Adhesive sheet

Abstract

The present invention provides an adhesive sheet having excellent workability and capable of being stored at room temperature. The adhesive sheet has: an adhesive layer composed of a composition for an adhesive layer containing an epoxy resin and a film-forming aid, and a coating layer formed on the adhesive layer and containing a thermoplastic resin. The coating layer contains at least one of an epoxy resin curing agent and an epoxy resin curing accelerator, and does not exhibit tackiness at room temperature. The heat generation ratio of the adhesive sheet after being placed at 40°C for 14 days is 80% or more. By heating the adhesive sheet to a temperature above the curing start temperature of the adhesive layer, at least a part of the coating layer disappears within the range from the interface between the adhesive layer and the coating layer to the surface of the coating layer.

Description

Technical Field

[0001] The present invention relates to an adhesive sheet, and more particularly, to an adhesive sheet having excellent workability and capable of being stored at room temperature for a long time. Background Art

[0002] Adhesive sheets are used in various fields such as reinforcement of rivet joints of building structural materials, adhesion of decorative panels for furniture or building materials, interior decorative materials for automobiles, interlayer adhesion or structural adhesion applications of carbon fiber reinforced plastics (CFRP), and adhesion applications of cover films for flexible electronic power substrates. The present applicant has proposed an adhesive sheet characterized by having: an adhesive layer composed of a composition for an adhesive layer containing a thermosetting resin; and a coating layer formed on the adhesive layer and containing a resin, the coating layer not showing stickiness at room temperature, and at least a part of the coating layer disappearing in the range from the interface between the adhesive layer and the coating layer to the surface of the coating layer by heating the adhesive sheet to a temperature equal to or higher than the curing start temperature of the adhesive layer (see Patent Document 1). With respect to the adhesive sheet of Patent Document 1, it is possible to prevent undesired sticking and adhesion phenomena during the operation before the adhesive layer is heated and cured, and excellent workability can be achieved. However, for the adhesive sheet of Patent Document 1, since the adhesive layer contains a main agent, a curing agent, and a curing accelerator, it cannot be stored at room temperature, and there is room for improvement in terms of storage stability.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2015-163694 Summary of the Invention

[0006] Accordingly, an object of the present invention is to provide an adhesive sheet capable of being stored at room temperature and having excellent workability.

[0007] In view of the above problems, the inventors of the present application conducted in-depth research and found that by adding at least one of an epoxy resin curing agent and an epoxy resin curing accelerator to a coating formed on a bonding layer composed of a composition for a bonding layer containing an epoxy resin and a film-forming aid, and a coating containing a thermoplastic resin formed on the bonding layer, the curing reaction in the bonding layer is inhibited, thereby obtaining a bonding sheet that can be stored at room temperature and has excellent workability, and the present invention was conceived. That is, the bonding sheet of the present invention is characterized by having: a bonding layer composed of a composition for a bonding layer containing an epoxy resin and a film-forming aid, and a coating formed on the bonding layer and containing a thermoplastic resin, the coating contains at least one of an epoxy resin curing agent and an epoxy resin curing accelerator, and does not show stickiness at room temperature, the heat generation ratio of the bonding sheet after being placed at 40 °C for 14 days is 80% or more, and by heating the bonding sheet to a temperature above the curing start temperature of the bonding layer, at least a part of the coating disappears in the range from the interface between the bonding layer and the coating to the surface of the coating.

[0008] The above film-forming aid and thermoplastic resin are preferably each at least one selected from phenoxy resin, polyvinyl acetal resin, polyester resin, and acrylic resin.

[0009] The epoxy resin curing agent contained in the above coating can be at least one selected from dicyandiamide, imidazole compounds, and tertiary amines.

[0010] In addition, the epoxy resin curing accelerator contained in the above coating can be at least one selected from imidazole compounds, tertiary amines, and phosphorus compounds.

[0011] The above coating may contain: at least one of the above epoxy resin curing agents and at least one of the above epoxy resin curing accelerators (wherein, substances of the same type as the above epoxy resin curing agent are not included).

[0012] In addition, for the bonding sheet of the present invention, the above bonding layer contains an epoxy resin curing agent, the epoxy resin curing agent is at least one selected from dicyandiamide, imidazole compounds, tertiary amines, and acid anhydrides, the above coating contains an epoxy resin curing accelerator, and the epoxy resin curing accelerator can also be at least one selected from imidazole compounds, tertiary amines, and phosphorus compounds (wherein, substances of the same type as the above curing agent are not included).

[0013] The adhesive sheet of the present invention is characterized in that the curing reaction of the epoxy resin is inhibited during storage, and when the adhesive sheet is heated during use, the components of the adhesive layer are mixed with the components of the coating formed on the upper part, the reaction is promoted, and curing is carried out. Therefore, the adhesive sheet of the present invention can be stored at room temperature, it is easy to ensure a storage place, refrigerated transportation is not required, and the costs for transportation and storage can be reduced. In addition, for a conventional adhesive sheet that needs to be stored refrigerated in order to inhibit the progress of the curing reaction at room temperature, when in use, in order to avoid the adverse effects of dew condensation on the adhesive sheet, it is opened only after it has adapted to room temperature. However, for the adhesive sheet of the present invention, since it can be stored at room temperature, it can be used immediately after being taken out, and the rapidization of the operation can also be expected.

[0014] It should be noted that the heating conditions during use of the adhesive sheet of the present invention are not particularly limited, and by adjusting the material composition of the adhesive layer and the coating, etc., a cured product of the epoxy resin can be obtained under heating conditions equivalent to those of an existing adhesive sheet. Detailed Embodiments

[0015] The embodiments of the present invention will be described in detail below, but the present invention is not construed as being limited thereto, and various changes, corrections, and improvements can be added based on the knowledge of those skilled in the art as long as the scope of the present invention is not exceeded.

[0016] It should be noted that in this specification, "~" indicating a numerical range means a range including the numerical values respectively described as its upper limit value and lower limit value. In addition, when only the unit of the upper limit value is described in the numerical range, it means that the lower limit value is also the same unit as the upper limit value.

[0017] In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value described in a certain numerical range can be replaced with the upper limit value or the lower limit value of another numerically described range.

[0018] In addition, in the numerical ranges described in this specification, the upper limit value or the lower limit value described in a certain numerical range can be replaced with the value shown in the examples.

[0019] In this specification, regarding the content or content ratio of each component in the composition, when there are multiple substances belonging to each component in the composition, unless otherwise specified, it means the total content or content ratio of the multiple substances present in the composition.

[0020] The adhesive sheet according to this embodiment is characterized by comprising: an adhesive layer composed of a composition for an adhesive layer containing an epoxy resin and a film-forming aid, and a coating layer formed on the adhesive layer and containing a thermoplastic resin, the coating layer containing at least one of an epoxy resin curing agent and an epoxy resin curing accelerator, and not showing stickiness at normal temperature, the heat generation ratio of the adhesive sheet after being placed at 40°C for 14 days being 80% or more, and by heating the adhesive sheet to a temperature equal to or higher than the curing start temperature of the adhesive layer, at least a part of the coating layer disappears within the range from the interface between the adhesive layer and the coating layer to the surface of the coating layer.

[0021] As described above, the adhesive sheet according to this embodiment is characterized in that the curing reaction of the epoxy resin in the adhesive layer can be suppressed at normal temperature. Therefore, any of the following configurations is adopted: (i) a configuration in which an epoxy resin curing agent and an epoxy resin curing accelerator are added to the coating layer and no epoxy resin curing agent and epoxy resin curing accelerator are added to the adhesive layer; (ii) a configuration in which an epoxy resin curing agent is added to the coating layer and an epoxy resin curing accelerator is added to the adhesive layer; (iii) a configuration in which an epoxy resin curing accelerator is added to the coating layer and an epoxy resin curing agent is added to the adhesive layer; and (iv) a configuration in which an epoxy resin curing agent is added to the coating layer and no epoxy resin curing agent and epoxy resin curing accelerator are added to the adhesive layer. The detailed content of each configuration will be described later.

[0022] Regarding the adhesive sheet according to this embodiment, the coating layer does not show stickiness (tackiness) at normal temperature, so that a reduction in workability due to stickiness or the like can be prevented. The presence or absence of the stickiness of the coating layer can be evaluated by the following method.

[0023] The sheet obtained by laminating the coating layer on a release film is cut into a size of 5 cm × 5 cm, and is laminated under the condition where the coating layers face each other and under the condition where the release film and the coating layer face each other, and is sandwiched between glass plates with a thickness of 1 mm. A load of 100 g is applied thereto, and after being left at normal temperature (25°C) for 24 hours, the load is removed, the glass plates are opened up and down, and the peeling state at this time is confirmed, thereby evaluating the stickiness of the coating layer. The specific evaluation criteria will be described later.

[0024] The adhesive sheet according to this embodiment is characterized in that the heat generation ratio after being placed at 40°C for 14 days measured by the method described later is 80% or more.

[0025] The heat generation ratio of the adhesive sheet according to this embodiment, which is 80% or more after being placed at 40°C for 14 days, can suppress the progress of the curing of the epoxy resin even when stored at room temperature. Therefore, the adhesive sheet according to this embodiment can be stored at room temperature, easily ensuring a storage place, without the need for refrigerated transportation, and can reduce the costs consumed in transportation and storage. In addition, for the adhesive sheet according to this embodiment, since it can be stored at room temperature, it can be used immediately after being taken out, and the acceleration of the operation can be expected.

[0026] The heat generation ratio after being placed at 40°C for 14 days is preferably 85% or more, more preferably 90% or more.

[0027] Regarding the adhesive sheet according to this embodiment, by heating to a temperature equal to or higher than the curing start temperature of the adhesive layer, at least a part of the coating disappears within the range from the interface between the adhesive layer and the coating to the coating surface. The so-called "coating disappearance" means that by applying heat exceeding the glass transition temperature of the resin forming the coating to the adhesive sheet according to this embodiment, the coating is softened, and thus the resin of the coating is mixed with the (pre-cured) epoxy resin forming the adhesive layer, thereby integrating with the adhesive layer, and the coating existing on the adhesive layer becomes visually non-existent.

[0028] It should be noted that the disappearance of the coating can be judged by the ratio (Pm / Pc) of the measured value (Pc) of the tensile shear adhesive strength between the steel plates A and B of the coating alone and the measured value (Pm) of the tensile shear adhesive strength between the steel plates A and B of the laminated product after heating. The specific method will be described later.

[0029] Hereinafter, the specific configuration of the adhesive sheet according to this embodiment will be described.

[0030] (1) Adhesive layer

[0031] The adhesive layer of the adhesive sheet according to this embodiment (hereinafter, also simply referred to as "adhesive layer") is formed of a composition for the adhesive layer containing an epoxy resin and a film-forming aid.

[0032] 1) Epoxy resin

[0033] The epoxy resin used in the adhesive layer is not particularly limited. Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, hydantoin type epoxy resin, biphenyl type epoxy resin, alicyclic epoxy resin, triphenylmethane type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, naphthol novolak type epoxy resin, dicyclopentadiene / phenol epoxy resin, alicyclic amine epoxy resin, aliphatic amine epoxy resin, and epoxy resins obtained by various modifications such as CTBN modification and halogenation of them. Among these, from the viewpoints of heat resistance and ease of obtaining, bisphenol A type epoxy resin and novolak type epoxy resin are preferred. In addition, these epoxy resins can be used alone or in combination of two or more. In order to improve the adhesiveness of the adhesive layer when processed into an adhesive sheet and ensure the flexibility when the adhesive sheet is processed into a roll, the epoxy resin used in the adhesive layer is preferably a mixture of an epoxy resin that is liquid at room temperature (25°C) and a solid epoxy resin.

[0034] The epoxy equivalent (WPE) of the epoxy resin used in the adhesive layer is preferably 150 or more, more preferably 180 or more, preferably 1000 or less, and more preferably 700 or less. When the WPE is less than 150, there are many crosslinking points, and a cured product with high heat resistance is obtained, but the toughness is low and it may become brittle. When the WPE is higher than 1000, there are few crosslinking points, and thus the heat resistance may be reduced. The "epoxy equivalent" is defined as the molecular weight of the epoxy resin per 1 epoxy group. Here, the "epoxy group" includes oxirane (ethylene oxide) which is an ether of a 3-membered ring, and in addition to the epoxy group in the narrow sense, it also includes glycidyl groups (including glycidyl ether groups and glycidyl ester groups). The WPE is determined by the method (perchloric acid-tetraethylammonium bromide method) described in JIS K7236, Method for Determining the Epoxy Equivalent of Epoxy Resins (2001), etc. It should be noted that in this specification, when a plurality of epoxy resins are used, the above-mentioned epoxy equivalent refers to the epoxy equivalent of the mixed epoxy resins.

[0035] 2) Film-forming aid

[0036] This embodiment is characterized in that the adhesive layer contains a film-forming aid. By adding a film-forming aid to the adhesive layer, no depressions, coating unevenness, etc. will occur on the surface of the adhesive layer obtained by coating and drying the composition for the adhesive layer, and thus the coatability can be improved.

[0037] As a film-forming auxiliary used in the adhesive layer, thermoplastic resins such as phenoxy resin, polyester resin, polyurethane resin, polyacetal resin, polyamide resin, polypropylene, polyvinyl butyral resin, polyvinyl acetal resin, polyvinyl acetate, nylon, and acrylic resin can be used; rubber materials such as polybutadiene, styrene-butadiene rubber, styrene-butadiene-styrene copolymer, styrene-ethylene-butene-styrene copolymer, butyl rubber, chloroprene rubber, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-acrylic acid copolymer, acrylonitrile-butadiene-styrene copolymer, natural rubber, isoprene rubber, chloroprene rubber, nitrile rubber, fluororubber, and acrylic rubber can be used, etc.

[0038] Among these, from the viewpoint of affinity with epoxy resin, it is preferable to use at least one selected from phenoxy resin, polyvinyl acetal resin, polyester resin, and acrylic resin. In addition, phenoxy resin, polyvinyl acetal resin, and polyester resin having a hydroxyl group are more preferable. These film-forming auxiliaries can be used alone or in combination of multiple kinds.

[0039] Phenoxy resin refers to a high-molecular-weight thermoplastic polyether resin based on diphenols such as bisphenol A and bisphenol F and epihalohydrins such as epichlorohydrin. The weight-average molecular weight of the phenoxy resin is preferably 20,000 to 100,000. When the weight-average molecular weight is 20,000 or more, film-forming properties can be imparted. On the other hand, when the weight-average molecular weight is 100,000 or less, the viscosity during the formation of the coating film does not become too high, and a smooth and uniform coating film can be obtained.

[0040] As the phenoxy resin, there is no particular limitation, and resins having one or more skeletons selected from bisphenol A skeleton, bisphenol F skeleton, bisphenol S skeleton, bisphenol acetophenone skeleton, novolak skeleton, biphenyl skeleton, fluorene skeleton, dicyclopentadiene skeleton, norbornene skeleton, naphthalene skeleton, anthracene skeleton, adamantane skeleton, terpene skeleton, and trimethylcyclohexanone skeleton can be cited.

[0041] As commercially available products of phenoxy resin, for example, product names such as PKHB, PKHC, PKHH, PKHJ (all manufactured by HUNTSMAN), jER (registered trademark) 1256, 4250, 4275 (all manufactured by Mitsubishi Chemical), YP-50, YP-50S, YP-70, ZX-1356-2, FX-316 (all manufactured by NIPPON STEEL Chemical&Material Co.,Ltd.) can be cited.

[0042] In addition, substances obtained by dissolving phenoxy resins with a solvent are also commercially available and can be used in the same manner. For example, jER 1256B40, 1255HX30, YX6954BH30, YX6954B35, YX8100BH30, YL7174BH40 (all manufactured by Mitsubishi Chemical Corporation), YP-40ASM40, YP-50EK35, YPB-40PXM40, ERF-001M30, YPS-007A30, FX-293AT40 (all manufactured by NIPPON STEEL Chemical&Material Co.,Ltd.), etc. can be cited. These phenoxy resins can be used alone or in combination of multiple types.

[0043] As the polyvinyl acetal resin, for example, the trade names S-LEC (registered trademark) KS-23Z, KS-1, KS-5, BX-1, BM-S (all manufactured by Sekisui Chemical Co., Ltd.) etc. can be cited.

[0044] As the polyester resin, for example, the trade name Vylon (registered trademark) series (manufactured by TOYOBO MMCorporation), the trade name Nichigo-POLYESTER TP series (manufactured by Mitsubishi Chemical Corporation), the trade name ELITEL (registered trademark) UE series (manufactured by UNITIKA LTD.), etc. can be cited.

[0045] The mass ratio of the epoxy resin to the film-forming aid in the adhesive layer (epoxy resin: film-forming aid) is preferably in the range of 3:1 to 20:1, more preferably in the range of 3:1 to 15:1, and particularly preferably in the range of 4:1 to 12:1. By adjusting the mass ratio of the epoxy resin to the film-forming aid in the adhesive layer to the above range, the depression and coating unevenness during the formation of the coating film of the composition for the adhesive layer are improved, the coatability is further enhanced, and an adhesive layer that can improve the surface tackiness, the peelability of the self-releasing film, and has excellent heat resistance can be obtained.

[0046] 3) Epoxy resin curing agent

[0047] The adhesive sheet according to the present embodiment is characterized in that it can suppress the progress of the curing reaction of the adhesive sheet at normal temperature.

[0048] Therefore, as described above, any of the following configurations needs to be adopted: (i) a configuration in which an epoxy resin curing agent and an epoxy resin curing accelerator are added to the coating, and no epoxy resin curing agent and epoxy resin curing accelerator are added to the adhesive layer; (ii) a configuration in which an epoxy resin curing agent is added to the coating and an epoxy resin curing accelerator is added to the adhesive layer; (iii) a configuration in which an epoxy resin curing accelerator is added to the coating and an epoxy resin curing agent is added to the adhesive layer; and (iv) a configuration in which an epoxy resin curing agent is added to the coating, and no epoxy resin curing agent and epoxy resin curing accelerator are added to the adhesive layer.

[0049] Regarding the configurations of (i), (ii), and (iv), the adhesive layer does not contain an epoxy resin curing agent. Therefore, hereinafter, the epoxy resin curing agent of the configuration of (iii) will be described.

[0050] In the configuration of (iii), the epoxy resin curing agent contained in the adhesive layer is at least one selected from dicyandiamide (DICY), imidazole compounds, tertiary amines, and acid anhydrides, and the coating contains at least one epoxy resin curing accelerator selected from imidazole compounds, tertiary amines, and phosphorus compounds. Among them, it is necessary that the epoxy resin curing accelerator contained in the coating and the epoxy resin curing agent contained in the adhesive layer are different types of compounds.

[0051] For example, when dicyandiamide is added as the epoxy resin curing agent to the adhesive layer, at least one of an imidazole compound, a tertiary amine, or a phosphorus compound can be added as the epoxy resin curing accelerator to the coating. For the adhesive sheet composed of such an adhesive layer and a coating, the curing reaction of the epoxy resin can be suppressed during storage at room temperature, and when the adhesive sheet is heated during use, the epoxy resin and the epoxy resin curing agent in the adhesive layer are mixed with the epoxy resin curing accelerator in the coating, and the curing reaction of the epoxy resin proceeds.

[0052] As the above-mentioned imidazole compounds, for example, 2-methylimidazole, 2-phenyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,4-diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-1,3,5-triazine, 2-ethyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, etc. can be cited.

[0053] As the above-mentioned tertiary amines, 2,4,6-tris(dimethylaminomethyl)phenol, 1,8-diazabicyclo[5.4.0]-7-undecene, triethylenediamine, N,N-dimethylbenzylamine, 4-dimethylaminopyridine, 2-dimethylaminomethylphenol, 1,5-diazabicyclo[4.3.0]-5-nonene, etc. can be cited.

[0054] Examples of the above-mentioned acid anhydrides include phthalic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, trimellitic anhydride, pyromellitic dianhydride, maleic anhydride, methylbicyclo[2.2.1]heptane-2,3-dicarboxylic anhydride, bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride, 4-methylcyclohexanone-1,2-dicarboxylic anhydride, bicyclo[2.2.1]heptane-2,3-dicarboxylic anhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,3,3',4-biphenyltetracarboxylic dianhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride, ethylene glycol bis(trimellitic anhydride), 4,4'-[propane-2,2-diylbis(1,4-phenyleneoxy)]diphthalic dianhydride, and the like.

[0055] In the composition of (iii), examples of commercially available products of dicyandiamide added to the adhesive layer include DICY7 (manufactured by Mitsubishi Chemical Corporation). In addition, examples of commercially available products of imidazole compounds include CUREZOL (registered trademark) 2MZA-PW, 2P4MHZ-PW, 2E4MZ, 2PHZ (all manufactured by Shikoku Kasei Kogyo Co., Ltd.). Examples of commercially available products of tertiary amines include the Ancamine (registered trademark) series (manufactured by Evonik), DBU (registered trademark), and U-CAT (registered trademark) series (all manufactured by San-apro).

[0056] The blending amount of the epoxy resin curing agent is calculated based on the equivalent ratio with the epoxy resin used, and the preferred range of the equivalent ratio is 0.2 to 2.0. For example, when the epoxy resin curing agent is dicyandiamide, it is preferably in the range of 2 to 20 parts by mass, more preferably in the range of 5 to 15 parts by mass, relative to 100 parts by mass of the epoxy resin. When the blending amount of the epoxy resin curing agent is less than 2 parts by mass, it is difficult to cure sufficiently, and the heat resistance, chemical resistance, etc., which are characteristics of the epoxy resin, may not be fully exhibited. On the other hand, if the blending amount exceeds 20 parts by mass, an excessive exothermic reaction occurs during curing, and the unreacted epoxy resin curing agent remains in the cured product, which may affect the resin properties.

[0057] 4) Epoxy resin curing accelerator

[0058] In the structure of (iii), when dicyandiamide is added as an epoxy resin curing agent in the adhesive layer, the imidazole compounds and tertiary amines added as epoxy resin curing accelerators in the coating can be the above-mentioned substances. As the phosphorus compound, organophosphines such as tributylphosphine, triphenylphosphine, and tri-p-tolylphosphine, salts such as triphenylborane-triphenylphosphine complex and tetrakis(4-methylphenyl)borane-tetraphenylphosphine complex can be cited. These epoxy resin curing accelerators only need not be of the same type as the epoxy resin curing agent contained in the adhesive layer, and can be used alone or in combination of multiple kinds.

[0059] As commercially available products of the phosphorus compound, HOKKO TPP (registered trademark), TPTP, TPP-S, TPP-K, TPP-MK (all manufactured by Kitakyo Chemical Industry Co., Ltd.) etc. can be cited.

[0060] In the present embodiment, since the epoxy resin curing accelerator is contained in a layer different from the epoxy resin and the epoxy resin curing agent, the epoxy resin curing accelerator can be blended without significantly affecting the storage stability of the adhesive sheet. When a substance that is solid at normal temperature is used as the epoxy resin curing accelerator, the blending amount of the epoxy resin curing accelerator is preferably 20 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin. By making the blending amount of the epoxy resin curing accelerator within the above range, a state with good dispersion stability and viscosity is achieved in the coating-forming coating liquid, and a coating with good smoothness can be produced. In addition, the residue of unreacted substances can be suppressed during heat curing, so an adhesive sheet with excellent heat resistance can be produced.

[0061] Next, the epoxy resin curing accelerator added to the adhesive layer in the structure of (ii) will be described.

[0062] As the above-mentioned epoxy resin curing accelerator, a phosphorus compound can be added. Imidazole compounds and tertiary amines themselves also function as epoxy resin curing agents, so they cannot be added as the epoxy resin curing accelerator in the structure of (ii). For the adhesive sheet composed of such an adhesive layer and a coating, the curing reaction of the epoxy resin can be suppressed during storage at normal temperature, and when the adhesive sheet is heated during use, the epoxy resin and the epoxy resin curing accelerator in the adhesive layer are mixed with the epoxy resin curing agent in the coating, and the curing reaction of the epoxy resin proceeds.

[0063] In the structure of (ii), the blending amount of the epoxy resin curing accelerator added to the adhesive layer is preferably set to, for example, 5 parts by mass or less with respect to 100 parts by mass of the epoxy resin. However, in the present embodiment, since the epoxy resin curing accelerator is contained in a layer different from the epoxy resin curing agent, even if the blending amount of the epoxy resin curing accelerator exceeds 5 parts by mass, it will not significantly affect the storage stability of the adhesive sheet.

[0064] 5) Other additives

[0065] In the composition for the adhesive layer that forms the adhesive layer, other additives that can be incorporated as optional components may also be added. For example, a thickener (such as amorphous silica, calcium carbonate, talc, etc.), a thermal foaming agent, a foaming aid, various fillers, a cell stabilizer, an antioxidant, an ultraviolet absorber, a flame retardant, a colorant, etc. may also be incorporated.

[0066] (2) Coating

[0067] The coating of the adhesive sheet according to this embodiment (hereinafter, also simply referred to as "coating") is formed on the above-mentioned adhesive layer and is formed of a composition containing a thermoplastic resin. The coating contains at least one of an epoxy resin curing agent and an epoxy resin curing accelerator and does not exhibit adhesiveness at normal temperature. Further, by heating to a temperature above the curing start temperature of the adhesive layer when using the adhesive sheet, at least a part of the coating disappears in the range from the interface between the adhesive layer and the coating to the surface of the coating, and at least a part of the heat-cured adhesive layer is exposed at the portion of the adhesive sheet that comes into contact with the adherend, whereby it functions as an adhesive sheet.

[0068] Hereinafter, the components constituting the coating will be described.

[0069] 1) Thermoplastic resin

[0070] As the thermoplastic resin used in the coating, the resin described as a thermoplastic resin among the film-forming aids used in the above-mentioned adhesive layer can be used. From the viewpoint of affinity with the epoxy resin, the thermoplastic resin is also preferably at least one selected from a phenoxy resin, a polyvinyl acetal resin, a polyester resin, and an acrylic resin. Among these, a phenoxy resin, a polyvinyl acetal resin, and a polyester resin having a hydroxyl group are more preferable. The thermoplastic resin can be used alone or in combination of multiple kinds.

[0071] Specifically, in the configuration where the film-forming aid used in the adhesive layer is a phenoxy resin and the thermoplastic resin used in the coating is a phenoxy resin and / or a polyvinyl acetal resin and / or a polyester resin having a hydroxyl group, and in the configuration where the film-forming aid used in the adhesive layer is a polyvinyl acetal resin and the thermoplastic resin used in the coating is a phenoxy resin and / or a polyvinyl acetal resin and / or a polyester resin having a hydroxyl group, more excellent affinity is achieved.

[0072] 2) Epoxy resin curing agent and / or epoxy resin curing accelerator

[0073] As described above, the adhesive sheet according to this embodiment is characterized in that the curing reaction of the epoxy resin in the adhesive layer is suppressed at normal temperature. Therefore, any of the following configurations needs to be adopted: (i) a configuration in which an epoxy resin curing agent and an epoxy resin curing accelerator are added to the coating layer, and no epoxy resin curing agent and epoxy resin curing accelerator are added to the adhesive layer; (ii) a configuration in which an epoxy resin curing agent is added to the coating layer and an epoxy resin curing accelerator is added to the adhesive layer; (iii) a configuration in which an epoxy resin curing accelerator is added to the coating layer and an epoxy resin curing agent is added to the adhesive layer; and (iv) a configuration in which an epoxy resin curing agent is added to the coating layer, and no epoxy resin curing agent and epoxy resin curing accelerator are added to the adhesive layer. Regarding the configuration of (iii), as described above, the configurations of (i), (ii), and (iv) will be described below.

[0074] (i) A configuration in which an epoxy resin curing agent and an epoxy resin curing accelerator are added to the coating layer, and no epoxy resin curing agent and epoxy resin curing accelerator are added to the adhesive layer

[0075] In this configuration, the epoxy resin curing agent added to the coating layer is preferably at least one selected from dicyandiamide, imidazole compounds, and tertiary amines, and the epoxy resin curing accelerator is preferably at least one selected from imidazole compounds, tertiary amines, and phosphorus compounds. Among them, substances of the same type as the above-mentioned epoxy resin curing agent are not included. The detailed content of each component is as described above.

[0076] Among the above, for the configuration in which dicyandiamide is used as the epoxy resin curing agent and an imidazole compound is used as the epoxy resin curing accelerator, the curing reaction of the epoxy resin is suppressed even during long-term storage at normal temperature, and during heating during use, the coating layer completely disappears, and more excellent adhesiveness can be achieved, which is preferable.

[0077] (ii) A configuration in which an epoxy resin curing agent is added to the coating layer and an epoxy resin curing accelerator is added to the adhesive layer

[0078] In this configuration, when an epoxy resin curing agent is added to the coating layer, the epoxy resin curing agent is preferably at least one selected from dicyandiamide, imidazole compounds, and tertiary amines. The detailed content of each component is as described above. Regarding the epoxy resin curing accelerator, it is also as described above.

[0079] (iv) A configuration in which an epoxy resin curing agent is added to the coating layer, and no epoxy resin curing agent and epoxy resin curing accelerator are added to the adhesive layer

[0080] In this configuration, when an epoxy resin curing agent is added to the coating, the epoxy resin curing agent is preferably at least one selected from imidazole compounds and tertiary amines. The details of each component are as described above. Among the above, for the configuration using an imidazole compound as the epoxy resin curing agent, even during long-term storage at room temperature, the progress of the curing reaction of the epoxy resin is suppressed, and during heating during use, the coating disappears, enabling excellent adhesiveness, which is preferable.

[0081] (3) Method for producing the adhesive sheet

[0082] The composition for the adhesive layer can be obtained by mixing, as needed, an epoxy resin curing agent or an epoxy resin curing accelerator, various additives, etc. in any order into the above-mentioned epoxy resin and film-forming aid. The mixing of the above raw materials can be carried out using a mixer or kneader such as a mixing roll, planetary mixer, butterfly mixer, kneader, single-screw or twin-screw extruder. The mixing temperature varies depending on the composition, and it is preferably carried out under conditions lower than the curing start temperature.

[0083] Each component of the composition for the adhesive layer is preferably adjusted such that the curing start temperature of the adhesive sheet formed by forming the composition for the adhesive layer into a sheet is 60°C or higher and 200°C or lower.

[0084] The adhesive layer is obtained by dissolving or dispersing the above-mentioned composition for the adhesive layer in a solvent, coating one or both sides of the substrate described below, and drying it as needed. It should be noted that the adhesive layer can also be obtained by coating the above-mentioned composition for the adhesive layer on the coating layer described below formed on a separately prepared release film and drying it as needed. In addition, the adhesive layer can also be obtained by coating the above-mentioned composition for the adhesive layer on one side of the substrate that has been subjected to a release treatment and drying it as needed.

[0085] Regarding the coating method of the coating liquid for forming the adhesive layer, there is no particular limitation, and conventionally known coating methods such as those using a wire bar, coater, brush, sprayer, roller, gravure coater, die coater, lip coater, comma coater, knife coater, reverse coater, spin coater, etc. can be used. It should be noted that the surface of the release film and the substrate to which the coating liquid for forming the adhesive layer is to be coated can be surface-treated as needed.

[0086] Regarding the drying method of the coating liquid for forming the adhesive layer, there is also no particular limitation, and conventionally known drying methods such as hot air drying and reduced-pressure drying can be used. Regarding the drying conditions, they can be appropriately set according to the type of the composition for the adhesive layer, the type of the solvent used in the coating liquid for forming the adhesive layer, the film thickness of the adhesive layer, etc., and usually drying is carried out at a temperature of about 60 to 200°C.

[0087] The thickness (t1) of the adhesive layer can be appropriately selected according to the use of the adhesive sheet. It is preferably in the range of 10 μm to 1000 μm, more preferably in the range of 30 μm to 400 μm, and particularly preferably in the range of 30 μm to 200 μm. By making the thickness of the adhesive layer 10 μm or more, for example, it can follow the adherend with unevenness, so that stable adhesive performance can be maintained. By making the thickness (t1) of the adhesive layer 1000 μm or less, it can be suitably used for applications requiring thinning.

[0088] As the solvent, the following solvents can be used alone or in combination of two or more: aromatic solvents such as toluene and xylene; ester solvents such as ethyl acetate, butyl acetate, methoxybutyl acetate, and methoxypropyl acetate; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ether solvents such as diethyl ether, dibutyl ether, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, propylene glycol monomethyl ether acetate, diethylene glycol dimethyl ether, and diethylene glycol methyl ethyl ether, etc.

[0089] As the base material, there is no particular limitation and it can be appropriately selected. Examples include films, non-woven fabrics, papers, etc. formed of synthetic resins such as polyethylene terephthalate, polyethylene naphthalate, polyethylene, polypropylene, polycarbonate, cellulose triacetate, aromatic polyamide, polyimide, polyamide, polyphenylene sulfide, polyetherimide, polyethersulfone, aromatic polyamide, and polysulfone. The base material is selected according to the use of the adhesive sheet. Especially in applications requiring insulation and heat resistance, polyimide films, aromatic polyamide non-woven fabric sheets, etc. are preferably used.

[0090] The thickness of the base material can be appropriately selected according to the application. For example, when the application is the bonding of various components of electronic devices requiring insulation described later, etc., the thickness of the base material is preferably 25 to 250 μm.

[0091] The composition for coating can be obtained by the following method: If necessary, an epoxy resin curing agent or an epoxy resin curing accelerator, various additives, etc. are mixed in the above-mentioned thermoplastic resin in any order. The mixing of the above raw materials can be carried out using a mixer or a kneader such as a mixing roll, a planetary mixer, a butterfly mixer, a kneader, a single-screw or twin-screw extruder, etc. The mixing temperature varies according to the composition, but it is preferably carried out under the condition of being lower than the curing start temperature.

[0092] The coating is obtained by the following method: The above-mentioned composition for coating is dissolved or dispersed in a solvent, coated on one or both sides of the above-mentioned base material, and dried if necessary. It should be noted that there is no particular limitation on the coating method and the drying method of the coating-forming coating liquid, and the same methods as the coating method and the drying method of the adhesive layer-forming coating liquid can be used.

[0093] The thickness (t2) of the coating is preferably 100% or less, more preferably 50% or less, and particularly preferably 30% or less of the thickness (t1) of the adhesive layer before heating. By making t2 100% or less of t1, the coating softens due to heat and can disappear well.

[0094] The mechanism of the coating disappearance is as follows. By applying heat exceeding the glass transition temperature of the resin forming the coating, the coating softens. As a result, the resin of the coating (thermoplastic resin) is mixed with the epoxy resin (before curing) forming the adhesive layer and integrated into the adhesive layer (introduced into the adhesive layer). As a result, the coating present on the adhesive layer becomes visually absent.

[0095] If t2 exceeds 100% of t1, it will not be sufficiently incorporated into the adhesive layer, and as a result, the disappearance of the coating may not proceed well. In this embodiment, t2 is preferably, for example, 0.5 μm or more and 600 μm or less, more preferably 1 μm or more and 200 μm or less, and particularly preferably 3 μm or more and 100 μm or less.

[0096] Regarding the coating, it is preferable to determine the resin forming the coating such that its glass transition temperature is preferably 60°C or more and lower than the curing temperature. If the glass transition temperature of the coating is lower than 60°C, the stickiness (tackiness) on the surface of the coating increases, and it may be difficult to obtain the effects of the present invention. On the other hand, if it exceeds the curing temperature, the coating does not soften sufficiently in the heating and curing temperature range of the adhesive layer, and thus the adhesive force brought by the adhesive layer may not be fully exerted.

[0097] The adhesive sheet of this embodiment can be produced by any of the wet method and the dry method.

[0098] The wet method is the following method: A coating-forming coating liquid obtained by dissolving or dispersing the components of the above coating in a solvent is applied to a substrate, and dried as needed to obtain a coating. An adhesive-layer-forming coating liquid obtained by dissolving or dispersing the components of the above adhesive layer in a solvent is prepared, applied to the above coating, and dried.

[0099] On the other hand, the dry method is, for example, the following method: The coating formed on a release film and the adhesive layer formed on a release film (different from the release film used for forming the coating) are laminated (bonded) to produce it.

[0100] <Use>

[0101] The adhesive sheet according to the present embodiment described above can be suitably used for, for example, strengthening the rivet joints of building structural materials, bonding decorative panels of furniture or building materials, interior decorative materials of automobiles, interlayer bonding or structural bonding applications of carbon fiber reinforced plastics (CFRP), bonding of cover films for flexible electronic circuit boards, etc. In addition, by using an insulating substrate in the adhesive layer, it can be used for bonding various components of electronic devices that require insulation, such as interlayer insulating films of electronic circuit boards.

[0102] Furthermore, by introducing a thermally conductive filler into the adhesive layer, it can be used for bonding an electronic device and a radiator.

[0103] By introducing a thermally expandable filler into the adhesive layer, and utilizing the void filling property based on thermal expansion, in addition to being used as a filling material for the gaps generated between an image display component fixed to an image display device (liquid crystal display, electroluminescent display, plasma display, etc.), an optical component (camera, lens, etc.) fixed to a portable electronic device (mobile phone, portable information terminal, etc.), and a frame (window part), it can also be used as a filling material for the gaps between coils with different phases adjacent to the coil ends of a stator used in a motor or a generator, the gaps in the slots of a stator core, etc., and is widely used in the electrical and electronic industries.

[0104] Examples

[0105] Hereinafter, the embodiments of the present invention will be described in more detail using examples, but the present invention is not limited by these examples. It should be noted that in the examples, unless otherwise specified, "%" and "parts" represent mass% and mass parts.

[0106] [Examples 1 to 24, Comparative Examples 1 to 5]

[0107] 1. Preparation of coating liquids for forming the adhesive layer and the coating

[0108] The respective components described in Tables 1 to 4 were mixed in a solid component ratio (in terms of mass), stirred and mixed together with separately prepared methyl ethyl ketone, and degassed under reduced pressure to prepare a coating liquid for forming the adhesive layer and a coating liquid for forming the coating. The total solid component in each coating liquid was set to 30% by mass to 50% by mass.

[0109] The raw materials used are as follows.

[0110] (A) Epoxy resin

[0111] (a1) Bisphenol A liquid resin (epoxy equivalent: 184 - 194 g / eq, liquid at room temperature)

[0112] (a2) Bisphenol A solid resin (epoxy equivalent: 600 - 700 g / eq, softening temperature: 78°C)

[0113] (a3) Bisphenol A solid resin (epoxy equivalent: 1700 - 2200 g / eq, softening temperature: 128 °C)

[0114] (B) Film-forming aid

[0115] (b1) Phenoxy resin (product name: PHENOXY PKHB (containing bisphenol A skeleton), glass transition temperature: 84 °C, weight average molecular weight: 32000, manufactured by HUNTSMAN)

[0116] (b2) Polyvinyl acetal resin (product name: S-LEC KS-23Z, glass transition temperature is 110 °C, manufactured by Sekisui Chemical Co., Ltd.)

[0117] (b3) Polyester resin (hydroxyl group-containing polyester resin, product name: Nichigo-POLYESTER TP-235, glass transition temperature: 65 °C, manufactured by Mitsubishi Chemical Corporation)

[0118] (C) Epoxy resin curing agent and / or epoxy resin curing accelerator

[0119] (c1) Dicyandiamide (50% particle size: 3 μm)

[0120] (c2) Imidazole compound

[0121] (c2-1) 2-Phenyl-4-methyl-5-hydroxymethylimidazole

[0122] (c2-2) 2,4-Diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-1,3,5-triazine

[0123] (c2-3) 2-Phenyl-4,5-dihydroxymethylimidazole

[0124] (c3) Acid anhydride

[0125] (c3-1) 3,3’,4,4’-Biphenyltetracarboxylic dianhydride

[0126] (c4) Phosphorus compound

[0127] (c4-1) Triphenylphosphine

[0128] (c4-2) Tris(p-tolyl)phosphine

[0129] (c5) Tertiary amine

[0130] (c5-1) 2,4,6-Tris(dimethylaminomethyl)phenol

[0131] 2. Preparation of the coating

[0132] A coating-forming coating solution having the composition shown in Tables 1 to 4 was used. Using a Baker coater, the specified coating-forming coating solution was coated on the release layer of the release film 1 (PET film with a thickness of 38 μm and a non-silicone release layer) such that the thickness of the dried coating became the thickness shown in Tables 1 to 4. Then, it was dried at 90°C for 3 minutes to obtain laminate 1 (a laminate of release film 1 and the coating).

[0133] 3. Production of the adhesive sheet

[0134] An adhesive layer-forming coating solution having the composition shown in Tables 1 to 4 was used. Using a Baker coater, the specified adhesive layer-forming coating solution was coated on the release layer of the release film 2 (PET film with a thickness of 38 μm and a non-silicone release layer) such that the thickness of the dried adhesive layer became the thickness shown in Tables 1 to 4. Then, it was dried at 90°C for 3 minutes to obtain laminate 2 (a laminate of release film 2 and the adhesive layer). The adhesive layer surface and the coating of laminate 1 were laminated while applying heat at 80°C, and then release film 1 and release film 2 were peeled off to obtain the adhesive sheets of the examples and comparative examples.

[0135] 4. Evaluation

[0136] For each of the obtained adhesive sheets of the examples and comparative examples, the following items were measured or evaluated using the following methods. The results are shown in Tables 1 to 4.

[0137] [Film thickness (t2) of the coating]

[0138] Regarding the adhesive sheets obtained in each of the examples and comparative examples, for laminate 1, the total thickness was measured using a micrometer, and the thickness of release film 1 was subtracted from the obtained measured value to calculate it.

[0139] [Film thickness (t1) of the adhesive layer]

[0140] Regarding the adhesive sheets obtained in each of the examples and comparative examples, for laminate 2, the total thickness was measured using a micrometer, and the thickness of release film 2 was subtracted from the obtained measured value to calculate it.

[0141] [Adhesiveness of the coating]

[0142] The laminate 1 (a laminate of release film 1 and the coating) in each of the adhesive sheets of the examples and comparative examples was cut into a size of 5 cm × 5 cm, and they were laminated under the conditions where the coatings faced each other and under the conditions where the release film and the coating faced each other, and a glass plate with a thickness of 1 mm was sandwiched. A load of 100 g was applied thereon, and after leaving them at room temperature for 24 hours, the load was removed, and the glass plate was opened up and down, and the peeling state at this time was confirmed to evaluate the adhesiveness of the coating.

[0143] Here, visually observe the state when the glass plate is opened up and down, and evaluate according to the following criteria.

[0144] ○: No peeling caused by contact between the coatings and between the release film and the coating

[0145] △: Peeling occurs under any one of the conditions

[0146] ×: Peeling occurs under any conditions

[0147] [Coatability]

[0148] During the production of the laminate 2, visually observe the state of the adhesive layer, and evaluate according to the following criteria.

[0149] 〇: It is possible to uniformly coat without depressions

[0150] △: Depressions are generated in a part

[0151] ×: Depressions are generated on the entire surface

[0152] [Operability]

[0153] Evaluate the state of the adhesive layer surface during the process of laminating the coating layer of the laminate 1 onto the adhesive layer surface of the laminate 2 according to the following criteria.

[0154] 〇: Not sticky

[0155] △: Sticky enough to hinder the operation

[0156] ×: Sticky enough to cause difficult operation

[0157] [Peelability]

[0158] Evaluate the peelability of the release film 1 and the release film 2 according to the following criteria.

[0159] 〇: Each release film can be easily peeled off

[0160] △: Only one of the release films on either side can be peeled off

[0161] ×: When attempting to peel off the release film, the adhesive sheet undergoes cohesive failure

[0162] [Tensile shear bond strength and disappearance of the coating]

[0163] The adhesive sheets of each example and comparative example were cut into 25 mm × 12.5 mm, placed on an SPCC steel plate (Steel Plate A) with a thickness of 1.6 mm in a manner where the adhesive layers were in contact, laminated using a hand roller (rubber-made) while applying heat at 60 °C, and then an SPCC steel plate with a thickness of 1.6 mm (Steel Plate B) was laminated on the coating and fixed with a spring clip. After placing this laminate in an oven heated to the temperature (curing temperature) shown in Tables 1 to 4 for 30 minutes, it was taken out, allowed to cool at room temperature, and then the spring clip was removed to prepare test pieces. Using a universal testing machine #5982 manufactured by Instron Corporation, at room temperature, Steel Plate A and Steel Plate B of the heated laminate were pulled in directions parallel to the adhesive surface and opposite to each other (shearing direction) at a speed of 5 mm / min, and thereby the shear bond strength (Pm) (unit: MPa) was measured. It should be noted that this evaluation was only carried out when all the above evaluations of coatability, operability, and peelability were "〇".

[0164] When the coating disappeared and the adhesive layer adhered to Steel Plate A and Steel Plate B, the shear bond strength increased compared to the case where only the coating adhered to the steel plate. Therefore, the release film of laminate 1 was peeled off, and the same operation as above was performed, and it was placed between Steel Plate A and Steel Plate B, and the shear bond strength (Pc) of the coating alone was measured. Then, using the ratio (Pm / Pc) of the measured value (Pc) of the shear bond strength of the coating alone and the measured value (Pm) of the shear bond strength between Steel Plate A and Steel Plate B of the heated laminate, the disappearance property of the coating was evaluated according to the following criteria.

[0165] ◎: When the value of (Pm / Pc) exceeds 110%

[0166] 〇: When the value of (Pm / Pc) exceeds 100% and is 110% or less

[0167] ×: When the value of (Pm / Pc) is 100% or less

[0168] [Storage Stability]

[0169] The adhesive sheets obtained in each example and comparative example were cut into specified sizes, and a plurality of specimens were prepared. The calorific value of the obtained specimens was measured by differential scanning calorimetry (DSC) as the initial calorific value Q0. In addition, release film 1 and release film 2 were laminated on the coating surface and the adhesive surface of another specimen respectively to obtain laminate 3. Laminate 3 was placed in a constant temperature bath set at 40 °C, and after 14 days, it was taken out from the constant temperature bath, allowed to cool, and after peeling off release film 1 and release film 2, the calorific value was measured by DSC as the calorific value Q1 after being placed at 40 °C. Based on the obtained Q0 and Q1, the calorific value ratio after being placed at 40 °C for 14 days was calculated using the following formula.

[0170] Heat generation ratio (%) after storage at 40°C for 14 days = (Heat generation amount after storage at 40°C (Q1) / Initial heat generation amount (Q0)) × 100

[0171] It should be noted that the measurement conditions for the heat generation amount based on DSC are as follows.

[0172] Measurement temperature: 30°C to 300°C, Heating rate: 10°C / min.

[0173] As shown in Table 1, it was confirmed that for the adhesive sheet of Comparative Example 1 in which dicyandiamide as an epoxy resin curing agent and an imidazole compound as an epoxy resin curing accelerator were added to the adhesive layer containing an epoxy resin and a phenoxy resin as a film-forming aid, the heat generation ratio after storage at 40°C for 14 days was as low as 60%. It is considered that the reason is that since dicyandiamide and the imidazole compound are contained in the adhesive layer, the curing reaction of the epoxy resin proceeds in an environment of 40°C.

[0174] On the other hand, for the configurations of Examples 1 and 2 in which dicyandiamide and the imidazole compound are contained in the coating layer and not in the adhesive layer, that is, (i) a configuration in which an epoxy resin curing agent and an epoxy resin curing accelerator are added to the coating layer and no epoxy resin curing agent and epoxy resin curing accelerator are added to the adhesive layer, it was confirmed that the heat generation ratio after storage at 40°C for 14 days was 100%, and the curing reaction of the epoxy resin was also suppressed in an environment of 40°C. Therefore, it can be said that the adhesive sheet of the present invention can be sufficiently stored at room temperature.

[0175] In addition, compared with Comparative Example 1, the tensile shear adhesive strength of Examples 1 and 2 in which dicyandiamide and the imidazole compound are contained in the coating layer also increased, and it was confirmed that the adhesive performance in the present invention was also improved. In Examples 1 and 2, the addition amounts of dicyandiamide and the imidazole compound were different, and it was confirmed that the characteristics were stable in a wide range. Thus, it was confirmed that in the present invention, by adding an epoxy resin curing agent and / or a curing accelerator equivalent to the prior art in which an epoxy resin curing agent and / or a curing accelerator is added to the adhesive layer, excellent storage stability and adhesive performance are obtained.

[0176] [Table 1]

[0177]

[0178] In Example 3, the evaluation results of the configuration (ii) in which an epoxy resin curing agent was added to the coating layer and an epoxy resin curing accelerator was added to the adhesive layer are shown. Here, the epoxy resin curing agent added to the coating layer was (c1) dicyandiamide, and as the epoxy resin curing accelerator added to the adhesive layer, (c4-2) triphenylphosphine as a (c4) phosphorus compound was used. Except for this, it was produced in the same manner as in Example 1.

[0179] As shown in Table 1, it was confirmed that Example 3 obtained excellent storage stability, high tensile shear bond strength, and good coatability, workability, and peelability. From these results, it was found that the configuration of (ii) can also achieve the effects of the present invention.

[0180] Regarding the adhesive sheet of Comparative Example 2 in which an imidazole compound (c2-1) was added to the adhesive layer and neither an epoxy resin curing agent nor an epoxy resin curing accelerator was added to the coating layer, it was confirmed that the heat generation ratio after being left at 40°C for 14 days was as low as 64%. Therefore, it was found that even when an imidazole compound was added alone to the adhesive layer, the curing reaction of the adhesive sheet proceeded. In contrast, for the configuration in which the same imidazole compound (c2-1) as the epoxy resin curing agent was added to the coating layer, that is, Example 4 in which an epoxy resin curing agent was added to the coating layer and neither an epoxy resin curing agent nor an epoxy resin curing accelerator was added to the adhesive layer, although the blending amount of (c2-1) was significantly increased, the heat generation ratio after being left at 40°C for 14 days was also 100%, and it was confirmed that the curing reaction of the epoxy resin was suppressed. In addition, compared with Comparative Example 2, in Example 4, the tensile shear bond strength was improved, and the effects of the present invention were confirmed. It should be noted that the coatability, workability, and peelability of the adhesive sheets of Example 4 and Comparative Example 2 were all good.

[0181] In Comparative Example 3 and Example 5 in which the imidazole compound as the epoxy resin curing agent was changed from (c2-1) to (c2-2), the same tendency was also observed, and the effects of the present invention were confirmed.

[0182] It should be noted that for Comparative Example 4 in which the film-forming aid was removed from the adhesive layer of Example 5, it was found that when the coating liquid was formed by coating the adhesive layer on the release sheet, depressions were generated on the entire surface, and a good adhesive layer could not be obtained.

[0183] In addition, in Example 6 in which (c2-3) 2-phenyl-4,5-dihydroxymethylimidazole was used as the imidazole compound, the heat generation ratio after being left at 40°C for 14 days was also 100%, the coatability, workability, and peelability were all good, and the effects of the present invention were observed.

[0184] Similar to Examples 4 to 6, Example 7 has the configuration of (iv) in which an epoxy resin curing agent is added to the coating layer and neither an epoxy resin curing agent nor an epoxy resin curing accelerator is added to the adhesive layer. In Examples 4 to 6, (c2) imidazole compound was added as the epoxy resin curing agent added to the coating layer, but in Example 7, (c5-1) 2,4,6-tris(dimethylaminomethyl)phenol of (c5) tertiary amine was used and made by changing the curing temperature.

[0185] As shown in Table 1, it was confirmed that Example 7 achieved excellent storage stability, high tensile shear bond strength, and good coatability, workability, and peelability. From these results, it was found that in the configuration of (iv), even when a tertiary amine was used as an epoxy resin curing agent in the coating layer, the effects of the present invention could be achieved.

[0186] Regarding Examples 8 to 12, all had the configuration of (iii) adding (c1) dicyandiamide as an epoxy resin curing agent to the adhesive layer and adding (c2-2) an imidazole compound as an epoxy resin curing accelerator to the coating layer. Except that the compounding amounts and compounding ratios of (c1) dicyandiamide and (c2-2) imidazole compound were as shown in Table 2, all were produced under the same conditions. It was found that excellent storage stability, high tensile shear bond strength, and good coatability, workability, and peelability were obtained in all of Examples 8 to 12.

[0187]

[0188] [Table 2]

[0189] Comparative Example 5 had a configuration in which the film-forming aid was removed from the adhesive layer of Example 9. Although good coatability was obtained, problems occurred in workability and peelability. Therefore, it was confirmed that in order to obtain good workability and peelability, the configuration of adding a film-forming aid to the adhesive layer as in the present invention was necessary.

[0190] In addition, regarding Example 13, except that the thermoplastic resin in the coating layer was changed from (b1) phenoxy resin to (b2) polyvinyl acetal, it was produced in the same manner as Example 9. The tensile shear bond strength of Example 13 was equivalent to that of Example 9, and the storage stability was improved compared to Example 7. Therefore, it was found that polyvinyl acetal could also be suitably used as the thermoplastic resin for the coating layer of the adhesive sheet of the present invention.

[0191] Regarding Example 14, except that the thermoplastic resin in the coating layer was changed from (b1) phenoxy resin to (b3) polyester resin, it was produced in the same manner as Example 9. The tensile shear bond strength and storage stability of Example 14 were improved compared to Example 9. Therefore, it was found that polyester resin could also be suitably used as the thermoplastic resin for the coating layer of the adhesive sheet of the present invention.

[0192] Table 3 shows the evaluation results of the adhesive sheets prepared by adding an epoxy resin curing agent to the adhesive layer and an epoxy resin curing accelerator to the coating layer. For Examples 15 and 16, dicyandiamide (c1), an epoxy resin curing agent, was added to the adhesive layer, and the type of (c4) phosphorus compound was changed and added as an epoxy resin curing accelerator to the coating layer. As shown in Table 3, it was found that the tensile shear adhesive strength and storage stability changed depending on the type of (c4) phosphorus compound. However, it was confirmed that both Examples 15 and 16 achieved excellent storage stability, high tensile shear adhesive strength, and good coatability, workability, and peelability. It should be noted that when Example 15 was compared with Example 16, it was confirmed that although there was no significant difference in storage stability, the tensile shear adhesive strength of Example 16 was significantly higher.

[0193] From the above results, it can be seen that in the structure of (iii), as the epoxy resin curing accelerator added to the coating layer, the (c4) phosphorus compound can be applied.

[0194] [Table 3]

[0195]

[0196] For Example 17, the type of the epoxy resin curing accelerator added to the coating layer was changed to the (c4) phosphorus compound, and 2,4,6-tris(dimethylaminomethyl)phenol (c5-1), which is a (c5) tertiary amine, was used. The curing temperature was changed from 150 °C to 130 °C, and otherwise, it was produced in the same manner as in Example 15 and the like. As shown in Table 3, it was confirmed that Example 17 also achieved excellent storage stability, high tensile shear adhesive strength, and good coatability, workability, and peelability.

[0197] From the above results, it can be seen that in the structure of (iii), as the epoxy resin curing accelerator added to the coating layer, the (c5) tertiary amine can also be applied. In addition, the curing temperature of the adhesive sheet of Example 17 is 130 °C, and it can be cured at a lower temperature than Examples 15 and 16. Therefore, its application in fields requiring low-temperature curability is expected.

[0198] Similar to Examples 8 to 17, Examples 18 to 20 in Table 3 show the evaluation results of the adhesive sheets prepared by adding an epoxy resin curing agent to the adhesive layer and an epoxy resin curing accelerator to the coating layer. In Examples 18 to 20, as the epoxy resin curing agent added to the adhesive layer, 3,3’,4,4’-biphenyltetracarboxylic dianhydride, which is a (c3) acid anhydride, was used, and the curing temperature was changed from 150°C to 190°C. In addition, as the epoxy resin curing accelerator added to the coating layer, 2,4-diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-1,3,5-triazine, which is a (c2) imidazole compound, was used in Example 18, and 2,4,6-tris(dimethylaminomethyl)phenol, which is a (c5) tertiary amine, was used in Examples 19 and 20 and the addition amount was changed for preparation.

[0199] It was confirmed that Examples 18 to 20 all achieved excellent storage stability, high tensile shear adhesive strength, and good coatability, operability, and peelability. Based on this result, in the configuration of (iii), an acid anhydride can also be used as the epoxy resin curing agent, and applications in uses that particularly require heat resistance can be expected.

[0200] In Table 4, as Examples 21 to 24, the evaluation results of the adhesive sheets prepared by adding an epoxy resin curing agent to the adhesive layer and an epoxy resin curing accelerator to the coating layer, in which the thicknesses of the coating layer and the adhesive layer were changed, are shown. For Examples 21 to 24, except for changing the thickness of the adhesive layer or the coating layer, they were all prepared by the same method as in Example 9. As shown in Table 4, it was confirmed that even when the thickness of the adhesive layer or the coating layer was changed, the tensile shear adhesive strength and storage stability of Examples 21 to 24 were equivalent to those of Example 9, and the respective thicknesses could be appropriately selected for use.

[0201]

[0202] [Table 4]

Claims

1. An adhesive sheet, characterized in that, comprising: an adhesive layer composed of a composition for an adhesive layer containing an epoxy resin and a film-forming aid and not containing an imidazole compound, and a coating layer formed on the adhesive layer and containing a thermoplastic resin, wherein the coating layer contains an epoxy resin curing agent and does not exhibit adhesiveness at room temperature, and the epoxy resin curing agent is at least one selected from dicyandiamide, imidazole compounds, and tertiary amines, the ratio of the initial heat generation amount Q0 of the adhesive sheet measured by differential scanning calorimetry to the heat generation amount Q1 after being placed at 40 °C for 14 days, i.e., Q1 / Q0×100% is 80% or more, by heating the adhesive sheet to a temperature above the curing start temperature of the adhesive layer, at least a part of the coating layer disappears in the range from the interface between the adhesive layer and the coating layer to the surface of the coating layer.

2. The adhesive sheet according to claim 1, wherein, The film-forming aid and the thermoplastic resin are each at least one selected from phenoxy resins, polyvinyl acetal resins, polyester resins, and acrylic resins.

3. The adhesive sheet according to claim 1, wherein, The coating layer further contains an epoxy resin curing accelerator, and the epoxy resin curing accelerator is at least one selected from imidazole compounds, tertiary amines, and phosphorus compounds and different in type from the epoxy resin curing agent.

4. The adhesive sheet according to claim 1, wherein, The adhesive layer contains an epoxy resin curing accelerator, and the epoxy resin curing accelerator is a phosphorus compound.

5. An adhesive sheet, characterized in that, comprising: an adhesive layer composed of a composition for an adhesive layer containing an epoxy resin and a film-forming aid and not containing an imidazole compound, and a coating layer formed on the adhesive layer and containing a thermoplastic resin, wherein the adhesive layer contains an epoxy resin curing agent, and the epoxy resin curing agent is at least one selected from dicyandiamide, tertiary amines, and acid anhydrides, the coating layer contains an epoxy resin curing accelerator and does not exhibit adhesiveness at room temperature, and the epoxy resin curing accelerator is at least one selected from imidazole compounds, tertiary amines, and phosphorus compounds and different in type from the epoxy resin curing agent, the ratio of the initial heat generation amount Q0 of the adhesive sheet measured by differential scanning calorimetry to the heat generation amount Q1 after being placed at 40 °C for 14 days, i.e., Q1 / Q0×100% is 80% or more, by heating the adhesive sheet to a temperature above the curing start temperature of the adhesive layer, at least a part of the coating layer disappears in the range from the interface between the adhesive layer and the coating layer to the surface of the coating layer.

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