JP2019214729A - Adhesive sheet - Google Patents

Abstract

To provide an adhesive sheet excellent in shape retention property after deformation while maintaining sufficient foaming performance and maintaining deformation state such as folding, and thereby being capable of completely filling gaps having a complex shape.SOLUTION: One formed from a raw material containing a thermoplastic resin having at least glass transition temperature (Tg) and thermal capacitance change (ΔCs) by glass transition, represented by a formula (ΔH/Φ) based on a width of each base lines (ΔH) and a rate of temperature rise (Φ) before and after shifting to a lower direction in a DSC curve of 60 to 420 mJ/(K g) is used as a resin sheet for a substrate of an adhesive sheet having an adhesive layer by a foamable adhesive composition.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an adhesive sheet suitable for use for filling various voids, for example.

  In manufacturing various electric components or electronic components, a gap (or a gap or a gap) existing between each member to prevent water from entering the inside or to insulate between two adjacent or opposed members. May be filled. As a technique for filling the gap, there is known a technique in which an adhesive sheet having a (foamable) adhesive layer provided on both surfaces of a resin sheet as an insulator is inserted into the gap and bonded by heating. Patent Document 1).

JP 2010-261030 A

The gaps between the above-mentioned members include those having a simple shape such as a straight line or a substantially straight line and those having a complicated shape having a bent portion such as an L-shape or a V-shape. The former gap can be filled with the adhesive sheet of Patent Document 1.
However, with respect to the latter gap, the technique according to Patent Document 1 uses a resin sheet having a high springback property (a property of returning to the original shape when folded into a U-shape or a V-shape) as the base material of the adhesive sheet. Therefore, it has been difficult to insert the adhesive sheet along the shape of the gap, that is, to deform the adhesive sheet so as to conform to the shape of the bent portion, and to keep the deformed state. As a result, gaps having complicated shapes cannot be completely filled, and the working efficiency has been reduced.

  An object of the present invention is to provide an adhesive capable of completely filling gaps having a complicated shape while maintaining a sufficient foaming performance while maintaining a deformed state such as bending, and excellent in shape retention after deformation. Is to provide a sheet.

  The present inventor has proposed that, by using a resin sheet formed of a raw material containing a thermoplastic resin having specific properties as a base material of an adhesive sheet having an adhesive layer, a gap having a bent portion with a complicated shape is used. Can be deformed so as to conform to the shape of the bent portion, and furthermore, can maintain the deformed state, in other words, a shape having a bent shape (corner portion) having excellent shape retention after deformation. Found that an adhesive sheet capable of completely filling complicated gaps was obtained, and completed the present invention.

That is, according to the present invention, an adhesive sheet having the following configuration is provided. Further, a method for manufacturing an electric component or an electronic component using the adhesive sheet having the following configuration is provided.
The adhesive sheet of the present invention has an adhesive layer on one side or both sides of a resin sheet. The adhesive layer is formed of a foamable adhesive composition. In this case, the resin sheet has at least a glass transition temperature (Tg) and a formula based on the width (ΔH) between each base line before and after shifting downward in the DSC curve and the rate of temperature rise (Φ). : Characterized by using a material formed from a raw material containing a thermoplastic resin having a heat capacity change (ΔCs) of 60 to 420 mJ / (K · g) due to glass transition represented by (ΔH / Φ).
A method of manufacturing an electric component or an electronic component according to the present invention is characterized in that the adhesive sheet of the present invention is placed in a gap including a bent portion existing between components, heated, and thermally foams the adhesive layer.

  The thermoplastic resin forming the resin sheet preferably has a glass transition temperature of 150 ° C. or higher. Preferably, the thermoplastic resin is a liquid crystal polymer, a para-aromatic polyamide, or a mixture thereof. It is preferable to use a resin sheet having a flame resistance of VTM-0 or more in a test according to UL94 standard.

  The adhesive composition forming the adhesive layer preferably contains a thermal foaming agent (more preferably, heat-expandable microspheres) and a thermosetting resin having a softening temperature of 105 ° C. or lower. The thermosetting resin preferably has a weight average molecular weight of 1650 or less, more preferably 800 or less. The thermosetting resin preferably has a weight average molecular weight of 450 or more. The thermosetting resin is preferably an epoxy resin. The thermal foaming agent is preferably contained in an amount of 1 to 30 parts by mass based on 100 parts by mass of the thermosetting resin contained in the adhesive composition.

  The adhesive sheet of the present invention preferably has a coat layer laminated on the adhesive layer. As the coating layer, for example, it is preferable to use a layer that does not show tack at room temperature but softens and disappears due to heat. The coat layer is formed of a resin. In this case, when the thermal foaming temperature of the thermal foaming agent is T1, the curing start temperature of the adhesive layer is T2, and the glass transition temperature of the coat layer is T3, it is preferable that the relationship of T3 <T1 ≦ T2 is satisfied. . At this time, T1 is more preferably 100 ° C to 200 ° C, T2 is more preferably 110 ° C to 250 ° C, and T3 is more preferably 60 ° C to 140 ° C.

  When laminating the coat layer on the adhesive layer, when the thickness of the adhesive layer before heat foaming is t1 and the thickness of the coat layer is t2, t2 ≦ 0.6 · t1 (the thickness of the coat layer is (60% or less of the thickness of the previous adhesive layer). At this time, t2 is more preferably 0.5 μm or more and 600 μm or less, and at that time, t1 is preferably 20 μm or more and 1000 μm or less.

  The adhesive sheet of the present invention is suitable for use in, for example, void filling, but is not particularly limited to this use.

  The size of the voids when used for filling voids is not particularly limited, and may be used for filling small voids of, for example, 1 mm or less (for example, about several tens μm to several hundred μm). The shape of the gap is not particularly limited, and may be applied not only to a gap having a simple shape (for example, a straight line which can be seen through or a substantially straight line having a gentle curve), but also to a gap having a complicated shape (for example, an L-shape). It can also be used for filling bent portions such as V-shaped or V-shaped portions (including those having one or more rounded small Rs).

  As the “small gap” in the present invention, for example, an image display member fixed to an image display device (a liquid crystal display, an electroluminescence display, a plasma display, etc.) or a portable electronic device (a mobile phone, a portable information terminal, etc.) Examples of the gap include a gap formed between a fixed optical member (camera, lens, or the like) and a housing (window), between coil windings of a motor or the like, or a butt portion of a metal material in a welded structure. Examples of the “gap having a complicated shape” include a gap (commonly referred to as a hem portion) formed between an automobile exterior material and a reinforcing plate, a screw thread, and the like.

  The adhesive sheet of the present invention uses, as the base material for laminating the adhesive layer, a material formed from a raw material containing a thermoplastic resin having specific properties, so that the gap having the bent portion follows the shape of the bent portion. And the deformed state can be maintained. That is, it is excellent in shape retention after deformation, and as a result, a gap having a complicated shape can be completely filled.

FIG. 1 is a schematic diagram showing a manner in which a baseline changes stepwise in a DSC curve as an example. FIG. 2 is a DSC curve obtained for a measurement sample prepared from the resin sheet used in Experimental Example 1. FIG. 3 is a DSC curve obtained for a measurement sample prepared from the resin sheet used in Experimental Example 2. FIG. 4 is a DSC curve obtained for a measurement sample prepared from the resin sheet used in Experimental Example 3. FIG. 5 is a DSC curve obtained for a measurement sample prepared from the resin sheet used in Experimental Example 5. FIG. 6 is a DSC curve obtained for a measurement sample prepared from the resin sheet used in Experimental Example 7. FIG. 7 is a DSC curve obtained for a measurement sample prepared from the resin sheet used in Experimental Example 8. FIG. 8 is a DSC curve obtained for a measurement sample prepared from the resin sheet used in Experimental Example 9. FIG. 9 is a DSC curve obtained for a measurement sample prepared from the resin sheet used in Experimental Example 4. FIG. 10 is a DSC curve obtained for a measurement sample prepared from the resin sheet used in Experimental Example 6. FIG. 11 is a cross-sectional view of a filling test device in the evaluation of fillability into corners. FIG. 12 is a schematic view showing a method of bending a U-shaped test piece in the evaluation of the filling property to the corners. FIG. 13 is a schematic view showing a method of inserting a U-shaped test piece into a filling test apparatus in the evaluation of filling properties into corners. FIG. 14 is a cross-sectional view when the filling test device is cut with the U-shaped test piece inserted into the filling test device. FIG. 15 is a cross-sectional view when the U-shaped test piece is inserted into the filling test device, heated and foamed, and then the filling test device is cut.

BL1: Baseline example before glass transition BL2: Baseline example after glass transition CP: Inflection point SP: Extrapolation start temperature 1: Stainless steel molded product 2: SPCC steel plate 3: Test piece obtained by molding an adhesive sheet into a U-shape 3 ': Test piece after heating and foaming 4: Filling test device 5: Cutting location

[Resin sheet]
The resin sheet used as the base material for the adhesive sheet of the present invention may be any resin sheet formed of a raw material containing a thermoplastic resin.
The thermoplastic resin used for forming the resin sheet has at least a glass transition temperature (Tg) and a heat capacity change (ΔCs = ΔH / φ) due to the glass transition of 60 to 420 mJ from the viewpoint of shape retention after deformation. / (K · g), preferably 60 to 200 mJ / (K · g).
The present inventor believes that a resin sheet formed of a raw material containing a thermoplastic resin having such properties can maintain shape retention after deformation, and as a result, if an adhesive sheet containing the resin sheet as a base material is used, the shape can be improved. Can completely fill complicated gaps.

  The “glass transition temperature” and the “heat capacity change due to the glass transition” referred to in the present invention are both defined by the explanation in the section of Examples.

The heat capacity change (ΔCs) value due to the glass transition described above is the energy difference between the glass region and the rubber region of the raw material constituting the resin sheet. In the glass region, the higher the energy level (ie, ΔCs is 60 mJ / (K · g) or more), and therefore, the more rigid the material is, the more strongly the external stress due to bending is affected, and as a result, , More likely to bend. In addition, since the structure is rigid, the shape can be maintained even after bending, and it is considered that shape retention after deformation is improved.
On the other hand, when the ΔCs value of the raw material for forming the resin sheet is low (less than 60 mJ / (K · g)), the rigidity is almost the same as that of the rubber region even in the glass region. Only a certain period of time, many actions to restore the deformation from its elasticity come to work. Therefore, the folded state cannot be maintained, and the shape retention after deformation is considered to be poor.
Further, in the case where the material for forming the resin sheet does not have Tg, such as polyimide, which cannot define the ΔCs value, it has a rigid structure, but exhibits excessive rigidity over a wide temperature range, and therefore, is required to be deformed by bending. Very large external stress is required. Also, it will be difficult to maintain the shape.

  Examples of the thermoplastic resin used for forming the resin sheet include polyethylene naphthalate (PEN), polycarbonate (PC), liquid crystal polymer (LCP), para-aromatic amide, and triacetyl cellulose. These can be used alone or in combination of two or more. Among these, the heat capacity change ΔCs due to the glass transition belongs to a more appropriate range (60 to 200 mJ / (K · g)). As a result, when formed into a sheet, the shape retention after deformation is excellent, and the adhesion is improved. It is preferable to use LCP, para-aromatic amide, triacetyl cellulose, or a mixture thereof because there is no deformation of the sheet even under high heat conditions during the resin curing process.

  PEN is produced, for example, from 2,6-naphthalenedicarboxylic acid and ethylene glycol and is formed into a film by a known method, but a commercially available product such as Teonex (manufactured by Teijin Dupont Film Co., Ltd.) may be used. .

  PC is manufactured using, for example, bisphenol A and phosgene (or diphenyl carbonate) as raw materials. When using phosgene, it is polymerized by interfacial polycondensation, and when using diphenyl carbonate, it is synthesized by transesterification polymerization, but the raw material and polymerization method are not particularly limited. Further, commercially available products, for example, Pure Ace (manufactured by Teijin Limited), Iupilon sheet (manufactured by Mitsubishi Gas Chemical Company), Sunroid Eco Sheet Polica (manufactured by Sumitomo Bakelite), Carboglass (manufactured by Asahi Glass Co., Ltd.) and the like may be used.

  LCP is typically an aromatic polyester that exhibits liquid crystallinity when melted, and can be usually synthesized from monomers such as aromatic diols, aromatic carboxylic acids, and hydroxycarboxylic acids. For example, Vexter (manufactured by Kuraray Co., Ltd.), VIAC (manufactured by Japan Gore-Tex Co., Ltd.), pericul (manufactured by Chiyoda Integre Co., Ltd.), and liquid crystal polymer cast film (manufactured by Kyodo Giken Kagaku) may be used.

The para-aromatic amide can be obtained by copolymerizing polyparaphenylene terephthalamide (PPTA) or a third component with the same, and as a film of the para-aromatic amide, a commercially available product such as Microtron (Toray) And Aramica (manufactured by Teijin Advanced Film Co., Ltd.).
Triacetylcellulose is obtained by reacting cellulose with acetic anhydride to acetylate cellulose molecules. As a triacetylcellulose film, a commercially available product such as Konica Minolta or Fuji Film is used. Is also good.

  The thermoplastic resin used for forming the resin sheet preferably has a Tg of 150 ° C. or higher, more preferably 200 ° C., from the viewpoint of reducing deformation due to heat during curing when used as an adhesive sheet. ° C or higher. Examples of such a thermoplastic resin include the above-described LCP, para-aromatic amide, and a mixture thereof.

  It is preferable that the thermoplastic resin used for forming the resin sheet has a relatively high molecular weight from the viewpoint of sheet forming properties. By setting the molecular weight to be high, it is easy to maintain the viscosity during sheet molding, and it is possible to form a thin film. The optimum weight average molecular weight of the thermoplastic resin differs depending on the type of the resin. For example, when polycarbonate is used, it is preferably at least 5,000, more preferably at least 10,000. When PEN is used, it is preferably at least 10,000, more preferably at least 20,000. When LCP is used, it is preferably 20,000 or more. When the weight average molecular weight is 100,000 or more, the viscosity becomes extremely high, and molding failure easily occurs. Therefore, the weight average molecular weight is preferably less than 100,000.

  The raw material used for forming the resin sheet may contain various additives in addition to the above-mentioned thermoplastic resin. The type of the additive is not particularly limited, and examples thereof include a heat stabilizer, a lubricant, a dispersant, a colorant, a fluorescent whitening agent, an antistatic agent, a flame retardant, an antibacterial agent, a fungicide, an ultraviolet absorber, and a light stabilizer. And general plastic additives such as antioxidants, plasticizers, defoamers, leveling agents, flow regulators, antifouling agents, pigments, dyes, and fine particles. When an additive is included, the amount of the additive can be, for example, about 0.1 to 10 parts by weight based on 100 parts by weight of the thermoplastic resin.

  The thickness of the resin sheet used for the adhesive sheet of the present invention can be appropriately selected depending on the size of the gap to be applied and the application. When the application is, for example, filling a gap having a width of 1 mm or less and having a bent portion, the thickness of the resin sheet is preferably, for example, 30 to 600 μm, and more preferably 30 to 500 μm.

  The resin sheet used for the adhesive sheet of the present invention uses a resin composition containing the above-described thermoplastic resin and an optional additive as a raw material, and is represented by a uniaxial stretching method, a biaxial stretching method, a non-stretching method, and the like. It can be obtained by forming into a film by a known method such as a melt extrusion method, a solution stretching method, and a calendar method.

  The resin sheet used for the adhesive sheet of the present invention, when the elastic modulus is low, poor conveyance occurs at the time of sheet processing, and wrinkles and the like are likely to be formed. Therefore, the tensile elastic modulus is preferably 2 MPa or more, more preferably 4 MPa or more. (Preferably 25 MPa or less, more preferably 20 MPa or less). The tensile modulus of the resin sheet is a value measured according to JIS K7127 “Plastic film and sheet tensile test method”.

  When the resin sheet used for the adhesive sheet of the present invention is used as an insulating material, it is preferable that the resin sheet is thinner as long as it has the same insulation reliability. Therefore, the insulating sheet having a dielectric breakdown voltage of 250 kV / mm or more is preferable. Are preferred. The upper limit of the breakdown voltage is not particularly limited, but is usually 500 kV / mm or less, preferably 400 kV / mm or less.

  The resin sheet used for the adhesive sheet of the present invention preferably has a flame retardancy of VTM-0 or higher in a test conforming to the UL94 standard from the viewpoint of safety when used as an insulating material when used. Here, “flame retardancy of VTM-0 or higher in a test according to UL94 standard” means a flame resistance test standard for thin plastic materials issued by Under Laboratories Inc. It means that it is determined to be 0, and furthermore, it means that it satisfies the self-extinguishing standard of 5VA, 5VB, V-0, V-1, and V-2 in a test according to the UL94 vertical combustion test.

  When the resin sheet used for the adhesive sheet of the present invention is used as an insulating material, it is assumed that the resin sheet is used in a high-temperature state. In order to ensure sufficient heat resistance, UL746B has a long-term heat resistance index of mechanical properties. It is preferable to use those having heat resistance of B or more.

[Adhesive layer]
In the adhesive sheet of the present invention, the adhesive layer laminated on one side or both sides of the resin sheet is not particularly limited as long as it is formed of a thermofoamable adhesive composition. An example is as follows.

  The adhesive layer according to an example is formed of a thermosetting foamable adhesive composition in which, when heated to a predetermined temperature or more, the volume increases, and a curing reaction proceeds to increase the adhesive force, and is formed at room temperature. Is likely to show tack or cracks. This adhesive composition contains at least a thermal foaming agent and a thermosetting resin having a softening temperature of 105 ° C. or less. By forming the adhesive layer by including a thermosetting resin having a softening temperature of 105 ° C. or lower, the adhesive layer shows tack at room temperature, cracks may occur, or cracks may occur.

In the present invention, "showing tack at room temperature" means that adhesion is confirmed by the following method.
A sheet in which an adhesive layer and a coat layer are laminated on a base material is cut into a size of 5 cm × 5 cm to prepare six adhesive sheets. Six sheets are laminated so that the coat layers of the adhesive sheet face each other, and then sandwiched between glass plates. After applying a load of 100 g on the above-mentioned laminate and leaving it to stand at room temperature (25 ° C.) for 24 hours, when the load is released and the glass plate is spread up and down, the coat layers of the respective adhesive sheets are brought into close contact with each other. It is said that peeling occurs between the base material of the adhesive sheet and the adhesive layer, that is, the coat layer shows tack at room temperature. On the other hand, when the glass plate is spread up and down and peels off between the coat layers that have been in contact with each other, the coat layer does not show tack at room temperature.
“Cracks occur” means that when the adhesive sheet is bent at 180 degrees, a crack occurs in the adhesive layer, and at least a part of the adhesive layer falls off or is in a state where it can fall off.

It is preferable to arrange a coat layer on the adhesive layer of the present embodiment. The coat layer is formed of a resin, does not show tack at room temperature, but softens and disappears due to heat.
In the present invention, "disappearing the coat layer" means, in principle, that the adhesive sheet of the present invention is softened by application of heat exceeding the glass transition temperature of the resin forming the coat layer, whereby the coat layer is softened. Means that the resin is mixed with the thermosetting resin (before curing) forming the adhesive layer to be integrated with the adhesive layer, and the coat layer existing on the adhesive layer is apparently absent. Specifically, the adhesive sheet is cut by a method described below, and its cross section is observed with a microscope, and at least a part of the coat layer disappears in a range from the interface between the adhesive layer and the coat layer to the coat layer surface. It is determined that the coat layer has disappeared when it exists. That is, in the present invention, even when the adhesive sheet after the adhesive layer is cured by heating, at least a part of the adhesive layer after the thermal curing is exposed at a portion in contact with the adherend, the “coating” The layer has disappeared. " That is, in interpreting “the disappearance of the coat layer” in the present invention, the degree of mixing of the resin forming the coat layer with the thermosetting resin (before curing) forming the adhesive layer may not be perfect. After the heat curing, the function as an adhesive layer may be exhibited on the sheet surface. It is sufficient that at least a part of the adhesive layer after the heat curing is exposed on the surface of the sheet at a portion in contact with the adherend of the adhesive sheet after the adhesive layer is cured by the heating. If all of the adhesive layer after heat curing is exposed on the sheet surface, it means that the coat layer existing on the adhesive layer is completely absent.

  In the present embodiment, when the thermal foaming temperature of the thermal foaming agent is T1, the curing start temperature of the adhesive layer is T2, and the glass transition temperature of the coat layer is T3, the relationship of T3 <T1 ≦ T2 may be satisfied. preferable. Details will be described later.

The resin contained in the adhesive composition for forming the adhesive layer of the present embodiment (hereinafter, may be referred to as an adhesive resin) is not particularly limited, and a thermoplastic resin or a thermosetting resin may be used. Can be.
Examples of the thermoplastic resin contained in the adhesive composition forming the adhesive layer of the present embodiment include, for example, natural rubber, butyl rubber, isoprene rubber, chloroprene rubber, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer , Ethylene-acrylate copolymer, polybutadiene resin, polypropylene resin, styrene-butadiene-styrene copolymer, styrene-ethylene-butylene-styrene copolymer, polyacetal resin, polyvinyl butyral resin, polyvinyl acetal resin, acrylonitrile-butadiene Copolymer, acrylonitrile-butadiene-acrylic acid copolymer, acrylonitrile-butadiene-styrene copolymer, polycarbonate resin, thermoplastic polyimide resin, thermoplastic siloxane-modified polyimide resin, 6-nylo And 6,6-polyamide resins such as nylon, a phenoxy resin, an acrylic resin, a polyester resin, or a fluorine resin. These thermoplastic resins can be used alone or in combination of two or more.
Examples of the thermosetting resin to be contained in the adhesive composition forming the adhesive layer of the present embodiment include, for example, epoxy resin, urethane resin, silicone resin, oxetane resin, phenol resin, (meth) acrylate resin, diallyl phthalate Resins, maleimide resins, polyimide resins, polyesterimide resins, polyamideimide resins, bismaleimide-triazine resins, polyetherimide resins, and the like. Further, a thermoplastic resin having a reactive group such as an epoxy group, a hydroxyl group, an amide group, a carboxyl group, a silanol group, and a mercapto group can be used as a thermosetting resin by adding a curing agent. Examples of such a thermosetting resin include a phenoxy resin, a polyester resin, and a polyamic acid resin.

  Among such thermosetting resins, in particular, epoxy resin, (meth) acrylate resin, phenoxy resin, polyester resin, polyimide resin, polyamic acid resin, polyetherimide resin, polyesterimide resin, polyamideimide resin, silicone resin, A maleimide resin, a bismaleimide-triazine resin, and the like are preferable, and any of these can be used alone or in combination. Of these, epoxy resins are preferred from the viewpoint of excellent curability and storage properties, and excellent heat resistance, moisture resistance, and chemical resistance of the cured product.

  Examples of the epoxy resin include bisphenol A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin, hydantoin epoxy resin, biphenyl epoxy resin, alicyclic epoxy resin, triphenylmethane epoxy resin, and phenol novolak. 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 various modifications such as CTBN modification and halogenation Among them, bisphenol A type epoxy resin and novolak type epoxy resin are preferable. These can be used alone or in combination of two or more.

  The epoxy resin generally has a viscosity at 190 ° C. of preferably 0.05 Pa · s or more, more preferably 0.1 Pa · s or more. In addition, it is usually preferably 3.0 Pa · s or less, more preferably 1.8 Pa · s or less. If the viscosity is too low, the foaming state of the thermal foaming agent cannot be maintained, and there is a possibility that continuous foaming or foam breakage may occur. If the viscosity is too high, the foaming external pressure becomes higher than the foaming internal pressure, so that the thermal foaming agent may not foam. The viscosity here is a value measured using a dynamic viscoelasticity measuring device (Bohlin C-VOR, manufactured by Malvern Instruments).

  The epoxy resin has an epoxy equivalent weight (WPE) of usually 150 or more, preferably 180 or more, and usually 1000 or less, preferably 700 or less. “Epoxy equivalent” is defined as the molecular weight of an epoxy resin per epoxy group. Here, the “epoxy group” includes oxacyclopropane (oxirane ring) which is a three-membered ring ether, and in addition to an epoxy group in a narrow sense, a glycidyl group (including a glycidyl ether group and a glycidyl ester group). Is included. WPE is determined by a method (perchloric acid-tetraethylammonium bromide method) described in JIS K7236, Determination of epoxy equivalent of epoxy resin (2001), or the like.

  The epoxy resin is semi-solid or solid at room temperature. In the case of a solid, the softening temperature is preferably 105 ° C. or lower, more preferably 95 ° C. or lower. Further, it is usually preferably 40 ° C. or higher, more preferably 45 ° C. or higher. If it is liquid at normal temperature, the viscosity during curing and foaming will decrease remarkably, and the foamed state of the epoxy resin will not be able to be maintained. Further, there is a possibility that the shape of the adhesive layer cannot be maintained.

  By forming the adhesive layer by including a thermosetting resin (preferably an epoxy resin) having a softening temperature of 105 ° C. or less, the resin is softened by heating, and thereby the thermal foaming agent is successfully foamed in the adhesive layer. Can be. If the softening temperature exceeds 105 ° C. even if it is lower than 105 ° C., cracks may occur in the adhesive layer. However, in the present invention, since the adhesive layer is covered with the coat layer, even if the adhesive layer is cracked, there is no possibility that the adhesive layer will fall off, and there is no problem in use.

By forming the adhesive layer by containing a thermosetting resin (preferably an epoxy resin) having a softening temperature of 60 ° C. or less, the above-mentioned action (the ability to effectively foam the thermal foaming agent in the adhesive layer by heating) In addition to the above, the occurrence of cracks in the adhesive layer can be suppressed, which can contribute to preventing the adhesive layer from falling off.
The softening temperature here is a value measured by a method defined by JIS K7234 (ring and ball method).

In the present embodiment, it is desirable to use a thermosetting resin having a weight average molecular weight of preferably 1650 or less, more preferably 800 or less. By forming the adhesive layer by containing a thermosetting resin having a weight average molecular weight of 1650 or less, the resin can be adjusted to be softer by heating and the coat layer can be eliminated, so that the adhesive performance is more favorably maintained. be able to. It is more preferable that the adhesive layer is formed by containing a thermosetting resin having a weight average molecular weight of 800 or less. This is because, in addition to the above operation (maintaining the adhesion performance), the occurrence of cracks in the adhesive layer can be suppressed.
In the present embodiment, the thermosetting resin contained in the adhesive composition preferably has a weight average molecular weight of 450 or more in order to facilitate the formation of a sheet. If the molecular weight is less than 450, the resin becomes almost liquid at room temperature, and the shape of the adhesive layer may not be maintained.

The thermal foaming agent to be contained in the adhesive composition forming the adhesive layer is not particularly limited, and for example, a known thermal foaming agent (pyrolytic type, expanded graphite, microencapsulated, etc.) may be appropriately used. It can be selected and used, and among them, microencapsulated ones (hereinafter, referred to as “thermally expandable microspheres”) can be preferably used.
Preferable examples of the heat-expandable microspheres include microspheres having a structure in which a foaming agent is sealed in an elastic outer shell and exhibiting a thermal expansion property (a property of expanding entirely by heating) as a whole. Can be.
Examples of the outer shell having elasticity include a heat-fusible substance and a substance that is destroyed by thermal expansion, such as vinylidene chloride-acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, and polysulfone. The one formed by the above can be cited as a preferred example.
Examples of the foaming agent include mainly substances which easily gasify and expand when heated, for example, hydrocarbons such as isobutane, propane and pentane. Commercially available heat-expandable microspheres include, for example, “Matsumoto Microsphere” series (trade name, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.), Advancel EM series (trade name, manufactured by Sekisui Chemical Co., Ltd.), Expancel (trade name, manufactured by Nippon Ferrite Co., Ltd.) ) And the like.

  The size of the heat-expandable microspheres may be appropriately selected depending on the use of the adhesive sheet, and specifically, may be about 10 to 20 μm in terms of mass average particle diameter. The heat-expandable microspheres may be used after adjusting the particle size distribution. The particle size distribution can be adjusted by removing particles having a relatively large particle size contained in the heat-expandable microspheres by using a centrifugal-type air classifier, a dry classifier, a sieving machine, or the like. Specifically, the standard deviation of the particle size distribution of the heat-expandable microspheres is preferably set to 5.0 μm or less.

  The expansion ratio of the heat-expandable microspheres is preferably 5 times or more, and more preferably 7 times or more. On the other hand, it is preferably at most 15 times, more preferably at most 12 times. In addition, it is preferable that the outer shell of the heat-expandable microspheres has a suitable strength so that it does not burst even when the heat-expandable microspheres expand to the predetermined expansion ratio.

  The amount of the heat-expandable microspheres is preferably at least 1 part by mass, more preferably at least 3 parts by mass, preferably at most 30 parts by mass, more preferably at most 20 parts by mass, based on 100 parts by mass of the adhesive resin. Hereinafter, it is more preferably 15 parts by mass or less.

  The thermal foaming agent preferably has a thermal foaming temperature (T1) of preferably 100 ° C. or higher, more preferably 150 ° C. or higher, preferably 200 ° C. or lower, more preferably 190 ° C. or lower. T1 corresponds to the thermal expansion temperature when using thermally expandable microspheres as the thermal foaming agent, and corresponds to the thermal decomposition temperature when using a thermal decomposition type foaming agent. The “thermal expansion temperature” is synonymous with the foaming start temperature, and in this embodiment, refers to the thermal expansion start temperature in TMA measurement, and does not mean the maximum thermal expansion temperature at which the volume expands to the maximum.

Examples of other thermal foaming agents include a pyrolytic foaming agent and expanded graphite. Pyrolytic blowing agents are classified into inorganic and organic.
Examples of the inorganic foaming agent include ammonium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, azides and the like. Examples of the organic blowing agent include water, chloroalkanes (eg, trichloromonofluoromethane, dichloromonofluoromethane, etc.), azo compounds (eg, azobisisobutyronitrile, azodicarbonamide (ADCA), Barium azodicarboxylate, etc.), hydrazine compounds (eg, paratoluenesulfonyl hydrazide, diphenylsulfone-3,3'-disulfonylhydrazide, 4,4'-oxybis (benzenesulfonylhydrazide), allylbis (sulfonylhydrazide), etc.) , Semicarbazide compounds (eg, ρ-toluylenesulfonyl semicarbazide, 4,4′-oxybis (benzenesulfonyl semicarbazide), etc.), and triazole compounds (eg, 5-morpholyl-1,2,3,4-thiatriazole, etc.) , - nitroso compounds (e.g., N, N'-dinitrosopentamethylenetetramine, N, N'-dimethyl -N, N'-dinitrosoterephthalamide, etc.), and the like.
These thermal foaming agents can be used alone or in combination of two or more.

  The amount of such a pyrolytic foaming agent is preferably at least 5 parts by mass, more preferably at least 10 parts by mass, preferably at most 30 parts by mass, more preferably at most 30 parts by mass, based on 100 parts by mass of the adhesive resin. 25 parts by mass or less.

When a thermosetting resin is used for the adhesive composition forming the adhesive layer, an optional component such as a curing agent may be contained in addition to the thermosetting resin and the heat-expandable microspheres described above. Examples of the curing agent include amide-based curing agents such as dicyandiamide (DICY) and aliphatic polyamide; amine-based curing agents such as diaminodiphenylmethane, metaphenylenediamine, ammonia, triethylamine, and diethylamine; bisphenol A, bisphenol F, and phenol novolak Phenolic curing agents such as resin, cresol novolak resin and p-xylene novolak resin; and acid anhydride curing agents such as methylnadic anhydride.
These curing agents can be used alone or in combination of two or more.

  The compounding amount of the curing agent is calculated from the equivalent ratio with the thermosetting resin to be used, and an appropriate range of the equivalent ratio is 0.8 to 3.0. For example, when the curing agent is dicyandiamide, the lower limit is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and the upper limit is preferably 30 parts by mass or less, relative to 100 parts by mass of the thermosetting resin. Parts or less is more preferable. For example, in the case of anhydrous methylnagic, the lower limit is preferably 60 parts by mass or more, more preferably 80 parts by mass or more, and the upper limit is preferably 240 parts by mass or less, relative to 100 parts by mass of the thermosetting resin. Parts or less is more preferable. If the amount of the curing agent is less than the above lower limit, curing may not be sufficiently performed, and characteristics such as heat resistance and chemical resistance of the thermosetting resin may not be sufficiently exhibited. On the other hand, when the compounding amount exceeds the upper limit, an excessive exothermic reaction occurs during curing, and the viscosity of the resin composition during curing decreases more than necessary, and it becomes difficult to maintain a sufficient foaming state finally. there is a possibility.

  A curing accelerator can be used together with the curing agent. Examples of the curing accelerator include imidazoles such as 2-methylimidazole, 2-methyl-4-ethylimidazole and 2-phenylimidazole; 1,8-diazabicyclo [5.4.0] undecene-7, triethylenediamine, Tertiary amines such as benzyldimethylamine; organic phosphines such as tributyl phosphine and triphenylphosphine; and the like. These can be used alone or in combination of two or more. The compounding amount of the curing accelerator is, for example, 5 parts by mass or less based on 100 parts by mass of the thermosetting resin.

  Other additives that can be blended as an optional component in the adhesive composition include, for example, natural rubber, isoprene rubber, styrene-butadiene rubber, chloroprene rubber, butadiene rubber, nitrile rubber, butyl rubber, fluorine rubber, acrylic rubber as an elastomer component And the like, solid or liquid rubbers, polyurethane, urethane prepolymer and the like. The compounding amount is 20 parts by mass or less, preferably 10 parts by mass or less, more preferably 5 parts by mass or less based on 100 parts by mass of the adhesive resin. Further, a foaming aid, various fillers, a foam stabilizer, an antioxidant, an ultraviolet absorber, and a coloring agent may be blended.

The adhesive composition of the present embodiment is obtained by mixing the above-described thermal foaming agent, adhesive resin, and, if necessary, a curing agent, a curing accelerator, a foaming aid, and various additives in any order. Can be obtained by The mixing of the raw materials can be performed using a mixing roll, a planetary mixer, a butterfly mixer, a kneader, a mixer such as a single-screw or twin-screw extruder, or a kneader. The mixing temperature varies depending on the composition, but it is necessary to perform the mixing at a temperature equal to or lower than the thermal foaming temperature (T1) of the thermal foaming agent.
In the adhesive composition of the present embodiment, it is desirable to mix each component so that the curing start temperature (T2) in the state of the adhesive layer formed in a sheet shape is preferably 110 ° C. or more and 250 ° C. or less.

The adhesive layer is obtained by applying the above-mentioned adhesive composition to one or both sides of a resin sheet used as a base material, and drying it as necessary. The adhesive layer can also be obtained by applying the above-mentioned adhesive composition on a coat layer described later formed on a release film prepared separately and drying it as necessary.
The thickness (t1) of the adhesive layer before foaming may be appropriately selected according to the use of the adhesive sheet, but the lower limit is preferably 20 μm or more, more preferably 30 μm or more, and the upper limit is 1000 μm or less, further 400 μm or less, Further, the thickness is preferably 200 μm or less. By setting the thickness of the adhesive layer to 20 μm or more, air bubbles generated by the foaming reaction are easily held in the adhesive layer. By setting the thickness (t1) of the adhesive layer to 1000 μm or less, it becomes possible to fill a narrow gap of 1 mm or less, for example.

[Coat layer]
In a preferred embodiment of the present embodiment, as the resin forming the coat layer disposed on the adhesive layer, for example, phenoxy resin, polyester resin, polyurethane resin, polyimide resin, siloxane-modified polyimide resin, polybutadiene, polypropylene, styrene-butadiene- Styrene copolymer, styrene-ethylene-butylene-styrene copolymer, polyacetal resin, polyvinyl butyral resin, polyvinyl acetal resin, butyl rubber, chloroprene rubber, polyamide resin, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-acrylic acid copolymer A thermoplastic resin such as coalesced, acrylonitrile-butadiene-styrene copolymer, polyvinyl acetate, and nylon can be used. These can be used alone or in combination of two or more. Among them, it is preferable to use a phenoxy resin, a polyester resin, or the like.
Examples of the polyester resin include Byron 200 (manufactured by Toyobo Co., Ltd.), Polyester TP220 (manufactured by Nippon Gohsei), Elitel KA series (manufactured by Unitika), and the like.

  The phenoxy resin refers to a high molecular weight thermoplastic polyether resin (* bisphenol type epoxy resin) based on diphenols such as bisphenol A and bisphenol F and epihalohydrin such as epichlorohydrin. The phenoxy resin preferably has a weight average molecular weight of 20,000 to 100,000.

  The phenoxy resin is not particularly limited, and includes a bisphenol A skeleton, a bisphenol F skeleton, a bisphenol S skeleton, a bisphenol acetophenone skeleton, a novolak skeleton, a biphenyl skeleton, a fluorene skeleton, a dicyclopentadiene skeleton, a norbornene skeleton, a naphthalene skeleton, and an anthracene. A skeleton having one or more skeletons selected from a skeleton, an adamantane skeleton, a terpene skeleton, and a trimethylcyclohexane skeleton is exemplified.

Commercially available phenoxy resins include, for example, trade names PKHB, PKHC, PKHH, PKHJ (all manufactured by InChem), jER 1256, jER 4250, jER 4275 (all manufactured by Mitsubishi Chemical Corporation), YP-50, YP -50S, YP-70, ZX-1356-2, FX-316, all manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.
Further, a phenoxy resin dissolved using a solvent is also commercially available, and is also used similarly. For example, jER 1256B40, jER 1255HX30, jER YX6954BH30, YX8100BH30, jER YL7174BH40 (all manufactured by Mitsubishi Chemical Corporation), YP-40ASM40, YP-50EK35, YPB-40PXM40, ERF-001M30, YPS-0093A Nippon Steel & Sumikin Chemical Co., Ltd.).

  These phenoxy resins can be used alone or in combination.

  In this embodiment, a curing agent such as an isocyanate or an organic peroxide may be further added to the thermoplastic resin, if necessary. Fine adjustment of the affinity with the adhesive layer is facilitated by appropriately selecting and blending the type and molecular weight of the curing agent. When blended, the blending amount of the curing agent (such as isocyanate) can be about 3 to 30 parts by mass with respect to 100 parts by mass of a polyester resin or a phenoxy resin.

  The coating layer is prepared by dissolving or dispersing the above-described resin (including a curing agent if included) in a solvent to form a coating liquid for forming a coating layer, and applying this to an adhesive layer laminated on a resin sheet. It is obtained by applying and drying. The coating layer can also be obtained by applying the coating liquid for forming a coating layer described above to a release film prepared separately and drying the coating liquid.

The thickness (t2) of the coat layer is preferably 60% or less of the thickness (t1) of the adhesive layer before heating (or before heating and foaming). By setting t2 to 60% or less of t1, the coat layer is softened by heat (for example, heating at about 60 ° C. or more and about 140 ° C. or less) under the condition that the composition is formed with an appropriate composition, and the coating layer is satisfactorily reduced. Can be eliminated.
The mechanism by which the coat layer disappears is as follows. The coat layer is softened by applying heat exceeding the glass transition temperature of the resin forming the coat layer. As a result, the resin of the coat layer is mixed with the adhesive resin (thermosetting resin or thermoplastic resin before curing described above) forming the adhesive layer, and is integrated with the adhesive layer (taken into the adhesive layer). As a result, the coat layer existing on the adhesive layer apparently does not exist. Form an adhesive layer

If the coat layer is too thick, it may not be sufficiently taken into the adhesive layer, and as a result, the disappearance of the coat layer may not proceed well. Further, when a thermal foaming agent is contained, the thermal foaming agent in the adhesive layer may not be sufficiently foamed, and foamability may be impaired.
In the present invention, as described above, at least a part of the heat-cured adhesive layer is exposed (contacted) to a portion of the adhesive sheet after the adhesive layer has been cured by heating, in contact with the adherend. In this case, it is determined that “the coat layer has disappeared”.
In the present embodiment, t2 is preferably, for example, 0.5 μm or more and 600 μm or less.

  It is desirable that the resin forming the coat layer is determined so that the glass transition temperature (T3) of the coat layer is preferably 60 ° C. or more and 140 ° C. or less. If the glass transition temperature (T3) of the coat layer is too low, the tackiness of the coat layer surface will increase, and the effect of the present invention may not be easily obtained. On the other hand, if T3 is too high, the coat layer does not sufficiently soften in the heat curing temperature range of the adhesive layer, so that the adhesive force of the adhesive layer may not be sufficiently exerted.

  In the present embodiment, it is preferable to determine the resin forming the coat layer in relation to the composition of the adhesive layer. By considering the affinity between the coat layer and the adhesive layer, when the coat layer is softened, it can be more easily taken into (penetrated) into the adhesive layer. Thereby, the thickness of the coat layer can be easily designed. For example, as an epoxy resin having a weight-average molecular weight of less than 800 to be contained in the adhesive composition forming the adhesive layer, NC2000L (Novolak type epoxy resin, Nippon Kayaku, epoxy equivalent 229 to 244, softening temperature 47 to 57) ° C), it is desirable to use bisphenol A type trade name PKHH as the resin for forming the coat layer.

  As described above, the adhesive sheet according to one embodiment of the present invention may be manufactured by sequentially forming an adhesive layer and a coat layer on one side or both sides of a resin sheet. Further, as described above, after a coat layer and an adhesive layer are sequentially formed on a release film prepared separately, a resin sheet may be laminated (laminated) thereon. Furthermore, it can also be produced by laminating (laminating) a release film having a coat layer formed thereon and a resin sheet having an adhesive layer formed thereon.

  The adhesive sheet of the present embodiment can be widely used for filling various gaps existing between members, such as manufacturing various electric or electronic components, joining a joint between a skin material and a reinforcing material of a vehicle body, and the like. In particular, it is useful for filling gaps having a narrow gap of 1 mm or less and / or a complicated shape having a bent portion. Specifically, the above-described various gaps can be completely filled by putting the adhesive sheet of the present embodiment into various gaps existing between the members, heating the adhesive sheet, and thermally foaming the adhesive layer.

  Hereinafter, the present invention will be specifically described based on experimental examples (including examples and comparative examples), but the present invention is not limited to these examples.

1. Measurement or Evaluation of Resin Sheet The following items were measured or evaluated for the resin sheet used in each example described below by the following method. The results are shown in Table 1 or Table 2.

(1) Glass transition temperature (Tg)
The glass transition temperature was determined as follows.
First, with respect to the resin sheets of Experimental Examples 1 to 3 and 5 to 9, those not subjected to the pretreatment were used as measurement samples. In addition, as for the resin sheet of Experimental Example 4, an endothermic reaction was observed at around 80 ° C., and it was difficult to detect the target glass transition temperature. .
Next, the temperature (° C.) and the heat flow (heat capacity: mJ / (s ·) of the above measurement sample were measured by differential scanning calorimetry (DSC) using a differential scanning calorimeter (DSC3200, manufactured by Mac Science) as a measuring device. g)) were respectively obtained on the XY plane on the horizontal axis (X axis) and the vertical axis (Y axis) (FIGS. 2 to 10).

  Generally, when the measurement sample undergoes glass transition, the specific heat capacity of the measurement sample changes before and after the glass transition, whereby the baseline (base line) changes stepwise (especially downward) near the glass transition temperature of the DSC curve. (Non-patent document published by the Engineering Information Center Publishing Department on December 29, 1985: "Basic / Application of Various Thermal Analysis Techniques and Measurement Data Collection", page 43). Therefore, next, focusing on a portion where the baseline is shifted downward from the obtained DSC curve, the original baseline before shifting downward (for example, the baseline indicated by “BL1” in FIG. 1) and the inflection Intersection (extrapolation start temperature, for example, indicated by “SP” in FIG. 1) of a tangent at a point (a point at which the upwardly convex curve changes to a downwardly convex curve; for example, the point indicated by “CP” in FIG. 1) ) Was taken as the glass transition temperature (unit: ° C.) of the measurement sample. The results are shown in Table 1.

(2) Heat capacity change due to glass transition (ΔCs)
The above 1. Using the DSC curve obtained for each measurement sample prepared in (1), the width between baselines (for example, “BL1” and “BL2” in FIG. 1) before and after shifting downward in the curve (ie, measurement) The difference between the baseline before and after the sample undergoes glass transition) is defined as the heat capacity change ΔH (unit: mJ / (s · g)), and this ΔH is defined as the rate of temperature rise Φ (unit: K / s) of the measurement sample. ) Was defined as the heat capacity change ΔCs (unit: mJ / (K · g)) due to the glass transition of the measurement sample (see the same page of the above non-patent document). The heat capacity change ΔH of each measurement sample was determined from the obtained DSC curves as shown in FIGS. The heating rate Φ was 10 K / s. The results are shown in Table 1.
In Experimental Example 4, an exothermic reaction peak was observed immediately after the glass transition temperature, but this is considered to be a liquid crystal phase transition. Therefore, the point before the start of the exothermic peak was set as a baseline value after the glass transition, and the exothermic reaction peak was determined. The heat capacity change (ΔCs) was calculated.

(3) Flame Retardancy The resin sheets of Experimental Examples 1 to 9 were subjected to a thin-material vertical burn test method and a vertical burn test method according to UL94 flame retardancy test standard for plastic materials issued by Under Laboratories, and a VTM rank was obtained. And V rank were determined and evaluated according to the following criteria. The sample size of the resin sheet used for the evaluation was 50 mm × 200 mm. The results are shown in Table 2.
◎: Those satisfying VTM-0 in the UL94 thin material vertical burning test and satisfying V-0 in the UL94 vertical burning test.
：: VTM-0 in the UL94 thin material vertical combustion test.
×: VTM-0 is not satisfied in the UL94 thin material vertical combustion test.

(4) Tensile modulus
The resin sheets of Experimental Examples 1 to 9 were measured in accordance with JIS K7113 (unit: MPa). Specifically, a resin sheet was punched out using a type 2 test piece, and a test was performed at a speed of 50 mm / min using a universal testing machine (manufactured by Instron), and calculated by the following equation. The results are shown in Table 2.

[Equation] E = (σ ₂ −σ ₁ ) / (ε ₂ −ε ₁ )
σ ₁ : tensile stress (MPa) measured at displacement ε ₁ = 0.0005
σ ₂ : tensile stress (MPa) measured at displacement ε ₂ = 0.0025

(5) Dielectric breakdown voltage The resin sheets of Experimental Examples 1 to 9 were measured in accordance with the short-time method of JIS C2110. Specifically, the test piece used was a resin sheet cut into a size of 50 mm × 50 mm. The test electrode used was a spherical brass electrode having a diameter of 12.5 mm, the pressure between the electrodes was set to 500 g, and the measurement was performed in silicone oil. Note that the voltage boosting speed was 1 kV / sec. The results are shown in Table 2.

(6) Shape Retention after Deformation The resin sheets of Experimental Examples 1 to 9 were cut into a size of 40 mm × 100 mm to prepare test pieces, which were mounted on a 10 mm thick rubber plate. Next, a metal plate having a thickness of 1 mm, a width of 50 mm, and a height of 50 mm was vertically pressed (pressed) under conditions of 12.5 kg / cm ² so as to face the test piece, and held for 30 seconds. Next, the bending angle of the test piece (the angle of the bent piece with respect to the rubber sheet surface) after 1 second from the pressure release as an evaluation of whether it can be deformed and 10 seconds after the pressure release as an evaluation of the shape retention after deformation. Was measured and evaluated according to the following criteria. The results are shown in Table 1.

：: A bend angle of 90 ° or more (deformable, good shape retention after deformation) both after 1 second of pressure release and 10 seconds after pressure release.
×: The bend angle after 1 second of pressure release is 45 degrees or more, and the bend angle after 10 seconds of pressure release is less than 45 degrees (deformation was possible, but shape retention after deformation was poor).
XX: Bending angle of less than 45 degrees (cannot be deformed) after 1 second of pressure release and 10 seconds after pressure release.

2. Preparation of Coating Solution for Forming Adhesive Layer The following components were uniformly mixed at the following solid content ratio (in terms of mass) and prepared. The total solid content in the coating liquid was 85%.

<Components of adhesive layer forming coating liquid>
-Thermosetting resin (novolak type epoxy resin): 100 parts by mass (NC-2000L, epoxy equivalent: 229 to 224 g / eq, softening temperature: 47 to 57 ° C, weight average molecular weight: 700 to 800, viscosity (190 ° C) : 0.11 dPa · s, manufactured by Nippon Kayaku Co., Ltd.)
Curing agent (solid content: 100%): 8.9 parts by mass (dicyandiamide (DICY), manufactured by Japan Epoxy Resin Co., Ltd.)
-Cure accelerator (solid content 100%): 0.5 parts by mass (Cureazole 2MZ-A, 2,4-diamino-6- [2'-methylimidazolyl- (1 ')]-ethyl-s-triazine, Shikoku (Manufactured by Kaseisha)
-Thermal foaming agent: 10 parts by mass (Matsumoto Microsphere F100M, thermally expandable microspheres, mass average particle size: 17 to 23 µm, thermal expansion temperature (synonymous with thermal foaming temperature T1): 120 ° C, maximum thermal expansion temperature: 160 ° C, expansion ratio: 10 times, manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.)

3. Preparation of Coating Layer Forming Coating Solution The following components were uniformly mixed and prepared at the following solid content ratio (mass conversion). The total solid content in the coating solution was 40%.
<Components of coating liquid for forming coat layer>
-Thermoplastic resin (bisphenol A type phenoxy resin): 100 parts by mass (PKHH, glass transition temperature (T3): 92 ° C, manufactured by InChem)
Curing agent (solid content: 75%): 10 parts by mass (Takenate 600, manufactured by Mitsui Takeda Chemical Co., NCO content: 43.3%)

4. Creating an adhesive sheet
[Preparation of adhesive layer and coat layer]
Using the coating liquid for forming an adhesive layer and the coating liquid for forming a coating layer having the above-described configuration, a coating film for forming a coating layer was formed on a release-treated surface of a release film (Biner No. 23, manufactured by Fujimori Kogyo Co., Ltd .; The working liquid was applied by a baker type applicator. Thereafter, by drying at 140 ° C. for 1 minute, a coat layer was formed with a thickness (t2) of 5 μm (laminated product a ′). Next, a coating liquid for forming an adhesive layer was applied to the surface of the coat layer in the same manner as described above. Thereafter, by drying at 120 ° C. for 1 to 2 minutes, an adhesive layer was formed with a thickness (t1) of 50 μm (laminated product a).
Further, an adhesive layer was formed on the release film in the same manner as described above except that the coat layer was not formed on the release film (laminated product b).

[Evaluation of adhesive layer and coat layer]
(1) Thermal foaming temperature (T1)
A dynamic viscoelasticity measuring device (DMA Q800, manufactured by TA Instruments) was used as a measuring device, and 0.5 mg of heat-expandable microspheres were transferred to aluminum having a diameter of 6.0 mm (inner diameter 5.65 mm) and a depth of 4.8 mm. The sample was placed in a cup, and an aluminum lid (5.6 mm, thickness: 0.1 mm) was placed on top of the thermally expandable microsphere layer to prepare a sample. The sample height was measured in a state where a force of 0.01 N was applied to the sample from above by a pressurizer. Heating is performed at a rate of 10 ° C./min from 20 ° C. to 300 ° C. in a state where a pressure of 0.01 N is applied, and the displacement of the pressurizer in the vertical direction is measured. The temperature at which displacement in the forward direction was started was defined as the thermal foaming temperature (T1). As a result, T1 was 120 ° C.

(2) Curing start temperature of adhesive layer (T2)
Using a differential scanning calorimeter (DSC3200, manufactured by Mac Science) as a measuring device, the DSC in a steady range when the temperature of the formed sheet-like adhesive layer resin was raised from room temperature to 300 ° C. at 10 ° C./min. The point where the baseline and the DSC rise line during the curing reaction intersect was defined as the curing start temperature (T2). As a result, T2 was 151 ° C.

(3) Glass transition temperature of coat layer (T3)
Using a differential scanning calorimeter (DSC3200, manufactured by Mac Science) as a measuring device, the DSC baseline change point when the temperature of the formed sheet-like coat layer resin is increased from room temperature to 300 ° C. at 10 ° C./min. Was taken as the glass transition temperature (T3). As a result, T3 was 92 ° C.

(4) Adhesive layer thickness (after heating)
The laminate a was cut into a size of 5 cm × 5 cm, placed on a 1 mm-thick SPCC steel plate so that the adhesive layer was in contact with the laminate, and the release film was peeled from the laminate a. Then, after being left in an oven heated to 190 ° C. for 30 minutes, it was taken out. Thereafter, the total thickness of the SPCC steel sheet and the adhesive layer (and the coat layer) was measured, and the thickness of the adhesive layer after heating was calculated by subtracting the thickness of the release film from the measured values. As a result, the thickness of the adhesive layer after heating was 325 μm. Therefore, the expansion ratio of the adhesive layer was 5.9 times.

(5) Cracking of the adhesive layer Regarding the laminated product a (with a coated layer) and the laminated product b (without a coated layer), before heating and foaming, any part on the adhesive layer side is bent to 180 degrees, and then the state of the adhesive layer Was visually confirmed.
As a result, cracks in the adhesive layer itself were not observed in both the laminates a and b, and the laminates were good.

(6) Disappearance of the coat layer The laminate a was placed on a 1 mm-thick SPCC steel sheet so that the adhesive layer was in contact with the laminate, and the release film was peeled off. Further, an SPCC steel sheet having a thickness of 1 mm was overlapped and fixed so as to form a gap twice as large as the sum of the thickness of the adhesive layer and the thickness of the coat layer. Then, after being left in an oven heated to 190 ° C. for 30 minutes, it was taken out. This was cut vertically so that the cross section of the SPCC steel sheet and the cross section of the adhesive layer (and the coat layer) could be confirmed, and the cross section was observed with a microscope to confirm the presence or absence of the coat layer. As a result, the coat layer disappeared and was adhered to the SPCC steel sheet.

  As described above, the adhesive layer and the coat layer used in the adhesive sheet of the present experimental example are appropriate for evaluation as an adhesive sheet.

[Create adhesive sheet]
[Experimental example 1]
While applying heat of 80 ° C. to both surfaces of a resin sheet (thickness: 50 μm, polyethylene naphthalate film: Teonex Q51, manufactured by Teijin Dupont Film Co., Ltd.) as a base material, the adhesive layer surface of the laminate a faces each other. After lamination, the release film was peeled off to obtain the adhesive sheet of Experimental Example 1.

[Experiment 2]
An adhesive sheet of Experimental Example 2 was obtained in the same manner as in Experimental Example 1, except that a resin sheet (thickness: 50 μm, polycarbonate film: Pure Ace, manufactured by Teijin Limited) was used as a substrate.

[Experimental example 3]
An adhesive sheet of Experimental Example 3 was obtained in the same manner as in Experimental Example 1, except that a resin sheet (thickness: 50 μm, para-aromatic amide film: Microtron (GQ type), manufactured by Toray Industries, Inc.) was used as the base material.

[Experimental Example 4]
An adhesive sheet of Experimental Example 4 was obtained in the same manner as in Experimental Example 1, except that a resin sheet (thickness: 50 μm, triacetyl cellulose film: 8VAW, manufactured by Konica Minolta) was used as a substrate.

[Experimental example 5]
An adhesive sheet of Experimental Example 5 was obtained in the same manner as in Experimental Example 1 except that a resin sheet (thickness: 50 μm, liquid crystal polymer (LCP) film: Vexter, manufactured by Kuraray Co., Ltd.) was used as a substrate.

[Experimental example 6]
An adhesive sheet of Experimental Example 6 was obtained in the same manner as in Experimental Example 1 except that a resin sheet (thickness: 50 μm, optical polyethylene terephthalate film: Lumirror U403 manufactured by Toray Industries, Inc.) was used as the base material.

[Experimental example 7]
An adhesive sheet of Experimental Example 7 was obtained in the same manner as in Experimental Example 1 except that a resin sheet (thickness: 50 μm, industrial polyethylene terephthalate film: Lumirror T60, manufactured by Toray Industries, Inc.) was used as the base material.

[Experimental Example 8]
An adhesive sheet of Experimental Example 8 was obtained in the same manner as in Experimental Example 1, except that a resin sheet (thickness: 50 μm, polyphenylene sulfide film: Torelina, manufactured by Toray Industries, Inc.) was used as the base material.

[Experimental example 9]
An adhesive sheet of Experimental Example 9 was obtained in the same manner as in Experimental Example 1 except that a resin sheet (thickness: 50 μm, polyimide film: Kapton 100H, manufactured by Toray DuPont) was used as a substrate.

5. Evaluation of Adhesive Sheet The following items were evaluated for the adhesive sheets obtained in Experimental Examples 1 to 9 by the following methods. Table 1 also shows the results.

(1) Fillability into corners Filling of a stainless steel molded product 1 in which a 0.3 mm thick stainless steel plate is formed into a U-shape is provided with a 10 mm × 15 mm × 1.5 mm thick SPCC steel plate 2 in a U-shape. Test device 4 was produced. (FIG. 11). The gap between the stainless molded product 1 and the SPCC steel plate 2 was 0.45 to 0.5 mm.

Next, the adhesive sheets obtained in Experimental Examples 1 to 9 were cut into a size of 10 mm × 14 mm. The cut adhesive sheet was bent at 90 degrees at 6 mm from both ends and formed into a U-shape to obtain a test piece 3 (FIG. 12).
Then, the test piece 3 was inserted into a U-shaped gap of the filling test device 4 (FIGS. 13 and 14). Next, it was left in an oven heated to 190 ° C. for 20 minutes, heated and foamed, and then taken out.
Thereafter, the filling test apparatus 4 is cut in a direction 5 perpendicular to the insertion direction of the test piece 3 (FIG. 13), and the filling state of the U-shaped gap is visually observed and by a microscope (Digital Microscope VHX, manufactured by Keyence Corporation). Observation was performed at 200 times, and the evaluation was performed based on the following criteria (FIG. 15).
A: The base material maintains a U-shape and fills the gaps at the corners (FIG. 15A).
〇: Deformation was observed from the U-shaped state of the base material, but the base material filled the gaps at the corners (FIG. 15B).
XX: The base material did not maintain the U-shape before the heating and foaming, and an unfilled portion occurred (FIG. 15C).

6). Discussion As shown in Table 1, in Experimental Examples 1 to 5, the resin sheet was made of a raw material (thermoplastic resin) having a sufficiently high heat capacity change ΔCs due to glass transition. As a result, a resin sheet having good shape retention after deformation was obtained. The adhesive sheets of Experimental Examples 1 to 5 used these resin sheets as a base material. After deforming the adhesive sheet into a U-shape, the shape was maintained, and the resin sheet and a stainless steel plate as an adherend were used. The adhesive layer was cured and foamed by heating in a state where the gap with the SPCC steel plate was kept equal, and the gap was completely filled. As a result, the adhesive sheets obtained in Experimental Examples 1 to 5 had good filling properties at the corners where the gap between the adherends was largest. At this time, the base material was deformed in Experimental Examples 1, 2, and 4, but in Experimental Examples 3 and 5, the base material was not deformed.
On the other hand, in Experimental Examples 6 to 8, although the resin sheet had a Tg, it was made of a raw material having a low ΔCs value. As a result, the resin sheet had poor shape retention after deformation. In addition, when the adhesive sheets in Experimental Examples 6 to 8 used these resin sheets as a base material, the shape could not be maintained after the adhesive sheets were deformed into a U-shape, and the adhesive sheets were adhered to the resin sheets. The adhesive layer was cured and foamed by heating in a state where the gap between the stainless steel plate and the SPCC steel plate was non-uniform, and unfilled portions were generated. As a result, the adhesive sheets obtained in Experimental Examples 6 to 8 had insufficient fillability to corners as compared with Experimental Examples 1 to 5.
Next, in Experimental Example 9, the resin sheet was made of a raw material having no Tg and in which ΔCs could not be defined. As a result, the resin sheet was not deformable by bending. In addition, when the adhesive sheet of Experimental Example 9 used this resin sheet as a base material, the adhesive sheet could not be deformed into a U-shape, and the gap between the resin sheet and the stainless steel plate and the SPCC steel plate as the adherends was reduced. The adhesive layer was cured and foamed by heating in an uneven state, and unfilled portions were generated. As a result, the adhesive sheet obtained in Experimental Example 9 had insufficient filling into corners as in Experimental Examples 6 to 8.

Claims (7)

An adhesive sheet having an adhesive layer of a foamable adhesive composition on at least one surface of the resin sheet,
The resin sheet has, as a raw material, at least a glass transition temperature (Tg) and is based on a width (ΔH) between base lines before and after a downward shift in a DSC curve and a heating rate (Φ). An adhesive sheet characterized by a formula (ΔH / Φ) containing a thermoplastic resin having a heat capacity change (ΔCs) by glass transition of 60 to 420 mJ / (K · g).   The adhesive sheet according to claim 1, wherein the resin sheet uses a thermoplastic resin having a glass transition temperature of 150 ° C or higher.   The adhesive sheet according to claim 1, wherein a resin sheet having a flame resistance of VTM-0 or more in a test conforming to UL94 standard is used.   The adhesive sheet according to any one of claims 1 to 3, wherein the adhesive composition forming the adhesive layer includes a thermal foaming agent and a thermosetting resin having a softening temperature of 105 ° C or lower.   Further comprising a coat layer laminated on the adhesive layer, made of resin, showing no tack at room temperature, but softening and disappearing by heat; and setting the thermal foaming temperature of the thermal foaming agent to T1, and curing the adhesive layer. 5. The adhesive sheet according to claim 4, wherein a relationship T3 <T1 ≦ T2 is satisfied, where T2 is the starting temperature and T3 is the glass transition temperature of the coat layer.   The adhesive sheet according to any one of claims 1 to 5, which is used for filling voids.   A method for producing an electric component or an electronic component, comprising: placing the adhesive sheet according to claim 6 in a gap including a bent portion existing between components, heating the adhesive sheet, and thermally foaming the adhesive layer.