KR20010053584A - Monomer-poor polyurethane bonding agent having an improved lubricant adhesion - Google Patents

Abstract

The present invention relates to polyurethane binders having a low content of high volatile residual monomers, substantially no transitions, and having improved lubricating adhesion. The present invention also relates to a process for producing the original binder and to an adhesive containing such polyurethane binder. The invention also provides for the preparation of adhesives, in particular one and two components, for example for bonding of mesh, material comprising paper, plastic and / or aluminum, coatings, in particular lacquers, dispersion paints, casting resins and shaped bodies. It relates to the use of a low-viscosity polyurethane binder (the binder has an isocyanate group (NCO group)) in the production of an adhesive containing.

Description

MONOMER-POOR POLYURETHANE BONDING AGENT HAVING AN IMPROVED LUBRICANT ADHESION}

The present invention is a low viscosity polyurethane binder containing isocyanate groups that only has a low content of readily volatile residual monomers, does not form substantially "migrates" and exhibits improved lubrication adhesion. It relates to a method and a polyurethane binder for producing a. The invention also relates to the production of adhesives, in particular single and two-component adhesives, for example for bonding paper, plastic and / or aluminum, coatings, in particular lacquers, emulsion paints and casting resins, as well as mesh-like materials of moldings. It relates to the use of a low viscosity polyurethane binder containing an isocyanate group (NCO group).

Isocyanate-terminated polyurethane prepolymers are known from the past. They are readily crosslinked or chain-extended with suitable compounds, typically polyhydric alcohols, to form high molecular weight materials. Polyurethane prepolymers have gained importance in many fields of use including, for example, the manufacture of adhesives, coatings, casting resins and moldings.

In order to obtain isocyanate-terminated polyurethane prepolymers, it is standard practice to react polyhydric alcohols with excess polyisocyanates, usually at least primarily diisocyanates. The molecular weight can be controlled at least approximately through the ratio of OH groups to isocyanate groups. The ratio of OH groups to isocyanate groups of 1: 1 or approximately 1: 1 generally leads to high molecular weights, and as a statistical average (if diisocyanate is used) one diisocyanate molecule binds to each OH group The ratio of OH: isocyanate groups is about 2: 1, so that oligomerization or chain extension does not ideally occur during the reaction.

In practice, however, the chain-extension reaction cannot be completely suppressed even in this last case, and as a result, at the end of the reaction, a certain amount of the component used in excess remains regardless of the reaction time. For example, when diisocyanates are used as excess components, a substantial proportion of these components generally remain in the reaction mixture for the same reasons as described above.

The presence of such components is particularly problematic when constituting these easily volatilized diisocyanates. The vapors of the diisocyanates are often harmful to the skin, and the use of products having such high volatilities of volatilized diisocyanates can be complicated by the user side, more specifically ambient air, to protect those involved in the processing of the product. Requires complex measures to keep clean for breathing.

Since protective measures and cleanliness measures generally involve significant costs, there is a need on the user side for a product having a low percentage content of diisocyanate which volatilizes easily depending on the isocyanate used.

As used herein, "easily volatilized" material means a material having a vapor pressure of about 0.0007 mmHg at about 30 ° C or having a boiling point of less than about 190 ° C (70 mPa).

When widely used bicyclic diisocyanates such as low viscosity diisocyanates, in particular diphenylmethane diisocyanate, are used instead of easily volatilized diisocyanates, polyurethane binders are generally obtained which have a viscosity outside the range suitable for simple processing. In this case, the viscosity of the polyurethane prepolymer can be lowered by the addition of a suitable solvent, but this is inconsistent with the absence of the solvent normally required. Another method for reducing viscosity without the use of solvents is an excess of monomeric polyisocyanate incorporated into the coating or bond (reactive diluent) during the subsequent curing process (after addition of the hardening agent, or by curing under the influence of moisture). Is to add.

While the viscosity of the polyurethane prepolymers can actually be reduced in this way, the generally incomplete reaction of the reactive diluents leads to the presence of free monomeric polyisocyanates that can "take" into the bonds or coatings, for example It may be present in the coating or bond, in some cases in the material itself which is coated or bonded. Corresponding constituents of the coating or bonding are often referred to by those skilled in the art as "implements". In contact with moisture, the isocyanate groups of the transition react continuously to form amino groups. It is assumed that aromatic amines normally formed in this way have a carcinogenic effect.

The implementation is often often unacceptable, especially in the packaging sector, because all implementations of the transition through the packaging material will cause contamination of the packaged product and the consumer will inevitably contact the transition when using the product.

Thus, such transitions are particularly undesirable in the field of packaging, especially in the packaging of food.

To avoid this drawback, EP-A 0 118 065 proposes to prepare polyurethane prepolymers by a two step process. In the first stage of the process, the monocyclic diisocyanate reacts with the polyhydric alcohol such that the ratio of OH groups: isocyanate groups is less than one, and in the second stage, the bicyclic diisocyanate is combined with the polyhydric alcohol and OH groups: The reaction is carried out in the presence of the prepolymer prepared in the first step so that the proportion of isocyanate groups is less than one. The ratio of OH groups to isocyanate groups of 0.65 to 0.8: 1, preferably 0.7 to 0.75: 1 is recommended for the second step. Prepolymers obtainable in this way still have viscosities of 2500 mPas, 7150 mPas and 9260 mPas at high temperatures (75 ° C. and 90 ° C.). Lubricant miscibility is not mentioned.

EP-A 0 019 120 relates to a two step process for the preparation of a resilient weathering sheet-like material. In the first step of the process, toluene diisocyanate (TDI) is reacted with at least equimolar amounts of the polyol and the reaction mixture obtained is then reacted with diphenylmethane diisocyanate (MDI) and polyol. Polyurethane binders obtainable in this way are said to be curable with water or moisture in the atmosphere. The method provides a product of relatively low viscosity, but the content of free volatilized free diisocyanate (TDI in this case) is still high (0.7% by weight) and to remove excess easily volatilized diisocyanate, for example For example, it can be reduced only by using a time-consuming and energy-intensive method such as thin layer distillation.

German patent DE 197 49 834.5, which is so far unpublished, relates to a low-monomer polyurethane binder and discloses a two-component polyurethane binder having a low monomer content and a low transition content.

For example, films used for the packaging of foods mainly have a high lubricant content. Representative lubricants are, for example, erucin acid amide (EAA) and are usually present in the film in an amount of at least about 400 ppm. Conventional adhesives used to bond such films to form laminates often exhibit degradation of the bondability of the laminate as the lubricant content of the films to be bonded increases. With modern efficient packaging machines, an increase in productivity has been achieved by significantly increasing the working speed of the machine. Films used for this purpose generally have a markedly increased lubricant content (usually at least 600 ppm) for relatively slow packaging machines. Unfortunately, many conventional adhesives exhibit unsatisfactory adhesion to films having a lubricant content of this grade. As a result, the laminate film obtained exhibits inadequate sealing seal adhesion, especially after curing.

Accordingly, a problem posed by the present invention is to provide a polyurethane binder having a low viscosity and a low residual content of easily volatilized diisocyanate of less than about 1% by weight. In the case of toluene diisocyanate (TDI), the residual content of readily volatilized isocyanates should be less than about 0.1% by weight.

Another problem addressed by the present invention is the provision of polyurethane binders having a low percentage content of "implementation", ie a low percentage content of monomeric polyisocyanates.

Another problem addressed by the present invention is to provide a method for producing a polyurethane binder having the above characteristics.

Another problem addressed by the present invention is, in addition to the above properties for easily volatilized isocyanate content and low transition content, further improved lubricant miscibility, i.e. bonding of films with high lubricant content, for example. To provide adhesives and polyurethane binders having improved seal closure adhesion or improved laminate bonding.

The present invention relates to a polyurethane binder characterized by the following: a low content of easily volatile isocyanate-functional monomers containing at least components A, B and C:

a) a polyurethane polymer containing at least two isocyanate groups or a mixture of at least two polyurethane prepolymers containing at least two isocyanate groups is present as component A, and the at least one polyurethane prepolymer comprises at least two differently bonded types of isocyanate groups Or two different polyurethane prepolymers, containing at least two differently bonded kinds of isocyanate groups, in one or more pairs having a lower reactivity to the isocyanate-reactive group than the other species,

b) as component B there is at least a bifunctional isocyanate which does not contain one nitrogen atom which is not part of the NCO group, or a mixture of two or more thereof,

c) As component C there is a mixture of at least difunctional isocyanates or mixtures of at least two isocyanates having an average of at least two functionalities, containing at least one nitrogen atom which is not part of the NCO or urethane group, per molecule of isocyanate.

As used herein, "low viscosity" means a Brookfield viscosity of less than 5,000 mPas at 50 ° C.

As used herein, the expression “polyurethane binder” is understood as a mixture of molecules each containing at least two isocyanate groups, the content of molecules having a molecular weight of at least 500 being at least about 50% by weight, preferably at least about 60% by weight or At least about 70% by weight.

Polyurethane prepolymers containing two or more isocyanate groups, or two or more polyurethane prepolymers containing two or more isocyanate groups, preferably containing two or more isocyanate groups, obtainable by reacting a polyol component having at least two functional isocyanates. Is used as component A.

As used herein, a "polyurethane prepolymer" is understood to be a compound obtained, for example, when the polyol component is reacted with a bifunctional or higher isocyanate. Thus, the expression "polyurethane prepolymer" includes both relatively low molecular weight compounds formed by the reaction of polyols with excess polyisocyanates and oligomeric or polymeric compounds, for example. The expression "polyurethane prepolymer" also includes, for example, compounds formed by the reaction of trivalent or tetravalent polyols with an excess molar amount of diisocyanate relative to the polyol. In this case, one molecule of the resulting compound has several isocyanate groups.

Unless otherwise indicated, the molecular weight for the polymerizable compound represents the number average molecular weight (Mn).

In general, the polyurethane prepolymers used for the purposes of the present invention have a molecular weight in the range of about 150 to about 15,000, or in the range of about 500 to about 10,000, for example about 5,000, but in particular about 700 to about 2,500 Have

In a preferred embodiment of the invention, the at least one polyurethane prepolymer present in the polyurethane prepolymer containing two isocyanate groups or the mixture of the polyurethane prepolymer containing two or more isocyanate groups is of two or more differently bonded species. Isocyanates, and at least one kind has a lower reactivity with respect to isocyanate-reactive groups than other or different kinds of isocyanate groups. Isocyanate groups (relative to one or more other isocyanate groups present in the polyurethane binder) having a relatively low reactivity to the isocyanate-reactive group are also referred to as "less reactive isocyanate groups" and are higher for isocyanate-reactive compounds. Corresponding isocyanate groups having reactivity are also referred to as "more reactive isocyanate groups".

Thus, according to the invention, for example, a bifunctional polyurethane prepolymer containing two differently bonded isocyanate groups can be used as component A, in which one isocyanate group is more reactive than the other isocyanate group. . Such polyurethane prepolymers can be obtained, for example, from reactions of dihydric alcohols with compounds containing, for example, two different isocyanate groups of difunctionality, which reactions are for example about each molecule of a dihydric alcohol. Is reacted with one molecule of a compound containing different isocyanate groups.

Trifunctional or higher polyurethane prepolymers may also be used as component A, in which case one molecule of the polyurethane prepolymer, for example, may contain different numbers of isocyanate groups that are less reactive and more reactive.

In another preferred embodiment, a mixture of two or more different polyurethane prepolymers can be used as component A. The mixture may be a polyurethane prepolymer having isocyanate groups in which each polyurethane molecule is identically bonded. Therefore, at least two different kinds of polyurethane molecules different in at least the properties of the isocyanate groups they have must be present in the mixture. In this embodiment, at least one more reactive and one less reactive kind of isocyanate group, ie a polyurethane molecule containing at least two reactive isocyanate groups and a polyurethane molecule containing at least two less reactive isocyanate groups, is present in the mixture as a whole. It must exist. In addition to molecules containing at least one identically bonded isocyanate group, the mixture may also contain other molecules having both at least one identically bonded isocyanate group and at least one differently bonded isocyanate group.

In addition, part of component A or component A, for example, by reaction of difunctional or higher alcohols with lower molecular weight diisocyanates having a molecular weight of about 400 or less in an equimolar amount (relative to the OH groups of the difunctional or higher alcohol) An abnormality can be formed.

In a preferred embodiment, the polyurethane prepolymer or mixture of two or more polyurethane prepolymers used as component A contains one or more urethane groups per molecule.

In another preferred embodiment of the invention, component A is prepared in two or more reactions:

c) In the first step, a polyurethane prepolymer is prepared from at least the bifunctional isocyanate and at least the first polyol component, the NCO: OH ratio is less than 2 and the free OH groups are still present in the polyurethane prepolymer,

d) in the second step, the other bifunctional or higher isocyanate groups react with the polyurethane prepolymer from the first step,

The isocyanate groups of the isocyanate added in the second stage have a higher reactivity to the isocyanate-reactive compound than at least a major percentage of isocyanate groups present in the polyurethane prepolymer from the first stage.

In another preferred embodiment, the other difunctional or higher isocyanates are added in an excess molar amount relative to the free OH groups of component A.

In another preferred embodiment, component A is prepared by the following two or more reactions:

e) In the first step, the polyurethane prepolymer is prepared from at least bifunctional isocyanate and at least the first polyol component, the NCO: OH ratio is less than 2 and the free OH groups are still present in the polyurethane prepolymer,

f) in the second step, other bifunctional or higher isocyanates and other polyol components are reacted with the polyurethane prepolymer from the first step,

The isocyanate groups of the isocyanate added in the second stage have a higher reactivity to the isocyanate-reactive compound than at least a major percentage of isocyanate groups present in the polyurethane prepolymer from the first stage.

According to the invention, in the preparation of component A in the second stage, the ratio of OH: NCO is preferably from about 0.001 to less than 1: 1, in particular from 0.005 to about 0.8: 1.

In one preferred embodiment of the invention, the OH: NCO ratio in the second stage is about 0.2 to 0.6: 1.

In another preferred embodiment of the invention, the OH: NCO ratio in the first stage is less than 1, in particular 0.5 to 0.7: 1, and the ratio is optionally maintained in the second stage.

As used herein, the expression “polyol component” includes a single polyol or a mixture of two or more polyols that can be used in the preparation of polyurethanes. Polyols are understood as polyhydric alcohols, ie compounds containing at least one OH group in the molecule.

Various polyols can be used as the polyol component for the preparation of component A. These include, for example, aliphatic alcohols containing 2 to 4 OH groups per molecule. OH groups can be primary or secondary. Suitable aliphatic alcohols are, for example, ethylene glycol, propylene glycol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol, heptane-1,7-diol, octane-1,8 -diol, and a person skilled in the art to extend the hydrocarbon chain with one stretch of CH _2, or including their advanced analogs or isomers which may be obtained by introducing a branched carbon chain. Other suitable are in the form of higher alcohols such as glycerol, trimethylolpropane, pentaerythritol and the oligomeric ethers of the above materials, either individually or mixtures of two or more of these ethers with each other.

Another suitable polyol component for the preparation of component A is the reaction product of low molecular weight polyhydric alcohols with alkylene oxides, so called polyethers. The alkylene oxides preferably contain 2 to 4 carbon atoms. Suitable reaction products of this kind are, for example, the reaction products of ethylene glycol, propylene glycol, isomeric butanediol or hexane diols with ethylene oxide, propylene oxide or butylene oxide or mixtures of two or more thereof. Also suitable are polyhydric alcohols, such as glycerol, trimethylolethane and / or trimethylolpropane, pentaerythritol or sugar alcohols, which form polyetherpolyols, with the reaction products of said alkylene oxides. Particularly suitable are polyetherpolyols having a molecular weight ranging from about 100 to about 10,000, preferably from about 200 to about 5,000. According to the present invention, polypropylene glycol having a molecular weight of about 300 to about 2,500 is most preferred. Other suitable polyol components for the preparation of component A are, for example, polyetherpolyols obtained by the polymerization of tetrahydrofuran.

The polyethers are starting compounds containing reactive hydrogen atoms and alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran or epichlorohydrin or mixtures of two or more thereof. React with a known method.

Suitable starting compounds are, for example, water, ethylene glycol, 1,2- or 1,3-propylene glycol, 1,4- or 1,3-butylene glycol, hexane-1,6-diol, octane-1, 8-diol, neopentylglycol, 1,4-hydroxymethyl cyclohexane, 2-methylpropane-1,3-diol, glycerol, trimethylolpropane, hexane-1,2,6-triol, butane-1, 2,4-triol, trimethylolethane, pentaerythritol, mannitol, sorbitol, methylglycoside, sugar, phenol, isononylphenol, resorcinol, hydroquinone, 1,2,2- or 1,1,2- Tris- (hydroxyphenyl) -ethane, ammonia, methylamine, ethylenediamine, tetra- or hexamethylenediamine, triethanolamine, aniline, phenylenediamine, 2,4- and 2,6-diaminotoluene and aniline / form Polyphenylpolymethylene polyamine obtainable by aldehyde condensation reaction.

Polyethers modified with vinyl polymers are also suitable for use as polyol components. Such products can be obtained for example by polymerizing styrene or acrylonitrile or mixtures thereof in the presence of polyethers.

Other suitable polyol components for the preparation of component A are polyesterpolyols having a molecular weight of about 200 to about 10,000. For example, it is possible to use low molecular weight alcohols, in particular ethylene glycol, diethylene glycol, neopentyl glycol, hexanediol, butanediol, propylene glycol, glycerol or trimethylolpropane and polyester polyols obtained by reacting caprolactone Do. Other suitable polyhydric alcohols for the preparation of polyesterpolyols are 1,4-hydroxymethylcyclohexane, 2-methylpropane-1,3-diol, butane-1,2,4-triol, triethylene glycol, tetraethylene Glycols, polyethylene glycols, dipropylene glycols, polypropylene glycols, dibutylene glycols and polybutylene glycols.

Other suitable polyesterpolyols can be obtained by condensation polymerization. For example, dihydric and / or trihydric alcohols can be condensed with less than equimolar amounts of dicarboxylic acids and / or tricarboxylic acids or reactive derivatives thereof to form polyesterpolyols. Suitable dicarboxylic acids are, for example, succinic acid and higher homologues thereof having up to 16 carbon atoms, unsaturated dicarboxylic acids such as maleic acid or fumaric acid, and aromatic dicarboxylic acids, especially isomeric phthalic acids such as phthalic acid, isophthalic acid or terephthalic acid . Citric acid and trimellitic acid are also suitable tricarboxylic acids, for example. Particularly suitable for the purposes of the present invention are at least one polyesterpolyol of the dicarboxylic acid and glycerol having a residual content of OH groups. Particularly suitable alcohols are hexanediol, ethylene glycol, diethylene glycol or neopentyl glycol, or mixtures of two or more thereof. Particularly suitable acids are isophthalic acid and adipic acid, and mixtures thereof.

In a particularly preferred embodiment of the invention, the polyols used as polyol components for the preparation of component A are, for example, polypropylene glycols and / or dipropylene glycols having a molecular weight of about 400 to about 2,500, and polyesterpolyols, preferably Preferably it is a polyester polyol obtainable by condensation polymerization of hexanediol, ethylene glycol, diethylene glycol or neopentyl glycol, or a mixture of two or more thereof and isophthalic acid or adipic acid, or mixtures thereof.

High molecular weight polyesterpolyols include, for example, reaction products of polyhydric, preferably dihydric alcohols (optionally with small amounts of trihydric alcohols) and polybasic, preferably dibasic carboxylic acids. Instead of the free polycarboxylic acids, the corresponding polycarboxylic anhydrides or the corresponding polycarboxylic esters and alcohols having 1 to 3 carbon atoms can also be used if possible. Polycarboxylic acids can be aliphatic, cycloaliphatic, aromatic or heterocyclic or both. These may optionally be substituted, for example with alkyl groups, alkenyl groups, ether groups or halogens. Suitable polycarboxylic acids are, for example, succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetra Chlorophthalic anhydride, endomethylene tetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimer fatty acids or trimer fatty acids, or mixtures of two or more thereof. Small amounts of monofunctional fatty acids may optionally be present in the reaction mixture.

The polyester may optionally contain a small percentage of terminal carboxyl groups. Polyesters obtainable from lactones such as ε-caprolactone, or hydroxycarboxylic acids such as ω-hydroxycaproic acid can also be used.

Polyacetals are also suitable polyol components. Polyacetals are compounds obtainable from glycerol, for example diethylene glycol or hexanediol, or mixtures thereof and formaldehyde. Polyacetals suitable for use according to the invention may also be obtained by the polymerization of cyclic acetals.

Other suitable polyols for the preparation of component A are polycarbonates. Polycarbonates are, for example, diols such as propylene glycol, butane-1,4-diol or hexane-1,6-diol, diethylene glycol, triethylene glycol or tetraethylene glycol, or mixtures of two or more thereof, and diaryl Obtainable by reaction with a carbonate, for example diphenylcarbonate or phosgene.

OH-functional polyacrylates are also suitable polyol components for the preparation of component A. The polyacrylates can be obtained, for example, by polymerization of ethylenically unsaturated monomers containing OH groups. Such monomers are obtainable, for example, by esterification of ethylenically unsaturated carboxylic acids and dihydric alcohols, in which the alcohol is generally present in a slight excess. Suitable ethylenically unsaturated carboxylic acids for this purpose are, for example, acrylic acid, methacrylic acid, crotonic acid or maleic acid. Corresponding OH-functional esters are, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl Acrylate or 3-hydroxypropylmethacrylate or a mixture of two or more thereof.

To prepare component A, the corresponding polyol component is reacted with at least bifunctional isocyanates. Suitable bifunctional or higher isocyanates for the preparation of component A are essentially isocyanates containing at least two isocyanate groups, but for the purposes of the present invention compounds generally containing 2 to 4 isocyanate groups, in particular diisocyanate groups, are preferred.

Bifunctional or higher isocyanates suitable as difunctional or higher isocyanates for the preparation of component A are described below.

The bifunctional or higher isocyanate is, for example, 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-isocyanatomethyl cyclohexane (isophorone diisocyanate, IPDI), 2,4- and 2,6-hexahydrotoluene diisocyanate, tetramethylxylylene diisocyanate (TMXDI), 1,3- and 1,4-phenylenediisocyanate, 2,4- or 2,6-toluenedi Isocyanate, diphenylmethane-2,4'-diisocyanate, diphenylmethane-2,2'-diisocyanate or diphenylmethane-4,4'-diisocyanate or a mixture of two or more of these diisocyanates.

According to the invention, other suitable isocyanates for the preparation of component A are, for example, trifunctional or higher isocyanates obtainable by oligomerization of diisocyanates. Examples of such trifunctional and higher polyisocyanates are triisocyanurates of HDI or IPDI or mixtures thereof or mixed triisocyanurates thereof.

In one preferred embodiment of the invention, diisocyanates containing two isocyanate groups of different reactivity are used for the preparation of component A. Examples of such diisocyanates are 2,4- and 2,6-toluene diisocyanate (TDI) and isophorone diisocyanate (IPDI). With such asymmetric diisocyanates, one isocyanate group generally reacts much faster with isocyanate-reactive groups, such as OH groups, while the remaining isocyanate groups react relatively slowly. Thus, in one preferred embodiment, monocyclic asymmetric diisocyanates containing two different isocyanate groups with different reactivity as described above are used for the preparation of component A.

In one particularly preferred embodiment, 2,4- or 2,6-toluene diisocyanate (TDI) or a mixture of two isomers, in particular pure 2,4-TDI, is used for the preparation of component A.

The polyurethane binder according to the invention contains, as component B, at least difunctional isocyanates and mixtures of two or more thereof which do not contain one nitrogen atom which is not part of the NCO group.

Component B can be formed, for example, of a bifunctional or higher isocyanate or a mixture of two or more isocyanates having an average functionality of about 2 or more.

In a preferred embodiment of the invention, component B is less reactive than isocyanate groups of the polyurethane prepolymers present in component A in which the NCO groups are present, for example, in urethanization, thiurethanation, non-urethanization or allopanlation reactions. It contains one or more of bi- or higher-functional isocyanate groups that are more reactive with NCO-reactive groups.

The isocyanate groups of the difunctional isocyanate present in component B may be different or substantially identical in their reactivity. In a preferred embodiment of the invention, bifunctional or higher isocyanates having the same reactivity of the isocyanate groups can be used as component B.

Component B generally has a molecular weight of about 2,000 or less. However, the molecular weight is preferably low, for example less than about 1,000, less than about 700, or less than about 400 g / mol.

According to the invention, for example 4,4'-diphenylmethane diisocyanate (MDI), 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and HDI, IPDI or TMXDI are Suitable for use as component B.

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

The polyurethane binder according to the invention contains at least about 3% by weight of component B relative to the total polyurethane binder. In a preferred embodiment, the polyurethane binder contains about 5 to about 25 weight percent of component B.

The polyurethane binders according to the invention preferably have a content of easily volatile isocyanate-functional monomers of less than 2% by weight or less than 1% by weight, or preferably less than 0.5% by weight. These limits are particularly readily volatile isocyanate compounds with only a limited risk potential for those involved in processing, for example isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tetramethylxylylene diisocyanate (TMXDI) or Applies to cyclohexanediisocyanate. In the case of certain isocyanate compounds which are readily volatilized, in particular those which present a serious danger to the person involved in processing, their content in the polyurethane binder according to the invention is preferably less than 0.3% by weight, more preferably 0.1% by weight. Less than%. Such specific isocyanate compounds include in particular toluene diisocyanate (TDI). In another preferred embodiment of the invention, the polyurethane binder has a TDI and HDI content of less than 0.05% by weight.

The polyurethane binder according to the invention contains, as component C, a mixture of two or more isocyanates or a mixture of two or more isocyanates having at least two average functionalities containing at least one nitrogen atom which is not part of the NCO or urethane group per isocyanate.

Therefore, NCO-containing carbodiimides obtainable by the reaction of diisocyanates under suitable reaction conditions and in the presence of suitable catalysts are suitable for use in component C.

Suitable isocyanates for forming carbodiimide are, for example, of O = C = NXN = C = O, wherein X is an aliphatic, cycloaliphatic or aromatic radical, preferably an aliphatic or cycloaliphatic radical having 4 to 18 carbon atoms. It is a compound having a general structure.

Examples of suitable isocyanates include 1,5-naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate (MDI), hydrogenated MDI (H ₁₂ -MDI), xylylene diisocyanate (XDI), tetramethylxylyl Ethylene diisocyanate (TMXDI), 4,4'-diphenyldimethylmethane diisocyanate, di- and tetraalkylenediphenylmethane diisocyanate, 4,4'-dibenzyldiisocyanate, 1,3-phenylenediisocyanate, 1, 4-phenylene diisocyanate, isomer of toluene diisocyanate (TDI), 1-methyl-2,4-diisocyanatocyclohexane, 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 diisocyanate, Phosphorus-containing diisocyanate, 4,4'-diisocyanatophenyl perfluoroethane, tetramethoxy moiety -1,4-diisocyanate, 1,4-butane diisocyanate, 1,6-hexane diisocyanate (HDI), dicyclohexyl methane diisocyanate, cyclohexane-1,4-diisocyanate, ethylene diisocyanate, phthalic acid- Bis-isocyanatoethyl ester; Diisocyanates containing reactive halogen atoms such as 1-chloromethylphenyl-2,4-diisocyanate, 1-bromomethylphenyl-2,6-diisocyanate, 3,3-bis-chloromethyl ether-4,4'- Diphenyl diisocyanate.

Other suitable diisocyanates are for example trimethylhexamethylene diisocyanate, 1,4-diisocyanatobutane, 1,12-diisocyanatododecane and dimer fatty acid diisocyanates. Tetramethylene, hexamethylene, undecane, dodecamethylene, 2,2,4-trimethylhexane, 1,3-cyclohexane, 1,4-cyclohexane, 1,3- and 1,4-tetramethylxylene, iso Poron, 4,4-dicyclohexylmethane and lysine ester diisocyanate are particularly suitable.

Particularly suitable are reaction (carbodiimide formation) products of MDI, TDI, HDI or IPDI, or mixtures of two or more thereof.

Other suitable are oligomerization and trimerization products of polyisocyanates which can be obtained by appropriate reaction of polyisocyanates, preferably diisocyanates, to form isocyanurate rings. Particularly suitable are those having an average degree of oligomerization of about 3 to about 5 when oligomerization products are used.

Suitable isocyanates for the reaction are the above-mentioned diisocyanates, with trimerized products of isocyanate HDI, MDI or IPDI being particularly preferred.

Polymeric isocyanates, for example obtained as bottom residues in the distillation of diisocyanates, are also suitable for use as component C. Particularly suitable are "polymerizable MDIs" which are obtainable from distillation residues during the distillation of MDI and which contain at least one nitrogen atom per molecule of isocyanate which is not part of the NCO or urethane groups.

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

Polyurethane binders having the advantages according to the invention can be prepared essentially by any method. However, the two methods described below prove to be particularly advantageous.

For example, polyurethane binders can be prepared directly by preparing component A, followed by the addition of components B and C simultaneously or continuously. Component B may optionally be added with other polyol components.

Accordingly, the present invention relates to a three or more step process for the production of polyurethane binders containing isocyanate groups, characterized by:

h) In the first step, the polyurethane prepolymer is made from at least bifunctional isocyanate and at least one polyol component,

i) in the second step, another bifunctional or higher isocyanate or mixture of two or more thereof which does not contain one nitrogen atom which is not part of the NCO group, and

j) in the third step a difunctional or higher isocyanate or a mixture of two or more isocyanates having at least two average functionalities is added (one or more isocyanates contain one or more nitrogen atoms that are not part of the NCO group),

The major percentage of isocyanate groups present at the end of the first stage has a lower reactivity to the isocyanate-reactive groups, especially OH groups, than the isocyanate groups of the bifunctional or higher isocyanates added in the second stage.

In principle, any of the polyol components already mentioned herein can be used as other polyol components.

In one advantageous embodiment, the ratio of OH: NCO in the first step of the process according to the invention is less than 1: 1. In one preferred embodiment, the ratio of OH groups to isocyanate groups in the first stage is about 0.4 to about 0.7: 1, in particular 0.5 to about 0.7: 1.

The reaction of the bifunctional or higher isocyanate with the polyol component of the first step can be carried out by any method known to those skilled in the art under the general rules for the preparation of polyurethanes. For example, the reaction can be carried out in the presence of a solvent. Suitable solvents are basically any solvents conventionally used in polyurethane chemistry, in particular esters, ketones, halogenated hydrocarbons, alkanes, alkenes and aromatic hydrocarbons. Examples of such solvents are methylene chloride, trichloroethylene, 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, methylethyl Ketone, tetrahydrofuran or tetrachloroethylene or mixtures of two or more of the aforementioned solvents.

If the reaction components themselves are liquid or one or more of the reaction components form a dispersion with a solution or other insufficiently liquid reaction component, there is no need to use a solvent. Reactions without using a solvent represent a preferred embodiment of the present invention.

To carry out the first step of the process according to the invention, the polyol is introduced into a suitable vessel, optionally with a suitable solvent and mixed. The bifunctional or higher isocyanates are then added with continuous mixing. In order to accelerate the reaction, the temperature is usually increased. Generally the reaction mixture is heated to about 40 to about 80 ° C. The exothermic reaction then started increases in temperature. The temperature of the mixture is maintained at about 70 to about 110 ° C, for example about 85 to 95 ° C, in particular about 75 to about 85 ° C, and the temperature is optionally adjusted by suitable external measures such as heating or cooling.

Catalysts commonly used in polyurethane chemistry may optionally be added to the reaction mixture to promote the reaction. Dibutyltin dilaurate or diazabicyclooctane (DABCO) is preferably added. If a catalyst is desired to be used, the catalyst is generally added to the reaction mixture in an amount of about 0.005% by weight, or about 0.01% by weight to about 0.2% by weight, based on the total mixture.

The reaction time of the first stage depends on the polyol component used, the bifunctional or higher isocyanate used, the reaction temperature and, if present, the 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 _H12 ) or toluene diisocyanate (TDI) or mixtures of two or more thereof are difunctional in the first step. It is preferably used as the above isocyanate.

In order to carry out the second step of the process according to the invention, one or more other bifunctional or more isocyanates or mixtures of two or more such isocyanates, which do not contain one nitrogen atom that is not part of the NCO group, optionally contain other polyol components. Together with the component A obtained in the first step. Any polyol or mixtures of two or more thereof from the groups of polyols listed above may be used as constituents of other polyol components, optionally present. However, polypropylene glycols having a molecular weight of about 400 to about 2,500, or polyesterpolyols having a high percentage or more, in particular a major percentage of aliphatic dicarboxylic acids, or mixtures of these polyols, are in the second step of the process according to the invention It is preferably used as a polyol component.

At least one polyisocyanate having a higher reactivity than the relatively low reactive isocyanate groups present in the prepolymer is free of two nitrogen atoms which are not part of the NCO group in the second step of the process according to the invention. It is used as an isocyanate more than functional. In other words, reactive isocyanate groups derived from bifunctional or higher isocyanate groups used from the beginning for the preparation of prepolymer A may be present in the prepolymer, the requirement for which is only a small number of isocyanate groups present in the prepolymer of component A. A higher reactivity, preferably a major percentage, is lower than the isocyanate groups of other difunctional or higher isocyanates added in the second step of the process according to the invention, which do not contain one nitrogen atom which is not part of the NCO group. Is to have.

Bicyclic aromatic symmetric diisocyanates are preferably used as other difunctional or higher isocyanates that do not contain one nitrogen atom that is not part of the NCO group. Bicyclic isocyanates include, for example, diphenylmethane-based diisocyanates, especially 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate. Include. Among the diisocyanates, diphenylmethane diisocyanate, especially 4,4'-diphenylmethane diisocyanate, is particularly preferred as the other difunctional or higher isocyanate of the second step of the process according to the invention.

Other bifunctional or higher isocyanates that do not contain one nitrogen atom that are not part of the NCO group are, in relation to the total amount of polyisocyanate used in all steps of the process according to the invention, from about 1 to about 50% by weight, preferably Is used in an amount of about 10 to about 30 weight percent, more preferably about 15 to about 25 weight percent.

In one preferred embodiment, the OH: NCO ratio of the second stage is about 0.2 to about 0.6: 1, in particular about 0.5: 1 or less. This means the OH: NCO ratio of the component added in the second step excluding all isocyanate groups derived from prepolymer A.

However, polyurethane binders with the advantages according to the invention can also be prepared by mixing the individual components D, E, F and G.

Accordingly, the present invention also provides a process for producing a low viscosity polyurethane binder containing isocyanate groups having a low content of easily volatilized isocyanate-functional monomers by mixing four components D, E, F and G, characterized by the following: It is about:

k) An isocyanate-functional polyurethane prepolymer obtainable by reacting a polyol component with a bifunctional or higher isocyanate is used as component D,

l) Other isocyanate-functional polyurethane prepolymers obtainable by reaction of the polyol component with other difunctional or higher isocyanates, wherein the isocyanate group has a higher reactivity to the isocyanate-reactive group than the isocyanate group of component D are used as component E ,

m) difunctional or higher isocyanates or mixtures of two or more thereof, which do not contain one nitrogen atom which is not part of the NCO group, are used as component F,

n) other difunctional or higher isocyanates or mixtures of two or more isocyanates having at least two average functionalities, where at least one isocyanate contains at least one nitrogen atom which is not part of the NCO group, is used as component G,

The amount of component G is at least 5% by weight, in particular at least 10% by weight, based on the total polyurethane binder after all the reactions between components D, E, F and G have occurred, at the end of the mixing, if present. Weighed to be present in the urethane binder.

The polyurethane binder according to the invention and the polyurethane binder prepared according to the invention preferably have a viscosity of less than 5000 mPas (measured by Brookfield RT DVII (Thermosell), spindle 27, 20 r.p.m., 50 ° C.).

As used herein, the expression “all reactions between components D, E, F and G, if present” refers to the reaction of an isocyanate group with a functional group containing an isocyanate-reactive hydrogen atom. In particular, for example, when component D or E or D and E contain free OH groups, the addition of component F generally leads to the reaction of the isocyanate groups of the component F with the free OH groups. This leads to a decrease in the content of component F. Thus, if a reaction is likely to occur that may result in a decrease in the proportion of component F, after all of the above reactions have been terminated, component F should be added in an amount such that the required minimum amount of component F is present in the polyurethane binder. .

Any of these polyols and mixtures of two or more of said polyols can be used as polyol components for the preparation of components D and E in the process according to the invention. The polyol components mentioned herein in particular suitable for the preparation of component A are also preferably used in the process according to the invention.

Prior studies on component B similarly apply to bifunctional or higher functional isocyanates or mixtures of two or more of these isocyanates to be used as component F which does not contain one nitrogen atom which is not part of the NCO group.

Prior studies on component C have similarly been conducted to mixtures of two or more isocyanates or an average of two or more isocyanates having an average of two or more functionalities of one or more isocyanates to be used as component G containing one or more nitrogen atoms that are not part of the NCO group. Apply.

The polyurethane binders according to the invention and the polyurethane binders prepared according to the invention are in particular easily volatile monomers containing isocyanate groups of less than 2% by weight or less than 1% by weight, less than 0.5% by weight, in particular less than about 0.1% by weight. It is noticeable by the fact that it has a very low content. In this respect, it is particularly emphasized that the process according to the invention does not require any separate process steps to remove easily volatilized diisocyanate components.

Another advantage of the polyurethane binders produced by the process according to the invention is that they have a viscosity in the range which is very advantageous for processing. In particular, the polyurethane binder produced by the process according to the invention has a viscosity of less than 5000 mPas (measured by Brookfield RT DVII (Thermosell), spindle 27, 20 r.p.m., 50 ° C.).

The polyurethane binders according to the invention are suitable for the bonding of objects to coatings, in particular, as such or in the form of solutions in an organic solvent, for example the solvent.

The invention therefore also relates to the preparation of adhesives, in particular single and two-component adhesives, coatings, in particular lacquers, emulsion paints and castings, of polyurethane binders according to the invention, or of polyurethane binders prepared by the method according to the invention. In addition to resins, it relates to moldings and coatings, and in particular for the bonding of articles, in particular for the bonding of films and for the production of laminated films.

The polyurethane binder according to the invention or the polyurethane binder made by one of the methods according to the invention is particularly suitable for bonding plastics and, in one preferred embodiment, plastic films metallized with plastic films, metals or metal oxides, and metals. Used to laminate foils, in particular aluminum foils.

The curing process, ie the crosslinking of the individual polyurethane binder molecules via the free isocyanate groups, can be carried out only under the influence of moisture in the atmosphere, ie without the need to add a curing agent. However, polyfunctional crosslinking agents, for example amines, or more specifically polyfunctional alcohols, are preferably added as curing agents (two-component systems).

Film laminates made from the products made according to the invention are safe for heat sealing. This is due to the reduced percentage of workable low molecular weight products in the polyurethane binder. During the heat sealing process, the preferred processing temperature of the adhesive prepared according to the present invention is about 30 to about 90 ° C.

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

o) polyurethane binders containing isocyanate groups according to the invention or polyurethane binders containing isocyanate groups produced by the process according to the invention are used as component H,

p) Compounds containing at least two functional groups reactive with isocyanate groups of component H with a molecular weight of 50,000 or less, or mixtures of two or more of these compounds, are used as component I.

Thus, any polyurethane binder according to the invention can be used as component H.

Compounds containing two or more functional groups reactive with the isocyanate groups of component F having a molecular weight of 2,500 or less or mixtures of two or more of these compounds are preferably used as component I. The at least two functional groups reactive with the isocyanate groups of component F may in particular be selected from amino groups, mercapto groups or OH groups. Compounds suitable for use in component G may contain amino groups, mercapto groups or OH groups individually or in mixtures.

The functionality of the compounds suitable for use in component I is generally at least about 2. Component I preferably has a percentage of compounds with higher functionality, for example 3, 4 or more. The overall (average) functionality of component I is for example at least about 2 (eg when only bifunctional compounds are used as component I), for example about 2.1, 2.2, 2.5, 2.7 or 3. Component I may optionally have higher functionality, such as about 4 or more.

Component I preferably contains a polyol having at least two OH groups. All polyols described above are suitable for use in component I as long as the limit of the upper limit of the molecular weight is satisfied.

Component I is generally such that the ratio of isocyanate groups of component H to the functional groups reactive with isocyanate groups of component H in component I is from about 5: 1 to about 1: 1, in particular from about 2: 1 to about 1: 1. Used in quantity.

Adhesives according to the invention generally have a viscosity (Brookfield RVT DVII, spindle 27, 20 r.p.m., 40 ° C.) of about 250 to about 10,000 mPas, in particular about 500 to about 8000 mPas or about 5000 mPas.

The adhesive according to the invention may optionally contain additives. The additive may constitute about 30% by weight of the total adhesive.

Suitable additives for use in accordance with the invention include, for example, plasticizers, stabilizers, antioxidants, dyes, light stabilizers and fillers.

Suitable plasticizers represent, for example, plasticizers which are preferred plasticizers based on phthalic acid esters esterified with phthalic acid, especially dialkylphthalates, straight alkanols having from about 6 to about 12 carbon atoms. Dioctylphthalate is particularly preferred.

Other suitable plasticizers are benzoate plasticizers, for example sucrosebenzoate, diethylene glycol dibenzoate and / or diethylene glycol benzoate, phosphate plasticizer, in which about 50 to about 95% of all hydroxyl groups are esterified. Agents such as t-butylphenyl diphenylphosphate, polyethyleneglycol and derivatives thereof such as diphenylether of poly (ethyleneglycol), liquid resin derivatives such as methyl esters of vegetable, vegetable or animal oils, For example glycerol esters of fatty acids and their polymerization products.

Stabilizers or antioxidants suitable for use as additives according to the invention include high molecular weight (Mn) sterically hindered phenols, polyhydric phenols and sulfur- and phosphorus-containing phenols. Suitable phenols for use as additives according to 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-methylene-bis- (2,6-di-tert-butylphenol); 4,4-thiobis- (6-tert-butyl-o-cresol); 2,6-di-tert-butylphenol; 6- (4-hydroxyphenoxy) -2,4-bis- (n-octylthio) -1,3,5-triazine; Di-n-octadecyl-3,5-di-tert-butyl-4-hydroxybenzyl phosphonate; 2- (n-octylthio) -ethyl-3,5-di-tert-butyl-4-hydroxybenzoate; And sorbitol hexa- [3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate].

Suitable light stabilizers are for example those sold under the trade name of Tinuvin (registered trademark, manufactured by Ciba Geigy).

In order to change certain properties, other additives may be incorporated into the additives according to the invention. Such other additives are, for example, dyes such as titanium dioxide, fillers such as talc, clay and the like. The adhesives according to the invention are suitable for use in small amounts of thermoplastic polymers or copolymers, such as ethylene / vinylacetate (EVA), ethylene / acrylic acid, ethylene / methacrylate and ethylene, which optionally provide additional elasticity, rigidity and strength to the adhesive. / n-butylacrylate copolymer may optionally be contained. Wetting properties of certain hydrophilic polymers such as polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl methyl ether, polyethylene oxide, polyvinyl pyrrolidone, polyethyl oxazoline or starch or cellulose esters, in particular adhesives It is possible to add acetate with a degree of substitution of less than 2.5, which increases the ratio, which is preferred according to the invention.

The following examples are intended to illustrate the invention and in no case limit the invention.

Example

Explanation of Raw Materials and Abbreviations in Table 1:

A1-A5: Adhesive Formulations 1-5

H: curing agent (polyol mixture), OHV = 138.8

PE1: Propylene glycol based polyether

PE2: Propylene Glycol Based Polyether

DEG: Diethylene Glycol

PES: Polyester based on dipropylene glycol with adipic acid, diethylene glycol, phthalic acid and two OH groups

PE3: Propylene Glycol Based Polyether

MDI-C: MDI Carbodiimide Dimer

HDI-T: HDI trimer

HDI-O: HDI oligomer

MDI-P: Polymerizable MDI (Distillation Column Bottom Residue)

ADR-1: OH: NCO addition ratio of component A and component B

ADR-T: Total OH: NCO Addition Ratio

V: Viscosity (Brookfield RVTD, 40 ℃)

MC: monomer content (% by weight of the total formulation)

m-TDI: monomeric TDI

m-MDI: monomeric MDI

OHV: OH value in [mg KOH / g]

NCO value: NCO content (% by weight of the total formulation)

NCO-F: Final NCO Content

Abbreviations and descriptions in Table 2

E1-8: Examples 1-8

C1-2: Comparative Examples 1 and 2

LS: Laminated Structure

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

F2: 70 μ thick polyethylene (PE) film with plasticizer content of 400 ppm of erucin acid amide (EAA)

F3: 60 μ thick polyethylene (PE) film with plasticizer content of 800 ppm of erucin acid amide (EAA)

(EAA) LA: Laminated Joint

SSA: Sealed Seal Joint

coh. AS: Cohesive Adhesive Splitting

adh. alt. : Alternating splices, splicing errors alternately in each material

The mixing ratio of the binder formulation to the curing agent is 1: 1 in Examples 1 to 8 and 100: 70 in Comparative Examples 1 and 2.

In all examples, the amount used is 2 g / m ² .

Claims (21)

A polyurethane binder, characterized by a low content of easily volatile isocyanate-functional monomer, containing at least components A, B and C: a) a polyurethane polymer containing at least two isocyanate groups or a mixture of at least two polyurethane prepolymers containing at least two isocyanate groups is present as component A, and the at least one polyurethane prepolymer comprises at least two differently bonded types of isocyanate groups Or two different polyurethane prepolymers, containing at least two differently bonded kinds of isocyanate groups, in one or more pairs having a lower reactivity to the isocyanate-reactive group than the other species, b) as component B there is at least a bifunctional isocyanate which does not contain one nitrogen atom which is not part of the NCO group, or a mixture of two or more thereof, c) As component C there is a mixture of at least difunctional isocyanates or mixtures of at least two isocyanates having an average of at least two functionalities, containing at least one nitrogen atom which is not part of the NCO or urethane group, per molecule of isocyanate. The polyurethane binder according to claim 1, wherein at least 5% by weight of component C is present with respect to the total polyurethane binder. The polyurethane binder according to claim 1 or 2, wherein the content of the easily volatilized monomer containing an isocyanate group is less than 1% by weight, and the content of toluene diisocyanate (TDI) is less than 0.1% by weight. The polyurethane binder according to any one of claims 1 to 3, wherein component A is prepared by the following two or more reactions: d) In the first step, the polyurethane prepolymer is prepared from at least bifunctional isocyanate and at least the first polyol component, the NCO: OH ratio is less than 2 and the free OH groups are still present in the polyurethane prepolymer, e) in the second step, other bifunctional or higher isocyanates are reacted with the polyurethane prepolymer from the first step, The isocyanate groups of the isocyanate added in the second stage have a higher reactivity to the isocyanate-reactive compound than at least a major percentage of isocyanate groups present in the polyurethane prepolymer from the first stage. 5. A polyurethane binder according to claim 4, wherein other difunctional or higher isocyanates are added in an excess molar amount relative to the free OH groups of component A. The polyurethane binder according to any one of claims 1 to 3, wherein component A is prepared by the following two or more reactions: f) In the first step, the polyurethane prepolymer is prepared from at least bifunctional isocyanate and at least the first polyol component, the NCO: OH ratio is less than 2 and the free OH groups are still present in the polyurethane prepolymer, g) in the second step, other bifunctional or higher isocyanates and other polyol components are reacted with the polyurethane prepolymer from the first step, The isocyanate groups of the isocyanate added in the second stage have a higher reactivity to the isocyanate-reactive compound than at least a major percentage of isocyanate groups present in the polyurethane prepolymer from the first stage. 7. A polyurethane binder according to claim 6, wherein other difunctional or higher isocyanates are added in an excess molar amount relative to the free OH groups of component A and the other polyol component. 8. The polyurethane binder according to claim 4, wherein the OH: NCO ratio in the second stage is from 0.1 to 1: 1, in particular from 0.2 to 0.6: 1. 9. 9. The polyurethane binder according to claim 4, wherein the OH: NCO ratio of the first stage is less than 1: 1, in particular 0.5 to 0.7: 1. Three or more processes for the production of polyurethane binders containing isocyanate groups, characterized by the following: h) In the first step, the polyurethane prepolymer is made from at least bifunctional isocyanate and at least one polyol component, i) In the second step, other difunctional or higher isocyanates or other difunctional or higher isocyanates and other polyol components are added, j) In the third step, a bifunctional or higher isocyanate or a mixture of two or more isocyanates having at least two average functionalities is added (one or more isocyanates contain one or more nitrogen atoms that are not part of the NCO group), The major percentage of isocyanate groups present at the end of the first stage has a lower reactivity to the isocyanate-reactive groups, especially OH groups, than the isocyanate groups of the bifunctional or higher isocyanates added in the second stage. The method of claim 10, wherein the OH: NCO ratio of the second stage is from 0.2: 1 to 0.6: 1. 12. The polyurethane binder according to claim 10 or 11, characterized in that the OH: NCO ratio of the first stage is less than 1: 1, in particular 0.4: 1 to 0.7: 1. 13. The isophorone diisocyanate (IPDI), tetramethylxylylene diisocyanate (TMXDI), hydrogenated diphenylmethane diisocyanate according to any one of claims 10 to 12, as the bifunctional or higher isocyanate in the first step. (MDI _H12 ) or toluene diisocyanate (TDI) is used. The process according to claim 11, wherein diphenylmethane diisocyanate (MD) is used as the other difunctional or higher isocyanate in the second step. A process for producing a low viscosity polyurethane binder containing isocyanate groups with a low content of easily isocyanate-functional monomers by mixing four components D, E, F and G, characterized by the following: k) An isocyanate-functional polyurethane prepolymer obtainable by reacting a polyol component with a bifunctional or higher isocyanate is used as component D, l) Other isocyanate-functional polyurethane prepolymers obtainable by reaction of the polyol component with other difunctional or higher isocyanates, wherein the isocyanate group has a higher reactivity to the isocyanate-reactive group than the isocyanate group of component D are used as component E , m) difunctional or higher isocyanates or mixtures of two or more thereof, which do not contain one nitrogen atom which is not part of the NCO group, are used as component F, n) other difunctional or higher isocyanates or mixtures of two or more isocyanates having at least two average functionalities, where at least one isocyanate contains at least one nitrogen atom which is not part of the NCO group, is used as component G, The amount of component G is at least 5% by weight, in particular at least 10% by weight, based on the total polyurethane binder after all the reactions between components D, E, F and G have occurred, at the end of the mixing, if present. Weighed to be present in the urethane binder. The method according to any one of claims 11 to 15, wherein the polyurethane binder has a viscosity of less than 5,000 mPas (measured by Brookfield RT DVII (Thermosell), spindle 27, 20 r.p.m., 50 ° C). Use of a polyurethane binder according to any one of claims 1 to 9, or a polyurethane binder prepared by the method according to any one of claims 10 to 16, comprising an adhesive, in particular a single component and a 2- The use of component adhesives, coatings, in particular lacquers, emulsion paints and casting resins, as well as moldings and coatings, and in particular of bonding of articles, in particular of bonding of films and of laminated films. Adhesives containing two components H and I: o) Component H is a polyurethane binder containing an isocyanate group according to any one of claims 1 to 9 or a polyurethane binder containing an isocyanate group prepared by the method according to any one of claims 10 to 16. Used as p) Compounds containing two or more functional groups reactive with the isocyanate groups of component F with a molecular weight of 50,000 or less or mixtures of two or more of these compounds are used as component I. 19. The adhesive according to claim 18, wherein a polyol containing at least two OH groups is used as component I. 20. The method according to claim 18 or 19, wherein the ratio of isocyanate groups of component H to functional groups reactive with isocyanate groups of component H in component I is from 5: 1 to 1: 1, in particular from 2: 1 to 1: 1. Adhesive, characterized in that component I is used in an amount to be. The adhesive according to any one of claims 18 to 20, having a viscosity of 500 to 6,500 cps (Brookfield, RVTD, 40 ° C).