DE19931997A1 - Polyurethane binder for adhesive, paint, dispersion dye and molding is prepared using different types of isocyanate prepolymer both with nitrogen solely and not solely in isocyanate groups - Google Patents

Abstract

Polyurethane (PU) binder comprises PU prepolymer prepared in a two-stage process using isocyanates both with and without nitrogen only in isocyanate groups. Polyurethane binder comprises: (a) an isocyanate-containing polyurethane (PU) prepolymer(s) with at least one having at least two differently bonded types of NCO groups or two prepolymer have pairwise at least two differently bonded types of NCO groups, where at least one type is less NCO reactive than the other; (b) an at least difunctional isocyanate(s) with no N excluding NCO groups; and (c) an at least difunctional isocyanate(s) with an average functionality of at least two and having at least one N per isocyanate not part of an NCO group. Independent claims are included for: (i) the preparation of the above binder by reacting an at least difunctional isocyanate and a polyol(s) to give a prepolymer, further adding another at least difunctional isocyanate(s) and optionally a further polyol and finally adding an isocyanate as per (c) above; and (ii) an adhesive comprising an isocyanate containing PU binder as above and an isocyanate reactive compound(s) of mol. wt. up to 50000.

Description

The present invention relates to a polyurethane binder, process for Production of a low-viscosity isocyanate group-bearing polyurethane binding means that has only a low content of volatile residual monomers, essentially does not form migrates and improves lubricant adhesion having. The invention further relates to the use of a low-viscosity, Isocyanate groups (NCO groups) carrying polyurethane binders from Her provision of adhesives, in particular one and two-component adhesives, for example for gluing sheet-like materials made of e.g. B. paper, Plastic and / or aluminum, coatings, especially paints, dispersions paints and casting resins as well as moldings.

Polyurethane prepolymers with isocyanate end groups have been known for a long time. she can with suitable compounds - mostly with polyfunctional alcohols - in chain extended or crosslinked to form high molecular weight substances in a simple manner. Polyurethane prepolymers have gained importance in many areas of application, so in the production of adhesives, coatings, casting resins and Molded articles.

It is to obtain polyurethane prepolymers with terminal isocyanate groups usual, polyfunctional alcohols with an excess of polyisocyanates in which Usually at least predominantly diisocyanates to react. Here leaves the molecular weight is at least approximately the ratio of OH- Control groups to isocyanate groups. While a ratio of OH groups to Isocyanate groups of 1: 1 or close to 1: 1 when fully converted to in Usually leads to high molecular weights, for example at a ratio of about 2: 1 when using diisocyanates on a statistical average to every OH  Group attached a diisocyanate molecule so that it is in the course of the reaction in Ideally, no oligomer formation or chain extension occurs.

In practice, however, chain extensions can also be used in the latter case usually not completely prevent reactions, which leads to the fact that at the end of the Implementation regardless of the reaction time a certain amount of im Excess component remains. Used as a surplus component For example, if diisocyanate is used, one does not usually remain insignificant proportion of this component due to the facts presented in the Reaction mixture.

A content of such substances is particularly disruptive when it is are volatile diisocyanates. The vapors of these diisocyanates are often harmful, and the use of products with a high The content of such volatile diisocyanates is required by the user complex measures to protect the people processing the product, especially complex measures to keep the breathing air clean.

Because protection and cleaning measures usually involve high financial Investments or costs are linked on the part of the user Need for products which, depending on the isocyanate used, have the lowest possible proportion of volatile diisocyanates.

In the context of the present text, such sub stamping understood that at about 30 ° C a vapor pressure of more than about 0.0007 mmHg or a boiling point less than about 19b ° C (70 mPa).

If, instead of the volatile diisocyanates, low volatile diisocyanates are used, especially the widespread bicyclic diisocyanates, for example Diphenylmethane diisocyanates, this is usually obtained with polyurethane binders a viscosity that is usually outside of that for easy processing methods usable range. In these cases, the viscosity of the  Polyurethane prepolymers are lowered by adding suitable solvents, which contradicts the often required freedom from solvents of such binders. A Another possibility to lower the viscosity while avoiding solvents consists in the addition of an excess of monomeric polyisocyanates, which in the As part of a later hardening process (after adding a hardener or by hardening under the influence of moisture) in the coating or bonding be installed (reactive thinner).

While the viscosity of the polyurethane prepolymers in this way actually Lich lower, the generally incomplete implementation of the reactive leads often thinner to a content of the bond or coating of free, monomeric polyisocyanates, for example within the coating or Gluing, or partly also in the coated or glued materials can walk in. Such components of a coating or adhesive are often referred to as "migrates" in specialist circles. Through contact with damp activity, the isocyanate groups of the migrates continuously become amino groups implemented. The aromatic amines usually produced in this way are in Suspected to have carcinogenic effects.

In the packaging sector in particular, migrates are often intolerable because of a Migration of migrates through the packaging material to a contamination nation of the packaged goods would lead and the consumer when consuming the Good things would inevitably come into contact with migrants.

Especially in the packaging area, especially in food packaging such migrates are therefore undesirable.

To avoid the disadvantages described above, EP-A 0 118 065 proposes Manufacture polyurethane prepolymers in a two-step process. Here will first in a first stage a monocyclic diisocyanate with a polyfunction nelle alcohol in the ratio OH groups: isocyanate groups <1 implemented and then in a second step with a bicyclic diisocyanate polyfunctional alcohols in the ratio OH groups: isocyanate groups <1 in  Presence of the prepolymer prepared in the first step for the reaction brought. In the second stage there is a ratio of OH groups: Isocyanate groups from 0.65 to 0.8, preferably 0.7 to 0.75 are proposed. The so Available prepolymers always show at high temperatures (75 ° C or 90 ° C) viscosities of 2500 mPas or 7150 mPas and 9260 mPas, over which Nothing is said about compatibility with lubricants.

EP-A 0 019 120 relates to a method for producing elastic, weatherproof flat fabrics. For this purpose, a two-stage procedure is proposed, in which in a first stage tolylene diisocyanate (TDI) with at least equimolar amounts a polyol reacted and the reaction product obtained then reacted with diphenylmethane diisocyanate (MDI) and a polyol becomes. The polyurethane binders obtainable in this way should be able to Cure with water or with humidity. The procedure described leads to products with a relatively low viscosity, the content of free, volatile diisocyanate (in this case TDI) is still high (0.7 wt .-%) and can only be reduced if time and energy consuming Methods for removing excess volatile diisocyanate, for example, thin-film distillation can be used.

The unpublished German patent application with the file number 197 49 834.5 relates to low-monomer polyurethane binders. A two is revealed component polyurethane binder with a low monomer content and low migratory content.

Films that are used, for example, for packaging food, often have a high content of lubricants. A common lubricant is for example erucic acid amide (ESA), often in amounts greater than about 400 ppm is contained in the film. Conventional adhesives used to glue such Foils used in composite films often show with increasing Lubricant content of the film to be glued deteriorates Association liability. Especially with modern, efficient packaging machines will increase productivity by significantly increasing the  Running speed of the packaging machines reached. The used here Films usually show compared to slower running packaging machines a significantly increased lubricant content, which is often 600 ppm or more can. Many conventional adhesives have the same adhesive strength in films with one Lubricant content of this magnitude, however, leaves something to be desired. As a result the film composites produced in this way show in particular after they have been made Hardening often results in poor seal seam adhesion.

The object of the invention was therefore to provide a polyurethane binder make the lowest possible viscosity and the lowest possible Residual content of less than about 1% by weight of volatile diisocyanates has, the residual content of volatile isocyanate in the case of Toluene diisocyanate (TDI) should be less than about 0.1% by weight.

Another object of the invention was to provide a polyurethane binder To make available the lowest possible proportion of "migrants", d. H., has the lowest possible proportion of monomeric polyisocyanates.

Another object of the invention was to provide a method with which a polyurethane binder with the above properties can be made.

Another object of the invention was to provide a polyurethane binder and a To provide glue in addition to the properties already mentioned with regard to its content of volatile isocyanates and, if possible low migratory content additionally improved lubricant compatibility, d. H., for example an improved bond or an improved Sealing seam adhesion when gluing films with a high lubricant content, having.

The invention relates to a polyurethane binder with a low content of volatile monomers bearing isocyanate groups, at least containing components A, B and C, in which

• a) a polyurethane prepo carrying at least two isocyanate groups lymeres, or a mixture of two or more at least two isocyanates group-containing polyurethane prepolymers as component A. is, wherein at least one polyurethane prepolymer at least two differently bound types of isocyanate groups or two ver different polyurethane prepolymers in pairs at least two under have differently bound types of isocyanate groups, of which at least one type has a lower reactivity with isocyanates reactive groups than the other species or species, and
• b) an at least difunctional isocyanate which has no nitrogen atom which is not part of an NCO group, or a mixture of two or more of them, as component B and
• c) an at least difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of minde at least two, the at least one nitrogen atom per isocyanate molecule points, which is not part of an NCO or urethane group, as Component C,

is included.

The term "low viscosity" is used in the context of the present invention Viscosity (measured according to Brookfield) understood that at 50 ° C less than 5000 mPas is.

The term "polyurethane binder" is used in the context of the present text a mixture of at least two isocyanate groups Molecules understood in which the proportion of molecules with a molecular weight of more than 500 at least about 50% by weight, preferably at least about 60% % By weight or at least about 70% by weight.

As component A, there is at least two isocyanate groups Polyurethane prepolymer, or a mixture of two or more at least two Isocyanate-bearing polyurethane prepolymers used, the preferred  as by reacting a polyol component with an at least difunk tional isocyanate is available.

A "polyurethane prepolymer" is used in the context of the present text understood a connection, such as that resulting from the implementation of a Polyol component with an at least difunctional isocyanate results. The term "Polyurethane prepolymer" thus includes both compounds with relative low molecular weight, such as from the implementation of a Polyols with an excess of polyisocyanate are formed, but so are oligomeric or polymeric compounds. Likewise from the term "Polyurethane prepolymers" are enclosed compounds such as. B. from the Reaction of a 3- or 4-valent polyol with a molar excess Diisocyanates, based on the polyol, are formed. In this case, enter Molecule of the resulting compound has multiple isocyanate groups.

Unless otherwise stated, molecular weight data relating to polymeric compounds relate to the number average molecular weight (M _n ).

As a rule, those used in the context of the present invention Polyurethane prepolymers 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 a preferred embodiment of the present invention, this has two Polyurethane prepolymers carrying isocyanate groups, or at least one of the im Mixture of two or more polyurethane prepoly bearing isocyanate groups present polyurethane prepolymers at least two different bound types of isocyanate groups, of which at least one type one has lower reactivity towards groups reactive with isocyanates than that other type or the other types of isocyanate groups. Isocyanate groups with one comparatively lower reactivity towards isocyanate-reactive groups pen (compared to at least one other in the polyurethane binder  present isocyanate group) are also referred to in the following text as "less reactive Isocyanate groups ", the corresponding isocyanate group with a higher reactivity towards compounds reactive with isocyanate groups also referred to as "more reactive isocyanate group".

Within the scope of the present invention, for example, difunctional polyurethane prepolymer can be used as component A, the two has differently bonded isocyanate groups, one of the isocyanate groups a higher reactivity towards groups reactive with isocyanates has than the other isocyanate group. Such a polyurethane prepolymer is for example from the reaction of a difunctional alcohol with two different, for example difunctional, isocyanate groups Compounds available, the reaction being carried out, for example, that on average each molecule of the difunctional alcohol with one molecule each of the different compounds carrying isocyanate groups reacts.

It is also possible to use a tri- or higher functional polyurethane prepolymer To use component A, wherein a molecule of the polyurethane prepolymer for example a different number of less reactive and more reactive Can have 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, where individual polyurethane molecules are each bound identically Wear isocyanate groups. So there must be at least two in the mixture Different types of polyurethane molecules are present, which are characterized at least by distinguish the types of isocyanate groups they carry. Overall, in Within this embodiment, at least one in such a mixture More reactive and a less reactive type of isocyanate groups, i. i.e., a poly urethane molecule with at least two reactive and one polyurethane molecule with at least two less reactive isocyanate groups are present. That `s how it is possible that the mixture in addition to molecules that are one or more identical  bound isocyanate groups, contains further molecules that contain either one or several identically bound isocyanate groups as well as one or more carry differently bound isocyanate groups.

Suitable as component A or at least as a component of component A. for example, the reaction products of di- or higher-functional alcohols with an at least equimolar amount (based on the OH groups of the di- or higher functional alcohol) on low molecular weight diisocyanates with a Molecular weight up to about 400.

In a preferred embodiment, this has been used as component A. Polyurethane prepolymers or the mixture of two or more polyurethane Prepolymers at least one urethane group per molecule.

In a preferred embodiment of the invention, component A is prepared by an at least two-stage reaction in which

• c) in a first stage from an at least difunctional isocyanate and at least one first polyol component is a polyurethane prepolymer is produced, wherein the NCO / OH ratio is less than 2 and in Polyurethane prepolymers are still free OH groups, and
• d) in a second stage with a further at least difunctional isocyanate the polyurethane prepolymer from the first stage is implemented,

wherein the isocyanate groups of the isocyanate added in the second stage are one have higher reactivity towards compounds reactive with isocyanates, than at least the predominant part of the in the polyurethane prepolymer from the First stage isocyanate groups.

In a further preferred embodiment, the further, at least difunctional isocyanate in molar excess, based on free OH groups Component A added.  

In a further preferred embodiment, component A is prepared by an at least two-stage reaction in which

• e) in a first stage from an at least difunctional isocyanate and at least one first polyol component is a polyurethane prepolymer is produced, wherein the NCO / OH ratio is less than 2 and in Polyurethane prepolymers are still free OH groups, and
• f) in a second stage, another at least difunctional isocyanate and another polyol component with the polyurethane prepolymer is implemented from the first stage,

wherein the isocyanate groups of the isocyanate added in the second stage are one have higher reactivity towards compounds reactive with isocyanates, than at least the predominant part of the in the polyurethane prepolymer from the First stage isocyanate groups.

It is preferred in the context of the present invention if in the production the component A in the second stage the ratio OH: NCO about 0.001 to is less than 1, in particular 0.005 to about 0.8.

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

In a further preferred embodiment of the invention, the first is Step the ratio OH: NCO less than 1, in particular 0.5 to 0.7, wherein if necessary, the conditions described for the second stage also can be met.

The term "polyol component" includes in the context of the present text single polyol or a mixture of two or more polyols used in the manufacture can be used by polyurethanes. Under a polyol, a poly understood functional alcohol, d. i.e., a connection with more than one OH Group in the molecule.  

A large number of polyols can be used as the polyol component for the production of component A. For example, these are aliphatic alcohols with 2 to 4 OH groups per molecule. The OH groups can be bound either primary or secondary. Suitable aliphatic alcohols include, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol and their higher homologs or isomers such as them arise for the person skilled in the art from a gradual extension of the hydrocarbon chain by one CH ₂ group or by introducing branches into the carbon chain. Highly functional alcohols such as, for example, glycerol, trimethylolpropane, pentaerythritol and oligomeric ethers of the substances mentioned with themselves or in a mixture of two or more of the ethers mentioned are also suitable.

Furthermore, as a polyol component for the production of component A Reaction products with low molecular weight polyfunctional alcohols Alkylene oxides, so-called polyethers, can be used. The alkylene oxides have preferably 2 to 4 carbon atoms. For example, the implementation is suitable products of ethylene glycol, propylene glycol, the isomeric butanediols or Hexanediols with ethylene oxide, propylene oxide and / or butylene oxide. Furthermore, too the reaction products of polyfunctional alcohols, such as glycerol, trimethylolethane and / or trimethylolpropane, pentaerythritol or sugar alcohols, with the named Alkylene oxides suitable for polyether polyols. Are particularly suitable Polyether polyols with a molecular weight of about 100 to about 10,000, preferably from about 200 to about 5,000. Is very particularly preferred Within the scope of the present invention polypropylene glycol with a molecular weight from about 300 to about 2,500. Also as a polyol component for the production of Component A is suitable for polyether polyols, such as those obtained from poly merization of tetrahydrofuran arise.

The polyethers are prepared in a manner known to those skilled in the art by reacting a Starting compound with a reactive hydrogen atom with alkylene oxides, for example ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran or epichlorohydrin or mixtures of two or more thereof.  

Suitable starting compounds are, for example, water, ethylene glycol, Propylene glycol 1,2 or 1,3, butylene glycol 1,4 or 1,3 hexanediol 1,6, octanediol 1,8, neopentyl glycol, 1,4-hydroxymethylcyclohexane, 2-methyl-1,3-propanediol, Glycerol, trimethylolpropane, hexanetriol-1,2,6, butanetriol-1,2,4 trimethylolethane, Pentaerythritol, mannitol, sorbitol, methylglycosides, sugar, phenol, isononylphenol, Resorcinol, hydroquinone, 1,2,2- or 1,1,2-tris- (hydroxyphenyl) -ethane, ammonia, Methylamine, ethylenediamine, tetra- or hexamethyleneamine, triethanolamine, aniline, Phenylenediamine, 2,4- and 2,6-diaminotoluene and polyphenylpolymethylene polyamines, how they can be obtained by aniline-formaldehyde condensation.

Also suitable for use as a polyol component are polyethers which pass through Vinyl polymers were modified. Such products are available, for example, by polymerizing styrene and / or acrylonitrile in the presence of polyethers become.

Also suitable as a polyol component for the production of component A, are polyester polyols with a molecular weight of about 200 to about 10,000. So For example, polyester polyols can be used by reaction of low molecular weight alcohols, especially ethylene glycol, diethylene glycol, Neopentyl glycol, hexanediol, butanediol, propylene glycol, glycerin or trimethylol propane with caprolactone. Also as polyfunctional alcohols Production of polyester polyols are suitable 1,4-hydroxymethylcyclohexane, 2- Methyl 1,3-propanediol, 1,2-butanetriol, triethylene glycol, tetraethylene glycol, Polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol and Polybutylene glycol.

Other suitable polyester polyols can be produced by polycondensation. So can be difunctional and / or trifunctional alcohols with a deficit Dicarboxylic acids and / or tricarboxylic acids, or their reactive derivatives Polyester polyols are condensed. Suitable dicarboxylic acids are for example succinic acid and its higher homologues with up to 16 C- Atoms, also unsaturated dicarboxylic acids such as maleic acid or fumaric acid  as well as aromatic dicarboxylic acids, especially the isomeric phthalic acids, such as Phthalic acid, isophthalic acid or terephthalic acid. Than are tricarboxylic acids for example, citric acid or trimellitic acid. As part of the Polyester polyols from at least one of the invention are particularly suitable called dicarboxylic acids and glycerol, which have a residual content of OH groups exhibit. Particularly suitable alcohols are hexanediol, ethylene glycol, Diethylene glycol or neopentyl glycol or mixtures of two or more of them. Particularly suitable acids are isophthalic acid or adipic acid or their Mixture.

In the context of the present invention, particularly preferably as a polyol component Polyols used to prepare component A are, for example Dipropylene glycol and / or polypropylene glycol with a molecular weight of approximately 400 to about 2,500, and polyester polyols, preferably polyester polyols, are available by polycondensation of hexanediol, ethylene glycol, diethylene glycol or neo pentylglycol or mixtures of two or more thereof and isophthalic acid or Adipic acid, or mixtures thereof.

High molecular weight polyester polyols include, for example Reaction products of polyfunctional, preferably difunctional alcohols (if necessary together with small amounts of trifunctional alcohols) and polyfunctional, preferably difunctional carboxylic acids. Instead of freer Polycarboxylic acids can (if possible) also the corresponding ones Polycarboxylic anhydrides or corresponding polycarboxylic esters with alcohols with preferably 1 to 3 carbon atoms. The polycarboxylic acids can be aliphatic, cycloaliphatic, aromatic and / or heterocyclic. she can optionally be substituted, for example by alkyl groups, Alkenyl groups, ether groups or halogens. As are polycarboxylic acids for example succinic acid, adipic acid, suberic acid, azelaic acid, sebacin acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, phthalic acid anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, Tetrachlorophthalic anhydride, endomethylene tetrahydrophthalic anhydride, Glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimer fat  acid or trimer fatty acid or mixtures of two or more thereof. If necessary, minor amounts of monofunctional fatty acids be present in the reaction mixture.

The polyesters may optionally have a small proportion of carboxyl end groups exhibit. From lactones, for example ε-caprolactone or hydroxycarboxylic acids, for example, ω-hydroxycaproic acid, available polyesters can also be used.

Polyacetals are also suitable as the polyol component. Among polyacetals are understood compounds as they from glycols, for example diethylene glycol or hexanediol with formaldehyde are available. Within the scope of the invention Polyacetals that can be used can also be polymerized cyclically Acetals can be obtained.

Polycar are also suitable as polyols for the production of component A. bonate. Polycarbonates can, for example, by the reaction of diols, such as Propylene glycol, 1,4-butanediol or 1,6-hexanediol, diethylene glycol, triethylene glycol or tetraethylene glycol or mixtures of two or more thereof Diaryl carbonates, for example diphenyl carbonate, or phosgene can be obtained.

Also suitable as polyol components for the production of components A are Polyacrylates bearing OH groups. These polyacrylates are available, for example through the polymerization of ethylenically unsaturated monomers that contain an OH Wear group. Such monomers are, for example, by the esterification of ethylenically unsaturated carboxylic acids and difunctional alcohols, the Alcohol is usually available in a slight excess. For this Suitable ethylenically unsaturated carboxylic acids are, for example, acrylic acid, Methacrylic acid, crotonic acid or maleic acid. Corresponding OH groups supporting esters are, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl meth acrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate or 3-hydroxypropyl methacrylate or mixtures of two or more thereof.  

The corresponding polyol component is used to produce component A. each reacted with an at least difunctional isocyanate. As at least difunctional isocyanate is used both for the production of component A. additionally any isocyanate with at least two isocyanate groups in question In the context of the present invention, however, compounds with two to four isocyanate groups, in particular with two isocyanate groups, are preferred.

Below, at least difunctional isocyanates are described, which as the at least difunctional isocyanate is suitable for the production of components A. are.

For example, these are: ethylene diisocyanate, 1,4-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-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 2,4- and 2,6- Hexahydrotolylene diisocyanate, tetramethylxylylene diisocyanate (TMXDI), 1,3- and 1,4- Phenylene diisocyanate, 2,4- or 2,6-tolylene diisocyanate, diphenylmethane-2,4'- diisocyanate, diphenylmethane-2,2'-diisocyanate or diphenylmethane-4,4'-diisocyanate or mixtures of two or more of the diisocyanates mentioned.

Likewise in the sense of the present invention as isocyanates for the production of Component A is suitable for tri-valent or higher isocyanates, such as those are obtainable by oligomerization of diisocyanates. Examples of such tri- and higher-value polyisocyanates are the triisocyanurates from HDI or IPDI or their mixtures or their mixed triisocyanurates.

In a preferred embodiment of the invention, the Component A used diisocyanates that have two isocyanate groups have different reactivity. Examples of such diisocyanates are 2,4- and 2,6-tolylene diisocyanate (TDI) and isophorone diisocyanate (IPDI). Not with such As a rule, an isocyanate group reacts clearly to symmetrical diisocyanates faster with groups reactive towards isocyanates, for example OH Groups, while the remaining isocyanate group is comparatively inert  is. In a preferred embodiment, the Component A uses a monocyclic, non-symmetrical diisocyanate, that over two isocyanate groups of the different reactivity described disposes.

For the production of component A, the use of 2,4- or 2,6-tolylene diisocyanate (TDI) or a mixture of the two isomers, especially the use of pure 2,4-TDI.

The polyurethane binder according to the invention contains a as component B. at least difunctional isocyanate, which has no nitrogen atom which is not part of an NCO group, or a mixture of two or more from that.

As component B are at least difunctional isocyanates or a Mixture of two or more such isocyanates, their average Functionality is at least about two.

In a preferred embodiment of the invention, component B contains at least one at least difunctional isocyanate, its NCO groups to compounds reactive with NCO groups, for example under Urethane, thiourethane, biuret or allophanate formation are more reactive than the less reactive isocyanate groups of the polyurethane contained in component A Prepolymers.

The isocyanate groups of the difunctional isocyanates contained in component B. may have a different or substantially identical reactivity exhibit. It is also possible in the context of a preferred embodiment to use at least difunctional isocyanates as component B of the invention, whose isocyanate groups have an identical reactivity.  

As a rule, component B has a molecular weight of up to about 2,000, however, the molecular weight is preferably lower, for example less than about 1,000, less than about 700 or less than about 400 g / mol.

For use as component B are within the scope of the present invention for example 4,4'-diphenylmethane diisocyanate (MDI), 2,2'-diphenylmethane di Isocyanate, 2,4'-diphenylmethane diisocyanate and HDI, IPDI or TMXDI are suitable.

In a preferred embodiment, 4,4'-diphenylmethane diisocyanate (MDI), 2,2'-diphenylmethane diisocyanate or 2,4'-diphenylmethane diisocyanate set.

The polyurethane binder according to the invention contains at least about 3% by weight component B, based on the entire polyurethane binder. In a In a preferred embodiment, the polyurethane binder contains about 5 to about 25 % By weight of component B.

The polyurethane binder according to the invention preferably has a content volatile monomers bearing isocyanate groups, of less than 2% by weight % or less than 1% by weight or preferably less than 0.5% by weight. This Limits apply in particular to volatile isocyanate compounds that have only one Limited risk potential for people involved in their processing have, for example for isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tetramethylxylylene diisocyanate (TMXDI) or cyclohexane diisocyanate. At certain volatile isocyanate compounds, especially those containing a high risk potential for people involved in their processing sen, their content in the polyurethane binder according to the invention is preferred less than 0.3% by weight and particularly preferably less than 0.1% by weight. To the the latter isocyanate compound belongs in particular to tolylene diisocyanate (TDI). In a further preferred embodiment of the invention, this Polyurethane binder has a TDI and HDI content of less than 0.05% by weight on.  

The polyurethane binder according to the invention contains a as component C. at least difunctional isocyanate or a mixture of two or more isocya naten with an average functionality of at least two has at least one nitrogen atom per isocyanate, which is not a component an NCO or urethane group.

The NCO groups, for example, are therefore suitable for use in component C. bearing carbodiimides, as obtained by reacting diisocyanates suitable conditions and catalysis are available.

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

Examples of suitable isocyanates are 1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), hydrogenated MDI (H ₁₂ MDI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), 4,4'-diphenyldimethylmethane diisocyanate, di- and Tetraalkylene diphenylmethane diisocyanate, 4,4'-dibenzyl diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, the isomers of tolylene diisocyanate (TDI), 1-methyl-2,4-diisocyanato-cyclohexane, 1,6-diisocyanato-2, 2,4-trimethylhexane, 1,6-diisocyanato-2,4,4-trimethylhexane, 1-isocyanatomethyl-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-ethyl ester , also diisocyanates with reactive halogen atoms, such as 1-chloromethylphenyl-2,4-dii socyanate, 1-bromomethylphenyl-2,6-diisocyanate, 3,3-bis-chloromethyl ether-4,4'-diphenyl diisocyanate.

Other usable diisocyanates are, for example, trimethylhexamethylene diisocyanate, 1,4-diisocyanatobutane, 1,1 2-diisocyanatododecane and dimer fat  acid diisocyanate. Particularly suitable are: tetramethylene, hexamethylene, Undecane, dodecamethylene, 2,2,4-trimethylhexane, 1,3-cyclohexane, 1,4- Cyclohexane, 1,3- or 1,4-tetramethylxylene, isophorone, 4,4-dicyclohexyl methane and lysine ester di-isocyanate.

The implementation products of MDI, TDI, HDI are particularly suitable or IPDI, or mixtures of two or more thereof, under Carbodi imidation.

The tri- and oligomerization products of the polyisocyanates are also suitable, as they are formed by the appropriate implementation of isocyanurate rings Polyisocyanates, preferably diisocyanates, are available. Become Oligomerization products used: those with are particularly suitable an average degree of oligomerization of about 3 to about 5.

Suitable isocyanates for the reaction are those already mentioned above, the Trimerization products of the isocyanates HDI, MDI or IPDI are particularly preferred are.

Also suitable for use as component C are the polymeric isocyanates, as, for example, as a residue in the distillation bottoms during the distillation of Diisocyanates arise. The "polymeric MDI" as is particularly suitable here is available in the distillation of MDI from the distillation residue and has at least one nitrogen atom per isocyanate, which is not a component an NCO or urethane group.

Component C is the polyurethane binder according to the invention in one added such that the total polyurethane binder is about 1 to about Contains 40% by weight of component C. In a preferred embodiment of the Invention contains about 5 to about 30% by weight of the polyurethane binder and in particular about 10 to about 22% by weight of component C.  

A polyurethane binder with the advantages of the invention can in principle can be produced in any way. However, two have proven to be particularly advantageous Proven procedures that are described below.

It is possible, for example, to pass the polyurethane binder directly through the Production of component A, with a subsequent consecutive or to produce simultaneous addition of components B and C. The addition of the Component B can optionally together with another polyol component.

Another object of the invention is therefore a process for the preparation of a polyurethane binder containing isocyanate groups, comprising at least three stages, in which

• h) in a first stage from an at least difunctional isocyanate and at least one polyol component is a polyurethane prepolymer is posed and
• i) in a second stage, another at least difunctional isocyanate, which has no nitrogen atom which is not part of an NCO Is group, or a mixture of two or more thereof and
• j) in a third stage an at least difunctional isocyanate or Mixture of two or more isocyanates with an average Functionality of at least two is added, with at least one Isocyanate has at least one nitrogen atom, which is not a component is an NCO group, wherein

the majority of those available after completion of the first stages Isocyanate groups have a lower reactivity than reactive with isocyanates Groups, especially against OH groups, has as the isocyanate groups of the at least difunctional isocyanate added in the second stage.

In principle, all of them can already be used as a further polyol component in this context Text called polyol components are used.  

It is advantageous if in the first stage of the method according to the invention OH: NCO ratio is less than 1. The ratio of OH groups to In a preferred embodiment, isocyanate groups are in the first stage about 0.4 to about 0.7, in particular more than 0.5 to about 0.7.

The reaction of a polyol component with the at least difunctional iso Cyanate in a first stage can be after in any manner known to the skilled worker the general rules of polyurethane production. The implementation can for example in the presence of solvents. As a solvent basically all solvents commonly used in polyurethane chemistry usable, in particular 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 acetate, 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 tetrachlorethylene or mixtures of two or more of the solvents mentioned.

If the reaction components themselves are liquid or at least one or several of the reaction components are not a solution or dispersion of another form sufficient liquid reaction components, so the use of Solvents are completely dispensed with. Such a solvent-free reaction is in Preferred within the scope of the present invention.

To carry out the first stage of the method according to the invention, the Polyol, optionally together with a suitable solvent, in one suitable vessel submitted and mixed. This is followed by continuing of mixing the addition of the at least difunctional isocyanate. For Accelerating the reaction usually increases the temperature. Usually is tempered to about 40 to about 80 ° C. The onset of exothermic reaction then causes the temperature to rise. The temperature of the batch  is at about 70 to about 110 ° C, for example at about 85 to 95 ° C or in particular kept at about 75 to about 85 ° C, optionally the on setting the temperature by suitable external measures, for example Heating or cooling.

If necessary, to accelerate the reaction in polyurethane chemistry usual catalysts are added to the reaction mixture. The is preferred Add dibutyltin dilaurate or diazabicyclooctane (DABCO). When a Catalyst use is desired, the catalyst is usually in an amount from about 0.005% or about 0.01% to about 0.2% by weight, based on the entire batch, added to the reaction mixture.

The reaction time for the first stage depends on the Polyolkom used component, of the at least difunctional isocyanate used, of the Reaction temperature and any catalyst present. The total reaction time is usually from about 30 minutes to about 20 Hours.

Isophorone diisocyanate (IPDI), tetramethylxylylene diisocyanate (TMXDI), hydrogenated diphenylmethane diisocyanate (MDI _HI2 ) or _tolylene diisocyanate (TDI) or a mixture of two or more thereof is preferably used as the at least difunctional isocyanate in the first stage.

To carry out the second stage of the method according to the invention Mixture with component A obtained in the first stage at least one wide one res at least difunctional isocyanate, which has no nitrogen atom which is not part of an NCO group, or a mixture of two or more such isocyanates, optionally together with a further polyol component implemented. As part of any further Polyol component can be any polyol from the group in the course of this Text of the polyols listed above or a mixture of two or more of which are used. However, preference is given to the second stage of the process according to the invention as a polyol component, a polypropylene glycol  with a molecular weight of about 400 to about 2500, or a polyester polyol with at least a high proportion, in particular a predominant proportion aliphatic dicarboxylic acids, or a mixture of these polyols.

As at least difunctional isocyanate, which has no nitrogen atom which is not part of an NCO group, is in the second stage of the Invention according to the method used at least one polyisocyanate, its isocyanate groups have a higher reactivity than those in the prepolymer Isocyanate groups with lower reactivity. That means it can be in the prepolymer reactive isocyanate groups are still present, from the original to the Her position of prepolymer A used at least difunctional isocyanate come. The only essential to the invention in this context is that at least a small proportion, preferably the predominant proportion, which in the Prepolymers of component A located isocyanate groups a lower Reactivity has at least as the isocyanate groups difunctional isocyanate, which has no nitrogen atom which is not a component an NCO group, which is in the second stage of the invention Process is added.

As the further at least difunctional isocyanate, which has no nitrogen atom which is not part of an NCO group is preferably a bicyclic, aromatic, symmetrical diisocyanate used. To the bicyclic isocya Examples include diisocyanates from the diphenylmethane series, in particular the 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate. Among the diisocyanates mentioned is the Use of diphenylmethane diisocyanate, especially 4,4'-diphe nylmethane diisocyanate, as the further at least difunctional isocyanate in Especially in the second stage of the method according to the invention prefers.

The further at least difunctional isocyanate, which has no nitrogen atom which is not part of an NCO group, is in the second stage in a  Amount from about 1 to about 50% by weight, preferably from 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 invention according to the procedure used.

In a preferred embodiment, the ratio in the second stage is OH: NCO about 0.2 to about 0.6, especially up to about 0.5. Below that is Ratio OH: NCO of the components added in the second stage understand, isocyanate groups originating from prepolymer A remain here disregarded.

However, a polyurethane binder with the advantages according to the invention can be used also produce by mixing individual components D, E, F and G.

The invention therefore also relates to a process for the preparation of a low-viscosity, isocyanate-bearing polyurethane binder with a low content of volatile, isocyanate-bearing monomers, comprising the mixing of four components D, E, F and G, in which

• k) as component D an isocyanate-bearing polyurethane pre polymeric, obtainable by reacting a polyol component with an at least difunctional isocyanate,
• l) as component E a further poly carrying isocyanate groups urethane prepolymer, obtainable by reacting a polyolcom component with a further at least difunctional isocyanate, whose isocyanate groups have a higher reactivity with Have isocyanate reactive groups than the isocyanate groups component D,
• m) as component F, an at least difunctional isocyanate which is not Has nitrogen atom which is not part of an NCO group is, or a mixture of two or more thereof, and
• n) as component G, another at least difunctional isocyanate or a mixture of two or more isocyanates with one average functionality of at least two, where  at least one isocyanate has at least one nitrogen atom which is not part of an NCO group,

is used, the amount of component G being such that after Completion of the mixing process and after completion of all between the Components D, E, F and G any reactions that may occur at least 5 % By weight, in particular at least 10% by weight, based on the total poly urethane binder, present on component G in the polyurethane binder.

The polyurethane binders according to the invention and those according to the invention Polyurethane binders produced preferably have a viscosity of less than 5000 mPas (measured with Brookfield RT DVII (Thermosell), spindle 27, 20 rpm, 50 ° C).

Among "all that may occur between components D, E, F and G Reactions "are reactions of Isocya in the context of the present invention nat groups understood with functional groups compared to isocyanates have reactive hydrogen atoms. Especially if, for example, the Components D or E, or D and E, still have free OH groups, leads the Addition of component F generally to a reaction of the isocyanate groups Component F with the free OH groups. This results in a reduction in the Content of component F. Accordingly, if reactions are to be expected, the can lead to a reduction in the proportion of component F, the Component F is added in such an amount that after connection of all of these reactions the required minimum amount of component F in the polyurethane binder is present.

As a polyol component for the production of components D and E in the context of The inventive method can all polyols and Mixtures of two or more of the polyols mentioned can be used. In particular, the polyol components that are used to produce component A in Framework of this text have been mentioned as particularly suitable preferably also used in the process according to the invention.  

For the at least difunctional isocyanate to be used as component F, the has no nitrogen atom which is not part of an NCO group, or a mixture of two or more such isocyanates, the explanations apply to Component B analog.

For the at least difunctional isocyanate to be used as component G or a mixture of two or more isocyanates with an average function nality of at least two, at least one isocyanate at least one Has nitrogen atom, which is not part of an NCO group, apply The explanations for component C are the same.

The polyurethane binder according to the invention and those according to the invention Polyurethane binders produced are particularly characterized in that they have an extremely low content of volatile, isocyanate groups Have monomers containing less than 2% by weight or less than 1% by weight is less than 0.5% and especially less than about 0.1% by weight. It should be particularly emphasized that the inventive method without separate process steps for the removal of volatile diisocyanate components gets along.

Another advantage of the polyu produced by the process according to the invention Rethane binder is due to the fact that they have a viscosity that in a very convenient area for processing. The viscosity of the after Polyurethane binder produced by the method according to the invention is in particular less than 5,000 mPas (measured with Brookfield RT DVII (Thermosell), spindle 27, 20 rpm, 50 ° C).

The polyurethane binders according to the invention are suitable in bulk or as Solution in organic solvents, for example in solvents as above have been described for coating objects, in particular for Gluing objects.  

The invention therefore also relates to the use of an inventive Polyurethane binder or a polyurethane binder that after a was produced according to the invention in the manufacture of adhesive substances, in particular one and two-component adhesives, coatings, ins special paints, emulsion paints and casting resins as well as moldings, as well for coating and in particular gluing objects, in particular for gluing foils and for the production of foil composites.

The polyurethane binder according to the invention or that according to one of the Invention Polyurethane binder produced according to the method is used in particular for Bonding of plastics and particularly preferred for laminating Plastic films, of plastic films vapor-coated with metal or with metal oxides, as well as metal foils, in particular aluminum foils.

The curing, d. H. the crosslinking of the individual polyurethane binder molecules via the free isocyanate groups, without the addition of further compounds, for example by hardener, can only be caused by air humidity. It is however preferred if polyfunctional crosslinking agents, for example amines, are used as hardeners or in particular polyfunctional alcohols can be added (two-component systems).

Film composites produced with the products produced according to the invention show high processing reliability when heat sealing. This is due to the diminisher portion of migratable, low molecular weight products in the polyurethane binders. An advantageous processing temperature for the Adhesives produced according to the invention lie between such processes about 30 and about 90 ° C.  

The invention also relates to an adhesive comprising two components H and I, wherein

• o) a polyurethane having isocyanate groups according to the invention binder or a polyurethane bond containing isocyanate groups medium, manufactured according to one of the inventions described above process according to the invention, as component H, and
• p) a compound with at least two compared to the isocyanate groups Component H reactive functional groups with a Molecular weight up to 50,000, or a mixture of two or more such compounds as component I.

is used.

Any component according to the invention is thus as component H binders can be used, as described in the context of the above text.

A component with at least two is preferably used as component I functional component reactive over the isocyanate groups of component F. Groups with a molecular weight of up to 2,500, or a mixture of two or more of such compounds. As at least two against the Isocyanate groups of component F are reactive functional groups in particular amino groups, mercapto groups or OH groups, where Compounds that can be used in component G, amino groups, Mercapto groups or OH groups in each case exclusively, or in a mixture can have.

The functionality of the compounds that can be used in component I is as follows Usually at least about two. Component I preferably has a portion higher functional connections, for example with a functionality of three, four or more, on. The total (average) functionality of component I is, for example, about two (e.g. if only difunctional compounds as Component I) or more, for example about 2.1, 2.2, 2.5, 2.7,  or 3. If necessary, component I can have an even higher functionality have, for example about four or more.

Component I preferably contains at least two OH groups Polyol. All are within the scope of this text for use in component I. Suitable polyols, provided they meet the restrictive criterion of Meet upper molecular weight limit.

Component I is usually used in an amount such that the ratio of Component H isocyanate groups with component H isocyanate groups reactive functional groups in component I about 5: 1 to about 1: 1, ins especially about 2: 1 to about 1: 1.

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

If necessary, the adhesive according to the invention can also contain additives. The additives can make up up to about 30 percent of the total adhesive % By weight.

Additives that can be used in the context of the present invention include for example plasticizers, stabilizers, antioxidants, dyes, Photo stabilizers or fillers.

Examples of plasticizers are plasticizers based on phthalic acid used, in particular dialkyl phthalates, phthalic acid esters as plasticizers are preferred, those with a about 6 to about 12 carbon atoms, linear alkanol were esterified. This is particularly preferred Dioctyl phthalate.

Benzoate plasticizers are also suitable as plasticizers, for example Sucrose benzoate, diethylene glycol dibenzoate and / or diethylene glycol benzoate  about 50 to about 95% of all hydroxyl groups have been esterified, Plasticizers, for example t-butylphenyl diphenyl phosphate, polyethylene glycols and their derivatives, for example diphenyl ether 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 their Polymerization products.

Stabilizers or antioxidants which can be used as additives in the context of the invention include sterically hindered phenols of high molecular weight (M _n ), polyfunctional phenols and sulfur- and phosphorus-containing phenols. Phenols which can be used as additives in the context 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-hydroxyphenyl) propionate; n-octadecyl-3,5-di-tert-butyl-4-hydroxyphenyl) propionate; 4,4-methylenebis (2,6-di-tert-butylphenol); 4,4-thiobis (6-tert-butyl-o cresol); 2,6-di4ert-butylphenol; 6- (4-hydroxyphenoxy) -2,4-bis (n-octylthio) -1,3,5-triazine; Di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate; 2- (n-octylthio) ethyl 3,5-di-tert-butyl-4-hydroxybenzoate; and sorbitol hexa [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate].

Suitable photostabilizers are, for example, those under the Names Thinuvin® (manufacturer: Ciba Geigy) are commercially available.

Further additives can be included in the adhesives according to the invention are used to vary certain properties. Among them, for example Dyes such as titanium dioxide, fillers such as talcum, clay and the like. If necessary, small amounts of can be present in the adhesives according to the invention thermoplastic polymers are present, for example ethylene vinyl acetate (EVA), Ethylene acrylic acid, ethylene methacrylate and ethylene-n-butyl acrylate copolymers If necessary, add additional flexibility, toughness and strength to the adhesive. It is also possible, and preferred within the scope of the present invention, adding certain hydrophilic polymers, for example polyvinyl alcohol, Hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl methyl ether, Polyethylene oxide, polyvinyl pyrrolidone, polyethylene oxazoline or starch or  Cellulose esters, especially the acetates with a degree of substitution of less than 2.5, which increase the wettability of the adhesives.

The invention is illustrated below by examples, which, however, do not restrict exert an effect.  

Examples Explanation of raw materials and abbreviations in table 1

K1-K5: Adhesive formulations 1 to 5
H: Hardener (polyol mixture), 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 propylene glycol
MDI-C: MDI carbodiimide dimer
HDI-T: HDI trimer
HDI-O HDI oligomer
MDI-P: polymeric MDI (residue from distillation bottoms)
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 contents in% by weight (based on the entire formulation)
m-TDI: monomeric TDI
m-MDI: monomeric MDI
OHZ: OH number in [mg KOH / g]
NCO value: NCO value in% by weight (based on the entire formulation)
NCO-F: final NCO value

Table 1

Adhesive formulations (all values, unless otherwise stated above, in% by weight)

Explanations and abbreviations in Table 2

B1-8: Examples 1 to 8
V1-2: Comparative Examples 1 and 2
VA: composite structure
F1: film made of polyethylene terephthalate (PETP) with a thickness of 12 μ
F2: film made of polyethylene (PE) with a thickness of 70 µ and a plasticizer content of 400 ppm erucic acid amide (ESA)
F3: Polyethylene (PE) film with a thickness of 60 µ and a plasticizer content of 800 ppm erucic acid amide
(ESA) VH: Group liability
SNH: Sealed seam liability
koh. KS: cohesive adhesive splitting
adh. alt .: Alternating adhesion, adhesion fracture takes place alternately on both composite materials.

The mixing ratio of adhesive preparation / hardener was 1/1 for B1 to B8, for V1 and V2 100 to 70.

The application amount in all examples was ² g / m ² .

Claims (21)

1. Polyurethane binder with a low content of volatile monomers bearing isocyanate groups, at least containing components A, B and C, in which

• a) a polyurethane prepolymer carrying at least two isocyanate groups, or a mixture of two or more polyurethane prepolymers containing at least two isocyanate groups is present as component A, at least one polyurethane prepolymer containing at least two differently bonded types of isocyanate groups or two different ones Polyurethane prepolymers in pairs have at least two differently bonded types of isocyanate groups, at least one of which has a lower reactivity towards groups reactive with isocyanates than the other type or the other types, and
• b) an at least difunctional isocyanate which has no nitrogen atom which is not part of an NCO group, or a mixture of two or more thereof, as component B and
• c) an 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 part of an NCO or urethane group, as component C,

is included. 2. Polyurethane binder according to claim 1, characterized in that at least 5% by weight of component C, based on the total Polyurethane binders are included.   3. Polyurethane binder according to claim 1 or 2, characterized in that the content of volatile monomers bearing isocyanate groups is less than 1% by weight, the content of tolylene diisocyanate (TDI) is less than 0.1% by weight. 4. Polyurethane binder according to one of claims 1 to 3, characterized in that component A is produced by an at least two-stage reaction in which

• d) a polyurethane prepolymer is prepared in a first stage from an at least difunctional isocyanate and at least one first polyol component, the NCO / OH ratio being less than 2 and free OH groups still present in the polyurethane prepolymer, and
• e) in a second stage, another at least difunctional isocyanate is reacted with the polyurethane prepolymer from the first stage,

wherein the isocyanate groups of the isocyanate added in the second stage have a higher reactivity towards compounds reactive with isocyanates than at least the predominant proportion of the isocyanate groups present in the polyurethane prepolymer from the first stage. 5. Polyurethane binder according to claim 4, characterized in that the further at least difunctional isocyanate in molar excess, based to 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 an at least two-stage reaction in which

• f) a polyurethane prepolymer is produced in a first stage from an at least difunctional isocyanate and at least one first polyol component, the NCO / OH ratio being less than 2 and free OH groups still present in the polyurethane prepolymer, and
• g) in a second stage, another at least difunctional isocyanate and another polyol component are reacted with the polyurethane prepolymer from the first stage,

wherein the isocyanate groups of the isocyanate added in the second stage have a higher reactivity towards compounds reactive with isocyanates than at least the predominant proportion of the isocyanate groups present in the polyurethane prepolymer from the first stage. 7. polyurethane binder according to claim 6, characterized in that the further at least difunctional isocyanate in molar excess, based free OH groups of component A and the other polyol component, is added. 8. Polyurethane binder according to one of claims 4 to 7, characterized shows that in the second stage the ratio OH: NCO between 0.1 and 1 lies and is in particular 0.2 to 0.6. 9. Polyurethane binder according to one of claims 4 to 8, characterized records that in the first stage the ratio OH: NCO less than 1, ins is particularly 0.5 to 0.7. 10. A method for producing an isocyanate group-bearing polyurethane binder, comprising at least three stages, in which

• h) in a first stage, a polyurethane prepolymer is produced from an at least difunctional isocyanate and at least one polyol component, and
• i) in a second stage, another at least difunctional isocyanate or another at least difunctional isocyanate and a further polyol component is added 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 having at least one nitrogen atom which is not part of an NCO group, where

the majority of the isocyanate groups present after completion of the first stage have a lower reactivity towards groups reactive with isocyanates, in particular towards OH groups, than the isocyanate groups of the at least difunctional isocyanate added in the second stage. 11. The method according to claim 10, characterized in that in the second stage the OH: NCO ratio is 0.2 to 0.6. 12. The method according to claim 10 or 11, characterized in that in the first stage the ratio OH: NCO less than 1, in particular 0.4 to 0.7 is. 13. The method according to any one of claims 10 to 12, characterized in that isophoronedi isocyanate (IPDI), tetramethylxylylene diisocyanate (TMXDI), hydrogenated diphenyl methane diisocyanate (MDI _K12 ) or tolylene diisocyanate (TDI) is used as the at least difunctional isocyanate in the first stage. 14. The method according to any one of claims 10 to 13, characterized in that in the second stage as the further at least difunctional isocyanate diphe nylmethane diisocyanate (MDI) is used. 15. A process for the preparation of a low-viscosity, isocyanate group-bearing polyurethane binder with a low content of volatile, isocyanate group-containing monomers, comprising the mixing of four components D, E, F and G, in which

• k) as component D, an isocyanate-bearing polyurethane prepolymer, obtainable by reacting a polyol component with a least difunctional isocyanate,
• l) as component E, a further polyurethane prepolymer carrying isocyanate groups, obtainable by reacting a polyol component with a further at least difunctional isocyanate, the isocyanate groups of which have a higher reactivity towards groups reactive with isocyanates than the isocyanate groups of component D,
• m) as component F, an at least difunctional isocyanate which has no nitrogen atom which is not part of an NCO group, or a mixture of two or more thereof, and
• n) as component G, a further at least difunctional isocyanate or a mixture of two or more isocyanates with an average functionality of at least two, at least one isocyanate having at least one nitrogen atom which is not part of an NCO group,

is used, the amount of component G being such that after completion of the mixing process and after completion of all reactions which may occur between components D, E, F and G, at least 5% by weight, in particular at least 10% by weight, based on the total polyurethane binder, present on component G in the polyurethane binder. 16. The method according to any 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 rpm, 50 ° C) having. 17. Use of a polyurethane binder according to one of claims 1 to 9, or produced by a method according to any one of claims 10 to 16, in the manufacture of adhesives, especially one and two-component ten adhesives, coatings, in particular paints, emulsion paints and Casting resins and moldings, and for coating and in particular Bonding objects, in particular for bonding foils and for the production of film composite materials.   18. Adhesive containing two components H and I, wherein

• o) an isocyanate group-containing polyurethane binder according to one of claims 1 to 9 or an isocyanate group-containing polyurethane binder, prepared according to one of claims 10 to 16, as component H, and
• p) a compound having at least two functional groups which are reactive toward the isocyanate groups of component H and having a molecular weight of up to 50,000, or a mixture of two or more such compounds, as component I.

is used. 19. Adhesive according to claim 18, characterized in that as component I a polyol carrying at least two OH groups is used. 20. Adhesive according to claim 18 or 19, characterized in that com component I is used in such an amount that the ratio of Component H isocyanate groups with component isocyanate groups H reactive, functional groups in component I 5: 1 to 1: 1, is in particular 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).