WO2019145170A1

WO2019145170A1 - Aqueous dispersion of a polyurethane comprising a cycloaliphatic compound with two secondary amino groups as chain extender

Info

Publication number: WO2019145170A1
Application number: PCT/EP2019/050749
Authority: WO
Inventors: Alexander Panchenko; Karl Haeberle; Matthaeus KOPCZYNSKI
Original assignee: Basf Se
Priority date: 2018-01-24
Filing date: 2019-01-14
Publication date: 2019-08-01

Abstract

An aqueous dispersion of a polyurethane wherein the polyurethane is obtained by reacting dior polyfunctional isocyanates, diols, a cycloaliphatic compound with two secondary amino groups and optionally further compounds.

Description

Aqueous dispersion of a polyurethane comprising a cycloaliphatic compound with two secondary amino groups as chain extender

Description

The present invention relates to an aqueous dispersion of a polyurethane wherein the polyurethane is obtained by reacting di- or polyfunctional isocyanates, diols, a cycloaliphatic compound with two secondary amino groups and optionally further compounds.

Aqueous polyurethane dispersions are often produced industrially using the process known as the“prepolymer mixing technique”. In that process polyurethanes are first prepared in an organic solvent and the resulting polyurethane solution is subsequently dispersed in water. During and/or after its dispersing in water the polyurethane can then have its molar mass increased further by chain extension. For such chain extension compounds with two primary amino groups and/or secondary amino groups are used, as disclosed in WO 2016/162215, US 2007/0197720 and US 6395824. The polyurethanes obtained by this process are used, for example, as binders in coatings and adhesives.

Often it is observed that films prepared from such the polyurethane dispersions show a yellowing when exposed to daylight for a certain time. Such yellowing has a severe negative impact on the suitability of such polyurethane dispersions for a variety of technical application. Hence, it is desired to have polyurethane dispersions with significantly reduced yellowing.

The synthesis of cycloaliphatic compounds with primary or secondary amino groups is described, for example, in DE-A 4404220, in Seung Geun Oh et al., Catalysis Communications 43 (2014), pages 79 - 83 or in PCT/EP2017/065864 (INV160115).

It was an object of this invention to provide polyurethane dispersions which are suitable to be used for technical applications, notably as binders in coatings or adhesives. The polyurethane should have good mechanical properties but should show as little yellowing as possible under daylight exposure.

Accordingly, the polyurethane dispersion described above and a process for the preparation of the polyurethane dispersion have been found.

To the cycloaliphatic compound with two secondary amino groups

The term "cycloaliphatic compound” shall mean a compound comprising at least one cycloaliphatic ring system. Furthermore, the cycloaliphatic compound comprises two secondary amino groups. In addition, the cycloaliphatic compound may comprise further groups, for example alkyl groups. The cycloaliphatic compound may also be a mixture of different cycloaliphatic compounds.

In a preferred embodiment, the cycloaliphatic compound has a molecular weight of at maximum 2000 g/mol, notably of at maximum 1000 g/mol.

More preferred is a cycloaliphatic compound with a molecular weight of at maximum 600 g/mol.

The cycloaliphatic compound may comprise one or more cycloaliphatic ring systems, notably one or two cycloaliphatic ring systems. The ring system may notably be an aliphatic five- or six- membered ring system.

Such cycloaliphatic compounds are notable the following compounds: a compound of formula I

a compound of formula II

or a mixture thereof, with R¹ and R² independently from one another representing an alkyl group with 1 to 12 carbon atoms and R³ representing hydrogen or an alkyl group with 1 to 12 carbon atoms; a compound of formula III

with R¹ and R² independently from one another representing an alkyl group with 1 to 12 carbon atoms; a compound of formula IV

with R¹ and R² independently from one another representing an alkyl group with 1 to 12 carbon atoms and a compound of formula V

Preferably, R¹ and R² in formulas I, II, III and IV independently from one another represent an alkyl group with 1 to 6 carbon atoms, notably with 1 to 4 carbon atoms. In a preferred embodiment, R¹ and R² are identical. In a more preferred embodiment, both R¹ and R² in formulas I, II, III and IV represent an alkyl group with 3 or 4 carbon atoms, notably an isobutyl group which is -CFh - CH (-CH3)₂ or an isopropyl group which is -CH-(CH3)2.

Preferably, R³ in formulas I and II represents a hydrogen atom or alkyl group with 1 to 6 carbon atoms, notably a hydrogen atom or an alkyl group with 1 to 4 carbon atoms.

More preferably, R³ in formulas I and II represents a hydrogen atom or a methyl group. In a particularly preferred embodiment, R³ is a methyl group.

In a preferred embodiment, the cycloaliphatic compound is a compound of formula I or II or a mixture thereof or a compound of formula V.

In a more preferred embodiment, the cycloaliphatic compound is a compound of formula I or II, or a mixture thereof.

In a particularly preferred embodiment, the cycloaliphatic compound is a compound of formula I, of formula II or a mixture of a compound of formula I and of a compound of formula II with both R¹ and R² representing an isopropyl group and R³ representing a methyl group.

In a most preferred embodiment, the cycloaliphatic compound is a mixture of a compound of formula I and of a compound of formula II with both R¹ and R² representing an isopropyl group and R³ representing a methyl group, in other words a mixture of N, N‘-diisopropyl-1 -methyl-2, 4- diamino-cyclohexane und N, N‘-diisopropyl-1 -methyl-2, 6-diamino-cyclohexane.

Preferred mixtures of a compound of formula I and of a compound of formula II comprise 70 to 90 % by weight, notably 75 to 85 % by weight of the compound of formula I, based on the total weight of both compounds.

Accordingly, such mixtures comprise 10 to 30 % by weight, notably 15 to 25 % by weight of the compound of formula II, based on the total weight of both compounds.

The synthesis of cycloaliphatic compounds with primary or secondary amino groups is well known in the art and is described, for example, in DE-A 4404220, in Seung Geun Oh et al., Catalysis Communications 43 (2014), pages 79 - 83 or in PCT/EP2017/065864 (INV1601 15). Mixtures of compounds of formula I and II may be obtained by mixing such compounds or by synthesis methods using mixtures as starting material, such as mixtures of 2,4 toluene and 2,6 toluene, respectively 2,4 toluene diamine and 2,6 toluene diamine.

Compound of formula V may be obtained by reacting 2 mols of acrylonitrile with isophorone; compound of formula V is available from BASF as Baxxodur® PC 136. Preferably, the polyurethane comprises 0.5 to 15% by weight, notably 1 to 12% by weight of the cycloaliphatic compound with two secondary amino groups.

In a more preferred embodiment, the polyurethane comprises 2 to 10% by weight, notably 3 to 9% by weight of the cycloaliphatic compound with two secondary amino groups.

The above weight percentages are based on the total weight of the polyurethane and relate to the cycloaliphatic compound in its polymerized form. The reaction of the secondary amino group with the isocyanate group is an addition reaction. No demerging compounds are formed. Hence, the molecular weight of the cycloaliphatic compound with two secondary amino groups and the molecular weight of the cycloaliphatic compound with two secondary amino groups in its polymerized form are identical.

To the polyurethane

The polyurethane is obtained by reacting di- or polyfunctional isocyanates, diols, a

cycloaliphatic compound with two secondary amino groups and optionally further compounds.

Specifically, the polyurethane is obtained by reacting

a) di- or polyfunctional isocyanates with 4 to 30 carbon atoms b) diols of which b.1 ) 10 to 100 mol%, based on the total amount of diols (b), have a molecular weight of from 500 to 5000 and b.2) 0 to 90 mol%, based on the total amount of diols (b), have a molecular weight of from 60 to 500 g/mol, c) further di- or polyfunctional compounds of which c.1 ) 5 to 100 mol % are the cycloaliphatic compound with two secondary

amino groups and c.2) 0 to 95 mol % are other di- or polyfunctional compounds than a), b) and d ) d) compounds other than the compounds a), b) and c) with at least one

isocyanate group or at least one isocyanato-reactive group and additionally at least one hydrophilic group or one potentially hydrophilic group and e) optionally compounds with one isocyanate group or one isocyanato-reactive group without hydrophilic groups or potentially hydrophilic groups

Di-functional isocyanates are compounds with two isocyanate groups, also referred to as diisocyanates.

Poly-functional isocyanates are compounds with at least three isocyanate groups, also referred to as polyisocyanates.

The di- or polyfunctional isocyanates may be aliphatic, aromatic and cycloaliphatic compounds which includes compounds that have combinations of (cyclo)aliphatic or aromatic groups.

Preferably, the di- or polyfunctional isocyanates do not comprise any other constituents than the isocyanate groups and hydrocarbon groups.

Usually a mixture of different di- or polyfunctional isocyanates is used. The NCO functionality of the mixture is preferably from 2 to 4.

The diisocyanates are preferably isocyanates having 4 to 20 carbon atoms. Examples of customary diisocyanates are aliphatic diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (1 ,6-diisocyanatohexane), octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate, esters of lysine diisocyanate, tetramethylxylylene diisocyanate, trimethylhexane diisocyanate or tetramethylhexane diisocyanate, cycloaliphatic diisocyanates such as 1 ,4-, 1 ,3- or 1 ,2- diisocyanatocyclohexane, trans/trans, the cis/cis and the cis/trans isomer of 4,4’- or 2,4’- di(isocyanatocyclohexyl)methane, 1-isocyanato-3,3,5-trimethyl-5- (isocyanatomethyl)cyclohexane (isophorone diisocyanate), 2,2-bis(4- isocyanatocyclohexyl)propane, 1 ,3- or 1 ,4-bis(isocyanatomethyl)cyclohexane or 2,4- or 2,6- diisocyanato-1-methylcyclohexane, and aromatic diisocyanates such as 2,4- or 2,6-tolylene diisocyanate and the isomer mixtures thereof, m- or p-xylylene diisocyanate, 2,4’- or 4,4’- diisocyanatodiphenylmethane and the isomer mixtures thereof, 1 ,3- or 1 ,4-phenylene diisocyanate, 1-chloro-2,4-phenylene diisocyanate, 1 ,5-naphthylene diisocyanate, diphenylene 4,4’-diisocyanate, 4,4’-diisocyanato-3,3’-dimethylbiphenyl, 3-methyldiphenylmethane 4,4’- diisocyanate, 1 ,4-diisocyanatobenzene or diphenyl ether 4,4’-diisocyanate.

Suitable diisocyanates are also the uretdiones of the above diisocyanates.

Mixtures of said diisocyanates may also be used. Preference is given to aliphatic and cycloaliphatic diisocyanates, and particular preference to isophorone diisocyanate, hexamethylene diisocyanate, meta-tetramethylxylylene diisocyanate (m-TMXDI) and 1 ,1-methylenebis[4-isocyanato]cyclohexane (H12MDI).

Suitable polyisocyanates include polyisocyanates containing isocyanurate groups,

polyisocyanates containing biuret groups, polyisocyanates containing urethane groups or allophanate groups, polyisocyanates containing oxadiazinetrione groups, uretonimine-modified polyisocyanates of linear or branched C₄-C2o-alkylene diisocyanates, cycloaliphatic

diisocyanates having 6 to 20 carbon atoms in all or aromatic diisocyanates having 8 to 20 carbon atoms in all, or mixtures thereof.

The diisocyanates and polyisocyanates which can be used preferably have an isocyanate group (calculated as NCO, molecular weight = 42) content of from 10 to 60% by weight based on the diisocyanate and polyisocyanate (mixture), more preferably from 15 to 60% by weight and very preferably from 20 to 55% by weight.

Preference is given to aliphatic and/or cycloaliphatic diisocyanates and polyisocyanates, examples being the abovementioned aliphatic and cycloaliphatic diisocyanates and

polyisocyanates or mixtures thereof.

Diols b.1) have a molecular weight of from 500 to 5000 g/mol, preferably from about 1000 to 3000 g/mol.

The diols b.1) are, in particular, polyesterdiols. Such polyesterdiols are preferably obtained by reacting dihydric alcohols with dibasic carboxylic acids. Instead of the free polycarboxylic acids it is also possible to use the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols, or mixtures thereof, to prepare the polyesterpolyols. The polycarboxylic acids can be aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic and can be unsubstituted or substituted, by halogen atoms, for example, and/or saturated or unsaturated. Examples are suberic, azelaic, phthalic, and isophthalic acid, phthalic,

tetrahydrophthalic, hexahydrophthalic, tetrachlorophthalic, endomethylenetetrahydrophthalic, glutaric and maleic anhydride, maleic acid, fumaric acid and dimeric fatty acids. Preference is given to dicarboxylic acids of the general formula HOOC- (CH2)_y-COOH, where y is a number from 1 to 20, preferably an even number from 2 to 20, examples being succinic, adipic, sebacic and dodecanedicarboxylic acids.

Examples of suitable dihydric alcohols are ethylene glycol, 1 ,2-propanediol, 1 ,3-propanediol,

1 ,3-butanediol, 1 ,4-butenediol, 1 ,4-butynediol, 1 ,5-pentanediol, neopentyl glycol,

bis(hydroxymethyl)cyclohexanes such as 1 ,4-bis(hydroxymethyl)cyclohexane, 2-methyl-1 ,3- propanediol and also diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol and polybutylene glycols. Preference is given to neopentylglycol and alcohols of the general formula HO-(CH2)_x-OH, where x is a number from 1 to 20, preferably an even number from 2 to 20. Examples of such alcohols are ethylene glycol, 1 ,4-butanediol, 1 ,6-hexanediol, 1 ,8 -octanediol and 1 ,12- dodecanediol.

Also suitable are polycarbonatediols, lactone-based polyesterdiols.

Further suitable diols b.1 ) are polyetherdiols. They are obtainable in particular by addition polymerization of ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide or epichlorohydrin with itself, in the presence, for example, of BF₃, or by addition reaction of these compounds, alone or in a mixture or in succession, onto starter components containing reactive hydrogens, such as alcohols or amines, examples being water, ethylene glycol, 1 ,2- propanediol, 1 ,3-propanediol, 2,2-bis(4-hydroxydiphenyl)propane or aniline. Particular preference is given to polytetrahydrofuran having a molecular weight of from 500 to 5000 g/mol and, in particular, from 1000 to 4500 g/mol.

Mixtures of different diols b.1) may be used.

It is possible to employ as diols b) not only the diols b.1 ) but also low molecular mass diols b.2) having a molecular weight of from about 50 to 500, preferably from 60 to 200 g/mol.

Compounds employed as monomers (b2) are notably short-chain alkanediols cited above for the preparation of polyesterpolyols, preference being given to the unbranched diols having from 2 to 12 carbons and an even number of carbons, and to 1 ,5-pentanediol and neopentyl glycol.

The proportion of the diols (b1), based on the total amount of diols (b), is preferably from 10 to 100 mol%, and the proportion of the diols (b2), based on the total amount of diols (b), is preferably from 0 to 90 mol%.

Compounds c) are further di- or polyfunctional compounds. Compounds c) are used for crosslinking or chain extension reactions.

Compound c.1) is the cycloaliphatic compound with two secondary amino groups. Preferred compounds c.1) are disclosed above.

Compounds c.2) are other di-or polyfunctional compounds than a), b) and c.1 ). They are notably compounds with at least three hydroxy groups or amino compounds other than c.1 ) having with at least two primary and/or secondary amino groups or compounds having at least one hydroxy groups and at least one primary or secondary amino group.

Preferably, 5 to 100 mol % of compounds c) are compounds c.1) and 0 to 95 mol % of compounds c) are compounds c.2). More preferably, 50 to 100 mol % of compounds c) are compounds c.1) and 0 to 50 mol % of compounds c) are compounds c.2).

Most preferably, 90 to 100 mol % of compounds c) are compounds c.1) and 0 to 10 mol % of compounds c) are compounds c.2).

In a particularly preferred embodiment compounds c.1) are used as compounds c), only.

Compound c.1) are preferably used in an amount to get a polyurethane with the content of c.1 ) of 0.5 to 15% by weight as already defined above, respectively with the preferred contents of c.1) as defined above.

Compounds d) are compounds with at least one isocyanate group or at least one isocyanato- reactive group and additionally at least one hydrophilic group or one potentially hydrophilic group. Due to the hydrophilic group or potentially hydrophilic group, compounds d) are different from compounds a), b) and c) which do not comprise such a hydrophilic group or potentially hydrophilic group.

In order to render the polyurethanes dispersible in water they are synthesized not only from compounds a), b) and c) but also from compound d).

In the text below the term“hydrophilic groups or potentially hydrophilic groups” is abbreviated to “(potentially) hydrophilic groups”. The hydrophilic groups can be nonionic or, preferably, ionic, i.e., cationic or anionic groups. A potentially hydrophilic group is a group which can be easily transformed into a hydrophilic group when it is intended to disperse the polyurethane in water. Such potentially hydrophilic groups are notably acid groups than can be transformed into hydrophilic groups by salt formation or tertiary amino groups that can be transformed into ionic groups by reacting them with an acid or by quaternization with alkylating agents.

The content of compounds d) in the polyurethane is preferably from 50 to 500 and more preferably from 80 to 300 mmol of d) per kg of polyurethane.

Examples of suitable nonionic hydrophilic groups include polyethylene glycol ethers made up of preferably from 5 to 100, more preferably from 10 to 80, repeating ethylene oxide units. The polyethylene glycol ethers may also contain propylene oxide units. Where such is the case the amount of propylene oxide units ought not to exceed 50%, preferably 30%, by weight based on the mixed polyethylene glycol ether.

Ionic hydrophilic groups are, in particular, anionic groups such as the sulfonate, the carboxylate and the phosphate group in the form of their alkali metal or ammonium salts and also cationic groups such as ammonium groups, especially protonated tertiary amino groups or quaternary ammonium group. Suitable compounds containing potentially anionic groups are usually aliphatic, cycloaliphatic, araliphatic or aromatic monohydroxycarboxylic and dihydroxycarboxylic acids which comprise in addition at least one alcoholic hydroxyl group or one primary or secondary amino group.

Of particular preference are compounds d) of the general formula

HO-R¹-CR³(COOH)-R²-OH in which R¹ and R² are each a Ci- to C₄-alkanediyl unit and R³ is a Ci- to C₄-alkyl unit. Most preferred are dimethylolbutyric acid and particularly dimethylolpropionic acid (DMPA).

Compounds d) with potentially ionic groups can be converted into the ionic form before or during or after the formation of the polyurethane. Preferably they are converted into the ionic form after the formation of the polyurethane, since the obtained ionic compounds often have only low solubility in the reaction mixture of compounds a), b) and c), but preferably before dispersing the obtained polyurethane in water, see process steps I) and II) below.

With particular preference, the obtained anionic hydrophilic groups are salts with an alkali metal ion or an ammonium ion as counterion. In one preferred embodiment, compound d) is a compound with a carboxylic acid group and a tertiary amino compound is added for converting the compound into the ionic form (salt formation).

Compounds e) are compounds with one isocyanate group or one isocyanato-reactive group without hydrophilic groups or potentially hydrophilic groups. As such compounds have only one reactive group, they may be used to limit the molecular weight of the polyurethane by chain termination. Examples are methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, sec-butanol, tert-butanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 1 ,3-propanediol monomethyl ether, n-hexanol, n-heptanol, n-octanol, n-decanol, n-dodecanol (lauryl alcohol) and 2-ethylhexanol.

If used at all, compounds e) are usually used in minor amounts, such as amounts of less than 1 mol per 10 mols of compounds b) and c).

Compounds a), b), c), d) and e) are preferably reacted in molar amounts such that the ratio A:B, whereby

A) is the molar amount of isocyanate groups and

B) is the sum of the molar amount of the hydroxyl groups and the molar amount of the

functional groups which are able to react with isocyanates in an addition reaction, is from 0.5:1 to 2:1 , preferably from 0.8:1 to 1.5 and more preferably from 0.9:1 to 1.2:1. With very particular preference the ratio A:B is as close as possible to 1 :1. The reaction of compounds a) to e) is a well know polyaddition reaction. The polyaddition reaction is preferably performed at temperatures of 20 to 180°C, preferably 50 to 150°C under atmospheric pressure.

The reaction times required normally extend from a few minutes to several hours. It is known within the field of polyurethane chemistry how the reaction time is influenced by a multiplicity of parameters such as temperature, monomer concentration and monomer reactivity.

For accelerating the reaction of the diisocyanates it is possible to use catalysts. Suitable catalysts are commonly known.

These are, for example, organic amines, particularly tertiary aliphatic, cycloaliphatic or aromatic amines, and/or Lewis-acidic organometallic compounds.

Preferred Lewis-acidic organometallic compounds are dimethyltin diacetate, dibutyltin dibutyrate, dibutyltin bis(2-ethylhexanoate), dibutyltin dilaurate, dioctyltin dilaurate, zirconium acetylacetonate and zirconium 2,2,6,6-tetramethyl-3,5-heptanedionate.

Bismuth, cobalt or cesium based catalysts may be used as well.

Suitable apparatus for the polyaddition reaction includes stirred tanks, particularly when solvents are used to ensure a low viscosity and effective heat removal.

If the reaction is carried out in bulk suitable equipment, because of the generally high viscosities and the generally short reaction times, includes in particular extruders, especially self-cleaning multiscrew extruders.

The polyurethane and the aqueous dispersion thereof are preferably obtained by

a process wherein

I) compounds a), b), d) and e) are reacted to a polyurethane in an organic solvent and

II) the polyurethane is dispersed in water, whereby components c) may be reacted in I) as well or may be added partially or totally during or after step II.

The organic solvent used in step I may be any solvent which solves compounds a) to e).

Preferred solvents have high miscibility with water, notably unlimited miscibility with water. Preferably, the organic solvent used has a boiling point of at maximum 100°C (normal pressure). A preferred solvent is, for example, acetone. Potentially ionic groups are preferably converted into the ionic form in step I, in particular after or at the end of the polyadditon reaction in step I, but before step II.

The organic solvent may be totally removed from the aqueous dispersion, if desired.

Alternatively, the solvent may remain totally or partially in the aqueous dispersion.

The average particle size (z-average) as measured by means of dynamic light scattering with the Malvern® Autosizer 2 C of the obtained polyurethane particles dispersed in water is generally <1000 nm, preferably <500 nm, more preferably <200 nm and very preferably between 20 and below 200 nm.

The dispersions generally have a solids content of from 10 to 75%, preferably from 20 to 65%, by weight and a viscosity of from 10 to 500 mPas (measured at a temperature of 20°C and at a shear rate of 250 S^'1 ) .

The dispersions prepared in accordance with the invention may additionally be mixed with other components typical for the cited applications, examples being surfactants, detergents, dyes, pigments, colour transfer inhibitors and optical brighteners.

The dispersions can be subjected to physical deodorization, if desired, following their preparation.

Physical deodorization may involve stripping the dispersion using steam, an oxygen-containing gas, preferably air, nitrogen or supercritical carbon dioxide in, for example, a stirred vessel, as described in DE-B 12 48 943, or in a counter current column, as described in DE-A 196 21 027.

The aqueous polyurethane formulations of the invention are suitable for coating and bonding substrates. They are notably suitable for coating or adhesively bonding wood, wood veneer, paper, paperboard, cardboard, textile, leather, nonwoven, plastics surfaces, glass, ceramic, mineral building materials, uncoated metals or coated metals.

They find application, for example, in the production of films or thin sheets, for impregnating textiles or leather, as dispersants, as pigment grinding agents, as primers, as adhesion promoters, as hydrophobicizers, as a laundry detergent additive or as an additive to cosmetic formulations, or for producing mouldings or preparing hydrogels.

In the context of their use as coating materials the polyurethane dispersions can be employed in particular as primers, surfacers, pigmented topcoat materials and clearcoat materials in the automotive refinishing or large-vehicle finishing sector. The coating materials are especially suitable for applications that call for particularly high application reliability, exterior weathering stability, optical qualities, solvent resistance, chemical resistance and water resistance, such as in automotive refinish and large-vehicle finishing. The polyurethanes comprising a cycloaliphatic compound with two secondary amino groups have good mechanical properties and show significantly less yellowing under daylight exposure as polyurethanes without such cycloaliphatic compounds with two secondary amino groups.

Examples

DETA diethylene triamine

DIP-MCDA N, N‘ diisopropylmethylcyclohexandiamine, mixture of 80 % by weight of 2,4- and 20 % by weight of 2,6-Isomer

DMPA dimethylol propionic acid

I PDA isophorone diamine

IPDI isophorone diisocyanate

HDI hexamethylene diisocyanate

PUD polyurethane dispersion

TEA triethyl amine

Example

400 g (0.20 mol) of a polyester diol made from adipic acid, isophthalic acid (molar ratio 1/1 ) and hecandiol-1 ,6 (OH-number 56) and 20.1 g (0.15 mol) DMPA were charged to a vessel and stirred at 65°C. Then 1 12.6 g (0.67 mol) H Dl und 150 g acetone were added followed by stirring of the obtained mixture at 70°C for 180 minutes. The mixture was diluted by adding 550 g acetone. The NCO-content of he obtained mixture was determined to be 2.13 % by weight (calculated: 2.18% by weight). Thereafter 12.0 g (0.12 mol) TEA were added. After 5 minutes 42.5 g (0.20 mol) DIP-MCDA were added within 10 minutes. After further 5 minutes 800 g of water were added within 15 minutes. Then a mixture of 8.2 g (0.08 mol) DETA and 100 g water were added. Finally, acetone was removed by distillation at reduced pressure.

A homogeneous PUD with small polyurethane particles was obtained. The PUD had a solids content of 36 % by weight.

Comparison example

400 g (0.20 mol) of a polyester diol made from adipic acid, isophthalic acid (molar ratio 1/1 ) and hecandiol-1 ,6 (OH-number 56) and 20.1 g (0.15 mol) DMPA were charged to a vessel and stirred at 65°C. Then 1 12.6 g (0.67 mol) HDI und 150 g acetone were added followed by stirring of the obtained mixture at 70°C for 180 minutes.

The mixture was diluted by adding 550 g acetone. The NCO-content of the obtained mixture was determined to be 2.13 % by weight (calculated: 2.18% by weight).

Thereafter 12.0 g (0.12 mol) TEA were added. After 5 minutes 34.0 g (0.20 mol) IPDA were added within 10 minutes. After further 5 minutes 800 g of water were added within 15 minutes. Then a mixture of 8.2 g (0.08 mol) DETA and 100 g water were added. Finally, acetone was removed by distillation at reduced pressure.

A homogeneous PUD with small polyurethane particles was obtained. The PUD had a solids content of 36 % by weight. Determination of yellowness of PUD films

15 g of the PUD of the example and of the comparison example were poured into round plastic cups with a diameter of 7 cm diameter. The PUD were kept at room temperature (about 21 °C) for two days and dry films of the PUDs were obtained.

The yellowness of the dry films was determined with a Minolta spectrophotometer cm-508i:

Yellowness of the PUD from example: 2,3

Yellowness of the PUD from the comparison example: 4,8

Claims

1 ) An aqueous dispersion of a polyurethane wherein the polyurethane is obtained by

reacting di- or polyfunctional isocyanates, diols, a cycloaliphatic compound with two secondary amino groups and optionally further compounds.

2) An aqueous dispersion according to claim 1 , wherein the cycloaliphatic compound is a compound of formula I

a compound of formula II

or a mixture thereof, with R¹ and R² independently from one another representing an alkyl group with 1 to 12 carbon atoms and R³ representing hydrogen or an alkyl group with 1 to 12 carbon atoms 3) An aqueous dispersion according to claim 2 wherein the cycloaliphatic compound is a mixture of compound of formula I and II with both R¹ and R² representing an isopropyl group and R³ representing a methyl group

4) An aqueous dispersion according to any of claims 1 to 3 wherein the polyurethane

comprises 0.5 to 15% by weight of the cycloaliphatic compound with two secondary amino groups

5) An aqueous dispersion according to any of claims 1 to 4 wherein the polyurethane is

obtained by reacting a) di- or polyfunctional isocyanates with 4 to 30 carbon atoms

b) diols of which

b.1 ) 10 to 100 mol%, based on the total amount of diols (b), have a molecular weight of from 500 to 5000 and

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

c) further di- or polyfunctional compounds of which

c.1 ) 5 to 100 mol % are the cycloaliphatic compound with two secondary amino groups and

c.2) 0 to 95 mol % are other di- or polyfunctional compounds than a), b) and d )

d) compounds other than compounds a), b) and c) with at least one isocyanate group or at least one isocyanato-reactive group and additionally at least one hydrophilic group or one potentially hydrophilic group and

e) optionally compounds with one isocyanate group or one isocyanato-reactive group without hydrophilic groups or potentially hydrophilic groups

6) Process for the preparation of an aqueous dispersion according to any of claims 1 to 5, wherein I) compounds a), b), d) and e) are reacted to a polyurethane in an organic solvent and

II) the polyurethane is dispersed in water, whereby components c) may be reacted in I) as well or may be added partially or totally during or after step II

7) The use of a polyurethane dispersion according to any off claims 1 to 6 for coating or adhesively bonding wood, wood veneer, paper, paperboard, cardboard, textile, leather, nonwoven, plastics surfaces, glass, ceramic, mineral building materials, uncoated metals or coated metals.