JP6067967B2 - Thermally expandable adhesive sheet and manufacturing method thereof - Google Patents

Description

  The present disclosure relates to an adhesive sheet for bonding these elements to each other while filling a space between the two elements, and a manufacturing method thereof.

  Epoxy adhesives are widely used for structural bonding because they have excellent heat resistance and high adhesive strength. Commonly used epoxy adhesives are liquid or pasty and have many uses. Moreover, the liquid epoxy adhesive can be manufactured with a simple manufacturing apparatus, and can impart various characteristics. However, liquid epoxy adhesives have many points to be controlled during use, such as viscosity adjustment according to the application, selection of coating method, and management of coating thickness during coating, which may cause problems in workability during use. .

  In order to solve such workability problems, an epoxy adhesive may be formed as a film. The film adhesive generally contains a latent curing agent and is classified as a one-component thermosetting adhesive. Since this thermosetting film adhesive is solid, the thickness can be easily controlled, and an appropriate adhesive layer can be formed by being sandwiched between adherends. However, since the manufacturing method is not simple and the adhesive thickness is also determined, there are limitations on the application.

  However, the film adhesive is superior to the liquid adhesive from the viewpoint of workability, and it is considered that the film adhesive exhibits its superiority in limited joining applications. For example, in the motor of a hybrid car, the coil is fixed to the stator core. FIG. 1 shows a schematic cross-sectional view of a stator core 100 and a coil 110 attached to the stator core 100. The coil is typically bonded to the stator core using a liquid epoxy adhesive. The conventional procedure for bonding the coil to the stator core is, for example, as follows. First, insulating paper is inserted between the coil and the stator core. Next, the liquid adhesive is poured into a gap (clearance) between the coil and the stator core and heated to cure the adhesive. Finally, excess cured adhesive is removed from the stator core. In this case, since the clearance between the coil and the stator core is very small and the adhesive hardly enters the clearance, a large amount of liquid adhesive must be used to completely fill the clearance. Thus, when bonding a coil to a stator core, a complicated process is required, and an adhesive must be used excessively.

  Patent Document 1 (Japanese Patent Laid-Open No. 5-179213) describes “an expandable adhesive comprising a liquid or viscous semi-solid uncured adhesive and an expandable material”.

  Patent Document 2 (Japanese Patent Laid-Open No. 2007-106963) states that “(a) a film-forming resin that is solid at room temperature, (b) a liquid or semi-solid epoxy resin at room temperature, (c) a latent curing agent, (d "A heat-expandable sheet-like adhesive composition characterized in that it is formed by forming a film of a component comprising (a) a thermally expandable capsule and (e) a lubricating fine particle powder".

Japanese Patent Laid-Open No. 5-179213 JP 2007-106963 A

  The present disclosure is capable of bonding these elements with high reliability while filling a space between two elements, such as a coil and a stator core. Provide a method.

  According to one embodiment of the present disclosure, a heat-resistant base material having a first surface and a second surface facing the first surface, and a thermally expandable epoxy formed on the first surface of the heat-resistant base material There is provided a heat-expandable adhesive sheet having a first adhesive layer containing an adhesive and a second adhesive layer containing a heat-expandable epoxy adhesive formed on the second surface of the heat-resistant substrate.

  According to another embodiment of the present disclosure, providing a heat resistant substrate having a first surface and a second surface facing the first surface, (a) an epoxy resin, (b) a latent curing agent, And (c) forming a first adhesive layer comprising a thermally expandable epoxy adhesive comprising a thermally expandable capsule on the first surface (a) an epoxy resin, (b) a latent curing agent, and (c) There is provided a method for producing a thermally expandable adhesive sheet, comprising forming a second adhesive layer including a thermally expandable epoxy adhesive including a thermally expandable capsule on the second surface.

  According to another embodiment of the present disclosure, a method of adhering a first element and a second element, wherein the thermally expandable adhesive sheet is disposed between the first element and the second element. And thermally curing the thermally expandable adhesive sheet to bond the first element and the second element while filling a space between the first element and the second element. A method is provided.

  According to another embodiment of the present disclosure, the first element includes a first element, a second element, and the heat-expandable thermally expandable adhesive sheet, wherein the first element is heat-cured by the heat-expandable adhesive sheet. An article is provided in which a space between the first element and the second element is filled and the first element and the second element are bonded.

  Since the heat-expandable adhesive sheet of the present disclosure includes a heat-resistant substrate, it can be used for various adhesive applications that require heat resistance. In addition, the first adhesive layer and the second adhesive layer of the heat-expandable adhesive sheet of the present disclosure include a heat-expandable epoxy adhesive, and the heat-expandable epoxy adhesive melts and expands when heated. Therefore, when using the thermally expandable adhesive sheet of the present disclosure, the space between the two elements to be bonded is filled with the expanded epoxy adhesive by thermosetting, and at the same time, the two elements are disposed between them. It can adhere | attach via an adhesive sheet. For example, the coil and the stator core can be bonded with high reliability by using the thermally expandable adhesive sheet of the present disclosure. Further, unlike the case where a liquid adhesive is used, the two elements can be bonded with fewer steps and fewer materials, so that productivity and economy can be greatly improved. For example, the process of bonding the coil and the stator core is completed by inserting a thermally expandable adhesive sheet and thermosetting.

  The above description should not be construed as disclosing all embodiments of the present invention and all advantages related to the present invention.

It is a schematic sectional drawing of the stator attached to the stator core and the stator core. It is sectional drawing of the thermally expansible adhesive sheet by one embodiment of this indication. It is the schematic which shows a mode that the thermally expansible adhesive sheet by one embodiment of this indication is bent and inserted in the recessed part of a stator core, and a coil is inserted there. It is sectional drawing of the test piece produced by the overlap shear strength (OLSS) test of the Example.

  Hereinafter, the present invention will be described in more detail for the purpose of illustrating representative embodiments of the present invention, but the present invention is not limited to these embodiments.

  In FIG. 2, sectional drawing of the thermally expansible adhesive sheet of one embodiment of this indication is shown. The heat-expandable adhesive sheet 10 includes a heat-resistant base material 20 having a first surface and a second surface facing the first surface, and a heat-expandable epoxy adhesive formed on the first surface of the heat-resistant base material. The first adhesive layer 30 includes a second adhesive layer 40 formed on the second surface of the heat-resistant base material and including a thermally expandable epoxy adhesive. Since this heat-expandable adhesive sheet contains a heat-resistant substrate, it can be used for various adhesive applications that require heat resistance. Further, when the heat-expandable adhesive sheet is heated to a predetermined temperature, the heat-expandable epoxy adhesive expands to increase the dimension of at least one dimension among the length, width, and thickness of the adhesive sheet. As a result, the space between the two elements to be bonded can be filled with the expanded epoxy adhesive, and at the same time, the two elements can be bonded via an adhesive sheet disposed between them.

  These adhesive layers are advantageously non-tacky (tack free) at the temperature at which the adhesive sheet is used. When the adhesive layer is non-tacky, the handleability and workability of the adhesive sheet can be further improved. For example, when a stator core and a coil are bonded, an adhesive sheet having a non-adhesive adhesive layer can be smoothly inserted into the gap between the stator cores, and the coil formed in the gap that becomes narrower when the adhesive sheet is inserted. It can be inserted more smoothly.

  Each of these adhesive layers may be continuous, or may be discontinuous composed of a plurality of stripes, dots, patterns and the like. Concavities and convexities such as embossing may be formed on the surface of the adhesive layer. Reduce the adhesiveness of the adhesive layer surface by making the adhesive layer discontinuous composed of stripes, dots, patterns, etc., or by forming irregularities such as embosses on the surface of the adhesive layer, or It can be made substantially non-tacky. In the heat-expandable adhesive sheet of the present disclosure, since the heat-expandable epoxy adhesive expands at the time of thermosetting, the discontinuity of the adhesive layer or the unevenness on the surface of the adhesive layer gives the in-plane uniformity of the adhesive force. The impact can be reduced or counteracted.

  The heat-resistant substrate means a substrate having heat resistance necessary for the intended application, and the kind thereof is not particularly limited. The melting temperature of the refractory substrate can generally be about 150 ° C. or higher or about 200 ° C. or higher. The continuous use temperature of the heat-resistant substrate can be about 100 ° C. or higher, or about 150 ° C. or higher when measured according to UL-746B. When the heat resistant substrate is a substrate containing an organic resin, the glass transition point of the organic resin can be about 80 ° C. or higher, about 140 ° C. or higher, or about 200 ° C. or higher.

  Examples of heat-resistant substrates that can be used include polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polyamide resins such as polycarbonate, polyarylate, polyurethane, polyamide, and polyetheramide, polyimide, polyetherimide, Polyimide resins such as polyamideimide, polysulfone resins such as polysulfone and polyethersulfone, polyetherketone resins such as polyetherketone and polyetheretherketone, films of organic resins such as polyphenylene sulfide and modified polyphenylene oxide, cellulose fibers Organic fibers such as polyester fiber, aramid fiber, and liquid crystal polymer fiber, or inorganic fibers such as glass fiber, metal fiber, and carbon fiber No woven or nonwoven substrates, glass plates, films of inorganic material such as a metal foil, sheet or plate, and the like laminates thereof and the like. A composite such as glass fiber reinforced plastic (GFRP) can also be used. For example, as a heat-resistant substrate, a woven fabric substrate or a nonwoven fabric substrate containing glass fibers, a glass substrate containing a glass fiber composite, a glass plate, a polyamide resin film, or a polyimide resin film is advantageously used. be able to. The adhesion between the heat-resistant substrate and the adhesive layer can be improved by subjecting the heat-resistant substrate to corona treatment or providing a primer layer.

  The heat resistant substrate may have insulating properties. The insulating heat-resistant substrate can have a dielectric breakdown voltage of about 50 kV / mm or more, about 100 kV / mm or more, or about 200 kV / mm or more when measured according to JIS C2151. It is advantageous to use a film of polyamide-based resin, polyimide-based resin, polysulfone-based resin, or polyetherketone-based resin as a heat-resistant substrate having insulating properties, and has excellent adhesiveness with an epoxy resin It is particularly advantageous to use polyetherimide films.

  The heat resistant substrate may have resilience. The resilience means a property that resists a force to bend the substrate. When a heat-resistant substrate having such a resilience is used, shape recoverability can be imparted to the adhesive sheet. For example, when such an adhesive sheet is inserted by being bent into a narrow gap, the adhesive sheet can be pressed and fixed to the inner wall of the gap by using the force generated by the shape recoverability of the adhesive sheet. As the heat-resistant substrate having resilience, for example, a woven fabric or a nonwoven fabric containing glass fibers can be used. In addition, when the nonwoven fabric containing glass fiber is used, the adhesiveness of the adhesive layer surface will fall, and the handleability and workability | operativity of an adhesive sheet may be able to be improved.

  The thickness of the heat resistant substrate can be, for example, about 10 μm or more, about 20 μm or more, or about 50 μm or more, about 5 mm or less, about 2 mm or less, or about 1 mm or less. In an application where an adhesive sheet is inserted into a narrow gap, such as adhesion between a stator core and a coil, it is desirable that the thickness be about 10 μm or more, or about 20 μm or more, about 500 μm or less, or about 300 μm or less.

  The first adhesive layer formed on the first surface of the heat-resistant substrate and the second adhesive layer formed on the second surface of the substrate include a thermally expandable epoxy adhesive. The thermally expandable epoxy adhesive contained in the first adhesive layer and the thermally expandable epoxy adhesive contained in the second adhesive layer may be the same or different. The thermally expandable epoxy adhesive can include (a) an epoxy resin, (b) a latent curing agent, and (c) a thermally expandable capsule. The latent curing agent can increase the adhesive force of the adhesive layer by curing the epoxy adhesive by heating. Thermally expandable capsules promote the expansion of the epoxy adhesive melted by heating. The thickness of the first adhesive layer and the second adhesive layer can be, for example, about 1 μm or more, about 5 μm or more, or about 10 μm or more, about 5 mm or less, about 2 mm or less, or about 1 mm or less. In applications where an adhesive sheet is inserted into a narrow gap, such as adhesion between a stator core and a coil, it is desirable that the thickness be about 1 μm or more, or about 5 μm or more, about 200 μm or less, or about 100 μm or less, respectively.

  The physical properties of the epoxy resin used, such as softening point, melt viscosity, glass transition point (Tg), storage elastic modulus, etc., are the adhesiveness and flexibility of the adhesive layer, fluidity during heating, and adhesive strength after curing. It is considered to be closely related to strength. For example, the softening point of the epoxy resin, the activation temperature of the latent curing agent described later, and the expansion start temperature of the thermally expandable capsule described later are closely related to each other. More specifically, in order to effectively exert the function of the thermally expandable adhesive sheet of the present disclosure, the softening point of the epoxy resin is equal to or lower than the activation temperature of the latent curing agent, and the thermally expandable capsule Advantageously, it is below the expansion start temperature. If the softening point of the epoxy resin is lower than the activation temperature of the latent curing agent, if the manufacturing process of the heat-expandable adhesive sheet includes a melt coating or a solution coating, the epoxy resin may be used during the coating process and the subsequent drying process. It is possible to prevent the resin from gelling. If the softening point of the epoxy resin is equal to or lower than the expansion start temperature of the thermally expandable capsule, the resin exhibits fluidity at the temperature at which the thermally expandable capsule expands, so that the thermally expandable epoxy adhesive can be sufficiently expanded. . The softening point of the epoxy resin is measured using a ring and ball softening point test method defined in JIS K 2207.

  As the epoxy resin, a mixture of a plurality of epoxy resins may be used. When a mixture of a plurality of epoxy resins is used, the physical properties of the epoxy resin such as softening point, melt viscosity, glass transition point (Tg), storage elastic modulus and the like can be easily and finely adjusted. For example, an epoxy resin having a relatively low softening point or a liquid epoxy resin contributes to improving the fluidity of the adhesive layer when heated and the flexibility before and after curing. Liquid epoxy resins can also be used to predisperse powdered or granular latent hardeners and thermally expandable capsules therein and mix uniformly with other epoxy resins. The use of a semi-solid or solid epoxy resin having a relatively high softening point can reduce the tackiness of the adhesive layer surface or make the adhesive layer surface non-tacky.

  Usable epoxy resins include bisphenol A type epoxy resins, dimer acid-modified bisphenol A type epoxy resins, bisphenol epoxy resins such as bisphenol F type epoxy resins, epoxy resins having an aliphatic skeleton such as hexanediol diglycidyl ether, p- Glycidylamine type epoxy resins such as aminophenol triglycidyl ether, novolac epoxy resins such as phenol novolac epoxy resins and cresol novolac epoxy resins, brominated epoxy resins, alicyclic epoxy resins, and mixtures thereof can be used. It is not limited. The epoxy resin may further contain a phenoxy resin (polyhydroxy polyether synthesized from bisphenols and epichlorohydrin) as a thermoplastic component. When a phenoxy resin is added, the film formability of the thermally expandable epoxy adhesive may be improved. For applications in which an article bonded using the thermally expandable adhesive sheet of the present disclosure is used at a high temperature (for example, about 200 ° C.), when a phenol novolac epoxy resin and / or a cresol novolac epoxy resin is used as a base resin, Since the glass transition point (Tg) of the cured adhesive layer is increased, a stable adhesive force can be exhibited even at high temperatures.

  Crystalline epoxy resin can be used as the solid epoxy resin. Crystalline epoxy resin is a non-sticky solid at room temperature, whereas the melt viscosity is greatly reduced above the melting point, and therefore acts as a reactive diluent above the melting point. For this reason, when the crystalline epoxy resin is included in the adhesive layer, the fluidity of the adhesive layer when heated can be further increased, which advantageously affects the thermal expansion of the adhesive layer. Further, since it is a non-tacky solid at room temperature, it is useful for reducing the tackiness of the surface of the adhesive layer or making the surface of the adhesive layer non-tacky. When the adhesive layer is formed by the melt coating method, the melt viscosity of the epoxy resin can be lowered to increase the speed of the melt coating by heating to the melting point of the crystalline epoxy resin or higher.

  The number average molecular weight of the epoxy resin is generally about 100 or more, or about 300 or more in terms of standard polystyrene, and can be about 100,000 or less, or about 60000 or less. The epoxy equivalent weight of the epoxy resin can generally be about 50 g / equivalent or more, or about 80 g / equivalent or more, about 50000 g / equivalent or less, or about 30000 g / equivalent or less. The epoxy resin is about 10 parts by weight or more, about 15 parts by weight or more, or about 20 parts by weight or more, about 95 parts by weight or less, about 90 parts by weight or less, or about 90 parts by weight, based on 100 parts by weight of the thermally expandable epoxy adhesive. It can be used in an amount of 85 parts by mass or less.

  The latent curing agent is a curing agent that has no activity to cure the epoxy resin at room temperature but can be activated by heating to cure the epoxy adhesive. For example, a conventionally known fine-grain latent curing agent is insoluble in an epoxy resin at room temperature, and can be solubilized and cured by heating. Conventional latent curing agents known as latent curing agents such as dicyandiamide and its derivatives, hydrazide compounds, boron trifluoride-amine complexes, finely divided imidazole compounds at room temperature, reaction of amine compounds with epoxy compounds A product (amine-epoxy adduct), a reaction product of an amine compound with an isocyanate compound or a urea compound (urea adduct), and the like can be used. A combination of two or more latent hardeners may be used. The latent curing agent is about 0.5 parts by mass or more, about 1 part by mass or more, about 2 parts by mass or more, or about 30 parts by mass or less, about 20 parts by mass or less, or about 100 parts by mass of epoxy resin. It can be used in an amount of 15 parts by mass or less. A combination of dicyandiamide and an amine-epoxy adduct (for example, trade name PN-50, manufactured by Ajinomoto Fine Techno Co., Ltd.) is particularly advantageous because it exhibits good storage stability at room temperature and has a suitable activation temperature. it can.

  As described above, the activation temperature of the latent curing agent is advantageously selected so that the softening point of the epoxy resin is equal to or lower than the activation temperature of the latent curing agent. Here, the activation temperature of the latent curing agent was DSC (Differential Scanning Calorimeter), and the temperature was raised from room temperature to 10 ° C./min using a mixture of the used epoxy resin and the latent curing agent as a sample. In the DSC curve obtained sometimes, it is defined as the temperature at the point where the tangent at the low temperature side where the calorific value is ½ of the peak intersects the baseline. The activation temperature of the latent curing agent can be selected from the range of, for example, about 80 ° C. or higher, or about 120 ° C. or higher, about 180 ° C. or lower, or about 160 ° C. or lower.

  The heat-expandable capsule is a microcapsule in which a thermoplastic resin having gas barrier properties is used as a shell, and a heat-expanding agent is included inside the shell. When the heat-expandable capsule is heated, the thermoplastic resin in the shell is softened, and the volume of the heat-expandable agent is increased, so that the capsule expands. For example, a low-boiling substance is used as the thermal expansion agent, and vaporization of the low-boiling substance is used for expansion of the capsule. The expansion start temperature of the thermally expandable capsule is desirably lower than the activation temperature of the latent curing agent. By doing in this way, it can prevent or control more effectively that an epoxy adhesive hardens before expanding. Further, as described above, the expansion start temperature of the thermally expandable capsule is advantageously selected so that the softening point of the epoxy resin is equal to or lower than the expansion start temperature of the thermally expandable capsule. Here, the expansion start temperature of the thermally expandable capsule is a temperature at which the volume change of the thermally expandable capsule occurs. The expansion start temperature of the thermally expandable capsule can be selected from the range of, for example, about 70 ° C. or higher, or about 100 ° C. or higher, about 200 ° C. or lower, or about 180 ° C. or lower.

  The amount and volume expansion coefficient of the thermally expandable capsule can be appropriately determined according to the strength and adhesive force required for the cured adhesive layer, the expansion coefficient required for the adhesive sheet, and the like. For example, the thermally expandable capsule is about 0.1 parts by weight or more, about 0.5 parts by weight or more, about 1 part by weight or more, about 50 parts by weight or less, based on 100 parts by weight of the thermally expandable epoxy adhesive. It can be used in an amount of 30 parts by weight or less, or about 20 parts by weight or less. The volume expansion coefficient of the thermally expandable capsule can be, for example, about 2 times or more, or about 5 times or more, about 100 times or less, or about 50 times or less.

  The heat-expandable epoxy adhesive includes, as an optional component, a phenolic antioxidant, an antioxidant such as a sulfur-based antioxidant, a reinforcing agent such as a core-shell type reinforcing agent, and a silane coupling agent such as an epoxy-modified alkoxysilane. Further, a thixotropic agent such as fumed silica and an inorganic filler such as alumina and boron nitride may be further included for the purpose of improving thermal conductivity and / or insulation.

  The thickness of the heat-expandable adhesive sheet including the heat-resistant substrate, the first adhesive layer and the second adhesive layer is, for example, about 10 μm or more, about 30 μm or more, or about 70 μm or more, about 15 mm or less, about 10 mm or less, or It can be about 5 mm or less. In an application where an adhesive sheet is inserted into a narrow gap, such as adhesion between a stator core and a coil, it is desirable that the thickness be about 10 μm or more, or about 30 μm or more, about 1 mm or less, or about 500 μm or less. The thermally expandable sheet may include a liner on the first adhesive layer and / or the second adhesive layer.

  The heat-expandable adhesive sheet of the present disclosure uses the heat-expandable epoxy adhesive composition containing the epoxy resin, the latent curing agent, and the heat-expandable capsule, and the optional component and / or solvent as necessary. Thus, the first adhesive layer can be formed on the first surface of the heat-resistant substrate, and the second adhesive layer can be formed on the second surface of the heat-resistant substrate. The heat-expandable epoxy adhesive composition can be applied onto a heat-resistant substrate by a conventionally known method such as a solution coating method, a melt coating method, a melt extrusion method, or a rolling method. The melt coating method can be carried out without a solvent, and does not require a solvent removal step, processing equipment, etc., and is advantageous in terms of productivity and economy. When using the melt coating method, it is advantageous that the epoxy resin comprises a crystalline epoxy resin. In this case, since the melt viscosity of the epoxy resin can be lowered by heating above the melting point of the crystalline epoxy resin, the speed of the melt coating can be increased. The adhesive layer can also be applied onto the heat resistant substrate by applying the thermally expandable epoxy adhesive composition on the liner to form an adhesive layer and laminating the heat resistant substrate thereon.

  A thermally expansible epoxy adhesive composition can be produced in the following procedures, for example. A latent curing agent and a thermally expandable capsule are dispersed in a liquid epoxy resin to prepare a liquid epoxy resin mixture. After the remaining epoxy resin and optional components are mixed, the liquid epoxy resin mixture is added and mixed there. The resulting mixture is applied to the liner using a melt coating process to form an adhesive layer. Next, the first adhesive layer is applied on the first surface of the substrate by laminating a heat resistant substrate on the adhesive layer formed on the liner. In the same manner, a second adhesive layer is applied on the second surface of the substrate.

  The thermally expandable adhesive sheet of the present disclosure can be used in various double-sided adhesive applications that require filling the space between two elements. For example, as shown in FIG. 3, the thermally expandable adhesive sheet 10 is inserted into the two gaps 102 of the stator core 100 by bending and inserted into the coil 110, and then, for example, at 120 to 180 ° C. for 10 minutes to 2 hours. The coil 110 can be bonded to the stator core 100 by heating.

  In this example, the materials shown in Table 1 below were used.

<Overlap shear strength (OLSS) test>
FIG. 4 shows a cross section of a test piece prepared by an overlap shear strength (OLSS) test. Heat is applied so that the first adhesive layer 30 is in contact with one of the steel plates inside the rectangular parallelepiped space defined by the two SPCC-SB steel plates 50 and the spacers 60 that are surface-treated by wiping with methyl ethyl ketone (MEK). An expandable adhesive sheet 10 was disposed. The steel plate had a length of 50 mm, a width of 25 mm, and a thickness of 1.6 mm, and the adhesive sheet was a rectangle of 12.5 mm × 25 mm. The thickness of the spacer was adjusted so that the thickness of the cured adhesive sheet was about 2.5 times the initial thickness. Next, it heated at 160 degreeC for 30 minute (s), the epoxy adhesive of the adhesive sheet was fuse | melted, expanded, and hardened, and the test piece of the OLSS test was produced. The shear strength when the two steel plates of the test piece were pulled in opposite directions at 25 ° C. and a tensile speed of 5 mm / min was defined as OLSS (MPa).

<Preparation of thermally expandable adhesive sheet>
The heat-expandable adhesive sheet was produced as follows. A liquid epoxy resin mixture was prepared by dispersing the latent curing agent and thermally expandable capsules in a liquid epoxy resin (YD-128 or MY0510). The remaining epoxy resin melted at 120 ° C. was mixed with the remaining components such as the core-shell toughening agent at 120 ° C. to prepare a molten epoxy resin mixture. The mixture obtained by mixing the liquid epoxy resin mixture and the molten epoxy resin mixture at 80 ° C. was applied to a liner (SLB-50WD) at 80 ° C. using a melt coating method to form an adhesive layer. The thickness of the adhesive layer after drying was 90 μm. Next, the first adhesive layer was applied onto the substrate by laminating a substrate (glass nonwoven fabric, polyetherimide film, or nylon nonwoven fabric) at 80 ° C. on the adhesive layer formed on the liner. A second adhesive layer was applied on the substrate by forming an adhesive layer in the same manner and laminating the resulting adhesive layer on the opposite side of the substrate. In this way, a thermally expandable adhesive sheet having a thickness of 250 μm was produced.

  The presence or absence of tackiness of the obtained thermally expandable adhesive sheet was judged by tactile sensation. Also, the coefficient of expansion of the thermally expandable adhesive sheet when heated at 160 ° C. for 30 minutes (sheet thickness after thermosetting / sheet thickness before thermosetting), and thermosetting at 160 ° C. for 30 minutes or 180 ° C. for 30 minutes The OLSS was evaluated. The composition and results are shown in Table 2 below.

Example 5 and Reference Example 1
When a crystalline epoxy resin (YSLV80XY) is mixed with an epoxy resin, the melt viscosity of the epoxy resin during heating can be effectively reduced. An example is shown in Table 3 below.

DESCRIPTION OF SYMBOLS 10 Thermal expansion adhesive sheet 20 Heat resistant base material 30 1st contact bonding layer 40 2nd contact bonding layer 50 Steel plate 60 Spacer 100 Stator core 102 Crevice 110 Coil
Some of the embodiments described herein are described in items [1]-[7].
[Item 1]
A heat-resistant substrate having a first surface and a second surface facing the first surface;
A first adhesive layer comprising a thermally expandable epoxy adhesive formed on the first surface of the heat resistant substrate;
A second adhesive layer comprising a thermally expandable epoxy adhesive formed on the second surface of the heat-resistant substrate;
A heat-expandable adhesive sheet.
[Item 2]
A thermally expandable epoxy adhesive contained in the first adhesive layer and the second adhesive layer,
(A) epoxy resin,
(B) a latent curing agent, and
(C) Thermally expandable capsule
The heat-expandable adhesive sheet according to item 1, comprising:
[Item 3]
Item 3. The thermally expandable adhesive sheet according to item 1 or 2, wherein the epoxy resin has a softening point not higher than an activation temperature of the latent hardener and not higher than an expansion start temperature of the thermally expandable capsule.
[Item 4]
The heat-expandable adhesive sheet according to any one of items 1 to 3, wherein the heat-resistant substrate is selected from the group consisting of a glass substrate, a polyamide resin film, and a polyimide resin film.
[Item 5]
Providing a heat-resistant substrate having a first surface and a second surface facing the first surface;
Forming on the first surface a first adhesive layer comprising (a) an epoxy resin, (b) a latent curing agent, and (c) a thermally expandable epoxy adhesive comprising a thermally expandable capsule,
Forming on the second surface a second adhesive layer comprising (a) an epoxy resin, (b) a latent curing agent, and (c) a thermally expandable epoxy adhesive comprising a thermally expandable capsule.
A method for producing a thermally expandable adhesive sheet.
[Item 6]
A method of bonding a first element and a second element, comprising:
The thermally expandable adhesive sheet according to any one of items 1 to 4 is disposed between the first element and the second element,
Heat curing the thermally expandable adhesive sheet to bond the first element and the second element while filling a space between the first element and the second element. .
[Item 7]
A first element, a second element, and the thermally expandable adhesive sheet according to any one of items 1 to 4, wherein the first element is thermally cured by the thermally expandable adhesive sheet. And the second element is filled, and the first element and the second element are bonded.

Claims (8)

A heat-resistant substrate having a first surface and a second surface facing the first surface;
A single thermally expandable first adhesive layer comprising a thermally expandable epoxy adhesive containing a crystalline epoxy resin formed on the first surface of the heat resistant substrate;
A heat-expandable adhesive sheet having a single heat-expandable second adhesive layer containing a heat-expandable epoxy adhesive containing a crystalline epoxy resin, formed on the second surface of the heat-resistant substrate. A thermally expandable epoxy adhesive contained in the first adhesive layer and the second adhesive layer,
(A) Epoxy resin (excluding crystalline epoxy resin),
(B) a latent curing agent,
The thermally expandable adhesive sheet according to claim 1, comprising (c) a thermally expandable capsule, and (d) a crystalline epoxy resin.   The thermally expandable adhesive sheet according to claim 2, wherein a softening point of the epoxy resin is not higher than an activation temperature of the latent hardener and not higher than an expansion start temperature of the thermally expandable capsule.   The heat-expandable adhesive sheet according to any one of claims 1 to 3, wherein the heat-resistant substrate is selected from the group consisting of a glass substrate, a polyamide resin film, and a polyimide resin film.   The thermally expandable adhesive sheet according to any one of claims 1 to 4, wherein at least one adhesive layer is discontinuous or has irregularities on the surface. Providing a heat-resistant substrate having a first surface and a second surface facing the first surface;
(A) including epoxy resin (excluding crystalline epoxy resin), (b) latent curing agent, (c) thermally expandable capsule, and (d) thermally expandable epoxy adhesive containing crystalline epoxy resin Forming a single thermally expandable first adhesive layer on the first surface;
(A) including epoxy resin (excluding crystalline epoxy resin), (b) latent curing agent, (c) thermally expandable capsule, and (d) thermally expandable epoxy adhesive containing crystalline epoxy resin A method for producing a thermally expandable adhesive sheet, comprising forming a single thermally expandable second adhesive layer on the second surface. A method of bonding a first element and a second element, comprising:
The thermally expandable adhesive sheet according to any one of claims 1 to 5 is disposed between the first element and the second element,
Heat curing the thermally expandable adhesive sheet to bond the first element and the second element while filling a space between the first element and the second element. .   A first element, a second element, and a heat-expandable adhesive sheet according to any one of claims 1 to 5, wherein the first element is heat-cured by the heat-expandable adhesive sheet. An article in which a space between an element and the second element is filled and the first element and the second element are bonded.

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