Adhesive sheet and method of use thereof

Abstract

To provide an adhesive sheet which enables easy recycling of a resin base material.SOLUTION: An adhesive sheet 10 includes a sheet-like base material 1, and an adhesive layer 3 which contains a foaming agent 5 and is formed on at least one surface of the base material 1. The foaming agent 5 is thermally expansible microcapsules, the adhesive layer 3 contains at least one of a chelate-based curing agent and an epoxy-based curing agent, and the whole adhesive layer 3 is peelable from an adherend 9 and the base material 1 by heating treatment after the adhesive layer 3 is bonded to the adherend.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 to which thermally expandable microspheres are added 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 the dicing process or back grinding process 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 materials have been promoted globally. Regarding adhesive sheets using a plastic base material, since it is often difficult to switch to a biodegradable material in terms of cost and performance, measures such as recovering and recycling the base material are being taken.

[0006] In the case of the adhesive sheet described in Patent Document 1, when peeled off from the adherend after use, the base material and adhesive peel off together. Therefore, after recovering the base material, a separate process is required to separate the base material from the adhesive layer, which can make it difficult to promote low-cost recycling.

[0007] The object of the present invention is to provide an adhesive sheet that allows the base material to be easily recycled. [Means for solving the problem]

[0008] An example of an adhesive sheet disclosed herein is an adhesive sheet comprising a sheet-like substrate and an adhesive layer formed on at least one surface of the substrate, comprising a foaming agent. The foaming agent is a thermally expandable microcapsule, and the adhesive layer comprises at least one of a chelating curing agent and an epoxy curing agent, and the entire adhesive layer becomes peelable from the substrate and the adherend by heat treatment after the adhesive layer is attached to the adherend. [Effects of the Invention]

[0009] According to the adhesive sheet disclosed herein, the entire adhesive layer becomes detachable from both the adherend and the substrate by heat treatment, thus facilitating the recycling of not only the adherend but also the substrate. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a cross-sectional view showing an adhesive sheet according to an embodiment of the present disclosure. [Figure 2] Figure 2(a) is a cross-sectional view showing the adhesive sheet according to the embodiment in a state attached to a substrate, and (b) is a diagram showing the adhesive sheet after being peeled off the substrate after heating. [Modes for carrying out the invention]

[0011] Figure 1 is a cross-sectional view showing an adhesive sheet, which is an example of an embodiment disclosed herein.

[0012] As shown in Figure 1, the adhesive sheet 10 of this embodiment comprises a sheet-shaped base material 1 and an adhesive layer 3 containing a foaming agent 5, which is formed on at least one surface of the base material 1. A release liner 7 protecting the adhesive layer 3 may be provided on the surface of the adhesive layer 3 opposite to the base material 1. The foaming agent 5 is, for example, a thermally expandable microcapsule that expands when heated above a predetermined temperature.

[0013] Figure 2(a) is a cross-sectional view showing the adhesive sheet 10 attached to the substrate, and (b) is a view showing the adhesive sheet 10 after being peeled off the substrate after heating.

[0014] As shown in Figures 2(a) and (b), in this embodiment, the adhesive sheet 10 expands when the foaming agent 5 is heated after the release liner 7 is peeled off and the adhesive layer 3 is attached to the adherend 9. As a result, the thickness and planar size of the adhesive layer 3 increase, and consequently, it becomes peelable from both the substrate 1 and the adherend 9. Here, "peelable" includes cases where it peels off naturally due to the heat treatment, and cases where it can be easily peeled off by simply touching the adhesive sheet 10, even without natural peeling.

[0015] In the adhesive sheet 10 of this embodiment, the entire adhesive layer 3 can be peeled off not only from the adherend 9 but also from the base material 1 by heating. Therefore, when the base material 1 is recovered and recycled, the step of removing the adhesive layer 3 becomes unnecessary. Furthermore, if the adherend 9 is recoverable, it is easy to reuse or recycle the adherend 9.

[0016] The adherend 9 is not particularly limited, but may include, for example, a wall, building materials, glass bottles, resin bottles such as polyethylene terephthalate (PET), semiconductor wafers, or ceramic green sheet laminates.

[0017] [Relationship between adhesive strength and adhesion to the substrate] Generally, in an adhesive sheet, the adhesive force between the adhesive layer and the base material is much greater than the force (adhesive force) required to peel it from the adherend. Therefore, even when the adhesive sheet is peeled 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 adhesive force between the adhesive layer and the base material is too strong, the adhesive layer cannot be peeled from the base material even when heated. Through repeated independent studies, they came up with the idea of making it possible to peel the base material and the adhesive layer during heating by making the adhesive force of the adhesive layer with respect to the adherend as large as possible while making the adhesive force between the base material and the adhesive layer as small as possible.

[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 particularly limited. As the constituent material, a material that can be separately collected and recycled is preferable, and for example, various papers, resin materials, etc. can be used. When the adhesive sheet 10 is used as a label for beverages or the like, a resin material, paper having water resistance, or the like is preferably used as the material of the base material 1.

[0020] The paper for the base material 1 may be fine paper, art paper, coated paper, gloss paper, cast coated paper, or the like. As the resin material for the base material 1, polyester resins such as PET, polyolefin resins such as polyethylene (PE) and polypropylene (PP), polyvinyl chloride (PVC), or the like may be used. The base material 1 may be formed of synthetic paper.

[0021] Known easy adhesion layers, antistatic layers, or the like may be provided on one or both surfaces of the base material 1. By forming an easy adhesion layer on the adhesive layer 3 side of the base material 1, the adhesive force between the base material 1 and the adhesive layer 3 can be strengthened within a range where the adhesive layer 3 can be peeled by heating. Also, when the adhesive sheet is used as a label, a printing layer can be formed on the easy adhesion layer. When the printing layer is not formed or when it is desired to reduce the adhesive force with the adhesive layer 3, it is not necessary to provide an easy adhesion layer on the surface of the base material 1 on the adhesive layer 3 side.

[0022] Considering that the base material 1 is recycled after peeling, it is preferable that it has a simple structure without using a particularly special material as much as possible. For example, if the base material 1 is formed of a single-layer PET film, when the 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 resin 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.

[0023] 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 coater, 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.

[0024] 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 it may be one selected from a rubber-based adhesive, an acrylic-based adhesive, an acrylic urethane-based adhesive, a urethane-based adhesive, and a polyester-based adhesive, or a mixture of two or more thereof.

[0025] When using an acrylic-based adhesive, it is preferable to use an epoxy-based curing agent or a chelate-based curing agent, or a mixture of both curing agents as a curing agent. When curing is performed using only an isocyanate-based curing agent, the adhesion between the adhesive layer and the base material becomes too strong, and the adhesive layer and the base material are difficult to peel even when heated. For this reason, for curing the adhesive, at least one of a chelate-based curing agent and an epoxy-based curing agent is used without using an isocyanate-based curing agent, or when using an isocyanate-based curing agent, it is preferable to suppress the total addition amount of the chelate-based curing agent and the epoxy-based curing agent to 20% by mass or less.

[0026] Based on the above, the cured adhesive layer 3 contains at least one of a chelating curing agent and an epoxy curing agent. In this specification, "the adhesive layer contains a curing agent" means not only that it contains unreacted curing agent molecules, but also that it contains molecules derived from the curing agent that are bound to the adhesive by a crosslinking reaction.

[0027] The amount of curing agent added to the adhesive may be 1 / 2 equivalent or more of the crosslinking point contained in the adhesive. The curing agent content in the adhesive layer 3 may be, for example, 0.01% by mass or more and 1.0% by mass or less when using an epoxy curing agent or a metal chelate curing agent. If the amount of curing agent added is less than 0.01 parts by mass per 100 parts by mass of the resin solids content of the adhesive, curing may be insufficient, or even if cured, the adhesion between the substrate 1 and the adhesive layer 3 may become too strong. If the amount of curing agent added exceeds 1.0 part by mass per 100 parts by mass of the resin solids content of the adhesive, the adhesion to the adherend may become too weak. When using an epoxy curing agent, by setting the amount added to less than 0.1% by mass per 100 parts by mass of the resin solids content of the adhesive, it is possible to maintain a relatively high adhesion strength of the adhesive layer to the adherend and substrate, and to make it less likely for the adhesive layer to transfer to the adherend side.

[0028] Since epoxy curing agents crosslink with acid groups in the adhesive molecule, when using epoxy curing agents, an adhesive containing acid groups in its molecule should be selected. In this case, the acid value of the adhesive is preferably 1.0 or higher. Here, the acid value is one of the indicators that represents the acid content and is expressed as the number of mg of potassium hydroxide required to neutralize 1 g of polymer containing carboxyl groups.

[0029] If the adhesive sheet 10 is not to be reattached once it has been attached to the substrate 9, the adhesion between the adhesive layer 3 and the substrate 1 may be reduced to the extent that the adhesive layer 3 transfers to the substrate 9 side when peeled off at room temperature.

[0030] A solvent-type adhesive that is insoluble in hot water can be used as the adhesive for forming the adhesive layer 3. In this case, since the adhesive layer 3 does not dissolve during hot water treatment, the cost of wastewater treatment can be reduced compared to when using an adhesive that is soluble in hot water.

[0031] In addition to the foaming agent 5, the adhesive layer 3 may also contain various known additives, such as tackifiers, plasticizers, antioxidants, heat stabilizers, fillers, and coupling agents, as long as the objectives of the present invention are not impaired.

[0032] The adhesive strength of the adhesive sheet 10 to the glass plate may be, for example, 0.1 N / 25 mm to 15.0 N / 25 mm or 0.4 N / 25 mm to 10.0 N / 25 mm at 24 hours after application, when the temperature is 23°C, relative humidity is 50%, peeling speed is 300 mm / min, and peeling angle is 180°. If the adhesive strength to glass is 0.1 N / 25 mm or more, when applied to a glass bottle as a label, it will not easily peel off the glass bottle at room temperature, and if it is 0.4 N / 25 mm or more, it will be even less likely to fall off the glass bottle. If the adhesive strength is 15.0 N / 25 mm or less, the adhesive layer 3 will peel off the adherend 9 more easily after the foaming agent 5 foams up due to heating, and if the adhesive strength is 10.0 N / 25 mm or less, the adhesive layer 3 will peel off the adherend 9 even more easily. Because the adhesive strength of the adhesive sheet 10 is not too strong, the adhesion force between the substrate 1 and the adhesive layer 3 can be made relatively small, and as a result, the substrate 1 and the adhesive layer 3 can be easily peeled off when heated.

[0033] The adhesive strength of the adhesive sheet 10 to the PET plate may be, for example, 0.1 N / 25 mm to 15.0 N / 25 mm or 0.5 N / 25 mm to 12.0 N / 25 mm at 24 hours after application, when the temperature is 23°C, relative humidity is 50%, peeling speed is 300 mm / min, and peeling angle is 180°. By having an adhesive strength of 0.1 N / 25 mm to 15.0 N / 25 mm or less to the PET plate, when the adhesive sheet 10 is applied to a PET container as a label, it will be difficult to peel off the container at room temperature, and will be easily peeled off the adherend 9 when heated.

[0034] The storage modulus of the adhesive layer 3 is not particularly limited, but for example, under conditions of 23°C, 50% relative humidity, and 1 Hz, it is 2.0 × 10⁻⁶. 4 Pa or more 1.0×10 6 It may be less than or equal to Pa, 4.0 × 10 4 Pa or more 6.0×10 5 A value of Pa or less is more preferable. Under conditions of 80°C, 50% relative humidity, and a frequency of 1 Hz, the storage modulus of the adhesive layer 3 is, for example, 1 × 10⁻⁶. 3 Pa or more 5×10 5 It may be less than Pa. If the storage modulus is too low at 23°C and near the foaming start temperature of the foaming agent (80°C in this case), the adhesive layer 3 will easily break during heat peeling, making it easier for the adhesive to remain on the adherend 9. Also, if the storage modulus is too high, the adhesive layer 3 will be difficult to peel off from the substrate 1 when heated under dry conditions. Note that even with the presence of the foaming agent 5, the storage modulus of the adhesive layer 3 at 23°C is close to the value when the foaming agent 5 is not present.

[0035] The thickness of the adhesive layer 3 varies depending on the type of adhesive used, but it may be, for example, 2 μm to 300 μm, preferably 10 μm to 200 μm, and more preferably 20 μm to 100 μm. If the thickness of the adhesive layer 3 is 2 μm or more, it can be made less likely to detach from the adherend 9 at room temperature. If the thickness of the adhesive layer 3 is 300 μm or less, it can be made less likely to cause cohesive failure when peeling after heat treatment, and contamination of the adherend 9 can be easily reduced. Also, if the content of the foaming agent 5 is the same, a thicker adhesive layer 3 expands more after heating, making it easier for the adhesive layer 3 to peel off from both the substrate 1 and the adherend 9, but from the viewpoint of reducing manufacturing costs, a thinner adhesive layer 3 is preferable.

[0036] The foaming agent 5 contained in the adhesive layer 3 may be a microcapsule containing a substance that readily gasifies and expands upon heating, such as isobutane, propane, or pentane, within an elastic shell. The shell is composed of a heat-meltable substance or a substance that expands or breaks upon thermal expansion. Examples of shell components include vinylidene chloride-acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, and polysulfone.

[0037] Microcapsules can be manufactured by known methods, such as coacervation or interfacial polymerization.

[0038] The foaming start temperature of the foaming agent 5 is not particularly limited, but from an energy-saving viewpoint, it is preferable to reduce the energy required to peel the adhesive layer 3 from the substrate 1 or adherend 9. For example, the foaming start temperature of the foaming agent 5 may be 50°C or higher and 100°C or lower. If the foaming start temperature is 50°C or higher, it is possible to suppress unintended peeling of the adhesive sheet 10 in summer, etc. If the foaming start temperature is 100°C or lower, the adhesive layer 3 can be peeled from the substrate 1 and adherend 9 by processing at relatively low temperatures, such as with hot water at 100°C or lower or in a dry state at 130°C or lower.

[0039] The temperature at which the foaming agent 5 expands to its maximum particle size may be approximately 100°C to 140°C. Similar to the foaming initiation temperature, a relatively low temperature is preferable because it reduces the energy consumed during heating.

[0040] As foaming agent 5, a commercially available product may be used. 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 Oil & Fat Pharmaceutical Co., Ltd. Examples include "Expancel" (grades: 053-40, 031-40, 007-40) manufactured by Ilight, "Daiform" (grades: M330, M430) manufactured by Kureha Chemical Industries, and "Advancel" (grades: EML101, EMH204, EHM301, EHM302, EHM303, EM304, EHM401, EM403, EM501) manufactured by Sekisui Chemical Co., Ltd.

[0041] The average particle size of the foaming agent 5 may be, for example, 1 μm to 50 μm, or 5 μm to 30 μm. If the average particle size is 1 μm or more, it becomes easier to increase the surface irregularities of both sides of the adhesive layer 3 after expansion due to heating, making it easier to peel the adhesive layer 3 from the substrate 1 and the adherend 9. Depending on the thickness of the adhesive layer 3, if the average particle size of the foaming agent 5 is 50 μm or less, the surface irregularities of the adhesive layer 3 before heating can be reduced, making it easier to reduce unintended peeling from the adherend 9. The average particle size of the foaming agent 5 may be about 5 times or less the thickness of the adhesive layer 3, preferably 3 times or less, and more preferably 1 time or less.

[0042] The volume change rate when the foaming agent 5 expands to its maximum extent compared to before heating may be, for example, 5 to 70 times, or 7 to 40 times. The volume change rate referred to here means the value measured by the method using a cylinder and piston described in the specification of Japanese Patent Publication No. 11-002615.

[0043] The content of the foaming agent 5 in the adhesive layer 3 depends on the adhesive used, but may be 5% by mass or more and 70% by mass or less relative to the total mass of the adhesive layer 3, 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. If the content of the foaming agent 5 is too low, the adhesive layer 3 will be difficult to peel off from the substrate 1 and the adherend 9 even when heated, and if the content of the foaming agent 5 is too high, the adhesive strength to the adherend 9 will likely be insufficient before heating.

[0044] By appropriately adjusting the average particle size, content, and volume change rate of the foaming agent 5 in the adhesive layer 3, the rate of increase in film thickness of the adhesive layer 3 after heat treatment can be made, for example, between 4 and 30 times, making it easier to peel the adhesive layer 3 from both the substrate 1 and the adherend 9 after heat treatment. The rate of increase in film thickness of the adhesive layer 3 may also be between 6 and 25 times. Here, the rate of increase in film thickness of the adhesive layer 3 after heat treatment is the value calculated by Equation 1.

[0045] (Thickness of the adhesive layer after heat treatment) / (Thickness of the adhesive layer before heat treatment) ... Formula 1 The thickness of the adhesive layer 3 before heat treatment shall be measured at 23°C and 50% relative humidity. The thickness of the adhesive layer 3 can be measured using a commercially available micrometer.

[0046] Patent Document 1 describes how providing a rubber-elastic intermediate layer between the adhesive layer 3 and the substrate 1 makes it easier to peel the adhesive sheet from the adherend after heating. However, in the adhesive sheet 10 of this embodiment, an intermediate layer is deliberately omitted, and the adhesive layer 3 is in direct contact with one side of the substrate 1. This configuration reduces the adhesion force between the substrate 1 and the adhesive layer 3, making it easier to peel the adhesive layer 3 from the substrate 1 after heating. Here, the substrate 1 includes any printing layer or easy-adhesion layer provided. Even if another layer is provided between the substrate 1 and the adhesive layer 3, it is preferable to keep the distance between the substrate 1 and the adhesive layer 3 to about 1 μm or less.

[0047] [Method for manufacturing adhesive sheets] In preparing the adhesive sheet 10 of this embodiment, first, a coating solution is prepared by adding a crosslinking agent and a predetermined amount of foaming agent 5 to the adhesive and mixing them. Next, the coating solution is applied to the release surface of a paper or resin film release liner 7 using a comma-type coater or the like to achieve a desired thickness after drying, and dried at a low temperature below the foaming start temperature of the foaming agent 5 to form an adhesive layer 3. Then, the coated surface of the release liner 7 is bonded to the substrate 1 to prepare the adhesive sheet 10, and then aging is performed, for example, at 40°C for about 72 hours.

[0048] In this case, when preparing an adhesive sheet to be used as a label, a printed layer with a predetermined design can be formed on at least one side of the substrate 1 using a known printing press before forming the adhesive layer 3. This printed layer may have a recycling information display area that indicates the peeling conditions for the substrate 1 and the adhesive layer 3, and that the substrate 1 is recyclable. This allows consumers and processing companies to properly recycle the adherend 9 and the substrate 1.

[0049] Alternatively, instead of this method, the above-mentioned coating liquid may be applied to the release surface of the release liner 7, the second release liner may be bonded to the coated surface of the release liner 7, and then the above-mentioned aging may be performed to create a so-called substrate-less adhesive layer 3. In this case, the second release liner can be peeled off the previously formed adhesive layer 3 and bonded to the substrate 1, and then the adhesive layer 3 can be bonded to the substrate 1 to create the adhesive sheet 10. With this method, the adhesive layer 3 can be bonded to the substrate 1 after it has been sufficiently cured, so the adhesion between the substrate 1 and the adhesive layer 3 can be suppressed. As a result, the adhesive layer 3 can be easily peeled off from the substrate 1 when the adhesive sheet 10 is heat-treated.

[0050] In the adhesive sheet 10 of this embodiment, the adhesive layer 3 is cured by at least one of a chelating curing agent and an epoxy curing agent, so that the adhesion force between the substrate 1 and the adhesive layer 3 does not become too strong. For this reason, the substrate 1 and the adhesive layer 3 can be easily separated by heating without first forming an adhesive layer 3 without a substrate.

[0051] [How to remove adhesive sheets] After attaching the adhesive sheet 10 of this embodiment to the adherend 9, in order to separate it into the adhesive layer 3 and the base material 1, it is sufficient to heat it to a temperature at which the adhesive layer 3 expands sufficiently. For example, if the expansion start temperature of the foaming agent 5 (microcapsules) is 50°C or higher and 100°C or lower, the adhesive layer 3 can be separated from both the base material 1 and the adherend 9 by immersion in hot water at a temperature between the expansion start temperature and 100°C, or by heating in a dry state at a temperature 10°C or higher than the expansion start temperature and 130°C or lower. However, the adhesive sheet 10 does not need to be separated under all of the above conditions; it is sufficient if it can be separated under at least one condition. Also, although the ease of separation from the adhesive sheet 10 varies depending on the material of the adherend 9, the heated adhesive layer 3 does not need to be able to be separated from all types of adherends; it is sufficient if it can be separated from at least one type of adherend. Considering actual use, it is preferable that it can be separated from at least one of PET and glass.

[0052] If the adherend 9 is immersable, such as a glass bottle or plastic bottle, or if it is altered by temperatures exceeding 100°C, hot water treatment may be performed. If the adherend 9 can withstand heating, heating may be performed in a dry state.

[0053] The adhesive sheet 10 of this embodiment allows for easy separation of the base material 1 and adhesive layer 3 from the adherend 9, even in a household setting, making it easy to separate the base material 1 and adherend 9 for recycling. Furthermore, if the specific gravity of the base material 1 is less than 1, when used as a container label for PET bottles, the base material 1 peeled off by hot water treatment can be easily separated and recovered in water from the adhesive layer 3 and PET bottle material (specific gravity approximately 1.38) by utilizing the difference in specific gravity. The specific gravity of the 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 adhesive layer 3 is less than 1, it becomes easier to recover the adhesive layer 3 separated from the base material 1 and adherend 9 by hot water treatment. If the specific gravity of the base material 1 differs from the specific gravity of the adhesive layer 3 by, for example, 0.1 or more, the adhesive sheet 10 after disassembly can be easily separated into materials by utilizing the difference in specific gravity.

[0054] Furthermore, when the adhesive sheet 10 attached to a PET bottle is processed at a recycling plant, the collected bottles are washed and crushed, and then subjected to heat treatment. This allows the entire crushed piece to be disassembled into the adherend 9 (PET bottle fragments), adhesive layer 3, and base material 1, significantly improving recycling efficiency compared to cases where only a portion of the fragments can be disassembled.

[0055] [Other configurations] The configuration of the adhesive sheet 10 described above is just one example of an embodiment, and the constituent materials, the thickness of each layer, physical properties, etc. can be changed as appropriate without departing from the spirit of the present invention. [Examples]

[0056] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0057] [Making adhesive sheets] <Example 1> A coating solution was prepared by adding 5.0 parts by mass of a commercially available liquid metal chelating curing agent (containing 3 wt% curing agent component) to 100 parts by mass of a commercially available liquid strong adhesive solvent-type acrylic adhesive A (resin solids content 50 wt%). To this adhesive composition, foaming agent A (manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd., trade name "Matsumoto Microsphere® HF-36D") was added at a concentration of 40% by mass relative to the resin solids content of the adhesive, and the mixture was combined to prepare a coating solution. Next, the above coating solution was applied to the release surface of a commercially available release liner using a known comma-type coater so that the thickness after drying was 20 μm, and the adhesive layer was formed by drying at 60°C for 3 minutes. After that, an adhesive sheet was prepared by laminating it to one side of a commercially available PET film (substrate). As the substrate, a PET film manufactured by Toyobo Co., Ltd. with a thickness of 50 μm (trade name "Cosmoshine® A4360"; specific gravity approximately 1.4) was used. Next, the adhesive sheet was aged under conditions of 40°C for 72 hours.

[0058] <Example 2> An adhesive sheet was prepared using the same method as in Example 1, except that the adhesive layer was coated to a thickness of 30 μm.

[0059] <Example 3> An adhesive sheet was prepared using the same method as in Example 1, except that the adhesive layer was coated to a thickness of 50 μm.

[0060] <Example 4> A coating solution was prepared by adding 0.5 parts by mass of a commercially available liquid epoxy curing agent (containing 5 wt% curing agent component) to 100 parts by mass of a commercially available liquid strong-tack acrylic adhesive A (resin solids content 50 wt%). The foaming agent A described above was then added at a concentration of 30% by mass relative to the resin solids content of the adhesive and mixed to prepare the coating solution. Next, the coating solution was applied to the release surface of a release liner so that the thickness after drying would be 30 μm, and the adhesive layer was formed by drying at 60°C for 3 minutes. After that, the adhesive sheet was bonded to one side of a commercially available PET film (substrate) to prepare the adhesive sheet. The adhesive sheet was then aged at 40°C for 72 hours. The content of the epoxy curing agent in the formed adhesive layer was approximately 0.05% by mass.

[0061] <Example 5> An adhesive sheet was prepared in the same manner as in Example 4, except that the adhesive layer was coated to a thickness of 50 μm.

[0062] <Example 6> An adhesive sheet was prepared in the same manner as in Example 5, except that the amount of epoxy curing agent added per 100 parts by mass of adhesive A was changed to 0.7 parts by mass, and the amount of foaming agent A added was set to 40% by mass relative to the resin solids content of adhesive A.

[0063] <Example 7> An adhesive sheet was prepared in the same manner as in Example 6, except that the amount of epoxy curing agent added to 100 parts by mass of adhesive A was changed to 0.8 parts by mass.

[0064] <Example 8> An adhesive sheet was prepared in the same manner as in Example 6, except that the amount of epoxy curing agent added to 100 parts by mass of adhesive A was changed to 0.9 parts by mass.

[0065] <Example 9> An adhesive sheet was prepared in the same manner as in Example 4, except that the amount of epoxy curing agent added to 100 parts by mass of adhesive A was 1.0 part by mass, and the adhesive layer was coated to a thickness of 20 μm.

[0066] <Example 10> An adhesive sheet was prepared in the same manner as in Example 9, except that the amount of foaming agent added was changed to 40% by mass relative to the resin solid content of adhesive A.

[0067] <Example 11> An adhesive sheet was prepared in the same manner as in Example 9, except that the adhesive layer was coated to a thickness of 30 μm.

[0068] <Example 12> An adhesive sheet was prepared in the same manner as in Example 11, except that the amount of foaming agent added was changed to 40% by mass relative to the resin solid content of adhesive A.

[0069] <Example 13> An adhesive sheet was prepared in the same manner as in Example 9, except that the adhesive layer was coated to a thickness of 50 μm.

[0070] <Example 14> An adhesive sheet was prepared in the same manner as in Example 13, except that the amount of foaming agent added was changed to 40% by mass relative to the resin solid content of adhesive A.

[0071] <Example 15> An adhesive sheet was prepared in the same manner as in Example 9, except that the amount of epoxy curing agent added per 100 parts by mass of adhesive A was 3.0 parts by mass, and the amount of foaming agent A added was 40% by mass relative to the resin solids content of adhesive A.

[0072] <Example 16> An adhesive sheet was prepared using the same method as in Example 15, except that the adhesive layer was coated to a thickness of 30 μm.

[0073] <Example 17> An adhesive sheet was prepared in the same manner as in Example 15, except that the adhesive layer was coated to a thickness of 50 μm.

[0074] <Example 18> An adhesive sheet was prepared in the same manner as in Example 15, except that the amount of epoxy curing agent added per 100 parts by mass of adhesive A was 5.0 parts by mass.

[0075] <Example 19> An adhesive sheet was prepared in the same manner as in Example 18, except that the adhesive layer was coated to a thickness of 30 μm.

[0076] <Example 20> An adhesive sheet was prepared in the same manner as in Example 18, except that the adhesive layer was coated to a thickness of 50 μm.

[0077] <Example 21> An adhesive sheet was prepared in the same manner as in Example 18, except that a commercially available solvent-type one-component acrylic adhesive B containing a metal chelating curing agent was used as the adhesive, and no epoxy curing agent was added. Adhesive B contains a metal chelating curing agent at a concentration of 10% by mass or less.

[0078] <Example 22> An adhesive sheet was prepared in the same manner as in Example 21, except that the amount of foaming agent added was changed to 50% by mass relative to the resin solid content of adhesive B.

[0079] <Example 23> An adhesive sheet was prepared in the same manner as in Example 22, except that the adhesive layer was coated to a thickness of 30 μm.

[0080] <Example 24> A coating solution was prepared by adding 0.6 parts by mass of a commercially available liquid epoxy curing agent (containing 5 wt% curing agent component) and 0.6 parts by mass of a commercially available metal chelating curing agent (containing 3 wt% curing agent component) to 100 parts by mass of a commercially available liquid solvent-type acrylic adhesive C (resin solids content 30 wt%). A foaming agent B (manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd., trade name "Matsumoto Microsphere® HF-48D") was added at a concentration of 30% by mass relative to the resin solids content of the adhesive, and the mixture was combined to prepare a coating solution. Next, the above coating solution was applied to the release surface of a release liner so that the thickness after drying was 30 μm, and the adhesive layer was formed by drying at 60°C for 3 minutes. After that, an adhesive sheet was prepared by laminating it to one side of a commercially available PET film (substrate). Next, the adhesive sheet was aged at 40°C for 72 hours.

[0081] <Example 25> An adhesive sheet was prepared in the same manner as in Example 24, except that the adhesive layer was coated to a thickness of 50 μm.

[0082] <Comparative Example 1> An adhesive sheet was prepared in the same manner as in Example 1, except that a foaming agent B was added at a concentration of 30% by mass relative to the resin solids content of the adhesive to an adhesive composition prepared by adding 3.0 parts by mass of a commercially available isocyanate-based curing agent (containing 45 wt% curing agent component) to 100 parts by mass of the acrylic adhesive A used in Example 5.

[0083] <Comparative Example 2> An adhesive sheet was prepared in the same manner as in Comparative Example 1, except that 4.0 parts by mass of the above-mentioned isocyanate-based curing agent was added to 100 parts by mass of acrylic adhesive A.

[0084] <Comparative Example 3> An adhesive sheet was prepared in the same manner as in Comparative Example 1, except that 5.0 parts by mass of the above-mentioned isocyanate-based curing agent was added to 100 parts by mass of acrylic adhesive A.

[0085] Table 1 shows the characteristics of the foaming agents A and B used in the above examples and comparative examples.

[0086] [Table 1]

[0087] [Evaluation of adhesive sheets] <Evaluation test for ease of peeling> Sample pieces were prepared by cutting the adhesive sheets made in each example and comparative example to a size of 2 cm x 7 cm, and the adhesive side of the sample piece was attached to an untreated glass plate or PET plate. For the hot water treatment, the glass plate or PET plate with the attached sample piece was placed in a beaker of 100°C hot water, and the presence or absence of natural peeling was visually checked after 5 minutes. In addition, the glass plate or PET plate with the attached sample piece was placed in a drying oven set to 120°C, and the presence or absence of natural peeling was visually checked after 5 minutes. In both conditions, if the adhesive layer did not peel off naturally, it was judged whether it could be peeled off by hand. If it peeled off naturally, it was judged as ◎ (Excellent); if it did not peel off naturally but could be easily peeled off by hand, it was judged as ○ (Good); if it did not peel off easily but could be peeled off carefully, it was judged as △ (Acceptable); and if it could not be peeled off, or if adhesive components remained on the adherend even if it could be peeled off, it was judged as × (Unacceptable).

[0088] <Measuring Adhesion> After peeling off the release liner from the adhesive sheet and attaching it to the substrate, the adhesive strength was measured 1 minute and 24 hours after attachment according to the method in accordance with JIS Z 0237. Specifically, test pieces of adhesive sheet cut to a width of 25 mm were attached to a glass plate or PET plate (the substrate) and left to stand at 23°C and 50% relative humidity for 1 minute or 24 hours. The force required to peel these test pieces off using a universal material testing machine under conditions of a peel angle of 180° and a peel speed of 300 mm / min was measured as the adhesive strength (N / 25 mm).

[0089] <Measurement of the storage modulus of the adhesive layer> Two adhesive compositions were prepared: one with 5.0 parts by mass of isocyanate-based curing agent added to 100 parts by mass of liquid adhesive A, and another with 8.0 parts by mass of the same curing agent added. Using these adhesive compositions, a substrate-less tape with an adhesive layer 50 μm thick was fabricated. This substrate-less tape was then aged at 40°C for 72 hours. Next, only the adhesive layer was laminated until the total thickness reached 1 mm, and then punched out to a diameter of 8 mm to produce tablets. These tablets were placed between plates of a rheometer (product name: AR2000ex), and the storage modulus G' and loss modulus G'' were measured at a frequency of 1 Hz, relative humidity of 50%, and strain of 0.05%, and tanδ was calculated. Measurements were taken at both 23°C and 80°C. The average values ​​of the storage modulus G' and loss modulus G'' measurements, obtained by adding 5.0 parts of curing agent and adding 8.0 parts of curing agent, were used.

[0090] Furthermore, for adhesive B, a substrate-less tape with a thickness of 50 μm was prepared, and then tablets with a diameter of 8 mm and a thickness of 1 mm were prepared using the method described above. The storage modulus G' and loss modulus G'' were measured for these tablets, and tanδ was calculated. For adhesive C, the storage modulus G' and other parameters were measured using the same method as for adhesives A and B, using an adhesive composition prepared by adding 0.6 parts by mass of epoxy curing agent and 0.6 parts by mass of metal chelate curing agent to 100 parts by mass of adhesive solution.

[0091] [Measurement results] The results of the adhesive strength measurements for each test specimen are shown in Tables 2 to 4. The results of the peelability test for each test specimen are shown in Tables 5 to 9. The measured storage modulus and tanδ of adhesives A to C at 23°C and 80°C are shown in Table 10. In Tables 2 to 4, "PT" means that the adhesive layer partially transferred to the adherend when the adhesive sheet was peeled from the adherend, and "AT" means that the adhesive layer completely transferred to the adherend.

[0092] [Table 2]

[0093] [Table 3]

[0094] [Table 4]

[0095] [Table 5]

[0096] [Table 6]

[0097] [Table 7]

[0098] [Table 8]

[0099] [Table 9]

[0100] [Table 10] From a comparison of Examples 1-3, 4-20, and Comparative Example 1, it was found that even when using the same adhesive, the adhesive strength to the substrate tended to be lower when using epoxy-based curing agents or metal chelate-based curing agents compared to when using isocyanate-based curing agents. In Comparative Example 1, where an isocyanate-based curing agent was used, the adhesive layer could not be separated from the substrate, whereas in the adhesive sheets using epoxy-based curing agents, metal chelate-based curing agents, or a mixture of both curing agents (Examples 24 and 25), the adhesive layer could be separated from both the substrate and the adherend.

[0101] Furthermore, while the conditions under which the adhesive layer could be peeled from the substrate were limited in the adhesive sheets of Examples 1-3 and 21-23 that used metal chelating curing agents, it was confirmed that in many cases, when a predetermined amount of epoxy curing agent was used (for example, Examples 6-20), the adhesive layer and substrate could be peeled off in both boiling water at 100°C and in a dry state at 120°C.

[0102] Furthermore, the results of the peelability evaluation in Examples 9-14 showed that, when the amount of foaming agent added was the same, a greater thickness of the adhesive layer resulted in better peeling between the adhesive layer and the substrate. [Industrial applicability]

[0103] The adhesive sheets disclosed herein can be used for a variety of applications as temporary fixing tapes or labels. [Explanation of symbols]

[0104] 1 Base material 3. Adhesive layer 5. Foaming agent 7. Release Liner 9 Adherent 10 Adhesive Sheets

Claims

1. A sheet-like substrate, An adhesive sheet comprising a foaming agent and an adhesive layer formed on at least one surface of the substrate, The foaming agent is a thermally expandable microcapsule, The adhesive layer contains at least one of a chelating curing agent and an epoxy curing agent. After the adhesive layer is attached to the adherend, a heat treatment is performed so that the entire adhesive layer can be peeled off from the adherend and the substrate. The adhesive sheet wherein the adhesive layer does not contain an isocyanate-based curing agent.

2. The adhesive sheet according to claim 1, wherein the adhesive layer contains an epoxy-based curing agent.

3. The adhesive sheet according to claim 2, wherein the content of the epoxy-based curing agent contained in the adhesive layer is 0.01% by mass or more and 1.0% by mass or less.

4. The adhesive sheet according to claim 1, wherein the adhesive strength to glass 24 hours after application, when the temperature is 23°C, relative humidity is 50%, peeling speed is 300 mm / min, and peeling angle is 180°, is 0.1 N / 25 mm or more and 15.0 N / 25 mm or less.

5. The adhesive sheet according to claim 1, wherein the content of the foaming agent contained in the adhesive layer is 5% by mass or more and 70% by mass or less of the total content of the adhesive layer.

6. The storage modulus of the adhesive layer under the conditions of 23°C, 50% relative humidity, and 1 Hz frequency is 2.0 × 10⁻⁶. ４ Pa or more 1.0×10 ６ It is less than or equal to Pa, The storage modulus of the adhesive layer under the conditions of 80°C, 50% relative humidity, and 1 Hz frequency is 1.0 × 10⁻⁶. ３ Pa or more 5.0×10 ５ The adhesive sheet according to claim 1, wherein the pressure is Pa or less.

7. The adhesive sheet according to claim 1, wherein the adhesive layer contains a curing agent in an amount equal to or greater than half the crosslinking point of the adhesive for forming the adhesive layer.

8. The adhesive sheet according to claim 1, wherein the adhesive layer is formed of a cured product of a solvent-type acrylic adhesive.

9. An adhesive sheet according to any one of claims 1 to 8, to be used as a label.

10. A method for using an adhesive sheet comprising a sheet-like substrate and an adhesive layer formed on at least one surface of the substrate, the adhesive layer containing a foaming agent which is a thermally expandable microcapsule, The adhesive layer contains at least one of a chelating curing agent and an epoxy curing agent, and does not contain an isocyanate curing agent. The process of attaching the adhesive layer of the adhesive sheet to the object to be attached, A method for using an adhesive sheet, comprising the step of heating the adhesive sheet to peel the adhesive layer from the adherend and also peeling it from the substrate.

11. A step of applying a coating liquid to the release surface of a release liner having a release surface, the coating liquid containing a foaming agent in the form of microcapsules, an adhesive, and at least one of a chelating curing agent and an epoxy curing agent, but not containing an isocyanate curing agent, and then drying it at a temperature below the foaming start temperature of the foaming agent to form an adhesive layer, A step of bonding the adhesive layer formed on the coated surface of the release liner to a sheet-like substrate. A method for manufacturing an adhesive sheet, comprising: A method for manufacturing an adhesive sheet, wherein the adhesive sheet is made peelable from the adherend and the substrate by a heat treatment after the adhesive layer is attached to the adherend.

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