Electrochemically debondable thiol-catechol functionality (TCC)-reversible adhesive system, and use

Abstract

The invention relates to an electrochemically debondable thiol-catechol functionality (TCC)-reversible adhesive system, wherein the reversible adhesive system comprises adhesive system components which react with one another to form a thiol-catechol functionality, and wherein the cured reversible adhesive system is debonded by electrochemical oxidation of the TCC catechols to form TCC quinones, and is characterised in that the reversible adhesive system is in the form of a two-component adhesive system, wherein the first adhesive system component is formed of bi- and / or trifunctional quinone compounds or mixtures of these components, and the second adhesive system component is formed of multithiols and / or mixtures which react with one another in a Michael-like reaction or general thiol-quinone addition, the thiol-catechol functionalities formed are present in the polymer backbone of the adhesive system, the reversible adhesive system comprises additives in the form of at least one conductive particle filler and at least one ionic liquid, and controlled debonding can be carried out by means of electrochemical switching by: switching off the adhesive strength of the reversible adhesive system until separation takes place, or reducing the adhesive strength of the reversible adhesive system up to the point of separability. The invention also relates to the use of the reversible adhesive system.

Description

[0001] Electrochemically detachable thiol catechol functionality (TCC) reversible adhesive system and use

[0002] The invention relates to an electrochemically debondable thiol catechol (TCC)-functionality reversible adhesive system, wherein the reversible adhesive system comprises adhesive system components that react with each other to form a thiol catechol functionality, and wherein the cured reversible adhesive system is debonded by electrochemical oxidation of the TCC catechols to TCC quinones, and an associated use.

[0003] Strong and durable structural adhesives are essential for modern production lines, but pose a challenge at the end of a product's life cycle, particularly for the recycling or repair of microelectronic devices. Effective methods for breaking such adhesives are increasingly in demand, and several triggers have already been investigated, including heat, light, chemical transformations, and electricity.

[0004] The class of TCC adhesives utilizes the potency, performance, and robustness of the interactive key sites of catechol functionalities and offers an interesting mechanism for detachment by oxidation of catechols to quinones.

[0005] The state of the art shows various works dealing with TCC adhesives and catechol adhesives, as well as the possibilities of removing them.

[0006] Lee H. et al. describe the different adhesive properties of catechol and quinone functionalities in detail in “Single-molecule mechanics of mussel adhesion”. Proc Natl Acad Sei USA. 2006; 103(35): 12999-3003. doi: 10.1073 / pnas.0605552103.

[0007] Akram Bhuiyan MS. et al. report the electrochemical application of catechol-containing adhesives underwater in “In Situ Deactivation of Catechol-Containing Adhesive Using Electrochemistry”. J Am Chem Soc. 2020; 142(10):4631-4638. doi: 10.1021 / jacs.9b11266.

[0008] More recently, Neubert TJ et al. published a report in “Redox-Triggered Debonding of Mussel-Inspired Pressure Sensitive Adhesives: Improving Efficiency Through Functional Design”.

[0009] Angewandte Chemie International Edition 2024; 63(44). doi: 10.1002 / anie.202408441 demonstrates debonding-on-demand for TCC-containing adhesives, using a chemical oxidizing agent as a trigger, which achieved a reduction in adhesive strength of up to 99% in a biohybrid DiDopa-TCC pressure-sensitive adhesive.

[0010] While the use of a chemical oxidizing agent has the advantage of providing triggers with suitable reactivity at specific times, the rigid adhesive surface of structural adhesives could complicate trigger accessibility. The electrochemical conversion of, for example, diDopa catechols to bisquinones occurs in a fairly controlled manner, as described in the previously mentioned "Redox-Triggered Debonding of Mussel-Inspired Pressure Sensitive Adhesives: Improving Efficiency Through Functional Design" by Neubert T. J. et al. (Angewandte Chemie International Edition 2024; 63(44). doi: 10.1002 / anie.202408441). This makes electrochemically triggered debonding of such adhesives via the oxidation mechanism a promising and ideal process for microelectronic devices, although it has not yet been demonstrated.

[0011] Electrically and electrochemically degradable structural adhesives are typically exposed to more extreme conditions during deactivation, often leading to superimposed decomposition reactions and making it difficult to carry out defined chemical transformations. These more extreme conditions are described, for example, in Leijonmarck S. et al. “Electrolytically assisted debonding of adhesives: An experimental investigation”.

[0012] International Journal of Adhesion and Adhesives 2012; 32:39-45. doi:

[0013] 10.1016 / j.ijadhadh.2011.09.003, CaglarS. „Debonding of carbon fiber veil interleaved adhesively bonded GFRP joints via Joule heating“. Composites Part B: Engineering 2022; 230: 109544. doi: 10.1016 / j.compositesb.2021.109544, Lee J. S. et al. ,,Debonding-on-Demand Adhesive Film using Internal Joule Heating Effect of the Steel-Aramid Braided Reinforcement“. Composite Structures 2022; 286(13): 115290. doi: 10.1016 / j.compstruct.2022.115290, Wu M. et al. „Interfacial Electrochemistry-Induced Detachable Adhesives with Ultra-High Bonding strentgh and Detaching Efficiency“. ACS Applied Materials & Interfaces 2022; 14(36): 41456-41467. doi: 10.1021 / acsami.2c12553, Inutsuka M. etal. „Electrical properties of adhesives designed for smart debonding by a pulsed discharge method“. The Journal of Adhesion 2023; 99(13): 1996-2010. doi: 10.1080 / 00218464.2023.2167600, Sun S. et al. „Environmental reliability and failure mechanism of ionic conductive adhesives“. Polymer 2023; 283: 126226. doi:

[0014] 10.1016 / j.polymer.2023.126226, Wei Y. et al. “Electrically Detaching Behavior and Mechanism of Ionic Conductive Adhesives”. Chinese Journal of Polymer Science 2023; 41: 1142-1154, doi: 10.1007 / s10118-023-2913-7, As Y. et al. “Electrically Detachable Ionic Conductive Epoxy Adhesives with High Bonding Strength”. ACS Applied Polymer Materials 2023; 5(9). doi:

[0015] 10.1021 / acsapm.3c01251 and Anduix-Canto et al. "Unraveling the Mechanism of Electrically Induced Adhesive Debonding: A Spectro-Microscopic Study". Advanced Materials Interfaces 2022; 9: 2101447 doi: 10.1002 / admi.202101447.

[0016] However, studies on soft, catechol-containing adhesives have clearly shown that the catechol-quinone equilibrium can be used for debonding applications.

[0017] Further publications concerning the debonding of electrically and electrochemically degradable structural adhesives in general can be found below. For example, US 2021 / 0002516 A1, EP 3591 020 A1, and EP 4194198 A1 disclose electrically removable adhesive films consisting of an acrylate-based adhesive with ionic liquids and (earth) alkali metal salts, applied to an electrically conductive layer. Ionic liquids are also used in adhesive manufacturing and selective debonding in CN 11630128 A.

[0018] From TW 201741146 A, the electrical unbonding of PU hot melt adhesives by using conductive inks is known.

[0019] EP 4050040 A1 and US 2022 / 0411673 disclose curable one-component, and WO 2021 / 115774 A1, EP 3835381 A1, and WO 2022 / 207300 A1 disclose curable two-component debonding adhesive compositions. The compositions are based on (meth)acrylate monomers (EP 4050040 A1, EP 3835381 A1), epoxy resin (US 2022 / 0411673, WO 2021 / 115774 A1), and polyols (WO 2022 / 207300 A1), respectively. Non-polymerizable electrolytes are used in EP 4050040 A1, US 2022 / 0411673, EP 3835381 A1 and WO 2022 / 207300 A1. WO 2021 / 115774 A1 uses a polymerizable ionic liquid.

[0020] Furthermore, WO 2021 / 259594 A1 describes a curable and electrochemically removable adhesive composition comprising a) at least one ethylene unsaturated non-ionic monomer, b) at least one polymerizable ionic compound and c) at least one radical initiator.

[0021] US 7,465,492 B2 describes an electrochemically bondable composition having a matrix functionality comprising a monomer from the group of (meth)acrylic acids and an electrolyte.

[0022] The problems with the prior art are essentially that while the use of chemical oxidizing agents to remove TCC adhesives provides triggers with suitable reactivity at certain times, the rigid adhesive surface of structural adhesives makes the accessibility of the trigger difficult.

[0023] Other existing solutions include the use of one of the components / additives selected from ionic liquids (IL), carbon particles, especially carbon black (CB) or catechols, as an admixture to the adhesive to be removed, requiring the application of high currents / voltages and / or slow debonding effects.

[0024] The present invention is based on several problems.

[0025] One object of the invention is to provide a TCC adhesive / a TCC adhesive system with which a reduction in the adhesive strength of the TCC adhesive can be achieved under electrochemically gentler conditions than before (use of lower currents / voltages) (reversible adhesive system).

[0026] Another task is to electrochemically reduce the adhesive strength of a TCC adhesive on a substrate, preferably on one electrode side, under gentler conditions.

[0027] Furthermore, it is an object of the invention to provide a TCC adhesive / a TCC adhesive system with which debonding effects can be achieved within a short time, preferably within minutes.

[0028] These problems are solved with an electrochemically debondable thiol-catechol (TCC)-reversible adhesive system according to the main claim. Furthermore, the solution is also achieved by a use according to the use claim. The electrochemically debondable thiol-catechol (TCC)-reversible adhesive system according to the invention, wherein the reversible adhesive system comprises adhesive system components that react with one another to form a thiol-catechol functionality, and wherein the cured reversible adhesive system is debonded by electrochemical oxidation of the TCC catechols to TCC quinones, is characterized in that

[0029] - the reversible adhesive system is designed as a two-component adhesive system,

[0030] wherein the first adhesive system component is formed from bi- and / or trifunctional quinone compounds or from mixtures of these components and the second adhesive system component is formed from multithiols and / or mixtures which react with each other in a Michael-type reaction or more generally thiol-quinone addition,

[0031] - the formed thiol-catechol functionalities are present in the polymer backbone of the adhesive system,

[0032] - the reversible adhesive system has additives in the form of at least one conductive particle filler and at least one ionic liquid and

[0033] - controlled delamination via electrochemical circuitry through:

[0034] - Deactivation of the adhesive strength of the reversible adhesive system until separation

[0035] or

[0036] - Reduction of the adhesive strength of the reversible adhesive system until separability is feasible.

[0037] The Michael-type addition reaction of thiols and quinones usually proceeds via a nucleophilic attack of the thiol component (thiol / thiolate) on the quinone, but can also proceed at least partially via radical addition mechanisms, whereby in both reaction pathways the thiol-catechol functionality inherent to the adhesive is formed, which is essential as an electrochemically switchable group.

[0038] In accordance with the requirements, sustainable reactive components and additives were used to construct reversible adhesive systems with thiol-catechol functionalities. Spiro-bis(guaiacol), synthesized from sustainable starting chemicals, was oxidized to spiro-bis(quinone) (SBQ), which was also produced from synthesized spiro-bis(catechol). SBQ was combined with multithiol mixtures from a broad range of renewable raw materials. Limonene-based dithiols (LSH), castor oil-based trithiols (COSH), and sunflower oil-based trithiols (SFSH) were used across the entire mixing range in variable ratios (e.g., COSH / LSH / SFSH = 0.6 / 0.3 / 0.0) and mixed with SBQ to create curable formulations.By adding renewable, conductive plant-based carbon (biochar) as well as green ionic liquids, the hardened adhesives became electrochemically addressable, which, at an activation voltage of 9 V, enabled controlled unbonding with a reduction in shear strength of up to 70-80% (e.g., from 9.7 MPa to 2.6 MPa, i.e., by 73%).

[0039] Separation can also be achieved by reducing the adhesive strength, so that actual separation only occurs subsequently, for example, through mechanical action. The mechanical action can be adjusted accordingly to the reduced adhesive strength. The lower the residual adhesive strength, the less force is ultimately required for separation. A defined debonding process occurs. Particularly preferably, the reversible adhesive system can be cured at a temperature between 9 °C and 150 °C, or between 40 °C and 130 °C, or between 90 °C and 120 °C for a duration of between 0.5 h and 48 h, or 5 h and 24 h, or 10 h and 18 h.

[0040] The voltage to be applied for controlled delamination by electrochemical circuitry can be between 0.5 V and 60 V or between 6 V and 24 V or between 8 V and 12 V, and the time period with applied voltage can be between 2 min and 60 min or between 5 min and 30 min or between 10 min and 25 min.

[0041] The conductive particle filler can also be made from conductive carbon particles, carbon nanotubes, carbon black, or mixtures of these components.

[0042] Furthermore, the ionic liquid may contain as cations 1-butyl-3-methylimidazolium and / or 1-butyl-1-methylperidinium and / or 1-ethyl-3-methylimidazolium and / or tetrabutylammonium and / or 1,3-diethylimidazolium or mixtures of these components. Anions may contain hexafluorophosphate and / or bistrifluoromethylsulfonylimide and / or tetrafluoroborate and / or dicyanamide or be formed from 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

[0043] Furthermore, the ionic liquid can be selected from the list or formed from a combination of the list and selected from the list:

[0044] 1-Ethyl-3-methyl-1H-imidazole-3-ium-methylsulfate;

[0045] 1-hexyl-3-methylimidazolium 2-(2-fluoroanilino)pyridinate;

[0046] 1-hexyl-3-methylimidazoliumimide;

[0047] 1-Butyl-1-methylpyrrolidinium 2-(2-fluoranilino)pyridinate;

[0048] 1-Butyl-1-methylpyrrolidiniumimide;

[0049] Trihexyl(tetradecyl)phospholium-2-(2-fluoranilino)-pyridinat;

[0050] Cyclohexyltrimethylammonium-bis(trifluormethylsulfonyl)imid;

[0051] Di(2-hydroxyethyl)ammoniumtrifluoracetat;

[0052] N,N-Dimethyl(2-hydroxyethyl)ammoniumoctanoat;

[0053] Methyltrioctylammonium-bis(trifluormethylsulfonyl)imid;

[0054] N-Ethyl-N,N,N,N-Tetramethylguanidiniumtrifluormethansulfonat;

[0055] Guanidiniumtrifluormethansulfonat;

[0056] 1-Butyl-4-methylpyridiniumbromid;

[0057] 1-Butyl-3-methylpyridiniumtetrafluoroborat;

[0058] 1-Butyl-3-hydroxymethylpyridiniumethylsulfat;

[0059] 1-Butyl-1-methylpyrrolidinium-bis(trifluormethylsulfonyl)imid;

[0060] 1-Butyl-methylpyrrolidinium-tris(pentafluorethyl)trifluorphosphat;

[0061] 3-Methylimidazoliumethylsulfat;

[0062] 1-Ethyl-3-methylimidazoliumchlorid;

[0063] 1-Ethyl-3-ethyl-methylimidazoliumbromid;

[0064] 1-Butyl-3-methylimidazoliumchlorid;

[0065] 1-Hexyl-3-methylimidazoliumchlorid;

[0066] 1-Octyl-3-methylimidazoliumchlorid;

[0067] 1-Methyl-3-octylimidazoliumchlorid;

[0068] 1-Propyl-3-methylimidazoliumiodid;

[0069] 1-Butyl-3-methylimidazoliumtetrafluoroborat;

[0070] 1-Butyl-3-methylimidazoliumtrifluormethansulfonat;

[0071] 1-Butyl-3-methylimidazoliumhexafluorphosphat;

[0072] 1-Ethyl-3-methylimidazoliumtrifluormethansulfonat;

[0073] 1-Butyl-2,3-dimethylimidazoliumtetrafluoroborat;

[0074] 1-Butyl-2,3-dimethylimidazoliumhexafluorphosphat;1-Butylimidazol;

[0075] 1-Methylimidazoliumtetrafluoroborat;

[0076] tetrabutylphosphonium tris(pentafluoroethyl)trifluorophosphate;

[0077] Trihexyl(tetradecyl)phosphonium tetrafluoroborate.

[0078] Both bi- and trifunctional quinone compounds can be used, which are generally pre-synthesized, isolated and used, but can also be produced from the multicatechol precursors by in situ oxidation.

[0079] The degree of functionalization of the thiol compounds used can range from 2 to 4.

[0080] In particular, the reversible adhesive system can be configured to have a quinone / thiol ratio window (Q / T) of Q / T = 1 / 0.3 to 1 / 5.0 or Q / T = 1 / 0.5 to 1 / 1.5 and / or 2 to 25 wt.% or 4 to 10 wt.% of conductive particle filler and / or 0.1 to 25 wt.% or 2 to 10 wt.% of ionic liquid.

[0081] Furthermore, the c[logP] partitioning coefficient of the thiols can cover a range between 0.27 and 29.38 based on the n-octanol-water partitioning coefficient (calculated using Chem3D, version 20.1.1 (PerkinElmer), where the thiols were treated as ethyl thioethers). Accordingly, both hydrophobic and hydrophilic thiol components and any mixtures thereof can be used.

[0082] The molecular weight of thiol compounds can also range from 180 to 1700 g / mol.

[0083] Furthermore, the aforementioned thiols, including mixtures thereof, can be used as lightly cross-linked statistical prepolymers, which expands the molecular weight range and statistically increases the number of thiol groups to multithiols in the range of 5-80.

[0084] Furthermore, the electrochemical circuit can be used to control the unbonding and deactivation or reduction of the adhesive strength of the adhesive system, with a reduced adhesive force of 25% to 90% or with a reduced adhesive force of at least 50% or, in particular, 50% to 75%.

[0085] Furthermore, a controlled unbonding and deactivation of the adhesive strength of the adhesive system with a pure adhesive system failure pattern can be achieved via the electrochemical circuit.

[0086] The electrochemical circuit can also be used to create a controlled unbonding and deactivation of the adhesive strength of the adhesive system on one electrode side.

[0087] The reversible adhesive system according to the invention can be used as an adhesive system that can be removed from a substrate and / or as an adhesive system that can be removed from a substrate, wherein the substrate comprises aluminium and / or steel and / or indium tin oxide-coated glass and / or carbon-doped polylactide and / or conductive surfaces such as metals and / or conductive coatings and / or conductive plastics and / or conductively impregnated plastics and / or conductive glasses and / or ITO and / or applied conductive layers and / or printed conductive inks and / or conductive adhesive tapes.

[0088] Overall, it can be stated that any electrically conductive materials or conductively modified non-conductors can be used as electrically detachable materials, ranging from glass to metals to conductive plastics.

[0089] Possible uses of the reversible adhesive system can be found.

[0090] - in the electronics sector,

[0091] - in the automotive sector,

[0092] - when bonding display glass to frame,

[0093] - when gluing batteries into devices and

[0094] - during the bonding of battery cells into battery packs.

[0095] With the TCC reversible adhesive system according to the invention, it becomes possible to switch the thiol-catechol functionalities to controlled oxidative mode by combining them with conductive particle fillers and ionic liquids. This leads to a reduction in adhesive strength, favored on one electrode side under gentler conditions. Controlled debonding and deactivation of the adhesive system's bond strength is possible within minutes.

[0096] The electrochemical currents are conducted by the conductive carbon particles into the adhesive bulk, so that catechol oxidation does not only occur locally at the electrode-adhesive interface, but is extended into the bulk. The ionic liquid provides the necessary ionic conductivity, reduces charging effects, controls the fracture pattern, and participates in the reductive half-cell reactions. This enables efficient transfer of the electrochemical oxidation of catechol to quinone in the TCC Reversible Adhesive System, which quickly (within 2-5 minutes) at low voltages (as low as 9 V) leads to clean, one-sided debonding (weakening of adhesion) of the adhesive system.Unlike other catechol-containing adhesives, the electrochemically reversible thiol-catechol (TCC) adhesive system according to the invention features catechol functionalities in the polymer backbone of the adhesive system, rather than in the side chains or as non-polymeric / low-molecular-weight additives. This results in improved adhesion to a substrate and improved cohesion within the adhesive system itself. Upon deactivation, these adhesion and cohesion properties are altered by the oxidation of the catechols to quinones, and the adhesive strength of the system to the substrate decreases significantly. Compared to catechol side-chain functionalities, TCC main-chain functionalities are considerably less susceptible to oxidative crosslinking ("radical dicatechol formation"), which occurs as a known side reaction (e.g., didopa formation) in catechol-containing polymers and additives and can counteract reversibility.

[0097] The invention is described below with reference to the accompanying illustrations in the description of the figures, which are intended to explain the invention and are not to be considered limiting.

[0098] A symmetrical connection of conductive aluminum substrates was used to apply electrical voltage and current.

[0099] They show:

[0100] Figure 1 shows an exemplary representation of the structural formulas of exemplary quinone components and exemplary thiol components of the electrochemically releasable thiol-catechol (TCC) reversible adhesive system according to the invention;

[0101] Figure 2 shows an exemplary graphical representation of the shear strength of a TQ / ETTMP700 adhesive system with and without conductive particle filler and ionic liquid on a substrate compared to a commercially available epoxy adhesive with the same additives in the form of a bar chart;

[0102] Figure 3 shows an exemplary graphical representation of the fracture patterns of the differently formulated TQ / ETTMP700 adhesive systems on a substrate according to Fig. 2; Figure 4 shows an exemplary graphical representation of cyclic voltamograms with two electrodes of an exemplary TQ / ETTMP700 adhesive system according to the invention and a commercially available epoxy adhesive with the same additives;

[0103] Figure 5 shows an exemplary FTIR analysis of an exemplary TQ / ETTMP700 adhesive system according to the invention before and after applying a voltage of 9 V for 30 min;

[0104] Figure 6 shows an exemplary schematic representation of the electrochemical debonding concept in an exemplary TQ / ETTMP700 adhesive system according to the invention:

[0105] Figure 7 shows a comparison of the placement of catechol functionalities in a thiol-catechol functionality (TCC) reversible adhesive system (left) and a conventional catechol adhesive system (right), and Figure 8 shows a comparison of the adhesion and cohesion effect of catechol functionalities in a thiol-catechol functionality (TCC) reversible adhesive system (left) and a conventional catechol adhesive system (right).

[0106] Fig. 1 shows an exemplary representation of the structural formulas of exemplary quinone components and exemplary thiol components of the electrochemically releasable thiol-catechol (TCC) reversible adhesive system 2 according to the invention, configured as a two-component adhesive system. Possible quinone components include triquinones such as TQ (4,4',4-(ethane-1,1,1-triyl)tris(cyclohexa-3,5-diene-1,2-dione)) and dichinones such as sBQ (3,3,3',3'-tetramethyl-2,2',3,3'-tetrahydro-1,T-spirobi[1 / 7-indene]-5,5',6,6'tetraone) and BQA (4,4'-(propane-2,2'-diyl)bis(cyclohexa-3,5-diene-1,2-dione)).Possible thiol components include dithiols such as EDET (2,2'-(ethane-1,2-diylbis(oxy))bis(ethane-1-thiol)) and LSH (limolen-based dithiol; 5-(1-mercaptopropan-2-yl)-2-methylcyclohexane-1-thiol), trithiols such as TTMP (1,1,1-tris(hydroxymethyl)ethane tris(3-mercaptopropionate)), ETTMP700 (ethoxylated trimethylolpropane tri(3-mercaptopropionate), Mn = 700 g / mol), ETTMP1300 (ethoxylated trimethylolpropane tri(3-mercaptopropionate), Mn = 1300 g / mol), COSH (castor oil-based trithiol; propane-1,2,3-triyl) (9Z,9'Z,9"Z)-tris(12-((3-mercaptopropanoyl)oxy)octadec-9-enoate)) and FLSH (sunflower oil-based trithiol; 18, 18'-((3-((9-mercaptoheptadecyl)oxy)propan-1,2-diyl)bis(oxy))bis(octadecane-9-thiol)) and tetrathiols such as GPM800 (pentaerythritol-tetrakis(propylene-2-mercaptoethan-1-ol)) as well as slightly crosslinked precondensates derived from the aforementioned thiols, which were statistically prepolymerized to multithiols.

[0107] Figures 2 to 6 below illustrate the electrochemical unbonding of the adhesive system trimere ortho-quinones (TQ) / ethoxylated trimethylolpropane tri (3-mercapto-propionate), Mn = 700 g / mol (ETTMP700). This is a specific example and is not to be considered limiting to the entirety of the invention. For the formation of a TCC reversible adhesive system 2 according to the invention, adhesive system components that form mutually adhesive thiol-catechol functionalities 2a, as shown in Figure 1, are generally suitable.

[0108] Figure 2 shows an exemplary graphical representation of the shear strength of a TQ / ETTMP700 adhesive system with and without conductive particle filler in the form of conductive carbon particles (CB) 3 and ionic liquid (IL) 4 on a substrate 1, compared to a commercially available epoxy adhesive with the same additives, in the form of a bar chart. The shear strength of these adhesive systems after storage at 200 °C for 30 minutes is also shown graphically.

[0109] To overcome the insulating properties of the two-component base adhesive system, conductive additives are required, as shown in the diagram. Through intensive iterative optimization, a formulation with remarkable bonding and release performance was developed. For this purpose, the two-component base adhesive system TQ / ETTMP7002, with a Q / T ratio of 1 / 0.8, is modified with 5 wt% conductive carbon / black (CB)3 and 5 wt% of an ionic liquid (IL)4, in this embodiment 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM-NTf2). The resulting two-component adhesive system 2 exhibits the following properties: an increased shear strength of 19.6 ± 0.7 MPa and ~20 MPa in overlap shear tests. Release is achieved by applying a constant voltage of 9 V in this example for a period of 30 minutes.This electrochemical circuit 5 leads to a pure adhesive failure at the negative electrode, resulting in a decrease in the original strength of 75%, with the bond breaking at ~5 MPa.

[0110] When analogous tests were carried out with a commercially available 2K epoxy adhesive, it proved to be unaffected by the application of stress before and after the formulation work with CB 3 and / or BMIM-NTf24.

[0111] Furthermore, the unfilled TQ / ETTMP700 adhesive system shows no debonding effects when voltage is applied and no current flows through the adhesive system layer.

[0112] In the absence of conductive carbon 3, the required ionic conductivity is only imparted to the TQ / ETTMP700 adhesive system by the addition of ionic liquid 4, but even the use of up to 30 wt% BMIM-NTf24 is not able to achieve electrochemical release properties.

[0113] This is a surprising effect, as ionic liquids are typically used as sole additives and, in other examples, actively participate in debonding mechanisms through electromigration and / or electrodecomposition. Interestingly, the cured TQ / ETTMP700 / IL formulation exhibits adhesive layer resistances in the MQ range and allows the flow of small currents. This result supports the hypothesis of an undefined dispersion of ionic liquid 4 within the adhesive system matrix, leading to discontinuous conductivity zones.

[0114] In general, ionic conductivity is preferred over electronic conductivity in electrochemical reactions. However, as can be seen from the diagram, the latter is improved independently in a control experiment by adding only conductive carbon 3 to the adhesive system base mixture, resulting in an ohmic resistance in the cured layer. In contrast to the negligible effects of the ionic liquid 4, the addition of 5 wt% conductive carbon s significantly facilitates the electrochemical debonding effects. Besides improving conductivity, adhesives filled with conductive carbon 3 exhibit a low resistance of 100–500 Ω.The application of 9 V for 30 minutes results in an approximately 80% reduction in shear strength from 14.5 ± 1.0 MPa to 2.1 ± 0.2 MPa, which is consistent with the strength reduction observed in the TQ / ETTMP700 adhesive system formulation 2 with the additives conductive carbon 3 and ionic liquid 4.

[0115] Fig. 3 shows an exemplary graphical representation of the fracture patterns of the differently formulated TQ / ETTMP700 adhesive systems on aluminium as substrate 1 according to Fig. 2. After performing a tensile shear test.

[0116] Neither the TQ / ETTMP700 adhesive system without additives nor the TQ / ETTMP700 adhesive system with conductive carbon 3 exhibits sufficient release of the adhesive system from the substrate 1. Only the TQ / ETTMP700 adhesive system 2 with conductive carbon 3 and ionic liquid 4 shows sufficient release of the adhesive system 2 to detach from the substrate 1.

[0117] The fracture patterns shown indicate a non-preferred mixed failure mode, suggesting synergy effects between the two fillers to achieve a clean debonding mechanism.

[0118] The differences in the debonding mechanisms were confirmed by a comparative analysis of the thermal signatures of the debonding process in the TQ / ETTMP700 adhesive system 2 filled with ionic liquid 4 and conductive carbon s and in the TQ / ETTMP700 adhesive system filled with conductive carbon s. IR camera tracking showed that the fully formulated adhesive system 2 became slightly warmer than room temperature during stress application, with peak temperatures of 26 °C, while the control filled with conductive carbon 3 exhibited a significant temperature rise to 75 °C. Given that the bonded aluminum samples 1 can be heated to 200 °C for 30 minutes without a significant decrease in shear strength, thermally induced debonding effects can be ruled out.

[0119] Figure 4 shows an exemplary graphic representation of cyclic voltamograms with two electrodes of an exemplary TQ / ETTMP700 adhesive system 2 according to the invention and a commercially available epoxy adhesive with the same additives.

[0120] The resistance of TQ / ETTMP700 adhesive systems 2 filled with ionic liquid 4 and conductive carbon 3 is only slightly higher (0.5–2 kΩ) than that of adhesive systems filled exclusively with conductive carbon 3. Both adhesive system samples exhibit some similarities. The application of the debonding trigger voltage initially results in high currents, both of which, for safety reasons, are limited to 1 A. Over time, the current decreases significantly, indicating a Faraday current in which the adhesive system layer not only conducts current as a resistance but also consumes current through chemical reactions.

[0121] This is demonstrated by the cyclic voltamograms shown at two electrodes, by measuring the adhesive system films between two aluminum substrates 1. Despite different formulations of the adhesive systems, they exhibit high faradaic currents occurring within a related potential window, suggesting possible redox reactions. Starting at 5 V, the current rises sharply, reaching peak values ​​of approximately 8 V. The electrochemical transformations appear to be irreversible, as inverse scans and subsequent scan cycles do not show currents of this magnitude. Increasing the scan rate reveals a systematic rise in the peak current and peak position, further supporting the faradaic origin of the current.

[0122] The system consisting of epoxy adhesive filled with conductive carbon 3 and ionic liquid 4 is used as a control experiment. The figure shows that in this system there is no electrochemical reaction and no Faraday current.

[0123] This leads to the conclusion that the electrochemical conversion is specifically associated with the TCC reversible adhesive 2 according to the invention. However, the interpretation of cyclic voltamograms with two electrodes in solid films is inherently difficult, since the setup precludes the separation of electrochemical oxidative and reductive half-reactions.

[0124] Fig. 5 shows an exemplary representation of an FTIR analysis of an exemplary TQ / ETTMP700 adhesive system 2 according to the invention before and after applying a voltage of 9 V for 30 min. The ortho-quinone vibration band is at 1664 cm⁻¹. -1 .

[0125] IR spectroscopic tracking of the ungluing process suggests the formation of a quinone species.

[0126] The illustrations clearly show that the transmission changes significantly over time in the region of the ortho-quinone vibration band of the electrochemical circuit.

[0127] Since the excess of quinone in the most efficient adhesive system (TQ / ETTMP700 (1 / 0.8)) 2 makes it difficult to draw a qualitative conclusion regarding the formation of new quinone groups, an alternative adhesive system composition is used for illustrative purposes in the FTIR analysis. A substoichiometric amount of quinones is used to detect a difference in the ortho-quinone vibrational band. A combination of TQ / ETTMP700 (1 / 1.1) 2 with conductive carbon 3 and ionic liquid 4 is used. With this composition as well, the addition of conductive carbon 3 and ionic liquid 4 leads to debonding effects, which are observed after applying a voltage of 9 V for 30 min at 85%, from μ = 7.4 ± 0.4 MPa to μ = 1.1 ± 0.1 MPa. The formation of an orthoquinone vibration band at 1664 cm' 1As shown in the figure, this can be observed after just 5 minutes and is still present after 30 minutes. This corresponds to the decay of the current over time. A brief application of the voltage is sufficient to induce a comparable degree of weakening in the bulk material. However, this leads to insufficient control of the fracture pattern of the delamination.

[0128] Furthermore, Fig. 6 shows an exemplary schematic representation of the electrochemical debonding concept in an exemplary TQ / ETTMP700 adhesive system 2 according to the invention.

[0129] Two substrates 1 are joined together by means of the electrochemically reversible thiol-catechol (TCC) adhesive system 2 according to the invention, filled with conductive carbon s and ionic liquid 4. The TCC adhesive 2 according to the invention has thiol-catechol functionalities 2a. By applying an electrochemical circuit 5, here 9 V for 30 minutes, the substrates 1 are re-bonded by the re-bonding of the TCC adhesive 2 through oxidation of the catechols to quinones 2b; the adhesive system 2 is re-bonded 6.

[0130] Figure 7 shows a comparison of the placement of catechol functionalities in a thiol-catechol (TCC) reversible adhesive system 2 (left) and a conventional catechol adhesive system (right). The thiol-catechol (TCC) reversible adhesive system 2 shown on the left is an adhesive system that features thiol-catechol functionalities 2a placed in the polymer backbone 7a. Side reactions between the catechol adhesion groups are suppressed due to the limited flexibility of the polymer backbone 7a. In the conventional catechol adhesive system shown on the right, the catechol functionalities 8 are located in the side chains 7b. Side reactions between the catechol adhesion groups are possible due to the increased flexibility of the side chains 7b.

[0131] Figure 8 shows a comparison of the adhesion and cohesion effects of catechol functionalities in a thiol-catechol (TCC) reversible adhesive system 2 (left) and a conventional catechol adhesive system (right). In the left figure, the catechol adhesion groups anchor the polymer network 7 to the substrate surface 1 (adhesion enhancement 9). Furthermore, the interactions of the catechol adhesion groups with each other within the TCC reversible adhesive system 2 ensure better cohesion (cohesion enhancement 10). In the right figure, the catechol adhesion groups anchor the polymer network 7 to the surface (adhesion enhancement 9). However, the interactions of the catechol adhesion groups with each other do not significantly contribute to the cohesion of the adhesive system, as the adhesion groups are not part of the polymer backbone 7a.

[0132] The decisive factor for the debonding effect in the TCC reversible adhesive system according to the invention is the combination of the three components (TCC adhesive mixture, carbon particles, ionic liquid).

[0133] Analogous formulations using a commercially available epoxy adhesive show that under the same conditions, there is no weakening of the adhesive strength.

[0134] Furthermore, the addition of only conductive particle filler leads to an unclean debonding process with high thermal peaks in the adhesive bulk up to 80°C. Conversely, ionic liquid alone, without conductive particle filler, shows no debonding effects of the TCC adhesive up to an increase of +30 wt.%. Thermally stimulated weakening could be ruled out by tests.

[0135] Furthermore, cyclic voltammographic analyses can demonstrate that an electrochemical reaction takes place in the cured adhesive bulk, which can additionally be correlated with the oxidation of the TCC group via infrared spectroscopic methods, thus proving the debonding mechanism to be a clean electrochemical reaction in the adhesive bulk.

[0136] Experimental checks show that all three components (TCC adhesive system, conductive particle filler, ionic liquid) are involved, with the Faraday currents (electrochemically effective potentials) being introduced from the conductive substrate (aluminum, ITO, steel, gold, copper, graphite on plastic) via the conductive particle filler into the adhesive bulk, where surprisingly a significantly enlarged interface with the adhesive can become electrochemically active mediated by the ionic liquid, whereby the ionic liquid causes ionic conductivity at the interface (adhesive / conductive particle filler) and, via plasticizer effects, induces local structural dynamics and can also provide the reductive half-cell reaction to promote TCC oxidation.

[0137] The use of the novel, electrochemically debondable thiol-catechol (TCC) reversible adhesive system according to the invention differs significantly from the application of catechol additives because low-molecular-weight additives preferentially improve adhesion at the interface and cannot contribute to polymer chain-polymer chain interaction to strengthen cohesion. In the TCC adhesive according to the invention, the catechols are incorporated into the polymer chain and demonstrably strengthen cohesion and adhesion, such that the oxidation of the TCC catechols to TCC quinones in the adhesive system reduces both cohesion and adhesion. Thus, the present two-additive-component TCC reversible adhesive system differs from the prior art, particularly in that this combination contributes to achieving the described mechanism for inducing debonding effects.

[0138] The electrochemically debondable thiol-catechol (TCC) reversible adhesive system according to the invention is a novel adhesive system which forms thiol-catechol compounds (TCCs) from trimeric ortho-quinone (TQ) and commercially available trithiols, which function both as network links and as adhesion promoters.

[0139] The developed two-component adhesive systems exhibit high shear strength on materials such as aluminum and demonstrate the potential for controlled debonding through the application of voltage. By adding conductive additives such as conductive carbon (CB) and an ionic liquid (IL), the adhesive system enables electrochemical debonding, reducing the adhesive strength by 72% after the application of a voltage. Applying a voltage of, for example, 9 V for 30 minutes not only results in a significant reduction in adhesive strength but also in a pure adhesive rupture pattern, allowing for clean and efficient removal of the adhesive.

[0140] Compared to conventional two-component epoxy adhesives, the TQ-based system exhibits superior debonding performance, making it a promising solution for recyclable structural adhesives where end-of-life separation is important. Reference list

[0141] 1 substrate

[0142] 2 TCC Reversible Adhesive System, TCC Reversible Adhesive 2a Thiol-Catechol Functionality

[0143] 2b Oxidation of catechols to quinones

[0144] 3 Conductive particle filler

[0145] 4 Ionic liquid

[0146] 5 Electrochemical Circuit

[0147] 6. Debonding of the adhesive system

[0148] 7 Polymer network

[0149] 7a Polymer backbone

[0150] 7b Polymer side chain

[0151] 8 Catechol Functionality

[0152] 9. Adhesion enhancement

[0153] 10 Cohesion enhancement

Claims

REQUIREMENTS 1. Electrochemically reversible adhesive system (2) with thiol catechol (TCC) functionality, wherein the reversible adhesive system (2) comprises adhesive system components that react with each other to form a thiol catechol functionality and wherein the cured reversible adhesive system (2) is re-bonded by electrochemical oxidation of the TCC catechols to TCC quinones; characterized by the fact that - the reversible adhesive system (2) is designed as a two-component adhesive system, wherein the first adhesive system component is formed from bi- and / or trifunctional quinone compounds or from mixtures of these components and the second adhesive system component is formed from multithiols with at least 2 thiol functionalities and / or mixtures of multithiols, which react with each other in a Michael-type reaction or thiol-quinone addition; - the formed thiol-catechol functionalities are present in the polymer backbone of the adhesive system (2); - the reversible adhesive system (2) comprises additives in the form of at least one conductive particle filler (3) and at least one ionic liquid (4) and - controlled delamination via electrochemical circuit (5) by: - Deactivation of the adhesive strength of the reversible adhesive system (2) until separation or - Reduction of the adhesive strength of the reversible adhesive system (2) to the point of separability is feasible.

2. Reversible adhesive system (2) according to claim 1 , characterized by the fact that a curing of the adhesive system (2) is possible at a temperature between 9 °C and 150 °C or between 40 °C and 130 °C or between 90 °C and 120 °C for a duration between 0.5 h and 48 h or 5 to 24 h or 10 h to 18 h.

3. Reversible adhesive system (2) according to claim 1 or 2, characterized by the fact that The voltage to be applied for controlled delamination by electrochemical circuit (5) is between 0.5 V and 60 V, or between 6 V and 24 V, or between 8 V and 12 V, and the time period with applied voltage is between 2 min and 60 min, or between 5 min and 30 min, or between 10 min and 25 min.

4. Reversible adhesive system (2) according to one of the preceding claims, characterized in that the conductive particle filler (3) is formed from conductive carbon particles or from carbon nanotubes or from carbon black or from mixtures of these components.

5. Reversible adhesive system (2) according to one of the preceding claims, characterized in that the ionic liquid (4) - containing 1-butyl-3-methylimidazolium and / or 1-butyl-1-methylperidinium and / or 1-ethyl-3-methylimidazolium and / or tetrabutylammonium and / or 1,3-diethylimidazolium as cations and as anions hexafluorophosphate and / or bistrifluoromethylsulfonylimide and / or tetrafluoroborate and / or dicyanamide or - is formed from 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or - selected is from the list or formed from a combination and selected is from the list: 1-Ethyl-3-methyl-1H-imidazole-3-ium-methylsulfate; 1-hexyl-3-methylimidazolium 2-(2-fluoroanilino)pyridinate; 1-hexyl-3-methylimidazoliumimide; 1-Butyl-1-methylpyrrolidinium 2-(2-fluoranilino)pyridinate; 1-Butyl-1-methylpyrrolidiniumimid; Trihexyl(tetradecyl)phospholium-2-(2-fluoranilino)-pyridinat; Cyclohexyltrimethylammonium-bis(trifluormethylsulfonyl)imid; Di(2-hydroxyethyl)ammoniumtrifluoracetat; N,N-Dimethyl(2-hydroxyethyl)ammoniumoctanoat; Methyltrioctylammonium-bis(trifluormethylsulfonyl)imid; N-Ethyl-N,N,N,N-Tetramethylguanidiniumtrifluormethansulfonat; Guanidiniumtrifluormethansulfonat; 1-Butyl-4-methylpyridiniumbromid; 1-Butyl-3-methylpyridiniumtetrafluoroborat; 1-Butyl-3-hydroxymethylpyridiniumethylsulfat; 1-Butyl-1-methylpyrrolidinium-bis(trifluormethylsulfonyl)imid;1 -Butyl-methylpyrrolidinium-tris(pentafluorethyl)trifluorphosphat; 3-Methylimidazoliumethylsulfat; 1-Ethyl-3-methylimidazoliumchlorid; 1-Ethyl-3-ethyl-methylimidazoliumbromid; 1-Butyl-3-methylimidazoliumchlorid; 1-hexyl-3-methylimidazolium chloride; 1-Octyl-3-methylimidazolium chloride; 1-methyl-3-octylimidazolium chloride; 1-propyl-3-methylimidazolium iodide; 1-Butyl-3-methylimidazolium tetrafluoroborate; 1-butyl-3-methylimidazolium trifluoromethanesulfonate; 1-Butyl-3-methylimidazolium hexafluorophosphate; 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate; 1-Butyl-2,3-dimethylimidazolium tetrafluoroborate; 1-Butyl-2,3-dimethylimidazolium hexafluorophosphate; 1-Butylimidazole; 1-methylimidazolium tetrafluoroborate; tetrabutylphosphonium tris(pentafluoroethyl)trifluorophosphate; Trihexyl(tetradecyl)phosphonium tetrafluoroborate.

6. Reversible adhesive system (2) according to one of the preceding claims, characterized in that the adhesive system (2) - a quinone / thiol ratio window (Q / T) of Q / T = 1 / 0.3 to 1 / 5.0 or Q / T = 1 / 0.5 to 1 / 1.5 and / or - 2 to 25 wt.% or 4 to 10 wt.% of conductive particle filler (3) and / or - comprising 0.1 to 25 wt.% or 2 to 10 wt.% of ionic liquid (4).

7. Reversible adhesive system (2) according to one of the preceding claims, characterized in that via the electrochemical circuit (5) controlled delamination by switching off or reducing the adhesive strength of the adhesive system (2) - adjustable with a reduced adhesive force of 25% to 90% or with a reduced adhesive force of at least 50% or 50% to 75% and / or - can be formed using a pure adhesive system fracture pattern.

8. Reversible adhesive system (2) according to one of the preceding claims, characterized in that via the electrochemical circuit (5) a controlled debonding can be achieved by switching off or reducing the adhesive strength of the adhesive system (2) on one electrode side.

9. Use of the reversible adhesive system (2) according to any one of the preceding claims as: - adhesive system removable from a substrate (1) and / or - a removable adhesive system from a substrate (1) wherein the substrate comprises aluminium and / or steel and / or indium tin oxide coated glass and / or carbon doped polylactide and / or conductive surfaces such as metals and / or conductive coatings and / or conductive plastics and / or conductively impregnated plastics and / or conductive glasses and / or ITO and / or applied conductive layers and / or printed conductive inks and / or conductive adhesive tapes.

10. Use of the reversible adhesive system (2) according to the preceding claim - in the electronics sector, - in the automotive sector, - when bonding display glass to frame, - when gluing batteries into devices and - during the bonding of battery cells into battery packs.

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