WO2015052213A1

WO2015052213A1 - Polymer, composition and use

Info

Publication number: WO2015052213A1
Application number: PCT/EP2014/071503
Authority: WO
Inventors: Ronald Tennebroek; Roel Johannes Marinus Swaans; DE Paul KOK
Original assignee: Dsm Ip Assets B.V.
Priority date: 2013-10-09
Filing date: 2014-10-08
Publication date: 2015-04-16
Also published as: WO2015052214A1

Abstract

There is described a process for preparing an aqueous dispersion of a polyurethane A (PUD) the process comprising the steps of: (a) reacting components one and three (and two and four where present) to form an acidic isocyanate terminated prepolymer that comprises anionic or potentially anionic functional groups thereon; where: (1) component one comprises 10 to 80% by weight of at least one polyisocyanate optionally containing at least one anionic or potentially anionic dispersing group; (2) optional component two comprises up to 15% by weight of at least one isocyanate reactive polyol containing at least one anionic or potentially anionic dispersing group; (3) component three comprises 15 to 85% by weight of at least one isocyanate reactive hydrophobic polyol other than component two if present, and having a weight average molecular weight greater than or equal to 500 Daltons; and (4) optional component four comprises up to 20% by weight of at least one isocyanate reactive polyol other than component three and two if present and having a weight average molecular weight less than 500 Daltons; where if component two is not present component one contains at least one anionic or potentially anionic dispersing group; where the mixture used in step (a) is substantially free of volatile amines and N- alkyl pyrrolidinones; (b) adding to the reaction mixture from step (a) an alkali metal neutralising agent in an amount from 0.05 to 6 parts by weight substantially to neutralise the isocyanate terminated prepolymer obtained from step (a); and (c) reacting the neutralised prepolymer from step (b) with an active hydrogen compound to extend the chain of the prepolymer to form an aqueous dispersion of polyurethane A. PUDs obtained from this method and coating compositions comprising the PUD with a vinyl polymer B are also described.

Description

POLYMER, COMPOSITION AND USE

The present invention relates to the field of polyurethanes especially urethane-acrylic based dispersions.

Urethane-acrylic (U-A) dispersions have good resistance to water, chemicals, solvents and abrasion and so are commonly used in coating compositions such as decorative and protective coatings.

To prepare stable aqueous urethane-acrylic dispersions, both the acrylic part and the polyurethane (PU) part must be dispersed in water. This can be achieved in part by surfactants and in part by incorporating suitable groups such as ionic or non-ionic hydrophilic groups in the polyurethane polymer either pendant to the polymer chain or in-chain. Such groups include anions such as carboxylic, sulfonic, sulphate or phosphate groups that are typically incorporated into the PU by reacting compounds containing reactive hydrogen and at least one suitable acid group (typically a carboxylic acid) with polyisocyanate to form the polyurethane component of the urethane-acrylic dispersion. It is undesirable that large amounts of acidic materials remain in the resultant dispersion thus a substantial part (if not all) of the acid present must be neutralised in the final product.

It is also desirable to reduce or eliminate the use of surfactants in an aqueous coating dispersions as the use of large amount of surfactant increases the water sensitivity of the coatings that are formed.

When simple inorganic bases (such as KOH) are added to neutralise anionic polyurethane dispersions to neutralise acid groups therein, they are found unsatisfactory. In general the viscosity of the polyurethane dispersion rises undesirably when strong inorganic bases are added. To prevent the dispersion destablising the polyurethane, it may be modified with large amounts of hydrophilic groups such as polyethoxy groups. The resultant films and coatings (whether the PU is modified or not) are also highly water sensitive (compared to PUD neutralised by other agents) unless a further agent is added to cross-link the polyurethane. So other neutralising agents are used to prepare commercially available PU dispersions, the most common of which are volatile amines such as the tertiary amine triethyl amine (TEA). These materials are readily available and evaporate from the final film.

However it is known that volatile amines also have various disadvantages. For example they readily evaporate volatile organic compounds (VOC) during the film formation causing unacceptable environmental pollution and/or poor indoor air quality when used indoors. The use of such materials may be more strictly regulated in the future. Therefore it is desirable to find an alternative method of providing stable aqueous urethane-acrylic dispersions and/or neutralising acidic materials used during their preparation.

Various alternatives have been proposed to improve the stability of aqueous urethane dispersions.

US 2968575 describes a PU latex dispersed in water using an emulsifier.

US 4,501 ,852 describes stable aqueous dispersions of polyurethane- ureas containing (i) 10-120 meq per 100 g of anionic groups chemically incorporated therein and (ii) up to about 10% by weight of hydrophilic chains containing ethylene oxide (EO) units. To counter the anionic groups the formulation contains a mixture of volatile and non volatile cations in a equivalent ratio from about 1 :4 to 4:1. The examples use as component (ii) a nonionic polyether monoalcohol of n-butanol, ethylene oxide and propylene oxide (in a molar ratio 83:17) having an OH-number of 26. This component aids dispersion but increases water sensitivity. The examples also use the undesirable NMP as a solvent.

US 4,701 ,480 describes aqueous polyurethane-urea dispersions with improved hydrolytic stability formed from an aqueous polyurethane-urea-dispersion containing carboxylic acid groups neutralized with volatile organic bases which are then converted to non volatile cations by adding alkali metal salts of organic or inorganic acids in an amount sufficient to displace at least a portion of the volatile organic bases. The volatile organic bases may be optionally removed by distillation under reduced pressure. All the examples contain NMP and distillation is undesirable because it uses large amounts of energy and may cause excessive foaming (as described in Example XVI of US 2010/0099967).

US 2006-0229409 describes polyurethane dispersions made from TMXDI with a special embodiment on page 9 where the use of metal hydroxides is mentioned. This is not exemplified in the examples nor is TMXDI a suitable

diisocyanate for use in coatings (it is too soft).

US 2010-0098867 (Costa) describes a method of making aqueous dispersions of carboxylated anionic polyurethanes that are free of volatile amines and do not contain any polyoxyethylene or polyoxypropylene side chains. First a prepolymer (containing 2-10% by weight of isocyanate groups and 10-100 meq of carboxylic groups) is prepared by reacting: a polyol with a carboxylic acid group; a non ionic polyol, and a (cyclo)aliphatic polyisocyanate. The prepolymer is dispersed in an aqueous solution of an alkaline metal hydroxide and then the prepolymer is chain extended with a polyamine.

EP1 153051 describes aqueous dispersions of anionic polyurethanes with pendant carboxylic acid groups that are neutralised with a reactive volatile amine compound (tertiary aminofunctional acrylic monomer (DMAEMA)) that is subsequently incorporated in the polymer backbone by radical polymerization. Unreacted free monomer remains in the final product which thus still contains volatile amines. The monomer may also contain impurities in the monomer and hydrolysis may generate the undesirable side product dimethylethanol amine.

W093/24551 describes an aqueous polyurethane polymer dispersion comprising the reaction product of: organic polyisocyanate; polyester polyol which incorporate polymerized units derived from dimer acid; nonionic and/or ionic dispersing groups and at least one of the following polymerized units: cyclo-aliphatic polyol of molecular weight (Mw) < 400; cyclo-aliphatic polyacid of MW < 400, aromatic polyol MW< 500, aromatic diacid Mw < 500 and an active hydrogen chain extending compound.

WO 2001 -027179 (Stahl) describes an anionic polyurethane dispersion which is neutralised by a tertiary amine functional urethane polymer or oligomer. Although the polymeric material is less volatile than reagents such as TEA, this method adds extra expense and complexity to preparation of the PU dispersion and is not completely successful at removing all acidic groups.

The applicant's co-pending applications PCT/EP2013/057457 (claiming priority from EP12163513.0) and PCT/EP2013/057455 (claiming priority from EP12163515.5) discloses similar compositions to those described herein, but where the component three is not specified to be hydrophobic (especially as hydrophobic is defined herein). The Examples of PCT/EP2013/057457 and PCT/EP2013/057455 and their priority documents (all of the contents of which are incorporated by reference) insofar as they may inadvertently overlap any aspect of the present invention are hereby disclaimed herein.

Surprising the applicant has found a means to stabilise aqueous dispersions of acrylate and anionic polyurethanes without the proceeding

disadvantages.

In particular the applicant has found that adding an alkali metal neutralising agent at an early stage in the process and using an isocyanate reactive hydrophobic polyol as component three reduces or avoids some or all of the preceding problems with the prior art.

Therefore broadly the invention comprises a process for preparing an aqueous dispersion of a polyurethane A the process comprising the steps of:

(a) reacting components one and three (and two and four where present) to form an acidic isocyanate terminated pre-polymer that comprises anionic or potentially anionic functional groups thereon; where:

(1 ) component one comprises 10 to 80% by weight of at least one polyisocyanate optionally containing at least one anionic or potentially anionic dispersing group;

(2) optional component two comprises up to 15% by weight of at least one isocyanate-reactive polyol containing at least one anionic or potentially anionic dispersing group;

(3) component three comprises 15 to 85% by weight of at least one isocyanate reactive hydrophobic polyol and having a weight average molecular weight greater than or equal to 500 Daltons optionally containing at least one anionic or potentially anionic dispersing group; and

(4) optional component four comprises up to 20% by weight of at least one isocyanate reactive polyol other than component three and two if present and having a weight average molecular weight less than 500 Daltons; where if component two is not present component one or three contains at least one anionic or potentially anionic dispersing group;

where the amounts of components one to four are expressed as a weight percentage calculated from the total amount of the above components (i.e. one and three and optional two and/or four where present) being 100%; and where the mixture used in step (a) is substantially free of volatile amines and N-alkyl pyrrolidinones;

(b) adding to the reaction mixture from step (a) an alkali metal neutralising agent in an amount from 0.05 to 6 parts by weight substantially to neutralise the isocyanate terminated prepolymer obtained from step (a);

where the amount (in weight parts) of the alkali metal neutralising agent is calculated based on the weight of alkali metal in the neutralising agent relative to the total amount of components one to four in step (a) being equal to 100 parts by weight; and (c) reacting the neutralised prepolymer from step (b) with an active hydrogen compound to extend the chain of the prepolymer to form an aqueous dispersion of polyurethane A.

Preferably in step (a) the process of the invention is free of tin catalysts, more preferably comprises catalysts selected from no catalyst and/or carboxylates of zinc, zirconium, copper, bismuth, titanium and/or molybdenum, most preferably is substantially free of any catalysts for any of the reaction steps.

As used herein hydrophobic denotes that a moiety (e.g. a molecule or part thereof) is a hydrophobe, a term which is well understood by those skilled in the art. Hydrophobes are usually substantially immiscible with (preferably insoluble in) water. Usefully hydrophobes may also be lipophilic, that is substantially miscible with (preferably soluble in) fats, oils, lipids, and/or non-polar materials such as hexane and/or toulene. More preferred hydrophobes are themselves substantially non polar or have a low polarity (for example may have a net difference in electronegativity between the atoms of the moiety of from 0 to 0.4 on the Pauling scale). Hydrophobes may also exhibit a high (>90°C) water contact angle (preferably > 100°C, more preferably > 120°C, most preferably > 150°C) when liquid water is applied to their surface.

Hydrophobicity (and its opposite hydrophilicity) denotes a relative property of a material. Therefore unless expressly stated herein it may not always be possible to set an absolute borderline between a hydrophobe and hydrophile. The relative and/or absolute hydrophobic character of a component, composition, monomer, oligomer and/or polymer described herein (such as component three) can nevertheless be determined by several different well known methods available to the person skilled in the art. Surface tension is one such method, water breakthrough pressure is another. For example a micro-porous membrane can prepared identically but from two different materials. The water flux through each membrane can be independently and separately measured by any suitable technique well-known to those skilled in the art to determine which of the test materials is relatively the more hydrophobic. Surface tension is another appropriate physical property that may be generally used to distinguish a hydrophobe from a hydrophile. For example surface tensions of materials such as polymers can be accurately determined by observing whether or not droplets of liquids such as water spontaneously spread on their surface (spreading indicates a hydrophile). In a preferred embodiment a material is denoted herein as hydrophobic (such as the hydrophobic polyols of component three) when it exhibits a water contact angle of more than 90° (preferably > 100°C, more preferably > 120°C, for example > 150°C).

Thus it will be understood that in a first embodiment of the present invention the hydrophobic polyol(s) of component three are hydrophobic insofar as relative to the other components one to four, they have a more hydrophobic character than any of the other components one, two and/or four that are present.

In another, second, embodiment of the present invention the hydrophobic polyol(s) of component three are hydrophobic insofar as they have an absolute hydrophobicity measured by having a water contact angle of at least 90°C.

In another third embodiment of the present invention the hydrophobic polyol(s) of component three are hydrophobic relative to the other components one to four and also by having a water contact angle of at least 90°C.

It is preferred that optional component two is a non-hydrophobe, but if component two is hydrophobic then component three and component two are not the same. As used herein the terms hydrophile and non-hydrophobe (as well as corresponding adjectives etc.) are used synonymously.

It will be seen that the sum of the amounts of ingredients given (a) and (b) together will total greater than 100 parts by weight.

In the process of the invention any of component(s) (1 ), (2) and/or (3) by themselves and/or in any combination may comprise at least one anionic or potentially anionic dispersing group. However it is preferred that the isocyanate component (1 ) does not contain an anionic or potentially anionic dispersing group but instead at least one such group comprises the polyol component (2).

Therefore in one embodiment of the process of the invention, step (a) comprises:

(a) reacting:

(1 ) 10 to 80% by weight of at least one polyisocyanate;

(2) 1 to 15% by weight of at least one isocyanate-reactive non-hydrophobic polyol comprising at least one anionic or potentially anionic dispersing group;

(3) 15 to 85% by weight of at least one isocyanate reactive hydrophobic polyol having a weight average molecular weight > 500 Daltons optionally containing at least one anionic or potentially anionic dispersing group; and (4) optionally up to 20% by weight of at least one isocyanate reactive polyol other than (2) and (3) and having a weight average molecular weight < 500 Dalton;

to form an acidic isocyanate terminated prepolymer that comprises anionic or potentially anionic functional groups and which is substantially free of volatile amines and N-alkyl pyrrolidinones (such as TEA, NMP or NEP).

Preferably step (b) occurs during or substantially immediately after step (a).

Without being bound by any mechanism it is believed that in step (b) the metal cation from the alkali metal neutralising agent forms a counterion for the anionic group thereon (and/or anionic group formed from the potential anionic groups thereon)

A further aspect of the invention provides a process for preparing an aqueous coating composition comprising bringing into initimate admixture components (i) and (ii):

(i) 10 to 95%, preferably 20 to 80%, more preferably 30 to 65% by weight of a polyurethane dispersion A obtained or obtainable by the process of the invention as described herein; and

(ii) 90 to 5%, preferably 80 to 20%, more preferably 70 to 35% by weight of a vinyl polymer B, wherein

(i) and (ii) add up to 100% and are calculated based on weight of solids (excluding the water); and where the composition (and both components (i) and (ii)) are substantially free of volatile amines and N-alkyl pyrrolidinones.

The Tg of polymer B preferably is greater than -10°C, preferably greater than 0°C, most preferred > 15°C.

As is well known, the glass transition temperature of a polymer is the temperature at which it changes from a glassy, brittle state to a plastic, rubbery state.

The glass transition temperatures may be determined experimentally using differential scanning calorimetry DSC, taking the peak of the derivative curve as Tg, or calculated from the Fox equation. Thus the Tg, in degrees Kelvin, of a copolymer having "n" copolymerised comonomers is given by the wt fractions W of each comonomer type and the Tg's of the homopolymers (in degrees Kelvin) derived from each comonomer according to the equation:

Tg Tg_! Tg₂ Tg_n The calculated Tg in degrees Kelvin may be readily converted to °C.

Preferably both components (i) and (ii) form different phases which are present in the same particles.

Based on the total amount of components one to four (where present) being 100% the weight percentage of each of these components in the compositions of the invention may be as follows.

Preferably component (1 ) (the polyisocyanate) is present in an amount from 15% to 70%, more preferably from 20% to 60%, most preferably 25% to 50% by weight.

Preferably component (2) (the anioinic isocyanate-reactive polyol) is present in an amount from 2% to 12%, more preferably from 3% to 10%, most preferably 4% to 7% by weight.

Preferably component (3) (the high (>500D) mw isocyanate-reactive hydrophobic polyol) is present in an amount from 20% to 80%, more preferably from 25% to 75%, most preferably 30% to 60% by weight.

Preferably optional component (4) (the low (<500D) mw isocyanate- reactive polyol) is present in an amount from 0.5% to 20%, more preferably from 1 % to 15%, most preferably 2% to 10% by weight.

Usefully the preceding components may also be present in the same number amounts given above where the percentages are replaced by relative parts by weight.

Based on the total amount of components one to four (where present) being 100 parts by weight the amount of other components in the compositions of the invention expressed as parts per weight may be as follows.

Preferably optional component (5) (the alkali metal neutralising agent) may be present in an amount from 0.1 to 6, more preferably from 0.2 to 5, most preferably 0.5 to 4 parts by weight.

Preferably further optional components (6) (which may be any other suitable additives well known to those skilled in the art) may be present in a total amount from 0.1 to 20, more preferably from 0.2 to 10, most preferably 0.5 to 5 parts by weight.

Usefully the preceding components may also be present in the same number amounts given above where the relative parts by weight are replaced by weight percentages based on the total amount of all the components being 100%. The term "alkali metal neutralising agent" denotes an alkali metal compound, preferably an alkali metal salt, that is sufficiently basic under the conditions (under which the polyurethane dispersion is prepared) to neutralise the acidic groups on the polymer. Without wishing to be bound by any mechanism it is believed that ions from the alkali metal neutralising agent act as counter ions to ionic groups formed from acidic groups on the polymer. Preferred alkali metal salts comprise cations such as potassium, sodium and/or lithium with sodium being more preferred. Preferred alkali metals salt comprise anions such as carbonate, bicarbonate, hydroxide and/or hydride, with hydroxide being more preferred. The most preferred alkali metal neutralising agents are sodium and/or potassium hydroxide.

The polyurethane dispersions of the invention may (unless indicated otherwise herein) be prepared conventionally using conventional polyols and isocyanates.

For example the polyisocyanate used in the present invention as component one may be selected from those described in WO2007-006586 as polyisocyanate component (i) (see from page 7, line 33 to page 8, line 20 - this passage incorporated herein by reference).

For example the NCO-reactive polyols used in the present invention as components two, three and four (subject to the other requirements for these components specified herein) may be selected from those described in WO2007-

006586 as components (ii), (iii) and/or (iv) (see from page 8, line 30 to page 9, line 24 - this passage also incorporated herein by reference)

Component one comprises a polyisocyanate. Suitable polyisocyanates may comprise aliphatic, cycloaliphatic, araliphatic, aromatic and/or polyisocyanates modified by the introduction of urethane, allophanate, urea, biuret, carbodiimide, uretonimine, urethdione or isocyanurate residues. Examples of suitable polyisocyanates include ethylene diisocyanate, 1 ,6-hexamethylene diisocyanate, isophorone diisocyanate, cyclohexane-1 , 4-diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, p-xylylene diisocyanate, α,α'-tetramethylxylene diisocyanate, 1 ,4- phenylene diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 4,4'- diphenylmethane diisocyanate, polymethylene polyphenyl polyisocyanates, 2,4'- diphenylmethane diisocyanate, 3(4)-isocyanatomethyl-1 -methyl cyclohexyl isocyanate, 1 ,5-naphthylene diisocyanate and mixtures thereof. Preferred polyisocyanates are isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, toluenediisocyanate and 4,4'-diphenylmethane diisocyanate. Components two, three and four comprises various polyols as defined herein. Suitable polyols may comprise propylene glycols, poly(propylene

oxide/ethylene oxide) copolymers, polytetrahydrofuran, polybutadiene, hydrogenated polybutadiene, poysiloxane, polyamide polyesters, isocyanate-reactive polyoxyethylene compounds, polyester, polyether, polyether ester, polycaprolactone, polythioether, polycarbonate, polyethercarbonate, polyacetal and polyolefin polyols.

Preferably component two comprises a polyol with an anionic or potential anionic dispersing group thereon.

Preferred anionic dispersing groups are carboxylic, phosphate, phosphonate or sulphonic acid groups. Preferred potentially anionic dispersing groups are precursors for the anionic dispersing groups described herein, i.e. groups which under the conditions of step (a) will transform into the anionic dispersing groups. Most preferred anionic dispersing groups are carboxylic or sulphonic acid groups.

Conversion to the salt form is achieved by neutralisation of anionic groups with an alkali metal neutralising agent during step (b). Most preferably dimethylol propanoic acid is used.

Component three comprises an isocyanate reactive hydrophobic polyol with a weight average molecular weight of greater than 500 daltons (high mw polyol). Preferably component three comprises polyols that (calculated based on the weight of the polyol being 100 wt%) comprise > 10 wt%, more preferably >20 wt%, even more preferably >30 wt%, most preferably > 40 wt% of diacids and/or dialcohols containing hydrophobic hydrocarbo moieties. The hydrocarbo moiet(ies) may comprise 8 or more carbon atoms, usefully have from 8 to 50, more usefully from 12 to 44 and most usefully from 16 to 36 carbon atoms. Conveniently the carbon atoms in such hydrocarbon moieties may form a carbon chain although preferred polyols may also comprise cyclic groups. It is especially preferred that component three comprises polyols that comprise > 10 wt %, more preferably > 20 wt%„ even more preferably >30 wt % and most preferably >40 wt% of a dimer fatty acid (calculated based on the weight of the polyol being 100 wt%).

As used herein, weight average molecular weight of a polymer is determined using Size Exclusion Chromatography performed on a Waters Alliance 2695 (pump, degasser and autosampler) with a Waters 410 differential refractive index detector and Shimadzu CTO-20AC column oven. The eluent was 1 ,1 ,1 ,3,3,3 hexafluoro isopropanol (HFIP) with the addition of 0.2M potassium trifluoro actetate (PTFA). The injection volume was 50μΙ. The flow was established at 0.8 ml/min. Two PSS PFG Linear XL columns (Polymer Standards Service) with a guard column (PFG PSS) were applied at a temperature of 40°C. The detection was performed with a differential refractive index detector. The sample solutions were prepared with a concentration of 5 mg solids in 2 ml HFIP (+ 0.2M PTFA), and the samples were dissolved for a period of 24 hours. Calibration is performed with eleven polymethyl methacrylate standards (polymer standard services), ranging from 500 to 2,000,000 g/mol. The calculation was performed with Empower 3 software (Waters) with a third order calibration curve. The molar mass distribution is obtained via conventional calibration and the molar masses are polymethyl methacrylate equivalent molar masses (g/mol).

In one preferred embodiment of the invention component three comprises carbonate moieties that (calculated based on the weight of the carbonate moiety being 100 wt%) comprise > 10 wt%, more preferably >20 wt%, even more preferably >30 wt%, most preferably > 40 wt% of dialcohols that comprise hydrocarbo moieties. The hydrocarbo moiet(ies) may comprise 8 or more carbon atoms, usefully have from 10 to 50, more usefully from 12 to 46, even more usefully from 16 to 44 and most usefully from 22 to 36 carbon atoms. Conveniently the carbon atoms in such hydrocarbon moieties may form a carbon chain

Preferred polyols that comprise component four may have one or more of the following properties: comprise short chains that impart greater rigidity to the resultant polyurethane A. Preferably the molecular weight is below 500 Dalton, more preferably below 350 Dalton, most preferably 250 Daltons (typical examples are neopentylglycol, cyclohexane dimethanol, hexane diol, trimethylolpropane)

In one embodiment of the invention it is preferred that the acrylic urethane of the invention and/or prepared according to the process of the invention is substantially free of any non-ionic functional polyols as it is believed that such components may deteriorate water resistance.

In a still further embodiment of the invention it is preferred that the polyurethane dispersions (PUD) and/or the urethane acrylics of or prepared in the present invention are permanently basic (i.e. after neutralisation with the alkali metal neutralising agent), preferably exhibiting a pH of > 8. Although PUDs and urethane acrylic coatings with a high pH were thought to be undesirable, the applicant has surprisingly found that they may solve some or all of the problems identified herein. Optionally additional surfactant may be added to facilitate dispersing the urethane however this is not preferred as it has a detrimental effect on the water resistance.

In the present invention it is preferred that the neutralising agent is added to the prepolymer as by pre-neutralizing the prepolymer urethanes with lower acid values can be synthesized which have improved water resistance. More preferably the neutralizing agent is added as aqueous solution to the prepolymer.

Preferred compositions of the invention have low acid values (AV), preferably the AV of the total composition is from 1 to 40 mg KOH / g, more preferably 2-20 mg KOH/g, most preferably 3-15 mg KOH/g.

Without wishing to be bound by any mechanism it is believed that (alkali) metal ion neutralized urethane-acrylic based dispersions contain sufficient hydrophobic polyols to compensate for the deteriorated chemical stain resistances, specifically water resistance and optionally may also be made without a tin catalyst so the composition may be tin free. Such urethane acrylic dispersions may be

advantageously used as coatings for surfaces such as floors.

A special embodiment of the present invention is a tin free aqueous dispersion of polyurethane A and optionally vinyl polymer B wherein said polyurethane A is prepared from components 1 , 2, 3 and optionally 4. These dispersions can be prepared without using any catalyst or alternatively carboxylates of zinc, zirconium, copper, bismuth, titanium and molybdenum may be employed as catalysts.

Another special embodiment of the present invention is a tin free aqueous dispersion of polyurethane A and optionally vinyl polymer B wherein said polyurethane A is prepared from tin free components 2, 3 and optionally 4. These components can be prepared without using any catalysts, via enzymatic catalysis or alternatively sulfonic acids or titanates may be employed as catalysts.

Another special embodiment of the present invention is an aqueous dispersion of polyurethane A and optionally vinyl polymer B wherein said polyurethane A is prepared from components 2 and/or 3 where the anionic dispersing group is a metal salt of a sulfonic acid (RS0₃H) group. Preferred are the Li, Na and K salts of sulphonated isophtalic acid.

Many other variations embodiments of the invention will be apparent to those skilled in the art and such variations are contemplated within the broad scope of the present invention. Further aspects of the invention and preferred features thereof are given in the claims herein.

Examples

The present invention will now be described in detail with reference to the following non limiting examples which is by way of illustration only.

Abbreviations:

DMPA = dimethylolpropionic acid

MMA = methyl methacrylate

n-BA = n-butylacrylate

BMA = butyl methacrylate

EDTA = ethylenediamine tetraacetic acid

Viscosity was determined with a Brookfield DV-I viscometer (spindle S61 , 60 rpm, 23°C)

Particle size distribution was measured on a Particle Size Distribution Analyser (PSDA) from Polymer Laboratories. Samples are diluted until a concentration of approximately 0,05%. Samples are filtered over 2 micron filtered and measured on Cartridge Type 2 (20nm to 1500nm).

Reagents and materials:

PL-PSDA Eluent concentrate: 0.04% Sodium azide solution (Polymer

Laboratories part no. 0850- 2000, 4x 100ml)

PL-PSDA Marker: 0.02 g 3-nitrobenzene sulfonic acid in 250ml Ultra pure water.

Standards: Latex Particle Size Standards from 2-1000 nm; KSTN0026, KSTN 0027, KSTN0028 and KSTN0033 t/m KSTN0039

Ultra pure demineralized water or HPLC grade water.

Syringe filters: regenerated cellulose, 0.45μηι membrane, Spartac Millex-AP 20 pre filter 25 MM, 2.0μηι membrane, Millipore.

For determining the particle size value, the median diameter is mentioned in the examples. When a broad particle size distribution is found, the diameter at peak value is mentioned. Comparative Example Comp A (= Example XI from US 2010/009867(Da Costa))

A reaction vessel, equipped with internal thermometer, stirrer and cooler, was filled, under nitrogen atmosphere and at room temperature, with 442.6 g of polypropylene ether glycol (having molecular weight 2,000 g/mol), 30.9 g of DMPA and 50.0 g of N-methylpyrrolidone. The mixture was heated to 40 °C and stirred for 30 minutes. 213.2 g Desmodur W (available from Bayer) was added under stirring to the homogeneous mixture which was then heated to 60°C for 30 minutes. The reaction temperature was brought to 100°C and maintained for 2 hours, until the titrimetric determination of the free NCO groups still present gave a calculated value of 4.12% by weight. 650 g of the obtained prepolymer, cooled to 65°C, are dispersed in 10 minutes under vigorous stirring into 1057.1 g of demineralised water cooled at 18°C and containing 10.84 g of potassium hydroxide. 65.2 g of a 15.5% aqueous solution of hydrazine are added in 10 minutes and a maximum temperature of 34°C is reached during the extension step. After 30 minutes stirring, the NCO peak in the IR spectrum at 2240 cm^"1 is disappeared and 1.780 g of BYK® 346 are added. The resulting amine free (but N-methyl pyrrolidone containing) polyurethane dispersion had a solids content of 34.3 wt %, a pH of 8.0 and a viscosity of 66 cps. The median particle size was 170 nm. Comparative Example Comp B

A 2000 cm³ flask equipped with a thermometer and overhead stirrer was charged with 99.66 g polypropylene glycol 1000 (OH-value = 1 12 mg KOH/g), 137.82 g polypropylene glycol 2000 (OH-value = 56 mg KOH/g), 172.48 g Desmodur W (available from Bayer), 21.58 g DMPA, 107.88 g MMA and 0.17 g butylated hydroxytoluene. This mixture was heated to 50°C and tin octoate (0.1 1 g) was added. The reaction was allowed to exotherm to 90° C. After the exotherm was complete the reaction was kept at 90° C for 2 hours. The isocyanate content of the prepolymer was 4.99% (theoretical 5.12%). 528.23 g of the obtained prepolymer was cooled to a temperature of 40°C and 186.65 g of a 5.68% KOH solution in demineralized water was added under vigorous stirring. Subsequently 744.78 g of demineralized water was added to the flask and the mixture was stirred until a homogeneous dispersion was obtained. After that, 53.19 g of a 15.5% hydrazine solution was added together with 17.6 g of water. The radical polymerization was initiated by the addition of 0.74 g of tertiary butyl hydroperoxide, 0.02 g of iron(ll)EDTA and a subsequent feed addition of 26.4 g of a 1 % solution of isoascorbic acid in demineralized water, over a period of 10 minutes. The batch was filtered through a filter cloth to remove any coagulum formed during the reaction. The resulting amine free polyurethane acrylic hybrid dispersion had a solids content of 34.3 wt %, a pH of 7.7 and a viscosity of 15 cps. The median particle size was 59 nm.

Example 1

A 2000 cm³ flask equipped with a thermometer and overhead stirrer was charged with 258.48 g Priplast 3192 (OH-value = 56 mg KOH/g, available from Croda), 152.21 g Desmodur W (available from Bayer), 21.62 g DM PA, 108.1 g MMA and 0.17 g butylated hydroxytoluene. This mixture was heated to 50°C. and tin octoate (0.1 1 g) was added. The reaction was allowed to exotherm to 90° C. After the exotherm was complete the reaction was kept at 90° C for 2 hours. The isocyanate content of the prepolymer was 4.23% (theoretical 4.52%). 528.5 g of the obtained prepolymer was cooled to a temperature of 40°C and 186.74 g of a 5.68% KOH solution in

demineralized water was added under vigorous stirring. Subsequently 731.05 g of demineralized water was added to the flask and the mixture was stirred until a homogeneous dispersion was obtained. After that, 46.92 g of a 15.5% hydrazine solution was added together with 35.21 g of water. The radical polymerization was initiated by the addition of 0.74 g of tertiary butyl hydroperoxide, 0.02 of iron(ll)EDTA and a subsequent feed addition of 26.4 g of a 1 % solution of isoascorbic acid in demineralized water, over a period of 10 minutes. The batch was filtered through a filter cloth to remove any coagulum formed during the reaction. The resulting amine free polyurethane acrylic hybrid dispersion had a solids content of 34.3 wt %, a pH of 7.5 and a viscosity of 18 cps. The median particle size was 69 nm.

Example 2

A polyester polyol was synthesized from the following components: Pripol 1009 (available from Croda, 49 wt%), adipic acid (12 wt%) and 1 ,4 cyclohexane dimethanol (39 wt%). The polyester polyol had a hydroxyl value of 1 13 mg KOH/g and an acid value of 0.47 mg KOH/g. A 2000 cm³ flask equipped with a thermometer and overhead stirrer was charged with 324.87 g of this polyester polyol, 253.51 g

Desmodur W (available from Bayer), 21.0 g DM PA, 150.04 g MMA and 0.35 g butylated hydroxytoluene. This mixture was heated to 50°C and tin octoate (0.35 g) was added. The reaction was allowed to exotherm to 90° C. After the exotherm was complete the reaction was kept at 90° C for 2 hours. The isocyanate content of the prepolymer was 5.23% (theoretical 5.42%). 333.4 g of the obtained prepolymer was cooled to a temperature of 40°C and 68.76 g of a 5.68% KOH solution in demineralized water and 8.15 g of Antarox CA-630 were added under vigorous stirring. Subsequently 533.9 g of demineralized water was added to the flask and the mixture was stirred until a homogeneous dispersion was obtained. After that, 39.94 g of a 15.5% hydrazine solution was added together with 20.52 g of water. Subsequently 0.82 g of Tego foamex 805, 294.9 g of demineralized water, 54.23 g of n-butyl acrylate, 127.36 g of methyl methacrylate and 23.49 g of butyl methacrylate were added and the mixture was stirred for one hour. After that, 2.37 g of tertiary butyl hydroperoxide and 0.03 g of iron(ll)EDTA were added. The radical polymerization of the (meth)acrylic monomers was initiated by a feed addition of 68.0 g of a 1 % solution of isoascorbic acid in demineralized water, over a period of 10 minutes. The batch was filtered through a filter cloth to remove any coagulum formed during the reaction. The resulting amine free polyurethane acrylic hybrid dispersion had a solids content of 34.7 wt %, a pH of 7.0 and a viscosity of 32 cps. The median particle size was 86 nm.

Formulations were prepared by slow addition of the additives

(mentioned in the Table 1 below) to the polyurethane dispersion, while stirring.

Table 1 : Formulations

Stain Resistance

The formulated examples, prepared and formulated as described above were cast onto a Leneta test chart using a wire rod at a wet film thickness of 125 micron. The cast films were then allowed to dry at room temperature for 1 hour, followed by ageing of the coatings at 50°C for 16 hours. The coatings were allowed to cool to room temperature for 1 hour. The stain resistance of the coated cards towards the following stains were then assessed: water, ethanol (48%), detergent (Andy, 50% solution), coffee, hot pan. In all cases, a spot (1 cm²) of the respective stain was placed on the coating and covered with a piece of filter paper and a watch glass. In case of the "hot pan test" a small glass beaker filled with boiling hot water was placed on cold water on a test chart. All mentioned spots were left for one hour; water, ethanol (48%) and detergent (50%) were also tested for 16 hours. After these periods, the spot was gently wiped off with a tissue and the film was assessed for its integrity. This was rated between 0 to 5, where 0 = film totally destroyed/strongly discoloured and 5 = film fully intact without any defects/discolouration. The results for the clear coatings are shown in Table 2.

Table 2: Properties

Key for table 2

Hardness = Konig hardness (seconds)

W = water

E48% = ethanol, 48% solution in demineralized water

A50% = Andy, 50% solution in deminerz=alized water (detergent)

C = coffee

HP = hot pan

Total score = sum of all individual scores on stain resistances

Claims

CLAIMS A process for preparing an aqueous dispersion of a polyurethane A the process comprising the steps of: (a) reacting components one and three (and two and four where present) to form an acidic isocyanate terminated prepolymer that comprises anionic or potentially anionic functional groups thereon; where: (1 ) component one comprises 10 to 80% by weight of at least one polyisocyanate optionally containing at least one anionic or potentially anionic dispersing group; (2) optional component two comprises up to 15% by weight of at least one isocyanate-reactive polyol containing at least one anionic or potentially anionic dispersing group; (3) component three comprises 15 to 85% by weight of at least one isocyanate reactive hydrophobic polyol other than component two if present, and having a weight average molecular weight greater than or equal to 500 Daltons optionally containing at least one anionic or potentially anionic dispersing group; and (4) optional component four comprises up to 20% by weight of at least one isocyanate reactive polyol other than component three and two if present and having a weight average molecular weight less than 500 Daltons; where if component two is not present component one or three contains at least one anionic or potentially anionic dispersing group; where the amounts of components one to four are expressed as a weight percentage calculated from the total amount of the above components (i.e. one and three and optional two and/or four where present) being 100%; and where the mixture used in step (a) is substantially free of volatile amines and N-alkyl pyrrolidinones; (b) adding to the reaction mixture from step (a) an alkali metal neutralising agent in an amount from 0.05 to 6 parts by weight substantially to neutralise the isocyanate terminated prepolymer obtained from step (a); where the amount (in weight parts) of the alkali metal neutralising agent is calculated based on the weight of alkali metal in the neutralising agent relative to the total amount of components one to four in step (a) being equal to 100 parts; and (c) reacting the neutralised prepolymer from step (b) with an active hydrogen compound to extend the chain of the prepolymer to form an aqueous dispersion of polyurethane A. A process as claimed in claim 1 , in which component three comprises polyols that contain >10 wt% (by weight of the polyol) of diacids and/or dialcohols containing hydrophobic hydrocarbo moieties having at least eight carbon atoms. A process as claimed in claim 2 in which component three comprises >20 wt%, (by weight of the polyol) of diacids and/or dialcohols containing hydrophobic hydrocarbo moieties having from eight to fifty carbon atoms. A process as claimed in any preceding claim, in which either component one or two or three comprise at least one anionic or potentially anionic dispersing group. A process as claimed in any preceding claim, in which step (a) comprises: (a) reacting:

(1 ) 10 to 80% by weight of at least one polyisocyanate;

(2) 1 to 15% by weight of at least one isocyanate-reactive non- hydrophobic polyol containing at least one anionic or potentially anionic dispersing group;

(3) 15 to 85% by weight of at least one isocyanate reactive

hydrophobic polyol and having a weight average molecular weight > 500 Daltons; and

(4) optionally up to 20% by weight of at least one isocyanate reactive polyol other than (2) and (3) and having a weight average molecular weight < 500 Dalton;

to form an acidic isocyanate terminated prepolymer that comprises anionic or potentially anionic functional groups and which is substantially free of volatile amines and N-alkyl pyrrolidinones.

A process as claimed in any preceding claim, in which step (b) occurs during or substantially immediately after step (a).

A process for preparing an aqueous coating composition comprising bringing into initimate admixture components (i) and (ii): (i) 10 to 95% by weight of a polyurethane dispersion A obtained or obtainable by the process as claimed in any preceding claim and

(ii) 90 to 5% by weight of a vinyl polymer B, where (i) and (ii) add up to 100% and are calculated based on weight of solids (excluding the water); and where the composition (and both components (i) and (ii)) substantially free of volatile amines and N-alkyl pyrrolidinones.

.A process as claimed in claim 7 in which the acid value (AV) of the total aqueous coating composition is from 1 to 40 mg KOH / g, more preferably from 2 to 20 mg KOH/g, most preferably from 3 to 15 mg KOH/g.

An aqueous dispersion of a polyurethane A, obtained or obtainable by a process as claimed in any claim 1 to 7.

An aqueous coating composition comprising a polyurethane A and a vinyl polymer B, obtained or obtainable by a process as claimed in claim 8. An article and/or substrate coated by a composition as claimed in claim 10. A method of coating an article and/or substrate comprising the steps of

(I) applying a coating composition as claimed in claim 10 to an article and/or substrate, and

(II) drying the coating thereon to obtain a coated article and/or substrate.