyl glycol, 1,6-hexane diol, 2-butyl-2-ethyl-1, 3-propane diol, 1,4-diclohexanedimethanol, diethylene glycol, 1,3-propanediol, hydrogenated bisphenol A, dimethylol propionic acid, 2,3,4,4-tetramethyl-1,3-cyclobutanediol, ethylene glycol, propylene glycol, 2,4-dimethyl- 2-ethylhexane-1,3-diol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, thiodiethanol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-xylylenediol, ethoxylated bisphenol A, 3-hydroxy-2,2-dimethylpropionate, methyl propanediol, 2-methyl-1,3-propanediol, hydroxypivalyl hydroxypivalate, vinyl cyclohexanediol, dipropylene glycol, dimethylol propionic acid, aromatic diol compounds, and mixtures thereof. 36. A powder coating composition, as defined in claim 34, wherein the diacid reagent includes an aromatic diacid reactant wherein the aromatic diacid reactant is aromatic acid, acid anhydride, or acid halide of terephthalic acid, phthalic acid, anhydride phthalic, dimethyl terephthalic acid, naphthalene dicarboxylate, tetrachlorophthalic acid, bis-glycol ester of terephthalic acid, isophthalic acid, t-butyl isophthalic acid, and mixtures thereof. 37. A powder coating composition, as defined in claim 34, wherein the diacid reagent includes an open chain aliphatic diacid reactant, wherein the open chain aliphatic diacid reactant is aliphatic acid, acid anhydride or acid acid halide of open chains of fumaric acid, adipic acid, azelaic acid, sebacic acid, dodecanoic acid, glutaric acid, succinic acid, oxalic acid, itaconic acid, dimeric fatty acids, maleic anhydride, succinic anhydride, chlordenedic acid, diglycolic acid, nadic acid, and mixtures thereof . 38. A powder coating composition, as defined in claim 34, wherein the diacid reagent includes a cycloaliphatic diacid reactant, wherein the cycloaliphatic diacid reactant is cycloaliphatic acid, cycloaliphatic anhydride or cycloaliphatic acid halide of acid 1, 4. - dicyclohexane dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, hexahydrophthalic acid, dimethyl cyclohexane dicarboxylic acid, and mixtures thereof. 39. A powder coating composition, as defined in claim 35, wherein the diol is selected from the group consisting of neopentyl glycol, 1,6-hexane diol, 2-butyl-2-ethyl-l, 3-propanediol, 1,4-cyclohexanedimethanol and its mixtures. 40. A powder coating composition, as defined in claim 36, wherein the diacid reactant is an acid, anhydride or aromatic acid halide of an aromatic acid selected from the group consisting of terephthalic acid, isophthalic acid, t-butyl isophthalic acid, and mixtures thereof. 41. A powder coating composition, as defined in claim 31, wherein the oligoester diol is the reaction product of a lactone selected from the group consisting of β-propiolactone, β-butyrolactone, β-and d-valerolac- tone, e-caprolactone, 3,5,5- and 3, 3, 5-trimethylcaprolactone, and mixtures thereof, and a dihydric compound. 42. A powder coating composition, as defined in claims 31 or 33, wherein the polyacid is at least one triacid. 43. A powder coating composition, as defined in claim 33, wherein the triacid is selected from the group consisting of trimellitic anhydride, citric acid, and mixtures thereof. 44. A powder coating composition, as defined in claim 43, wherein the triacid is trimellitic anhydride. 45. A powder coating composition, as defined in claim 31, wherein the hydroxyl-terminated, branched polyol oligoester has a hydroxyl functionality of about 1.5 to about 5.0.