MXPA00007749A - Polyester containing tertiary carboxyl groups, preparation method and thermosetting powder compositions containing same - Google Patents

Abstract

The invention concerns a polyester bearing tertiary carboxyl groups, characterised in that it consists of:(a) 8.1 to 35 moles of an aliphatic or cycloaliphatic of a polyol;(b) 9.1 to 36 moles of an aliphatic, cycloaliphatic or aromatic polycarboxylic acid;(c) 1.6 to 2.8 moles of an aliphatic, cycloaliphatic or aromatic compound comprising a tertiary carboxyl group and either a primary or secondary carboxyl group, or a primary or secondary hydroxyl group. Said polyester is prepared in several steps, the first steps consisting in the preparation of a polyester by condensation between (a) an aliphatic or cycloaliphatic polyol, and (b) an aliphatic, cycloaliphatic or aromatic polycarboxylic acid, the final step consisting in condensing said polyester with (c) an aliphatic, cycloaliphatic or aromatic compound comprising a tertiary carboxyl group and either a primary or secondary carboxyl group, or a primary or secondary hydroxyl group. Said polyester is used in thermosetting powder compositions, mixed with a crosslinking agent which is more particularly a&bgr;-hydroxylalkylamide. Said compositions provide coatings with excellent surface appearance, good flexibility and good resistance to poor weather conditions.

Description

POLYESTER CONTAINING TERBOARY CARBOXYL GROUPS, PROCESS FOR YOUR PREPARATION AND COMPOSITIONS IN POWDER THERMOENDUREABLE THAT CONTAINS DESCRIPTION OF THE INVENTION The present invention relates to novel polyesters containing tertiary carboxyl groups, to a process for their preparation and to thermosetting powder compositions containing, as a binder or substance, the polyesters and a crosslinking agent capable of being reacted with their carboxyl groups. The invention also relates to the use of these compositions for preparing paints and varnishes in powder form for making coatings, as well as for the coatings thus obtained. The powder compositions are well known in the state of the art and are widely used as paints and varnishes for coating a very varied range of objects. These powders have many advantages: on the one hand, the problems associated with the use of solvents are completely eliminated, on the other hand, the powders are 100% used, since only the powder in direct contact with the substrate is retained by that substrate , being the excess of REF: 122072 powder, in principle, fully recoverable and reusable. Accordingly, these powder compositions are preferred over coating compositions in the form of solutions in an organic solvent. Thermosetting powder compositions have already found a large opening in the coating of household goods, accessories for the motor vehicle industry, etc. They usually contain thermosetting organic compounds that are the binders for paint, fillers, pigments, catalysts and various additives to adapt their behavior for use. In addition there are also thermosetting powder compositions, thermoplastic compositions in powder form. These compositions comprise polymers that do not contain any of the reactive chemical groups. When this type of powder is heated in a substrate, the molten particles combine and propagate on the substrate to form a smooth and uniform coating. In contrast, the polymers used in the thermosetting powder compositions contain a reactive chemical group, for example, a carboxyl, hydroxyl or epoxide group. In this type of powder, it is added » .-teesa. S4i * ¡£?!. cr a crosslinking agent containing chemical groups that are reacted with those of the polymers when the powder is heated on the substrate. This results in hard coatings that are more resistant to chemical agents, which adhere better to metal surfaces and are not soft when exposed to high temperatures. However, the crosslinking of thermosetting powders creates a new series of problems when compared to thermoplastic powders. Mainly, the crosslinking can give rise to a lack of surface uniformity, which gives an appearance in the form of an orange peel. This is due to the fact that, during its heating, the powder is cross-linked before the dust particles have had the time to propagate by making a very uniform coating. Another consequence of this premature crosslinking is that air bubbles may remain trapped in the coating, which adversely affect its surface appearance, its adhesion to the substrate and its protective effect. Another problem encountered with thermosetting powder compositions is that they impart coatings that lack flexibility. When a coating is deposited on metal sheets intended to manufacture articles that will need to be bent at various angles, it is essential for the coating not to crack in the bending placement. In addition, it is essential for dust that is stable in storage. In other words, it must remain in a finely pulverulent state for a sufficiently long period, and should not be re-agglomerated, which means that the polymer used as a binder for the powder must have a sufficiently high vitreous transition temperature. Finally, when the thermosettable powder composition is intended to make coatings on articles that are part of architectural constructions, it is very important for these coatings to withstand bad times. In the latter case, it is common in practice to use amorphous polyesters, which carry carboxyl groups, which contain a majority of isophthalic acid as an acid constituent, as a mixture with triglycidyl isocyanurate (TGIC) as the crosslinking agent. This actually gives the coatings good resistance to photodegradation and hydrolysis of the ester groups, but the coatings thus obtained do not have good impact resistance. In addition, the TGIC is tending to be used less than previously, since it shows health problems and iJXij.S. Security, security Specifically, the TGIC is relatively t, its dose of lethal LD50 being 0.4 g / kg administered orally in rats, and it is mutagenic according to the mutagenicity test of Ames; It is also considered to give rise to allergic reactions, reflected by eczema and asthma. In this way, it has been attempted to replace TGIC with other crosslinking agents for polyesters bearing carboxyl groups. Among these, acrylic copolymers bearing epe groups have been used, as in patent EP 38635. However, binder substances containing these two types of compound give coatings whose impact strength and flexibility are not completely satisfactory. It has also been tried to use beta-hydroxyalkylamides as crosslinking agents for polyesters bearing carboxyl groups. The hydroxyl group located in the beta position relative to the amide group is highly reactive in the esterification of the carboxyl group in the polyesters, which leads to problems with respect to the rate of crosslinking of compositions containing this type of crosslinking agent. The reason for this is that, since this speed is high, the coating does not have enough time to propagate correctly when it melts, which leads to surface defects such as the formation of an outer shell in the shape of an orange peel. In addition, this esterification is carried out by a release of water, which does not have time to escape from the coating as it hardens, which also leads to surface defects. EP 322,834, for example, discloses thermosetting powder compositions containing essentially a polyester bearing carboxyl groups and a beta-hydroxyalkylamide, which is applied to a substrate and is then crosslinked at a temperature of 160 to 200 ° C. Despite the presence of benzoin in these compositions, which is added as a degassing agent, water bubbles and air remain trapped in the hardened coating after it has been melted and crosslinked, especially if the coating is relatively thick. In addition, the flow of the powder when it is melted is not optimal. Patent application WO 91/14745 discloses thermosetting powder compositions containing an amorphous polyester containing carboxyl groups, a talc semicris polyester containing carboxyl groups and a crosslinking agent. From 10 to 40% by weight of the semicrystalline polyester is preferably used in relation to polyesters in general, and the agent of crosslinking can be a beta-hydroxyalkylamide. The presence of talc semicris polyester in these compositions improves the mechanical properties of the coatings provided. However, the presence of these semicrystalline polyesters also increases the curing rate of these compositions, which could be a factor that disadvantages the satisfactory flow and degassing of these compositions when they melt, leading to surface defects in the coatings. Patent application EP 668,895 also discloses thermosettable powder compositions containing a polyester bearing carboxyl groups and a beta-hydroxyalkylamide. The polyesters of this patent application have a carboxyl group functionality of less than 2, obtained by adding monofunctional acids or alcohols during the synthesis of the polyester. By virtue of this reduced functionality, the polyester is less reactive, which makes the powder flow better when it melts and allows the air and water vapor bubbles to escape from the coating before it hardens, unlike the compositions in patent applications EP 322,834 and WO 91/14745. However, since the polyester contains chain ends that do not carry a reactive group, these ends do not participate in the formation of the three-dimensional network during the cross-linking of the powder, which reduces the resistance to solvents and the flexibility of the coatings thus obtained. As can be appreciated, it is not easy to find a thermosettable powder composition that by itself combines all the qualities that would be desired to be found in it, such as good storage stability, good flow when it fuses to give smoothness, tense appearance and lustrous that does not have an orange peel or bubble, good flexibility and good surface hardness, at the same time as good resistance to solvents, bad weather and hydrolysis. The present invention is directed to thermosettable powder compositions which combine the qualities listed in the foregoing, more particularly these compositions contain a beta-hydroxyalkylamide as a crosslinking agent. Accordingly, the present invention relates to a polyester carrying tertiary carboxyl groups, which allows more of these problems to be solved. Finding a good concession between the reactivity of the tertiary carboxyl groups in the polyester containing them, their functionality and their acid index (factor that is in correlation with the molecular weight and thus governs its viscosity, which is an essential factor for flow correct of the composition in the molten state), the coatings have been successfully produced, according to the present invention, the surface of these coatings have a very smooth and taut appearance, without any form of orange peel or bubbles retained in the coating. In addition, these coatings have very good flexibility and very good resistance to bad weather and hydrolysis. The invention also provides a specific process for preparing these polyesters in various stages, the tertiary carboxyl groups being mainly found at the end of the polyester chains. Finally, the invention relates to thermosetting powder compositions containing this polyester and a crosslinking agent, as well as for the use of these compositions for preparing paints and varnishes in powder, which give coatings that combine most of the properties favorable listed in the above.

One of the objects of the present invention is thus a polyester carrying tertiary carboxyl groups, characterized in that it consists of: (a) 8.1 to 35 moles of an aliphatic or cycloaliphatic polyol, (b) 9.1 to 36 moles of a polycarboxylic acid aliphatic, cycloaliphatic or aromatic, (c) 1.6 to 2.8 moles of an aliphatic, cycloaliphatic or aromatic compound containing, on the other hand, a tertiary carboxyl group, and, on the other hand, either a primary or secondary carboxyl group or a group primary or secondary hydroxyl. This number of moles of constituents in (a), (b) and (c) is relative to one mole of the polyester containing them. The aliphatic or cycloaliphatic polyol (a) is selected from neopentyl glycol, 2, 2-butylethyl-l, 3-propanediol, neopentyl glycol hydroxypivalate, 1,4-cyclohexane-dimethanol, trimethylolpropane, ditrimethylolpropane, pentaerythritol, etc. Preferably, from 40 to 100%, and still better from 60 to 100%, by weight of an aliphatic diol containing two primary hydroxy groups, in particular neopentyl glycol, is used in relation to the total weight of the polyols.

The aliphatic, cycloaliphatic or aromatic polycarboxylic acid (b) is chosen from isophthalic acid, terephthalic acid, phthalic acid or anhydride, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, etc. Preferably, from 85 to 100% by weight of an aromatic dicarboxylic acid, in particular terephthalic acid and / or isophthalic acid, is used in relation to the total weight of the polycarboxylic acids. The aliphatic, cycloaliphatic or aromatic compound (c) which contains, on the other hand, a primary or secondary carboxyl or hydroxyl group, can be represented by the following general formula I: wherein R1 and R2 signify, independently of each other, an alkyl group containing from 1 to 12 carbon atoms, a cycloalkyl group or an aryl group; Y represents a carboxyl or hydroxyl group; R3 represents a hydrogen atom or has the same meaning as R1 or R2; preferably, R3 represents a hydrogen atom. When Y represents a hydroxyl group in formula I, compound (c) is a hydroxyl acid containing a primary or secondary hydroxyl group, preferably a primary group, and a tertiary carboxyl group, which may be chosen from hydroxypivalic acid (or acid) 3-hydroxy-2,2-dimethylpropanoic acid), 3-hydroxy-2, 2-diphenylpropanoic acid, 3-hydroxy-2-methyl-2-phenylpropanoic acid, 2- (hydroxymethyl) -2- ethylbutanoic acid, 2-ethyl acid -2- (hydroxymethyl) butanoic, 2- (hydroxymethyl) -2-phenylbutanoic acid, 2- (hydroxymethyl) -3-methyl-2-phenylbutanoic acid, 2- (hydroxymethyl) -2-methylpentanoic acid, 2-ethyl- 2- (hydroxymethyl) pentanoic, 2- (hydroxymethyl) -2-propylpentanoic acid, 2- (hydroxymethyl) -2- phenyl-pentanoic acid, 2-ethyl-2- (hydroxymethyl) hexanoic acid, 2-butyl-2- acid (hydroxymethyl) hexanoic, 2- (hydroxymethyl) -2-phenylhexanoic acid, 2-heptyl-2- (hydroxymethyl) decanoic acid, etc. Among these compounds, hydroxypivalic acid is preferred. When Y represents a carboxyl group in the formula I, the compound (c) is a diacid containing a tertiary carboxyl group and a primary or secondary carboxyl group, preferably a primary group, which can be chosen from 2,2-dimethyl- succinic acid, 2-ethyl-2-methyl-succinic acid, 2,2-diethyl-succinic acid, 2-methyl-2-propylsuccinic acid, 2-isopropyl-2-methyl-succinic acid, 2-ethyl-2-propylsuccinic acid, 2, 2- acid dipropyl succinic acid, 2-hexyl-2-methylsuccinic acid, 2-heptyl-2-methyl-succinic acid, 2,2-bis (2-methylpropyl) succinic acid, 2,2-bis- (isobutyl) succinic acid, 2-decyl- 2-Methylsuccinic acid, 2-decyl-2-propylsuccinic acid, 2-methyl-2-phenylsuccinic acid, 2-ethyl-2-phenylsuccinic acid, 2-phenyl-2-propylsuccinic acid, 2-butyl-2-phenylsuccinic acid, 2-pentyl-2-phenylsuccinic acid, 2-hexyl-2-phenylsuccinic acid, 2-heptyl-2-phenylsuccinic acid, 2-octyl-2-phenylsuccinic acid, 2,2-diphenyl-succinic acid, etc. The anhydrides corresponding to all these acids can also be used. Among these compounds, 2,2-dimethylsuccinic acid or its anhydride is preferably used. The polyester carrying tertiary carboxyl groups according to the invention has an acid number from 15 to 50 mg KOH / g, preferably from 25 to 35 mg KOH / g, and a hydroxyl number from 0 to 10 mg KOH / g. Its weight average molecular weight varies from 1800 to 10,500, preferably from 2900 to 5000. The functionality of this polyester varies from 1.6 to 2.8, preferably from 1.85 to 2.25. Its ICI viscosity, measured by the cone / plate method at 200 ° C, varies from 10 mPa.s to 10,000 mPa. s and its vitreous transition temperature is between 45 and 85 ° C, when measured by differential scanning calorimetry (DSC), with an increased temperature of 20 ° C / minute. The standards applied to determine these values are described at the beginning of the examples that follow. Another object of the present invention is a process for preparing a polyester bearing tertiary carboxyl groups, characterized in that it is carried out in various stages, the first steps consist of preparing a prepolyester by condensation between (a) an aliphatic or cycloaliphatic polyol, and (b) an aliphatic, cycloaliphatic or aromatic polycarboxylic acid, the end of the step consists of condensing this prepolyester with (c) an aliphatic, cycloaliphatic or aromatic compound containing, on the one hand, a tertiary carboxyl group, and, on the other hand , either a primary or secondary carboxyl group or a primary or secondary hydroxyl group. More particularly, in this preparation process: (1) (i) a prepolymer carrying hydroxyl groups is prepared first by condensation between compounds (a) and (b), using a techiometric excess of the polyol (a) relative to the acid polycarboxylic acid (b), (ii) the prepolymer obtained in (1) (i) is then condensed with a polycarboxylic acid (b), with the exception, however, of terephthalic acid, to form a prepolymer carrying carboxyl groups, and (iii) finally, the prepolyester obtained in (1) (ii) is condensed with a compound (c) containing, on the one hand, a tertiary carboxyl group, and, on the other hand, a primary or secondary hydroxyl group; or alternatively, (2) (i) a prepolymer carrying hydroxyl groups is prepared first as in (1) (i), (ii) this prepolyester is then condensed with a compound (c) containing, on the one hand, a tertiary carboxyl group, and, . ^ a «« «ifa»? ^ l ^? a »on the other hand, a primary or secondary carboxyl group; or alternatively, (3) (i) a prepolymer carrying carboxyl groups is prepared first by condensation between compounds (a) and (b), using a stoichiometric excess of the polycarboxylic acid (b) relative to the polyol (a), with the except, however, of terephthalic acid, (ii) the prepolyester obtained in (3) (i) is then condensed with a compound (c) containing, on the one hand, a tertiary carboxyl group, and, on the other hand, a primary or secondary hydroxyl group. The compounds (a), (b) and (c) used to prepare the polyester bearing tertiary carboxyl groups are the same as those described above with respect to the polyester according to the invention. The molar amounts in which they are present are also the same. The acid number and hydroxyl number, molecular weight, functionality, viscosity and vitreous transition temperature values which characterize the polyesters obtained by this synthetic process are also those of the polyester bearing tertiary carboxyl groups according to the invention. This specific synthetic method, in which the compound (c) is used in the final stage of the synthesis, ensures the production of a polyester in which the tertiary carboxyl groups are mainly at the ends of the polyester chains, with virtually no have to react in everything. The primary and / or secondary and / or aromatic hydroxyl and carboxyl groups in the compounds (a) and (b) have, on the other hand, to be reacted together almost completely. It will be seen later in a comparative example, if an attempt is made to synthesize the polyester according to the invention in a simple step, using diols containing primary hydroxyl groups as compounds (a), these diols react with the tertiary carboxyl groups of the compound (c) of the formula I, in such a way that the latter compound is incorporated in a large amount in the polyester chain, in this way it is not possible to obtain a polyester according to the invention, in which the tertiary carboxyl groups are mainly at the end of the polyester chains.

Patent application EP 634,434 describes a linear polyester containing tertiary, aliphatic carboxyl groups as a constituent of a thermosettable powder composition. This polyester is synthesized in a simple step and contains: • at least one monofunctional compound comprising a primary or secondary group and / or at least one compound comprising a primary or secondary hydroxyl group and an aliphatic tertiary carboxyl group; • at least one aromatic or cycloaliphatic dicarboxylic acid comprising two aliphatic or aromatic secondary carboxyl groups; • at least one diol comprising two primary or secondary hydroxyl groups; • at least one dihydroxymonocarboxylic acid comprising a tertiary carboxyl group and two primary or secondary aliphatic hydroxyl groups. In this polyester, only the tertiary carboxyl groups remain unreacted, the other carboxyl groups have to be reacted completely with the hydroxyl groups. According to the examples within the patent application, all linear polyesters containing the prepared aliphatic tertiary carboxyl groups contain hydrogenated bisphenol A, which is a preferred compound according to the patent application, as the sole diol, i.e. a diol whose hydroxyl groups are secondary. In fact, the synthetic one-step method described in the patent application is, with the compounds used, only possible with secondary diols, which react with tertiary carboxyls with greater difficulty, but which can react with secondary carboxyls, such as those of hexahydrophthalic acid used in the examples, and which is the preferred compound according to the patent application. In contrast, as noted above, it is not possible to synthesize the polyesters bearing tertiary carboxyl groups of the present invention in a simple step. The polyesters prepared in the examples in the patent application have two drawbacks compared with those of the present invention. Specifically, the vast majority of the monomers used to prepare them are aliphatic and cycloaliphatic compounds, and it is known that this type of monomer gives polyesters whose resistance to bad weather is inadequate. In addition, the acid number of these polyesters ranges from 67.3 to 87.0 mg KOH / g, and these very high values increase the reactivity of these polyesters to the point of completely counterbalancing the beneficial effect of the reduced reactivity of the contained tertiary carboxyl groups, which is an obstacle to decrease or stop the crosslinking reaction, which is precisely the cause of favorable results obtained according to the present invention. The polyester carrying tertiary carboxyl groups according to the invention can be prepared by volume polycondensation, in two or three stages, using a standard polyester reactor, equipped with a stirrer, a distillation column connected to a condenser cooled with water , a nitrogen inlet and a thermometer connected to a temperature regulator. According to the three-step process of the invention (1), the polycarboxylic acids (b) are placed in the reactor with a stoichiometric excess of the polyols (a), with stirring, at a temperature of from 120 to 150 ° C. , under nitrogen and in the presence of an esterification catalyst. The temperature increases to 200-250 ° C, while the water begins to distill at 190 ° C. When the distillation is stopped at atmospheric pressure, the polyester carrying hydroxyl groups is cooled and a polycarboxylic acid (b) different from terephthalic acid (which is too insoluble according to this process) is added thereto. In this second stage, the carboxylation and an optional chain extension of the prepolyester are carried out, at a temperature of 250 ° C, first at atmospheric pressure and then under vacuum, until the desired prepolyester is obtained, according to its index of acid, its hydroxyl number and its viscosity. In a third step, the compound (c) bearing a tertiary carboxyl group and a primary or secondary hydroxyl group, between 180 and 200 ° C, is added with stirring. The reaction is continued at 225-250 ° C, under vacuum, until the desired acid and hydroxyl numbers and the desired viscosity are obtained. The usual additives can be added to the polyester carrying tertiary carboxyl groups, which are thus obtained, before the reactor is emptied. According to the two-step process of the invention (2), a prepolymer carrying hydroxyl groups is first prepared in the same manner as in the single step of the process (1). During the second step, compound (c) containing a tertiary carboxyl group and a primary or secondary carboxyl group is added between 180 and 200 ° C and with stirring. The reaction is continued at a temperature from 180 to 220 ° C, under vacuum, until the desired acid and hydroxyl numbers and the desired viscosity are obtained. An alternative for this second step consists in using the anhydride of the same compound (c), at a temperature from 160 to 200 ° C, with stirring, until the desired acid and hydroxyl numbers and the desired viscosity are obtained. The usual additives can be added to the polyester carrying tertiary carboxyl groups, which are thus obtained, before the reactor is emptied. According to the two-step process of the invention (3), a prepolymer carrying carboxyl groups is first prepared by adding a stoichiometric excess of one or more polycarboxylic acids (b), different from terephthalic acid (since it is too insoluble according to this process), to polyols (a) at a temperature from 120 to 150 ° C, under nitrogen and with stirring, in the presence of an esterification catalyst . The temperature increases to 200-250 ° C, while the water begins to distill at 190 ° C. When the distillation is stopped at atmospheric pressure, the condensation is continued under vacuum until the prepolyester is obtained iri? 1? - | M "= ii? Mm ^ Í ^ fl? < l« jf1 ?? -? < i ^^^. M '^ * ^ m ^^^^^^' 1 ^ ¡^ '^ - a ^ > .Wg &fc ^^ desired carrying carboxyl groups, according to their acid number, hydroxyl number and viscosity.In a third step, compound (c) bearing a tertiary carboxyl group is added and a primary or secondary hydroxyl group, between 180 ° and 200 ° C, with stirring, the reaction is continued at 225-250 ° C under vacuum, until the desired acid and hydroxyl numbers and the desired viscosity are obtained. the usual additives to the polyester carrying tertiary carboxyl groups, which is thus obtained, before the reactor is emptied Examples of an esterification catalyst which is used are tin derivatives, such as dibutyltin dilaurate, dibutyltin oxide or n-trioctanoate. -buttons, or titanium derivatives, such as tetrabutoxy ti tanate, 0 to 1% phenolic derivatives, such as Irganox 1010, can be added as antioxy dante, alone or with several stabilizers of the phosphite type, such as tributylphosphite. The present invention also relates to thermosettable powder compositions containing the polyester bearing tertiary carboxyl groups according to the invention and a crosslinking agent carrying functional groups capable of reacting the carboxyl groups of the polyester. The invention also relates to the preparation of powder varnishes and paints, as well as to the varnishes and powder paints obtained using these compositions. Finally, the invention also relates to a process for coating an article, preferably a metal article, which is characterized by applying a thermosettable powder composition, according to the invention, to the article by deposition with an electrostatic or triboelectric spray gun. or by deposition in a fluidized bed, followed by heating the coating thus obtained at a temperature from 160 to 225 ° C for a period of about 5 to 30 minutes. The crosslinking agent used to prepare the thermosetting powder compositions according to the invention is chosen from compounds containing functional groups capable of being reacted with the carboxyl groups of the polyester bearing tertiary carboxyl groups. Among these compounds which are used as crosslinking agents are: polyepoxylated compounds which are solids at ordinary temperature and which contain at least two epoxy groups per molecule, such as, for example, triglycidyl isocyanurate (such as the product sold under the name of Araldite PT 810 by the company Ciba-Geigy), although this is not preferred due to its toxicity, or the epoxy resin of Araldite PT 910 (from the same company), which contains a mixture of diglycidyl terephthalate and triglycidyl trimellitate 75 / 25, or alternatively the reaction product of 2,2-bis (4-hydroxy phenyl) -propane and epichlorohydrin, such as GT 7004 from the Ciba-Geigy company or Epikote 1055 from the Shell company. acrylic copolymers containing glycidyl groups, obtained from glycidyl methacrylate and / or glycidyl acrylate and from a (meth) acrylic monomer and optionally from an ethylenically monounsaturated monomer different from glycidyl (meth) acrylate and different from monomer (met) acrylic . An example of this type of acrylic copolymer is GMA252 expired by the company Estron Chemical Co. beta-hydroxyalkylamides containing at least one, preferably two, bis (beta-hydroxy-alkyl) amide groups, for example those mentioned in the applications of WO 91/14745, EP 322,834 and EP 473,380 and in the patents of the States^^ sft ^ «6 ^^ - * ^^^^ --- ^ g * w! '- ^^ i - ^' - E * - < - - ^ - and »-! *. * Tf ^ ^» ^ jg ^ Sass s United 4,727,111, 4,788,255 and 4,076,917. These beta-hydroxyalkylamides, which are preferred crosslinking agents according to the present invention, correspond to the following general formula II: wherein A represents a polyvalent organic group derived from saturated or unsaturated alkyl groups containing from 1 to 60 carbon atoms, or an aryl group, or a trialkenamino group containing from 1 to 4 carbon atoms, or a carboxy group alkenyl or alternatively an alkoxycarbonyl-quenyl group; R1 represents a hydrogen atom or an alkyl group containing from 1 to 5 carbon atoms, or alternatively a hydroxyalkyl group containing from 1 to 5 carbon atoms; R2 and R3 are identical or different and represent, independently, a hydrogen atom or a linear or branched alkyl group containing from 1 to 5 carbon atoms, it also being possible for one of the groups R2 and one of the groups R3 to form a cycloalkyl group with the carbon atom adjacent to it; m and n are between 1.6 and 2.0; preferably, A represents an alkyl group containing from 1 to 10 carbon atoms; R1 represents a hydrogen atom or a hydroxyalkyl group containing from 1 to 5 carbon atoms; R2 and R3 represent a hydrogen atom or a methyl or ethyl group. The preferred beta-hydroxyalkylamides correspond to the following general formula III: in which n varies from 0.2 to 1 and R3 can be a hydrogen atom (product sold under the name of Primid XL 552 by the company EMS) or a methyl group (product sold under the name of Primid QM 1260 by the company EMS ). The thermosetting powder compositions according to the invention may also contain, in addition to the polyester carrying tertiary carboxyl groups and the crosslinking agent, a talc semicris polyester bearing carboxyl groups, in a minor amount relative to polyesters in general, by example from 0 to 40% by weight. Such semicris talin polyesters are well known in the state of the art, for example, in patent application WO 91/14745. Its acid number is between 10 and 70 mg KOH / g, preferably between 15 and 40 mg KOH / g, and its weight average molecular weight varies from 1600 to 17,000, preferably from 2800 to 11200; they have a glass transition temperature from 10 to 50 ° C, a melting range from 70 to 150 ° C and an ICI viscosity from 10 to 10,000 mPa.s, at 175 ° C. The presence of these semicrystalline polyesters bearing carboxyl groups in the thermosetting compositions according to the invention can in certain cases contribute towards improvements p K.???& .., additional surface appearance, flexibility and resistance to weathering of coatings. The crosslinking agent described above is used in a proportion from 0.25 to 1.4, preferably from 0.5 to 1.05, equivalents of epoxy or beta-hydroxyalkyl groups, per equivalent of carboxyl groups that exist in the polyester bearing tertiary carboxyl groups and the semi-crystalline polyester bearing carboxyl groups which are optionally present. The thermosettable powder compositions according to the invention may contain, for example, from 97 to 60 parts by weight of the polyester carrying tertiary carboxyl groups and of the semicris talin polyester, and from 3 to 40 parts by weight of the crosslinking agent, with relation to the total weight of the polyesters and the crosslinking agent. The thermosettable powder compositions according to the invention may also contain various auxiliary substances conventionally used in the manufacture of powder paints and varnishes. Auxiliary substances optionally added to the thermosetting compositions according to the invention are, in theory, ultraviolet absorbing compounds, such as Tinuvin 900 (ex Ciba-Geigy Corp.) and light stabilizers based on sterically hindered amines. (for example Tinuvin 144 of Ciba-Geigy Corp.). A wide variety of pigments and fillers can also be added to the thermosetting compositions according to the invention. As examples of pigments and fillers, mention will be made of metal oxides such as titanium dioxide, iron oxide, zinc oxide, etc., metal hydroxides, metal powders, sulphides, sulfates, carbonates, silicates such as, for example, aluminum silicate, carbon black, talcum, kaolins, barites, ultramarine blue, lead blue, organic reds, organic coffees, etc. Auxiliary substances that will also be mentioned are fluid modifiers such as Resiflow PV5 (from Worlee) or Modaflo (from Monsanto), or Acronal 4F (from BASF), plasticizers such as dicyclohexyl phthalate, tri-phenylphosphate, auxiliary grinding agents, oils desiccants and degassing agents such as benzoin. These auxiliary substances are used in customary amounts, it being understood that if the thermosetting compositions according to the invention are used as varnishes, the addition of auxiliary substances with opacifying properties will be omitted.

For the preparation of the thermosetting powder compositions, the constituents of the composition are mixed dry, for example in a drum mixer. This mixture is then homogenized at a temperature within the range of 80 to 150 ° C in an extruder, for example a single screw-type extruder or a double screw extruder of A.P.V. Then, the extrudate is allowed to cool, is milled, optionally at very low temperature using liquid nitrogen, and sieved to obtain a powder whose particle size is between 10 and 150 microns. The powder paints and varnishes thus obtained are completely suitable for application to the article which is coated by conventional techniques, that is, by the well-known technique of deposition in a fluidized bed or by application using an electrostatic or triboelectric gun. In the latter case, known additives are added that increase the load in triboelectric systems. After they have been applied to the related article, the deposited coatings are cured by heating in an oven at a temperature of 160 to 225 ° C for a period of about 5 to 30 minutes to obtain complete crosslinking of the coating. The following examples illustrate the invention without being limited. In these examples, the determination of certain characteristic values was carried out according to the methods described below: the brightness: this is expressed as the intensity of the reflected light, as a percentage, in relation to the intensity of the incident light at an angle of 60 ° C, and measured according to the standard of ASTM D 523; Impact resistance: this is measured using a Gardner machine according to ASTM D 2794 standard. Cold-rolled steel panels provided with a cured coating are subjected to increased intensity impacts on the coated side (direct impact) and on the uncoated side (reverse impact). The largest impact that does not cause the crack coating is presented in kg.cm; The QUV accelerated aging test: chrome-plated aluminum panels provided with a cured coating to be tested are placed on a "QUV panel" test machine from the company Q-Panel Co. (Cleveland, USA), and submitted felrtjjfe ¡fa8lll -fe ^ "and • MOwrifrVTt. at various exposure cycles to UV lamps and humidity, at various temperatures. Among the various cycles of this type that are described in the ASTM G 53-88 standard, the coatings in the present case were subjected to a cycle of exposure for 8 hours to a fluorescent UVA lamp (wavelength 340 nm e intensity of 0.77 W / m2 / nm) that simulates the damaging effects of sunlight at 60 ° C, and 4 hours of water vapor condensation, with the lamp off, at 40 ° C; the change in brightness, measured at an angle of 60 °, is not observed, according to the standard of ASTM D 523. Every 200 hours of exposure to this test, the brightness retention is determined according to the equation: Retention% = 60 ° brightness after 200 hours of exposure x 100 brightness of 60 ° at the beginning of the experiment - the acid number and the hydroxyl number were determined by grinding according to the standards of DIN 53402 and 53240, and expressed as mg of HOH per gram of polyester; the vitreous transition temperature (Tg) and the melting point (Tm) were determined by differential scanning calorimetry (DSC) at a scanning speed of 20 ° C per minute; the number average molecular weight (Mn) of the polyesters was determined by gel permeation chromatography (GPC), with mono-dispersed polystyrene as the standard; the melt viscosity of the polyesters, expressed in mPa.s, was measured using an ICI cone and plate viscometer according to the standard of ASTM D 4287-88; it is also known as the "ICI viscosity" and was measured at the temperatures indicated in the examples; the resistance to acid hydrolysis of the coatings are indicated by the Delta-b * values according to the method for measuring the heats L * a * b * by the "Compagnie Internationale d 'Eclairage". To this, the ISO 3231 standard is applied, modifying, however, the amount of sulfur dioxide (2 1 instead of 0.2 1) (determination of the resistance to humid atmospheres containing sulfur dioxide). Chromed aluminum panels coated with formulation compositions C (compositions 20 to 22 and 25 according to the invention and comparative composition 32) are subjected to an acidic humid atmosphere for 25 cycles of successive test. A test cycle consists of placing the panels for 8 hours, at 45 ° C, in an atmosphere containing 2 liters of sulfur dioxide, followed by degassing at room temperature for 16 hours. After each cycle, the Delta-b * value is measured using a spectrophotometer with a measurement geometry of 0/45 °, with a D65 type light source. Using the ICD-L * a * b * method, eg value b * indicates a blue / yellow color variation. The green compositions in formulations C containing the yellow pigment Sicomin LS 1522 turns blue on exposure to acidic conditions, due to the destruction of pigment LS 1522, if the coatings do not protect the pigment too long due to a lack of resistance to acid hydrolysis conditions. At least, the Delta-b * value is high, at most, the resistance to acid hydrolysis conditions is high; a coating is considered to be sufficiently resistant to acid hydrolysis if its Delta-b * value is less than 5 after 25 cycles. Except where indicated otherwise, the parts indicated in the examples are part by weight. ^ '^^^ f ^ s ^ j ^ ß ^ ^ taf ^ S ^ - »* - ^ Example 1: Synthesis of three stages of a polyester containing tertiary carboxyl groups. First stage: 395.52 parts of neopentyl glycol are placed in a 4 neck round bottom flask fitted with a stirrer, a distillation column connected to a water cooled condenser, a nitrogen inlet and a thermometer connected to a temperature controller. The contents of the flask were heated to a temperature of 140 ° C, under nitrogen and with stirring, and 568.65 parts of terephthalic acid and 1.25 parts of n-butyltin trioctanoate were added thereto. The reaction is continued at 240 ° C and at atmospheric pressure until 95% of the theoretical amount of water has been removed by distillation and the reaction mixture is clear. A prepolymer containing hydroxyl groups was obtained, which had the following characteristics: acid number (IA): 7.6 mg KOH / g hydroxyl number (IOH): 56.6 mg KOH / g ICI viscosity at 175 ° C: 2200 mPa. s Second stage: 110.86 parts of isophthalic acid were added, 200 ° C, to the prepolymer obtained in the first stage and the mixture was heated to 230 ° C. After 2 hours to this At the temperature, and when the reaction mixture is clear, 1.0 part of tributyl phosphite and 1.0 part of n-butyltin trioctanoate were added thereto and the contents of the flask were placed under a pressure of 50 mmHg. After 3 hours at this temperature and under this pressure, the polyester obtained had the following characteristics: IA: 35.5 mg of KOH / g IOH: 2.5 mg of KOH / g ICI viscosity at 200 ° C: 5000 mPa. s Third stage: 69.38 parts of hydroxypivalic acid and 1.0 part of n-butyltin trioctanoate, at 180 ° C, were added to the prepolymer obtained in the second stage. The mixture was then heated gradually to 230 ° C. After about half an hour at this temperature, the reaction mixture was placed under a pressure of 50 mmHg when it became clear. After three hours at this temperature and under this pressure, the polyester had the character! following: IA: 34.2 mg of KOH / g IOH: 3.5 mg of KOH / g ICI viscosity at 200 ° C: 3500 mPa.s Tg (DSC, 20 ° C / min.): 53 ° C Mn: 2980 polyester containing tertiary carboxyl groups thus obtained was cooled to 180 ° C and removed from the flask.

Examples 2 to 5: Synthesis of three-stage polyesters containing tertiary carboxyl groups. Working in the same manner as in Example 1, a series of different polyesters containing tertiary carboxyl groups were prepared. The monomeric composition of these polyesters are given in Table 1, together with the characteristics obtained in the various steps. In Table 1, the various compounds used to prepare the polyesters are indicated by the following abbreviations: NPG: neopentyl glycol TMP: trimethylolpropane NHP: neopentyl glycol hydroxypivalate BEPD: 2,2-butylethyl-1,3-propanediol TPA: acid terephthalic iPA: isophthalic acid HPA: hydroxypivalic acid Catalyst: n-butyltin trioctanoate Antioxidant: tributyl phosphite M * tw, MAtfiui?, Ht? Y¡m. ~ .3i ^ to¿iMfa ^ < aas * S¿.4¿.3? £ > -f j Table 1 Example 2 Example 3 Example 4 Example 5 First stage NPG 405.9 359.7 312.0 388.0 NHP - 63.5 - - TMP - - - 7.14 BEPD - - 106.7 - TPA 583.6 561.5 557.1 340.42 iPA - - - 229.37 Catalyst 1.3 1.3 1.3 1.25 IA (mg KOH / g) 10.5 11.0 8.7 8.5 OHI (mg KOH / g) 61.2 60.2 58.7 56.0 ICI (175 ° C in mPa. S) 2000 1900 1500 2000 Second stage iPA 101.9 101.9 101.9 111.04 Catalyst 1.0 1.0 1.0 1.0 Antioxidant 1.0 1.0 1.0 1.0 IA (mg KOH / g) 28.7 28.5 28.2 35.0 OHI (mg KOH / g) 2.1 1.9 4.8 3.0 ICI (200 ° C in mPa. S) 7300 6800 5600 5500 Third stage HPA 54.3 54.3 54.3 69.38 Catalyst 1.0 1.0 1.0 1.0 AI (mg KOH / g) 28.0 27.8 28.5 34.0 IOH (mg KOH / g) 3.6 3.4 4.3 3.0 ICI (200 ° C in mPa. S) 5400 4600 4000 4000 Tg in ° C (DSC; 20 ° C / min.) 54 52 50 51 Mn 3550 3600 3420 3400 Example 6: Two-step synthesis of a polyester containing tertiary carboxyl groups. First stage 431.37 parts of neopentyl glycol were placed in a 4 neck round bottom flask fitted with a stirrer, a distillation column connected to a water cooled condenser, a nitrogen inlet and a thermometer connected to a temperature controller. The contents of the flask were heated to a temperature of 140 ° C, under nitrogen and with stirring, and 639.54 parts of terephthalic acid and 2.3 parts of n-butyltin trioctanoate were added thereto. The reaction was continued at 240 ° C and at atmospheric pressure until 95% of the theoretical amount of water had been removed by distillation. When the reaction mixture is clear, 0.1 part of tributyl phosphite was added thereto and placed under a pressure of 50 mmHg. After two hours at this temperature and under this pressure, a prepolymer containing hydroxyl groups was obtained which had the following characteristics: IA: 2.8 mg KOH / g IOH: 36.7 mg KOH / g Viscosity of ICI at 200 ° C: 5900 mPa.s Second stage: 75.14 parts of 2,2-dimethylsuccinic anhydride were added, at 180 ° C, to the prepolymer obtained in the first stage. After 2 hours at this temperature, and when the reaction mixture is clear, the polyester obtained had the character! following: IA: 33.5 mg KOH / g IOH: 2.9 mg KOH / g ICI viscosity at 200 ° C: 3900 mPa.s Mn: 3080 The polyester containing tertiary carboxyl groups thus obtained was cooled to 180 ° C and removed from the flask.

Example 7: Two-step synthesis of a semi-crystalline polyester containing primary carboxyl groups. First step: 459.4 parts of 1,6-hexanediol were placed in the same flask as in Example 1. The contents of the flask were heated to a temperature of 150 ° C under nitrogen and with stirring, and 579.5 parts of the flask were added thereto. terephthalic acid and 2.5 parts of n-butyltin trioctanoate. The reaction is continued at 235 ° C at atmospheric pressure until 95% of the theoretical amount of water has been distilled off. A prepolymer containing hydroxyl groups having the following characteristics was thus obtained: acid number: 5.0 mg KOH / g hydroxyl number: 53.0 mg KOH / g ICI viscosity at 175 ° C: 800 mPa.s Second stage: 101.3 parts of adipic acid were added, at 200 ° C, to the prepolymer obtained in the first stage and the mixture was heated to 235 ° C. After 2 hours at this temperature, 1.0 part of tributyl phosphite was added and the contents of the flask were placed under a pressure of 50 mmHg. After 2 hours at this temperature and under this pressure, the obtained polyester had the following characteristics: IA: 32.0 mg of KOH / g IOH: 0.5 mg of KOH / g ICI viscosity at 200 ° C: 1500 mPa.s Tg ( DSC, 20 ° C / min.) 28 ° C Melting range (DSC, 20 ° / min.): 100-130 ° C Mn: 3450. Semi-crystalline polyester bearing primary carboxyl groups, which was thus obtained, cooled to 160 ° C and removed.

Example 8: Synthesis of a stage of a semicrystalline polyester bearing primary carboxyl groups 500.0 parts of 1, -cyclohexanediol were placed, 655. 1 part of adipic acid and 2.5 parts of n-butyltin trioctanoate in the same flask as in Example 1. The mixture was then heated to 140 ° C, under nitrogen and with stirring, and the esterification of the water began to be extracted by distillation at 190 ° C, the heating was continued gradually at a temperature of 200 ° C. When the distillation at atmospheric pressure was stopped, 1.0 part of tributylphosphite and 1.0 part of n-butyltin trioctanoate were added and the contents of the flask were placed under a pressure of 50 mmHg. After 5 hours at this temperature and under this pressure, the polyester obtained had the following characteristics: acid number: 23.5 mg KOH / g hydroxyl number: 2.5 mg KOH / g ICI viscosity at 175 ° C 3600 mPa. s Viscosity of ICI at 150 ° C 8000 mPa.s Tg (DSC; 20 ° C / min.) 40 ° C Melting range: 90-130 ° C Mn: 4320 Semi-crystalline polyester bearing primary carboxyl groups obtained in this way cooled at 160 ° C and was removed.

Comparative Examples 9 to 13: Comparative Example 9 relates to the synthesis of two steps, according to the procedure in the first of two steps of Example 1, of a fully condensed linear polyester bearing aromatic carboxyl groups. This polyester is well known in the state of the art. In Comparative Example 10, a polyester very similar to that of Comparative Example 9 was synthesized, and was prepared in the same manner with complete condensation, but with introduction of a small amount of monomers known for its plasticizing effect. This linear polyester bearing aromatic carboxyl groups improves the melt flow of the powder containing it, by virtue of the presence of the plasticizing monomers. In Comparative Example 11, a polyester very similar to that of Comparative Example 9 was prepared, and was prepared in the same manner as in that example, but which stopped the synthesis before the condensation was complete. Due to its incomplete condensation, this linear polyester bearing aromatic carboxyl groups had a lower average molecular weight than the polyester of Comparative Example 9, which improves its melt flow, as well as lower fcncionality, which reduces the reactivity of the dust that contains it. Comparative Example 12 relates to a polyester containing the same monomers as the polyester of Example 1 according to the invention, but was prepared as in Example 1 in three steps, except that for steps 2 and 3 it was the reverse . Working in this way, it was observed that the hydroxypivalic acid was incorporated into the polyester in the second stage of the synthesis, by the reaction between the primary hydroxyl groups of the prepolymer bearing hydroxyl groups, obtained in the first stage, and the tertiary carboxyl group of hydroxypivalic acid, which leads to a prepolymer carrying hydroxyl groups derived from hydroxypivalic acid. The third stage of synthesis leads to a carboxylation with isophthalic acid, which gives a fully condensed polyester, without plasticizer bearing aromatic carboxyl groups, which is similar to the polyester of Comparative Example 9. In Comparative Example 13, an attempt was made for preparing a polyester having the same monomer composition as the polyester of Example 1 according to the invention, but carrying out the process in a single step, as in the patent application EP 634,434. This synthesis was not possible, since the polycondensation stopped at a very early stage to give a milky-looking reaction mixture in which the terephthalic acid precipitates in large quantities.

Table 2 summarizes the amounts of monomers used in the synthesis of the polyesters of Comparative Examples 9 to 12, as well as the synthetic steps and characteristics of the final polyesters and polyesters obtained. In this Table 2, the abbreviations used are the same as those in Table 1. In addition, the following abbreviations indicate the following: EG: ethylene glycol AdA: adipic acid Table 2 Example Example Example Example 9 10 11 12 First stage NPG 442200..11 377.3 426.8 3 39955..55 EG - 32.8 - - TPA 660033..99 543.5 613.6 5 56688..77 iPA - 67.2 - - Catalyst 11 ..33 1.3 1.3 1 1..33 IA (mg KOH / g) 9.6 7.0 8.9 9.5 IOH (mg KOH / g) 59.6 56.8 58.6 56.0 ICI (175 ° C in mPa.s) 1900 1600 2000 2500 Second stage iPA 113.1 83.9 104.1 - Ada - 34.3 - - HPA - - - 69.4 Catalyst 1.0 1.0 1.0 1.0 Antioxidant 1.0 1.0 1.0 1.0 IA (mg KOH / g) 34.0 32.1 30.8 6.5 OHI (mg KOH / g) 3.3 3.0 11.5 45.0 ICI (200 ° C in mPa. S) 4700 3100 4100 4200 (175 Mn 3000 3200 2650 - Tg in ° C (DSC; 20 ° C / min.) 55 53 52 - Third stage iPA 110.9 Catalyst 1.0 IA (mg KOH / g) 31.7 OHI (mg KOH / g) 2.0 ICI (200 ° C in mPa.s) - 5900 Tg in ° C (DSC; 20 ° C / min.) - - - 52 Mn - - - 3300 Example 14. Preparation of thermosettable powder compositions and characteristics of the coatings thus obtained. The agitation with the polyesters bearing tertiary carboxyl groups of Examples 1 to 6 according to the invention and with the polyesters bearing carboxyl groups obtained in Comparative Examples 9 to 12, was prepared a series of powders which can be used for the coating manufacturing. As seen in Table 3, the talc semicris polyesters obtained in Examples 7 and 8 were also added to some of these formulations. The following three different types of formulations were prepared, one white (formulation A), the other dark brown (formulation B) and the third green (formulation C): A) binder substance 700.0 parts titanium dioxide (1) 300.0 parts fluidity modifier (2) 10.0 parts benzoin 3.5 parts B) Binding substance 804.0 parts Bayferrox 130 (3) 45.0 parts Bayferrox 3950 (3) 140.0 parts FW 2 (4) 11.0 parts fluidity modifier (2) 10.0 parts benzoin 3.5 parts C) binder substance 670.0 parts titanium dioxide (1) 40.0 parts Sicomin L 1522 (5) 240.0 parts Heliogene Blue K 7090 (6) 10.0 parts Carbon Black Flammruss 101 (7) 40.0 parts fluidity modifier (2) 10.0 parts benzoin 3.5 parts (1) Kronos 2310 (Kronos) (2) Resiflow PV5 (Worlee) (3) (Bayer) (4) (Degussa) (5) (BASF) (6) (BASF) (7) Degussa The binder in these formulations always contains the crosslinking agent, as well as either the polyester carrying tertiary carboxyl groups according to the invention as the only polyester ( compositions 15 to 23 and 27), or a polyester mixed with a semicrystalline polyester bearing carboxyl groups (compositions 24 to 26), or, by comparison, a polyester bearing aromatic carboxyl groups (compositions 28 to 33), as indicated in Table 3. The compositions are prepared by dry mixing and homogenization of the various constituents in a twin screw extruder, at an extrusion temperature of 85 ° C. The homogenized mixture is then cooled and milled in a Retsch ZM100 grinder with a sieve diameter of 0.5 mm. The powder thus obtained is screened to obtain a particle size from 10 to 100 microns. In the case of compositions 24 to 26, which contain two polyesters, these are mixed in the melting state in a round bottom flask, prior to the operations described in the above. The compositions, formulated as described above, were applied, using an electrostatic spray gun of GEMA-Vols tatic PCG1, at a voltage of 60 kV, to cold-rolled steel plates, untreated, in a film thickness from 50 to 70 micrometers. This deposited coatings then undergo heating in a ventilated oven with air, at a temperature of 200 ° C, for a period of 15 minutes. The cured coatings thus obtained are subjected to the standard tests. The results obtained are presented in Table 3. In this table, the 1st column gives the number of the composition prepared in Example 14, the 2nd column, the type of formulation, A, B or C, the 3rd column, the number for the preparation of the polyester carrying tertiary carboxyl groups used, with the amount used (compositions 15 to 27) and of the comparative polyester bearing aromatic carboxyl groups (compositions 28 to 33), the 4th column, the example number for the preparation of the semicrystalline polyester bearing carboxyl groups, with the amount used (representing 10% by weight of the semicrystalline polyester, relative to the total weight of the polyesters; compositions 24 to 26), the 5th column, the nature and amount of the crosslinking agent used, with the following abbreviations: XL: Primid XL 552 from the company EMS, a beta-hydroxyalkylamide of the formula III in which R 3 represents a hydrogen atom; QM: Primid QM 1260 from the company EMS, a beta-hydroxyalkylamide of the formula III in which R 3 represents a methyl group; GMA: GMA252 from the company Estron Chemical Inc., an acrylic glycidyl copolymer. The 6th and 7th columns, the value of impact resistance and direct impact respectively, The 8th column, the visual evaluation of the quality of the surface appearance of the coatings, in which: (b) indicates a perfectly smooth and well tense appearance , similar to that of a mirror, (m) indicates a much poorer appearance than (b), with the beginning of a skin in the shape of an orange peel, (tm) indicates a skin appearance in the shape of a marked orange peel, the 9th column, the value Delta-b * (? b *), which indicates the resistance to hydrolysis, as explained at the beginning of the examples, the 10th column, the brightness, measured at an angle of 60 °. aMeaatf-itüHaw? »; - Table 3 Composition Type of Polyester Polyester Crosslinking agent Impact resistance Appearance? B * Form gloss containing semi-crystalline 60 ° tertiary carboxyl lane Direct Reverse 15 A EJ 1: 665.0 - XL: 35.0 200 200 b - 96 16 A EJ 2: 668.5 - XL: 31.5 180 180 b - 95 17 A EJ 6: 665.0 - XL: 35.0 160 140 b - 94 18 A EJ 1: 661.5 - QM: 38.5 200 200 b - 95 19 A EJ 3: 665.0 - QH: 35.0 180 160 b - 95 C EJ 1: 636.5 - XL: 33.5 180 180 b 5.0 92 21 C EJ 1: 633.2 - QM: 36.8 160 120 b 3.8 93 22 C EJ 4: 636.5 - QM: 33.5 160 140 b 4.0 92 23 B EJ 1: 759.8 - QM: 44.2 160 180 b - 95 VJI 24 A EJ 5: 598.5 EJ 7: 66.5 XL: 35.0 160 140 b - 93 C EJ 5: 569.9 EJ 7: 63.3 QM: 36.8 140 120 b 3.6 94 26 A EJ 5: 595.4 EJ 8: 66.1 QM: 38.5 160 160 b - 93 27 A EJ 1: 574.0 - GMA: 162 200 200 b - 95 28 * A EJ 9: 665.0 - XL: 35.0 180 160 tm - 94 29 * A EJ 11: 666.8 - XL: 33.2 80 60 m - 90 * A EJ 9: 661.5 - QM: 38.5 180 180 tm - 91 31 * A EJ 12: 666.8 - XL: 33.2 180 180 tm - 92 32 * C EJ 10: 636.5 - XL: 33.5 160 160 m 15 93 33 * B EJ 9: 759.8 - QM: 44.2 180 160 tm - 92 The compositions marked ** "ssee p prruueebbaann for comparative purposes As seen in Table 3, the coatings obtained with the compositions containing a polyester bearing tertiary carboxyl groups, according to the invention, have a surface of very high quality - which is smooth and well taut, without an appearance in shape of orange peel (compositions 15 to 27). These coatings also have very good flexibility (compositions 15, 18 and 27, for example), which is at least equal to, if not better than, the coatings in the state of the art (compositions 28, 30, 32 and 33). , for example), as shown by its impact resistance. The resistance to hydrolysis of these coatings is also very good, as shown by compositions 20 to 22 and 25 according to the invention. With the compositions also contain a semi-crystalline polyester (compositions 24 to 26), an additional improved surface appearance is obtained in certain cases; in contrast to the compositions in the patent application WO 91/14745, the addition of a semicrystalline polyester to the compositions according to the invention results in virtually no increase in the crosslinking speed. In contrast, the coatings obtained with the comparative compositions each have, one or different, defects. None of these coatings have a surface appearance that is as good with the compositions of the invention. Furthermore, it was noted that if it is desired to obtain a good surface appearance by using an incompletely condensed polyester, the deteriorated flexibility should be made to flow more easily in the melt (composition 29). If, for the same purpose, a composition containing a polyester prepared using plasticizing monomers (composition 32) was used, good flexibility was found, but the resistance to hydrolysis becomes very poor. In conclusion, it should be noted that by using polyesters bearing tarcyl carboxyl groups according to the invention in thermosetting powder compositions, coatings are obtained which have, simultaneously, excellent appearance, excellent flexibility and very good resistance to hydrolysis, i.e. , a combination of properties that can not be combined with the compositions containing polyesters bearing carboxyl groups of the state of the art.

Example 15. Resistance to bad weather of paint coatings. In this example, the weather resistance of the paint coatings obtained with the composition 23 according to the invention is compared with that of the coatings obtained with the composition 33 without being in accordance with the invention. The pigmented powders formulated according to type B, as described in Example 14, are applied by an electrostatic spray gun on chrome-plated aluminum panels under the same conditions as in Example 14. The coatings were subjected to an aging test accelerated to estimate the resistance to bad weather (Q-UV test), as described at the beginning of the examples. "Table 4 gives the gloss values for paint coatings, measured at an angle of 60 °, every 200 hours, until the reduction in brightness reaches approximately 50% of its initial value, this initial value is set at 100 %.

Table 4 Hours Composition 23 Composition 33 0 100 100 200 100 100 400 99 99 600 99 98 800 97 97 1000 93 92 1200 90 90 1400 85 84 1600 80 78 '1800 77 74 2000 66 65 2200 59 56 2400 55 52 2600 54 50 2800 49 46 3000 45 43 As can be seen in the reading of the Table 4, the coating obtained according to the invention, with a coating composition containing a polyester bearing tertiary carboxyl groups, has excellent resistance to bad weather, which is comparable to that of a coating obtained with a composition known in the state of the technique. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (20)

CLAIMS Having described the invention as above, the content of the following claims is claimed as property:

1. Polyester carrying tertiary carboxyl groups, characterized in that it consists of: (a) 8.1 to 35 moles of an aliphatic or cycloaliphatic polyol, (b) 9.1 to 36 moles of an aliphatic, cycloaliphatic or aromatic polycarboxylic acid, (c) 1.6 to 2.8 moles of an aliphatic, cycloaliphatic or aromatic compound containing, on the other hand, a tertiary carboxyl group, and, on the other hand, either a primary or secondary carboxyl group or a primary or secondary hydroxyl group, the number of moles of the constituents ( a), (b) and (c) is in relation to one mole of the polyester that contains them.

2. Polyester according to claim 1, characterized in that the polyol (a) is selected from neopentyl glycol, 2, 2-butylethyl-3, , í & *. propanediol, neopentyl glycol hydroxypivalate, 1,4-cyclohexanedimethanol, trimethylolpropane, ditrimethylolpropane and pentaerythritol.

3. Polyester according to any of claims 1 and 2, characterized in that the polyol (a) consists of from 40 to 100% by weight of neopentyl glycol, based on the total weight of the polyols (a).

4. Polyester according to any of claims 1 to 3, characterized in that the polycarboxylic acid (b) is chosen from isophthalic acid, terephthalic acid, phthalic acid or anhydride, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid and 1-cyclohexane-dicarboxylic acid.

5. Polyester according to any of claims 1 to 4, characterized in that the polycarboxylic acid (b) consists of 85 to 100% by weight of terephthalic acid and / or isophthalic acid, based on the total weight of the polycarboxylic acids (b) ).

6. Polyester according to any of claims 1 to 5, characterized in that the compound (c) is represented by the general formula I, wherein R1 and R2 signify, independently of each other, an alkyl group containing from 1 to 12 carbon atoms, a cycloalkyl group or an aryl group; Y represents a carboxyl or hydroxyl group; R3 represents a hydrogen atom or has the same meaning as R1 or R2.

7. Polyester according to any of claims 1 to 6, characterized in that the compound (c) represented by the general formula I is chosen from hydroxypivalic acid and 2, 2-dimethylsuccinic acid or anhydride.

8. Polyester according to any of claims 1 to 7, characterized in that it has an acid number from 15 to 50 mg KOH / g, a hydroxyl number from 0 to 10 mg KOH / g, a weight average molecular weight from 1800 to 10,500, a functionality from 1.6 to 2.8, a viscosity of ICI at 200 ° C from 10 to 10,000 mPa.s and a glass transition temperature of between 45 and 85 ° C.

9. Process for preparing a polyester bearing tertiary carboxyl groups, characterized in that it is carried out in various stages, the first stages consist of preparing a prepolyester by condensation between (a) an aliphatic or cycloaliphatic polyol, and (b) an aliphatic polycarboxylic acid, cycloaliphatic or aromatic, the end of the step consists of condensing this prepolyester with (c) an aliphatic, cycloaliphatic or aromatic compound containing, on the one hand, a tertiary carboxyl group, and, on the other hand, either a primary carboxyl group or secondary or a primary or secondary hydroxyl group.

10. Process for preparing a polyester according to claim 9, characterized in that: (1) (i) a prepolymer carrying hydroxyl groups is prepared first by condensation between compounds (a) and (b), using a stoichiometric excess of the polyol (a) ) with respect to the polycarboxylic acid (b), (ii) the prepolyester obtained in (1) (i) is then condensed with a polycarboxylic acid (b), with the exception, however, of terephthalic acid, to form a prepolyester which carries carboxyl groups, and (iii) lastly, the prepolyester obtained in (1) (ii) is condensed with a compound (c) containing, on the one hand, a tertiary carboxyl group, and, on the other hand, a primary or secondary hydroxyl group; or alternatively, (2) (i) a hydroxyl-bearing prepolyester is prepared first as in (1) (i), (ii) this prepolyester is then condensed with a compound (c) containing, on the one hand, a group tertiary carboxyl, and, on the other hand, a primary or secondary carboxyl group; or alternatively, (3) (i) a prepolymer carrying carboxyl groups is prepared first by condensation between compounds (a) and (b), using a stoichiometric excess of the polycarboxylic acid (b) relative to the polyol (a), with the exception, without However, of terephthalic acid, (ii) the prepolyester obtained in (3) (i) is then condensed with a compound (c) containing, on the one hand, a tertiary carboxyl group, and, on the other hand, a primary hydroxyl group or secondary

11. Process for preparing a polyester according to any of claims 9 and 10, characterized in that the compounds (a), (b) and (c) used to prepare the polyester are those of claims 2 to 7, because the molar amounts in which are present are those of claim 1 and because the characteristics of the obtained polyester are those of claim 8.

12. Thermosettable powder compositions, characterized in that they contain a polyester carrying tertiary carboxyl groups according to claims 1 to 11 and a crosslinking agent carrying functional groups capable of being reacted with carboxyl groups of the polyester.

13. Compositions according to claim 12, characterized in that the agent of Crosslinking is a polyepoxy compound or a beta-laidoxy alkylamide.

14. Compositions according to any of claims 12 and 13, characterized in that the crosslinking agent is a beta-hydroxyalkylamide of the formula III wherein n varies from 0.2 to 1 and R3 represents a hydrogen atom or a methyl group.

15. Compositions according to any of claims 12 to 14, characterized in that they also contain 0 to 40% by weight of a semicrystalline polyester bearing carboxyl groups, based on the total weight of this semicrystalline polyester and the polyester carrying tertiary carboxyl groups.

16. Compositions according to any of claims 12 to 15, characterized in that the semicrystalline polyester bearing carboxyl groups consists of the condensation product of a stoichiometric excess of an aliphatic, cycloaliphatic or aromatic polycarboxylic acid with an aliphatic or cycloaliphatic polyol, and because its index acid is between 10 and 70 mg KOH / g, its weight average molecular weight is 1600 to 17,000, its vitreous transition temperature is 10 to 50 ° C, its melting range is 70 to 150 ° C and its ICI viscosity is 10 to 10,000 mPa.s, at 175 ° C.

17. Compositions according to any of claims 12 to 16, characterized in that from 0.25 to 1.4 equivalents of carboxyl groups in the polyester bearing tertiary carboxyl groups and in the semicrystalline polyester bearing carboxyl groups, which is optionally present, are used per equivalent of functional groups in the crosslinking agent.

18. Compositions according to any of claims 12 to 17, characterized in that they also contain 0 to 10% by weight, relative to the total composition, of a compound that absorbs UV light and / or a light stabilizer such as sterically-laden amines. disabled, and the usual additives is.

19. Process for coating an article, preferably a metallic article, characterized in that a thermosetting powder composition according to any of claims 12 to 18 is applied to the article in a fluidized bed or by spray with an electrostatic or tribo-electrostatic spray gun. , and in that the coating thus obtained is subjected to heating at a temperature from 160 to 225 ° C, for a period from 5 to 30 minutes.

20. Items totally or partially covered by the process in accordance with the rei indication 19. ^^^^^^^^ É ^^^ g ^ ¡g ^^^^ g ^^^ »^^^ g ^^