HK1167420A - Low-solvent or solvent-free crosslinker dispersions with pyrazole-blocked isocyanate groups - Google Patents

Description

Low-solvent or solvent-free crosslinker dispersions containing pyrazole-blocked isocyanate groups

This application is a divisional application of the applicants' invention patent application entitled "Low solvent or solvent free crosslinker Dispersion containing pyrazole blocked isocyanate groups" filed on 30/5/2007 under application number 200710109808.3.

Cross Reference to Related Applications

The present application claims priority from german patent application No. 102006025313.2 filed on 31/5/2006 according to 35u.s.c. § 119(a) - (d).

Background

The invention relates to the production of aqueous, solvent-free or low-solvent, storage-stable PU crosslinker dispersions containing pyrazole-blocked isocyanate groups, to coating compositions produced from these dispersions and to their use in coatings.

In recent years, the use of aqueous paints and coating compositions has increased dramatically with increasingly stringent emission indications of solvent release during paint application. Although waterborne paint systems are currently available for many application areas, these systems generally do not achieve the high quality of conventional solvent-based paints in terms of solvent and chemical resistance, elasticity and mechanical durability.

Even aqueous paint systems based on aqueous polyurethane dispersions generally contain considerable amounts of solvents. Complete elimination of these solvents is generally not possible with polyurethane dispersions, since the preparation of such dispersions by means of prepolymers usually necessitates the use of solvents or generally requires the addition of so-called cosolvents (coalescents) to the dispersions in order to achieve a reduction in the minimum film-forming temperature. The co-solvent ensures that when a film is formed from the coating composition (even at or below room temperature), the hardness of the formed coating is sufficiently high. In addition, polyurethane dispersions and paint formulations generally lack storage stability in the absence of solvents.

The solvent N-methylpyrrolidone (NMP) is particularly widely used in the field of aqueous dispersions and paints. For example, EP-A0942023 describes carboxylic-hydrophilicized polyisocyanate crosslinker dispersions containing dimethylpyrazole-blocked isocyanate groups which contain NMP as cosolvent.

The solventless preparation of the dimethylpyrazole-terminated polyisocyanate crosslinkers described in EP-A0942023 by solvent elimination is not possible due to the increase in viscosity.

The nonionically hydrophilicized polyisocyanate crosslinker dispersions containing pyrazole-blocked isocyanate groups described in WO 1997012924 contain about 7% of butanediol as cosolvent. Butanediol, like NMP, is distinguished by a relatively high boiling point. Removal of the butanediol to prepare a solventless dispersion is not possible.

DE 19914885 describes polyurethane dispersions containing dimethylpyrazole-blocked isocyanate groups for the preparation of glass fibre sizes (sizes). These dispersions are prepared using organic solvents which, after dispersion in water, are removed from the dispersion by distillation. Example 1 describes the preparation using a 62% strength by weight acetone solution. These dispersions are made with 30% to 90% of the polyol component in the prepolymer having a molecular weight of at least 350 g/mol. Due to the high proportion of soft segments of the dispersions described, they cannot be used as crosslinker components for high-value coating compositions, since these paints do not achieve sufficient hardness.

DE 3613492 describes the acetone process for preparing cosolvent-free polyurethane-polyurea dispersions. The prepolymer, which in this case is not blocked, is prepared in a solution of a volatile organic solvent (e.g. acetone) in a concentration of 20 to 50% by weight, is then dispersed in water, and the solvent is removed by distillation.

In the process of EP-A0942023, 50% by weight or 62% by weight of acetone, as described in DE 19914885, are used instead of NMP to give dimethylpyrazole-terminated polyisocyanate crosslinkers which are not storage-stable.

It was therefore an object of the present invention to provide storage-stable polyurethane dispersions having pyrazole-blocked isocyanate groups, which can be obtained in a similar manner to that described in EP-A0942023, but which are solvent-free or low-solvent, in particular free of NMP or butanediol. Furthermore, coatings produced from these dispersions should have good film optical properties, good chemical resistance and pendulum hardness of more than 80 seconds.

Summary of The Invention

It has now been found that the above objects can be achieved by specific preparation processes. The present invention provides a process for preparing a dispersion of a blocked polyurethane prepolymer comprising:

I) preparing a blocked polyurethane prepolymer by reacting a) with b), c), d) and e):

a)100 equivalent% of at least one polyisocyanate,

b) 50-90 equivalent%, based on the isocyanate-reactive groups, of a thermally-eliminable blocking agent,

c) 5-45% by weight, based on the isocyanate-reactive groups, of a monohydroxycarboxylic acid as hydrophilicizing agent,

d) 0 to 25 equivalent%, based on isocyanate-reactive groups, of polyhydroxycarboxylic acids as hydrophilicizing agents,

e) from 0 to 15 equivalent%, based on the isocyanate-reactive groups, of a chain extender component which is at least difunctional or polyfunctional, based on the isocyanate-reactive groups, and has a molecular weight of from 32 to 350 g/mol,

wherein the content of the first and second substances,

i) step I) is carried out using a (partially) water-miscible organic solvent which is inert towards NCO groups and has a boiling point of less than 120 ℃ at 1013 mbar, and

ii) the components a) to e) and the organic solvent are used in such amounts that the content of the polyurethane prepolymer in the reaction solution after complete reaction is from 70% to 98% by weight,

II) at least partially deprotonating the carboxylic acid group with a base before, during or after step (III),

III) dispersing the polyurethane prepolymer solution obtained from step (I) in water, and

IV) distillation of the dispersion to completely remove the organic solvent, the distillation being carried out during or after step III).

The invention also provides dispersions obtainable by the process of the invention.

Detailed description of the preferred embodiments

In the above and in the claims, "completely removed" means that less than 5% by weight, preferably less than 3% by weight, more preferably less than 1.5% by weight of solvent remains in the dispersion after distillation.

The proportion of the reaction-participating substances is preferably: the equivalent ratio of isocyanate-reactive groups of isocyanate component a) to components b), c), d) and e) is from 1: 0.5 to 1: 1.7, more preferably from 1: 0.6 to 1: 1.5, and particularly preferably from 1: 0.7 to 1: 1.3.

Polyisocyanates suitable for use in a) are NCO-functional compounds known to the person skilled in the art, preferably having a functionality of 2 or more. These compounds are generally aliphatic, cycloaliphatic, araliphatic and/or aromatic diisocyanates or triisocyanates, and also those having imino groupsDiazinediones, isocyanurates, uretdiones, urethanes, allophanates, biurets, ureas, uretdiones,diazinetrione,Higher molecular weight derivatives of oxazolidinone, acylurea and/or carbodiimide structures, said derivatives also having two or more free NCO groups.

Examples of such diisocyanates or triisocyanates are 1, 4-butanediol, cyclohexane 1, 3-and 1, 4-diisocyanate, 1, 6-Hexamethylene Diisocyanate (HDI), 1-isocyanato-3, 3, 5-trimethyl-5-isocyanato-methylcyclohexane (isophorone diisocyanate, IPDI), methylene-bis (4-isocyanatocyclohexane), tetramethylxylylene diisocyanate (TMXDI), triisocyanatononane, Tolylene Diisocyanate (TDI), diphenylmethane-2, 4 ' -and/or 4, 4 ' -diisocyanate (MDI), triphenylmethane 4, 4 ' -diisocyanate, 1, 5-naphthalene diisocyanate, 4-isocyanatomethyloctane 1, 8-diisocyanate (nonane triisocyanate, triisocyanatononane, TIN) and/or 1, 6, 11-undecane triisocyanate and any desired mixtures of the above, and optionally mixtures of other diisocyanates, triisocyanates and/or polyisocyanates.

The isocyanate content of such polyisocyanates is generally from 0.5 to 50% by weight, preferably from 3 to 30% by weight, more preferably from 5 to 25% by weight.

Particular preference is given to using diisocyanates based on aliphatic and/or cycloaliphatic diisocyanatesHaving isocyanurate, urethane, allophanate, biuret, imino groupsDiazinedione,Higher molecular weight compounds of diazinetrione and/or uretdione groups.

Particular preference is given to using biuret, imino groups having biuret, based on 1, 6-hexamethylene diisocyanate, isophorone diisocyanate and/or 4, 4' -diisocyanatodicyclohexylmethaneHigher molecular weight compounds of diazinedione, isocyanurate and/or uretdione groups.

The blocking agents of component b) which are preferably used are 1H-pyrazoles, such as pyrazole, 3-methylpyrazole or 3, 5-dimethylpyrazole. Particularly preferably, 3, 5-dimethylpyrazole, which is readily available (for example, obtained by condensing hydrazine hydrate with acetylacetone), is used. In addition, mixtures of these blocking agents and mixtures thereof with other blocking agents, such as butanone oxime, acetone oxime, N-tert-butylbenzylamine and/or diisopropylamine, may be used.

Suitable monohydroxycarboxylic acids of component c) are, for example, 2-hydroxyacetic acid, 3-hydroxypropionic acid, 12-hydroxy-9-octadecanoic acid (ricinoleic acid), hydroxypivalic acid (2-hydroxymethyl-2-methylpropionic acid) or lactic acid. Hydroxypivalic acid is preferred.

Suitable polyhydroxycarboxylic acids of component d) are, for example, dihydroxycarboxylic acids, such as dimethylolacetic acid, 2-dimethylolbutyric acid, 2-dimethylolpentanoic acid, dihydroxysuccinic acid, dimethylolbutyric acid or dimethylolpropionic acid. Dimethylolpropionic acid is preferred.

In addition to the hydrophilization by means of at least one hydroxycarboxylic acid, it is also possible to use suitable compounds having a nonionic hydrophilization. Suitable nonionically hydrophilic compounds are, for example, polyoxyalkylene ethers which contain at least one hydroxyl or amino group. These polyethers are obtained by conventional methods by alkoxylation of suitable starter molecules.

Examples of suitable starter molecules are saturated monoalcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, the isomers pentanols, hexanols, octanols and nonanols, n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecanol, cyclohexanol, the isomeric methylcyclohexanols or hydroxymethylcyclohexane, 3-ethyl-3-hydroxymethyloxetane or tetrahydrofurfuryl alcohol, diethylene glycol monoalkylethers, such as diethylene glycol monobutyl ether, for example, unsaturated alcohols, such as allyl alcohol, 1-dimethylallyl alcohol or oleyl alcohol, aromatic alcohols, such as phenol, the isomeric cresols or methoxyphenols, araliphatic alcohols, such as benzyl alcohol, anisyl alcohol or cinnamyl alcohol, secondary monoamines, such as dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, di (2-ethylhexyl) amine, N-methyl-and N-ethylcyclohexylamine or dicyclohexylamine, and also heterocyclic secondary amines, such as morpholine, pyrrolidine, piperidine or 1H-pyrazole. Preferred starter molecules are saturated monoalcohols. Particular preference is given to using diethylene glycol monobutyl ether as starter molecule.

Alkylene oxides which are particularly suitable for the alkoxylation reaction are ethylene oxide and propylene oxide, which can be used in any order or as a mixture in the alkoxylation reaction. It is preferred that the ethylene oxide and propylene oxide blocks are added to the starter.

The polyoxyalkylene polyether is a simple polyethylene oxide polyether or a mixed polyoxyalkylene polyether in which at least 30 mol%, preferably at least 40 mol%, of the alkylene oxide units consist of ethylene oxide units. Preferred nonionic compounds are monofunctional mixed polyoxyalkylene polyethers containing at least 40 mol% of ethylene oxide units and not more than 60 mol% of propylene oxide units.

The amount of ethylene oxide units is less than 5 wt.%, preferably less than 3 wt.%, more preferably less than 2 wt.%, based on the total solids content of components a) to e).

Examples of suitable chain extender components e) include diols, triols and/or polyols. Examples are ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, 1, 2-propanediol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, 1, 3-propanediol, butane-1, 4-diol, butane-1, 3-diol, butane-2, 3-diol, pentane-1, 5-diol, hexane-1, 6-diol, 2-dimethyl-1, 3-propanediol, 1, 4-dihydroxycyclohexane, 1, 4-dimethylolcyclohexane, octane-1, 8-diol, decane-1, 10-diol, dodecane-1, 12-diol, trimethylolpropane, castor oil, glycerol and/or mixtures of the products optionally with other diols, triols and/or polyols. Additionally, ethoxylated and/or propoxylated diols, triols and/or polyols such as ethoxylated and/or propoxylated trimethylolpropane, glycerol and/or hexane-1, 6-diol may be used.

In addition, diamines, triamines and/or polyamines having primary and/or secondary amino groups can be used. Examples are ethylenediamine, 1, 3-propylenediamine, 1, 6-hexamethylenediamine, isophoronediamine, 4' -diaminodicyclohexylmethane, diethylenetriamine or hydrazine.

In addition, hydroxides such as adipic acid dihydroxide may also be used.

Mixtures of amines and alcohols may also be used, and compounds having mixed functionalities of different isocyanate-reactive groups may be used, such as N-methylethanolamine and N-methylisopropanolamine 1-aminopropanol, diethanolamine, 1, 2-hydroxyethylthiol or 1-aminopropanethiol.

Preferred chain extenders are butane-1, 4-diol, butane-1, 3-diol, hexane-1, 6-diol and/or trimethylolpropane. The molecular weight of the chain extender of component e) is preferably from 32 to 350 g/mol, more preferably from 62 to 200 g/mol.

To accelerate the urethanization, a catalyst may also be added to the reaction mixture. Examples of suitable catalysts include tertiary amines, tin compounds, zinc compounds or bismuth compounds or basic salts. Preference is given to dibutyltin dilaurate and dibutyltin octoate.

Suitable as (part of) the water-miscible solvent of component i) are aliphatic ketones or aliphatic or cycloaliphatic ethers. Examples of such solvents are acetone, methyl ethyl ketone, tert-butyl methyl ether or tetrahydrofuran. Preference is given to aliphatic ketones having from 3 to 6 carbon atoms. Acetone is particularly preferred.

Mixtures of the solvents may also be used.

The solvent is used in such an amount that the content of the polyurethane polymer in the reaction solution is 70 to 98% by weight, preferably 80 to 95% by weight.

The solvent may be added in portions or all at once. In each step, the addition is carried out before the dispersion. In a preferred mode, the solvent is added when some of the isocyanate groups have reacted while still some free isocyanate groups are present.

The removal of the solvent by distillation is preferably carried out in vacuo.

The advantage of this process is that the viscosity is reduced in the preparation of the prepolymer and that no significant amount of solvent is present in the dispersion.

Examples of deprotonating agents used in step II) are basic compounds such as ammonia, triethylamine, N-dimethylaminoethanol, dimethylcyclohexylamine, triethanolamine, methyldiethanolamine, diisopropanolamine, ethyldiisopropylamine, diisopropylcyclohexylamine, N-methylmorpholine, 2-amino-2-methyl-1-propanol or any desired mixtures thereof. Preferred deprotonating agents are 2-amino-2-methyl-1-propanol and tertiary amines such as triethylamine and N, N-dimethylethanolamine, particularly preferably N, N-dimethylethanolamine.

The amount of deprotonating agent is generally calculated such that the degree of deprotonation of the carboxylic acid groups present in the polyurethanes of the invention (molar ratio of amine used to acid groups present) is at least 40%, preferably from 70% to 130%, more preferably from 90% to 110%. The deprotonation step is carried out before, during and after the dispersing step. Preferably, however, the deprotonation step is carried out before the addition of water.

For dispersion in water according to step III), the polyurethane prepolymer solution may optionally be added to the dispersion water under strong shear (e.g., vigorous stirring), or the dispersion water may be added to the prepolymer solution with stirring. It is preferred to add water to the dissolved prepolymer.

After dispersion, in step IV), the solvent is completely removed by distillation (as described above). Preferably, the distillation is carried out in vacuo at a temperature of 20 to 70 deg.C (more preferably 30 to 50 deg.C). The vacuum is preferably set at 50-500 mbar, more preferably at 100-200 mbar. In this case, the desired temperature can first be set and the vacuum adjusted to the value required for the distillation or vice versa. In a preferred procedure, the vacuum is initially set at 100 and 200 mbar and the dispersion is then heated from room temperature to 40 ℃.

In a preferred embodiment of the process according to the invention, the polyisocyanate (component I) a)) is initially charged and is partially blocked with a portion of DMP (as blocking agent for component I) b)) in a first reaction stage at about 70 ℃. Preferably, in this first step, 25 to 60 equivalent% of the isocyanate groups are reacted. The remaining isocyanate-reactive components and solvent are then added successively and the reaction mixture is heated under reflux until no more isocyanate groups are detected. In a preferred embodiment, the acid groups are subsequently deprotonated in whole or in part with a base, then dispersed in water and the acetone removed under vacuum.

The dispersions of the invention have an average particle size (determined, for example, by LCS measurement, measured at 23 ℃ after dilution of the sample with about 100 volumes of deionized water, equipment: Malvern Zetasizer 100, Malvern Instr. Limited) of from 5 to 300 nm, preferably from 10 to 150 nm. This range applies to at least 90% of the particles, preferably at least 75%, more preferably at least 60%.

The solids content of the dispersion is preferably from 20 to 55% by weight, more preferably from 25 to 45% by weight.

The blocked polyisocyanate dispersions of the invention can be used, for example, for preparing bakeable coating compositions (stoving lacquers) for coating substrates, preferably substrates made of metal, mineral, glass, wood or plastic. For this purpose, the coating of the invention can be applied by spreading, knife coating, dipping, spraying (for example compressed air spraying or airless spraying) and electrostatic application (for example high-speed rotating belt application). The thickness of the dry film is, for example, 10 to 120 μm. The dry film can be cured by baking at a temperature of 90-190 deg.C, preferably 110-180 deg.C, more preferably 120-160 deg.C.

The invention therefore also provides for the use of the blocked polyurethane prepolymer dispersions of the invention for the preparation of coatings, adhesives, sealants and elastomers.

The invention also provides coatings, adhesives, sealants and elastomers obtainable using the dispersions of the invention.

The invention also provides substrates having a coating obtainable using the coating of the invention.

For the preparation of coatings (stoving lacquers), adhesives and elastomers, the polyisocyanate crosslinker dispersions of the invention having blocked isocyanate groups can be mixed with at least one difunctional isocyanate-reactive compound, examples being any desired polyol component, preferably in the form of an aqueous dispersion.

Such polyol components may be polyhydroxy polyesters, polyhydroxy polyurethanes, polyhydroxy polyethers, polycarbonate diols or hydroxyl-containing addition polymers, examples being conventional polyhydroxy polyacrylates, polyacrylate-polyurethanes and/or polyurethane-polyacrylates. The hydroxyl number of these components is generally from 20 to 200, preferably from 50 to 130 mg KOH/g. The hydrophilic modification of these polyhydroxyl compounds, which is generally necessary for the preparation of dispersions, is effected by customary methods, for example those described in EP-A-0157291, EP-A-0498156 or EP-A-0427028.

Other cross-linking during baking can also be carried out using mixtures of other alcohol-reactive compounds, for example amino cross-linker resins, such as melamine resins and/or urea resins.

The preparation of paints, inks, adhesives and other formulations from the dispersions of the invention is accomplished by conventional methods. Typical additives and other auxiliaries (examples are pigments, fillers, flow control agents, defoamers, catalysts) can be added to these formulations in addition to the blocked polyisocyanate and polyol.

Examples

Chemical product

Desmodur N 3300：

Isocyanurates based on 1, 6-hexamethylene diisocyanate, Bayer MaterialScience AG, Leverkusen, Germany

Desmodur W：

4, 4' -diisocyanatodicyclohexylmethane, Bayer MaterialScience AG, Leverkusen, Germany

Bayhydrol D 270：

Hydroxyl-containing aqueous polyester dispersions, Bayer MaterialScience AG, Leverkusen, Germany

Additol XW 395

Flow control aid/defoamer, UCB Chemical, St. Louis, USA

Surfynol 104

Flow control aids/defoamers, Air Products, Hattingen, Germany

Hydroxy pivalic acid

Perstorp Specialty Chemicals AB, Perstorp, Sweden

Other chemicals were purchased by chemical trade (Sigma-Aldrich Chemie GmbH, Taufkirchen, germany).

All percentages are by weight unless otherwise indicated.

All analytical tests involved a temperature of 23 ℃ unless otherwise indicated.

The reported viscosity was determined by rotational viscometry, which was carried out according to DIN 53019 at 23 ℃ using an rotational viscometer from Anton Paar Germany GmbH of Ostfildern, Germany.

The NCO content is determined by volume in accordance with DIN-EN ISO 11909, unless otherwise mentioned.

The reported particle size was determined from laser correlation spectroscopy (equipment: Malvern Zetasizer 1000, Malvern Instr. Limited).

The solids content was determined by the following steps: the weighed sample was heated at 120 ℃ and when a constant weight was reached, the sample was reweighed and the solids content calculated.

By infrared spectroscopy (2260 cm)^-1Band at (b) was monitored for free NCO groups.

As a storage test, the dispersions were testedPortioned 250 ml and stored at room temperature or 40 ℃. The respective storage times were recorded for the respective examples. The stability value was determined on the basis of a bottom area of 25cm²The resulting height of the precipitate in the vessel. A height of more than 0.5 mm is considered to be unstable.

1) Comparative example 1: cross-linker dispersions not according to the invention, prepared according to example 1 of EP-A0942023, but without NMP and co-solvent

To a standard stirring apparatus 200 grams (1 eq) of Desmodur N3300 was added and the initial charge was heated to 50 ℃ under nitrogen. A portion of 3, 5-Dimethylpyrazole (DMP) (48.0 g; 0.5 eq.) was then added to the melt in portions over 30 minutes. The melt was stirred at 70-80 ℃ until the isocyanate content was about 8.5%.

The melt was mixed with 29.0 g (0.25 eq) of hydroxypivalic acid and stirred at 65 ℃ until the isocyanate content reached 3.8%.

Then, another 24.0 g (0.25 eq) of DMP were added and the batch was stirred at 65 ℃ until no more isocyanate groups were detected by IR spectroscopy. At this point, the prepolymer became very viscous and partially entangled around the stirrer.

22.2 g (0.25 eq) of N, N-dimethylethanolamine were then added, stirred for 10 minutes and 451.4 g of 70 ℃ deionized water were added with vigorous stirring.

The properties of the resulting dispersion were as follows:

solid content: about 38 percent

pH: about 8.4

Viscosity: about 400mPas

Average particle size (LCS): 74 nm

Storage test: after storage at 40 ℃ for several days and at room temperature for two weeks, a large amount of precipitate formed.

The dispersion is not storage stable. Moreover, the preparability is problematic due to the high viscosity of the prepolymer.

2) Comparative example 2: the crosslinker dispersions not according to the invention, prepared according to example 1 of EP-A0942023, but without NMP, were prepared by the acetone method (acetone solution of prepolymer, 50% strength)

To a standard stirring apparatus 200 grams (1 eq) of Desmodur N3300 was added and the initial charge was heated to 50 ℃ under nitrogen. A portion of 3, 5-Dimethylpyrazole (DMP) (48.0 g; 0.5 eq.) was then added to the melt in portions over 30 minutes. The melt was stirred at 70-80 ℃ until the isocyanate content was about 8.5%. The melt was mixed with 29.0 g (0.25 eq) of hydroxypivalic acid and 302 g of acetone and stirred at 50-65 ℃ until the isocyanate content reached 1.8%.

Then, another 24.0 g (0.25 eq) of DMP were added and stirring was continued until no more isocyanate groups were detected by IR spectroscopy.

22.2 g (0.25 eq) of N, N-dimethylethanolamine were then added, followed by stirring for 10 minutes, and 451.4 g of 50 ℃ deionized water were added with vigorous stirring.

After removal of the acetone, distillation was carried out under vacuum (120 mbar) at about 40 ℃. The product was not a dispersion; and a large amount of white precipitate formed.

3) Comparative example 3: crosslinker Dispersion according to comparative example 2, but with an increased solids content in the prepolymer

The procedure described in comparative example 2 was repeated, using a 62% strength acetone solution of the prepolymer instead of the 50% solution.

In this case, too, no stable dispersion is formed.

4) Embodiment 1 of the present invention: the crosslinker dispersions of the invention, prepared according to example 1 of EP-A0942023, but without NMP, are prepared using small amounts of acetone (acetone solution of prepolymer, 95% strength)

The procedure described in comparative example 1 was repeated, but 16 g of acetone were added together with the hydroxypivalic acid. After the addition of deionized water, acetone was removed by distillation under vacuum (120 mbar) at about 40 ℃.

The properties of the resulting finely divided dispersion were as follows:

solid content: about 39 percent

pH: about 8.4

Viscosity: about 9600mPas

Average particle size (LCS): 36 nm

Storage test: can be stored stably at room temperature and 40 deg.C for at least 3 months.

5) Embodiment 2 of the present invention: the crosslinker dispersion according to the invention, prepared according to example 1 (acetone solution of prepolymer, concentration 85%)

The procedure described in comparative example 1 was repeated, but 45 g of acetone was added together with the hydroxypivalic acid. After the addition of deionized water, acetone was removed by distillation under vacuum (120 mbar) at about 40 ℃.

The properties of the resulting finely divided dispersion were as follows:

solid content: about 39 percent

pH: about 8.7

Viscosity: about 1300mPas

Average particle size (LCS): 38 nm

Storage test: can be stored stably at room temperature and 40 deg.C for at least 3 months.

6) Embodiment 3 of the present invention: the crosslinker dispersion according to the invention, prepared according to example 1 (acetone solution of prepolymer, concentration 70%)

The procedure described in comparative example 1 was repeated, but 129 g of acetone were added together with the hydroxypivalic acid. After the addition of deionized water, acetone was removed by distillation under vacuum (120 mbar) at about 40 ℃.

The properties of the resulting finely divided dispersion were as follows:

solid content: about 38 percent

pH: about 8.9

Viscosity: about 165mPas

Average particle size (LCS): 22 nm

Storage test: can be stored stably at room temperature and 40 deg.C for at least 3 months.

7) Example 4: the crosslinker dispersions of the invention, chain extended with a diol component, were prepared with a small amount of acetone (acetone solution of prepolymer, concentration 90%)

429.0 g (2.2 eq) of Desmodur N3300 was added to a standard stirring apparatus and the initial charge was heated to 70 ℃ under nitrogen. A portion of DMP (76.9 g; 0.8 eq.) was then added to the melt in portions over 30 minutes. The melt was stirred at 70 ℃ until the theoretical isocyanate content reached 11.62% or less than 11.62%.

The following components were added to the melt successively: 63 g of acetone; 11.8 grams (0.2 eq.) of 1, 6-hexanediol; 47.2 g (0.4 eq) of hydroxypivalic acid; and another portion of 57.7 grams (0.6 equivalents) of DMP. The mixture was then stirred at reflux until no isocyanate groups were detected by infrared spectroscopy. 39.2 g (0.44 eq) of N, N-dimethylethanolamine was then added, followed by stirring for 10 minutes, and 976.6 g of 50 ℃ deionized water were added with vigorous stirring. The acetone was distilled off under vacuum (120 mbar) at about 40 ℃ and the dispersion was stirred at this temperature for a further 3 hours.

The properties of the resulting finely divided dispersion were as follows:

solid content: about 37 percent

pH: about 8.7

Viscosity: about 1000mPas

Average particle size (LCS): 14 nm

Storage test: can be stored stably at room temperature and 40 deg.C for at least 3 months.

8) Example 5: the crosslinker dispersions of the invention were chain extended with a triol component and prepared with a small amount of acetone (acetone solution of prepolymer, concentration 90%)

The procedure described in inventive example 4 was repeated, but the corresponding amount of OH groups was added instead of hexanediol by means of trimethylolpropane.

The properties of the resulting finely divided dispersion were as follows:

solid content: about 37 percent

pH: about 8.9

Viscosity: about 3000mPas

Average particle size (LCS): 14 nm

Storage test: can be stored stably at room temperature and 40 deg.C for at least 3 months.

9) Embodiment 6 of the present invention: the crosslinker dispersions of the invention are chain extended with a triol component, as described in example 5, but using mixtures of different polyisocyanates

The procedure of inventive example 5 was repeated but a mixture of 174.0 grams of Desmodur N3300 and 26 grams of Desmodur W was added in place of Desmodur N3300.

The properties of the resulting finely divided dispersion were as follows:

solid content: about 37 percent

pH: about 9.0

Viscosity: about 950mPas

Average particle size (LCS): 20 nm

Storage test: can be stored stably at room temperature and 40 deg.C for at least 3 months.

10) Embodiment 7 of the present invention: the crosslinker dispersions of the invention were prepared by hybrid hydrophilization with hydroxypivalic acid and dimethylolpropionic acid using a small amount of acetone (acetone solution of prepolymer, concentration 90%)

The procedure described in inventive example 5 was repeated, but with the hexanediol replaced by the corresponding amount of OH groups of dimethylolpropionic acid (13.4 g), the proportion of hydroxypivalic acid was reduced by 25%.

The properties of the resulting finely divided dispersion were as follows:

solid content: about 37 percent

pH: about 8.9

Viscosity: about 3500mPas

Average particle size (LCS): 13 nm

Storage test: can be stored stably at room temperature and 40 deg.C for at least 3 months.

Table 1: performance testing

(number unit: gram)

Preparation of the paint formulations, baking and testing of the clear varnishes

^*VP LS 2310, commercially available aqueous polyisocyanate dispersion blocked with butanone oxime, solids content 38%, Bayer MaterialScience AG, Leverkusen, Germany.

(1)1 minute, the order of solvents was as follows: xylene/methoxypropyl acetate/ethyl acetate/acetone:

evaluation: 0 is preferably-5

The solvent described must have chemical resistance equal to or less than 4.

(2) According to DIN 53157 byThe method measures the pendulum hardness. The pendulum hardness must be at least 80 seconds.

(3) The flow time was determined in accordance with DIN 53211.

Similar tests cannot be carried out on the comparative examples, since these contain already a large amount of precipitate at the start of the test. These precipitates prevent reliable paint testing by performance testing.

The polyisocyanate dispersions of the invention were found to be storage stable and the bakeable coating compositions of the invention meet the criteria in terms of film optical properties, chemical resistance and pendulum hardness.

Comprising a cross-linking agentThe coating of VP LS 2310 has a number of disadvantages compared to coatings comprising the crosslinkers of the present invention (low solids content of the coating formulation at comparable flow times, poorer chemical resistance, lower film hardness).

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (14)

1. A method of preparing a dispersion of a blocked polyurethane prepolymer comprising:

I) preparing a blocked polyurethane prepolymer by reacting a) with b), c), d) and e):

a)100 equivalent% of at least one polyisocyanate,

b) 50-90 equivalent%, based on the isocyanate-reactive groups, of a thermally-eliminable blocking agent,

c) 5-45% by weight, based on the isocyanate-reactive groups, of a monohydroxycarboxylic acid as hydrophilicizing agent,

d) 0 to 25 equivalent%, based on isocyanate-reactive groups, of polyhydroxycarboxylic acids as hydrophilicizing agents,

e) from 0 to 15 equivalent%, based on the isocyanate-reactive groups, of a chain extender component which is at least difunctional or polyfunctional, based on the isocyanate-reactive groups, and has a molecular weight of from 32 to 350 g/mol,

wherein the content of the first and second substances,

i) step I) is carried out using a (partially) water-miscible organic solvent which is inert towards NCO groups and has a boiling point of less than 120 ℃ at 1013 mbar, and

ii) the components a) to e) and the organic solvent are used in such amounts that the content of the polyurethane prepolymer in the reaction solution after complete reaction is from 70% to 98% by weight,

II) at least partially deprotonating the carboxylic acid group with a base before, during or after step (III),

III) dispersing the polyurethane prepolymer solution obtained from step (I) in water, and

IV) distillation of the dispersion to completely remove the organic solvent, the distillation being carried out during or after step III).

2. The method of preparing a dispersion of a blocked polyurethane prepolymer according to claim 1 where the polyisocyanate is a polyisocyanate based on a compound selected from the group consisting of: 1, 6-hexamethylene diisocyanate, isophorone diisocyanate, 4' -diisocyanatodicyclohexylmethane and mixtures thereof.

3. The method of preparing a dispersion of end-capped polyurethane prepolymer of claim 1 wherein said end-capping agent is 1H-pyrazole.

4. The method of preparing a dispersion of end-capped polyurethane prepolymer of claim 1 wherein said monohydroxy carboxylic acid is hydroxypivalic acid.

5. The method of preparing a dispersion of a blocked polyurethane prepolymer of claim 1 wherein the polyhydroxycarboxylic acid is dimethylolpropionic acid.

6. The method of preparing a dispersion of end-capped polyurethane prepolymer of claim 1 wherein said chain extender is selected from the group consisting of: butane-1, 4-diol, butane-1, 3-diol, hexane-1, 6-diol, trimethylolpropane and mixtures thereof.

7. The method of preparing a dispersion of end-capped polyurethane prepolymer of claim 1 wherein said (portion of) water miscible solvent is an aliphatic ketone having 3 to 6 carbon atoms.

8. The method of preparing a dispersion of blocked polyurethane prepolymer according to claim 1 wherein the base used in step II) is selected from the group consisting of: 2-amino-2-methyl-1-propanol, triethylamine, N-dimethylethanolamine and mixtures thereof.

9. The method of preparing a dispersion of blocked polyurethane prepolymer of claim 1 wherein in step IV) the solvent is removed from the dispersion to reduce the solvent content to less than 3 weight percent.

10. The process for preparing a dispersion of blocked polyurethane prepolymers according to claim 1 wherein the equivalent ratio of isocyanate components I) a) to isocyanate-reactive groups of components I) b), c), d) and e) is from 1: 0.5 to 1: 1.7.

11. The method of preparing a dispersion of blocked polyurethane prepolymers according to claim 1 wherein step II) is performed before step III).

12. A dispersion of blocked polyurethane prepolymer obtained by the process of claim 1.

13. A composition comprising a dispersion of the blocked polyurethane prepolymer of claim 12, said composition selected from the group consisting of: coating compositions, adhesives, sealants, and elastomers.

14. A substrate having a coating obtained using the dispersion of claim 12.