WO2021023841A1

WO2021023841A1 - Water-resistant two-component structural adhesives

Info

Publication number: WO2021023841A1
Application number: PCT/EP2020/072189
Authority: WO
Inventors: Sebastian Benedikt STAPPERT; Wilhelm Kopp; Lutz Schmalstieg
Original assignee: Glue Tec Industrieklebstoffe Gmbh & Co. Kg
Priority date: 2019-08-07
Filing date: 2020-08-06
Publication date: 2021-02-11
Also published as: EP4010393A1; DE102019211865A1

Abstract

The present invention relates to a method for bonding substrates of the same or different type using two-component structural adhesives on the basis of aliphatic polyisocyanates and polyaspartic acid esters, and to a two-component structural adhesive, which contains said two components and has a high strength and water resistance when hardened.

Description

WATERPROOF TWO-COMPONENT STRUCTURAL ADHESIVES

The present invention relates to a method for bonding the same or different substrates with two-component structural adhesives based on aliphatic polyisocyanates and polyaspartic acid esters, as well as a two-component structural adhesive which has these two components and shows high strength in the cured state.

Reactive two-component adhesives (hereinafter also referred to as "2K adhesives") are now widely used for the structural bonding of substrates.

In structural bonding, the same or different substrates are permanently bonded to one another, the bonded component usually assuming a structural function.

Structural adhesives have a comparatively high internal strength - cohesion - and at the same time good adhesion to the substrate. A major advantage of the two-component structural adhesives is the relatively fast curing without restriction of layer thickness and the freedom from organic solvents. The curing is only dependent on the temperature and is essentially independent of the humidity or oxygen content of the environment.

Among other things, to differentiate elastic adhesives and sealants, structural adhesives are within the scope of the present application due to a tensile shear strength on roughened V2A steel according to DIN / EN 1465 (2009-07) of at least 7 MPa, preferably at least 10 MPa, more preferably at least 12 MPa marked.

Basically three different product groups have established themselves as two-component structural adhesives of the state of the art:

• Two-component epoxy resin adhesives based on a polyepoxy component and a polyamine and / or polymercaptan component, • Two-component acrylate adhesives based on acrylate copolymers that are cured radically with a peroxide component, and

• Two-component polyurethane adhesives based on a polyisocyanate component and a polyol and / or polyamine component.

Two-component epoxy resin adhesives are possibly the most important class of structural adhesives due to their variable property profile and their excellent adhesion to a wide variety of substrates. The problem with this class of structural adhesives, however, is the comparatively slow curing, especially at lower temperatures. These adhesives no longer harden reliably below a temperature of approx. 8 ° C. In addition, the tendency of aromatic epoxy resins to crystallize makes comparatively high demands on the correct storage temperature, which usually has to be between 5 and 25 ° C.

Two-component acrylate adhesives, on the other hand, cure much faster. However, the presence of odor-intensive and unhealthy acrylate monomers, such as methyl methacrylate, cyclohexyl methacrylate or tetrahydrofurfuryl methacrylate, is viewed as a disadvantage in these structural adhesives. Another problem with these structural adhesives is the relatively unfavorable relationship between correction time on the one hand and adequate assembly strength on the other. The radical formers used as hardener components such as organic peroxides or azo compounds also require strict adherence to the cold chain of mostly below 8 ° C in order to effectively slow down the decomposition of these substances.

Two-component polyurethane adhesives can be formulated in different ways and can therefore be used in a particularly diverse way as structural adhesives. Due to their high reactivity, aromatic isocyanates are predominantly used in reactive structural adhesives. The monomeric aromatic diisocyanates diphenylmethane diisocyanate -MDI- and toluylene diisocyanate -TDI- presumably have carcinogenic properties, which means that their use is limited. The hydrolysis products of the monomeric diisocyanates, aromatic diamines, are proven carcinogenic and are released from the adhesives through migration. Nowadays, therefore, low-monomer polyisocyanates based on TDI and / or MDI are often used, which are produced by oligomerization or prepolymerization of these isocyanates and are freed from monomeric diisocyanates by subsequent thin-film distillation. The polyisocyanates and / or isocyanate prepolymers obtained in this way are usually highly viscous or resinous, so that the products can only be made with the aid of solvents or Plasticizers can be processed into adhesives, which is disadvantageous in terms of adhesive technology and environmental aspects.

Aliphatic, low-monomer polyisocyanates based on isophorone diisocyanate and / or hexamethylene diisocyanate, on the other hand, are physiologically more favorable, but have a significantly lower reactivity compared to aromatic isocyanates, so that the curing of the adhesives is comparatively slow. For this reason, the aliphatic polyisocyanates have so far only been used in special applications for structural bonding.

Two-component polyurethane adhesives contain polyols such as polyester polyols, polyether polyols, polycarbonate polyols, polyacrylate polyols or low molecular weight polyalcohols as the second component. Since the reaction with the polyisocyanates proceeds relatively slowly, catalysts usually have to be added to accelerate the curing process. Some of these are toxic organotin compounds or strongly basic tertiary amine compounds. Even with the use of the catalyst systems mentioned, the curing rate is insufficient for many modern production processes or at least in need of improvement.

Much faster curing is achieved if the abovementioned polyols are partially or completely replaced by aromatic polyamine compounds. The polyaddition of the aromatic amines with the polyisocyanates takes place in minutes, so that with the help of this technology structural adhesives can be formulated which have a favorable ratio of correction time on the one hand to adequate assembly strength on the other. Disadvantages of these adhesives are their strong tendency to yellow and their poor reactivity at temperatures below approx. 5 ° C.

An overview of structural adhesives can be found, for example, in 'Bodo Müller and Walter Rath, Formulation of adhesives and sealants', 3rd edition, Vincentz Network 2015, S107 ff.

Another class of curable two-component systems is based on aliphatic polyisocyanates and amine-functional aspartic acid esters, as can be obtained by adding maleic acid and / or fumaric acid esters to polyamines. These are known in principle as paints and coating systems and are described by way of example in the following patent applications: EP 403 921, EP 0 573 860, US 6 605 684, EP 1 767 559, WO 2001/007504, WO 2001/007399, US 6 458 293, EP 1 426 397, DE 10 2006 002 153 A1 or WO 2004/033517 and the more recent patent applications EP 3 098 247 A1 and EP 3 115 388 A1. However, these applications do not give any indication of the possible use of such coating systems in structural bonds.

WO 2009-07 / 003596 relates to medical adhesives based on hydrophilic polyisocyanate prepolymers for surgery, in particular as tissue adhesive, WO 2011/138274 relates to polyisocyanate prepolymers which contain polyether carbonate polyols as a structural component, their production and their use as an isocyanate component in and Two-component systems for paints, adhesives and sealants. A common feature of these patent applications is that prepolymers containing special isocyanate end groups are used. In the context of the present invention, the observation was made that such prepolymer-based 2-component adhesives cure to form comparatively soft polymers with low mechanical strength and are therefore not suitable as structural adhesives.

In contrast to paints and coatings, structural adhesives must have a significantly higher internal strength - cohesion - and, with regard to adhesive joints of different dimensions, they must also be able to be applied in a significantly higher layer thickness. In addition, the requirements in structural adhesives for adhesion to different substrates are significantly higher than for a lacquer or a coating. Furthermore, the loads of a structural bond are fundamentally different than for paints or coatings: Static loads on the bonds are pressure and tensile loads as well as shear and peel loads.

Of particular relevance for structural adhesives in many applications is the water resistance (moisture resistance), which is often not (sufficiently) given, especially in the class of two-component polyurethane systems of the state of the art, such as those used as paints and coatings.

Furthermore, with structural adhesives, dynamic loads from shear or peeling movements are particularly relevant, as well as impact and shock loads, which are repeatedly the reason for the inadequate applicability of structural adhesives, especially at low temperatures. An overview of this problem can be found, for example, in 'Bodo Müller and Walter Rath, Formulation of adhesives and sealants, 3rd edition, Vincentz Network 2015, S291 ff. In summary, it can be stated that the structural adhesives of the state of the art do not fully meet the requirements of modern and fast manufacturing and bonding processes.

The object of the present invention was therefore to provide a new structural adhesive of comparatively high strength, especially when exposed to moisture, as well as a method for moisture-resistant bonding of substrates, this adhesive and this method overcoming or at least minimizing the aforementioned disadvantages of the prior art.

This and other object (s) are achieved with the provision of the method described below and with the two-component structural adhesive described below.

In one embodiment, the present invention relates to a two-component structural adhesive which has at least the following components:

(i) at least one polyisocyanate containing free isocyanate groups with an aliphatically bonded NCO group content of 14.0 to 24.0% by weight,

(ii) an amino-functional polyaspartic acid ester of the stereochemical general formula:

(iii) and optionally at least one further component selected from the group comprising: fillers, auxiliaries and additives wherein the structural adhesive in the cured state has a tensile shear strength of at least 7 MPa, preferably at least 10 MPa, more preferably at least 12 MPa, the tensile shear strength according to Standard DIN EN 1465: 2009 is measured between two test bodies made of roughened V2A steel.

In the context of the present invention, “stereochemically general” means that the structure should not be restricted in any way with regard to stereoisomerism, i.e. all stereoisomers of the present structural formulas should be included, i.e. in particular all enantiomers, diastereomers, rotational isomers, etc.

In a preferred embodiment, the structural adhesive has, in addition to the above-mentioned cycloaliphatic amino-functional polyaspartic acid ester (ii), at least one further amino-functional polyaspartic acid ester, namely an aliphatic amino-functional polyaspartic acid ester (ii ') of the stereochemical general formula:

In a further embodiment, the present invention relates to a method for the structural bonding of identical or different substrates with two-component structural adhesives, the method having at least the following steps:

(1) Providing a two-component structural adhesive that contains at least the following components:

(i) at least one polyisocyanate containing free isocyanate groups with an aliphatically bound NCO group content of 14.0 to 24.0% by weight

(ii) at least one amino-functional polyaspartic acid ester of the stereochemical general formula

(iii) and optionally at least one further component selected from the group comprising: fillers, auxiliaries and additives

(2) structural bonding of at least two identical or different substrates using at least the two-component structural adhesive from (1);

(3) Curing of the at least one bond from (2), so that in the cured state it has a tensile shear strength of at least 7 MPa, preferably at least 10 MPa, more preferably at least 12 MPa, the tensile shear strength according to standard DIN EN 1465: 2009 between two test specimens from roughened V2A steel is measured.

In a preferred embodiment, the structural adhesive in (1) has, in addition to the above-mentioned cycloaliphatic amino-functional polyaspartic acid ester (ii), at least one further amino-functional polyaspartic acid ester, namely an aliphatic amino-functional polyaspartic acid ester (ii ') of the stereochemically generally shown formula:

Unless otherwise stated, all percentages in the present disclosure relate to percent by weight (% by weight), in each case based on the total weight of the structural adhesive.

In embodiments of the present invention, the two-component structural adhesive contains, in addition to the above-mentioned components (i), and (ii) or (ii '), at least one further component (iii) which is at least one auxiliary or additive of the two-component structural adhesive . Preferred auxiliaries or additives are described below and in the claims.

The present invention is based on the observation that the two-component systems characterized in more detail here, based on the special or special amino-functional aspartic acid esters as described above, in combination with selected aliphatic polyisocyanates, are not only suitable as paints or coatings, but surprisingly also in the demanding Application as structural adhesives are particularly suitable because they have a particularly favorable ratio of sufficient correction time with rapid assembly strength at the same time, can be applied and used in a very wide temperature window, as well as bonds with excellent tensile shear strength, especially under water and Moisture exposure (see experimental data discussed below). This moisture resistance was determined according to DIN EN 204: 2016 between two test specimens made of beech wood after standardized storage under the influence of moisture. As delimiting tests have shown, linear aliphatic aspartic acid esters alone are typically not suitable for producing water-resistant bonds, as is demonstrated in the comparative examples listed below that are not according to the invention.

The method according to the invention and the two-component structural adhesive according to the invention are further characterized in particular by the following properties and advantages, which are at least partially, preferably all achieved together:

• favorable physiological properties of the raw materials used,

• good light and UV resistance of the bonds,

• Sufficient correction time with simultaneous rapid assembly strength,

• Application security in a temperature range from -10 ° C to + 40 ° C,

• Functional reliability in the temperature range from -20 ° C to 150 ° C.

• Permanently moisture and water-resistant bonding

Polyisocyanates which can be replaced as component i) are preferably modified with the aid of suitable modification reactions, such as. B. dimerization, trimerization, biuretization, allophanatization and / or urethanization of hexamethylene diisocyanate and / or isophorone diisocyanate, more preferably exclusively based on hexamethylene diisocyanate, preferably excess monomeric diisocyanate is then removed from the mixture by distillation, whereby the polyisocyanates residual monomer content Diisocyanate preferably <0.5%, preferably <0.3%, particularly preferably <0.1%, each based on the total mixture of the polyisocyanate mixture.

In embodiments of the invention, component i) has residual contents of monomeric diisocyanate of <0.5% by weight, preferably <0.3%, particularly preferably <0.1% by weight, based in each case on the total weight of the polyisocyanate mixture.

Polyisocyanates which are preferred as component i) are uretdione, isocyanurate, iminooxadiazinedione, urethane, allophanate, biuret and / or oxadiazinetrione group-containing derivatives of HDI which at 23 ° C. have a viscosity of 200 to 23,000 mPas io preferably 800 to 12,000 mPas, and preferably have an isocyanate group content of 14 to 24% by weight, preferably 15 to 23% by weight and an average isocyanate functionality of at least 2.5, preferably at least 3.0.

Suitable polyisocyanates are described by way of example in Laas et al. , J. Prakt. Chem. 336, 1994, 185-200, DE-A 1 670 666, DE-A 3 700 209, DE-A 3 900 053, EP-A 0 330 966, EP-A 0 336205, EP-A 0 339 396 and EP-A-0 798299.

Polyisocyanates based on hexamethylene diisocyanate with biuret structures and / or isocyanurate structures and / or iminooxadiazinedione structures are preferred as component i).

In a preferred embodiment of the present invention, polyisocyanate mixtures containing alkoxysilane groups are used as component i). Such polyisocyanate mixtures can be obtained by reacting polyisocyanates with functional silanes which have a functional group that can react with the isocyanate groups of the polyisocyanates, or by processes as described by way of example in DE 102009-07 047 964 A1 and DE 102007 032 666 A1.

The polyisocyanates which can be used according to the invention as component i) can be mixed with minor amounts of isocyanate prepolymers or provided as a mixture of the abovementioned polyisocyanates with a view to adapting the mixing ratios of the processable two-component mixture.

These are preferably the isocyanate prepolymers known in principle from polyurethane technology, which are produced by reacting aliphatic di- or polyisocyanates with higher molecular weight polyols, in particular polyether polyols, polyester polyols and / or polycarbonate polyols. In this case, only minor amounts of isocyanate prepolymers are preferably used for mixing, the mixture corresponding to the information given above with regard to isocyanate content and residual monomer content. The amounts of isocyanate prepolymers are preferably less than 25% by weight based on the total weight of component i), preferably less than 15% by weight, particularly preferably less than 10% by weight.

Hardener component (ii) in the context of the present invention is the cycloaliphatic amino-functional polyaspartic acid ester of the stereochemically general formula

either alone or in combination with at least one further amino-functional polyaspartic acid ester, in particular an aliphatic amino-functional polyaspartic acid ester (ii ') of the stereochemical general formula:

The production of the cycloaliphatic amino-functional polyaspartic acid ester (ii) takes place, for example, in a manner known per se by reacting diaminodicyclohexylmethane with maleic and / or fumaric acid diethyl ester, preferably within the temperature range from 0 to 100 ° C., the starting materials preferably being used in proportions such that each primary amino group at least one, preferably exactly one, olefinic double bond is omitted, it being possible for starting materials, which may have been used in excess, to be separated off by distillation after the reaction.

The reaction can take place in bulk or in the presence of suitable solvents such as methanol, ethanol, propanol or dioxane or mixtures of such solvents, the use of solvents being less preferred.

The aliphatic amino-functional polyaspartic acid ester (ii ‘) is prepared, for example, in a manner known per se by reacting 2-methyl-1,5-diaminopentane with diethyl maleic and / or fumarate in the aforementioned type for component (ii).

In embodiments, the two-component structural adhesives according to the invention can contain fillers, auxiliaries and additives that are advantageous as component (iii) in adhesive technology. These are, for example, inorganic and organic fillers, flame retardants, pigments, leveling agents, thixotropic agents, solvents or plasticizers or (other) viscosity regulators.

Solvents can optionally be used as component (iii) in small amounts to improve substrate wetting, ie in amounts of less than 5% by weight, preferably less than 2% by weight, particularly preferably less than 1% by weight, in each case on the total weight of the structural adhesive.

Suitable solvents are, in particular, the usual organic solvents such as, for example, ethyl acetate, butyl acetate, methoxypropyl acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, aromatic or (cyclo) aliphatic hydrocarbon mixtures or any mixtures of such solvents. In a preferred embodiment of the present invention, the structural adhesives contain, as component iii), inorganic flame retardants and, if appropriate, additional organic flame retardants.

As inorganic flame retardants, aluminum hydroxide and magnesium hydroxide are preferred, aluminum hydroxide in powder form with particle sizes of 0.1 μm to 100 μm being preferably used.

Particularly preferred organic flame retardants are phosphoric acid esters, such as triethyl phosphate, tributyl phosphate, tris-2-ethylhexyl phosphate, triphenyl phosphate, diphenyl octyl phosphate or tricresyl phosphate.

A combination of pulverulent aluminum hydroxide and tris-2-ethylhexyl phosphate is particularly preferably used as the flame retardant.

In addition to the flame retardants mentioned, or instead of them, the structural adhesives can also contain fillers as component (iii). Suitable fillers are sand, rock flour, quartz flour, talc, natural, ground or precipitated calcium carbonates, which can optionally be coated with fatty acids, barium sulfate (BaS0 ₄ , also called barite or barite), carbon black, and silicas, preferably highly disperse silicas from pyrolysis processes, also natural, artificial or artificially modified phyllosilicates.

These fillers are preferably incorporated into components (ii) / (ii ‘).

In principle, all organic and inorganic pigments known per se from coating technology, optionally as paste preparations, can be used as component (iii) as pigments. Such pigments are preferably incorporated into component (ii).

The two-component structural adhesives can also contain reactive thinners as component (iii), which are preferably incorporated into component (ii). For example, aspartic acid esters based on polyetheramines, as disclosed in WO 2014/151307 A1, can be used as reactive diluents.

Also suitable as reactive diluents are the low molecular weight polyols known per se from polyurethane chemistry, such as, for example. 1, 2-ethanediol, 1, 2-propanediol, 1, 4- or 1,3-butanediol, 1,6-hexanediol, 2-ethylhexanediol-1,3, 1, 8-octanediol, or dimer fatty alcohols. Diols containing ether groups, such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol or mixtures of such alcohols, can also be used.

The reactive diluents mentioned preferably have a mass fraction of less than 20%, preferably less than 15%, particularly preferably less than 10%, based on the total weight of the adhesive formulation.

To improve adhesion to substrates, higher molecular weight polyols of the type known per se from polyurethane chemistry can also be used in component (iii). These are, in particular, hydroxy-functional polyether polyols, polyester polyols, polycarbonate polyols and polyacrylate polyols, and also mixtures of the aforementioned polyols. Such polyols are preferably incorporated into component (ii).

The polyols mentioned are preferably used in a mass fraction of less than 20%, preferably less than 15%, particularly preferably less than 10%, based on the total weight of the adhesive formulation.

To (further) improve the adhesion to special substrates, the 2K structural adhesives according to the invention can preferably contain functional silanes as part of component (iii). In this context, γ-organofunctional silanes or α-organofunctional silanes are preferred.

3-mercaptopropyl-trimethoxysilane, 3-aminopropyl-trimethoxysilane, N-alkyl-3-aminopropyl-trimethoxysilane, N-aminoethyl-3-aminopropyl-trimethoxysilane, 3-ureidopropyl-trimethoxysilane, vinyltrimethoxysilane, and 3-methacryloxysilane-trimethoxysilane, and 3-methacryloxysiloxysilane, and 3-methacryloxysilypropyl-trimethoxysilane, and 3-methacryloxysilane propyl, 3-methacryloxysilane, and 3-methacryloxysilane, are particularly preferred corresponding triethoxysilane derivatives and dimethoxymethyl derivatives of the aforementioned functional silanes. Also preferred as silanes are tris [3- (trimethoxysilyl) propyl] isocyanurate and N-methyl [3- (trimethoxysilyl) propyl] carbamate, methacryloxymethyltrimethoxysilane, N-trimethoxysilylmethyl-O-methylcarbamate

Mixtures of the abovementioned silanes or else their oligomerization products can of course also be used in the context of component (iii). The named functional Silanes are preferably also used in amounts of less than 3% by weight, preferably less than 2% by weight, based on the total weight of the adhesive formulation.

To adjust the reaction rate, the 2K structural adhesives according to the invention can contain catalysts as component (iii). These are preferably catalysts such as water, carboxylic acids or Lewis acids such as formic acid, acetic acid, propionic acid, fatty acids or benzoic acid and also dicarboxylic acids such as oxalic acid or malonic acid and metal salts of metals such as aluminum, iron, lithium, magnesium, titanium, zinc or Zirconium of these carboxylic acids in solid or dissolved form.

In a preferred embodiment of the present invention, the 2K structural adhesives according to the invention contain water as a catalyst. The 2K structural adhesives according to the invention particularly preferably contain 0.1 to 1% by weight of water, based on the total weight of the adhesive formulation, in the context of component (iii).

In a preferred embodiment of the present invention, the 2K structural adhesives in the context of component (iii) contain aliphatic polyamines for rheology control. Such polyamines react faster than the aspartic acid esters of component (ii) and are incorporated into them. The rapid reaction of the polyamines results in a rapid increase in viscosity immediately after application. The polyamines of the type exemplified below can therefore advantageously be used for rheology control. Suitable amines are, in particular, aliphatic or cycloaliphatic polyamines with primary and / or secondary amine groups. Such polyamines are preferably used in amounts of less than 2% by weight, preferably less than 1% by weight, based on the total weight of the adhesive formulation.

Preferred polyamines are ethylenediamine, 1,2-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 2,5-diamino-2,5-dimethylhexane, 2,2,4- and / or 2,4,4- Trimethyl-1,6-diaminohexane, 1,1-diaminoundecane, 1,2-diaminododecane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 2,4- and / or 2,6-hexahydrotoluylenediamine, 2 , 4'- and / or 4,4'-diamino-dicyclohexylmethane or 3,3'-dimethyl-4,4'-diamino-dicyclohexyl-methane, 1,3-bis (aminomethyl) benzene and polyether polyamines and polyethylene polyamines such as diethylenetriamine or Triethylenetetramine. In principle, the reaction products of the diamines mentioned can also be replaced with derivatives of acrylic acid and / or methacrylic acid, even if this is less preferred. Other auxiliaries and additives (iii) that may be mentioned are, by way of example, deaerators, defoamers, wetting aids and anti-aging agents. Antioxidants, UV absorbers and free radical scavengers and corresponding combinations of these anti-aging agents may be mentioned at this point as anti-aging agents.

In the 2K structural adhesives according to the invention, components (i), (ii) / (ii ') and optionally (iii) are preferably used in a quantitative ratio (measured in% by weight based on the total weight of the adhesive formulation) so that the equivalent ratio (i.e. the molar ratio) of the isocyanate groups of component (i) to the amino groups and, if present, for example in the polyol, additional hydroxyl groups of components ii) / (ii ') and iii) from 0.9: 1 to 1.5: 1, preferably 1: 1 to 1.4: 1.

The 2K structural adhesives according to the invention preferably have a mass fraction of 35-65% by weight, preferably 40 to 60% by weight of component (i), a mass fraction of 25 to 65% by weight, preferably 35 to 55% by weight .-% of component (ii) or, if present, (ii) and (ii ') together, and 0 to 25% by weight of the optional component (iii), based in each case on the total weight of the adhesive formulation.

If both cycloaliphatic amino-functional polyaspartic acid esters (ii) and linear aliphatic amino-functional polyaspartic acid esters (ii ') are used, at least 5% by weight of component (ii), particularly preferably at least 10% by weight of component (ii), are based to the total weight of the adhesive formulation. At least 10% by weight to 95% by weight of the polyaspartic acid ester component of the cycloaliphatic amino-functional polyaspartic acid ester (ii) are further preferred, more preferably 20% by weight to 90% by weight, based in each case on the total weight of the polyaspartic acid ester component.

The inventors have found that the curing reaction time can be gradually adjusted as the content of the linear aliphatic polyaspartic acid ester (ii ‘) is successively increased.

The 2K structural adhesives are preferably formulated as two-component systems consisting of a resin component and a hardener component. The formulation is preferably such that the resin component contains all components (ii) / (ii ') and, if appropriate, iii). If necessary, solvents and viscosity regulators as well as anti-aging agents can be added in order to adjust the viscosities or the mixing ratios of the two components of component (i) so that two-component systems corresponding to a volume ratio of 1: 4 to 4: 1, preferably 2: 1 to 1: 2 and particularly preferably 1: 1 can be obtained.

The 2K structural adhesives according to the invention are typically reactive and can therefore normally only be processed with the aid of suitable metering systems with two chambers. These are preferably 2K cartridge systems in conjunction with suitable static mixers, as described by way of example in WO 2011/162728 and the secondary literature cited there. Particularly preferably replaceable within the scope of the present invention are double cartridge systems with child safety devices, as described in the German utility model application DE 202016102271 (U1).

The 2K structural adhesives according to the invention cure comparatively quickly and are formulated in such a way that, depending on the presence of catalysts of component (iii)

- in particular water - build up an assembly strength in a period of 2 minutes to 30 minutes, and reach their final strength in a period of 3 hours to 24 hours.

In the context of corresponding tests (see also examples below) it has been shown on the one hand that according to the invention a particularly favorable ratio of correction time on the one hand to assembly strength on the other is achieved. The adhesives according to the invention are particularly suitable for bonding wood substrates; the bonds here are characterized by excellent water resistance in accordance with DIN EN 204: 2016.

In the course of further tests (see also examples below) it has been shown, on the other hand, that, in particular by combining components (ii) and (ii '), a highly moisture-resistant bond can be produced in accordance with DIN EN 204: 2016, these adhesives being characterized by a particularly high reactivity. The 2K structural adhesives that can be used according to the invention show excellent adhesion to many organic and inorganic substrates, even without the addition of special adhesion promoters such as, for example, functional silanes of the type mentioned above.

The particularly strong adhesion to other organic substrates, in particular plastics or inorganic substrates, in particular metals and metal alloys, can be controlled in a targeted manner by adding the substances mentioned above in the context of component iii).

Overall, the present invention represents a significant advance in the structural connection of the same or different substrates.

In order to produce sufficient adhesion, it may be preferred according to the invention to prepare the substrate. This can be done by mechanical pretreatment such as roughening or sanding, but also by chemical pretreatment such as flame treatment, plasma or corona pretreatment, but also by using primers and adhesive primers.

Preferred primers are solutions of the functional silanes mentioned above as component iii) in organic solvents or solutions of chlorinated polyolefins and / or modified chlorinated polyolefins in organic solvents.

Such solutions of chlorinated polyolefins are particularly advantageous as primers if sufficient adhesion to non-polar plastics, in particular polyolefin plastics such as polypropylene, is to be achieved. The chlorinated polyolefins or modified chlorinated polyolefins preferably have a chlorine content of 10 to 25% by weight, based on the solids (solids content) of the chlorinated polyolefins. The chlorinated polyolefins or modified chlorinated polyolefins used preferably have a number average molecular weight of 8,000 to 50,000. The amount of chlorinated polyolefins used in the primer formulation is preferably 0.2 to 5.0% by weight, based in each case on the total weight of the primers and on the solids content of the chlorinated polyolefins. The chlorinated polyolefins used according to the invention are familiar to the person skilled in the art and are commercially available, for example, under the trade name Eastman ™ chlorinated polyolefins from Eastman Chemical Products, INC., T rapylenes from Tramaco or Hardlen from Toyo Kasei.

The 2K structural adhesives that can be replaced according to the invention can be adjusted to have a low to high viscosity with regard to the processing viscosity. They preferably have a viscosity, immediately after mixing, in the range from 1000 mPas to 100,000 mPas, preferably from 2000 mPas to 50,000 mPas, at a temperature of 23 ° C., the viscosity being determined rotationally viscometrically in accordance with DIN EN ISO 3219 becomes.

Low-viscosity formulations are used when substrates are to be glued virtually gap-free, i.e. with a gap size of less than 0.1 mm, higher-viscosity settings are used when gluing with a larger gap size or gap-bridging or when sloping or overhanging ones are to be glued off Substrates is to be avoided.

In the context of the present invention, the observation was made that adhesive bonds with surprisingly high internal strengths can be obtained according to the invention, so that bonds with a gap dimension of 0.1 mm to 5 mm can be produced with high strength.

The 2K structural adhesives can be processed in the method according to the invention in a much larger temperature window than 2K structural adhesives of the prior art. The two-component structural adhesives according to the invention cure reliably in a temperature range from -20 ° C to + 50 ° C. The cured adhesives also show outstanding impact strength at low temperatures down to -40 ° C and at the same time have excellent high temperature resistance in the temperature range up to 150 ° C. The following examples of formulations of structural adhesives are intended to explain the invention in more detail, but without restricting it. A comparison of the examples according to the invention with examples not according to the invention is intended to illustrate the technical advantages of the process according to the invention and of the cured structural adhesive.

Examples:

Polyisocyanate M):

Polyisocyanurate-polyisocyanate based on hexamethylene diisocyanate with an NCO content of 22% and a viscosity of 3000 mPas (23 ° C.), residual monomer content <0.1%, Desmodur Ultra N3300, commercial product from Covestro AG, Leverkusen

Polyisocyanate i2):

Polyisocyanurate-polyisocyanate based on hexamethylene diisocyanate with an NCO content of 23% and a viscosity of 1200 mPas (23 ° C.), residual monomer content <0.1%, Desmodur Ultra N3600, commercial product from Covestro AG, Leverkusen

Polyisocyanate i3): commercially available polyisocyanate based on hexamethylene diisocyanate with a biuret structure and an NCO content of 22% and a viscosity of 8000 mPas (23 ° C.), Desmodur N100, residual monomer content 0.25%, commercial product from Covestro AG, Leverkusen

Polyisocyanate i4): commercially available polyisocyanate (polyisocyanate prepolymer) based on hexamethylene diisocyanate with an isocyanurate structure, which is modified with a polyester diol with an NCO content of 11% and a viscosity of 6000 mPas (23 ° C.), Desmodur N 3800, residual monomer content 0.25 %, Commercial product from Covestro AG, Leverkusen

Polyaspartic acid ester 111)

Polyaspartic acid ester based on diaminodicclohexylmethane and maleic acid diethyl ester, amine number 200mg KOH / g, viscosity 1500 mPas (23 ° C), Desmophen NH1420, commercial product from Covestro AG, Leverkusen (product variant not purified by distillation) Polyaspartic acid ester N2)

Polyaspartic acid ester based on diaminodicvclohexylmethane and maleic acid diethyl ester, amine number 200mg KOH / g, viscosity 1500 mPas (23 ° C), Desmophen NH1423, commercial product from Covestro AG, Leverkusen (product variant purified by distillation)

Polyaspartic acid ester ii3)

Polyaspartic acid ester based on 2-methyl-1,5-diaminopentane and maleic acid diethyl ester, amine number 245 mg KOH / g, viscosity 90 mPas (23 ° C.), Desmophen NH1220, commercial product from Covestro AG, Leverkusen

Polyol containing ester groups iii1) slightly branched, highly viscous polyester polyol with an OH content of 4.3% and a viscosity> 100,000 mPas (23 ° C.), Desmophen 670, commercial product from Covestro AG, Leverkusen

General process description for the production of 2-component adhesives

Polyisocyanates or polyisocyanate mixtures of component i) are used as component A. To produce component B, components ii) / ii ‘) and iii) are intimately mixed in a commercially available laboratory dissolver.

In the case of hand application, components A and B are intimately stirred in the specified proportions in a disposable beaker for 30 seconds and then applied to a substrate with the aid of a glass rod. To determine the tensile shear strengths, the 2K adhesives were applied to one side of roughened V2A steel test specimens with a length of 100 mm and a width of 25 mm in accordance with DIN EN 1465: 2009-07, followed by an overlap length of 12 mm with a Gaps of 0.1 mm glued. The gap size is set by inserting spacers of the desired layer thickness in the non-wetted area of the test specimen. The correction time was determined as the time in which the two bonded test specimens can still be moved manually without any effort. The mounting strength was determined as that Time after which the bonded test specimens can be loaded with a mass of 1kg at one end if they are fixed horizontally.

The tensile shear strength was determined using a tensile testing machine (Shimadzu, AGS-X HC 20 KN) after a period of 24 hours (22 ° C., 40% relative humidity, test speed 1.3 mm / minute for metal and plastic substrates according to DIN EN 1465: 2009; test speed 50 mm / minute for wood substrates according to DIN EN 204: 2016 and DIN EN 205: 2016). The tensile strength values given in the table below were determined as the mean value, measured on at least three test specimens.

Example 1:

Production of a two-component structural adhesive with boiling water resistance D4 (DIN EN 204) (according to the invention)

Component A

50 wt .-% polyisocyanate i1)

Component B [mixture of components ii) and iii)]

46.0% by weight of polyaspartic acid ester ii1) 3.0% by weight of highly disperse silica (HDK H18 from Wacker Chemie AG, Burghausen [component iii)]

0.5% by weight of polyethylene polyamine, IPOX EH 2291, commercial product from Ipox Chemicals DE, Laupheim, [component iii)]

0.5 wt .-% 25% solution of zinc acetate dihydrate in demineralized water [component iii)]

The mentioned proportions of the components are combined gravimetrically in a plastic beaker and intimately mixed with one another for 30 seconds with the aid of a glass rod before they are applied to the respective substrates.

This structural adhesive hardens completely within 24 hours, even on a residual damp surface, and is given a D4 classification according to DIN EN 204 and thus corresponds to a boiling water-resistant wood structural adhesive.

Ratio NCO / NH + OH 1.09 (water included as reactive component)

Ratio i) to ii) + iii) 1: 1 (m / m)

Ratio i) to ii) + iii) 1.16: 1.10 (v / v)

Correction time: 5 minutes. Assembly strength: 15 minutes Shore D: 75 Example 2:

Component A

50.9% by weight polyisocyanate i3)

Component B [mixture of components ii) and iii)]

44.7% by weight polyaspartic acid ester ii1)

2.95% by weight of highly disperse silica (HDK H18 from Wacker Chemie AG,

Burghausen [component iii)]

0.25% by weight demineralized water [component iii)]

1.23% by weight of N- [3- (trimethoxysilyl) propyl] ethylenediamine, Geniosil GF 9,

Commercial product from Wacker Chemie AG, Burghausen [component iü)]

The two components A and B are filled into a 2K cartridge - Sulzer Mixpac 2K Adhesive A System, from Sulzer Mixpac AG, Haag Switzerland. It is applied in a volume ratio of 1: 1 using a Sulzer 2K mixer MAH 06-21 T from Sulzer Mixpac AG.

Ratio NCO / NH + OH 1.34 (water included as reactive component)

Ratio i) to ii) + iii) 1.14: 1.10 (m / m)

Ratio i) to ii) + iii) 1: 1 (v / v)

Correction time: 3 minutes. Assembly strength: 10 minutes Shore D: 80

Example 3:

Example 1 is repeated, but the polyaspartic acid ester N2) is used instead of polyaspartic acid ester ii1).

Ratio NCO / NH + OH 1.13 (water included as reactive component) Ratio i) to ii) + iii) 1.05: 1.00 (m / m) Ratio i) to ii) + iii) 1: 1 (v / v)

Correction time: 5 minutes. Assembly strength: 15 minutes Shore D: 75

Example 4:

Production of a two-component structural adhesive (according to the invention)

Component A:

51.3% by weight polyisocyanate i2)

Component B [mixture of components ii) and iii)]

36.0% by weight polyaspartic acid ester N2)

2.9% by weight of highly disperse silica (HDK H18 from Wacker Chemie AG,

Burghausen [component iii)]

9.3% by weight polyol having ester groups iii1) [component iii)]

0.5 wt .-% demineralized water [component iii)]

This structural adhesive cures completely within 24 hours. The adhesion on organic (beech wood), metallic (V2A and aluminum) and low-energy plastics (ABS, PVC) is particularly high and in all cases led to substrate failure or cohesive breakage on smooth V2A at 16 N / mm ²

Ratio NCO / NH + OH 1.21 (water included as reactive component) Ratio i) to ii) + iii) 1.16: 1.10 (m / m)

Ratio i) to ii) + iii) 1: 1 (v / v)

Correction time: 4 minutes. Assembly strength: 15 minutes Shore D: 70

Example 5:

Component A [mixture of components i1) and i4)]:

25% by weight polyisocyanate i1)

25 wt .-% polyisocyanate i4)

Component B [mixture of components ii) and iii)]

46.8% by weight polyaspartic acid ester N2)

3% by weight of highly disperse silica (HDK H18 from Wacker Chemie AG,

Burghausen [component iii)] 0.2% by weight demineralized water [component iii)]

Ratio NCO / NH + OH 1.05 (water included as reactive component)

Ratio i) to ii) + iii) 1.14: 1.10 (m / m)

Ratio i) to ii) + iii) 1: 1 (v / v)

Open time: 4 minutes. Assembly strength: 14 minutes Shore D: 60

Example 6:

Production of a two-component structural adhesive (not according to the invention)

Component A polyisocyanate i1)

Component B [mixture of components ii) and iii)] 97.5% by weight of polyaspartic acid ester N3), 0.5% by weight of demineralized water [component iii)]

2.0% by weight of 3,3'-dimethyl-4,4'-diamino-dicyclohexyl methane, Laromin C260, commercial product from BASF AG, Ludwigshafen [component iii)]

The two components A and B are filled into a 2K cartridge - Sulzer Mixpac 2K Adhesive A System, from Sulzer Mixpac AG, Haag Switzerland. It is applied in a volume ratio of 1: 1 using a Sulzer 2K mixer MAH 06-21T from Sulzer Mixpac AG.

This structural adhesive not according to the invention cures reliably within 24 hours even at a temperature of -18 ° C. The structural bonding of beech wood substrates did not allow classification as "water-resistant" according to D3 or D4 in the water resistance test according to DIN EN 204: 2016. An application in Indoor areas with frequent short-term or long-lasting effects of draining water or condensation and / or use when exposed to high humidity. outdoors is therefore not recommended.

Table 1: Comparison of technical adhesive data

Example 7:

Comparative example not according to the invention:

V2A test specimens were bonded using a commercially available two-component polyurethane adhesive 'Easy-Mix PU-90, polyurethane adhesive from Weicon GmbH, Münster, in accordance with the information given above. This adhesive has a correction time of 70 seconds at 23 ° C and an assembly strength of 9 minutes. The ratio of correction time to assembly strength is therefore considerably less favorable.

In an attempt to bond at a temperature of 0 ° C, this adhesive no longer cured.

Example 8:

Comparative example not according to the invention (analogous to WO 2009-07 / 003596)

166 g of the prepolymer from Example A1 of WO 2009-07 / 003596 were intimately mixed with 23.4 g of the polyaspartic acid ester N3) in a plastic beaker. The mixture had a processing time of 5 minutes at 23 ° C. V2A test specimens were glued to the fresh mixture according to the information given above without a gap and with a gap width of 1 mm. This adhesive has a correction time of 300 seconds at 23 ° C. and an assembly strength of 50 minutes. The tensile shear strength was determined with the aid of a tensile testing machine after a period of 48 hours. The tensile strengths were determined as a mean value, measured on three test specimens each with:

2.9 MPa (without gap)

2.7 MPa (1mm gap width)

This flexible adhesive is unsuitable for the production of structural bonds. The following examples illustrate advantageous properties of mixtures of cycloaliphatic and aliphatic polyaspartic acid esters:

Example 9:

Production of a two-component structural adhesive with water resistance D3 (DIN EN 204) (according to the invention)

Component A [mixture of components i1) and i4)] 18 wt .-% polyisocyanate i1)

36 wt .-% polyisocyanate i4)

Component B [mixture of components ii) N3) and iii)]

38.5% by weight polyaspartic acid ester ii1)

4% by weight polyaspartic acid ester N3)

3% by weight of highly disperse silica (HDK H18 from Wacker Chemie AG,

Burghausen, [component iii)]

0.5% by weight of polyethylene polyamine, IPOX EH 2291, commercial product from Ipox

Chemicals DE, Laupheim, [component iii)]

This structural adhesive hardens completely within 24 hours even on a residual moist surface and is given a D3 classification according to DIN EN 204 and thus corresponds to a waterproof wood structural adhesive. The adhesion to organic (beech wood) and low-energy plastics (ABS, PVC) is particularly high and led to substrate failure in all cases.

NCO / NH + OH ratio 1.18

Ratio i) to ii) + N3) + iii) 1.16: 1.10 (m / m)

Ratio i) to ii) + N3) + iii) 1: 1 (v / v)

Open time: 5 minutes. Assembly strength: 15 minutes Shore D: 65

Example 10:

Production of a two-component structural adhesive with water resistance D4 (DIN EN 204) (according to the invention)

Component A

45.5% by weight polyisocyanate i1)

Component B [mixture of components ii) N3) and iii)]

46.5% by weight polyaspartic acid ester ii1)

5.3% by weight polyaspartic acid ester N3) 2.7% by weight of highly disperse silica (HDK H18 from Wacker Chemie AG,

Burghausen [component iii)]

NCO / NH + OH ratio 1.22

Ratio i) to ii) + N3) + iii) 1.00: 1.20 (m / m)

Ratio i) to ii) + N3) + iii) 1.00: 1.13 (v / v)

Open time: 2:30 minutes. Assembly strength: 17 minutes Shore D: 80

Example 11:

Component A

45.5% by weight polyisocyanate i2)

Component B [mixture of components ii) N3) and iii)]

25.9% by weight polyaspartic acid ester ii1)

25.9% by weight polyaspartic acid ester N3)

2.7% by weight of highly disperse silica (HDK H18 from Wacker Chemie AG,

Burghausen [component iii)]

NCO / NH + OH ratio 1.22

Ratio i) to ii) + N3) + iii) 1.00: 1.20 (m / m)

Ratio i) to ii) + N3) + iii) 1.00: 1.13 (v / v)

Open time: 1 minute. Assembly strength: 8 minutes Shore D: 80 Example 12:

Component A 52.5% by weight polyisocyanate i1)

Component B [mixture of components ii), N3) and iii)]

4.2% by weight polyaspartic acid ester ii2)

40.4 wt .-% polyaspartic acid ester N3) 0.5 wt .-% polyethylene polyamine, IPOX EH 2291, commercial product of Ipox Chemicals DE, Laupheim, [component iii)])

2.4% by weight of highly disperse silica (HDK H18 from Wacker Chemie AG, Burghausen [component iii)]

This structural adhesive hardens completely within 24 hours even on a residual moist surface and is given a D3 classification according to DIN EN 204 and thus corresponds to a waterproof wood structural adhesive.

Ratio NCO / NH + OH 1.33 Ratio i) to ii) + N3) + iii) 1.00: 1, 10 (m / m) Ratio i) to ii) + N3) + iii) 1: 1 (v / v)

Open time: 1 minute. Assembly strength: 4 minutes Shore D: 80

Example 13:

Example 4 was repeated with the same amounts of polyisocyanate i3) instead of polyisocyanate i1).

The adhesive properties were comparable to those from Example 4.

NCO / NH + OH ratio 1.35

Ratio i) to ii) + N3) + iii) 1.00: 1.08 (m / m)

Ratio i) to ii) + N3) + iii) 1: 1 (v / v)

Open time: 30 seconds. Assembly strength: 2:30 minutes Shore D: 80 Example 14:

Component A

51, 33% by weight polyisocyanate i1)

Component B [mixture of components ii), N3) and iii)]

25.31% by weight of polyaspartic acid ester ii2) 12.65% by weight of polyaspartic acid ester N3) 7.30% by weight of polyol containing ester groups iii1) 0.49% by weight of polyethylene polyamine, IPOX EH 2291, commercial product from Ipox Chemicals DE , Laupheim, [component iii)]

0.24% by weight of demineralized water, [component iii)] 2.68% by weight of highly disperse silica (HDK H18 from Wacker Chemie AG, Burghausen [component iii)]

The two components A and B are intimately mixed in the plastic beaker for 30 seconds before they are applied to one side of the respective substrates with a glass rod. This structural adhesive hardens completely within 24 hours even on a residual moist surface and is given a D3 classification according to DIN EN 204 and thus corresponds to a waterproof wood structural adhesive.

Ratio NCO / NH + OH 1.18 Ratio i) to ii) + N3) + iii) 1.00: 1.05 (m / m) Ratio i) to ii) + N3) + iii) 1: 1 (v / v)

Open time: 60 seconds. Assembly strength: 3:30 minutes Shore-D: 65

Claims

1. Two-component structural adhesive that has at least the following components:

(i) at least one polyisocyanate containing free isocyanate groups with a content of aliphatically bound NCO groups of 14.0 to 24.0% by weight, which is essentially free of ester and / or ether and / or carbonate groups,

the structural adhesive in the cured state has a tensile shear strength of at least 7 MPa, preferably at least 10 MPa, more preferably at least 12 MPa, the tensile shear strength being measured according to standard DIN EN 1465: 2009-07 between two test specimens made of roughened V2A steel; preferably: the structural adhesive, in addition to the above-mentioned cycloaliphatic amino-functional polyaspartic acid ester (ii), also has at least one further amino-functional polyaspartic acid ester, namely an aliphatic amino-functional polyaspartic acid ester (ii ') of the stereochemical general formula:

2. A method for the structural bonding of identical or different substrates with two-component structural adhesives, the method comprising at least the following steps:

(1) Providing a two-component structural adhesive which contains at least the following components: i) at least one polyisocyanate having free isocyanate groups with a content of aliphatically bound NCO groups of 14.0 to 24.0% by weight, which is essentially free is of ester and / or ether and / or carbonate groups,

ii) at least one amino-functional polyaspartic acid ester (ii) of the stereochemical general formula:

preferably at least one further amino-functional polyaspartic acid ester, namely an aliphatic amino-functional polyaspartic acid ester (ii ') of the stereochemical general formula:

(2) structural bonding of at least two identical or different substrates using at least the structural adhesive from (1);

(3) Curing of the at least one bond from (2) so that in the cured state it has a tensile shear strength of at least 7 MPa, preferably at least 10 MPa, more preferably at least 12 MPa, the tensile shear strength according to standard DIN EN 1465: 2009-07 between two test pieces made of roughened V2A steel are measured.

3. Structural adhesive according to claim 1 or the method according to claim 2, wherein i) contains: i) at least one polyisocyanate containing free isocyanate groups based on hexamethylene diisocyanate with a content of aliphatically bound NCO groups of 17.0 to 23.5% by weight which is essentially free of ester and / or ether and / or carbonate groups.

4. Structural adhesive according to claim 1 or the method according to claim 2, characterized in that the structural adhesive has a mass fraction of 35 to 65 wt .-% of component (i), a mass fraction of 25 to 65 wt .-% of component (ii) / ( ii '), and a mass fraction of 0 to 25% by weight of the optional component (iii).

5. Structural adhesive according to claim 1 or the method according to claim 2, characterized in that, if both cycloaliphatic amino-functional polyaspartic acid ester (ii) and linear aliphatic amino-functional polyaspartic acid ester (ii ') are used, 10% by weight to 95% by weight of cycloaliphatic amino-functional polyaspartic acid ester (ii) are present, preferably 20% by weight to 90% by weight, based in each case on the total weight of polyaspartic acid ester (ii) plus (iii ').

6. Structural adhesive according to claim 1 or the method according to claim 2, wherein i) contains i) at least one polyisocyanate mixture containing alkoxysilane groups.

7. Structural adhesive or method according to one or more of claims 1 to 5, characterized in that the two-component structural adhesive contains at least one further component iii), this further component preferably containing water or being water.

8. Structural adhesive or method according to one or more of claims 1 to 7, characterized in that component iii) contains aliphatic and / or cycloaliphatic polyamines, and / or: that component iii) contains at least one adhesion promoter, preferably at least one functional silane , and / or: that the components iii) contain inorganic and / or organic flame retardants, and / or: that the components iii) contain highly disperse silicas, and / or: that the components iii) contain polyols.

9. Structural adhesive or method according to one or more of claims 1 to 8, characterized in that the two components i) on the one hand and components ii) and optionally iii) on the other hand are used in a volume ratio of 4: 1 to 1: 4 or: characterized that the two components i) and ii), optionally containing component iii), are used in a volume ratio of 2: 1 to 1: 2.

10. The method according to one or more of claims 2 to 9, characterized in that the two components in step (2) are applied to the two substrate surfaces using a 2K cartridge system with a static mixer.

11. Substrates, objects or articles, characterized in that they are obtained by means of a method and / or using a structural adhesive according to one or more of claims 1 to 10 and, in particular, are structurally glued and cured.