Adhesive tape, bonded assembly and method for electrically dissolving the bonded assembly

Abstract

The invention relates to an adhesive tape, to a bonded assembly, to a method for electrically dissolving the bonded assembly and to the use of the adhesive tape for bonding components in electronic devices, motor vehicles, medical devices and dental devices. The adhesive tape comprises at least one layer D of adhesive, where the adhesive of the adhesive layer D is a reactive, heat-activatable adhesive and comprises at least one electrolyte.

Description

[0001] Adhesive tape, bonded composite and method for electrically releasing the bonded composite

[0002] The invention relates to an adhesive tape, a bonded composite, a method for electrically releasing the bonded composite and the use of the adhesive tape for bonding components in electronic devices, automobiles, medical devices and dental devices.

[0003] Double-sided pressure-sensitive adhesive tapes are typically used to bond metal parts to plastics. The adhesive strength required is sufficient to fix and secure the metal components to the plastics. Steel, stainless steel, and aluminum are preferred metals. Plastics used include PVC, ABS, PC, or blends based on these plastics. However, the requirements for portable consumer electronics are constantly increasing. These items are becoming ever smaller, so the bonding surfaces are also shrinking. These conditions are particularly problematic for metal bonding to plastics. This can be achieved particularly effectively through the use of heat-activated films, which can develop particularly high adhesive strength upon activation.

[0004] Reactive heat-activated adhesives can be based on different polymers and crosslinking chemicals and mechanisms.

[0005] WO 2013 / 174650 A1, for example, discloses a heat-activatable adhesive based on a mixture of a nitrile rubber and a phenolic resin as reactive resin.

[0006] Recently, there has been increased interest in "debonding-on-demand" functionalities, driven by environmental regulations, end-customer awareness of sustainability, and increasing cost pressure in manufacturing. Application scenarios for debonding processes are classified into rework, repair, recycling, and processing aids.

[0007] Debonding technologies aim to achieve cohesive separation of the adhesive layer or adhesive detachment of the adhesive layer from the substrate. While the former requires cleaning of the substrate before rebonding, the latter does not require cleaning.

[0008] However, adhesive release technologies that guarantee the required high and permanently reliable bond strength are generally more difficult to implement or take a very long time to apply, such as removal by means of a solvent that infiltrates the substrate.

[0009] For example, cohesive-splitting adhesive bonds are currently predominantly used, particularly in the rework or repair of electronic devices such as smartphones and tablet computers. These adhesive bonds are often designed as pressure-sensitive adhesive tapes whose cohesion is reduced by increasing the temperature to such an extent that manual, cohesive separation of the bond is possible. This results in extensive rework to prepare the substrate surface, which is contaminated with adhesive residue, for rebonding.

[0010] In addition to heat-mediated separation processes, electrical separation processes are also being discussed. For example, EP 3031875 B1 discloses the reduction of the bond strength of an acrylate adhesive by applying a voltage.

[0011] However, reactive heat-activated adhesive bonds generally have very high bond strengths due to the chemical setting process.

[0012] These adhesive tape solutions are therefore not removable or only removable without damaging the substrates bonded to them and requiring a great deal of force.

[0013] The present invention is therefore based on the object of providing an adhesive tape comprising at least one adhesive layer D, wherein the adhesive of the adhesive layer D is a heat-activatable adhesive, wherein the adhesive tape should be removable from at least one substrate with minimal force. At the same time, the adhesive strength of the adhesive tape to the substrates to be bonded should not be adversely affected prior to removal.

[0014] The object is achieved according to the invention by the adhesive tape according to claim 1.

[0015] The adhesive tape according to the invention comprises an adhesive layer D, wherein the adhesive of the adhesive layer D is a reactive heat-activatable adhesive and contains at least one electrolyte.

[0016] By means of the electrolyte contained therein, the adhesive layer D can be electrically detached by applying a voltage. Surprisingly, it has been found that the reactive heat-activatable adhesive containing at least one electrolyte, and thus the adhesive tape comprising the heat-activatable adhesive, can be electrically detached from bonded substrates simply and quickly without great effort by applying a voltage, and at the same time, the adhesive strength of the adhesive tape to the substrates to be bonded is not negatively affected before the detachment.

[0017] Adhesive tapes and methods for electrically detaching or electrically reducing adhesive strength are known in principle in the prior art. As explained above, EP 3031875 B1 discloses such an electrical method. The electrically detachable adhesive is an acrylate-based one.

[0018] However, it was not foreseeable in this case that a film-like, heat-activated adhesive tape, with comparatively high bond strengths on various substrates, could be electrically removed after bonding without adversely affecting the adhesive tape's bond strength to the substrates to be bonded prior to removal. At the same time, removal is clean and easy.

[0019] In particular, it was not foreseeable that a comparatively rigid matrix in the adhesive film or adhesive tape, such as, for example, comprising a rubber, could be designed to be electrically removable and that the electrolyte would be compatible with the matrix at all and, furthermore, could migrate quickly enough through the matrix without negatively affecting the bond strength.

[0020] The adhesive tape according to the invention is preferably a double-sided adhesive tape. For the sake of simplicity, the adhesive tape according to the invention is also referred to as "adhesive tape" in the double-sided embodiments within the scope of the present invention.

[0021] The present invention relates to an adhesive tape that can be produced in any desired form, with adhesive tape rolls being preferred. The adhesive tape, particularly in web form, can be produced either in the form of a roll, i.e., wound upon itself in the shape of an Archimedean spiral, or as an adhesive strip, such as is obtained, for example, in the form of blanks or die-cuts.

[0022] The adhesive tape according to the invention is in particular in web form. A web is understood to be an object whose length (extension in the x-direction) is many times greater than its width (extension in the y-direction), and whose width is approximately, preferably exactly, uniform along the entire length.

[0023] The general term “adhesive tape”, synonymously also called “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.

[0024] In addition to the longitudinal dimension (x-direction) and width (y-direction), the adhesive tape also has a thickness (z-direction) perpendicular to both dimensions, with the width and longitudinal dimensions being many times greater than the thickness. The thickness is as uniform as possible across the entire surface area of ​​the adhesive tape, determined by its length and width, and preferably exactly the same within tolerances.

[0025] The statements apply analogously to the carrier layer(s) which, as part of the adhesive tape, form or form a layer in the x and y directions according to some preferred embodiments.

[0026] It is understood that the individual layers are arranged on top of each other along the z-direction.

[0027] All statements of the description apply to the adhesive tape according to the invention, the method according to the invention for producing the adhesive tape, the bonded composite according to the invention, the method according to the invention for producing the bonded composite as well as the method for electrically detaching the composite and the use of the adhesive tape according to the invention.

[0028] The invention also encompasses all features that are the subject matter of any dependent patent claims. Furthermore, the invention encompasses combinations of individual features with one another, including combinations of different degrees of preference. Thus, for example, the invention encompasses the combination of a first feature designated as "preferred" with a second feature designated as "particularly preferred." This also encompasses subject matter designated as "embodiments" with different degrees of preference.

[0029] The adhesive of adhesive layer D is described in more detail below.

[0030] The adhesive layer D contains at least one electrolyte.

[0031] An "electrolyte" is understood here as a chemical compound "that is dissociated into ions in the solid, liquid, or dissolved state and that moves in a directed manner under the influence of an electric field," as listed in the Wikipedia entry "Electrolyte" dated January 4, 2023. The electrolyte of the adhesive layer D is preferably selected from the group consisting of ionic liquids and metal salts, with ionic liquids being particularly preferred.

[0032] In particular, using one or more ionic liquids as electrolytes allows the adhesive tape to be easily removed without negatively affecting its adhesive properties. Ionic liquids have the advantage of being easily and homogeneously distributed throughout the polymer matrix of adhesives, and removal is faster than with other electrolytes.

[0033] Furthermore, the components of ionic liquids are non-volatile, especially at room temperature. Ionic liquids are also comparatively heat-stable, non-flammable, and chemically stable.

[0034] For the purposes of the present invention, ionic liquids are salts that are liquid at room temperature, i.e., 23 °C. Ionic liquids therefore contain anions and cations.

[0035] Ionic liquids are therefore particularly well suited as electrolytes in the separation process or process for electrical dissolution according to the invention.

[0036] When a voltage is applied, the anions migrate to the anodic side and the cations to the cathodic side. Without wishing to be limited to this, it can be assumed mechanistically that this leads to a reduction in the adhesive strength of the adhesive layer containing the ionic liquid to at least one substrate, thereby achieving an adhesive cleavage between the adhesive and the at least one substrate.

[0037] In principle, all ionic liquids are suitable for the present invention.

[0038] The ionic liquids used in the present invention contain at least one anion and at least one cation. It is also conceivable for the ionic liquid to comprise two or more types of anions and / or two or more types of cations. Furthermore, it is conceivable for two or more different ionic liquids to be added to the adhesive layer D, or for the adhesive layer D to then contain two or more different ionic liquids.

[0039] Preferably, the anion of the ionic liquid is selected from the group consisting of Surprisingly, this reduces the bond strength in reactive heat-activatable adhesives by applying a voltage, thus resulting in good electrical detachability of the adhesive tape according to the invention. In particular, this anion allows for particularly rapid (re-)detachment, and no residues remain.

[0040] Particularly preferably, the anion is selected from the group consisting of (CFsSC^N- and (FSO2)2N-.

[0041] These anions are particularly suitable because they achieve the best electrical detachability. In particular, detachment (and re-detachment) with these anions is particularly fast and leaves no residue.

[0042] Preferably, the cation of the ionic liquid is selected from the group consisting of imidazolium-based cations, pyridinium-based cations, pyrrolidine-based cations and ammonium-based cations.

[0043] Surprisingly, this reduces the bond strength in reactive heat-activatable adhesives by applying a voltage, thus resulting in good electrical detachability of the adhesive tape according to the invention. In particular, this anion allows for particularly rapid (re-)detachment, and no residues remain.

[0044] Particularly preferably, the cation is selected from the group consisting of imidazolium-based cations.

[0045] These cations are particularly well-suited because they achieve the best electrical detachability. In particular, detachment (and re-detachment) with these cations is particularly fast and leaves no residue.

[0046] Most preferably, the cation is selected from the group consisting of 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium. The cation is again preferred as 1-ethyl-3-methylimidazolium.

[0047] The electrolyte of adhesive layer D is particularly preferably selected from the group consisting of the ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM-FSI). Surprisingly, this results in a reduction in bond strength in reactive heat-activatable adhesives by applying a voltage, thus providing good electrical removability of the adhesive tape of the invention. In particular, (re-)removal with this anion is particularly rapid, and no residues remain.

[0048] It is preferred that the first adhesive layer D contains 2 to 20 wt.%, particularly preferably 5 to 18 wt.%, of electrolytes, preferably ionic liquids, based on the total amount of the adhesive.

[0049] With such a preferred or particularly preferred amount of electrolytes, in particular ionic liquids, a comparatively rapid electrical detachment is made possible, wherein at the same time the adhesion of the adhesive layer to the adjacent layers, in particular at least one substrate, is not adversely affected before detachment.

[0050] The mass of adhesive layer D is a reactive heat-activated adhesive.

[0051] Reactive heat-activated adhesives (also called “reactive adhesives”) are polymer systems that contain functional groups such that a chemical reaction takes place when heat is applied, whereby the adhesive chemically sets and produces greater internal strength.

[0052] Likewise, it may be advantageous to design the reactive adhesives in such a way that they become softer and / or more flowable at elevated temperatures in order to optimally adapt to the adhesive bond; this is achieved in particular and preferably by a thermoplastic component.

[0053] The chemical reaction mentioned and the physical melting result in a high bonding strength and thus adhesive effect.

[0054] The functional groups are also referred to as reactive groups. In the case of reactive heat-activatable adhesives within the scope of the present invention, these groups are particularly constituents of the polymers and / or other components of the adhesive, such as, in particular, resins, referred to in this context as reactive resins, and / or crosslinkers.

[0055] As the term "heat-activated" suggests, the activation that leads to the bonding effect occurs through the application of heat. This means that these adhesives are not activated at room temperature, especially at 23°C, meaning the mechanism that leads to permanent bonding is not triggered.

[0056] Preference is given to an adhesive tape according to the invention in which the heat-activatable adhesive is activated at temperatures of 110°C or more, and preferably at temperatures of 110°C to 250°C, particularly preferably at 120°C to 200°C. "Heat-activatable" is thus preferably understood to mean that activation takes place at a temperature of 110°C or more, and preferably at temperatures of 120°C to 250°C, particularly preferably 120°C to 200°C.

[0057] The duration of activation is preferably from 5 seconds to 10 minutes, particularly preferably from 5 seconds to 6 minutes.

[0058] According to preferred embodiments of the invention, the duration is 6 to 10 minutes, in particular at an activation temperature of, for example, 120 °C.

[0059] According to further preferred embodiments of the invention, the duration is 5 seconds to 1 minute, in particular 30 seconds, in particular at an activation temperature of, for example, 180 °C.

[0060] For high activation temperatures within the temperature ranges mentioned, a correspondingly short activation time is preferred, while for lower temperatures, a correspondingly longer activation time is chosen. This depends, in particular, on the desired bond strength.

[0061] Activation is also preferably carried out using pressure, also called compression pressure. The compression pressure is preferably from 1 to 30 bar, particularly preferably from 3 to 30 bar, very particularly preferably from 5 to 30, and again preferably from 5 to 15 bar, for example and in particular 10 bar.

[0062] Before activation, a so-called pre-lamination is preferably carried out to achieve optimal wetting of the substrate. This is achieved, for example, by preheating the substrates to be bonded.

[0063] For this purpose, the substrates to be bonded are preferably heated to a temperature of 95 to 120 °C. The adhesive layer is preferably applied to the respective substrate at a pressure of 2 to 6 bar for a duration of 3 to 10 seconds.

[0064] This ensures that the adhesive flows evenly onto the substrate before activation.

[0065] As a reactive heat-activatable adhesive, preference is given to using one based on a mixture of at least one nitrile rubber S1 and a reactive component, in particular a reactive resin.

[0066] The weight fraction of nitrile rubber S1 is preferably between 25 and 70%, particularly preferably between 30 and 60%, of the total composition of the reactive heat-activatable adhesive. The nitrile rubbers S1 preferably have an acrylonitrile content of 15 to 45%. Another criterion for the nitrile rubber S1 is the Mooney viscosity. Since high flexibility at low temperatures must be ensured, the Mooney viscosity should preferably be below 100 (Mooney ML 1 +4 at 100 °C; according to DIN 53523).

[0067] The proportion of reactive resins in the heat-activatable adhesive is preferably between 75 and 30 wt.%.

[0068] Reactive resins are understood to be short- to medium-chain oligomers or polymeric compounds, in particular with average molecular weights in the range up to 10,000 g / mol.

[0069] A particularly preferred group are epoxy resins. The weight-average molecular weight Mw of the epoxy resins is preferably from 100 g / mol up to a maximum of 10,000 g / mol for polymeric epoxy resins.

[0070] Preferably, the reactive resin is selected from the group consisting of phenol resins, melamine resins, terpene-phenol resins, epoxy resins and polyisocyanates.

[0071] 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.

[0072] Particularly preferably, at least one phenolic resin is included as the reactive resin. Novolak resins and resole resins, or combinations of novolak resins and resole resins, are particularly suitable.

[0073] Novolak resins are, in accordance with the expert understanding, polycondensates of phenol and formaldehyde under acidic conditions, with the formaldehyde-phenol ratio being in particular less than 1:1.

[0074] Resol resins are produced by polycondensation of phenol and formaldehyde under basic conditions.

[0075] According to particularly preferred embodiments of the invention, the adhesive contains a combination of at least one novolak resin and at least one resole resin. This allows a particularly high cohesion of this adhesive layer to be achieved, thus further optimizing the bond strength of the adhesive tape in the bonded assembly. To accelerate the reaction between the two components, crosslinkers and accelerators are optionally added to the mixture.

[0076] HMTA (hexamethylenetetramine) is preferred as a crosslinker.

[0077] According to particularly preferred embodiments of the invention, the reactive heat-activatable adhesive of the adhesive layer D is a reactive heat-activatable adhesive based on at least one mixture of at least one nitrile rubber S1 and at least one reactive component, in particular a reactive resin, wherein the reactive component is preferably at least one reactive resin selected from the group consisting of epoxy resins, melamine resins, phenolic resins, such as in particular novolak resins and resole resins, terpene-phenolic resins and polyisocyanates, wherein phenolic resins, in particular novolak resins and / or resole resins, are particularly preferred.

[0078] The adhesive of the adhesive layer D may also contain other conventional additives, such as catalysts, in particular zinc oxide (ZnO), fillers, pigments and anti-aging agents.

[0079] If an adhesive comes into contact with a layer from which so-called rubber toxins such as copper, manganese (II), iron (II), cobalt, or nickel ions can potentially be released, it is advantageous to add at least one type of metal deactivator, also known as a "metal scavenger." Specific examples include ADK-Stab CDA-1, CDA-1 H, CDA-6, and CDA-10, as well as ADK-Stab ZS-27 or ZS-90 from Adeka, Hostanox OSP1 from Clariant, Naugard XL-1 from SIGroup, and Irganox MD-1024 from BASF. Typical application amounts are up to 0.5 wt.% based on the total weight of the adhesive.

[0080] Another object of the present invention is a bonded composite comprising at least the following layers:

[0081] • A first substrate A; and

[0082] • A second substrate B; and

[0083] • An adhesive tape according to the invention which is arranged between the substrate A and the substrate B and bonds the substrates A and B together.

[0084] The present invention further provides a method for electrically dissolving the composite according to the invention, comprising at least the following method steps: i.) Applying a voltage to two different locations on the composite, wherein the voltage is preferably between 2 and 50 V. The voltage is applied according to step i.) of the method according to the invention for electrically dissolving the composite.

[0085] The voltage is in particular a direct voltage.

[0086] According to preferred embodiments of the invention, the voltage is from 3 to 12 V. Such a voltage can be applied in particular by using a battery located in the immediate vicinity of the bond, such as in particular and for example in a mobile phone, tablet, etc.

[0087] According to further preferred embodiments of the invention, the voltage is between 12 and 50 V. This comparatively high voltage allows for particularly rapid detachment; the voltage only needs to be applied for a few seconds.

[0088] The expert basically knows how to apply a voltage without causing unwanted short circuits.

[0089] The duration of the application of the voltage in step i.) can, in particular depending on the selected voltage, be from a few seconds, in particular 2 seconds, up to 900 seconds, preferably up to 600 seconds.

[0090] Of course, it is also conceivable that the voltage is applied for a longer period than 900 seconds, especially if the voltage is comparatively low.

[0091] By means of the method according to the invention for electrically detaching the composite according to the invention, the substrates A and B can be detached from one another quickly and easily without the need for excessive force.

[0092] If the layers do not separate from one another without further action after application of the voltage, the method according to the invention comprises at least the further method step: ii.) application of force to the adhesive layer D and / or the substrate A and / or the substrate B, so that the distance between the substrates A and B is increased.

[0093] The force that may still be required according to step ii.) is significantly lower than the adhesive force before applying the voltage according to step i.)

[0094] The voltage is applied according to step i.) at two different locations on the bonded composite according to the invention. The appropriate locations for applying the voltage depend on the structure of the adhesive tape and the bonded composite, and thus on the properties of the individual layers and the bonded substrates A and B.

[0095] Some preferred embodiments are described below. According to preferred embodiments, the adhesive tape is a transfer adhesive tape and consists of the adhesive layer D.

[0096] Such an adhesive tape can advantageously be electrically released again in a bonded composite with two substrates A and B in that both substrates A and B are electrically conductive. For this purpose, a voltage is then applied to substrates A and B, resulting in a migration of anions to the anode and of cations to the cathode in the adhesive. Without wishing to be bound to a particular theory, the inventors assume the following mechanism: Applying the voltage causes a migration of the electrolyte, in particular a separation of the anions and cations of an ionic liquid, in the adhesive layer D. This greatly reduces the adhesion of the adhesive layer D to substrate A and substrate B, and these layers detach from one another.

[0097] According to preferred embodiments of the present invention, the bonded composite thus comprises the following layers:

[0098] • A first substrate A which is electrically conductive; and

[0099] • A second substrate B which is electrically conductive; and

[0100] • An adhesive tape according to the invention, which consists of the adhesive layer D and is arranged between the substrate A and the substrate B and bonds the substrates A and B to one another.

[0101] According to further preferred embodiments, the adhesive tape comprises, in addition to the first adhesive layer D, at least the following layers:

[0102] • A second adhesive layer C; and

[0103] • at least one electrically conductive carrier layer T arranged between the layers D and C.

[0104] Such an adhesive tape can be adapted as a double-sided adhesive tape to a variety of different substrates via the second adhesive layer C. In principle, these can be the same substrates as in the previous embodiments, in which the adhesive tape is a transfer adhesive tape.

[0105] Such an adhesive tape can also be used, in particular and advantageously, to later separate substrates A and B from one another, of which only one is electrically conductive, for example the substrate A. According to preferred embodiments, either xi.) only the carrier layer T or xii.) the carrier layer T and the second adhesive layer C are designed to be electrically conductive.

[0106] In this way, a voltage can be applied to xi.) the electrically conductive carrier layer or xii.) to the second adhesive layer C as well as to the conductive substrate A.

[0107] The adhesive tape is advantageously bonded beforehand as a double-sided adhesive tape in such a way that the electrically detachable adhesive layer D is bonded to the conductive substrate A and the second adhesive layer is bonded to the substrate B, which may or may not be conductive.

[0108] Without wishing to be bound to a particular theory, the inventors assume the following mechanism: By applying the voltage, a migration of the electrolyte occurs, in particular a separation of the anions and cations of an ionic liquid, in the adhesive layer D. As a result, the adhesion of the adhesive layer D to the substrate A is greatly reduced and these layers detach from each other.

[0109] According to preferred embodiments of the invention, xi.) only the carrier layer is electrically conductive. A voltage can be applied to this layer particularly well, particularly and preferably if the carrier layer projects laterally beyond at least one of the adhesive layers.

[0110] According to further preferred embodiments of the invention, xii.) the carrier layer and the second adhesive layer C are electrically conductive. Such a structure has the advantage that the voltage can be applied to the adhesive layer C. A lateral overhang of the carrier layer is not necessary. The adhesive tape can therefore be easily produced, especially since layers D, T, and C can be punched together.

[0111] Preferably, the adhesive tape according to the embodiments described above consists of the three layers D, T and C. For this purpose, the term three-layer composite DTC is also used in the context of the present application.

[0112] According to preferred embodiments of the present invention, the bonded composite thus comprises the following layers:

[0113] • A first substrate A which is electrically conductive; and

[0114] • A second substrate B; and

[0115] • An adhesive tape according to the invention, which consists of the three-layer composite DTC and bonds the substrates A and B together in such a way that the adhesive layer D is bonded to the conductive substrate A. According to further preferred embodiments, the adhesive tape comprises, in addition to the first adhesive layer D, at least the following layers:

[0116] • A second adhesive layer C; and

[0117] • at least one first electrically conductive carrier layer T arranged between the layers D and C; and

[0118] • at least one second electrically conductive carrier layer T', which is arranged on the surface of the adhesive layer D opposite the first electrically conductive carrier layer T; and

[0119] • A third adhesive layer C', which is arranged on the surface of the second electrically conductive carrier layer T' opposite the first adhesive layer D.

[0120] Such an adhesive tape has at least the layer structure CTDT'-C' and can be adapted as a double-sided adhesive tape to a variety of different substrates via the adhesive layers C and C'.

[0121] In principle, these can be the same substrates as in the previous embodiments, in which the adhesive tape is a transfer adhesive tape or has the three-layer DTC structure.

[0122] Such an adhesive tape can, in particular and advantageously, also be used to later separate substrates A and B from each other, neither of which is electrically conductive.

[0123] According to preferred embodiments, either xi.) only the carrier layers T and T' or xii.) the carrier layers T and T' and the second adhesive layer C and / or the third adhesive layer C' are designed to be electrically conductive.

[0124] In this way, a voltage can be applied to xi.) the two electrically conductive carrier layers or xii.) to at least one of the adhesive layers C and C' and to one of the carrier layers or the other adhesive layer.

[0125] Analogous to the above embodiments, it is assumed that the application of the voltage causes a migration of the electrolyte, in particular a separation of the anions and cations of an ionic liquid, in the adhesive layer D. As a result, the adhesion of the adhesive layer D to the electrically conductive carrier layers T and T' is greatly reduced and these layers detach from one another.

[0126] According to preferred embodiments of the invention, xi.) only the carrier layers T and T are electrically conductive. A voltage can be applied to these layers particularly well, particularly and preferably if the carrier layers T and T' project laterally beyond at least one of the adjacent adhesive layers.

[0127] According to further preferred embodiments of the invention, xii.) the carrier layers T and T' and the second and third adhesive layers C and C', respectively, are electrically conductive. Such a structure has the advantage that the voltage can be applied to the adhesive layers C and C'. A lateral overhang of the carrier layers T and T' is not necessary. The adhesive tape can therefore be produced easily, particularly since the layers C, T, D, T', and C' can be punched together.

[0128] Preferably, the adhesive tape according to the embodiments described above consists of the five layers C, T, D, T', and C'. For this purpose, the term five-layer composite CTDT'-C' is also used in the present application.

[0129] According to preferred embodiments of the present invention, the bonded composite thus comprises the following layers:

[0130] • A first substrate A; and

[0131] • A second substrate B; and

[0132] • An adhesive tape according to the invention which consists of the five-layer composite CTDT-C' and bonds the substrates A and B together.

[0133] The electrically conductive substrate of all embodiments can be, for example, a metal housing of a mobile phone.

[0134] The electrically non-conductive substrate of all embodiments can in particular be a housing made of a non-conductive material, such as plastic, or a battery or other components that are not electrically conductive, such as loudspeakers.

[0135] A further object of the present invention is the use of the adhesive tape according to the invention for bonding components in electronic devices, automobiles, medical devices and dental devices.

[0136] The carrier layers T as well as T and T' of all the above-mentioned embodiments are electrically conductive.

[0137] These layers are described in more detail below. For simplicity, the term "electrically conductive carrier layer" or simply "carrier layer" is used. Depending on the above embodiments, this refers to the carrier layer T or the carrier layers T and T'. The carrier layers T and T' are independent of each other and can be identical or different from each other.

[0138] The electrically conductive carrier layer preferably comprises at least one metal.

[0139] The metal is particularly preferably selected from the group consisting of copper, nickel, zinc, tin, silver, gold, aluminum, iron, chromium, and alloys of these metals. The metal is most preferably selected from the group consisting of aluminum, zinc, copper, and nickel. Aluminum is most preferred.

[0140] Preferably, the electrically conductive carrier layer has a layer thickness, measured in the z-direction, i.e. parallel to the stacking direction of the layer arrangement, of 10 nm (nanometers) to 50 pm (micrometers).

[0141] According to preferred embodiments of the invention, the electrically conductive carrier layer comprises a) at least one metal foil, preferably an aluminum foil, and / or b) at least one electrically conductive textile comprising at least one metal, preferably selected from the group consisting of copper and nickel, and / or c) one or more layers of at least one vapor-deposited metal, preferably selected from the group consisting of copper and aluminum, and / or d) at least one grid made of metal and / or e) a metal-vapor-deposited foil.

[0142] In principle, it is also conceivable that layer T contains a combination of two or more of the above-mentioned possibilities.

[0143] Metal foils, such as, for example, and preferably, aluminum foils, are known to those skilled in the art. The metal foil, for example, and preferably, aluminum foil, preferably has a layer thickness, measured in the z-direction, i.e., parallel to the stacking direction of the layer arrangement, of 5 to 50 μm, particularly preferably 10 to 30 μm.

[0144] Electrically conductive textiles are known to those skilled in the art, particularly under the English term "conductive mesh." This is a textile fabric, for example made of PET (polyethylene terephthalate), coated with a metal, such as copper and / or nickel, which makes the fabric electrically conductive.

[0145] It is also known to the person skilled in the art that metals can be vapor-deposited directly as a monolayer or multiple layers onto surfaces, such as the surface of an adhesive layer here.

[0146] Within the scope of the present invention, the electrically conductive carrier layer can be provided by vapor deposition of metal onto the adhesive layer D or the adhesive layer C or the adhesive layer C'. Furthermore, metal grids of various dimensions are known to those skilled in the art. Metal grids with suitable layer thicknesses can be produced, for example, by a scrim of appropriately thin metal threads or by punching at least one film of appropriate layer thickness.

[0147] In the case of a metal-deposited film, in particular a non-conductive film is vapor-deposited with metal in order to make it electrically conductive. The material of the film can in principle be selected from all materials that are suitable for being vapor-deposited with metal and used as a carrier film in adhesive tapes. The material is in particular selected from polyesters and polyolefins, although a mixture of several materials is also conceivable. As polyesters, polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are particularly preferred. As polyolefins, polypropylene (PP) and polyethylene (PE) are particularly preferred. According to preferred embodiments, the material of the film is selected from the group consisting of PET, PEN, PE, and PP.

[0148] The preferred film is made of PET (polyethylene terephthalate). Such a film is dimensionally stable and therefore easy to process without significant stretching or tearing. This makes it possible to permanently apply a homogeneous and seamless metal layer, ensuring permanent electrical conductivity, particularly in the z-direction, across the entire film.

[0149] In the embodiments in which at least one electrically conductive carrier layer T or at least two electrically conductive carrier layers T and T' are present, it is preferred that these extend laterally beyond at least one adjacent adhesive layer in at least one direction of extension of the layer plane and thus have a lateral projection. A voltage can then be applied to this lateral projection in a simple manner.

[0150] In the case of the five-layer composite, the lateral projections of the electrically conductive carrier layers T and T' are arranged spatially separated from each other according to advantageous embodiments. This facilitates the application of voltage to these two projections.

[0151] In the case of vapor-deposited metal as a carrier layer, it is preferred that this carrier layer laterally projects only one adjacent adhesive layer in at least one extension direction of the layer plane and that the respective other adhesive layer serves as a mechanical support for this metal layer. In this case, the metal layer has no actual carrier function. Instead, the other adhesive layer acts as a carrier for the metal layer. For the sake of simplicity, the term carrier layer for the metal layer is retained in these embodiments. The layer thickness of the

[0152] Layer T in this case greater than or equal to 10 nm (nanometers), preferably 50 to 200 nm.

[0153] According to preferred embodiments of the invention, the electrically conductive carrier layer T or T and / or T' comprises a) at least one metal foil, preferably an aluminum foil, and / or b) at least one electrically conductive textile comprising at least one metal, preferably selected from the group consisting of copper and nickel, and / or d) at least one metal grid and / or e) a metal-vaporized foil, and projects beyond the first adhesive layer D and the second adhesive layer C or the first adhesive layer D and the second adhesive layer C and / or the first

[0154] Adhesive layer D and the third adhesive layer C' in at least one

[0155] Direction of extension.

[0156] This allows tension to be applied to the carrier layer in a simple and safe manner. At the same time, the adhesive tape can be manufactured in a comparatively simple manner.

[0157] According to preferred embodiments of the invention, the electrically conductive carrier layer T or T and / or T' comprises one or more layers, preferably one layer, of at least one vapor-deposited metal, preferably selected from the group consisting of copper and aluminum.

[0158] According to particularly preferred embodiments of the invention, the electrically conductive carrier layer T or T and / or T' e) comprises a metal-deposited film and projects beyond the first adhesive layer D in at least one direction of extension. In this case, the film is metal-deposited, in particular on one surface, and the respective carrier layer is bonded to the first adhesive layer D, and thus to the electrically detachable layer, via the metallized surface.

[0159] This allows a voltage to be applied to the carrier layer in a simple and safe manner.

[0160] Within the scope of the present invention, the term "laterally projecting" refers to any type of lateral projection of the layer or layers in question and means that the respective layer in question extends further, particularly in the "xy" plane and thus laterally—perpendicular to the stacking direction—than the reference layer. Instead of the term "lateral projection," the terms "lateral extension" or "lateral extension section" are also used within the scope of the present invention.

[0161] The term "lateral" here refers to any direction of extension of the layer plane "xy" perpendicular to the stacking direction of the layers "z." The term is thus independent of the geometric shape of the adhesive tape in the "xy" plane, which can be, for example, a rectangle, as is common for adhesive tapes (see above), but also a square or a circle.

[0162] Minor variations in the dimensions of the individual layers in the “xy” plane resulting from the punching process or similar forming processes are not addressed here, in particular since such minor material overhangs are not suitable for systematically applying tension to them due to their dimensions.

[0163] Adhesive layers C, or C and C', can in principle be based on the same materials as adhesive layer D, whereby the adhesives of layers C, or C and C', need not contain electrolytes, but may. Layers C, or C and C', preferably do not contain electrolytes.

[0164] According to some embodiments of the three-layer composite DTC described above, the adhesive layer C is electrically conductive.

[0165] Likewise, the adhesive layer C and / or the adhesive layer C' of the five-layer composite CTDT'-C' can also be designed to be electrically conductive.

[0166] These layers are explained in more detail below. For the sake of simplicity, the term "electrically conductive adhesive layer" is used where appropriate. Depending on the above embodiments, this refers to the adhesive layer C or the adhesive layers C and / or C'. Furthermore, for the sake of simplicity, the expression "the adhesive layers C or C and / or C"' is used, which refers to the respective layers in the described embodiments of the adhesive tape comprising at least the three-layer composite or at least the five-layer composite.

[0167] The adhesive layers C and C' are independent of each other and can be the same or different from each other.

[0168] For this purpose, the electrically conductive adhesive layer preferably contains at least one metal, such as in particular nickel, copper, silver, preferably in the form of electrically conductive metal particles and / or metallized particles, particularly preferably metal particles.

[0169] Metallized particles are in particular and preferably glass or polymer particles that are metallized with at least one metal, so that the previously electrically non-conductive particles are made electrically conductive by the metallization.

[0170] Particularly preferably, the electrically conductive adhesive layer contains electrically conductive particles selected from the group consisting of nickel particles, copper particles, and silver-plated copper particles. According to particularly preferred embodiments, the electrically conductive adhesive layer contains nickel particles.

[0171] The electrically conductive adhesive layer preferably contains 5 to 65% by weight, particularly preferably 20 to 40% by weight, very particularly preferably 25 to 35% by weight, of electrically conductive particles, in particular metal particles and / or metallized particles, based on 100% by weight, based on 100% by weight of polymers and adhesive resins contained.

[0172] The electrically conductive particles should preferably not be or not significantly larger than the respective thickness of the electrically conductive adhesive layer in the z-direction, measured with the light microscope.

[0173] The electrically conductive particles preferably have an average particle size of 1 to 10 pm, particularly preferably of 1 to 6 pm, again preferably of 3 to 5 pm, such as in particular 4 pm.

[0174] The electrically conductive adhesive layer is in particular electrically conductive at least in the z-direction.

[0175] However, it can also be electrically conductive in the xy plane. If the electrically conductive adhesive layer is designed to be electrically conductive only in the z direction, but not necessarily in the xy direction, a smaller amount of these materials is required according to preferred embodiments in which a metal, in particular metal particles, is added to achieve electrical conductivity. This optimizes the adhesive with regard to the required conductivity, adhesive strength, flow behavior, and cost.

[0176] In the context of the present invention, a layer is considered to be “electrically conductive” in particular if the resistance is less than 1 ohm, measured in the respective direction, here in particular in the z-direction, according to the standard MIL-DTL-83528C.

[0177] Regardless of whether the adhesive layers C or C and / or C' are electrically conductive, the following statements apply.

[0178] According to preferred embodiments of the invention, the adhesive layers C or C and / or C', like the adhesive layer D, are reactive heat-activatable adhesives based on at least one mixture of at least one nitrile rubber S1 and at least one reactive component, in particular a reactive resin, wherein all of the above statements apply to the adhesive of layer D. According to preferred embodiments of the invention, the same nitrile rubber S1 and the same reactive resin are used in the adhesive layers C or C and / or C' as in the adhesive layer D.

[0179] This allows similar substrates, referred to here as A and B, to be bonded together. Furthermore, this increases the aging and temperature resistance of the adhesive tape.

[0180] According to further preferred embodiments of the invention, an adhesive different from the adhesive of the adhesive layer D is used in the adhesive layers C or C and / or C'.

[0181] This allows the properties of the conductive layer to be particularly well adapted to the substrate(s) bonded via the adhesive layer C or C and / or C'. Since the adhesive layer C or C and / or C' preferably does not contain or need not contain an electrolyte, such as an ionic liquid, the components do not need to be adapted accordingly.

[0182] Preferably, the adhesive of the adhesive layer D is not pressure-sensitive and therefore preferably not a pressure-sensitive adhesive and the adhesive layer D is therefore preferably not a pressure-sensitive adhesive layer D.

[0183] According to preferred embodiments, the adhesive of the adhesive layers C or C and / or C' is also not a pressure-sensitive adhesive.

[0184] According to further preferred embodiments of the invention, the adhesive of the adhesive layers C or C and C' is a pressure-sensitive adhesive and the adhesive layer C or C and C' is thus a pressure-sensitive adhesive layer.

[0185] In the present invention, a pressure-sensitive adhesive is understood, as is generally customary, to be a substance that is permanently tacky and adhesive, particularly at room temperature. A characteristic of a pressure-sensitive adhesive is that it can be applied to a substrate by pressure and remains adhered there, whereby the pressure to be applied and the duration of this pressure are not further defined. In some cases, depending on the exact type of pressure-sensitive adhesive, the temperature and humidity, as well as the substrate, the application of short-term, minimal pressure, which does not go beyond a light touch for a brief moment, is sufficient to achieve the adhesion effect; in other cases, a longer exposure to high pressure may be necessary. Pressure-sensitive adhesives have special, characteristic viscoelastic properties that lead to their permanent tackiness and adhesiveness.They are characterized by the fact that when they are mechanically deformed, both viscous flow processes and the buildup of elastic restoring forces occur. The respective contribution of both processes is in a certain relationship to each other, depending on the precise composition, structure, and degree of crosslinking of the pressure-sensitive adhesive, as well as the speed and duration of the deformation and the temperature.

[0186] The viscous flow component is necessary to achieve adhesion. Only the viscous components, caused by macromolecules with relatively high mobility, enable good wetting and flow onto the substrate to be bonded. A high proportion of viscous flow leads to high pressure-sensitive adhesion (also referred to as tack or surface adhesion) and thus often also to high adhesive strength. Highly cross-linked systems, crystalline, or glass-like polymers, are generally not or at least only slightly tacky due to the lack of flowable components.

[0187] The proportional elastic restoring forces are necessary to achieve cohesion. They are caused, for example, by very long-chain and highly entangled macromolecules, as well as by physically or chemically cross-linked macromolecules, and enable the transfer of forces acting on an adhesive bond. They ensure that an adhesive bond can sufficiently withstand continuous loading, for example, in the form of permanent shear stress, over an extended period of time.

[0188] For a more precise description and quantification of the degree of elastic and viscous components as well as the relationship between the components, the storage modulus (G') and loss modulus (G"), which can be determined by means of Dynamic Mechanical Analysis (DMA, according to DIN EN ISO 6721), can be used. G' is a measure of the elastic component, G" a measure of the viscous component of a material. Both parameters depend on the deformation frequency and the temperature.

[0189] These parameters can be determined using a rheometer. The material under test is subjected to sinusoidal oscillating shear stress, for example, in a plate-on-plate arrangement. Shear stress-controlled devices measure the deformation as a function of time and the temporal offset of this deformation relative to the application of the shear stress. This temporal offset is referred to as the phase angle δ.

[0190] The storage modulus G' is defined as follows: G' = (T / Y) • cos(ö) (T = shear stress, y = deformation, ö = phase angle = phase shift between shear stress and deformation vector).

[0191] The definition of the loss modulus G is:

[0192] G" = (T / Y) *sin(ö) (T = shear stress, y = deformation, ö = phase angle = phase shift between shear stress and deformation vector).

[0193] A substance is generally considered to be pressure-sensitively adhesive and is defined as pressure-sensitively adhesive in the sense of the invention if, at room temperature, here defined as 23°C, in the deformation frequency range of 10° to 10 1 rad / sec G' at least partly in the range of 10 3 up to 10 7Pa and if G" also lies at least partly in this range. "Partially" means that at least a section of the G' curve lies within the window defined by the deformation frequency range from 10° to 10 1 rad / sec (abscissa) and the range of G' values ​​from 10 3 up to and including 10 7 Pa (ordinate). This applies accordingly to G".

[0194] Preferably, the pressure-sensitive adhesive has a deformation frequency range of 10° to 10 1 rad / sec at 23 °C a storage modulus G' and a loss modulus G" in the range of 10 3 up to 10 7 Pa, determined according to DIN EN ISO 6721 .

[0195] To achieve viscoelastic properties, the monomers on which the polymers underlying the pressure-sensitive adhesive are based, as well as any other components present in the pressure-sensitive adhesive, are selected in particular such that the pressure-sensitive adhesive has a glass transition temperature (according to DIN 53765) below the application temperature (i.e., usually below room temperature (23 °C)). By using suitable cohesion-enhancing measures, such as crosslinking reactions (formation of bridge-forming links between the macromolecules), the temperature range in which a polymer mass exhibits pressure-sensitive adhesive properties can be expanded and / or shifted. The application range of the pressure-sensitive adhesive can thus be optimized by adjusting the flowability and cohesion of the mass.

[0196] In particular, a pressure-sensitive adhesive has a glass transition temperature of < 23 °C, determined according to DIN 53765.

[0197] The present invention further relates to the production of the adhesive tape according to the invention. The adhesive of adhesive layer D and, depending on the embodiment, further adhesives are produced by known methods and formed into layers, in particular by spreading.

[0198] Furthermore, one or more drying steps may be carried out if necessary.

[0199] The lamination of several layers on top of one another takes place in a manner known to the person skilled in the art, the layers being placed on top of one another in such a way that, in particular, a layer composite DTC, where T is arranged between D and C, or C'-T'-DTC is obtained as a double-sided adhesive tape.

[0200] The provision of the carrier layers T or T' can be carried out in various ways, as already explained above.

[0201] It is thus conceivable that a) a metal foil, in particular an aluminum foil, and / or b) an electrically conductive mesh and / or d) at least one metal grid and / or e) a metal-coated PET film is placed between the respective adhesive layers.

[0202] Furthermore, c) metal particles can be vapor-deposited directly onto the surface of the adhesive layer D or C or C'.

[0203] A further object of the present invention is the production of a bonded composite using the adhesive tape according to the invention.

[0204] To activate the reactive, heat-activatable adhesive of the adhesive tape according to the invention, it is placed between the substrates to be bonded and heated, preferably using a pressing pressure. All of the above statements regarding the activation of the bonding mechanism apply. Furthermore, pre-lamination preferably takes place, as also stated above.

[0205] The adhesive tape according to the invention is in particular a double-sided adhesive tape in which, depending on the embodiment, two surfaces of the adhesive layer D (transfer adhesive tape) or one surface of the first adhesive layer D and one surface of the second adhesive layer C (three-layer composite DTC) or one surface each of the adhesive layers C and C' (five-layer composite CTDT'-C') are each available for bonding substrates.

[0206] The outer, exposed surfaces of the adhesive layers of the adhesive tape according to the invention can advantageously be provided with anti-adhesive materials such as a release paper or a release film, also called a liner. A liner can also be a material that is anti-adhesively coated on at least one side, preferably on both sides, such as, for example, material that is siliconized on both sides. A liner, or more generally a temporary carrier, is not a component of an adhesive tape but merely an aid for its production, storage and / or further processing by punching. Furthermore, in contrast to a permanent carrier, a liner is not firmly bonded to an adhesive layer, but rather functions as a temporary carrier, i.e. as a carrier that can be removed from the adhesive layer. In the present application, “permanent carriers” are synonymously also referred to simply as “carriers”.

[0207] The thickness of the individual adhesive layer(s) (in the z-direction) is preferably from 10 to 225 µm, particularly preferably from 15 to 150 µm, very particularly preferably from 20 to 100 µm, again very particularly preferably from 25 to 70 µm.

[0208] In the embodiments of the three-layer composite DTC and the five-layer composite CTDT'-C', the adhesive layers D and C or D and C as well as D and C' have different layer thicknesses according to preferred embodiments, wherein the thickness of the adhesive layer D is, for example, less than that of the adhesive layers C or C and C'.

[0209] According to further preferred embodiments, the layers D and C or D, C and C' have the same layer thickness.

[0210] If the thickness of layer D is too high, it may become uneconomically expensive due to the electrolytes it contains.

[0211] Preferred embodiments of the invention are explained and described in more detail below with reference to the accompanying figures. In the figures:

[0212] Fig. 1 is a simplified schematic cross-sectional view through a double-sided adhesive tape according to the invention in a preferred embodiment; and

[0213] Fig. 2 is a simplified schematic cross-sectional view through a double-sided adhesive tape according to the invention in a preferred embodiment; and

[0214] Fig. 3 is a simplified schematic cross-sectional view through a double-sided adhesive tape according to the invention in a preferred embodiment; and

[0215] Fig. 4 is a simplified schematic cross-sectional view through a bonded composite according to the invention of a preferred embodiment; and

[0216] Fig. 5 is a simplified schematic cross-sectional view through a bonded composite according to the invention to which a voltage is applied, in a preferred embodiment; and Fig. 6 is a simplified schematic cross-sectional view through a bonded composite according to the invention after a voltage has been applied and an adhesive split has thereby occurred; and

[0217] Fig. 7 is a simplified schematic cross-sectional view through a bonded composite according to the invention of a preferred embodiment; and

[0218] Fig. 8 is a simplified schematic cross-sectional view through a bonded composite according to the invention of a preferred embodiment.

[0219] As can be seen in Fig. 1, the adhesive layer D 1 is bonded to the carrier layer T 2 via one of its surfaces. The second adhesive layer C 3 is arranged on the surface of the carrier layer T opposite the layer D.

[0220] As can also be seen in Fig. 1, the layer composite represents a double-sided adhesive tape in which one surface of the adhesive layer D and one surface of the second adhesive layer C are each available for bonding.

[0221] Fig. 2 shows a preferred embodiment of the invention. Here, the electrically conductive carrier layer T 2 projects laterally beyond the adhesive layer D 1 and the second adhesive layer C 3 in at least one direction of extension of the layer plane, so that the electrically conductive carrier layer T 2 has a projection with at least one free surface 2 a.

[0222] Fig. 3 shows a further preferred embodiment of the invention. Here, the electrically conductive carrier layer T 2 projects laterally beyond the adhesive layer D 1 in at least one direction of extension of the layer plane, so that the electrically conductive carrier layer T 2 has a projection with a free area 2 a . In Fig. 3, the adhesive layer C 3 is designed such that it also has a projection relative to the layer D 1 . The carrier layer T 2 is, in particular, a PET film coated with aluminum on one side, the aluminized side being bonded to the layer D 1 .

[0223] Figure 4 shows a schematic representation of the bonded composite according to the invention in a preferred embodiment. As can be seen from Figure 4, the adhesive tape is arranged over the adhesive layer D 1 on a surface of the first substrate A 4 , the first substrate being electrically conductive.

[0224] Furthermore, the adhesive tape is arranged over the second adhesive layer C 3 on a surface of a second substrate B 5. Fig. 4 also shows, by way of example, that the electrically conductive carrier layer T 2 projects laterally beyond the adhesive layer D 1 in at least one direction of extension of the layer plane, so that the electrically conductive carrier layer T has a projection with a free surface 2 a.

[0225] A voltage can now be applied across this free surface 2a, as shown in the schematic representation in Fig. 5.

[0226] By applying the voltage, a migration of the electrolyte occurs, in particular a separation of the anions and cations of an ionic liquid, in the adhesive layer D 1.

[0227] As a result, the adhesion of the adhesive layer D 1 to the substrate A 4 is greatly reduced and these layers separate from each other, as can be seen in the schematic representation according to Fig. 6.

[0228] Figure 7 shows a further schematic representation of the bonded composite according to the invention in a preferred embodiment. As can be seen from Figure 7, the adhesive tape is arranged over the adhesive layer C 3 on a surface of the first substrate A 4.

[0229] Furthermore, the adhesive tape is arranged over the third adhesive layer C' 7 on a surface of a second substrate B 5.

[0230] Between the layers C 3 and C' 7 there is the electrically removable adhesive layer D 1 and two electrically conductive carrier layers T 2 and T' 6, with the layer D 1 being arranged between the carrier layers.

[0231] Fig. 7 also shows by way of example that the electrically conductive carrier layer T 2 and the electrically conductive carrier layer T' 6 each project laterally beyond the adhesive layer D 1 in at least one direction of extension of the layer plane, so that the electrically conductive carrier layer T has a projection with a free surface 2a and the electrically conductive carrier layer T' has a projection with a free surface 6a.

[0232] Fig. 8 shows a further schematic representation of the bonded composite according to the invention in a preferred embodiment, which is similar to the representation according to Fig. 7. In contrast to Fig. 7, however, the projections of the electrically conductive carrier layer T 2 and the electrically conductive carrier layer T' 6 point in different directions, so that the resulting free surfaces of these layers 2a and 6a, respectively, are spatially separated.

[0233] A voltage can now be applied across these free surfaces 2a and 6a, analogously to Figure 5. In contrast to the embodiment according to Figure 5, the voltage can be applied to surfaces 2a and 6a, so that none of the substrates A and B need be electrically conductive.

[0234] Applying the voltage causes the electrolyte to migrate, particularly the anions and cations of an ionic liquid to separate, within the adhesive layer D 1. This significantly reduces the adhesion of the adhesive layer D 1 to the carrier layers T 2 and / or T' 6, and causes these layers to separate from each other. In particular, detachment occurs at the layer to which the negative pole is applied.

[0235] The application of the voltage is simplified in the case of the spatially separated surfaces 2a and 6a according to Fig. 8.

[0236] The illustrations in Figs. 1 to 8 are, as stated, schematic representations. In particular, the layer thicknesses of the individual layers D, T, and C may differ from one another. Furthermore, substrates A and B are only schematically depicted as additional layers. These may, of course, have any other spatial geometry.

[0237] Some examples are described below to further clarify the invention.

[0238] Test methods

[0239] Unless otherwise stated, all measurements are conducted at 23 °C and 50% relative humidity. The mechanical and adhesive data were determined as follows:

[0240] Molecular weight M n , M w

[0241] The number average molecular weight M n or weight-average molecular weight M win this document refer to the determination by gel permeation chromatography (GPC). The determination is carried out on 100 μl of a clear-filtered sample (sample concentration 4 g / l). Tetrahydrofuran with 0.1 vol.% trifluoroacetic acid is used as the eluent. The measurement is carried out at 25 °C. A PSS-SDV column, 5 μm, 10 3 Ä, 8.0 mm * 50 mm (information here and below in the order: type, particle size, porosity, inner diameter * length; 1 Ä = 10 -10 m). For separation, a combination of columns of type PSS-SDV, 5 pm, 10 3 Ä and 10 5 Ä and 10 6 Ä with a diameter of 8.0 mm x 300 mm each (columns from Polymer Standards Service; detection using a Shodex RI71 differential refractometer). The flow rate is 1.0 ml per minute. Calibration is performed against PMMA standards (polymethyl methacrylate calibration) for polar molecules and against PS standards (polystyrene calibration) for other molecules.

[0242] thickness

[0243] The thickness of an adhesive layer can be determined by determining the thickness of a section of such an adhesive layer applied to a liner, defined in terms of its length and width, minus the (known or separately determinable) thickness of a section of the same dimensions of the liner used. The thickness of the adhesive layer can be determined using commercially available thickness gauges (touch-type testers) with an accuracy of less than 1 pm. If thickness variations are detected, the average value of measurements taken at at least three representative locations is given, thus, in particular, not measured at creases, folds, spots, and the like.

[0244] Just as with the thickness of an adhesive layer, the thickness of an adhesive tape (adhesive strip) or a carrier can be determined analogously using commercially available thickness gauges (touch gauges) with an accuracy of less than 1 pm. If thickness variations are detected, the average value of measurements taken at at least three representative locations is given, thus excluding creases, folds, spots, and the like.

[0245] Bonding strength

[0246] As a parameter for the quality of the bond achieved, the bond strength of the bonded composite is determined for the adhesive tapes under investigation. For this purpose, the bond strength is quantitatively determined in a dynamic tensile shear test based on DIN EN 1465 at 23 °C and 50% relative humidity for a test speed of 10 mm / min (results in N / mm 2= MPa). Steel test specimens were used, which were cleaned with acetone before bonding. The preparation of the test specimens and the layer thicknesses of the adhesive tapes correspond to the specifications below.

[0247] The mean value of three measurements is given.

[0248] The following inventive example of an inventive adhesive tape comprising at least one adhesive layer D was produced in the form of a transfer adhesive tape, bonded between substrates, and subsequently electrically released by applying a voltage. The adhesive of layer D was a heat-activatable adhesive that was not pressure-sensitive prior to activation. Inventive Example 1

[0249] The adhesive layer D was provided as follows:

[0250] 43 wt.% Nipol 1001 CG (nitrile rubber) from Zeon, 40 wt.% novolak resin Durez 33040 blended with 8% HMTA (Rohm and Haas), and 10 wt.% resol resin 9610 LW from Bakelite were prepared as a 30% solution in methyl ethyl ketone in a kneader. The kneading time was 20 h.

[0251] Subsequently, 7.0 wt. % of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) is added and also mixed intensively.

[0252] The heat-activated adhesive was then spread from solution onto a glassine release paper and dried at 80°C for 15 minutes. After drying, the film thickness was 30 μm.

[0253] To test the bond strength, the transfer adhesive tape consisting of the adhesive layer D was bonded between two steel plates as follows:

[0254] From the adhesive tape to be tested (covered on one side with release paper) 3 approx. 15 x 25 mm 2 large pieces cut out.

[0255] A steel test specimen (substrate) was placed on a hot plate preheated to 105 °C. After approximately 5 seconds of heating, the open side of the adhesive tape sample, not covered with release paper, was applied to a surface of the test specimen using tweezers and pressed flat with a rubber roller.

[0256] After cooling, the excess tape edges were trimmed and the release paper removed. A second test specimen was placed on a hot plate preheated to 105 °C for 5 seconds. The coated strip (adhesive tape on the first steel substrate) was applied to this with an overlap of exactly 10 mm and pressed down. The pre-laminated composite was then allowed to cool.

[0257] Subsequently, activation takes place by applying heat and pressure in a heating press.

[0258] In Example 1 according to the invention, heating was carried out for 8 minutes to a temperature of 120 °C at a pressure of 5 bar.

[0259] The resulting specimens were stored for 24 hours at room temperature and 50% RH (standard climate). The bond strength was determined according to the method described above and was 8.0 MPa.

[0260] Subsequently, a sample of the above-mentioned Example 1 was again prepared and tested for electrical re-detachability.

[0261] After bonding and activation, a voltage was applied to the two steel plates representing conductive substrates A and B.

[0262] The voltage was 48 V and was applied for 5 minutes.

[0263] The bond strength was determined according to the method given above and was 3.9 MPa.

[0264] By applying the voltage, the bond strength could be reduced.

[0265] Thus, it has surprisingly been possible to provide reactive heat-activated adhesive tapes or bonded composites comprising heat-activated adhesive tapes that can be electrically removed.

[0266] List of reference symbols

[0267] 1 adhesive layer D

[0268] 2 electrically conductive carrier layer T 2a free area of ​​the electrically conductive carrier layer T

[0269] 3 second adhesive layer C

[0270] 4 first substrate A

[0271] 5 second substrate B

[0272] 6 second electrically conductive carrier layer T' 6a free area of ​​the electrically conductive carrier layer T'

[0273] 7 third adhesive layer C'

Claims

Patent claims 1 . Adhesive tape comprising at least one adhesive layer D, wherein the adhesive of the adhesive layer D is a reactive heat-activatable adhesive and contains at least one electrolyte.

2. Adhesive tape according to claim 1, characterized in that the electrolyte of the adhesive layer D is selected from the group consisting of ionic liquids and metal salts, with ionic liquids being particularly preferred.

3. Adhesive tape according to claim 2, characterized in that the anion of the ionic liquid is selected from the group consisting of Br, AICI4-, AI2CI7-, NO3, BF4-, PF6-, CH3COO-, CF3COO-, CF3CO3-, CF3SO3-, (CF3SO2)2N-, (CF3SO2)3C-, ASF6-, SbF6-, CF3(CF2)3SO3-, (CF3CF2SO2)2N-, CF3CF2CF2COO _ , (FSO2)2N-, and is particularly preferably selected from (CF3SO2)2N- and (FSO2)2N-.

4. Adhesive tape according to claim 2 or 3, characterized in that the cation of the ionic liquid is selected from the group consisting of imidazolium-based cations, pyridinium-based cations, pyrrolidine-based cations and ammonium-based cations, and is particularly preferably selected from the group consisting of imidazolium-based cations, wherein the cation is particularly preferably selected from the group consisting of 1-ethyl-3-methylimidazolium and 1-butyl-3-methylimidazolium, wherein the cation is very particularly preferably 1-ethyl-3-methylimidazolium.

5. Adhesive tape according to one of the preceding claims, characterized in that the electrolyte of the adhesive layer D is selected from the group consisting of the ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM-FSI).

6. Adhesive tape according to one of the preceding claims, characterized in that the first adhesive layer D contains 2 to 20 wt.%, preferably 5 to 18 wt.%, of electrolytes, preferably ionic liquids, based on the total amount of the adhesive.

7. Adhesive tape according to one of the preceding claims, characterized in that the reactive heat-activatable adhesive of the adhesive layer D is based on at least one mixture of at least one nitrile rubber S1 and at least one reactive component, in particular a reactive resin, wherein the reactive component is preferably at least one reactive resin selected from the group consisting of epoxy resins, melamine resins, phenolic resins, such as in particular novolak resins and resole resins, terpene-phenolic resins and polyisocyanates, wherein phenolic resins, in particular novolak resins and / or resole resins, are particularly preferred.

8. Adhesive tape according to one of claims 1 to 7, characterized in that the adhesive tape is a transfer adhesive tape and consists of the adhesive layer D.

9. Adhesive tape according to one of claims 1 to 7, characterized in that it additionally comprises at least the following layers: • A second adhesive layer C; and • at least one electrically conductive carrier layer T arranged between the layers D and C.

10. Adhesive tape according to one of claims 1 to 7, characterized in that it additionally comprises at least the following layers: • A second adhesive layer C; and • at least one first electrically conductive carrier layer T arranged between the layers D and C; and • at least one second electrically conductive carrier layer T', which is arranged on the surface of the adhesive layer D opposite the first electrically conductive carrier layer T; and • A third adhesive layer C', which is arranged on the surface of the second carrier layer T' opposite the first adhesive layer D. 1 1. Adhesive tape according to claim 9 or 10, characterized in that the electrically conductive carrier layer T or the electrically conductive first carrier layer T and the electrically conductive second carrier layer T' comprise at least one metal, wherein the metal is selected from the group consisting of copper, nickel, zinc, tin, silver, gold, aluminum, iron, chromium and alloys of these metals, wherein the electrically conductive first carrier layer T and the electrically conductive second carrier layer T' are independently the same or different from one another.

12. Adhesive tape according to claim 11, characterized in that the electrically conductive carrier layer T or the electrically conductive first carrier layer T and the electrically conductive second carrier layer T' a) at least one metal foil, preferably an aluminum foil, and / or b) at least one electrically conductive textile comprising at least one metal, preferably selected from the group consisting of copper and nickel, and / or c) one or more layers of at least one vapor-deposited metal, preferably selected from the group consisting of copper and aluminum, and / or d) at least one grid made of metal and / or e) a metal-vapor-deposited foil, wherein the electrically conductive first carrier layer T and the electrically conductive second carrier layer T' are independently the same or different from one another.

13. Bonded composite comprising at least the following layers: • A first substrate A; and • A second substrate B; and • An adhesive tape according to any one of claims 1 to 12, which is arranged between the substrate A and the substrate B and bonds the substrates A and B together.

14. A method for electrically releasing the composite according to claim 13, comprising at least the following method steps: i.) applying a voltage to two different points of the composite, wherein the voltage is preferably from 2 to 50 V.

15. Use of the adhesive tape according to one of claims 1 to 12 for bonding components in electronic devices, automobiles, medical devices and dental devices.

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