MXPA01000635A - Monomer-poor polyurethane bonding agent having an improved lubricant adhesion - Google Patents

Abstract

The invention relates to a polyurethane bonding agent which has a low content of highly volatile residual monomers, which essentially forms no migrates and which has an improved lubricant adhesion. The invention also relates to a method for producing the inventive bonding agent and to an adhesive containing such a polyurethane bonding agent. In addition, the invention relates to the use of a low-viscous polyurethane bonding agent, said bonding agent carrying isocyanate groups (NCO groups), during the production of adhesives, especially adhesives containing one and two constituents, for example, provided for gluing web materials comprised of e.g. paper, plastic and/or aluminum, coatings, especially lacquers, dispersion paints, casting resins and shaped bodies.

Description

POLYURETHANE AGGLOMERATING AGENT WITH LOW CONTENT OF MONOMERS HAVING BETTER ADHESION OF THE LUBRICANT This invention relates to a polyurethane binder and to a process for producing low viscosity polyurethane binder containing isocyanate groups which have only a low content of easily volatile residual monomers, essentially non-migrating forms and which exhibit improved lubricant adhesion. The invention also relates to the use of a low viscosity polyurethane binder containing isocyanate groups (NCO groups) in the production of adhesives, more particularly, one-component and two-component adhesives, for example, for agglomerating materials of continuous forms, for example, paper, plastic and / or aluminum, coatings, more particularly lacquers, emulsion paints and molding resins as well as molded parts. Isocyanate terminated polyurethane prepolymers have been known for some time. These can quickly be elongated in their chain or crosslinked with suitable compounds, usually polyhydric alcohols, to form high molecular weight materials. Polyurethane prepolymers have become important in many fields of application, including for example the production of adhesives, coatings, molding resins and castings. To obtain isocyanate-terminated polyurethane prepolymers, it is common practice to react polyhydric alcohols with an excess of polyisocyanate, usually at least predominantly diisocyanates. The molecular weight can be controlled at least approximately by the ratio of the OH groups to the isocyanate groups. While a ratio of OH groups to isocyanate groups of about 1: 1 leads to generally high molecular weights, a statistical average of one molecule of diisocyanate - where diisocyanates are used - is attached to each OH group where the OH: isocyanate group ratio is approximately 2: 1, so that ideally no oligomerization or chain extension occurs in the course of the reaction. In practice, however, chain elongation reactions are impossible to eliminate completely, even in the latter case, with the result that, at the completion of the reaction, a certain amount of the component used in excess is left without having account in reaction time. If, for example, diisocyanate is used as the excess component, a generally considerable proportion of this component remains lagged in the reaction mixture for the reasons explained above.

The presence of such components is particularly problematic when they consist of readily volatile diisocyanates. The vapors of these diisocyanates are often harmful to the skin and the application of products with a high content of such volatile isocyanates requires measures to be developed by the user to protect the people involved in the processing of the product, more particularly measures of Elaboration to keep the surrounding air clean to breathe. Since protective measures and cleaning measures generally involve considerable expense, it is a necessity, on the part of the user, for products having a low percentage of content of easily volatile diisocyanates depending on the diisocyanate used. In the context of the present invention, substances "easily volatile" are understood to be substances having a vapor pressure, at about 30 ° C, of more than about 0.0007 mmHg or a boiling point of less than about 190 ° C (70 mPa). If the low volatility diisocyanates, more particularly, the widely used bicyclic diisocyanates, for example, diphenyl methane diisocyanates, are used in place of the readily volatile diisocyanates, polyurethane binders with a viscosity normally outside the appropriate range are obtained by processing methods. simple In cases such as this one, the viscosity of the polyurethane prepolymers can be reduced by the addition of suitable solvents, although this is not consistent with the absence of solvents normally demanded. Another way to reduce the viscosity without solvents is to add an excess of monomeric polyisocyanates that are incorporated in the bond or coatings (reactive diluent) in the course of a subsequent curing / hardening process (after the addition of a hardener or by curing under the influence of humidity). Since the viscosity of the polyurethane prepolymers can currently be reduced in this way, the generally incomplete reaction of reactive diluent often leads to the presence in the bond or coating, of free monomeric polyisocyanates that are capable of "migrating", for example within the lining or joint or, in some cases, even in the coated or aggrated materials themselves. Corresponding constituents of a coating or bond are often referred to by experts as "migrants". On contact with moisture, the isocyanate migrant groups are continuously reacting to form amino groups. It is suspected that the aromatic amines normally formed in this way have a carcinogenic effect. Migrants are often not tolerable, especially in the field of packaging, because any migration of migrants through the packaging material could result in contamination of the packaged product and the consumer could inevitably come into contact with the migrants when using the product. . Consequently, the migrants in question are undesirable especially in the field of packaging, especially in the packaging of food. To avoid the disadvantages described above, EP-A 0 118 065 proposes to produce polyurethane prepolymers by a two-stage process. In the first stage of this process, a monocyclic diisocyanate reacts with a polyhydric alcohol in a ratio OH group: isocyanate group of <1 and, in the second step, a bicyclic diisocyanate reacts with polyhydric alcohols in an OH group: isocyanate group ratio of < 1 in the presence of the prepolymer prepared in the first step. A ratio of OH groups to isocyanate groups of 0.65 to 0.8: 1 and, preferably, 0.7 to 0.75: 1 is proposed for the second-stage. The prepolymers obtainable in this manner still have viscosities of 2500 mPas, 7150 mPas and 9260 mPas at high temperatures (75 ° C and 90 ° C). Lubricant compatibility was not mentioned.

EP-A 0 019 120 refers to a two-stage process for the production of weather-resistant elastic materials in the form of a sheet. In the first step of this process, toluene diisocyanate (DIT) reacts with at least equimolar amounts of a polyol, and the reaction product obtained subsequently is reacted with diphenyl methane diisocyanate (MDI) and a polyol. The polyurethane binders obtained in this way are said to be capable of curing with water or with atmospheric humidity. Although the processes described give products with a relatively low viscosity, the content of readily volatile free diisocyanates (in the present case TDI) is still high (0.7% by weight) and can only be reduced when methods that consume time and intensive energy are used. , for example, thin layer distillation, to remove excess easily volatile diisocyanate. To date, the application of the unpublished German Patent DE 197 49 834.5 relates to low polyurethane binders in monomers, describing a bicomponent polyurethane binder with a low content of monomers and a low content of migrants. Films used, for example, for food packaging frequently have a high content of lubricants. A common lubricant is, for example, erucic acid amide (EAA) which is often present in the film in amounts of more than about 400 ppm. The conventional adhesives used to agglomerate such films to form laminates often show deterioration in layered adhesion with an increased lubricant content in the film to be bonded. An increase in productivity is achieved with modern efficient packaging machines by a considerable increase in the speed of operation of the machines. These films used for this purpose generally have a distinctly increased lubricant content - often 600 ppm or more - relative to relatively slow packing machines. Unfortunately, many conventional adhesives show unsatisfactory adhesion in films with a lubricant content of this order. As a result, laminated films produced in this way often show inadequate adhesion in the sealing of the joint, especially after curing. Accordingly, the problem solved by the present invention provides a polyurethane binder that will have a low viscosity and a low residual content of less than about 1% by weight of readily volatile diisocyanates. In the case of toluene diisocyanate (TDI), the residual content of the readily volatile isocyanate should be less than about 0.1% by weight. A further problem solved by the present invention was to provide a polyurethane binder having a low percentage content of "migrants", that is, a low percentage content of monomeric polyisocyanates. Another problem faced by the present invention was to provide a process for the production of a polyurethane binder with the aforementioned properties. Yet another problem solved by the invention was to provide a polyurethane binder and an adhesive which, in addition to the aforementioned properties in relation to its content of readily volatile isocyanates and a low content of migrants, should additionally have improved lubricant compatibility, i.e. example better adhesion of the laminate or better adhesion in the sealing of the joint in the agglomeration of films with a high content of lubricant. The present invention relates to a polyurethane binder with a low content of readily volatile isocyanate-functional monomers, containing at least components A, B and C, in which: a) a polyurethane polymer containing at least two isocyanate groups or a mixture of two or more polyurethane prepolymers containing at least two isocyanate groups are present as component A, at least one polyurethane prepolymer containing at least two differently bound types of isocyanate groups or two different polyurethane prepolymers containing at least two types of isocyanate groups differently bonded in pairs of which at least one type has a lower reactivity than isocyanate-reactive groups other than the other type (s), and b) at least one difunctional isocyanate that does not contain a nitrogen atom that is not part of an NCO group, or a mixture of two or more of the same, is present as component B and c) at least one difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two, containing at least one nitrogen atom that is not part of an NCO or urethane group Isocyanate molecule is present as component C. "Low viscosity" in the context of the present invention means a viscosity (Brookfield) at 50 ° C of less than 5,000 mPas. In the context of the present invention, the term "polyurethane binder" shall be understood to mean a mixture of molecules each containing at least two isocyanate groups, in which the content of molecules with a molecular weight of more than 500 is at least about 50% by weight and, preferably, at least about 60% by weight or about 70% by weight.

A polyurethane prepolymer containing at least two isocyanate groups or a mixture of two or more polyurethane prepolymers containing at least two isocyanate groups, which can preferably be obtained by reacting a polyol component with at least one difunctional isocyanate, are used as component A. In the context of the present invention, a "polyurethane prepolymer" is understood to be the compound that can be obtained, for example, when a polyol component is reacted with an at least difunctional isocyanate.

Accordingly, the term "polyurethane prepolymer" embraces relatively low molecular weight compounds, formed, for example, in the reaction of a polyol with an excess of polyisocyanate, and also oligomeric or polymeric compounds. The term "polyurethane prepolymer" also encompasses compounds formed, for example, in the reaction of a trihydric or tetrahydric polyol with a molar excess of diisocyanates, based on the polyol. In this case, a molecule of the resulting compound carries several isocyanate groups. The molecular weights in relation to the polymeric compounds represent the average molecular weight number (Mn), unless otherwise indicated. In general, the polyurethane prepolymers used for the purposes of the present invention have a molecular weight in the range from about 150 to about 15,000 or in the range from about 500 to about 10,000, for example, of the order of 5,000, but especially in the range from about 700 to about 2,500. In a preferred embodiment of the invention, the polyurethane prepolymer containing two isocyanate groups or at least one of the polyurethane prepolymers present in the polyurethane polymer mixture containing two or more isocyanate groups has at least two types of isocyanate groups differently. joined, of which at least one type has a lower reactivity towards the isocyanate-reactive groups than the other type or the other types of isocyanate groups. The isocyanate groups with a relatively low reactivity towards the isocyanate-reactive groups (by comparison with at least one other isocyanate group present in the polyurethane binder) are also referred to hereafter as "less reactive isocyanate groups" while the corresponding isocyanate group with higher Reactivity towards the isocyanate-reactive compounds is also referred to as the "most reactive isocyanate group". According to the present invention, therefore, a difunctional polyurethane prepolymer, for example, containing two isocyanate groups differently attached, one of the isocyanate groups having a greater reactivity towards the isocyanate salt reactive groups than the other isocyanate group, can be used as component A. A polyurethane prepolymer such as this can be obtained, for example, by the reaction of a dihydric alcohol with compounds containing two different isocyanate groups for example, difunctional, the reaction being carried out, for example, as In this way, on average, each molecule of the dihydric alcohol reacts with a molecule of the compounds containing different isocyanate groups. A trifunctional or higher polyurethane prepolymer can also be used as component A, in which case a molecule of the polyurethane prepolymer, for example, can contain a different number of less reactive and more reactive isocyanate groups. In another preferred embodiment, mixtures of two or more different polyurethane prepolymers can be used as component A. The mixtures mentioned can be polyurethane prepolymers in which the individual polyurethane molecules carry identically linked isocyanate groups. Accordingly, at least two different types of polyurethane molecules that differ at least in the nature of the isocyanate groups they carry must be present in the mixture. In this modality, at least one of the isocyanate groups of the most reactive type and one of the least reactive type, ie a polyurethane molecule containing at least two reactive isocyanate groups and a polyurethane molecule containing at least two less reactive isocyanate groups should be present in the mixture as a whole. In addition to the molecules containing one or more identically linked isocyanate groups, the mixture may also contain other molecules carrying one or more identically linked isocyanate groups and one or more isocyanate groups differently attached. Component A or at least part of component A can also be formed, for example, by the reaction products of difunctional or higher alcohols with an amount at least equimolar (based on the OH groups of the difunctional alcohol or higher) of weight diisocyanates low molecular weight with a molecular weight of up to about 400. In a preferred embodiment, the polyurethane prepolymer used as component A or the mixture of two or more polyurethane prepolymers contain at least one urethane group per molecule. In another preferred embodiment of the invention, component A is prepared by a reaction of at least two steps in which: c) in a first step, a polyurethane prepolymer is prepared from at least one isocyanate and at least one first polyol component, the NCO: OH ratio being less than 2 and still OH groups are still present in the polyurethane prepolymer, and d) in a second step, another at least difunctional isocyanate is reacted with the polyurethane prepolymer of the first stage , the isocyanate groups of the isocyanate added in the second stage having greater reactivity towards the isocyanate-reactive compounds than at least the predominant percentage of the isocyanate groups present in the polyurethane prepolymer of the first stage. In another preferred embodiment, the at least difunctional isocyanate is added in a molar excess, based on the free OH groups of component A. In another preferred embodiment, component A is prepared in a reaction of at least two steps in which e) in a first step, a polyurethane prepolymer is prepared from at least one difunctional isocyanate and at least one first polyol component, the ratio in NCO: OH being less than 2 and still the free OH groups present in the polyurethane prepolymer, and f) in a second step, another at least difunctional isocyanate and another polyol component are reacted with the polyurethane prepolymer of the first stage, the isocyanate groups of the isocyanate added in the second stage have a greater reactivity towards the compounds isocyanate reagents that at least the predominant percentage of the isocyanate groups present in the polyurethane prepolymer of the first stage. According to the invention, the OH: NCO ratio in the production of component A in the second stage is preferably about 0.001 to less than 1: 1, and more particularly, 0.005 to about 0.8: 1. In a preferred embodiment of the invention, the OH: NCO ratio in the second stage is about 0.2 to 0.6: 1. In another preferred embodiment of the invention, the relationship OH: NCO in the first stage is less than 1 and, more particularly, 0.5 to 0.7: 1, the relations described optionally being also maintained for the second stage. In the context of the present invention, the term "polyol component" encompasses a simple polyol or a mixture of two or more polyols that can be used for the production of polyurethanes. A polyol is understood as a polyhydric alcohol, that is, a compound that contains more than one OH group in the molecule. Various polyols can be used as the polyol component for the production of component A. These include, for example, aliphatic alcohols containing 2 to 4 OH groups per molecule. The OH groups can be primary and secondary. Suitable aliphatic alcohols include, for example, ethylene glycol, propylene glycol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, heptane-1,7-diol, octane-1. , 8-diol and higher homologs, or isomers thereof, which the expert can obtain by extension of the hydrocarbon chain by a CH2 group each time or by introduction of branches in the carbon chain. Also suitable are higher alcohols such as, for example, glycerol, trimethylolpropane, pentaerythritol and oligomeric ethers of any of the substances mentioned individually or in the form of mixtures with one another of two or more of the aforementioned ethers. Other polyol components suitable for the production of component A are the reaction products of low molecular weight polyhydric alcohols with alkylene oxides, also called polyethers. The alkylene oxides preferably contain 2 to 4 carbon atoms. Suitable reaction products of the type in question are, for example, the reaction products of ethylene glycol, isomers of butanediols or hexanediols with ethylene oxide, propylene oxide or butylene oxide or mixtures of two or more thereof. The reaction products of polyhydric alcohols, such as glycerol, trimethylolethane and / or trimethylolpropane, pentaerythritol or sugar alcohols, with the abovementioned alkylene oxides to form polyether polyols are also suitable. Polyether polyols with a molecular weight of from about 100 to about 10,000 and preferably in the range from about 200 to about 5,000 are particularly suitable. According to the invention, propylene glycol with a molecular weight of about 300 to about 2,500 is more particularly preferred. Other polyol components suitable for the production of component A are polyether polyols obtained, for example from the polymerization of tetrahydrofuran. The polyethers are reacted in a known manner by reacting an initial compound containing a reactive hydrogen atom with alkylene oxides, for example ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran or epichlorohydrin or mixtures thereof. two or more of them. Suitable starting compounds are, for example, water, ethylene glycol, 1,2- or 1,3-propylene glycol, 1,4- or 1,3-butylene glycol, hexane-1,6-diol, octane-1, 8-diol, neopentyl glycol, 1,4-hydroxymethyl cyclohexane, 2-methyl propane-1,3-diol, glycerol, trimethylol propane, hexane-1,2,6-triol, butane-1,2,4-triol , trimethylol ethane, pentaerythritol, mannitol, sorbitol, methyl glucosides, sugars, phenol, isononylphenol, resorcinol, hydroquinone, 1,2,2- or 1,1,2-tris- (hydroxyphenyl) -ethane, ammonia, methyl amine, ethylenediamine , tetra- or hexamethylenediamine, triethanolamine, aniline, phenylenediamine, 2,4- and 2,6-diaminotoluene and polyphenylpolymethylene polyamines which can be obtained by condensation of aniline / formaldehyde. Polyethers modified by vinyl polymers are also suitable for use as a polyol component. Products such as these may be obtained, for example, by polymerization of styrene or acrylonitrile or mixtures thereof in the presence of polyethers. Other polyol components suitable for the production of component A are polyester polyols with a molecular weight from 200 to about 10., 000 For example, it is possible to use polyester polyols obtained by reacting low molecular weight alcohols, more particularly ethylene glycol, diethylene glycol, neopentyl glycol, hexanediol, butanediol, propylene glycol, glycerol or trimethylol propane, with caprolactone. Other polyhydric alcohols suitable for the production of polyester polyols are 1,4-hydroxymethyl cyclohexane, 2-methyl propane-1,3-diol, butane-1,2,4-triol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene. glycol, polypropylene glycol, dibutylene glycol and polybutylene glycol. Other suitable polyester polyols can be obtained by polycondensation. In this manner, dihydric and / or trihydric alcohols can be condensed with less than the equivalent amount of dicarboxylic acids and / or tricarboxylic acids or reactive derivatives thereof to form polyester polyols. Suitable dicarboxylic acids are, for example, succinic acid and higher homologs thereof containing up to 16 carbon atoms, unsaturated dicarboxylic acids, such as maleic acid or fumaric acid, and aromatic dicarboxylic acids, more particularly the isomers of phthalic acid , such as phthalic acid, isophthalic acid or terephthalic acid. Citric acid and trimellitic acid, for example, are also suitable tricarboxylic acids. The polyester polyols of at least one of the mentioned dicarboxylic acids and glycerol, which have a residual content of OH groups, are particularly suitable for the purposes of the present invention. Particularly suitable alcohols are hexanediol, ethylene glycol, diethylene glycol or neopentyl glycol or mixtures of two or more thereof. Particularly suitable acids are isophthalic acid and adipic acid and mixtures thereof. In a particularly preferred embodiment of the invention, the polyols used as the polyol component for the production of component A are, for example, dipropylene glycol and / or polypropylene glycol with a molecular weight of from about 400 to about 2500 and polyester polyols, preferably polyester polyols obtained by condensation of hexanediol, ethylene glycol, diethylene glycol or neopentyl glycol or mixtures of two or more thereof and isophthalic acid or adipic acid or mixtures thereof. High molecular weight polyester polyols include, for example, the reaction products of polyhydric alcohols, preferably dihydric, (optionally together with small amounts of trihydric alcohols) and polybasic, preferably dibasic, carboxylic acids. Instead of free polycarboxylic acids, the corresponding polycarboxylic anhydrides or corresponding polycarboxylic acid esters with alcohols preferably containing 1 to 3 carbon atoms can also be used (where possible). The polycarboxylic acids can be aliphatic, cycloaliphatic, aromatic or heterocyclic or both. These can optionally be substituted, for example, by alkyl groups, alkenyl groups, ether groups or halogens. Suitable polycarboxylic acids are, for example, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylene anhydride. tetrahydrophthalic, glutaric anhydride, maleic acid, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, fatty acid dimer or fatty acid trimer or mixtures of two or more thereof, small amounts of monofunctional fatty acids can optionally be present in the reaction mixture. The polyesters may optionally contain a small percentage of terminal carboxyl groups. Polyesters obtainable from lactones, for example e-caprolactone, or hydroxycarboxylic acids, for example γ-hydroxycaproic acid can also be used. Polyacetals are also suitable polyol components. Polyacetals are compounds that can be obtained from glycols, for example diethylene glycol or hexanediol or mixtures thereof with formaldehyde. Polyacetals suitable for use, according to the invention, can also be obtained by polymerization of cyclic acetals. Other polyols suitable for the production of component A are polycarbonates, polycarbonates can be obtained, for example, by the reaction of diols, such as propylene glycol, butane-1,4-diol or hexane-1,6-diol, diethylene glycol , triethylene glycol or tetraethylene glycol or mixtures of two or more thereof, with diaryl carbonates, for example diphenyl carbonate or phosgene.

Polyacrylates with functional OH are also suitable polyol components for the production of component A. These polyacrylates are obtained, for example, by the polymerization of ethylenically unsaturated monomers containing an OH group. Monomers such as these are obtained, for example, by the esterification of ethylenically unsaturated carboxylic acids and dihydric alcohols, the alcohol generally being present in a slight excess. Ethylenically unsaturated carboxylic acids suitable for this purpose are, for example, acrylic acid, methacrylic acid, crotonic acid or maleic acid. The corresponding functional OH esters are, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate or 3-hydroxypropyl methacrylate or mixtures of two or more thereof. To produce the component A the corresponding polyol component is reacted with an isocyanate at least difunctional. The at least difunctional isocyanates suitable for the production of component A are basically any isocyanate containing at least two isocyanate groups although, in general, compounds containing 2 to 4 isocyanate groups, more particularly two isocyanate groups, are preferred for the purposes of present invention.

The at least difunctional isocyanates suitable as the at least difunctional isocyanate for the production of component A are described in the following. These at least difunctional isocyanates are, for example, ethylene diisocyanate, 1-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), cyclobutane-1,3-diisocyanate, cyclohexane-1, 3-, and 1,4-diisocyanate. and mixtures of two or more thereof, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethyl cyclohexane (isophorone diisocyanate, IPDI), 2,4- and 2,6-hexahydrotoluene diisocyanate, tetramethyl xylylene diisocyanate (TMXDI) ), 1,3-and 1,4-phenylene diisocyanate, 2,4- or 2,6-toluene diisocyanate, diphenyl methane-2,4'-diisocyanate, diphenylmethane-2,2 '-diisocyanate or diphenylmethane-4, 4 '-diisocyanate or mixtures of two or more of the aforementioned diisocyanates. According to the invention, other isocyanates suitable for the production of component A are trifunctional or higher isocyanates obtained, for example, by oligomerization of diisocyanates. Examples of such trifunctional and higher polyisocyanates are the triisocyanurates of HDI or IPDI or mixtures thereof or mixed triisocyanurates thereof. In a preferred embodiment of the invention, the diisocyanates contain two isocyanate groups which differ in their reactivity and are used for the production of component A. Examples of such diisocyanates are 2,4- and 2,6-toluene diisocyanate (TDI) and isophorone diisocyanate (IPDI). With non-symmetrical diisocyanates such as these, an isocyanate group generally reacts much faster with groups reactive to the isocyanates, for example OH groups, while the remaining isocyanate group reacts slowly in a comparative manner. Accordingly, in a preferred embodiment, a non-symmetrical monocyclic diisocyanate containing two isocyanate groups that differ in their reactivity, as described above, is used for the production of component A. In a particularly preferred embodiment, 2,4- or 2 , 6-toluene diisocyanate (TDI) or a mixture of the two isomers, but especially pure 2,4-TDI, is used for the production of component A. The polyurethane binder according to the invention contains an isocyanate at least difunctional which does not contains a nitrogen atom that is not part of a group NCO or a mixture of two or more thereof as component B. Component B can be formed, for example, by at least difunctional isocyanates or by a mixture of two or more diisocyanates with an average functionality of at least about two. In a preferred embodiment of the invention, the component B contains at least one difunctional isocyanate, at least of which the NCO groups are more reactive towards the groups reactive to the NCO, for example in a urethanization reaction, thiouretanization, biuretization or allophanatization, compared to the less reactive isocyanate groups of the polyurethane prepolymers present in component A. The isocyanate groups of the difunctional isocyanates present in component B may differ, or they can be substantially identical, in their reactivity. In a preferred embodiment of the invention, the at least difunctional isocyanates of which isocyanate groups are identical in their reactivity, can also be used as component B. Component B generally has a molecular weight of up to about 2,000. However, this molecular weight is preferably lower, for example, less than 1,000, less than about 700 or less than about 400 g / mol. According to the invention, 4,4'-diphenylmethane diisocyanate (MDI), 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and HDI, IPDI or TMXDI, for example, are suitable for use as component B In a preferred embodiment, 4,4'-diphenylmethane diisocyanate (MDI), 2,2'-diphenylmethane diisocyanate or 2,4'-diphenylmethane diisocyanate are used. The polyurethane binder according to the invention contains at least about 3% by weight of component B, based on the polyurethane binder as a total. In a preferred embodiment, the polyurethane binder contains from 5 to about 25% by weight of component B. The polyurethane binder according to the invention preferably has a content of readily volatile isocyanate functional monomers of less than 2% by weight or less of 1% by weight or preferably less than 0.5% by weight. These limits apply in particular to readily volatile isocyanate compounds which have only limited potential damage to those involved in their processing, for example isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tetramethyl xylylene diisocyanate (TMXDI) or cyclohexane diisocyanate. In the case of certain readily volatile isocyanate compounds, especially those which represent a serious risk to the people involved in their processing, their content of the polyurethane binder according to the invention is preferable less than 0.3% by weight and more preferably less than 0.1% in weigh. These particular isocyanate compounds include, especially toluene diisocyanate (TDI). In another preferred embodiment of the invention, the polyurethane binder has a TDI and HDI content of less than 0.05% by weight. The polyurethane binder according to the invention contains at least one difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two, which contains at least one nitrogen atom which is not part of an NCO or urethane group. isocyanate as component C. Accordingly, carbodiimides containing NCO obtained by reaction of diisocyanates under suitable conditions and in the presence of suitable catalysts are suitable for use in component C. Isocyanates suitable for the formation of carbodiimides are, for example, compounds with the general structure 0 = C = NXN = C = 0, wherein X is an aliphatic, alicyclic or aromatic radical, preferably an aliphatic or alicyclic radical with conditions of 4 to 18 carbon atoms. Examples of suitable isocyanates are 1, 5-naphthylene diisocyanate, 4,4 '-diphenyl methane diisocyanate (MDI), hydrogenated MDI (Hi2-MDI), xylylene diisocyanate (XDI), tetramethyl xylylene diisocyanate (TMXDI), 4,4' - diphenyl dimethyl methane diisocyanate, di- and tetraalkylene diphenyl methane diisocyanate, 4, '-dibenzyl diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, the isomers of toluene diisocyanate (TDI), 1-methyl-2, 4 -diisocyanatocyclohexane, 1,6-diisocyanato-2,2,4-trimethylhexane, 1,6-diisocyanato-2,4,4-trimethylhexane, 1-isocyanato-methyl-3-isocyanato-1,5,5-trimethyl cyclohexane (IPDI), chlorinated and brominated diisocyanates, diisocyanate containing phosphorus, 4,4'-diisocyanatophenyl perfluoroethane, tetramethoxybutane-1,4-diisocyanate, 1,4-butane diisocyanate, 1,6-hexane diisocyanate (HDI), dicyclohexylmethane diisocyanate, cyclohexane-1 , 4-diisocyanate, ethylene diisocyanate, bis-isocyanatoethyl ester of phthalic acid, diisocyanates containing reactive halogen atoms, such as l-chloromethylphenyl-2,4-diisocyanate, 1-bromomethylphenyl-2,6-diisocyanate, 3, 3 bis-chloromethyl-ether-4,4'-diphenyl diisocyanate. Other suitable diisocyanates are, for example, trimethyl hexamethylene diisocyanate, 1,4-diisocyanatobutane, 1,12 diisocyanate dodecane and fatty acid diisocyanate dimer. Tetramethylene, hexamethylene, undecane, dodecanomethylene, 2,2,4-trimethylhexane, 1,3-cyclohexane, 1,4-cyclohexane, 1,3- and 1,4-tetramethyl xylene, isophorone, 4,4-dicyclohexyl methane and lysine diisocyanate ester are particularly suitable. The reaction products (carbodiimide formation) of MDI, TDI, HDI or IPDI or mixtures of two or more thereof are especially suitable. Also suitable are the trimerization and oligomerization products of the polyisocyanates which can be obtained by reaction of suitable polyisocyanates, preferably diisocyanates, to form isocyanate rings. Oligomerization products are used, those which have a degree of oligomerization of an average of about 3 to 5 are particularly suitable. The isocyanates suitable for the reaction are the aforementioned diisocyanates, the trimerization products of the isocyanates HDI, MDI or IPDI being particularly preferred. The polymeric isocyanates obtained, for example, as bottom residues in the distillation of diisocyanates are also suitable for use as component C. The "polymeric MDI" which is obtained from the distillation residue in the distillation of MDI and which contains at least one Nitrogen atom that is not part of an NCO or urethane group per isocyanate molecule is particularly suitable. The component C is added to the polyurethane binder according to the invention in an amount such that the polyurethane binder as a whole contains from 1 to about 40% by weight of the component C. In a preferred embodiment of the invention, the polyurethane binder contains about 5 to about 30% by weight and more particularly from 10 to about 22% by weight of component C. A polyurethane binder with the advantages according to the invention can be produced in any form basically. However, two processes that have proved to be particularly advantageous are described below. For example, the polyurethane binder can be directly produced by preparing the component A and subsequently adding the components B and C simultaneously or successively. Component B can optionally be added together with another polyol component. Accordingly, the present invention also relates to a process of at least three steps for the production of a polyurethane binder containing isocyanate groups, characterized in that: h) in a first step, a polyurethane prepolymer is prepared from a at least one difunctional isocyanate and at least one polyol component i) in a second step, another at least difunctional isocyanate that does not contain a nitrogen atom that is not part of an NCO group or a mixture of two or more thereof, and j) in a third stage, an at least difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two is added, at least one isocyanate containing at least one nitrogen atom that is not part of an NCO group, the predominant percentage of the isocyanate groups present at the completion of the first stage has a lower reactivity towards the groups reactive to the isocyanates, more particularly to the OH groups, which Isocyanate groups of at least difunctional isocyanate added in the second stage. At first, any of the polyol components that have already been mentioned herein can be used as the polyol component. In an advantageous embodiment, the OH: NCO ratio in the first step of the process according to the invention is less than 1: 1. In a preferred embodiment, the ratio of OH groups to the isocyanate groups in the first stage is from 0.4 to about 0.7: 1 and, more particularly, more than 0.5 to about 0.7: 1. The reaction of a polyol component with the at least difunctional isocyanate in a first step can be carried out in any manner known to the skilled person under the general rules for producing polyurethanes. For example, the reaction can be carried out in the presence of solvents. Suitable solvents are, basically, any of the solvents commonly used in the chemistry of polyurethanes, more particularly: esters, ketones, halogenated hydrocarbons, alkanes, alkenes and aromatic hydrocarbons. Examples of such solvents are methylene chloride, trichlorethylene, toluene, xylene, butyl acetate, amyl acetate, isobutyl acetate, methyl isobutyl ketone, methoxybutyl acetate, cyclohexane, cyclohexanone, dichlorobenzene, diethyl ketone, diisobutyl ketone, dioxane, ethyl, ethylene glycol monobutyl ether acetate, ethylene glycol monoethyl acetate, 2-ethylhexyl acetate, glycol diacetate, heptane, hexane, isobutyl acetate, isooctane, isopropyl acetate, methyl ethyl ketone, tetrahydrofuran or tetrachloroethylene or mixtures of two or more of the solvents mentioned. If the components of the reaction by themselves are liquid or if at least one or more of the reaction components form a solution or dispersion of other reaction components not sufficiently liquid, it is not necessary to use solvents. A reaction without solvents represents a preferred embodiment of the invention. To carry out the first stage of the process according to the invention, the polyol is introduced into a suitable container, optionally together with a suitable solvent, and mixed. The at least difunctional isocyanate is then added with continuous mixing. To accelerate the reaction, the temperature is normally increased. In general, the reaction mixture is heated from 40 to about 80 ° C. The exothermic reaction then begins, provided by an increase in temperature. The temperature of the mixture is maintained from 70 to about 110 ° C, for example from 85 to 95 ° C or, more particularly, from about 75 to about 85 ° C, the temperature being optionally adjusted by external measurements, for example heating or cooling. The catalysts commonly used in polyurethane chemistry can optionally be added to the reaction mixture to accelerate the reaction. Dibutyl tin dilaurate or diazabicyclooctane (DABCO) is preferably added. If it is desired to use a catalyst, the catalyst is generally added to the reaction mixture in an amount from 0.005% by weight or approximately 0.01% by weight to about 0.2% by weight, based on the mixture as a whole. The reaction time for the first stage depends on the polyol component used, the at least difunctional isocyanate used, the reaction temperature used and whether any catalyst is present. The total reaction time is usually about 30 minutes to about 20 hours. Preferably it is used as the at least difunctional isocyanate in the first stage isophorone diisocyanate (IPDI), tetramethylene xylylene diisocyanate (TMXDI), hydrogenated diphenyl methane diisocyanate (MDIH? 2) or toluene diisocyanate (TDI) or a mixture of two or more thereof.

To carry out the second step of the process according to the invention, at least one other at least difunctional isocyanate that does not contain a nitrogen atom that is not part of an NCO group or a mixture of two or more such isocyanates reacts, optionally , together with another polyol component, in mixture with the component A obtained in the first stage. Any polyol of the group of polyols in the foregoing list, or a mixture of two or more thereof, can be used as a constituent of the other polyol component optionally present. However, a polypropylene glycol with a molecular weight from 400 to about 2,500 or a polyester polyol with at least a high percentage and, more particularly, a predominant percentage of aliphatic dicarboxylic acids or a mixture of these polyols is preferably used as the polyol component in the second step of the process according to the invention. At least one polyisocyanate of which the isocyanate groups has a higher reactivity than the isocyanate groups of relatively low reactivity present in the prepolymer is used as the at least difunctional isocyanate which does not contain a nitrogen atom which is not part of an NCO group in the second stage of the process according to the invention. In other words, reactive isocyanate groups originating from the at least difunctional isocyanate originally used for the production of prepolymer A may be present in the prepolymer, the only requirement being that at least a small percentage, preferably the predominant percentage of the isocyanate groups present in the prepolymer of component A should have less reactivity than the isocyanate groups of the at least difunctional isocyanate added in the second step of the process according to the invention which do not contain a nitrogen atom that is not part of an NCO group . Preferably, an aromatic, bicyclic, symmetrical diisocyanate is used as the at least difunctional isocyanate which does not contain a nitrogen atom that is not part of an NCO group. The bicyclic isocyanates include, for example, diisocyanates of the diphenylmethane series, more particularly 2, 2'-diphenyl methane diisocyanate, 2,4'-diphenyl methane diisocyanate and 4,4'-diphenyl methane diisocyanate. Of the diisocyanates mentioned, diphenyl methane diisocyanate, more particularly 4,4 '-diphenyl methane diisocyanate, is particularly preferred as the at least difunctional isocyanate for the second step of the process according to the invention. The other at least difunctional isocyanate that does not contain any nitrogen atom that is not part of an NCO group is used in the second stage in an amount from 1 to about 50% by weight, preferably in an amount from 10 to about 30. % by weight and more preferably in an amount from 15 to about 25% by weight, based on the total amount of polyisocyanates used in all stages of the process according to the invention. In a preferred embodiment, the OH: NCO ratio in the second stage is from 0.2 to about 0.6: 1 and, more particularly, to about 0.5: 1. But this means that the OH: NCO ratio of the components added in the second stage excludes any isocyanate group from the prepolymer A. However, a polyurethane binder with the advantages according to the invention can also be produced by mixing the components D, E, F and G. Accordingly, the present invention also relates to a process for the production of a low viscosity polyurethane binder containing isocyanate groups with a low content of easily volatile isocyanate functional monomers by mixing four components D, E, F and G, characterized in that: k) a polyurethane prepolymer with isocyanate function which is obtained by reaction of a polyol component with at least one difunctional isocyanate is used as a component D, 1) another polyurethane prepolymer with isocyanate function which is obtained by reacting a polyol component with another at least difunctional isocyanate, of which the isocyanate groups have a greater reactivity towards the isocyanate reactive groups than the isocyanate groups of component B, uses as component E, m) an at least difunctional isocyanate that does not contain a nitrogen atom that is not part of an NCO group or a mixture of two or more thereof, is used as component F and, n) another isocyanate less difunctional or a mixture of two or more isocyanates with an average functionality of at least two, at least one isocyanate containing at least one nitrogen atom that is not part of an NCO group, is used as component G, the amount of component being G measured so that at the completion of mixing and after all reactions, if any, taking place between components D, E, F and G have finished, at least 5% of the weight and more particulate At least 10% by weight of the component G is present in the polyurethane binder based on the polyurethane binder as a whole. The polyurethane binders according to the invention and the polyurethane binders produced according to the invention preferably have a viscosity of less than 5000 mPas (measured with a Brookfield RT DVII (Thermosell), needle 27, 20 r.p.m., 50 ° C).

In the context of the present invention, the expression "all reactions, if any, occurring between the components D, E, F and G" refers to the reactions of the isocyanate groups with functional groups containing reactive hydrogen atoms to isocyanates. The addition of component F, particularly when components D or E or D and E, for example, contain free OH groups, generally lead to a reaction of the isocyanate groups of component F with free OH groups. This leads to a reduction of the content of component F. Consequently, reactions capable of leading to a reduction in the proportion of component F are likely to occur, component F can be added in such a quantity, that after all these reactions have finished, the minimum required amount of component F is present in the polyurethane binder. Any of the polyols described above and mixtures of two or more of the mentioned polyols can be used as the polyol component for the production of components D and E in the process according to the invention. The particular polyol components mentioned in the present specification as particularly suitable for the production of component A are also preferably used in the process according to the invention. The above observations on component B apply similarly to the isocyanate at least difunctional to be used as component F that does not contain a nitrogen atom that is not part of an NCO group or a mixture of two such isocyanates plus [sic] . The above observations on component C are applied in a manner similar to the at least difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two - at least one isocyanate containing at least one nitrogen atom which is not part of an NCO group - to be used as component G. The polyurethane binder according to the invention and the polyurethane binders produced according to the invention are distinguished in particular by the fact that they have an extremely low content of isocyanate groups containing monomers easily volatile, which is less than 2% by weight or less than 1% by weight, less than 0.5% by weight and, more particularly, less than about 0.1% by weight. It is particularly emphasized in this regard, that the process according to the invention does not require any separate steps of the process to separate the easily volatile diisocyanate components. Another advantage of the polyurethane binders produced by the process according to the invention is that they have a viscosity that is in a very favorable range for processing. More particularly, the polyurethane binders produced by the process according to the invention have a viscosity lower than 5000 mPas (thus measured with a Brookfield RT DVII (Thermosell), needle 27, 20 r.p.m., 50 ° C). The polyurethane binders according to the invention are suitable for coating articles and, more particularly, for joining articles, as such or in the form of solutions in organic solvents, for example in the solvents described above. Accordingly, the present invention also relates to the use of a polyurethane binder according to the invention or a polyurethane binder produced by a process according to the invention in the production of adhesives, more particularly one-component and two-component adhesives. , coatings, more particularly lacquers, emulsion paints and molding resins, as well as castings and for coating and, more particularly, for joining articles, more particularly for joining films and for the production of laminated films. The polyurethane binder according to the invention or the polyurethane binder produced by one of the processes according to the invention is used in particular for joining plastics and, in a particularly preferred embodiment, for lamination of plastic films, plastic films plated with metals or with metal oxides and metal sheets, more particularly aluminum sheets. The curing process, ie the crosslinking of the individual polyurethane binder molecules through the free isocyanate groups, can be carried out only under the influence of atmospheric humidity, that is, without the need to add hardeners. However, polyfunctional crosslinking agents, for example amines or, more particularly, polyfunctional alcohols, are preferably added as hardeners (two-component systems). Laminates of films made with products produced according to the invention are safe for hot sealing. This is attributable to the reduced percentage of migratable products of low molecular weight in the polyurethane binders. The favorable processing temperature for the adhesives produced according to the invention in sealing processes by heating is between about 30 and about 90 ° C. The present invention also relates to an adhesive containing two components H and I, o) a polyurethane binder containing isocyanate groups according to the invention or a polyurethane binder containing isocyanate groups produced by the process according to the invention, used as component H and p) a compound containing at least two functional groups reactive to isocyanate groups of component H with a molecular weight of up to 50,000 or a mixture of two or more such compounds, being used as component I. Accordingly, any of the polyurethane binders according to the invention as described above can be used as component H. A compound containing at least two functional groups reactive to the isocyanate groups of the component F with a molecular weight of up to 2,500 or a mixture of two or more such compounds, preferably is used as component I. The at least two functional groups reactive to the isocyanate groups of the component F can be selected in particular from amino groups, groups mercapto or OH groups. Compounds suitable for use in component G may contain amino groups, mercapto groups or OH groups individually or as a mixture. The functionality of the compounds suitable for use in component I is generally at least about two. Component I preferably has a percentage of compounds with a higher functionality, for example with a functionality of three, four or more. The total (average) functionality of component I is for example about two (for example, when only difunctional compounds are used as component I) or more, for example about 2.1, 2.2, 2.5, 2.7 or 3. Component I may optionally have even greater functionality, for example of about 4 or greater. Component I preferably contains a polyol carrying at least two OH groups. Any of the polyols mentioned in the above are suitable for use in component I as long as they satisfy the limiting criterion of the upper molecular weight limit. Component I is generally used in an amount such that the isocyanate group ratio of component H for the isocyanate-reactive functional groups of component H in component I is about 5: 1 to about 1: 1 and, more particularly, about 2: 1 to about 1: 1. The adhesive according to the invention generally has a viscosity from about 250 to about 10,000 mPas and, more particularly, in the range from 500 up to about 8000 mPas or up to about 5000 mPas (Brookfield RVT DVII, needle 27, 20 r.p.m., 40 ° C). The adhesive according to the invention can optionally contain additives. The additives can constitute as much as about 30% by weight of the adhesive as a total. Suitable additives for use in accordance with the present invention include, for example, plasticizers, stabilizers, antioxidants, colorants, photostabilizers and fillers. Suitable plasticizers are, for example plasticizers based on phthalic acid, more particularly dialkyl phthalates, esters of phthalic acid esterified with a linear alkanol containing from 6 to about 12 carbon atoms representing the preferred plasticizers. Dioctyl phthalate is particularly preferred.

Other suitable plasticizers are benzoate plasticizers, for example sucrose benzoate, diethylene glycol dibenzoate and / or diethylene glycol benzoate, in which from 50 to about 95% of all hydroxyl groups have been esterified, phosphate plasticizers, for example t- butylphenyl diphenyl phosphate, polyethylene glycols and derivatives thereof, for example diphenyl ethers of poly (ethylene glycol), liquid resin derivatives, for example the methyl ester of hydrogenated resin, vegetable and animal oils, for example glycerol esters of fatty acids and polymerization products thereof. Suitable stabilizers or antioxidants for use as additives according to the invention include: sterically hindered phenols of high molecular weight (Mn), polyhydric phenols and phenols containing phosphorus and sulfur. Phenols suitable for use as additives of According to the invention are, for example, 1,3,5-trimethyl-2,4,6-tris- (3,5-diter-butyl-4-hydroxybenzyl) -benzene; Pentaerythritol tetrakis-3- (3,5-diter., Butyl-4-hydroxyphenyl) -propionate; n-octadecyl-3, 5-diter .butyl-4-hydroxy-phenyl) -propionate; 4, 4-methylene-bi8s- (2,6-diter .butylphenol); 4,4-thiobis (6-tert.butyl-o-cresol); 2, 6-diter. butylphenyl, 6- (4-hydroxyphenoxy) -2, -bis (n-octylthio) -1,3,5-triazine; di-n- ^ 10 octadecyl-3, 5-diter .butyl-4-hydroxybenzyl phosphonates; 2- (n-octylthio) -ethyl-3,5-diter .butyl-4-hydroxybenzoate; and sorbitol hexa- [3- (3, 5-diter-butyl-4-hydroxyphenyl) -propionate]. Suitable photostabilizers are, for example, those registered under the name of Tinuvin® 15 (manufactured: Ciba Geigy). Other additives can be incorporated in the adhesives according to the invention to vary certain properties. These other additives include, for example, colorants, such as titanium dioxide, fillers such as talc, clay and the like. The additives according to the invention can optionally contain small amounts of thermoplastic polymers or copolymers, for example ethylene / vinyl acetate (EVA) copolymers, ethylene / acrylic acid, ethylene / methacrylate and Ethylene / n-butyl acrylate which optionally provide the adhesive with additional flexibility, strength and strength. It is also possible - and preferred according to the invention - to add certain hydrophilic polymers, for example polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl methyl ether, polyethylene oxide, polyvinyl pyrrolidone, polyethyl oxazolines or starch or cellulose esters, more particularly acetates with a degree of substitution of less than 2.5, which increases the wettability of adhesives. The following examples are intended to illustrate the invention without limiting the invention in any way.

Examples Explanation of raw materials and abbreviations in Table 1: A1-A5: 1 to 5 H adhesive formulations: hardener (polyol mixture), OHV = 138.8 PEI: propylene glycol-based polyether PE2: propylene glycol-based polyether DEG : diethylene glycol PES: polyester based on adipic acid, diethylene glycol, phthalic acid and dipropylene glycol with two groups OH PE3: polyether based on propylene glycol MDI-C: MDI carbodiimide dimer HDI-T: HDI trimer HDI-0: HDI MDI-P oligomer: polymeric MDI (bottom distillation residue) (B ADR-1: OH: NCO addition ratio for component A and component B ADR-T: total addition ratio OH: NCO V: viscosity (Brookfield RVTD , 40 ° C) MC: monomer content in% by weight (based on formulations as a total) m-TDI: monomeric TDI fl m-MDI: monomeric MDI OHV: OH value in [mg KOH / g] NCO: NCO content in% by weight (based on formulations as a total) NCO-F: content NCO final nest Table 1. Adhesive formulations (all figures =% by weight unless otherwise indicated) Explanations and abbreviations in Table 2: El-8: Examples 1 to 8 Cl-2: Comparative examples 1 and 2 LS: Laminated structure Fl: Polyethylene terephthalate (PETP) film 12 μ thick F2: Polyethylene film with a plasticizer content of 400 ppm erucic acid amide (EAA) 70 μ thick F2: Polyethylene (PE) film with a plasticizer content of 800 ppm erucic acid amide (EAA) 60 μ thick (EAA) LA: Adhesion of the SSA laminate: Adhesion in the sealed joint coh.AS: Separation of the adhesive adhesive adh.alt: Alternating adhesion, the failure of the adhesion takes place alternately in both materials The mixing ratio of the preparation of the alenduring adhesive was 1: 1 in El at E8 and 100: 70 in Cl and C2. In all the Examples, the applied amount was 2 g / m2.

Table 2: Evaluation of the laminate

Claims (21)

1. A polyurethane binder with a low content of readily volatile isocyanate-functional monomers containing at least components A, B and C, in which: a) a polyurethane polymer containing at least two isocyanate groups or a mixture of two or more prepolymers of polyurethane containing at least two isocyanate groups, is present as component A, at least one polyurethane prepolymer containing at least two differently bound types of isocyanate groups or two different polyurethane prepolymers containing at least two differently bound types of isocyanate groups , in pairs of which at least one type has less reactivity towards the isocyanate-reactive groups than the other type (s), and b) at least one difunctional isocyanate which does not contain a nitrogen atom which is not part of an NCO group, or a mixture of two or more thereof, is present as component B and c) an at least difunctional isocyanate or a mixture of two or The isocyanates having an average functionality of at least two, which contains at least one nitrogen atom that is not part of an NCO or urethane group per isocyanate molecule, is present as component C.

2. The polyurethane binder as mentioned in claim 1 is characterized in that at least 5% by weight of component C, based on the polyurethane binder as a whole, is present.

3. The polyurethane binder as recited in claim 1 or 2, characterized in that the content of readily volatile monomers containing isocyanate groups is less than 1% by weight, the content of toluene diisocyanate (TDI) being less than 0.1. % in weigh. w?

4. The polyurethane binder as mentioned in any of claims 1 to 3 is characterized in that the component A is produced by at least one reaction in two steps in which: d) in a first step, a polyurethane prepolymer is it is prepared from at least one difunctional isocyanate and at least one first polyol component, the NCO: OH ratio being less than 2 and the free OH groups still present in the polyurethane prepolymer, and e) in a second stage, another isocyanate at least The difunctional is reacted with the polyurethane prepolymer of the first stage, the isocyanate groups of the isocyanate added in the second stage having a greater reactivity towards the compounds reactive to the isocyanates than at least The predominant percentage of the isocyanate groups present in the polyurethane prepolymer of the first stage.

5. The polyurethane binder as mentioned in claim 4, characterized in that the other at least difunctional isocyanate is added in a molar excess, based on the free OH groups of component A.

6. The polyurethane binder as mentioned in Component 1 is characterized in that the component A is produced in a reaction of at least two steps in which: f) in a first step, a polyurethane prepolymer is prepared from an at least difunctional isocyanate and minus a first polyol component, the NCO: OH ratio being less than 2 and still the free OH groups being present in the polyurethane prepolymer, and g) in a second step, another at least difunctional isocyanate and another polyol component are reacted with the polyurethane prepolymer of the first stage, the isocyanate groups of the isocyanate added in the second stage • having a greater reactivity towards the compounds reactive to the isocyanates than at least the predominant percentage of the isocyanate groups present in the polyurethane prepolymer of the first stage.

7. The polyurethane binder as recited in claim 6, characterized in that the other at least difunctional isocyanate is added in a molar excess, based on the free OH groups of component A and the other polyol component.

8. The polyurethane binder as mentioned in any of claims 4 to 7, characterized in that the OH: NCO ratio in the second stage is between 0.1 and 1: 1 and more particularly between 0.2 and 0.6: 1.

9. The polyurethane binder as mentioned in any of claims 4 to 8, characterized in that the OH: NCO ratio in the first stage is less than 1: 1 and more particularly between 0.5 and 0.7: 1.

10. A process of at least three stages for the production of a polyurethane binder containing isocyanate groups, characterized in that: h) in a first step, a polyurethane prepolymer is prepared from at least one isocyanate and at least one isocyanate polyol component, i) in a second step, another at least difunctional isocyanate or another at least difunctional isocyanate and another polyol component are added and j) in a third step, an at least difunctional isocyanate or a mixture of two or more isocyanates with a functionality average of at least two is added, at least one isocyanate containing at least one nitrogen atom that is not part of an NCO group, the predominant percentage of the isocyanate groups present at the end of the first stage having lower reactivity towards the isocyanate reactive groups , more flB particularly towards the OH groups, than the isocyanate groups of the at least difunctional isocyanate added in 5 the second stage.

11. The process as mentioned in claim 10, characterized in that the OH: NCO ratio in the second stage is 0.2: 1 to 0.6: 1.

12. The polyurethane binder as mentioned in claim 10 or 11, is characterized in what relation OH: NCO in the first stage is less than 1: 1 and more particularly 0.4: 1 to 0.7: 1.

13. The process as mentioned in any of claims 10 to 11, is characterized in that 15 isophorone diisocyanate (IPDI), tetramethyl xylylene diisocyanate (TMXDI), hydrogenated diphenyl methane diisocyanate (MDIH? 2) or toluene diisocyanate (TDI) are used as the at least difunctional isocyanate of the first stage. The process as mentioned in any of claims 11 to 13 characterized in that diphenyl methane diisocyanate (MD) is used as the other isocyanate at least difunctional in the second step. 15. A process for the production of a low viscosity polyurethane binder containing t groups Isocyanate with a low content of easily volatile isocyanate-functional monomers by mixing four components D, E, F and G, characterized in that: IB k) a polyurethane prepolymer with isocyanate function which is obtained by reaction of a polyol component with a At least difunctional isocyanate is used as component D, 1) another polyurethane prepolymer with isocyanate function which is obtained by reaction of a polyol component with at least one difunctional isocyanate, of which ^ Isocyanate groups have a greater reactivity towards the isocyanate-reactive groups than the isocyanate groups of component B, is used as component E, m) an at least difunctional isocyanate which does not contain a nitrogen atom which is not part of an NCO group or a mixture of two or more thereof, is used as component F and, n) another at least difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two, at least one isocyanate containing at least 20 isocyanates. a nitrogen atom that is not part of an NCO group, is used as component G, the amount of component G being measured so that, upon completion of mixing and after all reactions, if any, taking place between components D , E, F and G, 25 have finished, at least 5% by weight and more particularly at least 10% by weight - based on the polyurethane binder as a total - of component G is present in the polyurethane binder. The process as mentioned in any of claims 11 to 15, characterized in that the polyurethane binder has a viscosity of less than 5,000 mPas (measured with a Brookfield RT DVII (Thermosell), needle 27, 20 rpm, 50 ° C). 17. The use of the polyurethane binder claimed in * (B 10 any of claims 1 to 9 or produced by the process claimed in any of claims 10 to 16 in the production of adhesives, more particularly one component and two component adhesives, coatings, more particularly lacquers, emulsion paints and molding resins, as well as castings and for coating and, in particular, for joining articles, more particularly for bonding films and for the production of laminated films. two components H and I, 20 or) a polyurethane binder containing isocyanate groups according to any of claims 1 to 9 or a polyurethane binder containing isocyanate groups produced according to any of claims 10 to 16 being used as a component H and p) a compound containing at least two functional groups reactive to the isocyanate groups of the * flP component F with a molecular weight of up to 50,000 or a mixture of two or more such compounds, 5 being used as component I. 19. The adhesive as claimed in claim 18, characterized in that a polyol containing at least two OH groups is used as component I. 20. The adhesive as mentioned in claim 18 or 10, characterized in that the component I is used in an amount such that the ratio of isocyanate groups of component H to the functional groups reactive with the isocyanate groups of component H in component I is from 5: 1 to 1: 1 and more particularly from 2: 1 to 15 1: 1. The adhesive as mentioned in any of claims 18 to 20, characterized in that it has a viscosity of 500 to 6,500 cps (Brookfield, RVTD, 40 ° C). twenty