Adhesive device with high bonding strength

Abstract

The present invention provides an adhesive device in which the adhesive strength AS of the adhesive can be increased on demand from its initial state, ASi, to a bonded state, ASb, by application of one or more electric stimuli, and wherein the bonded state ASb exhibits a high adhesive strength of 2.1 N / cm or higher. The increase in adhesive strength from the initial state to the bonded state may realize a factor of ASb / ASi = 1.2 or greater, preferably 1.5 or greater, such as 2 or greater, such as 5 or greater or 10 or greater, 11.0 or greater, preferably as 13 or greater, 15 or greater for Test A of peel strength. Further disclosed is a method of increasing the adhesive strength of the adhesive device comprising the adhesive, comprising the application of one or more electric stimuli. The one or more stimuli may be applied using a controller that is operated manually by a user, or which follows a pre-defined program.

Description

[0001] tesa SE Norderstedt

[0002] ADHESIVE DEVICE WITH HIGH BONDING STRENGTH

[0003] TECHNICAL FIELD

[0004] The present invention relates to a device comprising an adhesive, which is able to achieve a high or even very high bonding strength, and its adhesion strength can be modified upon application of an electric stimulus (also referred to as electro-responsive adhesive in the following). The adhesive may be a pressure-sensitive adhesive (PSA). In one embodiment, the device is in the form of an adhesive tape that can be placed e.g. between electrically conductive surfaces. The adhesion strength of the electro- responsive adhesive can be modified, e.g. either increased or decreased, or both, on demand by the application of an electric stimulus to the adhesive, e.g. relative to an electrically conductive adherend surface.

[0005] BACKGROUND ART

[0006] Adhesives are used to bond two surfaces by creating strong contact at their interface. Depending on formulation, adhesives can be pressure-sensitive, heat-activated, light, moisture, or chemically cured. Nowadays adhesives are used in areas like packaging, construction, electronics, and healthcare. Modern applications require reworkability, easy removal, quick bonding, reusability, sensing, and adaptability, which conventional adhesives lack. To address these needs, newer adhesive systems are being developed that can alter their adhesion or bonding behavior when exposed to external stimuli such as light, mechanical stress, solvents, or magnetic fields. Among these, electricity is a popular stimulus due to its simple operation, accurate control, speed, and ability to target specific locations.

[0007] CN 106928881 A describes an electro-reversible adhesive made mainly by mixing starch and electrorheological species such as BaTiO CjC )?. The mixture has a gel-like consistency, but when an electric field is applied, it hardens and functions as an adhesive, achieving a higher bonding strength of up to 3.6 MPa at an electric field of 1.5 KV / m. Once the electric field turns off, it transforms to its original gel state, allowing easy debonding.

[0008] US 2005 / 274455 Al describes electro-active adhesive systems that consist of an adhesive matrix incorporated with various electro-active particles. The adhesion can be activated or altered by an electric field. Electrorheological fluid is used in the adhesive that changes the viscosity in response to an electric field. Once the electric field is cut off, the adhesion is then immediately significantly reduced. The patent also discussed other approaches, such as surface-responsive materials, shape memory, and liquid crystal polymers, to achieve electro-responsive functionality in adhesives.

[0009] US 2007 / 269659 Al, US 7,332,218 Bl, and US 6,620,308 B2 disclose structural adhesives in the form of liquid glues with electrolyte functionality. They are cured chemically through reactions involving epoxies and acrylics in a matter of hours to days, and a bonding strength of up to ~ 27 MPa was achievable. The strength can be further modified (e.g. reduced up to 90% from initial bonding) with the application of DC voltage up to 50 V.

[0010] US 6,254,954 Bl describes an adhesive tape comprising polyester, epoxy resin, and a cationic photoinitiator (photo acid generator), while CN 110643286 A is a photo base generator. The adhesive can be applied as a tacky film and, following additional curing (UV-C or e-beam), attains a lap shear strength of 6.9 MPa. However, bonding strength cannot be altered once it is cured. WO 2024 / 079548 Al discloses a semi-structural or structural adhesive composition comprising a comparable cationic curing mechanism, wherein the bonding strength of the adhesive decreases upon application of direct electric power.

[0011] WO 2021 / 115772 Al discloses a curable and debondable two-part adhesive system. The first part contains a (meth)acrylate monomer, a co-polymerizable acid, and an electrolyte, while the second part includes two curing agents for the monomers and a solubilizer. The adhesive provides strong initial bonding and allows for easy debonding when an electrical potential is applied.

[0012] US 2015 / 240136 Al describes a structural adhesive based on a thermosettable composition that becomes active at temperatures between 140 °C and 200 °C. In contrast, US 2008 / 0166513 Al discloses a heat- activated hotmelt adhesive in the form of a non-tacky sheet, which is activated by heating to 80-150 °C, enabling bonding by melting the adhesive matrix.

[0013] In addition to the adhesive systems mentioned above with various curing mechanisms, pressure-sensitive adhesives (PSA)s, even though they have low bonding strength, have also been developed that allow control of adhesion strength through external stimuli such as light, heat, or electricity.

[0014] WO 2023 / 165966 Al describes a pressure-sensitive adhesive composition comprising at least one base component selected from the group consisting of a polyacrylate pressure-sensitive adhesive and a synthetic rubber pressure-sensitive adhesive, a salt component and a (polymer) electrolyte component. The adhesive strength can be modified (e.g. decreased) by electricity.

[0015] WO 2021 / 202527 Al describes a pressure-sensitive adhesive comprising acrylic polymers, ionic liquids, vinyl compounds, and crosslinkers with electrically peelable features even under high temperature exposure. EP 3878482 Al and EP 3 858 929 Al describe a pressure sensitive adhesive with an electrical debonding function. The adhesive recovered its bonding strength over time after debonding. The composition of the adhesive is an acrylic / silicon / urethane-based polymer with ionic liquid.

[0016] EP 3858932 Al describes a method for separating an adherend with an electrolyte-based adhesive layer. The method entails applying a first voltage to create a potential difference across the thickness of the adhesive layer in order to reduce adhesion, allowing a bonding maintenance period for the adhesive force to recover, applying a second voltage to modify adhesion again, and finally separating the adhesive layer from the adherent. However, the peel adhesion for such an adhesive before and after voltage application and recovery within one hour was reported to be in the range of 6 to 8 N / 20 mm. The adhesive composition described therein contains a commercially available ionic polymer (e.g. SOMAREX 530: anionic polyacrylamide polymer).

[0017] TECHNICAL PROBLEM

[0018] In view of the above, traditional triggers like light, heat, pressure, chemical curing, or moisture are used to initiate bonding or increase bonding strength by curing or activating the adhesive, which requires direct exposure and is not suitable to locally activate the process without impacting adjacent areas of the substrate. This might be critical to sensitive systems. Many of these systems further require the use of materials or stimuli that are more difficult to provide at the place of use, such as high heat or UV radiation. Also, once curing is activated, it propagates automatically, resulting in less control over the system, limiting adjustment capabilities.

[0019] Other stimuli like electricity (DC voltage) are mostly used to decrease the bonding strength rather than to increase it. Only a few prior arts mentioned electro-responsive adhesives that temporarily increase adhesion strength, but here the increased adhesion strength immediately disappears when the electric stimulus is turned off or disconnected. This is unsuitable in case where strong adhesion is required even after the electric connection is disconnected.

[0020] Some prior art adhesives suffer from low or no initial tack to place the adhesive and need hours to days to obtain sufficiently high adhesive strength. In some heat-activated film adhesives, water vapor is produced as a byproduct, which may result in porous bonding structures, and which may also be less suitable for the bonding of water-sensitive objects. Also, moisture can be a factor contributing to corrosion, which is often also not desired. UV-activated structural bonding adhesive also comes with several disadvantages, as UV-C is mostly used to activate the adhesive, and the adhesive needs to be cured over several hours or days or even weeks to achieve maximum bonding strength. UV-C is also harmful to the human body, and protective measures may have to be taken. Further, most of the existing systems require significantly high pressure and sometimes heat to activate the adhesive, which may not be suitable for substrates that are sensitive to heat or pressure.

[0021] In view of the above, there remains a challenge to provide a suitable adhesive with already sufficient tack for initial adhesion to the target adherend, and which also allows the adhesion strength to be further enhanced on demand — offering more precise control and flexibility.

[0022] It is also desired a system that allows increasing adhesion strength in seconds or minutes from its initial values to several folds, on demand by a controllable external stimulus, without requiring a high external pressure or temperature or UV light and, of course, locally without affecting adjacent areas of the substrate, while preferably also not leading to the generation of water vapor due to the increased adhesion strength. Further and very importantly, the increased adhesion strength should remain even after the stimulus is removed.

[0023] OBJECTS OF THE INVENTION

[0024] It is therefore an object of the present invention to overcome one or more of the above-mentioned disadvantages of the adhesives of the prior art.

[0025] Specifically, it is one object of the present invention to provide a device comprising an adhesive with sufficient initial tackiness, where the adhesion strength of the adhesive can be increased to a level similar to or higher than structural bonding level within a short amount of time (for example within seconds or minutes) and on demand in a controllable manner.

[0026] Further, it is an object of the invention to provide a device comprising an adhesive that achieves this without the need for complicated equipment and without the need for protective gear.

[0027] In certain embodiments, it is a further object of the present invention to provide a device that satisfies these requirements while also allowing the adhesive strength to be reduced on demand, e.g. to allow disassembly.

[0028] In still further embodiments, it is an object of the present invention to provide a device that allows achieving high adhesive strength within minutes upon demand (bonding), which allows reducing adhesive strength in a controllable manner (debonding), and which allows increasing adhesive strength again to level similar or even high than after the first bonding (rebonding), i.e. where debonding and rebonding can be reversibly performed for a number of times, e.g. at least 2 or 3 times. SUMMARY OF THE INVENTION

[0029] The present invention provides the following embodiments:

[0030] 1. A device comprising an adhesive, wherein the adhesive strength of the adhesive can be increased by an electric stimulus from an initial state, AS;, to a bonded state, AS^ wherein AS, represents the adhesive strength in the initial state prior to application of an electric stimulus, and

[0031] ASb represents the adhesive strength after one or more electric stimuli for increasing bonding strength has been applied, and wherein in Test A of peel strength

[0032] ASj is in the range of up to 2 N / cm, and

[0033] ASb is 2.1 N / cm or higher, such as 10 N / cm or higher such as 25 N / cm or higher.

[0034] 2. The device according to embodiment 1, wherein in Test A of peel strength, ASb 's'nthe range of 2.1 N / cm or higher, such as 5.0 N / cm or higher, 7.0 N / cm or higher, 9.0 N / cm higher, 17 N / cm or higher, or 20 N / cm or higher or 25 N / cm or higher.

[0035] 3. The device according to embodiment or 2, which satisfies the condition ASb / AS; = 1.2 or greater, preferably 1.5 or greater, such as 2 or greater, such as 5 or greater or 10 or greater, 11.0 or greater, preferably as 13 or greater, 15 or greater for Test A of peel strength.

[0036] 4. A device according to any embodiments 1 to 3, wherein the adhesive comprises

[0037] (a) a polymer network that is formed by at least one of a single polymer (aO), which is a homopolymer or a random copolymer, two or more different polymers, comprising at least a first polymer (al) and a second polymer (a2), and a block copolymer that comprises at least a first segment (al') formed by repeating units derived from at least one first monomer and a second segment (a2') formed from at least one second monomer, the block copolymer optionally comprising one or more further segments,

[0038] (b) one or more of an ionic liquid (bl), an inorganic salt that is no ionic liquid (b2), and / or a linear polymer having oxyethylene or oxypropylene units.

[0039] 5. A device according to any embodiments 1 to 4 wherein the component (b) is present in a total amount of 0.1 to 80 % by weight, relative to the total weight of the adhesive. A device according to any embodiments 1 to 5wherein the component (b) is present in domains surrounded by the polymer network (a), the domains having an average size of 1 to 5,000 nm. A device according to any embodiments 1 to 6 wherein the adhesive does not exhibit a glass transition temperature or exhibits a glass transition temperature of 20 °C or lower, such as 10 °C or lower. A device according to any embodiments 1 to 7 wherein at least one, and preferably both, of the first polymer (al) and the second polymer (a2), respectively one or both of the repeating units forming the first (al') respectively second segment (a2') of the block copolymer, comprise a repeating unit containing one or more of O, N, S, Si, P, and B atoms in a side chain or main chain of the polymer. A device according to any embodiments 1 to 8, wherein the adhesive comprises one or more electro-responsive compounds selected from the group consisting of polymerizable zwitterionic monomers and / or non-polymerizable zwitterionic compounds, preferably one or more zwitterionic monomers. A device according to any embodiments 1 to 9, wherein the adhesive comprises nanoparticles, wherein the nanoparticles may optionally be surface functionalized, and wherein preferably the shape of the nanoparticles or surface functionalized nanoparticles may be spherical or non- spherical, wherein the non-spherical particles may take any form, including but not limited to rods, wires, tubes, cubes, prisms, disks, or branched structures like tetrapods, and / or wherein the nanoparticles or surface functionalized nanoparticles have an average diameter of from 1 to 1,000 nm, expressed as median value D Q in a particle size distribution determined by laser diffraction. A device according to any embodiments 1 to 10, wherein the adhesion strength of the adhesive having the adhesive strength AS, and / or AS^ can be decreased by an electric stimulus. The device according to any of embodiments 1 to 11 wherein the one or more electric stimuli are each a direct current (DC) voltage of 1 to 50 V, preferably 1 to 10 V, for a duration of 30 minutes or less, preferably 10 minutes or less, and / or wherein the number of electric stimuli is one, two or three, preferably one or two. The device according to any of embodiments Ito 12 wherein the device is in the form of an adhesive tape comprising a backing and one or more adhesive layer(s) each comprising an adhesive, wherein at least one of the one or more adhesive layers is formed by an adhesive as defined in any one of the preceding embodiments, and wherein preferably the backing is an electrically conductive backing, 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. The device is according to any of the preceding embodiments, wherein the device further comprises an electrically conductive backing in contact with the adhesive. The device according to any of the preceding embodiments, wherein the adhesive is a pressure sensitive adhesive and / or wherein the adhesive has ionic conductivity, preferably in the range of IO10S / cm to IO-3S / cm, and / or comprises one or more ionic liquids and / or one or more salts that are not ionic liquids, preferably lithium salt. The device according to embodiment 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(trifluoromethanesulfonyl)imide, trifluoromethanesulfonate, dicyanamide, nitrate, chloride, acetate, hydrogen sulfate, and methanesulfonate. The device according to embodiments 4 and 15, wherein the one or more inorganic salts, 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). The device according to any of embodiments 1 to 17, wherein the adhesive, 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, water, other ionic species, and organic or inorganic particles, such as electrically polarizable particles. A method of increasing the adhesive strength of an adhesive device as defined in any of the preceding embodiments, the method comprising the application of one, two or more electric stimuli for increasing the adhesive strength of the adhesive. The method according to embodiment 19, 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. The method according to embodiment 19 or 20, 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. The method according to embodiment 21, wherein the user or the pre-defined program provides electric stimuli for increasing voltage and / or duration. 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 a device as defined in any of embodiments 1 to 18, and a controller that applies an electric stimulus to the device, wherein the controller is operated manually by an operator or follows a pre-defined program.

[0040] Further embodiments and additional features of the above and the further embodiments will become apparent from the following description.

[0041] BENEFITS OF THE INVENTION

[0042] Electrically controlled (i.e. electro-responsive) adhesives provide significant benefits compared to prior technologies, mainly because of their precise and localized activation capabilities. This characteristic enables precise activation without affecting surrounding areas, which is particularly beneficial in intricate assemblies or delicate components. Moreover, electrical activation facilitates rapid and adjustable improvement of adhesive strength by voltage application, eliminating the necessity for cooling or curing processes linked to thermal or ultraviolet approaches. Unlike UV light, which requires direct exposure, electrical activation can penetrate opaque materials or enclosed structures, enhancing its versatility in enclosed or multilayer systems. This approach also reduces the possibility of heating the entire structure, which is crucial when handling temperature-sensitive materials like electronics, thin coatings, or biological surfaces.

[0043] The adjustability of the process through electrification control further distinguishes it from UV- or heat- cured adhesives. Moreover, electrical activation offers improved energy efficiency, especially when targeting small areas, thereby eliminating the need for energy-intensive lamps or ovens. This characteristic makes it well-suited for flexible, portable, and wearable devices, as it can be powered by small electrical circuits or batteries, making it ideal for mobile or low-footprint applications. Overall, electric activation gives faster, more targeted, and often adjustable control over adhesion, which opens new possibilities in smart materials and advanced manufacturing.

[0044] Unlike the adhesives of the prior art, the adhesive strength of the device of the present invention can be increased by means of simple methods, i.e., control of electromotive stimuli (e.g., application of DC voltage), without resorting to certain special conditions such as the use of UV-C radiation, high heat, or high pressure.

[0045] On top of that, the device has an electrically modifiable adhesion strength, e.g. an increase of adhesion strength, that can be controlled by the properties (e.g. rate, voltage, duration, waveform, polarity) of electric stimuli, such as DC voltages. Even after switching off or disconnecting the electric stimulus, e.g. the DC voltage, the adhesion strength remains at a high level.

[0046] Without wishing to be bound by theory, in comparison to prior art systems, the adhesive strength increase of the present invention may in one embodiment be due to electrophoretic effects (ion movements within the adhesive matrix under electric fields). Further, it is also contemplated that an electro-curing mechanism (e.g., crosslinking induced by electricity as described for liquid glue elsewhere in references Nat. Commun. 2015, 6, 8050; Macromolecules 2018, 51, 6661; ACS Appl. Bio Mater. 2019, 2, 2633) may occur. Basically, the mechanism may involve carbene-mediated crosslinking, which is different from conventional electron beam crosslinking.

[0047] In certain embodiments, the adhesive present in the device of the present invention comprises one or more ionic liquids, which may be a monomeric ionic liquid or a polymeric ionic liquid. It is contemplated that the incorporation of polymeric ionic liquids (PILs) with hard and soft segments may be responsible for the increase in adhesive strength. These PILs may enhance the adhesive properties by providing a balance between rigidity and flexibility, which improves ionic conductivity and mechanical properties. Balancing hard and soft segments may allow obtaining sufficient cohesive strength of the adhesive, while the soft segments form ion conduction paths. To this end, at the interface with the substrate (adherend) the presence of anions and cations in the PIL may increase the adhesion by the development of non- covalent interactions.

[0048] In an embodiment of the invention, the adhesive may comprise (or be) a ionogel. A ionogel is formed by a polymeric matrix that is impregnated with an ionic liquid, which may be a momomeric or polymeric ionic liquid, lonogels are formed by blending polymers and ionic liquids. In contrast to hydrogel structures, ionogels do not dry up and lose their softness. When appropriately chosen toughening approaches are taken ionogels can be ductile materials with high mechanical strength. In the context of toughening mechanisms, a polymer network can be formed by crosslinking. Alternatively, a polymer network structure can be formed by phase separation, where polymer rich units or domains contribute to mechanical strength, but the elastic soft units or domains allow an easy mixing with ionic liquids. Herein, the interaction of the ionic liquid (IL) with the polymer network, can contribute to effective energy dissipation. Additionally, reversible interactions at the interface with the adherend surface may occur due to the ionic liquid, which may be present or enriched at the adherend surface side of the adhesive, thereby contributing to high adhesive strength.

[0049] Additionally or alternatively, nanoparticles may be present in the adhesive that forms a part of the adhesive device of the present invention. The presence of nanoparticles with or without surface modification may contribute to an increased adhesion strength, for example by establishing a physical crosslinking withing the adhesive. In another approach, nanoparticles can form a rigid network around an elastic polymer, forming a separate network structure within the adhesive matrix network. Such a strong viscoelastic network may be supplemented with ionic liquid, allowing to toughen the network, to increase the responsiveness to an electric current, and / or to obtain high adhesion on various kinds of substrates.

[0050] The combination of the abovementioned factors with application of electric stimuli results in a significant improvement in adhesive strength. The present invention achieves high initial peel adhesion preferably on a conductive substrate, e.g. up to 2 N / cm. Further, by application of a moderate DC voltage of a short period of time, e.g. 1 to 50 V for 1 second to 30 minutes, the bonding strength increases significantly, reaching up to 25 N / cm or higher in the peel test (the below Test A).

[0051] DEFINITIONS

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Whenever ranges are specified below, the upper and lower limit are included, as is any value in between.

[0056] 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.

[0057] A "device" in the context of the present application is characterized in that it comprises an adhesive whose adhesive properties can be modified from at least an initial state to a bonded state. The adhesive may also be referred to as electro-responsive adhesive. The adhesive may be a PSA. The adhesive may have more than two adhesive states. Additional states may be a debonded state and a rebonded state.

[0058] The device may take any form or shape as long as it contains the adhesive, while the device may also contain additional components. In one embodiment, the device is a tape, i.e. an adhesive tape. In the embodiment of an adhesive tape, the device additionally contains at least a backing, which preferably is transparent or translucent. The backing may be coated with a primer. The backing may be electrically conductive. The device may also comprise additional components, such as electrical connections or a substrate to which the adhesive is adhesively bonded. The tape may have an adhesive layer on only one side of the backing (one-sided adhesive tape), or may have an adhesive layer on both sides of the backing (double-sided tape). In the latter case, at least one of the adhesive layers comprises or is formed by the electro-responsive adhesive, while the respective other layer may be formed from a an electro-reponsive adhesive or from an adhesive that has no electro-responsive properties, i.e. a conventional adhesive. Both the electro-responsive adhesive and the conventional adhesive may be pressure-sensitive adhesives (PSAs).

[0059] The device in the form of an 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.

[0060] The device may be a capacitor-like device, for example wherein an adhesive layer is disposed on an electrically conductive backing and / or an electrically conductive substrate / adherend, or two electrically conductive substrates sandwiching the adhesive (which may be a PSA), with or without interposing elements such as additional layers.

[0061] The adhesive tape according to one embodiment of the present invention is present more particularly 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.

[0062] 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. 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 one atop another along the z direction.

[0063] 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 or the 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.

[0064] 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.

[0065] 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.

[0066] 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. As a result of these forces of recovery, an adhesive bond is formed.

[0067] The term "initial adhesive strength" refers to the adhesion strength of the adhesive measured by Test A (peel adhesion) outlined below without and prior to applying any electric stimulus. In certain embodiments where the device is debondable and rebondable, the term however also encompasses an adhesive strength after debonding, as explained below, i.e. also encompasses a "debonded adhesive strength".

[0068] The term "bonding" refers to the application of an electric stimulus that leads to an increase in adhesion strength of the adhesive, as measured by Test A (described below) compared to its initial bonding state. Test A assesses peel strength in N / cm. A "bonded adhesion strength" refers to the adhesion strength that is observed after the stimulus has been applied, typically determined within a short period of time (e.g. 2 minutes) after the electric stimulus has been discontinued.

[0069] In certain embodiments, the device in the bonded state can be subjected to one or more electric stimuli for decreasing bonding strength, i.e. can be debonded. The term "debonding" refers to the application of an electric stimulus that reduces adhesion strength as compared to the "bonded" adhesion strength, i.e. the adhesion strength in the bonded state, as measured by Test A (described below). A "debonded adhesion strength" denotes the adhesion strength that is observed after an electric stimulus (e.g. voltage) for debonding (i.e. for reducing adhesive strength) has been applied, again typically determined within a short period of time (e.g. 2 minutes) after the electric stimulus has been discontinued. While the adhesive strength of a debonded adhesive is typically lower than the initial adhesive strength prior to application of any electric stimulus, the term also encompasses a reduction of the bond strength after it has been increased by an electric stimulus (bonding), back to its initially bonded adhesive strength or lower to allow for easy removal.

[0070] The term "rebonding" or "rebonded" refers to the adhesive strength of the adhesive as measured by Test A after a debonded adhesive is subjected to a (next) electric stimulus (e.g. voltage) that increases 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.

[0071] In embodiments where debonding and rebonding is possible, the rebonded adhesive strength is an embodiment of a bonded adhesive strength. Accordingly, in these embodiments an increase in adhesive strength from an initial state to a bonded state comprises a change from a state prior to application of any electric stimulus to a bonded state, and a change from a debonded state to a bonded state (i.e. a change from a debonded state to a rebonded state, where the debonded state is the initial state and the rebonded state is the bonded state).

[0072] The term "rebonding" refers to the third step in a sequence including subsequently initial bonding, debonding and rebonding, but also encompasses any further rebonding performed subsequently thereafter, e.g. in subsequent debonding-rebonding cycles, such as bonding-debonding-(first) rebonding- debonding- (next) rebonding, etc. The term "cycle" is defined as including at least the sequence: bonding- debonding, and a device of the present application may be suitable for 0, 1, 2, 3, 4, 5 or more of such cycles without a loss of adhesive strength in the second, third, or fourth rebonded state as compared to the adhesive strength in the first rebonding, or with a loss of adhesive strength that is less than 20%, preferably less than 10% in the second and third rebonding as compared to the first rebonding, each based on the same electric stimulus (voltage, duration, polarity) for each rebonding step. The term "ionic conductivity" refers to the conductivity that is caused by the movement of ions, e.g. in an adhesive layer, under an electromotive force (e.g. DC voltage), where the cations and anions are the charge carriers. In the present invention, the ionic conductivity may be determined by methods known in the art or by Test C: Ionic Conductivity set out below. In case of discrepancy, the result obtained by Test C prevails.

[0073] The term "adhesive strength" denotes refers to the adhesive strength in N / cm as determined by Test A below.

[0074] 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).

[0075] The term "electric stimulus" refers to any electric stimulus, and may thus include any current, voltage, polarity, duration, or frequency. The term may denote an alternating current (AC) or a direct current (DC) or a pulsed current and also alternating voltage (AC voltage), direct voltage (DC voltage), or pulsed voltage

[0076] 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 5 to 50 V, 5 to 20 V, or 10 to 50 V, and may be a AC or DC voltage, and preferably is a DC voltage. The duration of the electric stimulus is not particularly limited and may be from 0.1 to 10,000 seconds, such as from 30 to 1000 seconds or from 30 to 300 seconds.

[0077] 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 to change from a first to a second adhesive state, as well as the correlated change in optical states

[0078] The term "electrically conductive" is well understood by a skilled person. A possible threshold may be defined at a conductivity of 10 S / cm or higher, e.g. 102S / cm or higher or 103S / cm or higher.

[0079] DETAILED DESCRIPTION OF EMBODIMENTS

[0080] In its broadest aspect, the present invention relates to a device comprising an adhesive, wherein the adhesive strength of the adhesive can be modified (e.g. increased) by an electric stimulus from an initial state, ASj, to a bonded state, AS^, wherein ASj represents the adhesive strength in the initial state prior to application of an electric stimulus, and ASb represents the adhesive strength after one or more electric stimuli for increasing adhesive strength has been applied, and wherein in a peel strength Test A

[0081] AS j is in the range of up to 2 N / cm, and

[0082] ASb is 2.1 N / cm or higher, such as 10 N / cm or higher such as 25 N / cm or higher.

[0083] As derivable from the above, AS, is larger than ASb, which expresses that after application of an electric stimulus the adhesive strength of the adhesive in the initial state, AS,, is increased to the bonded adhesive strength ASb- The initial state is typically the state of the adhesive prior to application of any electric stimulus. However, if debonding and rebonding is possible, the initial state can also be a debonded state, i.e. the state of the adhesive after an electric stimulus for decreasing bonding strength has been applied. ASj is thus not particularly limited, as long as it falls within the ranges of adhesive strength indicated for Test A.

[0084] In certain embodiments, in Test A of peel strength, ASb 's'nthe range of 2.1N / cm or higher, such as 5.0N / cm or higher, 7.0N / cm or higher, 9.0 N / cm or higher, or 11.0 N / cm or higher, preferably as 13 N / cm or higher, 15 N / cm or higher, 17 N / cm or higher, or 20 N / cm or higher or 25 N / cm or higher.

[0085] While there is no particular upper limit, in practice the adhesion strength in the bonded state, AS^ may be 40 N / cm or less in Test A, such as 35 N / cm or less, 30 N / cm or less, 25 N / cm or less, 20 N / cm or less, 18 N / cm or less, 16 N / cm or less, 15 N / cm or less, 14 N / cm or less, or 13 N / cm or less.

[0086] The adhesion strength in the initial state, ASj, is 2.0 N / cm or less in Test A. This ensures good handleability and releasability prior to the application of the electric stimulus for increasing adhesion strength. Further, such values are sufficiently tacky to avoid undesired release of the adhesive.

[0087] While there is no particular lower limit for the adhesive strength in the initial state, in practice it may be 0.1 N / cm or more or 0.5 N / cm or more, in Test A; however, it may also be 1.0 N / cm or less or 1.5 N / cm or less.

[0088] In certain embodiments, the device of the present invention may be for single use, meaning that the adhesive strength can be increased only once by applying one or more electric stimuli, and the device may not be debondable without impairment of its properties or structural failure. In other embodiments, the device may be for multiple use, in which the device may be debonded and rebonded one or more times. This depends in particular on the composition of the adhesive. If debondable / rebondable properties are desired, in particular adhesive compositions comprising a zwitterionic compounds as described below in combination with an ionic liquid and an alkali metal salt, wherein the ionic liquid preferably includes both a protic ionic liquid, such as a primary or secondary ammonium ionic liquid such as ethylammonium nitrate, and a non-protic ionic liquid, may preferably be employed.

[0089] The electric stimuli for increasing adhesive strength is not particularly limited, and the one or more electric stimuli are each a direct current of 1 to 50 V (Volt), preferably 1 to 10 V, for a duration of 30 minutes or less, preferably 10 minutes or less, and / or wherein the number of electric stimuli is one, two or three, preferably one or two. Thus, in one embodiment, the one or more electric stimuli for increasing adhesion strength consists of a single electric stimulus of a direct current of 1 to 50 V, preferably 1 to 10 V, for a duration of 30 minutes or less, preferably 10 minutes or less.

[0090] In practice, of relevance are not only the absolute values of adhesion strength, but also the relative increase in adhesion strength after application of the one or more electric stimuli, i.e. the bonded adhesion strength ASj-, relative to the initial adhesion strength AS,. Preferably, the ratio AS^ / ASj is 1.2 or greater, preferably 1.5 or greater, such as 2 or greater, such as 5 or greater or 10 or greater, for Test A of peel strength. This ensures that there is significant increase and difference in removability between the initial and bonded state, and the adhesion strength in the bonded state may be sufficiently high for demanding applications, approaching or reaching levels required for structural bonding applications. The ratio ASj-j / ASj may also be 5.0 or greater, 7.5 or greater, 10.0 or greater, 12.5 or greater, 15.0 or greater, 20 or greater, 25 or greater, 30 or greater, 40 or greater, 50 or greater, 60 or greater, 70 or greater, 80 or greater, or 90 or greater. Here, ratios of 10 or higher are easier to achieve if AS, is small, i.e. 1 N / cm or less, while still ensuring high adhesive strength in the bonded state.

[0091] While there is no particular limitation in the ratio AS^ / ASj, in practice the ratio may be limited to 250 or less, such as 200 or less, 150 or less, or 100 or less.

[0092] In certain embodiments, the adhesive device is an adhesive tape that comprises an electro-responsive adhesive layer on one side of an electrically conductive backing material. The backing material may be any material having suitable properties and electrical conductivity, such as plastic films (e.g. PET films) that are metallized on at least one surface that is in contact with the adhesive, or which are inherently conductive due to the use of conductive polymers or polymers that are blended with conductive particles, such as carbonaceous materials such as carbon nanotubes. Examples of backings thus include a metal (e.g. copper, aluminum) foil, an electrically conductive polymer, or on insulating polymer film that has been treated to impart electrical conductivity, e.g. by providing a metallic film or electrically conductive coating on the polymer film, such as a tin-coated polyethylene terephthalate (Sn-PET).

[0093] The other side of the tape formed by the electro-responsive adhesive can then be laminated onto an electrically conductive substrate, such as an ASTM steel plate. For bonding, the positive terminal of a DC power source is connected at the edge of the conductive backing of the tape, while the negative terminal is connected to the edge of the substrate. When a voltage, e.g. of 5 to 50 V, is applied for sufficient time, e.g. 1 to 5 minutes, the adhesive's bonding strength to the substrate increases and maintains at an increased level even after the electric current is discontinued. In some embodiments, the bonded adhesive strength may be more than doubled, compared to its initial strength prior to application of voltage, confirming that the adhesion strength can be locally controlled by electromotive force.

[0094] Electro-responsive Adhesive

[0095] The adhesive comprised in the device of the present invention is able to increase adhesion strength upon application of an electric stimulus. Such an adhesive may be referred to as electro-responsive adhesive in the present invention. The electro-responsive adhesive is not particularly limited, yet preferred adhesives that may be used in the present invention will be explained below. The adhesive chemistry is not otherwise limited and may include adhesive chemistries such as acrylic adhesives, rubber-based adhesives, silicone adhesives, epoxy adhesives, vinyl based adhesives, polyurethane adhesives, cyanoacrylate adhesives, UV-curable adhesives.

[0096] Preferred electro-responsive adhesive are those exhibiting ionic conductivity. This can be achieved by including one or more ionic liquids and / or one or more salts that are no ionic liquids. The salts that are no ionic liquids may be selected from the group consisting of inorganic salts and organic salts. Ionic liquids are salts that are liquid at 25 °C and 1 atm. Here, the ionic conductivity is preferably in the range of IO10S / cm to 10'3S / cm at 25 °C. When ionic liquids are incorporated into the adhesive, an electrolyte adhesive is formed. This not only gives ion conductivity as well as adhesion properties.

[0097] Without wishing to be bound by theory, it is assumed that under electric force / field, the ionic species move within the adhesive. The cations move towards the negative electrode, while the anion moves towards the positive electrode. Without wishing to be bound by theory, it is considered that these movements improve interfacial contact between the adhesive and the electrodes as the ions push the adhesive chain to the electrodes, resulting in an increase in adhesion or bond strength. The salts may be ionic liquids and / or salts that are no ionic liquids, and may be inorganic or organic salts, with inorganic salts being fully inorganic and organic salts having at least an organic cation or anion. In one embodiment, both the cation and anion may be organic. An example of an inorganic cation is lithium (Li+)^

[0098] The present invention is not limited to any adhesive chemistries until some properties are fulfilled as enough ion conductive to activate the electrical responsive properties, better adhesion and cohesion.

[0099] In a preferred embodiment of the present invention, the electro-responsive adhesive comprises a polymeric matrix and one or more ionic liquids, which preferably include at least one protic ionic liquid, one or more selected from inorganic and organic salts that are no ionic liquids, and one or more zwitterionic compounds and / or one or more polymers comprising repeating units derived from zwitterionic monomers as part of the polymeric matrix. In a preferred embodiment, the electro-responsive adhesive is based on an acrylic adhesive matrix in which ionic species (inorganic and organic salts, ionic liquid and / or zwitterionic molecules) can be dissolved to make the electro-responsive adhesive. The preferred adhesive matrix should not be sensitive to moisture or not uptake too much moisture. Of course, it should be compatible with the salts. The preferred adhesive should contain as little moisture as possible, e.g. 0.1 wt.% or less or 0.05% by wt.% or less, relative to the total weight of the adhesive.

[0100] The preparation method of the adhesive or the device containing it is not particularly limited. Preferred adhesive preparation methods includes first the preparation of a UV-curable prepolymer (UV syrup) , followed by dissolving ionic species (salts, such as LiTFSI, zwitterionic compound, and / or (polymerizable or non-polymerizable) ionic liquid) in it together with one or more initiators, like Irgacure 184, optionally di- or triacrylate crosslinkers, or different plasticizers (PEG or carbonates). The resultant may then be UV cured (polymerization) on a conducive backing to provide an electro responsive adhesive tape that forms one embodiment of the present invention.

[0101] In the case of a solvent-borne adhesive system similar to DE102023108348A1, the salts are dissolved, and then the adhesive is coated and dried (crosslinked) to get the electro-responsive adhesive tape.

[0102] A further preferred adhesive matrix might also comprise acrylic polymer with ionic salts as well as electrocuring additives (e.g., diazirine molecules) either grafted / bonded to the acrylic polymer / other matrices (star shape / dendritic molecules) or as dispersion along with ionic salt in the adhesive matrix. Upon voltage application, a crosslinking reaction happens to the diazirine groups, resulting in an increase in the bonding strength.

[0103] Preferred electro curing additives are aryl-diazirines type as a carbene precursor due to high crosslinking efficiency; some are as 3-Phenyl-3-(trifluoromethyl)-3H-diazirine, 4-[3-(trifluoromethyl)-3H-diazirin-3- yl]benzoic acid, 4-[3-(trifluoromethyl)-3H-diazirin-3-yl]benzyl alcohol, 4-[3-(trifluoromethyl)-3H-diazirin- 3-yl]benzyl bromide,

[0104] 2-[3-[(prop-2-yn-l-yloxy)methyl]-3H-diazirin-3-yl]ethan-l-ol, 4-[3-(trifluoromethyl)-3H-diazirin-3- yl]benzylamine hydrochloride.

[0105] Inorganic salts

[0106] Inorganic salts are substances composed of a metal or ammonium cation and a non-carbon-based anion. They are typically formed when an acid combines with a base, although it can also form interactions with metals or metal oxides. Salts frequently dissolve in water and can conduct electricity in solution.

[0107] One common example is table salt, or sodium chloride. Most important properties should be that the salts can be dissolved in the adhesive system and generate cations and anions. This might be possible if the salt and adhesive matrix are compatible with polarities, electrostatic interaction, and adhesive has solvation abilities. Sometimes, the salt can be dissolved in solvents with high boiling points, then can be incorporated into the adhesive matrix. Common salts used include sodium chloride, potassium chloride, lithium chloride, sodium sulfate, potassium sulfate, lithium sulfate, ammonium chloride, sodium nitrate, potassium nitrate, lithium nitrate, magnesium sulfate, and calcium chloride.

[0108] The preferred salt system does not decompose under voltage and will not absorb too much moisture, which can generate gas formation and trigger delamination in the adhesive. The preferred salts should have enough electrophoretic movement to induce increases in bonding or adhesion strength once voltage is applied.

[0109] The preferred salts have a larger anion and smaller cation, as the larger anion-based salts are easy to dissolve in adhesive matrix and form less ion pairs. Also important is that during voltage application cations or anions do not decompose through electrolysis. So, the preferred system should have larger electrochemical stability windows (ECW).

[0110] Preferred salts are those of potassium, sodium and lithium, more preferably sodium and lithium, and even more preferably lithium. Examples thereof include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium perchlorate (LiCI04), lithium hexafluorophosphate (LiPFe), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiTf), and lithium bis(fluorosulfonyl)imide (LiFSI). Also, stannous chloride, zinc chloride, lithium perchlorate, and aluminum trihydrate, may be used.

[0111] Organic salts

[0112] Organic salts are ionic compounds formed from organic molecules that carry a positive or negative charge, paired with an oppositely charged counterion e.g. ionic liquid or polyionic liquid. They may be composed of organic cations and organic anions, or only one of cations and anions may be organic. Examples include the ammonium and alkali metal acetates, acetylacetonates and carbonates, e.g. lithium acetate.

[0113] Polymers salts are also one type of organic salt. These polymers contain charged groups along their polymer structure, paired with small counterions. These polymer salts are typically formed when a polymer with acidic or basic groups reacts with a base or acid. For example, poly(acrylic acid) can be neutralized with sodium hydroxide to form sodium polyacrylate, which contains negatively charged carboxylate groups and sodium counterions. Another example is polystyrenesulfonic acid, which becomes potassium polystyrenesulfonate when treated with potassium hydroxide. This polymer has sulfonate groups (SO3“) along the chain with potassium ions as counterions. Cationic examples include poly(diallyldimethylammonium chloride), which has fixed positive charges on the polymer and chloride as the counterion. These polymer salts behave as ionic species because they can dissociate in water or polar solvents, conduct ions, and participate in electrostatic interactions. Preferred salt of polymer might be Na or Li salt of acrylate.

[0114] Many surfactants are also organic salts. These are compounds that have a long hydrophobic tail and a charged headgroup, which allows them to dissolve in water and interact with both oils and polar substances. When the headgroup carries a charge, it forms salt with an oppositely charged ion, making the surfactant an organic salt.

[0115] For example, sodium dodecyl sulfate (SDS) has a negatively charged sulfate group and a sodium counterion. Cetyltrimethylammonium bromide (CTAB) has a positively charged ammonium group with a bromide counterion. Sodium stearate, a common soap, is made from stearic acid and sodium hydroxide and contains a carboxylate group paired with sodium. Also, polymeric ionic materials such as polystyrene sulfonate sodium salts, ethylene acrylic acid copolymers, and sulfonated polyesters are included for their functionality.

[0116] The organic salt may thus be polymeric or non-polymeric. Non-polymeric organic salts may be characterized by having a molecular weight of 1,000 g / mol or less, such as 600 g / mol or less or 500 g / mol or less, and by the absence of repeating units derived from monomers.

[0117] Ionic liquids

[0118] Preferred ionic liquids are protic ionic liquids, such as ammonium-based protic ionic liquids, i.e. containing a N+-H bond. These are in particular suitable if very high bonding strength is aimed at. The protic ionic liquid may have a cation that is a primary or secondary ammonium cation, i.e. a cation of the formula N+[H]m[R]n, wherein H is hydrogen, R is an organic group, e.g. a a straight or branched alkyl group, such as a C2-12alkyl group, m is 2 or 3, n is 1 or 2, and m+n=4. The counter-anion is not particularly limited and may be selected from the group consisting of tetrafluoroborate, hexafluorophosphate, bis(trifluoromethanesulfonyl)imide, trifluoromethanesulfonate, dicyanamide, nitrate, chloride, acetate, hydrogen sulfate, and methanesulfonate. An examples is. ethylammonium nitrate (EAN).

[0119] Other ionic liquids containing cations such as imidazolium, phosphonium, piperidinium, morpholinium, and pyrrolidinium, may also be employed. However, these may participate in an electrolysis reaction that can lead to debonding the adhesive under voltage application. As the high bonding strength of the present invention is in part due to electrophoretic effects, electrolysis reactions may be undesirable. Further, ionic liquids are hygroscopic in nature; therefore, electrolysis may occur due to the presence or absorption of moisture. In consequence, protic ionic liquids are preferred, are preferably used in combination with an adhesive matrix with hydrogen bonding capabilities within the matrix, such as those containing prepared from the monomers (al') and (a2') and unsaturated carboxylic acids or salts thereof, such acrylic acid or sodium acrylate. Further examples of ionic liquids that may be used in light of the above include those 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 / or wherein the anion of the one or more ionic liquids is selected from the group consisting of tetrafluoroborate, hexafluorophosphate, bis(trifluoromethanesulfonyl)imide, trifluoromethanesulfonate, dicyanamide, nitrate, chloride, acetate, hydrogen sulfate, and methanesulfonate.

[0120] Specific examples include l-ethyl-3-methylimidazolium bis(fluorosulfonyl) imide (EMIM FSI), l-ethyl-3- methylimidazolium bis(trifluoromethanesulfonyl) imide (EMIM TFSI), l-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIM TFSI), l-ethyl-3-methylimidazolium thiocyanate (EMIM SCN), 1- ethyl-3-methylimidazolium dicyanamide (designated as EMIM DCA), l-ethyl-3-methylimidazolium tetrafluoroborate (EMIM BF4), l-butyl-3-methylimidazolium tetrafluoroborate (BMIM BF4), 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), and 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 (Pyrl4 TFSI), 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 MeS04), 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), l-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 MeS04), 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), 1- Ethyl-3-methylimidazolium hexafluorophosphate (EMIM PFg), l-butyl-3-methylimidazolium hexafluorophosphate (BMIM PFg), 1-hexylpyridinium bis(trifluoromethylsulfonyl)imide (HexPy TFSI) In preferred embodiments, therefore an ionic liquid may be used that can be polymerized with the polymer backbone of the adhesive, thereby avoiding the risk of disintegration. This can be done using polymerizable ionic liquids, e.g. those wherein the cation contains an allyl or vinyl group that is then polymerized by light or heat activation. Some examples are: l-Allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, l-Allyl-3-methylimidazolium chloride, l-Allyl-3-methylimidazolium dicyanamide, l-Vinyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide (VEIm-TFSI), l-Vinyl-3- butylimidazolium bis(trifluoromethanesulfonyl)imide (VBIm-TFSI).

[0121] Other ionic species

[0122] Besides organic and inorganic salts, several other types of ionic species exist. These include zwitterions molecules, acids, bases, and molten salts. Among them preferred are zwitterionic materials. These are the molecules that have both positive and negative charges but are overall neutral (e.g. betains). They can be used as polymerizable zwitterionic monomers or non-polymerizable zwitterionic compounds.

[0123] According to preferred embodiments, the adhesive matrix of the present invention may comprise one or more zwitterionic compounds, and may in particular comprise repeating units derived from zwitterionic monomers. Exemplary zwitterionic monomers may include but are not limited to monomers based on phosphobetaine, carboxybetaine, sulfobetaine, or combinations thereof. Preferably, the one or more zwitterionic monomers comprise phosphobetaine monomers, carboxybetaine monomers, sulfobetaine monomers, or combinations thereof. Mixtures of different types of zwitterionic monomers may be used. The one or more zwitterionic monomers may contain acrylic functional groups. More preferably, one or more zwitterionic acrylic monomers are used in the mixture for preparing the adhesive employed in the present invention.

[0124] According to more preferred embodiments, the one or more polymerizable electro-responsive monomers, preferably zwitterionic monomers, that may be used to form repeating units contained in the adhesive employed in embodiments of the present invention include, but not limited to:

[0125] 2-methacryloyloxyethyl phosphorylcholine;

[0126] 2-[[2-(methacryloyloxy)ethyl]dimethylammonio]acetate;

[0127] 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propionate;

[0128] 3-[(3-acrylamidopropyl)dimethylammonio]propanoate;

[0129] 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propane-l-sulfonate;

[0130] 4-[[2-(methacryloyloxy)ethyl]dimethylammonio]butane-l-sulfonate;

[0131] 3-[[2-(acryloyloxy)ethyl]dimethylammonio]propane-l-sulfonate;

[0132] 3-[bis[2-(methacryloyloxy)ethyl](methyl)ammonio]propane-l-sulfonate;

[0133] 3-[(3-methacrylamidopropyl)dimethylammonio]propane-l-sulfonate;

[0134] 4-[(3-methacrylamidopropyl)dimethylammonio]butane-l-sulfonate. Alternatively or additionally, the adhesive employed in the present invention may comprise one or more non-polymerizable zwitterionic compounds. Compared to zwitterionic monomers which are polymerizable, the non-polymerizable zwitterionic compounds do not have any polymerizable groups. In the present invention, the use of a polymerizable zwitterionic monomer is preferred since its distribution in the adhesive, obtained by polymerizing the mixture, is generally easier to achieve. However, the use of a non-polymerizable zwitterionic compound is also possible provided that it can be dissolved in the mixture of the other components prior to preparation of the adhesive by polymerizing this mixture. In this case, no zwitterionic monomer is necessary, but the effects of the present invention may also be achieved by the non-polymerizable zwitterionic compound.

[0135] The non-polymerizable zwitterionic compounds may in principle be any type known to the skilled person. Exemplary non-polymerizable zwitterionic compounds may include but are not limited to phosphatidylcholine and non-polymerizable zwitterionic compounds based on phosphobetaine, carboxybetaine, sulfobetaine, or combinations thereof. Preferably the one or more non-polymerizable zwitterionic compounds are selected from the group comprising a zwitterionic polymer, obtained by polymerizing phosphobetaine monomers, carboxybetaine monomers, sulfobetaine monomers, or combinations thereof; phosphatidylcholine; and betaine, such as sulfobetaine, phosphobetaine and carboxybetaine. Mixtures of different types of non-polymerizable zwitterionic compounds may be used.

[0136] Polymer network

[0137] In certain embodiments, the adhesive comprises a polymer network that is formed by at least one of a single polymer (aO), which is a homopolymer or a random copolymer, two or more different polymers, comprising at least a first polymer (al) and a second polymer (a2), and a block copolymer that comprises at least a first segment (al') formed by repeating units derived from at least one first monomer and a second segment (a2') formed from at least one second monomer, the block copolymer optionally comprising one or more further segments,

[0138] The monomers forming the single polymer (aO) are not particularly limited, and a single monomer or two or more monomers may be used. The monomer(s) preferably include, or are entirely selected from, the monomers (al), (a2), and (a3) as defined below, and more preferably include one or more monomers selected from the monomers (al) and (a2). In one embodiment, the polymer (aO) does not contain oxyethylene or oxypropylene repeating units.

[0139] The two or more different polymers comprising a first polymer (al) and a second polymer (a2) are not particularly limited. In one embodiment, at least one of the first and the second polymer is a homopolymer or random copolymer as described for the polymer (aO), and both of the first and second polymer may be a homopolymer or copolymer described as the polymer (aO). In one embodiment, the two or more different polymers (al) and (a2) do not contain oxyethylene or oxypropylene repeating units. The block copolymer that comprises at least a first segment (al') formed by repeating units derived from at least one first monomer and a second segment (a2') formed from at least one second monomer, the block copolymer optionally comprising one or more further segments, is not particular limited. Each of the first, second and optionally third or further block segments may comprise repeating units derived from only one monomer, or may comprise repeating units derived from two or more monomers. The block segments thus differ from each other in the type of repeating units and / or their compositions.

[0140] The at least one first and the at least one second monomer forming the entirety or at least a part of the repeating units of the respective block polymer segments (al') and (a2') may be selected from monomers known to a skilled person, including in particular alkyl (meth)acrylates, e.g. C^.^Q alkyl (meth)acrylates, and the monomers (al), (a2) and (a3) defined below. In preferred embodiments, at least one or both of the first and second block segment is formed by repeating units derived from the monomers (al), (a2) and (a3), preferably (al) and / or (a2), as described below.

[0141] While the block copolymer may consist of the first and second block segment, optionally a third or further block segment is present. The third and further block segments are not particularly limited, yet may in one embodiment be formed by repeating units derived from the monomer (a3) as defined below.

[0142] The order or sequence of block segments is not particular limited. Examples of sequences of first block segments (al'), represented by A in the following, and second block sequences (a2'), represented by B in the following, and optional third and further block segments, represented by C in the following, include for example A-B, A-B-A, B-A-B, A-B-C, A-C-B, A-B-A-B, B-A-B-A, A-B-A-B-A, B-A-B-A-B, A-B-C-B-A, A-B-C-A- B, etc.

[0143] The first and second block segments (al') and (a2') differ in composition, and preferably differ in glass transition temperature. Here, the glass transition temperature of a polymer block is defined as the glass transition temperature (Tg) of a homopolymer or copolymer with the same repeating unit composition as the respective block segment, the homopolymer or copolymer having a weight-average molecular weight of about 100,00 as determined by gel permeation chromatography (GPC) using a polystyrene standard. The Tg is determined by dynamic scanning calorimetry (DSC). The difference in Tg between the polymer blocks is preferably 5°C or higher, such 10°C or higher, 15°C or higher, or 20°C or higher, e.g. 25°C or higher, or even 30 °C or higher. Additionally or alternatively, at least one of the first and second block segments has a Tg of 10 °C or less. While the Tg of the respective other block segment is not particularly limited, it may be 20°C or higher. By using a block copolymer comprising block segments with such different Tg's, it is possible to combine high adhesion strength with sufficient cohesive strength and rigidity of the polymer matrix. While the relative amounts of the first and second block segments (al') and (a2') is not particularly limited, each of them may form between 20 - 80 wt.% of the block copolymer.

[0144] In one embodiment, the block polymer does not contain a block segment comprising oxyethylene or oxypropylene repeating units. In addition, the adhesive comprising the polymer network comprises one or more of an ionic liquid (bl), an inorganic salt that is no ionic liquid (b2), and / or a linear polymer having oxyethylene or oxypropylene units. Here, the linear polymer having oxyethylene or oxypropylene units may be polyoxyethyle or polyoxypropylene. The ionic liquid and the inorganic salt that is no ionic liquid are discussed elsewhere herein, and the respective disclosure applies to the ionic liquid (bl) and the inorganic salt that is no ionic liquid (b2).

[0145] The polymer network formed thereby facilitates the incorporation of an ionic liquid, which may then lead to the formation of a ionogel. The ionogel may comprise domains of ionic liquid that are surrounded by the polymer network. The domains may exhibit an average size of 1 to 5,000 nm, expressed as the longest axis as observed e.g. by SEM or TEM in a cross-section of the adhesive for 100 randomly chosen domains.

[0146] The electro-responsive adhesive may be a pressure-sensitive adhesive. In preferred embodiments, the pressure sensitive adhesive is one 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 the (meth)acrylic esters containing at least one oxygen atom; and b) 20 to 80 wt % of acrylate monomer (a2) from the group of the (meth)acrylic esters and / or amides containing at least one nitrogen atom; and c) 0.0 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 d) 0.005 to 10 wt % of at least one initiator; and e) 0 wt % to 20 wt % of one or more ionic liquids; and f) 0 wt % to 20 wt % of one or more salts that are no ionic liquids; and g) optionally 1% to 20% 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 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 in the present invention, which forms the basis for the adhesive composition of the present invention, the solvent is disregarded when stating the weight fractions of the components.

[0147] The use of such a PSA allows obtaining a surprisingly high adhesive strength. 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.

[0148] In one such embodiment, the PSA employed in the present invention may be a polar polymer mixed with one or more ionic liquids. The polar polymer may be prepared by polymerization of monomer (aO') in the presence of crosslinker and may contain an excess of carboxyl groups. The presence of the said carboxyl groups allows for electrostatically interaction with the cations of ionic liquid, which increases the cohesive strength of the adhesive, resulting an increase in bonding strength of the adhesive assembly. The monomer (aO) may be one or more monomers as defined below for the monomer (al).

[0149] 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 both oxygen and 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, and (b) controlling the glass transition temperature (Tg) of the copolymer.

[0150] According to further embodiments, the adhesive composition preferably 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. The presence of zwitterionic compounds may facilitate achieving a higher AS^.

[0151] As outlined above, in one embodiment the adhesive further contains salts that are no ionic liquid (e.g., different Na and Li salts), facilitating the adhesive composition to be ionically conductive. The adhesive composition of the present invention may also contain an ionic liquid. The ionic liquid preferably is or includes a protic nitrogen-containing ionic liquid for the reasons outlined above, as this facilitates achieving a higher adhesion strength in the bonded state, ASj-,.

[0152] 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 electrochromic backing and cure it. 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.

[0153] Below a more detailed description of the monomers and other components that may be used in the preparation of the PSA present in the device of the present is given. As to the ionic liquids, those mentioned above can also be used in this specific embodiment.

[0154] Monomer (aO')

[0155] In one preferred embodiment, the adhesive, which may be a pressure-sensitive adhesive (PSA), is prepared by polymerizing a monomer (aO') or a mixture comprising two more monomers (aO') and optionally a crosslinker as to make, thereby forming a homopolymer or random copolymer (aO) forming a polymer network. Examples of the monomers (aO') include a (meth)acrylates with pendant carboxyl functional groups (-COOH), preferably used as a homopolymer, optionally in combination with one or more additional monomers capable of forming polar interactions with ionic liquids. The monomer (aO') is present in an amount of 20 to 80 wt %, such as from 35 wt % to 70 wt %, preferably 45 wt % to 68 wt %, more preferably 50 wt % to 66 wt %, based on the total weight of the mixture. The presence of higher amount of ionic liquid in the polymer network (aO) ensures pressure sensitive property.

[0156] The monomer (aO) may be a carboxylic acid-functional monomer comprising at least one carbon-carbon double bond (C=C) and at least one carboxyl group (-COOH), wherein the carboxyl group contains two oxygen atoms: one carbonyl oxygen (C=O) and one hydroxyl oxygen (-OH), intrinsic to the acid functionality. In certain embodiments, monomer (aO') may be selected from vinyl-terminated carboxylic acids, wherein the carboxyl group is separated from the vinyl group by an alkylene spacer of 0 to 3 carbon atoms. Preferred carboxylic acid-functional monomers have an alkylene spacer of 0 to 2 carbon atoms. More preferably an alkylene spacer of 0 to 1 carbon atoms.

[0157] In alternative embodiments, monomer (aO') may be selected from ester-linked carboxylic acid (meth)acrylates, wherein the vinyl group is part of an acrylate or methacrylate ester and the carboxylic acid group is located at the terminus of an alkylene spacer of 2 to 5 carbon atoms. Preferred ester-linked carboxylic acid (meth)acrylates have an alkylene spacer of 2 to 4 carbon atoms. More preferably an alkylene spacer of 2 to 3 carbon atoms.

[0158] Specific examples of monomers (aO) include those represented by formula (1) and formula (2): formula (1)

[0159] In present formula (1), R1is H or CH3, and n is an integer between 0 and 3, preferably 0 and 2, more preferably 0 and 1. In a preferred embodiment at least one monomer (aO') used has a value n between 0 and 3, preferably 0 and 1. Preferred are monomers, which are liquid at 25 °C.

[0160] Examples of the carboxylic acid-functional monomer include acrylic acid (AA, n = 0, R1= H), 3-butenoic acid (n = 1, R1= H), 4-pentenoic acid (n = 2, R1= H), 5-hexenoic acid (n = 3, R1= H).

[0161] In present formula (2), R1is H or CH3, and n is an integer between 2 and 5, preferably 2 and 4, more preferably 2 and 3. In a preferred embodiment at least one monomer (aO') used has a value n between 2 and 5, preferably 2 and 3. Preferred are monomers, which are liquid at 25 °C.

[0162] Further examples of the monomer (aO) include carboxylic acid (meth)acrylates, such as 2-carboxyethyl (meth)acrylate (n = 2, R1= H or CH3), 3-carboxypropyl (meth)acrylate (n = 3, R1= H or CH3), 4-carboxybutyl (meth)acrylate (n = 4, R1= H or CH3) or 5-carboxypentyl (meth)acrylate (n = 5, R1= H or CH3).

[0163] In formulations where the carboxylic acid-functional monomer is used in combination with ionic liquids, the oxygen content of the system may be further influenced by the ionic liquid's anionic component, which can participate in hydrogen bonding or electrostatic interactions with the carboxyl group. These interactions are critical for forming non-covalent crosslinks that contribute to the mechanical integrity of the resulting polymer network.

[0164] The polymerization may be carried out in the presence of an ionic liquid (IL), such as those selected from phosphonium or imidazolium-based salts, such as tributyl(methyl)phosphonium dimethyl phosphate (PP), l-ethyl-3-methylimidazolium methyl sulfate (PS), or similar ILs capable of forming strong non-covalent interactions with the carboxylic acid groups of the monomer. The IL acts both as a solvent and a physical crosslinker, forming electrostatic and hydrogen-bonding interactions with the polymer chains.

[0165] The single polymer (aO) may be a homopolymer or random copolymer, and is preferably a random copolymer, such as obtained by polymerizing two, three or four monomers as described above.

[0166] Monomer (al)

[0167] In one embodiment, the adhesive, which may be a PSA; is prepared by polymerizing a mixture comprising monomer (al) as component a) of the mixture. The monomer (al) is preferably an acrylate monomer from the group of the (meth)acrylic esters containing at least one oxygen atom. 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 70 wt %, preferably 45 wt % to 68 wt %, more preferably 50 wt % to 66 wt %, based on the total weight of the mixture.

[0168] 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 ester functionality 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.

[0169] 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.

[0170] 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 CHj 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 (3). formula (3)

[0171] In present formula (3), R1is H or CH3, R2is H, -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 5, preferably 0, 1, 2, 3 and 4. Preferred are monomers, which are liquid at 25 °C.

[0172] 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, R1=H, R2=CH2CH3), 2-[2-(2-methoxyethoxy)ethoxy]ethyl acrylate (n=3, R1=H, R2=CH3), diethylene glycol monomethyl ether methacrylate (n=2, R^CHs, R2=CH3), 2-ethoxyethyl methacrylate (n=l, R^CHs, R2=CH2CH3), 2-methoxyethyl methacrylate (n=l, R^CHs, R2=CH3) and ethylene glycol monoacetoacetate monomethacrylate (n=l, R1=CH3, R2=-C(=O)CH2C(=O)CH3). Acrylic acid (AA, n = 0, R1= H, R2= H) may also be mentioned as a structurally related (meth)acrylic compound.

[0173] Monomer (a2)

[0174] In one embodiment, the PSA may be prepared by polymerizing a mixture comprising monomer (a2). The monomer (a2) 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 (a2) may be contained or two or more thereof may be contained in combination. The one or more monomer(s) (a2) according to the invention are present in an amount of 20 wt % to 80 wt %, such as from 20 to 60 wt %, e.g. 20 to 55 wt %, preferably 22 wt % to 50 wt %, more preferably 24 wt % to 45 wt % based on the total weight of the mixture.

[0175] In a preferred embodiment, the monomer (a2) 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.

[0176] 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 CH2 group 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.

[0177] In the present invention, by use of the monomer (a2), 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.

[0178] In particular, with the use of the monomer (a2), a proper degree of polarity can be given to the acrylic copolymer and Tgcan be controlled.

[0179] In a preferred embodiment, the monomer (a2) is represented by the following formula (4). formula (4)

[0180] In present formula (4), R1is H or CH3, R2or R3is H, CH3, CH2OH, CH2CH2OH, CH3 or CH2CH3, preferably CH3 or CH2CH3.

[0181] In a preferred embodiment the monomer (a2) is liquid at 25 °C. In a preferred embodiment, the monomer (a2) is represented by CH2=CH-C(=O)-NR4R5, where R4is selected from the group of H ,-CH3, -CH2CH3, -CH2CH2CH3, CH2CH2OH, -CH2CH2CH2CH3, and R5is H or - CH3. This is preferably combined with the above preferred embodiment of (al).

[0182] 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).

[0183] 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.

[0184] 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.

[0185] 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,

[0186] Monomer (a3)

[0187] Optionally, the adhesive may be prepared by polymerizing a mixture comprising one or more acrylate monomers (a3), wherein the preferred one or more acrylate monomers (a3) are different from acrylate monomers (al) and (a2). If the mixture comprises monomer (a3') it may be present in an amount of 0.1 wt % to 20 wt %, preferably 5 wt % to 10 wt %, based on the total weight of the mixture.

[0188] The optionally present one or more acrylate monomers (a3) according to the present invention are not particularly limited and may for example be selected from the group consisting of acrylic acid, 2- hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, methyl acrylate, methyl methacrylate, isobornyl acrylate, 2-ethylhexyl acrylate, n-butyl acrylate, 2-octyl acrylate, n-heptyl acrylate, 2-ethylhexyl diglycol acrylate, and combinations thereof. Selecting a monomer (a3') allows to tailor properties of the adhesive composition. For example, by introducing a monomer unit comprising hydroxy groups, such as acrylic acid or 4-hydroxybutyl acrylate, polarity of the mixture may be increased resulting in an increased solubility of electro-responsive compounds, preferably zwitterionic monomers, and therefore in an improved bonding strength of the end product (i.e. a tape comprising the adhesive composition).

[0189] According to particularly preferred embodiments, the one or more acrylate monomers (a3) may be selected from the group consisting of n-butyl acrylate, 2-ethylhexyl acrylate, 4-hydroxybutyl acrylate, and combinations thereof.

[0190] The (a3) monomers may serve two functions. If the electro-responsive monomers are not directly soluble in the UV syrup or in the liquid electrolyte formulation (i.e., mixture of UV syrup, conducting salt and other ingredients), then they can first be solubilized in a hydroxy or carboxy group-containing (a3) monomers. Afterward, the adhesive formulation can then be made. If the adhesive strength needs to be increased, then monomers having more polar groups or monomers with a higher number of methylene groups as described above can be used.

[0191] Electro-responsive compounds

[0192] The adhesive may comprise 0.0 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. 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 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.

[0193] In a preferred embodiment, the one or more electro-responsive compounds are present in an amount of 0.1 wt % to 15 wt %, preferably 0.5 wt % to 10 wt %, more preferably 1 wt % to 5 wt %, based on the total weight of the adhesive. The adhesive may in principle comprise any type of electro-responsive compounds from the group of polymerizable zwitterionic monomers or non-polymerizable zwitterionic compounds, preferably zwitterionic monomers, known to the skilled person.

[0194] According to preferred embodiments, the adhesive of the present invention may comprise one or more zwitterionic monomers. Exemplary zwitterionic monomers may include but are not limited to monomers based on phosphobetaine, carboxybetaine, sulfobetaine, or combinations thereof. Preferably the one or more zwitterionic monomers comprise phosphobetaine monomers, carboxybetaine monomers, sulfobetaine monomers, or combinations thereof. Mixtures of different types of zwitterionic monomers may be used. The one or more zwitterionic monomers may contain acrylic functional groups. More preferably, one or more zwitterionic acrylic monomers are used in the mixture of the present invention.

[0195] According to more preferred embodiments, the one or more polymerizable electro-responsive monomers, preferably zwitterionic monomers, that may be contained in the mixture of the present invention include but not limited to:

[0196] 2-methacryloyloxyethyl phosphorylcholine;

[0197] 2-[[2-(methacryloyloxy)ethyl]dimethylammonio]acetate;

[0198] 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propionate;

[0199] 3-[(3-acrylamidopropyl)dimethylammonio]propanoate;

[0200] 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propane-l-sulfonate;

[0201] 4-[[2-(methacryloyloxy)ethyl]dimethylammonio]butane-l-sulfonate; 3-[[2-(acryloyloxy)ethyl]dimethylammonio]propane-l-sulfonate;

[0202] 3-[bis[2-(methacryloyloxy)ethyl](methyl)ammonio]propane-l-sulfonate;

[0203] 3-[(3-methacrylamidopropyl)dimethylammonio]propane-l-sulfonate;

[0204] 4-[(3-methacrylamidopropyl)dimethylammonio]butane-l-sulfonate.

[0205] Alternatively, the mixture used to prepare the adhesive comprised in the device of the present invention may comprise one or more non-polymerizable zwitterionic compounds. Compared to zwitterionic monomers which are polymerizable, the non-polymerizable zwitterionic compounds according to the embodiment of the present invention do not have any polymerizable group. In the present invention, the use of a polymerizable zwitterionic monomer is preferred since its distribution in the adhesive composition, obtained by polymerizing the mixture, is generally easier to achieve. However, the use of a non-polymerizable zwitterionic compound is also possible provided that it can be dissolved in the mixture of the other components prior to preparation of the adhesive composition by polymerizing this mixture. In this case, no zwitterionic monomer is necessary but the effects of the present invention may also be achieved by the non-polymerizable zwitterionic compound.

[0206] The non-polymerizable zwitterionic compounds may in principle be any type known to the skilled person. Exemplary non-polymerizable zwitterionic compounds may include but are not limited to phosphatidylcholine and non-polymerizable zwitterionic compounds based on phosphobetaine, carboxybetaine, sulfobetaine, or combinations thereof. Preferably the one or more non-polymerizable zwitterionic compounds are selected from the group comprising a zwitterionic polymer, obtained by polymerizing phosphobetaine monomers, carboxybetaine monomers, sulfobetaine monomers, or combinations thereof; phosphatidylcholine; and betaine, such as sulfobetaine, phosphobetaine and carboxybetaine. Mixtures of different types of non-polymerizable zwitterionic compounds may be used.

[0207] Nanoparticles

[0208] The adhesive, respectively the mixture for forming the adhesive, may comprise 10 wt% by weight or less of one or more nanoparticles, preferably 7 wt% by weight or less of one or more nanoparticles, more preferably 5 wt% by weight or less of one or more nanoparticles. The nanoparticles may or may not have a functionalized surface, but preferably have a functionalized surface.

[0209] Thus, preferably, the surface chemistry of one or more nanoparticles may be compatible or tailored, e.g. surface treated or functionalized, to bond or interact with the polymer matrix. This can be achieved by providing corresponding functional groups on the surface, or by providing a corresponding coating on the nanoparticles. Examples of functional groups include hydroxyl groups, e.g. silanol groups, oxide groups, or ethylenically unsaturated groups (e.g. vinyl groups) that may be bound to the nanoparticle surface via a linker group. Examples of the latter include e.g. silica particles that have been modified by reaction with a compound such as trimethoxyvinyl silane.

[0210] The shape of the (non-surface-functionalized) nanoparticles or surface functionalized nanoparticles may be spherical or non-spherical. If not spherical, the shape may take any form, including but not limited to rods, wires, tubes, cubes, prisms, disks, or branched structures like tetrapods. Here, a spherical nanoparticles denotes a particle having a sphericity of 0.8 or greater. Sphericity is defined as the ratio of the surface area of a sphere with the same volume as the particle to the particle's actual surface area. A perfectly spherical particle has a sphericity of 1, while less spherical, irregular particles have values less than 1.

[0211] The nanoparticles or surface functionalized nanoparticles have an average diameter of from 1 to 1,000 nm, preferably 10 nm to 1,000 nm, such as 100 to 1,000 nm, expressed as median value D5Q in a particle size distribution determined by laser diffraction.

[0212] The nanoparticles carrying reactive functional groups contain any element suitable to this purpose, which may present in oxidation state 0 (e.g. metal nanoparticles) or which may be present in other oxidation state, e.g. as in metal oxides or silicon oxide wherein the metal or silicon is in a positive oxidation state. The element may also be present in ionic form, e.g. as one or more ions, preferably one or three ions, more preferable one or two ions. The first, second and third ions may be selected from any desirable group of the periodic table, such as but not limited to group 1, 2, 11, 12, 13, 14, 15 or 16 of the periodic table. The first and / or second ion may be a transition metal ion, d-block or a f-block metal ion. Surface functionalized nanoparticles utilized in the present invention are preferably semiconductor nanoparticles, pigment or magnetic nanoparticles.

[0213] Encapsulating nanoparticles with free functional groups may in principle be nanoparticles, where the composition and microstructure may or may not change gradually across its dimensions, with or without an additional shell or multishell containing the desired reactive functional groups that represents reactive groups available for further bonding, known to the skilled person. The presence of a tailored shell allows for the integration of nanoparticles into polymer systems in ways that bare particles cannot, i.e. by providing covalent linkage points (e.g. vinyl groups) rather than just physical interaction. These covalent bonds dramatically increase the cross-link density of the polymer contained in the present invention of the adhesive device, thereby significantly improve stress transfer, yielding a higher bonding strength and stiffness of the polymer matrix.

[0214] The reactive functional groups may contain any appropriate binding group suitable to form covalent bonds or co-polymerize with polymer matrices. Preferably the binding group contains an atom such as, e.g., carbon, sulfur, nitrogen, oxygen, and / or phosphorous. The binding group may contain a species selected from the group consisting of a vinyl group, a thio group, an amino group, an oxo group a phospho group, a hydroxyl group, alkoxide, carboxylic acid, carboxylate ester, amine, nitro, polyethyleneglycol, sulfonic acid, sulfonate ester, phosphoric acid, phosphate ester, aldehydes, anhydrides and azides. The above are just a few examples. The key is that these functional groups are available on the nanoparticle's surface (e.g. formed by a shell after an encapsulation process), and they are strategically chosen to chemically react with a target polymer chemistry. By doing so, one ensures that when the nanoparticles are mixed with the polymer (or adhesive precursors), a chemical bond forms, locking the nano-fillers into the polymer matrix.

[0215] Initiator

[0216] The mixture for polymerization in the present invention, which forms the basis for the adhesive composition of this embodiment of the present invention, comprises 0.005 to 10 wt %, preferably 0.005 to 5 wt %, more particularly 0.01 to 3 wt %, based on the total weight of the mixture, of at least one initiator as component d) of the mixture. If a mixture of two or more initiators is used, the above weight fractions are based typically on the total amount of the initiators.

[0217] The term "initiator" as used in the present disclosure refers to a compound that generate radicals or cations upon exposure to UV light and heat. The initiator used in the present invention is preferably an initiator which initiates a radical polymerization. Accordingly, the polymerization taking place in accordance with the present invention is preferably a radical polymerization. Preferably, the initiator is a thermal initiator and / or photoinitiator, more preferably the initiator is a photoinitiator. According to a preferred embodiment, the adhesive composition is prepared by polymerizing a mixture comprising at least one, more preferably comprising at least two photoinitiators.

[0218] A thermal initiator is a compound that generates reactive species (free radicals, cations, or anions) upon exposure to heat. In the context of the present invention, the thermal initiator is not particularly limited. A photoinitiator is a compound that generates reactive species (free radicals, cations, or anions) when exposed to radiation (UV or visible). The photoinitiator typically comprises a UV initiator. Accordingly, the polymerization taking place in accordance with the present invention is preferably a UV polymerization.

[0219] The UV polymerization for syrup preparation and / or on the coated-out web may take place, for example, with the following photoinitiators, i.e. light-active initiators: 2,2-dimethoxy-2-phenylacetophenone (DMPA, 340 nm, 250 nm, Irgacure 651), 1-Hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184), 2-Hydroxy- 4'-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959), , 2,4,6- trimethylbenzoyldiphenylphosphine oxide (BAPO, 295 nm, 370 nm), iodonium (4-methylphenyl)[4-(2- methylpropyl)phenyl]hexafluorophosphate (242 nm), 2,2'-bithiophen-5-yl 4-N,N'-diethylaminophenyl ketone (THBP), 6,6'-(((lE,l'E)-(2,5-bis(octyloxy)-l,4-phenylene)bis(ethene-2,l-diyl))bis(4,l- phenylene))bis(l,3,5-triamine-2,4-diamine)) (400 nm). As well as the stated initiators it is possible to use other known initiators from the following classes: alpha-amino ketones, metallocenes, iodonium salts, alpha-hydroxy ketones, or phosphines. Thermal stability exists preferably up to at least 50°C.

[0220] Depending on the energy of the radicals formed on initiator scission, they may be limited to initiating the acrylate polymerization or may additionally produce crosslinking reactions as well, such as, for example, 2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-l,3,5-triazine (MTT). Crosslinking of the chain is unwanted during the polymerization or syrup preparation, in order to keep the viscosities low for the coating. In the second polymerization step in the case of UV polymerization, crosslinking, photoactive crosslinkers may be added. They may also be polymerized electively into the chains. When using 2-oxo-l,2-diphenylethyl acrylate (benzoin acrylate) or analogues thereof, polymerization in a UV tunnel at a wavelength between 300 and 400 nm produces polymers which, after the end of the polymerization in the UV tunnel, can be crosslinked briefly and intensely with UV radiation at 250 nm by activation of the benzoin acrylate units incorporated by polymerization. These crosslinkers may equally be incorporated by polymerization during a thermally initiated solution polymerization, and activated later, after drying, with UV radiation.

[0221] Benzophenone methacrylate (Visiomer 6976, 300 nm) and analogues thereof can also be used, with their known benefits and disadvantages. These initiators reduce the contamination with small molecules but require a greater time for reaction because of the biomolecular reaction. Crosslinking must take place under inert conditions.

[0222] According to preferred embodiments, a mixture of more than one initiator or multiple different initiators is used for different polymerization steps, for example, preparation of the UV syrup and final curing preferably done by UV polymerization or UV web polymerization. Preferably, a mixture of multiple initiators with different molar absorption coefficients is being used.

[0223] According to more preferred embodiments, 2,2-dimethoxy-2-phenylacetophenone (Irgacure 651) and 1- hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184) are used.

[0224] Inorganic salt that is not ionic liquid

[0225] The conducting salt may be selected based on its solubility in the mixture, cost, safety handling and longterm stability. For example, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) is considered to demonstrate improved moisture resistance. Lithium bis(fluorosulfonyl)imide (LiFSI) or lithiumtriflate (LiOTf), lithium difluoro(oxalato)borate (LiDFOB), or lithium bis(oxalato)borate (LiBOB) can also be used.

[0226] It is also possible to use other cations, such as Na+, K+, Cs+, Rb+, Ag+, Cu+, Cu2+, Mg2+, NH4+and other anions, such2)2N]‘, CF3SO3’, CH3CO2’, [B(C2O4)2] , [BF2(C2O4)2] , PFg" pure form or in a mixture. An anion such as PFg" is not preferred since they form toxic and corrosive gases such as HF on reaction with moisture.

[0227] The salt can also be a mixture of two or more salts, which may be beneficial for preventing corrosion of the conductive substrate or backing.

[0228] While the presence of the salt that is not ionic liquid (organic salt) is optional, in certain embodiments the salt is present in an amount of 0.1 wt % to 20 wt %, preferably 1 wt % to 10 wt %, more particularly 3 wt % to 8 wt %, based on the total weight of the mixture forming the basis for the adhesive composition.

[0229] Further additives

[0230] Optionally, the adhesive composition may be prepared by polymerizing a mixture further comprising additives as crosslinker, salt of acrylate, plasticizer, antioxidant, tackifier, corrosion inhibitor, oxygen scavenger, water, and a combination thereof, preferably in an amount of 0.01 wt % to 10 wt %, based on the total weight of the mixture. However, in order to facilitate high bonding strength in the bonded state, the additives preferably do not include water, or water is only present in amount of 0.1 wt% or less, based on the total weight of the mixture.

[0231] Generally, the compounds (e.g., Li salt, monomers, etc.) used for preparing the mixture forming the basis for the adhesive composition already contain traces of water. In addition, water is also taken up into the mixture upon its preparation and to the adhesive composition upon its use. In other words, the mixture and the adhesive composition may contain traces of water, e.g. 0.1 wt.% or less based on the total weight of the mixture, such as 0.01 wt. % or less. Water may however be added, and its addition may be more acceptable if debondable-rebondable properties are desired, yet this may be at the expense of the maximum adhesive strength in in the bonded state that can be achieved. When a low conductive ionic liquid is used, a larger amount of water may be required than when a high conductive ionic liquid is used. The mixture and the adhesive composition are therefore preferably stored under dry conditions.

[0232] In a further embodiment of the invention, the adhesive composition may be prepared by polymerizing a mixture further comprising a plasticizer, e.g. in an amount of 0.01 wt % to 10 wt %, preferably 0.05 to 5 wt % of plasticizer, as an optional additive. When the mixture forming the basis for the adhesive composition comprises a conventional plasticizer within above ranges, the presence of water can be avoided while debonding properties can still be achieved, yet again at the expense of maximum bonded adhesive strength that can be obtained. As explained above with respect to the presence of water, the amount of plasticizer in the mixture may be varied depending on the type of ionic liquid used. That is, when a low conductive ionic liquid is used, a larger amount of plasticizer may be required than when a high conductive ionic liquid is used.

[0233] Conventional plasticizers that may be used in the present invention include, for example, cyclic carbonates such as ethylene carbonate (EC), vinylene carbonate (VC), propylene carbonate (PC), butylene carbonate (BC) or fluoroethylene carbonate (FEC), linear carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC) or ethyl methyl carbonate (EMC), mixed carbonates, dimethylacetamide, ethyl methanesulfonate (EMS), gamma-butyrolactone, dimethyl sulfoxide, polyethylene oxide (PEO, also referred to as poly(ethylene glycol) i.e. PEG), "glymes" such as diglyme, triglyme, tetraglyme, ethylene glycol diacetate, ketones, or various ethers or polyethers, polypropylene oxides or block copolymer thereof, trimethylolpropane ethoxylate, or mixtures thereof. Particular preference in the present invention is given to the use of plasticizers that are based on polyethylene oxides, polypropylene oxides or block copolymers thereof, trimethylolpropane ethoxylate, or glymes.

[0234] The polyethylene oxides preferably have hydroxyl, (meth)acrylate, methoxy or ethoxy groups as chain ends. In the case of (meth)acrylate, polyethylene oxides with only one (meth)acrylate chain end are preferred. It is also possible to use mixtures of PEOs with and without (meth)acrylate chain ends. The chain end or chain ends with no (meth)acrylate groups are preferably hydroxy groups. Methoxy groups may further improve conductivity, and hydroxy groups may further improve adhesion strength to the substrates.

[0235] PEOs with (meth)acrylate groups function as monomers and will be copolymerized with monomers (al') and (a2'). This introduces long PEO chains as side groups into the polymer. In preferred embodiments, the chain length of the PEOs used is between 5 to 20 preferably 5 to 12 which corresponds to the number of consecutive ethylene oxide (-O-CH2-CH2-) repeat units in the polymer chain. An example of polymerizable PEOs is PEGMA480 and unpolymerizable is PEG200. In preferred embodiments, the plasticizer is selected from cyclic carbonates such as ethylene carbonate (EC), vinylene carbonate (VC), propylene carbonate (PC), butylene carbonate (BC) or fluoroethylene carbonate (FEC), linear carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC) or ethyl methyl carbonate (EMC), mixed carbonates, dimethylacetamide, ethyl methanesulfonate (EMS), gammabutyrolactone, dimethyl sulfoxide.

[0236] All the stated plasticizers may typically improve the solubility during the polymerization and, at the same time, act as an integral constituent of the final electrolyte. Adding plasticizer may increase softness of the adhesive, which reduced peel adhesion. Accordingly, a plasticizer or water is preferably absent if very high bonding strength is desired.

[0237] The mixture may comprise further ingredients like heteroaromatic substances like triazine. Such substances may help to improve the conductivity.

[0238] In order to optimize the technical adhesive properties, it is furthermore possible to admix the adhesive composition with resins. Resins are considered for the purposes of this present invention typically to be small molecule compounds to oligomeric and polymeric compounds having number-average molecular weights Mnof not more than 10 000 g / mol; they are not included in the polymer component. Tackifying resins for addition (peel adhesion-enhancing resins, i.e. tackifier) that can be used include all existing tackifier resins and those described in the literature. Representatives include the pinene resins, indene resins and rosins, their disproportionated, hydrogenated, polymerized, and esterified derivatives and salts, the aliphatic and aromatic hydrocarbon resins, terpene resins and terpene-phenolic resins, and also C5to Cg and other hydrocarbon resins. Any desired combinations of these and further resins may be used in order to adjust the properties of the resultant adhesive in line with requirements. Generally speaking, it is possible to use any resins or rosins which are compatible with (soluble in) the corresponding base polymer; reference may be made more particularly to all aliphatic, aromatic and alkylaromatic hydrocarbon resins, hydrocarbon resins based on pure monomers, hydrogenated hydrocarbon resins, functional hydrocarbon resins, and natural resins or hydrogenated rosins like methyl ester of hydrogenated rosin.

[0239] With the acrylate-based, adhesive composition, there is no need for the presence of tackifier resins, and so one outstanding variant constitutes the adhesive composition of the present invention wherein no resins have been added to the PSA. Such additions frequently possess adverse effects in the context of application for optical bonds. The resins used in the prior art as tackifier resins for acrylate PSAs are usually polar in nature, in order to achieve compatibility with the polyacrylate matrix. This usually leads to the use of aromatic tackifier resins, which on prolonged storage or on light exposure are subject to a yellowish discoloration.

[0240] Depending on the application, e.g. if no optical clarity is needed, tackifier resins may be used, preferably in a low range, preferably 0 to 5 wt %, more preferably 0.1 to 2 wt %. Other Electro-responsive Systems:

[0241] Some preferred systems include electrically polarizable particles, which can be made from a variety of natural, organic, and inorganic materials. Natural substances such as starch are one example, while carbon-based materials like fullerenes, carbon black, and carbon black grafted with polymers also serve this purpose effectively. In the category of inorganic materials, examples range from metallic and ceramic particles to compounds such as synthetic mica, silica gel, gypsum, lime, titanium oxide (including its hydrous form), metallic silicates, aluminum borate, colloidal silica, and plain silica.

[0242] Organic particles are also widely used, including water-absorbing resins such as those based on polyacrylic acid, along with thermoplastic polymers that carry carboxyl or ester groups, polyamides, and liquid crystalline polymers. To enhance their compatibility or performance, both organic and inorganic particles can be treated at the surface level. In addition, various salts are used, including alkali carboxylates like lithium laurate, potassium stearate, and sodium palmitate. Electrically functional organic semiconductors such as polyanilines, polythiophenes, and polyphenylenevinylenes also belong in this group. Other examples include magnetically responsive materials like iron oxide, along with functional polymeric or organometallic compounds such as phenoxy organometallic salts, silicone ionomer particles, polymeric salts, and metal polyoxo complexes that incorporate amino acids.

[0243] Susceptor particles— used for activation through thermal or electromagnetic energy— are commonly made from metals such as copper, aluminum, and gold, as well as metal alloys. Non-metallic conductors like silicon carbide also serve this function. Metal oxides such as ferrites and iron oxide are typical choices in this group.

[0244] BRIEF DESCRIPTION OF FIGURES

[0245] FIG. 1 schematically illustrates embodiments of an adhesive tape of the present invention, namely a single-layered adhesive transfer tape comprising layer (C) of adhesive.

[0246] FIG. 2 schematically illustrates embodiments of an adhesive tape of the present invention, namely a single-layered adhesive transfer tape comprising layer (D) of adhesive.

[0247] FIG. 3 schematically illustrates embodiments of an adhesive tape of the present invention, namely a double-layered adhesive transfer tape comprising a first adhesive layer (C) and a second adhesive layer (D), wherein both the layers are formed from different adhesives. FIG. 4 schematically illustrates embodiments of an adhesive tape of the present invention, namely a single-layered, single-sided adhesive tape comprising layer (C) of adhesive and an electrically conductive backing (T).

[0248] FIG. 5 schematically illustrates embodiments of an adhesive tape of the present invention, namely a single-layered, single-sided adhesive tape comprising layer (D) of adhesive and an electrically conductive backing (T).

[0249] FIG. 6 schematically illustrates embodiments of an adhesive tape of the present invention, namely a double-layered, single sided adhesive tape comprising - two adhesive layers (C and D), formed from different adhesives and layer (C) coated on an electrically conductive backing (T), and layer (D) coated on layer (C).

[0250] FIG. 7 schematically illustrates embodiments of an adhesive tape of the present invention, namely a double-sided adhesive tape comprising a backing (T) disposed between- two adhesive layers (C) and (D), wherein both the layers are formed from different adhesives.

[0251] FIG. 8 schematically illustrates embodiments of an adhesive tape device of the present invention, namely a single-layered, single-sided adhesive tape comprising layer (C) of adhesive and backing (T) laminated on an electrically conductive substrate (SI). The electrically conductive substrate serves as target adherend. Polarity signs indicate the applied voltage to the respective side of the assembly.

[0252] FIG. 9 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 and backing (T) laminated on an electrically conductive substrate (SI). The electrically conductive substrate serves as target adherend. Polarity signs indicate the applied voltage to the respective side of the assembly.

[0253] FIG. 10 schematically illustrates embodiments of an adhesive tape device of the present invention, namely a double-layered transfer adhesive tape comprising of two adhesive layers (C and D), formed from different adhesives and disposed between two electrically conductive substrates (SI and S2).

[0254] FIG. 11 schematically illustrates embodiments of an adhesive tape device of the present invention, namely a double-sided adhesive tape disposed between two electrically conductive substrates (SI and S2). The adhesive tape comprises a backing (T) disposed between - two adhesive layers (C) and (D), wherein both the layers are formed from different adhesives ADHESIVE TAPE COMPOSITION AND DESIGN

[0255] The following further illustrates possible compositions and configurations of the device of the present invention in the embodiment of an adhesive tape. However, they are in no way a limitation of the teachings or disclosure of the present invention as set forth herein.

[0256] According to preferred embodiments, the adhesive tape of the present invention is a pressure-sensitive adhesive tape.

[0257] The adhesive tape of the present invention comprises different structures and may include one or more layer (C) of adhesive or a layer (D) of adhesive or a combination thereof either in the form of a freestanding tape or in the form of a tape comprising backing T. The (C) or (D) of adhesive is not limited to the below examples.

[0258] The preferred adhesive layer (C) comprises a polymeric matrix made from a co- or terpolymer containing two distinct acrylic monomers (al) and (a2), along with electro-responsive zwitterionic compounds / monomers. Within this matrix, inorganic salts such as LiTFSI are incorporated at concentrations between 2 and 20 wt%.

[0259] Adhesive (C) may also be an adhesive matrix of polymer network formed from a copolymer composed of two different acrylic monomers (al) and (a2) or a polymer or a network of different polymers, in which inorganic salts such as LiTFSI are dissolved at concentrations ranging from 2 to 20 wt%.

[0260] Where the layer (D) of adhesive is based on acrylic adhesive prepared from two different acrylic monomers (al) and (a2) with dissolved organic salt (protic or aprotic ionic liquid) based on ammonium salt, e.g. ethylammonium nitrate (EAN) in wt % of 1 to 20.

[0261] Adhesive (D) may also be an adhesive matrix of polymer network formed from a copolymer composed of two different acrylic monomers (al) and (a2) or a polymer or a network of different polymers with dissolved organic salt [protic or aprotic ionic liquid] based on ammonium salt, e.g. ethylammonium nitrate (EAN) in wt % of 1 to 20.

[0262] Since adhesive layers (C) or (D) contain various types of salts, the electro-responsive tape of the present invention exhibits certain levels of ionic conductivity. These salts form different electrolytes within the adhesive, resulting in ionic conductivities at room temperature preferably in the range of 1O“10to 10“3S / cm, more preferably between 10“9and 10“5S / cm, and most preferably between 10“8and 10“3S / cm.

[0263] The backing (T) is an electrically conductive film that could be a metal foil or polymer film treated to induce electrical conductivity, which may consist of materials such as Sn-PET, PEDOT:PSS-primer-PET, or similar alternatives. For transfer tapes, no backing is not required. In the case of PEDOT:PSS-primer-PET backing, the PEDOT:PSS ink was coated onto a primer-treated PET film, where the primer is essentially a thin layer of acrylic adhesive.

[0264] The adhesive tape of the present invention may be a single layered, adhesive transfer tape (FIG. 1, adhesive (C), and 2, adhesive (D)). The adhesive tape may preferably be double layered, transfer tape (FIG. 3, adhesive (C) on (D)). Furthermore, the adhesive tape of the present invention may preferably be a single-layered, single-sided tape (FIG. 4, (C) coated on (T), and FIG. 5, (D) coated on (T)). The adhesive tape could be double-layered, single-sided tape (FIG. 6, (C), and (D), both on (T)). Alternatively, the adhesive tape of the present invention may be a single-layered, double-sided adhesive tape as shown in FIG. 7; (C) is on one side of (T), and (D) is on the other side.

[0265] The backing (T) in the different adhesive tape designs may laterally protrude beyond any of the other layers (D) and (C). A lateral protrusion is preferably in terms of connecting a direct-current (DC) voltage source to any of the layers. For example, when voltage is to be applied to a backing (T) that comprises only one side coated with a conductive coating on a polymer film, then, sufficient connection of the voltage source to such a carrier may be ensured if the backing protrudes the other layer(s). However, when voltage is to be applied to a double sided conductive coated polymer film or a completely conductive film, for example a metal foil backing (T), sufficient connection of the voltage source to such a layer may also be achieved without any protrusion.

[0266] According to an embodiment, the backing (T) is preferably a conductive backing. In other words, the material of the backing is not particularly limited but preferably electrically conductive. For example, the conductive backing (T) may be a metalized-polymer film, preferably a Sn-PET. A metalized backing usually comprises a polymer film (e.g., PET) coated with metal particles on one or both sides. For example, silver nanowires or conductive paint spray may be used, optionally together with a conductive primer. By applying this metal particle coating to a non-conductive polymer substrate, electrical conductivity may be achieved, making the metalized backing an alternative to purely metallic conductive materials such as steel. Poly-3, 4-ethylendioxythiophen indium tin oxide (PEDOT-ITO)-coated PET, PEDOT-coated metalized PET, PEDOT:PSS or Tos primed PET, CNT-coated PET or other chemically coated (e.g., chromate coated) metalized PET films can be used as an alternative to a metalized PET. The use of a chemically coated or a metal-free conductive backing such as a conductive carbon-coated or intrinsically conductive polymer film is beneficial to prevent the risk of corrosion of a metal-based backing. Primed PET means a PET film coated with a thin acrylic adhesive layer to enhance the anchorage of the PEDOT:PSS layer to the PET film.

[0267] In order to produce such adhesive as transfer tapes, the adhesive composition obtainable as set out above is advantageously coated in the desired layer thickness onto a temporary carrier (made in particular from anti-adhesive and / or anti-adhesively furnished materials, known interchangeably as liner materials, release materials or release liners, such as siliconized papers and polymer films. In principle, it is possible here to use all release materials that are suitable for polyacrylate PSAs. Particularly preferred for use are release liners with a PET carrier core.

[0268] It is also possible to use two clear release liners for such transfer adhesive tapes, wherein both release liners differ in their release forces, one liner has a tight release (known as tight liner) and the other has an easy release (known as easy liner), e.g., a siliconized PET liner.

[0269] According to preferred embodiments, in order to obtain an adhesive transfer tape of the present invention, such as shown in FIGs. 1, 2 and 3, the liquid electrolyte or adhesive precursor adhesive may be coated and then cured i.e., via UV web polymerization or curing between two release liners.

[0270] According to further preferred embodiments, in order to obtain a single-layered, single-sided adhesive tape of the present invention, such as shown in FIGs. 4 and 5, the adhesive is directly coated between a backing (T) and an easy-release liner and then subsequently cured. Where in FIG. 6, liquid electrolyte adhesive is coated on (T), covered with easy liner, and then cured to get the (C) of adhesive layer, and then liquid electrolyte adhesive composition (D) was coated after removal of easy liner and covered with another easy liner and cured to get the (D) of adhesive layer.

[0271] According to further preferred embodiments, in order to obtain a single layered, double-sided adhesive tape of the present invention, such as shown in FIG. 7, both sides of the backing (T) are coated with the liquid electrolyte adhesive (C) and (D) (where both are electro-responsive adhesives) and cover with easy release liners and then cured.

[0272] (a) TWO ELECTRICALLY CONDUCTIVE SURFACES (E.G., TWO SUBSTRATES OR ONE SUBSTRATE AND ONE BACKING)

[0273] To construct a device according to one embodiment of the present invention, an electro-responsive adhesive (FIG.s 1 to 7) is placed between two electrically conductive surfaces (FIG.s 8 to 11). Electrically conductive surfaces can either be two adherends or one adherend, and one backing. The adherend refers to the target substrate where the electro-responsive adhesive is applied, while the backing serves as the support layer for the adhesive. In the case of single- or double-sided tapes, a backing (denoted as (T) in the description) is required. However, for a transfer tape, no backing is necessary, as the tape is positioned directly between two conductive adherends.

[0274] Not every adherend may be suitable for that, as electrical conductivity may be required in case the electric stimulus for increasing adhesion strength cannot be provided differently. Examples of electrically conductive adherends include but are not limited to copper foil, stainless steel plate, aluminum substrate or foil, gold-coated surfaces, silver-coated substrates, nickel plating, titanium, ITO-coated glass, carbon- coated films, graphene films, metal-coated plastics, chromium-coated substrates, zinc-plated surfaces, conductive polymer coated film (e.g. PEDOT:PSS or Tos), tin-plated surfaces, silicon wafers with conductive coatings, and conductive carbon fiber composite substrates. From the examples, it is also clear that nonconductive substrates can also be used once coated with an electrically conductive layer with a higher conductive and smooth surface.

[0275] Preferred adherends or backing for the present invention are those that have smooth surfaces with better oxidation resistance and are more electrically conductive. Examples include stainless steel plates or silver- coated plastic substrates, but Sn-PET, AI-PET, or conductive polymer coated films e.g. PEDOT:PSS or Tos- primer-PET is preferred as conductive backing for the tape.

[0276] (b) APPLICATION OF ELECTRIC STIMULI IN DIFFERENT POLARITIES AND TIME SCALES WITH RESPECT TO THE CONDUCTIVE SURFACES

[0277] The bonding strength of the adhesive tape in the adhesive devices (e.g. FIG.s 8-11) can be adjusted by applying electric stimuli (electromotive forces) with varying polarities and durations. The electromotive force may consist of DC, AC, or pulsed voltages or current application. Preferred applied voltage is typically between 5 and 100 V, more preferably 10 to 50 V, and most preferably 10 to 30 V and with times range from 30 seconds to 50 minutes, more preferably 30 seconds to 30 minutes, and most preferably 30 seconds to 10 minutes.

[0278] In the configuration shown in FIG. 8, bonding strength increases (as confirmed by Test A) when substrate (SI) is connected to the negative terminal and backing (T) to the positive terminal of a DC power source. Applying a DC voltage enhances the bonding on the negative voltage side, leading to strong adhesion between adhesive (C) and substrate (SI).

[0279] Similar behavior can be observed for FIG. 9 setup with adhesive D; however, there the connection is different: substrate (SI) to positive and backing (T) to the negative side of the DC voltage source. The bonding strength increases to the positive side where a voltage is applied, resulting in strong bonding between D of the adhesive and (SI) of the substrate.

[0280] Adhesive devices constructed using either a double-layered transfer tape or a single-layered double-sided tape, as illustrated in FIG.s 10 and 11, can be used to bond two electrically conductive substrates.

[0281] In FIG 10, applying a negative DC voltage to substrate (SI) and a positive DC voltage to substrate (S2) results in a twofold or greater increase in bonding strength, compared to when no voltage is applied.

[0282] In FIG 11, applying a negative DC voltage to substrate SI and a positive voltage to backing (T) (next to adhesive layer (C)), and simultaneously applying a positive voltage to substrate (S2) and a negative voltage to its adjacent backing (T) (next to adhesive layer (D)), results in an increase in bonding strength, effectively joining substrates (SI) and (S2). The voltage level and duration play a key role in the bonding performance. It was observed that extending the voltage level and application time mostly leads to an increase in bonding strength, as confirmed by Test A.

[0283] The present invention relates to the use of the adhesive tape for bonding in the following applications: (i) between different metal surfaces or substrates coated with conductive materials where rapid development of final bonding strength is required; (ii) precise alignment and adjustable placement during assembly; (iii) sealing applications; (iv) situations requiring high bonding strength without the use of heat, light, or significant pressure; (v) sensing applications; (vi) consumer electronics; (vii) electronic packaging; (viii) semi-structural bonding applications; (ix) microelectronics; (x) battery mounting in electric vehicles or mobile devices; (xi) mounting of cell phone back covers; (xii) biomedical applications; (xiii) microfabrication, such as the transfer and positioning of small components; (xiv) applications requiring environmental or structural adaptability, including adjustment to surface conditions or structural changes; (xv) smart wearable electronics, such as health monitoring systems; (xvi) optoelectronics, for example, bonding of camera modules; and (xvii) printing plate mounting on printing sleeves in flexoprint processes.

[0284] METHOD and SYSTEM

[0285] The present invention also pertains to a method of increasing the adhesive strength of an adhesive device as defined herein claims, the method comprising the application of one, two or more electric stimuli for increasing the adhesive strength of the adhesive.

[0286] The one or more electric stimuli may have a voltage of 1 to 50 V and / or a duration of 1 second to 30 minutes, preferably 1 to 20 V, such as 2 to 10 Volt. 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. The program (software) may be stored in a computer (RAM or ROM) or in a data storage device such as a CD, a USB storage of flash storage, and may define certain conditions for applying the electric stimulus, e.g. related to time or pre-defined conditions, such as a signal from a sensor. The program may also include different sets of conditions are instructions that trigger the application of an electric stimulus for increasing or decreasing adhesive strength. Such conditions may include a signal from a sensor or an input by a user, optionally in combination with an authenticating mechanism authorizing the use to apply the electric stimulus.

[0287] In certain embodiments, the user or the pre-defined program provides two or more electric stimuli with increasing voltage and / or duration.

[0288] The present invention further pertains 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 system comprising a device as described herein, and a controller that applies an electric stimulus to the device, wherein the controller is operated manually by an operator or follows a pre-defined program.

[0289] EXAMPLES

[0290] 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.

[0291] RAW MATERIALS

[0292] (a) Acrylate monomer (aO):

[0293] - Acrylic acid (AA)

[0294] Acrylate monomer (al):

[0295] - 2-(2-Ethoxyethoxy)ethyl acrylate (EEEA or EDGA)

[0296] Acrylate monomer (a2):

[0297] - N,N-Dimethylacrylamide (DMAA)

[0298] (b) Zwitterionic compounds / monomers

[0299] - 2-(Methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate) (MPC) from TCI

[0300] - 3-[[2-(Methacryloyloxy)ethyl]dimethylammonio]propionate (CBMA) from TCI

[0301] (c) Photoinitiators:

[0302] - 2,2-Dimethoxy-2-phenylacetophenone (Irgacure 651) from Sigma-Aldrich

[0303] - 1-Hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184) from Sigma-Aldrich

[0304] (d) Organic salt (ionic liquids)

[0305] - Ethylammonium nitrate (EAN) from TCI

[0306] - l-Ethyl-3-methylimidazolium ethyl sulfate (EMIM EtS04) from Sigma-Aldrich

[0307] (e) Inorganic salts:

[0308] - Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) from Sigma-Aldrich

[0309] - Sodium chloride from Sigma-Aldrich

[0310] - Lithium triflate (LiOTf) also called: lithium trifluoromethanesulfonate) from Sigma-Aldrich

[0311] - Lithium tetrafluoroborate ( Li BF4) from Sigma-Aldrich

[0312] (f) Additional monomers (a3):

[0313] - 4-Hydroxybutyl acrylate (4-HBA) from TCI

[0314] - N-(2-hydroxyethyl) acrylamide from TCI - 2-Hydroxyethyl) acrylate from TCI

[0315] - Methyl methacrylate from TCI

[0316] (g) Additives (plasticizers, crosslinker and tackifier):

[0317] - Different types of PEGs (PEG 200, PEG 400 and similar kinds)

[0318] - Different types of carbonates as ethylene carbonate (EC), propylene carbonates (PC), vinylene carbonate (VC) and similar kinds

[0319] - PEGDA (460) from Sigma-Aldrich

[0320] - N,N'-methylene bis(acrylamide) and 1,6-hexanediol diacrylate

[0321] - Hercolyn-D

[0322] (h) Electrically conductive substrate / backing:

[0323] - Sn-PET or AI-PET

[0324] - PEDOT:PSS ink from Agfa

[0325] - ASTM steel plate

[0326] EXPERIMENTAL PART 1 - UV POLYMERIZATION

[0327] Example (I) demonstrates the preparation of single-layered, single-sided adhesive tape or adhesive transfer tape of the present invention by means of UV bulk polymerization. Disregarding solvents, the components used give a total of 100 wt %.

[0328] Different adhesive compositions of the invention (Examples 1 to 7) were produced with the successive steps of a) prepolymer preparation, i.e. UV syrup preparation; b) formulation of the liquid electrolyte, i.e., dissolving zwitterionic monomers / compounds, conducting salt, ionic liquid, photoinitiator and or other monomers or additives (plasticizer / crosslinker / tackifier) into the UV syrup; and c) coating and curing of the liquid electrolyte between the Sn-PET or PEDOT:PSS-primer-PET backing and a siliconized PET liner or between two siliconized PET liners. The curing process is related to UV polymerization. See the details below for steps a) to c):

[0329] Step a)

[0330] A mixture with a ratio of 65:35 of EDGA: DMAA (monomer (al'): monomer (a2') 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 N2 for 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 AT = 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. Step b)

[0331] 80 to 90 wt % of the UV syrup from step a) was mixed with the other components as set out in Table 1 below, such as 1 to 5 wt % of zwitterionic monomer (MPC or CBMA), 1 to 10 wt % of conducting salt (NaCI or LiTFSI, or LiFSI or LiOTf), 1 to 10 wt % of one of the ionic liquid (EAN) and 0.055 to 0.15 wt % of Irgacure 184 photoinitiator, 0 to 10 wt % of other acrylate monomers (a3'), such as 4-HBA and 0.1 to 5 wt % plasticizer (PEG 200) or tackifier. The mixture then continuously rolled on a rolling bench until every component had dissolved. The mixtures are referred to as liquid electrolytes when all components are dissolved.

[0332] Step c)

[0333] The liquid electrolyte from step b) was coated with a layer thickness of about 50 to 150 pm between two films, e.g., an Sn-PET or PEDOT:PSS-primer-PET film acting as a backing and a siliconized PET liner. When the liquid electrolyte is coated and cured between two siliconized liners to prepare an adhesive layer, and both liners are removed, an adhesive transfer tape (not comprising backing (T)) is provided. The transfer tape can also be double-layered adhesive tape containing (C) and (D) adhesive. In this case, (C) of adhesive is coated and cured between two siliconized liners, then the easy liner is removed, and (D) of adhesive is coated and cured on the (C) layer of adhesive.

[0334] When the liquid electrolyte is coated on an Sn-PET or PEDOT:PSS-primer-PET backing and covered by a siliconized PET liner and cured, then the siliconized PET liner is removed, a single-layered sided adhesive tape (comprising backing T) is provided.

[0335] Curing was then achieved with irradiation from fluorescent lamps (ACTINIC) with wavelength of 350 to 400 nm (UV-A) at an intensity of ~ 10 mW / cm2at the residence time in the irradiation tunnel being 250 to 500 seconds. This corresponds to a UV dose from 2500 to about 5000 mWs / cm2. Table 1 below presents the various adhesive compositions and the corresponding tapes, labeled as adhesive (C) and adhesive (D).

[0336] Table 1: Adhesive tape compositions of examples 1 to 7. Example (II) demonstrates the preparation of several adhesive tapes of the present invention following sequences:

[0337] (i) Preparation of several adhesive precursors

[0338] (ii) Coating and curing of the precursors

[0339] (i) Preparation of adhesive precursors: a polymerizable mixture was prepared in a glass reactor by mixing 40-70 wt% acrylic acid, or 2-hydroxyethyl methacrylate, or 40-70 wt% of a 60:40 mixture of acrylic acid and methyl methacrylate; 0.098-2 wt% N,N'-methylene bis(acrylamide) or 1,6-hexanediol diacrylate as a covalent crosslinker; and 0.071-1 wt% 2-hydroxy-l-[4-(hydroxyethoxy)phenyl]-2-methyl-l-propanone (Irgacure 2959) or 1-hydroxycyclohexyl phenyl ketone (Irgacure 184) as a photoinitiator, in 30-70 wt% of an ionic liquid (e.g. l-ethyl-3-methylimidazolium ethyl sulfate or l-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) as solvent. The solution was degassed by purging with Nzunder stirring for 30 min and then irradiated with UV light at 365 nm with an intensity of 0.5-5 mW / cm2. The solution was kept under constant stirring and polymerization continued. The UV lamp was switched off when the reaction temperature in the glass reactor increased by AT = 5-10 °C. The resulting adhesive precursor was cooled and stored in the absence of light. Depending on the tape formulation, additional monomers, crosslinkers and initiator or additives like Si-NP (1-30 wt%) could be incorporated into the adhesive precursor to improve the mechanical properties of the final tape.

[0340] (ii) Coating and curing of the precursors: the viscous precursors from step (i) were coated between two siliconized PET release liners (RF02 and RF12) at a thickness of 100-1000 pm using a doctor blade, followed by curing under a UV-A lamp (365 nm, 10 mW / cm2) for 5-60 min, corresponding to a total dose of 3,000-36,000 mW-s / cm2. During curing, the precursor underwent polymerization and crosslinking, forming the tape of the present invention. After removing both liners, a free-standing transfer tape was obtained. For single-sided or double-sided tape designs, the precursor solution was coated with a doctor blade onto an electrically conductive backing (e.g. metal foil or metalized PET e.g. Sn-PET or PEDOT:PSS- primer-PET). The exposed side of the precursor solution was then covered with a siliconized release liner (RF02), and the assembly was UV-cured as described above. A double-sided tape was prepared by additionally coating the opposite side of the conductive backing with the same precursor solution, followed by UV curing. Once the tape was prepared as described in sequence (ii), it was laminated onto electrically conductive substrates [e.g. ASTM steel plate]. For transfer and double-sided tapes, lamination was done between two ASTM steel plates, while for single-sided tapes it was applied to one ASTM steel plate. The lamination was carried out in a way that allowed connection of a DC voltage source to the device, specifically to the electrically conductive substrates, or to one substrate together with the conductive backing^ EXPERIMENTAL PART 2 - BONDING EXPERIMENT

[0341] A single-layered, single-sided adhesive tape [table 1] (100 mm long and 20 mm wide) was laminated onto an ASTM steel plate (similar construction as shown in FIG. 8 and 9) by gently applying hand pressure with a lamination squeegee, after removing the siliconized PET release liner. The other side of the adhesive tape already has Sn-PET or PEDOT:PSS-primer-PET as backing. The entire setup was then pressed by rolling it over five times back and forth using a 4 kg roller.

[0342] For the adhesive device of [T-D-Sl: FIG. 9], positive voltage was applied to SI (substrate) and negative to T (backing). On the other hand, negative voltage was applied to SI (substrate) and positive to T (backing) for the device of [T-C-Sl: FIG. 8], The applied voltage was in the range of 10 to 20 V for 1 to 2 min. After that, peel adhesion was measured following Test A, but with the DC voltage source cables disconnected from the substrates. Peel adhesion values are mentioned in Table 2; without voltage application, peel adhesions are in the range of 2 to 6.4 N / cm depending upon the thickness of the adhesive layer, but reach up to 10.5 N / cm after voltage application, confirming the increase of bonding strength. Peel values mentioned in Table 2 are the average of 2 individual measurements. Two separate measurements under identical conditions (same dwelling time): one without applied voltage and the other with applied voltage were done for each sample.

[0343] TEST METHODS

[0344] 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 pm to 150 pm.

[0345] Test A: Peel Adhesion

[0346] A single-layered, single-sided adhesive tape [FIGs 4 and 5, adhesive C or D] was cut with a width of 20 mm and a length of 150 mm. The adhesive tape was then laminated on a cleaned (using acetone after removing the protective film) ASTM steel plate upon removal of the siliconized PET liner. The other side of the adhesive tape was provided with an Sn-PET or PEDOT:PSS-primer-PET backing. Then the whole setup was pressed by rolling back and forth over five times using a 4 kg roller.

[0347] The setup was then vertically hooked to the bottom holder of a tensile testing instrument (ZwickRoell Z020), and the Sn-PET or PEDOT:PSS-primer-PET backing was attached to the upper holder of the instrument.

[0348] For peel adhesion measurement, the Sn-PET or PEDOT:PSS-primer-PET backing 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 steel substrate. The values reported here are the average of three individual measurements and denoted as "Initial bonding (no voltage)".

[0349] Test B: Ionic Conductivity

[0350] The ionic conductivity, more specifically DC conductivity, was measured by EIS (Electrochemical Impedance Spectroscopy). It was extracted from the log-log plot of the real part of the AC conductivity versus angular frequency by extrapolating the plateau region to the zero-frequency using the Dyre fit function (an empirical model describing charge transport 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, either single layered or double layered (no backing) 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. The measured temperature was 25°C.

[0351] Tab e 2: Results for the adhesive tapes of the present invention, examples 1 to 7.

Claims

Claims1. A device comprising an adhesive, wherein the adhesive strength of the adhesive can be increased by an electric stimulus from an initial state, AS,, to a bonded state, AS^, wherein AS j represents the adhesive strength in the initial state prior to application of an electric stimulus, andASb represents the adhesive strength after one or more electric stimuli for increasing bonding strength has been applied, and wherein in Test A of peel strengthASj is in the range of up to 2 N / cm, andASb is 2.1 N / cm or higher, such as 10 N / cm or higher such as 25 N / cm or higher.

2. The device according to claim 1, wherein in Test A of peel strength, ASb is in the range of 2.1 N / cm or higher, such as 5.0 N / cm or higher, 7.0 N / cm or higher, 9.0 N / cm higher, 17 N / cm or higher, or 20 N / cm or higher or 25 N / cm or higher.

3. The device according to claim 1 or 2, which satisfies the condition ASb / ASj = 1.2 or greater, preferably 1.5 or greater, such as 2 or greater, such as 5 or greater or 10 or greater, 11.0 or greater, preferably as 13 or greater, 15 or greater for Test A of peel strength.

4. A device according to any claims 1 to 3, wherein the adhesive comprises(a) a polymer network that is formed by at least one of a single polymer (aO), which is a homopolymer or a random copolymer, two or more different polymers, comprising at least a first polymer (al) and a second polymer (a2), and a block copolymer that comprises at least a first segment (al') formed by repeating units derived from at least one first monomer and a second segment (a2') formed from at least one second monomer, the block copolymer optionally comprising one or more further segments,(b) one or more of an ionic liquid (bl), an inorganic salt that is no ionic liquid (b2), and / or a linear polymer having oxyethylene or oxypropylene units.

5. A device according to any claims 1 to 4 wherein the component (b) is present in a total amount of 0.1 to 80 % by weight, relative to the total weight of the adhesive.

6. A device according to any claims 1 to 5 wherein the component (b) is present in domains surrounded by the polymer network (a), the domains having an average size of 1 to 5,000 nm.

7. A device according to any claims 1 to 6 wherein the adhesive does not exhibit a glass transition temperature or exhibits a glass transition temperature of 20 °C or lower, such as 10 °C or lower.

8. A device according to any claims 1 to 7 wherein at least one, and preferably both, of the first polymer (al) and the second polymer (a2), respectively one or both of the repeating units forming the first (al') respectively second segment (a2') of the block copolymer, comprise a repeating unit containing one or more of O, N, S, Si, P, and B atoms in a side chain or main chain of the polymer.

9. A device according to any claims 1 to 8, wherein the adhesive comprises one or more electro- responsive compounds selected from the group consisting of polymerizable zwitterionic monomers and / or non-polymerizable zwitterionic compounds, preferably one or more zwitterionic monomers.

10. A device according to any claims 1 to 9, wherein the adhesive comprises nanoparticles, wherein the nanoparticles may optionally be surface functionalized, and wherein preferably the shape of the nanoparticles or surface functionalized nanoparticles may be spherical or non- spherical, wherein the non-spherical particles may take any form, including but not limited to rods, wires, tubes, cubes, prisms, disks, or branched structures like tetrapods, and / or wherein the nanoparticles or surface functionalized nanoparticles have an average diameter of from 1 to 1,000 nm, expressed as median value D5Q in a particle size distribution determined by laser diffraction.

11. A device according to any claims 1 to 10, wherein the adhesion strength of the adhesive having the adhesive strength AS j and / or AS^ can be decreased by an electric stimulus.

12. The device according to any of claims 1 to 11 wherein the one or more electric stimuli are each a direct current (DC) voltage of 1 to 50 V, preferably 1 to 10 V, for a duration of 30 minutes or less, preferably 10 minutes or less, and / or wherein the number of electric stimuli is one, two or three, preferably one or two.

13. The device according to any of claims 1 to 12 wherein the device is in the form of an adhesive tape comprising a backing and one or more adhesive layer(s) each comprising an adhesive, wherein at least one of the one or more adhesive layers is formed by an adhesive as defined in any one of the preceding claims, and wherein preferably the backing is an electrically conductive backing, 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 is according to any of the preceding claims, wherein the device further comprises an electrically conductive backing in contact with the adhesive.

15. The device according to any of the preceding claims, wherein the adhesive is a pressure sensitive adhesive and / or wherein the adhesive has ionic conductivity, preferably in the range of IO10S / cmto 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(trifluoromethanesulfonyl)imide, trifluoromethanesulfonate, dicyanamide, nitrate, chloride, acetate, hydrogen sulfate, and methanesulfonate.

17. The device according to claims 4 and 15, wherein the one or more inorganic salts, 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).

18. The device according to any of claims 1 to 17, wherein the adhesive, which preferably is a pressuresensitive 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, water, other ionic species, and organic or inorganic particles, such as electrically polarizable particles.

19. A method of increasing the adhesive strength of an adhesive device as defined in any of the preceding claims, the method comprising the application of one, two or more electric stimuli for increasing the adhesive strength of the adhesive.

20. 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 a device as defined in any of claims 1 to 18, and a controller that applies an electric stimulus to the device, wherein the controller is operated manually by an operator or follows a pre-defined program.

Images