WO2009065899A1

WO2009065899A1 - Polymer composition

Info

Publication number: WO2009065899A1
Application number: PCT/EP2008/065927
Authority: WO
Inventors: Jacobus Loontjens; Konstantinos Diakoumakos
Original assignee: Dsm Ip Assets B.V.
Priority date: 2007-11-23
Filing date: 2008-11-20
Publication date: 2009-05-28

Abstract

The present invention relates to a composition comprising at least one polymer that comprises a functional group that reversibly reacts with isocyanate. The reversibility allows for damage to the coatings to be repaired.

Description

POLYMER COMPOSITION

The present invention relates to a composition comprising at least one polymer that comprises at least one functional group that reversibly reacts with isocyanate. The invention further relates to a process for preparing such a composition, a coating comprising such a composition, a process for coating a substrate and a coated substrate.

Conventional powder coatings offer a number of advantages over other coating systems. Typically, the powder coating composition comprises finely ground particles of pigment and binder, which are usually applied electrostatically to the substrate and then cured under heat. The binder comprises resin and crosslinker that react irreversibly to form a coating.

It would be advantageous to have a system that allowed for repair of scratches, scrapes, nicks, and other surface damage. Furthermore, it is advantageous for powder coatings systems to have good flow properties.

Powder coatings are generally known in the art and are for example described by Misev T.A. in Powder Coatings, Chemistry and Technology, John Wiley and Sons, Chichester, 1991.

The powder coating according to the invention may have improved optical properties, mechanical properties, chemical resistance against solvents (for example xylene, acetone, alcohols), moisture resistance, thermal resistance and outdoor resistance.

Optical properties include but are not limited to appearance properties, for example colour, gloss, light diffusion by a matt surface, transparency, translucency and opacity, the later of which is also referred to as hiding power.

Mechanical properties include but are not limited to toughness, strength, impact resistance, scratch resistance, flexibility, stiffness and abrasion resistance.

The present invention relates to a composition, preferably a coating composition, more preferably a powder coating composition, comprising at least one polymer that comprises a functional group that reversibly reacts with isocyanate to form a reversible network comprising a urethane, a urea or a combination thereof. The reversibility allows for damage to the coatings to be repaired. The present compositions may also have good properties such as flow and/or appearance. The term polymer and resin are used interchangeably herein to indicate the compound comprising a functional group that reversibly reacts with isocyanate.

The compositions according to the invention comprise at least one polymer. The polymer is preferably suitable for use in powder coating compositions or composite resin compositions. The polymer should comprise at least one functional group that reversibly reacts with isocyanate. Preferably the functional group has the general formula:

-A-X-H

wherein A is an electron withdrawing group, X is selected from O, S, N, NH, C, CH and CH₂.

As used herein, "electron withdrawing group" refers to an organic moiety comprising atoms that are more electron negative than aliphatic alkyl groups, in particular a methyl group (-CH₃) Preferably the functional group(s) is/are selected from:

and combinations thereof. Wherein Z is selected from N, O, F, Cl, Br, and I and R is selected from H, CH₃, OCH₃, COOCH₃, F, Cl, Br, I and NO₂.

As used herein, "isocyanate" refers to a compound having a NCO functionality, an NCS functionality, or a combination thereof.

As used herein, "urethane" refers to a -NH-C(=O)-X- group or a -NH-C(=S)-X- group or a combination of such groups. As used herein, "urea" refers to a -NH-C(=0)-X- group or a -NH-C(=S)-X- group or a combination of such groups, wherein X= NH.

The isocyanate and the functional group of the polymer should have a dissociation constant (Kd) of 1x10^"4 or greater, preferably 9x10^"4 or greater, preferably 26x10^"4 or greater, preferably 0.25 or greater, preferably 0.5 or greater, more preferably 0.75 or greater at a temperature of 200⁰C or less, preferably 190⁰C or less, preferably 175°C or less. Preferably the isocyanate does not significantly dissociate from the functional group at a temperature of 25°C or less, preferably 30⁰C or less, more preferably 45°C or less. The Kd may be calculated in the following manner:

_{Kd = ±}NCY_]tXH_L [-N(H)C(Y)X-] wherein Y is O or S and wherein [-NCY ], [-XH ] and [-N(H)C(Y)X-] are the mol/l concentrations of isocyanate, the functional group of the polymer and of the urethane or urea respectively.

Information on the reversibility of a urethane or urea crosslink may be obtained from studies of the rheological properties of the compositions such as dynamic mechanical analysis (DMA) measurements of a storage modulus (G'), a loss modulus (G"), a tan delta and/or a complex viscosity as a function of a temperature, or a time, or a frequency or combination thereof.

Preferably the dissociation constant of a compound is determined using hot-stage Fourier transform Infrared Spectroscopy as described in Journal of Polymer Science: Part A: Polymer Chemistry DOI: 10.1002/pola.21924, page 1557- 1570 by G. Sankar and S. Nasar. The dissociation constant may be determined by first recording a series of FTIR spectra of the compound at increasing temperatures until the height of the isocyanate absorption peak at about 2200 cm^"1 doesn't increase any more. This height is herein referred to as a maximum 2200 cm^"1 isocyanate absorbance. When the height of the isocyanate absorption peak at about 2200 cm^"1 doesn't increase any more with increasing temperature it is assumed that the maximum dissociation of the compound has been reached. The dissociation constant Kd at a certain temperature may be then determined by first determining the peak height (absorbance) of the isocyanate absorption peak at about 2200 cm^"1 at that certain - A -

temperature and thereafter expressed this peak height as a percentage of the maximum 2200 cm^"1 isocyanate absorbance, giving a measure of the isocyanate concentration. From this isocyanate concentration the Kd may be determined.

Preferably the isocyanate-reactive functional group of the polymer has a pKa 18 or less, preferably 16 or less, more preferably 15 or less, preferably 14 or less, even more preferably 13 or less at 25⁰C in water. Preferably the pKa is 1 or greater, preferably 5 or greater at 25⁰C in water. Measuring a pKa is within the skills of the person skilled in the art. Alternatively the skilled person may look up the pKa in a handbook such as Organic Chemistry, 3^rd edition, International Student Edition, J. B. Hendrickson, DJ. Cram, G. S. Hammons, Mc Graw-Hill Kogakusha Ltd, Tokyo , pages 303-307.

If the solubility of the compound is not sufficient to determine the pKa in water the skilled person knows how to solve this e.g. by performing the measurement in DMSO, acetonitrile, a mixture of dioxane/water or a mixture of methanol water.

In the polymer composition according to the invention the at least one polymer comprises a functional group that reversibly reacts with isocyanate. In one aspect of the invention the polymer as such comprises the functional group that reversibly reacts with isocyanate. In another aspect the of the invention the polymer comprising the functional group that reversibly reacts with isocyanate is obtained by reacting the polymer with a reactant to form the polymer comprising the functional group that reversibly reacts with isocyanate.

Examples of suitable polymers include, but are not limited to, polyesters, polycarbonates, polyethers, polyurethanes, epoxy resins, acrylic resins, phenolic resins, poly(ester-amide)s, polyamide, polyimide, poly(ester-imide), silicones, poly(ester-siloxane)s and combinations thereof.

The compositions herein comprises a polymer having a group that is capable of reversibly reacting with an isocyanate but they may additionally comprise other polymers that may utilize alternative crosslinking mechanisms.

The number average molecular weight (Mn in g/mol) of the resin is preferably between about 1 ,000 and about 20,000, preferably between about 1 ,200 and about 10,000, preferably between about 1 ,000 and about 7,000, more preferably between about 1 ,400 and about 6,000. Mn values may be measured using size exclusion chromatography (SEC). The resin may be amorphous, crystalline or semi-crystalline. An amorphous resin has a Tg but lacks a Tm. A crystalline resin has a Tm but lacks a Tg whilst a semi-crystalline resin has at least one Tg and at least one Tm. Preferably the resin is an amorphous solid at room temperature, preferably 25⁰C. The resin preferably has a viscosity lower than 300 Pa. s, preferably lower than 200 Pa. s, more preferably lower than 150 Pa. s (measured at 160⁰C, Rheometrics CP 5).

The glass transition temperature (T₉) of the resin is preferably greater than about -20 ⁰C , preferably greater than about -10⁰C, preferably greater than about 5°C, preferably greater than about 20⁰C, more preferably greater than about 35⁰C, even more preferably greater than about 45⁰C. The T₉ of the resin is preferably less than about 300⁰C, preferably less than about 250⁰C, preferably less than about 200⁰C, preferably less than about 100⁰C, more preferably less than about 85⁰C, even more preferably less than about 8O⁰C. The T₉ may be determined by differential scanning calorimetry (DSC) at a heating rate of 5 °C/min.

The resin itself can be prepared in ways known to the man skilled in the art, see for example "Powder Coatings, Chemistry and Technology" by T.A.Misev, John Wiley and Sons, 1991 , the whole book in general and Chapters 2 and 3 in particular, which are hereby incorporated by reference. More details about thermosetting power coatings may be found in chapter 3.

Preferably the resins for use herein are selected from polyesters, polycarbonates, polyethers, and combinations thereof. More preferred are polyesters. The polyesters can be fully saturated or bear some degree of unsaturation and when used in coating compositions may also be mixtures thereof. Suitable polyesters may be based for example on a condensation reaction between a linear aliphatic, branched aliphatic and cyclo-aliphatic polyalcohols and an aliphatic, cyclo-aliphatic and/or aromatic poly carboxylic acids or its anhydrides.

Polyesters for use herein can comprise polycarboxylic acid units of, for example, isophthalic acid, terephthalic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-oxybisbenzoic acid, 3,6-dichloro phthalic acid, tetrachloro phthalic acid, tetrahydro phthalic acid, trimellitic acid, pyromellitic acid, hexahydro terephthalic acid (cyclohexane dicarboxylic acid), hexachloro endomethylene tetrahydro phthalic acid, phthalic acid, azelaic acid, sebacic acid, decane dicarboxylic acid, adipic acid, succinic acid, maleic acid, fumaric acid, stearic acid and mixtures thereof. These acids may be used as such, or, in so far as available as their anhydrides, acid chlorides, and/or lower alkyl esters. Preferably, the polyester is based on at least one of isophthalic acid and/or terephthalic acid. Trifunctional or higher functional acids may be used also. Examples of suitable such acids include trimellitic acid or pyromellitic acid. These tri- or higher functional acids may be used to obtain branched polyesters.

Hydroxy carboxylic acids and/or optionally lactones and/or optionally lactides may also be used, for example, 12-hydroxy stearic acid, hydroxy pivalic acid and ε-caprolactone.

Monocarboxylic acids may also be used if desired. Examples of these acids are benzoic acid, tert.-butyl benzoic acid, hexahydro benzoic acid and saturated aliphatic monocarboxylic acids.

Useful polyalcohols, in particular diols, reactable with the carboxylic acids to obtain the polyester include aliphatic diols. Examples are 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-(4hydroxy-cyclohexyl)-propane (hydrogenated bisphenol-A), 1 ,4-dimethylolcyclohexane, diethylene glycol, dipropylene glycol, 2,2-bis[4-(2-hydroxy ethoxy)-phenyl] propane, the hydroxy pivalic ester of neopentyl glycol, 2-ethyl, 2-butyl propanediol-1 ,3 (butylethylpropane diol), 2-ethyl, 2-methyl propanediol-1 ,3 (ethylmethylpropane diol) and 2-methylpropanediol-1 ,3 (MP-Diol).

Tri- or higher functional alcohols may be used in order to obtain branched polyesters. Examples of such suitable polyols include glycerol, hexanetriol, trimethylol ethane, trimethylol propane, tris-(2-hydroxyethyl)-isocyanurate, penta erythritol and sorbitol. The polyester may be prepared according to conventional procedures by esterification or transesterification, optionally in the presence of customary esterifi cation catalysts for example dibutyltin oxide or tetrabutyl titanate. Alternatively, polyesters may also be prepared via a process which involves enzymes (enzymatic catalysis). The resin herein comprises a functional group that reversibly reacts with isocyanate. Preferably the group is selected from a compound containing phenol, caprolactam, imidazole, triazol, hydroxyl imines, malonic esters, and combinations thereof.

The present compositions comprise an isocyanate crosslinker. Examples of suitable isocyanates include hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), caprolactam blocked IPDI derivatives, uretdione of IPDI, TMXDI (tetramethylxylene diisocyanate), methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), thioisocyanates, derivatives, dimers, trimers, oligomers, and combinations thereof. Preferably the isocyanate is selected from blocked isocyanates, polymeric isocyanates, and combinations thereof. Preferred are blocked isocyanates such as caprolactam blocked IPDI derivatives, blocked hexamethylene diisocyanate (HDI), blocked isophorone diisocyanate (IPDI), blocked uretidione of IPDI, blocked TMXDI (tetramethylxylene diisocyanate), blocked methylene diphenyl diisocyanate (MDI), blocked toluene diisocyanate (TDI) and blocked thioisocyanates. In addition to the isocyanate crosslinker the compositions herein may comprise other crosslinkers. Any crosslinker or mixture of crosslinkers that is suitable for use (i.e. reactive) with the resin may be used herein. Various types of cross-linkers or mixtures of cross-linkers may be used herein. Classes of suitable crosslinkers include compounds bearing oxirane rings, epoxy resins and epoxy compounds such as bisphenol-A and bisphenol-F epoxy resins, Araldite®GT 7004, Araldite® PT 910, Araldite® PT 912, Epicote® 1002, Epikote® 828, DER™ 663, polyamides, (blocked) isocyanates, amino resins, polycarboxylic acids, acid anhydrides, polyphenols, betahydroxyalkylamides such as Primid®-like compounds, and combinations thereof. Examples of suitable compounds include polyphenols (for example polyphenols of the resol or novolac type), amino resins (for example alkylated melamine or benzoguanimine resins), triglycidylisocyanurate (TGIC), alkylated melamine such as hexamethoxy-methylmelamine (HMMM), triglycidyl trimillitate, epoxidized vegetable oil such as epoxidized linseed oil, benzoguanamine (derivative), and combinations thereof. It may be necessary to cure the composition comprising polymer and crosslinker in order to form the coating. Preferably the compositions herein are thermally cured. Other methods of curing include electromagnetic radiation, such as for example UV- or electron beam curing. Depending on the nature of the functional groups it is also possible to use two (dual-cure) or more types of curing processes e.g. radical cure.

The coatings herein preferably have a thickness of 400μm or less, more preferably 300μm or less, even more preferably 150μm or less.

The coatings herein preferably have a gloss at 20° of 60 or better i.e. more, more preferably of 70 or better i.e. more, more preferably of 80 or better i.e. more (as measured by Byk Gardner haze-gloss meter at a layer thickness of 60μm).

The coatings herein preferably have a gloss at 60° of 10 or better i.e. more, preferably 15 or more, preferably 20 or more, preferably 50 or more (as measured by Byk Gardner haze-gloss meter at a layer thickness of 60μm). The coatings herein preferably have a gloss at 85° of 2 or better i.e. more, preferably 5 or more, preferably 7 or more (as measured by Byk Gardner haze- gloss meter at a layer thickness of 60μm).

The coatings herein preferably have a haze of 250 or less, more preferably of 150 or less, more preferably of 100 or less (as measured by Byk Gardner haze-gloss meter at a layer thickness of 60μm).

The powder coating compositions herein generally comprises resin, an isocyanate crosslinker, and pigment and/or filler. Additionally other components can be added to the powder coating composition, for example flow control agents, antioxidants, anti-bridging agents, catalysts, fillers, dispersants, light-stabilizers e.g. quinones, (sterically hindered) phenolic compounds, phophonites, phosphites, thioethers, HALS (hindered amine light stabilizers), waxes, biocides, and degassing agents e.g. benzoine, cyclohexane dimethanol bisbenzoate. Suitable fillers are fore example metal oxides, silicates, carbonates, and sulphonates.

The coating compositions herein may be in any suitable form including solvent-borne compositions and powder coating compositions. Preferably the compositions herein are non-aqueous. Preferably the compositions are powder coating compositions. The present powder coating compositions are preferably solid compositions that are suitable for application as a powder onto a substrate. With solid is here and hereinafter meant a compound that is solid at room temperature, preferably at 25⁰C, at atmospheric pressure. The glass temperature (Tg) of the powder coating composition preferably lies at or above 20⁰C. Preferably the Tg lies above 35°C, more preferably above 45°C.

The present invention also relates to a process for the preparation of a coating composition. The process may be any process suitable for producing a coating composition. Preferably the process comprises the steps:

(a) providing a polymer as described herein;

(b) mixing the resin with pigment and crosslinker.

The present invention also relates to a process of applying a coating to a substrate wherein the present compositions, comprising polymer, crosslinker, and preferably pigment, are applied to a substrate and cured.

The present invention also relates to a substrate fully or partly coated with a coating composition, preferably powder coating composition, comprising polymer, crosslinker, and preferably pigment, as described herein. The substrate may be a heat-sensitive substrate. Examples of heat sensitive substrates are plastic, textile, leather, substrates comprising cellulose fibres, paper, cardboard, cork, wood such as solid wood, veneer, chip wood and wood composite material, for example particle board, high, medium or low density fibre board, plywood and other substrates that contain a significant amount of wood. Examples of plastic substrates include, unsaturated polyester based compositions, ABS, melamine-formaldehyde resins, polyethylene, polypropylene, polyamide, polyimide, poly(amide-co-imide) and polyethyleneterephthalate. The invention is also suitable for heat resistant substrates, such as for example metal, aluminium, copper, (galvanized) steel, cast iron, other alloys, glass, ceramic and bricks. The present invention further relates to the use of a binder comprising a thermo-reversible covalent bond between the resin and the crosslinker in a coating composition wherein the dissociation constant (Kd) is 1x10^"4 or greater preferably 9x10^"4 or greater, preferably 26x10^"4 or greater, preferably 0.25 or greater, preferably 0.5 or greater, more preferably 0.75 or greater at a temperature of 200⁰C or less, preferably 190⁰C or less, preferably 175°C or less.

As used herein, a thermo-reversible covalent bond refers to a chemical bond which dissociates and associates i.e. is reversible, the extent of which is determined by temperature.

The present invention further relates to a process for manufacturing a coated substrate comprising the steps, a) providing a substrate, b) optionally pre-treating and/or pre-heating the substrate, c) thereafter applying the coating composition according to the invention, d) thereafter curing the coating composition e) optionally applying a second cure step.

The process according to the invention is preferably used without the use of step b) and/ or e). Preferably the network formation of the compositions herein occurs as a result of a thermal treatment of the composition. Other methods of curing include electromagnetic radiation, such as for example UV- or electron beam curing. Depending on the nature of the functional groups it is also possible to use two (dual- cure) or more types of curing processes e.g. radical cure.

The process for manufacturing a coated substrate according to the invention can be used in various temperature regimes. The man skilled in the art can easily determine which temperature regime is most suitable for his application. The man skilled in the art also knows, or can easily determine, for how long the temperature should be maintained to obtain a satisfactory coating.

The invention also relates to a process for repairing a coating according to the invention comprising the steps: providing a substrate fully or partly coated with a coating according to the invention, thereafter heating the coating .

Usually thereafter the coating is cooled, preferably to room temperature, preferably 25⁰C.

The invention also relates to a process for improving the appearance of a coating according to the invention comprising the steps: providing a substrate fully or partly coated with a coating according to the invention, thereafter heating the coating .

The present invention has utility in the coatings field, preferably in the powder coating field. However, the underlining inventive concept may also be useful in other fields where repair of a polymeric networks or improvement of flow or of appearance would be advantageous such as adhesives, composite materials, and the like. For example, adhesive compositions comprising at least one polymer comprising a functional group that reversibly reacts with isocyanate and at least one isocyanate; characterised in that the dissociation constant of the isocyanate and the functional group is IxIO^"4 or greater, preferably 9x10^"4 or greater, preferably 26x10^"4 or greater, preferably 0.25 or greater, preferably 0.5 or greater, preferably 0.75 or greater at a temperature of 200⁰C or less, preferably 190⁰C or less, preferably 175°C or less. Or, adhesive compositions comprising at least one polymer comprising a functional group that reversibly reacts with isocyanate and at least one isocyanate; characterised in that the functional group has a pKa of 18 or less preferably 16 or less, preferably 15 or less, preferably 14 or less, more preferably 13 or less at 25⁰C in water. Preferably the pKa is 1 or greater, preferably 5 or greater at 25⁰C in water. The substrate may be coated with a primer coating layer using the composition according to the invention which is applied directly to the, optionally pretreated, substrate. The substrate may comprise a further coating layer comprising the coating composition according to the invention, such as a coating layer applied on top of another coating layer. The further coating layer may be a top coating layer.

A substrate may also be provided with more than one coating layer comprising the composition according to the invention, e.g. a primer coating layer and a top coating layer manufactured using the coating composition according to the invention. In an aspect of the invention the composition is a composite resin composition. The composite resin is reinforced with reinforcement fibres, often but not necessarily build up in layers of reinforcement fibers and composite resin, and/or filled with fillers like for example wood, paper, clay, talcum, etc. In this aspect a three dimension network with a thickness of at least 0.2 mm may be manufactured from the composite resin composition according to the invention. The three dimension network may for example be a free standing article. It has been found that curing a resin composition comprising reinforcement fibres and a polymer that comprises a functional group that reversibly reacts with isocyanate may result in reduced internal stress, that is caused by the polymerization shrinkage, in the obtained composite article and/or repair of micro cracks that may result from internal stresses. It has further been found that the reversibility allows for repair of delamination between different composite layers.

In an aspect of the invention the composition is a gel coat composition. A gel coat composition is primarily used for contact molding (hand or spray lay up). The gel coat provides a molded-in finished surface, and a weather and wear resistant coating over usually a glass reinforced composite resin. Typically the gel coat is formulated with thixotropic agents, fillers for flow properties, pigments to yield the desired color and additives with specific quality such as gel time and cure.

The polymer of the composite resin composition or the gel coat composition is preferably an unsaturated polyester resin and/or a vinyl ester resin.

The unsaturated polyester resin or vinyl ester resin may be any such resin as is known to the skilled man. Examples thereof can be found in a review article of M. Malik et al. in J. M. S. - Rev. Macromol. Chem. Phys., C40 (2&3), p.139-165 (2000). The authors describe a classification of such resins - on the basis of their structure - in five groups: (1 ) ortho resins; (2) iso- resins; (3) bisphenol-A-fumarates; (4) chlorendics, and (5) vinyl ester resins. Besides these classes of resins also so-called pure maleic resins and so-called dicyclopentadiene (DCPD) resins can be distinguished. Examples of suitable unsaturated polyester or vinyl ester resins to be used as basic resin systems in the resins of the present invention are, subdivided in the categories as classified by Malik et al., cited above.

(1 ) Ortho-resins: these are based on phthalic anhydride, maleic anhydride, or fumaric acid and glycols, such as 1 ,2-propylene glycol, ethylene glycol, diethylene glycol, triethylene glycol, 1 ,3-propylene glycol, dipropylene glycol, tripropylene glycol, neopentyl glycol or hydrogenated bisphenol-A. Commonly the ones derived from 1 ,2-propylene glycol are used in combination with a reactive diluent such as styrene.

(2) Iso-resins: these are prepared from isophthalic acid, maleic anhydride or fumaric acid, and glycols. These resins may contain higher proportions of reactive diluent than the ortho resins. (3) Bisphenol-A-fumarates: these are based on ethoxylated bisphenol-A and fumaric acid.

(4) Chlorendics: are resins prepared from chlorine/bromine containing anhydrides or phenols in the preparation of the unsaturated polyester resins.

(5) Vinyl ester resins: these are resins, which are mostly used because of their because of their hydrolytic resistance and excellent mechanical properties, as well as for their low styrene emission, are having unsaturated sites only in the terminal position, introduced by reaction of epoxy resins (e.g. diglycidyl ether of bisphenol-A, epoxies of the phenol-novolac type, or epoxies based on tetrabromobisphenol-A) with (meth)acrylic acid. Instead of (meth)acrylic acid also (meth)acrylamide may be used.

All of these resins, as can suitably used in the context of the present invention, may be modified according to methods known to the skilled man, e.g. for achieving lower acid number, hydroxyl number or anhydride number, or for becoming more flexible due to insertion of flexible units in the backbone, etc. The class of DCPD- resins is obtained either by modification of any of the above resin types by Diels-Alder reaction with cyclopentadiene, or they are obtained alternatively by first reacting maleic acid with dicyclopentadiene, followed by the resin manufacture as shown above.

The composition comprising the unsaturated polyester and/or vinyl ester resin preferably further comprises a reactive diluent. The reactive diluent can be chosen from all diluents capable of reacting with the ethylenic unsaturation of the resin, including vinyl monomers such as, for instance, vinyl esters, vinyl ethers, aromatic vinyl compounds, vinyl nitriles, acrylates or methacrylates. The amount is preferably at least 5 wt % and generally at most 80 wt % based on the unsaturated polyester resin and/or vinyl ester resin. Examples are styrene, α-methylstyrene, p-methyl-styrene, p-tertiary butylstyrene, vinyl toluene and (meth)acrylates such as methyl methacrylate (MMA), hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA), vinyl ethers, vinyl esters, butanediol dimethacrylate (BDDMA), triethylene glycol dimethacrylate (TEGDMA), trimethylolpropane trimethacryate (TMPTMA), phenoxyethyl methacrylate (PEMA). Preferably, the reactive diluent is a methacrylate and/or styrene. The composition comprising the unsaturated polyester and/or vinyl ester resin is preferably cured by using a radical initiator. Suitable radical initiators can be selected from peroxides, such as hydroperoxides, ketone peroxides and peresters, and from azo compounds like for example azo isobutyronitril (AIBN). All peroxides known to the skilled man for being used in curing of unsaturated polyester resins and vinyl ester resins can be used. Such peroxides include organic and inorganic peroxides, whether solid or liquid; also hydrogen peroxide may be applied. Examples are benzoyl peroxide, ditertiary butyl peroxide, cyclohexanone peroxide, tertiary butyl perbenzoate and tertiary butyl peroctoate, as well as photoinitiators sensitive to visible light or ultraviolet-sensitive photoinitiators. Examples of suitable peroxides are, for instance, peroxy carbonates (of the formula -OC(O)O-), peroxyesters (of the formula -C(O)OO-), diacylperoxides (of the formula - C(O)OOC(O)-), dialkylperoxides (of the formula -00-), etc. They can also be oligomeric or polymeric in nature. An extensive series of examples of suitable peroxides can be found, for instance, in US 2002/0091214-A1 , paragraph [0018]. The skilled man can easily obtain information about the peroxides and the precautions to be taken in handling the peroxides in the instructions as given by the peroxide producers.

The radical initiator is preferably an organic peroxide, or a combination of two or more organic peroxides. Examples of suitable organic peroxides are: tertiary alkyl hydroperoxides (such as, for instance, t-butyl hydroperoxide), and other hydroperoxides (such as, for instance, cumene hydroperoxide), peroxyesters or peracids (such as, for instance, t-butyl peresters, benzoyl peroxide, peracetates and perbenzoates, lauryl peroxide, including (di)peroxyesters), perethers (such as, for instance, peroxy diethyl ether), perketones (such as, for instance, methyl ethyl ketone peroxide). Often the organic peroxides used as curing agent are tertiary peresters or tertiary hydroperoxides, i.e. peroxy compounds having tertiary carbon atoms directly united to a -0-O-acyl or -OOH group. Clearly also mixtures of these peroxides with other peroxides may be used in the context of the present invention. The peroxides may also be mixed peroxides, i.e. peroxides containing any two of different peroxygen- bearing moieties in one molecule). Most preferably, however, the peroxide is a liquid peroxide. Handling of liquid peroxides when curing the resins for their final use is generally easier: they have better mixing properties and dissolve more quickly in the resin to be cured.

In particular it is preferred that the peroxide is selected from the group of perethers and perketones. The peroxide being most preferred in terms of handling properties and economics is methyl ethyl ketone peroxide (MEK peroxide).

The amount of radical initiator is usually between 0.05 and 5% (wt) calculated on the unsaturated components.

In an aspect of the invention the coating composition is provided as a two component system having a first component comprising at least one polymer comprising a functional group that reversibly reacts with an isocyanate and a second component comprising at least one isocyanate wherein the dissociation constant of the isocyanate and the functional group is 1x10^"4 or greater preferably 9x10^"4 or greater, preferably 26x10^"4 or greater, preferably 0.25 or greater, preferably 0.5 or greater, more preferably 0.75 or greater at a temperature of 200⁰C or less, preferably 190⁰C or less, preferably 175°C or less. This may be beneficial for storage purposes.

EXAMPLES

Example 1 Preparation of a polyester resin A polyester resin was prepared according to the formulation illustrated in table 1.

Table 1 : Composition of the polyester

FASCAT 4101 is an-butyl chloro tin (IV) dihydroxy esterification catalyst available from Atofina.

After the product was completely esterified, 120 g parahydroxy benzoic acid (phenolic hydroxyl pKa ~9) was added, and the polycondensation was continued to convert aliphatic hydroxyl groups into aromatic OH groups. Only 65 % of the aliphatic OH groups of the polyester was reacted with p-hydroxy benzoic acid to make sure all the p-hydroxy benzoic acid is esterified with the polyester and no free monomer remained after the polycondensation was finished. The resultant polyester was analyzed with NMR to determine the composition.

Example C (Comparative)

As a comparative Uralac ® P1580 (DSM N.V. The Netherlands) was used, this is a hydroxyl functional polyester comprising hydroxyl funtionality having a pKa greater than 18. The reference polyester does not comprise phenolic hydroxyl groups. Uralac ® P1580 is a powder coating resin suitable for use with a blocked isocyanate crosslinker.

In table 2 resin characteristics of polyester EX-1 and polyester EX-C are listed.

Table 2: Resin characterization

Glass transition temperature (Tg) measurements (inflection point) were carried out via differential scanning calorimetry (DSC) on a Mettler Toledo, TA DSC821 , in N₂ atmosphere and at a heating rate of 5°C/min. Viscosity measurements were carried out at 16O⁰C, on Rheometric Scientific CT 5 (Rm 265) (Mettler Toledo). A 30 mm spindle was used. The applied shear-rate was 70s^"1. The acid and hydroxyl values of the resins were determined via H¹-NMR.

Application The powder coating composition of the formulation is given in table 3.

The formulation mixture was extruded at 120⁰C using a Prism Twin Screw extruder. The extrudate was ground and sieved, and the sieving fraction smaller than 90 microns was used as powder paint.

Table 3: Powder coating composition PC-EX-1 according to the invention

Vestagon B 1530 is a commercial trifunctional blocked isocyanate available from Degussa.

Byk 361 is a flow additive available from Byk. Benzoin is a degassing agent obtainable from Caffaro SpA Italy.

Table 4: powder coating composition PC-EX-C (comparative)

The powder coating composition PC-EX-1 was applied on an aluminium ALQ panel and cured for 10 minutes at 200⁰C. The film thickness of the coating thus obtained was approximately 70 micron.

Two different scratches were made in the PC-EX1 coating thus obtained using a Gitterschnitt machine from Sikkens (8519-3). This is an apparatus that may be used to carry out a Gitterschnitt test (cross-cut adhesion test). Here it was used to make scratches in a defined manner. Two different scratches were made using different positions of a weight (3651 gram) resulting in scratches with different depth of indentation.

The panel with the scratches was placed in an oven at 190⁰C and heated for 30 minutes i.e. it was re-heated. The results for PC-EX-1 are given in table δ.Weight position 3 means that the weight which is used to create the scratch is at position 3 of the arm. Position 3 is further away, i.e. has a longer arm and thus scratched with increased force as compared to position 1. Table 5: Results of self healing of PC-EX-1

In an additional experiment a panel was coated with PC-EX-C and a panel was coated with PC-EX-1. After heating the coatings were provided with a scratch using the Gitterschnitt machine. The weight was at position 10. Position 10 indicates an even longer arm and thus induces scratches with more force than at position 3. The positions are equidistant.

The scratched coated panels were re-heated for 20 min. at 190⁰C.

Optical microscopy (Olympus AH-2 optical microscope) was used to assess differences in flow and healing effect of two powder coatings (PC-EX-1 and PC- EX-C).

From the microscopy pictures of cross-sections of the scratched coatings the following was observed. In both pictures it can be seen that at the location of the scratch the aluminum substrate is damaged; there is an indent. The coating of the comparative PC-EX-C is lacking at the bottom of the indent: in the middle of the scratch in the reference coating does not cover aluminum substrate, i.e. the substrate is bare in the middle of the scratch.

The PC-EX-1 coating, however, covers the whole surface of the aluminum substrate so also at the bottom of the indent: the coating has healed.

Claims

1. Composition comprising: a. at least one polymer comprising a functional group that reversibly reacts with isocyanate; b. at least one isocyanate; characterised in that the dissociation constant of the isocyanate and the functional group is 1x10^"4 or greater at a temperature of 200⁰C or less.

2. Composition comprising: a. at least one polymer comprising a functional group that reversibly reacts with isocyanate; b. at least one isocyanate; characterised in that the functional group has a pKa of 18 or less.

3. Composition according to Claim 1 or 2 wherein the functional group has the formula:

-A-X-H wherein A is an electron withdrawing group and X is selected from O, S, N, NH, C, CH and CH2.

4. Composition according to any preceding claim wherein the dissociation constant is 0.25 or greater at a temperature of 200⁰C or less.

5. Composition according to any preceding claim wherein the functional group(s) chosen from phenol, caprolactam, imidazole, triazol, hydroxyl imines, malonic esters, and combinations thereof.

6. Composition according to any preceding claim wherein the isocyanate is selected from blocked isocyanates, polymeric isocyanates, and combinations thereof.

7. Composition according to any preceding claim wherein the composition is a powder coating composition.

8. Composition according to any preceding claim wherein the composition is a solvent-borne, non-aqueous coating composition.

9. Composition according to any preceding claim wherein the composition is an adhesive composition.

10. Composition according to any preceding claim wherein the composition is a composite resin composition.

11. Substrate fully or partly coated with a coating composition according to any of Claims 1-10.

12. Use of a binder comprising a thermo-reversible bond between the resin and the crosslinker in a coating composition wherein the dissociation constant is 1x10^"4 or greater at a temperature of 200⁰C or less.

13. Process for manufacturing a coated substrate comprising the steps, providing a substrate, thereafter applying the coating composition according to any one of claims 1 to 10, thereafter curing the coating composition