JP6779346B2 - Adhesive sheet - Google Patents

Description

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

When manufacturing various electric parts or electronic parts, gaps (or gaps or gaps) existing between the two members in order to prevent water from entering the inside and to insulate between two adjacent or opposing members. May be filled. As a technique for filling the gap, a technique is known in which an adhesive sheet having (foamable) adhesive layers provided on both surfaces of a resin sheet which is an insulator is put in the gap and bonded by applying heat (). Patent Document 1).

Japanese Unexamined Patent Publication No. 2010-261030

As the gaps existing between the above-mentioned members, there are 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, in the technique according to Patent Document 1, a resin sheet having high springback characteristics (characteristics that return to the original shape when bent into a U-shape, V-shape, etc.) is used as the base material of the adhesive sheet. Therefore, it was difficult to insert the adhesive sheet so as to follow the shape of the gap, that is, to deform the adhesive sheet so as to follow the shape of the bent portion, and to maintain the deformed state. As a result, it is not possible to completely fill the gap having a complicated shape, and the work efficiency is lowered.

An object of the present invention is to maintain excellent foaming performance while maintaining a deformed state such as bending, and to have excellent shape retention after deformation. As a result, adhesion capable of completely filling gaps having a complicated shape. To provide a sheet.

The present inventor uses a resin sheet formed from a raw material containing a thermoplastic resin having specific properties as a base material of an adhesive sheet having an adhesive layer, so that a gap having a bent portion has a complicated shape. It is possible to deform the bent portion so as to follow the shape of the bent portion, and further, the deformed state can be maintained. In other words, the shape has excellent shape retention after deformation and has a bent portion (corner portion). The present invention has been completed by finding that an adhesive sheet capable of completely filling a complicated gap can be obtained.

That is, according to the present invention, an adhesive sheet having the structure shown below is provided. Further, a method for manufacturing an electric component or an electronic component using an 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 the resin sheet. The adhesive layer is formed of an effervescent adhesive composition. In this case, the formula is based on the width (ΔH) and the rate of temperature rise (Φ) between the baselines before and after the resin sheet has at least a glass transition temperature (Tg) and shifts downward in the DSC curve. : (ΔH / Φ), the thermal capacity change (ΔCs) due to the glass transition is 60 to 420 mJ / (K · g), which is formed from a raw material containing a thermoplastic resin.
The method for manufacturing an electric component or an electronic component of 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 the components and heated to heat-foam the adhesive layer.

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

The adhesive composition forming the adhesive layer preferably contains a heat 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 heat foaming agent is preferably contained in an amount of 1 to 30 parts by mass with respect to 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 coat 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 made of 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 to satisfy the relationship of T3 <T1 ≦ T2. .. At this time, T1 is more preferably 100 ° C. or higher and 200 ° C. or lower, T2 is more preferably 110 ° C. or higher and 250 ° C. or lower, and T3 is more preferably 60 ° C. or higher and 140 ° C. or lower.

When the coat layer is laminated 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 heat foaming). It is preferable to satisfy the relationship (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 t1 at that time 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 applications, but is not particularly limited to this application.

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

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

Since the adhesive sheet of the present invention is formed from a raw material containing a thermoplastic resin having specific properties as the base material on which the adhesive layer is laminated, it follows the shape of the bent portion of the gap having the bent portion. Can be deformed to, and the deformed state can be maintained. That is, it is excellent in shape retention after deformation, and as a result, it is possible to completely fill gaps having a complicated shape.

FIG. 1 is a schematic view showing how the baseline changes stepwise in the 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 the measurement sample prepared from the resin sheet used in Experimental Example 2. FIG. 4 is a DSC curve obtained for the 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 the measurement sample prepared from the resin sheet used in Experimental Example 7. FIG. 7 is a DSC curve obtained for the measurement sample prepared from the resin sheet used in Experimental Example 8. FIG. 8 is a DSC curve obtained for the measurement sample prepared from the resin sheet used in Experimental Example 9. FIG. 9 is a DSC curve obtained for the measurement sample prepared from the resin sheet used in Experimental Example 4. FIG. 10 is a DSC curve obtained for the measurement sample prepared from the resin sheet used in Experimental Example 6. FIG. 11 is a cross-sectional view of a filling test device for evaluating the filling property of a corner portion. FIG. 12 is a schematic view showing how to bend the U-shaped test piece in the evaluation of the filling property to the corner portion. FIG. 13 is a schematic view showing a method of inserting a U-shaped test piece into a filling test apparatus in evaluating the filling property of a corner portion. 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 filling test device is cut after the U-shaped test piece is inserted into the filling test device and heated and foamed.

BL1 ... Base line example before glass transition BL2 ... Base line example after glass transition CP ... Inflection point SP ... Supplementary starting 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 point

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

Both the "glass transition temperature" and the "heat capacity change due to the glass transition" referred to in the present invention are defined by the description 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 of 60 mJ / (K · g) or higher) and therefore the more rigid the material, the more strongly it is affected by the external stress due to bending, resulting in , More, seems to bend. Further, since it has a rigid structure, its shape can be maintained even after bending, and it is considered that the shape retention after deformation is improved.
On the other hand, when the ΔCs value of the raw material forming the resin sheet is low (less than 60 mJ / (K · g)), the rigidity of the glass region is almost the same as that of the rubber region, so that the influence of the external stress is applied to the external stress. It stays only for a certain amount of time, and many actions are taken to restore the deformation from its elasticity. Therefore, it is considered that the bent state cannot be maintained and the shape retention after deformation becomes poor.
Further, in the case of polyimide or the like in which the raw material for forming the resin sheet does not have Tg and therefore the ΔCs value cannot be defined, it has a rigid structure, but since it exhibits excessive rigidity over a wide temperature range, it is necessary to deform it by bending. Very large external stress is required. Also, it will be difficult to maintain its 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. Of these, the heat capacity change ΔCs due to the glass transition belongs to a more appropriate range (60 to 200 mJ / (K · g)), and as a result, the shape retention after deformation when formed into a sheet is excellent, and adhesion is achieved. It is preferable to use LCP, para-aromatic amide, triacetyl cellulose or a mixture thereof because the sheet is not deformed even under high heat conditions during the curing process of the agent resin.

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

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

The LCP is typically an aromatic polyester that exhibits liquid crystallinity when melted, and can usually be synthesized from a monomer such as an aromatic diol, an aromatic carboxylic acid, or a hydroxycarboxylic acid, and is commercially available as a film of the LCP. Products such as Vexter (manufactured by Kuraray), Viac (manufactured by Japan Goretex), Pelicule (manufactured by Chiyoda Integre), liquid crystal polymer cast film (manufactured by Kyodo Giken Kagaku Co., Ltd.) and the like may be used.

The para-aromatic amide can be obtained by copolymerizing polypara-phenylene terephthalamide (PPTA) or a third component thereof, and as a film of the para-aromatic amide, a commercially available product, for example, Mictron (Toray) Aramica (manufactured by Teijin Advanced Film Co., Ltd.) or the like may be used.
Triacetyl cellulose is obtained by reacting cellulose with acetic anhydride to acetylate cellulose molecules. As the triacetyl cellulose film, commercially available products such as those manufactured by Konica Minolta and Fuji Film are used. May be 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. It is above ℃. Examples of such a thermoplastic resin include the above-mentioned LCP, para-aromatic amide, and a mixture thereof.

The thermoplastic resin used for forming the resin sheet preferably has a relatively high molecular weight from the viewpoint of sheet film forming property. By increasing the molecular weight, it becomes easy to maintain the viscosity during sheet molding, and it becomes possible to mold into a thin film. The optimum weight average molecular weight of the thermoplastic resin varies depending on the type of resin, and for example, when polycarbonate is used, it is preferably 5000 or more, and more preferably 10000 or more. When PEN is used, it is preferably 10,000 or more, and more preferably 20,000 or more. When LCP is used, it is preferably 20000 or more. When the weight average molecular weight is 100,000 or more, the viscosity becomes very high and molding defects are likely to occur. Therefore, it 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 additive is not particularly limited, and for example, a heat stabilizer, a lubricant, a dispersant, a colorant, a fluorescent whitening agent, an antistatic agent, a flame retardant, an antibacterial agent, an antifungal agent, an ultraviolet absorber, and a light stabilizer. , Antioxidants, plasticizers, antifoaming agents, leveling agents, flow regulators, antifouling agents, pigments, dyes, fine particles and other general plastic additives. When the additive is contained, the amount of the additive added can be, for example, about 0.1 to 10 parts by weight with respect to 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, a width of 1 mm or less and filling of a gap 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 the above-mentioned thermoplastic resin and a resin composition containing an arbitrary 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 is obtained by forming a film by a known method such as a melt extrusion method, a solution stretching method, or a calendar method.

The resin sheet used for the adhesive sheet of the present invention has a tensile elastic modulus of 2 MPa or more, more preferably 4 MPa or more, because if the elastic modulus is low, transport defects occur during sheet processing and wrinkles and the like are likely to occur. (Preferably 25 MPa or less, more preferably 20 MPa or less). The tensile elastic modulus of the resin sheet is a value measured in accordance with JIS K7127 "Tensile test method for plastic film and sheet".

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 resin sheet has an insulating breakdown voltage of 250 kV / mm or more. It is preferable to have. The upper limit of the dielectric breakdown voltage is not particularly limited, but is usually 500 kV / mm or less, preferably 400 kV / mm or less.

When used as an insulating material, 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 according to the UL94 standard from the viewpoint of safety during use. Here, "flame retardancy of VTM-0 or higher in a test conforming to UL94 standard" means VTM-in a test conforming to the thin material vertical combustion test method of the flame retardancy test standard UL94 of plastic materials issued by Under Laboratories. It means that it is judged to be 0, and further, it means that it satisfies the self-digestion standard of 5VA, 5VB, V-0, V-1, V-2 in the test according to the vertical combustion test of UL94.

When the resin sheet used for the adhesive sheet of the present invention is used as an insulating material, it is assumed that it is used in a high temperature state, and in order to ensure sufficient heat resistance, the mechanical properties are measured by the UL746B long-term heat resistance temperature index. It is preferable that the material has heat resistance of class B or higher.

[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 by a heat-foamable adhesive composition. An example is as follows.

The adhesive layer according to one example is formed of a thermosetting, foamable adhesive composition whose volume increases and the curing reaction proceeds to increase the adhesive force when heated to a predetermined temperature or higher, and is formed at room temperature. It shows tack or cracks may occur. This adhesive composition contains at least a thermosetting agent and a thermosetting resin having a softening temperature of 105 ° C. or lower. By forming the adhesive layer by containing a thermosetting resin having a softening temperature of 105 ° C. or lower, the adhesive layer exhibits tack at room temperature, or cracks or may crack.

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 of the adhesive sheet are stacked so that the coat layers face each other, and then sandwiched between glass plates. After applying a load of 100 g on the laminate and allowing 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 each adhesive sheet are in close contact with each other. It is said that the base material of the adhesive sheet and the adhesive layer are in close contact with each other, that is, the coat layer exhibits tack at room temperature. On the other hand, when the glass plate is spread up and down, if it peels off between the coated layers that were in contact with each other, the coat layer does not show tack at room temperature.
The term "cracking" means that when the adhesive sheet is bent 180 degrees, the adhesive layer is cracked, and at least a part of the adhesive layer is removed or is in a state where it can be removed.

It is preferable to arrange a coat layer on the adhesive layer of the present embodiment. The coat layer is formed of a resin and does not show tack at room temperature, but is softened by heat and disappears.
In the present invention, "the coat layer disappears" means that, in principle, the adhesive sheet of the present invention is softened by applying heat exceeding the glass transition temperature of the resin forming the coat layer, whereby the coat layer is softened. By mixing with the thermosetting resin (before curing) that forms the adhesive layer, the resin is integrated with the adhesive layer, and the coat layer that was present on the adhesive layer apparently disappears. Specifically, the adhesive sheet is cut by a method described later, the cross section thereof is observed with a microscope, and at least a part of the coat layer disappears in the range from the interface between the adhesive layer and the coat layer to the surface of the coat layer. If so, it is judged that the coat layer has disappeared. That is, in the present invention, even when at least a part of the adhesive layer after heat curing is exposed on the portion of the adhesive sheet after the adhesive layer is cured by heating, which is in contact with the adherend, "coating". The layer has disappeared. " That is, in interpreting "the coat layer disappears" in the present invention, the degree of mixing of the resin forming the coat layer with the thermosetting resin forming the adhesive layer (before curing) does not have to be perfect. After heat curing, the surface of the sheet may function as an adhesive layer. At least, a part of the adhesive layer after heat curing may be exposed on the sheet surface at a portion of the adhesive sheet after the adhesive layer is cured by heating and in contact with the adherend. If the entire heat-cured adhesive layer is exposed on the sheet surface, it means that the coat layer that was present 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 can be satisfied. preferable. Details will be described later.

The resin contained in the adhesive composition 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 is used. Can be done.
Examples of the thermoplastic resin contained in the adhesive composition forming the adhesive layer of the present embodiment include natural rubber, butyl rubber, isoprene rubber, chloroprene rubber, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid copolymer. , Ethylene-acrylic acid ester copolymer, polybutadiene resin, polypropylene resin, styrene-butadiene-styrene copolymer, styrene-ethylene-butylene-styrene copolymer, polyacetal resin, polyvinyl butyral resin, polyvinyl acetal resin, acrylonitrile-butadiene Copolymers, acrylonitrile-butadiene-acrylic acid copolymers, acrylonitrile-butadiene-styrene copolymers, polycarbonate resins, thermoplastic polyimide resins, thermoplastic siloxane modified polyimide resins, polyamides such as 6-nylon and 6,6-nylon Examples thereof include a resin, a phenoxy resin, an acrylic resin, a polyester resin, and a fluororesin. These thermoplastic resins can be used alone or in combination of two or more.
Further, examples of the thermosetting resin contained in the adhesive composition forming the adhesive layer of the present embodiment include epoxy resin, urethane resin, silicone resin, oxetane resin, phenol resin, (meth) acrylate resin, and diallyl phthalate. Examples thereof include resins, maleimide resins, polyimide resins, polyesterimide resins, polyamideimide resins, bismaleimide-triazine resins, and polyetherimide resins. 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 also be used as a thermosetting resin by adding a curing agent. Examples of such a thermosetting resin include phenoxy resin, polyester resin, polyamic acid resin and the like.

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, Maleimide resin, bismaleimide-triazine resin and the like are preferable, and one or a plurality of these can be used alone or in combination. Of these, epoxy resins are preferable from the viewpoints of excellent curability and storage stability, heat resistance of cured products, moisture resistance, and chemical resistance.

Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, hidden in type epoxy resin, biphenyl type epoxy resin, alicyclic epoxy resin, triphenylmethane type epoxy resin, and phenol novolac. Type epoxy resin, cresol novolac type epoxy resin, naphthol novolac type epoxy resin, dicyclopentadiene / phenol epoxy resin, alicyclic amine epoxy resin, aliphatic amine epoxy resin, and various modifications such as CTBN modification and halogenation are performed on these. Of these, 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 viscosity of the epoxy resin at 190 ° C. is usually preferably 0.05 Pa · s or more, and more preferably 0.1 Pa · s or more. Further, it is usually preferably 3.0 Pa · s or less, and 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 risk of continuous foaming or foam breakage. 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 (WPE) of usually 150 or more, preferably 180 or more, and usually 1000 or less, preferably 700 or less. "Epoxy equivalent" is defined by the molecular weight of the epoxy resin per epoxy group. Here, the "epoxide group" contains an oxacyclopropane (oxylane 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). Includes. WPE is determined by JIS K7236, the method described in the method for determining the epoxy equivalent of an epoxy resin (2001) (perchloric acid-tetraethylammonium bromide method), or the like.

The epoxy resin is semi-solid or solid at room temperature, and in the case of a solid, the softening temperature is preferably 105 ° C. or lower, more preferably 95 ° C. or lower. Further, usually 40 ° C. or higher is preferable, and 45 ° C. or higher is more preferable. If it is liquid at room temperature, the viscosity decreases significantly during curing and foaming, and the foamed state of the epoxy resin cannot be maintained, which may lead to foam rupture and continuous foaming. In addition, the shape of the adhesive layer may not be maintained.

By containing a thermosetting resin (preferably an epoxy resin) having a softening temperature of 105 ° C. or lower to form an adhesive layer, the resin is softened by heating, whereby the thermal foaming agent is successfully foamed in the adhesive layer. Can be done. Even if the softening temperature is 105 ° C or lower, if it exceeds 60 ° C, the adhesive layer may be cracked. 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 risk of it falling 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 lower, the above-mentioned action (the heat foaming agent in the adhesive layer can be successfully foamed by heating). ), The occurrence of cracks in the adhesive layer can be suppressed, which can contribute to the prevention of the adhesive layer from falling off.
The softening temperature here is a value measured by a method defined by JIS K7234 (ring 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 maintained better. be able to. It is more preferable to form the adhesive layer by containing a thermosetting resin having a weight average molecular weight of 800 or less. This is because, in addition to the above action (maintaining the adhesive 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 so that it can be easily formed into a sheet. This is because if the molecular weight is less than 450, the resin becomes almost liquid at room temperature, so that the shape of the adhesive layer may not be maintained.

The thermal foaming agent 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 one, etc.) is appropriately used. Although it can be selected and used, among them, microencapsulated ones (hereinafter referred to as "thermally expanding microspheres") can be preferably used.
As a heat-expandable microsphere, a microsphere having a structure in which a foaming agent is sealed inside an elastic outer shell and exhibiting thermal expansion as a whole (property of expanding the whole by heating) is given as a preferable example. Can be done.
Examples of the elastic outer shell include heat-meltable substances and substances that are destroyed by thermal expansion, such as vinylidene chloride-acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethylmethacrylate, polyacrylonitrile, polyvinylidene chloride, and polysulfone. Can be mentioned as a preferable example.
As the foaming agent, substances that are easily gasified and expanded by heating, for example, hydrocarbons such as isobutane, propane, and pentane can be mainly mentioned. Commercially available products of thermally expandable microspheres include, for example, the trade name "Matsumoto Microsphere" series (manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.), Advancel EM series (manufactured by Sekisui Chemical Co., Ltd.), and Expandel (manufactured by Nippon Ferrite Co., Ltd.). ) Etc. can be mentioned.

The size of the heat-expandable microspheres may be appropriately selected depending on the use of the adhesive sheet, and specifically, the mass average particle size may be about 10 to 20 μm. The heat-expandable microspheres may be used after adjusting the particle size distribution. To adjust the particle size distribution, those having a relatively large particle size contained in the thermally expandable microspheres to be used may be classified and removed by a centrifugal force type wind classifier, a dry classifier, a sieving machine or the like. Specifically, it is preferable that the standard deviation of the particle size distribution of the thermally expandable microspheres is 5.0 μm or less.

The expansion coefficient of the heat-expandable microsphere is preferably 5 times or more, and more preferably 7 times or more. On the other hand, it is preferably 15 times or less, and more preferably 12 times or less. The outer shell of the heat-expandable microspheres preferably has an appropriate strength that does not burst even when the heat-expandable microspheres expand to the predetermined expansion coefficient.

The blending amount of the thermally expandable microspheres is preferably 1 part by mass or more, more preferably 3 parts by mass or more, preferably 30 parts by mass or less, and more preferably 20 parts by mass with respect to 100 parts by mass of the adhesive resin. Hereinafter, it is more preferably 15 parts by mass or less.

It is desirable that the thermal foaming temperature (T1) of the thermal foaming agent is preferably 100 ° C. or higher, more preferably 150 ° C. or higher, preferably 200 ° C. or lower, and more preferably 190 ° C. or lower. T1 corresponds to the thermal expansion temperature when a thermal expansion microsphere is used as the thermal foaming agent, and corresponds to the thermal decomposition temperature when a pyrolysis type foaming agent is used. The "thermal expansion temperature" is synonymous with the foaming start temperature, and in the present embodiment, it means the thermal expansion start temperature in the TMA measurement, and does not mean the maximum thermal expansion temperature at which the volume expands to the maximum.

In addition, examples of other thermal foaming agents include pyrolytic foaming agents and expanded graphite. Pyrolytic foaming agents are classified into inorganic and organic.
Examples of the inorganic foaming agent include ammonium carbonate, ammonium hydrogencarbonate, sodium hydrogencarbonate, ammonium nitrite, sodium borohydride, azides and the like. Examples of the organic foaming agent include water, alkane hydrochloride (for example, trichloromonofluoromethane, dichloromonofluoromethane, etc.), azo compounds (for example, azobisisobutyronitrile, azodicarboxylicamide (ADCA), etc.). 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.), Triazole compounds (eg, 5-morpholyl-1,2,3,4-thiatriazole, etc.) , N-nitroso compounds (eg, N, N'-dinitrosopentamethylenetetramine, N, N'-dimethyl-N, N'-dinitrosoterephthalamide, etc.), and the like.
These heat foaming agents can be used alone or in admixture of a plurality.

The blending amount of such a thermal decomposition type foaming agent is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and preferably 30 parts by mass or less, more preferably more preferably, with respect to 100 parts by mass of the adhesive resin. It is 25 parts by mass or less.

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

The blending amount of the curing agent is calculated from the equivalent ratio with the thermosetting resin used, and the 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, and 15 parts by mass with respect to 100 parts by mass of the thermosetting resin. Less than a part is more preferable. Further, for example, in the case of anhydrous methyl nagic, with respect to 100 parts by mass of the thermosetting resin, 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, 200 parts by mass. Less than a part is more preferable. If the blending amount of the curing agent is less than the above lower limit, it is difficult to cure sufficiently, and there is a possibility that the characteristics as a thermosetting resin such as heat resistance and chemical resistance cannot be sufficiently exhibited. On the other hand, if the blending amount exceeds the above upper limit value, an excessive exothermic reaction is accompanied during curing, the viscosity of the resin composition during curing is lowered more than necessary, and it becomes difficult to finally maintain a sufficient foamed state. there is a possibility.

A curing accelerator can be used in combination 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, and the like. Tertiary amines such as benzyldimethylamine; organic phosphines such as tributylposfin and triphenylphosphine; and the like can be mentioned. These can be used alone or in combination of two or more. The blending amount of the curing accelerator is, for example, 5 parts by mass or less with respect to 100 parts by mass of the thermosetting resin.

Other additives that can be added as optional components to the adhesive composition include, for example, natural rubber, isoprene rubber, styrene-butadiene rubber, chloroprene rubber, butadiene rubber, nitrile rubber, butyl rubber, fluororubber, and acrylic rubber as elastomer components. Such as solid or liquid rubbers, polyurethane, urethane prepolymer and the like can be mentioned. The blending amount is 20 parts by mass or less, preferably 10 parts by mass or less, and more preferably 5 parts by mass or less with respect to 100 parts by mass of the adhesive resin. Further, a foaming aid, various fillers, a foam stabilizer, an antioxidant, an ultraviolet absorber, and a colorant may be blended.

In the adhesive composition of the present embodiment, the above-mentioned thermal foaming agent, adhesive resin, and if necessary, a curing agent, a curing accelerator, a foaming aid, various additives, and the like are mixed in an arbitrary order. Can be obtained by The raw materials can be mixed using a mixer such as a mixing roll, a planetary mixer, a butterfly mixer, a kneader, a single-screw or twin-screw extruder, or a kneader. The mixing temperature varies depending on the composition, but it is necessary to carry out the mixing temperature below the heat foaming temperature (T1) of the heat 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 the form of a sheet is preferably 110 ° C. or higher and 250 ° C. or lower.

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 if necessary. The adhesive layer can also be obtained by applying the above-mentioned adhesive composition on a coat layer described later, which is formed on a separately prepared release film, and drying it if necessary.
The thickness (t1) of the adhesive layer before foaming may be appropriately selected depending on the intended use of the adhesive sheet, but the lower limit is preferably 20 μm or more, further 30 μm or more, and the upper limit is 1000 μm or less, further 400 μm or less. Furthermore, it is preferably 200 μm or less. By setting the thickness of the adhesive layer to 20 μm or more, it is easy to retain the bubbles generated by the foaming reaction in the adhesive layer. By setting the thickness (t1) of the adhesive layer to 1000 μm or less, it is possible to fill a narrow void of 1 mm or less, for example.

[Coat layer]
Examples of the resin forming the coat layer arranged on the adhesive layer in the preferred embodiment of the present embodiment include phenoxy resin, polyester resin, polyurethane resin, polyimide resin, siloxane-modified polyimide resin, polybutadiene, polypropylene, and 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 Thermoplastic resins 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. Of these, it is preferable to use a phenoxy resin, a polyester resin, or the like.
Examples of the polyester resin include trade name Byron 200 (manufactured by Toyobo Co., Ltd.), trade name Polyester TP220 (manufactured by Nippon Synthetic Chemical Co., Ltd.), and trade name Elitel KA series (manufactured by Unitika Ltd.).

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 epichlorohydrin 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 is not particularly limited. Examples thereof include those having one or more skeletons selected from a skeleton, an adamantan skeleton, a terpen skeleton, and a trimethylcyclohexane skeleton.

Commercially available products of phenoxy resin 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, etc. (all manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.) and the like can be mentioned.
In addition, a phenoxy resin dissolved in a solvent is also commercially available, and this is also used in the same manner. 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-007A Nippon Steel & Sumikin Chemical Co., Ltd.), etc.

These phenoxy resins can be used alone or in combination of two or more.

In the present embodiment, a curing agent such as isocyanate or organic peroxide may be further added to the thermoplastic resin, if necessary. By appropriately selecting and blending the type and molecular weight of the curing agent, it becomes easy to finely adjust the affinity with the adhesive layer. When blending, the blending amount of the curing agent (isocyanate or the like) can be about 3 to 30 parts by mass with respect to 100 parts by mass of polyester resin, phenoxy resin or the like.

For the coat layer, a coat layer forming coating liquid in which the above-mentioned resin (including a curing agent if blended) is dissolved or dispersed in a solvent is prepared, and this is applied to an adhesive layer laminated on a resin sheet. Obtained by applying and drying. The coat layer can also be obtained by applying the above-mentioned coat layer forming coating solution to a separately prepared release film and drying it.

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 60 ° C. or higher and 140 ° C. or lower) on the condition that it is formed with an appropriate composition, and this is satisfactorily formed. It can be extinguished.
The mechanism by which the coat layer disappears is as follows. The coat layer softens when heat exceeding the glass transition temperature of the resin forming the coat layer is applied. As a result, the resin of the coat layer is mixed with the adhesive resin (thermosetting resin before curing or thermoplastic resin described above) forming the adhesive layer and integrated with the adhesive layer (incorporated into the adhesive layer). As a result, the coat layer that was present on the adhesive layer apparently disappears. Form an adhesive layer

If the coat layer is too thick, it may not be sufficiently incorporated into the adhesive layer, and as a result, the disappearance of the coat layer may not proceed well. Further, when the heat foaming agent is contained, the heat foaming agent in the adhesive layer may not be sufficiently foamed, and the foamability may be impaired.
In the present invention, as described above, at least a part of the adhesive layer after heat curing is exposed (contacted) with the portion of the adhesive sheet after the adhesive layer is cured by heating and in contact with the adherend. For example, 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.

For the coat layer, it is desirable to determine the resin that forms the coat layer so that the glass transition temperature (T3) is preferably 60 ° C. or higher and 140 ° C. or lower. If the glass transition temperature (T3) of the coat layer is too low, the surface of the coat layer becomes sticky (tack), and the effect of the present invention may be difficult to obtain. On the other hand, if T3 is too high, the coat layer is not sufficiently softened 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 that forms the coat layer in relation to the composition of the adhesive layer. By considering the affinity between the coat layer and the adhesive layer, it is possible to facilitate the incorporation (penetration) into the adhesive layer when the coat layer is softened. 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 contained in the adhesive composition forming the adhesive layer, trade name NC2000L (novolac type epoxy resin, Nihon Kayaku, epoxy equivalent 229 to 244, softening temperature 47 to 57) ℃), it is desirable to use the bisphenol A type trade name PKHH as the resin forming the coat layer.

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

The adhesive sheet of the present embodiment can be widely used for manufacturing various electric parts or electronic parts, joining a joint portion between a skin material of a vehicle body and a reinforcing material, and filling a gap existing between each member. In particular, a narrow gap of 1 mm or less and / or a shape having a bent portion is useful for filling a complicated gap. Specifically, the adhesive sheet of the present embodiment is placed in various gaps existing between the members, heated, and the adhesive layer is thermally foamed, whereby the above-mentioned various gaps can be completely filled.

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. 1. Measurement or evaluation of resin sheet The following items were measured or evaluated by the following methods with respect to the resin sheet used in each example described later. 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 without the pretreatment were used as measurement samples. Further, regarding 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. Therefore, a sample heated at 80 ° C. for 10 minutes as a pretreatment was used as a measurement sample. ..
Next, the temperature (° C.) and heat flow (heat capacity. MJ / (s.)) Of the above-mentioned measurement sample were measured by differential scanning calorimetry (DSC) using a differential scanning calorimetry device (DSC3200, manufactured by MacScience) as a measuring device. A DSC curve was obtained on an XY plane with g)) on the horizontal axis (X axis) and the vertical axis (Y axis), respectively (FIGS. 2 to 10).

In general, when the measurement sample undergoes a glass transition, the specific heat capacity of the measurement sample changes before and after that, and as a result, the baseline changes stepwise (particularly downward) near the glass transition temperature of the DSC curve. It is known (see page 43 of the non-patent document published by the Publishing Department of the Engineering Information Center on December 29, 1985: "Basics / Applications of Various Thermal Analysis Technologies and Measurement Data Collection"). Therefore, next, paying attention to the portion where the baseline is shifted downward from the obtained DSC curve, the original baseline before the downward shift (for example, the baseline indicated by "BL1" in FIG. 1) and the inflection point. The intersection with the tangent line at a point (the point where the upwardly convex curve changes to the downwardly convex curve. For example, the point indicated by "CP" in FIG. 1) and the intersection (external start temperature. For example, "SP" in FIG. 1 indicates. Point) was defined as the glass transition temperature (unit: ° C.) of the measurement sample. The results are shown in Table 1.

(2) Change in heat capacity due to glass transition (ΔCs)
Above 1. Using the DSC curve obtained for each measurement sample prepared in (1), the width (that is, measurement) between the baselines (for example, "BL1" and "BL2" in FIG. 1) before and after the downward shift in the curve. The heat capacity change rate ΔH (unit: mJ / (s · g)) is defined as the difference between the baselines before and after the glass transition of the sample, and this ΔH is defined as the temperature rise rate Φ (unit: K / s) of the measurement sample. The value calculated by dividing by) is 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 degree of change in heat capacity ΔH of each measurement sample was determined from the obtained DSC curve as shown in FIGS. 2 to 10. The heating rate Φ was set to 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 since this is thought to be a liquid crystal phase transition, the point before the start of the exothermic peak was set as the baseline value after the glass transition, and it was due to the glass transition. The change in heat capacity (ΔCs) was calculated.

(3) Flame Retardant The resin sheets of Experimental Examples 1 to 9 were tested according to the thin material vertical combustion test method and vertical combustion test method of the flame retardancy test standard UL94 for plastic materials issued by Under Laboratories, and ranked as VTM. And V rank were judged 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.
⊚: A material that satisfies VTM-0 in the UL94 thin material vertical combustion test and V-0 in the UL94 vertical combustion test.
◯: A material satisfying VTM-0 in the UL94 thin material vertical combustion test.
X: A material that does not satisfy VTM-0 in the UL94 thin material vertical combustion test.

(4) Tension elastic modulus
The resin sheets of Experimental Examples 1 to 9 were measured according to JIS K7113 (unit: MPa). Specifically, the resin sheet was punched out using a type 2 test piece, tested at a speed of 50 mm / min using a universal testing machine (manufactured by Instron), and calculated by the following formula. 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 according to the short-time method of JIS C2110. Specifically, the test piece used was a resin sheet cut into 50 mm × 50 mm. A spherical brass electrode having a diameter of 12.5 mm was used as the test electrode, the pressure bonding force between the electrodes was 500 g, and the measurement was performed in silicone oil. 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 a test piece, which was then placed on a rubber plate having a thickness of 10 mm. Next, using a metal plate having a thickness of 1 mm, a width of 50 mm, and a height of 50 mm, the metal plate was vertically pressed (pressurized) under the condition 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 of pressurization release as an evaluation of whether or not it can be deformed and 10 seconds after pressurization release as an evaluation of shape retention after deformation. Was measured and evaluated according to the following criteria. The results are shown in Table 1.

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

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

<Components of adhesive layer forming coating liquid>
Thermosetting resin (novolac 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 (100% solid content): 8.9 parts by mass (dicyandiamide (DICY), manufactured by Japan Epoxy Resin Co., Ltd.)
-Curing accelerator (100% solid content): 0.5 parts by mass (Curesol 2MZ-A, 2,4-diamino-6- [2'-methylimidazolyl- (1')]-ethyl-s-triazine, Shikoku Made by Kaseisha)
-Heat foaming agent: 10 parts by mass (Matsumoto Microsphere F100M, heat-expandable microspheres, mass average particle size: 17 to 23 μm, heat expansion temperature (synonymous with heat foaming temperature T1): 120 ° C., maximum thermal expansion temperature: 160 ° C, expansion coefficient: 10 times, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.)

3. 3. Preparation of coating layer forming coating liquid The following constituent components were uniformly mixed at the following solid content ratio (mass conversion) to prepare. The total solid content in the coating liquid was 40%.
<Components of coating layer forming coating liquid>
-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., Ltd., NCO content: 43.3%)

4. Creating an adhesive sheet
[Creation of adhesive layer and coat layer]
Using the example of the adhesive layer forming coating liquid having the above-mentioned structure and the coating layer forming coating liquid, the coating layer forming coating is applied on the release-treated surface of the release film (Vina No. 23, manufactured by Fujimori Kogyo Co., Ltd., thickness 38 μm). The working liquid was applied with a baker type applicator. Then, the coat layer was formed to have a thickness (t2) of 5 μm by drying at 140 ° C. for 1 minute (laminated product a'). Next, the adhesive layer forming coating liquid was applied to the surface of the coat layer in the same manner as described above. Then, it was dried at 120 ° C. for 1 to 2 minutes to form an adhesive layer having 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 type, manufactured by TA instruments) is used as a measuring device, and 0.5 mg of thermally expandable microspheres are made of aluminum with a diameter of 6.0 mm (inner diameter 5.65 mm) and a depth of 4.8 mm. The sample was prepared by putting it in a cup and placing an aluminum lid (5.6 mm, thickness 0.1 mm) on the upper part of the heat-expandable microsphere layer. The height of the sample was measured with a force of 0.01 N applied to the sample from above with a pressurizer. With a pressure of 0.01 N applied, the presser is heated from 20 ° C. to 300 ° C. at a heating rate of 10 ° C./min, and the amount of displacement of the pressurizer in the vertical direction is measured. The displacement start temperature in the positive direction was defined as the thermal foaming temperature (T1). As a result, T1 was 120 ° C.

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

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

(4) Film thickness of the adhesive layer (after heating)
The laminated product a was cut into a size of 5 cm × 5 cm, placed on an SPCC steel plate having a thickness of 1 mm so that the adhesive layer was in contact with the laminated product a, and the release film was peeled off from the laminated product a. Then, it was left in an oven heated to 190 ° C. for 30 minutes and then taken out. Then, 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 reducing the thickness of the release film from the obtained measured values. As a result, the thickness of the adhesive layer after heating was 325 μm. Therefore, the foaming ratio of the adhesive layer was 5.9 times.

(5) Cracking of Adhesive Layer For laminated product a (with coat layer) and laminated product b (without coat layer), the state of the adhesive layer after bending any part on the adhesive layer side to 180 degrees before heat foaming. Was visually confirmed.
As a result, both the laminated product a and the laminated product b were good with no cracking of the adhesive layer itself.

(6) Disappearance of coat layer The laminated product a was placed on an SPCC steel plate having a thickness of 1 mm so that the adhesive layer was in contact with the sheet, and the release film was peeled off. Further, SPCC steel sheets having a thickness of 1 mm were laminated and fixed so as to form a gap twice the total thickness of the adhesive layer and the coat layer. Then, it was left in an oven heated to 190 ° C. for 30 minutes and then taken out. This was cut vertically so that the cross section on the SPCC steel sheet and 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 attached to the SPCC steel sheet.

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

[Creating an adhesive sheet]
[Experimental Example 1]
While applying heat of 80 ° C. to both surfaces of the resin sheet (thickness: 50 μm, polyethylene naphthalate film: Theonex Q51, manufactured by Teijin DuPont Film Co., Ltd.) as the base material so that the adhesive layer surfaces of the laminated product a face each other. After laminating, the release film was peeled off to obtain an adhesive sheet of Experimental Example 1.

[Experimental Example 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 base material.

[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: Mictron (GQ type), manufactured by Toray Industries, Inc.) was used as a 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 base material.

[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 base material.

[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: manufactured by Lumirror U403 Toray Industries, Inc.) was used as a 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 a 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: Torerina, manufactured by Toray Industries, Inc.) was used as a 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 base material.

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

(1) Fillability to corners Filling in which a 10 mm × 15 mm × 1.5 mm thick SPCC steel plate 2 is installed in the U-shaped portion of a stainless molded product 1 obtained by molding a stainless steel plate having a thickness of 0.3 mm into a U shape. The test device 4 was manufactured. (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. This cut adhesive sheet was bent at 90 degrees at 6 mm from both ends and formed into a U shape to form a test piece 3 (FIG. 12).
Then, the test piece 3 was inserted into the U-shaped gap of the filling test device 4 (FIGS. 13 and 14). Then, it was left in an oven heated to 190 ° C. for 20 minutes, heated and foamed, and then taken out.
After that, the filling test apparatus 4 is cut in a direction 5 orthogonal to the insertion direction of the test piece 3 (FIG. 13), and the filling status of the U-shaped gap is visually checked and by a microscope (digital microscope VHX, manufactured by KEYENCE). It was observed at 200 times and evaluated according to the following criteria (Fig. 15).
⊚: The base material maintains a U-shape and fills the gaps at the corners (FIG. 15 (a)).
〇: Deformation was observed from the U-shaped state of the base material, but the gaps at the corners were filled (Fig. 15 (b)).
XX: The base material did not retain the U-shape before heating and foaming, and an unfilled portion was generated (FIG. 15 (c)).

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 value of heat capacity change ΔCs due to glass transition. As a result, a resin sheet having good shape retention after deformation was obtained. Further, when these resin sheets were used as the base materials for the adhesive sheets of Experimental Examples 1 to 5, the adhesive sheets were deformed into a U shape and then retained in shape, and the resin sheet and the stainless steel plate as an adherend were retained. The adhesive layer was cured and foamed by heating while the gaps with the SPCC steel sheet were kept equal, and all the gaps were filled. As a result, the adhesive sheets obtained in Experimental Examples 1 to 5 had good filling property to the corners where the gap between the adherends was the largest. At this time, deformation was observed in the base material in Experimental Examples 1, 2 and 4, but no deformation was observed in the base material in Experimental Examples 3 and 5.
On the other hand, in Experimental Examples 6 to 8, the resin sheet was made of a raw material having Tg but a low ΔCs value, and as a result, the resin sheet had poor shape retention after deformation. Further, when these resin sheets were used as the base materials for the adhesive sheets in Experimental Examples 6 to 8, 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 body stainless plate and the SPCC steel plate was non-uniform, and an unfilled portion was generated. As a result, the adhesive sheets obtained in Experimental Examples 6 to 8 had insufficient filling property to the corners as compared with Experimental Examples 1 to 5.
Next, in Experimental Example 9, the resin sheet was made of a raw material that did not have Tg and could not define ΔCs, and as a result, the resin sheet was not deformable by bending. Further, in the adhesive sheet of Experimental Example 9, when this resin sheet was used as a base material, the adhesive sheet could not be deformed into a U shape, and there was a gap between the resin sheet and the stainless steel plate and SPCC steel plate which were adherends. The adhesive layer was cured and foamed by heating in a non-uniform state, and an unfilled portion was generated. As a result, the adhesive sheet obtained in Experimental Example 9 had insufficient filling property to the corners as in Experimental Examples 6 to 8.

Claims (7)

An adhesive sheet having an adhesive layer made of an effervescent adhesive composition on at least one side of the resin sheet.
The adhesive composition forming the adhesive layer contains a heat foaming agent and a thermosetting resin having a softening temperature of 105 ° C. or lower.
The resin sheet has a glass transition temperature (Tg) of more than 155 ° C. as a raw material thereof, and has a width (ΔH) and a heating rate (Φ) between each baseline before and after shifting downward in the DSC curve. An adhesive sheet comprising a thermoplastic resin having a heat capacity change (ΔCs) of 60 to 420 mJ / (K · g) due to glass transition, which is represented by the formula: (ΔH / Φ). The adhesive sheet according to claim 1, wherein the resin sheet uses a thermoplastic resin having a glass transition temperature of 200 ° C. or higher. The adhesive sheet according to claim 1 or 2, wherein a resin sheet having a flame retardancy of VTM-0 or higher is used in a test conforming to the UL94 standard. The adhesive sheet according to any one of claims 1 to 3, wherein the thermoplastic resin forming the resin sheet has a weight average molecular weight of 20,000 or more and less than 100,000. It is laminated on the adhesive layer, is made of resin, has a coat layer that does not show tack at room temperature but softens and disappears due to heat, and the thermal foaming temperature of the thermal foaming agent is T1, and the adhesive layer is cured. start temperature of T2, when the glass transition temperature of the coating layer was T3, the adhesive sheet according to claim 1, wherein satisfying the relation of T3 <T1 ≦ T2. The adhesive sheet according to any one of claims 1 to 5, which is used for filling voids. A method for manufacturing an electric component or an electronic component, which comprises placing the adhesive sheet according to claim 6 in a gap including a bent portion existing between the components and heating the adhesive layer to heat-foam the adhesive layer.