ITVA20100033A1 - AQUEOUS DISPERSIONS OF ANIONIC POLYURETHANE - Google Patents

Description

Description of the industrial invention entitled:

WATER DISPERSIONS OF ANIONIC POLYURETHANS

The present invention relates to aqueous dispersions of anionic polyurethanes prepared starting from specific hydrophobic polyols and to their use as filming agents for the coating of rigid surfaces, such as those of metals, plastic, glass and wood.

The aqueous dispersions of the invention allow to obtain excellent coatings in terms of durability, adhesion, hydrolytic resistance, resistance to bases and acids, hardness.

STATE OF THE ART

The surface of many artifacts, for example the surface of artifacts made of leather, plastic, wood, glass and metal, is treated with the aim of making it more homogeneous, or to protect it from wear due to time or atmosphere and / or to improve some aesthetic characteristics, such as transparency or opacity, rough or soft touch, color, and so on.

Normally, these effects are obtained through the application of film-forming polymers (coating) and, among the great variety of film-forming polymers, solvent-based polyurethanes are well known and appreciated in the sector, as they allow to produce films with excellent chemical resistance. and mechanics.

Aqueous dispersions of polyurethanes have also recently acquired an important role, also due to the growing attention paid by regulatory policies to lowering emissions of volatile organic compounds in the environment and, in particular, in the workplace.

Wanting to use polyurethanes in the form of aqueous dispersions for the coating, problems arise due to the fact that their dispersibility in water requires the inclusion of hydrophilic segments in the structure and these reduce the duration and hydrolytic stability of the films.

It is known in the field that unsaturated groups can be introduced into the polyurethanes which cause the film to cross-link and consequently improve its resistance; unfortunately, the yellowing of the film and the need for highly oxidative conditions for crosslinking are disadvantages connected to the presence of unsaturated groups in polyurethanes.

US 2003/0191273 describes the use of aqueous dispersions of polyurethanes prepared with alkanolamides of fatty acids as compositions for the coating; The coatings produced from these dispersions are reported to have good pendulum hardness, good scratch resistance and high gloss levels.

US 2008/0194757 discloses compositions of polyurethanes dispersed in water which contain a â € œnurateâ € compound bearing a long-chain alkyl group as a polyisocyanic component; it is reported that the compositions give coatings having excellent adhesion, resistance to water, atmospheric agents, corrosion, water and grease repellents.

Surprisingly, it has now been found that it is possible to obtain aqueous dispersions of anionic polyurethanes capable of providing durable films having excellent adhesion on rigid substrates, chemical resistance and hardness by incorporating in the polyurethane a particular hydrophobic polyol obtained by reacting a fatty alcohol with a diglycidyl ether. aromatic.

SUMMARY OF THE INVENTION

The present invention relates to aqueous dispersions containing from 20 to 50% by weight of anionic polyurethanes obtained by dispersing in water and extending with a polyamine a neutralized anionic prepolymer containing from 5 to 250 meq / 100 g on the dry basis of carboxylic groups and prepared by making react one or more aliphatic, cycloaliphatic or aromatic polyisocyanates with a mixture of polyols (P) which includes:

I) from 4 to 90% by weight of one or more hydrophobic polyols with mean 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 Ã ̈ a saturated, linear or branched C4-C30 alkyl chain, preferably C6-C22, or R is a phenyl radical substituted with a saturated, linear or branched C4-C10 alkyl chain, with an aromatic diglycidyl ether of formula (I):

O O

O O

R1

(THE)

where R1Ã is the radical (i):

(the)

in which R2 and R3 are one independently of the other Me, Et, or H;

or R1Ã a phenylene radical, optionally substituted with one or more alkyl groups and preferably with a methyl;

or R1Ã is a bis-phenylene radical, optionally substituted with one or more alkyl groups and preferably with a methyl; or R1Ã ̈ the radical (ii):

OR

OR

(ii) II) from 1 to 10% by weight of one or more anionic or potentially anionic polyols in twenty-two more reactive groups with respect to isocyanic groups and at least one carboxylic carboxylate group;

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

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

V) from 0 to 95% by weight of one or more polyalkylene diols selected from 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 NCO isocyanic groups of the polyisocyanates and the sum of all reactive - OH groups of the polyol mixture (P) is between 1.2 and 2.3.

According to another aspect, the invention relates to the use of the aqueous dispersions described above of anionic polyurethanes for the preparation of compositions for the coating of rigid substrates.

DETAILED DESCRIPTION

In one embodiment, components I), II), III), IV) and V) constitute at least 95% by weight of the polyol blend, the polyol blend further comprising 0 to 5% by weight of other polyols non-ionic having a molecular weight of less than 1,000 and containing two or more hydroxyl groups; examples of such usable non-ionic polyols are glycerol, pentaerythritol, neopentyl glycol, butanediol, 1,4-cyclohexanedimethanol, trimethylolpropane and its derivatives, such as propoxylated trimethylolpropane, polyfunctional polybutadienes and polyester polyols.

In a preferred embodiment, components I), II), III), IV) and V) constitute 100% by weight of the polyol mixture (P) of the prepolymer; in an even more preferred embodiment, components I), II), III), and IV) constitute 100% by weight of the polyol mixture. The hydrophobic polyol (I) does not contain epoxy groups and preferably represents from 5 to 75% by weight of the polyol mixture (P).

Advantageously, in the diglycidyl ether of formula (I) R1 is the radical (i) in which R2 and R3 are methyls.

The usable polyisocyanates have medium functionality - NCO between 2.0 and 2.3 and are preferably aliphatic or cycloaliphatic.

Examples of usable polyisocyanates are 4,4 '- dicyclohexyl-methanediisocyanate, 1-isocyanate-3- (isocyanatomethyl) -3,5,5-trimethylcyclohexane (or isophorone diisocyanate), tetramethylene diisocyanate, hexamethylene diisocyanate, and mixtures thereof.

The most preferred polyisocyanates are 4,4 '- dicyclohexyl-metanediisocyanate, 1-isocyanate-3- (isocyanatomethyl) -3,5,5-trimethylcyclohexane (or isophorone diisocyanate), hexamethylene diisocyanate, and mixtures thereof.

Polyisocyanates with an average NCO functionality greater than 2 s are obtained from the partial trimerization, biuretization, urethaneization or alloophanation of diisocyanates, such as isocyanate hexamethylene, isophorondisocyanate, 4,4 '- dicyclohexyl-methane-diisocyanate and their mixtures, or by mixing the aforesaid isocyanates with their products of trimerization, biuretization, urethanization or allophanation.

Component II) of the polyol mixture (P) is preferably a carboxylic acid substituted in position 2 by two hydroxymethyl groups, such as dimethylolpropionic acid, dimethylolbutanoic acid or their mixtures. The quantity of component II) in the mixture of polyols is chosen in such a way as to obtain a prepolymer that contains from 5 to 125 meq / 100 g on the dry basis of â € “COOH; the best results are obtained when this value is between 20 and 60.

Component III) of the polyol mixture (P) can be chosen from the polycarbonates obtained from the de-alcohol condensation of low molecular weight diols with dialkyl carbonates, from the de-phenol condensation of low molecular weight diols with diphenyl carbonates, or from the de-glycol condensation of low molecular weight diols with alkylene carbonates or dialkyl carbonates.

Examples of low molecular weight diols include 1,4-butanediol, 1,5-pentanediol, 1,6-hexandiol, ethylene glycol, propylene glycol, 3-methyl-1,5-pentanediol, nepentylglycol, diethylene glycol, 1,4 -cyclohexanodiol, 1,4-cyclohexanodimethanol and the like.

Examples of dialkyl carbonates include dimethyl carbonate and diethyl carbonate. An example of dialkylene carbonate is diethylene carbonate.

A particularly preferred example of polycarbonate diol is the poly (hexamethylene carbonate) diol, obtained from the condensation of 1,6-hexanediol with a dialkyl carbonate.

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

Component IV) of the polyol mixture (P) can be chosen from the polyesters obtained from the reaction of acids, anhydride esters or acyl halides with glycols.

Useful for the preparation of the aforesaid polyesters are, for example, maleic, succinic, adipic, suberic, sebacic, phthalic, terephthalic and isophthalic acids and possibly their corresponding acyl halides, esters and anhydrides.

Examples of suitable glycols are ethylene glycol, 1,4-butanediol, 1,3-propanediol, 1,2-propanediol, neopentylglycol, tetramethylene glycol, diethylene glycol, 1,6-hexanediol, 1,5-pentanediol; substituted alkylene glycol, such as 2,2-dimethyl-1,3-propanediol; cyclic glycols, such as 1,4-cyclohexanediol and 1,4-cyclohexanedimethanol, and aromatic glycols; these glycols are reacted with aliphatic, cycloaliphatic or aromatic dicarboxylic acids or with alkyl esters of alcohols having low molecular weight or with compounds which are capable of forming esters, so as to obtain polymers with relatively low molecular weight, and preferably having a melting below about 80 ° C.

It is also possible to use hydroxy-terminated polycaprolactone.

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

In a preferred embodiment, the polyester diol is selected from polyesters based on adipic and / or phthalic acid with 1,6-hexanediol, ethylene glycol, diethylene glycol, neopentylglycol, 1,4-butanediol or their mixtures. According to a preferred aspect, the polyols of the mixture (P) are free of units deriving from poly (oxyethylene) glycol.

The aqueous polyurethane dispersions of the present invention can be prepared: i) by reacting, in the proportions defined above, the polyisocyanates with the polyol mixture (P); ii) dispersing the prepolymer obtained in water; iii) adding a polyamine (chain extender) to the dispersion thus obtained and letting it react until all the isocyanate groups have disappeared.

Step i) is preferably carried out in the presence of an organic solvent or a mixture of organic solvents at a temperature between 40 and 110 ° C; however, it has been found that the use of hydrophobic polyol I) reduces the viscosity of the reaction mixture and therefore, advantageously, the amount of solvent required and the overall consumption of VOC in the synthesis.

Suitable solvents are commonly used solvents, such as N-methylpyrrolidone, N-ethylpyrrolidone, dipropylene glycol dimethyl ether, ethyl acetate, butyl acetate, ethylene glycol monomethyl or monoethyl ether acetate, 1-methoxypropyl-2-acetate, 3-methoxy-n- butyl acetate, acetone, 2-butanone, 4-methyl-2-pentanone, cyclohexanone, mixtures of aromatic solvents, carbonic esters, such as dimethyl carbonate, diethyl carbonate, 1,2-ethylene carbonate and 1,2-propylene carbonate, lactones, such as [beta] -propiolactone, [gamma] -butyrolactone, [epsilon] -caprolactone and [epsilon] -methylcaprolactone, but also solvents such as propylene glycol diacetate, diethylene glycol dimethyl ether, diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate and N-methylcaprolactam, or any mixture of such solvents.

The preferred solvents are N-ethylpyrrolidone and dipropylene glycol dimethyl ether.

The prepolymer obtained at the end of step i) is normally neutralized, preferably with tertiary amines, such as N-alkylmorpholines, trialkylamines, dialkanolamines, alkyldyalkanolamines, trialkanolamines and their mixtures, at a temperature below 90 ° C.

Thethylamine, dimethylethanolamine and N-methylmorpholine are particularly suitable for this purpose.

Neutralization can be carried out at the end of reaction stage i), in anhydrous environment, or during the following stage of dispersion of the prepolymer in water (stage ii).

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

The emulsifier can be chosen from nonionic, anionic and cationic surfactants; preferably, the emulsifier is a nonionic surfactant. The polyamines of stage iii) are preferably primary or secondary aliphatic diamines.

In stage iii) it is possible to use a mixture of polyamines.

Examples of usable polyamines are hydrazine, ethylene diamine, piperazine, 1,5-pentanediamine, 1,6-hexanediamine, isoforondiamine, diethylenetriamine, 2-methyl-1,5-pentanediamine and 4,4â € ™ -methylene-bis-cyclohexylamine.

The temperature and duration of stage iii) and the amount of polyamine are determined in such a way as to exhaust the free NCO groups present in the prepolymer and to obtain a stable and homogeneous dispersion of polyurethane, as is well known in the sector.

Any organic solvent present can be removed by distillation during stage iii) or at the end of stage iii).

Step iii) can be carried out by percolating the polyamine into the prepolymer dispersion maintained under mechanical stirring at a temperature below 40 ° C.

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

For the preparation of the compositions for the coating, the aqueous dispersions of anionic polyurethanes can be mixed with binders, preferably acrylics, with crosslinkers and / or with other additives, in order to further improve their application properties in the coating, such as for example the filming power, reduction or increase of opacification, the solution of surface problems such as orange peel, white spots and foam.

Examples of additives that can be added to coating compositions are leveling agents, wetting agents, fillers, pigments, waxes, surfactants, thickeners, coalescing agents, rust inhibitors, etc. The aqueous dispersions of anionic polyurethanes of the present invention can also be crosslinked with all crosslinkers known to those skilled in the art, such as water-dispersible polyisocyanates, blocked polyisocyanants, polyaziridines, carbodiimides, epoxysilanes and melamines.

The crosslinking agents can be added in quantities ranging from 1 to 10% on the dry basis of the dispersion.

Crosslinking can be useful for increasing the mechanical and chemical properties of the films.

The aqueous dispersions of anionic film-forming polyurethanes of the present invention and the compositions for the coating containing them can advantageously be used for the finishing of rigid substrates, such as plastics (for example polycarbonates, ABS and PVC), wood, glass and metals (for example aluminum, steel, iron and galvanized steels: GA, GL, GI and EGI).

The materials coated with the films obtained from the aqueous dispersions of the invention can be used for car interiors for the finishing of instruments or for the inside of the doors, on electronic products, such as mobile phones, i-Pod® and i- Pad®, for finishing metal surfaces such as the exterior of computers and televisions, and for continuous painting of metals.

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 were measured by means of Laser Correlation Spectroscopy (LCS) with a Coulter N4 Plus Instrument at a temperature of 25 ° C and an angle of 90 °.

EXAMPLES

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

POLYOL 1: polyester diol, adipate phthalate from 1,6-hexandiol, molecular weight 1,000 g / mol

POLYOL 2: polycarbonate diol, poly (hexamethylene carbonate) diol, molecular weight 1,000 g / mol

H-POLYOL 5: coco diethanolamide, molecular weight 213 g / mol H-POLYOL 6: oleic diethanolamide, molecular weight 269.7 g / mol DGEBA: bisphenol A diglycidyl ether, molecular weight 380 DMPA: dimethylolpropionic acid, molecular weight 134, 2 g / mol ALCOHOL C6: n-hexanol, molecular weight 102 g / mol

ALCOHOL C12: n-dodecanol, molecular weight 186 g / mol ALCOHOL C20: mono-alcohol C20 linear, molecular weight 298 g / mol NMP: N-methylpyrrolidone

NEP: N-ethylpyrrolidone

IPDI: isophorone isocyanate, molecular weight 222 g / mol

HMDI: 4.4â € ™ - dicyclohexyl-methan-diisocyanate, molecular weight 262 g / mol TEA: triethylamine, molecular weight 101.15 g / mol

HH: hydrazine hydrates, sol. 24.36% aqueous, molecular weight 32.04 g / mol

DEA: diethanolamine, molecular weight 105.14 g / mol

ADD: Byk 346 wetting agent

EXAMPLES 1.1-1.3

Examples 1.1-1.3 describe the preparation procedure of hydrophobic polyols based on DGEBA.

Example 1.1

Synthesis of H-POLYOL 1.

140.6 g (1.363 mol) of ALCOHOL C6 are charged into a reactor equipped with a thermometer, mechanical stirring and condenser, under nitrogen, and heated up to 65 ° C. 0.40 g of 40% KOH are added under stirring at 65 ° C.

259.4 g (0.682 mol) of DGEBA are then added and the reaction mixture is heated and maintained for about 4 hours at 120 ° C until the signals of the epoxy groups completely disappear; the titration of the epoxy groups is carried out in this and in the other examples according to the ASTM D1652-04 standard.

Once the epoxy groups have completely reacted, the reaction mixture is cooled to 80 ° C and 0.35 g of 85% phosphoric acid are added, obtaining the polyol H-POLYOL 1 (molecular weight 586 g / mol). Its hydroxyl number turns out to be 191 mg KOH / g. Example 1.2

Synthesis of H-POLYOL 2

186.0 g (1.363 mol) of C12 ALCOHOL are loaded into a reactor like that of Example 1.1 and heated up to 70 ° C. 0.75 g of 40% KOH are added. 190.0 g (0.5 mol) of DGEBA are then added and the reaction mixture is heated and maintained for about 4 hours at 120 ° C until the signals of the epoxy groups completely disappear. The reaction mixture is cooled to 80 ° C and 0.65 g of 85% phosphoric acid are added, obtaining the polyol H-POLYOL 2 (molecular weight 752 g / mol). Its hydroxyl number is 149 mg KOH / g.

Example 1.3

Synthesis of H-POLYOL 3

326.0 g (1.363 mol) of ALCOHOL C20 are loaded into a reactor like that of Example 1.1 and heated up to 100 ° C. 0.80 g of 40% KOH are added.

190.0 g (0.5 mol) of DGEBA are then added and the reaction mixture is heated and maintained for about 4 hours at 130 ° C until the epoxy group signals completely disappear.

The reaction mixture is cooled to 120 ° C and 0.80 g of 85% phosphoric acid are added, obtaining the polyol H-POLYOL 3.

Its hydroxyl number is 108 mg KOH / g.

Example 1.4

Synthesis of H-POLYOL 4

Example 1.4 describes the preparation of a hydrophobic polyol prepared by IPDI according to the prior art (H-POLYOL 4).

135.1 g of ALCOHOL C6 and 432.0 g of NEP are charged into a reactor equipped with a thermometer, mechanical stirring and condenser, under nitrogen, and at room temperature. 293.9 g of IPDI are added under stirring after about 30 minutes of homogenization of the mixture at 40 ° C.

The reaction mixture is then heated to 80 ° C and continued by reacting at 90 ° C, until the content of â € “NCO in the prepolymer is equal to 6.45%; the titration of the residual isocyanate groups is determined in this as in the other examples with the ASTM D2572 method.

The prepolymer is cooled to 80 ° C and 138.8 g of DEA is added slowly and mixing.

The polyol obtained (H-POLYOL 4) has a solid residue of 75% by weight (molecular weight 429.7 g / mol). The hydroxyl number is equal to 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 loaded into a reactor like that of Example 1.1.

155.6 g of HMDI are added under stirring after about 30 minutes of homogenizing the mixture at 40 ° C.

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

The reaction is then carried out at 95-100 ° C until the theoretical content of NCO in the prepolymer is reached (5.07%, in about 1 hour).

The prepolymer is then cooled to about 75 ° C and 14.9 g of neutralizing agent (TEA) are added.

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

The wetting agent ADD is added to the aqueous polyurethane dispersion which is then filtered on a cloth at 150 microns and brought to a solid content of 35% by weight. The dispersion obtained is transparent and stable.

Examples 2.2-2.4

Preparation of other aqueous dispersions according to the invention.

The procedure of Example 2.1 is followed by modifying the raw materials as indicated in Table 1 (quantity in grams).

Example 2.5 (comparative)

Example 2.1 is repeated without however adding the hydrophobic polyol and with the ingredients indicated in Table 1.

EXAMPLES 2.6-2.10

Preparation of other aqueous dispersions according to the known art.

The detailed list of raw materials and their quantities are shown in Table 1.

POLYOL 1 or POLYOL 2 and H-POLYOL 4, H-POLYOL 5 or H-POLYOL 6, DMPA and NMP are loaded into a reactor equipped with a thermometer, mechanical stirring and condenser, under nitrogen and at room temperature.

HMDI is added under stirring after having homogenized the mixture for about 30 minutes at 40 ° C.

The reaction mixture is brought and maintained at 60 ° C for 30 minutes.

The reaction is then carried out at 95-100 ° C, until the NCO content in the prepolymer is approximately equal to the theoretical one (for approximately 1 hour).

The prepolymer is brought to about 75 ° C and the neutralizer (TEA) is added under stirring.

After about 10 minutes and at an internal temperature of about 65 ° C, the prepolymer is dispersed in demineralized water under strong stirring, keeping the temperature below 35 ° C. The extension is performed by adding HH, as described in Table 1, at a temperature below 35 ° C. The wetting agent ADD is added to the aqueous polyurethane dispersion which is then filtered on cloth at 150 microns and brought to a solid content of 35% by weight. The dispersion obtained is transparent and stable.

TABLE 1

Example

2.1 2.2 2.3 2.4 2.5 * 2.6 * 2.7 * 2.8 * 2.9 * 2.10 * POLYOL 1 - 134.4 - 130.4 124.9 - 144.4 - - -POLYOL 2 138.7 - 134.6 - 43.6 148.6 - 131.0 147.0 146.7 H-POLYOL 1 26.6 27.5 - - - - - - - -H-POLYOL 2 - - 33.1 34.3 - - - - - -H-POLYOL 5 - - - - - 10.3 10.8 18.2 - -H-POLYOL 6 - - - - - - - - 13.1 -H-POLYOL 4 - - - - - - - - - 31.1 DMPA 20.9 20.8 20.8 20.9 20.8 20.8 20.8 20.8 20.8 21.6 NMP 80.0 80.0 80.0 80.0 80.0 80.0 80.0 80.0 80.0 80.0 HMDI 155.6 158.7 153.0 156.1 152.5 162.6 165.2 170.5 160.4 157.5 TEA 14.9 14.9 15.7 14.9 14.9 14.9 14.9 15.7 15.6 16.3 HH 47.8 48.7 49.1 47.9 46.8 49.6 50.7 54.7 51.4 50.5 ADD 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Water 514.6 513.8 512.8 514.5 515.4 513.1 512.1 508.0 510.8 495.3

Diameter

particle

(nm) 55 54 32 55 63 43 45 30 65. 40 * comparative

APPLICATION EXAMPLES

The application examples show the comparison between the results of coating carried out using dispersions of the known art and two dispersions according to the invention.

Mechanical, chemical and physical properties of glass or metal substrates coated with polyurethane dispersions are compared. The contact angle is measured on a coated aluminum substrate using a PGX Pocket Goniometer. The integrated pump releases 0.5 microliter water droplets and the collection chamber captures images of the single drop to determine the static contact angle at equilibrium.

The hardness of the films was measured with the ASTM D4366-95 method (Standard Test Method for Hardness of Coatings by Pendulum Damping Test), on glass.

The hydrolytic and ethanol resistance of the films was measured with the UNI EN 12720 method (Surface resistance to cold liquids) on glass.

Chemical resistance (NaOH, HCl) was determined by evaluating the coated glass substrate after immersion in an alkaline or acid solution (1% NaOH or 5% HCl) at a temperature of 55 ° C for 2 minutes. The results are expressed on a scale from 0 to 5 (0 = worst result, the coating is destroyed; 5 = best result, no effect on the coating).

The adhesion on metal substrate (aluminum and electrogalvanized steel) was determined with the ASTM D3359-09 method (Standard Test Method for Measuring by Tape Test). The results are

expressed on a scale from 0 to 5 (0 = worst result, the coating yes

completely destroys; 5 = best result, no effect on

coating).

The results are reported in Table 2.

TABLE 2

EXAMPLE

2.2 2.4 2.5 * 2.6 * 2.7 * 2.8 * 2.10 * Contact angle (°) 66.4 85.5 70.6 66.2 67.1 59.4 65.3 Resistance to EtOH

(min) 25 30 4 2 2 1 1 Resistance to H2O

(min) 120 50 30 60 30 10 240 Koenig hardness (s) 143 113 108 150 141 190 130 Adhesion (alum. A

36) ** 5 5 1 0 0 0 0 Adhesion (EGI) 5 5 3 0 0 0 0 Resistance to NaOH 5 4 2 3 3 3 3 Resistance to HCl 4 3 3 2 2 2 2

*comparative

** wet: substrate immersed in water for 4 hours and adhesion test 2 minutes after extraction

It can be observed that the contact angle of Example 2.4 is

significantly greater than that of the other examples, and this one

demonstrates a greater hydrophobicity of the coating.

The substrates coated with the dispersions of Examples 2.2 and 2.4 show a resistance to ethanol 6-7 times greater than those prepared without using a hydrophobic polyol and even more increased than those from the dispersions of the known art.

The hydrolytic resistance of the coatings of the present invention is good. Furthermore, the substrates coated with the dispersion of Examples 2.2 and 2.4 show good hardness and excellent adhesion both on aluminum and on steel in comparison with those prepared with the dispersions of the prior art. If the resistance to alkalis and acids is considered, the coatings prepared with the dispersions of the present invention show resistance better than or equal to those of the known art.

Claims (10)

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 neutralized anionic prepolymer containing from 5 to 250 meq / 100 g on the dry basis of carboxylic groups and prepared by reacting one or more aliphatic, cycloaliphatic or aromatic polyisocyanates with a mixture of polyols (P) which includes: I) from 4 to 90% by weight of one or more hydrophobic polyols having hydroxyl mean molar functionality from 2 to 3, hydroxyl number from 350 to 40 and obtained by reacting an alcohol ROH, in which R is a saturated alkyl chain, linear or branched C4-C30 or R is a phenyl radical substituted with a saturated, linear or branched C4-C10 alkyl chain, with an aromatic diglycidyl ether of formula (I): O O O O R1 (THE) where R1Ã is the radical (i): R2R3 (the) in which R2 and R3 are one independently of the other Me, Et, or H; or R1Ã a phenylene radical, optionally substituted with one or more alkyl groups; or R1Ã a bis-phenylene radical, optionally substituted with one or more alkyl groups; or R1Ã ̈ the radical (ii): OR OR (ii) II) from 1 to 10% by weight of one or more anionic or potentially anionic polyols having two or more groups reactive towards the isocyanic groups and at least one carboxyl or carboxylate group; III) from 0 to 95% by weight of one or more linear polycarbonate diols having molecular weight from 500 to 3,000; IV) from 0 to 95% by weight of one or more linear polyester diols having molecular weight from 500 to 4,000; V) from 0 to 95% by weight of one or more polyalkylene diols selected from 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 NCO isocyanic groups of the polysiocyanates and the sum of all reactive - OH groups of the mixture of polyols (P) is between 1.2 and 2.3. 2) Aqueous dispersions according to claim 1 wherein components I), II), III), IV) and V) constitute at least 95% by weight of the polyol mixture (P), the polyol mixture further comprising 0 to 5% by weight of other non-ionic polyols having a molecular weight of less than 1,000 and containing two or more hydroxyl groups. 3) Aqueous dispersions according to claim 2 wherein components I), II), III), IV) and V) constitute 100% by weight of the polyol mixture (P) of the prepolymer. 4) Aqueous dispersions according to claim 3 wherein components I), II), III), and IV) constitute 100% by weight of the polyol mixture (P). 5) Aqueous dispersions according to claim 1 wherein the polyol mixture (P) contains from 5 to 75% by weight of a hydrophobic polyol I) obtained by reacting an alcohol ROH in which R is a saturated C6-C22 branched alkyl chain or linear and R1Ã is the radical (i). 6) Aqueous dispersions according to claim 5 wherein R2 and R3 are methyls. 7) Aqueous dispersions according to claim 1 in which the neutralized anionic prepolymer is prepared from one or more aliphatic or cycloaliphatic polyisocyanates having an average functionality - NCO comprised between 2.0 and 2.3. 8) Aqueous dispersions according to claim 1 wherein component II) of the polyol mixture (P) is dimethylolpropionic acid, dimethylolbutanoic acid or their mixtures; component III) of the mixture of polyols (P) is poly (hexamethylene carbonate) diol having an average number molecular weight from 800 to 2,000; component IV) of the polyol mixture (P) is selected from polyesters based on adipic and / or phthalic acid with 1,6-hexanediol, ethylene glycol, diethylene glycol, neopentylglycol, 1,4-butanediol or their mixtures, and having an average number molecular weight from 800 to 3,000. 9) Aqueous dispersions according to any one of the preceding claims in which the polyols of the mixture (P) are free from units deriving from poly (oxyethylene) glycol. 10) Use of aqueous dispersions of anionic polyurethanes according to claims 1) to 9) for the preparation of compositions for coating rigid substrates.