JP7204971B1 - Expandable adhesive sheet and method for producing article - Google Patents

Abstract

A foamable adhesive sheet and a method for manufacturing an article using the sheet are provided. A foamable adhesive sheet (10) having a first adhesive layer (1), a substrate (2) and a second adhesive layer (3) in this order, wherein the composition of the first adhesive layer (1) and the second adhesive layer (1) 3, the first adhesive layer 1 and the second adhesive layer 3 contain a thermosetting adhesive, and at least one of the first adhesive layer 1 and the second adhesive layer 3 is foamed agent, and the foamable adhesive sheet after standing for 15 hours at a temperature of 60° C. and a humidity of 10% RH or less has a curl radius of 15 mm or more and a loop stiffness of 45 mN/10 mm or more. The foamable adhesive sheet 10 is provided. [Selection drawing] Fig. 1

Description

TECHNICAL FIELD The present disclosure relates to a foamable adhesive sheet and a method of manufacturing an article using the same.

Adhesives for bonding members together are widely used in various fields. For example, an adhesive is used when fixing one member to a hole or groove of the other member.

A liquid adhesive is mainly used as the adhesive when fixing the other member to a hole or groove of one member. However, in the case of a liquid adhesive, there is a problem that coating unevenness, extrusion, liquid dripping, etc. occur, which complicates the bonding process.

On the other hand, in recent years, it has been proposed to use a sheet-like adhesive containing a foaming agent (expandable adhesive sheet) instead of the liquid adhesive (see, for example, Patent Document 1). According to the foamable adhesive sheet, it is possible to suppress the occurrence of problems in the case of the liquid adhesive as described above.

Japanese Patent No. 6874867

When fixing the other member to a hole or groove of one member, for example, as described in Patent Document 1, a foam adhesive sheet is attached to the other member to temporarily fix it, and the hole of one member The other member to which the foamable adhesive sheet is attached is placed in the groove or the like, and then the foamable adhesive sheet is foamed and cured to bond and fix the two members.

When one member is fixed to the hole or groove of the other member, the gap between the two members tends to be narrowed. Therefore, the foamable adhesive sheet to be used is required to have a small overall thickness.

By the way, in a foamable adhesive sheet, it has been proposed to dispose adhesive layers on both sides of a substrate so that the properties of the two adhesive layers are different. For example, Patent Literature 1 discloses that two adhesive layers have different coefficients of expansion.

However, in a foamable adhesive sheet, if the two adhesive layers are different, curling may occur. In particular, when the thickness of the expandable adhesive sheet is reduced, curling tends to occur. In this case, there is a problem that the foamable adhesive sheet is prevented from sticking to the member, or the foamable adhesive sheet is lifted or peeled off. In such a case, the adhesiveness after foaming and curing is lowered and the reliability is lowered.

In addition, if the thickness of the expandable adhesive sheet is thin, the expandable adhesive sheet tends to sag under its own weight during transportation of the expandable adhesive sheet. For example, when an expandable adhesive sheet is transported by suction, if the expandable adhesive sheet is thin, both ends of the expandable adhesive sheet tend to sag under its own weight. Therefore, when the expandable adhesive sheet is conveyed by suction and attached to a member, there is a problem that the expandable adhesive sheet may be folded, twisted, bent, or entrapped by air bubbles during attachment. Furthermore, if the foamable adhesive sheet is attached to a member with such a problem, the foamable adhesive sheet will bulge. Another problem is that when the other member is inserted, the foam adhesive sheet is rubbed and peeled off. Even in such a case, the adhesiveness after foaming and curing is lowered and the reliability is lowered.

The present disclosure has been made in view of the above circumstances, and a main object of the present disclosure is to provide a foamable adhesive sheet capable of suppressing curling and having excellent sticking properties.

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

Another embodiment of the present disclosure includes an arrangement step of arranging the foamable adhesive sheet described above between a first member and a second member, heating the foamable adhesive sheet to foam and cure, and forming the first member and a bonding step of bonding the second member.

The foamable adhesive sheet according to the present disclosure can suppress curling and has an effect of being excellent in sticking properties.

1 is a schematic cross-sectional view illustrating an expandable adhesive sheet in the present disclosure; FIG. It is a schematic diagram explaining the measuring method of the curvature radius of curl. 1A and 1B are a schematic plan view and a cross-sectional view illustrating a loop stiffness measuring device; FIG. It is a schematic diagram explaining the measuring method of loop stiffness. It is a schematic diagram explaining the measuring method of loop stiffness. 1 is a schematic cross-sectional view illustrating an expandable adhesive sheet in the present disclosure; FIG. 1 is a schematic cross-sectional view illustrating an expandable adhesive sheet in the present disclosure; FIG. 1 is a process diagram illustrating a method of manufacturing an article in the present disclosure; FIG. 1 is a process diagram illustrating a method of manufacturing an article in the present disclosure; FIG. It is a schematic diagram explaining the evaluation method of sticking property.

Embodiments of the present disclosure will be described below with reference to the drawings and the like. However, the present disclosure can be embodied in many different modes and should not be construed as limited to the description of the embodiments exemplified below. In addition, in order to make the description clearer, the drawings may schematically show the width, thickness, shape, etc. of each part compared to the actual form, but this is only an example and limits the interpretation of the present disclosure. not something to do. In addition, in this specification and each figure, the same reference numerals may be given to the same elements as those described above with respect to the existing figures, and detailed description thereof may be omitted as appropriate.

In this specification, when expressing a mode in which another member is arranged on top of a certain member, the term “above” or “below” simply means that it is in contact with a certain member unless otherwise specified. , arranging another member directly above or below, and arranging another member above or below a certain member via another member. In addition, in this specification, when expressing a mode in which another member is arranged on the surface of a certain member, when simply describing “on the surface side” or “on the surface”, unless otherwise specified, It includes both the case of arranging another member directly above or directly below so as to be in contact with it, and the case of arranging another member above or below a certain member via another member.

In this specification, the term "sheet" also includes a member called "film". The term "film" also includes members called "sheets".

The foamable adhesive sheet and the method for manufacturing an article using the same according to the present disclosure will be described in detail below.

A. Foamable Adhesive Sheet The foamable adhesive sheet in the present disclosure is a foamable adhesive sheet having a first adhesive layer, a base material, and a second adhesive layer in this order, wherein the composition of the first adhesive layer and the above Different from the composition of the second adhesive layer, the first adhesive layer and the second adhesive layer contain a thermosetting adhesive, and at least one of the first adhesive layer and the second adhesive layer contains a foaming agent. The foamable adhesive sheet after standing for 15 hours at a temperature of 60° C. and a humidity of 10% RH or less has a curl radius of 15 mm or more and a loop stiffness of 45 mN/10 mm or more.

FIG. 1 is a schematic cross-sectional view illustrating an expandable adhesive sheet in the present disclosure. The expandable adhesive sheet 10 in FIG. 1 has a first adhesive layer 1, a substrate 2, and a second adhesive layer 3 in this order. The first adhesive layer 1 and the second adhesive layer 3 contain a thermosetting adhesive, and at least one of the first adhesive layer 1 and the second adhesive layer 3 further contains a foaming agent. Further, the expandable adhesive sheet 10 has a curl radius of curvature within a predetermined range after being left at a predetermined temperature and humidity for a predetermined time, and a loop stiffness within a predetermined range.

Here, when one member is adhesively fixed to the hole or groove of the other member, the gap between the two members tends to be narrowed as described above. Therefore, the foamable adhesive sheet to be used is required to have a small overall thickness. However, when the foamable adhesive sheet has a first adhesive layer, a substrate, and a second adhesive layer in this order, if the compositions of the first adhesive layer and the second adhesive layer are different, the thickness of the foamable adhesive sheet is If it is too thin, it will curl easily. In addition, if the thickness of the expandable adhesive sheet is thin, the expandable adhesive sheet tends to sag under its own weight during transportation of the expandable adhesive sheet.

On the other hand, in the present disclosure, when the composition of the first adhesive layer and the second adhesive layer are different because the radius of curvature of the curl after standing at a predetermined temperature and humidity for a predetermined time is within a predetermined range , curling can be suppressed even when the thickness of the expandable adhesive sheet is thin. Therefore, for example, when inserting a foamable adhesive sheet between two members, after placing the foamable adhesive sheet in a hole or groove of one member, the hole in the one member where the foamable adhesive sheet is placed When inserting the other member into a hole or groove, etc., after placing the foamable adhesive sheet on the other member, inserting the other member with the foamable adhesive sheet placed into the hole or groove of the other member In addition, insertability can be improved. Further, for example, when the tack of the first adhesive layer is lower than the tack of the second adhesive layer, the tack of the second adhesive layer is used to attach the surface of the second adhesive layer of the foamable adhesive sheet to the member. In this case, lifting and peeling of the expandable adhesive sheet from the member can be suppressed. Moreover, in the above case, it is possible to suppress the occurrence of folding, twisting, bending, entrapment of air bubbles, etc. of the foamable adhesive sheet at the time of attachment. Therefore, poor adhesion after foaming and curing can be suppressed.

In addition, the inventors of the present disclosure paid attention to the stiffness of the expandable adhesive sheet. When the foamable adhesive sheet is thick, it tends to have high rigidity, so it is thought that curling and sagging due to its own weight can be suppressed. However, when the gap between the two members is narrow, increasing the thickness of the expandable adhesive sheet deteriorates the insertability. As described above, since the thickness of the expandable adhesive sheet should be thin in the first place, it is not suitable to increase the thickness of the expandable adhesive sheet. In addition, when the thickness of the base material is large, the rigidity tends to be high, so it is thought that curling can be suppressed and sagging due to its own weight can be suppressed. However, if the thickness of the base material is increased, the thickness of the foamable adhesive sheet is also increased, resulting in poor insertability in the same manner as described above. In addition, if the thickness of the base material is made relatively thick while the thickness of the foamable adhesive sheet is kept thin, the thicknesses of the first adhesive layer and the second adhesive layer become relatively thin. Also, the adhesive properties and foaming properties of the second adhesive layer may deteriorate.

The inventors of the present disclosure conducted further studies and found that by setting the loop stiffness of the foamable adhesive sheet within a predetermined range, the foamable adhesive sheet can be prevented from sagging under its own weight.

Note that the loop stiffness is a parameter representing the stiffness of a sheet or film. The higher the loop stiffness value, the stiffer the sheet or film. Loop stiffness is used, for example, as a parameter representing the stiffness of sheets and films used as packaging materials, but it is not so common in the field of adhesive sheets.

Since the foamable adhesive sheet according to the present disclosure has a loop stiffness equal to or higher than a predetermined value, it is possible to increase stiffness. Therefore, it is possible to prevent the foamable adhesive sheet from sagging due to its own weight when the foamable adhesive sheet is transported. Therefore, for example, when an expandable adhesive sheet is adsorbed and conveyed and attached to a member, it is possible to prevent the expandable adhesive sheet from folding, twisting, bending, and entrapment of air bubbles during attachment. can. Therefore, sticking property can be improved. Furthermore, since it is possible to suppress the occurrence of bumps in the foamable adhesive sheet due to these defects, the other member to which the foamable adhesive sheet is attached is inserted into the hole or groove of one member. At the same time, the foamable adhesive sheet can be made resistant to rubbing. Therefore, peeling of the expandable adhesive sheet during insertion can be suppressed.

Therefore, by using the foamable adhesive sheet of the present disclosure, it is possible to achieve high adhesion strength, high reliability, and high quality adhesion.

Here, "adhesion" is a concept included in "adhesion". Adhesion is sometimes used to mean a temporary adhesion phenomenon, whereas adhesion is used to mean a substantially permanent adhesion phenomenon (Iwanami Shoten Rikagaku Jiten, 5th edition). The terms "tackiness" and "tackiness" refer to the property of adhering by pressure sensitivity and the adhesive force at that time.

As used herein, the terms "adhesiveness of the adhesive layer" and "adhesive strength of the adhesive layer" refer to the adhesiveness and adhesive strength of the adhesive layer prior to curing, unless there are special circumstances. In this specification, unless there are special circumstances, the terms "adhesiveness of the adhesive layer" and "adhesive strength of the adhesive layer" refer to the adhesiveness and adhesive strength of the cured adhesive layer.

Each configuration of the expandable adhesive sheet in the present disclosure will be described below.

1. Characteristics In the expandable adhesive sheet of the present disclosure, the curl radius of curvature after standing for 15 hours at a temperature of 60° C. and a humidity of 10% RH or less is 15 mm or more, preferably 20 mm or more, and more preferably 25 mm. That's it. When the radius of curvature is within the above range, curling can be suppressed. Therefore, for example, when inserting a foamable adhesive sheet between two members, after placing the foamable adhesive sheet in a hole or groove of one member, the hole in the one member where the foamable adhesive sheet is placed When inserting the other member into a hole or groove, etc., after placing the foamable adhesive sheet on the other member, inserting the other member with the foamable adhesive sheet placed into the hole or groove of the other member In addition, insertability can be improved. Further, for example, when the tack of the first adhesive layer is lower than the tack of the second adhesive layer, the tack of the second adhesive layer is used to attach the surface of the second adhesive layer of the foamable adhesive sheet to the member. In this case, lifting and peeling of the expandable adhesive sheet from the member can be suppressed. Moreover, in the above case, it is possible to suppress the occurrence of folding, twisting, bending, entrapment of air bubbles, etc. of the foamable adhesive sheet at the time of attachment. Therefore, poor adhesion after foaming and curing can be suppressed. On the other hand, the larger the radius of curvature, the smaller the curl, so the upper limit of the radius of curvature is not particularly limited.

When the foam adhesive sheet is used, for example, to bond coils and stators in a motor or to bond rotors and permanent magnets in an embedded magnet type motor, the length of the foam adhesive sheet is often about 100 mm. . Therefore, in the present disclosure, when the length of the test piece of the expandable adhesive sheet is 100 mm, it is practical if the test piece does not make one turn in the length direction, and the radius of curvature is set to 15 mm or more. bottom.

Moreover, in the thermosetting adhesive, curing shrinkage and heat shrinkage occur during the curing process. Curl results from this shrinkage. In general, thermosetting adhesives are considered to start shrinking at about 60°C. Therefore, since the main shrinkage factor of thermosetting adhesives is heat, in order to exclude the influence of humidity, in the present disclosure, the conditions are set to 60° C. for 15 hours, and the humidity is set to 10% RH or less.

Here, the radius of curvature of the curl of the expandable adhesive sheet can be measured by the following method.

First, a foamable adhesive sheet is cut into a square of 50 mm×50 mm to prepare a test piece for curl measurement. At this time, as shown in FIG. 2( a ), the directions of the sides of the square are the MD direction and the TD direction of the expandable adhesive sheet 10 . The MD direction of the expandable adhesive sheet refers to the longitudinal direction of the expandable adhesive sheet when the expandable adhesive sheet is produced in a long shape. Moreover, the TD direction of the expandable adhesive sheet refers to a direction perpendicular to the MD direction. The MD direction and TD direction of the foamable adhesive sheet can be specified by the following method. When the foamable adhesive sheet is elongated, the longitudinal direction of the foamable adhesive sheet is defined as the MD direction. Further, in the case where the foamable adhesive sheet is sheet-shaped, if it is known in advance that the base material, the first adhesive layer and the second adhesive layer have anisotropy, the base material and the first adhesive By measuring the tensile strength and elongation of the layer and the second adhesive layer, the MD direction and TD direction of the expandable adhesive sheet can be identified from these tensile strengths and elongation rates. In addition, when the foamable adhesive sheet is sheet-shaped and the anisotropy of the base material and the anisotropy of the first adhesive layer and the second adhesive layer are unknown, the foamable adhesive sheet may be set to a diameter of 50 mm. A test piece for direction measurement is prepared by cutting it into a circle of about 100 degrees, and the test piece for direction measurement is left at a temperature of 60 ° C., and the direction in which the test piece for direction measurement is curled is covered with the foaming adhesive sheet. can be regarded as the MD direction of

Next, the test piece for curl measurement is allowed to stand at a temperature of 60° C. and a humidity of 10% RH or less for 15 hours. At this time, when at least one of the first adhesive layer and the second adhesive layer has stickiness, the test piece for curl measurement is in a state where the surface of the adhesive layer having stickiness does not touch the surroundings. Above all, it is preferable that the test piece for curl measurement is in a state in which its own weight is not applied in the curl direction. Next, the chord length d of the curl of the test piece for curl measurement is measured as shown in FIG. 2(b). Then, the radius of curvature r is calculated using the following formula.
L=r×θ
d=2×r×sin(θ/2)
(In the above formula, L is the arc length, d is the chord length, r is the radius of curvature, and θ is the central angle.)
The chord length d is measured in each of the cases where the direction of the chord length d is the MD direction, the TD direction, and the 45° direction with respect to the MD direction, and the radius of curvature r is calculated. Then, among the curvature radii r in these cases, the smallest value is adopted. When the direction of the chord length d is the MD direction or the TD direction, the arc length L is 50 mm. Further, when the direction of the chord length d is set at 45° to the MD direction, the arc length L is L=50×√2=70.7 mm.

In the present disclosure, the curl radius of curvature of the foamable adhesive sheet can be controlled by adjusting the thickness and hardness of each layer, for example. For example, a thick substrate tends to have a large radius of curvature. Further, for example, if the hardness of the substrate is high, the radius of curvature tends to be large. Further, for example, when the hardness of the first adhesive layer is higher than the hardness of the second adhesive layer, the radius of curvature tends to increase as the thickness of the second adhesive layer increases. Further, when the hardness of the first adhesive layer and the second adhesive layer are approximately the same, the radius of curvature tends to be large if the thicknesses of the first adhesive layer and the second adhesive layer are approximately the same.

The hardness of the first adhesive layer and the second adhesive layer can be controlled by adjusting the composition of the first adhesive layer and the second adhesive layer. Further, in the first adhesive layer and the second adhesive layer, the lower the tack, the higher the hardness, and the higher the tack, the lower the hardness. Further, in the first adhesive layer and the second adhesive layer, the higher the storage elastic modulus, the higher the hardness, and the lower the storage elastic modulus, the lower the hardness. Further, in the first adhesive layer and the second adhesive layer, the higher the pencil hardness, the higher the hardness, and the lower the pencil hardness, the lower the hardness. Further, in the first adhesive layer and the second adhesive layer, if the coefficient of static friction is low, the hardness tends to be high, and if the pencil hardness is high, the hardness tends to be low.

The foamable adhesive sheet of the present disclosure has a loop stiffness of 45 mN/10 mm or more, preferably 75 mN/10 mm or more, and more preferably 100 mN/10 mm or more. Loop stiffness is a parameter that represents the stiffness of a film or sheet, as described above. Since the loop stiffness of the foamable adhesive sheet is within the above range, the foamable adhesive sheet can be made stronger. Therefore, when arranging the expandable adhesive sheet between the two members, it is possible to improve the insertability. In addition, for example, when the expandable adhesive sheet is conveyed by suction and attached to a member, it is possible to suppress the expandable adhesive sheet from sagging due to its own weight, thereby improving the attachment properties. On the other hand, the upper limit of loop stiffness is not particularly limited.

A method of measuring loop stiffness will be described below with reference to FIGS.

FIG. 3(a) is a schematic plan view showing a loop stiffness measuring device, and FIG. 3(b) is a sectional view taken along the line AA of FIG. 3(a). A test piece of the expandable adhesive sheet 10 is rectangular with long sides and short sides. In the present disclosure, the length L1 of the long side of the test piece of the expandable adhesive sheet 10 is 200 mm, and the length L2 of the short side is 10 mm. As the loop stiffness measuring device 30, a loop stiffness tester (DR) manufactured by Toyo Seiki Seisakusho Co., Ltd. can be used. The length L1 of the long side of the test piece of the expandable adhesive sheet 10 can be adjusted as long as the test piece of the expandable adhesive sheet 10 can be gripped by a pair of chuck portions 31, which will be described later.

The loop stiffness measuring instrument 30 has a pair of chuck portions 31 for gripping a pair of longitudinal ends of the test piece of the expandable adhesive sheet 10 and a support member 32 for supporting the chuck portions 31 . The chuck part 31 has a first chuck 31a and a second chuck 31b. The foamable adhesive sheet 10 is placed on the pair of first chucks 31a, and the second chuck 31b has not yet gripped the foamable adhesive sheet 10 with the first chucks 31a. As will be described later, the expandable adhesive sheet 10 is gripped between the first chuck 31a and the second chuck 31b of the chuck portion 31 during measurement. The second chuck 31b may be connected to the first chuck 31a via a hinge mechanism.

First, as shown in FIGS. 3(a) and 3(b), a test piece of the expandable adhesive sheet 10 is placed on the first chucks 31a of the pair of chuck portions 31 spaced apart by an interval L3. At this time, in the present disclosure, the interval L3 is set so that the length of the loop portion 41 (hereinafter also referred to as loop length) is 60 mm. Subsequently, as shown in FIG. 4( a ), the second chuck 31 b is attached to the first chuck 31 a by foam bonding so as to grip the ends of the test piece of the foam adhesive sheet 10 in the long side direction. The sheet 10 is placed on top of the test piece.

Next, as shown in FIG. 4B, at least one of the pair of chuck portions 31 is slid on the support member 32 in the direction in which the distance between the pair of chuck portions 31 is reduced. Thereby, the loop portion 41 can be formed in the expandable adhesive sheet 10 . The test piece of the expandable adhesive sheet 10 shown in FIG. 4(b) has a loop portion 41, a pair of intermediate portions 42 and a pair of fixing portions 43. The pair of fixing portions 43 are portions of the test piece of the expandable adhesive sheet 10 that are held by the pair of chuck portions 31 . The pair of intermediate portions 42 are portions of the test piece of the expandable adhesive sheet 10 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 expandable adhesive sheet 10 come into contact with each other. Thereby, the loop portion 41 having a loop length of 60 mm can be formed. The loop length of the loop portion 41 is defined by the position P1 where the surface of the second chuck 31b on the loop portion 41 side and the test piece of the foamable adhesive sheet 10 intersect, and the surface of the second chuck 31b on the loop portion 41 side. is the length of the test piece of the expandable adhesive sheet 10 between the position P2 where the test piece of the expandable adhesive sheet 10 intersects. When ignoring the thickness of the test piece of the expandable adhesive sheet 10, the above-mentioned interval L3 is a value obtained by adding 2×t to the length of the loop portion 41. As shown in FIG. t is the thickness of the second chuck 31b of the chuck portion 31;

Next, as shown in FIG. 5A, the posture of the chuck portion 31 is adjusted so that the projection direction Y of the loop portion 41 with respect to the chuck portion 31 is horizontal. For example, the posture of the chuck portion 31 supported by the support member 32 is adjusted by moving the support member 32 so that the normal direction of the support member 32 faces the horizontal direction. In the example shown in FIG. 5A , the projecting direction Y of the loop portion 41 matches the thickness direction of the chuck portion 31 . In addition, the load cell 35 is prepared at a position apart from the second chuck 31b in the projecting direction Y of the loop portion 41 .

Subsequently, as shown in FIG. 5(b), the load cell 35 is moved toward the loop portion 41 of the test piece of the expandable adhesive sheet 10 to bring the load cell 35 into contact with the loop portion 41. Then, as shown in FIG. A distance Z1 is the distance between the load cell 35 and the second chuck 31b of the chuck portion 31 .

After that, as shown in FIGS. 5B to 5C, 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 15 mm. A speed V for moving the load cell 35 is set to 5 mm/sec.

Next, as shown in FIG. 5(c), the load cell 35 is moved toward the chuck portion 31 by a distance Z2, and in a state in which the load cell 35 is pushing the loop portion 41 of the test piece of the expandable adhesive sheet 10, the loop The value of the load applied from the portion 41 to the load cell 35 is recorded. Among the load values thus obtained, the maximum value of the load is taken as the loop stiffness of the expandable adhesive sheet 10 . In this specification, unless otherwise specified, the environment during the loop stiffness measurement is a temperature of 23° C. and a relative humidity of 50%.

In the measurement of the loop stiffness of the foamable adhesive sheet, when the test piece of the foamable adhesive sheet 10 is placed in the loop stiffness measuring instrument 30, the inner surface 40x is the surface of the first adhesive layer, and the outer surface 40y is the second adhesive layer. Measurements are taken both in the case of arranging so as to be the surface of the layer and in the case of arranging so that the inner surface 40x is the surface of the second adhesive layer and the outer surface 40y is the surface of the first adhesive layer. Then, among the loop stiffnesses in these cases, the larger value is adopted.

In addition, when measuring the loop stiffness of the foamable adhesive sheet, if the foamable adhesive sheet has a separator as described later, the loop stiffness of the foamable adhesive sheet is measured after peeling off the separator. . This is because the separator is peeled off from the foamable adhesive sheet when the foamable adhesive sheet is placed between the two members.

In the present disclosure, the loop stiffness of the expandable adhesive sheet can be controlled, for example, by adjusting the thickness and hardness of each layer. For example, thicker substrates tend to have greater loop stiffness. Further, for example, when the hardness of the base material is high, the loop stiffness tends to increase. Further, for example, when the hardness of the first adhesive layer is higher than the hardness of the second adhesive layer, the loop stiffness tends to increase as the thickness of the first adhesive layer increases. Also, when the hardness of the first adhesive layer and the second adhesive layer is high, the loop stiffness tends to increase.

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

The foamable adhesive sheet in the present disclosure preferably has high adhesiveness after foaming and curing. After foaming and curing of the foamable adhesive sheet, the shear strength (adhesive strength) based on JIS K6850 corresponding to ISO 4587 may be, for example, 1.50 MPa or more, or 1.80 MPa or more at 23 ° C. Well, it may be 2.10 MPa or more. Further, the shear strength (adhesive strength) at 130° C. may be, for example, 0.50 MPa or more, 0.75 MPa or more, or 1.00 MPa or more. For example, a high-strength acrylic foam pressure-sensitive adhesive tape that does not require heating has a shear strength (adhesive strength) of about 1 MPa to 2 MPa at room temperature, and does not have heat resistance at 200.degree. Therefore, if the shear strength (adhesive strength) is within the above range at 23° C., there is superiority in terms of strength. Further, if the shear strength (adhesive strength) is within the above range at 130° C., it can be applied to applications requiring heat resistance such as those around automobile engines.

The foamable adhesive sheet in the present disclosure preferably has high electrical insulation after foaming and curing. After foaming and curing of the foamable adhesive sheet, the dielectric breakdown voltage based on JIS C2107 corresponding to IEC 60454-2 is, for example, preferably 3 kV or higher, more preferably 5 kV or higher. When the dielectric breakdown voltage is within the above range, it can be applied to rust prevention and around copper wires. In addition, the thermal conductivity of the foamable adhesive sheet after foaming and curing is, for example, preferably 0.05 W/mK or more, and more preferably 0.10 W/mK or more. When the thermal conductivity is within the above range, the parts can be miniaturized, and the curing reaction during heating can be accelerated.

2. First Adhesive Layer and Second Adhesive Layer In the present disclosure, the first adhesive layer and the second adhesive layer contain a thermosetting adhesive. At least one of the first adhesive layer and the second adhesive layer further contains a foaming agent. Also, the composition of the first adhesive layer and the composition of the second adhesive layer are different.

Here, the difference between the composition of the first adhesive layer and the composition of the second adhesive layer means the type and content of the main agent constituting the thermosetting adhesive, the type and content of the curing agent constituting the thermosetting adhesive, and It means that at least one of the content, the type and content of resin components other than the main agent constituting the thermosetting adhesive, the type and content of the foaming agent, and the type and content of the additive is different. .

Among them, it is preferable that the first adhesive layer and the second adhesive layer contain a thermosetting adhesive and a foaming agent, and that the composition of the first adhesive layer and the composition of the second adhesive layer are different.

(1) Properties of First Adhesive Layer and Second Adhesive Layer (a) Hardness In the present disclosure, the first adhesive layer and the second adhesive layer preferably have different hardnesses. If the first adhesive layer and the second adhesive layer have different hardnesses, the foamable adhesive sheet tends to curl. Therefore, the present disclosure is effective when the hardness of the first adhesive layer and the second adhesive layer are different.

The hardness of the first adhesive layer and the second adhesive layer is not particularly limited as long as it is a measurable hardness parameter for the first adhesive layer and the second adhesive layer. Further, as indices of hardness of the first adhesive layer and the second adhesive layer, for example, tackiness of the first adhesive layer and the second adhesive layer; thermophysical properties such as glass transition temperature of the first adhesive layer and the second adhesive layer; etc. can be used.

(b) Tack In the present disclosure, it is preferable that the first adhesive layer and the second adhesive layer have different tacks. Here, in general, the adhesive layer tends to become softer as the adhesiveness (tack) increases, and tends to become harder as the adhesiveness (tack) decreases. Therefore, if the first adhesive layer and the second adhesive layer have different tacks, the foamable adhesive sheet tends to curl. Therefore, the present disclosure is effective when the first adhesive layer and the second adhesive layer have different tacks.

Further, when the first adhesive layer and the second adhesive layer have different tacks, and the tack of the first adhesive layer is lower than the tack of the second adhesive layer, the tack of the first adhesive layer is, for example, 0 gf or more and 10 gf. It is preferable that the tack of the second adhesive layer is, for example, 10 gf or more and 500 gf or less. In this case, the tack of the first adhesive layer may be, for example, 5 gf or less, or 2 gf or less. Moreover, in this case, the tack of the second adhesive layer may be, for example, 30 gf or more, or may be 50 gf or more. Also, the tack of the second adhesive layer may be, for example, 400 gf or less, or 300 gf or less.

In the above case, since the first adhesive layer and the second adhesive layer have different tacks, the foamable adhesive sheet tends to curl. Therefore, the present disclosure is effective.

Further, in the above case, the tack of the second adhesive layer is within the above range, so that the second adhesive layer can have good adhesion to the member. Specifically, when the other member is adhesively fixed to a hole or groove of one member, the surface of the second adhesive layer of the foamable adhesive sheet is attached to the other member, and the hole of the one member is attached. When the other member to which the foamable adhesive sheet is attached is inserted into the groove or the like, and then the foamable adhesive sheet is foamed and cured to bond the one member and the other member, the second adhesive layer is within a predetermined range, the surface of the second adhesive layer of the foamable adhesive sheet can be attached to the other member using the tack of the second adhesive layer, and the second adhesive layer on the member can increase the adhesion of. As a result, peeling and displacement of the foamable adhesive sheet can be suppressed when the member to which the foamable adhesive sheet is attached is inserted into the hole or groove of the other member.

In the above case, the tack of the second adhesive layer is within the above range, so that the second adhesive layer can have good reworkability. Therefore, for example, in the adhesive fixing method described above, misalignment of the foamable adhesive sheet is corrected when the surface of the second adhesive layer of the foamable adhesive sheet is attached to the member using the tack of the second adhesive layer. be able to.

Further, in the above case, the tack of the second adhesive layer is within the above range, so that when the second adhesive layer is formed by a transfer method, for example, the floating of the second adhesive layer can be suppressed. Furthermore, as will be described later, when the separator is arranged on the side opposite to the substrate of the second adhesive layer, the tack of the second adhesive layer is within a predetermined range, so that the separator can be easily removed. It can be peeled off easily, and workability can be improved.

In the above case, the tack of the first adhesive layer is within the above range, so that the first adhesive layer can be made substantially non-tacky (tack-free), and the first adhesive with good slipperiness can be layered. Therefore, for example, in the above adhesive fixing method, when inserting the other member to which the foamable adhesive sheet is attached into the hole or groove of one member, the other member to which the foamable adhesive sheet is attached may The member can be smoothly inserted, and insertability can be improved. As a result, peeling and displacement of the expandable adhesive sheet can be suppressed. Further, in the above bonding and fixing method, when aligning the members by moving the other member with respect to the other member, the other member is inserted into the hole or groove of the one member while the other member is inserted. The other member can be smoothly moved with respect to the other member, and positioning can be easily performed.

Furthermore, in the above case, since the tack of the first adhesive layer is within the above range, the first adhesive layer is substantially non-tacky (tack-free), so that the slip property is good and the blocking resistance is good. The first adhesive layer can also have good properties. Therefore, it is possible to improve the handleability of the foamable adhesive sheet.

In the above case, as described above, the second adhesive layer has excellent adhesion to the member, and the first adhesive layer has excellent slipperiness. can be suppressed. Therefore, it suppresses the deterioration of the adhesiveness of the foamable adhesive sheet after foaming and curing due to peeling and misalignment of the foamable adhesive sheet, and also suppresses the adhesion of the foamable adhesive sheet after foaming and curing due to peeling and misalignment of the foamable adhesive sheet. Variation in intensity can be reduced. Therefore, in the above case, by using the foamable adhesive sheet of the present disclosure, high adhesive strength, high reliability, and high quality adhesion can be achieved.

On the other hand, the first adhesive layer and the second adhesive layer may have the same tack.

Also, both the first adhesive layer and the second adhesive layer may have low tack. In this case, the tacks of the first adhesive layer and the second adhesive layer are preferably, for example, 0 gf or more and less than 10 gf. In this case, the tacks of the first adhesive layer and the second adhesive layer may each be, for example, 5 gf or less, or 2 gf or less. When the tacks of the first adhesive layer and the second adhesive layer are within the above ranges, respectively, the first adhesive layer and the second adhesive layer can be made substantially non-tacky (tack-free) and slippery. It can be a good first adhesive layer and second adhesive layer. Therefore, for example, when inserting a foamable adhesive sheet between two members, after placing the foamable adhesive sheet in a hole or groove of one member, the hole in the one member where the foamable adhesive sheet is placed When inserting the other member into a hole or groove, etc., after placing the foamable adhesive sheet on the other member, inserting the other member with the foamable adhesive sheet placed into the hole or groove of the other member In addition, insertability can be improved. As a result, peeling and displacement of the expandable adhesive sheet can be suppressed. Further, when aligning the members by moving the other member with respect to one member, the other member is moved with respect to the one member while the foamable adhesive sheet is arranged between the two members. It can be moved smoothly and alignment can be easily performed. In addition, when the tacks of the first adhesive layer and the second adhesive layer are within the above ranges, respectively, the first adhesive layer and the second adhesive layer can have good blocking resistance. Therefore, it is possible to improve the handleability of the foamable adhesive sheet.

Here, the tack of the first adhesive layer and the second adhesive layer can be measured by a probe tack test conforming to JIS Z3284-3:2014. As the probe tack tester, for example, a tack tester "TAC-II" manufactured by RHESCA can be used. The details of the method for measuring the tackiness of the first adhesive layer and the second adhesive layer will be described in the Examples section below.

In the present disclosure, the tackiness of the first adhesive layer and the second adhesive layer can be controlled, for example, by adjusting the composition of each adhesive layer.

Specifically, in an adhesive layer containing an epoxy resin and a curing agent, the tackiness of the 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. can. On the other hand, in the adhesive layer containing an epoxy resin and a curing agent, if an epoxy resin that is liquid at room temperature or a curing agent that is liquid at room temperature is used, the adhesion of the adhesive layer tends to increase.

In addition, in the adhesive layer containing an epoxy resin and a curing agent, by including an epoxy resin with a high softening temperature or an epoxy resin with a large weight average molecular weight, the adhesiveness of the adhesive layer can be reduced. On the other hand, if an adhesive layer containing an epoxy resin and a curing agent contains an epoxy resin with a low softening temperature or an epoxy resin with a small weight-average molecular weight, the adhesion of the adhesive layer tends to increase. For example, the adhesive layer contains a plurality of types of epoxy resins with different softening temperatures. The tackiness of the adhesive layer can be reduced by containing other epoxy resins having a temperature higher than 10°C. Alternatively, for example, the adhesive layer contains a plurality of types of epoxy resins having different weight average molecular weights. By containing another epoxy resin having a weight average molecular weight of 300 or more, the adhesiveness of the adhesive layer can be reduced. More specifically, in the adhesive layer containing an epoxy resin and a curing agent, as described later, a first epoxy resin having a low softening temperature and a low molecular weight and a second epoxy resin having a high softening temperature and a high molecular weight are used as epoxy resins. By containing a two-epoxy resin, the adhesiveness of the adhesive layer can be reduced.

Further, in the adhesive layer containing the epoxy resin and the curing agent, the adhesiveness of the adhesive layer can be reduced by including an acrylic resin that is compatible with the epoxy resin, as will be described later.

Also, the addition of a tackifying resin (tackifier) to the adhesive layer tends to increase the tackiness of the adhesive layer.

If a curing agent that is liquid at room temperature is used, the adhesiveness tends to increase, but the storage stability may decrease. The adjustment preferably adjusts the tackiness of the adhesive layer.

(c) Storage Modulus In the present disclosure, it is preferable that the first adhesive layer and the second adhesive layer have different viscoelasticities. Here, in general, the adhesive layer tends to be harder as the storage elastic modulus is higher, and softer as the storage elastic modulus is lower. Therefore, if the first adhesive layer and the second adhesive layer have different storage elastic moduli, the foamable adhesive sheet tends to curl. Therefore, the present disclosure is effective when the storage elastic moduli of the first adhesive layer and the second adhesive layer are different.

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

In the above case, the storage elastic modulus of the second adhesive layer is within the above range, so that the second adhesive layer can have good adhesion to the member. Specifically, when the other member is adhesively fixed to a hole or groove of one member, the surface of the second adhesive layer of the foamable adhesive sheet is attached to the other member, and the hole of the one member is attached. When the other member to which the foamable adhesive sheet is attached is inserted into the groove or the like, and then the foamable adhesive sheet is foamed and cured to bond the one member and the other member, the second adhesive layer When the storage elastic modulus of is within a predetermined range, the adhesion of the second adhesive layer can be enhanced by following the unevenness of the member using the softness of the second adhesive layer. As a result, peeling and displacement of the foamable adhesive sheet can be suppressed when the member to which the foamable adhesive sheet is attached is inserted into the hole or groove of the other member.

In the above case, the storage elastic modulus of the second adhesive layer is within the above range, so that the second adhesive layer can have good reworkability. Therefore, for example, in the adhesive fixing method described above, misalignment of the foamable adhesive sheet is corrected when the surface of the second adhesive layer of the foamable adhesive sheet is attached to the member by utilizing the softness of the second adhesive layer. can do.

In the above case, since the storage elastic modulus of the second adhesive layer is within the above range, for example, when the second adhesive layer is formed by a transfer method, lifting and deformation of the second adhesive layer are suppressed. be able to. Furthermore, as described later, when the separator is arranged on the side opposite to the base material of the second adhesive layer, the storage elastic modulus of the second adhesive layer is within a predetermined range, so that the separator can be easily peeled off, and workability can be improved.

In the above case, the storage elastic modulus of the first adhesive layer is within the above range, so that the first adhesive layer can have good slipperiness. Therefore, for example, in the above adhesive fixing method, when inserting the other member to which the foamable adhesive sheet is attached into the hole or groove of one member, the other member to which the foamable adhesive sheet is attached may The member can be smoothly inserted, and insertability can be improved. As a result, peeling and displacement of the expandable adhesive sheet can be suppressed. Further, in the above bonding and fixing method, when aligning the members by moving the other member with respect to the other member, the other member is inserted into the hole or groove of the one member while the other member is inserted. The other member can be smoothly moved with respect to the other member, and positioning can be easily performed.

Furthermore, in the above case, the storage elastic modulus of the first adhesive layer is within the above range, so that the first adhesive layer can have good slip properties and good anti-blocking properties. Therefore, it is possible to improve the handleability of the foamable adhesive sheet.

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

Also, the storage elastic modulus of both the first adhesive layer and the second adhesive layer may be high. In this case, the storage modulus E′(25) at 25° C. of the first adhesive layer and the second adhesive layer is, for example, 1.0×10 ⁶ Pa or more and 1.0×10 ¹⁰ Pa or less. preferable. In this case, the storage modulus E'(25) of the first adhesive layer and the second adhesive layer may each be, for example, 1.0×10 ⁷ Pa or more. Since the storage elastic modulus E′(25) of the first adhesive layer and the second adhesive layer is within the above range, the first adhesive layer and the second adhesive layer have good slipperiness. It can be an adhesive layer. Therefore, for example, when inserting a foamable adhesive sheet between two members, after placing the foamable adhesive sheet in a hole or groove of one member, the hole in the one member where the foamable adhesive sheet is placed When inserting the other member into a hole or groove, etc., after placing the foamable adhesive sheet on the other member, inserting the other member with the foamable adhesive sheet placed into the hole or groove of the other member In addition, insertability can be improved. As a result, peeling and displacement of the expandable adhesive sheet can be suppressed. Further, when aligning the members by moving the other member with respect to one member, the other member is moved with respect to the one member while the foamable adhesive sheet is arranged between the two members. It can be moved smoothly and alignment can be easily performed. Further, by setting E'(25) of the first adhesive layer and the second adhesive layer within the above ranges, the first adhesive layer and the second adhesive layer can have good blocking resistance. Therefore, it is possible to improve the handleability of the foamable adhesive sheet.

Here, the storage elastic moduli of the first adhesive layer and the second adhesive layer can be measured, for example, by a dynamic mechanical property test conforming to JIS K7244-4:1999. As the dynamic mechanical property tester, for example, a dynamic viscoelasticity measuring device manufactured by TA Instruments can be used. Also, the measurement conditions can be attachment mode: compression mode, frequency: 1 Hz, temperature: 25° C., temperature increase rate: 10° C./min.

In the present disclosure, the 25° C. storage modulus of the first adhesive layer and the second adhesive layer can be controlled, for example, by adjusting the composition of each adhesive layer.

Specifically, in an adhesive layer containing an epoxy resin and a curing agent, the storage modulus of the adhesive layer can be increased by using an epoxy resin that is solid at room temperature or using a curing agent that is solid at room temperature. can be done. On the other hand, in the adhesive layer containing an epoxy resin and a curing agent, if an epoxy resin that is liquid at room temperature or a curing agent that is liquid at room temperature is used, the storage modulus of the adhesive layer tends to be low.

In addition, the storage modulus of the adhesive layer can be increased by including an epoxy resin with a high softening temperature or an epoxy resin with a large weight-average molecular weight in the adhesive layer containing an epoxy resin and a curing agent. . On the other hand, if an adhesive layer containing an epoxy resin and a curing agent contains an epoxy resin with a low softening temperature or an epoxy resin with a small weight-average molecular weight, the storage modulus of the adhesive layer tends to decrease. For example, the adhesive layer contains a plurality of types of epoxy resins with different softening temperatures. The storage elastic modulus of the adhesive layer can be increased by containing other epoxy resins having a temperature higher than 10°C. Alternatively, for example, the adhesive layer contains a plurality of types of epoxy resins having different weight average molecular weights. By containing another epoxy resin having a weight average molecular weight of 300 or more, the storage elastic modulus of the adhesive layer can be increased. More specifically, in the adhesive layer containing an epoxy resin and a curing agent, as described later, a first epoxy resin having a low softening temperature and a low molecular weight and a second epoxy resin having a high softening temperature and a high molecular weight are used as epoxy resins. By containing a two-epoxy resin, the storage elastic modulus of the adhesive layer can be increased.

In addition, the storage modulus of the adhesive layer can be increased by including an acrylic resin compatible with the epoxy resin in the adhesive layer containing the epoxy resin and the curing agent, as described later.

If a curing agent that is liquid at normal temperature is used, the storage modulus tends to decrease, but the storage stability may decrease. is preferably adjusted to adjust the storage modulus of the adhesive layer.

(d) Pencil hardness In the present disclosure, it is preferable that the first adhesive layer and the second adhesive layer have different surface pencil hardnesses. Here, in general, the adhesive layer tends to be harder as the pencil hardness of the surface is higher, and softer as the pencil hardness of the surface is lower. Therefore, if the surfaces of the first adhesive layer and the second adhesive layer have different pencil hardnesses, the foamable adhesive sheet tends to curl. Therefore, the present disclosure is effective when the surfaces of the first adhesive layer and the second adhesive layer have different pencil hardnesses.

When the pencil hardness of the surface of the first adhesive layer and the second adhesive layer is different, and the pencil hardness of the surface of the first adhesive layer is higher than the pencil hardness of the surface of the second adhesive layer, the surface of the first adhesive layer The pencil hardness is, for example, HB or more, and the pencil hardness of the surface of the second adhesive layer is preferably, for example, less than HB. In this case, the pencil hardness of the surface of the first adhesive layer may be, for example, HB or more and 2H or less, or F or more and 2H or less. Further, in this case, the pencil hardness of the surface of the second adhesive layer may be B or less, for example. If the tackiness of the second adhesive layer is high and the pencil hardness of the surface of the second adhesive layer cannot be measured, the pencil hardness of the surface of the second adhesive layer is considered to be 6B or less.

Further, in the above case, by setting the pencil hardness of the surface of the first adhesive layer within the above range, the slipperiness of the first adhesive layer can be improved, and the anti-blocking property of the first adhesive layer can also be improved. On the other hand, if the pencil hardness of the surface of the first adhesive layer is too high, the adhesion of the first adhesive layer to the base material may decrease.

Further, in the above case, the pencil hardness of the surface of the second adhesive layer is within the above range, so that the adhesion of the second adhesive layer to the member can be improved.

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

Moreover, the pencil hardness of the surfaces of the first adhesive layer and the second adhesive layer may both be high. In this case, the pencil hardness of each of the surfaces of the first adhesive layer and the second adhesive layer is preferably, for example, HB or higher, may be HB or higher and 2H or lower, or may be F or higher and 2H or lower. When the pencil hardness is within the above range, it is possible to improve slipperiness and anti-blocking property. On the other hand, if the pencil hardness is too high, the adhesion of the adhesive layer to the substrate may decrease.

Here, the pencil hardness can be determined according to JIS K5600. Specifically, the following methods are mentioned. First, an A4 size foam adhesive sheet is prepared and set on a glass plate. Next, according to JIS K5600, a pencil hardness tester (with a level) is used to measure the pencil hardness of the surface of the foamable adhesive sheet on which the adhesive layer to be tested is arranged. The measurement conditions are an angle of 45° from the horizontal state of the pencil, a load of 750 g, a test speed of 1 mm/sec, a test length of 20 mm, and a temperature of 23°C. The pencil hardness is defined as the maximum pencil hardness at which the surface of the adhesive layer of the expandable adhesive sheet is not damaged by visual inspection. As a pencil hardness tester, for example, KT-VF2378-12 manufactured by TQC can be used.

In the present disclosure, the pencil hardness of the surfaces of the first adhesive layer and the second adhesive layer can be controlled by, for example, the composition of the first adhesive layer and the second adhesive layer. Specifically, the pencil hardness can be controlled by the average particle size and content of the foaming agent contained in the adhesive layer. More specifically, the pencil hardness can be increased by increasing the average particle size of the foaming agent. Moreover, the pencil hardness can be increased by increasing the content of the foaming agent. Further, for example, the pencil hardness can be increased by including an inorganic filler in the adhesive layer. Further, for example, the pencil hardness can be increased by including a component having a rigid structure in the adhesive layer. Specifically, in the adhesive layer containing an epoxy resin and a curing agent, a phenol resin can be mentioned as a component having a rigid structure.

(e) Static Friction Coefficient In the present disclosure, it is preferable that the first adhesive layer and the second adhesive layer have different surface static friction coefficients. Here, in general, the adhesive layer tends to be harder as the surface friction coefficient is lower, and softer as the surface friction coefficient is higher. Therefore, when the static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer are different, the foamable adhesive sheet tends to curl. Therefore, the present disclosure is effective when the static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer are different.

When the static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer are different, and the static friction coefficient of the surface of the first adhesive layer is lower than the static friction coefficient of the surface of the second adhesive layer, the surface of the first adhesive layer The static friction coefficient is, for example, 0.34 or less, and the static friction coefficient of the surface of the second adhesive layer is preferably, for example, greater than 0.34. In this case, the static friction coefficient of the surface of the first adhesive layer may be, for example, 0.30 or less, or 0.26 or less. Also, the coefficient of static friction of the surface of the first adhesive layer may be, for example, 0.16 or more. Also, in this case, the coefficient of static friction of the surface of the second adhesive layer may be, for example, 0.38 or more.

Further, in the above case, the coefficient of static friction of the surface of the first adhesive layer is within the above range, so that the slipperiness of the first adhesive layer can be improved.

On the other hand, the surface static friction coefficient may be the same between the first adhesive layer and the second adhesive layer.

Also, the coefficients of static friction of the surfaces of the first adhesive layer and the second adhesive layer may both be high. In this case, the static friction coefficients of the surfaces of the first adhesive layer and the second adhesive layer may be, for example, 0.34 or less, 0.30 or less, or 0.26 or less. good. Also, the coefficient of static friction may be, for example, 0.16 or more. When the coefficient of static friction is within the above range, slipperiness can be improved.

Here, the static friction coefficient can be determined according to JIS K7125. Specifically, the following methods are mentioned. First, the expandable adhesive sheet is cut to 80 mm×200 mm. Subsequently, the foamable adhesive sheet was placed on a rectangular metal plate placed horizontally, and a sliding piece (63 mm x 63 mm, weight) was placed on the surface of the foamable adhesive sheet on which the adhesive layer to be tested was placed. 200 g, bottom: felt) is placed, and 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. The adhesive layer to be tested of the foam adhesive sheet is arranged. Calculate the coefficient of static friction between the surface and the metal plate. As a device, a friction measuring machine FRICTION TESTER TR-2 manufactured by Toyo Seiki Seisakusho can be used. As the metal plate, for example, a stainless plate made of SUS304 and having a surface roughness Ra of 0.05 μm can be used.

In the present disclosure, the coefficient of static friction of the surfaces of the first adhesive layer and the second adhesive layer is adjusted, for example, by adjusting the composition of the first adhesive layer and the second adhesive layer, or the surface of the first adhesive layer and the second adhesive layer can be controlled by adjusting the pencil hardness of Specifically, the coefficient of static friction can be controlled by the average particle size and content of the foaming agent contained in the adhesive layer. More specifically, the coefficient of static friction tends to decrease as the average particle diameter of the foaming agent increases. Moreover, when the content of the foaming agent increases, the coefficient of static friction tends to decrease. Further, when the pencil hardness of the surface of the adhesive layer increases, the static friction coefficient tends to decrease.

(2) Materials for First Adhesive Layer and Second Adhesive Layer The first adhesive layer and the second adhesive layer in the present disclosure contain a thermosetting adhesive. At least one of the first adhesive layer and the second adhesive layer further contains a foaming agent.

(a) Thermosetting adhesive As the thermosetting adhesive contained in the first adhesive layer and the second adhesive layer in the present disclosure, a thermosetting adhesive that is generally used for the adhesive layer of the foamable adhesive sheet is used. be able to. A thermosetting adhesive can be applied even when the member does not have transparency, such as a member made of metal.

Examples of thermosetting adhesives include epoxy resin-based adhesives, acrylic resin-based adhesives, phenolic resin-based adhesives, unsaturated polyester resin-based adhesives, alkyd resin-based adhesives, urethane resin-based adhesives, Thermosetting polyimide resin-based adhesives and the like are included.

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

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

(i) Epoxy resin The epoxy resin in the present disclosure is a compound that has at least one or more epoxy groups or glycidyl groups and is cured by a cross-linking polymerization reaction when used in combination with a curing agent. Epoxy resins also include monomers having at least one or more epoxy groups or glycidyl groups.

As the epoxy resin, an epoxy resin that is generally used for the adhesive layer of the foamable adhesive sheet can be used.

When the tack of the first adhesive layer is lower than the tack of the second adhesive layer, the thermosetting adhesive contained in the first adhesive layer with a low tack is the first epoxy resin and the second epoxy resin described later. It is preferable to contain a resin. Further, when the tackiness of both the first adhesive layer and the second adhesive layer is low, the thermosetting adhesive contained in the first adhesive layer and the second adhesive layer is an epoxy resin, which is the first epoxy resin described later. It is preferable to contain a second epoxy resin. Specifically, the thermosetting adhesive includes, as epoxy resins, a first epoxy resin having a softening temperature of 50° C. or higher and an epoxy equivalent of 5000 g/eq or lower, and the first epoxy resin having a softening temperature of It is preferable to contain a second epoxy resin having a higher weight average molecular weight of 20,000 or more. By using the first epoxy resin and the second epoxy resin in combination, the adhesiveness (tackiness) of the adhesive layer can be reduced, and a foamable adhesive sheet with good slipperiness can be obtained. Furthermore, it is possible to obtain an adhesive layer with good blocking resistance and adhesiveness after foaming and curing.

For example, when only improving the adhesiveness after foaming and 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 a low molecular weight (low epoxy equivalent) epoxy resin is used, for example, when the foamable adhesive sheet is wound into a roll, the low molecular weight (low epoxy equivalent) epoxy resins are assimilated with each other, causing blocking. easier.

On the other hand, when using a first epoxy resin having a relatively low softening temperature (relatively high crystallinity) and a low molecular weight (low epoxy equivalent weight), the first epoxy resin has a softening temperature or higher. When heated, it melts rapidly and turns into a low viscosity liquid. Therefore, it is easy to improve the adhesiveness after foaming and curing. On the other hand, since the first epoxy resin has relatively high crystallinity, it can suppress the occurrence of blocking as compared with an epoxy resin having relatively low crystallinity or an epoxy resin having no crystallinity. However, when only the first epoxy resin is used, the effect of suppressing the occurrence of blocking may be insufficient, or the tackiness (tackiness) of the adhesive layer may become too high. Therefore, by further using a second epoxy resin having a relatively high softening temperature (relatively low crystallinity) and a high molecular weight, it is possible to improve the effect of suppressing the occurrence of blocking and improve the adhesiveness of the adhesive layer. (tackiness) can be kept low.

On the other hand, when the tack of the first adhesive layer is lower than the tack of the second adhesive layer, the epoxy resin used in the second adhesive layer with a higher tack is liquid at room temperature, such as bisphenol A type epoxy resin or bisphenol F type epoxy resin. and an epoxy resin with a low softening point are preferably used. This is because the use of these epoxy resins facilitates adjustment of the tackiness of the second adhesive layer within a predetermined range.

The first epoxy resin and the second epoxy resin are described below.

(i-1) First Epoxy Resin The first epoxy resin has a softening temperature of 50° C. or higher and an epoxy equivalent of 5000 g/eq or lower. The first epoxy resin has a relatively low softening temperature (relatively high crystallinity) compared to the second epoxy resin described below. Since the first epoxy resin has relatively high crystallinity and a low molecular weight, it tends to improve adhesiveness and blocking resistance after foaming and curing. In addition, since the first epoxy resin has a low molecular weight, the crosslink density can be increased, and an adhesive layer having good mechanical strength, chemical resistance, and curability can be obtained. Also, the first epoxy resin is preferably an epoxy resin that is solid at room temperature (23° C.).

The softening temperature of the first epoxy resin is usually 50°C or higher, may be 55°C or higher, or may be 60°C or higher. On the other hand, the softening temperature of the first epoxy resin is, for example, 150° C. or less. The softening temperature can be measured by the ring and ball method according to JIS K7234.

The epoxy equivalent of the first epoxy resin is, for example, 5000 g/eq or less, may be 3000 g/eq or less, may be 1000 g/eq or less, or may be 600 g/eq or less. On the other hand, the epoxy equivalent of the first epoxy resin is, for example, 90 g/eq or more, may be 100 g/eq or more, or may be 110 g/eq or more. The epoxy equivalent can be measured by a method according to JIS K7236 corresponding 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.

The first epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher epoxy resin. .

Also, the weight average molecular weight (Mw) of the first epoxy resin is usually smaller than the weight average molecular weight (Mw) of the second epoxy resin described later. The Mw of the first epoxy resin is, for example, 6,000 or less, may be 4,000 or less, or may be 3,000 or less. On the other hand, Mw of the first epoxy resin is, for example, 400 or more. Mw is a value converted to polystyrene when measured by gel permeation chromatography (GPC).

The first epoxy resin has a melt viscosity at 150° C. of, for example, 0.005 Pa·s or more, may be 0.015 Pa·s or more, may be 0.03 Pa·s or more, or may be 0.05 Pa · s or more, or 0.1 Pa·s or more. If the melt viscosity is too low, good foamability 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 adhesion (tackiness) of the resulting adhesive layer may increase. The reason for this is that if the melt viscosity of the first epoxy resin is too low (if the crystallinity of the first epoxy resin is too high), the crystallinity will greatly decrease when compatible with the second epoxy resin or acrylic resin. , is presumed to be due to the decrease in the Tg of the adhesive layer. On the other hand, the first epoxy resin has a melt viscosity at 150° C. of, for example, 10 Pa·s or less, may be 5 Pa·s or less, or may be 2 Pa·s or less. If the melt viscosity is too high, the resulting adhesive layer may be less uniform. The melt viscosity was 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). It can be obtained by measuring using a thermocell of.

Next, the structure of the first epoxy resin will be described. Examples of the first epoxy resin include aromatic epoxy resins, aliphatic epoxy resins, alicyclic epoxy resins, and heterocyclic epoxy resins. Specific examples of the first epoxy resin include bisphenol A type epoxy resin, bisphenol type epoxy resin such as bisphenol F type epoxy resin, bisphenol A novolac type epoxy resin, novolak type epoxy resin such as cresol novolak type epoxy resin, urethane modified epoxy resin. Modified epoxy resins such as resins and rubber-modified epoxy resins can be used. Other specific examples include biphenyl-type epoxy resins, stilbene-type epoxy resins, triphenolmethane-type epoxy resins, alkyl-modified triphenolmethane-type epoxy resins, triazine nucleus-containing epoxy resins, dicyclopentadiene-modified phenol-type epoxy resins, Naphthalene-type epoxy resins, glycol-type epoxy resins, and pentaerythritol-type epoxy resins can be mentioned. The number of first epoxy resins may be one, or two or more.

The bisphenol A type epoxy resin can exist in a liquid state at room temperature or in a solid state at room temperature depending on the number of repeating units of the bisphenol skeleton. A bisphenol A type epoxy resin having, for example, 2 or more and 10 or less bisphenol skeletons in the main chain is solid at room temperature. In particular, bisphenol A-type epoxy resins are preferable because they can improve heat resistance.

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

In general formula (1), R ¹ is a group represented by C _m H _2m (m is 1 or more and 3 or less), and R ² and R ³ are each independently C _p H _2p+1 (p is 1 or more and 3 or less), and n is 0 or more and 10 or less.

In general formula (1), m in R ¹ is preferably 1, ie, R ¹ is -CH ₂ -. Likewise, it is preferred that p in R ² and R ³ is 1, ie R ² and R ³ are —CH ₃ . In addition, hydrogen atoms bonded to the benzene ring of general formula (1) may be substituted with other elements or groups.

The content of the first epoxy resin is, for example, 1 part by mass or more, may be 3 parts by mass or more, or may be 5 parts by mass or more, when the resin component contained in the adhesive layer is 100 parts by mass. 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 foaming and curing may deteriorate. On the other hand, when the resin component contained in the adhesive layer is 100 parts by mass, the content of the first epoxy resin is, for example, 90 parts by mass or less, may be 80 parts by mass or less, or may be 70 parts by mass or less. , may be 60 parts by mass or less, may be 50 parts by mass or less, or may be 40 parts by mass or less. If the content of the first epoxy resin is too high, the content of the second epoxy resin and the acrylic resin will be relatively small, resulting in non-adhesiveness, blocking resistance, adhesion to the substrate after foaming and curing, and It may not be possible to balance the crack resistance of the foam and the adhesion after foaming cure.

(i-2) Second Epoxy Resin The second epoxy resin has a softening temperature higher than that of the first epoxy resin and a weight average molecular weight of 20,000 or more. The second epoxy resin has a relatively high softening temperature (relatively low crystallinity) compared to the first epoxy resin described above. Since the second epoxy resin has relatively low crystallinity and a high molecular weight, it tends to improve blocking resistance. Furthermore, since the second epoxy resin has relatively low crystallinity and a high molecular weight, it is possible to suppress an increase in adhesiveness (tackiness) due to the first epoxy resin. Moreover, the second epoxy resin is preferably an epoxy resin that is solid at normal temperature (23° C.).

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

The epoxy equivalent weight of the second epoxy resin may be larger, smaller, or the same as the epoxy equivalent weight of the first epoxy resin. The epoxy equivalent of the second epoxy resin is, for example, 4000 g/eq or more, may be 5000 g/eq or more, or may be 6000 g/eq or more. On the other hand, the epoxy equivalent of the second epoxy resin is, for example, 20000 g/eq or less.

The second epoxy resin may be a monofunctional epoxy resin, a difunctional epoxy resin, a trifunctional epoxy resin, or a tetrafunctional or higher epoxy resin. .

The softening temperature of the second epoxy resin is usually higher than the softening temperature 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 higher, and may be 90° C. or higher. On the other hand, the softening temperature of the second epoxy resin is, for example, 180° C. or lower.

The configuration of the second epoxy resin is the same as the configuration of the first epoxy resin described above, so the description is omitted here.

The content of the second epoxy resin is, for example, 10 parts by mass or more, may be 15 parts by mass or more, or may be 20 parts by mass or more, when the resin component contained in the adhesive layer is 100 parts by mass. may be 25 parts by mass or more, may be 30 parts by mass or more, may be 35 parts by mass or more, may be 40 parts by mass or more, or may be 45 parts by mass or more. may If the content of the second epoxy resin is too small, the adhesiveness may increase and the blocking resistance may decrease. On the other hand, when the resin component contained in the adhesive layer is 100 parts by mass, the content of the second epoxy resin is, for example, 90 parts by mass or less, may be 85 parts by mass or less, or may be 80 parts by mass or less. or 75 parts by mass or less. If the content of the second epoxy resin is too high, the content of the first epoxy resin and the acrylic resin will be relatively small, resulting in non-stickiness, blocking resistance, adhesion to the substrate after foaming and curing, and It may not be possible to balance the crack resistance of the foam and the adhesion after foaming cure.

The ratio of the first epoxy resin to the total of the first epoxy resin and the second epoxy resin 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. % by mass or more. On the other hand, the ratio 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.

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

(ii) Acrylic resin When the thermosetting adhesive is an epoxy resin-based adhesive, the adhesive layer may further contain an acrylic resin compatible with the epoxy resin. Acrylic resin is a resin compatible with epoxy resin. Since the acrylic resin is compatible with the epoxy resin, it tends to improve the toughness of the adhesive layer. As a result, the adhesion after foaming and curing can be improved. Furthermore, it is believed that the acrylic resin acts as a compatibilizer for the foaming agent (for example, a foaming agent whose shell is an acrylonitrile copolymer resin), uniformly disperses and foams, thereby improving the adhesiveness after foaming and curing. . In addition, flexibility due to the acrylic resin is exhibited, and adhesion to the base material after foaming and curing and crack resistance after foaming and curing can be improved. In addition, since the acrylic resin is compatible with the epoxy resin, the hardness of the surface of the adhesive layer can be kept high. On the other hand, if the acrylic resin is incompatible with the epoxy resin, a flexible portion is formed on the surface of the adhesive layer, so that the interface with the adherend becomes less slippery, which may reduce workability.

Acrylic resins in the present disclosure are compatible with epoxy resins. Here, the fact that the acrylic resin is compatible with the epoxy resin can be confirmed, for example, by observing the cross section of the adhesive layer of the foamable adhesive sheet with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). It can be confirmed from the fact that micron-sized islands are not generated. More specifically, the average grain size of the islands is preferably 1 μm or less. Among them, the average grain size of the islands may be 0.5 μm or less, or may be 0.3 μm or less. The number of samples is preferably large, for example 100 or more. The area to be observed is in the range of 100 μm×100 μm, or in the range of thickness×100 μm when the thickness of the adhesive layer is 100 μm or less.

The weight average molecular weight (Mw) of the acrylic resin is, for example, 50,000 or more, may be 70,000 or more, or may be 100,000 or more. The crystallinity of the first epoxy resin is relatively high, and the melt viscosity (or dynamic viscoelasticity) during heating becomes too low. However, by using an acrylic resin with a certain molecular weight, it is possible to prevent the melt viscosity from becoming too low, and shrinkage hardly occurs during curing after foaming. Become. On the other hand, Mw of 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.).

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

The acrylic resin may have a storage modulus (E′) of 1×10 ⁶ Pa or less at the foaming initiation temperature. A low E′ at the start of foaming improves the fluidity and allows good foamability to be obtained. On the other hand, E′ at the foaming start temperature is, for example, 1×10 ⁵ Pa or more. Note that the foaming start temperature is a temperature that differs depending on the type of foaming agent. Moreover, when using two or more types of foaming agents, the starting temperature of the main foaming reaction is defined as the foaming start temperature.

The acrylic resin may have a storage modulus (E′) of 1×10 ⁵ Pa or more at the curing initiation temperature. As described above, shrinkage may occur during curing after foaming (between the completion of foaming of the foaming agent and the curing of the adhesive layer). can be suppressed, and good shape retention can be obtained. It should be noted that the curing start temperature is a different temperature depending on the type of curing agent. When two or more kinds of curing agents are used as the curing agent, the starting temperature of the main curing reaction is defined as the curing initiation temperature.

Further, the acrylic resin may have an average storage modulus (E′) of 1×10 ⁶ Pa or more at 0° C. or higher and 100° C. or lower. A high average value of E′ before foaming can provide good non-tackiness and anti-blocking properties. On the other hand, the average value of storage elastic modulus (E′) at 0° C. or higher and 100° C. or lower is, for example, 1×10 ⁸ Pa or lower.

The acrylic resin may have a polar group. Polar groups include, for example, epoxy groups, hydroxyl groups, carboxyl groups, nitrile groups, and amide groups.

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

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

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

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).

The acrylic copolymer may have no polar group, or may be a modified product into which the above-mentioned polar group is partially introduced. Since the modified product is easily compatible with the epoxy resin, the adhesiveness is further improved.

Among them, the acrylic resin is (meth)acrylic acid having a first polymer portion having a glass transition temperature (Tg) of 10°C or lower and a second polymer portion having a glass transition temperature (Tg) of 20°C or higher. Ester copolymers are preferred. Such a (meth)acrylic acid ester copolymer has a first polymer portion serving as a soft segment and a second polymer portion serving as a hard segment.

The manifestation of the above effects can be estimated as follows. By using an acrylic resin having both a soft segment and a hard segment, such as the above (meth)acrylate copolymer, the hard segment contributes to heat resistance, and the soft segment contributes to toughness or flexibility. , an adhesive layer having good heat resistance, toughness and flexibility can be obtained.

At least one of the first polymer portion and the second polymer portion contained in the (meth)acrylate copolymer has compatibility with the epoxy resin. Flexibility can be enhanced if the first polymer portion is compatible with the epoxy resin. Further, when the second polymer portion has compatibility with the epoxy resin, cohesiveness and toughness can be enhanced.

If either the first polymer portion or the second polymer portion is not compatible with the epoxy resin, the (meth)acrylic acid ester copolymer is a polymer portion that is compatible with the epoxy resin. It will have a compatible site and an incompatible site, which is a polymer portion that is not compatible with the epoxy resin. In this case, when the (meth)acrylic acid ester copolymer is added, the compatible sites are compatible with the epoxy resin, and the incompatible sites are not compatible with the epoxy resin, resulting in fine phase separation. As a result, a fine sea-island structure appears. As for the sea-island structure, the type of (meth)acrylic acid ester copolymer, the compatibility of the first polymer portion and the second polymer portion contained in the (meth)acrylic acid ester copolymer, and the degree of modification due to the introduction of polar groups. For example, a sea-island structure in which the compatible site of the cured epoxy resin and the (meth)acrylic acid ester copolymer is a sea, and the incompatible site of the (meth)acrylic acid ester copolymer is an island. and a sea-island structure in which the incompatible site of the (meth)acrylic acid ester copolymer is the sea, and the compatible site of the cured epoxy resin and the (meth)acrylic acid ester copolymer is an island. A sea-island structure in which the acrylic acid ester copolymer is the sea and the epoxy resin cured product is the island is exemplified. By having such a sea-island structure, stress can be easily dispersed, so interfacial failure can be avoided, and excellent adhesiveness can be obtained after foaming and curing.

The above (meth)acrylic acid ester copolymer is preferably a block copolymer among others. Block copolymers are preferred. Furthermore, the first polymer portion is the incompatible portion, the second polymer portion is the compatible portion, the first polymer portion is polymer block B, and the second polymer portion is polymer block A. A -BA block copolymer is preferred. By using such an ABA block copolymer as the acrylic resin, the compatible site of the cured epoxy resin and the (meth)acrylic acid ester copolymer becomes a sea and the (meth)acrylic acid ester copolymer. In the case of a sea-island structure in which the coalescing incompatible sites are islands, the island portions can be made smaller. In addition, in the case of a sea-island structure in which the incompatible site of the (meth)acrylic acid ester copolymer is the sea and the compatible site of the cured epoxy resin and the (meth)acrylic acid ester copolymer is an island, 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 island, the sea portion can be reduced.

Further, the (meth)acrylic acid ester copolymer may be a modified product obtained by introducing the above-described polar group into a part of the first polymer portion or the second polymer portion.

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

The Tg of the first polymer portion is calculated by the following formula based on the Tg (K) of each homopolymer described in "POLYMER HANDBOOK 3rd Edition" (published by John Wiley & Sons, Ink.) can ask.
₁ /Tg(K) ₌ W1 _/ Tg1 ₊ W2/Tg2 ₊ ...+Wn/ _Tgn
W _n ; mass fraction Tg _n of each monomer; Tg (K) of homopolymer of each monomer, Polymer Handbook (3rd Ed., J. Brandrup and EH Immergut, WILEY INTERSCIENCE) A posted value that is open to the public, such as an intermediate value, may be used. The same applies to the Tg of the second polymer portion, which will be described later.

The first polymer portion contained in the (meth)acrylic acid ester copolymer may be a homopolymer or a copolymer, but is preferably a homopolymer. The monomer component and polymer component constituting the first polymer portion may be any monomer component and polymer component capable of obtaining the first polymer portion having a Tg within a predetermined range. Acrylic acid ester monomers such as butyl acid, 2-ethylhexyl acrylate, isononyl acrylate, and methyl acrylate; other monomers such as vinyl acetate, acetal, and urethane; copolymers such as monomers and EVA.

The Tg of the second polymer portion contained in the (meth)acrylic acid ester copolymer is 20° C. or higher, within the range of 20° C. or higher and 150° C. or lower, especially in the range of 30° C. or higher and 150° C. or lower. , particularly in the range of 40°C or higher and 150°C or lower.

The second polymer portion contained in the (meth)acrylic acid ester copolymer may be a homopolymer or a copolymer, but is preferably a homopolymer. . The monomer component that constitutes the second polymer portion may be a monomer component capable of obtaining a second polymer portion having a Tg within a predetermined range. monomers, 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 above polar groups body.

Specific examples of the (meth)acrylic acid ester copolymer having the above first polymer portion and second polymer portion include the above MMA-BA-MMA copolymer.

The content of the acrylic resin is, for example, 1 part by mass or more, may be 3 parts by mass or more, or may be 5 parts by mass or more when the resin component contained in the adhesive layer is 100 parts by mass. It may be 7 parts by mass or more, or may be 10 parts by mass or more. If the content of the acrylic resin is too small, the adhesiveness to the base material after foaming and curing, the crack resistance after foaming and curing, and the adhesiveness after foaming and curing may decrease. On the other hand, when the resin component contained in the adhesive layer is 100 parts by mass, the content of the acrylic resin is, for example, 60 parts by mass or less, may be 50 parts by mass or less, or may be 40 parts by mass or less. may be 35 parts by mass or less, or may be 30 parts by mass or less. If the content of acrylic resin is too high, the content of the first epoxy resin and the second epoxy resin will be relatively small, resulting in non-stickiness, blocking resistance, adhesion to the substrate after foaming and curing, and It may not be possible to balance the crack resistance of the foam and the adhesion after foaming cure. Moreover, when the content of the acrylic resin is too large, the film strength may decrease.

(iii) Curing agent The curing agent in the present disclosure is a curing agent that causes a curing reaction by heat, and a curing agent that is generally used for epoxy resin adhesives can be used. The curing agent is preferably solid at room temperature (23° C.). Curing agents that are solid at room temperature can have longer storage stability (pot life) than curing agents that are liquid at room temperature. The curing agent may also be a latent curing agent. Moreover, a curing agent may be used alone, or two or more kinds thereof may be used.

When the tackiness of the first adhesive layer is lower than the tackiness of the second adhesive layer, both a curing agent that is solid at room temperature and a curing agent that is liquid at room temperature can be used in the second adhesive layer having a high tack. From the viewpoint of storage stability, it is preferable to use a curing agent that is solid at room temperature.

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

Specific examples of curing agents include imidazole curing agents, phenol curing agents, amine curing agents, acid anhydride curing agents, isocyanate curing agents, and thiol curing agents.

Examples of imidazole curing agents include imidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl -4-Methylimidazole, 2-isopropylimidazole, 2-phenylimidazole, carboxylic acid salts of imidazole compounds, adducts with epoxy compounds. Also, the imidazole-based curing agent preferably has a hydroxyl group. Since crystallization occurs due to hydrogen bonding between hydroxyl groups, the reaction initiation temperature tends to be high.

Examples of phenol-based curing agents include phenol resins. Furthermore, examples of phenolic resins include resol-type phenolic resins and novolac-type phenolic resins. A phenolic novolac resin having a Tg of 110° C. or less is particularly preferable from the viewpoint of adhesion to the base material after foaming and curing and cracking resistance after foaming and curing. A phenol-based curing agent and an imidazole-based curing agent may also be used together. In that case, it is preferable to use an imidazole curing agent as a curing catalyst.

Examples of amine curing agents include aliphatic amines such as diethylenetriamine (DETA), triethylenetetramine (TETA), metaxylylenediamine (MXDA); diaminodiphenylmethane (DDM), m-phenylenediamine (MPDA), diamino aromatic amines such as diphenylsulfone (DDS); alicyclic amines; and polyamidoamines. As the amine-based curing agent, a dicyandiamide-based curing agent such as dicyandiamide (DICY), an organic acid dihydrazide-based curing agent, an amine adduct-based curing agent, and a ketimine-based curing agent can be used.

Examples of acid anhydride curing agents include alicyclic acid anhydrides (liquid acid anhydrides) such as hexahydrophthalic anhydride (HHPA) and methyltetrahydrophthalic anhydride (MTHPA); trimellitic anhydride (TMA); Aromatic acid anhydrides such as pyromellitic anhydride (PMDA) and benzophenonetetracarboxylic acid (BTDA) are included.

Examples of isocyanate-based curing agents include blocked isocyanates.

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

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

(b) Foaming Agent In the present disclosure, at least one of the first adhesive layer and the second adhesive layer contains a foaming agent.

Among them, both the first adhesive layer and the second adhesive layer preferably contain a foaming agent. In this case, the adhesiveness of the first adhesive layer and the second adhesive layer after foaming and curing can be enhanced.

On the other hand, when only one of the first adhesive layer and the second adhesive layer contains a foaming agent and the foaming agent is a microcapsule-type foaming agent, the foaming agent is expected to function as a filler. Therefore, it is thought that there is a tendency for the adhesive layer containing the foaming agent to be hard and the adhesive layer not containing the foaming agent to be soft. Therefore, if only one of the first adhesive layer and the second adhesive layer contains a foaming agent, the foamable adhesive sheet is likely to curl. Therefore, it is considered that the present disclosure is effective when only one of the first adhesive layer and the second adhesive layer contains a foaming agent.

Moreover, when the hardness of the first adhesive layer is higher than the hardness of the second adhesive layer, the first adhesive layer having the higher hardness preferably contains a foaming agent. By containing the foaming agent in the first adhesive layer, the surface roughness is increased, the coefficient of friction is decreased, and the slipperiness is further improved.

As the foaming agent, a foaming agent that causes a foaming reaction by heat, and a foaming agent that is generally used for the adhesive layer of the foamable adhesive sheet can be used.

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

The softening temperature of the main agent of the thermosetting adhesive such as epoxy resin can be measured using the ring and ball softening temperature test method specified in JIS K7234.

Foaming agents include, for example, microcapsule-type foaming agents. The microcapsule-type foaming agent preferably has a core made of a thermal expansion agent such as a hydrocarbon, and a shell made of a resin such as an acrylonitrile copolymer.

As the foaming agent, for example, an organic foaming agent or an inorganic foaming agent may be used. Examples of organic foaming agents include azo foaming agents such as azodicarbonamide (ADCA), azobisformamide, and azobisisobutyronitrile, alkane fluoride foaming agents such as trichloromonofluoromethane, and paratoluenesulfonyl hydrazide. hydrazine foaming agents, semicarbazide foaming agents such as p-toluenesulfonyl semicarbazide, triazole foaming agents such as 5-morpholyl-1,2,3,4-thiatriazole, N such as N,N-dinitrosoterephthalamide - includes nitroso foaming agents. On the other hand, inorganic foaming agents include, for example, ammonium carbonate, ammonium hydrogencarbonate, ammonium nitrite, ammonium borohydride, and azides.

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. When the average particle size of the foaming agent is within the above range, the coefficient of static friction on the surface of the adhesive layer can be reduced, and the adhesive layer can have good lubricity. The average particle diameter of the foaming agent is preferably equal to or less than the thickness of the adhesive layer, and may be, for example, 44 μm or less, 30 μm or less, or 24 μm or less.

The average particle size of the foaming agent is the particle size at 50% of the integrated value in the particle size distribution determined by the laser diffraction scattering method. When measuring the average particle diameter of the foaming agent, the foaming agent is separated by dissolving the adhesive layer in a solvent. The solvent is not particularly limited as long as it can dissolve components other than the foaming agent contained in the adhesive layer, and is appropriately selected according to the type of thermosetting adhesive contained in the adhesive layer. For example, the solvent used for the adhesive composition used for forming the adhesive layer can be used. Specifically, methyl ethyl ketone, ethyl acetate, toluene, and the like can be used.

The content of the foaming agent is, for example, 0.5 parts by mass or more, may be 2 parts by mass or more, or may be 3 parts by mass or more, when the resin component contained in the adhesive layer is 100 parts by mass. may be 4 parts by mass or more, or 5 parts by mass or more. On the other hand, the content of the foaming agent is, for example, 25 parts by mass or less, may be 20 parts by mass or less, or may be 15 parts by mass or less with respect to 100 parts by mass of the resin component contained in the adhesive layer. . If the foaming agent content is too low, the coefficient of static friction on the surface of the adhesive layer may increase. On the other hand, if the content of the foaming agent is too high, the content of the thermosetting adhesive becomes relatively small, which may reduce the adhesiveness after foaming and curing.

(c) Other components The adhesive layer in the present disclosure may contain only an epoxy resin and an acrylic resin as resin components when, for example, the thermosetting adhesive is an epoxy resin-based adhesive. may further contain. Other resins include, for example, urethane resins.

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

The content of the resin component contained in the 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.

The adhesive layer optionally contains additives such as silane coupling agents, fillers, antioxidants, light stabilizers, UV absorbers, lubricants, plasticizers, antistatic agents, cross-linking agents, and colorants. You may have Silane coupling agents include, for example, epoxy-based silane coupling agents. Examples of fillers include inorganic fillers such as calcium carbonate, aluminum hydroxide, magnesium hydroxide, antimony trioxide, zinc borate, molybdenum compounds, and titanium dioxide. Examples of antioxidants include phenol antioxidants and sulfur antioxidants.

(3) Configuration of First and Second Adhesive Layers When the first and second adhesive layers contain a foaming agent, the first and second adhesive layers are, for example, 1.5 times or more, Foaming is possible at an expansion ratio of 15 times or less. The expansion ratio may be, for example, 3.5 times or more, 4 times or more, or 4.5 times or more. In the above case, the expansion ratio may be, for example, 9 times or less, 8.5 times or less, or 8 times or less.

Here, the expansion ratio can be determined by the following formula.
Expansion ratio (times) = thickness of adhesive layer after foaming and curing/thickness of adhesive layer before foaming and curing

The thickness of each of the first adhesive layer and the second adhesive layer is not particularly limited, but when the adhesive layer contains a foaming agent, it is preferably equal to or greater than the average particle size of the foaming agent, for example, 10 μm or more. , 15 μm or more, or 20 μm or more. On the other hand, the thickness of each of the first adhesive layer and the second adhesive layer is, for example, 200 μm or less, may be 150 μm or less, or may be 100 μm or less. If the thickness of the adhesive layer is too thin, it may not be possible to obtain sufficient adhesion to the substrate and adhesion after foaming and curing. Further, when the tack of the first adhesive layer is lower than the tack of the second adhesive layer, if the thickness of the first adhesive layer with low tack is too thin, foaming after standing for a predetermined time at a predetermined temperature and humidity The radius of curvature of the curl of the adhesive sheet may be reduced. On the other hand, if the adhesive layer is too thick, the surface quality may deteriorate.

Here, the thickness of the first adhesive layer and the thickness of the second adhesive layer are respectively the foamed adhesive sheet observed with a transmission electron microscope (TEM), a scanning electron microscope (SEM) or a scanning transmission electron microscope (STEM). It is a value measured from a cross-section in the thickness direction, and can be an average value of 10 randomly selected thicknesses. The same can be applied to the method of measuring the thickness of other layers of the expandable adhesive sheet.

The first adhesive layer and the second adhesive layer may be continuous layers or discontinuous layers. Examples of discontinuous layers include patterns such as stripes and dots. Moreover, the surfaces of the first adhesive layer and the second adhesive layer may have an uneven shape such as emboss.

The first adhesive layer and the second adhesive layer can be formed, for example, by applying an adhesive composition containing the above thermosetting adhesive and a foaming agent and removing the solvent. Examples of coating 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. is mentioned.

The adhesive composition may or may not contain a solvent. In addition, the solvent in the present specification has a broad meaning including not only a strict solvent (a solvent that dissolves a solute) but also a dispersion medium. Moreover, the solvent contained in the adhesive composition is volatilized and removed when the adhesive composition is applied and dried to form an adhesive layer.

The adhesive composition can be obtained by mixing each component described above, and kneading and dispersing the mixture as necessary. 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, and dispersers. , high-speed mixers, ribbon blenders, co-kneaders, intensive mixers, tumblers, blenders, dispersers, homogenizers, and ultrasonic dispersers.

3. Substrate The substrate in the present disclosure is disposed between the first adhesive layer and the second adhesive layer described above.

The substrate preferably has insulating properties. Moreover, it is preferable that the base material is in the form of a sheet. The base material may have a single layer structure or may have a multilayer structure. Further, the substrate may or may not have a porous structure inside.

Examples of base materials include resin base materials and non-woven fabrics.

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

Nonwoven fabrics include, for example, nonwoven fabrics containing fibers such as cellulose fibers, polyester fibers, nylon fibers, aramid fibers, polyphenylene sulfide fibers, liquid crystal polymer fibers, glass fibers, metal fibers, and carbon fibers.

The base material may be subjected to surface treatment in order to enhance adhesion with the first adhesive layer and the second adhesive layer.

The thickness of the substrate is preferably thinner than the thickness of the first adhesive layer or thinner than the thickness of the second adhesive layer, and is thinner than the thickness of the first adhesive layer and the thickness of the second adhesive layer Thinner than thick is more preferable. By making the thickness of the base material thinner than the thickness of the first adhesive layer and the thickness of the second adhesive layer, the thickness of the expandable adhesive sheet can be reduced, and the thickness of the first adhesive layer and the thickness of the second adhesive layer can be reduced. The thickness of the second adhesive layer can be relatively thick. Therefore, it is possible to reduce the thickness of the foamable adhesive sheet and improve the insertability without deteriorating the adhesive properties and foaming properties of the first adhesive layer and the second adhesive layer.

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

4. Curl Adjusting Layer The foamable adhesive sheet in the present disclosure may have a curl adjusting layer on the side of the second adhesive layer opposite to the substrate. For example, if the tackiness of the first adhesive layer is lower than the tackiness of the second adhesive layer, the foamable adhesive sheet tends to curl, but the curl adjusting layer is formed on the side of the second adhesive layer opposite to the substrate. By being arranged, curling can be suppressed.

For example, in the expandable adhesive sheet 10 shown in FIG. 6, the curl adjusting layer 4 is arranged on the side of the second adhesive layer 3 opposite to the base material 2 .

The curl adjusting layer may be, for example, a separator that protects the second adhesive layer or a fiber layer. Among them, the curl adjusting layer is preferably a separator. The separator is peelable, and when the foamable adhesive sheet is arranged between two members, the separator is peeled off from the foamable adhesive sheet, so that the thickness of the foamable adhesive sheet can be reduced. Insertability can be improved.

(1) Separator In the present disclosure, a separator may be arranged on the surface of the second adhesive layer opposite to the substrate.

The separator is not particularly limited as long as it can be peeled off from the second adhesive layer, and can have a strength sufficient to protect the second adhesive layer. Examples of such a separator include a release film, release paper, and the like. Moreover, the separator may have a single-layer structure or may have a multi-layer structure.

Examples of the separator having a single layer structure include a fluororesin film.

Moreover, examples of the separator having a multilayer structure include a laminate having a release layer on one side or both sides of a substrate layer. Examples of the substrate layer include resin films such as polypropylene, polyethylene, and polyethylene terephthalate, and paper such as woodfree paper, coated paper, and impregnated paper. The material for the release layer is not particularly limited as long as it has releasability. Examples include silicone compounds, organic compound-modified silicone compounds, fluorine compounds, aminoalkyd compounds, melamine compounds, acrylic compounds, polyester compounds, chain alkyl compounds and the like. These compounds can be of emulsion type, solvent type or non-solvent type.

(2) Fiber layer In the present disclosure, the fiber layer may be arranged on the surface of the second adhesive layer opposite to the base material. In the case where the second adhesive layer contains a thermosetting adhesive and a foaming agent, the fiber layer allows the thermosetting adhesive to permeate or permeate when the second adhesive layer foams and expands. layer.

Examples of forms of the fiber layer include nonwoven fabric, paper, felt, knitted fabric, and woven fabric.

Examples of fibers constituting the fiber layer include basalt fiber, vinylon fiber, polyarylate fiber, polyethylene fiber, polypropylene fiber, silicon carbide fiber, cellulose fiber, polyester fiber, nylon fiber, aramid fiber, polyphenylene sulfide fiber, and liquid crystal polymer fiber. , glass fiber, and the like.

The density of the fiber layer is not particularly limited as long as the thermosetting adhesive can be permeated or permeated when the second adhesive layer foams and expands. For example, 200 g/cm ³ or less, may be 100 g/cm ³ or less, or may be 50 g/cm ³ or less. If the density of the fibrous layer is too high, the number of voids in the fibrous layer will decrease, making it difficult for the thermosetting adhesive to permeate or permeate during foaming of the second adhesive layer. Adhesive strength may not be obtained. On the other hand, the density of the fiber layer is, for example, 3 g/cm ³ or more, may be 5 g/cm ³ or more, or may be 7 g/cm ³ or more.

Here, the density (g/cm ³ ) of the fiber layer can be calculated by dividing the basis weight (g/cm ² ) of the fiber layer by the thickness (cm) of the fiber layer.

The basis weight of the fiber layer can be measured by the following method. First, 10 fiber layer test pieces having a size of 100 mm×100 mm are taken, and the mass (g) of each test piece is measured. Next, the basis weight (g/cm ² ) of each test piece is calculated by dividing the mass (g) of each test piece by the area (cm ² ) of each test piece. The average value of the grammage of a total of 10 test pieces is calculated, and this average value is adopted as the grammage.

In addition, the density of the fiber layer can be adjusted by the manufacturing method and manufacturing conditions of the fiber layer.

The thickness of the fiber layer is not particularly limited as long as the thermosetting adhesive can be permeated or permeated when the second adhesive layer foams and expands. It may be 80 μm or less, or 60 μm or less. If the thickness of the fiber layer is too thick, the amount of permeation or permeation of the thermosetting adhesive during foaming of the second adhesive layer may decrease, and the adhesive strength of the second adhesive layer after foaming and curing may decrease. . On the other hand, the thickness of the fiber layer is, for example, 6 μm or more, may be 8 μm or more, or may be 10 μm or more. If the thickness of the fiber layer is too thin, blocking may occur when processed into a roll.

As a method of arranging the fiber layer on the surface opposite to the base material of the second adhesive layer, for example, a method of attaching the fiber layer using the adhesiveness of the second adhesive layer, a method of attaching the fiber layer separately from the second adhesive layer A method of attaching a fiber layer to a second adhesive layer via a layer having adhesiveness, a method of applying a solvent-diluted adhesive composition from above the fiber layer and drying it, and a heat lamination of the second adhesive layer and the fiber layer. or a method using a combination thereof.

5. First Intermediate Layer and Second Intermediate Layer The foamable adhesive sheet in the present disclosure may have a first intermediate layer between the substrate and the first adhesive layer. Also, the foamable adhesive sheet in the present disclosure may have a second intermediate layer between the substrate and the second adhesive layer. By arranging the first intermediate layer and the second intermediate layer, the adhesion of the first adhesive layer and the second adhesive layer to the substrate can be improved. Furthermore, by arranging the first intermediate layer and the second intermediate layer, for example, when the foamable adhesive sheet is folded, the stress applied to the bent portion is alleviated, and when the foamable adhesive sheet is cut, It is possible to relax the stress applied to the cut portion. As a result, it is possible to prevent the first adhesive layer and the second adhesive layer from lifting or peeling off from the substrate when the expandable adhesive sheet is bent or cut.

For example, in the expandable adhesive sheet 10 shown in FIG. 7, the first intermediate layer 5 is arranged between the base material 2 and the first adhesive layer 1, and the second intermediate layer A layer 6 is arranged. 5, the expandable adhesive sheet 10 has both the first intermediate layer 5 and the second intermediate layer 6, but may have only one of them.

The foamable adhesive sheet may have at least one of the first intermediate layer and the second intermediate layer, and for example, has only the first intermediate layer disposed between the substrate and the first adhesive layer. may have only a second intermediate layer disposed between the substrate and the second adhesive layer, the first intermediate layer disposed between the substrate and the first adhesive layer; It may have both a material and a second intermediate layer disposed between the second adhesive layer. Among them, it is preferable that the first intermediate layer is arranged between the base material and the first adhesive layer, and the second intermediate layer is arranged between the base material and the second adhesive layer.

The material contained in the first intermediate layer and the second intermediate layer should be a material that can improve the adhesion between the substrate and the first adhesive layer or the second adhesive layer and can relieve stress. It is not particularly limited, and is appropriately selected according to the materials of the base material, the first adhesive layer, and the second adhesive layer. Examples thereof include polyester, polyvinyl chloride, polyvinyl acetate, polyurethane, copolymers of at least two or more thereof, crosslinked products thereof, and mixtures thereof.

The crosslinked body is a crosslinked body obtained by crosslinking the above resin with a curing agent. Examples of curing agents include isocyanate-based curing agents. Further, for example, when the reactive group/NCO equivalent is 1, it is preferable to add the isocyanate-based curing agent at a ratio of 0.5% by mass or more and 20% by mass or less with respect to the resin.

Among them, the first intermediate layer and the second intermediate layer preferably contain a crosslinked resin. The crosslinked resin means a resin that does not melt even at high temperatures. This makes it possible to improve the adhesive strength at high temperatures, that is, the heat resistance.

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

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

6. Foamable Adhesive Sheet The thickness of the foamable adhesive sheet in the present disclosure is, for example, 10 μm or more, and may be 20 μm or more. On the other hand, the thickness of the expandable adhesive sheet is, for example, 1000 μm or less, and may be 200 μm or less.

The use of the expandable adhesive sheet in the present disclosure is not particularly limited. The foamable adhesive sheet in the present disclosure is used, for example, when the foamable adhesive sheet is placed between two members and then the foamable adhesive sheet is heated to foam and harden, thereby bonding the two members together. be able to. For example, when the tackiness of the first adhesive layer is lower than the tackiness of the second adhesive layer, the foamable adhesive sheet in the present disclosure is applied after the surface of the second adhesive layer of the foamable adhesive sheet is attached to the second member. The first member and the second member are bonded by inserting the second member to which the foamable adhesive sheet is attached into the hole or groove of the first member, and heating the foamable adhesive sheet to foam and harden it. It is preferably used in some cases. Further, for example, when the tackiness of the first adhesive layer and the second adhesive layer is low, the foamable adhesive sheet in the present disclosure is inserted between the first member and the second member, and the foamable adhesive sheet When bonding the first member and the second member by heating and foaming and curing; after placing the foaming adhesive sheet on the second member, the foaming adhesive sheet When bonding the first member and the second member by inserting the arranged second member and heating the foaming adhesive sheet to foam and harden; insert the foaming adhesive sheet into the hole or groove of the first member After arranging, the first member and the second member are joined by inserting the second member into the holes, grooves, etc. of the first member in which the expandable adhesive sheet is arranged, and heating the expandable adhesive sheet to foam and harden it. When adhering; etc., it is preferably used. Specifically, the foamable adhesive sheet in the present disclosure is used for bonding coils and stators in motors, and rotors and permanent magnets in embedded magnet motors.

The method for manufacturing the foamable adhesive sheet in the present disclosure is not particularly limited, and is appropriately selected according to the layer structure of the foamable adhesive sheet.

B. Method for manufacturing an article A method for manufacturing an article according to the present disclosure includes an arrangement step of arranging the foamable adhesive sheet described above between a first member and a second member, heating the foamable adhesive sheet to foam and cure, and a bonding step of bonding the first member and the second member.

FIGS. 8(a) and 8(b) are process charts showing an example of a method for manufacturing an article according to the present disclosure. First, as shown in FIG. 8(a), the expandable adhesive sheet 10 is arranged on the first member 20a and the second member 20b. Next, as shown in FIG. 8B, the first adhesive layer 1 and the second adhesive layer 3 of the foamable adhesive sheet 10 are heated to foam and harden. The first member 20a and the second member 20b are adhered (bonded) by the adhesive sheet 15 having the first adhesive layer 11 and the second adhesive layer 13 after foaming and curing. Thereby, the article 100 in which the adhesive sheet 15 is arranged between the first member 20a and the second member 20b is obtained.

9A to 9C are process diagrams showing another example of the method for manufacturing an article according to the present disclosure. First, as shown in FIG. 9A, the expandable adhesive sheet 10 is arranged on the second member 20b. At this time, in the foamable adhesive sheet 10, when the tack of the first adhesive layer 1 is lower than that of the second adhesive layer 3, the tack of the second adhesive layer 3 is used to foam the second member 20b. The surface of the second adhesive layer 3 of the adhesive sheet 10 is attached. Next, as shown in FIG. 9(b), the second member 20b on which the expandable adhesive sheet 10 is arranged is inserted into the hole of the first member 20a. Next, as shown in FIG. 9(c), the first adhesive layer 1 and the second adhesive layer 3 of the foamable adhesive sheet 10 are heated to foam and harden. The first member 20a and the second member 20b are adhered (bonded) by the adhesive sheet 15 having the first adhesive layer 11 and the second adhesive layer 13 after foaming and curing. Thereby, the article 100 in which the adhesive sheet 15 is arranged between the first member 20a and the second member 20b is obtained.

A method for manufacturing an article according to the present disclosure will be described below.

1. Foamable Adhesive Sheet In the method for manufacturing an article according to the present disclosure, the foamable adhesive sheet described above is used as the foamable adhesive sheet.

When the foamable adhesive sheet has a separator, the separator is removed from the foamable adhesive sheet when placing the foamable adhesive sheet between the first member and the second member.

The details of the foamable adhesive sheet have been described in the above section "A. Foamable adhesive sheet", so the description is omitted here.

2. Arrangement step In the arrangement step of the present disclosure, the method of arranging the foamable adhesive sheet between the first member and the second member depends on the configuration of the foamable adhesive sheet, the types of the first member and the second member, etc. selected as appropriate. For example, when the second member is adhesively fixed to the hole or groove of the first member, and the tack of the first adhesive layer in the foamable adhesive sheet is lower than the tack of the second adhesive layer, the foamable adhesive sheet After attaching the surface of the second adhesive layer of the foamable adhesive sheet to the second member using the tack of the second adhesive layer, the second member to which the foamable adhesive sheet is attached is inserted into the hole or groove of the first member. The method of disposing two members; using the tack of the second adhesive layer of the foam adhesive sheet to stick the surface of the second adhesive layer of the foam adhesive sheet to the hole or groove of the first member, and then foaming adhesive a method of arranging the second member in the hole or groove of the first member to which the sheet is attached; Further, for example, when the second member is adhesively fixed to the hole or groove of the first member, and when the tackiness of the first adhesive layer and the second adhesive layer in the foamable adhesive sheet is low, the first member and the second adhesive A method of disposing a foamable adhesive sheet between members; A method of disposing a second member having a foamable adhesive sheet in a hole or groove of the first member after disposing the foamable adhesive sheet on the second member. a method of disposing the foamable adhesive sheet in the holes or grooves of the first member, and then disposing the second member in the holes or grooves of the first member in which the foamable adhesive sheet has been disposed;

3. Adhesion Step In the adhesion step in the present disclosure, the foamable adhesive sheet is heated to foam and cure. The heating method is applicable even when the first member and the second member do not have transparency, such as metal members.

The heating conditions are appropriately set according to the type of thermosetting adhesive and foaming agent contained in the first adhesive layer and the second adhesive layer, the type of substrate, and the like. The heating temperature can be, for example, 130° C. or higher and 200° C. or lower. Also, the heating time can be, for example, 3 minutes or more and 3 hours or less.

Note that the present disclosure is not limited to the above embodiments. The above embodiment is an example, and any device that has substantially the same configuration as the technical idea described in the claims of the present disclosure and produces the same effect is the present invention. It is included in the technical scope of the disclosure.

[Manufacturing example]
First, adhesive compositions A and B having the following compositions were prepared.

<Adhesive composition A>
・ Acrylic resin (PMMA-PBuA-PMMA (acrylamide group in part), Tg: -20 ° C., 120 ° C., Mw: 150,000): 13 parts by mass ・ Epoxy resin A (bisphenol A novolac type, normal temperature solidification, 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, normal temperature solid, softening temperature: 110°C , Epoxy equivalent: 8000 g / eq, Mw: 50,000): 42 parts by mass Curing agent A (α-(hydroxy (or dihydroxy) phenylmethyl) -ω-hydropoly[biphenyl-4,4'-diylmethylene (hydroxy (or dihydroxy)phenylene methylene)]): 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., activity Range 155° C. to 173° C. (manufactured by Shikoku Kasei Co., Ltd., 2PHZ-PW)): 8 parts by mass Blowing 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

<Adhesive composition B>
・ Acrylic resin (PMMA-PBuA-PMMA (acrylamide group in part), Tg: -20 ° C., 120 ° C., Mw: 150,000): 40 parts by mass ・ Epoxy resin C (bisphenol A type, liquid at room temperature, epoxy equivalent : 184 to 194 g / eq): 45 parts by mass Epoxy resin D (diaminodiphenylmethane type, high viscosity liquid, epoxy equivalent: 110 to 130 g / eq): 65 parts by mass Epoxy resin E (silicone modification, epoxy equivalent: 1200 g /mol): 20 parts by mass Silane coupling agent (3-glycidoxypropyltrimethoxysilane): 2 parts by mass Curing agent B (phenol-formaldehyde polycondensate softening point 80 ° C., hydroxyl equivalent 104 g / mol): 6 parts by mass Curing catalyst (2-phenyl-4,5-dihydroxymethylimidazole, average particle size: 3 μm, melting point: 230° C., reaction initiation temperature: 145° C. to 155° C., active region: 155° C. to 173° C. (Shikoku Kasei Kogyo Co., Ltd. 2PHZ-PW)): 10 parts by mass ・Blowing 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: carbonization Hydrogen, Shell: Thermoplastic polymer: 20 parts by mass Solvent (methyl ethyl ketone): 114 parts by mass

[Example 1]
Polyethylene naphthalate (PEN film, manufactured by Toyobo Film Solution Co., Ltd., Teonex Q51, thickness 25 μm) was used as the base material. Further, 15 parts by mass of a curing agent (polyisocyanate) and 0.3 parts by mass of a catalyst (trisdimethylaminomethylphenol) are blended with respect to 100 parts by mass of the polyester polymer, and the solid content is 15% by mass. and diluted with methyl ethyl ketone (MEK) to prepare a resin composition. The resin composition was applied to one surface of the base material with a bar coater and dried in an oven at 100° C. for 1 minute to form a first intermediate layer having a thickness of 2 μm. Next, the adhesive composition A was applied to the surface of the first intermediate layer opposite to the substrate using an applicator so that the thickness after coating was 27 μm. Then, it was dried in an oven at 100° C. for 3 minutes to form a first adhesive layer.

Next, a release film (PET separator, manufactured by Nippa Co., Ltd., PET50×1-J2, thickness 50 μm) is used as a separator, and the adhesive composition B is applied to the release treatment surface of the release film. It was applied using an applicator so that the thickness afterward would be 51 μm. After that, it was dried in an oven at 100° C. for 3 minutes to form a second adhesive layer.

Next, the surface of the second adhesive layer of the laminate having the separator and the second adhesive layer was laminated to the surface of the base material of the laminate having the substrate, the first intermediate layer and the first adhesive layer. After that, the separator was peeled off. As a result, a foamable adhesive sheet was obtained in which the first adhesive layer, the first intermediate layer, the substrate, and the second adhesive layer were arranged in this order.

[Examples 2 to 5]
A foamable adhesive sheet was produced in the same manner as in Example 1, except that the thicknesses of the first adhesive layer and the second adhesive layer were set as shown in Table 2 below.

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

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

[Comparative Example 3]
A first intermediate layer was formed on the substrate in the same manner as in Example 1. Also, in the same manner as in Example 3, a second adhesive layer was formed on the separator. Next, the surface of the second adhesive layer of the laminate having the separator and the second adhesive layer was laminated to the surface of the substrate of the laminate having the substrate and the first intermediate layer. After that, the separator was peeled off. As a result, a foamable adhesive sheet was obtained in which the first intermediate layer, the substrate, and the second adhesive layer were arranged in this order.

[Comparative Examples 4-5]
A foamable adhesive sheet was produced in the same manner as in Comparative Example 3, except that the thickness of the second adhesive layer was set as shown in Table 2 below.

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

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

The tack of the second adhesive layer was also measured in the same manner as the tack of the first adhesive layer.

(2) Loop Stiffness A rectangular test piece having a width of 10 mm and a length of 200 mm was produced from the foamable adhesive sheet, and the loop stiffness was measured by the loop stiffness measurement method described above. A loop stiffness tester (DR) manufactured by Toyo Seiki Seisakusho Co., Ltd. was used as a measuring instrument. The environment during the measurement was a temperature of 23° C. and a relative humidity of 50%.

(3) Adhesiveness FIGS. 10(a) and 10(b) are schematic diagrams for explaining a method for evaluating the adhesiveness of a foamable adhesive sheet. The expandable adhesive sheet 10 was cut into a size of 10 mm in width and 100 mm in length to obtain a test piece. The jig 51 has a rectangular parallelepiped shape, and the lower surface 51a of the jig 51 has a rectangular shape, is flat, and is horizontal. A double-sided adhesive tape 52 ("Y-4920-25" manufactured by 3M) was attached to the lower surface 51a of the jig 51. As shown in FIG.

First, as shown in FIG. 10( a ), in a normal temperature and humidity environment, the surface of the double-sided adhesive tape 52 of the jig 51 is attached to the center of the expandable adhesive sheet 10 to fix the expandable adhesive sheet 10 . bottom. The pasting area was 10 mm×10 mm. At this time, 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 expandable adhesive sheet 10 .

Next, as shown in FIG. 10(b), the jig 51 was lifted vertically upward. Next, although not shown, a metal plate was placed below the expandable adhesive sheet lifted by the jig, and the jig was lowered vertically to adhere the expandable adhesive sheet to the metal plate. Then, the state of the expandable adhesive sheet was visually observed, and the stickability was evaluated according to the following criteria.
A: The foamable adhesive sheet was adhered without breaking or entrapment of air bubbles.
B: Folding of the foamable adhesive sheet and air bubble entrapment occurred.

From Table 2, the radius of curvature of the curl of the foamable adhesive sheet after standing at a predetermined temperature and humidity for a predetermined time is at least a predetermined value, and the loop stiffness of the foamable adhesive sheet is at least a predetermined value. In this case, it was confirmed that the sticking property was good.

REFERENCE SIGNS LIST 1 first adhesive layer 2 base material 3 second adhesive layer 4 curl adjusting layer 5 first intermediate layer 6 second intermediate layer 10 foamable adhesive sheet 15 adhesive sheet after foaming and curing 20a second First member 20b... Second member 100... Article

Claims (6)

A foamable adhesive sheet having a first adhesive layer, a substrate, and a second adhesive layer in this order,
The composition of the first adhesive layer and the composition of the second adhesive layer are different,
The first adhesive layer and the second adhesive layer contain a thermosetting adhesive,
At least one of the first adhesive layer and the second adhesive layer further contains a foaming agent, and the radius of curvature of the curl of the expandable adhesive sheet after standing for 15 hours at a temperature of 60° C. and a humidity of 10% RH or less is 15 mm or more,
A foamable adhesive sheet having a loop stiffness of 45 mN/10 mm or more. The expandable adhesive sheet according to claim 1, wherein said first adhesive layer and said second adhesive layer contain said foaming agent. The expandable adhesive sheet according to claim 1 or 2, wherein the thickness of the base material is thinner than the thickness of the first adhesive layer and the thickness of the second adhesive layer. 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, according to any one of claims 1 to 3. foam adhesive sheet. The expandable adhesive sheet according to any one of claims 1 to 4, which has a curl adjusting layer on the side of the second adhesive layer opposite to the base material. an arrangement step of arranging the expandable adhesive sheet according to any one of claims 1 to 5 between the first member and the second member;
a bonding step of heating the foamable adhesive sheet to foam and harden it to bond the first member and the second member;
A method for manufacturing an article.

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