Method for lowering bonding strength of adhesive layer

Abstract

The present invention provides: a method in which electrical pulses are applied to an article including a portion where two or more members have been bonded together by an adhesive layer containing an electroconductive filler, thereby lowering the bonding strength of the adhesive layer; and a method in which a member is taken out of the article using said method and the member or a functional component contained in the member is reused.

Description

Method for reducing the adhesive strength of an adhesive layer

[0001] The present invention relates to a method for reducing the adhesive strength of an adhesive layer in an article including a portion where two or more members are joined via an adhesive layer.

[0002] Communication terminal devices, home appliances, and other products that are no longer in use due to breakdowns or changes in their product lifecycles are collected by businesses and then disassembled and dismantled for recycling or reuse. Conventionally, this work has often been done by manually disassembling the products and then physically dismantling them using a crusher or similar. However, this type of work requires a lot of manpower, making it inefficient. In addition, dismantling using a crusher or similar machine can damage the dismantled components and the functional parts contained in them, which creates problems when reusing the components.

[0003] In view of these circumstances, various methods have been proposed in recent years for decomposing an object by generating a pulsed power discharge in a liquid.

[0004] For example, Patent Document 1 describes a method for recycling materials and / or products by pulsed power, which involves generating a series of discharges between at least two electrodes in a reactor containing a surrounding liquid and the material and / or product to be recycled, and exposing the material and / or product to the series of discharges, the discharge energy, voltage between the electrodes, switching time, and discharge frequency being selected so that the generated discharges generate an electric arc that passes through the material and / or product to be recycled and a mechanical shock wave that propagates across the material and / or product to be treated in the reactor.

[0005] Patent Document 2 also describes a method for pulverizing solids that have been condensed from non-metallic components or partially metallic components, and for breaking down homogeneous non-metallic solids into small pieces by rapidly discharging an electric energy accumulator, in which the solids are immersed in a non-conductive or weakly conductive processing liquid, the processing liquid being contained in a container, and in which a device consisting of a high-voltage electrode and an earth electrode protrudes into a mixture of the processing liquid and the solid, the ends of the electrodes being spaced apart by a predetermined distance, and a high-voltage pulse is applied between the end of the high-voltage electrode and the end of the earth electrode, generating shock waves in the solid and the liquid, thereby pulverizing and breaking down the solids into small pieces.

[0006] Furthermore, Patent Document 3 describes a method for fragmenting and / or weakening a pourable material using high-voltage discharges, the method comprising the steps of: a) providing an electrode unit associated with one or more high-voltage generators, to which high-voltage pulses can be supplied by the high-voltage generators; b) guiding a material stream of the pourable material past the electrode unit using a conveying device that carries the material stream, while immersing the material stream in a treatment liquid; and c) supplying high-voltage pulses to the electrode unit while guiding the material stream past the electrode unit, thereby causing a high-voltage breakdown through the material stream, wherein each electrode of the electrode unit is immersed from above in the treatment liquid, and the electrodes between which a high-voltage breakdown is caused are opposed to each other at a predetermined electrode distance transverse to the direction of guiding the material.

[0007] Furthermore, Patent Document 4 describes a method for disassembling an article, in which a substrate or an article including a substrate is disassembled by performing discharge multiple times in a liquid, the method comprising: a container for holding the liquid; a positive electrode and an earth electrode in the liquid in the container; and the substrate or the article including the substrate is placed in a discharge path between the positive electrode and the earth electrode in the liquid or in a region where a shock wave generated by the discharge propagates; measuring the peak value of the discharge current flowing in the discharge path during discharge; and controlling the discharge conditions so that the measured peak value of the discharge current remains constant.

[0008] However, the inventions described in Patent Documents 1 to 4 all have a high degree of randomness in the discharge path, and are not methods for selectively and locally dismantling an object. Therefore, there is a problem in that it is difficult to selectively and locally dismantle a specific part of an object of a certain size. Furthermore, the large shock waves in the liquid can cause functional impairment of the dismantled parts, which makes it difficult to reuse the parts.

[0009] Special Table of Contents No. 2012-517892 Publication of Japanese Patent Application Publication No. 9-75769 Publication of Special Publication No. 2018-506429 Publication of Japanese Patent Application Publication No. 2017-104796

[0010] Therefore, the problem that the present invention aims to solve is to provide a method that can efficiently remove components from an article and prevent damage to the components or functional components incorporated in the components by applying an electric pulse to reduce the adhesive strength of the adhesive layer that joins the components in the article.

[0011] The inventors therefore conducted extensive research and discovered that by applying an electric pulse to an article including a portion in which two or more components are joined via an adhesive layer containing a conductive filler, the adhesive strength of the adhesive layer can be reduced, allowing the components to be efficiently removed from the article and preventing damage to the components or functional components incorporated in the components, and thus arrived at the present invention.

[0012] That is, the present invention is a method for reducing the adhesive strength of an adhesive layer by applying an electric pulse to an article including a portion in which two or more components are joined via an adhesive layer containing a conductive filler.

[0013] According to the present invention, it is possible to selectively and locally dismantle specific portions of an object having a certain size that are bonded with an adhesive layer containing a conductive filler. Furthermore, since the adhesive layer contains a conductive filler, the number of pulse irradiations and the amount of energy consumed required for dismantling can be reduced, allowing the dismantling work to be completed in a short time. Furthermore, the functionality of the dismantled parts is less likely to be impaired, thereby improving the reuse rate of the dismantled components and functional parts within the components. Furthermore, when applying an electric pulse in the atmosphere, no container for pouring liquid is required.

[0014] 1 is a high-voltage pulse generator used in the method for reducing the adhesive strength of an adhesive layer of the present invention; FIG. 2 is a circuit diagram of a high-voltage pulse generator used in the method for reducing the adhesive strength of an adhesive layer of the present invention; FIG. 3 is an enlarged photograph of the adhesive layer on the steel plate after dismantling a test piece formed using the adhesive composition of Example 1; FIG. 4 is an enlarged photograph of the adhesive layer on the steel plate after dismantling a test piece formed using the adhesive composition of Example 2; FIG. 5 is an enlarged photograph of the adhesive layer on the steel plate after dismantling a test piece formed using the adhesive composition of Example 3; FIG. 6 is an enlarged photograph of the adhesive layer on the steel plate after dismantling a test piece formed using the adhesive composition of Example 4; FIG. 7 is an enlarged photograph of the adhesive layer on the steel plate after dismantling a test piece formed using the adhesive composition of Comparative Example 1.

[0015] The method of the present invention for reducing the adhesive strength of an adhesive layer will be described in detail below.

[0016] In the present invention, "reducing the adhesive strength of the adhesive layer" means that when the method of the present invention is applied to an article including a portion in which two or more members are joined via an adhesive layer, the tensile shear strength (adhesion strength) of the adhesive layer is reduced by 10% or more, assuming that the tensile shear strength of the adhesive layer when not applied is 100%.

[0017] First, the article used in the method of the present invention will be described. The article used in the method of the present invention includes a part in which two or more members are joined via an adhesive layer containing a conductive filler, and the adhesive layer containing a conductive filler is made of a cured product of an adhesive composition containing a conductive filler.

[0018] Examples of the conductive filler include carbon black, graphene, carbon nanotubes (CNTs), metal particles selected from copper, silver, nickel, silver-coated copper, gold-coated copper, silver-coated nickel, and gold-coated nickel, and metal-coated resin particles selected from acrylic resin particles or urethane resin particles coated with copper, silver, nickel, gold, or a mixture thereof. Among the above-mentioned conductive fillers, carbon black or copper is preferred, and carbon black is most preferred, from the viewpoint of the ease with which the adhesive layer breaks after an electric pulse is applied to members bonded via an adhesive layer containing the conductive filler.

[0019] The particle size of the conductive filler (or length in the case of carbon nanotubes) is not particularly limited and is appropriately selected depending on the desired thickness of the adhesive layer and the desired adhesive strength, and is used in the range of, for example, 0.01 to 1000 μm. Within the above range, the particle size (volume basis, D50) of the conductive filler is preferably 0.015 to 500 μm, more preferably 0.02 to 250 μm, even more preferably 0.02 to 50 μm, and most preferably 0.02 to 1 μm, from the viewpoint of the adhesive strength of the adhesive layer before the application of an electric pulse. Note that the particle size can be measured using a particle size distribution measuring device using laser diffraction.

[0020] Furthermore, the content of the conductive filler is preferably 0.1 vol% or more relative to the adhesive composition containing the conductive filler from the viewpoint of the ease of rupture of the adhesive layer after application of an electric pulse to members joined via the adhesive layer containing the conductive filler, and is preferably 40 vol% or less from the viewpoint of the adhesive strength of the adhesive layer before application of the electric pulse, more preferably 0.5 to 25 vol%, and even more preferably 1 to 10 vol%.

[0021] The adhesive composition is not particularly limited, and adhesive compositions that can be cured by heat, light, or the like can be used. Resins commonly used in adhesive compositions can be used for the adhesive composition, and examples of such resins include epoxy resins, acrylic resins, and urethane resins. Here, "resin" refers to a resin before it has been further polymerized with a curing agent or polymerization initiator. From the viewpoint of the adhesive strength of the adhesive layer before application of an electric pulse, the molecular weight of the resin is preferably 50 to 10,000, and more preferably 150 to 5,000. The molecular weight can be measured by SEC measurement.

[0022] Examples of epoxy resins include polyglycidyl ether compounds of mononuclear polyhydric phenol compounds such as hydroquinone, resorcinol, pyrocatechol, and phloroglucinol; and polynuclear polyhydric phenols such as dihydroxynaphthalene, biphenol, methylenebisphenol (bisphenol F), methylenebis(ortho-cresol), ethylidenebisphenol, isopropylidenebisphenol (bisphenol A), isopropylidenebis(ortho-cresol), tetrabromobisphenol A, 1,3-bis(4-hydroxycumylbenzene), 1,4-bis(4-hydroxycumylbenzene), 1,1,3-tris(4-hydroxyphenyl)butane, 1,1,2,2-tetra(4-hydroxyphenyl)ethane, thiobisphenol, sulfobisphenol, oxybisphenol, phenol novolac, orthocresol novolac, ethylphenol novolac, butylphenol novolac, octylphenol novolac, resorcinol novolac, and terpene phenol. polyglycidyl ether compounds of alcohol compounds; polyglycidyl ethers of polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, hexanediol, polyglycol, thiodiglycol, glycerin, trimethylolpropane, pentaerythritol, sorbitol, and bisphenol A-alkylene oxide adducts; maleic acid, fumaric acid, itaconic acid, succinic acid, glutaric acid, suberic acid, adipic acid, azelaic acid, sebacic acid, dimer acid, trimer acid, Homopolymers or copolymers of glycidyl esters of aliphatic, aromatic, or alicyclic polybasic acids, such as phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, trimesic acid, pyromellitic acid, tetrahydrophthalic acid, hexahydrophthalic acid, and endomethylenetetrahydrophthalic acid, and glycidyl methacrylate; epoxy compounds having a glycidylamino group, such as N,N-diglycidylaniline, bis(4-(N-methyl-N-glycidylamino)phenyl)methane, and diglycidyl orthotoluidine;Examples of suitable polyepoxy compounds include epoxidized cyclic olefin compounds such as vinylcyclohexene diepoxide, dicyclopentanediene diepoxide, 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate, 3,4-epoxy-6-methylcyclohexylmethyl-6-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate; epoxidized conjugated diene polymers such as epoxidized polybutadiene and epoxidized styrene-butadiene copolymers; heterocyclic compounds such as triglycidyl isocyanurate; urethane-modified epoxy resins, chelate-modified epoxy resins, and rubber-modified epoxy resins. These polyepoxy compounds may also be internally crosslinked with a terminal isocyanate prepolymer or polymerized with a polyvalent active hydrogen compound (such as a polyhydric phenol, polyamine, or polyphosphate ester).

[0023] The urethane-modified epoxy resin is obtained by reacting an epoxy resin having at least one hydroxyl group in the molecule with a polyurethane having a residual isocyanate group, and the polyurethane is obtained by reacting a polyhydroxy compound with a polyisocyanate compound. During the reaction, the polyisocyanate compound is used in an excess amount relative to the polyhydroxy compound.

[0024] The method for producing the epoxy resin containing at least one hydroxyl group is not particularly limited, but examples thereof include a method in which 1 to 10 equivalents of epichlorohydrin and an alkali metal hydroxide such as sodium hydroxide are reacted with 1 equivalent of the hydroxyl groups of a low-molecular-weight polyol (molecular weight of 50 or more and less than 500) having at least two hydroxyl groups at 40 to 150°C for 1 to 20 hours.

[0025] The low molecular weight polyol containing at least two hydroxyl groups is not particularly limited, but examples thereof include polyphenols, aliphatic polyols, and alicyclic polyols.

[0026] Examples of the polyphenols include bisphenol A, bisphenol F, tetrabromobisphenol A, phenol novolak, brominated phenol novolak, cresol novolak, brominated cresol novolak, 4,4'-dihydroxybiphenyl, and 1,1,2,2-tetrakis(hydroxyphenyl)ethane.

[0027] Examples of the aliphatic polyols include polyhydric alcohols such as ethylene glycol and propylene glycol, linear or branched low-molecular-weight polyols such as butanediol, pentanediol, hexanediol, octanediol, decanediol, glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, dipentaerythritol, and neopentyl glycol, and ethylene oxide or propylene oxide adducts thereof.

[0028] Examples of the alicyclic polyol include cyclohexanediol, cyclohexanetriol, cyclohexanedimethanol, isopropylidenedicyclohexanol, decalindiol, and tricyclodecane dimethanol.

[0029] Among the polyols having at least two hydroxyl groups described above, it is preferable to use polyphenols, which are highly reactive and easy to produce, and it is more preferable to use bisphenol A and / or bisphenol F, which are inexpensively available.

[0030] Examples of polyhydroxy compounds used to produce the polyurethane include polyether polyols, polyester polyols, polycarbonate polyols, polyesteramide polyols, acrylic polyols, and polyurethane polyols.

[0031] As the polyether polyol, from the viewpoint of the adhesive strength of the adhesive layer before the application of an electric pulse, an alkylene oxide adduct of a polyol is preferably used, and the alkylene oxide preferably has 2 to 4 carbon atoms.

[0032] Examples of polyols used to produce the polyether polyols include aliphatic dihydric alcohols such as ethylene glycol, propylene glycol, 1,4-butylene glycol (tetramethylene glycol), and neopentane glycol; glycerin, trioxyisobutane, 1,2,3-butanetriol, 1,2,3-pentanetriol, 2-methyl-1,2,3-propanetriol, 2-methyl-2,3,4-butanetriol, 2-ethyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol, and 4-propyl-3,4,5- Examples of suitable polyhydric alcohols include trihydric alcohols such as heptanetriol, 2,4-dimethyl-2,3,4-pentanetriol, pentamethylglycerin, pentaglycerin, 1,2,4-butanetriol, 1,2,4-pentanetriol, and trimethylolpropane; tetrahydric alcohols such as erythritol, pentaerythritol, 1,2,3,4-pentanetetrol, 2,3,4,5-hexanetetrol, 1,2,3,5-pentanetetrol, and 1,3,4,5-hexanetetrol; pentahydric alcohols such as adonite, arabidopsis, and xylitol; and hexahydric alcohols such as sorbitol, mannitol, and idit. Among these, dihydric to tetrahydric alcohols are preferred from the viewpoint of the adhesive strength of the adhesive layer before the application of an electric pulse, with propylene glycol, 1,4-butylene glycol, and glycerin being particularly preferred.

[0033] Examples of alkylene oxides constituting the above polyether polyol include ethylene oxide, propylene oxide, and butylene oxide (tetramethylene oxide). From the viewpoint of the adhesive strength of the adhesive layer before the application of the electric pulse, propylene oxide and butylene oxide are particularly preferred.

[0034] Examples of the polyester polyol include conventionally known polyesters produced from polycarboxylic acids and polyhydric alcohols, and polyesters obtained from lactones.

[0035] Examples of polycarboxylic acids used to produce polyester polyols include benzenetricarboxylic acid, adipic acid, succinic acid, suberic acid, sebacic acid, oxalic acid, methyl adipic acid, glutaric acid, pimelic acid, azelaic acid, phthalic acid, terephthalic acid, isophthalic acid, thiodipropionic acid, maleic acid, fumaric acid, citraconic acid, and itaconic acid.

[0036] Examples of polyols used to produce polyester polyols include ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, bis(hydroxymethylchlorohexane), diethylene glycol, 2,2-dimethylpropylene glycol, 1,3,6-hexanetriol, trimethylolpropane, pentaerythritol, sorbitol, glycerin, etc. In addition to these polyols, polyhydroxy compounds such as polytetramethylene glycol and polycaprolactone glycol can also be used in partial substitution.

[0037] Examples of the polycarbonate polyol include those obtained by a dephenolation reaction between a diol and diphenyl carbonate, a dealcoholization reaction between a diol and a dialkyl carbonate, or a deglycolization reaction between a diol and an alkylene carbonate. Examples of the diol include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, and 3,3-dimethylolheptane.

[0038] Examples of polyisocyanate compounds used to produce the polyurethane include propane-1,2-diisocyanate, 2,3-dimethylbutane-2,3-diisocyanate, 2-methylpentane-2,4-diisocyanate, octane-3,6-diisocyanate, 3,3-dinitropentane-1,5-diisocyanate, octane-1,6-diisocyanate, 1,6-hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate, lysine diisocyanate, triisocyanate, methyl ... Examples of the polyisocyanate include diisocyanate (TDI), xylylene diisocyanate, meta-tetramethylxylylene diisocyanate, isophorone diisocyanate (3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate), 1,3- or 1,4-bis(isocyanatomethyl)cyclohexane, diphenylmethane-4,4'-diisocyanate (MDI), dicyclohexylmethane-4,4'-diisocyanate (hydrogenated MDI), hydrogenated tolylene diisocyanate, and mixtures thereof. These polyisocyanate compounds may be isocyanurates obtained by trimerization.

[0039] The chelate-modified epoxy resin is obtained by reacting an epoxy resin with phosphoric acid, and further, a chelate-urethane-modified epoxy resin obtained by reacting an epoxy resin, phosphoric acid, and a polyurethane having an isocyanate group can also be used.

[0040] The rubber-modified epoxy resin may be an epoxy resin containing a rubber component obtained by homopolymerizing isoprene rubber, butadiene, styrene, acrylonitrile, chloroprene, or the like, or copolymerizing two or more of the components, and containing an epoxy group at the terminal.

[0041] As the acrylic resin, for example, a homopolymer or copolymer of a (meth)acrylic monomer (such as (meth)acrylic acid or an ester thereof) or a polymer of other monomers can also be used.

[0042] Other monomers include hydroxyalkyl acrylates such as methyl 2-(hydroxymethyl)acrylate, methyl 2-(1-hydroxyethyl)acrylate, ethyl 2-(hydroxymethyl)acrylate, and butyl 2-(hydroxymethyl)acrylate; styrene; halogenated styrenes such as chlorostyrene and bromostyrene; substituted styrenes such as vinyltoluene and α-methylstyrene; unsaturated nitriles such as acrylonitrile and methacrylonitrile; unsaturated acid anhydrides such as maleic anhydride and citraconic anhydride; and unsaturated imides such as phenylmaleimide and cyclohexylmaleimide. The acrylic resin may also be modified by reacting functional groups contained in the copolymer.

[0043] The acrylic resin can be obtained by polymerizing a monomer mixture containing methyl methacrylate and / or methyl acrylate in the presence of a radical polymerization initiator and a chain transfer agent.

[0044] Examples of urethane resins include polyurethane and block urethane resin.

[0045] As described above, polyurethane is obtained by reacting a polyhydroxy compound with a polyisocyanate compound. The polyhydroxy compound and isocyanate compound used in producing polyurethane may be the same as those described above for the urethane-modified epoxy resin.

[0046] The production of polyurethane by reacting a polyhydroxy compound with a polyisocyanate compound can be carried out by a conventional method.

[0047] As the blocked urethane resin, a blocked urethane resin obtained by blocking, with a blocking agent, polyurethane having an isocyanate (NCO) content of 0.1 to 10 mass % obtained by reacting a polyhydroxy compound with an excess amount of a polyisocyanate compound is preferably used.

[0048] Examples of blocking agents include active methylene compounds such as malonic acid diesters (diethyl malonate, etc.), acetylacetone, and acetoacetic acid esters (ethyl acetoacetate, etc.); oxime compounds such as acetoxime, methyl ethyl ketoxime (MEK oxime), and methyl isobutyl ketoxime (MIBK oxime); monohydric alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, heptyl alcohol, hexyl alcohol, octyl alcohol, 2-ethylhexyl alcohol, isononyl alcohol, and stearyl alcohol, or isomers thereof; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, and the like; glycol derivatives such as ethylene glycol monobutyl ether, ethyl diglycol, ethyl triglycol, ethylene glycol monobutyl ether, and butyl diglycol; amine compounds such as dicyclohexylamine; phenols such as phenol, cresol, ethylphenol, n-propylphenol, isopropylphenol, butylphenol, tert-butylphenol, octylphenol, nonylphenol, dodecylphenol, cyclohexylphenol, chlorophenol, bromophenol, resorcinol, catechol, hydroquinone, bisphenol A, bisphenol S, bisphenol F, and naphthol; ε-caprolactone, ε-caprolactam, and the like.

[0049] The blocking reaction for obtaining a blocked polyurethane from a polyurethane and a blocking agent can be carried out by a known reaction method.

[0050] As the blocked urethane resin, in addition to the blocked urethane resin obtained by reacting polyurethane with a blocking agent, a blocked isocyanate resin obtained by modifying a polyisocyanate compound (particularly an isocyanuric compound) with a blocking agent can also be used.

[0051] The amount of resin in the adhesive composition is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, of the adhesive composition from the viewpoint of the adhesive strength of the adhesive layer before the application of an electric pulse.

[0052] The adhesive composition used in the present invention may contain a latent curing agent or other curing agents, a curing catalyst, a polymerization initiator, and the like.

[0053] The latent curing agent may be at least one compound selected from the group consisting of dicyandiamide, modified polyamines, hydrazides, 4,4'-diaminodiphenyl sulfone, boron trifluoride amine complex salts, ureas, and melamine. Examples of the modified polyamine include epoxy addition-modified amines, amidation-modified amines, acrylate-modified amines, isocyanate-modified amines, and Mannich-modified amines.

[0054] Examples of amines for providing the modified polyamine include aliphatic polyamines such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyoxypropylenediamine, and polyoxypropylenetriamine; alicyclic polyamines such as isophoronediamine, menthenediamine, bis(4-amino-3-methyldicyclohexyl)methane, diaminodicyclohexylmethane, bis(aminomethyl)cyclohexane, N-aminoethylpiperazine, and 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxaspiro(5.5)undecane; m-phenylenediamine, p-phenylenediamine, and tolylene-2,4-diamine; mononuclear polyamines such as biphenylenediamine, 4,4-diaminodiphenylmethane, 2,5-naphthylenediamine, and 2,6-naphthylenediamine; aromatic polyamines such as biphenylenediamine, 4,4-diaminodiphenylmethane, 2,5-naphthylenediamine, and 2,6-naphthylenediamine; and imidazoles such as 2-methylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, and 2-aminopropylimidazole.

[0055] The other curing agents are not particularly limited as long as they are known curing agents, and examples thereof include phenolic resins, aliphatic amines, aromatic amines, acid anhydrides, polythiol compounds, and the like.

[0056] The amount of the latent curing agent or other curing agent to be added is preferably 1 to 100 parts by mass, and more preferably 2 to 50 parts by mass, per 100 parts by mass of the resin, from the viewpoint of the adhesive strength of the adhesive layer before the application of the electric pulse.

[0057] Examples of the curing catalyst include phosphines such as triphenylphosphine; phosphonium salts such as tetraphenylphosphonium bromide; imidazoles such as 2-methylimidazole, 2-phenylimidazole, 2-ethyl-4-methylimidazole, 2-undecylimidazole, 1-cyanoethyl-2-methylimidazole, and imidazole silane (for example, 2MUSIZ manufactured by Shikoku Chemical Industry Co., Ltd.); imidazole salts obtained by combining the above-mentioned imidazoles with trimellitic acid, isocyanuric acid, boron, or the like; benzyldimethylamine, 2 , 4,6-tris(dimethylaminomethyl)phenol and other amines; quaternary ammonium salts such as trimethylammonium chloride; ureas such as 3-(p-chlorophenyl)-1,1-dimethylurea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, 3-phenyl-1,1-dimethylurea (1,1-dimethyl-3-phenylurea), isophorone diisocyanate-dimethylurea, and tolylene diisocyanate-dimethylurea; and complex compounds of boron trifluoride with amines, ether compounds, etc. These curing catalysts may be used alone or in combination of two or more.

[0058] The amount of the curing catalyst to be added is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, per 100 parts by mass of the resin, from the viewpoint of the adhesive strength of the adhesive layer before the application of the electric pulse.

[0059] Examples of the polymerization initiator include a thermal radical polymerization initiator, a photoradical polymerization initiator, and a cationic polymerization initiator.

[0060] The thermal radical polymerization initiator is not particularly limited as long as it generates radicals upon heating, and conventionally known compounds can be used. Examples include azo compounds such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(methyl isobutyrate), 2,2'-azobis-2,4-dimethylvaleronitrile, and 1,1'-azobis(1-acetoxy-1-phenylethane); peroxides such as benzoyl peroxide, di-t-butylbenzoyl peroxide, t-butyl peroxypivalate, and di(4-t-butylcyclohexyl)peroxydicarbonate; and persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate.

[0061] The photoradical polymerization initiator is not particularly limited as long as it generates radicals upon irradiation with light, and conventionally known compounds can be used. Examples of such compounds include diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 4'-isopropyl-2-hydroxy-2-methylpropiophenone, 2-hydroxymethyl-2-methylpropiophenone, 2,2-dimethoxy-1,2-diphenylethan-1-one, p-dimethylaminoacetophenone, p-tert-butyldichloroacetophenone, p-tert-butyltrichloroacetophenone, p-azidobenzalacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, benzoin, benzoin methyl ether, benzoin ethyl ether, and benzoin. benzyl-based compounds such as benzil; benzophenone-based compounds such as benzophenone, methyl o-benzoylbenzoate, Michler's ketone, 4,4'-bisdiethylaminobenzophenone, 4,4'-dichlorobenzophenone, and 4-benzoyl-4'-methyldiphenyl sulfide; thioxanthone-based compounds such as thioxanthone, 2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone, 2-isopropylthioxanthone, and 2,4-diethylthioxanthone; and oxime ester compounds such as oxime ester compounds having a carbazole skeleton, oxime ester compounds having a diphenyl sulfide skeleton, and oxime ester compounds having a fluorene skeleton.

[0062] Other examples of the radical polymerization initiator include phosphine oxide compounds such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide, and titanocene compounds such as bis(cyclopentadienyl)-bis[2,6-difluoro-3-(pyr-1-yl)]titanium.

[0063] Commercially available radical polymerization initiators include ADEKA OPTOMER N-1414, N-1717, N-1919, ADEKA ARCLES NCI-831, NCI-930 (all manufactured by ADEKA Corporation); IRGACURE 184, IRGACURE 369, IRGACURE 651, IRGACURE 907, IRGACURE OXE 01, IRGACURE OXE 02, IRGACURE 784 (all manufactured by BASF Corporation); TR-PBG-304, TR-PBG-305, TR-PBG-309 and TR-PBG-314 (all manufactured by Tronly Corporation); and the like.

[0064] The cationic polymerization initiator may be any compound capable of releasing a substance that initiates cationic polymerization upon irradiation with energy rays or heat, but is preferably a double salt, which is an onium salt that releases a Lewis acid upon irradiation with energy rays, or a derivative thereof. Examples include aryldiazonium salts such as phenyldiazonium hexafluorophosphate, 4-methoxyphenyldiazonium hexafluoroantimonate, and 4-methylphenyldiazonium hexafluorophosphate; diaryliodonium salts such as diphenyliodonium hexafluoroantimonate, di(4-methylphenyl)iodonium hexafluorophosphate, di(4-tert-butylphenyl)iodonium hexafluorophosphate, and tolylcumyliodonium tetrakis(pentafluorophenyl)borate; and sulfonium salts such as a sulfonium cation and a hexafluoroantimony ion, a hexafluorophosphate ion, and a tetrakis(pentafluorophenyl)borate ion.

[0065] The amount of the polymerization initiator to be added is preferably 1 to 100 parts by mass, more preferably 2 to 50 parts by mass, per 100 parts by mass of the resin, from the viewpoint of the adhesive strength of the adhesive layer before the application of the electric pulse.

[0066] The adhesive composition used in the present invention may contain additives as needed. Examples of such additives include moisture adsorbents such as calcium oxide, non-reactive diluents (plasticizers) such as dioctyl phthalate, dibutyl phthalate, benzyl alcohol, and coal tar; fibrous fillers such as glass fiber, pulp fiber, synthetic fiber, and ceramic fiber; reinforcing materials such as glass cloth, aramid cloth, and carbon fiber; pigments; γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-N'-β-(aminoethyl)-γ-aminopropyltriethoxysilane, γ-anilinopropyltriethoxysilane, γ-glycidoxypropyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltriethoxysilane, vinyltriethoxysilane, N -β-(N-vinylbenzylaminoethyl)-γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and other silane coupling agents; lubricants such as candelilla wax, carnauba wax, Japan wax, Ibota wax, beeswax, lanolin, spermaceti, montan wax, petroleum wax, aliphatic wax, aliphatic esters, aliphatic ethers, aromatic esters, and aromatic ethers; thickeners; thixotropic agents; antioxidants; light stabilizers; ultraviolet absorbers; flame retardants; antifoaming agents; rust inhibitors; colloidal silica, colloidal alumina, and other commonly used additives may be contained, and adhesive resins such as xylene resins and petroleum resins may also be used in combination.

[0067] When an additive is added, the amount of the additive is preferably 100 parts by mass or less, and more preferably 50 parts by mass or less, per 100 parts by mass of the resin, from the viewpoint of the adhesive strength of the adhesive layer before the application of the electric pulse.

[0068] The adhesive composition containing the conductive filler used in the present invention is produced by mixing the adhesive composition with the conductive filler. The mixing method is not particularly limited, and a general method for mixing a filler with a resin composition, such as using a roll-type kneader, can be used.

[0069] The adhesive composition containing the conductive filler described above is used, for example, to bond two or more components that constitute an article. For example, by applying the adhesive composition containing the conductive filler to at least one of the components, placing the components on top of each other with the adhesive composition interposed therebetween, and curing the adhesive composition, an article can be obtained in which the components are bonded via an adhesive layer containing the conductive filler. The thickness of the adhesive layer is not particularly limited, but is within the range of 1 μm to 2 mm. The application method is also not particularly limited, and any common application method used to bond components can be used. The components may be conductors or insulators, or may be a combination of conductors and insulators. However, it is preferable for the components to include a conductor portion, because when applying an electric pulse to disassemble the article by applying the electric pulse, as described below, the electric pulse can be applied to the adhesive layer more efficiently by contacting an electrode with the conductor portion. Here, examples of conductors include metal materials such as copper, aluminum, and gold; and electrical conductors such as graphite and conductive polymers. Examples of insulators include electrical nonconductors such as glass, paper, and plastic.

[0070] The environment in which the electric pulse is applied in this method may be any environment that allows the desired electric pulse to be applied to the article. Such an environment may be in the atmosphere or in a liquid such as water. It may also be in a vacuum or reduced-pressure environment. In this method, the environment is preferably in the atmosphere, as this facilitates application of the electric pulse. Next, a method for applying an electric pulse in the atmosphere according to the present invention will be described. In this method, the "atmosphere" refers to any environment in which the electric pulse can be applied, such as an environment under atmospheric pressure. Note that "under atmospheric pressure" includes atmospheric pressure (1013.25 hPa) and pressures in the vicinity thereof, as well as pressures within the range of normal atmospheric pressure variations. The atmospheric pressure may be any pressure that allows the application of an electric pulse, such as a pressure in the range of 700 to 1300 hPa. The temperature in the atmosphere in which the electric pulse is applied may be any temperature range that allows the desired electric pulse to be applied to the article, such as a temperature range of -40°C to 150°C, preferably a temperature range of -20°C to 100°C, and particularly a temperature range of -10°C to 50°C. This is because it is easy to apply an electric pulse and because it is easy to suppress deterioration of the article to which the electric pulse is applied. The humidity of the atmosphere to which the electric pulse is applied may be within a temperature range in which a desired electric pulse can be applied to the article, and can be, for example, an environment with a relative humidity of 1% to 99%.

[0071] The application of the electric pulse is carried out, for example, by using a high-voltage pulse generator 1 as shown in Fig. 1. This device is not new, and any known high-voltage pulse generator can be used. For example, the high-voltage pulse generator using a Marx booster circuit described in Japanese Patent Laid-Open Publication No. 56-139090 can be used.

[0072] When dismantling components of a relatively large home appliance, it is possible to dismantle the object S while it is placed on the floor or workbench 2, but when dismantling a mobile communication terminal or the like, it is preferable to hold the object S on the workbench 2 with a clamping device or the like.

[0073] If the number of objects S to be dismantled is small, the objects S can be clamped using a vice, but if the number of objects S to be dismantled is large, it is preferable to use a dedicated workbench 2. As shown in Figure 1, the workbench 2 comprises a base 3 and a pair of clamping tools 4 and 5 provided on the base 3. One of the pair of clamping tools 4 and 5 is fixed on the base 3, and the other clamping tool 5 is configured to be slidable on the base 3.

[0074] In order to improve the efficiency of the dismantling work, it is preferable to use a pneumatic device to slide the clamping tool 5 and clamp the object S. In addition, it is preferable that the periphery of the work table 2 be surrounded by metal plates or resin plates to ensure safety.

[0075] A pair of electrodes (positive electrode 8 and negative electrode 9) are connected to the output terminals of the high-voltage pulse generator 1 using cables 6 and 7, and are configured to be able to contact any position on the surface of the object S to be disassembled. Specifically, the positive electrode 8 and negative electrode 9 are held by separate holders (not shown), which are fixed to the workbench 2 by magnets or the like. Therefore, each electrode can be easily contacted to any position on the surface of the object S. That is, the positive electrode 8 and negative electrode 9 can be contacted separately to the front and back surfaces of the object S, or the positive electrode 8 and negative electrode 9 can be contacted to the same front and back surfaces of the object S. Furthermore, since the method of the present invention is performed in the atmosphere, no container for pouring a liquid medium is required, and therefore the positive electrode 8 and negative electrode 9 can be easily contacted to any position on the object S.

[0076] Here, an example will be described in which the object S is, for example, a steel plate S1 and a steel plate S2 joined via an adhesive layer S3. In this case, when both of the members contacting the electrodes are conductors, it is possible to apply an electric pulse without any problems even if the electrodes are contacted at a position away from the area where the adhesive layer S3 is formed, for example, about 1 meter away. However, if the electrodes are contacted too far away, the electrical resistance and inductance of the steel plates may affect the discharge energy. Furthermore, when the members contacting the electrodes include an insulator, it is preferable to contact the electrodes at a position closer to the adhesive layer S3 so as not to impair the discharge energy.

[0077] By applying an electric pulse, an internal discharge occurs inside the adhesive layer S3, starting from the conductive filler, causing the resin around the conductive filler to gasify, creating voids in the adhesive layer S3 and making the adhesive layer S3 more susceptible to rupture.

[0078] A circuit diagram of the high-voltage pulse generator 1 is shown in Figure 2. As shown in this figure, this device is configured to charge a capacitor C from a DC power supply (charger), and then switch a mechanical switch to the discharge side (electrode side) to apply an electric pulse to the electrode in contact with the object S. By switching the mechanical switch between the charge side and the discharge side, charging and discharging can be repeated, making it possible to apply an electric pulse multiple times.

[0079] In this case, the charging voltage varies depending on the size of the area on the object where the adhesive layer is formed and the thickness of the adhesive layer, but is preferably in the range of 0.1 kV to 100 kV. The capacitance of the capacitor C is preferably 0.1 μF to 10 μF.

[0080] The number of times the electric pulse is applied varies depending on the size of the object S, etc., but if the number of times is too great, the components that make up the object may be damaged, and the components or functional components contained in the components may also be damaged. Therefore, it is preferable to apply the electric pulse 1 to 20 times, and more preferably 1 to 10 times.

[0081] After applying the electric pulse, the component can be removed and the remaining adhesive layer can be removed by cleaning or the like, allowing the component or the functional parts contained in the component to be reused. Examples of methods for removing the adhesive layer include manually removing the remaining adhesive layer, since its adhesive strength has decreased, mechanically scraping it off, and dissolving and removing the adhesive layer with a solvent. Examples of functional parts include home appliances, communication device terminals, toys, daily necessities, industrial equipment, and automotive interior parts.

[0082] The present invention will be specifically described below with reference to examples.

[0083] <Preparation of adhesive composition> Each component was placed in a container in the amounts shown in Table 1, and stirred with a spatula at 25°C for 5 minutes, followed by stirring using a planetary mixer and further stirring using a roll kneader to prepare an adhesive composition.

[0084]

[0085] Carbon black was added as a conductive filler to 100 parts by mass of the resulting adhesive composition in the amounts shown in Table 2 for Examples 1 to 3, and copper was added in Example 4, and mixed using a roll-type kneader to prepare adhesive compositions containing carbon black and copper. In Comparative Example 1, no conductive filler was added to the adhesive composition. The manufacturer names, trade names, particle diameters, and densities of the conductive fillers used in Examples 1 to 4 are shown in Table 3.

[0086]

[0087]

[0088] [Tensile Shear Test Method] <Preparation of Test Specimens> Test specimens for use in the tensile shear test method were prepared in accordance with JIS K 6850. Specifically, as shown in FIG. 1 , two identical steel plates S1 and S2 (conductors) (length: 10 cm, width: 2.5 cm, thickness: 1.6 cm) were prepared. The adhesive compositions of Examples 1 to 4 and Comparative Example 1 were applied to predetermined areas of one of the steel plates, S1, with a spatula to a film thickness of approximately 0.2 mm. Next, the other steel plate, S2 (conductor), was placed on top of the steel plate S1 to which the adhesive composition had been applied, so that the two plates overlapped only in the area where the adhesive composition had been applied. The steel plates S1 and S2, overlapping each other with the adhesive composition interposed therebetween, were then placed in a curing furnace, and the adhesive composition was cured at 180°C for 30 minutes to prepare test specimens in which the two steel plates S1 and S2 were joined via the adhesive layer S3.

[0089] <Application of Electric Pulse> Using the high-voltage pulse generator 1 shown in FIG. 1 in the laboratory atmosphere at room temperature, the test specimen was used as the object S. A pair of electrodes (positive electrode 8 and negative electrode 9) was placed on the rigid plates S1 and S2 joined via the adhesive layer S3. Each electrode was located approximately 5 cm away from the area where the adhesive layer S3 was formed, and abutted against the surface opposite the area where the adhesive layer S3 was formed. Next, as shown in the circuit diagram in FIG. 2, a capacitor C was charged to 2.4 μF with a charging voltage of 10 kV using a charger, and an electric pulse was applied to each electrode by switching the mechanical switch of the circuit to the electrode side (discharge side). The electric pulse was applied once or ten times.

[0090] <Measurement of tensile strength> A tensile shear test was performed on each test piece using the adhesive compositions of Examples 1 to 4 and Comparative Example 1, and the tensile strength of the test piece after application of an electric pulse and the tensile strength of the test piece without application of an electric pulse were measured. Specifically, for each test piece, one of the rigid plates was pulled in the opposite direction to the other steel plate at 25°C and 5 mm / min using a universal testing machine (AGIS-100kN manufactured by Shimadzu Corporation), and the tensile strength at the time when the steel plate S1 and the steel plate S2 peeled apart, i.e., when the adhesive layer S3 broke, was measured as the adhesive strength.

[0091] As shown in Table 4, the test pieces bonded via an adhesive layer not containing a conductive filler, as in Comparative Example 1, maintained their adhesive strength at 33 MPa even after 10 applications of an electric pulse, whereas the test pieces of Examples 1 to 3 were confirmed to have an adhesive strength that decreased from 34 MPa to 26 MPa (a decrease of about 24%) in Example 1, from 33 MPa to 15 MPa (a decrease of about 55%) in Example 2, and from 33 MPa to 11 MPa (a decrease of about 67%) in Example 3 after 10 applications of an electric pulse. It was also confirmed that the adhesive strength of Example 4 decreased from 23 MPa to 17 MPa (a decrease of about 26%) after one application of an electric pulse.

[0092]

[0093] <Observation of the Surface of the Adhesive Layer After Fracture> For each test piece using the adhesive compositions of Examples 1 to 4 and Comparative Example 1, enlarged photographs of the side of the adhesive layer S3 of each steel plate after a tensile shear test was performed after application of an electric pulse are shown in Figures 3 to 7, respectively. As shown in the photographs of Figures 3 to 5, the adhesive layer S3 containing carbon black had voids (areas surrounded by white dotted lines in the photographs) recognized as discharge traces V inside the adhesive layer S3. As shown in the photograph of Figure 6, the adhesive layer S3 containing copper particles in Example 4 also had voids (areas surrounded by white dotted lines in the photographs) recognized as discharge traces V inside the adhesive layer S3, although these were smaller than those in Examples 1 to 3. On the other hand, as shown in the photograph of Figure 7, for the adhesive layer S3 of Comparative Example 1 not containing a conductive filler, no discharge traces were observed inside the adhesive layer S3, and discharge traces V' were confirmed at the edge of the adhesive layer S3 (areas surrounded by black dotted lines in the photographs).

[0094] When an electric pulse is applied to a test piece whose adhesive layer contains a conductive filler, as in Examples 1 to 4, an internal discharge occurs within the adhesive layer, originating from the conductive filler, causing the resin to decompose and gasify, resulting in voids.

[0095] The method of the present invention for reducing the adhesive strength of an adhesive layer can be used when dismantling household electrical appliances, mobile communication terminals, etc. that are no longer in use due to breakdown or changes in the product life cycle.

[0096] REFERENCE SIGNS LIST 1 High voltage pulse generator 2 Work table 3 Base 4, 5 Clamping tool 6, 7 Cable 8 Positive electrode 9 Negative electrode S Object S1 Steel plate S2 Steel plate S3 Adhesive layer V, V' Discharge traces

Claims

1. A method for reducing the adhesive strength of an adhesive layer by applying an electric pulse to an article including a portion in which two or more members are joined via an adhesive layer containing a conductive filler.

2. The method of claim 1 , wherein the electrical pulse is applied in air.

3. the adhesive layer is made of a cured product of an adhesive composition containing the conductive filler, The method according to claim 1 , wherein the adhesive composition comprises at least one selected from the group consisting of an epoxy-based resin, an acrylic-based resin, and a urethane-based resin.

4. 2. The method according to claim 1, wherein the conductive filler is at least one selected from the group consisting of carbon black; graphene; carbon nanotubes (CNT); metal particles selected from copper, silver, gold, nickel, silver-coated copper, gold-coated copper, silver-coated nickel, and gold-coated nickel; and metal-coated resin particles selected from acrylic resin particles or urethane resin particles coated with copper, silver, nickel, gold, or a mixture thereof.

5. The method according to claim 1, wherein the content of the conductive filler in the adhesive composition is 0.1 to 40 vol % of the adhesive composition containing the conductive filler.

6. The method of claim 1 , wherein at least one of the two or more members comprises a conductive portion.

7. After carrying out the method according to any one of claims 1 to 6, A method of removing a component from the article and reusing the component or a functional part contained in the component.