WO2021116121A1 - Structural pressure-sensitive adhesive - Google Patents

Abstract

The present invention describes a structural pressure-sensitive adhesive comprising an epoxy-functionalized acrylate matrix, cationically polymerizable epoxy monomers and a Brønsted acid- or Lewis acid-releasing photoinitiator. The structural pressure-sensitive adhesive is stable even at elevated storage temperatures due to the photochemically induced polymerization of the epoxy monomers and surprisingly exhibits a synergy between the acrylate matrix and the epoxide matrix as a result of the simultaneously occurring crosslinking via the epoxy groups of the polyacrylate matrix. This is manifested in that the structural pressure-sensitive adhesive has the pressure-sensitive adhesive properties of the polyacrylate prior to exposure to UV or other actinic radiation and has the structural strength of an epoxy adhesive after irradiation. A further advantage of the cationic polymerization and of the simultaneously occurring crosslinking reaction is that the reaction after initiation can continue to react even in the absence of light and hence directly in the joint and, as a result, in contrast to a free-radical mechanism, curing of layer thicknesses of up to 1 mm is also possible.

Description

Structural pressure sensitive adhesive

The present invention relates to a structural pressure-sensitive adhesive which, due to the balanced adhesive and cohesive properties, is suitable for pre-fixing different parts to be joined without additionally causing squeezes during assembly, which can contaminate the parts to be joined or lead to optical defects. The structural pressure-sensitive adhesive is cured by actinic radiation, so that bond strengths of a similar order of magnitude as in the case of structural adhesives are achieved. Furthermore, despite the reactive components, such a structural pressure-sensitive adhesive should be storage-stable over a relatively long period of time at different temperatures and different atmospheric humidity. The invention further relates to the production of and products comprising the structural PSAs of the invention and to their use.

State of the art

The term “structural adhesive” is generally used for highly stressed adhesives which are intended to guarantee a possible structural design with high strength or rigidity with a largely uniform and favorable stress distribution. Furthermore, this term also characterizes the requirement for a bond to meet the mechanical and aging-related stresses placed on it permanently without failure. Chemically reacting polymer systems form the basis for structural adhesives. The hardening reaction can take place by supplying heat, mixing resin and hardener, humidity or UV radiation.

In chemically reacting systems, two reactants mixed with one another usually cause the adhesive layer to form (two-component reactive adhesives) or one reactant finds the second “component” required for the reaction in the chemical conditions of the adhesive joint (e.g. moisture) or this component is caused by an external stimulus such as thermal energy or UV radiation released (one-component reactive adhesives). These systems are mostly liquid in order to be easier to apply and so that the curing reaction can take place quickly and with high conversions due to better diffusion of the reactive components. However, this has the disadvantage that the adhesive can squeeze out and that the parts to be joined have to be fixed until they have set.

Pressure sensitive adhesives (PSA), in turn, are used in a variety of applications because they offer many desirable characteristics, such as removability and ease of use. For a more permanent and / or very smooth bond, some conventional PSAs do not have sufficient strength to retain and maintain their adhesion to certain substrates. Furthermore, when applied to certain materials, a conventional PSA may not be able to withstand the effects of elevated temperatures or high humidity. For example, the use of a PSA on polymethyl methacrylate and polycarbonate sheets, which are known to "outgass materials" and are difficult to bond, can cause blistering and delamination.

Structural pressure-sensitive adhesives, on the other hand, have, in addition to the customary polymers used in pressure-sensitive adhesives, additional thermally crosslinking components, as a result of which very high peel resistances are achieved, which can be of the order of magnitude of a structural adhesive.

Curable adhesives (e.g., heat or light cured) have been used in applications where substrates require significant durability and high strength adhesion. However, conventional curable adhesives are not typically provided as PSA, nor are they provided in a form that is easy to use, such as tape. For optical product applications (e.g. glazing), curable adhesives are desirable as they provide optically clear, strongly adhering laminates (e.g. layered substrates).

To achieve both strength and ease of use, hybrid compositions have been developed.

Conventional curable adhesives contain reactive chemical building blocks such as epoxy adhesives that contain epoxy groups. During hardening, these basic building blocks can be bonded to one another via the epoxy groups with the aid of a hardener connect and form a stable, three-dimensional network. This network formation is a major cause of the generally high strength and good adhesive properties of epoxy adhesives on many materials.

Hybrid compositions are characterized by the inclusion of further materials in this network structure. Possible solutions are primarily the creation of interpenetrating networks (IPN or penetration network) or other multiphase structures. A semi-interpenetrating network is understood to mean the combination of a linear uncrosslinked polymer and a first crosslinked polymer, the first crosslinked polymer being synthesized in the presence of the other. The uncrosslinked polymer penetrates the network of the crosslinked polymer and has the effect that the two components can hardly be physically separated due to entanglements and entanglements. This semi-interpenetrating network enables two polymers to combine properties, even if they are thermodynamically incompatible.

Such interpenetrating networks can be produced sequentially (from polymer A and monomer B) or simultaneously (from monomer A and monomer B). Preferably an elastomer and a glassy polymer, e.g. B. a polyurethane and a polyacrylate combined. Depending on the proportions, a reinforced elastomer or a resin with high impact strength is produced.

IPN systems can have very different chemical compositions. There are essentially two techniques for their synthesis:

The simultaneous technique consists in combining two linear polymers, prepolymers or monomers of types A and B with the respective crosslinking agents in the liquid state, i.e. in bulk, melt, solution or dispersion, and polymerizing or crosslinking them simultaneously. In doing so, substances must be selected that do not react with one another.

The sequential technique consists in swelling a crosslinked polymer A with a monomer of type B and then polymerizing or crosslinking the latter in situ with the addition of crosslinking agents. IPN systems are examples of polymer blends in which macroscopic phase separation does not appear. Typically, polymer blending results in multiphase systems due to the well-known thermodynamic incompatibility of most polymers. This incompatibility results from the relatively low gain in entropy when mixing polymers, which in turn is based on the fact that the great length of the chains limits their possibilities for contact. However, if products with a lower molecular weight are mixed and then polymerized and crosslinked simultaneously, kinetic control of the phase separation can be achieved.

Compared to conventional polymer blends, interpenetrating networks are characterized by better resistance to segregation and often advantageous mechanical properties. The degradation resistance of the interpenetrating networks is usually better than that of copolymers in which the incompatible polymers are covalently bonded to one another as blocks. This is why IPNs are also used in the field of adhesives.

Epoxy resin adhesives are known which additionally contain a further type of basic building blocks that form an independent network via a second chemical mechanism and cannot react with the epoxy-containing building blocks. When these adhesives cure, two independent adhesive networks are created that penetrate each other, i.e. IPNs. From a practical point of view, such systems consist of two adhesives in one system, whose properties ideally complement each other synergistically.

In general, epoxy resins are poorly miscible with other polymers. If the mixture is attempted anyway, polymers generally tend to separate the phases used. If, however, it is possible to mix the uncrosslinked or unpolymerized basic building blocks of the polymers and then to conduct their polymerization in such a way that the phase separation of the polymers formed is prevented, then synergy effects can be observed in the resulting polymer mixture. Properties such as adhesive strength or impact strength often result in significantly higher values than for the individual networks investigated separately (e.g. pure epoxy adhesives). The effect of the technology of the IPN modification of adhesives is therefore the use of synergy effects that only show in the combination of two networks, but cannot be observed in the individual networks. This often resulted in a maximization of desired properties and a possible minimization of undesired properties.

IPNs are also known from the field of PSAs and structural PSAs.

EP 0 621 931 B1 describes hybrid adhesives which are produced from an acrylate syrup - a mixture of polyacrylates dissolved in the remaining acrylate monomers - and epoxy monomers by means of a low conversion mixture, and thus form a simultaneous IPN. A pressure sensitive adhesive can only be obtained if the reaction stops before it is fully cured (B stage). In this state, the pressure-sensitive adhesive film must generally be stored in a cool place, which is a disadvantage.

WO 2004/060946 describes an adhesive composition which comprises an acrylate copolymer, acrylated oligomers and an initiator which starts a radical polymerization. A semi-IPN is formed, which leads to a highly transparent adhesive, which is achieved by combining acrylate copolymers with acrylate oligomers. The disadvantage is that these formulations are based purely on acrylates, some of which do not ensure sufficiently high bond strengths and the fact that similar classes of substances are combined with one another, so that the range of achievable synergistic effects is smaller than with different classes of substances.

WO 2012/061032 discloses adhesives in which a reactive isocyanate prepolymer has been dispersed in a styrene block copolymer pressure-sensitive adhesive and this prepolymer, after crosslinking by means of atmospheric moisture, forms a semi-IPN within the pressure-sensitive adhesive phase. These PSAs have the disadvantage that they have to be stored away from moisture.

EP 1 658 319 B1 describes a molding composition containing a mixture of interpenetrating polymers with a first phase of a crosslinked isobutene polymer and a second phase of a stiffening polymer, the (meth) acrylic and / or vinyl aromatic units comprises, wherein the first phase comprises the reaction product of an isobutene polymer with an average of at least 1,4 functional groups in the molecule and a crosslinking agent with an average of at least two functional groups in the molecule which are complementary to the functional groups of the isobutene polymer. The IPN can be produced simultaneously or sequentially - with the crosslinked isobutene phase as a presented network. Due to the crosslinking of the PIB, the examples do not disclose any pressure-sensitive adhesive molding compositions.

In order to improve the compatibility of the first phase with the second phase, the use of polymeric compatibilizers, e.g. polyethylene glycols, is proposed. The polymeric compatibilizers are preferably crosslinked. In this way, the polymeric compatibilizing agent can form a network which penetrates the first phase. The disadvantage of this type of compatibilization is the high complexity of the now ternary system, which makes it difficult to control the properties.

EP 2 160443 B1 discloses a semi-interpenetrating network with a first phase of a linear uncrosslinked isobutene polymer and a second phase of a crosslinked polymer, the crosslinked polymer being obtained by a crosslinking build-up reaction in the presence of the isobutene polymer. In the preferred embodiment, which is documented with examples, the crosslinked polymer is obtained by free-radical polymerization of ethylenically unsaturated monomers, in particular of styrene and methacrylates. However, it has been shown that such systems lose their strength significantly at temperatures above 80 ° C.

A common method for impact modification of high-strength reactive adhesives is the generation of a two-phase polymer morphology with a microheterodisperse phase of a thermoplastic or elastomeric polymer with a low glass transition temperature below -20 ° C in a continuous matrix of a polymer with a high glass transition temperature above 100 ° C. In general, there are discrete spherical soft phase domains with diameters between 0.1 and 10 μm distributed homogeneously in the matrix.

A common method for generating such two-phase morphologies, for. B. in epoxy resin adhesives is the addition of an end-group-modified, epoxy-reactive Polybutadiene-co-acrylonitrile copolymers for uncured epoxy resin. The thermoplastic polymer must be soluble in the uncured epoxy resin, but must be incompatible with the epoxy resin polymer in the course of the curing reaction, so that phase separation occurs during curing. When the gel point is reached, the phase separation process is stopped so that the thermoplastic or elastomeric polymer is present in the epoxy resin matrix in the form of microscopic spherical domains.

EP 1 456 321 B1 proposes a multi-phase reactive adhesive in which the binder matrix of the cured reactive adhesive has a continuous phase consisting of an optionally crosslinked polymer (P1) with a glass transition temperature above 100 ° C, preferably above 120 ° C, in which a hetero disperse phase consisting of individual continuous areas of a thermoplastic or elastomeric polymer P2 with a glass transition temperature of less than -30 ° C. is dispersed. Within this phase, formed by P2, another thermoplastic or elastomeric polymer P3 with a glass transition temperature of less than -30 ° C. is dispersed. Furthermore, a further heterodisperse phase composed of regions of the thermoplastic or elastomeric polymer P3 with a glass transition temperature of less than -30 ° C. is dispersed in the continuous phase P1, with P3 not being identical to P2. The continuous phase P1 is preferably an epoxy resin. No pressure-sensitive adhesives are described.

DE 10 2004 031 188 A1 and DE 103 615 40 A1 disclose adhesives which consist of at least a) an acid- or acid-anhydride-modified vinyl aromatic block copolymer and b) an epoxy-containing compound. Due to the chemical cross-linking of the resins with the elastomers, very high strengths are achieved within the adhesive film. In order to increase the adhesion, it is also possible to add tackifier resins that are compatible with the elastomer block of the block copolymers. Essentially, the epoxy resin acts as a crosslinking agent for the modified elastomers and, at most, forms its own second phase to a small extent, as a result of which these systems continue to show the general weakness of vinyl aromatic block copolymer PSAs, namely a low thermal shear strength.

WO 2012/177 337 A1 describes a UV-crosslinkable acrylate syrup containing epoxides. After making the prepolymer - the syrup - using UV-activated For free-radical polymerization, this is mixed with a cationic photoinitiator and, in addition to the remaining free-radically polymerizable monomers, epoxy monomers. The syrup is coated and then radically and cationically polymerized to the end on the web and at the same time crosslinked. This process and the product resulting from it are not suitable for subsequent cationic crosslinking, or the radical and the cationic photoinitiator must be coordinated with one another so that both are activated by a completely different wavelength range. However, the selection of commercially available initiators is very limited. Another disadvantage is the acid-functionalized ethylenic monomers in the acrylate, which are only described as optional but used in each example of the document, since this creates the risk of thermal initiation of the cationic polymerization and the products are therefore not storage-stable.

There is thus a continuing need for solutions to provide structural PSAs with specifically adjusted adhesion and cohesion properties.

Object of the invention

The object of the invention is therefore to provide a structural pressure-sensitive adhesive which, owing to its balanced adhesive and cohesive properties, is suitable for prefixing different parts to be joined without squeezing out which can contaminate the parts or lead to optical defects. The structural pressure-sensitive adhesive should achieve bond strengths of a similar order of magnitude as in the case of structural adhesives. Furthermore, despite the reactive components present, such a structural pressure-sensitive adhesive should be storage-stable over a long period of time at different temperatures and different humidity levels.

Solution of the task

It has surprisingly been found that, in particular, structural PSAs as described in claim 1 are particularly suitable for achieving the object. Such a structural pressure-sensitive adhesive of the invention contains an epoxy-functionalized acrylate matrix and a Bronsted or Lewis acid-releasing one Photoinitiator, at least one polyacrylate being used as the acrylate matrix, consisting of

(a1) 35 to 90% by weight, preferably 45 to 80% by weight, particularly preferably 45 to 70% by weight of acrylic acid esters and / or methacrylic acid esters with the formula (I)

(l), where R ^{1 is} H and / or —CH ₃ and R ^{2 are} linear and / or branched alkyl chains having 1 to 30 carbon atoms;

(a2) 5 to 30% by weight, preferably 10 to 25% by weight, particularly preferably 15 to 25% by weight, of olefinically unsaturated monomers with a cationically polymerizable functional group, preferably with an epoxy and / or oxetane - group, particularly preferably with a 3,4-epoxycyclohexyl group,

(a3) 5 to 30% by weight, preferably 10 to 25% by weight, particularly preferably 15 to 25% by weight, / V-vinyl-substituted lactams and (a4) 0 to 5% by weight of at least one Reactive diluent selected from the group consisting of acrylates, methacrylates and olefinically unsaturated monomers which are copolymerizable with components (a1) to (a3), the proportions by weight being based on the polyacrylate.

The structural PSA formulations of the invention thus comprise a polyacrylate containing cationically polymerizable functional groups, cationically polymerizable reactive diluents and a UV-activatable photoinitiator which, after activation, releases a proton. In particular, the chemical linkage of the two different polymer networks - the already existing polyacrylate network and the epoxy network formed by the cationic polymerization - contributes to the bond strength, which happens during the cationic polymerization initiated by the proton, although the inherent adhesive strength of the polyacrylate and the strength of the Epoxy network can be combined synergistically. In contrast to the state of the art, there is no longer an I PN after curing. The use of a UV-initiated curing mechanism, in turn, ensures storage stability. Furthermore, it has surprisingly been found that it is advantageous, in particular with regard to storage stability, that the polyacrylate does not contain any Contains acid functionalities and that instead / V-vinyllactams such as / V-vinylpyrrolidone or / V-vinylcaprolactam are used as both cohesion and adhesion-increasing comonomers.

In the following, the term “cationically polymerizable functional groups” is understood to mean all epoxy (oxirane) and / or oxetane groups or molecules comprising at least one of these functional groups, in particular 3,4-epoxycyclohexyl groups.

In the context of the invention, a polyacrylate is understood to be a polymer comprising monomers from the series of acrylic and / or methacrylic acid esters.

In the context of this document, a chemical linkage or crosslinking of the two polymer networks is understood to be a reaction between polymer macromolecules in which a further three-dimensional network is formed between these macromolecules in addition to the already existing ones. In the sense of the invention, this is achieved through the use of actinic (high-energy) radiation, such as ultraviolet rays, electron beams or radioactive rays. The initiation of the crosslinking by thermal energy is undesirable, since otherwise the storage stability of the structural PSAs of the invention is not guaranteed, but after the activation of the cationic polymerization by actinic radiation, which at the same time also leads to the crosslinking of the epoxy matrix with the polyacrylate containing cationically polymerizable groups, the thermal energy can be used to increase the efficiency of the crosslinking reaction and the polymerization. Furthermore, an increase in efficiency can also be achieved through mechanical influences (such as ultrasound) or through exothermic reaction processes in the reaction system.

Structural PSA formulations are understood according to the invention to mean mixtures and compositions which are at least crosslinkable (uncrosslinked and / or partially crosslinked, further crosslinkable) pressure-sensitively adhesive polyacrylates, optionally further polymers and cationic polymerizable monomers, with crosslinked polymer systems being present after polymerization and the simultaneous crosslinking of these preparations, which are suitable as structural pressure-sensitive adhesives. In this document, a pressure-sensitive adhesive is understood, as is customary in common parlance, to be a substance which - especially at room temperature - is permanently tacky and tacky (referred to as “pressure-sensitive adhesive” or also as “self-adhesive” in the context of this document). It is characteristic of a pressure-sensitive adhesive that it can be applied to a substrate by pressure and remains adhered there. Depending on the exact type of pressure-sensitive adhesive, the temperature and humidity as well as the substrate, short-term, minimal pressure, which does not go beyond a light touch for a brief moment, can be sufficient to achieve the adhesive effect; in other cases, too Long-term exposure to high pressure may be necessary. Pressure-sensitive adhesives have special, characteristic viscoelastic properties that lead to permanent tack and adhesiveness. They are characterized by the fact that when they are mechanically deformed, both viscous flow processes and the build-up of elastic restoring forces occur. Both processes are related to one another in terms of their respective proportions, depending on the exact composition, structure and degree of crosslinking of the pressure-sensitive adhesive under consideration as well as on the speed and duration of the deformation and on the temperature.

The structural pressure-sensitive adhesive obtained after curing, on the other hand, achieves very high peel resistances, which can be of the order of magnitude of a structural adhesive.

Before curing, the structural pressure-sensitive adhesive of the invention, like a conventional pressure-sensitive adhesive, can be applied in the form of a single-sided or double-sided adhesive tape, a roll of adhesive tape, an adhesive transfer tape, a die cut and other embodiments familiar to the person skilled in the art.

Activation by means of actinic radiation, in particular UV radiation, can take place before or after application to the parts to be joined. In the case of UV-transparent substrates, activation can also take place after application in the adhesive joint.

Detailed description of the invention

The present invention describes a structural pressure-sensitive adhesive comprising an epoxy-functionalized acrylate matrix, cationically polymerizable epoxy monomers and a Bnansted or Lewis acid releasing photoinitiator. Owing to the photochemically induced polymerization of the epoxy monomers, the structural pressure-sensitive adhesive is stable even at elevated storage temperatures and surprisingly shows a synergy between the acrylate and the epoxy matrix due to the simultaneous crosslinking via the epoxy groups of the polyacrylate matrix. This is expressed in the fact that the structural pressure-sensitive adhesive has the pressure-sensitive adhesive properties of the polyacrylate before exposure to UV or other actinic radiation and the structural strength of an epoxy adhesive after irradiation. Another advantage of the cationic polymerization and the simultaneous crosslinking reaction is that after initiation the reaction can continue to react even in the absence of light and thus directly in the joint and, in contrast to a radical mechanism, this also enables the hardening of layer thicknesses of up to 1 mm is.

Polyacrylate matrix

The basis of the structural pressure-sensitive adhesives and the structural pressure-sensitive adhesive tapes consisting of the aforementioned pressure-sensitive adhesives, which are produced by means of the process according to the invention, comprises all polyacrylates known to the person skilled in the art and / or mixtures comprising at least one polyacrylate which are suitable for producing pressure-sensitive adhesives. Particularly preferred are polyacrylates comprising at least one comonomer with a cationically polymerizable group and mixtures comprising at least one of the polyacrylates just mentioned.

wobei R¹ H und/oder -CH₃ und R² lineare und/oder verzweigte Alkylketten mit 1 bis 30 C-Atomen darstellen; In a particularly preferred variant, the matrix used for the UV-crosslinkable structural pressure-sensitive adhesives is polyacrylates, consisting of (a1) 35 to 90% by weight, preferably 45 to 80% by weight, particularly preferably 45 to 70% by weight, and acrylic acid esters / or methacrylic acid ester with the formula (I)

where R ¹ H and / or -CH ₃ and R ^{2 represent} linear and / or branched alkyl chains with 1 to 30 carbon atoms;

(a2) 5 to 30% by weight, preferably 10 to 25% by weight, particularly preferably 15 to 25% by weight, of olefinically unsaturated monomers with a cationically polymerizable one functional groups, preferably with epoxy and / or oxetane groups, particularly preferably with a 3,4-epoxycyclohexyl group,

(a3) 5 to 30% by weight, preferably 10 to 25% by weight, particularly preferably 15 to 25% by weight / V-vinyl-substituted lactams and

(a4) optionally further acrylates and / or methacrylates and / or olefinically unsaturated monomers (0 to 5% by weight) which are copolymerizable with components (a1) to (a3) and optionally have a functional one that does not give rise to any thermal cationic Polymerization of the epoxy monomers leads.

The weight data relate to the polymer.

For the monomers (a1), preference is given to using acrylic monomers comprising acrylic and methacrylic acid esters with alkyl groups consisting of 1 to 14 carbon atoms. Specific examples, without wishing to be restricted by this list, are methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, n-pentyl (meth) acrylate, n-hexyl (meth) acrylate, n-heptyl acrylate, n-octyl acrylate, n-nonyl acrylate, lauryl acrylate, stearyl (meth) acrylate, behenyl acrylate, and their branched isomers, such as, for example, 2-ethylhexyl acrylate, 2-propylhexyl acrylate. Further classes of compounds to be used, which can also be added in small amounts under (a1), are cyclohexyl (meth) acrylate and isobornyl (meth) acrylate.

wobei R³ H oder -CH₃, X -NR⁵- oder -O- , R⁵ H oder -CH₃ und R⁴ eine Epoxy- funktionalisierte (Hetero)hydrocarbylgruppe darstellen. Preference is given to using monomers of the formula (II) for the monomers (a2)

where R ³ H or -CH ₃ , X -NR ⁵ - or -O-, R ⁵ H or -CH ₃ and R ^{4 represent} an epoxy-functionalized (hetero) hydrocarbyl group.

The group R ^{4 more} preferably comprises linear, branched, cyclic or polycyclic hydrocarbons having 2 to 30 carbon atoms, which are functionalized with an epoxy group. The group R ⁴ particularly preferably comprises 3 to 10 carbon atoms, such as, for example, glycidyl (meth) acrylate. 3,4-epoxycyclohexyl-substituted monomers such as, for example, 3,4-epoxycyclohexylmethyl (meth) acrylate, are even more preferred, Preference is given to using / V-vinyllactams as (a3), N-vinylpyrrolidone, / V-vinylpiperidone and / V-vinylcaprolactam are particularly preferred. Monomers such as / V-vinylformamide, / \ / - methyl - / \ / - vinylacetamide and / V-vinylphthalimide are likewise included according to the invention in group (a3).

For the optional monomers (a4), preference is given to, for example, benzyl (meth) acrylate, phenyl (meth) acrylate, te / f-butylphenyl (meth) acrylate, phenoxyethyl (meth) acrlylate, 2-butoxyethyl (meth) acrylate, / V , / V-dimethylaminoethyl (meth) acrylate, L /, / V-diethylaminoethyl (meth) acrylate, tetrahydrofufurylacrylate, hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, cyanoethyl (meth) acrylate, allyl alcohol, acrylamide, N-tert-butyl acrylamide, / \ / - methylol (meth) acrylamide, / \ / - (butoxymethyl) methacrylamide, / \ / - (Ethoxymethyl) acrylamide, / V-isopropylacrylamide, styrene, methylstyrene and 3,4-dimethoxystyrene are used, this list not being exhaustive.

For the polymerization, the monomers are chosen so that the resulting polymers can be used as pressure-sensitive adhesives, in particular such that the resulting polymers have pressure-sensitive adhesive properties according to the "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (van Nostrand, New York 1989).

The glass transition temperature To of the polyacrylate results from the type and amount of the respective comonomers and is calculated from the Fox equation (G1) (cf. TG Fox, Bull. Am. Phys. Soc. 1956, 1, 123).

Here, n represents the running number over the monomers used, W _n the mass fraction of the respective monomer n (% by weight) and Tc _, n the respective glass transition temperature of the homopolymer from the respective monomers n in K.

The comonomers of a PSA are usually chosen so that the glass transition temperature of the polymers is below the application temperature, preferably T _G s 15 ° C. Due to the possibility of using epoxy monomers, which in the act as a plasticizer in the uncrosslinked state, the resulting glass transition temperature of the inventive polyacrylate matrix of the structural pressure-sensitive adhesive can markedly exceed the glass transition temperatures typical for pressure-sensitive adhesives. Nevertheless, the comonomer composition of the polyacrylate matrix according to the invention is chosen such that the glass transition temperature T _G S is 40.degree. C., preferably T _G <30.degree.

To produce the polyacrylate PSAs, it is advantageous to carry out conventional free-radical polymerizations or controlled free-radical polymerizations. For the free-radical polymerizations, preference is given to using initiator systems which additionally contain further free-radical initiators for the polymerization, in particular thermally decomposing free-radical-forming azo or peroxo initiators. In principle, however, all customary initiators familiar to the person skilled in the art for acrylates and / or methacrylates are suitable. The production of C-centered radicals is described in Houben-Weyl, Methods of Organic Chemistry, Vol. E 19a, pp. 60-147. These methods are preferably used in analogy.

Examples of radical sources are peroxides, hydroperoxides and azo compounds. Some non-exclusive examples of typical free radical initiators are potassium peroxodisulfate, dibenzoyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, cyclohexylsulfonylacetyl peroxide, diisopropyl percarbonate, benzopinacolate, benzopinacolate. The free-radical initiator used is particularly preferably 2,2′-azobis (2-methylbutyronitrile) (Vazo 67 ™ from DuPont).

The number average molecular weights M _{n of} the PSAs formed in the free radical polymerization are very preferably chosen such that they are in a range from 20,000 to 2,000,000 g / mol; PSAs with weight-average molecular weights M _w of 200,000 to 20,000,000 g / mol are preferably produced. The average molecular weight is determined using gel permeation chromatography (GPC).

The polymerization can be carried out in bulk, in the presence of one or more organic solvents, in the presence of water or in mixtures of organic solvents and water. The aim is to keep the amount of solvent used as low as possible. Suitable organic Solvents are pure alkanes (e.g. hexane, heptane, octane, isooctane), aromatic hydrocarbons (e.g. benzene, toluene, xylene), esters (e.g. ethyl acetate, propyl, butyl or hexyl acetate), halogenated Hydrocarbons (e.g. chlorobenzene), alkanols (e.g. methanol, ethanol, ethylene glycol, ethylene glycol monomethyl ether), ketones (e.g. acetone, butanone) and ethers (e.g. diethyl ether, dibutyl ether) or mixtures thereof . The aqueous polymerization reactions can be mixed with a water-miscible or hydrophilic cosolvent in order to ensure that the reaction mixture is in the form of a homogeneous phase during the monomer conversion. Advantageously usable cosolvents for the present invention are selected from the following group consisting of aliphatic alcohols, glycols, ethers, glycol ethers, pyrrolidines, / V-alkylpyrrolidinones, / V-alkylpyrrolidones, polyethylene glycols, polypropylene glycols, amides, carboxylic acids and salts thereof, esters, Organosulfides, sulfoxides, sulfones, alcohol derivatives, hydroxyether derivatives, amino alcohols, ketones and the like, as well as derivatives and mixtures thereof.

The polymerization time is - depending on the conversion and temperature - between 4 and 72 hours. The higher the reaction temperature that can be chosen, that is to say the higher the thermal stability of the reaction mixture, the shorter the reaction time that can be chosen.

To initiate the polymerization, the introduction of heat is essential for the thermally decomposing initiators. For the thermally decomposing initiators, the polymerization can be initiated by heating to 50 to 160 ° C., depending on the type of initiator.

For radical stabilization, nitroxides are used in a favorable procedure, such as. B. (2,2,5,5-Tetramethyl-1-pyrrolidinyl) oxyl (PROXYL), (2,2,6,6-tetramethyl-1-piperidinyl) oxyl (TEMPO), derivatives of PROXYL or TEMPO and other nitroxides familiar to the person skilled in the art.

A number of other polymerization methods, according to which the adhesives can be produced in an alternative procedure, can be selected from the prior art: WO 96/24620 A1 describes a polymerization process in which very specific radical compounds such as. B. phosphorus-containing nitroxides based on imidazolidine can be used. WO 98/44008 A1 discloses special nitroxyls based on morpholines, piperazinones and piperazinediones. DE 199 49 352 A1 describes heterocyclic alkoxyamines as regulators in controlled radical polymerizations.

Atom Transfer Radical Polymerization (ATRP) can advantageously be used as a further controlled polymerization method for the synthesis of block copolymers, the initiator preferably being monofunctional or difunctional secondary or tertiary halides and for the abstraction of the halide (s) Cu, Ni , Fe, Pd, Pt, Ru, Os-, Rh, Co, Ir, Ag or Au complexes can be used. The different possibilities of ATRP are also described in the documents of US Pat. No. 5,945,491 A, US Pat. No. 5,854,364 A and US Pat. No. 5,789,487 A.

A variant of the RAFT polymerization (reversible addition-fragmentation chain transfer polymerization) is carried out as a very preferred preparation process. The polymerization process is e.g. B. described in detail in the documents WO 98/01478 A1 and WO 99/31144 A1. Trithiocarbonates of the general structure R "'- S-C (S) -S-R"' (Macromolecules 2000, 33, 243-245) are particularly advantageously suitable for the preparation.

In a very advantageous variant, for example, the trithiocarbonates (TTC1) and (TTC2) or the thio compounds (THI1) and (THI2) are used for the polymerization, where F is a phenyl ring that is unfunctionalized or by alkyl or aryl substituents that are directly or via ester or ether bridges are linked, can be functionalized, can be a cyano group or a saturated or unsaturated aliphatic radical. The phenyl ring F can optionally carry one or more polymer blocks, for example polybutadiene, polyisoprene, polychloroprene or poly (meth) acrylate, which can be constructed according to the definition for P (A) or P (B), or polystyrene, to name just a few . Functionalizations can be, for example, halogens, hydroxyl groups, epoxy groups, nitrogen or sulfur-containing groups, without this list claiming to be exhaustive. (THl 1) <TH! 2)

In connection with the above-mentioned controlled radical polymerizations, preference is given to initiator systems which additionally contain further radical initiators for the polymerization, in particular the thermally decomposing radical-forming azo or peroxo initiators listed above. In principle, however, all of the customary initiators known for acrylates and / or methacrylates are suitable for this. It is also possible to use radical sources which only release radicals under UV irradiation.

Cationically polymerizable reactive diluents

The cationically polymerizable reactive diluents have at least one polymerizable functional group and include cyclic ethers such as epoxides (oxiranes, 1,2-epoxides), 1,3- (oxetanes) and 1,4-cyclic ethers (1,3- and 1, 4-epoxides) as well as alkyl vinyl ethers, styrene, p-methylstyrene, divinylbenzene, / V-vinyl-substituted compounds, 1-alkyl olefins (α-olefins), lactams and cyclic acetals. Epoxides and oxetanes are preferred, and 3,4-epoxycycohexyl-functionalized monomers are particularly preferred.

Furthermore, the cationically polymerizable reactive diluents according to the invention can be present as monomers or polymers, and they have an average molecular weight or a number average molecular weight of 58 g / mol to about 1,000 g / mol. The epoxides can be aliphatic, cycloaliphatic, aromatic or heterocyclic. The number of epoxy functionalities per molecule is preferably one to six, particularly preferably one to three. Preferred cationically polymerizable monomers are aliphatic, cycloaliphatic epoxides and glycidyl ethers, such as propylene oxide, epichlorohydrin, styrene oxide, vinyl cyclohexene oxide, cyclohexene oxide, vinyl cyclohexene dioxide, glycidol, Butadiene oxide, glycidyl metharylate, bisphenol A diglycidyl ether (e.g. Epon 828, Epon 825, Epon 1004, Epon 1001, Momentive Specialty Chemicals), dicyclopentadiene dioxide, epoxidized polybutadienes (e.g. Oxiron 2001, FMC Corp.), 1,4-butanediol diglycidether 2- Cyclohexanedicarboxylic acid diglycidyl ester, polyglycidether of phenolic resins based on resol or novolak (e.g. DEN 431, DEN 438, Dow Chemical), resorcinol diglycidyl ether and epoxidized silicones such as dimethylsiloxanes with glycidyl ether or epoxyxcyclohexane groups. 3,4-epoxycycohexyl-functionalized monomers, such as, for example, 3,4-epoxycyclohexyl methacrylate, 3,4-epoxycyclohexylmethyl methacrylate, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, 3,4-epoxy-6- methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate, bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate, 1,4-cyclohexanedimethanolbis (3,4-epoxycyclohexanecarboxylate) and 3,4-epoxycyclohexylmethyl-3 ^' , 4 ^{'-epoxycyclohexancarboxylat-} modified e-caprolactone (CAS-No. 139198-19-9 (Celloxide 2081, Fa. Daicel, Japan), and 151629-49-1 (Tetrachem, Fa. Hainan Zhongxin Chemical, China).

Mixtures of the aforementioned and all other cationically polymerizable reactive diluents known to the person skilled in the art are also inventive. Advantageous mixtures comprise two or more epoxides, whereby the epoxides have different molecular weights and can be grouped into those with a low molecular weight (M <200 g / mol), with a medium molecular weight range (200 g / mol <M <1,000 g / mol) and a high molecular weight (M> 1,000 g / mol). It can also be advantageous to use mixtures of epoxides with different numbers of epoxy groups. Optionally, further cationically polymerizable reactive diluents can be added.

The concentration of the epoxy monomer or the epoxy monomer mixture is advantageously chosen so that an epoxy concentration of 0.001 mmol epoxy / g polymer to 4 mmol epoxy / g polymer, preferably 0.01 mmol epoxy / g polymer to 2.5 mmol epoxy / g Polymer results.

Cationic photoinitiators

The cationic photoinitiator fragments by means of actinic radiation, preferably UV radiation, one or more of these fragments being a Lewis or Bronsted acid, which causes the cationic polymerization and the simultaneous crosslinking the polyacrylate catalyzes with the epoxy matrix that is being formed. Advantageous photoinitiators are thermally stable, do not lead to polymerization of the monomers even as a result of thermal activation, and are soluble both in the uncured and in the cured structural PSA formulation. “Thermally stable” means that the photoinitiator does not disintegrate at least at all process and processing temperatures. The photoinitiator is preferably stable up to temperatures of 200 ° C., ie does not disintegrate.

It is also advantageous that the acids released by fragmentation of the photoinitiator have a pKa <0.

The photoinitiators are ionic compounds, the cations are preferably based on organic onium structures, in particular on salts with aliphatic and aromatic groups IVA to VIIA (CAS nomenclature) centered onium cations, particularly preferably on I, S, P, Se-, N- and C-centered onium salts, selected from the group of the sulfoxonium, iodonium, sulfonium, selenonium, pyridinium, carbonium and phosphonium salts, even more preferably on the I and S centered onium salts such as sulfoxonium, diaryliodonium, triarylsulfonium, diarylalkylsulfonium, dialkylarylsulfonium and trialkylsulfonium salts.

The nature of the anion of the photoinitiator can influence the reaction rate and the conversion of the cationic polymerization. For example, JV Crivello and R. Narayan in Chem. Mater. 1992, 4, 692 a reactivity sequence of common counterions as follows: SbF ₆ > AsF ₆ > PF ₆ > BF4. The reactivity of the anion depends on the following factors: (1) the acidity of the Lewis or Bronsted acid released, (2) the degree of ion pair separation in the growing cationic chain and (3) the susceptibility of the anion to fluoride Abstraction and chain termination. Furthermore, B (C6Fs) 4 can be used as an anion.

Advantageous photoinitiators include bis (4-te / f-butylphenyl) iodonium hexafluoroantimonate (FP5034 ™ from Hampford Research Inc.), a mixture of triarylsulfonium salts (diphenyl- (4-phenylthio) phenylsulfonium hexafluoroantimonate and bis (4-diphenyl- sulfonio)) phenyl) sulfide hexafluoroantimonate) available as Syna PI-6976 ™ from Synasia, (4-methoxyphenyl) phenyliodonium triflate, bis (4-te / f-butylphenyl) iodonium camphor sulfonate, Bis (4-te / f-butylphenyl) iodonium hexafluoroantimonate, bis (4-te / f-butyl phenyl) iodonium hexafluorophosphate, bis (4-te / f-butylphenyl) iodonium tetrafluoroborate, bis (4-te / f-butyl phenyl ) iodonium triflate, [4- (octyloxy) phenyl] phenyliodonium hexafluorophosphate, [4- (octyloxy) phenyl] phenyliodonium hexafluoroantimonate, (4-isopropylphenyl) (4-methylphenyl) iodonium tetrakis (pentafluorophenyl) borate (available as Rhodium Silicones ™) borate 2074 , Bis (4-methylphenyl) iodonium hexafluorophosphate (available as Omnicat 440 ™ from IGM Resins), 4 - [(2-hydroxy-1-tetradecyloxy) phenyl] phenyliodonium hexafluoroantimonate, triphenylsulfonium hexafluoroantimonate (available as CT-548TM from Chitec Technology Corp.) , Diphenyl (4-phenylthio) phenylsulfonium hexafluorophosphate, diphenyl (4-phenylthio) phenylsulfonium hexafluoroantimonate, tris- [4- (4-acetyl-phenyl) sulfanylphenyl] sulfonium tetrakis (pentafluorophenyl) borate (available as Irgacure PAG® 290, BASF®) Bis (4- (diphenylsulfonio) phenyl) sulfide hexafluoroantimona t, although this list is not to be understood as exhaustive.

The concentration of the photoinitiator is chosen so that the desired degree of crosslinking and polymerization is achieved, which in turn can vary due to different layer thicknesses of the structural pressure-sensitive adhesive and that of the desired adhesive properties. The required photoinitiator concentration also depends on the quantum yield (the number of acid molecules released per absorbed proton) of the initiator, the pKa value of the acid, the permeability of the polymer matrix, the wavelength and duration of the irradiation as well as the temperature. In general, concentrations of 0.01 to 2 parts by weight, preferably 0.1 to 1.5 parts by weight, based on 100 parts by weight of the polyacrylate and of the cationically polymerizable monomers.

Furthermore, the use of photosensitizers or photo accelerators in combination with the photoinitiators is also within the meaning of the invention. Photosensitizers and photo accelerators change or improve the wavelength sensitivity of the photoinitiator. This is particularly advantageous when the absorption of the incident light by the initiator is insufficient. The use of photosensitizers and photo accelerators increases the sensitivity to electromagnetic, in particular actinic, radiation and thus allows shorter irradiation times and / or the use of radiation sources of lower power. Examples of photosensitizers and photo accelerators are pyrene, fluoranthene, xanthone, thioxanthone, benzophenone, acetophenone, benzil, benzoin and benzoin ether, chrysene, p-terphenyl, acenaphthene, naphthalene, phenanthrene, biphenyl and substituted derivatives of the aforementioned Called connections. If required, the amount of photosensitizer or photo accelerator is less than 10% by weight, preferably less than 1% by weight, based on the amount of photoinitiator.

The structural pressure-sensitive adhesive can additionally contain further additives, preference being given to tackifier resins, plasticizers, dyes, anti-aging agents, solid or hollow glass spheres, silica, silicates, nucleating agents, and blowing agents. The additives can be used provided they do not adversely affect the properties and the curing mechanism of the structural pressure-sensitive adhesive. The optional adhesive resins are advantageously used in amounts of up to 50% by weight, preferably up to 40% by weight, even more preferably up to 30% by weight, based on the polymer. Usually rosin esters, terpene-phenol, hydrocarbon and indene-coumarone resins can be used. The amount and type of adhesive resin can influence the wetting, the adhesive strength, the adhesion to substances of different polarity, the thermal stability and the tack.

Likewise for the purposes of the invention, the structural PSAs can be chemically crosslinked even before the UV activation in order to increase the internal strength (cohesion). Metal chelates, multifunctional isocyanates, multifunctional epoxides, multifunctional aziridines, multifunctional oxazolines or multifunctional carbodiimides are preferably used as crosslinkers.

The structural PSAs of the invention described above are outstandingly suitable for producing single-sided or double-sided adhesive tapes, it being possible to use all carrier materials familiar to the person skilled in the art. By way of example, but not by way of limitation, PET, PVC and PP films, paper, nonwovens, fabrics and foams can be used as carrier materials.

Structural pressure-sensitive adhesive tape products of the invention consisting of the structural pressure-sensitive adhesive formulations of the invention described above comprise:

(foamed and non-foamed) adhesive transfer tapes (linerless double-sided adhesive tapes)

Single sided adhesive tapes Double-sided adhesive tapes comprising at least one outer layer consisting of the structural pressure-sensitive adhesive formulations of the invention

Furthermore, it can be advantageous for the process and for anchoring the structural pressure-sensitive adhesive layer with other possible layers, a film based on polyester, polyamide, polymethacrylate, PVC, etc. or a viscoelastic foamed or non-foamed carrier based on polyacrylate or polyurethane, if a chemical anchor z. B. takes place via a primer.

For transport, storage or punching, the adhesive tape is preferably provided with a liner on at least one side, for example a silicone-coated film or a silicone paper.

Another advantageous embodiment of the invention is the use of a carrier-free adhesive for the self-adhesive tape. A carrier-free adhesive is an adhesive that does not have a permanent carrier, such as a polymer film or a fleece. Rather, in a preferred embodiment, the self-adhesive mass is only applied to a liner, that is to say a material which is only used temporarily to support the self-adhesive mass and to make it easier to apply. After the self-adhesive compound has been applied to the substrate surface, the liner is then removed and the liner is therefore not a productive component.

The PSAs of the invention can be produced from solution or from the melt. For the latter case, suitable manufacturing processes include both batch processes and continuous processes. Continuous production with the aid of an extruder and subsequent coating directly on a liner with or without a layer of adhesive is particularly preferred.

A particularly preferred process comprises the following steps: a) free-radical polymerization to produce the acrylate matrix; b) mixing with the photoinitiator releasing a Bronsted or Lewis acid and the optional reactive diluent; c) coating the polymer solution on a carrier material; d) thermal drying. The structural pressure-sensitive adhesive of the invention or an adhesive tape comprising at least one structural pressure-sensitive adhesive of the invention are used in particular for pre-fixing and subsequent final fixing of various parts to be joined, curing taking place by actinic radiation.

A preferred field of application of the structural pressure-sensitive adhesive of the invention or of the adhesive tape of the invention is the automotive industry, where there are many parts that have to be permanently and firmly bonded, or in the construction sector, e.g. for fixing panels or exterior facades.

The invention is explained in more detail below using the examples, without thereby restricting the invention.

Experimental part

Unless otherwise specified or stated, the sample preparations and measurements are carried out under standard conditions (25 ° C, 101325 Pa).

I, Stat sch e GJasü be rg angstem pe f atu r Tg

The static glass transition temperature is determined using dynamic differential calorimetry in accordance with DIN 53765. The information on the glass transition temperature Tg relates to the glass transition temperature Tg in accordance with DIN 53765: 1994-03, unless otherwise stated in the individual case.

II,. M g j e ku J arge weights

The average molecular weights (weight average M _w and number average M _n ) and the polydispersity D were determined by means of gel permeation chromatography (GPC). THF with 0.1% by volume of trifluoroacetic acid was used as the eluent. The measurement was carried out at 25 ° C. PSS-SDV, 5 μm, 103 Å (10-7 m), ID 8.0 mm × 50 mm was used as the guard column. The columns PSS-SDV, 5 μm, 103 Å (10-7 m), 105 Å (10-5 m) and 106 Å (10-4 m) each with ID 8.0 mm ^c 300 mm were used for separation. The sample concentration was 4 g / l, the flow rate 1.0 ml per minute. It was measured against PMMA standards. III _; . Solid matter content:

The solids content is a measure of the proportion of non-evaporable components in a polymer solution. It is determined gravimetrically by weighing the solution, then evaporating the vaporizable components in a drying cabinet for 2 hours at 120 ° C. and reweighing the residue.

JV, K _: value (after. Fl KENTSC HER):

The K value is a measure of the average molecular size of high polymer substances. For the measurement, one percent (1 g / 100 ml) toluene polymer solutions were prepared and their kinematic viscosities were determined using a VOGEL-OSSAG viscometer. After normalization to the viscosity of the toluene, the relative viscosity is obtained, from which the K value can be calculated according to FIKENTSCHER (Polymer 8/1967, 381 ff.)

V _; _ Quantitative assessment ng the shear strength: Static shear test SSZ A rectangular test sample of size 13 mm ^c 20 mm of the double-sided adhesive tape to be tested is placed between two steel plates (50 mm ^c 25 mm ^c 2 mm; material according to DIN EN 10088-2, type 1, 4301, surface quality 2R, cold-rolled and bright annealed, Ra = 25 - 75 nm) glued in such a way that the glued area of the test sample with both steel plates is 260 mm ² each, the steel plates are offset in parallel in the longitudinal direction, so that the test sample is glued in the middle between them and the steel plates protrude beyond the test sample on different sides. Then it is pressed for 1 min with a contact pressure of 100 N / cm ^2. After a specified expansion time (unless otherwise stated, 72 hours at room temperature), the test specimens prepared in this way are suspended from a shear test station with the one steel plate area protruding beyond the test specimen in such a way that the longitudinal direction of the steel plate is oriented downwards and the area protruding beyond the test specimen of the other steel plate is loaded with a selected weight at a specified temperature (measurements at room temperature and with 20 N load as well as at 70 ° C and with 10 N load; see information in the respective table). Test climate: standard conditions, 50% rel. Humidity. An automatic counter clock now determines the time until the failure of the test sample in minutes (falling off of the loaded steel plate).

.YLSchäj STRENGTH (adhesive strength) .KK A strip of the (pressure-sensitive) adhesive tape to be examined is placed in a defined width (standard: 20 mm) on a ground steel plate (stainless steel 302 according to ASTM A 666; 50 mm ^c 125 mm ^c 1.1 mm; shiny annealed surface; surface roughness Ra = 50 ± 25 nm arithmetic mean deviation from the baseline) glued by rolling over it ten times with a 5 kg steel roller. Double-sided adhesive tapes are reinforced on the back with a 36 μm thick rigid PVC film. Identical samples in each case are produced and either made available for an immediate measurement, stored and measured for 3 days or stored and measured for 14 days.

The prepared plate is clamped (fixed) in the test device and the adhesive strip is peeled off the plate via its free end on a tensile testing machine at a peel angle of 90 ° at a speed of 300 mm / min in the longitudinal direction of the adhesive tape. The force required for this is determined. The measurement results are given in N / cm (force normalized to the particular detached bond line) and averaged over three measurements. All measurements are carried out in an air-conditioned room at 23 ° C and 50% relative humidity.

VII, micro-shear test

This test is used to quickly test the shear strength of adhesive tapes when exposed to temperature.

Measurement sample preparation for micro-shear test:

An adhesive tape cut from the respective sample sample (length approx. 50 mm, width 10 mm) is stuck to a steel test plate cleaned with acetone, so that the steel plate protrudes beyond the adhesive tape on the right and left and that the adhesive tape extends over the upper edge of the test plate by 2 mm protrudes. The bond area of the sample is height width = 13mm 10mm. The bond point is then rolled over six times with a 2 kg steel roller at a speed of 10 m / min. The adhesive tape is reinforced flush with a sturdy adhesive strip that serves as a support for the displacement sensor. The sample is suspended vertically by means of the test plate.

Microshear test:

The sample to be measured is loaded at the lower end with a weight of 100 g. The test temperature is 40 ° C and the test duration is 30 minutes (15 minutes of loading and 15 minutes of unloading). The shear path after the specified test duration at constant temperature is given as the result in pm, namely as the maximum value ["max"; maximum shear distance due to 15 minute load]; as minimum value ["min"; Shear distance (“residual deflection”) 15 min after the load is removed; at The load is relieved by a return movement through relaxation] The elastic component is also given in percent ["elast"; elastic component = (max - min) · 100 / max] vm dynamic shear strength;

A square adhesive transfer tape with an edge length of 25 mm is glued in an overlapping manner between two steel plates and pressed for 1 minute with 0.9 kN (force P). After storage for 24 hours, the composite is tested in a tensile testing machine from ZWICK at 50 mm / min at 23 ° C. and 50% rel. Humidity separated in such a way that the two steel plates are pulled apart at an angle of 180 °. The maximum force is determined in N / cm ² .

IX P fobe tack test:

The probe tack measurement is carried out in accordance with ASTM D2979-01. A steel test plate is cleaned with acetone and then conditioned for 30 min at room temperature. The sample is then bonded to the plate in the form of a transfer tape free of bubbles and defined by being rolled over three times with a 2 kg roller at a speed of 150 mm / s. To pull the adhesive strip onto the substrate, the plate is placed in a climatic room at 23 ° C. and 50% relative humidity for 12 hours. Stored in moisture. The surface to be measured must be covered with a release paper, for example. The tacking stamp (cylindrical shape, diameter 6 mm, stainless steel) with which the measurement is carried out is cleaned with acetone and conditioned for 30 min at room temperature. The release paper is only removed from the adhesive strip immediately before the measurement. Before the measurement with the Texture Analyzer TA.XT plus (Stable Micro Systems, Ltd.), the force is calibrated with a 2kg weight and the measuring path is calibrated. 5 to 10 individual measurements are carried out for each sample and the mean value is calculated in each case.

Parameters: pre-speed: 1 mm / s, test speed: 0.01 mm / s, trigger force: 0.005 N, pull-off speed: 10 mm / s, contact time: 1 s, pressure force: 0.27 N.

For the evaluation of the samples, only the maximum force at the first force peak is given below. Table 1: Raw materials used:

H e rstelju n g Bas i s pol y m er Acl

A reactor conventional for radical polymerizations was charged with 35.0 kg of 2-ethylhexyl acrylate, 35.0 kg of butyl acrylate, 5.0 kg of 3,4-epoxycyclohexylmethyl methacrylate, 25.0 kg / V-vinylcaprolactam and 66.7 kg of acetone / isopropanol (96: 4) filled. After nitrogen gas had been passed through for 45 minutes with stirring, the reactor was heated to 58 ° C. and 50 g of Vazo 67, dissolved in 500 g of acetone, were added. The external heating bath was then heated to 70 ° C. and the reaction was carried out constantly at this external temperature. After 1 hour, another 50 g of Vazo 67, dissolved in 500 g of acetone, were added and, after 2 hours, the mixture was diluted with 10 kg of acetone / isopropanol mixture (96: 4). After 5.5 hours, 150 g of bis (4-te / f-butylcyclohexyl) peroxydicarbonate, dissolved in 500 g of acetone, were added; after 6 h 30 min, the mixture was diluted again with 10 kg of acetone / isopropanol mixture (96: 4). After 7 hours, a further 150 g of bis (4-te / f-butylcyclohexyl) peroxydicarbonate, dissolved in 500 g of acetone, were added and the heating bath was adjusted to a temperature of 60.degree. After a reaction time of 22 h, the polymerization was terminated and the mixture was cooled to room temperature. The product had a solids content of 50.2% and was dried. The resulting polyacrylate had a K value of 70.0, a weight average molecular weight of M _w = 19,975,000 g / mol, a number average molecular weight M _n = 37,734 g / mol and a static glass transition temperature of Tg = -10.0 ° C.

Production of base polymer Ac2

A reactor conventional for radical polymerizations was charged with 35.0 kg of 2-ethylhexyl acrylate, 35.0 kg of butyl acrylate, 5.0 kg of 3,4-epoxycyclohexylmethyl methacrylate, 25.0 kg / V-vinylpyrrolidone and 66.7 kg of acetone / isopropanol (94: 6) filled. After nitrogen gas had been passed through for 45 minutes with stirring, the reactor was heated to 58 ° C. and 50 g of Vazo 67, dissolved in 500 g of acetone, were added. The external heating bath was then heated to 75 ° C. and the reaction was carried out constantly at this external temperature. After 1 hour, another 50 g of Vazo 67, dissolved in 500 g of acetone, were added and after 4 hours the mixture was diluted with 12.1 kg of acetone / isopropanol mixture (94: 6). After 5 and after 7 h, 150 g of bis (4-te / f-butylcyclohexyl) peroxydicarbonate, each dissolved in 500 g of acetone, were re-initiated. After a reaction time of 22 h, the polymerization was terminated and the mixture was cooled to room temperature. The product had a solids content of 50.5% and was dried. The resulting polyacrylate had a K value of 69.5, a weight average molecular weight of M _w = 14,900,000 g / mol, a number average molecular weight of M _n = 40,129 g / mol and a static glass transition temperature of Tg = -15.0 ° C.

Manufacture of comparison comparator .YA3. (With.acryic acid and no ./V-VjnyNactam)

A reactor conventional for radical polymerizations was filled with 46.0 kg of 2-ethylhexyl acrylate, 46.0 kg of butyl acrylate, 5.0 kg of 3,4-epoxycyclohexylmethyl methacrylate, 3.0 kg of acrylic acid and 66.7 kg of acetone / isopropanol (94: 6) filled. After nitrogen gas had been passed through for 45 minutes with stirring, the reactor was heated to 58 ° C. and 50 g of Vazo 67, dissolved in 500 g of acetone, were added. The external heating bath was then heated to 75 ° C. and the reaction was carried out constantly at this external temperature. After 1 hour, another 50 g of Vazo 67, dissolved in 500 g of acetone, were added and after 4 hours the mixture was diluted with 12.1 kg of acetone / isopropanol mixture (94: 6).

After 5, the polymer was gelled and could not be used for further experiments. H first JJ ung V eralejspolymer VA4. (Without monomers with a kati njschp j mejjsjerbaren functional group:

A reactor conventional for radical polymerizations was charged with 37.5 kg of 2-ethylhexyl acrylate, 37.5 kg of butyl acrylate, 25.0 kg / V-vinylpyrrolidone and 66.7 kg of acetone / isopropanol (94: 6). After nitrogen gas had been passed through for 45 minutes with stirring, the reactor was heated to 58 ° C. and 50 g of Vazo 67, dissolved in 500 g of acetone, were added. The external heating bath was then heated to 75 ° C. and the reaction was carried out constantly at this external temperature. After 1 hour, another 50 g of Vazo 67, dissolved in 500 g of acetone, were added and after 4 hours the mixture was diluted with 12.1 kg of acetone / isopropanol mixture (94: 6).

After 5 and after 7 h, 150 g of bis (4-te / f-butylcyclohexyl) peroxydicarbonate, each dissolved in 500 g of acetone, were re-initiated. After a reaction time of 22 h, the polymerization was terminated and the mixture was cooled to room temperature. The product had a solids content of 50.1% and was dried. The resulting polyacrylate had a K value of 69.6, a weight average molecular weight of M _w = 14,700,000 g / mol, a number average molecular weight of M _n = 40,521 g / mol and a static glass transition temperature of Tg = -17.0 ° C.

H first IJ ung comparison spojymer VA5 (without A / _: yinyNactam)

A reactor conventional for radical polymerizations was charged with 47.5 kg of 2-ethylhexyl acrylate, 47.5 kg of butyl acrylate, 5.0 kg of 3,4-epoxycyclohexylmethyl methacrylate and 66.7 kg of acetone / isopropanol (96: 4). After nitrogen gas had been passed through for 45 minutes with stirring, the reactor was heated to 58 ° C. and 50 g of Vazo 67, dissolved in 500 g of acetone, were added. The external heating bath was then heated to 70 ° C. and the reaction was carried out constantly at this external temperature. After 1 hour, another 50 g of Vazo 67, dissolved in 500 g of acetone, were added and, after 2 hours, the mixture was diluted with 10 kg of acetone / isopropanol mixture (96: 4). After 5.5 hours, 150 g of bis (4-te / f-butylcyclohexyl) peroxydicarbonate, dissolved in 500 g of acetone, were added; after 6 h 30 min, the mixture was diluted again with 10 kg of acetone / isopropanol mixture (96: 4). After 7 hours, a further 150 g of bis (4-te / f-butylcyclohexyl) peroxydicarbonate, dissolved in 500 g of acetone, were added and the heating bath was adjusted to a temperature of 60.degree. After a reaction time of 22 h, the polymerization was terminated and the mixture was cooled to room temperature. The product had a solids content of 50.8% and was dried. The resulting polyacrylate had a K value of 86.6, a weight average molecular weight of Mw = 1,480,000 g / mol, a number average molecular weight Mn = 15,071 g / mol and a static glass transition temperature of Tg = -53.0 ° C.

Examples

Manufacture of the structure of adhesive adhesives. PSA 1 to PSA 12 as well as equal adhesive compounds VPSA13 to VPSA16

a⁾ ln diesem Fall kationisch polymerisierbares Monomer mit Oxetangruppen b⁾ In diesem Fall handelt es sich um eine Oxetankonzentration [mmol/g Polymer] Der Initiator wurde stets im Dunkeln und in Aceton gelöst zu der Klebemasseformulierung gegeben, welche anschließend unter starkem Rühren gut durchmischt wurde. Die folgenden Beispiele enthalten jeweils 1,35 Gew.-% Irgacure PAG 290 bezogen auf das Polymer. Table 2: Mass-specific information

a ^{) In} this case cationically polymerizable monomer with oxetane groups b ⁾ In this case it is an oxetane concentration [mmol / g polymer] The initiator was always added in the dark and dissolved in acetone to the adhesive formulation, which was then mixed thoroughly with vigorous stirring. The following examples each contain 1.35% by weight of Irgacure PAG 290 based on the polymer.

The finished formulation was diluted to a solids content of 30% with acetone and then coated from solution onto a siliconized release film (50 μm polyester). (Coating speed 2.5 m / min, drying tunnel 15 m, temperatures zone 1: 40 ° C., zone 2: 70 ° C., zone 3: 95 ° C., zone 4: 105 ° C.) The mass application in each case was 100 g / m ² . There was no difference in product properties between the

Drying was found at the temperatures given above or a significantly slower one at room temperature.

^c) Sofern keine Angaben zum Bruchbild gegeben werden, handelt es sich um ein kohäsives Versagen derTable 3: Bonding results

^c) If no information is given on the fracture pattern, it is a cohesive failure of the

Adhesive. To assess the suitability of the samples as PSA prior to UV irradiation, the bond strength on steel and the static shear resistance time at room temperature were determined. It has been shown that all structural pressure-sensitive adhesives according to the invention and the formulations with epoxy monomers or monomers with a cationically polymerizable group such as the bisoxetane Aron OXT-221 (PSA1 to PSA12) exhibit adhesive strengths comparable to a typical acrylate pressure-sensitive adhesive and good cohesion, the latter despite the There was no need for an additional chemical crosslinker. The comparison adhesives VPSA13 and VPSA14 also show good pressure-sensitive adhesive properties, whereas the comparison adhesives VPSA15 and VPSA16 clearly fail in the shear test and are therefore not suitable for pre-fixing the components to be bonded or for bonding after UV activation until the maximum degree of crosslinking is reached due to the lack of cohesion would fail without fixation.

UV crosslinking ... the. Structural adhesive fabrics PSA 1 ... to ... PSA 12 ... spwj each ... of the equivalent adhesive sizes VPSAI 3 to VPSA16

The previously produced, 100 .mu.m thick adhesive tape samples were each applied bubble-free to a steel plate. By regulating the lamp power and the rolling speed of the conveyor belt, this could be varied, the optimal dose being 80 mJ / cm ^{2 in} each case. After irradiating the open side, another steel plate was glued to the previously irradiated surface in accordance with measurement method VIII within 30 seconds. With longer times between UV irradiation and gluing, the surface was already so strongly crosslinked that the adhesion to the steel plate was no longer sufficient.

Table 4: Bonding properties after UV crosslinking

^d) Sofern keine Angaben zum Bruchbild gegeben werden, handelt es sich um ein kohäsives Versagen der Klebemasse. A = adhäsives Versagen

^d) If no information is given on the fracture pattern, it is a cohesive failure of the adhesive. A = adhesive failure

From the microshear paths it can be seen that the examples according to the invention both (PSA1 and PSA7) and with epoxy monomers crosslink very well after UV irradiation. Nevertheless, the samples show adequate adhesion and very good dynamic shear strength. In contrast, the absence of the cationically polymerizable group in the acrylate (VPSA13 and VPSA14) leads to a drastic drop in the dynamic shear strength. Although these compositions are suitable as pressure-sensitive adhesives prior to UV crosslinking, they do not achieve the bond strength desired for a structural pressure-sensitive adhesive. The comparative examples VPSA15 and VPSA16 show the desired dynamic shear strengths, at least as a result of the formulation with reactive epoxy monomers, but, as already shown above, these compositions are not suitable as pressure-sensitive adhesive.

Layer thickness dependent on the U Y network

^e) Sofern keine Angaben zum Bruchbild gegeben werden, handelt es sich um ein kohäsives Versagen derThe UV-activated cationic polymerization shows a so-called dark reaction, which means that, in contrast to a UV-activated radical reaction, the active species, namely the proton, is available for further reactions even after the UV source has been switched off. As a result, generally higher layer thicknesses can be crosslinked or be polymerized through, provided that the diffusion of the protons is not prevented. To check the dependency on the layer thickness, the structural pressure-sensitive adhesive PSA1 with 100, 200, 500 and 1000 .mu.m thick samples was examined with a constant dose. Table 5: Layer thickness dependency of PSA1 - dynamic shear strength

^e) If no information is given on the fracture pattern, it is a cohesive failure of the

Adhesive. A = adhesive failure

It has been shown that even the 1000 μm thick sample still has a sufficiently high bond strength.

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Uncrosslinked samples of the PSA1, PSA2 and PSA7 pressure-sensitive adhesive of the invention are stored at different temperatures in the dark for a week or a month and then reassessed by means of dynamic shear strength. A freshly coated sample is used as a reference, which is immediately crosslinked by means of UV radiation.

Table 6: Checking the temperature stability using dynamic shear strength ⁰

⁰ Unless information on the fracture pattern is given, it is a cohesive failure of the adhesive. A = adhesive failure Table 6 clearly shows that all samples can still be UV-crosslinked even after thermal storage and achieve the desired bond strength.

Claims

Claims 1. Structural pressure-sensitive adhesive comprising an epoxy-functionalized acrylate matrix and a Bronsted or Lewis acid releasing photoinitiator, characterized in that at least one polyacrylate is used as the acrylate matrix, consisting of (a1) 35 to 90% by weight, preferably 45 to 80% by weight, particularly preferably 45 to 70 wt .-% acrylic acid ester and / or methacrylic acid ester with the formula (I)

(I), where R ^{1 is} H and / or —CH ₃ and R ^{2 are} linear and / or branched alkyl chains having 1 to 30 carbon atoms; (a2) 5 to 30% by weight, preferably 10 to 25% by weight, particularly preferably 15 to 25% by weight, of olefinically unsaturated monomers with a cationically polymerizable functional group, preferably with an epoxy and / or oxetane - group, particularly preferably with a 3,4-epoxycyclohexyl group, (a3) 5 to 30% by weight, preferably 10 to 25% by weight, particularly preferably 15 to 25% by weight, / V-vinyl-substituted lactams and (a4) 0 to 5% by weight of at least one Reactive diluent selected from the group consisting of acrylates, methacrylates and olefinically unsaturated monomers which are copolymerizable with components (a1) to (a3), the proportions by weight being based on the polyacrylate. 2. Structural pressure-sensitive adhesive according to claim 1, characterized in that the monomers (a2) monomers of the formula II

where R ^{3 is} H or -CH3, X -NR ⁵ - or -O-, R ^{5 is} H or -CH3 and R ^{4 is} an epoxy-functionalized (hetero) hydrocarbyl group. 3. Structural PSA according to claim 1 or 2, characterized in that they have a number average molecular weight M _n of 20,000 to 2,000,000 g / mol and a weight average molecular weight M _w of 200,000 to 20,000,000 g / mol. 4. Structural pressure-sensitive adhesive according to at least one of claims 1 to 3, characterized in that the epoxy-functionalized acrylate matrix has a glass transition temperature of T _G S 40 ° C, in particular T _G S 30 ° C. 5. Structural pressure-sensitive adhesive according to at least one of claims 1 to 4, characterized in that it furthermore contains at least one cationically polymerizable reactive diluent. 6. Structural pressure-sensitive adhesive according to claim 5, characterized in that the cationically polymerizable reactive diluent is at least one cyclic ether, in particular an epoxide or an oxetane. 7. Structural pressure-sensitive adhesive according to claim 6, characterized in that the at least one reactive diluent (a4) has a functional group which does not lead to any thermal cationic polymerization of the cyclic ethers. 8. Structural pressure-sensitive adhesive according to at least one of claims 5 to 7, characterized in that the proportion of cationically polymerizable reactive diluent contains 0.001 to 4 mmol reactive diluent / g polyacrylate, in particular 0.01 to 2.5 mmol reactive diluent / g polyacrylate. 9. Structural pressure-sensitive adhesive according to at least one of claims 1 to 8, characterized in that the photoinitiator fragments by means of actinic radiation, in particular by means of UV radiation, where it is in particular a Bronsted acid. 10. Structural pressure-sensitive adhesive according to at least one of claims 1 to 9, characterized in that the photoinitiator is thermally stable. 11. Structural pressure-sensitive adhesive according to at least one of claims 1 to 10, characterized in that it contains 0.01 to 2 parts by weight, in particular 0.1 to 1.5 parts by weight of photoinitiator, based on 100 parts by weight of polyacrylate and cationically polymerizable reactive diluent. 12. An adhesive tape comprising at least one structural pressure-sensitive adhesive according to any one of claims 1 to 11. 13. A method for producing the adhesive composition according to any one of claims 1 to 11, characterized in that the method comprises the following steps: a) free-radical polymerization to produce the acrylate matrix; b) mixing with the photoinitiator releasing a Bronsted or Lewis acid and the optional reactive diluent; c) coating the polymer solution on a carrier material; d) Thermal drying. 14. Use of the structural pressure-sensitive adhesive according to any one of claims 1 to 11 or of the adhesive tape according to claim 12 for pre-fixing and subsequent final fixing of various parts to be joined, curing taking place by actinic radiation. 15. Use of the structural pressure-sensitive adhesive according to any one of claims 1 to 11 or of the adhesive tape according to claim 12 in the automotive industry or in the construction sector.