METHOD AND DEVICE FOR PRODUCING A REDUCED FOAMING POLYURETHANE DISPERSION

Description

[0001] The present invention relates to a method for producing a polyurethane dispersion, comprising the steps of: I) Providing polyurethane polymers and / or polyurethane prepolymers A) in a liquid phase comprising a first solvent which is miscible with water and which has a lower boiling point than water; II) In the event that isocyanate-functional polymers or isocyanate-functional prepolymers were provided in step I): adding NCO-reactive compounds so that at least a partial reaction with the polymers or prepolymers occurs; III) Distilling off the water-miscible first solvent to obtain an aqueous polyurethane dispersion; wherein the liquid phase in step I) continues to comprise water and / or water is added to the mixture obtained after step II) after step II) and foam bubbles formed during step III) are at least temporarily contacted with a second solvent, wherein the contact of the foam bubbles with the second solvent is effected by spraying from one or more spray nozzles.

[0002] In the production of low-solvent polyurethane dispersions, the polymer is initially dissolved in acetone and then dispersed in water. The acetone is subsequently removed by vacuum distillation. This process often generates large quantities of foam, necessitating a significant reduction in the distillation rate. This, in turn, lowers the space-time yield of the system. The addition of defoamers, which are frequently based on hydrophobic mineral oils or silicone oils, can only partially suppress foam formation. Furthermore, the presence of defoamers is undesirable in many products. For example, in paints, defoamers can cause flow problems.

[0003] DE 27 08 442 A1 relates to a process for the production of modified aqueous plastic dispersions, wherein liquid organic diisocyanates, optionally in the simultaneous presence of catalysts accelerating the isocyanate polyaddition reactions and / or the dimerization of isocyanate groups and / or the carbodiimidation of isocyanate groups and / or the trimerization of isocyanate groups, are introduced into non-sedimented aqueous plastic dispersions containing polyurethanes at room temperature, while mixing at a temperature at which visible foaming does not occur, the aforementioned temperature condition is maintained after the addition of the diisocyanate until at least 50% of the isocyanate groups of the introduced diisocyanate have reacted, and the reaction is optionally then completed by heating to temperatures up to 100 °C.

[0004] JP H04 372603 A discloses the production of water-soluble or water-swellable polymers. US2015 / 005444 A1 discloses a polyurethane prepolymer which is dissolved in acetone and extended with carbodihydrazide and diaminosulfonate. The resulting polyurethane is then dispersed by adding water. Subsequently, the acetone is distilled off under slight vacuum.

[0005] The present invention aims to provide a method in which less foaming occurs during the distillation of organic solvents. This objective is achieved by a method according to claim 1. Advantageous embodiments are specified in the dependent claims. They can be combined as desired, unless the context clearly indicates otherwise.

[0006] A process for producing a polyurethane dispersion includes the following steps: I) Providing polyurethane polymers and / or polyurethane prepolymers A) in a liquid phase comprising a first solvent which is miscible with water and which has a lower boiling point than water; II) In the event that isocyanate-functional polymers or isocyanate-functional prepolymers were provided in step I): adding NCO-reactive compounds so that at least a partial reaction with the polymers or prepolymers occurs; III) Distilling off the water-miscible first solvent to obtain an aqueous polyurethane dispersion; wherein the liquid phase in step I) continues to include water and / or water is added to the mixture obtained after step II) after step II).

[0007] During step III), foam bubbles formed are at least temporarily contacted with a second solvent, whereby the contact of the foam bubbles with the second solvent is effected by spraying from one or more spray nozzles.

[0008] Surprisingly, it was found that the second solvent introduced during distillation in step III) effectively destroys the foam bubbles. While not committing to a specific theory, it is assumed that a strong local fluctuation in interfacial tension occurs, destabilizing the foam lamellae and thus causing the bubbles to burst. This allows for a significantly faster distillation process.

[0009] The polymer or prepolymer A) can have an average NCO functionality of 0 to 6, preferably of ≥ 1.8 to ≤ 3.5. For their production, the polyisocyanate or polyisocyanates are used in a stoichiometric excess / deficiency, such that the polymer or prepolymer has terminal isocyanate groups or OH groups.

[0010] Particularly suitable solvents for the prepolymer are wholly or partially miscible with water in the temperature range of 10 °C to 120 °C, are non-reactive towards isocyanate groups, and can optionally be removed by distillation after preparation of the dispersion. It is also possible to use, in addition to the aforementioned solvents, other solvents that are immiscible or poorly miscible with water and are non-reactive towards isocyanate groups. Solvent mixtures consisting of several solvents that meet the aforementioned conditions are also suitable for preparing the dispersions according to the invention.

[0011] Preferred solvents are acetone, butanone, tetrahydrofuran, ethyl acetate, butyl acetate and / or dimethyl carbonate. Acetone is particularly preferred.

[0012] In one embodiment, the isocyanate-functional prepolymers A) are obtainable from the reaction of A1) organic polyisocyanates with A2) monomeric polyols and / or polymeric polyols with number-mean molecular weights of ≥ 400 g / mol to ≤ 8000 g / mol and OH functionalities of ≥ 1.5 to ≤ 6.

[0013] Suitable polyisocyanates (A1) are aromatic, araliphatic, aliphatic, or cycloaliphatic polyisocyanates. Mixtures of such polyisocyanates can also be used. Preferred polyisocyanates are selected from the group consisting of butylene diisocyanate, hexamethylene diisocyanate (HDI), 1,5-pentamethylene diisocyanate, isophorone diisocyanate (IPDI), 2,2,4 and / or 2,4,4-trimethylhexamethylene diisocyanate, the isomeric bis(4,4'-isocyanatocyclohexyl)methanes or mixtures thereof of any isomer content, isocyanatomomethyl 1,8-octane diisocyanate, 1,4-cyclohexylene diisocyanate, 1,4-phenylene diisocyanate, 2,4- and / or 2,6-toluene diisocyanate, 1,5-naphthylene diisocyanate, 2,4'- or 4,4'-diphenylmethane diisocyanate, triphenylmethane 4,4',4"-triisocyanate and their derivatives with urethane, isocyanurate, allophanate, biuret, Uretdione, iminooxadiazindeione structure. Mixtures thereof are also preferred.Particularly preferred are hexamethylene diisocyanate, isophorone diisocyanate, pentamethylene diisocyanate and the isomeric bis(4,4'-isocyanatocyclohexyl)methanes and mixtures thereof.

[0014] Suitable monomeric polyols A2) are, for example, short-chain, i.e. containing 2 to 20 carbon atoms, aliphatic, araliphatic or cycloaliphatic polyols. Examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 2-ethyl-2-butylpropanediol, trimethylpentanediol, positional isomers of diethyloctanediols, 1,3-butylene glycol, cyclohexanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, 1,2- and 1,4-cyclohexanediol, hydrogenated bisphenol A (2,2-bis(4-hydroxycyclohexyl)propane), 2,2-dimethyl-3-hydroxypropionic acid (2,2-dimethyl-3-hydroxypropyl ester). Preferred triols are 1,4-butanediol, 1,4-cyclohexanedimethanol, and 1,6-hexanediol. Examples of suitable triols are trimethylolethane, trimethylolpropane, or glycerol; trimethylolpropane is preferred.

[0015] The polymeric polyols A2) are compounds which are themselves composed of monomers and which, in addition to the mostly terminal isocyanate-reactive end groups, have further functional groups along the main chain.

[0016] Suitable higher molecular weight polyols are polyester polyols, polyacrylate polyols, polyurethane polyols, polycarbonate polyols, polyether polyols, polyester polyacrylate polyols, polyurethane polyacrylate polyols, polyurethane polyester polyols, polyurethane polyether polyols, polyurethane polycarbonate polyols and polyester polycarbonate polyols, polyether polyamines and polyamido polyamines; polyester polyols, polyether polyols and polycarbonate polyols are particularly preferred; polyester polyols are especially preferred.

[0017] The suitable polyester polyols are often composed of one or more aliphatic and / or aromatic and / or araliphatic dicarboxylic acids with one or more aliphatic and / or aromatic and / or araliphatic diols and are produced via a polycondensation process.

[0018] Suitable polyester polyols are the known polycondensates of di- and optionally tri- and tetraols, and di- and optionally tri- and tetracarboxylic acids, or hydroxycarboxylic acids, or lactones. Instead of the free polycarboxylic acids, the corresponding polycarboxylic anhydrides or corresponding polycarboxylic acid esters of lower alcohols can also be used to prepare the polyesters. Examples of suitable diols are ethylene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycols such as polyethylene glycol, as well as 1,2-propanediol, 1,3-propanediol, butanediol(1,3), butanediol(1,4), hexanediol(1,6) and isomers, neopentyl glycol, or hydroxypivalic acid neopentyl glycol esters, the latter three being preferred.To achieve a functionality ≥ 2, polyols with a functionality of 3 can be used to a certain extent, for example trimethylolpropane, glycerin, erythritol, pentaerythritol, trimethylolbenzene or trishydroxyethyl isocyanurate.

[0019] Preferred dicarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, cyclohexanedicarboxylic acid, adipic acid, azelaic acid, sebacic acid, glutaric acid, tetrachlorophthalic acid, maleic acid, fumaric acid, itaconic acid, malonic acid, cortic acid, 2-methyl succinic acid, succinic acid, 3,3-diethylglutaric acid, and 2,2-dimethyl succinic acid. Anhydrides of these acids are also suitable, provided they exist. For the purposes of the present invention, the anhydrides are therefore referred to as "acids." Monocarboxylic acids, such as benzoic acid and hexanecarboxylic acid, are also preferred, provided that the average functionality of the polyol is ≥2. Saturated aliphatic or aromatic acids, such as adipic acid or isophthalic acid, are preferred. Trimellitic acid may be used as a polycarboxylic acid, optionally in smaller quantities.

[0020] Hydroxycarboxylic acids suitable as reactants in the synthesis of a polyester polyol with terminal hydroxyl groups include, for example, hydroxycaproic acid, hydroxybutyric acid, hydroxydecanoic acid, hydroxystearic acid, and the like. Useful lactones include, among others, ε-caprolactone, butyrolactone, and their homologs.

[0021] Preferred are polyester polyols based on butanediol and / or neopentyl glycol and / or hexanediol and / or ethylene glycol and / or diethylene glycol with adipic acid and / or phthalic acid and / or isophthalic acid. Particularly preferred are polyester polyols based on butanediol and / or neopentyl glycol and / or hexanediol with adipic acid and / or phthalic acid.

[0022] Examples of polyether polyols include the polyaddition products of styrene oxides, ethylene oxide, propylene oxide, tetrahydrofuran, butylene oxide, epichlorohydrin, as well as their mixed addition and grafting products, and polyether polyols obtained by condensation of polyhydric alcohols or mixtures thereof and by alkoxylation of polyhydric alcohols, amines and amino alcohols.

[0023] Suitable hydroxy-functional polyethers exhibit OH functionalities of 1.5 to 6.0, preferably 1.8 to 3.0, OH numbers of 50 to 700, preferably 100 to 600 mg KOH / g solid, and molecular weights Mn of 106 to 4000 g / mol, preferably 200 to 3500, such as alkoxylation products of hydroxy-functional starter molecules like ethylene glycol, propylene glycol, butanediol, hexanediol, trimethylolpropane, glycerol, pentaerythritol, sorbitol, or mixtures of these and other hydroxy-functional compounds with propylene oxide or butylene oxide. Polypropylene oxide polyols and polytetramethylene oxide polyols with a molecular weight of 300 to 4000 g / mol are preferred. The particularly low molecular weight polyether polyols can be water-soluble at correspondingly high OH contents. However, water-insoluble polypropylene oxide polyols and polytetramethylene oxide polyols with a molecular weight of 500 - 3000 g / mol and mixtures thereof are particularly preferred.

[0024] The polycarbonate polyols in question are obtained by reacting carbonic acid derivatives, e.g., diphenyl carbonate, dimethyl carbonate, or phosgene, with diols. Examples of 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-bishydroxymethylcyclohexane, 2-methyl-1,3-propanediol, 2,2,4-trimethylpentanediol-1,3, dipropylene glycol, polypropylene glycols, dibutylene glycol, polybutylene glycols, bisphenol A, tetrabromobisphenol A, and also lactone-modified diols. Preferably, the diol component contains 40 to 100 wt% 1,6-hexanediol and / or hexanediol derivatives, preferably those which, in addition to terminal OH groups, have ether or ester groups, e.g. products obtained by reacting 1 mol of hexanediol with at least 1 mol, preferably 1 to 2 mol of ε-caprolactone or by etherification of hexanediol with itself to form di- or trihexylene glycol.Polyether polycarbonate polyols can also be used.

[0025] Polycarbonate polyols based on dimethyl carbonate and hexanediol and / or butanediol and / or ε-caprolactone are preferred. Polycarbonate polyols based on dimethyl carbonate and hexanediol and / or ε-caprolactone are particularly preferred.

[0026] Furthermore, it is possible that isocyanate-reactive cationic, potentially cationic, anionic, or potentially anionic and / or nonionic hydrophilizing agents A4) are already added during the synthesis of the prepolymers. Details on the hydrophilizing agents A4) are given below in the text.

[0027] In a further preferred embodiment, isocyanate-reactive compounds A3) with molecular weights of 62 to 399 g / mol are added in step II). The degree of chain elongation, i.e., the equivalent ratio of NCO-reactive groups of the compounds used for chain elongation and chain termination to free NCO groups of the prepolymer, is generally between 40 and 150%, preferably between 50 and 110%, and particularly preferably between 60 and 100%.

[0028] For chain extension of the prepolymers with compounds A3), amines can be used, for example, which do not have ionic or ionogenic, as well as anionically hydrophilizing groups. Organic di- or polyamines such as 1,2-ethylenediamine, 1,2- and 1,3-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, isophorone diamine, isomeric mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamine, 2-methylpentamethylenediamine, diethylenetriamine, 4,4-diaminodicyclohexylmethane, hydrazine hydrate, and / or dimethylethylenediamine are preferably used as component A3).

[0029] Furthermore, compounds that, in addition to a primary amino group, also contain secondary amino groups, or OH groups in addition to an amino group (primary or secondary), can also be used as component A3). Examples include primary / secondary amines such as diethanolamine, 3-amino-1-methylaminopropane, 3-amino-1-ethylaminopropane, 3-amino-1-cyclohexylaminopropane, 3-amino-1-methylaminobutane, and alkanolamines such as N-aminoethylethanolamine, ethanolamine, 3-aminopropanol, and neopentanolamine.

[0030] Furthermore, monofunctional isocyanate-reactive amine compounds can also be used as component A3), such as methylamine, ethylamine, propylamine, butylamine, octylamine, laurylamine, stearylamine, isononyloxypropylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, N-methylaminopropylamine, diethyl(methyl)aminopropylamine, morpholine, piperidine, or suitable substituted derivatives thereof, amidamines from diprimary amines and monocarboxylic acids, monoketim of diprimary amines, primary / tertiary amines such as N,N-dimethylaminopropylamine.

[0031] Dihydrazides such as adipic acid dihydrazide, oxalic acid dihydrazide, carbohydrazide, and succinic acid dihydrazide are also suitable as component A3). Longer-chain, amino-functional compounds such as polyetheramines ("jeffamines") are also suitable as component A3.

[0032] The preferred components A3) are 1,2-ethylenediamine, bis(4-aminocyclohexyl)methane, 1,4-diaminobutane, isophoronediamine, ethanolamine, diethanolamine and diethylenetriamine.

[0033] Low-molecular-weight polyols can also be used, for example, to extend the chain of prepolymers with compounds A3). Suitable low-molecular-weight polyols are short-chain aliphatic, araliphatic, or cycloaliphatic compounds containing 2 to 20 carbon atoms. Examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 2-ethyl-2-butylpropanediol, trimethylpentanediol, positional isomers of diethyloctanediols, 1,3-butylene glycol, cyclohexanediol, 1,4-cyclohexanedimethanol, 1,6-hexanediol, 1,2- and 1,4-cyclohexanediol, hydrogenated bisphenol A (2,2-bis(4-hydroxycyclohexyl)propane), 2,2-dimethyl-3-hydroxypropionic acid (2,2-dimethyl-3-hydroxypropyl ester). Preferred are 1,4-butanediol, 1,4-cyclohexanedimethanol and 1,6-hexanediol.Examples of suitable triols are trimethylolethane, trimethylolpropane or glycerol, trimethylolpropane is preferred.

[0034] Further examples of chain extenders (A3) are dihydrazides such as oxalic acid dihydrazide, carbohydrazide, and adipic acid dihydrazide; carbohydrazide and adipic acid dihydrazide are particularly preferred. Examples of suitable dithiols are 1,2-ethanedithiol, 1,3-propanedithiol, 1,4-butanedithiol, and 1,6-hexanedithiol. 1,2-Ethanedithiol and 1,6-hexanedithiol are particularly preferred.

[0035] Diols are preferably used as low molecular weight compounds (A3).

[0036] In a further embodiment, in step II), isocyanate-reactive cationic, potentially cationic, anionic, or potentially anionic and / or nonionic hydrophilizing agents A4) are added. The degree of chain elongation, i.e., the equivalent ratio of NCO-reactive groups of the compounds used for chain elongation and chain termination to free NCO groups of the prepolymer, is generally between 40 and 150%, preferably between 50 and 110%, and particularly preferably between 60 and 100%.

[0037] Dispersing compounds (hydrophilizing agents) A4) are those containing, for example, sulfonium, ammonium, phosphonium, carboxylate, sulfonate, or phosphonate groups, or groups that can be converted into the aforementioned groups by salt formation (potentially ionic groups), or polyether groups that can be incorporated into the macromolecules by existing isocyanate-reactive groups. The neutralizing agents necessary for salt formation can be added either stoichiometrically or in a deficit relative to the salt-forming group. To generate anionic groups, organic bases, such as tertiary amines, or inorganic bases, such as alkali metal hydroxides or ammonia, are added. Tertiary amines such as triethylamine, triethanolamine, or dimethylethanolamine are preferably used. Preferred suitable isocyanate-reactive groups are hydroxyl and amino groups.

[0038] Suitable ionic or potentially ionic compounds include, for example, mono- and dihydroxycarboxylic acids, dihydrohydroxydicarboxylic acids, mono- and diaminocarboxylic acids, mono- and dihydroxysulfonic acids, mono- and diaminosulfonic acids, as well as mono- and dihydroxyphosphonic acids or mono- and diaminophosphonic acids and their salts such as dimethylolpropionic acid, dimethylolbutyric acid, hydroxypivalic acid, N-(2-aminoethyl)alanine, 2-(2-aminoethylamino)ethanesulfonic acid, ethylenediaminepropyl or butylsulfonic acid, 1,2- or 1,3-propylenediamineethylsulfonic acid, malic acid, citric acid, glycolic acid, lactic acid, glycine, alanine, taurine, lysine, 3,5-diaminobenzoic acid, and an addition product of IPDIand acrylic acid (EP-A 0 916 647, Example 1) and its alkali and / or ammonium salts; the adduct of sodium bisulfite to 1,4-butenediol, polyethersulfonate, the propoxylated adduct of 2-butenediol and NaHSO₃, e.g., described in DE-A 2 446 440 (pages 5-9, formulas I-III), as well as building blocks convertible into cationic groups, such as N-methyldiethanolamine, as hydrophilic components. Furthermore, the salt of cyclohexylaminopropanesulfonic acid (CAPS) from WO-A 01 / 88006 can be used as an anionic hydrophilizing agent. Preferred ionic or potential ionic compounds are those possessing carboxyl or carboxylate and / or sulfonate groups and / or ammonium groups.

[0039] Preferred compounds are polyethersulfonate, dimethylolpropionic acid, tartaric acid, and dimethylolbutyric acid; polyethersulfonate and dimethylolpropionic acid are particularly preferred. Suitable nonionically hydrophilic compounds are, for example, polyoxyalkylene ethers containing at least one hydroxy or amino group. These polyethers contain 30 wt.% to 100 wt.% of building blocks derived from ethylene oxide. Linear polyethers with a functionality between 1 and 3 are suitable, as are compounds of the general formula: in which R1 and R2 independently each represent a divalent aliphatic, cycloaliphatic or aromatic residue with 1 to 18 C atoms, which may be interrupted by oxygen and / or nitrogen atoms, and R3 represents an alkoxy-terminated polyethylene oxide residue.

[0040] Non-ionically hydrophilizing compounds include, for example, monovalent polyalkylene oxide polyether alcohols, which on average contain 5 to 70, preferably 7 to 55 ethylene oxide units per molecule and can be accessed in a manner known per se by alkoxylation of suitable starter molecules.

[0041] Suitable starter molecules include, for example, saturated monoalcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, the isomers pentanols, hexanols, octanols and nonanols, n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecanol, cyclohexanol, the isomers 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 oleic alcohol, aromatic alcohols such as phenol, the isomers cresols or methoxyphenols, and araliphatic alcohols such as benzyl alcohol, anise alcohol or cinnamyl alcohol. Secondary monoamines such as dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, bis-(2-ethylhexyl)amine, N-methyl- and N-ethylcyclohexylamine or dicyclohexylamine, as well as heterocyclic secondary amines such as morpholine, pyrrolidine,Piperidine or 1H-pyrazole. Preferred starter molecules are saturated monoalcohols. Diethylene glycol monobutyl ether is particularly preferred as a starter molecule.

[0042] Suitable alkylene oxides for the alkoxylation reaction are in particular ethylene oxide and propylene oxide, which can be used in any order or in a mixture in the alkoxylation reaction.

[0043] The polyalkylene oxide polyether alcohols are either pure polyethylene oxide polyethers or mixed polyalkylene oxide polyethers whose alkylene oxide units consist of at least 30 mol%, preferably at least 40 mol%, ethylene oxide units. Preferred nonionic compounds are monofunctional mixed polyalkylene oxide polyethers containing at least 40 mol% ethylene oxide and at most 60 mol% propylene oxide units.

[0044] Particularly preferred are monohydroxy functional alkoxy polyethylene glycols such as MPEG 750 (Dow Chemical) and LB 25 (Covestro) and dihydroxy functional compounds with lateral polyethylene oxide units such as Ymer N 120 (Perstorp) or Tegomer D 3404.

[0045] A particularly preferred prepolymer is prepared from a polyester composed of adipic acid, 1,6-hexanediol, and neopentyl glycol, and hexamethylene diisocyanate. The polyester preferably has a molar mass of 1700 g / mol.

[0046] A particularly preferred chain-extending reagent is 2-(2-Aminoethylamino)ethanesulfonic acid.

[0047] The molar ratio of NCO to isocyanate-reactive groups for the synthesis of prepolymer A) can vary from 1.05 to 4.00, preferably from 1.2 to 3.0, and particularly preferably from 1.4 to 2.5. The prepolymers are synthesized by placing the appropriate polyol or a mixture of different polyols in a reaction vessel and then adding the polyisocyanate or the mixture of polyisocyanates at an elevated temperature. If mixtures of polyols and / or polyisocyanates are used, the individual reactants can be added at different times to achieve a targeted synthesis of the prepolymer. The reaction can take place either in the melt or in suitable inert solvents such as acetone or butanone. The reaction temperature is between 50 °C and 130 °C, and the reaction time is 1 to 24 hours.The urethanization reaction can be accelerated by using suitable catalysts. Catalysts known to those skilled in the art, such as triethylamine, 1,4-diazabicyclo-[2,2,2]-octane, tin dioctoate, dibutyltin dilaurate, or bismuth dioctoate, are suitable for this purpose and can be added initially or subsequently. Dibutyltin dilaurate is preferred. The reaction is usually complete when the NCO content no longer changes; reaction monitoring is typically carried out by titration. To ensure further processing of the prepolymer, low-viscosity prepolymers are generally advantageous. For this purpose, the prepolymer is dissolved in a suitable solvent, if this has not already been done during production. Low-viscosity prepolymers or prepolymer solutions are defined as systems whose viscosity is less than or equal to 10⁴ mPas at a shear rate of 40 s⁻¹.The prepolymer solution preferably has a solids content of > 40% and acetone is preferred as the solvent.

[0048] A preferred polyurethane dispersion to be produced according to the inventive process contains 9 to 60 wt.% of a polyisocyanate compound, 35 to 90 wt.% of an isocyanate-reactive polyol with a molar mass > 500 g / mol, 0.5 to 5 wt.% of an ionic or potentially ionic hydrophilizing agent, 0 to 10 wt.% of low molecular weight (C 2 to Cs) alcohols and 0.5 to 10 wt.% of a chain elongation amine which has no hydrophilic groups.

[0049] In a particularly preferred embodiment, the polyurethane dispersion contains at least one additive selected from the group consisting of 0.1 to 25.0 wt.% of a non-ionic hydrophilizing agent, 0.1 to 15.0 wt.% of a further polyol with a molar mass < 500 g / mol and 0.1 to 3.0 wt.% further auxiliary or additive substances, in particular emulsifiers, biocides, and antioxidants.

[0050] In a further preferred embodiment, the process is carried out such that the resulting polyurethane dispersion contains defoamers in a proportion of ≤ 1 wt%, based on the weight of the polyurethane. Preferably, the content is 0 wt% to ≤ 0.1 wt%, more preferably 0 wt% to ≤ 0.01 wt%. Most preferably, no defoamers are present in the resulting dispersion, whereby technically unavoidable impurities are included in this term. The defoamers can be, for example, silicone oils or paraffins.

[0051] In another preferred embodiment, the second solvent is identical to the first solvent. For example, distilled solvent can be condensed and then used as the second solvent to re-contact foam bubbles. This approach has the further advantage that no changes in product properties are expected, since no new substance is introduced into the product.

[0052] In another preferred embodiment, the first and second solvents are acetone.

[0053] The foam bubbles are brought into contact with the second solvent by spraying from one or more spray nozzles. The spray nozzle(s) are preferably arranged such that the cross-section of the container is uniformly covered with the spray droplets of the second solvent.

[0054] In another preferred embodiment, one or more spray nozzles are arranged in the vapor chamber within a vessel used for distillation.

[0055] In a further preferred embodiment, during distillation in step III), the vapor obtained is drawn off via at least one vapor tube, and the contact of the foam bubbles with the second solvent takes place in the vapor tube and / or at a distance of ≤ 1 m from the vapor tube. In this way, the amount of second solvent required can be further reduced. In this embodiment, contact in the vicinity (less than one meter away) of the vapor tube is preferred.

[0056] Generally, single-component nozzles are preferred for atomizing the second solvent, as these do not require the addition of an atomizing gas. The nozzle bore diameter must be matched to the desired pressure drop; the tendency of small bores to become clogged by potential solid deposits must also be taken into account.

[0057] When used in vapor tubes, commercially available solid cone or hollow cone nozzles can be used, arranged coaxially in the same direction or (preferably) in the opposite direction to the gas flow. The spray angle of the nozzles should preferably be small (preferably 30° or less) to minimize liquid loss to the vapor tube wall. The nozzle bore diameter should be selected such that the resulting pressure drop across the nozzles for the desired solvent flow is between 0.5 and 20 bar, preferably 1 to 10 bar, and particularly preferably 1 to 3 bar.

[0058] When used in the vapor chamber of the distillation vessel above the liquid level, commercially available flat jet nozzles are preferably employed. These are arranged so that the flat jet spreads horizontally above the liquid level, thus covering a large area of ​​the foam-filled gas space. Flat jet nozzles with large spray angles above 90°, and particularly preferably above 120°, are preferred. Depending on the geometry of the distillation apparatus, several nozzles can also be distributed in the headspace to ensure uniform spraying of the foam. The nozzle bore diameter is preferably selected such that the resulting pressure drop across the nozzles for the desired solvent flow is between 0.5 and 20 bar, preferably 1 to 10 bar, and particularly preferably 1 to 3 bar.The vertical position of the nozzles between the liquid level and the vapor pipe connection is preferably chosen so that, on the one hand, not too much spray is lost to the liquid level due to gravity and, on the other hand, not too much spray is carried away with the vapor stream; preferably, at the beginning of the distillation, a position at half the height between the liquid level and the vapor pipe connection is used.

[0059] Depending on the product characteristics, it may also be sufficient to install only a single commercially available flat jet nozzle directly below the vapor tube when used in the vapor chamber of the distillation boiler above the liquid level; regarding spray angle, bore diameter and pressure loss as well as vertical positioning of the nozzle, what has been said above applies accordingly.

[0060] The ideal droplet size can vary depending on the type of dispersion and influences both the contact with the foam to be destroyed and the entrainment in the vapor stream. Preferably, the droplets have a size of < 2000 µm and particularly preferably < 200 µm. Droplet sizes of < 10 µm are less advantageous due to the increased carryover in the vapor stream. The droplet size can be approximately influenced by selecting the nozzle orifice diameter and the pressure drop during spraying.

[0061] Depending on the temperature of the evaporated solvent, flash evaporation can occur during spraying; this is generally not preferred because very small droplets can form, which are carried along by the vapor gas stream and do not lead to a complete coverage of the foam-filled space with spray, as they are slowed down very quickly by the surrounding gas due to their low inertia and low sinking velocity.

[0062] In a further preferred embodiment, the second solvent is applied to the foam bubbles during step III) at a rate of ≥ 0.1 volume % / h to ≤ 20 (preferably ≤ 5) volume % / h, based on the volume of the dispersion present during step III).

[0063] In a further preferred embodiment, the second solvent is used in an amount of ≤ 100%, preferably ≤ 30% and particularly preferably ≤ 10% of the amount of solvent present before step III).

[0064] During step III), the amount of the second solvent applied per unit of time can be constant. However, in a further preferred embodiment, the amount of the second solvent applied during step III) varies over time. Preferably, the amount of solvent applied is reduced over the course of the process. It is also possible to apply the second solvent in pulses.

[0065] It is still preferred that contact with the second solvent only lasts as long as the foam bubbles reach a predetermined layer height. This can be monitored with a foam probe.

[0066] In a further preferred embodiment, the contact of the foam bubbles with the second solvent is carried out exclusively within a pressure range of ≥ 80 mPa to ≤ 500 mPa. This offers advantages in terms of explosion protection for the system.

[0067] Also disclosed is a device for carrying out the method according to the invention, comprising a vessel to which a vacuum can be applied and which is configured to hold a polyurethane dispersion that develops foam bubbles when a vacuum is applied. The device further comprises one or more nozzles through which a solvent can be applied to the foam bubbles.

[0068] This device can be set up to condense distilled solvent and reapply it to the foam bubbles.

[0069] The present invention and the disclosed device are explained by the following example and the Figure 1 explained in more detail, but without being limited to that.

[0070] FIG. 1 Figure 1 shows a device for carrying out the method according to the invention. This device can be a suitably modified distillation vessel. The vessel 100 contains the aqueous polyurethane dispersion 200, from which the organic solvent, such as acetone, is to be distilled off. When a vacuum is applied and, if necessary, the dispersion 200 is heated, gaseous solvent can be drawn off at the top of the vessel 100. This is represented by the mass stream 400. Furthermore, foam bubbles 300 are formed when the vacuum is applied.

[0071] The device has a nozzle 500 in the vapor chamber, from which a stream 600 of a second solvent can be applied to the foam bubbles 300 in the form of individual jets or drops 700. This causes the foam bubbles to burst, and there is no risk of material from the dispersion 200 being carried along overhead by the device.

[0072] The material stream 400 can be condensed and then re-enter the nozzle 500 in the form of the material stream 600 and applied to the foam bubbles 300. Example according to the invention: Production of a polyurethane urea dispersion with a strong foaming tendency

[0073] In a 500 L reactor with a distillation unit, 56 kg of a polyester composed of adipic acid, hexanediol, and neopentyl glycol with a mean molecular weight of 1700 g / mol and 5.5 kg of a hydrophilic monofunctional polyether based on ethylene oxide / propylene oxide (number-average molecular weight 2250 g / mol, OH number 25 mg KOH / g) were heated to 65 °C. Subsequently, 13.6 kg of isophorone diisocyanate (IPDI) were added and the mixture was stirred at 120 °C until the theoretical NCO value of 3.0% was reached.

[0074] The resulting prepolymer was dissolved under pressure by adding 134 kg of acetone and simultaneously cooled to 40 °C. Subsequently, a solution of 3.2 kg of isophorone diamine (IPDA) in 24 kg of water was added at 40 °C. Stirring time was 15 minutes.

[0075] The mixture was then dispersed by adding 162 kg of water within 10 minutes. Immediately afterwards, the crude dispersion was carefully evacuated. At a pressure of 300 mbar (temperature: 34 °C), intense foaming began, making further distillation impossible.

[0076] Only by spraying the foam surface in the reactor with acetone from a flat jet nozzle located above the liquid level (pre-pressure: 3 bar, spray angle: 120°, flow rate calibrated with water: 15 kg / h, droplet size: approx. 200 µm) according to the invention could the foam be instantly suppressed.

[0077] The distillation of the acetone still present in the reaction mixture at this point could thus be efficiently continued by further careful reduction of the pressure and slight increase in the reactor internal temperature. A brief, experimental cessation of the acetone spraying according to the invention after 5 hours of distillation time immediately resulted in strong foaming again, extending far into the vapor tube.

[0078] Therefore, the acetone spraying according to the invention was reactivated, which again suppressed foaming. Even when the acetone nozzle pressure was reduced to 1.8 bar, the foam suppression remained effective. The acetone spraying was stopped 30 minutes before the end of the distillation. Distillation was terminated at a pressure of 150 mbar and a reactor internal temperature of 49 °C. The total duration of the distillation was 7 hours.

[0079] A stable dispersion was obtained, with a residual acetone content of 0.8 wt.%.

Claims

1. Process for producing a polyurethane dispersion, comprising the steps of: I) providing polyurethane polymers and / or polyurethane prepolymers A) in a liquid phase comprising a first solvent which is miscible with water and has a lower boiling point than water; II) if isocyanate-functional polymers or isocyanate-functional prepolymers have been provided in step I): adding NCO-reactive compounds, such that at least partial reaction with the polymers or prepolymers occurs; III) distilling off the water-miscible first solvent, such that an aqueous polyurethane dispersion is obtained; wherein the liquid phase in step I) still comprises water and / or, after step II), water is added to the mixture obtained after step II), characterized in that foam bubbles formed during step III) are at least temporarily contacted with a second solvent, wherein the foam bubbles are contacted with the second solvent by spraying from one or more spray nozzles.

2. Process according to Claim 1, characterized in that the isocyanate-functional prepolymers A) are obtainable from the reaction of A1) organic polyisocyanates with A2) monomeric polyols and / or polymeric polyols having number-average molecular weights of ≥ 400 g / mol to ≤ 8000 g / mol and OH functionalities of ≥ 1.5 to ≤ 6.

3. Process according to Claim 1 or 2, characterized in that isocyanate-reactive compounds A3) having molecular weights of 62 to 399 g / mol are added in step II).

4. Process according to any of Claims 1 to 3, characterized in that isocyanate-reactive cationic, potentially cationic, anionic or potentially anionic and / or nonionic hydrophilizing agents A4) are added in step II).

5. Process according to any of Claims 1 to 4, characterized in that the process is performed in such a way that defoamers are present in the resultant polyurethane dispersion in a proportion of ≤ 1% by weight, based on the weight of the polyurethane.

6. Process according to any of Claims 1 to 5, characterized in that the second solvent is identical to the first solvent.

7. Process according to any of Claims 1 to 6, characterized in that the first and second solvents are acetone.

8. Process according to Claim 7, characterized in that the one or more spray nozzles are disposed in the vapor space within a vessel used for distillation.

9. Process according to any of Claims 1 to 8, characterized in that, in the distillative removal in step III), the vapor obtained is drawn off via at least one vapor tube and the foam bubbles are contacted with the second solvent in the vapor tube and / or at a distance of ≤ 1 m from the vapor tube.

10. Process according to any of Claims 1 to 9, characterized in that the second solvent is applied to the foam bubbles during step III) at a rate of ≥ 0.1% by volume / h to ≤ 20% (preferably ≤ 5%) by volume / h, based on the volume of the dispersion present during step III).

11. Process according to any of Claims 1 to 10, characterized in that the contacting of the foam bubbles with the second solvent is performed exclusively within a pressure range from ≥ 80 mPa to ≤ 500 mPa.

12. Process according to any of Claims 1 to 11, characterized in that the amount of the second solvent applied during step III) is variable over time.