AU7184598A - Aqueous polyurethane dispersions of polypropylene glycol having a low urea content - Google Patents

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AUSTRALIA

Patents Act 1990

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Application Number: Lodged: Invention Title: AQUEOUS POLYURETHANE DISPERSIONS OF POLYPROPYLENE GLYCOL HAVING A LOW UREA CONTENT The following statement is a full description of this invention, including the best method of performing it known to us BASPiAktengeseischaft -o.z o 80 66 Aqueous Polyurethane Dispersions of Polypropylene glycol Having a Low Urea Content The present invention relates to aqueous dispersions, containing a polyurethane to having a content of urea groups of not more than 110 mmollkg of solid material, composed of a) diisocyanates containing from 4 to 30 carbon atoms, b) polypropylene glycol having a molecular weight of from 1000 to 8000 provided that when the molecular weight is between 1000 and 2000, the arithmetic average hydroxyl functionality is from 1.99 to 2.00, when the molecular weight is between 2000 and 3000, the arithmetic average hydroxyl functionality is from 1.97 to 2.00, when the molecular weight is between 3000 and 4000, the arithmetic average hydroxyl functionality is from 1.90 to 2.00 is and when the molecular weight is between 4000 and 8000, the arithmetic average hydroxyl functionality is from 1.80 to 2.00, S c) optionally diols other than the polypropylene glycol which 25 c) have a molecular weight of from 500 to 5000 and/or c2) have a molecular weight of from 60 to 500 g/mol, 3o d) monomers other than the monomers to and containing at least one isocyanate group or at least one group that is reactive to isocyanate groups, which furthermore carry at least one hydrophilic group or a potentially hydrophilic group, by which means the polyurethanes are rendered water-dispersible.

e) optionally further polyvalent or polyhydric compounds other than the monomers to and containing reactive groups, which reactive groups are alcoholic hydroxyl groups or isocyanate groups and f) optionally monovalent or monohydric compounds other than the monomers to 4o and containing one reactive group, which is an alcoholic hydroxyl group or an isocyanate group.

Aqueous polyurethane dispersions having a low urea content and produced using polypropylene glycol are disclosed, for example, in EP-A 615,988. These compounds are recommended for use in bonding films, ie for the preparation of composite films.

The constituents mentioned are dihydric polyether alcohols. According to the teaching of this paper the polyether alcohols are obtained by polymerizing the corre- BASFAktieneseltschaft O.Z..0050148066 sponding monomers, which are recorded in said reference in the form of a list containing, inter alia propylene oxide, by base-catalyzed addition of these compounds to starter compounds such as amines or alcohols.

However, the person skilled in the art of polymer technology will possess general information to the effect that the polymerization of propylene oxide under these condi- Stions will not lead to strictly bifunctional compounds but to polymer mixtures contain- Iing, depending on the molecular weight, both polymers containing two alcoholic hydroxyl groups and compounds containing only one alcoholic hydroxyl group. The reason for this is that conventional alkaline catalysis causes a rearrangement of PO to allyl alcohol, which then functions as a monofunctional starter. This general information is given, for example, in the monograph Kunststoffhandbuch, Vol. 7 Polyurethane, 3rd Edition, page 61.

A detailed investigation on this is described in the publication "A New Generation of Polyether Polyols for the Urethane Industry" by S.D. Seneker and N. Barksby, presented at UTECH '96 in The Hague, Netherlands, March, 1996 (UTECH'96 Conf.

Book, Pap. (1996), Paper 46; Editors: Reed, David; Lee, Carole, Publisher: Crain Communications, London, UK). According to this publication, a polypropylene glycol 20 prepared by conventional methods and having a molecular weight of 1000 (hydroxy number 112) will have an average hydroxyl functionality of approximately 1.97, while one having a molecular weight of 2000 (hydroxyl number 56) will have an average hydroxyl functionality of about 1.93.

2 The person skilled in the art would according to this teaching not seriously consider using a strictly bifunctional polypropylene glycol for the preparation of polyurethane Sdispersions by the method proposed in EP-A 615,988, but would use the commercially available product prepared by the method described in said reference, which has a distinctly lower average functionality. At the time of filing the basic application 3o pertaining to EP-A 615,988 it was not yet possible to provide strictly bifunctional polypropylene glycols in amounts such as would have been required for the preparation of polyurethane dispersions on an industrial scale.

EP-A 741,152 discloses polyurethane dispersions prepared from polypropylene glycol. The polypropylene glycol used here has a content of unsaturated groups of 0.020 meaqg or less. We would point out that such polypropylene glycols have a hydroxyl functionality which deviates only slightly from 2.0. In the preferred process for the preparation of the polyurethanes a prepolymer containing terminal NCO groups is first of all produced, which, following dispersion in water, is caused to increase in 4 chain length using glycols or, preferably, amines. This method inevitably produces in each of the two specified cases polyurethanes having a comparatively high urea content, for in the case of chain growth incited by diols this is a result of the saponification reaction of the isocyanate groups with water which leads to the formation of urea as shown by the following equation: 2 RNCO H 2 0 R-NH-CO-NHR

CO

2 gI m I- I O.Z- 0050/48066 BASFAktienQesellschaR The competitive reaction take place at a velocity comparable to that leading to ur thane formation.

The dispersions of the prior art exhibit a good set of properties as film adhesives, particularly when polar materials are to be bonded to each other. In the case of nonr polar substrates such as polyolefins, the laminating strengths are still unsatisfactory however. The manufacturers of films therefore have a specia need for aqueous adhesive dispersions capable of creating a strong bond between polyolefin films and one or more other films, since composite films that at least partially comprise i0 polyolefins have a particularly interesting market value.

It is thus an object of the present invention to provide aqueous adhesive dispersions which can be used for the manufacture of composite films at least partially composed of polyolefins and having a particularly high laminating strength.

Accordingly, we have found the polyurethane dispersions defined above, a process for the nreparation thereof and composite films made using said polyurethane dispersion..

Suitable monomers are the diisocyanates usually employed in polyurethane chemistry.

Specific example are, in particular, diisocyanates X(NCO)2, where X stands for an aliphatic hydrocarbon radical containing from 4 to 12 carbon atoms, a cycloaliphatic or aromatic hydrocarbon radical containing from 6 to 15 carbon atoms or an araliphatic hydrocarbon radical containing from 7 to 15 carbon atoms stands. Exampies of such diisocyanates are tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 1, 4 diisocyanatocyclohexane, 1-isocyanatoo- 3,5,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), 2 ,2bis(4-isocyanatocyclo- 30 hexyl)propane, trimethylhexane diisocyanate, i,4-diisocyanatobenzene, 2,4-diisocyanatotoluene, 2 .6~diisocyanatotoluene, 4 4 ,diisocyanatodiphenylmethane, 2,4'diisocyanatodiphenylmethane, p-xylylene diisocyanate, tetramethylxylylene diisocyanate (TMXDI), the isomers of bis( 4 isocyanatocyclohexyl)methane such as the transltrans, the cislcis and the cisltrans isomers, and mixtures of said compounds.

Significant mixtures of these isocyanates are particularly the mixtures of the respective structural isomers of diisocyanatotluene and diisocyanatodiphenylmethane, a mixture of 80 mol% of 2,4-diisocyanatotoluene and 20 mol% of 2,6-diisocyanatotoluene being particularly suitable. Furthermore mixtures of aromatic isocy nates 4 such as 2 ,4diisocyanatotoluene andlor 2,6-diisocyanatotoluene with aliphatic or cycloaliphatic isocyanates such as hexamethylene diisocyanate or IPDI are particularly advantageous, the preferred proportions of the aliphatic and aromatic isocyanates being from 4:1 to 1:4.

The compounds may also be isocyanates which carry, in addition to te free isocyanate groups, other, hidden isocyanate groups, examples of which are uretdione or carbodiimide groups.

b

L

BS o.z. 005014806.

BASFAten eseschaf- 4 The polypropylene glycols preferably have an arithmetic average hydroxyl func tionality of from 1.97 to 2.00. Such polypropylen e generally known. The preparation thereof takes place in a particularly simple fashion using complexes of ®R for example, in DE-A 0,654,302 a n d U S zinc hexacyanocobaltate and is described, for example, in DE-A 0,654,302 and US 5,158,922.

SAs regards good film formation and elasticity, suitable diols differing from component are mainly diols of higher molecular weight which have a molecular to weight of from approximately 500 to 5000 and preferably from approximately 1000 to 3000 gimol.

The diols (cl) are, in particular, polyester polyols such as are described in Ullmanns Encyklopaedie der technischen Chemie, 4th edition, Vol. 19, pp 62-65. We prefer to use polyester polyols which are obtained by causing dihydric alcohols to react with divalent carboxylic acids. Instead of the free polycarboxylic acids, use can be made of.the corresponding polycarboxylic anhydrides or corresponding polycarboxylates of lower alcohols or mixtures thereof for the preparation of the polyester polyols The polycarboxylic acids can be aliphatic, cloaliphatic, araliph atic aromatic or heterocyclic and may optionally be substituted by, for example, halogen atoms andlor be unsaturated. The following may be specified as examples suberic acid, azelaic acid, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, ethyleetetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric 2. acid, and dimeric fatty acids. We prefer dicaroxylic acids of the general formula HOOC- (H 2 )y-COOH, where y is a number from 1 to 20, preferably an even number A from 2 to 20, examples being succinic acid, adipic acid, dodecanoic acid and sebacic acid.

3o Examples of suitable polyhydric alcohols are ethylene glycol, propane-,2-diol, pro- A pane-I,3-diol, butane-I,3-diol, butene-l,4-diol, butyne-1,4-diol, neopenty glycol, bis(hydroxymethyl)cyclohexanes such as 1,4-bis(hydroxymethyl)cyclohexane, 2-methylpropane-l ,3-diol, methylpentane diols, and also diethylene glycol, triethylene glycol, ttraethylene glyco), polyethylene glycol, dipropylene glycol 3s and polybutylene glycols. We prefer alcohols of the general formula HO-(CH 2 )x-OH, where x is a rumber from 1 to 20, preferably an even number from 2 to 20. Examples thereof are ethylene glycol, butane-1,4-diol, hexane-1,6-diol, octane-1,8-diol and dodecane-1,12-diol.

I Also suitable are polycarbonate diols, such as can be obtained by the reaction of phosgene with an excess of the low molecular weight alcohols specified as consituents of the polyester polyols.

Further suitable diols are polyester diols based on lactone, these being homopoiymers or copolymers of lactones, preferably terminal hydroxyl groups-containing addition products of actones on suitable bifunctional starting molecules. Preferred lactores are those derived from compounds of the general formula HO-(CH2)z- 1 r

I

B

s a

B

r i:k h ':i 7 s ~ii-" w b a r .i BASFAkienpes n I- .h-Ba 0 7 nnS0050I480 0 Z 00-5014806 COOH, where z is a number from I to 20. Examples are s-caprolactone, ppropiolactone, y-butyrolactone and/or methyl s-caprolactone or mixtures thereof.

Suitable starting components are for example the low molecular weight dihydric alco- Shols specified above as constituents of the polyester polyols. The corresponding 5 polymers of e-caprolactone are particularly preferred. Lower polyester diols or polyether diols may be used as starters for the preparation of lactone polymers, if desired. Instead of the polymers of lactones, the corresponding chemically equivalent polycondensates of the hydroxycarboxylic acids corresponding to the lactones may be used.

Other suitable monomers (cl) are polyether diols. They can be obtained, in particular, by polymerization of ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide or epichlorohydrin with itself, eg in the presence of BF 3 or by the addition of these compounds, optionally in admixture or successively, to starting components containing reactive hydrogen atoms, such as alcohols or amines, eg water, ethylene glycol, propane-1,2-diol, propane-1,3-diol, 1,2-bis(4-hydroxydiphenyl)propane or aniline. Particularly preferred is polytetrahydrofuran having a molecular weight of from 500 to 4500. However the use of such polypropylene glycols is not preferred.

Monomers (cl) which can also be used are polypropylene glycols which differ from the polypropylene glycols suitable as components These polypropylene glycols (cl) either have a molecular weight of less than 1000 glmol or, if the molecular weight is between 1000 and 5000, this polypropylene glycol has an arithmetic aver- 25 age hydroxyl functionality of less than 1.95.

Also suitable are polyhydroxy olefins, preferably those containing 2 terminal hydroxyl groups, eg a,,-dihydroxypolybutadiene, a,o-dihydroxypolymethacrylate or a,ow-dihydroxypolyacrylate, as monomers Such compounds are disclosed, for exam- 30 pie, in EP-A 0,622,378. Other suitable polyols are polyacetals, polysiloxanes and alkyd resins.

The polyols can also be used as mixtures in ratios of from 0.1:1 to 1:9.

The hardness and the modulus of elasticity of the polyurethanes can be raised, when the diols used are not only the diols (cl) but also diols (c2) having a molecular weight of from approximately 62 to 500, preferably from 62 to 200 g/mole. The monomers (c2) used are primarily the constituents of the short-chain alkanediols specified for the preparation of polyester polyols, where the unbranched diols having from 2 to 12 carbon atoms and an even number of carbon atoms and diol are preferred.

The molar ratio of the amount of the diols (c2) to the sum of the amount of polypropylene glycols and the diols (cl) is preferably from 0.1:1 to 5:1 and more prefera- ,4 bly from 0.1:1 to 2:1, whilst most preferably no diols (c2) are included.

The molar content of the dials based on the polypropylene glycol is gener- BASFAktienesellschaft 6 O.Z. 0050148066 ally not more than 50, but is preferably less than 20, and more preferably 0 mol%.

In order to make the polyurethanes water-dispersible, the polyurethanes are not only composed of the components and but also of monomers differing from the components and and carrying at least one isocyanate group or at least one isocyanate-reactive group and in addition at least one hydrophilic group or a group capable of being converted to hydrophilic groups. Below, the term "hydrophilic groups or potentially hydrophilic groups" is abbreviated to "(potentially) hydrophilic groups". The (potentially) hydrophilic groups react with isocyanates much more slowly than the functional groups of the monomers which are used for the synthesis of the main polymer chain.

The concentration of the components containing (potentially) hydrophilic groups based on the total amount of the components and is generally such that the molar magnitude of the (potentially) hydrophilic groups, based on the weight of all monomers to is from 30 to 1000, preferably from 50 to 500, and more preferably from 80 to 300, mmollkg.

The (potentially) hydrophilic groups can be non-ionic or preferably (potentially) ionic o hydrophilic groups.

Particularly suitable non-ionic hydrophilic groups are polyethylene glycol ethers comprising preferably from 5 to 100, more preferably from 10 to 80, recurring ethylene oxide units. The concentration of polyethylene oxide units is generally from 0 to 25 preferably from 0 to 6 wt%, based on the weight of all monomers to Preferred monomers containing non-ionic hydrophilic groups are polyethylene oxide S diols, polyethylene oxide monools the reaction products of a polyethylene glycol and a diisocyanate carrying a terminal etherified polyethylene glycol radical. Such diiso- 3o cyanates and processes for the preparation thereof are described in the patent specifications US 3,905,929 and US 3,920,598.

S" Ionic hydrophilic groups are primarily anionic groups such as the sulfonate, carboxylate and phosphate groups in the form of their alkali metal or ammonium salts and s3 also cationic groups such as ammonium groups, particularly protonized tertiary Samino groups or quaternary ammonium groups.

Potentially ionic hydrophilic groups are primarily those which can be converted by simple neutralisation, hydrolysis or quatemizing reactions to the aforementioned ionic 4 hydrophilic groups, that is to say for example, carboxylic acid groups, anhydride groups or tertiary amino groups.

(Potentially) ionic monomers are described in detail in, eg, Ullmanns Encyklopaedie der technischen Chemie, 4th Edition, Vol. 19, pp 3 1 1-313 and for example in DEs A 1,495,745.

(Potentially) cationic monomers of special significance are primarily monomers IS for example lAmins--- O.Z. 0050/48066 S containing tertiary amino groups, for exam tris(ra minoalyl)amines, (hydroxyalkyl)alkylamines,

N-

h ydroxyalkyldialkylamines, tris(amioalkyl)amiles N,N Nbis(aminoalkyl)alkylamines, N-aminoalkyldialkylamines, where the alkyl radicals and alkanediyl units in these tertiary amines independently contain from ar- S bon atoms. Also suitable are polyethers containing tertiary nitrogen atomsand preferably containing two terminal hydroxyl groups, such as can be prepared by alkoxylation of two amines having hydrogen atoms attached to amine nitrogen, eg methylamine, aniline, or N,N-dimethylhydrazine, in conventional manner. Such polyethers S generally have a molecular weight between 500 and 6000 glmole.

SThese tertiary amines are converted to the ammonium salts 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 Ci to C alkyl halides, eg bromides or chlorides.

Suitable monomers containing (potentially) anionic groups are usually aliphatic, cycloaliphatic, araliphatic or aromatic carboxylic acids and sulfonic acids carrying at Suitable monomers containing (p es and sulfonic ci Sary^igat least one alcoholic hydroxyl group or at least one primary or secondary amino group.

Preferred are dihydroxyalky arboxylic acids, primarily containing from 4 to 10 carbon Satoms, such as are also described in US-A 3,412,054.:We particularly prefer compounds of the general formula

COOH

HO--R _2--OH 25 i

R

3 in which R' and R 2 stand for a C1 to C4 alkanediyl unit and R 3 stands for a C, to C4 alkyl unit, especially dimethylolpropionic acid (DMPA).

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

Also suitable are dihydroxyl compounds having a molecular weight of more than 500 to 10000 g/mol and containing at least 2 carboxylate groups, which are disclosed in DE-A 3911,827 They cnann be prepared by the reaction of dihydroxyl compounds with tetroic dianhyd,, des such as pyromellitic dianhydride or cyclopentanetetroic dianhydride in a molar ratio of from 2:1 to 1.05:1, in a polyaddition reaction. Particularly 4o suitable dihydroxyl compounds are the monomers (c2) mentioned as chain extenders and also the diols (cl).

Suitable monomers containing isocyanate-reactive amino groups are amincarboxylic acids such as lysine, -alanine, the adducts, mentioned in DE-A 2,034,479, of 4 aliphatic diprmary diamines with A-unsaturated carboxylic acids such as N-2aminoethyl)-2-aminoethanecarbxyic acid and also the corresponding N-aminoalkylaminoalkylcarboxylic acids, where the alkanediyl units contain from 2 to 6 carbon i BAS FAktiengeselschaft 8 S atoms.

If monomers containing potentially ionic groups are u.

the ionic form before or during, but preferably after, the s tion, since the ionic monomers are frequently only sp mixture. We particularly prefer the carboxylate groups salts in which an alkali metal or ammonium ion is the cc Monomers containing amino groups reactive to iso in such amounts that the resulting urea content does nc The monomers which differ from the monomers (a to effect cross linkage or chain growth. They are gen alcohols.

Polyhydric alcohols which can serve to establish a spe specific cross-link density are for example trimethylol pr Monomers comprising more than divalent isocyana purpose. Commercially available compounds are for ex biuret of hexamethylene diisocyanate.

Monomers which may be optionally included, are n cohols. In general, the concentration thereof is not mor total molar amount of the monomers. These monof carry further functional groups such as olefinic groups to introduce functional groups into the polyurethane, S perse or cross-link the polyurethane or cause some oth polyurethane to take place. Examples of suitable mono propenyl-a,a-dimethylbenzyl isocyanate (TMI) and es acid such as hydroxyethyl acrylate or hydroxyethyl metl In the field of polyurethane chemistry it is generally kni weight of the polyurethanes by adjusting the conce monomers and the arithmetic mean of the number of molecule.

n 7 anniManRA u.L- uuuu.~vuu, sed, they can be converted to Sisocyanate polyaddition reacaringly soluble in the reaction s to be present in the form of ounterion cyanate groups are used only ot exceed 110 mmol/kg.

to are generally included erally polyhydric non-phenolic cific degree of branching or a opane, glycerol or sugar.

tes can be used for the same ample the isocyanurate or the nonoisocyanates and monoale than 10 mol%, based on the unctional compounds usually or carbonyl groups and serve vhich make it possible to diser polymer-like reaction of the mers for this purpose are isoters of acrylic or methacrylic lacrylate.

own how to set the molecular ntrations of the interreacting reactive functional groups per Normally the components to and also the respective molar amounts thereof are selected such that the ratio of A to B, where A) is the molar concentration of isocyanate groups and B) is the sum of the molar concentration of the hydroxyl groups and the molar concentration of the functional groups which can react with isocyanate in an addition reaction is from 0.5:1 to 1.08:1, preferably from 0.8:1 to 1.08:1, and more preferably from SBASFAktenqesellschaft O.Z 0050148066 So8:ls1 to 1:1. Most preferably the ratio A:B is as near to 1:1 as possible.

The content of urea groups in the polyurethanes is not more than 11Ommol/kg and is Spreferably less than 60 mmol/kg.

To prevent the polyurethanes or their prepoiymers from forming polyurethanes ha, ing a higher content of urea groups by reaction with water, it is necessary to avoid the use of polyurethanes or their prepolymers which have an NCO content above 220 mmol/kg of solid material prior to dispersion in water.

i t0 IFor the same reason preferably no monomers having primary or secondary amino groups are used for the preparation of the polyurethanes. If this should not be possible for some reason, care must be taken to ensure that the amount of such monomers used is restricted such that that the urea content does not exceed the stated S1 limits.

The monomers to used carry, on average, usually from 1.5 to 2.5, preferably from 1.9 to 2.1 and more preferably 2.0, isocyanate groups or functional groups, I' which can react with isocyanates in an addition reaction.

The polyaddition of the components to generally takes place at reaction temperatures of from 20 to 180 OC, preferably from 50 to 150 *C under standard pressure or under autogenous pressure.

2s The required reaction times may extend from a few minutes to several hours. In the field of polyurethane chemistry it is known how to influence the reaction time by means of a large number of parameters such as temperature, concentration of the monomers and reactivity of the monomers.

U 3o To accelerate the reaction of the diisocyanates use can be made of conventional S. catalysts such as dibutyltin dilaurate, tin(ll) octoate or diazabicyclo(2,2,2)octane.

Suitable polymerization equipment comprises stirred boilers, particulary when the supplementary use of solvents makes for low viscosity and good heat removal.

If the reaction is to be carried out in substance, extruders are particularly suitable on account of the high viscosities and very short reaction times usually involved, especially self-cleaning multiscrew extruders.

4 The preferred solvents are completely water-miscible, have a boiling point under standard pressure of from 40 to 100 °C and react with the monomers only slowly or not at all.

The dispersions are usually prepared by the "acetone process". In this case an ionic polyurethane is prepared from the components to in a water-miscible solvent boiling under standard pressure below 100 Water is added until a dispersion forms in which water is the coherent phase.

BASFAcienceseischa 10 O.Z. 0050148066 If a solvent has been used for the preparation of the polyurethane, the major part of the solvent is usually removed from the dispersion, for example by distillation under reduced pressure. The dispersions preferably have a solvent content of less than 10 wt% and are more preferably free from solvents.

The dispersions have in general a solids content of from 10 to 65 and preferably from to 55 wt% and a viscosity of from 10 to 500 mPAs (measured at a temperature of °C and a shearing rate of 250 s Hydrophobic auxiliaries, which may possibly be difficult to distribute homogeneously in the finished dispersion, such as phenol condensation resins of aldehydes and phenol or phenol derivatives or epoxy resin and other polymers, specified in DE-A S3,903,538, 4,309,079 and 4,024,567, which serve for example as adhesion promotors in polyurethane dispersions, can be added to the polyurethane or the prepolymer prior to dispersion, by the methods described in the aforementioned specifications.

The polyurethane dispersions can contain commercially available auxiliaries and additives such as foaming agents, defoaming agents, emulsifiers, thickeners and thixo- S 20 tropic agents, and colorants such as dyes and pigments.

S. The dispersions of the invention are suitable for coating and bonding a wide variety of objects. They are particularly suitable for the preparation of composite films by bonding together two or more films of different materials.

2" The film materials mainly used are polyethylene, polypropylene, particularly biaxially oriented polypropylene, polyamide, polyester, PVC, cellulose acetate, cellophane and metals such as tin and aluminum.

30 The polymer films, particularly the polyolefin films; may optionally be subjected to corona pretreatment.

The preparation of the composite films advantageously takes place by the generally known methods. !n this case the polyurethane dispersion is applied to at least one 3s and generally to only one of the films to be bonded. The coated films are in general dried for a short time and then pressed together or onto an uncoated substrate pref- *erably at a temperature of from 30 to 80 *C.

The bond obtained, and particularly the compound obtained, shows a high laminating io strength at room temperature, such as is otherwise generally only achievable with two-component systems using a cross-linking agent The laminating strength falls at high temperatures above, approximately, 60 Above ca 100 C, for example in boiling water, the composites can generally be Sreadily delaminated. This makes it possible to carry out separate recycling of the different films in the composite.

BASFAkieselischat O.Z. 0050/48066 An increase in the laminating strength at high temperatures may be achieved, if desired, for example by adding cross-linking agents containing free isocyanate groups.

Examples A. Preparation of the polyurethane dispersions Example io A mixture of 76.6 g (0.440 mol) of toluylene diisocyanate 80120, 410.2 g (0.200 mol) of a polypropylene glycol having an OH number of 54.7 and an unsaturation content of 0.005 meql g (Acclaim@ 2200 sold by Arco) having a calculated functionality of 1.99, 32.2 g (0.240 mol) of DMPA and 0.1 g of DBTL was caused to react over a period of 5 h at 95 C. The mixture was then cooled to 30 OC and the NCO content of the PUR was found to be 0.10 wt%, based on the PUR. The ratio of NCO groups to NCO-reactive groups was 1:1. The concentration of urea groups

=N-CO

N

was 0.07 wt% (12 mmol of urea per kg).

The mixture was then diluted with 450 g of acetone and 16.2 g (0.16 mol) of triethylamine and 800 g of water were stirred in. Following distillation of the acetone there was obtained an approximately 40 wt% strength aqueous polyurethane dispersion.

Comparative Example 1 (as per EP-A 615,998, Example 1) 5 A mixture of 76.6 g (0.440 mol) of toluylene diisocyanate 8020, 400 g (0.20 m) of a polypropylene glycol having an OH number of 56.0 and an unsauration content of 0.035 meqlg (determined by the iodine number method of Wies; Lupranol® 1000 sold by BASF having a calculated functionality of 1.93) 32.2 g (0.240 mol) of DMPA and 0.1 g of DBTL was caused to react over a period of 5 h at 95 The mixture Swasthen cooled to 35C and the NCO content of the PUR was found to be to S014 wt%, based on the PUR. The ratio of NCO groups to NCO-reactive groups was 1:1. The concentration of urea groups

N-CO-N

was 0.09 wt% (16 mmol of urea per kg).

3s The mixture was then diluted with 450 g of acetone and 16.2 g (0.16 mol) of triethylarnine and 800 g of water were stirred in. Following distillation of the acetone there was obtained an approximately 40 wt% strength aqueous polyurethane dispersion.

Comparative Example 2 (as per EP 741,152) A mixture of 42.1 g (0.242 mol) of toluylene diisocyanate 8120, 205.1 g (0.100 mol) of a polypropylene glycol having an OH number of 54.7 and an unsaturation content of 0.005 meqlg (Acclairn 2200 by Arco) 16.1 g (0.120 mol) of DMPA and 0.1 g of DBTL was caused to react over a period of 5 h at 95 The mixture was then a cooled to 35 °C and the NCO content of the PUR was found to be to 0.70 wt%, based on the PUR.

.o P SBASFAkengesellschaft 12 O.Z 0050/48066 The ratio of NCO groups to NCO-reactive groups was 1:1. The mixture was then diluted with 225 g of acetone and 8.1 g (0.08 mol) of triethylamine, and 360 g of water were stirred in, following which a solution of 1.3 g (0.022 mol) of ethylenediamine was stirred in. Following distillation of the acetone, there was obtained an approxis mately 40 wt% strength aqueous polyurethane dispersion.

The urea content was 161 mmoi of urea per kg.

B. Preparation of and Tests on Composite Films Composites were made from different polymer films and an aluminum foil and the peeling strength was then determined as a measure of the laminating strength.

SMore specifically, the polyurethane dispersion was applied in a concentration of is 4 g Im 2 using a 0.2 mm roll coater, to the surface of the film (which was coronapretreated in the case of polyolefin). The coated films were dried with a hot-air blower for approximately two minutes and pressed onto another film or foil in a roller press at i 70 'C and 6.5 bar at a rate of 5 m/min.

Following storage over 7 days at room temperature the peeling strength of the compound film in N/cm was determined using a tension tester. The test results are shown in Table 1.

Table 1 Peeling strengths in N/cm PPIPE PPlmetallized PET Example 3.1 2.2 Comparative Example 1 1.9.5 Comparative Example 2 1.1 1.3 ~ii3

I

I

Abbreviations: PP Polypropylene film PE Polyethylene film PET Polyethylene terephthalate film

Claims (6)

1. An aqueous dispersion, containing a polyurethane having a content of urea groups of not more than 110 mmol/kg of solid material, composed of a) a diisocyanate containing from 4 to 30 carbon atoms, b) polypropylene glycol having a molecular weight of from 1000 to 8000 provided that when the molecular weight is between 1000 and 2000, the arithmetic average o1 hydroxyl functionality is from 1.99 to 2.00, when the molecular weight is between 2000 and 3000, the arithmetic average hydroxyl functionality is from 1.97 to 2.00, when the molecular weight is between 3000 and 4000, the arithmetic average hy- droxyl functionality is from 1.90 to 2.00 is and when the molecular weight is be- tween 4000 and 8000, the arithmetic average hydroxyl functionality is from 1.80 to

2.00, J c) optionally a diol other than the polypropylene glycol which S cl) has a molecular weight of from 500 to 5000 and/or 20 c2) has a molecular weight of from-60 to 500 g/mol, Sd) a monomer other than the monomers to and containing at least one iso- cyanate group or at least one group that is reactive to isocyanate groups, which furthermore carries at least one hydrophilic group or a potentially hydrophilic group, by which means the polyurethane is rendered water-dispersible, e) optionally a further polyvalent or polyhydric compound other than the monomers so to and containing reactive groups which are alcoholic hydroxyl groups or isocyanate groups and f) optionally a monovalent or monohydric compound other than the monomers to and containing one reactive group which is an alcoholic hydroxyl group or an isocyanate group. 2. An aqueous dispersion as defined in claim 1, wherein the molar amount of the diol based on the amount of polypropylene glycol is from 0 to 50 mol%.

3. An aqueous dispersion as defined in claim 1 or claim 2, wherein the polyurethane contains dimethylolpropionic acid as component

4. An aqueous dispersion as defined in any of claims 1 to 3, wherein the polyure- thane contains toluylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexyl- methane diisocyanate or hexamethylene diisocyanate as component A process for the preparation of a composite film, wherein a dispersion as defined SBASFAkiengesellschaft 14 O.Z. 0050/48066 I in any of claims 1 to 4 is applied to a plastics film or metal foil which is bonded to Sone or more plastics films or metal foils to form a composite film.

6. A process for the preparation of a composite film as defined in claim 5 wherein a dispersion as defined in any of claims 1 to 4 is applied to a plastics film or metal foil which is bonded to one or more plastics films, one of which is a polyolefin film, or metal foils to form a composite film.

7. A composite film whenever produced by a process as defined in claim 5 or claim 6. DATED this 12th day of June 1998. BASF AKTIENGESELLSCHAFT WATEIMARK PATENT TRADEMARK ATTORNEYS T"A 290 BURWOOD ROAD HAWTHORN. VIC. 3122. *j i BASFAktien eselschaft 15 O.Z 005048066 Aqueous Polyurethane Dispersions of Polypropylene glycol having a Low Urea Con- tent Aqueous dispersions, containing a polyurethane having a content of urea groups of not more than 110 mmol/kg of solid material, composed of a) diisocyanates containing from 4 to 30 carbon atoms, b) polypropylene glycol having a molecular weight of from 1000 to 8000 provided that when the molecular weight is between 1000 and 2000, the arithmetic average hydroxyl functionality is from 1.99 to 2.00, when the molecular weight is between 2000 and 3000, the arithmetic average hydroxyl functionality is from 1.97 to 2.00, when the molecular weight is between 3000 and 4000, the arithmetic average hy- Is droxyl functionality is from 1.90 to 2.00 is and when the molecular weight is be- tween 4000 and 8000, the arithmetic average hydroxyl functionality is from 1.80 to 2.00, c) optionally diols other than the polypropylene glycol which cl) have a molecular weight of from 500 to 5000 andlor c2) have a molecular weight of from 60 to 500 g/mol, d) monomers other than the monomers to and containing at least one isocya- nate group or at least one group that is reactive to isocyanate groups, which fur- thermore carry at least one hydrophilic group or a potentially hydrophilic group, by which means the polyurethanes are rendered water-dispersible. e) optionally further polyvalent or polyhydric compounds other than the monomers to and containing reactive groups, which reactive groups are alcoholic hy- droxyl groups or isocyanate groups and 3 f) optionally monovalent or monohydric compounds other than the monomers to and containing one reactive group, which reactive group is an alcoholic hy- droxyl group or an isocyanate group.