CA2132905A1 - Water-dispersible polyurethanes - Google Patents

Abstract

Abstract of the Disclosure Polyurethanes which can be dispersed in water without emulsifier, obtained by partial reaction of an isocyanate-terminated urethane prepolymer with a salt of an acid having a hydrogen atom which is reactive toward isocyanate, followed by reaction of the remaining iso-cyanate groups with a chain-extending agent, are useful in binders for coating compositions and adhesives.

Description

2 1 3 ~
; 1 WATER-DISPERSIBLE POLYURETHANES

Backqround of the Invention The present invention relates to aqueous polyurethane dispersions which do not require emulsifier and can be used, for example, to produce coatings on fabrics, wood, paper, or metal surfaces.
Particularly favorable mechanical properties of polyurethane coatings such as hardness and resistance to abrasion, scratching, and impact, can be achieved using high molecular weight polyurethanes. High molecular weight polyurethanes, however, are difficult to handle in the melt because of their high viscosities, and it is therefore preferred to work in solvents. On the other hand, environmental considerations dictate that solvents are to bé eliminated if possible or minimized.
Dispersibility in water necessitates the presence of a sufficient number of hydrophilic groups in the polymer.
Aqueous polyurethane dispersions are described in DE-C 14 ~5 74~. In this case, dispersibility in water is achieved by adding on to the isocyanate-terminated prepolymers compounds which, in addition to containing an active hydrogen atom which reacts with the isocyanate group, also carry a salt-liXe group or a group capable of forming a salt, for example, a quaternized amino group.
Another embodiment which is described, is the reaction of the prepolymer with a compound which has an isocyanate group in addition to the group which is salt-like or capable of forming salts.
DE-C 14 95 847 describes a process for the preparation of anionic polyurethanes, in which polyisocyanates are reacted, in the presence of acetone as solvent, with essentially linear compounds having reactive hydrogen atoms and a molecular mass of from 300 to 10,000 g/mol. The compound reacted carries a carboxyl or sulfo group and at least one hydrogen atom which is reactive toward isocyanate.

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j r 2 DE-C 19 54 090 describes the preparation of salts of 2-(~-aminopropionamido)alkanesulfonic acid and their use as anionic component in the preparation of polyurethane dispersions.
DE-A 20 35 732 describes a process for the preparation of ~ salts of N-(~-aminoalkane)-~-aminoalkanesulfonic acid and their use as anionic component in the preparation of polyurethane dispersions which are free of emulsifier.
In the documents mentioned above, the starting component is a polyurethane prepolymer which at this stage still carries no ionic or ionogenic groups. The introduction of ionogenic structures enables dispersibility in water, but as described, the reactive isocyanate groups of the prepolymer are always fully used up by reaction. The introduction of these groups therefore puts a stop to addition polymerization. It is then no longer readily possible to raise the molecular mass subsequently in order to improve the mechanical properties. Although the text of these documents does indeed mêntion~the preparation from urethane prepolymers in a solvent-free melt, in the examples, the reactions are always carried out in a solvent, in order to prevent the viscosity from rising excessively.

Summary of the Invention :.. - ~ ,.
It is therefore an object of the present invention to p~ovide polyurethanes `and processes for their preparation and use, which polyurethanes can be dispersed in water without emulsifier, contain no solvent and, despite a high molecular mass, can be processed without problems.
In accordance with the objects, there has been provided a polyurethane which is dispersible in water without emulsifier, obtained by reaction of a portion of the isocyanate groups of an isocyanate-terminated urethane prepolymer with a salt of an acid having a hydrogen atom which is reactive toward isocyanate, .7 ~'., ,~. ,~
: 3 followed by reaction of remaining isocyanate groups with a chain-extending agent.
In accordance with the objects, there has also been provided a process of preparing a polyurethane which is dispersible in water without emulsifier comprising, reaction of a portion of the isocyanate groups of an isocyanate-terminated urethane prepolymer with a salt of an acid having a hydrogen atom which is reactive towards the isocyanate groups, followed by reaction of remaining isocyanate group with a chain-extending agent.
There has also been provided methods of using the polyurethane in adhesive and coating compositions and articles coated with the polyurethane.
Further objects, features, and advantages of the ~-invention will become apparent from the detailed description which follows. -... , - ---- :
Detailed Description ~ ~.,.'..:
The invention relates to polyurethanes which can be dispersed~in water without emulsifier and are obtained by partial reaction of an isocyanate-terminated urethane prepolymer with a salt of an acid having a hydrogen atom which is reactive toward isocyanate, followed by reaction of the remaining isocyanate groups with a chain-extending agent.
In this context the quantity of salt should be chosen such that only a fraction, generally from 20 to 80%, preferably from 30 to 60%, of the terminal isocyanate group is reacted. This makes it possible, by adding a suitable chain-extending agent, such as a polyamine, and an appropriate quantity of water, in a subsequent step, to carry out a chain extension. In this context the quantity of water should be calculated such that the rise in viscosity caused by the chain extension is compensated by this dilution.
Linear or branched polyurethanes are obtained which carry acid groups at the chain ends and have urea groups within the chain and/or at the branching sites. This ~.,~,, ~

~ 1 3 ~
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molecular structure leads to fine polyurethane dispersions which are stable on storage, are stable to hydrolysis, and give films displaying a high degree of resistance to swelling by water.
The isocyanate-terminated urethane prepolymers are prepared in any desired manner, such as by reacting one or more high molecular weight polyols A, if desired with the addition of low molecular weight polyols, polyamines or polythiols A', with one or more polyisocyanates B in the melt at, for example, from 60 to 130C.
Subsequently added to this polyisocyanate melt is a salt C of an acid having a hydrogen atom which is reactive toward isocyanate. Any salt of any acid may be used. Examples of appropriate acids include carboxylic, sulfonic or phosphonic acids, the molecule of which contains a hydroxyl or acidic amino group. The salt can be added in any desired manner to the prepolymer, for example, as a solid or in the form of an aqueous solution at a temperature below 100C. It is also possible to use mixtures of several such salts.
After~ this~reaction, one or more chain extenders is reacted with the remaining isocyanate groups. This is accomplished, for example, by either preparing a dispersion of the prepolymer by the addition of water, and then chain extension is accomplished by adding a chain-extender, such as a polyamine D (process I); or chain extension is first carried out by adding chain~
extender D in a small quantity of water to the prepolymer, followed by dispersion in a larger quantity of water (process II). It is also possible, in accordance with the invention, to dissolve the chain-extender D required for chain extension in the total quantity of dispersion water and therefore to add it to the isocyanate-containing urethane prepolymer at the same time as the water (process III). Likewise, chain extension can also be achieved by a partial hydrolysis of the isocyanate groups followed by reaction of the resulting amines with the remaining isocyanate groups (process IV). In all of the processes described, the ~ 1 3 ~
: ,~. 5 temperature of the dispersion water may vary, and be between 0 and 100C, with a range from 20 to 80C being preferred.
The high molecular weight polyols A which are suitable for the invention are any of those conventionally used in the preparation of polyurethanes.
They are chosen, for example, from any of the types of polyetherpolyols, polyesterpolyols, polylactonepolyols, and polycarbonatepolyols. Example of preferred polyols are as follows.
Suitable polyetherpolyols include compounds of the formula H - [ - O - (CHR) n~]m OH
in which '-15 R is hydrogen or a lower (C1 - C6) alkyl radical which may hav'e^'various substituents, n is a number from 2 to 6, and --m is a number from 10 to 120. -~ ' Examples are poly(oxytetramethylene) glycols, poly(oxye'thyle~e) glycols and poly(oxypropylene) glycols. ' The preferred polyetherpolyols are poly(oxypropylene) glycols having a molecular mass in the range from 400 to '~
5000 g/mol. ~; ~
The polyesterpolyols are generally prepared by -'`-''~~' esterifying any desired organic polycarboxylic acids or their anhydrides with desired organic polyols. The - --~
polycarboxylic acids and the polyols may be aliphatic or aromatic polycarboxylic acids and polyols. ''~
The polyols used for the preparation include alkylene ;~
glycols such as ethylene glycol, butylene glycol, neopentylglycol, hexane-1,6-diol and other glycols, such ~' ' as dimethylolcyclohexane, and trishydroxyalkylalkanes, such as trimethylolpropane, and tetrakishydroxyalkyl- ;
i alkanes, for example, pentaerythritol.
The acid component of the polyester polyols generally primarily comprises low molecular weight polycarboxylic -acids or their anhydrides having 2 to 18 carbon atoms in the molecule. Examples of suitable acids include - 2~3~3`3~
.~
;- 6 phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, maleic acid, glutaric acid, hexachloroheptanedi-carboxylic acid, alkyl- and alkenylsuccinic acids, for example, n-octenylsuccinic acid, n- and iso-dodecenylsuccinic acid, tetrachlorophthalic acid, trimellitic acid and pyromellitic acid. Instead of these acids it is also possible to use their anhydrides where these exist. ~ .
Dimeric and trimeric fatty acids can also be employed as polycarboxylic acids. Terephthalic acid, adipic acid and ~-`
maleic acid are particularly preferred.
The terms polyetherpolyols and polyesterpolyols also include products of this kind containing monomers with - -carboxylic acid, phosphonic acid or sulfonic acid groups.
Furthermore, it is also possible in the invention to use polyesterpoiyols which are derived from lactones.
These products are obtained by, for example, reacting an ~-caprolactone with a polyol. Products of this kind are ~ ;-`
described in US-A 3 169 945, which is incorporated by ;~
reference~in i~ts entirety. ~- -The polylactonepolyols obtained by this reaction are distinguished by the presence of a terminal hydroxyl group and by recurring polyester units which are derived from the lactone. These recurring molecular units may be ~ -of the formula O ........................................... ~ :`
'' 1 1 ` ~, - C - ( CHR~ n - CH 2 - :~
' '`: : .-in which n is an integer, preferably 4 to 6, and the -substituent R is hydrogen, an alkyl radical, a cycloalkyl radical or an alkoxy radical, with no substituent containing more than 12 carbon atoms.
The lactone used as starting material may be any desired lactone or any desired combination of lactones; -:
this lactone should contain at least 6 carbon atoms in ~:~3~ 3~

the ring, for example, 6 to 8 carbon atoms, and at least 2 substituents of hydrogen should be present on the carbon atom attached to the oxygen group of the ring.
The lactone used as starting material may be represented by the following formula:

CH2C CR 2 ~n C O
O
in which n and R are as defined above.
The lactones preferred in the invention are the ~-caprolactones in which n has the value 4. The most preferred lactone is unsubstituted ~-caprolactone, in which n has the value 4 and all the substituents R are hydrogen. This lactone is particularly preferred since it is available in large quantities and gives coatings having excellent properties. In addition, it is also possible to use various other lactones, singly or in combination.
Any aesired polyol can be used to react with the lactone. Examples of aliphatic polyols which are suitable for reaction with the lactone include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, dimethylolcyclohexane, trimethylolpropane and pentaerythritol.
Other suitable starting compounds A are polycarbonate-polyols or polycarbonatediols, for example, of the formula O

H O ~ O - C - O - R - ) n ~ O H

in which R is an alkylene radical. These OH-functional polycarbonates can be prepared by reacting polyols, such as propane-1,3-diol, butane-1,4-diol, hexane-1,6-diol, diethylene glycol, triethylene glycol, 1,4-bishydroxy-~ K j 1 ~ r~ -. ~:,, \., : 8 methylcyclohexane, 2,2-bis(4-hydroxycyclohexyl)propane, neopentylglycol,trimethylolpropane,andpentaerythritol, with dicarbonates such as dimethyl, diethyl or diphenyl carbonate, or with phosgene. Mixtures of such polyols also can be employed.
The polyetherpolyols, polyesterpolyols, polylactone-polyols and polycarbonatepolyols described above can be employed alone or together. Furthermore, these polyols A may also be employed together with different quantities of low molecular weight, isocyanate-reactive polyols, polyamines or polythiols A'. Examples of compounds of this kind are ethylene glycol, 1,2-propylene glycol or 1,3-propylene glycol, 1,4-butanediol or 1,3-butanediol, 1,6-hexanediol, the lower oligomers of the abovementioned diols, pentaerythritol, trimethylolpropane, ethylenediamine, propylenediamine, hexamethylenediamine and 1,2-dimercaptoethane. Compounds having mixed functional groups, for example, ethanolamine or 2-mercaptoethanol, are also suitable. Ethylene glycol, butanediol and hexanediol are particularly preferred.
Suitable polyisocyanates B are any in the art and include all (cyclo)aliphatic, aromatic or mixed aromatic-aliphatic diisocyanates as are conventionally employed in polyurethane chemistry.
Examples of suitable polyisocyanates include tri-methylene diisocyanates, tetramethylene diisocyanates, pentamethylene diisocyanates, hexamethylene diiso-cyanates, propylene diisocyanates, ethylethylene diiso-cyana~es, 2,3-dimethylethylene diisocyanates, 1-methyl-trimethylene diisocyanates, 1,3-cyclopentylene diiso-cyanates, 1,4-cyclohexylene diisocyanates, 1,2-cyclo-hexylene diisocyanates, 1,3-phenylene diisocyanates, 1,4-phenylene diisocyanates, 2,4-tolylene diisocyanates (TDI), 2,6-tolylene diisocyanates (TDI), 4,4'-biphenylene diisocyanates, 1,5-naphthylene diisocyanates, 1,4-naphthylene diisocyanates, l-isocyanatomethyl-5-iso-cyanato-1,3,3-trimethylcyclohexane (IPDI), bis(4-iso-cyanatocyclohexyl)methane, 4,4'-diisocyanatodiphenyl ether, 2,3-bis-(8-isocyanatooctyl) -4-octyl-5-hexylcyclo-2~3~
. `~. .-.
... g hexene, trimethylhexamethylene diisocyanates, tetramethylxylylene diisocyanates (TMXDI), isocyanurates of the above diisocyanates, and allophanates of the above diisocyanates. Mixtures of such di- or polyisocyanates can also be employed. TDI, TMXDI and IPDI are particularly preferred.
Suitable salts C of acids, preferably carboxylic, sulfonic, or phosphonic acids which carry a hydroxyl or amino group are derived from, for example, hydroxycarboxylic acids, such as glycolic acid, lactic acid, trichlorolactic acid, salicylic acid, 4-hydroxyiso~
phthalic acid, hydroxyterephthalic acid, 5,6,7,8-tetra-hydro-2-naphthol-3-carboxylic acid, 1-hydroxy-2-naphthoic acid, ~-hydroxypropionic acid and m-hydroxybenzoic acid;
aminocarboxylic acids such as anilidoacetic acid, 2-hydroxycarbazole-3-carboxylicacid,glycine, sarcosine, methionine, ~-alanine, ~-alanine, 6-aminocaproic acid, 6-benzoylamino-2-chlorocaproicacid,4-aminobutyricacid, aspartic acid, glutamic acid, histidine, anthranilic acid, 2-ethylaminobenzoic acid, N-(2-carboxylphenyl)-aminoacetic acid, 2-(3'-aminobenzenesulfonylamino)benzoic acid, 3-aminobenzoic acid, 4-aminobenzoic acid, N-phenyl-aminoacetic acid, 5-aminobenzenedicarboxylic acid and 5-(4'-aminobenzoyl-amino)-2-aminobenzoic acid;
hydroxysulfonicacidssuchas2-hydroxyethanesulfonic acid, 2-phenolsulfonic acid, 3-phenolsulfonic acid, 4-phenylsulfonic acid, 2,4-phenoldisulfonic acid, 1-naph-tholsulfonic acid, l-naphtholdisulfonic acid, 8-chloro-1-naphtholdisulfonic acid, l-naphtholtrisulfonic acid, 2-naphthol-1-sulfonic acid, 2-naphtholtrisulfonic acid, 2-hydroxy-6-sulfo-3-naphthoic acid and 2-hydroxy-carbazole-7-sulfonic acid;
aminosulfonic acids such as amidosulfonic acid, hydroxylaminemonosulfonicacid,hydrazinedisulfonicacid, sulfanilic acid, N-phenylaminomethanesulfonic acid, 4,6-dichloroaniline-2-sulfonic acid, 1,3-phenylene-diamine-4,6-disulfonic acid, N-acetyl-1-naphthylamine-3-sulfonic acid, 1-naphthylaminesulfonic acid, 2-naphthylaminesulfonic acid, naphthylaminedi-sulfonic . ~ 2 ~ 3 ," .9 .~ ~
~,.~,.~ .. .
;,.` ";.,. 1o acid, naphthylaminetrisulfonic acid, phenylhydrazine-2,5-disulfonic acid, 2,3-dimethyl-4-aminoazobenzene-4,5'-disulfonic acid, 4'-amino-4-(4-methoxyphenylazo)-2,2'-disulfonic acid, carbazole-2,7-disulfonic acid, taurine, methyltaurine, butyltaurine, 3-amino-5-sulfo-1-benzoic acid, 3-methylanilino-methanesulfonic acid, 6-nitro-1,3-dimethylbenzene-4-sulfamic acid, 2-aminophenol-4-sulfonic acid, 2-methoxyanilinomethanesulfonic acid, and 2-aminodiphenylaminesulfonic acid.
The salts of taurine and its derivatives are particularly preferred.
The cations in these salts can be selected from the alkali and alkaline earth metals, such as sodium potassium, rubidium, magnesium, and calcium, and from ammonium and its alkyl and aryl derivatives. Especially preferred are alkali and ammonium salts.
- To extend the chain of the urethane prepolymers, one or more chain extenders D are used. Chain extenders for isocyanate-terminated polyurethane prepolymers are selected from compounds that carry at least two groups that are react~ve towards isocyanate groups. If used in aqueous medium, like in this case, the reactivity of these groups in the chain extender has to be greater than that of water. Suitable highly reactive groups are primary and secondary amino groups, and thiol (mercaptan) groups. Chain extenders which can be used in the present invention therefore comprise polyamines, polymercaptans, and polyamino-polymercaptans with at least two isocyanate reactive groups per molecule; Preferably a polyamine is added which rea!cts with the remaining isocyanate groups.
Suitable polyamines are any known in the art, and include ethylenediamine (EDA), hexamethylenediamine (HMDA), 1,4-cyclohexylenediamine, diaminodiphenylmethane, diethylenetriamine (DETA), triethylenetetramine, tetra-ethylenepentamine, triaminobenzene, 2-methyl-1,5-diamino-pentane (Dytek A), the isomeric phenylenediamines, and hydrazine. Suitable polymercaptans are dimercapto toluene, and the ~,~-dimercapto alkanes like dimercapto ethane, dimercapto propane, dimercaptobutane and . ~ -~' h ~ O S
.~`~
,.`,~j~ 11 dimercaptohexane, and 2,3-dimercapto propanol (BAL).
Suitable Mercaptoamines include cysteamine and mercapto aniline. EDA, DETA, HMDA and Dytek A are particularly preferred.
The advantage of the product and process according ~-to the invention compared with the prior art are in the separation of the steps -a) introduction of ionic groups into the urethane prepolymer, and , ;,, b) chain extension, by using salts, preferably monofunctional salts (i.e., salts having one hydrogen atom which is reactive toward ~-isocyanate groups), partial reaction of the isocyanate-terminated prepolymer with the salt, and subsequent chain extension. It is possible in accordance with the -invention to carry out the reaction of the urethane , , , - - -:
prepolymer with the salt either in bulk or in a small quantity of water, and to carry out the subsequent chain extension likewise in water. In this way, it is generally possible to avoid the use of solvents.
In the prilor art, solvents are always employed in the preparation of the polyurethane and/or in the subsequent reaction with hydroxy- or amino-functional salts.
Although the oldest of the abovementioned documents, DE-C 14 95 745, talks of a reaction in the melt, all of the examples employ acetone as solvent. In the case of the preparation or reaction of polyurethanes of sufficiently high molecular weight, their high molecular mass will mean that the viscosity of the mixtures will be above the level which can be coped with in the melt. In accordance with the invention, on the other hand, poly-urethanes of high molecular mass are only formed when a sufficient quantity of water is present to dilute the solution and thus to reduce its viscosity.
The polyurethane dispersions which are obtainable from these components by processes I to IV described above are suitable for many applications, for example, for the production of coating compositions for wood, ', ~'.

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textiles and metals, as binders for water-dilutable adhesives or as resins for printing inks.
They are capable of being combined and are generally compatible with other aqueous solutions and dispersions of polymers, for example, acrylic and/or methacrylic polymers, polyurethane, polyurea resins, polyester resins and epoxy resins, thermoplastics based on polyvinyl acetate, polyvinyl chloride, polyvinyl ether, polychloro-prene and polyacrylonitrile, and ethylene-butadiene-styrene copolymers. They also can be combined withthickening substances based on carboxyl-containing polyacrylates or polyurethanes, hydroxyethylcellulose, polyvinyl alcohols and inorganic thixotropic agents, such as bentonite, sodium-magnesium and sodium-magnesium-fluorine-lithium silicates.
The polyurethane dispersions according to the invention can be applied to a wide variety of substrates, examples being ceramic, wood, glass, concrete, preferably plastics such as polycarbonate, polystyrene, polyvinyl chloride, polyester, poly(meth)acrylates, acrylonitrile-butadiene-styrene polymers and the like, and preferably metals such as iron, copper, aluminum, steel, brass, bronze, tin, zinc, titanium, magnesium and the like.
They adhere to the various substrates without adhesion-promoting primers or intermediate layers.
The polyurethane dispersions according to theinvention are suitable, for example, for the production of anticorrosion coatings and/or intermediate coatings for a wide variety of applications, in particular for the production of metallic and solid-color basecoats in multicoat paint systems for the sectors of automotive finishing and the coating of plastics, and for producing primers for the sector of plastics coating.
- Because of the short flash-off times of the basecoats based on the polyurethane dispersions according to the invention, the pigmented basecoat can be coated over with a clearcoat without a baking step (wet-on-wet method) and then the two coats can be baked together or subjected to forced drying. Basecoats prepared using the polyurethane ' ~``'~

h ~ a s dispersions according to the invention give paint films which are of substantially equal quality, regardless of the baking or drying temperature, so that they can be employed both as a refinish for motor vehicles and also as a stoving enamel in the production-line finishing of motor vehicles. Both applications result in paint films having a good adhesion to both the substrate and the original f`inish and having good resistance to humidity.
Furthermore, the brightness of the painted coat is not impaired to any notable extent after a humidity test.
In the formulation of water-dilutable coating materials using the polyurethane dispersions according to the invention, it is possible to add the crosslinking agents which are conventional in the paint industry, for example, water-soluble or water-emulsifiable melamine or benzoguanamine resins, polyisocyanates or prepolymers having terminal isocyanate groups, water-soluble or water-dispersible polyaziridines and blocked polyiso-cyanates. The aqueous coating systems may contain all known inorganic or organic pigments and/or dyes which are conventional in paint technology, as well as wetting agents, antifoams, leveling agents, stabilizers, catalysts, fillers, plasticizers and solvents.
The polyurethane dispersions according to the invention also may be used directly for joining any desired substrates. In order to achieve specific adhesive properties, the polyurethane dispersions according to the invention can be blended with other polymer dispersions or solutions as described above.
Furthermore, in order to improve the heat resistance and peel strength it is possible to add crosslinking agents such as, for example, polyisocyanates or prepolymers having terminal isocyanate groups, or water-soluble or water-emulsifiable melamine or benzoguanamine resins.
The adhesives which are based on the polyurethane dispersions according to the invention may contain additives which are conventional in adhesives technology, such as plasticizers, solvents, film binder auxiliaries, fillers and synthetic and natural resins. They are ' ~ ', ~ -.

2~3 ~9~S ` ~
".,,, ~- 14 specifically suitable for the production of adhesive bonds between substrates in the motor vehicle industry, for example, the adhesive bonding of interior fittings, and in the shoe industry, for example, for joining the sole of the shoe to the upper. The preparation and processing of the adhesives based on the polyurethane dispersions according to the invention are carried out by the conventional methods of adhesives technology as are employed for aqueous dispersion and solution adhesives.
10The invention is illustrated by the following non-limiting examples.

Example 1:
An amount of 330.6 g of a polyester made from adipic acid and 1,4-butanediol, having an OH number of 47.7, and 1517.6 g of neopentylglycol are placed together at 130C.
Amounts of 30.9 g of tolylene diisocyanate and 14.5 g of m-tetramethylxylylene diisocyanate are metered into this melt, which is stirred until the NCO value is 0.0%.
After cooling to 70C, 15.7 g of 1,6-hexanediol are added and, once~ this has dissolved, a further 69.8 g of m-tetramethylxylylene diisocyanate are metered in. At an NCO value of 1.8~, 68.5 g of a 25% strength aqueous solution of sodium taurinate are added and are stirred into the resin. After about 10 min, a solution of 2.4 g of ethylenediamine in 124 g of water is added and is stirred in homogeneously while the temperature is raised to 85C. After about 30 min, the mixture is diluted with 323.3`g of water to the final solids content (50%). A
dispersion is obtained which has a viscosity of 66 mPa.s, a pH of 7.4, an amine number <0.3, and an acid number of O . 9 .

Example 2~
An amount of 10.5 g of ethylene glycol is added to 330.6 g of a polyester made from adipic acid and 1,4 butanediol, having an OH number of 47.7. An amount of 41.2 g of tolylene diisocyanate is metered into this solution whlle the temperature is raised from 60 to 213~3~5 ~ ;-130C. As soon as the NCO value has reached 0.0%, the melt is cooled to 70C and a further 8.2 g of ethylene glycol are added. This solution is reacted further with 69.8 g of m-tetramethylxylylene diisocyanate. When an NC0 value of 1.5% has been reached, 66 g of a 25%
strength aqueous solution of sodium taurinate are added and are stirred in homogeneously. After about 10 min, a solution of 1.1 g of ethylenediamine in 111.4 g of water is metered in and is stirred in homogeneously over 30 min while the temperature is raised to 85C. After this, the :
mixture -is diluted with 318.2 g of water to the final solids content (50%). A dispersion is obtained which has a viscosity of 253 mPa.s, a pH of 7.4, an amine number <0.1 and an acid number of 0.9. ~ -.
While several embodiments of the invention have been described, it will be understood that it is capable of further modifications, and this application is intended to cover any variations, uses, or adaptations of the - -invention, following in general the principles of the -invention and.including such departures from the present ~--disclosure as to come within knowledgP or customary practice in the art to which the invention pertains, and as may be applied to the essential features hereinbefore -~
set forth and falling within the scope of the invention. -.. ~ . ~:

,, ~ , .. .....

:: : -:-,.,:~,, ~.

Claims (20)

1. A polyurethane dispersible in water without emulsifier, obtained by reaction of a portion of the isocyanate groups of an isocyanate-terminated urethane prepolymer, with a salt of an acid having a hydrogen atom which is reactive toward isocyanate, followed by reaction of remaining isocyanate groups with a chain-extending agent.

2. An aqueous polyurethane dispersion, comprising a polyurethane as claimed in claim 1.

3. An aqueous polyurethane dispersion as claimed in claim 2, obtained by dispersing in water the urethane prepolymer which has been reacted with the salt, and then adding the chain-extending agent which then reacts with remaining isocyanate groups.

4. An aqueous polyurethane dispersion as claimed in claim 2, obtained by adding the chain-extending agent in a quantity of water to the urethane prepolymer which has been reacted with the salt, and then reacting this chain-extending agent with remaining isocyanate groups, followed by dilution with a larger quantity of water.

5. An aqueous polyurethane dispersion as claimed in claim 2, obtained by adding the chain-extending agent together with the total quantity of dispersion water to the urethane prepolymer which has been reacted with salt, and then reacting the chain-extending agent with remaining isocyanate groups.

6. An aqueous polyurethane dispersion as claimed in claim 2, obtained by partial hydrolysis of the terminal isocyanate groups remaining after the urethane prepolymer has been reacted with the salt, to give a chain-extending agent with terminal amino groups, which are then reacted with the remaining terminal isocyanate groups of the nonhydrolyzed urethane prepolymers, with chain extension taking place.

7. A polyurethane, as claimed in claim 1, wherein the acid comprises taurine in solid or solution form.

8. A binder for coating compositions or adhesives, which comprises a polyurethane as claimed in claim 1.

9. An aqueous polyurethane dispersion as claimed in claim 2 which comprises no emulsifier.

10. An aqueous polyurethane dispersion as claimed in claim 2 which comprises no solvent.

11. An article coated with a composition which comprises a polyurethane as claimed in claim 1.

12. A polyurethane as claimed in claim 1, wherein the salt reacts with from 20 to 80% of the terminal isocyanate groups of the prepolymer.

13. A polyurethane as claimed in claim 1, wherein the chain-extending agent comprises a polyamine.

14. A polyurethane as claimed in claim 1, wherein the prepolymer is obtained by reaction of a polyol with a polyisocyanate.

15. A polyurethane as claimed in claim 14, wherein the polyol is selected from one or more of the group consisting of polyetherpolyols, polyesterpolyols, polylactonepolyols, and polycarbonatepolyols.

16. A polyurethane as claimed in claim 1, wherein the acid is selected from one or more of the group consisting of carboxylic acids, sulfonic acids, and phosphonic acids.

17. A process of preparing a polyurethane which is dispersible in water without emulsifier comprising reacting a portion of the isocyanate groups of an isocyanate-terminated urethane prepolymer with a salt of an acid having a hydrogen atom which is reactive towards the isocyanate groups, and then reacting remaining isocyanate groups with a chain-extending agent.

18. A process as claimed in claim 17, comprising dispersing in water the urethane prepolymer which has been reacted with the salt, and then adding the chain-extending agent which then reacts with remaining isocyanate groups.

19. A process as claimed in claim 17, comprising adding the chain-extending agent in a quantity of water to the urethane prepolymer which has been reacted with the salt, and then reacting this chain-extending agent with remaining isocyanate groups, and then diluting with a larger quantity of water.

20. A process as claimed in claim 17, comprising adding the chain-extending agent together with the total quantity of dispersion water to the urethane prepolymer which has been reacted with salt, and then reacting the chain-extending agent with remaining isocyanate groups.