Heat-expandable adhesive sheet

Abstract

To provide a heat-expandable adhesive sheet capable of sufficiently inhibiting separation between a base material and a heat-expandable layer under high-temperature environments during heating when expanding the heat-expandable layer and after thermal expansion.SOLUTION: A heat-expandable adhesive sheet includes a base material, an intermediate layer laminated on the base material, and a heat-expandable layer laminated on a surface of the intermediate layer on a side opposite to the base material. A broken interface in the case of applying shear force capable of breaking the heat-expandable adhesive sheet in a shear strength test at 200°C is present in the heat-expandable layer.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a thermal expansion adhesive sheet.

Background Art

[0002] In a thermal expansion adhesive sheet provided with a thermal expansion layer having adhesiveness on the surface of a base material, in order to suppress the peeling of the thermal expansion layer from the base material, it is conceivable to provide an intermediate layer that improves the adhesiveness between the base material and the thermal expansion layer (Patent Documents 1 and 2).

[0003] However, at present, a thermal expansion adhesive sheet that can sufficiently suppress the peeling between the base material and the thermal expansion layer not only during heating when expanding the thermal expansion layer but also in a high-temperature atmosphere after expansion and adhesion has not yet been provided.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention has been made in view of the above-described problems, and a main object thereof is to provide a thermal expansion adhesive sheet that can sufficiently suppress the peeling between the base material and the thermal expansion layer during heating and in a high-temperature atmosphere after expansion and adhesion.

Means for Solving the Problems

[0006] That is, the thermal expansion adhesive sheet according to the present invention is as follows. [1] A thermal expansion adhesive sheet comprising a base material, an intermediate layer laminated on the base material, and a thermal expansion layer laminated on the surface of the intermediate layer opposite to the base material, wherein the fracture interface when a shearing force capable of breaking the thermal expansion adhesive sheet is applied in a shear strength test at 200°C is present within the thermal expansion layer. The thermal expansion adhesive sheet is characterized by this. [2] The thermal expansion adhesive sheet according to [1], wherein the intermediate layer contains a resin having a carboxyl group, the acid value of the resin having a carboxyl group is 5 or more, and the thermal expansion layer contains a resin containing an epoxy group and a thermal expansion agent. [3] The thermal expansion adhesive sheet according to [1] or [2], wherein the thickness of the intermediate layer is 0.5 μm or more and 4 μm or less. [4] The thermal expansion adhesive sheet according to any one of [1] to [3], wherein the thermal expansion layer contains a curing agent for the epoxy resin, the curing agent is an amine-based resin, and the equivalent ratio of the curing agent to the epoxy resin (equivalent of the curing agent / epoxy equivalent) is 0.9 or less. [5] The thermal expansion adhesive sheet according to any one of [1] to [4], having a coefficient of kinetic friction of 0.6 or less. [6] The thermal expansion adhesive sheet according to any one of [1] to [5], wherein the thermal expansion start temperature of the thermal expansion agent contained in the thermal expansion layer is 100°C or more and 150°C or less. [7] A method for manufacturing a thermal expansion adhesive sheet comprising a base material, an intermediate layer laminated on the base material, and a thermal expansion layer laminated on the surface of the intermediate layer opposite to the base material, characterized in that the thermal expansion layer is laminated on the intermediate layer before performing a heating step for crosslinking the intermediate layer.

Advantages of the Invention

[0007] According to the present invention, it is possible to provide a thermal expansion adhesive sheet capable of sufficiently suppressing peeling between the base material and the thermal expansion layer during heating when expanding the thermal expansion layer and in a high-temperature atmosphere after expansion and adhesion.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0009] Hereinafter, a thermal expansion sheet according to an embodiment of the present invention will be described. <Thermal Expansion Adhesive Sheet> FIG. 1 is a schematic cross-sectional view showing the configuration of the thermal expansion adhesive sheet 1 according to this embodiment. The thermal expansion adhesive sheet 1 according to this embodiment can be used in various fields, for example, as a conductive material sheet for electronic devices or electronic devices, an insulating sheet for electronic devices or electronic devices, and the like. This thermal expansion adhesive sheet 1 is, for example, arranged inside a gap and heated at a high temperature such as 120°C or higher and 250°C or lower to bond two adherend surfaces facing each other with the gap in between. It includes a base material 10, thermal expansion layers 20 formed on both surfaces of the base material 10, and an intermediate layer 30 formed between the base material 10 and the thermal expansion layers 20.

[0010] When a shear force capable of breaking the thermal expansion adhesive sheet 1 is applied in the shear strength test at 200°C for the thermal expansion adhesive sheet 1 according to this embodiment, the fracture interface exists within the thermal expansion layer 20. By making the fracture interface exist within the thermal expansion layer 20, the adhesive strength between the base material 10 and the intermediate layer 30, and between the intermediate layer 30 and the thermal expansion layer 20 can be stabilized, and peeling of the thermal expansion layer 20 from the base material 10 after the high-temperature durability test (for example, 200°C for 500 hours) can be suppressed. In addition, the shear strength test is performed, for example, by sandwiching two sheets of the thermal expansion adhesive sheet 1 between two support plates, heating and expanding them, firmly adhering them to the two support plates, using this as a sample, and measuring the shear adhesion force when the two support plates of this sample are pulled in opposite directions along the surface direction of the thermal expansion adhesive sheet 1.

[0011] The shear adhesion force (shear strength (adhesion strength) based on JIS K6850) at which the thermal expansion adhesive sheet 1 after heating and expansion can be broken is preferably, for example, 2.0 MPa or more, more preferably 2.5 MPa or more, and even more preferably 3.0 MPa or more at 23°C. Further, the shear adhesion force at 200°C is preferably 0.4 MPa or more, more preferably 0.45 MPa or more, and particularly preferably 0.5 MPa or more. If the shear adhesion force at which shear failure is possible is 0.4 MPa or more at 200°C and the failure interface at that time exists within the thermal expansion layer 20, it is preferable because the adhesion force at the interfaces between the base material 10, the intermediate layer 30, and the intermediate layer 30 and the thermal expansion layer 20 is sufficiently high even after heating and expansion in a high-temperature environment. The high-temperature environment here refers to, for example, an environment of 100°C or more and 250°C or less. For example, when it is used for applications such as inserting and adhering between a stator core (also referred to as the first adherend) and a coil (also referred to as the second adherend) as described later, cases where it is constantly exposed to a temperature of 120°C or more and 160°C or less or instantaneously exposed to a high temperature of 170°C or more and 220°C or less due to heat generation by a motor, etc., can be cited.

[0012] The thermal expansion adhesive sheet 1 according to this embodiment preferably has high electrical insulation after being heated and expanded. The dielectric breakdown voltage of the thermal expansion adhesive sheet 1 based on JIS C 2107 is preferably, for example, 3 kV or more, and more preferably 5 kV or more. Further, the thermal conductivity of the thermal expansion adhesive sheet 1 after being heated and expanded is preferably, for example, 0.1 W / mK or more, and more preferably 0.15 W / mK or more. Note that these electrical insulation properties can be adjusted according to the type of base material used in the production of the thermal expansion adhesive sheet, the type of resin contained in the thermal expansion layer and the intermediate layer. Also, the electrical insulation can be improved by increasing the thickness of the thermal expansion adhesive sheet. Further, the thermal conductivity can be adjusted according to the type and content of the filler contained in the thermal expansion layer. Hereinafter, preferred configuration examples and production examples of the thermal expansion adhesive sheet 1 having such properties will be described.

[0013] <<Base material>> The base material 10 functions as a support material for supporting the thermal expansion layer 20.

[0014] Specifically, the base material 10 is preferably in the form of a sheet, and may have a single-layer structure or a laminated structure. Further, the base material 10 may or may not have a porous structure inside. The thickness of the base material 10 is preferably, for example, 1 μm or more and 125 μm or less, more preferably 10 μm or more and 75 μm or less, and particularly preferably 20 μm or more and 50 μm or less. For example, when the thermal expansion adhesive sheet 1 according to this embodiment is inserted into a motor slot and used, by giving the base material 10 a certain thickness, it is possible to suppress the thermal expansion adhesive sheet 1 from buckling when inserted into the motor slot. Also, by not making the thickness of the base material 10 too large, a sufficient winding space factor of the coil can be ensured. For these reasons as well, it is preferable to set the thickness of the base material 10 within the range described above.

[0015] The material of the base material 10 is not particularly limited and may be either an inorganic material or an organic material. For example, when electrical conductivity is required for the thermal expansion adhesive sheet 1, a metal film can be used, and when electrical insulation is required for the thermal expansion adhesive sheet 1, a resin film can be used.

[0016] The metal film is not particularly limited, and for example, copper foil and aluminum foil can be used. The thickness of the metal film is, for example, 1 μm or more and 100 μm or less, preferably 10 μm or more and 70 μm or less, and more preferably 15 μm or more and 50 μm or less. When a metal film is used as the material of the base material 10, the thermal conductivity of the thermal expansion adhesive sheet 1 can be increased compared to the case where an organic material is used.

[0017] Examples of the resin contained in the resin film include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyesters; polycarbonate; polyarylate; polyurethane; polyamide resins such as polyamide and polyetheramide; polyimide resins such as polyimide, polyetherimide, and polyamideimide; polysulfone resins such as polysulfone and polyethersulfone; polyether ketone resins such as polyether ketone and polyether ether ketone; polyphenylene sulfide (PPS); and modified polyphenylene oxide. The glass transition temperature of the resin is preferably, for example, 80°C or higher, and may be 140°C or higher or 200°C or higher. Also, a liquid crystal polymer (LCP) may be used as the resin.

[0018] In this embodiment, the base material 10 preferably has electrical insulation properties and preferably contains polyimide (PI) or polyethylene naphthalate (PEN). Polyimide and polyethylene naphthalate have high heat resistance and are suitable when the thermal expansion adhesive sheet 1 is thermally expanded and foam-cured by heating. Also, polyimide and polyethylene naphthalate are preferably highly insulating, for example, because the members can be insulated from each other by the thermally expanded adhesive sheet 1 after foam curing.

[0019] <<Thermal expansion layer>> The thermal expansion layer 20 is a layer that expands upon heating and exhibits adhesiveness. In this embodiment, it is formed on both sides of the base material 10 and forms the outermost surface of the thermally expanded adhesive sheet 1. The thermal expansion layer 20 may be a continuous layer that continuously covers the surfaces of the base material and the intermediate layer, or may be a discontinuous layer composed of a plurality of islands provided on the surface of the base material or the intermediate layer. Examples of the discontinuous layer include patterns such as stripes and dots. Also, the surface of the thermal expansion layer 20 may have an uneven shape such as an emboss.

[0020] The surface of the thermal expansion layer 20 may have adhesiveness to the extent that it can be temporarily fixed to the adherend, or the thermal expansion layer 20 before thermal expansion may be non-adhesive (tack-free). In the thermally expanded adhesive sheet 1 according to this embodiment, the coefficient of kinetic friction of the outer surface of the thermal expansion layer 20 (that is, the outermost surface of the thermally expanded adhesive sheet) is preferably, for example, 0.60 or less, more preferably 0.55 or less, and even more preferably 0.50 or less. Further, the coefficient of kinetic friction is preferably, for example, 0.15 or more. By making the thermally expanded adhesive sheet 1 have a coefficient of kinetic friction of 0.60 or less on the surface, for example, it is possible to obtain a thermally expanded adhesive sheet 1 that is easy to insert into the gaps between members such as motor slots and has good usability.

[0021] When the thermal expansion layers 20 are disposed on both surfaces of the base material 10 as in the thermal expansion adhesive sheet 1 according to the present embodiment, it is sufficient that the coefficient of kinetic friction of the outer surface of at least one of the two thermal expansion layers 20 is within the above range. Among them, it is preferable that the coefficients of kinetic friction of the outer surfaces of both of the two thermal expansion layers 20 are within the above range. The coefficient of kinetic friction of the outer surface of the thermal expansion layer 20 can be determined in accordance with JIS K7125. The coefficient of kinetic friction of the outer surface of the thermal expansion adhesive sheet can be adjusted, for example, by reducing the contact area with the adherend, such as providing irregularities on the surface of the outermost layer. Also, since the coefficient of kinetic friction tends to be small when using a resin having a high elastic modulus as the resin contained in the outermost layer, it can also be adjusted by the resin composition of the outermost layer.

[0022] When the coefficient of kinetic friction of the outer surface of the thermal expansion layer 20 is 0.60 or less, the slipperiness and insertability can be further improved. For example, when the thermal expansion adhesive sheet 1 is disposed between two members to bond the two members, the thermal expansion adhesive sheet 1 can be smoothly inserted into the gap between these members, or after the thermal expansion adhesive sheet 1 is disposed on one member, the other member can be smoothly inserted into the gap. Specific applications include, for example, the case of manufacturing a motor by bonding a stator core and a coil. As described above, for a thermal expansion adhesive sheet in which the coefficient of kinetic friction of the outer surface of the thermal expansion layer 20 is 0.60 or less, it can be smoothly inserted into the gap of the stator core, and the coil can be more smoothly inserted into the gap that becomes narrower after the adhesive sheet is inserted.

[0023] Further, in the thermal expansion layer 20 according to the present embodiment, in the expansion and curing process thereof, it is preferable that there is a minimum viscosity temperature at which the viscosity of the thermosetting resin is the lowest in the temperature range from the thermal expansion start temperature of the thermal expansion agent to the curing active temperature in the curing behavior. By using the thermal expansion adhesive sheet 1 having such properties, the resin can be cured after the thermal expansion layer is sufficiently expanded, so that the expansion rate and adhesiveness of the entire thermal expansion adhesive sheet 1 can be made optimal, which is preferable. The minimum viscosity temperature at which the viscosity of the thermosetting resin becomes the lowest can be determined, for example, from the relationship between the temperature measured by a viscoelasticity measuring device and the melt viscosity (complex viscosity) of the resin sample, as the temperature indicating the off-peak of the complex viscosity curve.

[0024] As a specific example of the thermal expansion layer 20 according to the present embodiment, those containing a thermosetting resin, a curing agent, and a thermal expansion agent can be mentioned. Examples of the thermosetting resin include epoxy resins. Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, hindered tolylene type epoxy resin, biphenyl type epoxy resin, alicyclic epoxy resin, triphenylmethane type epoxy resin, 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 epoxy resins obtained by various modifications of these. These can be used alone or in combination of multiple types.

[0025] The content of the thermosetting resin in the thermal expansion layer 20 is preferably 20 wt% or more and 80 wt% or less, more preferably 30 wt% or more and 70 wt% or less, and particularly preferably 40 wt% or more and 60 wt% or less.

[0026] As the curing agent, any agent that can cure the above-mentioned thermosetting resin can be used. For example, amide-based curing agents such as dicyandiamide and aliphatic polyamide; amine-based curing agents such as diaminodiphenylmethane, metaphenylenediamine, ammonia, triethylamine, and diethylamine; phenol-based curing agents such as bisphenol A, bisphenol F, phenol novolac resin, cresol novolac resin, and p-xylene novolac resin; acid anhydride-based curing agents, etc. can be widely used.

[0027] Any of the above-mentioned curing agents can be used without problems, and the content is not particularly limited. Among these, it is particularly preferable that the curing agent contains an amide-based curing agent, and the equivalent ratio (C / E) of a functional group (E) such as an epoxy group possessed by the thermosetting resin and a functional group (C) such as a carboxyl group capable of reacting with the functional group (E) possessed by the curing agent is 0.6 or more and 0.9 or less. By setting the equivalent ratio to 0.6 or more, a sufficient curing reaction can occur in the thermal expansion layer 20, and the strength of the thermal expansion layer 20 can be sufficiently increased. Further, by setting the equivalent ratio to 0.9 or less, a decrease in adhesive strength due to an excess of the curing agent is suppressed, and an excess epoxy resin that has not reacted with the curing agent is left to cause a crosslinking reaction between this epoxy resin and a resin having, for example, a carboxyl group contained in the intermediate layer 30, so that the adhesiveness at the interface between the intermediate layer 30 and the thermal expansion layer 20 can be ensured, which is preferable.

[0028] Depending on the combination of the thermosetting resin and the curing agent used, the suitable content of each component varies. However, in order to achieve the equivalent ratio as described above, the content of the curing agent in the thermal expansion layer is preferably 1% by mass or more and 40% by mass or less with respect to 100% by mass of the content of the thermosetting resin in the thermal expansion layer. For example, when an amide-based curing agent is used as the main component of the curing agent, the content of the curing agent in the thermal expansion layer is preferably 1% by mass or more and 15% by mass or less with respect to 100% by mass of the thermosetting resin contained in the thermal expansion layer. On the other hand, when a phenol-based curing agent is used as the main component of the curing agent, the content of the curing agent in the thermal expansion layer is preferably, for example, 5% by mass or more and 40% by mass or less with respect to 100% by mass of the thermosetting resin in the thermal expansion layer.

[0029] As the thermal expansion agent, it is preferable that the thermal expansion start temperature is 100°C or higher and 150°C or lower, and more preferably 120°C or higher and 130°C or lower. Specifically, inorganic blowing agents such as ammonium carbonate, ammonium bicarbonate, ammonium nitrite, ammonium borohydride, azides, etc., alkanes fluorides such as trichloromonofluoromethane, azo compounds such as azobisisobutyronitrile, hydrazine compounds such as paratoluenesulfonyl hydrazide, semicarbazide compounds such as p-toluenesulfonyl semicarbazide, triazole compounds such as 5-morpholyl-1,2,3,4-thiatriazole, N-nitroso compounds such as N,N'-dinitrosoterephthalamide, and other organic blowing agents, and microencapsulated blowing agents obtained by microencapsulating hydrocarbon solvents can be preferably used. Among them, it is more preferable to use a microcapsule type blowing agent. These may be used alone or in combination.

[0030] The content of the thermal expansion agent in the thermal expansion layer 20 is preferably 3 wt% or more and 19 wt% or less, more preferably 4 wt% or more and 17 wt% or less, and even more preferably 5 wt% or more and 15 wt% or less. If the content of the thermal expansion agent in the thermal expansion layer 20 is 3 wt% or more, the thermal expansion layer 20 can be sufficiently foamed, so that the adhesive strength can be improved, which is preferable. Also, if the content of the thermal expansion agent in the thermal expansion layer 20 is 19 wt% or less, a decrease in the adhesive strength due to excessive foaming of the thermal expansion layer 20 can be suppressed, and the content of the epoxy resin can be sufficiently ensured, so that the heat resistance can be suppressed, which is preferable.

[0031] The thermal expansion layer 20 may further contain a thermoplastic resin. Examples of the thermoplastic resin include at least one of a polyester resin, a butyral resin, a urethane resin, an acrylic resin, a carboxyl group-terminated butadiene nitrile rubber (CTBN), and an epoxy-modified butadiene. Among these, it is preferable to contain an elastomer-based resin as the thermoplastic resin, and it is more preferable to contain at least one of a butyral resin, an acrylic thermoplastic elastomer, and a urethane thermoplastic elastomer. When using two or more types of thermoplastic resins, it is preferable that the glass transition temperature Tg of at least one thermoplastic resin is 100°C or higher and 120°C or lower.

[0032] When the thermoplastic resin is contained in the thermal expansion layer 20, the content of the thermoplastic resin in the thermal expansion layer 20 is preferably 3 wt% or more and 30 wt% or less, more preferably 4 wt% or more and 20 wt% or less, and even more preferably 5 wt% or more and 15 wt% or less. By setting the content of the thermoplastic resin to 3 wt% or more, the flexibility and toughness of the thermal expansion layer 20 can be enhanced, and the adhesion of the thermal expansion layer to the base material can be further improved. Also, by setting the content of the thermoplastic resin to 30 wt% or less, when thermally expanded, the complex melt viscosity of the adhesive sheet when the thermal expansion start temperature of the thermal expansion agent contained in the thermal expansion adhesive sheet 1 is reached can be suppressed, and the thermal expansion layer 20 can be sufficiently expanded.

[0033] The thermal expansion layer 20 may further contain a filler. Examples of the filler include inorganic fillers such as aluminum oxide, magnesium oxide, calcium oxide, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, boron nitride, silicon nitride, silicon oxide, talc (magnesium silicate), titanium oxide, potassium titanate, and boehmite.

[0034] As the shape of the filler, various shapes such as polygonal, spherical, fibrous, scaly, acicular, and irregular can be used. When using a filler with a relatively high aspect ratio, it is preferable because the rigidity of the thermal expansion adhesive sheet 1, particularly the stiffness, can be improved. The aspect ratio is preferably 10 or more and 50 or less, and more preferably 20 or more and 40 or less. Examples of fillers with a relatively high aspect ratio include fibrous fillers, scaly fillers, and acicular fillers. Among them, it is particularly preferable to use acicular fillers because of their good dispersibility and high effect of improving the rigidity of the thermal expansion adhesive sheet 1.

[0035] The stiffness of the entire thermal expansion adhesive sheet obtained by incorporating the filler as described above in the thermal expansion layer 20 is, for example, 0.1 mN or more, and preferably 0.2 mN or more. On the other hand, the above stiffness is preferably, for example, 5.0 mN or less, and preferably 4.0 mN or less. By setting the stiffness within such a range, it can be expected that the shape retention of the thermal expansion adhesive sheet will be good. This stiffness can be calculated by cutting out a 25×25 mm sheet from the thermal expansion adhesive sheet and conducting a test using a Gurley-type tester (manufactured by Toyo Tester Kogyo Co., Ltd.) in accordance with JIS L 1085.

[0036] When the filler is incorporated in the thermal expansion layer 20, the content of the filler in the thermal expansion layer 20 is preferably 5 wt% or more and 50 wt% or less, more preferably 7 wt% or more and 35 wt% or less, and particularly preferably 10 wt% or more and 25 wt% or less. If the content of the filler in the thermal expansion layer 20 is 5 wt% or more, it is preferable because the thermal conductivity and the rigidity of the thermal expansion adhesive sheet 1 can be further improved. Also, if the content of the filler in the thermal expansion layer 20 is 50 wt% or less, the overexpression of thixotropy in the solution state of the adhesive containing the solvent before forming into a sheet can be suppressed, and the manufacturing limitations of the thermal expansion adhesive sheet 1 can be reduced.

[0037] The thickness of one layer of the thermal expansion layer 20 before thermal expansion is preferably 10 μm or more and 100 μm or less, more preferably 15 μm or more and 75 μm or less, and particularly preferably 20 μm or more and 50 μm or less.

[0038] <<Intermediate layer>> The intermediate layer 30 is for adhering the thermal expansion layer 20 to the base material 10 and is formed between the base material 10 and the thermal expansion layer 20. In the present embodiment, the intermediate layer 30 is formed on both surfaces of the base material 10. The intermediate layer 30 may be a continuous layer that continuously covers the surface of the base material, or may be a discontinuous layer composed of a plurality of islands.

[0039] It is preferable that the intermediate layer 30 has almost no cross-linked structure before laminating the thermal expansion layer 20 and can cause a cross-linking reaction with the thermal expansion layer 20 when the thermal expansion layer 20 is heated and expanded. In order to make the cross-linking reaction with the thermal expansion layer 20 sufficient, it is preferable that the intermediate layer 30 contains a resin containing a carboxyl group as a functional group. Also, for the same reason, it is preferable that the intermediate layer 30 according to the present embodiment does not contain a curing agent for curing the resin contained in the intermediate layer 30.

[0040] Examples of the resin containing a carboxyl group include polyester resins, such as polyesters and copolymers containing polyesters. Also, it is preferable that the acid value of the resin containing a carboxyl group is 5 or more. By setting the acid value to 5 or more, when the thermal expansion layer 20 is heated and expanded, the carboxyl group can be sufficiently cross-linked with the epoxy resin contained in the thermal expansion layer, so that the adhesive force between the intermediate layer 30 and the thermal expansion layer 20 can be sufficiently increased and the peeling of the thermal expansion layer 20 can be sufficiently suppressed.

[0041] The intermediate layer 30 is formed between the base material 10 and the thermal expansion layer 20, and preferably relieves the stress generated between the thermal expansion layer 20 and the base material 10. Therefore, it preferably contains a material with excellent flexibility. In addition to the resin described above, the intermediate layer 30 may also contain a filler for the purpose of improving heat resistance, thermal conductivity, and rigidity. As the filler, the same ones as those contained in the thermal expansion layer 20 can be used. The same type of filler may be used for the intermediate layer 30 and the thermal expansion layer 20, or different types of fillers may be used. When the intermediate layer 30 contains a filler, the content of the filler in the intermediate layer 30 is preferably 10 wt% or less. By setting the content of the filler in the intermediate layer 30 within the above-mentioned range, the area where the resin contained in the intermediate layer 30 and the resin contained in the thermal expansion layer 20 come into contact with each other can be sufficiently ensured. Therefore, it is preferable because the adhesive force between the intermediate layer 30 and the thermal expansion layer 20 can be maintained high.

[0042] In order to increase the expansion rate of the entire thermal expansion adhesive sheet 1, the intermediate layer 30 may contain a thermal expansion agent. The type of the thermal expansion agent can be the same as that contained in the thermal expansion layer 20. The same type can be used for the intermediate layer 30 and the thermal expansion layer 20, or different types can be used.

[0043] When the intermediate layer 30 contains a thermal expansion agent, the content of the thermal expansion agent in the intermediate layer is preferably less than the content of the thermal expansion agent in the thermal expansion layer. For example, it is preferably 25 wt% or less. More preferably, it is 10 wt% or less, and if it is 5 wt% or less, the possibility of the thermal expansion agent expanding between the base material and the intermediate layer can be sufficiently reduced, and the peeling between the intermediate layer 30 and the thermal expansion layer 20 can be sufficiently suppressed, which is particularly preferable.

[0044] The thickness of the intermediate layer 30 is preferably 0.1 μm or more and 10 μm or less, more preferably 0.3 μm or more and 7 μm or less, and particularly preferably 0.5 μm or more and 4 μm or less.

[0045] <Method for manufacturing a thermally expandable adhesive sheet>

[0046] The thermally expandable adhesive sheet 1 according to the present embodiment can be produced, for example, by the following procedures and methods. An intermediate layer composition in a varnish or slurry form in which a material for forming the intermediate layer 30 having the above-described configuration (for example, a polyester resin or the like) is dissolved or dispersed in an appropriate solvent is prepared. Further, a thermally expandable layer composition in a varnish or slurry form in which a material for forming the thermally expandable layer 20 having the above-described configuration (for example, a thermosetting resin, a curing agent, a thermoplastic resin, a filler, a thermal expansion agent) is dissolved or dispersed in an appropriate solvent is prepared.

[0047] Next, as shown in FIG. 2, for example, the intermediate layer composition is applied onto one surface of the base material 10 using, for example, a roll-to-roll film forming apparatus so that the thickness after drying becomes an arbitrary thickness. Examples of the coating method include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, dip coating, and the like. The intermediate layer composition applied to the surface of the base material by the method as described above is dried at a temperature of 50°C or more and 110°C or less, which is lower than the expansion start temperature of the thermally expandable layer 20, for a time of 30 seconds or more and 300 seconds or less to form the intermediate layer 30a.

[0048] Subsequently, the thermally expandable layer composition is continuously applied onto the intermediate layer 30a thus formed using a roll-to-roll film forming apparatus so that the thickness after drying becomes an arbitrary thickness. The thermally expandable layer composition applied onto the intermediate layer 30a is dried at a temperature of 50°C or more and 110°C or less for 30 seconds or more and 300 seconds to form the thermally expandable layer 20a.

[0049] Only when the intermediate layer 30a and the thermal expansion layer 20a are formed on one side of the base material, the roll is removed from the film forming apparatus, and the roll is reinstalled in the film forming apparatus in a direction in which the next layer can be formed on the surface of the base material 10 opposite to the surface on which the intermediate layer 30a and the thermal expansion layer 20a are formed. Then, by performing the same procedure as described above on the other side of the base material, the second intermediate layer 30b and the second thermal expansion layer 20b are formed on the base material 10, whereby the thermal expansion adhesive sheet 1 according to the present embodiment can be manufactured.

[0050] <Effect of the thermal expansion adhesive sheet according to the present embodiment> In the shear strength test at 200 °C (i.e., the same temperature as when the thermal expansion adhesive sheet 1 is thermally expanded and used for adhesion), the fracture interface when a shear force is applied until the thermal expansion adhesive sheet 1 is fractured exists within the thermal expansion layer 20. This indicates that the shear strength of not only the base material 10 but also the intermediate layer 30 of the thermal expansion adhesive sheet 1 is higher than that of the thermal expansion layer 20, and the adhesive force between the base material 10 and the intermediate layer 30 and between the intermediate layer 30 and the thermal expansion layer 20 is also sufficiently high, and in particular, the peeling of the thermal expansion layer 20 from the base material 10 can be sufficiently suppressed not only when the thermal expansion adhesive sheet 1 is heated and expanded but also in a high-temperature environment after heating and expansion.

[0051] Since the intermediate layer 30 is in a state where it is hardly crosslinked before the thermal expansion of the thermal expansion layer 20, a crosslinking reaction can occur between the intermediate layer 30 and the thermal expansion layer 20 when the thermal expansion adhesive sheet 1 is heated and expanded (when used for adhesion). As a result, the adhesive force between the thermal expansion layer 20 and the intermediate layer 30 can be increased when the thermal expansion layer 20 is easily peeled from the base material 10 during thermal expansion, and the peeling of the thermal expansion layer 20 can be suppressed more than before. In addition, since the intermediate layer 30 according to the present embodiment has a carboxyl group as a polar group, intermolecular forces such as hydrogen bonds and van der Waals forces act not only between the intermediate layer 30 and the thermal expansion layer 20 but also between the intermediate layer 30 and the base material 10, and the intermediate layer 30 and the base material 10 are strongly adhered. Therefore, after the thermal expansion adhesive sheet 1 according to the present embodiment is heated and expanded, the adhesive force between the thermal expansion layer 20 and the intermediate layer 30 and between the intermediate layer 30 and the base material 10 becomes sufficiently high. On the other hand, although the thermal expansion layer 20 according to the present embodiment is designed to have a sufficiently high cohesive force within the layer, the formation of an air layer inside due to heating expansion makes the cohesive force inside weaker than the adhesive force between the layers, and it is considered that cohesive failure occurs inside the thermal expansion layer 20. Regarding whether the intermediate layer 30 and the thermal expansion layer 20 are crosslinked, for example, it can be confirmed by observing an exothermic peak by DSC (differential scanning calorimetry) or observing the disappearance or decrease of the peak derived from the carboxyl group that existed before crosslinking by FT-IR (Fourier transform infrared spectroscopy). Further, when the intermediate layer 30 and the thermal expansion layer 20 are crosslinked, the adhesive force between these layers becomes sufficiently strong, and it is difficult to peel at the interface between the intermediate layer 30 and the thermal expansion layer 20 in the above-described shear strength test. When attempting to peel these, fracture occurs inside the thermal expansion layer 20. Therefore, it is also possible to determine the presence or absence of crosslinking based on whether these two layers can be peeled at the interface between the intermediate layer 30 and the thermal expansion layer 20.

[0052] Since the thermal expansion layer 20 contains an epoxy resin and the intermediate layer 30 contains a resin having a carboxyl group as a functional group, when the thermal expansion adhesive sheet 1 is heated and expanded, the thermal expansion layer 20 and the intermediate layer 30 can be surely crosslinked.

[0053] By setting the acid value of the resin having a carboxyl group as a functional group contained in the intermediate layer 30 to 5 or more, sufficient crosslinking can be formed between the thermal expansion layer 20, and the adhesive force between the intermediate layer 30 and the thermal expansion layer 20 can be further increased.

[0054] A heat expansion adhesive sheet 1 is provided with a base material 10, intermediate layers 30a and 30b formed on both surfaces of the base material 10 respectively, and heat expansion layers 20a and 20b formed on the outer sides of the intermediate layers 30 respectively. When manufacturing the heat expansion adhesive sheet 1 in which the intermediate layers 30a and 30b have heat resistance, it is necessary for the intermediate layers 30a and 30b to be thermosetting. Therefore, conventionally, it has been common to form the intermediate layer 30 by thermosetting before laminating the heat expansion layer 20 on the intermediate layer 30. However, in this conventional manufacturing method, when attempting to form the intermediate layer 30b on one side after laminating the intermediate layer 30a and the heat expansion layer 20a on one side, there is a problem that the previously formed heat expansion layer 20a expands.

[0055] Therefore, conventionally, as a method for manufacturing the heat expansion adhesive sheet 1 provided with the base material 10, intermediate layers 30a and 30b formed on both surfaces of the base material 10 respectively, and heat expansion layers 20a and 20b formed on the outer sides of the intermediate layers 30a and 30b respectively, as shown in FIG. 3, first, only the intermediate layers 30a and 30b are formed on both surfaces of the base material 10, and then the heat expansion layers 20a and 20b are formed on the outer sides of these intermediate layers 30a and 30b respectively. Such a process has been considered.

[0056] However, in such a manufacturing method, as shown in FIG. 3, four steps are required: the step of forming the intermediate layers 30a and 30b on both surfaces of the base material 10 respectively, and the step of forming the heat expansion layers 20a and 20b on the outer sides of these intermediate layers 30a and 30b respectively. Furthermore, since it is necessary to remove the roll from the apparatus and set it up again once between these four steps, compared to the manufacturing process of the heat expansion adhesive sheet 1 without the intermediate layer 30 shown in FIG. △, it takes more than twice the time and labor.

[0057] If attempting to manufacture the heat expansion adhesive sheet 1 with the intermediate layers 30a and 30b in almost the same time and labor as the heat expansion adhesive sheet 1 without the intermediate layer 30, as shown in FIG. 4, a special apparatus capable of laminating the intermediate layers 30a and 30b and the heat expansion layers 20a and 20b at once from both surfaces of the base material 10 is required.

[0058] On the other hand, according to the thermal expansion adhesive sheet 1 according to the present embodiment, as described above, after laminating the thermal expansion layers 20a and 20b without previously crosslinking the intermediate layers 30a and 30b, when the thermal expansion adhesive sheet 1 is used (that is, during heating when the thermal expansion layers 20a and 20b are thermally expanded), crosslinking is performed. Therefore, without preparing special equipment, the thermal expansion adhesive sheet 1 can be manufactured in almost the same time and effort as the manufacturing method of the thermal expansion adhesive sheet 1 without the intermediate layer 30.

[0059] <Modification example> The present invention is not limited to the above-described ones. For example, the thermal expansion adhesive sheet 1 according to the present invention does not necessarily have the intermediate layer 30 and the thermal expansion layer 20 provided on both sides of the base material 10, and may have the intermediate layer 30 and the thermal expansion layer 20 provided only on one side of the base material 10. A release paper may be further laminated on the outermost surface of the thermal expansion layer. In addition, various modifications of the embodiments and combinations of some of the embodiments may be made as long as they do not depart from the gist of the present invention.

Example

[0060] Hereinafter, the present invention will be described in more detail with specific examples, but it goes without saying that the present invention is not limited to these. Here, several types of thermal expansion adhesive sheets were manufactured as examples and comparative examples, and their physical properties were evaluated. <Manufacture of thermal expansion adhesive sheets according to Examples 1 to 3 and Comparative Examples 1 to 3> <<Formation of intermediate layer 30a>> An intermediate layer composition containing the components described in Table 2 below was applied onto the base material 10 using a baker-type applicator so that the thickness after drying would be the thickness described in Table 2. As the base material 10, Kapton (registered trademark) 100EN-S, a product name manufactured by Toray DuPont Co., Ltd., was used. This was dried at 80°C for 120 seconds to remove the solvent, thereby forming the intermediate layer 30a. In this example and the comparative examples, toluene and methyl ethyl ketone (MEK) were used as the solvent.

[0061] <<Formation of Thermal Expansion Layer 20a>> A thermal expansion layer composition containing the components described in Table 1 below was applied onto the intermediate layer 30a previously formed to have an arbitrary thickness after drying, using a baker-type applicator. By drying this at 110°C for 90 seconds to remove the solvent, the thermal expansion layer 20a was formed.

[0062]

Table 1

[0063] <<Formation of Intermediate Layer 30b>> The same intermediate layer composition as that of the intermediate layer 30a was applied onto the surface of the base material 10 opposite to the surface on which the intermediate layer 30a and the thermal expansion layer 20a were formed, using a baker-type applicator, so that the thickness after drying would be an arbitrary thickness. By drying this at 80°C for 120 seconds to remove the solvent, the intermediate layer 30b was formed.

[0064] <<Formation of Thermal Expansion Layer 20b>> The same thermal expansion layer composition as the thermal expansion layer 20a was applied onto the intermediate layer 30b using a baker-type applicator so that the thickness after drying would be an arbitrary thickness. By drying this at 110°C for 90 seconds to remove the solvent, the thermal expansion layer 20b was formed.

[0065] <Evaluation of the thermally expandable adhesive sheet> The following evaluation tests were respectively conducted on the thermally expandable adhesive sheets produced as described above. <<Shearing adhesive strength>> A 12.5×25 mm sheet was cut out from the thermally expandable adhesive sheet before heating and expansion, and this was used to conduct measurements according to the following procedure. Using a rubber roll at 110°C, the thermally expandable adhesive sheet was fixed to an SPCC plate, spacers with a thickness of 0.4 mm were placed on both sides of the thermally expandable adhesive sheet, another SPCC plate was further stacked thereon, and the gap between the SPCC plates was fixed using a fixing jig (such as a clamp), thereby producing a sample.

[0066] The temperature of the above sample was raised to 200°C at a rate of 50°C / min and heated at 200°C for 7 minutes to foam (3.2 times foaming) and cure the thermally expandable adhesive sheet in the sample. At this time, the gap between the two SPCC plates was fixed at 0.4 mm. Thereafter, using a universal testing machine (AGS-10kNX load cell capacity: 10kN, manufactured by Shimadzu Corporation), with the test atmosphere set to 200°C and the test speed set to 5 mm / min, the two SPCC plates of the above sample were pulled in opposite directions along the surface direction of the sample, and the applied pressure when the sample broke was measured as the shearing adhesive strength. In addition, the fracture interface after the test was observed, and the fracture interface was classified into the following A to C. The results are shown in Table 2. A: Cohesive failure of the thermal expansion layer B: Cohesive failure of the thermal expansion layer, but fracture near the intermediate layer C: Cohesive failure of the intermediate layer, or interfacial peeling between the thermal expansion layer and the intermediate layer

[0067] <<Substrate peeling during heating and expansion>> The thermal expansion adhesive sheet was cut into pieces of 50×50 mm, put into a heating furnace set at 160 °C for 10 minutes for foaming and curing, and then the appearance was visually checked, and the floating of the thermal expansion layer was evaluated according to the following criteria. The results are shown in Table 2. ×: The thermal expansion layer floats from the base material and peeling occurs. 〇: Neither floating nor peeling of the thermal expansion layer.

[0068] <<Confirmation of cracks in the expansion adhesive layer>> A 10×100 mm sheet was cut out from the thermal expansion adhesive sheet, bent 180 degrees, a load of 2 kg of copper was applied to the bent part for 5 seconds, and after releasing the load, the surface state of the thermal expansion adhesive sheet was visually observed, and the crackability of the thermal expansion layer was evaluated according to the following criteria. The results are shown in Table 2. ×: Cracks occur in the thermal expansion layer. 〇: No cracks in the thermal expansion layer.

[0069]

Table 2

[0070] <Discussion> From the results of the examples and comparative examples, when a shearing force capable of breaking the thermally expandable adhesive sheet is applied in the shear strength test at 200°C, the fracture interface exists within the thermally expandable layer. Comparing Examples 1 to 5 with Comparative Examples 1 to 3, in the thermally expandable sheet where the fracture interface exists within the thermally expandable layer, even when the composition is changed, the shear adhesive force at 200°C greatly exceeds 0.4 MPa. It was confirmed that not only the peeling during heating expansion can be suppressed, but also the peeling of the thermally expandable layer during use at a very high temperature of 200°C can be sufficiently suppressed. Also, if the intermediate layer is crosslinked in advance and then the thermally expandable layer is formed, the elastic modulus of the entire thermally expandable adhesive sheet increases and the stress relaxation effect decreases. On the other hand, in the case of the present invention where the thermally expandable layer is laminated without crosslinking the intermediate layer, the elastic modulus of the intermediate layer is suppressed to be low and the stress relaxation effect is high. Therefore, for example, even if the elastic modulus of the expandable adhesive layer disposed on the outside is high and it has a property of being easily cracked, the stress relaxation effect of the intermediate layer can suppress the cracking of the expandable adhesive layer when the expandable adhesive sheet is bent.

Industrial Applicability

[0071] According to the present invention, it is possible to provide a thermally expandable adhesive sheet capable of sufficiently suppressing the peeling between the base material and the thermally expandable layer during heating when the thermally expandable layer is expanded.

Explanation of Reference Numerals

[0072] 1 Thermally expandable adhesive sheet 10 Base material 20, 20a, 20b Thermally expandable layer 30, 30a, 30b Intermediate layer

Claims

1. A substrate; an intermediate layer laminated on the substrate; A thermally expandable adhesive sheet comprising a thermally expandable layer laminated on the surface of the intermediate layer opposite to the substrate, the intermediate layer is capable of undergoing a crosslinking reaction with the thermal expansion layer, A thermally expandable adhesive sheet characterized in that when a shear force sufficient to destroy the thermally expandable adhesive sheet is applied in a shear strength test at 200°C, the fracture interface is located within the thermally expandable layer.

2. A substrate, an intermediate layer laminated on the substrate; A thermally expandable adhesive sheet comprising a thermally expandable layer laminated on the surface of the intermediate layer opposite to the substrate, the thermal expansion layer contains a thermosetting resin and a curing agent, an equivalent ratio (C / E) of the functional group (E) of the thermosetting resin to the functional group (C) of the curing agent is 0.6 or more and 0.9 or less; A thermally expandable adhesive sheet characterized in that when a shear force sufficient to destroy the thermally expandable adhesive sheet is applied in a shear strength test at 200°C, the fracture interface is located within the thermally expandable layer.

3. The intermediate layer The thermal expansion adhesive sheet according to claim 1, characterized in that it contains a resin having functional groups that remain before the thermal expansion layer is heated and that can crosslink with the thermal expansion layer when the thermal expansion layer is heated and expanded.

4. The thermal expansion layer contains a thermosetting resin, The thermally expandable adhesive sheet according to claim 1 or 2, wherein the thermosetting resin is an epoxy resin.

5. the thermal expansion layer contains a curing agent, The thermally expandable adhesive sheet according to claim 1 or 2, wherein the curing agent is an amine-based curing agent or an amide-based curing agent.

6. A thermally expandable adhesive sheet as described in claim 1 or 2, wherein the intermediate layer contains a resin having a carboxy group.

7. The intermediate layer contains a resin having a carboxy group, The thermally expandable adhesive sheet according to claim 1 or 2, wherein the resin having a carboxy group has an acid value of 5 or more.

8. A thermally expandable adhesive sheet as described in claim 1 or 2, wherein the resin contained in the intermediate layer is a polyester resin.

9. 3. The thermally expandable adhesive sheet according to claim 1, wherein the thermal expansion agent contained in the thermally expandable layer has a thermal expansion starting temperature of 100°C or higher and 150°C or lower.

10. a substrate, an intermediate layer laminated on the substrate, and a thermal expansion layer laminated on a surface of the intermediate layer opposite to the substrate, the intermediate layer is capable of undergoing a crosslinking reaction with the thermal expansion layer, A method for producing a thermally expandable adhesive sheet in which the fracture interface exists within the thermally expandable layer when a shear force sufficient to destroy the thermally expandable adhesive sheet is applied in a shear strength test at 200°C, the method comprising laminating the thermally expandable layer on the intermediate layer before performing a heating step to crosslink the intermediate layer.

11. A method for producing an article comprising a first adherend, a second adherend, and a thermally expandable adhesive sheet, comprising:

3. A manufacturing method comprising: placing the thermally expandable adhesive sheet according to claim 1 or 2 between the first adherend and the second adherend; heating and expanding the thermally expandable adhesive sheet to fill a gap formed between the first adherend and the second adherend, thereby adhering the first adherend and the second adherend.

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