Reactive-adhesive tape for easy detaching

Abstract

The invention relates to an adhesive tape, designed and equipped to be removed after permanent bonding, comprising at least an adhesive layer that includes a reactive, structural adhesive, and to a method for detaching a permanent structural bond produced by such an adhesive tape.

Description

[0001] Reactive adhesive tape for easy removal

[0002] The present invention relates to an adhesive tape designed and configured to be separated after permanent bonding, comprising or consisting of at least one adhesive layer comprising a reactive, structural adhesive. Furthermore, the present invention encompasses a method for releasing a permanent structural bond created by such an adhesive tape.

[0003] In repair workshops and in the end-of-life recycling of electronic devices, the desire to be able to repair electronic devices or even automobiles or to dismantle and / or recycle them as far as possible is becoming increasingly important for ecological as well as economic reasons.

[0004] There are different types of electronic devices that differ in their recyclability and recycling rate:

[0005] • Large household appliances (also called white goods): for example washing machines, refrigerators and freezers, cookers;

[0006] • Small household appliances (also considered white goods): for example vacuum cleaners, coffee machines, microwaves;

[0007] • Information and communication technology devices: for example, computers, monitors, printers, mobile phones, telephones;

[0008] • Consumer electronics devices (also called brown goods): for example, televisions, video recorders, digital cameras.

[0009] Electrical and electronic devices, in particular, contain a multitude of substances and materials. If waste electrical and electronic devices are not disposed of properly, for example, with household waste, they can pose environmental risks due to the pollutants they sometimes still contain. In addition to pollutants such as heavy metals and CFCs, waste electrical and electronic devices also contain a number of valuable materials that need to be recovered and thus recycled. If waste electrical and electronic devices are disposed of properly, primary raw materials (and thus their costly extraction) can be replaced, making a significant contribution to conserving natural resources.

[0010] To achieve these goals, the German Act on the Placing on the Market, Return, and Environmentally Sound Disposal of Electrical and Electronic Equipment (ElektroG), implementing Directive 2012 / 19 / EU on Waste Electrical and Electronic Equipment (WEEE), establishes specific obligations for all relevant stakeholders (manufacturers, retailers, municipalities, owners, and disposal companies). Through waste prevention, reasonable testing of the possibilities for preparing entire devices or individual components for reuse, and requirements for the further recycling of waste, a significant contribution is to be made to conserving natural resources and reducing pollutant emissions.

[0011] Appropriate recycling-friendly designs are necessary that allow for debonding on demand. Recycling-friendly designs also include removable adhesive bonds. This is because, especially in small electronic devices, the trend toward permanently bonding parts structurally rather than mechanically detachably connecting them is rapidly increasing. As a rule, these components are intended to be permanently joined together using such structural bonding (according to DIN EN 923: 2006-01, structural bonding is demonstrably suitable for the production of load-bearing structures in which the adhesive bond can be subjected to a high percentage of the maximum breaking force over extended periods without failure). This should lead to a corresponding longevity and resilience of the bond or the product.Examples of components bonded in this way include touch panels, such as those used in computer monitors or mobile electronic devices. If one of the two components becomes damaged, the bonded assembly cannot be separated for component replacement or can only be separated with considerable effort (or force). There is also a risk that the undamaged component may be damaged during the separation process.

[0012] Thus, there is a need for an adhesive tape with unique properties, particularly with regard to their use in electronic devices, automotive devices, and medical devices, which, on the one hand, enables a permanent and secure (structural) bond between two components, while, on the other hand, allowing for a clean and secure separation of the components when necessary. A common problem with separating the components or the bond is that the removed adhesive tape rebonds under slight pressure, making separation of the bond difficult or messy. Furthermore, ideally, a substantially residue-free removal must be possible, which is only possible with a few adhesive tapes.

[0013] Removable adhesives or adhesive tapes are generally known in the state of the art, but especially in the field of pressure-sensitive adhesives.

[0014] For example, the company Tesa sells the tesa® Powerstrips (adhesive) adhesive strips with which objects can be easily attached to walls and the Powerstrips can later be removed without leaving any residue by slowly pulling the Powerstrip out using the handle parallel to the surface.

[0015] For example, EP 612 823 A1 discloses an adhesive film with at least three layers that can be easily removed from the adhered material by heat treatment. The adhesive film consists of a substrate with one (or two) pressure-sensitive elastic layer(s) made of synthetic or natural rubber, a heat-expandable layer containing foaming agents, and an adhesive layer. The advantage of this film is both its excellent adhesion to the adhered material and its excellent decrease in adhesion after heat treatment.

[0016] EP 1 033 393 A2 discloses a heat-removable, pressure-sensitive, two-layer adhesive film whose adhesive strength can decrease upon heating and can therefore be easily removed from an adhesive surface without contamination. The adhesive film comprises a heat-expandable layer containing heat-expandable microspheres that expands upon heating, and a non-heat-expandable pressure-sensitive adhesive layer thereon.

[0017] EP 1332191 A2 discloses a heat-peelable, pressure-sensitive adhesive film comprising a base material and a thermally expandable, pressure-sensitive adhesive layer containing thermally expandable microspheres. These microspheres partially have a particle size larger than the thickness of the thermally expandable, pressure-sensitive adhesive layer, and thus the adhesive surface has a specific roughness and a convex portion. This results in the adhesive film exhibiting excellent releasability after heating while maintaining excellent adhesion before heating, even when the surface area of ​​the adherend is relatively large.

[0018] WO 2021 / 176376 A1 discloses a method for removing a pressure-sensitive adhesive bond at a temperature between 100 °C and 150 °C. The bonding was achieved using a primer, and the choice of primer influences the removability.

[0019] The object of the present invention is therefore to provide an adhesive tape which, on the one hand, enables a permanent and secure (structural) bonding of two components to one another, but, on the other hand, enables a clean and secure separation of the components if necessary.

[0020] A further object of the present invention is therefore to provide an adhesive tape which, on the one hand, enables a permanent and secure (structural) bonding of two components to one another, but, on the other hand, allows a clean and secure separation of the components if necessary and does not re-bond to the component or components after separation.

[0021] A further object of the present invention is therefore to provide an adhesive tape which, on the one hand, enables a permanent and secure (structural) bonding of two components to one another, but, on the other hand, allows a clean and secure separation of the components if necessary and the adhesive tape can be removed from the component(s) without leaving any residue.

[0022] This object is achieved according to the invention by an adhesive tape as described in claim 1. Advantageous embodiments are recited in the subclaims. Furthermore, the invention includes a method for releasing a permanent structural bond between two components, achieved by means of an adhesive tape according to the invention, by heating the adhesive tape or heating the two 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] Accordingly, the present invention relates to an adhesive tape designed and configured to be separated after permanent structural bonding, comprising or consisting of at least one adhesive layer comprising a reactive, structural adhesive, characterized in that the reactive, structural adhesive comprises expandable microballoons having a starting temperature required for expansion of at least 94 °C.

[0024] The inventors have surprisingly discovered that after foaming the microballoons at temperatures of 115°C or more, the structural bond can be easily released; surprisingly, even residue-free detachment or removal from the substrate(s) is possible. Furthermore, the inventors have surprisingly discovered that incorporating expandable microballoons into a structural adhesive has no negative impact on the initial strength of the structural bond, and that the reactive adhesive tape can be processed without problems at conventional temperatures (in the range of 90°C to 100°C).

[0025] The foaming of the microballoons, which is necessary for easy release of the structural bond, takes place at temperatures of 115°C or more. Typical foaming temperatures are in the range of 120°C to 150°C, and the appropriate foaming temperature can be easily selected by a specialist based on their expertise. The heat input for foaming the microballoons can be achieved using conventional heat sources, such as a hot plate (heat press), oven, laser, IR radiation, or induction.

[0026] The at least one adhesive layer comprises a reactive, structural adhesive containing expandable microballoons. The microballoons in the structural, reactive adhesive have an initial expansion temperature of at least 94 °C.

[0027] In general, a reactive adhesive is understood to be an adhesive that cures under external influence, in particular under the influence of moisture or high-energy radiation or heat, to a technically relevant extent or with a significant change in at least one application-related property, thereby achieving structural bond strengths that significantly exceed the level of conventional pressure-sensitive adhesives or conventional pressure-sensitive adhesive tapes. Such adhesives are referred to as reactive structural adhesives in the context of this invention.

[0028] In principle, all known reactive or latent-reactive adhesives that lead to structural bonding are suitable as adhesives, hereinafter referred to as "reactive, structural adhesives," but especially heat-activated adhesives. Heat-activated adhesives can generally be divided into two categories: thermoplastic heat-activated adhesives and reactive heat-activated adhesives. a) Thermoplastic heat-activated adhesives, preferably with chemical bonding. Thermoplastic heat-activated adhesives (also called "hotmelt adhesives") are not or only weakly self-adhesive at room temperature. The adhesive is only activated by heat, melts, becomes flowable, and flexible.This is due to the adhesive's correspondingly high glass transition temperature, meaning that the activation temperature required to achieve sufficient tack is usually several tens to hundreds of degrees Celsius above room temperature. Due to the self-adhesive properties, an adhesive effect occurs even before the adhesive has set. After joining, these adhesives harden upon cooling and solidify physically (usually reversibly; thermoplastic materials), and possibly also chemically (usually irreversibly; thermoplastic-reactive materials), so that the adhesive effect is retained even in the cooled state and develops its final strength there. The more heat, pressure and / or time applied during the bonding process, the stronger the bond between the two materials to be bonded generally becomes.This allows maximum bond strengths to be achieved under technically easy processing conditions. Thermoplastics are defined as compounds as defined in Römpp (online version; 2016 edition, document ID RD-20-01271).

[0029] The described thermoplastic heat-activatable adhesives do not count as reactive structural adhesives within the meaning of this invention. b) Reactive heat-activatable adhesives

[0030] Reactive heat-activated adhesives (also referred to as "reactive adhesives") are polymer systems that contain functional groups such that a chemical reaction occurs upon application of heat, whereby the adhesive chemically sets and thus creates the adhesive effect. Reactive heat-activated adhesives generally do not become self-adhesive upon application of heat, so that the adhesive effect only occurs after setting. Reactive heat-activated adhesives are often not thermoplastic, but are realized using an elastomer-reactive resin system. The glass transition temperature is not important for the functionality of reactive systems. It can also be advantageous to design the reactive materials so that they become softer and / or more flowable at elevated temperatures in order to optimally adapt to the adhesive bond; this can be achieved, for example, using a thermoplastic component.Reactive heat-activatable adhesives are among the reactive structural adhesives within the meaning of this invention. Various reactive heat-activatable adhesives are described below that are outstandingly suitable as base adhesives for the reactive structural adhesive of the adhesive tape of the invention. Expandable microballoons, which have an initial expansion temperature of at least 94°C (required for expansion), are added to the base adhesives to obtain the reactive structural adhesive of the invention.

[0031] The reactive, structural adhesive of the adhesive tape according to the invention accordingly comprises expandable microballoons that have a required initial expansion temperature of at least 94°C and a base adhesive (the possible composition of which is described below). For the purposes of this invention, the base adhesive refers to the reactive, structural adhesive without the expandable microballoons.

[0032] For the purpose of the best possible processability by the end user, it is generally desirable for reactive adhesives themselves to have at least weakly pronounced pressure-sensitive adhesive properties; for example, if vertical or overhead processing is necessary. Therefore, the reactive, structural adhesive in the context of this invention can be pressure-sensitive (tacky) or can have pressure-sensitive adhesive properties, i.e. the property of forming a permanent bond to a substrate even under relatively light pressure. However, it is also possible for the reactive, structural adhesive to have no pressure-sensitive adhesive properties. This is useful if good (re-)positionability is desired; in such a case, it is preferred for the adhesive to be non-tacky at room temperature.Therefore, in a preferred embodiment, the reactive, structural adhesive of the adhesive tape according to the invention is not pressure-sensitively adhesive at room temperature or has no pressure-sensitive adhesive properties.

[0033] Without wishing to be bound by any theory, it is often assumed that a pressure-sensitive adhesive can be viewed as an extremely viscous liquid with an elastic component, which consequently exhibits characteristic viscoelastic properties that lead to permanent intrinsic tack and pressure-sensitive adhesive capacity. It is assumed that with corresponding pressure-sensitive adhesives, mechanical deformation leads to both viscous flow processes and the build-up of elastic restoring forces. The partial viscous flow serves to achieve adhesion, while the partial elastic restoring forces are particularly necessary to achieve cohesion. The relationships between rheology and pressure-sensitive tack are known in the art and are described, for example, in "Satas, Handbook of Pressure Sensitive Adhesives Technology", Third Edition, (1999), pages 153 to 203.To characterise the degree of elastic and viscous components, the storage modulus (G') and the loss modulus (G") are usually used, 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 and thus a pressure-sensitive adhesive if, at a temperature of 23°C in the deformation frequency range from 10° to 10. 1 rad / sec G' and G“ each at least partly in the range of 10 3 up to 10 7 Pa lie.

[0034] In one embodiment, the reactive structural adhesive of the invention comprises a polymer component formed from at least one thermoplastic polymer or an elastomer. Preferably, the thermoplastic polymer is a polyurethane.

[0035] According to one variant of the invention, a reactive adhesive or base adhesive is suitable as the reactive structural adhesive according to the invention, which comprises a polymer component formed from at least one thermoplastic polymer or an elastomer, 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 such thermoplastic polymers which have no C=C double bonds and no C=C triple bonds.

[0036] Such a base adhesive and an adhesive tape made therefrom are disclosed and described in detail in WO 2019 / 207125 A1.

[0037] Peroxides are then selected for which the 1-minute half-life temperature T(ti / 2 = 1 min) in solution (0.1 molar in monochlorobenzene) does not exceed 200 °C, preferably does not exceed 190 °C, very preferably does not exceed 180 °C.

[0038] The peroxides are in particular those which - in addition to meeting the above definition - also carry an organyl group on each oxygen atom. Accordingly, compounds of the general structure ROOR* are used as peroxides, where the radicals R and R' are organyl groups which can be chosen independently of one another or can be identical, and where R and R' can also be linked to one another so that a cycle is formed via the peroxy group (-OO-), so that a structure of the type results.

[0039] Organyl groups are organic residues - regardless of which functional group they contain - with one or, more rarely, several free valences on a carbon atom.Examples of these are acetonyl groups, acyl groups (for example acetyl groups, benzoyl groups), alkyl groups (for example methyl groups, ethyl groups), alkenyl groups (for example vinyl groups, allyl groups), alkynyl groups (propargyl groups), aminocarbonyl groups, ampicilloyl groups (residues derived from ampicillin), aryl groups (for example phenyl groups, 1-naphthyl groups, 2-naphthyl groups, 2-thiophenyl groups, 2,4-dinitrophenyl groups), alkylaryl groups (for example benzyl groups, triphenylmethyl groups), benzyloxycarbonyl groups (Cbz), tert-butoxycarbonyl groups (Boc), carboxy groups, (fluoren-9-ylmethoxy)carbonyl groups (Fmoc), furfuryl groups, glycidyl groups, haloalkyl groups (for example chloromethyl groups, 2,2,2-trifluoroethyl groups), indolyl groups, nitrile groups, Nucleosidyl groups, trityl groups, to name just a few.

[0040] Peroxides of the general structure ROOR* (also in cyclic form), for example, have the advantage over hydroperoxides that they do not release water in the form of primary decomposition products upon thermal activation of the adhesive. It is desirable to reduce volatile components with boiling points above 150 °C, preferably with boiling points above 120 °C, as much as possible, preferably to avoid them completely, in particular to prevent blistering in the bonded joint and thus its weakening. Accordingly, R and R' of the peroxides should particularly preferably be selected such that they also do not lead to the formation of highly volatile primary decomposition products—such as carbon dioxide or isopropanol.

[0041] In a preferred embodiment of this variant, the reactive, structural adhesive according to the invention comprises expandable microballoons which have an initial temperature required for expansion of at least 94°C; furthermore 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 thermoplastic polymers which have no C=C double bonds and no C=C triple bonds; wherein the at least one peroxide has the general structural formula ROOR', wherein R and R' each represent organyl groups or together represent a cyclic organyl group; and; wherein the peroxide in solution has a 1-minute half-life temperature of less than 200°C.

[0042] Adhesive layers produced from such a reactive, structural adhesive have proven to be excellently suited for prelamination and can be activated in the hot-pressing step to develop the final bond strength. This means that they possess the capacity for chemical reaction, in particular a rapid crosslinking and / or curing reaction, after appropriate activation. Activation occurs primarily thermally, i.e., through the application of heat. In principle, other activation methods—such as inductive, microwave, UV irradiation, laser treatment, and plasma treatment—are also known for latent-reactive adhesive tapes. However, activation very preferably occurs through the application of thermal energy, and the other activation methods can be used, in particular and optionally, in a complementary (additive) manner, for example, by admixing UV photoinitiators into the adhesive.

[0043] When heat is applied, the adhesive melts and provides excellent wetting of the substrate surfaces to be bonded. The crosslinking or curing reaction increases the adhesive's cohesion. This is achieved by using thermoplastic base polymers.

[0044] Thanks to the reactive bonding, the adhesive tapes are capable of generating high bond strengths to the substrates to which they are bonded. These bond strengths can, for example, exceed those of conventional pressure-sensitive adhesives by a factor of 10 or more.

[0045] At least one peroxide, or several peroxides used, are selected such that they exhibit comparatively high decomposition rates or short half-lives [ti / 2] at elevated temperatures – temperatures above their activation temperature. The decomposition rate of the peroxides is a characteristic criterion for their reactivity and is quantified by specifying the half-lives at specific temperatures [ti / 2(T)]. The half-life, as usual, represents the time after which half of the peroxide has decomposed under the given conditions. The higher the temperature, the shorter the half-life of the decomposition. Therefore, the higher the decomposition rate, the shorter the half-life.The half-life temperature [T(ti / 2)J] is the temperature at which the half-life corresponds to a given value, for example the 10-hour half-life temperature [T(ti / 2=1 Oh)] is the temperature at which the half-life of the substance under investigation is exactly 10 hours, the 1-minute half-life temperature [T(ti / 2=1 min)] is the temperature at which the half-life of the substance under investigation is exactly 1 minute, and accordingly.

[0046] The at least one peroxide, or the several peroxides used, are selected such that the 1-minute half-life temperature T(ti / 2= 1 min) in solution does not exceed 200 °C, preferably does not exceed 190 °C, very preferably does not exceed 180 °C.

[0047] The above condition is considered to be fulfilled in particular if the peroxide in question has a corresponding half-life temperature value at least in monochlorobenzene (0.1 molar solution).

[0048] Such half-lives can be determined experimentally (concentration determination using DSC or titration) and can also be obtained from the relevant literature. The half-lives can also be calculated from the specific constants for the respective peroxide, the Arrhenius frequency factor and the decay activation energy, for the given conditions. The following relationships apply:

[0049] - dc / dt = kc [1]

[0050] In (ci / c0) = -kt [2] ti / 2= In2 / k for c t (ti / 2) = c0 / 2 [3} k = A e Ea / RT [4] where Co = initial concentration c t = Concentration at time t

[0051] Ct(ti / 2) = concentration at half-life ti / 2 = half-life k = decay constant

[0052] A = Arrhenius frequency factor

[0053] Ea = activation energy for peroxide decomposition

[0054] R = general gas constant (R = 8.3142 J / (mol K))

[0055] T = absolute temperature The half-lives and half-life temperatures stated in this document refer to a 0.1 molar solution of the corresponding peroxide in monochlorobenzene, unless otherwise stated.

[0056] Using the constants Arrhenius frequency factor and decay activation energy, which can be researched for the respective conditions - such as the solvent used - or calculated from researched values, the half-lives and half-life temperatures can be converted to other conditions - such as in other solvents - and thus made comparable.

[0057] Preference is given to using peroxides that also have long half-lives at moderate temperatures—especially those significantly below their activation temperatures. This allows good latency behavior, i.e., good storage stability, of the thermally activatable adhesive films comprising the peroxides to be achieved. Accordingly, the at least one peroxide, or the several peroxides used, are selected such that their half-life at 80°C—i.e., for example, after a pre-lamination process—is at least 13.5 hours, in particular at least 22.5 hours, preferably at least 69 hours, and particularly preferably at least 700 hours.This enables the thermally activatable adhesive tape to have a sufficient processing and application time at 80 °C, in that after one hour at least 95% of the peroxide originally used (corresponding to ti / 2 = 13.5 h), in particular at least 97% (corresponding to ti / 2 = 22.5 h), preferably at least 99% (corresponding to ti / 2 = 69 h), particularly preferably at least 99.9% of the peroxide used is still present and thus not yet available for a reaction.

[0058] Such reactive, structural adhesives are preferably latent-reactive. Activatable adhesive systems are those that can be stored stably for extended periods without activation. Latent-reactive adhesive tapes are those that do not cure or only cure for a period of months under normal climate conditions (23 °C [296.15 K]; 50% RH) and particularly at elevated storage temperatures (especially up to 40 °C [316.15 K]) and are therefore storage-stable, but which can be activated and cure and / or crosslink at significantly higher temperatures. To guarantee a storage-stable system, the half-life under normal storage conditions - which can usually be up to 40 °C - should be high. Therefore, the peroxides used should preferably be selected such that their half-life at the storage temperature, preferably up to 40 °C, is sufficiently long that after 9 months (274 days) at least75%, preferably 85%, particularly preferably 95%, or most particularly preferably more than 95% of the peroxide is available for crosslinking. The corresponding half-lives can be determined using the relationships mentioned above.

[0059] Suitable peroxides are, for example, representatives from the following groups: dialkyl peroxides, diacyl peroxides, peroxy esters, peroxydicarbonates, peroxyketals, cyclic peroxides, for which the stated values ​​are realized with respect to 1-minute half-life temperature, preferably also with respect to half-life at 80 °C, more preferably also with respect to half-life at 40 °C.

[0060] The following are examples of some advantageously used representatives from the various groups for which this applies:

[0061] Dialkyl peroxides: di-tert.amyl peroxide, di-tert. -Butyl peroxide, tert-butyl cumyl peroxide,

[0062] Dicumyl-peroxid, 2,5-Dimethyl-2,5-di-(tert.-Butylperoxy)-hexan, 2,5- Dimethyl-2,5-di(tert.-butylperoxy)-hexyn-3, Di-(2-tert.-Butyl-peroxyiso- propyl)-benzen;

[0063] Diacylperoxide: Dibenzoylperoxid, Dilauroylperoxid, Diisobutyrylperoxid, Didecanoyl- peroxid, Di-(3,5,5-trimethyl-hexanoyl)-peroxid;

[0064] Ketonperoxide: Acetylacetonperoxid, Cyclohexanonperoxid, Methylethylketonperoxid,

[0065] Methyl-isobutylketon-peroxid;

[0066] Peroxyester: tert.- Butylperoxyacetat, tert.-Butylperoxybenzoat, tert.-Butylperoxy- diethylacetat, tert.-Amyl-peroxy-2-ethylhexylcarbonat, tert.-Butylperoxy- isopropylcarbonat, tert.-Butylperoxy-2-ethylhexyl-carbonat, tert.-Amyl- peroxy-2-ethylhexanoat, tert.-Butylperoxy-2-ethylhexanoat, 1 ,1 ,3,3- Tetramethylbutylperoxy-2-ethylhexanoat, tert.-Butylperoxy-3,5,5- trimethylhexanoat, tert.-Butyl-peroxyisobutyrat, tert.-Butylmonoperoxy- maleat, tert.-Amylperoxineodecanoat, tert.-Butyl-peroxyneodecanoat, Cumolperoxyneodecanoat, 1 ,1 ,3,3-Tetramethylbutyl-peroxyneodeca- noat, tert.-Butylperoxyneoheptanoat, tert.-Amylperoxypivalat, tert.- Butylperoxypivalat, 1 ,1 ,3,3-Tetramethylbutylperoxypivalat, 2,5-Di- methyl-2,5-di(2-ethylhexanoylperoxy)-hexan;

[0067] Peroxidicarbonate: Di-n-peroxidicarbonat, Di-(2-ethylhexyl)-peroxydicarbonat, Di-n- butylperoxy-dicarbonat, Dicetyl-peroxydicarbonat, Dimyristylperoxy- dicarbonat, Di-(4-tert.-Butylcyclohexyl)-peroxydicarbonat;

[0068] Peroxyketals: 1,1-di-(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di-(tert-butylperoxy)cyclohexane, 2,2-di-(tert-butylperoxy)butane; Cyclic peroxides. 3,6,9-Triethyl-3,6,9-trimethyl-1,4,7-triperoxonane.

[0069] Dicumyl peroxide (bis(1-methyl-1-phenylethyl)peroxide) is particularly advantageously used, which has the following half-lives: 812 h at 80 °C (corresponding to less than 0.1% of the original amount of peroxide at 80 °C within one hour), 10 h at 112 °C; 1 h at 132 °C; 0.1 h = 6 min at 154 °C; 1 min at 172 °C; all of the above values ​​in solution (0.1 molar monochlorobenzene).

[0070] Dicumyl peroxide is particularly preferred because it allows adhesive tapes to be obtained that are particularly stable in storage and also resistant to humid heat.

[0071] Therefore, in a particularly preferred embodiment of this variant, the reactive, structural adhesive according to the invention comprises expandable microballoons which have a starting temperature required for expansion of at least 94 °C; furthermore 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 wt. %, based on the total weight of the polymer component, of such thermoplastic polymers which have no C=C double bonds and no C=C triple bonds; wherein the at least one peroxide has the general structural formula ROOR', wherein R and R' each represent organyl groups or together represent a cyclic organyl group; wherein the peroxide in solution has a 1-minute half-life temperature of less than 200 °C; and wherein the peroxide comprises dicumyl peroxide.

[0072] Two or more peroxides can also be used. In this case, dicumyl peroxide is preferred as one of the two or more peroxides.

[0073] The peroxide(s) used, in particular dicumyl peroxide, are preferably selected - particularly depending on their reactivity - in an amount such that the resulting bond created with the adhesive tape has the desired properties and in particular meets the specifications in the push-out tests defined in more detail below (as a fresh sample at least 4 MPa, preferably even after defined storage in humid heat at least 3 MPa, more preferably after six weeks of storage in a standard climate no more than 10% loss, even further after six weeks of storage and storage in humid heat no more than 10% loss, see the respective information below for details). In order to meet these requirements, peroxide amounts - for example the amount of dicumyl peroxide - of at least 0.5 wt.%, advantageously at least 1 wt.%, particularly advantageously at least 2 wt.%, very particularly advantageously at least 3 wt.%, and at most 10 wt.% have proven to be suitable.-%, preferably a maximum of 8 wt.%, very preferably a maximum of 7 wt.%, based on the total weight of the base adhesive, has been found to be very advantageous.

[0074] Peroxides that do not meet the requirements include, for example, a variety of hydroperoxides, i.e., compounds of the general formula ROOH, where R is an organyl group. Accordingly, an adhesive tape according to the invention is preferred, wherein the latent-reactive adhesive is essentially free of hydroperoxides, wherein the proportion of hydroperoxides is 0.0001 wt.% or less, based on the total weight of the base adhesive.

[0075] The list of hydroperoxides that do not lead to the desired success includes, for example, cumene hydroperoxide, tert-butyl hydroperoxide, p-menthane hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, tert-amyl hydroperoxide, diisopropylbenzene monohydroperoxide.

[0076] It has been shown that these hydroperoxides are unable to form a good crosslinking effect during thermal activation of the adhesive within a sufficiently short processing time, thus producing the desired benefits. Furthermore, hydroperoxides can release volatile primary decomposition products upon thermal exposure (see also above).

[0077] In this variant of the invention, the latently reactive base adhesive comprises a polymer component consisting of a single polymer or composed of several polymers. At least one of the polymers forming the polymer component is a thermoplastic polymer that has no carbon-carbon double bonds or carbon-carbon triple bonds, i.e., it is a saturated polymer.

[0078] Saturated thermoplastic polymers make up at least 50 wt.% of the polymer component and can amount to up to 100 wt.% of the polymer component (based on the total weight of the polymer component), so that in the latter case, the polymer component is formed exclusively by one or more saturated thermoplastic polymers. If only one thermoplastic polymer is present, it is present in the polymer component in a proportion of 50 wt.% to 100 wt.%. The reactive, structural adhesive can be composed exclusively of the polymer component and the peroxide(s), in addition to the expandable microballoons.

[0079] Very preferably, polymers are used whose glass transition temperature is not more than -25 °C, particularly preferably not more than -35 °C. All information on glass transition temperatures in this document refers to the determination of the static glass transition temperature T Gby means of dynamic differential calorimetry (DSC) according to DIN 53765, namely to the glass transition temperature value T g according to DIN 53765:1994-03, unless otherwise stated in individual cases.

[0080] Low glass transition temperatures of the polymers used have had a beneficial effect on the good shock resistance properties of the composites produced with the corresponding adhesive tapes.

[0081] Suitable saturated thermoplastic polymers can advantageously be selected from the group of polyolefins (e.g., ethylene-vinyl acetate copolymers (EVA)), polyethers, copolyethers, polyesters, copolyesters, polyamides, copolyamides, polyacrylic acid esters, acrylic acid ester copolymers, polymethacrylic acid esters, methacrylic acid ester copolymers, thermoplastic polyurethanes, and chemically or physically crosslinked substances of the aforementioned compounds. Blends of various thermoplastic polymers, particularly from the aforementioned compound classes, can also be used. Semicrystalline (partially crystalline) thermoplastic polymers are particularly preferred.

[0082] Preferred examples are, in particular, semicrystalline polyolefins. Preferred polyolefins are produced from ethylene, propylene, butylene, and / or hexylene, whereby the pure monomers can be polymerized or mixtures of the monomers mentioned can be copolymerized. The polymerization process and the selection of the monomers allow the physical and mechanical properties of the polymer to be controlled, such as the softening temperature and / or specific mechanical properties.

[0083] Thermoplastic elastomers can preferably be used as thermoplastic polymers, either alone or in combination with one or more thermoplastic polymers from the aforementioned classes of compounds. Saturated semicrystalline thermoplastic elastomers are particularly preferred. Thermoplastic polymers with softening temperatures of less than 100°C are particularly preferred. In this context, the term "softening point" refers to the temperature at which the thermoplastic granules bond to themselves. Semicrystalline thermoplastic polymers advantageously have, in addition to their softening temperature (related to the melting of the crystallites), a glass transition temperature of at most 25°C, particularly as characterized above.

[0084] Very advantageous examples of thermoplastic elastomers in the sense of thermoplastic polymers are thermoplastic polyurethanes (TPII). Polyurethanes are polycondensates typically composed of polyols and isocyanates and containing soft and hard segments. The soft segments consist, for example, of polyesters, polyethers, polycarbonates, each preferably aliphatic in nature, and polyisocyanate hard segments. Depending on the type and ratio of the individual components, materials are available that can be used advantageously. Raw materials available to the skilled person for this purpose are mentioned, for example, in EP 0 894 841 B1 and EP 1 308 492 B1.

[0085] In a preferred embodiment of the invention, a thermoplastic polyurethane without multiple carbon-carbon bonds is used. The thermoplastic polyurethane preferably has a softening temperature of less than 100°C, in particular less than 80°C.

[0086] In a further preferred embodiment, a mixture of two or more saturated thermoplastic polyurethanes is used. The mixture of thermoplastic polyurethanes preferably has a softening temperature of less than 100°C, in particular less than 80°C.

[0087] In a particularly preferred embodiment, Desmomelt® 530 is used as the saturated thermoplastic polymer. Desmomelt® 530 is a largely linear, thermoplastic, highly crystallizing polyurethane elastomer commercially available from Covestro AG. Desmomelt can also be used together with other polymers—especially saturated thermoplastic polymers, preferably other saturated thermoplastic polyurethanes.

[0088] At least one adhesion-enhancing additive—also known as an adhesion promoter—is preferably added to the adhesive. Adhesion promoters are substances that improve the adhesive strength of the adhesive tape to the substrate to be bonded. This can be achieved, in particular, by increasing the wettability of the substrate surfaces and / or by forming chemical bonds between the substrate surface and the adhesive or components of the adhesive.

[0089] An advantageous embodiment relates to a base adhesive which is composed exclusively of the polymer component, the peroxides and the adhesion promoter - the latter in particular in the form of the silanes described below - and here in particular in such a way that exclusively one or more - in particular semi-crystalline - saturated thermoplastic polymers are used as the polymer component.

[0090] Silane coupling agents can be used advantageously as coupling agents. Compounds of the general form RR' are particularly suitable as coupling agents. a R“bSiX(3- a -b) where R, R' and R" are selected independently of one another and each denote a hydrogen atom bonded to the Si atom or an organic functionalized radical bonded to the Si atom, X denotes a hydrolyzable group, a and b are each 0 or 1, and where R, R' and R" or two representatives of this group can also be identical.

[0091] Compounds can also be used as adhesion promoters in which, in the presence of several hydrolyzable groups X, are not identical but differ from each other [according to the formula RR' a R“bSiXX' cX"d , with X, X', X" being independently selected hydrolyzable groups (of which two may be identical), c and d are each 0 or 1, with the proviso that a + b + c + d = 2.

[0092] Alkoxy groups are particularly used as hydrolyzable groups, so alkoxysilanes are particularly well-suited for use as adhesion promoters. The alkoxy groups of a silane molecule are preferably identical, but they can in principle be chosen differently.

[0093] Alkoxy groups, for example, are methoxy and / or ethoxy groups. Methoxy groups are more reactive than ethoxy groups. Methoxy groups can therefore provide better adhesion promotion due to faster reaction with the substrate surfaces, and the amount used can therefore be reduced if necessary. Ethoxy groups, on the other hand, have the advantage that, due to their lower reactivity, they have a smaller (possibly negative) impact on processing time, especially with regard to the desired moisture-heat stability.

[0094] Trialkoxysilanes R-SiX3 are preferred as adhesion promoters. Examples of suitable trialkoxysilanes are

[0095] Trimethoxysilane - wie N-(2-Aminoethyl)-3-aminopropyl-trimethoxysilan, N-Cyclohexyl-3- aminopropyl-trimethoxysilan, 3-Aminopropyl-trimethoxysilan, 3-llreidopropyl-trimethoxysilan, Vinyltrimethoxysilan, 3-Glycidoxypropyl-trimethoxysilan, 3-Methacryloxypropyl-trimethoxy- silan, Methacryloxymethyl-trimethoxysilan, N-Methyl-[3-(Trimethoxysilyl)propyl] carbamat, N- T rimethoxysilylmethyl-O-methylcarbamat, T ris-[3-(trimethoxysilyl)propyl]-isocyanurat, 3- Glycidoxypropyl-trimethoxysilan, Methyltrimethoxysilan, Isooctyltrimethoxysilan, Hexadecyl- trimethoxysilan, 3-Mercaptopropyl-trimethoxysilan, 3-Aminopropyl-trimethoxysilan, N-(2- Aminoethyl)-3-Aminopropyl-trimethoxysilan, N-Phenyl-3-aminopropyl-trimethoxysilan, N- Ethyl-3-aminoisobutyl-trimethoxysilan, Bis-[3-(trimethoxysilyl)propyl]amin, 3-lsocyanato- propyl-trimethoxysilan, 2-(3,4-Epoxycyclohexyl)-ethyl-trimethoxysilan;3-Methacryloxypropyl- trimethoxysilan, 3-Methacrylamidopropyl-trimethoxysilan, p-Styryltrimethoxysila, 3-Acryloxy- propyl-trimethoxysilan, N-(Vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilan hydro- chlorid; Triethoxysilane - wie N-Cyclohexyl-aminopropyl-triethoxysilan, 3-Aminopropyl- triethoxysilan, 3-llreidopropyl-triethoxysilan, 3-(2-Aminomethyl-amino)propyl-triethoxysilan, Vinyltriethoxysilan, 3-Glycidoxypropyl-triethoxysilan, Methyltriethoxysilan, Octyltriethoxysilan, Isooctyltriethoxysilan, Phenyltriethoxysilan, 1 ,2-Bis(triethoxysilan)ethan, 3-Octanonylthio-1- propyl-triethoxysilan; 3-Aminopropyl-triethoxysilan, Bis-[3-(triethoxysilyl)propyl]amin, 3- Isocyanatopropyl-triethoxysilan, 2-(3,4-Epoxycyclohexyl)-ethyl-triethoxysilan, 3- Methacryloxypropyl-triethoxysilan, 3-Methacrylamidopropyl-triethoxysilan, 3-Triethoxysilyl-N- (1 ,3-dimethylbutadien)propylamid; Triacetoxysilane - wie Vinyltriacetoxysilan, 3- Methacryloxypropyl-triacetoxysilan, Triacetoxyethylsilan;gemischte Trialkoxysilane - wie 3-Methacrylamidopropyl-methoxy-diethoxysilan, 3-Methacryl- amidopropyl-dimethoxy-ethoxysilan.;

[0096] Beispiele für geeignete Dialkoxysilane sind

[0097] Dimethoxysilane - wie N-(2-Aminoethyl)-3-aminopropyl-methyldimethoxysilan, Vinyldi- methoxy-methylsilan, (Methacryloxymethyl)-methyldimethoxysilan, Methacryloxymethyl- methyl-dimethoxysilan, 3-Methacryloxypropyl-methyldimethoxysilan, Dimethyldimethoxysilan, (Cyclohexyl)methyldimethoxysilan, Dicyclopentyl-dimethoxysilan, 3-Glycidoxypropyl-methyl- dimethoxysilan, 3-Mercaptopropyl-methyldimethoxysilan; Diethoxysilane - wie Dimethyldiethoxysilan, Gamma-Aminopropyl-methyl-diethoxysilan; 3- Glycidoxypropyl-methyldiethoxysilan, 3-Methacryloxypropyl-methyldiethoxysilan.

[0098] Ein Beispiel für ein Monooxysilan ist Trimethyloxysilan.

[0099] The amount of adhesion promoter added can generally be selected within a wide range, depending on the desired properties of the product and taking into account the raw materials selected for the adhesive tape. However, it has proven very advantageous if the amount of adhesion promoter used, based on the base adhesive used, is selected in the range of 0.5 to 20 wt.%, preferably in the range of 1 to 10 wt.%, particularly preferably in the range of 1.5 to 5 wt.%, and most preferably in the range of 2.5 to 3.5 wt.%.

[0100] Very high amounts of adhesion promoters used can have a strong plasticizing effect, so that - especially with regard to sufficiently stable films - it can be advantageous to choose the amount of adhesion promoter as low as possible, so that on the one hand the desired positive influence on the moisture-heat resistance is sufficiently large, but on the other hand the properties of the adhesive tape with regard to its dimensional stability and stability are not negatively influenced.

[0101] Details regarding the processing and production of the adhesive layer can be found in WO 2019 / 207125 A1.

[0102] According to a further variant of the invention, the liquid adhesive preparation disclosed and described in detail in DE 10 2021 200 580 A1 is suitable as the base adhesive for the reactive, structural adhesive for the adhesive tape according to the invention.

[0103] The preparation or composition for producing the adhesive or base adhesive comprises i) a thermoplastic, preferably (semi)crystalline, polymer component formed from at least one polymer containing functional groups that can react with isocyanate, ii) a crosslinker component formed from at least one isocyanate-containing particulate compound, x) a solvent component formed from at least one organic solvent, wherein the polymer component is substantially dissolved in the organic solvent, and wherein furthermore the isocyanate-containing component is substantially insoluble neither in the solvent-free polymer component nor in the organic solvent at room temperature (23 °C).

[0104] Components (i) and (ii) are components of the adhesive mass obtainable from the preparation, while component (x) serves mainly as a processing aid for the preparation (precursor of the adhesive mass).

[0105] In order to obtain the reactive, structural adhesives used in the present invention, the preparations described here are used as base adhesives and mixed with expandable microballoons.

[0106] The reactive, structural adhesive composition according to the invention, produced from this preparation, therefore comprises, in this variant, expandable microballoons which have a starting temperature required for expansion of at least 94 °C; a polymer component formed from at least one polymer containing functional groups that can react with isocyanate, and a crosslinker component formed from at least one isocyanate-containing particulate compound.

[0107] The term "at least one" is, as usual, to be understood as meaning that the thermoplastic, preferably (semi)crystalline, polymer component is formed from one or more polymers with functional groups that can react with isocyanate, and that the crosslinker component is formed from one or more isocyanate-containing particulate compounds, and that the solvent component is formed from one or more organic solvents. Where reference is made below to the properties of "the at least one" representative of the respective component, the described properties apply in particular to all representatives of the respective component, if several of them are present.

[0108] The terms "essentially" and "significantly" are used here in a manner that reflects their importance for the invention. If the polymer component is "essentially" dissolved in the organic solvent, minor undissolved portions of the polymer may be present, particularly provided they do not jeopardize the implementation of the teachings of the invention. If a reaction "essentially" does not take place, minor reaction processes that have already begun do not harm the invention. For example, reaction mechanisms that occur under heat usually exhibit minor reaction processes even at lower temperatures (see the theory of equilibrium reactions). By means of the preparation, a latent-reactive adhesive, particularly in film form, made from an organically dissolved polymer can be offered in a new way, which has particularly advantageous adhesive properties.

[0109] This is particularly surprising for the person skilled in the art, since this applies both to the use of surface-deactivated, isocyanate-containing, particulate compounds and to the use of non-surface-deactivated, particulate isocyanate-containing compounds as crosslinking components, although the person skilled in the art expressly excludes this through the publications "Lagerstable latent-reaktive Klebfolien" (Jörg Büchner, Wolfgang Henning, Horst Stepanski, Bolko Raffel; Adhäsion 7-8.05) and "Latent reaktiv und lagerfähig" (Jörg Büchner, Wolfgang Henning; Adhäsion 6 / 2007).

[0110] Similar to the prior art, the preparations for producing (in particular latent-reactive) base adhesives and latent-reactive adhesive tapes obtainable therefrom contain a thermoplastic component having a melting temperature, T(melt), and containing functional groups that can react with isocyanate, as well as an isocyanate-containing component that is particulate, in particular finely particulate (preferably with a particle size distribution with d50 < 50 pm, in particular < 15 pm). In contrast to the prior art, however, the polymer component and the isocyanate component are not dispersed in an aqueous medium; rather, the polymer is dissolved in an organic solvent, and the isocyanate compound is finely dispersed in this solvent.

[0111] The composition thus contains a polymer component (component (i)) formed from at least one polymer containing functional groups that can react with isocyanate (hereinafter also referred to as isocyanate-reactive polymer). This polymer component represents the polymeric basis for the adhesive that can be produced from the composition. In the composition according to the invention, the polymeric component (i) is present in organic solution.

[0112] For example, compounds functionalized with OH and / or NH2 groups and / or urethane groups are used as polymer components.

[0113] In a highly preferred procedure, the at least one isocyanate-reactive polymer is at least partially crystalline, i.e., a semicrystalline or crystalline polymer. (Semi)crystalline substances can be determined using differential scanning calorimetry (DSC) according to DIN 53765:1994-03. Amorphous substances exhibit glass transition temperatures, while (purely) crystalline substances exhibit melting temperatures. Glass transition temperatures are recognizable as steps, and melting temperatures as peaks in the thermogram. Semicrystalline substances can exhibit glass transition temperatures in addition to melting temperatures. In (semi)crystalline substances, at least one melting temperature is recognizable, whereas this does not occur in amorphous substances.

[0114] For (semi)crystalline polymers, it has been shown that the requirement of non-solubility of the particulate isocyanate-containing compound is generally better met in the prepared state, especially at room temperature, than in amorphous systems. Only upon heating the resulting adhesive, especially to the melting and / or decrystallization temperature, is sufficient compatibility between the polymer component and the crosslinker component achieved.

[0115] In a further preferred embodiment, the at least one isocyanate-reactive polymer is a polyurethane polymer, and even more preferably in conjunction with the above-mentioned advantageous embodiment, a crystalline or semi-crystalline polyurethane polymer, for example polyurethane esters.

[0116] Preferably, the thermoplastic polyurethane has a softening temperature and / or decrystallization temperature of less than 90 °C, preferably less than 80 °C, more preferably less than 70 °C.

[0117] In a particularly preferred embodiment, a hydroxyl-terminated, largely linear, thermoplastic, highly crystallizing polyurethane elastomer is used as the isocyanate-reactive polymer. Such a polymer is commercially available from Covestro AG under the name Desmomelt 530®.

[0118] However, less strongly crystallizing and / or branched and / or polyfunctional polymers may also be advantageous, for example, if a higher crosslinking density is advantageous with regard to even better chemical resistance and / or bonding strength and / or hardness. A mixture of two or more isocyanate-reactive polymers may be advantageous in order to adjust the properties to a favorable level.

[0119] The preparation further contains a crosslinker component for the polymers to be crosslinked, which is formed from at least one isocyanate-containing particulate component (component (ii)). The isocyanate compounds can be used in a surface-deactivated or non-surface-deactivated form. This represents an advantage over the prior art, which requires surface-deactivated isocyanate compounds for latently reactive adhesives.

[0120] Since the preparation represents at least a two-phase system, namely the polymer solution and the particulate isocyanate-containing component, a significant onset of the curing reaction does not occur in this state. Even after spreading the preparation onto a temporary or permanent carrier and drying, i.e., removing the solvent—completely or down to a small residual solvent content of a few percent—the composition can be stored for a long period without the curing reaction significantly starting, so that the applicability of the latently reactive adhesive tape obtained from this preparation is at least 3 months, preferably at least 6 months.more preferably at least 9 months or longer with the achievement of the required property profile (>= 2 MPa in the push-out test on anodized aluminum and / or polycarbonate and >= 1 MPa in the push-out test [very good PSA without humid heat storage or after chemical exposure] after humid heat storage [72 h at 60 °C and 95% relative humidity and / or 72 h at 85 °C and 85% relative humidity], preferably also >= 1 MPa in the push-out test after 72 h storage at 60 °C in oleic acid, even more preferably also >= 1 MPa in the push-out test after 72 h storage at 60 °C in a mixture of ethanol and water [75 parts by volume : 25 parts by volume]).

[0121] In a preferred procedure, toluene diisocyanate compounds (TDI compounds) are used in whole or in part as the isocyanate-containing component, such as TDI dimers (available, for example, as Dispercoll BL XP 2514® (aqueous dispersion of a reactive isocyanate based on TDI dimer; in this case preferably usable after removal of the water) or as Dancure 999® (1,3-bis(3-isocyanato-4-methylphenyl)-1,3-diazetidine-2,4-dione; solid)), and / or isophorone diisocyanates (IPDI).

[0122] In the simplest embodiment, the preparation consists only of a polymer and an isocyanate-containing compound in a solvent. The ratio of the polymer to the isocyanate-containing compound is selected such that the resulting latently reactive film exhibits the desired property profile. The skilled person advantageously uses the minimum amount of isocyanate-containing compound that is stoichiometrically necessary to crosslink the isocyanate-reactive groups of the polymer according to the invention.

[0123] Further advantageously, the person skilled in the art uses more than this necessary amount of isocyanate-containing compound, in particular in order to compensate for unintentional reactions of the isocyanate-containing compound, for example with residual moisture of the solvent used and / or moisture input via the atmospheric humidity, for example during storage and / or transport and / or application of the latently reactive adhesive tape according to the invention or when, for example, further isocyanate-reactive components are added to the formulation according to the invention.

[0124] It may also be advantageous to use higher amounts of the isocyanate-containing compound if, for example, the melt viscosity of the polymer and / or the melt viscosity of the latently reactive adhesive tape are high, so that sufficient solubility and / or migration capacity cannot be guaranteed within the required application time. In this case, the temperature-time relationship can be positively influenced by increasing the content of the isocyanate-containing compound. In this case, unreacted portions of the isocyanate-containing compound would remain in the adhesive tape after crosslinking.

[0125] It may also be advantageous to use less than the stoichiometrically required amount of isocyanate-containing compound according to the invention, for example if the polymer used is a branched and / or polyisocyanate-reactive polymer, in order to avoid an excessively high crosslinking density, possibly accompanied by embrittlement, or in order to achieve a property profile of the latently reactive adhesive tape produced from this preparation that is required for the application (for example viscoelastic).

[0126] Advantageously, 1 wt.% to 25 wt.%, particularly advantageously 2 wt.% to 15 wt.%, very particularly advantageously 4 wt.% to 10 wt.% of the components of the base adhesive are selected from isocyanate-containing compounds.

[0127] The solvent used is not taken into account in this calculation; it is to be understood merely as a processing aid to homogeneously blend the components of the formulation and to adjust a viscosity that enables coating of the formulation using the desired coating process to obtain the latently reactive adhesive tape in the desired layer thickness. The solvent component (x) can be an organic solvent or a mixture of mutually compatible organic solvents in which the polymer component is essentially soluble and the crosslinker component is essentially insoluble. In principle, the usual organic solvents can be selected; the solubility or insolubility of the components mentioned can be easily determined by a person skilled in the art using specialist knowledge.Examples of solvents that can be used are acetone and 2-butanone, although this is not intended to be limiting.

[0128] The preparation can optionally further comprise an adhesion promoter component (iii). This is formed in particular from at least one organofunctional silane compound, for example of the general formula R-SiXs, where R denotes an organically functionalized radical and X a hydrolyzable group. The organic group of the silane can effect a bond to the adhesive; for example, through a newly formed covalent bond. The organically functionalized radical R often represents a longer molecular moiety (spacer, frequently comprising an alkyl chain) which generally has a functional group and whose function is to bond to the substrate surface and / or to components of the adhesive. Typical functional groups are vinyl, methacrylic acid, glycidyl, epoxy, epoxide, amino, urea, or thiol groups. Hydrolyzable groups X include, for example, alkoxy groups and, more rarely, halogen groups.Advantageously used are, for example, epoxy- or epoxy-terminated silanes, compounds based on epoxy or epoxy silanes, and / or alkylphosphonic acids. Examples of silane compounds that can be used alone or together as adhesion promoter components are aminopropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane (commercially available under the name Glymo®), and ß-(3,4-epoxycyclohexyl)ethyltriethoxysilane (commercially available under the name CoatOSil 1770®).

[0129] Since silane-containing adhesion promoters are sensitive to hydrolysis, the organic solution-based preparation offers - compared to the aqueous systems known in the state of the art - an improved possibility for the use of mixed adhesion promoters in polyurethane-based adhesives.

[0130] The proportion of an adhesion promoter is advantageously 0.5 wt.% to 6 wt.%, particularly advantageously 1 wt.% to 4 wt.%, very particularly advantageously 1.5 wt.% to 3 wt.% of the base adhesive without solvent.

[0131] A preferred embodiment is that the composition of the preparation is final through components (i), (ii), and (x), i.e., no further components or additives are present apart from components (i), (ii), and (x). Another preferred embodiment of the invention comprises component (iii) in addition to components (i), (ii), and (x), but is otherwise final, i.e., it comprises no further components or additives apart from these four components.

[0132] A very preferred embodiment relates to a composition for producing a base adhesive from a hydroxyl-terminated, largely linear, thermoplastic, highly crystallizing polyurethane elastomer (Desmomelt 530®) (component (i)), dissolved in an organic solvent (component (x)), such as acetone or 2-butanone, and particulate, finely distributed TDI dimer dispersed in the solution (component (ii), in particular 1,3-bis(3-isocyanato-4-methylphenyl)-1,3-diazetidine-2,4-dione (DANCURE 999®).

[0133] From this preparation, together with the expandable microballoons, the reactive, structural adhesive composition according to the invention is produced. Therefore, a preferred variant of the reactive, structural adhesive composition according to the invention comprises expandable microballoons that have an initial expansion temperature of at least 94°C (e.g., Expancel® 043 WU 80); a polymer component formed from a hydroxyl-terminated, largely linear, thermoplastic, highly crystallizing polyurethane elastomer (Desmomelt 530®), and a crosslinker component formed from a TDI dimer (in particular, 1,3-bis(3-isocyanato-4-methylphenyl)-1,3-diazetidine-2,4-dione (DANCURE 999®).

[0134] The advantageous composition can be limited to the above three components (i), (ii) and (x), but in an advantageous further development can additionally contain one or more organofunctional silane compounds as adhesion promoter component (iii), such as glycidyloxypropyltrimethoxysilane and / or ß-(3,4-epoxycyclohexyl)ethyltriethoxysilane.

[0135] The advantageous composition can be limited to the above four components (i), (ii), (iii), and (x), but in an advantageous further development can additionally contain one or more components (iv) from the group of epoxides and / or epoxy compounds, comprising mono-, di-, tri-, or polyfunctional epoxides and / or epoxy compounds. These include, for example, compounds that are liquid / viscous at 23°C, such as N,N,N',N'-tetrakis(2,3-epoxypropyl)-m-xylene-a,a'-diamine and / or 7-oxabicyclo-[4.1,0]hept-3-ylmethyl 7-oxabicyclo[4.1,0]heptane-3-carboxylate and / or compounds with a melting / softening point above 23°C (so-called epoxy / epoxy resins) such as Epicion N-673.In a particularly preferred embodiment, the reactive, structural adhesive according to the invention comprises expandable microballoons which have a starting temperature required for expansion of at least 94 °C; a polymer component formed from at least one polymer containing functional groups that can react with isocyanate; a crosslinker component formed from at least one isocyanate-containing particulate compound; and at least one further component from the group of epoxides and / or epoxy compounds.

[0136] The advantageously described compositions may be limited to these components, but may also advantageously contain further additives and / or components (v), see below, such as in particular adhesive resins.

[0137] 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 adjusting specific adhesive properties. Special adhesive properties can be achieved, for example, by admixing amorphous polymers (e.g., polyetherurethanes or polyacrylates) and / or by admixing adhesive resins.

[0138] Adhesive resins can optionally be used for the present invention to adjust the pressure-sensitive adhesive properties of the adhesive film according to the invention or to make it pressure-sensitively adhesive in the first place. Adhesive resins, as frequently used for adhesives, differ from reactive components, the latter often also being called reactive resins. According to the general understanding of those skilled in the art, an "adhesive resin" is understood to be an oligomeric or polymeric resin that effects, increases, and / or influences the adhesion (tack, inherent stickiness) of the adhesive compared to an otherwise identical adhesive that does not contain an adhesive resin. Adhesive resins typically contain no reactive groups other than double bonds (in the case of unsaturated resins), since their properties should not change over the service life of the adhesive.In particular, adhesive resins, in contrast to the reactive component(s) (reactive resins), are oligomeric or polymeric compounds that do not participate or do not significantly participate in curing reactions.

[0139] Resins based on terpene phenol or rosin, such as partially or fully hydrogenated resins based on rosin and rosin derivatives, can be used as adhesive resins. Other suitable adhesive resins include 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 α3-carene, and hydrogenated polymers of preferably pure C5 and C8 aromatics. The aforementioned adhesive resins can be used alone or in mixtures.

[0140] The above-mentioned rosins include, for example, natural rosin, polymerized rosin, partially hydrogenated rosin, fully hydrogenated rosin, esterified products of these rosins (such as glycerol esters, pentaerythritol esters, ethylene glycol esters and methyl esters) and rosin derivatives (such as disproportionation rosin, fumaric acid modified rosin and lime modified rosin).

[0141] Adhesive resins based on acrylates and methacrylates can also be used according to the invention.

[0142] Reference is made to the presentation of the state of knowledge in the "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (van Nostrand, 1989), Chapter 25 "Tackifier Resins".

[0143] To produce such latent-reactive adhesives, the solvent in particular is largely removed until only a small residual solvent content, preferably not more than 2% by weight, more preferably not more than 1% by weight, most preferably not more than 0.5% by weight, remains in the preparation. This can be achieved in particular by heating, although the temperature of the adhesive should be below the activation temperature of the curing reaction. The solvent can be removed, for example, in a drying oven and / or a drying tunnel and / or by another technical solution that ensures that the drying temperature (of the formulation and / or the adhesive tape) remains below the activation temperature of the latent-reactive adhesive tape or is only exceeded for so long that the latent-reactive adhesive tape still exhibits the property profile after drying.

[0144] In another variant of the adhesive tape according to the invention, heat-activatable adhesives with a low activation temperature are used as the base adhesive for the reactive, structural adhesive. This is particularly advantageous because it makes it possible to bond even heat-sensitive materials without damaging them, thus enabling a material-friendly bond. Adhesives such as those described, for example, in WO 2013 / 127697 A1 can be advantageously used as heat-activatable base adhesives with a relatively low activation temperature—and are excellently suited for the adhesive layer made of a reactive, structural adhesive in the present document.In the sense of the heat-activatable adhesive layers, these are in particular latent-reactive base adhesives which contain: a) a thermoplastic polymer component with a melting temperature Tschmeiz in the range of 35 °C < Tschmeiz 90 °C, in particular 40 °C < Tschmeiz 60 °C, wherein the thermoplastic polymer component has functional groups which can react with isocyanate, and b) an isocyanate-containing crosslinker component which is present in particulate form in the thermoplastic component and is essentially deactivated in the region of the particle surface, wherein the particles have a light-off temperature TSchmelz VOU 40 °C < TSchmelz 100 °C, in particular 45 °C < TSchmelz 75 °C, and wherein TSchmelz — TSchmelz.

[0145] For the purposes of this description, T melting point is the melting temperature of the thermoplastic component, and T start is the temperature at which the isocyanate groups of the particles dispersed in the thermoplastic component are enabled to react with the functional groups of the thermoplastic polyurethane (for example, because they are distributed in the matrix with the thermoplastic polyurethane). In the case of blocked isocyanate groups, T start is linked to the deblocking temperature; in the case of microencapsulation, it is linked to the release of isocyanate from the microcapsules (for example, by melting the microcapsule shell); and in the case of isocyanates deactivated near the surface of the isocyanate particles, it is linked to the melting of the isocyanate particles.For the purposes of this invention, all blocked, microencapsulated, or isocyanate-containing systems known from the prior art that are deactivated at the particle surface and meet the specifications for TAnspring are conceivable. The thermoplastic polyurethanes and the isocyanate-containing component are preferably dispersible in an aqueous medium or dispersed in an aqueous medium.

[0146] To obtain the reactive, structural adhesives used in the present invention, the base adhesives described here are used and mixed with expandable microballoons. In this variant, the reactive, structural adhesive according to the invention therefore comprises expandable microballoons that have an initial expansion temperature of at least 94°C; a polymer component formed from at least one polymer containing functional groups that can react with isocyanate; and a crosslinker component formed from at least one isocyanate-containing particulate compound.In a preferred embodiment, the reactive, structural adhesive comprises expandable microballoons which have a starting temperature required for expansion of at least 94 °C; a thermoplastic polymer component with a melting temperature Tschmelzz in the range of 35 °C < Tschmelzz 90 °C, in particular 40 °C < Tschmelzz 60 °C, wherein the thermoplastic polymer component has functional groups which can react with isocyanate; and an isocyanate-containing crosslinker component which is present in particulate form in the thermoplastic component and is substantially deactivated in the region of the particle surface, wherein the particles have a starting temperature Tschmelzz of 40 °C < Tschmelzz 100 °C, in particular 45 °C < Tschmelzz — 75 °C, and wherein Tschmelzz — Tschmelzz.

[0147] The adhesives contain, in particular, a thermoplastic component that has a melting point, Tmelt, and contains functional groups that can react with isocyanate, as well as an isocyanate-containing component that is present in particulate form, in particular finely divided particulate form, dispersed in the thermoplastic component and is blocked, microencapsulated, or substantially deactivated in the region of the particle surface. Finely divided particulate means having a particle size distribution with d50 < 50 pm, with the particle size distribution preferably being < 15 pm. Latent-reactive adhesives are preferably based on so-called 1 K latent-reactive polyurethane, obtained from an aqueous polyurethane dispersion, preferably Dispercoll U® from Covestro AG; the isocyanate-containing component is one that is substantially deactivated in the region of the particle surface.

[0148] The particles have a light-off temperature, TAnspring , for which TSchmelz — TAnspring - TSchmelz is between 35 °C and 90 °C, preferably between 40 °C and 60 °C. TAnspring is between 40 °C and 120 °C, preferably at most 100 °C, very particularly preferably at most 90 °C. The lower limit is 50 °C, and 60 °C is particularly preferred.

[0149] Particularly preferred is TSchemiz < TAnspring, since this reliably prevents unwanted triggering of the crosslinking reaction during the production of the web-shaped latent-reactive adhesive tape.

[0150] The thermoplastic components used are preferably compounds functionalized with OH and / or NH2 groups. The thermoplastic component is very preferably at least a semicrystalline polyester polyurethane.

[0151] The latent-reactive base adhesive preferably contains an anionic, high-molecular polyurethane dispersion as a thermoplastic component, which has a melting temperature (in dried form) Tschmeiz of 35 °C < Tschmeiz 90 °C, in particular 40 °C < Tschmeiz 60 °C, and contains functional groups that can react with isocyanate, 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 U 2824 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).

[0152] The latent-reactive base adhesive preferably also contains toluene diisocyanate compounds (TDI compounds) such as Dispercoll BL XP 2514 (TDI dimer) and / or Aqualink U (dispersion of blocked TDI dimer) and / or isophorone diisocyanates (IPDI) such as Aqualink D (dispersion of blocked IPDI trimer) as an isocyanate-containing component, which is dispersed in particulate form, particularly in finely divided form, within the thermoplastic component and is blocked, microencapsulated, or essentially deactivated near the particle surface. The diisocyanates are used, for example, in the form of aqueous suspensions of the respective latent-reactive solid isocyanate. Aqualink is offered by Aquaspersions.The aforementioned diisocyanate products can be used as crosslinking components, particularly in combination with anionic, high-molecular-weight polyurethane dispersions as the thermoplastic component (such as the Dispercoll U products mentioned above). Other isocyanates, including monomeric and oligomeric compounds and polyisocyanates, can also be used.

[0153] The base adhesive may also contain other formulation components. These include thickeners, wetting agents, defoamers, fillers (e.g., thermally conductive), pigments (including coloring, whiteness adjustment, and / or blackening agents), catalysts, stabilizers, anti-aging agents, light stabilizers, and other polymers for adjusting specific adhesive properties. Specific adhesive properties can be achieved, for example, by admixing aqueous dispersions of amorphous polymers (e.g., polyether urethanes or polyacrylates) and / or aqueous resin dispersions (especially based on rosin esters) or liquid resins.

[0154] According to a further variant of the invention, an adhesive as disclosed and described in detail in WO 2013 / 174650 A1 is suitable as the base adhesive for the reactive, structural adhesive for the adhesive tape according to the invention.

[0155] The reactive, heat-activatable adhesive used can preferably be one based on a mixture of at least one nitrile rubber heat-activatable adhesive S1 and a reactive component, in particular a reactive resin. Expandable microballoons are added to this base adhesive to obtain the reactive, structural adhesives for the present invention.

[0156] Therefore, in this variant, the reactive, structural adhesive according to the invention comprises, in addition to expandable microballoons having a starting temperature of at least 94°C required for expansion, 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 invention comprises expandable microballoons having a starting temperature of at least 94°C required for expansion; at least one nitrile rubber S1; and a reactive component, in particular a reactive resin.

[0157] The weight fraction of the nitrile rubber S1 is preferably between 25 and 70 wt.%, particularly preferably between 30 and 60 wt.% of the total composition of the reactive heat-activatable base adhesive.

[0158] Nitrile rubbers S1 preferably have an acrylonitrile content of 15 to 45 wt.%. Another criterion for 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; according to DIN 53523). Commercial examples of such nitrile rubbers include Nipol™ N917 from Zeon Chemicals.

[0159] Reactive resins are understood to be, in particular, short- to medium-chain oligomers or polymeric compounds, especially with average molecular weights in the range up to 10,000 g / mol. The proportion of reactive resins in the heat-activatable adhesive is preferably between 75 and 30 wt.%. A very preferred group includes epoxy resins. The weight-average molecular weight Mw of the epoxy resins varies from 100 g / mol up to a maximum of 10,000 g / mol for polymeric epoxy resins.

[0160] The epoxy resins include, for example, the reaction product of bisphenol A and epichlorohydrin, epichlorohydrin, glycidyl ester, the reaction product of epichlorohydrin and p-amino phenol.

[0161] Preferred commercial examples are, for example, Araldite 6010, CY-28, ECN 1273, ECN 1280, MY 720, RD-2 from Ciba Geigy, DER 331, DER 732, DER 736, DEN 432, DEN 438, DEN 485 from Dow Chemical, Epon 812, 825, 826, 828, 830, 834, 836, 871, 872,1001, 1004, 1031 etc. from Shell Chemical and HPT™ 1071, HPT™ 1079 also from Shell Chemical. Examples of commercial aliphatic epoxy resins are vinylcyclohexane dioxides such as ERL-4206, ERL-4221, ERL 4201, ERL-4289 or ERL-0400 from Union Carbide Corp.

[0162] Novolak resins that can be used include, 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, Epicion N673 from DaiNippon Ink Chemistry or Epicote 152 from Shell Chemical.

[0163] Melamine resins can also be used as reactive resins, such as Cymel 327 and 323 from Cytec.

[0164] Phenolic resins are very preferred as reactive resins. Novolak resins, phenolic resole resins, or combinations of novolak resins and phenolic resins are excellent options. Examples of commercially available phenolic resins are YP 50 from Toto Kasei, PKHC from Union Carbide Corp, and BKR 2620 from Showa Union Gosei Corp.

[0165] Terpene phenolic resins, such as NIREZ 2019 from Arizona Chemical, can also be used as reactive resins.

[0166] Polyisocyanates such as Coronate L from Nippon Polyurethan Ind., Desmodur N3300 or Mondur 489 from Covestro can also be used as reactive resins.

[0167] In an advantageous embodiment of the base adhesive, adhesive strength-enhancing (tackifying) resins are also added; very advantageously, in a proportion of up to 30 wt.%, based on the total mixture of the heat-activatable adhesive. All known tackifying resins described in the literature can be used as tackifying resins. Examples include pinene, indene, and rosin resins, their disproportionated, hydrogenated, polymerized, and 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 desired.In general, all (soluble) resins compatible with S1 rubbers can be used, including all aliphatic, aromatic, and alkylaromatic hydrocarbon resins, hydrocarbon resins based on pure monomers, hydrogenated hydrocarbon resins, functional hydrocarbon resins, and natural resins. Reference is made to the current state of knowledge in the "Handbook of Pressure Sensitive Adhesive Technology" by Donatas Satas (3rd edition, Satas & Associates, 1999).

[0168] To accelerate the reaction between the two components, crosslinkers and accelerators can optionally be added to the mixture.

[0169] Suitable accelerators include imidazoles, commercially available as 2M7, 2E4MN, 2PZ-CN, 2PZ-CNS, P0505, L07N from Shikoku Chem. Corp., or Curezol 2MZ from Air Products. HMTA (hexamethylenetetramine) additives are also suitable as crosslinkers.

[0170] Amines, especially tert-amines, can also be used for acceleration.

[0171] In addition to reactive resins, plasticizers can also be used. In a preferred embodiment of the invention, plasticizers based on polyglycol ethers, polyethylene oxides, phosphate esters, aliphatic carboxylic acid esters, and benzoic acid esters can be used. Aromatic carboxylic acid esters, higher molecular weight diols, sulfonamides, and adipic acid esters can also be used.

[0172] In a further preferred embodiment, further additives are added to the blend, such as polyvinyl formal, polyacrylate rubbers, chloroprene rubbers, ethylene-propylene-diene rubbers, methyl-vinyl-silicone rubbers, fluorosilicone rubbers, tetrafluoroethylene-propylene copolymer rubbers, butyl rubbers, styrene-butadiene rubbers.

[0173] Polyvinyl butyrals are available under Butvar from Solutia, under Pioloform from Wacker, and under Mowital from Kuraray. Polyacrylate rubbers are available under Nipol AR from Zeon. Chloroprene rubbers are available under Baypren from Bayer. Ethylene propylene diene rubbers are available under Keltan from DSM, under Vistalon from Exxon Mobile, and under Buna EP from Bayer. Methyl vinyl silicone rubbers are available under Silastic from Dow Corning and under Silopren from GE Silicones. Fluorosilicone rubbers are available under Silastic from GE Silicones. Butyl rubbers are available under Esso Butyl from Exxon Mobile. Styrene butadiene rubbers are available under Buna S from Bayer, Europrene from Eni Chem, and under Polysar S from Bayer. Polyvinyl formals are available under Formva from Ladd Research.According to a further variant of the invention, an adhesive as disclosed and described in detail in WO 2010 / 145945 A1 is suitable as the base adhesive for the reactive, structural adhesive for the adhesive tape according to the invention.

[0174] The adhesive composition therein consists of (a) at least one acrylonitrile-butadiene copolymer, (b) at least one novolak resin, and (c) a formaldehyde donor as a hardener. Expandable microballoons are added to the described base adhesive composition to obtain the reactive, structural adhesives for the present invention. Therefore, in this variant, the reactive, structural adhesive composition according to the invention comprises expandable microballoons that have an initial expansion temperature of at least 94°C; at least one acrylonitrile-butadiene copolymer; at least one novolak resin; and a formaldehyde donor as a hardener.

[0175] The ratio of the acrylonitrile-butadiene copolymers to the novolak resins is advantageously in the range of 3:7 to 8:2, so that the acrylonitrile-butadiene copolymers are preferably present in a weight proportion of 30 to 80 wt.% and the novolak resins in a weight proportion of 20 to 70 wt.%, with components a. and b. adding up to 100 wt.% and based on the total weight of the base adhesive.

[0176] The novolak resin is particularly capable of chemically crosslinking at high temperatures with the help of the hardener. Crosslinking occurs primarily through chemical reaction of the novolak resins with the hardeners under heat and / or through reaction of the hardeners with the novolak resins and the polymer matrix under heat.

[0177] The activation temperatures for thermal crosslinking are significantly higher than room temperature, typically at least 100 °C or more. Preferred activation temperatures for thermal crosslinking, especially to ensure the required bond strength, are at least 120 °C, especially between 140 °C and 220 °C.

[0178] The base adhesive may be limited to the aforementioned components a. to c., but may also contain other components.

[0179] Ideally, the novolak resins and the hardeners (formaldehyde donors) are used in a ratio of 50:1 to 5:1 wt.% (novolak resins:hardener), preferably 20:1 to 7:1 wt.%. The adhesive is heat-activated, cross-links when heated, flows well onto the substrate to be bonded, exhibits good adhesion to polyimide, is short-term temperature-stable up to at least 288°C, and, in the uncross-linked state, is soluble or suspendable in organic solvents.

[0180] Acrylonitrile-butadiene copolymers, also known as acrylonitrile-butadiene rubbers, nitrile-butadiene rubbers, or simply nitrile rubbers, are particularly suitable for all acrylonitrile-butadiene rubbers with an acrylonitrile content of 15 to 55 wt.%. Copolymers of acrylonitrile-butadiene and isoprene can also be used. The proportion of 1,2-linked butadiene is variable. The aforementioned polymers can be hydrogenated to varying degrees; even fully hydrogenated polymers with a double bond content of less than 1% are usable. Nitrile-butadiene rubbers are polymerized either hot or cold.

[0181] Such systems are commercially available, for example, under the names Europrene from Eni Chem, Krynac and Perbunan from Bayer, or Nipol and Breon from Zeon. Hydrogenated systems are commercially available in varying degrees under the name Zetpol from Zeon or Therban from Lanxess. The aforementioned products are examples of systems that can be used advantageously according to the invention.

[0182] It has been shown that nitrile rubbers with higher acrylonitrile contents provide better adhesive performance. A high molecular weight is also advantageous for strong bonding, although care must be taken to ensure that the polymer can still be dissolved or suspended.

[0183] Nitrile rubbers 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 novolak resins, dissolve better in butanone.

[0184] Novolaks are soluble, meltable, non-self-curing, and storage-stable phenolic resins. They are produced by condensing formaldehyde and excess phenol in the presence of usually acidic catalysts.

[0185] Their crosslinking to form thermoset molded parts is achieved with the help of a hardener that releases formaldehyde, e.g., hexamethylenetetramine (urotropine). Due to steric hindrance, this crosslinking occurs more rapidly in the para-position than in the ortho-position. Therefore, novolak resins containing phenol units linked together in the ortho-position are preferred for particularly rapid crosslinking.

[0186] Examples of advantageously used novolak resins are the Durez products from Sumitomo Bakelite and / or the Plenco products from Plastics Engineering Company.

[0187] Different formaldehyde donors can be used as hardeners, such as hexmethylenetetramine (Hexa, HMTA, Urotropin) and / or different methylolamine derivatives such as trimethylolmelamine or hexamethylolmelamine.

[0188] The chemical crosslinking of the hardeners with the novolak resins achieves very high strength within the adhesive tape. The bond strength to the polyimide is also extremely high.

[0189] In order to increase adhesion, it is also advantageous to add adhesive resins (“tackifiers”) that are compatible with the elastomers.

[0190] Tackifiers used in heat-activatable adhesives include, 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 8-limonene; and hydrogenated polymers of, preferably, pure C8 and C9 aromatics. The aforementioned tackifier resins can be used alone or in mixtures. Tackifiers can advantageously be added in amounts of up to 20% by weight, based on the blended adhesive.

[0191] Small amounts of epoxy resins can also be used. To maintain storage stability, the amount of epoxy resin should preferably not exceed 10 wt.%.

[0192] Epoxy resins are defined as both monomeric and oligomeric compounds with more than one epoxy group per molecule. These can be reaction products of glycidyl esters or epichlorohydrin with bisphenol A or bisphenol F, or mixtures of the two. Epoxy novolac resins obtained by reacting epichlorohydrin with the reaction product of phenols and formaldehyde can also be used. Monomeric compounds with multiple epoxy end groups, which are used as thinners for epoxy resins, can also be used. Elastically modified epoxy resins can also be used.

[0193] Examples of advantageously usable epoxy resins are AralditeT 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.

[0194] Advantageously usable commercial aliphatic epoxy resins include vinylcyclohexane dioxides such as ERL-4206, 4221, 4201, 4289 or 0400 from Union Carbide Corp.

[0195] Advantageously used elasticized epoxy resins are available from Noveon under the name Hycar.

[0196] Advantageously usable epoxy thinners, monomeric compounds with several epoxy groups are, for example, Bakelite EPD KR, EPD Z8, EPD HD, EPD WF, etc. from Bakelite AG or Polypox R 9, R12, R 15, R 19, R 20 etc. from UCCP.

[0197] Additional additives that can be used optionally include:

[0198] • primary antioxidants such as sterically hindered phenols

[0199] • secondary antioxidants such as phosphites or thioethers

[0200] • other anti-aging agents such as sterically hindered amines

[0201] • Process stabilizers such as C radical scavengers

[0202] • Sunscreens such as UV absorbers

[0203] • Processing aids

[0204] • Fillers such as silicon dioxide, glass (ground or in the form of beads), aluminum oxides, zinc oxides, titanium dioxides, carbon blacks, metal powders, etc.

[0205] • Color pigments and dyes as well as optical brighteners • if necessary, other polymers, preferably of an elastomeric nature.

[0206] The above-mentioned and possibly other additives can be used alone or in combination with each other, in particular when their addition is intended to adjust the properties of the adhesive with regard to specific intended uses.

[0207] The elasticity of the crosslinked adhesive can be increased by using plasticizers. Examples of plasticizers include low-molecular-weight polyisoprenes, polybutadienes, polyisobutylenes, or polyethylene glycols and polypropylene glycols.

[0208] Because nitrile rubber's viscosity remains stable even at high temperatures, the adhesive does not leak from the bond joint during bonding and hot pressing. During this process, the novolak resins and, if present, the polymer matrix crosslink with the hardeners, resulting in a three-dimensional network.

[0209] The reactive structural adhesive comprises the microballoons in an amount of from 1 wt% to 25 wt%, in particular from 2 wt% to 20 wt%, more preferably from 5 wt% to 10 wt%, and most preferably about 10 wt%, based on the total weight of the reactive structural adhesive.

[0210] For the purposes of this invention, "microballoons" are understood to be elastic and thus expandable hollow microspheres with a thermoplastic polymer shell. These spheres are usually filled with low-boiling liquids or liquefied gas. Polyacrylonitrile, PVDC, PVC, or poly(meth)acrylates are particularly used as shell materials. Short-chain hydrocarbons, such as isobutane or isopentane, are particularly commonly used as low-boiling liquids, which are enclosed, for example, as liquefied gas under pressure in the polymer shell.

[0211] Microballoons generally serve as foaming agents. Heating the microballoons softens the outer polymer shell. At the same time, the propellant inside expands. The microballoons expand essentially irreversibly, expanding three-dimensionally. The expansion is complete when the internal and external pressures equalize. Since the polymer shell remains intact, a closed-cell, syntactically foamed foam is achieved.

[0212] Microballoons that have not yet been thermally activated and which accordingly still have their original expansion are referred to in the present invention as expandable microballoons (synonymous with unexpanded microballoons) and are not considered to be expanded microballoons in accordance with the understanding of those skilled in the art.

[0213] Expandable or unexpanded microballoons are available in a variety of designs, which can essentially be characterized by their size (usually 6 to 45 pm diameter D(0.5) in the unexpanded state) and the starting temperatures required for expansion (approx. 75 °C to approx. 220 °C). Examples of commercially available microballoons are the Expancel® DU types (DU = dry unexpanded) from Nouryon or Matsumoto® Microsphere from Matsumoto Yushi-Seiyaku Co., Ltd. Expandable or unexpanded microballoons are available, for example, as an aqueous dispersion with a microballoon mass fraction of approx. 40 to 45% or as polymer-bound products, for example in ethylene vinyl acetate, with a microballoon mass fraction of approx. 65%. However, within the scope of the present invention, it is preferred to use the expandable microballoons in powder form, wherein the powder preferably consists essentially of the expandable microballoons.

[0214] Important parameters for the expandable microballoons used according to the invention are the required starting temperature, the maximum temperature, and the particle size D(0.5), which can be found in the manufacturers' data sheets. According to the invention, a starting temperature of the expandable microballoons is preferably in the range of 94°C to 140°C, more preferably in the range of 95°C to 120°C, and most preferably in the range of 100°C to 110°C.

[0215] Those skilled in the art are aware that the starting temperature of the expandable microballoons directly correlates with the temperature (hereinafter referred to as the foaming temperature) that must be reached to enable good and easy separation of the bond. For example, the foaming temperature for optimal separation of the bond for an adhesive tape according to the invention with an adhesive layer made of a reactive, structural adhesive with expandable microballoons, which have a starting temperature required for expansion of at least 94°C, is approximately 120°C. Higher temperatures lead to faster expansion of the microballoons and thus to less time until the bond strength drops and separation is possible. At lower temperatures, it naturally takes longer until separation of the components is possible.The difference between the starting temperature and the optimal separation temperature is preferably in the range of 20-30°C, most preferably around 15°C. The foaming of the expandable microballoons, which is necessary for easy release of the structural bond, takes place at temperatures of 115°C or more. Typical foaming temperatures are in the range of 120°C to 150°C, preferably around 120°C. The suitable foaming temperature can be easily selected by a person skilled in the art based on their specialist knowledge. The heat input for foaming the microballoons can be achieved by conventional heat sources, such as a hot plate (heating press), oven, laser, IR radiation, or induction. In the context of this invention, the heat input is preferably achieved by a hot plate or a heating press.

[0216] According to the invention, the maximum temperatures of the expandable microballoons used are preferably at most 200 °C, in particular at most 180 °C and preferably at most 170 °C.

[0217] The starting temperature (Tstart) and the maximum temperature (T ma x) of microballoons can be determined using methods known to those skilled in the art, such as thermomechanical analysis (TMA). Here, the sample is heated at a constant rate (in the case of Expancel microballoons, at 20 °C / min), and the volume of the sample is measured. A temperature-volume diagram is created from this, from which the starting temperature (temperature at which the volume increase begins) and the maximum temperature (temperature with the maximum volume) can be determined or calculated.

[0218] The particle size D(0.5), determined by laser diffraction, of the expandable microballoons is typically between 5 pm and 40 pm, in particular between 16 pm and 24 pm. In a preferred embodiment, the adhesive tape according to the invention is characterized in that the expandable microballoons have a particle size D(0.5) (in the unexpanded state) between 16 pm and 24 pm. The inventors have surprisingly found that this particle size is ideal for adhesive layer thicknesses of 75 pm to 150 pm. For smaller adhesive layer thicknesses, a particle size D(0.5) of the expandable microballoons of less than 16 pm is preferred. Particle sizes D(0.5) of 25 pm or more are preferably used for adhesive layer thicknesses greater than 150 pm.

[0219] Particle size determination by laser diffraction can be performed, for example, with a Bettersizer S3 Plus particle analyzer from 3P Instruments. By default, the Bettersizer measurement is essentially a measurement of the volume distribution—converting the result into a numerical distribution is a mathematical process. The measurement results were presented as D v (0,1 )-, D v (0.5) and D v (0.9) values ​​are given, which are standard percentiles. D v (0.5) or D(0.5) is the size in micrometers (pm) at which 50% of the sample particles are smaller and 50% larger. This value is also called the mass median diameter (MMD) or the median of the volume distribution. D v (0.1 ) corresponds to the particle size below which 10% of the sample lies, and D v (0.9) of the particle size below which 90% of the sample lies.

[0220] Preferred types of expandable microballoons are Expancel® 043 DU 80 and Expancel® 043 WU 80 (both - T start : 94-1 14 °C; T max : 147-167 °C; D(0.5): 16-24 pm) from Nouryon and the Matsumoto Microsphere® F-100M and F-100MD (both - T s tart: 115-125 °C ; Tmax: 155-165 °C, D(0.5): 17-23 pm) from Matsumoto Yushi-Seiyaku Co., Ltd.

[0221] Adhesive tapes with reactive, structural adhesives that create a permanent, 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 the reactive, structural adhesive is called the activation temperature. This does not refer to the temperature typically used in the pre-lamination step to apply the adhesive tape to the first substrate to be bonded. This temperature is typically 10 to 20°C below the activation temperature and causes the adhesive to become tacky or sticky, but does not yet cause a curing reaction of the reactive, structural adhesive. For the purposes of this invention, only adhesive tapes with reactive, structural adhesives that are cured in a temperature range of 75°C to 140°C are to be considered.Therefore, the invention relates to an adhesive tape designed and configured to be separated after permanent bonding, comprising at least one or consisting of at least one adhesive layer comprising a reactive, structural adhesive, wherein the reactive, structural adhesive comprises expandable microballoons having a starting temperature required for expansion of at least 94 °C and wherein the reactive, structural adhesive has an activation temperature in the range of 75 °C to 140 °C.

[0222] Therefore, an important aspect for the selection of expandable microballoons is that the foaming temperature of the expandable microballoons is at least 5 °C above the activation temperature or the temperature range for activation, in particular at least 10 °C above the activation temperature or the temperature range for activation, and preferably at least 20 °C above the activation temperature or the temperature range for activation. The expandable microballoons are selected according to the activation temperature or the temperature range for activation of the reactive, structural adhesive so that foaming of the microballoons does not (accidentally) occur during curing of the adhesive, in order not to impair the permanent structural bond.In the case of the preferred expandable microballoons Expancel® 043 DU 80, Expancel® 043 WU 80, Matsumoto Microsphere® F-100M and Matsumoto Microsphere® F-100MD, the foaming temperature is 120 °C to 150 °C, so that they can be used in reactive, structural adhesives with an activation temperature in the range of 75 °C to 100 °C.

[0223] The 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 of the present invention is characterized in that the adhesive layer has a layer thickness of between 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.

[0224] The thickness of the adhesive layer is related to the selection of suitable expandable microballoons to ensure optimal separation or detachability of the adhesive layer after foaming of the microballoons by heat application. The inventors surprisingly found that the particle size D(0.5) of the expandable microballoons (in the unexpanded state) should be in the range of 20 to 30% of the thickness of the adhesive layer to ensure optimal detachability after foaming.

[0225] The adhesive tape according to the invention is a double-sided adhesive tape. Such an adhesive tape comprises or consists of at least one adhesive layer comprising a reactive, structural adhesive and, in the simplest case, is used in a single-layer form, as a transfer adhesive tape, applied to a removable (temporary) release material (also referred to as a release liner or liner to those skilled in the art). It is particularly preferred for the adhesive tape to be a transfer adhesive tape with at least one adhesive layer. A liner (release paper, release film) is not a component of an adhesive tape, but merely an aid for its production, storage, or further processing by die-cutting. Furthermore, unlike an adhesive tape carrier, a liner is not permanently bonded to an adhesive layer. Temporary release materials suitable for the adhesive according to the invention are known to those skilled in the art.

[0226] Suitable temporary covering materials include, for example, all release films and papers suitable for the adhesive of the invention, which are known from the prior art and which are equipped with a release layer on one or both sides and / or do not intrinsically form excessively strong bonds with the adhesive of the invention. Siliconized papers suitable for the adhesive of the invention are preferred. Two layers of a removable carrier material can also be used, so that the top and bottom sides of the adhesive film are covered, even when the product is not wound up.

[0227] The adhesive tape according to the invention comprises or consists of at least one adhesive layer comprising a reactive, structural adhesive, and can also contain a carrier material (backing) that remains in the product even after bonding. Such an adhesive tape is typically referred to as a double-sided adhesive tape. Films and papers, as well as non-crimp, woven, and knitted fabrics, are also suitable for this purpose. The surfaces of these carrier materials can each be independently pretreated chemically (primer, plasma) and / or physically (corona, flame, plasma) in such a way that particularly good anchoring of the adhesive layer to the carrier material can be achieved. Nonwovens are preferred. A layer of a permanent carrier reduces any tendency of the adhesive layer to be squeezed out laterally from the bond joint in the molten state under pressing conditions.

[0228] In this preferred case, flat structures made of individual fibers are used as the carrier nonwoven. All nonwovens defined according to the DIN EN 29092 standard can be used. The nonwoven consists of loosely arranged fibers which are not yet bonded to one another. The strength results from the fiber's own adhesion. A distinction is also made between bonded and unbonded nonwovens. The fibers are randomly distributed. The nonwovens can be differentiated according to the fiber material. The fiber materials used can be 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 aforementioned substances.The fibers can be strengthened mechanically by needling or water jets, chemically by adding binders or thermally by softening in a suitable gas stream, between heated rollers or in a steam stream.

[0229] In a very preferred embodiment of the invention, cellulose-based nonwovens are used. The basis weight of the nonwovens is preferably between 4 and 100 g / m 2 , particularly preferably between 10 and 70 g / m 2Such nonwovens are commercially available, for example, from Glatfelter. The thickness of these nonwovens is preferably between 20 and 100 μm, most preferably between 30 and 60 μm. Double-sided adhesive tapes with a carrier material can have adhesive layers of different thicknesses and / or, preferably, adhesive film layers of different types on the top and bottom sides. The use of different (pressure-sensitive) adhesive layers is possible in order to adjust the properties of the double-sided adhesive tape. The properties that can be influenced in this way include the thickness, stiffness, flexibility, temperature resistance, elasticity and flame resistance of the adhesive tape. If different adhesive layers are used, then both advantageously meet the requirements for the adhesive layers with a reactive, structural adhesive, as outlined above.It is also possible that in such systems one of the adhesive layers does not comprise a reactive, structural adhesive, but contains, for example, thermoplastic, heat-activated and / or pressure-sensitive adhesives.

[0230] The adhesive tape according to the invention, which comprises or consists of at least one adhesive layer (comprising a reactive, structural adhesive), can in principle have or consist of one or more adhesive layers in both variants (carrier-containing or carrier-free). At least the uppermost and lowermost layers are an adhesive layer comprising a reactive, structural adhesive, whereby these can differ in terms of thickness and / or type. If different adhesive layers are used, then both advantageously meet the requirements for the adhesive layers with a reactive, structural adhesive, as set out above. It is particularly preferred for the adhesive tape to be in the form of a transfer adhesive tape with an adhesive layer. Accordingly, in a preferred embodiment, the adhesive tape is characterized in that the adhesive tape is a transfer adhesive tape and consists of an adhesive layer.

[0231] Multilayer and carrier-containing adhesive products can have thicknesses of 10 pm to 2000 pm, preferably of 25 pm to 500 pm, particularly preferably of 75 pm to 300 pm.

[0232] The general term “adhesive tape” (pressure-sensitive adhesive tape), synonymously also “adhesive strip” (pressure-sensitive adhesive strip), encompasses, in the sense of this invention, all flat structures such as films or film sections extended in two dimensions, tapes with an extended length and a limited width, tape sections and the like, and ultimately also die-cuts or labels.

[0233] The adhesive tape thus has a longitudinal dimension (x-direction) and a width dimension (y-direction). The adhesive tape also has a thickness perpendicular to both dimensions (z-direction), with the width dimension and longitudinal dimension being many times greater than the thickness. The thickness is as uniform as possible, preferably exactly the same, across the entire surface area of ​​the adhesive tape, determined by its length and width.

[0234] At the end of the manufacturing process, the adhesive tape(s) according to the invention are usually wound into a roll in the shape of an Archimedean spiral, i.e., disc-shaped adhesive tape rolls known in technical terms as a "pancake." However, they can also be supplied by the meter, or alternatively, the adhesive tape can be wound like a textile yarn onto a core whose length is significantly greater than the width of the adhesive tape. By superimposing a rotational movement of the core and an axial movement of the core or of the adhesive tape guide member, the adhesive tape initially forms a first, radially innermost layer of helical windings. At the end of the first layer and the jump to the second layer, the orientation of the axial movement is inverted while the rotational movement remains unchanged.At the end of the second layer and the jump to the third layer, the orientation of the axial movement is inverted again, while the rotational movement remains unchanged, returning to the original orientation. Between each orientation reversal point, the pitch angle remains constant. In this way, numerous winding layers can be formed, each of which intersects the other (cross-wound coils).

[0235] Adhesive tapes according to the invention are preferably used in widths of 9 to 50 mm, in particular 19 to 25 mm. Roll widths of 10, 15, 19, 25, and 30 mm are typically selected. Alternatively, the laminates can be sold in bars or rolls, for example, in widths of 1000 to 1300 mm. These bars are typically processed into diecuts and thus prepared for composite production. The diecuts are produced either by a laser cutting process, by flatbed diecutting, or by rotary diecutting. The diecut typically has the dimensions of the first component but can also be somewhat smaller to allow for slight squeezing during the bonding process.

[0236] Substrates particularly suitable for bonding using the adhesive tape according to the invention are metals, glass, and / or plastics. The substrates to be bonded can be the same or different.

[0237] It may be necessary to pretreat the surfaces of the substrates to be bonded using a physical, chemical, and / or physico-chemical process. Applying a primer or adhesion promoter composition, for example, is advantageous in this case.

[0238] Suitable plastic substrates are, for example, acrylonitrile-butadiene-styrene copolymers (ABS), polycarbonates (PC), ABS / PC blends, PMMA, polyamides, glass fiber reinforced polyamides, polyvinyl chloride, polyvinylene fluoride, cellulose acetate, cycloolefin copolymers, liquid crystal polymers (LCP), polylactide, polyether ketones, polyetherimide, polyethersulfone, polymethacrylmethylimide, polymethylpentene, polyphenyl ether, polyphenylene sulfide, polyphthalamide, polyurethanes, polyvinyl acetate, styrene acrylonitrile copolymers, polyacrylates or polymethacrylates, polyoxymethylene, acrylic ester-styrene-acrylonitrile copolymers, polyethylene, polystyrene, polypropylene and / or polyesters such as polybutylene terephthalate (PBT) and / or polyethylene terephthalate (PET). Suitable metal substrates include aluminum, stainless steel, steel, magnesium, zinc, nickel, brass, copper, titanium, ferrous metals and austenitic alloys.The metal substrate is preferably anodized aluminum (e.g., E6EV1). Substrates can be painted, printed, vapor-deposited, or sputter-coated. The substrates to be bonded can take on any shape required for the use of the resulting composite body. In the simplest form, the substrates are flat. Furthermore, the substrates, especially glass, can be coated on their surfaces with a (particularly black) lacquer.

[0239] With the help of the adhesive tape according to the invention, excellent structural or (semi-)structural bonds can be achieved. "Structural or (semi-)structural bonding" refers in particular to a bond in which a potential fracture point upon stress on the adhesive bond does not necessarily have to be located in the adhesive layer or in the carrier material with the adhesive layer(s) between the components to be bonded, but can occur with equal probability at any other location on the objects bonded by the structural adhesive. The durability of the bond can therefore be as high as the durability of the bonded materials and may even exceed it.In the case of high-strength and / or resistant materials to be bonded, the expert speaks of (semi-)structural bonding if the bond strength is higher than that achieved with a (non-reactive, structural) pressure-sensitive adhesive (PSA).

[0240] The special feature of the adhesive tape according to the invention is that the stability of the structural bond lasts as long as the adhesive bond or the adhesive tape has not been heated or warmed to temperatures above the suitable foaming temperature by heat input. Since the foaming of the expandable microballoons takes place at temperatures of 115°C or more, depending on the type of expandable microballoon, the structural bond can be easily removed after the adhesive bond 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 invention therefore offers a significant advantage over conventional reactive structural adhesive tapes.

[0241] Generally, to activate the reactive, structural adhesive, the adhesive placed between the substrates to be bonded—particularly in the form of an adhesive tape—is heated. This initiates the reaction between the polymer component and the isocyanate-containing component, and the curing reaction takes place. A preferred design utilizes a heating press to apply the heat. The die of the heating press is made of aluminum, brass, or bronze, for example, and its shape is typically adapted to the contours of the metal part or the dimensions of the die-cut. After heat activation, the anodized aluminum part with the laminated adhesive product is removed from the molded part using at least one layer of adhesive tape. The entire process can also be automated.

[0242] Heat activation typically occurs at activation temperatures ranging from at least 60°C up to temperatures of 150 to 190°C. The activation temperature of the reactive, structural adhesive is related to the suitable foaming temperature of the expandable microballoons used, and the skilled person can select these two parameters based on their specialist knowledge. 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 of at least 80°C, and even more preferably of at least 110°C.

[0243] The adhesive tape according to the invention can be used in a process for bonding two components or substrate surfaces together using the adhesive tape. The process is fundamentally characterized in that the adhesive film is placed between the two substrate surfaces of the components, contacting them, and then cured by applying 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 effected by means of the adhesive tape according to the invention (carried out according to the described or another method for bonding two substrate surfaces) between two substrates A and B, as described herein, comprising: a) exposing the adhesive bond comprising a substrate A, the adhesive tape according to the invention and a substrate B (substrate A / adhesive tape / substrate B) to a temperature in a range from 115°C to 150°C, preferably of approximately 120°C; b) separating the adhesive bond into the individual substrates A and B along the adhesive tape according to the invention; and optionally c) removing the residues of the adhesive tape according to the invention from substrate A and / or substrate B.

[0244] Depending on the type, structure, and shape of the substrates or adhesive bond, the adhesive bond can be separated into its two individual substrates A and B, for example, by pushing, sliding, twisting, peeling, and / or levering. Depending on the type / pattern of breakage of the adhesive tape, residues of the adhesive tape may be present on both substrate A and substrate B, or the adhesive tape may remain completely on substrate A or substrate B after separation. In all cases, the residues of the adhesive tape can be removed, preferably by simply peeling them off and preferably without leaving any residue. The separated substrates A and / or B can be reused or bonded again, if necessary after cleaning.

[0245] The required (separation) temperature of 115 °C to 150 °C can be achieved by applying heat from conventional heat sources, such as a hot plate (heating press), furnace, laser, IR radiation, or induction. It is therefore preferred that the process is characterized in that in step a), the temperature is applied using a laser, a furnace, IR radiation, induction, or a hot plate (heating press).

[0246] After separating the adhesive tape from at least one substrate, preferably from at least two substrates, residues of the adhesive layer may remain on the substrate or substrates (also called components). The remaining parts of the adhesive layer on the substrate or substrates can preferably be easily removed by peeling. In a preferred variant, the method according to the invention is therefore characterized in that the residues of the adhesive layer can be removed without leaving any residue. The ability to remove the adhesive tape or adhesive layer without leaving any residue eliminates the high cleaning effort if the substrates are to be reused. Rebonding is possible with no or only very little cleaning effort.

[0247] The adhesive tape according to the invention can be used in particular wherever the demands on bonding quality—for example, with regard to bonding strength or durability—are high. This is the case, for example, in the field of electronic devices or automotive engineering, but also in many other areas. The adhesive is particularly suitable for bonding difficult substrates, small bonding surfaces—for example, small-area bonding in the consumer electronics sector—and / or different substrates to be bonded, especially in the electronics industry, to name just a few.

[0248] An exemplary use according to the invention relates to the bonding of anodized aluminum such as E6EV1 to a plastic. The plastic parts for consumer electronics components are preferably based on plastics that can be processed by injection molding. This group includes, for example, ABS, PC, ABS / PC blends, PMMA, polyamides, glass fiber reinforced polyamides, polyvinyl chloride, polyvinylene fluoride, cellulose acetate, cycloolefin copolymers, liquid crystal polymers (LCP), polylactide, polyether ketones, polyetherimide, polyethersulfone, polymethacrylmethylimide, polymethylpentene, polyphenyl ether, polyphenylene sulfide, polyphthalamide, polyurethanes, polyvinyl acetate, styrene acrylonitrile copolymers, polyacrylates or polymethacrylates, polyoxymethylene, acrylic ester styrene-acrylonitrile copolymers, polyethylene, polystyrene, polypropylene or polyester (e.g. PBT, PET). This list is not exhaustive.The components can take any shape required for the production of a component or housing for consumer electronics. In their simplest form, they are planar. However, 3D components are also quite common. The components can serve a wide variety of functions, such as housings, viewing windows, or stiffening elements. Polycarbonate, PMMA, or ABS are very preferred plastics.

[0249] The plastic parts can be painted or otherwise coated. Coatings used to functionalize or modify the surface of plastics include anti-reflective coatings, anti-fingerprint coatings, anti-scratch coatings, or decorative printing (so-called backprints). Furthermore, plastics can also be coated with (inorganic) layers, such as conductive layers. Indium tin oxide is particularly suitable as a conductive layer. Some of these coatings and layers are thermosensitive, thus necessitating the use of adhesive products that can be processed at low temperatures.

[0250] For an application cited as an example in consumer electronics articles, the adhesive tapes according to the invention are typically further processed into diecuts. These are produced, for example, by a laser cutting process, flatbed die-cutting, or rotary die-cutting. The diecut typically has the dimensions of the anodized aluminum part, but can also be somewhat smaller to allow for slight squeezing during the bonding process. There are a wide variety of possible applications for the adhesive tape according to the invention. The dismantling of touch panels has already been mentioned. Given the great importance of mobile phones, this is a particularly important application. On the one hand, a very strong and, above all, sealing bond for mobile phone displays is desired. On the other hand, it is often necessary to remove the display.The adhesive tape according to the invention is ideally suited for this purpose.

[0251] Finally, so-called "reworkability" is an issue that is becoming increasingly important. For example, in the automotive industry, the requirements for the separate disposal of products at the end of their life cycle are increasing. 1 It is therefore important that components made of different materials be separated into their individual components before disposal, even if these components were previously "inseparably" connected. The present invention enables a very strong and permanent connection of different components while still allowing their separation upon request. The invention therefore also relates to the use of the described adhesive tape according to the invention in the automotive industry.

[0252] Experimental part:

[0253] Chemicals used:

[0254]

[0255] General manufacturing instructions - for comparative examples 1 to 4 and 6 as well as examples 1 a to 4b and 6a and 6b:

[0256] The respective components were dispersed or homogeneously dissolved in methyl ethyl ketone according to their respective compositions, so that the total content of the aforementioned compositions in the solvent was 20 wt.%. The solution or dispersion was then coated, using known methods, onto a release paper known to those skilled in the art to be suitable for silane-containing compositions and dried in a suitable forced-air drying cabinet at 70 °C for 30 minutes, resulting in an adhesive tape of 100 pm (dry film thickness) in each case.

[0257] Comparative Example 1, Example 1 a and 1 b

[0258] Comparative example 2, examples 2a and 2b

[0259] Comparative example 3, examples 3a and 3b

[0260] Comparative Example 4, Examples 4a and 4b Comparative Example 6, Examples 6a and 6b

[0261] Push out - Results:

[0262] The push-out test allows for determination of the bond strength of an adhesive product in the direction of the adhesive layer normal. A circular first substrate (1) made of polycarbonate (PC, thickness 3 mm) with a diameter of 21 mm is provided, a second substrate (2) made of polycarbonate (PC, thickness 4 mm) – square with a side length of 40 mm – with a circular, centrally located opening (bore) of 9 mm in diameter, and the adhesive film sample to be tested, which was also cut (cut or punched) to a circular shape with a diameter of 21 mm.

[0263] A test specimen is produced from the three aforementioned components by precisely pre-laminating the adhesive tape with the free surface onto the substrate (1) (at 70 °C for 5 s). The temporary carrier is then removed, and this composite, with the now exposed side of the adhesive product, is concentrically pre-laminated onto the substrate (2) (also at 70 °C for 5 s), so that the circular recess of the substrate 2 is positioned exactly centrally above the circular first substrate 1 (bonding area thus 282 mm 2 ). Care is taken to ensure that the total exposure time (70 °C) during the pre-lamination process does not exceed 20 s. The entire composite is then pressed at 90 °C for 120 seconds at a pressure of 10 bar, creating the test specimen.

[0264] A portion of the produced test specimens is initially measured after compression and 24 hours of storage at 23°C and 50% relative humidity (see column 1 of Tables 1 & 2). Foaming is carried out using a hot plate at 150°C. Another portion of the produced test specimens is placed on the hot plate preheated to 150°C for 1 minute. The temperature input causes the expandable microballoons to expand and the adhesive film to foam. The push-out values ​​are measured for some of the test specimens directly after foaming (see column 2 of Tables 1 & 2). Yet another portion of the test specimens are not measured after foaming but are stored / reconditioned at room temperature (23°C) for 1 hour and only then are the push-out tests carried out (see column 3 of Tables 1 & 2).

[0265] The testing is carried out as follows: A tensile testing machine is equipped with a cylindrical punch (steel, diameter 7 mm) and the test specimen is clamped over the substrate (2) in a holder of the tensile testing machine such that the substrate (1) is only held in place by the adhesive and can be detached by applying sufficient pressure when the adhesive is released. The sample is fixed in such a way that any possible bending of the substrate (2) due to the application of force during the test is minimized. The cylindrical punch is pressed through the hole in substrate (2) perpendicular (i.e. parallel and opposite to the normal vector of the adhesive product surface) and centrically onto the exposed surface of the adhesive product at a constant speed of 10 mm / min. The tests are carried out in a standard test environment (23 °C at 50 % RH).The force measured is the force at which the bond fails and the substrate (1) separates from the substrate (2) (detachment of the bond, recognizable by a sudden drop in force). The force is standardized to the bonded area (N / mm). 2 Due to the natural scatter of the individual results, caused by the most frequent adhesion failure (failure at the interface between substrate and adhesive film, and by the frequently achieved high bond strengths frequently associated with deformation and / or cold flow of the substrates (structural bond strength), the arithmetic mean of three individual tests is calculated. The second line of the results table gives the respective standard deviation of the measured value and the third line the fracture pattern (A: adhesive, K: cohesive, M: mixed fracture).

[0266] Table 1 - Results of the push-out tests for the (comparative) examples 1 to 4 and 6

[0267] Table 1 shows that all comparative examples and all inventive examples exhibit excellent initial bond strengths (see column 1) and that the bond strengths drop 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 strengths is reversible. They rise back to their previous level after reconditioning the test specimens for 1 hour at 23°C (see column 3). In the inventive examples (see column 3), the increased temperature causes the microballoons to expand, and the resulting low bond strengths remain constant even after cooling or reconditioning.The bond strengths drop so much that the two substrates of the test specimen can be easily separated from each other and the remaining adhesive tape can be removed without leaving any residue.

[0268] Comparative Example 5 and Examples 5a, 5b, 5c and 5d

[0269] Manufacturing instructions - Comparative example 5 and examples 5a to 5d:

[0270] The adhesive tape was prepared from the quantities of Dispercoll U53, Dispercoll BL XP 2514, Borchigel 0625, and Expancel 043 Wil 80 listed in the table above. The formulation components were mixed as an aqueous dispersion in a drum with an anchor stirrer at 60 rpm for 15 minutes at room temperature. The solids content was adjusted to 46 wt.% by adding demineralized water. A web coating system was used to apply a coating to various temporary carriers using a doctor blade. The water was then removed in a drying tunnel at 40 °C for 15 minutes. Push-out results:

[0271] Table 2 - Results of the push-out tests for Comparative Example 1 and Examples 5a to 5d

[0272] Table 2 shows that Comparative Example 5 and Inventive Examples 5a to 5d exhibit excellent initial bond strengths (see column 1) and that the bond strengths drop 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 strengths is reversible. They rise back to their previous level after reconditioning the test specimens for 1 hour at 23°C (see column 3). In Inventive Examples 5a to 5d (see column 3), the increased temperature causes the microballoons to expand, and the resulting low bond strengths remain constant even after cooling or reconditioning.The bond strengths drop so much that the two substrates of the test specimen can be easily separated from each other and the remaining adhesive tape can be removed without leaving any residue.

Claims

Patent claims 1. Adhesive tape, designed and arranged to be separated after permanent bonding, comprising at least one or consisting of at least one adhesive layer which comprises a reactive, structural adhesive, characterized in that the reactive, structural adhesive comprises expandable microballoons which have a starting temperature required for expansion of at least 94 °C.

2. Adhesive tape according to claim 1, characterized in that the reactive, structural adhesive contains the microballoons in an amount of 1 wt.% to 25 wt.%, in particular from 2 wt.% to 20 wt.%, more preferably from 5 wt.% to 10 wt% and most preferably about 10 wt%.

3. Adhesive tape according to claim 1 or claim 2, characterized in that the starting temperature of the expandable microballoons 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. Adhesive tape according to one of claims 1 to 3, characterized in that the adhesive layer has a thickness between 25 pm and 750 pm, in particular between 50 pm and 300 pm.

5. Adhesive tape according to one of claims 1 to 4, characterized in that the expandable microballoons have a particle size D(0.5) of 16 to 24 pm.

6. Adhesive tape according to one of claims 1 to 5, characterized in that the adhesive tape is a transfer adhesive tape and consists of an adhesive layer.

7. Adhesive tape according to one of claims 1 to 6, characterized in that the reactive structural adhesive comprises a polymer component formed from at least one thermoplastic polymer or an elastomer.

8. Adhesive tape according to claim 7, characterized in that the thermoplastic polymer is a polyurethane.

9. Adhesive tape according to one of claims 1 to 8, characterized in that the reactive, structural adhesive further comprises at least one peroxide, and in that the polymer component comprises at least 50 wt.% of thermoplastic polymers which do not have C=C double bonds and C=C triple bonds.

10. Adhesive tape according to claim 9, characterized in that the at least one peroxide has the general structural formula ROOR', where R and R' each represent organyl groups or together represent a cyclic organyl group, and in that the peroxide in solution has a 1-minute half-life temperature of less than 200 °C.

11. Adhesive tape according to claim 9 or claim 10, characterized in that the peroxide comprises dicumyl peroxide.

12. Adhesive tape according to one of claims 1 to 8, characterized in that the polymer component is formed from at least one polymer which contains functional groups which can react with isocyanate, and the adhesive further comprises a crosslinker component formed from at least one isocyanate-containing particulate compound.

13. Adhesive tape according to claim 12, further comprising at least one further component from the group of epoxides and / or epoxy compounds.

14. Adhesive tape according to one of claims 1 to 7, characterized in that the reactive, structural adhesive comprises a mixture of at least one nitrile rubber S1 and a reactive component, in particular a reactive resin.

15. A method for releasing a permanent structural bond between two substrates A and B effected by means of an adhesive tape according to one of claims 1 to 14, comprising the following steps: a) exposing the adhesive bond substrate A / adhesive tape according to one of claims 1 to 14 / substrate B to a temperature in a range of 115 °C to 150 °C, preferably of approximately 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, characterized in that in step a) the temperature is controlled by using a heating plate, a heating press, an oven, a laser, IR radiation or induction, preferably by using a heating plate 17. Method according to claim 15 or claim 16, characterized in that the residues of the adhesive layer are removed without residue.

18. Use of an adhesive tape according to one of claims 1 to 14 in the Automotive industry.

19. Use of an adhesive tape according to one of claims 1 to 14 in the Electronics industry.

Images