Adhesive sheets, foam-forming properties, and manufacturing methods for products using those properties.

Abstract

DEPCT67 A foam-based adhesive sheet consisting of a primary adhesive layer, a substrate, and a secondary adhesive layer. In order, the first and second adhesive layers mentioned above include adhesive properties. Solidified, in which at least one of the above first adhesive layer and at least one of the above second adhesive layers constitutes the solid. Additionally, with foaming agent, the first adhesive layer listed above must have a force of 0 grams or more. Less than 10 grams of force; the tack of the second adhesive layer above is greater than or equal to 10 grams of force and less. Or equal to 500 grams of force, and the characteristic stiffness of the loop is greater than or equal to... 50 millinewtons / 10 millimeters;

Description

Foamable adhesive sheet and method for manufacturing article

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

[0002] Adhesives are widely used in various fields to bond components together. For example, adhesives are used to secure one component to a hole or groove in another component. Specifically, adhesives are used to secure permanent magnets in the holes in the core of interior permanent magnet motors.

[0003] Liquid adhesives are the mainstream adhesives used in motors, but liquid adhesives can have problems such as uneven application, spillage, and dripping, making the bonding process more complicated.

[0004] On the other hand, in recent years, it has been proposed to use a sheet-type adhesive containing a foaming agent (foamable adhesive sheet) instead of a liquid adhesive (see, for example, Patent Document 1). Foamable adhesive sheets can prevent the above-mentioned problems that occur with liquid adhesives.

[0005] Patent No. 6874867

[0006] For example, when fixing one component to a hole or groove in another component, as described in Patent Document 1, a foamable adhesive sheet is attached to the other component to temporarily fix it, and the other component with the foamable adhesive sheet attached is placed in the hole or groove in the one component, and then the foamable adhesive sheet is foamed and hardened, thereby adhesively fixing the two components together.

[0007] When one component is fixed to a hole, groove, or the like of another component, the gap between the two components tends to become narrow. Therefore, the foamable adhesive sheet used is required to have a thin overall thickness. However, if the foamable adhesive sheet is thin, it is likely to sag under its own weight during transport. For example, when a foamable adhesive sheet is transported by suction, a thin foamable adhesive sheet is likely to cause both ends of the foamable adhesive sheet to sag under its own weight. Therefore, when a foamable adhesive sheet is transported by suction and attached to another component, problems such as folding, kinking, warping, and air bubble entrapment can occur during attachment. Furthermore, if a foamable adhesive sheet is attached to another component in such a defective state, a protrusion will form in the foamable adhesive sheet, which can cause the foamable adhesive sheet to rub against a hole, groove, or the like of one component when the other component to which the foamable adhesive sheet is attached is inserted, resulting in peeling. In such cases, the adhesiveness after foaming and curing is reduced, resulting in low reliability.

[0008] In the adhesive fixing method described above, the adhesiveness of the foamable adhesive sheet is utilized to attach the foamable adhesive sheet to the other component for temporary fixation. However, if the adhesiveness of the foamable adhesive sheet is high, there is a problem that the insertability of the other component to which the foamable adhesive sheet is attached is reduced when inserting the other component into a hole, groove, etc. of the first component.

[0009] The first embodiment of the present disclosure has been made in consideration of the above circumstances, and has as its main object to provide a foamable adhesive sheet that is excellent in application properties and insertability.

[0010] Furthermore, when fixing one component to a hole or groove of the other component, for example, as described in Patent Document 1, a foamable adhesive sheet can be attached to the other component to temporarily fix it, and then the other component with the foamable adhesive sheet attached is placed in the hole or groove of the one component, and the foamable adhesive sheet is then foamed and hardened, thereby adhesively fixing the two components together.

[0011] When one component is fixed to a hole or groove in another component, the gap between the two components tends to be narrow, so the foamable adhesive sheet used is required to have a small overall thickness.

[0012] In the case of a foamable adhesive sheet, it has been proposed to arrange adhesive layers on both sides of a substrate and to make the properties of the two adhesive layers different. For example, Patent Document 1 discloses making the expansion coefficients of the two adhesive layers different.

[0013] However, when the two adhesive layers in a foamable adhesive sheet are different, curling may occur. This is particularly likely when the thickness of the foamable adhesive sheet is reduced. This can hinder the foamable adhesive sheet from adhering to a component, or can cause the foamable adhesive sheet to lift or peel. In such cases, the adhesive strength after foaming and curing is reduced, resulting in reduced reliability.

[0014] Furthermore, if the foamable adhesive sheet is thin, it is likely to sag under its own weight during transport. For example, when a foamable adhesive sheet is transported by suction, a thin foamable adhesive sheet is likely to cause both ends of the foamable adhesive sheet to sag under its own weight. Therefore, when a foamable adhesive sheet is transported by suction and attached to a component, problems such as folding, kinking, warping, and air bubble entrapment can occur during attachment. Furthermore, if a foamable adhesive sheet is attached to a component in such a defective state, a protrusion will form on the foamable adhesive sheet. This can cause the foamable adhesive sheet to rub against a hole or groove in one component, resulting in peeling. In such cases, the adhesive strength after foaming and curing is reduced, resulting in reduced reliability.

[0015] The second embodiment of the present disclosure has been made in consideration of the above-described circumstances, and has as its main object to provide a foamable adhesive sheet that can suppress curling and has excellent adhesion properties.

[0016] One implementation of the first embodiment of the present disclosure provides a foamable adhesive sheet having a first adhesive layer, a substrate, and a second adhesive layer in this order, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, and at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent, and the tack of the first adhesive layer is 0 gf or more and less than 10 gf, and the tack of the second adhesive layer is 10 gf or more and 500 gf or less, and the loop stiffness is 50 mN / 10 mm or more.

[0017] Another aspect of the first embodiment of the present disclosure provides a foamable adhesive sheet having, in this order, a first adhesive layer, a substrate, a second adhesive layer, and an adhesive layer, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive and a foaming agent, the adhesive layer contains a pressure-sensitive adhesive or a curable adhesive, the first adhesive layer has a tack of 0 gf or more and less than 10 gf, the adhesive layer has a tack of 10 gf or more, and a loop stiffness of 50 mN / 10 mm or more.

[0018] One implementation of the second embodiment of the present disclosure provides a foamable adhesive sheet having a first adhesive layer, a substrate, and a second adhesive layer in this order, wherein the composition of the first adhesive layer is different from the composition of the second adhesive layer, the first adhesive layer and the second adhesive layer contain a thermosetting adhesive, and at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent, and wherein after being left to stand for 15 hours at a temperature of 60°C and a humidity of 10% RH or less, the curl radius of curvature of the foamable adhesive sheet is 15 mm or more and the loop stiffness is 45 mN / 10 mm or more.

[0019] Another embodiment of the present disclosure provides a method for manufacturing an article, comprising: a placement step of placing the above-mentioned foamable adhesive sheet between a first member and a second member; and a bonding step of foaming and curing the foamable adhesive sheet to bond the first member and the second member together.

[0020] The foamable adhesive sheet according to the first embodiment of the present disclosure exhibits the effects of excellent adhesion and insertability.

[0021] Furthermore, the foamable adhesive sheet according to the second embodiment of the present disclosure exhibits the effect of being able to suppress curling and having excellent adhesion properties.

[0022] FIG. 1 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to the present disclosure. FIG. 2 is a schematic plan view and cross-sectional view illustrating an example of a loop stiffness measuring instrument. FIG. 3 is a schematic view illustrating a method for measuring loop stiffness. FIG. 4 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to the present disclosure. FIG. 5 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to the present disclosure. FIG. 6 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to the present disclosure. FIG. 7 is a process diagram illustrating an example of a method for manufacturing an article according to the present disclosure. FIG. 8 is a process diagram illustrating an example of a method for manufacturing an article according to the present disclosure. FIG. 9 is a schematic view illustrating a method for measuring the amount of sagging. FIG. 10 is a schematic view illustrating a method for measuring the radius of curvature of curl. FIG. 11 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to the present disclosure. FIG. 12 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to the present disclosure.

[0023] Embodiments of the present disclosure will be described below with reference to the drawings and the like. However, the present disclosure can be implemented in many different forms, and should not be construed as being limited to the description of the embodiments exemplified below. Furthermore, to clarify the explanation, the drawings may schematically depict the width, thickness, shape, etc. of each part compared to the actual form, but these are merely examples and are not intended to limit the interpretation of the present disclosure. Furthermore, in this specification and each drawing, elements similar to those previously described with reference to the preceding drawings will be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0024] In this specification, when describing a mode in which another component is placed on a certain component, the terms "above" or "below" are used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween. Also, in this specification, when describing a mode in which another component is placed on the surface of a certain component, the terms "on the surface side" or "on the surface" are used, unless otherwise specified, to include both a case in which another component is placed directly above or below a certain component so as to be in contact with the component, and a case in which another component is placed above or below a certain component with another component interposed therebetween.

[0025] In this specification, the term "sheet" also includes a member called a "film." The term "film" also includes a member called a "sheet."

[0026] Hereinafter, the present disclosure will be described separately as a first embodiment and a second embodiment.

[0027] I. First Embodiment First, a foamable adhesive sheet according to a first embodiment of the present disclosure and a method for producing an article using the same will be described.

[0028] A. Foamable Adhesive Sheet The foamable adhesive sheet of this embodiment has two embodiments, each of which will be described below.

[0029] A) First embodiment A first embodiment of the foamable adhesive sheet in this embodiment is a foamable adhesive sheet having a first adhesive layer, a substrate, and a second adhesive layer in this order, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent, the first adhesive layer has a tack of 0 gf or more and less than 10 gf, the second adhesive layer has a tack of 10 gf or more and 500 gf or less, and the loop stiffness is 50 mN / 10 mm or more.

[0030] Figure 1 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to this embodiment. The foamable adhesive sheet 10 in Figure 1 comprises, in this order, a first adhesive layer 1, a substrate 2, and a second adhesive layer 3. The first adhesive layer 1 and the second adhesive layer 3 contain a curable adhesive, and at least one of the first adhesive layer 1 and the second adhesive layer 3 further contains a foaming agent. The tack of the first adhesive layer 1 and the tack of the second adhesive layer 3 each fall within a predetermined range, and the loop stiffness of the foamable adhesive sheet 10 falls within a predetermined range.

[0031] In this embodiment, the tackiness of the second adhesive layer within a predetermined range allows the second adhesive layer to have good adhesion to the member. Specifically, when adhesively fixing one member to a hole, groove, or the like of another member, by attaching the second adhesive layer surface of the foamable adhesive sheet to the other member, inserting the other member to which the foamable adhesive sheet is attached into the hole, groove, or the like of the one member, and then foaming and curing the foamable adhesive sheet to bond the one member and the other member, the tackiness of the second adhesive layer within a predetermined range allows the second adhesive layer surface of the foamable adhesive sheet to be attached to the other member, thereby improving the adhesion of the second adhesive layer to the member. This prevents the foamable adhesive sheet from peeling off or shifting when inserting the other member to which the foamable adhesive sheet is attached into the hole, groove, or the like of the one member.

[0032] In this embodiment, the tackiness of the second adhesive layer is within a predetermined range, which allows the second adhesive layer to have good reworkability. Therefore, for example, in the above-mentioned adhesive fixing method, the tackiness of the second adhesive layer can be used to correct misalignment of the foamable adhesive sheet when attaching the second adhesive layer surface of the foamable adhesive sheet to one of the members.

[0033] In this embodiment, since the tackiness of the second adhesive layer is within a predetermined range, for example, when the second adhesive layer is formed by a transfer method, lifting of the second adhesive layer can be suppressed. Furthermore, as will be described later, when a second separator is disposed on the side of the second adhesive layer opposite the first adhesive layer, since the tackiness of the second adhesive layer is within a predetermined range, the second separator can be easily peeled off, thereby improving workability.

[0034] Furthermore, in this embodiment, since the tackiness of the first adhesive layer is equal to or less than a predetermined value, the first adhesive layer can be made substantially non-tacky (tack-free) and can have good slipperiness. Therefore, for example, in the above-described adhesive fixing method, when inserting a component to which a foamable adhesive sheet is attached into a hole, groove, or the like of one component, the component to which the foamable adhesive sheet is attached can be smoothly inserted, improving insertability. This prevents peeling and misalignment of the foamable adhesive sheet. Furthermore, in the above-described adhesive fixing method, when aligning the components by moving the other component relative to the first component, the other component can be smoothly moved relative to the first component while the other component is inserted into a hole, groove, or the like of the first component, facilitating alignment.

[0035] Furthermore, in this embodiment, the tackiness of the first adhesive layer is a predetermined value or less, and the first adhesive layer is substantially non-sticky (tack-free), so the first adhesive layer has good slip properties and good blocking resistance, which in turn improves the handleability of the foamable adhesive sheet.

[0036] Furthermore, in this embodiment, as described above, the second adhesive layer has excellent adhesion to the member, and the first adhesive layer has excellent slipperiness, so peeling and misalignment of the foamable adhesive sheet can be suppressed. Therefore, a decrease in the adhesive strength of the foamable adhesive sheet after foaming and curing due to peeling or misalignment of the foamable adhesive sheet can be suppressed, and variation in the adhesive strength of the foamable adhesive sheet after foaming and curing due to peeling or misalignment of the foamable adhesive sheet can be reduced. Therefore, by using the foamable adhesive sheet of this embodiment, high adhesive strength, high reliability, and high-quality adhesion can be achieved.

[0037] Here, when one component is adhesively fixed to a hole, groove, or the like of another component, the gap between the two components tends to narrow, as described above. Therefore, the foamable adhesive sheet used is required to have a thin overall thickness. However, if the foamable adhesive sheet is too thin, it is likely to sag under its own weight during transport. Therefore, the inventors of the present disclosure focused on the rigidity of the foamable adhesive sheet. A thicker foamable adhesive sheet tends to have a higher rigidity. However, since the foamable adhesive sheet must be thin to begin with, increasing the thickness of the foamable adhesive sheet is not suitable. Furthermore, when a foamable adhesive sheet has adhesive layers on both sides of a substrate, a thicker substrate tends to have a higher rigidity. However, if the thickness of the substrate is relatively increased while the thickness of the foamable adhesive sheet remains thin, the adhesive layer becomes relatively thin, which may result in a decrease in the adhesive and foaming properties of the adhesive layer. In general, adhesive layers tend to be softer as their tackiness increases, and harder as their tackiness decreases. Therefore, when a foamable adhesive sheet has an adhesive layer with tackiness, its rigidity tends to be low. The inventors of the present disclosure have discovered that by setting the loop stiffness of the foamable adhesive sheet within a predetermined range, it is possible to prevent the foamable adhesive sheet from sagging under its own weight. Furthermore, they have discovered that by making the first adhesive layer of the first and second adhesive layers substantially non-tacky (tack-free), it is possible to improve insertion ease while also increasing rigidity.

[0038] Loop stiffness is a parameter that indicates the stiffness of a sheet or film. The higher the loop stiffness value, the stiffer the sheet or film. Loop stiffness is used as a parameter to indicate the stiffness of sheets and films used in packaging materials, for example, but is not very common in the field of adhesive sheets.

[0039] The foamable adhesive sheet of this embodiment has a loop stiffness equal to or greater than a predetermined value, thereby enhancing stiffness. Therefore, sagging of the foamable adhesive sheet due to its own weight can be suppressed during transport. Therefore, for example, when a foamable adhesive sheet is transported by suction and attached to another component, folding, kinking, bending, air bubble entrapment, and the like of the foamable adhesive sheet during attachment can be suppressed. This improves attachment properties. Furthermore, since the occurrence of protrusions in the foamable adhesive sheet due to these defects can be suppressed, the foamable adhesive sheet is less likely to rub when inserting a component to which the foamable adhesive sheet is attached into a hole, groove, or the like of one component. Therefore, peeling of the foamable adhesive sheet during insertion can be suppressed. Therefore, from these points of view, the use of the foamable adhesive sheet of this embodiment can achieve high adhesive strength, high reliability, and high-quality adhesion.

[0040] Here, "adhesion" is a concept included in "bonding." The two are sometimes distinguished in that "adhesion" is used to mean a temporary adhesive phenomenon, while "bonding" is used to mean a substantially permanent adhesive phenomenon (Iwanami Shoten, Physics and Chemistry Dictionary, 5th Edition). "Adhesion" and "adhesive strength" refer to the property of adhesion through pressure and the adhesive strength at that time.

[0041] In this specification, unless otherwise specified, the terms "adhesion of the adhesive layer" and "adhesion strength of the adhesive layer" refer to the adhesion and adhesive strength of the adhesive layer before curing. In addition, in this specification, unless otherwise specified, the terms "adhesion of the adhesive layer" and "adhesion strength of the adhesive layer" refer to the adhesion and adhesive strength of the adhesive layer after curing.

[0042] Each component of the foamable adhesive sheet of this embodiment will be described below.

[0043] 1. Properties In this embodiment, the tackiness of the first adhesive layer is 0 gf or more and less than 10 gf, and may be 5 gf or less, or may be 2 gf or less. When the tackiness of the first adhesive layer is within the above range, the first adhesive layer can be made substantially non-sticky (tack-free), and can be made into a first adhesive layer with good sliding properties and blocking resistance.

[0044] In this embodiment, the tack of the second adhesive layer is 10 gf or more, 30 gf or more, or even 50 gf or more. If the tack of the second adhesive layer is too low, for example, in the above-mentioned adhesive fixing method, when the tack of the second adhesive layer is used to attach the second adhesive layer surface of the foamable adhesive sheet to the other component, the adhesion between the second adhesive layer and the other component may be reduced. Also, when inserting the other component to which the foamable adhesive sheet is attached into a hole or groove of one component, poor adhesion between the second adhesive layer and the other component may cause the foamable adhesive sheet to peel off or the position of the foamable adhesive sheet to shift, resulting in a reduction in the adhesion of the first adhesive layer and the second adhesive layer after foaming and curing, or variations in adhesive strength. Furthermore, the tack of the second adhesive layer may be 500 gf or less, 400 gf or less, or 300 gf or less. If the tackiness of the second adhesive layer is too high, reworkability will be reduced, and for example, in the above-mentioned adhesive fixing method, when using the tackiness of the second adhesive layer to attach the second adhesive layer surface of the foamable adhesive sheet to another component, it may become difficult to correct misalignment of the foamable adhesive sheet.

[0045] Here, the tackiness of the first adhesive layer and the second adhesive layer can be measured by a probe tack test. As a probe tack tester, for example, a tackiness tester "TAC-II" manufactured by RHESCA can be used. Details of the method for measuring the tackiness of the first adhesive layer and the second adhesive layer will be described in the Examples section below.

[0046] In this embodiment, the tackiness of the first adhesive layer can be adjusted to a predetermined range, for example, by adjusting the composition of the first adhesive layer. Specifically, the adhesiveness of the first adhesive layer can be reduced by using an epoxy resin that is solid at room temperature or a curing agent that is solid at room temperature in the first adhesive layer containing an epoxy resin and a curing agent. Furthermore, the adhesiveness of the first adhesive layer can be reduced by including an epoxy resin with a high softening temperature or an epoxy resin with a high weight-average molecular weight in the first adhesive layer containing an epoxy resin and a curing agent. For example, the adhesiveness of the first adhesive layer can be reduced by including multiple epoxy resins with different softening temperatures in the first adhesive layer, i.e., by including one epoxy resin and another epoxy resin with a softening temperature of 25°C or higher and 10°C or higher than the softening temperature of the first epoxy resin. Furthermore, for example, the adhesive strength of the first adhesive layer can be reduced by including multiple epoxy resins with different weight-average molecular weights in the first adhesive layer. That is, the first adhesive layer can include one epoxy resin and another epoxy resin with a weight-average molecular weight of 370 or more that is 300 or more greater than that of the first epoxy resin. More specifically, the adhesive strength of the first adhesive layer can be reduced by including a first epoxy resin with a low softening temperature and low molecular weight and a second epoxy resin with a high softening temperature and high molecular weight, as described below, in the first adhesive layer containing an epoxy resin and a curing agent. The adhesive strength of the first adhesive layer can be reduced by including an acrylic resin compatible with the epoxy resin, as described below, in the first adhesive layer containing an epoxy resin and a curing agent.

[0047] In this embodiment, the tackiness of the second adhesive layer can be controlled, for example, by adjusting the composition of the second adhesive layer. Specifically, when an epoxy resin that is liquid at room temperature or a curing agent is used in a second adhesive layer containing an epoxy resin and a curing agent, the adhesiveness of the second adhesive layer tends to increase. Furthermore, when an epoxy resin with a low softening temperature or an epoxy resin with a low weight-average molecular weight is added to a second adhesive layer containing an epoxy resin and a curing agent, the adhesiveness of the second adhesive layer tends to increase. Furthermore, adding a tackifier to the second adhesive layer tends to increase the adhesiveness of the second adhesive layer. Although using a curing agent that is liquid at room temperature tends to increase the adhesiveness, it may also decrease storage stability. Therefore, it is preferable to adjust the tackiness of the second adhesive layer by adjusting the properties and type of components other than the curing agent, such as the epoxy resin.

[0048] In this embodiment, the static friction coefficient of the surface of the first adhesive layer opposite the second adhesive layer is, for example, preferably 0.33 or less, or may be 0.30 or less, or may be 0.26 or less. When the static friction coefficient of the surface of the first adhesive layer is within the above range, the first adhesive layer can have good slip properties. Furthermore, the static friction coefficient may be, for example, 0.16 or more.

[0049] Here, the static friction coefficient of the surface of the first adhesive layer can be determined in accordance with JIS K7125, which corresponds to ISO 8295. Specifically, the static friction coefficient between the first adhesive layer of the foamable adhesive sheet and a metal plate is measured by the following method. First, the foamable adhesive sheet is cut into 80 mm x 200 mm pieces. Next, the foamable adhesive sheet is placed on a horizontally placed rectangular metal plate (SUS plate), and a sliding piece (63 mm x 63 mm, weight 200 g, bottom: felt) is placed on the first adhesive layer of the foamable adhesive sheet. The friction force is measured under conditions of a test speed of 100 mm / min, a test length of 50 mm, a load cell of 10 N, and a temperature of 23°C, and the static friction coefficient is calculated. For example, a friction measuring device such as the FRICTION TESTER TR-2 manufactured by Toyo Seiki Seisakusho, Ltd. can be used.

[0050] In this embodiment, the static friction coefficient of the surface of the first adhesive layer can be controlled, for example, by adjusting the composition of the first adhesive layer. Specifically, when the first adhesive layer further contains a foaming agent, the static friction coefficient of the surface of the first adhesive layer can be controlled by the average particle size, content, etc. of the foaming agent contained in the first adhesive layer. More specifically, as the average particle size of the foaming agent increases, the static friction coefficient of the surface of the first adhesive layer tends to decrease. Furthermore, as the content of the foaming agent increases, the static friction coefficient of the surface of the first adhesive layer tends to decrease.

[0051] In this embodiment, the arithmetic mean roughness (Ra) of the surface of the first adhesive layer opposite the second adhesive layer is, for example, preferably 0.3 μm or more, and may be 0.5 μm or more, or 0.7 μm or more. By having the Ra of the first adhesive layer within the above range, the first adhesive layer can have good slip properties. Furthermore, the Ra of the first adhesive layer may be, for example, 1.5 μm or less, 1.3 μm or less, or 1.1 μm or less.

[0052] The Ra of the first adhesive layer can be measured using a white light interferometer. Specifically, the Ra of the first adhesive layer can be measured using a white light interferometer NewView 7300 manufactured by Zygo Corporation, with an observation field of view of 0.55 mm × 0.55 mm and a sampling interval of 0.55 μm.

[0053] In this embodiment, the Ra of the first adhesive layer can be controlled, for example, by adjusting the composition of the first adhesive layer. Specifically, when the first adhesive layer further contains a foaming agent, the Ra of the first adhesive layer can be controlled by the average particle size, content, etc. of the foaming agent contained in the first adhesive layer. More specifically, as the average particle size of the foaming agent increases, the Ra of the first adhesive layer tends to increase. Furthermore, as the content of the foaming agent increases, the Ra of the first adhesive layer tends to increase.

[0054] The foamable adhesive sheet of this embodiment has a loop stiffness of 50 mN / 10 mm or more, preferably 75 mN / 10 mm or more, and more preferably 100 mN / 10 mm or more. When the loop stiffness of the foamable adhesive sheet is within this range, for example, when the foamable adhesive sheet is adsorbed and transported and attached to a member, the foamable adhesive sheet can be prevented from sagging due to its own weight, thereby improving attachment properties. Meanwhile, there is no particular upper limit to the loop stiffness.

[0055] As mentioned above, loop stiffness is a parameter that represents the stiffness of a film or sheet. A method for measuring loop stiffness will be described below with reference to FIGS.

[0056] FIG. 2(a) is a schematic plan view showing a loop stiffness measuring device, and FIG. 2(b) is a cross-sectional view taken along line A-A in FIG. 2(a). The test piece of the foamable adhesive sheet 10 is rectangular with long and short sides. In this embodiment, the length L1 of the long side of the test piece of the foamable adhesive sheet 10 is 200 mm, and the length L2 of the short side is 10 mm. The loop stiffness measuring device 30 can be a Loop Stiffness Tester (registered trademark) manufactured by Toyo Seiki Seisaku-sho, Ltd. The length L1 of the long side of the test piece of the foamable adhesive sheet 10 can be adjusted as long as the test piece of the foamable adhesive sheet 10 can be gripped by a pair of chucks 31, which will be described later.

[0057] The loop stiffness measuring device 30 has a pair of chuck portions 31 for gripping a pair of ends in the long side direction of the test piece of the foamable adhesive sheet 10, and a support member 32 for supporting the chuck portions 31. The chuck portions 31 have a first chuck 31a and a second chuck 31b. The foamable adhesive sheet 10 is placed on the pair of first chucks 31a, and the second chuck 31b has not yet gripped the foamable adhesive sheet 10 between itself and the first chuck 31a. As will be described later, during measurement, the foamable adhesive sheet 10 is gripped between the first chuck 31a and the second chuck 31b of the chuck portions 31. The second chuck 31b may be connected to the first chuck 31a via a hinge mechanism.

[0058] First, as shown in Figures 2(a) and (b), a test piece of the foamable adhesive sheet 10 is placed on the first chuck 31a of a pair of chuck sections 31 arranged with a distance L3 between them. In this embodiment, the distance L3 is set so that the length of the loop section 41 (described below, also referred to as the loop length) is 60 mm. The test piece of the foamable adhesive sheet 10 is also arranged so that the inner surface 40x is the surface of the first adhesive layer and the outer surface 40y is the surface of the second adhesive layer. Next, as shown in Figure 3(a), the second chuck 31b is placed on the test piece of the foamable adhesive sheet 10 so that the end of the long side of the test piece of the foamable adhesive sheet 10 is gripped between the first chuck 31a and the second chuck 31b.

[0059] Next, as shown in FIG. 3( b), at least one of the pair of chuck portions 31 is slid on the support member 32 in a direction that reduces the distance between the pair of chuck portions 31. This allows a loop portion 41 to be formed in the foamable adhesive sheet 10. The test piece of the foamable adhesive sheet 10 shown in FIG. 3( b) has a loop portion 41, a pair of intermediate portions 42, and a pair of fixing portions 43. The pair of fixing portions 43 are portions of the test piece of the foamable adhesive sheet 10 that are gripped by the pair of chuck portions 31. The pair of intermediate portions 42 are portions of the test piece of the foamable adhesive sheet 10 that are located between the loop portion 41 and the pair of intermediate portions 42. The chuck portion 31 is slid on the support member 32 until the inner surfaces 40x of the pair of intermediate portions 42 of the foamable adhesive sheet 10 come into contact with each other. This allows a loop portion 41 with a loop length of 60 mm to be formed. The loop length of the loop portion 41 is the length of the test piece of the foamable adhesive sheet 10 between position P1 where the surface of one second chuck 31b on the loop portion 41 side intersects with the test piece of the foamable adhesive sheet 10, and position P2 where the surface of the other second chuck 31b on the loop portion 41 side intersects with the test piece of the foamable adhesive sheet 10. If the thickness of the test piece of the foamable adhesive sheet 10 is ignored, the above-mentioned distance L3 is the value obtained by adding 2×t to the length of the loop portion 41, where t is the thickness of the second chuck 31b of the chuck portion 31.

[0060] Next, as shown in Fig. 4(a), the posture of the chuck portion 31 is adjusted so that the protruding direction Y of the loop portion 41 relative to the chuck portion 31 is horizontal. For example, the posture of the chuck portion 31 supported by the support member 32 is adjusted by moving the support member 32 so that the normal direction of the support member 32 is horizontal. In the example shown in Fig. 4(a), the protruding direction Y of the loop portion 41 coincides with the thickness direction of the chuck portion 31. Furthermore, a load cell 35 is prepared at a position away from the second chuck 31b in the protruding direction Y of the loop portion 41.

[0061] 4(b), the load cell 35 is moved toward the loop portion 41 of the test piece of the foamable adhesive sheet 10, and the load cell 35 is brought into contact with the loop portion 41. The distance Z1 is the distance between the load cell 35 and the second chuck 31b of the chuck portion 31.

[0062] 4B and 4C, the loop portion 41 is pressed by a distance Z2 toward the chuck portion 31 by the load cell 35. In this embodiment, the distance Z2 is set to 15 mm.

[0063] Next, as shown in Figure 4(c), the load cell 35 is moved a distance Z2 toward the chuck portion 31, and with the load cell 35 pressing into the loop portion 41 of the test piece of the foamable adhesive sheet 10, the value of the load applied to the load cell 35 from the loop portion 41 is recorded after it has stabilized. The load value obtained in this manner is the loop stiffness of the foamable adhesive sheet 10. Unless otherwise specified in this specification, the environment during loop stiffness measurement is a temperature of 23°C and a relative humidity of 50%.

[0064] When measuring the loop stiffness of a foamable adhesive sheet, if the foamable adhesive sheet has a first separator and a second separator as described below, the loop stiffness of the foamable adhesive sheet is measured after peeling off the first separator and the second separator.

[0065] In this embodiment, the loop stiffness of the foamable adhesive sheet can be controlled, for example, by adjusting the thickness and composition of the first adhesive layer, the thickness and composition of the second adhesive layer, and the thickness and composition of the substrate. For example, the thicker the substrate, the greater the loop stiffness. Also, for example, the thicker the first adhesive layer, the greater the loop stiffness. Therefore, it is preferable to adjust the thickness of each layer to obtain the desired loop stiffness. Also, adjusting the composition of the first adhesive layer to reduce the tack of the first adhesive layer tends to increase the loop stiffness.

[0066] The foamable adhesive sheet in this embodiment preferably has high adhesiveness after foaming and curing. After foaming and curing, the foamable adhesive sheet may have a shear strength (adhesive strength) at 23°C based on JIS K6850, which corresponds to ISO 4587, of, for example, 1.50 MPa or more, 1.80 MPa or more, or 2.10 MPa or more.

[0067] Furthermore, 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, a high-strength acrylic foam adhesive tape that does not require heating has a shear strength (adhesive strength) of approximately 1 MPa or more and 2 MPa or less at room temperature, and is not heat resistant 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. Furthermore, if the shear strength (adhesive strength) is within the above range at 130°C, it can be used in applications requiring heat resistance such as around an automobile engine.

[0068] The foamable adhesive sheet in this embodiment preferably has high electrical insulation after foaming and curing. After foaming and curing, the foamable adhesive sheet preferably has a breakdown voltage based on JIS C2107, which corresponds to IEC 60454-2, of, for example, 3 kV or more, more preferably 5 kV or more. Having the breakdown voltage within the above range enables application for rust prevention and around copper wires. Furthermore, after foaming and curing, the foamable adhesive sheet preferably has a thermal conductivity of, for example, 0.05 W / mK or more. Having the thermal conductivity within the above range allows for the miniaturization of parts and promotes the curing reaction during heating.

[0069] 2. First Adhesive Layer (1) Material of First Adhesive Layer The first adhesive layer in this embodiment contains a curable adhesive.

[0070] (a) Curable Adhesive The curable adhesive contained in the first adhesive layer in this embodiment can be a curable adhesive generally used in adhesive layers of foamable adhesive sheets. Examples of curable adhesives include heat-curable adhesives and photo-curable adhesives. Among these, heat-curable adhesives are preferred. Heat-curable adhesives can be applied even when the component does not have transparency, such as a metal component.

[0071] Examples of curable adhesives include epoxy resin adhesives, acrylic resin adhesives, phenolic resin adhesives, unsaturated polyester resin adhesives, alkyd resin adhesives, urethane resin adhesives, and thermosetting polyimide resin adhesives.

[0072] Among these, the curable adhesive is preferably an epoxy resin adhesive. That is, the curable 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., and have little shrinkage upon curing, making them suitable for a wide range of applications.

[0073] An example in which the curable adhesive is an epoxy resin adhesive will be described below.

[0074] (i) Epoxy Resin The epoxy resin in this embodiment is a compound that has at least one epoxy group or glycidyl group and cures by crosslinking polymerization in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

[0075] The epoxy resin can be any epoxy resin commonly used in the adhesive layer of a foamable adhesive sheet. In particular, the curable adhesive preferably contains a first epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5,000 g / eq or less, and a second epoxy resin having a softening temperature higher than that of the first epoxy resin and a weight-average molecular weight of 20,000 or more. By using a combination of the first epoxy resin and the second epoxy resin, the tackiness (stickiness) of the first adhesive layer can be reduced, resulting in a foamable adhesive sheet with excellent slip properties. Furthermore, a first adhesive layer with excellent blocking resistance and adhesion after foaming and curing can be obtained.

[0076] For example, when only improving adhesiveness after foaming and curing is desired, it is more effective to use a low molecular weight (low epoxy equivalent) epoxy resin than a high molecular weight (high epoxy equivalent) epoxy resin. However, when a low molecular weight (low epoxy equivalent) epoxy resin is used, for example, when the foamable adhesive sheet is wound into a roll, the low molecular weight (low epoxy equivalent) epoxy resins tend to assimilate with each other, resulting in blocking.

[0077] In contrast, when a first epoxy resin having a relatively low softening temperature (relatively high crystallinity) and a low molecular weight (low epoxy equivalent weight) is used, the first epoxy resin rapidly melts and changes into a low-viscosity liquid when heated to a temperature above its softening temperature. This facilitates improved adhesiveness after foaming and curing. Meanwhile, the first epoxy resin has relatively high crystallinity, which can suppress blocking compared to epoxy resins with relatively low crystallinity or no crystallinity. However, using only the first epoxy resin may result in insufficient blocking suppression or excessive tackiness of the first adhesive layer. Therefore, by further using a second epoxy resin having a relatively high softening temperature (relatively low crystallinity) and a high molecular weight, the blocking suppression effect can be improved and the tackiness of the first adhesive layer can be reduced.

[0078] (i-1) First Epoxy Resin The first epoxy resin has a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or lower. The first epoxy resin has a relatively low softening temperature (relatively high crystallinity) compared to the second epoxy resin described below. The first epoxy resin has relatively high crystallinity and a low molecular weight, which makes it easy to improve adhesion and blocking resistance after foaming and curing. Furthermore, the first epoxy resin has a low molecular weight, which allows for a high crosslink density, resulting in a first adhesive layer with excellent mechanical strength, chemical resistance, and curing properties. Furthermore, the first epoxy resin is preferably an epoxy resin that is solid at room temperature (23°C).

[0079] The softening temperature of the first epoxy resin is usually 50° C. or higher, and may be 55° C. or higher, or 60° C. or higher. On the other hand, the softening temperature of the first epoxy resin is, for example, 150° C. or lower. The softening temperature can be measured by the ring and ball method in accordance with JIS K7234.

[0080] The epoxy equivalent of the first epoxy resin is, for example, 5000 g / eq or less, or may be 3000 g / eq or less, 1000 g / eq or less, or 600 g / eq or less. On the other hand, the epoxy equivalent of the first epoxy resin is, for example, 90 g / eq or more, or may be 100 g / eq or more, or may be 110 g / eq or more. The epoxy equivalent can be measured by a method in accordance with JIS K7236, which corresponds to ISO 3001 (Plastics Epoxy Compounds—Determination of Epoxy Equivalent), and is the number of grams of resin containing 1 gram equivalent of epoxy groups.

[0081] The first epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0082] The weight-average molecular weight (Mw) of the first epoxy resin is usually smaller than the weight-average molecular weight (Mw) of the second epoxy resin described below. The Mw of the first epoxy resin is, for example, 6,000 or less, and may be 4,000 or less, or 3,000 or less. On the other hand, the Mw of the first epoxy resin is, for example, 400 or more. Mw is a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0083] The melt viscosity of the first epoxy resin at 150°C is, for example, 0.005 Pa·s or more, or may be 0.015 Pa·s or more, 0.03 Pa·s or more, 0.05 Pa·s or more, or 0.1 Pa·s or more. If the melt viscosity is too low, good foaming properties may not be obtained. Furthermore, if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), the resulting first adhesive layer may have high tackiness. This is presumably because if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), its crystallinity will be significantly reduced when it is mixed with the second epoxy resin or acrylic resin, resulting in a decrease in the Tg of the first adhesive layer. On the other hand, the melt viscosity of the first epoxy resin at 150°C is, for example, 10 Pa·s or less, or may be 5 Pa·s or less, or 2 Pa·s or less.

[0084] If the melt viscosity is too high, the uniformity of the resulting first adhesive layer may be reduced. The melt viscosity can be determined in accordance with JIS K6862, which corresponds to ISO 2555 (Determination of Brookfield RV viscosity for Resins in the liquid state or as emulsions or dispersions), by measurement using a Brookfield single-cylinder rotational viscometer and a thermocell for heating the solution.

[0085] Next, the composition of the first epoxy resin will be described. Examples of the first epoxy resin include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of the first epoxy resin 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 first epoxy resin may be one type or two or more types.

[0086] Bisphenol A epoxy resins can exist in a liquid state or a solid state at room temperature depending on the number of repeating units in the bisphenol skeleton. Bisphenol A epoxy resins having, for example, 2 to 10 bisphenol skeletons in the main chain are solid at room temperature. Bisphenol A epoxy resins are particularly preferred because they can improve heat resistance.

[0087] In particular, the first epoxy resin is preferably a bisphenol A novolac epoxy resin represented by the following general formula (1).

[0088]

[0089] In general formula (1), R １ is C ｍ H ２ｍ (m is 1 or more and 3 or less), and R ２ and R ３ are each independently C ｐ H ２ｐ＋１ (p is 1 or more and 3 or less), and n is 0 or more and 10 or less.

[0090] In general formula (1), R １ m in is 1, that is, R １ Ha-CH ２ Similarly, R ２ and R ３ p in is 1, that is, R ２ and R ３ Ha-CH ３ Furthermore, the hydrogen bonded to the benzene ring in general formula (1) may be substituted with other elements or other groups.

[0091] The content of the first epoxy resin, relative to 100 parts by mass of the resin component contained in the first adhesive layer, may be, for example, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 10 parts by mass or more, 15 parts by mass or more, or 25 parts by mass or more. If the content of the first epoxy resin is too low, the adhesiveness and blocking resistance after foaming and curing may be reduced. On the other hand, the content of the first epoxy resin, relative to 100 parts by mass of the resin component contained in the first adhesive layer, may be, for example, 90 parts by mass or less, 80 parts by mass or less, 70 parts by mass or less, 60 parts by mass or less, 50 parts by mass or less, or 40 parts by mass or less. If the content of the first epoxy resin is too high, the contents of the second epoxy resin and acrylic resin may be relatively low, which may make it impossible to achieve a balance between non-stickiness, blocking resistance, adhesion to substrates after foaming and curing, cracking resistance after foaming and curing, and adhesiveness after foaming and curing.

[0092] (i-2) Second Epoxy Resin The second epoxy resin has a softening temperature higher than that of the first epoxy resin and a weight-average molecular weight of 20,000 or more. The second epoxy resin has a relatively high softening temperature (relatively low crystallinity) compared to the first epoxy resin described above. The second epoxy resin has relatively low crystallinity and a high molecular weight, which makes it easy to improve blocking resistance. Furthermore, the second epoxy resin has relatively low crystallinity and a high molecular weight, which can suppress an increase in adhesion (tackiness) caused by the first epoxy resin. In addition, the second epoxy resin is preferably an epoxy resin that is solid at room temperature (23°C).

[0093] The weight average molecular weight (Mw) of the second epoxy resin is usually larger than the weight average molecular weight (Mw) of the first epoxy resin. The Mw of the second epoxy resin is usually 20,000 or more, or may be 30,000 or more, or may be 35,000 or more. On the other hand, the Mw of the second epoxy resin is, for example, 100,000 or less.

[0094] The epoxy equivalent of the second epoxy resin may be greater than, less than, or the same as the epoxy equivalent of the first epoxy resin. The epoxy equivalent of the second epoxy resin is, for example, 4000 g / eq or more, 5000 g / eq or more, or 6000 g / eq or more. On the other hand, the epoxy equivalent of the second epoxy resin is, for example, 20000 g / eq or less.

[0095] The second epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher functional epoxy resin.

[0096] The softening temperature of the second epoxy resin is usually higher than that of the first epoxy resin. The difference between the two temperatures is, for example, 10°C or higher, and may be 20°C or higher, or 30°C or higher. The softening temperature of the second epoxy resin is, for example, 80°C or higher, and may be 90°C or higher. On the other hand, the softening temperature of the second epoxy resin is, for example, 180°C or lower.

[0097] The constitution of the second epoxy resin is the same as that of the first epoxy resin described above, and therefore description thereof will be omitted here.

[0098] The content of the second epoxy resin, relative to 100 parts by mass of the resin component contained in the first adhesive layer, may be, for example, 10 parts by mass or more, 15 parts by mass or more, 20 parts by mass or more, 25 parts by mass or more, 30 parts by mass or more, 35 parts by mass or more, 40 parts by mass or more, or 45 parts by mass or more. If the content of the second epoxy resin is too low, the adhesiveness may be high and the blocking resistance may be reduced. On the other hand, the content of the second epoxy resin, relative to 100 parts by mass of the resin component contained in the first adhesive layer, may be, for example, 90 parts by mass or less, 85 parts by mass or less, 80 parts by mass or less, or 75 parts by mass or less. If the content of the second epoxy resin is too high, the contents of the first epoxy resin and acrylic resin may be relatively low, which may make it difficult to achieve a balance between non-stickiness, blocking resistance, adhesion to substrates after foaming and curing, cracking resistance after foaming and curing, and adhesion after foaming and curing.

[0099] The proportion of the first epoxy resin relative to the total of the first epoxy resin and the second epoxy resin is, for example, 5% by mass or more, or alternatively 10% by mass or more, or 15% by mass or more, or alternatively 20% by mass or more, while the proportion of the first epoxy resin is, for example, 80% by mass or less, or alternatively 75% by mass or less, or alternatively 60% by mass or less.

[0100] Furthermore, the total proportion of the first epoxy resin and the second epoxy resin to all epoxy resins contained in the first adhesive layer is, for example, 50% by mass or more, or may be 70% by mass or more, or 90% by mass or more, or may be 100% by mass.

[0101] (ii) Acrylic Resin When the curable adhesive is an epoxy resin-based adhesive, the first adhesive layer may further contain an acrylic resin compatible with the epoxy resin. The acrylic resin is a resin compatible with the epoxy resin. Because the acrylic resin is compatible with the epoxy resin, it is easy to improve the toughness of the first adhesive layer. As a result, the adhesiveness after foaming and curing can be improved. Furthermore, the acrylic resin acts as a compatibilizer for the foaming agent (e.g., a foaming agent whose shell is an acrylonitrile copolymer resin), uniformly dispersing and foaming, which is thought to improve the adhesiveness after foaming and curing. In addition, the flexibility of the acrylic resin can be exerted, improving adhesion to the substrate after foaming and curing and crack resistance after foaming and curing. Furthermore, the compatibility of the acrylic resin with the epoxy resin can maintain high hardness of the surface of the first adhesive layer. On the other hand, if the acrylic resin is incompatible with the epoxy resin, a flexible portion is formed on the surface of the first adhesive layer, making the interface with the adherend less slippery and reducing workability.

[0102] The acrylic resin in this embodiment is compatible with the epoxy resin. The compatibility of the acrylic resin with the epoxy resin can be confirmed, for example, by observing the cross section of the first adhesive layer of the foamable adhesive sheet with a scanning electron microscope (SEM) or a transmission electron microscope (TEM) and finding no micron-sized islands. 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 even 0.3 μm or less. A large number of samples is preferably used, for example, 100 or more. The area to be observed is within a range of 100 μm × 100 μm, or, if the thickness of the first adhesive layer is 100 μm or less, within a range of the thickness × 100 μm.

[0103] The weight-average molecular weight (Mw) of the acrylic resin is, for example, 50,000 or more, or may be 70,000 or more, or even 100,000 or more. The first epoxy resin has relatively high crystallinity, which can result in a low melt viscosity (or dynamic viscoelasticity) when heated, potentially causing shrinkage during curing after foaming (between the end of foaming of the foaming agent and the curing of the first adhesive layer). However, by using an acrylic resin with a certain molecular weight, it is possible to prevent the melt viscosity from becoming too low, making it less likely for shrinkage to occur during curing after foaming. Meanwhile, the Mw of the acrylic resin is, for example, 1,500,000 or less. The weight-average molecular weight of the acrylic resin can be measured by GPC (eluent: THF, standard: PS, sample: 20 μL, flow rate: 1 mL / min, column temperature: 40°C).

[0104] The glass transition temperature (Tg) of the acrylic resin is, for example, 90° C. or higher, and may be 100° C. or higher. On the other hand, the Tg of the acrylic resin is, for example, 180° C. or lower. Tg can be measured by thermal analysis such as a differential scanning calorimeter (DSC) in accordance with JIS K7121, which corresponds to ISO 3146.

[0105] The acrylic resin has a storage modulus (E') of 1 x 10 at the foaming initiation temperature. ６ A low E' at the foaming initiation temperature can improve fluidity and provide good foaming properties. On the other hand, E' at the foaming initiation temperature can be, for example, 1 x 10 ５ The foaming initiation temperature is a temperature that varies depending on the type of foaming agent. When two or more foaming agents are used, the foaming initiation temperature is the temperature at which the main foaming reaction begins.

[0106] The acrylic resin has a storage modulus (E') of 1 x 10 at the curing initiation temperature. ５Pa or more. As described above, shrinkage may occur during curing after foaming (between the end of foaming of the foaming agent and the curing of the first adhesive layer), but a large E' at the curing initiation temperature can suppress shrinkage and provide good shape retention. The curing initiation temperature varies depending on the type of curing agent. When two or more curing agents are used as the curing agent, the initiation temperature of the main curing reaction is taken as the curing initiation temperature.

[0107] The acrylic resin has an average storage modulus (E') of 1 x 10 at temperatures between 0°C and 100°C. ６ The average value of E' before foaming may be high, which allows for good non-stickiness and blocking resistance. On the other hand, the average value of the storage modulus (E') at temperatures from 0°C to 100°C may be, for example, 1 x 10 ８ Pa or less.

[0108] 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.

[0109] 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 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" 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. Of these, it is preferable that the acrylic resin contain a copolymer of two or more acrylic acid ester monomers (a (meth)acrylic acid ester copolymer).

[0110] Examples of the monomer component constituting the (meth)acrylic acid ester copolymer include the monomer components described in JP 2014-065889 A. The monomer component may have the polar group described above. Examples of the (meth)acrylic acid ester copolymer include an ethyl acrylate-butyl acrylate-acrylonitrile copolymer, an ethyl acrylate-acrylonitrile copolymer, and a 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.

[0111] 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. In these examples, "acrylic acid" also includes "methacrylic acid."

[0112] Specific examples of methacrylate-acrylate copolymers include acrylic copolymers such as methyl methacrylate-butyl acrylate-methyl methacrylate (MMA-BA-MMA) copolymer, which also includes block copolymers of polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (PMMA-PBA-PMMA).

[0113] The acrylic copolymer may have no polar groups, or may be a modified product in which the above-mentioned polar groups have been partially introduced. The modified product is highly compatible with epoxy resins, thereby further improving adhesion.

[0114] Among these, 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 lower and a second polymer portion having a glass transition temperature (Tg) of 20° C. or higher. Such a (meth)acrylic acid ester copolymer has the first polymer portion that becomes a soft segment and the second polymer portion that becomes a hard segment.

[0115] 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 a first adhesive layer having good heat resistance, toughness, and flexibility can be obtained.

[0116] 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. Furthermore, when the second polymer portion has compatibility with epoxy resins, cohesion and toughness can be increased.

[0117] When either the first polymer portion or the second polymer portion is incompatible with the epoxy resin, the (meth)acrylic acid ester copolymer has a compatible portion, which is a polymer portion that is compatible with the epoxy resin, and an incompatible portion, which is a polymer portion that is incompatible with the epoxy resin. In this case, when the (meth)acrylic acid ester copolymer is added, the compatible portion becomes compatible with the epoxy resin, and the incompatible portion becomes incompatible with the epoxy resin, causing fine phase separation. As a result, a fine sea-island structure is formed. The sea-island structure varies depending on the type of (meth)acrylic acid ester copolymer, the compatibility of the first polymer portion and the second polymer portion contained in the (meth)acrylic acid ester copolymer, and whether or not modification by introduction of polar groups has been performed, and examples include a sea-island structure in which the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible portions of the (meth)acrylic acid ester copolymer are the islands, a sea-island structure in which the incompatible portions of the (meth)acrylic acid ester copolymer are the sea and the compatible portions of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, and a sea-island structure in which the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands. The presence of such a sea-island structure makes it easier to disperse stress, thereby preventing interfacial failure and achieving excellent adhesion after foaming and curing.

[0118] The (meth)acrylic acid ester copolymer is preferably a block copolymer, and particularly preferably an A-B-A block copolymer in which a compatible portion is polymer block A and an incompatible portion is polymer block B. Furthermore, an A-B-A block copolymer in which a first polymer portion is an incompatible portion and a second polymer portion is a compatible portion, with the first polymer portion being polymer block B and the second polymer portion being polymer block A, is preferred. By using such an A-B-A block copolymer as the acrylic resin, in a case where a sea-island structure is formed in which the compatible portion of the cured epoxy resin and the (meth)acrylic acid ester copolymer is a sea and the incompatible portion of the (meth)acrylic acid ester copolymer is an island, the island portions can be made smaller. Furthermore, in a case where a sea-island structure is formed in which the incompatible portion of the (meth)acrylic acid ester copolymer is a sea and the compatible portion of the cured epoxy resin and the (meth)acrylic acid ester copolymer is an island, or in a case where the (meth)acrylic acid ester copolymer is a sea and the cured epoxy resin is an island, the sea portions can be made smaller.

[0119] 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.

[0120] The upper limit of the Tg of the first polymer portion contained in the (meth)acrylic acid ester copolymer is 10° C. or lower, preferably 0° C. or lower, and particularly preferably −10° C. or lower. On the other hand, the lower limit of the Tg can be −150° C. or higher, preferably −130° C. or higher, and particularly preferably −110° C. or higher.

[0121] The Tg of the first polymer portion can be calculated using the following formula based on the Tg(K) of each homopolymer described in "POLYMER HANDBOOK, Third Edition" (published by John Wiley & Sons, Inc.): 1 / Tg(K)=W １ / Tg １ +W ２ / Tg ２ +...+W ｎ / Tg ｎ W ｎ ; Mass fraction of each monomer Tg ｎTg (K) of the homopolymer of each monomer, and publicly available values ​​such as those in the Polymer Handbook (3rd Ed., J. Brandrup and E. H. Immergut, Wiley Interscience) may be used. The same applies to the Tg of the second polymer portion described below.

[0122] The first polymer portion contained in the (meth)acrylic acid ester copolymer may be either a homopolymer or a copolymer, but is preferably a homopolymer. The monomer component and polymer component constituting the first polymer portion may be any monomer component and polymer component that can give a first polymer portion having a Tg within a predetermined range, and examples thereof include acrylate monomers such as butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, and methyl acrylate, other monomers such as vinyl acetate, acetal, and urethane, polar group-containing monomers containing the above-mentioned polar groups, and copolymers such as EVA.

[0123] The lower limit of the Tg of the second polymer portion contained in the (meth)acrylic acid ester copolymer is 20° C. or higher, preferably 30° C. or higher, and particularly preferably 40° C. or higher. On the other hand, the upper limit of the Tg can be 150° C. or lower.

[0124] The second polymer portion contained in the (meth)acrylic acid ester copolymer may be either a homopolymer or a copolymer, but is preferably a homopolymer. The monomer component constituting the second polymer portion may be any monomer component capable of obtaining a second polymer portion having a Tg within a predetermined range, and examples thereof include acrylic acid ester monomers such as methyl methacrylate, other monomers such as acrylamide, styrene, vinyl chloride, amide, acrylonitrile, cellulose acetate, phenol, urethane, vinylidene chloride, methylene chloride, and methacrylonitrile, and polar group-containing monomers containing the above-mentioned polar groups.

[0125] A specific example of the (meth)acrylic acid ester copolymer having the first polymer portion and the second polymer portion is the above-mentioned MMA-BA-MMA copolymer.

[0126] The content of the acrylic resin, relative to 100 parts by mass of the resin component contained in the first adhesive layer, may be, 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. If the content of the acrylic resin is too low, adhesion to the substrate after foaming and curing, cracking resistance after foaming and curing, and adhesiveness after foaming and curing may be reduced. On the other hand, the content of the acrylic resin, relative to 100 parts by mass of the resin component contained in the first adhesive layer, may be, 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. If the content of the acrylic resin is too high, the contents of the first epoxy resin and the second epoxy resin will be relatively low, which may make it impossible to achieve a balance between non-stickiness, blocking resistance, adhesion to the substrate after foaming and curing, cracking resistance after foaming and curing, and adhesiveness after foaming and curing. Furthermore, if the content of the acrylic resin is too high, the film strength may be reduced.

[0127] (iii) Curing Agent As the curing agent in this embodiment, a curing agent generally used in epoxy resin adhesives can be used. The curing agent is preferably solid at room temperature (23°C). A curing agent that is solid at room temperature can extend storage stability (pot life) compared to a curing agent that is liquid at room temperature. The curing agent may also be a latent curing agent. The curing agent may also be a curing agent that undergoes a curing reaction due to heat, or a curing agent that undergoes a curing reaction due to light. The curing agents may also be used alone or in combination of two or more.

[0128] 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 will start early, and curing will occur with low flexibility and fluidity of the resin component, making it difficult to achieve uniform curing. 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. Note that when a highly heat-resistant resin such as a phenolic resin is used in addition to the epoxy resin, the resin component will deteriorate less, and 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).

[0129] 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.

[0130] 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, carboxylic acid salts of imidazole compounds, and adducts with epoxy compounds. Furthermore, it is preferable that the imidazole-based curing agent has a hydroxyl group. Crystallization occurs due to hydrogen bonding between the hydroxy groups, so the reaction initiation temperature tends to be high.

[0131] Examples of phenolic curing agents include phenolic resins. Further examples of phenolic resins include resol-type phenolic resins and novolac-type phenolic resins. From the viewpoints of adhesion to the substrate after foaming and curing and crack resistance after foaming and curing, phenolic novolac resins having a Tg of 110°C or less are particularly preferred. Furthermore, phenolic curing agents and imidazole-type curing agents may be used in combination. In this case, it is preferable to use an imidazole-type curing agent as a curing catalyst.

[0132] Examples of amine-based curing agents include aliphatic amines, aromatic amines, alicyclic amines, and polyamidoamines. Examples of the aliphatic amines include diethylenetriamine (DETA), triethylenetetramine (TETA), and metaxylylenediamine (MXDA). Examples of the aromatic amines include diaminodiphenylmethane (DDM), m-phenylenediamine (MPDA), and diaminodiphenylsulfone (DDS).

[0133] As the amine-based curing agent, a dicyandiamide-based curing agent such as dicyandiamide (DICY), an organic acid dihydrazide-based curing agent, an amine adduct-based curing agent, or a ketimine-based curing agent can be used.

[0134] Examples of acid anhydride curing agents include alicyclic acid anhydrides (liquid acid anhydrides) and aromatic acid anhydrides. Examples of the alicyclic acid anhydrides (liquid acid anhydrides) include hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA). Examples of the aromatic acid anhydrides include trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), and benzophenonetetracarboxylic acid (BTDA).

[0135] The isocyanate curing agent may, for example, be a blocked isocyanate.

[0136] Examples of thiol-based curing agents include ester-bonded thiol compounds, aliphatic ether-bonded thiol compounds, and aromatic ether-bonded thiol compounds.

[0137] The content of the curing agent is, for example, 1 part by mass or more and 40 parts by mass or less, based on 100 parts by mass of the resin component contained in the first adhesive layer. For example, when an imidazole-based curing agent is used as the main component of the curing agent, the content of the curing agent is preferably, for example, 1 part by mass or more and 15 parts by mass or less, based on 100 parts by mass of the resin component contained in the first adhesive 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 is preferably, for example, 5 parts by mass or more and 40 parts by mass or less, based on 100 parts by mass of the resin component contained in the first adhesive layer. Note that using an imidazole-based curing agent or a phenol-based curing agent as the main component of the curing agent means that the mass proportion of the imidazole-based curing agent or the phenol-based curing agent is the highest in the curing agent.

[0138] (b) Foaming Agent The first adhesive layer in this embodiment may or may not contain a foaming agent, but it is preferable that it contains a foaming agent. By containing a foaming agent, the surface roughness is increased, the friction coefficient is reduced, and the slipperiness is further improved. Therefore, of the first adhesive layer and the second adhesive layer, it is preferable that the first adhesive layer, which has low tack, contains a foaming agent.

[0139] The foaming agent may be any foaming agent generally used in the adhesive layer of a foamable adhesive sheet, and may be a foaming agent that undergoes a foaming reaction when exposed to heat or light.

[0140] The foaming initiation temperature of the foaming agent is preferably equal to or higher than the softening temperature of the base of the curable adhesive, such as an epoxy resin, and equal to or lower than the activation temperature of the curing reaction of the base of the curable adhesive, such as an epoxy resin. The foaming initiation temperature of the foaming agent is, for example, 70°C or higher, and may be 100°C or higher. If the foaming initiation temperature is too low, the reaction may start early, causing foaming to occur in a state where the flexibility and fluidity of the resin component are low, making it difficult to achieve uniform foaming. On the other hand, the foaming initiation temperature of the foaming agent is, for example, 210°C or lower. If the foaming initiation temperature is too high, the resin component may deteriorate.

[0141] The softening temperature of the base resin of the curable adhesive such as an epoxy resin can be measured using the ring and ball softening temperature test method specified in JIS K7234.

[0142] The foaming agent may be, for example, a microcapsule type foaming agent, which preferably has a core made of a thermal expansion agent such as hydrocarbon and a shell made of a resin such as acrylonitrile copolymer.

[0143] Furthermore, organic or inorganic blowing agents may be used as the blowing agent. Examples of organic blowing agents include azo blowing agents such as azodicarbonamide (ADCA), azobisformamide, and azobisisobutyronitrile; fluorinated alkane blowing agents such as trichloromonofluoromethane; hydrazine blowing agents such as paratoluenesulfonylhydrazide; semicarbazide blowing agents such as p-toluenesulfonylsemicarbazide; triazole blowing agents such as 5-morpholyl-1,2,3,4-thiatriazole; and N-nitroso blowing agents such as N,N-dinitrosoterephthalamide. On the other hand, examples of inorganic blowing agents include ammonium carbonate, ammonium bicarbonate, ammonium nitrite, ammonium borohydride, and azides.

[0144] 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. By having the average particle size of the foaming agent in the above range, the static friction coefficient of the surface of the first adhesive layer can be reduced, resulting in a first adhesive layer with good slipperiness. Furthermore, the average particle size of the foaming agent is preferably equal to or less than the thickness of the first adhesive layer, and may be, for example, 44 μm or less, 30 μm or less, or 24 μm or less.

[0145] The average particle size of the foaming agent is the particle size at 50% of the cumulative value in the particle size distribution determined by laser diffraction scattering. To measure the average particle size of the foaming agent, the first adhesive layer is dissolved in a solvent to separate the foaming agent. The solvent is not particularly limited as long as it can dissolve components other than the foaming agent contained in the first adhesive layer. It is appropriately selected depending on the type of curable adhesive contained in the first adhesive layer. For example, a solvent used in the adhesive composition used to form the first adhesive layer can be used. Specifically, methyl ethyl ketone, ethyl acetate, toluene, etc. can be used.

[0146] 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 first 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 first adhesive layer. If the content of the foaming agent is too low, the static friction coefficient of the surface of the first adhesive layer may be increased. Furthermore, if the content of the foaming agent is too high, the content of the curable adhesive will be relatively low, which may result in a decrease in adhesion after foaming and curing.

[0147] (c) Other Components In the present embodiment, when the curable adhesive is an epoxy resin adhesive, the first adhesive layer may contain only an epoxy resin and an acrylic resin as resin components, or may further contain other resins, such as urethane resins.

[0148] The total ratio of the first epoxy resin, the second epoxy resin and the acrylic resin to the resin components contained in the first adhesive layer is, for example, 70% by mass or more, or may be 80% by mass or more, or 90% by mass or more, or may be 100% by mass.

[0149] The content of the resin component contained in the first adhesive layer is, for example, 60% by mass or more, or may be 70% by mass or more, or 80% by mass or more, or may be 90% by mass or more.

[0150] The first adhesive layer may contain additives such as silane coupling agents, fillers, antioxidants, light stabilizers, UV absorbers, lubricants, plasticizers, antistatic agents, crosslinking agents, and colorants, as needed. 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.

[0151] (2) Configuration of the First Adhesive Layer When the first adhesive layer further contains a foaming agent, the first adhesive layer can be foamed at an expansion ratio of, for example, 4 times or more and 15 times or less. For example, when only the first adhesive layer of the first and second adhesive layers contains a foaming agent, the expansion ratio may be, for example, 5 times or more, 7 times or more, or 9 times or more. In this case, the expansion ratio may be, for example, 14 times or less, 13 times or less, or 12 times or less. On the other hand, when both the first adhesive layer and the second adhesive layer contain a foaming agent, the expansion ratio may be, for example, 5 times or more, 6 times or more, or 7 times or more. In this case, the expansion ratio may be, for example, 14 times or less, 12 times or less, or 10 times or less. If the expansion ratio is too small or too large, the adhesiveness after foaming and curing may be reduced.

[0152] Here, the expansion ratio can be calculated by the following formula: Expansion ratio (times) = thickness of first adhesive layer after foaming and curing / thickness of first adhesive layer before foaming and curing

[0153] The thickness of the first adhesive layer is not particularly limited, but when the first adhesive layer contains a foaming agent, it is preferably equal to or greater than the average particle size of the foaming agent, for example, 10 μm or more, or 15 μm or more, or even 20 μm or more. If the first adhesive layer is too thin, it may be difficult to obtain sufficient adhesion to the substrate and adhesion after foam curing. On the other hand, the thickness of the first adhesive layer is, for example, 200 μm or less, or may be 150 μm or less, or may be 100 μm or less. If the first adhesive layer is too thick, the surface quality may deteriorate.

[0154] Here, the thickness of the first adhesive layer is a value measured from a cross section of the foamable adhesive sheet in the thickness direction as 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 thicknesses measured at 10 randomly selected locations. The same method can be used to measure the thickness of other layers of the foamable adhesive sheet.

[0155] The first adhesive layer may be a continuous layer or a discontinuous layer. Examples of discontinuous layers include stripes and dots. The surface of the first adhesive layer may have an uneven shape such as an embossed shape.

[0156] The first adhesive layer can be formed, for example, by applying an adhesive composition containing the above-mentioned curable adhesive and a foaming agent, etc., and then removing the solvent. Examples of application methods 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.

[0157] The adhesive composition may or may not contain a solvent. In this specification, the term "solvent" is used in a broad sense to include 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.

[0158] The adhesive composition can be obtained by mixing the above-mentioned components and, if necessary, kneading and dispersing them. As a mixing and dispersing method, a general kneading disperser, such as a two-roll mill, a three-roll mill, a pebble mill, a tron ​​mill, a Szegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a desper, a high-speed mixer, a ribbon blender, a co-kneader, an intensive mixer, a tumbler, a blender, a desperzer, a homogenizer, or an ultrasonic disperser can be used.

[0159] 3. Second Adhesive Layer (1) Material for Second Adhesive Layer The second adhesive layer in this embodiment contains a curable adhesive.

[0160] (a) Curable Adhesive The curable adhesive contained in the second adhesive layer in this embodiment can be the same as the curable adhesive used in the first adhesive layer. In particular, the curable adhesive is preferably an epoxy resin adhesive.

[0161] An example in which the curable adhesive is an epoxy resin adhesive will be described below.

[0162] (i) Epoxy Resin The epoxy resin in this embodiment may be the same as the epoxy resin used in the first adhesive layer.

[0163] As the epoxy resin, an epoxy resin generally used for the adhesive layer of a foamable adhesive sheet can be used.

[0164] Examples of the epoxy resin include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of the epoxy resin may be the same as those of the first epoxy resin used in the first adhesive layer.

[0165] 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.

[0166] Among these, it is preferable to use, as the epoxy resin, an epoxy resin that is liquid at room temperature, such as a bisphenol A type epoxy resin or a bisphenol F type epoxy resin, or an epoxy resin with a low softening point, because by using these epoxy resins, it is easy to adjust the tackiness of the second adhesive layer within a predetermined range.

[0167] (ii) Acrylic Resin When the curable adhesive is an epoxy resin adhesive, the second adhesive layer may further contain an acrylic resin that is compatible with the epoxy resin. This can improve film-forming properties.

[0168] The acrylic resin may be the same as the acrylic resin used in the first adhesive layer.

[0169] (iii) Curing agent The curing agent in this embodiment can be the same as the curing agent used in the first adhesive layer. In addition, as the curing agent, a curing agent that is solid at room temperature or a curing agent that is liquid at room temperature can be used, but from the viewpoint of storage stability, it is preferable to use a curing agent that is solid at room temperature.

[0170] (b) Foaming Agent The second adhesive layer in this embodiment may or may not contain a foaming agent, but preferably contains a foaming agent. By containing a foaming agent in both the first adhesive layer and the second adhesive layer, the adhesiveness of the first adhesive layer and the second adhesive layer after foaming and curing can be improved.

[0171] The foaming agent may be the same as the foaming agent used in the first adhesive layer.

[0172] (c) Other Components In the present embodiment, when the curable adhesive is an epoxy resin adhesive, the second adhesive layer may contain only an epoxy resin and an acrylic resin as resin components, or may further contain other resins, such as urethane resins.

[0173] The total ratio of epoxy resin and acrylic resin to the resin components contained in the second adhesive layer is, for example, 70% by mass or more, or may be 80% by mass or more, or 90% by mass or more, or may be 100% by mass.

[0174] The content of the resin component contained in the second adhesive layer is, for example, 60% by mass or more, or may be 70% by mass or more, or 80% by mass or more, or may be 90% by mass or more.

[0175] The second adhesive layer may contain additives as needed, which may be the same as the additives used in the first adhesive layer.

[0176] (2) Configuration of the Second Adhesive Layer When the second adhesive layer further contains a foaming agent, the second adhesive layer can be foamed at an expansion ratio of, for example, 1.5 times or more and 12 times or less. For example, when both the first adhesive layer and the second adhesive layer contain a foaming agent, the expansion ratio may be, for example, 2 times or more, 3 times or more, or 4 times or more. In the above case, the expansion ratio may be, for example, 10 times or less, 9 times or less, or 8 times or less. If the expansion ratio is too small or too large, the adhesiveness after foaming and curing may be reduced.

[0177] The thickness of the second adhesive layer can be the same as the thickness of the first adhesive layer.

[0178] The second adhesive layer may be a continuous layer or a discontinuous layer. The surface of the second adhesive layer may have an uneven shape such as an embossed shape.

[0179] The method for forming the second adhesive layer can be the same as the method for forming the first adhesive layer.

[0180] 4. Substrate In this embodiment, the substrate is disposed between the first adhesive layer and the second adhesive layer.

[0181] The substrate preferably has insulating properties. 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.

[0182] Examples of the substrate include a resin substrate and a nonwoven fabric.

[0183] Resins contained in the resin substrate include polyester resins, polycarbonates, polyarylates, polyurethanes, polyamide resins, polyimide resins, polysulfone resins, polyetherketone resins, polyphenylene sulfide (PPS), modified polyphenylene oxides, etc. Examples of the polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), aromatic polyesters, etc. Examples of the polyamide resins include polyamides and polyetheramides. Examples of polyimide resins include polyimides, polyetherimides, polyamideimides, etc. Examples of polysulfone resins include polysulfones and polyethersulfones. Examples of polyetherketone resins include polyetherketones and polyetheretherketones, etc.

[0184] The glass transition temperature of the resin is, for example, 80° C. or higher, or may be 140° C. or higher, or may be 200° C. or higher. Furthermore, a liquid crystal polymer (LCP) may be used as the resin.

[0185] Examples of nonwoven fabrics 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.

[0186] The substrate may be subjected to a surface treatment to enhance adhesion to the first adhesive layer and the second adhesive layer.

[0187] The thickness of the substrate is preferably thinner than the thickness of the first adhesive layer and thinner than the thickness of the second adhesive layer. By making the thickness of the substrate thinner than the thicknesses of the first adhesive layer and the second adhesive layer, the thickness of the foamable adhesive sheet can be made thinner, and the thicknesses of the first adhesive layer and the second adhesive layer can be made relatively thick. Therefore, the thickness of the foamable adhesive sheet can be made thinner and insertion ease can be improved without reducing the adhesive properties or foaming properties of the first adhesive layer and the second adhesive layer.

[0188] Specifically, the thickness of the substrate is 200 μm or less, may be 100 μm or less, or may be 50 μm or less, and may be, for example, 2 μm or more, may be 5 μm or more, or may be 9 μm or more.

[0189] 5. Other Features (1) First Intermediate Layer and Second Intermediate Layer The foamable adhesive sheet of this embodiment may have a first intermediate layer between the substrate and the first adhesive layer. The foamable adhesive sheet of this embodiment may also have a second intermediate layer between the substrate and the second adhesive layer. The presence of the first intermediate layer or second intermediate layer can improve the adhesion of the first adhesive layer or second adhesive layer to the substrate. Furthermore, the presence of the first intermediate layer or second intermediate layer can, for example, alleviate stress at the bent portion when the foamable adhesive sheet is folded, or alleviate stress at the cut portion when the foamable adhesive sheet is cut. As a result, lifting or peeling of the first adhesive layer or second adhesive layer from the substrate can be suppressed when the foamable adhesive sheet is bent or cut.

[0190] For example, in the foamable adhesive sheet 10 shown in Fig. 5, a first intermediate layer 4 is disposed between the substrate 2 and the first adhesive layer 1, and a second intermediate layer 5 is disposed between the substrate 2 and the second adhesive layer 3. Although the foamable adhesive sheet 10 in Fig. 5 has both the first intermediate layer 4 and the second intermediate layer 5, it may have only one of them.

[0191] The foamable adhesive sheet may have at least one of a first intermediate layer and a second intermediate layer; for example, it may have only the first intermediate layer arranged between the substrate and the first adhesive layer, or it may have only the second intermediate layer arranged between the substrate and the second adhesive layer, or it 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.

[0192] The materials contained in the first intermediate layer and the second intermediate layer are not particularly limited as long as they can increase the adhesion between the substrate and the first adhesive layer or the second adhesive layer and can relieve stress, and are 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, polymers obtained by copolymerizing at least two or more of these, crosslinked products thereof, and mixtures thereof.

[0193] The crosslinked product is a crosslinked product obtained by crosslinking the above-mentioned resin with a curing agent. Examples of the curing agent include an isocyanate-based curing agent. Furthermore, for example, when the reactive group / NCO equivalent is 1, it is preferable to add the isocyanate-based curing agent in a ratio of 0.5 mass % to 20 mass % relative to the resin.

[0194] In particular, the first intermediate layer and the second intermediate layer preferably contain a crosslinked resin. Note that a crosslinked resin refers to a resin that does not melt even at high temperatures. This improves adhesive strength at high temperatures, i.e., heat resistance.

[0195] 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, 0.5 μm or more, or 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 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, heat resistance (adhesive strength at high temperatures) may be reduced.

[0196] 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 application methods 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.

[0197] (2) First Separator and Second Separator The foamable adhesive sheet in this embodiment may have a first separator on the side of the first adhesive layer opposite the second adhesive layer. Also, the foamable adhesive sheet in this embodiment may have a second separator on the side of the second adhesive layer opposite the first adhesive layer.

[0198] The first separator and the second separator are not particularly limited as long as they can be peeled 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. The first separator and the second separator may have a single-layer structure or a multi-layer structure.

[0199] An example of a separator having a single layer structure is a fluororesin film.

[0200] Further, examples of multilayer separators include laminates having a release layer on one or both sides of a substrate layer. Examples of substrate layers include resin films such as polypropylene, polyethylene, and polyethylene terephthalate, as well as paper such as fine paper, coated paper, and impregnated paper. The material for the release layer is not particularly limited as long as it has 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 emulsion-type, solvent-type, or solventless.

[0201] The first separator and the second separator may be the same or different. Preferably, the first separator has heavy releasability and the second separator has light releasability. In the foamable adhesive sheet, the first adhesive layer is substantially non-tacky (tack-free), while the second adhesive layer has tack. Therefore, for example, when bonding a rotor and a permanent magnet in an embedded magnet motor, after placing the foamable adhesive sheet on a second member, inserting the second member with the foamable adhesive sheet into a hole in the first member, by attaching the second adhesive layer of the foamable adhesive sheet to the second member and placing the first adhesive layer of the foamable adhesive sheet on the front side, the adhesion between the second member and the foamable adhesive sheet during insertion and the ease of inserting the second member with the foamable adhesive sheet can be improved. In this case, the first separator will peel from the second separator, and the first separator having heavy releasability and the second separator having light releasability can make the second separator easier to peel than the first separator.

[0202] Here, light peeling and heavy peeling refer to the degree of force required to peel the first separator and the second separator from the first adhesive layer and the second adhesive layer, respectively, and light peeling means that the peeling force is smaller than heavy peeling.

[0203] 6. Foamable Adhesive Sheet The thickness of the foamable adhesive sheet in this embodiment 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.

[0204] The use of the foamable adhesive sheet in this embodiment is not particularly limited. The foamable adhesive sheet in this embodiment can be used, for example, when two members are bonded together by placing the foamable adhesive sheet between them and then foaming and curing the foamable adhesive sheet. In particular, the foamable adhesive sheet in this embodiment is preferably used when a first member and a second member are bonded together by placing the foamable adhesive sheet on a second member, inserting the second member on which the foamable adhesive sheet is placed into a hole in a first member, and foaming and curing the foamable adhesive sheet.

[0205] The method for producing the foamable adhesive sheet in this embodiment is not particularly limited and may be appropriately selected depending on the layer structure of the foamable adhesive sheet. For example, the following two methods for producing a foamable adhesive sheet can be mentioned.

[0206] In the first method for producing a foamable adhesive sheet, for example, an adhesive composition for forming a first adhesive layer is first applied to one surface of a substrate and dried to form the first adhesive layer. Also, an adhesive composition for forming a second adhesive layer is applied to a second separator and dried to form the second adhesive layer. Next, a laminate of the substrate and the first adhesive layer and a laminate of the second separator and the second adhesive layer are laminated together. This results in a foamable adhesive sheet. A first intermediate layer and a second intermediate layer may also be formed. This method allows for efficient production of a foamable adhesive sheet, as the drying step for the first adhesive layer is performed only once.

[0207] In the second method for producing a foamable adhesive sheet, for example, an adhesive composition for forming a first adhesive layer is first applied to one surface of a substrate and dried to form a first adhesive layer. Next, an adhesive composition for forming a second adhesive layer is applied to the other surface of the substrate and dried to form a second adhesive layer. Subsequently, a second separator is laminated onto the second adhesive layer. This results in a foamable adhesive sheet. A first intermediate layer and / or a second intermediate layer may also be formed.

[0208] A) Second embodiment A second embodiment of the foamable adhesive sheet in this embodiment is a foamable adhesive sheet having, in this order, a first adhesive layer, a substrate, a second adhesive layer, and an adhesive layer, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive and a foaming agent, the adhesive layer contains a pressure-sensitive adhesive or a curable adhesive, the first adhesive layer has a tack of 0 gf or more and less than 10 gf, the adhesive layer has a tack of 10 gf or more, and the loop stiffness is 50 mN / 10 mm or more.

[0209] Figure 6 is a schematic cross-sectional view illustrating a foamable adhesive sheet according to this embodiment. The foamable adhesive sheet 10 in Figure 6 comprises, in this order, a first adhesive layer 1, a substrate 2, a second adhesive layer 3, and a pressure-sensitive adhesive layer 6. The first adhesive layer 1 and the second adhesive layer 3 contain a curable adhesive and a foaming agent, and the pressure-sensitive adhesive layer 6 contains a pressure-sensitive adhesive or a curable adhesive. The tack of the first adhesive layer 1 and the tack of the pressure-sensitive adhesive layer 6 are each within a predetermined range, and the loop stiffness of the foamable adhesive sheet 10 is also within a predetermined range.

[0210] In this embodiment, the tackiness of the adhesive layer within a predetermined range allows the adhesive layer to have good adhesion to the member. Specifically, when adhering and fixing one member to a hole, groove, etc. of another member, by adhering the adhesive layer surface of the foamable adhesive sheet to the other member, inserting the other member to which the foamable adhesive sheet is attached into the hole, groove, etc. of the one member, and then foaming and curing the foamable adhesive sheet to adhere the one member to the other member, the tackiness of the adhesive layer within the predetermined range allows the adhesive layer surface of the foamable adhesive sheet to be attached to the other member, thereby improving the adhesion of the adhesive layer to the member. This prevents the foamable adhesive sheet from peeling off or shifting when inserting the other member to which the foamable adhesive sheet is attached into the hole, groove, etc. of the one member.

[0211] Furthermore, in this embodiment, since the tackiness of the first adhesive layer is equal to or less than a predetermined value, the first adhesive layer can be made substantially non-tacky (tack-free) and can have good slipperiness. Therefore, for example, in the above-described adhesive fixing method, when inserting a component to which a foamable adhesive sheet is attached into a hole, groove, or the like of one component, the component to which the foamable adhesive sheet is attached can be smoothly inserted, improving insertability. This prevents peeling and misalignment of the foamable adhesive sheet. Furthermore, in the above-described adhesive fixing method, when aligning the components by moving the other component relative to the first component, the other component can be smoothly moved relative to the first component while the other component is inserted into a hole, groove, or the like of the first component, facilitating alignment.

[0212] Furthermore, in this embodiment, the tackiness of the first adhesive layer is a predetermined value or less, and the first adhesive layer is substantially non-sticky (tack-free), so the first adhesive layer has good slip properties and good blocking resistance, which in turn improves the handleability of the foamable adhesive sheet.

[0213] Furthermore, in this embodiment, as described above, the adhesive layer has excellent adhesion to the member, and the first adhesive layer has excellent slipperiness, so peeling and misalignment of the foamable adhesive sheet can be suppressed. Therefore, a decrease in the adhesive strength of the foamable adhesive sheet after foaming and curing due to peeling or misalignment of the foamable adhesive sheet can be suppressed, and variation in the adhesive strength of the foamable adhesive sheet after foaming and curing due to peeling or misalignment of the foamable adhesive sheet can be reduced. Therefore, by using the foamable adhesive sheet of this embodiment, high adhesive strength, high reliability, and high-quality adhesion can be achieved.

[0214] Furthermore, since the foamable adhesive sheet of this embodiment has a loop stiffness equal to or greater than a predetermined value, it can be made stiff. Therefore, when the foamable adhesive sheet is transported, it can be prevented from sagging under its own weight. Therefore, for example, when the foamable adhesive sheet is suction-transported and attached to another component, folding, kinking, bending, air bubble entrapment, and the like of the foamable adhesive sheet can be prevented during attachment. This improves attachment. Furthermore, since the occurrence of protrusions in the foamable adhesive sheet due to these defects can be prevented, when inserting a component to which the foamable adhesive sheet is attached into a hole, groove, or the like of one component, the foamable adhesive sheet is less likely to rub against the other component. Therefore, peeling of the foamable adhesive sheet during insertion can be prevented. Therefore, from these points of view, the use of the foamable adhesive sheet of this embodiment can achieve high adhesive strength, high reliability, and high-quality adhesion.

[0215] Each component of the foamable adhesive sheet of this embodiment will be described below.

[0216] 1. Characteristics The tackiness of the first adhesive layer in this embodiment is the same as the tackiness of the first adhesive layer in the first embodiment.

[0217] In this embodiment, the tackiness of the adhesive layer is 10 gf or more, 30 gf or more, or even 50 gf or more. If the tackiness of the adhesive layer is too low, for example, in the above-mentioned adhesive fixing method, when the adhesive layer surface of the foamable adhesive sheet is attached to the other member using the tackiness of the adhesive layer, the adhesion between the adhesive layer and the other member may be reduced. Also, when inserting the other member to which the foamable adhesive sheet is attached into a hole or groove of one member, poor adhesion between the adhesive layer and the other member may cause the foamable adhesive sheet to peel off or the position of the foamable adhesive sheet to shift, etc., which may result in a reduction in the adhesion of the first adhesive layer and the adhesive layer after foaming and curing, or variations in adhesive strength. Furthermore, the tackiness of the adhesive layer may be, for example, 500 gf or less, 400 gf or less, or 300 gf or less.

[0218] In this embodiment, the tackiness of the second adhesive layer is not particularly limited. In particular, the tackiness of the second adhesive layer is preferably less than 10 gf. In this case, the tackiness of the second adhesive layer can be the same as that of the first adhesive layer.

[0219] The method for measuring the tackiness of the first adhesive layer, the second adhesive layer and the pressure-sensitive adhesive layer is the same as that described in the first embodiment.

[0220] The method for controlling the tackiness of the first adhesive layer and the second adhesive layer is the same as that described in the first embodiment.

[0221] In this embodiment, the static friction coefficient of the surface of the first adhesive layer opposite the second adhesive layer and the arithmetic mean roughness (Ra) of the surface of the first adhesive layer opposite the second adhesive layer are the same as those described in the first embodiment above.

[0222] The loop stiffness of the foamable adhesive sheet of this embodiment is the same as that of the foamable adhesive sheet of the first embodiment. In this embodiment, when a test piece of the foamable adhesive sheet is placed on the loop stiffness measuring device, the test piece of the foamable adhesive sheet is positioned so that the inner surface is the surface of the first adhesive layer and the outer surface is the surface of the pressure-sensitive adhesive layer.

[0223] The adhesive properties and electrical insulating properties of the foamable adhesive sheet of this embodiment after foaming and curing are the same as those described in the first embodiment.

[0224] 2. First Adhesive Layer The first adhesive layer in this embodiment contains a curable adhesive and a foaming agent. The material and configuration of the first adhesive layer can be the same as those of the first adhesive layer in the first embodiment.

[0225] 3. Second Adhesive Layer The second adhesive layer in this embodiment contains a curable adhesive and a foaming agent. The material and configuration of the second adhesive layer may be the same as those of the first adhesive layer in the first embodiment, or may be the same as those of the second adhesive layer in the first embodiment.

[0226] 4. Adhesive Layer In this embodiment, the adhesive layer is disposed on the side of the second adhesive layer opposite the substrate, and contains a pressure-sensitive adhesive or a curable adhesive. The adhesive layer is substantially free of a foaming agent.

[0227] As the pressure-sensitive adhesive contained in the adhesive layer in this embodiment, a general pressure-sensitive adhesive can be used.

[0228] Furthermore, the curable adhesive contained in the adhesive layer in this embodiment can be the same as the curable adhesive used in the second adhesive layer.

[0229] The thickness of the adhesive layer is not particularly limited, but may be, for example, 2 μm to 100 μm, 3 μm to 75 μm, or 5 μm to 50 μm. If the adhesive layer is too thin, sufficient adhesiveness may not be obtained.

[0230] The adhesive layer may be a continuous layer or a discontinuous layer. Examples of discontinuous layers include stripes and dots. The surface of the adhesive layer may have an uneven shape such as an embossed shape.

[0231] The method for forming the adhesive layer can be the same as the method for forming the first adhesive layer and the second adhesive layer.

[0232] 5. Substrate In this embodiment, the substrate is disposed between the first adhesive layer and the second adhesive layer. The substrate is the same as the substrate in the first embodiment.

[0233] 6. Other Configurations (1) First Intermediate Layer and Second Intermediate Layer The foamable adhesive sheet in this embodiment may have a first intermediate layer between the substrate and the first adhesive layer. The foamable adhesive sheet in this embodiment may also have a second intermediate layer between the substrate and the second adhesive layer. The first intermediate layer and second intermediate layer are the same as the first intermediate layer and second intermediate layer in the first embodiment.

[0234] For example, in the foamable adhesive sheet 10 shown in Fig. 7, a first intermediate layer 4 is disposed between the substrate 2 and the first adhesive layer 1, and a second intermediate layer 5 is disposed between the substrate 2 and the second adhesive layer 3. Although the foamable adhesive sheet 10 in Fig. 7 has both the first intermediate layer 4 and the second intermediate layer 5, it may have only one of them.

[0235] (2) First Separator and Second Separator The foamable adhesive sheet in this embodiment may have a first separator on the side of the first adhesive layer opposite the second adhesive layer. The foamable adhesive sheet in this embodiment may also have a second separator on the side of the pressure-sensitive adhesive layer opposite the second adhesive layer. The first separator and second separator may be the same as the first separator and second separator in the first embodiment.

[0236] 7. Foamable Adhesive Sheet The thickness and uses of the foamable adhesive sheet in this embodiment are the same as those in the first embodiment.

[0237] The method for producing the foamable adhesive sheet in this embodiment is not particularly limited, and may be appropriately selected depending on the layer structure of the foamable adhesive sheet.

[0238] B. Method for Manufacturing an Article The method for manufacturing an article in this embodiment includes a disposing step of disposing the foamable adhesive sheet described above between a first member and a second member, and a bonding step of foaming and curing the foamable adhesive sheet to bond the first member and the second member together.

[0239] 8(a) to 8(c) are process diagrams illustrating an example of a method for manufacturing an article according to this embodiment. First, as shown in FIG. 8(a), the second adhesive layer 3 of the foamable adhesive sheet 10 is attached to the second member 20b. Next, as shown in FIG. 8(b), the second member 20b with the foamable adhesive sheet 10 disposed thereon is inserted into the hole in the first member 20a. Next, as shown in FIG. 8(c), the first adhesive layer 1 and the second adhesive layer 3 of the foamable adhesive sheet 10 are foamed and cured, for example, by heating. The first member 20a and the second member 20b are bonded (joined) by the adhesive sheet 13 having the first adhesive layer 11 and the second adhesive layer 12 after foaming and curing. This results in an article 100 in which the adhesive sheet 13 is disposed between the first member 20a and the second member 20b.

[0240] 9(a) to 9(c) are process diagrams showing another example of the method for manufacturing an article according to this embodiment. In Fig. 9(a), foamable adhesive sheets are attached to both sides of the second member 20b. The placement and adhesion steps are the same as those shown in Figs. 8(a) to 8(c).

[0241] The method for manufacturing an article according to this embodiment will be described below.

[0242] 1. Foamable Adhesive Sheet In the method for producing an article according to this embodiment, the foamable adhesive sheet used is the foamable adhesive sheet described above.

[0243] When the foamable adhesive sheet has a first separator or a second separator, the first separator or the second separator is peeled off from the foamable adhesive sheet when the foamable adhesive sheet is placed between the first member and the second member.

[0244] Details of the foamable adhesive sheet are described above in the section "A. Foamable adhesive sheet," so further description will be omitted here.

[0245] 2. Placement Step In the placement step of this embodiment, the method for placing the foam adhesive sheet between the first and second members is selected appropriately depending on the types of the first and second members, etc. For example, when the first member has a hole or groove and the second member is placed in the hole or groove of the first member, and the first and second members are fixed by adhesion, examples of the method include a method in which the second adhesive layer or adhesive layer surface of the foam adhesive sheet is attached to the second member using the tack of the second adhesive layer or adhesive layer of the foam adhesive sheet, and then the second member with the foam adhesive sheet attached is placed in the hole or groove of the first member, or a method in which the foam adhesive sheet is placed in the hole or groove of the first member, the second adhesive layer or adhesive layer surface of the foam adhesive sheet is attached to the hole or groove of the first member using the tack of the second adhesive layer or adhesive layer of the foam adhesive sheet, and then the second member is placed in the hole or groove of the first member with the foam adhesive sheet attached.

[0246] 3. Bonding Step In the bonding step of this embodiment, examples of the method for foaming and curing the foamable adhesive sheet include heating and light irradiation. Of these, it is preferable to foam and cure the foamable adhesive sheet by heating. Heating methods are also applicable even when the first and second members are not transparent, such as when the first and second members are made of metal.

[0247] The heating conditions are appropriately set depending on the types of curable adhesive and foaming agent contained in the first adhesive layer and the second adhesive layer, the type of substrate, etc. The heating temperature can be, for example, 130° C. or higher and 200° C. or lower. The heating time can be, for example, 3 minutes or higher and 3 hours or lower.

[0248] II. Second Embodiment Next, a foamable adhesive sheet according to a second embodiment of the present disclosure and a method for producing an article using the same will be described in detail.

[0249] A. Foamable Adhesive Sheet The foamable adhesive sheet in this embodiment is a foamable adhesive sheet having a first adhesive layer, a substrate, and a second adhesive layer in this order, wherein the first adhesive layer has a different composition from the second adhesive layer, the first adhesive layer and the second adhesive layer contain a thermosetting adhesive, and at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent, and wherein after being allowed to stand for 15 hours at a temperature of 60°C and a humidity of 10% RH or less, the foamable adhesive sheet has a curl radius of curvature of 15 mm or more and a loop stiffness of 45 mN / 10 mm or more.

[0250] Figure 1 is a schematic cross-sectional view illustrating an example of a foamable adhesive sheet according to this embodiment. The foamable adhesive sheet 10 in Figure 1 comprises, in this order, a first adhesive layer 1, a substrate 2, and a second adhesive layer 3. The first adhesive layer 1 and the second adhesive layer 3 contain a thermosetting adhesive, and at least one of the first adhesive layer 1 and the second adhesive layer 3 further contains a foaming agent. Furthermore, the foamable adhesive sheet 10 has a curl radius of curvature within a predetermined range after being left to stand for a predetermined time at a predetermined temperature and humidity, and also has a loop stiffness within a predetermined range.

[0251] Here, when one component is adhesively fixed to a hole or groove in another component, the gap between the two components tends to become narrow, as mentioned above. Therefore, the foamable adhesive sheet used is required to have a thin overall thickness. However, when a foamable adhesive sheet has a first adhesive layer, a substrate, and a second adhesive layer in this order, and the first adhesive layer and the second adhesive layer have different compositions, a thin foamable adhesive sheet is more likely to curl. Furthermore, a thin foamable adhesive sheet is more likely to sag under its own weight during transport.

[0252] In contrast, in this embodiment, the curl radius after standing for a predetermined time at a predetermined temperature and humidity is within a predetermined range, thereby suppressing curling even when the first adhesive layer and the second adhesive layer have different compositions and the foamable adhesive sheet is thin. Therefore, for example, when inserting a foamable adhesive sheet between two components, for example, by placing the foamable adhesive sheet in a hole or groove of one component and then inserting the other component into the hole or groove of the component with the foamable adhesive sheet placed in it, or by placing the foamable adhesive sheet in the other component and then inserting the other component with the foamable adhesive sheet placed in it into the hole or groove of the other component, the ease of insertion is improved. Furthermore, for example, when the tack of the first adhesive layer is lower than that of the second adhesive layer, using the tack of the second adhesive layer to attach the second adhesive layer surface of the foamable adhesive sheet to a component can prevent the foamable adhesive sheet from lifting or peeling from the component. Furthermore, in the above case, folding, kinking, warping, air bubble entrapment, and other problems occurring in the foamable adhesive sheet during attachment can be suppressed. Therefore, poor adhesion after foaming and curing can be suppressed.

[0253] The inventors of the present disclosure also focused on the rigidity of the foamable adhesive sheet. A thick foamable adhesive sheet tends to have higher rigidity, which is thought to suppress curling and sagging due to its own weight. However, when the gap between two components is narrow, increasing the thickness of the foamable adhesive sheet reduces insertion. Thus, since the foamable adhesive sheet must be thin to begin with, increasing the thickness of the foamable adhesive sheet is not appropriate. Furthermore, a thick substrate tends to have higher rigidity, which is thought to suppress curling and sagging due to its own weight. However, increasing the thickness of the substrate increases the thickness of the foamable adhesive sheet, which, as mentioned above, reduces insertion. Furthermore, if the thickness of the substrate is relatively increased while the thickness of the foamable adhesive sheet is kept thin, the thicknesses of the first and second adhesive layers become relatively thin, which may reduce the adhesive and foaming properties of the first and second adhesive layers.

[0254] After further investigation, the inventors of the present disclosure discovered that by setting the loop stiffness of the foamable adhesive sheet within a specific range, it is possible to prevent the foamable adhesive sheet from sagging under its own weight.

[0255] Loop stiffness is a parameter that indicates the stiffness of a sheet or film. The higher the loop stiffness value, the stiffer the sheet or film. Loop stiffness is used as a parameter to indicate the stiffness of sheets and films used in packaging materials, for example, but is not very common in the field of adhesive sheets.

[0256] The foamable adhesive sheet of this embodiment has a loop stiffness equal to or greater than a predetermined value, thereby increasing stiffness. Therefore, sagging of the foamable adhesive sheet due to its own weight can be suppressed during transport. Therefore, for example, when a foamable adhesive sheet is suction-transported and attached to a component, folding, kinking, bending, air bubble entrapment, and the like of the foamable adhesive sheet during attachment can be suppressed. This improves attachment properties. Furthermore, since the occurrence of protrusions in the foamable adhesive sheet due to these defects can be suppressed, the foamable adhesive sheet is less likely to rub when a component to which the foamable adhesive sheet is attached is inserted into a hole or groove in another component. Therefore, peeling of the foamable adhesive sheet during insertion can be suppressed.

[0257] Therefore, by using the foamable adhesive sheet of this embodiment, high adhesive strength, high reliability, and high quality adhesion can be achieved.

[0258] Here, "adhesion" is a concept included in "bonding." The two are sometimes distinguished in that "adhesion" is used to mean a temporary adhesive phenomenon, while "bonding" is used to mean a substantially permanent adhesive phenomenon (Iwanami Shoten, Physics and Chemistry Dictionary, 5th Edition). "Adhesion" and "adhesive strength" refer to the property of adhesion through pressure and the adhesive strength at that time.

[0259] In this specification, unless otherwise specified, the terms "adhesion of the adhesive layer" and "adhesion strength of the adhesive layer" refer to the adhesion and adhesive strength of the adhesive layer before curing. In addition, in this specification, unless otherwise specified, the terms "adhesion of the adhesive layer" and "adhesion strength of the adhesive layer" refer to the adhesion and adhesive strength of the adhesive layer after curing.

[0260] Hereinafter, each component of the foamable adhesive sheet in this embodiment will be described.

[0261] 1. Properties The foamable adhesive sheet of this embodiment exhibits a curl radius of 15 mm or more, preferably 20 mm or more, and more preferably 25 mm or more, after being left to stand for 15 hours at a temperature of 60°C and a humidity of 10% RH or less. Having the radius of curvature within the above range can suppress curling. Therefore, for example, when inserting a foamable adhesive sheet between two components, for example, by placing the foamable adhesive sheet in a hole or groove of one component and then inserting the other component into the hole or groove of the component with the foamable adhesive sheet placed therein, or by placing the foamable adhesive sheet on the other component and then inserting the other component with the foamable adhesive sheet placed therein into the hole or groove of the component, the ease of insertion can be improved. Furthermore, for example, when the tack of the first adhesive layer is lower than that of the second adhesive layer, and the tack of the second adhesive layer is used to attach the second adhesive layer surface of the foamable adhesive sheet to a component, lifting or peeling of the foamable adhesive sheet from the component can be suppressed. In addition, in the above case, the foamable adhesive sheet can be prevented from folding, buckling, bending, or trapping air bubbles during application, thereby preventing poor adhesion after foaming and curing. On the other hand, the larger the radius of curvature, the smaller the curl, so there is no particular upper limit for the radius of curvature.

[0262] When a foamable adhesive sheet is used to bond, for example, a coil and a stator in a motor, or a rotor and a permanent magnet in an embedded magnet motor, the length of the foamable adhesive sheet is often about 100 mm. Therefore, in this embodiment, when the length of a foamable adhesive sheet test piece is set to 100 mm, it is deemed practical as long as the test piece does not complete a full revolution in the length direction, and the radius of curvature is set to 15 mm or more.

[0263] Furthermore, in the case of a thermosetting adhesive, shrinkage occurs during the curing process due to hardening and thermal shrinkage. This shrinkage causes curling. Generally, it is thought that a thermosetting adhesive begins to shrink at around 60°C. Therefore, since the main cause of shrinkage of a thermosetting adhesive is heat, in this embodiment, in order to eliminate the influence of humidity, the conditions were set to 60°C, 15 hours, and humidity was set to 10% RH or less.

[0264] Here, the radius of curvature of the curl of the foamable adhesive sheet can be measured by the following method.

[0265] First, a foamable adhesive sheet is cut into a 50 mm x 50 mm square to prepare a test piece for curl measurement. In this case, as shown in FIG. 11( a), the side directions of the square are defined as the MD and TD directions of the foamable adhesive sheet 10. The MD direction of a foamable adhesive sheet refers to the longitudinal direction of the foamable adhesive sheet when the foamable adhesive sheet is manufactured in a continuous shape. The TD direction of a foamable adhesive sheet refers to the direction perpendicular to the MD direction. The MD and TD directions of a foamable adhesive sheet can be determined using the following method. When the foamable adhesive sheet is continuous, the longitudinal direction of the foamable adhesive sheet is defined as the MD direction. When the foamable adhesive sheet is in a sheet-like shape, if the substrate, first adhesive layer, and second adhesive layer are known to be anisotropic, the tensile strength and elongation of the substrate, first adhesive layer, and second adhesive layer can be measured, and the MD and TD directions of the foamable adhesive sheet can be determined from these tensile strengths and elongations. Furthermore, when the foamable adhesive sheet is in sheet form, and the anisotropy of the substrate or the anisotropy of the first adhesive layer and the second adhesive layer is unknown, the foamable adhesive sheet can be cut into a circle with a diameter of approximately 50 mm to prepare a test piece for direction measurement, and the test piece for direction measurement can be left to stand at a temperature of 60°C, and the direction in which the test piece for direction measurement curls can be considered to be the MD direction of the foamable adhesive sheet.

[0266] Next, the test piece for curl measurement is left to stand for 15 hours at a temperature of 60°C and a humidity of 10% RH or less. At this time, if at least one of the first adhesive layer and the second adhesive layer is adhesive, the test piece for curl measurement should be in a state where the adhesive layer surface does not touch the surroundings. In particular, it is preferable that the test piece for curl measurement be in a state where its own weight is not applied in the curl direction. Next, the chord length d of the curl of the test piece for curl measurement is measured as shown in FIG. 11(b). The radius of curvature r is calculated using the following formula: L = r × θ d = 2 × r × sin(θ / 2) (where L represents the arc length, d represents the chord length, r represents the radius of curvature, and θ represents the central angle). The chord length d is measured in the MD direction, the TD direction, and a direction at 45° to the MD direction, and the radius of curvature r is calculated. The smallest value of the radii of curvature r in these cases is used. When the direction of the chord length d is the MD or TD, the arc length L is 50 mm. When the direction of the chord length d is at a 45° angle to the MD, the arc length L is L = 50 × √2 = 70.7 mm.

[0267] In this embodiment, the radius of curvature of the curl of the foamable adhesive sheet can be controlled, for example, by adjusting the thickness and hardness of each layer. For example, the thicker the substrate, the larger the radius of curvature tends to be. Furthermore, for example, the higher the hardness of the substrate, the larger the radius of curvature tends to be. Furthermore, for example, if the hardness of the first adhesive layer is higher than that of the second adhesive layer, the thicker the second adhesive layer, the larger the radius of curvature tends to be. Furthermore, if the hardness of the first adhesive layer and the second adhesive layer are similar, the radius of curvature tends to be larger if the thicknesses of the first adhesive layer and the second adhesive layer are similar.

[0268] The hardness of the first adhesive layer and the second adhesive layer can be controlled by adjusting the composition of the first adhesive layer and the second adhesive layer. Furthermore, in the first adhesive layer and the second adhesive layer, low tack tends to increase hardness, and high tack tends to decrease hardness. Furthermore, in the first adhesive layer and the second adhesive layer, high storage modulus tends to increase hardness, and low storage modulus tends to decrease hardness. Furthermore, in the first adhesive layer and the second adhesive layer, high pencil hardness tends to increase hardness, and low pencil hardness tends to decrease hardness. Furthermore, in the first adhesive layer and the second adhesive layer, low static friction coefficient tends to increase hardness, and high pencil hardness tends to decrease hardness.

[0269] The foamable adhesive sheet of this embodiment has a loop stiffness of 45 mN / 10 mm or more, preferably 75 mN / 10 mm or more, and more preferably 100 mN / 10 mm or more. As described above, loop stiffness is a parameter that indicates the stiffness of a film or sheet. Having the loop stiffness of the foamable adhesive sheet within the above range can increase the stiffness of the foamable adhesive sheet. Therefore, when the foamable adhesive sheet is placed between two components, insertion can be improved. Furthermore, for example, when the foamable adhesive sheet is suction-transported and attached to a component, sagging of the foamable adhesive sheet due to its own weight can be suppressed, improving attachment. Meanwhile, there is no particular upper limit to the loop stiffness.

[0270] The method for measuring the loop stiffness is the same as that explained in the section "I. First embodiment A. Foamable adhesive sheet A) First embodiment 1. Properties" above, and therefore will not be explained here.

[0271] In measuring the loop stiffness of the foamable adhesive sheet, measurements are performed in both cases where the test piece of the foamable adhesive sheet 10 is placed in the loop stiffness measuring device 30 so that the inner surface 40x is the surface of the first adhesive layer and the outer surface 40y is the surface of the second adhesive layer, and where the inner surface 40x is the surface of the second adhesive layer and the outer surface 40y is the surface of the first adhesive layer. The larger of the loop stiffness values ​​obtained in these cases is used.

[0272] Furthermore, when measuring the loop stiffness of a foamable adhesive sheet, if the foamable adhesive sheet has a separator, as described below, the loop stiffness of the foamable adhesive sheet is measured after peeling off the separator, because the separator is peeled off from the foamable adhesive sheet when the foamable adhesive sheet is placed between two members.

[0273] In this embodiment, the loop stiffness of the foamable adhesive sheet can be controlled, for example, by adjusting the thickness and hardness of each layer. For example, the thicker the substrate, the greater the loop stiffness. Furthermore, for example, the higher the hardness of the substrate, the greater the loop stiffness. Furthermore, for example, when the hardness of the first adhesive layer is higher than that of the second adhesive layer, the thicker the first adhesive layer, the greater the loop stiffness. Furthermore, the higher the hardness of the first adhesive layer and the second adhesive layer, the greater the loop stiffness.

[0274] The method for controlling the hardness of the first adhesive layer and the second adhesive layer is as described above.

[0275] The foamable adhesive sheet of this embodiment preferably has high adhesiveness after foaming and curing. It is also preferable that the foamable adhesive sheet of this embodiment has high electrical insulation after foaming and curing. The explanation of these points is the same as that in the section "I. First Embodiment A. Foamable Adhesive Sheet A) First Embodiment 1. Characteristics" above, and therefore will not be repeated here.

[0276] 2. First Adhesive Layer and Second Adhesive Layer In this embodiment, the first adhesive layer and the second adhesive layer contain a thermosetting adhesive. At least one of the first adhesive layer and the second adhesive layer further contains a foaming agent. The composition of the first adhesive layer is different from the composition of the second adhesive layer.

[0277] Here, the composition of the first adhesive layer and the composition of the second adhesive layer are different means that at least one of the following is different: the type and content of the main agent constituting the thermosetting adhesive; the type and content of the curing agent constituting the thermosetting adhesive; the type and content of resin components other than the main agent constituting the thermosetting adhesive; the type and content of the foaming agent; and the type and content of additives.

[0278] In particular, it is preferable that the first adhesive layer and the second adhesive layer contain a thermosetting adhesive and a foaming agent, and that the composition of the first adhesive layer is different from the composition of the second adhesive layer.

[0279] (1) Characteristics of the First Adhesive Layer and the Second Adhesive Layer (a) Hardness In this embodiment, it is preferable that the first adhesive layer and the second adhesive layer have different hardnesses. If the hardnesses of the first adhesive layer and the second adhesive layer are different, the foamable adhesive sheet is likely to curl. Therefore, this embodiment is effective when the hardnesses of the first adhesive layer and the second adhesive layer are different.

[0280] The hardness of the first adhesive layer and the second adhesive layer is not particularly limited as long as it is a measurable hardness parameter for the first adhesive layer and the second adhesive layer. In addition, for example, the tack of the first adhesive layer and the second adhesive layer, or a thermal property such as the glass transition temperature of the first adhesive layer and the second adhesive layer, etc. can be used as an indicator of the hardness of the first adhesive layer and the second adhesive layer.

[0281] (b) Tack In this embodiment, it is preferable that the tackiness of the first adhesive layer and the second adhesive layer be different. Generally, the greater the adhesiveness (tackiness) of an adhesive layer, the softer it tends to be, and the weaker the adhesiveness (tackiness) of an adhesive layer, the harder it tends to be. Therefore, if the tackiness of the first adhesive layer and the second adhesive layer is different, the foamable adhesive sheet is likely to curl. Therefore, this embodiment is effective when the tackiness of the first adhesive layer and the second adhesive layer is different.

[0282] Furthermore, when the tackiness of the first adhesive layer and the second adhesive layer is different and the tackiness of the first adhesive layer is lower than that of the second adhesive layer, it is preferable that the tackiness of the first adhesive layer is, for example, 0 gf or more and less than 10 gf, and the tackiness of the second adhesive layer is, for example, 10 gf or more and 500 gf or less. In this case, the tackiness of the first adhesive layer may be, for example, 5 gf or less or 2 gf or less. In this case, the tackiness of the second adhesive layer may be, for example, 30 gf or more or 50 gf or more. In addition, the tackiness of the second adhesive layer may be, for example, 400 gf or less or 300 gf or less.

[0283] In the above case, the foamable adhesive sheet is prone to curling due to the difference in tack between the first adhesive layer and the second adhesive layer. For this reason, this embodiment is effective.

[0284] Furthermore, in the above case, the tackiness of the second adhesive layer within the above range allows the second adhesive layer to have good adhesion to the member. Specifically, when adhesively fixing one member to a hole, groove, etc. of another member by attaching the second adhesive layer surface of the foamable adhesive sheet to the other member, inserting the other member to which the foamable adhesive sheet is attached into the hole, groove, etc. of the one member, and then foaming and curing the foamable adhesive sheet to bond the one member and the other member, if the tackiness of the second adhesive layer is within the specified range, the tackiness of the second adhesive layer can be used to attach the second adhesive layer surface of the foamable adhesive sheet to the other member, thereby improving the adhesion of the second adhesive layer to the member. This prevents peeling or misalignment of the foamable adhesive sheet when inserting the other member to which the foamable adhesive sheet is attached into the hole, groove, etc. of the one member.

[0285] In the above case, the tackiness of the second adhesive layer within the above range allows the second adhesive layer to have good reworkability, and therefore, for example, in the above-mentioned adhesive fixing method, when the surface of the second adhesive layer of the foamable adhesive sheet is attached to a member by utilizing the tackiness of the second adhesive layer, misalignment of the foamable adhesive sheet can be corrected.

[0286] In the above case, by having the tackiness of the second adhesive layer within the above range, for example, when the second adhesive layer is formed by a transfer method, lifting of the second adhesive layer can be suppressed. Furthermore, as will be described later, when a separator is disposed on the side of the second adhesive layer opposite the substrate, by having the tackiness of the second adhesive layer within the specified range, the separator can be easily peeled off, thereby improving workability.

[0287] Furthermore, in the above case, by having the tack of the first adhesive layer within the above range, the first adhesive layer can be made substantially non-tacky (tack-free) and can have good slipperiness. Therefore, for example, in the above-mentioned adhesive fixing method, when inserting a component to which a foamable adhesive sheet is attached into a hole, groove, etc. of one component, the component to which the foamable adhesive sheet is attached can be smoothly inserted, improving insertability. This can prevent peeling and misalignment of the foamable adhesive sheet. Furthermore, in the above-mentioned adhesive fixing method, when aligning the components by moving the other component relative to the first component, the other component can be smoothly moved relative to the first component while the other component is inserted into a hole, groove, etc. of the first component, facilitating alignment.

[0288] Furthermore, in the above case, since the tackiness of the first adhesive layer is within the above range, the first adhesive layer is substantially non-tacky (tack-free), and therefore the first adhesive layer has good slip properties and good blocking resistance, which in turn improves the handleability of the foamable adhesive sheet.

[0289] Furthermore, in the above case, as described above, the second adhesive layer has excellent adhesion to the member, and the first adhesive layer has excellent slipperiness, so peeling and misalignment of the foamable adhesive sheet can be suppressed. Therefore, a decrease in the adhesive strength of the foamable adhesive sheet after foaming and curing due to peeling or misalignment of the foamable adhesive sheet can be suppressed, and variation in the adhesive strength of the foamable adhesive sheet after foaming and curing due to peeling or misalignment of the foamable adhesive sheet can be reduced. Therefore, in the above case, by using the foamable adhesive sheet of this embodiment, high adhesive strength, high reliability, and high-quality adhesion can be achieved.

[0290] On the other hand, the tackiness of the first adhesive layer and the second adhesive layer may be the same.

[0291] The tackiness of both the first adhesive layer and the second adhesive layer may be low. In this case, the tackiness of each of the first adhesive layer and the second adhesive layer is preferably, for example, 0 gf or more and less than 10 gf. In this case, the tackiness of each of the first adhesive layer and the second adhesive layer may be, for example, 5 gf or less, or even 2 gf or less. By having the tackiness of the first adhesive layer and the second adhesive layer each within the above range, the first adhesive layer and the second adhesive layer can be made substantially non-tacky (tack-free), resulting in first adhesive layer and second adhesive layer with good slipperiness. Therefore, for example, when inserting a foamable adhesive sheet between two components, the foamable adhesive sheet can be placed in a hole, groove, etc. of one component, and then the other component can be inserted into the hole, groove, etc. of the component with the foamable adhesive sheet placed thereon, or the foamable adhesive sheet can be placed in the other component, and then the other component with the foamable adhesive sheet placed thereon can be inserted into the hole, groove, etc. of the component. This improves insertion ease. This prevents peeling or misalignment of the foamable adhesive sheet. Furthermore, when aligning two components by moving one component relative to the other, the foamable adhesive sheet can be placed between the two components, allowing the other component to be moved smoothly relative to the first component, facilitating alignment. Furthermore, by ensuring that the tack of the first adhesive layer and the second adhesive layer is within the above range, the first adhesive layer and the second adhesive layer also have good blocking resistance. Therefore, the handleability of the foamable adhesive sheet can be improved.

[0292] Here, the tackiness of the first adhesive layer and the second adhesive layer can be measured by a probe tack test. As a probe tack tester, for example, a tackiness tester "TAC-II" manufactured by RHESCA can be used. Details of the method for measuring the tackiness of the first adhesive layer and the second adhesive layer will be described in the Examples section below.

[0293] In this embodiment, the tackiness of the first adhesive layer and the second adhesive layer can be controlled, for example, by adjusting the composition of each adhesive layer.

[0294] Specifically, the adhesive layer containing an epoxy resin and a curing agent can have a lower adhesive strength by using an epoxy resin that is solid at room temperature or a curing agent that is solid at room temperature, whereas the adhesive layer tends to have a higher adhesive strength by using an epoxy resin that is liquid at room temperature or a curing agent that is liquid at room temperature.

[0295] Furthermore, the adhesive layer containing an epoxy resin and a curing agent can have a reduced adhesive strength by incorporating an epoxy resin with a high softening temperature or an epoxy resin with a high weight-average molecular weight. On the other hand, the adhesive layer containing an epoxy resin and a curing agent tends to have a higher adhesive strength by incorporating an epoxy resin with a low softening temperature or an epoxy resin with a low weight-average molecular weight. For example, the adhesive layer can have a reduced adhesive strength by incorporating multiple epoxy resins with different softening temperatures, i.e., by incorporating one epoxy resin and another epoxy resin with a softening temperature of 25°C or higher and 10°C or higher than the softening temperature of the first epoxy resin. The adhesive layer can also have a reduced adhesive strength by incorporating multiple epoxy resins with different weight-average molecular weights, i.e., by incorporating one epoxy resin and another epoxy resin with a weight-average molecular weight of 370 or higher and 300 or higher than the weight-average molecular weight of the first epoxy resin. More specifically, in an adhesive layer containing an epoxy resin and a curing agent, the adhesive layer can be made to have a reduced adhesiveness by including, as the epoxy resin, a first epoxy resin having a low softening temperature and a low molecular weight, and a second epoxy resin having a high softening temperature and a high molecular weight, as described below.

[0296] Furthermore, in an adhesive layer containing an epoxy resin and a curing agent, the adhesive layer can be made to contain an acrylic resin that is compatible with the epoxy resin, as will be described later, thereby reducing the adhesiveness of the adhesive layer.

[0297] Furthermore, by adding a tackifier to the adhesive layer, the adhesive layer tends to have increased adhesiveness.

[0298] In addition, when a curing agent that is liquid at room temperature is used, the adhesiveness tends to increase, but storage stability may decrease. Therefore, it is preferable to adjust the tackiness of the adhesive layer by adjusting the properties and type of components other than the curing agent, such as the epoxy resin.

[0299] (c) Storage Modulus In this embodiment, it is preferable that the viscoelasticity of the first adhesive layer and the second adhesive layer be different. Generally, adhesive layers tend to be harder as their storage modulus increases, and softer as their storage modulus decreases. Therefore, if the storage moduli of the first adhesive layer and the second adhesive layer are different, the foamable adhesive sheet is likely to curl. Therefore, this embodiment is effective when the storage moduli of the first adhesive layer and the second adhesive layer are different.

[0300] When the storage modulus of the first adhesive layer and the second adhesive layer are different, and the storage modulus E'(25) of the first adhesive layer at 25 ° C. is higher than the storage modulus E'(25) of the second adhesive layer, the storage modulus E'(25) of the first adhesive layer is, for example, 1.0 × 10 ６ Pa or more, 1.0×10 １０ Pa or less, and the storage modulus E'(25) of the second adhesive layer is, for example, 1.0 x 10 ３ Pa or more, 1.0×10 ６ In this case, the storage modulus E′(25) of the first adhesive layer is preferably less than 1.0×10 Pa. ７ In this case, the storage modulus E′(25) of the second adhesive layer may be, for example, 1.0×10 ４ Pa or more, 1.0×10 ５ Pa or less.

[0301] Furthermore, in the above case, having the storage modulus of the second adhesive layer within the above range allows the second adhesive layer to have good adhesion to the member. Specifically, when adhesively fixing one member to a hole, groove, etc. of another member, by attaching the second adhesive layer surface of the foamable adhesive sheet to the other member, inserting the other member to which the foamable adhesive sheet is attached into the hole, groove, etc. of the one member, and then foaming and curing the foamable adhesive sheet to bond the one member to the other member, having the storage modulus of the second adhesive layer within the specified range allows the softness of the second adhesive layer to be utilized to conform to the unevenness of the member, thereby improving the adhesion of the second adhesive layer. This prevents peeling or misalignment of the foamable adhesive sheet when inserting the other member to which the foamable adhesive sheet is attached into the hole, groove, etc. of the one member.

[0302] In the above case, since the storage modulus of the second adhesive layer is within the above range, the second adhesive layer can have good reworkability. Therefore, for example, in the above-mentioned adhesive fixing method, the softness of the second adhesive layer can be used to correct misalignment of the foamable adhesive sheet when attaching the second adhesive layer surface of the foamable adhesive sheet to a member.

[0303] In the above case, by having the storage modulus of the second adhesive layer within the above range, for example, when the second adhesive layer is formed by a transfer method, lifting or deformation of the second adhesive layer can be suppressed. Furthermore, as will be described later, when a separator is disposed on the side of the second adhesive layer opposite the substrate, by having the storage modulus of the second adhesive layer within the predetermined range, the separator can be easily peeled off, thereby improving workability.

[0304] Furthermore, in the above case, by having the storage modulus of the first adhesive layer within the above range, the first adhesive layer can have good slip properties. Therefore, for example, in the above-mentioned adhesive fixing method, when inserting one component to which a foamable adhesive sheet is attached into a hole, groove, etc. of another component, the other component to which the foamable adhesive sheet is attached can be smoothly inserted, improving insertability. This prevents peeling and misalignment of the foamable adhesive sheet. Furthermore, in the above-mentioned adhesive fixing method, when aligning the components by moving the other component relative to one component, the other component can be smoothly moved relative to the one component while inserted into a hole, groove, etc. of the first component, facilitating alignment.

[0305] Furthermore, in the above case, since the storage modulus of the first adhesive layer is within the above range, the first adhesive layer can have good slip properties and good blocking resistance, thereby improving the handleability of the foamable adhesive sheet.

[0306] On the other hand, the first adhesive layer and the second adhesive layer may have the same storage modulus.

[0307] In addition, the storage modulus of both the first adhesive layer and the second adhesive layer may be high. In this case, the storage modulus E'(25) of the first adhesive layer and the second adhesive layer at 25°C is, for example, 1.0 x 10 ６ Pa or more, 1.0×10 １０ In this case, the storage modulus E'(25) of the first adhesive layer and the second adhesive layer is preferably 1.0 x 10 Pa or less. ７Pa or higher. By having the storage modulus E'(25) of the first adhesive layer and the second adhesive layer each within the above range, the first adhesive layer and the second adhesive layer can have good slipperiness. Therefore, for example, when inserting a foamable adhesive sheet between two components, the foamable adhesive sheet is placed in a hole, groove, etc. of one component, and then the other component is inserted into the hole, groove, etc. of the component with the foamable adhesive sheet placed thereon; or, after placing the foamable adhesive sheet on the other component, the other component with the foamable adhesive sheet placed thereon can be inserted into the hole, groove, etc. of the component. This improves insertion ease. This prevents peeling and misalignment of the foamable adhesive sheet. Furthermore, when aligning one component by moving the other component relative to the other component, the other component can be moved smoothly relative to the first component with the foamable adhesive sheet placed between the two components, facilitating alignment. Furthermore, by having the E'(25) of the first adhesive layer and the second adhesive layer each within the above range, the first adhesive layer and the second adhesive layer can have good blocking resistance. Therefore, the handleability of the foamable adhesive sheet can be improved.

[0308] The storage modulus of the first adhesive layer and the second adhesive layer can be measured, for example, by a dynamic mechanical property test in accordance with JIS K7244-4:1999. As a dynamic mechanical property tester, for example, a dynamic viscoelasticity measuring device manufactured by TA Instruments can be used. The measurement conditions can be attachment mode: compression mode, frequency: 1 Hz, temperature: 25°C, and heating rate: 10°C / min.

[0309] In this embodiment, the storage modulus at 25° C. of the first adhesive layer and the second adhesive layer can be controlled, for example, by adjusting the composition of each adhesive layer.

[0310] Specifically, the storage modulus of an adhesive layer containing an epoxy resin and a curing agent can be increased by using an epoxy resin that is solid at room temperature or a curing agent that is solid at room temperature, whereas the storage modulus of an adhesive layer containing an epoxy resin and a curing agent tends to be decreased by using an epoxy resin that is liquid at room temperature or a curing agent that is liquid at room temperature.

[0311] In addition, the storage modulus of the adhesive layer containing an epoxy resin and a curing agent can be increased by adding an epoxy resin with a high softening temperature or an epoxy resin with a large weight-average molecular weight, whereas the storage modulus of the adhesive layer tends to be decreased by adding an epoxy resin with a low softening temperature or an epoxy resin with a small weight-average molecular weight.

[0312] For example, the storage modulus of the adhesive layer can be increased by including multiple epoxy resins with different softening temperatures, i.e., by including one epoxy resin and another epoxy resin with a softening temperature of 25°C or higher that is 10°C or higher than the softening temperature of the first epoxy resin. Alternatively, the storage modulus of the adhesive layer can be increased by including multiple epoxy resins with different weight-average molecular weights, i.e., by including one epoxy resin and another epoxy resin with a weight-average molecular weight of 370 or higher that is 300 or higher than the weight-average molecular weight of the first epoxy resin. More specifically, in an adhesive layer containing an epoxy resin and a curing agent, the storage modulus of the adhesive layer can be increased by including a first epoxy resin with a low softening temperature and low molecular weight and a second epoxy resin with a high softening temperature and high molecular weight, as described below.

[0313] Furthermore, in an adhesive layer containing an epoxy resin and a curing agent, the storage modulus of the adhesive layer can be increased by adding an acrylic resin that is compatible with the epoxy resin, as will be described later.

[0314] In addition, when a curing agent that is liquid at room temperature is used, the storage modulus tends to be low, but storage stability may be reduced. Therefore, it is preferable to adjust the storage modulus of the adhesive layer by adjusting the properties and type of components other than the curing agent, such as the epoxy resin.

[0315] (d) Pencil Hardness In this embodiment, it is preferable that the first adhesive layer and the second adhesive layer have different surface pencil hardnesses. Generally, the higher the surface pencil hardness of an adhesive layer, the harder it tends to be, and the lower the surface pencil hardness, the softer it tends to be. Therefore, if the surfaces of the first adhesive layer and the second adhesive layer have different pencil hardnesses, the foamable adhesive sheet is likely to curl. Therefore, this embodiment is effective when the surfaces of the first adhesive layer and the second adhesive layer have different pencil hardnesses.

[0316] When the pencil hardness of the surface of the first adhesive layer and the second adhesive layer is different, and the pencil hardness of the surface of the first adhesive layer is higher than the pencil hardness of the surface of the second adhesive layer, it is preferable that the pencil hardness of the surface of the first adhesive layer is, for example, HB or higher, and the pencil hardness of the surface of the second adhesive layer is, for example, lower than HB. In this case, the pencil hardness of the surface of the first adhesive layer may be, for example, HB or higher and 2H or lower, or F or higher and 2H or lower. In this case, the pencil hardness of the surface of the second adhesive layer may be, for example, B or lower. Note that if the tack of the second adhesive layer is high and the pencil hardness of the surface of the second adhesive layer cannot be measured, the pencil hardness of the surface of the second adhesive layer is considered to be 6B or lower.

[0317] In the above case, by having the pencil hardness of the surface of the first adhesive layer within the above range, the slipperiness of the first adhesive layer can be improved, and the blocking resistance of the first adhesive layer can also be improved. On the other hand, if the pencil hardness of the surface of the first adhesive layer is too high, the adhesion of the first adhesive layer to the substrate may be reduced.

[0318] In the above case, by having the pencil hardness of the surface of the second adhesive layer within the above range, the adhesion of the second adhesive layer to the member can be improved.

[0319] On the other hand, the first adhesive layer and the second adhesive layer may have the same surface pencil hardness.

[0320] The pencil hardness of the surfaces of the first adhesive layer and the second adhesive layer may both be high. In this case, the pencil hardness of the surfaces of the first adhesive layer and the second adhesive layer is preferably, for example, HB or higher, and may be HB or higher and 2H or lower, or F or higher and 2H or lower. When the pencil hardness is within the above range, the slipperiness can be improved and the blocking resistance can also be improved. On the other hand, if the pencil hardness is too high, the adhesion of the adhesive layer to the substrate may be reduced.

[0321] Here, the pencil hardness can be determined in accordance with JIS K5600. Specifically, the following method can be used. First, an A4-sized foamable adhesive sheet is prepared and placed on a glass plate. Next, in accordance with JIS K5600, the pencil hardness of the surface of the foamable adhesive sheet on which the adhesive layer to be tested is disposed is measured using a pencil hardness tester (with a level). The measurement conditions are a pencil angle of 45° from the horizontal, a load of 750 g, a test speed of 1 mm / sec, a test length of 20 mm, and a temperature of 23°C. The maximum pencil hardness that does not visually scratch the surface of the adhesive layer of the foamable adhesive sheet is defined as the pencil hardness. For example, a KT-VF2378-12 manufactured by TQC can be used as the pencil hardness tester.

[0322] In this embodiment, the pencil hardness of the surfaces of the first adhesive layer and the second adhesive layer can be controlled, for example, by the composition of the first adhesive layer and the second adhesive layer. Specifically, the pencil hardness can be controlled by the average particle size and content of the foaming agent contained in the adhesive layer. More specifically, the pencil hardness can be increased by increasing the average particle size of the foaming agent. Furthermore, the pencil hardness can be increased by increasing the content of the foaming agent. Furthermore, the pencil hardness can be increased, for example, by including an inorganic filler in the adhesive layer. Furthermore, the pencil hardness can be increased, for example, by including a component having a rigid structure in the adhesive layer. Specifically, in an adhesive layer containing an epoxy resin and a curing agent, an example of the component having a rigid structure is a phenolic resin.

[0323] (e) Static Friction Coefficient In this embodiment, it is preferable that the static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer are different. Generally, adhesive layers tend to be harder as the surface friction coefficient decreases, and softer as the surface friction coefficient increases. Therefore, if the static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer are different, the foamable adhesive sheet is likely to curl. Therefore, this embodiment is effective when the static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer are different.

[0324] When the static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer are different, and the static friction coefficient of the surface of the first adhesive layer is lower than the static friction coefficient of the surface of the second adhesive layer, it is preferable that the static friction coefficient of the surface of the first adhesive layer is, for example, 0.34 or less, and the static friction coefficient of the surface of the second adhesive layer is, for example, greater than 0.34. In this case, the static friction coefficient of the surface of the first adhesive layer may be, for example, 0.30 or less, or may be 0.26 or less. Furthermore, the static friction coefficient of the surface of the first adhesive layer may be, for example, 0.16 or more. Furthermore, in this case, the static friction coefficient of the surface of the second adhesive layer may be, for example, 0.38 or more.

[0325] In the above case, the static friction coefficient of the surface of the first adhesive layer is within the above range, so that the slipperiness of the first adhesive layer can be improved.

[0326] On the other hand, the first adhesive layer and the second adhesive layer may have the same surface static friction coefficient.

[0327] The static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer may both be high. In this case, the static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer may each be, for example, 0.34 or less, 0.30 or less, or 0.26 or less. The static friction coefficients may be, for example, 0.16 or more. By having the static friction coefficients in the above range, slip properties can be improved.

[0328] Here, the static friction coefficient can be determined in accordance with JIS K7125. Specifically, the following method can be used. First, the foamable adhesive sheet is cut into 80 mm x 200 mm pieces. Next, the foamable adhesive sheet is placed on a horizontally placed rectangular metal plate, and a sliding piece (63 mm x 63 mm, weight 200 g, bottom: felt) is placed on the surface of the foamable adhesive sheet on which the adhesive layer to be tested is located. The friction force is measured under conditions of a test speed of 100 mm / min, a test length of 50 mm, a load cell of 10 N, and a temperature of 23°C, and the static friction coefficient between the surface of the foamable adhesive sheet on which the adhesive layer to be tested is located and the metal plate is calculated. A friction tester TR-2 manufactured by Toyo Seiki Seisakusho can be used as the device. Furthermore, the metal plate can be, for example, a stainless steel plate made of SUS304 and having a surface roughness Ra of 0.05 μm.

[0329] In this embodiment, the static friction coefficient of the surfaces of the first adhesive layer and the second adhesive layer can be controlled, for example, by adjusting the composition of the first adhesive layer and the second adhesive layer, or by adjusting the pencil hardness of the surfaces of the first adhesive layer and the second adhesive layer. Specifically, the static friction coefficient can be controlled by the average particle size and content of the foaming agent contained in the adhesive layer. More specifically, as the average particle size of the foaming agent increases, the static friction coefficient tends to decrease. Furthermore, as the content of the foaming agent increases, the static friction coefficient tends to decrease. Furthermore, as the pencil hardness of the surfaces of the adhesive layers increases, the static friction coefficient tends to decrease.

[0330] (2) Materials for the First and Second Adhesive Layers In this embodiment, the first and second adhesive layers contain a thermosetting adhesive. At least one of the first and second adhesive layers further contains a foaming agent.

[0331] (a) Thermosetting adhesive The thermosetting adhesive contained in the first adhesive layer and the second adhesive layer in this embodiment can be a thermosetting adhesive generally used in adhesive layers of foamable adhesive sheets. Thermosetting adhesives can be applied even to components that do not have transparency, such as metal components.

[0332] Examples of thermosetting adhesives include epoxy resin adhesives, acrylic resin adhesives, phenolic resin adhesives, unsaturated polyester resin adhesives, alkyd resin adhesives, urethane resin adhesives, and thermosetting polyimide resin adhesives.

[0333] 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., and have little shrinkage upon curing, making them suitable for a wide range of applications.

[0334] An example in which the thermosetting adhesive is an epoxy resin adhesive will be described below.

[0335] (i) Epoxy Resin The epoxy resin in this embodiment is a compound that has at least one epoxy group or glycidyl group and cures by a crosslinking polymerization reaction when used in combination with a curing agent. The epoxy resin also includes a monomer having at least one epoxy group or glycidyl group.

[0336] As the epoxy resin, an epoxy resin generally used for the adhesive layer of a foamable adhesive sheet can be used.

[0337] When the tack of the first adhesive layer is lower than that of the second adhesive layer, the thermosetting adhesive contained in the first adhesive layer having lower tack preferably contains the first epoxy resin and the second epoxy resin described below as the epoxy resin. Also, when the tack of both the first adhesive layer and the second adhesive layer is low, the thermosetting adhesive contained in the first adhesive layer and the second adhesive layer preferably contains the first epoxy resin and the second epoxy resin described below as the epoxy resin.

[0338] Specifically, the thermosetting adhesive preferably contains, as epoxy resins, a first epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5,000 g / eq or less, and a second epoxy resin having a softening temperature higher than that of the first epoxy resin and a weight-average molecular weight of 20,000 or more. By using a combination of the first epoxy resin and the second epoxy resin, the adhesive layer can be made less sticky (tacky), resulting in a foamable adhesive sheet with good slip properties. Furthermore, an adhesive layer with good blocking resistance and adhesion after foaming and curing can be obtained.

[0339] For example, when only improving adhesiveness after foaming and curing is desired, it is more effective to use a low molecular weight (low epoxy equivalent) epoxy resin than a high molecular weight (high epoxy equivalent) epoxy resin. However, when a low molecular weight (low epoxy equivalent) epoxy resin is used, for example, when the foamable adhesive sheet is wound into a roll, the low molecular weight (low epoxy equivalent) epoxy resins tend to assimilate with each other, resulting in blocking.

[0340] In contrast, when a first epoxy resin having a relatively low softening temperature (relatively high crystallinity) and a low molecular weight (low epoxy equivalent weight) is used, the first epoxy resin rapidly melts and changes into a low-viscosity liquid when heated to a temperature above its softening temperature. This facilitates improved adhesiveness after foaming and curing. Meanwhile, the first epoxy resin has relatively high crystallinity, which can suppress blocking compared to epoxy resins with relatively low crystallinity or no crystallinity. However, using only the first epoxy resin may result in insufficient blocking suppression or excessive tackiness of the adhesive layer. Therefore, by further using a second epoxy resin having a relatively high softening temperature (relatively low crystallinity) and a high molecular weight, the blocking suppression effect can be improved and the tackiness of the adhesive layer can be reduced.

[0341] On the other hand, when the tackiness of the first adhesive layer is lower than that of the second adhesive layer, it is preferable to use, as the epoxy resin for the second adhesive layer having a higher tackiness, an epoxy resin that is liquid at room temperature, such as a bisphenol A type epoxy resin or a bisphenol F type epoxy resin, or an epoxy resin with a low softening point, because the use of these epoxy resins makes it easier to adjust the tackiness of the second adhesive layer within a predetermined range.

[0342] The first epoxy resin and the second epoxy resin are similar to the explanations given in the sections "(i-1) First epoxy resin" and "(i-2) Second epoxy resin" in "I. First embodiment A. Foamable adhesive sheet A) First embodiment 2. First adhesive layer (1) Material of first adhesive layer (a) Curable adhesive (i) Epoxy resin," and therefore will not be explained here.

[0343] (ii) Acrylic Resin When the thermosetting adhesive is an epoxy resin-based 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. Because 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, the acrylic resin acts as a compatibilizer for the foaming agent (e.g., a foaming agent whose shell is an acrylonitrile copolymer resin), uniformly dispersing and foaming, which is thought to improve the adhesiveness after foaming and curing. In addition, the flexibility of the acrylic resin can be exerted, improving adhesion to the substrate after foaming and curing and crack resistance after foaming and curing. Furthermore, the compatibility of the acrylic resin with the epoxy resin can maintain high hardness on the surface of the adhesive layer. 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, making the interface with the adherend less slippery and reducing workability.

[0344] The explanation of the acrylic resin in this embodiment is the same as that in the section above titled "I. First embodiment A. Foamable adhesive sheet A) First embodiment 2. First adhesive layer (1) Material of first adhesive layer (a) Curable adhesive (ii) Acrylic resin," and therefore will not be repeated here.

[0345] (iii) Curing Agent The curing agent in this embodiment is a curing agent that undergoes a curing reaction by heat, and a curing agent generally used in epoxy resin adhesives can be used. The curing agent is preferably solid at room temperature (23°C). A curing agent that is solid at room temperature can extend storage stability (pot life) compared to a curing agent that is liquid at room temperature. The curing agent may also be a latent curing agent. The curing agent may be used alone or in combination of two or more types.

[0346] In addition, when the tackiness of the first adhesive layer is lower than that of the second adhesive layer, a curing agent that is solid at room temperature or a curing agent that is liquid at room temperature can be used in the second adhesive layer with higher tack, but from the viewpoint of storage stability, it is preferable to use a curing agent that is solid at room temperature.

[0347] The explanation of the curing agent is the same as that in the section "I. First embodiment A. Foamable adhesive sheet A) First embodiment 2. First adhesive layer (1) Materials for first adhesive layer (a) Curable adhesive (iii) Curing agent," and therefore will not be repeated here.

[0348] (b) Foaming Agent In this embodiment, at least one of the first adhesive layer and the second adhesive layer contains a foaming agent.

[0349] In particular, it is preferable that both the first adhesive layer and the second adhesive layer contain a foaming agent, in which case the adhesiveness of the first adhesive layer and the second adhesive layer after foaming and curing can be improved.

[0350] On the other hand, when only one of the first adhesive layer and the second adhesive layer contains a foaming agent, if the foaming agent is a microcapsule-type foaming agent, the foaming agent is expected to function as a filler. Therefore, it is thought that the adhesive layer containing the foaming agent tends to become hard, and the adhesive layer without the foaming agent tends to become soft. Therefore, when only one of the first adhesive layer and the second adhesive layer contains a foaming agent, it is thought that the foamable adhesive sheet is more likely to curl. Therefore, when only one of the first adhesive layer and the second adhesive layer contains a foaming agent, this embodiment is thought to be effective.

[0351] Furthermore, when the hardness of the first adhesive layer is greater than that of the second adhesive layer, the first adhesive layer having a higher hardness preferably contains a foaming agent, which increases the surface roughness, reduces the coefficient of friction, and improves the slipperiness.

[0352] The foaming agent is one that undergoes a foaming reaction when heated, and foaming agents that are generally used in adhesive layers of foamable adhesive sheets can be used.

[0353] The explanation regarding the foaming agent is the same as that in the section "I. First embodiment A. Foamable adhesive sheet a) First embodiment 2. First adhesive layer (1) Material of first adhesive layer (b) Foaming agent" above, and therefore will not be repeated here.

[0354] (c) Other Components In the present embodiment, when the thermosetting adhesive is an epoxy resin adhesive, the adhesive layer may contain only an epoxy resin and an acrylic resin as resin components, or may further contain other resins such as urethane resins.

[0355] The explanation of these other components is the same as that in the section above titled "I. First embodiment A. Foamable adhesive sheet a) First embodiment 2. First adhesive layer (1) Material of first adhesive layer (c) Other components," and therefore will not be repeated here.

[0356] (3) Configuration of the First Adhesive Layer and the Second Adhesive Layer When the first adhesive layer and the second adhesive layer contain a foaming agent, the first adhesive layer and the second adhesive layer can be foamed at an expansion ratio of, for example, 1.5 times or more and 15 times or less. The expansion ratio may be, for example, 3.5 times or more, 4 times or more, or 4.5 times or more. In the above case, the expansion ratio may be, for example, 9 times or less, 8.5 times or less, or 8 times or less.

[0357] Here, the expansion ratio can be calculated by the following formula: Expansion ratio (times) = thickness of adhesive layer after foaming and curing / thickness of adhesive layer before foaming and curing

[0358] The thicknesses of the first adhesive layer and the second adhesive layer are not particularly limited. However, if the adhesive layer contains a foaming agent, it is preferably equal to or greater than the average particle size of the foaming agent, for example, 10 μm or more, 15 μm or more, or even 20 μm or more. On the other hand, the thicknesses of the first adhesive layer and the second adhesive layer are, for example, 200 μm or less, 150 μm or less, or even 100 μm or less. If the adhesive layer is too thin, it may not be possible to obtain sufficient adhesion to the substrate and adhesion after foam curing. Furthermore, if the tack of the first adhesive layer is lower than that of the second adhesive layer, if the first adhesive layer with lower tack is too thin, the radius of curvature of the curl of the foamable adhesive sheet after standing at a predetermined temperature and humidity for a predetermined time may be small. On the other hand, if the adhesive layer is too thick, the surface quality may be deteriorated.

[0359] Here, the thicknesses of the first adhesive layer and the second adhesive layer are values ​​measured from a cross section of the foamable adhesive sheet in the thickness direction as 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 thicknesses measured at 10 randomly selected locations. The same method can be used to measure the thicknesses of other layers of the foamable adhesive sheet.

[0360] The first adhesive layer and the second adhesive layer may be continuous or discontinuous. Examples of discontinuous layers include stripes and dots. The surfaces of the first adhesive layer and the second adhesive layer may have an uneven shape such as an embossed shape.

[0361] The first adhesive layer and the second adhesive layer can be formed, for example, by applying an adhesive composition containing the above-mentioned thermosetting adhesive and a foaming agent, etc., and then removing the solvent. Examples of application methods 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.

[0362] The adhesive composition may or may not contain a solvent. In this specification, the term "solvent" is used in a broad sense to include 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.

[0363] The adhesive composition can be obtained by mixing the above-mentioned components and, if necessary, kneading and dispersing them. As a mixing and dispersing method, a general kneading disperser, such as a two-roll mill, a three-roll mill, a pebble mill, a tron ​​mill, a Szegvari attritor, a high-speed impeller disperser, a high-speed stone mill, a high-speed impact mill, a desper, a high-speed mixer, a ribbon blender, a co-kneader, an intensive mixer, a tumbler, a blender, a desperzer, a homogenizer, or an ultrasonic disperser can be used.

[0364] 3. Substrate The substrate in this embodiment is disposed between the first adhesive layer and the second adhesive layer.

[0365] The substrate preferably has insulating properties. 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.

[0366] The explanation regarding the substrate is the same as that given in the section "I. First embodiment A. Foamable adhesive sheet a) First embodiment 4. Substrate," and therefore will not be repeated here.

[0367] 4. Curl Control Layer The foamable adhesive sheet in this embodiment may have a curl control layer on the side of the second adhesive layer opposite the substrate. For example, if the tack of the first adhesive layer is lower than that of the second adhesive layer, the foamable adhesive sheet is likely to curl, but by arranging a curl control layer on the side of the second adhesive layer opposite the substrate, curling can be suppressed.

[0368] For example, in the foamable adhesive sheet 10 shown in FIG. 12, a curl control layer 7 is disposed on the surface of the second adhesive layer 3 opposite the substrate 2 .

[0369] The curl control layer may be, for example, a separator that protects the second adhesive layer, or a fiber layer. Among these, the curl control layer is preferably a separator. The separator is removable, and when the foamable adhesive sheet is placed between two components, the separator is removed from the foamable adhesive sheet, allowing the foamable adhesive sheet to be thinner and easier to insert.

[0370] (1) Separator In this embodiment, a separator may be disposed on the surface of the second adhesive layer opposite to the substrate.

[0371] The separator is not particularly limited as long as it can be peeled from the second adhesive layer, and it can have a strength sufficient to protect the second adhesive layer. Examples of such separators include release films and release papers. The separator may have a single-layer structure or a multi-layer structure.

[0372] An example of a separator having a single layer structure is a fluororesin film.

[0373] Further, examples of multilayer separators include laminates having a release layer on one or both sides of a substrate layer. Examples of substrate layers include resin films such as polypropylene, polyethylene, and polyethylene terephthalate, as well as paper such as fine paper, coated paper, and impregnated paper. The material for the release layer is not particularly limited as long as it has 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 emulsion-type, solvent-type, or solventless.

[0374] (2) Fiber Layer In this embodiment, a fiber layer may be disposed on the surface of the second adhesive layer opposite the substrate. When the second adhesive layer contains a thermosetting adhesive and a foaming agent, the fiber layer is a layer that allows the thermosetting adhesive to permeate or penetrate when the second adhesive layer foams and expands.

[0375] Examples of the form of the fiber layer include nonwoven fabric, paper, felt, knitted fabric, and woven fabric.

[0376] Examples of fibers that may be used to form the fiber layer include basalt fibers, vinylon fibers, polyarylate fibers, polyethylene fibers, polypropylene fibers, silicon carbide fibers, cellulose fibers, polyester fibers, nylon fibers, aramid fibers, polyphenylene sulfide fibers, liquid crystal polymer fibers, and glass fibers.

[0377] The density of the fiber layer is not particularly limited as long as it allows the thermosetting adhesive to pass through or penetrate when the second adhesive layer foams and expands, and may be, for example, 200 g / cm ３ or less, and 100 g / cm ３ or less, and ３ If the density of the fiber layer is too high, the voids in the fiber layer will be small, making it difficult for the thermosetting adhesive to penetrate or permeate the second adhesive layer when foaming, and there is a possibility that sufficient adhesive strength will not be obtained after the second adhesive layer is foamed and cured. On the other hand, the density of the fiber layer may be, for example, 3 g / cm ３ or more, and ３ 7 g / cm or more ３ It may be more than that.

[0378] Here, the density of the fiber layer (g / cm ３ ) is the basis weight (g / cm ２ ) by the thickness (cm) of the fiber layer.

[0379] The basis weight of the fiber layer can be measured by the following method. First, ten test pieces of the fiber layer, each measuring 100 mm x 100 mm, are taken, and the mass (g) of each test piece is measured. Next, the mass (g) of each test piece is multiplied by the area (cm) of each test piece. ２ ) to obtain the basis weight (g / cm ２ The average value of the basis weights of the 10 test pieces is calculated, and this average value is used as the basis weight.

[0380] The density of the fiber layer can be adjusted by the manufacturing method and manufacturing conditions of the fiber layer.

[0381] The thickness of the fiber layer is not particularly limited as long as it allows the thermosetting adhesive to permeate or penetrate when the second adhesive layer foams and expands, and may be, for example, 100 μm or less, 80 μm or less, or 60 μm or less. If the fiber layer is too thick, the amount of thermosetting adhesive that permeates or penetrates the second adhesive layer during foaming may be reduced, which may reduce the adhesive strength of the second adhesive layer after foaming and hardening. On the other hand, the thickness of the fiber layer may be, for example, 6 μm or more, 8 μm or more, or 10 μm or more. If the fiber layer is too thin, blocking may occur when the sheet is processed into a roll.

[0382] Methods for disposing a fiber layer on the side of the second adhesive layer opposite the substrate include, for example, a method of attaching the fiber layer by utilizing the adhesiveness of the second adhesive layer, a method of attaching the fiber layer to the second adhesive layer via a layer having adhesive properties different from the second adhesive layer, a method of applying a solvent-diluted adhesive composition onto the fiber layer and drying it, a method of heat-laminating the second adhesive layer and the fiber layer, or a combination of these methods.

[0383] 5. First Intermediate Layer and Second Intermediate Layer The foamable adhesive sheet of this embodiment may have a first intermediate layer between the substrate and the first adhesive layer. The foamable adhesive sheet of this embodiment may also have a second intermediate layer between the substrate and the second adhesive layer. The presence of the first intermediate layer or second intermediate layer can improve the adhesion of the first adhesive layer or second adhesive layer to the substrate. Furthermore, the presence of the first intermediate layer or second intermediate layer can, for example, reduce stress at the bent portion when the foamable adhesive sheet is folded, or reduce stress at the cut portion when the foamable adhesive sheet is cut. As a result, lifting or peeling of the first adhesive layer or second adhesive layer from the substrate can be suppressed when the foamable adhesive sheet is bent or cut.

[0384] For example, in the foamable adhesive sheet 10 shown in Fig. 13, a first intermediate layer 4 is disposed between the substrate 2 and the first adhesive layer 1, and a second intermediate layer 5 is disposed between the substrate 2 and the second adhesive layer 3. Although the foamable adhesive sheet 10 in Fig. 13 has both the first intermediate layer 4 and the second intermediate layer 5, it may have only one of them.

[0385] 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 disposed between the substrate and the first adhesive layer, may have only the second intermediate layer disposed between the substrate and the second adhesive layer, or may have both the first intermediate layer disposed between the substrate and the first adhesive layer and the second intermediate layer disposed between the substrate and the second adhesive layer. Of these, it is preferable that the first intermediate layer be disposed between the substrate and the first adhesive layer and the second intermediate layer be disposed between the substrate and the second adhesive layer.

[0386] The explanation regarding the materials, thickness, manufacturing method, etc. contained in the first intermediate layer and the second intermediate layer is the same as the explanation in the section above titled "I. First embodiment A. Foamable adhesive sheet A) First embodiment 5. Other configurations (1) First intermediate layer and second intermediate layer," and therefore will not be repeated here.

[0387] 6. Foamable Adhesive Sheet The thickness of the foamable adhesive sheet in this embodiment 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.

[0388] The use of the foamable adhesive sheet in this embodiment is not particularly limited. The foamable adhesive sheet in this embodiment can be used, for example, when placing the foamable adhesive sheet between two members and then heating the foamable adhesive sheet to foam and harden it, thereby bonding two members together. For example, when the tack of the first adhesive layer is lower than that of the second adhesive layer, the foamable adhesive sheet in this embodiment is preferably used when bonding the first member and the second member by attaching the second adhesive layer surface of the foamable adhesive sheet to the second member, inserting the second member to which the foamable adhesive sheet has been attached into a hole, groove, or the like of the first member, and heating the foamable adhesive sheet to foam and harden it. Furthermore, for example, when the tackiness of the first adhesive layer and the second adhesive layer is low, the foamable adhesive sheet of this embodiment is preferably used in the following cases: inserting a foamable adhesive sheet between a first member and a second member and heating the foamable adhesive sheet to foam and harden it, thereby adhering the first member and the second member; placing a foamable adhesive sheet on the second member, inserting the second member with the foamable adhesive sheet disposed thereon into a hole or groove of the first member, and heating the foamable adhesive sheet to foam and harden it, thereby adhering the first member and the second member; placing a foamable adhesive sheet in a hole or groove of the first member, inserting the second member with the foamable adhesive sheet disposed thereon into a hole or groove of the first member, and heating the foamable adhesive sheet to foam and harden it, thereby adhering the first member and the second member; Specifically, the foamable adhesive sheet of this embodiment is used to adhere the coil and stator in a motor, or the rotor and permanent magnet in an interior permanent magnet motor.

[0389] The method for producing the foamable adhesive sheet in this embodiment is not particularly limited, and may be appropriately selected depending on the layer structure of the foamable adhesive sheet.

[0390] B. Method for Manufacturing an Article The method for manufacturing an article in this embodiment includes a disposing step of disposing the foamable adhesive sheet described above 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 together.

[0391] 14(a) and 14(b) are process diagrams showing an example of a method for manufacturing an article according to this embodiment. First, as shown in FIG. 14(a), a foamable adhesive sheet 10 is placed on a first member 20a and a second member 20b. Next, the first adhesive layer 1 and the second adhesive layer 3 of the foamable adhesive sheet 10 are heated to foam and harden. As a result, as shown in FIG. 14(b), the first member 20a and the second member 20b are bonded (joined) by the adhesive sheet 15 having the foamed and hardened first adhesive layer 11 and second adhesive layer 13. This results in an article 100 in which the adhesive sheet 15 is placed between the first member 20a and the second member 20b.

[0392] 9(a) to 9(c) are process diagrams illustrating another example of a method for manufacturing an article according to this embodiment. First, as shown in FIG. 9(a), a foamable adhesive sheet 10 is placed on a second member 20b. If the tack of the first adhesive layer 1 of the foamable adhesive sheet 10 is lower than that of the second adhesive layer 3, the tack of the second adhesive layer 3 is utilized to attach the second adhesive layer 3 of the foamable adhesive sheet 10 to the second member 20b. Next, as shown in FIG. 9(b), the second member 20b on which the foamable adhesive sheet 10 is placed is inserted into the hole in the first member 20a. Next, as shown in FIG. 9(c), the first adhesive layer 1 and the second adhesive layer 3 of the foamable adhesive sheet 10 are heated to foam and harden. After foaming and hardening, the first member 20a and the second member 20b are bonded (joined) by the adhesive sheet 15 having the first adhesive layer 11 and the second adhesive layer 13. This results in an article 100 in which the adhesive sheet 15 is placed between the first member 20a and the second member 20b.

[0393] The method for manufacturing an article according to this embodiment will be described below.

[0394] 1. Foamable Adhesive Sheet In the method for producing an article according to this embodiment, the foamable adhesive sheet used is the foamable adhesive sheet described above.

[0395] When the foamable adhesive sheet has a separator, the separator is peeled off from the foamable adhesive sheet when the foamable adhesive sheet is disposed between the first member and the second member.

[0396] Details of the foamable adhesive sheet are described above in the section "A. Foamable adhesive sheet," so further description will be omitted here.

[0397] 2. Placement Step In the placement step of this embodiment, the method for placing the foamable adhesive sheet between the first and second members is selected as appropriate depending on the configuration of the foamable adhesive sheet, the types of the first and second members, etc. For example, when the second member is adhesively fixed to a hole or groove in the first member and the tackiness of the first adhesive layer in the foamable adhesive sheet is lower than that of the second adhesive layer, methods include: attaching the surface of the second adhesive layer of the foamable adhesive sheet to the second member by utilizing the tackiness of the second adhesive layer of the foamable adhesive sheet, and then placing the second member to which the foamable adhesive sheet has been attached in the hole or groove of the first member; and methods including: attaching the surface of the second adhesive layer of the foamable adhesive sheet to the hole or groove of the first member by utilizing the tackiness of the second adhesive layer of the foamable adhesive sheet, and then placing the second member in the hole or groove of the first member to which the foamable adhesive sheet has been attached. Other examples include a method in which, when a second member is adhesively fixed to a hole or groove in a first member and the tack of the first adhesive layer and second adhesive layer in the foamable adhesive sheet is low, the foamable adhesive sheet is placed between the first member and the second member; a method in which a foamable adhesive sheet is placed on the second member, and then the second member with the foamable adhesive sheet placed in the hole or groove in the first member; a method in which a foamable adhesive sheet is placed in the hole or groove in the first member, and then the second member is placed in the hole or groove in the first member with the foamable adhesive sheet placed in it; etc.

[0398] In the bonding step of this embodiment, the foamable adhesive sheet is heated to foam and harden. This heating method is applicable even when the first and second members are not transparent, such as when the first and second members are made of metal.

[0399] The heating conditions are appropriately set depending on the types of thermosetting adhesive and foaming agent contained in the first adhesive layer and the second adhesive layer, the type of base material, etc. The heating temperature can be, for example, 130° C. or higher and 200° C. or lower. The heating time can be, for example, 3 minutes or higher and 3 hours or lower.

[0400] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure.

[0401] I. Example of the first embodiment

[0402] [Production Examples] First, adhesive compositions 1 to 3 having the following compositions were prepared.

[0403] <Adhesive composition 1> Acrylic resin (PMMA-PBuA-PMMA (partially containing acrylamide groups), Tg: -20°C, 120°C, Mw: 150,000): 13 parts by mass Epoxy resin A (bisphenol A novolac type, solid at room temperature, softening temperature: 70°C, epoxy equivalent: 210 g / eq, Mw: 1300, melt viscosity at 150°C: 0.5 Pa s): 40 parts by mass Epoxy resin B (BPA phenoxy type, solid at room temperature, softening temperature: 110°C, epoxy equivalent: 8000 g / eq, Mw: 50,000): 42 parts by mass Curing agent A (α-(hydroxy(or dihydroxy)phenylmethyl)-ω-hydropoly[biphenyl-4,4'-diylmethylene(hydroxy(or dihydroxy)phenylenemethylene)]): 6 parts by mass Curing catalyst (2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction initiation temperature 145°C to 155°C, active region 155°C to 173°C (Shikoku Chemicals Corporation, 2PHZ-PW)): 8 parts by mass; Foaming agent (thermally expandable microcapsules, average particle size 10 μm to 16 μm, expansion initiation temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer): 13.5 parts by mass; Solvent (methyl ethyl ketone): 150 parts by mass

[0404] <Adhesive composition 2> Acrylic resin (PMMA-PBuA-PMMA (partially containing acrylamide groups), Tg: -20°C, 120°C, Mw: 150,000): 40 parts by mass Epoxy resin C (bisphenol A type, liquid at room temperature, epoxy equivalent: 184 to 194 g / eq): 45 parts by mass Epoxy resin D (diaminodiphenylmethane type, highly viscous liquid, epoxy equivalent: 110 to 130 g / eq): 65 parts by mass Epoxy resin E (silicone-modified, epoxy equivalent: 1200 g / mol): 20 parts by mass Silane coupling agent (3-glycidoxypropyltrimethoxysilane): 2 parts by mass Curing agent B (phenol-formaldehyde polycondensate, softening point 80°C, hydroxyl equivalent 104 g / mol): 6 parts by mass Curing catalyst (2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction initiation temperature 145°C to 155°C, active region 155°C to 173°C (Shikoku Chemicals Corporation, 2PHZ-PW)): 10 parts by mass Foaming agent: thermally expandable microcapsules, average particle size 10 μm to 16 μm, expansion initiation temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer: 20 parts by mass Solvent (methyl ethyl ketone): 114 parts by mass

[0405] <Adhesive composition 3> Acrylic resin (PMMA-PBuA-PMMA (containing a part of an acrylamide group), Tg: -20°C, 120°C, Mw: 150,000): 10 parts by mass Epoxy resin A (bisphenol A novolac type, solid at room temperature, softening temperature: 70°C, epoxy equivalent: 210 g / eq, Mw: 1300, melt viscosity at 150°C: 0.5 Pa s): 15 parts by mass Epoxy resin C (bisphenol A type, liquid at room temperature, epoxy equivalent: 184 to 194 g / eq): 23 parts by mass Epoxy resin F (aliphatic polyfunctional epoxy compound, epoxy equivalent: 173 g / eq): 13 parts by mass Silane coupling agent (3-glycidoxypropyltrimethoxysilane): 1 part by mass Curing agent B (phenol-formaldehyde polycondensate softening point 80°C, hydroxyl equivalent 104g / mol): 19 parts by mass; Curing catalyst (2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3µm, melting point: 230°C, reaction onset temperature 145°C to 155°C, active region 155°C to 173°C (Shikoku Chemicals Corporation, 2PHZ-PW)): 2 parts by mass; Foaming agent: thermally expandable microcapsules, average particle size 10µm to 16µm, expansion onset temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer: 8.5 parts by mass; Storage stabilizer (borate ester compound): 9 parts by mass; Solvent (methyl ethyl ketone): 39 parts by mass.

[0406] Example I-1: A polyethylene naphthalate (PEN) film (Teonex Q5100, manufactured by Toyobo Co., Ltd., thickness 25 μm) was used as the substrate. Furthermore, 15 parts by mass of a curing agent (polyisocyanate) and 0.3 parts by mass of a catalyst (trisdimethylaminomethylphenol) were blended with 100 parts by mass of polyester polymer, and the resulting mixture was diluted with methyl ethyl ketone (MEK) to a solids content of 15% by mass to prepare a resin composition. The resin composition was applied to one side of the substrate using a bar coater and dried in an oven at 100°C for 1 minute to form a first intermediate layer with a thickness of 2 μm. Next, the adhesive composition 1 was applied to the side of the first intermediate layer opposite the substrate using an applicator to a thickness of 50 μm after application. The resulting mixture was then dried in an oven at 100°C for 3 minutes to form a first adhesive layer.

[0407] Next, a release film (PET separator, manufactured by Nippa Corporation, PET50x1-J2, thickness 50 μm) was used as a second separator, and the adhesive composition 2 was applied to the release-treated surface of the release film using an applicator so that the thickness after application was 50 μm. Thereafter, the resultant was dried in an oven at 100°C for 3 minutes to form a second adhesive layer.

[0408] Next, the surface of the second adhesive layer of a laminate having a second separator and a second adhesive layer was laminated onto the surface of the substrate of a laminate having a substrate, a first intermediate layer, and a first adhesive layer, thereby obtaining a foamable adhesive sheet in which the first adhesive layer, the first intermediate layer, the substrate, the second adhesive layer, and the second separator were arranged in this order.

[0409] Example I-2 A foamable adhesive sheet was produced in the same manner as in Example I-1, except that the thickness of the first adhesive layer and the second adhesive layer was set to 45 μm.

[0410] Example I-3 A foamable adhesive sheet was produced in the same manner as in Example I-1, except that adhesive composition 3 was used to form the second adhesive layer, and the thickness of the second adhesive layer was 45 μm.

[0411] Comparative Example I-1 A foamable adhesive sheet was produced in the same manner as in Example I-1, except that adhesive composition 2 was used to form the first adhesive layer.

[0412] Comparative Example I-2 A foamable adhesive sheet was produced in the same manner as in Comparative Example I-1, except that a polyphenylene sulfide (PPS) film (Toray Industries, Inc., Torelina 25-3030, thickness 25 μm) was used as the substrate.

[0413] Comparative Example I-3 A foamable adhesive sheet was produced in the same manner as in Comparative Example I-1, except that the thickness of the substrate (PEN film) was 50 μm.

[0414] Comparative Example I-4 A foamable adhesive sheet was produced in the same manner as in Comparative Example I-1, except that a polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc., Lumirror #25-S105, thickness 50 μm) was used as the substrate.

[0415] [Evaluation] (1) Tack of the first adhesive layer and the second adhesive layer For the tack of the first adhesive layer, a tack tester "TAC-II" manufactured by RHESCA was used to press a 5 mm diameter cylindrical stainless steel probe against the surface of the first adhesive layer of the foamable adhesive sheet at a temperature of 25°C with a load of 10.0 gf and a speed of 30 mm / min, hold for 1.0 second, and then peel off at a speed of 30 mm / min, measuring the load at the time of peeling. This measurement was performed five times, and the average value was taken as the tack.

[0416] The tackiness of the second adhesive layer was measured in the same manner as the tackiness of the first adhesive layer. At this time, the second separator was peeled off from the foamable adhesive sheet, and then the tackiness of the second adhesive layer was measured.

[0417] (2) Loop Stiffness After peeling the second separator from the foamable adhesive sheet, a rectangular test piece with a width of 10 mm and a length of 200 mm was prepared, and the loop stiffness was measured by the above-mentioned loop stiffness measurement method. The measuring device used was a Loop Stiffness Tester (registered trademark) manufactured by Toyo Seiki Seisaku-sho, Ltd. The measurement was performed in an environment of 23°C temperature and 50% relative humidity.

[0418] (3) Drooping Amount Figures 10(a) and 10(b) are schematic diagrams illustrating a method for measuring the drooping amount of a foamable adhesive sheet. After peeling off the second separator, the foamable adhesive sheet 10 was cut into a size of 10 mm wide and 100 mm long to prepare a test piece. The jig 51 had a rectangular parallelepiped shape, and the lower surface 51a of the jig 51 was rectangular, flat, and horizontal. Double-sided adhesive tape 52 (Y-4920-25, manufactured by 3M) was attached to the lower surface 51a of the jig 51.

[0419] First, as shown in Figure 10(a), in a room temperature and humidity environment, the surface of double-sided adhesive tape 52 of jig 51 was attached to the center of foamable adhesive sheet 10 to fix the foamable adhesive sheet 10. The attached area was 10 mm x 10 mm. In this case, when the surface of double-sided adhesive tape 52 of jig 51 was attached to the surface of the first adhesive layer of foamable adhesive sheet 10, the adherend surface was defined as the first adhesive layer. On the other hand, when the surface of double-sided adhesive tape 52 of jig 51 was attached to the surface of the second adhesive layer of foamable adhesive sheet 10, the adherend surface was defined as the second adhesive layer.

[0420] Next, as shown in Figure 10(b), the jig 51 was lifted vertically upward. At this time, the end 10a of the foamable adhesive sheet 10 drooped vertically downward. Then, the surface S1 of the double-sided adhesive tape 52 of the jig 51 was used as a reference plane, and the vertical distance from this reference plane S1 to the end 10a of the foamable adhesive sheet 10 was measured, and this was taken as the sagging amount F. Three test pieces were prepared from the foamable adhesive sheet, and one measurement was made for each test piece. The sagging amount was calculated as the average value of the three test pieces.

[0421] (4) Adhesion: In the same manner as in the measurement of sagging amount described above, the double-sided adhesive tape side of the jig was attached to the center of the foamable adhesive sheet test piece, and the foamable adhesive sheet was then fixed. The jig was then lifted vertically upward. At this time, the double-sided adhesive tape side of the jig was attached to the surface of the first adhesive layer of the foamable adhesive sheet. Next, a metal plate was placed below the foamable adhesive sheet lifted by the jig, and the jig was lowered vertically downward to adhere the foamable adhesive sheet to the metal plate. The condition of the foamable adhesive sheet was then visually observed, and the adhesion was evaluated according to the following criteria. A: The foamable adhesive sheet was able to be attached without folding or air bubbles. B: The foamable adhesive sheet was folded or air bubbles were trapped.

[0422] (5) Insertability (Slipperiness of the First Adhesive Layer During Insertion) A foam adhesive sheet cut to 5.5 cm x 8.0 cm was prepared. A hollow cylinder 1 with an outer diameter of 22 mm, a thickness of 1.5 mm, and a length of 60 mm, and a hollow cylinder 2 with an outer diameter of 18 mm, a thickness of 1.0 mm, and a length of 80 mm were also prepared. The second separator was peeled off from the foam adhesive sheet, and the surface of the second adhesive layer was attached to the outer diameter of the cylinder 2 with the short side aligned circumferentially. The foam adhesive sheet was then positioned. The cylinder 2 was then slowly pushed by hand to insert it into the hollow gap of the cylinder 1, and the slipperiness of the first adhesive layer during insertion was evaluated. The evaluation criteria were as follows: A: No catching during insertion; B: catching during insertion (the first adhesive layer stuck to the cylinder 1, resulting in poor insertability).

[0423]

[0424]

[0425] Comparison of Examples I-1 to I-3 and Comparative Examples I-3 to I-4 with Comparative Examples I-1 to I-2 confirmed that when the loop stiffness was 50 mN / 10 mm or more, the amount of sagging was small and the adhesiveness was good. In addition, in Examples I-1 to I-3, the tack of the first adhesive layer and the tack of the second adhesive layer were each within the specified range, and therefore the insertability was also good.

[0426] II. Example of the second embodiment

[0427] [Production Example] First, adhesive compositions A and B having the following formulations were prepared.

[0428] <Adhesive composition A> Acrylic resin (PMMA-PBuA-PMMA (partially containing acrylamide groups), Tg: -20°C, 120°C, Mw: 150,000): 13 parts by mass Epoxy resin A (bisphenol A novolac type, solid at room temperature, softening temperature: 70°C, epoxy equivalent: 210 g / eq, Mw: 1300, melt viscosity at 150°C: 0.5 Pa s): 40 parts by mass Epoxy resin B (BPA phenoxy type, solid at room temperature, softening temperature: 110°C, epoxy equivalent: 8000 g / eq, Mw: 50,000): 42 parts by mass Curing agent A (α-(hydroxy(or dihydroxy)phenylmethyl)-ω-hydropoly[biphenyl-4,4'-diylmethylene(hydroxy(or dihydroxy)phenylenemethylene)]): 6 parts by mass Curing catalyst (2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction initiation temperature 145°C to 155°C, active region 155°C to 173°C (Shikoku Chemicals Corporation, 2PHZ-PW)): 8 parts by mass; Foaming agent (thermally expandable microcapsules, average particle size 10 μm to 16 μm, expansion initiation temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer): 13.5 parts by mass; Solvent (methyl ethyl ketone): 150 parts by mass

[0429] <Adhesive composition B> Acrylic resin (PMMA-PBuA-PMMA (partially containing acrylamide groups), Tg: -20°C, 120°C, Mw: 150,000): 40 parts by mass Epoxy resin C (bisphenol A type, liquid at room temperature, epoxy equivalent: 184 to 194 g / eq): 45 parts by mass Epoxy resin D (diaminodiphenylmethane type, highly viscous liquid, epoxy equivalent: 110 to 130 g / eq): 65 parts by mass Epoxy resin E (silicone-modified, epoxy equivalent: 1200 g / mol): 20 parts by mass Silane coupling agent (3-glycidoxypropyltrimethoxysilane): 2 parts by mass Curing agent B (phenol-formaldehyde polycondensate, softening point 80°C, hydroxyl equivalent 104 g / mol): 6 parts by mass Curing catalyst (2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230°C, reaction initiation temperature 145°C to 155°C, active region 155°C to 173°C (Shikoku Chemicals Corporation, 2PHZ-PW)): 10 parts by mass Foaming agent: thermally expandable microcapsules, average particle size 10 μm to 16 μm, expansion initiation temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer: 20 parts by mass Solvent (methyl ethyl ketone): 114 parts by mass

[0430] Example II-1: Polyethylene naphthalate (PEN film, manufactured by Toyobo Film Solutions Co., Ltd., Teonex Q51, thickness 25 μm) was used as the substrate. Furthermore, 15 parts by mass of a curing agent (polyisocyanate) and 0.3 parts by mass of a catalyst (trisdimethylaminomethylphenol) were blended with 100 parts by mass of polyester polymer, and the resulting mixture was diluted with methyl ethyl ketone (MEK) to a solids content of 15% by mass to prepare a resin composition. The resin composition was applied to one side of the substrate using a bar coater and dried in an oven at 100°C for 1 minute to form a first intermediate layer with a thickness of 2 μm. Next, the adhesive composition A was applied to the side of the first intermediate layer opposite the substrate using an applicator to a thickness of 27 μm after application. The resulting mixture was then dried in an oven at 100°C for 3 minutes to form a first adhesive layer.

[0431] Next, a release film (PET separator, manufactured by Nippa Corporation, PET50x1-J2, thickness 50 μm) was used as a separator, and the adhesive composition B was applied to the release-treated surface of the release film using an applicator so that the thickness after application was 51 μm. Thereafter, the resultant was dried in an oven at 100°C for 3 minutes to form a second adhesive layer.

[0432] Next, the second adhesive layer surface of a laminate having a separator and a second adhesive layer was laminated onto the substrate surface of a laminate having a substrate, a first intermediate layer, and a first adhesive layer. The separator was then peeled off. This resulted in a foamable adhesive sheet having the first adhesive layer, the first intermediate layer, the substrate, and the second adhesive layer arranged in this order.

[0433] Examples II-2 to II-5 Foamable adhesive sheets were prepared in the same manner as in Example II-1, except that the thicknesses of the first adhesive layer and the second adhesive layer were set to the thicknesses shown in Table 2 below.

[0434] Comparative Example II-1 A laminate having a substrate, a first intermediate layer, and a first adhesive layer was obtained in the same manner as in Example II-1, and this laminate was used as a foamable adhesive sheet.

[0435] Comparative Example II-2 A laminate having a substrate, a first intermediate layer, and a first adhesive layer was obtained in the same manner as in Example II-3, and this laminate was used as a foamable adhesive sheet.

[0436] Comparative Example II-3: A first intermediate layer was formed on a substrate in the same manner as in Example II-1. A second adhesive layer was formed on a separator in the same manner as in Example II-3. Next, the second adhesive layer surface of a laminate having a separator and a second adhesive layer was laminated onto the substrate surface of a laminate having a substrate and a first intermediate layer. The separator was then peeled off. This resulted in a foamable adhesive sheet in which the first intermediate layer, substrate, and second adhesive layer were arranged in this order.

[0437] Comparative Examples II-4 to II-5 Foamable adhesive sheets were prepared in the same manner as in Comparative Example II-3, except that the thickness of the second adhesive layer was set to the thickness shown in Table 2 below.

[0438] Comparative Example II-6 A foamable adhesive sheet was prepared in the same manner as in Example II-1, except that the thicknesses of the first adhesive layer and the second adhesive layer were set to the thicknesses shown in Table 2 below.

[0439] [Evaluation] (1) Tack of the first adhesive layer and the second adhesive layer For the tack of the first adhesive layer, a tack tester "TAC-II" manufactured by RHESCA was used to press a 5 mm diameter cylindrical stainless steel probe against the surface of the first adhesive layer of the foamable adhesive sheet at a temperature of 25°C with a load of 10.0 gf and a speed of 30 mm / min, hold for 1.0 second, and then peel off at a speed of 30 mm / min, measuring the load at the time of peeling. This measurement was performed five times, and the average value was taken as the tack.

[0440] The tack of the second adhesive layer was measured in the same manner as the tack of the first adhesive layer.

[0441] (2) Loop Stiffness A rectangular test piece 10 mm wide and 200 mm long was prepared from the foamable adhesive sheet, and the loop stiffness was measured using the above-mentioned loop stiffness measurement method. The measuring device used was a Loop Stiffness Tester (D-R) manufactured by Toyo Seiki Seisaku-sho, Ltd. The measurement was performed in an environment of 23°C temperature and 50% relative humidity.

[0442] (3) Adhesion: Figures 10(a) and 10(b) are schematic diagrams illustrating a method for evaluating the adhesion of a foamable adhesive sheet. The foamable adhesive sheet 10 was cut into a size of 10 mm wide and 100 mm long to prepare a test piece. The jig 51 had a rectangular parallelepiped shape, and the lower surface 51a of the jig 51 was rectangular, flat, and horizontal. Double-sided adhesive tape 52 (Y-4920-25, manufactured by 3M) was attached to the lower surface 51a of the jig 51.

[0443] 10( a), in a room temperature and humidity environment, the surface of double-sided adhesive tape 52 of jig 51 was attached to the center of foamable adhesive sheet 10 to fix foamable adhesive sheet 10. The attached area was 10 mm × 10 mm. At this time, the surface of double-sided adhesive tape 52 of jig 51 was attached to the surface of the first adhesive layer of foamable adhesive sheet 10.

[0444] Next, as shown in Figure 10(b), the jig 51 was lifted vertically upward. Next, although not shown, a metal plate was placed below the foamable adhesive sheet lifted by the jig, and the jig was lowered vertically downward to attach the foamable adhesive sheet to the metal plate. The condition of the foamable adhesive sheet was then visually observed, and the adhesion was evaluated according to the following criteria. A: The foamable adhesive sheet was able to be attached without folding or air bubbles forming. B: The foamable adhesive sheet was folded or air bubbles formed.

[0445] From Table 3, it was confirmed that the adhesiveness was good when the curl radius of the foamable adhesive sheet after being left to stand at a predetermined temperature and humidity for a predetermined time was equal to or greater than a predetermined value, and when the loop stiffness of the foamable adhesive sheet was equal to or greater than a predetermined value.

[0446] In addition, the present disclosure provides, for example, the following inventions.

[0447] [1] A foamable adhesive sheet having a first adhesive layer, a substrate, and a second adhesive layer in this order, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive, at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent, the first adhesive layer has a tack of 0 gf or more and less than 10 gf, the second adhesive layer has a tack of 10 gf or more and 500 gf or less, and the loop stiffness is 50 mN / 10 mm or more. [2] The foamable adhesive sheet according to [1], wherein the first adhesive layer contains the foaming agent. [3] The foamable adhesive sheet according to [2], wherein the first adhesive layer and the second adhesive layer contain the foaming agent. [4] A foamable adhesive sheet having a first adhesive layer, a substrate, a second adhesive layer, and a pressure-sensitive adhesive layer in this order, wherein the first adhesive layer and the second adhesive layer contain a curable adhesive and a foaming agent, the pressure-sensitive adhesive layer contains a pressure-sensitive adhesive or a curable adhesive, the first adhesive layer has a tack of 0 gf or more and less than 10 gf, the pressure-sensitive layer has a tack of 10 gf or more, and the loop stiffness is 50 mN / 10 mm or more. [5] The foamable adhesive sheet according to [4], wherein the second adhesive layer has a tack of 0 gf or more and less than 10 gf. [6] The foamable adhesive sheet according to any of [1] to [5], wherein the thickness of the substrate is thinner than the thickness of the first adhesive layer and the thickness of the second adhesive layer. [7] A foamable adhesive sheet having, in this order, a first adhesive layer, a substrate, and a second adhesive layer, wherein the composition of the first adhesive layer is different from the composition of the second adhesive layer, the first adhesive layer and the second adhesive layer contain a thermosetting adhesive, and at least one of the first adhesive layer and the second adhesive layer further contains a foaming agent, wherein the foamable adhesive sheet has a curl radius of 15 mm or more and a loop stiffness of 45 mN / 10 mm or more after being left to stand for 15 hours at a temperature of 60°C and a humidity of 10% RH or less. [8] The foamable adhesive sheet according to [7], wherein the first adhesive layer and the second adhesive layer contain the foaming agent. [9] The foamable adhesive sheet according to [7] or [8], wherein the thickness of the substrate is thinner than the thickness of the first adhesive layer and the thickness of the second adhesive layer.

[10] The foamable adhesive sheet according to any one of [7] to [9], wherein the first adhesive layer has a tack of 0 gf or more and less than 10 gf, and the second adhesive layer has a tack of 10 gf or more and 500 gf or less.

[11] The foamable adhesive sheet according to any one of [7] to

[10] , wherein the second adhesive layer has a curl control layer on the side opposite the substrate.

[12] A method for manufacturing an article, comprising: a positioning step of positioning the foamable adhesive sheet according to any one of [1] to

[11] between a first member and a second member; and a bonding step of heating the foamable adhesive sheet to foam and cure it, thereby bonding the first member and the second member.

[0448] DESCRIPTION OF SYMBOLS 1: First adhesive layer 2: Substrate 3: Second adhesive layer 4: First intermediate layer 5: Second intermediate layer 6: Pressure-sensitive adhesive layer 7: Curl control layer 10: Foamable adhesive sheet 15: Foamed and cured adhesive sheet 20a: First member 20b: Second member 100: Article

Claims

DEPCT671. A foam-forming adhesive sheet having a first adhesive layer, substrate, and second adhesive layer, respectively, which consists of such first and second adhesive layers containing a hardening adhesive, and at least one of such first and second adhesive layers contains an additional foaming agent. The tack of such first adhesive layer is greater than or equal to 0 gf and less than 10 gf, and the tack of such second adhesive layer is greater than or equal to 10 gf and less than or equal to 500 gf. Loop stiffness is greater than or equal to 50 mN / 10 mm.

2. A foam-forming adhesive sheet as specified in Reputation 1, in which such first adhesive layer contains the said foaming agent.

3. A foam-forming adhesive sheet as specified in Reputation 2, in which such first and second adhesive layers contain the said foaming agent. 4.A foam-forming adhesive sheet consisting of a primary adhesive layer, substrate, secondary adhesive layer, and subsequent adhesive layer, in sequence, comprising the aforementioned primary adhesive layer and the aforementioned secondary adhesive layer, comprising the aforementioned pressure-sensing adhesive and foam-forming adhesive; the aforementioned adhesive layer, comprising the aforementioned pressure-sensing adhesive or foam-forming adhesive; and the tag of the primary adhesive layer being greater than or equal to 0 gf and less than 10 gf; and the tag of the adhesive layer being greater than or equal to 10 gf; and loop stiffness being greater than or equal to 50 millinewtons / 10 mm.

5. A foam-forming adhesive sheet specified in claim 4 where the tag of the secondary adhesive layer is greater than or equal to 0 gf and less than 10 gf.

6. A foam-forming adhesive sheet specified in claim 1 where the thickness of the substrate is thinner than the thickness of the primary adhesive layer and the thickness of the secondary adhesive layer. 7.A foam-forming adhesive sheet having a first adhesive layer, substrate, and a second adhesive layer, respectively, composed of different components of the first and second adhesive layers; the first and second adhesive layers contain a terimosating adhesive; and at least one of the first and second adhesive layers contains an additional foaming agent; and the radius of curvature of the foam-forming adhesive sheet after static placement at 60°C and humidity less than or equal to 10%RH for 15 hours is greater than or equal to 15 mm²; loop stiffness is greater than or equal to 45 millinewtons / 10 mm².

8. The foam-forming adhesive sheet specified in claim 7 where the first and second adhesive layers contain the said foaming agent.

9. The foam-forming adhesive sheet specified in claim 7 where the thickness of the substrate is thinner than the thickness of the first and second adhesive layers. 10.

11. Foam-forming adhesive sheets specified in Reputation 7 where the tag of the first adhesive layer is greater than or equal to 0 g force and less than 10 g force, and the tag of the second adhesive layer is greater than or equal to 10 g force and less than or equal to 500 g force.

12. A manufacturing method of the product in which a placement step is arranged between the foam-forming adhesive sheets specified in Reputations 1 to 11 and between the first and second parts, and a bonding step is used to bond the first and second parts together by heating and causing the foam-forming adhesive sheets to foam and solidify.

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