WO1993004122A1

WO1993004122A1 - Polyester compositions containing phosphonium compounds

Info

Publication number: WO1993004122A1
Application number: PCT/US1992/007130
Authority: WO
Inventors: John Michael Beckerdite; Peter Charles Rooney
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1991-08-27
Filing date: 1992-08-24
Publication date: 1993-03-04
Anticipated expiration: 1994-02-27
Also published as: MX9204933A; CN1072193A; AU2568492A

Abstract

Acid terminated polyesters containing phosphonium compounds are disclosed which are useful, when admixed with an epoxy curing agent, in powder coating applications.

Description

POLYESTER COMPOSITIONS CONTAINING PHOSPHONIUM COMPOUNDS

The present invention pertains to the polyester compositions containing phosphonium salts as low-temperature or accelerated cure catalysts for the reaction of carboxyl-terminated polyesters with epoxy compounds to form thermosetting powder coatings. The invention also pertains to curable compositions comprising carboxyl- terminated polyesters, epoxy-containing compounds and phosphonium salts as well as powder coating compositions containing said curable compositions. Polyester powder coatings are a well-known type of thermosetting coatings. Carboxyl-group bearing polyesters are typically formulated with epoxide compounds to yield powders which can be applied to various substrates by electrostatic spraying orfluidized bed and then cured by baking. Since the uncatalyzed rate of reaction has been found to be too slow to suit the baking schedule established in the industry, the art has found it to be of practical necessity to bake these polyester/epoxy compositions in the presence of a curing catalyst. This is especially true for many of the higher molecular weight polyesters such as those frequently cured with

triglycidylisocyanurate (TGIC). Various cure catalysts are known to the art for the reaction of carboxyl- terminated polyesters with epoxides for use in powder coatings. Accelerators include choline chloride, benzyl trimethyl ammonium chloride, imidazole, 1-methylimidazole, 2- methyiimidazole and benzotriazoles as discussed in by Worles et al. in EP 395,185, by Heater in U.S. Patent 4,370,452, by Goring in U.S. Patent 4,507,441 , and by McLafferty et al. in U.S. Patent 4,910,287. Unfortunately, many of these compounds lack the thermal stability at liquid melt temperatures of the polyester (typically 200°C) needed to uniformly blend the cure catalyst into the polyester which results in discoloration of the polyester. As disclosed by McLafferty et al. in U.S. Patent No. 4,910,287 above, the use of 1-methylimidazole causes discoloration of the polyester when anhydrides are used to prepare the polyester. Although some discoloration can be tolerated in some systems, especially highly pigmented systems, it is undesirable in most cases.

It would be desirable, therefore, to have a cure catalyst that does not cause discoloration of the polyester, made using a wide variety of starting materials and heat histories, that still facilitates the carboxylic acid/ epoxy reaction.

The use of phosphonium compounds employed to catalyze the reaction of phenolic hydroxyl and carboxylic acid compounds with epoxides is well known. McLafferty et al. in U.S. Patent No. 4,910,287, mentioned above, discloses the use of triphenylphosphine as a cure catalyst for a carboxyl-terminated polyester with triglycidyl isocyanurate for the low-temperature or accelerated cure of carboxyl- terminated polyesters with epoxides suitable for powder coatings. This disclosure by McLafferty et al. does not disclose the use of the phosphonium compouds of the present invention as a cure catalyst for a carboxyl-terminated polyester with triglycidyl isocyanurate for the low-temperature or accelerated cure of carboxyl-terminated polyesters with epoxides suitable for powder coatings.

There are, however, many known examples of the utility of

phosphorous-containing materials as esterification/transesterification catalysts or as color stabilizers for polyesters that are not encompassed by the present invention. For example, Lazarus in U.S. Patent No. 3,641 ,111 discloses the use of

tetrabutylphosphonium chloride and other phosphorous-containing compounds for the direct esterification of terephthalic acid with an alkylene glycol. Brady in U.S. Patent No. 3,600,365 discloses the use of phosphines and quaternary phosphonium salts for the preparation of poly carboxylic acids from organic polyhalides and salts of polycarboxylic acids. Craun in U.S. Patent No. 4,742,096 and Craun et al. in U.S. Patent No. 4,749,728 disclose the use of phosphonium salts as transesterification catalysts for hydroxyl- functional materials with carboxylic esters.

It has been discovered that phosphonium salts can be used for the low- temperature or accelerated cure of carboxyl-terminated thermosettable polyesters with epoxy compounds such as triglycidyl isocyanurate (TGIC). The cure catalyst may be added to the polyester at any stage of the synthesis or can be added with the epoxy agent during the formulation, with additives if desired, before mixing or extrusion (melt- mixing) or after extrusion. Preferably, the phosphonium salt is added to a liquid melt of the polyester towards the end of the polyester synthesis but can be added at the beginning of the polyester synthesis if desired.

The present invention pertains to a polyester composition comprising (1) a carboxyl-containing thermosettable polyester, and (2) a phosphonium compound .

The present invention also pertains to a curable polyester composition comprising (1) a carboxyl-containing thermosettable polyester, (2) a phosphonium compound as a catalyst for the reaction between (1) and (3), and (3) a compound containing an average of more than one vicinal epoxy group per molecule as a curing agent for the polyester.

The present invention also pertains to a powder coating composition containing (A) a curable polyester composition comprising (1) a carboxyl-containing thermosettable polyester, (2) a phosphonium compound as a catalyst for the reaction between (1) and (3), and (3) a compound containing an average of more than one vicinal epoxy group per molecule as a curing agent for the polyester; and (B) at least one member selected from the group consisting of fillers, pigments, flow control agents, any combination thereof.

FORMULAS

The following formulas are used throughout this application.

Formula I

PHOSPHONIUM COMPOUND

The amount of the phosphonium catalyst to be employed depends upon the reactants used and the particular phosphonium catalyst used. In any event, an amount sufficient to produce the desired reaction is used.

The amount of phosphonium compound which can be employed in the present invention is from 0.0005 to 1.0, preferably from 0.005 to 0.5, more preferably from 0.05 to 0.2, percent by weight based upon the weight of the thermosettable polyester.

When the amount of the phosphonium compound is less than 0.0005 percent by weight, the rate of the cure of the thermosettable polyester with the epoxy compound may be too slow to suit industrial needs.

When the amount of the phosphonium compound is greater than 1.0 percent by weight, the rate of cure may be too fast. That is, the thermosettable polyester/epoxy system may cure upon storage, during extrusion and/or melt mixing or may cure too fast to form a coating with poor properties such as adhesion, impact, gloss, solvent resistance combinations thereof.

Suitable phosphonium compounds which can be employed herein include, but are not limited to those represented by formulas RRRP+X- or -XRRRP⁺-Z- P⁺RRRX- wherein each R is independently a hydrocarbyl or inertly substituted hydrocarbyl group, Z is a hydrocarbyl or inertly substituted hydrocarbyl group and X is any suitable anion.

The term "hydrocarbyl" as employed herein means any aliphatic, cycloaliphatic, aromatic, or aliphatic or cycloaliphatic substituted aromatic groups. The aliphatic groups can be saturated or unsaturated. Those R groups which are not aromatic contain from 1 to 20, preferably from 1 to 10, more preferably from 1 to 4 carbon atoms.

The term "inertly substituted hydrocarbyl group" means that the hydrocarbyl group can contain one or more substituent groups that does not enter into the reaction and does not interfere with the reaction between the epoxy compound and the polyester. Suitable such substituent groups include for example, NO₂, Br, Cl, I, F. Suitable anions include, for example, any of those described by Dante et al. in U.S. Patent No. 3,477,990, by Perry in U. S. Patent No. 3,948,855, by Tyler, Jr. et al. in U.S. Patent No. 4,366,295, by Marshall in U.S. Patent No. 4,634,757 and by Pham et al. in U.S. Patent No. 4,933,420. Particularly suitable anions include the halides such as, for example, chloride, bromide, iodide and the carboxylates as well as the carboxylic acid complexes thereof, such as formate, acetate, propionate, oxalate, trifluoroacetate, formate●formic acid complex, acetate●acetic acid complex, propionate●propionic acid complex, oxalate●oxalic acid complex, trifluoroacetate●trifluoroacetic acid complex. Also suitable anions include, for example, phosphate, and the conjugate bases of inorganic acids, such as, for example, bicarbonate, phosphate, tetrafluoroborate or biphosphate and conjugate bases of phenol, such as, for example phenate or an anion derived from bisphenol A. Some of the catalysts are commercially available; however those which are not can be readily prepared by the method described by Dante et al. in the aforementioned U.S. Patent No. 3,477,990, by Marshall in the aforementioned U.S. Patent No. 4,634,757 and by Pham et al. in the aforementioned U.S. Patent No.

4,933,420,. Examples of the above-mentioned phosphonium catalysts include, among others, methyltriphenyiphosphonium iodide, ethyltriphenylphosphonium iodide, propyrtriphenylphosphonium iodide, tetrabutylphosphonium iodide,

methyltriphenyiphosphonium acetate-acetic acid complex, ethyltriphenylphosphonium acetate·acetic acid complex, propyrtriphenylphosphonium acetate·acetic acid complex, tetrabutylphosphonium acetate-acetic acid complex, methyltriphenyiphosphonium bromide, ethyltriphenylphosphonium bromide, propyitriphenylphosphonium bromide, tetrabutylphosphonium bromide, ethyltriphenylphosphonium phosphate, benzyl-tri- para-tolylphosphonium chloride, benzyl-tri-para-tolylphosphonium bromide, benzyl-tri- para-tolylphosphonium iodide, benzyl-tri-meta-tolylphosphonium chloride, benzyl-tri- meta-tolylphosphonium bromide, benzyl-tri-meta-tolylphosphonium iodide, benzyl-tri- ortho-tolylphosphonium chloride, benzyl-tri-ortho-tolylphosphonium bromide, benzyl-tri- ortho-tolylphosphonium iodide, tetramethylene bis(triphenyl phosphonium chloride), tetramethylene bis(triphenyl phosphonium bromide), tetramethylene bis(triphenyl phosphonium iodide), pentamethylene bis(triphenyl phosphonium chloride),

pentamethylene bis(triphenyl phosphonium bromide), pentamethylene bis(triphenyl phosphonium iodide), hexamethylene bis(triphenyl phosphonium chloride), hexamethylene bis(triphenyl phosphonium bromide), hexamethylene bis(triphenyl phosphonium iodide), or any combination thereof.

Particularly suitable phosphonium compounds which can be employed herein include, for example, methyltriphenyiphosphonium iodide,

ethyltriphenylphosphonium iodide, tetrabutylphosphonium iodide,

methyltriphenyiphosphonium acetate-acetic acid complex, ethyrtriphenyiphosphonium acetate-acetic acid complex, tetrabutylphosphonium acetate-acetic acid complex, methyltriphenyiphosphonium bromide, ethyltriphenylphosphonium bromide, tetrabutylphosphonium bromide, ethyltriphenylphosphonium phosphate, benzyl-tri- para-tolylphosphonium chloride, benzyl-tri-para-tolylphosphonium bromide, benzyl-tri- para-tolylphosphonium iodide, benzyl-tri-meta-toϊylphosphonium chloride, benzyl-tri- meta-tolylphosphoniurn bromide, benzyl-tri-meta-toiylphosphonium iodide, benzyl-tri- ortho-tolylphosphonium chloride, benzyl-tri-ortho-tolylphosphonium bromide, benzyl-tri- ortho-tolylphosphonium iodide or any combination thereof.

The phosphonium compouds can be employed as is or they may be dissolved or dispersed in an organic carrier such as, for example, alcohols such as methanol, ethanol, propanol, glycol ethers such as, for example, ethylene glycol methyl ether, ethylene glycol n-butyl ether, propylene glycol methyl ether or any combination thereof.

When a solvent or diluent is employed, it can be employed in amounts such that the concentration of the phosphonium compound in the diluent is from 0.01 to 99.99, preferably from 25 to 99.99, more preferably from 50 to 99.99, percent by weight.

The phosphonium compounds can be added to the polyesters after they have been prepared or they can be added at the beginning of their preparation or they can be added at any point during their preparation.

POLYESTERS

The polyesters useful in the practice of the present invention are thermosettable carboxyl-terminated and are any of those suitable for the formulation of thermosetting powder coatings with epoxide group bearing compounds. This implies that the polyesters have a sufficiently high glass transition temperature to resist clumping when in powder form and subjected to normally encountered field conditions. It is preferred that the polyesters have a DSC obtained glass transition temperature (Tg) of at least 45°C, wherein the glass transition temperature is obtained by differential scanning calorimetry employing a heat-up rate of 10°C per minute in a nitrogen atmosphere. Thermosettable carboxyl-terminated polyesters having lower glass transition temperatures can be used, but special handling and/or additives may be required to resist the above-mentioned clumping. The thermosettable carboxyl- terminated polyester can have an acid number of 20-100, preferably from 20 to 60, more preferably from 20 to 40. It is preferred that they have a hydroxy! number less than 20, preferably less than 10, more preferably less than 7.

ORGANIC DICARBOXYLIC ACIDS or ANHYDRIDES or ESTERS

Suitable organic dicarboxylic acids which can be employed to prepare the thermosettable polyesters used herein include, for example, aliphatic, cycloaliphatic or aromatic diacids having from 2 to 20 carbon atoms. These diacids can be either saturated or unsaturated. Also suitable are the anhydrides thereof. Such diacids or anhydrides include, but are not limited to, adipic acid, terephthalic acid, oxalic acid, succinic acid, sebacic acid, fumaric acid, azelaic acid, suberic acid, phthalic acid, isophthalic acid, hexahydrophthalic acid, succinic anhydride, phthalic anhydride or any combination thereof. Particularly suitable such acids or anhydrides include, for example, terephthalic acid, isophthalic acid, adipic acid or any combination thereof.

Also suitable are the lower alkyl, C ₁ to C₄ esters of any of the aforementioned dicarboxylic acids. Particularly suitable such esters include, for example, the methyl, ethyl or propyl mono and diesters of adipic acid, terephthalic acid, oxalic acid, succinic acid, sebacic acis, fumaric acid, azelaic acid, suberic acid, phthalic acid, isophthalic acid, hexahydrophthalic acid, or any combination thereof. DIOL COMPOUNDS

Suitable diols (compounds containing two hydroxyl groups per molecule) which can be employed to prepare the polyesters used herein.include, for example, aliphatic, cycloaliphatic or aromatic diols which can be either saturated or unsaturated. These diols can have from 2 to 20, preferably from 2 to 12, more preferably from 2 to 8, carbon atoms per molecule. Such diols include, but are not limited to, ethylene glycol, propylene glycol, 1 ,4-butanediol, 1 ,3-butanediol, 1 ,2-butanediol, pentanediol, hexanediol, heptanediol, neopentyl glycol, nonanediol, decanediol, 2,2,4- trimethyl-1 ,3-pentanediol, diethylene glycol, dipropylene glycol,

cyclohexanedimethanol, 2-methyl-1 ,3-propanediol or any combination thereof.

Particularly suitable such diols include, for example, neopentyl glycol, ethylene glycol, cyclohexanedimethanol or any combination thereof.

POLYFUNCTIONAL REACTANTS

In some instances it is desirable to introduce chain branching into the polyester being prepared. In order to do this a tri- or poly-functional reactant is introduced into the reaction mixture. This tri- or poly-functional reactant can be either hydroxyl or acid or anhydride functional. Particularly suitable tri- or poly-functional reactants which can be employed herein include, for example, trimellitic anhydride, trimethylolpropane, glycerin, triethylolpropane, pentaerythritol or any combination thereof.

MONOFUNCTIONAL REACTANTS

In some instances, it is desirable to incorporate monofunctional compounds into the reaction to control molecular weight. Suitable such monofunctional reactants include, for example, benzoic acid, tert-butylbenzoic acid, phenylbenzoic acid, stearic acid, tert-butylphenol, benzyl alcohol, or any combination thereof.

These monofunctional compounds are employed in amounts of from 0.01 to 10, preferably from 1 to 8, more preferably from 2 to 5, weight percent based upon the total weight of reactants.

REACTION SOLVENTS If desired, the process for preparing polyesters can be conducted in the presence of a suitable solvent such as, for example, aromatic hydrocarbons, ethers, sulfones, chlorinated aromatic hydrocarbons, sulfolanes, sulfoxides or any combination thereof. Particularly suitable such solvents include, for example, toiuene, xylene, diphenyl ether, dimethyl sulfolane or any combination thereof. The solvent can be employed in amounts of from 40 to 95, preferably from 45 to 90, more preferably from 50 to 90, percent by weight based upon the weight of the reactants.

The diol, dicarboxylic acid and, when employed, the tri- or poly-functional compound and monofunctional compound, when employed, are employed in quantities and the reaction conducted such that the resultant acid terminated polyester contains the desired acid number. The desired acid number is less than 100, preferably less than 60, more preferably less than 40.

The acid terminated polyesters are usually prepared at temperatures usually employed in the preparation of polyester resins. Such temperatures are from 150°C to 270°C, preferably from 170°C to 270°C, more preferably from 180°C to 250°C. The reaction is conducted for a time sufficient to bring the reaction to the desired degree of completion. For the acid or carboxyl terminated polyesters of the present invention, the reaction is usually considered complete when the acid number of the reaction mixture is below 100, preferably below 60, more preferably below 40.

At temperatures below 150°C the reaction generally proceeds too slowly to suit industrial needs.

At temperatures above 270°C the polyester may become colored and/or by-product formation such as ethers may result. The reaction is conveniently conducted at pressures from 700 mm

Hg to 1500 mm Hg. The reaction temperature and pressure are balanced such that the water or low-boiling alcohol of reaction is removed as quickly as possible while not distilling the low-boiling reactants, generally glycols, from the reaction. It is generally advantageous to finish the reaction at reduced pressure, generally below 100 mm Hg, preferably below 50 mm Hg, more preferably below 10 mm Hg.

Pressures below 10 mm Hg are generally difficult to achieve on an industrial scale. At pressures above 1500 mm Hg, the rate of removal of water or low- boiling alcohol from the reaction is greatly reduced. The reaction temperature and pressure are balanced such that the water or low-boiling alcohol produced in the reaction, depending upon whether the starting material is an acid or a lower alkyl ester thereof, is removed as quickly as possible while not distilling off any low-boiling reactants.

The time required to achieve the desired degree of reaction depends upon many factors, such as heating and cooling capacity, reaction vessel size, particular reactants and catalyst,. Generally, for lab scale reactions up to 2 liters, the reaction is usually complete in less than 12 hours, preferably in less than 10 hours, more preferably in less than 8 hours.

It is anticipated that in most commercial production reactors used on an industrial scale, the time to essentially complete the reaction is less than 36 hours, preferably less than 30 hours, more preferably less than 24 hours.

The polyester resins are prepared in the presence of a suitable catalyst such as, for example, organotin compounds such as dibutyltin oxide, dimethyltin oxide, dibutyltin dilaurate, butylchlorotin dihydroxide, organotitanium compounds such as tetramethyl titanate, tetrabutyl titanate, vanadyl alcoholates such as vanadyl isopropylate and vanadyl isobutylate or any combination thereof. It is preferred to prepare the acid terminated polyesters in the presence of a catalyst composition comprising (1) at least one organotin salt of a carboxylic acid, and (2) either (a) at least one organotin oxide, or (b) at least one organostannoic acid, or (c) a combination of (a) and (b).

ORGANOTIN SALTS

Suitable organotin salts of a carboxylic acid which can be employed herein include, for example, those represented by the following formulas R-Sn(O₂CR'), R₂Sn(O₂R')₂, R₂Sn(O₂CR')(OCR'), R-Sn(O₂CR')₃ or

R-Sn(O₂CR')₂Y; wherein each R is the same or different and is an alkyl group having from

1 to 20, preferably from 1 to 12, more preferably from 1 to 8, carbon atoms, or an aryl, alkaryl or cycloalkyl group having from 6 to 14 carbon atoms. The R groups can be saturated or unsaturated and can be substituted or unsubstituted with such substituent groups as alkyl, aryl or cycloalkyl groups having from 1 to 20 carbon atoms, halogen, preferably chlorine or bromine, -NO₂,; and Y is a halogen, preferably chlorine or bromine. Such organotin salts of a carboxylic acid include, but are not limited to stannous acetate, stannous laurate, stannous octoate, stannous oleate, stannous oxalate, dibenzyltin diacetate, dibenzyltin distearate, dibutylmethoxytin acetate, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, dilauryltin diacetate, dioctyltin diacetate, dioctyltin dilaurate, diphenyltin diacetate, methyttin trilaurate, methyltin tris(2-ethylhexoate), butyltin triacetate, butyttin trilaurate, butyrtin tris(2-ethylhexoate), or any combination thereof. Particularly suitable such organotin salts of carboxylic acids include, for example, dibutyltin diacetate, dibutyltin dilaurate, stannous octoate, dioctyltin dilaurate or any combination thereof.

ORGANOTIN OXIDES

Suitable organotin oxides which can be employed herein include, for example, those represented by the formula R₂SnO wherein R is as defined above. Such organotin oxides include, but are not limited to bis(carbomethoxyethyl) tin oxide, diallyitin oxide, dibenzyltin oxide, dibutyltin oxide, dicyclohexyltin oxide, dilauryltin oxide, dimethyltin oxide, di-1-naphthyrtin oxide, dioctyltin oxide, diphenyltin oxide, divinyltin oxide, or any combination thereof. Particularly suitable organotin oxides include, for example, dibutyltin oxide, dimethyltin oxide or any combination thereof.

ORGANOSTANNOIC ACIDS

Suitable organostannoic acids which can be employed herein include, for example, those represented by the formula R-SnOOH or their corresponding anhydrides represented by the formula (R-SnO)₂O wherein R is as defined above. Such organostannoic acids or anhydrides thereof include, but are not limited to

phenylstannoic acid, chlorobenzylstannoic acid, 1-dodecyl-stannoic acid,

methylstannoic acid, 1-naphthylstannoic acid, butylstannoic acid, octyistannoic acid, their anhydrides, or any combination thereof. Particularly suitable organostannoic acids or anhydrides include, for example, butylstannoic acid, methylstannoic acid or any combination thereof.

CATALYST CONCENTRATION The tin catalysts which can be employed herein are employed in an amount which provides a total amount of catalyst of from 0.00 i to abut 3, preferably from 0.01 to 1.0, more preferably from 0.05 to 0.2 weight percent based upon the weight of the reactants.

The organotin salt of a carboxylic acid catalyst (component 1) is employed in an amount of from 0.01 to 99.99, preferably from 0.01 to 60, more preferably from 0.01 to 30 mole percent based upon the total amount of catalyst; and the organotin oxide and/or organostannoic acid catalyst (component 2) is employed in an amount of from 0.01 to 99.99, preferably from 50 to 99.99, more preferably from 70 to 99.99 mole percent based upon the total amount of catalyst.

CURING AGENT

The epoxy curing agent can be any epoxy that results in a thermosettable coating with acceptable properties. Examples of suitable epoxides include for example, triglycidyl isocyanurate or a related heterocyclic triepoxy compound such as methyl-substituted triglycidyl isocyanurate, 1 ,2,4-triglycidyl triazolidine-3,5-dione or diglycidylterephthalate or diglycidylhexahydroterephthalate or diglycidyl ethers of polyhydric phenols such as, for example, resorcinol, catecol and hydroquinone, the diglycidyl ethers of bisphenol and bisphenols such as, for example, bisphenol A, bisphenol F, bisphenol K, bisphenol S as well as the alkyl and halogen derivatives thereof such as the C-1 to C-4 alkyl, chlorine or bromine derivatives. Also suitable are the polyglycidyl ethers of the novalac resins prepared by reacting a phenol or alkyl or halogen substituted phenol with an aldehyde such as formaldehyde. These are disclosed by Nelson in U.S. Patent No. 4,390,680 which is incorporated herein by reference in its entirety. Preferably, the epoxide containing compounds are triglycidyl isocyanurate and the diglycidyl ethers of dihydroxyl containing compounds represented by the formulas I, II, III, IV or V wherein each A is independently a divalent hydrocarbyl group having from 1 to 12, more suitably from 1 to 8, most suitably from 1 to 4 carbon atoms; each A' is independently a divalent saturated or unsaturated aliphatic or cycloaliphatic group having grom 1 to 10, preferably from 1 to 6, more preferably from 1 to 4, carbon atoms; each R is independently hydrogen or an alkyl group having from 1 to 4 carbon atoms, preferably hydrogen or methyl, most preferably hydrogen; each X is independently hydrogen or a hydrocarbyl or hydrocarbyloxy group having from 1 to 12, preferably from 1 to 6, more preferably from 1 to 4, carbon atoms or a halogen, preferably chlorine or bromine; Z is a glycidyl group or an alkyl substituted glycidyl group, said substituent being an alkyl group having from 1 to 4 carbon atoms, preferably methyl; m has a value from 0 to 6, preferably from 0.1 to 5, more preferably from 0.1 to 4; m' has an average value from 0.1 to 6, preferably from 0.1 to 5, more preferably from 0.1 to 4; n has a value of zero or 1; and n' has a value from zero to 6, preferably from 0.1 to 5, more preferably from 0.1 to 4; p has an average value from 0 to 4, preferably from 0.01 to 3, more preferably from 0.1 to 3; and p' has an average value from 0 to 4, preferably from 0.01 to 3, more preferably from 0.1 to 3.

The quantity of the epoxy compound used in the binding agent with the thermosettable polyester resin depends on the acid number of the polyester resin and on the epoxy equivalent weight of the epoxy compound with which the polyester is combined, and is in general between from 0.80 to 1.30, preferably from 0.90 to 1.10, more preferably from 0.95 to 1.05 epoxy equivalents per carboxyl equivalent and is particularly preferred to approach stoichiometry, that is, one epoxy group per carboxyl group.

POWDER COATINGS

The powder coating compositions of the present invention comprise the curable compositions and one or more additives such as, for example, fillers, pigments, flow control agents, any combination thereof.

ADDITIVES The amounts of the additive compounds are those which provides the composition with the desired result. That is in the instance of pigments, they are added in amounts which provides the powder coating with the desired color. Usually, the amount is from 0.01 to 40, preferably from 0.01 to 15, more preferably from 0.1 to 10, percent by weight based upon the weight of the binder (combined weight of polyester resin plus curing agent).

Suitable pigments include, for example, carbon black, titanium dioxide, iron oxide, zinc sulfide, zinc oxide, lead chromate, phthalocyanine blue, chromium oxide or any combination thereof. The fillers are employed in amounts which provide the powder coating with the desired cost, hardness, volume, surface texture, corrosion resistance or the like. However, the fillers are usually employed in amounts of from 0 to 80, preferably from 2 to 75, more preferably from 5 to 50, percent by weight based upon the weight of the binder.

Suitable fillers include, for example, calcium carbonate, barium sutfate, wollastonite, kaolin clay, nephelin sulfate, quartz or any combination thereof. The flow control agents are employed in amounts which provide the powder coating with the desired surface aesthetics, anti-cratering action, pinhole-free surface, smoothness, adhesion, dry flow. However, the fillers are usually employed in amounts of from 0.01 to 20, preferably from 0.05 to 10, more preferably from 0.1 to 1.0, percent by weight based upon the weight of the binder.

Suitable flow control agents include, for example, polyacrylate oligomers, silicones, teflon, benzoin or any combination thereof.

The following examples are illustrative of the present invention but are not to be construed as to limiting the scope thereof in any manner.

The following compounds were employed in the Examples. TGIC is triglycidylisocyanurate. MEK is methylethyl ketone.

A-1 is ethyltriphenylphosphonium acetate·acetic acid (70 wt. percent in methanol).

A-2 is tetrabutylphosphonium acetate-acetic acid complex (70 wt. percent in methanol). l-1 is ethyltriphenylphosphonium iodide.

P-1 is ethyltriphenylphosphonium phosphate (30 wt. percent in methanol).

D.E.R.™ 663U is an advanced epoxy resin prepared from a diglyicidyl ether of bisphenol A having an EEW from 180 to 190 and bisphenol A, the advanced resin having an epoxide equivalent weight (EEW) of 730, commercially available from The Dow Chemical Company.

Uralac P-5400, is a saturated carboxylated polyester resin (commercially available from Dutch State Mines) having an acid number of 34 (acid equivalent weight of 1650) and a melt viscosity of 120 poise at 175°C.

Ruco 106, is a saturated hydroxyl-terminated polyester resin having a hydroxyl number of 44 (hydroxyl equivalent weight of 1275), commercially available from Ruco Polymer Corporation.

Pioester 4140 is a saturated hydroxyl-terminated polyester resin having a hydroxyl number of 41 (hydroxyl equivalent weight of 1368), commercially available from Pioneer Plastics.

Pioester 4248 is a saturated carboxylated polyester resin having an acid number of 27 (acid equivalent weight of 2078), commercially available from Pioneer Plastics.

Acid numbers were determined by dissolving 0.5-1 g of resin in 30mL dimethyl formamide (DMF) and titrating with 0.1 N KOH (in methanol) using

phenolphthalein as the indicator.

Viscosities were measured using a Research Equipment (London) Ltd. ICI Cone and Plate viscometer at 175°C using the "C" cone.

APHA color was measured on a Hellige Aqua Tester (Hellige Inc., Garden City, N.Y.) using 5g of sample and 45g of tetrahydrofuran (THF) and comparing the color of the solution (after sonication to fully dissolve the polyester) with color disk standards. The higher the APHA number, the darker the solution.

Methyl ethyl ketone (MEK. double rubs, which is an indication of solvent resistance, was determined by imparting double rubs on the coating side of the panel with a Q-tip that was rewetted every 50 double rubs with fresh MEK. The number of double rubs to metal is recorded. Gel times were measured at 180°C on a Thomas Electric Company (Cleveland, Ohio) Cure Plate using 1/4 teaspoon (0.7g) of the formulated powder. The powder was stroked with a wooden craft stick until the mixture gells. EXAMPLE 1

Use of tetrabutylphosphonium acetate●acetic acid complex (A-2) catalyst with a saturated carboxylated polyester Uralac P-5400 polyester resin (1200g) was heated in a 2 liter flask equipped with a heating mantle, stirrer, thermometer and nitrogen inlet and outlet to a temperature of 185°C whereupon 3.0g of A-2 catalyst (70 wt % in methanol) was added. The mixture was then raised to 200°C (in 10 min) and then stirred at 200°C for an additional 30 min whereupon the mixture was poured onto aluminum foil. The APHA color, measured using 10 wt % resin in THF, of the Uralac P-5400 was is 60 before heating and remained at 60 after heating in the presence of A-2 catalyst.

EXAMPLE 2 Comparison of cured properties of Uralac P-5400 with and without tetrabutyl phosphonium acetate●acetic acid complex (A-2) catalyst

Uralac P-5400 polyester and A-2 catalyst containing Uralac P-5400 polyester described in Example 1 were used in this comparison evaluation. The polyester (837g, 0.507 equivalent), triglycidylisocyanurate (TGIC; 63g, 0.636 equivalent) having an epoxy equivalent weight (EEW) of 99, TiO₂ (450g) and Resiflow P-67 (a flow modifier commercially available from Synthron, Inc.; 13.5g) were placed in a plastic bag, sealed and dry mixed to a homogeneous blend. The dry-mixed formulation is then extruded in a Buss-Condux PLK 46 single screw extruder (equipped with a 46mm diameter kneader screw operated at 100rpm) with Zone 1 at 55°C and Zone 2 at 110°C. The extrudate is passed through Buss-Condux Chill Rolls (6.5 in., 165.1 mm diameter), cooled and crushed. The crushed extrudate is then fine ground in a Brinkman ZM-1 Centrifugal Grinding Mill utilizing the 12-tooth grinding attachment and 0.75mm screen. The finely ground extrudate is sieved through a No.140 (150 mesh, 100um) standard test sieves (wire cloth). Portions of the -150 mesh powder coating formulation were applied via electrostatic spray with a Wagner EPM200 unit (set at 80-90kV) connected to a Wagner G-100 electrostatic Spray-O-Round sprayer onto 4" x 12" x 20 gauge (101.6mm x 304.8mm x 0.529mm) cold rolled steel, clean treatment Parker test panels (Parker Division, Hooker Chemicals and Plastics Corp.). The electrostatically coated panels were set in a Blue M Touchmatic convection-type oven and cured. After removal from the oven the panels were evaluated via the following test methods: coating thickness is determined per ASTM D1186 by utilizing a Fisher Model 650C film thickness tester. Surface gloss was determined per ASTM D523 (DIN 67530) using a BYK Chemie Model 4031 multi-gloss unit. Gardner forward and reverse impact strengths were determined per ASTM D2794 using a Gardner impact Tester, 46 inch (1.17m) tube length, 0-160 in-lb (0-18 J) tester with a four pound (1.81 kg) one-half inch (12.7mm) diameter cone. The are given in Table I.

* Not an example of the present invention.

a 180°C, seconds.

b Gardner impact forward/reverse, inch-lbs (J).

c Methyl ethyl ketone double rubs.

d 20760° gloss. EXAMPLE 3

Use of ethyltriphenylphosphonium iodide (l-1) catalyst with a saturated carboxylated polyester Commercially available Uralac P-5400 polyester (1200g), described in

Example 1, was heated to 180°C whereupon 1.2 g of I-1 was added. The polyester was raised to 200°C (in 10 min) and the polyester/l-1 was stirred at 200°C for an additional 30 min whereupon the mixture was poured onto aluminum foil. The APHA color, measured using 10 wt % resin in THF, of the Uralac P-5400 polyester was 60 before heating and was 80 after heating in the presence of I-1 catalyst. EXAMPLE 4

Comparison of cured properties of Uralac P-5400 with and without l-1 catalyst

Uralac P-5400 polyester and I-1 catalyst containing Uralac P-5400 polyester described in Example 3 were used in this comparison evaluation. The polyester (837g, 0.505 equivalents), TGIC (63g, 0.636 equivalents), TiO₂ (450g) and

Resiflow P-67 (a flow modifier; 13.5g) were placed in a plastic bag, sealed and dry mixed to provide a homogeneous dry blend which was further processed and evaluated using the method of Example 2. The are given in Table II.

* Not an example of the present invention.

a 180°C, seconds.

b Gardner impact forward/reverse, inch-lbs (J).

c Methyl ethyl ketone double rubs.

d 20760º gloss. EXAMPLE 5

Use of tetrabutyl phosphonium acetate●acetic acid complex (A-2) catalyst in Formulated Uralac P-5400 Powder

Tetrabutyl phosphonium acetate●acetic acid complex catalyst (A-2) was tested for its ability to shorten the gel time of the uncatalyzed formulated polyester powder described in Example 4. The A-2 catalyst was first dispensed via a 10 μL syringe onto the gel plate which was maintained at 180°C. The formulated polyester powder was immediately placed on the gel plate and, with stirring, the time taken for the powder to gel at 180°C was recorded. The results are given in Table III.

* Not an example of the present invention.

EXAMPLE 6

Use of l-1 catalyst in Formulated Uralac P-5400 Powder I-1 catalyst was tested for its ability to shorten the gel time of the uncatalyzed formulated polyester powder described in Example 4. The following amounts of I-1 were combined with 5.00±0.01g of the formulated Uralac P-5400 powder in a 2 ounce(59mL) jar. The were mixed on a mechanical shaker for 1 hour to facilitate mixing. One quarter tablespoon (0.7g) of the formulated polyester powder was placed on the gel plate maintained at 180°C and the time taken for the powder to gel was recorded. The are given in Table IV.

* Not an example of the present invention.

EXAMPLE 7

Addition of I-1 to Formulated P-5400 Powder and cure properties obtained

Uralac P-5400 polyester described in Example 1 was used in this comparison evaluation. The polyester (837g, 0.507 equivalents), TGIC (63g, 0.636 equivalents), TiO2 (450g) and Resiflow P-67 (a flow modifier; 13.5g) were placed in a plastic bag, sealed and dry mixed to provide a homogeneous dry blend which was further processed and evaluated using the method of Example 2. The results are given in Table V.

a 180°C, seconds.

b Gardner impact forward/reverse, inch-lbs (J).

c Methyl ethyl ketone double rubs.

d 20760° gloss. These results show the improvement of Impact properties and equal to or better MEK double rubs compared to uncatalyzed Uralac P-5400 described in Example 4. Further, these results point out the preferred method of adding the phosphonium salt catalyst to the polyester resin described in EExample 4 rather than to the formulated powder described here.

EXAMPLE 8

Storage stability of Uralac P-5400 Powders with and without catalyst

The storage stability of formulated Uralac P-5400 powder (uncatalyzed) was compared to the storage stability of tetrabutyl phosphonium acetate»acetic acid complex (A-2) catalyzed Uralac P-5400 powder described in Example 2 and to the storage stability of I-1 catalyzed Uralac P-5400 powder described in Example 4. In each case approximately 1 inch (25.4 mm) of powder was placed into 25 x 200 mm test tubes and then a 100 ±0.5 g weight was placed on top of the powder. The powders were heated in an air oven for 24 hours at 110°F (43.3°C). The powders were removed from the test tubes and cooled for 30 min. The powders were then graded on a scale of 1 -10 with 1 being poor and 10 being excellent. The uncatalyzed Uralac 5400 powder as well as the A-2 or I-1 containing powders all were graded 4.

EXAMPLE 9 Use of various phosphonium salts to accelerate the cure of a formulated carboxyl- terminated polyester.

The polyester used in this study was prepared in a 10 gallon reactor equipped with a heating jacket, temperature controller, agitator and a column packed with stainless steel wire mesh. To this reactor was charged:

Terephthalic acid 16946 g (102.00 moles)

Neopentyl glycol 11430 g (109.75 moles)

Trimethylol propane 222 g (1.65 moles)

Water 1700 g

Butyltin hydroxide oxide 31 g (0.11 wt. %)

This mixture was heated to 230°C and monitored periodically by measuring the acid number and viscosity using an I.C.I. cone and plate viscometer. After a viscosity of 72 poise at 175°C and an acid number of 5.5 was obtained isophthalic acid (2937g, 17.68 moles) was added. Vacuum was applied slowly until a final acid number of 36.5 and a 175°C viscosity of 189 was obtained. The resin was discharged from the reactor at this point. Formulated powder was prepared, by dry mixing polyester resin (930g, 0.605 equivalents), TGIC (70g, 0.707 equivalents) TiO₂ (500g) and Resiflow P-67 (a flow modifying agent, 15g were placed in a plastic bag, sealed and dry mixed to provide a homogeneous dry blend which was processed using the method of Example 2.

Several phosphonium salts were tested for their ability to shorten the gel time of the formulated powder described above . For solid catalysts ethyltriphenylphosphonium iodide (I-1), benzyltriphenylphosphonium chloride and benzyltritolylphosphonium chloride, 5.00 ±0.01 g of formulated powder was combined with the catalyst. The powder/catalyst were mixed on a mechanical shaker for 1 hr to facilitate mixing. Gel times were taken of 1/4 tablespoon (0.7g) of this powder at 180°C. For liquid catalysts tetrabutylphosphonium acetate● acetic acid complex (A-2, 70 wt % in MeOH) and ethyltriphenylphosphonium phosphate (P-1 , 30 wt % in MeOH), the liquid catalyst was first placed on the gel plate (180°C) via a 10 ul syringe and then the powder was immediately placed on the gel plate. The results are shown below. The gel time of the uncatalyzed powder was 285 sec.

(A) Powder + l-1

* Not an example of the present invention.

EXAMPLE 10 Use of A-2 with Carboxyl-terminated polyester and formulated properties

Polyester resin described in Example 9 (1200 g) was heated to 200°C in a 2 liter flask equipped with a heating mantle, thermometer, stirrer and a nitrogen inlet and outlet. To this molten resin was added either triphenyl phosphine (2.65 g) or tetrabutylphosphonium acetate●acetic acid complex (A-2) catalyst (3.7g). The resin was heated for an additional 30 min at 200°C and the polyester was then poured onto aluminum foil. Polyester resin (930 g, 0.605 equivalents) was formulated with TGIC (70 g, 0.707 equivalents), TiO₂ and Resiflow P-67 as described in Example 9 and then placed in a plastic bag, sealed and dry mixed to provide a homogeneous dry blend which was further processed and evaluated using the method of Example 2. In this case, the panels were cured in the oven at 180°C for 15 min. The results are given in Table VI.

* Not an example of the present invention.

a Stroke cure, 180°C, seconds.

b Gardner impact forward/reverse, inch-lbs (J)

c. MEK (methyl ethyl ketone) double rubs.

EXAMPLE 11

Discoloration Evaluation

Below are the APHA color results of the polyester described in Example 9 plus various agents compared with commercially available DSM P2400 polyester (Dutch State Mines). In each case, the polyester was melted at 200°C and the agents shown were added. Ten grams of each resin was placed in an aluminum pan in an air oven set at 220°C for 6 hours. APHA color was measured on a Hellige Aqua Tester (Hellige Inc.) using 5 g of sample and 45 g of tetrahydrofuran (THF) and comparing the color of the solutions with color disk standards. Higher APHA numbers correspond to darker solution colors. The results are given in Table VII.

0^a ) l

10

- -

Color(0)^a Color(6)^b

EXAMPLE 12

Use of of phosphonium salts for low temperature cure The polyester powders described in Example 9 were cured at 149°C and 120°C on a gel plate. The results are given in Table VIII.

A. Use of Example 9C for cure at 149°C.

* Not an example of the present invention

EXAMPLE 13

Use of A-2 for Low-temperature Cure of DSM P-5400 Polyester

DSM P-5400 polyester, described in Examplel , was heated to 200°C in a 5 liter flask equipped with a heating mantle, stirrer, thermometer, nitrogen inlet and outlet. Tetrabutylphosphonium acetate●acetic acid complex (A-2) catalyst (15.0g) was added at 200°C , the resin was stirred at this temperature for 30 min and then poured onto aluminum foil. The catalyzed resin and a control of P-5400 polyester were formulated accordingly:

* Not an example of the present invention.

These formulated were mixed separately in a plastic bag and then double extruded through the single screw extruder (zone 1=55°C, zone 2=110°C). The extrudates were then ground to pass through a #140 mesh screen as described in Example 2. The gel time (180°C) of uncatalyzed P-5400 powder was 311 sec whereas the gel time of the A-2 catalyzed powder was 70 sec. The powders were then electrostatically sprayed onto 4" x 12" (101.6mm x 304.8mm) steel panels and baked in an air oven. The results are given in Table IX.

* Not an example of the present invention.

a Gardner Impact forward/reverse, inch-lbs (J).

b Methyl ethyl ketone double rubs.

EXAMPLE 14

Preparation of Anhydride-based Polyester in Presence of A-2 The following polyester was prepared in a 2 liter flask equipped with a heating mantle, stirrer, thermometer, nitrogen inlet and outlet and connected to a column with stainless steel wire mesh. The flask was charged:

Terephthalic acid 847.1 g (5.1 moles)

Neopentyl glycol 618.55g (5.9 moles)

Butylchlorotin dihydroxide 1.5g (0.1 wt. %)

A-2 (70 wt. % in methanol) 2.65g (0.18 wt.%)

The mixture was heated to 250°C and monitored periodically by measuring the acid number and viscosity using a cone and plate viscometer. After a viscosity of 10 poise at 175°C and an acid number of 14 was obtained, the temperature was lowered to 200°C. Succinic anhydride (113 g, 1.13 moles) was added and the temperature then was slowly increased to 230°C. When an acid number of 37 was obtained, triphenyiphosphite (2.4 g, 0.15 wt. percent) was added. No color change occured. The resin was poured onto aluminum foil 15 minutes after addition of the triphenyiphosphite. APHA color of the poured resin was 15. EXAMPLE 15

Use of A-1 for the Cure of Carboxyl-terminated Polyester Containing High Hydroxyl Number with TGIC Commercially-available Pioneer Pioester 4248 (acid number = 27, hydroxyl number = 10) having an acid equivalent weight of 2077.8 was used in this study. The polyester (50.0 g, 0.024 equivalents), TGIC (3.76 g, 0.038 equivalents) and Ti0₂ (26.9 g) were combined in an 8 ounce (236 mL) jar and mixed on a mechanical shaker for 1 hr. The mixture was then ground into a fine powder using an electric minimixer. When A-1 was dispersed onto the gel plate via a 10 μl syringe with the powder, the gel time results (180°C) are given in Table X.

* Not an example of the present invention. EXAMPLE 16

Use of A-2 for the Cure of Carboxyl-terminated Polyester Containing High Hydroxyl Number with TGIC Commercially-available Pioneer Pioester 4248 (acid number = 27, hydroxyl number = 10) having an acid equivalent weight of 2077.8 was used in this study. The polyester (50.0 g, 0.024 equivalents), TGIC (3.76g, 0.038 equivalents) and TiO₂ (26.9 g were combined in an 8 ounce (236 mL) jar and mixed on a mechanical shaker for 1 hr. The mixture was then ground into a fine powder using an electric mini-mixer. When A-2 was dispersed onto the gel plate via a 10 μl syringe with the powder, the gel time results (180°C) are given in Table XII.

* Not an example of the present invention.

EXAMPLE 17

Use of A-2 for the Cure of Hydroxyl-terminated Polyesters with TGIC

Commercially-available Ruco 106 polyester (hydroxyl number = 44, acid number =14) having an acid equivalent weight of 4007 was used in this study. The polyester (30.0g, 0.007 equivalents), TGIC (3.54 g, 0.036 equivalents) and TiO₂ (16.1g) were combined in a 2 ounce (59 mL) jar and mixed on a mechanical shaker for 1 hour. The mixture was then ground into a fine powder using an electric mini-mixer for 8 seconds. This powder showed no sign of curing at 180°C when stirred up to 15 minutes(900 sec). When A-2 was dispensed onto the gel plate via a 10 μL syringe with the powder, the gel time results are given in Table XIII.

EXAMPLE 18

Use of A-2 for the Cure of Hydroxyl-terminated Polyesters with TGIC

Commercially-available Pioneer Pioester 4140 (hydroxyl number = 41 , acid number = 6) having an acid equivalent weight of 9350 was used in this study. The polyester (60.0 g, 0.006 equivalents), TGIC (5.74 g, 0.058 equivalents) and TiO₂ (32.1 g) were combined in an 8 ounce (236 mL) jar and mixed on a mechanical shaker for 1 hr. The mixture was then ground into a fine powder using an electric mini-mixer. This powder shows no signs of curing at 180°C when stirred up to 18 minutes. When tetrabutylphosphonium acetate●acetic acid complex (A-2) was dispersed onto the gel plate via a 10 μl syringe with the powder, the gel time results (180°C) are given in Table XIV.

* Not an example of the present invention.

When ethyltriphenylphosphonium acetate●acetic acid complex (A-1) catalyst was used in concentrations of 1.98, 4.94, 7.92, 11.88 and 15.84 mg catalyst per gram of Pioester 4140 powder, there was no sign of cure up to 900 seconds. When ethyl

triphenylphosphonium was used at concentrations of 0.28, 0.72, 1.38, 1.86 and 3.34 mg catalyst per gram of Pioester 4140 powder, there was no sign of cure up to 900 seconds. Finally, when ethyl triparatolylphosphonium was used (70 wt. % in methanol) at concentrations of 2.07, 10.36, 15.54 and 20.72 mg catalyst per gram of Pioester 4140 powder, there was no sign of cure up to 900 seconds.

EXAMPLE 19

Use of tetrabutyl phosphonium acetate●acetic acid complex (A-2) catalyst for the reaction of a carboxyl-terminated polyester with DEH 663U epoxy resin

Tetrabutyl phosphonium acetate»acetic acid complex catalyst (A-2) was tested for its ability to shorten the gel time of a formulated polyester powder made from commercially-available DSM 2695 polyester (450g, 0.562 equivalents; acid number =70, cone and plate viscosity at 175°C of 48 poise; Dutch State Mines) having an acid equivalent weight of 801.4, a portion of a commercial grade of a bisphenol A advanced diglycidyl ether of bisphenol A (336g, 0.46 equivalents; D.E.R. 663U, Dow Chemical Company) having an epoxide equivalent weight(EEW) of 730, barium sulfate (450g), Ti02 (300g), Resiflow P-67 (a flow modifier; 13.5g), benzoin (6g) and choline chloride (a cure catalyst; 2.25g) were placed in a plastic bag, sealed and dry mixed to provide a homogeneous dry blend which was further processed using the method of Example 2.

The A-2 catalyst was first dispensed via a 10 μL syringe onto the gel plate which was maintained at 180°C. The formulated polyester powder was immediately placed on the gel plate and, with stirring, the time taken for the powder to gel at 180°C was recorded. The results are given in Table XV.

* Not an example of the present invention.

Claims

1. A polyester composition characterized by consisting of (1) at least one carboxyl-containing thermosettable polyester, and (2) at least one phosphonium catalyst compound in an amount sufficient to catalyze the subsequent reaction between component (1) and a polyepoxide compound.

2. A polyester composition of Claim 1 wherein said

phosphonium compound is a phosphonium halide or phosphonium

carboxylate●carboxylic acid complex.

3. A polyester composition of Claim 1 wherein said

thermosettable carboxyl-containing polyester is any polyester with an acid number below 100; and said phosphonium compound is methyltriphenyiphosphonium iodide, ethyltriphenylphosphonium iodide, tetrabutylphosphonium iodide,

methyltriphenyiphosphonium acetate-acetic acid complex, ethyltriphenylphosphonium acetate-acetic acid complex, tetrabutylphosphonium acetate-acetic acid complex, methyltriphenyiphosphonium bromide, ethyltriphenylphosphonium bromide, tetrabutylphosphonium bromide, ethyltriphenylphosphonium phosphate, benzyl-tri- para-tolylphosphonium chloride, benzyl-tri-para-tolylphosphonium bromide, benzyl-tri- para-tolylphosphonium iodide, benzyl-tri-meta-tolylphosphonium chloride, benzyl-tri- meta-tolylphosphonium bromide, benzyl-tri-meta-tolylphosphonium iodide, benzyl-tri- ortho-tolylphosphonium chloride, benzyl-tri-ortho-tolylphosphonium bromide, benzyl-tri- ortho-tolylphosphonium iodide or any combination thereof.

4. A curable polyester composition characterized by consisting of (1) at least one carboxyl-containing thermosettable polyester, (2) at least one phosphonium compound as a catalyst for the reaction between (1) and (3), and (3) at least one compound containing an average of more than one vicinal epoxy group per molecule as a curing agent for the polyester.

5. A curable polyester composition of Claim 4 wherein said phosphonium compound is a phosphonium halide or phosphonium

carboxylate●carboxylic acid complex.

6. A curable polyester composition of Claim 4 wherein said carboxyl-containing thermosettable polyester is any polyester having an acid number below 100; said phosphonium compound is methyltriphenyiphosphonium iodide, ethyltriphenylphosphonium iodide, tetrabutylphosphonium iodide,

methyltriphenyiphosphonium acetate-acetic acid complex, ethyltriphenylphosphonium acetate-acetic acid complex, tetrabutylphosphonium acetate·acetic acid complex, methyltriphenyiphosphonium bromide, ethyltriphenylphosphonium bromide, tetrabutylphosphonium bromide, ethyltriphenylphosphonium phosphate, benzyl-tri- para-tolylphosphonium chloride, benzyl-tri-para-tolylphosphonium bromide, benzyl-tri- para-tolylphosphonium iodide, benzyl-tri-meta-tolylphosphonium chloride, benzyl-tri- meta-tolylphosphonium bromide, benzyl-tri-meta-tolylphosphonium iodide, benzyl-tri- ortho-tolylphosphonium chloride, benzyl-tri-ortho-tolylphosphonium bromide, benzyl-tri- ortho-tolylphosphonium iodide or any combination thereof; and said curing agent is triglycidylisocyanurate, a diglycidyl ether of a dihydric phenol, or any combination thereof.

7. A powder coating composition characterized by containing (A) a curable polyester composition comprising (1) at least one carboxyl-containing thermosettable polyester, (2) at least one phosphonium compound as a catalyst for the reaction between (1) and (3), and (3) at least one compound containing an average of more than one vicinal epoxy group per molecule as a curing agent for the polyester; and (B) at least one member selected from the group consisting of fillers, pigments, flow control agents, or any combination thereof.

8. A powder coating composition of Claim 7 wherein said phosphonium compound is a phosphonium halide or phosphonium

carboxylate●carboxylic acid complex.

9. A powder coating composition of Claim 7 wherein said carboxyl-containing thermosettable polyester is any polyester with an acid number below 100; said phosphonium compound is methyltriphenyiphosphonium iodide, ethyltriphenylphosphonium iodide, tetrabutylphosphonium iodide,

methyltriphenyiphosphonium acetate●acetic acid complex,

ethyltriphenylphosphoniumacetate●acetic acid complex, tetrabutylphosphonium acetate●acetic acid complex, methyltriphenylphosphonium bromide,

ethyltriphenylphosphonium bromide, tetrabutylphosphonium bromide,

ethyltriphenylphosphonium phosphate, benzyl-tri-para-tolylphosphonium chloride, benzyl-tri-para-tolylphosphonium bromide, benzyl-tri-para-tolylphosphonium iodide, benzyl-tri-meta-tolylphosphonium chloride, benzyl-tri-meta-tolylphosphonium bromide, benzyl-tri-meta-tolylphosphonium iodide, benzyl-tri-ortho-tolylphosphonium chloride, benzyl-tri-ortho-tolylphosphonium bromide, benzyl-tri-ortho-tolylphosphonium iodide or any combination thereof; and said curing agent is triglycidylisocyanurate, a diglycidyl ether of a dihydric phenol, or any combination thereof.