Debonding of a cured composition

Abstract

A method of debonding first and second substrates bonded together by a cured product of a cationically curable composition is disclosed. The composition comprises an epoxy component, expandable microspheres, and a cationic polymerisation initiator, wherein the microspheres contain an expanding agent that expands under heat, thus causing the microspheres to expand. The method comprises heating the cured product to cause thermal expansion of the microspheres, thereby reducing the tensile strength of the bond formed by the cured product by ≥50% and leading to at least partial debonding of the substrates. The microspheres may be 2-80 microns in diameter and may contain silica and a gas, especially an alkane gas like isobutane. The epoxy component may be 2-vinyloxyethylglycidyl ether and the initiator may comprise (4-isopropylphenyl)(4-methylphenyl)iodonium tetrakis(pentafluorophenyl)borate or an ammonium salt of tetrakis(pentafluorophenyl)boric acid. Preferably, the first substrate is an electronic component and the second substrate is a printed circuit board.

Description

Field

[0001] The present invention relates to a method of debonding of two substrates that are bonded together using a curable composition. The adhesive bond is formed by curing of the curable composition. In particular the present invention relates to a method of debonding where the bond has been formed by a cationically curable adhesive composition. The composition may include a photocationic polymerization initiator and / or a thermal cationic polymerization initiator. Optionally the composition is dual-curable adhesive composition. Such a dual-curable adhesive composition is curable through cationic polymerization by light irradiation and heating, a cured product thereof. Related Art

[0002] When products come to the end of their life cycle it is desirable to recycle them. Substrates which have been bonded together using a curable adhesive composition can be difficult to recycle as it may be difficult to separate the parts that have been bonded together. Methods of debonding have been developed which include heating and / or applying a separation force and / or using a solvent.

[0003] One end use application, where debonding is important, is the field of electronics where electronic components may be bonded to each other or to a substrate such as an integrated circuit board.

[0004] It is an objective of the present invention to provide a method of debonding of two substrates that are bonded together using a curable composition. In particular it is an objective of the present invention to provide a method of bonding where the bond has been formed by a dual curable adhesive composition. Summary

[0005] In one aspect, the present invention provides a method of debonding a first substrate from a second substrate, wherein the first substrate is bonded to the second substrate by the cure product of a cationically curable composition, the cationically curable composition comprising: (a) an epoxy component; (b) a cationic polymerization initiator; and (c) expandable microspheres; wherein the expandable microspheres contains an expanding agent which expands under application of heat and in turn causes the microspheres to expand, the method comprising the step of: subjecting the cure product to heat to thermally expand the microspheres, so that the thermal expansion of the microspheres reduces the tensile strength of the bond formed by the cure product by at least 50% thus causing at least partial debonding of the first substrate relative to the second substrate.

[0006] Compositions for use in the method of the invention are cationically curable.

[0007] Compositions for use in the method of the invention may include a thermal cationic polymerization initiator or a photocationic polymerization initiator or both.

[0008] Such an adhesive composition has excellent adhesive strength, is curable at a high reaction ratio at a low temperature.

[0009] Recyclability at the end of life of components within the electronic market is becoming a requirement from both a regulatory and ethical / environmental point of view. The present invention facilitates that.

[0010] The present invention eliminates the need for a debondable primer.

[0011] The invention enables recyclability of parts, including those bonded to printed circuit boards, at the end of product life by debonding of two components.

[0012] Debonding in the present invention is achieved by thermal treatment.

[0013] Such partial debonding allows for separation of substrates for reuse / recycling.

[0014] The first substrate may be an electronic component. The second substrate may also be an electronic component.

[0015] Optionally the second substrate may be a printed circuit board.

[0016] Suitable cationically curable compositions for use in the present invention are typically one-part, room temperature stable composition.

[0017] Suitable cationically curable compositions for use in the present invention are typically one part compositions and are typically stable at room temperatures.

[0018] Suitable cationically curable compositions for use in the present invention are typically activated by UV irradiation.

[0019] Often cationically curable compositions for use in the present invention have adjustable open times.

[0020] This cationically curable composition is typically a UV-activated delayed cure cationic epoxy adhesive that enables debonding with the use of heat. This adhesive has been developed for application to a printed circuit board, followed by activation with UV radiation.

[0021] Once activated such a cationically curable composition has an open time of more than 10 minutes (before build up in viscosity) allowing time for assembly of the substrates. Once assembled the adhesive reaches full cure over a 24 hour period at room temperature.

[0022] At the end of life of the product the bonded assembly can be heated to 150 C for 30 minutes to reduce the bond strength by more than 90% allowing disassembly and recycling of the parts that were bonded together.

[0023] Unless otherwise stated the term “alkyl” (including for example as used in the term alkylene) relates to materials having Ci-Cwsuch as Ci-Ce. Unless otherwise stated the term “aromatic” or “aryl” or “aralkyl” relates to materials having Ca-Czosuch as C3-C10. Epoxy Component

[0024] The epoxy component is a curable component of the composition of the invention.

[0025] The epoxy component is desirably present in an amount of from about 30 to about 70% by weight based on the total weight of the composition.

[0026] Optionally the epoxy component comprises an alicyclic epoxy compound.

[0027] Optionally the epoxy component comprises an oxetane compound.

[0028] Optionally the epoxy component comprises an aromatic glycidyl ether-based epoxy compound.

[0029] The epoxy component may comprise one or more at least bifunctional epoxycontaining compounds. At least “bifunctional” means that the epoxy-containing compound contains at least two epoxy groups. The epoxy component can comprise cycloaliphatic epoxides, aromatic and aliphatic glycidyl ethers, glycidyl esters or glycidyl amines and mixtures thereof.

[0030] Bifunctional cycloaliphatic epoxy compounds are well known in the state of the art and contain compounds carrying both a cycloaliphatic group and at least two oxirane rings. Exemplary compounds are 3-cyclohexenylmethyl-3-cyclohexyl carboxylate diepoxide, 3,4-epoxycyclohexylalkyl-3',4'-epoxy cyclohexane carboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-3',4'-epoxy-6-methyl cyclohexane carboxylate, vinyl cyclohexene dioxide, bis(3,4-epoxycyclohexylmethyl) adipate, dicyclopentadiene dioxide and 1,2-epoxy-6-(2,3-epoxypropoxy)hexahydro-4,7-methane indane and mixtures thereof.

[0031] Aromatic epoxy compounds can also be used in the compositions according to the present invention. Examples of aromatic epoxy compounds / resins are bisphenol-A epoxy resins, bisphenol-F epoxy resins, phenol novolac epoxy resins, cresol novolac epoxy resins, biphenyl epoxy resins, 4,4'-biphenyl epoxy resins, divinyl benzene dioxide, 2-glycidyl phenyl glycidyl ether, naphthalene diol diglycidyl ether, glycidyl ether of tris(hydroxyphenyl) methane and glycidyl ether of tris(hydroxyphenyl) ethane as well as mixtures thereof. In addition, all completely or partially hydrogenated analogues of aromatic epoxy resins can be used.

[0032] The epoxy component may comprise isocyanurates and other heterocyclic compounds substituted with epoxy-containing groups. Examples are triglycidyl isocyanurate and monoallyl diglycidyl isocyanurate.

[0033] The epoxy component may comprise polyfunctional epoxy resins of all resin groups mentioned, viscoplastic epoxy resins and blends of different epoxy resins can be used in the compositions according to the present invention.

[0034] A combination of several epoxy-containing compounds, at least one of which is bifunctional or of a higher functionality may be utilised.

[0035] Monofunctional epoxides can also be used as reactive diluents for the epoxy component / curable composition.

[0036] Examples of commercially available epoxy-containing compounds are products available under the trade names CELLOXIDE™ 2021P, CELLOXIDE™ 8000 by Daicel Corporation, Japan, EPIKOTE™ RESIN 828 LVEL, EPIKOTE™ RESIN 166, EPIKOTE™ RESIN 169 by Momentive Specialty Chemicals B. V., Netherlands, Epilox™ resins from the product series A, T and AF by Leuna Harze, Germany, or EPICLON™ 840, 840-S, 850, 850-S, EXA850CRP, 850-LC by DIC K. K., Japan, Omnilane 1005 and Omnilane 2005 by IGM Resins B.V., Syna Epoxy 21 and Syna Epoxy 06 by Synasia Inc., TTA21, TTA26, TTA60 and TTA128 by Jiangsu Tetra New Material Technology Co. Ltd.

[0037] Optionally in addition to the epoxy component, oxetane-containing compounds can be used as cationically curable components in the compositions. Methods for the manufacture of oxetanes are known from US Patent Publication No. 2017 / 0198093 A1.

[0038] Examples of commercially available oxetanes are bis(1-ethyl-3-oxetanyl-methyl) ether (DOX), 3-allyloxymethyl-3-ethyl oxetane (AQX), 3-ethyl-3-[(phenoxy)methyl] oxetanes (PDX), 3-ethyl-3-hydroxymethyl oxetanes (OXA), 1,4-bis[(3-ethyl-3-oxetanylmethoxy)methyl] benzene (XDO), 3-ethyl-3-[(2-ethylhexyloxy)methyl] oxetane (EHOX). Said oxetanes are commercially available by TOAGOSEI CO., LTD.

[0039] The epoxy component may comprise a non-aromatic glycidyl ether-based epoxy compound, such as 1,4-butanediol diglycidyl ether and 2-vinyloxyethylglycidyl ether.

[0040] The epoxy component may comprise an aromatic glycidyl ether-based epoxy compound. The aromatic glycidyl ether-based epoxy compound is not particularly limited as long as it is a compound having an aromatic hydrocarbon structure and a glycidyl ether group in the molecule. Desirably, the aromatic glycidyl ether-based epoxy compound has two or more aromatic hydrocarbon structures and two or more glycidyl ether groups in the molecule.

[0041] Examples of the aromatic glycidyl ether-based epoxy compound include a bisphenol type epoxy compound such as a bisphenol A type epoxy compound, a bisphenol F type epoxy compound, and a bisphenol S type epoxy compound; a novolac type epoxy compound such as a phenol novolac type epoxy compound and a cresol novolac type epoxy compound; and a biphenyl type epoxy compound.

[0042] The aromatic glycidyl ether-based epoxy compound desirably includes a bisphenol type epoxy compound, desirably includes at least one selected from a bisphenol A type epoxy compound and a bisphenol F type epoxy compound, and desirably includes at least a bisphenol A type epoxy compound. In general, the bisphenol A type epoxy compound and the bisphenol F type epoxy compound are produced by a reaction of epichlorohydrin with bisphenol A and bisphenol F, respectively. As one aspect of the present embodiment, the amount of the bisphenol A type epoxy compound and / or the bisphenol F type epoxy compound is desirably 80% by mass or more, and may be 100% by mass, based on the total amount of the aromatic glycidyl ether-based epoxy compound.

[0043] The aromatic glycidyl ether-based epoxy compounds may be used singly or in combinations of two or more thereof.

[0044] The aromatic glycidyl ether-based epoxy compound is desirably a liquid or a semi-solid at ordinary temperature (about 23°C), but a solid compound may be used after dissolving it. The epoxy equivalent of the aromatic glycidyl ether-based epoxy compound is not particularly limited, but is desirably 50 to 480, more desirably 60 to 450.

[0045] Examples of commercially available aromatic glycidyl ether-based epoxy compounds include Bisphenol A type epoxy compounds such as 840, 840S, 850, 850S, EXA-850CRP, 850LC, 860, 1050, and 1055 manufactured by DIC Corporation; Bisphenol F type epoxy compounds such as 830, 830S, 835, EXA830CRP, EXA830LVP, and EXA835LV manufactured by DIC Corporation; Bisphenol A type epoxy compounds such as 825, 827, 828, 1001, 1002 manufactured by Mitsubishi Chemical Corporation; Bisphenol F type epoxy compounds such as 806, 806H, and 807 manufactured by Mitsubishi Chemical Corporation; Bisphenol A type epoxy compounds such as RE-310S manufactured by Nippon Kayaku Co., Ltd.; Bisphenol F type epoxy compounds such as RE-303S-L manufactured by Nippon Kayaku Co., Ltd.; and NC-3000L and NC-2000L manufactured by Nippon Kayaku Co., Ltd.

[0046] The aromatic glycidyl ether-based epoxy compound can impart adhesive strength to the adhesive composition which is optionally a dual-curable adhesive composition.

[0047] The amount of the aromatic glycidyl ether-based epoxy compound is desirably 3 parts by mass or more, more desirably 5 parts by mass or more, further desirably 10 parts by mass or more, and still more desirably 15 parts by mass or more, (in relation to the lower limit of the amount present), and is desirably 45 parts by mass or less, more desirably 40 parts by mass or less, further desirably 35 parts by mass or less, and still more desirably 30 parts by mass or less, (in relation to the upper limit of the amount present), each based on 100 parts by mass of the total amount of the epoxy component. Toughening Component

[0048] It is desirable that an epoxy component of the present invention is toughened for example using a toughening component. For example the epoxy composition of the invention may include elastomeric materials optionally in the form of particles. One example of a toughening component are rubber particles, for example core shell rubber particles.

[0049] The toughening component is desirably present in an amount of from about 5 to about 30% by weight based on the total weight of the composition.

[0050] Suitable toughening components are set out below.

[0051] Rubber particles having a core-shell structure may be an additional component of the compositions of the present invention. Such particles generally have a core comprised of a polymeric material having elastomeric or rubbery properties (i.e., a glass transition temperature less than about 0° C., e.g., less than about -30° C.) surrounded by a shell comprised of a non-elastomeric polymeric material (i.e., a thermoplastic or thermoset / crosslinked polymer having a glass transition temperature greater than ambient temperatures, e.g., greater than about 50° C.). For example, the core may be comprised of a diene homopolymer or copolymer (for example, a homopolymer of butadiene or isoprene, a copolymer of butadiene or isoprene with one or more ethylenically unsaturated monomers such as vinyl aromatic monomers, (meth)acrylonitrile, (meth)acrylates, or the like) while the shell may be comprised of a polymer or copolymer of one or more monomers such as (meth)acrylates (e.g., methyl methacrylate), vinyl aromatic monomers (e.g., styrene), vinyl cyanides (e.g., acrylonitrile), unsaturated acids and anhydrides (e.g., acrylic acid), (meth)acrylamides, and the like having a suitably high glass transition temperature. The polymer or copolymer used in the shell may have acid groups that are crosslinked ionically through metal carboxylate formation (e.g., by forming salts of divalent metal cations).

[0052] The shell polymer or copolymer could also be covalently crosslinked through the use of monomers having two or more double bonds per molecule. Other rubbery polymers may also be suitably be used for the core, including polybutylacrylate or polysiloxane elastomer (e.g., polydimethylsiloxane, particularly crosslinked polydimethylsiloxane). The rubber particle may be comprised of more than two layers (e.g., a central core of one rubbery material may be surrounded by a second core of a different rubbery material or the rubbery core may be surrounded by two shells of different composition or the rubber particle may have the structure soft core, hard shell, soft shell, hard shell). In one embodiment of the invention, the rubber particles used are comprised of a core and at least two concentric shells having different chemical compositions and / or properties. Either the core or the shell or both the core and the shell may be crosslinked (e.g., ionically or covalently), as described, for example, in U.S. Pat. No. 5,686,509 (incorporated herein by reference in its entirety). The shell may be grafted onto the core. The polymer comprising the shell may bear one or more different types of functional groups (e.g., epoxy groups, carboxylic acid groups) that are capable of interacting with other components of the compositions of the present invention. In other embodiments, though, the shell is free of functional groups capable of reacting with other components present in the composition.

[0053] Typically, the core will comprise from about 50 to about 95 percent by weight of the rubber particles while the shell will comprise from about 5 to about 50 percent by weight of the rubber particles.

[0054] Preferably, the rubber particles are relatively small in size. For example, the average particle size may be from about 0.03 to about 2 pm or from about 0.05 to about 1 pm. In certain embodiments of the invention, the rubber particles have an average diameter of less than about 500 nm. In other embodiments, the average particle size is less than about 200 nm. For example, the core-shell rubber particles may have an average diameter within the range of from about 25 to about 200 nm or from about 50 to about 150 nm.

[0055] Methods of preparing rubber particles having a core-shell structure are well-known in the art and are described, for example, in U.S. Pat. Nos. 3,985,703, 4,180,529, 4,315,085, 4,419,496, 4,778,851, 5,223,586, 5,290,857, 5,534,594, 5,686,509, 5,789,482, 5,981,659, 6,111,015, 6,147,142 and 6,180,693, 6,331,580 and published U.S. application 2005-124761, each of which is incorporated herein by reference in its entirety. Rubber particles having a core-shell structure are also available from several commercial sources. The following core-shell rubbers are suitable for use in the present invention, for example: the core-shell particles available in powder form from Wacker Chemie under the tradename GENIOPERL, including GENIOPERL P22, P23, P52 and P53, which are described by the supplier as having crosslinked polysiloxane cores, epoxy-functionalized polymethylmethacrylate shells, polysiloxane content of about 65 weight percent, softening points as measured by DSC / DMTA of about 120 degrees C., and a primary particle size of about 100 nm, the core-shell rubber particles available from Rohm &Haas under the tradename PARALOID, in particular the PARALOID EXL 2600 / 3600 series of products, which are grafted polymers containing a polybutadiene core upon which is grafted a styrene / methylmethacrylate copolymer and having an average particle size of ca. 0.1 to about 0.3 pm; the core-shell rubber particles sold under the tradename DEGALAN by Roehm GmbH or Roehm America, Inc. (e.g., DEGALAN 4899F, which is reported to have a glass transition temperature of about 95° C.); the core-shell rubber particles sold by Nippon Zeon under the tradename F351; and the core-shell rubber particles sold by General Electric under the tradename BLENDEX.

[0056] Rubber particles having a core-shell structure may be prepared as a masterbatch where the rubber particles are dispersed in one or more epoxy components / resins such as a diglycidyl ether of bisphenol A. For example, the rubber particles typically are prepared as aqueous dispersions or emulsions. Such dispersions or emulsions may be combined with the desired epoxy component / resin or mixture of epoxy components / resins and the water and other volatile substances removed by distillation or the like. One method of preparing such masterbatches is described in more detail in European Patent Application EP 1632533, incorporated herein by reference in its entirety. For example, an aqueous latex of rubber particles may be brought into contact with an organic medium having partial solubility in water and then with another organic medium having lower partial solubility in water than the first organic medium to separate the water and to provide a dispersion of the rubber particles in the second organic medium. This dispersion may then be mixed with the desired epoxy component(s) / resin(s) and volatile substances removed by distillation or the like to provide the masterbatch. Other methods for preparing masterbatches of rubber particles having a core-shell structure stably dispersed in an epoxy component / resin matrix are described in U.S. Pat. Nos. 4,778,851 and 6,111,015, each incorporated herein by reference in its entirety. Preferably, the rubber particles are stably dispersed in the epoxy component / resin matrix, i.e., the core-shell rubber particles remain as separated individual particles with little or no agglomeration of the particles or precipitation (settling) of the particles from the masterbatch as the masterbatch is aged by standing at room temperature. The shell of the rubber particles may advantageously be functionalized to improve the stability of the masterbatch, although in another embodiment the shell is non-functionalized (i.e., does not contain any functional groups that react with any of the other components of the adhesive composition (such as the epoxy component / resin or curing agent) when that composition is cured).

[0057] Particularly suitable dispersions of rubber particles having a core-shell structure in an epoxy component / resin matrix are available from Kaneka Corporation. One suitable material available from Kaneka Corporation is their Kane Ace MX150 product.

[0058] For instance, the core may be formed predominantly from feed stocks of dienes such as butadiene, (meth)acrylates, ethylenically unsaturated nitrites such as acrylonitrile, and / or any other monomers that when polymerized or copolymerized yield a polymer or copolymer having a low glass transition temperature. The outer shells may be formed predominantly from feed stocks of (meth)acrylates such as methylmethacrylate, vinyl aromatic monomers such as styrene and / or ethylenically unsaturated halocarbons such as vinyl chloride and / or any other monomers that when polymerized or copolymerized yield a polymer having a higher glass transition temperature.

[0059] The core shell rubber may have an average particle size in the range of 0.07 to 10 pm, such as 0.1 to 5 pm or 0.1 to 10 pm or 0.2 to 2 pm.

[0060] The core shell rubber made in this way may be dispersed in an epoxy matrix or a phenolic matrix. Examples of epoxy matrices include the diglycidyl ethers of bisphenol A, F or S, or bisphenol, novolac epoxies, and cycloaliphatic epoxies. Examples of phenolic resins include bisphenol-A based phenoxies.

[0061] The polymer constituting the rubber particle core preferably is an elastic material comprised of (in polymerized form) not less than 50% by weight of at least one monomer selected from the group consisting of a diene monomer (conjugated diene monomer) and a (meth)acrylate monomer and less than 50% by weight of another copolymerizable vinyl monomer. In the present invention, (meth)acrylate means acrylate and / or methacrylate.

[0062] Suitable conjugated diene monomers include, for example, butadiene, isoprene, chloroprene, and the like, among which butadiene is particularly preferable. The (meth)acrylate monomers may include, for example, butyl acrylate, 2-ethylhexyl acrylate, lauryl methacrylate, and the like, among which butyl acrylate and 2-ethylhexyl acrylate are particularly preferable. These can be used alone or as a mixture of two or more thereof.

[0063] The total amount of conjugated diene monomer and / or (meth)acrylate monomer is preferably not less than 50% by weight, more preferably not less than 60% by weight, based on the total weight of the monomers used to make the core polymer.

[0064] The core polymer may be comprised not only of conjugated diene monomer(s) and / or (meth)acrylate monomers but also one or more vinyl monomers copolymerizable therewith. The vinyl monomers copolymerizable with the conjugated diene monomer or (meth) acrylate monomer include, but are not limited to, monomers selected from the group consisting of aromatic vinyl monomers and vinyl cyanide monomers. Suitable aromatic vinyl monomers include, for example, styrene, a-methylstyrene and vinyl naphthalene, and suitable vinyl cyanide monomers include, for example, acrylonitrile, methacrylonitrile and other substituted acrylonitriles. These can be used alone or in combination thereof.

[0065] The amount of these copolymerizable vinyl monomers used is preferably less than 50% by weight, more preferably less than 40% by weight, based on the total weight of the monomers used to prepare the core polymer.

[0066] To adjust the degree of crosslinkage, a multifunctional monomer may be contained as a component in the synthesis of the core copolymer. Examples of multifunctional monomers include compounds containing two or more carbon-carbon double bonds such as divinyl benzene, butane diol di(meth)acrylate, triallyl(iso)cyanurate, allyl(meth)acrylate, diallyl itaconate, diallyl phthalate, and the like. The amount of the multifunctional monomer used is typically not higher than 10% by weight, preferably not higher than 5% by weight, more preferably not higher than 3% by weight, based on the total weight of the monomers used to prepare the core polymer.

[0067] To adjust the molecular weight of the core polymer or the extent to which the core polymer is crosslinked, a chain transfer agent may be used. For example, C5 to C20 alkyl mercaptans can be used for this purpose. The amount of the chain transfer agent used is typically not higher than 5% by weight, more preferably not higher than 3% by weight, based on the total weight of the core polymer monomers.

[0068] As mentioned previously, polysiloxane rubbers can be employed as the core polymer in the core-shell rubber particles, either alone or in combination with other core polymers. The polysiloxane may, for example, be comprised of di-alkyl or aryl substituted silyloxy units such as dimethyl silyloxy, methylphenyl silyloxy and diphenyl silyloxy. It may be preferable to introduce a crosslinked structure into the polysiloxane by using a multifunctional alkoxy silane compound partially in combination therewith during polymerization or by radically reacting a silane compound having a vinyl reactive group introduced in it or using other methods, if necessary.

[0069] Preferably, the composition of the polymer used for the shell layer has sufficient affinity for epoxy component / resin such that the resulting rubber-like core-shell particles can be dispersed stably in the form of primary particles in the epoxy component / resin.

[0070] The polymer comprising the shell layer preferably has been graft-polymerized with and substantially bonded to the polymer constituting the rubber particle core. It is desired that preferably not less than 70% by weight, more preferably not less than 80% by weight and still more preferably not less than 90% by weight of the polymer constituting the shell layer is covalently bonded to the polymer comprising the particle core.

[0071] The shell layer polymer may contain moieties or units derived from monomers reactive with the epoxy component / resin or with a curing agent. A functional group of the reactive monomer contained in the shell layer polymer is preferably one capable of chemically reacting with the epoxy component / resin or the curing agent present in the adhesive compositions of the present invention.

[0072] The polymer constituting the shell layer is preferably a polymer or copolymer obtained by copolymerizing at least one component selected from alkyl (meth)acrylates, aromatic vinyl compounds and vinyl cyanide compounds. Particularly when the shell layer is desired to be chemically reactive at the time of curing the adhesive composition, it is preferable from the viewpoint of high reactivity with the epoxy group or the epoxy curing agent that the polymer constituting the shell layer contain at least one monomer selected from the group consisting of (meth)acrylates having a reactive group, such as hydroxyalkyl (meth)acrylates, aminoalkyl (meth)acrylates, epoxyalkyl (meth)acrylates, epoxy alkyl vinyl ethers, unsaturated acid derivatives, (meth)acrylamide derivatives and maleimide derivatives, in addition to the alkyl (meth)acrylate(s), aromatic vinyl compound(s) and / or vinyl cyanide compound(s).

[0073] Suitable alkyl (meth)acrylates include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and the like. The aromatic vinyl monomers that are suitable include styrene, a-methylstyrene, and the like. Suitable vinyl cyanides include (meth)acrylonitrile and the like.

[0074] (Meth)acrylates having reactive groups include, for example, 2-hydroxyethyl (meth)acrylate, 2-aminoethyl (meth)acrylate and glycidyl (meth)acrylate. Suitable epoxy alkyl vinyl ethers include glycidyl vinyl ether. Suitable unsaturated acid derivatives include a,p-unsaturated acids, a,p-unsaturated acid anhydrides, (meth)acrylic acid, itaconic acid and crotonic acid. The (meth)acrylamide derivatives that are suitable include (meth)acrylamide (including N-substituted derivatives thereof). Suitable maleimide derivatives include maleic imide. These can be used alone or in combination thereof.

[0075] The ratio (by weight) of the core layer shell layer in the rubber particles is in the range of preferably 50:50 to 95:5, more preferably 60:40 to 90:10.

[0076] The rubber particles having a core-shell structure can be produced by any method known in the art, such as emulsion polymerization, suspension polymerization, micro-suspension polymerization and the like. In particular, a process involving emulsion polymerization is preferred Photocationic polymerization initiator component

[0077] The photocationic polymerization initiator component is desirably present in an amount of from about 0.5 to about 10% by weight based on the total weight of the composition. Note that parts by weight and % by weight were in the copied text below

[0078] Onium compounds from the group of aryl sulfonium salts and aryl iodonium salts as well as combinations thereof may be used as the photocationic polymerization initiator component.

[0079] Aromatic aryl sulfonium salts suitable as photolatent acids are described, for example, in the following patent publication no.s WO 2003 / 072567 or WO 2003 / 008404. Suitable aryl iodonium salts are disclosed in patent publication no. WO 1998 / 002493 or U.S. Patent No. 6,306,555.

[0080] In addition, onium salts suitable as photolatent acids are described by J. V. Crivello and K. Dietliker in “Photoinitiators for Free Radical, Cationic &Anionic Photopolymerisation”, Vol. Ill of “Chemistry &Technology of UV &EB Formulation for Coatings, Inks &Paints”, 2nd ed., J. Wiley and Sons / SITA Technology (London), 1998.

[0081] For example, HSO4", PFe", SbFe", AsFe", Cl", Br", I", CIO4", PO4", SOaCFs", tosylate, aluminates or a borate anion such as BF4" and B(CeF6)4" can serve as anions of the sulfonium or iodonium salts. For higher polymerization rates, barely nucleophilic complex anions are preferred. Aryl sulfonium and aryl iodonium salts may be used, for example with hexafluoroantimonate as a counter ion.

[0082] Photolatent acids based on onium salts with aluminate anions as disclosed in patent publication no.s EP 3 184 569 A1 or WO 2017 035 551 A1 are also suitable.

[0083] Photoinitiators based on triaryl sulfonium commercially available as photolatent acids are available under the trade names Chivacure 1176, Chivacure 1190 by Chitech, Irgacure 290, Irgacure 270, Irgacure GSID 26-1 by BASF, Speedcure 976 and Speedcure 992 by Lambson, TTA UV-692, TTA UV-694 by Jiangsu Tetra New Material Technology Co., Ltd. or UVI-6976 and UVI-6974 by Dow Chemical Co.

[0084] Photoinitiators based on diaryl iodonium commercially available as photolatent acids are, for example, available under the brand names UV1242 or UV2257 by Deuteron and Bluesil 2074 by Bluestar.

[0085] The photoinitiator component can be activated by irradiation with actinic radiation of a wavelength A of 200 to 600 nm, particularly preferably of a wavelength A of 250 to 365 nm. If necessary, the photoinitiator can be combined with a suitable sensitizer.

[0086] Based on the total weight of the composition, the photoinitiator is contained in a proportion of 0.5 to 10 wt.%, but preferably in proportions of 0.3 to 3 wt.%.

[0087] The photocationic polymerization initiator component is typically a salt represented by A'ETthat generates a cationically active species when irradiated with light (desirably ultraviolet light). Here, the cation A+ is desirably an aromatic iodonium ion or an aromatic sulfonium ion, for example.

[0088] The aromatic iodonium ion is represented by the following formula: Ar1-I+-Ar2

[0089] In this formula, it is desirable that the groups Ar1 and Ar2 bonded to l+ be both independently aromatic group, and particularly optionally substituted phenyl groups.

[0090] The aromatic sulfonium ion is represented by the following formula: Ar’ Ar?—s + Ar3

[0091] In this formula, it is desirable that Ar1, Ar2, and Ar3 bonded to the center S+ be each independently aryl group, and particularly optionally substituted phenyl group. Examples of the substituent include an alkyl group, a hydroxy group, a carboxyl group, an alkoxy group, an aryloxy group, an alkylcarbonyl group, an arylcarbonyl group, an aralkylcarbonyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an aralkyloxycarbonyl group, an alkylcarbonyloxy group, an arylcarbonyloxy group, an aralkylcarbonyloxy group, an alkoxycarbonyl oxy group, an aryloxycarbonyloxy group, an aralkyloxycarbonyloxy group, an arylthiocarbonyl group, an arylthio group, an alkylthio group, an aryl group, a heterocyclic hydrocarbon group, an alkyl sulfinyl group, an aryl sulfinyl group, an alkylsulfonyl group, an arylsulfonyl group, and a hydroxy (poly)alkyleneoxy group.

[0092] An initiator in which the anion B' is a B(aryl)4‘ ion, such as B(C6F5)4‘, may be included. Examples of the B(aryl)4_ include B(CeF4OCF3)4' and B(CeF4CF3)4', in addition to B(C6Fs)4'. Initiators in which the anion B' is a B(aryl)4' ion tend to bring about a high curing rate.

[0093] In order to further improve the adhesiveness, an initiator in which the anion B‘ is an anion other than the B(aryl)4~ ion may be included. Examples of the anion B’ include PFe', [(Rf)bPFe-b]- (Rf represents an alkyl group in which 80% or more of the hydrogen atoms are replaced with fluorine atoms, b represents the number thereof and is an integer of 1 to 5, and each Rf may be the same or different), AsFe', and BF4'

[0094] Examples of the photocationic polymerization initiator include (4-hydroxyphenyl)methylbenzylsulfonium tetrakis(pentafluorophenyl)borate, 4-(4-biphenylylthio)phenyl-4-biphenylylphenylsulfonium tetrakis(pentafluorophenyl)borate, 4-(phenylthio)phenyldiphenylsulfonium phenyltris(pentafluorophenyl)borate, [4-(4-biphenylylthio)phenyl]-4-biphenylylphenylsulfonium phenyltris(pentafluorophenyl)borate, diphenyl[4-(phenylthio)phenyl]sulfonium tris(pentafluoroethyl)trifluorophosphate, diphenyl[4-(phenylthio)phenyl]sulfonium tetrakis(pentafluorophenyl)borate, diphenyl[4-(phenylthio)phenyl]sulfonium hexafluorophosphate, 4-(4-biphenylylthio)phenyl-4-biphenylylphenylsulfonium tris(pentafluoroethyl)trifluorophosphate, bis[4-(diphenylsulfonio)phenyl]sulfide phenyltris(pentafluorophenyl)borate, [4-(2-thioxanthonylthio)phenyl]phenyl-2-thioxanthonylsulfonium phenyltris(pentafluorophenyl)borate, and compounds represented by the following formulae:

[0095] Examples of commercially available products that may be used as the photocationic polymerization initiator include CPI-1 OOP, CPI-101 A, CPI-200K, CPI-2108, CPI-310B, CPI-310FG, CPI-410S and IK-1 manufactured by San-Apro Ltd.; Irgacure 250 and Irgacure 270 manufactured by Ciba Specialty Chemicals Inc.; and BLUESIL PI 2074 manufactured by Elkem.

[0096] These photocationic polymerization initiators may be used singly or in combinations of two or more thereof.

[0097] One suitable photocationic polymerization initiator component is (4-isopropylphenyl)(4-methylphenyl)iodonium tetrakis(pentafluorophenyl)borate.

[0098] The amount of the photocationic polymerization initiator is not particularly limited, but it is desirably 0.1 parts by mass or more, and more desirably 0.5 parts by mass or more, (in relation to the lower limit of the amount present), and is desirably 10 parts by mass or less, and more desirably 5 parts by mass or less, (in relation to the upper limit of the amount present), each based on 100 parts by mass of the total amount of the epoxy component.

[0099] In view of reducing toxicity, it is desirable that the amount of an antimony-containing compound be low in the photocationic polymerization initiator. The amount of an antimony-containing compound is desirably 3% by mass or less, more desirably 1% by mass or less, and further desirably 0% by mass, based on the total mass of 100% by mass of the photocationic polymerization initiator. Thermal cationic polymerization initiator component

[00100] The thermal cationic polymerization initiator is a compound that generates cationically active species by heat and cannot generate a practical amount of a cationically active species by light irradiation. The thermal cationic polymerization initiator is also a salt represented by A+B~. In the present embodiment, the temperature at which the cationically active species is generated is low, and it is desirably 60°C or higher, and more desirably 70°C or higher, (in relation to the lower limit of the temperature range), and is desirably 120°C or lower, more desirably 100°C or lower, further desirably 90°C or lower, and still more desirably 80°C or lower, (in relation to the upper limit of the temperature range).

[00101] The thermal cationic polymerization initiator desirably includes a compound in which the anion B' is an anion species (such as a tetrakis(pentafluorophenyl)borate compound) represented by the following formula: F F .., , B 'tV.ZF F F

[00102] The cation species A+ of the tetrakis(pentafluorophenyl)borate compound is desirably an ammonium cation represented by the following formula: Va wherein Y1, Y2, Y3, and Y4 each independently represent a hydrogen atom, linear, branched-chain, or cyclic alkyl group having 1 to 20 carbon atoms, or aryl group. It is desirable that at least one of Y1, Y2, Y3, and Y4 be an aryl group.

[00103] In compositions described herein any alkyl group has 1 to 20 carbon atoms, and desirably 1 to 15 carbon atoms.

[00104] Examples of an alkyl group that may be in composition described herein include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, and a cyclohexyl group.

[00105] Examples of the aryl group include a phenyl group.

[00106] The alkyl group or aryl group may have a substituent. Examples of the substituent that the alkyl group may have include a phenyl group, an alkoxy group having 1 to 15 carbon atoms, and a hydroxy group. When the alkyl group has a substituent, the number of carbon atoms of the substituent is not included in the number of carbon atoms of the alkyl group. Examples of the substituent that the aryl group may have include an alkyl group having 1 to 15 carbon atoms, a hydroxyalkyl group having 1 to 15 carbon atoms, and an alkoxy group having 1 to 15 carbon atoms (desirably an alkoxy group having 1 to 8 carbon atoms, and more desirably a methoxy group and an ethoxy group), and a phenylthio group.

[00107] In one aspect of the present embodiment, it is desirable that the A+ of the thermal cationic polymerization initiator A+B- be a quaternary ammonium cation. It is desirable that in the above formula (c-2), Y1, Y2, Y3, and Y4 be each independently linear, branched-chain, or cyclic alkyl group having 1 to 20 carbon atoms, or aryl group. It is more desirable that two of Y1, Y2, Y3, and Y4 be each independently optionally substituted aryl group, and at the same time that the remaining two be each independently optionally substituted alkyl group having 1 to 15 carbon atoms (desirably alkyl group having 1 to 8 carbon atoms, and more desirably alkyl group having 1 to 3 carbon atoms).

[00108] Examples of the thermal cationic polymerization initiator include dimethylphenyl(4-methoxybenzyl)ammonium tetrakis(pentafluorophenyl)borate, dimethylphenyl(4-methylbenzyl)ammonium hexafluorotetrakis(pentafluorophenyl)borate, methylphenyldibenzylammonium tetrakis(pentafluorophenyl)borate, phenyltribenzylammonium tetrakis(pentafluorophenyl)borate, and dimethylphenyl(3,4-dimethylbenzyl)ammonium tetrakis(pentafluorophenyl)borate. Among these, dimethylphenyl(4-methoxybenzyl)ammonium tetrakis(pentafluorophenyl)borate is desirable. Examples of commercially available products include CXC1821 (trade name, manufactured by King Industries, Inc.).

[00109] These thermal cationic polymerization initiators may be used singly or in combinations of two or more thereof.

[00110] The thermal cationic polymerization initiator may comprise a tetrakis(pentafluorophenyl)borate compound.

[00111] Thermal cationic polymerization initiator may comprise the ammonium salt of tetrakis(pentafluorophenyl)boric acid. Expandable microsphere component

[00112] Desirably the microspheres are from about 2 to about 80pm in diameter. This size of particle has been found to effect suitable debonding.

[00113] Optionally the microspheres contain a gas such as an alkane gas. The gas expands under the application of suitable heat and the expansion of the microspheres stresses the bond and facilitates debonding.

[00114] The microspheres may contain butane, for example isobutane.

[00115] Optionally the microspheres contain silica, for example colloidal silica, such as silane modified colloidal silica.

[00116] The microspheres may have a density of from about 1 to about 30g / cm3.

[00117] The microspheres may have a particle size distribution D50 of 58pm ± 20 pm as measured according to ISO 22412.

[00118] The expandable microsphere component is desirably present in an amount of from about 10% to about 50% by weight based on the total weight of the composition.

[00119] Suitably the spheres are made of an expandable polymer.

[00120] Suitable expandable microspheres include those sold under the trade name Expancel™ including which are available from Nouryon in Amsterdam in The Netherlands. Expancel™ 051DU40 is one suitable material. Other suitable expandable microspheres include those sold by Kureha Corporation based in Japan. Antioxidant Components

[00121] The cationically curable composition used in the method of the invention may also contain at least one stabilizer / antioxidant. These compounds are added to protect the adhesive from degradation caused by reaction with oxygen induced by such things as heat, light, or residual catalyst from the raw materials such as the tackifying resin. For example, of interest are antioxidants capable of inhibiting free radicals generated by redox reactions.

[00122] The antioxidant component is desirably present in an amount of from about 0.01 to about 1 % by weight based on the total weight of the composition.

[00123] Among the applicable stabilizers or antioxidants included herein are high molecular weight hindered phenols and multifunctional phenols such as sulfur and phosphorous-containing phenol. Hindered phenols are well known to those skilled in the art and may be characterized as phenolic compounds which also contain sterically bulky radicals in close proximity to the phenolic hydroxyl group thereof. In particular, tertiary butyl groups generally are substituted onto the benzene ring in at least one of the ortho positions relative to the phenolic hydroxyl group. The presence of these sterically bulky substituted radicals in the vicinity of the hydroxyl group serves to retard its stretching frequency, and correspondingly, its reactivity; this hindrance thus providing the phenolic compound with its stabilizing properties. Representative hindered phenols include; 1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)-benzene; pentaerythrityl tetrakis-3(3,5-d i-tert-butyl-4-hydroxyphenyl)-propionate; n-octadecyl-3(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate; 4,4'-methylenebis(2,6-tert-butyl-phenol); 4,4'-thiobis(6-tert-butyl-o-cresol); 2,6-di-tertbutylphenol; 6-(4-hydroxyphenoxy)-2,4-bis(n-octyl-thio)-1,3,5 triazine; di-n-octylthio)ethyl 3,5-di-tert-butyl-4-hydroxy-benzoate; and sorbitol hexa[3-(3,5-d i-tert-butyl-4-hydroxy-phenyl)-propionate],

[00124] Such antioxidants are commercially available from the BASF company and include IRGANOX® 565, 1010, 1076 and 1726 which are hindered phenols. These are primary antioxidants which act as radical scavengers and may be used alone or in combination with other antioxidants such as phosphite antioxidants like IRGAFOS 168 antioxidant available from BASF. Phosphite catalysts are considered secondary catalysts and are not generally used alone. These are primarily used as peroxide decomposers. Other available catalysts are CYANOX® LTDP available from Cytec Industries and ETHANOX® 330 available from Albemarle Corp. Many such antioxidants are available either to be used alone or in combination with other such antioxidants. These compounds are added in small amounts, typically less than about 10 wt.%, and have no effect on other physical properties. Flexibiliser Components

[00125] The cationically curable composition used in the method of the invention may also contain at least one flexibiliser.

[00126] The flexibiliser component is desirably present in an amount of from about 2.5 to about 20% by weight based on the total weight of the composition.

[00127] The flexibiliser component may be one or more reactive flexibilisers and may be one or more alcohols.

[00128] Polyols of a higher molecular weight can be used to flexibilise the compositions used in the present invention. For example, suitable polyols are available based on polyethers, polyesters, polycaprolactones, polycarbonates or (hydrogenated) polybutadiene diols.

[00129] Examples of commercially available polyols of a higher molecular weight are products available under trade names Eternacoll L UM-90 (1 / 1), Etemacoll UHC50-200 by UBE Industries Ltd., Capa™ 2200, Capa™ 3091 by Perstorp, Liquiflex H by Petroflex, Merginol 901 by HOBUM Oleochemicals, Placcel 305, Placcel CD 205 PL by Deicel Corporation, Priplast 3172, Priplast 3196 by Croda, Kuraray Polyol F-3010, Kuraray Polyol P-6010 by Kuraray Co., Ltd., Krasol LBH-2000, Krasol HLBH-P3000 by Cray Valley or Hoopol S-1015-35 or Hoopol S-1063-35 by Synthesia Internacional SLU.

[00130] One suitable flexibiliser is polyester diol. Adhesion Promoter Components

[00131] The cationically curable composition used in the method of the invention may also contain at least one adhesion promoter.

[00132] The adhesion promoter component is desirably present in an amount of from about 0.1 to about 5% by weight based on the total weight of the composition.

[00133] For example, an organosilane can be optionally contained in the curable composition so as to improve bond strengths.

[00134] Examples of organosilanes include but are not limited to: vinyl chlorosilane, vinyl tri methoxysilane, vinyl triethoxysilane, 2-(3,4-epoxy cyclohexyl)ethyl trimethoxysilane, glycidyloxypropyltrimethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-glycidoxypropyl 15 methyldiethoxysilane, 3-glycidoxypropyl diethoxysilane, 3-glycidoxypropyl triethoxysilane, p-styryl trimethoxysilane, 3-methacryloxypropyl triethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-methacryloxypropylmethyl dimethoxysilane, 3-methacryloxypropylmethyl diethoxysilane, 3-acryloxypropyl trimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyl dimethoxysilane, N-2-(aminoethyl)-3-aminopropyl tri methoxysilane, N-2-(aminoethyl)-3- 20 aminopropylmethyl triethoxysilane, 3-aminopropyl trimethoxysilane, 3-aminopropyl triethoxysilane, 3-triethoxysilyI-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyl trimethoxysilane, 3-chloropropyl trimethoxysilane, 3-mercaptopropylmethyl dimethoxysilane, 3-mercaptopropyl trimethoxysilane, bis(triethoxysilylpropyl)tetrasulfide, 3- isocyanatepropyl triethoxysilane, or the like, which may be used alone or in any combination. Filler / Rheology Modifier Components

[00135] The cationically curable composition used in the method of the invention may also contain at least one filler / rheology modifier.

[00136] The filler / rheology modifier component is desirably present in an amount of from about 0.01 to about 10% by weight based on the total weight of the composition.

[00137] Filler / rheology modifier contemplated for optional use include, for example, aluminum nitride, boron nitride, silicon carbide, diamond, graphite, beryllium oxide, magnesia, titanium oxide, silicas, such as fumed silica or fused silica, alumina, perfluorinated hydrocarbon polymers (for example polytetrafluroethylene), thermoplastic polymers, thermoplastic elastomers, mica, glass powder and the like. Optionally, the particle size of these fillers will be about 20 pm or less.

[00138] As regards silicas, the silica may have a mean particle diameter on the nanoparticle size; that is, having a mean particle diameter on the order of 10~9 meters. Silica nanoparticles can be pre-dispersed in epoxy resins, and may be selected from those available under the tradename NANOPOX, from Nanoresins, Germany. NANOPOX is a tradename for a product family of silica nanoparticle reinforced epoxy resins showing an outstanding combination of material properties. The silica phase consists of surface-modified, synthetic SiOznanospheres with less than 50 nm diameter and an extremely narrow particle size distribution. The SiOz nanospheres are agglomerate-free dispersions in the epoxy resin matrix resulting in a low viscosity for resins containing up to 50 wt % silica.

[00139] A commercially available example of the NANOPOX products particularly desirable for use herein includes NANOPOX A610 (a 40 percent by weight dispersion in a cycloaliphatic epoxy resin matrix). The NANOPOX products are believed to have a particle size of about 5 nm to about 80 nm, though the manufacturer reports less than 50 nm.

[00140] Other filler / rheology modifiers include, for example, lithopone, zirconium silicate, hydroxides, such as hydroxides of calcium, aluminum, magnesium, iron and the like, diatomaceous earth, carbonates, such as sodium, potassium, calcium, and magnesium carbonates, oxides, such as zinc, magnesium, chromic, cerium, zirconium and aluminum oxides, calcium clay, fumed silicas, silicas that have been surface treated with a silane or silazane such as the AEROSIL products available from Evonik Industries, silicas that have been surface treated with an acrylate or methacrylate such as AEROSIL R7200 or R711 available from Evonik Industries, precipitated silicas, untreated silicas, graphite, synthetic fibers and mixtures thereof. Examples of treated fumed silicas include polydimethylsiloxane-treated silicas, hexamethyldisilazane-treated silicas and other silazane or silane treated silicas. Such treated silicas are commercially available, such as from Cabot Corporation under the tradename CAB-O-SIL ND-TS and Evonik Industries under the tradename AEROSIL, such as AEROSIL R805.

[00141] Other filler / rheology modifiers include talcs, clays, silicas and treated versions thereof, carbon blacks and micas.

[00142] The filler / rheology modifier component may be in the form of particles (spherical particles, beads, and elongated particles), fibres, and combinations thereof. Photosensitiser Components

[00143] The cationically curable composition used in the method of the invention may also contain at least one photosensitiser.

[00144] The photosensitiser component is desirably present in an amount of from about 0.01 to about 5% by weight based on the total weight of the composition.

[00145] The photosensitiser may be a thioxanthone-based photosensitiser. This class of photosensitiser includes this 2-isopropylthioxanthen-9-one (2-ITX), 4-isopropylthioxanthone (4-ITX) and 2,4-diethylthioxanthone (DETX), 1-chloro-4-propoxythioxanthone (CPTX) among others, and can be used in combination with each other or individually.

[00146] The photosensitiser is useful to absorb light and transfer energy to other chemical species that do not absorb light at the wavelengths being used. For example the photosensitiser may transfer energy to the photocationic polymerization initiator component. Detailed Description

[00147] The present invention has been tested as follows.

[00148] A composition as set out in Table 1 below was prepared: Component % by weight based on the total weight of the composition 1,4-Butanediol diglycidyl ether 12.5% Kane Ace MX150 (Polybutadiene Core Shell Rubber dispersed in Bisphenol A epoxy resin) 41.2% Expancel™ 051DU40 (Thermally expanding microspheres) 29.9% Butylated hydroxytoluene (BHT) 0.1% (4-lsopropylphenyl)(4-methylphenyl)iodonium tetrakis(pentafluorophenyl)borate 2.0% Polyester Diol 10.3% Glycidyloxypropyltrimethoxysilane 0.6% Hydrophobic amorphous fumed silica 2.2% 2-lsopropylthioxanthen-9-one 1.3% Total 100% Table 1

[00149] Composition above was applied to FR4 PCB substrate as a 400pm thick film. It was then UV activated at 130mW / cm2 from a 405nm LED for 6 seconds. 125pm spacer beads was applied over the activated adhesive and an Ink Coated Glass substrate was applied to the activated adhesive with the ink coated side in contact with the adhesive.

[00150] The composition / bond allowed to cure for 24 hours at room temperature (RT).

[00151] Bond made is bond area of 25.4mm x25.4 mm between the FR4 PCB substrate and the Ink Coated Glass substrate. This assembly was prepared a number of times to facilitate the tests set out below.

[00152] The tensile strength of the bond was tested by pulling the Ink Coated Glass substrate away from the FR4 PCB substrate in a plane which is at 90 degrees to the FR4 PCB substrate. The pulling rate was 2 mm / minute. The tensile strength was tested under a number of conditions as set out below.

[00153] Results were as follows: • Initial Strengths: 1.1 MPa • Post Humid Strengths (3 days 65°C, 95% RH): 1,4MPa • Post Humid Strengths (7 days 65°C, 95% RH): 0.8MPa

[00154] All testing above resulted in mixed mode failure with all of the following occurring: substrate failure of the FR4 PCB substrate; adhesion failure off FR4 PCB substrate; adhesion failure off the ink coated glass; and cohesive failure.

[00155] The assembly was also subjected to thermal debonding conditions of 150°C for 30 minutes and allowed to return to room temperature. The assembly was then loaded into the tensile tester to be tested at 2mm per minute but all bonds failed in hand while loading into the test machine so no strengths could be recorded. All bonds resulted in adhesive failure off FR4 PCB substrate.

[00156] A composition as set out in Table 2 below was prepared: 2-vinyloxyethylglycidyl ether 9.58% 1,4-Butanediol diglycidyl ether 7.19% ExpancelTM 051DU40 (Thermally expanding microparticles) 28.65% Kane Ace MX150 (Polybutadiene Core Shell Rubber dispersed in Bisphenol A epoxy resin) 39.47% Butylated hydroxytoluene (BHT) 0.10% (4-lsopropylphenyl)(4-methylphenyl)iodonium tetrakis(pentafluorophenyl)borate 1.92% Polyester Diol 9.77% Glycidyloxypropyltrimethoxysilane 0.57% Hydrophobic amorphous fumed silica 1.50% 2-lsopropylthioxanthen-9-one 1.25% Total 100% Table 2

[00157] The composition was applied, used to bond together substrates and tested, all as set out above for Example 1.

[00158] Results were as follows: • Initial Strengths: 1.2 MPa • Post Humid Strengths (3 days 65°C, 95% RH): 0.9MPa • Post Humid Strengths (7 days 65°C, 95% RH): 0.9MPa

[00159] All testing above resulted in mixed mode failure with all of the following occurring: substrate failure of the Ink Coated Glass substrate; adhesion failure off FR4 PCB substrate; adhesion failure off the ink coated glass; and cohesive failure.

[00160] The assembly was also subjected to thermal debonding conditions of: 1: 130°C for 30 minutes, allowed to cool to room temperature and then tested as above. The results here were 0.46MPa, with adhesive failure off the Ink Coated Glass substrate. 2: 130°C for 30 minutes, allowed to cool to room temperature and then tested in the same way as above. The results here were 0.66MPa, with adhesive failure off the Ink Coated Glass substrate. 3: 150°C for 30 minutes, and then tested within 2 minutes of removal from the oven as above. The results where were 0.04MPa, with adhesive failure off the off FR4 PCB substrate.

[00161] The words “comprises / comprising” and the words “having / including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[00162] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

Claims

1. A method of debonding a first substrate from a second substrate, wherein the first substrate is bonded to the second substrate by the cure product of a UV-activated delayed cationically curable composition, the cationically curable composition comprising: (a) an epoxy component;(b) a cationic polymerization initiator; and(c) expandable microspheres, wherein the expandable microspheres contains an expanding agent which expands under application of heat and in turn causes the microspheres to expand,the method comprising the step of: subjecting the cure product to heat to thermally expand the microspheres, so that the thermal expansion of the microspheres reduces the tensile strength of the bond formed by the cure product by at least 50% of the initial tensile strength thus causing at least partial debonding of the first substrate relative to the second substrate.LOCM 2. A method according to Claim 1 wherein the first substrate is an electronicLO component.1— 3. A method according to according to any preceding claim wherein the secondsubstrate is a printed circuit board.

4. A method according to any preceding claim wherein the microspheres are from about 2 to about 80 pm in diameter.

5. A method according to any preceding claim wherein the expandable microspheres contain a gas such as an alkane gas.

6. A method according to any preceding claim wherein the microspheres contain butane.

7. A method according to claim 6 wherein the microspheres contain isobutane.

8. A method according to any preceding claim wherein the microspheres contain silica.01 05 259. A method according to claim 8, wherein the colloidal silica is a silane modified colloidal silica.

10. A method according to any preceding claim wherein the epoxy component comprises an alicyclic epoxy compound.

11. A method according to any preceding claim wherein the epoxy component additionally comprises an oxetane compound.

12. A method according to any preceding claim wherein the epoxy component comprises a glycidyl ether-based epoxy compound such as a non-aromatic glycidyl ether-based epoxy compound.

13. A method according to claim 13, wherein the non-aromatic glycidyl ether-based epoxy compound may be 2 vinyloxyethylglycidyl ether.

14. A method according to any preceding claim wherein the cationic polymerization initiator comprises a photocationic polymerization initiator.

15. A method according to Claim 14 wherein the photocationic polymerization initiator is a tetrakis(pentafluorophenyl)borate16. A method according to claims 15 wherein the photocationic polymerization initiator compound is (4-lsopropylphenyl)(4-methylphenyl)iodonium tetrakis(pentafluorophenyl)borate.

17. A method according to any preceding claim wherein the cationic polymerization initiator comprises a thermal cationic polymerization r.

18. A method according to claim 17 wherein the thermal cationic polymerization is a tetrakis(pentafluorophenyl)borate compound initiator19. A method according to claim 18 wherein the thermal cationic polymerization initiator is a tetrakis(pentafluorophenyl)borate compound.

20. A method according to Claim 19 wherein the thermal cationic polymerization initiator comprises the ammonium salt of tetrakis(pentafluorophenyl)boric acid.

21. A method according to any preceding claim wherein the epoxy component comprises an aromatic glycidyl ether-based epoxy compound.01 05 25Application No: GB2406614.4Claims searched: 1-16Examiner: Dr Paul MintonDate of search: 29 October 2024Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X 1,4-6,9,11-16 International Journal of Adhesion and Adhesives, 59, 2015, BANEA et al, "Debonding on command of adhesive joints for the automotive industry", pages 14-20. See particularly Section 2 (Experimental details). X 1-5,9,11-16 US2024 / 059827 Al (OTSU et al) see particularly paragraph [0120] and Examples 1-14. X 1,4,5,9,11 -16 International Journal of Adhesion and Adhesives, Vol. 23, 2003, NISHIYAMA et al, "Dismantlement behavior and strength of dismantlable adhesive including thermallyexpansive particles", pages 377-382. See particularly Sections 2 (Materials) and 6 (Discussion). X 1,4,5,9,11 -16 at least WO2021 / 251099 Al (UNIV KYUSHU) see particularly WPI Abstract Accession No. 2021-E40352 and claims 1 &12. X 1,4,5,9,11 -16 at least CN105694790 A (MAT INST CHINA ACAD) see particularly WPI Abstract Accession No. 2016-42340Y, Example 3, and claims 1 &10. X 1,9,11-16 at least Journal of the Adhesion Society of Japan, Vol. 42, No. 9, 2006, KISHI et al, "Design of dismantlable structural adhesives with high temperature performance", pages 356-363. See particularly Section 2.1, Figure 10, and English Abstract on page 363.X Document indicating lack of novelty or inventive step A Document indicating technological background and / or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO &US patent documents classified in the following areas of the UKCX :Worldwide search of patent documents classified in the following areas of the IPCB32B; C09J______________________________________________________The following online and other databases have been used in the preparation of this search report SEARCH-PATENT, SEARCH-NPLInternational Classification:Subclass Subgroup Valid From C09J 0011 / 02 01 / 01 / 2006 B32B 0007 / 12 01 / 01 / 2006 B32B 0043 / 00 01 / 01 / 2006 C09J 0005 / 06 01 / 01 / 2006 C09J 0163 / 00 01 / 01 / 2006