MXPA01006123A - Aqueous dispersion of a polyurethane containing blocked reactive sites - Google Patents

Abstract

The invention relates to an aqueous dispersion of a crosslinkable polyurethane obtained by chain extension of a polyurethane prepolymer with a compound containing hydrazone functions having general formula (1), wherein Q<1>and Q<2>is a hydrazone functional group of formula (2), H or R<1>, R and R<1>in formula (1) is an organic group which has no reactivity towards the hydrazone function, R<2>and R<3>in formula (2) is an organic group which has no reactivity towards the hydrazone function or is H, x has a value from 1 to 10, and is preferably from 1 to 4 with the proviso that at least one of the groups Q<1>or Q<2>is of formula (2). The invention relates also to a process for a preparation of an aqueous dispersion of a crosslinkable polyurethane containing hydrazone functions, and to the application of the aqueous dispersion of a crosslinkable polyurethane together with a polyisocyanate, a polyketone - or a polyepoxide - functional material onto a substrate.

Description

AQUEOUS DISPERSION OF A POLYURETHANE CONTAINING BLOCKED REAGENT SITES The present invention relates to an aqueous dispersion of a crosslinkable polyurethane obtained by chain extension of a polyurethane prepolymer with a hydrazone-containing compound having the general formula: (1) R - (- N Q1 x wherein Q1 and Q2 is a functional group hydrazone of the formula (2), H or R1 (2) O I I - CH2 - CH2 - C - NH - N = CR2 R3 R and R1 in the formula (1) is an organic group that has no reactivity towards the hydrazone function, R2 and R3 is an organic group that has no reactivity towards the hydrazone functions, provided that at least one of the groups Q1 or Ql2 in the formula (1) is of the formula (2). It relates to a process for the preparation of said polyurethane dispersion, to a process for the preparation of a crosslinked film or a coated substrate and to the crosslinked film or coated substrate obtained.

INTRODUCTION It is well known that the performance and properties of coatings and films of aqueous polyurethane dispersions can be increased with the incorporation of crosslinkable groups in the main chain of the polymer and the crosslinking of said oligomers with relevant crosslinkers. For the application on thermosensitive substrates, such as hides and artificial leathers, the low temperature baking types are of special interest. An overview of crosslinking of the low temperature baking type for polyurethane dispersions is presented in EP-507407. This application further discloses an improved crosslinking system wherein carboxylic acid functional polymers are crosslinked by functional carbodiimide polymers or oligomers containing additional reactive functional groups, which contribute to crosslinking. An alternative crosslinking system is disclosed in US4598121, which comprises incorporating a functional chain extender hydrazide into a polyurethane and crosslinking the polyurethane with formaldehyde. Since the use of formaldehyde-type crosslinkers is expected to cause environmental problems, other types of compounds that are reactive towards the hydrazide function became of interest as crosslinkers, such as functional isocyanate, functional ketone functional or exoxy functional compounds. Research has shown that, due to the reactivity of these groups towards the hydrazide function, especially of the isocyanate functional compounds, the pot life of the polyurethane functional hydrazide together with the crosslinkers was limited. In addition, polyurethane dispersions containing hydrazide functions turned yellow in stability tests. We have now developed a new aqueous dispersion of a crosslinkable polyurethane wherein a product containing blocked reactive sites is incorporated into the polymer chain. The obtained aqueous polyurethane dispersion combined with a relevant crosslinker is suitable for the preparation of a crosslinked film or a crosslinked coating on a substrate. SUMMARY OF THE INVENTION The present invention provides an aqueous dispersion of a crosslinkable polyurethane obtained by chain extension and / or chain termination of an isocyanate-functional polyurethane prepolymer with a hydrazone-containing compound having the general formula: (1) R - (- N - Q1) x I where Q1 and Q2 is a hydrazone functional group of the formula (2), H, or R1 (2) 0 11 CH2 - CH2 - C - NH - N = CR2 R2 R and R1 in formula (1) is an organic group that has no reactivity to the hydrazone function, R2 and R3 in the formula (2) is an organic group that does not have reactividada towards the hydrazone function, x has a value of 1 to 10 , and is preferably from 1 to 4 provided that at least one of the groups Q1 or Q2 is of the formula (2). In an aqueous solution at a pH greater than 7 the hydrazone function is stable, but at a lower pH, or during drying at elevated temperatures the hydrazone function in the polyurethane reacts with water under the formation of a ketone and a hydrazide function of the formula (3) 0 II-CH2-CH2-C-NH-NH2 The resulting hydrazide-containing product can be cross-linked and / or chain-extended by a polyisocyanate, a polyketone or a polyepoxy functional material.As the product of the formula (1) is used as chain extender and / or chain terminator group for isocyanate functional polyurethane prepolymers at least one of the Q groups must be a hydrogen. The invention therefore includes the aqueous dispersion of a polyurethane containing as a chain extender or chain terminating group a hydrazone functional compound of the formula (1), wherein at least one of the groups Q1 or Q2 is H. it appears that under aqueous conditions only the NH or NH2 function of the product of formula (1) reacts with an isocyanate functional material under formation of a urea function, while the hydrazone function remains intact. In the presence of only one reactive hydrogen amine in formula (1), the functional isocyanate material is only covered. More preferably the product of the formula (1) contains two or more reactive amine hydrogen functions and can chain and / or crosslink a polyisocyanate functional material to obtain an aqueous dispersion of a polyurethane containing hydrazone functions. Accordingly, the present invention relates to an aqueous dispersion of a polyurethane which preferably contains as a chain extender a hydrazone functional product, which contains at least two amino functional groups of hydrogen.

Generally the product of the general formula () which is used as a chain extender in the aqueous polyurethane dispersion is prepared by reacting a functional hydrazide compound of the formula (4) R N-P1) wherein P1 and P2 is a hydrazide functional group of the formula (3) or is H, or is R1, R and R1, and x are as in the formula (1) provided that at least one of the groups P1 or P2 has the formula (3) with an equimolar amount of a functional compound ketone of formula R2 R3C = 0 Where R2 and R3 are as in the formula (2). The hydrazide functional compound is prepared from a polyamine by a method such as described in US 4598121.

The polyamine has the structure according to formula (4) wherein the functional group hydrazide P was originally hydrogen. According to this method the polyamine is reacted first with an alkyl acrylate after which the functional compound aminopropionate of alkyl is reacted with hydrazine.

The functional compound hydrazide is an alkylamine functional hydrazide, a cycloalkylamine, an arylamine, an alkylpolyamine, a cycloalkylpolyamine, an arylpolyamine, an alkylamino-cycloalkylamine, a polyalkoxyamine, a polyalkoxypolyamine, an aminoalkylamine, an amino-poly (alkyl-amine). The preferred functional hydrazide compound can be selected from a 5-amino-1,3,3-trimethylcyclohexanemethylamine functional hydrazide, methylpentanediamine, diaminohexane, 3,3'-dimethyl-4,4'-diaminodiylhexylmethane, 4,4'-diamino. -dicyclohexylmethane, a polyoxypropylenediamine with a molecular weight of about 230, 400, or 2000, a polyoxyethylenediamine with a molecular weight of about 600, 900, 2000, 4000 or 6000, a polyalkoxyethyleneamine with a molecular weight of about 600, 1000, 2000, a polyoxypropylenetriamine with a molecular weight of about 470, a long-chain alkylamine with an average molecular weight of 140 to 550, a (long chain alkyl) -aminopropylamine with an average molecular weight of 280 to 360. The ketone which is used for the blocking of the hydrazide function in the preparation of the product of the formula (1) is preferably acetone or butyl ketone. The product of formula (1) is a polyamine that is modified by replacing an N-H function by an N-hydrazone function. The amount of hydrazone functions can be varied from 0.1-1 equimolar amount with respect to the NH-functions in the polyamine. Furthermore, the invention relates to the process for the preparation of the aqueous dispersion of a crosslinkable polyurethane containing hydrazone functions comprising: "dispersion of an isocyanate functional polyurethane prepolymer in water, optionally in the presence of neutralizing agents and / or surfactants "chain extension of the prepolymer with a hydrazone functional product containing at least two amino functional groups of hydrogen, optionally in the presence of a surfactant, during or after dispersion in water. Isocyanate functional polyurethane prepolymer can be anionic, cationic or non-ionic and is prepared in a conventional manner EP 308115 presents an overview of suitable polyols and polyisocyanates for such polyurethane prepolymers The polyurethane dispersion can become self-crosslinking when The polyurethane contains hydrazone and ketone functions The invention therefore provides a process for the preparation of a self-crosslinkable aqueous dispersion of a functional ketone and hydrazone polyurethane using an isocyanate functional prepolymer containing ketone functions in the described method. these types of prepolymer s is described in US 4983662. Aqueous crosslinkable polyurethane dispersions containing hydrazone functions obtained by the process of the invention can be used as coating compositions in conjunction with a crosslinking material. Accordingly the invention provides a process for the preparation of a crosslinked film or a crosslinked coating on a substrate comprising the steps of: "mixing the polyurethane dispersion entrusted with the hydrazone functional groups of the invention with a functional polyisocyanate, polyketone or polyepoxy functional material. or aqueous dispersion thereof wherein the ratio of functional groups is hydrazone: isocyanate or ketone is from 0.5 to 1.5 and wherein the ratio of hydrazone: epoxy is from 0.3 to 1.2, "apply said mixture On a substrate "evaporation of water / solvents When an aqueous dispersion of a polyurethane containing both ketone and hydrazone functions is used, a self-crosslinking system is obtained, therefore the invention includes the preparation of a crosslinked film or a crosslinked coating. on a substrate comprising: "applying the dispersion of functional polyurethane hydrazone and ketone on a substrate and ulando the same by "evaporation of water and / or solvents Another option is that the products of the formula (1) are not incorporated in a polyurethane structure, but are used as functional products of pure hydrazone. Coating in conjunction with a crosslinking material Accordingly, the invention provides for the preparation of a crosslinked film or a crosslinked coating on a substrate comprising: "preparing a mixture of a hydrazone functional material according to formula (1) where Q is not H with a poly-epoxy or polyketone functional material, or with an aqueous dispersion of a polyepoxy or polyketone functional material, and preferably with an aqueous dispersion of a polyisocyanate functional material in which the functional group ratio is hydrazone: isocyanate or ketone is from 0.5 to 1.5 and wherein the ratio of hydrazone: epoxy is from 0.3 to 1.2, "applying the mixture on a substrate" evaporation of water and / or solvents. The functional products of hydrazone or polyurethane dispersions offer, together with a crosslinker, a coating material having comparable performance and properties and sometimes even better than those described in EP507407. Especially crosslinking with a functional polyisocyanate material is very efficient. Hydrazone functional polyurethane dispersions have a better resistance to yellowing than those of the functional hydrazide polyurethanes described in US4598121. In combination with polyisocyanates as a crosslinker, the dispersions of the functional polyurethanes hydrazone have a longer pot life than the dispersions of the functional polyurethanes hydrazide. The reason is that the protection of the hydrazide function by acetone is stable in water at pH > 7 and the isocyanate function can only react with the hydrazide function after the acetone has been released during the formation of the film. In addition, crosslinking with polyisocyanate-, polyketone-, or polyepoxy functional materials is a method that presents fewer environmental problems than the crosslinking of functional compounds hydrazide with formaldehyde, as described in US4598121. Many additional ingredients can also be found present in the application and crosslinking stage, for example fillers, dyes, pigments, silicones, agents which have the objective of achieving a matt effect, flow agents, and the like. These additional ingredients can be used when there is not or there is little interference with the crosslinking function, or, if there is interference, this contributes to an optimal application result. The functional products hydrazone and aqueous dispersions of polyurethanes in combination with the functional material polyisocyanate, polyketone or polyepoxy can be used in adhesives, sealants, printing ink and coatings. These can be applied to any substrate, including leather or artificial leather, metals, wood, glass, plastics, paper, cardboard, textile, non-wovens, fabrics, foams and the like by conventional methods, including spraying, flow coating, coating by roller, with brush, dip, dispersion and the like. Various aspects and embodiments of the present invention are illustrated through the following examples. These examples are merely illustrative and are not intended to limit the invention as claimed below. Examples Example 1-6 Preparation of products containing hydrazone functional groups of the formula (1). Functional hydrazide amines were prepared by the method described in US-4598121 by reacting 1 mole of a mono- or polyamine with ethylacrylate, followed by the reaction of the obtained ethyl aminopropionate functional product with a stoichiometric amount of hydrazine hydrate. A stoichiometric amount of acetone was added to the functional hydrazide compound at room temperature during stirring. An increase in temperature from about 20 to 50 degrees C was recorded due to the exothermic reaction. The reaction mixture was stirred for 30 min and cooled. The ratio of amine or polyamine to the ethylacrylate and thus to the hydrazone functions and hydrazide functions obtained is presented in Table I. The amine concentration of the obtained hydrazone functional compounds was verified by titration with 1M solution of stearyl isocyanate in toluene and methoxy propylacetate. The hydrazone function remained intact during the titration for at least 5 min at the turning point. The final point was detected with the appearance of an isocyanate signal at 2240 cm "1 by IR-spectroscopy The amine concentration is presented in Table I. Table I Hydrazone functional products of the formula (1) a: Jeffamine T- 403 is a polyoxyethylene triamine containing 6, 4 meq amino / g functions obtained from Huntsman.1 Example 7-12 Preparation of polyether functional hydrazone dispersions based on polyether. Under a nitrogen atmosphere 426 g (0.213 mol) of a polypropylene diol with a molecular weight of 2000, 340 g (0.340 mol) of a polypropylene diol with a molecular weight of 1000 and 46.9 g (0.350 mol) of Dimethylolpropanoic acid was heated to 70 degrees C during stirring. 444 g (2 mol) of 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (hereinafter referred to as IPDI) was added and the mixture was heated to 100 degrees C and stirred for 2 hours to form a polyurethane prepolymer. After 1 hour of reaction time, 0.1 g of tinoctoate was added as a catalyst. The reaction was cooled and the amount of remaining NCO appeared to be 5.20%. 100 g of the polyurethane prepolymer was mixed with 3.22 g of triethylamine and the mixture was dispersed in 120 g of water during intensive agitation. The products of Examples 1, 2, 4, and 1 + 5 or 1 + 6 were diluted 1: 1 with water in an amount as mentioned in Table II. The mixtures were added to the dispersed prepolymer in the space of 5 min and the dispersion was stirred for 30 min. The NCO signals in the infrared spectra to 2240 cm-1 disappeared. The products were adjusted to a quantity of solid of 35% with water. In Example 7 hydrazine was used in a comparative example to obtain a polyurethane dispersion without hydrazone functions. The pH and hydrazone functionalities of the products are presented in Table II. Table II Chain extension and / or chain termination of a polyurethane prepolymer dispersion a) hydrazine was used in a comparative example to obtain a polyurethane dispersion are hydrazone functions. Example 13 Preparation of a functional polyurethane ketone. Under a nitrogen atmosphere 182.33 g (0.13 mol) of a polyester diol with an OH number of 80 and containing ketone functions (can be obtained from NeoResins as PEC-205), 12.06 g (0.09 g) mol) of dimethylolpropanoic acid and 94.4 g of N-methylpyrrolidone was heated to 70 degrees C during stirring. 88.8 g (0.4 mol) of IPDI were added and the mixture was heated to 100 degrees C and stirred for 2 hours to form a polyurethane prepolymer. After 1 hour of reaction time, 0.04 g of tinoctoate was added as a catalyst. The reaction was cooled and the amount of remaining NCO appeared to be 2.87%. 110 g of the polyurethane prepolymer was mixed with 2.75 g of triethylamine and the mixture was dispersed in 120 g of water during intensive agitation. 1.79 g of hydrazine hydrate in 4.2. g of water was added in the space of 5 min and the dispersion was stirred for 30 min. The NCO-signal in IR-spectrum at 2240 cm-1 disappeared. The product was characterized by a solid amount of 35%, a viscosity of 300 cps, a pH of 8.0, opaque appearance. The results of assays of the product as the functional crosslinking agent ketone are presented in Example 14. Example 14 This example relates to the evaluation of the crosslinked and non-crosslinked films of the products of example 7 and example 8. Films with a thickness of 200 and 600 Dm were prepared and dried at room temperature of: "the products of example 7 and example 8," of the product combination of example 8 and the example 8 + 3 with an equivalent amount of XR-5553, which is an NCO crosslinker that can be obtained from Stahl Holland, "of the product combination of Example 8 and an equivalent amount of Eurepox 756/67 W, which is a Witco epoxy functional resin," of the product combination of Example 8 and an equivalent amount of the functional ketone product of the Example 13. The mechanical properties, percentages of expansion in ethanol and yellow staining of the films were tested. The results obtained are established in the Table III. These results show that the crosslinking of the polyurethane functional hydrazone with the isocyanate functional crosslinker is more efficient as indicated by: "a higher film tension is obtained with respect to the other crosslinking systems," a lower elongation is obtained with respect to the other crosslinking systems, "a low uptake of ethanol is obtained," the films do not turn yellow * the films can be re-coated The addition of additional hydrazone functions by adding 5% of the product of example 3 and the corresponding amount of the crosslinker of isocyanate results in a film with a higher crosslink density which is indicated by a lower elongation. Table III Crosslinking of functional hydrazone polyurethanes with various crosslinkers Notes regarding table III a) Mpa is megapascal (106 Nm-2). The mechanical properties and the elongation were measured with films that were stretched to a thickness of 600 Om on an MTS Synergie 200 device. The values at 10M, 25M, 50M, 100M, 200M and 300M present tensile strengths of the films stretching the same to 10, 25, 50, 100, 200 and 300% respectively. b) elong. is the maximum elongation before the breaking of the film measured on an MTS Synergie 200 device. c) incr. prisoner is the proportional weight increase of a film stretched at 200 Dm and submerged in water for 20 min at 20 degrees C. d) yellow, is the yellow coloration of a film when stored for 1 week at 80 degrees C. Example 15 Preparation of a polyurethane functional ketone and hydrazone dispersion based on polycarbonate. Under a nitrogen atmosphere 302 g (0.151 mol) of a polycarbonate diol with a molecular weight of 2000 obtainable from Stahl USA as PC-1122, 121.13 g (0.0864 mol) of a polyester diol with an OH number of 80 and containing ketone functions (can be obtained from NeoResins as PEC-205), 26.00 g (0.194 mol) of dimethylolpropanoic acid and 261 g of N-methyl-pyrollidone were heated at 70 degrees C during agitation. 159.84 g (0.72 mol) of IPDI were added and the mixture was heated to 95 degrees C and stirred for 2 hours to form a polyurethane prepolymer. After 1 hour of reaction time, 0.04 g of tinoctoate was added as a catalyst. The reaction was cooled and the amount of remaining NCO appeared to be 2.82%. 200 g of the polyurethane prepolymer was mixed with 3.99 g of triethylamine and the mixture was slowly added to 304.16 g of water containing 22.16 g of product of example 1, 1.02 g of triethylamine and 6 g of dioctyl sulfosuccinate of sodium during agitation. The dispersion was stirred for 30 min. The signal-NCO in the IP-spectrum at 2240 cm "1 disappeared, the product was characterized by a solid amount of 30%, a viscosity of 300 cps, a pH of 8.8, an opaque appearance, a hydrazone functionality of 0.106 meq / g and a ketone functionality of 0.099 meq / g.

Claims (13)

RE IVINDICATIONS 1. Aqueous dispersion of a polyurethane containing blocked reactive sites with an aqueous dispersion of a crosslinkable polyurethane characterized in that it is obtained by chain extension of a polyurethane prepolymer with a hydrazone-containing compound having the general formula: (1) R - (- N - Q1) x Q2 where Q1 and Q2 is a hydrazone functional group of the formula (2), H or R1 (2: O - CH2 - CH2 - C - NH - N = CR) R
1. R and R1 in the formula (1) is an organic group that has no reactivity towards the hydrazone function. R2 and R3 in the formula (2) is an organic group that has no reactivity towards the hydrazone function. X has a value from 1 to 10, and is preferably from 1 to 4 provided that at least one of the groups Q1 or Q2 has the formula (2).
2. 2. Aqueous dispersion of a polyurethane of the claim containing as a chain extender or chain terminating group a hydrazone functional compound of the formula (1), characterized in that at least one of the groups Q1 or Q2 is H. 3. Aqueous dispersion of a polyurethane of claim 1 or 2 characterized in that said hydrazone functional product contains at least two hydrogen functional amino groups. 4. The aqueous polyurethane dispersion of claims 1-3, characterized in that the chain extender or chain termination group is prepared by reacting a hydrazide functional compound of the formula (4) R - (- N - P1 x wherein P1 and P2 is a hydrazide functional group of the formula (3), H,
3. R1 (3) O - CH2 CH2 - C NH - NH2
4. R and R1 and x are as in formula (1) provided that at least one of the groups R1 or P2 has the formula (3) with an equimolar amount of a functional ketone compound of the formula R2 R3C = 0 wherein R2 and R3 are as in formula (1) and (2) of claim 1.
5. 5. Aqueous dispersion of a polyurethane of claims 1-4, characterized in that the hydrazide functional compound of claim (4) is a functional alkylamine hydrazide, a cycloalkylamine, an arylamine, an alkylpolyamine, a cycloalkylpolyamine, an arylpolyamine, an alkylaminocycloalkyl amine, a plialcoxyamine, a polyalcoypylamine, an aminoalkylamine, an alkylamine, an amino-poly (alkylamine).
6. 6. Aqueous dispersion of a polyurethane of claims 1-5, characterized in that the hydrazide functional compound of claims 4 and 5 is preferably a 5-amino-1,3,3-trimethylcyclohexanemethylamine functional hydrazide, methylpentanediamine, diaminohexane, 3, 3 '-dimethyl-4,4'-diaminodicylohexy-methane, 4,4'-diaminodicyclohexylmethane, a polyoxypropylenediamine with a molecular weight of about 230, 400, or 2000, a polyoxyethylenediamine with a molecular weight of about 600, 900, 2000, 4000 or 6000, a polyalkoxyethyleneamine with a molecular weight of about 600, 1000, 2000, a polyoxypropylenetriamine with a molecular weight of about 470, a long-chain alkylamine with an average molecular weight of 140 to 550, a (long-chain alkyl) aminopropylamine with an average molecular weight of 280 to 360.
7. 7. Aqueous dispersion of a polyurethane of claims 1-6, characterized in that the ketone of claim 4 is acet. Ona or butyl ketone.
8. 8. A process for the preparation of an aqueous dispersion of a crosslinkable polyurethane containing hydrazone functions of claims 1-7, characterized in that it comprises: dispersing an isocyanate functional polyurethane prepolymer in water, optionally in the presence of neutralizing agents and / or surfactants "chain extension of the prepolymer with a hydrazone functional product containing at least two hydrogen functional amino groups according to claim 1-7, optionally in the presence of a surfactant, during or after dispersion in water.
9. 9. The process according to claim 8, characterized in that a hydrazone functional product according to claim 2 is used as a chain extender and / or concealing agent.
10. 10. The process for the preparation of a self-crosslinkable aqueous dispersion of a functional polyurethane ketone and hydrazone using an isocyanate functional prepolymer containing ketone functions in the method of claim 8 or 9.
11. 11. A process for the preparation of a crosslinked film or a crosslinked coating on a substrate, characterized in that it comprises: "mixing the polyurethane dispersion according to claims 1-7 with a dispersion or functional material of polyisocyanate, polyketone or polyepoxy characterized in that the functional group ratio is hydrazone: isocyanate or ketone is from 0.5 to 1.5 and wherein the ratio of hydrazone: epoxy is from 0.3 to 1.2, "applying said mixture on a substrate" evaporation of water and / or solvents. process for the preparation of a crosslinked film or a crosslinked coating on a substrate by crosslinking the dispersion of polyurethane functional ketone and hydrazone according to claim 10, characterized in that it comprises: "applying the dispersion on a substrate and crosslinking it by evaporation of water and / or solvents. 13. A process for the preparation of a crosslinked film or a crosslinked coating on a substrate characterized in that it comprises: "preparation of a mixture of a hydrazone functional material according to claim 1 characterized in that Q is not H and claims 4-7 with a functional material of poly-epoxy or polyketone, with an aqueous dispersion of a functional material of poly-epoxy or polyketone, and, preferably with a functional material of dispersible polyisocyanate in water or an aqueous dispersion of a functional material of polyisocyanate wherein The ratio of functional groups is hydrazone: isocyanate or ketone is from 0.5 to 1.5 and wherein the ratio of hydrazone: epoxy is from 0.3 to 1.2, "applying said mixture on a substrate and" evaporating water and / or solvents. SUMMARY The invention relates to an aqueous dispersion of a crosslinkable polyurethane which is obtained by chain extension of a polyurethane prepolymer with a hydrazone-containing compound having the general formula: (1) R - (- N - Q1) x Q2 wherein Q1 and Q2 is a hydrazone functional group of the formula (2), H or R1 (2) 0 -CH2-CH2-C-NH-N = CR .2 R, - > 3 ~ R and R1 in the formula (1) is an organic group that has no reactivity towards the hydrazone function, R2 and R3 in the formula (2) is an organic group that has no reactivity towards the hydrazone function or is H, X it has a value from 1 to 10, and is preferably from 1 to 4 provided that at least one of the groups Q 1 or Q "is of the formula (2). The invention also relates to a process for a preparation of an aqueous dispersion of a crosslinkable polyurethane containing hydrazone functions, and to the application of the aqueous dispersion of a crosslinkable polyurethane together with a functional material of polyisocyanate, polyketone or polyepoxide on a substrate.