WO2005003247A1

WO2005003247A1 - Method for bonding substrates by using polyurethane adhesives

Info

Publication number: WO2005003247A1
Application number: PCT/EP2004/006889
Authority: WO
Inventors: Andre Burghardt; Karl Häberle; Ulrike Licht; Bernd Meyer-Roscher
Original assignee: Basf Aktiengesellschaft
Priority date: 2003-07-07
Filing date: 2004-06-25
Publication date: 2005-01-13
Also published as: DE10330749A1

Abstract

The invention relates to a method for bonding substrates having different surface energies, and is characterized in that the adhesive used for bonding is comprised of, at least 15 % by weight, a polyurethane (water or other organic solvents having a boiling point lower than 150 °C at 1 bar not being counted), the adhesive is applied to the substrate having the lower surface energy, and the obtained adhesive-coated substrate is bonded to the substrate having the higher surface energy.

Description

Process for bonding substrates with polyurethane adhesives

description

The invention relates to a method for bonding substrates with different surface energies, characterized in that the adhesive used for the bonding consists of at least 15% by weight of a polyurethane (water or other organic solvents with a boiling point below 150 ° C at 1 bar not calculated), the adhesive is applied to the substrate with the lower surface energy and the resulting adhesive-coated substrate is bonded to the substrate with the higher surface energy.

Aqueous polyurethane dispersions are often used as the adhesive. It is also common practice to add a crosslinking agent to the dispersion in order to ensure sufficient heat resistance of the adhesive bond. Isocyanates are frequently used as crosslinkers, but because of their short life in an aqueous environment, which generally does not exceed one working day, they can only be added to the adhesive dispersion shortly before use. Carbodimides and aziridines are also known as crosslinkers. Polyurethane dispersions containing carbodiimides are e.g. in DE-A-10000656 or DE-A-10001777.

In general, the highest possible strength of the adhesive composite is desired. In this context, it would be advantageous to use a method by which the strength can be increased without the chemical composition of a given adhesive, e.g. by adding other additives.

The object of the present invention was to provide a corresponding method.

Accordingly, the process defined at the outset was found.

In the method according to the invention, two substrates are glued together.

An essential feature of the method is that the adhesive is applied to the substrate with the lower surface energy. In addition, the other substrate (with the higher surface energy) can be coated with adhesive; preferably only the substrate with the lower surface energy is coated with adhesive. This is a measure of the surface energy of the substrates to be bonded

Contact angle of a drop of water on the substrate surface. A little

Contact angle means a flat distribution of the drop on the surface and extensive wetting of the surface.

The smaller the contact angle, the greater the surface energy of the

Substrate.

The contact angle of a drop of water is determined at 21 ° C, 1 bar by known methods, e.g. determined by visual evaluation or projection of the drop contour with image analysis.

The substrate with the lower contact angle is the substrate with the larger surface energy.

The advantages of the method according to the invention become particularly clear with larger differences in the contact angle, e.g. if the difference is more than 10, in particular more than 20 ° degrees of angle.

Substrates with low surface energy are e.g. Substrates with surfaces made of non-polar substances.

Examples of substrates with low surface energy are synthetic polymers, e.g. Polyolefins such as pvc; polyethylene; Polypropylene, polybutadiene or ABS called.

Substrates with higher surface energy are e.g. Substrates with surfaces made of polar substances.

Examples of substrates with higher surface energy include Wood, paper, leather or textiles made from natural fibers.

The adhesive to be used according to the invention essentially consists of at least one polymeric binder and optionally additives such as fillers, thickeners, defoamers, etc. The additives may also include crosslinking agents.

The polymeric binder is preferably present as a solution or dispersion in water or another solvent with a boiling point below 150 ° C. (1 bar). Water is particularly preferred. The water or other solvents are not included in the weight of the composition of the adhesive.

The polymeric binder is a polyurethane or a mixture of different polymeric binders which contains at least one polyurethane.

The adhesive consists in total of at least 15% by weight, preferably at least 30% by weight, particularly preferably at least 50% by weight, in particular at least 70% by weight or at least 90% by weight polyurethane.

In a particular embodiment, the adhesive contains only a polyurethane or a mixture of polyurethanes as a binder.

The polyurethanes predominantly consist of polyisocyanates, in particular diisocyanates on the one hand and, as reactants, polyester diols, polyether diols or their mixtures on the other hand.

The polyurethane is preferably composed of at least 40% by weight, particularly preferably at least 60% by weight and very particularly preferably at least 80% by weight, of diisocyanates, polyether diols and / or polyester diols.

The polyurethane preferably has a softening point or melting point in the range from -50 to 150 ° C., particularly preferably from 0 to 100, and very particularly preferably from 10 to 90 ° C.

The polyurethane particularly preferably has a melting point in the above temperature range.

For this purpose, the polyurethane preferably contains polyester diols in an amount of more than 10% by weight, based on the polyurethane.

Overall, the polyurethane is preferably composed of:

a) diisocyanates,

b) diols, of which b 10 to 100 mol%, based on the total amount of diols (b), have a molecular weight of 500 to 5000 g / mol, b ₂₎ 0 to 90 mol%, based on the total amount of diols (b) Have a molecular weight of 60 to 500 g / mol,

c) monomers different from the monomers (a) and (b) with at least one isocyanate group or at least one group which is reactive toward isocyanate groups and which additionally carry at least one hydrophilic group or a potentially hydrophilic group, thereby causing the water dispersibility of the polyurethanes,

d) optionally further polyvalent compounds with reactive groups which differ from the monomers (a) to (c) and which are alcoholic hydroxyl groups, primary or secondary amino groups or isocyanate groups and

e) optionally monohydric compounds different from the monomers (a) to (d) having a reactive group which is an alcoholic hydroxyl group, a primary or secondary amino group or an isocyanate group.

Particularly worth mentioning as monomers (a) are diisocyanates X (NCO) ₂ , where X is an aliphatic hydrocarbon radical having 4 to 15 carbon atoms, a cycloaliphatic or aromatic hydrocarbon radical having 6 to 15

Carbon atoms or an araliphatic hydrocarbon radical having 7 to 15 carbon atoms. Examples of such diisocyanates are tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 1,4-diisocyanatocyclohexane, 1-isocyanato-3,5,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), 2,2-bis (4-isocyanatocyclohexyl) propane, trimethylhexane , 1,4-diisocyanatobenzene, 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene, 4,4'-diisocyanatodiphenylmethane, 2,4'-diisocyanatodiphenylmethane, p-xylylene diisocyanate, tetramethylxylylene diisocyanate (TMXDI), the isomers of the bis - (4-isocyanatocyclohexyl) methane (HMDI) such as the trans / trans, the cis / cis and the cis / trans isomer and mixtures consisting of these compounds.

Such diisocyanates are commercially available. The mixtures of the respective structural isomers of diisocyanatotoluene and diisocyanatodiphenylmethane are particularly important as mixtures of these isocyanates, and the mixture of 80 mol% 2,4-diisocyanatotoluene and 20 mol% 2,6-diisocyanatotoluene is particularly suitable. Furthermore, the mixtures of aromatic isocyanates such as 2,4-diisocyanatotoluene and / or 2,6-diisocyanatotoluene with aliphatic or cycloaliphatic isocyanates such as hexamethylene diisocyanate or IPDI are particularly advantageous, the preferred mixing ratio of the aliphatic to aromatic isocyanates being 4: 1 to 1: 4 ,

In addition to the abovementioned, isocyanates which, in addition to the free isocyanate groups, have other blocked isocyanate groups, e.g. Wear uretdione groups.

With regard to good film formation and elasticity, diols (b) which can be used are primarily higher molecular weight diols (b1) which have a molecular weight of about 500 to 5000, preferably of about 1000 to 3000 g / mol. It is the number average molecular weight Mn. Mn is obtained by determining the number of end groups (OH number).

The diols (b1) can be polyester polyols which are known, for example, from Ullmanns Encyklopadie der Technische Chemie, 4th edition, volume 19, pages 62 to 65. Polyester polyols are preferably used which are obtained by reacting dihydric alcohols with dihydric carboxylic acids. Instead of the free polycarboxylic acids, the corresponding polycarboxylic anhydrides or corresponding polycarboxylic esters of lower alcohols or their mixtures can also be used to prepare the polyester polyols. The polycarboxylic acids can be aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic and optionally substituted, for example by halogen atoms, and / or unsaturated. Examples include: suberic acid, azelaic acid, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride, endomethylene tetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic acid, fatty acid, maleic acid, maleic acid, fatty acid, maleic acid, maleic acid, fatty acid. Dicarboxylic acids of the general formula HOOC- (CH ₂ ) _y - COOH are preferred, where y is a number from 1 to 20, preferably an even number from 2 to 20, for example succinic acid, adipic acid, sebacic acid and dodecanedicarboxylic acid.

Examples of polyhydric alcohols are ethylene glycol, propane-1,2-diol, propane-1,3-diol, butane-1,3-diol, butene-1,4-diol, butyne-1,4-diol, pentane-1 , 5-diol, neopentyl glycol, bis (hydroxymethyl) cyclohexanes such as 1, 4-bis (hydroxymethyl) cyclohexane, 2-methylpropane-1, 3-diol, methylpentanediols, furthermore diethylene glycol, triethylene glycol, Tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol and polybutylene glycols. Alcohols of the general formula HO- (CH ₂ ) _x -OH are preferred, where x is a number from 1 to 20, preferably an even number from 2 to 20. Examples include ethylene glycol, butane-1, 4-diol, hexane-1, 6-diol, octane-1, 8-diol and dodecane-1, 12-diol. Neopentyl glycol is also preferred.

Furthermore, polycarbonate diols, such as those e.g. can be obtained by reacting phosgene with an excess of the low molecular weight alcohols mentioned as synthesis components for the polyester polyols.

If appropriate, polyester diols based on lactone can also be used, which are homopolymers or copolymers of lactones, preferably terminal products having hydroxyl groups, which are addition products of lactones to suitable difunctional starter molecules. Preferred lactones are those which are derived from compounds of the general formula HO- (CH ₂ ) ₂ - COOH, where z is a number from 1 to 20 and an H atom of a methylene unit is also by a d to C - Alkyl radical can be substituted. Examples are e-caprolactone, β-propiolactone, g-butyrolactone and / or methyl-e-caprolactone and mixtures thereof. Suitable starter components are, for example, the low molecular weight dihydric alcohols mentioned above as the structural component for the polyester polyols. The corresponding polymers of e-caprolactone are particularly preferred. Lower polyester diols or polyether diols can also be used as starters for the preparation of the lactone polymers. Instead of

Lactone polymers can also use the corresponding chemically equivalent polycondensates of the hydroxycarboxylic acids corresponding to the lactones.

Polyether diols are in particular by polymerization of ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, styrene oxide or epichlorohydrin with themselves, for example in the presence of BF ₃ or by addition of these compounds, if appropriate in a mixture or in succession, to starting components with reactive hydrogen atoms, such as alcohols or amines, for example Water, ethylene glycol, propane-1,2-diol, propane-1,3-diol, 2,2-bis (4-hydroxyphenyl) propane or aniline are available. Polypropylene oxide, polytetrahydrofuran with a molecular weight of 240 to 5000, and especially 500 to 4500, are particularly preferred. B _1} only includes polyether diols which consist of less than 20% by weight of ethylene oxide. Polyether diols with at least 20% by weight are hydrophilic polyether diols which belong to monomers c).

If necessary, polyhydroxyolefins can also be used, preferably those with 2 terminal hydroxyl groups, e.g. α, -ω-Dihydroxypolybutadien, α, -ω-Dihydroxypolymethacrylester or α, -ω-Dihydroxypolyacrylester as monomers (d). Such compounds are known for example from EP-A 0622378. Other suitable polyols are polyacetals, polysiloxanes and alkyd resins.

At least 95 mol% of the diols bi _{) are} preferably polyether diols. Particularly preferred diols b _{1} are} exclusively polyether diols.

The hardness and the modulus of elasticity of the polyurethanes can be increased if, in addition to the diols (b1), low molecular weight diols (b2) with a diol (b)

Molecular weight of about 60 to 500, preferably from 62 to 200 g / mol, are used.

The structural components of the short-chain alkanediols mentioned for the production of polyester polyols are primarily used as monomers (b2), the unbranched diols having 2 to 12 carbon atoms and an even number of carbon atoms, as well as pentane-1, 5-diol and neopentyl glycol to be favoured.

Examples of diols b ₂ > are ethylene glycol, propane-1,2-diol, propane-1,3-diol, butane-1,3-diol, butene-1,4-diol, butyne-1,4-diol, pentane -1,5-diol, neopentyl glycol, bis-

(hydroxymethyl) cyclohexanes such as 1,4-bis (hydroxymethyl) cyclohexane, 2-methylpropane-1,3-diol, methylpentanediols, furthermore diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, polypropylene glycol, dibutylene glycol and polybutylene glycol. Alcohols of the general formula HO- (CH ₂ ) _x -OH are preferred, where x is a number from 1 to 20, preferably an even number from 2 to 20. Examples include ethylene glycol, butane-1, 4-diol, hexane-1, 6-diol, octane-1, 8-diol and dodecane-1, 12-diol. Neopentyl glycol is also preferred.

The proportion of the diols (bi), based on the total amount of the diols (b), is preferably 10 to 100 mol% and the proportion of the monomers (b ₂ ), based on the total amount of the diols (b), 0 to 90 mol% , The ratio of the diols (b1) to the monomers (b2) is particularly preferably 0.1: 1 to 5: 1, particularly preferably 0.2: 1 to 2: 1. In order to achieve the water dispersibility of the polyurethanes, they contain

Polyurethanes from components (a), (b) and (d) different monomers (c) which have at least one isocyanate group or at least one group which is reactive towards isocyanate groups and moreover at least one hydrophilic group or a group which can be converted into a hydrophilic group , wear as

Building component. In the following text, the term "hydrophilic groups or potentially hydrophilic groups" is abbreviated to "(potentially) hydrophilic groups". The

(Potentially) hydrophilic groups react with isocyanates much more slowly than the functional groups of the monomers, which serve to build up the main polymer chain.

The proportion of components with (potentially) hydrophilic groups in the total amount of components (a), (b), (c), (d) and (e) is generally such that the molar amount of the (potentially) hydrophilic groups, based on the amount by weight of all monomers (a) to (e), 30 to 1000, preferably 50 to 500 and particularly preferably 80 to 300 mmol / kg.

The (potentially) hydrophilic groups can be nonionic or preferably (potentially) ionic hydrophilic groups.

Particularly suitable nonionic hydrophilic groups are polyethylene glycol ethers composed of preferably 5 to 100, preferably 10 to 80, repeating ethylene oxide units. The content of polyethylene oxide units is generally 0 to 10, preferably 0 to 6% by weight, based on the amount by weight of all monomers (a) to (e).

Preferred monomers with nonionic hydrophilic groups are polyethylene oxide diols with at least 20% by weight of ethylene oxide, polyethylene oxide monools and the reaction products of a polyethylene glycol and a diisocyanate which carry a terminally etherified polyethylene glycol residue. Such diisocyanates and processes for their preparation are specified in US Pat. Nos. 3,905,929 and 3,920,598.

Ionic hydrophilic groups are above all anionic groups such as the sulfonate, carboxylate and phosphate groups in the form of their alkali metal or ammonium salts, and also cationic groups such as ammonium groups, in particular protonated tertiary amino groups or quaternary ammonium groups.

Potentially ionic hydrophilic groups are primarily those which can be converted into the abovementioned by simple neutralization, hydrolysis or quaternization reactions ionic hydrophilic groups, for example carboxylic acid groups or tertiary amino groups.

(Potentially) ionic monomers (c) are e.g. described in detail in Ulimann's Encyclopedia of Industrial Chemistry, 4th edition, volume 19, pages 311-313 and, for example, in DE-A 1 495 745.

As (potentially) cationic monomers (c), especially monomers with tertiary amino groups are of particular practical importance, for example: tris (hydroxyalkyl) amines, N, N'-bis (hydroxyalkyl) alkylamines, N-hydroxyalkyl dialkylamines, tris - (Aminoalkyl) amines, N, N'-bis (aminoalkyl) alkylamines, N-aminoalkyl dialkylamines, the alkyl radicals and alkanediyl units of these tertiary amines independently of one another consisting of 1 to 6 carbon atoms. Furthermore, polyethers containing tertiary nitrogen atoms come with preferably two terminal hydroxyl groups, such as those e.g. by alkoxylation of two amines containing hydrogen atoms bonded to amine nitrogen, e.g. Methylamine, aniline or N, N'-dimethylhydrazine, which are accessible in a conventional manner, into consideration. Such polyethers generally have a molecular weight between 500 and 6000 g / mol.

These tertiary amines are converted into the ammonium salts either with acids, preferably strong mineral acids such as phosphoric acid, sulfuric acid, hydrohalic acids or strong organic acids or by reaction with suitable quaternizing agents such as C to C ₆ alkyl halides or benzyl halides, for example bromides or chlorides.

Suitable monomers with (potentially) anionic groups are usually aliphatic, cycloaliphatic, araliphatic or aromatic carboxylic acids and sulfonic acids which carry at least one alcoholic hydroxyl group or at least one primary or secondary amino group. Are preferred

Dihydroxyalkyl carboxylic acids, especially those with 3 to 10 carbon atoms, as are also described in US Pat. No. 3,412,054. In particular, compounds of the general formula (c-i)

in which R ¹ and R ^{2 is} a C to C ₄ alkanediyl (unit) and R ^{3 is} a C to C alkyl (unit) and especially dimethylolpropionic acid (DMPA) is preferred. Corresponding dihydroxysulfonic acids and dihydroxyphosphonic acids such as 2,3-dihydroxypropanephosphonic acid are also suitable.

Otherwise suitable are dihydroxyl compounds with a molecular weight above 500 to 10,000 g / mol with at least 2 carboxylate groups, which are known from DE-A 3 911 827. They can be obtained by reacting dihydroxyl compounds with tetracarboxylic dianhydrides such as pyromellitic dianhydride or cyclopentantetracarboxylic dianhydride in a molar ratio of 2: 1 to 1.05: 1 in a polyaddition reaction. Particularly suitable dihydroxyl compounds are the monomers (b2) listed as chain extenders and the diols (b1).

Suitable monomers (c) with amino groups reactive towards isocyanates are aminocarboxylic acids such as lysine, ß-alanine or the adducts of aliphatic diprimeric diamines with a, ß-unsaturated carboxylic or sulfonic acids mentioned in DE-A 2034479.

Such compounds obey, for example, the formula (c ₂ ) H ₂ NR ⁴ -NH-R ⁵ -X (c ₂ )

in the

R ⁴ and R ⁵ independently of one another for ad- to C ₆ -alkanediyl unit, preferably ethylene

and X represents COOH or SO ₃ H.

Particularly preferred compounds of the formula (c ₂ ) are the N- (2-aminoethyl) -2-aminoethane carboxylic acid and the N- (2-aminoethyl) -2-aminoethanesulfonic acid or the corresponding alkali metal salts, Na being a particularly preferred counterion.

Also particularly preferred are the adducts of the abovementioned aliphatic diprimeric diamines with 2-acrylamido-2-methylpropanesulfonic acid, such as those e.g. are described in DE-B 1 954090.

If monomers with potentially ionic groups are used, they can be converted into the ionic form before, during, but preferably after the isocyanate polyaddition, since the ionic monomers are often difficult to dissolve in the reaction mixture. The sulfonate or carboxylate groups in the form of their salts with an alkali ion or a

Ammonium ion as counter ion.

The monomers (d), which differ from the monomers (a) to (c) and which may also be constituents of the polyurethane, are generally used for crosslinking or chain extension. They are generally more than dihydric non-phenolic alcohols, amines with 2 or more primary and / or secondary amino groups and compounds which, in addition to one or more alcoholic hydroxyl groups, carry one or more primary and / or secondary amino groups.

Alcohols with a higher valence than 2, which can serve to set a certain degree of branching or crosslinking, are e.g. Trimethylolpropane, glycerin or sugar.

Also suitable are monoalcohols which, in addition to the hydroxyl group, carry another isocyanate-reactive group, such as monoalcohols having one or more primary and / or secondary amino groups, e.g. Monoethanolamine.

Polyamines with 2 or more primary and / or secondary amino groups are used above all if the chain extension or crosslinking is to take place in the presence of water, since amines generally react with isocyanates faster than alcohols or water. This is often necessary when aqueous dispersions of cross-linked polyurethanes or high molecular weight polyurethanes are desired. In such cases, the procedure is to use prepolymers

Produces isocyanate groups, disperses them rapidly in water and then chain-lengthens or cross-links by adding compounds with several isocyanate-reactive amino groups.

Suitable amines are generally polyfunctional amines of

Molecular weight range from 32 to 500 g / mol, preferably from 60 to 300 g / mol, which contain at least two amino groups selected from the group of primary and secondary amino groups. Examples include diamines such as diaminoethane, diaminopropane, diaminobutane, diaminohexane, piperazine, 2,5-dimethylpiperazine, amino-3-aminomethyl-3,5,5-trimethyl-cyclohexane (isophorone diamine, IPDA), 4,4'-diaminodicyclohexylmethane, 1 , 4-diaminocyclohexane, aminoethylethanolamine, hydrazine, hydrazine hydrate or triamines such as diethylenetriamine or 1, 8-diamino-4-aminomethyloctane. The amines can also be in blocked form, for example in the form of the corresponding ketimines

(see e.g. CA-A 1 129 128), ketazines (see e.g. US-A 4269 748) or amine salts

(see US-A 4292226) are used. Oxazolidines, as are used, for example, in US Pat. No. 4,192,937, are blocked polyamines which are used for the chain extension of the polyurethanes according to the invention

Prepolymers can be used. When using such capped

Polyamines are generally used with the prepolymers in the absence of

Water mixed and this mixture then mixed with the dispersion water or part of the dispersion water so that the corresponding polyamines are released hydrolytically.

Mixtures of di- and triamines are preferably used, particularly preferably mixtures of isophoronediamine (IPDA) and diethylenetriamine (DETA).

The polyurethanes preferably contain 1 to 30, particularly preferably 4 to 25 mol%, based on the total amount of components (b) and (d) of a polyamine with at least 2 amino groups reactive towards isocyanates as monomers (d).

For the same purpose, higher than divalent isocyanates can also be used as monomers (d). Commercially available compounds are, for example, the isocyanurate or the biuret of hexamethylene diisocyanate.

Monomers (e) which may be used are monoisocyanates, monoalcohols and monoprimary and secondary amines. In general, their proportion is at most 10 mol%, based on the total molar amount of the monomers. These monofunctional compounds usually carry further functional groups such as olefinic groups or carbonyl groups and are used to introduce functional groups into the polyurethane which enable the polyurethane to be dispersed or crosslinked or further polymer-analogously converted. Monomers such as isopropenyl-a, a-dimethylbenzyl isocyanate (TMI) and esters of acrylic or methacrylic acid such as hydroxyethyl acrylate or hydroxyethyl methacrylate are suitable for this.

Coatings with a particularly good property profile are obtained above all if essentially only aliphatic diisocyanates, cycloaliphatic diisocyanates or araliphatic diisocyanates are used as monomers (a).

This monomer combination is excellently supplemented as component (c) by diaminosulfonic acid alkali salts; especially through the N- (2-aminoethyl) -2- aminoethanesulfonic acid or its corresponding alkali salts, the Na salt being the most suitable, and a mixture of DETA / IPDA as component (d).

It is generally known in the field of polyurethane chemistry how the molecular weight of the polyurethanes can be adjusted by choosing the proportions of the monomers reactive with one another and the arithmetic mean of the number of reactive functional groups per molecule.

Components (a) to (e) and their respective molar amounts are normally chosen so that the ratio A: B with

A is the molar amount of isocyanate groups and

B the sum of the molar amount of the hydroxyl groups and the molar amount of the functional groups which can react with isocyanates in an addition reaction

0.5: 1 to 2: 1, preferably 0.8: 1 to 1.5, particularly preferably 0.9: 1 to 1.2: 1. The ratio A: B is very particularly preferably as close as possible to 1: 1.

The monomers (a) to (e) used usually carry an average of 1.5 to 2.5, preferably 1.9 to 2.1, particularly preferably 2.0 isocyanate groups or functional groups which can react with isocyanates in an addition reaction ,

The polyaddition of components (a) to (e) to produce the polyurethane is preferably carried out at reaction temperatures of up to 180 ° C., preferably up to 150 ° C. under normal pressure or under autogenous pressure.

The production of polyurethanes or of aqueous polyurethane dispersions is known to the person skilled in the art.

Polymers obtainable by radical polymerization of ethylenically unsaturated compounds (monomers) are suitable as further binders, which may be used in a mixture with polyurethanes.

Such polymers preferably consist of at least 40% by weight, preferably at least 60% by weight, particularly preferably at least 80% by weight, of so-called main monomers. The main monomers are selected from CrC ₂ o-alkyl (meth) acrylates, vinyl esters of carboxylic acids containing up to 20 C atoms, vinyl aromatics with up to 20 C atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers containing 1 to 10 C atoms Alcohols, aliphatic hydrocarbons with 2 to 8 carbon atoms and one or two double bonds or mixtures of these monomers.

Examples include (meth) acrylic acid alkyl esters with a CrC ₁₀ alkyl radical, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate.

Mixtures of the (meth) acrylic acid alkyl esters are also particularly suitable.

Vinyl esters of carboxylic acids with 1 to 20 C atoms are e.g. Vinyl laurate, stearate, vinyl propionate, vinyl versatic acid and vinyl acetate.

Suitable vinylaromatic compounds are vinyltoluene, a- and p-methylstyrene, a-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and preferably styrene. Examples of nitriles are acrylonitrile and methacrylonitrile.

The vinyl halides are chlorine, fluorine or bromine-substituted ethylenically unsaturated compounds, preferably vinyl chloride and vinylidene chloride.

Examples of vinyl ethers include Vinyl methyl ether or vinyl isobutyl ether. Vinyl ethers of alcohols containing 1 to 4 carbon atoms are preferred.

As hydrocarbons with 2 to 8 carbon atoms and one or two olefinic

Double bonds include ethylene, propylene, butadiene, isoprene and chloroprene.

Preferred main monomers are the C to CIO alkyl acrylates and methacrylates, in particular C to C ₈ alkyl acrylates and methacrylates and vinyl aromatics, in particular styrene and mixtures thereof.

Methyl acrylate, methyl methacrylate, ethyl acrylate, n-butyl acrylate, n-hexyl acrylate, octyl acrylate and 2-ethylhexyl acrylate, styrene and mixtures of these monomers are very particularly preferred.

In addition to the main monomers, the polymer can contain further monomers, for example monomers with carboxylic acid, sulfonic acid or phosphonic acid groups. Carboxylic acid groups are preferred. Examples include acrylic acid, methacrylic acid, itaconic acid, maleic acid or fumaric acid. Further monomers are, for example, monomers containing hydroxyl groups, in particular CrC ₀ -hydroxyalkyl (meth) acrylates, (meth) acrylamide.

Phenyloxyethyl glycol mono (meth) acrylate, glycidyl acrylate, glycidyl methacrylate, amino (meth) acrylates such as 2-aminoethyl (meth) acrylate may also be mentioned as further monomers.

Crosslinking monomers may also be mentioned as further monomers.

The polymer particularly preferably consists of at least 40% by weight, in particular at least 60% by weight and very particularly preferably at least 80% by weight, of C 1 -C ₂₀ -, in particular C 1 -C ₁₀ alkyl (me-h) acrylates ,

In a preferred embodiment, the polymers are prepared by emulsion polymerization, so it is an emulsion polymer.

However, the manufacture can e.g. also by solution polymerization and subsequent dispersion in water.

In summary, the adhesive is preferably an aqueous adhesive. For this purpose, the polymeric binder is preferably in the form of an aqueous dispersion. Further additives can easily be added to the aqueous dispersion of the polymeric binder.

Other additives include Fillers, thickeners, defoamers etc. into consideration.

Crosslinkers, such as compounds with carbodimide groups, isocyanate groups or aziridine groups, are also particularly suitable.

The crosslinkers can also be attached to polymers, e.g. the above polymeric binders.

Compounds with carbodiimide groups are preferred as crosslinking agents, since aqueous dispersions which contain such compounds are stable on storage; Furthermore, dried adhesive coatings can still be used after several weeks, e.g. after more than 4 or more than 8 weeks are glued with unchanged high strength.

According to the method according to the invention, the substrate with the lower surface energy is coated with adhesive. The coating can be made according to usual Order process take place. After coating, drying is carried out, preferably at room temperature or at temperatures up to 80 ° C., in order to remove water or other solvents.

If necessary, the adhesive can also be applied to both substrates on both sides. Preferably, only the substrate with the lower surface energy is coated.

The amount of adhesive applied is preferably 0.5 to 100 g / m ² , particularly preferably 2 to 80 g / m ² , very particularly preferably 10 to 70 g / m ² .

When using adhesives with carbodiimides as crosslinkers, the coated and dried substrates can be stored. If the substrates are flexible, they can be wound on drums.

To glue to the substrate with the higher surface energy, the parts to be glued are put together. The temperature in the adhesive layer is preferably 20 to 200 ° C, particularly preferably 30 to 180 ° C. For this purpose, the coated flexible substrate can suitably be heated to appropriate temperatures.

The bonding is preferably carried out under pressure, for example the parts to be bonded can be pressed together with a pressure of 0.05 to 5 N / mm ² .

The composites obtained are characterized by high mechanical strength even at elevated temperatures (heat resistance) or under rapidly changing climatic conditions (climatic resistance). Compared to a method in which only the substrate with the higher surface energy is coated, the strength achieved is significantly higher.

Claims

claims

1. A method for bonding substrates with different surface energies, characterized in that the adhesive used for the bonding consists of at least 15% by weight of a polyurethane (water or other organic solvents with a boiling point below 150 ° C. at 1 bar not calculated), the adhesive is applied to the substrate with the lower surface energy and the resulting adhesive-coated substrate is bonded to the substrate with the higher surface energy.

2. The method according to claim 1, characterized in that the polyurethane is composed of at least 60 wt .-% of diisocyanates, polyether diols and / or polyester diols.

3. The method according to claim 3, characterized in that the polyurethane has a melting point or softening point in the range of -50 to 150 ° C.

4. The method according to any one of claims 1 to 5, characterized in that the adhesive contains a crosslinker for the polyurethane or the polyurethane is self-crosslinking

5. The method according to claim 4, characterized in that the crosslinker is compounds having isocyanate groups or carbodiimide groups or, in the case of the self-crosslinking polyurethane, isocyanate groups or carbodiimide groups are bound to the polyurethane.

6. The method according to claim 5, characterized in that the crosslinker is a compound having carbodiimide groups or, in the case of the self-crosslinking polyurethane, carbodiimide groups are bound to the polyurethane.

7. The method according to any one of claims 1 to 8, characterized in that an aqueous adhesive is used to produce the substrate coated with adhesive and the polyurethane is in the form of an aqueous dispersion

8. The method according to any one of claims 1 to 7, characterized in that it is substrates made of wood or plastic in the substrates to be bonded.

9. The method according to any one of claims 1 to 8, characterized in that the substrate with the low surface energy is a polymer film

10. The method according to any one of claims 1 to 8, characterized in that the substrate with the higher surface energy is a substrate made of natural or synthetic fibers or chips.

11. The method according to any one of claims 1 to 9, characterized in that the adhesive is applied to the substrate with the lower surface energy, optionally drying to remove water or organic solvents and the adhesive layer in the subsequent bonding to the substrate with the higher surface energy is heated to temperatures of 20 to 200 ° C.

12. The method according to claim 11, characterized in that the substrate with the lower surface energy is a polymer film and this polymer film is wound up after coating with the adhesive and after drying, if appropriate,

13. Substrate composites obtainable by a method according to one of claims 1 to 12.