Adhesive sheet, bonded body, and method for separating bonded body

Abstract

The present invention pertains to an adhesive sheet having a band shape and provided with an adhesive layer, said adhesive sheet comprising a slanted part formed in a tapering shape such that the width thereof tapers toward one end of the adhesive sheet in the longitudinal direction.

Description

Pressure-sensitive adhesive sheet, joined body, and method for separating joined body

[0001] The present invention relates to a pressure-sensitive adhesive sheet, a bonded body, and a method for separating the bonded body.

[0002] In electronic component manufacturing processes, etc., there is an increasing demand for rework to improve yield and recycling by disassembling and recovering components after use. To meet such demands, double-sided pressure-sensitive adhesive sheets that have a certain degree of adhesive strength and also a certain degree of releasability are sometimes used to join components in electronic component manufacturing processes, etc. Patent Documents disclosing prior art related to this type of releasable pressure-sensitive adhesive sheet include Patent Documents 1 and 2.

[0003] Patent Documents 1 and 2 describe adhesive products with tabs that include an extensible adhesive sheet and tabs provided at the ends of the adhesive sheet.

[0004] Furthermore, as a double-sided pressure-sensitive adhesive sheet that achieves both adhesive strength and releasability, a pressure-sensitive adhesive sheet (electrically peelable pressure-sensitive adhesive sheet) is known that includes an electrically peelable pressure-sensitive adhesive layer made of an electrically peelable pressure-sensitive adhesive composition that peels off when a voltage is applied to the adhesive layer (Patent Document 3).

[0005] Japanese Patent Publication No. 2017-75231 Japanese Patent Publication No. 2017-75228 International Publication No. 2017 / 064925

[0006] However, the tab-equipped adhesive products described in Patent Documents 1 and 2 prevent deformation or damage to the adherend by providing a tab at the end of an extensible adhesive sheet, and no consideration has been given to adhesive sheets that do not have extensibility, and there is a demand for adhesive sheets with better releasability.

[0007] The present invention was conceived under these circumstances, and has an object to provide a pressure-sensitive adhesive sheet having excellent adhesive strength and better releasability, a bonded structure having excellent adhesive strength and good releasability, and a method for separating such a bonded structure.

[0008] As a result of extensive research, the present inventors have found that the above object can be achieved by using a pressure-sensitive adhesive sheet having a specific structure.

[0009] The present invention has the following configurations. [1] A band-shaped pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer, the pressure-sensitive adhesive sheet comprising an inclined portion formed in a tapered shape with a width that tapers toward one end in the longitudinal direction of the pressure-sensitive adhesive sheet. [2] The pressure-sensitive adhesive sheet according to [1], comprising a tab provided at the end. [3] The pressure-sensitive adhesive sheet according to [1] or [2], wherein the ratio of the length of the inclined portion to the length of the pressure-sensitive adhesive sheet in the longitudinal direction is 5% or more. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3], wherein the ratio of the width of the end to the width of the pressure-sensitive adhesive sheet is 50% or less. [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4], wherein the pressure-sensitive adhesive layer is an electrically peelable pressure-sensitive adhesive layer whose adhesive strength decreases upon application of a voltage. [6] The pressure-sensitive adhesive sheet according to [5], wherein the electrically peelable pressure-sensitive adhesive layer contains a polymer and an ionic liquid. [7] The pressure-sensitive adhesive sheet according to [6], wherein the anion of the ionic liquid is at least one selected from the group consisting of bis(fluorosulfonyl)imide anion and bis(trifluoromethanesulfonyl)imide anion. [8] The pressure-sensitive adhesive sheet according to [6] or [7], wherein the cation of the ionic liquid is at least one selected from the group consisting of nitrogen-containing onium cations, sulfur-containing onium cations, and phosphorus-containing onium cations. [9] A bonded body comprising the pressure-sensitive adhesive sheet according to any one of [1] to [8], a first adherend, and a second adherend.

[10] The method for separating a bonded body according to [9], wherein separation of the first adherend and the second adherend is initiated from an outer edge of a portion of the first adherend or the second adherend joined by the inclined portion of the pressure-sensitive adhesive sheet.

[0010] The present invention provides a pressure-sensitive adhesive sheet and an assembly having excellent adhesive strength and good releasability, and also provides a method for separating an assembly having good releasability.

[0011] FIG. 1 is a schematic top view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. FIG. 2 is a perspective view schematically illustrating another configuration example (embodiment) of a pressure-sensitive adhesive sheet according to an embodiment of the present invention. FIGS. 3(a), 3(b), and 3(c) are schematic cross-sectional views of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. FIG. 4 is a cross-sectional view showing an example of a laminate structure of a pressure-sensitive adhesive sheet according to the present invention. FIG. 5 is a cross-sectional view showing another example of a laminate structure of a pressure-sensitive adhesive sheet according to the present invention. FIG. 6 is a schematic cross-sectional view showing an example of an end portion of the pressure-sensitive adhesive sheet shown in FIG. 1. FIG. 7 is a schematic cross-sectional view of a bonded body in which a first adherend and a second adherend are bonded together using a pressure-sensitive adhesive sheet according to a modified embodiment of the present invention. FIG. 8 is a top view schematically illustrating one configuration example (embodiment) of a pressure-sensitive adhesive sheet in a state where it is attached to a first adherend and a second adherend. FIG. 9 is a view for explaining a method of producing a test sample in the examples.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes in detail the preferred embodiments of the present invention, but the present invention is not limited to the following preferred embodiments.

[0013] In this specification, the term "band shape" refers to a shape that extends linearly and has a width (length in a direction perpendicular to the linear extension direction). The band shape has a predetermined length in the linear extension direction and a width that is shorter than the length, and is a concept that encompasses rectangular and strip shapes. Therefore, the band shape can be rephrased as elongated. The band shape according to one embodiment has a shape that extends linearly, but may also have a shape that extends curvedly, and may include a shape that has both a linear and a curved portion. The width of the band shape does not have to be constant.

[0014] In this specification, the term "tab" is used to mean a "knob" that serves as the starting point (starting point of pulling) when pulling the adhesive sheet, and other elements (shape, material, etc.) are not particularly limited. Typically, a tab is large enough to be held with fingers and has a shape that can be held with fingers (e.g., a flat rectangular shape). However, since there are also embodiments in which the tab can be pulled using a machine or tool, it does not need to be large enough to be held with fingers, and there are no restrictions on the shape. For example, a tab with perforations can be pulled by inserting a hook through the perforations, so it can be very small. A typical tab is planar and continuous with the adhesive sheet, and preferably does not stretch when pulled, or if it does stretch, it has lower stretchability than the adhesive sheet.

[0015] [Adhesive Sheet] The adhesive sheet according to an embodiment of the present invention is a strip-shaped adhesive sheet having an adhesive layer, and includes a tapered portion formed in a width that tapers toward one end of the adhesive sheet in the longitudinal direction. By including the inclined portion, when peeling the adhesive sheet from an adherend, applying stress to the adherend around the inclined portion allows for peeling with less force than peeling from other locations, resulting in excellent peelability. This eliminates the need to apply a large stress to a portion of the interface between the adhesive layer and the adherend for peeling, and has the advantage of preventing deformation of the adherend. Figure 1 is a top view schematically illustrating one configuration example (embodiment) of an adhesive sheet according to an embodiment of the present invention. The adhesive sheet 100 shown in Figure 1 includes an inclined portion 40 formed in a tapered shape at one end of the adhesive sheet 100 in the longitudinal direction, with the width tapering toward one end 41. In Figure 1, the dotted portion with an inclined length L2 indicates the inclined portion 40. In FIG. 1 , the width tapers linearly toward one end 41 (hereinafter sometimes simply referred to as "end 41"), but it may also taper in a curved manner. The pressure-sensitive adhesive sheet according to the embodiment of the present invention may have a tab provided at the end. For example, a tab 50 having a length L3 (tab length L3) may be provided at end 41. The width of the tab in FIG. 1 is the same as the width W2 of the end, but the width of the tab and the width W2 of the end may be different.

[0016] 2 is a perspective view schematically illustrating another example of the configuration (embodiment) of the pressure-sensitive adhesive sheet according to the embodiment of the present invention. The pressure-sensitive adhesive sheet 100 shown in FIG. 2 further includes a substrate 20, and includes pressure-sensitive adhesive layers 10 disposed on both sides of the substrate 20.

[0017] The other end of the adhesive sheet 100 in the longitudinal direction (the end opposite to the end 41) may or may not have an inclined portion 40.

[0018] The PSA sheet 100 having such a shape can exhibit good adhesive strength to rectangular adherends (for example, housings and components (e.g., batteries) of electronic devices such as personal computers, mobile phones, smartphones, digital cameras, tablet PCs, portable music players, portable game consoles, and chargers). The PSA sheet 100 also has a band shape.

[0019] In FIG. 1 , the total length L of the pressure-sensitive adhesive sheet 100 is the sum of the inclined length L2, which is the length of the inclined portion, and the length L1 of the portion other than the inclined portion. In an embodiment of the present invention, the ratio of the length of the inclined portion 40 (inclined length L2) to the longitudinal length L (total length L) of the pressure-sensitive adhesive sheet 100 is preferably 5% or more. By setting the ratio of the inclined length L2 to 5% or more, peeling can be performed with less force, and the peeling force (force required for peeling) can be reduced. The ratio of the inclined length L2 to the longitudinal length L (total length L) of the pressure-sensitive adhesive sheet is more preferably 10% or more, and even more preferably 20% or more. Furthermore, from the viewpoint of maintaining adhesive strength, the ratio of the inclined length L2 to the longitudinal length L (total length L) of the pressure-sensitive adhesive sheet is preferably 100% or less, and more preferably 70% or less.

[0020] The ratio of the edge width W2 to the width W of the adhesive sheet is preferably 90% or less, more preferably 75% or less, and even more preferably 50% or less. By setting the ratio of the edge width W2 to 50% or less, peeling can be performed with less force, and the peeling force (the force required for peeling) can be reduced. In an embodiment of the present invention, the ratio of the edge width W2 to the width W of the adhesive sheet 100 is preferably 50% or less. Furthermore, from the viewpoint of maintaining adhesive strength, the ratio of the edge width W2 to the width W of the adhesive sheet is more preferably 10% or more, and even more preferably 20% or more. The width W of the adhesive sheet is the width of the portion of the band-shaped adhesive sheet other than the inclined portion. Furthermore, when the inclined length L2 and the longitudinal length L of the adhesive sheet (total length L) are equal, the width W of the adhesive sheet is defined as the length of the edge on the side opposite to the width W2 of one edge.

[0021] The width of the adhesive sheet 100 tapers toward the edge 41, and at the edge 41 shown in Fig. 1, the edge width W2 is narrower than the width W by the lengths of the inclined widths W1 and W3. The lengths of the inclined widths W1 and W3 may be the same or different, but from the viewpoint of adhesiveness, it is preferable that the inclined widths W1 and W3 are the same length.

[0022] Although it depends on the shape and size of the adherend and the location of application, PSA sheets with the above ratio (L / W) of approximately 2 or more tend to have excellent releasability and handleability. There is no particular upper limit for the above ratio (L / W), but from the standpoint of strength, handleability, etc., the above ratio (L / W) may be approximately 50 or less.

[0023] The pressure-sensitive adhesive sheet according to the embodiment of the present invention has a band shape, and may have a band-shaped portion in part, for example. The pressure-sensitive adhesive sheet typically has a linearly extending shape as in the above embodiment, but is not limited thereto. It may also have a curved shape or a shape that combines linear and curved lines (e.g., a dogleg shape, a square-shaped, an arc-shaped, a wavy, a zigzag, etc.). The pressure-sensitive adhesive sheet according to the present embodiment may be, for example, in the form of a roll, a sheet, or a leaf. Alternatively, the pressure-sensitive adhesive sheet may be processed into various shapes. The term "pressure-sensitive adhesive sheet" also includes the meaning of "pressure-sensitive adhesive tape." That is, the pressure-sensitive adhesive sheet according to the present embodiment may be a tape-shaped pressure-sensitive adhesive tape.

[0024] (Configuration of Pressure-Sensitive Adhesive Sheet) The pressure-sensitive adhesive sheet according to an embodiment of the present invention includes a pressure-sensitive adhesive layer. Fig. 3(a) is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to an embodiment of the present invention. The pressure-sensitive adhesive sheet 110 shown in Fig. 3(a) may be a substrate-less double-sided pressure-sensitive adhesive sheet consisting only of the pressure-sensitive adhesive layer 10.

[0025] The pressure-sensitive adhesive sheet according to an embodiment of the present invention may further include a substrate and a pressure-sensitive adhesive layer disposed on at least one surface of the substrate. (b) of Fig. 3 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to an embodiment of the present invention. This pressure-sensitive adhesive sheet 120 further includes a substrate 20 and pressure-sensitive adhesive layers 10 disposed on both surfaces of the substrate 20. (c) of Fig. 3 is a schematic cross-sectional view of a pressure-sensitive adhesive sheet according to an embodiment of the present invention. This pressure-sensitive adhesive sheet 130 includes a substrate 20 and a pressure-sensitive adhesive layer 10 disposed on one surface of the substrate 20. The pressure-sensitive adhesive sheets shown in (b) and (c) of Fig. 3 may have an exposed extension extending beyond the pressure-sensitive adhesive layer 10 in the surface extension direction of the substrate 20, and this extension may be the tab 50 in Fig. 1.

[0026] The pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet preferably exhibits adhesiveness by pressure-bonding. The pressure-sensitive adhesive sheet (substantially the pressure-sensitive adhesive layer) may be a pressure-sensitive adhesive sheet that exhibits adhesiveness at room temperature (25°C), or may be a pressure-sensitive adhesive sheet that exhibits adhesiveness by heating. A pressure-sensitive adhesive sheet that exhibits adhesiveness by heating may exhibit adhesiveness in a state cooled to room temperature after heating.

[0027] The pressure-sensitive adhesive layer 10 may also be an electrically releasing pressure-sensitive adhesive layer. In the case of a pressure-sensitive adhesive sheet 120 in which pressure-sensitive adhesive layers 10 are disposed on both sides of a substrate 20 as shown in FIG. 3(b), either one of the pressure-sensitive adhesive layers 10 or both of the pressure-sensitive adhesive layers 10 may be electrically releasing pressure-sensitive adhesive layers. A pressure-sensitive adhesive sheet (electrically releasing pressure-sensitive adhesive sheet) containing an electrically releasing pressure-sensitive adhesive layer preferably firmly bonds members when no voltage is applied, and can be peeled with little force when a voltage is applied. By providing the above-described inclined portion 40, the electrically releasing pressure-sensitive adhesive sheet can reduce the stress required to initiate peeling when peeled from the outer edge of the portion bonded by the inclined portion. When a voltage is applied, cleavage peeling can be achieved by applying a slight stress to a portion of the interface between the pressure-sensitive adhesive layer and the adherend, preferably to the outer edge of the portion bonded by the inclined portion. This eliminates the need to apply a large stress to a portion of the interface between the pressure-sensitive adhesive layer and the adherend for peeling, which has the advantage of preventing deformation of the adherend.

[0028] Here, cleavage peeling refers to peeling along the interface between the pressure-sensitive adhesive layer and the adherend. Cleavage peeling allows for easy peeling of the entire interface between the pressure-sensitive adhesive layer and the adherend, eliminating the need to apply significant stress to a portion of the interface between the pressure-sensitive adhesive layer and the adherend through peeling or the like, and offering the advantage of not deforming the adherend. In embodiments of the present invention, cleavage peeling may or may not be natural peeling, but natural peeling is preferred. Natural peeling refers to peeling (cleavage) along the interface between the adherend and the pressure-sensitive adhesive layer, occurring naturally without applying stress to a portion of the interface between the pressure-sensitive adhesive layer and the adherend. Natural peeling also includes peeling in a stationary state, natural peeling during transfer to a subsequent process, and peeling between the adherend and the pressure-sensitive adhesive layer due to the weight of the adherend or the pressure-sensitive adhesive layer itself. Examples of cleavage peeling other than natural peeling include peeling of the pressure-sensitive adhesive layer from one end of the adherend by applying slight stress to a portion of the interface between the pressure-sensitive adhesive layer and the adherend without deforming or destroying the pressure-sensitive adhesive layer or the adherend.

[0029] When the pressure-sensitive adhesive layer 10 of the pressure-sensitive adhesive sheet of the present embodiment is an electrically peelable pressure-sensitive adhesive layer, the pressure-sensitive adhesive sheet may further include, in addition to the pressure-sensitive adhesive layer, a substrate, a conductive layer, a conductive substrate, an intermediate layer, an undercoat layer, etc. When the pressure-sensitive adhesive layer 10 of the pressure-sensitive adhesive sheet of the present embodiment is an electrically peelable pressure-sensitive adhesive layer, the pressure-sensitive adhesive sheet may further include another pressure-sensitive adhesive layer that does not have electrical peeling properties.

[0030] The electrically peelable pressure-sensitive adhesive sheet of this embodiment may have a separator (release liner) for the purpose of protecting the surface of the electrically peelable pressure-sensitive adhesive layer and other pressure-sensitive adhesive layers, but the release liner is not included in the electrically peelable pressure-sensitive adhesive sheet of this embodiment.

[0031] When the pressure-sensitive adhesive layer 10 in the pressure-sensitive adhesive sheet of the present embodiment is an electrically releasing pressure-sensitive adhesive layer, the structure is not particularly limited, but preferred examples include pressure-sensitive adhesive sheet X2, the layer structure of which is shown in FIG. 4, and pressure-sensitive adhesive sheet X3, the layer structure of which is shown in FIG. 5. Pressure-sensitive adhesive sheet X2 is a substrate-attached double-sided pressure-sensitive adhesive sheet having a layer structure of a pressure-sensitive adhesive layer 2, a conductive substrate 5 (substrate 3 and conductive layer 4), and a electrically releasing pressure-sensitive adhesive layer 1. Pressure-sensitive adhesive sheet X3 is a substrate-attached double-sided pressure-sensitive adhesive sheet having a layer structure of a pressure-sensitive adhesive layer 2, a conductive substrate 5 (substrate 3 and conductive layer 4), a electrically releasing pressure-sensitive adhesive layer 1, a conductive substrate 5 (substrate 3 and conductive layer 4), and a pressure-sensitive adhesive layer 2. In the conductive substrate 5 of pressure-sensitive adhesive sheets X2 and X3 shown in FIGS. 4 and 5, the substrate 3 is not essential, and only the conductive layer 4 may be present. Furthermore, pressure-sensitive adhesive sheet X2 in FIG. 4 may be a single-sided pressure-sensitive adhesive sheet without the pressure-sensitive adhesive layer 2.

[0032] In the adhesive sheet X2 according to an embodiment of the present invention, for example, as shown in FIG. 6 , the conductive substrate 5 may have an exposed extension portion that extends beyond the electrically peelable adhesive layer 1 and the adhesive layer 2 in the surface extension direction of the conductive substrate 5, and the extension portion may be a tab 50.

[0033] Furthermore, in such a configuration, electrical connection between one terminal of the voltage application device or the DC power supply device and the current-carrying substrate can be easily achieved via the extending portion of the current-carrying substrate.

[0034] The electrically releasing pressure-sensitive adhesive sheet may be a double-sided electrically releasing pressure-sensitive adhesive sheet, as shown in a modified example in FIG. 7 . The electrically releasing pressure-sensitive adhesive sheet shown in FIG. 7 has a laminated structure in which an electrically conducting substrate 5 and an adhesive layer 2 are laminated on both sides of an electrically releasing pressure-sensitive adhesive layer 1. In the modified example shown in FIG. 7 , the double-sided electrically releasing pressure-sensitive adhesive sheet may be attached to a first adherend 15 on one side of the adhesive layer 2, and to a second adherend 16 on the other side of the adhesive layer 2. Furthermore, as shown in FIG. 7 , the double-sided electrically releasing pressure-sensitive adhesive sheet may have an exposed extension extending beyond one of the electrically conducting substrates 5 and the first adherend 15 in the surface extension direction, and the extension may be a tab 50. In such a configuration, electrical connection between one terminal of a device to which voltage is applied and the electrically conducting substrate 5 is easily achieved via the extension. As shown in FIG. 7 , the conductive layer 4 in the extension is preferably not exposed from the viewpoint of corrosion prevention, and may be covered by the electrically releasing pressure-sensitive adhesive layer 1. The extension may also be a tab 50 .

[0035] The substrate 3 is not particularly limited, but examples thereof include paper-based substrates such as paper, fiber-based substrates such as cloth and nonwoven fabric, plastic-based substrates such as films and sheets made of various plastics (polyolefin-based resins such as polyethylene and polypropylene, polyester-based resins such as polyethylene terephthalate, acrylic resins such as polymethyl methacrylate, etc.), and laminates thereof. The substrate may have a single layer structure or a multi-layer structure. The substrate may be subjected to various treatments such as back surface treatment, antistatic treatment, and primer treatment as necessary.

[0036] The conductive layer 4 is not particularly limited as long as it is a layer having conductivity, but may be a metal substrate such as a metal (e.g., aluminum, magnesium, copper, iron, tin, gold, etc.) foil or a metal plate (e.g., aluminum, magnesium, copper, iron, tin, silver, etc.), a conductive polymer, or the like, or may be a metal vapor deposition film provided on the substrate 3.

[0037] The conductive substrate 5 is not particularly limited as long as it is a substrate having a conductive layer (conductive), but examples thereof include a substrate having a metal layer formed on the surface thereof, such as a substrate having a metal layer formed on the surface thereof by plating, chemical vapor deposition, sputtering, etc. Examples of the metal layer include the metals, metal plates, conductive polymers, etc. exemplified above.

[0038] 3(a) is an electrically peelable pressure-sensitive adhesive sheet, the adherends on both sides preferably have metal adherends. In the case of pressure-sensitive adhesive sheet X2, the adherend on the electrically peelable pressure-sensitive adhesive layer 1 side preferably has a metal adherend.

[0039] Examples of metal-coated surfaces include conductive surfaces made of metals whose main components are aluminum, copper, iron, magnesium, tin, gold, silver, and lead, with aluminum being preferred. Examples of adherends having a metal-coated surface include sheets, parts, and plates made of metals whose main components are aluminum, copper, iron, magnesium, tin, gold, silver, and lead. Adherends other than those having a metal-coated surface include, but are not limited to, fiber sheets such as paper, cloth, and nonwoven fabric, and various plastic films and sheets.

[0040] From the viewpoint of initial adhesive strength, the thickness of the electrically peeling pressure-sensitive adhesive layer 1 is preferably 1 μm or more and 1000 μm or less. The upper limit of the thickness of the electrically peeling pressure-sensitive adhesive layer 1 is more preferably 500 μm, even more preferably 100 μm, and particularly preferably 30 μm, and the lower limit is more preferably 3 μm, even more preferably 5 μm, and particularly preferably 8 μm. When the pressure-sensitive adhesive sheet is a substrate-less double-sided pressure-sensitive adhesive sheet (pressure-sensitive adhesive sheet 110 shown in FIG. 3(a)) consisting of only one pressure-sensitive adhesive layer (electrically peeling pressure-sensitive adhesive layer), the thickness of the pressure-sensitive adhesive layer (electrically peeling pressure-sensitive adhesive layer) is the thickness of the pressure-sensitive adhesive sheet.

[0041] From the viewpoint of adhesive strength, the thickness of the pressure-sensitive adhesive layer 2 is preferably 1 μm or more and 2000 μm or less. The upper limit of the thickness of the pressure-sensitive adhesive layer 2 is more preferably 1000 μm, even more preferably 500 μm, and particularly preferably 100 μm, and the lower limit is more preferably 3 μm, even more preferably 5 μm, and particularly preferably 8 μm.

[0042] The thickness of the substrate 3 is preferably 10 μm or more and 1000 μm or less. The upper limit of the thickness is more preferably 500 μm, even more preferably 300 μm, and particularly preferably 100 μm, and the lower limit is more preferably 12 μm, even more preferably 25 μm.

[0043] The thickness of the conductive layer 4 is preferably 0.001 μm or more and 1000 μm or less. The upper limit of the thickness is more preferably 500 μm, even more preferably 300 μm, even more preferably 50 μm, and even more preferably 10 μm, and the lower limit is more preferably 0.01 μm, more preferably 0.03 μm, and even more preferably 0.05 μm.

[0044] The thickness of the conductive substrate 5 is preferably 10 μm or more and 1000 μm or less. The upper limit of the thickness is more preferably 500 μm, even more preferably 300 μm, and particularly preferably 100 μm, and the lower limit is more preferably 12 μm, even more preferably 25 μm.

[0045] The surface of the pressure-sensitive adhesive layer (electrically releasable pressure-sensitive adhesive layer and other pressure-sensitive adhesive layers) of the pressure-sensitive adhesive sheet of this embodiment may be protected by a separator (release liner). The release liner is not particularly limited, but examples include release liners in which the surface of a substrate (liner substrate) such as paper or plastic film is treated with silicone, and release liners in which the surface of a substrate (liner substrate) such as paper or plastic film is laminated with a polyolefin resin. The thickness of the release liner is not particularly limited, but is preferably 10 μm or more and 100 μm or less.

[0046] The thickness of the pressure-sensitive adhesive sheet of this embodiment is preferably 20 μm or more and 3000 μm or less. The upper limit of the thickness is more preferably 1000 μm, even more preferably 300 μm, and particularly preferably 200 μm, and the lower limit is more preferably 30 μm, and even more preferably 50 μm.

[0047] In particular, in the case of the pressure-sensitive adhesive sheet X2 shown in Fig. 4, the thickness of the pressure-sensitive adhesive sheet is preferably 50 µm or more and 2000 µm or less. The upper limit of the thickness is more preferably 1000 µm, and even more preferably 200 µm, and the lower limit is more preferably 80 µm, and even more preferably 100 µm.

[0048] In particular, in the case of the pressure-sensitive adhesive sheet X3 shown in Fig. 5, the thickness of the pressure-sensitive adhesive sheet is preferably 100 µm or more and 3000 µm or less. The upper limit of the thickness is more preferably 1000 µm, and even more preferably 300 µm, and the lower limit is more preferably 150 µm, and even more preferably 200 µm.

[0049] [Adhesive Layer] The adhesive layer can be formed from an adhesive composition, which preferably contains a polymer. The adhesive layer may be an electrically peelable adhesive layer whose adhesive strength decreases upon application of a voltage. The adhesive layer formed from the adhesive composition according to the embodiment of the present invention preferably has excellent heat resistance. An adhesive layer with excellent heat resistance can also be used in the manufacturing process of electronic devices that are exposed to high temperatures. The adhesive layer is preferably an electrically peelable adhesive layer whose adhesive strength decreases upon application of a voltage, and the electrically peelable adhesive layer preferably contains a polymer and an electrolyte, and more preferably contains a polymer and an ionic liquid. Furthermore, when the adhesive layer is an electrically peelable adhesive layer, the adhesive strength decreases sufficiently upon application of a voltage, allowing for cleavage peeling.

[0050] The pressure-sensitive adhesive composition according to an embodiment of the present invention will be described below. In this specification, the adhesive strength when no voltage is applied is sometimes referred to as "initial adhesive strength." The property of adhesive strength decreasing upon voltage application is sometimes referred to as "electrical releasability," and a large rate of decrease in adhesive strength upon voltage application is sometimes referred to as "excellent electrical releasability."

[0051] <Components of Pressure-Sensitive Adhesive Composition> (Polymer) The pressure-sensitive adhesive composition of the present embodiment preferably contains a polymer. In the present embodiment, the polymer is not particularly limited as long as it is a general organic polymer compound, and is, for example, a polymer or partial polymer of a monomer. The monomer may be one type of monomer or a mixture of two or more types of monomers. Note that a partial polymer refers to a polymer in which at least a part of the monomer or monomer mixture is partially polymerized.

[0052] The polymer in this embodiment is not particularly limited as long as it is normally used as a pressure-sensitive adhesive and has adhesive properties, and examples thereof include acrylic polymers, rubber polymers, vinyl alkyl ether polymers, silicone polymers, polyester polymers, polyamide polymers, urethane polymers, fluorine-based polymers, and epoxy polymers. The polymers can be used alone or in combination of two or more.

[0053] When the pressure-sensitive adhesive layer is an electrically peelable pressure-sensitive adhesive layer, a high dielectric constant of the polymer is preferred in order to increase the dielectric constant of the components other than the ionic liquid and improve the electrical peelability. From this perspective, the polymer in this embodiment preferably contains at least one selected from the group consisting of polyester polymers and acrylic polymers having carboxyl groups and / or hydroxyl groups. Because polyester polymers have easily polarizable hydroxyl groups at their terminals, and because acrylic polymers having carboxyl groups and / or hydroxyl groups have easily polarizable carboxyl groups and / or hydroxyl groups, the use of these polymers allows for the production of polymers with relatively high dielectric constants. The total content of the polyester polymer and the acrylic polymer having carboxyl groups and / or hydroxyl groups in the polymer of this embodiment is preferably 60% by mass or more, more preferably 80% by mass or more. Furthermore, in particular, to improve cost, productivity, and initial adhesive strength, the polymer in this embodiment is preferably an acrylic polymer. That is, the pressure-sensitive adhesive composition of this embodiment is preferably an acrylic pressure-sensitive adhesive composition containing an acrylic polymer as the polymer.

[0054] The acrylic polymer preferably contains a monomer unit derived from a (meth)acrylic acid alkyl ester (the following formula (1)) having an alkyl group having 1 to 14 carbon atoms. Such a monomer unit is suitable for obtaining a large initial adhesive strength. Furthermore, when the pressure-sensitive adhesive layer is an electrically peelable pressure-sensitive adhesive layer, the alkyl group R ｂ The number of carbon atoms in CH is preferably small, particularly preferably 8 or less, and more preferably 4 or less. ２ = C(R ａ ) COOR ｂ (1) [R in formula (1)] ａ is a hydrogen atom or a methyl group, and R ｂ is an alkyl group having 1 to 14 carbon atoms which may have a substituent.

[0055] Examples of (meth)acrylic acid alkyl esters having an alkyl group having 1 to 14 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, sec-butyl (meth)acrylate, 1,3-dimethylbutyl acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, and 2-ethylbutyl (meth)acrylate. acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-tridecyl (meth)acrylate, n-tetradecyl (meth)acrylate, and 2-methoxyethyl acrylate. Of these, n-butyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, and 2-methoxyethyl acrylate are preferred. The (meth)acrylic acid alkyl esters having an alkyl group having 1 to 14 carbon atoms can be used alone or in combination of two or more.

[0056] The proportion of the (meth)acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms relative to all monomer components (100% by mass) constituting the acrylic polymer is not particularly limited, but is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more. When the proportion of the (meth)acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms is 70% by mass or more, a large initial adhesive strength is easily obtained.

[0057] For the purpose of improving cohesive strength, heat resistance, crosslinkability, etc., the acrylic polymer preferably contains, in addition to a monomer unit derived from a (meth)acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms, a monomer unit derived from a polar group-containing monomer copolymerizable therewith. The monomer unit can impart crosslinking points and is suitable for obtaining high initial adhesive strength. Furthermore, when the pressure-sensitive adhesive layer is an electrically peelable pressure-sensitive adhesive layer, it preferably contains a monomer unit derived from a polar group-containing monomer, also from the viewpoint of increasing the relative dielectric constant of components other than the ionic liquid and improving electrical peelability.

[0058] Examples of polar group-containing monomers include carboxyl group-containing monomers, hydroxyl group-containing monomers, cyano group-containing monomers, vinyl group-containing monomers, aromatic vinyl monomers, amide group-containing monomers, imide group-containing monomers, amino group-containing monomers, epoxy group-containing monomers, vinyl ether monomers, N-acryloylmorpholine, sulfo group-containing monomers, phosphate group-containing monomers, and acid anhydride group-containing monomers. Among these, carboxyl group-containing monomers, hydroxyl group-containing monomers, and amide group-containing monomers are preferred from the viewpoint of excellent cohesiveness, and carboxyl group-containing monomers are particularly preferred. Carboxyl group-containing monomers are particularly suitable for obtaining high initial adhesive strength. Polar group-containing monomers can be used alone or in combination of two or more.

[0059] Examples of carboxyl group-containing monomers include acrylic acid, methacrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Acrylic acid is particularly preferred. The carboxyl group-containing monomers can be used alone or in combination.

[0060] Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl)methyl (meth)acrylate, N-methylol (meth)acrylamide, vinyl alcohol, allyl alcohol, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, and diethylene glycol monovinyl ether. 2-Hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are particularly preferred. The hydroxyl group-containing monomers may be used alone or in combination of two or more.

[0061] Examples of amide group-containing monomers include acrylamide, methacrylamide, N-vinylpyrrolidone, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N,N'-methylenebisacrylamide, N,N-dimethylaminopropylacrylamide, N,N-dimethylaminopropylmethacrylamide, and diacetoneacrylamide. The amide group-containing monomers can be used alone or in combination of two or more.

[0062] Examples of cyano group-containing monomers include acrylonitrile and methacrylonitrile.

[0063] Examples of vinyl group-containing monomers include vinyl esters such as vinyl acetate, vinyl propionate, and vinyl laurate, with vinyl acetate being particularly preferred.

[0064] Examples of aromatic vinyl monomers include styrene, chlorostyrene, chloromethylstyrene, α-methylstyrene, and other substituted styrenes.

[0065] Examples of imide group-containing monomers include cyclohexylmaleimide, isopropylmaleimide, N-cyclohexylmaleimide, and itaconimide.

[0066] Examples of amino group-containing monomers include aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, and N,N-dimethylaminopropyl (meth)acrylate.

[0067] Examples of epoxy group-containing monomers include glycidyl (meth)acrylate, methyl glycidyl (meth)acrylate, and allyl glycidyl ether.

[0068] Examples of vinyl ether monomers include methyl vinyl ether, ethyl vinyl ether, and isobutyl vinyl ether.

[0069] The proportion of the polar group-containing monomer relative to the total monomer components (100% by mass) constituting the acrylic polymer is preferably 0.1% by mass or more and 35% by mass or less. The upper limit of the polar group-containing monomer proportion is more preferably 25% by mass, even more preferably 20% by mass, and the lower limit is more preferably 0.5% by mass, even more preferably 1% by mass, and particularly preferably 2% by mass. When the proportion of the polar group-containing monomer is 0.1% by mass or more, cohesive strength is easily obtained, so that adhesive residue is less likely to remain on the adherend surface after peeling the electrically-release pressure-sensitive adhesive layer, and the electrical releasability is improved. Furthermore, when the proportion of the polar group-containing monomer is 30% by mass or less, it is easy to prevent the electrically-release pressure-sensitive adhesive layer from excessively adhering to the adherend and causing heavy peeling. In particular, when the proportion is 2% by mass or more and 20% by mass or less, it is easy to achieve both releasability from the adherend and adhesion between the electrically-release pressure-sensitive adhesive layer and other layers.

[0070] Furthermore, the monomer components constituting the acrylic polymer may contain a polyfunctional monomer in order to introduce a crosslinked structure into the acrylic polymer and make it easier to obtain the required cohesive strength.

[0071] Examples of polyfunctional monomers include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, divinylbenzene, and N,N'-methylenebisacrylamide. The polyfunctional monomers can be used alone or in combination of two or more.

[0072] The content of the polyfunctional monomer relative to the total monomer components (100% by mass) constituting the acrylic polymer is preferably 0.1% by mass or more and 15% by mass or less. The upper limit of the polyfunctional monomer content is more preferably 10% by mass, and the lower limit is more preferably 3% by mass. When the content of the polyfunctional monomer is 0.1% by mass or more, the flexibility and adhesiveness of the electrically peelable pressure-sensitive adhesive layer are easily improved, which is preferable. When the content of the polyfunctional monomer is 15% by mass or less, the cohesive force is not too high, and appropriate adhesiveness is easily obtained.

[0073] Polyester-based polymers are typically polymers having a structure formed by condensation of a polycarboxylic acid such as a dicarboxylic acid or a derivative thereof (hereinafter also referred to as a "polycarboxylic acid monomer") with a polyhydric alcohol such as a diol or a derivative thereof (hereinafter referred to as a "polyhydric alcohol monomer").

[0074] The polycarboxylic acid monomer is not particularly limited, but examples thereof include adipic acid, azelaic acid, dimer acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 4-methyl-1,2-cyclohexanedicarboxylic acid, dodecenylsuccinic anhydride, fumaric acid, succinic acid, dodecanedioic acid, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, maleic acid, maleic anhydride, itaconic acid, citraconic acid, and derivatives thereof. The polycarboxylic acid monomers can be used alone or in combination of two or more.

[0075] The polyhydric alcohol monomer is not particularly limited, but examples thereof include ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 2-methyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,5-pentanediol, 2-ethyl-2-butylpropanediol, 1,9-nonanediol, 2-methyloctanediol, 1,10-decanediol, and derivatives thereof. The polyhydric alcohol monomers can be used alone or in combination of two or more.

[0076] The polymer of this embodiment may also contain an ionic polymer. The ionic polymer is a polymer having an ionic functional group. When the polymer contains an ionic polymer, the relative dielectric constant of the polymer increases, improving the electro-separation properties. When the polymer contains an ionic polymer, the content of the ionic polymer is preferably 0.05 parts by mass or more and 2 parts by mass or less per 100 parts by mass of the polymer.

[0077] In this embodiment, the polymer can be obtained by (co)polymerizing monomer components. The polymerization method is not particularly limited, but examples thereof include solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization (active energy ray polymerization). In particular, from the viewpoints of cost and productivity, solution polymerization is preferred. When copolymerized, the polymer may be any of a random copolymer, a block copolymer, an alternating copolymer, a graft copolymer, and the like.

[0078] The solution polymerization method is not particularly limited, but examples thereof include a method in which a monomer component, a polymerization initiator, etc. are dissolved in a solvent and heated to polymerize, thereby obtaining a polymer solution containing a polymer.

[0079] As the solvent used in the solution polymerization method, various common solvents can be used. Examples of such solvents (polymerization solvents) include organic solvents such as aromatic hydrocarbons such as toluene, benzene, and xylene; esters such as ethyl acetate and n-butyl acetate; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. The solvents can be used alone or in combination of two or more.

[0080] The amount of the solvent used is not particularly limited, but is preferably 10 parts by mass or more and 1,000 parts by mass or less relative to the total monomer components (100 parts by mass) constituting the polymer. The upper limit of the amount of the solvent used is more preferably 500 parts by mass, and the lower limit is more preferably 50 parts by mass.

[0081] The polymerization initiator used in the solution polymerization method is not particularly limited, but examples thereof include peroxide-based polymerization initiators, azo-based polymerization initiators, etc. Examples of the peroxide-based polymerization initiator are not particularly limited, but examples thereof include peroxycarbonate, ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, and peroxyester, and more specific examples thereof include benzoyl peroxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, and 1,1-bis(t-butylperoxy)cyclododecane, etc. The azo polymerization initiator is not particularly limited, but examples thereof include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylpropionate)dimethyl, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 1,1'-azobis(cyclohexane-1-carbonitrile), 2,2'-azobis(2,4,4-trimethylpentane), 4,4'-azobis Examples of polymerization initiators include 4-cyanovaleric acid, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(2-methylpropionamidine) disulfate, 2,2'-azobis(N,N'-dimethyleneisobutylamidine) hydrochloride, and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] hydrate. The polymerization initiators can be used alone or in combination of two or more.

[0082] The amount of the polymerization initiator used is not particularly limited, but is preferably 0.01 to 5 parts by mass relative to the total monomer components (100 parts by mass) constituting the polymer. The upper limit of the amount of the polymerization initiator used is more preferably 3 parts by mass, and the lower limit is more preferably 0.05 parts by mass.

[0083] In the solution polymerization method, the heating temperature when polymerizing by heating is not particularly limited, but is, for example, 50° C. to 80° C. The heating time is not particularly limited, but is, for example, 1 hour to 24 hours.

[0084] The weight-average molecular weight of the polymer is not particularly limited, but is preferably 100,000 or more and 5,000,000 or less. The upper limit of the weight-average molecular weight is more preferably 4,000,000, even more preferably 3,000,000, and the lower limit is more preferably 200,000, even more preferably 300,000. When the weight-average molecular weight is 100,000 or more, the cohesive force is reduced, and the problem of adhesive residue remaining on the adherend surface after peeling off the electrically-peeling pressure-sensitive adhesive layer can be effectively suppressed. Furthermore, when the weight-average molecular weight is 5,000,000 or less, the problem of insufficient wettability on the adherend surface after peeling off the electrically-peeling pressure-sensitive adhesive layer can be effectively suppressed.

[0085] The weight-average molecular weight is obtained by measurement by gel permeation chromatography (GPC). More specifically, for example, measurement is performed using a GPC measurement device under the trade name "HLC-8220GPC" (manufactured by Tosoh Corporation) under the following conditions, and the weight-average molecular weight can be calculated in terms of a standard polystyrene. (Weight-average molecular weight measurement conditions) Sample concentration: 0.2 mass% (tetrahydrofuran solution) Sample injection amount: 10 μL Sample column: TSKguard column SuperHZ-H (1 column) + TSKgel SuperHZM-H (2 columns) Reference column: TSKgel SuperH-RC (1 column) Eluent: tetrahydrofuran (THF) Flow rate: 0.6 mL / min Detector: differential refractometer (RI) Column temperature (measurement temperature): 40°C

[0086] The glass transition temperature (Tg) of the polymer is not particularly limited, but is preferably 0° C. or lower because this can suppress a decrease in the initial adhesive strength, more preferably −10° C. or lower, and even more preferably −20° C. or lower. Furthermore, if it is −40° C. or lower, the rate of decrease in adhesive strength due to voltage application becomes particularly large, so it is particularly preferred, and most preferably −50° C. or lower.

[0087] The glass transition temperature (Tg) can be calculated, for example, based on the following formula (Y) (Fox formula): 1 / Tg=W1 / Tg1+W2 / Tg2+ ... +Wn / Tgn (Y) [In formula (Y), Tg is the glass transition temperature (unit: K) of the polymer, Tgi (i = 1, 2, ... n) is the glass transition temperature (unit: K) when monomer i forms a homopolymer, and Wi (i = 1, 2, ... n) is the mass fraction of monomer i in all monomer components] The above formula (Y) is a calculation formula when a polymer is composed of n types of monomer components, i.e., monomer 1, monomer 2, ..., monomer n.

[0088] The glass transition temperature when a homopolymer is formed refers to the glass transition temperature of a homopolymer of the monomer, and refers to the glass transition temperature (Tg) of a polymer formed using only a certain monomer (sometimes referred to as "monomer X") as the monomer component. Specific values ​​are listed in "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989). The glass transition temperature (Tg) of a homopolymer not described in this document refers to a value obtained, for example, by the following measurement method. Specifically, 100 parts by mass of monomer X, 0.2 parts by mass of 2,2'-azobisisobutyronitrile, and 200 parts by mass of ethyl acetate as a polymerization solvent are placed in a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, and the mixture is stirred for 1 hour while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, the temperature is raised to 63°C and the reaction is allowed to proceed for 10 hours. The mixture is then cooled to room temperature to obtain a homopolymer solution with a solids concentration of 33% by mass. Next, this homopolymer solution is cast onto a release liner and dried to prepare a test sample (sheet-like homopolymer) with a thickness of approximately 2 mm. Approximately 1 to 2 mg of this test sample is weighed into an aluminum open cell, and the reversing heat flow (specific heat component) behavior of the homopolymer is measured using a temperature-modulated DSC (trade name "Q-2000" manufactured by TA Instruments) at a heating rate of 5°C / min under a nitrogen atmosphere of 50 ml / min. With reference to JIS-K-7121, the glass transition temperature (Tg) of the homopolymer is determined as the temperature at the point where a line equidistant in the vertical direction from a line extending the low-temperature baseline and the high-temperature baseline of the obtained reversing heat flow intersects with the curve representing the stepwise change in the glass transition.

[0089] The content of the polymer in the pressure-sensitive adhesive composition of the present embodiment is preferably 50% by mass or more and 99.9% by mass or less, relative to the total amount of the pressure-sensitive adhesive composition (100% by mass), with the upper limit being more preferably 99.5% by mass, even more preferably 99% by mass, and the lower limit being more preferably 60% by mass, even more preferably 70% by mass. However, when the pressure-sensitive adhesive composition contains a solvent, it is preferable that the content of the polymer relative to the total amount of the pressure-sensitive adhesive composition excluding the solvent be in the above range.

[0090] When the pressure-sensitive adhesive layer is an electrically releasing pressure-sensitive adhesive layer, the electrolyte contained in the electrically releasing pressure-sensitive adhesive layer is a substance that can be ionized into anions and cations, and examples of such electrolytes include ionic liquids, alkali metal salts, and alkaline earth metal salts. From the viewpoint of realizing good electrical peelability in the electrically releasing pressure-sensitive adhesive layer, the electrolyte contained in the electrically releasing pressure-sensitive adhesive layer is preferably an ionic liquid. Ionic liquids are salts that are liquid at room temperature (about 25°C) and contain anions and cations.

[0091] (Ionic Liquid) The ionic liquid in this embodiment is not particularly limited as long as it is a molten salt (room-temperature molten salt) composed of a pair of anion and cation and is liquid at 25° C. Examples of anions and cations are given below, but among the ionic substances obtained by combining these, those that are liquid at 25° C. are ionic liquids, and those that are solid at 25° C. are not ionic liquids but are ionic solids described below.

[0092] The anion of the ionic liquid is, for example, (FSO ２ ) ２ N － , (CF ３ SO ２ ) ２ N － , (CF ３ CF ２ SO ２ ) ２ N － , (CF ３ SO ２ ) ３ C － ,Br － , AlCl ４ － , Al ２ Cl７ － , NO ３ － , B.F. ４ － , P.F. ６ － , C.H. ３ COO － , C.F. ３ COO － , C.F. ３ CF ２ CF ２ COO － , C.F. ３ SO ３ － , C.F. ３ (CF ２ ) ３ SO ３ － , AsF ６ － , SbF ６ － , and F(HF) ｎ － Among them, the anion is (FSO ２ ) ２ N － [bis(fluorosulfonyl)imide anion], and (CF ３ SO ２ ) ２ N － Anions of sulfonylimide compounds such as bis(trifluoromethanesulfonyl)imide anion are preferred because they are chemically stable and suitable for improving electrical peeling properties.

[0093] As the cation in the ionic liquid, nitrogen-containing onium, sulfur-containing onium, and phosphorus-containing onium cations are preferred because they are chemically stable and suitable for improving electrical peeling properties, and imidazolium-based, ammonium-based, pyrrolidinium-based, and pyridinium-based cations are more preferred.

[0094] Examples of imidazolium cations include 1-methylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1-propyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-pentyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, 1-heptyl-3-methylimidazolium cation, 1-octyl-3-methylimidazolium cation, 1-nonyl-3-methylimidazolium cation, 1-undecyl-3-methylimidazolium cation, and 1-dodecyl-3-methylimidazolium cation. imidazolium cation, 1-tridecyl-3-methylimidazolium cation, 1-tetradecyl-3-methylimidazolium cation, 1-pentadecyl-3-methylimidazolium cation, 1-hexadecyl-3-methylimidazolium cation, 1-heptadecyl-3-methylimidazolium cation, 1-octadecyl-3-methylimidazolium cation, 1-undecyl-3-methylimidazolium cation, 1-benzyl-3-methylimidazolium cation, 1-butyl-2,3-dimethylimidazolium cation, and 1,3-bis(dodecyl)imidazolium cation.

[0095] Examples of pyridinium cations include 1-butylpyridinium cation, 1-hexylpyridinium cation, 1-butyl-3-methylpyridinium cation, 1-butyl-4-methylpyridinium cation, and 1-octyl-4-methylpyridinium cation.

[0096] Examples of pyrrolidinium cations include 1-ethyl-1-methylpyrrolidinium cation and 1-butyl-1-methylpyrrolidinium cation.

[0097] Examples of ammonium-based cations include tetraethylammonium cation, tetrabutylammonium cation, methyltrioctylammonium cation, tetradecyltrihexylammonium cation, glycidyltrimethylammonium cation, and trimethylaminoethylacrylate cation.

[0098] From the viewpoint of increasing the rate of decrease in adhesive strength when a voltage is applied, it is preferable to select a cation having a molecular weight of 160 or less as the constituent cation of the ionic liquid. ２ ) ２ N － [bis(fluorosulfonyl)imide anion] or (CF ３ SO ２ ) ２ N － Particularly preferred is an ionic liquid containing a bis(trifluoromethanesulfonyl)imide anion and a cation having a molecular weight of 160 or less. Examples of the cation having a molecular weight of 160 or less include a 1-methylimidazolium cation, a 1-ethyl-3-methylimidazolium cation, a 1-propyl-3-methylimidazolium cation, a 1-butyl-3-methylimidazolium cation, a 1-pentyl-3-methylimidazolium cation, a 1-butylpyridinium cation, a 1-hexylpyridinium cation, a 1-butyl-3-methylpyridinium cation, a 1-butyl-4-methylpyridinium cation, a 1-ethyl-1-methylpyrrolidinium cation, a 1-butyl-1-methylpyrrolidinium cation, a tetraethylammonium cation, a glycidyltrimethylammonium cation, and a trimethylaminoethyl acrylate cation.

[0099] Furthermore, as the cation of the ionic liquid, cations represented by the following formulas (2-A) to (2-D) are also preferred.

[0100]

[0101] R in formula (2-A) １ represents a hydrocarbon group having 4 to 10 carbon atoms (preferably a hydrocarbon group having 4 to 8 carbon atoms, more preferably a hydrocarbon group having 4 to 6 carbon atoms), which may contain a heteroatom; R ２ and R ３are the same or different and represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms (preferably a hydrocarbon group having 1 to 8 carbon atoms, more preferably a hydrocarbon group having 2 to 6 carbon atoms, and even more preferably a hydrocarbon group having 2 to 4 carbon atoms), and may contain a heteroatom. However, when a nitrogen atom forms a double bond with an adjacent carbon atom, R ３ does not exist.

[0102] R in formula (2-B) ４ represents a hydrocarbon group having 2 to 10 carbon atoms (preferably a hydrocarbon group having 2 to 8 carbon atoms, more preferably a hydrocarbon group having 2 to 6 carbon atoms), which may contain a heteroatom; R ５ , R ６ , and R ７ are the same or different and represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms (preferably a hydrocarbon group having 1 to 8 carbon atoms, more preferably a hydrocarbon group having 2 to 6 carbon atoms, and even more preferably a hydrocarbon group having 2 to 4 carbon atoms), which may contain a heteroatom.

[0103] R in formula (2-C) ８ represents a hydrocarbon group having 2 to 10 carbon atoms (preferably a hydrocarbon group having 2 to 8 carbon atoms, more preferably a hydrocarbon group having 2 to 6 carbon atoms), which may contain a heteroatom; R ９ , R １０ , and R １１ are the same or different and represent a hydrogen atom or a hydrocarbon group having 1 to 16 carbon atoms (preferably a hydrocarbon group having 1 to 10 carbon atoms, more preferably a hydrocarbon group having 1 to 8 carbon atoms), which may contain a heteroatom.

[0104] In formula (2-D), X represents a nitrogen, sulfur, or phosphorus atom; １２ , R １３ , R １４ , and R １５ are the same or different and represent a hydrocarbon group having 1 to 16 carbon atoms (preferably a hydrocarbon group having 1 to 14 carbon atoms, more preferably a hydrocarbon group having 1 to 10 carbon atoms, even more preferably a hydrocarbon group having 1 to 8 carbon atoms, and particularly preferably a hydrocarbon group having 1 to 6 carbon atoms), which may contain a heteroatom. However, when X is a sulfur atom, R １２ does not exist.

[0105] The molecular weight of the cation in the ionic liquid is, for example, 500 or less, preferably 400 or less, more preferably 300 or less, even more preferably 250 or less, particularly preferably 200 or less, and most preferably 160 or less. It is usually 50 or more. It is believed that the cation in the ionic liquid has the property of migrating to the cathode side in the electrically releasing pressure-sensitive adhesive layer upon application of a voltage, and being biased toward the interface between the electrically releasing pressure-sensitive adhesive layer and the adherend. For this reason, in the present invention, the adhesive strength during voltage application decreases relative to the initial adhesive strength, resulting in electro-releasability. Cations with a small molecular weight, such as a molecular weight of 500 or less, are suitable for facilitating the migration of cations to the cathode side in the electrically releasing pressure-sensitive adhesive layer and increasing the rate of decrease in adhesive strength upon application of a voltage.

[0106] Examples of commercially available ionic liquids include "ELEXEL AS-110," "ELEXEL MP-442," "ELEXEL IL-210," "ELEXEL MP-471," "ELEXEL MP-456," and "ELEXEL AS-804" manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; "HMI-FSI" manufactured by Mitsubishi Materials Corporation; and "CIL-312" and "CIL-313" manufactured by Nippon Carlit Co., Ltd.

[0107] The ionic conductivity of the ionic liquid is preferably 0.1 mS / cm or more. More preferably, it is 1 mS / cm or more, even more preferably 3 mS / cm or more, even more preferably 5 mS / cm or more, even more preferably 10 mS / cm or more, particularly preferably 15 mS / cm or more, and most preferably 20 mS / cm or more. There is no particular upper limit, but by having the above ionic conductivity, the adhesive strength is sufficiently reduced even at low voltages. The ionic conductivity can be measured, for example, by the AC impedance method using a Solartron 1260 frequency response analyzer.

[0108] The content (blending amount) of the ionic liquid in the pressure-sensitive adhesive composition of this embodiment is preferably 0.5 parts by mass or more relative to 100 parts by mass of the polymer from the viewpoint of reducing adhesive strength during voltage application, and preferably 30 parts by mass or less from the viewpoint of increasing initial adhesive strength. From the same viewpoint, it is more preferably 20 parts by mass or less, even more preferably 15 parts by mass or less, particularly preferably 10 parts by mass or less, and most preferably 5 parts by mass or less. Furthermore, it is more preferably 0.6 parts by mass or more, even more preferably 0.8 parts by mass or more, particularly preferably 1.0 part by mass or more, and most preferably 1.5 parts by mass or more.

[0109] (Other Components) The pressure-sensitive adhesive composition of the present embodiment may contain one or more components other than the polymer and the ionic liquid (hereinafter, sometimes referred to as "other components"), as needed, within a range that does not impair the effects of the present invention. Hereinafter, other components that may be contained in the pressure-sensitive adhesive composition of the present embodiment will be described.

[0110] The pressure-sensitive adhesive composition of the present embodiment may contain an ionic additive. As the ionic additive, for example, an ionic solid can be used.

[0111] The ionic solid is an ionic substance that is solid at 25° C. There are no particular limitations on the ionic solid, but for example, a solid ionic substance obtained by combining an anion and a cation as exemplified in the section describing the ionic liquid above can be used. When the pressure-sensitive adhesive composition contains an ionic solid, the content of the ionic solid is preferably 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the polymer.

[0112] The pressure-sensitive adhesive composition of the present embodiment may contain a crosslinking agent, if necessary, for the purpose of improving creep resistance and shear resistance by crosslinking the polymer. Examples of crosslinking agents include isocyanate-based crosslinking agents, carbodiimide-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, and amine-based crosslinking agents. Examples of isocyanate-based crosslinking agents include toluene diisocyanate and methylene bisphenyl isocyanate. Examples of epoxy-based crosslinking agents include N,N,N',N'-tetraglycidyl-m-xylylene diamine, diglycidyl aniline, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, and 1,6-hexanediol diglycidyl ether. When a crosslinking agent is contained, the content thereof is preferably 0.1 parts by mass or more and 50 parts by mass or less relative to 100 parts by mass of the polymer. The crosslinking agents may be used alone or in combination of two or more.

[0113] The pressure-sensitive adhesive composition of the present embodiment may contain polyethylene glycol, if necessary, to aid in the movement of the ionic liquid when a voltage is applied. As the polyethylene glycol, one having a number average molecular weight of 200 to 6000 can be used. When polyethylene glycol is contained, the content is preferably 0.1 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the polymer.

[0114] The pressure-sensitive adhesive composition of the present embodiment may contain a conductive filler as needed to impart conductivity to the pressure-sensitive adhesive composition. The conductive filler is not particularly limited, and a commonly known or commonly used conductive filler can be used, such as graphite, carbon black, carbon fiber, or metal powder such as silver or copper. When a conductive filler is contained, the content is preferably 0.1 parts by mass or more and 200 parts by mass or less relative to 100 parts by mass of the polymer.

[0115] The pressure-sensitive adhesive composition of the present embodiment may also contain various additives such as fillers, plasticizers, antioxidants, antioxidants, pigments (dyes), flame retardants, solvents, surfactants (leveling agents), rust inhibitors, adhesion-imparting resins, corrosion inhibitors, and antistatic agents. The total content of these components is not particularly limited as long as the effects of the present invention are achieved, but is preferably 0.01 parts by mass or more and 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the polymer.

[0116] Examples of fillers include silica, iron oxide, zinc oxide, aluminum oxide, titanium oxide, barium oxide, magnesium oxide, calcium carbonate, magnesium carbonate, zinc carbonate, pyrophyllite clay, kaolin clay, and calcined clay. Examples of plasticizers that can be used include known and commonly used plasticizers used in general resin compositions, such as oils such as paraffin oil and process oil, liquid rubbers such as liquid polyisoprene, liquid polybutadiene, and liquid ethylene-propylene rubber, tetrahydrophthalic acid, azelaic acid, benzoic acid, phthalic acid, trimellitic acid, pyromellitic acid, adipic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, citric acid, and derivatives thereof, dioctyl phthalate (DOP), dibutyl phthalate (DBP), dioctyl adipate, diisononyl adipate (DINA), and isodecyl succinate. Examples of antioxidants include hindered phenol compounds, aliphatic and aromatic hindered amine compounds, etc. Examples of antioxidants include butylhydroxytoluene (BHT) and butylhydroxyanisole (BHA). Examples of pigments include inorganic pigments such as titanium dioxide, zinc oxide, ultramarine, red iron oxide, lithopone, lead, cadmium, iron, cobalt, aluminum, hydrochloride, and sulfate, as well as organic pigments such as azo pigments and copper phthalocyanine pigments. Examples of rust inhibitors include zinc phosphate, tannic acid derivatives, phosphate esters, basic sulfonates, and various rust-preventive pigments. Examples of adhesion promoters include titanium coupling agents and zirconium coupling agents. Examples of antistatic agents generally include quaternary ammonium salts or hydrophilic compounds such as polyglycolic acid and ethylene oxide derivatives. Examples of tackifying resins include rosin-based tackifying resins, terpene-based tackifying resins, phenol-based tackifying resins, hydrocarbon-based tackifying resins, ketone-based tackifying resins, as well as polyamide-based tackifying resins, epoxy-based tackifying resins, and elastomer-based tackifying resins. These tackifying resins can be used alone or in combination of two or more.Examples of corrosion inhibitors include carbodiimide compounds, adsorption inhibitors, and chelating-type metal deactivators. For example, those described in JP 2019-059908 A can be used.

[0117] The conductive substrate 5 is not particularly limited as long as it includes the substrate 3 and the conductive layer 4. For example, it may be a substrate in which a conductive layer is formed on the surface of the substrate 3, and it may be a substrate in which the conductive layer is formed on the surface of the substrate exemplified above by a method such as plating, chemical vapor deposition, or sputtering.

[0118] The electrically peelable pressure-sensitive adhesive sheet can be attached to a conductive material to form a bonded body. Examples of conductive materials include adherends such as metal-coated surfaces. Examples of metal-coated surfaces include surfaces made of metals primarily composed of aluminum, copper, iron, magnesium, tin, gold, silver, and lead, with aluminum being preferred. Examples of adherends having a metal-coated surface include sheets, parts, and plates made of metals primarily composed of aluminum, copper, iron, magnesium, tin, gold, silver, and lead. Adherends other than those having a metal-coated surface include, but are not limited to, fiber sheets such as paper, cloth, and nonwoven fabric, and various plastic films and sheets.

[0119] (Method for manufacturing pressure-sensitive adhesive sheet) The pressure-sensitive adhesive sheet of this embodiment can be manufactured by a known or commonly used manufacturing method. For the electrically peelable pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet of this embodiment, a method can be used in which a solution of the pressure-sensitive adhesive composition of this embodiment, if necessary, dissolved in a solvent, is applied to a release liner, followed by drying and / or curing. For the other pressure-sensitive adhesive layer, a method can be used in which a solution of a pressure-sensitive adhesive composition that does not contain an ionic liquid or an additive, if necessary, is dissolved in a solvent, is applied to a release liner, followed by drying and / or curing. The solvents and release liners listed above can be used.

[0120] For application, a conventional coater (for example, a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, a spray roll coater, etc.) can be used.

[0121] By the above method, an electrically releasable pressure-sensitive adhesive layer and other pressure-sensitive adhesive layers can be produced.

[0122] (Method for electrically peeling adhesive sheet) When peeling the adhesive sheet of this embodiment from the adherend, it is preferable to start peeling from the inclined portion, and if the adhesive sheet has a tab at the end of the inclined portion, it is preferable to peel it by pulling the tab perpendicular to the adherend surface.

[0123] When the adhesive layer in the adhesive sheet of this embodiment is an electrically releasing adhesive layer, it is preferable to apply a voltage to the electrically releasing adhesive layer to generate a potential difference in the thickness direction of the electrically releasing adhesive layer, thereby reducing the adhesive strength, and then start peeling from the adherend from the inclined portion of the adhesive sheet. For example, when the adhesive sheet has a metal-coated surface on both sides, the adhesive strength can be reduced and peeled off by passing electricity through the metal-coated surfaces on both sides and applying a voltage to the electrically releasing adhesive layer. When the adhesive sheet X2 has a metal-coated surface on the electrically releasing adhesive layer side, the adhesive strength can be reduced and peeled off by passing electricity through the conductive adherend and the conductive layer 4 and applying a voltage to the electrically releasing adhesive layer. In the case of adhesive sheet X3, peeling can be achieved by passing electricity through the conductive layer 4 on both sides and applying a voltage to the electrically releasing adhesive layer. It is preferable to apply electricity by connecting terminals to one end and the other end of the adhesive sheet so that a voltage is applied to the entire electrically releasing adhesive layer. When the adherend has a metal surface, the one end and the other end may be part of the adherend having a metal surface. When peeling, water may be added to the interface between the metal surface and the electrically peelable pressure-sensitive adhesive layer before applying a voltage.

[0124] The voltage and voltage application time applied during electrical peeling are not particularly limited as long as the pressure-sensitive adhesive layer or pressure-sensitive adhesive sheet can be peeled from the adherend. The preferred ranges for these are shown below. The applied voltage is preferably 1 V or more, more preferably 3 V or more, and even more preferably 6 V or more. It is also preferably 100 V or less, more preferably 50 V or less, even more preferably 30 V or less, and particularly preferably 15 V or less. The voltage application time is preferably 60 seconds or less, more preferably 40 seconds or less, even more preferably 20 seconds or less, and particularly preferably 10 seconds or less. In such cases, workability is excellent. The shorter the application time, the better, but it is usually 1 second or more.

[0125] (Uses of Pressure-Sensitive Adhesive Sheets) Conventional peeling technologies include adhesive layers that are cured and peeled by ultraviolet (UV) irradiation, and adhesive layers that peel by heat. Pressure-sensitive adhesive sheets using such adhesive layers cannot be used in cases where ultraviolet (UV) irradiation is difficult or where heat damages the adherend. Pressure-sensitive adhesive sheets according to embodiments of the present invention have excellent peeling strength without using ultraviolet (UV) or heat, and therefore can be easily cleaved and peeled by applying voltage without damaging the adherend. Due to the above properties, pressure-sensitive adhesive sheets according to embodiments of the present invention are suitable for use in fixing secondary batteries (e.g., lithium-ion battery packs) used in mobile devices such as smartphones, mobile phones, laptops, video cameras, and digital cameras to the housings of such devices. Pressure-sensitive adhesive sheets according to embodiments of the present invention are also suitable for use in fixing components in semiconductor manufacturing processes and inspections (e.g., ceramic capacitors, lithium-ion batteries, etc.). Furthermore, pressure-sensitive adhesive sheets according to embodiments of the present invention are suitable for use in protecting components in metal processing processes (e.g., stainless steel plates for railways, etc.).

[0126] In addition, examples of rigid members that can be bonded with the pressure-sensitive adhesive sheet according to the embodiment of the present invention include silicon substrates for semiconductor wafers, sapphire substrates for LEDs, SiC substrates and metal-based substrates, TFT substrates and color filter substrates for displays, and base substrates for organic EL panels. Examples of fragile members that can be bonded with the double-sided pressure-sensitive adhesive sheet include semiconductor substrates such as compound semiconductor substrates, silicon substrates for MEMS devices, passive matrix substrates, surface cover glass for smartphones, OGS (One Glass Solution) substrates in which a touch panel sensor is attached to the cover glass, organic substrates and organic-inorganic hybrid substrates mainly composed of silsesquioxane, flexible glass substrates for flexible displays, and graphene sheets.

[0127] [Jointed structure and method for separating the joined structure] Next, the joined structure and the method for separating the joined structure will be described. The joined structure of this embodiment is a joined structure including the pressure-sensitive adhesive sheet, a first adherend, and a second adherend. That is, the joined structure of this embodiment is a joined structure in which the first adherend and the second adherend are joined by the pressure-sensitive adhesive sheet described above.

[0128] Fig. 8 is a top view schematically showing one configuration example (embodiment) of a bonded structure in which a first adherend 15 and a second adherend 16 are bonded together by a pressure-sensitive adhesive sheet 100. In the bonded structure shown in Fig. 8, the pressure-sensitive adhesive sheet 100 has double-sided adhesiveness to bond the first adherend 15 and the second adherend 16. The pressure-sensitive adhesive sheet 100 also has a linear strip shape. In Fig. 8, the pressure-sensitive adhesive sheet 100 is sandwiched between the first adherend 15 and the second adherend 16, and is adhered to the first adherend 15 and the second adherend 16. Specifically, the adhesive surfaces of the pressure-sensitive adhesive sheet 100 are adhered to the first adherend 15 and the second adherend 16, respectively.

[0129] The method for separating a bonded body according to the present embodiment is a method for separating a bonded body in which separation of the first and second adherends is initiated from the outer edge of the portion of the first and second adherends joined by the inclined portion of the pressure-sensitive adhesive sheet. In FIG. 8 , separation of the first and second adherends is preferably initiated from the outer edge 17 of the first adherend 15. Furthermore, when the pressure-sensitive adhesive sheet 100 has a tab, as shown in FIG. 1 and FIG. 9 described later in the Examples, separation may be achieved by pulling the tab in a direction perpendicular to the adherend surface. Because the pressure-sensitive adhesive sheet has an inclined portion, initiating separation from the outer edge of the portion joined by the inclined portion reduces the stress required to initiate peeling of the pressure-sensitive adhesive sheet. This eliminates the need to apply a large stress to a portion of the interface between the pressure-sensitive adhesive layer and the adherend, and provides advantages such as preventing deformation of the adherend.

[0130] When the pressure-sensitive adhesive layer 10 in the pressure-sensitive adhesive sheet 100 of this embodiment is an electrically peelable pressure-sensitive adhesive layer, the first adherend 15 and the second adherend 16 may be adherends having a metal adhesion surface. Examples of adherends having a metal adhesion surface include those made of a metal primarily composed of aluminum, copper, iron, magnesium, tin, gold, silver, lead, etc., with aluminum being preferred. When the pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet of this embodiment is an electrically peelable pressure-sensitive adhesive layer, it is preferable to apply a voltage to the electrically peelable pressure-sensitive adhesive layer to generate a potential difference in the thickness direction of the electrically peelable pressure-sensitive adhesive layer, thereby reducing the adhesive strength, and then initiate separation of the first adherend and the second adherend from their outer edges.

[0131] Examples of the bonded body of this embodiment include a bonded body comprising adherends (first adherend and second adherend) having metal adhesion surfaces on both sides of an electrically peeling pressure-sensitive adhesive layer 1 which is a pressure-sensitive adhesive sheet; a bonded body which is bonded by pressure-sensitive adhesive sheet X2 and comprises a first adherend having a metal adhesion surface on the electrically peeling pressure-sensitive adhesive layer 1 side and a second adherend on the pressure-sensitive adhesive layer 2 side; a bonded body which is bonded by pressure-sensitive adhesive sheet X3 and comprises adherends (first adherend and second adherend) on both sides of pressure-sensitive adhesive layer 2;

[0132] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0133] (Preparation of Acrylic Polymer Solution) As monomer components, n-butyl acrylate (BA): 87 parts by mass, 2-methoxyethyl acrylate (MEA): 10 parts by mass, acrylic acid (AA): 3 parts by mass, and ethyl acetate: 150 parts by mass as a polymerization solvent were charged into a separable flask and stirred for 1 hour while introducing nitrogen gas. After removing oxygen from the polymerization system in this way, 2,2'-azobisisobutyronitrile (AIBN): 0.2 parts by mass was added as a polymerization initiator, and the temperature was raised to 63 ° C. and reacted for 6 hours. Thereafter, ethyl acetate was added to obtain an acrylic polymer solution with a solids concentration of 40% by mass.

[0134] Example 1 (Preparation of Electrically Peelable Pressure-Sensitive Adhesive Layer) 100 parts by mass of the acrylic polymer (solution) obtained above, 0.4 parts by mass of crosslinking agent V-05, 4 parts by mass of ionic liquid AS-110, additives (3 parts by mass of adsorptive inhibitor AMINE O, 0.3 parts by mass of Irgacor DSSG, and 0.8 parts by mass of chelating-type metal deactivator Irgamet 30), and ethyl acetate were added and stirred and mixed to obtain an electrically peelable pressure-sensitive adhesive composition (solution) adjusted to a solids concentration of 25% by mass. The obtained electrically peelable pressure-sensitive adhesive composition (solution) was applied to a uniform thickness using an applicator onto the release-treated surface of a polyethylene terephthalate release liner (trade name "MRF38", manufactured by Mitsubishi Plastics, Inc.) whose surface had been release-treated. Next, the resultant was heated and dried at 150°C for 3 minutes, and the release-treated surface of a polyethylene terephthalate release liner (product name "MRE38", manufactured by Mitsubishi Plastics, Inc.) with a release treatment on the surface was laminated onto the adhesive using a hand roller to obtain an electrically peelable adhesive layer 50 μm thick.

[0135] The abbreviations for the ionic liquid, crosslinking agent, adsorptive inhibitor, and chelating-type metal deactivator are as follows:

[0136] (Ionic liquid) AS-110: cation: 1-ethyl-3-methylimidazolium cation, anion: bis(fluorosulfonyl)imide anion, trade name "ELEXEL AS-110", manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. (Crosslinking agent) V-05: polycarbodiimide resin, trade name "CARBODILITE V-05", manufactured by Nisshinbo Chemical Inc. (Adsorption inhibitor) AMINE O: 2-(8-heptadecen-1-yl)-4,5-dihydro-1H-imidazole-1-ethanol, trade name "AMINE O", manufactured by BASF Japan Ltd. Irgacor DSSG: sodium sebacate, trade name "Irgacor DSSG", manufactured by BASF Japan Ltd. (Chelate-forming metal deactivator) Irgamet 30: N,N-bis(2-ethylhexyl)-[(1,2,4-triazol-1-yl)methyl]amine, trade name "Irgamet 30", manufactured by BASF Japan Ltd.

[0137] (Preparation of electrically peelable pressure-sensitive adhesive sheet) The polyethylene terephthalate release liner (MRE38) from the obtained electrically peelable pressure-sensitive adhesive layer was peeled off, and the conductive layer side of a metal layer-attached film (product name "Metal Me TS", manufactured by Toray Advanced Film Co., Ltd., thickness 50 μm), which is a laminate comprising an electrically conductive layer (metal layer (aluminum vapor-deposited layer)) and a substrate (polyethylene terephthalate (PET)) laminated in this order, was bonded to the surface of the exposed electrically peelable pressure-sensitive adhesive layer to form Laminate 1. Furthermore, double-sided tape (product name "No. 56405", manufactured by Nitto Denko Corporation) was bonded to the substrate side surface of Laminate 1 to form Laminate 2, which had an electrically peelable pressure-sensitive adhesive layer on one side and another pressure-sensitive adhesive layer on the other side. The double-sided tape was bonded so that Laminate 1 protruded (extended) 30 mm beyond the other pressure-sensitive adhesive layer. The laminate 2 was cut to a size of 20 (W) mm width, 90 mm total length (L), and 30 mm tab length (L3), and was cut into a band shape with an inclined portion having an inclined width W1 of 5 mm, an end width W2 of 10 mm, an inclined width W3 of 5 mm, an inclined length L2 of 30 mm, an overall length L of 90 mm, a tab width of 10 mm, and a tab length L3 of 30 mm in Figure 9, to form the adhesive sheet (electrically peelable adhesive sheet) of Example 1.

[0138] (Production of bonded structure) The polyethylene terephthalate release liner (MRF38) was peeled off from the electrically peeling pressure-sensitive adhesive sheet obtained above, and a stainless steel plate (SUS304BA, size: 60 mm × 130 mm) was attached as a conductive adherend to the peeled surface so that tab 50 of the electrically peeling pressure-sensitive adhesive sheet (adhesive sheet X2) protruded from the adherend (second adherend 16), and pressed back and forth once with a 2 kg roller. Furthermore, the release liner on the other pressure-sensitive adhesive layer side was peeled off, and an acrylic plate (40 mm × 100 mm, thickness 3 mm) was attached as first adherend 15 to the peeled surface, and pressure-bonded at 5 kg for 10 seconds and left to stand in an environment of 23°C for 30 minutes, thereby obtaining a bonded structure consisting of SUS304BA plate / electrically peeling pressure-sensitive adhesive layer (adhesive sheet) / acrylic plate as shown in Figure 9.

[0139] (Adhesion Test) The bonded structure prepared by the above method was used as a test sample and subjected to an adhesion test. Using a peel tester (trade name "Small Desktop Tester EZ-SX", manufactured by Shimadzu Corporation), the tab portion of the adhesive sheet was pulled vertically while holding down the SUS304BA plates in the bonded structure, and the adhesive strength (tab side) was measured (pulling speed: 150 mm / min, peeling temperature: 23°C). Furthermore, for the bonded structure prepared, the end opposite to the tab side of the adhesive sheet was pulled vertically while holding down the SUS304BA plates in the bonded structure, and the adhesive strength (opposite side) was measured (pulling speed: 150 mm / min, peeling temperature: 23°C). The ratio of the adhesive strength (tab side) to the adhesive strength (opposite side) was calculated.

[0140] (Electric Peel Force Test) The bonded body prepared by the above method was used as a test sample and an electric peel force test was performed. Before peeling, a negative electrode was attached to the SUS304BA plate of the bonded body, and a positive electrode was attached to the aluminum vapor-deposited surface of the metal layer-covered film. A voltage of 50 V was applied for 10 seconds, and then the adhesive force was measured while the voltage was still applied. The electric peel force (on the tab side and the opposite side) was measured, and the ratio of the peel force (on the tab side) to the peel force (on the opposite side) was calculated in the same manner as in the adhesive force test described above.

[0141] (Shear Adhesion Strength Test) The bonded structure produced by the above method was used as a test sample and subjected to a shear adhesion strength test. The tensile shear adhesion strength between the SUS304BA plate and the acrylic plate in the bonded structure was measured using a tensile tester (manufactured by Minebea, model number: TG-100kN). The measurement was carried out at 25°C and a pulling rate of 5 mm / min. The obtained measurement value was converted into a value per unit area to obtain the shear adhesion strength.

[0142] [Examples 2 to 12] Pressure-sensitive adhesive sheets and joined bodies were produced in the same manner as in Example 1, except that the shape of the pressure-sensitive adhesive sheet was changed as shown in Tables 1 and 2. In addition, for Examples 11 and 12, the size of the stainless steel plate was changed to 60 mm × 200 mm, and the size of the acrylic plate was changed to 40 mm × 180 mm.

[0143] Comparative Example 1 A pressure-sensitive adhesive sheet and a bonded body were produced in the same manner as in Example 1, except that the shape of the pressure-sensitive adhesive sheet was changed to a band shape with no inclined portion, a width of 20 mm, a length of 90 mm, and a tab width of 20 mm.

[0144] Comparative Example 2 A pressure-sensitive adhesive sheet and a bonded body were produced in the same manner as in Example 1, except that the shape of the pressure-sensitive adhesive sheet was changed to a strip shape with no inclined portion, a width of 40 mm, a length of 90 mm, and a tab width of 40 mm.

[0145] Comparative Example 3 An adhesive sheet and a bonded body were produced in the same manner as in Example 1, except that the shape of the adhesive sheet was changed to a band shape with no inclined portion, a width of 40 mm, a length of 180 mm, and a tab width of 40 mm, the size of the stainless steel plate was changed to 60 mm × 200 mm, and the size of the acrylic plate was changed to 40 mm × 180 mm.

[0146] The results obtained for Examples 1 to 12 and Comparative Examples 1 to 3 are shown in Tables 1 and 2.

[0147]

[0148]

[0149] The results in Tables 1 and 2 show that the adhesive sheets of Examples 1 to 12, which have a tapered inclined portion, have a lower peel force from the tab side compared to Comparative Examples 1 to 3, which do not have an inclined portion, and therefore can be peeled with less stress. Furthermore, the peel force tended to decrease when the width of the end (end 41) was made smaller than the width of the adhesive sheet. Similarly to Example 1, a decrease in peel force was also confirmed in Examples 11 and 12, in which the overall length of the adhesive sheet was increased. It was shown that the greater the ratio of the inclined length to the overall length of the adhesive sheet, the lower the peel force, and that the smaller the width of the end (the thinner the tab), the lower the peel force.

[0150] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0151] The present invention provides a pressure-sensitive adhesive sheet and an assembly having excellent adhesive strength and good releasability, and also provides a method for separating an assembly having good releasability.

[0152] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2021-057809) filed on March 30, 2021, the contents of which are incorporated herein by reference.

[0153] 100, 110, 120, 130, X2, X3 Adhesive sheet 2, 10 Adhesive layer 1 Electrically peelable adhesive layer 3, 20 Substrate 4 Conductive layer 5 Current-carrying substrate 15 First adherend 16 Second adherend 17 Outer edge portion 40 Sloped portion 41 End portion 50 Tab W Width W1 Sloped width W2 End width W3 Sloped width L Total length L1 Length other than sloped portion L2 Sloped length L3 Tab length

Claims

1. A band-shaped adhesive sheet having an adhesive layer, the adhesive sheet having a tapered portion whose width tapers toward one end in the longitudinal direction of the adhesive sheet.

2. The adhesive sheet of claim 1, further comprising a tab provided at said end.

3. The adhesive sheet according to claim 1 or 2, wherein the ratio of the length of said inclined portion to the longitudinal length of said adhesive sheet is 5% or more.

4. An adhesive sheet according to any one of claims 1 to 3, wherein the ratio of the width of said end portion to the width of said adhesive sheet is 50% or less.

5. The adhesive sheet according to any one of claims 1 to 4, wherein the adhesive layer is an electrically peelable adhesive layer whose adhesive strength decreases upon application of a voltage.

6. The adhesive sheet according to claim 5, wherein the electrically peelable adhesive layer contains a polymer and an ionic liquid.

7. The pressure-sensitive adhesive sheet according to claim 6, wherein the anion of the ionic liquid is at least one selected from the group consisting of bis(fluorosulfonyl)imide anion and bis(trifluoromethanesulfonyl)imide anion.

8. The pressure-sensitive adhesive sheet according to claim 6 or 7, wherein the cation of the ionic liquid is at least one selected from the group consisting of nitrogen-containing onium cations, sulfur-containing onium cations, and phosphorus-containing onium cations.

9. A bonded body comprising the pressure-sensitive adhesive sheet according to any one of claims 1 to 8, a first adherend, and a second adherend.

10. A method for separating a bonded body as described in claim 9, comprising starting separation of the first adherend and the second adherend from the outer edge of a portion of the first adherend or the second adherend joined by the inclined portion of the adhesive sheet.