EP2176612A1

EP2176612A1 - Method for the drying of foams composed of aqueous pu dispersions

Info

Publication number: EP2176612A1
Application number: EP08759363A
Authority: EP
Inventors: Meike Niesten; Steffen Hofacker; Thorsten Rische; Sebastian Dörr; Thorsten KRÄMER; Hartwig Kempkes; Jens Hepperle
Original assignee: Bayer MaterialScience AG
Current assignee: Covestro Deutschland AG
Priority date: 2007-07-11
Filing date: 2008-07-01
Publication date: 2010-04-21
Also published as: US20090018224A1; BRPI0814621A2; CA2693508A1; KR20100032887A; WO2009007037A1; TW200918584A; RU2010104471A; EP2015014A1; JP2010532798A; CN101730827A

Abstract

The invention relates to the drying of foams by means of microwave radiation, where the foams are obtained from aqueous polyurethane dispersions (PU dispersions).

Description

Process for drying foams from aqueous PU dispersions

The invention relates to the microwave drying of foams, which are preferably obtained from aqueous PU dispersions.

In the coating of substrates, increasingly aqueous binders, in particular polyurethane dispersions, are used.

Due to their excellent foamability and the advantageous properties of coatings and foams produced therefrom, such as good abrasion resistance, scratch, kink and hydrolysis resistance, polyurethane dispersions are particularly suitable for applications in the field of upholstery, occupational safety and automobile interior trim. Thus, it is possible to produce in one operation foam pads with a relatively high layer thickness, as they are otherwise possible only with solvent-containing high solids Beschichtungsmittteln (DE 10 2004 060 139).

Since foams based on aqueous polyurethane dispersions are also largely free from organic solvents and isocyanate monomers, they can also be used without further pretreatment or purification for cosmetic and medical applications.

Foams made from aqueous PU dispersions are typically prepared by foaming, application of the foam to a support and subsequent physical drying. To speed up the drying, warm air is usually used. This technique of drying, however, is only suitable for foam thicknesses of a maximum of 3 mm based on the wet foam layer to be dried. For layers of greater thickness, the problem arises that the foam dries only superficially and moisture from the interior is increasingly difficult to escape. This leads to an inhomogeneous and in some cases greatly delayed drying behavior.

There was therefore a need for a process for drying foams from aqueous PU dispersions, which leads to homogeneous, i.e., over the entire foam cross-section, dried foams even with wet foam thicknesses of more than 3 mm in an appropriate time and to obtain the foam structure.

The drying of aqueous paints, in particular paints based on aqueous polyurethane dispersions by means of microwave radiation, is known, for example, from EP-A 880 001, DE-A 4 121 203 or US 2004/0253452. However, these are always paint films with layer thicknesses of a maximum of 100 μm, which are usually bubble-free, ie without any type of foam structures. It has now surprisingly been found that microwave radiation is also suitable for drying foams which are produced from aqueous PU dispersions while retaining their foam structure, it being possible to achieve uniform drying of the foam over the entire foam cross section.

The invention therefore relates to a process for drying water-moist foams, preferably those which are obtainable from aqueous PU dispersions and optionally further constituents by foaming, in which the moist foam is exposed to microwave radiation.

Drying in the context of the present invention means lowering the water content of a foam to be dried.

Water moisture in connection with the present invention means a water content based on the total foam of at least 10 wt .-%, preferably 15 to 60 wt .-%, particularly preferably 35 to 60 wt .-%.

For the purposes of the invention, microwave radiation is understood as meaning electromagnetic radiation in the wavelength range from 300 MHz to 300 GHz. Radiation in the frequency ranges 2.0 to 3.0 GHz and 0.8 to 1.5 GHz are preferred. Particularly preferred frequencies are 2.2 to 2.6 and 0.85 to 1.0 GHz. Most preferably, the frequencies are 2.45 GHz (+0.1 GHz) and 0.915 GHz (+0.05 GHz).

Suitable aqueous PU dispersions, which are based on the foams to be dried, are all dispersions of polyurethanes and / or polyurethane polyureas known to the person skilled in the art in aqueous media.

Preference is given to polyurethane-polyurea dispersions.

The PU dispersions preferably have solids contents of 40 to 63% by weight.

Such PU dispersions are preferably obtainable in which

A) isocyanate-functional prepolymers

al) aliphatic or cycloaliphatic polyisocyanates

a2) polymeric polyols having number average molecular weights of 400 to 8000 g / mol and OH functionalities of 1.5 to 6, a3) optionally hydroxy-functional, ionic or potentially ionic and / or nonionic hydrophilicizing agents,

getting produced,

B) whose free NCO groups then in whole or in part with

bl) amino-functional compounds having molecular weights of 32 to 400 g / mol and / or

b2) amino-functional, ionic or potentially ionic hydrophilicizing agents

are reacted under chain extension and the prepolymers are dispersed in water before or after step B), wherein optionally contained potentially ionic groups can be converted by partial or complete reaction with a neutralizing agent in the ionic form.

Isocyanate-reactive groups are, for example, amino, hydroxy or thiol groups.

In al) typically 1,6-hexamethylene diisocyanate, isophorone diisocyanate, the isomeric bis (4,4'-isocyanatocyclohexyl) methanes and mixtures thereof are used.

It is likewise possible to use modified diisocyanates having uretdione, isocyanurate, urethane, allophanate, biuret, iminooxadiazinedione and / or oxadiazinetrione structures and those of unmodified polyisocyanates having more than 2 NCO groups per molecule, such as Isocyanatomethyl-l, 8-octane diisocyanate (nonane triisocyanate) or triphenylmethane-4,4 ', 4'-triisocyanate.

The compounds of component al) are particularly preferably polyisocyanates or polyisocyanate mixtures of the abovementioned type with exclusively aliphatically and / or cycloaliphatically bonded isocyanate groups and an average NCO functionality of the mixture of 2 to 4, preferably 2 to 2.6 and more preferably 2 to 2.4.

As components in a2) polymeric polyols having number average molecular weights of 400 to 6000 g / mol, particularly preferably from 600 to 3000 g / mol are used. These preferably have OH functionalities of from 1.8 to 3, particularly preferably from 1.9 to 2.1.

Such polymeric polyols, which are known per se in polyurethane coating technology, are polyester polyols, polycarbonate polyols, polyether polyols, polyacrylate polyols, polyether polyols and polyether polyols. polyester polyols and polyethercarbonate polyols. These can be used in a2) individually or in any mixtures with one another.

The polymeric polyols of the aforementioned type used are preferably those having an aliphatic skeleton. Preference is given to using aliphatic polycarbonate polyols, polyester polyols, polyether polyols or any mixtures thereof.

Preferred embodiments of the PUR dispersions to be used preferably comprise as component a2) a mixture of polycarbonate polyols and polytetramethylene glycol polyols, the proportion in the mixture being from 35 to 70% by weight of polytetramethylene glycol polyols and from 30 to 65% by weight polycarbonate polyols Assuming that the sum of the weight percentages of the polycarbonate and polytetramethylene glycol polyols gives 100% by weight.

Hydroxy-functional, ionic or potentially ionic hydrophilicizing agents a3) are understood as meaning all compounds which have at least one isocyanate-reactive hydroxyl group and at least one functionality such as -COOY, -SO ₃ Y, -PO (OY) ₂ (Y, for example = H ⁺ , NH ₄ ⁺ , Metal cation), -NR ₂ , -NR ₃ ⁺ (R = H, alkyl, aryl), which, when interacting with aqueous media, enter a pH-dependent dissociation equilibrium and thus be negatively, positively or neutrally charged can.

Suitable ionically or potentially ionically hydrophilic compounds according to the definition of component a3) are, for example, mono- and dihydroxycarboxylic acids, mono- and dihydroxy-sulfonic acids, and mono- and dihydroxyphosphonic acids and their salts, such as dimethylolpropionic acid, dimethylolbutyric acid, hydroxypivalic acid, malic acid, citric acid, glycol acid, lactic acid, the propoxylated adduct of 2-butenediol and NaHSO ₃ , for example described in DE-A 2 446 440 (page 5-9, formula I-Iü) and compounds which can be converted into cationic groups, for example amine -based, building blocks such as N-methyl-diethanolamine as hydrophilic structural components.

Preferred ionic or potentially ionic hydrophilicizing agents of component a3) are those of the abovementioned type which have an anionic, preferably hydrophilic, effect via carboxy or carboxylate and / or sulfonate groups.

Particularly preferred ionic or potentially ionic hydrophilicizing agents are those which contain carboxyl and / or sulfonate groups as anionic or potentially anionic groups, such as the salts of dimethylolpropionic acid or dimethylolbutyric acid.

Suitable nonionically hydrophilicizing compounds of component a3) are, for example, polyoxyalkylene ethers which contain at least one hydroxyl group as the isocyanate-reactive group. Examples are the monohydroxy-functional, on average 5 to 70, preferably 7 to 55 ethylene oxide units per molecule having Polyalkylenoxidpolyetheralkohole as they are accessible in a conventional manner by alkoxylation of suitable starter molecules (eg in Ulimann's Encyclopedia of Industrial Chemistry, 4th Edition, Volume 19 , Verlag Chemie, Weinheim pp. 31-38).

These are either pure polyethylene oxide ethers or mixed polyalkylene oxide ethers, wherein they contain at least 30 mol%, preferably at least 40 mol%, based on all the alkylene oxide units present of ethylene oxide units.

Particularly preferred nonionic compounds are monofunctional mixed polyalkylene oxide polyethers which have 40 to 100 mol% of ethylene oxide and 0 to 60 mol% of propylene oxide units.

Suitable starter molecules for such nonionic hydrophilicizing agents are saturated monohydric alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, the isomers pentanols, hexanols, octanols and nonanols, n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecanol, cyclohexanol, the isomeric methylcyclohexanols or hydroxymethylcyclohexane, 3-ethyl-3-hydroxymethyloxetane or tetrahydrofurfuryl alcohol, diethylene glycol monoalkyl ethers, such as diethylene glycol monobutyl ether, unsaturated alcohols such as allyl alcohol, 1,1 Dimethylalcohol or oleic alcohol, aromatic alcohols, such as phenol, the isomeric cresols or methoxyphenols, araliphatic alcohols, such as benzyl alcohol, anisole or cinnamyl alcohol, secondary monoamines, such as dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, bis (2-ethylhexyl) -amine, N-methyl and N-ethylcyclohexylamine or dicyclohexylamine, and heterocyclic secondary amines wi e morpholine, pyrrolidine, piperidine or 1H-pyrazole. Preferred starter molecules are saturated monoalcohols of the abovementioned type. Particular preference is given to using diethylene glycol monobutyl ether or n-butanol as starter molecules.

Alkylene oxides which are suitable for the alkoxylation reaction are, in particular, ethylene oxide and propylene oxide, which can be used in any desired order or else as a mixture in the alkoxylation reaction.

As component bl) can di- or polyamines such as 1, 2-ethylenediamine, 1,2- and 1,3-diaminopropane, 1, 4-diaminobutane, 1, 6-diaminohexane, isophoronediamine, isomer mixture of 2,2,4- and 2,4,4-trimethylhexamethylenediamine, 2-methylpentamethylenediamine, diethylenetriamine, and 4,4-diaminodicyclohexylmethane and / or dimethylethylenediamine. In addition, as component bl), it is also possible to use compounds which, in addition to a primary amino group, also have secondary amino groups or, besides an amino group (primary or secondary), also OH groups. Examples of these are primary / secondary amines, such as diethanolamine, 3-amino-1-methylaminopropane, 3-amino-1-ethylaminopropane, 3-amino-1-cyclohexylaminopropane, 3-amino-1-methylaminobutane, alkanolamines such as N-aminoethyl-ethanolamine , Ethanolamine, 3-aminopropanol, neopentanolamine.

Further, as component bl), it is also possible to use monofunctional amine compounds, for example methylamine, ethylamine, propylamine, butylamine, octylamine, laurylamine, stearylamine, isononyloxypropylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, N-methylaminopropylamine, diethyl (methyl) aminopropylamine, Moφholin, piperidine, or suitable substituted derivatives thereof, amide amines from diprimary amines and monocarboxylic acids, mono- ketime of diprimary amines, primary / tertiary amines, such as N, N-dimethylaminopropylamine.

Preference is given to using 1,2-ethylenediamine, 1,4-diaminobutane, isophoronediamine and diethylenetriamine.

By ionic or potentially ionic hydrophilizing compounds of component b2) are meant all compounds containing at least one isocyanate-reactive amino group and at least one functionality such as -COOY, -SO ₃ Y, -PO (OY) ₂ (Y, for example = H ⁺ , NH ₄ ⁺ , metal cation) which, upon interaction with aqueous media, undergoes a pH-dependent dissociation equilibrium and in this way may be positively, negatively or neutrally charged.

Suitable ionically or potentially ionically hydrophilicizing compounds are, for example, mono- and diaminocarboxylic acids, mono- and diaminosulfonic acids and mono- and diaminophosphonic acids and their salts. Examples of such ionic or potentially ionic hydrophilicizing agents are N- (2-aminoethyl) -β-alanine, 2- (2-aminoethylamino) -ethanesulfonic acid, ethylenediamine-propyl- or -butylsulfonic acid, 1,2-or 1,3-propylenediamine-β-ethylsulfonic acid, glycine, alanine, taurine, lysine, 3,5-diaminobenzoic acid and the addition product of IPDI and acrylic acid (EP-A 0 916 647, Example 1). Furthermore, cyclohexylaminopropanesulfonic acid (CAPS) from WO-A 01/88006 can be used as anionic or potentially anionic hydrophilicizing agent.

Preferred ionic or potentially ionic hydrophilicizing agents b2) are those which contain carboxyl and / or sulfonate groups as anionic or potentially anionic groups, such as the salts of N- (2-aminoethyl) -β-alanine, 2- (2- Amino-ethylamino) ethanesulfonic acid or the addition product of IPDI and acrylic acid (EP-A 0 916 647, Example 1). For the hydrophilization, preference is given to using a mixture of anionic or potentially anionic hydrophilicizing agents and nonionic hydrophilicizing agents.

The ratio of NCO groups of the compounds from component al) to NCO-reactive groups of components a2) to a3) in the preparation of the NCO-functional prepolymer is 1.2 to 3.0, preferably 1.3 to 2, 5th

The amino-functional compounds in step B) are used in such an amount that the equivalent ratio of isocyanate-reactive amino groups of these compounds to the free isocyanate groups of the prepolymer is 50 to 125%, preferably between 60 to 120%.

In a preferred embodiment, anionic and nonionic hydrophilicized polyurethane dispersions are used, the components al) to a3) and b1) to b2) being used for their preparation in the following amounts, the individual amounts adding up to 100% by weight:

From 10 to 30% by weight of component al),

65 to 85% by weight a2),

0.5 to 14 wt .-% sum of component bl)

0.1 to 13.5 wt .-% sum of components a3) and b2), wherein based on the total amounts of components al) to a3) 0.5 to 3.0 wt .-% of anionic or potentially anionic hydrophilicizing agents used become.

Particularly preferred embodiments of the polyurethane dispersions (I) comprise as component al) isophorone diisocyanate and / or 1,6-hexamethylene diisocyanate and / or the isomeric bis (4,4'-isocyanatocyclohexyl) methanes in combination with a2) a mixture of polycarbonate po - lyols and polytetramethylene glycol polyols.

The preparation of such polyurethane dispersions can be carried out in one or more stages in homogeneous or multistage reaction, in some cases in disperse phase. After complete or partial polyaddition from al) to a3), a dispersing, emulsifying or dissolving step takes place. This is followed, if appropriate, by a further polyaddition or modification in disperse phase.

In this case, all known from the prior art methods such. Example, prepolymer mixing method, acetone method or Schmelzdispergierverfahren can be used. Preference is given to proceeding by the acetone process. For the preparation by the acetone process are usually the components a2) to a3), which may have no primary or secondary amino groups and the polyisocyanate cyanate component al) for the preparation of an isocyanate-functional polyurethane prepolymer completely or partially and optionally with one with water Miscible but diluted with isocyanate inert solvent and heated to temperatures ranging from 50 to 120 ⁰ C. To accelerate the isocyanate addition reaction, the catalysts known in polyurethane chemistry can be used.

Suitable solvents are the customary aliphatic, ketofunctional solvents such as acetone, 2-butanone, which may be added not only at the beginning of the preparation, but optionally also in parts later. Preference is given to acetone and 2-butanone.

Subsequently, the components of al) to a3), which are optionally not added at the beginning of the reaction, are metered in.

The reaction of the components al) to a3) to the prepolymer takes place partially or completely, but preferably completely. Thus, polyurethane prepolymers containing free isocyanate groups are obtained in bulk or in solution.

Subsequently, in a further process step, if not yet done or only partially done, the resulting prepolymer with the aid of aliphatic ketones such as acetone or 2-butanone.

The aminic components b1), b2) can optionally be used individually or in mixtures in water- or solvent-diluted form in the process according to the invention, it being possible in principle for any order of addition to be possible.

When water or organic solvents are used as the diluent, the diluent content in the chain-extending component used in B) is preferably 30 to 95% by weight.

The dispersion preferably takes place after the chain extension. For this purpose, the dissolved and chain-extended polyurethane polymer is optionally added either under strong shearing, such as strong stirring, either in the dispersing water or, conversely, the dispersing water is stirred to the chain-extended polyurethane polymer solutions. Preferably, the water is added to the dissolved chain-extended polyurethane polymer. The solvent still present in the dispersions after the dispersion step is then usually removed by distillation. A removal already during the dispersion is also possible.

The residual content of organic solvents in the dispersions essential to the invention is typically less than 1.0% by weight, preferably less than 0.3% by weight, based on the total dispersion.

The pH of the dispersions essential to the invention is typically less than 9.0, preferably less than 8.0.

In the production of the foams to be dried, in addition to the PU dispersions, foam auxiliaries (IT), thickeners (HI) and other auxiliaries and additives (IV) may also be used.

Suitable foam assistants (II) are commercially available stabilizers, such as water-soluble fatty acid amides, sulfosuccinamides, hydrocarbon sulfonates, sulfates or fatty acid salts, the lipophilic radical preferably containing from 12 to 24 carbon atoms, alkyl polyglycosides, etc.

Preferred foam assistants (Df) are alkanesulfonates or sulfates having 12 to 22 carbon atoms in the hydrocarbon radical, alkylbenzenesulfonates or sulfates having 14 to 24 carbon atoms in the hydrocarbon radical or fatty acid amides or fatty acid salts having 12 to 24 carbon atoms.

The aforementioned fatty acid amides are preferably fatty acid amides of mono- or di- (C 2-3 -alkanol) -amines. Fatty acid salts may be, for example, alkali metal salts, amine salts or unsubstituted ammonium salts.

Such fatty acid derivatives are typically based on fatty acids such as lauric, myristic, palmitic, oleic, stearic, ricinoleic, behenic or arachidic, coconut, tallow, soybean and their hydrogenation products.

Particularly preferred foam auxiliaries (IT) are sodium lauryl sulfate, sulfosuccinamides and ammonium stearates, and mixtures thereof.

For the purposes of the invention, thickeners (DT) are compounds which make it possible to adjust the viscosity of the resulting mixture of I-IV in such a way that it promotes the production and processing of the foam according to the invention. Commercially available thickeners are suitable as thickeners, such as natural organic thickeners, such as dextrins or starch, organically modified natural products, such as cellulose ethers or hydroxyethyl cellulose, fully synthetic organic, eg Polyacrylic acids, polyvinylpyrrolidones, poly (meth) acrylic compounds or polyurethanes (associative thickeners) and inorganic thickeners, eg Betonite or silicic acids. Preference is given to using organically fully synthetic thickeners. Particular preference is given to using acrylate thickeners, which are optionally further diluted with water before addition. Preferred commercially available thickeners are, for example, Mirox ^® AM (BGB Stockhausen GmbH, Krefeld, Germany), Walocel® ^® MT 6000 PV (Wolff Cellulosics GmbH & Co KG, Walsrode, Germany), Rhéolate ^® 255 (Elementies Specialties, Gent, Belgium), Collacral® ^® VL (BASF AG, Ludwigshafen, Germany), Aristoflex® ^® AVL (Clariant, Sulzbach, Germany)

Possibly. In component (IV) contained auxiliaries and additives may, for. As surface-active substances, abrasive waxes, internal release agents, fillers, dyes, pigments, flame retardants, hydrolysis, microbicides, flow control agents, antioxidants such as 2,6-di-tert-butyl-4-methylphenol, UV absorber type 2-hydroxyphenyl benzotriazole or light stabilizers of the type substituted on the nitrogen atom unsubstituted HALS compounds such as Tinuvin ^® 292 and Tinuvin ^® 770 DF (Ciba specialties GmbH, Lampertheim, DE) or other commercially customary stabilizers, as they (for example, in "light stabilizers for coatings" A. Valet, Vincentz Verlag, Hannover, 1996 and "Stabilization of Polymeric Materials" (H. Zweifel, Springer Verlag, Berlin, 1997, Appendix 3, pp. 181-213), or any mixtures of these compounds.

Usually, 80 to 99.5 wt .-% of the PU dispersion, 0 to 10 wt .-% of component (H), 0 to 10 wt .-% of component (III) are used in the production of foam, wherein the amounts are based on the corresponding anhydrous components (I) to (HI) are obtained and the sum of the anhydrous individual components added to 100 wt .-%.

80 to 99.5% by weight of the PU dispersion, 0.1 to 10% by weight of component (II) and 0.1 to 10% by weight of component (II) are preferably used in the production of foam, wherein the quantities are based on the corresponding anhydrous components (I) to (IH) and the sum of the anhydrous individual components added to 100 wt .-%.

Foaming may be accomplished by the introduction of air and / or under the action of appropriate shear energy (e.g., mechanical stirring) or by commercial propellants. Preference is given to the entry of air under the action of appropriate shear energy.

The foamed composition can be applied in a variety of ways to a variety of surfaces or in molds such as, for example, casting, knife coating, rolling, brushing, spraying or spraying; as well as shaping by an extrusion process is possible. While the foamed material before drying has a preferred foam density of 200 to 900 g / l, particularly preferably 250 to 600 g / l, the density of the resulting foams after drying is preferably 50 to 700 g / l, more preferably 200 to 550 g / l.

The actual drying takes place by the action of microwave radiation within the aforementioned frequency ranges.

The power introduced at the aforementioned frequencies is preferably 250 to 6000 W, more preferably 500 to 4000 W per kilogram of foam to be dried.

Furthermore, in addition to the use of microwave radiation, it is also possible to use a combination of microwave radiation and conventional thermal drying by heating the foam to be dried by means of IR radiation and / or hot air. It is immaterial whether the two types of drying are used in parallel or successively. In the case of successive drying by means of microwave radiation and thermal treatment, it is preferred to first perform a drying by means of microwave radiation and then to carry out the thermal treatment.

By the method according to the invention it is possible to dry foams homogeneously up to a height of 50 mm, the term height being related to the spatial direction in which the foam has the smallest extent.

In a preferred embodiment of the process, sheet-like foams, as can be produced by casting, are dried to a height of up to 30 mm.

Also preferred is the drying of foam strands, as are preferably obtained in the extrusion, with a height and width of the strand of 1 to 30 mm, preferably a height of 5 to 30 mm and a width of 1 to 30 mm.

Furthermore, the drying of foams, as they can be obtained by means of a mold casting process, is preferred, the foams each having an extent of 1 to 30 mm, based on their width and length.

The foams according to the invention can also be applied in a plurality of layers, for example to produce particularly high foam deposits, onto a wide variety of substrates or cast into molds.

In addition, the foamed compositions according to the invention can also be used in combination with other carrier materials such as textile carriers, paper, etc., for example by prior application (eg coating). Best drying results are achieved when foams with a height of 1 to 30 mm, preferably 1 to 20 mm, as they can be prepared by knife coating, casting or extrusion can be used for drying.

The inventive method allows a number of new application forms such as casting molding, extrusion, optionally followed by cutting. Particularly good foams are also obtained by drying the undried foam in a powder form, e.g. Starch or silica, are poured and then dried in the microwave.

To produce higher foam thicknesses, these can also be applied in a plurality of layers to a wide variety of substrates or cast into molds.

Examples:

Unless otherwise indicated, all percentages are by weight.

The solids contents were determined according to DIN-EN ISO 3251.

NCO contents were determined volumetrically in accordance with DIN-EN ISO 11909, unless expressly stated otherwise.

Substances used and abbreviations:

Diaminosulphonate: NH ₂ -CH ₂ CH ₂ -NH-CH ₂ CH ₂ -SO ₃ Na (45% in water)

Desmophen ^® C2200: polycarbonate polyol, OH number 56 mg KOH / g, number average molecular weight 2000 g / mol (Bayer MaterialScience AG, Leverkusen, DE)

PolyTHF ^® 2000: Polytetramethylenglykolpolyol, OH number 56 mg KOH / g, number average molecular weight 2000 g / mol (BASF AG, Ludwigshafen, DE)

PolyTHF ^® 1000: Polytetramethylenglykolpolyol, OH number 112 mg KOH / g, number-average number average molecular weight 1000 g / mol (BASF AG, Ludwigshafen, DE)

Polyether LB 25: (monofunctional polyether based on ethylene oxide / propylene oxide based number-average molecular weight 2250 g / mol, OH number 25 mg KOH / g (Bayer MaterialScience AG, Leverkusen, DE)

Stokal ^® STA: 30% ammonium stearate in water, foam stabilizer (Bozzetto GmbH, Krefeld, DE)

Aristoflex AVL: Dispersion of a sulfonic acid and emulsifier in caprylic / capric acid triglyceride (Clariant, Muttenz, Switzerland)

Loxanol K12P: sodium lauryl sulphate (Cognis, Dusseldorf, DE)

The determination of the mean particle sizes (indicated by the number average) of the PUR dispersions was carried out by means of laser correlation spectroscopy (instrument: Malvern Zetasizer 1000, Malver Inst. Limited). Example 1: PUR dispersion (component D

761.3 g of Desmophen ^® C2200, 987.0 g of PolyTHF ^® 2000, 375,4g PolyTHF ^® 1000 and 53.2 g polyethers LB 25 were heated to 70 ⁰ C. Then, at 70 ⁰ C within 5 min was added a mixture of 237.0 g of hexamethylene diisocyanate and 313.2 g of isophorone diisocyanate and stirring under reflux was continued until the theoretical NCO value was reached. The finished Prepoly- mer was dissolved with 4850 g of acetone at 50 ⁰ C and then a solution of 1.8 g 25.1 g E thylendiamin, 61.7 g diaminosulphonate, 116.5 g of isophoronediamine and 1030 g of water within 10 min. The stirring time was 10 min. Thereafter, it was dispersed by adding 1061 g of water. This was followed by removal of the solvent by distillation in vacuo and a storage-stable dispersion having a solids content of 60% was obtained.

Examples 2 to 7: Preparation of the foams of the invention

10000 g of the dispersion (I) obtained from Example 1 were mixed with 90 g of Loxanol K12P (II), 150 g of Stokal STA (II), 150 g of Aristoflex AVL (EI) and then by adding air using a Hansamixer top mix Foam density was 500 g / l The foam was applied in 15 cm wide layers of 3, 5, 8, 10, 13 and 15 mm on a release paper (VEZ Mat, Sappi, Brussels, Belgium) Finally, the foams produced in this way were tested on a porous fabric (Sefar Propyltex.) In a test microwave oven MWT k / 1.2-3 LK reg. From EL-A Verfahrenstechnik (Heidelberg, DE) 05-1000 / 45mm mesh size, Sefar GmbH, Wasserburg, Germany) placed 5 cm above the microwave base and dried for 30 min at 30% power (3.6 kW at maximum power).

FIG. 1 shows that, regardless of the layer thickness, it was possible to observe constant weight of the foams to be dried after 30 minutes. The case occurred weight loss compared to the wet foam material corresponded to the expected value due to the water contained.

Examples 8 to 13: Comparative Examples

10000 g of the dispersion (I) obtained from Example 1 were mixed with 90 g of Loxanol K12P (IT), 150 g of Stokal STA (HI), 150 g of Aristoflex AVL (IV) and then by adding air using a Hansamixer top mix -K ((Hansa Industrie Mixer GmbH, Heiligenrode, DE) foamed foam density was 500 g / l.) The foam was in 15 cm wide Schich- 3, 5, 8, 10, 13 and 15 mm on a release paper (VEZ Mat, Sappi, Brussels, Belgium). Subsequently, the material was dried in a circulating air oven with a temperature profile of 60 ^° C. (30 minutes), 90 ^° C. (30 minutes) and 110 ^° C. (15 minutes).

As can be seen from FIG. 2, it was only possible to obtain a dried material after 75 minutes at a layer thickness of only 3 mm. For all the others, no weight stability or the final weight of the dry foam expected on the basis of the water content was reached after 75 minutes. Regardless of the degree of drying, all foams had an irregular foam structure (such as voids and bubbles).

Example 14 Inventive Example (Extrusion)

10,000 g of the dispersion (I) obtained from Example 1 were mixed with 90 g of Loxanol K12P (IQ), 150 g of Stokal STA (HI), 150 g of Aristoflex AVL (IV) and then by adding air using a Hansamixer top mix Foam density was 500 g / l. Thereafter, 470 grams of the foamed paste was passed through a 15 mm diameter tube in strips on release paper (VEZ, Mat, Sappi , Brussels, Belgium) and applied on a porous tissue (Sefar Propyltex 05-1000 / 45mm mesh size, Sefar GmbH, Wasserburg, Germany) in a MWT k / 1,2-3 LK reg. Microwave oven of the Firmal EL-A process technology (Heidelberg, DE) , Germany) 5 cm above the microwave floor and dried at 30% power (3.6 kW at maximum power) for 30 minutes.

In this case, a weight loss of 188 g (40 wt.%) Was measured according to the amount of water originally contained in the foam. The foam had a fine uniform structure.

Claims

Claims:

1. A process for drying foams, in which the water-moist foam is exposed to microwave radiation.

2. The method according to claim 1, characterized in that the water-moist foam to be dried has a water content of 15 to 60 wt .-%.

3. The method according to claim 1 or 2, characterized in that as microwave radiation electromagnetic radiation having a frequency in the range of 2.0 to 3.0 GHz or 0.8 to 1.5 GHz is used.

4. The method according to any one of claims 1 to 3, characterized in that in parallel, before or after the drying by means of microwave radiation additionally takes place a thermal drying.

5. The method according to any one of claims 1 to 4, characterized in that the water-moist foam to be dried is obtainable from aqueous PU dispersions and optionally further components by foaming.

6. The method according to claim 5, characterized in that it is the PU dispersions to polyurethane or polyurethane-polyurea dispersions having a retained content of 40 to 63 wt .-% is.

7. The method according to claim 5 or 6, characterized in that these PU dispersions are obtainable, in which

A) isocyanate-functional prepolymers

al) aliphatic or cycloaliphatic polyisocyanates

a2) polymeric polyols having number average molecular weights of 400 to 8000 g / mol and OH functionalities of 1, 5 to 6,

a3) optionally hydroxy-functional, ionic or potentially ionic and / or nonionic hydrophilicizing agents,

getting produced,

B) whose free NCO groups then in whole or in part with bl) amino-functional compounds having molecular weights of 32 to 400 g / mol and / or

b2) amino-functional, ionic or potentially ionic hydrophilicizing agents

are reacted under chain extension and the prepolymers are dispersed in water before or after step B), optionally containing potentially ionic

Groups can be converted by partial or complete reaction with a neutralizing agent in the ionic form.

8. The method according to claim 7, characterized in that in the preparation of the PU dispersions as component al) isophorone diisocyanate and / or 1, 6-hexamethylene diisocyanate and / or the isomeric bis (4,4'-isocyanatocyclohexyl) methanes in Combination with a2) a mixture of polycarbonate polyols and polytetramethylene glycol polyols can be used.

9. The method according to any one of claims 1 to 8, characterized in that the water-moist foams before drying a foam density of 250 to 600 g / l and after drying have a foam density of 200 to 550 g / l.

10. The method according to any one of claims 1 to 8, characterized in that the water-moist foams are sheet-like foams with a maximum height of 30 mm, to strand-shaped foams with a height of 5 to 30 mm and a width of 1 to 30 mm o- to molded bodies with an extension in each case based on length, width and height of 1 to 30 mm.