HRP20000902A2 - Monomer-poor polyurethane bonding agent having an improved lubricant adhesion - Google Patents

Description

The present invention relates to a polyurethane binder for the production of a low-viscosity, isocyanate group-bearing polyurethane binder, which has only an insignificant content of volatile monomer residues, essentially does not create migrations and has improved adhesion of lubricants. Furthermore, the invention relates to the use of a low-viscosity, isocyanate group (NCO-group) bearing polyurethane binder in the production of adhesives, especially one- and two-component adhesives, for example for gluing strip materials from e.g. paper, plastic and/or aluminum coatings, especially lacquers , dispersive paints and casting resins, as well as body shaping.

Polyurethane - prepolymers with isocyanate end groups have been known for a long time. They can be easily chain-extended or combined with high-molecular substances with suitable compounds - mostly polyfunctional alcohols. Polyurethane-prepolymers are important in many areas of application, such as in the production of adhesives, layering, casting resins and shaped bodies.

In order to obtain polyurethane-prepolymers with terminal isocyanate groups, it is usual to react polyfunctional alcohols with an excess of polyisocyanates, as a rule at least predominantly diisocyanates. In doing so, the molecular weight can be at least approximately adjusted above the OH-groups to isocyanate group. While the ratio of OH-groups to isocyanate groups of 1:1 or approximately 1:1 in the case of complete conversion leads to generally high molecular weights, for example in the case of a ratio of 2:1 when diisocyanate is used in the statistical mean of each OH-group, one is attached diisocyanide molecule, so that in the course of the reaction, in the ideal case, the formation of oligomers or chain elongation does not occur.

In practice, however, even in the last mentioned case, chain extension reactions cannot be avoided in most cases, which leads to the fact that at the end of the conversion, regardless of the reaction time, there remains a certain amount of components that were added to an excessive extent. If, for example, diisocyanate is added as an excess component, as a rule, a not insignificant part of this component remains in the reaction mixture.

The content of such substances is particularly disturbing, when it comes to volatile diisocyanates. The vapors of these diisocyanates are often harmful to health and the use of products with a high content of such volatile diisocyanates requires, from the manufacturer, expensive measures to protect the health of the people who process these products, so that the air remains clean.

As protective measures and cleaning measures usually require high financial investments or costs, there is a need for products that, depending on the applied isocyanate, preferably have a low proportion of volatile diisocyanates on the part of those who use these substances.

Volatile substances are understood to mean those, which at approximately 30ºC show a vapor pressure of more than about 0.0007 mmHg or a boiling point of less than about 190ºC (70 mPa) - within the scope of this text.

If highly volatile diisocyanates are used instead of volatile diisocyanates, especially widespread bicyclic diisocyanates, e.g. diphenylmethane diisocyanates, as a rule, polyurethane binders with a viscosity that usually lies outside the usable range for simple processing methods are obtained. In these cases, the viscosity of the polyurethane prepolymer can be lowered by adding suitable solvents, which is in contrast to the often required lack of solvent in such binders. A further possibility to reduce the viscosity while avoiding solvents is the addition of an excess of monomeric polyisocyanates, which in the later curing process (after adding a hardener or curing under the influence of moisture) can be incorporated into the layering or gluing (reactive thinner).

While the viscosity of the polyurethane-prepolymer can really be lowered in this way, as a rule, the incomplete conversion of the reactive thinner often leads to retention of stickiness or layering on free, monomeric polyisocyanates, which can, for example, within the layering or adhesive layer or partially "walk away" into the layered or glued materials. Such component parts of the layer-layer or glued part are often referred to in professional circles as "migrates". In contact with moisture, the isocyanate groups migrate, constantly turning it into amino groups. Aromatic amines usually formed are suspected of having carcinogenic effects.

Especially in the area of packaging, migrations are often not tolerated, because the penetration of migrations through the packaging material could lead to contamination of the packaged goods and the consumer would come into contact with migrations when enjoying the goods.

Especially in the field of packaging, especially with foodstuffs, such migrations are therefore undesirable.

To avoid the above-mentioned disadvantages, EP-A 118 065 proposes to produce polyurethane-prepolymers in a two-stage process. In the first step, a monocyclic diisocyanate with a polyfunctional alcohol in the ratio of OH- group: isocyanate of group<1 is first converted, and then in the second step into a bicyclic diisocyanate with polyfunctional alcohols in a ratio of OH- group: isocyanate of group<1 in the presence of in the first step produced prepolymers leads to a reaction. In the second stage, a ratio of OH-groups: isocyanate groups of 0.65 to 0.8, preferably 0.7 to 0.75, is suggested. thus obtained prepolymers even at high temperatures (75°C and 90°C) still show a viscosity of 2500 mPas and 9260 mPas, and nothing is said about compatibility with a lubricant.

EP-A 0 019 120 relates to a process for the production of an elastic, weather-resistant surface. For this, a two-stage procedure is proposed, in which in the first stage, toluene diisocyanate (TDI) is reacted with at least equimolar amounts of polyol, and the resulting reaction product is processed with diphenylmethane diisocyanate (MDI) and one polyol. The polyurethane binder or agents obtained in this way should harden in contact with water or moisture in the air. Although the described procedure leads to a low viscosity product, the content of free volatile diisocyanate (in the current case TDI) is still high (0.7 wt.%) and can only be reduced when time- and energy-demanding methods are applied to remove the excess, volatile diisocyanate, for example by thin-layer distillation.

Unpublished German patent application number 197 49 834.5 relates to monomer-poor polyurethane binders. It shows a two-component polyurethane binder with a low monomer content and an insignificant proportion of migrates.

Foils, for example, are used in food packaging, they often have a high content of sliding agents. A common sliding agent is, for example, erucic acid amide (ESA), which is often present in more than about 400 ppm in the film. Conventional adhesives, which are used for bonding such foils in connections, show often with an increase in the content of slip agents for gluing the foil or. Foil to be glued, deterioration of adhesion. Especially with modern, rationally working packaging machines, an increase in productivity is achieved by significantly increasing the speed of the packaging machines. The films used in this case with slower packaging machines generally show a significantly higher content of slip agents, which can often be 66 ppm or more. Many conventional adhesives have a reduced adhesive force with foils whose slip content is in this size class. As a result, such foil-bound goods - especially after hardening, have poor strength in sealing seams - joints.

Therefore, it was the task of the invention to make available a polyurethane binder, preferably with a low viscosity and preferably with a negligible content of volatile diisocyanates, less than approximately 1 wt. %, whereby the rest of volatile isocyanate, in the case of toluene diisocyanate (TDI), should be less than 0.1 wt.%.

A further task of the invention was to make available a polyurethane binder that has the smallest possible proportion of "migrates", i.e. preferably an insignificant proportion of monomeric polyisocyanates.

A further task of the invention was to make available a process by which a polyurethane binder with the above properties can be produced.

A further task of the invention was to make available a polyurethane binding agent and adhesive, which, in addition to the already known properties in terms of their content of volatile isocyanates and, if possible, a small proportion of migrates, additionally shows even better tolerability of lubricants, i.e., for example, improved joining of bindings and sealed seams when gluing foils with a high content of slip agent.

The subject of the invention is a polyurethane binder with a low content of volatile isocyanate groups carrying monomers, which contain at least components A, B, and C, of which

a) one polyurethane prepolymer bearing at least two isocyanate groups or a mixture of two or more or at least two isocyanate group bearing polyurethane prepolymers as component A, wherein at least one polyurethane prepolymer has at least two different types of isocyanate groups bound or two different polyurethane -prepolymer of groups in pairs with at least two differently bound types of isocyanate groups, of which at least one type shows a lower reactivity against isocyanate-reactive groups than the other type or types, and

b) one difunctional isocyanate, which does not contain a nitrogen atom, which is not an integral part of an NCO group, or a mixture of one or more, as component B and

c) one at least difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two, which shows at least one nitrogen atom per isocyanate molecule, and which is not an integral part of any NCO- or urethane group, as component C,

In the context of the present invention, the term "low viscosity" means a viscosity (measured according to Brookfield) which at 50°C is at least 5000 mPas.

The term "polyurethane binder" in the context of the existing text means a mixture of always at least two isocyanate groups containing molecules, where the proportion of molecules with a molecular weight of more than 500 is approximately 50% by weight, preferably at least 60% by weight or at least approximately 70% by weight.

Component A uses a polyurethane polymer consisting of at least two isocyanate groups or a mixture of two or more polyurethane polymers bearing at least two isocyanate groups, which can be obtained by converting one polyol component with at least one difunctional isocyanate.

In the context of this text, "polyurethane prepolymers" means a compound obtained, for example, by converting one polyol component with at least one difunctional isocyanate. The term "polyurethane-prepolymers" thus includes compounds with a relatively low molecular weight, which are formed, for example, from the conversion of one polyol with an excess of polyisocyanate, but it also includes oligomeric and polymeric compounds. Likewise, the term "polyurethane-prepolymers" includes compounds, which are formed from the conversion of a 3- or 4-valent polyol with a molar excess of diisocyanate, taken per polyol. In this case, one molecule of the resulting compound carries several isocyanate groups.

Molecular weight data relating to polymer compounds refer, unless otherwise stated, to the mean molecular weight (Mn).

As a rule, the polyurethane prepolymers used in the first invention have a molecular weight of about 150 to about 15,000, or about 500 to about 10,000, for example about 5,000, but especially about 700 to about 2,500.

In the embodiment that is preferred within the scope of this invention, a polyurethane-prepolymer with two isocyanate groups, or at least one in a mixture of two or more isocyanate groups, is shown, carrying a polyurethane-prepolymer of at least two differently bound types of isocyanate groups, of which at least one garden shows lower reactivity compared to groups with stronger reactivity or to another type, or other types of isocyanate groups. Isocyanate groups with comparatively lower reactivity compared to those with isocyanate reactive groups (compared to at least one other isocyanate group present in the polyurethane binder) will be described in the following text as "less reactive isocyanate groups, and the corresponding isocyanate group with higher reactivity compared to reactive compounds with isocyanate groups are also referred to as "more reactive isocyanate groups".

Within the framework of the present invention, therefore, one difunctional polyurethane prepolymer can be used as component A, which shows two differently bound isocyanate groups, whereby one of the isocyanate groups has a higher reactivity towards isocyanate reactive groups than the other isocyanate group. One such polyurethane-prepolymer can be obtained from the conversion of a difunctional alcohol with a compound that carries two different, for example, difunctional groups, whereby the conversion is carried out in such a way that, on average, each difunctional alcohol molecule reacts with always one molecule of different isocyanate groups.

It is also possible to insert tri- or multi-functional polyurethane prepolymer into component A, whereby one molecule of polyurethane prepolymer can have, for example, a different number of more or less reactive isocyanate groups.

In the context of a further form of performance which is preferred, mixtures of two or more different polyurethane prepolymers are used as component A. The said mixture can be polyurethane prepolymers in which individual polyurethane molecules carry identically bound isocyanate groups. Therefore, there must be at least two different types of polyurethane molecules in the mixture, which differ at least in the type of isocyanate groups they carry. In total, within this form of performance, there must be at least one more reactive and one less reactive type of isocyanate groups in such a mixture, i.e. one polyurethane molecule with at least two reactive and one polyurethane molecule with at least two less reactive isocyanate groups. It is also possible for the mixture to contain, in addition to molecules that carry one or more identically bonded isocyanate groups, further molecules that carry both one and more identically bonded isocyanate groups, as well as one or more differently bonded isocyanate groups.

As component A or at least as an integral part of component A, conversion products of di- or polyfunctional alcohols with at least one equimolecular amount (taken on the OH – groups of di- or polyfunctional alcohol) of low molecular weight diisocyanates with a molecular weight of up to about 400 are also suitable.

In the embodiment that primarily shows component A used polyurethane-prepolymer or a mixture of two or more polyurethane-prepolymers per molecule with at least one urethane group.

In a suitable embodiment of the invention, component A is produced using at least a two-step reaction in which

d) in the first stage, one polyurethane-prepolymer is produced from at least one difunctional isocyanate and at least one first polyol component, where the NCO/OH ratio is less than 2, and there are still free groups in the polyurethane-prepolymer, and

e) in a second stage, one further difunctional isocyanate with polyurethane-prepolymer from the first stage is converted,

whereby the isocyanate group in the second stage of added isocyanate shows increased reactivity towards isocyanate-reactive compounds, but the least predominant share of isocyanate groups in the polyurethane-prepolymers of the first stage.

In a further assumed form of performance, a further, at least difunctional isocyanate in molar excess, based on free OH-groups, is added to component A.

In a further preferred embodiment, component A is produced by a single, at least two-step reaction, in which

f) in a first stage, a polyurethane-prepolymer is produced from at least one difunctional isocyanate and at least one first polyol component, where the NCO/OH ratio is less than 2, and there are still free groups in the polyurethane-prepolymers and

g) in a second stage, one further at least difunctional isocyanate and one further polyol component with polyurethane-polymer from the first stage is converted,

where the isocyanate groups of the isocyanate added in the second stage have a higher reactivity compared to the compounds with isocyanates of a more reactive state, but at least as a predominant part in the polyurethane-prepolymers of the first stage existing isocyanate groups.

Within the framework of the present invention, it is preferred that, in the production of component A in the second stage, the OH:NCO ratio is approximately 0.001 to less than 1, especially 0.005 to some 0.8.

In a preferred embodiment of the present invention, the OH:NCO ratio in the second stage is approximately 0.2 to 0.6.

In a further assumed embodiment of the invention, the OH:NCO ratio in the first stage is less than 1, especially 0.5 to 0.7, whereby in a given case the ratios for the second stage can also be maintained.

In the following text, the term "polyol components" includes a single polyol or a mixture of two or more polyols, which can be used for the production of polyurethane. By polyol is meant a polyfunctional alcohol, for example a compound with more than OH- group in the molecule as a polyol component for the production of component A, a large number of polyols can be used. For example, they are aliphatic alcohols with 2 to 4 OH - groups per molecule. These molecules can be primarily or secondarily bound. Suitable aliphatic alcohols include, for example, ethylene glycol, propylene glycol, butanediol-1.4m, pentadiol-1.5, hexanediol-1.6, heptanediol 1.7m, octanediol 1.8 and their higher homologues or isomers, as for the expert they are created from the gradual lengthening of the hydrocarbon chain by always one CH2 group or by inserting branches into the hydrocarbon chain. Also suitable are higher functional alcohols such as glycerine, trimethylolpropane, pentaerythritol, as well as oligomeric ethers of the mentioned ingredients alone or in a mixture of two or more of the mentioned ethers together.

Furthermore, conversion products of low molecular weight polyfunctional alcohols from alkylene glycols, isomeric butanediols or hexanediols with ethylene oxide, propylene oxide and/or butylene oxide can be used as polyol components for the production of component A. Furthermore, conversion products of polyfunctional alcohols, such as glycerin, trimethylolethane and/or trimethylolpropane, pentaerythritol or sugar alcohols, and the aforementioned alkylene oxides into polyether polyols are also suitable. Particularly suitable are polyester polyols with a molecular weight of about 100 to 10,000, preferably of about 200 to 5,000. The most suitable within the scope of the present invention is polypropylene glycol with a molecular weight of about 300 to approximately 2,500. polyether polyols are also suitable as a polyol component for the production of component A, as, for example, they arise from the polymerization of tetrahydrofuran.

Polyethers are converted in a manner known to the expert by converting one initial or of the starting compound with a reactive hydrogen atom with alkylene oxides, eg ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran or epichloridine or a mixture of two or more of them.

Suitable starting compounds are, for example, water, ethylene glycol, propylene glycol-1,2 or -1,3, butylene glycol, 1,4-hydroxymethylcyclohexane, 2-methyl-1,3-propanediol, glycerin, trimethylolpropane, hexanetriol-1,2,6 , butanetriol-1,2,4, trimethylolethane, pentaerythritol, mannitol, sorbitol, methylglucosides, sugar, phenol, isonsylphenol, resorcinol, hydroquinone, 1,2,2-or 1,1,2-tris-(hydroxyphenyl)-ethane, ammonia, methylamine, ethylenediamine, tetra- or hexamethyleneamine, triethanolamine, analine, phenylenediamine, 2,4- and 2,6-diaminotoluene and polyphenylpolymethylenepolyamines, as they can be obtained by aniline-formaldehyde condensation.

Polyethers, which are modified by means of vinyl polymers, are also suitable for use as polyol components. Such products can be obtained when styrene and/or acrylonitrile is polymerized in the presence of polyether.

Polyester polyols are also suitable as polyol components for the production of component A, polyester polyols with a molecular weight of approximately 10,000. Thus, for example, polyester polyols produced by converting low molecular weight alcohols, especially ethylene glycol, diethylene glycol, neopentyl glycol, hexadiol, butanediol, propylene glycol, glycerin or trimethylolpropane with caprolactone. The polyfunctional alcohols 1,4-hydroxymethylcyclohexane, 2-methyl-1,3-propanediol, butanetriol-1,2,4, triethyleneglycol, tetraarylmglycol, polyethyleneglycol, dipropyleneglycol, polypropyleneglycol, dibutyleneglycol and polybutyleneglycol are also suitable for the production of polyester polyols.

Further suitable polyester polyols can be produced by polycondensation. Thus, difunctional and/or trifunctional alcohols with a small addition of dicarboxylic and/or tricarboxylic acid or their derivatives can be condensed into polyester polyols. Suitable dicarboxylic acids are, for example, succinic acid and its higher homologues with up to 16 C atoms, unsaturated dicarboxylic acids such as malvinic acid or fumaric acid as well as aromatic dicarboxylic acids, especially isomeric phthalic acids, such as phthalic acid, isophthalic or terephthalic acid. Suitable tricarboxylic acids are, for example, citric acid or trimethyl acid. Within the scope of the invention, polyester polyols from at least one of the mentioned dicarboxylic acids and glycerin, which show the remainder of OH- groups, are particularly suitable. Particularly suitable alcohols are hexanediol, ethylene glycol, diethylene glycol or neopentyl glycol or a mixture of two or more. Particularly suitable acids are isophthalic or adipic acid or their mixture.

High molecular weight polyesters include, for example, conversion products of polyfunctional, preferably difunctional alcohols (in this case together with minor amounts of trifunctional alcohols) and polyfunctional, preferably difunctional carboxylic acids. Instead of free polycarboxylic acids, suitable polycarboxylic acid anhydrides or suitable polycarboxylic acid esters with alcohols, preferably with 1 to 3 carbon atoms, can be used (if possible). Polycarboxylic acids can be aliphatic, cycloaliphatic, aromatic and/or heterocyclic. In a given case, they can be substituted, for example, by alkyl groups, alkylene groups, ether groups or halogens. Examples of polycarboxylic acids are succinic acid, adipic acid, cork acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylenetetrahydrophthalic anhydride, glutaric anhydride. acids, malvinic acid, malvinic acid anhydride, fumaric acid, dimer fatty acid or trimer fatty acid or suitable mixtures of two or more. In this case, minor amounts of monofunctional fatty acids can also exist in the reaction mixture.

Polyesters may in a given case show a minimal proportion of carboxylene groups. Polyesters, which are obtained from lactones, eg -caprolactone or hydroxycarboxylic acids, eg ω-hydroxycaproic acid, can also be used.

Polyacetals are also suitable as polyol components. Polyacetals are compounds obtained from glycols, eg diethylglycol or hexadiol with formaldehyde. Polyacetals that can be used in the scope of the invention can also be obtained by polymerization of cyclic acetals.

Furthermore, polycarbonates are suitable as polyols for the production of component A. Polycarbonates can be obtained, for example, by reacting diols, such as propylene glycol, butanediol-1,4 or hexadiol-1,6, diethyleneglycol, triethyleneglycol or tetraethyleneglycol or a mixture of two or more of them with diacrylates, for example diphenylcarbonate or forgen.

Polyacrylates that carry OH groups are also used as polyol components for the production of component A. These polyacrylates can, for example, be obtained by polymerization of ethylenically saturated monomers, which carry one OH- group. Such monomers can be obtained by esterification of ethylenically unsaturated carboxylic acids and difunctional alcohols, where the alcohol is slightly in excess. Suitable ethylenically unsaturated carboxylic acids are, for example, acrylic acid, methacrylic-crotonic or malvinic acid. Esters bearing appropriate OH groups are, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropylacrylate, 3-hydroxypropylacrylate or 3-hydroxypropylmethacrylate or mixtures of two or more of them.

For the production of component A, the corresponding polyol component is converted with at least one difunctional isocyanate. In principle, every isocyanate with at least two isocyanate groups can be used as the least difunctional isocyanate, as a rule, compounds with two to four isocyanate groups, especially with two, are preferred within the scope of this invention.

In the following, the least difunctional isocyanate is described, which is suitable as the least or least suitable isocyanate for the production of component A.

These are, for example: ethylene diisocyanate, 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate (HDI), cyclobutane-1,3-diisocyanate, cyclohexane-1,3 and 1,4-diisocyanate, as well as mixtures of two or more of them . or 2,6 toluene diisocyanate, diphenyl-methane-2,4-diisocyanate, diphenylmethane-2,2-diisocyanase or diphenylmethane-4,4-diisocyanate or mixtures of two or more of the said diisocyanates.

Likewise, in terms of this invention, suitable isocyanates for the production of component A are tri- or multivalent isocyanates, which can be obtained, for example, by oligomerization of diisocyanates. Examples of such tri- or multivalent polyisocyanates are HDI or IPDI triisocyanates or mixtures thereof or mixed triisocyanaurates thereof. In a preferred embodiment, diisocyanates are used for the production of component A, which have two isocyanate groups of different reactivity.

Examples of such diisocyanates are 2,3- and 2,6-toluene diisocyanate (DTI) and isophorone diisocyanate (IPDI). In such unsymmetrical diisocyanates, as a rule, one isocyanate group reacts significantly faster compared to isocyanate reactive groups, eg OH-groups, while the remaining isocyanate group - in comparison - reacts slowly. In the preferred embodiment, a monocyclic, non-symmetrical diisocyanate, which has two isocyanate groups described, of different reactivity, is used for the production of component A.

The use of 2,4- or 2,6-toluenediisocyanate (TDI) or a mixture of both isomers, and in particular the use of pure 2,4-TDI, was especially assumed for the production of component A.

The polyurethane binder according to the invention contains as component B at least one difunctional isocyanate, which does not have a nitrogen atom that is not an integral part of an NCO group, or a mixture of two or more of them.

As component B, for example, at least difunctional isocyanates or a mixture of two or more such isocyanates, whose average functionality is at least approximately two, are suitable.

In a preferred embodiment, component B contains at least one at least difunctional isocyanate, the NCO groups of which are more reactive than the NCO groups of reactive compounds, e.g. under the formation of urethane-, triourethane-, biuret- or allophanates, rather than less reactive isocyanate groups of component A with polyurethane-prepolymer content.

Isocyanate groups in component B, i.e. difunctional isocyanates, can show different or essentially identical reactivity. It is also possible within the framework of the assumed embodiment of the invention to use the least difunctional isocyanates as component B, which isocyanate groups show identical reaction ability.

As a rule, component B has a molecular weight of about 2,000, the advantage is that the molecular weight is lower, for example less than 1,000, such as 700 or 400 g/mol.

Suitable for use as component B within the scope of the present invention are, for example, 4,4'-diphenylmethane diisocyanate as well as HD, IPDI or ZMXDI.

In one presumptive embodiment, 4,4'-diphenylmethane diisocyanate (MDI), 2,2'-diphenylmethane diisocyanate or 2,4'-diphenylmethane diisocyanate is used.

The polyurethane binder according to the invention contains at least approximately 3% by weight of component B based on the total polyurethane binder. In a preferred embodiment, the polyurethane binding agent preferably contains 5 to 25% by weight of component B.

The polyurethane binder according to the invention advantageously shows a content of volatile, isocyanate groups carrying monomers of less than 2% by weight or less than 1% by weight. %, or less than 0.5 wt.% is preferred. These limits are particularly valid for volatile isocyanate compounds, which present only a limited hazard potential for the persons handling them, eg for isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tetramethylxylylene diisocyanate (TMXDI) or cyclohexanediisocyanate. In the case of certain highly volatile isocyanate compounds, especially those that represent a high potential danger for people who work with them, the content of polyurethane binders is less than 0.3 wt.%, and especially advantageously, less than 0.1 wt.%.

Toluyl diisocyanate (TDI) is among the last mentioned isocyanate compounds. In a further preferred embodiment of the present invention, the polyurethane binder has a TDI and HDI content of less than 0.05% by weight.

Polyurethane binder according to the invention as component C at least one difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two, which show at least one nitrogen atom per isocyanate, which is not an integral part of an NCO or urethane group.

For this reason, NCO groups in carbidimides, which can be obtained by converting diisocyanates under suitable conditions and catalysis, are suitable for use in component C.

Isocyanates suitable for the formation of cardodiimides are, for example, compounds of the general structure O=C=N-X-N=C=O, where X is an aliphatic, alicyclic or aromatic residue, preferably an aliphatic or alicyclic residue with 4 to 18 carbon atoms.

Examples of suitable isocyanates include 1,5-naphthylene diisocyanate, 4,4`-diphenylmethane diisocyanate (MDI), hydrogenated MDI (H12MDI), xylene diisocyanate (XDI), tetramethylxylene diisocyanate (TMXDI), 4,4 ́-dibenzyl diisocyanate, 1,3 - phenyl diisocyanate, 1,4-phenylenediisocyanate, isomers of toluene diisocyanate (TDI), 1-methyl-2,4-diisocyanato-cyclohexane, 1,6-diisocyanato-2,2,4-trimethylhexane, 1,6-diisocyanato-2,4 ,4-trimethylhexane, 1-isocyanomethyl-3-isocyanato-1,5,5-trimethylcyclohexane (IPDI), chlorinated and brominated diisocyanates, phosphorus-containing diisocyanates, 4,4`-diisocyanatophenylperfluoroethane, tetramethoxybutane-1,4-diisocyanate, butane -1,4-diisocyanate, hexane-1,6-diisocyanate (HDI), dicyclohexylmethane diisocyanate, cyclohexane-1,4-diisocyanate, ethylene diisocyanate, phthalic acid-bis-isocyanato-ethylester, further diisocyanates with reactive halogen atoms, such as 1-chloromethylphenyl -2,4-diisocyanate, 1-bromo-ethylphenyl-2,6-diisocyanate, 3,3-bis-chloromethylether-4,4`-diphenyl-diisocyanate ijanat.

Further applicable diisocyanates are, for example, trimethylhexa-methylene diisocyanate, 1,4-diisocyanatobutane, 1,12-diisocyanatododecane and fatty acid dimer diisocyanate. Particularly suitable are tetramethylene-hexamethylene-, undecane-dodecamethylene-2,2,4-trimethylhexane, 1,3-cyclohexane, 1,2-cyclohexane, 1,3-resp. 1,4-tetramethylxylene, isophorone-4,4-dicyclohexyl-methane and lysine ester-diisocyanate.

Particularly suitable conversion products are MDI, TDI, HDI or IPDI or mixtures of two or more of them, with the formation of carbodiimide.

Furthermore, the tri- and oligomerization products of polyisocyanates, which can be obtained by forming isocyanate rings through suitable conversion of polyisocyanates, are preferred, diisocyanates are preferred. If oligomerization products are used, then those with an average degree of oligomerization pd of 3 to some 5 are particularly suitable.

The isocyanates suitable for conversion are those already mentioned above, whereby the isocyanate trimerization products HDI, MDI or IPDI have a particular advantage.

Isocyanate polymers are also suitable for use with component C, as they appear as a residue in the distillation sludge during diisocyanate distillation. "Polymer MDI" is particularly suitable for this, which is obtained during the distillation of MDI from the distillation residue, and has at least one nitrogen atom per isocyanate, which is not an integral part of any NCO or urethane group.

Component C is added to the polyurethane binder according to the invention to such an extent that the entire polyurethane binder contains approximately 1 to 4 wt.% of component C. In a preferred embodiment, the polyurethane binder contains about 5 to some 30 wt.%, and especially on occasion 10 to some 22 wt.% of component C.

The polyurethane binder with the advantages of the invention can be produced in any desired manner. The procedure described below proved to be a particularly suitable method:

For example, it is possible for the polyurethane binder to be produced directly by the production of component A, with the subsequent or simultaneous addition of components B and C. The addition of component B may be carried out as needed together with one further polyol component.

A further object of the invention is therefore a process for the production of a polyurethane binder with isocyanate groups, comprising at least three stages, in which:

h) in the first stage, polyurethane-prepolymer is produced from at least one difunctional isocyanate and at least one polyol component, and

i) in another step, one further, at least difunctional, isocyanate is added, which does not contain a nitrogen atom that is not an integral part of an NCO group, or a mixture of two or more of them, and

j) in a third stage, one at least difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two is added, whereby one (at least one) isocyanate has a nitrogen atom, which is not an integral part of any NCO group, whereby

the predominant part of the existing isocyanate group, after the end of the first stage, has a lower reactivity towards isocyanate reactive groups, especially OH-groups, than isocyanate groups in the second stage added at least or at least difunctional isocyanate.

As a further polyol component, all the polyol components already mentioned in this text can be used.

It is advantageous when, in the first stage of this process, the OH:NCO ratio is less than 1. The ratio of OH-groups to isocyanate groups in the assumed form of performance in the first stage is about 0.4 to about 0.7, especially more than 0.5 up to some 0.7.

The conversion of a polyol component with at least a difunctional isocyanate in a first stage can be carried out in a manner that is known in a first stage, it can be carried out in a manner that is known to every expert according to the general rules of polyurethane production. The conversion can, for example, take place in the presence of a solvent.

In principle, all wastes common in polyurethane chemistry can be used as solvents, especially esters, ketones, halogenated hydrocarbons, alkanes, alkenes and aromatic hydrocarbons. Examples of such agents are methylene chloride, trichloroethylene, toluene, xylene, butyl acetate, amyl acetate, isobutyl acetate, methylisobutyl ketone, methoxybutyl acetate, cyclohexane, cyclohexanone, dichlorobenzene, diethyl ketone, diisobutyl ketone, dioxane, ethyl acetate, ethylene glycol monobutylene acetate, ethylene glycol monoethyl acetate, 2-ethylhexyl acetate, glycol diacetate, heptane, hexane. , isobutylacetate, isooctane, isopropylacetate, methylethylketone, tetrahydrofuran or tetrachloroethylene or mixtures of two or more of the mentioned solvents.

When the reaction components are liquid or at least one or more reaction components create a solution or dispersion, insufficient liquid components, then the addition of solubilizers can be completely dispensed with. One such solvent-free reaction is preferred within the scope of this invention.

To carry out the first stage of the process according to the invention, polyol is placed, if necessary together with a suitable solvent, in a suitable container and mixed. Then, while continuing to mix, at least the difunctional isocyanate is added. To speed up the reaction, the temperature is usually raised. As a rule, it is heated to 40°C to some 80°C. The resulting exothermic reaction further leads to an increase in temperature. The temperature of the mixture is maintained at about 70 to 110 °C, for example at about 85 to 95 °C or especially at approximately 75 to 85 °C, if necessary, the temperature is adjusted by suitable external measures, for example by cooling or heating.

In this case, catalysts common in polyurethane chemistry can be added to this reaction mixture to speed up the reaction. The addition of dibutylzinc laurate or diazabicyclooctane (DABCO) is preferred. When it is desired to use a catalyst, as a rule, the catalyst is added in an amount of about 0.005 wt.% or some 0.01- wt.% taken from the entire prepared quantity.

The duration of the reaction for the first stage depends on the polyol component used, the least difunctional isocyanate used and the reaction temperature. As well as from the possibly existing catalyst. The total duration of the reaction is usually 30 minutes to 20 hours per occasion.

As the least difunctional isocyanate, isophorone diisocyanate (IPDI), tetramethylxylene diisocyanate (TMXDI), hydrogenated diphenylmethane diisocyanate (MDUH12) or toluene diisocyanate (TDI) or a mixture of two or more of them is added.

To carry out the second stage of the process according to the invention of a mixture which in the first stage contains component A and has at least one further difunctional diisocyanate, which does not have a nitrogen atom without an NCO group, or a mixture of two or more such isocyanates, in a given case converted with a further polyol component. Any polyol from the group of polyols listed in this text or a mixture of two or more of them can be used as an integral part of the existing further polyol component. However, in the second step of the process according to the invention, a polypropylene glycol with a molecular weight of approximately 400 to approximately 2500, or a polyester polyol with at least one particularly high proportion of aliphatic dicarboxylic acids or a mixture of these polyols is preferred as the polyol component.

As the least difunctional isocyanate that does not have a nitrogen atom that is not an integral part of an NCO-group, in the second step according to the invention, at least one polyisocyanate is added, whose isocyanate groups show higher reactivity than isocyanate groups found in less reactive prepolymers. This means that there may be reactive isocyanate groups in prepolymers, which originate from the least difunctional isocyanate originally used for the production of prepolymer A. In this regard, it is important for the invention that at least a small proportion, predominantly a larger proportion in the prepolymers of component A, of the existing isocyanate groups show lower reactivity than the isocyanate groups of a further - at least difunctional isocyanate, which does not have a single nitrogen atom that is not an integral part of the NCO group , which is added in the second stage of the process according to the invention.

As a further, least difunctional isocyanate, which does not have a nitrogen atom that is not an integral part of the NCO group, the best bicyclic, aromatic, symmetrical diisocyanate is used. Bicyclic isocyanates include, for example, diphenylmethane diisocyanates, especially 2,2`-diphenylmethane diisocyanate, 2,4`-diphenylmethane diisocyanate and 4,4`-diphenylmetadiisocyanate. Of the mentioned diisocyanates, special preference is given to diphenylmethane diisocyanate, especially 4,4`-diphenylmethane diisocyanate, as a further at least difunctional isocyanate within the second stage of the process according to the invention.

A further at least difunctional isocyanate, which does not have a nitrogen atom that is not an integral part of the NCO-group, is used in the second step.

An amount of about 1 to about 50% by weight, preferably about 10 to about 30% by weight, and especially in an amount of about 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 one presumptive embodiment, the second-stage OH:NCO ratios are approximately 0.2 to 0.6, particularly some 0.5. By this should be understood the OH:NCO ratio in the second stage, the added components of the isocyanate group originating from prepolymer A are not taken into account here.

Polyurethane binder with advantages according to the invention can also be obtained by mixing individual components D, E, F and G.

Likewise, the subject of the invention is a process for the production of a low-viscosity, isocyanate group-bearing polyurethane binder with a low content of easily volatile monomers that bear isocyanate groups, including the mixing of four components D, E, F and G, in which

k) is, as component D, a polyurethane-prepolymer with an isocyanate group, which is obtained by converting one polyol component with one at least difunctional isocyanate,

l) as component E, a further polyurethane-prepolymer bearing one further isocyanate group, obtained by converting one polyol component with at least one difunctional isocyanate, whose isocyanate groups have a higher reactivity towards isocyanate-reactive groups than the isocyanate groups of component D,

m) as component F at least one difunctional isocyanate, which does not have a nitrogen atom that is not an integral part of an NCO group, or a mixture of two or more of them, and

n) as component G, one further, at least difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two, whereby at least one isocyanate has at least one nitrogen atom, which is not an integral part of an NCO group,

wherein the amount of component G is measured in such a way that after the end of the mixing process and after the end of all of the components of the end of the mixing process and after the end of all of the components of D, E, F and G in the given case of the unfolding reaction, there is at least 5 wt.%, and especially at least 10 wt.% taken on the entire polyurethane binder, on component G in the polyurethane binder.

Polyurethane binders and experimentally produced polyurethanes exhibit an assumed viscosity of less than 5000 mPas (measured with a Brookfield RT DVII Ttermosell, spindle 27, 20o/min, 50°C).

Under "all reactions that take place between components D, E, F and G and in the given case reactions" within the scope of the present invention is meant the reactions of isocyanate groups with functional groups, which have reactive hydrogen atoms in relation to isocyanates. In particular, when components D or E, or D and E, still have free OH-groups, the addition of component F usually leads to the reaction of isocyanate groups of component F with free OH-groups. This results in a decrease in the content of component F. Therefore, when reactions are expected that could lead to a decrease in the proportion of component F, component F must be added to such an extent that after the completion of all these reactions there is the required minimum amount of component F in the polyurethane binder asset.

As a polyol component for the production of components D and E within the scope of the process of the invention, all the above-described polyols and mixtures of two or more mentioned polyols can be used. Especially those polyol components, which are listed as particularly suitable for the production of component A in this text, are primarily used in the process according to the invention.

At least the difunctional isocyanate used for component F, and which does not have a nitrogen atom that is not an integral part of an NCO-group, or a mixture of two or more such isocyanates, are valid for them in addition to component B as analogous.

For component G, at least difunctional isocyanatyl mixtures of two or more isocyanates with an average functionality of two, where at least one isocyanate shows a nitrogen atom, which is not an integral part of any NCO group, are valid analogously to component C.

The polyurethane binder according to the invention and the polyurethane binders produced according to the invention are particularly distinguished by having an extremely low content of volatile monomers, which amounts to less than 2 wt.%, or less than 1 wt.%, less than 0.5 wt.% , and especially less than some 0.1 wt.%. It should be noted that the process according to the invention can work without special steps for removing volatile diisocyanate components.

A further advantage according to the method according to the invention of the production of polyurethane binders is based on the fact that they show viscosity, which lies on processing, in a suitable area. The viscosity of the polyurethane compositions produced according to this invention is especially less than 5,000 mPas (measured with Brookfield RT DVII (Thermosell), spindle 27, 20 rpm, 50°C).

Polyurethane binders according to the invention are suitable as a substance or solution in organic solvents, for example solvents as described above, for layering objects, especially gluing objects.

The subject of the invention is therefore also the application of a polyurethane binder according to the invention or a polyurethane binder produced according to one method according to the invention, in the production of adhesives, especially one- and two-component adhesives, layering, especially lacquers, dispersion paints and resins for casting as well as molded bodies, as well as for coating and especially gluing objects, especially for gluing foils and producing materials for the production of packaging foils.

The polyurethane binder according to the invention, and the polyurethane binder produced by a single process, can primarily be used for gluing artificial material, and especially for laminating plastic foils, metal or metal oxides scalded with plastic foils, as well as metal foils, and especially aluminum foils.

Hardening, i.e. wetting individual molecules of the polyurethane binder to free isocyanate groups, can be done without adding further compounds, for example hardeners, only with moisture in the air. It is better when, for example, polyfunctional binding agents (ernetzers) are added as hardeners, eg amines or especially polyfunctional alcohols (two-component systems).

With the products produced according to the invention - foils - these have a high degree of processing safety during hot gluing (sealing). This can be related to the reduced proportion of low molecular weight products in polyurethane binders. The suitable processing temperature of the adhesive produced according to the invention lies between 30° and some 90° for such products.

Likewise, the subject of the invention is an adhesive, which contains two components H and I, in which it is used

o) polyurethane binder containing isocyanate groups or polyurethane binder with isocyanate groups produced according to one or more of the processes described above by production as component H, and

p) a compound with at least two functional groups capable of reacting with the isocyanate groups of component H with a molecular weight of up to 50,000, or a mixture of two or more components, as component I.

Any polyurethane binder according to the invention, as described in the context of this text, can be used as component H.

As component I, a compound with a molecular weight of up to 2,500, or a mixture of two or more such compounds, is preferably used. Amino groups, mercaptogroups or OH-groups are particularly suitable as at least two isocyanate groups of component F. Aminogroups, mercaptogroups or OH-groups are particularly suitable, and the compounds that can be used in component G are aminogroups, mercaptogroups or OH-groups either exclusively or in a mixture.

Functionality in the component and usable connections amount to at least two as a rule. The advantage is shown by component I in the share of multifunctional compounds, eg functionalities of three, four or more. The total (average) functionality of component I is, for example, two per occasion (when, for example, only difunctional compounds are used as component I), or more, for example some 2,1, 2,2,, 2,5, 2,7 or 3. In a given case, component I can have an even higher functionality, for example four or more.

It is an advantage when component I contains polyols with at least two OH-groups. The polyols mentioned in this text are suitable for use in component I, if they meet the limiting criterion of the upper limit of molecular weight.

As a rule, component I is used in such quantities that the ratio of the isocyanate groups of component H to the reactive isocyanate groups of component H, functional groups of component I is approximately 5:1 to 1:1, especially some 2:1 to some 1:1.

The adhesive according to the invention generally exhibits a viscosity of about 250 to about 10,000 mPas, especially approximately 500 to about 8,000 or up to about 5,000 mPas (Brookfield RVT DVII, spindle 27, 20 rpm, 40°C)

In this case, the adhesive according to the invention can receive some additional substances. Additional substances can have a share of some 30% by weight in the overall adhesive.

Additional substances within the scope of the present invention include e.g. softeners, stabilizers, antioxidants, dyes, photostabilizers or fillers.

As plasticizers, e.g., phthalic acid-based plasticizers, especially dialkyl phthalates, are used, whereby preference is given to phthalic acid esters, which are esterified with a linear alcohol with about 6 to about 12 carbon atoms. Particular preference is given to dioctylphthalate.

Also suitable as softeners are benzoate softeners, for example sucrose benzoate, diethylene glycol dibenzoate and/or diethylene glycol benzoate, in which approximately 50 to some 98% of all hydroxyl groups are esterified. Phosphate softeners, eg t-butylphenyldiphenylphosphate, polyethylene glycols and their derivatives, eg diphenylether poly(ethyleneglycol), liquid resin derivatives, eg glycerin ester of fatty acids and their polymerization products.

Stabilizers or antioxidants that can be used in the scope of the invention as additional substances include sterically hindered phenols of high molecular weight (Mn), polyfunctional phenols and phenols that contain sulfur and phosphorus. Phenols that cannot be used as additives in the scope of the invention are, for example, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl)benzene; pentaerythritol tetrakis-3-(3,5-di-tert-butyl-4-hydroxybenzyl) propionate; n-octadecyl-3,5-di-tert-butyl-4-hydroxyphenyl) propionate; 4,4-methylenebis(2,6-di-tert-butyl-phenol); 4,4-thiobis(6-tert-butyl-o-cresol); 2,6-di-tert-butylphenol; 6-(4-hydroxyphenoxy)-2,4-bis(n-octyl-thio)-1,3,5-triazine; di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonates; 2-(n-octylthio)ethyl-3,5-di-tert-butyl – 4-hydroxybenzoate; and Sorbithexa[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].

Suitable photostabilizers are, for example, those that can be obtained in the store under the name Thinuvin® (manufacturer: Ciba-Geigy)

Further additional materials can be used in the adhesives according to the invention to vary certain properties. Among them can be, for example, coloring agents such as titanium dioxide, fillers such as talc, clay, etc. In a given case, very small amounts of thermoplastic polymers can also be added to the adhesives according to the invention, for example ethylene vinyl acetate (EVA), ethylene acrylic acid, ethylene methacrylate and ethylene-n-butylacrylate polymers, which give the adhesive additional flexibility, toughness and strength if necessary.

It is also possible, and within the scope of the present invention it is preferred, to add certain hydrophilic polymers, e.g. polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl methyl ether, polyethylene oxide, polyvinylpyrrolidone, poloethyloxazoline or starch or cellulose ester, especially acetates with a degree of substitution less than 2.5 which increase the wetting of the glue.

The invention is further explained by examples, which, however, do not have a limiting effect.

EXAMPLES

Explanations of raw materials and abbreviations in Table 1:

K1-K5: glue formulation from 1 to 5

H: hardener (mixture of polyols) OHZ=138.8

PE1: polyether based on propylene glycol

PE2: polyether based on propylene glycol

DEG : diethylene glycol

PES: polyester based on adipic acid, diethylene glycol, phthalic acid and dipropylene glycol with 2 OH groups

PE3: polyether based on polyethylene glycol

MDI-C: MDI-carbodiimide dimer

HDI-T: HDI trimmer

HDI-O: HDI-oligomer

MDI-P: polymeric MDI (distillation sludge residue)

ADV-1: OH/NCO addition ratio for component A and component B

ADV-G: addition ratio OH/NCO total

V: viscosity (Brookfield RVTD, 40°C)

MC: monomer content in wt.% (based on the entire formulation)

m-TDI: monomeric TDI

m-MDI: monomeric MDI

OHZ: number of OH in [mg KOH/g]

NCO-value: NCO-value in wt.% (taken for the entire formulation)

NCO-F: end value of NCO

TABLE 1:

Glue formulas (all types, unless otherwise stated in wt.%)

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Explanations and abbreviations in Table 2:

B1-8: examples 1 to 8

V1-2: comparative examples 1 and 2

VA: mixture composition

F1: polyethylene terephthalate (PETP) film with a thickness of 12μ

F2: polyethylene (PE) film with a thickness of 70μ and a softener content of 400 ppm erucic acid amide (ESA)

F3: polyethylene (PE) film with a thickness of 60μ and a softener content of 800 ppm erucic acid amide

(ESA)VH: bond strength

SNH: strength of the sealed seam

koh.KS: cohesive separation of glue

adh.alt.: alternating adhesion, adhesion failure occurs alternately on both bonding materials

The ratio of the mixture of adhesive preparation/hardener for B1 to B8 was 1/1, a

at V1 and V2 100:70.

The amount of application was 2 g/m2 in all examples.

TABLE 2: Evaluation of compounds

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Claims (21)

1. Polyurethane binder with a low content of volatile isocyanate groups carrying monomers, indicated by the fact that they contain at least components A, B, and C in which a) One polyurethane-prepolymer bearing at least two isocyanate groups or a mixture of two or more polyurethane-prepolymers with at least two isocyanate groups, contained as component A, wherein at least one polyurethane-prepolymer contains two differently bound types of isocyanate groups or two different polyurethanes -prepolymers in a pair have two differently bound types of isocyanate groups, of which at least one type has a lower reactivity towards isocyanate reactive groups than one or the other type or other types, and b) as component B, one at least difunctional isocyanate, which does not have a nitrogen atom that is not an integral part of an NCO group, or a mixture of two or more of them, and c) as component C, one at least difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two, which has at least one nitrogen atom per isocyanate, which is not an integral part of any NCO or urethane group. 2. Polyurethane binder characterized in that, according to claim 1, at least 5% by weight of component C, taken on the entire polyurethane binder, is contained. 3. Polyurethane binder according to claims 1 or 2, characterized in that the content of volatile, monomer-bearing isocyanate groups is less than 1 wt.%, while the content of toluene diisocyanate (TDI) is less than 0.1 wt.%. 4. Polyurethane binder, according to claims 1 to 3, characterized in that component A is produced by at least a two-step reaction, in which d) in the first stage of production from at least one difunctional isocyanate and at least one polyol component, a polyurethane-prepolymer, where the NCO/OH ratio is less than 2, and there are still free OH-groups in the polyurethane-prepolymer, and e) in the second stage, one further at least difunctional isocyanate is converted with the polyurethane-prepolymer from the first stage, whereby the isocyanate groups of the isocyanate added in the second stage have a higher reactivity towards isocyanates than the majority of the isocyanate groups from the first stage in polyurethane-prepolymers. 5. Polyurethane binder according to one of claims 1 to 3, characterized in that a further at least difunctional isocyanate in molar excess, based on the free OH – groups of component A, is added. 6. Polyurethane binder according to one of claims 1 to 3, characterized in that component A is produced by one at least two-step reaction, in which f) in the first stage, one polyurethane-prepolymer is produced from at least one difunctional isocyanate and at least one first polyol component, where the NCO/OH ratio is less than 2, and there are still free groups in the polyurethane-prepolymer, and g) that in the second stage one at least difunctional isocyanate is converted with one further polyol component with the polyurethane-prepolymer of the first stage, wherein the isocyanate groups added to the second stage have a higher reactivity towards the isocyanate reactive compounds than the existing isocyanate groups at least the predominant share in the polyurethane-prepolymers from the first stage. 7. Polyurethane binders according to claim 6, indicated by the fact that the further at least difunctional isocyanate in molar excess, taken on the free OH-groups of component A and further polyol components, and added 8. Polyurethane binders according to one of claims 4 to 7, characterized in that in the second stage the OH:NCO ratio lies between 0.01 and 1 and in particular amounts to 0.2 to 0.6. 9. Polyurethane binder according to one of claims 4 to 8, characterized in that in the first stage the OH:NCO ratio is less than 1, especially 0.6 to 0.7. 10. Process for the production of polyurethane-prepolymer bearing isocyanate groups, characterized by the fact that it includes at least three stages, in which h) in the first stage, polyurethane-prepolymer is produced from at least one difunctional isocyanate and at least one polyol component, and i) in the second stage, one further at least difunctional isocyanate and further polyol component i is added j) in the third stage, one at least difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two is added, whereby at least one isocyanate has at least one nitrogen atom, which is not an integral part of an NCO-group, whereby the predominant share of isocyanate groups after the conclusion of the first stage has a lower reactivity towards isocyanates of reactive groups, especially OH-groups, than isocyanate groups in the second stage of added at least difunctional isocyanate. 11. The method according to claim 10, characterized in that in the second stage the ratio is OH:NCO 0.2 to 0.6. 12. Process according to claims 10 or 11, characterized in that in the first stage the OH:NCO ratio is less than 1, and especially 0.4 to 0.7. 13. The method according to one of claims 10 to 12, characterized in that isophorone diisocyanate (IPDI), tetramethylxylene diisocyanate (TMXDI), hydrogenated diphenylmethane diisocyanate (MDIH12) or toluene diisocyanate (TDI) is used as at least difunctional isocyanate in the first stage. 14. The method according to one of claims 10 to 13, characterized in that in the second stage diphenylmethane diisocyanate (MDI) is used as a further at least difunctional isocyanate. 15. Process for the production of a low-viscosity isocyanate group carrier polyurethane binder with a low content of easily volatile monomers of the carrier isocyanate group, characterized by the fact that it includes the mixing of four components D, E, F and G, in which it is applied k) as component D, one polyurethane-prepolymer bearing isocyanate groups, which are obtained by converting one polyol component with one at least difunctional isocyanate, l) as component E, one further polyurethane-prepolymer bearing isocyanate groups, which are obtained by converting one polyol component with one further at least difunctional isocyanate, whose isocyanate groups show higher reactivity against isocyanates of reactive groups than isocyanate groups of component D, m) as component F, one at least difunctional isocyanate, which does not have any nitrogen atom that is not an integral part of one NCO-group or a mixture of two or more of them, and n) as component G, one further at least difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two, whereby at least one isocyanate shows at least one nitrogen atom, which is not an integral part of an NCO group, wherein the amount of component G is measured in such a way that after the end of the mixing process and after the end of all the reactions taking place between components D, E, F and G, there are at least 5% by weight, especially at least 10% by weight, based on the entire polyurethane binder , from component G in the polyurethane binder. 16. The method according to one of claims 10 to 15, characterized in that the polyurethane binder has a viscosity of less than 5,000 mPas (measured with Brookfield RT DVII (Thermosell), spindle 27, 20 rev/min, 50°C). 17. Application of a polyurethane binder according to claims 1 to 9, or made according to one process according to one of claims 10 to 16, characterized by the fact that in the production of adhesives, especially one- or two-component adhesives, layering, especially lacquers, dispersive paints and resins for casting, as well as shaped bodies, as well as for layering and especially gluing objects, especially for gluing foils and for the production of materials for binding with foil. 18. Adhesive, which contains two components H and I, indicated that it is applied o) polyurethane binder having isocyanate groups according to claims 1 to 9 or polyurethane binder with isocyanate groups made according to claims 10 to 16, as component H and p) a compound with at least two reaction-capable functional groups opposite to the isocyanate groups of component H with a molecular weight of up to 50,000 or a mixture of two or more such compounds, as component I. 19. Adhesive according to claim 18, characterized in that one of at least two OH-group bearing polyols is used as component I. 20. Adhesive according to claim 18 or 19, characterized in that component I is applied in such amounts that the ratio of isocyanate groups of component H to isocyanate groups of component H to reactive groups in component I amounts to 5:1 to 1:1, especially 2: 1 to 1:1. 21. Adhesive according to one of claims 18 to 20, characterized in that it has a viscosity of 500 to 6,500 mPas (Brookfield RVTD, 40°C)