Pressure-sensitive adhesive

Abstract

Provided is a pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer, in which the pressure-sensitive adhesive layer can be formed without using a special material, the pressure-sensitive adhesive sheet can stably maintain a stuck state with a high pressure-sensitive adhesive force in a normal state after being stuck to an object, and the pressure-sensitive adhesive sheet can be easily peeled off without leaving the pressure-sensitive adhesive layer on the surface of the object because the pressure-sensitive adhesive force decreases without applying a strong pressure when the pressure-sensitive adhesive sheet is peeled off from the object at any intended timing.SOLUTION: A pressure-sensitive adhesive sheet 1 comprising a substrate 11 and a pressure-sensitive adhesive layer 12 provided on the substrate 11, wherein the pressure-sensitive adhesive layer 12 contains microcapsules 13 having a median size of 7 μm or more, the microcapsules 13 are unevenly distributed in a region of the pressure-sensitive adhesive layer 12 on the side opposite to the substrate 11 side, the thickness T12 of the pressure-sensitive adhesive layer 12 is 1.2 times or more the median size of the microcapsules 13, and the substrate 11 is paper or synthesized paper.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet. [Background technology]

[0002] Adhesive sheets with an adhesive layer are widely used as adhesive labels, adhesive tapes, etc. Some adhesive sheets maintain a stable adherence state with high adhesive strength to an object to which they are attached under normal conditions after attachment, but when they are peeled from the object, it is sometimes desired that the adhesive strength be reduced so that the adhesive layer can be easily peeled off without remaining on the object.

[0003] As an adhesive sheet that can be easily peeled off from an object, a pressure-sensitive adhesive sheet with an adhesive layer containing an acrylic adhesive and microcapsules, the microcapsules containing a crosslinking agent and a softener for the acrylic adhesive, and which is broken by pressure, has been disclosed (see Patent Document 1). After this adhesive sheet has been applied to an object, when it is to be peeled off from the object, pressure is applied to the adhesive layer to break the microcapsules, and the crosslinking agent released from the microcapsules spreads throughout the adhesive layer together with the softener, crosslinking the acrylic adhesive, gradually losing the adhesiveness of the adhesive layer and improving cohesion, making it easier to peel the adhesive sheet off the object.

[0004] Another PSA sheet that can be easily peeled from an object is disclosed in Patent Document 2, which discloses a double-sided PSA sheet having adhesive layers on both sides of an easily dismantled layer, the easily dismantled layer containing a binder and thermally expandable microcapsules, facilitating peeling of the object from another object. After both sides of this double-sided PSA sheet are attached to the object, when the double-sided PSA sheet is peeled from the object, the easily dismantled layer is heated to expand the thermally expandable microcapsules. This breaks the easily dismantled layer, allowing the adhesive layer to be easily peeled from the side of the object that is not in direct contact with it.

[0005] An adhesive containing a release agent and a foaming agent has been disclosed as an adhesive that can be easily peeled off from an object (see Patent Document 3). After this adhesive is applied to an object, when the adhesive is to be peeled off from the object, energy is irradiated onto the adhesive, causing the release agent to migrate toward the object and the foaming agent to burst. This causes the object to float off the adhesive, allowing the adhesive to be easily peeled off from the object.

[0006] As an adhesive mechanism that allows easy peeling when peeling from an object, an adhesive mechanism has been disclosed in which a primer layer is provided between a substrate and a pressure-sensitive adhesive layer, an anthracene dimer is incorporated into the primer layer, and the chemical bond in the anthracene dimer is broken by light or heat (see Patent Document 4). In this adhesive mechanism, the substrate and the pressure-sensitive adhesive layer are usually bonded to each other by a chemical bond via the anthracene dimer, but by irradiating the primer layer with light or applying heat, the chemical bond in the anthracene dimer is broken and the pressure-sensitive adhesive layer can be easily peeled from the substrate. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 7-34051 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-119438 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-286464 [Patent Document 4] Japanese Patent Application Publication No. 2022-50299 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the adhesive sheet disclosed in Patent Document 1, the microcapsules are covered with a resilient acrylic adhesive in the adhesive layer. Therefore, unless strong pressure is applied to the adhesive layer, the microcapsules cannot be sufficiently destroyed, making it difficult to peel the adhesive sheet from the target object. Patent Document 1 describes that the microcapsules can be destroyed by applying low pressure, but this has actually been found to be incorrect. Furthermore, when strong pressure is applied to the adhesive layer, the adhesion between the adhesive layer in the adhesive sheet and the target object increases, increasing the peel strength, which at least partially offsets the effect of reduced peel strength caused by the destruction of the microcapsules, making it difficult to peel the adhesive sheet from the target object.

[0009] The double-sided PSA sheet disclosed in Patent Document 2 has the problem that although the objects on both sides can be separated, the PSA layer remains on the surface of the object. Objects with the PSA layer remaining in this way are not suitable for reuse, and their uses are limited. Similarly, the adhesive disclosed in Patent Document 3 also has the problem of the adhesive remaining on the surface of the object.

[0010] The adhesive mechanism disclosed in Patent Document 4 requires a primer layer in addition to the adhesive layer, and an anthracene dimer is required, which is a special material and is very expensive, which is a problem.

[0011] The present invention addresses the problem of providing an adhesive sheet having an adhesive layer, which can be formed without using any special material, which can maintain a stable adhered state with high adhesive strength in the normal state after being attached to an object, and which, when peeled from the object at any desired timing, has low adhesive strength without the application of strong pressure, and can be easily peeled off without leaving any adhesive layer on the surface of the object. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention employs the following configuration. [1] A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer provided on the substrate, An adhesive sheet, wherein the adhesive layer contains microcapsules having a median diameter of 7 μm or more, the microcapsules are unevenly distributed in a region of the adhesive layer opposite the substrate, the thickness of the adhesive layer is 1.2 times or more the median diameter of the microcapsules, and the substrate is paper or synthetic paper. [2] The adhesive sheet according to [1], wherein, when the adhesive surface of the adhesive layer opposite the substrate side is viewed in plan, the ratio of the surface area of ​​the microcapsules exposed on the adhesive surface to the area of ​​the adhesive surface is 50 to 90%. [Effects of the Invention]

[0013] According to the present invention, there is provided an adhesive sheet having an adhesive layer, which can be constructed without using special materials, which can maintain a stable adhered state with high adhesive strength in the normal state after being attached to an object, and which, when peeled from the object at any desired time, has a low adhesive strength without the application of strong pressure, and can be easily peeled off without leaving any adhesive layer remaining on the surface of the object. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a pressure-sensitive adhesive sheet according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view for schematically illustrating an example of a method of using a pressure-sensitive adhesive sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] ◇Adhesive sheet An adhesive sheet according to one embodiment of the present invention comprises a substrate and an adhesive layer provided on the substrate, wherein the adhesive layer contains microcapsules having a median diameter of 7 μm or more, the microcapsules being unevenly distributed in an area of ​​the adhesive layer opposite the substrate, the thickness of the adhesive layer being 1.2 times or more the median diameter of the microcapsules, and the substrate is paper or synthetic paper. The adhesive sheet of this embodiment has such a configuration that the adhesive layer can be formed without using special materials, and in the normal state after being attached to the object, it can maintain a stable attached state with high adhesive strength, and when it is time to peel it off from the object at any desired time, the adhesive strength decreases without the need for strong pressure, and it can be easily peeled off without leaving any adhesive layer remaining on the surface of the object.

[0016] The degree of adhesive strength of the adhesive sheet to the object under normal conditions after the adhesive sheet of this embodiment has been attached to the object can be determined, for example, using as an indicator the adhesive strength measured by the method described below (sometimes referred to in this specification as "normal adhesive strength"). That is, a slice of the adhesive sheet measuring 25 mm x 100 mm was prepared, and the entire exposed surface (adhesion surface) of the adhesive layer in the slice was placed on the exposed surface of a polyethylene terephthalate (PET) film fixed to a hard support to prepare a laminate. The laminate was placed on the horizontal surface with the hard support in contact with the horizontal surface and the exposed surface of the substrate in the slice facing upward. A roll having a mass of 2 kg was then pressed against the exposed surface of the substrate in the slice over the entire longitudinal area of ​​the slice. The slice is rolled back and forth to apply pressure, and the slice and PET film are bonded together to prepare a test piece. Immediately after preparation, the test piece is left to stand at a temperature of 23°C and a relative humidity of 50% (50% RH). Under these conditions, the slice is peeled from the PET film at a peel rate of 300 mm / min so that the angle between the peeled surfaces of the test piece is 180° (180° peel). The peel force measured at this time is used as the normal adhesive force of the adhesive sheet. The hard support is preferably made of metal, and more preferably a metal plate. The thickness of the PET film is preferably 80 to 120 μm. The test piece immediately after preparation is preferably left standing under conditions of a temperature of 23°C and 50% RH for (12) hours or more.

[0017] In the pressure-sensitive adhesive sheet of this embodiment, the normal adhesive strength is preferably 4.9 N / 25 mm or more, and may be, for example, either 5.8 N / 25 mm or more or 6.7 N / 25 mm or more. On the other hand, a pressure-sensitive adhesive sheet having a normal adhesive strength of 10 N / 25 mm or less can be more easily realized.

[0018] After the adhesive sheet of this embodiment is attached to an object, pressure is applied to the adhesive sheet at any desired timing, and the adhesive sheet is then peeled off from the object. The degree of adhesive force of the adhesive sheet to the object can be determined, for example, using as an indicator the adhesive force measured by the method described below (sometimes referred to in this specification as "adhesive force at disassembly"). That is, a test piece identical to that used when measuring the normal adhesive strength described above is prepared, and after allowing this test piece to stand as in the case of measuring the normal adhesive strength, the test piece after standing is used under these conditions (temperature 23°C, 50% RH), and a metal roll is rolled over the exposed surface of the substrate in the section over the entire longitudinal area of ​​the section, thereby applying a pressure of 10 MPa to the section from the substrate side to the PET film side of the section, and immediately after applying pressure, the section is peeled from the PET film at a peel speed of 300 mm / min so that the angle between the peel surfaces of the pressurized test piece is 180° (performed a 180° peel), and the peel force measured at this time is used as the adhesive strength of the pressure-sensitive adhesive sheet when dismantled.

[0019] In the pressure-sensitive adhesive sheet of this embodiment, the adhesive strength at the time of disassembly is preferably 2 N / 25 mm or less, and may be, for example, either 1 N / 25 mm or less or 0.7 N / 25 mm or less. On the other hand, a pressure-sensitive adhesive sheet having an adhesive strength of 0.1 N / 25 mm or more when disassembled can be more easily realized.

[0020] The overall configuration of the pressure-sensitive adhesive sheet of this embodiment will be described below. FIG. 1 is a cross-sectional view schematically showing an example of the pressure-sensitive adhesive sheet of the present embodiment. In addition, the drawings used in the following explanation may show enlarged essential parts for the sake of convenience in order to make the features of the present invention easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality.

[0021] The adhesive sheet 1 shown here is configured to include a substrate 11 and an adhesive layer 12 provided on the substrate 11. More specifically, in the pressure-sensitive adhesive sheet 1, one surface 11a of the substrate 11 (the surface on the pressure-sensitive adhesive layer 12 side) and one surface 12b of the pressure-sensitive adhesive layer 12 (the surface on the substrate 11 side) are in direct contact with each other. The other surface 11b of the substrate 11 (the surface opposite to the pressure-sensitive adhesive layer 12 side) is an exposed surface. The adhesive sheet 1 further includes a release paper 9 provided on the other surface 12a of the adhesive layer 12 (the surface opposite to the substrate 11 side).

[0022] The adhesive layer 12 contains microcapsules 13 with a median diameter of 7 μm or more, and the microcapsules 13 are concentrated in the area opposite the substrate 11 side of the adhesive layer 12 (the other surface 12a side of the adhesive layer 12).

[0023] In the adhesive sheet 1, the thickness T of the adhesive layer 12 12 is 1.2 times or more the median diameter of the microcapsules 13.

[0024] The substrate 11 is paper or synthetic paper.

[0025] The release paper 9 is an optional component of the adhesive sheet 1, and the adhesive sheet 1 does not necessarily have to include the release paper 9.

[0026] When using the adhesive sheet 1, the release paper 9 is removed, and then the other surface 12a of the adhesive layer 12, which is thereby exposed, is attached to an object. In other words, the other surface 12a of the adhesive layer 12 is the surface that is attached to the object.

[0027] The adhesive sheet of this embodiment is not limited to the adhesive sheet 1 shown in Figure 1, and some of the configuration may be changed, deleted, or added to the one shown in Figure 1 as long as the effects of the present invention are not impaired. For example, the pressure-sensitive adhesive sheet 1 shown in Fig. 1 includes a substrate 11, a pressure-sensitive adhesive layer 12, and a release paper 9, but the pressure-sensitive adhesive sheet of the present embodiment may or may not include other layers that do not fall into any of these categories. The type and location of the other layers can be selected arbitrarily depending on the purpose and are not particularly limited. However, in the adhesive sheet of this embodiment, it is preferable that the substrate and the adhesive layer are provided in direct contact with each other, and it is preferable that no other layers other than the release paper are provided on the surface of the adhesive layer opposite the substrate side. Next, each component of the pressure-sensitive adhesive sheet of this embodiment will be described in detail.

[0028] <<Adhesive layer>> The adhesive layer contains an adhesive and the microcapsules, and is a layer that is attached to an object when the adhesive sheet is attached to the object. The adhesive layer may or may not contain other components that do not fall into the category of either an adhesive or the microcapsules.

[0029] The adhesive layer may contain only one type of adhesive, the microcapsules, and the other components, or two or more types of adhesive, and if two or more types are contained, the combination and ratio thereof can be selected arbitrarily.

[0030] The adhesive layer may consist of one layer (single layer), or may consist of two or more layers. When it consists of multiple layers, these multiple layers may be the same or different from each other, and the combination of these multiple layers is not particularly limited.

[0031] In this specification, not limited to the case of pressure-sensitive adhesive layers, "multiple layers may be the same or different from one another" means "all layers may be the same, all layers may be different, or only some layers may be the same," and further, "multiple layers are different from one another" means "at least one of the constituent materials and thicknesses of each layer is different from one another."

[0032] The adhesive layer can be formed, for example, using an adhesive composition containing the components for constituting the adhesive layer (for example, the adhesive, the microcapsules, and optionally the other components, and optionally a solvent). The method for forming the pressure-sensitive adhesive layer and the method for producing the pressure-sensitive adhesive sheet will be described in detail later.

[0033] The median diameter of the microcapsules contained in the adhesive layer is 7 μm or more. As the microcapsules have a particle diameter equal to or greater than a specific value, when the adhesive sheet of this embodiment is peeled off from an object at any desired time, the adhesive sheet can be easily peeled off without applying strong pressure and without leaving any adhesive layer on the surface of the object.

[0034] In order to enhance the above-mentioned effects, the median diameter of the microcapsules is preferably 9 μm or more, and may be, for example, any one of 11 μm or more, 14 μm or more, and 17 μm or more. On the other hand, in order to maintain a stable adhered state with high adhesive strength under normal conditions after the adhesive sheet has been applied to an object, it is preferable that the median diameter of the microcapsules is 30 μm or less.

[0035] In this specification, unless otherwise specified, the term "median diameter" refers to the median diameter of the volume particle size distribution of particles measured using a particle size distribution measuring device. On the other hand, since acrylic pressure-sensitive adhesives are transparent, when the pressure-sensitive adhesive layer contains an acrylic pressure-sensitive adhesive as a pressure-sensitive adhesive, the microcapsules inside the pressure-sensitive adhesive layer can be observed using an optical microscope. Therefore, it is also possible to count the size and number of microcapsules from the image data of the pressure-sensitive adhesive layer obtained using the optical microscope by means of image analysis or the like, and calculate the median diameter of the microcapsules from the results.

[0036] In the pressure-sensitive adhesive sheet, the thickness of the pressure-sensitive adhesive layer is at least 1.2 times the median diameter of the microcapsules. Because the thickness of the pressure-sensitive adhesive layer is relatively large compared to the median diameter (particle diameter) of the microcapsules, when the pressure-sensitive adhesive sheet is applied to an object, the pressure-sensitive adhesive can be in sufficient contact with the object, and the pressure-sensitive adhesive sheet can then be stably maintained in its applied state with high adhesive strength under normal conditions.

[0037] In order to enhance the above-mentioned effect, the thickness of the adhesive layer is more preferably 1.4 times or more the median diameter of the microcapsules, and may be, for example, 1.8 times or more, 2.5 times or more, or 3.2 times or more. On the other hand, there is no particular upper limit to the multiple of the thickness of the pressure-sensitive adhesive layer relative to the median diameter of the microcapsules. For example, in order to avoid the pressure-sensitive adhesive layer from becoming excessively thick, the thickness of the pressure-sensitive adhesive layer is preferably 10 times or less the median diameter of the microcapsules.

[0038] The thickness of the pressure-sensitive adhesive layer is not particularly limited as long as it satisfies the condition of the multiple of the thickness of the pressure-sensitive adhesive layer relative to the median diameter of the microcapsules described above, but is preferably 10 to 70 μm, and may be, for example, any of 10 to 41 μm and 39 to 70 μm, or any of 10 to 27 μm, 25 to 41 μm, 39 to 57 μm, and 55 to 70 μm. When the thickness of the pressure-sensitive adhesive layer is at least the lower limit, the structure of the pressure-sensitive adhesive layer can be more stably maintained. When the thickness of the pressure-sensitive adhesive layer is at most the upper limit, excessive thickness of the pressure-sensitive adhesive layer can be avoided, and, for example, the pressure-sensitive adhesive sheet can be made thinner. Here, "thickness of the adhesive layer" means the thickness of the entire adhesive layer, and for example, the thickness of an adhesive layer consisting of multiple layers means the total thickness of all layers that make up the adhesive layer.

[0039] The thickness of the pressure-sensitive adhesive layer can be measured, for example, using a paper thickness measuring device. In this case, as will be described later in the Examples, a plurality of measurement points are arbitrarily selected on the surface of the pressure-sensitive adhesive layer so as not to cause bias in these positions, the thickness of the pressure-sensitive adhesive layer is measured at these measurement points, and the maximum and minimum values ​​of these measurements are excluded to calculate an average value of two or more measurements, and this average value can be used as the thickness of the pressure-sensitive adhesive layer. In this way, the thickness of the pressure-sensitive adhesive layer can be determined with higher accuracy. The measurement points are four or more (for example, 4 to 6). The thickness of the pressure-sensitive adhesive layer can also be measured in the form of a laminate in which the pressure-sensitive adhesive layer is laminated with some kind of film or sheet. In this case, the thickness of the laminate is determined using the method described above, and the thickness of the film or sheet before laminating the pressure-sensitive adhesive layer is also determined using the method described above. The thickness of the film or sheet is then subtracted from the thickness of the laminate (calculating [thickness of the laminate] - [thickness of the film or sheet]), thereby determining the thickness of the pressure-sensitive adhesive layer with higher accuracy. In this case, the film or sheet may be, for example, a substrate or release paper constituting the pressure-sensitive adhesive sheet.

[0040] In the pressure-sensitive adhesive layer, the microcapsules are unevenly distributed in the region opposite the substrate side, and the amount of microcapsules in the region opposite the substrate side is significantly greater than the amount of microcapsules in the region on the substrate side. Microcapsules may be present in the region of the pressure-sensitive adhesive layer on the substrate side, but the smaller the amount of microcapsules, the better, and it is more preferable that no microcapsules are present.

[0041] More specifically, it is preferable that the amount of microcapsules is greater in a region located at a distance of at least 1 / 5 of the thickness of the adhesive layer from the surface of the adhesive layer opposite the substrate side (in other words, the surface that is attached to the object; for example, in the adhesive sheet 1 shown in Figure 1, the other surface 12a of the adhesive layer 12) in the thickness direction of the adhesive layer than in other regions, and the amount of microcapsules may also be greater in a region located at a distance of 1 / 2 of the thickness of the adhesive layer in the thickness direction of the adhesive layer than in other regions. However, these are just examples of the manner in which the microcapsules may be unevenly distributed in the pressure-sensitive adhesive layer, and the uneven distribution of the microcapsules is not limited to these.

[0042] For example, in the region of the adhesive layer opposite the substrate side, the amount of microcapsules in the unevenly distributed region, which can be determined to have a larger amount of microcapsules than in other regions of the adhesive layer, is preferably 5 to 25% by mass relative to the total amount of the adhesive layer.

[0043] It is preferable that the microcapsules are exposed on the surface of the pressure-sensitive adhesive layer opposite the substrate side. By unevenly distributing the microcapsules in the pressure-sensitive adhesive layer in this way, when the pressure-sensitive adhesive sheet is peeled off from the object at any desired timing, the pressure-sensitive adhesive sheet can be easily peeled off without applying strong pressure and without leaving any of the pressure-sensitive adhesive layer on the surface of the object, which is an even greater effect.

[0044] The degree to which the microcapsules are exposed on the surface of the adhesive layer opposite the substrate side can be determined using the ratio of the surface area of ​​the exposed microcapsules on the surface (adhesive surface) to the area of ​​the surface (adhesive surface) when the surface (adhesive surface) of the adhesive layer opposite the substrate side, when viewed in a plane ([surface area of ​​the exposed microcapsules on the adhesive surface when viewed in a plane] / [area of ​​the adhesive surface when the adhesive surface of the adhesive layer is viewed in a plane] × 100). The proportion (sometimes referred to herein as "the proportion of the area of ​​the microcapsules in the application surface of the pressure-sensitive adhesive layer") can be calculated by the method described in the Examples below.

[0045] The ratio is preferably 50% or more, and may be, for example, any one of 55% or more, 60% or more, and 65% or more. The higher the ratio, the greater the effect of being able to easily peel the PSA sheet from the object at any desired time without applying strong pressure and without leaving any PSA layer on the surface of the object. On the other hand, in order to maintain a stable adhered state with high adhesive strength under normal conditions after the adhesive sheet has been applied to an object, the above ratio is preferably 90% or less. That is, the ratio is preferably 50 to 90%, and may be, for example, any one of 55 to 90%, 60 to 90%, and 65 to 90%.

[0046] <Adhesive> The adhesive contained in the adhesive layer may be a known adhesive and is not particularly limited. Examples of the adhesive include adhesive resins such as acrylic resins having adhesive properties.

[0047] Examples of the acrylic resin include a resin having a structural unit derived from a (meth)acrylic acid alkyl ester. The acrylic resin may or may not further have other structural units, such as a structural unit derived from (meth)acrylic acid, in addition to the structural unit derived from the (meth)acrylic acid alkyl ester.

[0048] In this specification, the term "(meth)acrylic acid" is a concept that encompasses both "acrylic acid" and "methacrylic acid."

[0049] In the pressure-sensitive adhesive layer, the ratio of the pressure-sensitive adhesive content to the total mass of the pressure-sensitive adhesive layer ([pressure-sensitive adhesive content in pressure-sensitive adhesive layer (parts by mass)] / [total mass of pressure-sensitive adhesive layer (parts by mass)]×100) is preferably 60 to 99 mass%, more preferably 70 to 97 mass%, and even more preferably 80 to 95 mass%. When this ratio is equal to or greater than the lower limit, the adhesive strength of the pressure-sensitive adhesive layer becomes greater. When this ratio is equal to or less than the upper limit, the effect obtained by the pressure-sensitive adhesive layer containing components other than the pressure-sensitive adhesive (for example, the microcapsules) becomes greater.

[0050] <Microcapsules with a median diameter of 7 μm or more> The microcapsules contained in the pressure-sensitive adhesive layer are configured by encapsulating a core substance in an outer shell (wall material). The microcapsules may be any known microcapsules as long as they have a median diameter of 7 μm or more, and are not particularly limited.

[0051] In this specification, unless otherwise specified, the term "microcapsules" simply means "microcapsules with a median diameter of 7 μm or more."

[0052] Outer shell Examples of materials constituting the outer shell of the microcapsules include polyurea, polyurethane, polyamide, gelatin, and melamine-formaldehyde resin (also known as melamine resin).

[0053] The material constituting the outer shell of the microcapsules may be one type only, or two or more types, and when two or more types are used, the combination and ratio of the materials can be selected arbitrarily.

[0054] Examples of the polyurea include a polymer of a polyisocyanate compound having two or more isocyanate groups (-N=C=O) in one molecule and a polyamine compound having two or more amino groups (-NH2) in one molecule.

[0055] [Polyisocyanate compounds] The polyisocyanate compound is preferably a trimethylolpropane adduct of a polyisocyanate compound (sometimes referred to herein as a "polyisocyanate compound-TMP adduct") and a polymethylene polyphenyl polyisocyanate (sometimes referred to herein as "polymeric MDI"). That is, the polyurea preferably contains both a polymer of a polyisocyanate compound-TMP adduct and a polyamine compound, and a polymer of polymeric MDI and a polyamine compound. By providing a pressure-sensitive adhesive layer containing such microcapsules, the pressure-sensitive adhesive sheet can more effectively achieve the above-mentioned effects of the present invention.

[0056] Among the polyisocyanate compound-TMP adducts, examples of the aliphatic polyisocyanate compound-TMP adducts (trimethylolpropane adducts of aliphatic polyisocyanate compounds) include aliphatic diisocyanate-TMP adducts such as a trimethylolpropane adduct of pentamethylene diisocyanate, a trimethylolpropane adduct of hexamethylene diisocyanate, a trimethylolpropane adduct of 2,4,4-trimethylhexamethylene diisocyanate, a trimethylolpropane adduct of isophorone diisocyanate, a trimethylolpropane adduct of dicyclohexylmethane-4,4'-diisocyanate, and a trimethylolpropane adduct of dicyclohexylmethane-2,4'-diisocyanate.

[0057] Among the polyisocyanate compound-TMP adducts, examples of aromatic polyisocyanate compound-TMP adducts (trimethylolpropane adducts of aromatic polyisocyanate compounds) include aromatic diisocyanate-TMP adducts such as a trimethylolpropane adduct of tolylene-2,4-diisocyanate, a trimethylolpropane adduct of tolylene-2,6-diisocyanate (in this specification, a trimethylolpropane adduct of tolylene diisocyanate may be referred to as a "TDI-TMP adduct"), a trimethylolpropane adduct of xylylene-1,3-diisocyanate, and a trimethylolpropane adduct of xylylene-1,4-diisocyanate.

[0058] The polyisocyanate compound-TMP adduct used in forming the polyurea (in other words, the structural unit of the polyurea derived from the polyisocyanate compound-TMP adduct) may be one type or two or more types, and when two or more types are used, the combination and ratio thereof can be selected arbitrarily.

[0059] The polymeric MDI is represented by the following general formula (P1).

[0060] [ka] (wherein n is an integer of 0 or more).

[0061] In the general formula (P1), n ​​may be an integer of 0 or more, for example, 0-300.

[0062] The NCO content of the polymeric MDI can be adjusted appropriately and may be, for example, 30 to 33 mass %.

[0063] The polymeric MDI used in forming the polyurea (in other words, the structural units of the polyurea derived from the polymeric MDI) may be one type or two or more types, and when two or more types are used, the combination and ratio thereof can be selected arbitrarily.

[0064] In terms of high reactivity in the polymerization reaction with the polyamine compound and the formation of a more robust polyurea, the polyisocyanate compound-TMP adduct is preferably an aromatic polyisocyanate compound-TMP adduct, more preferably an aromatic diisocyanate-TMP adduct, and even more preferably a TDI-TMP adduct.

[0065] In the polyurea, the amount of the structural units derived from the polyisocyanate compound-TMP adduct relative to the amount of the structural units derived from the polymeric MDI is preferably 0.6 to 12 times by mass, more preferably 0.8 to 10 times by mass, and even more preferably 1 to 8.5 times by mass. By providing a pressure-sensitive adhesive layer containing such microcapsules, the pressure-sensitive adhesive sheet can more effectively achieve the effects of the present invention described above.

[0066] [Polyamine compounds] The polyamine compound is preferably an organic polyamine compound. Preferred examples of the organic polyamine compounds include aliphatic polyamine compounds having a structure in which two or more hydrogen atoms (-H) of an aliphatic hydrocarbon are substituted with amino groups (-NH2); and NH-substituted aliphatic polyamine compounds having a structure in which one or more methylene groups (-CH2-) of the aliphatic polyamine compounds are substituted with groups represented by the formula "-NH-".

[0067] The polyamine compound is preferably an aliphatic polyamine compound having a cyclic aliphatic hydrocarbon group, more preferably an aliphatic polyamine compound having both a cyclic aliphatic hydrocarbon group and a chain aliphatic hydrocarbon group, and even more preferably an organic polyamine compound having a structure in which hydrogen atoms bonded to two or more different carbon atoms constituting the ring skeleton of a cycloalkane are substituted with aminoalkyl groups. Such organic polyamine compounds include, for example, 1,3-bisaminomethylcyclohexane.

[0068] The amine compound used when forming the polyurea (in other words, the structural units of the polyurea derived from the amine compound) may be one type or two or more types, and when two or more types are used, the combination and ratio thereof can be selected arbitrarily.

[0069] It is particularly preferable that the polyurea contains both a polymer of a polyisocyanate compound-TMP adduct and an aliphatic polyamine compound having both a cyclic aliphatic hydrocarbon group and a chain aliphatic hydrocarbon group, and a polymer of polymeric MDI and an aliphatic polyamine compound having both a cyclic aliphatic hydrocarbon group and a chain aliphatic hydrocarbon group. In such polyurea, the proportion of the total amount of the structural units derived from the polyisocyanate compound-TMP adduct, the structural units derived from polymeric MDI, and the structural units derived from the aliphatic polyamine compound having both a cyclic aliphatic hydrocarbon group and a chain aliphatic hydrocarbon group, relative to the total amount of structural units (([amount (parts by mass) of structural units derived from the polyisocyanate compound-TMP adduct in the polyurea] + [amount (parts by mass) of structural units derived from polymeric MDI in the polyurea] + [amount (parts by mass) of structural units derived from the aliphatic polyamine compound having both a cyclic aliphatic hydrocarbon group and a chain aliphatic hydrocarbon group in the polyurea]) / [total amount of structural units in the polyurea (parts by mass)] × 100) is preferably 80% by mass or more, more preferably 90% by mass or more, and may be, for example, any one of 95% by mass or more, 97% by mass or more, and 99% by mass or more. When the ratio is equal to or greater than the lower limit and the pressure-sensitive adhesive sheet is provided with a pressure-sensitive adhesive layer containing such microcapsules, the above-described effects of the present invention can be more favorably achieved. On the other hand, the proportion is 100% by mass or less.

[0070] ·Core material Examples of the core material of the microcapsules include plasticizers that are liquid at room temperature.

[0071] In this specification, "room temperature" means a temperature that is neither particularly cold nor hot, that is, an ordinary temperature, and examples thereof include temperatures of 15 to 25°C.

[0072] Examples of the plasticizer include esters such as monoesters, diesters, and triesters of monobasic acids having 1 to 18 carbon atoms or polybasic acids having 1 to 18 carbon atoms and polyalkylene glycols or monohydric alcohols having 20 or less carbon atoms other than polyalkylene glycols; esters of saturated fatty acids having 12 to 18 carbon atoms or unsaturated fatty acids having 12 to 18 carbon atoms and polyalkylene glycols or dihydric to tetrahydric alcohols other than polyalkylene glycols; esters such as diesters, triesters, and tetraesters of hydroxy acids and monobasic acids or alcohols; fatty acid esters in which the unsaturated site is epoxidized with peroxides or the like; and phosphate esters.

[0073] Preferred plasticizers include, for example, ether ester plasticizers (plasticizers having both an ether bond and an ester bond); and ester plasticizers such as fatty acid esters (plasticizers having an ester bond but no ether bond).

[0074] The core substance encapsulated in the microcapsules may be one type only, or two or more types. When two or more types are encapsulated, the combination and ratio of the two or more types can be selected arbitrarily.

[0075] In the adhesive layer, the ratio of the content of microcapsules having a median diameter of 7 μm or more to the content of adhesive ([content of microcapsules having a median diameter of 7 μm or more in adhesive layer (parts by mass)] / [content of adhesive in adhesive layer (parts by mass)]×100) is preferably 1.5 to 40 mass%, more preferably 2.5 to 30 mass%, and even more preferably 5 to 20 mass%. When this ratio is equal to or greater than the lower limit, the effect obtained by the adhesive layer containing the microcapsules is further enhanced. When this ratio is equal to or less than the upper limit, excessive use of the microcapsules is suppressed. Here, the "content of microcapsules" may be equivalent to the total content of components other than water in the aqueous dispersion of microcapsules, for example, when the aqueous dispersion of microcapsules described below is used in the production of the PSA composition. The ratio is usually the same as the ratio of the content of microcapsules with a median diameter of 7 μm or more to the content of adhesive in the adhesive composition (e.g., the second adhesive composition described below) ([content of microcapsules with a median diameter of 7 μm or more in the adhesive composition (parts by mass)] / [content of adhesive in the adhesive composition (parts by mass)]×100).

[0076] <Method for manufacturing microcapsules with a median diameter of 7 μm or more> The microcapsules can be produced by known methods depending on the type of microcapsule. For example, the microcapsules having a polyurea-containing shell can be produced by interfacially polymerizing the polyisocyanate compound and the polyamine compound in the presence of a core substance. For example, the microcapsules whose shell is made of polyurethane can be produced by interfacially polymerizing the polyisocyanate compound and a polyhydroxy compound having two or more hydroxyl groups (-OH) in one molecule in the presence of a core substance. For example, the microcapsules whose shell is made of polyamide can be produced by interfacially polymerizing a polycarboxylic acid having two or more carboxy groups (-C(=O)-OH) in one molecule, or a polycarboxylic acid derivative (-C(=O)-X (wherein X is a leaving group) in which one or more of the carboxy groups are substituted with a leaving group such as a chlorine atom), with the polyamine compound in the presence of a core substance. For example, the microcapsules whose shell is made of gelatin can be produced by a complex coacervation method in which gelatin is cationized and then vigorously mixed with an anionic polymer in the presence of a core substance under emulsifying conditions. For example, the microcapsules whose shell is made of melamine-formaldehyde resin can be produced by polymerizing melamine and formaldehyde in the presence of a core substance under emulsifying conditions.

[0077] In this specification, a compound whose structure has been modified is referred to as a "derivative" of the compound. Examples of structural modifications include the substitution of one or more hydrogen atoms with groups other than hydrogen atoms. In this specification, unless otherwise specified, the term "group" includes not only an atomic group formed by bonding multiple atoms but also a single atom.

[0078] The median diameter of the microcapsules can be adjusted by known methods. For example, the median diameter of the microcapsules can be adjusted by adjusting the conditions for forming the outer shell of the microcapsules. More specifically, the median diameter of the microcapsules can be adjusted by adjusting the type of material for forming the outer shell of the microcapsules, the type of core substance, the stirring speed of the reaction solution or emulsion for the shell formation reaction, etc.

[0079] The obtained microcapsules can be used for producing a PSA composition, for example, in the form of a dispersion dispersed in a reaction solution obtained by carrying out a microcapsule-forming reaction, or in the form of a post-treated dispersion obtained by carrying out a known post-treatment on the dispersion. Examples of such dispersions include aqueous dispersions of microcapsules obtained by any of the above-mentioned microcapsule-forming reactions (production methods). The obtained microcapsules can be used in the production of a pressure-sensitive adhesive composition in the form of a dried product obtained by, for example, removing them from the reaction solution, washing them by a known method if necessary, and then drying them.

[0080] <Other ingredients> The other components contained in the pressure-sensitive adhesive layer can be selected arbitrarily depending on the purpose, and are not particularly limited. Examples of the other components include tackifying resins; additives such as neutralizing agents, leveling agents, antifoaming agents, viscosity modifiers, preservatives, plasticizers, fillers, colorants, silane coupling agents, and crosslinking agents; other resins that do not fall into the category of either adhesive resins or tackifying resins; etc. These other components may be known.

[0081] In the pressure-sensitive adhesive layer, the ratio of the total content of the pressure-sensitive adhesive and microcapsules having a median diameter of 7 μm or more to the total mass of the pressure-sensitive adhesive layer (([adhesive content in the pressure-sensitive adhesive layer (parts by mass)] + [content of microcapsules having a median diameter of 7 μm or more in the pressure-sensitive adhesive layer (parts by mass)]) / [total mass of the pressure-sensitive adhesive layer (parts by mass)] × 100) is preferably 80 mass% or more, and may be, for example, 85 mass% or more, 90 mass% or more, 95 mass% or more, or 98 mass% or more. When the ratio is equal to or greater than the lower limit, the pressure-sensitive adhesive layer can be formed without using special materials, and in a normal state after being attached to an object, the adhesive layer can maintain a stable attachment state with high adhesive strength, and when it is time to peel it off from the object at a desired timing, the adhesive strength is reduced without the application of strong pressure, and the pressure-sensitive adhesive layer can be easily peeled off without remaining on the surface of the object, thereby further enhancing the effects of the present invention. On the other hand, the proportion is 100% by mass or less. The ratio is usually the same as the ratio of the total content of the adhesive and microcapsules with a median diameter of 7 μm or more to the total content of components that do not vaporize at room temperature in the adhesive composition (for example, the second adhesive composition described below) (([content of adhesive in the adhesive composition (parts by mass)] + [content of microcapsules with a median diameter of 7 μm or more in the adhesive composition (parts by mass)]) / [total content of components that do not vaporize at room temperature in the adhesive composition (parts by mass)] × 100).

[0082] <<Base material>> The substrate is a structure for improving the strength of the PSA sheet by stably maintaining the structure of the PSA layer. Furthermore, the substrate enables the PSA sheet, after being attached to an object, to be peeled off from the object at any desired timing, without the need to apply a strong pressure to the PSA sheet, thereby reducing the adhesive strength of the PSA layer. Furthermore, when the adhesive sheet is an adhesive label, the exposed surface of the substrate (the surface opposite to the adhesive layer side) serves as a recording area for information by printing or the like.

[0083] The substrate is not particularly limited as long as it is paper or synthetic paper.

[0084] The paper may be any paper known in the art. For example, the paper may be a sheet containing only natural fibers (e.g., pulp) constituting the paper, or a sheet containing the natural fibers as a main component and not containing a synthetic resin as a main component. As long as the paper has a layer containing such natural fibers, it may or may not have other layers laminated thereon. Examples of the paper include waterproof paper, wood-free paper, art paper, coated paper, cast-coated paper, and resin-coated paper.

[0085] The synthetic paper may be any known material in the art. For example, synthetic paper may be a sheet containing only synthetic resin, or a sheet containing synthetic resin as a main component and other components. As long as the synthetic paper has a layer containing such a synthetic resin, it may or may not have other layers laminated thereon. The layer other than the layer containing synthetic resin may be a layer containing the natural fiber.

[0086] When the paper or synthetic paper contains a synthetic resin, the synthetic resin may be in the form of either a fiber or a non-fiber.

[0087] The substrate may consist of one layer (single layer), or may consist of two or more layers. When the substrate consists of multiple layers, these multiple layers may be the same or different from each other, and the combination of these multiple layers is not particularly limited.

[0088] The thickness of the substrate is not particularly limited as long as the substrate is in the form of a sheet or film, but is preferably 10 to 300 μm, more preferably 20 to 200 μm, and particularly preferably 30 to 150 μm. When the thickness of the substrate is equal to or greater than the lower limit, the strength of the pressure-sensitive adhesive sheet is increased. When the thickness of the substrate is equal to or less than the upper limit, excessive thickness of the substrate can be avoided, and, for example, the pressure-sensitive adhesive sheet can be made thinner. Here, the "thickness of the substrate" means the thickness of the entire substrate, and for example, the thickness of a substrate consisting of multiple layers means the total thickness of all layers that make up the substrate.

[0089] The substrate may be a commercially available product or may be manufactured by a known method.

[0090] <<Release paper>> The release paper is not particularly limited and may be any known paper. The release paper may be, for example, one that is configured to include paper or a resin film with a release treatment layer provided on one or both sides thereof.

[0091] <<Adhesive sheet manufacturing method>> The pressure-sensitive adhesive sheet of the present embodiment can be produced by providing the pressure-sensitive adhesive layer on the substrate. More specifically, for example, the method is as follows. That is, a first adhesive composition is prepared which contains the adhesive, and optionally the other components, and optionally the solvent, and which does not contain the microcapsules or contains a trace amount of the microcapsules.

[0092] The solvent is a component that makes the first pressure-sensitive adhesive composition liquid and reduces its viscosity, and may be, for example, either water or an organic solvent. For example, when an aqueous solution or aqueous dispersion of a pressure-sensitive adhesive is used as the pressure-sensitive adhesive, the water in the aqueous solution or aqueous dispersion corresponds to the solvent. For example, when an aqueous dispersion of microcapsules is used as the microcapsules, the water in the aqueous dispersion corresponds to the solvent.

[0093] In this specification, unless otherwise specified, the term "solvent" refers not only to a component capable of dissolving a solute in a solution, but also to a component that serves as a dispersion medium in a dispersion.

[0094] The first adhesive composition can be prepared by blending the adhesive, optionally the other components, optionally the solvent, and optionally the microcapsules, and thoroughly stirring these blended components. The order of mixing the components when producing the adhesive is not particularly limited. For example, when a solvent is added, the solvent may be mixed with the adhesive, the other components, or the microcapsules in advance, or may be mixed alone without being mixed with these components. The temperature at which the components are mixed is not particularly limited as long as the components do not deteriorate, and may be adjusted appropriately depending on the types of components, etc., but is usually preferably 15 to 30°C. The time for stirring the ingredients may be adjusted as appropriate depending on the total amount of the first pressure-sensitive adhesive composition to be produced, the stirring method, etc., and may be, for example, 10 minutes to 2 hours.

[0095] Next, the first adhesive composition is applied to the release-treated surface of the release paper, and the applied first adhesive composition is dried to form a first adhesive layer on the release-treated surface of the release paper, which contains the adhesive and, if necessary, the other components, and which does not contain the microcapsules or contains a trace amount of the microcapsules.

[0096] Next, one side of the substrate is bonded to the exposed surface of the first pressure-sensitive adhesive layer (the surface opposite to the release paper side) to produce a laminate of the first pressure-sensitive adhesive layer and the substrate with the release paper attached.

[0097] A second PSA composition containing the PSA, the microcapsules, and optionally the other components and optionally the solvent is prepared separately, with the ratio of the microcapsule content in the second PSA composition to the total mass of the second PSA composition being higher than the ratio of the microcapsule content in the first PSA composition to the total mass of the first PSA composition. The adhesive, microcapsules, other components and solvent contained in the second adhesive composition may be the same as or different from the adhesive, microcapsules, other components and solvent contained in the first adhesive composition, respectively.

[0098] The second pressure-sensitive adhesive composition can be prepared in the same manner as the first pressure-sensitive adhesive composition described above, except that either or both of the types and amounts of the ingredients may be different.

[0099] Next, the release paper is removed from the first adhesive layer in the laminate, and the second adhesive composition is applied to the exposed surface of the first adhesive layer (the surface opposite the substrate side).The second adhesive composition after application is dried, thereby forming a second adhesive layer containing the adhesive, the microcapsules, and, if necessary, the other components, on the surface of the first adhesive layer opposite the substrate side. As a result, a pressure-sensitive adhesive sheet according to the present embodiment is obtained, in which the substrate, first pressure-sensitive adhesive layer, and second pressure-sensitive adhesive layer are laminated in this order in the thickness direction, the first pressure-sensitive adhesive layer contains no microcapsules or a trace amount of microcapsules, the ratio of the microcapsule content in the second pressure-sensitive adhesive layer to the total mass of the second pressure-sensitive adhesive layer is higher than the ratio of the microcapsule content in the first pressure-sensitive adhesive layer to the total mass of the first pressure-sensitive adhesive layer, and the laminate of the first and second pressure-sensitive adhesive layers forms a pressure-sensitive adhesive layer. In this pressure-sensitive adhesive sheet, the microcapsules are unevenly distributed in the second pressure-sensitive adhesive layer, which corresponds to the region of the pressure-sensitive adhesive layer opposite the substrate side.

[0100] Here, we have described the case where a pressure-sensitive adhesive sheet is produced by applying a second pressure-sensitive adhesive composition to the exposed surface of the first pressure-sensitive adhesive layer to form a second pressure-sensitive adhesive layer, but pressure-sensitive adhesive sheets can also be produced by methods other than this. For example, as in the case of the first adhesive layer, a second adhesive composition is applied to the release-treated surface of a release paper and dried to form a second adhesive layer on the release-treated surface of the release paper, and the exposed surface of this second adhesive layer (the surface opposite to the release paper) is bonded to the exposed surface of the first adhesive layer in the laminate, thereby obtaining an adhesive sheet with a release paper and a configuration similar to that described above.

[0101] In any of the above manufacturing methods, the first pressure-sensitive adhesive composition and the second pressure-sensitive adhesive composition can be applied by a known method using, for example, various coaters such as an air knife coater, curtain coater, die coater, blade coater, roll coater, gate roll coater, bar coater, rod coater, gravure coater, gravure offset coater, etc.; or an apparatus such as a wire bar coater.

[0102] In any of the above manufacturing methods, the first pressure-sensitive adhesive composition and the second pressure-sensitive adhesive composition can be dried by a known method, such as room temperature drying such as static drying at room temperature or room temperature air drying; or heated drying such as heated air drying. Drying conditions such as drying temperature and drying time can be appropriately set depending on the drying method. For example, when drying at room temperature, the drying temperature may be 15 to 25°C and the drying time may be 12 to 36 hours. When drying by heating, the drying temperature may be 80 to 120°C and the drying time may be 1 minute to 12 hours.

[0103] <<How to use the adhesive sheet>> The adhesive sheet of this embodiment can be used, for example, by attaching the exposed surface of the adhesive layer in the adhesive sheet opposite the substrate side (in other words, the attachment surface) to an object, maintaining the adhesive state of the adhesive sheet in this state for a certain period of time, and then, at any timing when it is desired to peel the adhesive sheet from the object, applying pressure to the adhesive layer from the outside of the substrate side of the adhesive sheet, and then peeling the adhesive sheet from the object. According to this method of use, under normal conditions after the adhesive sheet has been attached to an object, the adhesive sheet can be maintained in a stable attached state with high adhesive strength, and when the adhesive sheet is to be peeled off from the object, the adhesive strength of the adhesive layer decreases without the need for applying strong pressure to the adhesive sheet (more specifically, the adhesive layer), and the adhesive sheet can be easily peeled off without any adhesive layer remaining on the surface of the object. Hereinafter, the method of using the pressure-sensitive adhesive sheet of this embodiment will be described in more detail with reference to the drawings.

[0104] 2 is a cross-sectional view for schematically illustrating an example of a method of using the pressure-sensitive adhesive sheet of the present embodiment. Here, the method of use will be described using the pressure-sensitive adhesive sheet 1 shown in FIG. 1 as an example. In FIG. 2, the same components as those shown in FIG. 1, which have already been described, are denoted by the same reference numerals as in FIG. 1, and detailed description thereof will be omitted.

[0105] In the method of use, first, as shown in Figure 2(a), the adhesive sheet 1 after removing the release paper 9 from the adhesive layer 12 is used, and the exposed surface (in other words, the exposed surface or the other surface) 12a of the adhesive layer 12 opposite the substrate 11 side is attached to the object 8, and the adhesive sheet 1 is kept attached in this state for a certain period of time.

[0106] Here, the pressure-sensitive adhesive layer 12 is newly divided into a microcapsule unevenly distributed region 122 on the side opposite the substrate 11, and the other microcapsule non-unevenly distributed region 121. In other words, the microcapsule non-unevenly distributed region 121 and the microcapsule unevenly distributed region 122 are integrated to form the pressure-sensitive adhesive layer 12. The microcapsule non-unevenly distributed region 121 shown here does not contain microcapsules, but may contain a trace amount of microcapsules.

[0107] The microcapsule unevenly distributed region 122 of the adhesive layer 12 can be formed, for example, using the second adhesive composition, and the microcapsule non-unevenly distributed region 121 of the adhesive layer 12 can be formed, for example, using the first adhesive composition.

[0108] The interface between the microcapsule non-uniformly distributed region 121 and the microcapsule unevenly distributed region 122 may or may not be observable, and whether it is observable may depend on the composition of these regions. However, even if the interface is not observable, the microcapsule unevenly distributed region 122 can be identified by focusing on the distribution of microcapsules 13 in the pressure-sensitive adhesive layer 12. For example, if a region in the thickness direction of the pressure-sensitive adhesive layer 12 is found where there are no microcapsules at all or only a trace of microcapsules, and where it can be considered that there are essentially no microcapsules, then the other region can be identified as the microcapsule unevenly distributed region 122 of the pressure-sensitive adhesive layer 12.

[0109] When the adhesive sheet 1 is attached to the object 8, the thickness T 12 is 1.2 times or more the median diameter of the microcapsules 13, the exposed area of ​​the adhesive on the other surface 12a of the adhesive layer 12 (the attachment surface opposite to the substrate 11 side) is at least a certain value, and the other surface 12a of the adhesive layer 12 exhibits sufficient adhesive strength. Therefore, in the normal state after the adhesive sheet 1 is attached to the object 8, the adhesive state of the adhesive sheet 1 can be maintained stably with high adhesive strength. In contrast, if the thickness of the adhesive layer is less than 1.2 times the median diameter of the microcapsules and is thin, the exposed area of ​​the adhesive on the other side of the adhesive layer becomes small, and the adhesive sheet 1 cannot be maintained in a stable state even under normal conditions.

[0110] When adhering the adhesive sheet 1 to the object 8, the pressure applied to the adhesive sheet 1 is preferably 0.05 to 1 MPa. By doing so, the adhesive state of the adhesive sheet 1 can be maintained stably with higher adhesive strength in the normal state after the adhesive sheet 1 is adhered to the object 8.

[0111] In the adhesive sheet 1 shown in Figure 2(a) that remains attached to the object 8, the ratio of the surface area of ​​the microcapsules 13 exposed on the other side 12a of the adhesive layer 12 (the attachment side opposite the substrate 11) to the area of ​​said other side 12a typically does not change from before the adhesive sheet 1 is attached. As explained above, this ratio calculated by viewing the other side 12a in a plan view is preferably 50% or more and 90% or less. In particular, when this ratio is 90% or less, the adhesive sheet 1 can be maintained in an attached state more stably with high adhesive strength.

[0112] In the method of use, next, as shown in FIG. 2(b), pressure P is applied to the pressure-sensitive adhesive sheet 1 from the outside on the substrate 11 side toward the pressure-sensitive adhesive layer 12 at any desired timing. As a result, as shown in FIG. 2(c), all of the microcapsules 13 in the adhesive layer 12 (the microcapsule-distributed region 122) are crushed in the direction of the pressure P (in other words, for example, in the thickness direction of the adhesive layer 12). However, since there is no need to increase the pressure P more than necessary, rupture of the microcapsules 13 is avoided. This deformation of the microcapsules 13 increases the ratio of the surface area of ​​the microcapsules 13 exposed on the other surface 12a (the attachment surface opposite to the substrate 11) of the adhesive layer 12 to the area of ​​the other surface 12a, compared to before the pressure P was applied. As a result, the contact area between the adhesive on the other surface 12a and the object 8 becomes smaller than before the pressure P was applied. This reduces the adhesive force of the adhesive sheet 1 to the object 8.

[0113] In this case, since the substrate 11 is paper or synthetic paper, when pressure P is applied to the adhesive sheet 1, the pressure is efficiently transmitted to the adhesive layer 12. This is because paper or synthetic paper is soft, and pressure is easily transmitted to the unevenly distributed region of the adhesive layer 12 where the microcapsules 13 are located, not only when the paper or synthetic paper is thin but also when the paper or synthetic paper is thick. As a result, the microcapsules 13 are easily deformed. Furthermore, since the median diameter of the microcapsules 13 contained in the adhesive layer 12 is 7 μm or more, and is a size above a specific value, the effect of the adhesive strength decreasing as the microcapsules 13 deform can be fully obtained. In contrast, when the substrate is neither paper nor synthetic paper, but is another substrate such as a resin sheet, the other substrate is harder than paper or synthetic paper, and this tendency is particularly strong when the other substrate is thick, making it difficult for pressure to be transmitted to the adhesive layer, and the effect of reducing adhesive strength is not fully achieved. Furthermore, if the median diameter of the microcapsules is less than 7 μm, the area ratio does not increase sufficiently even if the microcapsules are deformed, and therefore the effect of reducing adhesive strength cannot be fully achieved. Furthermore, even when the microcapsules are uniformly dispersed in the adhesive layer, the area ratio does not increase sufficiently, and therefore the effect of reducing adhesive strength is not sufficiently obtained.

[0114] The pressure P applied to the pressure-sensitive adhesive sheet 1 is preferably 2 to 40 MPa, more preferably 4 to 30 MPa, and even more preferably 6 to 20 MPa. When the pressure P is equal to or greater than the lower limit, the area ratio increases more than before the pressure P was applied. When the pressure P is equal to or less than the upper limit, excessive pressure P can be avoided. Even if the microcapsules 13 are deformed, rupture can be avoided with high precision.

[0115] When pressure P is applied to the adhesive sheet 1, rupture of the microcapsules 13 is avoided as described above, and therefore the core substance encapsulated in the microcapsules 13 does not leak out of the microcapsules 13 from the time the adhesive sheet 1 is attached to the time it is peeled off. Therefore, the core substance is irrelevant to the effect achieved by the adhesive sheet 1.

[0116] In the method of use, the adhesive sheet 1 is then peeled off from the object 8, as shown in Figure 2(d). At this time, because the adhesive strength of the adhesive sheet 1 to the object 8 has decreased, the adhesive layer 12 (more specifically, the microcapsule unevenly distributed region 122 of the adhesive layer 12) does not remain on the surface 8a of the object 8 (the surface on the adhesive sheet 1 side), and the adhesive sheet 1 can be easily peeled off. [Example]

[0117] The present invention will be described in more detail below with reference to specific examples, although the present invention is not limited to the examples shown below.

[0118] [Example 1] <<Production of Second Pressure-Sensitive Adhesive Composition>> <Production of microcapsules> The desired microcapsules were produced by the interfacial polymerization method described below. That is, polyvinyl alcohol (JP-24, emulsifier, manufactured by Japan Vinyl Acetate & Poval Co., Ltd.) (8.6 g) was added to distilled water (171.4 g), stirred at 50°C for 1 hour to form a solution, and then cooled to 25°C to obtain a polyvinyl alcohol aqueous solution (the first solution) with a concentration of 4.8% by mass.

[0119] Separately, at room temperature, a TDI-TMP adduct (Takenate (registered trademark) D-103 manufactured by Mitsui Chemicals, Inc.) (25 g) and polymeric MDI (Millionate MR-200 manufactured by Tosoh Corporation, NCO content 31.3% by mass) (5 g) were added to a polyether ester plasticizer (ADEKA Cizer RS-700 manufactured by ADEKA Corporation) (65 g), and the mixture was stirred until the resulting mixture became transparent, thereby obtaining a mixed solution in which all of these components were dissolved (the second solution).

[0120] At room temperature, the entire amount of the mixed solution was added to the entire amount of the polyvinyl alcohol aqueous solution, and the resulting mixed solution was stirred for 3 minutes using a homogenizer (manufactured by Primix Corporation) at a rotation speed of 3000 rpm to obtain an emulsion (the emulsification process).

[0121] To the entire amount of the obtained emulsion, 1,3-bisaminomethylcyclohexane (Tokyo Chemical Industry Co., Ltd.) (6.8 g) and distilled water (40 g) were added, and the reaction solution was stirred at 80°C and 500 rpm for 2 hours with an anchor blade to carry out interfacial polymerization (the polymerization step).

[0122] As a result of the above, microcapsules having an outer shell made of polyurea containing a polymer of 1,3-bisaminomethylcyclohexane and a TDI-TMP adduct and a polymer of 1,3-bisaminomethylcyclohexane and polymeric MDI, and encapsulating the plasticizer as a core material, were obtained as an aqueous dispersion.

[0123] <Evaluation of Microcapsules> [Mean diameter measurement of microcapsules] The median diameter of the microcapsules was measured using a particle size distribution analyzer (Sysmex Corporation, "CDA-1000X") and the aqueous dispersion obtained above. The results are shown in Table 1.

[0124] <Production of second pressure-sensitive adhesive composition> At room temperature, the aqueous dispersion of microcapsules (4 parts by mass) obtained above was added to an aqueous acrylic adhesive ("BPW6441" manufactured by Artience) (1 part by mass), and the resulting mixture was stirred to obtain a liquid second adhesive composition. In the obtained second pressure-sensitive adhesive composition, the ratio of the content of microcapsules to the content of acrylic pressure-sensitive adhesive was approximately 200% by mass.

[0125] <<Adhesive sheet manufacturing>> As the first adhesive composition, an aqueous acrylic adhesive ("BPW6441" manufactured by Artience) was coated onto the release-treated surface of the release paper, and the coating was dried by heating at 105°C for 2 minutes to form a first adhesive layer on the release paper. Synthetic paper (Yupo (registered trademark) manufactured by Yupo Corporation, a synthetic paper containing polypropylene and inorganic filler) was used as the substrate, and the exposed surface of the first adhesive layer (the surface opposite the release paper) was attached to one side of the synthetic paper, and then the release paper was removed from the first adhesive layer. Next, the second adhesive composition obtained above was applied to the exposed surface of the first adhesive layer (the surface opposite the synthetic paper side), and the resulting mixture was left to stand for 24 hours under conditions of a temperature of 23°C and a relative humidity of 50% (50% RH), thereby drying the second adhesive composition and forming a second adhesive layer.

[0126] As a result of the above, an adhesive sheet was obtained comprising a substrate made of synthetic paper, a first adhesive layer provided on one side of the substrate, and a second adhesive layer provided on the side of the first adhesive layer opposite the substrate side. In this pressure-sensitive adhesive sheet, the microcapsules were unevenly distributed in the region of the pressure-sensitive adhesive layer, which was a laminate of the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer, on the side opposite to the substrate side. In the pressure-sensitive adhesive layer, the content of the acrylic pressure-sensitive adhesive relative to the total mass of the pressure-sensitive adhesive layer was approximately 90 mass %.

[0127] The thickness of the pressure-sensitive adhesive layer was measured by the following method. That is, five measurement points were arbitrarily selected on the surface of the adhesive sheet so as not to cause bias in these positions. Then, using a paper thickness measuring device ("MEI-11" manufactured by Citizen Co., Ltd.), the thickness of the adhesive sheet was measured at these five measurement points, and the maximum and minimum values ​​were excluded from these measurements to calculate the average of the three measured values, and this average value was used as the thickness of the adhesive sheet. Separately, the thickness (average value of the three thickness measurements of the substrate) of the substrate before laminating the first adhesive layer was determined in the same manner as in the case of the adhesive sheet, and the thickness of the substrate was subtracted from the thickness of the adhesive sheet (calculating [thickness of adhesive sheet] - [thickness of substrate]) to determine the thickness of the adhesive layer. As a result, as shown in Table 1, the thickness of the adhesive layer (total thickness of the first adhesive layer and the second adhesive layer) was 20 μm, and the thickness of the substrate was 80 μm.

[0128] <<Evaluation of adhesive sheets>> <Calculation of [Adhesive layer thickness] / [Median diameter of microcapsules]> The thickness of the adhesive layer and the median diameter of the microcapsules were used to calculate the ratio [thickness of the adhesive layer] / [median diameter of the microcapsules]. The results are shown in Table 1.

[0129] <Calculation of the ratio of the area of ​​microcapsules to the adhesive surface of the adhesive layer> Using a scanning electron microscope, the exposed surface of the adhesive layer of the adhesive sheet obtained above (the surface opposite to the substrate, i.e., the application surface) was photographed in three separate areas at a magnification of 250x, and three sets of image data were obtained. At this time, the total area of ​​the photographed areas was approximately 0.6 mm 2 (=approximately 0.2 mm × approximately 3 mm). Then, in this photographed area (i.e., the application surface), the area of ​​the region where the microcapsules were exposed and the area of ​​the region where the microcapsules were not exposed were determined, and from these values, the ratio of the area of ​​the microcapsules to the application surface of the adhesive layer was calculated. The results are shown in Table 1.

[0130] <Measurement of normal adhesive strength of adhesive sheets> A 25mm x 100mm section was cut from the pressure-sensitive adhesive sheet obtained above. The entire exposed surface (adhesion surface) of the pressure-sensitive adhesive layer in this section was placed on the exposed surface of a polyethylene terephthalate (PET) film (100µm thick) fixed to a metal plate. Then, a laminate of this section, the PET film, and the metal plate was placed on the horizontal surface with the metal plate in contact with the horizontal surface, with the exposed surface of the substrate in the laminate (section) facing upward. In this state, a 2kg roll was rolled back and forth twice over the entire length of the section on the exposed surface of the substrate in the section, applying a pressure of approximately 0.4MPa to the section from the substrate side to the PET film side, thoroughly bonding the section and the PET film. In this way, a test piece for measuring adhesive strength was prepared.

[0131] Immediately after preparation, the test piece was left to stand for 24 hours under conditions of a temperature of 23°C and a relative humidity of 50% (50% RH). Next, under these conditions, the section (adhesive sheet) of the test piece after standing was peeled from the PET film. At this time, the peeling speed was set to 300 mm / min, and 180° peeling was performed so that the angle between the two peeled surfaces (the adhesive surface of the section and the surface to which the PET film section was attached) formed by the peeling was 180°. The peel force at this 180° peeling was then measured, and this was adopted as the normal adhesive force of the adhesive sheet, and its level was evaluated according to the following criteria. The results are shown in Table 1. [Judgment criteria] A: The adhesive sheet has a normal adhesive strength of 4.9N / 25mm or more, which is sufficiently high. B: The normal adhesive strength of the adhesive sheet is less than 4.9 N / 25 mm, which is low.

[0132] <Measurement of adhesive strength when dismantling adhesive sheet> A test piece identical to the test piece used in measuring the normal adhesive strength was separately prepared, and this test piece was left standing in the same manner as in measuring the normal adhesive strength. Next, using the test piece after standing under conditions of 23°C and 50% RH, a metal roll was rolled across the exposed surface of the substrate in the entire longitudinal direction of the test piece, applying a pressure of approximately 10 MPa to the test piece from the substrate side to the PET film side. Immediately after pressing, the peel force at 180° peeling was measured using the same method as for measuring the normal adhesive force described above, and this was used as the adhesive force when the adhesive sheet was disassembled, and its level was evaluated according to the following criteria. The results are shown in Table 1. [Judgment criteria] A: The adhesive strength of the adhesive sheet when disassembled is 1N / 25mm or less, which is extremely low. B: The adhesive strength of the adhesive sheet when dismantled is greater than 1N / 25mm and less than 2N / 25mm, meaning that the adhesive strength when dismantled is low. C: The adhesive strength of the adhesive sheet when disassembled is over 2N / 25mm, and the adhesive strength when disassembled is high.

[0133] <Evaluation of the effect of suppressing the adhesive layer from remaining on the surface of the target object> After measuring the adhesive strength during disassembly, the area of ​​the surface of the object (PET film) where the adhesive sheet had been attached was visually observed. The effectiveness of suppressing the adhesive layer from remaining on the surface of the object after peeling off the adhesive sheet was evaluated based on the presence or absence of the adhesive layer remaining, and if so, the amount of the remaining adhesive layer, according to the following criteria. The results are shown in Table 1. [Evaluation criteria] A: No adhesive layer remains at all, and the effect of suppressing residue is high. B: Although a small amount of adhesive layer remains, there is no problem in reusing the object after peeling off the adhesive sheet, and a sufficient effect of suppressing residue is observed. C: More than a trace amount of adhesive layer remains, hindering reuse of the object after peeling off the adhesive sheet, and no or only a low effect of suppressing residue is observed.

[0134] <<Production and evaluation of microcapsules, production of second adhesive composition, and production and evaluation of adhesive sheet>> [Examples 2 to 3] The adhesive sheets were manufactured and evaluated in the same manner as in Example 1, except that the thickness of the first adhesive layer was increased by increasing the amount of coating of the first adhesive composition during the manufacture of the adhesive sheet, and the thickness of the adhesive layer was changed from 20 μm to 30 μm (Example 2) or 50 μm (Example 3). These results are shown in Table 1.

[0135] [Example 4] Microcapsules were produced and evaluated in the same manner as in Example 1, except that in the emulsification step, the rotation speed during stirring using a homogenizer was changed from 3000 rpm to 1800 rpm. The obtained microcapsules differed from the microcapsules obtained in Example 1 in terms of their median diameter. A second PSA composition was produced in the same manner as in Example 1, except that these microcapsules (more specifically, the aqueous dispersion of microcapsules) were used. Furthermore, an adhesive sheet was manufactured and evaluated in the same manner as in Example 1, except that this second adhesive composition was used when manufacturing the adhesive sheet, and the thickness of the first adhesive layer was increased by increasing the coating amount of the first adhesive composition, so that the thickness of the adhesive layer was 30 μm instead of 20 μm. These results are shown in Table 1.

[0136] [Example 5] <<Production of Second Pressure-Sensitive Adhesive Composition>> <Production of microcapsules> The desired microcapsules were produced according to the following procedure. That is, sodium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) (0.7 g) and styrene-maleic anhydride copolymer (Monsanto Company's Scripset (registered trademark) 520) (5.1 g) were added to distilled water (159.2 g), stirred at 80°C for 2 hours, and then cooled to 25°C to obtain an aqueous solution of styrene-maleic acid copolymer with a concentration of 3.5 mass%.

[0137] Separately, at room temperature, distilled water (20 g) was added to 7.0 g of a 37% by mass aqueous formaldehyde solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a 9.6% by mass aqueous formaldehyde solution, and a small amount of dilute sodium hydroxide solution was added thereto to adjust the pH of the aqueous formaldehyde solution to 9.0.

[0138] Melamine monomer (manufactured by Tokyo Chemical Industry Co., Ltd.) (3.4 g) was added to the entire amount of the aqueous formaldehyde solution at room temperature, and the mixture was stirred at 80° C. for 10 minutes to obtain a melamine-formaldehyde mixed solution.

[0139] At room temperature, a polyether ester plasticizer (ADEKA Cizer RS-700, manufactured by ADEKA Corporation) (65 g) was added to the entire amount of the styrene-maleic acid copolymer aqueous solution, and the resulting mixture was stirred for 3 minutes using a homogenizer (manufactured by Primix Corporation) at a rotation speed of 3500 rpm to obtain an emulsion.

[0140] The entire amount of the melamine-formaldehyde mixed solution was added to the entire amount of the resulting emulsion, and the reaction solution was stirred at 80° C. with an anchor blade rotating at 500 rpm for 2 hours to carry out polymerization. Next, the reaction solution was cooled to 25°C, and then a small amount of diluted aqueous sodium hydroxide solution was added thereto to adjust the pH of the reaction solution to 7.0.

[0141] As a result, microcapsules having an outer shell made of melamine-formaldehyde resin and encapsulating the plasticizer as a core material were obtained as an aqueous dispersion.

[0142] <Evaluation of Microcapsules> The microcapsules obtained above were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0143] <Production of second pressure-sensitive adhesive composition, and production and evaluation of pressure-sensitive adhesive sheet> A second liquid PSA composition was produced in the same manner as in Example 1, except that the aqueous dispersion of microcapsules obtained above was used.

[0144] <<Adhesive sheet manufacturing>> Except for using the second pressure-sensitive adhesive composition obtained above, a pressure-sensitive adhesive sheet was produced and evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0145] <<Production and evaluation of microcapsules, production of second adhesive composition, and production and evaluation of adhesive sheet>> [Example 6] An adhesive sheet was produced and evaluated in the same manner as in Example 1, except that high-quality paper ("Multi-Cut Paper White" manufactured by TOPPAN EDGE Co., Ltd.) was used as the substrate instead of the synthetic paper. The thickness of the substrate was 89 μm. The results are shown in Table 2.

[0146] [Comparative Example 1] Microcapsules were produced and evaluated in the same manner as in Example 1, except that the rotation speed during stirring using a homogenizer in the emulsification step was changed from 3000 rpm to 7000 rpm. The obtained microcapsules differed from the microcapsules obtained in Example 1 in terms of their median diameter. A second PSA composition was produced in the same manner as in Example 1, except that these microcapsules (more specifically, the aqueous dispersion of microcapsules) were used. Furthermore, an adhesive sheet was manufactured and evaluated in the same manner as in Example 1, except that this second adhesive composition was used when manufacturing the adhesive sheet, and the thickness of the first adhesive layer was increased by increasing the coating amount of the first adhesive composition, so that the thickness of the adhesive layer was 30 μm instead of 20 μm. These results are shown in Table 2.

[0147] Comparative Example 2 An adhesive sheet was produced and evaluated in the same manner as in Comparative Example 1, except that the thickness of the first adhesive layer was increased by further increasing the coating amount of the first adhesive composition during production of the adhesive sheet, and the thickness of the adhesive layer was changed from 30 μm to 50 μm. The results are shown in Table 2.

[0148] Comparative Example 3 An adhesive sheet was produced and evaluated in the same manner as in Example 1, except that the thickness of the first adhesive layer was reduced by reducing the coating amount of the first adhesive composition during production of the adhesive sheet, so that the thickness of the adhesive layer was 10 μm instead of 20 μm. The results are shown in Table 3.

[0149] [Comparative Examples 4 to 5] Pressure-sensitive adhesive sheets were produced and evaluated in the same manner as in Example 4, except that the thickness of the first pressure-sensitive adhesive layer was reduced by reducing the coating amount of the first pressure-sensitive adhesive composition during production, and the thickness of the pressure-sensitive adhesive layer was changed from 30 μm to 10 μm (Comparative Example 4) or 20 μm (Comparative Example 5). The results are shown in Table 3.

[0150] Comparative Example 6 Except for using a PET film (thickness: 100 μm) instead of the synthetic paper, a pressure-sensitive adhesive sheet was produced and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0151] Comparative Example 7 <<Production of Pressure-Sensitive Adhesive Composition>> At room temperature, the aqueous dispersion of microcapsules obtained in Example 1 (1 part by mass) was added to an aqueous acrylic adhesive ("BPW6441" manufactured by Artience) (10 parts by mass), and the resulting mixture was stirred to obtain a liquid comparative adhesive composition.

[0152] <<Production and evaluation of adhesive sheets>> The comparative adhesive composition obtained above was coated onto the release-treated surface of a release paper and dried by heating at 105°C for 2 minutes to form a microcapsule-containing adhesive layer on the release paper. The synthetic paper was used as a substrate, and the exposed surface of the microcapsule-containing adhesive layer (the surface opposite the release paper) was attached to one side of the synthetic paper, and then the release paper was removed from the microcapsule-containing adhesive layer. As a result, a pressure-sensitive adhesive sheet was obtained that included a synthetic paper substrate and a microcapsule-containing adhesive layer provided on one side of the substrate. In this pressure-sensitive adhesive sheet, the microcapsules were uniformly distributed throughout the entire area of ​​the microcapsule-containing adhesive layer.

[0153] The pressure-sensitive adhesive sheet obtained above was evaluated in the same manner as in Example 1. The results are shown in Table 4.

[0154] [Table 1]

[0155] [Table 2]

[0156] [Table 3]

[0157] [Table 4]

[0158] As described above, the pressure-sensitive adhesive sheets of Examples 1 to 6 were constructed without using any special materials. As is clear from the above results, in Examples 1 to 6, the normal adhesive strength of the adhesive sheet was 5 N / 25 mm or more (5 to 8 N / 25 mm), and the adhesive sheet exhibited high adhesive strength and a stable adhesion state in the normal state after being attached to the object. On the other hand, in Examples 1 to 6, the pressure applied to the adhesive sheet when peeling it from the object was 10 MPa, which was not a strong pressure, but the adhesive strength of the adhesive sheet when dismantled was 2 N / 25 mm or less (0.2 to 2 N / 25 mm), so the adhesive strength when peeling the adhesive sheet was low and the adhesive sheet could be easily peeled from the object. Moreover, no adhesive layer remained on the surface of the object after peeling.

[0159] In Examples 1 to 6, the median diameter of the microcapsules was 10 μm or more (10 to 20 μm), the thickness of the adhesive layer was 20 to 50 μm, and the thickness of the adhesive layer was 1.5 times or more (1.5 to 5 times) the median diameter of the microcapsules.

[0160] In Examples 1 to 6, the area ratio of the microcapsules to the applied surface of the pressure-sensitive adhesive layer was approximately 70%, which was consistent with the above evaluation results.

[0161] When calculating the proportion of the area of ​​the microcapsules on the adhesive surface of the adhesive layer, the microcapsules exposed on the adhesive surface were observed, and it was found that in all of Examples 1 to 6, all or almost all of the microcapsules were intact.

[0162] In contrast, in Comparative Examples 1, 2, and 7, the adhesive strength of the adhesive sheet during disassembly was 4.5 N / 25 mm or more, and the adhesive strength was high when the adhesive sheet was peeled off, making it difficult to peel the adhesive sheet from the object. Moreover, the adhesive layer clearly remained on the surface of the object after peeling.

[0163] In Comparative Examples 1 and 2, the median diameter of the microcapsules was 5 μm, which was too small. In Comparative Example 7, the microcapsules were uniformly dispersed in the adhesive layer. For these reasons, in Comparative Examples 1, 2 and 7, the effect of the pressure-sensitive adhesive layer containing microcapsules was not sufficiently obtained.

[0164] In Comparative Examples 3 to 5, the normal adhesive strength of the adhesive sheets was 4.5 N / 25 mm or less, which was low, and the adhesive sheets could not be stably applied under normal conditions. In Comparative Examples 3 to 5, the value of [adhesive layer thickness] / [median diameter of microcapsules] was less than 1, and the median diameter (particle diameter) of the microcapsules was too large relative to the thickness of the adhesive layer. As a result, when the adhesive sheet was attached to an object, the adhesive did not make sufficient contact with the object.

[0165] In Comparative Example 6, the normal adhesive strength of the adhesive sheet was 4.5 N / 25 mm, meaning that the adhesive sheet could not be stably attached under normal conditions. Furthermore, in Comparative Example 6, the adhesive strength of the adhesive sheet when disassembled was 4 N / 25 mm, meaning that the adhesive sheet could not be easily peeled off from the object. In the pressure-sensitive adhesive sheet of Comparative Example 6, the substrate was a PET film, and was neither paper nor synthetic paper. [Industrial Applicability]

[0166] The present invention can be used as an adhesive sheet that can be attached to an object and then peeled off from the object at any desired timing, and is suitable as an adhesive label, for example. [Explanation of symbols]

[0167] 1... adhesive sheet, 11... substrate, 11a... one surface of the substrate, 12... adhesive layer, 122... area of ​​uneven distribution of microcapsules in the adhesive layer, 12a... attachment surface of the adhesive layer opposite to the substrate side, 13... microcapsules with a median diameter of 7 μm or more, T 12 Adhesive layer thickness

Claims

1. A pressure-sensitive adhesive sheet comprising a substrate and a pressure-sensitive adhesive layer provided on the substrate, The pressure-sensitive adhesive layer contains microcapsules having a median diameter of 7 μm or more, the microcapsules are unevenly distributed in a region of the pressure-sensitive adhesive layer opposite to the substrate, The thickness of the pressure-sensitive adhesive layer is 1.2 times or more the median diameter of the microcapsules, The adhesive sheet, wherein the substrate is paper or synthetic paper.

2. 2. The pressure-sensitive adhesive sheet according to claim 1, wherein, when the adhesive surface of the pressure-sensitive adhesive layer is viewed in plan on the side opposite the substrate, the ratio of the area of ​​the surface of the microcapsules exposed on the adhesive surface to the area of ​​the adhesive surface is 50 to 90%.

Images