EP1165714A1

EP1165714A1 - Thermosetting powder compositions for preparing coatings with slight shine low brilliance

Info

Publication number: EP1165714A1
Application number: EP99969427A
Authority: EP
Inventors: Luc Moens; Kris Buysens; Daniel Maetens
Original assignee: UCB SA
Current assignee: UCB SA
Priority date: 1998-09-22
Filing date: 1999-09-10
Publication date: 2002-01-02
Also published as: WO2000017279A1; AU5977199A; BE1012176A3

Abstract

The invention concerns thermosetting powder compositions comprising as binding agent a mixture of a hyperbranched polyol, a polyester containing hydroxyl groups, optionally a semi-crystalline polyester containing hydroxyl groups and a blocked isocyanate as crosslinking agent. Said thermosetting powder compositions produce coatings with low brilliance when they are cured.

Description

Thermosetting powder compositions for the preparation of low gloss coatings.

DESCRIPTION. The present invention relates to thermosetting powder compositions comprising as a binder a mixture of a hyperbranched polyol, a polyester containing hydroxyl groups, optionally a semi-crystalline polyester containing hydroxyl groups and a blocked isocyanate as crosslinking. In particular, the invention relates to thermosetting powder compositions which, by firing, give coatings of low gloss.

The invention also relates to the use of these compositions for the preparation of powder paints and varnishes providing coatings of low gloss, as well as to the coatings obtained from these compositions. The term "low gloss" used to qualify the coatings described in this specification means that these coatings have a gloss, measured according to ASTM D523 at 60 °, ranging from 0 to 70%. In fact, this term encompasses coatings which can be described as "semi-matt" for glosses ranging from 31 to 70%, or "matt ^" for glosses ranging from 0 to 30%, according to the same standard. At present, thermosetting compositions in the form of powders are widely used as paints and varnishes for coating the ^most diverse objects. The advantages of these powders are numerous; on the one hand the problem of solvents is completely eliminated, on the other hand the powders are used at 100%, since only the powder in direct contact with the substrate is retained by the latter, the excess of powder being, in principle, fully recoverable and reusable. This is why these powder compositions are preferred over coating compositions which are in the form of solutions in an organic solvent.

Thermosetting powder compositions have already found a wide outlet in the construction of household appliances, garden furniture, accessories for the automotive industry, etc. They generally contain an organic thermosetting binder, fillers, pigments, catalysts and various additives to adapt their behavior to their use. There were mainly two types of thermosetting powder compositions; on the one hand, those which contain as a binder a mixture of polymers with carbon groups such as a polyester or a carboxylated polyacrylate and of epoxidized compounds, mainly triglycidyl isocyanurate and, on the other hand, those which contain as binder a mixture of polymers with hydroxyl groups, the most. often a hydroxylated polyester with isocyanates blocked with phenol, caprolactam. by the uretdione, etc.

Powder compositions generally give coatings which have good adhesion to the metal substrate (steel or aluminum), good resistance to impact and to solvents, and excellent resistance to weathering.

More recently, semi-crystalline polyesters have been described, used alone or in admixture with amorphous polyesters, for the preparation of powdered thermosetting compositions. These polyesters contain carboxyl or hydroxyl functions, and they are used with the usual crosslinkers for this type of polyester. This type of composition provides coatings which have a better balance, compared to the amorphous polyesters used alone, of properties such as flexibility and surface equality.

However, most of these powder compositions provide, after melting and curing, coatings having a high gloss. The gloss measured at an angle of 60 °, according to standard ASTM D523, is very often equal to, or even greater than 90%.

However, there is an increasing need to be able to have available paints and varnishes in powder form which provide matt coatings, or of low gloss, of good quality, for example for the coating of certain accessories of the automobile industry such as rims. wheels, bumpers, etc. or for the coating of metal panels and beams used in construction.

However, it is not easy to obtain coatings which at the same time have a low gloss appearance and good properties such as impact resistance, flexibility, adhesion, resistance to chemical agents and to weathering. usual glossy coatings, etc.

Various methods have already been proposed for obtaining powder paints and varnishes providing matt coatings. However, experience has shown that it is difficult to produce a powder paint capable of providing, under the usual conditions of extrusion and baking, a mat finish in a completely reliable and reproducible manner.

According to one of these methods, one or more specific matting agents such as silica, talc, chalk and metal salts are introduced into the powder composition, in addition to the conventional binder and pigments. However, the reduction in gloss is often insufficient and there is a marked deterioration in the properties of the paint coatings, for example a lack of adhesion to the metal substrate. To remedy these drawbacks, it is proposed in European patent 165.207 to incorporate waxes, for example polyolefin wax and metal salts (for example zinc 2-benzothiazolethiolate) in thermosetting powder compositions based on polyesters with terminal carboxyl groups and epoxidized compounds such as triglycidylisocyanurate. Likewise, in US Pat. No. 4,242,253, calcium carbonate and finely divided polypropylene particles are proposed as additives for producing low-gloss coatings. The disadvantage of this system is that the inorganic fillers, often incorporated in large quantities, can damage the extruders and harm the desired surface appearance of the coating obtained, which often has a rough and irregular appearance. In addition, the waxes easily migrate to the surface, which causes unacceptable variations in the degree of mattness of the coating during its natural aging. In addition, the fact of having to add additional charges entails additional expenditure and constitutes in itself a disadvantage. According to American patent 3,842,035, it is known to produce a mat finish using a coating composition obtained by dry mixing of two thermosetting powder compositions which have been extruded separately. One of these is a slowly hardening composition (long gel time) and the other is a fast hardening composition (short gel time). By this system, it is possible to obtain, after baking, a matt coating without the need to add a particular matting agent to the powder composition. The major drawback of this system is that it requires dry mixing of large quantities of formulated powders, which is not easy to achieve, especially on an industrial scale. In addition, since this mixture cannot be done continuously, but by batches of powder, it is not easy to obtain the same degree of mattness for the coatings by passing from a batch of powder to the other. Finally, the powder which is reused in the application of paints to substrates may not have the same composition as the initial powder, which also results in a change in the degree of dullness obtained. There are also other systems intended to obtain matt coatings in which two polymers of different nature or reactivity are used, as well as one or more crosslinking agents, so as to induce two distinct crosslinking mechanisms, or else two very different reaction rates. In these systems, the preparation of the powder is carried out in a single step unlike the process described in American patent 3,842,035. It is then possible to produce in a single extrusion, a powder paint capable of forming coatings of very low gloss. By way ^of example, in Japanese patent applications 154,771 / 88, 316,472 / 7 and 98,671 / 1, discloses resin compositions for powder matt paint comprising a mixture of a branched hydroxyl-containing polyester having a high hydroxyl index with another hydroxylated polyester having a lower hydroxyl number, in predetermined proportions, and a blocked isocyanate as crosslinking agent. These compositions provide, after crosslinking, matt coatings having good mechanical properties and good weather resistance.

In Japanese patent application 293.867 / 6, these are three different polyesters, hydroxyl group pesters, which are used with a crosslinking agent to prepare compositions which provide coatings the degree of matting of which is controlled by the amount of the constituents.

European patent application 366,608 describes powder paints obtained by extrusion and providing matt coatings, but two crosslinking agents are used. These powder paints contain an epoxy resin, in particular diglycidyl ether of bisphenol A, a polycarboxylic acid, such as, for example, 2,2,5,5-tetra- (β-carboxyethyl) -cyclopentanone as the first crosslinking agent, and a saturated polyester terminated with carboxyl groups, tolylbiguanide or dicyandiamide as the second crosslinking agent.

The use of compounds which give two reaction systems of different nature to form matt coatings is described for example in European patent 104,424. It offers the preparation of a powder using only one extrusion. This powder contains as a binder both a hydroxylated resin such as a polyester containing hydroxyl groups and a polyepoxide compound such as triglycidyl isocyanurate and it contains a particular crosslinking agent which contains in its molecule both carboxyl groups (to react with the epoxy compound) and blocked isocyanate groups (to react with the hydroxylated resin). In patent application WO 92/01756, thermosetting powder compositions are described comprising at least one semi-crystalline polyester carrying hydroxyl groups, at least one amorphous polyester carrying hydroxyl groups, at least one acrylic copolymer carrying hydroxyl groups and a blocked polyisocyanate as crosslinking agent. The coatings obtained from these compositions have a gloss of less than 35, at an angle of 60 °, good mechanical properties and good pencil hardness.

The main disadvantage of the powder paints obtained by extrusion described in the patents cited above is that the conditions Extrusion, such as adjusting the temperatures, the shear gradient, etc., are very critical and make it particularly difficult to obtain a coating having a well reproducible degree of mattness from a well defined composition. In particular, the difficulty is to find a composition which produces, under the usual conditions of extrusion, a matt coating in a completely reliable and reproducible manner.

Another disadvantage lies in the fact that most of the known compositions which give matt coatings have poor impact resistance. In conclusion, it can be seen that the various thermosetting powder compositions proposed to date for obtaining matt or low-gloss coatings, all still have a certain number of drawbacks.

It therefore remains advantageous to find thermosetting powder compositions which can provide coatings of low gloss and which do not have the defects of known compositions.

In accordance with the present invention, it has been made the surprising discovery that by using as a binder a mixture of a hyperbranched polyol, of an amorphous polyester containing hydroxyl groups, optionally accompanied by a semi-crystalline polyester containing hydroxyl groups, and of a blocked isocyanate as crosslinking agent, it is possible to obtain thermosetting powder compositions giving coatings of low gloss which are well reproducible and having good mechanical properties and excellent weather resistance without this being necessary to add specific additives to produce the mattness of the coatings, and in a single extrusion. The present invention therefore relates to thermosetting powder compositions comprising a mixture of compounds containing hydroxyl groups and of an isocyanate blocked as crosslinking agent, which are characterized in that the mixture comprises: (a) 5 to 50 parts by weight d a hyperbranched polyol, (b) 2.5 to 95 parts by weight of an amorphous polyester containing hydroxyl groups. (c) 0 to 90 parts by weight of a semi-crystalline polyester containing hydroxyl groups, the parts by weight being calculated on the whole of the mixture of the compounds containing hydroxyl groups, and (d) a polyiso yanate blocked at the right level from 5 to 50 parts by weight relative to the total weight of the compounds (a), (b), (c) and (d).

The hyperbranched pol ols used according to the present invention belong to the more general family of dendritic molecules, well described in the work. "Denditric Molecules", GR NEWKOME et al., VCH Publ. (1996), more particularly in Chapter 6. These hyperbranched polyols consist of a central monomer or polymer core comprising several identical functional groups, for example hydroxyl groups, that it is reacted with a functional group, such as a carboxyl group, of a branched molecule comprising at least two functional groups different from the first, such as hydroxyl groups. This first extension with branching of the central nucleus is called first generation. Each subsequent generation that can be grafted onto the previous one leads to the formation of a highly branched molecule, which can be represented by a tree-like appearance, where the number of functional groups found at the periphery of the tree increases to as the number of generations increases. Thanks to this very specific molecular structure, hyperbranched polyols have unique properties, such as low polydispersity (with 1 <Mw / Mn <2) and low melt viscosity, even when the molecular weight increases with the number of generations.

Structures of this type of hyperbranched polyols and their preparation methods are described in patent application WO 96/12754 for example. These hyperbranched polyols consist of: i) a central monomer or polymer core which is a compound carrying at least one epoxy group or a reaction product of a polyepoxidized compound still having at least one reactive epoxy group (such as for example l, 2-epoxy-3- allyloxypropane, l-allyloxy-2,3-epoxypropane, l, 2-èρoxy-3-phenoxypropane, l-glycidyloxy-2-ethylhexane, diglycidyl ether of bisphenol A, isocyanurate triglydicyl, diglycidyl terephthalate, epoxy soybean oil or acid, polyvinyl alcohol epoxide, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, etc.), and ii) at least a generation of a branched monomer or polymer having a chain-extending role and having at least three reaction groups, among which, ^{on the} one hand, at least one is a hydroxyl or hydroxyalkyl group and at least one is a carboxyl group , or on the other hand, one is a hydroxyl or hydroxy group alkyl and at least one is a terminal epoxide group (such as preferably 2,2-dimethylolpropionic acid, but also alpha, alpha-bis- (hydroxylmethyl) -butyric acid, alpha, alpha, alpha acid -tris- (hydroxymethyl) - acetic), alpha acid, alpha-bis- (hydroxymethyl) -valeric, alpha acid, alpha- bis- (hydroχ- / methyl) -propionic acid, 3,5- dihydroxybenzoic acid, alpha acid, beta-dihydroxypropionic acid, citric acid, d- or 1-tartaric acids, dihydroxymaloic acid, d-glyconic acid, etc.), and, optionally, iii) generation of a monomer or polymer having a chain extender role and ^spacing groups and having two reactive groups, one of which is a hydroxy or hydroxyalkyl group, and the other a carboxyl group or epoxy terminal (such as hydroxypivalic acid, hydroxypropionic acid, hydroxyvaleric acid, glycolide, deltavalerolactone, beta-propriolactone, epsilon-caprolactone, etc.).

As an example of this type of hyperbranched polyol, mention may be made of the reaction product of the diglycidyl ether of bisphenol A as component i) with dimethylolpropionic acid as component ii). A hyperbranched polyol belonging to the class of polyesters is thus obtained.

Other examples of hyperbranched polyols of the type of polyesters and of their preparation are given in patent application WO 93 / 17060. These hyperbranched polyesters consist of: i) a central monomer or polymer core chosen from an aliphatic, cycloaliphatic diol or aromatic, a triol, a tetrol (such as ditrimethylolpropane, ditrimethylolethane, pentaerythritol, alkoxylated or not, glycerol, neopentylglycol, dimethylolpropane, 1,3-dioxane-5,5-dimethanol, etc.) sugar such as sorbitol or mannitol, an anhydroene aheptitol, dipentaerythritol, an alpha-alkylglucoside, or else the reaction product of an alkyleneox of or one of its derivatives with one or more hydroxyl groups of the abovementioned alcohols; ii) at least one generation of a branched monomer or polymer having a chain-extending role and having at least three reaction groups, among which, ^{on the} one hand, at least two are hydroxyl groups, one or more of these groups which may be substituted by a hydroxyalkyl group and the other is a carboxyl group, and on the other hand, two are hydroxyl groups and one is a carboxyl group (for example, preferably acid 2, 2-dimethylolpropionic acid, but also alpha, alpha-bis- (hydroxymethyl) -butyric acid, alpha, alpha, alpha-tris- (hydroxymethyl) -acetic acid, alpha acid, alpha-bis- (hydroxymethyl) - valeric, alpha, alpha-bis- (hydroxymethyl) -propionic acid, 3,5-dihydroxybenzoic acid, etc.).

As an example of this type of hyperbranched polyol, mention may be made of the reaction product of pentaerythritol, ethoxylated or not, or ditrimethylolpropane as component i) with dimethylolpropionic acid as component ii). The amorphous polyesters containing hydroxyl groups which can be used in the compositions according to the present invention are polyesters which are well known in the state of the art and commonly used in the formulations of paints and varnishes in powder form for the production of coatings. The amorphous polyesters containing hydroxyl groups used in the thermosetting compositions according to the invention have a hydroxyl number of 10 to 100, and preferably from 20 to 50 mg of KOH / g.

These amorphous polyesters containing hydroxyl groups also have the following characteristics:

- an acid number less than or equal to 15 mg of KOH / g; a number average molecular weight of between 950 and 15,000, preferably between 2,000 and 8,500, measured by gel permeation chromatography (GPC) with polystyrene of polydispersity equal to 1 for calibration; - a glass transition temperature (Tg) from 45 ° C to 100 ° C (measured by DSC with a heating rate of 20 ° C per minute, according to standard ASTM D 3418-82;

- A viscosity in the molten state of 100 to 20,000 mPa.s measured at 200 ° C with a cone / plate viscometer (known as "ICI viscosity"), according to standard ASTM D 4287-88.

The acid component of the amorphous polyester used in the thermosetting compositions in accordance with the present invention contains from 70 to 100 mole% of isophthalic and / or terephthalic acid, the 0 to 30 mole% of remaining acids consisting of one or more other aliphatic, and / or cycloaliphatic and / or aromatic polycarboxylic acids having 4 to 15 carbon atoms such as fumaric acid, maleic acid, phthalic acid, acids 1, 2-, 1, 3- or 1, 4- cyclohexanedicarboxylic, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1, 12-dodecanedioic acid, etc., or their corresponding anhydrides. The use of a polycarboxylic acid comprising at least three carboxyl groups or its anhydride, for example trimellitic acid (or anhydride) or pyromellitic acid, allows the preparation of branched amorphous polyesters.

The alcoholic constituent of the amorphous polyester used in the thermosetting compositions in accordance with the present invention contains from 60 to 100 mol% of neopentylglycol. The 0 to 40 mole% of the remaining alcohols consist of one or more other aliphatic and / or cycloaliphatic polyols having from 2 to 15 carbon atoms chosen from ethylene glycol, propylene glycol, 1,4-b anediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, 2-methyl-1,3-proρanediol, 2-butyl-2-ethyl-1,3-propanediol, bisphenol A hydrogenated and neopentylglycol hydroxypivalate. For the preparation of branched amorphous polyesters, trihydroxylated or tetrahydroxylated polyols such as trimethylolpropane, ditrimethylolpropane, trimethylolethane, pentaerythritol and their mixtures are advantageously used. . The semi-crystalline polyesters containing hydroxyl groups according to the invention have the following characteristics:

- A hydroxyl number of 10 to 100 mg of KOH / g, preferably 20 to 50 mg of KOH / g; - an acid number less than or equal to 15 mg KOH / g; a number average molecular weight of between 1,000 and 15,000, preferably between 2,000 and 8,500, measured as the amorphous polyester described above; a well-defined melting point of 50 to 150 ° C, determined by differential scanning calorimetry (or DSC) according to standard ASTM D 3418-82; a viscosity of 50 to 50,000 mPa.s at 175 ° C, measured by the cone / plate method (viscosity HERE), according to standard ASTM D 4287-88;

- a glass transition temperature equal to or greater than -20 ° C;

- a crystallinity greater than or equal to 5 Joules / g, and preferably 10 Joules /, according to standard ASTM D 3418-82

These semi-crystalline polyesters are chosen from two types of compounds, (Cl) or (C2).

The acid component of the semi-crystalline polyester (C1) containing hydroxyl groups contains 85 to 100 mole% of terephthalic acid, 1,4-cyclohexanedicarboxylic acid or 1,12-docecanedioic acid and optionally up to 15 moles % of one or more other aliphatic, cycloaliphatic or aromatic di- or polycarboxylic acids, such as maleic acid, fumaric acid, isophthalic acid, phthalic acid, 1,2-cyclohexanedicarboxylic acid, l 1,3-cyclohexanedicarboxylic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid. These acids can be used in the form of the free acid or their functional derivatives, in particular in the form of the anhydride. The use of a polycarboxylic acid (or its anhydride) comprising at least three carboxyl groups, for example trimellitic acid (or anhydride) or pyromellitic acid, allows the preparation of branched polyesters. In addition, these di- or polycarboxylic acids can be used alone or as a mixture, but preferably they are used alone.

The alcohol component of the semi-crystalline polyester (C1) containing hydroxyl groups contains 85 to 100 mole% of a saturated aliphatic diol with straight chain. Examples of diols which can be used are ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,14-tetradecanediol, 1,16-hexadecanediol, etc. The alcoholic constituent of. semi-crystalline polyester (Cl), can also contain up to 15 mol% of one or more other aliphatic or cycloaliphatic diols or polyols, such as, for example, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol or bisphenol A hydrogen. For the preparation of branched polyesters, trihydroxylated or tetrahydroxylated polyols, such as trimethylolpropane, ditrimethylolpropane or pentaerythritol and their mixtures, are advantageously used.

The acid component of the semi-crystalline polyester (C2) containing hydroxyl groups contains 85 to 100 mole% of a saturated aliphatic straight chain dicarboxylic acid. Examples of the acids which can be used are succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, acid 1, 12 -dodecanedioic, etc. These acids can be used in the form of free acids or their functional derivatives, in particular in the form of anhydrides. In addition, these acids can be used alone or as a mixture, but preferably they are used alone. The acid component of the semi-crystalline polyester (C2) containing hydroxyl groups may also contain up to 15 mol% of one or more other aliphatic, cycloaliphatic or aromatic di- or polycarboxylic acids having from 4 to 8 carbon atoms, such as as maleic acid, fumaric acid, terephthalic acid, phthalic acid, isophthalic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4 acid - cyclohexanedicarboxylic. The use of a polycarboxylic acid (or its anhydride) comprising at least three carboxyl groups, for example trimellitic acid (or anhydride) or pyromellitic acid, allows the preparation of branched polyesters. In addition, these di- or polycarboxylic acids can be used alone or as a mixture, but preferably they are used alone.

The alcohol component of the semi-crystalline polyester (C2) containing hydroxyl groups contains 85 to 100 mol% of 1,4-cyclohexanediol or 1,4-cyclohexanedimethanol or ethylene glycol. The alcoholic constituent of this semi-crystalline polyester (C2) can also contain up to 15 mol% of one or more other aliphatic or cycloaliphatic di- or polyols having from 2 to 15 carbon atoms such as propylene glycol, 1 , 4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol and hydrogenated bisphenol A. For the preparation of branched polyesters, trihydroxylated or tetrahydroxylated polyols, such as trimethylolpropane, ditrimethylolpropane, trimethylolethane or pentaerythritol, etc., are advantageously used.

Semi-crystalline or amorphous polyesters containing hydroxyl groups are prepared according to conventional methods of synthesis of polyesters by t: sterification in one or more stages. If one proceeds in one stage to obtain the polyesters, a stoichiometric excess of one or more diols or polyols is reacted together with one or more suitable di- or polycarboxylic acids.

To obtain a semi-crystalline or amorphous polyester containing hydroxyl groups in two stages, a polyester containing carboxyl groups is first prepared from a stoichiometric excess of one or more di- or polycarboxylic acids and one or more diols or polyols and the polyester containing carboxyl groups thus obtained is then esterified with one or more other suitable diols or polyols to obtain a semi-crystalline or amorphous polyester containing hydroxyl groups.

For the preparation of semi-crystalline or amorphous polyesters containing hydroxyl groups, a conventional reactor is generally used provided with a stirrer, an inert gas (nitrogen) inlet, a distillation column connected to a cooled condenser. with water and a thermometer connected to a thermoregulator. The esterification conditions used for the preparation of these polyesters are conventional, namely that it is possible to use a conventional esterification catalyst derived from tin, such as dibutyltin oxide, dibutyltin dilaurate, trioctoate of n-butyltin or titanium derivative, such as tetrabutyl titanate, in a proportion of 0 to 1% by weight of the reagents, and optionally add antioxidants such as the phenolic compounds IRGANOX 1010 (CIBA-GEIGY) or IONOL CP

(SHELL), alone or with stabilizers of phosphonite or phosphite type, such as tributyl phosphite or triphenyl phosphite, in an amount of 0 to 1% by weight of the reactants.

The polyesterification is generally carried out at a temperature which is gradually increased from 130 ° C. to approximately 180 to 250 ° C., first under normal pressure, then under reduced pressure while maintaining these conditions until a polyester having the desired hydroxyl and / or acid number and viscosity. The degree of esterification is followed by determining the amount of water formed during the reaction and the properties of the polyester obtained, for example, the hydroxyl number, the acid number, the molecular weight and / or viscosity.

At the end of the polycondensation, when the polyester is still in the molten state, catalysts can be added thereto to accelerate the crosslinking reaction, at a rate of 0 to 1.5% by weight relative to the polyesters. Among these catalysts, mention may be made of organic tin compounds, such as dibutyltin dilaurate, dibutyltin dimaleate, dibutyltin oxide, tin octanoate, l, 3-diacetoxy-l, l, 3,3-tetrabutyldistanoxane and similar compounds.

Hyperbranched polyols, amorphous polyesters containing hydroxyl groups and semi-crystalline polyesters containing hydroxyl groups described above are intended to serve mainly as binders, together with crosslinking agents, in the preparation of thermosetting powder compositions usable in particular as varnishes and paints suitable for application according to the deposition technique by means of an electrostatic spray gun or triboelectric or according to the technique of deposition in a fluidized bed. This is why the present invention also relates to the use of the thermosetting powder compositions in accordance with the invention for the preparation of powder varnishes and paints, as well as to the powder varnishes and paints obtained using these compositions. Finally, it also relates to a process for coating an article, preferably metallic, which is characterized by the application to said article of a thermosetting powder composition in accordance with the invention by spraying with an electrostatic spray gun or triboelectrically or by deposition in a fluidized bed followed by ^a baking of the coating thus obtained at a temperature of 150 to 220 ° C for a period from about 5 to 35 minutes.

The crosslinking agent used for the preparation of the thermosetting powder compositions in accordance with the invention is chosen from compounds containing functional groups capable of reacting with the hydroxyl groups of the hyperbranched polyol and of the polyesters. Among these compounds, blocked polyisocyanates are used as crosslinking agents.

The blocked polyisocyanates used as crosslinking agents according to the present invention are compounds well known in the art. They are commercially available or they can be prepared according to well described methods. When the powders are cooked to prepare coatings according to the invention, these polyisocyanates are released and the isocyanate groups react with the hydroxyl groups present on the hyperbranched polyol, on the amorphous polyester and on the semi-crystalline polyester if the powder contains them , which causes cross-linking of the polymer chains.

As examples of blocked polyisocyanates, mention may be made of those based on isophorone diisocyanate blocked with epsilon-caprolactam, commercially available under the brands HULS B1530, RUCO NI-2 and CARGILL 2400. Mention may also be made of 2 , 4-toluene diisocyanate blocked by epsilon-caprolactam, commercially available under the brand CARGILL 2450, as well as hexamethylene diisocyanate blocked with phenol. The polyisocyanate preferably used as a crosslinking agent belongs to the group of isophorone diisocyanates blocked with epsilon-caprolactam. In addition to their commercial availability, these compounds are described in US patents 3,822,240, 4,150,211 and 4,212,962. Another class of blocked polyisocyanates useful as crosslinkers in thermosetting powder compositions consists of the ^adducts of dimer l, 3-diazetidine-2,4-dione derivative of isophorone diisocyanate with a diol, in which the molar ratio between the isocyanate and hydroxyl groups is from 1 / 0.5 to 1 / 0.9, and the molar ratio between the diazetidinedione and the diol is from 2/1 to 6/5; in these adducts, the content of free isocyanate groups is not higher than 8% by weight, their molecular weight ranges from 500 to 4,000 and their melting temperature ranges from 70 to 130 ° C. Such adducts can be prepared according to the method described in US Pat. No. 4,413,079 by reacting the diazetidinedione dimer of isophorone diisocyanate, preferably free of trimer, with diols using quantities of reagents such that a molar ratio between the isocyanate and hydroxyl groups ranging from 1 / 0.5 to 1 / 0.9, preferably from 1 / 0.6 to 1 / 0.8, is obtained; such an adduct has a molecular weight of 1,450 to 2,800, preferably, and a melting temperature of 85 to 120 ° C; the preferred diol is 1,4-butanediol. Such an adduct is commercially available under the brand HULS BF 1540, or under the brand CRELAN LS2147 from BAYER.

The amount of blocked polyisocyanate used as crosslinking agent in the compositions according to the invention varies according to different factors, such as the characteristics of the particular hyperbranched polyol used, as well as those of the amorphous and semi-crystalline polyesters; other factors varying the amount of crosslinker to be used are the nature and characteristics of the latter, the degree of pigment load, the desired properties of the coatings to be prepared using the compositions, etc. Typically, the amount of crosslinking agent to be used to prepare coatings having a good combination of properties is of the order of 5 to 50% by weight, and preferably 25 to 40% by weight, calculated on the total weight hyperbranched polyol, amorphous polyester containing hydroxyl groups, semi-crystalline polyester containing hydroxyl groups optionally present, and crosslinking agent.

According to the present invention, from the compounds containing hydroxyl groups, 5 to 50 parts by weight of a hyperbranched polyol are chosen, and preferably from 10 to 30 parts by weight, from 2.5 to 95 parts by weight of an amorphous polyester containing hydroxyl groups, and preferably from 50 to 90 parts by weight, and from 0 to 90 parts by weight of a semi-crystalline polyester containing hydroxyl groups, and preferably from 0 to 40 parts by weight, these parts by weight being calculated on the total weight of the compounds containing hydroxyl groups. According to the invention, it has surprisingly been found that the incorporation of a hyperbranched polyol into the thermosetting powder compositions makes it possible to obtain coatings whose reproducibility can be very easily controlled very reproducibly depending on the amount of the hyperbranched polyol and its generation number, as will be seen later in the examples. Other coating properties, such as flexibility, surface appearance, resistance to chemicals and weathering, are excellent. In particular if the semi-crystalline polyester is added to the compositions, an improvement in the mechanical properties of the coatings is obtained. In addition, all these results are obtained in a single extrusion of the powder.

The thermosetting powder compositions according to the invention can also contain various auxiliary substances conventionally used in the manufacture of powder paints and varnishes.

The auxiliary substances possibly added to the thermosetting compositions in accordance with the invention are inter alia ultraviolet ray absorbing compounds such as Tinuvin 900 (from CIBA-GEIGY Corp.), light stabilizers based on hindered amines (by example Tinuvin 144 from CIBA-GEIGY Corp.). The compositions in accordance with the invention can contain up to 10% by weight thereof relative to the weight of the polyesters. A variety of pigments and mineral fillers can also be added to the thermosetting compositions according to the invention. Examples of pigments and fillers that may be mentioned are metal oxides such as titanium dioxide, iron oxide, zinc oxide, etc., metal hydroxides, metal powders, sulfides, sulfates, carbonates, silicates such as for example aluminum silicate, carbon black, talc, kaolins, barytes, iron blues, lead blues, organic reds, organic browns, etc. Mention will also be made, as auxiliary substances, of fluidity regulating agents such as Resiflo PV5 (from WORLEE) or Modaflow (from MONSANTO), or Acronal 4F (from BASF), and degassing agents such as benzoin. These auxiliary substances are used in usual quantities, it being understood that if the thermosetting compositions according to the invention are used as varnish, the addition of auxiliary substances having opacifying properties will be omitted.

For the preparation of the thermosetting powder compositions, the hyperbranched polyol, the amorphous polyester, the semi-crystalline polyester, the crosslinking agent and the various auxiliary substances conventionally used for the manufacture of powder paints and varnishes are dry mixed. example in a drum mixer. This mixture is then homogenized to a temperature in the range of 80 to 150 ° C in an extruder, for example a Buss-Ko-Kneder single screw extruder or a twin screw extruder of the Prism or APV type Then, the extrudate is allowed to cool, it is grinds, optionally cryogenically using liquid nitrogen, and is sieved to obtain a powder whose particle size is between 10 and 150 micrometers.

The powder paints and varnishes thus obtained are perfectly suitable for application to the article to be coated by traditional techniques, that is to say by the well-known technique of deposition in a fluidized bed or by application with an electrostatic or triboelectric spray gun. . In the latter case, additives that are known to add charge in triboelectric systems are optionally added.

After having been applied to the article concerned, the coatings deposited are cured by baking in an oven at a temperature of 160 to 220 ° C. for a period of approximately 5 to 35 minutes in order to obtain complete crosslinking of the coating.

The examples which follow illustrate the invention without limiting it. Unless otherwise indicated, the parts cited in the examples are parts by weight.

Example 1.

Synthesis of an amorphous polyester containing hydroxyl groups. In a four-necked flask equipped with an agitator, a distillation column connected to a water-cooled condenser, a nitrogen admission tube and a thermometer connected to a thermoregulator, we introduce 410.9 parts of neopentylglycol, 21.6 parts of ethylene glycol and 25.7 parts of trimethylolpropane. The contents of the flask are heated to about 130 ^α C, with stirring and under a stream of nitrogen, and 687, 1 parts of terephthalic acid and 2.5 parts of n-butyltin trioctoate are then added to it as catalyst. The mixture is heated in a nitrogen atmosphere and with stirring to a temperature of about 230 ° C; the water formed begins to distill around 180 ° C. When the distillation under atmospheric pressure stops, a portion of tributylphosphite is added, and a vacuum of 50 mm Hg is gradually established.

After three hours of heating at 230 ° C. and under 50 mm Hg, the mixture is cooled to 180 ° C., then the flask is emptied while the polyester is still in the molten state and allowed to cool. The amorphous polyester containing hydroxyl groups thus obtained has the following characteristics: hydroxyl number 47 mg KOH / g ^acid number of 3 mg KOH / g

- viscosity HERE at 200 ° C 3.800 mPa.s

- Tg (DSC, 20 ° C / min) 58 ° C

(determined by differential scanning calorimetry (or DSC), with a heating rate of 20 ° C per minute).

Example 2

Synthesis ^of an amorphous polyester containing hydroxyl groups. According to the procedure of Example 1, 434.3 parts of neopentylglycol, 22.2 parts of trimethylolpropane, 689.7 parts of isophthalic acid and 2.5 parts of n-butyltin trioctoate are reacted as catalyst. The reaction is continued at 220 ° C under atmospheric pressure until 95% of the amount of water has distilled and the reaction mixture is transparent. 1.0 part of tyle tribe phosphite is then added, a vacuum of 50 mm Hg is gradually established and the heating is continued for 3 hours under vacuum and at the same temperature. The amorphous polyester containing hydroxyl groups obtained has the following characteristics: hydroxyl number 27 mg KOH / g acid number 0.9 mg KOH / g - ICI viscosity at 200 ° C 6,400 mPa.s

- Tg (DSC; 20 ° C / min) 56 ° C

Example 3

Synthesis of an amorphous polyester containing hydroxyl groups. According to the procedure of Example 1, 435.1 parts of neopentylglycol, 14.7 parts of trimethylolpropane, 691, 9 parts of isophthalic acid and 2.5 parts of n-butyltin trioctoate are reacted as catalyst. The reaction is continued at 220 ° C under atmospheric pressure until 95% of the amount of water has distilled and the reaction mixture is transparent. 1.0 part of tributyl phosphite is then added, a vacuum of 50 mm Hg is gradually established and the heating is continued for 3 hours under vacuum and at the same temperature. The amorphous polyester containing hydroxyl groups obtained has the following characteristics: ^hydroxyl number 17.6 mg KOH / g ^acid number 1, 2 mg KOH / g

- viscosity HERE at 200 ° C 14,000 mPa.s

- Tg (DSC; 20 ° C / min) 59 ° C. The polyester is cooled to 180 ° C. and 2.5 parts of phosphite of tri- (2,4-di-tert.butylphenyl) and 2.5 are added thereto. parts of octadecyl-3- (3,5-di-tert.butyl-4-hydroxyphenyl) propionate. After 1 hour of stirring, the polyester is discharged from the reactor.

Example 4.

Synthesis of a semi-crystalline polyester containing hydroxyl groups of the type (C l).

In the same reactor as in Example 1, a mixture of 396.5 parts of 1, 6-hexanediol, 71 1, 3 parts of 1, 12-dodecanedioic acid and 2.5 parts of n trioctoate are placed. -butyltin. The reaction mixture is heated, with stirring and under nitrogen, ^until a temperature of about 140 ° C at which the reaction water begins to distil. Heating is gradually continued until the temperature is 225 ° C. When the distillation under atmospheric pressure stops, 1.0 part of tributyl phosphite is added to the reaction mixture, which is placed under a vacuum of 50 mm Hg. After three hours under this pressure and at 225 ° C., the polyester obtained has the following characteristics:

- hydroxyl number 28.4 mg KOH / g acid number 1.0 mg KOH / g

- ICI viscosity at 100 ° C <100 mPa.s - Melting temperature (Tm) 65 ° C

(DSC, 20 ° C./min) The semi-crystalline polyester containing hydroxyl groups is cooled to 160 ° C. and 10 parts of Tinuvin 144 and 20 parts of Tinuvin 900 are added thereto. After one hour of stirring, the polyester contained in the balloon.

Example 5.

In the same reactor as in Example 1, a mixture of 367.9 parts of 1,6-hexanediol, 717.0 parts of 1,12-dodecanedioic acid, 23.8 parts of trimethylolpropane, and 2 , 5 parts of n-butyltin trioctoate. The reaction mixture is heated, with stirring and under nitrogen, to a temperature of about 140 ° C, at which the reaction water begins to distill. We continue gradually heating up to the temperature of 225 ° C. When the distillation under atmospheric pressure stops, 1.0 part of tributyl phosphite is added to the reaction mixture, which is placed under a vacuum of 50 mm Hg. After three hours under this pressure and at 225 ° C., the polyester obtained has the following characteristics: hydroxyl number 31, 6 mg of KOH / g

- acid number 0.3 mg KOH / g

- viscosity HERE at 125 ° C 3.000 mPa.s

- Melting temperature (Tm) 62 ° C (DSC, 20 ° C / min)

The semi-crystalline polyester containing hydroxyl groups is cooled to 160 ° C. and 10 parts of Tinuvin 144 and 20 parts of Tinuvin 900 are added thereto. After one hour of stirring, the polyester contained in the flask is recovered.

Example 6.

In the same reactor as in Example 1, a mixture of 501.9 parts of 1,6-hexanediol, 631, 7 parts of terephthalic acid and 2.5 parts of n-butyltin trioctoate is placed. The reaction mixture is heated, with stirring and under nitrogen, to a temperature of about 140 ° C, at which the reaction water begins to distill. Heating is gradually continued until the temperature is 225 ° C. When the distillation at atmospheric pressure stops, 1.0 part of tributyl phosphite is added to the reaction mixture, which is placed under a vacuum of 50 mm Hg. Heating is continued until the polyester obtained has the following characteristics: hydroxyl number 51 mg KOH / g acid number 2 mg KOH / g

- viscosity HERE at 150 ° C 1,800 mPa.s - Tm (DSC, 20 ° C / min) 132 ° C

When the temperature reaches 180 ° C, the polyester is discharged. Examples 7, 8 and 9.

Hyperbranched polyols.

The hyperbranched polyols of these examples consist of a central nucleus which is the ethoxylated pentaerythritol. Dimethylolpropionic acid is grafted onto this core, to make a hyperbranched polyol of the second, third and fourth generation, which constitutes Examples 7, 8 and 9 respectively, as described in patent application WO 93/17060 to examples 27, 28 and 29 respectively. These hyperbranched polyols are commercially available under the brand name BOLTORN from the company PERSTORP.

Table I shows the characteristics of the hyperbranched polyol of each of these three examples.

In Table I: the 1st line gives the number of the example as well as the number of generations; the second line the hydroxyl number, in mg of KOH / g;

- the third line, the acid number, in mg KOH / g;

- the 4th line the ICI viscosity in mPa.s, measured at 125 ° C;

- the 5th line the number average molecular weight (Mn).

Table at I Ex 7 Ex 8 Ex 9

2nd generation 3rd generation 4th generation

IQH (mg KOH / g); 490 - 520 480 - 510 470 - 500

I _A (mg KOH / g)! 2 - 9 6 - 10 7 - 11

Viscosity HERE (mPa.s). 1,400 8,400 34,000 at 125 ° C!

Molecular weight (Mn) 1,770 3,660 7,240

Examples 10 to 24.

Preparation of powdered thermosetting compositions and properties of the coatings obtained using them.

A series of powders which can be used for the manufacture of coatings are prepared, according to the following two different formulations, one of white color (formulation A) and the other of dark brown color (formulation B): A) Binder 700.0 parts

Titanium dioxide (1) 300.0 parts

Fluidity control agent (2) 10.0 parts

Benzoïne 3.5 games

B) Binder 700.0 parts

Bayferrox 130 (3) 45.0 games

Bayferrυx 3950 (3) 140.0 parts

FW 2 (4) 11.0 games

DURCAL (5) 104.0 parts

Fluidity control agent (2) 10.0 parts

Benzoïne 3.5 games (1) Kronos 2310 (KRONOS)

(2) Resiflo PV5 (WORLEE)

(3) (BAYER)

(4) (DEGUSSA) (5) (OMYA)

The binder of these formulations contains either a mixture of hyperbranched polyol and amorphous polyester containing hydroxyl groups (compositions 17 to 20), or, a mixture of hyperbranched polyol, amorphous polyester containing hydroxyl groups and semi-crystalline polyester containing hydroxyl groups (compositions 10 to 16 and 21 to 24), as indicated in Table II.

Dibutyltin dilaurate was also added to these formulations as a crosslinking catalyst, in an amount of 0.6% by weight relative to the semi-crystalline and amorphous polyesters.

For the preparation of the powder compositions, the hyperbranched polyol, the amorphous polyester and the semi-crystalline polyester can be used as a mixture or as separate resins. The constituents can be mixed, either in the molten state in a conventional flask until the mixture is homogeneous, or by using an extruder, for example of the Betol BTS type.

Next, the powders are prepared by dry mixing and homogenizing the binder, a blocked polyisocyanate as crosslinking agent and the various auxiliary substances conventionally used for the manufacture of powder paints and varnishes. The mixture is homogenized and extruded at a temperature of 85 ° C. in a twin screw extruder, of the Prism 16 mm L / D 15/1 type (from the company PRISM). The extrudate is cooled and ground in a grinder such as the Retsch ZM 100 having meshes of 0.5 mm (from the company RETSCH). Finally, the powder is sieved to obtain a particle size between 10 and 100 micrometers.

The various thermosetting powder compositions thus prepared are listed in Table II. The powders, formulated as described above, are applied with the electrostatic spray gun GEMA-Volstatic PCG 1, at a voltage of 60 kV, on cold-rolled steel panels, untreated, in a film thickness of 50 to 70 micrometers. The coatings deposited are then subjected to a baking in an oven ventilated with ^air at a temperature of 200 ° C, for a period of 15 minutes. The hardened coatings thus obtained are subjected to conventional tests. The results obtained are reported in Table II.

In this table, the 1st column gives the number of the example of the composition prepared, the 2nd column the type of formulation A or B used, the 3rd column the number of the example of preparation of the amorphous polyester containing hydroxyl groups used in the composition prepared, as well as the quantity used of this polyester, in parts by weight, the 4th column the number of the example of preparation of the semi-crystalline polyester containing hydroxyl groups used in the composition prepared, as well as the quantity used of this polyester, in parts by weight, the 5th column the number of the example describing the hyperbranched polyol used in the composition prepared, as well as the quantity of this polyol used, in parts by weight, the 6th column the nature and quantity of the blocked polyisocyanate used as crosslinking agent, in parts by weight; in this column, the abbreviations have the following meaning: BF 1540: the composition of this polyisocyanate is given above in this specification. It is a product marketed by Hϋls. Cargill 2,400: isophorone diisocyanate blocked by epsilon-caprolactam; B 1530: isophorone diisocyanate blocked by epsilon-caprolactam. the 7th column the value of the gloss at an angle of 60 °, in%, according to the standard ASTM D523, the 8th column first the value of the resistance to direct impact (CD), in kg.cm, according to the standard ASTM D2794, and then the value of the resistance to reverse impact (CI), in kg.cm, according to standard ASTM D2794.

Tableat i II

Compositions Type of Polyesters Polyesters Polyols Nature and quantity Brilliant Flexibility of the examples hyperbranched semi-crystalline amorphous formulation of isocyanate at 60 ° (kg. Cm) n ° of the examples of the examples of the blocked examples n ° n ° n ° CD CI

EX 10 A Ex 3: 396.2 Ex 5: 38.7 Ex 9: 68.3 BF 1540: 196.7 57 120 160

EX 11 A Ex 3: 355.5 Ex 5: 34.2 Ex 9: 85.5 BF 1540: 224.8 38 80 80

Ex 12 A Ex 3: 281.6 Ex 5: 26.0 Ex 9: 111.4 BF 1540: 281.0 29 80 60

Ex 13 A Ex 2: 380, 1 Ex 4: 36.9 Ex 9: 65.2 Cargill: 217.8 25 160 200

EX 14 A Ex 2: 272.8 Ex 4: 25.0 Ex 9: 107.2 Cargill: 295.0 10 80 60

EX 15 A Ex 2: 307.8 Ex 4: 28.9 Ex 7: 96.3 B 1530: 267.0 45 120 80

EX 16 A Ex 2: 307.8 Ex 4: 28.9 Ex 9: 96.3 B 1530: 267.0 27 80 80

EX 17 A Ex 1: 326.2 Ex 7: 92.8 B 1530: 281.0 40 100 80

EX 18 A Ex 1: 326.2 Ex 8: 92.8 B 1530: 281.0 35 80 80 g

EX 19 A Ex 1: 326.2 Ex 9: 92.8 B 1530: 281.0 26 80 80

EX 20 A Ex 1: 445, 1 Ex 9: 44.2 B 1530: 210.8 60 80 80

EX 21 A Ex 1: 298.3 Ex 6: 27.9 Ex 9: 92.8 B 1530: 281.0 24 120 120

EX 22 A Ex 1: 405.4 Ex 6: 39.7 Ex 9: 44.2 B 1530: 210.8 63 200 200

EX 23 A Ex 2: 307.8 Ex 4: 28.9 Ex 8: 96.3 B 1530: 267.0 34 100 100

EX 24 B Ex 2: 346.7 Ex 4: 38.5 Ex 8: 83.8 B 1530: 231.0 42 140 140

The coatings obtained with the various powder compositions according to Examples 10 to 24 all have a smooth and regular surface appearance, without any defect such as pinholes or craters, and a matt or semi-matt appearance.

The examples clearly show that a reduction in gloss is obtained with an increase in the amount of hyperbranched polyol. Thus in Examples 10 to 12, we see the gloss at 60 ° pass from 57 to 29, for amounts of the same hyperbranched polyol of Example 9 ranging from 68.3 parts to 111.4 parts, the other constituents of these compositions being identical. Similarly, in Examples 13 and 14, gloss is seen from 25 to 10 of the amounts of the same polyol hyperbranched of ^Example 9 from 65.2 parts to 107.2 parts, the other constituents of these Examples 13 and 14 being identical to each them, but different from those of examples 10 to 12. The comparison of examples 21 and 22 makes it possible to draw exactly the same conclusion.

Furthermore, it is also found that with the same amounts of the hyperbranched polyol in a powder composition of which the other constituents are identical, a reduction in gloss is obtained with an increase in the number of generations in the polyol. This is how, by comparing examples 15, 16 and 23, we see that we obtain a gloss of 45 (example 15) for the second generation polyol of example 7, while the gloss is 27 (Example 16) for the fourth generation polyol of Example 9. The same conclusion is necessary when comparing Examples 17 to 19.

On the other hand, it is found that the flexibility of the coatings improves when the powder compositions contain a semi-crystalline polyester containing hydroxyl groups, as shown by the comparison of Examples 19 with 21, and 20 with 22 respectively.

It can therefore be seen that the present invention provides a very versatile and flexible means for producing coatings of a desired degree of mattness, by playing on parameters such as the quantity and the number of generations of the hyperbranched polyol, as well as, to a lesser extent , on the nature of the crosslinking agent and of the polyesters.

Example 25.

Weather resistance of paint coatings.

In this example, the weather resistance of paint coatings obtained with the mixture of hyperbranched polyol, amorphous polyester and semi-crystalline polyester of the composition of Example 24, in accordance with the invention, is compared with that of 'A coating obtained with a composition not in accordance with the invention. The pigmented powders formulated are applied with an electrostatic spray gun to chromated aluminum panels under the same conditions as in Example 24.

The coatings were subjected to an accelerated aging test in order to assess their resistance to weathering (Q-UV test).

The weather resistance measurements were carried out in a very harsh environment, that is to say by means of a Q-UV device for accelerated aging measurement (from the Q Panel Co) in which the plasters are subjected to intermittent effects of water vapor condensation (4 hours at 50 ° C, lamps off) as well as deterioration effects due to sunlight simulated by fluorescent UV lamps (UVA 340nm lamps; 1 = 0 , 77 W / m ^ / nm) for 8 hours at 60 ° C, according to standard ASTM G53-88. For this type of lamp, there is a good correlation with the effects of natural sunlight, which is not the case with UVB lamps, emitting mainly at the wavelength of 313 nm.

For paint coatings, the gloss values measured at an angle of 60 ° are measured according to standard ASTM D523, every 200 hours.

For the composition of Example 24, a reduction of 50% in the initial value of the gloss is observed after 6,200 hours. The comparison composition, formulated according to type B, contains an amorphous polyester containing hydroxyl groups, consisting of terephthalic acid and neopentylglycol, of hydroxyl index of 30 mg KOH / g, as well as the blocked polyisocyanate B 1530 marketed by the firm HULS (described in examples 10 to 24), in a ratio 88 / 12. For this composition, a reduction of 50% in the initial value of the gloss is observed, which is 92% after only 2,400 hours.

Claims

CLAIMS.

1. Thermosetting powder compositions comprising a mixture of compounds containing hydroxyl groups and of a polyisocyanate blocked as crosslinking agent, characterized in that the mixture comprises:

(a) 5 to 50 parts by weight of a hyperbranched polyol,

(b) 2.5 to 95 parts by weight of an amorphous polyester containing hydroxyl groups,

(c) 0 to 90 parts by weight of a semi-crystalline polyester containing hydroxyl groups, the parts by weight being calculated on the whole of the mixture of the compounds containing hydroxyl groups, and,

(d) a blocked polyisocyanate, in an amount of 5 to 50 parts by weight relative to the total weight of the compounds (a), (b), (c) and (d).

2. Compositions according to claim 1, characterized in that the hyperbranched polyol is of the polyester type and in that it is the reaction product of: i) a polyepoxidized compound still having at least one reactive epoxide group, with ii) at at least one generation of a branched monomer or polymer having a chain-extending role and having at least three reaction groups, among which, on the one hand, at least one is a hydroxyl or hydroxyalkyl group and at least one is a group carboxyl, or on the other hand, one is a hydroxyl or hydroxyalkyl group and at least one is a terminal epoxy group, and, optionally, with iii) a generation of a monomer or polymer having a role of chain extension and d 'group spacing, and having two reaction groups, one of which is a hydroxyl or hydroxyalkyl group, and the other a terminal carboxyl or epoxide group.

3. Compositions according to claim 1, characterized in that the hyperbranched polyol is of the polyester type and in that it is the reaction product of i) a central monomer or polymer core chosen from an aliphatic, cycloaliphatic or aromatic diol, a triol, a tetrol, a sugar such as sorbitol or mannitol, an anhydroene aheptitol, dipentaerythritol, an alpha-alkylglucoside, or the reaction product of an alkylene oxide or of one of its derivatives with one or more hydroxyl groups of aforementioned alcohols, with ii) at least one generation of a branched monomer or polymer having a chain-extending role and having at least three reaction groups, of which, on the one hand, at least two are hydroxyl groups, one or more of these groups being able to be substituted by a hydroxyalkyl group and the other is a carboxyl group, and on the other hand, two are hydroxyl groups and one is a carboxyl group.

4. Compositions according to any one of claims 1 to 3, characterized in that the amorphous polyester containing hydroxyl groups comprises an acid constituent which contains from 70 to 100 mol% of isophthalic and / or terephthalic acid, the 0 to 30 moles% of remaining acids consisting of one or more other aliphatic, and / or cycloaliphatic and / or aromatic polycarboxylic acids having from 4 to 15 carbon atoms, and an alcoholic constituent which contains from 60 to 100 moles% of neopentylglycol , the 0 to 40 mol% of the remaining alcohols being made up of one or more other aliphatic and / or cycloaliphatic polyols having from 2 to 15 carbon atoms.

5. Compositions according to any one of claims 1 to 4, characterized in that the amorphous polyester containing hydroxyl groups has a hydroxyl number of 10 to 100, and preferably from 20 to 50 mg of KOH / g, a acid number less than or equal to 15 mg of KOH / g, a number average molecular weight of between 950 and 15,000, preferably between 2,000 and 8,500, a glass transition temperature (Tg) from 45 ° C to 100 ° C and a melt viscosity of 100 to 20,000 mPa.s measured at 200 ° C with a cone / plate viscometer.

6. Compositions according to any one of claims 1 to 5, characterized in that the semi-crystalline polyester containing hydroxyl groups is chosen from 2 types of polyesters (Cl) and (C2) in which, for

(Cl) the acid component of the polyester (Cl) contains 85 to 100 mole% of terephthalic acid, 1,4-cyclohexanedicarboxylic acid or acid

1,12-docecanedioic and from 0 to 15 mol% of one or more other di- or polycarboxylic acids aliphatic, cycloaliphatic or aromatic, and the alcoholic constituent of the polyester (Cl) contains 85 to 100 mol% of a saturated aliphatic diol with straight or branched chain and from 0 to 15 mol% of one or more other aliphatic or cycloaliphatic diols or polyols, and for (C2) the acid constituent of the polyester (C2) contains from 85 to 100 mol% of a straight chain saturated aliphatic dicarboxylic acid of 0 to 15 mole% of one or more other aliphatic, cycloaliphatic or aromatic di- or polycarboxylic acids having 4 to 8 carbon atoms, and the alcoholic constituent of polyester (C2) contains 85 at 100 moles% of

1,4-cyclohexanediol or 1,4-cyclohexanedimethanol or ethylene glycol and from 0 to 15 mol% of one or more other aliphatic or cycloaliphatic di- or polyols having from 2 to 15 carbon atoms.

7. Compositions according to any one of claims 1 to 6, characterized in that the semi-crystalline polyester containing hydroxyl groups has a hydroxyl number of 10 to 100 mg of KOH / g, preferably from 20 to 50 mg of KOH / g, an acid number less than or equal to 15 mg of KOH / g, a number average molecular weight of between 1,000 and 15,000, preferably between 2,000 and 8,500, a well-defined melting point of 50 to 150 ° C, a viscosity of 50 to 50,000 mPa.s at 175 ° C, measured by the cone / plate method, and a glass transition temperature equal to or greater than -20 ° C.

8. Compositions according to any one of claims 1 to 7, characterized in that the blocked polyisocyanate is chosen from isophorone diisocyanate blocked with epsilon-caprolactam, 2,4-toluene diisocyanate blocked with epsilon-caprolactam and the adduct of the dimer of isophorone diisocyanate 1,3-diazetidine-2,4-dione with a diol.

9. Compositions according to any one of claims 1 to 8, characterized in that they also contain up to 1% by weight of a crosslinking catalyst and up to 10% by weight of at least one stabilizer chosen from compounds absorbing ultraviolet rays and / or sterically hindered amines, relative to the total weight of the constituents (a), (b), (c) and (d).

10. A method of coating an article, preferably metallic, characterized in that a thermosetting powder composition according to any one of claims 1 to 9 is applied to said article, by deposition by spraying with an electrostatic or triboelectric gun or by deposition in a fluidized bed and in that the coating thus obtained is subjected to baking at a temperature of 150 to 220 ° C., for a period of approximately 5 to 35 minutes.

11. Varnishes and paints obtained with the thermosetting powder compositions according to any one of claims 1 to 9.

12. Low gloss coatings obtained from thermosetting powder compositions according to any one of claims 1 to 10.

13. Articles coated entirely or partially by the process according to claim 10.