WO2007142600A1

WO2007142600A1 - An electrochemically weakable adhesive composition

Info

Publication number: WO2007142600A1
Application number: PCT/SE2007/050401
Authority: WO
Inventors: Tommi Remonen; Petronella Norberg
Original assignee: Stora Enso Ab
Priority date: 2006-06-05
Filing date: 2007-06-05
Publication date: 2007-12-13

Abstract

The present invention relates to an electrochemically weakable adhesive composition, possessing adhesive properties to provide an adhesive bond to an electrically conducting surface and sufficient ion conductive properties to enable a weakening of said adhesive bond at the application of a voltage across the adhesive composition, wherein said composition comprises at least one ionic compound in an effective amount to give said ion conductive properties and wherein said ion compound has a melting point of no more than 120 ºC

Description

AN ELECTROCHEMICALLY WEARABLE ADHESIVE COMPOSITION

Field of invention

The present invention relates to an electrochemically weakable adhesive. The invention further relates to a laminate structure comprising said electrically weakable adhesive, a method of producing the laminate structure, a method of preparing an electrically weakable adhesive and a method for delaminating a laminate structure.

Technical Background

It is well known in the art that polymer chains can be broken by the application of a voltage. This is for example discussed in a review article by G. S. Shapoval (Cathodic initiation of reactions of macromolecule formation and degradation, Theoretical and Experimental Chemistry, Volume 30, Number 6, November 1995) .

US 6,620,308 B2 discloses a material for use in the airplane industry. The composition disclosed in US 6,620,308 B2 is developed for use as coatings and adhesives and is capable of releasing when subjected to a voltage current. The composition has a matrix functionality and an electrolyte functionality, wherein the electrolyte functionality is provided by a block copolymer or a graft copolymer. The matrix functionality provides an adhesive bond to a substrate, and the electrolyte functionality provides sufficient ionic conductivity to the composition to support a faradic reaction at an interface with an electrically conductive surface in contact with the composition, whereby the adhesive bond is weakened at the interface. The composition may be a phase-separated composition having first regions of substantially matrix functionality and second regions of substantially electrolyte functionality. US 6,620,308 further relates to a bonded structure comprising two electrically conductive surfaces and the electrochemically disbondable composition. The electrochemically disbondable composition disclosed in US 6,620,308 is suitable for use in various industrial applications. The voltage required to break the adhesive bonds in the composition disclosed in US 6,620,308 is quite high and the releasing time, i.e. the time needed to supply voltage to the adhesive for the adhesive bonds to be broken, is long. This limits its field of applications and makes it unsuitable for use in, e.g., packaging or distribution of products. Another problem with the electrochemically disbondable composition disclosed in US 6,620,308 is that it exhibits inconsistent disbonding, especially when one or both of the conductive surfaces to which it is bonded to is not a continuously conducting material, e.g. when the surfaces consist of graphite or conducting polymers printed on a non-conducting surface. Moreover, the composition disclosed in US 6,620,308 is complex since it requires several additives in order to provide sufficient ion conductivity and plasticizers to achieve proper viscous properties.

WO20070115675 provides a package adapted to be opened by the application of a voltage. The package comprises an electrically weakable adhesive incorporated in its opening. When a voltage is applied across the electrically weakable adhesive, the adhesive bonds are weakened or broken whereby the package can be opened. However, the electrically weakable adhesives previously known in the art, such as the one described in US 6,620,308, are developed for industrial use and not particularly suitable for use in packages in contact with a consumer.

Summary of invention It is an object of the invention to provide an electrochemically weakable adhesive which requires low voltages to weaken the bonds and which gives rise to short releasing times.

Another object of the invention is to provide an electrically weakable adhesive suitable for a wide field of applications and which adhesive enables a wide range of materials of the conductive surface to which the adhesive is bound.

Yet another object of the invention is to provide an electrically weakable adhesive suitable for use in packaging- and or distribution of products, e.g. in the opening of a package.

These objects, as well as other advantages, have been achieved in accordance with the invention with an electrochemically weakable adhesive composition, possessing adhesive properties to provide at least one adhesive bond to an electrically conducting surface and sufficient ion conductive properties to enable a weakening of said adhesive bond at the application of a voltage across the adhesive composition, wherein said composition comprises at least one ionic compound in an effective amount to give said ion conductive properties and wherein said ion compound has a melting point of no more than 120 ⁰C The term "electrochemically weakable adhesive" as used herein is an adhesive that possesses adhesive properties as well as ion conductive properties, which adhesive forms adhesive bonds to an electrically conductive surface in contact with said composition and which bonds are weakened or broken at the application of a voltage to said adhesive. The adhesive thus possesses sufficient ion conductive properties to enable an electrochemical reaction, e.g. a faradic reaction, to occur at the adhesive bonds. Most preferably, the adhesive bond is broken by the electrochemical reaction. Thus, most preferably the adhesive is an electrochemically breakable adhesive.

The adhesive comprising an ionic compound with a melting point of no more than 120 ⁰C of the present invention enhances the contact between the compounds providing the conductive properties of the adhesive and the conductive surfaces to which the adhesive is bound. The viscous properties of the ionic compound with such a low melting point enable it to migrate into all irregularities of the conductive surface. This enables weakening of the adhesive bonds at low voltages and the use of a wide range of materials of the conducting surface to which the adhesive can be bound. Moreover, unlike ordinary salts and conductive polymers, it is possible to choose the hydrophilicity of an ionic compound with a melting point of no more than 120 ⁰C so that it improves the wetting of the conductive surface to which the adhesive is bound. An enhanced contact between the compounds that provide the ionic properties of the adhesive and the conductive surface enables weakening of the adhesive bonds at lower voltages and at shorter releasing times. The hydrophilicity can be changed by choosing an appropriate ionic liquid or a blend of ionic liquids.

In one preferred embodiment of the present invention, the ionic compound with a melting point of no more than 120 ⁰C, providing the ion conductive properties, is hydrophobic. These hydrophobic ionic compounds include, but are not limited to; l-hexyl-3- methylimidazolium 2- (2-fluoroanilino) -pyridinate, 1- hexyl-3-methylimidazolium imide, 1-butyl-l-methyl- pyrrolidinium 2- (2-fluoroanilino) -pyridinate, 1-butyl-l- methyl-pyrrolidinium imide, trihexyl (tetradecyl) phospholium 2- (2-fluoroanilino) - pyridinate or mixtures of any of the above. Hydrophobic ionic compounds with a melting point of no more than 120 ⁰C, e.g. hydrophobic ionic liquids and/or hydrophobic ionic eutectic liquids, are less sensitive to humidity changes and wet conditions that are usual in, e.g., the packaging industry. Thus, electrically weakable adhesives comprising hydrophobic ionic compounds with a melting point of no more than 120 ⁰C are suitable for use in ,e.g., packaging or in distribution of products.

Moreover, hydrophobic ionic compounds improve the wetting of hydrophobic materials whereby the adhesive can be used in laminates with a wider range of materials of the conductive surface. This is especially advantageous when the conducting surface consists of conducting polymer inks, since conducting polymer inks used in wet conditions usually are hydrophobic.

The possibility to set/choose the hydrophilicity of the ionic compound with a melting point of no more than 120 ⁰C, enables the formation of nano-sized co-continous networks in the adhesive, with ion conducting channels, without the need of further additives. This can be achieved by choosing the right combination of solvents and ionic liquids, e.g. by dispersing a hydrophobic ionic liquid in a water based adhesive or vice versa. The formation of ion conducting channels in the adhesive facilitates the electrochemical reaction at the adhesive bonds and, thus, enables weakening of the adhesive bonds at lower voltages and at shorter releasing times. An ionic compound having a melting point of no more than 120 ⁰C provides softening properties to the composition, whereby additives such as plasticizers, are not necessary. The ionic properties of an electrochemically weakable composition normally increase with increased softening properties. However, the addition of plasticizers usually give rise to weakened adhesive properties. The addition of an ionic compound with a melting point below 120 ⁰C, provides the necessary softening properties to the adhesive, but makes it possible to achieve an unaffected or even an increased adhesive strength of the adhesive.

Due to the unique solvating properties of ionic compounds with a melting point below 120 ⁰C, the adhesive can comprise high amounts of the ionic compounds, whereby the ionic conductivity can be increased and, consequently, lower voltages are needed to break the adhesive bonds. In a preferred embodiment, the adhesive comprises an ionic compound having a melting point below 120 ⁰C in an amount of at least 10 %, most preferably 20%, by weight. In another preferred embodiment, the ionic compound is present in an amount of at least 30 % by weight.

Preferably, the ionic compound is in a liquid state when the adhesive is to be weakened or broken by applying of a voltage across the adhesive. When the ionic compound is in a liquid state, the desired ionic conductive and viscous properties of the adhesive are achieved. In most applications, e.g. in packages and/or distribution of products, the weakening of the adhesive usually is performed at temperatures at or below 120 ⁰C. In one preferred embodiment, the ionic compound providing the ionic conductive properties of the adhesive, has a melting point of no more than 100 ⁰C, most preferably of no more than 80 ⁰C. This enables the use of the adhesive also at lower temperatures without affecting the ion- conductive properties. In some embodiments, the ionic compound providing the ionic conductive properties has a melting point of no more than 50 ⁰C, or as low as 25 ⁰C or 0 ⁰C. The possibility to choose the melting point by choosing the appropriate ionic compound can, e.g., be used in packages for frozen food. The package can be provided with an electrically weakable adhesive and an electrical circuit providing voltage to the adhesive.

When the package is frozen, at e.g. -25°C, and the ionic compound is in a solid phase, the ionic conductive properties of the adhesive might not be sufficient to give rise to an electrochemical reaction and, consequently, the adhesive bonds are not weakened or broken. However, when the user thaws the frozen package to room temperature or in a microwave oven to temperatures above the room temperature, the ionic compound turn into a liquid phase and, consequently, provides sufficient ionic properties to the adhesive to enable an electrochemical reaction weakening or breaking the adhesive bond, whereby the package can be opened.

The ionic compound providing the ionic conductive properties of the adhesive can be an ionic liquid. Ionic liquids are salts that are liquid at low temperatures - many at room temperature or below - and that in a molten form are composed wholly of ions. Conventional molten salts exhibit a high melting point (i.e., 801 ⁰C for sodium chloride and 614 °C for lithium chloride Ionic liquids, however, remain liquid at or below room temperature. The adopted upper melting temperature limit for the classification "ionic liquid" is 100 ⁰C. Examples of suitable ionic liquids include, but are not limited to; ammonium ionic liquids, e.g. alkylammonium salts, such as cyclohexyltrimethylammonium bis (trifluormethylsulfonyl) imid or methyltrioctylammonium bis (trifluormethylsulfonyl) imide, di (2- hydrozyethyl) ammonium trifluoroaetate, N, N-dimethyl (2- hydroxyethyl) ammonium octanoate, methyltrioctylammonium bis (trifluoromethylsulfonyl) imide, guanidium ionic liquids, such as N-ethyl-N-N-N-N-tetramethylguanidinium trifluorometanesulfonate, guanidinium trifluoromethanesulfonate, pyridines, e.g. alkylpyridinium salts, such as 1- butyl-4-methylpyridinium bromide, l-buthyl-3- methylpyridinium tetrafluoroborate or l-butyl-3- hydroxymethylpyridinium ethylsulfate, pyrrolidines, such as 1-butyl-l-methylpyrrolidinium bis (trifluoromethylsulfonyl) imide, 1-butyl- methylpyrrolidinium tris (pentafluoroethyl) trifluorophosphate, or imidazoles, e.g., N-N . -dialkylimidazolium salts, such as -3-methyl imidazolium ethylsulfate, 1. -ethyl-3-methylimidazolium chloride, l-ethyl-31-ethyl -methylimidazolium bromide, 1- butyl-3-methylimidazolium chloride, l-hexyl-3- methylimidazolium chloride, l-octyl-3-methylimidazolium chloride, l-methyl-3-octylimidazolium chloride, 1-propyl- 3-methylimidazolium iodide, l-butyl-3-methylimidazolium tetrafluoroborate, l-butyl-3-methylimidazolium trifluoromethanesulfonate, l-butyl-3-methylimidazolium hexafluorophosphate, l-butyl-2, 3-dimethylimidazolium tetrafluoroborate, l-butyl-2, 3-dimethylimidazolium hexafluorophosphate, 1-butylimidazol, 1-methylimidazolium tetrafluoroborate, isouroniums/thiouroniums, phosphoniums, such as tetrabutylphosphonium tris (pentafluoroethyl) trifluorophosphate, trihexyl (tetradecyl) phosphonium tetrafluoroborate, or mixtures of any of the above. In one preferred embodiment of the invention, the ionic liquid comprises a surface active ionic liquid, i.e. an ionic liquid comprising both hydrophobic groups and hydrophilic groups. This group of ionic liquids include, but are not limited to, ionic liquids consisting of an imidazolium cation polar group and a hydrophobic tail, such as l-dodecyl-3-methylimidazolium bromide or 1- (2-acrylolyxyundecyl) -3-methylimidazole, and ionic liquids formulated from imidazole cations with appended perfluoro tails. The surface active ionic liquid forms micelle networks in the adhesive composition without the need of further additives. This facilitates the electrochemical reaction at the adhesive bonds and enables weakening of the bonds at lower voltages and at shorter releasing times.

In another preferred embodiment of the invention, the ionic compound providing the ionic properties of the adhesive is an ionic eutectic mixture or a eutectic solvent. A eutectic mixture is a mixture of two or more solid phases at a composition that gives rise to a melting point that is lower than the individual components, i.e. at a composition that has the lowest melting point or a melting point close to the lowest melting point of the mixture. The eutectic mixture suitable for use in an electrochemically weakable adhesive include, but are not limited to; Fenline 200 (phenol/Choline Cholride) , Clycerine 200 (Glycerol/Choline Choliride) , Fluoline 200 (Trifluoroacetic Acid/Choline Chloride) , Maline 200 (Malonic Acid (Choline Chloride), Ethaline 197 (Ethylene Glycol/Choline Chloride), Reline 203 (Urea/Choline Chloride), Oxaline 100 (Oxalic Acid/Choline Chloride), Ciline 200 (Citric Acid/Choline Chloride) , all supplied by ScioniX Ltd. The ionic liquid or the eutectic mixture can be eatable or nearly eatable. This enables the use of the electrochemically weakable adhesive in contact with a consumer, e.g. in packaging or in distribution of products. Examples of nearly eatable ionic liquids suitable are Reline203 (urea/chlorine chloride), Ciline 200 (citric acid/chlorine chloride) or D- Fructose/chlorine chloride (supplied by ScioniX Ltd) .

The adhesive properties of the adhesive composition can be provided by at least one polymer, including, but not limited to, a polymer selected from the group consisting of epoxies, acrylics, polyesters, urethanes, polyamides, vinyls and phenolics. The polymer should be present in an amount of at least 10%, preferably in an amount of at least 25 % by weight of the total adhesive composition .

The electrochemically weakable adhesive can, e.g., be an electrochemically weakable hot-melt adhesive, an electrochemically weakable contact adhesive, an electrochemically weakable pressure sensitive adhesive or an electrochemicaly weakable thermoset adhesive. The adhesive can comprise further additives, such as hardeners, solvents, plasticizers, etc. not mentioned herein but known in the art. Preferably, the adhesive of the present invention has an ionic conductivity of above 10^"11 S/cm², preferably above 10^~9 S/cm², such as above 10^~7 S/cm², and most preferably above 10^~5 S/cm² . An ion conductivity of above lO^'11 S/cm² enables an electrochemical reaction to occur at the adhesive bonds, whereby the bonds are weakened or broken. An adhesive with an ion conductivity of above 10^~9 S/cm², such as above 10^~7 S/cm², and most preferably above 10^~5 S/cm², requires less voltage in order to break or weaken the bonds . The electrochemically weakable adhesive of the invention can further comprise polyethylene glycol. The presence of polyethylene glycol in the adhesive composition contributes to the formation of stable, ion conducting, channels. Preferably, polyethylene glycol is present in the composition at an amount of at least 1 % by weight, preferably in an amount of at least 5%. Most preferably, polyethylene glycol is present in an amount within the range of 5% to 10%. Preferably, the weight ratio of polyethylene glycol to ionic compound with a melting point of no more than 120 ⁰C is about 3:1 to about 1:3. Most preferably, the weight ratio of polyethylene glycol to ionic compound with a melting point of no more than 120 ⁰C is 1:1. The adhesive composition of the invention can further comprise a salt, i.e. an ordinary salt with a melting point of above 120 ⁰C, dissolved in the ionic compound with a melting point of no more than 120 ⁰C. The salt further improves the ionic conductive properties of the adhesive composition. The salt can, e.g., be selected from the group consisting of alkali metal, alkaline earth and ammonium salts. Most preferably, the salt includes an anion comprising at least one acidic proton, adding proton conducting functionality to the composition, e.g. bisulfite (HSO4^") , dihydrogen phosphate (H2PO4^") , hydrogen phosphate (HPO4^2~) , bicarbonate (HCO3^~) or boric acid. Preferably, the salt is present in the adhesive in an amount of at least 1% by weight, preferably in an amount within the range of 5-10% by weight of the composition. In another preferred embodiment of the present invention, the adhesive composition comprises conductive- or non-conductive particles, preferably of nano and/or micro size. Alternatively or additionally, the adhesive composition can comprise fibers, preferably of nano and/or micro size. The particles and/or the fibers further contribute to the formation of ion conducting channels. Preferably, the particles are added to the composition in an amount of at least 1 % by weight of the composition. Rod-like particles are preferably added within range of 1% - 10 % by weight of the total composition, while spherical or essentially spherical particles are preferably added within the range of 10 % - 25 %, most preferably within the range of 15 - 20% by weight of the total composition. Preferably, the fibers are added to the composition in an amount of at least 1%, more preferably within the range of 1% - 10% and most preferably within the range of 2% -5%.

The electrically weakable adhesive according to the invention is suitable for use in packaging and/or distribution of products. The adhesive may, e.g., be used in the opening of a package. A first and a second portion of a package, which portions form the opening of the package, might be provided with at least one conductive surface and the electrically weakable adhesive of the invention. When the package is to be opened, a voltage is applied across the adhesive whereby bonds in the adhesive is weakened and/or broken and the package can be opened. The laminate of the present invention is particularly useful in packaging solutions, since it enables weakening of the adhesive bonds at low voltages and at short releasing times. Furthermore, the ionic liquid of the invention enables the use of a wide range of materials of the conductive surfaces to which the adhesive is bound, e.g. printed conducting surfaces of graphite and/or conducting polymers. This is especially advantageous when the conductive surfaces are printed on ordinary packaging materials, such as paper, plastic or combinations thereof . The invention further relates to a laminate structure comprising a first and a second electrically conducting surface and a layer of an electrically weakable adhesive composition arranged between said surfaces , which electrically weakable adhesive composition comprises an ionic compound with a melting point of no more than 120 ⁰C. Preferably, the electrically conducting surfaces are arranged at a distance from each other and the electrically weakable adhesive composition partly bridges said distance. The electrically weakable adhesive composition can bridge the whole distance between the conducting surfaces. Alternatively, the distance is bridged by the electrically weakable adhesive composition and a second layer formed of an electrically conductive adhesive. The thickness of the layer of the electrically weakable adhesive composition can be, e.g., 10-500 μm, such as within the range of 100-200 μm or within the range of 200 - 500 μm. Thinner layers, e.g. within the range of 10 - 200, are advantageous since the material consumption is decreased. However, thicker layers, e.g. within the range of 200 - 500 μm, can enable resealing of the laminate due to its sticky properties. The high ion conductive properties of the adhesive according to the invention make it possible to have thick layers of the adhesive on the conductive surfaces and still obtain the weakening of the adhesive bonds at the application of a voltage.

The conducting surfaces of the laminate can be of any conducting material, e.g. metals. In one preferred embodiment, the conducting surfaces comprise carbon, e.g. graphite. Alternatively, the conducting surfaces are of conducting polymers. Carbon based materials, e.g. graphite, and conducting polymers can be easily printed on a non conducting surface and are therefore particularly suitable for use as conducting surfaces in packaging and distribution of products. The use of the adhesive composition according to the invention facilitates the use of printed conducting surfaces. In another preferred embodiment, the laminate structure of the invention further comprise a continuous web impregnated with an electrically weakable adhesive comprising an ionic compound with a melting point of no more than 120 ⁰C. The term "impregnated" as used herein shall mean that the web has been coated and/or saturated with the adhesive. This can be achieved by coating the web with the adhesive and by letting the adhesive at least partly be absorbed by the web or by soaking the web in a solution of the adhesive. The porous, continuous web impregnated with an ionic compound with a melting point of no more than 120 ⁰C form stable channels for the ions whereby the ion conductivity is increased and the laminate is easily delaminated at the application of a voltage to the adhesive. Moreover, by providing a laminate structure with a porous, continuous web impregnated with an electrically weakable adhesive, undesired short-circuiting of the laminate is avoided. Furthermore, an even layer of the electrically weakable adhesive composition is accomplished and the whole surface of the electrically conducting surface is in contact with the electrically weakable adhesive. In this way, the adhesive is evenly weakened and separated from the electrically conducting surface at the application of a voltage. The thickness of the continuous web is preferably within the range of 10 -100 μm, most preferably within the range of 50 - 80 μm.

In one preferred embodiment of the present invention, the porous, continuous web comprises natural and/or synthetic fibers. Fibrous materials are flexible and facilitate the manufacture of webs with a predetermined thickness. Moreover, the use of fibers makes it possible to optimize the porosity of the web to achieve the desired ion conductivity. In this way, lower voltages are needed in order to weaken the adhesive bonds. Preferably, the porous continuous web is of a fiberglass cloth, which is an easily manufactured, flexible material particularly suitable for the above purposes. The web can also be of a porous paper. Paper requires quite low concentrations of the electrically weakable adhesive and is a relative inexpensive raw material .

In yet another preferred embodiment, the web is of an ion exchange textile. In this embodiment, ion exchange groups are grafted onto a non-woven textile. In this way, the ion conductive properties of the electrically weakable adhesive are further enhanced whereby lower voltages are needed in order to weaken the adhesive. The ion exchange group grafted onto the non-woven textile can be of a strong or of a weak cat ion exchanger, such as, e.g., sulfonic acid, carboxylic acid, phosphoric acid, phenolic, arsenic or selenonic or of a strong or of a weak anion exchanger, such as, e.g., a quaternary amine, a tertiary amine, a secondary amine, or a primary amine. Preferably, the ion exchange group is of a cat ion exchanger, most preferably of a sulfonic acid.

In yet another preferred embodiment, the porous, continuous web has an ion conductivity similar to the one of the electrically weakable adhesive, e.g. an ion conductivity of above 10^~9 S/cm², preferably above 10^~7

S/cm². In this way, the adhesive bonds can be weakened at lower voltages. Most preferably, the porous continuous web has an ion conductivity of above 10^~5 S/cm², which would make it possible to break adhesive bonds at even lower voltages.

The laminate may further comprise a second and/or a third layer of an electrically weakable adhesive which adhesive comprises an ionic compound with a melting point of no more than 120 ⁰C, provided between the porous continuous web and one or both of the electrically conducting surfaces. These additional layers improve the wetting of the conductive surfaces by the adhesive, whereby the strength of the adhesive bonds is increased.

The above objectives have also been achieved by a method of producing a laminate structure, the method comprising the steps of providing a first and a second electrically conducting surface; applying a layer of an electrically weakable adhesive comprising an ionic compound with a melting point of no more than 120 ⁰C on one of the conducting surfaces and pressing the conducing surfaces together. The method can also comprise a step of providing a second layer of a conducting, non-electrcally weakable, adhesive on the layer of an electrically weakable adhesive before the step of pressing the conducting surfaces together. This facilitates the manufacture of the laminate, since it enables the pre- manufacturing of a laminate comprising one conducting surface and a layer of an electrically weakable adhesive. Furthermore, undesired short circuit of the laminate is avoided.

In another preferred embodiment of the invention, the method comprises the steps of providing a solution of an electrically weakable adhesive comprising an ionic compound with a melting point of no more than 120 ⁰C; impregnating a porous continuous web with said solution whereby an impregnated porous continuous web is achieved; drying said impregnated porous continuous web; placing said dried, impregnated porous continuous web between said first and second electrically conducting surfaces and pressing the electrically conducting surfaces together at an increased temperature. The method of producing a laminate structure according to the invention facilitates the pre- manufacturing of a laminate that can be delaminated by the application of a voltage. The pre-manufacturing of a porous web impregnated with an electrically weakable adhesive facilitates the handling of the adhesive.

Furthermore, the method according to the invention makes it easier to apply an even layer of the electrically weakable adhesive between the conductive surfaces and it facilitates the achievement of a predetermined distance between the conductive surfaces. Moreover, the use of a porous continuous web, impregnated with the electrically weakable adhesive composition, makes it possible to press the laminate at higher pressures, since short-circuiting is prevented. The invention further relates to a method for delaminating, i.e. disbonding, the laminate structure described above by applying a voltage across the electrically weakable adhesive composition. The voltage applied may be either alternating or direct depending upon the desired manner of weakening of the electrically weakable adhesive. The voltage may e.g. be applied by an external source, such as a battery, by electromagnetic waves, or by designing the laminate with active surfaces, i.e. the conductive surfaces to which the adhesive is bound, of different materials with different electrode potentials, thereby forming an internal battery. If the two active surfaces are connected, e.g. by moving a switch to a position where it connects the two active surfaces, a closed circuit is formed and current will flow through the electrically weakable adhesive thereby causing the adhesive bond to break or to weaken. For example, copper and graphite can be used as active surfaces with different potentials. This design will create a flow of direct current between the active surfaces via the electrically weakable adhesive.

The invention further relates to a method for preparing an electrically weakable adhesive, comprising the steps of; dispersing a hydrophobic polymer in a water solution forming a dispersion of the polymer; dissolving a hydrophilic ionic compound having a melting point of no more than 120 ⁰C in the water phase of the solution; and evaporating the water; or dispersing a hydrophilic polymer in a non-polar solvent; dissolving a hydrophobic ionic compound having a melting point of no more than 120 ⁰C in the non-polar solvent .

In this way, a two phase system comprising ion- conducting channels is easily formed. The method of preparing an electrically weakable adhesive according to the invention can involve further steps, such as evaporation of the solvent, obvious to the skilled person. Moreover, further additives, e.g. solvents and/or surface active materials e.g. soaps or surface active ionic liquids, not mentioned herein but used in the art to stabilize emulsions and dispersion, can also be added to the dispersions and/or solutions.

Detailed description of the invention

The invention is described in more details with reference to some examples below. It is to be understood that the invention is not limited to the particular process steps and materials disclosed herein.

Example 1

A trial was performed, wherein l-ethyl-3-methyl imidazolium ethylsulfate (EMIM-ES) was added to a commercially available epoxy adhesive (Loctite Super Epoxy) . Three samples were prepared, wherein EMIM-ES was added in an amount of 10%, 20% and 30% by weight of the total adhesive composition. EMIM-ES was added to the binding part of the epoxy in each sample whereupon the hardener was added to the mixture. The composition samples were used to glue aluminium foils together, whereby three laminates were manufactured. Thereafter, the electrical resistance was measured. Table 1 shows the amount EMIM-ES and the resistance for each sample. As can be seen in table 1, the resistance decreases with increasing ionic liquid concentration.

Table 1

A voltage was applied across each laminate. All laminates showed delamination, i.e. disbonding, at 25 V within 5 minutes. At lower voltages, 10 V for 10 min, delamination of sample 2 was observed within 5 minutes. Delamination was observed on the anode electrode.

Example 2

In another trial, l-octyl-3-methylimidazolium chloride (OMI-Cl) and TiO2 particles, with a particle size of 2-3 μm, was added to a commercially available hot melt adhesive (Thermelt 869, supplied by Limgrossen AB) in an amount of 17,6 % OMI-Cl and 20 % TiO2 by weight of the total adhesive composition. The hot melt adhesive was melted in a steel can in a furnace and the additives were added stirring the composition in a blender machine. Thereafter, the adhesive composition was allowed to solidify. The thereby produced composition was used to glue aluminum foils together. The adhesive composition was melted and applied onto two surfaces of aluminum foil whereupon the two aluminum foils were heated and pressed together. In this way, totally six laminates were prepared.

A 25 V potential difference was applied across three of the prepared laminates. All of the laminates delaminated, i.e. disbonded, within 5 minutes at the application of 25 V. A 10 V potential difference was applied across the other three laminates. Two of the laminates were delaminated within 5 minutes at the application of 10V.

Example 3

A trial was performed in which l-ethyl-3-methyl- imidazolium-ethylsulfate, EMIM-ES (ECOENG 121, supplied by Solvent Innovation) was added to a commercially available epoxy adhesive, DER 652-PMK65, supplied by DOW. Dicy (diacyanidamide) and 2-MI (2-methyleimidazole) were dissolved in the EMIM-ES, whereupon the EMIM-ES was added to the epoxy adhesive. The ingredients were mixed for 30 minutes at room temperature. The components were present in the thereby prepared composition in accordance with table 2.

Table 2

About 30 ml of the thereby prepared composition was poured onto a (1080) fibreglass web (148 mm by 210 mm, with a thickness of 60 μm, treated with aminosilane) . The composition was distributed by a doctor blade on the fibreglass web and left to wet it for 30 seconds. After 30 seconds, the excess of the adhesive was scraped off. The fibreglass web impregnated with the adhesive was hardened, hanging in an oven, for 5 minutes at 150 ⁰C. Thereafter, the impregnated fibreglass web was arranged between two aluminium foils with thicknesses of 40 μm. The laminate was pressed at about 8 bar and 170 ⁰C for 7 minutes . A 27 V potential difference was applied across the laminate, whereupon the laminate delaminated after 14 seconds .

Example 4

Another trial was performed in which EMIM-ES (ECOENG 121) and Polyethylene glycol (PEG 400) were added to a commercially available epoxy adhesive (DER 652-PMK65, supplied by DOW) . Prior to the addition to the epoxy adhesive, Dicy and 2-MI were dissolved in the EMIM-ES. The components were present in the thereby prepared composition in accordance with table 3.

Table 3

About 30 ml of the composition was poured onto a (1080) fibreglass web (150 mm by 200 mm, with a thickness of 60 μm, treated with aminosilane) . The composition was distributed by a doctor blade on the fibreglass web and left to wet it for 30 seconds. After 30 seconds, the excess of the adhesive was scraped off. The fibreglass web impregnated with the adhesive was hardened, hanging in an oven, for 5 minutes at 150 ⁰C. Thereafter, the impregnated fibreglass web was arranged between two aluminium foils with thicknesses of 40 μm. The laminate was pressed at about 8 bar and 170 ⁰C for 7 minutes.

A 27 V potential difference was applied across the laminate, whereupon the laminate delaminated after 10 seconds .

Example 5

Another trial was performed wherein l-ethyl-3-methyl imidazolium ethylsulfate, EMIM-ES (ECOENG 121, supplied by Solvent Innovation) , was applied to an EVA-based adhesive (Instant Pak 2300) in an amount of 25-30 % by weight as calculated on the total adhesive composition. The EVA-based adhesive (Instant Pak 2300) was first heated into a liquid state, whereupon the EMIM-ES was applied stirring the adhesive composition. The composition was applied at a thickness of about 150 μm between two aluminium foil electrodes. A 25 V potential difference was applied across the electrodes. Delamination was observed within 5 minutes.

Example 6

The electrically weakable adhesive composition prepared in example 5 was used to glue two printed electrodes of carbon together. The printed electrodes were prepared by screen printing Dupont Carbon 7102 in a manual screen printing machine on a double coated kraft board (CKB 185 gsm, supplied by Stora Enso Skoghall AB) . The printed carbon was hardened in an oven at 120 ⁰C for 5 minutes. The composition described in example 5 was applied on one of the printed carbon electrodes whereafter the electrodes were pressed together forming a laminate structure.

A 25 V potential difference was applied between the printed carbon electrodes. Delamination was observed within 5 minutes. Delamination occurred at the carbon anode electrode.

Example 7

A trial was performed in order to investigate the effect of the amount ionic liquid on the maximum breaking load of the adhesive. Three adhesive compositions were prepared wherein butyl-3-methylimidazolium chloride (BMI- CL) were added to a commercially available epoxy adhesive (Loctite Super Epoxy) in amounts of 10 %, 20 % and 30 % by weight of the total adhesive composition, and another three adhesive compositions were prepared wherein EMIM-ES were added to a commercially available epoxy adhesive (Loctite, Super Epoxy) in amounts of 10 %, 20 %, and 30 % by weight of the total adhesive composition. The thereby prepared adhesive compositions were used to glue aluminum foils together. Two aluminum foils were glued together by each adhesive composition, i.e. totally six laminates were prepared. In addition, a reference laminate was prepared by gluing two aluminum foils together with the super epoxy adhesive without the addition of an ionic liquid. The breaking load was investigated in a tensile testing machine. The maximum forces needed to break the adhesive bonds were measured. Fig. 1 shows how the maximum breaking load varies with different amounts of ionic liquid in the adhesive. As can be seen in fig. 1, the maximum breaking load increases with an increased amount of BMI-Cl, but decreases with an increased amount of EMIM-ES.

In comparison with the reference, the breaking load is less than the reference with a small amount of BMIM- Cl, but on the same level as the reference at a higher amount of BMIM-Cl (15 %) . The breaking load is a lot higher than the reference with a small amount of EMIM-ES, (5 %) but lower than the reference with a high amount of EMIM-ES (15 %) .

The addition of EMIM-ES to the adhesive makes it possible to achieve a three-folded increase of the breaking load. The addition of EMIM-ES in an amount within the range of 0 - 10 % gives the highest breaking load. The results show that it is possible to achieve a higher, or an unaffected, breaking load with the addition of an ionic liquid.

Claims

Patent claims

1. An electrochemically weakable adhesive composition, possessing adhesive properties to provide an adhesive bond to an electrically conducting surface and sufficient ion conductive properties to enable a weakening of said adhesive bond at the application of a voltage across the adhesive composition, wherein said composition comprises at least one ionic compound in an effective amount to give said ion conductive properties and wherein said ion compound has a melting point of no more than 120 ⁰C

2. An electrochemically weakable adhesive composition according to claim 1, wherein the ionic compound has a melting point of no more than 100 ⁰C.

3. An electrochemically weakable adhesive composition according to any one of claims 1 or 2, wherein the ionic compound is hydrophobic.

4. An electrochemically weakable adhesive composition according to any one of claims 1 - 3, wherein the ionic compound comprises at least one ionic liquid

5. An electrochemically weakable adhesive composition according to any one of claims 1 - 4, wherein the adhesive comprises at least one surface active ionic liquid

6. An electrochemically weakable adhesive composition according to any one of claims 1-5, wherein the ionic compound is an eutectic mixture.

7. An electrochemically weakable adhesive composition according to any one of claims 1-6, wherein the adhesive properties are provided by at least one polymer .

8. An electrochemically weakable adhesive composition according to claim 7, wherein the polymer is selected from the group consisting of epoxies, acrylics, polyesters, urethanes, polyamides, vinyls and phenolics, and combinations thereof.

9. An electrochemically weakable adhesive composition according to any one of claims 1 or 2, wherein said adhesive composition has an ionic conductivity of above 10 ^~9 S/cm², preferably above 10 ^~5 S/cm².

10. An electrochemically weakable adhesive composition according to any one of claims 1-9, wherein the composition comprises the ionic compound at an amount of at least 10%, most preferably at an amount of at least 20%, by weight of the total adhesive composition.

11. An electrochemically weakable adhesive composition according to any one of claims 1-10, wherein the composition comprises the ionic compound at an amount of at least 30 % by weight.

12. An electrochemically weakable adhesive composition according to any one of claims 1 - 11, wherein said adhesive composition further comprises polyethylene glycol.

13. An electrochemically weakable adhesive composition according to any one of claims 1 - 12, further comprising a salt dissolved in the ionic compound with a melting point of no more than 120 C.

14. An electrochemically weakable adhesive composition according to claim 13, wherein said salt includes an anion comprising at least one proton.

15. An electrochemically weakable adhesive composition according to any one of claims 1- 14, further comprising conductive- and/or non-conductive particles.

16. An electrochemically weakable adhesive composition according to any one of claims 1-15, further comprising fibers.

17. A laminate structure comprising a first electrically conducting surface, a second electrically conducting surface and an electrically weakable adhesive composition according to any one of claims 1-16.

18. A laminate structure according to claim 17, wherein at least one of said electrically conducting surfaces comprises carbon.

19. A laminate structure according to claim 18, wherein said electrically conducting surfaces consist of graphite .

20. A laminate structure according to any one of claims 17-19, wherein at least one of said electrically conducting surfaces comprises a conducting polymer.

21. A laminate structure according to any one of claims 17-20, wherein said electrically conducting surfaces are printed on non-conducting surfaces.

22. A laminate structure comprising a first electrically conducting surface, a second electrically conducting surface and a porous, continuous web impregnated with an electrically weakable adhesive according to any one of claims 1-16 provided between said first and second active surfaces.

23. A laminate structure according to claim 22, wherein the porous continuous web comprises natural and/or synthetic fibres.

24. A laminate structure according to claim 23, wherein the porous continuous web/fabric is of a fibreglass cloth.

25. A laminate structure according to claim 22, wherein the porous continuous web/fabric is of an ion- exchange textile.

26. A laminate structure according to any one of the claims 22 - 25, wherein the porous, continuous web has an ion conductivity of above 10 ^~9 S/cm².

27. A method of producing a laminate structure comprising the steps of; providing a first and a second electrically conducting surface; applying a layer of an electrically weakable adhesive according to any one of claims 1 - 16 on one of the conducting surfaces; pressing the conducing surfaces together.

28. A method of producing a laminate structure comprising the steps of; providing a first and a second electrically conducting surface, providing a solution of an electrically weakable adhesive composition according to any one of claims 1 - 16, impregnating a porous continuous web in said electrically weakable adhesive, drying said impregnated porous continuous web/fabric placing said impregnated web between said first and second electrically conducting surfaces and pressing the electrically conducting surfaces together at an increased temperature to form the laminate structure

29. A method for preparing an electrically weakable adhesive, comprising the steps of; dispersing a hydrophobic polymer in a water solution forming a dispersion of the polymer, dissolving a hydrophilic ionic compound having a melting point of no more than 120 ⁰C in the water solution; or dispersing a hydrophilic polymer in a non-polar solvent forming a dispersion of the polymer, dissolving a hydrophobic ionic compound having a melting point of no more than 120 ⁰C in the water solution.

30. A method for delaminating a laminate structure according to any one of claims 17-26 by applying a potential difference across the electrochemically weakable adhesive.