Adhesive sheet

Abstract

To provide an adhesive sheet that allows for easier removal from an adherend by heating.SOLUTION: An adhesive sheet 10 includes a sheet-like substrate 5, and an adhesive layer 3 that includes a foamer 13 and is formed on at least one side of the substrate 5. The foamer 13 is a thermally expandable microcapsule. The side of the adhesive layer 3 remote from the substrate 5 is provided with irregularities.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The technology disclosed in this specification relates to an adhesive sheet in which an adherend and an adhesive layer can be peeled off 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 a dicing process or a back grinding process of a semiconductor wafer.

[0003] For example, Patent Document 1 describes an example of an adhesive sheet having a plastic base material, an adhesive layer, and a rubber-like 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 increased, and the recycling of various materials has been promoted worldwide. For example, if a label attached to an adherend can be peeled off by heating, the reuse or recycling of the adherend becomes easy. However, in the adhesive sheet described in Patent Document 1, the ease of peeling from the adherend during heating varies greatly depending on conditions such as the types of the adhesive and the thermally expandable microspheres and the thickness of the adhesive layer. Therefore, the configuration of an adhesive sheet that can be easily peeled off from an adherend regardless of the types of the adhesive and the thermally expandable microspheres is desired.

[0006] The object of the present invention is to provide an adhesive sheet that can be more easily peeled off from an adherend by heating. [Means for solving the problem]

[0007] An example of an adhesive sheet disclosed herein comprises a sheet-like substrate and an adhesive layer containing a foaming agent, formed on at least one surface of the substrate. The foaming agent is a thermally expandable microcapsule, and the surface of the adhesive layer opposite to the substrate has irregularities, so that the adhesive sheet peels off from the adherend upon heating. [Effects of the Invention]

[0008] The adhesive sheets disclosed herein make it easier to remove them from the adherend by heating. [Brief explanation of the drawing]

[0009] [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 is a plan view of the adhesive sheet shown in Figure 1, after the release liner has been peeled off, as seen from the adhesive layer side. [Figure 3] Figure 3(a) is a photograph showing the results of the peelability test of the adhesive sheet prepared in Example 1 on a glass plate, and (b) is a photograph showing the results of the peelability test of the adhesive sheet prepared in Comparative Example 1. [Modes for carrying out the invention]

[0010] Figure 1 is a cross-sectional view showing an adhesive sheet, which is an example of an embodiment disclosed herein. Figure 2 is a plan view of the adhesive sheet shown in Figure 1, with the release liner removed, as seen from the adhesive layer side.

[0011] As shown in Figure 1, the adhesive sheet 10 of this embodiment comprises a sheet-shaped base material 5 and an adhesive layer 3 containing a foaming agent 13, which is formed on at least one surface of the base material 5. A release liner 1 protecting the adhesive layer 3 may be provided on the surface of the adhesive layer 3 opposite to the base material 5. The foaming agent 13 is, for example, a thermally expandable microcapsule that expands when heated above a predetermined temperature.

[0012] The surface of the adhesive layer 3 opposite to the base material 5 has irregularities formed on it. Here, the term "irregularities" as used herein includes cases where only recesses such as grooves are formed when viewed from a certain reference plane, or cases where only protrusions are formed. In the example shown in Figures 1 and 2, a grid-like groove 9 is formed on the lower part of the adhesive layer 3 (the part opposite to the base material 5). That is, multiple protrusions 7 are formed on the surface of the adhesive layer 3 opposite to the base material 5 at regular intervals in the vertical and horizontal directions. The shape of the protrusions 7 is not particularly limited, but as shown in Figures 1 and 2, they may have a frustoconical shape with a quadrilateral horizontal cross-section and a trapezoidal cross-section in the thickness direction.

[0013] In order to form grooves 9 in the adhesive layer 3, a grid-like pattern of protrusions 11 is provided on the release surface of the release liner 1 in the example shown in Figure 1. Such protrusions 11 can be easily formed by known methods such as embossing or printing using UV ink. The adhesive surface of the adhesive layer 3 may also be formed using methods other than the release liner 1.

[0014] The width of the grooves 9 extending in the vertical and horizontal directions is not particularly limited, but may be, for example, 50 μm to 800 μm, or approximately 100 μm to 500 μm. The length of the base portion of the protrusion 7 shown in Figure 2 in the vertical and horizontal directions may be, for example, 100 μm to 800 μm, or 150 μm to 500 μm. The depth of the grooves 9 is not particularly limited, but may be, for example, 10 μm to 100 μm, or 15 μm to 60 μm.

[0015] Although not shown, the horizontal cross-section of the convex portion 7 may be circular, triangular, pentagonal, hexagonal, etc. other than a quadrilateral. Further, in the example shown in FIG. 1, each convex portion 7 is a part of the integrally formed adhesive layer 3, but the adhesive layer 3 may not be integrally formed, and may be composed of a plurality of convex portions 7 dispersed at a predetermined interval from each other.

[0016] With the above configuration, the contact area of the adhesive layer 3 with the adherend is smaller than the planar area of the adhesive layer 3. The contact area of the adhesive layer 3 with the adherend is preferably, for example, 20% or more and 60% or less of the entire planar area, and more preferably 30% or more and 50% or less.

[0017] A plurality of grooves communicating from one end to the other end may be provided on the surface of the adhesive layer 3 opposite to the base material 5. In this case, it is possible to prevent the formation of air pockets when the adhesive sheet 10 is attached to the adherend, and it becomes easier to maintain a beautiful attachment state.

[0018] In the adhesive sheet 10 of the present embodiment, after the release liner 1 is peeled off and the adhesive layer 3 is attached to the adherend, the foaming agent 13 expands by heating. For this reason, the thickness of the adhesive layer 3 increases and the planar size also increases, and as a result, it becomes possible to peel off from the adherend. Here, "peelable" includes both the case of natural peeling by heat treatment and the case of easily peeling by simply lightly touching the adhesive sheet 10 without natural peeling.

[0019] In the adhesive sheet 10 of the present embodiment, since irregularities are formed in the adhesive layer 3, the foaming agent 13 can be surely foamed by heating as compared with the case where the surface of the adhesive layer 3 is flat. As a result, the adhesive sheet 10 can be more surely peeled off from the adherend. Therefore, according to the adhesive sheet 10 of the present embodiment, it can be easily peeled off by heating regardless of the type of the adhesive or the foaming agent, the thickness of the adhesive layer, etc.

[0020] The adherent body 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 laminate such as a semiconductor wafer or a ceramic green sheet, or the like.

[0021] The base material 5 may be made of paper or a resin film. The paper for the base material 5 may be, for example, high-quality paper, art paper, coated paper, gloss paper, or cast-coated paper. As the resin material for the base material 5, a polyester resin such as PET, a polyolefin resin such as polyethylene (PE) or polypropylene (PP), or polyvinyl chloride (PVC) may be used. The base material 5 may be formed of synthetic paper. When considering the environment, part or all of the resin component contained in the base material 5 can be a biomass resin or a biodegradable resin derived from organisms.

[0022] A known easy-adhesion layer, an antistatic layer, or the like may be provided on one or both surfaces of the base material 5. By forming an easy-adhesion layer on the adhesive layer 3 side of the base material 5, the adhesion force between the base material 5 and the adhesive layer 3 can be strengthened. Also, when the adhesive sheet is used as a label, a printing layer can be formed on the easy-adhesion layer. When not forming the printing layer or when it is desired to reduce the adhesion force with the adhesive layer 3, it is not necessary to provide an easy-adhesion layer on the surface of the base material 5 on the adhesive layer 3 side.

[0023] The thickness of the base material 5 is not particularly limited, and may be, for example, 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 5 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 5 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. The adhesive used for forming the adhesive layer 3 is not particularly limited, and may be one selected from rubber-based adhesives, acrylic adhesives, acrylic urethane adhesives, silicone adhesives, urethane adhesives, and polyester adhesives, or a mixture of two or more thereof.

[0025] When using an acrylic adhesive, it is preferable to use an isocyanate-based curing agent, an epoxy-based curing agent, a chelating curing agent, or a mixture of these curing agents as the curing agent. 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 3.0% by mass or less. 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 5 and the adhesive layer 3 may become too strong. If the amount of curing agent added exceeds 3.0 parts by mass per 100 parts by mass of the resin solids content of the adhesive, the adhesive strength to the adherend may become too weak.

[0026] 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.

[0027] In addition to the foaming agent 13, the adhesive layer 3 may contain various known additives, such as tackifiers, plasticizers, antioxidants, heat stabilizers, fillers, coupling agents, and antistatic agents, to the extent that the objectives of the present invention are not impaired.

[0028] 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 substrate more easily after the foaming agent 13 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 substrate even more easily.

[0029] For the adhesive sheet 10, when the temperature is 23°C, relative humidity is 50%, peeling speed is 300 mm / min, and peeling angle is 180°, and the adhesive strength to glass at 1 minute after application is A (N / 25 mm), and the adhesive strength to glass at 24 hours is B (N / 25 mm), the value of B / A may be between 1.0 and 1.4. Having a B / A value within this range allows for achieving an adhesive strength close to that at 24 hours in a short time after application.

[0030] 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, but will be easily peeled off the substrate when heated.

[0031] The adhesive strength of the adhesive sheet 10 to the stainless steel BA plate may be, for example, 0.1 N / 25 mm to 15.0 N / 25 mm or less, or 0.4 N / 25 mm to 10.0 N / 25 mm or less, 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°.

[0032] The storage modulus of the adhesive layer 3 is not particularly limited, but for example, under conditions of 23°C, 50% relative humidity, and a frequency of 1 Hz, it is 1.0 × 10⁻⁶. 3 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 5.0×10 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. Also, if the storage modulus is too high, the adhesive layer 3 will be difficult to peel off from the adherend when heated under dry conditions. Note that even with the presence of the foaming agent 13, the storage modulus of the adhesive layer 3 at 23°C is close to the value when the foaming agent 13 is not present.

[0033] The thickness of the adhesive layer 3 varies depending on the type of adhesive used, but 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 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 can be easily reduced. Also, if the content of the foaming agent 13 is the same, a thicker adhesive layer 3 expands more after heating and is easier to peel from the adherend, but from the viewpoint of reducing manufacturing costs, a thinner adhesive layer 3 is preferable.

[0034] The foaming agent 13 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 materials include vinylidene chloride-acrylonitrile copolymer, polyvinyl alcohol, polyvinyl butyral, polymethyl methacrylate, polyacrylonitrile, polyvinylidene chloride, and polysulfone. Microcapsules can be manufactured by known methods, such as coacervation or interfacial polymerization.

[0035] The foaming start temperature of the foaming agent 13 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 5 or adherend. For example, the foaming start temperature of the foaming agent 13 may be 50°C or higher and 100°C or lower. A foaming start temperature of 50°C or higher can suppress unintended peeling of the adhesive sheet 10 in summer, etc. A foaming start temperature of 100°C or lower allows the adhesive layer 3 to be peeled from the substrate 5 and adherend 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.

[0036] The temperature at which the foaming agent 13 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.

[0037] A commercially available product may be used as the foaming agent 13. 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.

[0038] The average particle size of the foaming agent 13 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 5 and the adherend. Depending on the thickness of the adhesive layer 3, if the average particle size of the foaming agent 13 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. The average particle size of the foaming agent 13 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.

[0039] Furthermore, if the protrusion 7 is a truncated square pyramid, it is preferable that the average particle size of the foaming agent 13 is less than the length of one side of the protrusion 7. If the particle size of the foaming agent 13 is larger than the size of the protrusion 7, the foaming agent 13 may not be able to penetrate into the protrusion 7, which may make it difficult for the foaming agent 13 to peel off due to thermal expansion.

[0040] The volume change rate when the foaming agent 13 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.

[0041] The content of the foaming agent 13 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 13 is too low, the adhesive layer 3 will be difficult to peel off from the substrate 5 and the adherend even when heated, and if the content of the foaming agent 13 is too high, the adhesive strength to the adherend will likely be insufficient before heating.

[0042] By appropriately adjusting the average particle size, content, and volume change rate of the foaming agent 13 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 the adherend. 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.

[0043] (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.

[0044] Furthermore, Patent Document 1 describes how providing a rubber-elastic intermediate layer between the adhesive layer 3 and the base material 5 makes it easier to peel the adhesive sheet from the adherend after heating. In the adhesive sheet 10 of this embodiment, an intermediate layer may also be provided between the adhesive layer 3 and the base material 5.

[0045] [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 13 to the adhesive and mixing them. Next, the coating solution is applied to the release surface of the release liner 1 made of paper or resin film using a comma-type coater or the like to achieve a desired thickness after drying, and the adhesive layer 3 is formed by drying at a low temperature below the foaming start temperature of the foaming agent 13. Then, the coated surface of the release liner 1 is bonded to the substrate 5 to prepare the adhesive sheet 10, and then aging is performed, for example, at 40°C for about 72 hours.

[0046] 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 5 using a known printing press before forming the adhesive layer 3. This printed layer may have a recycling information display area that indicates the conditions for peeling from the adhesive layer 3. This allows consumers and processing companies to properly recycle the adherend.

[0047] Alternatively, instead of this method, the above-mentioned coating liquid may be applied to the release surface of the release liner 1, the second release liner may be bonded to the coated surface of the release liner 1, and then the above-mentioned aging may be performed to create a so-called substrate-less adhesive layer 3. In this case, the adhesive sheet 10 can be produced by peeling the second release liner off the previously formed adhesive layer 3 and then bonding it to the substrate 5.

[0048] [How to remove adhesive sheets] To remove the adhesive sheet 10 of this embodiment from an adherend after it has been attached to the adherend, the adhesive sheet 10 should be heated to a temperature at which the adhesive layer 3 expands sufficiently. For example, if the expansion start temperature of the foaming agent 13 is 50°C or higher and 100°C or lower, the adhesive layer 3 can be removed from the adherend 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 disassembled under all of the above conditions; 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, the heated adhesive layer 3 does not need to be able to peel from all types of adherends; it is sufficient if it can peel from at least one type of adherend. Considering actual use, it is preferable that it can be peeled from at least one of PET, glass, and metal.

[0049] If the adherend is immersable, such as a glass bottle or PET bottle, or if it is altered by temperatures exceeding 100°C, hot water treatment may be performed. If the adherend can withstand heating, heating may be performed in a dry state.

[0050] The adhesive sheet 10 of this embodiment can be easily separated from the adherend, for example, even in a household, so the adherend can be easily separated and recycled. Furthermore, if the specific gravity of the base material 5 is less than 1, when used as a container label for PET bottles, the adhesive sheet 10 that has been peeled off by hot water treatment can be easily separated from the PET bottle material (specific gravity approximately 1.38) in water by utilizing the difference in specific gravity, making it easier to recover.

[0051] [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]

[0052] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0053] [Making adhesive sheets] <Example 1> A coating solution was prepared by adding 2.5 parts by mass of a commercially available liquid isocyanate-based curing agent (containing 45 wt% curing agent component) to 100 parts by mass of a commercially available liquid solvent-type acrylic adhesive A (50 wt% resin solids content). Foaming agent A (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 mixed. Next, the above coating solution was applied to the release surface of a release liner using a known comma-type coater so that the thickness after drying was 50 μm, and the adhesive layer was formed by drying at 80°C for 3 minutes. After that, an adhesive sheet was prepared by laminating it to one side of a commercially available PET film (substrate). Release paper "MX2" manufactured by Nichiei Shinka Co., Ltd. was used as the release liner. This release liner had a grid-like convex structure formed on its release surface, with a width of 170 μm in the MD direction and 190 μm in the TD direction. The upper end of the opening in the recess was a square with sides of 280 μm. The depth of the opening was 33 μm.

[0054] As the base material, a PET film manufactured by Toray Industries, Inc. with a thickness of 50 μm (product name "Lumirror® S28"; specific gravity approximately 1.4) was used. Next, the adhesive sheet was aged under conditions of 40°C for 72 hours.

[0055] <Comparative Example 1> An adhesive sheet was prepared in the same manner as in Example 1, except that a commercially available release liner (E7002, manufactured by Toyobo Co., Ltd.) having a flat release surface was used as the release liner.

[0056] Table 1 shows information on the foaming agents used.

[0057] [Table 1]

[0058] [Evaluation of adhesive sheets] <Evaluation test of ease of peeling> Sample pieces were prepared by cutting the adhesive sheets made in Example 1 and Comparative Example 1 to a size of 80 mm x 80 mm. The adhesive side of the sample piece was then attached to an untreated glass plate or BA (stainless steel) plate. After 24 hours, the glass plate or BA 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 15 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 ○ (good); if it did not peel off naturally but could be easily peeled off by hand, 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).

[0059] <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 the substrate, which was a glass plate or BA plate, 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).

[0060] <Measurement of the storage modulus of the adhesive layer> An adhesive composition was prepared by adding 2.5 parts of an isocyanate-based curing agent to 100 parts by mass of liquid adhesive A. A substrate-less tape with an adhesive layer 50 μm thick was fabricated using this adhesive composition. Next, this substrate-less tape was aged at 40°C for 72 hours. Then, only the adhesive layer was laminated until the total thickness reached 1 mm, and then punched out to a size of 8 mm in diameter 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 under conditions of frequency 1 Hz, relative humidity 50%, and strain 0.05%, and tanδ was calculated. Measurements were taken at both 23°C and 80°C.

[0061] <Method for calculating the contact area ratio> The release liner was peeled off the adhesive sheet and bonded to a transparent PET film, then pressed down by passing a 2kg rubber roller back and forth twice. In this state, an arbitrary area of ​​the adhesive sheet (a square area of ​​1cm in the flow direction x 1cm in the width direction) was photographed using a microscope, and the contact area ratio (i.e., contact area percentage) was calculated by "100 × (total contact area between the PET film and the adhesive layer) / (total area of ​​the area)".

[0062] [Measurement results] Table 2 shows the measurement results of the storage modulus of the adhesive layer. Table 3 shows the measurement results of the adhesive strength of each test piece. Table 4 shows the results of the peelability test of each test piece. Figures 3(a) and (b) show the results of the peelability test on glass plates. Figure 3(a) shows the results of the adhesive sheet made in Example 1, and Figure 3(b) shows the results of the adhesive sheet made in Comparative Example 1.

[0063] [Table 2]

[0064] [Table 3]

[0065] [Table 4] As shown in Table 4, the adhesive sheet of Example 1, which used a release liner with an uneven release surface, peeled off naturally upon heating, whereas the adhesive sheet of Comparative Example 1, which used a release liner with a flat release surface, could not be peeled off upon heating. Although there was no significant difference between the adhesive sheet of Example 1 and the adhesive sheet of Comparative Example 1 in the adhesive strength measurement results shown in Table 3, only the adhesive sheet of Example 1 peeled off naturally when heated. This confirms that forming an uneven surface on the adhesive layer facilitates natural peeling upon heating.

[0066] Furthermore, the contact area ratio of the adhesive sheet in Example 1 was 37%, while the contact area ratio of the adhesive sheet in Comparative Example 1 was 100%. [Industrial applicability]

[0067] The adhesive sheets disclosed herein can be used for a variety of applications as temporary fixing tapes or labels. [Explanation of symbols]

[0068] 1. Release Liner 3. Adhesive layer 5. Foaming agent 7. Convex part 9 grooves 10 Adhesive Sheets 11 protrusion 13 Foaming agent

Claims

1. A sheet-like base material, A foaming agent is included, and an adhesive layer is formed on at least one surface of the substrate, An adhesive sheet comprising a release liner having a release surface, provided on the side of the adhesive layer opposite to the substrate, wherein The foaming agent is a thermally expandable microcapsule, A groove is formed on the side of the adhesive layer opposite to the substrate. The release surface of the release liner is provided with protrusions for forming the grooves in the adhesive layer. The depth of the groove in the adhesive layer is 15 μm or more and 60 μm or less. An adhesive sheet that peels off from the adherend when heated.

2. The adhesive sheet according to claim 1, wherein a plurality of grooves communicating from one end to the other are provided on the side of the adhesive layer opposite to the substrate.

3. The adhesive sheet according to claim 1, wherein the contact area of ​​the adhesive layer with respect to the adherend is 20% or more and 60% or less of the total planar area of ​​the adhesive layer.

4. The storage modulus of the adhesive layer at 23°C and 1 Hz is 1.0 × 10⁻⁶. ３ Pa or more 1.0×10 ６ The adhesive sheet according to claim 1, wherein the pressure is Pa or less.

5. 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.

6. The adhesive sheet according to claim 5, wherein, when the temperature is 23°C, relative humidity is 50%, peeling speed is 300 mm / min, and peeling angle is 180°, the adhesive strength to glass at 1 minute after application is A (N / 25 mm), and the adhesive strength to glass at 24 hours is B (N / 25 mm), the value of B / A is 1.0 or more and 1.4 or less.

7. The adhesive sheet according to any one of claims 1 to 6, 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.

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