Method for manufacturing foamed adhesive sheets and articles

Abstract

To provide a foamable adhesive sheet excellent in adherence and insertability.SOLUTION: A foamable adhesive sheet comprising a first adhesive layer, a base material, 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 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 a loop stiffness is 50 mN / 10 mm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a foamed adhesive sheet and a method for manufacturing an article using the same. [Background technology]

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

[0003] Liquid adhesives are the most common type of adhesive used in motors. However, liquid adhesives have problems such as uneven application, overflow, and dripping, which complicate the bonding process.

[0004] On the other hand, in recent years, it has been proposed to use a sheet-type adhesive containing a foaming agent (foaming adhesive sheet) instead of liquid adhesive (see, for example, Patent Document 1). Foaming adhesive sheets can suppress the occurrence of problems that occur with liquid adhesives as described above. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6874867 [Overview of the project] [Problems that the invention aims to solve]

[0006] For example, when fixing one member to a hole or groove in the other member, as described in Patent Document 1, a foam adhesive sheet can be attached to the other member for temporary fixing, the other member with the foam adhesive sheet attached can be placed in the hole or groove of the first member, and then the foam adhesive sheet can be foamed and hardened to bond the two members together.

[0007] When fixing one component to a hole or groove in the other component, the gap between the two components tends to narrow. Therefore, the foam adhesive sheet used must be thin overall. However, if the foam adhesive sheet is thin, it tends to sag under its own weight during transport. For example, when transporting a foam adhesive sheet using suction, if the foam adhesive sheet is thin, both ends of the foam adhesive sheet tend to sag under its own weight. Therefore, when transporting a foam adhesive sheet using suction and attaching it to another component, problems such as bending, creasing, sagging, and air bubbles getting trapped occur during attachment. Furthermore, if a foam adhesive sheet is attached to another component with such defects, bulges will form on the foam adhesive sheet. This can cause the foam adhesive sheet to rub against the other component when inserting the other component with the foam adhesive sheet attached into the hole or groove of the first component, leading to peeling. In such cases, the adhesive properties after foam curing decrease, resulting in lower reliability.

[0008] Furthermore, in the adhesive fixing method described above, the tackiness of the foam adhesive sheet is used to temporarily fix the other member by attaching the foam adhesive sheet to it. However, if the tackiness of the foam adhesive sheet is high, there is a problem that the insertability of the other member to which the foam adhesive sheet has been attached decreases when inserting it into holes or grooves in the other member.

[0009] This disclosure is made in view of the above circumstances, and its main purpose is to provide a foamed adhesive sheet with excellent adhesive properties and insertability. [Means for solving the problem]

[0010] One embodiment of the present disclosure is a foaming adhesive sheet having a first adhesive layer, a base material, 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 tack of the first adhesive layer is 0 gf or more and less than 10 gf, 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.

[0011] Another embodiment of the present disclosure is a foaming adhesive sheet having a first adhesive layer, a base material, a second adhesive layer, and an adhesive layer in this order, 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 tack of the first adhesive layer is 0 gf or more and less than 10 gf, the tack of the adhesive layer is 10 gf or more, and the loop stiffness is 50 mN / 10 mm or more.

[0012] Another embodiment of the present disclosure provides a method for manufacturing an article, which includes an arranging step of arranging the above-mentioned foaming adhesive sheet between a first member and a second member, and an adhering step of foaming and curing the foaming adhesive sheet to adhere the first member and the second member.

Advantages of the Invention

[0013] The foaming adhesive sheet in the present disclosure has the effect of being excellent in adhesiveness and insertability.

Brief Description of the Drawings

[0014] [Figure 1] It is a schematic cross-sectional view illustrating the foaming adhesive sheet in the present disclosure. [Figure 2] It is a schematic plan view and a cross-sectional view illustrating a loop stiffness measuring instrument. [Figure 3] It is a schematic diagram for explaining a method of measuring loop stiffness. [Figure 4]It is a schematic diagram for explaining a method of measuring loop stiffness. [Figure 5] It is a schematic cross-sectional view illustrating the foaming adhesive sheet in the present disclosure. [Figure 6] It is a schematic cross-sectional view illustrating the foaming adhesive sheet in the present disclosure. [Figure 7] It is a schematic cross-sectional view illustrating the foaming adhesive sheet in the present disclosure. [Figure 8] It is a process diagram illustrating a method for manufacturing an article in the present disclosure. [Figure 9] It is a process diagram illustrating a method for manufacturing an article in the present disclosure. [Figure 10] It is a schematic diagram for explaining a method of measuring the sag amount.

Embodiments for Carrying Out the Invention

[0017] Furthermore, in this specification, "sheet" also includes a component called "film."

[0018] The foamed adhesive sheet and the method for manufacturing articles using the same as described herein will be explained in detail below.

[0019] A. Foamed adhesive sheet The foamed adhesive sheet described herein has two embodiments. Each embodiment will be described below.

[0020] I. First Embodiment A first embodiment of the foamed adhesive sheet in this disclosure is a foamed 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 tack of the first adhesive layer is 0 gf or more and less than 10 gf, 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.

[0021] Figure 1 is a schematic cross-sectional view illustrating a foamed adhesive sheet in this embodiment. The foamed adhesive sheet 10 in Figure 1 has a first adhesive layer 1, a substrate 2, and a second adhesive layer 3 in that order. 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. In addition, the tack of the first adhesive layer 1 and the tack of the second adhesive layer 3 are within a predetermined range, and the loop stiffness of the foamed adhesive sheet 10 is within a predetermined range.

[0022] In this embodiment, by having the tack of the second adhesive layer within a predetermined range, a second adhesive layer with good adhesion to the member can be achieved. Specifically, when bonding one member to a hole or groove in one member, the surface of the second adhesive layer of the foam adhesive sheet is attached to the other member, the other member with the foam adhesive sheet attached is inserted into the hole or groove in the first member, and then the foam adhesive sheet is foamed and cured to bond the first member and the other member, by having the tack of the second adhesive layer within a predetermined range, the surface of the second adhesive layer of the foam adhesive sheet can be attached to the other member using the tack of the second adhesive layer, thereby improving the adhesion of the second adhesive layer to the member. As a result, when inserting the other member with the foam adhesive sheet attached into the hole or groove in the first member, peeling or displacement of the foam adhesive sheet can be suppressed.

[0023] Furthermore, in this embodiment, by having the tack of the second adhesive layer within a predetermined range, a second adhesive layer with good reworkability can be achieved. Therefore, for example, in the above adhesive fixing method, when attaching the surface of the second adhesive layer of the foam adhesive sheet to one of the members using the tack of the second adhesive layer, the misalignment of the foam adhesive sheet can be corrected.

[0024] Furthermore, in this embodiment, since the tack of the second adhesive layer is within a predetermined range, lifting of the second adhesive layer can be suppressed, for example, when the second adhesive layer is formed by a transfer method. Moreover, as will be described later, when the second separator is placed on the side of the second adhesive layer opposite to the first adhesive layer, the tack of the second adhesive layer being within a predetermined range allows the second separator to be easily peeled off, thereby improving workability.

[0025] Furthermore, in this embodiment, since the tack of the first adhesive layer is below a predetermined value, the first adhesive layer can be made substantially non-adhesive (tack-free), resulting in a first adhesive layer with good sliding properties. Therefore, for example, in the above adhesive fixing method, when inserting the other member to which the foam adhesive sheet is attached into a hole or groove of the other member, the other member to which the foam adhesive sheet is attached can be inserted smoothly, improving insertability. This suppresses peeling and displacement of the foam adhesive sheet. Also, in the above adhesive fixing method, when aligning the members by moving the other member relative to the other member, the other member can be moved smoothly relative to the first member while it is inserted into a hole or groove of the other member, making alignment easy.

[0026] Furthermore, in this embodiment, since the tack of the first adhesive layer is below a predetermined value and the first adhesive layer is substantially non-adhesive (tack-free), the first adhesive layer can be made to have good slipperiness and good blocking resistance. Therefore, the handling of the foamed adhesive sheet can also be improved.

[0027] 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, which can suppress peeling and displacement of the foamed adhesive sheet. Therefore, it is possible to suppress the decrease in adhesiveness of the foamed adhesive sheet after foaming and curing due to peeling and displacement of the foamed adhesive sheet, and to reduce the variation in adhesive strength of the foamed adhesive sheet after foaming and curing due to peeling and displacement of the foamed adhesive sheet. Thus, by using the foamed adhesive sheet of this embodiment, it is possible to achieve high adhesive strength, high reliability, and high quality adhesion.

[0028] Here, when one component is bonded and fixed to a hole or groove in the other component, as described above, the gap between the two components tends to narrow. Therefore, the foam adhesive sheet used needs to be thin overall. However, if the foam adhesive sheet is thin, it tends to sag under its own weight during transport. Therefore, the inventors of this disclosure focused on the stiffness of the foam adhesive sheet. A thicker foam adhesive sheet tends to have higher stiffness. However, since the foam adhesive sheet needs to be thin to begin with, increasing its thickness is not suitable. Also, when the foam adhesive sheet has adhesive layers on both sides of the substrate, a thicker substrate tends to have higher stiffness. However, if the thickness of the substrate is relatively increased while the thickness of the foam adhesive sheet remains thin, the thickness of the adhesive layer becomes relatively thin, which may reduce the adhesive properties and foaming properties of the adhesive layer. Furthermore, generally speaking, in adhesive layers, the greater the tackiness, the softer the layer tends to be, and the less tackiness, the harder it tends to be. Therefore, when a foamed adhesive sheet has an adhesive layer with tackiness, it tends to have low rigidity. The inventors of this disclosure have found that by setting the loop stiffness of the foamed adhesive sheet within a predetermined range, it is possible to suppress the foamed adhesive sheet from sagging due to its own weight. Moreover, they have found that by making the first adhesive layer of the two adhesive layers substantially non-tack-free, it is possible to improve insertability while also increasing rigidity.

[0029] Loop stiffness is a parameter that represents the rigidity 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 represent the rigidity of sheets and films used in packaging materials, for example, but it is not very common in the field of adhesive sheets.

[0030] In the foamed adhesive sheet of this embodiment, the loop stiffness is greater than a predetermined value, thus increasing its rigidity. Therefore, when the foamed adhesive sheet is transported, it is possible to suppress the sagging of the foamed adhesive sheet due to its own weight. Thus, for example, when the foamed adhesive sheet is transported by suction and attached to another member, it is possible to suppress the occurrence of bending, twisting, bending, and air bubble entrapment of the foamed adhesive sheet during attachment. Thus, the adhesive properties can be improved. Furthermore, since it is possible to suppress the occurrence of bulges in the foamed adhesive sheet due to these defects, it is possible to reduce friction of the foamed adhesive sheet when inserting the other member to which the foamed adhesive sheet has been attached into holes or grooves of the other member. Thus, it is possible to suppress the peeling of the foamed adhesive sheet during insertion. Therefore, from these points as well, by using the foamed adhesive sheet of this embodiment, high adhesive strength, high reliability, and high quality adhesion can be achieved.

[0031] Here, "adhesion" is a concept included in "bonding." Adhesion is sometimes used to mean a temporary bonding phenomenon, while bonding is sometimes used to mean a substantially permanent bonding phenomenon (Iwanami Shoten Dictionary of Physics and Chemistry, 5th Edition). "Adhesion" and "adhesion force" refer to the property of bonding upon pressure and the adhesive force at that time.

[0032] In this specification, "adhesion of the adhesive layer" and "adhesion strength of the adhesive layer" refer to the tackiness and adhesion strength of the adhesive layer before curing, unless otherwise specified. Furthermore, in this specification, "adhesion of the adhesive layer" and "adhesion strength of the adhesive layer" refer to the tackiness and adhesion strength of the adhesive layer after curing, unless otherwise specified.

[0033] The following describes the various components of the foamed adhesive sheet in this embodiment.

[0034] 1.Characteristics In this embodiment, the tack of the first adhesive layer is 0 gf or more and less than 10 gf, and may be 5 gf or less, or 2 gf or less. 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), resulting in a first adhesive layer with good slipperiness and blocking resistance.

[0035] In this embodiment, the tack of the second adhesive layer is 10 gf or more, may be 30 gf or more, or may be 50 gf or more. If the tack of the second adhesive layer is too low, for example, in the adhesive fixing method described above, when using the tack of the second adhesive layer to attach the surface of the second adhesive layer of the foam adhesive sheet to the other member, there is a possibility that the adhesion between the second adhesive layer and the other member will decrease. Also, when inserting the other member to which the foam adhesive sheet has been attached into a hole or groove of the first member, poor adhesion between the second adhesive layer and the other member may cause the foam adhesive sheet to peel off or shift position, which may reduce the adhesion between the first adhesive layer and the second adhesive layer after foam curing, or cause variations in adhesive strength. Furthermore, the tack of the second adhesive layer is 500 gf or less, may be 400 gf or less, or may be 300 gf or less. If the tack of the second adhesive layer is too high, the reworkability will decrease. For example, in the adhesive fixing method described above, when using the tack of the second adhesive layer to attach the surface of the second adhesive layer of the foam adhesive sheet to the other member, it may become difficult to correct any misalignment of the foam adhesive sheet.

[0036] Here, the tack of the first and second adhesive layers can be measured by a probe tack test in accordance with JIS Z3284-3:2014. For example, the tacking tester "TAC-II" manufactured by RHESCA can be used as the probe tack tester. Details of the measurement method for the tack of the first and second adhesive layers will be described in the Examples section below.

[0037] In this embodiment, the tack of the first adhesive layer can be set to a predetermined range by, for example, adjusting the composition of the first adhesive layer. Specifically, in the first adhesive layer containing epoxy resin and curing agent, the tackiness 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. Furthermore, in the first adhesive layer containing epoxy resin and curing agent, the tackiness of the first adhesive layer can be reduced by including an epoxy resin with a high softening temperature or an epoxy resin with a large weight-average molecular weight. For example, the tackiness of the first adhesive layer can be reduced by including multiple types of epoxy resins with different softening temperatures in the first adhesive layer, that is, by including one epoxy resin and another epoxy resin whose softening temperature is 25°C or higher and at least 10°C higher than the softening temperature of the first epoxy resin. Furthermore, for example, the tackiness of the first adhesive layer can be reduced by including multiple types of epoxy resins with different weight-average molecular weights in the first adhesive layer, that is, by including one epoxy resin and another epoxy resin having a weight-average molecular weight of 370 or more and being at least 300 greater than the weight-average molecular weight of the first epoxy resin. More specifically, in the first adhesive layer containing epoxy resin and a curing agent, as described later, the tackiness 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 the epoxy resin. Also, in the first adhesive layer containing epoxy resin and a curing agent, as described later, the tackiness of the first adhesive layer can be reduced by including an acrylic resin that is compatible with the epoxy resin.

[0038] In this embodiment, the tack of the second adhesive layer can be controlled, for example, by adjusting the composition of the second adhesive layer. Specifically, in a second adhesive layer containing epoxy resin and a curing agent, using an epoxy resin that is liquid at room temperature or a curing agent that is liquid at room temperature tends to increase the tackiness of the second adhesive layer. Furthermore, in a second adhesive layer containing epoxy resin and a curing agent, including an epoxy resin with a low softening temperature or an epoxy resin with a small weight-average molecular weight also tends to increase the tackiness of the second adhesive layer. Additionally, adding a tackifier to the second adhesive layer tends to increase its tackiness. However, while using a curing agent that is liquid at room temperature tends to increase tackiness, it may reduce 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.

[0039] In this embodiment, the static friction coefficient of the surface of the first adhesive layer opposite the second adhesive layer is preferably 0.33 or less, may be 0.30 or less, or 0.26 or less. By having the static friction coefficient of the surface of the first adhesive layer within the above range, a first adhesive layer with good sliding properties can be obtained. Alternatively, the static friction coefficient may be 0.16 or more.

[0040] 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 foamed adhesive sheet and the metal plate is measured by the following method. First, the foamed adhesive sheet is cut to 80 mm x 200 mm. Next, the foamed adhesive sheet is placed on a rectangular metal plate (SUS plate) that is placed horizontally, and a sliding piece (63 mm x 63 mm, weight 200 g, bottom surface: felt) is placed on the first adhesive layer of the foamed adhesive sheet. The friction force is measured under the 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 machine FRICTION TESTER TR-2 manufactured by Toyo Seiki Seisakusho Co., Ltd. can be used as the apparatus.

[0041] 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, if 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 and content 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. Also, as the content of the foaming agent increases, the static friction coefficient of the surface of the first adhesive layer tends to decrease.

[0042] In this embodiment, the arithmetic mean roughness (Ra) of the surface of the first adhesive layer opposite the second adhesive layer is preferably, for example, 0.3 μm or more, but may also 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, a first adhesive layer with good slipperiness can be obtained. Alternatively, 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.

[0043] Here, the Ra of the first adhesive layer can be measured using a white light interferometer. Specifically, using a Zygo NewView7300 white light interferometer, the Ra of the first adhesive layer can be measured with an observation field of view of 0.55 mm × 0.55 mm and a sampling interval of 0.55 μm.

[0044] 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, if the first adhesive layer further contains a foaming agent, the Ra of the first adhesive layer can be controlled by the average particle size and content 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. Also, as the content of the foaming agent increases, the Ra of the first adhesive layer tends to increase.

[0045] In the foamed adhesive sheet of this embodiment, the loop stiffness is 50 mN / 10 mm or more, preferably 75 mN / 10 mm or more, and more preferably 100 mN / 10 mm or more. Because the loop stiffness of the foamed adhesive sheet is within the above range, for example, when the foamed adhesive sheet is adsorbed and transported and attached to a component, it is possible to suppress the sagging of the foamed adhesive sheet due to its own weight, thereby improving adhesion. On the other hand, there is no particular upper limit to the loop stiffness.

[0046] Loop stiffness, as mentioned above, is a parameter that represents the rigidity of a film or sheet. The method for measuring loop stiffness will be explained below with reference to Figures 2 to 4.

[0047] Figure 2(a) is a schematic plan view showing the loop stiffness measuring instrument, and Figure 2(b) is a cross-sectional view taken along line AA of Figure 2(a). The test specimen of the foamed adhesive sheet 10 is rectangular in shape, having a long side and a short side. In this embodiment, the length L1 of the long side of the test specimen of the foamed adhesive sheet 10 is 200 mm, and the length L2 of the short side is 10 mm. As the loop stiffness measuring instrument 30, the Loop Stiffness Tester (registered trademark) manufactured by Toyo Seiki Seisakusho Co., Ltd. can be used. The length L1 of the long side of the test specimen of the foamed adhesive sheet 10 is adjustable as long as the test specimen of the foamed adhesive sheet 10 can be gripped by the pair of chuck parts 31 described later.

[0048] The loop stiffness measuring instrument 30 includes a pair of chucks 31 for gripping a pair of long-side ends of a test specimen of the foamed adhesive sheet 10, and a support member 32 for supporting the chucks 31. The chucks 31 have a first chuck 31a and a second chuck 31b. The foamed adhesive sheet 10 is placed on the pair of first chucks 31a, and the second chuck 31b does not yet grip the foamed adhesive sheet 10 between itself and the first chucks 31a. As will be described later, during measurement, the foamed adhesive sheet 10 is gripped between the first chucks 31a and the second chucks 31b of the chucks 31. The second chuck 31b may be connected to the first chuck 31a via a hinge mechanism.

[0049] First, as shown in Figures 2(a) and (b), a test specimen of the foamed adhesive sheet 10 is placed on the first chuck 31a of a pair of chucks 31 that are spaced apart by an interval L3. In this embodiment, the interval L3 is set so that the length of the loop portion 41 (hereinafter also referred to as the loop length), which will be described later, is 60 mm. The test specimen of the foamed adhesive sheet 10 is positioned 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 specimen of the foamed adhesive sheet 10 so as to grip the end of the test specimen in the long-side direction between it and the first chuck 31a.

[0050] Next, as shown in Figure 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 foamed adhesive sheet 10. The test piece of the foamed adhesive sheet 10 shown in Figure 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 the parts of the test piece of the foamed adhesive sheet 10 that are gripped by the pair of chuck portions 31. The pair of intermediate portions 42 are the parts of the test piece of the foamed 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 foamed 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 foam adhesive sheet 10 test specimen between the position P1 where the loop portion 41 side surface of one second chuck 31b intersects with the test specimen of the foam adhesive sheet 10, and the position P2 where the loop portion 41 side surface of the other second chuck 31b intersects with the test specimen of the foam adhesive sheet 10. The above-mentioned interval L3 is the length of the loop portion 41 plus 2 × t, where t is the thickness of the second chuck 31b of the chuck portion 31.

[0051] Next, as shown in Figure 4(a), the orientation of the chuck portion 31 is adjusted so that the protrusion direction Y of the loop portion 41 relative to the chuck portion 31 is horizontal. For example, the orientation 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 Figure 4(a), the protrusion direction Y of the loop portion 41 coincides with the thickness direction of the chuck portion 31. Also, a load cell 35 is prepared at a position away from the second chuck 31b in the protrusion direction Y of the loop portion 41.

[0052] Next, as shown in Figure 4(b), the load cell 35 is moved toward the loop portion 41 of the test piece of the foamed adhesive sheet 10, and the load cell 35 is brought into contact with the loop portion 41. Distance Z1 is the distance between the load cell 35 and the second chuck 31b of the chuck portion 31.

[0053] Subsequently, as shown in Figures 4(b) to 4(c), the load cell 35 pushes the loop portion 41 toward the chuck portion 31 by a distance Z2. In this embodiment, the distance Z2 is set to 15 mm.

[0054] Next, as shown in Figure 4(c), the load cell 35 is moved a distance Z2 toward the chuck portion 31, and while the load cell 35 is pressing down on the loop portion 41 of the foamed adhesive sheet 10 test piece, the load value applied from the loop portion 41 to the load cell 35 is recorded after it stabilizes. The load value obtained in this way is defined as the loop stiffness of the foamed adhesive sheet 10. In this specification, unless otherwise specified, the environment during the measurement of loop stiffness is a temperature of 23°C and a relative humidity of 50%.

[0055] Furthermore, when measuring the loop stiffness of a foamed adhesive sheet, if the foamed adhesive sheet has a first separator and a second separator, as described later, the loop stiffness of the foamed adhesive sheet should be measured after peeling off the first separator and the second separator.

[0056] In this embodiment, the loop stiffness of the foamed 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, a thicker substrate tends to result in greater loop stiffness. Also, for example, a thicker first adhesive layer tends to result in greater loop stiffness. Therefore, it is preferable to adjust the thickness of each layer to obtain the desired loop stiffness. Furthermore, adjusting the composition of the first adhesive layer to reduce its tack tends to increase loop stiffness.

[0057] In this embodiment, it is preferable that the foamed adhesive sheet has high adhesive properties after foaming and curing. After foaming and curing of the foamed adhesive sheet, the shear strength (adhesive strength) according to JIS K6850 corresponding to ISO 4587 may be, for example, 1.50 MPa or more, 1.80 MPa or more, or 2.10 MPa or more at 23°C. Furthermore, the above shear strength (adhesive strength) may be, for example, 0.50 MPa or more, 0.75 MPa or more, or 1.00 MPa or more at 130°C. For example, in the case of high-strength acrylic foam adhesive tape that does not require heating, the shear strength (adhesive strength) is about 1 MPa to 2 MPa at room temperature and has no heat resistance at 200°C. Therefore, if the above shear strength (adhesive strength) is within the above range at 23°C, there is an advantage in terms of strength. Furthermore, if the above shear strength (adhesive strength) is within the above range at 130°C, it becomes possible to apply it to applications around automobile engines and other applications requiring similar heat resistance.

[0058] In this embodiment, it is preferable that the foamed adhesive sheet has high electrical insulation properties after foaming and curing. After foaming and curing of the foamed adhesive sheet, the dielectric breakdown voltage according to JIS C2107 corresponding to IEC 60454-2 is preferably, for example, 3kV or higher, and more preferably 5kV or higher. Having the dielectric breakdown voltage within the above range makes it possible to apply it for rust prevention and around copper wires. Furthermore, after foaming and curing of the foamed adhesive sheet, it is preferable that the thermal conductivity is, for example, 0.05 W / mK or higher. Having the thermal conductivity within the above range makes it possible to miniaturize the components and promote the curing reaction during heating.

[0059] 2.First adhesive layer (1) Material of the first adhesive layer In this embodiment, the first adhesive layer contains a curable adhesive.

[0060] (a) Curing adhesive In this embodiment, the curable adhesive included in the first adhesive layer can be a curable adhesive generally used for the adhesive layer of foamed adhesive sheets. Examples of curable adhesives include heat-curing adhesives and light-curing adhesives. Among these, heat-curing adhesives are preferred. Heat-curing adhesives can be applied even when the component is not transparent, such as a metal component.

[0061] 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.

[0062] In particular, the curable adhesive is preferably an epoxy resin-based adhesive. That is, the curable adhesive preferably contains epoxy resin and a curing agent. Generally, epoxy resin-based adhesives have excellent mechanical strength, heat resistance, insulation, and chemical resistance, and exhibit low curing shrinkage, making them suitable for a wide range of applications.

[0063] The following explanation will provide an example of a case where the curing adhesive is an epoxy resin-based adhesive.

[0064] (i) epoxy resin The epoxy resin in this embodiment is a compound having at least one epoxy group or glycidyl group, which undergoes a crosslinking polymerization reaction and hardens when used in combination with a curing agent. The epoxy resin also includes monomers having at least one epoxy group or glycidyl group.

[0065] As the epoxy resin, epoxy resins generally used for the adhesive layer of foamed adhesive sheets can be used. In particular, the curable adhesive preferably contains a primary epoxy resin having a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or less, and a secondary epoxy resin having a softening temperature higher than the primary epoxy resin and a weight-average molecular weight of 20,000 or more. By using a combination of the primary and secondary epoxy resins, the tackiness of the primary adhesive layer can be reduced, and a foamed adhesive sheet with good slipperiness can be obtained. Furthermore, a primary adhesive layer with good blocking resistance and adhesion after foam curing can be obtained.

[0066] For example, if the goal is solely to improve adhesion after foam curing, 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 using a low molecular weight (low epoxy equivalent) epoxy resin, for example, when the foamed adhesive sheet is wound into a roll, the low molecular weight (low epoxy equivalent) epoxy resins tend to assimilate with each other, making blocking more likely.

[0067] In contrast, when using a primary epoxy resin with a relatively low softening temperature (relatively high crystallinity) and low molecular weight (low epoxy equivalent), the primary epoxy resin rapidly melts and changes into a low-viscosity liquid when the temperature exceeds the softening temperature. Therefore, it is easier to improve adhesion after foaming and curing. On the other hand, because the primary epoxy resin has relatively high crystallinity, it can suppress the occurrence of blocking compared to epoxy resins with relatively low crystallinity or epoxy resins that do not have crystallinity. However, if only the primary epoxy resin is used, the blocking suppression effect may be insufficient, or the tackiness of the first adhesive layer may become too high. Therefore, by further using a secondary epoxy resin with a relatively high softening temperature (relatively low crystallinity) and high molecular weight, the blocking suppression effect can be improved, and the tackiness of the first adhesive layer can be kept low.

[0068] (i-1) Primary epoxy resin The first epoxy resin has a softening temperature of 50°C or higher and an epoxy equivalent of 5000 g / eq or less. Compared to the second epoxy resin described later, the first epoxy resin has a relatively lower softening temperature (relatively higher crystallinity). Because the first epoxy resin has relatively high crystallinity and a low molecular weight, it is easy to improve the adhesion and blocking resistance after foam curing. In addition, because the first epoxy resin has a low molecular weight, a high crosslinking density can be achieved, resulting in a first adhesive layer with good mechanical strength, chemical resistance, and curability. Furthermore, it is preferable that the first epoxy resin is an epoxy resin that is solid at room temperature (23°C).

[0069] The softening temperature of primary epoxy resin is typically 50°C or higher, but may also be 55°C or higher, or even 60°C or higher. On the other hand, the softening temperature of primary 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.

[0070] The epoxy equivalent of the primary epoxy resin is, for example, 5000 g / eq or less, but may also 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 primary epoxy resin is, for example, 90 g / eq or more, but may also be 100 g / eq or more, or 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.

[0071] The first epoxy resin may be a monofunctional epoxy resin, a bifunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or more functional epoxy resin.

[0072] Furthermore, the weight-average molecular weight (Mw) of the primary epoxy resin is usually smaller than the weight-average molecular weight (Mw) of the secondary epoxy resin, which will be discussed later. The Mw of the primary epoxy resin is, for example, 6,000 or less, may be 4,000 or less, or 3,000 or less. On the other hand, the Mw of the primary epoxy resin is, for example, 400 or more. Mw is the polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0073] The first epoxy resin has a melt viscosity at 150°C of, for example, 0.005 Pa·s or higher, but may also be 0.015 Pa·s or higher, 0.03 Pa·s or higher, 0.05 Pa·s or higher, or 0.1 Pa·s or higher. If the melt viscosity is too low, good foaming properties may not be obtained. Also, if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), the tackiness of the resulting first adhesive layer may be high. This is presumed to be 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 decreases significantly when it is compatible with the second epoxy resin or acrylic resin, and the Tg of the first adhesive layer decreases. On the other hand, the first epoxy resin has a melt viscosity at 150°C of, for example, 10 Pa·s or less, but may also be 5 Pa·s or less, or 2 Pa·s or less. If the melt viscosity is too high, the uniformity of the resulting first adhesive layer may decrease. The melt viscosity can be determined in accordance with JIS K6862, which corresponds to ISO 2555 (Resins in the liquid state or as emulsions or dispersions: Determination of Brookfield RV viscosity), by measuring it using a Brookfield-type single-cylinder rotational viscometer and a thermocell for heating the solution.

[0074] Next, the composition of the primary epoxy resin will be described. Examples of primary epoxy resins include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of primary epoxy resins include bisphenol-type epoxy resins such as bisphenol A type epoxy resin and bisphenol F type epoxy resin, novolac-type epoxy resins such as bisphenol A novolac type epoxy resin and cresol novolac type epoxy resin, and modified epoxy resins such as urethane-modified epoxy resin and rubber-modified epoxy resin. Other specific examples include biphenyl-type epoxy resin, stilbene-type epoxy resin, triphenolmethane-type epoxy resin, alkyl-modified triphenolmethane-type epoxy resin, triazine nucleus-containing epoxy resin, dicyclopentadiene-modified phenol-type epoxy resin, naphthalene-type epoxy resin, glycol-type epoxy resin, and pentaerythritol-type epoxy resin. The primary epoxy resin may consist of one type or two or more types.

[0075] Bisphenol A type epoxy resins can exist in a liquid or solid state at room temperature, depending on the number of repeating units in the bisphenol skeleton. Bisphenol A type epoxy resins in which the main chain of bisphenol skeletons is, for example, 2 to 10 are solid at room temperature. Bisphenol A type epoxy resins are particularly preferable because they can improve heat resistance.

[0076] In particular, the first epoxy resin is preferably a bisphenol A novolac type epoxy resin represented by the following general formula (1).

[0077] [ka]

[0078] In general formula (1), R 1 C m H 2m It is a group represented by (m is between 1 and 3), and R 2 and R 3is, independently of each other, a group represented by C p H 2p+1 (where p is 1 or more and 3 or less), and n is 0 or more and 10 or less.

[0079] In general formula (1), m in R 1 is preferably 1, that is, R 1 is preferably -CH2-. Similarly, p in R 2 and R 3 is preferably 1, that is, R 2 and R 3 are preferably -CH3. Further, the hydrogen bonded to the benzene ring of general formula (1) may be substituted with other elements or other groups.

[0080] When the content of the first epoxy resin is based on 100 parts by mass of the resin component contained in the first adhesive layer, for example, it is 1 part by mass or more, and may be 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 small, the adhesiveness and blocking resistance after foam curing may decrease. On the other hand, when the content of the first epoxy resin is based on 100 parts by mass of the resin component contained in the first adhesive layer, for example, it is 90 parts by mass or less, and may be 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 large, the contents of the second epoxy resin and the acrylic resin will be relatively small, and it may not be possible to balance the non-stickiness, blocking resistance, adhesion to the base material after foam curing, crack resistance after foam curing, and adhesiveness after foam curing.

[0081] (i-2) Second epoxy resin The second epoxy resin has a higher softening temperature than the first epoxy resin and a weight-average molecular weight of 20,000 or more. Compared to the first epoxy resin mentioned above, the second epoxy resin has a relatively higher softening temperature (relatively lower crystallinity). Because the second epoxy resin has relatively low crystallinity and high molecular weight, it is easier to improve blocking resistance. Furthermore, because the second epoxy resin has relatively low crystallinity and high molecular weight, it can suppress the increase in tackiness caused by the first epoxy resin. In addition, it is preferable that the second epoxy resin is a solid epoxy resin at room temperature (23°C).

[0082] The weight-average molecular weight (Mw) of the secondary epoxy resin is usually greater than that of the primary epoxy resin. The Mw of the secondary epoxy resin is typically 20,000 or more, but may be 30,000 or more, or even 35,000 or more. On the other hand, the Mw of the secondary epoxy resin may be, for example, 100,000 or less.

[0083] 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. For example, the epoxy equivalent of the second epoxy resin may be 4000 g / eq or more, 5000 g / eq or more, or 6000 g / eq or more. On the other hand, for example, the epoxy equivalent of the second epoxy resin may be 20000 g / eq or less.

[0084] The second epoxy resin may be a monofunctional epoxy resin, a bifunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or more functional epoxy resin.

[0085] The softening temperature of the second epoxy resin is usually higher than that of the first epoxy resin. The difference between the two is, for example, 10°C or more, may be 20°C or more, or may be 30°C or more. The softening temperature of the second epoxy resin is, for example, 80°C or more, and may be 90°C or more. On the other hand, the softening temperature of the second epoxy resin is, for example, 180°C or less.

[0086] The composition of the second epoxy resin is the same as that of the first epoxy resin described above, so its description is omitted here.

[0087] The content of the secondary epoxy resin 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, when the resin components contained in the first adhesive layer are considered to be 100 parts by mass. If the content of the secondary epoxy resin is too low, the tackiness may increase and the blocking resistance may decrease. On the other hand, the content of the secondary epoxy resin 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, when the resin components contained in the first adhesive layer are considered to be 100 parts by mass. If the content of the secondary epoxy resin is too high, the content of the primary epoxy resin and acrylic resin will be relatively low, and it may not be possible to balance non-tackiness, blocking resistance, adhesion to the substrate after foam curing, crack resistance after foam curing, and adhesion after foam curing.

[0088] The proportion of the first epoxy resin to the total of the first and second epoxy resins is, for example, 5% by mass or more, may be 10% by mass or more, may be 15% by mass or more, or may be 20% by mass or more. On the other hand, the above proportion of the first epoxy resin is, for example, 80% by mass or less, may be 75% by mass or less, or may be 60% by mass or less.

[0089] Furthermore, the total ratio 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, may be 70% by mass or more, may be 90% by mass or more, or may be 100% by mass.

[0090] (ii) Acrylic resin When the curable adhesive is an epoxy resin-based adhesive, the first adhesive layer may further contain an acrylic resin that is compatible with the epoxy resin. The acrylic resin is a resin that is 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 adhesion after foam curing can be improved. Furthermore, it is thought that the acrylic resin acts as a compatibilizer for the foaming agent (for example, a foaming agent whose shell is an acrylonitrile copolymer resin), and by uniformly dispersing and foaming, the adhesion after foam curing is improved. In addition, the flexibility of the acrylic resin is exhibited, which can improve the adhesion to the substrate after foam curing and the crack resistance after foam curing. Also, because the acrylic resin is compatible with the epoxy resin, the hardness of the surface of the first adhesive layer can be kept high. On the other hand, if the acrylic resin is incompatible with the epoxy resin, flexible parts will be formed on the surface of the first adhesive layer, which may make the interface with the adherend less slippery and reduce workability.

[0091] In this embodiment, the acrylic resin is compatible with the epoxy resin. This compatibility can be confirmed, for example, by observing the cross-section of the first adhesive layer of the foamed adhesive sheet with a scanning electron microscope (SEM) or transmission electron microscope (TEM) and noting the absence of micron-sized islands. More specifically, the average island particle size is preferably 1 μm or less. In particular, the average island particle size may be 0.5 μm or less, or 0.3 μm or less. A large sample size is preferred, for example, 100 or more. The observation area is a range of 100 μm × 100 μm, or, if the thickness of the first adhesive layer is 100 μm or less, a range of thickness × 100 μm.

[0092] The weight-average molecular weight (Mw) of the acrylic resin is, for example, 50,000 or more, but may also be 70,000 or more, or 100,000 or more. Primary epoxy resins have relatively high crystallinity, which can lead to excessively low melt viscosity (or dynamic viscoelasticity) during heating, potentially causing shrinkage during curing after foaming (the period from when the foaming of the foaming agent is finished until the first adhesive layer hardens). However, by using an acrylic resin with a certain molecular weight, it is possible to suppress the melt viscosity from becoming too low, making shrinkage during curing after foaming less likely. On the other hand, 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 substance: PS, sample: 20 μL, flow rate: 1 mL / min, column temperature: 40°C).

[0093] The glass transition temperature (Tg) of acrylic resin is, for example, 90°C or higher, and may also be 100°C or higher. On the other hand, the Tg of acrylic resin is, for example, 180°C or lower. The Tg can be measured by thermal analysis such as differential scanning calorimeter (DSC), in accordance with JIS K7121, which corresponds to ISO 3146.

[0094] Acrylic resin has a storage modulus (E') of 1 × 10⁻¹⁰ at the foaming initiation temperature. 6 It may be less than Pa. A low E' at the start of foaming improves fluidity and allows for good foaming. On the other hand, E' at the foaming start temperature is, for example, 1 × 10⁻⁶. 5 The temperature must be above Pa. Note that the foaming initiation temperature varies depending on the type of foaming agent. Furthermore, if two or more foaming agents are used, the foaming initiation temperature shall be the temperature at which the primary foaming reaction begins.

[0095] Acrylic resin has a storage modulus (E') of 1 × 10⁻¹⁰ at the curing start temperature. 5It may be Pa or higher. As mentioned above, shrinkage may occur during curing after foaming (from the time the foaming of the foaming agent is finished until the first adhesive layer hardens), but shrinkage can be suppressed by having a large E' at the curing start temperature, and good shape retention can be obtained. Note that the curing start temperature is different depending on the type of curing agent. Also, when two or more curing agents are used, the curing start temperature is the start temperature of the main curing reaction.

[0096] Furthermore, the average storage modulus (E') of acrylic resin at temperatures between 0°C and 100°C is 1 × 10⁻⁶ 6 It may be Pa or higher. A high average value of E' before foaming allows for good non-stick and blocking resistance. On the other hand, the average value of the storage modulus (E') between 0°C and 100°C is, for example, 1 × 10⁻⁶ 8 It is below Pa.

[0097] Acrylic resins may have polar groups. Examples of polar groups include epoxy groups, hydroxyl groups, carboxyl groups, nitrile groups, and amide groups.

[0098] The acrylic resin is a homopolymer of acrylic acid ester monomers, and may be a mixed component containing two or more of the above homopolymers, or a copolymer of two or more acrylic acid ester monomers, and may be a component containing one or more copolymers. Furthermore, the acrylic resin may be a mixed component of the above homopolymer and the above copolymer. The term "acrylic acid" in acrylic acid ester monomers also includes the concept of methacrylic acid. Specifically, the acrylic resin may be a mixture of a polymer of methacrylate and a polymer of acrylate, or it may be an acrylic acid ester polymer such as acrylate-acrylate, methacrylate-methacrylate, or methacrylate-acrylate. In particular, it is preferable that the acrylic resin contains a copolymer of two or more acrylic acid ester monomers ((meth)acrylic acid ester copolymer).

[0099] Examples of monomer components constituting the (meth)acrylic acid ester copolymer include the monomer component described in Japanese Patent Publication No. 2014-065889. The above monomer component may have the polar group described above. Examples of the above (meth)acrylic acid ester copolymer include ethyl acrylate-butyl acrylate-acrylonitrile copolymer, ethyl acrylate-acrylonitrile copolymer, and butyl acrylate-acrylonitrile copolymer. Note that "acrylic acid" such as methyl acrylate and ethyl acrylate also includes "methacrylic acid" such as methyl methacrylate and ethyl methacrylate.

[0100] As the above (meth)acrylic acid ester copolymer, block copolymers are preferred, and acrylic block copolymers such as methacrylate-acrylate copolymers are even more preferred. Examples of (meth)acrylates constituting the acrylic block copolymer include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, and benzidyl acrylate. These "acrylic acids" also include "methacrylic acid."

[0101] Specific examples of methacrylate-acrylate copolymers include acrylic copolymers such as methyl methacrylate-butyl acrylate-methyl methacrylate (MMA-BA-MMA) copolymers. MMA-BA-MMA copolymers also include block copolymers of polymethyl methacrylate-polybutyl acrylate-polymethyl methacrylate (PMMA-PBA-PMMA).

[0102] The acrylic copolymer does not necessarily have polar groups, or it may be a modified product in which the aforementioned polar groups are partially introduced. Since the above modified product is easily compatible with epoxy resin, its adhesive properties are further improved.

[0103] In particular, the acrylic resin is preferably a (meth)acrylic acid ester copolymer having a first polymer portion with a glass transition temperature (Tg) of 10°C or less and a second polymer portion with a glass transition temperature (Tg) of 20°C or more. Such a (meth)acrylic acid ester copolymer has a first polymer portion that becomes a soft segment and a second polymer portion that becomes a hard segment.

[0104] The manifestation of the above effects can be estimated as follows: By using an acrylic resin that has both soft and hard segments, such as the (meth)acrylic acid ester copolymer described above, the hard segments contribute to heat resistance, and the soft segments contribute to toughness or flexibility, thus resulting in a first adhesive layer with good heat resistance, toughness, and flexibility.

[0105] At least one of the first polymer portion and the second polymer portion contained in the above (meth)acrylic acid ester copolymer is compatible with epoxy resin. When the first polymer portion is compatible with epoxy resin, flexibility can be increased. Furthermore, when the second polymer portion is compatible with epoxy resin, cohesiveness and toughness can be increased.

[0106] If either the first or second polymer portion is incompatible with the epoxy resin, the (meth)acrylic acid ester copolymer will have a compatible portion that is compatible with the epoxy resin and an incompatible 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, while the incompatible portion does not, resulting in 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 primary and secondary polymer portions contained in the (meth)acrylic acid ester copolymer, and whether or not it is modified by the introduction of polar groups. For example, there are sea-island structures in which the compatible parts of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible parts of the (meth)acrylic acid ester copolymer are the islands, or in which the incompatible parts of the (meth)acrylic acid ester copolymer are the sea and the compatible parts of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, or in which the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands. Having such a sea-island structure makes it easier to distribute stress, thus avoiding interfacial fracture and resulting in excellent adhesion after foam curing.

[0107] The above (meth)acrylic acid ester copolymer is preferably a block copolymer, and more preferably an ABA block copolymer in which the compatible parts are polymer block A and the incompatible parts are polymer block B. Furthermore, it is preferable that the first polymer portion is the incompatible part and the second polymer portion is the compatible part, with the first polymer portion being polymer block B and the second polymer portion being polymer block A. By using such an ABA block copolymer as the acrylic resin, in the case of a sea-island structure in which the compatible parts of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the sea and the incompatible parts of the (meth)acrylic acid ester copolymer are the islands, the island portion can be reduced. Also, in the case of a sea-island structure in which the incompatible parts of the (meth)acrylic acid ester copolymer are the sea and the compatible parts of the cured epoxy resin and the (meth)acrylic acid ester copolymer are the islands, or in the case of a sea-island structure in which the (meth)acrylic acid ester copolymer is the sea and the cured epoxy resin is the islands, the sea portion can be reduced.

[0108] Furthermore, 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 portion or the second polymer portion.

[0109] The Tg of the first polymer portion contained in the above (meth)acrylic acid ester copolymer is 10°C or lower, and can be in the range of -150°C or higher and 10°C or lower, more particularly in the range of -130°C or higher and 0°C or lower, and especially in the range of -110°C or higher and -10°C or lower.

[0110] Furthermore, the Tg of the first polymer portion can be calculated using the following formula, based on the Tg(K) of each homopolymer listed in "POLYMERHANDBOOK Third Edition" (published by John Wiley & Sons, Inc.). 1 / Tg(K)=W1 / Tg1+W2 / Tg2+····+W n / Tg n W n ; Mass fraction of each monomer Tgn ;This refers to the Tg(K) of the homopolymer of each monomer, and you can use publicly available values ​​such as those found in the Polymer Handbook (3rd Ed., J. Brandrup and E. Himmergut, WILEY INTERSCIENCE). The same applies to the Tg of the second polymer portion, which will be discussed later.

[0111] The first polymer portion included in the above (meth)acrylic acid ester copolymer may be a homopolymer or a copolymer, but a homopolymer is preferred. The monomer and polymer components constituting the first polymer portion may be any monomer and polymer components that can obtain a first polymer portion with a predetermined Tg, and examples include acrylic acid ester 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 including the polar group mentioned above, and copolymers such as EVA.

[0112] The Tg of the second polymer portion contained in the above (meth)acrylic acid ester copolymer is 20°C or higher, and can be within the range of 20°C to 150°C, more particularly within the range of 30°C to 150°C, and especially within the range of 40°C to 150°C.

[0113] Furthermore, the second polymer portion included in the (meth)acrylic acid ester copolymer may be a homopolymer or a copolymer, but a homopolymer is preferred. The monomer component constituting the second polymer portion may be any monomer component that can obtain a second polymer portion with a predetermined Tg, and examples 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, methacrylonitrile, and polar group-containing monomers including the polar group mentioned above.

[0114] A specific example of a (meth)acrylic acid ester copolymer having the above-mentioned first polymer portion and second polymer portion is the above-mentioned MMA-BA-MMA copolymer.

[0115] The acrylic resin content 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, when the total resin components in the first adhesive layer are considered to be 100 parts by mass. If the acrylic resin content is too low, the adhesion to the substrate after foam curing, the crack resistance after foam curing, and the adhesiveness after foam curing may decrease. On the other hand, the acrylic resin content may be, for example, 60 parts by mass or less, when the total resin components in the first adhesive layer are considered to be 100 parts by mass, 50 parts by mass or less, 40 parts by mass or less, 35 parts by mass or less, or 30 parts by mass or less, when the total resin components in the first adhesive layer are considered to be 100 parts by mass. If the acrylic resin content is too high, the content of the first epoxy resin and the second epoxy resin will be relatively low, and it may not be possible to balance non-stick properties, blocking resistance, adhesion to the substrate after foam curing, crack resistance after foam curing, and adhesiveness after foam curing. Also, if the acrylic resin content is too high, the film strength may decrease.

[0116] (iii) Hardener In this embodiment, a curing agent commonly 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 has a longer 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. Furthermore, the curing agent may be one that undergoes a curing reaction with heat, or one that undergoes a curing reaction with light. The curing agent may be used alone, or two or more types may be used.

[0117] The reaction initiation temperature of the curing agent is, for example, 110°C or higher, and may also be 130°C or higher. If the reaction initiation temperature is too low, the reaction may start too early, and curing may occur with low flexibility and fluidity of the resin components, making uniform curing difficult. 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 components may deteriorate. In addition to epoxy resin, if a heat-resistant resin such as phenolic resin is used, the deterioration of the resin components is less, so the reaction initiation temperature of the curing agent may be, for example, 300°C or lower. The reaction initiation temperature of the curing agent can be determined by differential scanning calorimetry (DSC).

[0118] Specific examples of curing agents 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.

[0119] 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, carboxylate salts of imidazole compounds, and adducts with epoxy compounds. Furthermore, it is preferable that the imidazole-based curing agent has hydroxyl groups. Because crystallization occurs through hydrogen bonding between hydroxyl groups, the reaction initiation temperature tends to be high.

[0120] Examples of phenolic curing agents include phenolic resins. Examples of phenolic resins include resol-type phenolic resins and novolac-type phenolic resins. From the viewpoint of adhesion to the substrate after foam curing and crack resistance after foam curing, phenolic novolac resins with a Tg of 110°C or lower are particularly preferred. Furthermore, a phenolic curing agent and an imidazole-type curing agent may be used in combination. In that case, it is preferable to use an imidazole-type curing agent as a curing catalyst.

[0121] Examples of amine-based curing agents include aliphatic amines such as diethylenetriamine (DETA), triethylenetetramine (TETA), and metaxylylenediamine (MXDA); aromatic amines such as diaminodiphenylmethane (DDM), m-phenylenediamine (MPDA), and diaminodiphenylsulfone (DDS); alicyclic amines; and polyamidoamines. In addition, dicyandiamide-based curing agents such as dicyandiamide (DICY), organic acid dihydrazide-based curing agents, amine adduct-based curing agents, and ketimine-based curing agents can be used as amine-based curing agents.

[0122] Examples of acid anhydride-based curing agents include alicyclic acid anhydrides (liquid acid anhydrides) such as hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA); and aromatic acid anhydrides such as trimellitic anhydride (TMA), pyromellitic anhydride (PMDA), and benzophenonetetracarboxylic acid (BTDA).

[0123] Examples of isocyanate-based curing agents include blocked isocyanates.

[0124] Examples of thiol-based curing agents include ester-bonded thiol compounds, aliphatic ether-bonded thiol compounds, and aromatic ether-bonded thiol compounds.

[0125] The curing agent content is, for example, 1 part by mass or more and 40 parts by mass or less, when the resin component contained in the first adhesive layer is considered to be 100 parts by mass. For example, when an imidazole-based curing agent is used as the main component of the curing agent, the curing agent content is preferably, for example, 1 part by mass or more and 15 parts by mass or less, when the resin component contained in the first adhesive layer is considered to be 100 parts by mass. On the other hand, when a phenol-based curing agent is used as the main component of the curing agent, the curing agent content is preferably, for example, 5 parts by mass or more and 40 parts by mass or less, when the resin component contained in the first adhesive layer is considered to be 100 parts by mass. 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 largest in the curing agent.

[0126] (b) foaming agent In this embodiment, the first adhesive layer may or may not contain a foaming agent, but it is preferable that it contains a foaming agent. The inclusion of a foaming agent increases the surface roughness, decreases the coefficient of friction, and further improves the slipperiness. Therefore, of the first and second adhesive layers, it is preferable that the first adhesive layer, which has lower tack, contains a foaming agent.

[0127] As the foaming agent, a foaming agent commonly used in the adhesive layer of foamed adhesive sheets can be used. Furthermore, the foaming agent may be one that undergoes a foaming reaction upon heating, or one that undergoes a foaming reaction upon exposure to light.

[0128] The foaming initiation temperature of the foaming agent is preferably above the softening temperature of the main component of the curable adhesive, such as epoxy resin, and below the activation temperature of the curing reaction of the main component of the curable adhesive, such as epoxy resin. The foaming initiation temperature of the foaming agent is, for example, 70°C or higher, and may also be 100°C or higher. If the foaming initiation temperature is too low, the reaction may start too early, and foaming may occur with low flexibility and fluidity of the resin component, 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.

[0129] Furthermore, the softening temperature of the main component of curable adhesives such as epoxy resins can be measured using the ring-spherical softening temperature test method specified in JIS K7234.

[0130] Examples of foaming agents include microencapsulated foaming agents. Microencapsulated foaming agents preferably have a core made of a thermal expandable agent such as a hydrocarbon, and a shell made of a resin such as an acrylonitrile copolymer.

[0131] Furthermore, as a blowing agent, for example, organic blowing agents or inorganic blowing agents may be used. Examples of organic blowing agents include azo blowing agents such as azodicarbonamide (ADCA), azobisformamide, and azobisisobutyronitrile; fluoride alkane blowing agents such as trichloromonofluoromethane; hydrazine blowing agents such as p-toluenesulfonyl hydrazide; semicarbazide blowing agents such as p-toluenesulfonyl semicarbazide; 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.

[0132] 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 within 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 less than or equal to the thickness of the first adhesive layer, for example, it may be 44 μm or less, 30 μm or less, or 24 μm or less.

[0133] The average particle size of the foaming agent is the particle size at 50% of the integrated particle size distribution determined by laser diffraction scattering. Furthermore, when measuring 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, and can be 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.

[0134] The foaming agent content is, for example, 0.5 parts by mass or more, but may be 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 foaming agent content is, for example, 25 parts by mass or less, but may be 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 foaming agent content is too low, the static friction coefficient of the surface of the first adhesive layer may increase. Also, if the foaming agent content is too high, the content of the curable adhesive will be relatively low, which may reduce the adhesiveness after foaming and curing.

[0135] (c) Other ingredients In this embodiment, the first adhesive layer may contain only epoxy resin and acrylic resin as resin components, or it may further contain other resins, for example, when the curable adhesive is an epoxy resin-based adhesive.

[0136] The total ratio of the primary epoxy resin, secondary epoxy resin, and acrylic resin to the resin component contained in the first adhesive layer is, for example, 70% by mass or more, may be 80% by mass or more, may be 90% by mass or more, or may be 100% by mass.

[0137] The resin component content in the first adhesive layer is, for example, 60% by mass or more, may be 70% by mass or more, may be 80% by mass or more, or may be 90% by mass or more.

[0138] The first adhesive layer may optionally contain additives such as silane coupling agents, fillers, antioxidants, light stabilizers, UV absorbers, lubricants, plasticizers, antistatic agents, crosslinking agents, and colorants. 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 phenolic antioxidants and sulfur-based antioxidants.

[0139] (2) Composition of the first adhesive layer If the first adhesive layer further contains a foaming agent, the first adhesive layer can be foamed at a foaming ratio of, for example, 4 times or more and 15 times or less. For example, if only the first adhesive layer contains a foaming agent, the foaming ratio may be, for example, 5 times or more, 7 times or more, or 9 times or more. Also, in the above case, the foaming ratio may be, for example, 14 times or less, 13 times or less, or 12 times or less. On the other hand, if both the first adhesive layer and the second adhesive layer contain a foaming agent, the foaming ratio may be, for example, 5 times or more, 6 times or more, or 7 times or more. Also, in the above case, the foaming ratio may be, for example, 14 times or less, 12 times or less, or 10 times or less. If the foaming ratio is too small or too large, the adhesiveness after foaming and curing may decrease.

[0140] Here, the expansion ratio can be calculated using the following formula. Foaming ratio (times) = Thickness of the first adhesive layer after foaming and curing / Thickness of the first adhesive layer before foaming and curing

[0141] The thickness of the first adhesive layer is not particularly limited, but if the first adhesive layer contains a foaming agent, it is preferably greater than or equal to the average particle size of the foaming agent, for example, 10 μm or more, but may also be 15 μm or more, or 20 μm or more. If the first adhesive layer is too thin, it may not be possible to obtain sufficient adhesion to the substrate and adhesion after foaming and curing. On the other hand, the thickness of the first adhesive layer is, for example, 200 μm or less, but may also be 150 μm or less, or 100 μm or less. If the first adhesive layer is too thick, the surface quality may deteriorate.

[0142] Here, the thickness of the first adhesive layer is measured from a cross-section in the thickness direction of the foamed adhesive sheet observed by a transmission electron microscope (TEM), scanning electron microscope (SEM), or scanning transmission electron microscope (STEM), and can be the average of the thicknesses of 10 randomly selected locations. The same method can be used to measure the thickness of other layers of the foamed adhesive sheet.

[0143] The first adhesive layer may be a continuous layer or a discontinuous layer. Examples of discontinuous layers include patterns such as stripes and dots. The surface of the first adhesive layer may also have an uneven shape such as an embossed surface.

[0144] The first adhesive layer can be formed, for example, by applying an adhesive composition containing the above-mentioned curable adhesive and foaming agent, 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, dip coating, and the like.

[0145] The adhesive composition may or may not contain a solvent. In this specification, "solvent" has a broad meaning, including not only a strict solvent (a solvent that dissolves the solute) but also a dispersion medium. Furthermore, any solvent contained in the adhesive composition is removed by volatilization when the adhesive composition is applied and dried to form an adhesive layer.

[0146] Adhesive compositions can be obtained by mixing the above-mentioned components and kneading and dispersing them as necessary. Suitable mixing and dispersion methods include general kneading and dispersing machines such as two-roll mills, three-roll mills, pebble mills, thron mills, Szegvari attritors, high-speed impeller dispersers, high-speed stone mills, high-speed impact mills, despersers, high-speed mixers, ribbon blenders, conespers, intensive mixers, tumblers, blenders, despersers, homogenizers, and ultrasonic dispersers.

[0147] 3.Second adhesive layer (1) Material of the second adhesive layer The second adhesive layer in this embodiment contains a curable adhesive.

[0148] (a) Curing adhesive The curable adhesive included 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.

[0149] The following explanation will provide an example of a case where the curing adhesive is an epoxy resin-based adhesive.

[0150] (i) epoxy resin The epoxy resin in this embodiment can be the same as the epoxy resin used in the first adhesive layer described above.

[0151] As the epoxy resin, epoxy resins generally used for the adhesive layer of foamed adhesive sheets can be used.

[0152] Examples of epoxy resins include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of epoxy resins can be the same as the specific examples of the first epoxy resin used in the first adhesive layer described above.

[0153] The epoxy resin may be a monofunctional epoxy resin, a bifunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or more functional epoxy resin.

[0154] In particular, it is preferable to use epoxy resins that are liquid at room temperature, such as bisphenol A type epoxy resin or bisphenol F type epoxy resin, and epoxy resins with a low softening point. This is because using these epoxy resins makes it easier to adjust the tack of the second adhesive layer within a predetermined range.

[0155] (ii) Acrylic resin If the curable adhesive is an epoxy resin-based adhesive, the second adhesive layer may further contain an acrylic resin compatible with the epoxy resin. This can improve film-forming properties.

[0156] The acrylic resin can be the same as the acrylic resin used in the first adhesive layer described above.

[0157] (iii) Hardener The curing agent in this embodiment can be the same as the curing agent used in the first adhesive layer described above. In addition, both a curing agent that is solid at room temperature and 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.

[0158] (b) foaming agent In this embodiment, the second adhesive layer may or may not contain a foaming agent, but it is preferable that it contains a foaming agent. By having both the first and second adhesive layers contain a foaming agent, the adhesion between the first and second adhesive layers after foaming and curing can be improved.

[0159] The foaming agent can be the same as the foaming agent used in the first adhesive layer described above.

[0160] (c) Other ingredients In this embodiment, the second adhesive layer may contain only epoxy resin and acrylic resin as resin components, or it may further contain other resins, for example, when the curable adhesive is an epoxy resin-based adhesive.

[0161] The total ratio of epoxy resin and acrylic resin to the resin component contained in the second adhesive layer is, for example, 70% by mass or more, may be 80% by mass or more, may be 90% by mass or more, or may be 100% by mass.

[0162] The resin component content in the second adhesive layer is, for example, 60% by mass or more, may be 70% by mass or more, may be 80% by mass or more, or may be 90% by mass or more.

[0163] The second adhesive layer may contain additives as needed. The additives may be the same as those used in the first adhesive layer.

[0164] (2) Composition of the second adhesive layer If the second adhesive layer further contains a foaming agent, the second adhesive layer can be foamed at a foaming ratio of, for example, 1.5 times or more and 12 times or less. For example, if both the first and second adhesive layers contain a foaming agent, the foaming ratio may be, for example, 2 times or more, 3 times or more, or 4 times or more. In the above case, the foaming ratio may also be, for example, 10 times or less, 9 times or less, or 8 times or less. If the foaming ratio is too low or too high, the adhesiveness after foaming and curing may decrease.

[0165] The thickness of the second adhesive layer can be the same as the thickness of the first adhesive layer.

[0166] The second adhesive layer may be a continuous layer or a discontinuous layer. Furthermore, the surface of the second adhesive layer may have an uneven shape, such as an embossed surface.

[0167] The method for forming the second adhesive layer can be the same as the method for forming the first adhesive layer described above.

[0168] 4.Base material In this embodiment, the substrate is placed between the first adhesive layer and the second adhesive layer described above.

[0169] The base material is preferably insulating. Furthermore, the base material is preferably in sheet form. The base material may have a single-layer structure or a multi-layer structure. The base material may or may not have a porous structure internally.

[0170] Examples of substrates include resin substrates and nonwoven fabrics.

[0171] Examples of resins included in the resin substrate include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyesters; polycarbonate; polyarylate; polyurethane; polyamide resins such as polyamide and polyetheramide; polyimide resins such as polyimide, polyetherimide, and polyamideimide; polysulfone resins such as polysulfone and polyethersulfone; polyetherketone resins such as polyetherketone and polyetheretherketone; polyphenylene sulfide (PPS); and modified polyphenylene oxide. The glass transition temperature of the resin is, for example, 80°C or higher, may be 140°C or higher, or 200°C or higher. Liquid crystal polymer (LCP) may also be used as the resin.

[0172] Examples of nonwoven fabrics include those 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.

[0173] The substrate may be surface-treated to improve adhesion with the first and second adhesive layers.

[0174] The thickness of the base material 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 base material thinner than the thickness of the first and second adhesive layers, the thickness of the foamed adhesive sheet can be reduced, while the thickness of the first and second adhesive layers can be made relatively thicker. Therefore, the thickness of the foamed adhesive sheet can be reduced and the insertability improved without reducing the adhesive properties or foaming properties of the first and second adhesive layers.

[0175] Specifically, the thickness of the substrate is 200 μm or less, may be 100 μm or less, or 50 μm or less. Furthermore, the thickness of the substrate is, for example, 2 μm or more, may be 5 μm or more, or 9 μm or more.

[0176] 5. Other components (1) First mesolayer and second mesolayer The foamed adhesive sheet in this embodiment may have a first intermediate layer between the substrate and the first adhesive layer. Alternatively, the foamed adhesive sheet in this embodiment may have a second intermediate layer between the substrate and the second adhesive layer. The presence of the first and second intermediate layers improves the adhesion of the first and second adhesive layers to the substrate. Furthermore, the presence of the first and second intermediate layers can, for example, alleviate stress on the bent portion when the foamed adhesive sheet is folded, or alleviate stress on the cut portion when the foamed adhesive sheet is cut. As a result, lifting and peeling of the first and second adhesive layers from the substrate can be suppressed when the foamed adhesive sheet is bent or cut.

[0177] For example, in the foamed adhesive sheet 10 shown in Figure 5, a first intermediate layer 4 is placed between the base material 2 and the first adhesive layer 1, and a second intermediate layer 5 is placed between the base material 2 and the second adhesive layer 3. In Figure 5, the foamed adhesive sheet 10 has both the first intermediate layer 4 and the second intermediate layer 5, but it may have only one of them.

[0178] The foamed adhesive sheet may have at least one of a first intermediate layer and a second intermediate layer. For example, it may have only a first intermediate layer placed between the substrate and the first adhesive layer, or only a second intermediate layer placed between the substrate and the second adhesive layer, or it may have both a first intermediate layer placed between the substrate and the first adhesive layer and a second intermediate layer placed between the substrate and the second adhesive layer.

[0179] The materials included in the first and second intermediate layers are not particularly limited as long as they can improve the adhesion between the substrate and the first and second adhesive layers and relieve stress, and are appropriately selected depending on the materials of the substrate, the first adhesive layer, and the second adhesive layer. Examples include polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, polymers obtained by copolymerizing at least two of these, crosslinked products thereof, and mixtures thereof.

[0180] The crosslinked material is a crosslinked material obtained by crosslinking the above-mentioned resin with a curing agent. Examples of curing agents include isocyanate-based curing agents. Furthermore, for example, when the reactive group / NCO equivalent is set to 1, it is preferable to add the isocyanate-based curing agent to the resin in a ratio of 0.5% by mass or more and 20% by mass or less.

[0181] In particular, the first and second intermediate layers preferably contain a cross-linked resin. A cross-linked resin is one that does not melt even at high temperatures. This improves the adhesive strength at high temperatures, i.e., the heat resistance.

[0182] The thickness of the first and second intermediate layers 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 and second intermediate layers are too thin, the effect of suppressing the peeling of the first and second adhesive layers from the substrate when the foamed adhesive sheet is bent and cut may not be sufficiently obtained. On the other hand, the thickness of the first and second intermediate layers may be, for example, 4 μm or less, or 3.5 μm or less. Since the first and second intermediate layers themselves do not usually have high heat resistance, if the first and second intermediate layers are too thick, the heat resistance (adhesion strength at high temperatures) may decrease.

[0183] The first and second intermediate layers 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.

[0184] (2) First separator and second separator In this embodiment, the foamed adhesive sheet may have a first separator on the side of the first adhesive layer opposite to the second adhesive layer. Furthermore, in this embodiment, the foamed adhesive sheet may have a second separator on the side of the second adhesive layer opposite to the first adhesive layer.

[0185] The first and second separators are not particularly limited as long as they can be peeled off from the first and second adhesive layers, and can have sufficient strength to protect the first and second adhesive layers. Examples of such first and second separators include release films and release paper. Furthermore, the first and second separators may have a single-layer structure or a multi-layer structure.

[0186] Examples of single-layer separators include fluororesin-based films.

[0187] Furthermore, examples of multilayer separators include laminates having release layers on one or both sides of a base layer. Examples of base layers include resin films such as polypropylene, polyethylene, and polyethylene terephthalate, and papers such as fine paper, coated paper, and impregnated paper. The material of the release layer is not particularly limited as long as it has release properties, and examples include silicone compounds, organic compound-modified silicone compounds, fluorine compounds, amino alkyd compounds, melamine compounds, acrylic compounds, polyester compounds, and long-chain alkyl compounds. These compounds can be used in emulsion, solvent, or solvent-free forms.

[0188] The first separator and the second separator may be the same or different. In particular, it is preferable that the first separator has heavy peelability and the second separator has light peelability. In a foamed adhesive sheet, the first adhesive layer is substantially non-adhesive (tack-free), and the second adhesive layer has tack. Therefore, for example, when bonding a rotor and permanent magnets in an embedded magnet type motor, if the foamed adhesive sheet is placed on the second member and then the second member with the foamed adhesive sheet is inserted into the hole of the first member, the adhesion between the second member and the foamed adhesive sheet, and the ease of inserting the second member with the foamed adhesive sheet can be improved by attaching the side of the second adhesive layer of the foamed adhesive sheet to the second member and making the side of the first adhesive layer of the foamed adhesive sheet the outer surface. In this case, since the second separator will be the first to peel off, having the first separator have heavy peelability and the second separator have light peelability makes it easier to peel off the second separator than the first separator.

[0189] Furthermore, "light peeling" and "heavy peeling" refer to the degree of force required to separate the first and second separators from the first and second adhesive layers, respectively. Light peeling means that the peeling force is less than that of heavy peeling.

[0190] 6. Foamed adhesive sheet In this embodiment, the thickness of the foamed adhesive sheet is, for example, 10 μm or more, and may be 20 μm or more. On the other hand, the thickness of the foamed adhesive sheet is, for example, 1000 μm or less, and may be 200 μm or less.

[0191] The use of the foamed adhesive sheet in this embodiment is not particularly limited. The foamed adhesive sheet in this embodiment can be used, for example, to bond two members together by placing the foamed adhesive sheet between them and then foaming and curing the foamed adhesive sheet. In particular, the foamed adhesive sheet in this embodiment is preferably used when bonding the first and second members by placing the foamed adhesive sheet on the second member, inserting the second member with the foamed adhesive sheet into the hole of the first member, and then foaming and curing the foamed adhesive sheet.

[0192] The method for manufacturing the foamed adhesive sheet in this embodiment is not particularly limited and can be appropriately selected depending on the layer structure of the foamed adhesive sheet. For example, the following two methods for manufacturing the foamed adhesive sheet can be given.

[0193] In the first method for manufacturing a foamed adhesive sheet, for example, first, an adhesive composition for forming a first adhesive layer is applied to one side of a substrate and dried to form the first adhesive layer. Next, an adhesive composition for forming a second adhesive layer is applied to a second separator and dried to form the second adhesive layer. Then, the laminate of the substrate and the first adhesive layer is laminated with the laminate of the second separator and the second adhesive layer. This yields a foamed adhesive sheet. A first intermediate layer and a second intermediate layer may also be formed. In this method, since there is only one drying step for the first adhesive layer, a foamed adhesive sheet can be manufactured efficiently.

[0194] In the second method for manufacturing a foamed adhesive sheet, for example, first, an adhesive composition for forming a first adhesive layer is applied to one surface of the 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 yields a foamed adhesive sheet. A first intermediate layer and a second intermediate layer may also be formed.

[0195] II. Second Embodiment A second embodiment of the foamed adhesive sheet in this disclosure is a foamed 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 tack of the first adhesive layer is 0 gf or more and less than 10 gf, the tack of the adhesive layer is 10 gf or more, and the loop stiffness is 50 mN / 10 mm or more.

[0196] Figure 6 is a schematic cross-sectional view illustrating a foamed adhesive sheet in this embodiment. The foamed adhesive sheet 10 in Figure 6 has, in this order, a first adhesive layer 1, a substrate 2, a second adhesive layer 3, and an adhesive layer 6. The first adhesive layer 1 and the second adhesive layer 3 contain a curable adhesive and a foaming agent, and the adhesive layer 6 contains a pressure-sensitive adhesive or a curable adhesive. Furthermore, the tack of the first adhesive layer 1 and the tack of the adhesive layer 6 are within a predetermined range, and the loop stiffness of the foamed adhesive sheet 10 is within a predetermined range.

[0197] In this embodiment, by having the tack of the adhesive layer within a predetermined range, an adhesive layer with good adhesion to the member can be obtained. Specifically, when one member is to be bonded to a hole or groove in one member, the adhesive surface of the foam adhesive sheet is attached to the other member, the other member with the foam adhesive sheet attached is inserted into the hole or groove in the first member, and then the foam adhesive sheet is foamed and hardened to bond the first and second members, by having the tack of the adhesive layer within a predetermined range, the tack of the adhesive layer can be used to attach the adhesive surface of the foam adhesive sheet to the other member, thereby improving the adhesion of the adhesive layer to the member. As a result, when inserting the other member with the foam adhesive sheet attached into the hole or groove in the first member, peeling or displacement of the foam adhesive sheet can be suppressed.

[0198] Furthermore, in this embodiment, since the tack of the first adhesive layer is below a predetermined value, the first adhesive layer can be made substantially non-adhesive (tack-free), resulting in a first adhesive layer with good sliding properties. Therefore, for example, in the above adhesive fixing method, when inserting the other member to which the foam adhesive sheet is attached into a hole or groove of the other member, the other member to which the foam adhesive sheet is attached can be inserted smoothly, improving insertability. This suppresses peeling and displacement of the foam adhesive sheet. Also, in the above adhesive fixing method, when aligning the members by moving the other member relative to the other member, the other member can be moved smoothly relative to the first member while it is inserted into a hole or groove of the other member, making alignment easy.

[0199] Furthermore, in this embodiment, since the tack of the first adhesive layer is below a predetermined value and the first adhesive layer is substantially non-adhesive (tack-free), the first adhesive layer can be made to have good slipperiness and good blocking resistance. Therefore, the handling of the foamed adhesive sheet can also be improved.

[0200] Furthermore, in this embodiment, as described above, the adhesive layer has excellent adhesion to the material, and the first adhesive layer has excellent slipperiness, which can suppress peeling and displacement of the foamed adhesive sheet. Therefore, it is possible to suppress the decrease in adhesiveness of the foamed adhesive sheet after foaming and curing due to peeling and displacement of the foamed adhesive sheet, and to reduce the variation in adhesive strength of the foamed adhesive sheet after foaming and curing due to peeling and displacement of the foamed adhesive sheet. Thus, by using the foamed adhesive sheet of this embodiment, it is possible to achieve high adhesive strength, high reliability, and high quality adhesion.

[0201] Furthermore, in the foamed adhesive sheet of this embodiment, the loop stiffness is above a predetermined value, making it highly rigid. Therefore, when the foamed adhesive sheet is transported, it is possible to suppress the sagging of the foamed adhesive sheet due to its own weight. Thus, for example, when the foamed adhesive sheet is transported by suction and attached to another member, it is possible to suppress the occurrence of bending, twisting, bending, and air bubble entrapment of the foamed adhesive sheet during attachment. Thus, the adhesive properties can be improved. Moreover, since it is possible to suppress the occurrence of bulges in the foamed adhesive sheet due to these defects, it is possible to reduce friction of the foamed adhesive sheet when inserting the other member to which the foamed adhesive sheet has been attached into holes or grooves of the other member. Thus, it is possible to suppress the peeling of the foamed adhesive sheet during insertion. Therefore, from these points as well, by using the foamed adhesive sheet of this embodiment, it is possible to achieve high adhesive strength, high reliability, and high quality adhesion.

[0202] The following describes the various components of the foamed adhesive sheet in this embodiment.

[0203] 1.Characteristics The tack of the first adhesive layer in this embodiment is the same as the tack of the first adhesive layer in the first embodiment described above.

[0204] In this embodiment, the tack of the adhesive layer is 10 gf or more, may be 30 gf or more, or may be 50 gf or more. If the tack of the adhesive layer is too low, for example, in the adhesive fixing method described above, when using the tack of the adhesive layer to attach the adhesive surface of the foam adhesive sheet to the other member, there is a possibility that the adhesion between the adhesive layer and the other member will decrease. Also, when inserting the other member to which the foam adhesive sheet has been attached into a hole or groove of the one member, poor adhesion between the adhesive layer and the other member may cause the foam adhesive sheet to peel off or shift position, which may reduce the adhesion between the first adhesive layer and the adhesive layer after foam curing, or cause variations in adhesive strength. Furthermore, the tack of the adhesive layer is, for example, 500 gf or less, may be 400 gf or less, or may be 300 gf or less.

[0205] In this embodiment, the tack of the second adhesive layer is not particularly limited. In particular, the tack of the second adhesive layer is preferably less than 10 gf. In this case, the tack of the second adhesive layer can be the same as that of the first adhesive layer.

[0206] The method for measuring the tack of the first adhesive layer, the second adhesive layer, and the adhesive layer is the same as that described in the first embodiment above.

[0207] Furthermore, the method for controlling the tack of the first and second adhesive layers is the same as that described in the first embodiment above.

[0208] In this embodiment, the static friction coefficient of the surface of the first adhesive layer opposite to the second adhesive layer, and the arithmetic mean roughness (Ra) of the surface of the first adhesive layer opposite to the second adhesive layer are the same as those described in the first embodiment above.

[0209] The loop stiffness of the foamed adhesive sheet in this embodiment is the same as that of the foamed adhesive sheet in the first embodiment described above. In this embodiment, when placing a test piece of the foamed adhesive sheet on the loop stiffness measuring instrument, the test piece of the foamed 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 adhesive layer.

[0210] The adhesive properties and electrical insulation properties of the foamed adhesive sheet after foaming and curing in this embodiment are the same as those described in the first embodiment above.

[0211] 2.First adhesive layer The first adhesive layer in this embodiment contains a curable adhesive and a foaming agent. The material and composition of the first adhesive layer can be the same as those of the first adhesive layer in the first embodiment described above.

[0212] 3.Second adhesive layer The second adhesive layer in this embodiment contains a curable adhesive and a foaming agent. The material and composition of the second adhesive layer may be the same as those of the first adhesive layer in the first embodiment, or the same as those of the second adhesive layer in the first embodiment.

[0213] 4. Adhesive layer In this embodiment, the adhesive layer is positioned on the side opposite to the substrate of the second adhesive layer and contains a pressure-sensitive adhesive or a curing adhesive. Furthermore, the adhesive layer substantially does not contain a foaming agent.

[0214] In this embodiment, a general-purpose pressure-sensitive adhesive can be used as the pressure-sensitive adhesive included in the adhesive layer.

[0215] 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.

[0216] The thickness of the adhesive layer is not particularly limited, but for example, it may be between 2 μm and 100 μm, between 3 μm and 75 μm, or between 5 μm and 50 μm. If the adhesive layer is too thin, sufficient adhesiveness may not be obtained.

[0217] The adhesive layer may be a continuous layer or a discontinuous layer. Examples of discontinuous layers include patterns such as stripes and dots. The surface of the adhesive layer may also have an uneven shape such as embossing.

[0218] 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.

[0219] 5.Base material In this embodiment, the substrate is placed between the first adhesive layer and the second adhesive layer described above. The substrate is the same as the substrate in the first embodiment.

[0220] 6. Other components (1) First mesolayer and second mesolayer The foamed adhesive sheet in this embodiment may have a first intermediate layer between the substrate and the first adhesive layer. Alternatively, the foamed adhesive sheet in this embodiment may have a second intermediate layer between the substrate and the second adhesive layer. The first and second intermediate layers are the same as those in the first embodiment described above.

[0221] For example, in the foamed adhesive sheet 10 shown in Figure 7, a first intermediate layer 4 is placed between the base material 2 and the first adhesive layer 1, and a second intermediate layer 5 is placed between the base material 2 and the second adhesive layer 3. In Figure 7, the foamed adhesive sheet 10 has both the first intermediate layer 4 and the second intermediate layer 5, but it may have only one of them.

[0222] (2) First separator and second separator In this embodiment, the foamed adhesive sheet may have a first separator on the side of the first adhesive layer opposite to the second adhesive layer. Alternatively, the foamed adhesive sheet may have a second separator on the side of the adhesive layer opposite to the second adhesive layer. The first and second separators can be the same as those in the first embodiment described above.

[0223] 7. Foamed adhesive sheet The thickness and application of the foamed adhesive sheet in this embodiment are the same as in the first embodiment described above.

[0224] The method for manufacturing the foamed adhesive sheet in this embodiment is not particularly limited and can be appropriately selected depending on the layer structure of the foamed adhesive sheet.

[0225] B. Method of manufacturing articles The method for manufacturing an article in this disclosure comprises a placement step of placing the above-mentioned foaming adhesive sheet between a first member and a second member, and an bonding step of foaming and curing the foaming adhesive sheet to bond the first member and the second member.

[0226] Figures 8(a) to 8(c) are process diagrams showing an example of a method for manufacturing an article according to this disclosure. First, as shown in Figure 8(a), the surface of the second adhesive layer 3 of the foamed adhesive sheet 10 is attached to the second member 20b. Next, as shown in Figure 8(b), the second member 20b with the foamed adhesive sheet 10 is inserted into the hole of the first member 20a. Then, as shown in Figure 8(c), the first adhesive layer 1 and the second adhesive layer 3 of the foamed 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. As a result, an article 100 is obtained with the adhesive sheet 13 placed between the first member 20a and the second member 20b.

[0227] Figures 9(a) to 9(c) are process diagrams illustrating other examples of the method for manufacturing an article according to this disclosure. In Figure 9(a), foam adhesive sheets are attached to both sides of the second member 20b. The placement and bonding processes are the same as those in Figures 8(a) to 8(c).

[0228] The method for manufacturing articles as described in this disclosure is described below.

[0229] 1. Foamed adhesive sheet In the method for manufacturing an article described herein, the foamed adhesive sheet described above is used as the foamed adhesive sheet.

[0230] If the foamed adhesive sheet has a first separator and a second separator, when placing the foamed adhesive sheet between the first and second members, the first separator and the second separator should be peeled off from the foamed adhesive sheet before use.

[0231] Further details regarding the foamed adhesive sheet are described in section "A. Foamed Adhesive Sheet" above, so an explanation will be omitted here.

[0232] 2.Placement process In the arrangement process described herein, the method for arranging the foam adhesive sheet between the first member and the second member is appropriately selected depending on the types of the first member and the second member. For example, when the first member has holes or grooves and the second member is to be arranged in the holes or grooves of the first member, and the first member and the second member are to be fixed by adhesive, one method is to use the tack of the second adhesive layer or adhesive layer of the foam adhesive sheet to attach the surface of the second adhesive layer or adhesive layer of the foam adhesive sheet to the second member, and then arrange the second member with the foam adhesive sheet attached in the holes or grooves of the first member. Another method is to arrange the foam adhesive sheet in the holes or grooves of the first member, use the tack of the second adhesive layer or adhesive layer of the foam adhesive sheet to attach the surface of the second adhesive layer or adhesive layer of the foam adhesive sheet to the holes or grooves of the first member, and then arrange the second member in the holes or grooves of the first member with the foam adhesive sheet attached.

[0233] 3.Gluing process In the bonding process described herein, methods for foaming and curing the foamed adhesive sheet include, for example, heating or light irradiation. Among these, foaming and curing the foamed adhesive sheet by heating is preferred. The heating method is applicable even when the first and second members are not transparent, such as when they are made of metal.

[0234] The heating conditions are set appropriately depending on the type of curable adhesive and foaming agent contained in the first and second adhesive layers, 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.

[0235] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure. [Examples]

[0236] [Manufacturing example] First, adhesive compositions 1 to 3 with the following compositions were prepared.

[0237] <Adhesive composition 1> • Acrylic resin (PMMA-PBuA-PMMA (partially containing acrylamide groups), Tg: -20℃, 120℃, 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 • Hardener 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 range: 155°C to 173°C (manufactured by Shikoku Chemicals, Inc., 2PHZ-PW)): 8 parts by mass • Foaming agent (thermally expandable microcapsules, average particle size 10 μm to 16 μm, expansion start 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

[0238] <Adhesive composition 2> • Acrylic resin (PMMA-PBuA-PMMA (partially containing acrylamide groups), Tg: -20℃, 120℃, Mw: 150,000): 40 parts by mass • Epoxy resin C (Bisphenol A type, liquid at room temperature, epoxy equivalent: 184-194 g / eq): 45 parts by mass • Epoxy resin D (diaminodiphenylmethane type, high viscosity liquid, epoxy equivalent: 110-130 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 • Hardening agent B (phenol-formaldehyde polycondensate, softening point 80°C, hydroxyl group 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 range: 155°C to 173°C (manufactured by Shikoku Chemicals Co., Ltd., 2PHZ-PW)): 10 parts by mass • Foaming agent: Thermally expandable microcapsules, average particle size 10 μm to 16 μm, expansion start 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

[0239] <Adhesive composition 3> • Acrylic resin (PMMA-PBuA-PMMA (partially containing acrylamide groups), Tg: -20℃, 120℃, 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: 184-194 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 • Hardening agent B (phenol-formaldehyde polycondensate, softening point 80°C, hydroxyl group equivalent 104 g / mol): 19 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 range: 155°C to 173°C (manufactured by Shikoku Chemicals, Inc., 2PHZ-PW)): 2 parts by mass • Foaming agent: Thermally expandable microcapsules, average particle size 10 μm to 16 μm, expansion start temperature 123°C to 133°C, maximum expansion temperature 168°C to 178°C, core: hydrocarbon, shell: thermoplastic polymer: 8.5 parts by mass • Preservative stabilizer (boric acid ester compound): 9 parts by mass • Solvent (methyl ethyl ketone): 39 parts by mass

[0240] [Example 1] A polyethylene naphthalate (PEN) film (Teonex Q5100, manufactured by Toyobo Co., Ltd., 25 μm thick) was used as the substrate. A resin composition was prepared by mixing 15 parts by mass of a curing agent (polyisocyanate) and 0.3 parts by mass of a catalyst (trisdimethylaminomethylphenol) with 100 parts by mass of polyester polymer, and then diluting with methyl ethyl ketone (MEK) to a solid content of 15% by mass. 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 substrate opposite to the first intermediate layer using an applicator to a thickness of 50 μm after coating. It was then dried in an oven at 100°C for 3 minutes to form a first adhesive layer.

[0241] Next, a release film (PET separator, manufactured by Nipper Co., Ltd., PET50×1-J2, 50 μm thick) was used as the second separator. The adhesive composition 2 described above was applied to the release-treated surface of the release film using an applicator so that the thickness after coating was 50 μm. After that, it was dried in an oven at 100°C for 3 minutes to form the second adhesive layer.

[0242] 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. This resulted in a foamed 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.

[0243] [Example 2] A foamed adhesive sheet was prepared in the same manner as in Example 1, except that the thickness of the first and second adhesive layers was set to 45 μm.

[0244] [Example 3] A foamed adhesive sheet was prepared in the same manner as in Example 1, except that adhesive composition 3 was used to form the second adhesive layer and the thickness of the second adhesive layer was set to 45 μm.

[0245] [Comparative Example 1] A foamed adhesive sheet was produced in the same manner as in Example 1, except that the adhesive composition 2 was used for forming the first adhesive layer.

[0246] [Comparative Example 2] A foamed adhesive sheet was produced in the same manner as in Comparative Example 1, except that a polyphenylene sulfide (PPS) film (manufactured by Toray Industries, Inc., Torelina 25-3030, thickness 25 μm) was used as the base material.

[0247] [Comparative Example 3] A foamed adhesive sheet was produced in the same manner as in Comparative Example 1, except that the thickness of the base material (PEN film) was 50 μm.

[0248] [Comparative Example 4] A foamed adhesive sheet was produced in the same manner as in Comparative Example 1, except that a polyethylene terephthalate (PET) film (manufactured by Toray Industries, Inc., Lumirror #25-S105, thickness 50 μm) was used as the base material.

[0249] [Evaluation] (1) Tack of the first adhesive layer and the second adhesive layer Regarding the tack of the first adhesive layer, using a tacking tester "TAC-II" manufactured by RHESCA, a cylindrical stainless steel probe with a diameter of 5 mm was pressed against the surface of the first adhesive layer of the foamed adhesive sheet at a temperature of 25°C, a load of 10.0 gf, and a speed of 30 mm / min, held for 1.0 second, and then peeled off at a speed of 30 mm / min, and the load at the time of peeling was measured. This measurement was performed 5 times, and the average value was taken as the tack.

[0250] Similar to the tack of the first adhesive layer, the tack of the second adhesive layer was also measured. At this time, after peeling the second separator from the foamed adhesive sheet, the tack of the second adhesive layer was measured.

[0251] (2) Loop stiffness After peeling off the second separator from the foaming 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-described method for measuring loop stiffness. As the measuring instrument, a loop stiffness tester (registered trademark) manufactured by Toyo Seiki Seisakusho Co., Ltd. was used. The environment during measurement was a temperature of 23°C and a relative humidity of 50%.

[0252] (3) Sag amount Figs. 10(a) to (b) are schematic diagrams for explaining the method of measuring the sag amount of the foaming adhesive sheet. The foaming adhesive sheet 10 was cut into a size of 10 mm in width and 100 mm in length after peeling off the second separator to obtain a test piece. Further, the jig 51 has a rectangular parallelepiped shape, and the lower surface 51a of the jig 51 is rectangular, flat, and horizontal. Further, a double-sided adhesive tape 52 (「Y-4920-25」manufactured by 3M) was attached to the lower surface 51a of the jig 51.

[0253] First, as shown in Fig. 10(a), in a normal temperature and normal humidity environment, the surface of the double-sided adhesive tape 52 of the jig 51 was attached to the center of the foaming adhesive sheet 10 to fix the foaming adhesive sheet 10. The sticking area was 10 mm × 10 mm. At this time, when the surface of the double-sided adhesive tape 52 of the jig 51 was attached to the surface of the first adhesive layer of the foaming adhesive sheet 10, the adherend surface was defined as the first adhesive layer. On the other hand, when the surface of the double-sided adhesive tape 52 of the jig 51 was attached to the surface of the second adhesive layer of the foaming adhesive sheet 10, the adherend surface was defined as the second adhesive layer.

[0254] Next, as shown in Fig. 10(b), the jig 51 was lifted vertically upward. At this time, the end portion 10a of the foaming adhesive sheet 10 sagged vertically downward. Then, with the surface S1 of the double-sided adhesive tape 52 of the jig 51 as the reference surface, the vertical distance from this reference surface S1 to the end portion 10a of the foaming adhesive sheet 10 was measured, and this was defined as the sag amount F. The sag amount was calculated as the average value of three test pieces prepared from the foaming adhesive sheet, with one measurement for each test piece.

[0255] (4) Affixability In the same manner as the measurement of the amount of sagging described above, the double-sided adhesive tape side of the jig was attached to the center of the foam adhesive sheet test piece to fix the foam adhesive sheet, and then the jig was 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 foam adhesive sheet. Next, a metal plate was placed below the foam adhesive sheet that was lifted by the jig, and the jig was lowered vertically downward to adhere the foam adhesive sheet to the metal plate. The condition of the foam adhesive sheet was then observed visually, and the adhesion properties were evaluated according to the following criteria. A: The foam adhesive sheet was applied without any creases or air bubbles. B: The foamed adhesive sheet was creased and air bubbles were trapped inside.

[0256] (5) Insertability (slipperiness of the first adhesive layer during insertion) A foamed adhesive sheet cut to 5.5 cm x 8.0 cm, 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 prepared. The second separator was peeled off the foamed adhesive sheet, and the surface of the second adhesive layer was attached to the outer diameter of cylinder 2 so that the shorter side was facing circumferentially, and the foamed adhesive sheet was placed there. Then, cylinder 2 was slowly pushed by hand and inserted into the hollow gap of cylinder 1, and the slipperiness of the first adhesive layer at that time was evaluated. The evaluation criteria were as follows. A: There is no resistance when inserting it. B: There is resistance during insertion (the first adhesive layer sticks to cylinder 1, making insertion difficult).

[0257] [Table 1]

[0258] [Table 2]

[0259] From a comparison between Examples 1-3 and Comparative Examples 3-4 and Comparative Examples 1-2, it was confirmed that when the loop stiffness is 50 mN / 10 mm or more, the amount of sagging is reduced and the adhesive properties are good. In addition, in Examples 1-3, the tack of the first adhesive layer and the tack of the second adhesive layer were within the specified range, resulting in good insertability. [Explanation of symbols]

[0260] 1 … First adhesive layer 2...Base material 3...Second adhesive layer 4 … First middle layer 5…Second intermediate layer 10… Foamed adhesive sheet 15… Adhesive sheet after foam curing 20a ... First component 20b ... Second member 100 … Goods

Claims

1. A foamed adhesive sheet having a first adhesive layer, a substrate, and a second adhesive layer in this order, 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 tack of the first adhesive layer is 0 gf or more and less than 10 gf. The tack of the second adhesive layer is 10 gf or more and 500 gf or less. A foamed adhesive sheet having a loop stiffness of 50 mN / 10 mm or more.

2. The foamed adhesive sheet according to claim 1, wherein the first adhesive layer contains the foaming agent.

3. The foaming adhesive sheet according to claim 2, wherein the first adhesive layer and the second adhesive layer contain the foaming agent.

4. A foamed adhesive sheet having a first adhesive layer, a substrate, a second adhesive layer, and an adhesive layer in this order, 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 curing adhesive, The tack of the first adhesive layer is 0 gf or more and less than 10 gf. The tack of the adhesive layer is 10 gf or more. A foamed adhesive sheet having a loop stiffness of 50 mN / 10 mm or more.

5. The foamed adhesive sheet according to claim 4, wherein the tack of the second adhesive layer is 0 gf or more and less than 10 gf.

6. The foamed adhesive sheet according to any one of claims 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 placement step of placing the foamed adhesive sheet according to any one of claims 1 to 6 between the first member and the second member, A bonding step of foaming and curing the foamed adhesive sheet to bond the first member and the second member, A method for manufacturing an article, comprising:

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