GB2503700A - A long-shelf life aqueous coating composition - Google Patents

Abstract

A long-shelf life aqueous coating composition, comprising water-dispersed polymer binder, such as an acrylate polymer binder, with a carbonyl-hydrazide cross-linking system, such as adipic dihydrazide, and one or more volatile mono-carbonyl entities, such as mono-ketones, such as methyl ethyl ketone, methyl iso-butyl ketone, mono-aldehydes and mixtures thereof (which retard cross-linking). Also disclosed is a long-shelf life cross-linkable vinyl copolymer dispersion comprising an aqueous solution of a water-soluble oligomer having a number average molecular weight Mn within the range of from 500-50,000 and a glass transition temperature (Tg) within the range of 10-150°C, and which oligomer is derived from a monomer system comprising 1-45 weight % of acid co-monomer(s), 0.5 to 20 weight % of crosslinking co-monomer(s), and 98.5-50 weight % of non-acid functional, non­-crosslinking co-monomer(s), the oligomer having cross-linkable carbonyl or hydrazide functional groups. The dispersion optionally comprises an aqueously dispersed hydrophobic polymer having a number average molecular weight Mn, higher than that of the oligomer, the dispersed polymer optionally having functional groups for imparting crosslink ability; a polyhydrazide or polycarbonyl crosslinking agent being react-able with the crosslinker functional groups of the oligomer and one or more volatile mono-carbonyl entities reversibly reactive with the hydrazide cross-linking groups (which retard crosslinking). A wood stain formulation comprising the long-shelf life aqueous coating composition is also disclosed.

Description

AQUEOUS CROSSLINKABLE POLYMER DISPERSIONS WITH IMPROVED

STABILITY.

BACKGROUND TO THE INVENTION

FIELD OF THE INVENTION

The invention pertains to crosslinkable aqueous polymer dispersions and the synthesis thereof The invention further pertains to a coating composition comprising said crosslinkable aqueous polymer dispersons; to a paint formulation comprising said crosslinkable aqueous polymer dispersons; and to an article coated with the coating composition or the paint formulation.

DESCRIPTION OF THE RELATED ART

Recent changes in the legislation concerning the emission of organic solvents have led to a growing interest in waterborne coating systems for industrial applications.

Waterbome coating systems have been used already for a long time in applications where the decorative aspects of the coating are of more importance than the protective properties. The aqueous polymer dispersions that arc used as binders in such coatings are often prepared by means of emulsion polymerization processes. A general description of emulsion polymerization process is given E.W. Duck in Encyclopaedia of Polymer Science and Technology, 1966, John Wiley & Sons, Inc.,Vol 5, p 801-859.

Duc to increasingly stringcnt laws conccrning the allowable contcnts of volatile organic compounds in coatings, major efforts have been made to minimize the use of organic co-solvents in water borne coatings based on acrylic binders. However, in water borne coatings that use acrylic polymers as the main binder, the final hardness after curing of an applied coating film is affected by a reduction in the amount of organic co-solvents in the coating formulation. For some coating applications a minimum hardness is required, for example if a high blocking-resistance or mar-resistance is important.

The hardness of a fmal coating can be increased by introducing a cross-linking mechanism into the coating composition. Introducing a cross-linking mechanism by provision of an oligomer with cross-linking groups and optionally cross-linking groups on the dispersed polymer is a well known method to improve some of the properties (e.g. water and chemical resistance) of aqueous polymer dispersions when they are used in coating applications.

Waterborne cross-linking coating compositions are commonly supplied as either one-package (1K) or two-package (2K) systems. In a one-package system, the polymer dispersion is pre-combined with a cross-lii*er, and is sealed in a single package for storage as a pre-prepared coating composition. In two-package systems, the binder and cross-linker are provided to the consumer in separate packets and are mixed by the consumer shortly before application to a substrate.

Curing of one-package systems occurs when the coating composition is exposed to an external environment, at ambient temperature or by baking the coating after application.

In two-package systems, curing occurs upon mixing and hence reaction of the binder and the erosslinker.

Two-package systems suffer from the disadvantage that mixing of the components must be carried out by the consumer requiring accurate measurement and often specialized mixing equipment. One-package systems do not suffer this disadvantage, but may suffer problems with shelf-life because the crosslinking reactants are in contact in the single package during storage. In order to be used as a one component coating, the combination of the erosslinkable polymer dispersion and the crosslinking compound must be stable, meaning that the reactive components must co-exist in a single composition that is shelf-stable.

A preferred one-package system makes use of the known carbonyl-hydrazide cross-linking system. In such a system the hyrdazide groups react with earbonyl groups by condensation reaction to form hydrazone linking bonds between polymer chains.

Water-borne polymer dispersions based on such cross-linking systems possess a good combination of performance properties for use in aqueous coating compositions.

Examples of such compositions arc described in patcnt applications US6730740 and EPII2S 949.

In such carbonyl-hydrazide crosslinking systems, crosslinking of the polymers takes place on drying through formation of a Schiffs base. Removal of water from the system, such as by evaporation during air drying, drives the reaction to the crosslinked product as illustrated in the below example scheme. Since water evaporation drives the reaction, it is possible to cure such compositions at ambient temperatures.

polymor-4 HNIRL'INH_2 0 oiymer ( CH3 Hi NH2 H3C polymer polymo pclymer.olmer r't NH.NHI&R)&NgNHyL1 polymer 2 H20 polymer It is typical, and preferred, in aqueous coating compositions having carbonyl-hydrazide erosslinking systems that the carbonyl-functional groups are provided on binder polymers/oligomers, and the hydrazide-functional groups are provided on the crosslinkers. However, it is also possible that the carbonyl-functionality can be provided on the crosslinker and the hydrazide functionality can be provided on the binder polymer/oligomer. Alternatively, both carbonyl and hydrazide functionality can be provided on the polymer/oligomer binder allowing the molecules of the polymettoligomer binder to link directly to one another without the need for an additional crosslinker component.

Aqucous dispcrsions of coating compositions having carbonyl-hydrazidc crosslinking systems provide useful aqueous coating compositions, and are desirable because of their low VOC requirements, and good performance properties.

However, the use of one packagc systems of aqueous polymer dispersions containing carbonyl-hydrazide cross-linking systems is resicted because of a limited shelf-life.

After a storage period it is not uncommon for these one-package systems to suffer deleterious effects such as viscosity increase, agglomeration, and yellowing.

Thus there is a general need for aqueous polymer dispersions containing carbonyl-hydrazide cross-linking systems that offer longer shelf-life than currently provided for inthe art.

Patents US 4,210,565 and EP 16518 describe the addition of pre-formed hydrazones as cross-linkers, to a composition. This method is not attractive as the hydrazones must be prepared separately, and their solutions (in ketones or ketone/water mixtures) must avoid high solids contents to prevent crystallization.

EP 332326, NL 1013299, CA 2347883, US 6,544,592, describe the preparation of polyurethanes with amongst others pendant hydrazide or hydrazone groups. The aim in these documents is to include pendant hydrazide groups in the polyurethane. Use is made of hydrazones because hydrazide groups arc too unstable for direct incorporation during the polyurethane synthesis. EP 332326 describes the use of a mixture of hydrazide / hydrazone functional polyurethanes and vinyl polymer bearing chain-pendent hydrazide / hydrazone functional groups. Also here it appears that use is made of hydrazones because hydrazide groups are too unstable for direct incorporation during the polyurethane synthesis. EP 1129146; US 6,579,932; and W0200024837, describe incorporation of hydrazidc into polyurethane polymers. Also here it appears that use is made of hydrazones because hydrazide groups are too unstable for direct incorporation during the polyurethane synthesis EP 0219047 describes in its examples the use of hydrazones in secondary emulsions, (that is, vinyl polymers prepared by solution polymerization that are post-emulsified in water). It does not disclose examples with vinyl copolymer dispersions prepared by emulsion polymerization. For realizing a system that does not gel, they preferably use a very high excess of ketones or aldehydes which is very undesirable for environmental and work place reasons.

BRIEF SUMMARY OF THE INVENTION

According to the present invention there is provided a process for the preparation of an aqueous dispersed polymer coating composition comprising the steps of: i) providing an aqueous binder system comprising a water-dispersed polymer binder, wherein the binder system is provided with a earbony-hydrazide cross-linking system; and ii) adding to the aqueous binder system one or more volatile (boiling point <200°C) mono-carbonyl entities reversibly reactive with the hydrazide groups of the cross-linking system.

According to another aspect of the invention there is provided an aqueous coating composition comprising, a) an aqueous dispersed polymer binder, preferably an acrylate polymer binder; and b) water; wherein the aqueous coating composition is provided with a carbonyl-hydrazide cross-linking system; characterized in that: the composition frirther compriscs one or morc volatilc (boiling point <200°C) mono-carbonyl entities reversibly reactive with the hydrazide of the cross-linking system, whcrein thc molar ratio of thc onc or morc mono-carbonyl cntitics to hydrazidc groups is from 0.1 to 5; more preferably from 0.1 to 4; more preferably 0.1 to 3; more preferably 0.1 to 2; more preferably 0.1 to 1; more preferably 0.1 to <1; and most preferably 0.1 to 0.95. More preferably the ratio will have a lower limit of 0.2, more preferably 0.3, more preferably 0.3, more preferably 0.4, and most preferably 0.5.

Without wishing to be bound by theory, the present inventors believe that in the present one-pack carbonyl-hydrazide compositions, the reaction of carbonyl-hydrazide cross-linking systems may already proceed to a deleterious extent during storage, despite being in an aqueous environment. This can significantly influence a number of properties of the coating composition, but will especially affect the viscosity, and hence application properties of thc composition. This is a particular issue with compositions containing low molecular weight oligomers as part of the binding systems.

The inventors have now found that blocking the hydrazidc crosslinker with a low molecular weight, volatile ketone or aldehyde stabilizes the viscosity of crosslinkable polymer dispersion in one-package aqueous coatings.

Surprisingly the present inventors have found that compositions according to this invention can be made by using a limited amount of ketone or aldehyde or even an amount smaller than equivalent relative to the hydrazide equivalent. Surprisingly we also found that also stable compositions can be prepared at temperatures not only at °C but even at room temperature.

So surprisingly it was found that even compositions that are described in this invention that do not suffer gelling problems on storage, still show an improvement with respect to viscosity stability. It was found that the addition of the previous mentioned amounts of kctones or aldehydcs has a vety positive effect on the speed to reach the equilibrium viscosity when changing storage temperature. Where the reference takes in the region of weeks to reach equilibrium, the compositions from this invention can obtain the equilibrium within hours or a few days depending on the amount of kctonc or aldehyde added and on the difference in changing the storage temperature. This is an attractivc tool for the paint formulator as he has more freedom to maneuver.

DETAILED DESCRIPTION OF THE INVENTION.

Tn a preferred embodiment of the invention there is provided a crosslinkablc vinyl copolymer dispersions useful for coatings comprising: a) An aqueous solution ofan acid-frmnctional oligomer built from olcfinically unsaturated monomers, said oligomcr having a number average molecular weight M within the range of from 500 to 50,000 and a glass transition temperature (Tg) within the range of 10 to 150°C, and which oligomer is derived from a monomer system comprising 1-45 weight % of acid comonomer(s), 0.5 to 20 weight % of crosslinking comonomer(s), and 98.5 -50 weight % of non-acid functional, non-crosslinking comonomer(s), and said acid functionality rendering the oligomer water-soluble per se or by neutralization, and said oligomer also having functional groups provided by said crosslinking comonomer(s) for imparting crosslinkability when the aqueous polymer composition is subsequently dried, b) optionally conducting an aqueous emulsion polymerization process of at least one olefinically unsaturated monomer in the presence of the aqueous solution of the oligomer, to form an aqueous dispersion of a hydrophobic (high molecular weight) polymer having a number average molecular weight M11 higher than that of the oligomer, said high molecular weight polymer optionally having functional groups for imparting erosslinkability when the aqueous vinyl copolymer composition is subsequently dried, and c) combining the aqneoius dispersion from b) with a blocked hydrazide (hydrazone) functional compound prepared in-situ or as such as crosslinking agent by addition of the erosslinking agent after the polymerization in step b) and/or performing the polymerization in the presence of the crosslinking agent, said crosslinking agent being reactable with the crosslinker ifinctional groups of the oligomer and (if present) of the polymer on subsequent drying and deblocking of the hydrazide group to effect crosslinking. Optionally the hydrazone crosslinking agent can be formed by first adding the low molecular weight carbonyl functional compound to the vinyl copolymcr dispersion, followed by adding the dihydrazide, the ratio between the mono-carbonyl compound relative to the hydrazide compound being from 0.5 to 5.

Preferably the erosslinkable vinyl copolymer dispersion is an ambient temperature crosslinkable vinyl copolymer dispersion. By this is meant that it can crosslink at an ambient temperature even if in practice heating is used to speed up drying.

By ambient temperature is meant 20 ± S °C.

Preferably the aqueous composition of the invention comprises 0 to 50 wt%, more preferably 0 to 40 wt% and most preferably 0 to 35 wt% of organic co-solvent by weight of the vinyl copolymer.

The weight percent ratio of oligomer to polymer is preferably in the range of from 10:90 to 90:10, more preferably 25:75 to 75:25 and most preferably between 35:65 to 65:35.

The Tg of an oligomer or polymer herein stands for the calculated glass transition temperature and is well known to be the temperature at which a polymer changes from a glassy, brittle state to a rubbery state. T2 values may be calculated using the well-known Fox equation. The Fox equation, which is well known in the art, is represented by the formula: 1/T = Wi/L(1) + W2/T2) + W3/T(3) + wherein W1, N2, N3, etcetera, are the weight fractions of the comonomers (1), (2), and 3), (etcetera), and Tg(l), Tg(2), Tg(3) mean the glass transition temperatures of their respective homopolymers. Glasstransition values for homopolymers given in the Polymer Flandbook, 41!] edition (editors: J. Brandrup, E.H. Immergut, E.A. Grulke, John Wiley & Sons, Inc. 1999) are used to perform the calculation. The calculated Tg in degrees Kelvin may be readily converted to degrees Celcius. Preferably the Tg of the oligomer is in the range of from 10 °C to 150 °C and more preferably in the range of from 25 °C to 125 °C.

The number and weight average molecular weights (M11 and Mw) of the oligomer and the resulting vinyl eopolymer may be determined by using gel permeation chromatography (GPC) using a polymer, such as polystyrene, of known molecular weight as a standard and THF as an cluent.

Preferably the M11 of the oligomer is in the range of from 500 Wmol and 50,000 g/mol, more preferably 2,500 g/mol to 25,000 Wmol and most preferably 5,000 g/mol and 15,000 g/mol.

The oligomer and the polymer of the crosslinking vinyl copolymer are derived from free-radically polymerizable olefinically unsaturated monomers, which are also usually referred to as vinyl monomers, and can contain polymerized units of a wide range of such vinyl monomers, especially those commonly used to make binders for the coatings industry.

Examples of vinyl monomers which maybe used include but are not limited to olefinically unsaturated vinyl monomers such as I,3-butadiene, isoprene, divinyl benzene, aromatic vinyl monomers such as styrene, alpha-methyl styrene; vinyl monomers such as acrylonitrile, methacrylonitrilc; vinyl halides such as vinyl chloride; vinylidene halides such as vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl laurate; vinyl esters of versatic acid such as VeoVa 9 and VeoVa 10 (VeoVa is a trademark of Hexion); heterocyclic vinyl compounds; alkyl esters of mono-olefinically unsaturated dicarboxylic acids such as di-n-butyl maleate and di-n-butyl fumarate and, in particular, esters of acrylic acid and methacrylic acid of formula CH2=CR5-COOR4 wherein R5 is H or methyl and R4 is optionally substituted C1 to C20, more preferably C1 to Cg, alkyl, cycloalkyl, aryl or (alkyl)aryl which are also known as acrylic monomers, examples of which are methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)aerylate (all isomers), 2-ethylhexyl meth)acrylate, isopropyl (methacrylate, propyl meth)acrylate (all isomers), and hydroxyalkyl (meth)acrylates such as hydroxyethyl methaciylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate and their modified analogues like Tone M-100 (Tone is a trademark of Union Carbide Corporation). Other olefinically unsaturated monomers that can be used are those monomers that contain a fatty acid derived ester-group such as oleyl (meth)acrylate, linoleyl (meth)acrylate, and linolenyl (meth)acrylate, synthesis of these monomers is described in J. Appl. Poly.

Sei., 30, 4571-4582 (1985), the analogue vinyl esters or monomers derived from the addition reaction between glycidyl (mcth)acrylate and a fatty acid such as mentioned in British patent application GB 2237276. These monomers can provide auto-oxidative drying properties polymer part of the vinyl copolymer. Other monomers that can be used comprise the vinyloxazo line diesters of unsaturated fatty acids like such as Dapro FX 521 commercially available from Elementis Specialities.

Particularly preferred is a vinyl monomer system comprising at least 40 wt%, more preferably at least 50 wt% and especially at least 60 wt% of one or more vinyl monomers of the formula CFI2=CR5COOR4 as defined above. Such a preferred polymer andior oligomer is defined herein as an acrylic polymer and an acrylic oligomer respectively. Particularly preferred acrylic monomers include butyl (meth)acrylate (all isomers), methyl (meth)acrylate, octyl (meth)acrylate (all isomers) and ethyl (mcth)acrylatc. Other preferred vinyl monomers include (meth)acrylic amides, (meth)acrylonitrile and vinyl acetate. The other vinyl monomers in such acrylic polymeric baekbones and/or macromonomer may include one or more of the other vinyl monomers mentioned above, and/or may include ones different to such other vinyl monomers.

The vinyl monomers may also include vinyl monomers carrying functional groups as exemplified below. Such functional vinyl monomers may be iniroduced directly in the vinyl copolymer by free radical polymerization, or alternatively the functional group may be introduced by a reaction of a reactive precursor into the oligomer or polymer using a reactive compound carrying a functional group.

For the sake of clarity by a carbonyl functionality in this specification (unless specified otherwise) is meant the carbonyl functionality of a ketone or aldehyde group. Such carbonyl functional groups in a vinyl polymer are normally chain-pendant and/or terminal groups. Examples of vinyl monomers which bear carbonyl functional groups include acrolein, methacrolein, crotonaldehyde, 4-vinylbenzaldehyde, vinyl alkyl ketones of 4 to 7 carbon atoms such as vinyl methyl ketone. Further examples include acrylamido pivalaldehyde, methactylamido pivalaldehyde, 3-acrylamidomethyl-anisaldehyde, diacetone acrylate and diacetone methacrylate, and keto-containing amides such as diacetone acrylamide. A preferred vinyl monomer carrying earbonyl functional groups is diaeetone acrylamide.

Preferably the vinyl copolymer comprises 0.5 to 10 wt% and more preferably 2 to 5 wt°% of carbonyl functional vinyl monomer(s).

Preferably the oligomer comprises 0 to 20 wt°%, more preferably 0 to 10 wt%, and most preferably 0 to 5 wt% of carbonyl functional vinyl monomer(s).

The polymer and/or oligomer may optionally contain other functional groups.

Water-dispersing functional groups provide the property of seif-dispersibility, stability and solubility in water. The water dispersing groups may be ionic, potentially ionic, non-ionic or a mixture of such water-dispersing groups. Ionic water-dispersing groups need to be in their dissociated (i.e. salt) form to effect their water-dispersing action, If they are not dissociated they are considered as potential ionic groups which become ionic upon dissociation. The ionic water-dispersing groups are preferably fully or partially in the fbmi of a salt in the final composition of the invention. Ionic water-dispersing groups include cationic water-dispersing groups such as basic amine -10 -groups, quatemary ammo nium groups and anionic water-dispersing groups such as acid groups, for example phosphoric acid groups, suiphonic acid groups, and carboxylic acid groups.

Preferably any ionic water-dispersing groups are anionic water-dispersing groups.

Preferred vinyl monomers providing anionic or potentially anionic water-dispersing groups include (meth)acrylic acid, itaconic acid, maleic acid, .beta.-carboxyethyl acrylate, monoalkyl maleates (for example monomethyl maleate and monoethyl maleate), citraconic acid, styrene sulphonic acid, vinylbenzyl sulphonic acid, vinylsulphonic acid, acryloyloxyalkyl sulphonic acids (e.g. acryloyloxymethyl sulphonic acid), 2-acrylamido-2-alkylalkane sulphonic acids (for example 2-acrylamido-2-methylethane suiphonic acid), 2-methacrylamido-2-alkylalkane suiphonic acids (for example 2-methacrylamido-2-methylethanesulphonic acid), mono(acryloyloxyalkyl)phosphates (for example, mono(acryloyloxyethyl)phosphate and mono(3-acryloyloxypropyl) phosphates) and mono(methacryloyloxyalkyl) phosphates.

The polymer and/or oligomer may comprise functional vinyl monomers that may become cationic upon addition of acid, such as dimethyl aminoethyl (meth)acrylate, dimethyl aminopropyl (meth)acrylate, and dimethylamino propyl (meth)acrylamide.

Such potentially ionic functional vinyl monomers may contribute to improved adhesion and may also improve stability or appearance on specific substrates such as Preferably the vinyl copolymer comprises 0 to 20 wt°h, more prekrably 0 to 10 wt % and most prcfcrably 0 to 5 wt % of vinyl monomers carrying anionic water-dispersing groups. Preferably the oligomcr comprises 0 to 50 wt°%, more preferably 0 to 25 wt% and most preferably 0 to 10 wt % of vinyl monomers carrying anionic water-dispersing groups.

Preferably the polymer couqnises 0 to 20 wt%, more preferably 0 to 15 wt%, most preferably 0 wt% of vinyl monomers carrying anionic water-dispersing groups.

Non-ionic water-dispersing groups may be in-chain, pendant or temiinal groups.

Preferably non-ionic water-dispersing groups are pendant polyoxyalkylene groups, more preferably polyoxyethylene groups such as methoxy(polyethyleneoxide (meth)acrylate) or hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate.

Preferred vinyl monomers providing non-ionic water-dispersing groups include alkoxy polyethylene glycol (meth)actylates, hydroxy polyethylene glycol -11- (meth)acrylates, alkoxy prolyproplene glycol (meth)acrylates and hydroxy polypropylene glycol methjaciylates, preferably having a number average molecular weight of from 350 to 3000 g/mol. Examples of such vinyl monomers which are commercially available include w-methoxypolyethylene glycol (meth)acrylate. Other vinyl monomers providing non-ionic water-dispersing groups include methacrylamidemono(methacryloyloxethyl) phosphate).

Such non-ionic functional vinyl monomers may contribute to improved stability and improved pigment and subsfrate wetting. Preferably the vinyl copolymer comprises 0 to 20 wt%, more preferably 0 to 15 wt%, most preferably 0 to 10 wt%, especially 0 to 5 wt% and most especially 0 wt% of vinyl monomers canying non-ionic water-dispersing groups.

Preferably the oligomer comprises 0 to 15 wt%, more preferably 0 to 10 wt% and most preferably 0 to 5 wt% of vinyl monomers carrying non-ionic water-dispersing groups.

Preferably the polymer comprises 0 to 20 wtYo, more preferably 0 to 15 wt%, most preferably 0 to 10 wt% and especially 0 to 5 wt% of vinyl monomers carrying non-ionic water-dispersing groups.

In a preferred embodiment of the invention, the oligomer is a macromonomer of Formula (1) CH2C(R1)-CH2-[X]m (1) Where R1 = optionally substituted aryl, -C(O)OR2 or -C(O)NR2 R3; R2 = -H, -CH3 or optionally substituted C1, to C18 alkyl, cycloalkyl, aryl (alkyl)aryl; R3 = -H -Cl-I3 or optionally substituted C1 to C18 alkyl, cycloalkyl, aryl (allcyl)aryl; X = residue of vinyl monomer; and m = an integer in the range of from 2 to 1750.

Preferably m is in the range of from 20 to 1300 and more preferably m is in the range of from 70 to 900.

Preferably the macromonomer of Formula 1 comprises: i) 10 to 98 wt% of CH2=CR6-COOR7 where R6 is H or methyl and R7 is optionally substituted alkyl or cycloalkyl of ito 20 carbon atoms; ii) 0 to 40 wt% of aromatic vinyl monomers; iii) 0 to 10 wt% of vinyl monomers carrying anionic water-dispersing groups; i) 0 to 20 wt % of carbonyl functional vinyl monomers; v) 0 to 20 wt% of vinyl monomers not in 1) to iv); whore i) + ii) + iii) + iv) + v) add up to 100%.

Preferably the polymer comprises: -12 -i) 10 to 98 wt % of CH2=CR6-COOR7 where R6 is H or methyl and R7 is optionally substituted alkyl or cycloalkyl of Ito 20 carbon atoms; ii) 0 to 40 wt % of aromatic vinyl monomers; iii) 0 to 20 wt % of vinyl monomers carrying anionic water-dispersing groups; iv) 0.6 to 20 wt % of carbonyl functional vinyl monomers; v) 0 to 88.8 wt % ofviny monomers not in i) to iv); where 1)-F II) + Iii) + iv) + v) add up to 100%.

The preferred pH range for the resulting aqueous crosslinkable vinyl copolymer is in between 6 to 10, more preferably from 7 to 9 General methods for preparing aqueous vinyl polymers are reviewed in the Journal of Coating Technology, volume 66, number 839, pages 89 to 105 (1995).

The oligomer and the polymer are preferably prepared by free radical polymerization.

The free radical polymerization can be performed by techniques well known in the art, for example, by emulsion polymerization, solution polymerization, suspension polymerization or bull polymerization.

Furthermore the free radical polymerization may be carried out as a batch or as a semi-continuous polymerization process.

The oligomer may be prepared by any known technique and may include directly synthesizing the oligomer in an aqueous process, i.e. in the presence of water (for example by emulsion polymerization, suspension polymerization, micro-suspension polymerization or mini emulsion polymerization), or by solution polymerization where the solution may be water or any organic solvent.

If the solvent is water the monomers are preferably soluble in water.

Preferably the oligomer is prepared by solution polymerization, emulsion polymerization or suspension polymerization.

Preferably the oligomer is prepared by an aqueous process.

Preferably the continuous phase of the aqueous process comprises> 50 wt%, more preferably> 80 wt% and most preferably >95 wt% of water.

Most preferably the oligomcr is prepared by an aqueous emulsion polymerization process.

Preferably the polymer is prepared in an aqueous process.

-13 -Preferably the polymer is prepared by solution polymerization or emulsion polymerization.

Most preferably the polymer is prepared by an aqueous emulsion polymerization process.

The process for preparing the vinyl copolymer may be carried out in a number of modes including but not limited to polymerizing all of the oligomer and vinyl monomers in one batch, pre-charging the oligomer to a reactor and subsequently feeding in the vinyl monomers in one or more stages and/or using a gradient feeding technique (or vice versa), feeding both oligomer and vinyl monomers to a reactor (optionally pre-charged with some oligomer), preparing a vinyl copolymer by feeding the vinyl monomers to the oligomer which is simultaneously fed into a reactor (optionally pre-charged with some oligomer or continuously feeding a mixture of oligomer and vinyl monomers into a reactor.

Preferably the free-radical polymerization is effected by heating the reactor contents to a temperature in the range of from 30 to 100°C and more preferably in the range of from 30 to 90 °C.

A free-radical polymerization of vinyl monomers will require the use of free-radical-yielding initiator to initiate the vinyl polymerization. Suitable free-radical-yielding initiators include inorganic peroxides such as K, Na or ammonium persulphate, hydrogen peroxide, or percarbonates; organic peroxides, such as acyl peroxides including e.g. benzoyl peroxide, allyl hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide; dialkyl peroxides such as di-t-butyl peroxide; peroxy esters such as t-butyl perbenzoatc and the like; mixtures may also be used.

The pcroxy compounds arc in some cases advantageously used in combination with suitable reducing agents (redox systems) such as Na or K pyrosulphite or bisulphite, and iso-ascorbic acid. Metal compounds such as Fe. EDTA (EDTA is ethylene diaminc tctra acetate) may also be used as part of the rcdox initiator system. Azo functional initiators may also be used. Preferred azo-initiators include azobis(isobutyronitrile), 2,2'-azo-bis(2-methyl butane nitrile) (ANBN); and 4,4'-azobis(4-cyanovaleric acid). It is possible to use an initiator partitioning between the aqueous and organic phases, e.g. a combination of t-butyl hydroperoxide, iso-ascorbic acid and Fe. EDTA. The amount of initiator or initiator system to use is conventional, e.g. within the range 0.05 to 6 wt% based on the total vinyl monomer(s) used.

Preferred initiators for preparing the oligomer include ammonium persuiphates, -14 - sodium persuiphates, potassium persuiphates, azobis(isobutyronitrilc) andior 4,4'-azobis(4-cyanovaleric acid). Preferred initiators for preparing the polymer include redox systems and persuiphates as described above.

A further amount of initiator may optionally be added at the end of the polymerization process to assist the removal of any residual vinyl monomers.

The oligomer, when it is a macromonomer may be prepared by a number of processes including but not limited to the use of catalytic chain transfer agents, diarylethene or high temperature processes (such as those described in US 5,710,227).

Molecular weight control of the oligomer may be provided by using chain-transfer agents such as mercaptans and halogenated hydrocarbons or by catalytic chain transfer agents such as mentioned Cobalt-agents.

Suitable chain-transfer agents include mercaptans such as n-dodecylmercaptan, n-octylmercaptan, t-dodecylmercaptan, mercaptoethanol, iso-octyl thioglycolurate, C2 to C8 mercapto carboxylic acids and esters thereof such as 3-mercaptopropionic acid and 2-mercaptopropionic acid; and halogenated hydrocarbons such as carbon tetrabromide and bromo trichloromethane.

(iS 4,403,003 to Backhousc and US 4,973,621 to Buter describe vinyl copolymer dispersions with so-called core-shell morphology; where the core-particle is composed of a high molecular weight hydrophobic polymer and the shell polymer, that is surrounding the core-particle, is a carboxylated polymer of lower molecular weight. The viscosity of these vinyl copolymer dispersions shows a strong dcpcndcncc on the molecular weight of thc carboxylated polymer, cspecially at pH valucs abovc 7 whcrc thc acid groups in thc shcll polymcr arc prcscnt in thc salt-form, rendering the shell copolymer alkali-swellable or soluble. Control of the molecular weight of the carboxylated shell copolymer and hence the viscosity behavior in a coating application is difficult. Therefore it can be advantageous to first synthesize the acid-functional shell copolymer, using the appropriate means known to the person skilled in the art to control molecular weight and than emulsion polymerize the higher molecular weight core polymer in its presence. In order to do so, the carboxylated shell polymer is often (partially) solubilized in the aqueous medium by the addition of a base to neutralize (part) of the acid-functional groups. Performing emulsion polymerization in the presence of a carboxylated oligomer has been described in the prior art, for example in US 4,151,143 to Blank et al. or EP-338486 to Morgan et. al. -15 -So called inverted core-shell latexes are also known from an article by Lee and Ishikawa (J. Poly. Sci., 21, 147-154 (1983)). In these products, the second stage polymer becomes the core domain and is encapsulated by the first-stage polymer. The molecular weight of the oligomers can be controlled by the use of an appropriate initiation system, or by the use of commonly known chain transfer agents.

Also numerous references have been made to the use of carboxylated oligomers that have been produced by a high temperature process. For example US 5.284.894 to Wasyliw et al. describes an emulsion polymerization process where acrylic monomers arc emulsion polymcrizcd in the presence an alkaline aqueous solution of a styrene/alpha-methyl styrene/acrylic acid copolymer that was obtained by high temperature solution or bulk polymerization. A special feature of these high temperature polymerized carboxylated oligomers is that they possess ultimate ethylenically unsaturated double bonds. This double bond allows them to participate in the subsequent polymerization step. Oligomcrs having an ultimate cthylcnically unsaturated double bond are also referred to as "macromonomers". Macromers are included in the definition of oligomer as used in the description of the invention.

Besides the use of high temperature polymerization, other routes have been described to introduce terminal double bonds. The main advantage of these other routes is the fact that they can be used in an emulsion polymerization process, making a so-called "one-pot" synthesis possible.

US 2007/0043 156 Al and US 6,872,789 describe the use of alpha-methyl styrene dimer as an addition fragmentation agent in emulsion polymerization processes to provide molecular weight control and introduce terminal double bonds in the oligomer.

Also the use of a catalytic chain-transfer agent allows control over the molecular weight of the oligomer as well as creating terminal unsaturated groups.

In catalytic chain-transfer polymerization a free radical polymerization is carried out using a free radical forming initiator and a catalytic amount of a selected transition metal complex acting as a catalytic chain transfer agent, and in particular cobalt chelate complexes. Such a technique has been described extensively in the literature.

Various literature references, such as N. S. Enikolopyan et al, J.Polym.Chcm.Ed, Vol 19, 879 (1981), discloses the usc of cobalt II porphyrin complexes as chain transfer agents in free radical polymerization, while US 4,526,945 discloses the use of dioxime complexes of cobalt Ii for such a purpose. Various other publications, e.g. US -16 - 4,680,354, EP-A-0196783, EP-A-0199436 and EP-A-0788518 describe the use of certain other types of cobalt Ii chelates as chain-transfer agents for the production of oligomers of vinyl monomers by free radical polymerization.

Yet another method to synthesize oligomer with a well defined molecular weight and a termin& double bond is the USC of diarylethene. ThC use of diaryethene is described in detail in W. Bremser et al, Prog. Org. Coatings, 45, (2002), 95 and JP 3135151, DE 10029802 and US 2002/0013414. A commonly used diarylethene includes diphenylethene.

Introducing erosslinking groups in thC oligomer and optionally in the polymer is a well known method to improve some of the properties of these vinyl copolymer dispersions when they are used in coating applications such as water and chemical resistance. Such compositions are known from the prior at for example US 5,498,659, (iS 6,730,740 or EP 0 758 364 B2.

Surfactants can be utilized in order to assist in the dispersion of the emulsification of the vinyl copolymer in water (even if it is self-dispersible). Suitable surfactants are ionic or non-ionic surfactants. Examples of anionic emulsifiers are: potassium laurate, potassium stearate, potassium oleate, sodium decyl sulphate, sodium dodeeyl sulphate, and sodium rosinate. Examples of non-ionic emulsifiers are: linear and branched alkyl and alkylaryl polyethylene glycol ethers and thioethers and linear and branched alkyl and alkylaryl polypropylene glycol ethers and thioethers, alkylphenoxypoly(ethylenoxyethanols such as the adduct of I mole of nonylphenol to 5-50 moles of ethylene oxide, or the alkali salt or ammonium salt of the sulphate or the phosphate of said adduct.

Also surfactants containing an olefinicaly unsaturated group that can participate in a free radical polymerization can be used. Suitable polymerizable surfactants include hemi-esters of maleic anhydride of the formula M+.-OOC-CH=CHCOOR wherein R is C6 to C22 alkyl and M+ is Na-I-, K+, Li-I-, NH4-I-, or a protonated or quaternary amine. Polyoxyethylene alkylphenyl ethers with an ethylenically unsaturated bond sold under the tradename Noigen® RN (cx Montello, Inc.) such as NOIGEN RN- 10M, NOIGEN RN-20, NOIGEN RN-30, NOIGEN RN-40'', and NOIGEN RN- 5065FM or the sulphate thereof sold under the tradename 1-litenol® BC (cx Montello, Inc.) such as HITENOL BC10TM, HITENOL BC1025TM, HITENOL BC20TM, HITENOL BC2020TM, HITENOL BC30TM. MAXEMULTM 6106 (available from -17 -Uniquema), which has both phosphonatc cstcr and cthoxy hydrophilicity, a nominal Cl 8 alkyl chain with an acrylate reactive group. Other representative reactive surfactants with phosphate ester functionalities suitable for such reactions include, but are not limited to, MAXEMUL1 6112, MAXEMUL1 5011, MAXEMULTM 5010 (all available from Croda Industrial Specialties). Alternative reactive surfactants suitable for use with various embodiments of the present invention include sodium allyloxy hydroxypropyl sulphonate (available from Rhodia as SIPOMER COPS1TM), ADEKA REASOAP SR'ER series such as ADEKA REASOAP ER-b, ER-20, ER-and ER-40, Akeda Reasope SR-b, SR-20, SR-30 (all available from Asahi Denka Co., Ltd.) and allylsulphosuccinate derivatives (such as TREM LT40TM (available from Cognis)).

The amount of surfactant used is preferably 0 to 15 wt%, more preferably 0 to 8 wt%, still more preferably 0 to 5 wt%, especially 0.1 to 3 wt% and most especially 0.3 to 2 wt% based on the weight of the vinyl copolymer.

By a hydrazide functional compound, is meant a compound bearing a carbonyl-reactive functional group of formula -Nl-INH2 that is reactablc for blocking with a monoketone or monoaldehyde of at least two carbon atoms to form a hydrazone. The blocking reaction can be performed prior to the addition to the vinyl copolymer dispersion or in-situ by adding the mono-carbonyl compound to the vinyl copolymer dispersion after addition of the dihydrazidc, or by adding the monocarbonyl compound prior to the addition of the dihydrazidc compound. Preferred blocked hydrazidc functional compounds include but arc not limited to dicarboxylic acid bis-hydrazones, specific examples being oxalic acid dihydrazone, malonic acid dihydrazone, succinic acid dihydrazone, adipic acid dihydrazone, phthalic acid dihydrazone, tcrephthalic acid dihydrazonc, glutaric acid dihydrazone and sebacic acid dihydrazone, cyclohexane dicarboxylic acid bis-hydrazones, azelaic acid bis-hydrazones.

More preferred examples include adipic acid dihydrazone, succinic acid dihydrazone and glutaric acid dihydrazonc.

Preferably the ratio of blocked hydrazidc functional groups to carbonyl functional groups in the vinyl copolymer is in the range of from 0.1 to 1.00 and most preferably 0.50 to 0.95.

-18 -The hydrazonc curing agcnts can be prepared by known processes such as by hydrazinolysis of carboxylic ester groups of the precursor dicarboxylic acid followed by the reaction with a ketone or aldehyde group containing compound. The chemistry and other reactions are described in The Chemistry of Hydrazides,' H. Paulsen and D. Stoyc, Chapter 10, pp. 515-600 in The Chemistry of Amidcs', H. Zabicky, Ed., Interscience Publishers, New York, New York, 1970.

The hydrazone crosslinker can be prepared separately and added to the vinyl copolymer dispersion. Preferably, the hydrazone crosslinker is prepared in-situ by adding low molecular ketone or aldchydc to the vinyl graft copolymcr dispersion afready containing a dihydrazide. The conversion of dihydrazide to dihydrazone in the resulting crosslinking vinyl copolymer dispersion can be followed by means of capillary gas chromatography. When the hydrazide is blocked using an in-situ conversion to the hydrazone, the equivalence ratio of ketone or aldehyde to hydrazide is preferably 0.5 to 10, more preferably 0.75 to 5 and most preferably 0.95 to 2.

In a preferred embodiment of the invention the dihydrazide is blocked with a mixture of two different ketones or aldehydes. In this way crystallization of the resulting dihydrazonc from the aqueous phase is prevented. Preferred carbonyl blocking agents are volatile having a boiling point below 250 °C, preferably below 200 °C, more preferably below 150 "C, and most preferably below 125 "C. Preferably the blocking compounds have only one carbonyl function. More preferably the mono-carbonyl blocking compounds arc kctoncs Preferred combinations of ketones arc acetone / methyl ethyl kctonc, methyl ethyl ketone / methyl isobutyl ketone. When mixtures of ketones are used a 50:50 ratio seems to produce the best results.

Tf desired the aqueous vinyl copolymer dispersion of the invention can be used in combination with other polymer compositions which are not according to the invention.

Furthermore the composition of the invention is particularly suitable for use in coatings or coating compositions. Such coating compositions can be pigmented or unpigmented.

-19 -The aqueous composition of the present invention maybe applied to a variety of substrates including wood, board, metals, stone, concrete, glass, cloth, leather, paper, plastics, foam and the like, by any conventional method including brushing, dipping, flow coating, spraying, flexo printing, gravure printing, ink-jet printing, any other graphic arts application methods and the like.

The aqueous carrier medium is removed by natural drying or accelerated drying (by applying heat) to form a coating.

Accordingly, in a further embodiment of the invention there is provided a coating, a polymeric film, a printing ink and/or an overprint lacquer obtainable from an aqueous composition of the present invention. It has also been found that the aqueous composition of the invention is suitable for use as an adhesive, accordingly there is also provided an adhesive obtainable from an aqueous composition of the present invention. Types of adhesives include pressure sensitive adhesives, hot melt, contact and laminating adhesives.

The aqueous composition of the invention may contain conventional ingredients, some of which have been mentioned above; examples include pigments, dyes, emulsifiers, surfactants, plastieisers, thickeners, heat stabilisers, levelling agents, anti-cratering agents, fillers, sedimentation inhibitors, UV absorbers, antioxidants, drier salts, organic co-solvents, wetting agents and the like introduced at any stage of the production process or subsequently.

Optionally an external crosslinking agent may be added to the aqueous composition of the invention to aid crosslinking during or after drying. External crosslinking agent include polyisocyanates, amino resins such as melamine-and ureumformadehyde resins, polyaziridines, carbodimides, epoxy resins an solutions of transistion metal salts such as zinc or zirconium ammonium carbonate.

The solids content of the aqueous composition of the invention is preferably within the range of from 20 to 60 wt% and most preferably within the range of from 30 to 50 wt%.

EXAMPLE S

-20 -Example 1. Preparation of a crosslinkable vinyl copolymer dispersion containing a dihydrazide crosslinker.

Example 1.4 -Preparation of a carbonyl functional carboxylated oliogomer A carbonyl-functional carboxylated oligomer for use in a composition according to the present invention can be obtained in the following way.

A reactor was charged with the components according to Table I.

Table I

Component, amounts in parts by weight (pbw) Amount (pbw) Demineralized water 133,9 35% sol. in water of nonylphenol 15 ethyloxide sulfate sodium 0,7 salt 80% solution in water of nonylphenol 20 ethyloxide 0,6 Dodecylbenzene sulfonic acid (free acid, 100% active) 0,5 Sodium hydroxide solution (33%) 0,2 The charged reactor was heated to 90°C under a nitrogen blanket. When the batch had reached 90°C, a first initiator solution containing 0,3 pbw sodium persulfate in 2,2 pbw demineralized water was added. A pre-emulsion was made according to the

following Table II.

Table II

Component Amount (pbw) Demineralized water 223,5 35% solution in water of nonylphenol 15 ethyloxide sulfate 4,2 sodium salt 80% solution in water ofnonylphenol 20 ethyloxide 3,7 Dodecylbenzene sulfonic acid (100%, free acid) 3,0 -21 -Sodium hydroxide solution (33%) 1,1 2-hydroxyethyl methacrylate 5,2 Methacrylic acid 36,8 Methyl methacrylate 76,1 Butyl acrylate 34,6 Styrene 19,7 Mercapto ethanol 2,4 This pre-emulsion was dosed in 120 minutes. Simultaneously a second initiator containing 2,0 pbw sodium persulfate and 38,6 pbw demineralized water was dosed in minutes. After this addition, the batch was kept at 90°C for 30 minutes. When the batch was cooled to 70°C. A solution of 31,5 pbw ammonia (25%) and 376,2 pbw of demineralized water was then added as a neutralization to dissolve the polymer. The solution was cooled to 30°C.

Example 1.B. Polymerization of a higher molecular weight core copolymer in the presence of the oligomer from example l.A

Table Ill

Reactor charge Amount (pbw) Stabilizing resin of Example 1 196,6 The batch was heated to 90°C. A pre-emulsion was made of the following components:

Table IV

Pre-emulsion Amount (pbw Oligomer of example l.A 458,7 Styrene 71,7 2-ethylbexyl actylate 105,2 Methyl methacrylate 84,0 Mcthacrylic acid 8,6 -22 -Nouryctyl® MA 123 8,6 Diacetone acrylamide 8,6 Nourycryl MA123 is a 50% solution in methyl methacrylate of ethylene ureum ethylmethacrylate from AkzoNobel.

An initiator solution was made according to the following Table V.

Table V

Initiator solution Amount (pbw) Demineralized water 56,2 Sodium persulfate 0,8 When the batch reached 90°C, this pre-emulsion was dosed in 180 minutes and the initiator was dosed in 195 minutes. The batch was kept at 90°C for an additional 30 minutes and then cooled down to 30°C. The pH of the batch was then adjusted to 7,5 with a 25% ammonia solution. Subsequently the following solution was added:

Table VI

Finishing Example 1.B Adipic dihydrazide Proxel® XL2 1,0 Proxel® XL2 is a compound based on benzoisothiazolone. Proxel® is a trademark of Arch Chemicals.

Example 2. Preparation of a crosslinkable vinyl copolymer dispersion containing a dihydrazonc crosslinker.

A crosslinking vinyl copolymer dispersion was synthesized using the method and ingredients used in example 1. To this vinyl copolymer dispersion was added an amount of a mixture consisting of 50 parts methyl ethyl ketonc and 50 parts methyl iso-butyl ketone that is equivalent to the concentration of hydrazide groups from the adipic dihydrazide in order to convert the hydrazide groups to hydrazone groups.

-23 -Examples 3 and 4. Coating compositions.

25,1 pbw of the dispersions of Example I or Example 2 was mixed with 75,2 pbw demineralized water, I pbw of a dispersant (e.g., Orotan® 1124 of Rohm and l-laas), 0,5 pbw defoamer (e.g., Dehydran® 1620 of Cognis), 1 pbw aminomethyl propanol, and 175,5 pbw titanium dioxide. This mixture was ground until the mean particle size was less than 10 m. This premix was then mixed further with 17,6 pbw demineralized water, I pbw defoamer(e.g., Dehydran® 1620 of Cognis), 1,5 pbw polyether modified dimethyl siloxane copolymer (e.g., Byk® 333 of Byk Chemie), 20,1 pbw butyl glycol, 5,0 pbw of a rheology modifier (e.g., Acrysol® RM 5 solution of Rohm and Haas) 2,5 pbw Forbest® 600 from Lucas Meyer GmbH, and 2,5 pbw dibutyl phthalate. This mixture was then added, under agitation, to the pigment paste, after which the whole was added to 668,7 pbw of the dispersions of Example 1 and 2.

The resulting coating compositions are: Example 3: containing the crosslinking vinyl copolymer dispersion from example I Example 4: containing the crosslinking vinyl copolymer dispersion from example 2 Both coating compositions were put in an oven at a temperature of 50 °C for a period of 6 months. After this period applications were made of both coating compositions.

We found that the viscosity of example 3 had increased considerably compared to that of the coating composition of example 4. Also the coating composition of example 3 contained gel-like particles, making a proper smooth application using a doctor-blade on glass impossible. From the observations above it is clear that using a hydrazone crosslinker is beneficial for viscosity stability of the coating.

-24 -

Claims (20)

1. CLAIMS1. A process for the preparation of an aqueous dispersed polymer coating composition comprising the steps of: i) providing an aqueous binder system comprising a water-dispersed polymer binder, wherein the binder system is provided with a carbonyl-hydrazide cross-linking system; and ii) adding to the aqueous binder system one or more volatile mono- carbonyl entities reversibly reactive with the hydrazide groups of the cross-linking system.
2. 2. The process of claim 1 wherein the polymer binder comprises carbonyl and/or hydrazidc flinctional groups, and optionally the carbonyl-hydrazide cross-linking system comprises a crosslinker having carbonyl and/or hydrazide functional groups for reaction with the functional groups of the polymer binder to give crosslrnking.
3. 3. The process of claim 2 wherein the crosslinker is a dihydrazide, preferably adipic dihydrazide.
4. 4. The process of claim 1, 2, or 3 wherein the mono-carbonyl entities are selected from the group consisting of mono-ketones, mono-aldehydes, and mixtures thereof
5. 5. The process of claim 1,2 or 3 wherein the one or more mono-carbonyl entities are added to a molar ratio with the hydrazide groups of from 0.1 to 5; more preferably from 0.1 to 4; more preferably 0.1 to 3; more preferably 0.1 to 2; more preferably 0.1 to 1; more preferably 0.1 to <1; and most preferably 0.1 to -25 - 095. More preferably the ratio will have a lower limit of 0.2, more preferably 0.3, more preferably 0.3, more preferably 0.4, and most preferably 0.5.
6. 6. The process of any ofclaims I to 4 wherein two or more mono-carbonyl cntities arc added.
7. 7. The process of any of claims 1 to 6 wherein the aqueous binder system comprises a polymer binder having earbonyl functional groups and a erosslinker having hydrazide frmnctional groups.
8. 8. The process of any of dams I to 7 wherein the polymer binder has a number average molecular weight in the range of 500 and 50000, preferably 1000 to 50000, and more preferably 2000 to 20000.
9. 9. An aqueous coating composition obtainable by the process of any of claims I to 8.
10. 10. An aqueous coating composition comprising, a) an aqueous dispersed polymer binder, preferably an aerylate polymer binder; and b) water (wt% water:polymer binder); wherein the aqueous coating composition is provided with a earbonyl-hydrazide cross-linking system; characterized in that: the composition further comprises one or more volatile (boiling point <200°C) mono-carbonyl entities reversibly reactive with the hydrazide of the cross-linking system, wherein the molar ratio of the one or more mono-earbonyl entities to hydrazide groups is from 0.1 to 5; more preferably from 0.1 to 4; more preferably 0.1 to 3; more preferably 0.1 to 2; more preferably 0.1 to 1; more preferably 0.1 to <1; and most -26 -preferably 0.1 to 0.95. More preferably the ratio will have a lower limit of 0.2, more preferably 0.3, more preferably 0.3, more preferably 0.4, and most preferably 0.5.
11. 11. An aqueous coating composition according to claim 10, wherein two or more of thc mono-carbonyl cntitics arc providcd.
12. 12. Thc aqueous coating composition according to claim 10 or 11 comprising i) 10 to 90% by weight solids of the polymer binder ii) 0 to 70% by weight solids of a crosslinker; iii) 0.01 to 5% by weight of one or more mono-carbonyl entities; and iv) 15 to 90% by weight of water; wherein I) to iv) add up to 100%
13. 13. The aqueous coating composition according to claim 10, 11 or 12 comprising 0.01% to 4%, more preferably 0.05% to 3%, even more preferably 0.10% to 2%, and most preferably 0.15% to 1% by weight of one or more mono-carbonyl entities.
14. 14. A paint formulation comprising the coating composition according to any of claims 10 to 13 and a pigment, and optionally coating additives and/or organic solvents.
15. 15. A wood stain formulation comprising the coating composition according to any of claims 10 to 13.
16. 16. An article coated with the coating composition of claim 10 to 13, the paint formulation of claim 14, or the wood stain of claim 15.-27 -
17. 17. Use of one or more volatile mono-carbonyl entities to stabilize the viscosity of an aqueous coating composition comprising, a) an aqueous dispersed polymer binder, preferably an acrylate polymer binder; and b) water; wherein the aqueous coating composition is provided with a carbonyl-hydrazidc cross-linking system.
18. 18. A crosslinkable vinyl copolymcr dispersion comprising: a) an aqueous solution of a water-soluble oligomer having a number average molecular weight M. within the range of from 500 to 50,000 and a glass transition temperature (Tg) within the range of 10 to 150°C, and which oligomer is derived from a monomer system comprising 1-45 weight % of acid comonomcr(s), 0.5 to 20 weight % of crosslinking comonomers), and 98.5-50 weight % of non-acid functional, non-crosslinking comonomcr(s), said oligomcr having crosslinkable carbonyl or hydrazidc flrnctional groups, b) optionally comprising an aqucously dispersed hydrophobic polymer having a number average molecular weight M11 higher than that of the oligomer; the dispersed polymer optionally having functional groups for imparting crosslinkability; c) a polyhydrazide or polycarbonyl crosslinking agent being reactable with the crosslinker functional groups of the oligomer and (if present) of the hydrophobic polymer; and d) one or more volatile mono-carbonyl entities reversibly reactive with the hydrazide cross-linking groups.
19. 19. A crosslinlcable vinyl copolymer dispersions according to claim 18 wherein the weight percent ratio of oligomer to polymer is in the range of from 10:90 to 90:10, preferably 25:75 to 75:25 and most preferably between 35:65 to 65:35.-28 -
20. 20. An aqueous composition according to any of claims 18 to 19 where the hydrazide crosslinker is adipic dihydrazide 21 An aqueous composition according to any of claims 18 to 20 that contains 0 to 50 wt%, more preferably 0 to 40 wt% and most preferably 0 to 35 wt% of organic co-solvent by weight of the vinyl copolymer.22. The composition according to any of claims 18 to 21 wherein the ratio between the mono-carbonyl compound relative to the hydrazide compound is from 0.5 to 5.23. The composition according to any of claims 18 to 22 wherein the number average molecular weight M1, of the oligomer is in the range of from 2,500 gi'mol to 25,000 g/mol and most preferably 5,000 g/mol and 15,000 g/mol.24. The composition according to any of claims 18 to 23 wherein the vinyl copolymer comprises 0.5 to 10 wt% and more preferably 2 to 5 wt% of carbonyl thnctional vinyl monomer(s) and the oligomer comprises 0 to 20 wt%, more preferably 0 to 10 wt%, and most preferably 0 to 5 wt% of carbonyl functional vinyl monomer(s).25. The composition according to any of claims 18 to 24 wherein the oligomer contains at least one double bond capable of participating in a radical polymerization.26. The composition according to any of claims 18 to 25 wherein the oligomer is synthesized using a sulfur containing chain transfer agent; or the oligomer is synthesized using a catalytic chain transfer agent; or the oligomer is synthesized using an addition fragmentation polymerization; or the oligomcr is synthesized using diarylethylene; or the oligomer is synthesized using a high temperature process resulting in oligomers with a terminal double bond.27. A process for the preparation of an aqueous dispersed polymer coating composition comprising the steps of: a) providing an aqueous solution of an acid-functional oligomer built from olefinically unsaturated monomers, said oligomer having a number average molecular weight M within the range of from 500 to 50,000 and a glass transition temperature (Tg) within the range of 10 to 150°C, and which oligomcr is derived from a monomer system comprising 1-45 weight % of acid comonomer (s), 0.5 to 20 weight % of carbonyl functional crosslinking comonomer(s), and 98.5-50 weight % of non-acid functional, -29 -non-crosslinking comonomcr(s), and said acid functionality rendering the oligomcr water-soluble per se or by neutralization, and said oligomer also having thnctional groups provided by said crosslinking comonomer(s) for imparting crosslinkability when the aqueous polymer composition is subsequently dried, b) optionally conducting an aqueous emulsion pcdymcrization process of at least one olefInically unsaturated monomer in the presence of the aqueous solution of the oligomer, to form an aqueous dispersion of a hydrophobic polymer having a number average molecular weight M1, higher than that of the oligomer, said polymer optionally having carbonyl functional groups for imparting crosslinkability when the aqueous polymer composition is subsequently dried, and c) combining the aqueous dispersion from b) with a polyhydrazone cross-linker by either: i) preparing the polyhydrazone in-situ by reaction of a polyhydrazide with one or more volatile mono-carbonyl entities; or ii) direct addition of a preformed polyhydrazone product of a polyhydrazide and one or more volatile mono-carbonyl entities subsequent to step b) and/or performing the polymerization in the presence of the crosslinking agent 28. An aqueous composition according to claim 27 where the carbonyl functional vinyl monomer is diacetone acrylamide.29. An aqueous composition according to claim 27 or 28 wherein the hydrazone crosslinkcr is derived from the reaction of a mono-carbonyl compound, mono-kctone, or mono-aldehyde with adipic dihydrazide.30. The composition according to any of claims 27 to 29 wherein the ratio between the mono-carbonyl compound relative to the hydrazidc compound is from 0.5 to 5.-30 -