Waterborne polyurethane coating composition

Abstract

The present invention relates to a waterborne polyurethane dispersion, wherein the dispersion comprises (a) a polyurethane (I) which comprises -NH-CO-HN-NH-CO-(R)n-CO-NH-NH-CO-NH- linkages, and -NH-CO-HN-NH-CO-(R)n-CO-NH-NH2 terminal groups, and (b) one or more dihydrazides B according to formula H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and in case n is 1, R is an aliphatic hydrocarbon group having from 1to 18 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, wherein the polyurethane (I) is obtained by at least:- providing an isocyanate group-functional prepolymer A composition comprising an isocyanate group-functional prepolymer A, wherein the isocyanate group-functional prepolymer A is obtained by reacting at least one or more polyisocyanates with aliphatic reactivity and one or more polyols, - adding one or more chain extending compounds having isocyanate-reactive groups to the isocyanate group-functional prepolymer A composition, and - reacting at least the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups, wherein the one or more chain extending compounds comprise, consist essentially of, or consist of the one or more dihydrazides B according to formula (X); wherein the reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the substantial absence of ketone- and / or aldehyde-functional organic solvents; and wherein the dispersion comprises the one or more dihydrazide B with formula (X) in an amount of at least 1000 ppm, based on the solids content of the dispersion, wherein the amount of the dihydrazide B with formula (X) in the dispersion is determined with the method as specified in the description.

Description

WATERBORNE POLYURETHANE COATING COMPOSITIONTechnical Field

[0001] The present invention relates to a waterborne polyurethane dispersion and its preparation method. The present invention also relates to an ink, coating or primer composition comprising the waterborne polyurethane dispersion. The present invention also relates to an ink, coating or primer layer, respectively, obtained by drying the waterborne polyurethane ink, coating or primer composition according to the present invention. Further, the present invention relates to objects comprising an ink, coating and / or primer layer according to the present invention.Background

[0002] It is well recognized that adhesion to plastic substrates and in particular hydrophobic plastic substrates, such as polyolefin substrates and in particularly polypropylene substrates, is generally hard to achieve. The adhesion of the coating to the plastic substrate is mainly determined by surface tension characteristics of the coating and the substrate and interdiffusion of the coating into the substrate. Surface tension will directly influence a coating's ability to wet out, to penetrate, and to adhere to the surface. It is generally seen that the lower the surface tension of the substrate, the more problematic it is to get good adhesion of the coating on the substrate. The surface tension of the coating ideally should be lower than the surface tension of the substrate to enable wetting of the coating on the surface of the substrate. Efficient wetting will maximize the adhesion. Surface roughness may also be an important parameter in certain cases as "mechanical interlocking" is another way to improve adhesion. Interdiffusion is the main adhesion mechanism for amorphous plastics, especially in the case of solvent based coating systems. The solvent is used to diffuse the polymer of the coating into the plastic substrate to provide for molecular interlocking. Ideally, this solvent should be selected from those that are good solvents for the polymers of the coating composition, and for the polymer constituting that of the plastic substrate. From an environmental point of view there is however an increasing need to reduce the amount of organic solvents in such coating compositions. In this respect waterborne binders are clearly preferred over conventional solventborne binders. The use of waterborne binders in coating compositions for application to hydrophobic plastic substrates may however give issues regarding wetting and or polymer interdiffusion. A common method to enhance the coating adhesion to hydrophobic plastics with a relatively low surface tension like polyolefins is toemploy surface pretreating processes. Surface treatments include chemical and physical methods such as chemical etching and corona discharge, and typically result in the formation of polar groups on the surface such as pendant hydroxyl, chloro, amino and carboxyl groups. The introduction of polar groups on the plastic substrate surface can provide improved wetting and potential chemical interaction with the applied coating composition, which can result in improved adhesion.

[0003] EP 0 646 609 Bl discloses aqueous hydrazine-terminated polyurethane dispersions.

[0004] However, as will be demonstrated, the adhesion of such coatings to in particular hydrophobic substrates, more in particular polypropylene substrates is inferior.

[0005] Consequently, there is a need for waterborne polyurethane dispersions which can be applied to provide layers with improved adhesion to in particular hydrophobic substrates, more in particular polypropylene substrates.Brief Summary

[0006] The present invention relates to a waterborne polyurethane dispersion that comprises:(a) a polyurethane (I) which comprises -NH-CO-HN-NH-CO-(R)n-CO-NH-NH-CO-NH- linkages and -NH-CO-HN-NH-CO-(R)n-CO-NH-NH2 terminal groups, and(b) one or more dihydrazides B according to formula (X): H2N-NH-CO-(R)n-CO-NH-NH^ (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 18 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, wherein the amount of dihydrazide B with formula (X) in the dispersion is at least 1000 ppm, based on the solids content of the dispersion, wherein the amount of the dihydrazide B with formula (X) in the dispersion is determined with the method as specified further herein.

[0007] The present invention also relates to a process for preparing such waterborne polyurethane dispersions.

[0008] The present invention also relates to an ink or coating or primer composition comprising such a waterborne polyurethane dispersion.

[0009] The present invention also relates to an ink or a coating or a primer layer obtained from such an ink or coating or primer composition.

[0010] The present invention further relates to an article comprising such an ink, coating and / or primer layer.Detailed Description[Oi l] For all upper and / or lower boundaries of any range given herein, the boundary value is included in the range given, unless specifically indicated otherwise. Thus, when saying from x to y, means including x and y and also all intermediate values.

[0012] The current invention is directed to a waterborne polyurethane dispersion, wherein the dispersion comprises:(a) a polyurethane (I) which comprises:-NH-CO-HN-NH-CO-(R)n-CO-NH-NH-CO-NH- linkages, and -NH-CO-HN-NH-CO-(R)n-CO-NH-NH2terminal groups, and(b) one or more dihydrazides B according to formula H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, wherein in case n is 0, the formula (X) simplifies to H2N-NH-CO-CO-NH-NH2, and in case n is 1, R is an aliphatic hydrocarbon group having from 1 to 18 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, wherein the polyurethane (I) is obtained by at least:(1) providing an isocyanate group-functional prepolymer A composition comprising an isocyanate group-functional prepolymer A, wherein the isocyanate group-functional prepolymer A is obtained by reacting at least one or more polyisocyanates with aliphatic reactivity and one or more polyols,(2) adding one or more chain extending compounds having isocyanate-reactive groups to the isocyanate group-functional prepolymer A composition, and(3) reacting at least the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups, wherein the one or more chain extending compounds comprise, consist essentially of, or consist of one or more dihydrazides B according to formula (X); wherein the reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the substantial absence of ketone- and / or aldehyde-functional organic solvents; and wherein the dispersion comprises the one or more dihydrazide B with formula (X)in an amount of at least 1000 ppm, based on the solids content of the dispersion, wherein the amount of the dihydrazide B with formula (X) in the dispersion is determined with the method as specified further herein.

[0013] It has surprisingly been found that the waterborne polyurethane dispersions of the invention are able to provide layers with improved adhesion to in particular hydrophobic substrates, more in particular polypropylene substrates.

[0014] The waterborne dispersion according to the present invention can be used as cohesive component (binder) in inks, coatings and / or primers. In a preferred embodiment of the invention, the waterborne dispersion according to the current invention is used as a primer composition.

[0015] The present invention is therefore also directed to a primer composition comprising the waterborne dispersion according to the present invention.

[0016] The present invention is also directed to a process for preparing a waterborne polyurethane dispersion comprising:(a) a polyurethane (I) which comprises -NH-CO-HN-NH-CO-(R)n-CO-NH-NH-CO-NH- linkages and -NH-CO-HN-NH-CO-(R)n-CO-NH-NH2 terminal groups, and(b) one or more dihydrazides B according to formula (X): H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when is 1, R is an aliphatic hydrocarbon group having from 1 to 18 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, wherein the process comprises:(1) providing an isocyanate group-functional prepolymer A composition comprising an isocyanate group-functional prepolymer A, wherein the isocyanate group-functional prepolymer A is obtained by reacting at least one or more polyisocyanates with aliphatic reactivity and one or more polyols,(2) adding one or more chain extending compounds having isocyanate-reactive groups to the isocyanate group-functional prepolymer A composition, and(3) reacting at least the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups, wherein the one or more chain extending compounds comprise, consist essentially of, or consist of one or more dihydrazides B according to formula (X); wherein the one or more dihydrazide B with formula (X) are added to the isocyanate group- functional prepolymer A composition in such an amount that the one or more dihydrazides B with formula (X) are present in the dispersion in an amount of at least 1000 ppm, based on the solids content of the dispersion, wherein the amount of the dihydrazide B with formula (X) in the dispersion is determined with the method as specified further herein; andwherein the reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the substantial absence of ketone- and / or aldehyde-functional organic solvents.

[0017] The -NH-CO-HN-NH-CO-(R)n-CO-NH-NH-CO-NH- linkages and the-NH-CO-HN-NH-CO-(R)n-CO-NH-NH2 terminal groups are introduced into the polyurethane (I) by reacting an isocyanate group-functional prepolymer with one or more dihydrazide B according to formula H2N-NH-CO-(R)n-CO-NH-NH2 (X) (wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 18 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms), wherein an at least equimolar amount, preferably an excess molar amount, of hydrazide groups from the dihydrazide B is available for the reaction between the isocyanate group-functional prepolymer A with said one or more hydrazide B. The amount of the one or more dihydrazide B with formula (X), which is present in the dispersion as a result of the at least equimolar amount of hydrazide groups from the dihydrazide B that was available for the reaction between the isocyanate group-functional prepolymer A with said one or more hydrazide B, is at least 1000 ppm, based on the solids content of the dispersion, wherein the amount of H2N- NH-CO-(R)n-CO-NH-NH2 that is present in the dispersion is determined with the method as further specified herein. The amount of the one or more dihydrazide B according to formula H2N-NH-CO-(R)n-CO-NH-NH2 that is present in the dispersion is, based on the solids content of the dispersion, preferably at least 1100 ppm, or at least 1200 ppm, or at least 1300 ppm, or at least 1400 ppm, or at least 1500 ppm, or at least 1600 ppm, or at least 1700 ppm, or at least 1800 ppm, or at least 1900 ppm, or at least 2000 ppm, or at least 2100 ppm, or at least 2200 ppm, or at least 2300 ppm, or at least 2400 ppm, or at least 2500 ppm, or at least 2600 ppm, or at least 2700 ppm, or at least 2800 ppm, or at least 2900 ppm, or at least 3000 ppm, or at least 3100 ppm, or at least 3200 ppm, or at least 3300 ppm, or at least 3400 ppm, or at least 3500 ppm, or at least 3600 ppm, or at least 3700 ppm, or at least 3800 ppm, or at least 3900 ppm, or at least 4000 ppm, or at least 4100 ppm, or at least 4200 ppm, or at least 4300 ppm, or at least 4400 ppm, or at least 4500 ppm, or at least 4600 ppm, or at least 4700 ppm, or at least 4800 ppm, or at least 4800 ppm, or at least 4900 ppm, or at least 5000 ppm. The amount of H2N-NH-CO-(R)n-CO-NH-NH2 in the dispersion, based on the solids content of the dispersion, is preferably at most 300000 ppm. The minimum amount of H2N-NH-CO- (R)n-CO-NH-NH2thatis present in the dispersion of the present invention is at least the amount of H2N-NH-CO-(R)n-CO-NH-NH2 that was available for the reaction between the isocyanate group-functional prepolymer A with said one or more hydrazide B but did not takepart in said reaction. Preferably, the minimum amount of H2N-NH-CO-(R)n-CO-NH-NH2 that is present in the dispersion of the present invention is the amount of H2N-NH-C0-(R)n-C0- NH-NH2that was available for the reaction between the isocyanate group-functional prepolymer A with said one or more hydrazide B but did not take part in said reaction.The maximum amount of H2N-NH-CO-(R)n-CO-NH-NH2thatis present in the dispersion of the present invention is the sum of at least the amount of H2N-NH-CO-(R)n-CO-NH-NH2 added to the isocyanate group-functional prepolymer A composition but that had not reacted with free isocyanate groups in the prepolymer A composition and the amount of H2N-NH- C0-(R)n-C0-NH-NH2 that is optionally introduced in the dispersion after having prepared the polyurethane (I). Preferably, the amount of H2N-NH-CO-(R)n-CO-NH-NH2thatis present in the dispersion of the present invention is the amount of H2N-NH-CO-(R)n-CO-NH-NH2 that was available for the reaction between the isocyanate group-functional prepolymer A with said one or more hydrazide B but did not take part in said reaction. The amount of H2N-NH- C0-(R)n-C0-NH-NH2 in the dispersion, based on the solids content of the dispersion, is more preferably at most 290000 ppm, even more preferably at most 280000 ppm, even more preferably at most 270000 ppm, even more preferably at most 260000 ppm, even more preferably at most 250000 ppm, even more preferably at most 240000 ppm, even more preferably at most 230000 ppm, even more preferably at most 220000 ppm, even more preferably at most 210000 ppm, even more preferably at most 200000 ppm, even more preferably at most 190000 ppm, even more preferably at most 180000 ppm, even more preferably at most 170000 ppm, even more preferably at most 160000 ppm, even more preferably at most 150000 ppm, even more preferably at most 140000 ppm, even more preferably at most 130000 ppm, even more preferably at most 120000 ppm, even more preferably at most 110000 ppm, even more preferably at most 100000 ppm, even more preferably at most 90000 ppm, even more preferably at most 80000 ppm, even more preferably at most 75000 ppm. The amount of the one or more dihydrazide B according to formula H2N-NH-CO-(R)n-CO-NH-NH2 that is present in the dispersion is determined with the method as further specified herein and is given based on the solids content of the dispersion.

[0018] The isocyanate group-functional prepolymer A is obtained by reacting at least one or more polyisocyanates with aliphatic reactivity and one or more polyols. Reacting at least (1) one or more polyisocyanates with aliphatic reactivity with (2) one or more polyols is carried out with a molar excess of polyisocyanates with aliphatic reactivity and thus results in a prepolymer A composition comprising isocyanate group-functional prepolymer A andunreacted polyisocyanate(s) with aliphatic reactivity. The isocyanate group-functional prepolymer A preferably comprises as building blocks: (a) at least one polyisocyanate with aliphatic reactivity, (b) at least one isocyanate-reactive polyol with ionic or potential ionic water-dispersing groups (which become ionic when deprotonated), and (c) at least one isocyanate-reactive polyol different from component (b). The isocyanate group-functional prepolymer A is preferably obtained with a melt process.

[0019] A polyisocyanate with aliphatic reactivity is a polyisocyanate in which all of the isocyanate groups are directly bonded to aliphatic or cycloaliphatic hydrocarbon groups, irrespective of whether aromatic hydrocarbon groups are also present. The polyisocyanate with aliphatic reactivity (component (a)) is preferably selected from the group consisting of ethylene diisocyanate, 1,5-pentane diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 2,2,4- trimethyl-l,6-hexamethylene diisocyanate, isophorone diisocyanate (IPDI), cyclohexane- 1,4- diisocyanate, di cyclohexylmethane diisocyanate such as 4,4’ -di cyclohexylmethane diisocyanate (4,4’-H12 MDI), m-xylylene diisocyanate, p-tetramethylxylene diisocyanate (p- TMXDI) (and its meta isomer m-TMXDI) and any combination of any two or more thereof. More preferably, the polyisocyanate with aliphatic reactivity (component (a)) is selected from the group consisting of 1,5-pentane diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 2,2,4-trimethyl-l,6-hexamethylene diisocyanate, isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate such as 4,4’-dicyclohexylmethane diisocyanate (4,4’- H12MDI) and any combination of any two or more thereof. Even more preferably, the polyisocyanate with aliphatic reactivity (component (a)) is selected from the group consisting of isophorone diisocyanate (IPDI), di cyclohexylmethane diisocyanate such as 4,4’- dicyclohexylmethane diisocyanate (4,4’-H12 MDI) and any combination of any two or more thereof. Even more preferably, the polyisocyanate with aliphatic reactivity (component (a)) is isophorone diisocyanate. Further examples are derivatives based on the afore mentioned diisocyanates having a uretdione, allophanate, biuret, iminooxadiazine dione and / or oxadiazine trione structure with two or more isocyanate groups. Mixtures of the polyisocyanates can be used as well. Preferably, the amount of polyisocyanates with more than two isocyanate groups is below 20 wt.%, more preferably below 15 wt.%, more preferably below 10 wt.%, and especially below 5 wt.% of the total amount of polyisocyanate with aliphatic reactivity. The amount of polyisocyanate with aliphatic reactivity, relative to the total weight of components used to prepare the isocyanate group-functional prepolymer A, is preferably from 10 to 50 wt.%, more preferably from 15 to 45 wt.%, even more preferably from 20 to 40 wt.%, even more preferably from 27 to 37 wt.%, most preferably from 30 to 35 wt.%.

[0020] The one or more polyols preferably comprise at least one isocyanatereactive polyol containing ionic and / or potential ionic water-dispersing groups (which become ionic when deprotonated) (component (b)), more preferably the one or more polyols comprise at least one isocyanate-reactive polyol containing potential ionic water-dispersing groups (which become ionic when deprotonated), even more preferably the one or more polyols comprise at least one isocyanate-reactive polyol containing potential anionic water-dispersing groups (which become anionic when deprotonated). The amount of the isocyanate-reactive polyol containing ionic and / or potential ionic water-dispersing groups (component (b)), relative to the total weight of components used to prepare the isocyanate group-functional prepolymer A, is preferably from 0.1 to 15 wt.%, more preferably from 1 to 10 wt.%, even more preferably from 2 to 8 wt.%, even more preferably from 3 to 6 wt.%. As used herein, potentially ionic water-dispersing group means a group, which under the conditions of the polyurethane preparation reaction, can be converted into an ionic group by salt formation (i.e., deprotonating the group by a base). Preferred ionic water-dispersing groups are anionic waterdispersing groups. Preferred anionic water-dispersing groups are carboxylic, phosphoric and / or sulphonic acid groups. Most preferred anionic water-dispersing groups are carboxylic acid groups. Examples of polyols with potentially anionic water-dispersing groups include carboxyl containing diols, for example dihydroxy alkanoic acids such as 2,2-dimethylolpropionic acid (DMPA; CAS number 4767-03-7), or 2,2-dimethylolbutanoic acid (DMBA; CAS number 10097-02-6). The anionic water-dispersing groups are preferably fully or partially in the form of a salt. Conversion to the salt form is optionally effected by neutralisation of the isocyanate group-functional prepolymer A with a base as neutralizing agent. The base used to neutralise the potentially anionic water-dispersing groups is preferably one or more tertiary amine. Preferred tertiary amines are trialkylamines. Most preferably, the neutralizing agent is triethylamine. Preferred isocyanate-reactive polyols containing potentially anionic waterdispersing groups are dihydroxy alkanoic acids, preferably 2,2-dimethylolpropionic acid and / or 2,2-dimethylolbutanoic acid. A very suitable isocyanate-reactive polyol containing potentially anionic water-dispersing groups is 2,2-dimethylolpropionic acid (DMPA). The neutralising agent is preferably used in such an amount that the molar ratio of the ionic and potentially ionic water dispersing groups to the neutralising groups of the neutralising agent are in the range of from 0.3 to 1.5, more preferably from 0.5 to 1.2, even more preferably from 0.6 to 1.05, even more preferably from 0.8 to 1.05, most preferably from 0.8 to 1.0.

[0021] The one or more polyols usually further includes at least one isocyanatereactive polyol different from component (b) (component (c)). Component (c) may be selectedfrom any of the chemical classes of polyols that can be used in polyurethane synthesis and is different than any other component (b). Component (c) preferably has an OH number of from 25 to 225 mg KOH / g solids. More preferably the OH number of component (c) is within the range of from 35 to 190 mg KOH / g solids, more preferably within the range of from 45 to 125 mg KOH / g solids. The OH number can be measured by titration of a known mass of alcohol according to ASTM D4274 and is expressed as mg KOH / g. Preferred polyols have a hydroxy functionality of 2. The amount of isocyanate-reactive polyol different from component (b), relative to the total weight of components used to prepare the isocyanate group-functional prepolymer A, is preferably from 35 to 89.9 wt.%, more preferably from 45 to 84 wt.%, even more preferably from 52 to 78 wt.%, even more preferably from 57 to 70 wt.%, most preferably from 59 to 67 wt.%. Preferred components (c) are polyols which may be selected from any of the chemical classes of polyols that can be used in polyurethane synthesis. In particular the polyol may be a polyester polyol, a polyesteramide polyol, a polyether polyol, a polythioether polyol, a polycarbonate polyol, a polyacetal polyol, a polyvinyl polyol and / or a polysiloxane polyol. The isocyanate-reactive polyol (c), which is different from component (b), is preferably selected from the group consisting of polyether polyols, polyester polyols, polysiloxane polyols, polycarbonate polyols, and any combination of any two or more thereof. More preferably, the isocyanate-reactive polyol (c) is selected from the group consisting of polyether polyols, polyester polyols, polycarbonate polyols, and any combination of any two or more thereof. Even more preferably, the isocyanate-reactive polyol (c) is selected from the group consisting of polyether polyols, polyester polyols, and any combination thereof. Preferred polyester polyols have a hydroxy functionality of 2 and are preferably obtained by reacting one or more diol with one or more dicarboxylic acids. Preferred polyether polyols are polypropylene glycol and polytetrahydrofuran. In a preferred embodiment, the isocyanatereactive polyol (c) is one or more polyether polyol that is preferably selected from one or more polypropylene glycol and / or one or more polytetrahydrofuran. In another preferred embodiment, the isocyanate-reactive polyol (c) consists of one or more polyester polyol and one or more polyether polyol, wherein the weight ratio of the polyester polyol(s) to the polyether polyol(s) is preferably from 5:95 to 80:20, more preferably from 5:95 to 70:30, more preferably from 15:85 to 50:50, even more preferably from 25:75 to 40:60.

[0022] Preferably, the amount of the one or more polyisocyanate with aliphatic reactivity (component (a)) is from 10 to 50 wt.%, the amount of the one or more isocyanatereactive polyol containing ionic and / or potential ionic water-dispersing groups (component (b)) is from 0.1 to 15 wt.% and the amount of the one or more isocyanate-reactive polyol differentfrom component (b) (component (c)) is from 35 to 89.9 wt.%, whereby the amounts are given relative to the total weight of components used to prepare the isocyanate group-functional prepolymer A. More preferably, the amount of the one or more polyisocyanate with aliphatic reactivity (component (a)) is from 15 to 45 wt.%, the amount of the one or more isocyanatereactive polyol containing ionic and / or potential ionic water-dispersing groups (component (b)) is from 1 to 10 wt.% and the amount of the one or more isocyanate-reactive polyol different from component (b) (component (c)) is from 45 to 84 wt.%, whereby the amounts are given relative to the total weight of components used to prepare the isocyanate group-functional prepolymer A. Even more preferably, the amount of the one or more polyisocyanate with aliphatic reactivity (component (a)) is from 20 to 40 wt.%, the amount of the one or more isocyanate-reactive polyol containing ionic and / or potential ionic water-dispersing groups (component (b)) is from 2 to 8 wt.% and the amount of the one or more isocyanate-reactive polyol different from component (b) (component (c)) is from 52 to 78 wt.%, whereby the amounts are given relative to the total weight of components used to prepare the isocyanate group-functional prepolymer A. Even more preferably, the amount of the one or more polyisocyanate with aliphatic reactivity (component (a)) is from 27 to 37 wt.%, the amount of the one or more isocyanate-reactive polyol containing ionic and / or potential ionic waterdispersing groups (component (b)) is from 3 to 6 wt.% and the amount of the one or more isocyanate-reactive polyol different from component (b) (component (c)) is from 57 to 70 wt.%, whereby the amounts are given relative to the total weight of components used to prepare the isocyanate group-functional prepolymer A. Most preferably, the amount of the one or more polyisocyanate with aliphatic reactivity (component (a)) is from 30 to 35 wt.%, the amount of the one or more isocyanate-reactive polyol containing ionic and / or potential ionic waterdispersing groups (component (b)) is from 3 to 6 wt.% and the amount of the one or more isocyanate-reactive polyol different from component (b) (component (c)) is from 59 to 67 wt.%, whereby the amounts are given relative to the total weight of components used to prepare the isocyanate group-functional prepolymer A. Preferably, the amounts of component (a), component (b) and component (c) add up to 100 wt.%, i.e., the components charged in the polymerization to prepare the isocyanate group-functional prepolymer A preferably consist of component (a), component (b) and component (c).

[0023] The polyurethane (I) is obtained by reacting at least the isocyanate group- functional prepolymer A with one or more chain extending compounds having isocyanatereactive groups, wherein the one or more chain extending compounds comprise, consist essentially of, or consist of one or more dihydrazides B according to formula H2N-NH-CO-(R)n-C0-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 18 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms. Suitable examples of the dihydrazides B are oxalyl dihydrazide (CAS number 996-98-5), malonic acid dihydrazide (CAS number 3815-86-9), succinic acid dihydrazide (CAS number 4146-43-4), glutaric acid anhydride (CAS number 1508-67-4), adipic acid dihydrazide (CAS number 1071-93-8), pimelic acid dihydrazide (CAS number 13043-98-6), suberic acid dihydrazide (CAS number 20247-84-1), azelaic acid dihydrazide (CAS number 4080-95-9) and sebacic acid dihydrazide (CAS number 925-83-7). Preferably, n is 0 (i.e., R is not present and the dihydrazide (B) being oxalyl dihydrazide (CAS number 996- 98-5)), or n is 1 (i.e., R is present) and R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms. More preferably, n is 1 and R is an aliphatic hydrocarbon group having from 2 to 8 carbon atoms. Even more preferably, n is 1 and R is an aliphatic hydrocarbon group having from 2 to 5 carbon atoms. Most preferably, the dihydrazide (B) with formula (X) is adipic acid dihydrazide (R = C4H ) (CAS number 1071-93-8).

[0024] The molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate groups of the prepolymer A composition is preferably in the range of from 1.0 to 4.5. More preferably the molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate groups of the prepolymer A composition is at least 1.1, even more preferably at least 1.2, even more preferably at least 1.3, even more preferably at least 1.4. More preferably the molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate groups of the prepolymer A composition is at most 2.0, even more preferably at most 1.8. Most preferably, the molar ratio of isocyanatereactive groups of the chain extending compounds to free isocyanate groups of the prepolymer A composition is from 1.2 to 1.8. The molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate (NCO) groups of the prepolymer A composition (also referred to as the degree of chain extension or the extension degree) is calculated by dividing the molar amount of isocyanate-reactive groups of the chain extending compounds by the molar amount of free isocyanate groups of the prepolymer A composition.

[0025] As used herein, chain extending compounds with isocyanate-reactive groups are amine functional compounds comprising two or more primary amine groups, amine functional compounds comprising two or more secondary amine groups, compounds comprising two or more hydrazide groups or amine functional compounds comprising one or more primary amine group and one or more secondary amine group. For example, diethylenetriamine comprises two primary amine groups and one secondary amine group, andhydrazine comprises two primary amine groups. Examples of chain extending compounds other than the dihydrazides B with formula (X) are polyamines such as 1,2-ethylenediamine, 1,2- and 1,3 -diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, isophoronediamine, isomer mixture of 2,2,4- and 2,4,4-trimethylhexamethylendiamine, 2- methylpentam ethylenediamine, di ethylenetriamine, 1,3- and 1,4-xylylenediamine, a, a, a ', a '-tetramethyl-1,3- and -1,4-xylylenediamine, 4,4’ -diaminodi cyclohexylmethane and dimethylethylenediamine. Preferably the chain extending compounds other than the dihydrazides B with formula (X) do not comprise hydrazine or a derivative thereof like for example methylhydrazine and 1,2-dimethylhydrazine.

[0026] The molar amount of isocyanate-reactive groups of the chain extending compounds is the sum of the molar amount of hydrazide groups present in the dihydrazides B with formula (X) and the molar amount of isocyanate-reactive groups present in the chain extending compounds other than the dihydrazides B with formula (X). The molar amount of isocyanate-reactive groups of the chain extending compounds is calculated by adding the molar amounts of amine groups (NH or NH2 groups) and the molar amounts of hydrazide groups present in the chain extending compounds. The dihydrazide B with formula (X) has two isocyanate-reactive NH2 groups since for hydrazides the -NH- group connected to the carbonyl group is not considered an isocyanate-reactive group. Thus, one mol of dihydrazide B with formula (X) has two moles of isocyanate-reactive groups.

[0027] In case the chain extending compound is added as a mixture of one or more dihydrazide B and one or more compounds comprising primary amine groups and / or secondary amine groups, it is believed that these primary and or secondary amine functional chain extending compounds react much faster than the dihydrazide B. Therefore, it is assumed that all the amine groups of the chain extending compounds comprising primary amine groups and / or secondary amine groups have reacted prior to the hydrazide groups of the dihydrazide(s) B. Therefore, the molar amount of isocyanate groups of the prepolymer A composition available for the reaction with hydrazide groups is calculated as the molar amount of free isocyanate groups of the prepolymer A composition minus the molar amount of primary and secondary amine groups present in the chain extending compounds comprising primary amine groups and / or secondary amine groups.

[0028] The ratio of the molar amount of hydrazide groups of the dihydrazide B to the molar amount of free isocyanate groups of the prepolymer A composition available for the reaction with hydrazide groups is preferably in the range of from 1.0 to 4.5. More preferably the ratio of the molar amount of hydrazide groups of the dihydrazide B to the molar amount offree isocyanate groups of the prepolymer A composition available for the reaction with hydrazide groups is at least 1.1, even more preferably at least 1.2, even more preferably at least 1.3, even more preferably at least 1.4. More preferably the ratio of the molar amount of hydrazide groups of the dihydrazide B to the molar amount of free isocyanate groups of the prepolymer A composition available for the reaction with hydrazide groups is at most 2.0, even more preferably at most 1.8. Most preferably, the ratio of the molar amount of hydrazide groups of the dihydrazide B to the molar amount of free isocyanate groups of the prepolymer A composition available for the reaction with hydrazide groups is from 1.2 to 1.8.

[0029] Free isocyanate groups of the prepolymer A composition are defined herein as any unreacted isocyanate group in the prepolymer A composition, whereby unreacted isocyanate groups in the prepolymer A composition are terminal isocyanate groups of the prepolymer A as well as isocyanate groups of unreacted polyisocyanates that are present in the prepolymer A composition. The amount of free isocyanate groups of the prepolymer A composition is determined after the prepolymer reaction has finished, i.e., when the measured NCO content of the prepolymer A composition (determined with the method as described further herein) is found close to or preferably equal to or lower than that of the theoretical NCO content of the prepolymer A composition. The theoretical NCO content of the prepolymer A composition is the molar amount of isocyanate groups that would theoretically remain in the prepolymer A composition if all the isocyanate-reactive groups of the compounds used to prepare the prepolymer A composition had reacted with the isocyanate groups of the isocyanate-group containing compounds used to prepare the prepolymer A composition.

[0030] The one or more chain extending compounds having isocyanate-reactive groups preferably comprise at least 5 mol%, more preferably at least 10 mol%, even more preferably at least 15 mol%, even more preferably at least 20 mol%, even more preferably at least 25 mol%, even more preferably at least 30 mol%, even more preferably at least 35 mol%, even more preferably at least 40 mol%, even more preferably at least 45 mol%, even more preferably at least 50 mol%, even more preferably at least 55 mol%, even more preferably at least 60 mol%, even more preferably at least 65 mol%, even more preferably at least 70 mol%, even more preferably at least 75 mol%, even more preferably at least 80 mol%, even more preferably at least 85 mol%, even more preferably at least 90 mol%, even more preferably at least 95 mol%, most preferably 100 mol%, of one or more dihydrazides B according to formula: H2N-NH-CO-(R)n-CO-NH-NH2 (X), relative to the total amount of chain extending compounds having isocyanate-reactive groups.

[0031] The reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups (also referred to as the chain extension reaction) is carried out in the substantial absence of ketone- and / or aldehyde- functional organic solvents. Examples of ketone-functional organic solvents are methyl ethyl ketone and acetone. It is well known that aldehyde-functional groups and ketone-functional groups react in a reversible manner with hydrazide groups resulting in Schiff base functional groups. Thus, the presence of aldehyde- and / or ketone- functional organic solvents will disturb the chain extension reaction between the hydrazide of the dihydrazide B and the isocyanate groups of the isocyanate group functional prepolymer A and is therefore to be prevented.

[0032] The amount of ketone- and / or aldehyde-functional organic solvents that is present during said reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is preferably such that the amount of ketone- and / or aldehyde-functional organic solvents in the dispersion of the present invention is, relative to the isocyanate group-functional prepolymer A composition, at most 5 wt.%, preferably at most 2 wt.%, more preferably at most 1 wt.%, more preferably at most 0.5 wt.%, more preferably at most 0.1 wt.%, more preferably at most 0.05 wt.%, more preferably at most 0.01 wt.%, more preferably at most 0.005 wt.%, more preferably at most 0.001 wt.%. Even more preferably, said reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the absence of ketone- and / or aldehyde-functional organic solvents.

[0033] The reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is preferably carried out in the presence of one or more neutralizing agents which are not reactive with isocyanate groups, such as for example tertiary amines. The reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is preferably carried out in the presence of one or more trialkylamines, more preferably in the presence of triethylamine. The reaction of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is preferably carried out in the absence of neutralizing agents which are reactive with isocyanate groups, such as ammonia and N,N-dimethylethanolamine. This is because ammonia for example reacts with isocyanate and this reaction will disturb the chain extension reaction between the hydrazide of the dihydrazide B and the isocyanate groups of the isocyanate group functional prepolymer A and is therefore to be prevented. The reaction of the isocyanate group- functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is therefore preferably carried out in the presence of one or more tertiary amines. Preferred tertiary amines are trialkylamines. Most preferred tertiary amine is triethylamine.

[0034] The amount of the one or more dihydrazides B with formula (X) that are added to the isocyanate group-functional prepolymer A composition is preferably from 1 to 50 wt.%, more preferably from 1 to 25 wt.%, more preferably from 1 to 20 wt.%, more preferably from 2 to 18 wt.%, more preferably from 4 to 16 wt.%, more preferably from 6 to 14 wt.%, more preferably from 6 to 14 wt.%, even more preferably from 8 to 12 wt.%, whereby the amount is given relative to the total solids content of the dispersion.

[0035] To reduce disturbing of the chain extension reaction between the hydrazide of the dihydrazide B and the isocyanate groups of the isocyanate group functional prepolymer A, the polyurethane (I) is preferably free of ketone groups which are reactive with hydrazide groups, more preferably the polyurethane (I) is preferably free of carbonyl groups (which include ketone groups and aldehyde groups) which are reactive with hydrazide groups. The polyurethane (I) is therefore also preferably free of allyl groups which are reactive with hydrazide groups. More preferably, the polyurethane (I) is free of ketone groups which are reactive with hydrazide groups and free of allyl groups which are reactive with hydrazide groups. Even more preferably, the polyurethane (I) is free of carbonyl groups (which include ketone groups and aldehyde groups) which are reactive with hydrazide groups and free of allyl groups which are reactive with hydrazide groups. Even more preferably, to further reduce disturbing of the chain extension reaction between the hydrazide of the dihydrazide B and the isocyanate groups of the isocyanate group functional prepolymer A, the chain extension reaction is effected in the substantial absence of functional groups which are reactive with hydrazide groups, whereby said one or more functional groups are other than isocyanate groups. Most preferably, the chain extension reaction is effected in the absence of functional groups which are reactive with hydrazide groups, whereby said one or more functional groups are other than isocyanate groups.

[0036] The polyurethane (I) preferably comprises ethylene oxide groups in an amount of at most 10 wt.%, more preferably of at most 7 wt.%, more preferably of at most 5 wt.%, even more preferably of at most 3 wt.%, relative to the polyurethane (I), since the water resistance of the layer obtained from a composition comprising the dispersion of the present invention can be improved by reducing the amount of ethylene oxide groups in the polyurethane (I).

[0037] The waterborne polyurethane dispersion according to the invention preferably has an acid value in the range of from 1 to 75 mg KOH / g solids of the dispersion, more preferably from 2 to 50 mg KOH / g solids of the dispersion, even more preferably from 5 to 40 mg KOH / g solids of the dispersion, even more preferably from 5 to 30 mg KOH / g solids of the dispersion, even more preferably from 10 to 20 mg KOH / g solids of the dispersion. As used herein, the acid value AV of the dispersion is calculated with the following method: AV [mg KOH / g solids of the dispersion] =(sum of acid groups present in the dispersion (in moles) / solids content of the dispersion)* 56.1 * 1000.

[0038] The waterborne polyurethane dispersion according to the invention preferably has a solids content in the range of from 5 to 40 wt.%, more preferably from 10 to 35 wt.%, even more preferably from 15 to 35 wt.%, even more preferably from 20 to 35 wt.%, whereby the solids content of the dispersion is determined with the method as further described herein. The solids of the dispersion preferably consists essentially of, or consists of polyurethane (I) and the one or more chain extending compounds having isocyanate-reactive groups.

[0039] The pH of the dispersion is preferably at least 4, more preferably at least 6, even more preferably at least 7, and the pH of the dispersion is preferably at most 9.

[0040] The process of the present invention to prepare the waterborne polyurethane dispersion according to the present invention preferably comprises: a) Preparing a melt comprising isocyanate group-functional prepolymer A by reacting at least (a) at least one polyisocyanate with aliphatic reactivity, (b) at least one isocyanatereactive polyol with potential anionic groups, and (c) at least one isocyanate-reactive polyol different from component (b) in the melt, b) either dispersing the melt in an aqueous phase comprising neutralization agent and chain extending compound that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula:H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, or either neutralizing the isocyanate-terminated prepolymer by adding neutralizing agent to the melt and subsequently dispersing the melt comprising neutralized isocyanate- terminated prepolymer in water comprising chain extending compound that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula:H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, or either dispersing the melt in an aqueous phase comprising neutralization agent and subsequently adding the chain extending compound, said chain extending compound is optionally present in water, that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula:H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, or either neutralizing the isocyanate-terminated prepolymer by adding neutralizing agent to the melt, subsequently dispersing the melt comprising neutralized isocyanate-terminated prepolymer in water and subsequently adding the chain extending compound, said chain extending compound is optionally present in water, that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula: H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms.

[0041] More preferably, the process of the present invention to prepare the waterborne polyurethane dispersion according to the present invention comprises: a) Preparing a melt comprising isocyanate group-functional prepolymer A by reacting at least (a) at least one polyisocyanate with aliphatic reactivity, (b) at least one isocyanatereactive polyol with potential anionic groups, and (c) at least one isocyanate-reactive polyol different from component (b) in the melt, b) either neutralizing the isocyanate-terminated prepolymer by adding neutralizing agent to the melt and subsequently dispersing the melt comprising neutralized isocyanate- terminated prepolymer in water comprising chain extending compound that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula: H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, or either neutralizing the isocyanate-terminated prepolymer by adding neutralizing agent to the melt, subsequently dispersing the melt comprising neutralized isocyanate-terminated prepolymer in water and subsequently adding the chain extending compound, said chainextending compound is optionally present in water, that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula:H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms.

[0042] The neutralization agent is preferably one or more tertiary amines, preferably one or more trialkylamines, more preferably the neutralization agent is triethylamine.

[0043] The amount of chain extending compound according to formula (X) that is used in the process of the present invention, relative to the total solids content of the dispersion, is preferably from 1 to 50 wt.%, more preferably from 1 to 25 wt.%, more preferably from 1 to 20 wt.%, more preferably from 2 to 18 wt.%, more preferably from 4 to 16 wt.%, more preferably from 6 to 14 wt.%, more preferably from 6 to 14 wt.%, even more preferably from 8 to 12 wt.%.

[0044] The present invention further relates to an ink or coating or primer composition comprising the waterborne polyurethane dispersion as described herein above or obtained with the process as described herein above. The polyurethane can be used as cohesive component (binder) in inks, coatings and / or primers.

[0045] The present invention further relates to an ink or coating or primer layer obtained by drying the ink or coating or primer composition according to the present invention.

[0046] The present invention further relates to a primer layer obtained by drying the primer composition of the present invention which primer layer increases the adhesion of label coatings, UV-curable inks, dry or oil based liquid toners, inkjet inks, or soft-feel resins to a substrate.

[0047] The present invention further relates to an article comprising such an ink, a coating and / or a primer layer. The ink, coating or primer layer is preferably adhered to at least a part of a substrate or layer comprising, consisting essentially of, or consisting of a hydrophobic plastic. The hydrophobic plastic is preferably polyethylene, polypropylene, biaxially oriented polypropylene BOPP or polyethylene terephthalate PET. More preferably, the hydrophobic plastic is biaxially oriented polypropylene. Preferably, the hydrophobic plastic has been corona treated. Preferably, the waterborne dispersion according to the current invention is used as a primer composition. The article of the present invention therefore preferably comprises a primer layer obtained by drying a primer composition comprising the waterborne dispersion of the current invention. The primer layer preferably has a dry filmthickness in the range of from 10 to 2000 nm, preferably from 20 to 1250 nm, more preferably from 50 to 500 nm, wherein the dry film thickness is measured as described in the description. The article of the present invention that comprises a primer layer obtained by drying a primer composition comprising the waterborne dispersion of the current invention preferably further comprises a coating onto the primer layer which preferably comprises polyvinylidene chloride (PVDC) and / or (meth)acrylic (co)polymer.

[0048] The present invention further relates to a food contact packaging comprising an article according to the current invention. Food contact packaging refers to packaging that may come into direct contact with the packaged food product.

[0049] Various aspects of the subject matter described herein are set out in the following numbered clauses:

[0050] Clause 1. A waterborne polyurethane dispersion, wherein the dispersion comprises(a) a polyurethane (I) which comprises:-NH-CO-HN-NH-CO-(R)n-CO-NH-NH-CO-NH- linkages, and -NH-CO-HN-NH-CO-(R)n-CO-NH-NH2terminal groups, and(b) one or more dihydrazides B according to formula H2N-NH-CO-(R)n-CO-NH-NH2(X), wherein n is 0 or 1, and in case n is 1, R is an aliphatic hydrocarbon group having from 1 to 18 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, wherein the polyurethane (I) is obtained by at least: providing an isocyanate group-functional prepolymer A composition comprising an isocyanate group-functional prepolymer A, wherein the isocyanate group-functional prepolymer A is obtained by reacting at least one or more polyisocyanates with aliphatic reactivity and one or more polyols, adding one or more chain extending compounds having isocyanate-reactive groups to the isocyanate group-functional prepolymer A composition, and reacting at least the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups, wherein the one or more chain extending compounds comprise, consist essentially of, or consist of the one or more dihydrazides B according to formula (X); wherein the reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the substantial absence of ketone- and / or aldehyde-functional organic solvents; andwherein the dispersion comprises the one or more dihydrazide B with formula (X) in an amount of at least 1000 ppm, based on the solids content of the dispersion, wherein the amount of the dihydrazide B with formula (X) in the dispersion is determined with the method as specified herein.

[0051] Clause 2. A waterborne polyurethane dispersion of clause 1, wherein the molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate groups present in the prepolymer A composition is at least 1.0, preferably at least 1.1, even more preferably at least 1.2, even more preferably at least 1.3, even more preferably at least 1.4, and at most 4.5, preferably at most 2.0, even more preferably at most 1.8.

[0052] Clause 3. A waterborne polyurethane dispersion of clause 1 or clause 2, wherein the one or more chain extending compounds comprise at least 5 mol%, more preferably at least 10 mol%, even more preferably at least 15 mol%, even more preferably at least 20 mol%, even more preferably at least 25 mol%, even more preferably at least 30 mol%, even more preferably at least 35 mol%, even more preferably at least 40 mol%, even more preferably at least 45 mol%, even more preferably at least 50 mol%, even more preferably at least 55 mol%, even more preferably at least 60 mol%, even more preferably at least 65 mol%, even more preferably at least 70 mol%, even more preferably at least 75 mol%, even more preferably at least 80 mol%, even more preferably at least 85 mol%, even more preferably at least 90 mol%, even more preferably at least 95 mol%, most preferably 100 mol%, of one or more dihydrazides B according to formula: H2N-NH-CO-(R)n-CO-NH-NH2 (X), relative to the total amount of chain extending compounds having isocyanate-reactive groups.

[0053] Clause 4. A waterborne polyurethane dispersion, wherein the dispersion comprises(a) a polyurethane (I) which comprises:-NH-CO-HN-NH-CO-(R)n-CO-NH-NH-CO-NH- linkages, and -NH-CO-HN-NH-CO-(R)n-CO-NH-NH2terminal groups, and(b) one or more dihydrazides B according to formula H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and in case n is 1, R is an aliphatic hydrocarbon group having from 1 to 18 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, wherein the polyurethane (I) is obtained by at least: providing an isocyanate group-functional prepolymer A composition comprising an isocyanate group-functional prepolymer A, wherein the isocyanate group-functional prepolymer A is obtained by reacting at least one or more polyisocyanates with aliphatic reactivity and one or more polyols,adding one or more chain extending compounds having isocyanate-reactive groups to the isocyanate group-functional prepolymer A composition, and reacting at least the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups, wherein the molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate groups present in the prepolymer A composition is at least 1.0, preferably at least 1.1, even more preferably at least 1.2, even more preferably at least 1.3, even more preferably at least 1.4, and at most 4.5, preferably at most 2.0, even more preferably at most 1.8; wherein the one or more chain extending compounds comprise at least 5 mol%, more preferably at least 10 mol%, even more preferably at least 15 mol%, even more preferably at least 20 mol%, even more preferably at least 25 mol%, even more preferably at least 30 mol%, even more preferably at least 35 mol%, even more preferably at least 40 mol%, even more preferably at least 45 mol%, even more preferably at least 50 mol%, even more preferably at least 55 mol%, even more preferably at least 60 mol%, even more preferably at least 65 mol%, even more preferably at least 70 mol%, even more preferably at least 75 mol%, even more preferably at least 80 mol%, even more preferably at least 85 mol%, even more preferably at least 90 mol%, even more preferably at least 95 mol%, most preferably 100 mol%, of one or more dihydrazides B according to formula: H2N-NH-CO- (R)n-CO-NH-NH2 (X), relative to the total amount of chain extending compounds having isocyanate-reactive groups; wherein the reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the substantial absence of ketone- and / or aldehyde-functional organic solvents.

[0054] Clause 5. The waterborne polyurethane dispersion of any of clause 1 to clause 4, wherein the dispersion comprises the one or more dihydrazide B with formula (X) in an amount, based on the solids content of the dispersion, of at least 2000 ppm, preferably of at least 3000 ppm, more preferably of at least 4000 ppm, even more preferably of at least 5000 ppm, wherein the amount of the one or more dihydrazide B with formula (X) is determined with the method as specified herein.

[0055] Clause 6. The waterborne polyurethane dispersion of any of clause 1 to clause 5, wherein the dispersion comprises the one or more dihydrazide B with formula (X) in an amount, based on the solids content of the dispersion, of at most 300000 ppm, preferably of at most 250000 ppm, more preferably of at most 200000 ppm, even more preferably of at most150000 ppm, even more preferably of at most 100000 ppm, even more preferably of at most 75000 ppm, wherein the amount of the one or more dihydrazide B with formula (X) is determined with the method as specified herein.

[0056] Clause 7. The waterborne polyurethane dispersion of any of clause 1 to clause 6, wherein n is 0 (i.e., the dihydrazide (B) being oxalic dihydrazide (CAS number 996- 98-5)) or n is 1 and R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms.

[0057] Clause 8. The waterborne polyurethane dispersion of any of clause 1 to clause 6, wherein n is 1 and R is an aliphatic hydrocarbon group having from 2 to 8 carbon atoms, preferably from 2 to 5 carbon atoms.

[0058] Clause 9. The waterborne polyurethane dispersion of any of clause 1 to clause 6, wherein the dihydrazide (B) is adipic acid dihydrazide (R = (CH^) (CAS number1071-93-8).

[0059] Clause 10. The waterborne polyurethane dispersion of any of clause 1 to clause 9, wherein the molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate groups present in the prepolymer A composition is at least 1.0, preferably at least 1.1, even more preferably at least 1.2, even more preferably at least 1.3, even more preferably at least 1.4, and at most 4.5, preferably at most 2.0, even more preferably at most 1.8.

[0060] Clause 11. The waterborne polyurethane dispersion of any of clause 1 to clause 9, wherein the molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate groups in the prepolymer A composition is from 1.2 to 1.8.

[0061] Clause 12. The waterborne polyurethane dispersion of any of clause 1 to clause 11, wherein the amount of ketone- and / or aldehyde-functional organic solvents that is present during said reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is such that the amount of ketone- and / or aldehyde-functional organic solvents, relative to the isocyanate group- functional prepolymer A composition, is at most 5 wt.%, preferably at most 2 wt.%, more preferably at most 1 wt.%, more preferably at most 0.5 wt.%, more preferably at most 0.1 wt.%, more preferably at most 0.05 wt.%, more preferably at most 0.01 wt.%, more preferably at most 0.005 wt.%, more preferably at most 0.001 wt.%.

[0062] Clause 13. The waterborne polyurethane dispersion of any of clause 1 to clause 11, wherein said reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the absence of ketone- and / or aldehyde-functional organic solvents.

[0063] Clause 14. The waterborne polyurethane dispersion of any of clause 1 to clause 13, wherein said reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the presence of one or more neutralizing agents which are not reactive with isocyanate groups, preferably in the presence of one or more tertiary amines, preferably in the presence of one or more trialkylamines, most preferably in the presence of triethylamine.

[0064] Clause 15. The waterborne polyurethane dispersion of any of clause 1 to clause 14, wherein, prior to reaction with said one or more chain extending compounds having isocyanate-reactive groups, the isocyanate group-functional prepolymer A is deprotonated with one or more neutralizing agents, wherein the one or more neutralizing agents are one or more trialkylamines, preferably the neutralizing agent is triethylamine.

[0065] Clause 16. The waterborne polyurethane dispersion of any of clause 1 to clause 15, wherein the one or more chain extending compounds having isocyanate-reactive groups consist essentially of, or consist of, one or more dihydrazides B according to formula:H2N-NH-CO-(R)n-CO-NH-NH2 (X).

[0066] Clause 17. The waterborne polyurethane dispersion of any of clause 1 to clause 16, wherein the isocyanate group-functional prepolymer A comprises as building blocks:(a) At least one polyisocyanate with aliphatic reactivity,(b) At least one isocyanate-reactive polyol with ionic or potential ionic water-dispersing groups (which become ionic when deprotonated), and(c) At least one isocyanate-reactive polyol different from component (b).

[0067] Clause 18. The waterborne polyurethane dispersion of clause 17, wherein the isocyanate-reactive polyol with potential ionic groups (b) is a dihydroxy alkanoic acid, preferably 2,2-dimethylolpropionic acid and / or 2,2-dimethylolbutanoic acid, more preferably, 2,2-dimethylolpropionic acid (DMPA).

[0068] Clause 19. The waterborne polyurethane dispersion of clause 17 or clause18, wherein the isocyanate-reactive polyol (c), which is different from component (b), is selected from the group consisting of polyether polyols, polyester polyols, and any combination thereof.

[0069] Clause 20. The waterborne polyurethane dispersion of any of clause 17 to clause 19, wherein the isocyanate-reactive polyol (c), which is different from component (b), is one or more poly ether polyol.

[0070] Clause 21. The waterborne polyurethane dispersion of any of clause 17 to clause 19, wherein the isocyanate-reactive polyol (c), which is different from component (b), consists of one or more polyester polyol and one or more polyether polyol, wherein the weight ratio of the polyester polyol(s) to the polyether polyol(s) is preferably from 5:95 to 80:20, more preferably from 5:95 to70:30, more preferably from 15:85 to 50:50, even more preferably from 25:75 to 40:60.

[0071] Clause 22. The waterborne polyurethane dispersion of any of clause 19 to clause 21 , wherein the one or more poly ether polyol is selected from one or more polypropylene glycol and / or one or more polytetrahydrofuran.

[0072] Clause 23. The waterborne polyurethane dispersion of any of clause 17 to clause 22, wherein the polyisocyanate with aliphatic reactivity is selected from the group consisting of ethylene diisocyanate, 1,5-pentane diisocyanate, 1,6-hexam ethylene diisocyanate (HDI), 2,2,4-trimethyl-l,6-hexamethylene diisocyanate, isophorone diisocyanate (IPDI), cyclohexane-l,4-diisocyanate, dicyclohexylmethane diisocyanate such as 4,4’- dicyclohexylmethane diisocyanate (4,4’-H12 MDI), p-tetramethylxylene diisocyanate (p- TMXDI) (and its meta isomer m-TMXDI) and any combination of any two or more thereof, preferably the polyisocyanate with aliphatic reactivity (component (a)) is selected from the group consisting of 1,5-pentane diisocyanate, 1,6-hexamethylene diisocyanate (HDI), 2,2,4- trimethyl-l,6-hexamethylene diisocyanate, isophorone diisocyanate (IPDI), di cyclohexylmethane diisocyanate such as 4,4’ -di cyclohexylmethane diisocyanate (4,4’-H12 MDI) and any combination of any two or more thereof, more preferably, the polyisocyanate with aliphatic reactivity (component (a)) is selected from the group consisting of isophorone diisocyanate (IPDI), di cyclohexylmethane diisocyanate such as 4,4’ -di cyclohexylmethane diisocyanate (4,4’-H12 MDI) and any combination of any two or more thereof, even more preferably, the polyisocyanate with aliphatic reactivity (component (a)) is isophorone diisocyanate.

[0073] Clause 24. The waterborne polyurethane dispersion of any of clause 1 to clause 23, wherein the polyurethane (I) is free of ketone groups which are reactive with hydrazide groups.

[0074] Clause 25. The waterborne polyurethane dispersion of any of clause 1 to clause 24, wherein the polyurethane (I) is free of allyl groups which are reactive with hydrazide groups.

[0075] Clause 26. The waterborne polyurethane dispersion of any of clause 1 to clause 25, wherein said reacting of at least the isocyanate group-functional prepolymer A withsaid one or more chain extending compounds having isocyanate-reactive groups is effected in the substantial absence of functional groups which are reactive with hydrazide groups, whereby said one or more functional groups are other than isocyanate groups.

[0076] Clause 27. The waterborne polyurethane dispersion of any of clause 1 to clause 26, wherein the ratio of the molar amount of hydrazide groups of the dihydrazide B to the molar amount of free isocyanate groups of the prepolymer A composition available for the reaction with hydrazide groups is at least 1.0, preferably at least 1.1, even more preferably at least 1.2, even more preferably at least 1.3, even more preferably at least 1.4, and at most 4.5, preferably at most 2.0, even more preferably at most 1.8, most preferably the ratio of the molar amount of hydrazide groups of the dihydrazide B to the molar amount of free isocyanate groups of the prepolymer A composition available for the reaction with hydrazide groups is from 1.2 to 1.8.

[0077] Clause 28. The waterborne polyurethane dispersion of any of clause 1 to clause 27, wherein the dispersion has an (calculated) acid value in the range of from 1 to 75 mg KOH / g solids of the dispersion, preferably from 2 to 50 mg KOH / g solids of the dispersion, more preferably from 5 to 40 mg KOH / g solids of the dispersion, even more preferably from 5 to 30 mg KOH / g solids of the dispersion, even more preferably from 10 to 20 mg KOH / g.

[0078] Clause 29. The waterborne polyurethane dispersion of any of clause 1 to clause 28, wherein the polyurethane (I) comprises ethylene oxide groups in an amount of at most 10 wt.%, preferably of at most 7 wt.%, more preferably of at most 5 wt.%, even more preferably of at most 3 wt.%, relative to the polyurethane (I).

[0079] Clause 30. The waterborne polyurethane dispersion of any of clause 1 to clause 29, wherein the dispersion has a solids content in the range of from 5 to 40 wt.%, preferably from 10 to 35 wt.%, more preferably from 15 to 35 wt.%, even more preferably from 20 to 35 wt.%.

[0080] Clause 31. The waterborne polyurethane dispersion of any of clause 1 to clause 30, wherein the amount of the one or more dihydrazides B with formula (X) that are added to the isocyanate group-functional prepolymer A composition is from 1 to 50 wt.%, preferably from 1 to 25 wt.%, preferably from 1 to 20 wt.%, more preferably from 2 to 18 wt.%, more preferably from 4 to 16 wt.%, more preferably from 6 to 14 wt.%, more preferably from 6 to 14 wt.%, even more preferably from 8 to 12 wt.%, whereby the amount is given relative to the total solids content of the dispersion.

[0081] Clause 32. The waterborne polyurethane dispersion of any of clause 1 to clause 31, wherein the pH of the dispersion is at least 4, preferably at least 6, more preferably at least 7, and the pH of the dispersion at most 9.

[0082] Clause 33. A process for preparing the waterborne polyurethane dispersion of any of clause 1 to clause 32, wherein the process comprises:(1) Reacting at least one or more polyisocyanates with aliphatic reactivity and one or more polyols to obtain an isocyanate group-functional prepolymer A composition comprising an isocyanate group-functional prepolymer A,(2) Adding one or more chain extending compounds having isocyanate-reactive groups to the isocyanate group-functional prepolymer A composition, and(3) Reacting at least the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups, wherein the one or more chain extending compounds comprise, consist essentially of, or consist of one or more dihydrazides B according to formula (X), wherein the one or more dihydrazide B with formula (X) are added to the isocyanate group-functional prepolymer A composition in such an amount that the one or more dihydrazides B with formula (X) are present in the dispersion in an amount of at least 1000 ppm, based on the solids content of the dispersion, wherein the amount of the dihydrazide B with formula (X) in the dispersion is determined with the method as specified herein; and wherein the reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the substantial absence of ketone- and / or aldehyde-functional organic solvents.

[0083] Clause 34. A process for preparing the waterborne polyurethane dispersion of any of clause 1 to clause 32, wherein the process comprises:(1) Reacting at least one or more polyisocyanates with aliphatic reactivity and one or more polyols to obtain an isocyanate group-functional prepolymer A composition comprising an isocyanate group-functional prepolymer A,(2) Adding one or more chain extending compounds having isocyanate-reactive groups to the isocyanate group-functional prepolymer A composition, and(3) Reacting at least the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups, wherein the molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate groups present in the prepolymer A composition is at least 1.0, preferably at least 1.1, even more preferably at least 1.2, even more preferably at least 1.3, even morepreferably at least 1.4, and at most 4.5, preferably at most 2.0, even more preferably at most 1.8; wherein the one or more chain extending compounds comprise at least 5 mol%, more preferably at least 10 mol%, even more preferably at least 15 mol%, even more preferably at least 20 mol%, even more preferably at least 25 mol%, even more preferably at least 30 mol%, even more preferably at least 35 mol%, even more preferably at least 40 mol%, even more preferably at least 45 mol%, even more preferably at least 50 mol%, even more preferably at least 55 mol%, even more preferably at least 60 mol%, even more preferably at least 65 mol%, even more preferably at least 70 mol%, even more preferably at least 75 mol%, even more preferably at least 80 mol%, even more preferably at least 85 mol%, even more preferably at least 90 mol%, even more preferably at least 95 mol%, most preferably 100 mol%, of one or more dihydrazides B according to formula: H2N-NH-CO- (R)n-CO-NH-NH2 (X), relative to the total amount of chain extending compounds having isocyanate-reactive groups; and wherein the reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the substantial absence of ketone- and / or aldehyde-functional organic solvents.

[0084] Clause 35. The process of clause 33 or clause 34, wherein the process comprises: a) Preparing a melt comprising isocyanate group-functional prepolymer A by reacting at least (a) at least one polyisocyanate with aliphatic reactivity, (b) at least one isocyanatereactive polyol with potential anionic groups, and (c) at least one isocyanate-reactive polyol different from component (b) in the melt, b) either dispersing the melt in an aqueous phase comprising neutralization agent and chain extending compound that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula:H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, or either neutralizing the isocyanate-terminated prepolymer by adding neutralizing agent to the melt and subsequently dispersing the melt comprising neutralized isocyanate- terminated prepolymer in water comprising chain extending compound that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula:H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, or either dispersing the melt in an aqueous phase comprising neutralization agent and subsequently adding the chain extending compound, said chain extending compound is optionally present in water, that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula:H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, or either neutralizing the isocyanate-terminated prepolymer by adding neutralizing agent to the melt, subsequently dispersing the melt comprising neutralized isocyanate- terminated prepolymer in water and subsequently adding the chain extending compound, said chain extending compound is optionally present in water, that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula:H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms.

[0085] Clause 36. The process of clause 33 or clause 34, wherein the process comprises: a) Preparing a melt comprising isocyanate group-functional prepolymer A by reacting at least (a) at least one polyisocyanate with aliphatic reactivity, (b) at least one isocyanatereactive polyol with potential anionic groups, and (c) at least one isocyanate-reactive polyol different from component (b) in the melt, b) either neutralizing the isocyanate-terminated prepolymer by adding neutralizing agent to the melt and subsequently dispersing the melt comprising neutralized isocyanate- terminated prepolymer in water comprising chain extending compound that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula: H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n is 1, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, or either neutralizing the isocyanate-terminated prepolymer by adding neutralizing agent to the melt, subsequently dispersing the melt comprising neutralized isocyanate-terminated prepolymer in water and subsequently adding the chain extending compound, said chain extending compound is optionally present in water, that comprises, consists essentially of, or consists of one or more dihydrazides B according to formula:H2N-NH-CO- Rn-CO-NH-NH2 (X), wherein n is 0 or 1, and, when n isl, R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms.

[0086] Clause 37. The process of clause 35 or clause 36, wherein the neutralization agent is one or more tertiary amines, preferably one or more trialkylamines, more preferably the neutralization agent is tri ethyl amine.

[0087] Clause 38. The process of any of clause 33 to clause 37, wherein the amount of chain extending compound according to formula (X) that is used in the process, relative to the total solids content of the dispersion, is from 1 to 50 wt.%, preferably from 1 to 25 wt.%, more preferably from 1 to 20 wt.%, more preferably from 2 to 18 wt.%, more preferably from 4 to 16 wt.%, more preferably from 6 to 14 wt.%, more preferably from 6 to 14 wt.%, even more preferably from 8 to 12 wt.%.

[0088] Clause 39. An ink or coating or primer composition comprising the waterborne polyurethane dispersion of any of clauses 1 to 32 or obtained with the process of any of clause 33 to clause 38.

[0089] Clause 40. An ink or coating or primer layer obtained from the ink or coating or primer composition of clause 39.

[0090] Clause 41. An article comprising an ink, a coating and / or a primer layer of clause 40.

[0091] Clause 42. The article of clause 41, wherein the article comprises a primer layer obtained from a primer composition comprising the waterborne polyurethane dispersion of any of clause 1 to clause 32 or obtained with the process of any of clause 33 to clause 38.

[0092] Clause 43. An article comprising (1) a substrate comprising, consisting essentially of, or consisting of hydrophobic plastic, and (2) an ink or coating or primer layer that is disposed on at least a part of the substrate, wherein the ink or coating or primer layer is obtained from the ink or coating or primer composition of clause 39.

[0093] Clause 44. The article of clause 43, wherein the article comprises (1) a substrate comprising, consisting essentially of, or consisting of hydrophobic plastic, and (2) a primer layer that is disposed on at least a part of the substrate, wherein the primer layer is obtained from the primer composition of clause 39.

[0094] Clause 45. The article of any of clause 41 to clause 44, wherein the primer layer has a dry film thickness in the range of from 10 to 2000 nm, preferably from 20 to 1250 nm, more preferably from 50 to 500 nm, wherein the dry film thickness is measured as described in the description.

[0095] Clause 46. The article of any of clause 43 to clause 45, wherein the hydrophobic plastic comprises, consists essentially of, or consists of polyethylene, polypropylene, biaxially oriented polypropylene and / or PET, wherein the hydrophobic plastic preferably has been corona treated.

[0096] Clause 47. The article of any of clause 44 to clause 46, wherein the article further comprises a coating onto the primer layer.

[0097] Clause 48. The article of clause 47, wherein the coating comprises polyvinylidene chloride (PVDC) and / or (meth)acrylic (co)polymer.

[0098] Clause 49. A food contact packaging comprising the article of any of clause41 to clause 48.Examples

[0099] The following examples further illustrate the invention but, of course, should not be construed as in any way limiting its scope. Unless otherwise specified, all parts, percentages and ratios are on a weight basis. All analyses and measurements were carried out at 23°C, unless otherwise stated.

[0100] Table 1 describes the raw materials and reagents used to prepare the dispersions of the present examples and comparative experiments.Table 1

[0101] The following test methods were applied.Solids

[0102] The solids content (wt.%) of a dispersion was determined via the following method: A test portion of approximately 1 gram dispersion is weighed into an aluminum dish with a diameter of 100 mm equipped with a glass filter pad (Machery -Nagel MN85 / 90, 90 mm diameter). The weight loss of the dispersion was subsequently determined after drying the test portion in a HB43-S halogen moisture analyzer from Mettler Toledo at a temperature of 75°C until constant weight.Amount of free dihydrazide with formula H2N-NH-CO-(R)n-CO-NH-NH2 (X) in the dispersion

[0103] Free dihydrazide residuals were quantified using a derivatization approach, followed by ultra-high performance liquid chromatography (UHPLC) with ultraviolet (UV) detection. Dihydrazides of >99 wt.% purity were dissolved in ultrapure water to obtain calibration standards in the area of interest (typical 1-1000 mg / kg). 1.0 mL of aqueous dihydrazide was transferred to a 2 mL HPLC vial, after which 50 pL of acetone was added. This mixture was homogenized for 60 minutes at room temperature prior to analysis.

[0104] Samples were prepared by diluting 0.5 gram of dispersion with 5.0 mL of ultrapure water in a 10 mL test tube. After mixing, 0.5 mL of a 10 wt.% calcium chloride solution was added to precipitate the polymer fraction. This mixture was left to stand at room temperature until a clear upper layer is obtained (typically within 1 hour). In certain cases, a short centrifugation step using a tabletop centrifuge (10 minutes at 20.000 rpm) was applied to remove particulate matter from the clear aqueous phase. 1.0 mL of the aqueous phase was transferred to a 2 mL HPLC vial, after which 50 pL of acetone was added. This mixture was homogenized for 60 minutes at room temperature prior to analysis. Any dihydrazide present in calibration standards or samples of dispersions was derivatized with acetone to form the corresponding di-imine, which provides UV absorption in the low-UV wavelength range (200-240 nm).Analysis of both derivatized calibration standards and derivatized samples was performed by separation using reversed phase liquid chromatography, using an Acquity H-Class UPLC (consisting of quaternary pump, autosampler, column oven and photodiode array detector) equipped with a HSS T3 C18 column (including a guard column of similar chemistry). The column oven was kept at 40°C, flow rate was kept constant at 0.4 mL / min. 1.0 pL of derivatized calibration standard or derivatized sample was injected onto the system, after which a gradient was applied from 95% water, 5% acetonitrile (1 min isocratic elution) to60% water, 40% acetonitrile in 5 minutes. Two cleaning phases were applied (towards an eluent composition of 1% water, 99% acetonitrile in 0.5 min, and after that towards 1% water, 99% tetrahydrofuran) after which re-equilibration was performed towards the initial conditions in 0.5 min followed by a 3.5-min wait step prior to the next injection. Total analysis time was 10 min. The various derivatized dihydrazides were chromatographically separated according to their relative polarity. In this method the derivatized dihydrazides eluted between 3 and 7 minutes. For instance, malonic dihydrazide derivate eluted at 3.18 minutes, azelaic-, suberic-, oxalic-, succinic-, glutaric-, adipic-, and pimelic dihydrazide derivatives eluted at 5.23, 4.80, 3.29, 3.21, 3.50, 3.90 and 4.36 minutes, respectively. Detection was performed using UV detection at 230 nm. The peak area of the separated (derivatized) dihydrazides in the calibration standards of known concentration are fitted to a calibration curve, which was compared with the peak area of the same dihydrazides in the samples of the dispersions and corrected for the dilution factor used in the method. After correction for the solids content of the dispersion, the amount of free dihydrazide (in ppm) in the sample, based on the solids content of the dispersion, was obtained. pH

[0105] The pH of a sample was determined according to the ISO 976:2013.Samples were measured at room temperature using a Metrohm 691 pH-meter equipped 10 with a combined glass electrode and a PT- 1000 temperature sensor. The pH-meter was calibrated using buffer solutions of pH 7.00 and 9.21 prior to use.NCO content

[0106] The NCO content of a sample is determined based on the ASTM D2572-19. In the procedure, the sample is dissolved in toluene and reacted with excess n- dibutylamine. The excess of n-dibutylamine is subsequently back-titrated with standard IN hydrochloric acid (HC1). The difference in titration volume between the sample and a blank is the measure of the isocyanate content on solids, according to the following formula: %NCOsolids=[(Vb - Vm) * N * 4.2] / (A * s / 100) where%NCOsolids is the isocyanate content on solids, Vb is the volume of HC1 used in the blank, Vm is the volume of HC1 used in the sample, N is the normality of the HC1 solution, A is the sample weight in grams and s is the solids content of the sample in wt.%. Measurements are performed in duplicate using a potentiometric endpoint on a Metrohm 702SM Titrino titrator (accepting the measurement if the difference between duplicates is < 0.1%NCO).Viscosity

[0107] The apparent viscosity (or equally the viscosity) was measured at room temperature at 60 rpm, according to ISO 2555-2018 on a Brookfield DVE-LV viscometer (single-cylinder geometry). The spindle was selected from the spindles S62, S63 or S64, using the lowest-numbered spindle (i.e., the largest spindle) that yields a reading between 10% and 100% torque.Dry film thickness

[0108] The weight of 10 uncoated samples of a dimension of 20 by 20 centimeters and the coated and the weight of 10 coated samples of a dimension of 20 by 20 centimeters were measured. Based on the weight difference between the coated and uncoated samples and the density of the coating which was taken as 1.18 g / cm3, the dry film thickness of the applied coating was obtained.Preparation of waterborne polyurethane dispersions

[0109] Comparative Example 1A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (45.0 gram), pTHFlOOO (488.2 gram) and IPDI (366.8 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.2 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.7% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (33.1 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 265.2 gram of this composition to a mixture of 24.6 gram of adipic acid dihydrazide (0.6 stoichiometric amount (SA), defined as the molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate groups present in the prepolymer composition) in 1110.3 gram demineralized water at room temperature in 60 minutes. The dispersion was stirred for a further 1 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 20.0 wt%; pH = 6.8; Viscosity = 5 mPa.s.

[0110] Comparative Example 2Comparative Example 2 was prepared according to Example 2 in EP 0 646 609 B 1.

[0111] Example 1A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (45.0 gram), pTHFlOOO (488.2 gram) and IPDI (366.8 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.2 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.7% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (33.1 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 237.5 gram of this composition to a mixture of 51.4 gram of adipic acid dihydrazide (1.4 SA) in 1111.3 gram demineralized water at room temperature in 60 minutes. The dispersion was stirred for a further 1 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 19.9 wt%; pH = 7.5; Viscosity = 5 mPa.s

[0112] Example 2A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (45.0 gram), pTHFlOOO (488.2 gram) and IPDI (366.8 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.2 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.7% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (33.1 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 85.1 gram of this composition to 366.7 gram demineralized water at room temperature in 60 minutes. Next, 18.3 gram of adipic acid dihydrazide (1.4 SA) and 30 gram of demineralized water were added to the dispersion and the dispersion was stirred for a further 2 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 20.2 wt%; pH = 7.4; Viscosity = 4 mPa.s.

[0113] Example 3A I L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (25.0 gram), pTHFlOOO (271.2 gram) and IPDI (203.8 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.10 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.4% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (18.5 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 74.9 gram of this composition to 267.8 gram demineralized water at room temperature in 60 minutes. Next, 13.1 gram of succinic acid dihydrazide (1.4 SA) and 66.0 gram of demineralized water were added to the dispersion and the dispersion was stirred for a further 2 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 19.6 wt%; pH = 7.2; Viscosity = 5 mPa.s.

[0114] Example 4A I L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (25.0 gram), pTHFlOOO (271.2 gram) and IPDI (203.8 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.1 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.7% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (18.9 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 243.8 gram of this composition to a mixture of 45.0 gram of adipic acid dihydrazide (1.2 SA) in 1111.1 gram demineralized water at room temperature in 60 minutes. The dispersion was stirred for a further 1 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 19.8 wt%; pH = 7.5; Viscosity = 4 mPa.s.

[0115] Example 5A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (60.0 gram), pTHFlOOO (651.0 gram) and IPDI (489.0 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.24 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours.The NCO content of the resultant urethane prepolymer composition was 7.5% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (44.9 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 177.3 gram of this composition to a mixture of 106.5 gram of adipic acid dihydrazide (4.0 SA) in 1113.5 gram demineralized water at room temperature in 60 minutes. The dispersion was stirred for a further 1 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 20.5 wt%; pH = 7.4; Viscosity = 5mPa.s.

[0116] Example 6A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (60.0 gram), pTHFlOOO (651.0 gram) and IPDI (489.0 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.24 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.5% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (44.9 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 74.9 gram of this composition to 267.8 gram demineralized water at room temperature in 60 minutes. Next, 19.6 gram of azelaic acid dihydrazide (1.4 SA) and 100.0 gram of demineralized water were added to the dispersion and the dispersion was stirred for a further 4 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 18.3 wt%; pH = 7.4; Viscosity = 5 mPa.s.

[0117] Example 7A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (60.0 gram), pTHFlOOO (651.0 gram) and IPDI (489.0 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.24 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.5% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (44.9 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 82.4 gram of this composition to 296.0 gram demineralized water at room temperature in 60 minutes. Next, 20.1 gram of suberic aciddihydrazide (1.4 SA) and 100.0 gram of demineralized water were added to the dispersion and the dispersion was stirred for a further 4 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 19.1 wt%; pH = 7.7; Viscosity = 5 mPa.s.

[0118] Example 8A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (60.0 gram), pTHFlOOO (651.0 gram) and IPDI (489.0 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.24 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.5% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (44.9 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 83.6 gram of this composition to 298.0 gram demineralized water at room temperature in 60 minutes. Next, 19.0 gram of pimelic acid dihydrazide (1.4 SA) and 100.0 gram of demineralized water were added to the dispersion and the dispersion was stirred for a further 4 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 19.7 wt%; pH = 7.5; Viscosity = 5 mPa.s.

[0119] Example 9A I L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (32.5 gram), pTHFlOOO (352.6 gram) and IPDI (264.9 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.13 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.5% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (23.7 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 108.2 gram of this composition to 406.7 gram demineralized water at room temperature in 60 minutes. Next, 15.4 gram of oxalic acid dihydrazide (1.4 SA) and 70.0 gram of demineralized water were added to the dispersion and the dispersion was stirred for a further 4 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 18.9 wt%; pH = 6.9; Viscosity = 5 mPa.s.

[0120] Example 10A I L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (32.5 gram), pTHFlOOO (352.6 gram) and IPDI (264.9 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.13 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.5% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (23.7 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 106.5 gram of this composition to 401.0 gram demineralized water at room temperature in 60 minutes. Next, 17.0 gram of malonic acid dihydrazide (1.4 SA) and 75.0 gram of demineralized water were added to the dispersion and the dispersion was stirred for a further 4 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 20.0 wt%; pH = 7.5; Viscosity = 6 mPa.s.

[0121] Example 11A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (50.0 gram), pTHFlOOO (542.5 gram) and IPDI (407.5 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.20 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.3% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (37.4 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 281.2 gram of this composition to 970.0 gram demineralized water at room temperature in 60 minutes. Next, 6.9 gram of ethylene diamine (EDA) (0.5 SA) and 21 gram of demineralized water were added to the dispersion and the dispersion was stirred for a further 5 min after which 36.9 g of adipic acid dihydrazide (0.9 SA) was added to the dispersion and the dispersion was stirred for another 4 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 23.3 wt%; pH = 7.5; Viscosity = 5 mPa.s.

[0122] Example 12A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (50.0 gram), pTHFlOOO (542.5 gram) and IPDI (407.5 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.20 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.3% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (37.4 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 281.2 gram of this composition to a mixture of 6.9 gram of ethylene diamine (EDA) (0.5 SA), 36.9 g of adipic acid dihydrazide (0.9 SA) in 991.1 gram demineralized water at room temperature in 60 minutes. The dispersion was stirred for another 4 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 23.3 wt%; pH = 7.9; Viscosity = 6 mPa.s.

[0123] Comparative Example 3A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (50.0 gram), pTHFlOOO (542.5 gram) and IPDI (407.5 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.20 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.65% on solids (theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (37.4 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 271.5 gram of this composition to a mixture of 20.0 gram of ethylene diamine (EDA) (1.4 SA) in 1030.1 gram demineralized water at room temperature in 60 minutes. The dispersion was stirred for another 4 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 21.1 wt%; pH = 10.8; Viscosity = 64 mPa.s.

[0124] Example 13A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (50.0 gram), pTHFlOOO (542.5 gram) and IPDI (407.5 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.20 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.65% on solids(theoretically 7.7%). The prepolymer composition was cooled down to 75°C and TEA (37.4 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 181.5 gram of this composition to a mixture of 37.6 gram of glutaric dihydrazide (1.4 SA) in 1001.2 gram demineralized water at room temperature in 60 minutes. The dispersion was stirred for another 4 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 21.3 wt%; pH = 7.7; Viscosity = 5 mPa.s.

[0125] Example 14A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (25.0 gram), pTHFlOOO (67.8 gram), CAPA2077A (203.4 gram) and IPDI (203.8 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.10 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 5.59% on solids (theoretically 6.57%). The prepolymer composition was cooled down to 75°C and TEA (18.5 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 271.6 gram of this composition to a mixture of 43.8 gram of adipic acid dihydrazide (1.4 SA) in 1170.1 gram demineralized water at room temperature in 60 minutes. The dispersion was stirred for another 4 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 20.6 wt%; pH = 7.8; Viscosity = 5 mPa.s.

[0126] Example 15A 2 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (25.0 gram), pTHFlOOO (271.2 gram), IPDI (183.4 gram) and DesW (20.4 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.10 gram of dibutyl tin dilaureate was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 7.00% on solids (theoretically 7.48%). The prepolymer composition was cooled down to 75°C and TEA (18.5 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 271.5 gram of this composition to a mixture of 51.6 gram of adipic dihydrazide (1.4 SA) in 1030.1 gram demineralized water at room temperature in 60 minutes. The dispersion was stirred for another 4 h after which itwas filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 22.9 wt%; pH = 7.7; Viscosity = 18 mPa.s.

[0127] Example 16A 3 L flask equipped with a thermometer and overhead stirrer was charged with dimethylolpropionic acid (69.0 gram), PPG1000 (1292.3 gram), Ymer™ N120 (230.0 gram) and IPDI (708.7 gram). The reaction mixture was placed under N2 atmosphere, heated to 50°C and 0.3 gram of DBTDL was added. The mixture was allowed to exotherm and kept at 90°C for 2 hours. The NCO content of the resultant urethane prepolymer composition was 3.91% on solids (theoretically 4.13%). The prepolymer composition was cooled down to 75°C and TEA (52.0 gram) was added and the resulting mixture was stirred for 15 minutes. A dispersion of the resultant composition was made by feeding 699 gram of this composition to a mixture of 68.5 gram of adipic dihydrazide (1.2 SA) in 1742.3 gram demineralized water at room temperature in 60 minutes. The dispersion was stirred for another 4 h after which it was filtered over a 400 mesh filter. The dispersion thus obtained had the following characteristics: Solids = 29.9 wt%; pH = 7.8; Viscosity = 43 mPa.s.The amount of free dihydrazide in the dispersion of Comparative Examples 1-2 and Examples 1-16 was determined with the method as described herein above. The results (based on the solids content of the dispersion) are reported in Table 2.Table 2: Amount of free dihydrazide in the dispersion, based on the solids content of the dispersionTesting of the heat seal strength of primer layer obtained from the dispersions of Comparative Examples 1-3 and Examples 1-16

[0128] The waterborne dispersion of Comparative Examples 2,3 and Examples11-16 were diluted to 20 wt.% solids with demi water. These dispersions and the dispersions of Comparative Example 1 and Examples 1-10 were applied as a primer layer on a biaxially- oriented polypropylene film (Label -Lyte™ 29-LL-210, obtained from Jindal Films, having a thickness of 29 micrometer and corona treated with 60 Watt / m2) with a 6 micron wire rod.The film was dried for 20 seconds at 80°C in an oven and a primer layer was obtained. The primer layer has a coat weight of 1.1 to 1.2 gram per square meter.On top of the primer layer, an acrylic heat seal coating composition was applied. This coating composition was obtained by formulating NeoCryl® FL-721 (obtained from Covestro AG) with 6 wt.% Michem® Lube 160 (obtained from Michelman, Inc.) and 0.2 wt.% Syloid® 7000 silica (obtained from W.R. Grace & Co.). The formulation was diluted to 10 wt. % solids with demi water and applied on top of the primed biaxially-oriented polypropylene film. The application was done with a 12 micron wire rod. The heat seal coating composition was dried for 20 seconds at 80°C in an oven. In this way a coat weight of 1.2 gram per square meter was applied for the heat seal coating. This coated substrate was stored for 12 days at room temperature RT.Two coated substrates were heat sealed together with the coating side facing each other. The heat-sealing was done with a Brugger HSG-C heat sealer (B rugger Feinmechanik GmbH). The heat sealer was equipped with a flat, heated metal jaw (the upper one) and a flat Teflon jaw (the lower one). Both jaws have a dimension of 2 cm x 15 cm.The heat seal conditions were: temperature 130 °C, dwell time 0.2 seconds and heat seal pressure of 780 N.After heat sealing, the film was cooled down to room temperature. The heat sealed film was cut in 4 sealed test specimens of 1 inch width and a length of 15 cm, with the heat seal joint in the middle of the length.The strength of the heat seal joint was measured in a 180° peel test using an Instron tensiometer (Instron tensile tester 3343 from Illinois Tool Works Inc.) with a load cell of 500 N, which was connected to a computer provided with software of Instron. Each leg of a sealed test specimen was clamped in the tensile tester. The sealed area of the specimen was approximately equidistant between the grips of the tensile tester. The specimen was aligned in the grips so that the heat seal joint was perpendicular to the direction of pull. The tensile strength was determined at a testing speed of 300 mm / min. The tensile strength was determined as the maximum force encountered as the specimen is stressed to failure. The tensile strengths are reported in Table 3.When subjecting the waterborne dispersions of the present invention (if applicable, diluted to 20 wt.% solids with demi water) to the tensile strength test as described above, the tensile strength (heat seal strengths @130°C 12 days room temperature) is preferably at least 100 g / inch, more preferably at least 125 g / inch, even more preferably at least 150 g / inch, evenmore preferably at least 175 g / inch, even more preferably at least 200 g / inch, even more preferably at least 225 g / inch, even more preferably at least 250 g / inch.Table 3: Heat seal strengths @130°C 12 days RT

Claims

What is claimed is:

1. A waterborne polyurethane dispersion, wherein the dispersion comprises(a) a polyurethane (I) which comprises:(1) -NH-CO-HN-NH-CO-(R)n-CO-NH-NH-CO-NH- linkages, and(2) -NH-CO-HN-NH-CO-(R)n-CO-NH-NH2terminal groups, and(b) one or more dihydrazides B according to formula H2N-NH-CO-(R)n-CO-NH-NH2 (X), wherein n is 0 or 1, and in case n is 1, R is an aliphatic hydrocarbon group having from 1 to 18 carbon atoms or R is a cycloaliphatic hydrocarbon group having from 5 to 12 carbon atoms, wherein the polyurethane (I) is obtained by at least: providing an isocyanate group-functional prepolymer A composition comprising an isocyanate group-functional prepolymer A, wherein the isocyanate group-functional prepolymer A is obtained by reacting at least one or more polyisocyanates with aliphatic reactivity and one or more polyols, adding one or more chain extending compounds having isocyanatereactive groups to the isocyanate group-functional prepolymer A composition, and reacting at least the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups, wherein the one or more chain extending compounds comprise, consist essentially of, or consist of the one or more dihydrazides B according to formula (X); wherein the reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the substantial absence of ketone- and / or aldehyde- functional organic solvents; and wherein the dispersion comprises the one or more dihydrazide B with formula (X) in an amount of at least 1000 ppm, based on the solids content of the dispersion, wherein the amount of the dihydrazide B with formula (X) in the dispersion is determined with the method as specified in the description.

2. The waterborne polyurethane dispersion according to claim 1, wherein the dispersion comprises the one or more dihydrazide B with formula (X) in an amount, based on the solids content of the dispersion, of at least 2000 ppm, preferably of at least 3000 ppm, more preferably of at least 4000 ppm, even more preferably of at least 5000 ppm, wherein the amount of the one or more dihydrazide B with formula (X) is determined with the method as specified in the description.

3. The waterborne polyurethane dispersion according to any of the preceding claims, wherein the dispersion comprises the one or more dihydrazide B with formula (X) in an amount, based on the solids content of the dispersion, of at most 300000 ppm, preferably of at most 250000 ppm, more preferably of at most 200000 ppm, even more preferably of at most 150000 ppm, even more preferably of at most 100000 ppm, even more preferably of at most 75000 ppm, wherein the amount of the one or more dihydrazide B with formula (X) is determined with the method as specified in the description.

4. The waterborne polyurethane dispersion according to any of the preceding claims, wherein n is 0 (i.e., the dihydrazide (B) being oxalic dihydrazide (CAS number 996- 98-5)) or n is 1 and R is an aliphatic hydrocarbon group having from 1 to 10 carbon atoms, preferably having from 2 to 8 carbon atoms, more preferably from 2 to 5 carbon atoms.

5. The waterborne polyurethane dispersion according to any of claims 1 to 3, wherein the dihydrazide (B) is adipic acid dihydrazide (R = (CH^) (CAS number 1071-93-8).

6. The waterborne polyurethane dispersion according to any of the preceding claims, wherein the molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate groups present in the prepolymer A composition is at least 1.0, preferably at least 1.1, even more preferably at least 1.2, even more preferably at least 1.3, even more preferably at least 1.4, and at most 4.5, preferably at most 2.0, even more preferably at most 1.8; most preferably the molar ratio of isocyanate-reactive groups of the chain extending compounds to free isocyanate groups present in the prepolymer A composition is from 1.2 to 1.8.

7. The waterborne polyurethane dispersion according to any of the preceding claims, wherein the amount of ketone- and / or aldehyde-functional organic solvents that is present during said reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is such that the amount of ketone- and / or aldehyde-functional organic solvents, relativeto the isocyanate group-functional prepolymer A composition, is at most 5 wt.%, preferably at most 2 wt.%, more preferably at most 1 wt.%, more preferably at most 0.5 wt.%, more preferably at most 0.1 wt.%, more preferably at most 0.05 wt.%, more preferably at most 0.01 wt.%, more preferably at most 0.005 wt.%, more preferably at most 0.001 wt.%, most preferably said reacting of the isocyanate group- functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the absence of ketone- and / or aldehyde- functional organic solvents.

8. The waterborne polyurethane dispersion of any of the preceding claims, wherein, prior to reaction with said one or more chain extending compounds having isocyanate-reactive groups, the isocyanate group-functional prepolymer A is deprotonated with one or more neutralizing agents, wherein the one or more neutralizing agents are one or more trialkylamines, preferably the neutralizing agent is triethylamine.

9. The waterborne polyurethane dispersion according to any of the preceding claims, wherein the one or more chain extending compounds having isocyanate-reactive groups consist essentially of, or consist of, one or more dihydrazides B according to formula: H2N-NH-CO-(R)n-CO-NH-NH2 (X).

10. The waterborne polyurethane dispersion according to any of claims 1 to 9, wherein the one or more chain extending compounds having isocyanate-reactive groups comprise at least 5 mol%, more preferably at least 10 mol%, even more preferably at least 15 mol%, even more preferably at least 20 mol%, even more preferably at least 25 mol%, even more preferably at least 30 mol%, even more preferably at least 35 mol%, even more preferably at least 40 mol%, even more preferably at least 45 mol%, even more preferably at least 50 mol%, even more preferably at least 55 mol%, even more preferably at least 60 mol%, even more preferably at least 65 mol%, even more preferably at least 70 mol%, even more preferably at least 75 mol%, even more preferably at least 80 mol%, even more preferably at least 85 mol%, even more preferably at least 90 mol%, even more preferably at least 95 mol%, most preferably 100 mol%, of one or more dihydrazides B according to formula: H2N-NH-CO-(R)n-CO-NH-NH2 (X), relative to the total amount of chain extending compounds having isocyanate-reactive groups.

11. The waterborne polyurethane dispersion according to any of the preceding claims, wherein the ratio of the molar amount of hydrazide groups of the dihydrazide B to themolar amount of free isocyanate groups of the prepolymer A composition available for the reaction with hydrazide groups is at least 1.0, preferably at least 1.1, even more preferably at least 1.2, even more preferably at least 1.3, even more preferably at least 1.4, and at most 4.5, preferably at most 2.0, even more preferably at most 1.8, most preferably the ratio of the molar amount of hydrazide groups of the dihydrazide B to the molar amount of free isocyanate groups of the prepolymer A composition available for the reaction with hydrazide groups is from 1.2 to 1.8.

12. The waterborne polyurethane dispersion according to any of the preceding claims, wherein the isocyanate group-functional prepolymer A comprises as building blocks:(a) At least one polyisocyanate with aliphatic reactivity,(b) At least one isocyanate-reactive polyol with ionic or potential ionic waterdispersing groups (which become ionic when deprotonated), and(c) At least one isocyanate-reactive polyol different from component (b).

13. The waterborne polyurethane dispersion according to claim 12, wherein the isocyanate-reactive polyol (c), which is different from component (b), is selected from the group consisting of polyether polyols, polyester polyols, and any combination thereof.

14. The waterborne polyurethane dispersion according to any of the preceding claims, wherein the polyurethane (I) is free of ketone groups which are reactive with hydrazide groups and / or free of allyl groups which are reactive with hydrazide groups.

15. The waterborne polyurethane dispersion according to any of the preceding claims, wherein the dispersion has an (calculated) acid value in the range of from 1 to 75 mg KOH / g solids of the dispersion, preferably from 2 to 50 mg KOH / g solids of the dispersion, more preferably from 5 to 40 mg KOH / g solids of the dispersion, even more preferably from 5 to 30 mg KOH / g solids of the dispersion, even more preferably from 10 to 20 mg KOH / g16. A process for preparing the waterborne polyurethane dispersion according to any of the preceding claims, wherein the process comprises:(1) Reacting at least one or more polyisocyanates with aliphatic reactivity and one or more polyols to obtain an isocyanate group-functional prepolymer A composition comprising an isocyanate group-functional prepolymer A,(2) Adding one or more chain extending compounds having isocyanate-reactive groups to the isocyanate group-functional prepolymer A composition, and(3) Reacting at least the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups, wherein the one or more chain extending compounds comprise, consist essentially of, or consist of one or more dihydrazides B according to formula (X); wherein the one or more dihydrazide B with formula (X) are added to the isocyanate group-functional prepolymer A composition in such an amount that the one or more dihydrazides B with formula (X) are present in the dispersion in an amount of at least 1000 ppm, based on the solids content of the dispersion, wherein the amount of the dihydrazide B with formula (X) in the dispersion is determined with the method as specified in the description; and wherein the reacting of the isocyanate group-functional prepolymer A with said one or more chain extending compounds having isocyanate-reactive groups is carried out in the substantial absence of ketone- and / or aldehyde-functional organic solvents.

17. A primer composition comprising the waterborne polyurethane dispersion according to any of claims 1 to 15 or obtained with the process according to claim 16.

18. An article comprising a primer layer obtained from a primer composition as claimed in claim 17.

19. The article of claim 18, wherein the article comprises (1) a substrate comprising, consisting essentially of, or consisting of hydrophobic plastic, and (2) a primer layer that is disposed on at least a part of the substrate, wherein the primer layer is obtained from the primer composition as claimed in claim 17.

20. The article of claim 19, wherein the hydrophobic plastic comprises, consists essentially of, or consists of polyethylene, polypropylene, biaxially oriented polypropylene and / or PET, preferably the hydrophobic plastic comprises, consists essentially of, or consists of biaxially oriented polypropylene, wherein the hydrophobic plastic preferably has been corona treated.

21. A food contact packaging comprising the article according to any of claims 18 to 20.

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