Adhesive sheet

Abstract

To provide an adhesive sheet capable of easily recycling a resin base material.SOLUTION: An adhesive sheet 10 comprises: a resin base material 1; and an adhesive layer 3 which includes a blowing agent 5 and is formed on at least one surface of the base material 1. The blowing agent 5 is a thermally expandable microcapsule, and the entire adhesive layer 3 can be peeled off from an adherend 9 and the base material 1 by heat treating after adhering the adhesive layer 3 to the adherend 9.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The technology disclosed in this specification relates to an adhesive sheet that can be peeled not only between an adherend and an adhesive layer but also between a base material and the adhesive layer by heating.

Background Art

[0002] An adhesive sheet for temporarily fixing an article having a base material and an adhesive layer added with thermally expandable microspheres has been conventionally known. After this adhesive sheet is attached to an adherend, the adhesive layer can be expanded by heating to peel the adhesive layer from the adherend. Therefore, this adhesive sheet is used in dicing processes and back grinding processes of semiconductor wafers.

[0003] For example, Patent Document 1 describes an example of an adhesive sheet having a plastic base material, an adhesive layer, and a rubbery organic elastic layer provided between the base material and the adhesive layer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, environmental awareness has been increasing, and the reduction of non-biodegradable plastic waste and the recycling of plastic materials have been promoted worldwide. Regarding adhesive sheets using plastic base materials, it is often difficult to switch to biodegradable materials from the viewpoints of cost and performance, so measures such as recovering and recycling the base materials are being taken.

[0006] Here, when the pressure-sensitive adhesive sheet described in Patent Document 1 is peeled off from the adherend after use, the base material and the pressure-sensitive adhesive are peeled off integrally. For this reason, after collecting the base material, an operation of separating the base material and the pressure-sensitive adhesive layer is separately required, and it may be difficult to recycle at low cost.

[0007] An object of the present invention is to provide a pressure-sensitive adhesive sheet capable of easily recycling a resin base material.

Means for Solving the Problems

[0008] An example of the pressure-sensitive adhesive sheet disclosed in this specification is a pressure-sensitive adhesive sheet including a resin base material and a pressure-sensitive adhesive layer formed on at least one surface of the base material and containing a foaming agent. The foaming agent is a thermally expandable microcapsule, and the entire pressure-sensitive adhesive layer can be peeled off from the adherend and the base material by heat treatment after the pressure-sensitive adhesive layer is attached to the adherend.

Effects of the Invention

[0009] According to the pressure-sensitive adhesive sheet disclosed in this specification, since the entire pressure-sensitive adhesive layer can be peeled off not only from the adherend but also from the base material by heat treatment, the recycling of the base material becomes easy.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0011] FIG. 1 is a cross-sectional view showing a pressure-sensitive adhesive sheet, which is an example of the embodiment disclosed in this specification.

[0012] As shown in FIG. 1, the pressure-sensitive adhesive sheet 10 of the present embodiment includes a resin base material 1 and a pressure-sensitive adhesive layer 3 containing a foaming agent 5 and formed on at least one surface of the base material 1. A release liner 7 for protecting the pressure-sensitive adhesive layer 3 may be provided on the surface of the pressure-sensitive adhesive layer 3 opposite to the base material 1. The foaming agent 5 is, for example, a thermally expandable microcapsule and expands when heated to a predetermined temperature or higher.

[0013] FIG. 2(a) is a cross-sectional view showing the pressure-sensitive adhesive sheet according to the embodiment in a state of being attached to an adherend, and (b) is a view showing the pressure-sensitive adhesive sheet in a state of being peeled from the adherend after heating.

[0014] As shown in FIGS. 2(a) and (b), after the release liner 7 is peeled off and the pressure-sensitive adhesive layer 3 is attached to the adherend 9, the pressure-sensitive adhesive sheet 10 of the present embodiment is heated, whereby the foaming agent 5 expands. For this reason, the thickness of the pressure-sensitive adhesive layer 3 increases and the planar size also increases, and as a result, it becomes detachable from both the base material 1 and the adherend 9. Here, "detachable" includes the case of natural detachment by heat treatment and the case of easy detachment by merely lightly touching the pressure-sensitive adhesive sheet 10 without natural detachment.

[0015] In the pressure-sensitive adhesive sheet 10 of the present embodiment, since the entire pressure-sensitive adhesive layer 3 can be detached from not only the adherend 9 but also the base material 1 by heating, when the base material 1 is recovered and recycled, the removal process of the pressure-sensitive adhesive layer 3 becomes unnecessary. Further, when the adherend 9 is recyclable, it becomes easy to reuse or recycle the adherend 9.

[0016] The adherend 9 is not particularly limited, and may be, for example, a wall, a building material, a glass bottle, a resin bottle such as polyethylene terephthalate (PET), a semiconductor wafer, or a ceramic green sheet laminate.

[0017] [Relationship between Adhesive Force and Adhesion to Substrate] Generally, in an adhesive sheet, the adhesion between the adhesive layer and the base material is much greater than the force (adhesive force) required to peel it off from the adherend. Therefore, even when the adhesive sheet is peeled off from the adherend, the adhesive layer does not remain on the adherend side.

[0018] However, the inventors of the present application noticed that if the adhesion between the adhesive layer and the base material is too strong, the adhesive layer cannot be peeled off from the base material even when heated. Through repeated independent studies, they conceived that by making the adhesion between the base material and the adhesive layer as small as possible while making it greater than the adhesive force to the adherend, the base material and the adhesive layer can be peeled off during heating.

[0019] [Configuration of Adhesive Sheet] In the adhesive sheet 10 of the present embodiment, the base material 1 is a sheet-like support, and the constituent material is not limited as long as it mainly contains a resin material. Examples of the resin material include polyester resins such as PET, polyolefin resins such as polyethylene (PE) and polypropylene (PP), and polyvinyl chloride (PVC). The base material 1 may be formed of synthetic paper.

[0020] A known easy-adhesion layer, antistatic layer, or the like may be provided on one or both surfaces of the base material 1. By forming an easy-adhesion layer on the side of the base material 1 where the adhesive layer 3 is located, the adhesion between the base material 1 and the adhesive layer 3 can be strengthened within a range where the adhesive layer 3 can be peeled off by heating. Also, when the adhesive sheet is used as a label, a printing layer can be formed on the easy-adhesion layer. If the printing layer is not formed or if it is desired to reduce the adhesion to the adhesive layer 3, the easy-adhesion layer may not be provided on the surface of the base material 1 on the side of the adhesive layer 3.

[0021] Considering that the base material 1 is recycled after peeling, it is preferable that a special material is not used as much as possible and that it has a simple structure. For example, if the base material 1 is formed of a single-layer PET film, when the pressure-sensitive adhesive sheet of the present embodiment is attached to a PET bottle as a label, it can be easily recovered together with the PET derived from the bottle after peeling by heat treatment. Further, when the base material 1 is formed of a material having a specific gravity of less than 1, such as synthetic paper or a polyolefin film, the base material 1 after peeling by heat treatment can be easily separated and recovered from the PET derived from the bottle and the adhesive layer due to the difference in specific gravity.

[0022] The thickness of the base material 1 is not particularly limited, and for example, it may be 1 μm or more and 300 μm or less, preferably 5 μm or more and 200 μm or less, and more preferably 10 μm or more and 150 μm or less. If the thickness of the base material 1 is 1 μm or more, it is easy to use with a general coating machine, and if it is 5 μm or more, it is easy to handle. If the thickness of the base material 1 is 300 μm or less, an increase in manufacturing cost can be suppressed.

[0023] The adhesive layer 3 is formed of a cured product of an adhesive and contains a foaming agent 5. The adhesive used for forming the adhesive layer 3 is not particularly limited, and may be one selected from rubber-based adhesives, acrylic-based adhesives, acrylic urethane-based adhesives, urethane-based adhesives, and silicone-based adhesives, or a mixture of two or more thereof. The silicone-based adhesive may be a peroxide-curing type or an addition-curing type.

[0024] When using an acrylic-based adhesive, as a curing agent, one or a mixture of two or more selected from known isocyanate-based curing agents, chelate-based curing agents, and epoxy-based curing agents can be used.

[0025] As the adhesive for forming the adhesive layer 3, a solvent-based adhesive insoluble in hot water can be used. In this case, since the adhesive layer 3 does not dissolve during heat treatment, the cost required for wastewater treatment can be reduced compared to the case of using an adhesive soluble in hot water.

[0026] In the adhesive layer 3, various known additives such as tackifiers, plasticizers, antioxidants, heat stabilizers, fillers, coupling agents, etc. may be appropriately added as long as the object of the present invention is not impaired other than the foaming agent 5.

[0027] The adhesive force of the adhesive sheet 10 to the glass plate may be, for example, 1.0 N / 25 mm or more and 10.0 N / 25 mm or less, or 1.5 N / 25 mm or more and 5.0 N / 25 mm or less at 24 hours after pasting when the temperature is 23 °C, the relative humidity is 50%, the peeling speed is 300 mm / min, and the peeling angle is 180°. If the adhesive force to glass is 1.0 N / 25 mm or more, it is not easily peeled from the glass bottle at room temperature when pasted on the glass bottle as a label, and if it is 1.5 N / 25 mm or more, it becomes more difficult to fall off from the glass bottle. If the adhesive force is 6.0 N / 25 mm or less, the adhesive layer 3 can be easily peeled from the adherend 9 after the foaming agent 5 foams by heating. Since the adhesive force of the adhesive sheet 10 is not too strong, the adhesion between the base material 1 and the adhesive layer 3 can be made relatively small, and as a result, the peeling between the base material 1 and the adhesive layer 3 during heating can be facilitated.

[0028] The adhesive force of the adhesive sheet 10 to the PET plate may be, for example, 1.0 N / 25 mm or more and 10.0 N / 25 mm or less, or 1.5 N / 25 mm or more and 6.0 N / 25 mm or less at 24 hours after pasting when the temperature is 23 °C, the relative humidity is 50%, the peeling speed is 300 mm / min, and the peeling angle is 180°. When the adhesive force to the PET plate is within the range of 1.0 N / 25 mm or more and 10.0 N / 25 mm or less, the adhesive sheet 10 is not easily peeled from the container at room temperature when pasted on the PET container as a label, and can be easily peeled from the adherend 9 by heating.

[0029] The storage elastic modulus of the adhesive layer 3 containing the foaming agent 5 is not particularly limited. For example, at 23 °C, relative humidity 50%, and frequency 1 Hz, it may be 4.5×10 4 Pa or more and 5×10 6 Pa or less, or 2×10 5 Pa or more and 1×106 It is more preferable if it is below Pa. If the storage elastic modulus is too low, it is likely to break inside the adhesive layer 3 during heat peeling, so the adhesive is likely to remain on the adherend 9. On the other hand, if the storage elastic modulus is too high, the adhesive layer 3 is difficult to peel from the base material 1 when heated under dry conditions.

[0030] When the gel fraction of the adhesive layer 3 immediately after being formed on the base material 1 is A% and the gel fraction of the adhesive layer 3 after being treated at 40°C and 50% relative humidity for 72 hours after production is B%, if the increase rate of the gel fraction obtained by 100×(B - A) / B is 5% or less, it is possible to prevent the adhesion force between the base material 1 and the adhesive layer 3 from becoming too strong, so it is preferable.

[0031] The thickness of the adhesive layer 3 varies depending on the type of adhesive used. For example, it may be 2 μm or more and 300 μm or less, preferably 10 μm or more and 200 μm or less, and more preferably 20 μm or more and 100 μm or less. If the thickness of the adhesive layer 3 is 2 μm or more, it can be made difficult to fall off from the adherend 9 at room temperature. If the thickness of the adhesive layer 3 is 300 μm or less, it is possible to make it difficult to cause cohesive failure during peeling after heat treatment, and it is easy to reduce the contamination of the adherend 9. Also, when the content rate of the foaming agent 5 is the same, the thicker the adhesive layer 3, the larger it expands after heating, so the adhesive layer 3 is easier to peel from both the base material 1 and the adherend 9. However, from the viewpoint of reducing the manufacturing cost, it is preferable that the thickness of the adhesive layer 3 is smaller.

[0032] The foaming agent 5 contained in the adhesive layer 3 may be, for example, microcapsules in which a substance that easily gasifies and expands by heating, such as isobutane, propane, pentane, etc., is encapsulated in a shell having elasticity. The shell is composed of a heat-melting substance or a substance that is broken by thermal expansion. Examples of the constituent material of the shell include vinylidene chloride - acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, polysulfone, etc.

[0033] Microcapsules can be produced by known methods, such as the coacervation method, the interfacial polymerization method, etc.

[0034] The foaming start temperature of the foaming agent 5 is not particularly limited, but from the viewpoint of energy saving, it is preferable that the energy required for peeling the adhesive layer 3 from the base material 1 or the adherend 9 can be reduced. For example, the foaming start temperature of the foaming agent 5 may be 50°C or higher and 100°C or lower. By the foaming start temperature being 50°C or higher, it is possible to suppress the unintended peeling of the adhesive sheet 10 in summer or the like. By the foaming start temperature being 100°C or lower, the adhesive layer 3 can be peeled from the base material 1 and the adherend 9 by treatment at a relatively low temperature, such as treatment with hot water at 100°C or lower or drying at 130°C or lower.

[0035] The temperature at which the foaming agent 5 expands to the maximum particle size may be about 100°C or higher and 140°C or lower. Similar to the foaming start temperature, this temperature is also preferably relatively low because the energy consumption during heating can be reduced.

[0036] Commercially available products may be used as the foaming agent 5. Specific examples of commercially available products include "Matsumoto Microsphere" (grades: F-30, F-30D, F-36D, F-36LV, F-50, F-50D, F-65, F-65D, HF-36D, HF-48D, FN-100SS, FN-100SSD, FN-180SS, FN-180SSD, F-190D, F-260D, F-2800D) manufactured by Matsumoto Yushi Seiyaku Co., Ltd., "Expancel" (grades: 053-40, 031-40, 007-40) manufactured by Nippon Fillite Co., Ltd., "Daiform" (grades: M330, M430) manufactured by Kureha Chemical Industry Co., Ltd., "Advancell" (grades: EML101, EMH204, EHM301, EHM302, EHM303, EM304, EHM401, EM403, EM501) manufactured by Sekisui Chemical Co., Ltd., etc.

[0037] The average particle size of the foaming agent 5 may be, for example, 1 μm or more and 50 μm or less, or may be 5 μm or more and 30 μm or less. If the average particle size is 1 μm or more, it becomes easier to increase the unevenness on both sides of the pressure-sensitive adhesive layer 3 after expansion by heating, and the pressure-sensitive adhesive layer 3 can be easily peeled from the base material 1 and the adherend 9. Although it depends on the thickness of the pressure-sensitive adhesive layer 3, if the average particle size of the foaming agent 5 is 50 μm or less, the unevenness on the surface of the pressure-sensitive adhesive layer 3 before heating can be reduced, and it becomes easier to reduce unintentional peeling from the adherend 9. The average particle size of the foaming agent 5 may be about 5 times or less, preferably 3 times or less, and more preferably 1 time or less, the thickness of the pressure-sensitive adhesive layer 3.

[0038] The volume change rate when the foaming agent 5 expands most compared to before heating may be, for example, about 5 times or more and 60 times or less, or may be 7 times or more and 40 times or less. The volume expansion rate here means a value measured by the method using the cylinder and piston described in the specification of JP-A-11-002615.

[0039] The content of the foaming agent 5 in the pressure-sensitive adhesive layer 3 may be 5% by mass or more and 70% by mass or less, preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 50% by mass or less, based on the mass of the entire pressure-sensitive adhesive layer 3, although it depends on the pressure-sensitive adhesive used. If the content of the foaming agent 5 is too low, the pressure-sensitive adhesive layer 3 is difficult to peel from the base material 1 and the adherend 9 even when heated, and if the content of the foaming agent 5 is too high, the adhesive force to the adherend 9 before heating tends to be insufficient.

[0040] By appropriately adjusting the average particle size, content, volume change rate, etc. of the foaming agent 5 in the pressure-sensitive adhesive layer 3, the film thickness increase rate of the pressure-sensitive adhesive layer 3 after the heat treatment can be, for example, 4 times or more and 30 times or less, so that the pressure-sensitive adhesive layer 3 can be easily peeled from both the base material 1 and the adherend 9 after the heat treatment. The film thickness increase rate of the pressure-sensitive adhesive layer 3 may be 6 times or more and 25 times or less. Here, the film thickness increase rate of the pressure-sensitive adhesive layer 3 after the heat treatment is a value calculated by Equation 1. (Thickness of the pressure-sensitive adhesive layer after heat treatment) / (Thickness of the pressure-sensitive adhesive layer before heat treatment) ··· Equation 1 The thickness of the adhesive layer 3 before the heat treatment shall be measured at 23°C and a relative humidity of 50%. The thickness of the adhesive layer 3 can be measured using a commercially available micrometer.

[0041] Note that Patent Document 1 describes that by providing an intermediate layer having rubber elasticity between the adhesive layer 3 and the base material 1, it becomes easier to peel the adhesive sheet after heating from the adherend. However, in the adhesive sheet 10 of the present embodiment, an intermediate layer is not deliberately provided, and the adhesive layer 3 is in direct contact with one surface of the base material 1. With this configuration, it is possible to reduce the adhesive force between the base material 1 and the adhesive layer 3, and it becomes easier for the adhesive layer 3 to peel from the base material 1 after heating. Here, the base material 1 shall include a printing layer and an easy-adhesion layer. Even if another layer is provided between the base material 1 and the adhesive layer 3, it is preferable that the distance between the base material 1 and the adhesive layer 3 is about 1 μm or less.

[0042] [Method for manufacturing an adhesive sheet] When manufacturing the adhesive sheet 10 of the present embodiment, first, a crosslinking agent and a predetermined amount of foaming agent 5 are added to the adhesive and mixed to prepare a coating liquid. Next, the coating liquid is applied to the release surface of the release liner 7 made of paper or a resin film by a comma coater or the like so as to have a desired thickness after drying, and dried at a low temperature of 100°C or lower to form the adhesive layer 3. Next, after the coated surface of the release liner 7 is bonded to the base material 1 to produce the adhesive sheet 10, aging is performed at, for example, 40°C for about 72 hours.

[0043] Here, when manufacturing an adhesive sheet to be used as a label, a printing layer with a predetermined design may be formed on at least one surface of the base material 1 using a known printing machine before forming the adhesive layer 3. A recycling information presentation area indicating the peeling conditions of the base material 1 and the adhesive layer 3, and that the base material 1 is recyclable, etc. may be formed in this printing layer. This enables consumers and processors to appropriately recycle the adherend 9 and the base material 1.

[0044] Alternatively, instead of this method, after applying the above coating liquid to the release surface of the release liner 7, a second release liner is bonded to the coated surface of the release liner 7, and then the above aging is performed to produce an adhesive layer 3 in a so-called substrate-less state. In this case, after peeling the second release liner from the previously formed adhesive layer 3 and bonding it to the substrate 1, the adhesive sheet 10 can be produced by bonding the adhesive layer 3 to the substrate 1. According to this method, since the adhesive layer 3 can be bonded to the substrate 1 after being sufficiently cured, it is possible to suppress the increase in the adhesive strength between the substrate 1 and the adhesive layer 3. As a result, when the adhesive sheet 10 is heat-treated, the adhesive layer 3 can be easily peeled from the substrate 1.

[0045] [Method of disassembling the adhesive sheet] After the adhesive sheet 10 of the present embodiment is attached to the adherend 9, in order to disassemble it into the adhesive layer 3 and the substrate 1, it is sufficient to heat it to a temperature at which the adhesive layer 3 expands sufficiently. For example, when the expansion start temperature of the foaming agent 5 (microcapsule) is 50°C or higher and 100°C or lower, the adhesive layer 3 can be peeled from both the substrate 1 and the adherend 9 by immersion in hot water at a temperature equal to or higher than the expansion start temperature and 100°C or lower, or by heating in a dry state at a temperature 10°C or higher and 130°C or lower than the expansion start temperature. However, the adhesive sheet 10 does not necessarily have to be disassembled under all the above conditions, and it is sufficient if it can be disassembled under at least one condition. Also, although the ease of peeling from the adhesive sheet 10 varies depending on the material of the adherend 9, etc., the adhesive layer 3 after heating does not necessarily have to be peelable from all types of adherends, and it is sufficient if it can be peeled from at least one type of adherend. Considering actual use, it is preferable that it can be peeled from at least one of PET and glass.

[0046] When the adherend 9 can be immersed like a glass bottle or a PET bottle, or when it is denatured by heat exceeding 100°C, hot water treatment may be performed. When the adherend 9 can withstand heating, heating in a dry state may be performed.

[0047] The pressure-sensitive adhesive sheet 10 of this embodiment can be easily separated from the adherend 9 and the base material 1 even at home, for example. Therefore, the base material 1 and the adherend 9 can be easily separated and recycled. Further, if the specific gravity of the base material 1 is less than 1, when used as a container label such as a PET bottle, the base material 1 peeled off by heat treatment can be easily separated from the pressure-sensitive adhesive layer 3 and the PET bottle material (specific gravity of about 1.38) in water using the difference in specific gravity and recovered. The specific gravity of the pressure-sensitive adhesive layer 3 after foaming by heat decreases as the content of the foaming agent 5 increases, and may be at least less than 1. If the specific gravity of the pressure-sensitive adhesive layer 3 is less than 1, it becomes easy to recover the pressure-sensitive adhesive layer 3 separated from the base material 1 and the adherend 9 by heat treatment. If the specific gravity of the base material 1 differs from that of the pressure-sensitive adhesive layer 3 by, for example, 0.1 or more, the pressure-sensitive adhesive sheet 10 after disassembly can be easily separated into materials using the difference in specific gravity.

[0048] Further, when the pressure-sensitive adhesive sheet 10 attached to a PET bottle or the like is processed in a recycling factory, after the recovered bottle is washed and crushed, by performing heat treatment, the adherend 9 (PET bottle piece), the pressure-sensitive adhesive layer 3, and the base material 1 can be disassembled in the whole crushed small pieces. Therefore, the recycling efficiency can be significantly improved as compared with the case where only some small pieces can be disassembled.

[0049] [Other configurations] The configuration of the pressure-sensitive adhesive sheet 10 described above is an example of the embodiment, and the constituent materials, the thickness of each layer, physical properties, etc. can be appropriately changed without departing from the spirit of the present invention.

Example

[0050] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

[0051] <Example 1> To an adhesive composition A prepared by adding 3.0 parts by mass of a commercially available isocyanate-based curing agent to 100 parts by mass of a commercially available re-peelable type acrylic adhesive, a foaming agent A (manufactured by Matsumoto Yushi Seiyaku Co., Ltd., trade name "Matsumoto Microsphere (registered trademark) HF-36D") was added in an amount of 20% by mass based on the resin solid content of the adhesive and mixed to prepare a coating liquid. Next, using a known comma coater, the above coating liquid was applied to the release surface of the first release liner (heavy release side) so that the thickness after drying would be 20 μm, and after drying at 60°C for 3 minutes to form an adhesive layer, the release surface of the second release liner (light release side) was bonded to produce a base material restape having an adhesive layer. After aging this base material restape under the conditions of 40°C, relative humidity 50%, and 72 hours, the second release liner was peeled off and the adhesive layer was attached to one surface of the base material to produce an adhesive sheet. As the base material, a PET film (trade name "Cosmo Shine (registered trademark) A4360"; specific gravity of about 1.4) manufactured by Toyobo Co., Ltd. with a thickness of 50 μm was used.

[0052] <Example 2> An adhesive sheet was produced in the same manner as in Example 1, except that the addition amount of the foaming agent A was 10% by mass based on the resin solid content of the adhesive, and the thickness of the adhesive layer was 30 μm.

[0053] <Example 3> An adhesive sheet was produced in the same manner as in Example 2, except that the addition amount of the foaming agent A was 20% by mass based on the resin solid content of the adhesive.

[0054] <Example 4> An adhesive sheet was produced in the same manner as in Example 1, except that a foaming agent B (manufactured by Matsumoto Yushi Seiyaku Co., Ltd., trade name "Matsumoto Microsphere (registered trademark) HF-48D") was used as the foaming agent, and the drying conditions of the coating liquid were changed to 70°C for 3 minutes.

[0055] <Example 5> An adhesive sheet was produced in the same manner as in Example 4, except that the addition amount of the foaming agent B was 30% by mass based on the resin solid content of the adhesive.

[0056] <Example 6> An adhesive sheet was produced in the same manner as in Example 4, except that the thickness of the adhesive layer was 30 μm.

[0057] <Example 7> An adhesive sheet was produced in the same manner as in Example 6, except that the addition amount of foaming agent B was 30% by mass based on the resin solid content of the adhesive.

[0058] <Example 8> An adhesive sheet was produced in the same manner as in Example 4, except that the thickness of the adhesive layer was 50 μm.

[0059] <Example 9> An adhesive sheet was produced in the same manner as in Example 8, except that the addition amount of foaming agent B was 30% by mass based on the resin solid content of the adhesive.

[0060] <Example 10> An adhesive sheet was produced in the same manner as in Example 9, except that the base material was changed to synthetic paper (manufactured by Upo Corporation, trade name "Upo Tack (registered trademark) base paper SGS80"; specific gravity 0.83) with a thickness of 80 μm.

[0061] <Example 11> An adhesive sheet was produced in the same manner as in Example 1, except that the addition amount of foaming agent A was 30% by mass based on the resin solid content of the adhesive.

[0062] <Example 12> An adhesive sheet was produced in the same manner as in Example 11, except that the thickness of the adhesive layer was 30 μm.

[0063] <Example 13> An adhesive sheet was produced in the same manner as in Example 11, except that the addition amount of foaming agent A was 40% by mass based on the resin solid content of the adhesive.

[0064] <Example 14> An adhesive sheet was produced in the same manner as in Example 12, except that the addition amount of foaming agent A was 40% by mass based on the resin solid content of the adhesive.

[0065] <Example 15> An adhesive sheet was produced in the same manner as in Example 11, except that the addition amount of foaming agent A was 50% by mass based on the resin solid content of the adhesive.

[0066] <Example 16> An adhesive sheet was produced in the same manner as in Example 12, except that the addition amount of foaming agent A was 50% by mass based on the resin solid content of the adhesive.

[0067] <Comparative Example 1> An adhesive sheet was produced in the same manner as in Example 2, except that an adhesive composition B obtained by adding 1.0 part by mass of the above isocyanate-based curing agent to 100 parts by mass of the acrylic-based adhesive used in Example 1 was used.

[0068] <Comparative Example 2> A coating liquid was prepared by adding 30% by mass of foaming agent B to the adhesive composition A based on the resin solid content of the adhesive and mixing. This coating liquid was applied to the release surface of a commercially available release liner using a comma coater so that the thickness after drying was 50 μm, dried at 70 °C for 3 minutes to form an adhesive layer, and then transferred to one surface of a substrate (trade name "Cosmo Shine (registered trademark) A4360") to produce an adhesive sheet. Then, it was aged under the conditions of 40 °C, 50% relative humidity, and 72 hours.

[0069] <Comparative Example 3> An adhesive sheet was produced in the same manner as in Example 2, except that the addition amount of foaming agent A was 3% by mass based on the resin solid content of the adhesive.

[0070] The characteristics of foaming agents A and B used in the above examples and comparative examples are shown in Table 1.

[0071]

Table 1

[0072] [Measurement method] <Evaluation test of peelability> The adhesive surface of the sample pieces prepared by cutting out the pressure-sensitive adhesive sheets produced in each of the examples and comparative examples into a size of 2 cm × 7 cm was bonded to a glass plate or a PET plate without surface treatment. Regarding the hot water treatment, the glass plate or PET plate to which the sample piece was attached was put into hot water at 90°C in a beaker, and the presence or absence of spontaneous peeling was visually confirmed after 5 minutes. Also, the glass plate or PET plate to which the sample piece was attached was put into a drying oven set at 120°C, and the presence or absence of spontaneous peeling was visually confirmed after 5 minutes. In both conditions, when the adhesive layer did not peel off spontaneously, it was determined whether it could be peeled off by hand. When it peeled off spontaneously, it was rated as ◎ (excellent), when it did not peel off spontaneously but could be easily peeled off by hand, it was rated as 〇 (good), when it was not easily peeled off but could be peeled off carefully, it was rated as △ (acceptable), and when it could not be peeled off or the adhesive component remained on the adherend even after peeling, it was rated as × (unacceptable).

[0073] <Confirmation of the increase rate of gel fraction> Regarding Examples 1 to 16 and Comparative Examples 1 and 3, the release liner was removed from the base material restape including the adhesive layer used for the production of the pressure-sensitive adhesive sheet, and about 0.3 g to 0.5 g of the adhesive layer was collected as a test specimen, and its exact mass G1 was measured. Next, the test specimen was immersed in ethyl acetate at 23°C and a relative humidity of 50% for 96 hours, and the solution containing the test piece was filtered using a 300-mesh filter cloth to obtain the insoluble component in ethyl acetate. Next, the insoluble component was dried at 100°C for 2 hours to measure the mass G2 of the insoluble matter. The gel fraction A was calculated by the following formula 2.

[0074] Gel fraction A (%) = 100 × G2 / G1 ··· (Formula 2) Next, after the base material restapes used in each of the examples and comparative examples were allowed to stand at 40°C and a relative humidity of 50% for 72 hours as an aging treatment, the gel fraction B was calculated for each test specimen by the same method as described above. The increase rate of the gel fraction of the treated test specimen was calculated based on the formula of 100 × (B - A) / B.

[0075] Regarding the pressure-sensitive adhesive sheet produced in Comparative Example 2, a coating solution containing blowing agent B and pressure-sensitive adhesive composition A was applied onto a release liner so that the thickness after drying would be 50 μm, dried, and then another release liner was laminated thereto to produce a substrate-less tape. The release liner was removed from this substrate-less tape, and 0.3 g to 0.5 g of only the pressure-sensitive adhesive layer was collected as a test piece, and its gel fraction A was measured. Further, after the test piece was allowed to stand at 40°C and 50% relative humidity for 72 hours, its gel fraction B was measured. The increase rate of the gel fraction of the processed test piece was calculated based on the formula of 100×(B - A) / B.

[0076] <Measurement of Adhesive Force> After peeling off the release liner of the pressure-sensitive adhesive sheet and attaching it to an adherend, the adhesive forces 1 minute and 24 hours after attachment were measured by a method conforming to JIS Z 0237. Specifically, a test piece of the pressure-sensitive adhesive sheet cut to a width of 25 mm was attached to a glass plate or a PET plate as the adherend and then allowed to stand at 23°C and 50% relative humidity for 1 minute or 24 hours. The force required to peel these test pieces at a peeling angle of 180° and a peeling speed of 300 mm / min using a universal material testing machine was measured as the adhesive force (N / 25 mm).

[0077] <Measurement of Film Thickness Increase Rate of Pressure-Sensitive Adhesive Layer> A test piece having a size of 25 mm × 40 mm was cut out from the pressure-sensitive adhesive sheet, and the thickness of the pressure-sensitive adhesive layer before the heat treatment was measured using a micrometer. Next, after the test piece was heat-treated in a drying oven at 120°C, the thickness of the pressure-sensitive adhesive layer was measured using a micrometer. Then, the film thickness increase rate was determined by the following formula 1.

[0078] (Thickness of pressure-sensitive adhesive layer after heat treatment) / (Thickness of pressure-sensitive adhesive layer before heat treatment) ··· Formula 1 <Measurement of Storage Elastic Modulus of Pressure-Sensitive Adhesive Layer> A pressure-sensitive adhesive layer having a thickness of 50 μm was prepared using a coating liquid obtained by adding blowing agent A at 20% by mass and 50% by mass, respectively, based on the resin solid content of the pressure-sensitive adhesive to the above-described pressure-sensitive adhesive composition A to a base material-less tape. Next, this base material-less tape was aged under the conditions of 40 ° C., 50% relative humidity, and 72 hours. Next, only the pressure-sensitive adhesive layer was laminated until the total thickness reached 1 mm, and then punched into a size of 8 mm in diameter to produce a tablet. This tablet was sandwiched between the plates of a rheometer (product name: AR2000ex), and the storage elastic modulus G' was measured under the conditions of a frequency of 1 Hz, 23 ° C., 50% relative humidity, and a strain of 0.05%.

[0079] [Measurement Results] The evaluation results of peelability, the measurement results of adhesive strength, and the calculation results of the increase rate of gel fraction before and after aging are shown in Tables 2 to 4.

[0080] [Table 2]

[0081] [Table 3]

[0082] [Table 4] The storage elastic moduli of the pressure-sensitive adhesive layer added with 20% by mass of blowing agent A (used in Examples 1 and 3) and the pressure-sensitive adhesive layer added with 50% by mass of blowing agent A (used in Examples 15 and 16) are shown in Table 5.

[0083] [Table 5] From the results of Examples 1, 2, 4, and 5 shown in Table 2, it was found that when the adherend is PET or glass, the adhesion between the pressure-sensitive adhesive layer and the base material tends to be greater than the adhesion between the pressure-sensitive adhesive and the adherend. However, in Examples 1 to 16, it was confirmed that the pressure-sensitive adhesive layer could be peeled off from both the base material and the adherend under at least one condition.

[0084] From the results of the peelability evaluation of Examples 2, 3, 7, 16 and Comparative Example 3, it was confirmed that the greater the amount of the foaming agent added, the easier it was to peel. Also, from the results of Examples 4 to 9, it was found that when the amount of the foaming agent added was the same, the greater the thickness of the pressure-sensitive adhesive layer, the better the peeling of the pressure-sensitive adhesive layer and the base material.

[0085] From the results of Comparative Example 1 shown in Table 4, the adhesion to glass after 24 hours of pasting at 23°C was relatively large, and the amount of the foaming agent added was relatively small at 10% by mass. A plurality of conditions that made it difficult to peel the pressure-sensitive adhesive layer from the base material overlapped, and it was confirmed that the pressure-sensitive adhesive layer was difficult to peel from the adherend and the base material.

[0086] Also, in the pressure-sensitive adhesive sheets produced in Examples 1 to 10, the increase rate of the gel fraction after aging was 5% or less (specifically, less than 1%). However, in the pressure-sensitive adhesive sheet produced in Comparative Example 2, the gel fraction of the pressure-sensitive adhesive layer immediately after production was 0%, and the increase rate of the gel fraction after aging was 100% (see Table 3). In particular, from the comparison between Examples 9 and 10 and Comparative Example 2, it was confirmed that reducing the adhesion between the base material and the pressure-sensitive adhesive layer by previously curing the pressure-sensitive adhesive layer was advantageous for peeling the pressure-sensitive adhesive layer and the base material.

Industrial Applicability

[0087] The pressure-sensitive adhesive sheet disclosed in this specification can be used for various purposes as a tape or label for temporary fixing.

Explanation of Signs

[0088] 1 Base material 3 Pressure-sensitive adhesive layer 5 Foaming agent 7 Release liner 9 Adherend 10 Pressure-sensitive adhesive sheet

Claims

1. A pressure-sensitive adhesive sheet comprising a resin substrate and a pressure-sensitive adhesive layer formed of a cured product of a pressure-sensitive adhesive containing a curing agent and a foaming agent, the pressure-sensitive adhesive layer being formed on at least one surface of the substrate, wherein the foaming agent is a thermally expandable microcapsule, and the entire pressure-sensitive adhesive layer can be peeled off from the adherend and the substrate by heat treatment after the pressure-sensitive adhesive layer is attached to the adherend, when the gel fraction of the pressure-sensitive adhesive layer immediately after it is formed on the substrate is A%, and the gel fraction of the pressure-sensitive adhesive layer after being treated at 40 °C and 50% relative humidity for 72 hours after production is B%, the rate of increase in the gel fraction determined by 100×(B - A) / B is 5% or less.

2. The pressure-sensitive adhesive sheet according to Claim 1, wherein the expansion start temperature of the foaming agent is 50 °C or higher and 100 °C or lower, and the heat treatment is washing with hot water at a temperature equal to or higher than the expansion start temperature and 100 °C or lower, or heating in a dry state at a temperature 10 °C or higher and 130 °C or lower than the expansion start temperature.

3. The pressure-sensitive adhesive sheet according to Claim 1 or 2, wherein the glass adhesion at 24 hours after pasting, when the temperature is 23 °C, the relative humidity is 50%, the peeling speed is 300 mm / min, and the peeling angle is 180°, is 1.0 N / 25 mm or more and 10.0 N / 25 mm or less.

4. The pressure-sensitive adhesive sheet according to any one of Claims 1 to 3, wherein the content of the foaming agent contained in the pressure-sensitive adhesive layer is 5% by mass or more and 70% by mass or less of the entire pressure-sensitive adhesive layer.

5. The pressure-sensitive adhesive sheet according to any one of Claims 1 to 4, wherein the heat treatment is treatment at 120 °C in a drying oven, and the film thickness increase rate of the pressure-sensitive adhesive layer after the heat treatment, determined by (the thickness of the pressure-sensitive adhesive layer after the heat treatment) / (the thickness of the pressure-sensitive adhesive layer before the heat treatment) ··· Formula 1 is 4 times or more and 30 times or less.

6. The pressure-sensitive adhesive sheet according to any one of Claims 1 to 5,

7. The storage elastic modulus of the adhesive layer under the conditions of 23°C, 50% relative humidity, and a frequency of 1 Hz is 4.5×10 ４ Pa or more and 5.0×10 ６ Pa or less. The adhesive sheet The pressure-sensitive adhesive sheet according to any one of Claims 1 to 6, wherein the pressure-sensitive adhesive layer is in direct contact with one surface of the substrate.

8. The pressure-sensitive adhesive sheet according to any one of Claims 1 to 7, wherein the specific gravity of the substrate is less than 1, and the specific gravity of the pressure-sensitive adhesive layer after being peeled off from the substrate by heating is 1 or less.

9. The pressure-sensitive adhesive sheet according to any one of Claims 1 to 8, ​ An adhesive sheet in which the specific gravity of the base material is different by 0.1 or more from the specific gravity of the adhesive layer after peeling from the base material by heating.

10. In the adhesive sheet according to any one of Claims 1 to 9, An adhesive sheet used as a label.

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