Foamable adhesive sheet and manufacturing method of structure

Abstract

To provide a foamable adhesive sheet capable of obtaining excellent foaming properties and adhesion properties suitable for a prescribed gap, and to provide a manufacturing method of a structure using the foamable adhesive sheet.SOLUTION: A foamable adhesive sheet includes an adhesion layer. The adhesion layer includes a thermosetting adhesive agent and a foaming agent. When a displacement is measured by a thermomechanical measurement in the foamable adhesive sheet, with its temperature risen at a prescribed rate while applying a compressive load, a sum total of an initial thickness of the foamable adhesive sheet and a displacement magnitude at a prescribed temperature of 160°C or higher and lower than 200°C is 100% to 308%, inclusive, based on a clearance set value 100%.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a foamable adhesive sheet and a method for producing a structure using the same. [Background technology]

[0002] Adhesives for bonding members together are used in a variety of fields, and many bonding methods are known.

[0003] For example, Patent Documents 1 and 2 disclose adhesive sheets containing a foaming agent (foamable adhesive sheets). A known method of using a foamable adhesive sheet is to place the foamable adhesive sheet between components, and then heat the foamable adhesive sheet to foam and harden it, thereby bonding the components together.

[0004] Such a foamable adhesive sheet is required to have foaming properties for filling the gaps between members, and adhesive properties for bonding members together. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2000-53944 A [Patent Document 2] Patent No. 6223477 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the foamable adhesive sheet is heated to foam and harden, both foaming and hardening occur, making it difficult to balance foaming and hardening, resulting in problems such as a decrease in foaming ratio and a decrease in adhesive strength. As such, it has been difficult to adjust the balance between foaming ratio and adhesive strength, making it difficult to obtain the desired foaming and adhesive properties.

[0007] The present disclosure has been made in consideration of the above-mentioned situation, and has as its main object to provide a foamable adhesive sheet and a method for manufacturing a structure using a foamable adhesive sheet that can obtain excellent foaming properties and adhesive properties suitable for a specified gap. [Means for solving the problem]

[0008] One embodiment of the present disclosure provides a foamable adhesive sheet having an adhesive layer, the adhesive layer containing a thermosetting adhesive and a foaming agent, wherein when a compressive load is applied to the foamable adhesive sheet, the temperature is raised at a predetermined heating rate, and the displacement is measured by thermomechanical measurement, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature of 160°C or more and less than 200°C is 100% or more and 308% or less with respect to a gap setting value of 100%.

[0009] Another embodiment of the present disclosure provides a method for manufacturing a structure, comprising: a positioning step of positioning a foamable adhesive sheet having an adhesive layer between a first member and a second member; and a bonding step of heating the foamable adhesive sheet to foam and harden it, thereby bonding the first member and the second member, wherein the adhesive layer contains a thermosetting adhesive and a foaming agent, and the foamable adhesive sheet is subjected to thermomechanical measurement to apply a compressive load, heat the sheet at a predetermined heating rate, and measure the displacement. The sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature of 160°C or more and less than 200°C is 100% or more and 308% or less relative to a gap setting value of 100%, and the gap setting value is the distance of the gap after the foamable adhesive sheet is positioned between the first member and the second member.

[0010] Another embodiment of the present disclosure provides a method for manufacturing a structure, comprising: a positioning step of positioning a foamable adhesive sheet having an adhesive layer between a first member and a second member; and a bonding step of heating the foamable adhesive sheet to foam and harden it, thereby bonding the first member and the second member, wherein the adhesive layer contains a thermosetting adhesive and a foaming agent; the heating temperature in the bonding step is 150°C or higher and lower than 200°C; and the foamable adhesive sheet is heated to the heating temperature at a predetermined heating rate by applying a compressive load and measuring the displacement by thermomechanical measurement, and the sum of the initial thickness and the amount of displacement of the foamable adhesive sheet is set to be 121% or higher and 168% or lower with respect to a gap setting value of 100%, and the gap setting value is the distance of the gap after the foamable adhesive sheet is positioned between the first member and the second member. Effect of the Invention

[0011] The present disclosure can provide a foamable adhesive sheet that is capable of obtaining excellent foaming properties and adhesive properties suitable for a specified gap, and a method for producing a structure using the foamable adhesive sheet. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to the present disclosure. [Diagram 2] 1 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to the present disclosure. [Diagram 3] 1 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to the present disclosure. [Figure 4] 1 is a graph illustrating a TMA curve for a foamable adhesive sheet. [Diagram 5] 1 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to the present disclosure. [Figure 6] 1A to 1C are process diagrams illustrating a method for manufacturing a structure according to the present disclosure. [Figure 7] 1 is a graph illustrating a TMA curve for a foamable adhesive sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The following describes the embodiments of the present disclosure with reference to the drawings. However, the present disclosure can be implemented in many different forms, and is not to be construed as being limited to the description of the embodiments exemplified below. In addition, the drawings may be schematic in terms of the width, thickness, shape, etc. of each part compared to the actual form in order to make the explanation clearer, but these are merely examples and do not limit the interpretation of the present disclosure. In addition, in this specification and each figure, elements similar to those described above with respect to the previous figures may be given the same reference numerals, and detailed explanations may be omitted as appropriate.

[0014] In this specification, when describing a mode in which another component is disposed on a certain component, the term "above" or "below" includes both a case in which another component is disposed directly above or below a certain component so as to be in contact with the component, and a case in which another component is disposed above or below a certain component with another component interposed therebetween, unless otherwise specified. In addition, in this specification, when describing a mode in which another component is disposed on the surface of a certain component, the term "on the surface side" or "on the surface" includes both a case in which another component is disposed directly above or below a certain component so as to be in contact with the component, and a case in which another component is disposed above or below a certain component with another component interposed therebetween, unless otherwise specified.

[0015] In this specification, the term "sheet" also includes members called "films." In addition, the term "films" also includes members called "sheets." In addition, the numerical ranges in this specification are average value ranges.

[0016] In order to fill the gap between components and bond the components together, the foamable adhesive sheet needs to have foaming properties such that the thickness of the foamable adhesive sheet after foaming and hardening is at least equal to or larger than the gap between the components. However, as mentioned above, it is difficult to balance the foaming ratio and adhesive strength in the foamable adhesive sheet. Therefore, there is still room for further study on foaming properties and adhesive properties suitable for the desired gap.

[0017] Conventionally, the foaming characteristics of a foamable adhesive sheet have been evaluated, for example, by the foaming ratio of the foamable adhesive sheet. Generally, the foaming ratio of a foamable adhesive sheet refers to the foaming ratio when the foamable adhesive sheet is foamed and cured in a state where no external pressure is applied to the foamable adhesive sheet.

[0018] On the other hand, when a foamable adhesive sheet is used to bond components together, the foamable adhesive sheet is foamed and cured while sandwiched between components, and therefore the foamable adhesive sheet is foamed and cured while being subjected to external pressure. Therefore, the measurement conditions for the expansion ratio of a foamable adhesive sheet are significantly different from the actual foaming and curing conditions of the foamable adhesive sheet.

[0019] In contrast, when measuring the foaming characteristics of a foamable adhesive sheet by thermomechanical measurement (TMA), the foamable adhesive sheet is heated while a compressive load is applied, and the displacement associated with the thermal expansion of the foamable adhesive sheet is measured. In this case, the foamable adhesive sheet is foamed and cured while a certain degree of compressive load is applied to the foamable adhesive sheet. Therefore, the measurement conditions of the thermomechanical analysis can be closer to the actual foaming and curing conditions of a foamable adhesive sheet than the measurement conditions of the expansion ratio of a conventional foamable adhesive sheet. Therefore, it is considered that the thermomechanical measurement can obtain a measurement value that reflects the foaming and curing behavior of the foamable adhesive sheet.

[0020] Therefore, the inventors of the present disclosure focused on the foaming characteristics of the foamable adhesive sheet measured by thermomechanical measurement, and as a result of extensive research into the foaming characteristics and adhesive characteristics of the foamable adhesive sheet, found that there is a correlation between the amount of displacement when the foaming characteristics of the foamable adhesive sheet are measured by thermomechanical measurement and the adhesive strength of the foamable adhesive sheet after foaming and curing. They also found that when the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement measured by thermomechanical measurement is within a predetermined range for the target gap, the adhesive strength of the foamable adhesive sheet after foaming and curing is high. The present disclosure is based on such findings.

[0021] The foamable adhesive sheet and the method for producing the structure according to the present disclosure will be described in detail below.

[0022] A. Foam adhesive sheet The foamable adhesive sheet of the present disclosure is a foamable adhesive sheet having an adhesive layer, the adhesive layer containing a thermosetting adhesive and a foaming agent, and when the foamable adhesive sheet is subjected to a compressive load, heated at a predetermined heating rate, and displacement is measured by thermomechanical measurement, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature of 160°C or more and less than 200°C is 100% or more and 308% or less with respect to a gap setting value of 100%.

[0023] The foamable adhesive sheet of the present disclosure will be described with reference to the drawings. FIGS. 1 to 3 are schematic cross-sectional views illustrating the foamable adhesive sheet of the present disclosure. The foamable adhesive sheet 10 in FIG. 1 has an adhesive layer 1. The foamable adhesive sheet 10 in FIG. 2 has a first adhesive layer 1a and a second adhesive layer 1b. The foamable adhesive sheet 10 in FIG. 3 has a first adhesive layer 1a, a substrate 2, and a second adhesive layer 1b in this order. The adhesive layer 1, the first adhesive layer 1a, and the second adhesive layer 1b all contain a thermosetting adhesive and a foaming agent.

[0024] 4 is a graph showing an example of a thermomechanical measurement (TMA) curve in which a compressive load is applied to a foamable adhesive sheet, the temperature is increased at a predetermined heating rate, and the displacement is measured, with the horizontal axis representing temperature and the vertical axis representing displacement. In the foamable adhesive sheet of the present disclosure, the sum of the initial thickness of the foamable adhesive sheet and the displacement at a predetermined temperature in the TMA curve as shown in FIG. 4 is within a predetermined range for the gap setting value.

[0025] In the foamable adhesive sheet of the present disclosure, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a given temperature measured by thermomechanical measurement is within a given range for the gap setting, so that excellent foaming and adhesive properties suitable for the gap setting can be obtained. Thus, the foamable adhesive sheet can be made optimal for filling the gap between components and bonding components together for the gap setting.

[0026] Hereinafter, each component of the foamable adhesive sheet according to the present disclosure will be described.

[0027] 1.Characteristics In the foamable adhesive sheet of the present disclosure, when a compressive load is applied, the temperature is raised at a predetermined heating rate, and the displacement is measured by thermomechanical measurement, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature of 160°C or more and less than 200°C is 100% or more and 308% or less with respect to a gap setting value of 100%. The sum of the initial thickness of the foamable adhesive sheet and the amount of displacement is preferably 112% or more and 308% or less, and more preferably 138% or more and 308% or less, with respect to a gap setting value of 100%. By having the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement within the above range, foaming properties and adhesive properties suitable for the gap setting value can be obtained.

[0028] Here, the thermomechanical measurement is performed by the following method. First, the foamable adhesive sheet is punched out with a φ4 mm jig to prepare a sample. Next, the sample is placed in an aluminum container with φ5 mm, and an aluminum plate with φ4 mm is placed on the sample. Next, thermomechanical measurement is performed under the conditions of temperature: 25°C to 250°C, heating rate: 20°C / min, load: 10 mN, and compression mode to measure the displacement associated with the expansion or contraction of the sample. Then, the amount of displacement at a predetermined temperature is obtained. As a thermomechanical measurement device, for example, a thermomechanical analyzer TMA7100 manufactured by Hitachi High-Tech Science Corporation can be used.

[0029] The amount of displacement at a given temperature refers to the amount of displacement associated with expansion when a given temperature is reached, with the amount of displacement at 25°C in the TMA curve being set at 0. The unit of displacement is "μm."

[0030] In addition, when determining the amount of displacement at a predetermined temperature, the predetermined temperature is any temperature between 160°C and 200°C. This is because when the predetermined temperature is within the above range, the foamable adhesive sheet can have good heat resistance. Therefore, it can be applied to applications requiring heat resistance around the engine of an automobile or similar. In addition, if the predetermined temperature is lower than the above range, the amount of displacement at the predetermined temperature tends to be small. Therefore, the adhesive strength may decrease. In this case, there is a possibility that interface destruction may easily occur between the adhesive sheet and the member after foaming and hardening. Here, in the microcapsule type foaming agent, a thermal expansion agent such as a hydrocarbon is encapsulated inside the shell made of resin. In the case of the microcapsule type foaming agent, when heated, the resin constituting the shell softens and the pressure of the thermal expansion agent such as a hydrocarbon increases, causing the microcapsule type foaming agent to expand. Since the shell becomes thinner due to expansion, if heating is continued, the thermal expansion agent will escape from the microcapsule type foaming agent, causing the microcapsule type foaming agent to shrink. Therefore, in the case of the microcapsule type foaming agent, the amount of displacement tends to decrease after reaching the maximum amount of displacement in the TMA curve. Therefore, if the predetermined temperature is higher than the above range, the amount of displacement at the predetermined temperature will be small, and as a result, there is a possibility that the adhesive strength will decrease. Therefore, in the present disclosure, the above-mentioned predetermined temperature is set to any temperature between 160°C or more and less than 200°C.

[0031] In the foamable adhesive sheet, the amount of displacement can be controlled, for example, by adjusting the particle size and content of the foaming agent. For example, when the particle size of the foaming agent is large, the amount of displacement tends to be large. On the other hand, when the particle size of the foaming agent is small, the amount of displacement tends to be small. Also, for example, when the content of the foaming agent is high, the amount of displacement tends to be large. On the other hand, when the content of the foaming agent is low, the amount of displacement tends to be small.

[0032] The initial thickness of the foamable adhesive sheet is the thickness of the foamable adhesive sheet before foaming, and refers to the thickness of the foamable adhesive sheet at room temperature after a sample of the foamable adhesive sheet is set in a thermomechanical measuring device. Specifically, as described above, the foamable adhesive sheet is first punched out with a φ4 mm jig to prepare a sample. Next, the sample is placed in an aluminum container with a φ5 mm, and an aluminum plate with a φ4 mm is placed on the sample. In this state, the expansion / compression probe of the thermomechanical measuring device is brought into contact with the aluminum plate at a load of 100 mN, and the thickness after the aluminum plate and the sample are brought into contact sufficiently smoothly is taken as the initial thickness of the foamable adhesive sheet. Note that, when the foamable adhesive sheet has a separator, the initial thickness of the foamable adhesive sheet refers to the thickness of the foamable adhesive sheet excluding the separator. The unit of the initial thickness of the foamable adhesive sheet is "μm".

[0033] The gap setting value is preferably, for example, 100 μm or more and 500 μm or less, and more preferably 200 μm or more and 400 μm or less. The present disclosure is suitable for the case where the gap setting value is relatively small as described above. The definition of the gap setting value will be described later. The unit of the gap setting value is "μm".

[0034] In addition, the foamable adhesive sheet of the present disclosure preferably has a high adhesive strength after foaming and curing. The shear strength (adhesive strength) based on JIS K6850 corresponding to ISO 4587 may be, for example, 1.50 MPa or more, 1.80 MPa or more, or 2.10 MPa or more at 23°C. In addition, the shear strength (adhesive strength) may be, for example, 0.50 MPa or more, 0.75 MPa or more, or 1.00 MPa or more at 130°C. For example, in a high-strength acrylic foam adhesive tape that does not require heating, the shear strength (adhesive strength) is about 1 MPa or more and 2 MPa or less at room temperature, and does not have heat resistance at 200°C. Therefore, if the shear strength (adhesive strength) is within the above range at 23°C, it has an advantage in terms of strength. In addition, if the shear strength (adhesive strength) is within the above range at 130°C, it can be applied to applications that require heat resistance around an automobile engine or similar.

[0035] In addition, the foamable adhesive sheet of the present disclosure preferably has high electrical insulation after foaming and curing. After foaming and curing of the foamable adhesive sheet, the dielectric breakdown voltage based on JIS C2107 corresponding to IEC 60454-2 is, for example, preferably 3 kV or more, more preferably 5 kV or more. When the dielectric breakdown voltage is within the above range, it is possible to apply it to rust prevention and around copper wires. Furthermore, after foaming and curing of the foamable adhesive sheet, the thermal conductivity is, for example, preferably 0.1 W / mK or more, more preferably 0.15 W / mK or more. When the thermal conductivity is within the above range, it is possible to miniaturize the parts and promote the curing reaction during heating.

[0036] 2.Adhesive layer The adhesive layer in the present disclosure contains a thermosetting adhesive and a foaming agent.

[0037] (1) Material (a) Foaming agent The foaming agent in the present disclosure is a foaming agent that undergoes a foaming reaction by heat. As the foaming agent, a foaming agent generally used in the adhesive layer of a foamable adhesive sheet can be used.

[0038] The foaming start temperature of the foaming agent is preferably equal to or higher than the softening temperature of the base of the thermosetting adhesive such as epoxy resin, and equal to or lower than the activation temperature of the curing reaction of the base of the thermosetting adhesive such as epoxy resin. The foaming start temperature of the foaming agent is, for example, 70°C or higher, and may be 100°C or higher. If the foaming start temperature is too low, foaming may start early, and foaming may occur in a state where the flexibility and fluidity of the resin component are low, making it difficult to generate uniform foaming. On the other hand, the foaming start temperature of the foaming agent is, for example, 210°C or lower. If the foaming start temperature is too high, the resin component may deteriorate.

[0039] The softening temperature of the base material of a thermosetting adhesive such as an epoxy resin can be measured using the ring and ball softening temperature test method specified in JIS K7234.

[0040] The foaming agent may be, for example, a microcapsule type foaming agent, which preferably has a thermal expansion agent such as a hydrocarbon as a core and a resin such as an acrylonitrile copolymer as a shell.

[0041] In addition, for example, organic or inorganic foaming agents may be used as the foaming agent. Examples of organic foaming agents include azo foaming agents such as azodicarbonamide (ADCA), azobisformamide, and azobisisobutyronitrile, fluorinated alkane foaming agents such as trichloromonofluoromethane, hydrazine foaming agents such as paratoluenesulfonylhydrazide, semicarbazide foaming agents such as p-toluenesulfonylsemicarbazide, triazole foaming agents such as 5-morpholyl-1,2,3,4-thiatriazole, and N-nitroso foaming agents such as N,N-dinitrosoterephthalamide. On the other hand, examples of inorganic foaming agents include ammonium carbonate, ammonium hydrogen carbonate, ammonium nitrite, ammonium borohydride, and azides.

[0042] The foaming agent may be used alone or in combination of two or more kinds.

[0043] The average particle size of the foaming agent may be, for example, 10 μm or more, 13 μm or more, or 17 μm or more. The average particle size of the foaming agent is preferably equal to or less than the thickness of the adhesive layer, and may be, for example, 44 μm or less, 30 μm or less, or 24 μm or less.

[0044] The average particle size of the foaming agent is the particle size at 50% of the cumulative value in the particle size distribution obtained by the laser diffraction scattering method. In addition, when measuring the average particle size of the foaming agent, the adhesive layer is dissolved in a solvent to separate the foaming agent. The solvent is not particularly limited as long as it is a solvent capable of dissolving components other than the foaming agent contained in the adhesive layer, and is appropriately selected according to the type of thermosetting adhesive contained in the adhesive layer. For example, a solvent used in the adhesive composition used to form the adhesive layer can be used. Specifically, methyl ethyl ketone, ethyl acetate, toluene, etc. can be used.

[0045] The expansion ratio at the maximum expansion temperature of the foaming agent is, for example, 1.5 times or more, and may be 3 times or more. On the other hand, the expansion ratio at the maximum expansion temperature of the foaming agent is, for example, 15 times or less, and may be 10 times or less.

[0046] The content of the foaming agent is, for example, 0.5 parts by mass or more, 2 parts by mass or more, 3 parts by mass or more, 4 parts by mass or more, or 5 parts by mass or more, based on 100 parts by mass of the resin component contained in the adhesive layer. On the other hand, the content of the foaming agent is, for example, 25 parts by mass or less, 20 parts by mass or less, or 15 parts by mass or less, based on 100 parts by mass of the resin component contained in the adhesive layer. If the content of the foaming agent is too high, the content of the thermosetting adhesive is relatively low, so that the adhesive strength after foaming and curing may decrease.

[0047] (b) Thermosetting adhesive The thermosetting adhesive in the present disclosure may be a thermosetting adhesive generally used for the adhesive layer of a foamable adhesive sheet. The thermosetting adhesive may be applied even when the member does not have transparency, such as a metal member.

[0048] Examples of thermosetting adhesives include epoxy resin adhesives, acrylic resin adhesives, phenol resin adhesives, unsaturated polyester resin adhesives, alkyd resin adhesives, urethane resin adhesives, and thermosetting polyimide resin adhesives.

[0049] Among them, the thermosetting adhesive is preferably an epoxy resin adhesive. That is, the thermosetting adhesive preferably contains an epoxy resin and a curing agent. In general, epoxy resin adhesives are excellent in mechanical strength, heat resistance, insulating properties, chemical resistance, etc., have small shrinkage upon curing, and can be used in a wide range of applications.

[0050] Hereinafter, an example will be described in which the thermosetting adhesive is an epoxy resin adhesive.

[0051] (i) Epoxy resin The epoxy resin in the present disclosure is a compound that has at least one epoxy group or glycidyl group and is cured by a crosslinking polymerization reaction in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

[0052] Examples of epoxy resins include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of epoxy resins include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins, novolac-type epoxy resins such as bisphenol A novolac-type epoxy resins and cresol novolac-type epoxy resins, and modified epoxy resins such as urethane-modified epoxy resins and rubber-modified epoxy resins. Other specific examples include biphenyl-type epoxy resins, stilbene-type epoxy resins, triphenolmethane-type epoxy resins, alkyl-modified triphenolmethane-type epoxy resins, triazine nucleus-containing epoxy resins, dicyclopentadiene-modified phenol-type epoxy resins, naphthalene-type epoxy resins, glycol-type epoxy resins, and pentaerythritol-type epoxy resins. The epoxy resin may be one type or two or more types.

[0053] Bisphenol A type epoxy resins can exist in a liquid state at room temperature or in a solid state at room temperature depending on the number of repeating units of the bisphenol skeleton. Bisphenol A type epoxy resins having, for example, 2 to 10 bisphenol skeletons in the main chain are solid at room temperature. In particular, bisphenol A type epoxy resins are preferred in that they can improve heat resistance.

[0054] The epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0055] (ii) Acrylic resin In the present disclosure, when the thermosetting adhesive is an epoxy resin adhesive, the adhesive layer may further contain an acrylic resin compatible with the epoxy resin. The acrylic resin is a resin compatible with the epoxy resin. Since the acrylic resin is compatible with the epoxy resin, it is easy to improve the toughness of the adhesive layer. As a result, the adhesiveness after foaming and curing can be improved. Furthermore, it is considered that the acrylic resin acts as a compatibilizer for the foaming agent (for example, a foaming agent whose shell part is an acrylonitrile copolymer resin), and uniformly disperses and foams, thereby improving the adhesiveness after foaming and curing. In addition, the flexibility of the acrylic resin is exerted, and the adhesion to the substrate after foaming and curing and the crack resistance after foaming and curing can be improved. In addition, the compatibility of the acrylic resin with the epoxy resin allows the hardness of the surface of the adhesive layer to be kept high. On the other hand, if the acrylic resin is incompatible with the epoxy resin, a soft portion is formed on the surface of the adhesive layer, so that the interface with the first member and the second member becomes difficult to slip, and the workability may be reduced.

[0056] The acrylic resin in the present disclosure is compatible with the epoxy resin. Here, the compatibility of the acrylic resin with the epoxy resin can be confirmed, for example, by the absence of micron-sized islands when the cross section of the adhesive layer is observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). More specifically, the average particle size of the islands is preferably 1 μm or less. In particular, the average particle size of the islands may be 0.5 μm or less, or may be 0.3 μm or less. It is preferable that the number of samples is large, for example, 100 or more. The area to be observed is in the range of 100 μm × 100 μm, or in the case where the thickness of the adhesive layer is 100 μm or less, in the range of the thickness × 100 μm.

[0057] The acrylic resin may have a polar group, such as an epoxy group, a hydroxyl group, a carboxyl group, a nitrile group, or an amide group.

[0058] The acrylic resin may be a homopolymer of an acrylic acid ester monomer, a mixed component containing two or more of the above homopolymers, or a copolymer of two or more of the acrylic acid ester monomers, a component containing one or more copolymers. The acrylic resin may also be a mixed component of the above homopolymer and the above copolymer. The "acrylic acid" of the acrylic acid ester monomer also includes the concept of methacrylic acid. Specifically, the acrylic resin may be a mixture of a methacrylate polymer and an acrylate polymer, or an acrylic acid ester polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. Among them, the acrylic resin preferably contains a copolymer of two or more of the acrylic acid ester monomers ((meth)acrylic acid ester copolymer).

[0059] Examples of the monomer components constituting the (meth)acrylic acid ester copolymer include the monomer components described in JP 2014-065889 A. The monomer components may have the above-mentioned polar group. Examples of the (meth)acrylic acid ester copolymer include ethyl acrylate-butyl acrylate-acrylonitrile copolymer, ethyl acrylate-acrylonitrile copolymer, and butyl acrylate-acrylonitrile copolymer. Note that "acrylic acid" such as methyl acrylate and ethyl acrylate also includes "methacrylic acid" such as methyl methacrylate and ethyl methacrylate.

[0060] The (meth)acrylic acid ester copolymer is preferably a block copolymer, and more preferably an acrylic block copolymer such as a methacrylate-acrylate copolymer. Examples of (meth)acrylates constituting the acrylic block copolymer include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and benzidyl acrylate. These "acrylic acids" also include "methacrylic acid."

[0061] Specific examples of methacrylate-acrylate copolymers include acrylic copolymers such as methyl methacrylate-butyl acrylate-methyl methacrylate (MMA-BA-MMA) copolymers. MMA-BA-MMA copolymers also include block copolymers of polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (PMMA-PBA-PMMA).

[0062] The acrylic copolymer may not have a polar group, or may be a modified product having the above-mentioned polar group partially introduced therein. The modified product is easily compatible with the epoxy resin, and therefore the adhesiveness is further improved.

[0063] Among them, the acrylic resin is preferably a (meth)acrylic acid ester copolymer having a first polymer portion having a glass transition temperature (Tg) of 10° C. or less and a second polymer portion having a glass transition temperature (Tg) of 20° C. or more. Such a (meth)acrylic acid ester copolymer has a first polymer portion that becomes a soft segment and a second polymer portion that becomes a hard segment. By adding such a copolymer, the toughness of the adhesive layer after curing is improved, and the adhesive strength can be further increased.

[0064] The manifestation of the above-mentioned effect can be presumed as follows: By using an acrylic resin having both a soft segment and a hard segment, such as the above-mentioned (meth)acrylic acid ester copolymer, the hard segment contributes to heat resistance, and the soft segment contributes to toughness or flexibility, so that an adhesive layer having good heat resistance, toughness, and flexibility can be obtained.

[0065] At least one of the first polymer portion and the second polymer portion contained in the (meth)acrylic acid ester copolymer has compatibility with epoxy resins. When the first polymer portion has compatibility with epoxy resins, flexibility can be increased. When the second polymer portion has compatibility with epoxy resins, cohesion and toughness can be increased.

[0066] The (meth)acrylic acid ester copolymer is preferably a block copolymer, and more preferably an ABA block copolymer in which a compatible portion is polymer block A and an incompatible portion is polymer block B. Furthermore, it is more preferably an ABA block copolymer in which a first polymer portion is an incompatible portion and a second polymer portion is a compatible portion, and the first polymer portion is polymer block B and the second polymer portion is polymer block A.

[0067] The (meth)acrylic acid ester copolymer may be a modified product in which the above-mentioned polar group is introduced into a part of the first polymer segment or the second polymer segment.

[0068] A specific example of the (meth)acrylic acid ester copolymer having the above-mentioned first polymer portion and second polymer portion is the above-mentioned MMA-BA-MMA copolymer.

[0069] The content of the acrylic resin is, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 7 parts by mass or more, or 10 parts by mass or more, when the resin component contained in the adhesive layer is 100 parts by mass. If the content of the acrylic resin is too small, the adhesiveness after foaming and curing and the adhesion of the adhesive layer to the substrate may be reduced. On the other hand, the content of the acrylic resin is, for example, 60 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 35 parts by mass or less, or 30 parts by mass or less, when the resin component contained in the adhesive layer is 100 parts by mass. If the content of the acrylic resin is too high, the film strength may be reduced.

[0070] Furthermore, as described below, when the foamable adhesive sheet has a first adhesive layer and a second adhesive layer as adhesive layers, the acrylic resin content in the first adhesive layer and the second adhesive layer may be the same or different from each other.

[0071] (iii) Hardener As the curing agent in the present disclosure, a curing agent generally used in an epoxy resin adhesive can be used.

[0072] The curing agent is preferably a solid at 23°C. A curing agent that is a solid at 23°C can extend the storage stability (pot life) compared to a curing agent that is a liquid at 23°C. The curing agent may be a latent curing agent. The curing agent is usually a curing agent that undergoes a curing reaction by heat. The curing agent may be used alone or in combination of two or more types.

[0073] The reaction initiation temperature of the curing agent is, for example, 110°C or higher, and may be 130°C or higher. If the reaction initiation temperature is too low, the reaction starts early, and curing occurs in a state where the flexibility and fluidity of the resin component is low, and uniform curing may be difficult to occur. On the other hand, the reaction initiation temperature of the curing agent is, for example, 200°C or lower. If the reaction initiation temperature is too high, the resin component may deteriorate. In addition to the epoxy resin, when a resin with high heat resistance, such as a phenolic resin, is used, the resin component is less deteriorated, so the reaction initiation temperature of the curing agent may be, for example, 300°C or lower. The reaction initiation temperature of the curing agent can be determined by differential scanning calorimetry (DSC).

[0074] Specific examples of the curing agent include imidazole-based curing agents, phenol-based curing agents, amine-based curing agents, acid anhydride-based curing agents, isocyanate-based curing agents, and thiol-based curing agents.

[0075] Examples of imidazole-based curing agents include imidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-isopropylimidazole, 2-phenylimidazole, carboxylates of imidazole compounds, and adducts with epoxy compounds. It is also preferable that the imidazole-based curing agent has a hydroxyl group. Since crystallization occurs due to hydrogen bonds between hydroxyl groups, the reaction initiation temperature tends to be high.

[0076] Examples of phenol-based curing agents include phenol resins. Examples of phenol resins include resol-type phenol resins and novolac-type phenol resins. From the viewpoint of adhesion to the substrate after foaming and curing and crack resistance after foaming and curing, phenol-type novolac resins having a Tg of 110° C. or less are particularly preferred. Also, phenol-based curing agents and imidazole-based curing agents may be used in combination. In this case, it is preferable to use an imidazole-based curing agent as a curing catalyst.

[0077] Examples of the amine-based curing agent include aliphatic amines such as diethylenetriamine (DETA), triethylenetetramine (TETA), and metaxylylenediamine (MXDA); aromatic amines such as diaminodiphenylmethane (DDM), m-phenylenediamine (MPDA), and diaminodiphenylsulfone (DDS); alicyclic amines; and polyamidoamines. In addition, examples of the amine-based curing agent that can be used include dicyandiamide-based curing agents such as dicyandiamide (DICY), organic acid dihydrazide-based curing agents, amine adduct-based curing agents, and ketimine-based curing agents.

[0078] Examples of acid anhydride curing agents include alicyclic acid anhydrides (liquid acid anhydrides) such as hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA); and aromatic acid anhydrides such as trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), and benzophenonetetracarboxylic acid (BTDA).

[0079] The isocyanate-based curing agent may, for example, be a blocked isocyanate.

[0080] Examples of the thiol-based curing agent include ester-bonded thiol compounds, aliphatic ether-bonded thiol compounds, and aromatic ether-bonded thiol compounds.

[0081] Among them, it is preferable to use a curing agent other than the imidazole-based curing agent in combination with the imidazole-based curing agent, and in that case, it is preferable to use the imidazole-based curing agent as a curing catalyst.

[0082] The content of the curing agent is, for example, 1 part by mass or more and 40 parts by mass or less when the resin component contained in the adhesive layer is 100 parts by mass. For example, when an imidazole-based curing agent is used as the main component as the curing agent, the content of the curing agent is, for example, 1 part by mass or more and 15 parts by mass or less when the resin component contained in the adhesive layer is 100 parts by mass. On the other hand, when a phenol-based curing agent is used as the main component as the curing agent, the content of the curing agent is, for example, 5 parts by mass or more and 40 parts by mass or less when the resin component contained in the adhesive layer is 100 parts by mass. In addition, using an imidazole-based curing agent or a phenol-based curing agent as the main component as the curing agent means that the mass ratio of the imidazole-based curing agent or the phenol-based curing agent is the highest in the curing agent.

[0083] (c) Other ingredients In the adhesive layer of the present disclosure, for example, when the thermosetting adhesive is an epoxy resin adhesive, the adhesive layer may contain only the above-mentioned epoxy resin and acrylic resin as the resin component, or may further contain other resins, such as urethane resin.

[0084] The total proportion of epoxy resin and acrylic resin to the resin components contained in the adhesive layer is, for example, 70 mass% or more, optionally 80 mass% or more, optionally 90 mass% or more, or optionally 100 mass%.

[0085] The content of the resin component in the adhesive layer is, for example, 60% by mass or more, optionally 70% by mass or more, optionally 80% by mass or more, or optionally 90% by mass or more.

[0086] The adhesive layer may contain additives such as silane coupling agents, fillers, antioxidants, light stabilizers, ultraviolet absorbers, lubricants, plasticizers, antistatic agents, crosslinking agents, and colorants, as necessary. Examples of silane coupling agents include epoxy-based silane coupling agents. Examples of fillers include inorganic fillers such as calcium carbonate, aluminum hydroxide, magnesium hydroxide, antimony trioxide, zinc borate, molybdenum compounds, and titanium dioxide. Examples of antioxidants include phenol-based antioxidants and sulfur-based antioxidants.

[0087] (2) Adhesive layer The thickness of the adhesive layer is not particularly limited, but is preferably equal to or greater than the average particle size of the foaming agent. The thickness of the adhesive layer is, for example, 10 μm or more and 200 μm or less, may be 15 μm or more and 150 μm or less, or may be 20 μm or more and 100 μm or less. If the adhesive layer is too thin, there is a possibility that the adhesion to the substrate and the adhesiveness after foaming and curing cannot be sufficiently obtained. In addition, if the adhesive layer is too thick, there is a possibility that the surface quality will deteriorate.

[0088] Here, the thickness of the adhesive layer is a value measured from a cross section in the thickness direction of the foamable adhesive sheet observed with a transmission electron microscope (TEM), a scanning electron microscope (SEM), or a scanning transmission electron microscope (STEM), and can be the average value of the thicknesses at 10 randomly selected points. The same method can be used to measure the thicknesses of other layers of the foamable adhesive sheet.

[0089] The adhesive layer may be a continuous layer or a discontinuous layer. Examples of discontinuous layers include stripes, dots, and other patterns. The surface of the adhesive layer may have an uneven shape such as an embossed shape.

[0090] The adhesive layer can be formed, for example, by applying an adhesive composition and removing the solvent. Examples of the application 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, and dip coating.

[0091] The adhesive composition may or may not contain a solvent. In this specification, the solvent is used in a broad sense including not only a strict solvent (a solvent that dissolves a solute) but also a dispersion medium. The solvent contained in the adhesive composition is volatilized and removed when the adhesive composition is applied and dried to form an adhesive layer.

[0092] The adhesive composition can be obtained by mixing the above-mentioned components and kneading and dispersing them as necessary.As a mixing and dispersing method, a general kneading and dispersing machine, for example, a two-roll mill, a three-roll mill, a pebble mill, a tron ​​mill, a Szegvari attritor, a high-speed impeller dispersing machine, a high-speed stone mill, a high-speed impact mill, a disperser, a high-speed mixer, a ribbon blender, a co-kneader, an intensive mixer, a tumbler, a blender, a disperser, a homogenizer, or an ultrasonic dispersing machine can be used.

[0093] The foamable adhesive sheet of the present disclosure may have an adhesive layer, and may have, for example, only one adhesive layer, or may have a first adhesive layer and a second adhesive layer as the adhesive layer. In addition, when the foamable adhesive sheet of the present disclosure has a first adhesive layer and a second adhesive layer as the adhesive layer, the sheet may have the first adhesive layer and the second adhesive layer in this order, or the sheet may have the first adhesive layer, the substrate, and the second adhesive layer in this order. When a substrate is disposed between the first adhesive layer and the second adhesive layer, the handleability and workability of the foamable adhesive sheet can be improved. On the other hand, when the foamable adhesive sheet does not have a substrate, the thickness of the entire foamable adhesive sheet can be reduced. Therefore, for example, the foamable adhesive sheet can be inserted into a narrow gap.

[0094] 3.Base material The foamable adhesive sheet of the present disclosure has a first adhesive layer and a second adhesive layer as adhesive layers, and may have a substrate between the first adhesive layer and the second adhesive layer.

[0095] The substrate is preferably insulating. The substrate is preferably in the form of a sheet. The substrate may have a single layer structure or a multi-layer structure. The substrate may or may not have a porous structure inside.

[0096] Examples of the substrate include a resin substrate and a nonwoven fabric.

[0097] Examples of the resin contained in the resin substrate include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyester; 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; polyetherketone resins such as polyetheretherketone and polyetheretherketone; polyphenylene sulfide (PPS); and modified polyphenylene oxide. The glass transition temperature of the resin is, for example, 80° C. or higher, may be 140° C. or higher, or may be 200° C. or higher. In addition, a liquid crystal polymer (LCP) may be used as the resin.

[0098] Examples of the nonwoven fabric include nonwoven fabrics containing fibers such as cellulose fibers, polyester fibers, nylon fibers, aramid fibers, polyphenylene sulfide fibers, liquid crystal polymer fibers, glass fibers, metal fibers, and carbon fibers.

[0099] The substrate may be subjected to a surface treatment in order to enhance adhesion to the adhesive layer.

[0100] The thickness of the substrate is not particularly limited, and is, for example, from 2 μm to 200 μm, or may be from 5 μm to 100 μm, or may be from 9 μm to 50 μm.

[0101] 4.Other configurations The foamable adhesive sheet of the present disclosure may have other components, in addition to the adhesive layer and substrate described above, as necessary.

[0102] (1) Middle Class The foamable adhesive sheet of the present disclosure may have a first intermediate layer between the substrate and the first adhesive layer. The foamable adhesive sheet of the present disclosure may have a second intermediate layer between the substrate and the second adhesive layer. By disposing the first intermediate layer or the second intermediate layer, the adhesion of the first adhesive layer or the second adhesive layer to the substrate can be improved. Furthermore, by disposing the first intermediate layer or the second intermediate layer, for example, the stress applied to the bent portion when the foamable adhesive sheet is folded can be alleviated, or the stress applied to the cut portion when the foamable adhesive sheet is cut can be alleviated. As a result, the lifting or peeling of the first adhesive layer or the second adhesive layer from the substrate can be suppressed when the foamable adhesive sheet is bent or cut.

[0103] For example, in the foamable adhesive sheet 10 shown in Fig. 5, a first intermediate layer 3a is disposed between the substrate 2 and the first adhesive layer 1a, and a second intermediate layer 3b is disposed between the substrate 2 and the second adhesive layer 1b. Note that, although the foamable adhesive sheet 10 in Fig. 5 has both the first intermediate layer 3a and the second intermediate layer 3b, it may have only one of them.

[0104] The foamable adhesive sheet may have at least one of a first intermediate layer and a second intermediate layer, and may, for example, have only the first intermediate layer arranged between the substrate and the first adhesive layer, may have only the second intermediate layer arranged between the substrate and the second adhesive layer, or may have both the first intermediate layer arranged between the substrate and the first adhesive layer and the second intermediate layer arranged between the substrate and the second adhesive layer. Of these, it is preferable that the first intermediate layer is arranged between the substrate and the first adhesive layer, and the second intermediate layer is arranged between the substrate and the second adhesive layer.

[0105] The material contained in the first intermediate layer and the second intermediate layer is not particularly limited as long as it can increase the adhesion between the substrate and the first adhesive layer or the second adhesive layer and can relieve stress, and is appropriately selected depending on the materials of the substrate, the first adhesive layer, and the second adhesive layer, etc. Examples include polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, a polymer obtained by copolymerizing at least two or more of these, a crosslinked product thereof, and a mixture thereof.

[0106] The crosslinked product is a crosslinked product obtained by crosslinking the above-mentioned resin with a curing agent, such as an isocyanate-based curing agent.

[0107] In particular, the first intermediate layer and the second intermediate layer preferably contain a crosslinked resin. The crosslinked resin is one that does not melt even at high temperatures. This can improve the adhesive strength at high temperatures, i.e., heat resistance.

[0108] The thickness of the first intermediate layer and the second intermediate layer is not particularly limited, but may be, for example, 0.1 μm or more, may be 0.5 μm or more, or may be 1 μm or more. If the first intermediate layer or the second intermediate layer is too thin, the effect of suppressing peeling of the first adhesive layer or the second adhesive layer from the substrate when the foamable adhesive sheet is bent or cut may not be sufficiently obtained. On the other hand, the thickness of the first intermediate layer and the second intermediate layer may be, for example, 4 μm or less, or may be 3.5 μm or less. Since the first intermediate layer and the second intermediate layer themselves usually do not have high heat resistance, if the first intermediate layer or the second intermediate layer is too thick, the heat resistance (adhesive strength at high temperatures) may decrease.

[0109] The first intermediate layer and the second intermediate layer can be formed, for example, by applying a resin composition and removing the solvent. Examples of the application 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, and dip coating.

[0110] (2) Separator The foamable adhesive sheet according to the present disclosure may have a first separator on the side of the first adhesive layer opposite the second adhesive layer, and may have a second separator on the side of the second adhesive layer opposite the first adhesive layer.

[0111] The first separator and the second separator are not particularly limited as long as they can be peeled off from the first adhesive layer and the second adhesive layer, and can have a strength sufficient to protect the first adhesive layer and the second adhesive layer. Examples of such first separators and second separators include release films and release papers. In addition, the first separator and the second separator may have a single-layer structure or a multi-layer structure.

[0112] An example of a separator having a single layer structure is a fluororesin film.

[0113] In addition, examples of the separator having a multi-layer structure include laminates having a release layer on one or both sides of a substrate layer. Examples of the substrate layer include resin films such as polypropylene, polyethylene, and polyethylene terephthalate, and papers such as fine paper, coated paper, and impregnated paper. Materials for the release layer are not particularly limited as long as they have releasability, and examples include silicone compounds, organic compound-modified silicone compounds, fluorine compounds, aminoalkyd compounds, melamine compounds, acrylic compounds, polyester compounds, and long-chain alkyl compounds. These compounds can be any of emulsion type, solvent type, and solventless type.

[0114] 5. Foam adhesive sheet The thickness of the foamable adhesive sheet in the present disclosure is, for example, 10 μm or more, and may be 20 μm or more. On the other hand, the thickness of the foamable adhesive sheet is, for example, 1000 μm or less, and may be 200 μm or less. The thickness of the foamable adhesive sheet here is different from the initial thickness of the foamable adhesive sheet described above.

[0115] The use of the foamable adhesive sheet in the present disclosure is not particularly limited. The foamable adhesive sheet in the present disclosure can be used, for example, when two members are bonded together by disposing the foamable adhesive sheet between them and then foaming and curing the foamable adhesive sheet by heating. Specifically, the foamable adhesive sheet in the present disclosure is used for bonding the coil and stator in a motor, or the rotor and permanent magnet in an embedded magnet motor.

[0116] The method for producing the foamable adhesive sheet of the present disclosure is not particularly limited.

[0117] For example, when the foamable adhesive sheet has only one adhesive layer and does not have a substrate, an adhesive layer can be formed by applying an adhesive composition to one side of a separator and drying the adhesive composition, after which the separator can be peeled off.

[0118] Also, for example, when the foamable adhesive sheet has a first adhesive layer and a second adhesive layer as adhesive layers and has no substrate between the first adhesive layer and the second adhesive layer, a method can be exemplified in which an adhesive composition for forming the first adhesive layer is applied to a first separator and dried to form a first adhesive layer, an adhesive composition for forming the second adhesive layer is applied to a second separator and dried to form a second adhesive layer, and a laminate of the first separator and the first adhesive layer and a laminate of the second separator and the second adhesive layer are laminated together. After that, the first separator and the second separator may be peeled off.

[0119] Also, for example, when the foamable adhesive sheet has a first adhesive layer, a substrate, and a second adhesive layer in this order, a method can be mentioned in which the first adhesive layer and the second adhesive layer are formed by applying and drying an adhesive composition to both sides of the substrate, respectively. The first adhesive layer and the second adhesive layer can be formed sequentially or simultaneously. Also, for example, a method can be mentioned in which the first adhesive layer is formed by applying and drying an adhesive composition to one side of the substrate, and the second adhesive layer is formed by applying and drying an adhesive composition to one side of the separator, and the second adhesive layer and the separator are laminated to the other side of the substrate.

[0120] B. Method of Manufacturing the Structure The method for producing a structure according to the present disclosure has two embodiments, each of which will be described below.

[0121] 1. First embodiment A first embodiment of the method for manufacturing a structure according to the present disclosure is a method for manufacturing a structure, comprising: a positioning step of positioning a foamable adhesive sheet having an adhesive layer between a first member and a second member; and a bonding step of heating the foamable adhesive sheet to foam and harden it, thereby bonding the first member and the second member, wherein the adhesive layer contains a thermosetting adhesive and a foaming agent, and the foamable adhesive sheet is subjected to thermomechanical measurement in which a compressive load is applied to the foamable adhesive sheet, the temperature is raised at a predetermined heating rate, and the displacement is measured. The sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature of 160°C or more and less than 200°C is 100% or more and 308% or less with respect to a gap setting value of 100%, and the gap setting value is the distance of the gap after the foamable adhesive sheet is positioned between the first member and the second member.

[0122] 6(a)-(b) are process diagrams illustrating a method for producing a structure of this embodiment. First, as shown in FIG. 6(a), a foamable adhesive sheet 10 is disposed between a first member 20a and a second member 20b. Next, as shown in FIG. 6(b), the adhesive layer of the foamable adhesive sheet 10 is foamed and cured by heating. The first member 20a and the second member 20b are bonded (joined) by the foamed and cured adhesive sheet 11. This results in a structure 100 in which the adhesive sheet 11 is disposed between the first member 20a and the second member 20b.

[0123] Furthermore, in the foamable adhesive sheet of this embodiment, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a given temperature in the TMA curve as shown in FIG. 4 is within a given range for the gap setting value.

[0124] The gap setting value is the distance of the gap after the foamable adhesive sheet is disposed between the first member and the second member. For example, in Fig. 6(a), the sum of the distances d1 and d2 of the gaps G1 and G2 after the foamable adhesive sheet 10 is disposed between the first member 20a and the second member 20b is the gap setting value.

[0125] In the manufacturing method of the structure of this embodiment, the above-mentioned foamable adhesive sheet is used. Therefore, it is possible to obtain excellent foaming characteristics and adhesive characteristics suitable for the gap setting value. Therefore, in order to fill the gap between the members and to bond the members to each other, it is possible to select and use a foamable adhesive sheet that is optimal for the gap setting value.

[0126] The foamable adhesive sheet used in the method for producing a structure of this embodiment and each step of the method for producing a structure of this embodiment will be described below.

[0127] (1) Foamable adhesive sheet In the foamable adhesive sheet used in this embodiment, when a compressive load is applied to the foamable adhesive sheet, the temperature is raised at a prescribed heating rate, and the displacement is measured by thermomechanical measurement, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a prescribed temperature of 160°C or higher and lower than 200°C falls within a prescribed range for the gap setting value.

[0128] The foamable adhesive sheet may be the same as the foamable adhesive sheet described above.

[0129] In this embodiment, the gap setting value is the gap distance after the foamable adhesive sheet is disposed between the first member and the second member.

[0130] (2) Placement process The positioning step in this embodiment is a step of positioning a foamable adhesive sheet having an adhesive layer between the first member and the second member.

[0131] The method of arranging the foamable adhesive sheet between the first member and the second member is appropriately selected depending on the type of the first member and the second member. For example, the method includes a method of arranging a foamable adhesive sheet on one of the first member and the second member, and arranging the other member on the surface side of the foamable adhesive sheet opposite to the one member; a method of inserting a foamable adhesive sheet into the gap between the first member and the second member; a method of arranging a foamable adhesive sheet in a hole or groove of the first member, and then inserting a second member into the gap after arranging the foamable adhesive sheet in the hole or groove of the first member, and the like. In addition, for example, when the first member has a hole or groove and the second member is arranged and bonded in the hole or groove of the first member, a method of attaching a foamable adhesive sheet to the second member, and then arranging the second member to which the foamable adhesive sheet is attached, in the hole or groove of the first member; a method of attaching a foamable adhesive sheet to the hole or groove of the first member, and then arranging the second member in the hole or groove of the first member to which the foamable adhesive sheet is attached, and the like.

[0132] The first member and the second member are appropriately selected depending on the application of the structure. The first member and the second member are preferably members that require adhesion and insulation. For example, motor parts can be mentioned. Specifically, the coil and stator of a motor, and the rotor and permanent magnet of an embedded magnet type motor can be mentioned.

[0133] (3) Adhesion process The bonding step in this embodiment is a step of foaming and curing the foamable adhesive sheet by heating, thereby bonding the first member and the second member.

[0134] The heating temperature in the bonding step is preferably set so that the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a predetermined temperature is 100% or more and 308% or less, more preferably 112% or more and 294% or less, relative to the gap setting value of 100% when the foamable adhesive sheet is heated at a predetermined heating rate under a compressive load by thermomechanical measurement, and the displacement is measured. If the heating temperature is lower than the above range, the amount of displacement is small, so that foaming is insufficient and the adhesive strength may decrease. In this case, there is a possibility that interface failure may easily occur between the adhesive sheet and the first or second member after foaming and hardening. Also, as described above, in the case of a microcapsule type foaming agent, the amount of displacement tends to decrease after reaching the maximum amount of displacement in the TMA curve. Therefore, if the heating temperature is higher than the above range, the amount of displacement decreases after reaching the maximum amount of displacement, and as a result, the thickness of the adhesive layer at the time of foaming cannot be maintained, and the adhesive strength may decrease.

[0135] Specifically, the heating temperature is preferably 160° C. or higher and 190° C. or lower. By keeping the heating temperature within the above range, the heat resistance can be improved. Therefore, the composition can be applied to the surroundings of automobile engines and other applications requiring similar heat resistance.

[0136] 2. Second embodiment A second embodiment of the method for manufacturing a structure according to the present disclosure is a method for manufacturing a structure, comprising: a positioning step of positioning a foamable adhesive sheet having an adhesive layer between a first member and a second member; and a bonding step of heating the foamable adhesive sheet to foam and harden it, thereby bonding the first member and the second member, wherein the adhesive layer contains a thermosetting adhesive and a foaming agent, the heating temperature in the bonding step is 150°C or higher and lower than 200°C, and the foamable adhesive sheet is heated to the heating temperature at a predetermined heating rate by thermomechanical measurement while applying a compressive load, and the displacement is measured. The sum of the initial thickness and the displacement of the foamable adhesive sheet is set to be 121% or higher and 168% or lower with respect to a gap setting value of 100%, and the gap setting value is the distance of the gap after the foamable adhesive sheet is positioned between the first member and the second member.

[0137] 7 is a graph showing an example of a thermomechanical measurement (TMA) curve in which a compressive load is applied to a foamable adhesive sheet, the temperature is raised to a predetermined temperature at a predetermined heating rate, and the displacement is measured, with the horizontal axis representing time and the vertical axis representing displacement. In the manufacturing method of the structure of this embodiment, the heating temperature in the bonding step is set to 150°C or higher and lower than 200°C, and the sum of the initial thickness of the foamable adhesive sheet and the displacement in the TMA curve for the foamable adhesive sheet as shown in FIG. 7, for example, is set to be within a predetermined range with respect to the gap setting value.

[0138] In the foamable adhesive sheet of this embodiment, by setting the heating temperature in the bonding step to 150° C. or higher and lower than 200° C., and by setting the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement measured by thermomechanical measurement of the foamable adhesive sheet within a predetermined range for the gap setting, it is possible to obtain excellent foaming and adhesive properties suited to the gap setting. Thus, the heating conditions in the bonding step can be optimized for the gap setting.

[0139] Conventionally, the heating conditions during foaming and curing of a foamable adhesive sheet are set based on, for example, the foaming start temperature of the foaming agent, the maximum foaming temperature of the foaming agent, and the curing start temperature of the adhesive. For example, Patent Document 2 discloses that the heating conditions satisfy the relationship T1≦T2 when the thermal foaming temperature (foaming start temperature) of the thermal foaming agent is T1 and the curing start temperature of the adhesive layer is T2. However, when the inventors of the present disclosure investigated the heating conditions during foaming and curing of a foamable adhesive sheet, it was found that even when the foaming start temperature of the foaming agent and the curing start temperature of the adhesive layer have a predetermined relationship, the adhesive strength may decrease. Note that the foaming start temperature and maximum foaming temperature of the foaming agent are foaming characteristics of the foaming agent alone, and cannot be said to be foaming characteristics of the foamable adhesive sheet.

[0140] In contrast, in this embodiment, the heating conditions are set based on the initial thickness of the foamable adhesive sheet and the amount of displacement measured by thermomechanical measurement of the foamable adhesive sheet. As described above, the measurement conditions of the thermomechanical analysis can be made close to the foaming and curing conditions of the actual foamable adhesive sheet. Therefore, it is considered that the thermomechanical measurement can obtain a measurement value that reflects the foaming and curing behavior of the foamable adhesive sheet.

[0141] The foamable adhesive sheet used in the method for producing a structure of this embodiment and each step of the method for producing a structure of this embodiment will be described below.

[0142] (1) Foamable adhesive sheet The foamable adhesive sheet used in this embodiment has an adhesive layer, and the adhesive layer contains a thermosetting adhesive and a foaming agent.

[0143] The adhesive layer in the foamable adhesive sheet can be the same as the adhesive layer described in the above section "A. Foamable adhesive sheet 2. Adhesive layer."

[0144] Other configurations of the foamable adhesive sheet may be similar to those described above in the section "A. Foamable adhesive sheet."

[0145] (2) Placement process The positioning step in this embodiment is a step of positioning a foamable adhesive sheet having an adhesive layer between a first member and a second member. The positioning step and the first and second members can be the same as those in the first embodiment.

[0146] (3) Adhesion process The bonding step in this embodiment is a step of foaming and curing the foamable adhesive sheet by heating, thereby bonding the first member and the second member.

[0147] In this embodiment, the heating temperature in the bonding step is set to 150°C or more and less than 200°C, and when the foamable adhesive sheet is heated to the heating temperature at a predetermined heating rate by thermomechanical measurement while applying a compressive load, and the displacement is measured, the sum of the initial thickness and the amount of displacement of the foamable adhesive sheet is 121% or more and 168% or less with respect to the gap set value of 100%. In particular, it is preferable to set the heating temperature in the bonding step to 150°C or more and less than 200°C, and the sum of the initial thickness and the amount of displacement of the foamable adhesive sheet is 149% or more and 168% or less with respect to the gap set value of 100%. By setting the heating temperature within the above range, the heating conditions in the bonding step can be optimized with respect to the gap set value.

[0148] Here, the thermomechanical measurement is performed by the following method. First, the foamable adhesive sheet is punched out with a φ4 mm jig to prepare a sample. Next, the sample is placed in an aluminum container with φ5 mm, and an aluminum plate with φ4 mm is placed on the sample. Next, thermomechanical measurement is performed under the conditions of a temperature of 25°C to a predetermined heating temperature, a heating rate of 20°C / min, a load of 10 mN, and a compression mode, and the displacement associated with the expansion or contraction of the sample is measured. As a thermomechanical measurement device, for example, a thermomechanical analyzer TMA7100 manufactured by Hitachi High-Tech Science Corporation can be used.

[0149] Specifically, the heating temperature is preferably 160° C. or higher and 190° C. or lower. By keeping the heating temperature within the above range, the heat resistance can be improved. Therefore, the composition can be applied to the surroundings of automobile engines and other applications requiring similar heat resistance.

[0150] The gap setting value is the same as the gap setting value described in the above section "A. Foamable adhesive sheet."

[0151] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits similar effects is included in the technical scope of the present disclosure. EXAMPLES

[0152] [Manufacturing examples I~III] First, an adhesive composition was prepared having the composition shown in Table 1 below. Details of each material shown in Table 1 are shown below.

[0153] Acrylic resin: PMMA-PBuA-PMMA (partially acrylamide groups), Tg: -20℃, 120℃, Mw: 150,000 Epoxy resin A: Bisphenol A novolac type, solid at room temperature, softening temperature: 70°C, epoxy equivalent: 210g / eq, Mw: 1300, melt viscosity at 150°C: 0.5Pa s Epoxy resin B: BPA phenoxy type, solid at room temperature, softening temperature: 110℃, epoxy equivalent: 8000g / eq, Mw: 50,000 Epoxy resin C: Bisphenol A type, liquid at room temperature, epoxy equivalent: 184~194g / eq Epoxy resin D: Diaminodiphenylmethane type, highly viscous liquid, epoxy equivalent: 110-130g / eq Epoxy resin E: silicone modified, epoxy equivalent: 1200g / mol Hardener 1: α-(hydroxy(or dihydroxy)phenylmethyl)-ω-hydropoly[biphenyl-4,4'-diylmethylene(hydroxy(or dihydroxy)phenylenemethylene)] Hardener 2: 2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction start temperature: 145°C to 155°C, active region: 155°C to 173°C (Shikoku Chemical Industry Co., Ltd., 2PHZ-PW)

[0154] Thermal foaming agent 1: Thermal expansion microcapsule, average particle size 13μm, expansion start temperature 123~133℃, maximum expansion temperature 168~178℃, core: hydrocarbon, shell: thermoplastic polymer Thermal foaming agent 2: Thermal expansion microcapsule, average particle size 21μm, expansion start temperature 120~130℃, maximum expansion temperature 175~190℃, core: hydrocarbon, shell: thermoplastic polymer Silane coupling agent: 3-glycidoxypropyltrimethoxysilane Solvent: Methyl ethyl ketone

[0155] [Table 1]

[0156] [Manufacturing Examples 1-9] As a substrate, a polyethylene naphthalate film (PEN film, Toyobo Film Solutions Co., Ltd., Teonex Q51, thickness 25 μm) was prepared with an intermediate layer having a thickness of 5 μm or less on one surface. Next, the adhesive composition was applied to the surface of the substrate opposite to the intermediate layer using an applicator so that the thickness after drying was 45 μm. Then, the substrate was dried in an oven at 100° C. for 3 minutes to form a first adhesive layer.

[0157] Next, the adhesive composition was applied to the surface of the intermediate layer opposite to the substrate using an applicator so that the thickness after drying was 45 μm, and then dried in an oven at 100° C. for 3 minutes to form a second adhesive layer.

[0158] Next, a release film (PET separator, Nippa Corporation, PET50x1-J2, thickness 50 μm) was laminated as a second separator on the surface of the second adhesive layer of the laminate having the first adhesive layer, substrate, intermediate layer, and second adhesive layer in this order. This resulted in a foamable adhesive sheet in which the first adhesive layer, substrate, intermediate layer, second adhesive layer, and second separator were arranged in this order.

[0159] [Table 2]

[0160] [Rating 1] (1) Thermomechanical Analysis (TMA) As a thermomechanical measuring device, a thermomechanical analyzer TMA7100 manufactured by Hitachi High-Tech Science Corporation was used. First, the foamable adhesive sheet was punched out with a φ4mm jig to prepare a sample. Next, the sample was placed in an aluminum container with a φ5mm so that the second adhesive layer was at the bottom, and an aluminum plate with a φ4mm was placed on the sample. In this state, the expansion and compression probe of the thermomechanical measuring device was brought into contact with the sample at a load of 100mN, and the thickness of the sample after the aluminum plate and the sample were brought into contact sufficiently smoothly was taken as the initial thickness of the foamable adhesive sheet. Next, a thermomechanical measurement was performed under the conditions of temperature: 25°C to 250°C, heating rate: 20°C / min, load: 10mN, and compression mode, and the displacement due to the expansion or contraction of the sample was measured. Then, the amount of displacement at each temperature was determined.

[0161] (2) Adhesive strength Two metal plates (cold-rolled steel plate SPCC-SD) with a thickness of 1.6 mm, width of 25 mm, and length of 100 mm were prepared. A spacer was placed at one end of one of the metal plates with a gap of 15 mm. The thickness of the spacer was 300 μm (thickness of five sheets of Kapton tape P-221 made by Nitto Denko Corporation) or 370 μm (thickness of two sheets of Kapton tape P-221 made by Nitto Denko Corporation and one sheet of fluororesin adhesive tape 8410 made by Teraoka Seisakusho). In addition, the foamable adhesive sheet was cut into a size of 12.5 mm x 25 mm. The separator was peeled off from the foamable adhesive sheet. Next, the foamable adhesive sheet was placed between the spacers, and another metal plate was placed so that one end of the metal plate overlapped, and fixed with a clip to obtain a test piece. The test piece was then placed in a thermal oven (manufactured by Yamato Scientific Co., Ltd., DN610) and heated to foam and cure the first and second adhesive layers of the foamable adhesive sheet under the following heating conditions: heating rate: 20°C / min, heating temperatures: 160°C, 180°C, and 200°C.

[0162] The shear strength (adhesive strength) of the heated test piece was measured in accordance with JIS K6850 using a tensile tester Tensilon RTF1350 (manufactured by A&D Co., Ltd.) under the measurement conditions of a tensile speed of 10 mm / min and a temperature of 23°C.

[0163] [Table 3]

[0164] As shown in Test Nos. 1 to 9, in the foamable adhesive sheets of Production Examples 1 to 6, the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement at a prescribed temperature of 160°C or more and less than 200°C, measured by TMA, was within a prescribed range for the gap setting. In the case of these foamable adhesive sheets, a comparison of Test Nos. 1 to 9 with Test Nos. 10 to 12 revealed that the adhesive strength was high when the heating temperature in the bonding step was 160°C or more and 190°C or less.

[0165] [Rating 2] (1) Thermomechanical Analysis (TMA) As the thermomechanical measuring device, a thermomechanical analyzer TMA7100 manufactured by Hitachi High-Tech Science Corporation was used. First, the foamable adhesive sheet was punched out with a φ4mm jig to prepare a sample. Next, the sample was placed in an aluminum container with a φ5mm so that the second adhesive layer was at the bottom, and an aluminum plate with a φ4mm was placed on the sample. In this state, the expansion and compression probe of the thermomechanical measuring device was brought into contact with the sample at a load of 100mN, and the thickness of the sample after the aluminum plate and the sample were brought into contact sufficiently smoothly was taken as the initial thickness of the foamable adhesive sheet. Next, a thermomechanical measurement was performed under the conditions of a temperature rise rate of 20°C / min, a load of 10mN, and a compression mode from a temperature of 25°C to the final temperature, and the displacement associated with the expansion or contraction of the sample was measured. At this time, the final temperatures were 150°C, 160°C, 180°C, 190°C, and 200°C.

[0166] (2) Adhesive strength The shear strength (adhesive strength) was measured in the same manner as in Evaluation 1. Regarding the heating conditions for the foamable adhesive sheet, the heating temperatures were 150°C, 160°C, 180°C, 190°C, and 200°C.

[0167] [Table 4]

[0168] From Table 2, it can be seen that the adhesive strength is high when the heating temperature in the bonding process is greater than or equal to 150°C and less than 200°C, and when the temperature is such that the sum of the initial thickness of the foamable adhesive sheet and the amount of displacement measured by TMA is within a specified range relative to the gap setting value. [Explanation of symbols]

[0169] 1 … Adhesive layer 1a … First adhesive layer 1b…Second adhesive layer 2...Base material 3a … First intermediate layer 3b…Second intermediate layer 10... Foam adhesive sheet 11 ... Adhesive sheet after foaming and hardening 20a … First member 20b … Second member 100 … structure

Claims

1. A foamable adhesive sheet having an adhesive layer, The adhesive layer contains a thermosetting adhesive and a foaming agent, The foamable adhesive sheet is used in a case where the foamable adhesive sheet is disposed between a first member and a second member, and then the foamable adhesive sheet is heated to foam and harden the foamable adhesive sheet, thereby bonding the first member and the second member; The distance of the gap after the foamable adhesive sheet is disposed between the first member and the second member is defined as a gap setting value, and the gap setting value is defined as D; In the foamable adhesive sheet, a compressive load is applied, the temperature is increased at a predetermined heating rate, and the displacement is measured by thermomechanical measurement. When the initial thickness of the foamable adhesive sheet is T 1 and the amount of displacement at a predetermined temperature of 160° C. or more and less than 200° C. is δ 1 , The gap setting value D is 100 μm or more and 500 μm or less, A foamable adhesive sheet, wherein the sum (T 1 + δ 1 ) of the initial thickness T 1 and the displacement δ 1 of the foamable adhesive sheet and the gap set value D are within a region surrounded by the straight lines represented by the following formulas (1) to (4) in a graph with the sum (T 1 + δ 1 ) (μm) of the initial thickness T 1 and the displacement δ 1 of the foamable adhesive sheet on the horizontal axis and the gap set value D (μm) on the vertical axis. D=T 1 +δ 1 (1) D=(T 1 +δ 1 ) / 3.08 (2) D = 100 (3) D = 500 (4)

2. The adhesive layer includes a first adhesive layer and a second adhesive layer, The foamable adhesive sheet according to claim 1 , comprising the first adhesive layer, a substrate, and the second adhesive layer in this order.

3. A positioning step of positioning a foamable adhesive sheet having an adhesive layer between a first member and a second member; a bonding step of foaming and curing the foamable adhesive sheet by heating to bond the first member and the second member; A method for producing a structure having the following steps: The adhesive layer contains a thermosetting adhesive and a foaming agent, The distance of the gap after the foamable adhesive sheet is disposed between the first member and the second member is defined as a gap setting value, and the gap setting value is defined as D; In the foamable adhesive sheet, a compressive load is applied, the temperature is increased at a predetermined heating rate, and the displacement is measured by thermomechanical measurement. When the initial thickness of the foamable adhesive sheet is T 1 and the amount of displacement at a predetermined temperature of 160° C. or more and less than 200° C. is δ 1 , The gap setting value D is 100 μm or more and 500 μm or less, A method for manufacturing a structure, wherein the sum (T 1 + δ 1 ) of the initial thickness T 1 and the displacement δ 1 of the foamable adhesive sheet and the gap setting value D are within a region surrounded by the straight lines represented by the following formulas (1) to (4) in a graph having the sum (T 1 + δ 1 ) (μm) of the initial thickness T 1 and the displacement δ 1 of the foamable adhesive sheet on the horizontal axis and the gap setting value D (μm) on the vertical axis. D=T 1 +δ 1 (1) D=(T 1 +δ 1 ) / 3.08 (2) D = 100 (3) D = 500 (4)

4. A method for manufacturing the structure described in claim 3, wherein the heating temperature in the bonding process is 160°C or higher and 190°C or lower.

5. A method for manufacturing a structure as described in claim 3 or claim 4, wherein the foamable adhesive sheet has a first adhesive layer and a second adhesive layer as the adhesive layers, and has the first adhesive layer, a substrate, and the second adhesive layer in this order.

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