Adhesive strength testing device, adhesive strength testing method, and expandable adhesive

Abstract

To provide an adhesive strength testing device capable of testing a tensile adhesive strength in the thickness direction of an expansive adhesive with higher accuracy than before.SOLUTION: Provided is an adhesive strength testing device for testing a tensile adhesive strength of an expandable adhesive with respect to a predetermined material, the testing device including: a pair of test pieces made of the material; a spacer; a holding member that presses the test pieces facing each other via the spacer and holds the test pieces such that a space is formed between facing surfaces of the test pieces; and a tensile member that has a first attachment portion attached to a tensile force generator that generates a tensile force and a second attachment portion attached to each of the test pieces from which the holding structure has been removed, the facing surfaces being bonded to each other by the expandable adhesive disposed in the space, and that transmits the tensile force generated by the tensile force generator to each of the test pieces to pull the test pieces in a direction in which the facing surfaces are separated from each other.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an adhesive strength testing device for testing the adhesive strength of an expansive adhesive, and an adhesive strength testing method using this testing device. [Background technology]

[0002] As a test device for testing the shear adhesive strength in the thickness direction of an adhesive, a device such as that disclosed in Non-Patent Document 1 is known. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] JIS K 6849 "Test method for tensile bond strength of adhesives" Summary of the Invention [Problem to be solved by the invention]

[0004] When testing the adhesive strength of an expandable adhesive using this conventional test method, the expandable adhesive placed between the metal pieces must expand and adhere to the metal pieces. The adhesive strength of an expandable adhesive is affected by its expansion coefficient. For example, if the expandable adhesive expands too much and the internal voids become too large, the adhesive strength will decrease. On the other hand, if the expansion coefficient of the expandable adhesive is insufficient, the adhesion to the adherend will decrease, and the adhesive strength will also decrease. Therefore, in order to accurately measure the adhesive strength of an expandable adhesive, it is necessary to adjust the expansion coefficient to a constant value suitable for measurement. However, since it is difficult to control the expansion rate of the expansive adhesive with the conventional testing device described above, it is difficult to accurately test the shear adhesive strength (tensile adhesive strength) in the thickness direction of the expansive adhesive.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an adhesive strength testing device that can test the tensile adhesive strength in the thickness direction of an expandable adhesive with greater accuracy than conventional devices. [Means for solving the problem]

[0006] That is, the present invention is as follows. [1] A test for testing the tensile adhesion of an expansive adhesive to a predetermined material, comprising: A pair of test pieces made of the material; A spacer; a holding member that presses the test pieces against each other via the spacer to form a space between the opposing surfaces of the test pieces; and an adhesive strength testing device comprising: a first mounting portion attached to a tensile force generator that generates a tensile force; a second mounting portion attached to each test piece from which the holding structure has been removed, the first mounting portion being attached to a tensile force generator that generates a tensile force; and a tensioning member that transmits the tensile force from the tensile force generator to each test piece and pulls the opposing surfaces in directions away from each other. [2] The adhesive strength testing device described in [1] is characterized in that the holding member comprises a pair of flat plate-like members and a pressing member that engages with each of the flat plate-like members and applies a force to each of the flat plate-like members in a direction that brings them closer to each other, and holds each of the test pieces between the flat plate-like members. [3] An adhesion testing apparatus as described in [1] or [2], characterized in that the test pieces are arranged so that parts of them overlap when viewed from a direction perpendicular to the opposing surfaces (hereinafter also referred to as the planar direction), and the spacer is interposed in the overlapping parts to form the space. [4] An adhesive strength testing device according to any one of [1] to [3], characterized in that each test piece is a rectangular plate and is arranged in a cross shape when viewed from the planar direction. [5] The adhesive strength testing device according to [3], characterized in that the second attachment portion of the tension member is attached to a portion of each test piece other than the overlapping portion. [6] The tension member comprises a main body member and a protruding member that protrudes integrally from both sides of the main body member, and the first mounting portion is provided on the main body member, and the second mounting portion is provided on the protruding member. [7] A method for testing the tensile adhesion of an expansive adhesive to a predetermined material, comprising: a space forming step of pressing and holding a pair of test pieces made of the material together with a spacer interposed therebetween, and forming a space between opposing surfaces of the test pieces by the spacer; an adhesive placement step of placing an expandable adhesive in the space (before or after the space forming step); a bonding step of expanding the expandable adhesive while the test pieces are pressed and held together, and bonding the opposing surfaces of the test pieces together with the expandable adhesive; a pressure-holding release step of releasing the pressure-holding of the test pieces after the test pieces are bonded together with the expansive adhesive; a pulling step of pulling each test piece in a direction in which the opposing surfaces move apart after the pressing and holding releasing step. [8] An expansive adhesive having a tensile adhesive strength of 3.0 MPa or more in the thickness direction as measured using the adhesive strength tester described in [1] to [6]. [9] A method for manufacturing an article comprising a first adherend, a second adherend, and an adhesive layer formed from an expandable adhesive, comprising: The expandable adhesive according to [8] is placed between the first adherend and the second adherend; and a bonding step of expanding the expandable adhesive to fill a gap between the first adherend and the second adherend, thereby bonding the first adherend and the second adherend. [Effects of the Invention]

[0007] According to the present invention, an adhesive strength testing device can be provided that can test the tensile adhesive strength in the thickness direction of an expansive adhesive with greater accuracy than conventional devices. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing an assembled structure of a test piece and a holding member of an adhesive strength testing device according to an embodiment of the present invention. [Figure 2] 2A to 2C are schematic diagrams illustrating the structure of each part of the test piece and the holding member in FIG. 1. [Figure 3] FIG. 2 is a schematic diagram showing a structure in which a mounting member is attached to a test piece according to the present embodiment. [Figure 4] 4 is a schematic diagram illustrating the structure of each part of the test piece and mounting member in FIG. 3. [Figure 5] 1A to 1C are schematic diagrams illustrating an adhesive strength testing method according to an embodiment of the present invention. [Figure 6] 1A to 1C are schematic diagrams illustrating an adhesive strength testing method according to an embodiment of the present invention. [Figure 7] 1A to 1C are schematic diagrams illustrating an adhesive strength testing method according to an embodiment of the present invention. [Figure 8] 1A to 1C are schematic diagrams illustrating an adhesive strength testing method according to an embodiment of the present invention. [Figure 9] 3 is a cross-sectional photograph of an adhesive layer in an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the present invention will be described in detail with reference to exemplary embodiments, although the present invention is not limited thereto.

[0010] <Configuration of Adhesion Strength Testing Device> The adhesion testing device 100 according to this embodiment tests the tensile adhesion in the thickness direction of an expansive adhesive for a predetermined material.

[0011] As shown in Figures 1 to 4, the adhesive strength testing device 100 includes, for example, a pair of test pieces 1 made of the material, a spacer 2, a holding member 3 that presses the test pieces 1 against each other via the spacer 2 and holds them so that a space S is formed between the opposing surfaces of the test pieces 1, and a tensioning member 4 that transmits the tensile force from the tensile force generator T to the test pieces 1 and pulls the opposing surfaces in a direction away from each other, the opposing surfaces of which are bonded together by a first mounting portion 41a attached to a tensile force generator T that generates a tensile force and the expandable adhesive G arranged in the space S, and has a second mounting portion 42a that is attached to each test piece 1 from which the holding member 3 has been removed.

[0012] The test pieces 1 are rectangular strip-shaped flat plates of equal thickness, as shown in Figure 1 or Figure 2, for example. As mentioned above, the test pieces 1 are formed from a predetermined material, and it is preferable to use a material that is the target of testing the adhesive strength of the expanding adhesive G to be tested, but here a steel plate is used. It is more preferable to use an SPCC material or the like, which is characterized by a relatively smooth surface, as the material for the test pieces 1.

[0013] If the test piece 1 itself is deformed when pulled by the tensile force generated by the tensile force generator T, it will be impossible to measure only the tensile adhesive strength in the thickness direction of the expandable adhesive G adhered to the test piece 1, so it is preferable that the test piece 1 does not deform under forces within the range of the tensile adhesive strength in the thickness direction of the expandable adhesive G. Although it depends on the pulling force, if the test piece 1 is a steel plate such as that described above, its thickness is preferably more than 0.6 mm, more preferably 1 mm or more, and even more preferably 1.5 mm or more, within the range of the tensile adhesive strength in the thickness direction of the expandable adhesive G.

[0014] On the other hand, if the thickness of the test piece 1 is too large, when the expandable adhesive G is expanded by heating, the heat capacity of the test piece 1 is large and it is difficult to control the heat supplied to the expandable adhesive G, so the thickness of the test piece 1 is preferably 10 mm or less, more preferably 8 mm or less, and even more preferably 6 mm or less.

[0015] The test pieces 1 are arranged so that parts of them overlap when viewed from a direction perpendicular to the opposing surfaces (hereinafter also referred to as a planar direction), and are fixed by a holding member so that the spacer 2 is interposed in the overlapping parts to form the space S. In this embodiment, as shown in Figure 1 or Figure 2, the two test pieces 1 are arranged so as to form a cross when viewed from the planar direction.

[0016] The spacer 2 is a strip-shaped flat plate with a uniform thickness, as shown in Fig. 1 or 2, for example. Here, two spacers 2 are arranged as a pair of spacers. The spacers 2 are preferably fixed in advance to one of the test pieces 1 so that their long dimension is parallel to the short dimension of the test piece 1 and so that they are spaced a uniform distance apart. The positions at which the spacers 2 are fixed are preferably symmetrical with respect to the center line of the test piece 1 in the long dimension.

[0017] The holding member 3 includes, for example, a pair of flat plate-like members 31 each having an equal square shape, and a pressing member 32 that engages with holes drilled at the four corners of the flat plate-like members 31.

[0018] The pressing member 32 is, for example, a screw and a nut as shown in Figure 1 or Figure 2. By tightening the nut or the screw, a force is applied to the flat plate-like members in a direction that moves them toward each other.

[0019] The holes formed in the flat plate-like member 31 are arranged to avoid the two test pieces 1 mentioned above so that they are not hidden by these two test pieces 1 when viewed from the planar direction.

[0020] As shown in FIG. 3 or 4, the tension member 4 is composed of a rectangular parallelepiped main body member 41 and a pair of protruding members 42 that protrude symmetrically from the bottom of the main body member 41 on both sides.

[0021] The main body member 41 is provided with a first mounting portion 41a, and the protruding member 42 is provided with a second mounting portion 42a.

[0022] The first mounting portion 41a is, for example, a through hole provided on the vertical center line of the main body member 41, and a mounting bracket T1 of the tensile force generator T is attached to this through hole.

[0023] The second attachment portions 42a are, for example, through-holes that pass vertically through each of the protruding members 42. These through-holes overlap with the insertion holes 1a provided at both ends of the test piece 1 (portions where the test pieces 1 do not overlap each other), and the tensile member 4 can be attached to the test piece 1 by inserting screws into these holes and tightening them with nuts.

[0024] The tensile force generator T is not particularly limited, and a commercially available tensile force generator that has been conventionally used to test the tensile adhesive strength of adhesives can be used.

[0025] <Adhesion strength test method> The method and procedure for testing the tensile adhesive strength in the thickness direction of the expansive adhesive G using the adhesive strength testing device 100 according to this embodiment is as follows, as shown in, for example, FIGS.

[0026] First, a pair of test pieces 1 made of a predetermined material are pressed together with a spacer 2 interposed therebetween, and a space S of a predetermined size is formed between the opposing surfaces of each test piece 1 by the spacer 2 (space forming step).

[0027] Next, an expansive adhesive G is placed in the space S (adhesive placing step). Note that this adhesive placing step may be performed before the space forming step.

[0028] After the adhesive placement step, while the test pieces 1 are pressed and held together, the expandable adhesive G is expanded to bond the opposing surfaces of the test pieces 1 together with the expandable adhesive G (bonding step). There are no particular limitations on the method for expanding the expandable adhesive G, and it may be expanded by heating or any other method suitable for the expandable adhesive G to be tested.

[0029] After the test pieces 1 are bonded together with the expansive adhesive G, the pressing member 32 is removed from the test pieces 1 to release the pressing and holding of the test pieces 1 together (pressing and holding releasing step).

[0030] After the pressure holding release step, the second mounting portion 42a of the tensioning member 4 is attached to each test piece 1, and a tension force generator T is attached to the first mounting portion 41a of the tensioning member 4, thereby pulling each test piece 1 in the direction in which the opposing surfaces move apart (tensile step).

[0031] The tensile force generated by the tensile force generator T in this tensile step is gradually increased, the maximum tensile force when the expandable adhesive G peels off from the test piece 1 is measured, and the tensile adhesive force in the thickness direction of the expandable adhesive G is calculated based on the value of this maximum tensile force (adhesion force calculation step). Specifically, the maximum tensile force [N] is calculated by multiplying the maximum tensile force (unit: Newton [N]) measured by a pressure sensor (load cell) provided in the tensile force generator T by the area of ​​contact with the test piece (unit: mm 2 ) the adhesive strength (unit: MPa) in the thickness direction of the expanding adhesive can be calculated. This adhesive strength calculation step may be performed by an information processing unit included in the tensile tester, or may be calculated manually by a user based on a signal output from the tensile tester.

[0032] <Effects of the adhesive strength testing device or adhesive strength testing method according to this embodiment> The adhesion testing apparatus 100 and adhesion testing method configured as described above include a pair of test pieces 1 made of the material, a spacer 2, and a holding member 3 that presses the test pieces 1 together facing each other via the spacer 2, forming a space S between the opposing surfaces of the test pieces 1. By adjusting the position and / or thickness of the spacer 2, the size of the space S can be set to a constant size suitable for the test, and the expansion rate of the expandable adhesive G can be adjusted to a constant condition. As a result, the adhesive strength of the expandable adhesive G in the thickness direction can be evaluated more accurately than before.

[0033] Since the test pieces 1 are provided with a holding member that presses the test pieces 1 against each other via the spacer 2, the positional relationship between the two test pieces 1 is not changed by the force of the expansion of the expandable adhesive G until the expandable adhesive G expands and hardens. Therefore, when pulling the expandable adhesive G with the tensile force generator T, a force can be applied directly to the expandable adhesive G in its thickness direction, and as a result, the tensile adhesive force in the thickness direction can be measured as accurately as possible.

[0034] By attaching a tensile force generator T to the first mounting portion 41a of the tension member 4, each test piece 1 is pulled in the direction in which the opposing surfaces move apart, so that a wide range of commercially available tensile force generators that have been conventionally used can be used.

[0035] Since all components are symmetrical about a central axis extending in the direction in which the pulling force is applied (thickness direction of the expandable adhesive G), a pulling force can be applied straight in the thickness direction of the expandable adhesive G. <Expansive adhesive>

[0036] The expandable adhesive G having a tensile adhesion strength of 3.0 MPa or more in the thickness direction measured by the adhesion testing apparatus 100 and adhesion testing method according to this embodiment is also part of the present invention.

[0037] The expandable adhesive G of this embodiment can be used in the manufacture of an article comprising a first adherend, a second adherend, and an adhesive layer formed from an expandable adhesive, the method including a bonding step of bonding the first adherend and the second adherend by placing the expandable adhesive G between the first adherend and the second adherend and expanding the expandable adhesive G to fill the gap between the first adherend and the second adherend.

[0038] By using an expandable adhesive G having a tensile adhesion of 3.0 MPa or more in the thickness direction measured using the adhesion testing apparatus 100 and adhesion testing method of this embodiment, it is possible to manufacture articles with higher reliability than conventional products.Such an expandable adhesive can be used in a variety of fields, for example, as a conductive sheet for electronic equipment or electronic devices where high reliability in adhesion in the thickness direction is required, or as an insulating sheet for electronic equipment or electronic devices.More specifically, it can be suitably used for inserting it between a rotor core (also referred to as the first adherend) and a magnet (also referred to as the second adherend) in an automobile drive motor to bond them together.

[0039] More specifically, in expandable adhesives used to secure magnets in rotors of drive motors for automobiles and the like, stress is exerted not only in the plane direction (XY direction) of the magnets to prevent them from popping out of the motor, but also in the thickness direction (Z direction) of the expandable adhesive due to the different thermal expansion behaviors of the rotor and magnets. Furthermore, with the recent development of EV-compatible motors and the like, rotor components such as those described above are required to have increasingly higher rotation speeds, and it is thought that centrifugal force will also exert even greater stress in the Z direction than before. Therefore, expandable adhesives used in these components are required to have highly reliable tensile adhesive strength in the Z direction. Therefore, an expandable adhesive G suitable for such applications has a tensile adhesion strength in the thickness direction of 3.0 MPa or more, as measured using the adhesion testing apparatus 100 and adhesion testing method according to this embodiment.

[0040] Examples of the expansive adhesive G having a tensile adhesion amount in the thickness direction of 3.0 MPa or more measured using the adhesion testing apparatus 100 and adhesion testing method according to this embodiment include the following.

[0041] The expandable adhesive G contains, for example, an epoxy resin, a curing agent, and a foaming agent.

[0042] Examples of epoxy resins include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins and bisphenol F-type epoxy resins, novolac-type epoxy resins such as bisphenol A novolac-type epoxy resins and cresol novolac-type epoxy resins, and modified epoxy resins such as urethane-modified epoxy resins and rubber-modified epoxy resins. Specific examples include biphenyl-type epoxy resins, stilbene-type epoxy resins, triphenolmethane-type epoxy resins, alkyl-modified triphenolmethane-type epoxy resins, and triazine nucleus-containing epoxy resins, and the like, and the composition may contain one or more of these.

[0043] It is more preferable to use an epoxy resin that is solid at room temperature, as this improves the slipperiness when inserting into gaps between components to be filled and fixed, making it easier to insert into narrow gaps.

[0044] The content of the epoxy resin in the adhesive layer formed from the expandable adhesive is preferably 20% by mass or more and 80% by mass or less, when the total amount of the adhesive layer is taken as 100% by mass.

[0045] The curing agent may be any agent capable of curing the epoxy resin described above, and may be one or more of a wide variety of agents, such as amide-based curing agents such as dicyandiamide and aliphatic polyamide; amine-based curing agents such as diaminodiphenylmethane, metaphenylenediamine, ammonia, triethylamine, and diethylamine; phenol-based curing agents such as bisphenol A, bisphenol F, phenol novolac resin, cresol novolac resin, and p-xylene novolac resin; and acid anhydride-based curing agents.

[0046] While any of the curing agents described above can be used without any problems and there are no particular restrictions on the amount of curing agent used, it is particularly preferred that the curing agent contains an amide-based curing agent and that the equivalent ratio (C / E) between the functional group (E) of the thermosetting resin, such as an epoxy group, and the functional group (C) of the curing agent, such as a carboxyl group, which is capable of reacting with the functional group (E), is 0.6 or more and 0.9 or less. By setting the equivalent ratio to 0.6 or more, a sufficient curing reaction can occur in the expandable adhesive, thereby sufficiently increasing the strength of the expandable adhesive.

[0047] The preferred content of each component varies depending on the combination of epoxy resin and curing agent used. However, to achieve the aforementioned equivalent ratio, the content of curing agent in the adhesive layer formed from the expandable adhesive is preferably 1% by mass or more and 40% by mass or less relative to 100% by mass of the epoxy resin in the adhesive layer. For example, when an amide-based curing agent is used as the main curing agent, the content of curing agent in the adhesive layer is preferably 1% by mass or more and 15% by mass or less relative to 100% by mass of the epoxy resin contained in the adhesive layer. On the other hand, when a phenol-based curing agent is used as the main curing agent, the content of curing agent in the adhesive layer is preferably 5% by mass or more and 40% by mass or less relative to 100% by mass of the epoxy resin in the adhesive layer.

[0048] As the foaming agent, it is preferable to use thermally expandable microcapsules, which can form closed cells and disperse stress. These thermally expandable microcapsules contain a thermal expansion agent, such as hydrocarbon, inside a shell made of resin. When such thermally expandable microcapsules are heated, the resin that makes up the shell softens, and the pressure of the thermal expansion agent, such as hydrocarbon, increases, causing the thermally expandable microcapsules to expand. This expansion thins the shell, and if the microcapsules are heated further, the thermal expansion agent escapes from the microcapsules, causing them to shrink. The temperature just before this shrinkage begins is called the maximum expansion temperature. It is preferable that the foaming agent has a maximum expansion temperature within ±20°C of the curing exothermic peak temperature in the DSC curve of the epoxy resin described above obtained by a differential scanning calorimeter. By using a foaming agent with such a maximum expansion temperature, it is possible to increase the thickness of the expandable adhesive sheet when the expandable adhesive is heated and expanded and then cooled to room temperature.

[0049] The content of the foaming agent in the adhesive layer formed from the expandable adhesive is preferably 3% by mass or more and 32% by mass or less, more preferably 4% by mass or more and 24% by mass or less, and even more preferably 5% by mass or more and 16% by mass or less, based on the total adhesive layer. By containing a foaming agent of 3% by mass or more, sufficient foaming can be achieved in the expandable adhesive, improving adhesive strength. Furthermore, by containing a foaming agent of 32% by mass or less, a decrease in adhesive strength due to excessive foaming can be suppressed, a decrease in heat resistance can be suppressed, and foaming agent cell breakage can be suppressed. By suppressing cell breakage, bubbles are prevented from becoming interconnected, thereby suppressing a decrease in adhesive strength in the thickness direction and in the plane direction. If the density of the foaming agent is too high, cell breakage can occur easily, particularly in the surface layer of the adhesive layer (the interface between the adhesive layer and the adherend), forming a layered structure in which interconnected bubbles are stacked in layers along the thickness direction. If such a layered structure is formed, the adhesive layer is likely to crack from the interconnected bubbles, running parallel to the plane of the adhesive layer, resulting in a decrease in adhesive strength in the thickness direction. A foaming agent content of 32% by mass or less in the expandable adhesive is preferred because it suppresses cell breakage in the surface layer of the adhesive layer and suppresses a decrease in adhesive strength in the thickness direction.

[0050] The expandable adhesive according to this embodiment may further contain a thermoplastic resin. The thermoplastic resin may include, for example, at least one of polyester resin, butyral resin, urethane resin, acrylic resin, carboxyl-terminated butadiene nitrile rubber (CTBN), and epoxy-modified butadiene. Among these, it is preferable to include an elastomer-based resin as the thermoplastic resin, such as butyral resin, acrylic thermoplastic elastomer, and urethane thermoplastic elastomer, and one or more of these may be included. When two or more types of thermoplastic resins are used, it is preferable that the glass transition temperature Tg of at least one of the thermoplastic resins is 100°C or higher and 120°C or lower.

[0051] When a thermoplastic resin is contained, the content of the thermoplastic resin in the adhesive layer formed by the expandable adhesive is preferably 3% by mass or more and 30% by mass or less, more preferably 4% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less. By making the content of the thermoplastic resin 3% by mass or more, the flexibility and toughness of the adhesive layer can be increased. Furthermore, by making the content of the thermoplastic resin 30% by mass or less, when the expandable adhesive is thermally expanded, the complex melt viscosity of the expandable adhesive when it reaches the thermal expansion starting temperature of the foaming agent can be suppressed, and the expandable adhesive can be sufficiently expanded.

[0052] The expandable adhesive may further include a filler. Examples of fillers include inorganic fillers such as aluminum oxide, magnesium oxide, calcium oxide, aluminum hydroxide, magnesium hydroxide, magnesium carbonate, boron nitride, silicon nitride, silicon oxide, talc (magnesium silicate), titanium oxide, potassium titanate, and boehmite.

[0053] The filler may have a variety of shapes, including polygonal, spherical, fibrous, scaly, needle-like, and irregular shapes. Fillers with a relatively high aspect ratio are preferably used because the fillers entangle with each other in the resin, thereby increasing the strength of the adhesive layer in the planar and thickness directions, thereby improving the rigidity, particularly the bending resistance, of the adhesive layer formed from the expandable adhesive. The aspect ratio is preferably 10 to 50, and more preferably 20 to 40. Examples of fillers with a relatively high aspect ratio include fibrous fillers, scaly fillers, and needle-like fillers. Needle-like fillers are particularly preferred due to their good dispersibility and their high effect of improving the rigidity of the adhesive layer.

[0054] The bending resistance of the adhesive layer obtained by incorporating the above-mentioned filler into the expandable adhesive is, for example, 0.1 mN or more, preferably 0.2 mN or more. On the other hand, the bending resistance is, for example, preferably 5.0 mN or less, more preferably 4.0 mN or less. By setting the bending resistance within this range, it is expected that the shape retention of the adhesive layer will be good. The bending resistance can be calculated by testing a test piece prepared by cutting a 25 x 25 mm sheet from the adhesive layer using a Gurley-type testing machine (manufactured by Toyo Tester Kogyo Co., Ltd.) in accordance with JIS L 1085.

[0055] When a filler is contained in the expandable adhesive, the filler content in the adhesive layer formed by the expandable adhesive is preferably 5% by mass or more and 50% by mass or less, more preferably 7% by mass or more and 35% by mass or less, and particularly preferably 10% by mass or more and 25% by mass or less. A filler content of 5% by mass or more in the adhesive layer is preferable because it can further improve the thermal conductivity and rigidity of the adhesive layer. Furthermore, a filler content of 50% by mass or less in the adhesive layer can suppress excessive thixotropy in the expandable adhesive before curing, minimizing limitations on the production of adhesive sheets and articles using this expandable adhesive.

[0056] When using a thermoplastic resin, it is difficult to dissolve the thermoplastic resin in a solvent if it remains in large chunks. Therefore, it is necessary to crush the thermoplastic resin beforehand. However, when using a thermoplastic resin with a relatively low elastic modulus, the crushed thermoplastic resin fragments may quickly block, making it difficult to dissolve again. In such cases, the aforementioned blocking can be suppressed by sprinkling a filler on the thermoplastic resin while crushing it. This anti-blocking filler is contained in the expandable adhesive together with the thermoplastic resin. Although a wide variety of fillers as described above can be used as the anti-blocking filler, it is preferable that the filler has a large particle size and a high Mohs hardness, because the large particle size of the filler can prevent contact between thermoplastic resins, and the high Mohs hardness can prevent the filler from being crushed during pulverization, resulting in a reduction in the filler particle size. The average particle size of the blocking filler is preferably 0.05 μm or more from the viewpoint of suppressing secondary aggregation, and is preferably 5 μm or less from the viewpoint of preventing appearance problems when the adhesive is molded into a sheet. The average particle size of the blocking filler is more preferably 0.1 μm or more and 2 μm or less. Furthermore, the Mohs hardness of the blocking filler is preferably relatively high, but is preferably 5 or less from the viewpoint of preventing metal contamination due to damage to the equipment used when crushing the thermoplastic resin.

[0057] The expandable adhesive may be used by placing only an adhesive layer formed by foaming and curing the expandable adhesive between the adherend, or it may be used as an adhesive sheet comprising a substrate and an adhesive layer laminated on one or both sides of the substrate. When an adhesive sheet is formed with a substrate, the substrate also functions as a support material, thereby improving handleability and workability.

[0058] The thickness of the adhesive layer is not particularly limited, but is preferably equal to or greater than the average particle size of the foaming agent. For example, it is 10 μm or more, or may be 15 μm or more, or may be 20 μm or more. If the adhesive layer is too thin, it may be difficult to obtain sufficient adhesion to the substrate and adhesion after foaming and curing. On the other hand, the thickness of the adhesive layer is, for example, 100 μm or less, or may be 75 μm or less, or may be 50 μm or less. If the adhesive layer is too thick, the surface quality may deteriorate, and if it is made into a roll product, the expanding adhesive may ooze out.

[0059] When an adhesive sheet is formed by laminating a substrate and an adhesive layer, the substrate functions as a support material that supports the adhesive layer. The substrate is preferably insulating. The substrate is preferably in the form of a sheet. The substrate may have a single layer structure or a multi-layer structure. The substrate may or may not have a porous structure inside. Examples of the substrate include a resin substrate and a nonwoven fabric.

[0060] Examples of materials that may constitute the substrate as described above include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate (PEN), and aromatic polyester; polycarbonate; polyarylate; polyurethane; polyamide resins such as polyamide and polyetheramide; polyimide resins such as polyimide, polyetherimide, and polyamideimide; polysulfone resins such as polysulfone and polyethersulfone; polyetherketone resins such as polyetherketone and polyetheretherketone; polyphenylene sulfide (PPS); and modified polyphenylene oxide.

[0061] The glass transition temperature of these resins is preferably, for example, 80° C. or higher, and may be 140° C. or higher, or may be 200° C. or higher. Furthermore, liquid crystal polymers (LCPs) may be used as the resin.

[0062] Among the above-mentioned materials, the substrate preferably contains polyimide (PI) or polyethylene naphthalate (PEN). Polyimide and polyethylene naphthalate have high heat resistance and are suitable for use in cases where the expandable adhesive is thermally expanded by heating to foam and harden. Polyimide and polyethylene naphthalate are also preferred because they have high insulating properties and can insulate components from each other using an adhesive layer after foaming and hardening, for example.

[0063] The thickness of the substrate is preferably, for example, 1 μm to 125 μm, more preferably 10 μm to 75 μm, and particularly preferably 20 μm to 50 μm. For example, when the expandable adhesive according to this embodiment is used in a motor slot or the like, by providing a certain thickness to the substrate, it is possible to prevent the expandable adhesive from buckling when inserted into the motor slot. Furthermore, by not making the substrate too thick, it is possible to ensure a sufficient space factor for the coil.

[0064] As described above, when an adhesive layer is laminated on a substrate, the adhesive layer can be formed, for example, by applying an expandable adhesive to the substrate and then removing the solvent. Examples of application methods include roll coating, reverse roll coating, transfer roll coating, gravure coating, gravure reverse coating, comma coating, rod coating, blade coating, bar coating, wire bar coating, die coating, lip coating, and dip coating.

[0065] The adhesive layer may be a continuous layer or a discontinuous layer. Examples of such patterns include stripes and dots. In addition, the surface of the adhesive layer may be embossed or the like. The surface may have a concave-convex shape.

[0066] The adhesive layer may or may not have tackiness. The adhesive layer's tackiness can improve adhesion to the adherend. Specifically, when one adherend is adhesively fixed to a hole, groove, or the like of another adherend, an adhesive sheet is attached to the other adherend, the other adherend with the adhesive sheet attached is inserted into the hole, groove, or the like of the first adherend, and the expandable adhesive forming the adhesive layer is then foamed and cured to bond the two adherends together. In this case, if the tackiness of the adhesive layer is within a predetermined range, the adhesive layer's tackiness can be used to improve adhesion of the adhesive sheet to the other adherend when attaching the foamable adhesive sheet to the other adherend. This can prevent the adhesive sheet from peeling off or shifting when the other adherend with the adhesive sheet attached is inserted into the hole, groove, or the like of the first adherend. Furthermore, by making the surface of the adhesive layer substantially tack-free, it is possible to improve the sliding properties. If the surface of the adhesive layer is non-tacky, for example, when bonding a stator core and a coil, an adhesive sheet having a non-tacky adhesive can be inserted more smoothly into the gap in the stator core, and the coil can be inserted more smoothly into the gap that has become narrower due to the insertion of the adhesive sheet.

[0067] As described above, when the substrate and the adhesive layer are laminated, an intermediate layer may be further provided between the substrate and the adhesive layer. The provision of the intermediate layer can improve the adhesion of the adhesive layer to the substrate. Furthermore, the provision of the intermediate layer can, for example, alleviate stress on the bent portion when the adhesive sheet is folded, or alleviate stress on the cut portion when the adhesive sheet is cut. As a result, lifting or peeling of the adhesive layer from the substrate can be suppressed when the adhesive sheet is bent or cut.

[0068] The intermediate layer is formed on one or both sides of the substrate, and may be a continuous layer that continuously covers the surface of the substrate, or a discontinuous layer made up of a plurality of islands.

[0069] It is preferable that the intermediate layer has almost no cross-linked structure before the adhesive layer is laminated, and that a cross-linking reaction can occur between the intermediate layer and the adhesive layer when the adhesive layer is heated and expanded. In order to ensure a sufficient cross-linking reaction with the adhesive layer, it is preferable that the intermediate layer contains a resin containing a carboxyl group as a functional group. For the same reason, it is also preferable that the intermediate layer according to this embodiment does not contain a curing agent for curing the resin contained in the intermediate layer.

[0070] Examples of resins containing a carboxyl group include polyester resins, polyesters, copolymers containing polyesters, and the like. Furthermore, the acid value of the resin containing a carboxyl group is preferably at least 5. By setting the acid value to at least 5, the carboxyl group can be sufficiently crosslinked with the epoxy resin contained in the adhesive layer when the adhesive layer is thermally expanded, and therefore the adhesive strength between the intermediate layer and the adhesive layer can be sufficiently increased, and peeling of the adhesive layer from the intermediate layer can be sufficiently suppressed.

[0071] The intermediate layer is formed between the substrate and the adhesive layer and preferably relieves stress generated between the adhesive layer and the substrate, and therefore preferably contains a material with excellent flexibility. In addition to the resins described above, the intermediate layer may contain a filler for the purpose of improving heat resistance, thermal conductivity, and rigidity.

[0072] The filler may be the same as that contained in the adhesive layer. The intermediate layer and the adhesive layer may contain the same type of filler or different types of fillers. When the intermediate layer contains a filler, the filler content in the intermediate layer is preferably 10% by mass or less. By setting the filler content in the intermediate layer within the above-mentioned range, a sufficient contact area between the resin contained in the intermediate layer and the resin contained in the adhesive layer can be ensured, which is preferable because it is possible to maintain high adhesive strength between the intermediate layer and the adhesive layer.

[0073] In order to increase the expansion rate of the adhesive sheet as a whole, the intermediate layer may contain an expansion agent. The type of expanding agent that can be used may be the same as that contained in the adhesive layer. The same type of agent may be used in the intermediate layer and the adhesive layer, or different types may be used.

[0074] When the intermediate layer contains an expanding agent, the content of the expanding agent in the intermediate layer is preferably less than the content of the foaming agent in the adhesive layer, for example, preferably 25% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less, since this sufficiently reduces the possibility of the expanding agent expanding between the substrate and the intermediate layer and sufficiently suppresses peeling between the intermediate layer and the adhesive layer.

[0075] The thickness of the intermediate layer is preferably from 0.1 μm to 10 μm, more preferably from 0.3 μm to 7 μm, and particularly preferably from 0.5 μm to 4 μm.

[0076] A release layer may be laminated on the surface of the adhesive layer, so that the release layer can be peeled off before the expandable adhesive is expanded and cured. The release layer is not limited to one formed by applying a release agent, but may also be one formed from an adhesive-permeable material such as nonwoven fabric that allows the expansive adhesive to pass through.

[0077] Specific examples of release agents include organic heat-melting polymers such as paraffin and long-chain alkyl compounds, and inorganic fine particles such as silicone, calcium carbonate, and silicon oxide fine particles. Among these, long-chain alkyl compounds are preferred from the standpoint of the storage stability and adhesiveness of the adhesive sheet.

[0078] Other examples of usable release agents include thermoplastic resins such as phenoxy resin, polyester resin, polyurethane resin, polyimide resin, siloxane-modified polyimide resin, polybutadiene, polypropylene, styrene-butadiene-styrene copolymer, styrene-ethylene-butylene-styrene copolymer, polyacetal resin, polyvinyl butyral resin, polyvinyl acetal resin, butyl rubber, chloroprene rubber, polyamide resin, acrylonitrile-butadiene copolymer, acrylonitrile-butadiene-acrylic acid copolymer, acrylonitrile-butadiene-styrene copolymer, polyvinyl acetate, and nylon. These can be used alone or in combination. Among these, phenoxy resin, polyester resin, and the like are preferred.

[0079] The phenoxy resin is not particularly limited, and examples thereof include those having one or more skeletons selected from a bisphenol A skeleton, a bisphenol F skeleton, a bisphenol S skeleton, a bisphenolacetophenone skeleton, a novolac skeleton, a biphenyl skeleton, a fluorene skeleton, a dicyclopentadiene skeleton, a norbornene skeleton, a naphthalene skeleton, an anthracene skeleton, an adamantane skeleton, a terpene skeleton, and a trimethylcyclohexane skeleton.

[0080] The release agent may further contain a curing agent such as an isocyanate or an organic peroxide in addition to the thermoplastic resin as described above, as necessary. By appropriately selecting and adding the type and molecular weight of the curing agent, it becomes easy to fine-tune the affinity with the adhesive layer. When the release agent contains a curing agent, the content of the curing agent is preferably 3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the thermoplastic resin.

[0081] The adhesive-permeable material is preferably a sheet-like material having a structure with at least a plurality of holes penetrating from one main surface to the other. By providing such a structure with a plurality of holes, the expandable adhesive, which is in contact with only one of the main surfaces of the release layer (i.e., the adhesive-permeable material) before heating, can penetrate the holes and reach the other main surface of the release layer upon expansion. The adhesive-permeable material preferably has a glass transition temperature higher than the curing initiation temperature of the expandable adhesive constituting the adhesive layer. Examples of such adhesive-permeable materials include nonwoven fabrics or paper based on natural fibers, chemical fibers, or mixtures thereof. Exemplary nonwoven fabrics include cellulose-based nonwoven paper, glass nonwoven fabric, aramid-based nonwoven fabric, polyolefin-based nonwoven fabric, polysulfone-based nonwoven fabric, polyaramid nonwoven fabric, polyphenylsulfide-based nonwoven fabric, polyester-based nonwoven fabric, nylon-based nonwoven fabric, and liquid crystal polymer (LCP)-based nonwoven fabric. Such nonwoven fabrics / papers have multiple through holes on the inside, so that an expandable adhesive in contact with one of the major surfaces can penetrate the inside of the nonwoven fabric / paper and reach the other major surface under certain conditions.

[0082] The basis weight of the nonwoven fabric or paper mentioned above is at least 10 g / m 2 , preferably 11 g / m 2 The thickness of the nonwoven fabric / paper is preferably 50 μm or less, and more preferably 47 μm or less.

[0083] As an example of the expansive adhesive as described above, one having the following composition was prepared and tested using the adhesive strength testing device according to this embodiment. <Expansive adhesive A> Epoxy resin A (cresol novolac type, solid at room temperature, epoxy equivalent 209-219 g / eq): 13 parts by weight Epoxy resin B (bisphenol A type, solid at room temperature, epoxy equivalent 450-500g / eq): 36 parts by weight Epoxy resin C (bisphenol A type, liquid at room temperature, viscosity 120-150, epoxy equivalent 184-194 g / eq): 7 parts by weight Hardener A (dicyandiamide finely ground powder, 50% particle size 3 μm): 1.5 parts by weight Curing agent B (dicyandiamide-type latent curing agent, ADEKA Hardener EH4351S manufactured by ADEKA Corporation): 1.5 parts by weight Curing catalyst A (imidazole-type latent curing agent, ADEKA Hardener EH5046S): 0.05 parts by weight Curing catalyst B (2-ethyl-4-methylimidazole): 0.05 parts by mass Elastomer (ethylene acrylic rubber, Tg -31°C, Mooney viscosity ML(1+4)100°C 17.5): 56 parts by weight Foaming agent A (thermal expandable microcapsules, average particle size 6 μm to 11 μm, expansion start temperature 120 to 130°C, maximum expansion temperature 145 to 155°C, core: hydrocarbon, shell: thermoplastic polymer): 10 parts by mass Solvent (methyl ethyl ketone): 45 parts by weight

[0084] <Expansive adhesive B> Expansive adhesive B was prepared using the same composition and procedure as above, except that blowing agent B below was used instead of blowing agent A. Foaming agent B (thermal decomposition type foaming agent, azodicarbonamide, decomposition temperature: 145°C, generated gas amount: 130 ml / g): 10 parts by mass

[0085] <Formation of adhesive layer> Each of the expandable adhesives having the above-described compositions was formed into a sheet shape according to the following specific procedure. The release film used was HY-US20 (PET separator, thickness 38 μm) manufactured by Higashiyama Film Co., Ltd. Next, the above-mentioned expanding adhesive was applied to the release-treated surface of this release film using a Baker applicator so that the thickness after drying would be 50 μm. This was dried at 100°C for 120 seconds to remove the solvent, thereby forming an adhesive layer.

[0086] <Adhesion strength evaluation> An adhesive sheet of 10 x 10 mm was cut out from the adhesive layer (thickness 50 µm) prepared as described above before expansion and curing, and this was used for measurements according to the following procedure. The adhesive sheet was fixed to the test piece, an SPCC plate (3.2 mm thick), using a rubber roll heated to 100°C, and spacers (125 μm thick) were placed on both sides of the adhesive sheet. Another SPCC plate was then placed on top of it, stacked at a 90° angle when viewed from above, and a holding member was used to fix the gap between the SPCC plates, thereby preparing a sample. Next, this sample was placed in a heating furnace set at 155°C for 34 minutes, then removed from the heating furnace and allowed to cool naturally to room temperature, at which point the expansion rate of the expanding adhesive was 2.5 times. After the expansion and hardening were completed, the holding member was removed, and the SPCC plate test piece was attached to the mounting member. This mounting member was placed in a universal testing machine, and the shear adhesive strength of the sample in the Z direction was measured using the universal testing machine at a test speed of 2 mm / min.

[0087] <Test Results> The adhesive layer formed with adhesive composition A had a shear adhesive strength (tensile adhesive strength) in the Z direction of 5.6 MPa. On the other hand, the adhesive layer formed with adhesive composition B had a shear adhesive strength (tensile adhesive strength) in the Z direction of 0.1 MPa or less. As can be seen from the cross-sectional view of the adhesive layer shown in Figure 9, the adhesive layer formed with adhesive composition B, which uses a thermally decomposable foaming agent as a foaming agent, has internal open cells. In contrast, the adhesive layer formed with adhesive composition A, which uses thermally expandable microcapsules as a foaming agent, has internal closed cells. As a result, the adhesive layer formed with adhesive composition A has almost no open cells that could serve as the starting point for fracture of the adhesive layer when a shear adhesive strength (tensile adhesive strength) in the Z direction is applied, and the bubbles are uniformly dispersed, which is thought to have resulted in a significantly greater shear adhesive strength in the Z direction than the adhesive layer formed with resin composition B. [Explanation of symbols]

[0088] 100... Adhesion testing equipment 1. Test piece 2 Spacer 3. Holding member 31 Flat plate member 32 Pressing member 4. Tensile member 41 Main body member 41a···First mounting part 42 Protruding member 42a Second mounting part S...Space G. Expandable adhesive

Claims

1. 1. Testing the tensile adhesion of an expandable adhesive to a predetermined material, comprising: A pair of test pieces made of the material; A spacer; a holding member that presses the test pieces against each other via the spacer to form a space between the opposing surfaces of the test pieces; and an adhesive strength testing device comprising: a first mounting portion attached to a tensile force generator that generates a tensile force; a second mounting portion attached to each test piece from which the holding member has been removed, the first mounting portion being attached to a tensile force generator that generates a tensile force; and a tension member that transmits the tensile force from the tensile force generator to each test piece and pulls the opposing surfaces in directions away from each other.

2. The holding member is a pair of flat plate-like members; and a pressing member that engages with each of the flat plate-like members and applies a force to the flat plate-like members in a direction that causes the flat plate-like members to approach each other; 2. An adhesive strength testing apparatus according to claim 1, wherein each of said test pieces is sandwiched and held between said flat plate-like members.

3. An adhesive strength testing apparatus as described in claim 1, characterized in that each test piece is arranged so that parts of it overlap when viewed from a direction perpendicular to the opposing surface (hereinafter also referred to as the planar direction), and the spacer is interposed in the overlapping part to form the space.

4. 4. An adhesive strength testing apparatus according to claim 3, wherein each of said test pieces has a rectangular plate shape and is arranged so as to form a cross shape when viewed in said planar direction.

5. 4. An adhesive strength testing device according to claim 3, wherein the second attachment portion of the tension member is attached to a portion of each of the test pieces other than the overlapping portion.

6. An adhesive strength testing apparatus as described in claim 5, wherein the tension member comprises a main body member and protruding members that protrude integrally from both sides of the main body member, the first mounting portion being provided on the main body member, and the second mounting portion being provided on the protruding members.

7. 1. A method for testing the tensile adhesion of an expandable adhesive to a predetermined material, comprising: a space forming step of pressing and holding a pair of test pieces made of the material together with a spacer interposed therebetween, and forming a space between opposing surfaces of the test pieces by the spacer; An adhesive placement step of placing an expandable adhesive in the space before or after the space forming step; a bonding step of expanding the expandable adhesive while the test pieces are pressed and held together, and bonding the opposing surfaces of the test pieces together with the expandable adhesive; a pressure-holding release step of releasing the pressure-holding of the test pieces after the test pieces are bonded together with the expansive adhesive; a pulling step of pulling each test piece in a direction in which the opposing surfaces move apart after the pressing and holding releasing step.

8. An expandable adhesive having a tensile adhesive strength of 3.0 MPa or more in the thickness direction measured using the adhesive strength testing device according to any one of claims 1 to 6.

9. Contains an epoxy resin, a curing agent, and a foaming agent, 9. The expandable adhesive of claim 8, wherein the foaming agent is capable of forming closed cells.

10. The expandable adhesive according to claim 8 , which contains a filler, and the filler is one or more of a fibrous filler, a scaly filler, and a needle-like filler.

11. A method for manufacturing an article comprising a first adherend, a second adherend, and an adhesive layer formed from an expandable adhesive, comprising: Disposing the expandable adhesive of claim 8 between the first adherend and the second adherend; and a bonding step of expanding the expandable adhesive to fill a gap between the first adherend and the second adherend, thereby bonding the first adherend and the second adherend.

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