WO2011124602A1

WO2011124602A1 - Aqueous anionic polyurethane dispersions

Info

Publication number: WO2011124602A1
Application number: PCT/EP2011/055337
Authority: WO
Inventors: Gabriele Costa; Franco Federici; Mariuccia De Luca; Irena Amici Kroutilova; Thierry Bossi; Arianna Benetti; Giovanni Floridi; Giuseppe Li Bassi
Original assignee: Lamberti Spa
Priority date: 2010-04-08
Filing date: 2011-04-06
Publication date: 2011-10-13
Also published as: IT1399424B1; KR101791283B1; EP2556097A1; CN102822220A; ITVA20100033A1; CN102822220B; KR20130040833A

Abstract

Aqueous anionic polyurethane dispersions based on specific hydrophobic polyols are useful as filming agents for fhe coating of rigid surfaces like metal, plastics, glass and wood and provide coatings with excellent durability, adhesion, hydrolyfic and alkali/acid resistance and hardness.

Description

AQUEOUS ANIONIC POLYURETHANE DISPERSIONS

The present disclosure relates to aqueous anionic polyurethane dispersions based on specific hydrophobic polyols and to their use as filming agents for the coating of rigid surfaces like metal, plastics, glass and wood.

The aqueous dispersions of the disclosure provide coatings with excellent durability, adhesion, hydrolytic and alkali/acid resistance and hardness. STATE OF THE ART.

The surface of many manufactured articles, by way of example made from leather, plastic, wood, glass and metal, is treated with the purpose of making it more homogenous, or of protecting it from the wear of the time or the atmosphere and/or in order to improve certain aesthetic properties, such as high or low opacity, soft or rough touch, colour, and the like.

Normally, these effects are obtained through the application of filming polymers (coating) and, among the great variety of filming polymers, solvent borne polyurethanes are now well known and appreciated in the field of coatings, because they can yield films having excellent chemical and mechanical resistance.

Aqueous dispersions of polyurethanes have also recently acquired a relevant role, also because of the increasing attention paid by the regulatory policies in lowering the emissions of low volatile organic compounds in the environment and, particularly, in working areas.

When polyurethanes in the form of aqueous dispersions are considered for coating, some problems arise from the fact that their dispersibility in water requires the inclusion of hydrophilic segments that inherently reduce the durability and the hydrolytic stability of the films.

It is known in the art to introduce in the polyurethanes unsaturated groups that cause crosslinking in the film and consequently can improve the chemical resistance of the coating; unfortunately, yellowing of the film and the need for strong oxidative conditions for crosslinking are drawbacks connected with the presence of unsaturated groups in the polyurethanes.

US 2003/0191273 describes the use of aqueous dispersions of polyurethanes based on fatty acid alkanolamides as coating compositions; the coatings produced from these dispersions are said to have good pendulum hardness, good heelmark resistance and high gloss.

US 2008/0194757 describes water dispersed polyurethane compositions that contain a nurate compound having a long chain alkyl group as the polyisocyanate component; the compositions are said to provide coating films excellent in adhesiveness, water resistance, weather resistance, corrosion resistance, water and oil repellency.

Surprisingly it has now been found that it is possible to obtain aqueous dispersions of anionic polyurethanes that are able to give durable films having excellent adhesiveness on rigid substrates, chemical resistance and hardness by incorporating in the polyurethane a particular hydrophobic polyol obtained by reacting a fatty alcohol with an aromatic diglycidyl ether. SUMMARY OF THE INVENTION

The present invention provides aqueous dispersions containing from 20 to 50% by weight of anionic polyurethanes obtained by dispersing in water and extending with a polyamine a neutralised anionic prepolymer containing from 5 to 125 meq/100 g dry matter of carboxylic groups and prepared by reacting one or more aliphatic, cycloaliphatic or aromatic polyisocyanates with a mixture of polyols (P) comprising:

I) from 4 to 90 w†% of one or more hydrophobic polyol having average molar hydroxyl functionality from 2 to 3, hydroxyl number from 350 to 40 (mg KOH/g) and obtained by reacting an alcohol ROH, in which R is a branched or linear, saturated C4-C30, preferably C0-C22, alkyl chain or R is a branched or linear, saturated C4-C 10 alkyl phenyl radical, with an aromatic diglycidyl ether of formula (I):

(I)

in which Ri is the radical (i)

(i)

in which R2, R3 are each independently Me, Et or H;

or Ri is phenylene, optionally substituted with one or more alkyl group, preferably methyl groups; or Ri is biphenylene, optionally substituted with one or more alkyl group, preferably methyl groups;

or Ri is fhe radical (ii):

II) from 1 to 10 w†% of one or more anionic or potentially anionic polyols having two or more groups reactive towards fhe isocyanafe group and at least one carboxylic or carboxylate group;

III) from 0 to 95 w†% of one or more linear polycarbonate diol having molecular weight from 500 fo 3,000;

IV) from 0 to 95 w†% of one or more linear polyester diol having molecular weight from 500 fo 4,000;

V) from 0 to 95 w†% of one or more polyoxyalkylene diols selected among poly(oxypropylene) glycol and poly(oxyfetramefhylene) glycol,

the polyisocyanafes and the mixfure of polyols (P) being in such proportions that: a) fhe ratio between fhe isocyanafe groups NCO of the polyisocyanafe and the sum of all reactive -OH groups of the mixfure of polyols (P) is comprised between 1 .2 and 2.3.

According fo another aspect, fhe invention relates fo fhe use of the aforesaid aqueous anionic polyurethane dispersions for the preparation of coating compositions. DETAILED DESCRIPTION OF THE INVENTION

In one embodiment, the components I), II), III), IV) and V) sum up to at least 95 w†% of the mixture of polyols, the mixture of polyols further comprising from 0 to 5 w†% of other nonionic polyols having molecular weight below 1 ,000 and containing two or more hydroxyl groups; examples of such utilizable nonionic polyols are glycerol, pentaerythritol, neopentylglycol, butanediol, 1 ,4-cyclohexanedime†hanol, trimethylolpropane and its derivatives, such as propoxylated trimethylolpropane, polyfunctional polybutadienes and polyesters polyols. In a preferred form of this embodiment the components I), II), III), IV) and V) sum up to 100 % by weight of the polyol mixture (P) of the prepolymer; in even a more preferred embodiment the components I), II), III) and IV) sum up to 100 w†% of the mixture of polyols.

The hydrophobic polyol I) contains no epoxy groups and preferably represents from 5 to 75 w†% of the mixture of polyols.

Advantageously, in the aromatic diglycidyl ether of formula (I) Ri is the radical (i) in which R2, R3 are methyl groups.

The polyisocyanates that can be used have an average -NCO functionality comprised between 2.0 and 2.3 and are preferably aliphatic or cycloaliphatic.

Examples of useful polyisocyanates are 4,4' - dicyclohexyl-methane- diisocyanate, 1 -lsocyana†o-3-(isocyana†ome†hyl)-3,5,5- trimethylcyclohexane (or isophoronediisocyanate), tetramethylene diisocyanate, hexamethylene diisocyanate, and mixtures thereof. The most preferred polyisocya nates are 4,4' - dicyclohexyl-methane- diisocyanate, 1 -isocyana†e-3-isocyana†e-me†hyl-3,5,5- frimefhylcyclohexane (or isophoronediisocyanafe) and hexamefhylenediisocyanafe, and mixture thereof.

Polyisocyanates having average -NCO functionality higher than 2 are obtained by partial trimerization, biurethization, urethanization or allophanation of diisocya nates, such as hexamethylendiisocyanate, isophoronediisocyanate, 4,4' - dicyclohexylmethanediisocyanate and mixtures thereof, or by mixing the aforesaid diisocyanates with their trimerization, biurethization, urethanization or allophanation products.

Component II) of the mixture of polyols (P) is preferably a carboxylic acid which is substituted in the position 2 by two hydroxymethyl groups, such as dimethylolpropanoic acid, dimethylolbutanoic acid or mixtures thereof. The amount of component II) in the mixture of polyols is chosen to obtain a prepolymer containing from 5 to 125 meq/100 g dry matter of -COOH groups; best results are obtained when this value is comprised between 20 and 60.

Component III) of the mixture of polyols (P) may be selected among polycarbonates obtained by de-alcohol condensation reaction of low molecular diols with dialkyl carbonate, de-phenol condensation reaction of low molecular diols with diphenyl carbonates, or de-glycol

condensation reaction of low molecular diols with alkylene carbonates or dialkyl carbonates.

Examples of the low molecular diols include 1 ,4-bu†anediol, 1 ,5- pentanediol, 1 ,6-hexanediol, ethylene glycol, propylene glycol, 3-me†hyl- l ,5-pen†anediol, neopentyl glycol, diethylene glycol, 1 ,4-cyclohexanediol, 1 ,4-cyclohexanedime†hanol and the like. Examples of the dialkyl carbonate include dimethyl carbonate and diethyl carbonate. An example of dialkylene carbonate is diethylene carbonate.

A particularly preferable example of the polycarbonate diol is

poly(hexame†hylene carbona†e)diol obtained by condensation reaction of 1 ,6-hexanediol with dialkyl carbonate.

The polycarbonate diol has preferably a number average molecular weight from 800 to 2,000.

Component IV) of the mixture of polyols (P) may be selected among polyesters obtained from the reaction of acids, esters, anhydrides or acyl halides with glycols.

Useful for the preparation of said polyesters are, by way of example, maleic acid, succinic acid, adipic acid, suberic acid, sebacic acid, phthalic acid, terephthalic acid and isophthalic acid, and possibly their correspondent acyl halides, anhydride and esters.

Examples of suitable glycols are ethylene glycol, 1 ,4-butanediol, 1 ,3- propanediol, 1 ,2-propanediol, neopentyl glycol, tetramethylene glycol, diethylene glycol, 1 ,6-hexanediol, 1 ,5-pen†anediol; substituted alkylene glycol, such as 2,2-dime†hyl-l ,3-propane diol; cyclic glycols, such as 1 ,4- cyclohexanediol and 1 ,4-cyclohexanedime†hanol, and aromatic glycols; these glycols are reacted with aliphatic, cycloaliphatic or aromatic dicarboxylic acids or with alkyl esters of low molecular weight alcohols or with compounds which are able to form ester linkages, to obtain polymers having relatively low molecular weight, and preferably having melting point below about 80°C.

Hydroxyl terminated polycaprolactone can also be used.

The polyester diol has preferably a number average molecular weight of from 800 to 3,000.

In a preferred embodiment the polyester diol is selected among polyesters based on adipic and/or phthalic acid with 1 ,6-hexanediol, ethylene glycol, diethylene glycol, neopentyl glycol, 1 ,4-butanediol or mixture thereof.

According to a preferred embodiment, the polyols of the mixture (P) are free from units deriving from poly(oxyethylene) glycol.

The aqueous dispersions of anionic polyurethanes of the invention can be prepared by: i) reacting, in the above defined proportions, the polyisocya nates with the mixture of polyols (P) ; ii) dispersing the obtained prepolymer in water; iii) adding a polyamine (chain extender) to the so obtained dispersion and allowing it to react until all isocyanate groups have disappeared.

Step i) is preferably carried out in the presence of an organic solvent or an organic solvent mixture at temperature between 40 and 1 1 0 °C; however it has been found that the use of the hydrophobic polyol I) reduces the viscosity of the reaction mixture and thus, advantageously, the amount of solvent that is needed and the overall consumption of VOC in synthesis. Suitable solvents are customary solvents, such as N-me†hylpyrrolidone, N- ethylpyrrolidone, dipropylene glycol dimethyl ether, ethyl acetate, butyl acetate, ethylene glycol monomethyl or monoethyl ether acetate, 1 - methoxypropyl 2-ace†a†e, 3-me†hoxy-n-bu†yl acetate, acetone, 2- butanone, 4-me†hyl-2-pen†anone, cyclohexanone, mixtures containing, in particular, aromatics, carbonic esters, such as dimethyl carbonate, diethyl carbonate, 1 ,2-ethylene carbonate and 1 ,2-propylene carbonate, lactones, such as [be†a]-propiolac†one, [gamma]-bu†yrolac†one, [epsilon]-caprolac†one and [epsilon]-me†hylcaprolac†one, but also solvents such as propylene glycol diacetate, diethylene glycol dimethyl ether, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate and N-me†hylcaprolac†am or any desired mixtures of such solvents. Preferred solvents are N-e†hylpyrrolidone and dipropylene glycol dimethyl ether.

The prepolymer obtained at the end of step i) is normally neutralized, preferably with tertiary amines, like N-alkylmorpholines, trialkylamines, dialkylalkanolamines, alkyldialkanolamines, trialkanolamines and mixtures thereof, at a temperature below 90 °C.

Triethylamine, dimethylethanolamine and N-me†hylmorpholine are particularly suited for this scope.

The neutralization can be carried out at the end of the reaction step i), in anhydrous environment, or during the subsequent prepolymer dispersion in water (step ii).

Step ii) is carried out pouring the prepolymer into water under mechanical stirring, optionally in the presence of an emulsifier, or vice versa.

The emulsifier can be chosen between nonionic, anionic and cationic surfactants; preferably, the emulsifier is a nonionic surfactant. The polyamines of step iii) are preferably tertiary and secondary aliphatic diamines.

In step iii) it is possible to use a mixture of polyamine.

Examples of suitable polyamines are hydrazine, ethylenediamine, piperazine, 1 ,5-pentanediamine, 1 ,6-dihexanediamine, isophoronediamine, diethylenetriamine, 2-me†hyl-l ,5-pen†anediamine and 4,4'-me†hylene-bis-cyclohexylamine.

The temperature and duration of step iii) and the amount of polyamine are determined to exhaust the free -NCO groups which are present in the pre-polymer and to obtain a fine, stable and homogeneous polyurethane dispersion, as it is well known in the art.

The organic solvent which is possibly present can be removed by distillation during step iii) or at the end of step iii).

Step iii) of the method of the invention may be carried out percolating the polyamine in the dispersion of the prepolymer maintained under stirring at temperature below 40 °C.

The Brookfield ® viscosity of the anionic polyurethane aqueous dispersions of the present invention is generally comprised between 50 and 2,000 mPa*s.

For the preparation of coating compositions, the anionic aqueous polyurethane dispersions can be mixed with crosslinkers, binders, preferably acrylic binders, and/or other additives, in order to further improve their performance in coating, such as the film-forming capability, and to reduce or increase opacity, to avoid the development of "orange peel" or "fish-eyes" effects and foam. Examples of additives that can be added to the coating composition are levelling, wetting agents, fillers, pigments, waxes, surfactants, thickeners, coalescing agents, rust inhibitors, etc.

The anionic polyurethane of the aqueous dispersions of the present invention can also be crosslinked with all crosslinking agents known to those skilled in the art, such as hydrodispersible polyisocyanates, blocked polyisocya nates, polyaziridines, carbodiimides, epoxysilanes and melamines.

Crosslinking agents are generally added in an amount comprised between 1 and 10% on dry weight of the dispersion.

The cross-linking can be useful in order to increase the mechanical and chemical properties of the films.

The film forming anionic polyurethane aqueous dispersions of the present invention and the coating compositions containing them are advantageously used for the finishing of rigid substrate, such as plastics (by way of example polycarbonates, ABS and PVC), wood, glass, and metal (by way of example aluminium, steel, galvanized iron and steel: GA, GL, Gl and EGI).

The materials coated with the films obtained from the aqueous dispersions of the invention can be used for car interiors to finish the instrumentations or the internal side of car doors, on electronic products like mobile phones, i-Pods® and i-Pads®, on metallic surfaces such as computer cases and television cases, for coil coating. In the following examples the synthesis of hydrophobic polyols and the preparation of aqueous dispersions according to the present invention are reported.

The particle size of the dispersions has been measured by means of Laser Correlation Spectroscopy (LCS) with a Coulter N4 Plus Instrument at temperature 25°C and angle 90°.

EXAMPLES

The following materials, as listed bellow, were used in the examples described afterwards.

POLYOL 1 : Polyester based diol, adipate-phthalate of 1 ,6-hexandiol, molecular weight 1 ,000 g/mol

POLYOL 2 : Polycarbonate based diol, poly(hexame†hylene carbona†e)diol, molecular weight 1000 g/mol

H-POLYOL 5: coco diethanolamide, molecular weight 213 g/mol

H-POLYOL 6: oleic diethanolamide, molecular weight 269.7 g/mol

DGEBA: diglycidyl ether of Bisphenol A, molecular weight 380 g/mol DMPA: dimethylolpropanoic acid, molecular weight 134,2 g/mol

ALCOHOL C6: n-hexanol, molecular weight 102 g/mol

ALCOHOL CI 2: n-dodecanol, molecular weight 186 g/mol

ALCOHOL C20: linear C20 monoalcohol, molecular weight 298 g/mol NMP : N-me†hyl-pyrrolidone,

NEP : N-e†hyl-pyrrolidone

IPDI: isophorondiisocyanate, molecular weight 222 g/mol

HMDI: 4,4'-dicyclohexyl-me†hane-diisocyana†e, molecular weight 262 g/mol TEA: Triethylamine, molecular weight 101 ,15 g/mol

DEA: Diethanolamine, molecular weight 105, 1 4 g/mol

HH: Hydrazine hydrated, 24.36% aq. sol., molecular weight 32,04 g/mol ADD: wetting agent Byk 346

EXAMPLE 1.1 -1.3

Examples 1 .1 -1 .3 describe the preparation procedure of DGEBA based hydrophobic polyols.

Example 1.1

Synthesis of H-POLYOL 1 .

140.6 g (1 .363 mol) of ALCOHOL C6 are charged in a reactor equipped with thermometer, mechanical stirrer and condenser, under nitrogen atmosphere and are heated up to 65°C. 0.40 g of KOH 40% are added under stirring at 65°C.

259.4 g (0.682 mol) of DGEBA are then added and the reaction mixture is heated up and maintained for about 4 hours at 120°C till the total disappearance of epoxy groups.

The titration of the epoxy groups is determined in this and all the other examples according to the norm ASTM D l 652-04.

Once reached the full epoxy conversion the reaction mixture is cooled down to 80°C and 0.35 g of phosphoric acid 85% are added, obtaining the polyol H-POLYOL 1 (molecular weight 586 g/mol) . The OH-number is 191 mg KOH/g.

Example 1.2

Synthesis of H-POLYOL 2. 186.0 g (1 mol) of ALCOHOL C I 2 are charged in a reactor according to the procedure of the Example 1 .1 , heated up to 70°C, then 0.75 g of KOH 40% are added.

190.0 g (0.5 mol) of DGEBA are then added and the reaction mixture is heated up to 120°C and maintained till the disappearance of epoxy groups (about 4 hrs) .

The reaction mixture is then cooled down to 80°C and 0.65 g of phosphoric acid 85% are added, obtaining the polyol H-POLYOL 2 (molecular weight 752 g/mol) . The OH-number is 1 49 mg KOH/g.

Example 1.3

Synthesis of H-POLYOL 3

326.0 g ( 1 mol) of ALCOHOL C20 are charged in a reactor according to the procedure of the Example 1 .1 , heated up to 100°C, then 0.80 g of KOH 40% are added.

190.0 g (0.5 mol) of DGEBA are then added and the reaction mixture is heated up to 1 30°C and maintained till the disappearance of epoxy groups (about 1 2 hrs) .

The reaction mixture is then cooled down to 120°C and 0.80 g of phosphoric acid 85% are added, obtaining the polyol H-POLYOL 3. The OH-number is 108 mg KOH/g.

EXAMPLE 1.4

Synthesis of H-POLYOL 4

Example 1 .4 describes the preparation of an IPDI based hydrophobic polyol according to the prior art (H-POLYOL 4) . 135.1 g of ALCOHOL C6, 432.0 g of NEP are charged in a reactor equipped with thermometer, stirrer and condenser, under nitrogen atmosphere and at room temperature.

293.9 g of IPDI are added under stirring after approximately 30 minutes of homogenization of the mixture at 40°C.

The reaction mixture is then heated up to 80°C and the reaction is carried out at 90°C, until the content of NCO groups in the prepolymer is equal to 6.45%.

The titration of the residual isocyanate groups is determined in this and all the other examples according to the standard method ASTM D2572.

The prepolymer is cooled down to 80°C and 138.8 g of DEA are slowly added under stirring.

The obtained polyol (H-POLYOL 4) has solid residue content of 75% by weight (molecular weight 429.7). The OH-number is 261 mg KOH/g.

Example 2.1

Preparation of an aqueous dispersion according to the invention.

138.7 g of POLYOL 2 and 26.6 g of H-POLYOL 1 , 20.9 g of DMPA and 80 g of NMP are charged in a reactor according to the Ex. 1 .1 . 155.6 g of HMDI are added under stirring after approximately 30 minutes of homogenization of the mixture at 40°C.

The reaction mixture is then heated up and maintained for 30 minutes at 60°C.

The reaction is carried out at 95-100°C, until the content of NCO groups in the prepolymer is equal to the theoretical value of 5.07% (approximately 1 hour). The prepolymer is then cooled down to approximately 75°C and 14.9 g of the neutralizing agent TEA is added under stirring.

After about 10 minutes and at internal temperature of 65°C the prepolymer is dispersed in demineralized water under strong stirring at temperature below 35°C. The extension is carried out adding 47.8 g of the diamine HH (24.36 % aqueous solution), as described in Table 1 , at temperature below 35°C.

The wetting agent ADD is added to the obtained polyurethane dispersion that is then filtered with a 150 μιτι canvas and brought to solid residue content of 35% by weight. The dispersion obtained results clear and stable.

EXAMPLES 2.2-2.4

Preparation of other aqueous dispersions according to the present invention.

The procedure described in the Example 2.1 is followed modifying the ingredients as shown in Table 1 , where amounts are reported in grams. Example 2.5 (comparative)

The procedure described in the Example 2.1 is followed without the use of any hydrophobic polyol and with the ingredients reported in Table 1 .

EXAMPLES 2.6-2.10 (comparative)

Preparation of other aqueous dispersions according to the prior art.

The detailed list of ingredients and their quantities are reported in Table 1 . POLYOL 1 or POLYOL 2 and H-POLYOL 4, H-POLYOL 5 or H-POLYOL 6, DMPA and NMP are charged in a reactor equipped with thermometer, stirrer and condenser, under nitrogen atmosphere and at room temperature. HMDI is added under stirring after approximately 30 minutes of homogenization of the mixture at 40°C.

The reaction mixture is then heated up and maintained for 30 minutes at 60°C.

The reaction is carried out at 95-100°C, until the content of NCO groups in the prepolymer is equal to the theoretical value (approximately 1 hour). The prepolymer is then cooled down to approximately 75°C and the neutralizing agent TEA is added under stirring.

After about 10 minutes and at internal temperature of 65°C the prepolymer is dispersed in demineralized water under strong stirring at temperature below 35°C. The extension is carried out adding the chain extender HH as described in Table 1 at temperature below 35°C.

APPLICATION EXAMPLE

In the application examples the comparison between the results of a coating treatment carried out by using prior art dispersions and two dispersions according to the invention is showed.

The mechanical, physical and chemical properties of glass or metal substrates coated with the polyurethane dispersions were compared. The contact angle on a coated aluminium substrate is measured using the Pocket Goniometer PGX. The integrated pump delivers accurate water droplets in steps of 0.5 μΙ and the built-in camera captures single droplet images to determine the static contact angle at 'equilibrium'.

TABLE 1

""comparative

The hardness of the films have been determined according to the standard method ASTM D4366-95 (Standard Test Method for Hardness of Organic Coatings by Pendulum Damping Test) on a glass substrate. The hydrolytic and ethanol resistance of the films have been determined by the standard method UNI EN 12720 (Surface Resistance to Cold Liquids) on glass.

The chemical resistance (NaOH, HCI) has been determined by the evaluation of the coated glass specimen after their immersion in alkali or acid solution (1 % NaOH or 5% HCI) at temperature of 55°C for 2 min. Results are expressed following the scale: 0=worst, coating destroyed, 5=best, no effect.

The adhesion on a metal substrate (aluminium and electro-galvanized steel) has been determined by the standard method ASTM D3359-09 (Standard Test Method for Measuring Adhesion by Tape Test). Results are expressed following the scale: 0=worst, coating destroyed, 5=best, no effect.

The results are reported in Table 2.

It can be seen that the Contact angle of Ex. 2.4 is significantly increased with respect to all the others, showing that the coating is more hydrophobic.

The substrates coated with the dispersion of Examples 2.2 and 2.4 show 6-7 times better resistance to ethanol in respect to those prepared without the use of any hydrophobic polyol and even more with respect to the dispersions according to the prior art.

The H20 (hydrolytic) resistance of the coatings according to the present invention is good. TABLE 2

Comparative

** Wet conditions: Panel immersed in water for 4 hrs and adhesion fesf run within 2 minutes after extraction.

Moreover, the substrates coated with the dispersion of Examples 2.2 and 2.4 show good hardness and excellent adhesion both on aluminium and steel substrate with respect to those prepared with the dispersions of the prior art.

When alkali/acid resistance is considered the coatings prepared with the dispersions of the present invention exhibits equal or better resistance than the coating of the prior art.

Claims

1 ) Aqueous dispersions containing from 20 to 50% by weight of anionic polyurethanes obtained by dispersing in water and extending with a polyamine a neutralised anionic prepolymer containing from 5 to 125 meq/100 g dry matter of carboxylic groups and prepared by reacting one or more aliphatic, cycloaliphatic or aromatic polyisocyanates with a mixture of polyols (P) comprising:

I) from 4 to 90 w†% of one or more hydrophobic polyol having average molar hydroxyl functionality from 2 to 3, hydroxyl number from 350 to 40 and obtained by reacting an alcohol ROH, in which R is a branched or linear, saturated C4-C3o alkyl chain or R is a branched or linear, saturated C4-C10 alkyl phenyl radical, with an aromatic diglycidyl ether of formula (I):

and R₂, R3 are each independently Me, Et or H;

or Ri is phenylene, optionally substituted with one or more alkyl group;

or Ri is biphenylene, optionally substituted with one or more alkyl group;

or Ri is the radical (ii):

(ii)

II) from 1 to 10 w†% of one or more anionic or potentially anionic polyols having two or more groups reactive towards the isocyanate group and at least one carboxylic or carboxylate group;

III) from 0 to 95 w†% of one or more linear polycarbonate diol having molecular weight from 500 to 3,000;

IV) from 0 to 95 w†% of one or more linear polyester diol having molecular weight from 500 to 4,000;

V) from 0 to 95 w†% of one or more polyoxyalkylene diols selected among poly(oxypropylene) glycol and poly(oxytetramethylene) glycol,

the polyisocyanates and the mixture of polyols (P) being in such proportions that: a) the ratio between the isocyanate groups NCO of the polyisocyanafe and the sum of all reactive -OH groups of the mixture of polyols (P) is comprised between 1 .2 and 2.3.

2) Aqueous dispersions according to claim, in which the components I), II), III), IV) and V) sum up to at least 95 w†% of the mixture of polyols, the mixture of polyols further comprising from 0 to 5 w†% of other nonionic polyols having molecular weight below 1 ,000 and containing two or more hydroxyl groups.

3) Aqueous dispersions according to claim 2 in which the components I), II), III), IV) and V) sum up to 100 % by weight of the polyol mixture (P) of the prepolymer.

4) Aqueous dispersions according to claim 3 in which the components I), II), III) and IV) sum up to 100 w†% of the mixture of polyols.

5) Aqueous dispersions according to claim 1 in which the mixture of polyols (P) comprises from 5 to 75 w†% of the one or more hydrophobic polyol I) obtained by reacting an alcohol ROH in which R is a branched or linear, saturated C6-C22 alkyl chain, and Ri is the radical (i):

7) Aqueous dispersions according†o claim 1 in which the neutralised anionic prepolymer is prepared from one or more aliphatic or cycloaliphatic polyisocya nates having an average -NCO functionality comprised between 2.0 and 2.3.

8) Aqueous dispersions according to claim 1 in which the component II) of the mixture of polyols (P) is dimethylolpropanoic acid, dimethylolbutanoic acid or mixtures thereof; the component III) of the mixture of polyols (P) is poly(hexame†hylene carbona†e)diol having number average molecular weight from 800 to 2,000; the component IV) of the mixture of polyols (P) is selected among polyesters based on adipic and/or phthalic acid with 1 ,6- hexanediol, ethylene glycol, diethylene glycol, neopentyl glycol, 1 ,4-bu†anediol and mixture thereof, and having number average molecular weight of from 800 to 3,000.

9) Aqueous dispersions according to any of the preceding claims in which the polyols of the mixture (P) are free from units deriving from poly(oxyethylene) glycol.

10) Use of an aqueous dispersion of any of claims from 1 to 9 for the preparation of coating compositions.