MXPA00005833A

MXPA00005833A - Powder thermosetting compositions for preparing coatings with low gloss finish

Info

Publication number: MXPA00005833A
Application number: MXPA/A/2000/005833A
Authority: MX
Inventors: Luc Moens; Buysens Kris; Daniel Maetens
Original assignee: Ucb Sa
Priority date: 1997-12-18
Filing date: 2000-06-13
Publication date: 2001-07-03

Abstract

The invention concerns powder thermosetting coating compositions comprising (a) an amorphous polyester containing carboxyl groups, rich in isophthalicacid and neopentylglycol, optionally branched with a polycarboxylic acid or a polyol containing at least three functional groups;(b) a semicrystalline polyester containing carboxyl groups prepared from one or several saturated aliphatic dicarboxylic acids with linear chain, and from a saturated aliphatic diol with linear or cyclic chain optionally branched with a polycarboxylic acid or with a polyol containing at least three functional groups, and having a melting point (Tm) of at least 40°C and an acid value of 5 to 50 mg of KOH/g, and (c) a cross-linking agent. Said compositions are useful for preparing powder paints and varnishes providing excellent quality coatings whereof the brilliance, measured at an angle of 60°, according to the ASTM D 523 standard is always less than 50%, that is half-gloss or matt coatings.

Description

THERMOPENDENTAL COMPOSITIONS IN POWDER TO PREPARE COATINGS WITH LOW BRIGHT FINISH DESCRIPTION OF THE INVENTION The present invention relates to thermosetting powder compositions comprising, as a binder, a mixture of an amorphous polyester, a semi-crystalline polyester and a crosslinking agent, which provide, by firing, low-gloss coatings, in particular matt coatings. The invention also relates to the use of these compositions. for the preparation of paints and powder varnishes that provide low gloss coatings, as well as the low gloss coatings obtained from these compositions. Currently, thermosetting powder coating compositions are widely used as paints and varnishes to provide protective coatings that last on the most diverse objects. Powder coating compositions have numerous advantages in relation to coating compositions which are in the form of REF.120401 solution in an organic solvent; on the one hand, the safety and environmental problems caused by the organic solvents are completely suppressed, on the other hand, while the solvent-based coating compositions have the drawback of being able to be particularly in certain types of applications only at 60% or less of the applied coating composition is contacted with the substrate and this part that is not contacted with the substrate is not recoverable. Powder coating compositions are used 100%, since only the powder in contact with the substrate it is retained by this one, being the excess of powder, in principle, entirely recoverable and reusable. This is why these powder compositions are preferred in relation to coating compositions which are presented in the form of solutions in an organic solvent. Generally, the powder coating compositions contain a thermosetting organic binder and optionally fillers, pigments, catalysts and various additives to adapt their behavior to their use. The preparation of these thermosetting powders is done in the following manner. The polyester (s), the crosslinking agent, the optional heat, the pigments, the fillers and other additives in the proportions required to obtain a paint or a powder varnish are dry mixed at room temperature. The mixture obtained in this way is passed to an extrusion press to produce a homogenization in a molten phase at a temperature generally comprised between 80 and 150 ° C. The mixture is allowed to cool as it leaves the ion press, is crushed and sieved to obtain a powder having the desired geometry, comprised between 10 and 150 microns. The powder paints and varnishes obtained in this way are applied in a manner known per se, by means of an electrostatic or triboelectric spray gun or by the fluid bed deposition technique on the object to be coated. The object coated in this way is then heated in an oven where the melting and crosslinking of the binder is carried out at an elevated temperature. The hard coatings obtained from the compositions of thermosettable powder coatings must have a smooth, uniform appearance, without defects and, above all, free of "orange peel"; They must have good mechanical and chemical properties and good weather resistance.

Furthermore, it is essential that the powder coating compositions remain in the form of free flowing powders for a sufficient period after their manufacture and conditioning, without agglomeration during transport and storage. Commonly available commercially available thermosetting powder coating compositions contain as a binder a mixture of an amorphous polyester containing carboxyl or hydroxyl groups having a glass transition temperature (Tg) of between 45 and 80 ° C., with a crosslinking agent having functional groups capable of reacting with the carboxyl or hydroxyl groups of the polyester. The amorphous polyesters used in these compositions are those obtained from aromatic dicarboxylic acids such as terephthalic acid or isophthalic acid and, optionally, dicarboxylic acids such as adipic acid and various polyols such as neopentyl glycol, ethylene glycol, trimethylpropane, etc. . - These compositions based on amorphous polyesters are stable to storage and produce coatings of excellent quality, among others a surface without apparent defects and good mechanical properties. Among these compositions, compositions based on amorphous polyesters rich in isophthalic acid provide coatings that are highly prized for their excellent performance in outdoor exposure. However, these compositions based on amorphous polyesters provide, after firing, coatings having a very high gloss. The brightness, measured at an angle of 60 °, according to ASTM D 523, is often more than 90%. Also, powder coating compositions have already been proposed in which the binder contains a semi-crystalline polyester. Thus, in European patent 521 992, the proposed binder is constituted by a mixture of at least one semicrystalline polyester having an acid number of 10 to 70 mg KOH per gram, and at least one amorphous polyester having a temperature of vitreous transition (Tg) of at least 30 ° C and an acid number of 15 to 90 mg KOH per gram, with a crosslinking agent, which may be an epoxidized compound, a compound containing activated hydroxyl or thiol groups or an oxazolila.

The polyesters are talis icris are characterized by one or more glass transition temperatures (Tg) not exceeding 55 ° and a net melting point of 50 to 200 ° C. According to this patent, the semi-crystalline polyesters differ from the amorphous polyesters in the fact that the semicris talinos polyesters have a heterogeneous morphology (they are kept in a mixture of phases), they are opaque and of white color at room temperature, they present low viscosity in the state of fusion, are more insoluble in organic solvents and have a regularity of m and large. The semi-synthetic talc polyesters described and used in the embodiments of this patent are those obtained by polycondensation from dicarboxylic acids comprising an aromatic or aliphatic cycle such as terephthalic acid and 1-cyclohexanedicarboxylic acid and from saturated aliphatic diols linear chain such as 1,6-hexanediol and 1, 10-decanediol; linear aliphatic dicarboxylic acids such as adipic acid, succinic acid or 1,12-dodecanedioic acid are also added. The amorphous polyesters used are the polyesters containing carboxyl groups commonly used in powder paints and varnishes; these polyesters can be rich in isophthalic acid in order to obtain coatings intended for outdoor which have a good weathering. According to this patent, the presence of the semicrystalline polyester in the binder provides a coating having an excellent appearance, free of "orange peel" and improved mechanical properties. However, as Table 1 shows at the end of the description of this patent, the coatings obtained from these compositions all have a very high gloss; the brightness, measured at an angle of 60 °, according to ASTM D 523, can vary between 82 and 87%. In US Pat. No. 5,373,084, thermosettable powder coating compositions are proposed which comprise as a binder a mixture of a semi-crystalline polyester, an amorphous polyester and a crosslinking agent. The particular crystalline polyesters proposed in this patent are those obtained by esterification of a linear chain saturated aliphatic dicarboxylic acid, mainly 1,2-dodecanedioic acid, with a straight chain saturated aliphatic diol, mainly 1,6-hexanediol and optionally incorporating a trifunctional polyol such as trimethylolpropane or glycerol or a functional polycarboxylic acid such as trimelyl acid to obtain branched polyesters. These semicrystalline polyesters have an acidity or basicity index of about 20 to 120, preferably about 30 to 80 mg KOH per gram and a melting point of 40 to 200 ° C, preferably 60 to 150 ° C. The amorphous polyesters used are amorphous polyesters containing conventional hydroxyl or carboxyl groups; these polyesters preferably have a glass transition temperature (Tg) of at least 50 ° C and a basic or acid number of about 25 to 80 mg of KOH per gram. However, it will be noted that the only amorphous polyethers described and used in this patent are amorphous polyesters rich in terephthalic acid, in which the acid constituent contains at least 50 mole% terephthalic acid and in which the alcohol constituent contains at least 50 mol% neopentyl glycol and up to 10 mol% trimethylpropane; however, amorphous polyesters rich in isophthalic acid are not mentioned in this patent.

The particular semicrystalline polyesters proposed in this patent act primarily as reactive plasticizers. In the embodiments, it is shown that when the powder composition contains a small amount of semicrystalline plasticizer polyester (at most 10% by weight) calculated based on the total weight of the polyesters, amorphous and semi-crystalline) the composition provides coatings that have improved properties, in this case, a smooth appearance with little "orange peel", a brightness measured at an angle of 60 °, according to ASTM D 523 from 96 to 97 %, good pencil hardness and excellent mechanical properties. However, like European patent 521,992 cited above, US patent 5,373,084 does not disclose the possibility of obtaining coatings. which have a low gloss, for example coatings in which the brightness measured at an angle of 60 °, according to ASTM D 523 was less than 50%. However, there is a growing need for thermosetting powder coatings and varnishes that provide coatings that have a low gloss, for example, satin or semi-gloss coatings or matt coatings, usable, inter alia, for the coating of certain industry accessories. of the automobile such as the joints of the wheels, the para-collisions, etc., or even for the coating of the panels and metal doors used in the construction. Various methods have already been proposed for obtaining paints and powder varnishes that provide coatings that exhibit low gloss. However, experience has shown that it is difficult to make a paint or varnish capable of providing, under the usual extrusion and firing conditions, a matte or satin finish in a fully reliable and reproducible manner. According to one of these methods, it is introduced into the composition of the. powder, in addition to the binder and conventional pigments, one or more opacifying agent (s) such as silica, talc, chalk and metal salts. However, the reduction in gloss is often insufficient and a marked alteration of the properties of the paint layers has been observed, such as a lack of adhesion on the metal substrate. To remedy these drawbacks, in European patent 165,207, it is proposed to incorporate waxes, for example a polyolefin wax and metal salts (for example zinc 2-benzothiazolothiolate) in thermosetting powder compositions based on polyesters terminated in carboxyl groups and epoxidized compounds such as triglycidyl isocyanurate. Likewise, in US Pat. No. 4,242,253, calcium carbonate and finely divided propylene particles are proposed as additives for the production of low gloss coatings. The drawback of this system is that the inorganic fillers, often incorporated in significant quantities, can damage the extrusion presses used in the preparation of the powders and damage the appearance of the coveted surface of the obtained coating, which often has an appearance rough and irregular. On the other hand, the added waxes migrate easily to the surface, which cause significant variations in the degree of opacity of the coating during the course of its natural aging. In addition, the fact of having to add additional charges in large quantities entails an additional expense and is in itself a drawback. According to US Pat. No. 3,842,035, the embodiment of a matte finish is known as a coating composition obtained by dry blending of two thermosetting powder compositions which have been exhumed separately. One of these is a composition that hardens slowly (long gel time) and the other composition that hardens quickly (short gel time). By this system it is possible after firing, a matte coating without a particular opacifying agent to the powder composition being necessary. The biggest drawback of this system is the need to dry mix large amounts of powder already formulated, which is not easy to do, especially on an industrial scale. Also, as this mixture can not be done continuously, but only in batches of powderIt is not easy to obtain the same degree of opacity for the coatings going from one batch of powder to another. Finally, the powder that is recovered after a first spray and is reused as paint, may not have the same composition as the powder before the first spray, which also implies an evolution in the degree of opacity obtained. There are still other systems designed to obtain matt coatings in which two polymers of different nature or reactivity are used, as well as one or more crosslinking agents, in such a way that they induce two different crosslinking mechanisms, or two very different reaction speeds. . In these systems, the preparation of the powder is carried out in a single step, unlike the process described in the American patent 3,842,035. It is therefore possible to produce in a single extrusion a paint or a powder varnish capable of forming coatings of very low gloss. By way of example, in Japanese Patent Application 154,771 / 88, a resin composition for powdery matte paints is described, comprising a mixture of a branched polyester containing hydroxyl groups having a high basicity index, with another polyester which it contains hydroxyl groups having a lower basicity index, in certain proportions, and a blocked isocyanate as a crosslinking agent. This composition provides a matte coating having good mechanical properties and good weather resistance. International patent application WO 92101756 discloses powder coating compositions comprising a mixture that both enclose (1) a semicrystalline polyester containing hydroxyl groups having a basicity index of 20 to 100, (2) a amorphous polyester containing hydroxyl groups having a basicity index of from 20 to 120, (3) an acrylic polymer containing hydroxyl groups and (4) a blocked polyisocyanate as the crosslinking agent. The semi-synthetic talc polyesters used are those in which the acid constituent contains from 85 to 95 mol% of terephthalic acid and from 5 to 15 mol% of 1,4-cyclo-hexanedicarboxylic acid and in which the alcohol constituent contains an aliphatic diol of linear chain. From these compositions, low-gloss coatings are obtained (the gloss, measured at an angle of 60 °, according to ASTM D 523, does not exceed 35%), which has good mechanical properties and good pencil hardness . In the European patent application 366,608, powder paints obtained in an extrusion and providing matt coatings are described, but these contain two crosslinking agents. These powder coatings contain an epoxy resin, in particular of the diglycidyl ether of bisphenol A, a polycarboxylic acid, such as for example 2, 2, 5, 5-tetra (β-carboxyethyl) -cyclopentanone as the first cross-linking agent, and a saturated polyester terminated in carboxyl groups, tolylbiguanide or dicyandiamide as the second crosslinking agent.

Finally, the use of active compounds in two different reaction systems for the production of matt coatings is described, for example, in European Patent 104,424. In this patent, it is proposed to prepare a powder by carrying out only one extrusion. This powder contains as a binder a resin containing hydroxyl groups such as a polyester containing hydroxyl groups and a polyepoxidated compound such as triglycidyl isocyanurate, and encloses a particular crosslinking agent comprising carboxyl groups in its molecule (to react with the epoxidized compound) and blocked isocyanate groups (to react with the resin containing hydroxyl groups). The main disadvantage of the powder paints and varnishes obtained in an extrusion described in the patents cited above, is that the properties of the powders obtained are very sensitive to variations in the extrusion conditions, such as the extrusion temperature, the shearing, etc., and as the precise adjustment of these conditions is not easy, it is difficult to constantly produce coatings having the same degree of opacity from a well-defined composition. In particular, the problem is to find a composition that produces under the usual extrusion conditions a low gloss coating in a totally reliable and reproducible manner. In European Patent 551,064, it is proposed to solve this problem by using thermosettable powder coating compositions containing as a binder a mixture of a linear polyester containing carboxyl groups having an acid number comprised between 20 and 50 mg of KOH and a acrylic copolymer containing glycidyl groups obtained from 5 to 30% by weight of acrylate or glycidyl methacrylate and from 70 to 95% by weight of methyl methacrylate. These powder compositions make it possible to obtain coatings of good quality which have a very low gloss. In fact, the brightness, measured at an angle of 60 °, according to the ASTM D 523 standard is always less than 15%. In addition, these matt coatings have a smooth surface without defects, good adhesion on metal surfaces and excellent weather resistance. In addition, the properties of these powders are only slightly or not at all sensitive to the variations of the extrusion conditions, which means that a given composition practically always produces a matt coating that has substantially the same degree of opacity. However, it has been proven that matt coatings obtained from these compositions do not withstand mechanical deformations since the mechanical properties of these coatings are insufficient in particular the resistance to direct and reverse shocks. In conclusion, it can be seen that the different powder compositions proposed up to now for obtaining low gloss coatings still have a certain number of drawbacks. There is therefore a need to have thermosettable powder compositions capable of producing low gloss coatings that do not have the defects of the compositions of the prior art. In accordance with the present invention, it has surprisingly been found that using as an binder an amorphous polyester containing carboxyl, aryl groups in isophthalic acid, with a semicrystalline polyester containing carboxyl groups, prepared more particularly from a saturated aliphatic dicarboxylic acid of chain linear and of a linear or cyclic chain saturated aliphatic diol and an appropriate crosslinking agent, it is possible to obtain thermosettable powder compositions capable of producing low gloss coatings in a totally reliable and reproducible manner and having good mechanical properties and an excellent weather resistance. Therefore, the subject of the present invention is a powdery, self-hardening compositions comprising a mixture of an amorphous polyester as a binder., of a semicrystalline polyester and a crosslinking agent characterized in that the binder comprises (a) an amorphous polyester containing carboxyl groups, rich in. isophthalic acid, prepared from an acid constituent comprising from 55 to 100% by mol of isophthalic acid, from 0 to 45% by mol of at least one dicarboxylic acid other than isophthalic acid and from 0 to 10% by mol of a polycarboxylic acid containing at least 3 carboxyl groups and of an alcoholic constituent comprising from 60 to. 100 mol% neopentyl glycol, from 0 to 40 mol% of at least one hydroxylated compound different from neopentyl glycol and from 0 to 10 mol% of a polyhydroxy compound containing at least 3 hydroxyl groups, the amorphous polyester having a vitreous transition temperature (Tg) of at least 50 ° C and an acid number of 15 to 100 mg KOH / g. (b) a semicrystalline polyester containing carboxyl groups prepared well (bl) from a straight chain saturated aliphatic dicarboxylic acid having from 4 to 16 carbon atoms and from a saturated straight chain saturated diol having 2 to 4 carbon atoms; to 16 carbon atoms and optionally a polycarboxylic acid containing at least 3 carboxyl groups or of a polyol containing at least 3 hydroxyl groups, either (b2) from 40 to 100 mol% of a saturated aliphatic dicarboxylic acid of straight chain having from 10 to 16 carbon atoms and from 0 to 60% by mole of a straight chain saturated aliphatic dicarboxylic acid having from 4 to 9 carbon atoms, calculated on the total of dicarboxylic acids, of a diol cycloaliphatic having from 3 to 16 carbon atoms and optionally from a polycarboxylic acid having at least 3 carboxyl groups or from a polyol having at least 3 hydroxyl groups, having the poly steres semicris talinos a melting point (Tm) of at least 40 ° C and an acid number of 5 to 50 mg KOH / g, and (c) a crosslinking agent. The amorphous polymers containing carboxyl groups, rich in isophthalic acid, used in the compositions according to the invention, are polyesters having a high content of isophthalic acid, normally used in the formulations of paint and powder varnishes for the production of coatings which They offer excellent performance in outdoor exposure. According to the invention, the acid constituent of these amorphous polyesters rich in isophthalic acid must contain at least 55% in -moles of isophthalic acid and can even be completely constituted by isophthalic acid (100% by mole). The acidic constituent of these amorphous polyesters can also contain up to 45% by mole of an aromatic, aliphatic or cycloaliphatic dicarboxylic acid other than isophthalic acid, glutaric acid, adipic acid, pimelic acid, -suberic acid, azelaic acid , sebacic acid, fumaric acid, maleic acid, 1,3- and 1,4-cyclohexanedicarboxylic acid and mixtures of these compounds and up to 10% by mole of a polycarboxylic acid containing at least 3 carboxyl groups, such as trimellitic acid and pyromellitic acid. These acids can be used in the form of free acid, or optionally, in the form of anhydride, or even in the form of an ester with a lower aliphatic alcohol. The alcoholic constituent of these amorphous polyesters must contain at least 60 mole% of neopentyl glycol, it can also consist entirely of neopentyl glycol (100 mole%). The alcoholic constituent of these amorphous polyesters may also contain up to 40% by mole of an aliphatic, cycloaliphatic or aromatic dihydroxy compound different from neopentyl glycol such as ethylene glycol, propylene glycol, 1-butanediol, 1,6-hexanediol, 2-methyl-l, 3-propanediol, 2-butyl-2-ethyl-l, 3-propanediol, 1,4-cyclohexanedimethanol, the hydrogenated bisphenol A, the neopentyl glycol hydroxypivalate and mixtures of these compounds and up to 10% by weight of a polyhydroxy compound containing at least 3 hydroxyl groups such as trimethylolpropane, di trimethylpropane, pentaerythritol and mixtures thereof. Amorphous polyesters containing carboxyl groups, rich in isophthalic acid, which can according to the invention have an acid number of 15 to 100 mg of KOH per gram, preferably 30 to 70 mg of KOH per gram and have a glass transition temperature (Tg) which rises to at least 50 ° C so that the polyesters remain solid at the entrapment temperature (20 to 50 ° C) and preferably ranges from 50 to 80 ° C. The number average molecular weight (Mn) of these amorphous polymers is between 1,100 and 11,500, preferably between 1,600 and 8,, 500. The viscosity in the molten state (measured with a cone / cup viscometer according to ASTM D 4287-8) of these amorphous polyesters can vary from 100 to 15.00 mPa.s at 200 ° C.

The semi-crystalline polyesters containing carboxyl groups used in the compositions according to the invention are semicrystalline polyesters having a particular chemical constitution. It is chosen between two types of polyesters (bl) or (b2). The polyesters (bl) are prepared by polyesterification of a straight chain saturated aliphatic dicarboxylic acid having from 4 to 16 carbon atoms with a saturated aliphatic diol having from 2 to 16 carbon atoms. Preferably, these polyesters are linear, but branched polyesters in which the branching is introduced by polycarboxylic acid containing at least 3 carboxyl groups such as trimellitic acid, di-trimethylolpropane and pentaerythritol can also be used, these compounds being used in the ratio of 0 to 10% in moles on all the monomers. Examples of saturated aliphatic straight-chain dicarboxylic acids which can be used with succinic acid, glutaric acid, pi-aic acid, suberic acid, acelaic acid, sebacic acid, 1,2-dodecanedioic acid, These acids they can be used mixed, but they are preferably used alone. 1,2-Dodecanedioic acid is preferred. Examples of straight-chain saturated aliphatic diols that can be used are ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,1-decanediol, 1,1-dodecanediol, 1,14-tetradecanediol, 1,16 hexadecanediol. These diols can be mixed, but are preferably used alone. 1,6-hexanediol is preferably used. Semi-crystalline polyesters (b2) are prepared from 40 to 100% by mole of a straight chain saturated aliphatic dicarboxylic acid having from 10 to 16 carbon atoms and from 0 to 60% by mole of a saturated aliphatic dicarboxylic acid linear chain having 4 to 9 carbon atoms, calculated on the set of these dicarboxylic acids. It is also possible to use from 40 to 95% by mole of the acid having from TI 0 to 16 carbon atoms and from 5 to 60% by mole of the acid having from 4 to 9 carbon atoms. The alcoholic constituent of these polyesters is a cycloaliphatic diol having from 3 to 16 carbon atoms. Preferably, these polymers are linear, but can likewise branched polyesters in which the branching is introduced by means of a polycarboxylic acid containing at least 3 carboxyl groups such as trimellitic or pyromellitic acid or of a polyol such as trimethylpropane, di-trimethylolpropane and pentaerythritol. These compounds having at least 3 functions are used in a ratio of 0 to 10% by mole over the group of monomers that enter the polyester composition. Examples of linear chain saturated aliphatic dicarboxylic acids having 10 to 16 carbon atoms are 1,10-decanedioic acid, 1,1-undecanedioic acid, 1,2-dodecanedioic acid, 1,4-tetradecanedioic acid , 1,15-pentadecanedioic acid and 1,16-hexadecanedioic acid. Preferably 1,2-dodecanedioic acid is used alone or as a mixture. Examples of straight chain saturated aliphatic dicarboxylic acids having from 4 to 9 carbon atoms which can be used are succinic acid, glutaric acid, pimelic acid, suberic acid, acelaic acid. These acids may be used mixed but preferably alone. Examples of cycloaliphatic diols having from 3 to 16 carbon atoms that can be used are 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A, 2, 2, 4-tetramethyl-1, 3- Cyclobutanediol and 4,8-bis (hydroxymethyl) -trotyclo- [5.2.1. O2'6] dean. These diols can be used mixed, but are preferably used alone. Preferably, 1,4-cyclohexanediol or cyclohexanedimethanol are used. The talc semicris polyesters containing carboxyl groups which can be used according to the invention have an acid number of 5 to 50 mg of KOH per gram, preferably 5 to 30 mg KOH per gram; preferably, these polyesters have a basicity index that does not exceed 5 mg KOH per gram. These semicrystalline polyesters are solid products at room temperature characterized by a melting point (Tm) between 40 and 90 ° C. The number average molecular weights (Mn) of these semicris talin polyesters are between 2,200 and 25,000 and preferably between 2,800 and 11,220. The viscosity in the molten state measured with a cone / pan viscometer according to AS.TM D 4287-88) of these semicrystalline polyesters can vary from 50 mPa.s to 100 ° C to 10,000 mPa.s at 150 ° C. It has been found with surprise that only thermosetting powder compositions containing both an amorphous polyester rich in isophthalic acid and a particular semicrystalline polyester prepared by polyesterification of a straight chain saturated aliphatic dicarboxylic acid with a saturated aliphatic chain diol linear or cycloaliphatic, such as those described above in detail, are capable of providing low gloss or matt coatings, which exhibit good mechanical properties and excellent weather resistance. In fact, it has been observed that powders of identical composition, but in which the amorphous polyester rich in isophthalic acid is replaced by an amorphous polyester rich in terephthalic acid of the type described and used in US Pat. No. 5,373,084, after the cooking a coating having a very high gloss (comparative example I). Furthermore, it has been observed that powders of identical composition but in which the particular semicrystalline polyester according to the invention are replaced by a semicrystalline polyester which is not according to the invention of the type described and used in European Patent 521,992 and based on essentially in the terephthalic acid and 1,6-hexanediol, they give after coating a coating which also has a very high gloss (comparative examples II and III).

The amorphous polyesters rich in isophthalic acid and the semicrystalline polyesters used according to the invention are prepared according to conventional methods of synthesis of polyesters, using an excess of acid in relation to alcohol so that a polyester containing carboxyl groups having the index is obtained of desired acidity. The amorphous polyesters containing carboxyl groups rich in isophthalic acid can be prepared according to one or two step synthesis methods. In the latter case, in the first step, a polyester containing hydroxyl groups is prepared from, on the one hand, isophthalic acid and optionally one or more polycarboxylic acid (s) different from the acid-isophthalic acid (or its functional derivatives), and on the other hand, an excess of neopentyl glycol and optionally one or more di- and / or polyhydroxy compound (s) and in the second step, the polyester containing hydroxyl groups is esterified. obtained in this manner, with an appropriate dicarboxylic acid, preferably isophthalic acid, to obtain an amorphous polyester containing carboxyl groups, rich in isophthalic acid.

Semi-crystalline polyesters containing carboxyl groups are generally prepared according to a one-step process, from an appropriate aliphatic or cycloaliphatic diol and from an excess of the appropriate aliphatic dicarboxylic acid, optionally incorporating a polycarboxylic acid or a polyol in the mixture. reaction in the case where it is desired to obtain a branched semicrystalline polyester. Generally, the synthesis of these polyesters is carried out in a conventional reactor equipped with a stirrer, an inert gas inlet (for example nitrogen), a distillation column attached to a condenser and a thermometer fixed to a thermoregulator. The esterification conditions are classical, knowing that a usual esterification catalyst can be usedeither a tin derivative, such as dibutyltin dilaurate, dibutyltin oxide or n-butyltin trioctanoate, or a titanium derivative such as tetrabutyl titanate in a ratio of 0.01 to 1% by weight of reagents. An antioxidant of the phenolic type, such as Irganox 1010 (sold by Ciba-Geigy), can optionally be added alone or mixed with a stabilizer such as, for example, tributyl phosphite, in a ratio of 0.01 to 1% by weight of reagents. The polyesterification is generally carried out at a temperature that is progressively increased from approximately 130 ° C to approximately 180 to 250 ° C, first at normal pressure, then at reduced pressure maintaining this temperature until obtaining a polyester having the Basicity Index and / or of desired acidity. When two steps proceed to prepare the amorphous polyesters rich in isophthalic acid, the reaction mixture containing hydroxyl groups obtained in the first step is allowed to cool to 200 ° C, the amount is added. The desired temperature of the dicarboxylic acid is brought to 230-240 ° C and this temperature is maintained, initially under normal pressure, then under reduced pressure, until an amorphous polyester containing carboxyl groups having the desired acid number is obtained . The degree of esterification is followed by determining the amount of water formed during the course of the reaction and the properties of the polyester obtained, for example, the acid number, the basicity index, the molecular weight, the temperature of the vitreous transition (Tg), the melting point (Tm) and the viscosity in the molten state. At the end of the synthesis, when the polyester is still in the molten state, a known crosslinking catalyst may be optionally added, in a ratio of 0.01 to 1.5% by weight of the polyester. These catalysts may be of the amine type such as 2-phenylimidazoline, of the phosphine type such as triphenylphosphine or phosphonium ammonium salts such as tetrapropylammonium chloride, tetrabutylammonium bromide, benzyltriphenylphosphonium chloride or ethyltriphenylphosphonium bromide. . The polyester is then discharged from the reactor, melted in a thick layer, allowed to cool and crushed into grains having an average dimension ranging from a fraction of mm to a few m. The amorphous polyester containing carboxyl groups, rich in isophthalic acid, the semicrystalline polyester containing carboxyl groups and the crosslinking agent together form the base binder of the thermosetting powder coating compositions according to the invention. In the thermosettable powder coating compositions according to the invention, the amount of amorphous polyester rich in isophthalic acid generally represents about 60 to 87% by weight and the amount of semi-solid polyester about 13 to 40% by weight calculated based on the weight total of the amorphous and semicrystalline polyesters. However, it has been observed that the gloss measured at an angle of 60 ° according to ASTM D 523, of the coatings obtained decreases when the amount of amorphous polyester decreases and the amount of semicrystalline polyester increases. This is why, in the compositions according to the invention, the amount of amorphous polyester rich in isophthalic acid preferably represents 60 to 82% by weight and the amount of the semicrystalline polyester preferably 18 to 40% by weight calculated based on the total weight of amorphous and semicrystalline polyesters. The crosslinking agents which may be used in the compositions according to the invention, are all organic compounds having functional groups capable of reacting with the carboxyl groups of polyesters to produce crosslinking of the binder. Typical crosslinking agents are, for example, the polyepoxidized compounds and the ß-hydroxyalkyl idas. Particularly preferred crosslinking agents are triglycidyl isocyanurate (Araldite PT 810 sold by Ciba-Geigy), the 75/25 mixture of diglycidol terephthalate and triglycidyl trimellitate (Araldite PT 910 sold by Ciba-Geigy), acrylic copolymers containing glycidyl groups such as GMA 252 sold by ESTRON and bis (N, N-dihydroxyethyl) adipamide (PRIMID XL 552 sold by EMS). In the thermosetting coating compositions according to the invention the ratio of the amount between the amorphous and semi-crystalline polyesters containing carboxyl groups on the one hand, and the crosslinking agent on the other, is such that there are 0.5 to 1.5 equivalents of carboxyl groups per equivalent of functional groups (e.g., epoxy groups) in the crosslinking agent. The crosslinking agent is preferably used in an amount of about 4 to 25% by weight calculated based on the total weight of the binder. The pvd coating compositions according to the invention therefore generally contain, as binder (a) 45 to 83% by weight amorphous polyester rich in isophthalic acid, (b) from 13 to 30% by weight semicrystalline polyester and (b) c) from 4 to 25% by weight crosslinking agent, and preferably (a) from 45 to 78% by weight amorphous polyester rich in isophthalic acid, (b) from 18 to 30% by weight semicrystalline polyester oy (c) ) from 4 to 25% by weight of crosslinking agent. The present invention also relates to the use of thermosetting powder coating compositions according to the invention, for the preparation of powder coatings and paints which provide low gloss coatings, preferably matt coatings, as well as varnishes and powder paints obtained with the help of these compositions. The powder varnishes and paints according to the invention can be prepared by homogeneously mixing the amorphous polyester rich in isophthalic acid, the semicrystalline polyester and the crosslinking agent with the various auxiliaries conventionally used for the production of varnishes and powder paints. This homogenization is carried out, for example, by first mixing, dry at room temperature, the amorphous polyester, the semicrystalline polyester, the crosslinking agent, and the various auxiliary substances in a mixer, for example a drum mixer and then passing through the mixture thus obtained to an extrusion press, for example a single screw extrusion press of the Buss-Ko-Kneter type or a twin screw extrusion press of the PRISM or APV type to produce a homogenization in a molten phase at a temperature located in the range of 80 to 150 ° C. The extrudate is then allowed to cool, crushed and sieved to obtain a powder whose particle size is between 10 and 150 microns. If desired, the amorphous polyester, rich in isophthalic acid and the semicrystalline polyester, can be blended into the molten state in the synthesis reactor or in an extrusion press such as an BETOL BTS 40 extrusion press before being added in the form of a mixture to the Other ingredients of the composition for dry mixing at room temperature. However, it is more convenient to add the two polyesters separately to the other ingredients of the powder composition. The auxiliary substances which can be added to the thermosettable powder compositions are, for example, pigments and dyes such as titanium dioxide, iron oxides, zinc oxide, etc., metal hydroxides, metal powders, sulfides, sulphates, carbonates, silicates such as ammonium silicate, carbon black, talcum, kaolins, barium sulfates, iron blues, lead blues, organic reds, organic browns, etc., fluidity regulating agents such as Resiflow PV5 (from WOR-LEE), Modaflow (from MONSANTO) or Acronal 4F (from BASF) and degassing agents such as benzoin, etc. These auxiliary substances are used in usual amounts, understanding that if the thermosetting compositions according to the invention are used as varnishes, the addition of opacifying substances will be increased. Ultraviolet ray absorbing compounds such as Tinuvin 900 from Ciba-Geigy and light stabilizers based on spherical impeding amines can also be added, such as Tinuvin 144 from Ciba-Geigy. The subject of the present invention is also a process for obtaining a low-gloss coating on an article, in which a thermosetting powder coating composition according to the invention as described above is applied to the article and subjected to the article thus coated at high temperature cooking for a duration sufficient to obtain complete crosslinking of the coating. The compositions of thermosettable powder coatings can be applied to articles of various dimensions, in particular on articles in glass, ceramic and metal such as steel or aluminum, by known techniques for depositing powders, that is, by spray application. sprayer in an electrostatic field where the powder is loaded under a voltage of 30 to _100 kV by means of a high-voltage direct current or, with a tribo-electric spray gun in which the powder is charged by friction or even by the well-known deposit technique in fluid bed. After being applied to the corresponding article, the deposited powders are baked in a furnace at a temperature comprised between 140 and 200 ° C for a duration that can reach 30 minutes to melt the powder particles and to form a homogeneous film that is install perfectly on the substrate and to finally obtain the cross-linking and the complete hardening of the coating. The compositions of thermosettable powder coatings according to the present invention allow to obtain coatings having a low gloss. In fact, the brightness, measured at an angle of 60 °, according to the ASTM D 523 standard of these coatings always increases to a value of less than 50%. Furthermore, as already explained above, it is possible to obtain coatings having different gloss levels depending on the amount of amorphous polyester and the amount of semicrystalline polyester or used in these compositions. Thanks to the present invention, therefore, after the firing, coatings having the desired gloss level can be obtained by simply choosing a powder composition containing the required proportions of amorphous and semi-crystalline polyester. However, it is necessary to take into account the fact that the nature of the crosslinking agent is equally important for the level of gloss of the coatings obtained after firing (see example 11 below). Some preliminary tests allowed to determine easily the composition that is convenient to obtain a coating that presents the desired level of brightness.

As shown in more detail in the examples that follow, thanks to the present invention, it is therefore possible to prepare paints and powder coatings capable of providing coatings having the required gloss level for the application in question, ie coatings satin or semi-gloss in which the brightness measured at an angle of 60 °, according to ASTM D 523 is less than 50%, or matt coatings in which the brightness, measured under the same conditions, is less than 35%. In addition, the powder thermosetting compositions according to the present invention are capable of producing low gloss coatings having a number of other advantageous properties, among others a smooth, uniform appearance, free of surface defects and free of "orange peel". , good mechanical properties and excellent resistance to weathering and U rays. Obtaining a satin or matte finish is therefore not accompanied by an alteration of the other properties of the coatings as is often the case for powder compositions of the state of the art, capable of producing low gloss coatings.

Finally, another important advantage of the compositions of thermosetting powder coatings according to the present invention, in relation to powder compositions of the state of the art, resides in the fact that their properties are only little or not at all sensitive to the variations of the extrusion conditions and that these compositions therefore make it possible to continuously produce low gloss, satin or matt coatings, which have substantially the same degree of gloss or opacity. The following examples illustrate the invention without limiting it. In these examples, the determination of certain characteristic values has been carried out according to the methods described below: - the brightness: it is expressed in intensity of the reflected light, in percentage, in relation to the intensity of the incident light under an angle 60 ° and measured according to ASTM D 523; - the impact resistance is measured by means of a Gardner apparatus according to ASTM D 2794. Cold-rolled steel panels with a hard coating are subjected to shocks of increasing intensity on the coated side (direct impact) and on the uncoated side (reverse impact). The highest shock that does not cause cracking of the coating is indicated in kg. cm; pencil hardness: determined by means of a hardness tester according to WOLFF WILBRON (ASTM D 3363 standard); the hardness indicated is that of the hardest pencil that does not cause notches in the coating according to a scale that goes from 6B (the softest) to 6H (the hardest); QUV accelerated aging test: chromium-plated aluminum panels fitted with a hard coating to be analyzed in a "QUV Panel" test device from the company Q-Panel Co (Cleveland-United States) and subjected to several cycles of exposure to UV lamps and moisture, at different temperatures. Among the different cycles of this type described according to ASTM G 53-88, in the present case, the coatings are subjected to a cycle of 8 hours of exposure with a fluorescent UVA lamp (wavelength of 340 nm and intensity of 0.77 W / m2 / nm) that simulates the harmful effects of sunlight at 60 ° C, and 4 hours of condensation of water vapor, matte lamp, at 40 ° C; the evolution of the brightness is recorded, measured at an angle of 60 °, according to ASTM D 523. After 3,000 hours of exposure to this ensayo, the brightness retention is determined according to the equation:% retention = brightness at 60 ° after 3,000 hours of exposure x 100% brightness at 60 ° at the beginning of the experience and also the delta E ink change, calculated according to the ASTM D standard of 2244; - the acid number and the basicity index are determined by titration according to DIN 53402 and DIN 53240 expressed in mg KOH per gram of polyester; - the vitreous transition temperature (Tg) and the melting point (Tm) are 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 according to the equation: Mh Functionality X 56,100 where IA is the acid number expressed in mg KOH per gram of polyester, - the viscosity in the molten state of the polyesters expressed in mPa.s has been measured with a cone / plate viscometer from ICI according to ASTM D 4287-88; also referred to as "ICI viscosity" and has been measured at the temperatures indicated in the examples. Unless indicated otherwise, the parts cited in the examples are parts by weight.

Example 1 - Synthesis of amorphous polyesters. a) in one step In a 4-neck 10-liter flask equipped with a stirrer, a nitrogen inlet, a distillation column attached to a water-cooled condenser and a thermometer attached to a thermoregulator, a mixture of 399.6 parts ( 3.84 moles) of neopentyl glycol and 22.2 parts (0.16 moles) of trimethylolpropane. The mixture is heated under agitation and nitrogen to a temperature of about 130 ° C and 722.9 parts (4.35 moles) of isophthalic acid and 2.5 parts of n-butyltin trioctanoate are added as the esterification catalyst. The temperature of the reaction mixture is then progressively increased to 230 ° C. Begin to distill water from the reactor at 180 ° C. When the distillation of water under atmospheric pressure is completed, a vacuum of 50 mm Hg is progressively established. The temperature of the reaction mixture is maintained for 3 hours at 230 ° C and under a pressure of 50 mm Hg. Finally, the polyester obtained at 180 ° C is allowed to cool and is discharged from the reactor. The polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 32 mg KOH / g basicity number 2 mg KOH / g Viscosity ICI (at 200 ° C) 8000 mPa.s Vitreous transition temperature (Tg) 59 ° C (DSC at 20 ° C / minute) Average molecular weight in number (Mn) 5423 (theoretical). b) in two steps, step. In a reactor as described in a) above, a mixture of 423.5 parts is introduced (4.07 moles) of neopentyl glycol and 22.2 parts (0.16 moles) of trimethylpropane. The mixture is heated under stirring and nitrogen to a temperature of about 130 ° C and 121.8 parts (0.733 moles) of terephthalic acid, 487.1 parts (2.93 moles) of isophthalic acid and 2.3 parts of n-butyltin trioctanoate are added as a catalyst of esterification. The reaction is continued at 220 ° C under atmospheric pressure until approximately 95% of the theoretical amount of water is distilled. A transparent polyester containing hydroxyl group is obtained having the following characteristics: basicity index 59 mg KOH / g acid number 12 mg KOH / g Viscosity ICI (at 175 ° C) 2200 mPa.s 2nd step The polyester obtained in the first step is allowed to cool to 200 ° C and 110.9 parts (0.67 moles) of isophthalic acid are added. The mixture is then heated progressively to 230 ° C. The mixture is kept at this temperature for 2 hours and when the reaction mixture becomes clear, a vacuum of 50 mm Hg is progressively established. The reaction is continued for 3 hours at 230 ° C under a pressure of 50 mm Hg. The polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 31 mg KOH / g basicity index 3 mg KOH / g Viscosity ICI (at 200 ° C) 6600 mPa.s Vitreous transition temperature (Tg) 57 ° C (DSC at 20 ° C / minute) Average molecular weight in number (Mn) 5423 (theoretical). c) According to the two-step operation described in b) above, still another amorphous polyester containing carboxyl groups, rich in isophthalic acid, is prepared. In the first step, a polyester containing hydroxyl groups from 423.5 parts is prepared in the same manner as in b) above. (4.07 moles) of neopentyl glycol, 304.5 parts (1.83 moles) of tgerephthalic acid, 304.5 parts (1.83 moles) of isophthalic acid and 2.3 parts of n-butyltin trioctanoate as the esterification catalyst. The reaction is carried out at 230 ° C under atmospheric pressure (instead of 220 ° C). The transparent polyester containing hydroxyl groups has the following characteristics: basicity index 57 mg KOH / g acid number 13 mg KOH / g ICI viscosity (at 175 ° C) 1200 mPa.s In the second step, a polyester is prepared in the same way as in b) above. contains carboxyl groups; 110.9 parts are added (0.67 moles) of isophthalic acid as in b) above. The polyester containing carboxyl groups obtained in this way possesses the following characteristics: Acidity index 32 mg KOH / g basicity index 2.1 mg KOH / g Viscosity ICI (at 200 ° C) 3000 mPa.s Vitreous transition temperature (Tg) 53 ° C (DSC at 20 ° C / minute) Average molecular weight in number (Mn) 3740 (theoretical). d) By way of comparison, an amorphous polyester containing carboxyl groups, rich in terephthalic acid, is also prepared according to the two-step operation described in b) above; it contains a lower amount of isophthalic acid (16.2 mole%) and a larger amount of terephthalic acid (83.8 mole%). In the first step, a polyester containing hydroxyl groups is prepared in the same manner as in b) above from 417.8 parts (4.02 moles) of neopentyl glycol, 600.7 parts (3.62 moles) of terephthalic acid and 2.2 parts of trioctanoate of n-butyl as an esterification catalyst. The reaction is carried out at 240 ° C under atmospheric pressure (instead of at 220 ° C). The transparent polyester containing hydroxyl groups has the following characteristics: basicity index 61 mg KOH / g acid index 8 mg KOH / g ICI viscosity (at 200 ° C) 1200 mPa.s In the second step, a polyester containing carboxyl groups is prepared in the same manner as in b) above, but 117.1 parts are added (0.7 moles) of isophthalic acid (instead of 110.9 parts); the mixture is progressively heated to 240 ° C (instead of at 230 ° C) it is kept at this temperature for 3 hours. When the reaction mixture becomes clear, a vacuum of 50 mm Hg is gradually established and the reaction is continued for 4 hours at 240 ° C and under a pressure of 50 mm Hg.

The polyester containing carboxyl groups obtained in this way possesses the following characteristics: Acidity index 33 mg KOH / g basicity index 3 mg KOH / g Viscosity ICI (at 200 ° C) 4700 mPa.s Vitreous transition temperature (Tg) 57 ° C (DSC at 20 ° C / minute) Average molecular weight in number (Mn) 3740 (theoretical) The polyester obtained is allowed to cool to 200 ° C and 1.3 parts of ethyltriphenyl-phosphonic bromide (crosslinking catalyst) are added After one hour of stirring the mixture, the polyester is discharged from the reactor. step described in a) above, another amorphous polyester containing carboxyl groups rich in isophthalic acid is prepared, from 424.9 parts of neopentyl glycol, 722.2 parts of isophthalic acid and 2.3 parts of n-butyltin trioctanoate as the esterification catalyst.

The polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 31.5 mg KOH / g ICI viscosity (at 200 ° C) 2900 mPa.s Vitreous transition temperature (Gg) 52 ° C (DSC at 20 ° C / minute) Example 2 - Synthesis of semicrystalline polyesters. a) In a reactor as described in Example 1, a mixture of 739.9 parts (3.21 moles) of 1,2-dodecanedioic acid, 369.2 parts (3.12 moles) of 1,6-hexanediol and 2.5 parts of trioctanoate of n-butyl as the esterification catalyst. The mixture is heated, with stirring and nitrogen, to a temperature of about 140 ° C, at which temperature the reactor water begins to distill. Then, the temperature of the reaction mixture is progressively raised to 225 ° C. When the distillation of the water under atmospheric pressure is finished, 1.0 parts of n-butyl trioctanoate are added and a vacuum of 50 mm Hg is progressively established. The temperature of the reaction mixture is maintained for 3 hours at 225 ° C and under a pressure of 50 mm Hg. The semicrystalline polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 11.5 mg KOH / g basicity index 0.5 mg KOH / g Viscosity ICI (at 150 ° C) 7000 mPa.s Vitreous transition temperature (Tg) 67 ° C (DSC at 20 ° C / minute) Average molecular weight in number (Mn) 11220 (theoretical).

The polyester obtained is allowed to cool to 160 ° C and 10 parts of Tinuvisn 144 (light stabilizer) and 20 parts of Tinuvisn 900 (UV light absorber) are added. After one hour of stirring the mixture, the polyester is discharged from the reactor, allowed to cool to room temperature and obtained in the form of a white solid product. b) According to the mode of operation described in a) above, another semicrystalline polyester is prepared from 750.7 parts (3.26_ moles) of 1,2-dodecanedioic acid, 353.7 parts (2.99-moles) of 1,6-hexanediol and 2.5 parts of trioctanoate of nt > I use it as an esterification catalyst. The semicrystalline polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 29.5 mg KOH / g basicity index 0.6 mg KOH / g Viscosity ICI (at 100 ° C) 2000 mPa.s Vitreous transition temperature (Tg) 65 ° C (DSC at 20 ° C / minute) Average molecular weight in number (Mn) 3740 (theoretical).

The polyester obtained is allowed to cool to 160 ° C and 10 parts of Tinuvin 144 and 20 parts of Tinuvin 900 are added. After one hour of stirring the mixture, the polyester is discharged from the reactor, allowed to cool to room temperature and It gets in the form of a white solid product. c) According to the mode of operation described in a) above, another semicrystalline polyester is prepared from 750.2 parts (3.25 moles) of 1,2-dodecanedioic acid, 351.2 parts (2.97 moles) of 1,6-hexanediol and 9,567 parts. (0.07 mol) - of trimethylolpropane and 2.5 parts of n-butyl triooctanoate as the esterification catalyst. The semicrystalline polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 21.3 mg KOH / g basicity index 0.9 mg KOH / g Viscosity ICI (at 100 ° C) 4000 mPa.s Vitreous transition temperature (Tg) 63 ° C (DSC at 20 ° C / minute) Average molecular weight in number (Mn) 7012 (theoretical).

The polyester obtained is allowed to cool to 160 ° C and 10 parts of Tinuvin 144 and 20 parts of Tinuvin 900 are added. After one hour of stirring the mixture, the polyester is discharged from the reactor, allowed to cool to room temperature and It gets in the form of a white solid product. d) According to the mode of operation described in a) above, another semicrystalline polyester is prepared from 897.4 parts (3.90 moles) of 1,2-dodecanedioic acid, 236.4 parts (3.81 moles) of ethylene glycol and 2.5 parts of trioctanoate of n-butyl as the esterification catalyst. The polyester is crystalline containing carboxyl groups obtained in this way possesses the following characteristics: acid number 8.02 mg KOH / g basicity index 2.5 mg KOH / g Viscosity ICI (at 150 ° C) 7200 mPa.s Vitreous transition temperature (Tg) 76 ° C (DSC at 20 ° C / minute) Average molecular weight in number (Mn) 11220 (theoretical).

The polyester obtained is allowed to cool to 160 ° C and 10 parts of Tinuvin 144 and 20 parts of Tinuvin 900 are added. After one hour of stirring the mixture, the polyester is discharged from the reactor, allowed to cool to room temperature and It gets in the form of a white solid product. e) By way of comparison, a semicrystalline polyester containing carboxyl groups which is not according to the invention is also prepared in the following manner: acid number 21.3 mg KOH / g basicity index 0.9 mg KOH / g Viscosity ICI (a 100 ° C) 4000 mPa.s Melting point (Tm) 63 ° C (DSC at 20 ° C / minute) Average molecular weight in number (Mn) 7012 (theoretical).

The polyester obtained is allowed to cool to 160 ° C and 10 parts of Tinuvin 144 and 20 parts of Tinuvin 900 are added. After one hour of stirring the mixture, the polyester is discharged from the reactor, allowed to cool to room temperature and get in the form zde a white solid product. d) According to the described operation mode. in a) above, another semicrystalline polyester is prepared from 897.4 parts (3.90 moles) of 1,2-dodecanedioic acid, 236.4 parts (3.81 moles) of ethylene glycol, and 2.5 parts of n-butyl trioctanoate as the esterification catalyst. The semicrystalline polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 8.0 mg KOH / g basicity index 2.5 mg KOH / g ICI viscosity (at 150 ° C) 7200 mPa.s Melting point ( Tm) 76 ° C (DSC at 20 ° C / minute) Average molecular weight in number (Mn): 11220 (theoretical).

The polyester obtained is allowed to cool to 160 ° C and 10 parts of Tinuvin 144 and 20 parts of Tinuvin 900 are added. After one hour of stirring the mixture, the polyester is discharged from the reactor, allowed to cool to room temperature and It gets in the form of a white solid product. e) By way of comparison, a semicrystalline polyester containing carboxyl groups which is not according to the invention is also prepared in the following manner: In a reactor as described in Example 1, 453.4 parts (3.84 moles) of 1,6-hexanediol are introduced. The contents of the reactor are heated to 150 ° C to melt the product and 589.9 parts (3.55 moles) of terephthalic acid and 2.3 parts of trioctanoate are added as the esterification catalyst. The reaction is continued at 235 ° C under atmospheric pressure until 95% of the theoretical amount of water is distilled. A polyester containing hydroxyl groups is obtained which has the following characteristics: basicity index 40 mg KOH / g acid number 5 mg KOH / g ICI viscosity (at 175 ° c, 800 mPa.s 2nd step The polyester obtained in the first step is cooled to 200 ° C and 91.7 parts (0.55 moles) of isophthalic acid are added. The mixture is then heated progressively to 235C, the mixture is kept at this temperature for 2 hours, 1.0 part of tributylphosphite is added as a stabilizer and a vacuum of 50 mm Hg is progressively established. The temperature of the reaction mixture is maintained for 2 hours at 235 ° C and under a pressure of 50 inm Hg. The semi-crystalline polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 32 mg KOH / g basicity index 0.5 mg KOH / g ICI viscosity (at 150 ° C) 7200 mPa.s Melting point ( Tm) 130 ° C (DSC at 20 ° C / minute) Average molecular weight in number (Mn) 3740 (theoretical).

The polyester obtained is allowed to cool to 160 ° C and 10 parts of Tinuvin 144 and 20 parts of Tinuvin 900 are added. After one hour of stirring the mixture, the polyester is discharged from the reactor, allowed to cool to room temperature and It gets in the form of a white solid product. f) By way of comparison, a semicrystalline polyester is prepared in exactly the same manner as in d) above, from 458.24 parts (3.88 moles) of 1,6-hexanediol and 589.2 parts (3.55 moles) of terephthalic acid (in the first step) and 91.4 parts (0.62 moles) of adipic acid (in the second step). The semicrystalline polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 34 mg KOH / g basicity index 3 mg KOH / g ICI viscosity (at 200 ° C) 700 mPa.s Melting point (Tm) 129 ° C (DSC at 20 ° C / minute) Number average molecular weight (Mn) 3400 (theoretical), This semicrystalline polyester has the same characteristics as the semicrystalline polyester described in the example of European patent 521,992. At the end of the synthesis, the polyester obtained is allowed to cool and 10 parts of Tinuvin 144 and 20 parts of Tinuvin 900 are added. After an hour of stirring the mixture, the polyester is discharged from the reactor, it is left to cool to room temperature , and they are obtained in the form of a white solid product. g) According to the mode of operation described in a) above, another semicrystalline polyester is prepared from 757.8 parts of 1,2-dodecanedioic acid, 351.2 parts, of 1,4-cyclohexanediol and 2.5 parts of n-butyl trioctanoate as esterification catalyst. The semicrystalline polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 31.3 mg KOH / g ICI viscosity (at 150 ° C) 1500 mPa.s Melting point (Tm) 65 ° C (DSC at 20 ° C) ° C / minute) h) According to the mode of operation described in a) above, another semicrystalline polyester is prepared from 700.1 parts of 1,12-dodecanedioic acid, 399.8 parts of 1,4-cyclohexanediol and 2.5 parts of n-butyl trioctanoate as the catalyst of esterification. The semicrystalline polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 33.4 mg KOH / g ICI viscosity (at 150 ° C) 1500 mPa.s Melting point (Tm) 47 ° C (DSC at 20 ° C / minute) i) According to the mode of operation described in a) above, another semicrystalline polyester is prepared from 709.4 parts of 1,12-dodecanedioic acid, 369.74 parts of 1,4-cyclohexane-dimethanol and 2.5 parts of n-butyl trioctanoate. as an esterification catalyst. The semicrystalline polyester containing carboxyl groups obtained in this way possesses the following characteristics: acid number 33.0 mg KOH / g ICI viscosity (at 150 ° C) 3400 mPa.s Melting point (Tm) 45 ° C (DSC at 20 ° C / minute) Examples 3 to 15 and comparative examples I, II and III -Preparation of thermosettable powder coating compositions. 16 powder thermosetting compositions are prepared in the following manner. An amorphous polyester containing carboxyl groups prepared as described in Example 1, a semi-crystalline polyester containing carboxyl groups prepared as described in Example 2, a cross-linking agent and various auxiliary substances used, is dry-mixed at room temperature. conventionally for the manufacture of powder paints. The nature and quantities of these products are indicated in Table I below. The mixture is homogenized in a twin screw extrusion press (PRISM 16 mm L / D 15/1) at an extrusion temperature of 85 ° C. The extrudate is cooled, crushed and crushed in a RETSCH ZM 100 crusher (0.5 μm sieve), then sieved to form a powder whose particle size is between 10 and 100 microns. To evaluate the properties of the coatings obtained with these compositions, the obtained powders are deposited by spraying with the help of an electrostatic spray gun GemaVols tatic PCG 1 on cold-rolled steel panels, under a voltage of 60 to 100 kV, with In order to obtain a film thickness comprised between 50 and 70 microns. The panels coated in this way are then transferred to an air-ventilated oven, where the deposited compositions are subjected to 15 minutes of cooking at a temperature of 200 ° C. The obtained hard coatings have all, a smooth, uniform appearance and without defects such as craters, pitting or "orange peel". The different compositions and the properties of the coatings obtained are described in Table I below. abla 1 ro 1 5 Table I (continued) v J (1) i comparative title (2) triglycidyl isocyanurate (Anfite PT S10 of Ciba Geigy) (3) mix 75/25 of diglydyl terephthalate and triglycidyl trimellilate (Ataldite 910 of Oba-Geig) (4) bis (N ^ -dil.droxyethyl) adipimide (Priraid XL-552 from EMS) (5) Kronos 3IO (Ciba-Oeigy) (6) Res¡flowPV5 (Worlee Chemie) (7) polyester described in Example U of European Patent 521,992 () beodl chloride MIMmo It is seen that only the compositions according to the invention contain both an amorphous polyester rich in isophthalic acid and a semi-crystalline polyester prepared from a straight chain saturated aliphatic dicarboxylic acid (1,2-dodecanedioic acid) and an aliphatic diol saturated linear chain (1,6-hexanediol or ethylene glycol) or a cycloaliphatic diol (1,4-cyclohexanediol or 1,4-cyclohexanedimethanol) give coatings in which the brightness is less than 50%. The composition of Comparative Example I containing an amorphous polyester rich in terephthalic acid gives a coating that is very bright (81% brightness). In the same way, the compositions of Comparative Example II and of Example III containing a semicrystalline polyester which is not according to the invention, based essentially on terephthalic acid and 1,6-hexanediol (as in the embodiments of European Patent 521,992), they give coatings that are very bright (84-86% brightness). In addition, the coatings obtained from these compositions have a resistance to shock and a flexibility that is less good. It is also seen that when a polyepoxided compound is used as a crosslinking agent in the composition and the amount of semicrystalline polyester increases (from 15 to 25% by weight) and the amount of amorphous polyester decreases (from 85 to 75% by weight) in relation to the total weight of polyester, it goes from a brightness of 44% to a brightness of 18% (compare examples 10 and 3). Therefore, a coating having the desired gloss level can be produced, either a matt coating (examples 3 to 9), or a satin or semi-gloss coating (examples 10 and 11), only by choosing the powder composition provided by this coating in a timely manner. brightness level. Examples 16 and 17 and comparative examples IV to VI - Preparation of thermosettable powder coating compositions. In these examples and comparative examples, 5 thermosettable powder compositions are prepared according to the mode of operation described in the previous examples 3 to 15, in order to obtain dark brown paints and to analyze the properties of the obtained coatings. The different compositions and the properties of the coatings obtained are described in Table II below.

The hard coatings obtained from these compositions all have a smooth, uniform and flawless appearance.

Table II Examples of dark brown paintings.

Composition (Ink tn atoles) 16 17 1V (1) V (l) Vl. { l) Policiicr Nnorfo lid example 1. »633.6 635.6 747.7 of example l.b. 591.2 59Í.2 PolüHer scancmulina of example 2J HW of example 2 ?. 149.S of the example le. (I) - 149.5 112.2 - Assist in crosslinking? (2) Í6J 56.3 J6.3 56.3 J6J Black iron oxide (3) 5 45 45 45 45 Black Oxide Oxide (4) MO 140 140 140 140 Carbon black (5) II U 11 11 1! B Fluidity regulating agent (6.} 10 10 10 10 10 Betuoina JÍ JJ 3, i 3.J 3.5 Properties Gloss (60-) 32 15 90 «7 Shock resistance (kg.cm) direct 100 120 60 0 inverse 100 200 120 40 0 Duuia lUpa 11 211 11 211 211 (1) comparative title (2) isoctaruaio de mgl idilo (? RaJdiic PT »J0 lie C? B * -Gc? Gy.}. (3) Dayfcpox 130 (BA SEE) (4) Dsyfcmn 3950 (BAVER) (5) FW 2 (DEGUSSA) (4) Rcuflow PVJ (oilic Chcmie) Table II shows that the compositions according to the invention (examples 16 and 17) give low gloss coatings , whereas the compositions that are not according to the invention (comparative examples IV and V) containing a semicrystalline polyester based essentially on terephthalic acid and 1,6-hexanediol, give very bright coatings (gloss of 85 to 90%) .

Example 8 - Resistance to the weathering of the coatings. In this example, the excellent behavior with respect to the weathering of the low gloss coatings obtained from the compositions according to the invention is evidenced. To this end, the coatings obtained with the dark brown paints prepared in examples 16 and 17 and the comparative examples IV, V and VI (whose "composition is given in table II) in terms of its weather resistance have been analyzed. The powder paints to be analyzed are deposited by projection with the aid of an electrostatic spray gun Ge a-Vols tatic PCG 1 on chrome-plated aluminum panels, under a voltage of 60 to 100 kV. 50 to 70 microns. The coatings obtained after cooking for 15 minutes at 200 ° C are subjected to the accelerated aging analysis (QUV test described above), in order to evaluate the resistance to UV and moisture. The change in Delta dye E according to ASTM D 2244 and gloss retention, measured at an angle of 60 °, according to ASTM D 523 after 3,000 hours of exposure is determined. are reproduced in Table III in which: the first column indicates the composition analyzed the second column change of delta dye E calculated according to ASTM D 2244 after 3,000 exposure hours, the third column the brightness retention, measured under an angle of 60 °, according to ASTM D 523 after 3,000 hours of exposure, and expressed as a percentage of its initial value at the beginning of the experience.

Table III Accelerated Envelopment of Coatings Delta Composition E Gloss Retention (%) of Example 16 5.3 63 of Example 17 3.5 82 of Example IV (1) 16.8 32 of Example V (1) 15.1 41 of Example VI (1) 4.8 92 (1) by way of comparison The results in Table III show that the low-gloss coatings initially obtained with the compositions according to the invention have a remarkable resistance to weathering (examples 16 and 17). This weather resistance is comparable to that obtained with compositions based on amorphous polyesters rich in isophthalic acid, commercially available and reputed for their excellent performance in outdoor exposure (comparative example VI). The presence of semicrystalline polyesters based on 1,2-dodecanedioic acid and 1,6-hexanediol in the compositions according to the invention does not greatly affect the weather resistance of the hard coatings obtained.

In Table III it is seen that it is not the same as regards the compositions of the state of the art that contain a semicrystalline polyester of the type used in the embodiments of the European patent 521,992, based essentially on acid terephthalic and 1, 6-hexanediol. Indeed, the coatings obtained with these compositions are strongly damaged by exposure to UV lamps and humidity; the delta dye change E is very considerable and the brightness drops below 50% of its initial value after 3,000 hours of exposure (comparative examples IV and V). 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

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

1. Thermosetting powder coating compositions comprising, as a binder, a mixture of an amorphous polyester, a semicrystalline polyester and a crosslinking agent, characterized in that the binder comprises: (a) an amorphous polyester containing carboxyl groups, rich in acid isophthalic, prepared from an acid constituent comprising from 55 to 100% by mole of isophthalic acid, from 0 to 45% by mole of at least one dicarboxylic acid other than isophthalic acid and from 0 to 10% by mole of an acid polycarboxylic containing at least 3 carboxyl groups and of an alcoholic constituent comprising from 60 to 100 mole% of neopentyl glycol, from 0 to 40 mole% of at least one dihydroxy compound different from neopentyl glycol and from 0 to 10 mole% of a polyhydroxy compound containing at least 3 hydroxyl groups, the amorphous polyester having a glass transition temperature (Tg) of at least 50 ° C and an acid number of 15 to 100 mg KOH / g; (b) a semicrystalline polyester containing carboxyl groups prepared either (bl) from a saturated aliphatic dicarboxylic acid with a straight chain having from 4 to 16 carbon atoms and from an aliphatic diol saturated with a straight chain having from 2 to 16 carbon atoms and optionally of a polycarboxylic acid containing at least 3 carboxyl groups or of a polyol containing at least 3 hydroxyl groups, or (b2) of 40 to 100 mole% of an aliphatic dicarboxylic acid with a chain selected linear of 1,11-undecanedioic acid, 1,1-dodecanedioic acid, 1,3-tridecandioic acid, 1,14-tetradecanedioic acid, 1,1-pentadecanediaic acid and 1,6-hexadecanedioic acid and 0 to 60% by mole of an aliphatic dicarboxylic acid with a straight chain having from 4 to 9 carbon atoms, calculated with respect to the total of the dicarboxylic acids of a cycloaliphatic diol having from 3 to 16 carbon atoms and opc preferably a polycarboxylic acid having at least 3 carboxyl groups or a polyol having at least 3 hydroxyl groups, the semicrystalline polyesters having a melting point (Tm) of at least 40 ° C and an acid number of 5 to 50 mg of KOH / g; and (c) a crosslinking agent.

2. Compositions according to claim 1, characterized in that the amorphous polyester (a) has a vitreous transition temperature of 50 to 80 ° C and an acid number of 30 to 70 mg of KOH per gram.

3. Compositions according to any of claims 1 and 2, characterized in that the amorphous polyester (a) has at least one of the following characteristics: a number average molecular weight between 1100 and 11,500 and a viscosity in the molten state of 100 to 15,000 mPa.s at 200 ° C.

4. Compositions according to any of claims 1 to 3, characterized in that the acid constituent of the amorphous polyester (a) contains, apart from isophthalic acid, up to 45% by mole of a dicarboxylic acid selected from terephthalic acid, phthalic acid, succinic acid , glutaric acid, adipic acid, piicic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, 1,3-cyclohexane-dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and mixtures of these compounds.

5. Compositions according to any of claims 1 to 4, characterized in that the alcoholic constituent of the amorphous polyester (a) contains, apart from neopentyl glycol, up to 40 mol of a dihydric compound selected from ethylene glycol, propylene glycol, 1,4-butanediol, , 6-hexanediol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,4-cyclohexanedimethane-1, hydrogenated bisphenol A, neopentyl glycol hydroxypivalate and mixtures of these compounds.

6. Compositions according to any of claims 1 to 5, characterized in that the semicrystalline polyester (b) has a melting point of between 40 and 90 ° C, an acid number of 5 to 30 mg of KOH per gram and an index of hydroxyl not exceeding 5 mg KOH per gram.

7. Compositions according to any of claims 1 to 6, characterized in that the semicrystalline polyester (b) has at least one of the following characteristics: a number average molecular weight between 2200 and 25,000 and a viscosity in the molten state from 50 mPa . to 100 ° C to 10,000 mPa.s at 150 ° C.

8. Compositions according to any of claims 1 to 7, characterized in that the semicrystalline polyester (bl) is the polyesterification product of 1,2-dodecandioic acid with 1,6-hexanediol.

9. Compositions according to any of claims 1 to 7, characterized in that the semicrystalline polyester (b2) is the polyesterification product of 1,2-dodecanedioic acid with 1,4-cyclohexanediol or 1,4-cyclohexanedimethanol.

10. Compositions according to any of claims 1 to 9, characterized in that the amount of amorphous polyester (a) represents approximately 60 to 87% by weight and the amount of semicrystalline polyester (b) represents approximately 13 to 40% by weight calculated with respect to to the total weight of the amorphous polyester (a) and the semicrystalline polyester (b).

11. Compositions according to any of claims 1 to 9, characterized in that the amount of amorphous polyester represents 60 to 82% by weight and the amount of semicrystalline polyester (b) represents 18 to 40% by weight calculated with respect to the total weight of the amorphous polyester (a) and semicrystalline polyester (b).

12. Compositions according to any of claims 1 to 11, characterized in that the crosslinking agent (c) is a solid polyol compound.

13. Compositions according to any of claims 1 to 11, characterized in that the crosslinking agent (c) is a beta-hydroxy-alkylamide.

14. Compositions according to any of claims 1 to 13, characterized in that the ratio of the amount of amorphous polyester (a) to the semicrystalline polyester (b) containing carboxyl groups, on the one hand, for the amount of the crosslinking agent (c) ), on the other hand, is such that there are 0.5 to 1.5 equivalents of carboxyl groups per equivalent of functional groups in the crosslinking agent.

15. Compositions according to any of claims 1 to 14, characterized in that the crosslinking agent (c) is present in an amount of about 4 to 25% by weight calculated with respect to the total weight of the binder.

16. Compositions according to any of claims 1 to 15, characterized in that the binder comprises from 45 to 83% by weight of the amorphous polyester (a), from 13 to 30% by weight of the semicrystalline polyester (b) and from 4 to 25% by weight, of the crosslinking agent (c).

17. Compositions according to any of claims 1 to 15, characterized in that the binder comprises from 45 to 78% by weight of the amorphous polyester (a), from 18 to 30% by weight of the semicrystalline polyester (b) and from 4 to 25% by weight of the crosslinking agent (c).

18. Varnishes and paints obtained with the thermosettable powder compositions according to any of claims 1 to 17.

19. Process for obtaining a low gloss coating on an article, characterized in that a thermosettable powder coating composition is applied according to any of claims 1 to 17 to the article and in that the article is cured in this way at a temperature of 140. at 200 ° C for a time that can reach 30 minutes.

20. Satin and matt coatings obtained from thermosettable powder compositions according to any of claims 1 to 17.

21. Articles coated entirely or partially using the process according to claim 19.