WO1998055550A1

WO1998055550A1 - Powder-paint binder composition

Info

Publication number: WO1998055550A1
Application number: PCT/NL1998/000320
Authority: WO
Inventors: Dirk Armand Wim Stanssens; Rudolfus Antonius Theodorus Maria Van Benthem; Patrick Herman Marie Hendriks
Original assignee: Dsm N.V.
Priority date: 1997-06-06
Filing date: 1998-06-02
Publication date: 1998-12-10
Also published as: NL1006251C2; AU7677998A

Abstract

Thermally stable, moisture-curable powder-paint binder composition with a glass transition temperature of ≥ 30 °C or a melting temperature of ≥ 30 °C, comprising a polymer and optionally a crosslinker. At least one of these components contains a moisture-latent reactive group. The polymer is selected from the group consisting of a saturated polyester, unsaturated polyester, polyacrylate, polyurethane, polycarbonate, polybutadiene, polystyrene, polysiloxane or a copolymer hereof. The moisture-latent reactive group is a moisture-latent amine group, a hydrolysable silyl group, a moisture-latent alcohol, a moisture-latent acid, a moisture-latent aldehyde group or a moisture-latent ketone group.

Description

POWDER-PAINT BINDER COMPOSITION

The invention relates to a powder-paint binder composition.

As it appears from the article "Rheology of Powder Coatings" by Sunil Kadam et al . (February 1992, Paint India/77) , efforts are being made to find powder- paint systems that simultaneously show good flow behaviour, good storage stability and good reactivity. In prior art powder-paint binder systems chemical curing by means of crosslinking of the powder paint takes place simultaneously with the heating and melting of the powder that has been applied to the substrate. If such a system has a high reactivity, this will lead to good hardening of the coating at the usual heating cycles and oven temperatures, resulting in good mechanical and chemical properties. However, it is very difficult to obtain the desired storage stability and flow behaviour. If a system has a low reactivity, this will lead to a good storage stability and a good flow behaviour. However, longer heating times and higher temperatures will be required in the cure cycle to obtain the desired coating properties.

The binder composition according to the invention is a thermally stable, moisture-curable powder-paint binder composition having a glass transition temperature of -> 30°C or a melting temperature of ≥ 30°C comprising a polymer and optionally a crosslinker wherein at least one of the polymer and/or the crosslinker contains moisture-latent reactive groups. A thermally stable moisture curable powder- paint binder composition is a binder composition which, on exposure to temperatures of <. 150°C for 15 minutes and under exclusion of moisture, undergoes less than 20% of the reactions leading to chain lengthening or crosslinking. The moisture-latent reactive groups are exposed to moisture after the powder's flow stage, after which curing to a powder coating takes place.

Preferably the powder paint composition contains, or contained before the flow phase, less than 0.1 wt . % water (relative to the powder paint composition) .

The use of the composition of the invention ensures that the chemical curing by means of crosslinking can take place after the heating and melting of the powder, by exposing the coated substrate to moisture. This ensures both the desired storage stability and very good flow behaviour provided that the absorption of moisture by one of the components of the powder paint composition is avoided. After the applied coating has been exposed to moisture, sufficient reactivity for the chemical curing can be obtained by means of crosslinking, which ensures the desired coating properties. No crosslinking will take place unless one of the components of the powder paint composition or the coating absorbs moisture.

A moisture-latent reactive group is a reactive group that does not react with other reactive groups in the binder system at temperatures between 0°C and 200°C but that can react with moisture at this temperature. Reaction with water causes the chemical structure of the reactive group to change, as a result of which reactions may take place with different reactive groups in the binder system.

A reactive group is part of a molecule that can react with another, optionally different, reactive group so that a chemical bond is formed between the two reacting groups. Hence, a chemical bond is formed also between the molecules, for example polymers, to which the reactive groups are attached.

During the exposure to moisture the relative humidity is usually between about 20% and 100% (at temperatures between 10°C and 200°C) , preferably between about 40% and 99%.

A very important advantage of moisture-latent curing, according to the invention, is that the powder paint's flow behaviour is (as a result of heat) entirely separated from the curing reaction. A result of this is that powder coatings with very good flow behaviour can be obtained.

Another advantage of the process of heating and curing described above is the relatively low temperature that is required for good flow behaviour. This makes the use on heat-sensitive substrates such as wood, paper and plastic possible too.

The moisture-latent reactive groups are attached to the polymer and/or the crosslinker.

If it is necessary or desirable to use a crosslinker, the moisture-latent reactive groups may be attached to the crosslinker. The other, optionally also moisture-latent, or the same reactive groups that are reactive with the crosslinker ' s reactive groups modified by exposure to moisture, may be attached to the polymer. Consequently the binder composition can comprise a) a polymer containing moisture-latent groups and a crosslinker or b) a polymer and a crosslinker containing moisture- latent groups or c) a polymer containing moisture-latent groups and a crosslinker containing moisture-latent groups. It is also possible for the moisture-latent reactive groups to be attached to one or more polymers when the use of an additional crosslinker is not necessary or desirable. In that case other, optionally also moisture-latent , or the same reactive groups that are reactive with the reactive groups modified by exposure to moisture, are attached to the same polymer or to one of the polymers .

The number average reactive groups per polymer chain can be varied depending on the application. However, this number will generally be between about 1.5 and about 10, preferably between 2 and 4 groups per polymer chain.

If the moisture-latent groups are attached to the crosslinker, they can, after reacting with moisture, react with optionally moisture-latent reactive groups attached to the polymer, which may or may not have reacted with moisture.

In the synthesis of the individual components of the binder composition, during the combination of the various components to obtain the ultimate binder composition and in the processing of the binder to a powder paint by means of the usual techniques such as crushing, grinding, extrusion, cooling, sieving and spraying, the conditions are preferably chosen such that no or virtually no moisture can be absorbed or react with moisture latent reactive groups.

Preferably, the binder composition and the powder paint composition are processed in an inert, dry atmosphere of nitrogen or argon, or in dried air (for example with < 20% relative humidity at a temperature of between 0°C and 130°C) .

Depending on its composition and/or the temperature, a binder or powder paint can absorb moisture more or less easily. A polymer will, for example, show a lesser tendency to absorb moisture at temperatures lower than the glass transition temperature. The temperature and humidity during processing can be adjusted depending on the tendency to absorb moisture.

Suitable polymers are, for example, saturated polyester, unsaturated polyester, polyacrylate, polyurethane, polycarbonate, polystyrene, polybutadiene, polysiloxane or a copolymer thereof. Preferably saturated polyesters and polyacrylates are used.

Examples of suitable moisture-latent reactive groups are moisture-latent amine groups, hydrolysable silyl groups, moisture-latent alcohols, moisture-latent acids, moisture-latent aldehyde groups and moisture- latent keton groups.

Preferably hydrolysable silyl groups and moisture-latent amine groups are used.

Examples of suitable moisture-latent amine groups are ketimine, aldimine, oxazolidine and silazanes groups. Examples of suitable hydrolysable silyl groups are silicon-containing reactive groups according to formula (I) :

R¹ I

A - Si - R² (I)

A. where at least one of the R¹, R² or R³ groups is hydrolysable and is chosen from the group comprising

(C;-C_2O) alkoxy, alkoxy containing (Cι-C₂₀) ether groups or (C1-C20) carboxylate and where A is a non-hydrolysable (Cι-C₁₀) alkyl radical or a (C1-C20) alkoxy radical. One or two of the R¹, R² or R³ groups may be a

(C1-C20) alkyl group.

The silane may be bound to one of the aforementioned polymers or crosslinkers via side group

A or may be used as a crosslinker as such. Preferably A is a (C₂-C₅) alkyl radical and

R¹, R² and R³ are (Cι-C₄) alkoxy groups.

According to a further preferred embodiment A is a C₃ radical and R¹, R² and R³ are (Cι-C₂) alkoxy groups. The C₃ radical is preferably unsubstituted. Examples of suitable moisture-latent alcohols are silyl ethers, acetals and ketals.

Examples of suitable moisture-latent acids are silyl esters, carboxyl esters and alkenyl esters. Examples of suitable moisture-latent aldehydes or ketones are acetals, ketals, alkenyl ethers, alkenyl esters, aldemines and ketimines.

Polyesters that can be used are generally based on the residues of aliphatic polyalcohols and polycarboxylic acids. The polycarboxylic acids are generally selected from the group comprising aromatic and cycloaliphatic polycarboxylic acids because these acids usually have a Tg-raising effect on the polyester. In particular use is made of dibasic acids. Examples of polycarboxylic acids are isophthalic acid, terephthalic acid, hexahydroterephthalic acid, 2 , 6-naphthalene dicarboxylic acid and 4, 4-oxybisbenzoic acid and, subject to availability, their anhydrides, acid chlorides or lower alkyl esters such as the dimethyl ester of naphthalene dicarboxylic acid. Although not required, the carboxylic acid component generally contains at least about 50 mol.%, preferably at least about 70 mol.%, isophthalic acid and/or terephthalic acid.

Other suitable aromatic cycloaliphatic and/or acyclic polycarboxylic acids are for example 3,6- dichlorophthalic acid, tetrachlorophthalic acid, tetrahydrophthalic acid, hexahydroterephthalic acid, hexachloroendomethylene tetrahydrophthalic acid, phthalic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, adipic acid, sebacic acid, trimellitic acid and maleic acid. These other carboxylic acids can be used usually in amounts of at most 50 mol . % of the total amount of carboxylic acids. These acids can be used as such or, subject to availability, in the form of their anhydrides, acid chlorides or lower alkyl esters.

Suitable polyalcohols, in particular diols, that can be caused to react with the carboxylic acids to obtain the polyester include aliphatic diols such as ethylene glycol, propane-1, 2-diol, propane-1, 3-diol, butane-1, 2-diol, butane-1, 4 -diol, butane-1, 3-diol, 2,2- dimethylpropanediol-1, 3 (= neopentyl glycol) , hexane- 2,5-diol, hexane-1, 6-diol, 2 , 2-bis- (4-hydroxy- cyclohexyl) -propane (hydrogenated bisphenol-A) , 1,4- dimethylolcyclohexane, diethylene glycol, dipropylene glycol and 2,2-bis [4-2-hydroxylethoxy) -phenyl] ropane, the hydroxypivalic ester of neopentyl glycol.

Small amounts, such as less than about 4 wt.%, but preferably less than 2 wt.%, of triols or triacids can be used to obtain branched polyesters. Examples of suitable polyols and polyacids are glycerol, hexanetriol, trimethylolethane, trimethylolpropane, tris- (2-hydroxyethyl) -isocyanurate and trimellitic acid.

The polyesters are prepared via the usual methods, through esterification or re-esterification, optionally in the presence of the usual esterification catalysts such as dibutyl tin oxide or tetrabutyl titanate. The preparation conditions and the COOH/OH ratio can be chosen such that end products are obtained that have an acid number or hydroxyl value within the range of values aimed at .

The polyester may be crystalline or amorphous. Preferably the polyester is amorphous. Mixtures of crystalline and amorphous polyesters can also be used. Amorphous polyesters have a viscosity that usually lies between 100 and 8000 dPas (measured at 158°C, Emila) . Crystalline polyesters usually have a viscosity of between about 2 and about 200 dPas .

Polyacrylates, such as epoxy-, carboxy- and hydroxy-reactive polyacrylates, are described in the patents US Patent No. 3,752,870, US Patent No. 3,787,340 and US Patent No. 3,758,334 and in the US patent No. 3,787,633, incorporated herein by reference.

The polymer's Tg generally lies between about 30°C and about 120°C. To obtain optimum storage stability, the Tg is preferably higher than 50°C. For processing of the polymer, the Tg is preferably lower than 100°C.

In the preparation of a polyester or polyacrylate containing hydrolysable silyl groups use can be made of a hydroxyl- or acid-functional polyester or polyacrylate that can react with a hydrolysable compound containing a silyl group according to formula (II) :

R¹

I

X-A- Si - R² (II)

A.

where X is a reactive group that can react with hydroxyl, acid or ester groups, where A is an organic radical, optionally substituted, containing (1-20) carbon atoms and - where at least one of the R¹, R² or R³ groups is hydrolysable and is chosen from the groups comprising (Cι-C₂o) alkoxy, alkoxy containing (Ci- C₂o) ether groups or (C1-C20) carboxylate.

Suitable reactive groups X are, for example, isocyanates, epoxies, amines and thiols.

Suitable examples of hydrolysable compounds containing silyl groups that can react with acid groups are : 3-glycidoxypropyltriethyoxysilane, 3-glycidoxypropyltrimethoxysilane,

3-glycidoxypropyltri (2-methoxyethoxy) silane, beta- (3 , 4-epoxycyclohexyl) ethyltrimethoxysilane and beta- (3 , 4-epoxycyclohexyl) ethyltriethoxysilane. Suitable examples of hydrolysable compounds containing silyl groups that can react with ester groups are :

3-aminopropyltrimethoxysilane,

3-aminopropyltriethoxysilane, bis (3-trimethoxysilylpropyl) amine, bis (3-triethoxysilylpropyl) amine, β-mercaptopropyltriethoxysilane and β-mercaptopropyltrimethoxysilane.

Suitable examples of hydrolysable compounds containing silyl groups that can react with hydroxyl groups are 3-isocyanatopropyltrimethoxysilane and 3- isocyanatopropyltriethoxysilane .

It is also possible to use as a starting material a polyester containing hydroxyl groups that reacts successively with a diisocyanate and with a silyl compound that can react with isocyanate.

Suitable examples of diisocyanates include

1, 4-diisocyanato-4-methyl-pentane, 1, 5-diisocyanato-5- methylhexane, 3 (4) -isocyanatomethyl-1- methylcyclohexylisocyanate, 1, 6-diisocyanato-6-methyl- heptane, 1, 5-diisocyanato-2, 2 , 5-trimethylhexane and

1, 7-diisocyanato-3 , 7-dimethyloctane, and 1-isocyanato- l-methyl-4- (4-isocyanatobut-2-yl) -cyclohexane, 1- isocyanato-1, 2, 2-trimethyl-3- (2-isocyanato-ethyl) - cyclopentane, 1-isocyanato-l, 4-dimethyl-4- isocyanatomethyl-cyclohexane, 1-isocyanato-l, 3- dimethyl-3-isocyanatomethyl-cyclohexane, 1-isocyanatol■ n-butyl -3- (4-isocyanatobut-1-yl) -cyclopentane, and 1- isocyanato-1 , 2 -dimethyl-3 -ethyl-3 - isocyanatomethylcyclopentane, respectively.

Suitable silyl compounds that can react with isocyanate are

3-aminopropyltrimethoxysilane,

Preferably the reaction between the polyester or polyacrylate containing hydroxyl groups and the diisocyanate takes place in the presence of a catalyst . Suitable catalysts are described in

W097/46517.

Most preferably A is 1, 3-propylene,

X is an isocyanate and the polymer is a hydroxyfunctional polyester or polyacrylate. Another method for preparing a hydrolysable polyacrylate containing silyl groups is by using as a starting material a copolymer of polymerisable ethylenically unsaturated monomers and a compound according to formula (III) :

R¹

R^

where y is an ethylenically unsaturated polymerisable group or a chain transfer group, where A is an organic radical, optionally substituted, that contains (1-20) carbon atoms and where at least one of the R¹, R² or R³ groups is hydrolysable and is chosen from the groups comprising (Cι-C₂o) alkoxy, alkoxy containing (Ci- C₂o) ether groups or (Cι-C₂o) carboxylate. One or two of the R¹, R² or R³ groups may be a (Cι-C₂o) alkyl group.

Suitable ethylenically unsaturated polymerisable groups are for example (meth) acrylates . Suitable chain transfer groups are for example thiols.

In case Y is a chain transfer group the silyl group is attached to one of the polymer chain's two ends after the synthesis.

Examples of ethylenically unsaturated monomers include (Cι-C₆) alkyl (meth) acrylates and styrenes

Examples of suitable compounds according to formula (III) are: vinyl triethoxysilane, vinyl trimethoxysilane, vinyl tri (2-methoxyethoxy) silane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3 -methacryloxypropylmethyldimethoxysilane and, 3-mercaptopropyltri (m) ethoxysilane .

Preferably A is 1 , 3-propylene and Y is a (meth) acrylate group. The compounds containing blocked amine groups are preferably used as crosslinkers in combination with a polymer containing reactive groups that can react with amine groups. The blocked amines are preferably derived from aliphatic amines with a functionality of -> 2. It is also possible to use a polyacrylate containing blocked amine groups as a starting material, while using a compound containing two or more reactive groups that can react with amine groups as a crosslinker. Preferably the reactive group that can react with amine groups is a cyclic carbonate, for example as described in BE-A-1009543 , an α, β-unsaturated ester or ketone or an isocyanate.

In the preparation of a polyester or polyacrylate containing blocked amine groups use can be made of a polyester or polyacrylate containing hydroxyl groups that reacts with, successively, a diisocyanate _ and a blocked dialkylenetriamine or a blocked N- alkylalkylenediamine . Another way of preparing a polyacrylate containing blocked amine groups is by using an ethylenically unsaturated polymerisable compound containing an isocyanate group as a comonomer. The acrylate polymer thus obtained reacts with blocked dialkylenetriamines or blocked N-alkyl- alkylenediamines .

An example of a suitable compound containing isocyanate groups is 3-isopropenyl- (α,α) - dimethylbenzylisocyanate . Suitable examples of a blocked dialkyltriamine are bis-ketimines and bis-aldimines of diethylenetriamine and bis (hexa) methylenetriamine . Suitable examples of blocked N-alkyl-alkylenediamines are the aldimines of N-ethyl-ethylenediamine, N-methyl- ethylenediamine, N- (m) ethyl-1, 3-propanediamine and N- (m) ethyl-1 , 6-hexanediamine . According to a preferred embodiment of the invention the binder composition comprises a polymer, preferably a polyester or a polyacrylate, having cyclic carbonate units and a crosslinker containing moisture latent groups, preferably amine groups. The amount of cyclic carbonate units generally ranges between about 0 , 2 and about 3 and preferably between 0 , 5 and 2 mequivalents/gram.

The invention is also directed to a moisture curable powder paint composition comprising a crystalline (co-) crosslinking compound.

Due to the presence of the crystalline (co-) crosslinking compound improved blocking stability and improved flow are obtained. Crystallization of the compound in the extruded powder paint composition is helpful in preventing blocking of the powder due to coagulation as a result of using an amorphous resin with a Tg close to the stoving temperatures, for example a Tg of between about 30°C and about 40°C. When such a powder is applied to the substrate and heated to flow, the melting of the crystalline compound will lower the melt viscosity of the powder composition, thus enhancing the flow. Preferably the crystalline compound has a melting point of between about 40°C and about 180°C, preferably between 50°C and 150°C in the extruded powder paint composition. According to a further preferred embodiment of the invention the crystalline compound is a crystalline adduct of a compound having two or more isocyanate groups and a compound containing at least one group being able to react with isocyanate and containing at least one hydrolysable group is added to the binder composition comprising the polymer and the crosslinker containing the moisture latent reactive groups. The adduct is preferably equimolar. Examples of suitable hydrolysable compounds are

3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, bis (3-trimethoxysilylpropyl) amine, bis (3-triethoxysilylpropyl) amine, β-mercaptopropyltriethoxysilane and β-mercaptopropyltrimethoxysilane .

Most preferably the adduct is based on hexane diisocyanate and 3-aminopropyltri (m) ethoxysilane . According to another preferred embodiment of the invention the binder composition comprises a) a polymer functionalized with a hydrolysable compound according to formula (II) and b) a cristalline adduct of a compound having two or more isocyanate groups and a compound containing at least one group being able to react with isocyanate and containing at least one hydrolysable group.

Preferably the polymer is a polyester or a polyacrylate. Most preferably the polymer is a hydroxyl functional polyester having a hydroxyl value between 10 and 50 mg KOH/gram resin.

The composition generally comprises between 80-98% by weight of a) and 2-20% by weigth b) .

According to another preferred embodiment of the invention the binder composition comprises a) a copolymer of a polymerisable ethylenically unsaturated monomer and a compound according to formula (III) and b) a cristalline adduct of a compound having two or more isocyanate groups and a compound containing at least one group being able to react with isocyanate and containing at least one hydrolysable group.

Suitable ethylenically unsaturated monomers include (Cx-Cg) alkyl (meth) acrylates and styrenes.

The composition generally comprises between about 80 and 98% by weight of a) and between about 2 and 20% by weight of b)

The preparation of powder paints and the chemical reactions for curing these powder paints into cured coatings are described in general terms in, for example, 'Powder Coatings' (Wiley and Son, 1991) by Misev (pages 44-54, 148 and 225-226) herein by reference .

It is also possible to use additives in the powder coating systems of the invention if desired. The additives preferably contain no water. Examples of additives are pigments, fillers, degassing agents, flow-promoting agents and stabilisers. Pigments are, for example, inorganic pigments, such as titanium dioxide, zinc sulphide, iron oxide and chromium oxide, and also organic pigments such as azo compounds. Fillers comprise for example metal oxides, silicates, carbonates and sulphates.^' Other additives that may be used are stabilisers such as primary and/or secondary antioxidants and UV-stabilisers such as quinones, (sterically hindered) phenolic compounds, phosphonites, phosphites, thioethers and HALS compounds (hindered amine light stabilisers) . Examples of degassing agents are benzoin and cyclohexane dimethanol bisbenzoate. The plasticizers include, for example, polyalkylacrylates, fluorohydrocarbons and silicon oils. Other additives are for example additives to improve triboelectrification, such as sterically hindered tertiary amines.

Powder paints according to the invention can be applied in the usual manner, for example, by electrostatically spraying the powder onto an earthed substrate and curing the coating by exposing it to heat at a suitable temperature for a sufficient length of time. The applied powder can for example be heated in a gas oven, an electric oven or with the aid of infrared radiation. Preferably the powder or the coating will absorb as little moisture as possible during the flow stage.

Thermosetting coatings of powder paint (coating) compositions intended for industrial applications are described further in general terms in Misev, pp. 141-173 (1991) .

Compositions according to the present invention can be used in powder coatings intended for use on metal, wooden and plastic substrates. Examples are industrial general -purpose top coatings, coatings for machinery and also cans, household and other small equipment. The coatings are also very suitable for use in the automotive industry for coating external and/or internal parts of vehicles such as cars.

The invention will be elucidated with reference to the following, non-limiting examples.

Example I Moisture-curing powder coating based on a cyclic carbonate-functional resin and a blocked amine crosslinker

Step l: preparation of MiBK-blocked DAB- (PA) _± 52 g of N,N,N' ,N' -tetrakis (3-aminopropyl) -

1,4-diaminobutane (DAB-(PA) from DSM), 150 g of methyl isobutyl ketone (MiBK) and 200 ml of toluene were introduced into a 500-ml round-bottomed flask fitted with a stirrer, a thermometer and a Dean-Stark distillation still head. After 4 hours' reaction at

120°C (boiling point of azeotropic water/toluene) 12 ml of water had been collected. The reaction was stopped at this point and the excess toluene and MiBK were removed via a Rotavapor. 58.5 g of pure product was obtained.

Step 2: conversion of αlycidyl methacrylate into cyclic carbonate (GMACC)

93 g of glycidyl methacrylate and 2 g of potassium iodide were dissolved in 100 g of methoxypropanol . At a temperature of 120°C C0₂ was passed through via a gas lead-through tube. The reaction was titrimetrically followed via the number of epoxide end groups. The reaction was ended after 15 hours' reaction, when the epoxy number had dropped from 3.5 meq/g to 0.06 meq/g. After further processing via extraction 120 g of product with a purity of >98% was obtained.

Step 3: preparation of a cyclic carbonate-functional polyacrylate 3.26 parts of toluene were heated to 110°C in a 2 -litre reactor. In 3 hours, a mixture of 4.15 parts of methyl methacrylate, 0.47 parts of butyl acrylate, 0.88 parts of GMACC obtained according to Step 2 and 0.22 parts of Luperox 575™ were added drop by drop to this. After all the monomers had been added 0.04 parts of Luperox 575™ were used for further initiation. After 2 hours' reaction at 130°C, of which half an hour in a vacuum (removal of toluene) , the product was poured out. The product was yellow, had a Tg of 68°C (determined via method TM 2076 of DSM Resins) and a viscosity (E/165, determined via method TM2005, DSM Resins) of 350-400P.

Step 4: preparation of a clear-coat binder composition based on the products obtained in Steps 1 and 3 350 g of cyclic carbonate-functional polyacrylate (obtained according to Step 3) was mixed with 2.3 g of plasticizer (BYK 361), 3 g of benzoin and 56 g of MiBK-blocked DAB (PA) ₄ (obtained according to Step 1) using a Buss kneader at 100°C, extruded using a PRISM twin-screw extruder at 110°C, ground and sieved to <90 um. The powder was electrostatically sprayed. Good flow behaviour was obtained after the powder had been melted at 110°C for 10 minutes (visual inspection) . No setting had yet taken place after the melting; acetone resistance 12 ADR determined via acetone test in which an acetone resistance of >100 ADR is regarded as complete setting, 25 -100 ADR as partial setting and <25 ADR as no setting) . After the coated test panels had been in a climate-controlled oven at 90°C and 90 % relative humidity for 4 hours the coating was found to have set completely (acetone resistance >100 ADR) .

Example II: moisture-curing powder coating based on an alkoxysilane-functional resin

Step 1: drying of polyester powder-coating resin

A polyester resin based on isophthalic acid and neopentyl glycol with a hydroxyl value of 30 g of KOH/g of resin, an acid number of < 1 mg of KOH/g of resin, a functionality of 2, a Tg of 53°C (method TM 2076, DSM Resins) , Mn 4500, Mw/Mn 2.3 and a water content of 3 mg/g of resin was melted in a heated glass reactor and heated to 160°C. 1 ml of p-xylene was added, which was subsequently evaporated in a vacuum until the resin no longer contained any volatile compounds. This procedure was repeated four times. After this treatment the resin contained < 0.2 mg of water/g of resin; the other properties were as those of the basic resin.

Step 2: preparation of a triethoxysilane-functional polyester powder-coating resin

1.0 g of dibutyl tin diacetate was added as a catalyst to the polyester resin dried in step 1 (500 g) in melted condition in the reactor (160°C) , in an inert atmosphere, followed by 68 g of 3- isocyanatopropyltriethoxysilane. After 30 minutes' reaction at 160°C the resin was poured out in an inert atmosphere and cooled with the exclusion of damp air. The resin's characteristics: Tg: 38°C (method TM 2076, DSM Resins), Mn: 5600, Mw/Mn : 2.7 and - viscosity (E/165, method TM2005, DSM Resins) : 150- 180P.

Step 3 : preparation of a clear-coat binder composition based on products from Steps 1 and 2 3 g of BYK 361 (flow-promoting agent) and 1.5 g of benzoin (degassing agent) were added to 569 grams of the triethoxysilane-functional resin obtained in Step 2 in melted condition in the reactor at 160°C, in an inert atmosphere. The resin was poured out in an inert atmosphere and cooled with the exclusion of damp air. After the resin had been crushed, it was ground and sieved (<90 μ) with the exclusion of damp air. After the powder had been exposed to a controlled climate of 23°C and 50% relative humidity for 2 weeks no significant increase in the melt viscosity was found to have occurred at 165° C: 150-210P (E/165 method TM2005, DSM Resins) .

The powder was electrostatically sprayed onto aluminium test panels. Very good flow behaviour was obtained after the powder had been melted at 120°C for

15 minutes (visual inspection) . No setting had yet taken place after the melting (acetone resistance: 14 ADR) . After the coated test panels had been in a climate-controlled oven at 90°C and 90 % relative humidity for 4 hours the coating proved to have set completely (acetone resistance: >100 ADR), the impact resistance was 60 inch pound (reverse impact resistance) and the Kδnig hardness was 255 seconds. The coating had a very good appearance, was very transparent and had a good gloss .

Claims

C L A I M S

1. A thermally stable, moisture-curable powder-paint binder composition having a glass transition temperature of >.30┬░C or a melting temperature of ΓëÑ. 30┬░C comprising a polymer and optionally a crosslinker wherein at least one of the polymer and/or the crosslinkers contains a moisture-latent reactive group.

2. The composition according to Claim 1, characterised in that the polymer is a saturated polyester, an unsaturated polyester, polyacrylate, polyurethane, polycarbonate, polybutadiene, polystyrene, polysiloxane or a copolymer hereof.

3. The composition according to Claim 2, characterised in that the polymer is a saturated polyester or a polyacrylate.

4. The composition according to any one of Claims 1-

3, characterised in that the moisture-latent reactive group of the polymer is a moisture-latent amine group, a hydrolysable silyl group, a moisture-latent alcohol, a moisture-latent acid, a moisture-latent aldehyde group or a moisture- latent ketone group.

5. The composition according to any one of Claims 1-

4, characterised in that the moisture-latent reactive group of the crosslinker is a moisture- latent amine group, a hydrolysable silyl group, a moisture-latent alcohol, a moisture-latent acid, a moisture-latent aldehyde group or a moisture- latent ketone group.

6. The composition according to any one of Claim 4-5, characterised in that the moisture-latent reactive group is a moisture-latent amine group or a hydrolysable silyl group.

7. The composition according to Claim 6, characterised in that the moisture-latent amine group is a ketimine, aldimine, oxazolidine or silazane group.

8. The composition according to Claim 6, characterised in that the hydrolysable silyl group is a silicon-containing reactive group according to formula (I) :

R¹

where at least one of the R¹, R² or R³ groups is hydrolysable and is chosen from the group comprising (C╬╣-C₂o) alkoxy, alkoxy containing (Ci- C₂o) ether groups or (C1-C20) carboxylate and where A is a non-hydrolysable (C╧ç-C╬╣o) alkyl radical or a (C3.-C20) alkoxy radical.

9. A powder paint composition according to any one of Claims 1-8 comprising a crystalline

(co-) crosslinking compound.

10. The composition according to Claim 9 characterized in that the crystalline crosslinking compound is an adduct of a compound having two or more isocyanate groups and a compound containing at least one group being able to react with isocyanate and containing at least one hydrolysable group.

11. The composition according to any one of Claims 9- 10, comprising a) a polymer functionalised with a hydrolysable compound according to formula (II)

R¹

X-A- Si R' (ID

R^J

where X is a reactive group that can react with hydroxyl, acid or ester groups, - where A is an organic radical, optionally substituted, containing (1-20) carbon atoms and where at least one of the R¹, R² or R³ groups is hydrolysable and is chosen from the groups comprising (Ci-C2o) alkoxy, alkoxy containing

(C1-C20) ether groups or (C1-C20) carboxylate and b) the adduct of a compound having two or more isocyanate groups and a compound containing at least one group being able to react with isocyanate and containing at least one hydrolysable group.

12. The composition according to Claim 11, characterized in that A = 1, 3-propylene, X = isocyanate and the polymer is a hydroxy functional polyester or a hydroxy functional polyacrylate.

13. The composition according to any one of Claims 9- 10 comprising a) a copolymer of polymerisable ethylenically unsaturated monomers and the compound according to formula (III)

R¹

where y is an ethylenically unsaturated polymerisable group or a chain transfer group , - where A is an organic radical, optionally substituted, that contains (1-20) carbon atoms and where at least one of the R¹, R² or R³ groups is hydrolysable and is chosen from the groups comprising (C₁-C₂₀) alkoxy, alkoxy containing (C╬╣-C₂o) ether groups or (C╬╣-C₂o) carboxylate and b) the adduct of a compound having two or more isocyanate groups and a compound containing at least one group being able to react with isocyanate and containing at least one hydrolysable group.

14. The composition according to Claim 12, characterized in that A is 1, 3-propylene and Y is a (meth) acrylate derivative.

15. A composition according to any one of Claims 1-14 characterized in that the binder composition comprises a polymer having cyclic carbonate units,

16. A process for obtaining a partially or wholly coated substrate comprising applying a powder paint composition comprising the composition according to any one of Claims 1-15 to a substrate and subsequently exposing the moisture-latent reactive groups to moisture after the flow stage thereby curing said powder paint .

17. A powder paint composition comprising the moisture curable composition according to any one of Claims 1-15 and further comprising one or more additives selected from the group consisting of pigments, fillers, degassing agents, flow-promoting agents and stabilizers.

18. A partly or wholly coated substrate, wherein the coating has wholly been obtained from a powder paint according to Claim 17 or via the process according to Claim 16.