CN102822220B - Aqueous anionic polyurethane dispersions - Google Patents

Abstract

Aqueous anionic polyurethane dispersions based on specific hydrophobic polyols as film formers for coating rigid surfaces such as metal, plastic, glass and wood, and provide excellent durability, adhesion to coatings , hydrolysis resistance and alkali/acid resistance and hardness.

Description

Waterborne Anionic Polyurethane Dispersion

The present invention relates to aqueous anionic polyurethane dispersions based on specific hydrophobic polyols and to their use as film formers for coating rigid surfaces such as metal, plastic, glass and wood.

The aqueous dispersions of the present invention provide coatings with excellent durability, adhesion, hydrolysis and acid/alkali resistance, and hardness.

Background technique

The surfaces of many manufactured articles, such as those made of leather, plastic, wood, and metal, require treatment to make the surface more uniform, or to protect the surface from abrasion over time or exposure to the atmosphere, and/or Improve certain aesthetic properties, such as higher or lower opacity, soft or hard touch, and color.

Usually, these effects are obtained by applying a film-forming polymer (coating), among many different film-forming polymers today solvent-borne polyurethanes are well known and valued in the field of coatings because they can produce coatings with excellent chemical resistance. and mechanically resistant film.

Likewise, water-based dispersions of polyurethanes are now being used due to the increased regulatory focus on reducing emissions of low VOCs to the environment, especially in work areas.

When considering coating polyurethanes in the form of aqueous dispersions, some problems arise because their ability to disperse in water requires the inclusion of hydrophilic segments, which inherently reduce the durability and Hydrolytic stability.

It is known in the art that the introduction of unsaturated groups into polyurethane causes cross-linking of the film and thus can improve the chemical resistance of the coating; unfortunately, the disadvantage associated with the presence of unsaturated groups in polyurethane is that the film Yellow and requires strong oxidative conditions for crosslinking.

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

US 2008/0194757 describes water-dispersible polyurethane compositions containing uric acid (nurate) compounds having long-chain alkyl groups as the polyisocyanate component; said compositions are said to provide coating films with Excellent adhesion, water resistance, weather resistance, corrosion resistance, water resistance and oil resistance.

Surprisingly, it has now been found that it is possible to obtain aqueous dispersions of anionic polyurethanes which, by incorporation of specific hydrophobic polyols into the polyurethane, allow durable films to have excellent properties on rigid substrates. Adhesion, chemical resistance, and hardness, the specific hydrophobic polyols are obtained by reacting fatty alcohols with aromatic diglycidyl ethers.

Summary of the invention

The present invention provides an aqueous dispersion containing 20 to 50% by weight of anionic polyurethane obtained by the following steps: an anionic prepolymer dispersed in water and extended and neutralized with a polyamine, the anionic Type prepolymers containing from 5 to 125 meq/100g dry weight of carboxylic acid groups, prepared by reacting one or more aliphatic polyisocyanates, cycloaliphatic polyisocyanates or aromatic polyisocyanates with a mixture of polyols (P) To prepare, the mixture of polyols (P) comprises the following components I), II), III), IV) and V):

I) 4 to 90% by weight of one or more hydrophobic polyols having an average molar hydroxyl functionality of 2 to 3 and a hydroxyl number of 350 to 40 (mg KOH/g), and passing Obtained by reacting the alcohol ROH with an aromatic diglycidyl ether, wherein R is a branched or linear saturated _C4 - _C30 alkyl chain, preferably a branched or linear saturated _C6 - _C22 alkyl chain , or R is a branched or linear saturated C ₄ -C ₁₀ alkylphenyl group, wherein the aromatic diglycidyl ether has the following chemical formula (I):

where _R1 is group (i):

wherein each of R ₂ and R ₃ is independently Me, Et or H;

or _R is phenylene optionally substituted by one or more alkyl groups, preferably methyl groups;

or _R is biphenylene optionally substituted by one or more alkyl groups, preferably methyl groups;

or _R1 is group (ii):

II) 1 to 10% by weight of one or more anionic or potentially anionic polyols having two or more isocyanate-reactive groups and at least one carboxyl or carboxylate group;

III) 0 to 95% by weight of one or more linear polycarbonate diols with a molecular weight of 500 to 3000;

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

V) 0 to 95% by weight of one or more polyoxyalkylene diols selected from poly(oxypropylene) glycols and poly(oxytetramethylene) glycols,

The ratio of polyisocyanate to polyol mixture (P) is such that the ratio of the isocyanate groups NCO of said polyisocyanate to the sum of all reactive -OH groups contained in said polyol mixture (P) is 1.2 and 2.3 between.

According to another aspect, the invention relates to the use of the aforementioned aqueous anionic polyurethane dispersions for the preparation of coating compositions.

Detailed description of the invention

In one embodiment, components I), II), III), IV) and V) together constitute at least 95% by weight of a mixture of polyols which also contains 0 to 5% by weight of other non- Ionic polyols, said other nonionic polyols having a molecular weight below 1000 and containing two or more hydroxyl groups; examples of useful nonionic polyols are: glycerol, pentaerythritol, neopentyl glycol Alcohols, butanediol, 1,4-cyclohexanedimethanol, trimethylolpropane and their derivatives such as propoxylated trimethylolpropane, polyfunctional polybutadiene and polyester polyols.

In a preferred embodiment, components I), II), III), IV) and V) together constitute 100% by weight of the mixture of polyols (P) of the prepolymer; in a more preferred embodiment, the components The subdivisions I), II), III) and IV) together represent 100% by weight of the mixture of polyols.

Hydrophobic polyols I) contain no epoxy groups, preferably 5 to 75% by weight of the mixture of polyols.

Preferably, in the aromatic diglycidyl ether of formula (I), R ₁ is group (i), wherein R ₂ , R ₃ are methyl groups.

Polyisocyanates which can be used have an average NCO functionality between 2.0 and 2.3 and are preferably aliphatic or cycloaliphatic polyisocyanates.

Examples of useful polyisocyanates are 4,4'-dicyclohexyl-methane-diisocyanate, 1-isocyanato-3-(isocyanatomethyl)-3,5,5-trimethylcyclohexane ( or isophorone diisocyanate), 1,4-butane diisocyanate, 1,6-hexamethylene diisocyanate and mixtures thereof.

The most preferred polyisocyanates are 4,4'-dicyclohexyl-methane-diisocyanate, 1-isocyanate-3-isocyanate-methyl-3,5,5-trimethylcyclohexane (or isophorone di isocyanate) and 1,6-hexamethylene diisocyanate and mixtures thereof.

Partial trimerization, biuretization, urethanization of diisocyanates such as 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate and mixtures thereof or allophanation, or by mixing the aforementioned diisocyanates with their trimerization, biuretization, urethanization or allophanation products to obtain an average NCO functionality higher than 2 of polyisocyanates.

Component II) of the mixture of polyols (P) is preferably a carboxylic acid substituted in position 2 by two methylol groups, for example dimethylolpropionic acid, dimethylolbutyric acid or mixtures thereof.

The amount of component II) in the mixture of polyols is chosen so as to obtain a prepolymer containing 5 to 125 meq/100 g dry weight of COOH groups; most preferably said value is between 20 and 60.

Polycarbonate can be obtained through the dehydration condensation reaction of low molecular weight diol and dialkyl carbonate, polycarbonate can be obtained through the dephenol condensation reaction of low molecular weight diol and diphenyl carbonate, or the polycarbonate can be obtained by low molecular weight diol and The polyol mixture (P) component III) is selected among the polycarbonate options from the dealcoholation condensation reaction of alkylene carbonate or dialkyl carbonate.

Examples of the low molecular weight diols include 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, ethylene glycol, propylene glycol, 3-methyl-1,5-pentanediol alcohol, neopentyl glycol, diethylene glycol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol, etc. Examples of the dialkyl carbonate include dimethyl carbonate and diethyl carbonate. An example of a dialkylene carbonate is diethylene carbonate.

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

Preferably, the polycarbonate diol has a number average molecular weight of 800 to 2000.

Component IV) of the mixture of polyols (P) may be chosen from polyesters obtained by reaction of acids, esters, anhydrides or acid halides with diols.

For example, maleic acid, succinic acid, adipic acid, suberic acid, sebacic acid, phthalic acid, terephthalic acid and isophthalic acid, and possibly their corresponding acid halides, anhydrides and esters can be used in the preparation of the polyester.

Examples of suitable diols are ethylene glycol, 1,4-butanediol, 1,3-propanediol, 1,2-propanediol, neopentyl glycol, tetramethylene glycol, diethylene glycol, 1,6 - hexanediol, 1,5-pentanediol; substituted alkylene glycols such as 2,2-dimethyl-1,3-propanediol; cyclic diols such as 1,4-cyclohexanediol and 1 , 4-cyclohexanedimethanol and aromatic diols; these diols are reacted with aliphatic, cycloaliphatic or aromatic dicarboxylic acids or with alkyl esters of low molecular weight alcohols or with Compounds that can form ester linkages are reacted to yield lower molecular weight polymers, preferably having a melting point of less than about 80°C.

Hydroxyl-terminated polycaprolactones may also be used.

Preferably, the polyester diol has a number average molecular weight of 800 to 3,000.

In a preferred embodiment, the polyester diol is selected from the group based on adipic acid and/or phthalic acid and 1,6-hexanediol, ethylene glycol, diethylene glycol, neopentyl glycol, 1,4 - Polyesters of butanediol or mixtures thereof.

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

Aqueous dispersions of the anionic polyurethanes according to the invention can be prepared by: i) reacting a mixture (P) of polyisocyanates and polyols in the ratios defined above; ii) dispersing the resulting prepolymer in water ; iii) Add polyamine (chain extender) to the resulting dispersion and allow it to react until all isocyanate groups disappear.

Preferably, step i) is carried out at a temperature between 40 and 110° C. in the presence of an organic solvent or a mixture of organic solvents; however, it was found that the use of a hydrophobic polyol I) reduces the viscosity of the reaction mixture and thus, advantageously reduces the synthesis The amount of solvent required and the total consumption of VOC.

Suitable solvents are customary solvents such as N-methylpyrrolidone, N-ethylpyrrolidone, dipropylene glycol dimethyl ether, ethyl acetate, butyl acetate, ethylene glycol monomethyl ether acetate or ethylene glycol Monoethyl ether acetate, 1-methoxypropyl 2-acetate, 3-methoxy-n-butyl acetate, acetone, 2-butanone, 4-methyl-2-pentanone, Cyclohexanone, especially mixtures containing aromatic esters, carbonates, such as dimethyl carbonate, diethyl carbonate, 1,2-ethylene carbonate and 1,2-propylene carbonate, lactones, such as [β]-propiolactone, [γ]-butyrolactone, [ε]-caprolactone, and [ε]-methylcaprolactone, as well as solvents such as propylene glycol diacetate, diglyme diethylene glycol ethyl ether acetate, diethylene glycol butyl ether acetate and N-methylcaprolactam or any desired mixtures of said solvents. Preferred solvents are N-ethylpyrrolidone and dipropylene glycol dimethyl ether.

The prepolymer obtained at the end of step i) is usually neutralized, preferably with tertiary amines such as N-alkylmorpholines, trialkylamines, dialkylalkanolamines, alkyldialkanolamines, trialkylamines, Alkanolamines and their mixtures at temperatures below 90°C.

Triethylamine, dimethylethanolamine and N-methylmorpholine are particularly suitable in this range.

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

Step ii) is carried out by pouring the prepolymer into water, preferably in the presence of an emulsifier, or vice versa, while mechanically stirring.

The emulsifier may be selected from nonionic, anionic and cationic surfactants; preferably, the emulsifier is a nonionic surfactant.

The polyamine in step iii) is preferably a tertiary aliphatic amine or a secondary aliphatic amine.

Mixtures of polyamines may be used in step iii).

Examples of suitable polyamines are hydrazine, ethylenediamine, piperazine, 1,5-pentanediamine, 1,6-dihexanediamine, isophoronediamine, diethylenetriamine, 2-methyl -1,5-pentanediamine, and 4,4'-methylene-bis-cyclohexylamine.

The determination of the temperature and duration of step iii) and the amount of polyamine to deplete the free NCO groups present in the prepolymer and to obtain a fine, stable and homogeneous polyurethane dispersion is well known in the art.

Organic solvents that may be present can be removed by distillation during step iii) or at the end of step iii).

Step iii) of the process of the invention can be carried out by infiltrating the dispersion of the prepolymer with the polyamine, kept under stirring and at a temperature below 40°C.

Brookfield of the inventive anionic polyurethane aqueous dispersion The viscosity is usually between 50 and 2000 mPa*s.

To prepare coating compositions, anionic aqueous polyurethane dispersions can be mixed with crosslinkers, binders (preferably acrylic binders) and/or other additives to further improve their coating properties e.g. Film strength and reduce or increase opacity to avoid "orange peel" effect or "fish eye" effect and foaming.

Examples of additives that may be added to the coating composition are leveling agents, wetting agents, fillers, pigments, waxes, surfactants, thickeners, coalescing agents, rust inhibitors, and the like.

The anionic polyurethanes of the aqueous dispersions of the invention can be crosslinked with any crosslinking agent known to the person skilled in the art, such as water-dispersible polyisocyanates, blocked polyisocyanates, polyethyleneimine pyridine, carbodiimide, epoxysilane, and melamine.

The amount of crosslinker added is usually between 1 and 10% based on the dry weight of the dispersion.

Crosslinking is useful to enhance the mechanical and chemical resistance of the film.

The film-forming anionic polyurethane aqueous dispersions of the present invention and coating compositions containing said film-forming anionic polyurethane aqueous dispersions are preferably used for finishing rigid substrates, such as plastics (such as polycarbonate, ABS and PVC), Wood, glass and metal (e.g. aluminium, steel, galvanized iron and galvanized steel: GA, GL, GI and EGI).

Materials coated with films obtained by means of the aqueous dispersions of the invention can be used in vehicle interiors, for finishing instrument panels or inside doors, in electronic products such as mobile phones, and Can be used on metal surfaces such as computer housings or television housings and for coil coating.

In the following examples, the synthesis of hydrophobic polyols and the preparation of aqueous dispersions according to the invention are reported.

The particle size of the dispersion was measured by laser correlation spectroscopy (LCS) with a Coulter N4 Plus instrument at a temperature of 25°C and an angle of 90°.

Example

The materials listed below were used in the examples described below:

Polyol 1: polyester-based diol, adipate-phthalate of 1,6-hexanediol, molecular weight 1000 g/mol

Polyol 2: polycarbonate-based diol, poly(hexamethylene carbonate) diol, molecular weight 1000 g/mol

H-Polyol 5: Cocodiethanolamide with a molecular weight of 213 g/mol

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

DGEBA: Diglycidyl ether of bisphenol A with a molecular weight of 380 g/mol

DMPA: Dimethylolpropionic acid, molecular weight 134,2 g/mol

Alcohol C6: n-hexanol with a molecular weight of 102 g/mol

Alcohol C12: n-dodecyl alcohol with a molecular weight of 186 g/mol

Alcohol C20: linear C20 monohydric alcohol with a molecular weight of 298 g/mol

NMP: N-methyl-pyrrolidone

NMP: N-ethyl-pyrrolidone

IPDI: Isophorone diisocyanate with a molecular weight of 222 g/mol

HMDI: 4,4'-dicyclohexyl-methane-diisocyanate, molecular weight 262g/mol

TEA: Triethylamine, molecular weight 101, 15g/mol

DEA: Diethanolamine, molecular weight 105, 14g/mol

HH: Hydrazine hydrate, 24.36% aqueous solution, molecular weight 32,04g/mol

ADD: Wetting agent Byk 346

Example 1.1-1.3

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

Example 1.1

Synthesis of H-polyol 1.

Under a nitrogen atmosphere, 140.6 g (1.363 mol) of alcohol C6 were added to a reactor equipped with a thermometer, mechanical stirrer and condenser and heated to 65 °C. 0.40 g of 40% KOH was added with stirring at 65°C.

Then 259.4 g (0.682 mol) of DGEBA were added and the reaction mixture was heated to 120°C and maintained at this temperature for about 4 hours until all the epoxy groups disappeared.

In this and all other examples titration of epoxy groups was determined according to standard ASTM D1652-04.

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

Example 1.2

Synthesis of H-polyol 2.

According to the process of Example 1.1, 186.0 g (1 mole) of alcohol C12 was added to the reactor, heated to 70 ° C, and then 0.75 g of 40% KOH was added.

Then 190.0 g (0.5 mol) of DGEBA were added and the reaction mixture was heated to 120°C and maintained at this temperature until the epoxy groups disappeared (about 4 hours).

The reaction mixture was then cooled to 80°C and 0.65 g of 85% phosphoric acid was added to give H-polyol 2 (molecular weight 752 g/mol). The OH number is 149 mg KOH/g.

Example 1.3

Synthesis of H-polyol 3.

According to the procedure of Example 1.1, 326.0 g (1 mole) of alcohol C20 was added to the reactor, heated to 100° C., and then 0.80 g of 40% KOH was added.

Then 190.0 g (0.5 mol) of DGEBA were added and the reaction mixture was heated to 130°C and maintained at this temperature until the epoxy groups disappeared (about 12 hours).

The reaction mixture was then cooled to 120°C and 0.80 g of 85% phosphoric acid was added to give 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 (H-polyol 4) according to the prior art.

Under nitrogen atmosphere and room temperature, 135.1 g of alcohol C6, 432.0 g of NEP were added into a reactor equipped with a thermometer, a stirrer and a condenser.

After the mixture was homogenized at 40° C. for about 30 minutes, 293.9 g of IPDI were added with stirring.

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

In this and all other examples the titration of residual isocyanate groups was determined according to standard method ASTM D2572.

The prepolymer was cooled to 80°C, and 138.8 g of DEA were slowly added with stirring.

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

Example 2.1

Aqueous dispersions of the invention are prepared.

According to example 1.1, 138.7 g of polyol 2 and 26.6 g of H-polyol 1, 20.9 g of DMPA and 80 g of NMP were charged into the reactor. After the mixture had been homogenized at 40° C. for about 30 minutes, 155.6 g of HMDI were added with stirring.

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

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% (about 1 hour).

The prepolymer was then cooled to about 75°C and 14.9 g of neutralizing agent TEA was added with stirring.

After about 10 minutes and at an internal temperature of 65°C, the prepolymer was dispersed in demineralized water with vigorous stirring and a temperature below 35°C. At temperatures below 35 °C, 47.8 g of diamine HH (24.36% in water) was added as described in Table 1 for increment.

The wetting agent ADD was added to the resulting polyurethane dispersion, which was then filtered through a 150 μm canvas so that the solid residue content reached 35% by weight. The resulting dispersion is clear and stable.

Example 2.2-2.4

Other aqueous dispersions of the invention were prepared.

Following the procedure described in Example 2.1, the ingredients were changed as shown in Table 1 in grams.

Embodiment 2.5 (comparative example)

The procedure as described in Example 2.1 was followed without any hydrophobic polyols and the ingredients reported in Table 1 were used.

Embodiment 2.6-2.10 (comparative example)

Other aqueous dispersions of the prior art were prepared.

A detailed list of ingredients and their amounts are reported in Table 1.

Under nitrogen atmosphere and room temperature, add polyol 1 or polyol 2 and H-polyol 4, H-polyol 5 or H-polyol 6, DMPA and NMP to the reaction set with thermometer, stirrer and condenser device.

When the mixture was homogenized at 40°C for about 30 minutes, HMDI was added with stirring.

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

The reaction is carried out at 95-100°C until the content of NCO groups in the prepolymer is equal to the theoretical value (about 1 hour).

The prepolymer was then cooled to about 75°C and the neutralizing agent TEA was added with stirring.

After about 10 minutes and at an internal temperature of 65°C, the prepolymer was dispersed in demineralized water with vigorous stirring and a temperature below 35°C. Add chain extenders HH as described in Table 1 to extend at temperatures below 35°C.

The wetting agent ADD was added to the resulting polyurethane dispersion, which was then filtered through a 150 μm canvas so that the solid residue content reached 35% by weight. The resulting dispersion is clear and stable.

Application example

In the application examples, a comparison of the results between a coating treated with a dispersion of the prior art and a coating treated with two dispersions according to the invention is shown.

Compare the mechanical, physical and chemical properties of glass or metal substrates coated with polyurethane dispersions.

Contact angle measurements on coated aluminum substrates were performed using a portable goniometer PGX. An integrated pump delivers precise droplets in 0.5μl steps, and a built-in camera captures images of individual droplets to determine the static contact angle at "equilibrium".

Table 1

*Comparative example

The hardness of the films was determined on glass substrates according to the standard method ASTM D4366-95 (Standard Test Method for Hardness of Organic Coatings by Pendulum Damping Test).

The hydrolysis resistance and ethanol resistance of the films were determined on glass by standard method UNIEN 12720 (Surface resistance to cold liquids).

Chemical resistance (NaOH, HCl) was evaluated by immersing coated glass specimens in alkaline or acidic solutions (1% NaOH or 5% HCl) at a temperature of 55°C for 2 minutes. The results are expressed by the following scale: 0=worst, coating destroyed, 5=best, no effect.

Adhesion on metal substrates (aluminum and zinc-galvanized steel) was determined by standard method ASTM D3359-09 (Standard Test Method for Adhesion by Tape Test). The results are expressed by the following scale: 0=worst, coating destroyed, 5=best, no effect.

The results are shown in Table 2.

It can be seen that the contact angle of Example 2.4 is significantly increased relative to all other examples, showing that the coating is more hydrophobic.

Substrates coated with the dispersions of Examples 2.2 and 2.4 had 6-7 times better resistance to ethanol relative to those prepared without any hydrophobic polyol, compared to dispersions according to the prior art , the substrates coated with the dispersions of Examples 2.2 and 2.4 had even better ethanol resistance.

The H ₂ O resistance (hydrolysis resistance) of the coating according to the invention is good.

Table 2

*Comparative example

**Wet Conditions: Panels were submerged in water for 4 hours and tested for adhesion within 2 minutes of removal.

Furthermore, the substrates coated with the dispersions of Examples 2.2 and 2.4 exhibit good hardness and excellent adhesion to both aluminum and steel substrates relative to substrates prepared from dispersions according to the prior art. Compatibility.

When considering alkali and acid resistance, the coatings prepared with the dispersions of the present invention exhibit alkali and acid resistance equal to or better than prior art coatings.

Claims (10)

1. Aqueous dispersion containing 20 to 50% by weight of anionic polyurethane obtained by: anionic prepolymer dispersed in water and augmented with polyamines , the anionic prepolymer contains 5 to 125meq/100g dry weight carboxylic acid groups, and by making one or more aliphatic polyisocyanate, cycloaliphatic polyisocyanate or aromatic polyisocyanate and the mixture of polyol ( The reaction of P) is prepared, and the mixture (P) of described polyhydric alcohol comprises following I), II), III), IV) and V): I) 4 to 90% by weight of one or more hydrophobic polyols having an average molar hydroxyl functionality of 2 to 3 and a hydroxyl number of 350 to 40, obtained by combining the alcohol ROH with the aromatic Reaction of diglycidyl ether is obtained, wherein R is a branched or linear saturated C ₄ -C ₃₀ alkyl chain, or R is a branched or linear saturated C ₄ -C ₁₀ alkylphenyl group, wherein The aromatic diglycidyl ether has the following chemical formula (I): where _R is the group (i): Each of R ₂ and R ₃ is independently Me, Et or H; or _R is phenylene optionally substituted with one or more alkyl groups; or _R is biphenylene optionally substituted with one or more alkyl groups; or R ₁ is group (ii): II) 1 to 10% by weight of one or more anionic or potentially anionic polyols having two or more groups reactive towards isocyanate groups and at least one carboxyl or carboxylate group; III) 0 to 95% by weight of one or more linear polycarbonate diols with a molecular weight of 500 to 3000; IV) 0 to 95% by weight of one or more linear polyester diols having a molecular weight of 500 to 4,000; V) 0 to 95% by weight of one or more polyoxyalkylene diols selected from poly(oxypropylene) glycols and poly(oxytetramethylene) glycols, The ratio of polyisocyanate to polyol mixture (P) is such that the ratio of the isocyanate groups NCO of said polyisocyanate to the sum of all reactive -OH groups contained in said polyol mixture (P) is 1.2 and 2.3 between. 2. The aqueous dispersion according to claim 1, wherein said components I), II), III), IV) and V) together represent at least 95% by weight of the mixture of polyols, said polyhydric The mixture of alcohols also contains 0 to 5% by weight of other nonionic polyols having a molecular weight below 1000 and containing two or more hydroxyl groups. 3. Aqueous dispersion according to claim 2, characterized in that the components I), II), III), IV) and V) together account for 100% of the mixture (P) of polyols of the prepolymer weight%. 4. The aqueous dispersion according to claim 3, wherein the components I), II), III) and IV) together represent 100% by weight of the mixture of polyols. 5. Aqueous dispersion according to claim 1, characterized in that the polyol mixture (P) comprises 5 to 75% by weight of one or more hydrophobic polyols I) obtained by making the alcohol ROH Reaction to obtain, wherein R is a branched or linear saturated C ₆ -C ₂₂ alkyl chain, and R ₁ is group (i): 6. The aqueous dispersion according to claim 5, wherein _R2 , _R3 are Me. 7. The aqueous dispersion according to claim 1, characterized in that the neutralized polyisocyanate is prepared from one or more aliphatic or cycloaliphatic polyisocyanates having an average NCO functionality between 2.0 and 2.3 Anionic prepolymers. 8. The aqueous dispersion according to claim 1, wherein component II) of the mixture of polyols (P) is dimethylolpropionic acid, dimethylolbutyric acid or mixtures thereof; Component III) of the mixture of polyols (P) is poly(hexamethylene carbonate) glycol with a number average molecular weight of 800 to 2000; component IV) of the mixture of polyols (P) is selected from from polyesters based on adipic and/or phthalic acid with 1,6-hexanediol, ethylene glycol, diethylene glycol, neopentyl glycol, 1,4-butanediol and mixtures thereof, and several The average molecular weight is 800 to 3000. 9. The aqueous dispersion as claimed in any one of the preceding claims, characterized in that the mixture of polyols (P) is free of units derived from poly(oxyethylene)glycols. 10. Use of the aqueous dispersion as claimed in any one of claims 1 to 9 for the preparation of coating compositions.