In W099/16810 a thermosetting powder-paint composition is described that comprises a carboxyl group or anhydride group containing polymer and a linear or branched condensation polymer with at least one hydroxy alkyl amide endgroup, that is preferably a P-hydroxy alkyl amide.

The described thermosetting powder-paint compositions are cured into a coating by means of a circulation oven at a minimum temperature of 180°C and for the duration of 15 minutes. Shorter durations are possible, however a higher temperature must compensate for the shorter time.

In the industries where these coating compositions are being used, a drive exists towards lower curing temperatures. This drive is dictated by the need to lower the costs of the coating process. However the lower curing temperatures must be compensated for by an increase in curing time to obtain sufficient mechanical properties of the final coating. An increase in time would lead to a reduction in output of an existing coating plant. To obtain the same output the capacity should be increased by investments in hardware, which is not desirable from an economic point of view.

Therefore the industry is in an urgent need of coating systems that can be cured at lower temperatures without the need to increase the curing time and still retaining sufficient mechanical properties.

In EP-0.664. 325 coating systems are described that comprise linear carboxyl functional polyesters and (3-hydroxy alkyl amides. The carboxyl functional polyesters are synthesized from specified bifunctional monomeric carboxylic acids and bifunctional alcohols. The carboxylic acid used is a mixture of at least isophthalic acid and at least one other specified dicarboxylic acid. The alcohol is a mixture from at least one branched aliphatic diol and at least one other further specified alcohol. The obtained polyesters can be cured at a temperature of 180°C during 10 minutes by using Primidi XL 552 (EMS), a P-hydroxy alkyl amide compound. However a

disadvantage of the coating systems based on these components is that the color of the obtained coatings after the curing cycle is not satisfactory, because the coating suffers of yellowing. This phenomenon especially occurs when the curing of the coating takes place in a gas-oven. Therefore it is an object of the invention to supply a binder composition comprising at least one carboxyl functional polyester and at least one P- hydroxy alkyl amide, which can be cured in 10 minutes at a temperature of 180°C while resulting in a coating with improved colour properties and sufficient mechanical properties.

This object has been reached by the use of a binder composition comprising at least one carboxyl functional polyester and at least one P-hydroxy alkyl amide, wherein at least one of the carboxyl functional polyesters is a modified polyester wherein the modification of the polyester has taken place with a salt-forming phosphorus compound.

It has surprisingly been found that in addition to the improvement in reactivity, which results in curing at lower temperatures for a shorter period of time, also an improvement is reached in the gloss and also in the adhesion between the cured coating and the substrate. A further additional advantage is that the amount of anti-oxidant that is necessary in the coating composition according to the invention can be lower than with coating compositions in the prior art, while retaining good properties.

A lower level of anti-oxidant is not only from an economic point of view very interesting; it is also from an environmental point of view important. Some anti-oxidants have in the long range a detrimental effect on the environment, especially the aquatic environment.

Therefore any possibility to decrease the amount of such a compound is very desirable.

Here and hereinafter with binder composition is meant the total of resins and crosslinkers. With coating composition is meant the binder composition with the pigments and additives. With coating is meant the paint after curing.

The binder composition according to the invention comprises at least one carboxyl functional modified polyester wherein the modification of the polyester has taken place with a salt-forming phosphorus compound. The binder composition according to the invention can in addition to this carboxyl-functional modified polyester comprise other resins either modified or not. Examples of other suitable resins are polyurethanes, polyacrylates, polyesters. When other resins are combined with the carboxyl-functional modified polyester, preferably polyesters are used. Preferably these

polyesters are also carboxyl-functional modified polyesters as in that case best results are obtained in relation to the reactivity combined with the color.

The binder composition according to the invention comprises at least one P-hydroxy alkyl amide. The binder composition according to the invention can in addition to this (3-hydroxy alkyl amide comprise other (3-hydroxy alkyl amides.

The binder composition according to the invention comprises the at least one carboxyl functional polyester and the at least one hydroxy alkyl amide in a certain ratio to obtain in the end a suitable coating. This ratio, Q, is defined in formula I : wherein: K is the number of carboxylgroups on the modified polyester, L is the number of phosphorus derived groups on the modified polyester that are reactive towards the hydroxy groups on the (3-hydroxy alkyl amide, M is the number of the hydroxy groups on the (3-hydroxy alkyl amide.

The ratio Q is preferably between 0,5 and 1,5, more preferred between 0,75 and 1,25.

The amount of modifying agent is chosen in such a way to reach the desired level. The person skilled in the art can, without undue burden, easily perform this. Preferably between 0,1 and 5 w% phosphorus based on the weight of the modified polyester is present. With a too low level of phosphorus present the reactivity is not increased enough to be able to cure the coating composition in a short time at a relatively low temperature. With a too high level of phosphorus the appearance of the final surface after curing is not satisfactory. With more preference between 0,25 and 3 w% phosphorus based on the weight of the modified polyester is present. Most preferred is a range between 0,5 and 2 w%.

The carboxyl-functional modified polyester can be prepared according to methods known to the person skilled in the art, for example in a one-step or two-step process. For example reference can be made to the book:"Powder Coatings, Chemistry and Technology"by T. A. Misev, John Wiley & Sons, 1991, page 147-152.

In the two-step process first a hydroxyl-functional polyester is prepared according to known methods and in a second step the hydroxyl-functional polyester is modified with both a suitable amount of salt-forming phosphorus compound and a compound able to convert a hydroxyl-functional polyester into a carboxyl- functional polyester, to obtain the carboxyl-functional modified polyester according to

the invention. The compound able to convert a hydroxyl-functional polyester into a carboxyl-functional polyester is a compound that has groups that are reactive towards hydroxyl-groups and that has in addition to those groups at least one carboxyl-group, for example trimellitic anhydride.

The modification of the hydroxyl-functional polyester results in a carboxyl-functional polyester wherein part of the hydroxyl groups has been replaced by phosphorus containing groups and the other part of the hydroxyl groups has been turned into carboxyl groups. The phosphorus containing groups can be located either in the backbone of the polyester or in the side chains of the polyester.

In the one-step synthesis all components that are used for the preparation of a hydroxyl-functional polyester are combined with the salt-forming phosphorus compound and a compound able to convert a hydroxyl-functional polyester into a carboxyl-functional polyester, to obtain the carboxyl-functional modified polyester according to the invention.

A hydroxyl-functional polyester can for example be obtained by causing polyhydric alcohols to react with acids or acid anhydrides by choosing a certain molar ratio of the polyhydric alcohols and the acids or acid anhydrides. This ratio may vary for example between 1.2 : 1.0 and 1.0 : 1.0 for the preparation of the hydroxyl-functional polyester.

Suitable polyhydric alcohols for the preparation of the polyester can have an aliphatic or aromatic nature. Suitable aliphatic polyhydric alcohols for preparing the hydroxyl-functional polyesters have a functionality of at least two and can contain from 2-24 carbon atoms. They include for example ethylene glycol, diethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, 2,2, 4-trimethylpentanediol- (1, 3), 1, 6-hexanediol, neopentyl glycol, 2-methyl-1, 3- propanediol, 2-ethyl-2-butyl-1, 3-propanediol, trimethylpentanediol, hydroxypivalic neopentyl glycol ester, tricyclodecane dimethanol, cyclohexane dimethanol, hydrogenated diphenylol propane, trimethylolpropane and/or pentaerythritol. Preferably NPG (neopentyl glycol) or TMP (trimethylolpropane) is used.

Suitable aromatic polyhydric alcohols for preparing the hydroxyl- functional polyesters have a functionality of at least two and can contain from 2-24 carbon atoms. They include for example bisphenol A bis (hydroxyethyl) ether.

Suitable aliphatic polybasic carboxylic acids for preparing the polyesters have a functionality of at least two and can contain from 2-36 carbon atoms.

They can have a straight or branched chain. Preferably aliphatic polybasic carboxylic

acids are used with 6-16 carbon atoms. They include for example adipic acid, fumaric acid, sebacic acid, tetrahydrophthalic acid, hexahydroterephthalic acid, decane dicarboxylic acid, succinic acid, maleic acid, hexahydrophthalic acid, azelaic acid and/or dimerised fatty acids or their corresponding acid anhydrides for example tetrahydrophthalic anhydride, succinic anhydride, maleic anhydride and/or hexahydrophthalic anhydride.

Suitable aromatic polybasic carboxylic acids for preparing the polyesters have a functionality of at least two and can contain from 2-36 carbon atoms.

Preferably aromatic polybasic carboxylic acids are used with 6-16 carbon atoms. They include for example phthalic acid, isophthalic acid and/or terephthalic acid, dimethyl terephthalate ester or acid anhydrides for example phthalic anhydride, trimellitic anhydride, 1, 8-naphthalic anhydride and pyromellitic anhydride. Preferably isophthalic acid or terephthalic acid is used.

Although in principle aliphatic and aromatic polybasic carboxylic acids are suitable, it is preferred to use a polyester that doesn't contain adipic acid derived building blocks in the polyester chain. It is even more preferred to use a polyester that doesn't contain aliphatic acid derived building blocks. It was surprisingly found that with these preferred polyesters the flow is improved. Additionally also better mechanical properties were obtained.

When not all objects of the present invention as described above need to be reached at the same time, but the main object is to improve the mechanical properties also carboxyl functional polyesters without adipic acid (and more generally without aliphatic acid) derived building blocks and without phosphorous modification can be used.

The carboxyl-functional modified polyester preferably contains at least one aromatic monomer, either the acid or the alcohol. When the polyester is to be used in a powder coating the glass temperature should be high enough. A high glass temperature can be reached by incorporating monomers with an aromatic character into the polyester chain.

The polyester according to the invention can be branched by incorporating tri-or more functional polycarboxylic acids or the corresponding anhydrides and/or tri-or more functional polyol components in an amount of at most 15 mol %, preferably between 6 and 12 mol % to the total acid component or polyol component. These branched polyesters result in an improved adhesion and flexibility of the finally cured coating.

The esterification reaction in the polyester synthesis is carried out under conditions well-known to the man skilled in the art. Preferably the reaction is carried out in a nitrogen atmosphere at temperatures of between 180°C and 260°C.

The polyester-forming reaction, the esterification, can take place in the presence of one or more catalysts. Examples of suitable catalysts are dibutyl tin oxide, tin chloride, butyl chlorotin dihydroxide (FASCATC) or tetrabutyloxytitanate. The reaction water released during the reaction can be removed by distillation. The desired degree of esterification is reached by means of azeotropic distillation or vacuum in the last phase.

The carboxyl-functional modified polyester is obtained by modification of the hydroxyl-functional polyester with a salt-forming phosphorus compound. Suitable salt-forming phosphorus compounds include for example phosphoric acid, phosphorous acid, phosphinic acid, phenylphosphinic acid, phosphinous acid, organic acid phosphate, phosphorous oxychloride, alkyl esters of phosphoric acid, anhydrides of phosphoric acid, hydrogen containing salts of phosphoric acid, hypo-phosphorous acid and mixtures thereof for example tri-butylphosphite. Preferably phosphoric acid is used.

The binder composition according to the invention comprises in addition to the at least one carboxyl-functional polyester at least one P-hydroxy alkyl amide. The carboxyl groups on the polyester can react with the functional ( (3-hydroxy) groups on the (3-hydroxy alkyl amide to form a network. The (3-hydroxy alkyl amide is preferably a linear or branched condensation polymer containing ester groups and at least one amide group in the backbone, having at least one hydroxy alkyl amide endgroup and having a weight average molecular mass of > 800 g/mol. With more preference the P-hydroxy alkyl amide with a weight average molecular mass of > 800 g/mol has at least two groups according to formula ll : in which R4 R6 - =-C-C-HH, H, (Ci-C24) (cyclo) alkyl or (C6-C1o) aryl, R5 H

B = (C2-C24), optionally substituted, aryl or (cyclo) alkyl aliphatic diradical, and R', R2, R3, R4, R5 and R6 may, independently of one another, be the same or different, H, (C6-C10) aryl or (C1-C8) (cyclo) alkyl radical.

With even more preference the (3-hydroxy alkyl amide has at least two groups according to formula 11 wherein R3and R6 are both methyl, R', R2, R4, R5 all are hydrogen and B is C6H4-diradical.

The binder composition according to the invention can, in principle, be used in all kinds of coating systems. However it is advantageously used in powder coating systems. The performance and the characteristics of the finally obtained powder coating after curing of the coating composition are influenced by several factors. For example the glass transition temperature of the binder plays an important role in the (storage) stability of the powder coating composition. In case the glass transition temperature is low the mobility of the components in the powder coating composition is relatively high, resulting in a system that is not powder stable. As a consequence the powder coating composition cannot be stored for a considerable time. The necessary glass temperature for a certain powder coating composition depends on the storage conditions. In countries with a relatively high ambient temperature binders with a higher glass transition temperature are needed. For practical reasons it is widely accepted that the glass transition temperature (Tg) of the powder coating should not be lower than 40°C. Another factor of influence for the behavior of a powder coating composition is the particle size. The smaller the particles, the better the leveling of the coating. Also the amount of pinholes, orange peel and shrinkage during curing are positively influenced when using smaller particles. The person skilled in the art of powder coatings knows or can without undue experimentation determine the most suitable parameters for a powder coating composition.

The invention also relates to a process for the preparation of a binder composition according to the invention, wherein at least one carboxyl-functional modified polyester is combined with at least one P-hydroxy alkyl amide in a mixing device. Preferably the mixing device is operated at a temperature below 160°C.

The coating composition according to the invention will generally contain at least one component chosen from the list comprising pigments, anti- oxidants, hindered amine light stabilizers, degassing agents, fillers and/or wetting agents.

The coating composition according to the invention is generally applied onto a substrate. The substrate is not particularly critical, examples are aluminum and (phosphatized) steel. It is in particular the temperature at which the curing takes place that determines whether the substrate is suitable or not. Some substrates, generally referred to as the heat-sensitive substrates, are less suitable as a higher risk exists that the substrate itself will deteriorate in some way or another.

The invention also relates to a process for coating a substrate with a coating composition according to the invention by applying the coating composition onto the substrate and curing it. The coating composition can be applied by means known to the person skilled in the art, reference can for example be made to"Powder Coatings, Chemistry and Technology"by T. A. Misev, John Wiley & Sons, 1991, page 324-349. For example use can be made by a corona charging gun or tribo charging gun. Curing can be effected through various means, for example thermal curing, electron beam curing and/or UV-curing. Thermal curing can take place in various types of ovens, for example gas oven, electrical oven or infrared oven. Preferably the curing takes place at a temperature of maximally 180°C and during a time of maximally 10 minutes. The substrate in general can be wholly or partly coated depending on its use.

The invention also relates to the wholly or partly coated substrate wherein the coating is obtained by the process according to the invention.

The wholly or partly coated substrates according to the invention can be used for both indoor and outdoor applications.

Examples Experiment 1 : Preparation of a carboxvl functional polyester modified with phosphorus (0.5 w% P) A 6-litre reactor vessel fitted with a thermometer, a stirrer and a distillation device, was filled with the monomers for the first step as listed in Table I.

Stirring was then applied and a light nitrogen flow was passed over the reaction mixture while the temperature was being raised to 200°C. The temperature was gradually raised further to a maximum of 250°C, and the reaction water was distilled off. The reaction was continued until the acid value of the polyester resin was below 8 mg KOH/g.

Subsequently, the monomers for the second step, trimellitic acid and phosphoric acid, were added at a temperature of 180°C. The temperature was then

raised to 225°C. When setpoint was reached pull vacuum and after 5 minutes adjusted the setpoint on 195°C. Additionally the viscosity was determined to be 40 with a Rheomat Plate Plate viscosimeter (Pa. s, at 160°C). The acid value was determined to be 84 mg KOH/g.

Table 1: Components for polyester synthesis Component Amount (g) First step Adipic acid 244.4 Terephtalic acid 2858.4 Ethane diol 206.6 Neopentylglycol 1784.4 n-Butyl chloro tin (IV) dihydroxide 2.52 Distearyl pentaerythritol diphosphite 5.10 Second step Trimellitic anhydride 443.8 Phosphoric acid 89.6 Experiment)) : Preparation of a carboxyl functional polyester modified with phosphorus (0. 5 w% P), without adipic acid building blocks A 6-litre reactor vessel fitted with a thermometer, a stirrer and a distillation device, was filled with the monomers for the first step as listed in Table 2.

Stirring was then applied and a light nitrogen flow was passed over the reaction mixture while the temperature was being raised to 200°C. The temperature was gradually raised further to a maximum of 250°C, and the reaction water was distilled off. The reaction was continued until the acid value of the polyester resin was below 8 mg KOH/g.

Subsequently, the monomers for the second step, trimellitic acid and phosphoric acid, were added at a temperature of 180°C. The temperature was then raised to 225°C. When setpoint was reached pull vacuum and after 5 minutes adjust the setpoint on 195°C. Additionally the viscosity was determined to be 20 with a Rheomat Plate Plate viscosimeter (Pa. s, at 160°C). The acid value was determined to be 74 mg KOH/g.

Table 2: Components for polyester synthesis Component Amount (g) First step Terephtalic acid 2746.4 Ethane diol 45.0 Neopentylglycol 1774.6 n-Butyl chloro tin (IV) dihydroxide 2.26 Distearyl pentaerythritol diphosphite 3.86 Second step Trimellitic anhydride 443. 8 Phosphoric acid 89.6

Experiment III : Preparation of a carboxyl functional polyester without adipic acid building blocks A 6-litre reactor vessel fitted with a thermometer, a stirrer and a distillation device, was filled with the monomers for the first step as listed in Table 3.

Stirring was then applied and a light nitrogen flow was passed over the reaction mixture while the temperature was being raised to 200°C. The temperature was gradually raised further to a maximum of 250°C, and the reaction water was distilled off. The reaction was continued until the acid value of the polyester resin was below 8 mg KOH/g.

Subsequently, the monomer for the second step, trimellitic acid, was added at a temperature of 180°C. The temperature was then raised to 225°C. When setpoint was reached, after one hour the viscosity was determined to be 16 with a Rheomat Plate Plate'viscosimeter (Pa. s, at 160°C). The acid value was determined to be 74 mg KOH/g.

Table 3: Components for polyester synthesis Component Amount (g) First step Terephtalic acid 2746.4 Ethane diol 45.0 Neopentylglycol 1774.6 n-Butyl chloro tin (IV) dihydroxide 2.26 Distearyl pentaerythritol diphosphite 3.86 Second step Trimellitic anhydride 515.8

Comparative Experiment A: Preparation of a polyester without phosphorus A 6-litre reactor vessel fitted with a thermometer, a stirrer and a distillation device, was filled with the monomers for the first step as listed in Table 4.

Stirring was then applied and a light nitrogen flow was passed over the reaction mixture while the temperature was being raised to 200°C. The temperature was gradually raised further to a maximum of 250°C, and the reaction water was distilled off. The reaction was continued until the acid value of the polyester resin was below 8 mg KOH/g.

Subsequently, the monomer for the second step, trimellitic acid, was added at a temperature of 180°C. The temperature was then raised to 225°C. When setpoint was reached, after one hour the viscosity was determined to be 26 with a Rheomat Plate Plate viscosimeter (Pa. s, at 160°C). The acid value was determined to be 74 mg KOH/g.

Table 4: Components for polyester synthesis Component Amount (g) First step Adipic acid 233.9 Terephtalic acid 2870. 7 Ethane diol 201.4 Neopentylglycol 1759.2 n-Butyl chloro tin (IV) dihydroxide 2.50 Distearyl pentaerythritol diphosphite 4.24 Second step Trimellitic anhydride 584.0

Example 1-111 and Comparative Example A: Preparation of a coating composition Powder paint compositions were prepared consisting of a B-hydroxy alkyl amide resin as described in Experiment I of WO 01/68781, pigment and or filler (see table 5), Resiflow@ PV5 (flow agent) and degassing agent benzoin. This powder composition was added to the granulated polyester resin according to Experiment I, II, III or Comparative Experiment A respectively. The amounts of the ingredients of the coating compositions are shown in Table 5.

The powder paint was prepared by mixing and extrusion in a PRISM extruder at 120°C. The composition was ground in the usual manner. The extrudate was cooled, milled and sieved and the fraction with particle size between 50-90 um was collected and used as the powder paint. The powder paint was electrostatically sprayed (Corona) onto aluminium test panels (Al-46). After a cure of 10 minutes at 180°C in a circulation oven the panels were tested. The test results are shown in Table 5.

Table 5: Powder paint composition and test results Exp. I Exp. II Exp. III Comp. Exp. A Polyester resin (g) 163.2 166.9 166.9 166.9 ß-Hydroxy alkyl amide resin (g) 36.8 33.1 33.1 33.1 Pigment (g) 100.0 2.0 2.0 100.0 Filler (g) - 84.0 84.0 - Resiflow PV5 (g) 3.0 3.0 3.0 3.0 Benzoin (g) 0.8 0.8 0.8 0.8 Pigment Kronos# 2160 Special Black# 100 Special Black# 100 Kronos# 2160 Filler - Blanc fixe Micro# Blanc Fixe Micro# Endgroup TMA TMA TMA TMA Functionality 4 4 4 4 Acid Value (mg KOH/g resin) 84 74 74 74 Amount of P (w%) 0.5 0.5 0 0 Flow good good good good Appearance ok ok ok ok Haze 36 38 50 52 20° gloss 85 85 85 84 60° gloss 94 94 94 94 Exp. I Exp. II Exp. III Comp. Exp. A Color b* 15'180° 0,6 0,5 3,1 3,2 Color b* 10'200° 3,2 3,3 4,5 4,4 Overbake color b* 1hr 220°C 6,4 6,6 9,5 9,8 Reversed Impact 10'200°C pass pass pass pass Reversed Impact 15'180°C pass pass pass pass Reversed Impact 10' 180°C no impact pass pass no impact Gradient (°C) 171 168 172 176 TMA = trimellitic anhydride<BR> Acid value is determined in mg KOH/g polyester<BR> Flow is determined according to the PCI-scale<BR> Appearance is determined visually<BR> Haze is determined according to ASTM D 523<BR> Gloss is determined according to ASTM D 523<BR> Overbake color is determined after 1 hour at 220°C<BR> Reversed Impact is determined with 60 inchpound at an AI-46 substrate