WO1995003350A1

WO1995003350A1 - Crosslinkable coating compositions

Info

Publication number: WO1995003350A1
Application number: PCT/GB1994/001467
Authority: WO
Inventors: Stephen George Yeates; Mark Thomas; Richard Andrew Brown; Donald Westwood
Original assignee: Zeneca Limited
Priority date: 1993-07-21
Filing date: 1994-07-07
Publication date: 1995-02-02
Also published as: GB9315092D0; AU7080294A

Abstract

Crosslinkable liquid carrier-based coating composition comprising a polyester(s) having acetoacetyl group functionality and a polyamine compound(s) having at least two acetoacetyl-reactive amino groups per molecule, wherein said polyester(s) has an acid value which is « 1 mgKOH/g.

Description

CROSSLINKABLE COATING COMPOSITIONS

The present invention relates to crosslinkable liquid carrier- based coating compositions in which the basis of the crosslinkability is provided by the reaction in an applied coating between the functional groups of an acetoacetyl-functional polyester and a polyamine used in the formulation of the compositions.

The provision of polymeric coatings from coating compositions for use on a variety of substrates for various purposes (eg, protective, decorative, adhesive or sealant purposes) is well known. It is also well known to improve the performance of such coatings by causing them to become crosslinked (cured) during and/or after coating film formation. For this purpose it is known to employ crosslinkable coating compositions whereby the composition includes components which react to cause crosslinking when a coating is formed from the composition - such as a polymer having reactive functional groups and a coreactant material (which could e.g. be a non- polymeric or oligomeric material or another polymer) having 2 or more groups reactable with those of the functionalised polymer. Such reaction (to cause crosslinking) is of course not intended to take place to any unacceptable degree until actual coating from the composition is effected. As might be imagined, many such coating compositions have a very short pot-life, i.e. a very short period of time before unacceptable premature crosslinking occurs in the composition (as manifested by a very large increase in viscosity and subsequent gelation) . Consequently, it is necessary with such coating compositions to employ them for coating very quickly after they have been prepared from their individual constituents. A potentially useful and known class of coating compositions comprise an acetoacetyl-functional polymer, e.g. an acrylic polymer or a polyester, and a polyamine. Such compositions are described, e.g. in Journal of Coating Technology, Vol. 61 (771) pages 31-37, 1989, and it is postulated that crosslinking occurs by means of enamine formation between the enolic acetoacetyl groups and the amine groups. Such compositions can be aqueous-based and non aqueous liquid-based. The problem with such compositions, however, is that their working pot-life is extremely short, being of the order of a few minutes to a few hours before premature crosslinking and gelation occurs. It has been proposed to increase the pot-life of compositions of this type by blocking the amine groups of the polyamine with a ketone or aldehyde to form corresponding ketimine or aldimine compounds prior to mixing with the acetoacetyl-functional polymer; examples of such compositions are disclosed in US Patent 4772680. On coating formation, exposure to adventitious moisture results in regeneration of the free amine groups which are then available to effect crosslinking. Nevertheless such compositions also have their disadvantages. The ketimine or aldimine group is very moisture sensitive and as such water must, in practice, be rigorously excluded from the stored compositions. This can result in problems when using pigmented systems: thus normally pigments tend to be wet or hydrated, and such products would therefore prematurely trigger the amine deblocking; therefore anhydrous pigments are required - but this in turn begets other problems such as how to effectively employ anhydrous pigments such that they will not absorb moisture; anhydrous pigments are also more expensive. In addition to this, there is a very limited choice of commercially available suitable ketimines or aldimines for use as the hardener. To widen this choice it would be necessary to effect a prior ketimation or aldimation of an amine oneself, thereby incurring unwelcome additional expense. In practice, therefore, the use of such a system may restrict the choice of available coreactant (hardener) for the acetoacetyl- functional polymer, even though there is a very wide range of suitable commercially available unblocked (free) polyamines.

It is disclosed in passing by Witzeman et al, Poly . Mater. Sci. and Eng., UIL, 1000-1006 (1990) that the pot life of compositions containing acetoacetyl-functional polymer and polyamine may be significantly extended by the addition of monacetoacetyl compounds such as methyl acetoacetate to the composition. However, Witzeman et al also state that the use of such an expedient causes the ultimate properties of the system to suffer, implying that it is not a viable way forward to achieve extended pot life in such compositions. In our copending application PCT/GB/00496 there is nevertheless described certain of such compositions having a selected range of the ratio of acetoacetyl groups from the monoacetoacetyl compound to acetoacetyl groups from the polymer which not only possess extended pot life but also provide coatings of excellent properties.

We have now discovered yet a further development in the achievement of compositions of this type which possess improved pot life and provide coatings of excellent properties.

Thus, we have now discovered certain novel liquid carrier-based crosslinkable coating compositions comprising acetoacetyl-functional polyesters^' and free (i.e. unblocked) polyamines which have considerably improved pot-life without the necessity for incorporating a monofunctional acetoacetyl compound or for blocking the amine groups by ketimation or aldimation.

According to the present invention there is provided a crosslinkable liquid carrier-based coating composition comprising a polyester(s) having acetoacetyl group functionality and a polyamine compound(s) having at least two acetoacetyl-reactive amino groups per molecule, wherein said polyester(s) has an acid value which is ≤l mg KOH/g. There is also provided according to the invention a method of preparing a crosslinkable liquid carrier-based coating composition which method comprises formulating, in a liquid carrier medium, components which comprise a polyester(s) having acetoacetyl group functionality and a polyamine compound(s) having at least two acetoacetyl-reactive amino groups per molecule, wherein said polyester(s) has an acid value which is ≤l mg KOH/g.

There is further provided according to the invention the use of a coating composition as defined supra for the provision of crosslinked coating on a substrate.

There is yet further provided according to the invention a crosslinked coating derived from a coating composition as defined supra.

The coating compositions of the present invention provide several advantages, many of which are not enjoyed by the compositions of the prior art employing acetoacetyl-functional polyester polymers and blocked polyamines (ketimines or aldimines) . For example, they can be derived using any suitable polyamine hardener, which does not need to be blocked prior to incorporation into the composition. They are not sensitive to moisture and consequently no special precautions need to be taken in this regard during storage; also they are equally suited to providing conventionally pigmented (i.e. using conventional non-anhydrous pigments) and clear coatings. Furthermore they do not require the incorporation of volatile monofunctional acetoacetates to provide improved pot-life (although they can be incorporated if desired) . In spite of this, they surprisingly do posses excellent pot-life. Moreover, they are often suitable for ambient or subambient temperature or slightly elevated temperature curing, although of course higher temperature curing can also be effected if appropriate.

One may achieve the synthesis of an acetoacetyl-functional polyester (as discussed in more detail later) by reacting an acid component with a hydroxyl component and employing an appropriate stoichiometric excess of hydroxy-functional reactants over acid-functional reactants in order to yield a hydroxyl-functional precursor polyester polymer (a polyester polyol) which may then be acetocetylated to form the final acetoacetyl-functional polyester. It has been standard procedure when synthesising polyester polyols for use in crosslinking systems to ensure that a finite acid value (typically ≥5 mg KOH/g) is present for ease of processing and ultimate substrate adhesion. We have now discovered that, surprisingly, if one deliberately ensures that the acid value of the precursor polyester polyol, and hence of the final acetoacetyl-functional polyester, is ≤l mg KOH/g, then the pot-life of the polyester/polyamine composition is considerably improved.

While it was known from R.J. Clements et al, Proc. XVIth International Conf. In Organic Coatings Tech., Athens, 1990, pp 127-142, that strong acids such as p-toluene sulphonic acid catalytically accelerate crosslinking in compositions based on acetoacetyl-functional acrylic polymers and polyamines, it is most surprising that by merely reducing the acid value of an acetoacetyl-functional polyester from ≥5 to ≤l one can achieve a considerably enhanced protection from premature crosslinking as discussed supra, particularly when one takes into consideration that typical acid groups providing the acid value in the polyester polymer will be the second acid group of weak carboxylic acids or anhydrides such as adipic acid, terephthalic acid, or phthalic anhydride (pKa 4.5-5.5) (typically used in polyester synthesis) which would not be expected to have much, if any, effect regarding the catalysis of crosslinking.

Generally speaking the acid value of the polyester will be in the range of from 0 to 0.7 mg KOH/g.

The compositions of the invention may be organic liquid-based or they may be water-based. By an organic liquid-based coating composition is meant a composition in which the components are carried in a liquid medium of which at least one organic liquid is the principle component (greater that 50 wt. % of the carrier medium say, and more usually at least 80 wt. %) ; minor quantities of water may optionally be present. By an aqueous- based coating composition is meant a composition in which the components are carried in a liquid medium of which water is the principle component (greater than 50 wt. % of the carrier medium say, and more usually at least 80 wt.%); minor quantities of organic liquid(s) may optionally be present. In the compositions of the invention, one or both of the acetoacetyl-functional polyester, and the polyamine may be dissolved in the liquid carrier medium, and in the case of organic liquid-based compositions it is not uncommon for both types of component to be dissolved therein. If a component is not truly dissolved in the liquid carrier medium it may alternatively be dispersed in the liquid carrier medium, i.e. exist in the form of a dispersion of non-solubilized particles or droplets (depending on whether it is a solid or liquid) rather than as properly solubilized material. Thus, e.g. the acetoacetyl-functional polyester could be present in the form of colloidally dispersed particles (i.e. in latex form), while the polyamine compound could be present in the form of colloidally dispersed particles or droplets (depending on whether it is in solid or liquid form) . Thus, one or both of the acetoacetyl functionalized polyester, and the polyamine components may be dispersed (rather than dissolved) in the liquid carrier medium.

In the compositions of the invention it is preferred that the ratio of the number of acetoacetyl groups of the acetoacetyl functional polymer(s) to the number of acetoacetyl-reactive amino groups of the polyamine compound(s) is within the range of from 0.5 to 2 more preferably from 0.8 to 1.5, in order to achieve the best possible cure rates. A ratio at or very near to 1 is particularly preferred (say 0.9 to 1.1) .

By an acetoacetyl group in this specification is meant a group having the formula:

CH₃-C-CH₂-C- (1)

where the methyl group may optionally be mono, di or tri-substituted (for example so as to provide therewith a higher alkyl group of 2 to 10 carbon atoms, usually 2 to 4 carbon atoms) and the methylene group may optionally be monosubstituted (usually by alkyl of 1 to 4 carbon atoms, particularly methyl) . The methyl group could also, in principle, be replaced by a cyclic hydrocarbyl group (optionally substituted) such as an optionally substituted phenyl group or an optionally substituted heterocyclic group, and such alternative groupings are also considered to be acetoacetyl groups for the purpose of this specification. A polymer-bound acetoacetyl group will normally be provided in the environment of an acetoacetate grouping of formula:

0 0

II II

CH₃-C-CH₂-C-0- (2)

or an acetoacetamide grouping of formula:

O O Rl

II II I CH₃-C-CH₂-C-N- (3)

or a 1,3 diketone grouping of formula:

where R¹ is hydrogen or a monovalent hydrocarbyl radical such as an

(optionally substituted) alkyl, aryl, aralkyl or alkaryl radical (usually of 1 to 10, particularly 1 to 6 carbon atoms) and R² is a divalent hydrocarbyl radical such as an (optionally substituted) alkylene, arylene, aralkylene or alkarylene radical (usually of 1 to 20, particularly 1 to 10 carbon atoms) .

It is preferred, however, that the acetoacetyl group is provided by an acetoacetate or acetoacetamide group, and more preferably by an acetoacetate group.

By an acetoacetyl-reactive amino group is meant an amino group which will react with an acetoacetyl group to form a covalent bond between the compounds containing the groups. Such groups are normally acetoacetyl- reactive primary amino (-NH₂) and/or secondary amino (-NH-) groups. In the particular context of this specification, we are including acetoacetyl- reactive nitrogen bound -NH₂ groups (such as in the hydrazino grouping -NHNH₂) as examples of amino groups as well as the more preferred carbon- bound acetoacetyl-reactive amino groups.

Turning now specifically to the acetoacetyl-functional polyester. Such a polymer may be prepared by first forming a precursor hydroxy- functional polyester polymer, i.e. a polyester polyol having acetoacetylatable precursor hydroxyl groups, and converting these precursor hydroxyl groups at least in part to acetoacetyl groups using an appropriate acetoacetylating agent such as diketene or (via transesterification) a lower alkyl (e.g. Cl to C5) ester of acetoacetic acid, such as methyl acetoacetate, ethyl acetoacetate and (in particular) t-butyl acetoacetate. It is well known that polyesters, which contain carbonyloxy (i.e.

-C(=0)-0-) linking groups may be prepared by a condensation polymerisation process in which an acid component (including ester-forming derivatives thereof) is reacted with a hydroxyl component. The acid component may be selected from one or more polybasic carboxylic acids such as di-or tricarboxylic acids or ester-forming derivatives thereof such as acid halides, anhydrides or esters. The hydroxyl component may be one or more polyhydric alcohols or phenols (polyols) such as diols, triols, etc. The reaction to form a polyester may be conducted in one or more stages (as is well known) . It would also be possible to introduce in-chain unsaturation into the polyester by employing as part of the acid component an olefinically unsaturated dicarboxylic acid.

When preparing an acetoacetyl-functional polyester a precursor polyester having acetoacetylatable precursor hydroxyl groups is first formed as mentioned above. This may be achieved by including an appropriate polyol(s) having two or more hydroxyl groups per molecule in the polyester synthesis. (If only a polyol(s) with two hydroxyl groups per molecule(s) were used, i.e. a diol, it would of course be necessary to use an appropriate stoichiometric excess in relation to the acid component to ensure that the resulting precursor polyester was hydroxyl-terminated. It is therefore better to also include a polyol(s) with 3 or more hydroxyl groups as part of the hydroxyl component in order to provide lateral hydroxyl groups in the resulting polyester; the presence of terminal hydroxyl groups would then be optional, although one could still have terminal as well as lateral hydroxyl groups if desired) . There are numerous carboxylic acids (or their ester forming derivatives) which can be used in polyester synthesis for the provision of the acid component. One can e.g. mention C4 to C20 aliphatic, alicyclic and aromatic dicarboxylic acids (or higher functionality acids) or their ester- forming derivatives (such as anhydrides, acid chlorides, or lower alkyl esters) . Specific examples include adipic acid, fumaric acid, maleic acid, succinic acid, itaconic acid, sebacic acid, nonanedioic acid, decanedioic acid, l,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, and tetrahydrophthalic acid. Anyhydrides include succinic, maleic, phthalic and hexahydrophthalic anhydrides.

Similarly there are numerous polyols which may be used in polyester synthesis for the provision of the hydroxyl component. The polyol (s) preferably have from 2 to 6 (2 to 3) hydroxyl groups per molecule.

Suitable polyols with two hydroxy groups per molecule include diols such as 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2,2- dimethyl-l,3-propanediol (neopentyl glycol), 2-butyl-2-ethyl-propylene diol, the 1,2-, 1,3-, and 1,4-, cyclohexanediols and the corresponding cyclohexane dimethanols, diethylene glycol, dipropylene glycol, and diols such as alkoxylated bisphenol A products, e.g. ethoxylated or propoxylated bisphenol A. Suitable polyols with three hydroxy groups per molecule include triols such as trimethylolpropane (1,1,1-tris (hydroxmethyl) ethane) . Suitable polyols with four or more hydroxy groups per molecule include pentaerythritol (2,2-bis (hydroxymethyl) - 1,3-propanediol) and sorbitol (1,2,3,4,5,6-hexahydroxyhexane) .

The precursor polyester polyols often usefully have a Mn within the range 300 to 5,000, a Tg within the range -40 to 120°C, and a hydroxyl number of 30 to 250 mg KOH/g. The acid value of the precursor ester polymer, as mentioned above, will, unless special precautions or expedients are undertaken, normally be at least 5 mg KOH/g, usually 5-20 (5-10) mg KOH/g.

For the purposes of the invention, the low acid value of the acetoacetyl-functional polyester is normally achieved by ensuring that precursor polymer itself has an acid value of 0 to 1 mg KOH/g. (It would in principle be possible to reduce the acid-value of a high acid-value acetoacetyl-functional polyester, but this is less preferred.) This may be achieved in several ways. For example, in the polyester synthesis, the polymerisation reaction between the hydroxyl and acid components can be forced so as to obtain full conversion, either azeotropically or with vacuum. However, this is not preferred since as the acid value gets to below 5, the reaction rate slows considerably and the product begins to discolour especially at low hydroxyl concentrations. Alternatively, the residual acid groups of a polyester polyol of acid value ≥5 mg KOH/g can be neutralised by titrating with base (e.g. KOH/methanol) such that the free acid level drops to ≤l mg KOH/g. In another alternative the residual acid groups may be removed by chemically converting the carboxylic acid groups of a polyester polyol of acid value ≥5 mg KOH/g to non-acid groups. For example the polyester polyol may be reacted with a monoepoxide compound such as CARDURA E10 to as to convert the carboxylic acid groups to those of formula:

0 II -C-0-CH₂-CH- (5)

OH

and such a reaction may be performed at low temperatures to give a clean product. Acetoacetylation of the precursor hydroxyl-functional polyester of low acid value may then be effected to yield the required acetoacetyl- functional polyester. The acetoacetyl functionality should normally be within the range of from 2 to 5, more usually 2 to 4. By acetoacetyl functionality is meant the average number of acetoacetyl groups per polymer molecule. The hydroxyl value of the acetoacetyl functional polymer will usually be within the range of from 0 to 200 mg KOH/g, more usually 0 to 150 mg KOH/g.

The specific polymerisation techniques for making polyesters are extremely well known and need not be described here in detail. Suffice to say that they are usually carried out in the melt using catalysts such as tin-based catalysts and with the provision for removing the water or alcohol formed from the condensation reaction (although one can, of course, by using appropriate reagents effect polyester synthesis where water or alcohol is not eliminated) . Turning next to the polyamine(s) component of the composition of the invention. Such materials can in principle be low molecular weight materials, oligomeric materials or polymeric materials.

The polyamine may e.g. have primary and/or secondary amino groups and have from 2 to 10 (more often 2 to 6) such amino groups per molecule, and 2 to 200 carbon atoms.

Suitable examples of polyamines with 2 such amino groups include diamines such as ethylenediamine, propylenediamine, butylenediamine, pentamethylenediamine, hexamethylenediamine, decamethylenediamine, 4,7- dioxadecane-l,10-diamine, dodecamethylenediamine, 4,9-dioxadodecane-l,12- diamine, 7-methyl-4,10-dioxatridecane-l,13-diamine, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, 4,4' -diaminodicyclohexyl methane, isophoronediamine, bis (3-methyl-4-aminocyclohexyl)methane, urea, 2,2-bis(4- aminocyclohexyl)propane, 3-amino-l- (methylamino)propane, 3-amino-l- (cyclohexylamino)propane and N- (2-hydroxyethyl) ethylenediamine. Suitable polyamines with 3 such amino groups per molecule, include polyamines such as tris (2-aminoethyl)amine, bis(3-aminopropy1) methylamine, melamine and products of the JEFFAMINE (Registered Trade Mark) T series represented by the formula:

CH₃ where E is the residue of an aliphatic triol and x, y and z are integers the sum of which is from 5 to 85 (this may not be a whole number if the product is a mixture of compounds with differing x, y and/or z) . JEFFAMINE D series products with 2 amino groups are also suitable.

Other suitable polyamines with from three to ten amino groups per molecule are polyalkylene polyamines represented by the formula:

H₂N—(R³ NH s R⁴-NH₂ (7)

where the group R⁴ and the n groups R³ which may be the same or different, are (cyclo)alkylene groups of from 1 to 6 (and. preferably from 1 to 4) carbon atoms, and n is an integer from 1 to 8 and preferably from l to 4. Examples of polyamines of formula (7) are diethylenetriamine, dipropylenetriamine and dibutylenetriamine.

Other suitable polyamines which could be used include the adducts of an amino compound with a polyfunctional epoxy, isocyanate, maleinate, fumarate or (meth)acryloyl compound, such that the resulting material has two or more amino groups (primary or secondary) per molecule. Many examples of such polyamines are disclosed in US Patent 4772680 reference to which is incorporated herein.

It would also be possible to employ as the polyamine compound, polyhydrazides such as those dicarboxylic acid bishydrazides of formula:

H₂N-NH-C(=0) -R^s-C(=0) -NH-NH₂ (8) where R⁵ is a covalent bond or a polyalkylene (preferably polymethylene) or alicyclic group having from 1 to 34 carbon atoms. Examples of suitable dihydrazides include oxalic acid dihydrazide, malonic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, adipic acid dihydrazide, cyclohexane dicarboxylic acid bis-hydrazide, azelaic acid bis- hydrazide, and sebacic acid dihydrazide.

The polyamine compound could also in principle be an organic polymer with an average of at least 2 acetoacetyl-reactive amino groups per molecule, such as an olefinic polymer, a polyester polymer or a polyurethane polymer, having lateral and/or terminal amino groups (more usually at least lateral amino groups) . Such a polymer is, in particular an olefinic polymer bearing at least lateral amino groups. An olefinic polymer bearing chain-pendant (lateral) amine functionality is preferably a copolymer formed by first preparing, using a free-radical-initiated polymerisation process, a precursor copolymer comprising polymerised units of at least one olefinically unsaturated monomer having an amine precursor group(s) (i.e. a group which may be subsequently reacted to provide a pendant amine group) and at least one other olefinically unsaturated monomer (i.e. a monomer which does not provide an amine precursor group) , and subsequently reacting at least a proportion of the amine precursor groups to provide chain-pendant amine functional groups. For example, the amine precursor groups may be carboxyl groups, which may be converted to provide amine groups by an imination reaction using an alkylene imine such as ethylene imine or propylene imine. It may be mentioned here that additional to the advantages of the coating compositions discussed supra, the use of an acetoacetyl-functional polyester polymer therein itself provides advantages which are independent of these other advantages. Thus an acetoacetyl-functional polymer will generally have a lower solution viscosity in comparison to the corresponding non acetoacetylated polymer at a given solids content, thereby allowing the use of less organic liquid in organic liquid-based compositions in which the components are dispersed or dissolved, or in' other words allows a composition with a comparatively higher solids content. In such compositions the acetoacetyl groups of the polymer also enhances polymer solubility in the organic liquid carrier. In water-based compositions, the acetoacetyl groups of the polyester polymer facilitates emulsification of the polymer, thereby improving its dispersion in the composition (although of course the polymer could also have groups for imparting water- emulsifiability or even water-solubility) .

The liquid carrier medium of the composition of the invention will be comprised at least in part (and usually at least predominantly) by an organic liquid(s) or by water. Examples of organic liquids, in many cases acting as a solvent for all the components, include aliphatic or aromatic hydrocarbons such as xylene and toluene, ketones such as methyl amyl ketone and methyl isobutyl ketone, esters such as ethyl acetate, ethers, alcohols and nitroalkanes such as nitropropane. The coating compositions of the invention usually have a non- volatiles content within the range of from 40 to 100 weight %, more usually 50 to 90 weight %. (By non-volatiles are meant solids, or non-volatile liquids such as might be provided by some low molecular weight polymers.) The polyester and polyamine components of the composition may be brought together by simple admixture using any suitable mixing technique. Once formulated, the composition is often storage-stable for a long period of time. Once the liquid carrier medium has been removed, crosslinking will occur, although this may take some time to develop fully, e.g. depending on criteria such as the temperature at which the curing is effected.

As discussed supra, many of the compositions described above often cure conveniently at or near to ambient temperature, e.g. at temperatures of from -5 to 35°C, and are thus suitable for non-factory or on-site applications where it would be difficult to apply elevated temperatures. Of course, the compositions may also be cured at higher temperatures, e.g. 35 to 200°C, particularly in locations where the means to apply such elevated temperatures is more convenient (as in a factory building) .

The components of the compositions of the invention are best supplied for use in the form of "two-pack" systems in which the acetoacetyl- functional polymer(s) and the polyamine(s) are kept in separate packs until formulation is effected. Once formulation of all the components is carried out the composition has good storage stability, allowing the user considerable flexibility as to when he chooses to undertake the actual coating operation.

The coating compositions of the invention may be employed to provide different types of coatings (e.g. protective, decorative, adhesive or sealant coatings) on a variety of substrates. They are particularly useful for providing heavy duty maintenance coatings on metal substrates such as steel. For example, they are suitable for coating steelwork structures such as bridges and industrial plants and for coating containers such as steel drums. Another particularly useful application for the coating compositions of the invention which may be mentioned is in the provision of contact adhesive compositions, especially aqueous-based, where, for example the polyamine compound is an organic polymer bearing amino groups (particularly an olefinic polymer bearing at least lateral amino groups) .

Substrates to which the compositions may be applied include metal, wood, leather, cloth, paper and plastics substrates. The coatings may be applied to the substrate by any conventional method such as by brushing, dipping, flow coating, roller coating, and spraying.

The compositions of the invention may also contain other added ingredients, such as pigments, emulsifiers, surfactants, thickeners, catalysts, heat or uv stabilizers, plasticisers, levelling agents, anti- cratering additives, fillers, fire retardants, antifoam agents, rheology control agents, antioxidants, and other organic polymers.

The present invention is now illustrated further by reference to the following examples. Unless otherwise specified all parts, percentages and ratios are on a weight basis. The prefix C before an example denotes that it is comparative.

In the examples the following abbreviations are used

AcAc = Acetoacetyl

AV = acid value

HV = hydroxyl value

NPG = neopentyl glycol

TMG = trimethylol propane BEPD = 2-butyl-2-ethyl-propylene diol

TA = terephthalic acid

IPA = isophthalic acid

AA = adipic acid

Fn(OH) = hydroxyl functionality Fn(AcAc) = acetoacetyl functionality

MAK = methyl amyl ketone

MIBK = methyl isobutyl ketone

Examples Cl. C2. 3. 4 and 5 The examples compare the following compositions comprising AcAc functional polyester and polyamine.

1) compositions, Examples Cl and C2. which incorporate high AV polyesters Pl and P2 as typically found in the literature, and which show very rapid viscosity development and hence short pot life.

2) compositions, Examples 3, 4 and 5, which incorporate very low AV polyesters, Ql, Q2 and Q3 and which show much slower viscosity build up with time and hence longer pot life.

The examples are chosen so as to cover a broad range of functionality and molecular weight to show that this is not the controlling factor, and also two ways of achieving low AV in the polyester: either by forcing the reaction which gives high glycol loss (polyester Ql) , or by reaction with the epoxide Cardura ElO which is more gentle and controllable (polyesters Q2, Q3) .

The recipes for synthesizing the polyesters Pl, P2, Ql, Q2, Q3 are shown in the following Table 1. The table also gives properties of the polyester polyols (i.e. precursor polyesters) and of the final functionalised polyesters, i.e. the acetoacetylated polyesters.

The synthetic procedure for the high AV polyester Pl is now set out as typical. (i) Synthesis of Precursor Polyesterpolyol. Glycols and acids were charged, as given in Table 1, to the reactor under nitrogen. The reactor temperature was raised to 175°C over 1 hour, agitation being started as soon as possible. The reactor temperature was raised to 235°C maintaining a steady reflux such that the distillation column head temperature did not exceed 101°C. Reaction was allowed to proceed to an AV=20-30 mgKOH/g, progress being monitored by the rate of water off-take. The reactor was then placed under mild vacuum (ca. 150 mbar) until a final AV=5 mgKOH/g was achieved. The final AV of the resulting polyester polyol (precursor polymer) was 5 mgKOH/g and HV was 110 mgKOH/g. The solid polyol was then isolated.

(ii) Synthesis of Acetoacetylated Polyester. 768g of the polyester polyol were heated to 120-140°C and 232g of t-butyl acetoacetate added dropwise over 4 hours. The t-butanol evolved was removed under reduced pressure distillation. The acetoacetylated polyester was then thinned with xylene to 65% w/w solids. The AV of the acetoacelylated polyester was unchanged from that of the precursor polyester. The degree of conversion of OH to acetoacetate was determined by 1H NMR to be 95%.

The synthetic procedure for the low AV polyester Q3 is now set out as typical.

(i) Synthesis of Precursor Polyesterpolyol. The procedure was as above for step ^"(i) in the synthesis of Pl, but taken to AV=5.8 mgKOH/g. The resin was then cooled to 200°C, 37g Cardura ElO added, and the resin held for 30 minutes at which point AV=< 0.5 mgKOH/g, with a HV=113 mgKOH/g. The solid polyol was then isolated.

(ii) Synthesis of Acetoacetylated Polyester. The procedure was as above for step (ii) in the synthesis of Pl but taking 500g polyol with 167g t- butylacetoacetate. The acetoacetylated polyester was then thinned with 1:1 w/w MAK: MIBK to 79% w/w solids. The AV of the acetoacetylated polyester was unchanged from that of the precursor polymer. The degree of conversion of OH to acetoacetate was again 95%.

The polyesters were used for the preparation of crosslinkable compositions using the formulations shown in Table 2. JEFFAMINE T 403 is a triamine of formula:

CH₂- (OCH₂CH) ₃₍ H₂ CH₃ CH₃CH₂C-CH₂- (0CH₂CH) yNH₂ I CH₃ CH₂- (OCH₂CH) _zNH₂

CH₃

where x + y + z is approximately 5.3 . JEFFAMINE D400 is a diamine of formula :

H₂NCHCH₂- (0CH₂CH) JIHj CH₃ CH₃

where x is 5 to 6 .

The compositions were stored at 25°C and their stabilities assessed periodically after increasing time periods by measuring their cone and plate viscosities (25°C) . The results are shown in Table 2. It will be noted that the invention compositions of Examples 3, 4, and 5 had significantly improved pot life in comparison to the comparative compositions of Examples Cl and C2. All the compositions were of equivalent performance in all respects except that the high AV ones had a marginally faster initial drying rate. Therefore the invention compositions allow, improved pot life without loss of performance.

Table 1: Preparation of Polyesters

High AV Low AV

Polyester Code Pl P2 Ql Q2 Q3

CoπtDosition (σ Charσed)

NPG 357.5 427 825 842 551

TMP 77.5 40 188 161 53.6

BEPD - - - - 96

TA 116 61 282 664 272

IPA 353 354 857 664 450

AA 96 180 234 - 124

Cardura ElO - - - 80 37

Polvester Polvol

HV(mgKOH/g) 110 102 84.5 119 113

AV(mgKOH/g) 5 4 0.45(**) 0.1 <0.5

Fn(OH) 2.81 2.31 3.56 2.53 2.22

Mid-point Tg (OC) 14.5 5.5 - - -

Punctional±sed

Polvester (*)

%-Acetoacetylation 95 98 95 95 95

Fn(AcAc) 2.67 2.26 3.38 2.4 2.11

Mid-Point Tg (OC) -4.5 -15.9 - 1.7 -

(*) Acetoacetylation by reaction of polyol with t-butyl acetoacetate (**) Low AV by driving esterification reaction and losing glycol Table 2: Compositions of Polvester and Polyamine

Formulation of Exs. Ex.Cl Ex.C2 Ex.3 Ex.4 Ex.5

Polyester used Pl P2 Ql Q2 Q3

Solid Polyester (g) 13 14 12 14 39.5

Solvent Xylene Xylene Xylene MAK:MIBK MAK:MIBK (1:1) (1:1)

Wt.Solvent (g) 7 8 8 6 10.5

Jeffamine T403 (g) 3.07 3.1 2.27 3.54 4.77

Jeffamine D400 (g) - - - - 6.5

Antifoam (drops) 2 2 2 2 2

Storaσe Time (mins) ICI Cone/Plate Viscosity (poises)

(25°C)

0 1.7 1.6 1.6 1.4 1.5

30 14 5.9 1.7 2 2.2

60 Gel 13.5 2.5 2.6 3

120 Gel 5.3 4.2 4.25

180 - 5.4 5.5

240 11 9 5.75

720 Gel Gel Gel

Claims

1. Crosslinkable liquid carrier-based coating composition comprising a polyester(s) having acetoacetyl group functionality and a polyamine compound(s) having at least two acetoacetyl-reactive amino groups per molecule, wherein said polyester(s) has an acid value which is < 1 mg KOH/g.

2. Composition according to claim 1 wherein the acid value of said polyester(s) is within the range of from 0 to 0.7 mgKOH/g.

3. Composition according to either claim 1 or claim 2 wherein said composition is organic liquid-based.

4. Composition according to either claim 1 or claim 2 wherein said composition is water-based.

5. Composition according to any one of the preceding claims wherein the ratio of the number of acetoacetyl groups of the acetoacetyl functional polyester(s) to the number of acetoacetyl-reactive amino groups is within the range of from 0.5 to 2.

6. Composition according to any one of the preceding claims wherein said polyester-based acetoacetyl groups are provided by acetoacetate groups of formula ,0 0

II II CH₃-C-CH₂-C-0-

or by acetoacetamide groups of formula

0 O R¹

II II I CH₃-C-CH₂-C-N-

where R¹ is hydrogen or a monovalent hydrocarbyl radical.

7. Composition according to any one of the preceding claims wherein said acetoacetyl-functional polyester(s) of said composition has been made by first forming a precursor hydroxyl-functional polyester and converting the hydroxyl groups thereof at least in part to acetoacetyl groups with an acetoacetylating agent.

8. Composition according to claim 7 wherein the precursor hydroxyl- functional polyester(s) before acetoacetylation has an acid value of <.1 mgKOH/g thereby to provide an acid value of <.1 mgKOH/g in the resulting acetoacetyl-functional polyester(s) .

9. Composition according to claim 8 wherein the precursor hydroxyl- functional polyester(s) as initially made has an acid value of at least 5 mgKOH/g and this is reduced to an acid value of < 1 mgKOH/g before acetoacetylation.

10. Composition according to claim 9 wherein the reduction to an acid value of < 1 mgKOH/g in the precursor hydroxyl-functional polyester(s) is effected by reaction with a monoepoxide compound.

11. Method of preparing a crosslinkable liquid carrier-based coating composition which method comprises formulating, in a liquid carrier medium, components which comprise a polyester(s) having acetoacetyl group functionality and a polyamine compound(s) having at least two acetoacetyl groups per molecule, wherein said polyester(s) has an acid value of < 1 mgKOH/g.

12. Use of a coating composition according to any one of claims 1 to 10 for the provision of crosslinked coating on a substrate.

13. Use according to claim 12 wherein said use is for the provision of a maintenance coating on a metal substrate.

14. Use according to claim 12 wherein said use is for the provision of a contact adhesive.

15. A crosslinked coating derived from a coating composition according to any one of claims 1 to 10.