HK1073858A - Aqueous polyurethane dispersions for producing coatings with soft feel effect - Google Patents

Description

Aqueous polyurethane dispersions for producing soft-touch effects

Cross reference to related patent applications

This patent application claims priority under 35 u.s.c. § 199(a) to (d) of german patent application No. 10323306.2 filed 5, 30, 2003.

Technical Field

The present invention relates to novel coating compositions based on aqueous polyurethane dispersions, to a process for preparing them and to their use for producing soft-touch coatings having low haze and VOC values.

Background

A wide variety of ionically modified Polyurethanes (PU) and their aqueous formulations are described in the prior art. A review of various aqueous PU products and methods for their preparation is described, for example, in "Houben-Weyl: methoden der Organischen Chemie, Volume E20, 1659-. By virtue of their mechanical strength, high adhesion to various substrates, solvent resistance and gloss, they are widely used, for example, in coatings for plastics.

When plastic parts are used, for example, in automotive interiors, however, an effect known as "fogging" or "fogging" occurs. This means that deposits are formed which refract the light strongly and appear on the inner surface of the window, in particular the windscreen. The agents responsible for this phenomenon are low molecular weight components of the plastic parts, which migrate and deposit on the inner surface of the window over time with the aid of sunlight and heat. This effect can be significantly reduced by using "low-fogging" polyurethanes, as described in EP-A579988, US-A5,545,675, or EP-A1153951.

In order to improve the tactile properties of plastic parts, in particular in motor vehicle interiors, so-called soft-touch coatings have increasingly been used in recent years.

"Soft touch effect" for purposes of the present invention means a particular tactile sensation (feel) of the coating surface; the feel can be described using terms 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 sheet coated with a conventional clear coat or finish material and made, for example, from ABS, Makrolon * (polycarbonate, bayer ag) or Plexiglas * (polymethyl methacrylate) feels cold and smooth. In order to adapt to the tendency to avoid the emission of solvents into the environment, it has been observed in recent years that aqueous soft-touch coatings based on polyurethane chemistry have been established, as disclosed in the teaching of DE-A4406159. These coatings also have good resistance and protection to plastic substrates in terms of excellent soft touch effect. However, it has subsequently been found that these coatings and coatings have a pronounced fogging effect, which is to some extent attributable to their increased development in automobile interiors.

Low-fogging soft-touch coatings based on aqueous polyurethane systems are not known to date, so it is an object of the present invention to provide novel aqueous coating compositions for producing soft-touch coatings having particularly low haze and VOC values.

Disclosure of Invention

The present invention relates to an aqueous coating composition comprising:

A) an aqueous formulation of at least one ionically modified, substantially hydroxyl-free polyurethane and/or polyurethane urea,

B) an aqueous formulation of at least one ionically modified, hydroxyl-containing polyurethane and/or polyurethane urea, and

C) at least one cross-linking agent.

Component a) was synthesized from the following compounds:

A1) one or more polyols having a number average molecular weight (Mn) of > 500 Dalton and an average OH functionality of > 1.5, substantially free of components which are volatile at temperatures of > 150 ℃ and pressures of < 10 mbar,

A2) optionally one or more polyols having a number average molecular weight (Mn) of 62 to 499 daltons and an OH functionality of 2 or more,

A3) optionally one or more hydrophilic compounds having an ethylene oxide content of 50% by weight and a number average molecular weight (Mn) of more than 400 Dalton, which contains at least one NCO-reactive group,

A4) one or more polyisocyanates selected from the group consisting of,

A5) optionally one or more aliphatic polyamines having a number average molecular weight (Mn) of 60 to 300 daltons and at least two primary or secondary amino groups or hydrazine, and

A6) one or more compounds which contain at least one NCO-reactive hydrogen atom or at least one NCO group and at the same time at least one ionic or potentially ionic group and which are different from the compounds A1) to A5) described above.

The invention also relates to coatings obtainable from the above-mentioned aqueous coating compositions and to substrates coated with these coatings.

The present invention further relates to soft touch coatings comprising the above-described polyhydroxy compounds as component A1).

Detailed Description

Other than in the examples, or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, etc. used in the specification and claims are to be understood as modified in all instances by the word "about".

The object on which the invention is based can now be achieved by using special polyester polyols which have been pretreated by distillation.

The present invention provides an aqueous coating composition comprising:

A) an aqueous formulation of at least one ionically modified, essentially hydroxyl-free polyurethane and/or polyurethane urea,

B) an aqueous formulation of at least one ionically modified, hydroxyl-containing polyurethane and/or polyurethane urea, and

C) at least one cross-linking agent, wherein,

D) optionally, auxiliary agents and additives, and optionally,

characterized in that component A) is synthesized from the following compounds:

A1) one or more polyhydroxyl compounds having a number-average molecular weight (Mn) of > 500 Dalton and an average OH functionality of > 1.5, from which components which are volatile under these distillation conditions have been removed at a temperature of > 150 ℃ and a pressure of < 10 mbar,

A2) optionally one or more polyols having a number average molecular weight (Mn) of 62 to 499 daltons and an OH functionality of 2 or more,

A3) optionally one or more hydrophilic compounds having an ethylene oxide content of 50% by weight and a number average molecular weight (Mn) of more than 400 Dalton, which contains at least one NCO-reactive group,

A4) one or more polyisocyanates selected from the group consisting of,

A5) optionally one or more aliphatic polyamines having a number average molecular weight (Mn) of 60 to 300 daltons and at least two primary or secondary amino groups or hydrazine, and

A6) one or more compounds containing at least one NCO-reactive hydrogen atom or at least one NCO group and simultaneously at least one ionic or potentially ionic group and being different from the compounds A1) -A5) described above;

and methods for their preparation.

For the purposes of the present invention, essentially free of hydroxyl groups means an OH number of less than 6mg KOH/g, preferably less than 2.5mg KOH/g.

For the purposes of the present invention, ionic groups are functional groups which carry a positive or negative charge, for example-COO^-，-SO₃ ^-，-NR₂H⁺，-NH₃ ⁺. The term ionically modified polyurethane or polyurethaneurea as used herein refers to a polyurethane or polyurethaneurea that has been treated or reacted or modified in some manner so as to contain these ionic groups.

For the purposes of the present invention, a potentially ionic group is a functional group having a covalent bond which can be readily converted into the corresponding salt, for example-COOM, -SO, by addition of a base or acid as the pH of the solution changes₃M (wherein M ═ H, NR)₄ ⁺Metal ion) or-NR₂/-NR₂H⁺or-NH₂/-NH₃ ⁺。

As compounds of component A1), preference is given to using organic compounds having a number average molecular weight (Mn) of 500-10000 Dalton, more preferably 600-5000 Dalton, still more preferably 1000-3000 Dalton and an average hydroxyl functionality of preferably from 1.5 to 6, more preferably from 1.8 to 3.

Particularly preferably, the compounds of component A1) are compounds of the abovementioned type based on polyesters, polylactones or polycarbonates and/or known copolymers.

The compounds used as a1) according to the invention are freed of volatile components by distillation before their use. The distillation is preferably carried out continuously in a thin-film evaporator at a temperature of 150 ℃ or more, preferably 170 ℃ and 230 ℃ or more, preferably 180 ℃ and 220 ℃ under a reduced pressure of 10 mbar or less, preferably 2 mbar or less, more preferably 0.5 mbar or less. The low molecular weight, non-reactive volatile fraction is separated from the polyol under these conditions. 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.

In one embodiment of the invention, the compound for a1) is substantially free of low molecular weight, non-reactive volatile fractions. As used herein, substantially free means that the material is present only as an incidental impurity, and depending upon the particular material, is present in an amount of less than 1 weight percent, in some cases less than 0.5 weight percent, and in other cases less than 0.2 weight percent based on the weight of the component, e.g., A1).

Suitable polyester polyols of component A1) are linear or branched polyester polyols, such as can be prepared in a known manner from aliphatic, cycloaliphatic or aromatic dicarboxylic or polycarboxylic acids and/or their anhydrides, such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, nonanedicarboxylic acid, decanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid or 1, 2, 4-trimellitic acid and also anhydrides, such as phthalic anhydride, 1, 2, 4-trimellitic anhydride or succinic anhydride or mixtures thereof, and polyols, such as ethylene glycol, di-, tri-, tetraethylene glycol, 1, 2-propanediol, di-, tri-, tetrapropylene glycol, 1, 3-propanediol, 1, 4-butanediol, 1, 3-butanediol, 2, 3-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 2, 2-dimethyl-1, 3-propanediol, 1, 4-dihydroxycyclohexane, 1, 4-dimethylolcyclohexane, 1, 8-octanediol, 1, 10-decanediol, 1, 12-dodecanediol, 2, 2, 4-and/or 2, 4, 4-trimethyl-1, 3-pentanediol or mixtures thereof, optionally with the use of small amounts of higher polyfunctional polyols, such as trimethylolpropane, glycerol or pentaerythritol. Suitable polyols for preparing the polyester polyols also include aromatic di-and polyhydroxy compounds. The di-and polyhydroxy compounds can be used in any desired mixtures, linear aliphatic and/or cycloaliphatic polyhydroxy compounds being preferred. Instead of the free carboxylic acids or the corresponding polycarboxylic anhydrides, it is also possible to use the corresponding polycarboxylic esters of lower alcohols or mixtures thereof for preparing the polyesters.

The polyester polyols can of course also be homopolymers or copolymers of lactones, which are preferably obtained by addition reaction of lactones or lactone mixtures, such as butyrolactone,. epsilon. -caprolactone and/or methyl-. epsilon. -caprolactone, with suitable difunctional and/or higher polyfunctional starter molecules, such as the abovementioned low molecular mass polyols, as synthesis components for polyester polyols.

Hydroxyl-containing polycarbonates are also suitable as polyhydroxy components, examples being those prepared by reacting diols such as 1, 4-butanediol and/or 1, 6-hexanediol with diaryl carbonates, for example diphenyl carbonate, dialkyl carbonates, such as dimethyl carbonate, or phosgene.

Particularly preferred compounds of component A1) are polyester diols based on adipic acid and diols such as 1, 4-butanediol, 1, 6-hexanediol and/or 2, 2-dimethyl-1, 3-propanediol (neopentyl glycol), and also copolymers of 1, 6-hexanediol with epsilon-caprolactone and diphenyl carbonate and 1, 6-hexanediol polycarbonate diol.

In addition to polyols of the type mentioned above, component A1) may also comprise up to 50% by weight of polyether polyols known per se in polyurethane chemistry, such as polyadducts of the class of the styrene oxides, ethylene oxide, propylene oxide, tetrahydrofuran, butylene oxide or epichlorohydrin, and also mixed addition products and graft products thereof, and also polyols obtained by condensation of polyols or mixtures thereof and polyols obtained by alkoxylation of polyfunctional alcohols, amines and amino alcohols. Preferably, however, a1) contains no polyether polyol.

The invention further provides the use of a polyol according to A1) in soft-touch coatings.

The compound of component a2) is a low molecular weight polyol having a number average molecular weight Mn of 62 to 499 dalton. Suitable examples include the polyols, in particular diols, mentioned above for the preparation of the polyester polyols of component A1), and also low molecular weight polyester diols, such as bis (hydroxyethyl) adipate, or short-chain homo-and mixed addition products of ethylene oxide or propylene oxide prepared starting from aromatic diols.

Preferred compounds of component A2) are 1, 2-ethanediol, 1, 4-butanediol, 1, 6-hexanediol, 2, 2-dimethyl-1, 3-propanediol, trimethylolpropane and glycerol, particularly preferably 1, 4-butanediol and 1, 6-hexanediol.

Suitable hydrophilic compounds of component A3) which are also optionally used have a number average molecular weight of at least 400 Dalton, preferably at least 500 Dalton and more preferably 1200 and 4500 Dalton and correspond to the general formula (I):

H-Y′-X-Y-R (I)

wherein

R is a monovalent hydrocarbon group having 1 to 12 carbon atoms, preferably an unsubstituted alkyl group having 1 to 4 carbon atoms,

x is a polyalkylene oxide chain having from 5 to 90, preferably from 20 to 70, monomer units and an ethylene oxide content of at least 50% by weight, preferably at least 65% by weight, based on the compounds of the formula (I).

Y and Y ' are each independently of the other oxygen or-NR ' -, where R ' corresponds to R or hydrogen according to its definition.

In addition to ethylene oxide, the radical X may also contain propylene oxide, butylene oxide and/or styrene oxide units; the preferred comonomer is propylene oxide.

The above-mentioned monofunctional, hydrophilic polyethers are prepared in a similar manner to those in DE-A2314512, DE A2314513 or U.S. Pat. No. 3,3905929,3920598 by alkylating monofunctional starters such as N-butanol or N-methylbutylamine using ethylene oxide and optionally further alkylene oxides such as propylene oxide.

As compounds of component A3), preference is given to using copolymers of the abovementioned type of ethylene oxide and propylene oxide having an ethylene oxide fraction of more than 50% by weight, more preferably from 55 to 89% by weight, based on the corresponding compounds of A3).

Suitable compounds of component A4) include any desired organic compound containing at least two free isocyanate groups per molecule, such as diisocyanates X (NCO)₂Wherein X is a divalent aliphatic hydrocarbon group having 4 to 12 carbon atoms, a divalent cycloaliphatic hydrocarbon group having 6 to 15 carbon atoms, a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms or a divalent araliphatic hydrocarbon group having 7 to 15 carbon atoms, which may be used alone or in mixtures with one another. Further examples of compounds which can be used as the diisocyanate component are described, for example, by W.Siefken in Justus LiebigsAnnalen der Chemie, 1949, page 56275-.

It is not important whether these isocyanates are prepared by the phosgene process or the phosgene-free process.

Naturally, it is also possible to use, as compounds of component A4), higher polyfunctional polyisocyanates known per se in polyurethane chemistry, or modified polyisocyanates known per se, for example containing carbodiimide, allophanate, isocyanurate, urethane, biuret and/or iminooxadiazinedione groups, if appropriate in certain proportions.

Preference is given to using tetramethylene diisocyanate, methylpentamethylene diisocyanate, Hexamethylene Diisocyanate (HDI), dodecamethylene diisocyanate, 1, 4-diisocyanatocyclohexane, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 2, 4 ' -and/or 4, 4 ' -diisocyanato-dicyclohexylmethane, 2, 2-bis (4-isocyanatocyclohexyl) propane, 1, 4-diisocyanatobenzene, 2, 4-diisocyanatotoluene, 2, 6-diisocyanatotoluene, 4, 4 ' -diisocyanatodiphenylmethane, 2, 2 ' -and 2, 4 ' -diisocyanatodiphenylmethane, 1, 3- (bis-2-isocyanatoprop-2-yl) benzene (TMXDI), 1, 3-and 1, 4-diisocyanatomethylbenzene (XDI), and mixtures of these compounds. Particular preference is given to hexamethylene diisocyanate, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethyl-cyclohexane and also 2, 4 '-and/or 4, 4' -diisocyanatodicyclohexylmethane or modified oligomeric polyisocyanates of the abovementioned type.

Suitable compounds of component A5) include aliphatic and/or cycloaliphatic primary and/or secondary polyamines having at least 2 primary or secondary amino functions, which may be used individually or as mixtures. Suitable ones include not only low molecular weight polyamines such as 1, 2-ethylenediamine, 1, 6-hexamethylenediamine, 1-amino-3, 3, 5-trimethyl-5-aminomethylcyclohexane (isophoronediamine), piperazine 1, 4-diaminocyclohexane, bis- (4-aminocyclohexyl) methane, adipic dihydrazide or diethylenetriamine and hydrazine or hydrazine hydrate but also polyetherpolyamines formally obtained by replacing the hydroxyl groups in the above polyether polyols with amino groups. Such polyether polyamines can also be prepared by reacting the corresponding polyether polyols with ammonia and/or primary amines.

Preference is given to 1, 2-ethylenediamine, 1, 6-hexamethylenediamine, 1-amino-3, 3, 5-trimethyl-5-aminomethylcyclohexane (isophoronediamine), piperazine 1, 4-diaminocyclohexane, bis (4-aminocyclohexyl) methane, adipic dihydrazide or diethylenetriamine and hydrazine or hydrazine hydrate, particular preference to 1-amino-3, 3, 5-trimethyl-5-aminomethylcyclohexane (isophoronediamine), 1, 2-ethylenediamine, piperazine or diethylenetriamine.

Suitable compounds of component A6) have at least one isocyanate-reactive hydrogen atom or at least one isocyanate group and at the same time at least one ionic group or one potentially ionic group.

Examples of compounds described here include tertiary amino group-containing alcohols of the type already exemplified in U.S. Pat. No. 4, 3479310, hydroxycarboxylic acids, hydroxysulfonic acids, aminocarboxylic acids or aminosulfonic acids. Instead of these synthesis components, it is also possible to use the corresponding salt derivatives, i.e. their quaternization and/or neutralization products. Suitable quaternizing and/or neutralizing agents for converting potentially ionic groups into ionic groups are likewise mentioned as examples in US-B3479310. Where a potentially ionic synthesis component is used, the at least partial conversion of the potentially ionic groups into ionic groups by quaternization or neutralization is carried out after or during the preparation of the polyurethane polyurea.

Preferred compounds of component A6) are those which contain at least two isocyanate-reactive groups in at least one ionic group or one potentially ionic group. Particularly preferred are compounds which, in addition to two hydroxyl groups or two primary or secondary amino groups, also contain one anionic or potentially anionic group.

Examples of suitable compounds of component A6) are diols carrying carboxyl and/or carboxylate groups, such as 2, 2-bis (hydroxymethyl) alkanoic acids, for example dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutyric acid, dimethylolvaleric acid or dihydroxysuccinic acid, and also diamines and polyamines carrying sulfonic acid or sulfonate groups.

More particularly preferred are dimethylolpropionic acid, alkali metal salts of N- (2-aminoethyl) -2-aminoethanesulfonic acid.

The component A) according to the invention can be prepared according to known preparation methods, for example as described in D.Dieterich in Houben-Weyl: methoden der Organischen Chemie, Vol E20, 1671-. Preferably according to the acetone process described herein.

In the acetone process, the synthesis of aqueous formulations of ionically modified polyurethanes and polyurethaneureas is carried out in a multi-step process.

In a first step, prepolymers containing isocyanate groups are synthesized from synthesis components a1) to a4) and optionally a 6). Wherein the amounts of the individual components used here are such that a ratio of NCO groups to the sum of OH and NH groups (isocyanate index) of from 1.1 to 3.5, preferably from 1.3 to 2 is obtained. The isocyanate content of the prepolymer obtained is from 1.5 to 7.5% by weight, preferably from 2 to 4.5% by weight and more preferably from 2.5 to 3.5% by weight. Furthermore, when calculating the amounts of synthesis components A1) to A4), care should be taken to ensure that the prepolymer to be prepared has an arithmetic number average functionality of from 1.80 to 3.50, preferably from 1.95 to 2.25.

In a second step, the prepolymer prepared in step 1 is dissolved in an organic, at least partially water-miscible solvent which does not carry isocyanate-reactive groups, such as acetone, 2-butanone, tetrahydrofuran, dioxane or mixtures of these solvents. A preferred solvent in this regard is acetone. The amount of solvent should be such that a solids content of 30 to 70 wt.%, preferably 35 to 60 wt.%, more preferably 40 to 55 wt.% can be obtained.

In a third step, the isocyanate-containing prepolymer solution from step 2 is reacted with amino-functional component a5) and optionally with component a6), if the latter has not been added in step 1, or is only partially added, to chain extend to a high molecular weight polyurethane resin. The amounts of component A5) and optionally A6) here are calculated such that from 0.3 to 0.93mol, preferably from 0.5 to 0.85mol, of isocyanate-reactive groups of component A5) and optionally A6) are present per mol of isocyanate groups in the dissolved prepolymer. The resulting ionically modified polyurethane or polyurethaneurea has an arithmetic number average isocyanate functionality of from 1.55 to 3.10, preferably from 1.90 to 2.35. The number average molecular weight (Mn) is 4500-.

In the fourth step, the high molecular weight polyurethane resin is precipitated in the form of a fine dispersion by adding water. The amount of water is calculated so that the formulation after step 5 has a solids content of 30-70 wt%, preferably 35-60 wt%, more preferably 40-55 wt%.

If potentially ionic compounds are used as synthesis component A6), they must be converted into the ionic form by addition of a suitable base or acid before precipitating the polymer with water. Bases which can be used include tertiary amines, such as triethylamine, triisopropylamine, ethyldiisopropylamine, triethanolamine, or triisopropanolamine, or, although not preferred, inorganic bases such as alkali metal or alkaline earth metal hydroxides, carbonates or bicarbonates may also be used.

In a fifth step, the organic solvent present is removed completely or partly by distillation, if appropriate under reduced pressure.

The proportion of component A3) is preferably less than 10 mol%, based on the amount of polyisocyanate A4) used, in order to ensure the desired high molecular weight structure of the polyurethane elastomer. In the case of more than 10% by weight of A3), it is advantageous to additionally use a trifunctional isocyanate-reactive component as constituent of component A2).

In a preferred embodiment of the present invention for the preparation of component A), 30.0 to 83.5 parts by weight of component A1), 0 to 30 parts by weight, preferably 0 to 15 parts by weight of component A2), 0 to 10 parts by weight, preferably 1 to 10 parts by weight of component A3), 15 to 50 parts by weight, preferably 20 to 40 parts by weight of component A4), 0.5 to 13 parts by weight, preferably 1 to 5 parts by weight of component A5) and 1 to 8 parts by weight, preferably 1.5 to 5.5 parts by weight of component A6) are used in the above-described multistage acetone process, wherein the sum of the amounts of the individual components A1) to A6) is 100 and the polymeric intermediates and end products obtained correspond to the statements given above.

In a particularly preferred embodiment of the present invention, the above starting materials are calculated such that a substantially hydroxyl-free ionically modified polyurethane and/or polyurethane polyurea dispersion is obtained having an ionic group content of from 1.5 to 50, preferably from 3.0 to 35 and more preferably from 3.5 to 15mmol/100g solids and the OH group content corresponds to an OH number of less than 6mg KOH/g, preferably less than 2.5mg KOH/g.

In an equally particularly preferred embodiment of the present invention, the above-mentioned starting materials are calculated so as to obtain a substantially hydroxyl-free ionic modified polyurethane and/or polyurethane polyurea dispersion which, in addition to ionic groups, contains from 0.1 to 20% by weight, preferably from 0.5 to 10% by weight and more preferably from 0.9 to 4% by weight, based on solids, of nonionic hydrophilic groups in the form of polyethylene oxide units.

To prepare component B) according to the invention, first of all, OH-or NH-functional polymers (polyurethane resins) are prepared and then converted into aqueous dispersions.

Polymer preparation is normally carried out in a similar manner to EP-A0355682, page 4, lines 39-45. In this procedure, one or more polyisocyanates according to the definition of component a4) above and one or more compounds of components a1) -A3) and a6) above are used to prepare isocyanate-functional prepolymers, and in a second reaction step, by reaction with compounds according to the definition of component a2) and/or a5) above in a nonaqueous medium, OH-or NH-functional polymers are obtained.

In addition, it is possible to prepare the OH-and/or NH-containing polyurethane resins directly by reacting compounds according to the definitions of the above components A1) -A6) in a nonaqueous medium as described in EP-A0427028, page 4, line 54 to page 5, line 1.

The OH components according to the definition of A1) which can be used for preparing component B) can be subjected to a distillation step under reduced pressure, as with A1), but are not essential. The distillation conditions set were the same as described above.

The process for preparing the polyurethane resins B) by reaction of the above-mentioned compounds is generally carried out at temperatures of from 0 to 140 ℃, preferably from 50 to 130 ℃ and more particularly from 70 to 110 ℃, depending on the reactivity of the isocyanates used. In addition, suitable catalysts, such as those commonly used in polyurethane chemistry, may also be used. Examples 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 polyurethane resin is preferably prepared in the presence of a solvent that is not reactive with isocyanate. Particularly suitable for this purpose are water-compatible solvents, such as ethers, ketones and esters, and also N-methylpyrrolidone. The amount of these solvents is advantageously not more than 30% by weight, preferably in the range from 5 to 25% by weight, based in each case on the sum of polyurethane resin B) and solvent.

The acid groups introduced in the polyurethane resin B) can be neutralized by adding a base. Suitable bases are amines or inorganic bases, such as ammonia or sodium or potassium hydroxide. Preference is given to tertiary amines with or without OH groups, for example trialkylamines having from 1 to 12, preferably from 1 to 6, carbon atoms in each alkyl radical. Suitable examples include trimethylamine, triethylamine, methyldiethylamine, tripropylamine, diisopropylethylamine, or dialkylmonoalkanolamines and trialkanolamines. The preferred alkanolamine is dimethylethanolamine. The neutralizing agent is generally used in a molar ratio of about 0.3: 1 to 1.3: 1, preferably about 0.4: 1 to 1: 1, based on the acid groups of the prepolymer.

The neutralization of the COOH groups is carried out at temperatures of from room temperature to +80 ℃, preferably from 40 to 80 ℃ and can be carried out before, during or after the preparation of the resin. Preferably, this neutralization step is carried out after preparation.

In a subsequent step, the hydroxyl-functional polyurethane resin is converted into an aqueous dispersion by adding water or by introducing it into water.

The aqueous polyurethane resin dispersion (compound of component B) obtained according to the process described hereinbefore generally has a number average molecular weight Mn of 1000-30000 Dalton, preferably 1500-10000 Dalton, an acid number of from 10 to 80mg KOH/g, 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 combining suitable crosslinkers C), it is possible to prepare not only one-component coatings but also two-component coatings, depending on the reactivity of the crosslinker or, where appropriate, the blocking of the crosslinker.

By one-component coating material is meant, in the sense of the present invention, a coating composition in which the binder component and the crosslinker component can be stored together without any significant or any harmful crosslinking reaction occurring for subsequent use. This crosslinking reaction only takes place at the time of application, after activation of the crosslinker. This activation can be obtained, for example, by raising the temperature.

By two-component coating materials is meant, in the sense of the present invention, coating compositions whose binder component and crosslinker component have to be stored in separate containers because of their high reactivity. The two components are mixed only shortly before application and they are generally able to react without further activation.

In order to accelerate the crosslinking reaction, it is, however, also possible to use catalysts or to use elevated temperatures. Examples of suitable crosslinkers include polyisocyanate crosslinkers as described in "lackkunsharze", h.wagner, h.f.sarx, Carl Hannser Verlag Munich, 1971, amide-and amine-formaldehyde resins, phenolic resins, aldehyde and ketone resins, such as phenyl-formaldehyde resins, resol resins, furan resins, urea resins, urethane resins, triazine resins, melamine resins, benzoguanamine resins, cyanimide resins, aniline resins.

As crosslinking agent C), polyisocyanates having free isocyanate groups are preferably used, since the resulting aqueous polyurethane coatings exhibit a particularly high level of industrial coating properties. Examples of suitable crosslinkers C) include lacquer polyisocyanates, such as polyisocyanates which contain uretdione, biuret, isocyanurate or iminooxadiazinedione groups and are prepared from hexamethylene diisocyanate, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethyl-cyclohexane (IPDI) or 2, 4 '-and/or 4, 4' -diisocyanatodicyclohexylmethane, for example those described in J.Prakt.chem./chem.ZTg.1994, 336, 185-zapropane 200. In this connection, preference is given to using the low-viscosity type as described in EP-A0798299 or DE-A19800286. Also suitable, although not preferred, are lacquer polyisocyanates containing urethane groups and based on 2, 4-and/or 2, 6-diisocyanatotoluene or 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane and low molecular weight polyols such as trimethylolpropane, the isomeric propyleneglycols or butyleneglycols, or any desired mixtures of these polyols.

If desired, the compounds containing free isocyanate groups can be converted into less reactive derivatives by reaction with blocking agents, these less reactive derivatives then being reacted only after activation (for example at elevated temperature). Examples of suitable blocking agents for these polyisocyanates include monoalcohols such as methanol, ethanol, butanol, hexanol, cyclohexanol and benzyl alcohol, oximes such as acetoxime, methyl ethyl ketoxime and cyclohexanone oxime, lactams such as epsilon-lactam, phenols, amines such as dipropylamine, benzyl-tert-butylamine or dibutylamine, dimethylpyrazole or triazole, and also dimethyl malonate, diethyl malonate or dibutyl malonate or cyclopentanone carboxyalkyl esters.

Preference is given to using low-viscosity, hydrophobic or hydrophilicized polyisocyanates which contain free isocyanate groups and are based on aliphatic, cycloaliphatic, araliphatic and/or aromatic isocyanates, more preferably on aliphatic or cycloaliphatic isocyanates, since in this way a particularly high level of resistance can be achieved in the coating films. The advantages of the binder dispersions of the invention are most clearly shown in combination with these crosslinking agents. These polyisocyanates generally have a viscosity (23 ℃) of from 10 to 3500 mPas. These polyisocyanates can be used, if necessary, as a blend with small amounts of inert solvents in order to reduce the viscosity to a number within the stated range. Triisocyanatononane can also be used alone or in mixtures as crosslinker component C).

The components A) and B) described here are generally sufficiently hydrophilic so that the dispersibility of the crosslinker C) (where the substances are not in any case water-soluble or water-dispersible) is ensured.

However, it is also possible to hydrophilize the crosslinkers C). Such water-soluble or water-dispersible, optionally blocked polyisocyanates can be obtained, for example, by modification with carboxylate, sulfonate and/or polyoxyethylene groups and/or polyoxyethylene/polyoxypropylene groups.

Hydrophilization of the polyisocyanates C) 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 suitable are the polyisocyanates containing allophanate groups described in EP-A-959087, page 3, lines 39-51, 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, as described in DE-A10007821, page 2, line 66 to page 3, line 5, and also polyisocyanates hydrophilicized with ionic groups (sulfonic acid, phosphonic acid groups), as described in DE-A10024624, page 3, lines 13 to 33. Hydrophilization by addition of emulsifiers customary in industry is likewise possible.

It will be appreciated that the use of mixtures of different crosslinker resins C) is generally also suitable.

As optional component D), it is possible to use the customary coating auxiliaries and additives which are added to the aqueous components A) and B) before, during or after their preparation, and also to the crosslinker component C). Examples of such adjuvants and additives include defoamers, thickeners, pigments, dispersants, delusterants, catalysts, anti-skinning agents, anti-settling agents or emulsifiers, and may include additives to enhance the desired soft touch effect and mixtures or combinations thereof.

In addition to the inventively essential components A) to D), the aqueous coating compositions of the invention may optionally comprise further binders or dispersions, for example those based on polyesters, polyurethanes, polyethers, polyepoxides or polyacrylates, and, if desired, pigments and further auxiliaries and additives known to the coatings industry.

The invention further provides for the use of the aqueous coating compositions of the invention as paints and coating systems for surfaces, for example of mineral building materials, for coating and sealing wood and wood-based materials, for coating metal surfaces (metallic coatings), for coating and painting asphalt or bitumen coverings, for coating and sealing various plastic surfaces (plastic coatings) and for high-gloss varnishes. However, they are particularly suitable for producing soft-touch effect coatings which ensure good solvent resistance and in particular good resistance to sun exposure (tanning liquor test). These coating compositions are preferably used for plastic coatings or wood coatings, wherein the curing is usually carried out at temperatures of from room temperature to 130 ℃. This two-component technique with non-blocked polyisocyanate crosslinkers allows the use of comparatively low curing temperatures in the above-mentioned range.

The aqueous coating compositions of the present invention are generally used in single coat coatings, or in clearcoat or topcoat films (topmost films) for multi-coat systems.

The coating can be formed by any of various spraying methods such as compressed air spraying, airless spraying or electrostatic spraying methods using a one-component or, where appropriate, two-component spraying device. However, the paint and coating compositions comprising the binder dispersions of the invention can also be applied by other methods, for example brushing, rolling or knife coating.

Examples

All chemicals used were purchased and used without further purification.

All percentages are considered to be wt% unless otherwise specified.

The average particle size was determined by laser correlation spectroscopy using a Zetasizer 1000 from Malvern Instruments Ltd, Worcestershire GB.

The flow-through viscosity of the dispersions was determined in accordance with DIN EN ISO 2431 using a DIN flow cup with a 4mm nozzle (Ford 4mm cup).

The viscosity measurements were carried out according to DIN EN ISO 3219 at a shear rate of 40s-1 in the form of rotational viscosity with Viscolab * LC3 from Paar Physica, Ashland, USA.

Polyurethane dispersion i (pud i): bayhydrol * PR240, available from Bayer AG, Leverkusen: a hydroxyl free aliphatic polyester polyurethane dispersion having a solids content of 40 + -1 wt.%, a pH of about 7.0 and a run-off time (23 ℃) of < 70 s.

Polyurethane dispersion ii (pud ii): bayhydrol * VP LS 2305, available from Bayer AG, Leverkusen: a hydroxyl free aliphatic polyester polyurethane dispersion having a solids content of 40 + -1 wt.%, a pH of 7.0 and a run-off time (23 ℃) of 20 s.

Polyurethane dispersion iii (pud iii): bayhydrol * XP 2429, available from bayer ag, levirkusen: a hydroxyl-functionalized aliphatic polyester polyurethane dispersion having a solids content of 55 ± 2 wt.%, a pH of 7.0 and a viscosity of 600mPas (23 ℃).

Polyisocyanate i (pic i): bayhydur * 3100, available from Bayer AG, levikusen: an aliphatic polyisocyanate having a solids content of 100% by weight, a viscosity (23 ℃) of 3800mPas and an isocyanate content of 17.4%.

Example 1 (polyesterdiol I)

5400g of a mixed ester of adipic acid, hexanediol and neopentyl glycol having an OH number of 66 were freed of low-boiling components using a customary laboratory film evaporator at an elevated temperature of 200 ℃ and a vacuum of 0.1 mbar with a metering rate of 300 g/h. The condensation temperature was 50 ℃.

5100g of a polyester diol I having an OH number of 56 was thus obtained.

Example 2 (polyester diol II)

5000g of caprolactone-hexanediol polycarbonate diol mixed ester having a number average molecular weight of 2000 Dalton (OH number 56; Desmophen * VPLS 2391, Bayer AG, Leverkusen, DE) were freed from low-boiling components using a customary laboratory film evaporator at an elevated temperature of 180 ℃ and a vacuum of 0.1 mbar with a metering rate of 300 g/h. The condensation temperature was 50 ℃.

4920g of a polyesterdiol II having an OH number of 52 are obtained.

Example 3 (polyester polyol I)

A15L reaction vessel with stirrer, heating device and water separator with cooling device was charged with 1281g of phthalic anhydride, 5058g of adipic acid, 6387g of hexane-1, 6-diol and 675g of neopentyl glycol, and the initial charge was heated to 140 ℃ over 1 hour under nitrogen. It is heated to 220 ℃ over a further 9 hours, at which temperature the condensation proceeds until an acid number of less than 3 is reached. The polyester polyol obtained had a viscosity of 54 seconds (determined as the flow time of an 80% solution of the polyester in methoxypropyl acetate in a DIN 4 cup at 23 ℃) and an OH number of 160mg KOH/g.

Example 4

420.5g of polyesterdiol I were placed in a 3.6L tank with a flat ground connection equipped with a heating device, reflux condenser and stirrer and dehydrated at 20 mbar and 100 ℃ for 60 minutes. 4.7g of hexane-1, 6-diol are added at 65 ℃ and the mixture is stirred until completely homogeneous. Subsequently, 75.5g of hexamethylene diisocyanate were added and after the exothermic reaction had subsided, the mixture was heated to 110 ℃. After a reaction time of 7 hours, a constant isocyanate content of 2.8% (theoretical 3.3%) was measured. The prepolymer was dissolved in 900g of anhydrous acetone and cooled to 38 ℃. An overhead-mounted dropping funnel was used to add a solution of 11.3g of sodium N- (2-aminoethyl) -2-aminoethanesulfonate and 4.3g of ethylenediamine in 150g of distilled water. After a reaction time of 15 minutes, the product was dispersed with 625g of distilled water. Acetone was removed under vacuum to obtain a fine dispersion having a solids content of 40 ± 1 wt% and a pH of 7.0.

Example 5

1700g of polyester diol I and 58.5g of a polyether monool having an OH number of 25 and prepared from n-butanol, ethylene oxide and propylene oxide (molar ratio 83: 17) were placed in a 3.6L pot with a flat ground connection fitted with a heating apparatus, reflux condenser and stirrer and the initial charge was dehydrated at 20 mbar and 100 ℃ for 60 minutes. The vacuum was then broken with nitrogen. Then, 250g of 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethyl-cyclohexane (isophorone diisocyanate) and 190g of hexamethylene diisocyanate are added and the mixture is stirred at 100 ℃ until it has an isocyanate content of 4.75%. After cooling the mixture to 50-60 ℃, 3900g of anhydrous acetone was added. The acetone solution was cooled to 45 ℃. Subsequently, a mixture of 107g of 1-amino-3, 3, 5-trimethyl-5-aminomethyl-cyclohexane (IPDA) in 210g of anhydrous acetone was injected. After the exothermic reaction subsides, a solution of 22g of sodium N- (2-aminoethyl) -2-aminoethanesulfonate and 5g of hydrazine monohydrate in 250g of water is added. After 10 minutes of subsequent stirring, 3500g of water were slowly introduced with vigorous stirring. A blue-white dispersion of the solid in a mixture of water and acetone was formed. After removal of the acetone by distillation, an aqueous dispersion having a solids content of 40. + -. 1% by weight remains. The particle diameter was measured by laser correlation spectroscopy, and a value of 210nm was obtained. The dispersion had a flow-out time of 22 seconds.

Example 6

1170g of polyester polyol I are introduced under nitrogen into a 6L reaction vessel having a cooling, heating and stirring device, and the initial charge is heated to 130 ℃ together with 1140g of polyester diol II, 90g of trimethylolpropane, 120g of dimethylolpropionic acid, 125g of N-methylpyrrolidone and 3.8g of tin (II) octanoate and homogenized for a further 30 minutes. It is then cooled to 80 ℃ and 480g of hexamethylene diisocyanate are added with vigorous stirring, and the mixture is heated to 140 ℃ using an exotherm and held at this temperature until no NCO groups can be detected.

Subsequently, the polyurethane obtained is cooled to 90-100 ℃ and 39g of dimethylethanolamine (degree of neutralization 50%) are added, and the mixture is homogenized for 15 minutes and dispersed with 2270g of demineralized water. The aqueous polyurethane resin dispersion thus obtained had an OH content of 1.4% (as 100%), an acid number of 18 (as 100%), an average particle size of 120nm and a viscosity of approximately 1700mPas at a solids content of 51.3% by weight (23 ℃ C.; D ═ 40 s-1).

Examples 7 to 13

VOC and haze values were determined according to the recommendation 278 "thermal desorption analysis method for characterizing organic emissions of non-metallic automotive materials" by Verband der deutschen automobilinddusie [ german automotive industry association ]:

examples	7	8	9	10	11	12	13
								PUD I	100
PUD II		100			52.5
								Example 4			100
Example 5				100		52.5	52.5
								PUD III					40.5	40.5
Example 6							40.5
								PIC I					7.0	7.0	7.0
Film thickness [ mu ] m]	76	53	59	59	76	84	73
								VOC[mg/kg]	324	233	4	8	211	111	61
Haze [ mg/kg]	526	526	10	14	480	334	213

The amount is in parts by weight.

If the VOC and haze values of examples 7 and 8 are compared with those of examples 9 and 10, the improvement of the dispersions of the invention over the prior art is very surprising. Even in the case of the standard system of aqueous 2K soft touch coatings (example 11), replacing some (example 12) or all (example 13) of the synthetic components with components according to the invention significantly reduced VOC and haze values.

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 (15)

1. An aqueous coating composition comprising:

A) an aqueous formulation of at least one ionically modified, substantially hydroxyl-free polyurethane and/or polyurethane urea,

B) an aqueous formulation of at least one ionically modified, hydroxyl-containing polyurethane and/or polyurethane urea, and

C) at least one cross-linking agent.

Wherein component a) is synthesized from the following compounds:

A1) one or more polyols having a number average molecular weight (Mn) of > 500 Dalton and an average OH functionality of > 1.5, substantially free of components which are volatile at temperatures of > 150 ℃ and pressures of < 10 mbar,

A2) optionally one or more polyols having a number average molecular weight (Mn) of 62 to 499 daltons and an OH functionality of 2 or more,

A3) optionally one or more hydrophilic compounds having an ethylene oxide content of 50% by weight and a number average molecular weight (Mn) of more than 400 Dalton, which contains at least one NCO-reactive group,

A4) one or more polyisocyanates selected from the group consisting of,

A5) optionally one or more aliphatic polyamines having a number average molecular weight (Mn) of 60 to 300 daltons and at least two primary or secondary amino groups or hydrazine, and

A6) one or more compounds which contain at least one NCO-reactive hydrogen atom or at least one NCO group and at the same time at least one ionic or potentially ionic group and which are different from the compounds A1) to A5) described above.

2. An aqueous coating composition according to claim 1, wherein an organic compound based on a polyester, a polylactone or a polycarbonate having a number average molecular weight (Mn) of 500-10,000 dalton and an average hydroxyl functionality of 1.5 to 6 is used as compound of component A1).

3. An aqueous coating composition according to claim 1, wherein a low molecular weight polyol having a number average molecular weight of from 62 to 499 daltons is used as compound of component a 2.

4. An aqueous coating composition according to claim 1, wherein the compound of component A3) is a monohydroxy-functionalized polyether based on ethylene oxide or ethylene oxide-propylene oxide.

5. An aqueous coating composition according to claim 1, wherein component a6) uses a compound having two hydroxyl primary or secondary amino groups and one anionic or potentially anionic group.

6. Coating obtained from an aqueous coating composition according to claim 1.

7. A substrate coated with the coating according to claim 6.

8. Soft feel coatings comprising a polyol according to claim 1, component A1).

9. The aqueous coating composition of claim 1 comprising D) auxiliaries and additives selected from the group consisting of defoamers, thickeners, pigments, dispersants, matting agents, catalysts, antiskinning agents, antisettling agents, emulsifiers and mixtures or combinations thereof.

10. An aqueous coating composition according to claim 2, wherein a low molecular weight polyol having a number average molecular weight of from 62 to 499 daltons is used as compound of component a 2.

11. An aqueous coating composition according to claim 2, wherein the compound of component A3) is a polyhydroxy-functionalized polyether based on ethylene oxide or ethylene oxide-propylene oxide.

12. An aqueous coating composition according to claim 3, wherein the compound of component A3) is a monohydroxy-functionalized polyether based on ethylene oxide or ethylene oxide-propylene oxide.

13. An aqueous coating composition according to claim 2, wherein the compounds of component A6) having two hydroxyl primary or secondary amino groups and one anionic or potentially anionic group are used.

14. An aqueous coating composition according to claim 3, wherein the compounds of component A6) having two hydroxyl primary or secondary amino groups and one anionic or potentially anionic group are used.

15. An aqueous coating composition according to claim 4, wherein the compounds of component A6) having two hydroxyl primary or secondary amino groups and one anionic or potentially anionic group are used.