HK1100674A - Coating agent composition - Google Patents

Description

Coating composition

The present invention relates to coating compositions which are stable to thermal yellowing, to a process for their preparation and to their use.

Polyurethane-polyurea dispersions (PU dispersions) and aqueous formulations of PU dispersions are known from the prior art. Various types of PU dispersions and their aqueous formulations and a summary of the preparation processes can be found, for example, in Houben-Weyl: "Methoden der Organischen Chemie", volume E20, page 1659-1692 or "Ullmann's Encyclopedia of Industrial chemistry" (1992), volume A21, page 677-682. By virtue of their combination of advantageous properties such as mechanical strength, high adhesion to different substrates, solvent resistance, gloss, etc., they can be used extensively, for example, as paints and coatings. An important field of application for aqueous formulations of ionically modified PU dispersions is in the field of painting of plastic parts.

Aesthetic and technical requirements mean that the plastic parts are generally painted in order to protect the plastic from external influences, such as sunlight, chemicals, heat and mechanical stress, to obtain specific colors and color effects, to mask defects on the plastic surface or to give it a pleasant feel (touch). In order to improve the tactile properties of plastic parts, so-called soft-feel coatings have been increasingly used in recent years. "Soft feel effect" for purposes of the present invention refers to the specific tactile sensation (feel) of the coated surface; the feel can be described using words such as velvet-like, soft, rubber-like, warm, etc., however, for example, the surface of a painted vehicle body or an unpainted polymer sheet or a surface coated with a conventional clear coat or top coat and composed of ABS, Makrolon ® (polycarbonate, Bayer AG) or plexiglas (polymethyl methacrylate), for example, feels cold and smooth. In response to the tendency to prevent solvent emissions into the environment, the development of waterborne soft-feel coatings based on polyurethane chemicals has been seen in recent years, as disclosed in the teaching of DE 4406159. In addition to the excellent soft-feel effect, these coatings also form coatings with good resistance and protection of the plastic substrate. However, it has now been found that these coatings and coatings often have only inadequate yellowing stability.

It is therefore an object of the present invention to provide coatings which, in addition to the above-mentioned mechanical and tactile properties, also result in coatings having a significantly higher stability to thermal yellowing and/or a significantly lower level of thermal yellowing than prior art coatings.

As described in DE-A4406159, the plastics coating portions having the desired soft-touch properties are composed of PU dispersions which do not contain significant amounts of hydroxyl functional groups.

The prior art has disclosed a large number of stabilizers and additives which reduce the thermal yellowing of the binder. However, in the above field of aqueous PU dispersions without a large number of hydroxyl functions, the yellowing-inhibiting effect of these systems is inadequate, or they lead to a reduction in the industrial application properties of the dispersions and coatings, for example a reduction in the stress-strain properties (Ing-Dehnangsverhalter), or poor compatibility with other paint or coating components. Known additives also tend to migrate out of the formed coating, such that over time, undesirable fogging and a decrease in yellowing stability are formed.

U.S. Pat. No. 5,137,967 describes a process for preparing carboxylate-containing PU dispersions which are stable to thermal yellowing and are prepared by the so-called prepolymer mixing process. To obtain yellowing stability, hydrazine is used to chain extend the prepolymer and Dimethylaminoethanol (DMAE) is used as the neutralizing amine for the carboxylic acid groups.

DE-A3238169 describes a process for preparing PU dispersions using hydrazine or hydrazide as additive or chain extender. Only anionic carboxylate-functionalized PU dispersions prepared by a prepolymer mixing method are described.

Hydrazine and hydrazides as chain extenders in polyurethanes are known in principle, for example, from U.S. Pat. No. 4, 4147679 or DE-A2314513. In some cases they are also used in admixture with other chain extenders, such as diamines (US-a 3415768). They are used to improve the flexibility, hardness, resistance and drying of the coating.

It has now been found that coatings comprising non-functionalized PU dispersions prepared by the defined process using hydrazine as chain extender component meet the desired properties without the addition of specific external stabilizers/additives and without impairing the above-mentioned mechanical and tactile properties required in the coating.

The present invention therefore provides a coating comprising:

I) dispersions of one or more polyurethanes and/or polyurethane-ureas which do not contain hydroxyl groups (PU dispersions)

II) an aqueous solution or dispersion of one or more ionically modified, hydroxyl-containing polyurethanes and/or polyurethane-ureas of ingredients other than component I), and

III) at least one crosslinking agent and

IV) optionally other film-forming resins,

characterized in that the PU dispersions used in I) are obtained by the following steps:

A) polyurethane prepolymers containing NCO groups were first prepared by reacting component a1) with a2) to a 6):

A1) polyisocyanates

A2) Polymeric polyols and/or polyamines having a number average molecular weight of 400-8000g/mol

A3) Optionally low molecular weight compounds having a number average molecular weight of 17 to 400g/mol, selected from the group consisting of mono-and polyols, mono-and polyamines and aminoalcohols,

A4) isocyanate-reactive ionic or potentially ionic hydrophilic compounds and/or

A5) Isocyanate-reactive nonionically hydrophilicizing compounds

A6) Optionally in an aliphatic ketone as solvent,

with the proviso that all of components A1) to A5) contain no primary or secondary amino groups,

B) dissolving the prepolymer obtained from step A) in an aliphatic ketone or, if the preparation is carried out in the presence of A6), optionally diluting the prepolymer solution by further addition of an aliphatic ketone, and

C) reacting the remaining free NCO groups of the prepolymer with a chain extender component comprising C1) and C2):

C1) hydrazine and/or hydrazine hydrate

C2) Optionally compounds which meet the provisions of components A2), A3), A4) and/or A5),

the premise is that:

the compounds of component C2) containing primary and/or secondary amino groups,

c1) and C2) in such a total amount that a calculated degree of chain extension of 40 to 200% and

c1) and C2) in such a proportion that at least 40% of the free isocyanate groups are chain-extended with amino groups of component C1) and/or terminated with amino groups of component C1).

Suitable polyisocyanates of component A1) are aromatic, araliphatic, aliphatic or cycloaliphatic polyisocyanates, which are known per se to the person skilled in the art and may also contain iminooxadiazinedione, isocyanurate, uretdione, urethane, allophanate, biuret, urea, oxadiazinetrione, oxazolidinone, acylurea and/or carbodiimide structures. They may be used in A1) alone or as any desired mixtures with one another.

Examples of suitable aromatic, araliphatic, aliphatic or cycloaliphatic polyisocyanates are diisocyanates and/or triisocyanates having a molecular weight in the range from 140-400g/mol, which can be obtained by phosgenation or by phosgene-free processes, for example by thermal urethane cleavage, and which contain aliphatic, cycloaliphatic, araliphatic and/or aromatic structuresLinked isocyanates, for example 1, 4-diisocyanatobutane, 1, 5-diisocyanatopentane, 1, 6-diisocyanatohexane (HDI), 2-methyl-1, 5-diisocyanatopentane, 1, 5-diisocyanato-2, 2-dimethylpentane, 2, 2, 4-and/or 2, 4, 4-trimethyl-1, 6-diisocyanatohexane, 1, 10-diisocyanatodecane, 1, 3-and 1, 4-diisocyanatocyclohexane, 1, 3-and 1, 4-bis (isocyanatomethyl) cyclohexane, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 4, 4 '-diisocyanatodicyclohexylmethane (Desmodur ® W, Bayer AG, Leverkusen), 4-isocyanatomethyl-1, 8-octane diisocyanate (triisocyanatononane, TIN), omega' -diisocyanato-1, 3-dimethylcyclohexane (H)₆XDI), 1-isocyanato-1-methyl-3-isocyanatomethylcyclohexane, 1-isocyanato-1-methyl-4-isocyanatomethylcyclohexane, bis (isocyanatomethyl) norbornane, 1, 5-naphthalene diisocyanate, 1, 3-and 1, 4-bis (2-isocyanatoprop-2-yl) benzene (TMXDI), 2, 4-and 2, 6-diisocyanatotoluene (TDI), in particular the 2, 4-and 2, 6-isomers and the technical-grade mixtures of the two isomers 2, 4 '-and 4, 4' -diisocyanatodiphenylmethane (MDI), 1, 5-diisocyanatonaphthalene, 1, 3-bis (isocyanatomethyl) benzene (XDI) and any desired mixtures of the compounds mentioned.

Preference is given to using polyisocyanates or polyisocyanate mixtures of the type mentioned above in A1) which contain exclusively aliphatically and/or cycloaliphatically bonded isocyanate groups.

Particular preference is given to hexamethylene diisocyanate, isophorone diisocyanate and the isomeric bis (4, 4' -isocyanatocyclohexyl) methanes and also mixtures thereof.

Importantly, the compounds used in A2) -A5) need only be free of primary and/or secondary amine functional groups in order to be prepared. In contrast, in the sense of chain extension, compounds which meet the definition of components a2) to a5), but additionally contain primary and/or secondary amino groups, can be used in C2).

The polymeric polyols or polyamines meeting the definition of component A2) are generally derived from polyacrylates, polyesters, polylactones, polyethers, polycarbonates, polyestercarbonates, polyacetals, polyolefins and polysiloxanes and preferably have a functionality of from 1.5 to 4 based on NCO-reactive functional groups.

Particularly preferred polymeric polyols are those of the above-described type having a number average molecular weight of 600-2500g/mol and an OH functionality of 2-3.

Polycarbonates containing hydroxyl groups which meet the definition of component A2) can be obtained by reacting carbonic acid derivatives, for example diphenyl carbonate, dimethyl carbonate or phosgene, with diols.

Examples of suitable such diols include ethylene glycol, 1, 2-and 1, 3-propanediol, 1, 3-and 1, 4-butanediol, 1, 6-hexanediol, 1, 8-octanediol, neopentyl glycol, 1, 4-bis-hydroxymethylcyclohexane, 2-methyl-1, 3-propanediol, 2, 2, 4-trimethylpentane-1, 3-diol, dipropylene glycol, polypropylene glycol, dibutylene glycol, polybutylene glycol, bisphenol A, tetrabromobisphenol A and lactone-modified diols. Preferably, the diol component contains from 40 to 100% by weight of hexanediol, preferably 1, 6-hexanediol and/or hexanediol derivatives, particularly preferably derivatives which, in addition to terminal OH groups, contain ether or ester groups, for example products obtained by reacting 1mol of hexanediol with at least 1mol, preferably 1 to 2mol, of caprolactone (e.g.DE-A1770245), or dihexylene or trihexylene glycol formed by the self-etherification of hexanediol. The preparation of such derivatives is known, for example, from DE-A1570540. It is also possible to use the polyether-polycarbonate diols described in DE-A3717060.

The hydroxyl polycarbonates are preferably linear, but may, if desired, also be branched owing to the incorporation of polyfunctional components, in particular low molecular weight polyols. Examples suitable for this purpose include glycerol, trimethylolpropane, hexane-1, 2, 6-triol, butane-1, 2, 4-triol, trimethylolpropane, pentaerythritol, p-cyclohexanediol, mannitol, and sorbitol, methyl glycoside, and 1, 3, 4, 6-dianhydrohexitols.

Suitable polyether polyols meeting the definition of component A2) are the polytetramethylene glycol polyethers known per se in polyurethane chemistry, which can be prepared, for example, by cationic ring-opening polymerization of tetrahydrofuran.

Other suitable polyether polyols are polyethers, for example polyols prepared from styrene oxide, propylene oxide, butylene oxide or epichlorohydrin, in particular propylene oxide, using starter molecules.

Examples of suitable polyester polyols meeting the definition of component a2) include reaction products of polyhydric alcohols, preferably dihydric alcohols and optionally additional trihydric alcohols, with polybasic, preferably dibasic carboxylic acids. Instead of the free polycarboxylic acids it is also possible to use the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols or mixtures thereof for preparing the polyesters. The polycarboxylic acids may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic in nature and may optionally be substituted (for example by halogen atoms) and/or unsaturated.

In this process, a compound satisfying the definition of component A3) may be added to terminate the polyurethane prepolymer.

Compounds suitable for this purpose are, for example, aliphatic monoalcohols or monoamines of the stated molecular weight range having from 1 to 18 carbon atoms, such as ethanol, N-butanol, ethylene glycol monobutyl ether, 2-ethylhexanol, 1-octanol, 1-dodecanol, 1-hexadecanol, diethylamine, dibutylamine, ethanolamine, N-methylethanolamine, N, N-diethanolamine, amines of the Jeffamin ® M series (Huntsman Corp. in Belgium Europe) or amino-functionalized polyethylene oxides and polypropylene oxides.

In addition, polyols, aminopolyols or polyamines having a number average molecular weight of less than 400g/mol can be used in the process. These compounds which may be mentioned by way of example include:

a) alkanediols and/or triols, for example ethylene glycol, 1, 2-and 1, 3-propanediol, 1, 4-and 2, 3-butanediol, 1, 5-pentanediol, 1, 3-dimethylpropanediol, 1, 6-hexanediol, neopentyl glycol, 1, 4-cyclohexanedimethanol, 2-methyl-1, 3-propanediol, 2-ethyl-2-butylpropanediol, trimethylpentanediol, positionally isomeric diethyloctanediols, 1, 2-and 1, 4-cyclohexanediols, hydrogenated bisphenol A [2, 2-bis (4-hydroxycyclohexyl) propane ], 2, 2-dimethyl-3-hydroxypropionic acid (2, 2-dimethyl-3-hydroxypropyl ester), trimethylolethane, a trimethylolpropane or a glycerol, in which the glycerol is a glycerol,

b) ether glycols, such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, 1, 3-butanediol or hydroquinone dihydroxyethyl ether,

c) ester diols of the general formulae (I) and (II),

HO-(CH₂)_x-CO-O-(CH₂)_y-OH (I)

HO-(CH₂)_x-O-CO-R-CO-O-(CH₂)_x-OH (II)

wherein

R is an alkylene or arylene group having 1 to 10 carbon atoms, preferably 2 to 6 carbon atoms,

x is 2 to 6 and

y is 3 to 5.

For example, delta-hydroxybutyl-epsilon-hydroxy-hexanoate, omega-hydroxyethyl-gamma-hydroxybutyrate, adipic acid (. beta. -hydroxyethyl) ester, bis (. beta. -hydroxyethyl) terephthalate, and

d) diamines and polyamines, such as 1, 2-diaminoethane, 1, 3-diaminopropane, 1, 6-diaminohexane, 1, 3-and 1, 4-phenylenediamine, 4, 4 ' -diphenylmethanediamine, isophoronediamine, isomer mixtures of 2, 2, 4-and 2, 4, 4-trimethylhexamethylenediamine, 2-methylpentamethylenediamine, diethylenetriamine, 1, 3-and 1, 4-xylylenediamine, α, α, α ', α ' -tetramethyl-1, 3-and-1, 4-xylylenediamine, 4, 4-diaminodicyclohexylmethane, amino-functionalized polyethylene oxide or polypropylene oxide (which are commercially available from huntsman corp. of the european belgium under the name Jeffamin ®, series D), diethylenetriamine and triethylenetetramine. Other suitable diamines in the sense of the present invention include substituted hydrazines, such as N-methylhydrazine, N, N' -dimethylhydrazine and their homologues as well as hydrazides of adipic acid, beta-methyladipic acid, sebacic acid, hydroxypropionic acid (Hydracrylspheradien ure) and terephthalic acid, ureido-alkylene hydrazides, such as beta-ureidopropionohydrazide (as described, for example, in DE-A1770591), ureido-alkylene carbazepines, such as 2-ureidoethyl carbazepine (as described, for example, in DE-A1918504), or semicarbazide compounds, such as beta-aminoethyl semicarbazide-carbonate (as described in DE-A1902931).

By ionically and potentially ionically hydrophilic compound is meant a compound containing at least one isocyanate-reactive group and at least one functional group, such as-COOY, -SO₃Y，-PO(OY)₂(Y is e.g. ═ H, NH₄ ⁺Metal cations), -NR₂，-NR₃ ⁺(R ═ H, alkyl, aryl) which, upon interaction with aqueous media, reaches an optionally pH-dependent dissociation equilibrium, and thus can have a negative, positive or neutral charge.

Preferred isocyanate reactive groups are hydroxyl or amino groups.

Suitable ionically or potentially ionically hydrophilicizing compounds which meet the definition of component A4) are, for example, mono-and dihydroxycarboxylic acids, mono-and diaminocarboxylic acids, mono-and dihydroxysulfonic acids, mono-and diaminosulfonic acids, and also mono-and dihydroxyphosphonic acids or mono-and diaminophosphonic acids and their salts, for example dimethylolpropionic acid, dimethylolbutyric acid, hydroxypivalic acid, N- (2-aminoethyl) - β -alanine, 2- (2-aminoethylamino) ethanesulfonic acid, ethylenediamine propyl-or-butylsulfonic acid, 1, 2-or 1, 3-propylenediamine- β -ethanesulfonic acid, malic acid, citric acid, glycolic acid, lactic acid, glycine, alanine, taurine, lysine, 3, 5-diaminobenzoic acid, adducts of IPDI and acrylic acid (EP-A0916647, example 1) and their alkali metal and/or ammonium salts; adducts of sodium bisulfite with 2-butene-1, 4-diol, polyethersulfonates, 2-butanediol and NaHSO₃Propoxylated adducts of (A) and (B)Such as described in DE-A2446440 (pages 5 to 9, formulae I to III), and compounds which contain structural units which can be converted into cationic groups, for example amine-type structural units, such as N-methyldiethanolamine, as hydrophilic synthesis components. It is also possible to use Cyclohexylaminopropanesulfonic Acid (CAPS) as in WO 01/88006 as compound satisfying the definition of component a 4).

Preferred ionic or potentially ionic compounds are those having carboxyl or carboxylate groups and/or sulfonate groups and/or ammonium groups.

Particularly preferred ionic compounds are those which contain carboxyl and/or sulfonate groups as ionic or potentially ionic groups, for example salts of N- (2-aminoethyl) -beta-alanine, salts of 2- (2-aminoethylamino) ethanesulfonic acid or of adducts of IPDI and acrylic acid (EP-A0916647, example 1) and salts of dimethylolpropionic acid.

Suitable nonionically hydrophilicizing compounds meeting the definition of component A5) are, for example, polyoxyalkylene ethers which contain at least one hydroxyl or amino group. These polyethers comprise a proportion of from 30 to 100% by weight of structural units derived from ethylene oxide. Suitable ones include polyethers of linear structure having a functionality of 1 to 3, but also compounds of the general formula (III):

wherein

R¹And R²Independently of one another, are divalent aliphatic, cycloaliphatic or aromatic radicals having from 1 to 18 carbon atoms, which may be interrupted by oxygen and/or nitrogen atoms, and

R³is an alkoxy terminated polyethylene oxide group.

Nonionically hydrophilicizing compounds also include, for example, monoalkene polyalkylene oxide polyether alcohols having an average of from 5 to 70, preferably from 7 to 55, ethylene oxide units/molecule, such as are obtained in a manner known per se by alkoxylation of suitable starter molecules (for example Ullmanns Encyclopadider tehnischen Chemie, 4 th edition, volume 19, Verlag Chemie, Weinheim, pages 31 to 38).

Examples of suitable starter molecules are saturated monoalcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, the isomeric 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 monoalkyl ethers, such as diethylene glycol monobutyl ether, unsaturated alcohols, such as allyl alcohol, 1, 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, monoamines, such as dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, bis (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 suitable for the alkoxylation reaction are, in particular, ethylene oxide and propylene oxide, which can be used in the alkoxylation reaction in any order or as a mixture.

The polyalkylene oxide polyether alcohols are linear (reine) polyethylene oxide polyethers or mixed polyalkylene oxide polyethers at least 30 mol%, preferably at least 40 mol%, of whose alkylene oxide units consist of ethylene oxide units. Preferred nonionic compounds are monofunctional mixed polyalkylene oxide polyethers containing at least 40 mol% ethylene oxide units and not more than 60 mol% propylene oxide units.

In this process, preference is given to using combinations of ionic and nonionic hydrophilicizing agents which meet the definitions of components A4) and A5). Particularly preferred combinations are those of nonionic and anionic hydrophilicizing agents.

The chain extension in step C) is carried out using hydrazine and/or its hydrates as component C1). Preferably, hydrazine monohydrate is used.

If desired, further chain extenders may also be used in component C2). They satisfy the above definitions for the compounds suitable for A2) -A5), with the proviso that the compounds used in C2) contain-NH₂And/or NH groups.

In this process, preference is given to using from 7 to 45% by weight of component A1), from 50 to 91% by weight of component A2), from 0 to 30% by weight of component A3), from 0 to 12% by weight of component A4), from 0 to 15% by weight of component A5), from 0.1 to 5.0% by weight of C1) (based on pure hydrazine N₂H₄) And 0 to 15% by weight of C2), where the sum of A4) and A5) is 0.1 to 27% by weight and the sum of all components is 100% by weight.

In particular, in the process, from 10 to 30% by weight of component A1), from 65 to 90% by weight of component A2), from 0 to 10% by weight of component A3), from 0 to 10% by weight of component A4), from 0 to 15% by weight of component A5), from 0.1 to 3.0% by weight of C1) (based on pure hydrazine N, are used₂H₄) And 0 to 10% by weight of C2), where the sum of A4) and A5) is 0.1 to 25% by weight and the sum of all components is 100% by weight.

In this process, it is more particularly preferred to use from 8 to 27% by weight of component A1), from 65 to 85% by weight of component A2), from 0 to 8% by weight of component A3), from 0 to 10% by weight of component A4), from 0 to 15% by weight of component A5), from 1.0 to 2.5% by weight of C1) (based on pure hydrazine N, based on pure hydrazine₂H₄) And 0 to 8% by weight of C2), where the sum of A4) and A5) is 0.1 to 25% by weight and the sum of all components is 100% by weight.

The process for preparing the aqueous PU dispersions can be carried out in one or more stages in homogeneous phase or, in the case of multistage reactions, partly in dispersed phase. Complete or partial polyaddition of A1) to A5) is followed by a dispersing, emulsifying or dissolving step. This is optionally followed by further polyaddition or modification in the disperse phase.

The aqueous PU dispersions can be prepared using the acetone process known from the prior art or variants thereof. In Methoden der organischen Chemie (Houben-Weyl, Additional and complementary Volumes to the 4)^thEdition, Volume E20, H.Bartl and J.Falbe, Stuttgart, New York, Thieme 1987, page 1671-. The acetone process is preferred.

Generally, in step A) of the process, all or part of the components A2) -A5) which should not contain any primary or secondary amino groups and the polyisocyanate component A1) used for preparing the polyurethane prepolymer are introduced as initial charge, optionally diluted with a water-miscible, but isocyanate-inert solvent A6), and heated to a relatively high temperature, preferably from 50 to 120 ℃.

Suitable solvents are the customary aliphatic ketone-functional solvents, such as acetone, butanone, which can be added not only at the beginning of the preparation but also later, if desired, in portions. Acetone and butanone are preferred. The reaction may be carried out at atmospheric pressure or elevated pressure, for example above the atmospheric boiling temperature of a solvent such as acetone.

In this process, it is also possible to include in the initial charge known catalysts, such as triethylamine, 1, 4-diazabicyclo [2.2.2] octane, dibutyltin oxide, tin dioctoate or dibutyltin dilaurate, tin bis (2-ethylhexanoate) or other organometallic compounds, to accelerate the isocyanate addition reaction, or to meter them in later. Dibutyltin dilaurate is preferred.

Subsequently, any constituents from A1) to A5) which have optionally not been added at the beginning of the reaction are metered in.

In the case of preparing the polyurethane prepolymer in step A), the molar ratio of isocyanate groups to isocyanate-reactive groups is from 1.0 to 3.5, preferably from 1.1 to 3.0, more preferably from 1.1 to 2.5.

The reaction of components A1) to A5) to form the prepolymer is partial or complete, but preferably complete. The extent of reaction was monitored by tracking the NCO content of the reaction mixture. This can be done not only by measuring the sample taken using spectroscopy, e.g. infrared or near infrared spectroscopy, but also by determining the refractive index of the sample taken or by chemical analysis of the sample taken, e.g. by titration. In this way, a polyurethane prepolymer containing free isocyanate groups is obtained as such or in solution.

The preparation of the polyurethane prepolymers of A1) and A2) -A5) is followed or during partial or complete salt formation of the anionic and/or cationic dispersing groups, if the starting molecules have not already been carried out. In the case of anionic groups, this is carried out using bases such as ammonia, ammonium carbonate or ammonium bicarbonate, trimethylamine, triethylamine, tributylamine, diisopropylethylamine, dimethylethanolamine, diethylethanolamine, triethanolamine, potassium hydroxide or sodium carbonate, preferably triethylamine, triethanolamine, dimethylethanolamine or diisopropylethylamine.

The molar amount of base is 50-100%, preferably 60-90% of the molar amount of anionic groups. In the case of cationic groups, dimethyl sulfate or succinic acid are used. If only non-ionic hydrophilic compounds A5 containing ether groups are used), the neutralization step is omitted. Neutralization can also be carried out simultaneously with the dispersion, the water for dispersion already containing the neutralizing agent.

Subsequently, in a further step B) of the process, if not carried out or carried out only partly in step A), the prepolymer obtained is dissolved with an aliphatic ketone, for example acetone or butanone.

In step C) of the process, component C1) and possibly NH₂-and/or NH-functional component C2) with the remaining isocyanate groups. The chain extension/termination may be carried out in the solvent before dispersion, during dispersion, or in the water after dispersion.

If the chain extension in C2) is used, the definition of A4) is satisfied and NH is contained₂Or NH groups, the prepolymer is preferably chain extended prior to dispersion.

The degree of chain extension, in other words the equivalent ratio of NCO-reactive groups of the compounds used for chain extension in C1) and optionally C2) to free NCO groups of the prepolymer is generally 40-200%, preferably 70-180%, more preferably 80-160%, still more preferably 101-150%, wherein C1) is added in an amount such that at least 40%, preferably at least 50%, more preferably at least 70% of the NCO groups have reacted with the compounds of component C1).

To terminate the prepolymer, it is also possible in C2) to additionally employ monoamines, for example diethylamine, dibutylamine, ethanolamine, N-methylethanolamine or N, N-diethanolamine.

The amine components C1) and optionally C2) can optionally be used individually or in admixture in the process of the invention in water-or solvent-diluted form, in principle any order of addition being possible.

If water or an organic solvent is used as the diluent, the diluent content is preferably 70 to 95 wt%.

For chain extension, it is preferred to add only component C1) with compounds from C2) which meet the specification of a4), and then as long as compounds from C2) which meet the specification of a2) and/or A3) are added.

The process for preparing the PU dispersions from the prepolymers is normally carried out after chain extension (step C). For this purpose, if desired, the dissolved and chain-extended polyurethane polymer is introduced into the dispersion water with strong shear, for example strong stirring, or, conversely, the dispersion water is stirred into the prepolymer solution. The water is preferably added to the dissolved prepolymer.

In principle, further chain extension can be carried out after the dispersion step by adding additional amounts of C1) and C2), but preferably chain extension is carried out just before dispersion.

The solvent still present in the dispersion after the dispersion step is then normally removed by distillation. Removal during dispersion is likewise possible.

The dispersions thus obtained have a solids content of from 10 to 70% by weight, preferably from 25 to 65% by weight and more preferably from 30 to 65% by weight.

Depending on the degree of neutralization and the amount of ionic groups, the dispersion can be prepared very finely, so that it has almost the appearance of a solution, but very coarse formulations are also possible and are likewise sufficiently stable.

Furthermore, polyacrylates can be used to modify the aqueous PU dispersions obtainable. For this purpose, emulsion polymerization of ethylenically unsaturated monomers is carried out in these polyurethane dispersions, as described in DE-A1953348, EP-A0167188, EP-A0189945 and EP-A0308115, examples being esters of (meth) acrylic acid and alcohols having from 1 to 18 carbon atoms, styrene, vinyl esters or butadiene.

These monomers may contain, in addition to one or more olefinic double bonds, functional groups such as hydroxyl, epoxy, hydroxymethyl or acetoacetoxy groups.

The constituents of component II) are generally prepared by first allowing an isocyanate-functional prepolymer to be prepared from compounds which meet the definitions of components A1) to A5) and, in a second reaction step, by reaction with compounds which meet the definitions of components A3) and C1) in a nonaqueous medium to give an OH-and/or NH-functional polyurethane, as described in EP-A0355682, page 4, lines 39 to 45. In addition, the preparation can be carried out by: the polyurethane resins containing OH and/or NH groups are formed directly by reacting components A1) -A5) in a nonaqueous medium, as described in EP-A0427028, page 4, line 54 to page 5, line 1.

The compounds satisfying the definition of component A2) used for the synthesis of the prepolymer may be, but need not necessarily be, subjected beforehand to a distillation step under reduced pressure. For this purpose, these compounds are preferably distilled continuously in a thin-film evaporator at temperatures ≥ 150 ℃, preferably 170-. Under these conditions, a low molecular weight, non-reactive volatile fraction is separated. In the course of the distillation, from 0.2 to 15% by weight, preferably from 0.5 to 10% by weight, more preferably from 1 to 6% by weight, of the volatile fraction are separated off.

Depending on the reactivity of the isocyanates used, the prepolymer preparation is generally carried out at temperatures of from 0 to 140 ℃. To accelerate the urethanization reaction, suitable catalysts may be used, such as those known to those skilled in the art for accelerating the NCO/OH reaction. Examples of such catalysts are tertiary amines, such as triethylamine or diazobicyclooctane, organotin compounds, such as dibutyltin oxide, dibutyltin dilaurate or tin bis (2-ethylhexanoate), or other organometallic compounds.

The prepolymer preparation is preferably carried out in the presence of a solvent which is inert towards isocyanates. Particularly suitable for this purpose are water-compatible solvents, such as ethers, ketones and esters, and N-methylpyrrolidone. The amount of solvent is advantageously not more than 30% by weight, preferably from 10 to 25% by weight, based in each case on the sum of polyurethane resin and solvent.

The acid groups thus obtained, which are introduced into the prepolymer, are at least partially neutralized. This can be carried out during or after prepolymer preparation or during or after dispersion in water by adding a suitable neutralizing agent. For this purpose, preference is given to using tertiary amines, for example trialkylamines having from 1 to 12, preferably from 1 to 6, carbon atoms in each alkyl radical. Examples thereof include trimethylamine, triethylamine, methyldiethylamine, tripropylamine and diisopropylethylamine. These alkyl groups may also carry hydroxyl groups, for example, as in the case of dialkylmonoalkanolamines, alkyldialkanolamines and trialkanolamines. An example of these is dimethylethanolamine, which is preferably used as neutralizing agent. As neutralizing agent, it is also possible to optionally use inorganic bases, such as ammonia or sodium or potassium hydroxide. The neutralizing agent is generally used in a molar ratio of neutralizing agent to acid groups of the prepolymer of about 0.3: 1 to 1.3: 1, preferably about 0.4: 1 to 1: 1.

This neutralization step is preferably carried out after the prepolymer preparation, in principle at temperatures of from 0 to 80 ℃ and preferably from 40 to 80 ℃.

Thereafter, the hydroxyl-functional polyurethane is converted into an aqueous dispersion by the addition of water or by introduction into water.

The resins of the PU dispersions of component II) obtained according to the above-described procedure generally have a number average molecular weight Mn of 1000-30000, preferably 1500-10000, an acid number of from 10 to 80, preferably from 15 to 40mg KOH/g and an OH content of from 0.5 to 5% by weight, preferably from 1.0 to 3.5% by weight.

By combination with a suitable crosslinker of component HI), it is possible to prepare not only one-component coatings but also two-component coatings, depending on the reactivity of the crosslinker or the blocking, if appropriate. For the purposes of the present invention, by one-component coating is meant a coating composition in which the binder component and the crosslinker component can be stored together without any significant or detrimental degree of crosslinking reaction occurring for subsequent use. The crosslinking reaction is only carried out at the time of application, after activation of the crosslinking agent. This activation can be obtained, for example, by raising the temperature.

Two-component coatings for the purposes of the present invention are coating compositions in which the binder component and the crosslinker component have to be stored in separate containers due to the high reactivity. The two components are mixed just shortly before application, at which point they typically react without further activation. However, catalysts or relatively high temperatures may also be used in order to accelerate the crosslinking reaction.

Examples of suitable crosslinkers include polyisocyanate crosslinkers, amide-and amine-formaldehyde resins, phenolic resins, aldehyde resins and ketone resins, for example phenol-formaldehyde resins, for example resole resins, furan resins, urea resins, urethane resins, triazine resins, melamine resins, benzoguanamine resins, cyanamide resins, aniline resins, as described in "lackkunsize", h.wagner, h.f.sarx, Carl han ver Munich, 1971.

As crosslinking agents of component III), polyisocyanates having free isocyanate groups are preferably used, since the aqueous polyurethane coatings obtained exhibit particularly high levels of technical-grade coating properties. Examples of suitable crosslinkers III) include 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethyl-cyclohexane, hexamethylene diisocyanate, 1, 4-diisocyanatocyclohexane or bis- (4-isocyanatocyclohexane) methane or 1, 3- (bis-2-isocyanatopropyl-2) -benzene, or polyisocyanates containing uretdione, biuret, isocyanurate or iminooxadiazinedione groups based on lacquer polyisocyanates, for example hexamethylene diisocyanate, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane or bis- (4-isocyanatocyclohexane) methane, or polyisocyanates containing urethane groups and based on one aspect 2, 4-and/or 2, 6-diisocyanatotoluene or 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane and, on the other hand, low molecular weight polyhydroxyl compounds such as trimethylolpropane, isopropylpropanediol or butanediol or any desired mixtures of such polyhydroxyl compounds.

Where appropriate, the compounds containing free isocyanate groups can be converted into less reactive derivatives by reaction with so-called blocking agents, these less reactive derivatives then being reacted only after activation, for example at relatively high temperatures. Suitable blocking agents for these polyisocyanates are, for example, monoalcohols, such as methanol, ethanol, butanol, hexanol, cyclohexanol, benzyl alcohol, oximes, such as acetoxime, methyl ethyl ketoxime and cyclohexanone oxime, lactams, such as epsilon-caprolactam, phenols, amines, such as diisopropyl-or dibutyl-amine, tert-butyl benzyl amine, dimethylpyrazole or triazole, and also dimethyl malonate, diethyl malonate or dibutyl malonate.

Preference is given to using low-viscosity, hydrophobic or hydrophilic polyisocyanates of the type mentioned above which contain free isocyanate groups and are based on aliphatic, cycloaliphatic, araliphatic and/or aromatic isocyanates, more preferably aliphatic or cycloaliphatic isocyanates, since in this way a particularly high level of film resistance can be achieved. These polyisocyanates generally have a viscosity (23 ℃) of from 10 to 3500 mPas.

If necessary, the polyisocyanate may be used as a blend with a small amount of an inert solvent in order to reduce the viscosity to a level within the range. Triisocyanatononane can also be used, alone or as a mixture, in component III).

The components I) and II) described here are generally sufficiently hydrophilic to ensure dispersibility of the hydrophobic crosslinkers of component III). However, if desired, external emulsifiers, as known to the person skilled in the art, can also be added.

However, it is additionally possible to use water-soluble or water-dispersible blocked polyisocyanates in component III), such as those obtained by modification with carboxylate groups, sulfonate groups and/or polyethylene oxide/polypropylene oxide groups.

Hydrophilization of polyisocyanates can be achieved, for example, by reaction with a deficiency of monohydric hydrophilic polyether alcohols. The preparation of such hydrophilicized polyisocyanates is described, for example, in EP-A0540985, page 3, line 55 to page 4, line 5. Also highly suitable are the polyisocyanates containing allophanate groups described on page 3, lines 39-51 of EP-A-959087, which are prepared by reacting low-monomer-content polyisocyanates with polyethylene oxide polyether alcohols under allophanatization conditions. Also suitable are water-dispersible polyisocyanate mixtures based on triisocyanatononane and described in DE-A10007821, page 2, line 66 to page 3, line 5, and also polyisocyanates hydrophilicized with ionic groups (sulfonates, phosphonates) as described in DE 10024624, page 3, lines 13 to 33. Hydrophilization can additionally be achieved by addition of emulsifiers customary in industry.

Of course, it is also possible in principle to use mixtures of different crosslinker resins of the type described above in component III).

As further film-forming resins of component IV), suitable are polymers which are dispersible, emulsifiable or soluble in water and which are different from the constituents of components I) to III). Examples of these are optionally epoxy-containing polyesters, polyurethanes, acrylic polymers, vinyl polymers such as polyvinyl acetate, polyurethane dispersions, polyacrylic dispersions, polyurethane-polyacrylate hybrid dispersions, polyvinyl ether and/or polyvinyl ester dispersions, polystyrene and/or polyacrylonitrile dispersions. The solids content of the film-forming resins used in component IV) is preferably from 10 to 100% by weight, more preferably from 30 to 100% by weight.

The ratio of crosslinker III) and compounds of component II) and optionally IV) which are reactive therewith should be chosen such that the ratio of the reactive groups of the crosslinker (NCO groups in the case of isocyanates) to the groups reactive toward the crosslinker (for example OH groups) of II) and IV) is from 0.5: 1.0 to 3.5: 1.0, preferably from 1.0: 1.0 to 3.0: 1.0, more preferably from 1.0: 1.0 to 2.5: 1.0.

The mixture of components I), II) and IV) preferably contains from 5 to 95% by weight, more preferably from 25 to 75% by weight, of component II), wherein the amounts of I) and IV) are selected such that the total amount of I), II) and IV) is 100% by weight.

As customary coating auxiliaries and additives, substances known to the skilled worker, such as defoamers, thickeners, pigments, dispersing assistants, matting agents, catalysts, antiskinning agents, antisettling agents and/or emulsifiers, and also additives which enhance the desired soft-feel effect, can be present in the coating compositions of the invention. The point in time at which these additives/auxiliaries are added to the coating materials of the invention or incorporated into them during preparation is immaterial.

The aqueous coating materials of the invention are suitable for all fields of application in which aqueous paints and coating systems are used which have stringent requirements with regard to the surface quality/resistance of the films, for example the coating of surfaces of mineral building materials, the coating and sealing of wood and wood-type materials, the coating of metal surfaces (metal coating), the coating and lacquering of asphalt or bitumen coverings, the coating and sealing of various plastic surfaces (plastic coating) and high-gloss varnishes.

However, they are particularly suitable for producing soft-feel effect coatings which are stable to thermal yellowing and ensure good solvent resistance and particularly good sun protection cream resistance (tanning lotion test). Such coatings are preferably used for plastic coating or wood coating, wherein the curing is usually carried out at temperatures from room temperature to 130 ℃. The two-component technology with non-blocked polyisocyanate crosslinkers allows the use of comparatively low curing temperatures in the above-mentioned range.

The aqueous coating materials of the invention are generally used for clearcoats or topcoats (top-most films) of single-coat coatings or multicoat systems.

The coating of the present invention can be formed by a variety of spray methods, such as air pressure spray, airless spray or electrostatic spray methods, using a single component or, as desired, a two component spray device. However, it is also possible to apply the paints and coatings containing the binder dispersions of the invention by other methods, for example by brushing, rolling or knife coating.

Examples

All percentages are to be understood as being percentages by weight unless otherwise specified.

Materials and abbreviations used

Diaminosulfonate:

NH₂-CH₂CH₂-NH-CH₂CH₂-SO₃na (45% aqueous solution)

Bayhydrol®2429：

Aliphatic hydroxyl-functional polyester-polyurethane dispersions having a solids content of 55% are from bayer ag, levkusen, germany.

BYK 348：

Wetting agent (BYK-Chemie from Wesel, Germany)

Tego-Wet KL 245 (50% aqueous solution):

flow additive (Degussa AG, Essen, Germany)

Bayhydur®3100：

A hydrophilic, aliphatic polyisocyanate based on Hexamethylene Diisocyanate (HDI) having an isocyanate content of 17.4%; bayer Siamese ex Levokusen, Germany

Bayhydur®VPLS 2306：

A hydrophilic, aliphatic polyisocyanate based on Hexamethylene Diisocyanate (HDI) having an isocyanate content of 8.0%; bayer Siamese ex Levokusen, Germany

Desmodur®XP 2410：

A low viscosity aliphatic polyisocyanate based on hexamethylene diisocyanate having an isocyanate content of 24.0%; bayer Siamese ex Levokusen, Germany

MPA: acetic acid 1-methoxy-2-propyl ester

The solids content was determined in accordance with DIN-EN ISO 3251. The NCO content is determined volumetrically in accordance with DIN-EN ISO 11909 unless specified otherwise. Yellowing (b)^*，Δb^*Values) were determined by the CIELAB method (DIN 5033).

Example 1: comparative example

Bayhydrol ® PR 240 (anionically hydrophilicized PU dispersions having a solids content of 40% and an average particle size of 100-300nm from Bayer AG, Leverkusen, Germany)

Example 2: comparative example

Bayhydril ® VP LS 2305 (anionic and nonionic hydrophilicized PU dispersions having a solids content of 40% and an average particle size of 100-300nm, from Bayer AG, Leverkusen, Germany)

Example 3:

1453.5g of polyester PE 170HN (polyester polyol, OH number 66mg KOH/g, number average molecular weight 1700g/mol from Bayer AG, Leverkusen, Germany), 64.1g of polyether LB 25 (monofunctional polyethers based on ethylene oxide/propylene oxide having a number average molecular weight of 2250g/mol and an OH number of 25mg KOH/g, Bayer AG, Leverkusen, Germany) and 0.1g of Desmorapid ® Z (dibutyltin dilaurate, Bayer AG, Leverkusen, Germany) were heated to 65 ℃. Subsequently, a mixture of 432.3g of isophorone diisocyanate and 343.9g of acetone was added at 65 ℃ over the course of 5 minutes, and the mixture was stirred under reflux until the theoretical NCO value was reached. The finished prepolymer was dissolved with 2298.5g of acetone at 50 ℃ and then a solution of 40.6g of hydrazine hydrate, 48.5g of isophoronediamine and 421.1g of water was metered in over a period of 10 minutes. After addition of 60.1g of the diaminosulphonate over the course of 5 minutes, stirring was continued for 15 minutes, and then the batch was dispersed by adding 2608.4g of water over the course of 10 minutes. Thereafter, the solvent was removed by vacuum distillation to obtain a storage-stable dispersion having a solid content of 41.0%.

Example 4:

1530.0g of polyester PE 170 (polyester polyol, OH number 66mg KOH/g, number-average molecular weight 1700g/mol, from Bayer AG, Leverkusen, Germany), 67.5g of polyether LB 25 (monofunctional polyethers based on ethylene oxide/propylene oxide, having a number-average molecular weight of 2250g/mol, OH number of 25mg KOH/g, from Bayer AG, Leverkusen, Germany) and 0.1g of Desmorapid ® Z (dibutyltin dilaurate, from Bayer AG, Leverkusen, Germany) were heated to 65 ℃. Subsequently, 537.1g of Desmodur ® W (bis (4, 4' -isocyanatocyclohexyl) methane, from Bayer AG, Leverkusen, Germany) and 355.0g of acetone were added over the course of 5 minutes at 65 ℃ and the mixture was stirred under reflux until the theoretical NCO value was reached. The finished prepolymer was dissolved with 1766.0g of acetone at 50 ℃ and a solution of 50.0g of hydrazine hydrate, 51.0g of isophoronediamine and 401.3g of water was metered in over a period of 10 minutes. After addition of 63.3g of the diaminosulphonate over the course of 5 minutes, stirring was continued for 15 minutes, and the batch was then dispersed by adding 2915.0g of water over a period of 10 minutes. Thereafter, the solvent was removed by vacuum distillation to obtain a storage-stable dispersion having a solid content of 41.0%.

Table 1 describes the composition of the coating of the present invention. To prepare the coatings, each dispersion of part I (see table 1) was introduced as an initial charge, the additive (part II) was added and the components were stirred together for 30 minutes. This was followed by addition of a crosslinker (part III). After stirring together for 5 minutes, these coatings were applied by spraying on glass and Makrofol ® sheets (bayer ag, luverkusen, germany). After application, the sheets were flash dried at 23 ℃ for 10 minutes, then dried at 80 ℃ for 30 minutes and at 60 ℃ for 16 hours. The dry film thickness was 20 microns.

Table 1: coating material

Examples	5 (comparison)	6 (comparison)	7	8	9 (comparison)	10 (comparison)	11	12
									Moiety I
Bayhydrol®XP 2429	50	50	50	50	50	50	50	50
									PU Dispersion of example 1	68.8	-	-	-	68.8	-	-	-
PU Dispersion of example 2	-	68.8	-	-	-	68.8	-	-
									PU Dispersion of example 3	-	-	67.1	-	-	-	67.1	-
PU Dispersion of example 4	-	-	-	67.1	-	-	-	67.1
									Part II
Byk 348	0.8	0.8	0.8	0.8	0.8	0.8	0.8	0.8
									Tego-Wet KL 245	0.6	0.6	0.6	0.6	0.6	0.6	0.6	0.6
Softened water	84.0	84.0	85.6	85.6	85.5	85.5	87.1	87.1
									Part III
B' dur 3100; 75% MPA solution	11.4	11.4	11.4	11.4	-	-	-	-
									B 'dur VP LS 2360/D' dur XP 2410; 75% MPA solution	-	-	-	-	12.4	12.4	12.4	12.4
Total of	215.6	215.6	215.5	215.5	218.1	218.1	218.0	218.0

The coated and dried sheets were then subjected to heat loads of 90 ℃ and 120 ℃ and monitored for yellow change over time with CIELAB measurements (see tables 2-5).

Table 2: yellowing value of glass stored at 90 DEG C

Glass	Layer thickness	0h	500h	1000h	1500h	2000h	2500h
								Examples	[μm]	b*	Δb*	Δb*	Δb*	Δb*	Δb*
5 (comparison)	20	1.83	0.96	1.27	1.55	1.76	1.90
								6 (comparison)	20	1.80	0.79	1.24	1.34	1.57	1.77
7	20	1.72	0.82	0.90	1.15	1.36	1.45
								8	20	1.79	0.82	0.93	1.04	1.39	1.41
9 (comparison)	20	1.79	1.09	1.41	1.66	1.88	2.03
								10 (comparison)	20	1.71	0.87	1.45	1.61	1.98	2.18
11	20	1.76	0.75	0.99	1.09	1.23	1.26
								12	20	1.74	0.82	1.14	1.20	1.64	1.62

Table 3: yellowness index of Makrofol ® stored at 90 ℃

Makrofol®	Layer thickness	0h	500h	1000h	1500h	2000h	2500h
								Examples	[μm]	b*	Δb*	Δb*	Δb*	Δb*	Δb*
5 (comparison)	20	1.51	0.89	1.37	1.48	1.55	1.78
								6 (comparison)	20	1.58	0.56	1.15	1.33	1.61	1.77
7	20	1.58	0.43	1.19	0.98	1.06	1.52
								8	20	1.49	0.55	0.96	0.80	1.13	1.30
9 (comparison)	20	1.54	0.66	1.33	1.19	1.55	1.71
								10 (comparison)	20	1.50	0.61	1.16	1.07	1.51	1.69
11	20	1.57	0.49	0.96	0.91	1.18	1.16
								12	20	1.46	0.76	1.07	1.08	1.42	1.49

Table 4: yellowing value of glass stored at 120 DEG C

Glass	Layer thickness	0h	100h	250h	500h
						Examples	[μm]	b*	Δb*	Δb*	Δb*
5 (comparison)	20	1.83	1.87	3.23	4.58
						6 (comparison)	20	1.80	1.41	2.93	4.73
7	20	1.72	0.75	1.38	2.62
						8	20	1.79	0.78	1.99	3.35
9 (comparison)	20	1.79	2.11	3.87	5.30
						10 (comparison)	20	1.71	2.53	4.69	6.61
11	20	1.76	0.68	1.69	2.87
						12	20	1.74	0.63	2.01	3.46

Table 5: yellowness index of Makrofol ® stored at 120 ℃

Makrofol	Layer thickness	0h	100h	250h	500h
						Examples	[μm]	b*	Δb*	Δb*	Δb*
5 (comparison)	20	1.51	1.22	1.97	2.70
						6 (comparison)	20	1.58	0.59	1.20	2.05
7	20	1.58	0.35	0.87	1.65
						8	20	1.49	0.41	0.91	1.83
9 (comparison)	20	1.54	2.01	2.33	3.74
						10 (comparison)	20	1.50	0.84	1.73	2.76
11	20	1.57	0.46	0.83	1.68
						12	20	1.46	0.79	1.35	2.40

These yellowing values demonstrate that the coatings according to the invention (examples 7, 8, 11 and 12) exhibit significantly lower yellowing values after heat exposure on glass and plastics (Makrofol ®, Bayer AG, Leverkusen, Germany) compared with the prior art systems (examples 5, 6, 9 and 10).

Moreover, the inventive coatings of examples 7, 8, 11 and 12 have mechanical and tactile properties comparable to those of the prior art examples (examples 5, 6, 9 and 10).

Claims (10)

1. A coating, the coating comprising:

I) dispersions of one or more polyurethanes and/or polyurethane-ureas which do not contain hydroxyl groups (PU dispersions)

II) an aqueous solution or dispersion of one or more ionically modified, hydroxyl-containing polyurethanes and/or polyurethane-ureas of ingredients other than component I), and

III) at least one crosslinking agent and

IV) optionally other film-forming resins,

characterized in that the PU dispersions used in I) are obtained by the following steps:

A) polyurethane prepolymers containing NCO groups were first prepared by reacting component a1) with a2) to a 6):

A1) a polyisocyanate,

A2) polymeric polyols and/or polyamines having a number average molecular weight of 400-8000g/mol,

A3) optionally low molecular weight compounds having a number average molecular weight of 17 to 400g/mol, selected from the group consisting of mono-and polyols, mono-and polyamines and aminoalcohols,

A4) isocyanate-reactive ionic or potentially ionic hydrophilic compounds and/or

A5) Isocyanate-reactive nonionically hydrophilicizing compounds

A6) Optionally in an aliphatic ketone as solvent,

with the proviso that all of components A1) to A5) contain no primary or secondary amino groups,

B) dissolving the prepolymer obtained from step A) in an aliphatic ketone or, if the preparation is carried out in the presence of A6), optionally diluting the prepolymer solution by further addition of an aliphatic ketone, and

C) reacting the remaining free NCO groups of the prepolymer with a chain extender component comprising C1) and C2):

C1) hydrazine and/or hydrazine hydrate

C2) Optionally compounds which meet the provisions of components A2), A3), A4) and/or A5),

the premise is that:

the compounds of component C2) containing primary and/or secondary amino groups,

c1) and C2) in such a total amount that a calculated degree of chain extension of 40 to 200% and

c1) and C2) in such a proportion that at least 40% of the free isocyanate groups are chain-extended with amino groups of component C1) and/or terminated with amino groups of component C1).

2. The coating according to claim 1, characterized in that in the preparation of the PU dispersions of step B) and optionally of step A), acetone or butanone is used as solvent.

3. The method according to claim 1 or 2In the preparation of PU dispersions, 8 to 27% by weight of component A1), 65 to 85% by weight of component A2), 0 to 8% by weight of component A3), 0 to 10% by weight of component A4), 0 to 15% by weight of component A5), 1.0 to 2.5% by weight of C1) (based on pure hydrazine N) are used in steps A) to C) for the preparation of the PU dispersions₂H₄) And 0 to 8% by weight of C2), where the sum of A4) and A5) is 0.1 to 25% by weight and the sum of all components is 100% by weight.

4. Coating according to any one of claims 1 to 3, characterized in that in the preparation of the PU dispersions the amounts of C1) and C2) are such that a calculated chain extension of 101-150% is obtained.

5. The coating according to any one of claims 1 to 4, characterized in that in III), polyisocyanates are used as crosslinking agents.

6. The coating according to claim 5, characterized in that the ratio of NCO groups of component III) to OH groups of components II) and IV) is from 1.0: 1.0 to 2.5: 1.0.

7. The coating according to any one of claims 1 to 6, characterized in that the mixture of components I), II) and IV) contains 25 to 75 wt.% of component II), and the amounts of I) and IV) are selected such that the total amount of I), II) and IV) is 100 wt.%.

8. Use of a coating according to any one of claims 1-7 for the preparation of a coating.

9. A coating formed using the coating material according to any one of claims 1 to 7.

10. A substrate coated with a coating according to claim 9.