Polyurethane-based adhesive with switchable debonding

Abstract

The present invention relates to an electrically releasable polyurethane-based adhesive composition, the use of this composition for bonding substrates and a method for debonding substrates bonded by means of the electrically releasable adhesive composition.

Description

[0001] Polyurethane-Based Adhesive with Switchable Debonding

[0002] The present invention relates to an electrically releasable polyurethane-based adhesive composition, the use of this composition for bonding substrates and a method for debonding substrates bonded by means of the electrically releasable adhesive composition.

[0003] State of the Art

[0004] Adhesives are often used in the assembly of finished products. They are used in place of mechanical connecting members such as screws, bolts and rivets to join substrates while keeping labor costs low and improving adaptability in the manufacturing process. Adhesives distribute stress evenly, reduce the possibility of fatigue and seal against corrosion. Modern high-strength adhesive systems are therefore often multifunctional, but still have insufficient reversibility of the bond. However, the ability to easily release the bond offers many advantages.

[0005] Switchable adhesives in the sense of a targeted deactivation of adhesion ("Debonding on Demand" = DoD) are therefore a long-cherished dream of the adhesives industry. The advantages of reversible bonding are obvious; repair and recycling have been drastically simplified. This applies both to complex technical constructions (e.g. replacing a defective cell phone display) and to simpler bonded parts (e.g. plastic laminates I packaging). Even one-time switchability (irreversible release of the substrates after bonding) would have considerable added value for the majority of technical applications.

[0006] A combination of controllable external influences is possible in order to weaken a bond and induce debonding / delamination in a targeted manner. High-strength structural adhesives are subject to changing mechanical stress as well as frequent temperature and humidity fluctuations, which must not lead to component part failure even during long-term use. Examples of such processes are described, for example, in U.S. Patent No. 4,171 ,240, U.S. Patent No. 7,407,704 and U.S. Patent No. 4,729,797.

[0007] Temperature as a control parameter is only suitable to a limited extent, as structural adhesives are used in particular for components subjected to thermal stress which must not lose their strength. In addition, a component part or device may often only be heated up to a certain temperature range for bonding so that components or thermoplastics are not damaged. The separation of substrates by means of temperature can also be time-consuming. This can impair the efficiency of production processes. The use of UV light is limited to transparent substrates and the use of solvents is not an environmentally friendly process. The introduction of chemically addressable predetermined breaking points, such as acetals as pH-sensitive and hydrolysable covalent cross-linking groups, is also not suitable for structural bonding due to high minimum technical requirements at prolonged service life.

[0008] EP 3262132 A1 discloses a reactive hot-melt adhesive composition comprising an isocyanate- functional polyurethane polymer and an organic or inorganic salt which loses at least part of its adhesiveness when an electrical voltage is applied, thus enabling detachment of substrates which have been bonded with this adhesive.

[0009] When realizing the switchability of structural adhesives, it is also important that the final properties of the adhesive, i.e. the absorption of high forces and bonding even under heavy loads, are retained.

[0010] To overcome the disadvantages mentioned, there is a need for innovative adhesive compositions that enable a more efficient and gentle separation of substrates. The ideal solution should also be environmentally friendly, fast (quick release of substrates from each other, increasing the efficiency of production processes) and adaptable to different applications while, at the same time, minimizing the risk of substrate damage.

[0011] Brief Description of the Invention

[0012] Surprisingly, it has now been found that the object described above is solved by the present invention. The present invention relates to an electrically releasable adhesive composition comprising:

[0013] (i) at least one conductive salt,

[0014] (ii) at least one polymer comprising at least one monomer unit per polymer chain according to formula (1): Formula (1) wherein

[0015] Ri and R2 are independently selected from the group consisting of hydrogen, linear or branched, substituted or unsubstituted alkanes or alkenes with up to 20 carbon atoms and 1 to 6 heteroatoms selected from O, S and N, substituted or unsubstituted cycloalkylene, cycloalkenylene or arylene having up to 20, preferably up to 12 carbon atoms, particularly preferably 6 carbon atoms, substituted or unsubstituted heterocycloalkylene, heterocycloalkenylene or heteroarylene with up to 20 carbon atoms and 1 to 6 heteroatoms selected from O, S and N, linear or branched, substituted or unsubstituted alkylcycloalkylene, alkenylcycloalkylene, alkylcycloalkenylene, alkenylcycloalkenylene, alkylarylene or alkenylarylene with up to 20 carbon atoms, linear or branched, substituted or unsubstituted heteroalkylcycloalkylene, heteroalkenylcycloalkylene, heteroalkylcycloalkenylene, heteroalkenylcycloalkenylene, heteroalkylarylene or heteroalkenylarylene with up to 20 carbon atoms and 1 to 6 heteroatoms, selected from O, S and N, and linear or branched, substituted or unsubstituted heteroalkylheterocycloalkylene, heteroalkenylheterocycloalkylene, heteroalkylheterocycloalkenylene, heteroalkenylheterocycloalkenylene, heteroalkylheteroarylene or heteroalkenylheteroarylene with up to 20 carbon atoms and 1 to 6 heteroatoms, selected from O, S and N, n is an integer of 2 or 3, preferably 2, and the polymer is a polyurethane.

[0016] According to the present invention, the electrically releasable adhesive composition may comprise a resin binder. The resin binder may be a thermoplastic resin binder or a thermoset resin binder selected from the group consisting of phenoxy resins, polyesters, thermoplastic urethanes, phenolic resins, thermoplastic acrylic polymers, acrylic block copolymers, acrylic polymers with tertiary alkylamide functionality, polysiloxane polymers, polystyrene copolymers, polyvinyl polymers, divinylbenzene copolymers, polyetheramides, polyvinyl acetals, polyvinyl butyrals, polyvinyl acetols, polyvinyl alcohols, polyvinyl acetates, polyvinyl chlorides, methylene polyvinyl ethers, cellulose acetates, styrene acrylonitriles, amorphous polyolefins, polyacrylonitriles, ethylene vinyl acetate copolymers, ethylene vinyl acetate terpolymers, functional ethylene vinyl acetates, ethylene acrylate copolymers, ethylene-acrylate terpolymers, ethylene-butadiene copolymers and / or block copolymers, styrene-butadiene block copolymers, vinyl resins, acrylic resins, phenolic resins, epoxy resins, maleimide resins, bismaleimide resins, polyimide resins and silicone-containing resins, and combinations thereof.

[0017] According to the present invention, the electrically releasable adhesive composition may further comprise a solvent. The solvent may be selected from the group consisting of butyl glycol acetate, 1 ,4-butanediol diglycidyl ether, p-tert-butylphenyl glycidyl ether, allyl glycidyl ether, glycerol diglycidyl ether, butyl diglycol, 2-(2-butoxyethoxy)ethyl ester, acetic acid, 2- butoxyethyl ester, butyl glycol, 2-butoxyethanol, isophorone, 3,3,5-trimethyl-2-cyclohexen-1- one, dimethyl succinate, dimethyl glutarate, dimethyl adipate, acetic acid, dipropylene glycol (mono)methyl ether, propyl acetate, glycidyl ether of alkylphenol and dimethyl ester of adipic, glutaric and succinic acid and combinations thereof. Alternatively, the electrically releasable adhesive composition may be free of solvents.

[0018] According to the present invention, the tensile shear strength of the cured electrically releasable adhesive composition can be reduced by at least 50%, preferably by at least 60% and particularly preferably by at least 70% when applying a voltage of more than 1 V, preferably more than 2 and particularly preferably more than 5 V.

[0019] According to the present invention, applying a voltage to the electrically releasable adhesive composition may cause the polymer to decompose, releasing the compound according to formula (2) Formula (2) where Ri, R2and n are as defined in formula (1).

[0020] According to the present invention, Ri and R2may be independently selected from the group consisting of:

[0021] (i) para substituted-,

[0022] (ii) para, meta substituted-,

[0023] (iii) meta, meta substituted-, or

[0024] (iv) unsubstituted arylene with up to 20, preferably up to 12 carbon atoms, particularly preferably 6 carbon atoms, wherein the substituent is electron-withdrawing or electron-donating.

[0025] The electron-withdrawing substituent may be selected from the group consisting of:

[0026] (i) halogenated, preferably fluorinated, alkanes with up to 10 carbon atoms,

[0027] (ii) thiocyanate group, (iii) cyanate group,

[0028] (vi) nitro group, and

[0029] (vii) nitrile group; and / or the electron donating substituent may be selected from the group consisting of

[0030] (i) alkanes with up to 10 carbon atoms, and

[0031] (ii) alkoxy groups with up to 10 carbon atoms, preferably methoxy group.

[0032] According to the present invention, the polymer can be a random copolymer of the monomer according to formula (1) and at least one di- or polyisocyanate. The polymer may be a block copolymer, preferably a triblock copolymer, of at least one polyurethane and at least one further polymer, wherein the at least one polyurethane or the at least one further polymer comprises at least one monomer according to formula (1), wherein the at least one further polymer may be selected from the group consisting of polyester, polyether, and polyamide.

[0033] The present invention also relates to the use of the above-described electrically releasable adhesive composition for bonding two substrates.

[0034] The present invention also relates to a method for irreversibly releasing at least two substrates bonded by the above-described electrically releasable adhesive composition, comprising applying an electrical voltage to one of the at least two substrates and / or the bonding agent. The electrical voltage may be between 1 and 100 V, preferably between 2.5 and 75 V, more preferably between 5 and 48 and particularly preferably between 10 and 30 and / or may be applied over a time of from 1 second to 30 minutes, preferably from 10 seconds to 20 minutes and particularly preferably from 30 seconds to 5 minutes.

[0035] Figures

[0036] Figures 1A and 1 B show schematically the mode of operation of the switchable debonding by breaking bonds within the polymer chain under the influence of voltage (for example, for oligomers linked by the monomer according to formula (3)). Electricity is intended to cause the adhesive to fail in a targeted manner in order to simplify repair and recycling.

[0037] Figure 2 shows electrochemical characterization with CV: bond breakage occurs in all bond types.

[0038] Figures 3A-D show the debonding of the electrically releasable adhesive composition on aluminum substrates. Detailed Description of the Invention

[0039] The detailed and specific embodiments of the invention described below are for illustrative purposes only, i.e., various modifications may be made without departing from the invention. The present invention is limited only by the appended claims.

[0040] All embodiments disclosed and claimed herein may be implemented and practiced in view of the disclosure without undue experimentation.

[0041] The content of the documents referred to herein is to be understood in its entirety as part of this document.

[0042] The present invention is the realization of the solution to one or more of the above problems and relates to an electrically releasable adhesive composition comprising:

[0043] (i) at least one conductive salt,

[0044] (ii) at least one polymer comprising at least one monomer unit per polymer chain according to formula (1): Formula (1) wherein

[0045] Ri and R2are independently selected from the group consisting of hydrogen, linear or branched, substituted or unsubstituted alkanes or alkenes with up to 20 carbon atoms and 1 to 6 heteroatoms selected from O, S and N, substituted or unsubstituted cycloalkylene, cycloalkenylene or arylene with up to 20, preferably up to 12 carbon atoms, particularly preferably 6 carbon atoms, substituted or unsubstituted heterocycloalkylene, heterocycloalkenylene or heteroarylene with up to 20 carbon atoms and 1 to 6 heteroatoms selected from O, S and N, linear or branched, substituted or unsubstituted alkylcycloalkylene, alkenylcycloalkylene, alkylcycloalkenylene, alkenylcycloalkenylene, alkylarylene or alkenylarylene with up to 20 carbon atoms, linear or branched, substituted or unsubstituted heteroalkylcycloalkylene, heteroalkenylcycloalkylene, heteroalkylcycloalkenylene, heteroalkenylcycloalkenylene, heteroalkylarylene or heteroalkenylarylene with up to 20 carbon atoms and 1 to 6 heteroatoms, selected from O, S and N, and linear or branched, substituted or unsubstituted heteroalkylheterocycloalkylene, heteroalkenylheterocycloalkylene, heteroalkylheterocycloalkenylene, heteroalkenylheterocycloalkenylene, heteroalkylheteroarylene or heteroalkenylheteroarylene with up to 20 carbon atoms and 1 to 6 heteroatoms, selected from O, S and N, n is an integer of 2 or 3, preferably 2, and the polymer is a polyurethane.

[0046] The compositions of the invention have a matrix functionality and an electrolyte functionality. The electrolyte functionality ensures sufficient conductivity. This electrolyte functionality is achieved by the use of at least one conductive salt. The matrix functionality of the composition provides the adhesive properties required for the intended use. This matrix functionality is achieved by the at least one polymer.

[0047] The adhesiveness of the composition is weakened by the application of an electrical voltage to the connecting line between the composition and at least one surface to which it is adhered. Without wishing to be bound by any particular theory regarding the mode of action, it is believed that application of a voltage to the electrically releasable adhesive composition as shown in Figure 1B results in bond breaking within the polymer chains, which is enabled bythe presence of the at least one monomer unit according to formula (1) in each polymer chain. Applying a voltage to the electrically releasable adhesive composition may result in decomposition of the polymer with release of the compound according to formula (2) Formula (2) wherein Ri, R2 and n are as defined in formula (1), i.e. an electrochemical change of the (substituted) hydroquinone to an analogous ketal takes place. This reaction is electrochemically irreversible.

[0048] Bond breakage within the polymer chains leads to a reduction in adhesive properties. This is reflected by a reduction of tensile shear strength. According to the present invention, the tensile shear strength of the cured electrically releasable adhesive composition can be reduced by at least 50%, preferably by at least 60% and particularly preferably by at least 70% by applying a voltage of more than 1 V, preferably more than 2 and particularly preferably more than 5 V.

[0049] As demonstrated by the experimental data in the present application, adhesive compositions according to the present invention exhibit the property that they lose their tensile shear strength when subjected to electricity. This is already achieved at a low voltage. Also, the effective DoD using the present invention requires only short exposure times.

[0050] The adhesive composition allows for easy and controlled separation of bonded substrates by applying an electrical voltage. This can be particularly useful in applications where a reversible bond is required. The composition can be used for different substrates and in different industries, including electronics, automotive and packaging.

[0051] The composition may contain various polymers and resin binders, which allows the adhesive properties to be adapted to specific requirements. The resin binder may be a thermoplastic resin binder or a thermosetting resin binder selected from the group consisting of phenoxy resins, polyesters, thermoplastic urethanes, phenolic resins, thermoplastic acrylic polymers, acrylic block copolymers, acrylic polymers with tertiary alkylamide functionality, polysiloxane polymers, polystyrene copolymers, polyvinyl polymers, divinylbenzene copolymers, polyetheramides, polyvinyl acetals, polyvinyl butyrals, polyvinyl acetols, polyvinyl alcohols, polyvinyl acetates, polyvinyl chlorides, methylene polyvinyl ethers, cellulose acetates, styrene acrylonitrile, amorphous polyolefins, polyacrylonitrile, ethylene vinyl acetate copolymers, ethylene vinyl acetate terpolymers, functional ethylene vinyl acetates, ethylene acrylate copolymers, ethylene acrylate terpolymers, ethylene-butadiene copolymers and / or block copolymers, styrene-butadiene block copolymers, vinyl resins, acrylic resins, phenolic resins, epoxy resins, maleimide resins, bismaleimide resins, polyimide resins and silicone-containing resins, as well as combinations thereof.

[0052] According to the present invention, the electrically releasable adhesive composition may further comprise a solvent. The solvent may be selected from the group consisting of butyl glycol acetate, 1 ,4-butanediol diglycidyl ether, p-tert-butylphenyl glycidyl ether, allyl glycidyl ether, glycerol diglycidyl ether, butyl diglycol, 2-(2-butoxyethoxy)ethyl ester, acetic acid, 2- butoxyethyl ester, butyl glycol, 2-butoxyethanol, isophorone, 3,3,5-trimethyl-2-cyclohexen-1- one, dimethyl succinate, dimethyl glutarate, dimethyl adipate, acetic acid, dipropylene glycol (mono)methyl ether, propyl acetate, glycidyl ether of alkylphenol and dimethyl ester of adipic, glutaric and succinic acid and combinations thereof.

[0053] In some embodiments, the adhesive composition is free of solvent, which is more environmentally friendly and reduces health risks. The ability to avoid solvents contributes to more sustainable production and application.

[0054] Conductive Salt

[0055] The electrically releasable adhesive composition according to the invention comprises at least one conductive salt. Conductive salts are used to increase the electrical conductivity of the composition. The choice of conductive salt depends on various factors, including the desired conductivity, chemical compatibility with other components of the adhesive, processing properties and cost.

[0056] Sufficient conductivity of the adhesive composition can be easily determined by preparing a composition and applying a voltage. If a current flow is observed, sufficient conductivity can be assumed. Higher conductivities generally allow for shorter debonding times.

[0057] The adhesive compositions can have a conductivity in the range of 10 to 150 S / cm at room temperature.

[0058] The at least one conductive salt can be solid or liquid at 25 °C and 1013 mbar, i.e. the conductive salts include both solid salts and the so-called ionic liquids.

[0059] Examples of such conductive salts are silver nitrate (AgNO3), copper salts (e.g. copper(ll) chloride, CuCI2), nickel salts (e.g. nickel(ll) chloride, NiCI2), iron(lll) chloride (FeCI3), alkali and alkaline earth metal salts (e.g. lithium perchlorate, l_iCIO4), tetrabutylammonium hexafluorophosphate (TBAPF6), iodine salts (e.g. sodium iodide, Nal), conductive polymer salts (e.g. polyaniline derivatives) or combinations thereof.

[0060] The at least one conductive salt is preferably an iodine salt and particularly preferably sodium iodide or potassium iodide.

[0061] The conductive salts can be dissolved or dispersed in the composition.

[0062] Salts of organic acids may also be used, such as Li, Na or K salts of aliphatic C2-6 mono- or dicarboxylic acids, aromatic mono- or dicarboxylic acids and trifluoromethanesulfonic acids. In one embodiment, a quaternary organic compound is used as the cation, wherein the anion consists of the above-mentioned acid anions or halides. In a further preferred embodiment, organic compounds containing sulfone groups are used as the anion, either as part of a cyclic structure, such as acesulfams or saccharinates, or as part of a linear structure, such as trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)imide or trifluoromethanecarbonyltrifluoromethanesulfonylimide.

[0063] The cationic quaternary organic compounds that can be used include, among others, tetraalkylphosphonium, trialkylsulfonium, tetraalkylammonium, N-alkyl-substituted cyclic 5- or 6-membered ring amines, N-alkyl-substituted aromatic 5-membered ring imidazolines, where the alkyl group can be a linear aliphatic alkyl radical with 1 to 12 carbon atoms. The alkyl radicals may be identical or different and may optionally also be substituted with an OH group. In principle, the various anions and cations can be combined with each other as long as the resulting compounds have the properties of a salt.

[0064] Examples of suitable cationic groups include:

[0065] (i) tetraalkyl-substituted N-compounds such as N-tetrabutylammonium, N-trimethyl-N- butylammonium, N-triethyl-N-benzylammonium, N,N-dimethyl-cyclohexylamine, N-methyl-N- trioctylammonium;

[0066] (ii) OH-functionalized tetraalkylamines, such as trimethyl-hydroxyethylammonium (choline), acetylcholine, N-methyl-N-hydroxyethyl-cyclohexylamine;

[0067] (iii) trialkyl-substituted S-compounds, such as triethylsulfonium, trimethylsulfonium;

[0068] (iv) 5-membered N-heterocycles, such as N-alkylimidazolium derivatives, such as 1- methyl-3-ethyl-imidazolium, 1-ethyl-3-methyl-imidazolium, 1-butyl-3-methylimidazolium, 1- hexadecyl-3-methyl-imidazolium, 1 -methyl-3-octyl-imidazolium, 1 -methyl-3-nonyl- imidazolium, 1-heptyl-3-methyl-imidazolium, 1-ethyl-2-methyl-imidazolium, 1-propyl-4-methyl- imidazolium, 1-propyl-2-methyl-imidazolium, 1 ,2-dimethyl-3-propyl-imidazolium;

[0069] (v) 6-membered N-heterocycles, e.g. alkyl-substituted pyridinium, pyrrolidinium or piperidinium compounds, such as 1 -butyl-pyridinium, 1-butyl-3-methyl-pyridinium, 1-butyl-4- methyl-pyridinium, 1-propyl-3-methyl-pyridinium, 1 -butyl-3-propyl-piperidinium, 1-butyl-1- methyl-pyrrolidinium, 1 -butyl-3-methyl-pyrrolidinium, 1 -hexyl-3-methyl-pyrrolidinium.

[0070] In a preferred embodiment, the salt should have a melting temperature of above 40 °C. It is also preferred that the organic or inorganic salt does not react with the isocyanate-functional polyurethane polymer or with atmospheric water. Examples of suitable organic anions include tetrafluoroborate, trifluoromethanesulfonate, aromatic dicarboxylates such as phthalic acid and its isomers, sulfonate group-containing compounds such as acesulfams, saccharinates, bis(trifluoromethanesulfonyl)imide or trifluoromethane carbonyl-trifluoromethanesulfonylimide. Preferred are trifluoromethanesulfonate salts, in particular the alkali metal salts, especially lithium trifluoromethanesulfonate.

[0071] The conductive salt is included in the adhesive composition in an amount sufficient to provide the required ionic conductivity. The actual amount of conductive salt used in a particular composition depends on the ionic conductivity of the polymer and the ability of the salt to form a continuous conduction path within the composition. While a continuous path is not essential, it does promote the efficiency of the process. If the ions must tunnel through areas of higher resistance, higher voltages and longer times are required for detachment. The at least one conductive salt may be present in an amount of from 1 to 30% by weight, preferably from 1 to 16% by weight, more preferably from 2 to 10% by weight and most preferably from 2 to 6% by weight, based on the total weight of the adhesive composition.

[0072] Polar Additive

[0073] The adhesive composition may comprise at least one polar compound as an additive, which is different from the at least one polyurethane polymer and the at least one conductive salt.

[0074] The polar compound is also referred to here as a "solvation matrix". Such polar compounds can promote the miscibility of the other components with the at least one salt.

[0075] The salt and the solvating matrix can form a suspension, dispersion or solution.

[0076] Preferably, the salts remain within the solvating matrix. This improves the structural and chemical integrity of the adhesive, while the salt can migrate through the matrix when a voltage is applied.

[0077] The polar compounds may include polymers such as polyphosphazenes, polymethylene sulfides, polyoxyalkylene glycols, polyethyleneimines, polyethyleneamines and the like.

[0078] Polyols are also suitable. These include aliphatic polyols with 2 to 120 hydroxyl groups. These typically have a molecular weight of up to 1 ,000 g / mol, preferably up to 500 g / mol. Polyols with 3 to 6 OH groups are preferred. Examples include neopentylglycol, pentaerythritol, glycerol, monosaccharides and sugar alcohols such as glucose, arabinose, xylose, mannitol, sorbitol, arabinose and other compounds with plural OH groups.

[0079] Preferably, the polar compound does not contain any functional H-acid groups, i.e. preferably the polar compound is an aprotic polar compound. This ensures that the polar compound does not adversely affect the storage stability.

[0080] One group of suitable polar compounds are polyethers, in particular polyethylene glycols and polypropylene glycols. Particularly suitable are capped polyethers, i.e. reaction products of polyether polyols in which hydroxyl groups have been converted in such a way that the polyethers inlcude only up to one H-acidic functional group, preferably no H-acidic functional group. Polyethers, preferably end-capped polyethers, with a molecular weight of less than 10,000 g / mol, preferably from 350 to 5,000 g / mol, are particularly suitable.

[0081] Suitable capped polyethers are allyl alcohol ethoxylate, methylene-capped; allyl alcohol ethoxylate propoxylate, methylene-capped (EO / PO random); allyl alcohol ethoxylate, allyl- endcapped; allyl alcohol ethoxylate propoxylate, allyl-endcapped (EO / PO random); allyl alcohol ethoxylate, epoxygroup-capped; allyl alcohol ethoxylate propoxylate, epoxygroup- capped (EO / PO random); allyl alcohol ethoxylate propoxylate, butyl-capped (EO / PO random); allyl alcohol ethoxylate, acetyl-capped; allyl alcohol ethoxylate propoxylate, acetyl-capped (EO / PO random); methyl alcohol ethoxylate, epoxy-capped; methyl ethoxylate propoxylate, epoxy-capped; butyl alcohol ethoxylate, epoxy-capped; butyl alcohol ethoxylate propoxylate, epoxy-capped (EO / PO random); fatty alcohol polyoxyethylene ether, methylene-capped; fatty alcohol polyoxyethylene ether, butyl-capped; nonylphenol polyoxyethylene ether, butyl- capped; polyethylene glycol) dimethyl ether; polyethylene glycol) methyl ether methacrylate; poly(ethylene glycol) methyl ether; poly(ethylene glycol) methyl ether acrylate; poly(ethylene glycol) methyl ether acrylate; poly(ethylene glycol) diglycidyl ether; poly(ethylene glycol) dimethyl ether; poly(ethylene glycol) ethyl ether methacrylate; poly(ethylene glycol) dimethyl acrylate; poly(ethylene glycol) divinyl ether; polyethylene glycol) butyl ether; polyethylene glycol) methyl ether tosylate; poly(ethylene glycol) behenyl ether methacrylate solution; poly(ethylene glycol) methyl ether tosylate; poly(ethylene glycol) tetra hydrofurfuryl ether; poly(ethylene glycol) octyl ether; poly(ethylene glycol) phenyl ether acrylate; polyethylene glycol bis(2-ethylhexanoate) (PEG-bis(2EH)) and mixtures thereof. Polyethylene glycol bis(2- ethylhexanoate) is particularly suitable. Dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) can also be used as at least one polar compound.

[0082] In various embodiments, the polar compounds have a melting point below the melting temperature of the adhesive, preferably below 100 °C, more preferably below 80 °C, even more preferably below 60 °C.

[0083] The polar compounds can be used in amounts of 0 to 25% by weight, preferably 5 to 15% by weight, based on the total weight of the adhesive composition.

[0084] Polymer

[0085] The polymer has at least one monomer unit per polymer chain according to formula (1) as shown above.

[0086] The polymer is a polyurethane, which can be a polyurethane without block structure or a block copolymer, preferably a triblock copolymer, of at least one polyurethane and at least one other polymer. If the polyurethane is a di- or triblock copolymer as shown above, either the at least one polyurethane block or the at least one block of the other polymer comprises the at least one monomer according to formula (1). The at least one other polymer may be selected from the group consisting of polyester, polyether, and polyamide. This means that the polyurethane can be a hybrid polymer which has further polymeric units in addition to the urethane units.

[0087] The polyurethane according to the invention is obtainable by reacting at least one polyol with at least one polyisocyanate. In general, the components used to synthesize the polyurethane are selected in such a way that meltable, non-crosslinked products are formed. The type of polyols and isocyanates used, in particular the polyols used, are decisive for the melting behavior and the viscosity.

[0088] The polymer can also consist of polyurethane oligomer units which are covalently linked by the at least one monomer according to formula (1) to form a polymer.

[0089] The polyurethane can be a random copolymer of the monomer according to formula (1) and at least one di- or polyisocyanate. In this case, the monomer according to formula (1) assumes the function of the polyol. The polyurethanes described herein can also be obtained from polyurethane prepolymers of polyisocyanates and polyols as defined herein (i.e. the polyol can be at least one compound according to formula (3)), which can be NCO- or OH-functionalized. For NCO-functionalized polyurethane prepolymers (corresponding to a polyisocyanate), the at least one polyisocyanate may be used in an amount such that NCO groups are present in a molar excess relative to the hydroxyl groups of the at least one polyol. Consequently, the NCO / OH equivalent ratio may be more than 1 , preferably between 1 and 2, particularly preferably between 1 .2 and 1.8. The content of free NCO can be in the range of 0.1 to 5% by weight of the polyurethane prepolymer, preferably 1 to 2.5% by weight. For OH-functionalized polyurethane prepolymers (corresponding to a polyol), the above applies accordingly, with the polyol being used in molar excess. The polyurethane prepolymer may have a molecular weight Mn between 500 and 10,000 g / mol, preferably between 1 ,000 and 7,000 g / mol and most preferably between 1 ,000 and 6,000 g / mol. The OH value of the polyurethane prepolymer may be greater than 20, preferably greater than 30 and most preferably greater than 50. The OH value of the polyurethane may be less than 150. The OH value of the polyurethane may be between 20 and 10, preferably between 30 and 150 and most preferably between 50 and 150.

[0090] The polyurethane imparts the required adhesive properties to the adhesive composition, including tack, adhesion, cohesion, melting behavior and stability. These basic properties can optionally be controlled by additives and auxiliaries which are commonly used and are known to the skilled person.

[0091] Thus, the present invention can be used for 1 K and 2K adhesives. The electrically releasable adhesive composition may be a 1 K or a 2K system. 2K systems have two components tailored to each other, one of which contains the curing agent, and which are mixed immediately before or during application and thus brought to reaction. In 1K formulations, on the other hand, an initiator (or curing agent) is integrated directly into the adhesive, which is activated by temperature, light or moisture.

[0092] The molecular weight Mn of the polyurethane in the adhesive composition may be between 10,000 and 250,000 g / mol, preferably between 50,000 and 150,000 g / mol

[0093] In the molten state, the polyurethane should have a viscosity of between 1 ,000 and 100,000 mPa s, preferably 2,000 to 50,000 mPa s, particularly preferably 3,000 to 10,000 mPa s. The polyurethane may be present in the adhesive composition in amounts of about 20 to about 90% by weight, preferably 40 to 90% by weight, based on the total weight of the adhesive composition.

[0094] The OH value of the polyurethane can be greater than 20, preferably greater than 30, and most preferably greater than 50. The OH value of the polyurethane can be less than 150. The OH value of the polyurethane may be between 20 and 10, preferably between 30 and 150 and most preferably between 50 and 150.

[0095] Polyols

[0096] Polyols are one of the main components in the production of polyurethanes. They react with isocyanates to form the polymer structure. Polyols may be selected from the group consisting of polyether polyols, polyester polyols, polycarbonate polyols, polyacetal polyols, polyamide polyols, polyesteramide polyols, polyalkylene polyether polyols, polythioether polyols and mixtures thereof, preferably polyether polyols, polyester polyols, polycarbonate polyols and mixtures thereof.

[0097] Polyether polyols such as poly(oxypropylene)glycol or poly(oxyethylene)glycol are produced by the polymerization of epoxides such as ethylene oxide or propylene oxide. They offer good hydrolytic stability and flexibility. According to the present invention, the polyether polyols include polyalkylene glycol homo- or copolymers, in particular homo- or copolymers of polypropylene glycol, homo- or copolymers of polyethylene glycol, homo- or copolymers of polytetramethylene glycol or polypropylene glycol / polyethylene glycol block copolymers.

[0098] The polyether polyol can have a molecular weight Mn in the range from 200 to 5000, preferably 300 to 4000 g / mol and particularly preferably 400 to 3000 g / mol.

[0099] Polyester polyols such as poly(adipic acid-co-ethanediol) or poly(neopentylglycol-adipate) are produced by the polycondensation of dicarboxylic acids with diols. They offer high mechanical strength and chemical resistance. The dicarboxylic acids can be aliphatic, cycloaliphatic or aromatic acids and / or their derivatives such as anhydrides, esters or acid chlorides. Specific examples are succinic acid, glutaric acid, adipic acid, pimelic acid, cork acid, azelaic acid or sebacic acid, phthalic acid, terephthalic acid, isophthalic acid, trimellitic acid, phthalic anhydride, tetrahydrophthalic anhydride, glutaric anhydride, maleic acid, maleic anhydride, fumaric acid, dimeric fatty acid and dimethyl terephthalate. Examples of suitable polyols are monoethylene glycol, 1 ,2-propanediol, 1 ,3-propanediol, 1 ,4-butanediol, 3-methylpentane-1 ,5- diol, neopentyl glycol (2,2-dimethyl-1 ,3-propanediol), 1 ,6-hexanediol, 1 ,8-octane glycol, cyclohexanedimethanol, 2-methylpropane-1 ,3-diol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol, polypropylene glycol, dibutylene glycol, tributylene glycol, tetrabutylene glycol and polybutylene glycol. Alternatively, polyester polyols can be obtained by ring-opening polymerization of cyclic esters, preferably s-caprolactone.

[0100] The polyester polyol may have a melting temperature Tm> 0 °C, preferably > 40 °C and / or a molecular weight Mn in the range from 400 to 5,000 g / mol, preferably 400 to 3,000 g / mol, more preferably 800 to 2,500 g / mol, most preferably 1 ,000 to 2,000 g / mol.

[0101] Polycarbonate polyols can be obtained by the reaction of carbonic acid derivatives, e.g. diphenyl carbonate, dimethyl carbonate or phosgene, with diols. Suitable examples of such diols are ethylene glycol, 1 ,2- and 1 ,3-propanediol, 1 ,3- and 1 ,4-butanediol, 1 ,6-hexanediol, 1 ,8-octanediol, neopentylglycol, 1 ,4-bishydroxymethylcyclohexane, 2-methyl-1 ,3-pro- panediol, 2,2,4-trimethylpentanediol-1 ,3, dipropylene glycol, polypropylene glycols, dibutylene glycol, polybutylene glycols, bisphenol A, bisphenol F, tetrabromobisphenol A, and lactone- modified diols. The diol component of the polycarbonate polyols preferably contains 40 to 100% by weight of hexanediol, preferably 1 ,6-hexanediol.

[0102] The polycarbonate polyols can be linear or branched. The branching is achieved by incorporating polyfunctional components, in particular low-molecular polyols. Suitable examples of these low molecular weight polyols are glycerol, trimethylolpropane, hexanetriol- 1 ,2,6, butanetriol-1 ,2,4, trimethylolpropane, pentaerythritol, quinitol, mannitol, sorbitol, methyl glycoside, or 1 ,3,4,6-dianhydrohexite.

[0103] Suitable polycarbonate polyols are available under the trademarks Desmophen® C3200 (Bayer) and Kuraray® C2050 (poly-(3-methyl-1 ,5-pentanediol, 1 ,6-hexanediol)carbonate).

[0104] Other polyols, in particular diols, can be used in combination with the above. Such diols may be monomeric diols, such as 1 ,4-butanediol. The diol may also be the compound according to formula (3). Suitable polyols are also hydroxy-functionalized polymers, e.g. hydroxyfunctionalized siloxanes, and polyols containing additional functional groups, such as vinyl or amino groups.

[0105] Isocyanates Isocyanates react with polyols to form the urethane bonds that form the backbone of the polyurethane. Any compound containing at least two isocyanate groups (i.e. polyisocyanates) may be considered for use as a polyisocyanate in the context of the present invention.

[0106] The polyisocyanate may be a diisocyanate, preferably selected from the group consisting of methylene diphenyl diisocyanate (MDI), toluene 2,4-diisocyanate (TDI), hexamethylene diisocyanate (HDI), polymeric di phenyl methane diisocyanate (PMDI), isophorone diisocyanate (IPDI), methylene-4,4-bis(cyclohexyl)diisocyanate (H12MDI) and mixtures thereof.

[0107] The incorporation of polyisocyanates with more than two isocyanate groups, in particular a triisocyanate, is conceivable and can even be advantageous under certain circumstances. Such polyisocyanates can act as crosslinkers. In this case, polyisocyanates based on isophorone diisocyanate are preferred.

[0108] Isocyanates can be divided into two main categories: aromatic isocyanates and aliphatic isocyanates. Aromatic isocyanates such as methylene diphenyl diisocyanate (MDI) or toluene diisocyanate (TDI) offer a fast reaction time and high strength but are less UV-resistant. Aliphatic isocyanates such as hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI) offer better UV resistance and the resulting isocyanate-functional polyurethane polymer is less reactive towards the organic or inorganic salts used as solvating matrix or other compounds such as polar compounds or additives. This leads to improved storage stability.

[0109] Although both aliphatic and aromatic polyisocyanates are contemplated within the scope of the present invention, it is preferred that the polyisocyanate is an aliphatic polyisocyanate. Particularly preferred aliphatic diisocyanates include isophorone diisocyanate, hexamethylene diisocyanate and mixtures thereof. Suitable polyisocyanates are commercially available, for example, under the trademark Desmodur® from Covestro.

[0110] Additives

[0111] Additives are added to improve or modify specific properties of the polyurethane. These include stabilizers, plasticizers, fillers and flame retardants.

[0112] Stabilizers such as phenolic antioxidants or UV stabilizers improve the thermal and oxidative stability of the polyurethane. Plasticizers such as phthalates or adipates increase the flexibility and processability of the polyurethane.

[0113] Fillers such as calcium carbonate, clays, carbon black, pigments, talc or silica improve the mechanical properties and reduce costs.

[0114] Flame retardants such as halogenated compounds or phosphorus compounds increase the fire resistance of the polyurethane.

[0115] It is particularly advantageous to use cost-effective additives that offer improved properties, such as improved initial strength before setting and increased curing speed. Initial strength before setting is particularly important for reactive hot melt adhesives as it allows the adhesive to achieve good bond strength immediately after application while maintaining the desired open- and set-times. A high curing speed enables faster utilization of the formulation components. High initial strength, long open-times and high curing speed are particularly beneficial for certain moisture-reactive adhesives for end-use applications, e.g., board lamination and product assembly.

[0116] The adhesive composition may also comprise additional polymers that are suitable for adhesive applications. These include polyamides, polyacrylates and polyesters. However, these are only used in amounts of less than 30 wt.%, preferably less than 20 wt.%, more preferably less than 10 wt.% and most preferably less than 5 wt.%, based on the total weight of the adhesive composition. The adhesive composition may be substantially free or free of other polymers suitable for the adhesive application.

[0117] Monomer Unit

[0118] According to the present invention, the at least one monomer unit per polymer chain prior to the reaction may be a monomer of the general formula (3): Formula (3) wherein

[0119] Ri and R2are independently selected from the group consisting of hydrogen, linear or branched, substituted or unsubstituted alkanes or alkenes with up to 20 carbon atoms and 1 to 6 heteroatoms selected from O, S and N, substituted or unsubstituted cycloalkylene, cycloalkenylene or arylene with up to 20, preferably up to 12 carbon atoms, particularly preferably 6 carbon atoms, substituted or unsubstituted heterocycloalkylene, heterocycloalkenylene or heteroarylene with up to 20 carbon atoms and 1 to 6 heteroatoms selected from O, S and N, linear or branched, substituted or unsubstituted alkylcycloalkylene, alkenylcycloalkylene, alkylcycloalkenylene, alkenylcycloalkenylene, alkylarylene or alkenylarylene with up to 20 carbon atoms, linear or branched, substituted or unsubstituted heteroalkylcycloalkylene, heteroalkenylcycloalkylene, heteroalkylcycloalkenylene, heteroalkenylcycloalkenylene, heteroalkylarylene or heteroalkenylarylene with up to 20 carbon atoms and 1 to 6 heteroatoms, selected from O, S and N, and linear or branched, substituted or unsubstituted heteroalkylheterocycloalkylene, heteroalkenylheterocycloalkylene, heteroalkylheterocycloalkenylene, heteroalkenylheterocycloalkenylene, heteroalkylheteroarylene or heteroalkenylheteroarylene with up to 20 carbon atoms and 1 to 6 heteroatoms, selected from O, S and N, and n is an integer of 2 or 3, preferably 2.

[0120] The DoD properties, in particular the sensitivity to the applied voltage, can be adjusted via the various substituents, which means that the tensile shear strength can be effectively reduced even at a very low electrical voltage.

[0121] In formula (3), Ri and R2 may be independently selected from the group consisting of:

[0122] (i) para substituted-,

[0123] (ii) para, meta substituted-,

[0124] (iii) meta, meta substituted-, or

[0125] (iv) unsubstituted arylene with up to 20, preferably up to 12 carbon atoms, particularly preferably 6 carbon atoms, wherein the substituent is electron-withdrawing or electron-donating. The electron-withdrawing substituent may be selected from the group consisting of:

[0126] (i) halogenated, preferably fluorinated, alkanes with up to 10 carbon atoms,

[0127] (ii) thiocyanate group,

[0128] (iii) cyanate group,

[0129] (vi) nitro group, and

[0130] (vii) nitrile group; and / or the electron donating substituent may be selected from the group consisting of

[0131] (i) alkanes with up to 10 carbon atoms, and

[0132] (ii) alkoxy groups with up to 10 carbon atoms, preferably methoxy group. According to the present invention, different monomers according to the general formula (3) may be used as the at least one monomer.

[0133] According to the present invention, the at least one monomer may be according to any one of formulae (4) to (16) or a combination of two or more thereof:

[0134]

[0135] Formula (16)

[0136] Use

[0137] The present invention also relates to the use of the above-described electrically releasable adhesive composition for bonding two substrates.

[0138] The adhesive composition typically melted at temperatures of, for example, up to 220 °C, preferably 80 to 120 °C, and is then applied to a substrate in a flowable state. The viscosity of the composition is preferably in the range of 500 to 25,000 mPa s at an application temperature of 80 °C to 120 °C (Brookfield Thermosel RVT, EN ISO 2555). Immediately afterwards, the second substrate is pressed against the adhesive layer and a physical adhesive bond is formed after cooling. The cooled adhesive layers may be amorphous, but they may also comprise crystalline components.

[0139] Devices for melting and applying the composition are known to the skilled person.

[0140] The thickness of the adhesive layer can be selected depending on the desired application. The layer thickness is typically 5 to 1 ,000 pm, in particular 10 to 500 pm.

[0141] Process for Irreversible Debonding

[0142] The present invention also relates to a method for irreversibly releasing at least two substrates bonded by the electrically releasable adhesive composition described above, comprising applying an electrical voltage to one of the at least two substrates and / or the bonding agent. After a certain reaction time, the two substrates can be separated from each other by normal tension or lateral shear. The rate of loss of adhesion can be influenced by the amount and type of salts.

[0143] The electrical voltage can be between 1 and 100 V, preferably between 2.5 and 75 V, more preferably between 5 and 48 and particularly preferably between 10 and 30 and / or can be applied over a time from 1 second to 30 minutes, preferably from 10 seconds to 20 minutes and particularly preferably from 30 seconds to 5 minutes.

[0144] The release of the adhesion can be triggered by a single stimulus (electricity). To accelerate the process, a second stimulus can additionally be applied. This second stimulus can be heat. The combination of electric current and heat leads to even easier detachment. However, the application of heat is optional.

[0145] Thus, in addition to the effect of electricity, heating up to 80°C is conceivable, in particular from 35 to 70°C. This temperature is not sufficient to make the adhesive flowable, but together with the applied voltage only leads to a loss of adhesion. It is possible that the heat increases the conductivity.

[0146] Methods for heating the substrates and / or the adhesive layer are known to those skilled in the art and include the effect of hot gas, such as hot air, and the effect of radiation sources, such as IR or NIR radiation. It is also possible to heat the adhesive layer with ultrasound.

[0147] Manufacturing Process

[0148] Methods for preparing the adhesive composition as described herein are known in the art. Such methods may include the addition of additives and excipients to the polyurethane in the molten state using known equipment such as static mixers, dissolvers, kneaders and extruders. The adhesive is then cooled and can be stored.

[0149] In various embodiments of the present invention, the method of manufacture comprises mixing a reactive polyurethane adhesive with the conductive salt and optionally one or more additives, wherein the mixing is carried out at a temperature such that the composition remains in a molten state.

[0150] Definitions

[0151] The "substrate" can be any type of substrate, including metal (such as steel or aluminum), wood (or wood-based material), plastic (such as PVC, PUR rigid foam, PS rigid foam, PC / ABS), textiles (such as polyester, cotton, blended fabric), plasterboard, stone, ceramic, concrete, glass, cork, paper, cardboard and combinations thereof. Preferably, the substrates are cleaned on the surface to be bonded. Optionally, additional primer layers or other coatings can also be applied. The substrates may be solid and rigid, but in other embodiments flexible substrates, such as single or multi-layer films, may also be used for bonding. The two substrates can be made of the same or different materials.

[0152] "NCO" as used herein refers to the isocyanate group -N=C=O.

[0153] In the context of the present invention, "standard conditions" are synonymous with "normal temperature and normal pressure", which are defined as a temperature of 20 ± 1 °C and an absolute pressure of 101.325 kPa (1 atm).

[0154] Unless otherwise stated herein, atmospheric pressure is understood to be 101.325 kPa. Unless otherwise stated herein, room or ambient temperature is understood to be 21 ±1 °C. Unless otherwise stated, all measurements and procedures disclosed herein are to be understood as having been performed under standard conditions.

[0155] Unless expressly stated otherwise, all percentages given herein with respect to the compositions or formulations refer to weight percentages (wt%) based on the total weight of the respective composition. Preferably, these percentages refer to weight percentages (wt%) based on the total weight of the respective dried composition.

[0156] Unless expressly stated otherwise, numerical values given without decimal places refer to the full value with one decimal place. For example, 99 % stands for 99.0 %.

[0157] In the context of the present application, the term "substantially free" refers to a situation where the compound / solvent / etc. from which the composition or material in question is substantially free may nevertheless be present in small amounts (e.g., as impurities in other components present in the composition in question - for example, commercially available solvents may contain small amounts of, for example, acetone or methyl ethyl ketone as undesirable impurities), but which do not affect the desired properties attributed to the compositions of the present technology. "Substantially free" in this context may mean that the compound, solvent, etc., from which the subject composition or material is substantially free may be present in an amount of 1000 ppm or less, 750 ppm or less, 500 ppm or less, 300 ppm or less, 200 ppm or less, 100 ppm or less, 50 ppm or less, or 10 ppm or less.

[0158] The mentioning of a document in this document is not an admission that the said document or its contents are part of the general knowledge of the person skilled in the art.

[0159] The term "comprise" as used herein is synonymous with "include" and does not exclude additional elements or process steps not listed. According to the present invention, the term "comprising" also includes the term "consisting essentially of" or "consisting of", i.e. that "comprising" may be replaced by the other terms in alternative embodiments, wherein "consisting of' excludes any element or step not expressly mentioned and "consisting essentially of" allows the inclusion of additional elements or steps not mentioned which do not substantially affect the essential or fundamental features of the composition or process in question. If a range of numbers is specified herein, this range is continuous and includes both the minimum and maximum values of the range as well as any value between these minimum and maximum values. If a range refers to integers, each integer between the minimum and maximum values of such a range is included. If several ranges are specified to describe a characteristic or property, these ranges can be combined. This means that, unless expressly stated otherwise, all ranges disclosed herein are to be understood as including all subranges contained therein. For example, a specified range of "1 to 10" is to be understood as including all subranges between the minimum value of 1 and the maximum value of 10, including the values 1 and 10. Exemplary subranges of the range 1 to 10 include 1 to 6.1 , 3.5 to 7.8 and 5.5 to 10. The disclosed upper and lower limits for quantity, range and ratio may be combined independently of each other.

[0160] Any feature of the invention to be present in a particular range or amount may, in a corresponding embodiment, be combined with the other features of this embodiment, and the other features may be present in the ranges or amounts disclosed herein for said other features.

[0161] All ranges and quantities for a feature of one embodiment may be combined with all ranges and quantities of the other features in that embodiment. For example, ranges or values indicated as preferred, more preferred, or most preferred for one feature or component of the invention may be combined with any range or amount indicated for any other feature or component of the embodiment, regardless of whether the range or amount indicated for the other element is designated as preferred, more preferred, most preferred, etc., or is disclosed without such a designation or indication.

[0162] The singular forms used herein (e.g. "a" or "the") include the plural, unless the context clearly indicates otherwise.

[0163] The term "at least one" as used herein includes, but is not limited to, 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10 or more. With respect to an ingredient, the term refers to the type of ingredient and not to the absolute number of molecules. To clarify the foregoing, "at least one alcohol" means at least one type of alcohol, i.e. that one type of alcohol or a mixture of several different alcohols may be meant. The same applies to expressions referring to a higher number (e.g. "at least two", "at least three", etc.), each starting with a higher number (e.g. 2, 3, 4, 5, 6, 7, 8, 9, 10 or more for "at least two"; 3, 4, 5, 6, 7, 8, 9, 10 or more for "at least three"; etc.).

[0164] The terms "approximately", "about" or "approx." used herein in connection with a numerical value refer to a deviation of ±10%, preferably ±5% and particularly preferably ±1%, with respect to the numerical value indicated. Unless expressly stated otherwise, information on molar mass always refers to the number average molar mass (Mn). Unless otherwise stated, all molecular weights given are those determined by gel permeation chromatography according to DIN 55672-1 with THF as eluent. In the present description, the terms isocyanate content, NCO content, NCO value and isocyanate value are used interchangeably.

[0165] In the present description, hydroxyl number, OH value and OH number are interchangeable terms.

[0166] Examples

[0167] The examples given below are merely illustrative of certain embodiments of the invention and in no way limit the scope of the invention described herein and claimed in the patent claims.

[0168] Unless explicitly stated otherwise, all syntheses and measurement methods of parameters were carried out at room or ambient temperature, i.e. at 21 ± 1 °C, and atmospheric pressure.

[0169] Unless explicitly stated otherwise, technically pure reagents were used.

[0170] All reagents used in the examples described below were purchased commercially under the product names indicated.

[0171] Measurement methods

[0172] Molar mass

[0173] The number-average and weight-average molecular weight can be calculated from the end group analysis (OH numbers according to DIN EN ISO 4629) and the functionality of the compound or determined by gel permeation chromatography according to DIN 55672-1 with THF as eluent.

[0174] Viscosity

[0175] The viscosity was determined at 100°C using Brookfield Thermosel RVT according to EN ISO 2555.

[0176] NCO value

[0177] The isocyanate content was determined in accordance with DIN EN ISO 1 1909.

[0178] OH value

[0179] The hydroxyl value was determined in accordance with DIN EN ISO 4629. NCO / OH ratio

[0180] The NCO / OH equivalent ratio can be calculated from the OH value and the NCO value.

[0181] Melting point Tm

[0182] The melting point was determined by differential scanning calorimeter (DSC) according to ISO 1 1357-3. In particular, the peak of an endothermic peak observed when the temperature is increased from -50°C to 250°C at a rate of 10°C / minute was considered as the melting temperature.

[0183] Tensile shear strength

[0184] The tensile shear strength was determined in accordance with DIN EN 1465:2009.

[0185] Experimental Data:

[0186] Polyurethanes

[0187] First, the following polyurethane prepolymers with terminal OH groups were prepared:

[0188] The preparation was carried out by polyaddition of the compound according to formula (4) and isophorone diisocyanate (IPDI) at 60°C with stirring and a reaction time of 3 hours. The ratios of the compound according to formula (4) to IPDI were weighed according to the molecular weights given in Table 1. The molecular weight and / or OH value of the prepolymers were varied.

[0189] Table 1 : Polyurethane prepolymers prepared

[0190] The resulting polyurethane prepolymers with terminal OH groups were first mixed with PPG 400 (polypropylene glycol with an Mw of 400 g / mol and terminal hydroxyl groups) and reacted with polymeric methylene diphenyl diisocyanate (MDI, DesmodurVKS 20) to form the adhesive (2K). The weight of the components and the parameters of the resulting adhesives are summarized in Table 2. Table 2: Polyurethane adhesives prepared

[0191] Adhesive Compositions

[0192] The adhesives were heated until a melt was reached (up to 70 °C) and kept in a molten state. An electrolyte composition was then added in appropriate amounts, followed by mechanical stirring (70 rpm) for about 10 minutes to thoroughly disperse the conductive material (conductive salt) until homogeneity was achieved. The proportions of the components in % by weight of the adhesive compositions are summarized in Table 3.

[0193] Table 3: Prepared adhesive compositions and their components in wt.%

[0194] DPK = Disflamoll from Clariant AG, diphenyl cresyl phosphate

[0195] DoD - Tensile shear strength

[0196] The adhesive compositions described above were each applied to aluminum in order to bond aluminum-aluminum plates.

[0197] The tensile shear strength in MPa was determined with simultaneous application of a voltage.

[0198] Ex.1

[0199] At a voltage of 30 V, failure of the adhesive was observed with an adhesive strength of 0.12 MPa (control = 3.5 MPa).

[0200] The tensile shear strength decreased by 96% at a voltage of 30 V.

[0201] Figure 3A shows the fracture patterns (adhesive failure on one side) after applying stress. It can be clearly seen that the aluminum substrate has no residue of the adhesive composition. In addition, the adhesive composition turned yellow. The yellow coloration indicates the formation of the corresponding ketal according to formula (2) by exposure to electricity starting

[0202] Ex.2

[0203] At a voltage of 20 V, failure of the adhesive was observed with an adhesive strength of 1.2 MPa (control = 3.8 MPa). The tensile shear strength decreased by 68% at a voltage of 20 V.

[0204] Figure 3B shows the fracture patterns (adhesive failure on one side) after applying a voltage. It can be clearly seen that the aluminum substrate has no residue of the adhesive composition. In addition, the adhesive composition turned yellow. The yellow coloration indicates the formation of the corresponding ketal according to formula (2) by exposure to electricity starting from the hydroquinone according to formula (4) (which is part of the polyurethane as shown in formula (1)).

[0205] Ex.3

[0206] At a voltage of 10 V, failure of the adhesive was observed with an adhesive strength of 1.4 MPa (control = 3.8 MPa).

[0207] The tensile shear strength decreased by 63 % at a voltage of 10 V.

[0208] Figure 3C shows the fracture patterns (adhesive failure on one side) after applying a voltage. It can be clearly seen that the aluminum substrate has no residue of the adhesive composition.

[0209] In addition, the adhesive composition turned yellow. The yellow coloration indicates the formation of the corresponding ketal according to formula (2) by exposure to electricity starting from the hydroquinone according to formula (4) (which is part of the polyurethane as shown in formula (1)).

[0210] Ex.4

[0211] At a voltage of 40 V, failure of the adhesive was observed with an adhesive strength of 0.15 MPa (control = 3.6 MPa).

[0212] The tensile shear strength decreased by 95% at a voltage of 40 V.

[0213] Figure 3D shows the fracture patterns (adhesive failure on one side) after applying a voltage. It can be clearly seen that the aluminum substrate has no residue of the adhesive composition. In addition, the adhesive composition turned yellow. The yellow coloration indicates the formation of the corresponding ketal according to formula (2) by exposure to electricity starting from the hydroquinone according to formula (4) (which is part of the polyurethane as shown in formula (1)). Ex.5 (Comparison)

[0214] At a voltage of 40 V, failure of the adhesive was observed with an adhesive strength of 3.5 MPa (control = 3.6 MPa).

[0215] The tensile shear strength decreased by 3 % at a voltage of 40 V. The voltage has no influence on the adhesive strength.

[0216] The examples given above show that adhesive compositions according to the invention have the property that they significantly lose their tensile shear strength when subjected to electricity. This is already achieved at a low voltage. Also, the effective DoD using the present invention requires only short exposure times.

Claims

Claims1 . An electrically releasable adhesive composition comprising(i) at least one conductive salt,(ii) at least one polymer comprising at least one monomer unit per polymer chain according to formula (1):Formula (1) whereinRi and R2are independently selected from the group consisting of hydrogen, linear or branched, substituted or unsubstituted alkanes or alkenes with up to 20 carbon atoms and 1 to 6 heteroatoms selected from O, S and N, substituted or unsubstituted cycloalkylene, cycloalkenylene or arylene with up to 20, preferably up to 12 carbon atoms, particularly preferably 6 carbon atoms, substituted or unsubstituted heterocycloalkylene, heterocycloalkenylene or heteroarylene with up to 20 carbon atoms and 1 to 6 heteroatoms, selected from O, S and N, linear or branched, substituted or unsubstituted alkylcycloalkylene, alkenylcycloalkylene, alkylcycloalkenylene, alkenylcycloalkenylene, alkylarylene or alkenylarylene with up to 20 carbon atoms, linear or branched, substituted or unsubstituted heteroalkylcycloalkylene, heteroalkenylcycloalkylene, heteroalkylcycloalkenene, heteroalkenylcycloalkenene, heteroalkylarylene or heteroalkenylarylene with up to 20 carbon atoms and 1 to 6 heteroatoms, selected from O, S and N, and linear or branched, substituted or unsubstituted heteroalkylheterocycloalkylene, heteroalkenylheterocycloalkylene, heteroalkylheterocycloalkenylene, heteroalkenylheterocycloalkenylene, heteroalkylheteroarylene or heteroalkenylheteroarylene with up to 20 carbon atoms and 1 to 6 heteroatoms, selected from O, S and N, n is an integer of 2 or 3, preferably 2, and wherein the polymer is a polyurethane, andwherein the at least one conductive salt is present in an amount of from 1 to 16% by weight, based on the total weight of the adhesive composition.

2. The electrically releasable adhesive composition according to claim 1 , wherein the adhesive composition comprises a resin binder.

3. The electrically releasable adhesive composition according to any one of the preceding claims, wherein the adhesive composition further comprises a solvent.

4. The electrically releasable adhesive composition according to claims 1 or 2, wherein the adhesive composition is free of solvents.

5. The electrically releasable adhesive composition according to claim 3, wherein the solvent is selected from the group consisting of butyl glycol acetate, 1 ,4-butanediol diglycidyl ether, p-tert-butylphenyl glycidyl ether, allyl glycidyl ether, glycerol diglycidyl ether, butyl diglycol, 2-(2-butoxyethoxy)ethyl ester, acetic acid, 2-butoxyethyl ester, butyl glycol, 2- butoxyethanol, isophorone, 3,3,5-trimethyl-2-cyclohexen-1-one, dimethyl succinate, dimethyl glutarate, dimethyl adipate, acetic acid, dipropylene glycol (mono)methyl ether, propyl acetate, glycidyl ether of alkylphenol and dimethyl ester of adipic, glutaric and succinic acid and combinations thereof.

6. The electrically releasable adhesive composition according to one of claims 2 to 5, wherein the resin binder is a thermoplastic resin binder ora thermosetting resin binder selected from the group consisting of phenoxy resins, polyesters, thermoplastic urethanes, phenolic resins, thermoplastic acrylic polymers, acrylic block copolymers, acrylic polymers with tertiary alkylamide functionality, polysiloxane polymers, polystyrene copolymers, polyvinyl polymers, divinylbenzene copolymers, polyetheramides, polyvinyl acetals, polyvinyl butyral, polyvinyl acetols, polyvinyl alcohols, polyvinyl acetates, polyvinyl chlorides, methylene polyvinyl ethers, cellulose acetates, styrene acrylonitriles, amorphous polyolefins, polyacrylonitriles, ethylene vinyl acetate copolymers, ethylene vinyl acetate terpolymers, functional ethylene vinyl acetates, ethylene acrylate copolymers, ethylene acrylate terpolymers, ethylene butadiene copolymers and / or block copolymers, styrene butadiene block copolymers, vinyl resins, acrylic resins, phenolic resins, epoxy resins, maleimide resins, bismaleimide resins, polyimide resins, and silicone-containing resins, as well as combinations thereof.

7. The electrically releasable adhesive composition according to one of the preceding claims, wherein the tensile shear strength of the cured electrically releasable adhesive composition is reduced by at least 50%, preferably by at least 60% and particularly preferably by at least 70% by applying a voltage of more than 1 V, preferably more than 2 V, and particularly preferably more than 5 V.

8. The electrically releasable adhesive composition according to one of the preceding claims, wherein application of a voltage causes decomposition of the polymer to release the compound according to formula (2)Formula (2) wherein Ri, R2and n are defined as in claim 1.

9. The electrically releasable adhesive composition according to one of the preceding claims, wherein Ri and R2are independently selected from the group consisting of(i) para substituted-,(ii) para, meta substituted-,(iii) meta, meta substituted-, or(iv) unsubstituted arylene with up to 20, preferably up to 12 carbon atoms, particularly preferably 6 carbon atoms, the substituent being electron-withdrawing or electron-donating.

10. The electrically releasable adhesive composition according to claim 9, wherein the electron-withdrawing substituent is selected from the group consisting of(i) halogenated, preferably fluorinated, alkanes with up to 10 carbon atoms,(ii) thiocyanate group,(iii) cyanate group,(vi) nitro group, and(vii) nitrile group; and / or the electron donating substituent is selected from the group consisting of(i) alkanes with up to 10 carbon atoms, and(ii) alkoxy groups with up to 10 carbon atoms, preferably methoxy group.

11. The electrically releasable adhesive composition according to one of the preceding claims, wherein the polymer is a random copolymer of the monomer according to formula (1) and at least one di- or polyisocyanate.

12. The electrically releasable adhesive composition according to one of the preceding claims, wherein the polymer is a block copolymer, preferably a triblock copolymer, of at least one polyurethane and at least one further polymer, wherein the at least one polyurethane or the at least one further polymer comprises at least one monomer according to formula (1), wherein the at least one further polymer is selected from the group consisting of polyester, polyether, and polyamide.

13. Use of the electrically releasable adhesive composition according to one of claims 1 to 11 , for bonding at least two substrates.

14. A method of irreversibly releasing at least two substrates bonded by the adhesive composition according to one of claims 1 to 12, comprising applying an electrical voltage to one of the at least two substrates and / or the adhesive.

15. The method according to claim 14, wherein:(i) the electrical voltage is between 1 and 100 V, preferably between 2.5 and 75 V, particularly preferably between 5 and 48 and especially preferably between 10 and 30 V; and / or(ii) the electrical voltage is applied for a time of 1 second to 30 minutes, preferably from 10 seconds to 20 minutes and in particular preferably from 30 seconds to 5 minutes

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