MXPA06004399A - Polyurethane dispersions having improved film-forming properties - Google Patents

Abstract

The present invention relates to a process for preparing an aqueous coating composition by I) preparing a polyurethane dispersion that is free from NMP and other solvents

Description

POLYURETHANE DISPERSIONS WITH BEST MOVIE FORMATION PROPERTIES DESCRIPTION OF THE INVENTION The invention relates to a process for the preparation of aqueous polyurethane coating agents, free of solvent and to paints thus prepared with better film-forming properties. In order to reduce the emissions of organic solvents, aqueous coating agents are increasingly used instead of systems containing solvents. An important class of aqueous paint binders are the polyurethane dispersions already described in the state of the art. It is mainly possible to obtain solvent-free polyurethane dispersions (hereinafter referred to as PUD) according to the mixed acetone process or according to the mixed procedure of the prepolymer. However, especially PUDs, which must form film to give coatings that harden at room temperature or below, need a coalescing agent that reduces the minimum temperature of film formation. In many applications N-methylpyrrolidone (NMP) has been maintained as a single solvent, since it is not reactive towards isocyanate groups and is therefore suitable for reducing the viscosity in the formation of the prepolymer.

REF.:171507 In addition to this the NMP can dissolve the dimethylolpropionic acid frequently used in the chemistry of the PUD. In this way it is ensured that sufficient hydrophilic centers are incorporated in the form of carboxylate groups into the polyurethane backbone. However, it has been shown that NMP is a substance harmful to fruits and therefore the replacement of this solvent is necessary. DE-A 3613492 discloses a process for preparing free dispersions of co-solvents according to the so-called acetone process. In this document, an organic solution of 20 to 50% of a hydrophilic polyurethane is prepared, for example by an elongated chain in acetone, and then it is transformed by addition with water to a dispersion. After distilling off the acetone, a solvent-free dispersion is obtained. These dispersions also preferably have a nonionic hydrophilicity and can be dried at room temperature to give hard, clear films. If a reduction of the film-forming temperature or a drying delay were necessary, coalescence co-solvents such as diacetone-alcohol, NMP, ethylene glycol monobutyl ether or diethylene glycol monobutyl ether in amounts <L> would be used together; 5% by weight (based on the dispersion) (column 11, lines 58 to 65). It is disadvantageous in these systems that the products present a resistance to water and ethanol not enough and the use of co-solvent co-solvents is indicated to achieve adequate processing. Equally disadvantageous in this process is the comparatively large amount of solvent that must be removed by distillation after the dispersing step. The object of the present invention was to provide exclusively ionic hydrophilicized polyurethane dispersion paints which are free of solvent and NMP. Furthermore, the coating agents according to the invention should have better film-forming properties and the coatings prepared therefrom have good resistance to chemicals and water, as well as have hardness greater than 75 seconds of pendulum. Surprisingly, this objective has been achieved by providing hardness-regulated polyurethane dispersions, which are prepared with a low-boiling solvent, which is distilled off after dispersion, and then high-point ethylene or propylene glycol ethers are added thereto. of boiling point (boiling point> 150 ° C) and optionally thickeners and / or leveling agents and / or defoamers and / or other paint coadjuvants. These solvent-containing dispersion paints form films, especially on absorbent substrates better than those with other cosolvents such as, for example, NMP, which are used in the same amounts. Dispersions containing glycolic cosolvents have minimum film formation temperatures below 20 ° C and lead to hard coatings, especially high quality with very good film optics, which can also be processed on absorbent substrates such as wood. Therefore, the present invention provides a process for the preparation of aqueous coating agents, characterized in that I) a dispersion of solvent-free polyurethane and NMP is prepared, in which 1.1) a first step is obtained in a first step. NCO prepolymer solution in a concentration of 66 to 98% by weight of a solvent having a boiling point below 100 ° C at normal pressure by reaction of: a) one or more polyisocyanates, b) one or more polyols with average molecular weights Mn from 500 to 6000, c) one or several polyols with average molecular weights from 62 to 500, d) one or more compounds containing an ionic group or a group capable of forming an ionic group, 1. 2) in a second stage the prepolymer of NCO 1.1) is dispersed in water, performing before, during or after the dispersion an at least partial neutralization of the ionic groups, 1.3) in a third stage a chain elongation with e) a or several polyamines with average molecular weights Mn lower than 500 and 1.4) in a fourth stage the solvent is completely removed by distillation and then added together or separately to the polyurethane (I) II dispersion) from 1 to 7% by weight of an ethylene or propylene glycol ether as well as III) other paint additives. Aqueous coating compositions obtained according to the process according to the invention are also the object of the present invention. The polyruetane dispersion according to the invention preferably contains a hard segment (HS) content between 50 and 85% by weight, particularly preferably between 55 and 85% by weight. 75% by weight, increasing the amount of isocyanate referred to the amount of solid to between 35 and 55% by weight, preferably 39 and 50% by weight. The acid number of the solid resin is between 12 and 30 mg of KOH / g of solid resin, preferably 15 and 28 mg KOH / g solid resin. The solid segment content is calculated as follows: 100 * [Mass a) + Mass. { c) + Mass. { d) + Mass. { e)] jMase a, b, c, d, é) As component a), the polyisocyanates normally used in polyurethane chemistry are suitable, such as, for example, diisocyanates of the formula R1 (NC0) 2, in which R1 represents an aliphatic hydrocarbon radical having 4 to 12 carbon atoms, a cycloaliphatic hydrocarbon radical with 6 to 15 carbon atoms, an aromatic hydrocarbon radical with 6 to 15 carbon atoms or an araliphatic hydrocarbon radical with 7 to 15 carbon atoms. Examples of preferred diisocyanates are tetramethylene diisocyanate, hexamethylene diisocyanate, 4,4'-diisocyanatodiphenylmethane, 2,4'-diisocyanatodiphenylmethane, 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene or, a, a ', a'-tetramethyl-m- or p -xylenediisocyanate as well as mixtures of the aforementioned diisocyanates. Especially preferred diisocyanates are l-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate) and 4,4'-diisocyanatodicyclohexylmethane. Optionally, small amounts of isocyanates can be used, for example, trifunctional and / or higher, and thereby a degree of branching or crosslinking is guaranteed. determined from polyurethane. The amount of the polyisocyanate to be used is governed by its functionality and is dimensioned so that the NCO prepolymer can still be stirred and dispersed. Isocyanates of this type are obtained, for example, by reacting difunctional isocyanates with one another, so that a part of their isocyanate groups are derivatized giving isocyanurate groups, biuret, allophanate, uretdione or carbodiimide. Also suitable are those polyisocyanates hydrophilized by ionic groups. Examples of isocyanates of this type are described in EP-A 510438, in which polyisocyanates are reacted with carboxylic compounds with OH functionality. The hydrophilized polyisocyanates are furthermore obtained by reaction of polyisocyanates with compounds reactive towards isocyanates carrying sulfuric acid groups. Polyisocyanates of this type can have high functionalities, for example of more than 3. Suitable polymer polyols b) have a molecular weight range (Mn) of from 500 to 6000, preferably from 500 to 3000 and more preferably from 650 to 2500. The OH functionality is at least 1.8 to 3, preferably 1.9 to 2.2, and particularly preferably 1.92 to 2.0. The polyols are, for example, polyesters, polyethers based on propylene oxide and / or tetrahydrofuran, polycarbonates, polyester carbonates, polyacetals, polyolefins, polyacrylates and polysiloxanes. Polyesters, polyethers, polyester carbonates and polycarbonates are preferred. Polyesters, polyethers, polyester carbonates and bifunctional polycarbonates are especially preferred. Mixtures of the polymer polyols b) described are also suitable. Additionally, b) fatty acid-containing polyesters, b) which are obtained by esterification or transesterification product of fatty acids or desiccant and / or non-desiccant oils with polyol compounds can also be used in admixture with the b) polyols. less bifunctional, as described, for example, in EP-A 0017199 (page 10, line 27 to page 11, line 31). Preferably, tri- and tetrafunctional hydroxylic components, such as, for example, trimethylolethane, trimethylolpropane, glycerin or pentaerythritol, are preferably used as polyol compounds. As a polyol b), partially dehydrated castor oil, which is obtained by heat treatment of castor oil with acid catalysis, is also suitable and is described in EP-A 0709414 (page 2, lines 37 to 40). Also suitable as polyols are b) those disclosed in DE-A 19930961 (page 2, lines 46 to 54, page 2, line 67 to page 3, line 3). There Aliphatic and cycloaliphatic monocarboxylic acids with 8 to 30 carbon atoms are reacted, such as, for example, oleic acid, lauric acid, linoleic acid, linolenic acid with castor oil in the presence of glycerin. Also suitable are polyols bl) transesterification products of castor oil and one or more other triglycerides. Especially preferred as components are b) fatty acid-containing, bisfunctional components on statistical average with respect to OH groups, which contain glycerin or trimethylolpropane units. Transesterification products with average OH functionalities of 2 from castor oil with some other oil other than castor oil are very especially preferred in this respect. The polyesters bl) containing fatty acid are preferably used with polyols b) having an Mn of 650 to 2500 g / mol and OH functionalities of 1.92 to 2. The polyesters bl) containing fatty acid are used with particular preference with polyols b) having a Ma of 650 to 2500 g / mol, OH functionalities of 1.92 to 2 and are selected from the group of esters, ethers, carbonates or sterescarbonate. Polyols c) of low molecular weight with a molecular weight range (Mn) of 62 to 500, preferably of 62 to 400 and especially preferably of 90 to 300 are the alcohols bifunctionals normally used in polyurethane chemistry, such as, for example, ethanediol, 1,2- and 1,3-propanediol, 1,2-, 1,3- and 1,4-butanediol, 1,5-pentanediol, 1, 6-hexanediol, neopentyl glycol, cyclohexane-1, -dimethanol, 1,2- and 1,4-cyclohexanediol, 2-ethyl-2-butylpropanediol, diols containing oxygen from ether, such as, for example, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol , tripropylene glycol, polyethylene glycols, polypropylene glycols or polybutylene glycols as well as mixtures of these products. Monofunctional alcohols with 2 to 22, preferably 2 to 18, carbon atoms can also be added in part. These include, for example, ethanol, 1-propanol, 2-propanol, primary butanol, secondary butanol, n-hexanol, and its isomers, 2-ethylhexyl alcohol, ethylene glycol monomethyl ether, diethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol butyl ether, dipropylene glycol monobutyl ether, tripropylene glycol monobutyl ether, 1-octanol, 1-dodecanol, 1-hexadecanol, lauryl alcohol and stearyl alcohol. The trifunctional alcohols of higher functionality of the indicated molecular weight range can be used together in part in a quantity, so that the polymer solution can be stirred. Neutralization components for anionic dispersions are suitable tertiary amines, ammonia as well as alkali hydroxides known to the person skilled in the art. The cationic resins are carried by protonation or quaternization to the water-soluble form. Suitable as component d) are low molecular weight compounds which contain ionic groups or are capable of forming an ionic group, such as, for example, dimethylolpropionic acid, dimethylolbutyric acid, hydroxypropivalic acid, (meth) acrylic acid reaction products and polyamines ( example, DE-A 19750186, page 2, lines 52 to 57) or polyol components containing sulfonate groups such as, for example, the propoxylated adduct of sodium hydrogensulfite in 2-butenediol or those described in EP-A 0364331 ( page 6, lines 1 to 6), of polyester salts constituted by sulfoisophthalic acid. Also suitable are OH-functional compounds containing cationic groups or units which can be converted into cationic groups, such as, for example, N-methyldiethanolamine. Preferred are components containing carboxylic acid groups. Especially preferred is dimethylolpropionic acid. Preferably the NCO prepolymer does not contain nonionic hydrophilizing agents. Chain extenders e) take into account aminopolyols or polyamines with a molecular weight of less than 500, such as, for example, hydrazine, ethylenediamine, 1,4- diaminobutane, isophoronediamine, 4,4'-diaminodicyclohexylmethane, ethanolamine, diethanolamine, piperazine or diethylenetriamine. In addition to the use of polyfunctional compounds reactive towards isocyanates, the termination of the polyurethane prepolymer with monofunctional alcohols or amines can also be considered, in order to regulate the molecular weight of the polyurethane. Preferred compounds are aliphatic monoalcohols or monoamines with 1 to 18 carbon atoms. Ethanol, n-butanol, ethylene glycol monobutyl ether, 2-ethylhexanol, 1-octanol, 1-dodecanol, 1-hexadecanol or N-dialkylamines are particularly preferably used. Solvents for the preparation of the polyurethane dispersion I) are those which boil under normal pressure below 100 ° C, do not have groups that are reactive towards isocyanates and, in addition, are soluble in water. In addition, the solvent must be able to be distilled off from the prepared dispersion. Examples of solvents of this type are acetone, methyl ethyl ketone, tert-butyl methyl ether or tetrahydrofuran. The preparation of the solvent-free, aqueous polyurethane dispersions runs in four stages. First, the preparation of the NCO prepolymer is carried out by reacting an excess of component a) with components b), c) and d). In this respect, the prepolymer of NCO should present an NCO functionality < 2,3. The solvent can be added before, during or after the prepolymerization in the amount that generates a solution at 66 to 98%, preferably at 75 to 95%. A neutralizing agent necessary for the neutralization of the potentially ionic groups may already be present at the beginning of the reaction, but must be incorporated later into the finished prepolymer, if it is not added to the water for dispersion. However, the amount of neutralization amine can also be partitioned before the dispersion between the organic and the aqueous phases. In a second step, the dispersion is carried out, in which the water is either added to the resin or conversely the resin to the water under conditions of sufficient shear stress. In the third stage the chain elongation is carried out, where the quantity of the components e) reagents against isocyanate containing nitrogen are dimensioned so that they can be reacted from 25 to 105%, preferably from 55 to 100% , with particular preference from 60 to 90% of the isocyanate groups. The remaining isocyanate groups react with chain elongation with the water present. The complete separation by distillation of the solvent is preferably carried out under vacuum and constitutes the fourth stage. "Solvent-free" in the sense of the present application means that the dispersion presents = 0.9% in weight, preferably = 0.5% by weight, with particular preference = 0.3% by weight of solvent. The solid content of the solvent-free dispersion is between 25 and 65% by weight. A solid range of 30 to 50% by weight, particularly preferably 34 to 45% by weight, is preferred. For the preparation of the coating agent according to the invention, the solvent-free dispersion is added from 1 to 7% by weight, preferably from 1 to 5% by weight (based on the dispersion of I) of an ether II) ethylene - or propylene glycol with OH monofunctionality or a mixture of such ethers II). Examples of ethylene or propylene glycol ethers with OH monofunctionality of this type are etilglicolmetiléter, etilglicoletiléter, dietilglicoletiléter, dietilglicolmetiléter, trietilglicolmetiléter, butylglycol, butyldiglycol, propylene glycol methyl ether, dipropylene glycol, tripropylene glycol, propilenglicolbutiléter, propilenglicolmonopropiléter, dipropilenglicolmonopropiléter, propilenglicolfeniléter and etilenglicolfeniléter. Preferred are ethyl glycol monomethyl ether, butyl glycol, butyl diglycol, propylene glycol monomethyl ether and propylene glycol monobutyl ether. It is preferred to add the ether or the mixture of ethers, as long as the components are soluble in water, as a solution watery with agitation. The water-insoluble components are added slowly to the dispersion with stirring. In part, ethylene or propylene glycol ethers, which do not have OH groups, can also be used, such as, for example, ethylene glycol dimethyl ether, triethyl glycol dimethyl ether, diethyl glycol dimethyl ether or Proglyde DMM (dipropylene glycol dimethyl ether) from Dow Chemicals (Schwalbach, Germany). Coating additives (III) are added to the coating agent containing co-solvents at the end. Paint additives are, for example, defoamers, deaerators, thickeners, leveling and surface additives. It is preferred to add a commercial antifoam first with agitation. For this purpose, mineral oil defoamers, silicone defoamers and also silicone-free polymeric antifoams as well as polyethersiloxane copolymers are taken into account. Suitable deaerators are polyacrylates, dimethylpolysiloxanes, organically modified polysiloxanes, such as, for example, polyoxyalkyldimethylsiloxanes and fluorosilicones. Furthermore, thickeners are used which make it possible to adjust the viscosity of the coating agents according to the invention in correspondence with the application process. Thickeners are suitable as thickeners commercial products such as, for example, natural organic thickeners, for example dextrins or starches, organically modified natural substances, for example cellulose ethers or hydroxyethylcellulose, completely synthetic organic substances, for example poly (meth) acrylic or polyurethane compounds as well as thickeners inorganic, for example, bentonites or silicic acids. It is preferred to use fully synthetic organic thickeners. It is preferred to use especially acrylate thickeners which, if appropriate, are further diluted with water before the addition. Leveling or surface additives can also be added as silicone additives, ionogenic or non-ionogenic acrylates or low molecular weight surfactant polymers. Silicone surfactants that wet the substrate can also be added, such as, for example, polyether-modified polydimethylsiloxanes. The addition of components II) and III) can be carried out preferably spread over time as described above, however these can also be incorporated at the same time, by adding the solvents containing ether and the paint additives together or a mixture of ether-containing solvents and paint additives to the polyurethane dispersion I). It also can add the mixture of additives III) and solvents containing ether II) to the dispersion I). Paint preparation is carried out at temperatures between 5 and 50 ° C, preferably between 20 and 35 ° C. The coating agents obtained according to the invention can be applied as a one-component system (1C) of physical drying or also as a two-component system (2C). The object of the present invention is therefore also the use of the aqueous coating agents according to the invention as binders in one-component systems (1C) or as a binder constituent in a two-component system (2C). In the 2C systems, the dispersions according to the invention are hardened preferably with the hydrophilic and / or hydrophobic paint polyisocyanates known to the person skilled in the art. In the use of the paint polyisocyanates it may be necessary to dilute these with amounts of cosolvent, to achieve a good mixture of the polyisocyanates with the dispersion. Solvents which are used here are solvents which are non-reactive towards isocyanate groups, such as, for example, ethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethyl glycol dimethyl ether, Proglyde® DMM (dipropylene glycol dimethyl ether), butyl acetate, methoxybutyl or dibasic esters, such as those marketed by the DuPont company. The coating agents according to the invention can be applied to discrete substrates, for example, wood, metal, plastic, paper, leather, textiles, felt, glass or mineral substrates as well as already coated substrates. An especially preferred use is the use of the aqueous coating agents according to the invention for the preparation of coatings on absorbent substrates such as, for example, wood or mineral open-pore substrates. The coating agents according to the invention can be used as such or in combination with other adjuvants and additives of the paint technology, such as fillers and pigments. The application of the coating agents containing the polyurethane dispersion according to the invention can be carried out in a known manner, for example by painting, pouring, scraping, spraying, spraying, spraying, rolling or dipping.

Examples Table 1: Components used Precursor of the polyester oligomer In a 5 1 reactor with distillation column, 3200 g of castor oil and 1600 g of soybean oil and 2.0 g of dibutyltin oxide are introduced. A stream of nitrogen (5 1 / h) was conducted through the reactants. It was heated in the period of 140 minutes to 240 ° C and after 6 hours at 240 ° C it was cooled. The OH number was 108 mg KOH / g, the acid number 2.5 mg KOH / g. Dispersion 1 205.5 g of a polyester (adipic acid, 1,6-hexanediol, OH number 66 mg KOH / g), 19 g of dimethylolpropionic acid and 58.0 g of 1,6-hexanediol were dehydrated. ° C to vacuum. It was then cooled to 55 ° C, 124.2 g of acetone and 226.9 g of Desmodur® I were successively added and boiled under reflux, until an NCO content of 3.9 wt% was obtained (content in Theoretical NCO of 4.0%). It was adjusted again to 55 ° C and 12.9 g of triethylamine was added to the clear solution, which was stirred well. The complete neutralized prepolymer solution (55 ° C) was dispersed with vigorous stirring in 770 g of water, which was placed at a temperature of 30 ° C. After the dispersion it was stirred for 5 minutes, before being added in the period of 5 minutes. minutes a solution of 4.2 g of hydrazine hydrate and 9.2 g of ethylenediamine, dissolved in 90 g of water. Then the acetone at 40 ° C under vacuum (12 kPa) completely by distillation. For the reaction of the remaining isocyanate groups, it was stirred at 40 ° C until NCO was no longer observed by IR spectroscopy. After cooling to 30 ° C it was filtered through a T5500 filter by Seitz. Characteristic data of the polyurethane dispersion: Average particle size: 60 nm (laser correlation spectroscopy, LCS) pH (20 ° C) (20% aqueous solution): 7.8 Solids content: 35.0% Content in hard segment: 61% acid index (based on solid resin): 15.5 mg KOH / g Dispersion 2 140.3 g of the oligomeric polyester precursor was added to a mixture of 181.0 g of PolyTHF® 2000 , 37.2 g of dimethylolpropionic acid and 18.3 g of 1,6-hexanediol at 55 ° C 89.9 g of acetone and 19.6 g of triethylamine were added and mixed. 275.4 g of Desmodur® were added and the reaction mixture was heated to reflux until an NCO content of 4.3% was obtained. 500 g of the prepolymer were dispersed with vigorous stirring in 720 g of water, which was placed at a temperature of 30 ° C. After 5 minutes a solution of 4.2 g of hydrazine hydrate was added over the period of 5 minutes. 6.2 g of ethylenediamine in 73 g of water. For the complete reaction of the isocyanate groups was stirred at 45 ° C until no NCO was evidenced by IR spectroscopy. After cooling, filtration was performed through a T5500 filter from Seitz. Characteristic data of the polyurethane dispersion: Average particle size (LCS): 60 nm pH (20 ° C) (10% aqueous solution): 8.4 Solid content: 35.0% Hard segment content: 52% acid number (based on the solid resin): 23.3 mg KOH / g Comparative dispersion 3 (containing NMP) 300.7 g of a polyester (adipic acid, 1,6-hexanediol) were dehydrated; OH number 66 mg KOH / g), 27.8 g of dimethylolpropionic acid and 84.8 g of 1,6-hexanediol at 110 ° C under vacuum. It was then cooled to 90 ° and obtained by the addition of 181.7 g of NMP * a clear solution to which 332.1 g of Desmodur® I were added at 70 ° C. It was stirred at 90 ° C to a NCO of 3.8% by weight (theoretical NCO content of 4.0% by weight). Then 21.0 g of triethylamine were added at 70 ° C and stirred for 10 minutes. 700 g of the neutralized solution were dispersed with vigorous stirring in 810 g of water, which was placed at a temperature of 30 ° C. After the dispersion it was stirred for 5 minutes, before a solution of 4 was added over the period of 5 minutes. , 2 g of hydrazine hydrate and 9.2 g of ethylenediamine, dissolved in 90 g of water. For the reaction of the isocyanate groups, it was stirred at 40 ° C until NCO was no longer detected by IR spectroscopy. After cooling to 30 ° C it was filtered through a T5500 filter by Seitz. Characteristic data of the polyurethane dispersion: Average particle size (LCS): 60 nm pH (20 ° C) (10% aqueous solution): 7,8 Solids content: 35.0% Co-solvent content: 8.3 % * It is tested to reduce the amount of NMP, so that a dispersion with a cosolvent content of 5% results, thus generating a highly viscous resin melt that can no longer be completely dispersed. Comparative Example 4 (containing NMP) 339 g of PolyTHF® 2000, 248 g of the polyester oligomer precursor, 70 g of dimethylolpropionic acid, 34 g of 1,6-hexanediol and 186 g of N-methylpyrrolidone were heated to 70 ° C. C and shaken, until a clear solution was generated. Then 516 g of Desmodur® W were added and heated to 100 ° C. It was stirred at this temperature until the NCO content of 4.6% was reached and then cooled to 70 ° C. They were added at this temperature 39 g of triethylamine. 500 g of this solution were dispersed with vigorous stirring in 640 g of water, which was placed at a temperature of 30 ° C. After dispersion it was stirred for 5 minutes before a solution of 4.1 g of hydrazine hydrate and 10.2 g of ethylenediamine in 100 g of water was added over the course of 5 minutes. For the complete reaction of the isocyanate groups, it was stirred at 45 ° C until NCO was no longer detected by IR spectroscopy. After cooling to 30 ° C it was filtered through a T5500 filter by Seitz. Characteristic data of the polyurethane dispersion: Average particle size (LCS): 45 nm pH (20 ° C) (10% aqueous solution): 8.2 Solids content: 35.0% Co-solvent content: 5.1 % Comparative Example 5 500.0 g of a polyester of adipic acid as well as 1,6-hexanediol and neopentyl glycol (in molar ratio 0.65: 0.35) of OH index 66 and 59.0 g of a second were mixed polyester of adipic acid as well as 1,6-hexanediol of OH number 133 with 31.5 g of 1,4-butanediol, 43 g of a polyether of a mixture of 84% ethylene oxide and 16% propylene oxide , initiated on n-butanol (OH number 26), 40.2 g of dimethylolpropionic acid and 13.4 g of trimethylolpropane and reacted at 70 ° C with 488.0 g of Demodur® I until the NCO content of the NCO prepolymer had reached 7.3%. The generated prepolymer was dissolved in 2420 g of acetone and 30.3 g of triethylamine were added at 30 ° C.

An aqueous solution of 24 g of ethylenediamine, 10.3 g of diethylenetriamine and 310 g of water in the range of 5 minutes was then added to the prepolymer solution. After this was stirred for 15 minutes, 2110 g of water were added with intensive stirring. From the dispersion generated, the acetone was removed under reduced pressure. Characteristic data of the polyurethane dispersion: Average particle size: 115 nm pH (20 ° C) (10% aqueous solution): 7.4 Solid content: 35.0% Film forming properties of the dispersions Divided the cosolvent-free dispersion 2 was diluted with different cosolvent / water mixtures or, as long as the cosolvent was not miscible with water, directly with a cosolvent (these are indicated in table 2 with *). The dispersions containing co-solvent obtained were applied with a doctor blade in a wet film layer thickness of 210 μm on a glass plate. After the drying at 20 ° C of the films, the evaluation was carried out (table 2). As a comparison, comparative dispersion 4 was applied (content in cosolvent of 5.1%) without other additions with the same layer thickness. After drying, it resulted in a smooth, transparent and crack-free film. Table 2: Films obtained from the cosolvent-free dispersion 2 by adding different amounts of cosolvent / cosolvent. 2% thickeners (on the dispersion) of a 5% solution of Acrysol® RM 8 were added.

Codisolvent Codisolven e Co-solvent at 3% on 5% on dispersion Butylglycol dispersion Smooth, Smooth-free, Crack-free fissures Butildiglicol Smooth, Smooth-free, Crack-free fissures Trip opi1englicol Smooth, Smooth-free, Crack-free fissures Dowanol® TPnB Smooth, Smooth-free, Crack-free fissures Dowanol® PnB Smooth, Smooth-free, Crack-free fissures N- Many fissures Few fissures long methylpyrrolidone long on the edge Film formation properties as well as hardnesses of different dispersions with different cosolvent contents (s) were studied (see tables 3 and 4). 2% thickeners (on the dispersion) of a 5% solution of Acrysol® RM 8 were added as thickeners. Resistance to ethanol and water in films applied on wood was carried out. The coatings were dried one day before at room temperature. The ethanol resistance was determined by placing a cotton pad soaked with ethanol over the coating for five minutes. The buffer was covered with a small beaker. The procedure was carried out analogously with water as the test substance, but the treatment was left for 24 hours on the coating. Rating of the resistances 1 = bad, coating destroyed 5 = very good, invariable coating Table 3: Properties of film formation and hardness Table 4: Comparison of 2C systems that were diluted with • NMP or butyl diglycol It is noted that in relation to this date, the best method known to the applicant or to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Claims (13)

CLAIMS Having described the invention as above, the content of the following claims is declared as property:

1. Process for the preparation of aqueous coating agents, characterized in that I) a dispersion of solvent-free polyurethane and NMP is prepared, in which 1.1) firstly a NCO prepolymer solution in a concentration of 66 to 98% by weight of a solvent having a boiling point below 100 ° C at normal pressure by reaction of: a) one or more polyisocyanates, b) one or more polyols with average molecular weights Mn from 500 to 6000, c) one or several polyols with average molecular weights of 62 to 500, d) one or more compounds containing an ionic group or a group capable of forming an ionic group, 1.

2) in a second stage the NCO prepolymer

1. 1) is dispersed in water, carried out before, during or after the dispersion a at least partial neutralization of the ionic groups, 1.

3) in a third step a chain elongation with e) one or more polyamines with average molecular weights Mn less than 500 and 1.4) in a fourth stage the solvent is completely removed by distillation and then or 1 to 7% by weight of an ethylene or propylene glycol ether as well as III) other paint additives are added together or separately to the polyurethane (I) II dispersion) 2. Aqueous coating agent obtained in accordance with claim 1. Aqueous coating agent according to claim 2, characterized in that the polyurethane dispersion has a hard segment content (HS) between 50 and 85% by weight, the amount of isocyanate being increased by the amount of solid to between 35 and 55% by weight.

4. Aqueous coating agent according to claim 2, characterized in that the acid number of the solid resin is between 12 and 30 mg of KOH / g of solid resin.

Aqueous coating agent according to claim 2, characterized in that polyols b) are used in combination with polyesters b) containing fatty acid.

6. Aqueous coating agent according to claim 5, characterized in that the components b) are bisfunctional fatty acid-containing components on statistical average with respect to the OH groups, which contain glycerin or trimethylolpropane units.

7. Aqueous coating agent according to claim 5, characterized in that the components bl) are products of transesterification, with average OH functionalities of 2, of castor oil with another oil other than castor oil.

Aqueous coating agent according to claim 5, characterized in that the polyols have an Mn of 650 to 2500 g / mol, OH functionalities of 1.92 to 2 and are selected from the group of esters, ethers, carbonates or sterescarbonate .

Aqueous coating agent according to claim 2, characterized in that they are component II) ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, butyl diglycol, propylene glycol monomethyl ether or propylene glycol monobutyl ether.

10. Use of the aqueous coating agents according to claim 2 as a binder in one component systems (1C).

11. Use of the aqueous coating agents according to claim 2 as a binder constituent in a two component system (2C).

12. Use of the aqueous coating agents according to claim 2 for the preparation of coatings on absorbent substrates.

13. Use according to claim 12, characterized in that the absorbent substrates are wood or mineral substrates with an open pore.