Electrothermally separable backing, adhesive tape and use thereof, method for separating the adhesive tape, and method for activating the adhesive tape

Abstract

The present invention relates to an electrothermally separable backing for an adhesive tape, an electrothermally separable pressure-sensitive double-sided adhesive tape comprising the backing, an electrothermally activatable and electrothermally separable thermally-reactive double-sided adhesive tape comprising the backing, and an electrothermally separable bonded body formed using the double-sided adhesive tape.

Description

tesa SENorderstedtElectrothermally separable backing, adhesive tape and use thereof, method for separating the adhesive tape, and method for activating the adhesive tapeTECHNICAL FIELD

[0001] The present invention relates to an electrothermally separable backing for an adhesive tape, an electrothermally separable pressure-sensitive double-sided adhesive tape comprising the backing, an electrothermally activatable and electrothermally separable thermally-reactive double-sided adhesive tape comprising the backing, and an electrothermally separable bonded body formed using the double-sided adhesive tape.BACKGROUND

[0002] Thermally separable double-sided adhesive tapes are known in the art, and they are often used to temporarily bond substrates to be assembled. When it is desired to disassemble the temporarily bonded substrates, for example to allow maintenance, replacement or refurbishment operations, or for securing articles during packaging or transportation, the assembly bonded using such double-sided adhesive tape can be easily detached by applying a thermal stimulus to such adhesive tape to cause a physical or chemical change of the adhesive in the adhesive tape, thereby reducing the adhesive force of the adhesive tape within the bonding face.

[0003] In order to generate the above-mentioned thermal stimulus, it is known to add electrically conductive components, such as electrically conductive particles, to the adhesive of the adhesive tape or, in the case of an adhesive tape having, for example, two layers of adhesive, to one of the layers of adhesive. When an external voltage is applied, the electrically conductive components would generate heat, and the generated heat causes the adhesive or the layer of adhesive toundergo a physical or chemical change that leads to thermal separation thereof. Such adhesive tapes are known as electrothermally separable or electrically de-bondable adhesive tapes, and are most often used for temporary bonding of non-conductive substrates such as wood, paper, cardboard, plastic, glass, concrete, ceramics and stone. These substrates are not easy or relatively difficult to be damaged under heating, and as long as the purpose of thermally separating the bonded components is achieved, it is not necessary to consider too much about the design of the structure of the adhesive tape itself and the suitability of the electrically conductive components to prevent thermal damage to the substrates.

[0004] Electrothermally separable adhesive tapes, specifically for electronic devices that are very sensitive to heat, are also known, as described in US2014287299A1. Such adhesive tapes are often used to bond electrically conductive substrates, such as components in electronic devices. For the purpose of preventing the current applied to initiate separation from being conducted away by the electrically conductive substrates, it is necessary to additionally use an insulating carrier in the adhesive tape to separate the electrically conductive material in the adhesive tape from the substrates to be bonded, which increases the complexity of the adhesive tape design and the cost of adhesive tape manufacture. In addition, for such adhesive tapes used in heatsensitive electronic devices, it is more important that the heating efficiency of the electrically conductive material of the adhesive tape should be controlled within an appropriate range. If the heating efficiency is too low, it would take significantly longer to reach the temperature that causes thermal separation of the adhesive or the layer of adhesive, which obviously involves significant time costs. If the heating efficiency is excessively pursued, the electrically conductive material would heat up rapidly and unevenly, thereby easily generating hot spots in the adhesive tape, which in turn would lead to the risk of damage to the bonded substrates.

[0005] Furthermore, to prevent damage to the substrates such as components in electronic devices, US2014287299A1 teaches rapid generation of heat within a heat generating layer as an adhesive tape member, such that the layer of adhesive separates from the adhesive tapestructure before a damaging amount of heat penetrates it. However, such operation is difficult to achieve in practice, especially in precisely controlling the time at which heat is generated and the time point at which the layer of adhesive separates. In addition, such operation requires the application of a very high voltage, which is extremely disadvantageous from the point of view of safety of use, and it does not fundamentally solve the problem of overheating.

[0006] In general, from the point of view of operational safety, the external voltage applied to the electrothermally separable adhesive tape should be lower than 32 V as much as possible, i.e., lower than the body safety voltage. In addition, in order to meet the high temperature environmental testing requirements of existing electronic products, for the electrothermally separable adhesive tape applied to an electronic device, a separation temperature of no more than 85 °C should be set, i.e., the temperature at which separation of the adhesive tape structure occurs. Under such circumstances, it is still needed to develop an electrothermally separable adhesive tape for heat-sensitive electronic devices. When a voltage lower than the body safety voltage is applied to the electrothermally separable adhesive tape, heat can be stably and particularly uniformly generated within the adhesive tape, so that the adhesive tape structure can be effectively separated without the risk of thermal damage to the substrates to which it is bonded.

[0007] On the other hand, a thermally activatable adhesive tape is an adhesive tape that requires heating to activate its tackiness. It is used to provide strong adhesion after heating, and is suitable for occasions where a high strength is required. An adhesive tape is typically consisting of a substrate (such as polyester, polyimide, etc.) and a hot melt adhesive. Adhesives are generally non-tacky at normal temperatures, but become tacky upon heating. When used, the adhesive tape needs to be heated to a specific temperature, usually between 120 °C and 180 °C, depending on the product and applications, to activate the adhesive. Therefore, a thermally activatable adhesive tape has a stronger adhesive strength than a traditional pressure-sensitive adhesive tape, and the higher the thermal activation temperature, the more complete the curing and thehigher the interfacial adhesive force. However, the high interfacial bonding strength also brings problems such as disassembly, repairment, reworking and difficulties in recycling of the thermally activatable adhesive tape bonded body. Moreover, a traditional thermally activatable adhesive tape is activated and cured by transferring heat to the adhesive tape through heat transfer means such as hot platens and ovens. For a non-heat-resistant bonded material, it is difficult to use a thermally activatable adhesive tape for bonding.

[0008] The use of the thermally activatable adhesive tape comprising the electrothermally separable backing of the present invention enables in-situ heating, thereby lowering the temperature of the entire bonded body, avoiding thermal damage to the bonded body, and effectively solving the problem of later disassembly through electrothermal separation technology.SUMMARY OF THE INVENTION

[0009] Accordingly, the present invention provides an electrothermally separable backing for adhesive tape and an electrothermally separable double-sided adhesive tape comprising the same, wherein separation and activation of the adhesive tape structure can be achieved by applying a voltage to a layer of electrically conductive material comprised by the backing. Specifically, in the case when a voltage lower than the body safety voltage is applied, the layer of electrically conductive material can stably and uniformly generate heat in a high electric heating efficiency, and heat the thermally separable material to a temperature of its initial melting point or higher to lose its cohesive force and interfacial molecular force, so that the layer of thermally separable material and the layer of adhesive the layer of electrically conductive material lose bonding strength, and the adhesive tape structure is effectively separated. The heat of the layer of electrically conductive material reaches a peak after a voltage is applied for a certain period of time, and a balance between heating and thermal diffusion is maintained to effectively avoid overheating of the backing. In particular, the overheat protection effect is more remarkable when the layer of electrically conductive material is a film of cured product of a polymer ink comprisingelectrically conductive particles. On the one hand, polymer ink comprising electrically conductive particles according to the present invention can stably and uniformly generate heat in a high electric heating efficiency in the case where a voltage that is lower than the body safety voltage is applied. On the other hand, as the temperature rises, resistance of such a layer of electrically conductive material increases and the current conduction effect weakens, thereby further preventing the temperature of the layer of electrically conductive material from rising to too high to achieve more effective overheat protection. At the same time, when the heat of the layer of electrically conductive material passes through the backing and the layer of adhesive, and reaches the bonded substrates, the temperature of the bonded substrates is at least 30 °C lower than that of the layer of electrically conductive material or less than 80 °C, thereby effectively avoiding the risk of thermal damage to the bonded substrates, especially electronic elements. Further, the backing is particularly useful for a thermally activatable and electrothermally separable adhesive tape. The heat generated when a voltage is applied to the backing not only causes the adhesive tape structure to separate, but also transfers through the backing to the thermally activatable reactive adhesive, thereby activating the thermally activatable reactive adhesive to undergo a thermal crosslinking reaction to firmly adhere to the bonded substrates.

[0010] According to one embodiment of the present invention, the electrothermally separable backing for adhesive tape is constructed as a single layer or multiple layers, wherein the electrically conductive part in the backing has a surface resistance of 0.1 to 10 Q / square, preferably 0.1 to 5 Q / square, more preferably 0.1 to 1 Q / square, and most preferably 0.1 to 0.5 Q / square, at room temperature. The electrothermally separable backing for adhesive tape, which is constructed as multiple layers, preferably two layers, comprises at least one layer of electrically conductive material and at least one layer of thermally separable material applied on at least one surface of the layer of electrically conductive material. The electrothermally separable backing for adhesive tape, which is constructed as a single layer, is a single layer of thermally separable material comprising an electrically conductive material.

[0011] According to preferred embodiments of the present invention, the electrically conductive part in the electrothermally separable backing for adhesive tape has a surface resistance of 0.1 to 8 Q / square, preferably 0.1 to 2.5 Q / square, more preferably 0.1 to 0.4 Q / square, and most preferably 0.1 to 0.3 Q / square, at room temperature.

[0012] According to other preferred embodiments of the present invention, the electrically conductive part in the electrothermally separable backing for adhesive tape has a surface resistance of 1 to 10 Q / square, preferably 2 to 10 Q / square, further preferably 5 to 10 Q / square, particularly preferably 8 to 10 Q / square, and more preferably 9 to 10 Q / square, at room temperature.

[0013] Surprisingly, the inventors found that, when the surface resistance of the electrically conductive part in the backing, in particular the layer of electrically conductive material or the single layer of thermally separable material comprising the electrically conductive material, is set within the above resistance range, the backing can stably and uniformly generate heat that causes the thermally separable material to separate in the case where an external voltage of < 32 V, preferably < 10 V, more preferably < 5 V is applied, and the electric heating efficiency reaches 1 °C / s or higher, which is beneficial for the practical and safe operation and high separation efficiency of the adhesive tape. Moreover, the heat of the electrically conductive part reaches a peak after a certain period of time, and a balance between heating and thermal diffusion is maintained, wherein the thermal equilibrium temperature is between 80 and 180 °C, which can effectively avoid overheating of the backing. When the surface resistance of the electrically conductive part in the backing, in particular the layer of electrically conductive material or the single layer of thermally separable material comprising the electrically conductive material, is < 0.1 Q / square, the difference between the surface resistance and the resistance of a wire that is commonly used for the application of an external voltage is less than 2 orders of magnitude, whereby there is a large voltage division in said wire, so that heating of the wire occurs. When the surface resistance of the electrically conductive part in the backing, inparticular the layer of electrically conductive material or the single layer of thermally separable material comprising the electrically conductive material, is > 10 Q / square, the electric heating efficiency is greatly reduced and the thermal equilibrium temperature at which heat reaches a peak is also greatly reduced. To achieve an electric heating efficiency of 1 °C / s or higher, a voltage of > 32 V needs to be applied to it, which would pose safety issues.

[0014] According to a preferred embodiment of the present invention, the layer of electrically conductive material in the multilayer backing is an alloy foil or a film of cured product of a polymer ink comprising electrically conductive particles.

[0015] According to a further preferred embodiment of the present invention, the layer of electrically conductive material in the multilayer backing is an alloy foil, and the metal composition of the alloy foil comprises two of more selected from the group consisting of aluminum, iron, nickel, chromium, copper, lead and zinc, more preferably iron-nickel alloy.

[0016] According to a further preferred embodiment of the present invention, the layer of electrically conductive material in the multilayer backing is a film of cured product of a polymer ink comprising electrically conductive particles, and the layer of electrically conductive material has a surface resistance of 0.1 to 0.5 Q / square, preferably 0.1 to 0.4 Q / square, and in particular 0.1 to 0.3 Q / square, at room temperature.

[0017] The polymer ink comprising electrically conductive particles as described above are particularly suitable for use in the present invention. This polymer ink, so-called positive temperature coefficient (PTC) ink, is a heating resistive element whose current conducting region is consisting of a material having a positive temperature coefficient (PTC) relative to its resistance. On the one hand, the film of the cured product of the polymer ink comprising electrically conductive particles having the surface resistance according to the present invention can stably and uniformly generate heat in a high electric heating efficiency when a fixed voltage is applied.On the other hand, its resistance increases as the temperature rises, so the current conduction effect weakens as the temperature rises. In the case of a fixed voltage power supply, the input current can be reduced, preventing the temperature of the layer of electrically conductive material from rising to too high to achieve more effective overheat protection.

[0018] The electrically conductive particles that can be used in the polymer ink of the present invention are not particularly limited, as long as they cause the layer of electrically conductive material to have a specific surface resistance according to the present application. Preferably, the electrically conductive particles can be selected form the group consisting of metal particles, alloy particles, metal fibers, carbon nanotubes, and monolayer or multilayer graphene. Further preferably, the electrically conductive particles can be particles formed of silver, copper, aluminum, iron, nickel or alloy materials thereof.

[0019] According to a further preferred embodiment of the present invention, the content of the electrically conductive particles in the film of cured product of a polymer ink comprising electrically conductive particles is 42.5 to 90 wt%, particularly 42.5 to 90 wt%, preferably 43 to 90 wt%, especially 45 to 85 wt%, further preferably 45 to 80 wt%, and more particularly preferably 43 to 50 wt%.

[0020] According to a preferred embodiment of the present invention, the polymer ink is selected from the group consisting of polyacrylate resin, polyurethane, epoxy resin, and polyolefin block copolymer.

[0021] According to a further preferred embodiment of the present invention, the polymer ink further comprises a foaming agent, and the content of the foaming agent in the polymer ink is less than or equal to 25 wt%, preferably less than or equal to 20 wt%, relative to the polymer. The use of such a polymer ink comprising a foaming agent is preferred for the purpose ofachieving overheat protection of the layer of electrically conductive material and for applications of shock protection.

[0022] The foaming agent that can be used in the polymer ink of the present invention is not particularly limited. It is preferably to use foamable microspheres (for example, expandable microspheres) or azo foaming agents.

[0023] "Microspheres" are understood to mean a hollow microbead, which is elastic and therefore expandable in its ground state, and which has a thermoplastic polymer shell. These hollow microspheres are filled with a low boiling point liquid or a liquefied gas. The shell materials used are in particular polyacrylonitrile, PVDC, PVC or polyacrylates. Suitable low-boiling liquids are in particular hydrocarbons from lower alkanes such as isobutane or isopentane, which are encapsulated as liquefied gases in a polymer shell under pressure.

[0024] The action on the microspheres, in particular by the action of heat, leads to softening of the polymer shell. At the same time, the blowing gas present in the liquid state inside the shell is converted into its gaseous form. This results in irreversible extension and three-dimensional expansion of the microspheres. Expansion ends when the internal and external pressures are in equilibrium. Since the polymer shell is retained, a closed-cell foam is obtained. The closed-cell foam is filled in the layer of electrically conductive material to increase the resistance value of the layer of electrically conductive material, thereby reducing the current conduction effect, preventing the temperature of the layer of electrically conductive material from rising too high, and achieving an overheat protection effect.

[0025] According to the present invention, "expandable" microspheres means that the microspheres may be unexpanded or partially expanded, and in both cases may be further expanded, i.e., expandable.

[0026] Many types of expandable microspheres, which differ substantially in size and the onset temperature required for their expansion (75 to 220 °C), are commercially available. An example of commercially available unexpanded microspheres is Expancel® DU (DU - dry unexpanded) product from Akzo Nobel. The expandable microsphere product is also available in the form of an aqueous dispersion with a solid / microsphere content of about 40 to 45 wt%, and also in the form of a polymer-bound microsphere (masterbatch), for example in ethylene-vinyl acetate with a microsphere concentration of about 65 wt%.

[0027] According to a preferred embodiment of the present invention, the film of the cured product of the polymer ink comprising electrically conductive particles can be obtained by printing or coating the polymer ink on a release film and then drying in an oven. There is no particular limitation on the printing or coating method, and it is preferable to apply the polymer ink by screen printing, blade coating and slit coating.

[0028] According to a particularly preferred embodiment of the invention, the thermally separable material in the multilayer backing or the thermally separable material constituting the single-layer backing is a non-adhesive, in particular a non-pressure-sensitive adhesive thermoplastic material. Under such circumstances, the thermally separable material has a melt initiation temperature of no less than 60 °C, and a peak melting temperature of no less than 80 °C and no more than 120 °C, under differential scanning calorimetry (DSC) test conditions. It is advantageous for the separation of the adhesive tape that the melting temperature of the thermally separable material is lower than the thermal equilibrium temperature of the layer of electrically conductive material. When a voltage is applied to the backing and the layer of electrically conductive material generates heat and heats up to and above the melt initiation temperature of the thermally separable material, cohesive force and interfacial intermolecular forces between the backing layers are lost, resulting in separation of the adhesive tape.

[0029] According to a further preferred embodiment of the present invention, the thermally separable material is selected form the group consisting of polyolefins and copolymers of polyolefins, and the copolymers of polyolefins are selected from the group consisting of ethylenevinyl acetate polymer (EVA), ethylene-acrylic acid polymer (EAA), ethylene-methacrylic acid polymer (EMAA), and ethylene-ethyl acrylate or ethylene-butyl acrylate polymer.

[0030] When the thermally separable material of the present invention comprises polyolefins, it is preferable to use polyethylene, polypropylene, especially uniaxially and biaxially oriented polyethylene and polypropylene.

[0031] The method that can be used to prepare the multilayer backing of the present invention is not particularly limited, as long as the layer of thermally separable material of the backing is ultimately bonded to the layer of electrically conductive material by intermolecular forces. In the case where an alloy foil is selected as the layer of electrically conductive material of the present invention, it is preferable to apply solvent-based polyolefin, water-based polyolefin or waterbased ethylene-vinyl acetate polymer slurry on the alloy foil by means of screen printing, blade coating and slit coating, and then dry, thereby obtaining a double-layer backing.

[0032] The method that can be used to prepare the single-layer backing of the present invention is not particularly limited, either. A simpler way is to blend a solvent-based polyolefin, a waterbased polyolefin or a water-based ethylene-vinyl acetate polymer with the electrically conductive material and optionally other additives, and then apply the mixture onto a release film, for example by screen printing, blade coating and slit coating, and then dry, for example in an oven.

[0033] According to a further preferred embodiment of the present invention, the layer of electrically conductive material in the multilayer backing has a thickness of 1 to 30 pm, preferably 5-25 pm, and further preferably 10-20 pm, and the layer of thermally separable material has a thickness of 1 to 30 pm, preferably 5-25 pm, and further preferably 10-20 pm.

[0034] According to a preferred embodiment of the present invention, the backing of the invention may be provided in the form of a die-cut, such as a rectangular-shaped or annularshaped die-cut. In particular, for an annular-shaped die-cut, voltage can be applied thereto in a series circuit or a parallel circuit.

[0035] Although the invention has been described separately for different configurations of the backing, it should be understood that it is not excluded that features or materials encompassed by the multilayer backings can also be applied to the single-layer backing, and vice versa. Various combinations and variations can be made by those skilled in the art without departing from the spirit and scope of the present invention.

[0036] In a second aspect, the present invention provides an electrothermally separable doublesided adhesive tape, comprising the backing as described above, and one or more layer(s) of adhesive applied in each case to the upper and lower sides of the backing, respectively. Based on this backing, various layers of adhesive can be applied to the backing according to application requirements to obtain a double-sided adhesive tape that meets customer's requirements, thereby allowing more flexibility in the design of the electrothermally separable adhesive tape. In some embodiments, an electrically insulating adhesive is preferred.

[0037] According to a further preferred embodiment of the invention, the adhesive is selected from the group consisting of a pressure-sensitive adhesive, a foamed adhesive and a thermally activatable reactive adhesive.

[0038] A thermally activatable reactive adhesive generally refer to an adhesive that do not have tackiness at room temperature and can only be brought into sufficient adhesion by heating to a substrate to be bonded to produce an adhesive connection to the substrate. "Heating" generally refers to exposure to a temperature in the range of about 60 to about 200 °C.

[0039] In principle, all thermally activatable reactive adhesives known in the art can be used in the present invention. However, the preferred thermally activatable reactive adhesives of the present invention comprise reactive components, also called as "reactive resins", in which heating initiates a cross-linking process, and after the cross-linking reaction is completed, a permanent and stable connection can be ensured even under pressure. Such a thermally activatable reactive adhesive preferably also comprises an elastic component, for example an adhesive comprising 50 to 95 wt% of a bondable polymer and 5 to 50 wt% of an epoxy resin or a mixture of several epoxy resins. The bondable polymer advantageously comprises 40 to 94 wt% of acrylic and / or methacrylic compounds of the general formula CH2 =C(Ri )(COOR2 ) (Ri here represents a group selected from H and CH3, and R2 represents a group selected from H and a linear or branched alkyl chain having 1 to 30 carbon atoms); 5 to 30 wt% of a first copolymerizable vinyl monomer having at least one acid group, in particular a carboxylic acid group and / or a sulfonic acid group and / or a phosphonic acid group; 1 to 10 wt% of a second copolymerizable vinyl monomer having at least one epoxy or anhydride functional group; and 0 to 20 wt% of a third copolymerizable vinyl monomer having at least one functional group that is different from the functional groups of the first copolymerizable vinyl monomer and the functional groups of the second copolymerizable vinyl monomer. This sticky substance can activate bonding quickly. Another thermally activatable reactive adhesive that can be used and provide particular advantages comprises 40 to 98% by weight of an acrylate-containing block copolymer, 2 to 50% by weight of a resin component, and 0 to 10% by weight of a curing agent component. The resin component comprises one or more resins selected from the group consisting of epoxy tackifying resins, novolac resins, and phenolic resins. The curing agent component is used to crosslink the acrylate-containing block copolymer with the resin component. More preferably, the thermally activatable layer of adhesive of the present invention is a thermosetting thermally activatable adhesive film based on a low temperature curable type of polyester.

[0040] Advantageously, the pressure-sensitive adhesives useful in the adhesive tapes of the present invention include polyacrylate polymers. This is a polymer obtainable by free radical polymerization of acrylic monomers (which are also understood to mean methacrylic monomers) and optionally further co-polymerizable monomers.

[0041] According to the invention, it may be polyacrylates that are cross-linkable with epoxy groups. Therefore, the monomers or comonomers used can preferably be functional monomers that are cross-linkable with epoxy groups; monomers used here include in particular monomers having acid groups (especially carboxylic acid, sulfonic acid or phosphoric acid groups) and / or hydroxyl groups and / or anhydride groups and / or epoxy groups and / or amine groups; and monomers containing carboxylic acid groups are preferred. It is particularly advantageous when the polyacrylate comprises polymerized acrylic acid and / or methacrylic acid.

[0042] Further monomers that can be used as comonomers for polyacrylates are, for example, acrylates and / or methacrylates having up to 30 carbon atoms, vinyl esters of carboxylic acids having up to 20 carbon atoms, vinyl aromatics having up to 20 carbon atoms, ethylenically unsaturated nitriles, vinyl halides, vinyl ethers of alcohols comprising 1 to 10 carbon atoms, aliphatic hydrocarbons having 2 to 8 carbon atoms and 1 or 2 double bonds, or mixtures of these monomers.

[0043] Preference is given to using polyacrylates that is obtainable from the following monomer compositions: i) acrylates and / or methacrylates of the formula:CH2=C(RI)(COOR2) wherein Ri - H or CH3, and R2- H or a linear, branched or cyclic, saturated or unsaturated hydrocarbon group having 1 to 30, in particular 4 to 18 carbon atoms, ii) ethylenically unsaturated monomers having functional groups of the type already defined as being reactive with epoxy groups,iii) optionally further acrylates and / or methacrylates and / or ethylenically unsaturated monomers which are copolymerizable with component (i).

[0044] The monomers of component (i) are in particular plasticizing and / or non-polar monomers. For monomer (i), acrylic monomers are preferably used, which include acrylates and methacrylates having alkyl groups comprising 4 to 18 carbon atoms, preferably 4 to 9 carbon atoms. Examples of such monomers are n-butyl acrylate, n-butyl methacrylate, n-pentyl acrylate, n-pentyl methacrylate, n-pentyl acrylate, n-hexyl acrylate, hexyl methacrylate, n-heptyl acrylate, n-octyl acrylate, n-octyl methacrylate, n-nonyl acrylate, isobutyl acrylate, isooctyl acrylate, isooctyl methacrylate, and branched isomers thereof such as 2-ethylhexyl acrylate or 2- ethylhexyl methacrylate.

[0045] For component (ii), it is preferred to use monomers having functional groups selected from those listed below: hydroxyl, carboxyl, sulfonic or phosphonic acid groups, anhydrides, epoxides, amines.

[0046] Particularly preferred examples of monomers of component (ii) are acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, aconitic acid, dimethacrylic acid, -acryloyloxy propionic acid, trichloroacrylic acid, vinylacetic acid, vinylphosphonic acid, itaconic acid, maleic anhydride, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, 6-hydroxyhexyl methacrylate, allyl alcohol, glycidyl acrylate, and glycidyl methacrylate.

[0047] For component (iii), monomers mentioned by way of example are: methyl acrylate, ethyl acrylate, propyl acrylate, methyl methacrylate, ethyl methacrylate, benzyl acrylate, benzyl methacrylate, sec-butyl acrylate, tert-butyl acrylate, phenyl acrylate, phenyl methacrylate, isobornyl acrylate, isobornyl methacrylate, tert-butylphenyl acrylate, tert-butylphenyl methacrylate, dodecyl methacrylate, isodecyl acrylate, lauryl acrylate, n-undecyl acrylate, stearylacrylate, tridecyl acrylate, behenyl acrylate, cyclohexyl methacrylate, cyclopentyl methacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, 2-butoxyethyl methacrylate, 2-butoxyethyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, 3,5-dimethyladamantyl acrylate, 4-cumylphenyl methacrylate, cyanoethyl acrylate, cyanoethyl methacrylate, 4-biphenyl acrylate, 4-biphenyl methacrylate, 2-naphthyl acrylate, 2-naphthyl methacrylate, tetra hydrofurfuryl acrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, 2-butoxyethyl acrylate, 2-butoxyethyl methacrylate, 3- methoxymethyl acrylate, 3-methoxybutyl acrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, 2-phenoxyethyl methacrylate, butyl diethylene glycol methacrylate, ethylene glycol acrylate, ethylene glycol monomethacrylate, methoxypolyethylene glycol methacrylate 350, methoxypolyethylene glycol methacrylate 500, propylene glycol monomethacrylate, butoxydiethylene glycol methacrylate, ethoxytriethylene glycol methacrylate, octafluoropentyl acrylate, octafluoropentyl methacrylate, 2,2,2-trifluoroethyl methacrylate, 1, 1,1, 3,3,3- hexafluoroisopropyl acrylate, 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 2, 2, 3,3,3- pentafluoropropyl methacrylate, 2,2,3,4,4,4-hexafluorobutyl methacrylate, 2, 2, 3, 3, 4,4,4- heptafluorobutyl acrylate, 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, 2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctyl methacrylate, dimethylaminopropyl acrylamide, dimethylaminopropyl methacrylamide, N-(l-methylundecyl) acrylamide, N-(n- butoxymethyl) acrylamide, N-(butoxymethyl) methacrylamide, N-(ethoxymethyl) acrylamide, N- (n-octadecyl) acrylamide, and N,N-dialkyl substituted amides such as N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N-benzyl acrylamide, N-isopropyl acrylamide, N-tert-butyl acrylamide, N-tert-octyl acrylamide, N-hydroxymethyl acrylamide, N-hydroxymethyl methacrylamide, acrylonitrile, methacrylonitrile, vinyl ethers such as vinyl methyl ether, ethyl vinyl ether, vinyl isobutyl ether, vinyl esters such as vinyl acetate, vinyl chloride, vinyl halides, vinylidene chloride, vinylidene halide, vinyl pyridine, 4-vinyl pyridine, N-vinyl phthalimide, N-vinyl lactam, N-vinyl pyrrolidone, styrene, p-methylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, 3,4- dimethoxystyrene, macromonomers such as 2-polystyrene-ethyl methacrylate (molecularweight Mw of 4000-13000 g / mol), poly (methyl methacrylate)-ethyl methacrylate (Mw of 2000- 8 000 g / mol).

[0048] It may also be advantageous to select the monomers of component (iii) such that they comprise functional groups that facilitate subsequent radiation-chemical crosslinking (e.g. by e- beam, UV). Suitable co-polymerizable photo-initiators are, for example, benzoin acrylates and acrylate-functionalized benzophenone derivatives. Monomers that contribute to crosslinking by electron radiation are, for example, tetra hydrofurfuryl acrylate, N-tert-butyl acrylamide, allyl acrylate, but this list is not exhaustive.

[0049] Preferably, the foamed adhesive useful in the adhesive tape of the present invention is a foamed pressure-sensitive adhesive. Regarding the foaming of the adhesive, the foaming agents stated above for the polymer ink can be used, and will not be described redundantly here.

[0050] In particular, the electrothermally separable backing of the present invention is particularly suitable for use in a double-sided adhesive tape comprising a thermally activatable reactive adhesive. In this case, the heat generated when a voltage is applied to the backing may not only cause the releasable material layer to separate from the adhesive tape structure, but may also be transferred through the backing to the thermally activatable reactive adhesive, thereby activating the thermally activatable reactive adhesive and producing adhesion to the bonded substrates. The thermally activatable reactive adhesive has a reaction starting temperature of no less than 40 °C and a reaction peak temperature of no more than 120 °C, under DSC test conditions. It is advantageous for activation of the thermally activatable reactive adhesive that the starting reaction temperature of the thermally activatable reactive adhesive is lower than the thermal equilibrium temperature of the layer of electrically conductive material. When the heat generated when a voltage is applied to the backing rises to and above the reaction starting temperature of the thermally activatable reactive adhesive, the adhesive is activated to cause crosslinking reaction and produce adhesion to the bonded substrates.

[0051] In a third aspect, the present invention provides an electrothermally separable bonded body, sequentially comprising a first substrate, the electrothermally separable double-sided adhesive tape according to the present invention as described above, and a second substrate, wherein the first substrate and / or the second substrate are electrically conductive or non- electrica lly conductive substrates.

[0052] In a fourth aspect, the present invention provides a method for separating an electrothermally separable adhesive tape, comprising: providing the double-sided adhesive tape or the bonded body according to the present invention as described above, applying a voltage of no more than 32 V, preferably no more than 10 V, further preferably no more than 3 V, more preferably no more than 2 V and especially no more than 1.5 V, to the layer of electrically conductive material or the single layer of thermally separable material comprisingthe electrically conductive material, the conductive material generates heat and heats the thermally separable material to its starting melting point or a higher temperature, causing the adhesive tape to separate. As mentioned above, the thermal equilibrium temperature of the layer of electrically conductive material is 80-180 °C. When the heat passes through the backing and the layer of adhesive to the bonded substrates, the temperature of the bonded substrates is at least 30 °C lower than that of the layer of electrically conductive material, thereby effectively avoiding the risk of thermal damage to the bonded substrates, especially electronic elements.

[0053] In a fifth aspect, the present invention provides a method for activating an electrothermally separable adhesive tape, comprising: providing the double-sided adhesive tape according to the present invention as described above, wherein the adhesive is a thermally activatable reactive adhesive; applying a voltage of no more than 32 V, preferably no more than 10 V, further preferably no more than 3 V, more preferably no more than 2 V and especially no more than 1.5 V to the layer of electrically conductive material or the single layer of thermally separable material comprising the electrically conductive material, the conductive materialgenerates heat and heats the thermally activatable reactive adhesive to its reaction starting temperature or a higher temperature, causing the adhesive to crosslink and producing adhesion to the first substrate and / or the second substrate.

[0054] Finally, the present invention relates to use of the backing as described above or a doublesided adhesive tape comprising the backing in an electronic device. The backing of the present invention or the double-sided adhesive tape comprising the backing is particularly advantageous when used in a heat-sensitive electronic device. On the one hand, when it is necessary to disassemble a component, in particular an electrically conductive component, of an electronic device that is temporarily bonded using the double-sided adhesive tape of the present invention, for example to allow maintenance, replacement or refurbishment operations or for fixing the component during packaging or transportation, the layer of electrically conductive material in the backing or the layer of thermally separable material comprising the electrically conductive material can be made to generate heat stably and particularly uniformly by applying a voltage lower than the body safety voltage to the adhesive tape of the present invention, such that the adhesive tape structure with the backing can be separated in a safe, controllable and easy to operate manner without the risk of thermal damage to components of the electronic device during disassembly.ADVANTAGEOUS EFFECTS

[0055] The present invention develops an electrothermally separable backing, an electrothermally separable pressure-sensitive double-sided adhesive tape comprising the backing, and an electrothermally activatable and electrothermally separable thermally-reactive double-sided adhesive tape by designing the structure and materials of the backing. The layer of electrically conductive material or the layer of thermally separable material comprising the electrically conductive material can stably and uniformly generate heat in an electric heating efficiency of no less than 1 °C / s under the condition of applying a voltage lower than the body safety voltage, and heat the thermally separable material to its melt initiation temperature orhigher to lose its cohesion and interfacial molecular force, so that the adhesive tape is effectively separated. The method of the present invention is safe to operate and efficient in separation.

[0056] The heat of the layer of electrically conductive material reaches a peak after a voltage is applied for a certain period of time, and a balance between heating and thermal diffusion is maintained, wherein the thermal equilibrium temperature is between 80 and 180 °C, which can effectively avoid overheating of the backing. In particular, the overheat protection effect is more remarkable when the layer of electrically conductive material is a film of cured product of a polymer ink comprising electrically conductive particles. On the one hand, the film of the cured product of the polymer ink comprising the electrically conductive particles having the surface resistance according to the present invention can stably and uniformly generate heat in a higher electric heating efficiency when being applied a voltage. On the other hand, as the temperature rises, resistance of such a layer of electrically conductive material increases and the current conduction effect weakens, thereby effectively preventing the temperature of the layer of electrically conductive material from rising to too high to achieve more effective overheat protection. At the same time, when the heat of the layer of electrically conductive material passes through the backing and the layer of adhesive, and reaches the bonded substrates, the temperature of the bonded substrates is at least 30 °C lower than that of the layer of electrically conductive material or less than 80 °C, thereby effectively avoiding the risk of thermal damage to the bonded substrates, especially electronic elements.

[0057] In another aspect, the backing of the present invention is also particularly suitable for an electrothermally activatable and electrothermally separable thermally-reactive double-sided adhesive tape. The heat generated when a voltage is applied to the backing can not only cause the adhesive tape structure to separate, but also transfer through the backing to the thermally activatable reactive adhesive, thereby activating the thermally activatable reactive adhesive to undergo a thermal crosslinking reaction to firmly adhere to the bonded substrates.BRIEF DESCRIPTION OF DRAWINGS

[0058] The above and other aspects, features and advantages of embodiments according to the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0059] Fig. 1 shows a schematic structural diagram of an electrothermally separable adhesive tape according to an embodiment of the present invention, which includes a backing composed of a layer f of electrically conductive material and a layer g of thermally separable material that is applied on its surface, and layers h of adhesive that are attached to both sides of the backing;

[0060] Fig. 2 shows a schematic structural diagram of an electrothermally separable adhesive tape according to an embodiment of the present invention, which includes a backing composed of a single layer j of electrically conductive and thermally separable material, and the layers h of adhesive that are attached to both sides of the backing;

[0061] Fig. 3 shows a schematic diagram of the surface resistance and electric heating efficiency test of the layer of electrically conductive material;

[0062] Fig. 4 shows a schematic diagram of the holding power (persistent adhesivity) test at room temperature;

[0063] Fig. 5 shows a schematic diagram of the holding power test under conditions for electrothermal separation;

[0064] Fig. 6 shows a schematic diagram of the vertical push-out force test at room temperature;

[0065] Fig. 7 shows a schematic diagram of the vertical push-out force test under conditions for electrothermal separation;

[0066] Fig. 8 shows the temperature of the layer of electrically conductive material over time and the electrical heating efficiencies.DETAILED DESCRIPTION

[0067] TEST METHODS

[0068] Melting temperature of the thermally separable materials

[0069] The melt initiation temperature and melting point of the polymer material as the thermally separable material were measured using DSC. 5 mg of a thin film sample prepared from a non-thermally treated thermally separable material according to the method for preparing a layer of thermally separable material as described in Examples was weighed into an aluminum crucible (volume 25 pL), and sealed with a perforated lid. Measurements were carried out using DSC 250 (from TA), and the process was carried out under inert nitrogen. The sample was first cooled to-70 °C, then heated to 250 °C at a heating rate of 10 °C / min, and cooled again to-70 °C. A subsequent second heating curve was also run at 10 °C / min, and the change in heat capacity was recorded. The melting of the polymer appeared as an endothermic peak in the DSC curve. The temperature corresponding to the intersection of the extrapolated baseline and a tangent drawn at the maximum slope of the curve at which the corresponding endothermic peak transition began was the melt initiation temperature of the polymer. The temperature at which the endothermic peak reached its maximum was the melting point of the polymer.

[0070] Surface resistance

[0071] The surface resistance test of the layer of electrically conductive material was carried out with reference to the two-point probe method in MIL-DTL-83528C method. A sample of the layer of electrically conductive material was cut into a rectangle with a side length of 25.4 mm, and placed on the surface of a non-conductive material. The temperature of the sample was regulated using a heating table or an oven. The probe shown in Fig. 3 was placed on the top surface of the material to be tested, wherein the entire width of the component was such that itshould be in contact with each electrode. After the stabilizer was on for 30 seconds, the resistance R on the ohmmeter was recorded. The surface resistance p was calculated according to ASTM D991 as follows: p _ R _d

[0072] R - measured resistance in ohms.

[0073] d - distance between the two electrodes, i.e. 2.54 centimeters.

[0074] L - length of the electrode, i.e. 2.54 centimeter.

[0075] Electric heating efficiency of the layer of electrically conductive material

[0076] This test was used to determine the change in temperature of the conductive heating layer over time under a 3 V DC power supply, and the temperature of the conductive heating layer when heat generation and heat diffusion reached equilibrium.

[0077] For this purpose, the entire test environment was carried out in a windless constant temperature chamber, the sample of the layer of electrically conductive material was cut into a rectangle with a side length greater than 25.4 mm and placed on the surface of the non- conductive material. The probe shown in Fig. 3 was placed on the top surface of the material to be tested, wherein the entire width of the component was such that it should be in contact with each electrode. The electrodes and the DC power supply were connected, and a thermocouple was used to detect the temperature of the adhesive surface. The temperature of the layer of electrically conductive material at different time points was recorded. Based on the recorded time and temperature values, a curve was plotted. The maximum slope of the curve, i.e., the electric heating efficiency value of the material, was calculated.

[0078] Holding power of the adhesive tape

[0079] The holding power of the adhesive tape was evaluated by testing the shear resistance of the adhesive tape both at room temperature and under conditions for electrothermal separation.The adhesive tape to be tested was bonded to a steel plate, a weight (1 kg) was loaded on the perforated test steel plate, and holding time (min) was recorded. The longer the holding time at room temperature, the better; and the shorter the holding time under conditions for electrothermal separation, the better the separation effect.

[0080] As shown in Fig. 4, a sample of the double-sided adhesive tape was cut into a size of 10 mm x 25 mm. A first side of the adhesive tape sample was attached to a cleaned test steel plate (material 1.4301, DIN EN10088-2, surface 2R, surface roughness Ra - 30 to 60 nm, thickness 1 mm), and a second side of the adhesive tape sample was attached to a cleaned perforated test steel plate.

[0081] If the layer of adhesive was a pressure-sensitive adhesive, a rubber-coated 2 kg steel roller was used to tumble back and forth twice on the adhesive tape at a speed of 10 m / s, and it was soaked for 20 minutes in an environment with a temperature of 23 ± 1 °C and a humidity of 50 ± 5%.

[0082] If the layer of adhesive was a thermally activatable reactive adhesive and there was no layer of electrically conductive material in the adhesive tape, a temperature-controlled laminator was used to hold the assembly with the attached test plate at 110 ° C and 1 MPa for 5 minutes, and soak for 24 hours in an environment with a temperature of 23 ± 1 °C and a humidity of 50 ± 5%.

[0083] If the layer of adhesive was a thermally activatable reactive adhesive, and a layer of electrically conductive material and a layer of thermally separable material were used as backings in the adhesive tape, metal sheets could be used on both sides of the adhesive tape to connect the layer of electrically conductive material, and wires could be used to connect to a DC power supple. As shown in Fig. 5, a voltage of 3 V was applied to the sample for 5 minutes, and at thesame time, a pressure of 1 MPa was applied to the entire assembly. It was soaked for 24 hours in an environment with a temperature of 23 ± 1 °C and a humidity of 50 ± 5%.

[0084] If it was for the purpose of testing the shear resistance of the adhesive tape at room temperature, a weight of 1 kg was hung on the perforated test steel plate, and the shear resistance of the adhesive tape sample was observed.

[0085] If it was for the purpose of testing the electrothermally separable function of the adhesive tape, a weight of 1 kg was hung on the perforated test steel plate, and then both sides of the adhesive tape were connected to a DC power supple to apply a voltage of 3 V. The shear resistance of the adhesive tape sample was observed. At the same time, a thermocouple was used to measure the maximum temperatures on the back of the steel plate and inside of the adhesive tape during the process of thermal separation by energization.

[0086] Results recording and failure analysis: If the perforated test plate fell off completely within 10 000 minutes, the maximum adhesive holding time, the failure mode, and the failure interface of adhesive tape were recorded. If the failure interface was the layer of adhesive and the test steel plate layer, it was determined as adhesive failure. If the failure interface was the layer of adhesive and the thermally separable layer, it was determined as the failure of the intermolecular force between the adhesive and the thermally separable layer. If the failure interface was inside of the thermally separable layer, it was determined as cohesive failure of the thermally separable layer. If the failure interface was the layer of adhesive and the layer of electrically conductive material, it was determined as the failure of the intermolecular force between the adhesive and the layer of electrically conductive material. If the failure interface was the layer of electrically conductive material and the thermally separable layer, it was determined as the failure of the intermolecular force between the layer of electrically conductive material and the thermally separable layer. If the perforated test panel did not fall off completely within 10 000 minutes, the holding time was recorded as greater than 10000 minutes.

[0087] Temperatures of the adhesive tape and the steel plate during the process of electrothermal separation process

[0088] During the test of the holding power under the conditions for electrothermal separation, a thermocouple was used to measure the maximum temperature on the back of the steel plate and inside of the adhesive tape simultaneously during the process of thermal separation by energization.

[0089] Vertical push-out force test

[0090] This test was used to test the resistance of the layer of adhesive of the adhesive tape to vertical separation both at room temperature and during the process of electrothermal separation. For this purpose, a circular adhesive tape cut to be tested with an outer ring diameter of 15 mm and an inner ring diameter of 10 mm was bonded to a perforated steel plate with holes of 10 mm in diameter, the holes were ensured to be aligned, and then a disc of steel plate with a diameter of 15 mm was placed on top of the adhesive tape, as shown in Fig. 6.

[0091] If the layer of adhesive was a pressure-sensitive adhesive, a rubber-coated 2 kg steel roller was used to tumble back and forth twice on the adhesive tape at a speed of 10 m / s, and it was soaked for 20 minutes in an environment with a temperature of 23 ± 1 °C and a humidity of 50 ± 5%.

[0092] If the layer of adhesive was a thermally activatable reactive adhesive and there was no layer of electrically conductive material in the adhesive tape, a temperature-controlled laminator was used to hold the assembly with the attached test plate at 110 ° C and 1 MPa for 5 minutes, and soak for 24 hours in an environment with a temperature of 23 ± 1 °C and a humidity of 50 ± 5%.

[0093] If the layer of adhesive was a thermally activatable reactive adhesive, and a laminated structure of a layer of electrically conductive material and a layer of thermally separable materialwas used in the adhesive tape, metal sheets could be used on both sides of the adhesive tape to connect the layer of electrically conductive material, and wires could be used to connect to a DC power supple. As shown in Fig. 6, a voltage of 3 V was applied to the sample for 5 minutes, and at the same time, a pressure of 1 MPa was applied to the entire assembly. It was soaked for 24 hours in an environment with a temperature of 23 ± 1 °C and a humidity of 50 ± 5%.

[0094] If it was for the purpose of testing the vertical separation resistance of the adhesive tape at room temperature, the steel plate disc was pushed out from the perforated steel plate side at a speed of 10 mm / min at room temperature using a tensile machine with an impact head, and the push-out force and the adhesive tape failure mode when the assembly was seperated and when failure of the adhesive tape occurred were recorded.

[0095] If it was for the purpose of testing the electrothermal separation function of the adhesive tape, both sides of the adhesive tape were connected to a DC power supple, a voltage of 3 V was applied, and a push-out force of 10 N was applied to the steel plate disc from the perforated steel plate side using a tensile machine with an impact head, as shown in Fig. 7. Duration of the applied voltage and the adhesive tape failure mode when the assembly was separated and when failure of the adhesive tape occurred were recorded.

[0096] The failure mode and the failure interface of adhesive tape: If the failure interface was the layer of adhesive and the test steel plate layer, it was determined as adhesive failure. If the failure interface was the layer of adhesive and the thermally separable layer, it was determined as the failure of the intermolecular force between the adhesive and the thermally separable layer. If the failure interface was inside of the thermally separable layer, it was determined as cohesive failure of the thermally separable layer. If the failure interface was the layer of adhesive and the layer of electrically conductive material, it was determined as the failure of the intermolecular force between the adhesive and the layer of electrically conductive material. If the failure interface was the layer of electrically conductive material and the thermally separablelayer, it was determined as the failure of the intermolecular force between the layer of electrically conductive material and the thermally separable layer.0097] Table 1: List of raw materials

[0098] Examples

[0099] I. Preparation of the layer of electrically conductive material - film of cured product of a polymer ink comprising electrically conductive particles

[0100] The components shown in Table 2 were dissolved in propylene glycol methyl ether at a solid weight percentage of 50%. The solution was coated onto a PET release substrate with a coating bar, and dried in a drying oven at 70 °C for 90 minutes. The thickness of the polymer conductive layer after drying was 15 microns.

[0101] Table 2: Composition of the polymer conductive material layer

[0102] II. Preparation of layers of thermally separable material

[0103] The thermally separable material b shown in Table 1 was diluted in xylene solvent at a solid weight percentage of 20%, and the thermally separable material c was diluted in deionized water solvent at a solid weight percentage of 20%. The solutions were coated onto a PET release substrate with a coating bar, and dried in a drying oven at 120 °C for 5 minutes. The thickness of the thermally separable layer after drying was 5 microns. The melting temperatures of the thermally separable materials are shown in Table 3.

[0104] Table 3: Melting temperatures of the thermally separable materials

[0105] III. Preparation of a single layer of thermally separable material comprising conductive particles

[0106] The thermally separable material b and the conductive powder i of nickel as shown in Table 1 were diluted in xylene solvent at a solid weight percentage of 20%, and mixed. The solution was coated onto a PET release substrate with a coating bar, and dried in a drying oven at 120 °C for 5 minutes. The thickness of the single layer of thermally separable material comprising conductive particles was 5 microns.

[0107] Table 4: Composition of the single layer of thermally separable material comprising conductive particles

[0108] IV. Preparation of thermally separable adhesive tape

[0109] The backings, which were constructed as a single layer or two layers, respectively, were prepared using the following layers:

[0110] Layer of electrically conductive materials: conductive layer a of alloy; and polymer conductive material layers 1, 2, 3, each with a thickness of 15 microns

[0111] Layers of thermally separable material: layer b and layer c of thermally separable material, each with a thickness of 5 microns

[0112] Single layer of thermally separable material comprising conductive particles: layer SI of electrically conductive material, with a thickness of 5 microns

[0113] Preparation of electrothermally separable adhesive tape with a backing that is constructed as two layers

[0114] Each of the layer f of electrically conductive material and the layer g of thermally separable material as shown in Table 5 was subjected to nitrogen plasma treatment, stacked, and then fully rolled using a rubber-coated steel roll at a speed of 10 m / s under a pressure of 8 kg and a temperature of 100 °C, and soaked for 24 hours in an environment with a temperature of 23 ± 1 °C and a humidity of 50 ± 5%.

[0115] Both sides of the soaked laminated structure of the layer f of electrically conductive material and the layer g of thermally separable material were subjected to nitrogen plasma treatment, and then the layer h of adhesive as shown in Table 5 was attached to both sides, respectively. A rubber-coated steel roller was used to perform fully rolling at a speed of 10 m / sunder a pressure of 8 kg and a temperature of 60 °C, and soaked for 24 hours in an environment with a temperature of 23 ± 1 °C and a humidity of 50 ± 5%. Finally, an electrothermally separable adhesive tape with a 4-layer structure as shown in Fig. 1 was obtained.

[0116] Preparation of electrothermally separable adhesive tape with a backing that is constructed as a single layer

[0117] Both sides of the single layer j of thermally separable material comprising electrically conductive particles were subjected to nitrogen plasma treatment, and then the layer h of adhesive as shown in Table 6 was attached to both sides, respectively. A rubber-coated steel roller was used to perform fully rolling at a speed of 10 m / s under a pressure of 8 kg and a temperature of 60 °C, and soaked for 24 hours in an environment with a temperature of 23 ± 1 °C and a humidity of 50 ± 5%. Finally, an electrothermally separable adhesive tape with a 3-layer structure as shown in Fig. 2 was obtained.

[0118] Table 5: Material composition of each layer of the electrothermally separable adhesive tape

[0119] Table 6: Material composition of each layer of the electrothermally separable adhesive tape

[0120] Table 7: Reaction temperatures of thermally activatable reactive adhesives under DSC test conditions

[0121] Table 8: Surface resistance of layers of electrically conductive materials at different temperatures

[0122] Table 9: Temperatures of layers of electrically conductive material over time, and electrical heating efficiencies123] Table 10: Properties of the electrothermally separable adhesive tapes

[0124] Analysis of results

[0125] According to the surface resistance test results of the layers of electrically conductive materials at different temperatures (see Table 8), the surface resistance of the layers of conductive alloys remained stable at room temperature and a high temperature. The surface resistance of the polymer conductive material layer increased as the temperature increased. When the temperature reached 130 °C, the resistance of the polymer conductive material layer1 at 130 °C became 2.8 times that at room temperature. The polymer conductive material layer2 exhibited a resistance greater than 1 000 ohm / square at 130 °C, indicating that it became a poor conductor, which helped to add a mistake-proof (or fool-proof) function when the adhesive tape with such material was electrically heated. That is, the operator could complete the operation correctly without special attention or professional knowledge, so as to avoid the risk of material damage caused by excessive temperature of components bonded with adhesive tape due to personnel errors or use of wrong voltages, and realize overheat protection.

[0126] The electric heating efficiency test results (see Fig. 8) of the layers of electrically conductive material showed that when the surface resistance of the layer of electrically conductive material was maintained between 0.1 and 10 ohms / square (such as conductive layer a of alloy, polymer conductive material layer 1), a heating efficiency of >1 °C / s could be achieved at a voltage of 3 V, and the temperature tended to stabilize after 150 s. Moreover, the generation and diffusion of heat of the layers of electrically conductive material reached equilibrium, and the maximum temperature was maintained between 80 and 180 °C. In contrast, when the surface resistance of the layer of electrically conductive material was > 10 ohm / square (polymer conductive material layer 3), the electric heating efficiency of the layer of electrically conductive material at a voltage of 3 V was significantly too low (about 0.1 °C / s), and its equilibrium temperature did not exceed 45 °C, which was not enough to provide the thermally separable function of the adhesive tape and the thermally activatable function of the thermally activatable adhesive tape.

[0127] Examples 1 and 3 related to thermally activatable adhesive tapes using different layers of electrically conductive materials. The thermally activatable adhesive tape of Comparative Example 1 did not include a layer of electrically conductive material and a layer of thermally separable material. By means of electrothermal activation, the holding power and the adhesion in vertical direction of the original tape (Comparative Example 1) could be achieved. After voltage and current were applied to samples of Example l and Example 3, they were both able to achieve adhesion failure within 3 minutes, which facilitated separation of the assemblies of the adhesive tapes, and the failure mode in the holding power test under conditions for electrothermal separation and the vertical push-out force test under conditions for electrothermal separation was cohesive failure of the thermally separable layer. The reason was that the layer of electrically conductive material heated the layer of thermally separable material due to the electrothermal effect, causing the temperature of the layer of thermally separable material to rise above the melting point, thereby losing its cohesive force, so that when the adhesive tape was subjected to a shear stress, the layer of thermally separable material exhibited cohesive failure phenomenon.

[0128] Examples 2 and 4 related to pressure-sensitive adhesive tapes using different layers of electrically conductive materials, and still had the holding power and the adhesion in vertical direction of the original adhesive tape (Comparative Example 2). After voltage and current were applied to samples of Example 2 and Example 4, they were both able to achieve adhesion failure within 2 minutes, which facilitated separation of the assemblies of the adhesive tapes, and the failure modes in the holding power test under conditions for electrothermal separation and the vertical push-out force test under conditions for electrothermal separation were cohesive failure of the thermally separable layer, and failure of intermolecular force between adhesive and thermally separable layer. The reason was that Examples 2 and 4 used pressure-sensitive adhesives, and the pressure-sensitive adhesives themselves would present a phenomenon of viscosity decrease at a high temperature. Under the influence of comprehensive factors, the presented failure mode would be a mixed failure mode of cohesive failure of the thermallyseparable layer, and failure of intermolecular force between adhesive and thermally separable layer.

[0129] Example 5 used a single layer of thermally separable material comprising electrically conductive particles as the layer of thermally separable material, which combined both functions of the layer of electrically conductive material and the layer of thermally separable material. In the test results, its holding power and vertical push-out force at room temperature were at the same level as in Example 4, and also achieved the same function of electrothermal separation after voltage and current were applied, which was reflected in the phenomenon that a holding power failure occurred after 190 seconds of energization, and the vertical push-out force decreased after 200 seconds of energization.

[0130] In the holding power test under conditions for electrothermal separation of Examples 1, 2, 3, 4 and 5, the temperature on the back of the steel plate and the temperature of the adhesive tape were recorded, respectively. It was found that the temperatures on the back of the test steel plates in Examples 1 to 3 were all lower than 100 °C, and the temperatures on the back of the test steel plates in Examples 4 and 5 were even lower than 80 °C. This phenomenon helped to control the problem that the temperature of the entire bonded assembly was too high and the bonded assembly was damaged in the process of electrothermal separation using the electrothermally separable adhesive tape of the present invention.

[0131] In Example 5, both the temperature on the back of the steel plate and the temperature of the adhesive tape were lower than those of Examples 1 to 4. Moreover, the temperature on the back of the steel plate was measured to be lower than 80 °C. This was due to the fact that the source of heat of the entire assembly was from the layer of electrically conductive material of the adhesive tape, and when heat was transferred to the bonded steel plate, it would be dispersed due to the heat transfer and the thermal resistance between the layers of materials,resulting in a phenomenon where the temperature of the back plate was lower than the temperature of the adhesive tape.

Claims

Claims1. An electrothermally separable backing for an adhesive tape, which is constructed as a single layer or multiple layers, wherein the electrically conductive part in the backing has a surface resistance of 0.1 to 10 Q / square, preferably 0.1 to 5 Q / square, more preferably 0.1 to 1 Q / square, and most preferably 0.1 to 0.5 Q / square, at room temperature, the electrothermally separable backing for an adhesive tape, which is constructed as multiple layers, preferably two layers, comprises at least one layer of electrically conductive material and at least one layer of thermally separable material applied on at least one surface of the layer of electrically conductive material, the electrothermally separable backing for an adhesive tape, which is constructed as a single layer, is a single layer of thermally separable material comprising an electrically conductive material.

2. The backing as claimed in claim 1, wherein the layer of electrically conductive material is an alloy foil, and the metal composition of the alloy foil comprises two of more selected from the group consisting of aluminum, iron, nickel, chromium, copper, lead and zinc, more preferably iron-nickel alloy.

3. The backing as claimed in claim 1, wherein the layer of electrically conductive material is a film of cured product of a polymer ink comprising electrically conductive particles.

4. The backing as claimed in claim 1, wherein the layer of electrically conductive material is a film of cured product of a polymer ink comprising electrically conductive particles, and the layer of electrically conductive material has a surface resistance of 0.1 to 0.5 Q / square at room temperature.

5. The backing as claimed in claim 4, wherein the electrically conductive particles are selected form the group consisting of metal particles, alloy particles, metal fibers, carbon nanotubes, and monolayer or multilayer graphene, and the content of the electrically conductive particles in the film of cured product of a polymer ink comprising electrically conductive particles is 42.5 to 90 wt%, and the polymer ink is selected from the group consisting of polyacrylate resin, polyurethane, epoxy resin, and polyolefin block copolymer.

6. The backing as claimed in claim 4 or 5, wherein the polymer ink further comprises a foaming agent, and the content of the foaming agent is less than or equal to 25 wt%, preferably less than or equal to 20 wt%, relative to the polymer.

7. The backing as claimed in claim 6, wherein the foaming agent is foamable microspheres or azo foaming agents.

8. The backing as claimed in claim 1 or 2, wherein the thermally separable material is a non- pressure-sensitive adhesive thermoplastic material.

9. The backing as claimed in claim 8, wherein the thermally separable material has a melt initiation temperature of no less than 60°C and a peak melting temperature of no less than 80°C and no more than 120°C, under DSC test conditions.

10. The backing as claimed in claim 1 or 2, wherein the thermally separable material is selected form the group consisting of polyolefins and copolymers of polyolefins, and the copolymers of polyolefins are selected from the group consisting of ethylene-vinyl acetate polymer (EVA), ethylene-acrylic acid polymer (EAA), ethylene-methacrylic acid polymer (EMAA), and ethyleneethyl acrylate or ethylene-butyl acrylate polymer.

11. The backing as claimed in claim 1, wherein the layer of electrically conductive material has a thickness of 1 to 30 pm, and the layer of thermally separable material has a thickness of 1 to 30 pm.

12. The backing as claimed in claim 1 or 2, wherein when being applied with a voltage of no more than 10 V, the layer of electrically conductive material or the single layer of thermally separable material comprising the electrically conductive material homogeneously heats up at an electric heating efficiency of greater than 1 °C / s, the heat reaches its peak after a certain period of time, and the balance between heating and thermal diffusion is maintained, wherein the thermal equilibrium temperature is 80 to 180°C.

13. An electrothermally separable double-sided adhesive tape, comprising the backing as claimed in any one of claims 1 to 11 and one or more layer(s) of adhesive applied in each case to both sides of the backing, wherein the adhesive is preferably an electrically insulating adhesive.

14. The electrothermally separable double-sided adhesive tape as claimed in claim 13, wherein the adhesive is selected from the group consisting of a pressure sensitive adhesive and a thermally activatable reactive adhesive.

15. The electrothermally separable double-sided adhesive tape as claimed in claim 13, wherein the adhesive is a thermally activatable reactive adhesive, and the thermally activatable reactive adhesive has a reaction starting temperature of no less than 40°C and a reaction peak temperature of no more than 120°C, under DSC test conditions.

16. An electrothermally separable bonded body, sequentially comprising a first substrate, the electrothermally separable double-sided adhesive tape as claimed in claim 13, and a second substrate, wherein the first substrate and / or the second substrate are electrically conductive or non-electrically conductive substrates.

17. A method for separating an electrothermally separable adhesive tape, comprising:- providing the double-sided adhesive tape or the bonded body as claimed in any one of claims 13 to 16,- applying a voltage of no more than 10 V to the layer of electrically conductive material or the single layer of thermally separable material comprising the electrically conductive material,- the layer of electrically conductive material or the single layer of thermally separable material comprising the electrically conductive material heating up at an electric heating efficiency of no less than 1 °C / s and heating the thermally separable material to its melt initiation temperature or higher, so that the layer of thermally separable material loses the bond strength with the layer of electrically conductive material and / or the layer of adhesive, or the single layer of thermally separable material comprising an electrically conductive material loses the bond strength with the layer of adhesive, in order to achieve the separation of the adhesive tape.

18. A method for activating an electrothermally separable adhesive tape, comprising:- providing the double-sided adhesive tape as claimed in claim 14 or 15, wherein the adhesive is a thermally activatable reactive adhesive,- applying a voltage of no more than 10 V to the layer of electrically conductive material or the single layer of thermally separable material comprising the electrically conductive material,- the layer of electrically conductive material or the single layer of thermally separable material comprising the electrically conductive material heating up at an electric heating efficiency of no less than 1 °C / s, and heating the thermally activatable reactive adhesive to the reaction starting temperature or higher, so that the thermally activatable reactive adhesive undergoes crosslinking and bonds with the first substrate and / or the second substrate.

19. Use of the backing as claimed in any one of claims 1 to 12 or the double-sided adhesive tape as claimed in any one of claims 13 to 15 in an electronic device.

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