Device capable of bonding and debonding on demand

Abstract

The present invention provides an adhesive device in which ion-conductive adhesives are positioned between two electrically conducive surfaces, either one backing and one substrate or both substrates. When a negative DC voltage is applied to the substrate, the adhesion strength of the tape decreases, allowing debonding from the substrate. In contrast, applying a positive DC voltage increases the adhesion strength, enabling bonding. This process can be repeated to achieve at least one cycle of bonding, debonding, and rebonding of the adhesive tape to the conductive substrate.

Description

[0001] DEVICE CAPABLE OF BONDING AND DEBONDING ON DEMAND

[0002] TECHNICAL FIELD

[0003] The present invention relates to a device comprising an adhesive with electrically adjustable adhesion properties, enabling bonding, debonding, and rebonding to surfaces by application of a corresponding electric stimulus.

[0004] BACKGROUND ART

[0005] Electrically debondable adhesives can alter their adhesion strength in response to an electrical stimulus, typically direct current (DC) voltage. This makes them useful in applications that require on-demand separation of the adhesive from electrically conductive surfaces with minimal to no effort, with no surface damage, and little to no residue.

[0006] WO 2023 / 165966 Al discloses a pressure-sensitive adhesive (PSA) composition that includes a base component, either a polyacrylate or synthetic rubber PSA along with a salt and a (polymer) electrolyte component that enables detachment when a DC voltage is applied. Also described is a PSA tape consisting of an electrically conductive backing and at least one layer of this adhesive composition. The tape adheres to conductive surfaces under pressure and can be debonded by applying DC voltage, preferably combined with heat.

[0007] WO 2024 / 204367 Al describes systems in which metal / carbon particles are incorporated into resin matrices or used commercially predefined intrinsically conductive polymer-coated film [Staclear NCF or Daiclea DC-75] to achieve electrically conductive backing. Then a solvent-borne acrylic ion conductive adhesive is applied and cured by drying and crosslinking. This provides reliable electrical debonding performance even after high temperature and high humidity conditioning. These configurations are inadequate for demonstrating reliable functionalities (e.g. bonding, and rebonding, and cycling).

[0008] EP 3 858 932 Al describes a separation method for an adherend comprising a first voltage application step in order to allow for debonding of an electrolyte-containing adhesive layer from an adherend, a bonding maintenance step of recovering the adhesive force, a second voltage application step, and a separation step of separating the electrolyte-containing adhesive layer and the adherend. However, the peel adhesion of the adhesive before and after voltage application and upon recovery of one hour was reported to be in the range of 6 to 8 N / 20 mm, which is still low for various applications. Similar bond recovery after electrical debonding was also mentioned in EP 3878482 Al, EP 3858929 Al, and WO 2006 / 050340 A2.

[0009] CN 106928881 A describes an electro-reversible adhesive derived mostly from starch and electrorheological species such as BaTiO(C2O4)2. Under normal conditions, the mixture has a gellike consistency; however, when an electric field is applied, it hardens and acts as an adhesive, producing a bonding strength of up to 3.6 MPa at 1.5 KV / m. When the electric field is turned off, it returns to its original gel condition, allowing for easy debonding.

[0010] US 2005 / 274455 Al describes electro-active adhesive systems, which include an adhesive matrix and a variety of electro-active particles. One example system is the use of electrorheological fluid in the adhesive matrix, which changes viscosity under an electric field. When the electric field is turned off, adhesion is significantly decreased. One problem of this system is that the adhesion and the subsequent bonding of the substrate diminish as the electricity is cut off, which limits applicability where permanent, or longer-time bonding is needed, also in the absence of an electric stimulus.

[0011] WO 2024 / 079548 Al describes a semi-structural or structural adhesive composition that provides initial bonding strength when activated by UV-C light. The adhesive can then be debonded by applying a direct current (DC) voltage across the bonded substrates. However, the reduction in adhesive strength is limited— only about 50 % to 69 % drop from the initial strength after applying 50 V for 3 minutes, and in some examples, reaching up to 83 % in 5 minutes.

[0012] TECHNICAL PROBLEM

[0013] In view of the above, many electrically debondable adhesives such as PSA described in the prior art suffer from low initial bonding strength, i.e. bonding strength prior to application of any electric stimulus. A further disadvantage is their long recovery time (defined as the time without electric stimulus between debonding and rebonding) that is required to provide sufficient bonding strength upon rebonding, so that rapid rebonding after debonding is not possible.

[0014] Electrical debondable adhesives can be categorized as either pressure-sensitive adhesives (PSA) or structural bonding types. Both systems bring some common advantages, as PSA does not need an extra curing step and can be easily applied to the surface by hand pressure but suffers from low bonding strength. Structural adhesives offer higher bonding strength but are non-tacky at room temperature. They require an additional activation step and take hours to even weeks to reach their final bonding strength. Both may be debondable under electric voltage with different performance levels, but one thing is common: the adhesive cannot be used in a sequence like bonding, debonding, and rebonding which is in fact a need for many modern applications for circular economy, in particular where the allowed time window between debonding and rebonding is limited.

[0015] For PSA tapes of the prior art, slight reworking is possible, but when the tape is rebonded after debonding, the obtained adhesion strength does not reach the adhesion strength upon first bonding and may be even lower than the initial adhesion strength. Even if the polarity of the DC voltage is changed after debonding to effect rebonding, the bonding strength does not increase or increase only very little; rather, anchorage failure between the backing and adhesive frequently occurs. While some electro-responsive adhesives of the prior art address some of these problems, they often have stimulus-dependent bonding properties; for example, once the electric stimulus [DC or AC voltage] is cut off, the adhesion disappears, making them unsuitable or undesirable for many applications where permanent application of an electric stimulus is undesired or not feasible.

[0016] Hence, new devices are required which allow reducing the recovery time between debonding and rebonding while allowing to obtain sufficiently high initial adhesion strength and sufficiently high rebonded adhesion strength, also allowing a sufficiently low debonded adhesive strength. Put differently, there is still a need for an adhesive device that provides sufficient initial bonding strength and allows the strength to be adjusted— either increased or decreased— on demand by switching the polarity of an applied stimulus such as a DC voltage. The device should be able to debond cleanly from substrates with little to no residue and, with a further electric stimulus, enable rebonding. The debonding-rebonding cycle should be repeatable multiple times without significant loss of adhesion. Further, the adhesive strength after debonding and rebonding should remain in their respective debonded or rebonded state without the need for permanent application of an electric stimulus.

[0017] Moreover, the adhesive should quickly regain its ability to provide high adhesion strength when rebonded again after debonding, bonding and rebonding both being caused by an electric stimulus. Further, after rebonding, the adhesion strength should remain at a high level even after the electric stimulus is turned off. SUMMARY OF INVENTION

[0018] It is therefore an object of the present invention to address one or more of the above-mentioned disadvantages of the adhesive devices of the prior art.

[0019] Specifically, it is an object of the present invention to provide a device comprising an adhesive that is able to provide for suitable initial adhesive strength. The adhesive strength of the adhesive can be increased or decreased on demand within a short period of time (for example within seconds or minutes) by an electric stimulus (e.g. an electromotive force), such as application of a DC (direct current), AC (alternating current), VDC (volts direct current), VAC (volts alternating current), pulsed DC (pulsed direct current), pulsed AC (pulsed alternating current), without resorting to certain special conditions such as the use of UV-C radiation, high heat, or high pressure.

[0020] The adhesive can be easily bonded, debonded and rebonded on demand by controlling the electric stimuli, e.g. different DC voltages that may be applied at different time scales and polarities, to thereby effect bonding, debonding, and rebonding. Here, a debonding-rebonding cycle can be repeated several times, and no or only a short recovery time is required after debonding before rebonding becomes possible.

[0021] In addition, in one aspect this invention is intended to enable fine tuning of the adhesion between two structures even from a remote position. Additionally, sustainability concepts such as recyclability, and reworkability by re / adjustment positioning of the objects during production are provided by the adaptability of the adhesive device.

[0022] The present invention includes the following embodiments:

[0023] 1. A device comprising an adhesive (A) whose adhesive strength can be modified by respective electric stimuli from an initial state to a first bonded state, from a first bonded state to a first debonded state, and from a first debonded state to a first rebonded state,

[0024] wherein the device has

[0025] an initial adhesive strength ASj,

[0026] a first bonded adhesive strength ASfoi,

[0027] a first debonded adhesive strength ASj^, and

[0028] a first rebonded adhesive strength ASri;

[0029] and which satisfies the following conditions:

[0030]

[0031] ASrl> (0.75 x ASbl).

[0032] wherein

[0033] ASj represents the adhesive strength prior to application of an electric stimulus (ES),

[0034] ASb1represents the adhesive strength after a first electric stimulus for increasing bonding strength (ES+1) has been applied,

[0035] ASJ represents the adhesive strength after a first electric stimulus for decreasing bonding strength (ES’l) has been applied, and

[0036] ASrrepresents the adhesive strength after a second electric stimulus for increasing bonding strength (ES+2) has been applied.

[0037] 2. A device comprising an adhesive (A) whose adhesive strength can be modified by respective electric stimuli from a first bonded state to a first debonded state, and from a first debonded state to a first rebonded state,

[0038] wherein the device has

[0039] a first bonded adhesive strength ASb,

[0040] a first debonded adhesive strength ASJI, and

[0041] a first rebonded adhesive strength ASr;

[0042] and which satisfies the following conditions:

[0043] ASdi < ASb, and

[0044] ASri> (0.75 x ASbi).

[0045] wherein

[0046] ASb1represents the adhesive strength after a first electric stimulus for increasing bonding strength (ES+1) has been applied,

[0047] ASJI represents the adhesive strength after a first electric stimulus for decreasing bonding strength (ES’l) has been applied, and

[0048] ASr1represents the adhesive strength after a second electric stimulus for increasing bonding strength (ES+2) has been applied.

[0049] 3. The device according to embodiment 1, which satisfies the condition ASJI^ 1.0 x ASj, preferably ASJI^ (0.5 x ASj), more preferably ASJI^ (0.1 x ASj) or ASJI^ (0.01 x ASj)

[0050] 4. The device according to any of the preceding embodiments, which satisfies the condition

[0051] ASri> (1.0 x ASbi),

[0052] preferably ASri> (1.0 x ASbi), more preferably ASri> (1.2 x ASbi), still more preferably ASri> (1.5 xASbl). 5. The device according to any one of the preceding embodiments, which satisfies the condition ASri> (0.8 x AS i) when the time between the electric stimuli ES-1 and ES+2 is 24 hours or less, such as 10 hours or less, e.g. 5 hours or less, 3 hours or less, or 2 hours or less, preferably 1 hour or less, more preferably 30 minutes or less or 20 minutes or less, further preferably 10 minutes or less, 5 minutes or less, or 1 minute or less.

[0053] 6. The device according to any one of the preceding embodiments, wherein the device has a second debonded state having an adhesive strength ASd2and a second rebonded state having an adhesive strength ASr2, and satisfies the following conditions:

[0054]

[0055] wherein AS^ represents the adhesive strength after a second electric stimulus for decreasing bonding strength (ES’2) has been applied, and

[0056] ASr2 represents the adhesive strength after a third electric stimulus for increasing bonding strength (ES+^) has been applied.

[0057] 7. The device according to embodiment 6, wherein

[0058]

[0059] 8. The device according to any one of the preceding embodiments, wherein the device has an n-th debonded state having an adhesive strength ASdnand n-th rebonded state having an adhesive strength ASrn, and satisfies the following conditions:

[0060]

[0061] and more preferably

[0062]

[0063] wherein n is an integer of 3 or greater, such as from 3 to 100, from 3 to 50, from 3 to 40, from 3 to 30, from 3 to 20, from 3 to 10 or from 3 to 5, and

[0064] wherein AS^ represents the adhesive strength after a n-th electric stimulus for decreasing bonding strength (ES+n) has been applied, and

[0065] ASrnrepresents the adhesive strength after an n+lth electric stimulus for increasing bonding strength (ES-n+l) has been applied.

[0066] 9. The device according to any one of embodiments 6 to 8, wherein

[0067]

[0068] wherein n is an integer of 3 or greater, such as from 3 to 10 or from 3 to 5.

[0069] 10. The device according to any one of the preceding embodiments, wherein the adhesive strength in the bonded state and the one or more rebonded state(s) is within the range of 3.0 to 40.0 N / cm, and the adhesive strength in the one or more debonded states is in the range of 0.1 to 2.5 N / cm.

[0070] 11. The device according to any one of the preceding embodiments, wherein ASri> (1.0 x ASfoi), and preferably ASri> (1.3 x AS^i).

[0071] 12. The device according to any one of the preceding embodiments, wherein the electric stimulus is selected from the group consisting of a DC (direct current), AC (alternating current), VDC (volts direct current), VAC (volts alternating current), Pulsed DC (pulsed direct current), Pulsed AC (pulsed alternating current), and preferably is selected from an VDC (volts direct current), VAC (volts alternating current), Pulsed DC (pulsed direct current).

[0072] 13 The device according to any one of the preceding embodiments, wherein the electric stimulus is a direct or alternating current with a voltage of 0.5 - 230 V, or a pulsed current or voltage.

[0073] 14. The device according to any one of the preceding embodiments, wherein all electric stimuli for increasing adhesive strength are identical, symmetrical or asymmetrical to each other and include a DC voltage of 15 V for 1 minute, and all stimuli for decreasing adhesive strength are identical, symmetrical or asymmetrical and include a direct current voltage of 15 V for 1 minute with reversed polarity direct current voltage for increasing adhesive strength. 15. The device according to any one of the preceding embodiments, which is in the form of an adhesive tape comprising a carrier and an adhesive layer comprising the adhesive (A), and wherein preferably the carrier is an electrically conductive carrier, such as for example a metal foil, an electrically conductive polymer, or on insulating polymer that has been treated to impart electrical conductivity, e.g. by providing a metallic film on a polymer foil.

[0074] 16. The device is according to any one of the preceding embodiments, wherein the device further comprises an electrically conductive substrate in contact with the adhesive (A).

[0075] 17. The device according to any one of the preceding embodiments, wherein the adhesive (A) is a pressure-sensitive adhesive and / or wherein the adhesive has ionic conductivity, preferably in the range of 10-10S / cm to 10-3S / cm, and / or comprises one or more ionic liquids and / or one or more salts that are not ionic liquids, preferably a lithium salt.

[0076] 18. The device according to embodiment 17,

[0077] wherein the cation of the one or more ionic liquids is selected from the group consisting of imidazolium-based cations, pyridinium-based cations, pyrrolidinium-based cations, piperidinium-based cations, phosphonium-based cations, sulfonium-based cations, morpholinium-based cations, ammonium-based cations, and a combination thereof;

[0078] and / or

[0079] wherein the anion of the one or more ionic liquids is selected from the group consisting of tetrafluoroborate, hexafluorophosphate, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, trifluoromethanesulfonate, dicyanamide, nitrate, chloride, acetate, hydrogen sulfate, and methanesulfonate.

[0080] 19. The device according to embodiment 17 or 18, wherein the ionic liquid is selected from the group comprising 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMIM FSI), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMIM TFSI), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIM TFSI), 1-ethyl-3-methylimidazolium thiocyanate (EMIM SCN), 1-ethyl-3-methylimidazolium dicyanamide (EMIM DCA), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM BF4), 1-butyl-3-methylimidazolium thiocyanate (BMIM SCN), 1-allyl-3-methylimidazolium dicyanamide (AllylMIM DCA), 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (AllylMIM TFSI), 1-ethyl-3-vinylimidazolium bis(trifluoromethylsulfonyl) imide (EVIM TFSI), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide (Pyr13 TFSI), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl) imide (Pyr13 FSI), N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl) imide (Pyr14 FSI), 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide, 1-butyl-1-methylpyrrolidinium dicyanamide (Pyr14 DCA), 1-butyl-1-methylpyrrolidinium triflate (Pyr14 OTf), 1-ethyl-3-methylimidazolium triflate (EMIM OTf), 1-butyl-3-methylimidazolium triflate (BMIM OTf), 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide (DiMIM BTA), 1-butyl-3-methylimidazolium tricyanomethanide (BMIM TCM), 1-butyl-3-methylimidazolium methyl sulfate (BMIM MeSO4), 1,3-diethylimidazolium bis(trifluoromethylsulfonyl) imide (DiEIM TFSI), N-butyl-N-methylpyrrolidinium tricyanomethanide (Pyr14 TCM), diethylmethylsulfonium bis(trifluoromethylsulfonyl) imide (S122 TFSI), 1-propyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide (Pro4Pic TFSI), 1-ethyl-3-methylimidazolium ethyl sulfate (EMIM EtSO4), triethylsulfonium bis(trifluoromethylsulfonyl) imide (S222 TFSI), 1-(2-methoxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (MeOEMIM TFSI), 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl) imide (PMIM TFSI), 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (Pyr14 TFSI), 1-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl) imide, 1,3-dimethylimidazolium methyl sulfate (DiMIM MeSO4), 1-ethylimidazolium bis(trifluoromethylsulfonyl) imide (EIM TFSI), 1-ethyl-3-methylimidazolium methanesulfonate (EMIM OMs), 1-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl) imide (Et4Pic TFSI), 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide (EDiMIM TFSI), 2-methyl-1-propylpyridinium bis(trifluoromethylsulfonyl) imide (Pro2Pic TFSI), 1-ethyl-3-methylimidazolium acetate (EMIM OAc), 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIM PF6), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF6), 1-hexylpyridinium bis(trifluoromethylsulfonyl)imide (HexPy TFSI).

[0081] 20. The device according to the embodiment 17, wherein the one or more salts that are no ionic liquids, which preferably comprises a lithium salt, are selected from the group consisting of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithiumtriflate (LiOTf), lithium difluoro(oxalato)borate (LiDFOB), and lithium bis(oxalato)borate (Li BOB).

[0082] 21. The device according to any one of the preceding embodiments, wherein the adhesive (A), which preferably is a pressure-sensitive adhesive, further comprises one or more additives, e.g. plasticizers that are preferably selected from the group consisting of poly(alkylene) glycols such as polyethylene glycol, carbonates, and water.

[0083] 22. The device according to any of the preceding embodiments, wherein the adhesive (A) is selected from the group consisting of acrylic adhesives, other vinyl-based adhesives, rubberbased adhesives, silicone adhesives, epoxy adhesives, polyurethane adhesives, cyanoacrylate adhesives, and UV-curable adhesives, which are preferably pressure-sensitive adhesives, and wherein the adhesive (A) is more preferably an acrylic pressure-sensitive adhesive.

[0084] 23. The device according to any one of the preceding embodiments, wherein the adhesive (A) is a pressure-sensitive adhesive that is prepared by polymerizing a mixture comprising at least the following components: a) 20 to 80 wt % of acrylate monomer (al) from the group of (meth)acrylic esters containing at least one oxygen atom; and

[0085] b) 20 to 80 wt % of acrylate monomer (a 2) from the group of (meth)acrylic esters and / or amides containing at least one nitrogen atom; and

[0086] c) 0 wt % to 15 wt % of one or more electro-responsive compounds from the group of polymerizable zwitterionic monomers and / or non-polymerizable zwitterionic compounds, preferably one or more zwitterionic monomers; and

[0087] d) 0.005 to 10 wt % of at least one initiator; and

[0088] e) 0 wt % to 20 wt % of one or more ionic liquids; and

[0089] f) 0 wt % to 20 wt % of one or more salts that are not ionic liquids; and

[0090] g) optionally 1 wt % to 20 wt % by weight of one or more acrylate monomers (a3), wherein the one or more acrylate monomers (a3) are different from acrylate monomers (al) and (a2); and

[0091] h) optionally additives,

[0092] wherein the weight fractions of the components are based on the total weight of the mixture.

[0093] 24. The device according to any of the preceding embodiments, wherein the device is in the form of an adhesive tape comprising the adhesive (A) on one or both sides of a carrier, wherein the carrier is preferably electrically conductive on a side where the adhesive (A) is present.

[0094] 25. The device according to embodiment 24, wherein the device in the form of an adhesive tape further comprises an electrically conductive layer and / or a primer layer between the backing and the adhesive (A).

[0095] 26. The device according to any one of embodiment 24 or 25, wherein the device in the form of an adhesive tape that comprises one or more layers of adhesive, wherein at least one of the one or more layers of adhesive is formed by an adhesive (A), and wherein the other one of the at least one or more layers is also formed by an adhesive (A) or is formed from an adhesive whose adhesive strength cannot be modified by an electric stimulus, the one or more layers being present on the same side or on opposite sides of a carrier.

[0096] 27. The device according to embodiment 26, which comprises a layer formed by the adhesive (A) and a layer formed by an adhesive whose adhesive strength cannot be modified by an electric stimulus, wherein the layers are present on the same side or on opposite sides of a carrier, and wherein the adhesive whose adhesive strength cannot be modified by an electric stimulus exhibit no ionic conductivity. 28. The device according to embodiment 27, wherein the adhesive (A) and that adhesive whose adhesive strength cannot be modified by an electric stimulus are present on opposite sides of a carrier, and wherein both of the adhesives are in contact with an electrically conductive substrate.

[0097] 29. The device according to any of the preceding embodiments, which comprises one or more layers of adhesive (A) that are in contact with each other, wherein the one or more layers differ in composition and in the magnitude of their change in adhesive strength, expressed in N / cm, upon application of the same electric stimulus.

[0098] 30. The device according to embodiment 29, which consists of the one or more layers that are in contact with each other, or which consists of the one or more layers that are in contact with each other and conductive substrates on either side of the layers.

[0099] 31. The device according to embodiment 29, wherein the one or more layers of adhesive (A) are provided on the same side of the carrier, such that the layer of adhesive (A) exhibiting the smaller change in adhesive strength upon application of the electric stimulus is provided in contact with the carrier, or wherein the layers are proved such that the layer of adhesive (A) exhibiting the larger change in adhesive strength upon application of the electric stimulus is provided in contact with the substrate.

[0100] 32. The device according to embodiment 31, wherein the adhesive layer formed from the adhesive (A) that is not in contact with the carrier is in contact with a conductive substrate.

[0101] 33. A method of modifying the adhesive strength of an adhesive device as defined in any of the preceding embodiments, the method comprising the application of one or more electric stimuli for increasing and / or decreasing the adhesive strength of the adhesive.

[0102] 34. The method according to embodiment 33, wherein the one or more electric stimuli have a voltage of 1 to 50 V and / or a duration of 1 second to 30 minutes.

[0103] 35. The method according to embodiment 33 or 34, wherein the one or more electric stimuli are applied by using a controller that is operated by a user or are applied using a controller according to a pre-defined program or automatically in response to a signal received from an external source, the signal being provided via RF, remote control, other wired or wireless communication methods, or by an external wired power supply.

[0104] 36. The method according to embodiment 35, wherein the user or the pre-defined program provides electric stimuli of increasing voltage and / or duration. 37. The method according to any one of embodiments 33 to 36, wherein two or more electric stimuli are applied in sequence, at least two of the stimuli having opposite polarity or are adapted to achieve different levels of adhesive strength.

[0105] 38. The method of embodiment 37, wherein the stimuli that are adapted to achieve different levels of adhesive strength both are electric stimuli for increasing adhesive strength, ES+, and are adapted to provide different rebonded adhesive strengths as well as decreasing adhesive strength, ES⁻ and are adapted to provide different debonded adhesive strengths.

[0106] 39. An adhesive system capable of modifying the adhesive strength of an adhesive, preferably a pressure-sensitive adhesive, by applying one or more electric stimuli, the system comprising

[0107] a device as defined in any one of embodiments 1 to 32, and

[0108] a controller that is configured to apply an electric stimulus to the device.

[0109] wherein the controller is operated manually by an operator or automatically following a pre-defined program.

[0110] Further aspects and features of the present invention will become apparent from the following description.

[0111] DETAILED DESCRIPTION OF THE INVENTION

[0112] DEFINITIONS

[0113] The "comprising" is used open-endedly and requires the presence of the recited components of features, while additional components of features are not excluded. The term however also encompasses the more restrictive meanings "consisting of" and "consisting essentially of", unless the context dictates otherwise. The term "consisting essentially of" requires the presence of other features or components and allows for the presence of other features or components as long as the objects of the present invention are not impaired.

[0114] The expression "laterally protrude" refers in the context of the present invention to any kind of lateral protrusion of the layer or layers in question and means that the layer in question extends further, particularly in the "xy" plane and hence laterally - perpendicular to the stack direction -than does the reference layer. In place of the term "lateral protrusion", terms used in the context of the present invention include "lateral extension" or "lateral extension portion". The term "lateral" is referenced here to any direction of extent of the layer plane "xy" perpendicularly to the stack direction of the layers "z". The term is therefore independent in particular of the geometric shape of the adhesive tape in the "xy" plane, which for example may be a rectangle, as is usual for adhesive tapes (see above), or else may be a square or a circle. Minor fluctuations in the dimensions of the individual layers in the "xy" plane, resulting from the die-cutting process or similar shaping processes, are not addressed herewith, in particular since such slight projections of material, in view of the dimensions, are incapable of receiving a voltage applied thereto as planned and they do not imply any additional effort in production, thus being not brought about by means of an additional method step.

[0115] The present invention embraces all the features which are subjects of any dependent claims. Further, the present invention embraces combinations of individual features with one another, including at different preference levels. The present invention thus embraces, for example, the combination of a first feature identified as being "preferred" with a second feature identified as being, e.g., "particularly preferred". In this context, subjects identified as part of "embodiments", likewise at different preference levels, are also embraced. In other words, where the present description refers to different levels of preferences, combinations of these preferred embodiments and / or features shall also be deemed as disclosed if this combination is technically meaningful.

[0116] Whenever ranges are specified below, the upper and lower limit are included, as is any value in between.

[0117] Physical properties referred to below are generally determined at 25 °C and 1 atm pressure, unless a specific test method is indicated or the circumstances require otherwise. Properties can be determined by methods known in the art or by specific test methods indicated below. In case of discrepancy, the specific test methods below prevail.

[0118] The term "conventional adhesive" is used to denote an adhesive that is not electro-responsive.

[0119] The terms "first", "second", "third", etc. are used in the present invention to distinguish between different elements, states or properties. These terms are not to be understood as implying any particular order of elements or magnitude of a physical state or property. In the present invention, a "second" element or state could be named "first" element or state, and vice versa, without changing the subject matter.

[0120] The term "initial bonding" or "initially bonded" refers to the adhesion strength of the adhesive measured by Test A (Peel Adhesion) outlined below without and prior to applying any electric stimulus.

[0121] The term "debonding" refers to the application of an electric stimulus ES~ that decreases the adhesive strength of the adhesive, the adhesive being in the initial, bonded or rebonded state prior to application of the electric stimulus. The term "debonded adhesive strength" refers to the adhesion strength of the adhesive as measured by Test A (described below), after a first electric stimulus (e.g. voltage) for debonding (i.e. for reducing adhesive strength, ES~, e.g. ES-1 for the first debonding) has been applied, i.e. in the debonded state. The adhesive strength of a debonded adhesive is lower than the initial adhesive strength.

[0122] The term "bonding" refers to the process of applying an electric stimulus ES+1 for increasing adhesive strength of the electrically responsive adhesive, the adhesive being in its initial state, thereby bonding the adhesive to a substrate (also referred to as adherend in the present invention). The bonding is thus the first application of an electric stimulus ES+1 for increasing adhesion strength, prior to any debonding or rebonding.

[0123] The term "bonded adhesive strength" refers to the adhesive strength that is observed in the Test A after an electric stimulus ES+1 for increasing bonding strength has been applied to an adhesive in the initial state. The first "bonded state" refers to an adhesive having the bonded adhesive strength AS^i. The bonded state is optional, as a device may be subjected to debonding when it is in an initial bonded state, in which case no bonded state exists.

[0124] The term "rebonding" refers to the application of an electric stimulus ES+to an adhesive that previously has been exposed to an electric stimulus for reducing the adhesion strength ES~, i.e. to a debonding process.

[0125] The term "rebonding" refers to the third step in a sequence including subsequently initial bonding, debonding and rebonding, or the second step in sequence including debonding and rebonding, and encompasses any rebonding performed after a debonding step, such as in one or more debonding-rebonding cycles, such as bonding-debonding-(first) rebonding-(second) debonding- (second) rebonding, etc.

[0126] The term "cycle" is defined as including at least the sequence: debonding - rebonding, and a device of the present application may be suitable for 2, 3, 4, 5 or more of such cycles without a significant loss of adhesive strength in the first, second, third, or fourth rebonded state as compared to the adhesive strength in the (first) bonded state or a preceding rebonded state, or with a loss of adhesive strength that is 50 % or less, such as 40 % or less, 30 % or less, and preferably 20 % or less, more preferably 10 % or less, in the second and third rebonding as compared to the first rebonding or the preceding rebonding, etc., each assessed based on the same electric stimulus (voltage, duration, polarity) for each rebonding step.

[0127] The term "rebonded adhesive strength" refers to the adhesive strength of the electrically responsive adhesive as measured by Test A after a debonded adhesive has been subjected to an electric stimulus (e.g. voltage) for increasing the adhesive strength as compared to the adhesive strength before the electric stimulus is applied. The rebonded adhesive strength is higher than the debonded adhesion strength, and may be lower, higher or the same as the initial adhesive strength, and is typically higher than the initial adhesive strength. It may be as high or higher than the bonded adhesive strength.

[0128] The term "bonded adhesive strength" denotes the adhesive strength that is observed after applying an electric stimulus for increasing adhesive strength ES+1 to a device in the initial adhesive state, i.e. in the state prior to the application of any electric stimulus.

[0129] The term "first debonded adhesive strength" denotes the adhesive strength that is observed after applying an electric stimulus for decreasing adhesive strength ES-1 to a device in the initial or bonded adhesive state, i.e. in the state prior to the application of any electric stimulus or in the state after application of an electric stimulus for increasing adhesive strength.

[0130] The term "first rebonded adhesive strength" refers to the adhesive strength of the electrically responsive adhesive as measured by Test A after a once debonded adhesive, i.e. an adhesive having the first debonded adhesive strength, has been subjected to an electric stimulus (e.g. voltage) ES+2 for increasing the adhesive strength as compared to the adhesive strength before the electric stimulus is applied. If there is no first electric stimulus has been applied for bonding, ES+1, from the initial state,, ES+2 may be the first electric stimulus for increasing adhesive strength that is applied to the device, and in this case the adhesive strength before the electric stimulus is applied is the initial adhesive strength.

[0131] In the present invention, ionic conductivity may be determined by methods known in the art or by Test B: Ionic Conductivity set out below. In case of discrepancy, the result obtained by Test B prevails.

[0132] The term "adhesive property" denotes any property of an adhesive that is of relevance in practice to exert the adhesive function. The adhesive property may in particular refer to the adhesive strength, determined in N / cm as determined by Test A below.

[0133] The term "adhesive state" denotes the state of the adhesive, such as a PSA, in particular in relation to its adhesive properties. The adhesive state may be characterized by the adhesive strength as determined by the below Test A (Peel adhesion). The absolute difference in adhesive strength between a) a bonded or rebonded state and b) a debonded adhesive states may be 1 N / cm or more, 2 N / cm or more, e.g. 3 N / cm or more, 4 N / cm or more, or 5 N / cm or more, such as 6 N / cm or more, 7 N / cm or more, or 8 N / cm or more. While there is no particular upper limit, it may be 40 N / cm or less, such as 35 N / cm or less, 30 N / cm or less, 25 N / cm or less, or 20 N / cm or less, or 15 N / cm or less.

[0134] The term "electric stimulus" refers to any electric stimulus, and may thus include any voltage, duration, or frequency. The term may denote of a DC (direct current), AC (alternating current), VDC (volts direct current), VAC (volts alternating current), Pulsed DC (pulsed direct current), Pulsed AC (pulsed alternating current). The alternating current may have a sinusoidal waveform or may have a rectangular wave form, and the shape of the waveform is not particularly limited. In one embodiment, the electric stimulus has a voltage of 1 to 100 V, such as 1 to 50 V, 1 to 10 V, or 10 to 50 V, and may be a direct or alternating current, and preferably is a direct current. The duration of the electric stimulus is not particularly limited and may be from 0.1 to 10,000 seconds, such as from 0.5 to 1000 seconds or from 1 to 300 seconds.

[0135] The polarity of the electric stimulus, e.g. in DC form, is not particularly limited. Amongst others, the polarity may be the decisive factor for an electric stimulus to increase or decrease bonding strength of an adhesive.

[0136] The term "carrier" is used to denote a structural element that provides support for a layer of an adhesive, meanwhile provides electrical conductivity. The carrier may consist of only one layer which provides both supporting and electrical conductivity functions, as will be described below. Or may be formed by a backing film having a primer layer or having a primed surface, on which optionally an electrically conductive layer is provided. The primed layer or primer, and the optional electrically conductive layer, may be provided on only one or on both sides of a backing film to thereby form the carrier.

[0137] The term "electrically conductive" is well understood by a skilled person. A possible threshold may be defined at a conductivity of 1 S / cm or higher, 10 S / cm or higher, such as 100 S / cm or higher, e.g. 103S / cm or higher, 104S / cm or higher or 105S / cm or higher.

[0138] The electric stimulus may be for increasing (ES+) or for decreasing (ES_) adhesive strength. Here, "+" and "-" do not relate to the polarity of the electric stimulus, but to the effect on the adhesive strength.

[0139] An adhesive whose adhesive strength can be modified by respective electric stimuli from an initial state to a first bonded state, from a first bonded state to a first debonded state, and from a first debonded state to a first rebonded state may also be referred to as electro-responsive adhesive or as adhesive (A) in the present invention.

[0140] The number designating the electric stimulus, such es ES+nand ES’n(where n is a positive integer) denotes the number of electric stimuli for increasing or decreasing adhesive strength, respectively, that are or have been applied to the device, thereby effecting n number of (re) bonding and debonding, respectively. In ES’n, n denotes the number of times an electric stimulus has been applied for debonding. In ES+n, (n-1) denotes the number of times an electric stimulus has been applied for rebonding, with ES+1 denoting the electric stimulus for the (first) bonding, prior to any debonding. In the method of the present invention and in the use of the device of the invention, ES+1 may be omitted if the initial adhesion strength is sufficient for the intended application. A pressure-sensitive adhesive or adhesive composition is understood in the invention, as is customary in the general usage, as a material which at least at room temperature is permanently tacky and also adhesive. A characteristic of a pressure-sensitive adhesive is that it can be applied by pressure to a substrate and remains adhering there, with no further definition of the pressure to be applied orthe period of exposure to this pressure. In general, though in principle dependent on the precise nature of the pressure-sensitive adhesive and also on the substrate, the temperature and the atmospheric humidity, the influence of a minimal pressure of short duration, which does not go beyond gentle contact for a brief moment, is enough to achieve the adhesion effect, while in other cases a longer-term period of exposure to a higher pressure may also be necessary.

[0141] Pressure-sensitive adhesives have particular, characteristic viscoelastic properties which result in the permanent tack and adhesiveness. A feature of these adhesives is that when they are mechanically deformed, there are processes of viscous flow and there is also development of elastic forces of recovery. The two processes have a certain relationship to one another in terms of their respective proportion, in dependence not only on the precise composition, the structure and the degree of crosslinking of the pressure-sensitive adhesive, but also on the rate and duration of the deformation, and on the temperature.

[0142] The proportional viscous flow is necessary for the achievement of adhesion. Only the viscous components, frequently brought about by macromolecules with relatively high mobility, permit effective wetting and effective flow onto the substrate where bonding is to take place. A high viscous flow component results in high pressure-sensitive adhesiveness (also referred to as tack or surface stickiness) and hence often also in high adhesion. Highly crosslinked systems, crystalline polymers, or polymers with glasslike solidification lack flowable components and are in general devoid of tack or possess only little tack at least.

[0143] The proportional elastic forces of recovery are necessary for the achievement of cohesion. They are brought about, for example, by very long-chain macromolecules with a high degree of coiling, and also by physically or chemically crosslinked macromolecules, and they allow the transmission of the forces that act on an adhesive bond.

[0144] DESCRIPTION OF EMBODIMENTS

[0145] The present invention provides a device, such as an adhesive tape, which possesses excellent reworking function, i.e. which is capable of (initial) bonding, debonding and rebonding, and which therefore can be used one or more times without significantly losing its adhesive properties.

[0146] The device, e.g. in the form of an adhesive tape, can preferably be debonded from at least one substrate (adherend) without remnants upon application of an electric stimulus (electromotive force). Especially, the adhesive strength may be decreased by at least 90 % from its initial bonding strength (no voltage) in less than 2 min after the application of DC voltage. More surprisingly, the device present invention can achieve an adhesion strength (peel adhesion on steel) of up to 15 N / cm, up to 20 N / cm, or even higher from its initial adhesion strength (e.g. 3 to 7 N / cm, without voltage application) by applying DC voltage, which is much higher than that of certain adhesive tapes disclosed in the prior art having electrical debonding functions.

[0147] In the broadest aspect, the present invention provides a device comprising an adhesive whose adhesive strength can be modified by respective electric stimuli from an initial state to a first bonded state, from a first bonded state to a first debonded state, and from a first debonded state to a first rebonded state, wherein the device has

[0148] an initial adhesive strength ASj,

[0149] a first bonded adhesive strength AS i,

[0150] a first debonded adhesive strength ASdi, and

[0151] a first rebonded adhesive strength ASr;

[0152] and which satisfies the following conditions:

[0153]

[0154] wherein

[0155] ASj represents the initial adhesive strength prior to application of an electric stimulus, ASbi represents the bonded adhesive strength after a first electric stimulus for increasing bonding strength (ES+1) has been applied,

[0156] ASdi represents the debonded adhesive strength after a first electric stimulus for decreasing bonding strength (ES’l) has been applied, and

[0157] ASrirepresents the rebonded adhesive strength after a second electric stimulus for increasing bonding strength (ES+2) has been applied.

[0158] Herein, the adhesive strength refers to the peel strength in N / cm as determined by Test A described below.

[0159] As derivable from the above, the adhesive strength in the (first) bonded state AS^i is higher than in the initial state. Thus, the device allows increasing the adhesive strength from the "natural" initial adhesive strength, prior to application of any electric stimulus, by applying a first electric stimulus for increasing adhesive strength, ES+1. This is however optional if the initial adhesive strength is already sufficient for the intended use. ASj is not particularly limited and depends on the nature of the adhesive material, such as a PSA. In certain embodiments, ASj is in the range of up to 8 N / cm, e.g. from 1 to 7 N / cm, such as from 3 to 6 N / cm.

[0160] ASfoi is not particularly limited, as long as it is higher than ASj. In certain embodiments, ASbiis in the range of 6 N / cm or greater, such as 7 N / cm or greater, 8 N / cm or greater, 9 N / cm or greater, preferably 10 N / cm or greater, 11 N / cm or greater, 12 N / cm or greater, 13 N / cm or greater, 14 N / cm or greater, or 15 N / cm or greater. While there is no particular upper limit, ASbimay be 40 N / cm or less, 35 N / cm or less, 30 N / cm or less, 25 N / cm or less, or 20 N / cm or less.

[0161] ASJI is not particularly limited as long as it is less than ASbi. In certain embodiments, ASJI is 6 N / cm or less, 5 N / cm or less, 4 N / cm or less, 3 N / cm or less, 2.5 N / cm or less or 2.0 N / cm or less, or even 1.5 N / cm or less or 1.0 N / cm or less. Preferably, ASJI is less then 1.0 N / cm, more preferably 0.5 N / cm or less, such as 0.3 N / cm or less.

[0162] ASridenotes the adhesive strength upon first rebonding, i.e. the adhesive strength of a device that has been debonded once upon rebonding, the debonding and rebonding being effected by respective electric stimuli ES'l and ES+2.

[0163] The absolute value of ASriis not particularly limited, as long as it satisfies ASri> (0.75 x ASbi). This means that ASriis at least 75 % of the adhesive strength that is observed upon first bonding. This requirement thus expresses that the device of the present invention can be rebonded with sufficiently high strength. In certain embodiments, the device satisfies the relationship ASri> (0.80 x ASfoi), ASri> (0.85 x ASb]J, ASri> (0.90 x ASb], ASri> (0.95 x ASb], or ASri> (1.00 x ASbi). While the latest expresses that the adhesive strength upon first rebonding is as high as upon first bonding, it is a very surprising finding of the present invention that in certain embodiments ASrican be even higher than ASbi. In certain embodiments, the device thus satisfies the condition ASri> (1.05 x AS^i), ASri> (1.10 x AS^i), ASri> (1.15 x ASbi), preferably ASrl> (1.20 x ASbl), ASrl> (1.25 x ASbl), ASrl> (1.30 x ASbl), ASrl> (1.35 x ASbl), ASrl> (1.40 x ASbi), or ASri> (1.45 x ASbi), and more preferably ASri> (1.50 x ASbi).

[0164] While there is no particular upper limit, in practice one may expect that ASri< (4.0 x ASbi), such as ASri< (3.0 x ASbi) or ASri< (2.5 x ASbi).

[0165] In certain embodiments, the device satisfies the condition ASj^^ ASj, preferably ASj^ (0.5 x ASj), more preferably ASJI^ (0.2 x ASj) or ASj^ (0.1 x ASj). Thus, the first debonded adhesive strength is lower than the initial adhesive strength (the "natural" adhesive strength prior to application of any electric stimulus), and is preferably 50 % or less, such as 20 % or 10 % or less thereof. While the first debonded adhesive strength ASJI is in practice preferably as low as possible, the device may satisfy ASj^ (0.005 x ASj). In one embodiment, the adhesive strength in the first bonded state and the 1strebonded state, and preferably also in subsequent rebonded states, is each within the range of 3.0 to 40.0 N / cm, e.g. from 5.0 to 30.0 N / cm, preferably from 7.0 to 20.0 N / cm, or from 7.5 to 18.0 N / cm, such as from 8.0 to 17.0 N / cm, and the adhesive strength in each of the one or more debonded states is in the range of 0.05 to 2.5 N / cm, such as from 0.10 to 2.0 N / cm, preferably from 0.10 to 0.50 N / cm.

[0166] A skilled person will realize that the absolute value of ASj depends mainly on the composition and chemistry of the adhesive, while for AS^, ASj and ASrin addition the type, magnitude and / or duration of the electrical stimulusfor increasing ordecreasing adhesive strength will have an impact on the obtained adhesive strength. While the above conditions apply regardless of the type, magnitude or duration, in one embodiment these conditions apply when the electric stimuli are selected from the group consisting of an alternating (AC) current, or direct (DC) current, or a pulsed current, such as wherein the electric stimuli are a direct or alternating current with a voltage of 0.5 - 230 V, or a pulsed current, such as wherein all electric stimuli for increasing adhesive strength are identical to each other and include a direct current voltage of 15 V for 1 minute, and all stimuli for decreasing adhesive strength are identical and include a direct current voltage of 15 V for one minute with reversed polarity to the electric stimuli for increasing adhesive strength.

[0167] Further, it is one advantage of the present invention that the above conditions can be met with no or only a short period of time between the electric stimuli for decreasing (debonding) and increasing (rebonding) adhesive strength. Thus, in certain embodiments the conditions are met when the time between ES’nand ES+(n+l) (where n is a positive integer of 1 or greater, such as from 1 to 10 or from 1 to 5, e.g. 2, 3, or 4) is 24 hours or less, such as 10 hours or less, e.g. 5 hours or less, 3 hours or less, preferably 120 minutes or less, such as 60 minutes or less, 45 minutes or less, 30 minutes or less, 20 minutes or less, more preferably 15 minutes or less, 10 minutes or less, or 5 minutes or less, e.g. 2 minutes or less or 1 minute or less.

[0168] For example, in one embodiment, the device of the present invention satisfies the condition ASri> (0.75 x AS i) when the time between the electric stimuli ES-1 and ES+2 is 2 hours or less, preferably 1 hour or less, more preferably 30 minutes or less or 20 minutes or less. While there is no particular lower limit, in practice 1 minute or more, such as 5 minutes or more, may be necessary to satisfy the above conditions in order to provide the adhesive with sufficient time for relaxation.

[0169] It is a further advantage of the present invention that not only the time between the electric stimuli for decreasing and increasing can be kept short while satisfying the above conditions in relation to ASJI and ASri, but also more generally for AS^ and ASrn(where n is a positive integer of 1 or greater, such as from 1 to 10 or from 1 to 5, e.g. 2, 3, or 4), i.e. that the device of the present invention allows multiple debonding-rebonding cycles while maintaining a high adhesion strength in the 2ndand further rebonded states and a low adhesion in the 2ndand further debonded states even at short times between the electric stimuli for debonding and rebonding. Here, the absolute values for the adhesion strength in the 2ndand further debonded states AS^ri (with n being a positive integer of 2 or greater, such as from 2 to 10 or 2 to 5, such as 2, 3, 4, and 5) preferably fall within the ranges given above in N / cm for the first debonded state, and the absolute values for the adhesion strength in the 2ndand further rebonded states ASrn(with n being a positive integer of 2 or greater, such as from 2 to 10 or 2 to 5, such as 2, 3, 4, and 5) preferably fall within the ranges given above in N / cm for the first and subsequent rebonded states.

[0170] In certain embodiments, the device has a second debonded state having an adhesive strength ASJ2 and a second rebonded state having an adhesive strength ASr2, and satisfies the following conditions AS^ < (1.5 x ASJI) and ASr2 > (0.5 x ASri), wherein AS^ represents the adhesive strength after a second electric stimulus for decreasing bonding strength (ES’2) has been applied, i.e. in the second debonded state, and ASr2 represents the adhesive strength after a third electric stimulus for increasing bonding strength (ES+^) has been applied, i.e. in the second rebonded state. These conditions specify that the adhesive strength in the second debonded state, AS^, is at most 50 % higher than in the first debonded state, and that the adhesive strength in the second rebonded state, ASr2, is at least 50 % of the adhesive strength in the first rebonded state. Satisfying these criteria ensures a reusability of the device, which may be in the form of an adhesive tape. Preferably, the device satisfies AS^ < (1.4 x ASj^) and ASr2 > (0.6 x ASri) or AS^ < (1.3 x ASJI) and ASr2 > (0.7 x ASri), more preferably AS^ < (1.2 x ASj^) and ASr2 > (0.8 x ASri).

[0171] In preferred aspect of the present invention, the device satisfies the criteria AS^ < (1.1 x ASJI) and ASr2 > (0.9 x ASri), more preferably AS^ < (1.0 x ASj^) and ASr2 > (1.0 x ASri). While not required for reusability, the device may satisfy the requirement AS^ < (0.9 x ASj^) and ASr2 > (1.1 x ASri), implying better removability (lower adhesive strength) in the second debonded state as compared to the first debonded state, and higher adhesive strength in the second rebonded state as compared to the first rebonded state.

[0172] While the above embodiment specifies these properties for the second debonded / rebonded state (the second cycle of debonding-rebonding, n=2), the above conditions and relationships preferably apply also in subsequent cycles. Accordingly, in one embodiment, the device of the present invention has an n debonded state having an adhesive strength ASdnand n’^ rebonded state having an adhesive strength ASrn, and satisfies the following conditions:

[0173] ASjn < (1.5 x AS^n-i) and ASrn≥ (0.5 x ASrn-1)

[0174] preferably

[0175]

[0176] wherein n is an integer of 3 or greater, such as from 3 to 100, from 3 to 50, from 3 to 40, from 3 to 30, from 3 to 20, from 3 to 10 or from 3 to 5, and

[0177] wherein ASdnrepresents the adhesive strength after an n-th electric stimulus for decreasing bonding strength (ES+n) has been applied, i.e. in the n^ debonded state, and

[0178] ASrnrepresents the adhesive strength after an n+lth electric stimulus for increasing bonding strength (ES’n+l) has been applied, i.e. in the n^ rebonded state.

[0179] These conditions specify that the adhesive strength in the n^ debonded state, ASdn, is at most 50 % higher than in the previous (n-l^) debonded state, and that the adhesive strength in the n*h rebonded state, ASrn, is at least 50 % of the adhesive strength in the preceding rebonded state, and that preferably the threshold is at most 30 %, more preferably or at most 20%, respectively preferably at least 70%, more preferably at least 80%. Satisfying these criteria ensures reusability of the device, which may in the form of an adhesive tape.

[0180] In a preferred aspect of the present invention, the device satisfies the criteria ASdn< (1.1 x ASd(n-1)) and ASrn> (0.9 x ASr(n-ij), more preferably ASdn < (1.0 x ASd(n-l)) and ASrn> (1.0 x ASr(n_ l. While not strictly required for reusebility, the device may satisfy the requirement ASdn< (0.9 xA$d(n-1)) and ASrn> (1.1 x ASr(n_ij), implying better removability (lower adhesive strength) in the n^ debonded state as compared to the preceding (n-lth) debonded state, and higher adhesive strength in the nthrebonded state as compared to the preceding (n-lth)rebonded state. These relationships preferably apply for n being 3 or greater, such as such as from 3 to 100, from 3 to 50, from 3 to 40, from 3 to 30, from 3 to 20, from 3 to 10, or from 3 to 5.

[0181] The adhesive used in the device of the present invention is not particularly limited as long as it allows realizing the features described above and set out in the claims. The adhesive preferably contains ionic species and is preferably ion conductive, preferably in the range of 10-10S / cm to 10-3S / cm, as this facilitates the electro-responsive properties and allows the conduction of a current my movement of the ions. The adhesive may comprise one or more ionic liquids and / or one or more salts that are no ionic liquids, preferably a lithium salt. This is because one way to achieve Ionic conductivity is to include an ionic liquid in the adhesive formulation, optionally in combination with a salt that is no ionic liquid, in particular a lithium salt. The adhesive comprising one or more ionic liquids and / or one or more salts that are no ionic liquids may be a pressure-sensitive adhesive (PSA).

[0182] In one embodiment, the PSA used in the device of the present invention comprises one or more selected from acrylic adhesives, rubber-based adhesives, silicone adhesives, epoxy adhesives, polyurethane adhesives, cyanoacrylate adhesives, UV-curable adhesives; an ionic liquid, and optionally a salt that is no ionic liquid. In one embodiment, the PSA comprises an acrylic adhesive, an ionic liquid and a salt that is no ionic liquid, which is preferably a lithium salt.

[0183] An ionic liquid is a salt that is in the liquid state at or near room temperature. It is made up entirely of ions— typically a bulky, asymmetric organic cation and a weaker coordinating anion. When ionic liquids are incorporated into the adhesive an electrolyte adhesive is formed. This not only gives ionic conductivity as well as adhesive properties. A salt that is no ionic liquid is thus a salt that is a solid at room temperature (25°C).

[0184] Common cation of ionic are imidazolium, pyridinium, pyrrolidinium, ammonium, phosphonium, cholinium, morpholinium, piperidinium, guanidinium, thiazolium based and anions are tetrafluoroborate, hexafluorophosphate, bis(trifluoromethanesulfonyl)imide, trifluoromethanesulfonate, dicyanamide, nitrate, chloride, acetate, hydrogen sulfate, methanesulfonate.

[0185] The ionic liquid is preferably selected from the group comprising 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMIM FSI), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMIM TFSI), l-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIM TFSI), l-ethyl-3-methylimidazolium thiocyanate (EMIM SCN), l-ethyl-3-methylimidazolium dicyanamide (EMIM DCA), l-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM BF4), l-butyl-3-methylimidazolium thiocyanate (BMIM SCN), l-allyl-3-methylimidazolium dicyanamide (AllylMIM DCA), l-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (AllylMIM TFSI), l-ethyl-3-vinylimidazolium bis(trifluoromethylsulfonyl) imide (EVIM TFSI), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide (Pyrl3 TFSI), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl) imide (Pyrl3 FSI), N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl) imide (Pyrl4 FSI), l-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide, 1-butyl-l-methylpyrrolidinium dicyanamide (Pyrl4 DCA), 1-butyl-l-methylpyrrolidinium triflate (Pyrl4 OTf), l-ethyl-3-methylimidazolium triflate (EMIM OTf), l-butyl-3-methylimidazolium triflate (BMIM OTf), 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide (DiMIM BTA), l-butyl-3-methylimidazolium tricyanomethanide (BMIM TCM), l-butyl-3-methylimidazolium methyl sulfate (BMIM MeSO4), 1,3-diethylimidazolium bis(trifluoromethylsulfonyl) imide (DiEIM TFSI), N-butyl-N-methylpyrrolidinium tricyanomethanide (Pyrl4 TCM), diethylmethylsulfonium bis(trifluoromethylsulfonyl) imide (S122 TFSI), l-propyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide (Pro4Pic TFSI), l-ethyl-3-methylimidazolium ethyl sulfate (EMIM EtSO4), triethylsulfonium bis(trifluoromethylsulfonyl) imide (S222 TFSI), l-(2-methoxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (MeOEMIM TFSI), 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl) imide (PMIM TFSI), 1-butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (Pyrl4 TFSI), l-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl) imide, 1,3-dimethylimidazolium methyl sulfate (DiMIM MeSO4), 1-ethylimidazolium bis(trifluoromethylsulfonyl) imide (EIM TFSI), l-ethyl-3-methylimidazolium methanesulfonate (EMIM OMs), l-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl) imide (Et4Pic TFSI), l-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide (EDiMIM TFSI), 2-methyl-l-propylpyridinium bis(trifluoromethylsulfonyl) imide (Pro2Pic TFSI), l-ethyl-3-methylimidazolium acetate (EMIM OAc), l-ethyl-3-methylimidazolium hexafluorophosphate (EMIM PFe), l-butyl-3-methylimidazolium hexafluorophosphate (BMIM PFe), 1-hexylpyridinium bis(trifluoromethylsulfonyl)imide (HexPy TFSI).

[0186] Ionic liquids or conducting salts may be used to give ionic conductivity. To enhance ionic conductivity, one or more plasticizers may be added to the adhesive formulation, which may be a PSA formulation. Common plasticizers are various PEG, different carbonates and water.

[0187] In one embodiment, the electro-responsive adhesive (A) is a PSA that is prepared by polymerizing a mixture comprising at least the following components:

[0188] a) 20 to 80 wt % of acrylate monomer (al) from the group of the (meth)acrylic esters containing at least one oxygen atom; and

[0189] b) 20 to 80 wt % of acrylate monomer (a 2) from the group of the (meth)acrylic esters and / or amides containing at least one nitrogen atom; and

[0190] c) 0 wt % to 15 wt % of one or more electro-responsive compounds from the group of polymerizable zwitterionic monomers and / or non-polymerizable zwitterionic compounds, preferably one or more zwitterionic monomers; and

[0191] d) 0.005 to 10 wt % of at least one initiator; and

[0192] e) 0 wt % to 20 wt % of one or more ionic liquids; and

[0193] f) 0 wt % to 20 wt % of one or more conducting salts; and

[0194] g) optionally 1 wt % to 20 wt % by weight of one or more acrylate monomers (a3), wherein the one or more acrylate monomers (a3) are different from acrylate monomers (al) and (a2); and

[0195] h) optionally additives, wherein the weight fractions of the components are based on the total weight of the mixture. All weight ratios of components present in the mixture are chosen to add up to 100 wt %. However, if a solvent is present in the mixture for polymerization, the solvent is disregarded when stating the weight fractions of the components.

[0196] The use of such a PSA as adhesive (A) allows obtaining a surprisingly high adhesive strength upon rebonding. The PSA may be prepared a two-step process (also described in further detail below), including: (i) the provision of a mixture, including UV syrup preparation and liquid electrolyte formulation, followed by (ii) polymerization, including curing by UV web polymerization or UV polymerization to obtain the adhesive composition that is employed in one embodiment of the present invention.

[0197] In one such embodiment, the PSA employed in the present invention is a pressure-sensitive adhesive polymer (random / statistical copolymer) electrolyte composition. The copolymer structure is prepared by polymerizing monomers (al) and (a2) and therefore contains units derived from these monomers also containing oxygen and optionally nitrogen atoms. The ratio of the unit containing at least one oxygen atom and the unit containing at least one nitrogen atom corresponds to the weight ratio of monomer (al) to monomer (a2) as defined in further detail below and which is adjusted to achieve several properties such as: (a) high polarity to dissolve enough conducting salts and electro-responsive compounds, preferably zwitterionic monomers, (b) controlling the glass transition temperature (Tg) of the copolymer, and (c) making the adhesive effectively debondable. The latter cause can be explained as follows.

[0198] Without wishing to be bound by theory, it is assumed that debonding occurs by reactive dissolution of the PSA when an ionic liquid is present. This means that when e.g. a DC voltage is applied, the cation of the ionic liquid is expected to form an N-heterocyclic carbene or similar reactive species by abstracting a proton from the cations, specifically the cation of the ionic liquid containing a proton at the C2 position. This carbene species then modifies or reacts with the bonding side of the adhesive, facilitating debonding. A similar mechanism has been experimentally demonstrated for the solubilization of cellulose, proteins and polymers. It is also possible that debonding occurs by physical dissolution (no reaction) or similar processes. The latter is more likely if the C2 carbon of the cation of the ionic liquid does not have a proton. In this scenario, migration of the ionic liquid to the adhesive-adherend interface causes physical solubilization of the adhesive, resulting in debonding. Of course, both processes can occur during debonding along with another process as gas evaluation, most probably H2gas, which facilitates debonding by mechanical stress. The gas release makes the adhesive surface porous.

[0199] In one embodiment, the adhesive composition contains one or more electro-responsive compounds from the group of polymerizable zwitterionic monomers or non-polymerizable zwitterionic compounds, preferably one or more zwitterionic monomers. The one or more electro-responsive compounds are ionic species having both cation and anion in their structure, which enable the adhesive tape comprising the adhesive composition of the present invention responsive to electric fields. More preferably, the electro-responsive compounds are zwitterionic compounds. In particular, zwitterionic compounds are molecules that contain both positive and negative charges but are overall neutral. In one embodiment, the amount of the one or more electro-responsive compounds is from 0.1 to 15 wt %, preferably from 1 wt % to 10 wt % of the adhesive composition.

[0200] As outlined above, in one embodiment the PSA further contains salts that are no ionic liquids (e.g., different Na and Li salts), facilitating the adhesive composition to be ion conductive. The adhesive composition may also contain an ionic liquid. The conducting salt aids in the solubilization of electro-responsive compounds, preferably zwitterionic monomers, and contributes to the entire adhesive becoming more electro-responsive.

[0201] In certain embodiments, the initial peel adhesion, i.e. the initial adhesive strength, as measured with Test A described hereinafter (cf. experimental section) before the application of a DC voltage source ranges from 2.5 N / cm to 5 N / cm. After voltage application, i.e. after application of the first electric stimulus for increasing first bonding strength ES+1, the peel adhesion, i.e. the adhesive strength in the first bonded state, may increase to values higher than 5 N / cm, such as 6 N / cm or higher, or from to 8 N / cm to 12 N / cm. The same range applies for rebonded states, in particular the first, second, and / or third rebonded state as achieved after application of the electric stimuli ES+2, ES+^ and ES+4, respectively.

[0202] After applying an electric stimulus ES~ for decreasing adhesive strength, the adhesive state in the debonded state is preferably less than 2.5 N / cm, such as 2.0 N / cm or less, 1.5 N / cm or less, 1.0 N / cm or less, or 0.5 N / cm or less. This applies to the first debonded state after application of the electric stimulus ES'l, but also applies to subsequent debonded states, such as the second, third or fourth debonded state as observed after application of the electric stimuli ES'2, ES’3 and ES~ 4, respectively.

[0203] After the preparation of adhesive mass with bulk or solution or UV prepolymer methods, the adhesive is mixed with ionic liquids / plasticizers / curing agents (e.g., initiators or crosslinkers) or other additives (tackifier) to formulate the ion conductive liquid adhesive. The next step is to coat the adhesive on the electrically conductive layer of the carrier and cure it.

[0204] In an embodiment, a UV syrup-based acrylic adhesive is mixed with one or more ionic liquids and then applied to the electrically conductive layer on a backing film and UV cured to obtain an adhesive tape. This is preferable over a solvent cast method, as the curing here is polymerization that increases the anchorage of the adhesive to the electrically conductive layer as well as increasing the anchorage to the electrically conductive layer and backing film. Below a more detailed description of the monomers that may be used in the preparation of the PSA present as adhesive (A) in the device of the present invention is given.

[0205] Monomer (al):

[0206] In one embodiment, the PSA is prepared by polymerizing a mixture comprising monomer (al) as component a) of the mixture. The monomer (al) is an acrylate monomer from the group of the (meth)acrylic esters, preferably containing at least one oxygen atom in the alcohol moiety. In the mixture, the one monomer (al) may be contained or two or more thereof may be contained in combination. The one or more monomer(s) (al) according to the invention are present in an amount of 20 to 80 wt %, such as from 35 wt % to 72 wt %, e.g. 35 to 70 wt %, preferably 45 wt % to 68 wt %, more preferably 50 wt % to 66 wt %, based on the total weight of the mixture.

[0207] The monomer (al) contains preferably at least two oxygen atoms, even more preferably 2 to 20 oxygen atoms. To the skilled person it is clear that the at least one oxygen atom (or the at least two oxygen atoms) in the acrylate monomer is (are) present in addition to the two O atoms (oxygen atoms) of the ester functionality, i.e. (C=O)O. In other words, monomer (al) in total contains at least three oxygen atoms, namely the two oxygen atoms of the ester functionality and an additional oxygen atom. Preferably, monomer (al) in total contains at least four oxygen atoms, namely the two oxygen atoms of the esterfunctionality and two additional oxygen atoms. The at least one oxygen atom (or the at least two oxygen atoms) is (are) typically present in the hydrocarbon part of the alcohol component of the (meth)acrylic ester. The expression "hydrocarbon part" as used herein is the part of the ester which is introduced by an alcohol upon reaction with the carboxylic functional group of acrylic acid to form the ester.

[0208] In a preferred embodiment, the monomer (al) is from the group of (meth)acrylic esters having 4 to 44 carbon atoms, preferably 7 to 44 carbon atoms, or the monomer (al) and at least one oxygen atom or at least two oxygen atoms as described above. More preferably monomer (al) is from the group of (meth)acrylic esters having 4 to 30 carbon atoms and comprising at least one oxygen atom, more preferred 8 to 30 carbon atoms and at least 2 oxygen atoms.

[0209] Preferred (meth)acrylic esters contain the at least one oxygen atom (or the at least two oxygen atoms in the hydrocarbon part of the alcohol component of the ester, wherein at least one non-adjacent CH2 group is replaced by O. The hydrocarbon part of the alcohol component may be branched, unbranched or cyclic, saturated, or unsaturated, aliphatic or aromatic, substituted or unsubstituted, preferably it is branched or unbranched, saturated or unsaturated, and aliphatic since aromatic groups may cause color. In a more preferred embodiment, the hydrocarbon part of the alcohol component is based on polyethylene oxide (PEO). The PEO can be linear or branched, and preferably is linear. In an even more preferred embodiment, the monomer (al) is based on the following formula (1).

[0210]

[0211] formula (1)

[0212] In present formula (1), R1is H or CH3, R2is H, linear or branched C^-Cig alkyl, aryl, hydroxy (C^-C^g) alkyl, -C(=O)CH2C(=O)CH3, -CH3 or -CH2CH3, preferably CH3 or CH2CH3, and n is an integer between 0 and 18, preferably 0 and 15, more preferably 0 and 11. In a preferred embodiment at least one monomer (al) used has a value n between 0 and 11, preferably 0, 1, 2,3 or 4. Preferred are monomers that are liquid at 25 °C.

[0213] Examples of the (meth)acrylic esters include butyl acrylate (BA, n = 0, R1= H, R2= -CH2CH2CH2CH3), 2-ethylhexyl acrylate (EHA, n = 0, R1= H, R2= -CH2CH(CH2CH3)CH3), 2-(2-ethoxyethoxy)ethyl acrylate) (EEEA, also designated as EDGA, n = 2, RT= H, R2=-CH2CH3), 2-[2-(2-methoxyethoxy)ethoxy]ethyl acrylate (n = 3, R1= H, R2= -CH3), diethylene glycol monomethyl ether methacrylate (n = 2, RT= CH3, R2= -CH3), 2-ethoxyethyl methacrylate (n = 1, Rx= CH3, R2= -CH2CH3), 2-methoxyethyl methacrylate (n=l, R1= CH3, R2= -CH3) and ethylene glycol monoacetoacetate monomethacrylate (n = 1, R1= CH3, R2= -C(=O)CH2C(=O)CH3).

[0214] Monomer (a2):

[0215] In one embodiment, the PSA may be prepared by polymerizing a mixture comprising monomer (a2) as component b) of the mixture. The monomer (a 2) is an acrylate monomer from the group of the (meth)acrylic esters or amides containing at least one nitrogen atom. In the mixture, one monomer (a 2) may be contained or two or more thereof may be contained in combination. The one or more monomer(s) (a 2) according to the invention are present in an amount of 20 wt % to 80 wt %, such as from 20 to 48 wt %, preferably 22 wt % to 38 wt %, more preferably 24 wt % to 36 wt % based on the total weight of the mixture.

[0216] In a preferred embodiment, the monomer (a 2) is from the group of (meth)acrylic esters or amides having 4 to 25 carbon atoms, more preferably 5 to 15 carbon atoms, and even more preferably 5 to 9 carbon atoms. Those ranges refer to the (meth)acrylic esters and (meth)acrylic esters amides. This achieves particularly good characteristics with regard to the object to be achieved. The monomer (a2) is from the group of (meth)acrylic esters or amides having at least one nitrogen atom within the molecule and may have one nitrogen atom or two or more nitrogen atoms. Moreover, because the monomer (a2) has an (meth)acrylic functionality within the molecule, the monomer (a2) is a monofunctional monomer. The monomer (a2) is a component copolymerizable with the monomer (al). This achieves particularly good characteristics with regard to the object to be achieved.

[0217] If monomer (a2) is a (meth)acrylic ester, the at least one nitrogen atom (or the at least two nitrogen atoms) is (are) typically present in the hydrocarbon part of the alcohol component of the (meth)acrylic ester, wherein at least one non-adjacent CH2group is replaced by N. The hydrocarbon part of the alcohol component may be branched, unbranched or cyclic, saturated, or unsaturated, aliphatic or aromatic, substituted or unsubstituted, preferably it is branched or unbranched, saturated or unsaturated, and aliphatic since aromatic groups may cause color.

[0218] In the present invention, by use of the monomer (a 2), a proper degree of polarity can be given to the acrylic copolymer. This can provide a pressure-sensitive adhesive sheet that keeps a high adhesive force and adhesion reliability (particularly, repulsion resistance and holding power) when the sheet is bonded and can be easily peeled off from an adherend when the sheet is peeled. This achieves particularly good characteristics with regard to the object to be achieved.

[0219] In particular, with the use of the monomer (a 2), a proper degree of polarity can be given to the acrylic copolymer and Tgcan be controlled.

[0220] In a preferred embodiment, the monomer (a2) is based on the following formula (2).

[0221]

[0222] formula (2)

[0223] In present formula (2), R1is H or CH3, R2or R3is -H, -CH3, -CH2OH, -CH2CH2OH, -CH3or -CH2CH3, preferably -CH3or -CH2CH3.

[0224] In a preferred embodiment the monomer (a2) is liquid at 25 °C, however, solid monomers at 25 °C may also be used. Examples of the (meth)acrylamides include (meth)acrylamide, N-alkyl (meth)acrylamide, and N, N-dialkyl (meth)acrylamide. Examples of the N-alkyl (meth)acrylamide include N-methyl (meth)acrylamide, N-ethyl (meth)acrylamide, N-n-butyl (meth)acrylamide, and N-octyl acrylamide. Further, examples thereof include amino group-containing (meth)acrylamides such as dimethylaminoethyl (meth)acrylamide and diethylaminoethyl (meth)acrylamide. Next, examples of the N, N-dialkyl (meth)acrylamide include N, N-dimethyl (meth)acrylamide, N, N-diethyl (meth)acrylamide, N, N-dipropyl (meth)acrylamide, N, N-diisopropyl (meth)acrylamide, N, N-di(n-butyl) (meth)acrylamide, N, N-di(t-butyl) (meth)acrylamide, N, N-dimethyl acrylamide (R1= H, R2= -CH3 R3= -CH3) and N, N-dimethyl methacrylamide (R1= CH3, R2= -CH3, R3= -CH3).

[0225] Further, examples of the (meth)acrylamides also include cyclic (meth)acrylamides having an N-acryloyl group such as (meth)acryloyl morpholine (like 4-acryloylmorpholine), (meth)acryloyl pyrrolidone, and (meth)acryloyl pyrrolidine. This achieves particularly good characteristics with regard to the object to be achieved.

[0226] Further, examples of the (meth)acrylamides also include N-dialkylaminoalkyl (meth)acrylamide monomers having an N-dialkylaminoalkyl group such as N-[3-(dimethylamino)propyl]acrylamide, N-[2-(dimethylamino)ethyl]acrylamide, N-[2-(diethylamino)ethyl]-acrylamide. This achieves particularly good characteristics with regard to the object to be achieved.

[0227] Further, examples of the (meth)acrylamides include N-hydroxylalkyl (meth)acrylamide monomers having a hydroxyalkyl group having 1 to 4 carbon atoms. Examples of the N-hydroxylalkyl (meth)acrylamide monomers having a hydroxyalkyl group having 1 to 4 carbon atoms include N-methylol (meth)acrylamide, N-(2-hydroxyethyl)acrylamide, N-(2-hydroxyethyl)methacrylamide, N-(2-hydroxypropyl)acrylamide, N-(2-hydroxypropyl)methacrylamide, N-(l-hydroxypropyl)acrylamide, N-(l-hydroxypropyl)methacrylamide, N-(3-hydroxypropyl)acrylamide, N-(3-hydroxypropyl)methacrylamide, N-(2-hydroxybutyl)acrylamide, N-(2-hydroxybutyl)methacrylamide, N-(3-hydroxybutyl)acrylamide, N-(3-hydroxybutyl)methacrylamide, N-(4-hydroxybutyl)acrylamide,

[0228] In the embodiment described above but also for all other embodiments of the electro-responsive adhesive (A), an ionic liquid is optionally yet preferably present. If an ionic liquid is present, the amount of one or more ionic liquids e) may be from 0.1 wt % to 20 wt %; and the amount of one or more salts f) that are not ionic liquids is 0 wt % to 20 wt %. As the requirement of the present invention are more easily satisfied, preferably one of, and more preferably both of the one or more ionic liquids e) and the one or more salts f) are present. Incidentally, this applies also to other electro-responsive adhesives (A), i.e. those that do not contain the unit (al) and (a2). The amount of the one or more ionic liquids is preferably 0.1 % by weight or higher, such as 0.5% by weight or higher, 1.0 % by weight or higher, more preferably 1.5 % by weight or higher, 2.0 % by weight or higher, 2.5 % by weight or higher, or 3.0 % by weight or higher, but is 20 % by weight or less, preferably 15 % by weight or less, or 10 % by weight or less, such as 8.0 % by weight or less. This applies to the totality of ionic liquid.

[0229] Further, the amount of the one or more salts that are not ionic liquids is preferably 0.1 % by weight or higher, such as 0.5 % by weight or higher, 1.0 % by weight or higher, more preferably 1.5 % by weight or higher, 2.0% by weight or higher, 2.5 % by weight or higher, or 3.0% by weight or higher, but is 20 % by weight or less, preferably 15 % by weight or less, or 10 % by weight or less, such as 8.0 % by weight or less. This applies to the totality of salts that are no ionic liquids.

[0230] Common cations of ionic liquids include imidazolium, pyridinium, pyrrolidinium, ammonium, phosphonium, cholinium, morpholinium, piperidinium, guanidinium, thiazolium based. Common anions include tetrafluoroborate, hexafluorophosphate, bis(trifluoromethanesulfonyl)imide, trifluoromethanesulfonate, dicyanamide, nitrate, chloride, acetate, hydrogen sulfate, and methanesulfonate.

[0231] The ionic liquid is preferably selected from the group comprising 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMIM FSI), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMIM TFSI), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIM TFSI), 1-ethyl-3-methylimidazolium thiocyanate (EMIM SCN), 1-ethyl-3-methylimidazolium dicyanamide (EMIM DCA), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM BF4), 1-butyl-3-methylimidazolium thiocyanate (BMIM SCN), 1-ethyl-3-vinylimidazolium bis(trifluoromethylsulfonyl) imide (EVIM TFSI), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide (Pyr13 TFSI), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl) imide (Pyr13 FSI), N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl) imide (Pyr14 FSI), 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide, 1-butyl-1-methylpyrrolidinium dicyanamide (Pyr14 DCA), 1-butyl-1-methylpyrrolidinium triflate (Pyr14 OTf), 1-ethyl-3-methylimidazolium triflate (EMIM OTf), 1-butyl-3-methylimidazolium triflate (BMIM OTf), 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide (DiMIM BTA), 1-butyl-3-methylimidazolium tricyanomethanide (BMIM TCM), 1-butyl-3-methylimidazolium methyl sulfate (BMIM MeSO4), 1,3-diethylimidazolium bis(trifluoromethylsulfonyl) imide (DiEIM TFSI), N-butyl-N-methylpyrrolidinium tricyanomethanide (Pyr14 TCM), diethylmethylsulfonium bis(trifluoromethylsulfonyl) imide (S122 TFSI), 1-propyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide (Pro4Pic TFSI), 1-ethyl-3-methylimidazolium ethyl sulfate (EMIM EtSO4), triethylsulfonium bis(trifluoromethylsulfonyl) imide (S222 TFSI), 1-(2-methoxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (MeOEMIM TFSI), 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl) imide (PMIM TFSI), 1-butyl-l-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (Pyrl4 TFSI), l-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl) imide, 1,3-dimethylimidazolium methyl sulfate (DiMIM MeSO4), 1-ethylimidazolium bis(trifluoromethylsulfonyl) imide (EIM TFSI), l-ethyl-3-methylimidazolium methanesulfonate (EMIM OMs), l-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl) imide (Et4Pic TFSI), l-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide (EDiMIM TFSI), 2-methyl-l-propylpyridinium bis(trifluoromethylsulfonyl) imide (Pro2Pic TFSI), l-ethyl-3-methylimidazolium acetate (EMIM OAc), l-ethyl-3-methylimidazolium hexafluorophosphate (EMIM PFe), l-butyl-3-methylimidazolium hexafluorophosphate (BMIM PFe), 1-hexylpyridinium bis(trifluoromethylsulfonyl)imide (HexPy TFSI).

[0232] Ionic liquids are not limited to the above examples; the cation can also carry vinyl- or allyl-functional groups, allowing the ionic liquid to be covalently integrated into a polymer matrix via radical polymerization. These polymerizable ionic liquids not only offer ionic conductivity like conventional ILs but also enable the formation of stable polymer networks. Examples include 1-allyl-3-methylimidazolium dicyanamide (AllylMIM DCA), l-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (AllylMIM TFSI), l-vinyl-3-ethylimidazolium bis(trifluoromethylsulfonyl)imide (VEIMTFSI), l-vinyl-3-butylimidazolium hexafluorophosphate (VBIMPF6), and similar types.

[0233] Ionic liquids or conducting salts are preferably used to give ionic conductivity, and they should preferably be compatible / soluble with the adhesive matrix, e.g. in order to avoid phase separation / degradation. To enhance ionic conductivity, plasticizers may be added to the adhesive formulation. Common plasticizers are various PEG, different carbonates and water.

[0234] The one or more salts that are no ionic liquids are not particularly limited, but are preferably salts of the alkali metals, more preferably lithium. In one preferred embodiment, the salt comprises a lithium salt selected from the group consisting of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithiumtriflate (LiOTf), lithium difluoro(oxalato)borate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0235] After the preparation of an adhesive mass by bulk or solution or UV prepolymer methods, the adhesive may be mixed with ionic liquids / plasticizers / curing agents (e.g., initiators or crosslinkers) or other additives (tackifier) to formulate the ion conductive liquid adhesive also called as liquid electrolyte. The next step is to coat the ion conducive adhesive on a substrate, e.g. an electrically conductive carrier, and cure it. In a preferred embodiment, the adhesive is a UV syrup-based acrylic adhesive, mixed with ionic liquids. This may be applied to a variety of substrates, e.g. to the electrically conductive coating on a primed PET backing, and then UV cured to obtain a device of the present invention, e.g. in the form of an adhesive tape. This is preferable to a solvent cast method, as the curing often is a polymerization plus crosslinking reaction (optional) that may increase the anchorage of the adhesive to the electrically conducive coating as well as increase the anchorage to a backing film.

[0236] If the device includes two distinct adhesive layers, the first layer may comprise an acrylic adhesive matrix containing inorganic salts like LiTFSI and a zwitterionic compound, including a polymerizable zwitterionic monomer. Alternatively, it may contain an acrylic adhesive with an ammonium-based protic ionic liquid such as EAN. The second adhesive layer may be an acrylic adhesive incorporating an ionic liquid, as described herein. Both adhesives are preferably ionically conductive. Further, in one embodiment the two distinct adhesive layers are formed from different adhesive compositions, each of which is an electro-responsive adhesive (A). Where the magnitude of the increase or decrease in adhesive strength upon application of an electric stimulus ES+respectively ES-is different for the two electro-responsive adhesives (A), selective bonding and debonding on demand is facilitated, as also discussed below in respect of FIG.s 4, 5, 6 and 10 – 15.

[0237] BRIEF DESCRIPTION OF FIGURES

[0238] FIG. 1 schematically illustrates embodiments of an adhesive tape of the present invention, namely a single-layered, single-sided adhesive tape comprising layer (D) of adhesive (A) and an electrically conductive carrier (T). The electrically conductive carrier (T) can be defined as a combination of a backing film (F), primer layer (P) and electrically conductive layer (EC).

[0239] FIG. 2 schematically illustrates embodiments of an adhesive tape of the present invention, namely a double-sided adhesive tape comprising an electrically conductive carrier (T) disposed between layer (D) of adhesive (A) and a layer 2S of conventional adhesive.

[0240] FIG. 3 schematically illustrates embodiments of an adhesive tape of the present invention, namely a double-sided adhesive tape comprising an electrically conductive carrier (T) disposed between two layers (D) of adhesive (A).

[0241] FIG. 4 schematically illustrates embodiments of an adhesive tape of the present invention, namely a double-layered adhesive transfer tape comprising a first adhesive layer (D) and a second adhesive layer (C), wherein both the layers are formed from different adhesives (A). FIG. 5 schematically illustrates embodiments of an adhesive tape of the present invention, namely a double-layered, single-sided adhesive tape comprising two adhesive layers (D) and (C), wherein both the layers are formed from different adhesives (A), coated on an electrically conductive carrier (T).

[0242] FIG. 6 schematically illustrates embodiments of an adhesive tape of the present invention, namely a double-layered, double-sided adhesive tape comprising a carrier (T) disposed between a first layer comprising two adhesive layers (D) and (C), wherein both the layers are formed from different adhesives (A), and a second layer 2S of conventional adhesive.

[0243] FIG. 7 schematically illustrates embodiments of an adhesive tape device of the present invention, namely a single-layered, single-sided adhesive tape comprising layer (D) of adhesive (A) and carrier (T) laminated on an electrically conductive substrate S. Electrically conductive substrate serves as target adherend.

[0244] FIG. 8 and FIG. 9 schematically illustrate the bonding and debonding setup, respectively, for the adhesive device from FIG. 7.

[0245] FIG. 10 schematically illustrates embodiments of an adhesive tape device of the present invention, comprising, namely a double-layered transfer tape comprising a first adhesive layer (D) and a second adhesive layer (C), wherein both the layers are formed from different adhesives (A), disposed between two electrically conductive substrates (S).

[0246] FIG. 11 and FIG. 12 schematically illustrate the bonding and debonding setup, respectively, for the adhesive device from FIG. 10.

[0247] FIG. 13 schematically illustrates embodiments of an adhesive tape device of the present invention, comprising, namely a double-layered, single-sided tape comprising a first adhesive layer (D) and a second ion-conductive adhesive layer (C), wherein both the layers are formed from different adhesives (A), and a carrier layer (T) disposed on an electrically conductive substrate (S).

[0248] FIG. 14 and FIG. 15 schematically illustrate the (re) bonding and debonding setup, respectively, for the adhesive device from FIG. 13.

[0249] DEVICE DESIGNS

[0250] The device of the present invention may take any form or shape. In one embodiment, the device is or comprises an adhesive tape. In the embodiment of an adhesive tape, the device contains in addition to the adhesive (typically present in the form of an adhesive layer) at least a carrier. The carrier may take the form of a backing that preferably is electrically conductive. This can be achieved by using a backing that is as such electrically conductive, such as a metal foil, by providing a conductive coating, or by blending an insulating backing material (such as a polymer, e.g. PET) with conductive particles.

[0251] The adhesive tape may take any desired converted form, with adhesive tape rolls being preferred. The adhesive tape, more particularly in web form, may be produced either in the form of a roll, i.e., in the form of an Archimedean spiral rolled up onto itself, or as an adhesive strip, of the kind obtained in the form of die-cuts, for example.

[0252] The device of the present invention also includes a capacitor-like device, for example wherein an electro-responsive adhesive layer is disposed on an electrically conductive carrier and / or a substrate / adherend, or wherein two electrically conductive substrates sandwich the electro-responsive adhesive, such as an electro-responsive PSA, with or without interposing elements such as additional layers.

[0253] The adhesive tape according to one embodiment of the present invention may be present in web form. A web refers to an object whose length (extent in x direction) is greater by a multiple than its width (extent in y direction), e.g., by a x:y ratio of at least 10:1, and the width is approximately, preferably exactly, the same along the entire length.

[0254] The general expression "adhesive tape" synonymously also called "adhesive strip", in the sense of the present invention encompasses all sheetlike structures, such as two-dimensionally extended films or film portions, tapes with extended length and limited width, tape portions and the like, lastly also die cuts or labels.

[0255] As well as the lengthwise extent (x direction) and widthwise extent (y direction), the adhesive tape also has a thickness (z direction), extending perpendicularly to both extents, with the widthwise extent and lengthwise extent being greater by a multiple than the thickness. The thickness is extremely similar, preferably exactly the same, over the entire two-dimensional extent of the adhesive tapes as defined by length and width. The statements apply analogously to the carrier, which as an integral constituent of the adhesive tape forms a layer in x and y directions. It will be appreciated that the individual layers are disposed on top of another along the z direction.

[0256] In one embodiment, the present invention pertains to a device as defined in the claims, which is a capacitor-like adhesive device comprising:

[0257] a) a primed backing film that is primed on at least one side thereof; b) an electrically conductive coating on the primed side of the backing film;

[0258] c) an electro-responsive adhesive (A) prepared directly on said electrically conductive coating by polymerization or crosslinking; and

[0259] d) an electrically conductive substrate disposed on the side of the adhesive c);

[0260] wherein the device is configured to bond strength increase (bond) of the adhesive tape formed by a), b) and c) to the electrically conductive substrate d) upon application of a first electric stimulus ER+1between the electrically conductive coating and the conductive substrate;

[0261] wherein the adhesive device is further configured to debond from the electrically conductive substrate d) upon application of an electric stimulus for decreasing adhesion strength, ER-1, which may be an electric stimulus with opposite in polarity to the first electric stimulus ER+1;

[0262] wherein the electrical stimuli comprises a DC (direct current), AC (alternating current), VDC (volts direct current), VAC (volts alternating current), Pulsed DC (pulsed direct current), Pulsed AC (pulsed alternating current), preferably a direct current (DC) or alternating current (AC), or pulsed voltage; and

[0263] wherein preferably the adhesive tape, formed by the above components a), b) and c), in the device is capable of repeatedly switching adhesion strength under applied electromotive force, enabling bonding, debonding, and rebonding of the tape to the electrically conductive adherend's surface.

[0264] According to an embodiment of the capacitor-like adhesive device, an electro-responsive adhesive (A) is placed between an electrically conductive coating present on a backing (the backing and the electrically conductive coating together forming a carrier) and an electrically conductive substrate. The adhesive strength of the tape to an electrically conducive substrate's surface can be controlled by properties of the electric stimulus, e.g. voltage polarity, voltage level, and duration of the applied voltage. For example, an electrically conductive coating of PEDOT: PSS [Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)] or PEDOT: Tos [Poly(3,4-ethylenedioxythiophene):p-toluenesulfonate] or carbon may be applied onto a primed PET film to prepare the carrier of this embodiment of the present invention. An electro-responsive adhesive layer may then coated on top to form a single-layered, single-sided adhesive tape. When the resulting tape formed by the components a), b) and c) is laminated onto a conductive substrate such as a steel plate (the adherend d), an adhesive device of this embodiment of the present invention is realized. Upon applying a positive DC voltage forming the electric stimulus ES+1to the steel plate (bonding), the adhesive strength between the tape and the steel plate is increased. While reversing the polarity of the DC voltage [negative voltage to the steel plate], i.e. upon application of the stimulus ES-1, adhesive strength is reduced, allowing the tape to be removed easily and cleanly, with little or no residue from the steel plate. This bonding-debonding process can be repeated multiple times by applying respective stimuli or increasing and decreasing adhesive strength, i.e. in the order

[0265]

[0266] The ability to provide for such repeated bonding and debonding is not achieved in the prior art, where debonding typically occurs on the side where the negative DC voltage is applied (i.e. at the cathode side)— whether it's the substrate or the backing or carrier. If debonding occurs at the side of the backing or carrier, this is usually considered a structural failure (anchorage failure) of the device rather than true debonding, given that the device is thereby disassembled or destroyed. True debonding usually refers to the adhesive separating cleanly from the substrate with little or no residue. It is a surprising finding of the present invention is that debonding occurs only at the electrically conductive substrate side, even when the polarity is reversed (i.e., negative voltage applied to the backing or carrier); instead of causing anchorage failure, the bonding strength of the adhesive tape to the substrate increases.

[0267] In preferred embodiments, the priming means increasing the anchorage strength between the electrically conductive coating and the backing. This might be achieved by physical priming (e.g., flame treatment or corona / plasma treatment) or chemical priming (e.g., curing a very thin adhesive layer or several layers on the film backing by UV light or temperature) or depositing transparent conductive oxides [e.g., Indium tin oxide (ITO)] or carbon nanotubes. Curing means here polymerization or crosslinking.

[0268] In preferred embodiments, the electrically conductive coating comprises materials that exhibit adequate electrical conductivity and hydrophobicity. In one embodiment, the carrier having the conductive coating may be a metalized polymer film. The coating must be resistant to corrosion in electrolyte-rich environments, should offer good weatherability, and form a strong bond with the carrier. In the present invention, this layer may for example be applied onto a primed surface of a backing by either in situ polymerization of monomers of intrinsically conductive polymers or by directly coating an aqueous dispersion or viscous ink onto the primed surface.

[0269] In the above embodiment, the backing having the conductive coating is considered as a carrier. Typically, a backing is non-conductive, such as made from insulating polymers like PET. This may be replaced by a carrier that is inherently conductive, e.g. a metal foil, by a conductive polymer, in which case a conductive coating can be dispensed with. All of these may jointly refer to as electrically conductive carrier.

[0270] The adhesive, as present in e.g. the adhesive tape of the invention, is not limited to particular chemistries, but the preferred system is preparation by in a two-step process (also described in further detail below), including: (i) the provision of a mixture, including UV syrup preparation and liquid electrolyte formulation with ionic liquids, followed by (ii) polymerization, including curing by UV web polymerization or UV polymerization directly on the electrically conductive carrier, e.g. on an electrically conductive coating on a primed backing.

[0271] According to further embodiments, the present invention also includes a device that additionally contains electrically conductive substrates or surfaces of interest where the adhesive is applied. The whole assembly is also a device in accordance with an embodiment of the present invention, and may be referred to as an adhesive device. In a preferred embodiment, this substrate / surface is smoother and / or more electrically conductive than the electrically conductive carrier, e.g. the electrically conducive coating present on the primed backing of the adhesive tape forming one aspect of the present invention. Further, the substrate / surface may have better corrosion resistance.

[0272] A device of the present invention may also exhibit an alternative constitution of a capacitor-like device. In this embodiment, the device comprises:

[0273] a) an electrically conducive carrier;

[0274] b) a first adhesive prepared directly on said electrically conductive carrier by polymerization or crosslinking;

[0275] c) a second adhesive coated directly on the first adhesive;

[0276] d) an electrically conductive substrate disposed on the side of the second adhesive; and e) means for applying an electromotive forces [e.g., DC voltages], preferably with different polarities;

[0277] wherein the adhesive device is designed to increase the bonding strength (bond) of the adhesive to the electrically conductive substrate when a first electric stimulus ES+is applied between the electrically conductive carrier and the substrate;

[0278] wherein the adhesive device is further designed to decrease the bonding strength (debond) of the adhesive tape from the electrically conductive substrate when a second electric stimulus ES~ of opposite polarity is applied.

[0279] Here, at least one, and preferably both, of the first and second adhesives are electro-responsive adhesives (A), as explained above. In addition, at least one, and preferably both, of the first and second adhesive are preferably ionically conductive and may in this case include an ionic liquid and / or a salt other than an ionic liquid.

[0280] The above embodiment realizes a double-layered adhesive tape device design. Where the first adhesive is an electro-responsive ionically conductive adhesive containing inorganic salt (LiTFSI) and zwitterionic species, the second adhesive may be different, e.g. comprising ionic liquid (for example of EMIM FSI type) but lacking zwitterionic species. This double-layer structure and voltage value and time all together may ensure that no debonding from the carrier side or the side where the first adhesive layer is present occurs, as the electro-responsive properties of the first and second adhesives differ. Here, also only one of the adhesives may be electro-responsive, in which case an ionic liquid, and optionally one or more salts that are no ionic liquid, is merely present in order to ensure ionic conductivity of the adhesive.

[0281] In certain embodiments, the first layerformed from an adhesive (A) comprises an acrylic adhesive matrix and an inorganic salt, e.g. LiTFSI and additionally, a zwitterionic compound, for example including one or more zwitterionic monomers, to provide for ionic conductivity. Alternatively, it may include an ammonium-based protic ionic liquid like ethylammonium nitrate (EAN) in the acrylic adhesive matrix. The second adhesive layer formed from an adhesive (A) differs, e.g. contains an acrylic adhesive matrix with an ionic liquid— such as EMIM FSI— as the ionic conductor. The electrically conductive carrier can be a metalized polymer film, such as Sn-coated PET. This second aspect provides a double-layered, single-sided adhesive tape according to the present invention. By applying an additional adhesive layer (either comprising a conventional adhesive or an electro-responsive adhesive) on the opposite side of the carrier, a double-sided tape can also be formed. If no carrier is used, a double-layered transfer tape is constructed instead.

[0282] Without wishing to be bound by theory, it is assumed that debonding occurs by reactive dissolution of the adhesive. This means that when the DC voltage is applied, the cation of the ionic liquid is expected to form an N-heterocyclic carbene or similar reactive species by abstracting a proton from the cations, specifically the cation of the ionic liquid containing a proton at the C2 position. This carbene species then modifies or reacts with the bonding side of the adhesive, facilitating debonding. A similar mechanism has been experimentally demonstrated for the solubilization of cellulose, proteins and polymers. It is also possible that debonding occurs by physical dissolution (no reaction) or similar processes. The latter is more likely if the C2 carbon of the cation of the ionic liquid does not have a proton. In this scenario, migration of the ionic liquid to the adhesive-adherend interface causes physical solubilization of the adhesive, resulting in debonding. Of course, both processes can occur during debonding along with another process as gas evaluation, most probably H2gas. The gas release makes the adhesive surface porous and aids in debonding. As per definition, debonding means adhesion failure from the substrate. This typically happens when negative DC voltage is applied to substates and positive to the carrier as already explained that cation accumulation or cathodic gas formation is the reason for debonding. But interestingly, in the positive side where anion goes, it even increases the adhesion between adhesive and the carrier. Therefore, once the polarity of the DC voltage changes, adhesion increases between the substrate and adhesive and resulting, debonding from the adhesive and carrier side. The present invention addresses the problem, assured that the debonding should always happen to the one side, from substrates side, meaning that reversal of the polarity does not initiate debonding from the carrier side. This allows us to achieve bonding and rebonding just by applying positive DC voltage to substrate and debonding just by applying negative DC voltage to substrate.

[0283] In one aspect of the present invention, to ensure that the debonding does not occur at the adhesive and carrier interface, an intrinsically electrically conductive hydrophobic polymer may be used either directly coated from aqueous or viscous ink of them or by in-situ polymerized from the monomer / their derivatives of them on the primed backing (carrier) with a higher thickness. The primer is basically a thin adhesive layer that may work as a bridge to the coating and carrier. Alternatively, nonmetallic conductive filler particles (carbon / similar kinds) may be coated on the primed backing (carrier). Finally, an ion-conductive adhesive is directly polymerized on the electrically conducive layer side of the carrier to ensure enough anchorage to the carrier. All these measures ensure that no debonding occurs when a negative DC voltage is applied to the carrier, enabling even increase of bonding strength to the positive side and finally, without losing the ability to debond from the substrate side once the polarity is reversed. As mentioned above, in such a tape design that represents one embodiment of the present invention, the carrier is preferably electrically conducive in order to provide a closed electric circuit transferring the electric stimulus to the adhesive.

[0284] The second aspect (another embodiment) of the present invention relates to a multilayer aspect with a different tape design, with or without backing (or with or without carrier). In this concept, two distinct adhesive layers are used, one referred to as adhesive layer (C), and the other as adhesive layer (D). In one embodiment, adhesive layer (D) enables debonding when an electric stimulus (for example, negative voltage, such as negative DC) is applied, while adhesive layer (C) supports bonding when a voltage of opposite polarity (e.g. positive voltage, such as positive DC) is applied. Adhesive layer (C) also helps prevent unintentional debonding. By simply controlling the polarity of the applied voltage, bonding, debonding, and rebonding can be affected as needed.

[0285] BACKING

[0286] A backing, constituting or forming part of a carrier, is not just a film to support the adhesive layer but rather an important part of the tape. This could be made from plastic, metal, textiles, and so on. A normal adhesive layer is thin, sticky, and, overall, not a free-standing, like material. A backing is therefore needed to provide support, dimensional stability, strength, flexibility, and ease of handling. It acts as the carrier for the adhesive layer, protects the adhesive before application, and determines the mechanical, thermal, and electrical properties of the tape. The backing can also influence the tape's resistance to moisture, heat, chemicals, and environmental exposure. Common backing films are polyethylene terephthalate (PET), polypropylene (PP), Polyethylene (PE), polyvinyl chloride (PVC), Polyimide (PI), cellulose acetate, Kraft paper, crepe paper, nonwoven fabric, aluminum foil, copper foil, polyester fabric, glass cloth, rayon fabric, foam (e.g., polyethylene foam, polyurethane foam), PTFE (polytetrafluoroethylene), silicone-coated paper or film, fluoropolymer films, polycarbonate (PC), nylon. Metal or metalized films are not suitable forthe current invention unless it has corrosion resistance. A backing can also be made of natural fabric (cotton, linen, wool, silk, hemp, or ramie) or synthetic fabric (acrylic or spandex) or from a composite fabric (poly-cotton, cotton-spandex, or wool-acrylic).

[0287] The backing is not limited to the materials mentioned above. Its purpose is to provide sufficient mechanical strength and to enable strong anchorage to the electrically conductive layer, or to both the primer and the electrically conductive layer, to form a suitable carrier.

[0288] In a preferred embodiment, backing films are polyethylene terephthalate) (PET) and poly(propylene) (PP) films with different thicknesses.

[0289] In one aspect, a metalized backing can be used as backing having a conductive coating e.g. aluminum-coated PET (AI-PET), copper-coated PET (Cu-PET), silver-coated PET (Ag-PET), nickel-coated PET (Ni-PET), tin-coated PET (Sn-PET). Of course, also other conductive materials can be used, such as ITO-coated PET (ITO-PET).

[0290] PRIMER LAYER

[0291] A priming / primer is a surface treatment or intermediary layer used to promote adhesion between a substrate or backing material to the adhesive. It functions as a compatibility bridge, increasing bonding strength and longevity.

[0292] The inventive adhesive tape includes multiple layers, such as a backing layer followed by an electrically conducive layer, forming a carrier. Due to the differing chemistries and surface polarities of these materials, the use of a primer is essential to achieve a stable, uniform coating of the electrically conducive layer and to ensure strong adhesion to the backing film. The reason for priming in this invention is to improve the anchorage of the electrically conductive layer to the backing film instead of the substrate and adhesive, as in typical applications.

[0293] Priming could be done by physical treatment like flame / corona / plasma to increase polar groups to the backing surface that can hold the electrically conducive coating better as well as increase compatibility to achieve uniform coating. This is beneficial when the electrically conducive material is applied from polar aqueous dispersion.

[0294] Another physical priming is chemical etching, which increases the roughness of the backing to make more surface area. This process induces a slightly opaque appearance due to the rough surface structure. This is sometimes beneficial if the compatibility of the primer and substrates is completely different. For example, coating a fluorinated chemical in solution due to its low surface energy seems to be very difficult; however, making the surface rough can solve the issue. Mechanical surface treatment (e.g. sandblasting or abrasion) can increase the roughness of the backing and enhance the anchorage of the electrical conductive layer to the backing.

[0295] The application of a thin adhesive layer or adhesion promoter onto the backing substrate is a chemical priming method, serving as a bridging layer between the backing and the electrically conductive coating. Typically, single or several thin layers of adhesive are coated on the backing and then UV or thermally cured. As the adhesive layer is sticky and has polar or unipolar groups that help to bind the electrically conductive layer to the backing. If the electrically conductive layer is coated with press, then even the layer is adsorbed, which further increases the anchorage. While the priming may be non-reactive, chemical priming can also be reactive, where the primer forms a bond through a chemical reaction with the backing surface. Reactive chemical priming includes using silanes, isocyanates, epoxies, or anhydrides that bond covalently with hydroxyl, amine, or other reactive groups on the backing surface. The backing surface is first pretreated (e.g. by plasma, corona, UV, acid, or base) to introduce reactive groups like -OH or -NH2, then a reactive primer is applied to form covalent bonds with those groups.

[0296] Sometimes different inorganic coatings also act as primers. For example, TCO coating on PET film also increases the binding of the electrically conductive layer, as well as giving it better electrical conductivity.

[0297] The preferred priming for the invention is both physical and chemical priming [reactive and nonreactive]. Chemical priming includes creating a very thin adhesive layer on the backing film and then UV curing or crosslinking. The adhesive could be from any chemistry, such as acrylic, synthetic rubber, or PU-based, until several criteria are fulfilled, such as it should be weatherresistant (e.g., not weaken in a high relative humidity environment), allow the electrically conductive material to be coated uniformly, sufficiently optically clear and finally, strong anchorage to the backing. Examples include acrylic adhesive from EDGA, DMAA, BA, MA, Benzyl acrylate, AA monomer, irgacure photo initiators 184 / 651, and crosslinkers like PEGDA, glycerol triacrylate, and crosslinkers with epoxy groups. Another preferred primed carrier is transparent conductive coating (TCO), e.g. ITO / FTO-coated film, as it shows faster response time during bonding, deboning or rebonding due to higher electrical conductivity of the transparent oxides. Also, it suffers a bit weaker anchorage with the electrically conductive layer than the adhesive-coated backing.

[0298] In a further embodiment, the present invention uses priming / primer to the backing to increase anchorage strength with adhesive and carrier It can also be used without priming if the anchorage of the electrically conductive layer is enough to do the (re) bonding and debonding operation to the adhesive device. Priming is optional, and priming types do not limit the scope of the present invention.

[0299] ELECTRICALLY CONDUCTIVE LAYER

[0300] An electrically conductive layer is a material layer capable of conducting electricity. It is typically used in devices or systems where electrical current needs to flow across or through a surface. In adhesive tapes or multilayer materials, this layer may play a crucial role in enabling electrical interaction, such as sensing, heating, or electrically controlled debonding.

[0301] Not all materials may be suitable for that, and high electrical conductivity may be an important requirement. Some examples are metal foils: stainless steel or aluminum, or copper foil. Conductive polymers: PEDOT: PSS and PEDOT: Tos are popular due to their flexibility, processability, and stability. They can be coated or polymerized on PET backing films. Carbonbased materials: polymer binder-dispersed carbon black, graphite, graphene, and carbon nanotubes can be coated on prepared film. These materials conduct well, are stable, and affordable. Fine silver, copper, or nickel particles can be employed in conductive coatings. They must be safeguarded against corrosion, especially in humid or long-term voltage systems. Some systems use conductive woven or nonwoven fabrics coated or implanted with conductive fillers as the mechanical backing and conducting layer. Inks and pastes with conductive particles in a polymer matrix can be printed as thin films on various substrates.

[0302] Preferred materials used in the current invention are intrinsically conductive polymers such as poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT: PSS), poly(3,4-ethylenedioxythiophene):p-toluenesulfonate (PEDOT: Tos), poly(3,4-propylenedioxythiophene) (ProDOT), poly(dioxythiophenes), poly(3,4-dialkylthiophenes), polyaniline (PANI), polypyrrole (PPy), poly(2,5-thienylenevinylene), polythiophene, polythiophene derivatives, metallo-supramolecular polymers, polyacetylene, poly(p-phenylene vinylene), polyfluorene, polycarbazole, and polybithiophene. As well as PEDOT, PANI, ProDOT and their derivatives e.g. obtained from modified monomer structures including alkyl-substituted EDOT, EDOT-OH, Br-EDOT, EDOT-NH₂, EDOT-COOH. As the PEDOT is a composite material and needs counter anion which is not limited but could be PSS⁻ (poly(styrenesulfonate)), Tos" (p-toluenesulfonate), CI04“ (perchlorate), BF4“ (tetrafluoroborate), PF6“ (hexafluorophosphate), OTf" (triflate), DBSA" (dodecylbenzenesulfonate), CSA" (camphorsulfonate), NO3“ (nitrate), SO42-(sulfate), HS04“ (hydrogen sulfate), TFSI" (bis(trifluoromethanesulfonyl)imide), Cl" (chloride), Br“ (bromide), I" (iodide), F" (fluoride), CF3SO3“ (trifluoromethanesulfonate), CH3SO3“ (methanesulfonate), acetate (CH3COO“), citrate, phosphate, they should have sufficient electrical conductivity.

[0303] The electrically conductive layer may be prepared on the primed backing film. The preferred materials are intrinsically conductive polymers. There are many ways to prepare the intrinsically conductive electrically conducive coating on the backing film. One is directly coating the materials (PEDOT: PSS) from aqueous or solvent dispersion, and another is coating the monomers (EDOT) and in situ polymerizing them on the backing. Also, gas-phase or UV polymerization is possible. The present invention is not limited to a particular method. Preferred is directly coating the ink or aqueous dispersion on the primer side of the backing, as it is easy and does not need any rinsing steps like the in-situ polymerization.

[0304] Another preferred material is carbon-based coating, including graphene, carbon nanotubes (CNTs), reduced graphene oxide (rGO), pyrolytic carbon, carbon paint, carbon nanofibers, graphite, amorphous carbon, carbon black, conductive carbon ink, fullerene-based coatings, carbon-loaded polymers coatings and carbon fiber coatings. These materials are often applied as thin films on primed backing layers to provide electrical conductivity in the carrier. Carbon-coated surfaces can be polished to smooth them to enhance electrical conductivity.

[0305] In the second aspect of the present invention, the backing may also be a metalized PET film beyond conducive polymers, such as aluminum-coated PET (AI-PET), copper-coated PET (Cu-PET), silver-coated PET (Ag-PET), nickel-coated PET (Ni-PET), tin-coated PET (Sn-PET) and ITO-coated PET (ITO-PET).

[0306] ADHEREND OR SUBSTRATE

[0307] The adherend or substrate is the target substrate of the device that shall come in contact with the adhesive. Together with the adherend, the device of the present invention can form a capacitor-like adhesive device. Not every adherend may be suitable for that. High electrical conductivity facilitates the formation of such a device. Some examples of adherends include copper plate / foil, stainless steel plate, aluminum plate / foil, gold-coated surfaces, silver-coated substrates, nickel plating, titanium, ITO-coated glass, carbon-coated films, graphene films, metal-coated plastics (metalized film Sn-PET or AI-PET), chromium-coated substrates, zinc-plated surfaces, tin-plated surfaces, silicon wafers with conductive coatings, and conductive carbon fiber composite substrates. From the examples, it is also clear that non-conductive adherents can also be used; in this case it is generally preferred that they are coated with an electrically conductive coating, e.g. one having a higher conductivity than the underlying surface, and preferably and smooth surface.

[0308] Preferred adherends of the present invention are those that have smooth surfaces with better oxidation resistance and are electrically conductive. Examples include stainless steel plates or silver-coated plastic substrates.

[0309] ADHESIVE TAPE DESIGN

[0310] The following further illustrates possible configurations of the adhesive tape of the present invention. However, they are in no way a limitation of the teachings or disclosure of the present invention as set forth herein.

[0311] According to preferred embodiments, the adhesive tape of the present invention is a pressuresensitive adhesive tape. As described above, the adhesive tape of the present invention comprises different structures.

[0312] FIG. 1 depicts an embodiment of the device of the present invention in the form of a singlelayered, single-sided adhesive tape according to the first aspect of the present invention. The adhesive tape comprises an electrically conductive layer (EC) on a primer (P), backing film (F), forming the carrier (T) and on the electrically conductive layer side of the carrier (T), an adhesive layer formed by the adhesive (A), i.e. the layer (D). Another adhesive 2S may be provided on the other side of the carrier, as illustrated in FIG. 2. The adhesive 2S may be a conventional doublesided transfer tape, i.e. an adhesive whose adhesive strength cannot be modified by applying an electric stimulus.

[0313] FIG. 3 illustrates a single-layered, double-sided adhesive tape according to the first aspect of the present invention. The tape comprises, or consists of, a carrier (T) formed by a backing film (F) that is primed (P) on both sides, followed by an electrically conductive coating (EC) applied to each primed surface. Adhesive layers (D) formed from the adhesive (A) are formed on both conductive sides of the carrier (T). FIG. 4 shows a double-layered transfer tape according to the second aspect of the present invention consisting of one layer (D) of an adhesive (A), e.g. one containing an ionic liquid (such as EMIM FSI) as an ionic conductor, and another layer C of adhesive containing either a lithium salt (e.g., LiTFSI) or an ammonium-based ionic liquid (e.g. EAN) as well as zwitterionic compound. The tape has no carrier (T). The adhesive in layer (C) is based on an acrylic copolymer or terpolymer (with zwitterionic monomer) combined with Li salts or ammonium-based ionic liquids (EAN), which are different from the ion conductor used in layer D of adhesive.

[0314] FIG. 5 illustrates a double-layered, single-sided adhesive tape according to the second aspect of the present invention. The tape preferably consists of an electrically conductive carrier (T) and two ion conductive adhesive layers: first (C) of adhesive on the conductive side and then adhesive (D) on the (C) of adhesive side.

[0315] FIG. 6 illustrates a double-layered, double-sided adhesive tape according to the second aspect of the present invention. The tape preferably consists of an electrically conductive carrier T and two ion conductive adhesive layers: first (C) of adhesive on the conductive side and then adhesive (D) on the © of adhesive side and on the other side of the carrier a double-sided tape (2S) (e.g. tesa tape).

[0316] From the FIGs, it is also evident that the electrically conductive carrier T should slightly extend beyond the adhered surfaces (e.g. conductive substrates) and adhesive layers (C and D) to allow space for voltage connection. However, in the case of a transfer tape (FIG. 4) where the adhesive is placed between two conductive substrates or plates, the opposite side of the plate provides enough access for voltage connection, so such protrusion is not necessary. The protrusion should not lead to any short circuiting, meaning the conductive surfaces on both sides of the ion conductive adhesive must not come into direct contact with each other.

[0317] PREPARATION OF DEVICE AND METHOD FOR MODIFYING THE ADHESION STRENGTH

[0318] When the device of the present invention in any form is disposed on an electrically conductive substrate, another embodiment of an adhesive device of the present invention is constructed (FIG. s 7-15).

[0319] FIG. 7 shows an adhesive device, according to an embodiment of the invention, constructed by a single-layered, single-sided tape (FIG. 1) disposed on an electrically conductive substrate (S). In this setup, connecting the negative terminal of DC voltage source to the conductive carrier (T) and the positive terminal of DC voltage source to the substrate (S) and applying a DC voltage for example 5 to 50 V for 30 s to 5 min, increases the adhesion strength between the adhesive layer (D, comprising the adhesive (A)) and the conductive substrate (S), thereby achieving bonding of the adhesive tape (D) to the conductive substrate S (FIG. 8). However, if the connection is reversed, e.g. the negative terminal of the DC voltage source is connected to the substrate (S) and the positive terminal is connected to the carrier (T), and a DC voltage, preferably in the range of 10 to 50 V, for 30 s to 5 min, is applied, the adhesion strength of (D) of adhesive with respected to electrically conductive (S) substrate decreases, thereby facilitating debonding of the adhesive tape from the substrate (S) (FIG. 9).

[0320] In another preferred embodiment based on the second aspect of the present invention, a doubled layered transfer tape containing adhesive layers (C) and (D)— shown in FIG. 4— can be used to bond two electrically conductive substrates (S and S), as illustrated in FIG. 10. In this setup, by applying a DC voltage and controlling the polarity, the adhesion strength between the tape and both substrates (S and S) can be increased or decreased. For example, when a positive DC voltage is applied to substrate (S) adjacent to adhesive (D) and a negative voltage to substrate (S) adjacent to adhesive (C) (FIG. 11), the adhesion between adhesive (D) and substrate (S) adjacent to adhesive (D) and adhesive (C) and substrate (S) adjacent to adhesive (C) increases, resulting in strong bonding. Now, if the polarity of the DC voltage is reversed, applying a negative DC voltage to substrate (S) adjacent to adhesive (D) and a positive voltage to (S) adjacent to adhesive (C) (FIG. 12), the adhesion between adhesive (D) and substrate (S) adjacent to adhesive (D) decreases, thereby debonding from side (S) adjacent to adhesive (D). Meanwhile, the adhesion between adhesive (C) and substrate (S) adjacent to adhesive (C) remains its bonding strength. The preferred DC voltage range is between 5 and 50 V for 30 seconds to 5 minutes.

[0321] In another preferred embodiment following the second aspect of the present invention, a double-layered, single-sided tape structure (FIG. 5) with adhesive layers (C) and (D) on an electrically conductive carrier (T) can be assembled on a conductive substrate (S), as illustrated in FIG. 13. In this setup, by applying a DC voltage and controlling the polarity, the adhesion strength between the tape and substrate (S) can be increased or decreased. For example, when a positive DC voltage is applied to substrate (S) and a negative voltage to carrier (T) (FIG. 14), the adhesion between adhesive D and substrate (S), and adhesive (C) and carrier (T) increases, resulting in strong bonding. If the polarity of the DC voltage is reversed, applying a negative DC voltage to substrate (S) and positive to carrier (T), the adhesion between adhesive (D) and substrate S decreases, enabling debonding from the side of substrate (S) (FIG. 15). Meanwhile, the adhesion between adhesive (C) and electrically conductive carrier (T) remains its bonding strength, e.g. it does not change so much. The preferred DC voltage range is between 5 and 20 V for 30 seconds to 5 minutes. The adhesive tape in the described adhesive device can be reused multiple times for bonding, debonding, and rebonding. For instance, after debonding, the same tape can be reapplied to the substrate and bonded again by applying electrical stimulus (e.g. DC voltage). Debonding can then be triggered by reversing the polarity of the applied DC voltage. The tape remains functional for repeated use by simply laminating it onto an electrically conductive substrate and applying DC voltage. This cycle can be repeated without a significant loss in adhesive strength compared to the initial bonding.

[0322] Methods, SYSTEM and Uses

[0323] As derivable from the above, the device of the present invention can be used in a method of modifying the adhesive strength of the device, the method comprising the application of one or more electric stimuli for increasing and / or decreasing the adhesive strength of the adhesive. Here, the one or more electric stimuli may be a DC (Direct Current), AC (Alternating Current), VDC (Volts Direct Current), VAC (Volts Alternating Current), Pulsed DC (Pulsed Direct Current), Pulsed AC (Pulsed Alternating Current), and may preferably have a DC voltage of 1 to 50 V and / or a duration of 1 second to 30 minutes. Preferably, the DC voltage or current can be supply from a battery, a DC bench power supply, a potentiostat / galvanostat, an AC-to-DC adapter, a DC-DC converter, a USB power source or power bank, or a solar panel with a regulator. The method may involve one or more cycles of debonding-rebonding, such as 2 or more cycles, 3 or more cycles, or 4 or more cycles, e.g. 5 or more cycles. There is no particular upper limit, but in practice 10 or less of such cycles may be needed.

[0324] The present invention also relates to an adhesive system capable of modifying the adhesive strength of an adhesive, preferably a pressure-sensitive adhesive, by applying one or more electric stimuli, the adhesive system comprising a device as described above; and a controller that is configured to apply an electric stimulus to the device. The controller can control a DC power supply, RFID systems, printed batteries, capacitors, energy-harvesting circuits, and / or may also operate remotely via wireless interfaces such as Bluetooth, WiFi, or NFC.

[0325] In the adhesive system, the one or more electric stimuli may be applied using a controller that is operated by a user (i.e., manual operation) or are applied using a controller according to a predefined program (automatic operation). In one embodiment, the user or the pre-defined program provides electric stimuli of increasing voltage and / or duration over several cycles, for example to thereby compensate for a possible loss in the magnitude of the change of adhesion strength over several cycles. The automatic operation may also involve further variables or conditions, e.g. the fulfilment of pre-defined criteria. Such criteria may e.g. involve conditions that are acquired by a sensor, such as temperature or humidity, or may include a security of ID check in order to avoid unauthorized usage. The security or ID check may involve identification of an individual by software means, or a password check.

[0326] In further embodiments, the present invention also relates to use of device, e.g. in the form of the above-described adhesive tape, for bonding, debonding, and rebonding application in: (i) joining different conductive surfaces or substrates; (ii) robotics, preferably in the manufacturing of robotic gripping arm; (iii) haptic devices; (iv) debonding applications; (v) sealing applications; (vi) applications where high bonding strength or debonding is needed without application of heat, light or pressure; (vii) sensing applications; (viii) consumer electronics; (ix) electronic packaging; (x) semi-structural type bonding applications; (xi) microelectronics; (xii) battery mounting for EVs or cell phones with reusable functions; (xiii) cell phone back cover mounting, (xiv) biomedical applications; (xv) recycling applications (e.g., disassembly and reassembly of products); (xvi) microfabrication (e.g., transfer and positioning of small components); (xvii) environmental and structural adaptability (adaptability to surface conditions or structural changes); (xviii) application in smart wearable electronics (e.g., health monitoring); and (xix) optoelectronics (e.g., bonding camera modules). This device is also intended to enable repair of structures, recyclability of articles for a reduced carbon dioxide footprint and automatization of processes; (xx) printing plate mounting on printing sleeves in flexoprint processes; (xxi) pick and place; (xxii) bin picking; (xxiii) assembly; (xxiv) machine tending; (xxv) tool changing; (xxvi) inspection and quality control; (xxvii) collaborative robotics; (xxviii) stain free handling; (xxix) micro-assembly; (xxx) optical component placement; (xxxi) temporary fixturing during machining; (xxxii) adaptive handling of soft or fragile items; (xxxiii) reversible gripping for testing stations; (xxxiv) non-mechanical holding in sterile environments; and (xxxv) gentle release systems for automated packaging.

[0327] EXAMPLES

[0328] The present invention is illustrated below by a number of examples. The examples described below illustrate particularly advantageous versions of the present invention, without wishing thereby to subject the present invention to any unnecessary limitation.

[0329] RAW MATERIALS

[0330] (a) Backing films:

[0331] PET film of different thicknesses

[0332] Etched film

[0333] Fabric (cloth) PP film

[0334] Sn-PETor AI-PET

[0335] (b) Electrically conductive coating materials:

[0336] PEDOT: PSS aqueous dispersion from Ossila

[0337] PEDOT: PSS ink from Sigma Aldrich

[0338] PEDOT: PSS nano particles aqueous dispersion from Sigma Aldrich

[0339] EDOT monomer with different derivatives from TCI

[0340] Aqueous carbon ink / paint (Liquiwire™) from Manchester Nanomaterials Ltd

[0341] (c) Acrylate monomers:

[0342] 2-(2-Ethoxyethoxy)ethyl acrylate (EEEA or EDGA)

[0343] N, N-Dimethylacrylamide (DMAA)

[0344] Butyl acrylate (BA)

[0345] Benzyl acrylate

[0346] Methyl acrylate (MA)

[0347] Acrylic acid (AA)

[0348] 2-(Methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate) (MPC) from TCI 3-[[2-(Methacryloyloxy)ethyl]dimethylammonio]propionate (CBMA) from TCI

[0349] (d) Initiators:

[0350] 2,2-Dimethoxy-2-phenylacetophenone (Irgacure 651) from Sigma-Aldrich

[0351] 1-Hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184) from Sigma-Aldrich

[0352] Vazo 67 and Perkadox 16

[0353] (e) Ionic liquids

[0354] 1-Ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM FSI) from Proionic

[0355] 1-Butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide (BMPip TFSI) from Iolitec 1,3-Dimethylimidazolium bis(trifluoromethylsulfonyl)imide (DiMIM TFSI) from Iolitec Triethylsulfonium bis(trifluoromethylsulfonyl)imide (S222 TFSI) from Iolitec

[0356] 1-Methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Pyr13 FSI) from TCI 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI) from Proionic

[0357] 1-Ethyl-3-methylimidazolium hexafluorophosphate (EMIM PF₆) from Sigma-Aldrich 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM PF₆) from Sigma-Aldrich 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI) from Iolitec 1-Butyl-3-methylimidazoliumtetrafluoroborat (BMIM BF₄) from Sigma-Aldrich

[0358] (f) Ionically conducting salts: Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) from Sigma-Aldrich Lithium Sodium chloride from Sigma-Aldrich

[0359] Lithium triflate (LiOTf), lithium triflouromethanesulfonate) from Sigma-Aldrich Lithium tetrafluoroborate (LiBF4) from Sigma-Aldrich

[0360] (g) Electrically conductive substrate / adherend:

[0361] ASTM steel plate

[0362] (h) Other materials):

[0363] Water as plasticizer

[0364] Crosslinkers: Erisys 240, polyethylene glycol) diacrylate (PEGDA)

[0365] Oxidant: Iron(III) p-toluenesulfonate hexahydrate from Sigma Aldrich

[0366] Butanol from Sigma Aldrich

[0367] Different types of PEGs (PEG 200, PEG 400 and similar kinds)

[0368] Different types of carbonates as ethylene carbonate (EC), vinylene carbonate (VC)

[0369] EXPERIMENTAL EXAMPLE 1:

[0370] Example 1 demonstrates the preparation of a single-layered, single-sided adhesive tape (FIG. 1) as well as using this tape to construct an adhesive device (FIG. 7) according to the first aspect of the present invention, following sequences:

[0371] i. Primer preparation and coating on the backing film

[0372] ii. Electrically conductive materials coating on the primed backing

[0373] iii. Ion-conducive adhesive coating on the electrically conductive side of the carrier iv. Ion-conducive adhesive tape lamination to the electrically conductive surface or substrate to construct the adhesive device of the present invention.

[0374] (i) Primer preparation and coating on the backing film: a mixture with a ratio of 45:55 wt % of EDGA: DMAA acrylic monomers was prepared in a glass reactor. 0.0063 wt % of Irgacure 651 photoinitiator was added to the mixture. The mixture was degassed under stirring with purging N2for 30 min and then irradiated by UV light at a wavelength of 365 nm with an intensity of 0.5 mW / cm2. The mixture was kept under constant stirring, and polymerization continued. The UV lamp was turned off when the reaction temperature in the glass reactor increased to ΔT = 26 °C. The resulting UV syrup was allowed to cool down and kept away from light. In the UV syrup, 0.15 % Irgacure 184 was added to prepare the primer formulation. In the next step, the primer was coated on PET and PP backing of different thicknesses and cured by UV light at 4000 to 5000 mW·s / cm2. The thickness of the primer is controlled in the range of 1 to 10 microns. Another variant of a primer was prepared from a solvent-borne acrylic adhesive, described in DE102023108348 Al, in example 3, consisting of butyl acrylate, methyl acrylate, benzyl acrylate, and acrylic acid monomers. The primer formulation contained 30 wt % (solid content) of the adhesive and epoxy-functionalized crosslinker (Erisys GA 240) of 0.075 wt % in ethyl acetate with respect to the solid content of the adhesive. The primer solution was coated on PET backing with a doctor blade and dried at 120 °C for 15 min and then 50 °C for 5 days. On top of this primer, another primer was coated, e.g. UV syrup-based, as explained above. This double-layered coating improves the weathering resistance as well as enables stable coating of the electrically conductive ink materials.

[0375] (ii) Electrically conductive coating preparation on the primed backing: In two different ways the coating was prepared as:

[0376] (1st) using PEDOT: PSS ink or aqueous dispersion or carbon ink, and

[0377] (2nd) in-situ EDOT polymerization using iron(III) p-toluenesulfonate hexahydrate in butanol.

[0378] For the 1stway, commercially available PEDOT: PSS or carbon ink was directly applied on the already prepared primed PET or PP or etched PET film as backing from the step (i), then covered by a siliconized liner (RF02) and passed through two rubber rollers with no gap between them. This process allows the formation of a very thin layer (less than 1 micron) of ink on the primer side of the carrier. Also, a strong anchorage is achieved due to the adsorption of the ink to the primer surface. After that, the whole setup was dried at 90 °C for 5 to 10 min, then another drying step for 10 min after removal of the siliconized liner (RF02). For the PEDOT: PSS or carbon ink aqueous dispersion, the coating was done using a doctor blade coater directly on the primed PET carrier from step (i) and then drying at 90 °C for 10 min.

[0379] For the 2ndway, the EDOT solution was prepared in butanol with iron(III) p-toluenesulfonate hexahydrate in a mole ratio of 1:2.3. The solution was coated by doctor blade on the PET or PP of different thickness and dried afterwards for 5 to 10 min at 80°C. This results in a bluish PEDOT: Tos film due to the EDOT polymerization. After that, the film was rinsed with water to remove the unreacted EDOT monomers and excess oxidant. The obtained PEDOT: Tos coated carrier was air dried afterwards. The carrier prepared is named as [PEDOT: PSS or PEDOT: Tos-primer-PET], which means the carrier consists of either a PEDOT: PSS or PEDOT: Tos layer on top, then a primer layer in the middle, and then the bottom PET film as backing.

[0380] Finally, the obtained electrically conductive layers look blue when PEDOT:PSS or Tos coated and have a surface resistance of between 15 and 4000 Ω / sq. The carbon ink coated film looks black with surface resistances between 50 and 1000 Ω / sq. (iii) Ion-conductive adhesive coating on the electrically conductive carrier: several adhesive compositions of the invention were produced with the successive steps of a) prepolymer preparation, i.e., UV syrup preparation; b) formulation of the liquid electrolyte, i.e., dissolving ionic liquid, photoinitiator, and / or other monomers or additives (plasticizer) and crosslinkers into the UV syrup; and c) coating and curing of the liquid electrolyte between the conducive side of the carrier e.g. (PEDOT: PSS or PEDOT: Tos-primer-PET) or (carbon-primer-PET) and a siliconized PET liner (RF02). The curing process is related to UV polymerization. See the details below for steps a) to c).

[0381] Step a)

[0382] A mixture with a ratio wt % of 60:40 EDGA: DMAA acrylic monomer was prepared in a glass reactor. 0.0063 wt % Irgacure 651 photoinitiator was added to the mixture. The mixture was degassed under stirring with purging N2for 30 min and then irradiated by UV light at a wavelength of 365 nm with an intensity of 0.5 mW / cm2. The mixture was kept under constant stirring and polymerization continued. The UV lamp was turned off when the reaction temperature in the glass reactor increased to ΔT = 26 °C. The resulting UV syrup was allowed to cool down and kept away from light. The syrups obtained had a viscosity in the range of 3500 cP to 6500 cP with a refractive index of 1.44 to 1.45.

[0383] The UV syrup from step a) was blended with other components as listed in Table 1. To prepare adhesive D, which follows the first aspect of the present invention, the formulation includes: 80-90 wt % UV syrup from step a), 5-15 wt % of an ionic liquid selected from EMIM FSI, BMIM TFSI, EMIM TFSI, EMIM BF4, BMIM BF4, S222 TFSI, or BMPip TFSI, 0.055-0.15 wt % of Irgacure 184 as the photoinitiator, 0.5-5 wt % of a plasticizer selected from such as PEG 200 or water, or a carbonate-based solvent, and 0.5-2 wt % of a crosslinker.

[0384] For the second aspect of the present invention, adhesive (C) is prepared using 80-90 wt % UV syrup from step a), 1-10 wt % of more or more salts selected from LiTFSI or LiOTf or LiBF4, or LiPF6or ethylammonium nitrate (EAN), 0.055-0.15 wt % Irgacure 184 photoinitiator, and up to 10 wt % of additional monomers, such as zwitterionic monomers like CMBA or MPC alone or together. The mixture was then continuously rolled on a rolling bench until all components were dissolved. The mixtures are referred to as liquid electrolytes when all components are dissolved.

[0385] The liquid electrolytes from step b) were coated with a layer thickness of about 50 to 150 μm between two films, e.g. (PEDOT: PSS or PEDOT: Tos-primer-PET) or (carbon-primer-PET) carrier and a siliconized PET liner, then UV cured. The coating was done in a way that some parts of the electrically conductive layer were kept uncoated to make electrical connection with the external DC power supply needed for debonding / rebonding operations. Upon removal of the siliconized PET liner, a single-layered, single-sided adhesive tape (comprising carrier T) is provided. Curing was then achieved with irradiation from fluorescent lamps (ACTINIC) with wavelength of 350 to 400 nm (UV-A) at an intensity of 14 mW / cm2at the residence time in the irradiation tunnel being 200 to 360 seconds. This corresponds to a UV dose from 2800 to about 5000 mW.s / cm2.

[0386] An adhesive tape based on the second aspect of the present invention was also prepared, as illustrated in FIG. 4. This double-layered transfer tape consists of two distinct adhesive compositions (C and D), and is produced through the following steps. First, adhesive layer (C) is coated and cured between two siliconized release liners. After curing, one of the liners is removed, and adhesive composition (D) is coated on top of layer (C) and then UV-cured. The adhesive layer (D) already contains a release liner. Both liners are peeled off, and the tape is applied in the configuration of FIG. 10 to bond two electrically conductive substrates.

[0387] A double-layered, single-sided adhesive tape was also prepared. In this version, adhesive (C) was coated onto a Sn-PET carrier, followed by coating and curing of (D) of adhesive layer on top of (C) of adhesive layer. Although this results in a single-sided tape, it can be easily converted into a double-sided tape by applying a standard double-sided adhesive tape to the PET side of the Sn-PET carrier (e.g. FIG. 6).

[0388] If the adhesive tape was left to dwell for several days in a lab environment, interfacial contact is improved between the adhesive and the electrically conductive layer, as well as the adhesive absorbing some moisture from the air, which results in faster bonding / debonding operations. Single-sided tape samples with ITO-primed carrier also show faster response due to the higher electrical conductivity of the transparent conductive oxides (TCOs). For the (C) adhesive, it is preferable to limit the moisture content as otherwise the risk of anchorage failure due to the electrolysis of water during voltage application may increase.

[0389] (iv) Ion-conducive adhesive tape lamination to the conductive surface or substrate to construct an adhesive device according to an embodiment of the present invention (e.g. FIG.s 7, 10 and 13).

[0390] The device in the form of an adhesive tape as prepared in sequence (iii) was laminated to an electrically conductive substrate, such as a steel plate. Lamination was carried out in a manner that enables connection of the DC voltage source to the device, specifically to the electrically conductive layer and the conductive carrier. The following Table 1 shows the different adhesive tape compositions like C and D of the present invention. Table 1: Examples of adhesive tape compositions used to demonstrate the (re) bonding and debonding functions of the present

[0391] invention.

[0392]

[0393]

[0394]

[0395]

[0396] Example 15 [second aspect of the present invention] is prepared by first applying adhesive C onto the Sn side of the Sn-PET carrier, followed by coating adhesive D on top of the C layer, forming a double-layered, single-sided adhesive tape.

[0397] TEST METHODS

[0398] Unless otherwise indicated, all measurements were conducted at 23 °C and 50 % relative humidity. Unless indicated otherwise, moreover, the measurements of the adhesive tape were carried out with an adhesive layer with a thickness of 50 μm to 150 μm.

[0399] Test A: Peel Adhesion

[0400] A single-layered, single-sided adhesive tape (according to first aspect, FIG. 1) was cut with a width of 20 mm and a length of 150 mm. The adhesive tape was applied onto a cleaned ASTM steel plate (cleaned with acetone after removing the protective film) by gentle hand pressure using a lamination squeegee, after peeling off the siliconized PET liner [FIG. 7], The other side of the adhesive tape already has carrier based on PEDOT: PSS or PEDOT: Tos, or carbon ink coated on a PP or PET or etched PET film. Then the whole setup was pressed by rolling back and forth over five times using a 4 kg roller.

[0401] The setup was then vertically hooked to the bottom holder of a tensile testing instrument (ZwickRoell Z020), and the carrier (e.g. PEDOT: PSS-primer-PET or carbon-primer-PET) was attached to the upper holder of the instrument.

[0402] For peel adhesion measurement, the PEDOT: PSS-primer-PET or carbon-primer-PET carrier was pulled off at an angle of 180° with a velocity of 300 mm / min. The maximum force was recorded in N / cm for a complete peel of the adhesive tape from the ASTM steel substrate. The values reported here are the average of three individual measurements.

[0403] Test B: Ionic Conductivity

[0404] The ionic conductivity, more specifically DC conductivity was measured by EIS (Electrochemical Impedance Spectroscopy) from the log-log plot of real part of the AC conductivity over an angular frequency by extrapolating the plateau region to the zero-frequency using the Dyre fit function (e.g. empirical model for frequency-dependent conductivity in disordered systems). Measurements were done by a BioLogic VMP-300 in the mode of PEIS (potentio EIS) with a constant voltage amplitude of 10 mV and a frequency range from 7 MHz to 1 Hz. A transfer tape (no carrier) of circular dimension with a diameter of 18 mm was applied between two circular steel plate electrodes. The tape thickness was 50 pm to 150 pm. Test C: Surface Resistance

[0405] Surface resistance was measured using a NAGY SD-510 Sheet Resistivity Meter from INNOVENT e. V. Technologieentwicklung Jena. The materials tested included PEDOT: PSS, PEDOT: Tos, carbon ink, and a tin (Sn) layer coated on a primed PET or only on a PET backing.

[0406] EXPERIMENTAL EXAMPLE 2 -

[0407]

[0408] A single-layered, single-sided adhesive tape [according to first aspect of the invention, FIG. 1] of 100 mm in length and 20 mm in width was laminated to an ASTM steel plate (also referred to as substrate S above, FIG. 7) by removing the siliconized PET release liner. The other side of the adhesive tape already has carrier e.g., PEDOT: PSS-primer-PET or carbon-primer-PET. The entire setup was then pressed by rolling it over five times back and forth using a 4 kg roller. Various experiments were carried out at different voltages, polarities, and time durations to investigate the electrically adjustable bonding, debonding, and rebonding behavior of the adhesive tape in the adhesive device of the present invention, as summarized in Table 2 below.

[0409] For the debonding experiment, the carrier (e.g. PEDOT: PSS-primer-PET or carbon-primer-PET) of the adhesive (acting as the anode) was connected to the positive terminal of the DC voltage source, while the ASTM steel plate (acting as the cathode) was connected to the negative terminal of a DC voltage source [DC power supply: Kiprim DC605S], After that, a DC voltage in the range of 5 to 50 V was applied for 30 s to 5 min. Then, peel adhesion was measured following Test A, but with the DC voltage source cables disconnected from both the substrate and the carrier. The bonding strength decrease of the adhesive tape with respect to the ASTM steel plate was confirmed by a decrease in peel adhesion values from its initial condition (without voltage application). For each sample, an additional peel test was performed separately to determine the initial peel strength value, denoted as [Initial bonding (no voltage)] in Table 2.

[0410] For the (re) bonding experiment, the same sample was laminated to the ASTM steel plate with hand lamination pressure and dwell for (30 s to 2 min). In this state, the peel adhesion value of the tape is basically significantly lower than the initial bonded state (without voltage application). Then the carrier (e.g. PEDOT: PSS-primer-PET or carbon-primer-PET) of the adhesive (acting as the cathode) was connected to the negative terminal of the DC voltage source (e.g. DC power supply: Kiprim DC605S), while the ASTM steel plate (acting as the anode) was connected to the positive terminal of the DC voltage source. After that, a DC voltage in the range of 5 to 50 V for 30 s to 5 min was applied. Then, peel adhesion was measured following Test A, but with the DC voltage source cables disconnected from both the substrate and the carrier. The bonding strength increase of the adhesive tape with respect to the ASTM steel plate was confirmed by an increase in peel adhesion value from its debonded condition. Peel adhesion testing at the bonded state of the adhesive tape can cause mixed failure— where adhesive remains both on the ASTM steel plate and on the carrier— or may lead to carrier deformation, like coiling, especially with thicker backings. This sometimes makes it difficult to perform rebonding tests on the same sample. Thus, the tape should not be fully peeled in the bonded state. Instead, only a small portion of the tape can be gently pulled to check the bonding. Full peeling should be done in the debonding state.

[0411] Table 2: Results.

[0412]

[0413]

Claims

CLAIMS1. A device comprising an adhesive (A) whose adhesive strength can be modified by respective electric stimuli from an initial state to a first bonded state, from a first bonded state to a first debonded state, and from a first debonded state to a first rebonded state,wherein the device hasan initial adhesive strength ASj,a first bonded adhesive strength ASbi,a first debonded adhesive strength ASd1, anda first rebonded adhesive strength ASri;and which satisfies the following conditions:whereinASj represents the adhesive strength prior to application of an electric stimulus,ASb1represents the adhesive strength after a first electric stimulus for increasing bonding strength (ES+1) has been applied,ASdi represents the adhesive strength after a first electric stimulus for decreasing bonding strength (ES’l) has been applied, andASr1represents the adhesive strength after a second electric stimulus for increasing bonding strength (ES+2) has been applied.

2. A device comprising an adhesive (A) whose adhesive strength can be modified by respective electric stimuli from a first bonded state to a first debonded state, and from a first debonded state to a first rebonded state,wherein the device hasa first bonded adhesive strength ASbi,a first debonded adhesive strength ASd1, anda first rebonded adhesive strength ASri;and which satisfies the following conditions:whereinASb1represents the adhesive strength after a first electric stimulus for increasing bonding strength (ES+1) has been applied,ASJI represents the adhesive strength after a first electric stimulus for decreasing bonding strength (ES’l) has been applied, andASr1represents the adhesive strength after a second electric stimulus for increasing bonding strength (ES+2) has been applied.

3. The device according to claim 1, which satisfies the condition ASd1≤ 1.0 x ASi, preferably ASd1≤ (0.5 x ASi), more preferably ASd1≤ (0.1 x ASi) or ASd1≤ (0.01 x ASi).

4. The device according to any of the preceding claims, which satisfies the conditionASri> (1.0 x AS i),preferably ASri> (1.0 x ASbi), more preferably ASri> (1.2 x ASbi), still more preferably ASri> (1.5 xASbl).

5. The device according to any one of the preceding claims, which satisfies the condition ASr1≥ (0.8 x ASb1) when the time between the electric stimuli ES-1and ES+2is 24 hours or less, such as 10 hours or less, e.g. 5 hours or less, 3 hours or less, or 2 hours or less, preferably 1 hour or less, more preferably 30 minutes or less or 20 minutes or less, further preferably 10 minutes or less, 5 minutes or less, or 1 minute or less.

6. The device according to any one of the preceding claims, wherein the device has a second debonded state having an adhesive strength ASd2and a second rebonded state having an adhesive strength ASr2, and satisfies the following conditions:wherein AS^ represents the adhesive strength after a second electric stimulus for decreasing bonding strength (ES’2) has been applied, andASr2 represents the adhesive strength after a third electric stimulus for increasing bonding strength (ES+^) has been applied.

7. The device according to claim 6, wherein8. The device according to any one of the preceding claims, wherein the device has an nthdebonded state having an adhesive strength ASdnand nthrebonded state having an adhesive strength ASrn, and satisfies the following conditions:and more preferablywherein n is an integer of 3 or greater, andwherein ASdnrepresents the adhesive strength after an n^ electric stimulus for decreasing bonding strength (ES+n) has been applied, andASrnrepresents the adhesive strength after an n+lth electric stimulus for increasing bonding strength (ES’n+l) has been applied.

9. The device according to any one of claims 6 to 8, whereinwherein n is an integer of 3 or greater, such as from 3 to 10 or from 3 to 5.

10. The device according to any one of the preceding claims, wherein the adhesive strength in the first bonded state and the one or more rebonded state(s) is within the range of 3.0 to 40.0 N / cm, and the adhesive strength in the one or more debonded states is in the range of 0.1 to 2.5 N / cm.

11. The device according to any one of the preceding claims, wherein the electric stimulus is selected from the group consisting of a DC (Direct Current), AC (Alternating Current), VDC (Volts Direct Current), VAC (Volts Alternating Current), Pulsed DC (Pulsed Direct Current), Pulsed AC (Pulsed Alternating Current), and preferably is selected from an VDC (Volts Direct Current), VAC (Volts Alternating Current), Pulsed DC (Pulsed Direct Current).

12. The device according to any one of the preceding claims, wherein all electric stimuli for increasing adhesive strength are identical to each other and include a direct current voltage of 15 V for 1 minute, and all stimuli for decreasing adhesive strength are identical and include a direct current voltage of 15 V for 1 minute with reversed polarity direct current voltage for increasing adhesive strength.

13. The device according to any one of the preceding claims, which is in the form of an adhesive tape comprising a carrier and an adhesive layer comprising the adhesive (A), and wherein preferably the carrier is an electrically conductive carrier, such as for example a metal foil, an electrically conductive polymer, or on insulating polymer that has been treated to impart electrical conductivity, e.g. by providing a metallic film on a polymer foil.

14. The device according to any one of the preceding claims, wherein the device further comprises an electrically conductive substrate in contact with the adhesive (A).

15. The device according to any one of the preceding claims, wherein the adhesive (A) is a pressure-sensitive adhesive and / or wherein the adhesive has ionic conductivity, preferably in the range of 10-10S / cm to 10-3S / cm, and / or comprises one or more ionic liquids and / or one or more salts that are not ionic liquids, preferably a lithium salt.

16. The device according to claim 15,wherein the cation of the one or more ionic liquids is selected from the group consisting of imidazolium-based cations, pyridinium-based cations, pyrrolidinium-based cations, piperidinium-based cations, phosphonium-based cations, sulfonium-based cations, morpholinium-based cations, ammonium-based cations, and a combination thereof;and / orwherein the anion of the one or more ionic liquids is selected from the group consisting of tetrafluoroborate, hexafluorophosphate, bis(fluorosulfonyl)imide, bis(trifluoromethanesulfonyl)imide, trifluoromethanesulfonate, dicyanamide, nitrate, chloride, acetate, hydrogen sulfate, and methanesulfonate.

17. The device according to claim 15 or 16, wherein the ionic liquid is selected from the group comprising 1-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMIM FSI), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMIM TFSI), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIM TFSI), 1-ethyl-3-methylimidazolium thiocyanate (EMIM SCN), 1-ethyl-3-methylimidazolium dicyanamide (EMIM DCA), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM BF4), 1-butyl-3-methylimidazolium thiocyanate (BMIM SCN), 1-allyl-3-methylimidazolium dicyanamide (AllylMIM DCA), 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (AllylMIM TFSI), 1-ethyl-3-vinylimidazolium bis(trifluoromethylsulfonyl) imide (EVIM TFSI), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide (Pyr13 TFSI), N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl) imide (Pyr13 FSI), N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl) imide (Pyr14 FSI), 1-butyl-3-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide, 1-butyl-1-methylpyrrolidinium dicyanamide (Pyr14 DCA), 1-butyl-1-methylpyrrolidinium triflate (Pyr14 OTf), 1-ethyl-3-methylimidazolium triflate (EMIM OTf), 1-butyl-3-methylimidazolium triflate (BMIM OTf), 1,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide (DiMIM BTA), 1-butyl-3-methylimidazolium tricyanomethanide (BMIM TCM), 1-butyl-3-methylimidazolium methyl sulfate (BMIM MeSO4), 1,3-diethylimidazolium bis(trifluoromethylsulfonyl) imide (DiEIM TFSI), N-butyl-N-methylpyrrolidinium tricyanomethanide (Pyr14 TCM), diethylmethylsulfonium bis(trifluoromethylsulfonyl) imide (S122 TFSI), 1-propyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide (Pro4Pic TFSI), 1-ethyl-3-methylimidazolium ethyl sulfate (EMIM EtSO4), triethylsulfonium bis(trifluoromethylsulfonyl) imide (S222 TFSI), 1-(2-methoxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (MeOEMIM TFSI), 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl) imide (PMIM TFSI), 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (Pyr14 TFSI), 1-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl) imide, 1,3-dimethylimidazolium methyl sulfate (DiMIM MeSO4), 1-ethylimidazolium bis(trifluoromethylsulfonyl) imide (EIM TFSI), 1-ethyl-3-methylimidazolium methanesulfonate (EMIM OMs), 1-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl) imide (Et4Pic TFSI), 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide (EDiMIM TFSI), 2-methyl-1-propylpyridinium bis(trifluoromethylsulfonyl) imide (Pro2Pic TFSI), 1-ethyl-3-methylimidazolium acetate (EMIM OAc), 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIM PF6), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF6), 1-hexylpyridinium bis(trifluoromethylsulfonyl)imide (HexPy TFSI).

18. The device according to any one of claims 15 to 17, wherein the one or more salts that are not ionic liquids, which preferably comprises a lithium salt, are selected from the group consisting of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithiumtriflate (LiOTf), lithium difluoro(oxalato)borate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

19. The device according to any of the preceding claims, wherein the adhesive (A) is selected from the group consisting of acrylic adhesives, other vinyl-based adhesives, rubber-based adhesives, silicone adhesives, epoxy adhesives, polyurethane adhesives, cyanoacrylate adhesives, and UV-curable adhesives, which are preferably pressure-sensitive adhesives, and wherein the adhesive (A) is more preferably an acrylic pressure-sensitive adhesive.

20. The device according to any one of the preceding claims, wherein the adhesive (A) is a pressure-sensitive adhesive that is prepared by polymerizing a mixture comprising at least the following components:a) 20 to 80 wt % of acrylate monomer (al) from the group of (meth)acrylic esters containing at least one oxygen atom; andb) 20 to 80 wt % of acrylate monomer (a 2) from the group of (meth)acrylic esters and / or amides containing at least one nitrogen atom; andc) 0 wt % to 15 wt % of one or more electro-responsive compounds from the group of polymerizable zwitterionic monomers and / or non-polymerizable zwitterionic compounds, preferably one or more zwitterionic monomers; andd) 0.005 to 10 wt % of at least one initiator; ande) 0 wt % to 20 wt % of one or more ionic liquids; andf) 0.0 wt % to 20 wt % of one or more salts that are not ionic liquids; andg) optionally 1 wt % to 20 wt % by weight of one or more acrylate monomers (a3), wherein the one or more acrylate monomers (a3) are different from acrylate monomers (al) and (a2); andh) optionally additives,wherein the weight fractions of the components are based on the total weight of the mixture.

21. The device according to any of the preceding claims, wherein the device is in the form of an adhesive tape comprising the adhesive (A) on one or both sides of a carrier, wherein the carrier is preferably electrically conductive on a side where the adhesive (A) is present.

22. The device according to claim 24, wherein the device in the form of an adhesive tape further comprises an electrically conductive layer and / or a primer layer between the backing and the adhesive (A).

23. A method of modifying the adhesive strength of an adhesive device as defined in any of the preceding claims, the method comprising the application of one or more electric stimuli for increasing and / or decreasing the adhesive strength of the adhesive.

24. An adhesive system capable of modifying the adhesive strength of an adhesive, preferably a pressure-sensitive adhesive, by applying one or more electric stimuli, the system comprisinga device as defined in any one of claims 1 to 22, anda controller that is configured to apply an electric stimulus to the device;wherein the controller is operated manually by an operator or automatically following a pre-defined program.

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