HK1032975A - Polyurethane binding agents having a low content of highly volatile monomers - Google Patents
Polyurethane binding agents having a low content of highly volatile monomers Download PDFInfo
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- HK1032975A HK1032975A HK01103562.1A HK01103562A HK1032975A HK 1032975 A HK1032975 A HK 1032975A HK 01103562 A HK01103562 A HK 01103562A HK 1032975 A HK1032975 A HK 1032975A
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Description
The invention relates to polyurethane adhesives and to a method for producing low-viscosity polyurethane adhesives having isocyanate groups, wherein the polyurethane adhesives, despite their low viscosity, have only a low amount of volatile residual monomers and do not substantially migrate. The invention also relates to the use of a low-viscosity polyurethane adhesive with isocyanate groups (NCO groups) for producing adhesives, in particular one-component and two-component adhesives, for example for bonding web materials consisting of paper, plastic or aluminum or mixtures of two or more thereof; the use of coatings, in particular paints, dispersion pigments and casting resins, and also mouldings.
Polyurethane prepolymers with isocyanate end groups have been known for a long time. They can be chain extended in a simple manner with suitable hardeners, mostly polyfunctional alcohols, to high molecular weight materials or to form crosslinks. Polyurethane prepolymers are of interest in many fields of application, such as the production of adhesives, coatings, casting resins and moldings.
To obtain isocyanate-terminated polyurethane prepolymers, polyfunctional alcohols are generally reacted with an excess of polyisocyanates, generally at least and predominantly diisocyanates. The molecular weight is in this case adjusted at least approximately by the ratio of hydroxyl groups to isocyanate groups. Although a ratio of hydroxyl groups to isocyanate groups of 1: 1 or close to 1: 1 generally leads to high molecular weights, for example in the case of diisocyanates having a ratio of about 2: 1, a statistical average of one diisocyanate molecule per hydroxyl group is pendant, so that in the ideal case no oligomers and no chain extension occur during the reaction.
In practice, such a chain extension reaction is naturally not prevented, and therefore the reaction is terminated independently of the reaction time, leaving a certain amount of the components used in excess. If, for example, an excess of diisocyanate is charged, the component residual amounts are generally not insignificant, based on the fact described in the reaction mixture.
The interference effect is particularly pronounced when the substances present are volatile diisocyanates. The steam of diisocyanates is generally unhealthy and the use of such products with high contents of volatile diisocyanates requires complex measures from the perspective of the user to protect the person working with the product, in particular measures to purify the air.
Since protection and cleaning measures usually lead to high capital investment or costs, there is a need from the user's point of view for products which, depending on the isocyanate used, contain as low as possible volatile diisocyanate components.
As used herein, "volatile" materials are those that have a vapor pressure above about 0.0007 mmHg or a boiling point below about 190℃ (70mPa) at about 30℃.
If the volatile diisocyanates are replaced by less volatile diisocyanates, in particular by widely spaced bicyclic diisocyanates, such as diphenylmethane diisocyanate, the viscosity of the polyurethane adhesives obtained is generally outside the range required by simple processing methods. In these cases, the viscosity of the polyurethane prepolymer can be reduced by adding suitable solvents, which is in contrast to the most demanding solvent-free process. Another possibility for avoiding the use of solvents and reducing the viscosity is the addition of excess polyisocyanate monomers, which are embedded in the coating or adhesive layer (reactive diluents) in the scope of the hardening process which is carried out later (hardening after addition of the hardener or by the influence of humidity).
Although the viscosity of the polyurethane prepolymer is actually reduced in this way, incomplete reaction of the reactive diluent generally leads to free polyisocyanate monomers in the adhesive layer or coating, which can "roam" into, for example, the coating or adhesive layer or also partly within the coated or bonded material. This component of the coating or bonding layer is known in the industry as "migrates". The isocyanate groups of the migrates are continuously converted into amino groups by contact with moisture. The aromatic amines thus formed are generally suspected of carcinogenic effect.
In the packaging field in particular, migration is often intolerable, since the migration of the migration through the packaging material leads to contamination of the packaged goods and the consumer must come into contact with this migration when using the goods.
Such migration is particularly undesirable in the field of packaging, particularly in the field of food packaging.
To avoid the above-mentioned disadvantages, it is proposed, from EP-A0118065, that the production of polyurethane prepolymers is divided into two operations. Here, first, in a first step, a monocyclic diisocyanate and a polyfunctional alcohol are reacted in a ratio of hydroxyl groups to isocyanate groups of less than 1, and then, in a second step, a bicyclic diisocyanate and a polyfunctional alcohol are reacted in a ratio of carboxyl groups to isocyanate groups of less than 1 and in the presence of the prepolymer produced in the first step. In the second step, the ratio of hydroxyl groups to isocyanate groups is preferably 0.65 to 0.8, more preferably 0.7 to 0.75. The prepolymer thus obtained still had a viscosity of 2500mPas or 7150mPas and 9260mPas at high temperature (75 ℃ or 90 ℃).
DE-A3401129 relates to a process for producing mixed polyurethane prepolymers in which polyfunctional alcohols are first reacted with the faster reacting isocyanate groups of an asymmetric diisocyanate to give slower reacting groups, whereupon the reaction product incorporates a symmetric diisocyanate whose likewise reactive isocyanate groups react faster than the slower reacting groups of the first-mentioned polyfunctional isocyanate compounds. The polyurethane prepolymers described have a high viscosity and thus a high processing temperature, allowing application only under conditions which allow a high processing temperature.
EP-A0019120 relates to a process for producing elastic, weather-resistant planar objects. Therefore, a two-step process is provided: in a first step Toluene Diisocyanate (TDI) is reacted with at least an equimolar amount of a polyol and the resulting reaction product is subsequently reacted with diphenylmethane diisocyanate (MDI) and a polyol. The polyurethane adhesive thus obtained should be capable of hardening with water or moisture in the air. Although the process described leads to products of relatively low viscosity, the content of free, volatile diisocyanates (TDI in this case) is still high (0.7% by weight) and is only reduced when time-consuming and energy-consuming methods are used to remove excess, volatile diisocyanates, for example thin-layer distillation.
Composite membranes are often used in high temperature applications such as food cooking. However, when the film is subjected to high temperatures, as are commonly encountered in cooking food, delamination often occurs in the adhesive field in composites made with conventional adhesives.
It is therefore an object of the present invention to provide polyurethane adhesives which have the lowest possible viscosity and the lowest possible residual content of volatile diisocyanates of less than about 1% by weight, where the residual content of volatile isocyanates in the case of Toluene Diisocyanate (TDI) is less than about 0.1% by weight.
It is a further object of the invention to provide a polyurethane adhesive which allows processing at as low a processing temperature as possible.
It is a further object of the present invention to provide a polyurethane adhesive having as low a "migrant" content, i.e. having as low a polyisocyanate monomer content as possible.
It is yet another object of the present invention to provide a polyurethane adhesive whereby thin film composite structures can be produced that exhibit no or only minimal delamination at elevated temperatures.
It is another object of the present invention to provide a process that produces a polyurethane adhesive having the above characteristics.
The invention relates to a polyurethane adhesive with a low content of volatile isocyanate-containing monomers, comprising at least components A and B, of which: (a) a polyurethane prepolymer having at least two isocyanate groups or a mixture of two or more polyurethane prepolymers having at least two isocyanate groups as component a, wherein the polyurethane prepolymer having two isocyanate groups or the mixture of two or more polyurethane prepolymers having isocyanate groups contains at least two different combinations of isocyanate groups of which at least one type is less reactive towards isocyanate-reactive groups than the other type or types, (B) an at least difunctional isocyanate as component B having a lower molecular weight than the polyurethane prepolymer contained in component a and having higher reactivity towards isocyanate-reactive compounds than the type contained in component a and having lower reactivity towards isocyanate-reactive compounds.
Low viscosity in the context of the present invention means a viscosity of less than 5000mPas at 50 ℃ (measured according to the Brookfield method).
The term "polyurethane adhesive" as referred to herein means a mixture of molecules each containing at least two isocyanate groups, wherein the molecular weight of the molecules above 500 is at least about 50 wt%, preferably at least about 60 wt%, or about 70 wt%.
As component A there is used a polyurethane prepolymer having at least two isocyanate groups or a mixture of two or more polyurethane prepolymers having at least two isocyanate groups, which is preferably obtained by reaction of a polyol component with an at least difunctional isocyanate.
By polyurethane prepolymer is meant herein a compound obtained, for example, from the reaction of a polyol component and an at least difunctional isocyanate. The term "polyurethane prepolymer" includes both relatively low molecular weight compounds, such as those resulting from the reaction of a polyol and an excess of a polyisocyanate, and oligomers or polymers. The term "polyurethane prepolymer" also includes compounds which are formed, for example, by reacting a tri-or tetrahydric polyol with a molar excess of diisocyanate, based on the polyol. In this case, the compound obtained has a plurality of isocyanate groups in the molecule.
Based on the molecular weight data of the polymer compounds, the average molecular weight (Mn) is the index average molecular weight, provided that no further indications are given.
Typically, the polyurethane prepolymers used in the present invention have a molecular weight of from about 500 to about 15,000, or from about 500 to about 10,000, such as 5,000, especially from about 700 to about 2,500.
The polyurethane prepolymer having two isocyanate groups or the mixture of two or more polyurethane prepolymers having isocyanate groups has at least two different types of isocyanate groups, at least one of which is less reactive with respect to isocyanate reactive groups than the other isocyanate group or groups. In comparison, an isocyanate group which is less reactive, i.e. less reactive towards isocyanate-reactive groups (at least compared to other isocyanate groups present in a polyurethane binder), is hereinafter referred to as "less reactive isocyanate group", and a corresponding isocyanate group which is more reactive towards isocyanate-reactive compounds is also referred to as reactive isocyanate group.
For example, difunctional polyurethane prepolymers having two different combinations of isocyanate groups, one of which has a relatively higher reactivity towards isocyanate-reactive groups than the other, can be used as component A in the present invention. Such polyurethane prepolymers can be obtained by reacting difunctional alcohols with two different, for example difunctional, isocyanate-containing compounds, in such a way that on average each molecule of the difunctional alcohol reacts with each molecule of the compound having a different isocyanate group.
It is likewise possible to use tri-or higher-functional polyurethane prepolymers as component A, where one molecule of the polyurethane prepolymer may have different numbers of low-reactive and high-reactive isocyanate groups.
In addition, mixtures of two or more polyurethane prepolymers can be used as component A in the present invention. The so-called mixtures are polyurethane prepolymers in which each molecule carries isocyanate groups of the same chemical combination type, where in total at least one highly reactive and one less reactive isocyanate group must be present in the mixture. It is likewise possible for the mixture to contain, in addition to molecules carrying one or more isocyanate groups of the same type, other molecules which carry one or more isocyanate groups of the same type, but also one or more isocyanate groups of a different type.
The polyurethane adhesive according to the invention contains, in addition to component A, an at least difunctional isocyanate whose molecular weight is lower than that of the polyurethane prepolymer contained in component A and whose isocyanate groups have a relatively higher reactivity with respect to isocyanate-reactive compounds than the low-reactive isocyanate groups contained in component A.
Typically, component B has a molecular weight of up to about 1000, preferably up to 720 or less, for example about 550, 500, 450, 400 or less. Suitable as component B are, for example, low molecular weight diisocyanates or reaction products of difunctional or higher-functional alcohols having a molecular weight of up to about 300, based on the hydroxyl groups of the difunctional or higher-functional alcohols, with an at least equimolar amount of such low molecular weight diisocyanates. Also suitable as component B are, for example, the terpolymerization products of difunctional isocyanates, isocyanurates.
The polyurethane adhesives according to the invention contain at least 5 wt.%, based on the total amount of polyurethane adhesive, of component B.
The polyurethane adhesives according to the invention preferably contain readily volatile monomers with isocyanate groups, from less than 2% by weight or 1% by weight or preferably less than 0.5% by weight. This range is particularly suitable for isocyanate compounds which are volatile and have only a limited potential for harm to the workers working with them, such as isophorone diisocyanate (IPDI), Hexamethylene Diisocyanate (HDI), tetramethylxylylene diisocyanate (TMXDI) or cyclohexyl diisocyanate. For certain readily volatile isocyanate compounds, in particular those which are potentially dangerous to the person working with them, their proportion in the polyurethane adhesive according to the invention is preferably less than 0.3% by weight, in particular less than 0.1% by weight. The isocyanate compounds just mentioned include, in particular, Toluene Diisocyanate (TDI). In a further preferred embodiment of the invention, the polyurethane adhesive contains less than 0.05% by weight of TDI and HDI.
In a preferred embodiment of the invention, the polyurethane adhesives according to the invention additionally contain, in addition to components A and B, component H, an at least trifunctional isocyanate.
Suitable isocyanates which are at least trifunctional are, for example, the trimerization or oligomerization products of polyisocyanates which have already been explained above, as are obtained by suitable reaction of polyisocyanates, preferably diisocyanates, to form isocyanurate ring structures. If an oligomerization product is used, preference is given to those oligomerization products whose degree of oligomerization averages from about 3 to 5.
Suitable isocyanates for producing the terpolymers are the diisocyanates already mentioned above, preference being given here in particular to the terpolymerization products of the isocyanates HDI, MDI or IPDI.
Also suitable as component H are polymers of isocyanates, for example those which are residues of the still bottoms which are formed during the distillation of diisocyanates. Particularly suitable here are polymers of MDI, such as are obtainable from distillation bottoms in the distillation of MDI.
In a preferred embodiment of the invention, use is made of trimer isocyanurate T1890 (manufacturer: Bayer AG) of, for example, Desmodur N3300, Desmodur N100, IPDI or triphenylmethane triisocyanate.
Component H is preferably used in an amount of about 1 to about 30% by weight, in particular between about 5 and about 25% by weight, for example about 12 to about 20% by weight.
In a preferred embodiment of the invention, component A is obtained by at least two reaction steps, namely: (c) in a first step, a polyurethane prepolymer is obtained from an at least difunctional isocyanate and at least one first polyol component, wherein the NCO/OH ratio is less than 2 and free hydroxyl groups are also present in the polyurethane prepolymer. (d) In the second step, another at least difunctional isocyanate is reacted with the polyurethane prepolymer obtained in the first step, wherein the isocyanate groups of the isocyanate added in the second step have a higher reactivity than the isocyanate-reactive compounds than at least the major part of the isocyanate groups present in the polyurethane prepolymer obtained in the first step.
In another preferred embodiment, a molar excess of further at least difunctional isocyanates is added, the moieties of the further at least difunctional isocyanates which are not reacted with hydroxyl groups, based on the free hydroxyl groups of component A, being component B.
In a further preferred embodiment component A is obtainable by a reaction in at least two stages, namely: (e) in a first step, a polyurethane prepolymer is formed from an at least difunctional isocyanate and at least one first polyol component, the NCO/OH ratio being less than 2 and the polyurethane prepolymer also having free hydroxyl groups, and (f) in a second step, an additional at least difunctional isocyanate and a further polyol component are reacted with the polyurethane prepolymer obtained in the first step, the isocyanate groups of the isocyanate added in the second step having a higher reactivity towards isocyanate-reactive compounds than at least the predominant isocyanate groups contained in the polyurethane prepolymer obtained in the first step.
In another preferred embodiment, a molar excess of further at least difunctional isocyanates is added, based on the free hydroxyl groups of component A and the further polyol component, the fraction of the further at least difunctional isocyanates which is not reacted with hydroxyl groups being component B.
It is preferred within the scope of the present invention that the OH/NCO ratio in the second stage for component A is from about 0.001 to less than 1, especially from 0.005 to about 0.8.
In a preferred embodiment of the invention, the OH/NCO ratio of the second step is about 0.2 to about 0.6.
In a further preferred embodiment of the invention, the OH to NCO ratio in the first step is less than 1, in particular from 0.5 to 0.7, where the above-mentioned ratio may be observed in the second step.
The term "polyol component" as used herein includes a single polyol or a mixture of two or more polyols and is contemplated for use in the production of polyurethanes. Polyols are understood to be polyfunctional alcohols, i.e. compounds having more than one hydroxyl group in the molecule.
As the polyol component for producing component A, it is possible to use a large amount of a polyol. For example, fatty alcohols containing 2 to 4 hydroxyl groups per molecule. The hydroxyl group may be primary or secondary. Suitable aliphatic alcohols include ethylene glycol, propylene glycol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 7-heptanediol, 1, 8-octanediol and their higher homologues or isomers, such as those skilled in the art, in which a stepwise increase in the carbon chain or branching off from the carbon chain per methylene group is observed. Also suitable are high-functional alcohols, such as glycerol, trimethylolpropane, pentaerythritol, and also the abovementioned substances and the underlying oligopolyethers themselves or mixtures of two or more of the abovementioned ethers.
As the polyol component for producing component A, furthermore, the reaction products of low molecular weight polyfunctional alcohols with alkylene oxides, so-called polyethers, can be used. The alkylene oxide preferably has 2 to 4 carbon atoms. Suitable examples are the products of the reaction of ethylene glycol, propylene glycol, the isomeric butanediols or hexanediols with ethylene oxide, propylene oxide or butene oxide, or mixtures of two or more of the foregoing. Also suitable are polyfunctional alcohols, such as glycerol, trimethylolethane or trimethylolpropane, pentaerythritol or sugar alcohols, or polyether polyols formed by reacting mixtures of two or more of the above with the alkylene oxides. Particularly suitable are polyether polyols having a molecular weight of from about 100 to about 10,000, preferably from about 200 to about 5,000. More particularly preferred are polypropylene glycols within the scope of the present invention having a molecular weight of from about 300 to about 2,500. Also suitable as polyol components for producing component A are polyether polyols, for example those obtained by the polymerization of tetrahydrofuran.
Polyethers are obtained in a manner familiar to the skilled worker by reacting starting compounds having reactive hydrogen atoms with alkylene oxides, for example ethylene oxide, propylene oxide, butylene oxide, styrene oxide, tetrahydrofuran or epichlorohydrin or mixtures of two or more thereof.
Suitable starter compounds are, for example, water, ethylene glycol, 1, 2-or 1, 3-propanediol, 1, 4-or 1, 3-butanediol, 1, 6-hexanediol, 1, 8-octanediol, neopentyl glycol, 1, 4-hydroxymethylcyclohexane, 2-methyl-1, 3-propanediol, glycerol, trimethylolpropane, 1, 2, 6-hexanetriol, 1, 2, 4-butanetriol, trimethylolethane, pentaerythritol, mannitol, sorbitol, methylglucoside, sugars, 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 polyphenyl polymethylene polyamines, e.g. it can be obtained by condensation polymerization of amine aldehydes, or from mixtures of two or more of the above.
Also suitable as polyol component are polyethers which are modified by vinyl polymers. Such products are obtained, for example, by polymerization of styrene nitriles or acrylonitrile or mixtures thereof in the presence of polyethers.
Also suitable as polyol components for producing component A are polyester polyols having a molecular weight of from about 200 to about 10,000. Polyester polyols which are formed by reacting low molecular weight alcohols, in particular ethylene glycol, diethylene glycol, neopentyl glycol, hexanediol, butanediol, propylene glycol, glycerol or trimethylolpropane, with caprolactone may be used. Also suitable as polyfunctional alcohols for the production of the polyester polyols are 1, 4-hydroxymethylcyclohexane, 2-methyl-1, 3-propanediol, 1, 2, 4-butanetriol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol and polybutylene glycol.
Other suitable polyester polyols can be obtained by polycondensation. Difunctional and/or trifunctional alcohols and an excess of dicarboxylic acids and/or tricarboxylic esters, or their reactive derivatives, can be polycondensed to form polyester polyols. Suitable dicarboxylic acids are, for example, succinic acid and its higher homologues having up to 16 carbon atoms, furthermore unsaturated dicarboxylic acids, such as maleic acid or fumaric acid, and aromatic dicarboxylic acids, in particular phthalic acid isomers, such as phthalic acid, isophthalic acid or terephthalic acid. Examples of tricarboxylic acids are citric acid or trimellitic acid. Suitable within the scope of the present invention are polyester polyols of at least one of the abovementioned dicarboxylic acids and glycerol, which have hydroxyl groups remaining. 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 or adipic acid or mixtures thereof.
Particularly preferred within the scope of the present invention are polyol components for the production of component A, such as dipropylene glycol and/or polypropylene glycol having a molecular weight of from about 400 to about 2500, and polyester polyols, preferably polyester polyols obtained by polycondensation of hexanediol, ethylene glycol, diethylene glycol or neopentyl glycol or mixtures of two or more thereof with phthalic acid or adipic acid or mixtures thereof.
High molecular weight polyester polyols include, for example, the reaction product of a multifunctional, preferably difunctional alcohol (possibly with a small amount of trifunctional alcohol) and a multifunctional, preferably difunctional carboxylic acid. Instead of the free polycarboxylic acids, it is also possible to use the corresponding polyanhydrides or the corresponding polycarboxylic esters with alcohols having preferably from 1 to 3 carbon atoms. The polycarboxylic acids may be aliphatic, cycloaliphatic, aromatic or heterocyclic or both. They may also be substituted, for example by alkyl, alkenyl, ether or halogen atoms. As polycarboxylic acids there may be mentioned succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylenetetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimeric or trimeric fatty acids or mixtures of two or more of these. Minor amounts of monofunctional fatty acids may also be present in the reaction mixture.
The polyesters may also have a small number of terminal carboxyl groups. Polyesters obtained from lactones, for example epsilon-caprolactone, or hydroxycarboxylic acids, for example omega-hydroxycaproic acid, may likewise be used.
Also suitable as polyol components are polyaldehydes. The so-called polyaldehyde acetal compounds are, for example, obtained by reacting a diol, for example diethylene glycol or hexanediol or mixtures thereof, with formaldehyde. Within the scope of the present invention, the polyaldehydes used can likewise be obtained by condensation of cyclic acetals.
Further suitable polyols for the production of components A and B are polycarbonates. Polycarbonates can be obtained by reacting 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, with diaryl carbonates, for example diphenyl carbonate, or phosgene.
Polyol components which are likewise suitable as production component A are polyacrylates with hydroxyl groups. These polyacrylates can be obtained by polymerization of ethylenically unsaturated monomers having hydroxyl groups. These monomers are obtained, for example, by esterification of ethylenically unsaturated carboxylic acids with difunctional alcohols, in which case a slight excess of alcohol is generally present. Suitable ethylenically unsaturated carboxylic acids for this purpose are, for example, acrylic acid, methacrylic acid, crotonic acid or maleic acid. Corresponding hydroxyl-bearing esters such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate or 3-hydroxypropyl methacrylate or mixtures of two or more thereof.
The corresponding polyol components are reacted separately with at least difunctional isocyanates in the production of component A. As at least difunctional isocyanates it is possible to produce component A, it being preferred for substantially each isocyanate to carry at least two isocyanate groups, in general also within the scope of the present invention to prefer compounds having from 2 to 4 isocyanate groups, in particular two isocyanate groups.
Subsequently, at least difunctional isocyanates are described which are suitable as at least difunctional isocyanates for the production of component A.
Examples are: ethane diisocyanate, 1, 4-tetramethyldiisocyanate, 1, 6-Hexamethyldiisocyanate (HDI), cyclobutyl-1, 3-diisocyanate, cyclohexyl-1, 3-and 1, 4-diisocyanates and mixtures of two or more thereof, 1-isocyanato-3, 3, 5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate, IPDI), 2, 4-and 2, 6-hexahydrotoluylene diisocyanate, tetramethylxylene diisocyanate (TMXDI), 1, 3-and 1, 4-phenyl diisocyanate, 2, 4-or 2, 6-toluylene diisocyanate, diphenylmethane-2, 4' -diisocyanate, diphenylmethane-2, 2 '-diisocyanate or diphenylmethane-4, 4' -diisocyanate or mixtures of two or more of the aforementioned diisocyanates.
Suitable isocyanates for producing component A in the sense of the present invention are tri-or higher isocyanates, which are obtainable, for example, by oligomerization of diisocyanates. Examples of these tri-or higher polyisocyanates are triisocyanurates from HDI or IPDI or mixtures thereof or mixed triisocyanurates thereof.
The diisocyanates used for the production of component A in a preferred embodiment of the present invention are those having two isocyanate groups with different reactivity. Examples of such diisocyanates are 2, 4-and 2, 6-Tolylene Diisocyanate (TDI) and isophorone diisocyanate (IPDI). For such asymmetric diisocyanates, in general one isocyanate group reacts relatively significantly faster with isocyanate-reactive groups, such as hydroxyl groups, while the remaining isocyanate groups are likewise reactive. In a preferred embodiment, component A is produced using a monocyclic, unsymmetrical diisocyanate which has more than two of the different reactive isocyanate groups mentioned above.
The production of component A is particularly preferably carried out using 2, 4-or 2, 6-Tolylene Diisocyanate (TDI) or a mixture of the two isomers, in particular using pure 2, 4-TDI.
The production of component B can be carried out using at least difunctional isocyanates, which ensure that at least the major proportion of the isocyanate groups of component B remaining after the end of the reaction with the polyol component is more reactive than the major proportion of the isocyanate groups in component A. The production of component B preferably uses difunctional isocyanates whose reactivity of the isocyanate groups is as identical as possible. In particular symmetrical isocyanates, preference being given here to symmetrical aromatic difunctional isocyanates. More particularly preferred for the production of component B are diisocyanates of the bicyclic, aromatic, symmetrical diphenylmethane series, in particular MDI.
The polyurethane adhesives having the advantages of the present invention can be obtained in essentially any manner. The following two methods prove particularly advantageous.
For example, the polyurethane adhesive can be produced directly by producing component A and then adding component B.
It is likewise possible to use the compounds desired as component B already in the production of component A and to add them in such an excess that the desired final content of component B is achieved.
The invention also relates to a process for producing low-viscosity, isocyanate-containing polyurethane adhesives, comprising at least two steps, namely: (g) in a first step, a polyurethane prepolymer is produced from an at least difunctional isocyanate and at least one polyol component. (h) In a second step, a further at least difunctional isocyanate or a further at least difunctional isocyanate and a further polyol component. In the presence of a polyurethane prepolymer. Here, the major proportion of the isocyanate groups present after the end of the first step is relatively less reactive with isocyanate-reactive groups, in particular hydroxyl groups, than the isocyanate groups of the at least difunctional isocyanate added in the second step, in which the OH to NCO ratio is from about 0.2 to about 0.6.
As further polyol component it is possible to use essentially all polyol components already described herein.
Preferably, the OH to NCO ratio in the first step of the process of the present invention is less than 1. In a preferred embodiment, the OH to NCO ratio in the first step is from about 0.4 to about 0.7, in particular from 0.5 to about 0.7.
The reaction of the polyol component and the at least difunctional isocyanate in the first step can be carried out in a manner familiar to the person skilled in the art according to the general rules of polyurethane production. For example, the reaction may be carried out in a solvent. As solvents there may be used essentially all solvents which are customarily used in polyurethane chemistry, in particular esters, ketones, halogenated hydrocarbons, alkanes, alkenes and aromatic hydrocarbons. Examples of such solvents are dichloromethane, 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 acetate, ethylene glycol monoethyl acetate, 2-ethylhexyl acetate, ethylene glycol diacetate, heptane, hexane, isobutyl acetate, isooctane, isopropyl acetate, methyl ethyl ketone, tetrahydrofuran or tetrachloroethylene or mixtures of two or more of the above solvents.
If the reaction components themselves flow or at least one or more of the reaction components form a solution or dispersion of another reaction component which has insufficient flow, the use of solvents can be dispensed with altogether. This solvent-free reaction is preferred in the present invention.
The first step of the process of the present invention is carried out by initially charging the vessel with the polyol, optionally together with a suitable solvent, and mixing. Then, mixing is continued while adding the at least difunctional isocyanate. The temperature is usually raised to accelerate the reaction. The temperature is generally adjusted to about 40 ℃ to about 80 ℃. The exothermic reaction applied then raises the temperature. The temperature of the mix is maintained at about 70 to 110 ℃, for example at about 85 to 95 ℃ or in particular at about 75 to about 85 ℃, the temperature being adjusted, if necessary, by suitable external measures, for example heating or cooling.
The reaction may also be accelerated by the addition of catalysts customary in polyurethane chemistry to the reaction mixture. Preference is given to adding dibutyltin dilaurate or azobicyclooctane (DABCO). When a catalyst is desired, the catalyst is typically added to the reaction mixture in an amount of about 0.005 wt% or about 0.01 wt% to about 0.2 wt%, based on the total mix.
The time of the first reaction step depends on the polyol component used, on the at least difunctional isocyanate used, on the reaction temperature and on the catalyst which may be present. Typically the total reaction time is from about 30 minutes to about 20 hours.
Preferred as at least difunctional isocyanates in the first step are isophorone diisocyanate (IPDI), tetramethylxylene diisocyanate (TMXDI), hydrogenated diphenylmethane diisocyanate (MDI)H12) Or Toluene Diisocyanate (TDI) or a mixture of two or more thereof.
According to the process of the invention, the second reaction step is carried out by reacting at least one further at least difunctional isocyanate with one further polyol component in the mixture of components A obtained in the first reaction step. Any polyols selected from the polyols listed above or mixtures of two or more thereof may be used herein as an integral part of the other polyol component. In the process according to the invention, polypropylene glycols having a molecular weight of from about 400 to about 2500, or at least polyester polyols having a high, in particular predominantly aliphatic dicarboxylic acid component, or mixtures of these alcohols are preferably used as polyol component in the second step.
According to the inventive method, at least one polyisocyanate is used as the at least difunctional isocyanate in the second step, the isocyanate groups of which have a higher reactivity than the isocyanate groups present in the prepolymer. That is to say that it is also possible for reactive isocyanate groups to be present in the prepolymer, which result from the at least difunctional isocyanates initially used for the production of prepolymer A, the essence of the invention being that the major proportion of the isocyanate groups present in prepolymer A have a lower reactivity than the isocyanate groups of the other at least difunctional isocyanates added in the second stage of the process according to the invention.
As further at least difunctional isocyanates preference is given to bicyclic, aromatic, symmetrical diisocyanates. Examples of diisocyanates belonging to the bicyclic group are diisocyanates of the diphenylmethane group, in particular 2, 2 ' -diphenylmethane diisocyanate, 2, 4 ' -diphenylmethane diisocyanate, and 4, 4 ' -diphenylmethane diisocyanate. The diisocyanates are particularly preferably diphenylmethane diisocyanate, in particular 4, 4' -diphenylmethane diisocyanate, as further at least difunctional isocyanates in the second step of the process according to the invention.
The amount of at least difunctional isocyanate used in the second step is from about 5 to about 95% by weight, preferably from about 20 to about 95% by weight, in particular from about 40 to about 90% by weight, based on the total amount of polyisocyanate used in all steps of the process of the present invention.
In a preferred embodiment, in the second step, the OH to NCO ratio is from about 0.2 to about 0.6, in particular to about 0.5. NCO of the second-stage application component is not taken into account by the isocyanate groups of prepolymer A.
The polyurethane adhesives with the advantages of the invention are likewise obtainable by mixing the individual components C, D and E.
Also disclosed is a process for producing low-viscosity, low-volatility isocyanate-containing polyurethane adhesives comprising the mixing of components C, D, E, where (i) an isocyanate-containing polyurethane prepolymer as component C is obtainable by reacting a polyol component with an at least difunctional isocyanate, (j) an additional isocyanate-containing polyurethane prepolymer as component D is obtainable by reacting a polyol with an additional at least difunctional isocyanate, the isocyanate-reactive groups of which are relatively more reactive than the isocyanate groups of component C, (g) an additional class of at least difunctional isocyanates as component E is obtainable with a lower molecular weight than components C and D, the isocyanate-reactive groups of which are relatively more reactive than the isocyanate groups of component C, wherein the amount of component E is metered in such a way that the content of component E in the polyurethane adhesive is at least 5% by weight, in particular at least 10% by weight, after the end of the mixing process and after the termination of the possible reaction between all components C, D and E.
The polyurethane adhesives according to the invention and the polyurethane adhesives produced according to the invention have a preferred viscosity of less than 5000mPas (measured by Brookfield RT DVII (Thermosell) spindle 27, 20U/min, 50 ℃ method).
By all possible reactions between components C, D and E is meant within the scope of the present invention the reaction of isocyanate groups with functional groups having hydrogen atoms which are relatively isocyanate-reactive. Especially when, for example, component C or D or C and D also contain free hydroxyl groups, the addition of component E will generally result in the isocyanate groups of component E reacting with the free hydroxyl groups. As a result, the content of component E is reduced. Accordingly, if the desired reaction results in a reduction in the composition of component E, then component E is added in such an amount that when all of this is done, component E has the minimum amount required in the polyurethane binder.
The polyol components for components C and D produced according to the process of the present invention may be used with the polyols described above and also mixtures of two or more thereof. In particular, the particularly suitable polyol components used herein for the production of component A are also preferably used in the process of the present invention.
The at least difunctional isocyanates used as component E have a lower molecular weight than components C and D and their isocyanate groups are more reactive than the isocyanate groups of component C, and this applies analogously to component B.
In a preferred embodiment of the present invention, further, at least trifunctional isocyanates can be added as component H after the two steps already described above have been completed. Suitable as at least trifunctional isocyanates are the polyisocyanates already mentioned above having at least three NCO groups or the ternary or higher polymerization products of the difunctional isocyanates mentioned.
The polyurethane adhesives of the invention and those produced according to the invention are distinguished in particular by a particularly low content of volatile isocyanate-containing monomers, below 2% by weight or below 1% by weight, below 0.5% by weight, in particular below about 0.1% by weight. It is to be emphasized in particular that the process of the invention has no separate working step to exclude the volatile diisocyanate component.
Another advantage of the polyurethane adhesive produced by the process of the invention is based on the fact that its viscosity number lies in a very processing-friendly range. The polyurethane adhesives produced by the process according to the invention have a viscosity of in particular less than 5000mPas (measured by the Brookfield RT DVII (Thermosell), Spindel 27, 20U/min, 50 ℃ method).
The polyurethane adhesives according to the invention are suitable for coating objects, in particular for bonding objects, in bulk or as solutions in organic solvents, for example the solvents mentioned above.
The invention also relates to the use of the polyurethane adhesives according to the invention or of the polyurethane adhesives produced by the process according to the invention for producing adhesives, in particular one-component and two-component adhesives, coatings, in particular paints, disperse dyes and casting resins, and also molded bodies, and also coatings, in particular adhesive bonds, in particular film bonds, of objects, and for producing film composites.
The polyurethane adhesives according to the invention or the polyurethane adhesives produced by the process according to the invention are used in particular for the bonding of plastics, particularly preferably for the casting of plastic films, plastic films deposited with metals or metal oxides, and metal films, in particular aluminum films.
The hardening, i.e. the crosslinking of each polyurethane binder molecule by free isocyanate groups, can be effected solely by the action of air humidity without the addition of a hardening agent. However, it is preferred to add polyfunctional crosslinkers as hardeners, for example ammonia or in particular polyfunctional alcohols (two-component systems).
The film composite produced from the products produced according to the invention exhibits a high degree of processing safety with regard to heat sealing. This is due to the reduction of low molecular weight products that can migrate in the polyurethane adhesive. The advantageous processing temperatures of the adhesives produced according to the invention are between about 30 and about 90 ℃ for such processes.
The invention likewise relates to adhesives comprising two components F and G, wherein (i) polyurethane adhesives having isocyanate groups according to the invention or polyurethane adhesives having isocyanate groups produced by the process according to the invention, (j) compounds having at least two functional groups which are reactive with respect to the isocyanate groups of component F and have a molecular weight of up to 2500 or mixtures of two or more such compounds are used as component G.
As component F, any of the polyurethane adhesives according to the invention can be used, as described above.
Preference is given to using as component G compounds having at least two functional groups which are reactive toward the isocyanate groups of component F and have a molecular weight of up to 2500 or mixtures of two or more such compounds. Particularly suitable as at least two functional groups reactive toward the isocyanate groups of component F are amino groups, thiol groups or hydroxyl groups, where the applicable compounds of component G may each have an amino group, thiol group or hydroxyl group, alone or in mixtures.
The functionality of the compounds which can be used in component G is generally at least about 2. Preferred are compounds of component G having high functionality, e.g. 3, 4 or more functionality. The total functionality (average) of component G is, for example, about 2 (e.g.when only difunctional compounds are used as component G), or more, for example 2.1, 2.2, 2.5 or 2.7 or 3. It is also possible for component G to have still higher functionalities, for example 4 or more.
Component G preferably comprises a polyol having at least two hydroxyl groups. All polyols explained above are suitable for use in component G, provided they meet the criteria of the upper limit of the molecular weight.
Component G is generally used in an amount such that the ratio of isocyanate groups of component F to functional groups of component G which are reactive with the isocyanate groups of component F is from about 5: 1 to about 1: 1, especially from about 2: 1 to about 1: 1.
The adhesives according to the invention generally have a viscosity of from about 250 to about 10,000 mPas, in particular from about 500 to about 8,000 or to about 5,000 mPas (Brookfield RVT DVII, Spindel 27, 20 Upm, 40 ℃ C.).
It is possible that the adhesive of the invention also contains additives. The additives comprise up to about 30 wt% of the total adhesive.
Additives which are usable within the scope of the present invention are, for example, softeners, stabilizers, antioxidants, pigments, light stabilizers or fillers.
As softeners, for example, use is made of softeners based on phthalic acid, in particular dialkyl phthalates, preference being given here to phthalate esters as softeners which are esterified with linear alcohols having from about 6 to about 12 carbon atoms. Dioctyl phthalate is particularly preferred here.
Also suitable as softeners are benzoate softeners, such as sucrose benzoate, diethylene glycol dibenzoate and/or diethylene glycol dibenzoate in which from about 50% to about 95% of all hydroxyl groups have been esterified, phosphate softeners, such as tert-butylphenyl diphenyl phosphate, polyethylene glycol and its derivatives, such as the diphenyl ether of polyethylene glycol, liquid rosin derivatives, such as the methyl ester of hydrogenated rosin, vegetable and animal oils, such as fatty acid glycerides and polymerization products thereof.
Stabilizers or antioxidants useful as additives in the present invention are high molecular weight (Mn) hindered phenols, polyfunctional phenols and sulfur and phosphorus containing phenols. Phenols which may be used as additives in the present invention are, for example, 1, 3, 5-trimethyl-2, 4, 6-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) phenol; pentaerythritol tetrakis (3- (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate, n-octadecyl-3, 5-di-tert-butyl-4-hydroxyphenyl propionate, 4-methylenebis (2, 6-di-tert-butylphenol), 4-thiobis (6-tert-butyl-o-cresol), 2, 6-di-tert-butylphenol, 6- (4-hydroxyphenoxy) -2, 4-bis (n-octylthio) -1, 3, 5-triazine, bis (n-octadecyl) -3, 5-di-tert-butyl-4-hydroxybenzylurea, 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 available under the trade name Thiinuvin_(manufacturer: Ciba Geigy).
Other additives may be used together in the adhesive of the present invention to modify certain properties. Examples of these are pigments, such as titanium dioxide, fillers, such as talc, china clay and the like. There may be small amounts of thermoplastic polymers or copolymers in the adhesives of the invention, such as ethylene/vinyl acetate (EVA), ethylene/acrylic acid, ethylene/methacrylate, and ethylene/n-butyl acrylate copolymers, which may impart additional softness, toughness, and hardness to the adhesive. It is likewise possible within the scope of the invention to preferably add certain hydrophilic polymers, for example polyvinyl alcohol, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl methyl ether, polyvinyl oxygen, polyvinyl pyrrolidone, polyethyloxazoline or starch or cellulose esters, in particular acetates with a degree of substitution below 2.5, which can improve the wettability of the adhesive.
Next, the present invention is explained by examples, but this does not produce a limiting effect. List of abbreviations used in the examples: DPG = dipropylene glycol PPG = polypropylene glycol TDI = toluene diisocyanate (2, 4-isomer) MDI =4, 4' -diphenylmethane diisocyanate PE = isophthalic acid/adipic acid/diethylene glycol/dipropylene glycol based polyester NCO = isocyanate group content OHZ = number of hydroxyl groups M = molecular weight d = day Verh = ratio VH = composite adhesion SNH = seal adhesion OPA = oriented polyamide PEK088Blend of LLDPE/LDPE with a thickness of about 70 μm, Mildenberger and Willing.
Examples 1 to 9 were produced according to the following process:
in the first step, the polyol component is added and mixed uniformly. The isocyanate was then added and the temperature of the reaction mixture was raised to 50 ℃. The temperature then rises sharply by the exothermic reaction between isocyanate groups and hydroxyl groups, and is maintained at this temperature after reaching 90 ℃ by cooling.
The components of the second step were added to the reaction product of the first step and the temperature of the mixture was adjusted to 85 ℃. Stirring for one hour.
In example 9, the first step and the second step were each produced separately, and then the resultant products were mixed.
Examples 10, 11 and 12 were carried out using isophorone diisocyanate (IPDI) as the first isocyanate component.
The results are listed in table 1 below.
Table 1: examples 1 to 12
| Examples | 1 | 2 | 3 | 4 | 5 | 6 | ||
| OHZ | Equivalent weight | |||||||
| Step 1 | ||||||||
| TDI | 19.0 | 18.1 | 17.1 | 19.6 | 22.0 | 17.1 | ||
| PPG | 10 | 17 | 12 | 5 | 3 | 12 | ||
| PPG | 8 | 4 | 8 | 10 | 8 | 8 | ||
| DPG | 4 | 2 | 3 | 6 | 8 | 3 | ||
| PE | 0 | 0 | 0 | 0 | 0 | 0 | ||
| OH/NCO ratio | 0.555 | 0.556 | 0.588 | 0.588 | 0.588 | 0.588 | ||
| NCO equivalent weight | 0.218 | 0.208 | 0.196 | 0.2250 | 0.253 | 0.196 | ||
| OH equivalent | 0.121 | 0.115 | 0.116 | 0.1323 | 0.149 | 0.116 | ||
| NCO/OH ratio | 1.8 | 1.8 | 1.7 | 1.7 | 1.7 | 1.7 | ||
| Terminal NCO content | 9.9 | 9.4 | 8.5 | 9.6 | 10.7 | 8.5 | ||
| 1 st step size | 41.0 | 41.1 | 40.1 | 40.6 | 41.0 | 40.1 | ||
| Step 2 | ||||||||
| MDI | 38.8 | 38.3 | 39.7 | 38.6 | 37.1 | 38.2 | ||
| PPG | 10 | 10 | 10 | 10 | 10 | 10 | ||
| PPG | 10 | 10 | 10 | 10 | 10 | 15 | ||
| DPG | 0 | 0 | 0 | 0 | 0 | 0 | ||
| PE | 10 | 10 | 10 | 10 | 10 | 10 | ||
| Step 2 OH/NCO ratio | 0.29 | 0.294 | 0.284 | 0.292 | 0.303 | 0.2535 | ||
| NCO equivalent in step 2 | 0.31 | 0.306 | 0.318 | 0.31 | 0.297 | 0.3053 | ||
| OH equivalent in step 2 | 0.09 | 0.09 | 0.09 | 0.09 | 0.09 | 0.0774 | ||
| NCO/OH addition ratio in step 2 | 3.44 | 3.40 | 3.53 | 3.43 | 3.29 | 3.94 | ||
| NCO/OH Total addition ratio | 2.50 | 2.50 | 2.50 | 2.40 | 2.30 | 2.60 | ||
| Total amount of | 109.8 | 109.3 | 109.8 | 109.2 | 108.1 | 108.2 | ||
| Terminal NCO | 12.1 | 11.8 | 11.8 | 12.0 | 12.1 | 12.0 | ||
| Viscosity at 40 ℃: | 9000 | 9300 | 5800 | 9370 | 14500 | 4190 | ||
| viscosity 50 ℃: | 3300 | 3530 | 2220 | 3320 | 4660 | 1770 | ||
| ％NCO(1d) | 11.80％ | 12％ | 12.1％ | 12.2％ | ||||
| MDI | 17.00％ | 16.0％ | / | 17.1％ | 16.6％ | |||
| TDI | 0.10％ | 0.10％ | / | 0.08％ | 0.09％ | 0.1％ | ||
TABLE 1 continuation
| Examples | 7 | 8 | 9/1 | 9/2 | 9/3 | ||
| Step 1 | Step 2 | Separate feed mixing | |||||
| Separation of | Separation of | ||||||
| Charging of | Charging of | ||||||
| OHZ | Equivalent weight | ||||||
| Step 1 | |||||||
| TDI | 21.7 | 21.7 | 17.1 | ||||
| PPG | 13.5 | 13.5 | 12 | ||||
| PPG | 25.5 | 25.5 | 8 | ||||
| DPG | 0 | 0 | 3 | ||||
| PE | 26.645 | 26.645 | 0 | ||||
| OH/NCO ratio | 0.714 | 0.714 | 0.588 | ||||
| NCO equivalent weight | 0.249 | 0.249 | 0.196 | ||||
| OH equivalent | 0.178 | 0.178 | 0.116 | ||||
| NCO/OH ratio | 1.4 | 1.4 | 1.77 | ||||
| Terminal NCO content | 3.4 | 3.4 | 8.5 | ||||
| 1 st step size | 87.3 | 87.3 | 40.1 | ||||
| Step 2 | |||||||
| MDI | 12.2 | 33.9 | 38.2 | ||||
| PPG | 0 | 0 | 5 | ||||
| PPG | 0 | 0 | 15 | ||||
| DPG | 0.575 | 0.575 | 0 | ||||
| PE | 0 | 0 | 10 | ||||
| Step 2 OH/NCO ratio | 0.088 | 0.032 | |||||
| NCO equivalent in step 2 | 0.098 | 0.271 | 0.3058 | ||||
| OH equivalent in step 2 | 0.009 | 0.009 | 0.0774 | ||||
| NCO/OH addition ratio in step 2 | 31.67 | 3.95 | |||||
| NCO/OH Total addition ratio | 2.79 | 3.95 | |||||
| Total amount of | 100.1 | 121.8 | 68.2 | ||||
| Terminal NCO | 6.7 | 11.5 | 14.1 | ||||
| Viscosity at 40 ℃: | viscosity of | 20000 | 3470 | 103000 | 1330 | 4600 | |
| Viscosity 50 ℃: | viscosity of | 7200 | 1420 | / | / | 1770 | |
| ％NCO(1d) | 7.10％ | 11.10％ | 9.00％ | 14.10％ | 12.40％ | ||
| MDI | / | / | / | 28.00％ | 18％ | ||
| TDI | / | / | 0.80％ | / | 0.30％ | ||
TABLE 1 continuation
| Examples | 10 | 11 | 12 | ||
| OHZ | Equivalent weight | ||||
| First step | |||||
| IPDI | 21.1 | 19.3 | 17.l | ||
| PPG400 | 256 | 219 | l0.3 | 10.64 | 10.64 |
| PPGl000 | 113 | 497 | 19.5 | 7.09 | 7.09 |
| DPG | 836 | 67 | 0 | 2.66 | 2.66 |
| PE218 | 137 | 410 | 20.4 | 0 | 0 |
| PE23l | 110 | 510 | 0 | 0 | 0 |
| Stanclere TL | 0.01 | 0.075 | 0.075 | ||
| NCO equivalent weight | 0.1905 | 0.1741 | 0.1537 | ||
| OH equivalent | 0.1360 | 0.1024 | 0.1024 | ||
| The addition ratio is X: 1 | 1.4 | 1.7 | 1.5 | ||
| Terminal NCO | 3.2 | 7.6 | 5.7 | ||
| 1 st step size | 71.3 | 39.7 | 37.4 | ||
| Step 2 | |||||
| MDI | 28.1 | 54.6 | 77.1 | ||
| PPG400 | 0 | 14.4 | 20.304 | ||
| PPG1000 | 0 | 15.2 | 21.432 | ||
| DPG | 0.45 | 0 | 0 | ||
| PE218 | 0 | 14.9 | 21.009 | ||
| NCO equivalent in step 2 | 0.2249 | 0.4371 | 0.6164 | ||
| OH equivalent in step 2 | 0.0067 | 0.1327 | 0.1871 | ||
| NCO/OH addition ratio in step 2 | 33.56 | 3.29 | 3.30 | ||
| NCO/OH Total addition ratio | 2.91 | 2.60 | 2.66 | ||
| Total amount of | 99.9 | 138.9 | 177.2 | ||
| Terminal NCO | 11.5 | 11.4 | 11.4 | ||
| Viscosity at 40 ℃: | 6000 | 4910 | 5600 | ||
| viscosity 50 ℃: | 2800 | 1960 | 2120 | ||
| ％NCO(24h) | 11.55％ | 12.20％ | 12.10％ | ||
| MDI (Mixed material) | 22.70％ | 20.00％ | 20.00％ | ||
| IPDI (Mixed material) | ＜1％ | ＜1％ | ＜1％ | ||
Table 2:
| examples | 13 | ||
| OHZ | Equivalent weight | ||
| Step 1 | |||
| TDI | 15.7 | ||
| PPG400 | 265 | 212 | 9.9 |
| PPG1000 | 111 | 506 | 6.6 |
| PPG2000 | 55 | 1020 | 8.58 |
| DPG | 835 | 67 | 2.502 |
| NCO equivalent weight | 0.1803 | ||
| OH equivalent | 0.1054 | ||
| The addition ratio is X: 1 | 1.71 | ||
| Terminal NCO | 7.3 | ||
| 1 st step size | 43.3 | ||
| Step 2 | |||
| MDI | 31.9 | ||
| PPG400 | 4.104 | ||
| PPG1000 | 12.402 | ||
| PE218 | 8.208 | ||
| NCO equivalent in step 2 | 0.2552 | ||
| OH equivalent in step 2 | 0.0647 | ||
| NCO/OH addition ratio in step 2 | 3.95 | ||
| NCO/OH Total addition ratio | 2.56 | ||
| 1 st and 2 nd step size | 99.99 | ||
| Terminal NCO | 11.2 | ||
| Step 3 | |||
| Desmodur 3300 | 20 | ||
| NCO equivalent in step 3 | 0.1026 | ||
| Total amount of | 119.9 | ||
| Terminal NCO | 12.9 | ||
| Viscosity 40 deg.C | 4200mPas | ||
| Colour(s) | Transparent yellow |
Table 3: application to the adhesion test of the polyurethane adhesive prepared in example 6
TABLE 3
| Composite structure | Coating g/m2 | Web speed m/min | VH unprinted N/15 mm | SNHN／15mm |
| OPA／PEK088 | 1．9 | 100 | 11.6 PE-elongation | 52.1 composite structural failure |
| OPA／PEK088 | 1．5 | 100 | 11.7 PE-elongation | 55.1 seal edge failure |
| OPA／PEK088 | 1．1 | 100 | 11.1 PE-elongation | 55.4 seal edge failure |
Migration test:
the transport content was determined as follows (cf. Deutsche LebensmittetlRundschau, 87:, (1991), 280-281):
a bonded film composite bag produced by the adhesive of the present invention was filled with 3% acetic acid and allowed to stand at 70 ℃ for two hours. The bag contents are then diazotized, azo coupled with N (1-naphthyl) ethylenediamine, at C18Concentrate on column. The concentration of the azo pigment is then determined photometrically.
The experimental results can be obtained from table 4 below.
Table 4: migration test results
| Migration volume (days of experience) | Composite material |
| 01.07.97 (4 days) | 9．7μg AHCL／100ml |
| 9.7 μ g AHCL/100 ml 07.07.97 (10 days) | 3．8μg AHCL／100ml |
| 11.07.97 (14 days) | 0．93μg AHCL／100ml |
| 21.07.97 (24 days) | ＜0．2μg AHCL／100ml |
Claims (22)
1. A polyurethane adhesive having a low content of volatile monomers with isocyanate groups, which adhesive contains at least components A and B, wherein (a) a polyurethane prepolymer having at least two isocyanate groups or a mixture of two or more polyurethane prepolymers having at least two isocyanate groups is contained as component A, here, the polyurethane prepolymer having two isocyanate groups or the mixture composed of two or more polyurethane prepolymers having isocyanate groups of at least two different compound types, at least one type of isocyanate-reactive groups being less reactive than one or more other types, (B) an at least difunctional isocyanate as component B, the molecular weight of which is lower than that of the polyurethane prepolymer contained in component A, and the reactivity of its isocyanate groups with respect to isocyanate-reactive compounds is higher than that of the low-reactive isocyanate groups contained in component A.
2. The polyurethane adhesive of claim 1, wherein component B is present in an amount of at least 5 weight percent of the total polyurethane adhesive.
3. A polyurethane adhesive as claimed in claim 1 or 2, characterised in that the content of volatile, isocyanate-containing monomers is less than 1% by weight, and the content of toluene diisocyanate is less than 0.1% by weight.
4. A polyurethane adhesive as claimed in one of claims 1 to 3, characterized in that it contains an at least trifunctional isocyanate as component H.
5. A polyurethane adhesive as claimed in any of claims 1 to 4, characterized in that component A is produced by an at least two-step reaction in which (c) in a first step a polyurethane prepolymer is produced from an at least difunctional isocyanate and at least one first polyol component, wherein the NCO/OH ratio is less than 2 and free hydroxyl groups remain in the polyurethane prepolymer, and (d) in a second step an additional at least difunctional isocyanate is reacted with the polyurethane prepolymer obtained in the first step, wherein the isocyanate groups of the isocyanate added in the second step are more reactive with respect to the isocyanate-reactive compounds than at least a major proportion of the isocyanate groups present in the polyurethane prepolymer obtained in the first step.
6. Polyurethane adhesive according to claim 5, characterized in that a molar excess of other types of at least difunctional isocyanates is added, based on the free OH groups of component A, where the part of the other types of at least difunctional isocyanates which does not react with OH groups is component B.
7. Polyurethane adhesive according to one of claims 1 to 4, characterized in that component A is produced by an at least two-step reaction in which:
(c) in a first step, a polyurethane prepolymer is produced from an at least difunctional isocyanate and at least one first polyol component, wherein the NCO/OH ratio is less than 2, the polyurethane prepolymer also contains free OH groups,
(d) in a second step, an additional type of at least difunctional isocyanate and an additional type of polyol component are reacted with the polyurethane prepolymer obtained in the first step, wherein the isocyanate groups of the isocyanate added in the second step are more reactive towards isocyanate-reactive compounds than at least a major portion of the isocyanate groups in the polyurethane prepolymer obtained in the first step.
8. The polyurethane adhesive of claim 7, wherein: a molar excess of the other type of at least difunctional isocyanate is added, based on the free OH of component a and the other type of polyol component, where the part of the other type of at least difunctional isocyanate that is not reactive with hydroxyl groups is component B.
9. Polyurethane adhesive according to one of claims 5 to 8, characterised in that the OH to NCO ratio in the second step is from 0.1 to less than 1, in particular from 0.2 to 0.6.
10. Polyurethane adhesive according to one of claims 5 to 9, characterized in that the OH to NCO ratio in the first step is less than 1, in particular 0.5 to 0.7.
11. A process for producing a low viscosity isocyanate-bearing polyurethane adhesive comprising at least two steps, wherein:
(c) in a first step, a polyurethane prepolymer is produced from an at least difunctional isocyanate and at least one polyol component,
(d) in the second step, an additional at least difunctional isocyanate, or an additional at least difunctional isocyanate and an additional polyol component, are reacted in the presence of the polyurethane prepolymer, the reactivity of the major part of the isocyanate groups present after the end of the first step with respect to isocyanate-reactive groups, in particular with respect to hydroxyl groups, being higher than the isocyanate groups of the at least difunctional isocyanate added in the second step, the OH/NCO ratio in the second step being from 0.2 to 0.6.
12. The process as claimed in claim 11, wherein the OH to NCO ratio in the first step is less than 1, in particular from 0.4 to 0.7.
13. The process of claim 11 or 12, wherein isophorone diisocyanate (IPDI), tetramethylxylylene diisocyanate (TMXDI), hydrogenated diphenylmethane diisocyanate (MDI) are used as the at least difunctional isocyanate in the first stepH12) Or Toluene Diisocyanate (TDI).
14. The process as claimed in one of claims 11 to 13, characterized in that diphenylmethane diisocyanate (MDI) is used as the other at least difunctional isocyanate in the second step.
15. A process for producing low-viscosity, isocyanate-containing polyurethane adhesives having a low content of volatile isocyanate-containing monomers, which comprises mixing three components C, D and E, where
(c) The isocyanate group-containing polyurethane prepolymer used as component C is obtainable by reacting a polyol component with an at least difunctional isocyanate,
(d) the use of other types of polyurethane prepolymers with isocyanate groups as component D is obtainable by reacting a polyol component with an other type of at least difunctional isocyanate whose isocyanate groups are more reactive towards isocyanate-reactive groups than the isocyanate groups of component C,
(g) as component E, an additional at least difunctional isocyanate is used, which has a lower molecular weight than components C and D and whose isocyanate groups are more reactive than the isocyanate groups of component C with respect to isocyanate-reactive groups, the amount of component E being such that, after the end of the mixing process and after all possible reactions between components C, D and E have ended, component E makes up at least 5% by weight, in particular at least 10% by weight, of the polyurethane binder.
16. The process according to any one of claims 11 to 15, characterized in that: the polyurethane adhesive has a viscosity of less than 5000mPas, as measured by Brookfield RT DVII (Thermosell), Spindel 27, 20U/min, 50 ℃.
17. The process as claimed in any of claims 11 to 16, characterized in that an at least trifunctional isocyanate is added as component H in the third step.
18. Use of the polyurethane adhesive according to one of claims 1 to 10 or produced according to the process of one of claims 11 to 17 for producing adhesives, in particular one-component and two-component adhesives, coatings, in particular paints, dispersion pigments and casting resins, and also molded bodies, and for coating, in particular bonding, of objects, in particular for bonding films, for producing film composites.
19. An adhesive comprising components F and G, use thereof
(i) The polyurethane adhesive having isocyanate groups according to one of claims 1 to 10 or the polyurethane adhesive having isocyanate groups produced according to one of claims 11 to 17 as component F,
(j) as component G, a compound having at least two functional groups reactive with the isocyanate groups of component F and having a molecular weight of up to 2500 or a mixture of two or more such compounds is used.
20. The adhesive according to claim 19, wherein a polyol having at least two hydroxyl groups is used as component G.
21. The adhesive according to claim 19 or 20, characterized in that component G is used in such an amount that the ratio between the isocyanate groups of component F and the functional groups reactive with the isocyanate groups of component F is 5: 1 to 1: 1, in particular 2: 1 to 1: 1.
22. An adhesive according to any of claims 19 to 21, characterized in that the viscosity is from 500 to 8000cps, as measured by the Brookfield RVT DII, Spindel 27, method at 40 ℃.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19749834.5 | 1997-11-11 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| HK1032975A true HK1032975A (en) | 2001-08-10 |
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