HK1054757B - Highly functional polyisocyanate mixtures which are dispersable in water - Google Patents

Description

Water-dispersible, high-functionality polyisocyanate mixtures

The present invention relates to polyether-modified water-dispersible polyisocyanate mixtures, to a process for their preparation and to their use as starting materials for the preparation of polyurethane plastics, in particular as water-soluble or water-dispersible crosslinkers for paint binders or binder components which contain groups capable of reacting with isocyanate groups.

With the increasing environmental awareness, water-dispersible polyisocyanates have gained in importance in recent years in different fields of application.

Water-dispersible polyisocyanates now play a special role as crosslinker components for water-dilutable two-component polyurethane (2C PUR) paints. In combination with aqueous polyol dispersions, they make it possible to form solvent-free lacquer systems which have cured at room temperature to form high-quality coatings which are by no means inferior to conventional paints with respect to solvent resistance and resistance to chemicals or mechanical loads (see, for example, EP-A-0358979, EP-A-0469389, EP-A-0496210, EP-A-0542105, EP-A-0543228, EP-A-0562282, EP-A-0562436, EP-A-583728, DE-A-4129951, DE-A-4226242, DE-A-4226243, DE-A-4226270).

In addition, water-dispersible polyisocyanate preparations are also important additives for water-dispersible adhesives. With their help, for example, the heat resistance and water resistance of ｃA glue joint of different materials can be significantly improved (see, for example, EP-A-0061628 and EP-A-0206059).

Furthermore, water-dispersible polyisocyanates can be used as crosslinker components for aqueous dispersions in textile finishing (EP-A-0560161 or WO95/30045) or in formaldehyde-free inks for textiles (EP-A-0571867 or DE-A-19533218), and polyisocyanates are also suitable, for example, as auxiliaries for the moisture enhancement of paper manufacture (EP-A-0564912, EP-A-0582166, EP-A-0707113, WO96/20309 and WO 97/04169).

In fact, nonionic polyisocyanates modified with polyethers to become hydrophilic have gained acceptance in these fields of application. The preparation of such water-dispersible polyisocyanates is described in a large number of documents.

Urethanes formed from organic, in particular aromatic polyisocyanates and polyethylene glycol monoalkyl ethers containing at least 5 ethylene oxide units constitute, according to the teaching of DE-A-2415435, for example, surface-active substances which are capable of producing stable aqueous emulsions of aromatic polyisocyanates according to GB-A-1444933 and DE-A-2908844.

Aromatic polyisocyanates which are hydrophilically modified by conversion with alkylene oxide polyethers are also known from EP-A-0061628 and EP-A-0095594. These products are used in the form of aqueous emulsions, in particular in the field of adhesives.

EP-A-0206059 has as its subject ｃA water-dispersible (cyclo) aliphatic polyisocyanate preparation. They contain, as emulsifiers, conversion products formed from polyisocyanates and monovalent or polyvalent polyoxyalkylene alcohols composed of at least one polyether chain comprising at least 10 ethylene oxide units, and are likewise used as additives for aqueous adhesives.

EP-0516277 describes the hydrophilization of special polyisocyanates containing tertiary bound isocyanate groups by conversion with monovalent polyalkylene oxide polyesters and the use of these products as crosslinkers for aqueous coatings.

For the use of advanced, light-resistant lacquers, polyisocyanate mixtures described in EP-A-0540985 and U.S. Pat. No. 4,5200489, obtainable by urethanizing aliphatic and/or cycloaliphatic lacquer polyisocyanates with short-chain polyoxyethylene polyether alcohols containing less than 10 ethylene oxide units, on statistical average, have proved particularly valuable.

From EP-A-0645410 and EP-A-0680983 it is known that water-dispersible polyisocyanates for crosslinking agents for aqueous lacquers for wood and furniture are based on 2, 4(6) -diisocyanatotoluene (TDI) or mixtures of TDI and 1, 6-diisocyanatohexane (HDI), which also contain, as hydrophilic component, ｃA urethane formed from ｃA polyisocyanate and ｃA monofunctional polyethylene oxide polyether alcohol.

In addition to these purely nonionic, hydrophilic polyisocyanates containing polyether urethanes, polyether-modified water-dispersible polyisocyanates are also described which, in order to improve the emulsifying action or to obtain special effects, also comprise ionic groups, such as sulfonate groups (see, for example, EP-A-0703255) or amino or ammonium groups (see, for example, EP-A-0582166 and EP-A-0707113). The described ionically/nonionically modified polyisocyanates are generally not very suitable for use in paints. They are preferably used as environmentally friendly textile finishes and as moisture enhancers for paper manufacture.

Despite the wide acceptance in the market place due to the extremely broad range of applications, the prior art water-dispersible polyisocyanates modified with polyetherurethanes suffer from a number of fundamental disadvantages.

Owing to the extremely high maximum viscosity to be overcome during dispersion, water-dispersible polyisocyanates prepared using high molecular weight polyether alcohols, for example in the case of pure polyethylene oxide polyethers having a starting average molecular weight of approximately 700, can frequently only be used homogeneously in aqueous media by means of considerable shear forces, for example high-speed stirrers. In addition, the products described, in particular in order to obtain the high emulsifier contents required for particularly fine particle dispersions which are stable for precipitation, often have a tendency to crystallize.

On the other hand, by using shorter polyether chains it is possible to obtain water-dispersible polyisocyanates which are easily stirrable in water to form stable dispersions without any tendency to crystallize even with a high degree of hydrophilisation, i.e.a high content of ethylene oxide units. However, since the polyoxyalkylene polyether used for modification has a low molecular weight, the isocyanate group and the average isocyanate functionality steadily decrease with increasing degree of hydrophilicity. In fact, in most of the aforementioned fields of application-for example as crosslinker components for paints and coatings-there is a very demanding requirement for highly hydrophilic polyisocyanates which can be emulsified into particularly fine particles and have a high NCO content and a functionality as high as possible.

DE-A-19822891 describes for the first time a process for preparing water-dispersible polyisocyanate mixtures which do not have the abovementioned disadvantages. In this case, low-monomer-content polyisocyanates composed of at least two diisocyanate molecules are converted with monofunctional polyethylene oxide polyether alcohols under allophanatization conditions such that at least 60 mol%, preferably at least 80 mol%, particularly preferably at least 90 mol%, of the urethane groups initially formed by the NCO/OH reaction continue to react to form allophanate groups. The resulting polyisocyanate mixtures having a degree of allophanation of at least 60% are much easier to stir and are present in the aqueous system in the form of finer particles, even if the degree of hydrophilization is significantly lower, than water-dispersible polyisocyanates prepared using polyether alcohols of the same structure in which the polyether chains are linked to the polyisocyanate via urethane bonds. They differ from previously known polyisocyanate mixtures which contain polyether chains and are equally and better dispersible in water by a higher content of isocyanate groups and a higher functionality.

It has been found that polyisocyanate mixtures which have likewise been prepared under allophanation conditions from low-monomer polyisocyanates composed of at least two diisocyanate molecules and monofunctional polyoxyethylene polyether alcohols exhibit a markedly improved dispersibility in water in comparison with the polyether allophanates described in DE-A-19822891, provided that the allophanation reaction ends before the degree of allophanation reaches 60%. In this way, water-dispersible polyisocyanate mixtures can be prepared which, in addition to the dispersibility being increased again, at the same time exhibit the advantage of having a higher NCO content, are suitable for all the abovementioned fields of application of hydrophilic polyisocyanates, in particular as starting materials for the preparation of polyurethane plastics, most particularly as crosslinkers for aqueous binders or binder components in coating systems.

Although the preparation of polyisocyanates containing allophanate groups is described as subject matter in some publications, for example EP-A-0000194, EP-A-0303150, EP-A-0682012, US-A-5380792 or US-A-5086175, however, conventional polyether alcohols are also listed as possible starting materials for the alcohols for preparing the products, and in addition to these, in EP-A-0000194, EP-A-0303150, EP-A-0682012, in a long list of starting isocyanates, polyisocyanates having a functionality > 2 are also mentioned by way of all inclusion, for example, the trimer of HDI or 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), the person skilled in the art is not at all able to derive any particular indication from any of the abovementioned publications: the conversion products of low-monomer polyisocyanates prepared under allophanatization conditions with an allophanatization degree of from 20 to 59% and monofunctional polyoxyethylene polyether alcohols in water stir considerably more easily and form stable emulsions in the form of finer particles than polyisocyanate mixtures of the same composition prepared by urethanization according to methods known in the art or by the method described in DE-A-19822891.

The invention provides water-dispersible polyisocyanate mixtures based on aliphatic, cycloaliphatic, araliphatic and/or aromatic diisocyanates having

a) An average isocyanate functionality of at least 2.0,

b) isocyanate group content (calculated as NCO; molecular weight 42) from 5.0 to 25.0 wt.%, and

c) content of ethylene oxide units (in C) incorporated in the polyether chain₂H₄Measuring O; molecular weight 44) from 2 to 50 wt.%, so that, on statistical average, the polyether chain contains from 5 to 35 ethylene oxide units,

characterized in that the polyether chain is linked to two polyisocyanate molecules by allophanate groups in a ratio of 20 to 59 mol.%, each polyisocyanate molecule being synthesized from at least two diisocyanates.

The present invention also provides a process for preparing the water-dispersible polyisocyanate mixtures, characterized in that: make it

A) A polyisocyanate component having an (average) NCO functional group content of 2.0 to 5.0, an aliphatically, cycloaliphatically, araliphatically and/or aromatically bound isocyanate group content (calculated as NCO; molecular weight 42) from 8.0 to 27.0 wt.% and a monomeric diisocyanate content of less than 1 wt.%, and

B) a monovalent polyoxyalkylene polyether alcohol comprising, on a statistical average, 5 to 35 ethylene oxide units,

reacting with one another while maintaining an NCO/OH equivalent ratio of from 6: 1 to 400: 1, so that from 20 to 59% of the urethane groups initially formed by the NCO/OH reaction continue to react to form allophanate groups, and furthermore the type and quantity ratio of the starting components are selected such that the resulting conversion products satisfy the conditions stated under a) to c).

The invention also provides the use of the polyisocyanate mixtures as starting materials for polyurethane plastics.

Finally, the invention also provides the use of the polyisocyanate mixtures as crosslinkers for water-soluble or water-dispersible lacquer binders or lacquer binder components in the preparation of coatings, wherein the coatings are prepared by using aqueous coating agents based on the binders or binder components.

The component a) used in the process of the present invention has an (average) NCO functionality of 2.0 to 5.0, preferably 2.3 to 4.5, and an isocyanate group content of 8.0 to 27.0 wt.%. Preferably 14.0-24.0 wt.%, with a monomeric diisocyanate content of less than 1 wt.%, preferably less than 0.5 wt.%. It consists of at least one organic polyisocyanate containing aliphatically, cycloaliphatically, araliphatically and/or aromatically bound isocyanate groups.

For the polyisocyanate or polyisocyanate mixture of component A) it is any polyisocyanate containing uretdione, isocyanurate, allophanate, biuret, iminooxadiazinedione and/or oxadiazinetrione structures, which is prepared by simple modification of aliphatic, cycloaliphatic, araliphatic and/or aromatic diisocyanates and is synthesized from at least two diisocyanates, as described, for example, in the following publications: J.Prakt.chem.336(1994)185-200, DE-A-1670666, DE-A-1954093, DE-A-2414413, DE-A-2452532, DE-A-2641380, DE-A-3700209 and DE-A-3900053, DE-A-3928503 or EP-A-0336205, EP-A-0339396 and EP-A-0798299.

Suitable diisocyanates for preparing the polyisocyanates are any diisocyanates having aliphatically, cycloaliphatically, araliphatically and/or aromatically bonded isocyanate groups of molecular weight 140 and obtained by phosgenation or without phosgene involvement, for example by thermal decomposition of urethanes, such as 1, 4-diisocyanatobutane, 1, 6-diisocyanatohexane (HDI), 2-methyl-1, 5-diisocyanatopentane, 1, 5-diisocyanato-2, 2-dimethylpentane, 2, 2, 4-or 2, 4, 4-trimethyl-1, 6-diisocyanatohexane, 1, 10-diisocyanatodecane, 1, 3-and 1, 4-diisocyanatocyclohexane, 1, 3-and 1, 4-bis- (isocyanatomethyl) -cyclohexane, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 4, 4 ' -diisocyanatodicyclohexylmethane, 1-isocyanato-1-methyl-4 (3) -isocyanatomethylcyclohexane, bis- (isocyanatomethyl) -norbornane, 1, 3-and 1, 4-bis- (2-isocyanato-prop-2-yl) -benzene (TMXDI), 2, 4-and 2, 6-diisocyanatotoluene (TDI), 2, 4 ' -and 4, 4 ' -diisocyanatodiphenylmethane, 1, 5-diisocyanatonaphthalene or a mixture of any of the foregoing diisocyanates.

The starting components A) are preferably polyisocyanates or polyisocyanate mixtures of the stated type which contain exclusively aliphatically and/or cycloaliphatically bound isocyanate groups.

The starting components A) are particularly preferably polyisocyanates or polyisocyanate mixtures containing isocyanurate structures based on HDI, IPDI and/or 4, 4' -diisocyanatodicyclohexylmethane.

Component B) is a monovalent polyoxyalkylene polyether alcohol which, on statistical average, contains 5 to 35, preferably 7 to 30, ethylene oxide units per molecule, such as are obtainable by alkoxylation of suitable starter molecules in a manner known per se (see, for example, Ullmanns encyclopenta die der thchnischen Chemie, Vol. 4, 19, Verlag Chemie, Weinheim, pp. 31 to 38).

Suitable starter molecules for preparing the polyether alcohols B) used in the process according to the invention are, for example: saturated monoalcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, sec-butanol, the isomeric pentanols, hexanols, octanols and nonanols, n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecanol, cyclohexanol, the isomeric methylcyclohexanols or hydroxymethylcyclohexane, 3-ethyl-3-hydroxymethyloxetane or tetrahydrofurfuryl alcohol; unsaturated alcohols such as allyl alcohol, 1, 1-dimethylallyl alcohol or oleyl alcohol, aromatic alcohols such as phenol, the isomeric cresols or methoxyphenols, araliphatic alcohols such as benzyl alcohol, anisyl alcohol or cinnamyl alcohol; secondary monoamines such as dimethylamine, diethylamine, dipropylamine, diisopropylamine, dibutylamine, diisobutylamine, bis- (2-ethylhexyl) amine, N-methyl-and N-ethylcyclohexylamine or dicyclohexylamine, and also heterocyclic secondary amines such as morpholine, pyrrolidine, piperidine or 1H-pyrazole.

Preferred starter molecules are saturated monoalcohols having up to 4 carbon atoms. It is particularly preferred to use methanol as starter molecule.

Alkylene oxides suitable for the alkylation are, in particular, ethylene oxide and propylene oxide, which may be added in any desired sequence or else in a mixture during the alkylation.

Polyoxyalkylene polyether alcohols B) are either pure polyoxyethylene polyethers or mixed polyoxyalkylene polyethers, in which the oxyalkylene units contain at least 30 mol.%, preferably at least 40 mol.%, of oxyethylene units.

Preferred starting components B) for the process according to the invention are pure polyethylene glycol monomethyl ether alcohols which comprise, on statistical average, from 7 to 30, particularly preferably from 7 to 25, ethylene oxide units.

Optionally, and less preferably, the process of the invention can be accompanied, in addition to the use of the stated polyether alcohols B), by the use of auxiliary amounts of other compounds as hydrophilic structural components, which compounds are reactive with isocyanates and contain anionic or cationic groups, such as carboxylate, sulfonate or ammonium groups.

To carry out the process according to the invention, the starting components A) and B) are reacted with one another at from 40 ℃ to 180 ℃, preferably from 50 ℃ to 150 ℃, while maintaining an NCO/OH equivalent ratio of from 6: 1 to 400: 1, preferably from 8: 1 to 140: 1, so that from 20 to 59 mol%, preferably from 25 to 59 mol%, particularly preferably from 30 to 59 mol%, of the urethane groups initially formed by the NCO/OH reaction continue to react to allophanate groups.

To promote the allophanatization reaction, the process of the present invention may optionally employ a suitable catalyst. To this end, they may be the allophanatization catalysts which are generally known, such as metal carboxylates, metal chelates or tertiary amines as described in GB-A-0994890, alkylating agents as described in U.S. Pat. No. 3, 3769318 or strong acids as described in EP-A-0000194.

Suitable allophanatization catalysts are in particular zinc compounds, such as zinc (II) stearate, zinc (II) n-octoate, zinc (II) 2-ethyl-1-hexanoate, zinc (II) naphthenate or zinc (II) acetylacetonate, tin compounds, such as tin (II) n-octoate, tin (II) 2-ethyl-1-hexanoate, tin (II) laurate, dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin dimaleate or dioctyltin diacetate, aluminum tris (ethylacetoacetate), iron (III) chloride, potassium octoate, compounds of manganese, cobalt or nickel, and also strong acids, such as trifluoroacetic acid, sulfuric acid, hydrochloric acid, hydrobromic acid, phosphoric acid or perchloric acid or mixtures of any of the abovementioned catalysts.

Although less preferred, suitable catalysts for the process of the invention are also those which, in addition to catalyzing the allophanatization reaction, also catalyze the trimerization of isocyanate groups to form isocyanurate structures, such catalysts being described, for example, in EP-A-0649866, page 4, line 7 to page 5, line 15.

Preferred catalysts for the process of the present invention are zinc compounds of the type described above. Particular preference is given to using zinc (II) n-octanoate, zinc (II) 2-ethyl-1-hexanoate and/or zinc (II) stearate.

The catalyst, if any, is added in the process of the invention in an amount of from 0.001 to 5% by weight, preferably from 0.005 to 1% by weight, relative to the total amount of the reaction mixture.

The addition to the reaction mixture may be in any manner. It is thus possible, for example, to mix any selected catalysts into the polyisocyanate component A) and/or the polyether component B) before the actual conversion begins. Similarly, it is also possible to add the catalyst to the reaction mixture at any time during the urethanization reaction or, if a two-step reaction step is used, also after urethanization, i.e. when the NCO content has reached a value theoretically corresponding to complete conversion of the isocyanate and hydroxyl groups.

According to the process of the invention, the progress of the conversion can be followed by titrimetric analysis of the NCO content. After the determination of the NCO content, the reaction is preferably terminated if the degree of allophanation, i.e.the percentage of urethane groups formed in the reaction mixture from polyether alcohols and polyisocyanates which have been converted into allophanate groups, which can be calculated from the NCO content, reaches 25 to 59%, particularly preferably 30 to 59%. Control of a purely thermal reaction can be effected, for example, by cooling the reaction mixture to room temperature. However, when it is preferred to concomitantly use an allophanate catalyst of the type described, the reaction is generally terminated by addition of a suitable catalyst poison, for example an acid chloride such as benzoyl chloride or isophthaloyl dichloride.

In addition, the type of starting components and the quantitative ratios within the stated numerical ranges in the process according to the invention are selected in the following manner: so that the resulting polyisocyanate mixtures satisfy the values under the conditions a) to c), wherein a) the average NCO functionality is preferably from 2.2 to 9.0, particularly preferably from 2.5 to 5.4, b) the NCO content is preferably from 6.0 to 23.0% by weight, particularly preferably from 8.5 to 22.0% by weight, and c) the content of ethylene oxide units bound to polyether chains is preferably from 5 to 40% by weight, particularly preferably from 7 to 25% by weight.

The values stated for the NCO functionality of the products obtained by the process of the invention relate to the values which can be determined by calculation from the type and functionality of the starting components, according to the following formula:

wherein x represents the proportion of urethane groups which have been converted into allophanate groups in the process according to the invention. The functionality fNCO of the starting polyisocyanate a) can be calculated from the NCO content and the molecular weight determined, for example by Gel Permeation Chromatography (GPC) or vapor pressure permeation.

The process of the invention can optionally be carried out in a suitable solvent which is inert towards isocyanate groups. Suitable solvents are, for example, the known conventional lacquer solvents, such as ethyl acetate, butyl acetate, ethylene glycol monomethyl ether acetate or ethylene glycol monoethyl ether acetate, 1-methoxypropyl-2-acetate, 3-methoxy-n-butyl acetate, acetone, 2-butanone, 4-methyl-2-pentanone, cyclohexanone, toluene, xylene, chlorobenzene, white spirit, highly substituted aromatics, such as those sold under the name Solventnaphtha^*，Solvesso^*，Shellsol^*，Isopar^*，Nappar^*And Diasol^*Carbonates such as dimethyl carbonate, diethyl carbonate, 1, 2-ethylene carbonate and 1, 2-propylene carbonate, lactones such as beta-propiolactone, gamma-butyrolactone, epsilon-caprolactone, epsilon-methyl caprolactone, and solvents such as propylene glycol diacetate, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, diethylene glycol ethyl ether acetate and diethylene glycol butyl ether acetate, N-methylpyrrolidone and N-methylcaprolactam, or any mixture of the above solvents.

The products obtained by the process of the invention consist of transparent, virtually colorless polyisocyanate mixtures of the abovementioned composition which are readily dispersible in water without high shear forces but merely by stirring, so that, in order to obtain stable aqueous dispersions with respect to precipitation at a given composition and molecular weight distribution of the polyether segments, a considerably lower total ethylene oxide unit content is sufficient than in the case of the water-dispersible polyisocyanate mixtures of the prior art obtained by urethanization with polyether alcohols of the same composition and molecular weight distribution. The process of the invention therefore relates to the preparation of highly hydrophilic polyisocyanates which are stable to crystallization and have the same or better dispersibility in water than known polyisocyanate mixtures comprising polyether urethanes and which are distinguished by a higher content of isocyanate groups and a higher functionality. The process of the invention also gives products having a higher NCO content, in addition to a further increase in dispersibility, at the same polyether content as compared with the allophanate-modified polyisocyanate mixtures described in DE-A-19822891 (degree of allophanation of at least 60%).

The excellent dispersibility with low ethylene oxide content in compounds having a high NCO content and high functionality constitutes an advantage, in particular for the use of the polyisocyanate mixtures according to the invention in water-soluble 2C PUR lacquers, since in this way highly crosslinked coatings can be obtained which, in addition to very good solvent-and chemical-resistant properties, in particular also have excellent water resistance owing to the low content of hydrophilic groups.

Before emulsification, other non-hydrophilic polyisocyanates, in particular polyisocyanate lacquers of the type mentioned above, may optionally be added to the polyisocyanate mixtures obtained by the process of the invention, the quantitative ratios being preferably chosen such that the resulting polyisocyanate mixtures satisfy the abovementioned conditions a) to c), so that they likewise constitute the polyisocyanate mixtures of the invention, since the latter generally consist of a mixture of (i) and (ii):

(i) the polyisocyanates modified to be hydrophilic according to the invention, and

(ii) unmodified polyisocyanates of the exemplified type.

In the above mixtures, the products obtained by the process according to the invention act as emulsifiers for the subsequently added non-hydrophilic polyisocyanate moieties.

The polyisocyanate mixtures according to the invention constitute valuable starting materials for the preparation of polyurethane plastics by the isocyanate polyaddition process.

The polyisocyanate mixtures used for this purpose are preferably used in the form of aqueous emulsions, in combination with polyhydroxyl compounds dispersed in water, which aqueous emulsions enable the reaction to be carried out in aqueous two-component systems.

The polyisocyanate mixtures according to the invention are particularly preferably used as crosslinkers for lacquer binders or binder components which are dissolved or dispersed in water and have groups which are reactive with isocyanate groups, in particular alcoholic hydroxyl groups, in the production of coatings by using aqueous coating compositions based on said binders or binder components. For this purpose, the crosslinking agent can be combined with the binder or binder component, optionally in emulsified form, by any method or by simple mixing before the treatment of the coating agent using a two-component spray gun.

In this context, mention may be made, as lacquer binding agent or lacquer binding agent component, for example, of polyacrylates which are dissolved or dispersed in water and contain hydroxyl groups, in particular those having a molecular weight of 1000-10000, organic polyisocyanates being used as crosslinking agents, which constitute valuable two-component binders; or a water-dispersible, optionally urethane-modified, hydroxyl-containing polyester resin of the type known in polyester chemistry and alkyd chemistry. Suitable reaction components for the polyisocyanate mixtures according to the invention are in principle all binders which are soluble or dispersible in water and which contain groups which are capable of reacting with isocyanates. They also include, for example, water-dispersible polyurethanes or polyureas which are capable of crosslinking with polyisocyanates owing to the active hydrogen atoms present in the urethane and urea groups.

When the polyisocyanate mixtures according to the invention are used as crosslinker components for aqueous lacquer binding agents, they are generally used in amounts which correspond to an equivalent ratio of NCO groups to groups which are capable of reacting with NCO groups, in particular alcoholic hydroxyl groups, of from 0.5: 1 to 2: 1.

The polyisocyanate mixtures according to the invention can also optionally be incorporated in auxiliary amounts into non-functionalized aqueous lacquer binders in order to achieve very specific properties, for example as an additive for improving adhesion.

The polyisocyanate mixtures according to the invention can of course also be used in aqueous one-component PUR stoving systems in combination with the abovementioned aqueous lacquer binders and lacquer binder components in protected form with protective agents (blocking agents) known per se from polyurethane chemistry. Suitable protecting agents are, for example, diethyl malonate, acetoacetate, acetoxime, butanone oxime, epsilon-caprolactam, 3, 5-dimethylpyrazole, 1, 2, 4-triazole, dimethyl-1, 2, 4-triazole, imidazole or any mixture of these protecting agents.

The lower surface of the aqueous coating formed by means of the polyisocyanate mixtures according to the invention can be any substrate, such as metal, wood, glass, stone, ceramic materials, concrete, hard and soft plastics, textiles, leather and paper, which can optionally be provided with a conventional primer before coating.

In general, the aqueous coating compositions prepared from the polyisocyanate mixtures according to the invention, optionally with the incorporation of auxiliaries and additives customary in the paint industry, such as flow-control agents, colorants, fillers, flatting agents or emulsifiers, have good paint properties already dried at room temperature.

Of course, they can also be dried at elevated temperatures under forced conditions or dried at temperatures up to 260 ℃.

Owing to their excellent emulsifiability in water, which enables them to be distributed homogeneously, in particular finely divided, in aqueous lacquer binders, the use of the polyisocyanate mixtures according to the invention as crosslinkers for aqueous polyurethane lacquers leads to coatings having outstanding optical properties, in particular high surface gloss, flow and high transparency.

In addition to their preferred use as crosslinkers for aqueous 2C PUR paints, the polyisocyanate mixtures according to the invention are also particularly suitable as crosslinkers for water-dispersible adhesives, coatings for leather and textiles or printing pastes for textiles, as AOX-free paper-making auxiliaries or as additives for inorganic building materials, for example concrete compositions or mortar compositions.

The following examples further illustrate the invention. "degree of allophanation" means the percentage of urethane groups formed from polyether alcohols and polyisocyanates which have been converted to allophanates-this percentage can be calculated from the NCO content. All percentages are by weight.

Examples

Example 1

850g (4.39 equivalents) of an isocyanurate group-containing 1, 6-diisocyanatohexane (HDI) -based polyisocyanate having an NCO content of 21.7%, an average NCO functionality of 3.5 (according to GPC), a monomeric HDI content of 0.1% and a viscosity of 3000mPa.s (23 ℃) are mixed at 100 ℃ under dry nitrogen with 150g (0.30 equivalents) of a monofunctional polyethylene oxide polyether starting with methanol having an average molecular weight of 500, corresponding to an NCO/OH equivalent ratio of 14.6: 1, over the course of 30min, and stirring is continued at this temperature until the NCO content of the mixture has fallen to 17.2% corresponding to complete urethanization after about 2 hours. The allophanatization reaction was started by adding 0.01g 2-zinc ethyl-1-hexanoate (II). The temperature of the reaction mixture rose to 103 ℃ due to the heat released by the reaction. The progress of the reaction can be followed by NCO titration. After the NCO content had reached 16.7%, the reaction was stopped by adding 0.01g of benzoyl chloride and the reaction mixture was cooled to room temperature. The virtually colorless, transparent polyisocyanate mixtures obtained according to the invention have the following characteristic data:

solid content: 100 percent

NCO content: 16.6 percent

NCO functionality: 3.6

Viscosity (23 ℃): 6300mPa.s

Ethylene oxide content: 14.0 percent

Degree of allophanation: 46 percent.

Example 2

850g (4.39 equivalents) of the HDI isocyanurate group-containing polyisocyanate based on HDI described in example 1 were mixed at 100 ℃ under dry nitrogen within 30min with 150g (0.30 equivalents) of the polyethylene oxide polyether described in example 1 corresponding to an NCO/OH equivalent ratio of 14.6: 1, and stirring was continued at this temperature until after about 2 hours the NCO content of the mixture had fallen to 17.2% corresponding to complete urethanization. The allophanatization reaction was started by adding 0.01g 2-zinc ethyl-1-hexanoate (II). The temperature of the reaction mixture rose to 105 ℃ due to the heat released by the reaction. The progress of the reaction can be followed by NCO titration. After the NCO content had reached 16.9%, the reaction was stopped by adding 0.01g of benzoyl chloride and the reaction mixture was cooled to room temperature. The virtually colorless, transparent polyisocyanate mixtures obtained according to the invention have the following data:

solid content: 100 percent

NCO content: 16.8 percent

NCO functionality: 3.5

Viscosity (23 ℃): 4800mPa.s

Ethylene oxide content: 14.0 percent

Degree of allophanation: 31 percent.

Example 3

830g (4.58 equivalents) of an HDI-based polyisocyanate comprising isocyanurate groups and having an NCO content of 23.2%, an average NCO functionality of 3.2 (according to GPC), a monomeric HDI content of 0.2% and a viscosity of 1200mPa.s (23 ℃) were mixed at 100 ℃ under dry nitrogen with 170g (0.49 equivalents) of a monofunctional polyethylene oxide polyether starting with methanol and having an average molecular weight of 350, corresponding to an NCO/OH equivalent ratio of 9.3: 1, over the course of 30min, and the NCO content of the mixture was then reduced to 17.2% corresponding to complete urethanization after further stirring at this temperature until about 2 hours. The allophanatization reaction was started by adding 0.01g 2-zinc ethyl-1-hexanoate (II). The temperature of the reaction mixture rose to 108 ℃ due to the heat released by the reaction. The progress of the reaction can be followed by NCO titration. After the NCO content had reached 16.5%, the reaction was stopped by adding 0.01g of benzoyl chloride and the reaction mixture was cooled to room temperature. The virtually colorless, transparent polyisocyanate mixtures obtained according to the invention have the following characteristic data:

solid content: 100 percent

NCO content: 16.3 percent

NCO functionality: 3.2

Viscosity (23 ℃): 2400mPa.s

Ethylene oxide content: 15.4 percent

Degree of allophanation: and 43 percent.

Example 4 (comparative example according to DE-A-19822891)

850g (4.39 equivalents) of the HDI-based polyisocyanate containing isocyanurate groups described in example 1 are mixed at 100 ℃ under dry nitrogen within 30min with 150g (0.30 equivalent) of the polyether alcohol described in example 1 and then stirred further at this temperature until after approximately 2 hours the NCO content of the mixture has fallen to 17.2% corresponding to complete urethanization. The allophanatization reaction was started by adding 0.01g 2-zinc ethyl-1-hexanoate (II). The temperature of the reaction mixture rose to 104 ℃ due to the heat released by the reaction. At the end of the exothermic reaction, about 30min after addition of the catalyst, the reaction was stopped by addition of 0.01g of benzoyl chloride and the reaction mixture was cooled to room temperature. The virtually colorless, transparent polyisocyanate mixtures obtained were characterized by the following data:

solid content: 100 percent

NCO content: 16.0 percent

NCO functionality: 3.9

Viscosity (23 ℃): 7400mPa.s

Ethylene oxide content: 14.0 percent

Degree of allophanation: 92 percent.

Example 5 (comparative example according to EP-A-0206059)

850g (4.39 equivalents) of the HDI-based polyisocyanate containing isocyanurate groups described in example 1 are stirred at 100 ℃ under dry nitrogen, mixed with 150g (0.30 equivalent) of the polyether alcohol described in example 1 within 30min and stirred at this temperature until after about 2 hours the NCO content of the mixture has fallen to 17.2% corresponding to complete urethanization. After cooling the reaction mixture to room temperature, a colorless, transparent polyisocyanate mixture was obtained which was characterized by the following data:

solid content: 100 percent

NCO content: 17.2 percent of

NCO functionality: 3.3

Viscosity (23 ℃): 3600mPa.s

Ethylene oxide content: 14.0 percent

Degree of allophanation: 0 percent.

Example 6 (comparative example according to EP-A-0206059)

800g (4.13 equivalents) of the HDI-based polyisocyanate containing isocyanurate groups described in example 1 are stirred at 100 ℃ under dry nitrogen, mixed with 200g (0.40 equivalent) of the polyether alcohol described in example 1 within 30min and stirred at this temperature until after about 2 hours the NCO content of the mixture has fallen to 15.7% corresponding to complete urethanization. After cooling the reaction mixture to room temperature, a colorless, transparent polyisocyanate mixture was obtained which was characterized by the following data:

solid content: 100 percent

NCO content: 15.7 percent

NCO functionality: 3.2

Viscosity (23 ℃): 3700mPa.s

Ethylene oxide content: 18.7 percent

Degree of allophanation: 0 percent.

Example 7 (comparative example according to DE-A-19822891)

830g (4.58 equivalents) of the HDI-based polyisocyanate containing isocyanurate groups described in example 3 are mixed at 100 ℃ under dry nitrogen with 170g (0.49 equivalents) of the polyether alcohol described in example 3 within 30min and then stirred further at this temperature until after about 2 hours the NCO of the mixture has fallen to 17.2% corresponding to complete urethanization. The allophanatization reaction was started by adding 0.01g of 2-zinc ethyl-1-hexanoate (II). The temperature of the reaction mixture rose to 108 ℃ due to the heat released by the reaction. At the end of the exothermic reaction, approximately 20min after addition of the catalyst, the reaction was stopped by addition of 0.01g of benzoyl chloride and the reaction mixture was cooled to room temperature. The resulting colorless, transparent polyisocyanate mixtures were characterized by the following data:

solid content: 100 percent

NCO content: 15.2 percent

NCO functionality: 3.8

Viscosity (23 ℃): 2900mPa.s

Ethylene oxide content: 15.4 percent

Degree of allophanation: 95 percent.

Example 8 (comparative example according to EP-A-0540985)

830g (4.58 equivalents) of the HDI-based polyisocyanate containing isocyanurate groups described in example 3 are mixed at 100 ℃ under dry nitrogen with 170g (0.49 equivalents) of the polyether alcohol described in example 3 within 30min and then stirred further at this temperature until after about 2 hours the NCO of the mixture has fallen to 17.2% corresponding to complete urethanization. After cooling the reaction mixture to room temperature, a colorless, transparent polyisocyanate mixture was obtained with the following characteristic data:

solid content: 100 percent

NCO content: 17.2 percent of

NCO functionality: 2.9

Viscosity (23 ℃): 1600mPa.s

Ethylene oxide content: 15.4 percent

Degree of allophanation: 0 percent.

Example 9 (emulsion preparation)

In each case 28g of the polyisocyanate mixture obtained in examples 1, 2 and 3 and the reference polyisocyanate obtained in examples 4, 5, 6 and 7 were diluted with 12g of 1-methoxypropyl-2-acetate and introduced into a conical flask with 100g of deionized water and stirred for 1min with a 900 rpm electromagnetic stirrer. As a measure of the dispersibility of the different polyisocyanate mixtures, the average particle size of the emulsions formed was measured with a "Zetasizer" instrument from Malvern Instruments. The following table shows the measured values:

polyisocyanate mixtures derived from	Degree of allophanation [% ]]	Average particle size [ nm ]]
			Example 1	46	75
Example 2	31	83
			Example 4 (reference)	92	174
Example 5 (reference)	0	434
			Example 6 (reference)	0	88
Example 3	43	118
			Example 7 (reference)	95	169
Example 8 (reference)	0	696

Comparison shows that the polyisocyanate mixtures prepared according to the invention (examples 1, 2, 3) exhibit distinctly better dispersibility than polyisocyanate mixtures of the same overall composition prepared according to DE-A-19822891 (examples 4 and 7) and polyisocyanate mixtures of the same overall composition prepared according to EP-A-0206059 (example 5) and EP-A-0540985 (example 9), in which the polyether chains are exclusively linked to the polyisocyanates viｃA urethane bonds. In order to obtain ｃA similarly good dispersibility, the polyurethane-modified polyisocyanate mixtures prepared according to EP-A-0206059 (example 6) require ｃA significantly higher content of ethylene oxide units than the polyisocyanate mixtures according to the invention (examples 1 and 2).

Example 10 (use)

100 parts by weight of an aqueous, cosolvent-free, hydroxy-functional polyacrylate dispersion having a solids content of 43% and a hydroxyl content of 2.5%, based on the solid resin, consisting essentially of 48.0% of methyl methacrylate, 27.4% of propyleneOlefine acid n-butyl ester, 21.6% hydroxy-C₃Alkyl methacrylates (addition product of propylene oxide to methacrylic acid) and 3.0% acrylic acid) with 0.5 part by weight of a commercially available defoamer (Foamaster)^*TCX, Henkel). 16.0 parts by weight of the polyisocyanate according to example 1 of the invention (corresponding to an equivalent ratio of isocyanate groups to alcoholic hydroxyl groups of 1: 1) are added, the mixture is homogenized by intensive stirring (2000 rpm), and the solids content is subsequently adjusted to 40% by adding water.

For comparison, in each case a clear lacquer was prepared in the same way from the following components: 100 parts by weight of the above-mentioned hydroxy-functional polyacrylate dispersion and 16.6 parts by weight of the polyisocyanate obtained from example 4 according to DE-A-19822891 and 15.5 parts by weight of the polyisocyanate obtained from example 5 according to EP-A-0206059 (in each case corresponding to an equivalent ratio of isocyanate groups to alcoholic hydroxyl groups of 1: 1).

In all cases, the treatment time for the ready-to-use ingredients was about 3 hours. The lacquer was applied as a wet film with a thickness of 150 μm (about 60 μm dry thickness) on a glass plate and exposed to air under forced conditions (30min/60 ℃) for 15 minutes. The resulting film layer of the paint had the following properties:

polyisocyanate derived from	Example 1	Example 4 (comparative)	Example 5 (comparative)
				Gloss 20 °	86	85	75
Gloss, Visiona)	0	1	3
				Haze degree	22	57	147
Pendulum hardness [ s ]]After 1d/7db)	99/137	106/139	84/125
				Solvent resistancec)Water (30min) isopropanol/water 1: 1(1min) MPA/xylene 1: 1(1min) butanediol (1min) acetone (1min)	00000	00000	22223

a) Evaluation: 0 (very good) -5 (bad)

b) Pendulum hardness according to K * nig (DIN53157)

c) Evaluation: 0-5(0 ═ paint film unchanged; 5 ═ complete dissolution)

The comparison shows that the coatings obtained with the polyisocyanate mixtures according to the invention (example 1) differ from the paint films prepared with the polyisocyanate mixtures according to DE-A-19822891 (example 4) having ｃA higher degree of allophanation in that the emulsifiability is better and the haze is low, and that, in addition, the coatings according to the invention also exhibit considerably higher solvent and water resistance than the paint films obtained with the polyisocyanate mixtures according to EP-A-0206059 (example 5).

Claims (10)

1. Water-dispersible polyether-modified polyisocyanate mixtures based on aliphatic, cycloaliphatic, araliphatic and/or aromatic diisocyanates having

a) An average isocyanate functionality of 2.2 to 5.4,

b) an isocyanate group content of 8.5-22.0 wt.%, and

c) the content of incorporated ethylene oxide units in the polyether chains is from 7 to 25 wt.%, so that, on statistical average, the polyether chains contain from 7 to 30 ethylene oxide units,

characterized in that the polyether chain is linked in a proportion of 20 to 59 mol% via allophanate groups to two polyisocyanate molecules, each of which is synthesized from at least two diisocyanates.

2. A water-dispersible polyisocyanate mixture according to claim 1, characterized in that the polyether chains are linked in a proportion of 20 to 59 mol% via allophanate groups to polyisocyanate molecules, each polyisocyanate molecule containing two isocyanurate groups.

3. Water-dispersible polyisocyanate mixture according to claim 1, characterized in that the polyether chains are linked in a proportion of 20 to 59 mol% via allophanate groups to polyisocyanate molecules, each polyisocyanate molecule containing two isocyanurate groups and containing exclusively aliphatically and/or cycloaliphatically bound isocyanate groups.

4. A process for preparing a water-dispersible polyisocyanate mixture according to claim 1, characterized in that: make it

A) A polyisocyanate component having an average functionality of from 2.3 to 4.5, an aliphatic, cycloaliphatic, araliphatic and/or aromatic bound isocyanate group content of from 14.0 to 24.0 wt.%, a monomeric diisocyanate content of less than 0.5 wt.%, and

B) a monovalent polyoxyalkylene polyether alcohol comprising, on statistical average, 7 to 30 ethylene oxide units,

reacting with one another while maintaining an NCO/OH equivalent ratio of from 8: 1 to 140: 1, so that from 20 to 59% of the urethane groups initially formed by the NCO/OH reaction continue to react to form allophanate groups, and, in addition, the type and quantity ratios of the starting components are selected such that the resulting conversion product meets the conditions as claimed in claim 1.

5. A process as claimed in claim 4, wherein polyisocyanates containing isocyanurate groups and based on 1, 6-diisocyanatohexane, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane and/or 4, 4' -diisocyanatodicyclohexylmethane are used as polyisocyanate component A).

6. Process according to claim 4, characterized in that the conversion is carried out in the presence of a catalyst which promotes the formation of allophanate groups.

7. A process as claimed in claim 6, characterized in that an organozinc compound is used as allophanation catalyst.

8. Process according to claim 6, characterized in that zinc (II) n-octanoate, zinc (II) 2-ethyl-1-hexanoate and/or zinc (II) stearate are used as allophanatization catalysts.

9. Use of the polyisocyanate mixtures according to claim 1 as starting materials for the preparation of polyurethane plastics.

10. Use of the polyisocyanate mixtures according to claim 1 as crosslinkers for water-soluble or water-dispersible lacquer binders or lacquer binder components in the preparation of coatings using aqueous coating agents based on the abovementioned binders or binder components.