EP1851281A1

EP1851281A1 - Aqueous polyurethane dispersions with a small content of cyclic compounds

Info

Publication number: EP1851281A1
Application number: EP06708156A
Authority: EP
Inventors: Andre Burghardt; Bärbel MEYER; Karl Häberle; Karl-Heinz Schumacher; Ulrike Licht
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2005-02-11
Filing date: 2006-02-09
Publication date: 2007-11-07
Also published as: DE102005006551A1; WO2006084881A1; KR20070104462A; CN101115811A; BRPI0607955A2; JP2008530292A; MX2007009193A; US20080139741A1

Abstract

The invention relates to aqueous dispersions containing a polyurethane and composed of: a) diisocyanates; b) diols, of which b1) 10 to 100 mol %, (in relation to the total quantity of the diols in (b)) have a molecular weight of between 500 and 5000 and b2) 0 to 90 mol %, (in relation to the total quantity of the diols in (b)) have a molecular weight of between 60 and 500 g/mol; c) monomers that differ from the monomers in (a) and (b) and that comprise at least one isocyanate group or at least one group that reacts with isocyanate groups, said monomers comprising in addition at least one hydrophilic group or a potential hydrophilic group, which induces the water dispersibility of the polyurethanes; d) optionally additional polyvalent compounds, which differ from the monomers in (a) to (c) and which comprise reactive groups, the latter being alcoholic hydroxyl groups, primary or secondary amino groups or isocyanate groups; and e) optionally monovalent compounds, which differ from the monomers in (a) to (d) and which comprise a reactive group, the latter being an alcoholic hydroxyl group, a primary or secondary amino group or an isocyanate group. Said dispersions are characterised in that the diols b1) contain less than 0.5 parts by weight cyclic compounds for 100 parts by weight diols b1).

Description

Aqueous polyurethane dispersions with a low content of cyclic compounds

description

The present invention relates to aqueous dispersions containing a polyurethane composed of

S) diisocyanates,

b) Diols, of which

bi) 10 to 100 mol%, based on the total amount of diols (b), have a molecular weight of 500 to 5000, and

b ₂ ) 0 to 90 mol%, based on the total amount of diols (b), have a molecular weight of 60 to 500 g / mol,

c) monomers other than monomers (a) and (b) having at least one isocyanate group or at least one isocyanate group-reactive group further having at least one hydrophilic group or a potentially hydrophilic group, thereby causing the water dispersibility of the polyurethanes;

d) optionally other polyfunctional compounds which differ from the monomers (a) to (c) and have reactive groups which are alcoholic hydroxyl groups, primary or secondary amino groups or isocyanate groups, and

e) optionally monovalent compounds other than monomers (a) to (d), having a reactive group which is an alcoholic compound

Hydroxyl group, a primary or secondary amino group or an isocyanate group,

characterized in that the diols b1 contain less than 0.5 parts by weight of cyclic compounds per 100 parts by weight of diols b1.

Furthermore, the invention relates to methods for coating, bonding and impregnation of articles made of different materials with these dispersions, the coated, bonded and impregnated articles coated with these dispersions, and the use of the dispersions of the invention as hydrolysis-resistant coating materials. The use of aqueous dispersions containing polyurethanes (in short: PU dispersions) as binders in adhesives, in particular laminating adhesives, or coating materials, eg for textile or leather, or in paints is known.

A disadvantage is that the raw materials used, in particular the diols b1, cyclic compounds such. contain cyclic esters or cyclic ethers. These cyclic compounds generally have no isocyanate-reactive groups, so that they are present in the polyurethane even after the preparation. If the polyurethanes are processed into adhesives or coatings, the cyclic compounds remain partly in the polymer and exert an undesired softening effect there. On the other hand, the cyclic compounds can migrate from the adhesives or coatings produced therewith when using the PU dispersions and contribute significantly to the so-called fogging effect. It is also common that the cyclic compounds migrate to the interface of the adhesive or coating film where they reduce the adhesion of the film to the substrate.

It is known from DE-A 103 24 306 that polyurethane dispersions which are prepared from polyhydroxyl compounds which have been freed of volatile compounds by distillation under certain conditions are suitable for producing low-fogging coatings.

Accordingly, the aqueous dispersions defined above were found. The aqueous dispersions according to the invention comprise polyurethanes which, in addition to other monomers, are derived from diisocyanates a, preference being given to using those diisocyanates which are customarily used in polyurethane chemistry.

To be mentioned in particular as monomers (a) diisocyanates X (NCO) ₂ , wherein X is an aliphatic hydrocarbon radical having 4 to 12 carbon atoms, a cycloaliphatic or aromatic hydrocarbon radical having 6 to 15 carbon atoms or an araliphatic hydrocarbon radical having 7 to 15 carbon atoms stands. Examples of such diisocyanates are tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 1,4-diisocyanatocyclohexane, 1-isocyanato-3,5, 5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), 2,2-bis (4-isocyanatocyclohexyl) propane , Trimethylhexandiisocyanat, 1, 4-diisocyanatobenzene, 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene, 4,4'-diisocyanato-diphenylmethane, 2,4'-diisocyanatodiphenyl methane, p-xylylene diisocyanate, tetramethylxylylene diisocyanate (TMXDI), the isomers of bis (4-isocyanatocyclohexyl) methane (HMDI) such as the trans / trans, the cis / cis and the cis / trans isomers, and mixtures consisting of these compounds. Such diisocyanates are available commercially.

Particularly suitable mixtures of these isocyanates are the mixtures of the respective structural isomers of diisocyanatotoluene and diisocyanato-diphenylmethane; in particular, the mixture of 80 mol% of 2,4-diisocyanatotoluene and 20 mol% of 2,6-diisocyanatotoluene is suitable. Furthermore, the mixtures of aromatic isocyanates such as 2,4-diisocyanatotoluene and / or 2,6-diisocyanatotoluene with aliphatic or cycloaliphatic isocyanates such as hexamethylene diisocyanate or IPDI are particularly advantageous, the preferred mixing ratio of the aliphatic to aromatic isocyanates 4: 1 to 1 : 4.

For the construction of the polyurethanes can be used as compounds in addition to the aforementioned also isocyanates, in addition to the free isocyanate groups further blocked isocyanate groups, e.g. Wear uretdione groups.

With regard to good film formation and elasticity, suitable diols (b) are primarily relatively high molecular weight diols (b1) which have a molecular weight of about 500 to 5000, preferably about 1000 to 3000 g / mol.

The diols (b1) are, in particular, polyesterpolyols which are known, for example, from Ullmanns Encyklopadie der technischen Chemie, 4th Edition, Volume 19, pages 62 to 65. Preference is given to using polyesterpolyols which are obtained by reacting dihydric alcohols with dibasic carboxylic acids. Instead of the free polycarboxylic acids, it is also possible to use the corresponding polycarboxylic acid anhydrides or corresponding polycarboxylic acid esters of lower alcohols or mixtures thereof to prepare the polyesterpolyols. The polycarboxylic acids may be aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic and may optionally be substituted, for example by halogen atoms, and / or unsaturated. Examples which may be mentioned are: suberic acid, azelaic acid, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylenetetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimer fatty acids. Preferred are dicarboxylic acids of the general formula HOOC- (CH 2) _y - COOH, where y is a number from 1 to 20, preferably an even number from 2 to 20, for example succinic acid, adipic acid, sebacic acid and dodecanedicarboxylic acid.

Examples of suitable polyhydric alcohols are ethylene glycol, propane-1,2-diol, propane-1,3-diol, butane-1,3-diol, butene-1,4-diol, butyne-1,4-diol, pentane-1 , 5-diol, neopentyl glycol, bis (hydroxymethyl) cyclohexanes such as 1, 4-bis (hydroxymethyl) cyclohexane, 2-methylpropane-1, 3-diol, methylpentanediols, furthermore diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol , Dipropylene glycol, polypropylene glycol, dibutylene glycol and polybutylene glycols into consideration. Alcohols of the general formula HO-- (CKb) _x -OH, where x is a number from 1 to 20, preferably an even number from 2 to 20. Examples of these are ethylene glycol, butane-1, 4-diol, hexane-1, 6-diol, octane-1, 8-diol and dodecane-1, 12-diol. Further preferred is neopentyl glycol.

Also included are polycarbonate diols, e.g. by reaction of phosgene with an excess of the mentioned as synthesis components for the polyester polyols low molecular weight alcohols, into consideration.

Also suitable are lactone-based polyesterdiols, which are homopolymers or copolymers of lactones, preferably terminal hydroxyl-containing addition products of lactones onto suitable difunctional starter molecules. Preferred lactones are those which are derived from compounds of the general formula where z is a number from 1 to 20 and an H atom of a methylene unit may also be substituted by a C 1 to C 4 alkyl radical. Examples are e-caprolactone, β-propiolactone, g-butyrolactone and / or methyl-e-caprolactone and mixtures thereof. Suitable starter components are, for example, the low molecular weight dihydric alcohols mentioned above as the synthesis component for the polyesterpolyols. The corresponding polymers of e-caprolactone are particularly preferred. Lower polyester diols or polyether diols can also be used as starters for the preparation of the lactone polymers. Instead of the polymers of lactones, it is also possible to use the corresponding, chemically equivalent polycondensates of the hydroxycarboxylic acids corresponding to the lactones.

In addition, suitable monomers (b1) are polyether diols. They are in particular by polymerization of ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide or epichlorohydrin with themselves, e.g. in the presence of BF3 or by addition of these compounds, optionally in admixture or sequentially, to starting components having reactive hydrogen atoms, such as alcohols or amines, e.g. Water, ethylene glycol, propane-1, 2-diol, propane-1, 3-diol, 1, 2-bis (4-hydroxydiphenyl) propane or aniline available. Particularly preferred is polytetrahydrofuran having a molecular weight of 240 to 5000, and especially 500 to 4500.

Also suitable are polyhydroxyolefins, preferably those having 2 terminal hydroxyl groups, e.g. a, -w-dihydroxypolybutadiene, a, -w-Dihydroxypolymethacrylester or a, -w-Dihydroxypolyacrylester as monomers (d). Such compounds are known, for example, from EP-A 0622378. Further suitable polyols are polyacetals, polysiloxanes and alkyd resins.

The polyols can also be used as mixtures in a ratio of 0.1: 1 to 1: 9. The hardness and modulus of elasticity of the polyurethanes can be increased if, as diols (b), low molecular weight diols (b2) having a molecular weight of from about 60 to 500, preferably from 62 to 200, g / mol are used in addition to the diols (b1).

The diols b1 contain less than 0.5, in particular less than 0.2 and very particularly preferably less than 0.1% by weight of cyclic compounds. These cyclic compounds are, in particular, cyclic esters and cyclic ethers. They appear as by-products in the preparation of the polyester or polyether ols. The molecular weight of the cyclic compounds is generally less than 500 g / mol, in particular less than 300 g / mol.

The cyclic compounds can be removed from diols b1 before further reacting these diols. These can z. B. the diols are subjected to a distillative treatment. The content of cyclic compounds may also be reduced by the introduction of gases such as e.g. Nitrogen, argon, steam or carbon dioxide can be reduced.

Also by treatment with suitable washing liquids, e.g. Water, the content of cyclic compounds can be reduced.

The monomers (b2) used are in particular the synthesis components of the short-chain alkanediols mentioned for the preparation of polyester polyols, the unbranched diols having 2 to 12 carbon atoms and an even number of carbon atoms and pentane-1, 5-diol and neopentyl glycol to be favoured.

Preferably, the proportion of the diols (b1), based on the total amount of the diols (b) is 10 to 100 mol% and the proportion of the monomers (b2), based on the total amount of the diols (b) 0 to 90 mol%. The ratio of the diols (b1) to the monomers (b2) is particularly preferably 0.1: 1 to 5: 1, particularly preferably 0.2: 1 to 2: 1.

In order to achieve the water-dispersibility of the polyurethanes, the polyurethanes, in addition to the components (a), (b) and, if appropriate, (d) are monomers (c) which are different from components (a), (b) and (d) and which are at least one Isocyanate group or at least one isocyanate-reactive group and, moreover, at least one hydrophilic group or a group which can be converted into a hydrophilic group carry constructed. In the following text, the term "hydrophilic groups or potentially hydrophilic groups" is abbreviated to "(potentially) hydrophilic groups". The (potentially) hydrophilic groups react much more slowly with isocyanates than the functional groups of the monomers which serve to build up the polymer main chain. The proportion of components having (potentially) hydrophilic groups in the total amount of components (a), (b), (c), (d) and (e) is generally such that the molar amount of (potentially) hydrophilic groups, based on the amount by weight of all monomers (a) to (e), 30 to 1000, preferably 50 to 500 and particularly preferably 80 to 300 mmol / kg.

The (potentially) hydrophilic groups may be nonionic or, preferably, (potentially) ionic hydrophilic groups.

Suitable nonionic hydrophilic groups are, in particular, polyethylene glycol ethers of preferably 5 to 100, preferably 10 to 80, ethylene oxide repeat units. The content of polyethylene oxide units is generally 0 to 10, preferably 0 to 6 wt .-%, based on the amount by weight of all monomers (a) to (e).

Preferred monomers with nonionic hydrophilic groups are polyethylene oxide diols, polyethylene oxide monools and the reaction products of a polyethylene glycol and a diisocyanate which carry a terminally etherified polyethylene glycol radical. Such diisocyanates and processes for their preparation are given in the patents US-A 3,905,929 and US-A 3,920,598.

Ionic hydrophilic groups are especially anionic groups such as the sulfonate, the carboxylate and the phosphate group in the form of their alkali metal or ammonium salts and cationic groups such as ammonium groups, in particular protonated tertiary amino groups or quaternary ammonium groups.

Potentially ionic hydrophilic groups are, above all, those which can be converted by simple neutralization, hydrolysis or quaternization reactions into the above-mentioned ionic hydrophilic groups, e.g. Carboxylic acid groups or tertiary amino groups.

(Potentially) ionic monomers (c) are e.g. in Ullmann's Encyclopedia of Industrial Chemistry, 4th Edition, Volume 19, pp.311-313 and for example in DE-A 14 95 745 described in detail.

As (potentially) cationic monomers (c), especially monomers having tertiary amino groups are of particular practical importance, for example: tris- (hydroxyalkyl) -amines, N, N'-bis (hydroxyalkyl) -alkylamines, N-hydroxyalkyl-dialkylamines, Ths (aminoalkyl) -amines, N, N'-bis (aminoalkyl) -alkylamines, N-aminoalkyl-dialkylamines, wherein the alkyl radicals and alkanediyl units of these tertiary amines independently of one another consist of 1 to 6 carbon atoms. Furthermore, tertiary nitrogen atoms containing polyether having preferably two terminal hydroxyl groups, such as, for example, by alkoxylation of two bonded to the atomic hydrogen atoms having suitable amines, for example methylamine, aniline or N, N'-dimethylhydrazine, in per se conventional manner, into consideration. Such polyethers generally have a molecular weight between 500 and 6000 g / mol.

These tertiary amines are reacted either with acids, preferably strong mineral acids such as phosphoric acid, sulfuric acid, hydrohalic acids or strong organic acids or by reaction with suitable quaternizing agents such as Cr to Cε-alkyl halides or benzyl halides, e.g. Bromides or chlorides into which ammonium salts are converted.

Suitable monomers with (potentially) anionic groups are usually aliphatic, cycloaliphatic, araliphatic or aromatic carboxylic acids and sulfonic acids which carry at least one alcoholic hydroxyl group or at least one primary or secondary amino group. Preference is given to dihydroxyalkylcarboxylic acids, especially having 3 to 10 carbon atoms, as also described in US Pat

3,412,054 are described. In particular, compounds of the general formula

(Ci)

R ³ Ho -R ¹ CR-OH (d)

COOH

in which R ¹ and R ^{2 is} a Cr to GrAlkandiyl unit and R ^{3 is} a Cr to C ₄ - alkyl unit and, in particular, dimethylolpropionic acid (DMPA) is preferred.

Also suitable are corresponding dihydroxysulfonic acids and dihydroxyphosphonic acids, such as 2,3-dihydroxypropanephosphonic acid.

Otherwise suitable are dihydroxyl compounds having a molecular weight above 500 to 10,000 g / mol with at least 2 carboxylate groups, which are known from DE-A 39 11 827. They are obtainable by reacting dihydroxyl compounds with tetracarboxylic acid dianhydrides such as pyromellitic dianhydride or cyclopentanetetracarboxylic dianhydride in a molar ratio of 2: 1 to 1:05 in a polyaddition reaction. Particularly suitable dihydroxyl compounds are the monomers (b2) listed as chain extenders and also the diols (b1).

Suitable monomers (c) with isocyanate-reactive amino groups are amino carboxylic acids such as lysine, β-alanine or the adducts of aliphatic diprimary diamines mentioned in DE-A 20 34 479 to α, β-unsaturated carboxylic or sulfonic acids into consideration. Such compounds obey, for example, the formula (C2)

H ₂ NR ¹ NH-RX ^(c2) in the

R ⁴ and R ^{5 are} independently of one another a d- to Cδ-alkanediyl unit, preferably ethylene

and X is COOH or SO ₃ H.

Particularly preferred compounds of the formula (c ₂ ) are N- (2-aminoethyl) -2-aminoethanecarboxylic acid and also N- (2-aminoethyl) -2-aminoethanesulfonic acid or the corresponding alkali metal salts, Na being particularly preferred as the counterion.

Further particularly preferred are the adducts of the abovementioned aliphatic diprimary diamines with 2-acrylamido-2-methylpropanesulfonic acid, as described, for example, in US Pat. in DE Patent 19 54 090 are described.

If monomers having potentially ionic groups are used, their conversion into the ionic form may take place before, during, but preferably after the isocyanate polyaddition, since the ionic monomers are often difficult to dissolve in the reaction mixture. The sulfonate or carboxylate groups are particularly preferably in the form of their salts with an alkali metal ion or an ammonium ion as the counterion.

The monomers (d), which are different from the monomers (a) to (c) and which are optionally also constituents of the polyurethane, generally serve for crosslinking or chain extension. They are generally more than dihydric non-phenolic alcohols, amines having 2 or more primary and / or secondary amino groups and compounds which carry one or more primary and / or secondary amino groups in addition to one or more alcoholic hydroxyl groups.

Alcohols of higher valency than 2, which can serve to set a certain degree of branching or crosslinking, are e.g. Trimethylolpropane, glycerine or sugar.

Also suitable are monoalcohols which, in addition to the hydroxyl group, carry a further isocyanate-reactive group, such as monoalcohols having one or more primary and / or secondary amino groups, for example monoethanolamine. Polyamines having 2 or more primary and / or secondary amino groups are used especially when the chain extension or crosslinking is to take place in the presence of water, since amines usually react faster than alcohols or water with isocyanates. This is often required when aqueous dispersions of high molecular weight crosslinked polyurethanes or polyurethanes are desired. In such cases, the procedure is to prepare prepolymers with isocyanate groups, to rapidly disperse them in water and then to chain extend or crosslink them by adding compounds containing several isocyanate-reactive amino groups.

Amines suitable for this purpose are generally polyfunctional amines of the molecular weight range from 32 to 500 g / mol, preferably from 60 to 300 g / mol, which contain at least two amino groups selected from the group of primary and secondary amino groups. Examples of these are diamines such as diaminoethane, diamino propanes, diaminobutanes, diaminohexanes, piperazine, 2,5-dimethylpiperazine, amino-3-aminomethyl-3,5,5-trimethylcyclohexane (isophoronediamine, IPDA), 4,4'-diaminodicyclo - hexylmethane, 1, 4-diaminocyclohexane, aminoethylethanolamine, hydrazine, hydrazine hydrate or triamines such as diethylenetriamine or 1,8-diamino-4-aminomethyloctan.

The amines may also be in blocked form, e.g. in the form of the corresponding ketimines (see, for example, CA-A 1 129 128), ketazines (see, for example, US-A 4,269,748) or amine salts (see US-A 4,292,226). Also oxazolidines, as used for example in US Pat. No. 4,192,937, are blocked polyamines which can be used for the preparation of the polyurethanes according to the invention for chain extension of the prepolymers. When using such capped polyamines they are generally mixed with the prepolymers in the absence of water and this mixture is then mixed with the dispersion water or a part of the dispersion water, so that the corresponding polyamines are hydrolytically released.

Preference is given to using mixtures of di- and triamines, particularly preferably mixtures of isophoronediamine (IPDA) and diethylenetriamine (DETA).

The polyurethanes preferably contain from 1 to 30, particularly preferably from 4 to 25, mol%, based on the total amount of components (b) and (d), of a polyamine having at least 2 isocyanate-reactive amino groups as monomers (d).

Alcohols with a value higher than 2, which can serve to set a certain degree of branching or crosslinking, are, for example, trimethylolpropane, glycerol or sugar. For the same purpose higher than divalent isocyanates can also be used as monomers (d). Commercially available compounds are, for example, the isocyanurate or the biuret of hexamethylene diisocyanate.

Monomers (e), which are optionally used, are monoisocyanates, monohydric alcohols and monoprimary and secondary amines. In general, their proportion is at most 10 mol%, based on the total molar amount of the monomers. These monofunctional compounds usually carry further functional groups, such as olefinic groups or carbonyl groups, and serve to introduce functional groups into the polyurethane, which make possible the dispersion or crosslinking or further polymer-analogous reaction of the polyurethane. Suitable for this purpose are monomers such as isopropenyl-α, α-dimethylbenzyl isocyanate (TMI) and esters of acrylic or methacrylic acid such as hydroxyethyl acrylate or hydroxyethyl methacrylate.

In the field of polyurethane chemistry, it is well known how the molecular weight of the polyurethanes can be adjusted by selecting the proportions of the monomers reactive with one another and the arithmetic mean of the number of reactive functional groups per molecule.

Normally, the components (a) to (e) and their respective molar amounts are chosen so that the ratio A: B with

A) the molar amount of isocyanate groups and

B) the sum of the molar amount of the hydroxyl groups and the molar amount of the functional groups which can react with isocyanates in an addition reaction

0.5: 1 to 2: 1, preferably 0.8: 1 to 1, 5, particularly preferably 0.9: 1 to 1, 2: 1. Most preferably, the ratio A: B is as close as possible to 1: 1.

The monomers (a) to (e) used carry on average usually 1.5 to 2.5, preferably 1.9 to 2.1, particularly preferably 2.0 isocyanate groups or functional groups which can react with isocyanates in an addition reaction ,

The polyaddition of components (a) to (e) for the preparation of the polyurethane present in the aqueous dispersions of the invention is carried out at reaction temperatures of 20 to 18O ⁰ C, preferably 50 to 15O ⁰ C under atmospheric pressure or under autogenous pressure.

The required reaction times are in the range of 1 to 20 hours, in particular in the range of 1, 5 to 10 hours. It is in the field of polyurethane chemistry Known how the reaction time is influenced by a variety of parameters such as temperature, concentration of monomers, reactivity of the monomers.

Rührkessel come into consideration as polymerization, especially when provided by the concomitant use of solvents for a low viscosity and good heat dissipation.

Preferred solvents are immiscible with water indefinitely, have a boiling point at atmospheric pressure of 40 to 100 ⁰ C and do not react or only slowly with the monomers.

Most often, the dispersions are prepared by one of the following methods:

After the "acetone process" is miscible with water and in a boiling solvent at atmospheric pressure under an ionic polyurethane 100 ⁰ C of the components (a) to (c). Add enough water to form a dispersion in which water is the coherent phase.

The "prepolymer mixing process" differs from the acetone process in that it does not produce a fully reacted (potentially) ionic polyurethane, but first a prepolymer bearing isocyanate groups. The components are chosen so that the ratio A: B is greater than 1, 0 to 3, preferably 1, 05 to 1, 5. The prepolymer is first dispersed in water and then optionally crosslinked by reaction of the isocyanate groups with amines carrying more than 2 isocyanate-reactive amino groups, or chain-extended with amines bearing 2 isocyanate-reactive amino groups. Chain extension also occurs when no amine is added. In this case, isocyanate groups are hydrolyzed to amino groups, which react with remaining isocyanate groups of the prepolymers with chain extension.

Usually, if a solvent was used in the preparation of the polyurethane, most of the solvent is removed from the dispersion, for example by distillation at reduced pressure. The dispersions preferably have a solvent content of less than 10% by weight and are particularly preferably free from solvents.

The dispersions generally have a solids content of 10 to 75, preferably from 20 to 65 wt .-% and a viscosity of 10 to 500 m Pas (measured at a temperature of 2O ⁰ C and a shear rate of 250 S ^"1 ).

Due to the use of diols b1 with a low content of cyclic compounds, the polyurethane dispersions also have a content of less than 0.5% by weight. in particular less than 0.2 parts by weight and very particularly preferably less than 0.1 parts by weight per 100 parts by weight of polyurethane (solid).

The low content of cyclic compounds in b1 or in the polyurethane dispersion is achieved by separating the cyclic compounds already from the diols b1 before their reaction (see above).

The polyurethane dispersions are suitable as binders for adhesives, coating agents for a wide variety of substrates, including textiles and leather, and in particular for paints.

The adhesives, coating compositions or paints may consist solely of the polyurethane dispersion or contain further constituents.

They may contain commercially available auxiliaries and additives such as blowing agents, defoamers, emulsifiers, thickeners and thixotropic agents, colorants such as dyes and pigments, tackifying resins (tackifiers).

The dispersions according to the invention are suitable for coating objects made of metal, plastic, paper, textile, leather or wood, by applying them by the generally customary methods, for example. by spraying or knife coating in the form of a film on these objects and the dispersion dries.

The aqueous dispersions of the invention are notable i.a. due to a higher modulus of elasticity, a higher tensile strength, a lower elongation at break and improved adhesion to the substrate.

Claims

claims

1. Aqueous dispersions containing a polyurethane, composed of

a> diisocyanates,

b) Diols, of which

b2) 0 to 90 mol%, based on the total amount of diols (b), have a molecular weight of 60 to 500 g / mol,

c) monomers other than monomers (a) and (b) having at least one isocyanate group or at least one isocyanate-reactive group which additionally carry at least one hydrophilic group or a potentially hydrophilic group, thereby causing the water-dispersibility of the polyurethanes,

d) optionally other polyfunctional compounds other than the monomers (a) to (c), having reactive groups which are alcoholic hydroxyl groups, primary or secondary amino groups or isocyanate groups, and

e) optionally monovalent compounds other than the monomers (a) to (d), having a reactive group which is an alcoholic hydroxyl group, a primary or secondary amino group or an isocyanate group,

characterized in that the diols bi contain less than 0.5 parts by weight of cyclic compounds per 100 parts by weight of diols b1.

2. Aqueous dispersions according to claim 1, wherein as diisocyanates (a) 1-isocyanato-SSδ-trimethyl-S-isocyanatomethylcyclohexane (IPDI), tetramethylxylylene diisocyanate (TMXDI) and bis (4-isocyanatocyclohexyl) methane (HMDI) be used.

3. Aqueous dispersions according to claims 1 or 2, wherein at least 50% by weight of the diols (bi) are polyesterdiols or polytetrahydrofuran.

4. A process for coating articles of metal, plastic, paper, textile, leather or wood, characterized in that applying an aqueous dispersion according to claims 1 to 3 in the form of a film on these objects and the dispersion is dried.

5. A process for bonding articles of metal, plastic, paper, textile, leather or wood, characterized in that applying an aqueous dispersion according to claims 1 to 3 in the form of a film on one of these objects and before or after drying of the film with another object.

6. A process for the impregnation of articles of textile, leather or paper, characterized in that soaking these articles with the aqueous dispersion according to claims 1 to 3 and then dried.

7. articles which are coated, bonded or impregnated with the aqueous dispersion according to claims 1 to 3.

8. Use of the aqueous dispersions according to claims 1 to 3 as a coating for objects made of metal, plastic, paper, textile, leather or

Wood.