Reactive adhesive tape easy to separate

Abstract

The invention relates to an adhesive tape designed and equipped to be removed after permanent adhesion, comprising at least one adhesive layer comprising a reactive structural adhesive, and to a method for separating a permanent structural adhesion produced by such an adhesive tape.

Description

Technical Field

[0001] The present invention relates to an adhesive tape embodied and configured to be separated after permanent bonding, the adhesive tape comprising or consisting of at least one adhesive layer comprising a reactive structural adhesive compound. Furthermore, the invention comprises a method for undoing a permanent structural bond produced with the aid of such an adhesive tape. Background Art

[0002] In repair workshops or in end-of-life recycling of electronic devices, the desire to be able to repair electronic devices or cars, or to dismantle and / or recycle them as far as possible, is becoming increasingly important not only for environmental reasons but also for economic reasons.

[0003] There are different kinds of electronic devices that differ in their recyclability and the degree to which they can be recycled:

[0004] Large household appliances (also known as white goods): for example, washing machines, refrigerators and freezers, stoves;

[0005] Small household appliances (also included in white goods): for example, vacuum cleaners, coffee makers, microwave ovens;

[0006] Information and communications technology devices: for example, computers, monitors, printers, cellular phones, telephones;

[0007] Consumer electronics (also called brown goods): for example, televisions, VCRs, and digital cameras.

[0008] Electrical and electronic devices, in particular, contain a large amount of substances and materials. If discarded electrical and electronic equipment is not properly handled, i.e., for example, by household waste disposal, environmental risks may arise due to the pollutants that are still present to a certain extent. In addition to pollutants such as heavy metals and HCFCs, discarded electrical and electronic equipment also includes a large number of recyclable materials that must be recovered and therefore recycled. On the other hand, if discarded electrical and electronic equipment is properly disposed of, primary raw materials (and therefore their resource-intensive extraction) can be replaced and a significant contribution can be made to the conservation of natural resources.

[0009] To achieve these goals, Germany's law on the sale, take-back and environmentally sound disposal of electrical and electronic equipment (Elektro- und Elektronikgerätegesetz – ElektroG) implements Directive 2012 / 19 / EU on waste electrical and electronic equipment (WEE) and imposes specific obligations on all relevant actors (manufacturers, trade, municipalities, owners, disposal operators). The aim is to make a significant contribution to the conservation of natural resources and the reduction of pollutant emissions through waste prevention, appropriate testing of the feasibility of preparing entire equipment items or individual components for reuse, and additional waste recycling requirements.

[0010] A suitable recycling-friendly design is needed that enables disassembly as needed and when needed ("debonding on demand"). A recycling-friendly design includes adhesive bonding that can be separated again. In particular, in small electronic devices, there is a strong increasing trend towards structurally bonded components, usually permanently, rather than connecting them in a way that can be mechanically released. Typically, these components should be permanently bonded to each other by such structural bonding (according to DIN EN 923:2006-01, structural bonding has been proven to be suitable for producing load-bearing structures, wherein adhesive bonding can withstand stress at a high percentage of the maximum breaking force over a long period of time without failure). This should result in the corresponding lifespan and load-bearing capacity of the adhesive and / or product. An example of a component connected in this way is a touch panel, such as the touch panel used in a computer screen or mobile electronic device. In the event that one of the two components is damaged, the bonded assembly cannot be separated for the purpose of replacing the component at all, or can only be separated by high (force) effort. There is also the risk of damaging the undamaged component during separation.

[0011] Therefore, there is a need, especially with regard to their use in electronic, automotive and medical devices, for adhesive tapes having unique properties which, on the one hand, allow two components to be permanently and firmly (structurally) bonded to one another, but on the other hand allow the components to be cleanly and reliably separated as and when desired.

[0012] When it comes to separating or bonding components, a common problem is that the removed tape will re-adhere under slight pressure, thus making the bond separation difficult or messy. In addition, ideally, separation must be possible with virtually no residue, which is only possible with a few tapes.

[0013] Re-detachable adhesives or adhesive tapes are generally known from the prior art and in particular in the field of pressure-sensitive adhesives.

[0014] For example, the (pressure-sensitive) adhesive strips sold by Tesa , with which objects can be easily mounted on the wall and the Powerstrip can later be removed without residue by slowly pulling it out with a finger-hold parallel to the substrate.

[0015] For example, EP 612 823 A1 discloses an adhesive film having at least three layers that can be easily separated from an adhered material by heat treatment. The adhesive film is composed of a substrate having one (or two) pressure-sensitive elastic layers of synthetic or natural rubber, a heat-expandable layer containing a foaming agent, and an adhesive layer. The advantages of this film are excellent bond strength to the materials to be adhered and excellent reduction in bond strength after heat treatment.

[0016] EP 1 033 393 A2 discloses a heat-separable, pressure-sensitive, two-layer adhesive film whose peel adhesion can be reduced upon heating and which can therefore be easily removed from the adhesive surface without contamination. The adhesive film comprises a heat-expandable layer containing heat-expandable microspheres and expanding upon heating, and a non-heat-expandable, pressure-sensitive adhesive layer on top.

[0017] EP 1 332 191 A2 discloses a heat-peelable pressure-sensitive adhesive film comprising a base material and a heat-expandable pressure-sensitive adhesive layer containing heat-expandable microspheres. Some of these microspheres have a particle size larger than the thickness of the heat-expandable pressure-sensitive adhesive layer, and thus the adhesive surface has a specific roughness and protrusions. This results in the adhesive film exhibiting excellent peeling properties after heating while maintaining excellent adhesion before heating, even when the surface area of ​​the adhesive substrate is relatively large.

[0018] WO 2021 / 176376 A1 discloses a method for separating bonded pressure-sensitive adhesives at temperatures between 100° C. and 150° C. The bonding in this case is carried out using a primer, and the choice of the primer influences the re-separability. Summary of the Invention

[0019] One object of the present invention is therefore to provide an adhesive tape which, on the one hand, allows a permanent and secure (structural) bonding of two components to one another, but, on the other hand, allows a clean and reliable separation of the components as and when desired.

[0020] A further object of the present invention is therefore to provide an adhesive tape which, on the one hand, allows two components to be permanently and firmly (structurally) bonded to one another, but, on the other hand, allows the components to be separated cleanly and reliably as needed and when required, without re-bonding to one or more components after separation.

[0021] A further object of the present invention is therefore to provide an adhesive tape which, on the one hand, allows two components to be permanently and firmly (structurally) bonded to one another, but on the other hand allows the components to be cleanly and reliably separated as needed and when required, and which can be separated from one component or components without any residue.

[0022] According to the invention, this object is achieved by an adhesive tape as claimed in claim 1. Advantageous embodiments are described in the dependent claims. The invention also relates to a method for releasing a permanent structural bond between two components, produced with the adhesive tape according to the invention, by heating the adhesive tape or heating both components or exposing them to heat and then separating the components. Furthermore, the invention includes proposed uses of the laminate according to the invention.

[0023] The present invention therefore relates to an adhesive tape embodied and configured to be separated after permanent structural bonding, said adhesive tape comprising or consisting of at least one adhesive layer comprising a reactive structural adhesive, characterised in that the reactive structural adhesive comprises expandable microspheres having an expansion onset temperature of at least 94° C.

[0024] The inventors have surprisingly found that after foaming the microspheres at 115°C or higher, the structural bond can be easily released and, surprisingly, can even be separated or removed from one or more substrates without residue. Furthermore, the inventors have surprisingly found that the introduction of expandable microspheres into the structural adhesive has no negative impact on the initial strength of the structural bond and that the reactive tapes can also be processed at conventional temperatures (in the range of 90°C to 100°C) without problems.

[0025] For easy release of structural bonds, it is essential to foam the microspheres at a temperature of 115°C or higher. Conventional foaming temperatures range from 120°C to 150°C, and a person skilled in the art can readily select an appropriate foaming temperature based on their expertise. Heat for foaming the microspheres can be introduced by conventional heat sources, such as a hot plate (hot press), an oven, a laser, IR radiation, or induction.

[0026] The at least one adhesive layer comprises a reactive structural adhesive containing expandable microspheres. The microspheres in the structural reactive adhesive have an expansion onset temperature of at least 94°C. DETAILED DESCRIPTION

[0027] In general, reactive adhesives are understood to be adhesives that cure under external influences, in particular under the influence of moisture or high-energy radiation or heat, to a technically relevant degree or with a significant change in at least one application-relevant property, and in the process achieve structural bond strengths that far exceed the standards of conventional pressure-sensitive adhesives or conventional pressure-sensitive adhesive tapes. Such adhesives are referred to in the context of the present invention as reactive structural adhesives.

[0028] Suitable adhesives are, in principle, all known reactive or potentially reactive adhesives which lead to structural bonds, hereinafter referred to as “reactive structural adhesives”, but in particular heat-activatable adhesives.

[0029] Heat-activatable adhesives can be divided essentially into two categories, namely thermoplastic heat-activatable adhesives and reactive heat-activatable adhesives.

[0030] a) Thermoplastic heat-activatable adhesive, preferably with chemical consolidation

[0031] Thermoplastic heat-activatable adhesives (also called "hot melt adhesives") are not self-adhesive or only weakly self-adhesive at room temperature. The adhesive is activated, melted, and becomes fluid and flexible only by heat. The correspondingly high glass transition temperature of the adhesive is responsible for this, so that the activation temperature for achieving sufficient adhesion is Usually tens to one hundred degrees Celsius Above room temperature. Due to its self-adhesive properties, the adhesive effect occurs before the adhesive solidifies. After joining, these adhesives, during cooling and consolidation, physically bond (usually reversibly; thermoplastic materials) and, optionally, also chemically bond (usually irreversibly; thermoplastic reactive materials) so that the adhesive effect is maintained even in the cooled state, where it develops its ultimate strength. The more heat, pressure and / or time applied during bonding, the stronger the bond between the two materials to be bonded will generally become. In this way, maximum bond strength can be regularly achieved under technically easy processing conditions. Thermoplastics are those compounds defined in Römpp (Online version, 2016 edition, document code RD-20-01271).

[0032] The thermoplastic heat-activatable adhesives described are not reactive structural adhesives in the sense of the present invention.

[0033] b) Reactive heat-activated adhesives

[0034] Reactive heat-activatable adhesives (also called "reactive adhesives") are polymer systems that have functional groups in such a way that a chemical reaction occurs when heat is supplied, wherein the adhesive chemically binds and thus causes an adhesive effect. Reactive heat-activatable adhesives do not usually become self-adhesive when heat is supplied, so that the adhesive effect only occurs after solidification. Reactive heat-activatable adhesives are usually not thermoplastic, but are realized by elastomer / reactive resin systems. The glass transition temperature is not important for the function (functionality) of the reactive system. It is also advantageous that the reactive compounds can be designed in such a way that they become softer and / or more fluid at elevated temperatures in order to best conform to the adhesive bond; this can be achieved, for example, by thermoplastic components.

[0035] Reactive heat-activatable adhesives are reactive structural adhesives within the meaning of the present invention. Various reactive heat-activatable adhesives are described below that are highly suitable for use as the base adhesive for the reactive structural adhesive of the adhesive tape according to the present invention. The base adhesive is mixed with expandable microspheres having an expansion onset temperature of at least 94°C to produce the reactive structural adhesive according to the present invention.

[0036] The reactive structural adhesive of the adhesive tape according to the invention thus comprises expandable microspheres having an expansion onset temperature of at least 94° C. and a base adhesive (the possible compositions of which are explained further below). In the context of the present invention, the reactive structural adhesive without expandable microspheres is referred to as the base adhesive.

[0037] For optimal processability for the end user, it is generally also desirable that the reactive adhesive itself has at least weakly significant pressure-sensitive adhesive properties; for example, when vertical or overhead handling is required. Therefore, the reactive structural adhesive within the scope of the present invention can be a pressure-sensitive adhesive (tacky) or can have pressure-sensitive adhesive properties, i.e. the ability to form a permanent connection with the adhesive base even under relatively weak applied pressure. However, it is also possible that the reactive structural adhesive does not have pressure-sensitive adhesive properties. This is useful if good (re)positioning capabilities are desired; in such cases, it is preferred that the adhesive is not pressure-sensitive adhesive at room temperature. Therefore, in a preferred embodiment, the reactive structural adhesive of the adhesive tape of the present invention is not a pressure-sensitive adhesive or does not have pressure-sensitive adhesive properties at room temperature.

[0038] In the prior art, pressure-sensitive adhesives are widely used in the art to produce adhesives having high viscosity and high performance. The pressure-sensitive adhesives of the present invention ... Storage modulus (G') and loss modulus (G'') are generally used to characterize the degree of elastic and viscous components, which can be determined by means of dynamic mechanical analysis (DMA), for example using a rheometer, as disclosed, for example, in WO 2015 / 189323. In the context of the present invention, an adhesive is preferably understood to be pressure-sensitive adhesive and therefore to be a pressure-sensitive adhesive which, when subjected to a temperature of 23° C. at 10 0 to 10 1 rad / s, G' and G'' are each at least partially within the range of 10 3 to 10 7 Within the range of Pa.

[0039] In one embodiment, the reactive structural adhesive according to the present invention comprises a polymer component formed from at least one thermoplastic polymer or elastomer. The thermoplastic polymer is preferably polyurethane.

[0040] According to a variant of the invention, the reactive structural adhesive of the invention is suitably a reactive adhesive or base adhesive comprising a polymer component formed from at least one thermoplastic polymer or elastomer, in particular a thermoplastic polyurethane, and comprising at least one peroxide, wherein the polymer component comprises at least 50% by weight, based on the total weight of the polymer component, of a thermoplastic polymer having no C=C double bonds and no C≡C triple bonds.

[0041] Such a base adhesive and the adhesive tape produced therefrom are disclosed in WO 2019 / 207125 A1 and are described in detail.

[0042] The selected peroxide is then in solution (0.1 molar in monochlorobenzene) at a 1 minute half-life temperature of Those which do not exceed 200°C, preferably do not exceed 190°C, very preferably do not exceed 180°C.

[0043] In particular, peroxides are those which, in addition to meeting the above definition, carry an organic radical on each oxygen atom. Thus, compounds used as peroxides are those of the general structure ROO-R', wherein the radicals R and R' may be selected independently of one another or may be the same organic radical, and wherein R and R' may also be linked to one another so as to form a cyclic moiety via the peroxy group (-OO-), resulting in a structure of the following type: .

[0044] Organic radicals are organic radicals having one, or more often two or more, free valences on a carbon atom, regardless of the functional groups they contain. Examples, to name a few, are acetonyl, acyl (e.g., acetyl, benzoyl), alkyl (e.g., methyl, ethyl), alkenyl (e.g., vinyl, allyl), alkynyl (propargyl), aminocarbonyl, ampicilloyl (a radical derived from ampicillin), aryl (e.g., phenyl, 1-naphthyl, 2-naphthyl, 2-thienyl, 2,4-dinitrophenyl), alkylaryl (e.g., benzyl, triphenylmethyl), benzyloxycarbonyl (Cbz), tert-butoxycarbonyl (Boc), carboxyl, (fluoren-9-ylmethoxy)carbonyl (Fmoc), furfuryl, glycidyl, haloalkyl (e.g., chloromethyl, 2,2,2-trifluoroethyl), indolyl, nitrile, nucleosidyl, and trityl.

[0045] Peroxides of the general structure ROO-R' (also in cyclic form) have advantages over hydroperoxides, for example, in that they do not release water as a primary cleavage product during thermal activation of the adhesive. It is desirable to minimize volatile components with a boiling point above 150° C., preferably above 120° C., and preferably to completely avoid them, in particular to avoid bubbling at the bonding site and thus weakening it. Therefore, R and R' of the peroxide are particularly preferably selected in such a way that they also do not lead to the formation of volatile primary cleavage products. Examples include carbon dioxide and isopropyl alcohol.

[0046] In a preferred embodiment of this variant, the reactive structural adhesive of the present invention comprises expandable microspheres having an expansion onset temperature of at least 94°C; in addition, a polymer component formed from at least one thermoplastic polymer, in particular a thermoplastic polyurethane; and at least one peroxide; wherein, based on the total weight of the polymer component, the polymer component comprises at least 50% by weight of a thermoplastic polymer having no C=C double bonds and no C≡C triple bonds; wherein the at least one peroxide has the general structural formula ROO-R', wherein R and R' each represent an organic group or together represent a cyclic organic group; and wherein the peroxide has a 1 minute half-life temperature in solution of less than 200°C.

[0047] Adhesive layers produced from such reactive structural adhesive compounds have proven to be excellently pre-laminated and can be activated in a hot pressing step to develop the final adhesive strength; that is, they contain the capability for chemical reactions, in particular for rapid crosslinking and / or curing reactions, after corresponding activation. Activation is particularly thermal. That is, through the supply of heat In principle, various activation methods are known, for example inductively, by microwaves, by irradiation with UV radiation, laser treatment, plasma treatment, including for latently reactive adhesive tapes. However, activation is very preferably achieved by supplying thermal energy, and further activation methods can particularly and optionally be used in addition (additively), for example by adding UV photoinitiators to the adhesive.

[0048] During the application of heat, the adhesive melts and is able to wet the substrate surface to be bonded excellently, and a crosslinking or curing reaction increases the cohesion of the adhesive. This is achieved by using a thermoplastic base polymer.

[0049] Thus, reactive bonding means that the adhesive tapes are able to develop high bond strengths to the substrates to which they are bonded. The bond strengths may, for example, exhibit orders of magnitude exceeding those of conventional pressure-sensitive adhesives by a factor of 10 or more.

[0050] The at least one peroxide or the two or more peroxides used are selected in such a way that at elevated temperature At temperatures above its activation temperature Have a relatively high decay rate or a short half-life The decay rate of a peroxide is a characteristic criterion of its reactivity and is expressed by its half-life at certain temperatures. The half-life is quantified by the regulations of the peroxide, where the half-life generally represents the time after which half of the peroxide decays under specified conditions. The higher the temperature, the shorter the half-life of decay. Therefore, the higher the decay rate, the lower the half-life.

[0051] Half-life temperature is the temperature at which the half-life corresponds to a predetermined value: for example, the 10-hour half-life temperature The temperature at which the half-life of the substance being studied is exactly 10 hours, and the temperature at which the half-life is 1 minute It is the temperature at which the half-life of the substance being studied is exactly 1 minute, and so on.

[0052] The at least one peroxide or the two or more peroxides used are selected in such a way that the 1 minute half-life temperature in the solution is Not more than 200°C, preferably not more than 190°C, very preferably not more than 180°C.

[0053] The above conditions are considered to be met if the peroxide in question has a corresponding half-life temperature value at least in monochlorobenzene (0.1 molar solution).

[0054] Such half-lives can be determined experimentally (concentration determination by DSC or titration) and can also be found in the relevant literature. The half-life can also be obtained by calculating the constants of the Arrhenius frequency factor and the decay activation energy specific to the specific peroxide for the specified conditions. The following relationship applies here:

[0055]

[0056]

[0057]

[0058]

[0059] Where c0 = initial concentration

[0060] c t = concentration at time t

[0061] = concentration at half-life

[0062] t 1 / 2 = half-life

[0063] k = decay constant

[0064] A = Arrhenius frequency factor

[0065] Ea = activation energy of peroxide decay

[0066] R = general gas constant (R = 8.3142 J / (mol∙K))

[0067] T = absolute temperature

[0068] Unless stated separately otherwise, the half-lives and half-life temperatures stated in this document refer to a 0.1 molar solution of the corresponding peroxide in monochlorobenzene.

[0069] Using constants for the Arrhenius frequency factor and the decay activation energy, which can be studied or calculated from studyable values ​​for the corresponding conditions, e.g. the solvent used, the half-life and the half-life temperature can be converted to different conditions, e.g. in other solvents, thus making them comparable.

[0070] Preferably, use at moderate temperatures Especially at temperatures significantly below its activation temperature Peroxides that also have a high half-life. This allows for achieving good latency behavior, i.e. good storage stability, for heat-activatable adhesive films comprising peroxides. Therefore, the at least one peroxide or peroxides used are selected in such a way that they have a half-life at 80°C of That is, for example, after the pre-lamination process is at least 13.5 hours, in particular at least 22.5 hours, preferably at least 69 hours, particularly preferably at least 700 hours. Thus, for heat-activatable adhesive tapes, it becomes possible to have sufficient processing and application time at 80° C. for at least 95% of the initially used peroxide (corresponding to ), in particular at least 97% (corresponding to ), preferably at least 99% (corresponding to ), particularly preferably at least 99.9% of the peroxide used is still present after 1 hour and is therefore not yet available for the reaction.

[0071] Such reactive structural adhesives are preferably latently reactive. Latently reactive adhesive systems are those that can be activated and are stable for a long time to store without activation. Latently reactive adhesive tapes are those that are: ; 50% RH) and especially at elevated storage temperatures (especially up to ) do not cure, or cure only within a period of several months, and are therefore stable in storage, but they can be activated and they cure and / or crosslink at significantly higher temperatures. To ensure a storage-stable system, the half-life is 200 Å under conventional storage conditions. It can usually be up to about 40°C It should be high. Therefore, the peroxides used should preferably be selected such that their half-life at storage temperature, preferably also up to 40° C., is sufficiently long that after 9 months (274 days) at least 75%, preferably 85%, particularly preferably 95%, or very preferably more than 95% of the peroxide is still available for crosslinking. The corresponding half-life can be determined using the above-mentioned relationship.

[0072] Suitable peroxides are, for example, representatives from the following group:

[0073] Dialkyl peroxides, diacyl peroxides, peroxyesters, peroxydicarbonates, peroxyketals, cyclic peroxides, for which the stated values ​​are achieved with respect to the 1 minute half-life temperature, preferably also with respect to the half-life at 80° C., further preferably also with respect to the half-life at 40° C.

[0074] The following are some examples of representatives from different groups that can be used advantageously:

[0075] Dialkyl peroxides: di-tert-amyl peroxide, di-tert-butyl peroxide, tert-butyl cumyl peroxide, dicumyl peroxide (dicumyl peroxide), 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di(tert-butylperoxy)hex-3-yne, di(2-tert-butylperoxyisopropyl)benzene;

[0076] Diacyl peroxides: dibenzoyl peroxide, dilauroyl peroxide, diisobutyryl peroxide, didecanoyl peroxide, di(3,5,5-trimethylhexanoyl) peroxide;

[0077] Ketone peroxides: acetylacetone peroxide, cyclohexanone peroxide, methyl ethyl ketone peroxide, methyl isobutyl ketone peroxide;

[0078] Peroxyesters: tert-butyl peroxyacetate, tert-butyl peroxybenzoate, tert-butyl peroxydiethyl acetate, tert-amyl peroxy-2-ethylhexyl carbonate, tert-butyl peroxyisopropyl carbonate, tert-butyl peroxy-2-ethylhexyl carbonate, tert-amyl peroxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate Tetramethylbutyl peroxide, tert-butyl peroxy-3,5,5-trimethylhexanoate, tert-butyl peroxyisobutyrate, tert-butyl monoperoxymaleate, tert-amyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, cumene peroxyneodecanoate, peroxyneodecanoic acid Tetramethylbutyl peroxide, tert-butyl peroxyneoheptanoate, tert-amyl peroxypivalate, tert-butyl peroxypivalate, peroxypivalic acid Tetramethylbutyl ester, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane;

[0079] Peroxydicarbonates: di-n-peroxydicarbonate, di(2-ethylhexyl) peroxydicarbonate, di-n-butyl peroxydicarbonate, dicetyl peroxydicarbonate, dimyristyl peroxydicarbonate, di(4-tert-butylcyclohexyl) peroxydicarbonate;

[0080] Peroxyketals: 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(tert-butylperoxy)cyclohexane, 2,2-di(tert-butylperoxy)butane;

[0081] Cyclic peroxide: 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxynonane.

[0082] Particularly advantageously used is dicumyl peroxide (bis(1-methyl-1-phenylethyl) peroxide), which has the following half-life: hours (equivalent to less than 0.1% of the initial amount of peroxide at 80°C in 1 hour), hours; in hours; in Hour = 6 minutes; min; all above values ​​are in solution (0.1 mol, monochlorobenzene).

[0083] Particular preference is given to selecting dicumyl peroxide, since this enables adhesive tapes which are particularly storage-stable and also resistant to humidity and heat to be obtained.

[0084] Thus, in a particularly preferred embodiment of this variant, the reactive structural adhesive of the present invention comprises expandable microspheres having an expansion onset temperature of at least 94°C; in addition, a polymer component formed from at least one thermoplastic polymer, in particular a thermoplastic polyurethane; and at least one peroxide; wherein the polymer component comprises at least 50% by weight, based on the total weight of the polymer component, of a thermoplastic polymer having no C=C double bonds and no C≡C triple bonds; wherein the at least one peroxide has the general structural formula ROO-R', wherein R and R' each represent an organic group or together represent a cyclic organic group; wherein the peroxide has a 1 minute half-life temperature in solution of less than 200°C; and wherein the peroxide comprises dicumyl peroxide.

[0085] It is also possible to use two or more peroxides. In a preferred procedure, dicumyl peroxide is then selected as one of the two or more peroxides.

[0086] The peroxide(s) used, in particular dicumyl peroxide, are preferably Especially according to their reactivity The amount is selected so that the resulting bond produced with the adhesive tape has the desired properties and, in particular, meets the requirements further defined below in the push-out test (at least 4 MPa as a fresh sample, preferably at least 3 MPa even after defined damp heat storage, further preferably no more than 10% loss after six weeks of storage under standard conditions, and furthermore no more than 10% loss after six weeks of storage and damp heat storage; for details, see the corresponding information later below). To meet these requirements, the amount of peroxide is based on the total weight of the base adhesive. For example, the amount of dicumyl peroxide A minimum of 0.5% by weight, advantageously a minimum of 1% by weight, particularly advantageously a minimum of 2% by weight, very particularly advantageously a minimum of 3% by weight, and a maximum of 10% by weight, preferably a maximum of 8% by weight, very preferably a maximum of 7% by weight has proven to be very advantageous.

[0087] Peroxides that do not meet these requirements are, for example, large amounts of hydroperoxides, i.e., compounds of the general formula ROOH, where R is an organic radical. Therefore, preferred are adhesive tapes according to the invention in which the latently reactive adhesive is essentially free of hydroperoxides, with the proportion of hydroperoxides being 0.0001% by weight or less, based on the total weight of the base adhesive.

[0088] A list of hydroperoxides that do not produce the desired results includes, for example, cumene hydroperoxide, t-butyl hydroperoxide, p-menthane hydroperoxide, Tetramethylbutyl hydroperoxide, tert-amyl hydroperoxide, diisopropylbenzene monohydroperoxide.

[0089] It has been found that these hydroperoxides cannot form good crosslinks during the thermal activation of the adhesive within a sufficiently short processing time and produce the desired advantages. In addition, hydroperoxides can release volatile primary cleavage products under thermal stress (see also above).

[0090] In this variant of the invention, the latently reactive base adhesive has a polymer component consisting of a single polymer or a plurality of polymers, at least one of which is a thermoplastic polymer having no carbon-carbon double bonds and no carbon-carbon triple bonds, i.e., a saturated polymer.

[0091] The saturated thermoplastic polymer comprises at least 50% by weight of the polymer component and can be up to 100% by weight of the polymer component (based on the total weight of the polymer component), so that in the latter case, the component is formed solely from one or more saturated thermoplastic polymers. If only one thermoplastic polymer is present, it is present in the polymer component at 50% to 100% by weight.

[0092] In addition to the expandable microspheres, the reactive structural adhesive may also consist solely of a polymer component and one or more peroxides.

[0093] Very preferably, polymers are used whose glass transition temperature is not more than -25° C., more preferably not more than -35° C. Unless otherwise stated in individual cases, all information on glass transition temperature within the scope of this document refers to the static glass transition temperature T determined by means of differential scanning calorimetry (DSC) in accordance with DIN 53765. g, and specifically refers to the glass transition temperature value T according to DIN 53765:1994-03 g .

[0094] The low glass transition temperature of the polymers used has a favorable effect on the good impact resistance of components produced with corresponding adhesive tapes.

[0095] Suitable saturated thermoplastic polymers can advantageously be selected from the group consisting of polyolefins (e.g., ethylene-vinyl acetate copolymers (EVA)), polyethers, copolyethers, polyesters, copolyesters, polyamides, copolyamides, polyacrylates, acrylate copolymers, polymethacrylates, methacrylate copolymers, thermoplastic polyurethanes, and chemically or physically crosslinked substances of the aforementioned compounds. Blends of various thermoplastic polymers, in particular those from the aforementioned classes of compounds, can also be used. Particular preference is given to using semicrystalline (partially crystalline) thermoplastic polymers.

[0096] Preferred examples are polyolefins, especially semicrystalline polyolefins. Preferred polyolefins are prepared from ethylene, propylene, butene, and / or hexene, wherein in each case the monomers may be polymerized in their pure form or mixtures of the monomers mentioned may be copolymerized. The physical and mechanical properties of the polymers, such as the softening temperature and / or specific mechanical properties, can be controlled via the polymerization process and by the nature of the monomers.

[0097] As thermoplastic polymers, thermoplastic elastomers may be used, alone or in combination with one or more thermoplastic polymers from the above-mentioned classes of compounds. Particular preference is given to using saturated semicrystalline thermoplastic elastomers.

[0098] Particularly preferred are thermoplastic polymers having a softening temperature of less than 100° C. In this context, the term softening point refers to the temperature at which the thermoplastic pellets adhere to themselves. If they are semicrystalline thermoplastic polymers, they advantageously have, in addition to their softening temperature (which is associated with the melting of the crystals), a glass transition temperature of not more than 25° C., in particular as characterized above.

[0099] A very advantageous example of a thermoplastic elastomer in the sense of a thermoplastic polymer is thermoplastic polyurethane (TPU). Polyurethane is a condensation polymer that is typically formed from a polyol and an isocyanate and contains soft segments and hard segments. The soft segments are composed, for example, of polyesters, polyethers, polycarbonates (each preferably aliphatic in nature) and hard polyisocyanate segments. Depending on the properties and the proportions used of the individual components, advantageously usable materials can be obtained. Raw materials available to the skilled person for this purpose are specified, for example, in EP 0 894 841 B1 and EP 1 308 492 B1.

[0100] In a preferred embodiment of the present invention, a thermoplastic polyurethane without multiple CC bonds is used. The thermoplastic polyurethane preferably has a softening temperature of less than 100°C, in particular less than 80°C.

[0101] In another preferred embodiment, a mixture of two or more saturated thermoplastic polyurethanes is used. The thermoplastic polyurethane mixture preferably has a softening temperature of less than 100°C, in particular less than 80°C.

[0102] In a particularly preferred embodiment, Used as a saturated thermoplastic polymer. is a substantially linear thermoplastic highly crystalline polyurethane elastomer commercially available from Covestro AG. Desmomelt can also be combined with other polymers In particular saturated thermoplastic polymers, preferably other saturated thermoplastic polyurethanes Use together.

[0103] Preferably, at least one adhesion enhancing additive Also called adhesion promoter Adhesion promoters are substances that improve the adhesive strength of the adhesive tape on the substrate to be bonded. This can occur, in particular, by increasing the wettability of the substrate surface and / or forming chemical bonds between the substrate surface and the adhesive or components of the adhesive.

[0104] An advantageous embodiment relates to a base adhesive consisting solely of a polymer component, a peroxide and an adhesion promoter The latter are in particular in the form of the silanes described hereinafter And in particular in such a way that one or more Especially semi-crystalline A saturated thermoplastic polymer is used as the sole polymer component.

[0105] Silane adhesion promoters can advantageously be used as adhesion promoters. Silane adhesion promoters used are in particular those of the general formula A compound wherein R, R' and R'' are selected independently of one another and each represent a hydrogen atom bonded to a Si atom or an organic functionalized group bonded to a Si atom, X represents a hydrolyzable group, a and b are each 0 or 1, and wherein R, R' and R'' or two representatives of this group may also be identical.

[0106] It is also possible to use the following compounds as adhesion promoters: wherein, in the case of the presence of a plurality of hydrolyzable groups X, said groups are not identical but differ from one another [corresponding to the formula , wherein X, X' and X" are independently selected hydrolyzable groups (however, two of them may be the same), and c and d are each 0 or 1, provided that ].

[0107] Alkoxy groups are used in particular as hydrolyzable groups, and alkoxysilanes are therefore used in particular as adhesion promoters. Preferably, the alkoxy groups of the silane molecules are identical; however, in principle, they can be selected differently.

[0108] For example, methoxy and / or ethoxy groups are selected as alkoxy groups. Methoxy groups are more reactive than ethoxy groups. Therefore, methoxy groups can have a better adhesion-promoting effect by reacting more quickly with the substrate surface, and thus, optionally, the amount used can be reduced. On the other hand, ethoxy groups have the following advantages: due to their lower reactivity, they have a lower (possibly negative) impact on processing time, especially for desired wet heat stability.

[0109] Trialkoxysilane For use as adhesion promoters are preferred. Examples of suitable trialkoxysilanes are

[0110] Trimethoxysilane For example, N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane, N-cyclohexyl-3-aminopropyl-trimethoxysilane, 3-aminopropyl-trimethoxysilane, 3-ureidopropyltrimethoxysilane, vinyltrimethoxysilane, 3-glycidoxypropyl-trimethoxysilane, 3-methacryloxypropyl-trimethoxysilane, methacryloxymethyl-trimethoxysilane, N-methyl[3-(trimethoxysilyl)propyl]carbamate, N-trimethoxysilylmethyl-O-methylcarbamate, tris[3-(trimethoxysilyl)propyl]isocyanurate, 3-glycidoxypropyl-trimethoxysilane, methyltrimethoxysilane, isooctyltrimethoxysilane, hexadecyltrimethoxysilane , 3-mercaptopropyl-trimethoxysilane, 3-aminopropyl-trimethoxysilane, N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane, N-phenyl-3-aminopropyl-trimethoxysilane, N-ethyl-3-aminoisobutyl-trimethoxysilane, bis[3-(trimethoxysilyl)propyl]amine, 3-isocyanatopropyl-trimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl-trimethoxysilane; 3-methacryloyloxypropyl-trimethoxysilane, 3-methacrylamidopropyl-trimethoxysilane; p-phenylenediamine, 3-acryloyloxypropyl-trimethoxysilane, N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride; triethoxysilane For example, N-cyclohexylaminopropyl-triethoxysilane, 3-aminopropyl-triethoxysilane, 3-ureidopropyl-triethoxysilane, 3-(2-aminomethyl-amino)propyltriethoxysilane, vinyltriethoxysilane, 3-glycidoxypropyl-triethoxysilane, methyltriethoxysilane, octyltriethoxysilane, isooctyltriethoxysilane, phenyltriethoxysilane, 1,2-bis(triethoxysilane)ethane, 3-octanoylthio-1,2-dimethylthiosilane, -propyl-triethoxysilane; 3-aminopropyl-triethoxysilane, bis[3-(triethoxysilyl)propyl]amine, 3-isocyanatopropyl-triethoxysilane, 2-(3,4-epoxycyclohexyl)ethyl-triethoxysilane, 3-methacryloyloxypropyl-triethoxysilane, 3-methacrylamidopropyl-triethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutadiene)propylamide; triacetoxysilane For example, vinyl triacetoxysilane, 3-methacryloxypropyl-triacetoxysilane, triacetoxyethylsilane;

[0111] Mixed trialkoxysilanes For example, 3-methacrylamidopropyl-methoxy-diethoxysilane, 3-methacrylamidopropyl-dimethoxy-ethoxysilane.

[0112] Examples of suitable dialkoxysilanes are

[0113] dimethoxysilane For example, N-(2-aminoethyl)-3-aminopropyl-methyldimethoxysilane, vinyldimethoxy-methylsilane, (methacryloyloxymethyl)-methyldimethoxysilane, methacryloxymethyl-methyl-dimethoxysilane, 3-methacryloyloxypropyl-methyldimethoxysilane, dimethyldimethoxysilane, (cyclohexyl)methyldimethoxysilane, dicyclopentyl-dimethoxysilane, 3-glycidoxypropyl-methyldimethoxysilane, 3-mercaptopropyl-methyldimethoxysilane;

[0114] Diethoxysilane For example, dimethyldiethoxysilane, γ-aminopropyl-methyl-diethoxysilane; 3-glycidoxypropyl-methyldiethoxysilane, 3-methacryloxypropyl-methyldiethoxysilane.

[0115] An example of a monooxysilane is trimethoxysilane.

[0116] The amount of adhesion promoter added can in principle be selected within a wide range, depending on the desired properties of the product and taking into account the selected raw materials of the adhesive tape. However, it has proven very advantageous to use an adhesion promoter in an amount within the range of 0.5% to 20% by weight, preferably within the range of 1% to 10% by weight, particularly preferably within the range of 1.5% to 5% by weight, and even more preferably within the range of 2.5% to 3.5% by weight, based on the base adhesive used.

[0117] The very high amounts of adhesion promoters used can have a strong plasticizing effect, making it possible to advantageously Especially for sufficiently stable membranes The amount of adhesion promoter is chosen to be as low as possible, so that on the one hand the desired positive effect on the resistance to moisture and heat is sufficiently great, while on the other hand the properties of the adhesive tape with regard to its dimensional integrity and stability are not too adversely affected.

[0118] Details on the processing and production of the adhesive layer can be found in WO 2019 / 207125 A1.

[0119] As base adhesive for the reactive structural adhesive for the adhesive tape according to the invention, according to another variant of the invention, the liquid adhesive preparation disclosed and described in detail in DE 10 2021 200 580 A1 is suitable.

[0120] The preparation or composition for producing the adhesive or base adhesive comprises

[0121] i) a thermoplastic, preferably (semi-)crystalline polymer component, which is formed from at least one polymer containing functional groups reactive toward isocyanates,

[0122] ii) a crosslinker component formed from at least one isocyanate-containing particulate compound,

[0123] x) a solvent component formed from at least one organic solvent,

[0124] wherein the polymer component is substantially soluble in the organic solvent, and wherein additionally the isocyanate-containing component is substantially insoluble neither in the solvent-free polymer component nor in the organic solvent at room temperature (23°C).

[0125] Components (i) and (ii) here are constituents of the adhesive obtainable from the formulation, whereas component (x) serves primarily as a processing aid for the formulation (precursor of the adhesive).

[0126] To obtain the reactive structural adhesive used in the present invention, the formulation described herein for use as a base adhesive is mixed with expandable microspheres.

[0127] Thus, in this variant, the reactive structural adhesive according to the invention produced from this formulation comprises expandable microspheres having an expansion onset temperature of at least 94° C., a polymer component formed from at least one polymer containing functional groups capable of reacting with isocyanates, and a crosslinker component formed from at least one isocyanate-containing particulate compound.

[0128] Generally, the term "at least one" is understood to mean that the thermoplastic, preferably (semi-)crystalline polymer component is formed from one or more polymers having functional groups reactive with isocyanates, the crosslinker component is formed from one or more isocyanate-containing particulate compounds, and the solvent component is formed from one or more organic solvents. If reference is made below to a property representing "at least one" of the respective components, the described property applies in particular to all representatives of the respective component, if two or more of them are present.

[0129] The terms "substantially" and "significantly" are used herein in a manner determined by the meaning of the present invention. If the polymer component is "substantially" soluble in the organic solvent, small amounts of undissolved polymer components may be present, particularly if they do not jeopardize the implementation of the teachings of the present invention. If a reaction does not occur "substantially," reaction processes that occur to a minor extent do not impair the present invention. For example, reaction mechanisms that occur under thermal conditions generally exhibit smaller reaction events even at lower temperatures (in this respect, see the theory of equilibrium reactions).

[0130] By means of this preparation, latently reactive adhesives comprising organically dissolved polymers and having particularly advantageous adhesive properties can be provided in a novel manner, in particular in the form of films.

[0131] This was particularly surprising to the person skilled in the art, since this applies both to the use of surface-deactivated particulate isocyanate-containing compounds as crosslinker components and to the use of non-surface-deactivated particulate isocyanate-containing compounds as crosslinker components, although this was explicitly excluded by the person skilled in the art due to the publications “Lagerstabile latent-reaktive Klebfolien” [Storage-stable latent-reactive adhesive films] (Jörg Büchner, Wolfgang Henning, Horst Stepanski, Bolko Raffel; Adhäsion 7-8.05) and “Latentreaktiv und lagerfähig” [Latently reactive and storable] (Jörg Büchner, Wolfgang Henning; Adhäsion 6 / 2007).

[0132] Similar to the prior art, the formulation for producing (particularly latently reactive) base adhesives and latently reactive tapes obtainable therefrom comprises a thermoplastic component having a melting temperature T(melt) and containing functional groups reactive with isocyanates, and an isocyanate-containing component in granular, especially finely granular (preferably with a , in particular a particle size distribution of <15 μm). However, in contrast to the prior art, the polymer component and the isocyanate component are not dispersed in an aqueous environment, but rather the polymer is dissolved in an organic solvent and the isocyanate compound is finely dispersed in this solvent.

[0133] The composition thus contains a polymer component (component (i)) formed from at least one polymer containing functional groups reactive with isocyanates (hereinafter also referred to as an isocyanate-reactive polymer). This polymer component forms the polymeric basis for the adhesive that can be produced from the composition. In the composition according to the invention, polymer component (i) is in an organic solution.

[0134] For example, polymer components used are those compounds which are functionalized with OH and / or NH2 groups and / or urethane groups.

[0135] In a very preferred method, at least one isocyanate-reactive polymer is an at least semi-crystalline polymer, i.e., a semi-crystalline or crystalline polymer. (Semi)crystalline substances can be determined by differential scanning calorimetry (DSC) according to DIN 53765:1994-03. In the case of amorphous substances, a glass transition temperature occurs; in the case of (pure) crystalline substances, a melting temperature occurs. The glass transition temperature can be seen as a step, and the melting temperature can be seen as a peak in the thermogram. Semi-crystalline substances can have a glass transition temperature and a melting temperature. At least one melting temperature is detectable for (semi)crystalline substances, while this does not occur for amorphous substances.

[0136] For (semi)crystalline polymers, it has been found that the requirement for the insolubility of the particulate isocyanate-containing compound herein In the state of preparation, therefore especially at room temperature Sufficient compatibility of the polymer component and the crosslinker component is generally achieved better than with amorphous systems. Sufficient compatibility of the polymer component and the crosslinker component is only achieved when the adhesive obtained later is heated, in particular to the melting and / or decrystallization temperature.

[0137] In another preferred embodiment, the at least one isocyanate-reactive polymer is a polyurethane polymer, and more preferably in combination with the above-mentioned advantageous embodiments, a crystalline or semi-crystalline polyurethane polymer, such as a polyurethane ester.

[0138] Preferably, the thermoplastic polyurethane has a softening temperature and / or a decrystallization temperature of less than 90°C, preferably less than 80°C, more preferably less than 70°C.

[0139] In a particularly preferred embodiment, a hydroxyl-terminated, essentially linear, thermoplastic, highly crystalline polyurethane elastomer is used as the isocyanate-reactive polymer. Such a polymer is available, for example, from Covestro AG under the name get.

[0140] However, if a higher crosslink density is advantageous, less highly crystalline and / or branched and / or multifunctional polymers may also be advantageous, for example with regard to even better chemical resistance and / or bond strength and / or hardness. It may be advantageous to have a mixture of two or more isocyanate-reactive polymers in order to adjust the properties in an advantageous manner.

[0141] The preparation also contains a crosslinker component for the polymer to be crosslinked, which is formed from at least one isocyanate-containing particulate component (component (ii)).

[0142] The isocyanate compounds can be used in either surface-deactivated or non-surface-deactivated form. This represents an advantage over the prior art, which necessarily required surface-deactivated isocyanate compounds for use in latently reactive adhesives.

[0143] Since the formulation represents at least a two-phase system, namely the polymer solution and the particulate isocyanate-containing component, no substantial onset of the curing reaction occurs in this state. Even after the formulation has been applied to a temporary or permanent support and dried, i.e., the solvent has been completely removed or reduced to a small residual solvent content of a few percent, the composition can still be stored for a long time without a significant onset of the curing reaction, thereby ensuring the usability of the latently reactive adhesive tape obtained from the formulation for at least 3 months, preferably at least 6 months, even more preferably at least 9 months or more, in which the desired property profile is achieved (in the push-out test on anodized aluminum and / or polycarbonate). , and in the push-out test after damp heat storage [72 hours at 60°C and 95% relative humidity and / or 72 hours at 85°C and 85% relative humidity] [very good PSA in the absence of damp heat storage or after chemical loading], preferably in oleic acid after storage at 60 ° C for 72 hours in the push-out test Even more preferably, after storage at 60° C. for 72 hours in a mixture of ethanol and water [75 volume fraction: 25 volume fraction], the ).

[0144] In a preferred procedure, toluene diisocyanate compounds (TDI compounds) are used in whole or in part as the isocyanate-containing component, such as TDI dimer (e.g., (aqueous dispersion of reactive isocyanates based on TDI dimer, preferably usable after removal of water) or as (1,3-bis(3-isocyanato-4-methylphenyl)-1,3-diazetidine-2,4-dione; solid)), and / or isophorone diisocyanate (IPDI).

[0145] In a very simple embodiment, the formulation consists only of the polymer and the isocyanate-containing compound in a solvent.The ratio between the polymer and the isocyanate-containing compound is selected so that the resulting latently reactive film has the desired property profile.

[0146] Advantageously, the skilled worker uses the minimum amount of isocyanate-containing compound which is stoichiometrically necessary for crosslinking the isocyanate-reactive groups of the polymer according to the invention.

[0147] The skilled person may also advantageously use more isocyanate-containing compounds than is necessary, in particular to compensate for undesired reactions of the isocyanate-containing compounds, for example with residual moisture of the solvents used and / or moisture introduced via atmospheric humidity, for example during storage and / or transport and / or application of the latently reactive adhesive tapes according to the invention, or when, for example, further isocyanate-reactive components are added to the formulations according to the invention.

[0148] It may also be advantageous to use higher amounts of isocyanate-containing compounds, for example if the melt viscosity of the polymer and / or the latently reactive adhesive tape is so high that sufficient solubility and / or transferability within the required application time cannot be ensured. Increasing the content of isocyanate-containing compounds can positively influence the temperature-time relationship. In this case, unreacted portions of the isocyanate-containing compound will remain in the adhesive tape after crosslinking.

[0149] It may also be advantageous to use less than the stoichiometrically necessary amount of the isocyanate-containing compound according to the invention, for example if the polymer used is a branched and / or poly(poly)isocyanate-reactive polymer, in order to prevent an excessively high crosslinking density (which may be accompanied by embrittlement) or to achieve the desired (e.g. viscoelastic) property profile for the application in the latently reactive adhesive tapes prepared from the formulation.

[0150] Advantageously, 1% to 25% by weight, particularly advantageously 2% to 15% by weight, very particularly advantageously 4% to 10% by weight, of the components of the base adhesive are selected from isocyanate-containing compounds.

[0151] The solvents used are not taken into account in this calculation and are to be understood only as processing aids in order to combine the components of the formulation homogeneously and to set a viscosity which allows the formulation to be applied in the desired coating process to obtain the latent reactive tape in the desired layer thickness.

[0152] As solvent component (x), an organic solvent or a mixture of mutually compatible organic solvents can be used in which the polymer component is substantially soluble and the crosslinker component is substantially insoluble. In principle, conventional organic solvents can be selected; the solubility or insolubility of the components mentioned herein can be readily determined by the skilled person with the aid of expert knowledge. Examples of useful solvents are acetone and 2-butanone, without limiting the scope of the invention to these solvents.

[0153] The formulation may optionally further include an adhesion promoter component (iii). This component is particularly formed by at least one organofunctional silane compound, such as an organofunctional silane compound of the general formula R-SiX3, wherein R represents an organofunctional group and X represents a hydrolyzable group. The organic group of the silane can produce attachment to the adhesive; for example, by a newly formed covalent bond. The organofunctional group R often represents a longer molecular part (a spacer, often including an alkyl chain), which usually has a functional group and its function is to attach to the substrate surface and / or to the component of the adhesive. Typical functional groups are vinyl, methacrylic acid, glycidyl, epoxy, epoxide, amino, urea or thiol groups. For example, alkoxy and more rare halogen groups are used as hydrolyzable groups X. Advantageously, for example, epoxy or epoxide-terminated silanes, compounds based on epoxy or epoxidosilanes and / or alkylphosphonic acids can be used. Examples of silane compounds which can be used alone or together in the sense of adhesion promoter components are aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane (which may also be referred to as Commercially available) and β-(3,4-epoxycyclohexyl)ethyltriethoxysilane (available under the name commercially available).

[0154] Since silane-containing adhesion promoters are sensitive to hydrolysis, formulations based on organic solutions offer improved possibilities for using incorporated adhesion promoters in polyurethane-based adhesives compared to the aqueous systems known from the prior art.

[0155] The proportion of adhesion promoter is advantageously 0.5% to 6% by weight, particularly advantageously 1% to 4% by weight, very particularly advantageously 1.5% to 3% by weight, of the solvent-free base adhesive.

[0156] In a preferred embodiment, the composition of the preparation of components (i), (ii) and (x) is decisive. That is, apart from components (i), (ii) and (x), no further components or adjuvants are present. A further preferred embodiment of the present invention comprises, in addition to components (i), (ii) and (x), component (iii), but is otherwise decisive and therefore has no further components or adjuvants besides these four components.

[0157] A very preferred embodiment relates to a composition for producing a base adhesive comprising:

[0158] - Hydroxyl terminated, essentially linear, thermoplastic, highly crystalline polyurethane elastomer ( ) (component (i)), dissolved in:

[0159] - an organic solvent (component (x)), such as acetone or 2-butanone,

[0160] - and finely divided TDI dimer in granular form dispersed in solution (component (ii), in particular 1,3-bis(3-isocyanato-4-methylphenyl)-1,3-diazetidine-2,4-dione ( ).

[0161] From this formulation, together with expandable microspheres, a reactive structural adhesive according to the invention is prepared. Therefore, a preferred variant of the reactive structural adhesive according to the invention comprises expandable microspheres (e.g. );

[0162] A hydroxyl-terminated, substantially linear, thermoplastic, highly crystalline polyurethane elastomer ( ) formed polymer components, and

[0163] TDI dimer (especially 1,3-bis (3-isocyanato-4-methylphenyl) -1,3-diazetidine-2,4-dione ( ) formed by the cross-linking agent component.

[0164] Advantageous compositions can be limited to the three components (i), (ii) and (x) mentioned above, but in an advantageous further development they can additionally contain one or more organofunctional silane compounds as adhesion promoter component (iii), for example glycidoxypropyltrimethoxysilane and / or β-(3,4-epoxycyclohexyl)ethyltriethoxysilane.

[0165] Advantageous compositions may be limited to the four components (i), (ii), (iii) and (x) mentioned above, but in an advantageous further development they may additionally contain one or more components (iv) from the group of epoxides and / or epoxy compounds, including monofunctional, difunctional, trifunctional or polyfunctional epoxides and / or epoxy compounds. These include, for example, compounds that are viscous / liquid at 23° C., such as Tetrakis(2,3-epoxypropyl)-m-xylene Diamines and / or 7-oxabicyclo[4.1.0]hept-3-ylmethyl 7-oxabicyclo[4.1.0]heptane-3-carboxylate and / or compounds having a melting / softening point above 23° C. (so-called epoxides / epoxy resins), for example Epiclon N-673.

[0166] In a particularly preferred embodiment, the reactive structural adhesive of the present invention comprises: expandable microspheres having an expansion onset temperature of at least 94°C; a polymer component formed from at least one polymer containing functional groups reactive with isocyanates; a crosslinker component formed from at least one isocyanate-containing particulate compound; and at least one additional component from the group of epoxides and / or epoxy compounds.

[0167] The advantageously described compositions may be limited to these components, but may additionally advantageously also comprise further additives and / or components (v), see below, such as in particular tackifier resins.

[0168] These include thickeners, wetting agents, defoamers, fillers (e.g. thermally and / or electrically conductive), organic and / or inorganic (color) pigments, organic and / or inorganic fillers, catalysts, anti-aging agents, light stabilizers and other polymers for setting specific adhesive properties. Specific adhesive properties can be set, for example, by adding amorphous polymers (e.g. polyetherurethanes or polyacrylates) and / or by adding tackifier resins.

[0169] In this case, a tackifier resin may optionally be used in the present invention to set the pressure-sensitive adhesive properties of the adhesive film according to the present invention or in fact to make it pressure-sensitive. The tackifier resins conventionally used in adhesives are different from reactive components; the latter are often also referred to as reactive resins. According to the general understanding of those skilled in the art, "tackifier resin" is understood to mean an oligomeric or polymeric resin that causes or increases and / or affects the adhesion (stickiness, inherent viscosity) of the adhesive compared to an adhesive that does not contain any tackifier resin but is otherwise identical. Typically, tackifier resins do not contain any reactive groups except double bonds (in the case of unsaturated resins) because their properties should not change during the life of the adhesive. In particular, tackifier resins are oligomeric or polymeric compounds that do not participate or do not significantly participate in the curing reaction compared to reactive components (reactive resins).

[0170] Tackifier resins that can be used are, for example, terpene-phenolic or rosin-based resins, such as partially or fully hydrogenated resins based on rosin and rosin derivatives. Further suitable tackifier resins are hydrogenated polymers of dicyclopentadiene, partially, selectively, or fully hydrogenated hydrocarbon resins based on C5, C5 / C9, or C9 monomer streams, polyterpene resins based on α-pinene and / or β-pinene and / or δ-limonene and / or Δ3-carene, and preferably hydrogenated polymers of pure C8 and C9 aromatic compounds. The aforementioned tackifier resins can be used individually or in mixtures.

[0171] The above-mentioned rosin includes, for example, natural rosin, polymerized rosin, partially hydrogenated rosin, fully hydrogenated rosin, esterified products of these rosin types (such as glycerol ester, pentaerythritol ester, ethylene glycol ester and methyl ester) and rosin derivatives (such as disproportionated rosin, fumaric acid-modified rosin and lime-modified rosin).

[0172] Tackifier resins based on acrylates and methacrylates can also be used according to the invention.

[0173] Reference may be made to the state of knowledge presented in "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (van Nostrand, 1989), Chapter 25 "Tackifier Resins".

[0174] To produce such a latently reactive adhesive, the solvent is removed in particular until only a small residual solvent fraction remains in the formulation, preferably not more than 2% by weight, particularly preferably not more than 1% by weight, and very preferably not more than 0.5% by weight. This can be done, in particular, by heating, but the temperature of the adhesive should be below the activation temperature of the curing reaction. The solvent removal can be carried out, for example, in a drying oven and / or drying tunnel and / or another technical solution that ensures that the drying temperature (of the formulation and / or adhesive tape) remains below the activation temperature of the latently reactive adhesive tape or only exceeds it for so long that the latently reactive adhesive tape still has its property profile after drying.

[0175] In another embodiment of the adhesive tape according to the invention, a heat-activatable adhesive with a low activation temperature is used as the base adhesive for the reactive structural adhesive compound. This is particularly advantageous because even heat-sensitive materials can be bonded without damaging them, and thus material-friendly bonding is possible.

[0176] As a heat-activatable base adhesive and heat-activatable base adhesives which are very well suited for adhesive layers consisting of reactive structural adhesives as in this document With a relatively low activation temperature, adhesives such as those described, for example, in WO 2013 / 127697 A1 can advantageously be used. The heat-activatable adhesive layer is in particular a latently reactive base adhesive containing:

[0177] a) Thermoplastic polymer component, its melting temperature exist ,in particular within the range wherein the thermoplastic polymer component has functional groups reactive with isocyanate, and

[0178] b) an isocyanate-containing crosslinker component, which is dispersed in particular in the thermoplastic component and is essentially inactivated in the region of the particle surface, wherein the starting temperature of the particles is for ,in particular , and among them .

[0179] For the purpose of this specification, is the melting temperature of the thermoplastic component, and is the temperature at which the isocyanate groups of the particles dispersed in the thermoplastic component are able to react with the functional groups of the thermoplastic polyurethane (e.g. because they are distributed in the matrix with the thermoplastic polyurethane). In the case of blocked isocyanate groups, is related to the deblocking temperature; in the case of microencapsulation, to the release of the isocyanate from the microcapsules (e.g. by melting the microcapsule shell); and in the case of isocyanates deactivated in the surface region of the isocyanate particles, to the melting of the isocyanate particles. For the purposes of the present invention, all isocyanate-containing systems known from the prior art which are blocked, microencapsulated or deactivated in the region of the particle surface are conceivable, provided that they meet the requirements for The thermoplastic polyurethane and the isocyanate-containing component are preferably dispersible or dispersed in an aqueous medium.

[0180] To obtain the reactive structural adhesive used in the present invention, the base adhesive described herein is used and mixed with expandable microspheres. Thus, in this variant, the reactive structural adhesive according to the present invention comprises: expandable microspheres having an expansion starting temperature of at least 94°C, a polymer component formed from at least one polymer containing functional groups capable of reacting with isocyanates, and a crosslinker component formed from at least one isocyanate-containing particulate compound. In a preferred embodiment, the reactive structural adhesive comprises: expandable microspheres having an expansion starting temperature of at least 94°C; a thermoplastic polymer component having a crosslinker ... ,in particular Melting temperature in the range wherein the thermoplastic polymer component has functional groups reactive with isocyanates; and an isocyanate-containing crosslinker component, particularly dispersed in the thermoplastic component and substantially inactivated in the region of the particle surface, wherein the particles have ,in particular Starting temperature , and among them .

[0181] The adhesive particularly contains a The thermoplastic component comprises a thermoplastic component containing functional groups that can react with isocyanates, and an isocyanate-containing component that is in particulate form, especially fine particulate form, dispersed in the thermoplastic component and is blocked, microencapsulated or substantially inactivated in the region of the particle surface. Fine particulate form means having The latently reactive adhesive is preferably based on an aqueous polyurethane dispersion, preferably from Covestro AG. So-called 1K latently reactive polyurethanes are obtained; the isocyanate-containing component is a component which is essentially deactivated in the region of the particle surface.

[0182] The particles have an initial temperature ,in . Between 35°C and 90°C, preferably between 40°C and 60°C. Between 40° C. and 120° C., preferably up to 100° C., very preferably up to 90° C. As a lower limit, 50° C. is preferred and 60° C. is particularly preferred.

[0183] Particularly preferably , since in this way an unwanted triggering of a crosslinking reaction during the production of the latently reactive adhesive tape in web form can be safely avoided.

[0184] The thermoplastic component used preferably comprises a compound functionalized with OH and / or NH2 groups. Very preferably, the thermoplastic component is at least one semicrystalline polyester polyurethane.

[0185] The latently reactive base adhesive preferably contains an anionic, high molecular weight polyurethane dispersion as thermoplastic component, which has ,in particular Melting temperature (in dry form) and contain functional groups that can react with isocyanates, for example in the form of commercially available products from the above-mentioned Dispercoll U family, such as Dispercoll U53, Dispercoll U54, Dispercoll U56, Dispercoll U 8755, Dispercoll U XP 2815, Dispercoll VP KA 8758, Dispercoll U XP 2682, Dispercoll U2824 XP, Dispercoll U XP 2701, Dispercoll U XP 2702, Dispercoll U XP 2710 and / or Dispercoll BL XP 2578 (Dispercoll is a registered trademark of Covestro AG).

[0186] The latently reactive base adhesive also preferably contains a toluene diisocyanate compound (TDI compound), such as Dispercoll BL XP 2514 (TDI dimer) and / or Aqualink U (dispersion of blocked TDI dimers) and / or isophorone diisocyanate (IPDI), such as Aqualink D (dispersion of blocked IPDI trimers), as the isocyanate-containing component. These are dispersed in particulate form, particularly finely particulate form, in the thermoplastic component and are blocked, microencapsulated, or substantially deactivated in the region of the particle surface. The diisocyanates are used, for example, in the form of aqueous suspensions of the corresponding latently reactive solid isocyanates. Aqualink is available from Aquaspersions. In particular, in combination with anionic high-molecular-weight polyurethane dispersions (such as the aforementioned Dispercoll U products) as the thermoplastic component, the aforementioned diisocyanate products can serve as crosslinker components. Other isocyanates, including monomeric and oligomeric compounds as well as polyisocyanates, can also be used.

[0187] The basic adhesive can also contain other formulation ingredients. These include thickeners, wetting agents, defoamers, fillers (e.g., thermally conductive), pigments (including reagents for coloring, whiteness regulation and / or blackening), catalysts, stabilizers, anti-aging agents, light stabilizers, and other polymers for setting specific adhesive properties. Specific adhesive properties can be set, for example, by adding an aqueous dispersion of an amorphous polymer (e.g., polyether urethane or polyacrylate) and / or by adding an aqueous resin dispersion (especially based on rosin ester) or a liquid resin.

[0188] As base adhesive for the reactive structural adhesive for the adhesive tape according to the invention, according to another variant of the invention, adhesives as disclosed and described in detail in WO 2013 / 174650 A1 are suitable.

[0189] As reactive heat-activatable adhesives, preferably adhesives based on a mixture of at least one nitrile rubber heat-activatable adhesive S1 and a reactive component, in particular a reactive resin, can be used. This base adhesive is mixed with expandable microspheres to obtain the reactive structural adhesive used in the present invention.

[0190] Therefore, in this variation, the reactive structural adhesive according to the present invention comprises, in addition to expandable microspheres having an expansion onset temperature of at least 94°C, a mixture of at least one nitrile rubber S1 and a reactive component, in particular a reactive resin. In other words, the reactive structural adhesive according to the present invention comprises expandable microspheres having an expansion onset temperature of at least 94°C; at least one nitrile rubber S1; and a reactive component, in particular a reactive resin.

[0191] The weight fraction of the nitrile rubber S1 is preferably between 25% and 70% by weight, particularly preferably between 30% and 60% by weight, of the total composition of the reactive, heat-activatable base adhesive.

[0192] The nitrile rubber S1 preferably has an acrylonitrile content of 15% to 45% by weight. Another criterion for the nitrile rubber S1 is the Mooney viscosity. Since high flexibility at low temperatures must be ensured, the Mooney viscosity should preferably be below 100 (Mooney ML 1+4 at 100° C.; correspondingly DIN 53523). Commercial examples of such nitrile rubbers are, for example, the nitrile rubbers from Zeon Chemicals. .

[0193] Reactive resins, in particular short-chain to medium-chain oligomers or polymeric compounds, in particular have an average molecular weight in the range of up to 10,000 g / mol. The proportion of reactive resins in the heat-activatable adhesive is preferably between 75% and 30% by weight. A particularly preferred group includes epoxy resins. For polymeric epoxy resins, the weight-average molecular weight M of the epoxy resin is preferably 10000 g / mol. w Varies from 100 g / mol up to 10 000 g / mol.

[0194] Epoxy resins include, for example, the reaction product of bisphenol A and epichlorohydrin; epichlorohydrin glycidyl ester; and the reaction product of epichlorohydrin and p-aminophenol.

[0195] Preferred commercial examples include Araldite 6010, CY-28, ECN 1273, ECN 1280, MY 720, RD-2 from Ciba Geigy; DER 331, DER 732, DER 736, DER 432, DEN 438, DEN485 from Dow Chemical; Epon 812, 825, 826, 828, 830, 834, 836, 871, 872, 1001, 1004, 1031, etc. from Shell Chemical; and also from Shell Chemical. 、 .

[0196] Examples of commercially available aliphatic epoxy resins include vinylcyclohexane dioxide, such as ERL-4206, ERL-4221, ERL 4201, ERL-4289, or ERL-0400 from Union Carbide Corp.

[0197] Novolac resins which can be used are, for example, Epi-Rez 5132 from Celanese, ESCN-001 from Sumitomo Chemical, CY-281 from Ciba Geigy, DEN 431, DEN 438, Quatrex 5010 from Dow Chemical, RE 305S from Nippon Kayaku, Epiclon N673 from Dainippon Ink Chemistry or Epicote 152 from Shell Chemical.

[0198] Melamine resins, such as Cymel 327 and 323 from Cytec, can also be used as reactive resins.

[0199] In a highly preferred procedure, phenolic resins are used as reactive resins. Novolac resins, resol resins, or combinations of novolac resins and phenolic resins are very suitable. Examples of commercially available phenolic resins used are YP 50 from Toto Kasei, PKHC from Union Carbide Corp., and BKR 2620 from Showa Union Gosei Corp.

[0200] Terpene phenolic resins, such as NIREZ 2019 from Arizona Chemical, can also be used as reactive resins.

[0201] Polyisocyanates, such as Coronate L from Nippon Polyurethane Ind., Desmodur N3300 or Mondur 489 from Covestro, can also be used as reactive resins.

[0202] In an advantageous form of the base adhesive, a peel adhesion enhancing (tackifying) resin is also added; very advantageously, in a fraction of up to 30% by weight, based on the total mixture of heat-activatable adhesives. All previously known tackifier resins described in the literature can be used as the tackifying resin to be added without exception. Representative examples include pinene, indene and rosin resins, their disproportionated, hydrogenated, polymerized, esterified derivatives and salts, aliphatic and aromatic hydrocarbon resins, terpene resins and terpene phenolic resins, as well as C5, C9 and other hydrocarbon resins. Any combination of these and other resins can be used to adjust the properties of the resulting adhesive as needed. Generally, all resins that are compatible (soluble) with rubber S1 can be used, in particular all aliphatic, aromatic and alkyl aromatic hydrocarbon resins, hydrocarbon resins based on pure monomers, hydrogenated hydrocarbon resins, functional hydrocarbon resins, and natural resins. The state of knowledge presented in "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (3rd edition, Satas & Associates, 1999) should be explicitly stated.

[0203] To accelerate the reaction between the two components, crosslinkers and accelerators may optionally also be added to the mixture.

[0204] Suitable accelerators include, for example, imidazoles, commercially available as 2M7, 2E4MN, 2PZ-CN, 2PZ-CNS, P0505, L07N from Shikoku Chem. Corp., or Curezol 2MZ from Air Products. In addition, HMTA (hexamethylenetetramine) additives are suitable as crosslinking agents.

[0205] Furthermore, amines, especially tertiary amines, can also be used for acceleration.

[0206] In addition to reactive resins, plasticizers can also be used. Here, plasticizers based on polyglycol ethers, polyethylene oxide, phosphoric acid esters, aliphatic carboxylic acid esters and benzoic acid esters can be used in preferred embodiments of the present invention. In addition, aromatic carboxylic acid esters, higher molecular weight glycols, sulfonamides and adipic acid esters can also be used.

[0207] In another preferred embodiment, additional additives are added to the blend, such as polyvinyl formal, polyacrylate rubber, chloroprene rubber, ethylene-propylene-diene rubber, methyl-vinyl-silicone rubber, fluorosilicone rubber, tetrafluoroethylene-propylene copolymer rubber, butyl rubber, styrene-butadiene rubber.

[0208] Polyvinyl butyral is available as Butvar from Solutia, as Pioloform from Wacker, and as Mowital from Kuraray. Polyacrylate rubber is available as Nipol AR from Zeon. Chloroprene rubber is available as Baypren from Bayer. Ethylene-propylene-diene rubber is available as Keltan from DSM, Vistalon from Exxon Mobil, and Buna EP from Bayer. Methyl-vinyl-silicone rubber is available as Silastic from Dow Corning and as Silopren from GE Silicones. Fluorosilicone rubber is available as Silastic from GE Silicones. Butyl rubber is available as EssoButyl from Exxon Mobil. Styrene-butadiene rubber is available as Buna S from Bayer, as Europrene from Eni Chem, and as Polysar S from Bayer. Polyvinyl formal is available as Formva from Ladd Research.

[0209] As base adhesive for the reactive structural adhesive for the adhesive tape according to the invention, according to a further variant of the invention, adhesives as disclosed and described in detail in WO 2010 / 145945 A1 are suitable.

[0210] The adhesive comprises: (a) at least one acrylonitrile-butadiene copolymer, (b) at least one novolac resin, and (c) a formaldehyde donor as a curing agent. The base adhesive is mixed with expandable microspheres to produce the reactive structural adhesive used in the present invention. Thus, in this variation, the reactive structural adhesive according to the present invention comprises: expandable microspheres having an expansion onset temperature of at least 94°C; at least one acrylonitrile-butadiene copolymer; at least one novolac resin; and a formaldehyde donor as a curing agent.

[0211] The ratio of acrylonitrile-butadiene copolymer to novolac resin is advantageously in the range of 3:7 to 8:2, so that the weight fraction of acrylonitrile-butadiene copolymer is preferably 30% to 80% by weight and the weight fraction of novolac resin is preferably 20% to 70% by weight, with components a. and b. adding up to up to 100% by weight and referring to the total weight of the base adhesive.

[0212] Novolac resins can be chemically crosslinked at elevated temperatures using a curing agent. Crosslinking occurs exclusively through a thermal chemical reaction of the novolac resin with the curing agent and / or a thermal reaction of the curing agent with the novolac resin and the polymer matrix.

[0213] The activation temperature for thermal crosslinking is significantly above room temperature, typically at least 100° C. or higher. Preferred activation temperatures for thermal crosslinking, in particular to ensure the required bond strength, are at least 120° C., in particular between 140° C. and 220° C.

[0214] The base adhesive may be limited to the above-mentioned components a. to c., but may optionally also include additional ingredients.

[0215] Ideally, the novolac resin and the curing agent (formaldehyde donor) are used in a ratio of 50:1 to 5:1 wt % (novolac resin:curing agent), preferably 20:1 to 7:1 wt %.

[0216] The adhesive is heat-activatable, crosslinks under hot conditions and flows well to the substrates to be bonded under hot conditions, exhibits good adhesion to polyimides, is temperature-stable for short periods of time up to at least 288°C, and is soluble or suspendable in organic solvents in the non-crosslinked state.

[0217] Acrylonitrile-butadiene copolymers, also known as acrylonitrile-butadiene rubber, nitrile-butadiene rubber, or simply nitrile rubber, can be used, in particular all acrylonitrile-butadiene rubbers with an acrylonitrile content of 15% to 55% by weight. Copolymers of acrylonitrile-butadiene and isoprene can also be used. The fraction of 1,2-linked butadiene can vary. These polymers can be hydrogenated to varying degrees; fully hydrogenated polymers with a double bond content of less than 1% can also be used. Nitrile-butadiene rubbers are either hot-polymerized or cold-polymerized.

[0218] Commercially, such systems are available, for example, under the names Europrene from Eni Chem, Krynac and Perbunan from Bayer or Nipol and Breon from Zeon; hydrogenated systems are available in various grades under the names Zetpol from Zeon or Therban from Lanxess. The aforementioned products are examples of systems that can be advantageously used according to the invention.

[0219] It has been found that nitrile rubbers with higher acrylonitrile contents produce better adhesive properties. A high molecular weight also contributes to strong adhesion; care must be taken to ensure that the polymer remains available for solution or suspension.

[0220] Nitrile rubber can be dissolved or suspended in short-chain alcohols and ketones such as ethanol or butanone. Butanone is preferred because the remaining components, especially the novolac resin, can be better dissolved in butanone.

[0221] Novolacs are soluble, meltable, non-self-curing and storage-stable phenolic resins. They are usually prepared by condensing formaldehyde and an excess of phenol in the presence of an acidic catalyst.

[0222] Their crosslinking with thermosetting moldings takes place with the aid of formaldehyde-releasing curing agents, such as hexamethylenetetramine (urotropin).

[0223] Due to steric hindrance, this crosslinking is faster in the para position than in the ortho position. Therefore, novolac resins containing phenol units linked together in the ortho position are preferred for particularly rapid crosslinking.

[0224] Examples of novolac resins which can be used advantageously are, for example, the Durez products from Sumitomo Bakelite and / or the Plenco products from Plastics Engineering Company.

[0225] Various formaldehyde donors can be used as curing agents, for example hexamethylenetetramine (hexa, HMTA, methenamine) and / or various methylolamine derivatives, for example trimethylolmelamine or hexamethylolmelamine.

[0226] Due to the chemical crosslinking of the hardener with the novolac resin, very high strength is achieved within the tape. However, the bond strength to the polyimide is also very high.

[0227] To increase adhesion, it is also possible in advantageous procedures to add tackifier resins ("tackifiers") which are compatible with the elastomers.

[0228] For example, non-hydrogenated, partially or fully hydrogenated resins based on rosin and rosin derivatives, hydrogenated polymers of dicyclopentadiene, non-hydrogenated, partially, selectively or fully hydrogenated hydrocarbon resins based on C5, C5 / C9 or C9 monomer streams, polyterpene resins based on α-pinene and / or β-pinene and / or δ-limonene, and preferably hydrogenated polymers of pure C8 and C9 aromatic compounds can be used as tackifiers in heat-activatable adhesives. The aforementioned tackifier resins can be used alone or in mixtures. The tackifier can advantageously be added in an amount of up to 20% by weight, based on the blended adhesive.

[0229] Small amounts of epoxy resins may also be used. To maintain storage stability, the amount of epoxy resin should preferably not exceed 10% by weight.

[0230] Epoxy resins are understood to include monomeric and oligomeric compounds having more than one epoxy group per molecule. These may be reaction products of glycidyl esters or epichlorohydrin with bisphenol A or bisphenol F, or mixtures thereof. Epoxy novolac resins obtained by reacting epichlorohydrin with the reaction product of phenol and formaldehyde may also be used. Monomeric compounds having multiple epoxy end groups may also be used, which serve as diluents for epoxy resins. Elastomer-modified epoxy resins may also be used.

[0231] Examples of epoxy resins that can be used advantageously are Araldite T 6010, CY-281, ECN 1273, ECN 1280, MY 720, RD-2 from Ciba Geigy, DER 331, 732, 736, DEN 432 from Dow Chemicals, Epon 812, 825, 826, 828, 830 etc. from Shell Chemicals, HPT 1071, 1079 also from Shell Chemicals, Bakelite EPR 161, 166, 172, 191, 194 etc. from Bakelite AG.

[0232] Commercially available aliphatic epoxy resins which can advantageously be used are, for example, vinylcyclohexane dioxide, for example ERL-4206, 4221, 4201, 4289 or 0400 from Union Carbide Corp.

[0233] Advantageously, elastomeric epoxy resins which can be used are available from Noveon under the name Hycar.

[0234] Advantageously, epoxy diluents (monomeric compounds with multiple epoxy groups) that can be used are, for example, Bakelite EPD KR, EPD Z8, EPD HD, EPD WF, etc. from Bakelite AG, or Polypox R9, R12, R15, R19, R20, etc. from UCCP.

[0235] Other additives that may optionally be utilized are:

[0236] Primary antioxidants, such as sterically hindered phenols

[0237] Secondary antioxidants such as phosphites or thioethers

[0238] Other antioxidants such as sterically hindered amines

[0239] Processing stabilizers, such as C-radical scavengers

[0240] Light stabilizers, such as UV absorbers

[0241] Processing aids

[0242] Fillers, such as silica, glass (ground or in the form of beads), alumina, zinc oxide, titanium dioxide, carbon black, metal powders, and the like.

[0243] Color pigments and dyes and optical brighteners

[0244] Optionally, further polymers, preferably of the elastomeric kind, are used.

[0245] The above-mentioned and any additional additives may be used alone or in combination with one another, particularly when the properties of the adhesive are to be adjusted for a particular application by the addition of such additives.

[0246] Plasticizers can be used to increase the elasticity of the cross-linked adhesive. For example, low molecular weight polyisoprene, polybutadiene, polyisobutylene, or polyethylene glycol, and polypropylene glycol can be used as plasticizers.

[0247] Since nitrile rubber does not have too low a viscosity even at high temperatures, the adhesive does not escape from the bondline during bonding and hot pressing. In this process, the novolac resin and the associated polymer matrix are crosslinked with the curing agent to produce a three-dimensional network.

[0248] The reactive structural adhesive includes microspheres in an amount of 1 to 25 wt %, specifically 2 to 20 wt %, preferably 5 to 10 wt %, and most preferably about 10 wt %, based on the total weight of the reactive structural adhesive.

[0249] "Microspheres" in the present invention are understood to mean hollow microspheres that are elastic and therefore expandable in their ground state, and have a thermoplastic polymer shell. These beads are usually filled with a low-boiling liquid or liquefied gas. The shell materials used are, in particular, polyacrylonitrile, PVDC, PVC, or poly(meth)acrylates. In particular, short-chain hydrocarbons, such as isobutane or isopentane, which are encapsulated under pressure as liquefied gases in the polymer shell, are conventional as low-boiling liquids.

[0250] Microspheres are typically used as a blowing agent. Heating the microspheres softens the outer polymer shell. Simultaneously, the blowing agent inside expands. This causes irreversible extension and three-dimensional expansion of the microspheres. Expansion ends when the internal and external pressures equalize. Because the polymer shell remains, the result is a closed-cell, synthetically expanded foam.

[0251] Microspheres that have not been heat activated and therefore still have their original expansion are referred to as expandable microspheres within the scope of the present invention (equivalent to unexpanded microspheres) and are not considered expanded microspheres according to the skilled person's understanding.

[0252] Expandable or unexpanded microspheres are useful in many embodiments and can be characterized essentially by their size (typically 6 to 45 μm diameter D(0.5) in the unexpanded state) and their expansion onset temperature (about 75° C. to about 220° C.). Examples of commercially available microspheres are GLUTAMATE® from Nouryon. Type (DU = Dry Unexpanded), or from Matsumoto Yushi-Seiyaku Co, Ltd Microspheres. Expandable or unexpanded microspheres are available, for example, as aqueous dispersions with a microsphere mass content of about 40% to 45%, or as polymer-bound products, for example in ethylene vinyl acetate, with a microsphere mass content of about 65%. However, within the scope of the present invention, it is preferred to use expandable microspheres in the form of a powder, wherein the powder preferably consists essentially of expandable microspheres.

[0253] Important parameters of the expandable microspheres used according to the invention are the desired onset temperature, the maximum temperature and the particle size D(0.5), which can be found in the manufacturer's data sheets. According to the invention, it is preferred that the onset temperature of the expandable microspheres is in the range of 94°C to 140°C, more preferably in the range of 95°C to 120°C, most preferably in the range of 100°C to 110°C.

[0254] The skilled person knows that the starting temperature of the expandable microspheres is directly related to the temperature (hereinafter referred to as the foaming temperature) that must be reached in order to allow a good and easy separation of the bond. For example, the foaming temperature for optimal separation of the adhesive layer of an adhesive layer having a reactive structural adhesive and expandable microspheres having an expansion starting temperature of at least 94°C is about 120°C. Higher temperatures lead to faster expansion of the microspheres and therefore to less time until the bond strength has decreased and separation is possible. At lower temperatures, the components naturally need longer to become separable. The distance between the starting temperature and the optimal separation temperature is preferably in the region of 20-30°C, most preferably about 15°C.

[0255] The expansion of the expandable microspheres is carried out at a temperature of 115°C or higher, which is necessary for easy separation of structural bonds. Conventional foaming temperatures range from 120°C to 150°C, preferably at about 120°C. A skilled person can easily select an appropriate foaming temperature based on their professional knowledge. The heat for foaming the microspheres can be introduced by common heat sources, such as a hot plate (hot press), an oven, a laser, IR radiation, or induction. In the context of the present invention, the heat input is preferably achieved by means of a hot plate or a hot press.

[0256] According to the present invention, the maximum temperature of the expandable microspheres used is preferably not greater than 200°C, in particular not greater than 180°C, and preferably not greater than 170°C.

[0257] The starting temperature of the microspheres (T 起始 ) and maximum temperature ( ) can be determined according to methods known to the skilled person, such as thermomechanical analysis (TMA). Here, the sample is heated at a constant rate (20°C / min in the case of Expancel microspheres), and the volume of the sample is measured and used to create a temperature-volume diagram, from which the onset temperature (temperature at which the volume increase begins) and the maximum temperature (temperature with the maximum volume) can be determined or calculated.

[0258] The particle size D(0.5) of the expandable microspheres, measured by laser diffraction, is typically between 5 μm and 40 μm, in particular between 16 μm and 24 μm. In a preferred embodiment, the adhesive tape according to the invention is characterized in that the expandable microspheres have a particle size D(0.5) of between 16 μm and 24 μm (in the unexpanded state). The inventors surprisingly discovered that this particle size is ideal for adhesive layer thicknesses of 75 μm to 150 μm. At lower adhesive layer thicknesses, the expandable microspheres preferably have a particle size D(0.5) of less than 16 μm. A particle size D(0.5) of 25 μm or greater is preferably used for adhesive layer thicknesses of greater than 150 μm.

[0259] Particle size determination by laser diffraction can be performed, for example, with the "Bettersizer S3Plus" particle analyzer from 3P Instruments. By default, the Bettersizer measurement is essentially a measurement of the volume distribution. Converting the results into a quantitative distribution is a mathematical process. The measurement results are reported as 、 and values, which are standard percentiles. Or D(0.5) is the size in micrometers (μm) at which 50% of the sample particles are smaller and 50% are larger. This value is also called the mass median diameter (MMD) or the median of the volume distribution. The particle size below which 10% of the samples are The particle size below which 90% of the samples fall.

[0260] A preferred type of expandable microsphere is that from Nouryon and (Both : 94-114°C; :147-167°C;D(0.5): 16-24µm), and from Matsumoto Yushi-Seiyaku Co., Ltd and F-100MD (both : 115-125°C; :155-165°C; D(0.5): 17-23 µm).

[0261] Adhesive tapes with a reactive structural adhesive that creates a permanent and structural bond between two components are typically exposed to temperatures in the range of 75°C to 180°C to cure the reactive structural adhesive. The minimum temperature required to cure a reactive structural adhesive is called the activation temperature. This does not necessarily refer to the temperature typically used to apply the tape to the first substrate to be bonded during the pre-lamination step (pre-lamination). This temperature is typically 10 to 20°C below the activation temperature and causes the adhesive to become (pressure-sensitive) tacky or sticky, but does not yet cause the curing reaction of the reactive structural adhesive. The scope of the present invention only covers adhesive tapes with a reactive structural adhesive that cures at a temperature in the range of 75°C to 140°C. Therefore, the present invention relates to an adhesive tape embodied and configured to be separated after permanent bonding, comprising or consisting of: at least one adhesive layer comprising a reactive structural adhesive, wherein the reactive structural adhesive comprises expandable microspheres having an expansion onset temperature of at least 94°C, and wherein the reactive structural adhesive has an activation temperature in the range of 75°C to 140°C.

[0262] Therefore, it is important for the selection of expandable microspheres that the foaming temperature of the expandable microspheres is at least 5°C higher than the activation temperature or the temperature range for activation, in particular at least 10°C higher than the activation temperature or the temperature range for activation, and preferably at least 20°C higher than the activation temperature or the temperature range for activation. The expandable microspheres are selected according to the activation temperature or the temperature range for activation of the reactive structural adhesive so that no (unintentional) foaming of the microspheres occurs during the curing of the adhesive, so as not to affect the permanent structural bond. In the preferred expandable microspheres 、 、 and In the case of PTFE, the foaming temperature is 120°C to 150°C, making them useful for reactive structural adhesives with activation temperatures in the range of 75°C to 100°C.

[0263] The present invention relates to an adhesive tape comprising or consisting of at least one adhesive layer. The at least one adhesive layer of the adhesive tape according to the invention is characterized in that the adhesive layer has a layer thickness of at least 5 μm and at most 1000 μm. Preferably, the thickness is between 25 μm and 750 μm, and more preferably between 50 μm and 300 μm. The layer thickness is particularly preferably 100 μm.

[0264] The thickness of the adhesive layer is related to the selection of suitable expandable microspheres to ensure optimal separation or separability of the adhesive layer after the microspheres are foamed by heat input. The inventors have surprisingly found that the particle size D(0.5) of the expandable microspheres (in the unexpanded state) should be in the range of 20 to 30% of the thickness of the adhesive layer to ensure optimal separability after foaming.

[0265] The adhesive tape according to the invention comprises a double-sided adhesive tape. Such an adhesive tape comprises or consists of at least one adhesive layer comprising a reactive structural adhesive and is used in the simplest case as a single-layer adhesive transfer tape, applied to a removable (temporary) backing material (also referred to as release material or known to the skilled person as a release liner or liner). Particularly preferably, the adhesive tape is present as an adhesive transfer tape having at least one adhesive layer. The liner (release paper, release film) is not part of the adhesive tape, but merely an aid to its production and / or storage or further processing by die-cutting. In addition, the liner cannot be firmly connected to the adhesive layer in contrast to the adhesive tape carrier. Temporary backing materials suitable for the adhesive according to the invention are known to the skilled person.

[0266] For example, all release films and papers known from the prior art that are suitable for the adhesive of the present invention and that are provided with a release layer on one or both sides and / or that do not inherently form excessively high bonds with the adhesive of the present invention are suitable as temporary backing materials. Siliconized papers that are suitable for the adhesive of the present invention are preferred. It is also possible to use a two-layer releasable carrier material so that the top and bottom sides of the adhesive film are covered even when the product is not in roll form.

[0267] Adhesive tape according to the present invention comprises at least one adhesive layer or is made of at least one adhesive layer, and described adhesive layer comprises reactive structural adhesive and also can contain carrier material (carrier), and it even still remains in the product after bonding.Such adhesive tape is typically called as double-sided tape.Film and paper are the possible selections that are used for this purpose, but can also be the scrim of laying and the fabric of weaving and knitting.The surface of these carrier materials can be carried out chemical pretreatment (primer, plasma) and / or physical pretreatment (corona, flame, plasma) independently of one another, makes to realize the especially good anchoring of adhesive layer on carrier material.Nonwoven fabric is preferred.The lamella (ply) of permanent carrier has reduced any trend that adhesive layer is laterally squeezed out from bonding joint under pressing condition in molten state.

[0268] In this preferred embodiment, a sheet structure made of individual fibers is used as a carrier nonwoven. All nonwovens defined according to standard DIN EN 29092 can be used. Nonwovens are composed of loosely folded fibers that are not yet connected to each other. Strength is generated by inherent fiber adhesion. There are also distinctions between consolidated and non-consolidated nonwovens. The fibers are statistically distributed. Nonwovens can be distinguished based on the fiber material. Mineral fibers such as glass, mineral wool or basalt, animal fibers such as silk or wool, plant fibers such as cotton, cellulose, chemical fibers such as polyamide, polypropylene, polyphenylene sulfide, polyacrylonitrile, polyimide, polytetrafluoroethylene, aramid or polyester, or mixtures of the above substances are usable fiber materials. The fibers can be mechanically consolidated by needle punching or water jetting, chemically consolidated by adding an adhesive, or thermally consolidated by softening in a suitable air flow, between heated rollers or in a steam flow.

[0269] In a very preferred version of the invention, a cellulose-based nonwoven is used. The basis weight of the nonwoven is preferably between 4 and 100 g / m 2 between 10 and 70 g / m 2 Such nonwovens are commercially available, for example, from Glatfelter. The thickness of these nonwovens is preferably between 20 and 100 μm, particularly preferably between 30 and 60 μm.

[0270] Double-sided tape with carrier material can carry adhesive layers of different thicknesses and / or preferably different types of adhesive film layers on top and bottom. Different (pressure-sensitive) adhesive layers can be used to regulate the character of double-sided tape. The character that can be affected in this way comprises the thickness, rigidity, flexibility, temperature resistance, elasticity and the flame retardancy of adhesive tape. If different adhesive layers are used, then both of them advantageously meet the requirement for the adhesive layer with reactive structural adhesive as described above. It is also possible that, in such a system, one of the adhesive layers does not include reactivity, structural adhesive, but contains for example thermoplastic, heat-activatable and / or pressure-sensitive adhesive.

[0271] The adhesive tape according to the invention, which comprises at least one adhesive layer (which comprises a reactive, structural adhesive) or consists thereof, can in principle comprise or consist of one adhesive layer or multiple adhesive layers in two variants (with or without a carrier). At least the topmost and bottommost layers are adhesive layers which comprise a reactive structural adhesive and which may differ in thickness and / or properties. If different adhesive layers are used, both of them advantageously meet the requirements for an adhesive layer with a reactive structural adhesive as described above. It is particularly preferred that the adhesive tape is present as an adhesive transfer tape having one adhesive layer. Accordingly, the adhesive tape in a preferred embodiment is characterized in that the adhesive tape is an adhesive transfer tape and consists of an adhesive layer.

[0272] The multilayered, carrier-containing adhesive product can have a thickness of 10 μm to 2000 μm, preferably 25 μm to 500 μm, particularly preferably 75 μm to 300 μm.

[0273] In the context of the present invention, the general expression "adhesive tape" (pressure-sensitive adhesive tape) or synonymously "adhesive strip" (pressure-sensitive adhesive strip) covers all sheet-like structures, such as films or film parts extending in two dimensions, tapes, tape parts, etc. with an extended length and a limited width, and finally also die-cut parts or labels.

[0274] The adhesive tape thus has a longitudinal extent (x-direction) and a transverse extent (y-direction). The adhesive tape also has a thickness (z-direction) that extends perpendicular to the two extents, with the transverse and longitudinal extents being many times greater than the thickness. The thickness is very substantially the same, preferably completely the same, over the entire surface of the adhesive tape, as determined by its length and width.

[0275] At the end of the production process, the adhesive tape according to the present invention or a plurality of adhesive tapes according to the present invention are typically wound into a roll in the form of an Archimedean spiral, i.e., a disc-shaped tape roll, which is called a "pancake" in technical language. However, the adhesive tape can also be provided by a meter, or alternatively, the adhesive tape can be wound onto a core like a textile yarn, the length of the core being much greater than the width of the adhesive tape. By superimposing the rotational movement of the core and the axial movement of the core or the adhesive tape guide member, the adhesive tape first forms the first radially innermost layer of helical turns. To complete the first layer and jump to the second layer, the orientation of the axial movement is reversed, wherein the rotational movement remains unchanged. To complete the second layer and jump to the third layer, the orientation of the axial movement is reversed again, i.e., returned to the original orientation, while the rotational movement remains unchanged. The tilt angle remains constant between each orientation reversal point. In this way, multiple layers of turns can be formed, in which the turns cross each other (cross-wound coils).

[0276] The adhesive tape according to the present invention is preferably used with a width of 9 to 50 mm, particularly 19 to 25 mm. The selected width of the roll is generally 10 mm, 15 mm, 19 mm, 25 mm and 30 mm. Alternatively, the laminate can be sold as a log or roll with a width of, for example, 1000 to 1300 mm. This log material is usually processed into die-cut pieces, which can be used for composite production. The die-cut pieces are produced by laser cutting, flatbed die cutting or rotary die cutting. The die-cut piece usually has the dimensions of the first component, but it can also be slightly smaller to allow for a slight oozing process during the joining process.

[0277] Substrates that are particularly suitable for bonding via the adhesive tape according to the invention are metal, glass and / or plastic.The substrates to be bonded can be identical or different.

[0278] It may be necessary to pretreat the surfaces of the substrates to be bonded by physical, chemical and / or physicochemical methods. For example, the application of a primer or an adhesion promoter composition is advantageous.

[0279] Suitable plastic substrates include acrylonitrile butadiene styrene (ABS), polycarbonate (PC), Blends, PMMA, polyamide, glass fiber reinforced polyamide, polyvinyl chloride, polyvinylidene fluoride, cellulose acetate, cycloolefin copolymer, liquid crystal polymer (LCP), polylactide, polyetherketone, polyetherimide, polyethersulfone, polymethacryloylmethylimide, polymethylpentene, polyphenylene oxide, polyphenylene sulfide, polyphthalamide, polyurethane, polyvinyl acetate, styrene-acrylonitrile copolymer, polyacrylate or polymethacrylate, polyoxymethylene, acrylate-styrene-acrylonitrile copolymer, polyethylene, polystyrene, polypropylene and / or polyester, such as polybutylene terephthalate (PBT) and / or polyethylene terephthalate (PET). Suitable metal substrates for use are, for example, aluminum, stainless steel, steel, magnesium, zinc, nickel, brass, copper, titanium, ferrous metals and austenitic alloys. Preferably, the metal substrate comprises anodized aluminum (e.g., E6EV1). The substrate may have been painted, printed or coated by vapor deposition or sputtering. The substrate to be bonded can take any shape required for the use of the resulting composite element. In the simplest form, the substrate is flat. In addition, the substrate, in particular glass, can be provided with a coating (in particular black) on its surface.

[0280] The adhesive tapes according to the invention make it possible to achieve outstanding structural or (semi-)structural bonds. "Structural or (semi-)structural bonds" are, in particular, bonds in which the potential breaking point upon loading of the bonded components does not necessarily have to lie in the adhesive layer or layers between the components to be bonded, or in the carrier material, but can occur with equal probability at any other point of the objects bonded by the structural adhesive. Consequently, the electrical resistance of the bond can be as high as the electrical resistance of the bonded materials and can even exceed it. In the case of high-strength and / or resistant materials to be bonded, the skilled artisan refers to a (semi-)structural bond if the bond strength is higher than that of (non-reactive, structural) pressure-sensitive adhesives (PSAs).

[0281] A special feature of the adhesive tape according to the present invention is that the structural bond's resistance persists as long as the bonded component or the adhesive tape is not heated or heated by heat input to temperatures above the appropriate foaming temperature. Because the foaming of the expandable microspheres occurs at temperatures of 115°C or higher, depending on the type of expandable microspheres, simple separation of the structural bond is possible after the bonded component or the adhesive tape has been exposed to these temperatures. This is not possible with conventional structural bonds, and the adhesive tape according to the present invention therefore offers significant advantages over conventional reactive structural adhesive tapes.

[0282] Typically, to activate reactive structural adhesives, the adhesive, particularly in the form of a tape, is heated between the substrates to be bonded. In this case, the reaction of the polymer component with the isocyanate-containing component begins, and the curing reaction proceeds. To introduce heat, a hot press is used in a preferred embodiment. The ram of the hot press is made, for example, of aluminum, brass, or bronze, and its shape is generally adapted to the contour of the metal part or the size of the die-cut piece. After heat activation, the anodized aluminum part with the laminated adhesive product having at least one layer of tape is removed from the formed part. The entire operation can also be automated.

[0283] Thermal activation typically occurs at an activation temperature of at least 60°C up to a temperature of 150 to 190°C. The activation temperature of the reactive, structural adhesive is proportional to the appropriate foaming temperature of the expandable microspheres used, and skilled artisans can select these two parameters based on their expertise. In a preferred embodiment, the adhesive tape according to the invention is characterized in that the reactive structural adhesive has an activation temperature of at least 75°C, preferably at least 80°C, and even more preferably at least 110°C.

[0284] The adhesive tape according to the invention can be used in a method for bonding two components or substrate surfaces together using an adhesive tape. The essential feature of the method is that an adhesive film is placed between two substrate surfaces of the components, in each case brought into contact, and then cured using heat (in a temperature range of 75°C to 140°C). The present invention therefore further relates to a method for releasing a permanent structural bond between two substrates A and B as described herein, produced using the adhesive tape according to the invention (performed according to the described method or another method for bonding two substrate surfaces), comprising:

[0285] a) exposing the adhesive assembly consisting of substrate A, the adhesive tape according to the invention and substrate B (substrate A / adhesive tape / substrate B) to a temperature in the range of 115° C. to 150° C., preferably about 120° C.;

[0286] b) separating the bonded assembly into the individual substrates A and B along the adhesive tape according to the invention; and optionally

[0287] c) Removing the residues of the adhesive tape according to the invention from substrate A and / or substrate B.

[0288] Separation of the bonded assembly into the two separate substrates A and B can be performed, for example, by pressing, pushing, twisting, peeling, and / or prying, depending on the type, structure, and shape of the substrates or bonded assembly. Depending on the tape's breakage mode / pattern, tape residue may be present on both substrates A and B, or the tape may remain completely on substrate A or B after separation. In all cases, the tape residue can be removed, preferably by simply peeling it off, and preferably without residue. The separated substrates A and / or B can be reused or re-bonded, if necessary, after cleaning.

[0289] The desired (separation) temperature of 115° C. to 150° C. can be achieved by heat input from common heat sources, such as a hot plate (hot press), an oven, a laser, IR radiation or induction. Therefore, preferably, the process is characterized in that, in step a), the temperature is achieved by using a laser, an oven, by IR radiation, by induction, or by a hot plate (hot press).

[0290] After separating the adhesive tape from at least one substrate, preferably from at least two substrates, residues of the adhesive layer may be present on one or more substrates (also referred to as components). Preferably, the remaining portion of the adhesive layer on the one or more substrates can be easily removed by peeling. Therefore, in a preferred embodiment, the method according to the invention is characterized in that the residues of the adhesive layer can be removed without residue. If the substrate is to be reused, the possibility of removing the adhesive tape or adhesive layer without any residue eliminates the high cost / effort of cleaning. Re-bonding is possible with no or only very little cleaning effort.

[0291] The adhesive tape according to the invention can be used in particular in applications where the adhesive quality requirements For example, regarding bond strength or fatigue resistance This is the case, for example, in the field of electronics or in automotive construction, as well as in many other areas. Adhesives are very suitable for difficult-to-bond substrates, small bonding surfaces, For example, in the field of consumer electronics, small area bonding and / or different substrates to be bonded, to name a few, especially in the electronics industry.

[0292] An illustrative application according to the present invention involves bonding anodized aluminum, such as E6EV1, to plastic. For consumer electronic components, the plastic parts are preferably based on plastics that can be processed by injection molding. For example, this group includes: ABS, PC, ABS / PC blends, PMMA, polyamide, glass-fiber-reinforced polyamide, polyvinyl chloride, polyvinylidene fluoride, cellulose acetate, cyclic olefin copolymers, liquid crystal polymers (LCP), polylactide, polyetherketone, polyetherimide, polyethersulfone, polymethacryloylmethylimide, polymethylpentene, polyphenylene oxide, polyphenylene sulfide, polyphthalamide, polyurethane, polyvinyl acetate, styrene-acrylonitrile copolymers, polyacrylates or polymethacrylates, polyoxymethylene, acrylate-styrene-acrylonitrile copolymers, polyethylene, polystyrene, polypropylene, or polyesters (e.g., PBT, PET). This list is not intended to be complete. Components can take any shape required for manufacturing components or housings for consumer electronic products. In their simplest form, they are planar. However, three-dimensional components are also quite common. For example, components can have various functions, such as housings, viewing windows, or reinforcement elements. The plastic used is very preferably polycarbonate, PMMA or ABS.

[0293] Plastic parts can be painted or coated in other ways. Paints used for functionalizing / modifying the surface of plastics are, for example, antireflective coatings, antifingerprint coatings, antiscratch coatings, or decorative prints (so-called backprinting). Furthermore, plastics can also be provided with (inorganic) layers, such as conductive layers. Indium tin oxide is particularly suitable as a conductive layer. Some of these paints and layers are heat-sensitive and therefore require the use of adhesive products that can be processed at low temperatures.

[0294] For use in consumer electronics, for example, the adhesive tapes according to the invention are often further processed into die-cut parts. These are produced, for example, by laser cutting, flatbed die-cutting, or rotary die-cutting. The die-cut parts are usually the size of the anodized aluminum parts, but they can also be slightly smaller to allow for slight bleed-through during the bonding process.

[0295] The adhesive tapes of the present invention offer numerous potential applications. Touch panel disassembly has already been mentioned. Given the importance of cell phones, this is a particularly important application area. On the one hand, cell phone displays require a very strong and, most importantly, leak-tight bond. On the other hand, it is often necessary to remove the display in practice. The adhesive tapes of the present invention are ideally suited for this purpose.

[0296] Finally, so-called "reprocessability" is a topic that is becoming increasingly important. In the automotive industry, for example, there is an increasing demand for a single type of disposal of products at the end of their life cycle. Therefore, it is crucial that components made of different materials be separated back into their individual components before they are disposed of, even if they were previously "inseparably" connected to one another. The present invention allows for a very strong and permanent connection of different components while still allowing them to be separated as needed. Therefore, the present invention also relates to the use of the adhesive tape according to the invention described in the automotive industry.

[0297] Experimental part:

[0298] Chemicals used :

[0299]

[0300] General Production Instructions For Comparative Examples 1 to 4 and 6, and for Examples 1a to 4b and 6a and 6b:

[0301] Depending on the respective composition, the corresponding components are dispersed or dissolved homogeneously in methyl ethyl ketone so that the total content of the aforementioned components in the solvent is 20% by weight. The solution or dispersion is then applied by known methods onto suitable release paper known to the person skilled in the art for silane-containing compositions and dried in a suitable circulating air drying cabinet at 70° C. for 30 minutes to give in each case an adhesive tape of 100 μm (dry film density).

[0302] Comparative Example 1, Examples 1a and 1b

[0303]

[0304] Comparative Example 2, Examples 2a and 2b

[0305]

[0306] Comparative Example 3, Examples 3a and 3b

[0307]

[0308] Comparative Example 4, Examples 4a and 4b

[0309]

[0310] Comparative Example 6, Examples 6a and 6b

[0311]

[0312] Launch results:

[0313] The push-out test allows conclusions to be drawn about the adhesive strength of the adhesive product in the normal direction of the adhesive layer. The following is provided: a circular first substrate (1) made of polycarbonate (PC, thickness 3 mm) with a diameter of 21 mm, a second substrate (2) made of polycarbonate (PC, thickness 4 mm) A square with a side length of 40 mm A circular, centrally arranged opening (hole) having a diameter of 9 mm, and an adhesive film sample to be examined, which is also made (cut to size or punched) into a circle having a diameter of 21 mm.

[0314] The test specimens were produced from the three components described above by precisely pre-laminating the adhesive tape produced from the free surface onto substrate (1) (at 70° C. for 5 seconds). The temporary carrier was then removed and the assembly with the now exposed side of the adhesive product was concentrically pre-laminated onto substrate (2) (also at 70° C. for 5 seconds), i.e. so that the circular opening in substrate 2 was arranged exactly centrally above the circular first substrate 1 (bonding area was therefore 282 mm). 2 ) in this way. Care was taken to ensure that the total time of exposure to temperature (70°C) during the pre-lamination process did not exceed 20 seconds. The entire assembly was then pressed at 90°C for 120 seconds under a pressure of 10 bar to obtain the test specimen.

[0315] After 24 hours of storage at 23°C and 50% relative humidity, one cohort of the test specimens produced was measured "initial" after pressing (see column 1 of Tables 1 and 2). Foaming was carried out using a hot plate at 150°C. In this case, another cohort of test specimens produced was placed on a hot plate preheated to 150°C for 1 minute. Due to the temperature input, the expandable microspheres expanded and the adhesive film foamed. For one cohort of test specimens, the push-out value was measured directly after foaming (see column 2 of Tables 1 and 2). Similarly, another cohort of test specimens was not measured after foaming, but was stored / repaired at room temperature (23°C) for 1 hour and only then subjected to the push-out test (see column 3 of Tables 1 and 2).

[0316] The test is as follows: a tensile testing machine is equipped with a cylindrical die (steel, 7 mm diameter) and the test sample is clamped into the mounting of the tensile testing machine via the substrate (2) in such a way that the substrate (1) is held only by bonding and can be separated by releasing the bond by sufficient pressure. The sample is fixed in such a way that any bending of the substrate (2) caused by the forces applied during the test is minimized. With the help of the cylindrical die, the sample is pressed vertically (i.e. parallel to and opposite to the normal vector of the adhesive product surface) and centrally through the hole in the substrate (2) onto the exposed surface of the adhesive product at a constant speed of 10 mm / min; the test is carried out under standard test conditions (23°C, 50% RH). The force at which the bond fails and the substrate (1) is separated from the substrate (2) is recorded (release of the adhesive bond, which can be identified by a sudden drop in force). The reported force is normalized to the bond area ( Due to the natural scatter of the individual results, due to the common occurrence of adhesive failure (failure at the substrate-adhesive film interface), and due to the high bond strengths generally achieved, often combined with deformation of the substrate and / or cold flow (structural bond strength), the arithmetic mean was calculated from three individual tests. The second row of the results table indicates the standard deviation of each measurement value, and the third row indicates the fracture mode (A: adhesive, C: cohesive, M: mixed fracture).

[0317] Table 1 (Comparative) Results of the Push-Out Test of Examples 1 to 4 and 6

[0318]

[0319] Table 1 shows that all comparative examples and all examples according to the invention have excellent initial bond strengths (see column 1), and that the bond strengths drop very sharply after the test specimens have been exposed to 150°C for 1 minute (see column 2). In the case of the comparative examples, this is solely due to the temperature, and the reduction in bond strength is reversible. After reconditioning the test specimens at 23°C for 1 hour, they return to their previous level (see column 3). In the examples according to the invention (see column 3), the increased temperature causes the microspheres to expand, and the resulting low bond strength remains constant even after cooling or reconditioning. The bond strength is reduced so much that the two substrates of the test specimens can be easily separated from each other, and the remaining tape can be separated without any residue.

[0320] Comparative Example 5 and Examples 5a, 5b, 5c and 5d

[0321]

[0322] Production Instructions Comparative Example 5 and Examples 5a to 5d:

[0323] The adhesive tape was produced from Dispercoll U53, Dispercoll BL XP 2514, Borchigel 0625, and Expancel 043 WU 80 in the amounts described in the table above. The formulation components were mixed as aqueous dispersions in a drum with an anchor stirrer at room temperature at 60 l / min for a period of 15 minutes. The solids content was adjusted to 46% by weight by adding demineralized water. The coatings were produced on various temporary supports using a web coating system using a doctor blade. The water was then removed in a drying tunnel at 40°C for 15 minutes.

[0324] Launch results:

[0325] Table 2 Comparative Example 1 and Examples 5a to 5d Push-out Test Results

[0326]

[0327] Table 2 shows that Comparative Example 5 and Examples 5a to 5d according to the invention have excellent initial bond strength (see column 1), and that the bond strength drops very sharply after the test specimens have been exposed to 150°C for 1 minute (see column 2). In the case of Comparative Example 5, this is solely due to the temperature, and the reduction in bond strength is reversible. After reconditioning the test specimens at 23°C for 1 hour, they return to their previous level (see column 3). In the case of Examples 5a to 5d according to the invention (see column 3), the increased temperature causes the microspheres to expand, and the resulting low bond strength remains constant even after cooling or reconditioning. The bond strength drops so much that the two substrates of the test specimen can be easily separated from each other, and the remaining adhesive tape can be separated without any residue.

Claims

1. An adhesive tape embodied and configured to be separated after permanent bonding, comprising or consisting of: at least one adhesive layer comprising a reactive structural adhesive, It is characterized by: The reactive structural adhesive includes expandable microspheres having an expansion onset temperature of at least 94°C.

2. The adhesive tape according to claim 1, It is characterized by: The reactive structural adhesive contains microspheres in an amount of 1 to 25 wt %, particularly 2 to 20 wt %, more preferably 5 to 10 wt %, and most preferably about 10 wt %.

3. The adhesive tape according to claim 1 or claim 2, It is characterized by: The onset temperature of the expandable microspheres is in the range of 94°C to 140°C, more preferably in the range of 95°C to 120°C, most preferably in the range of 100°C to 110°C.

4. The adhesive tape according to any one of claims 1 to 3, It is characterized by: The adhesive layer has a thickness of between 25 μm and 750 μm, in particular between 50 μm and 300 μm.

5. The adhesive tape according to any one of claims 1 to 4, It is characterized by: The expandable microspheres have a particle size D(0.5) of 16 to 24 μm.

6. The adhesive tape according to any one of claims 1 to 5, It is characterized by: The adhesive tape is an adhesive transfer tape and consists of an adhesive layer.

7. The adhesive tape according to any one of claims 1 to 6, It is characterized by: The reactive structural adhesive includes a polymer component formed from at least one thermoplastic polymer or elastomer.

8. The adhesive tape as claimed in claim 7, It is characterized in that The thermoplastic polymer is polyurethane.

9. The adhesive tape according to any one of claims 1 to 8, It is characterized by: The reactive structural adhesive further comprises at least one peroxide and wherein The polymer component comprises at least 50% by weight of a thermoplastic polymer having no C=C double bonds and no C≡C triple bonds.

10. The adhesive tape as claimed in claim 9, It is characterized by: The at least one peroxide has the general structural formula ROO-R', wherein R and R' each represent an organic group or together represent a cyclic organic group, And in The peroxide has a one minute half-life temperature in solution of less than 200°C.

11. The adhesive tape as claimed in claim 9 or claim 10, It is characterized by: The peroxide includes dicumyl peroxide.

12. The adhesive tape according to any one of claims 1 to 8, It is characterized by: The polymer component is formed from at least one polymer containing functional groups capable of reacting with isocyanate, and The adhesive further comprises a crosslinker component formed from at least one isocyanate-containing particulate compound.

13. The adhesive tape as claimed in claim 12, Also includes: At least one other component is selected from the group consisting of epoxides and / or epoxy compounds.

14. The adhesive tape according to any one of claims 1 to 7, It is characterized by: The reactive structural adhesive comprises a mixture of at least one nitrile rubber S1 and a reactive component, in particular a reactive resin.

15. Method for releasing a permanent structural bond of two substrates A and B, the permanent structural bond being produced with the aid of an adhesive tape as claimed in any one of claims 1 to 14, the method comprising the following steps: a) exposing the bonded substrate A / adhesive tape as claimed in any one of claims 1 to 14 / substrate B assembly to a temperature in the range of 115° C. to 150° C., preferably about 120° C.; and b) separating the adhesive tape from at least one substrate, preferably from at least two substrates.

16. The method according to claim 15, wherein In step a), the temperature is brought about by using a hot plate, a hot press, an oven, a laser, IR radiation or induction, preferably by using a hot plate.

17. The method of claim 15 or claim 16, wherein: The remaining portion of the adhesive layer was removed without residue.

18. Use of the adhesive tape as claimed in any one of claims 1 to 14 in the automotive industry.

19. Use of the adhesive tape according to any one of claims 1 to 14 in the electronics industry.

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