Color-changeable adhesive sheet

Abstract

The pressure-sensitive adhesive sheet (X), which is a color-changeable pressure-sensitive adhesive sheet, is provided with a base material (10) and a pressure-sensitive adhesive layer (21). The base material (10) has a first surface (10a) and a second surface (10b) on the opposite side from the first surface (10a). The adhesive layer (21) is disposed on the first surface (10a). The substrate (10) includes a color-changeable layer (12) that can change color by an external stimulus. A first color change width (W1) of a color change region formed in the color change layer (12) by linearly applying an external stimulus to the color change layer (12), and a second color change width (W2) of a color change region after the color change layer (12) is further subjected to a heat treatment at 85 DEG C for 168 hours satisfy 0.5 < = W2 / W1 < = 1.5.

Description

Technical Field

[0001] The present invention relates to a color-changeable adhesive sheet. Background Art

[0002] Display panels such as organic EL panels have a laminated structure including elements such as a pixel panel and a cover member. In the manufacturing process of such a display panel, in order to adhere the elements contained in the laminated structure to each other, for example, a transparent adhesive sheet can be used. As such a transparent adhesive sheet, an adhesive sheet without a substrate and a double-sided adhesive sheet with a substrate can be cited.

[0003] In addition, as a transparent adhesive sheet disposed on the light emitting side (image display side) of a pixel panel in a display panel, it has been proposed to use an adhesive sheet having a colored portion pre-formed at a predetermined portion of the sheet for imparting design, shielding, anti-reflection, etc. Such an adhesive sheet is described, for example, in the following Patent Document 1. Patent Document 1 specifically describes an adhesive sheet having a colored portion containing a carbon black pigment.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2017-203810 Summary of the invention

[0007] Problems to be solved by the invention

[0008] However, in the manufacturing process of display panels, when an adhesive sheet with a pre-formed colored portion is used, after the adhesive sheet is attached to an adherend, it is not possible to reliably detect the presence of foreign matter and bubbles between the adherend and the colored portion of the adhesive sheet. For the attachment of adhesive sheets in the manufacturing process of display panels, it is required to be able to reliably inspect the presence of foreign matter and bubbles between the adherend and the adhesive sheet after the attachment.

[0009] On the other hand, from the viewpoint of ensuring the function of the colored portion provided on the transparent adhesive sheet for a display panel, it is required to suppress the deterioration of the colored portion.

[0010] The present invention provides a color-changing pressure-sensitive adhesive sheet which can change color at least partially after being attached to an adherend and is suitable for suppressing deterioration of the color-changed portion.

[0011] Solutions to the problem

[0012] The present invention [1] includes a color-changing adhesive sheet, comprising: a substrate having a first surface and a second surface opposite to the first surface, and an adhesive layer arranged on the first surface, the substrate including a color-changing layer that can change color by external stimulation, a first color-changing width W1 of a color-changing region formed in the color-changing layer by linearly applying the external stimulation to the color-changing layer, and a second color-changing width W2 of the color-changing region after the color-changing layer is further heated at 85°C for 168 hours, satisfying 0.5≤W2 / W1≤1.5.

[0013] The present invention [2] includes the color-variable pressure-sensitive adhesive sheet described in [1] above, wherein the color-variable layer contains a polymer component having a glass transition temperature of 40° C. or higher and a colorant capable of developing color in response to the external stimulus.

[0014] The present invention [3] includes the color-variable adhesive sheet described in [2] above, wherein the colorant is a color-developing compound that develops color by reacting with an acid, and the color-variable layer further contains a photoacid generator.

[0015] The present invention [4] comprises the color-variable adhesive sheet according to any one of the above [1] to [3], wherein the average transmittance at a wavelength of 400 nm to 700 nm is 70% or more before the external stimulus is applied.

[0016] The present invention [5] includes the color-changeable adhesive sheet according to [1] to [4], further comprising an adhesive layer disposed on the second surface.

[0017] The present invention [6] includes the color-variable adhesive sheet according to any one of [1] to [5], wherein the substrate further comprises a substrate film and has a multilayer structure including the substrate film and the color-variable layer.

[0018] The present invention [7] comprises the color-variable adhesive sheet according to any one of [1] to [5] above, wherein the substrate is a color-variable layer.

[0019] Effects of the Invention

[0020] As described above, the color-changing adhesive sheet of the present invention includes a color-changing layer that can be colored by external stimulation. Therefore, after the color-changing adhesive sheet is attached to the adherend, the color-changing portion of the sheet (at least a portion of the sheet when viewed from above) is given an external stimulus, so that the portion can be locally changed in color. For such a color-changing adhesive sheet, the presence or absence of foreign matter and bubbles between the sheet and the adherend can be checked after attachment and before the color-changing portion is formed.

[0021] In addition, for the color-changing adhesive sheet, as described above, the first color-changing width W1 of the color-changing region formed in the color-changing layer by applying an external stimulus in a linear manner to the color-changing layer and the second color-changing width W2 of the color-changing region after the heat treatment under the above-mentioned given conditions satisfy 0.5≤W2 / W1≤1.5. Such a color-changing adhesive sheet is suitable for suppressing the degradation of the color-changing portion after the color-changing portion is formed in the color-changing layer by applying an external stimulus. Suppression of degradation of the color-changing portion in the color-changing layer helps to maintain the functional characteristics of the color-changing portion such as appearance design, shielding, and anti-reflection.

[0022] It is also possible to consider that the above-mentioned colorant is simply added to the adhesive layer instead of in the substrate to make the adhesive layer change color. However, colorants such as color-developing compounds tend to be more easily thermally diffused in the adhesive layer than in the substrate, and therefore, the color-changing portion formed in the adhesive layer is easily degraded due to the color development of the colorant. In contrast, in the color-changing adhesive sheet of the present invention, the substrate includes a color-changing layer that can change color, and the color-changing portion formed in the color-changing layer is less likely to degrade than the color-changing portion formed in the adhesive layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic cross-sectional view of one embodiment of the color-changeable pressure-sensitive adhesive sheet of the present invention.

[0024] FIG. 2 shows an example of a method of using the color-changeable pressure-sensitive adhesive sheet of the present invention. Figure 2A The steps of preparing the color-changeable pressure-sensitive adhesive sheet and the member (adherend) are shown. Figure 2B The step of bonding the components to each other via the color-changeable adhesive sheet is shown. Figure 2C The following is a step of forming a color-changing portion on a base material of a color-changing pressure-sensitive adhesive sheet.

[0025] Figure 3 1 is a cross-sectional schematic diagram of a modified example of the color-changing adhesive sheet of the present invention. The color-changing adhesive sheet of this modified example is a single-sided adhesive sheet with a substrate. In this modified example, the color-changing layer is arranged on the side of the substrate opposite to the adhesive layer.

[0026] Figure 4 2 is a schematic cross-sectional view of another variation of the color-changing adhesive sheet of the present invention. The color-changing adhesive sheet of this variation is a single-sided adhesive sheet with a substrate. In this variation, the color-changing layer is disposed on the adhesive layer side of the substrate.

[0027] Figure 5 1 is a schematic cross-sectional view of another modified example of the color-changing adhesive sheet of the present invention. The color-changing adhesive sheet of this modified example is a double-sided adhesive sheet with a color-changing substrate.

[0028] Explanation of symbols

[0029] X adhesive sheet (color-changing adhesive sheet)

[0030] H thickness direction

[0031] 10. Substrate

[0032] 10a Page 1

[0033] 10b Side 2

[0034] 11. Base film

[0035] 12 Color-Changeable Layers

[0036] 12a Discoloration part

[0037] 21, 22 Adhesive layer

[0038] 31 Component 1

[0039] 32 Component 2 DETAILED DESCRIPTION

[0040] As an embodiment of the color-changing adhesive sheet of the present invention, an adhesive sheet X is as follows Figure 1 As shown, the adhesive sheet X includes a substrate 10 and adhesive layers 21 and 22. Specifically, the adhesive sheet X includes an adhesive layer 21 (first adhesive layer), a substrate 10, and an adhesive layer 22 (second adhesive layer) in this order in the thickness direction H. The adhesive sheet X is developed in a direction (surface direction) perpendicular to the thickness direction H.

[0041] The substrate 10 has a first surface 10a and a second surface 10b on the opposite side to the first surface 10a. The adhesive layer 21 is arranged on the first surface 10a side of the substrate 10. In the present embodiment, the adhesive layer 21 is arranged on the first surface 10a. That is, the adhesive layer 21 is in contact with the first surface 10a. The adhesive layer 21 has an adhesive surface 21a on the opposite side to the substrate 10. The adhesive layer 22 is arranged on the second surface 10b side of the substrate 10. In the present embodiment, the adhesive layer 22 is arranged on the second surface 10b. That is, the adhesive layer 22 is in contact with the second surface 10b. The adhesive layer 22 has an adhesive surface 22a on the opposite side to the substrate 10. In addition, in the present embodiment, the substrate 10 has a multilayer structure including a substrate film 11 and a variable color layer 12. The substrate 10 preferably has a substrate film 11 and a variable color layer 12 arranged on the substrate film 11. In such a substrate 10 , the substrate film 11 and the color-variable layer 12 are in contact with each other. Figure 1The substrate 10 in which the color-changing layer 12 is arranged on the side of the adhesive layer 22 is shown as an example. In this case, the adhesive sheet X has an adhesive layer 21, a substrate film 11, a color-changing layer 12, and an adhesive layer 22 in the thickness direction H in sequence. Such an adhesive sheet X can be used, for example, as an optically transparent adhesive sheet (optical adhesive sheet) arranged on the image display side of a pixel panel in a display panel (having a laminated structure including elements such as a pixel panel and a cover member). That is, the adhesive sheet X is a color-changing adhesive sheet for optical purposes. As a display panel, for example, an organic EL panel can be cited.

[0042] The color-changing layer 12 contains a polymer component and a colorant. The colorant can develop color by an external stimulus described later. The color-changing layer 12 is, for example, a resin cured layer formed of a color-changing resin composition containing a polymer component and a colorant. The portion of such a color-changing layer 12 that is subjected to an external stimulus can change color. Therefore, according to the adhesive sheet X, by applying an external stimulus to the color-changing portion of the color-changing layer 12 after the adhesive sheet X is attached to the adherend, the color-changing layer 12 can be partially changed in color. According to such an adhesive sheet X, the presence or absence of foreign matter and bubbles between the adhesive sheet X and the adherend can be inspected after attachment and before the color-changing portion of the color-changing layer 12 is formed.

[0043] In the adhesive sheet X, a first color change width W1 of a color change region formed in the color change layer 12 by applying a linear external stimulus to the color change layer 12, and a second color change width W2 of the color change region after the color change layer 12 is further heated at 85° C. for 168 hours satisfy the following formula (1).

[0044] 0.5≤W2 / W1≤1.5 ···(1)

[0045] Such a structure is suitable for suppressing the deterioration (penetration, fading, uneven color tone, etc.) of the discoloration part formed in the variable color layer 12, and therefore, it helps to maintain the functional characteristics of the discoloration part. From this point of view, the ratio of W2 to W1 (W2 / W1) is 0.5 or more, preferably 0.7 or more, more preferably 0.8 or more, and more preferably 0.9 or more. In addition, it is 1.5 or less, preferably 1.3 or less, more preferably 1.2 or less, and more preferably 1.1 or less. In addition, when the ratio (W2 / W1) of the adhesive sheet X set for the pixel panel such as the organic EL panel is less than 0.5, sometimes the metal wiring of the pixel panel cannot be completely covered, and the sufficient anti-reflection function based on the above-mentioned discoloration part cannot be ensured. When the ratio (W2 / W1) of the adhesive sheet X set for the pixel panel such as the organic EL panel exceeds 1.5, sometimes the above-mentioned discoloration part will block a part of the emitted light from the light-emitting element of the pixel panel, and the light extraction efficiency in the pixel panel cannot be fully ensured.

[0046] As described above, the adhesive sheet X can change the color of at least a portion of the color-changing layer 12 after being attached to an adherend, and is suitable for suppressing the degradation of the color-changing portion of the color-changing layer 12. Suppression of degradation of the color-changing portion in the color-changing layer 12 helps maintain the functional characteristics of the color-changing portion, such as design, shielding, and anti-reflection.

[0047] The substrate film 11 is a film having a supporting function. The substrate film 11 is, for example, a flexible transparent resin film. Examples of the material of the substrate film 11 include polyester resins, polyolefin resins, polycarbonate resins, polyethersulfone resins, polyarylate resins, melamine resins, polyamide resins, cellulose resins, and polystyrene resins. Examples of polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate. Examples of polyolefin resins include polyethylene, polypropylene, and cycloolefin polymers (COP). From the viewpoint of transparency and strength, polyester resins are preferably used, and PET is more preferably used.

[0048] The substrate film 11 may contain an ultraviolet absorber. As the ultraviolet absorber, for example, benzotriazole ultraviolet absorbers, hydroxyphenyltriazine ultraviolet absorbers, benzophenone ultraviolet absorbers, salicylate ultraviolet absorbers, cyanoacrylate ultraviolet absorbers, and nickel complex salt ultraviolet absorbers can be cited. The ultraviolet absorber can be used alone or in combination of two or more. As a commercially available product of a resin film with an ultraviolet absorber, for example, "KC2UA" (cellulose triacetate film) manufactured by Konica Minolta can be cited. In addition, the substrate film 11 can be a film formed by a material that has ultraviolet absorption even without the ultraviolet absorber. As such an ultraviolet absorbing film, for example, a polyimide film can be cited. As a commercially available product of a polyimide film, for example, "Kapton 200H" manufactured by Toray DuPont Co., Ltd. can be cited.

[0049] From the viewpoint of ensuring the handling properties of the adhesive sheet X, the thickness of the base film 11 is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 15 μm or more. From the viewpoint of thinning the adhesive sheet X, the thickness of the base film 11 is preferably 200 μm or less, more preferably 150 μm or less, further preferably 100 μm or less, and particularly preferably 80 μm or less.

[0050] As described above, the color-changing resin composition forming the color-changing layer 12 contains a polymer component and a colorant. The polymer component is a molding material of the color-changing layer 12. As the polymer component, for example, thermoplastic resins and thermosetting resins can be cited. As the thermoplastic resin, for example, polyester resins, polyvinyl chloride resins, acrylic resins, and cellulose resins can be cited. As the polyester resin, for example, homopolymer polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN) can be cited. As the polyester resin, saturated copolymer polyester resins can also be cited. Saturated copolymer polyester resins refer to resins that do not substantially contain carbon-carbon unsaturated bonds in polyester resins generated by polycondensation reactions of monomer components including dicarboxylic acids and diols used to form homopolymer polyester resins (PET, PBT, PEN, etc.) and dicarboxylic acids (different types of dicarboxylic acids) and / or diols (different types of diols) different from them. Examples of different dicarboxylic acids include succinic acid, adipic acid, terephthalic acid, and isophthalic acid. Examples of different dicarboxylic acids include ethylene glycol, 1,4-butanediol, diethylene glycol, 1,3-propylene glycol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, and cyclohexanediol. Examples of thermosetting resins include polyurethane resins, epoxy resins, and phenolic resins.

[0051] The glass transition temperature (Tg) of the polymer component is higher than the glass transition temperature of the base polymer described later for the adhesive layers 21 and 22. From the viewpoint of suppressing the thermal diffusion of the colorant as a low molecular weight component in the variable color layer 12, the glass transition temperature of the polymer component is preferably 40°C or more, more preferably 60°C or more, and further preferably 80°C or more. The glass transition temperature of the polymer component is preferably 200°C or less, more preferably 170°C or less, and further preferably 90°C or less. The glass transition temperature of the polymer component is set to a value measured by differential scanning calorimetry (DSC) (the same applies to the glass transition temperature of the base polymer described later). The specific method for measuring the glass transition temperature of the polymer component is described later in the examples.

[0052] The external stimulus for causing the colorant to develop color may include, for example, light irradiation and heating, depending on the type of the colorant. The type of light in the irradiation may include, for example, ultraviolet light, visible light, and infrared light, and ultraviolet light is preferred from the perspective of the diversity of the equipment used.

[0053] The coloring agent is preferably a color-developing compound that develops color by reacting with an acid. When the coloring agent is a color-developing compound, the color-variable layer 12 further contains a photoacid generator.

[0054] Examples of the color-developing compound include a leuco dye, a triarylmethane dye, a diphenylmethane dye, a fluorane dye, a spiropyran dye, and a rhodamine dye. The color-developing compound may be used alone or in combination of two or more.

[0055] Examples of the colorless dye include 2'-anilino-6'-(N-ethyl-N-isopentylamino)-3'-methylspiro[phthalide-3,9'-[9H]xanthene], 3-dibutylamino-6-methyl-7-anilinofluoran, 3-dipropylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-dimethylanilinofluoran, and 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindol-3-yl)-4-azaphthalide.

[0056] Examples of triarylmethane dyes include p,p',p"-tris-dimethylaminotriphenylmethane. Examples of diphenylmethane dyes include 4,4-bis-dimethylaminophenylbenzhydryl benzyl ether. Examples of fluorane dyes include 3-diethylamino-6-methyl-7-chlorofluoran. Examples of spiropyran dyes include 3-methylspirobinaphthopyran. Examples of rhodamine dyes include rhodamine-B-anilinolactam.

[0057] From the viewpoint of ensuring good colorability in the color-variable layer 12, the color-developing compound is preferably a colorless dye, and more preferably 2'-anilino-6'-(N-ethyl-N-isopentylamino)-3'-methylspiro[phthalide-3,9'-[9H]xanthene].

[0058] From the viewpoint of ensuring good colorability in the color-variable layer 12, the amount of the color-developing compound is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and further preferably 1.5 parts by mass or more relative to 100 parts by mass of the polymer component. From the viewpoint of ensuring good solubility / dispersibility of the color-developing compound in the polymer component, the amount is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and further preferably 5 parts by mass or less.

[0059] The photoacid generator is excited by irradiation with light of a given wavelength or wavelength range, causing an acid generation reaction, thereby generating an acid. The acid generation reaction is, for example, a decomposition reaction of the photoacid generator. The wavelength of the light that causes the decomposition reaction varies depending on the type of the photoacid generator.

[0060] Examples of the photoacid generator include those that generate acid by ultraviolet irradiation. Compound. Compounds such as Cations and anions It is provided in salt form. Cations such as sulfonium and iodine Examples of anions include Cl - Br - ,I - 、ZnCl3 - 、HSO3 - 、BF4 - PF6 - 、AsF6 - 、SbF6 - 、CH3SO3 - CF3SO3 - 、C4F9HSO3 - 、(C6F5)4B - , and (C4H9)4B - The photoacid generator may be used alone or in combination of two or more. Preferred examples of the photoacid generator include sulfonium and (C6F5)4B - of Salt, Sulfonium and C4F9HSO3 - of Salt and iodine With C4F9HSO3 - of Salt.

[0061] From the viewpoint of ensuring good colorability in the color-variable layer 12, the amount of the photoacid generator is preferably 100 parts by mass or more, more preferably 300 parts by mass or more, and even more preferably 500 parts by mass or more relative to 100 parts by mass of the color-developing compound. From the viewpoint of ensuring durability of the hue of the adhesive sheet X, the amount is preferably 1000 parts by mass or less, more preferably 900 parts by mass or less, and even more preferably 800 parts by mass or less.

[0062] From the viewpoint of ensuring good colorability in the color-variable layer 12, the amount of the photoacid generator is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 5 parts by mass or more per 100 parts by mass of the polymer component. From the viewpoint of ensuring the durability of the adhesive sheet X, the amount is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 12 parts by mass or less.

[0063] The color-changing resin composition may contain other components as required. Examples of other components include solvents, antioxidants, antistatic agents, and sensitizers. Examples of solvents include ethyl acetate, methyl ethyl ketone, and toluene.

[0064] The color-changing layer 12 can be formed, for example, by applying the above-mentioned color-changing resin composition (varnish) on the base film 11 to form a coating film, and then drying and curing the coating film. When a thermoplastic resin is used as a polymer component, the color-changing resin composition can be prepared by dissolving and dispersing the polymer component, a colorant, and other components as required in a solvent. When a thermosetting resin is used as a polymer component, the color-changing resin composition can be prepared by dissolving and dispersing the monomer component forming the polymer component, a colorant, and other components as required in a solvent.

[0065] From the viewpoint of ensuring good colorability in the color-variable layer 12, the thickness of the color-variable layer 12 is preferably 3 μm or more, more preferably 7 μm or more, and even more preferably 10 μm or more. From the viewpoint of reducing the thickness of the adhesive sheet X, the thickness of the color-variable layer 12 is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 30 μm or less.

[0066] From the viewpoint of suppressing the thermal diffusion of the colorant as a low molecular weight component in the color-changing layer 12, the glass transition temperature of the color-changing layer 12 is preferably 40° C. or higher, more preferably 60° C. or higher, and further preferably 80° C. or higher. From the viewpoint of ensuring good processability of the base film 11, the glass transition temperature of the color-changing layer 12 is preferably 120° C. or lower, more preferably 100° C. or lower, and further preferably 90° C. or lower. The glass transition temperature of the color-changing layer 12 is preferably higher than the glass transition temperature of the adhesive layers 21 and 22.

[0067] From the viewpoint of ensuring the handling properties of the adhesive sheet X, the thickness of the substrate 10 is preferably 8 μm or more, more preferably 15 μm or more, and further preferably 20 μm or more. From the viewpoint of reducing the thickness of the adhesive sheet X, the thickness of the substrate 10 is preferably 300 μm or less, more preferably 200 μm or less, further preferably 150 μm or less, and particularly preferably 100 μm or less.

[0068] Adhesive layer 21 is a pressure-sensitive adhesive layer formed by an adhesive composition (the first adhesive composition). The adhesive composition includes a base polymer. As a base polymer, it is an adhesive component that exhibits adhesiveness. As a base polymer, for example, acrylic polymers, polyurethane polymers, polyamide polymers, and polyvinyl ether polymers can be cited. The base polymer can be used alone or in combination of two or more. From the viewpoint of ensuring good adhesiveness and transparency in the adhesive layer 21, as a base polymer, an acrylic polymer is preferably used.

[0069] The acrylic polymer is a copolymer containing a monomer component of (meth)acrylate at a ratio of 50% by mass or more. "(Meth)acrylic acid" refers to acrylic acid and / or methacrylic acid. As the (meth)acrylate, an alkyl (meth)acrylate can be preferably used, and an alkyl (meth)acrylate having an alkyl group with 1 to 20 carbon atoms can be more preferably used.

[0070] Examples of the alkyl (meth)acrylate include alkyl (meth)acrylates having a linear or branched alkyl group having 1 to 20 carbon atoms. Examples of such alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, and tert-butyl (meth)acrylate. Nonyl acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, isotridecyl (meth)acrylate, tetradecyl (meth)acrylate, isotetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate. The alkyl (meth)acrylate can be used alone or in combination of two or more. As the alkyl (meth)acrylate, from the viewpoint of achieving a balance between softness and adhesiveness in the adhesive sheet 10, it is preferred to use at least one first alkyl (meth)acrylate having a relatively large alkyl carbon number selected from the alkyl (meth)acrylate having an alkyl group with 1 to 12 carbon atoms, and at least one second alkyl (meth)acrylate having a relatively small alkyl carbon number. The first alkyl (meth)acrylate is preferably at least one selected from 2-ethylhexyl acrylate and dodecyl acrylate. The second alkyl (meth)acrylate is preferably at least one selected from methyl methacrylate and n-butyl acrylate.

[0071] From the viewpoint of appropriately expressing basic properties such as adhesiveness in the adhesive layer 21, the proportion of the (meth)acrylic acid alkyl ester in the monomer component is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. This proportion is, for example, 99% by mass or less.

[0072] The monomer component may include a copolymerizable monomer that can copolymerize with the (meth) alkyl acrylate. As the copolymerizable monomer, for example, a monomer having a polar group may be mentioned. As the monomer containing a polar group, for example, a hydroxyl group-containing monomer, a monomer having a ring containing a nitrogen atom, and a carboxyl group-containing monomer may be mentioned. The monomer containing a polar group helps to modify the acrylic polymer by introducing crosslinking points into the acrylic polymer, ensuring the cohesive force of the acrylic polymer, etc. For the modification of the acrylic polymer, the monomer containing a polar group may be included in the hard segment or in the soft segment.

[0073] The copolymerizable monomer preferably includes at least one selected from a hydroxyl group-containing monomer, a monomer having a ring containing a nitrogen atom, and a carboxyl group-containing monomer. More preferably, the copolymerizable monomer includes a hydroxyl group-containing monomer and / or a monomer having a ring containing a nitrogen atom.

[0074] Examples of the hydroxyl-containing monomer include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. As the hydroxyl-containing monomer, 2-hydroxyethyl (meth)acrylate can be preferably used, and 2-hydroxyethyl acrylate can be more preferably used.

[0075] The ratio of the hydroxyl-containing monomer in the monomer component is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoint of introducing a cross-linked structure into the acrylic polymer and ensuring the cohesive force in the adhesive layer 21. From the viewpoint of adjusting the polarity of the acrylic polymer (related to the compatibility of various additive components in the adhesive layer 21 with the acrylic polymer), the ratio is preferably 30% by mass or less, and more preferably 20% by mass or less.

[0076] Examples of the monomer having a nitrogen atom-containing ring include N-vinyl-2-pyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyl oxazole, N-(meth)acryloyl-2-pyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-vinylmorpholine, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1,3- Oxazine-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinyliso As the monomer having a ring containing a nitrogen atom, N-vinyl-2-pyrrolidone can be preferably used.

[0077] From the viewpoint of ensuring the cohesive force in the adhesive layer 21 and the adhesion of the adhesive layer 21 to the adherend, the proportion of the monomer having a ring containing a nitrogen atom in the monomer component is preferably 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more. From the viewpoint of adjusting the glass transition temperature of the acrylic polymer and adjusting the polarity of the acrylic polymer (related to the compatibility of various additive components in the adhesive layer 21 with the acrylic polymer), the proportion is preferably 30% by mass or less, and more preferably 20% by mass or less.

[0078] Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid.

[0079] From the viewpoint of introducing a crosslinked structure into the acrylic polymer, ensuring the cohesive force in the adhesive layer 21, and ensuring the adhesion of the adhesive layer 21 to the adherend, the proportion of the carboxyl group-containing monomer in the monomer component is preferably 1% by mass or more, more preferably 3% by mass or more, and further preferably 5% by mass or more. From the viewpoint of adjusting the glass transition temperature of the acrylic polymer and avoiding the risk of corrosion of the adherend caused by acid, the proportion is preferably 30% by mass or less, and more preferably 20% by mass or less.

[0080] The monomer component may contain other copolymerizable monomers. Examples of other copolymerizable monomers include acid anhydride monomers, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, alkoxy group-containing monomers, and aromatic vinyl compounds.

[0081] The copolymerizable monomers may be used alone or in combination of two or more.

[0082] The acrylic polymer can be formed by polymerizing the above-mentioned monomer components. Examples of the polymerization method include solution polymerization, bulk polymerization, and emulsion polymerization, and preferably solution polymerization. Examples of the polymerization initiator include a thermal polymerization initiator. The amount of the polymerization initiator used is, for example, 0.05 parts by mass or more, and, for example, 1 part by mass or less, relative to 100 parts by mass of the monomer components.

[0083] Examples of the thermal polymerization initiator include an azo polymerization initiator and a peroxide polymerization initiator. Examples of the azo polymerization initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis(2-methylpropionic acid) dimethyl ester, 4,4'-azobis-4-cyanovaleric acid, azobisisovaleronitrile, 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis[2-(5-methyl-2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(2-methylpropionamidine) disulfate, and 2,2'-azobis(N,N'-dimethyleneisobutylamidine) dihydrochloride. As a peroxide polymerization initiator, dibenzoyl peroxide, t-butyl peroxymaleate, and lauroyl peroxide are mentioned, for example.

[0084] From the viewpoint of ensuring the cohesive force in the adhesive layer 21, the weight average molecular weight of the base polymer is preferably 100,000 or more, more preferably 300,000 or more, and further preferably 500,000 or more. The weight average molecular weight is preferably 5,000,000 or less, more preferably 3,000,000 or less, and further preferably 2,000,000 or less. The weight average molecular weight of the acrylic polymer can be measured by gel permeation chromatography (GPC) and calculated by polystyrene conversion.

[0085] The glass transition temperature (Tg) of the base polymer is preferably 0° C. or lower, more preferably -10° C. or lower, and further preferably -20° C. or lower. The glass transition temperature is, for example, -80° C. or higher.

[0086] From the viewpoint of introducing a crosslinked structure into the base polymer, the adhesive composition may contain a crosslinking agent. Examples of the crosslinking agent include isocyanate crosslinking agents, epoxy crosslinking agents, Azoline crosslinking agent, an aziridine crosslinking agent, a carbodiimide crosslinking agent, and a metal chelate crosslinking agent. The crosslinking agent may be used alone or in combination of two or more.

[0087] As the isocyanate crosslinking agent, for example, toluene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and polymethylene polyphenyl isocyanate can be mentioned. In addition, as the isocyanate crosslinking agent, derivatives of these isocyanates can also be mentioned. As the isocyanate derivative, for example, isocyanurate modified bodies and polyol modified bodies can be mentioned. Examples of commercially available isocyanate crosslinking agents include CORONATE L (trimethylolpropane adduct of toluene diisocyanate, manufactured by Tosoh), CORONATE HL (trimethylolpropane adduct of hexamethylene diisocyanate, manufactured by Tosoh), CORONATE HX (isocyanurate of hexamethylene diisocyanate, manufactured by Tosoh), and TAKENATE D110N (trimethylolpropane adduct of xylylenediisocyanate, manufactured by Mitsui Chemicals).

[0088] Examples of the epoxy crosslinking agent include bisphenol A, epichlorohydrin type epoxy resins, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diamine glycidyl amine, N,N,N',N'-tetraglycidyl meta-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

[0089] From the viewpoint of ensuring the cohesive force of the adhesive layer 21, the amount of the crosslinking agent is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.07 parts by mass or more, relative to 100 parts by mass of the base polymer. From the viewpoint of ensuring good adhesion in the adhesive layer 21, the amount of the crosslinking agent is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less, relative to 100 parts by mass of the base polymer.

[0090] When a cross-linked structure is introduced into the base polymer, a cross-linking catalyst may be used to effectively carry out the cross-linking reaction. Examples of the cross-linking catalyst include dibutyltin dilaurate, tetra-n-butyl titanate, tetraisopropyl titanate, ferric acetylacetonate (NACEM ® Iron (III)), and butyltin oxide, and dibutyltin dilaurate can be preferably used. The amount of the crosslinking catalyst used is, for example, 0.0001 parts by mass or more, and for example, 1 part by mass or less, based on 100 parts by mass of the base polymer.

[0091] When a crosslinking catalyst is used, a crosslinking inhibitor that can be removed from the adhesive composition afterwards can also be matched in the adhesive composition. When dibutyltin dilaurate is used as a crosslinking catalyst, acetylacetone can be preferably used as a crosslinking inhibitor. In this case, in the adhesive composition, acetylacetone is coordinated to dibutyltin dilaurate, and the crosslinking reaction of the crosslinking agent relative to the base polymer is suppressed. In the manufacturing process described later of the adhesive sheet X, after the adhesive composition is applied to the substrate to form a coating film, acetylacetone can be volatilized by heating at a desired time, thereby removing it from the coating film. Thus, the crosslinking reaction of the crosslinking agent can be carried out.

[0092] The amount of the cross-linking inhibitor to be blended is, for example, 100 parts by mass or more, and for example, 5000 parts by mass or less, relative to 100 parts by mass of the cross-linking catalyst.

[0093] The adhesive composition may contain other components as necessary. Examples of other components include a silane coupling agent, an ultraviolet absorber, a tackifier, a plasticizer, a softener, an antioxidant, a surfactant, and an antistatic agent.

[0094] Examples of the ultraviolet absorber include benzotriazole ultraviolet absorbers, hydroxyphenyltriazine ultraviolet absorbers, benzophenone ultraviolet absorbers, salicylate ultraviolet absorbers, cyanoacrylate ultraviolet absorbers, and nickel complex salt ultraviolet absorbers. The ultraviolet absorbers may be used alone or in combination of two or more.

[0095] From the viewpoint of ensuring sufficient adhesion to the adherend, the thickness of the adhesive layer 21 is preferably 10 μm or more, more preferably 15 μm or more, and further preferably 20 μm or more. From the viewpoint of handling and thinning of the adhesive sheet X, the thickness of the adhesive layer 21 is preferably 300 μm or less, more preferably 200 μm or less, further preferably 100 μm or less, and particularly preferably 50 μm or less.

[0096] From the viewpoint of ensuring the transparency of the adhesive layer 21, the average transmittance of the adhesive layer 21 at a wavelength of 400 nm to 700 nm is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. Depending on the use of the adhesive sheet X, the average transmittance of the adhesive layer 21 at a wavelength of 400 nm to 700 nm may be, for example, 50% or less.

[0097] Adhesive layer 22 is a pressure-sensitive adhesive layer formed by an adhesive composition (the second adhesive composition). The second adhesive composition comprises a base polymer and other components used as required. The composition of the second adhesive composition may be the same as or different from the composition of the first adhesive composition described above. From the viewpoint of ensuring mutual homogeneity / equal properties in adhesive layers 21, 22, it is preferred that the composition of the second adhesive composition is the same as the composition of the first adhesive composition. When the properties of adhesive layers 21, 22 are homogeneous / equal, it is possible to use the adhesive sheet X as a double-sided adhesive sheet without distinguishing between the front and back with good operating efficiency, therefore preferred.

[0098] From the viewpoint of ensuring sufficient adhesion to the adherend, the thickness of the adhesive layer 22 is preferably 10 μm or more, more preferably 15 μm or more, and further preferably 20 μm or more. From the viewpoint of handling and thinning of the adhesive sheet X, the thickness of the adhesive layer 22 is preferably 300 μm or less, more preferably 200 μm or less, further preferably 100 μm or less, and particularly preferably 50 μm or less.

[0099] From the viewpoint of ensuring the transparency of the adhesive layer 22, the average transmittance of the adhesive layer 22 at a wavelength of 400 nm to 700 nm is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. Depending on the use of the adhesive sheet X, the average transmittance of the adhesive layer 22 at a wavelength of 400 nm to 700 nm may be, for example, 50% or less.

[0100] From the viewpoint of ensuring the transparency of the adhesive sheet X, the average transmittance T1 of the adhesive sheet X at a wavelength of 400nm to 700nm (the average transmittance before the color-changing layer 12 changes color) is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more. Specifically, such a configuration is suitable for inspecting the presence or absence of foreign matter and bubbles between the adhesive sheet X and the adherend after the adhesive sheet X is attached to the adherend. Depending on the use of the adhesive sheet X, the average transmittance T1 of the adhesive sheet X at a wavelength of 400nm to 700nm can be, for example, 50% or less.

[0101] The pressure-sensitive adhesive sheet X can be produced, for example, as follows.

[0102] First, a substrate 10, an adhesive layer 21, and an adhesive layer 22 are prepared. The substrate 10 can be produced by forming the color-changing layer 12 on the substrate film 11 as described above. The adhesive layer 21 can be formed by applying a first adhesive composition on a first release liner to form a coating film and then drying the coating film. The adhesive layer 22 can be formed by applying a second adhesive composition on a second release liner to form a coating film and then drying the coating film.

[0103] Next, the adhesive layer 21 is bonded to the first surface 10a of the substrate 10, and the adhesive layer 22 is bonded to the second surface 10b. Thus, an adhesive sheet X sandwiched between the first release liner and the second release liner can be obtained. When the adhesive sheet X is used, the release liner can be peeled off from the adhesive sheet X as needed.

[0104] The adhesive layer 21 can be formed by applying a first adhesive composition on the first surface 10a of the substrate 10 to form a coating film and then drying the coating film. The adhesive layer 22 can be formed by applying a second adhesive composition on the second surface 10b of the substrate 10 to form a coating film and then drying the coating film. By such a method, the adhesive sheet X can also be manufactured.

[0105] Figure 2A to Figure 2C An example of a method of using the pressure-sensitive adhesive sheet X is shown. This method includes a preparation step, a bonding step, and a color-changing portion forming step.

[0106] First, in the preparation process, such as Figure 2A As shown, a pressure-sensitive adhesive sheet X, a first member 31, and a second member 32 are prepared. The first member 31 is, for example, a display panel such as an organic EL panel. The first member 31 may also be other electronic devices and optical devices.

[0107] The second member 32 is, for example, a transparent substrate. Examples of the transparent substrate include a transparent plastic substrate and a transparent glass substrate.

[0108] Next, in the bonding process, Figure 2B As shown, the first member 31 and the second member 32 are joined via the adhesive sheet X. Thus, a laminate Z is obtained. In the laminate Z, the adhesive sheet X is arranged in contact with one surface of the first member 31 in the thickness direction, and the second member 32 is arranged in contact with one surface of the adhesive sheet X in the thickness direction.

[0109] After the bonding step, the presence or absence of foreign matter and bubbles between the members 31 and 32 and the adhesive sheet X is inspected as necessary.

[0110] Next, in the color changing portion forming process, as Figure 2C As shown, an external stimulus is applied to the color-changing layer 12 in the stacked body Z, and a color-changing portion 12a is formed in the color-changing layer 12. For example, the color-changing layer 12 is illuminated from the transparent second member 32 side through a mask pattern (not shown) for masking a given area in the color-changing layer 12. As a result, the portion of the color-changing layer 12 that is not masked by the mask pattern changes color. In the color-changing layer 12, when a color-developing compound and a photoacid generator are used as a colorant, an acid is generated by the photoacid generator in the portion of the color-changing layer 12 that is illuminated, and the color-developing compound develops color by reacting with the acid. As a result, a color-changing portion 12a is formed in the color-changing layer 12.

[0111] As the light source for illumination in this process, for example, ultraviolet LED lamp, high pressure mercury lamp and metal halide lamp can be cited. In addition, in the illumination of this process, a wavelength cut-off filter for cutting off a part of the wavelength range of the light emitted from the light source can be used as needed.

[0112] For example, as described above, the adhesive sheet X can be used for bonding between components. When the first component 31 is a display panel such as an organic EL panel, by providing the color-changing portion 12a in a pattern shape corresponding to (i.e., facing) a metal wiring formed on a pixel panel provided on the panel, external light reflection on the metal wiring can be suppressed.

[0113] As described above, the adhesive sheet X (color-changing adhesive sheet) of the present invention includes a color-changing layer 12 that can develop color by external stimulation in the substrate 10. Therefore, after the adhesive sheet X is attached to the adherend, the color-changing portion (at least a portion of the sheet when viewed from above) in the adhesive sheet X can be locally changed in color by applying an external stimulus. For such an adhesive sheet X, after attachment and before the color-changing portion is formed, the presence or absence of foreign matter and bubbles between the adhesive sheet X and the adherend can be detected.

[0114] In addition, for the adhesive sheet X, the first color change width W1 of the color change area formed in the color change layer 12 by applying the external stimulus in a linear form to the color change layer 12 as described above, and the second color change width W2 of the color change area after the heat treatment (85° C., 168 hours) satisfy 0.5≤W2 / W1≤1.5. Such an adhesive sheet X is suitable for suppressing the degradation (bleeding, fading, uneven color tone, etc.) of the color change part 12a after the color change part 12a is formed in the color change layer 12 by applying the external stimulus.

[0115] As described above, the adhesive sheet X can change the color of at least a portion of the color-changing layer 12 after being attached to an adherend, and is suitable for suppressing the degradation of the color-changing portion 12a of the color-changing layer 12. Suppression of degradation of the color-changing portion in the color-changing layer 12 helps maintain the functional characteristics of the color-changing portion 12a, such as design, shielding, and anti-reflection.

[0116] The adhesive sheet X may also be Figure 3 A single-sided adhesive sheet as shown. Figure 3 The adhesive sheet X shown is similar to Figure 1 The same is true for the adhesive sheet X shown. Specifically, Figure 3 The adhesive sheet X includes a substrate 10 and an adhesive layer 21 disposed on the first surface 10a side of the substrate 10. In addition, the adhesive sheet X may also be Figure 4 A single-sided adhesive sheet as shown. Figure 4 The adhesive sheet X shown is similar to Figure 1 The same is true for the adhesive sheet X shown. Specifically, Figure 4 The pressure-sensitive adhesive sheet X includes a substrate 10 and a pressure-sensitive adhesive layer 22 disposed on the second surface 10b side of the substrate 10. The pressure-sensitive adhesive sheet X, which is a single-sided pressure-sensitive adhesive sheet, can be used as a marking transfer sheet, for example.

[0117] like Figure 5 As shown, the adhesive sheet X may include a color-changing substrate 10A instead of the substrate 10. The color-changing substrate 10A has both the supporting function of the substrate film 11 and the color-changing function of the color-changing layer 12. Such a color-changing substrate 10A can be prepared, for example, by applying a color-changing resin composition containing a polymer component, a colorant, and other components as required on a release liner to form a coating film and then drying the coating film. The color-changing substrate 10A can be prepared by extrusion molding of the color-changing resin composition. The polymer component, the colorant and other components are the same as those described above for the color-changing layer 12. From the viewpoint of ensuring the handling properties of the adhesive sheet X and the good colorability of the color-changing substrate 10, the thickness of the color-changing substrate 10A is preferably 8 μm or more, more preferably 15 μm or more, and further preferably 20 μm or more. From the viewpoint of reducing the thickness of the adhesive sheet X, the thickness of the substrate 10 is preferably 300 μm or less, more preferably 200 μm or less, further preferably 150 μm or less, and particularly preferably 100 μm or less. In addition, the adhesive sheet X having the color-changing substrate 10A may be a single-sided adhesive sheet. That is, the adhesive sheet X having the color-changing substrate 10A may also have a Figure 5 The illustrated structure does not include the adhesive layer 21 or the adhesive layer 22 (not shown).

[0118] Example

[0119] The present invention is specifically described below with reference to the following embodiments, but the present invention is not limited to the embodiments. In addition, the specific numerical values ​​of the following amounts (contents), physical property values, parameters, etc. can be replaced with the upper limit (numerical value defined in the form of "below" or "less than") or the lower limit (numerical value defined in the form of "above" or "exceeding") of the amounts (contents), physical property values, parameters, etc. corresponding to them recorded in the above-mentioned "Specific Embodiments" part.

[0120] [Example 1]

[0121] <Preparation of base material>

[0122] First, the first polyester resin P1 (trade name "Elitel UE-3210", a saturated copolymerized polyester resin, manufactured by UNITIKA Corporation) was dissolved in ethyl acetate to obtain a resin solution. The resin solution contained 33% by mass of the first polyester resin P1. Next, 0.25 parts by mass (solid content conversion amount) of an isocyanate crosslinking agent (trade name "TAKENATE D110N", a 75% ethyl acetate solution of a trimethylolpropane adduct of xylylenediisocyanate, manufactured by Mitsui Chemicals, Inc.) as a crosslinking agent, 0.01 parts by mass (solid content conversion amount) of dibutyltin dilaurate (trade name "OL-1", a 1% ethyl acetate solution, manufactured by Tokyo Fine Chemical Co., Ltd.) as a crosslinking catalyst, 3 parts by mass of acetylacetone as a crosslinking inhibitor (ligand for the crosslinking catalyst), 2 parts by mass of a colorless pigment (trade name "S-205", manufactured by Yamada Chemical Industry Co., Ltd.) as a color-developing compound, and 7 parts by mass of a photoacid generator (trade name "CPI-310B", manufactured by San-Apro Co., Ltd.) were added to the resin solution per 100 parts by mass of the first polyester resin P1, and the mixture was mixed to prepare a color-changing resin composition.

[0123] Next, the color-changing resin composition was applied to a PET film (trade name "T912E75UE80", polyester film, thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) as a substrate film to form a coating film. Next, the coating film was dried and cured by heating at 150° C. for 3 minutes. Thus, a color-changing layer with a thickness of 25 μm was formed on the substrate film. The substrate (substrate film / color-changing layer) in Example 1 was prepared as described above. The color-changing layer of the substrate in Example 1 contains the first polyester resin P1 as a polymer component.

[0124] <Formation of Adhesive Layer>

[0125] First, in a reaction vessel equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen inlet pipe, at 60° C., in a nitrogen atmosphere, a mixture containing 63 parts by mass of 2-ethylhexyl acrylate (2EHA), 9 parts by mass of methyl methacrylate (MMA), 13 parts by mass of 2-hydroxyethyl acrylate (HEA), 15 parts by mass of N-vinyl-2-pyrrolidone (NVP), 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 233 parts by mass of ethyl acetate as a solvent was stirred for 7 hours (polymerization reaction). Thus, a polymer solution containing an acrylic polymer was obtained. The weight average molecular weight (Mw) of the acrylic polymer in the polymer solution was 1.2 million.

[0126] Next, to the polymer solution, 0.25 parts by mass (solid content conversion amount) of an isocyanate crosslinking agent (trade name "TAKENATE D110N", manufactured by Mitsui Chemicals, Inc.) as a crosslinking agent, 0.01 parts by mass (solid content conversion amount) of dibutyltin dilaurate (trade name "OL-1", manufactured by Tokyo Fine Chemical Co., Ltd.) as a crosslinking catalyst, and 3 parts by mass of acetylacetone as a crosslinking inhibitor were added and mixed per 100 parts by mass of the acrylic polymer to prepare an adhesive composition.

[0127] Next, the adhesive composition was applied to the release-treated surface of the first release liner (trade name "Diafoil MRF # 38", polyester film, manufactured by Mitsubishi Chemical Corporation) with a thickness of 38 μm and a release treatment on one side to form a coating film. Next, the coating film was dried by heating at 132° C. for 3 minutes. Thus, an adhesive layer with a thickness of 25 μm was formed on the first release liner. Next, the release-treated surface of the second release liner (trade name "Diafoil MRE # 38", polyester film, manufactured by Mitsubishi Chemical Corporation) with a thickness of 38 μm and a release treatment on one side was attached to the adhesive layer on the first release liner. Then, an aging treatment was performed at 60° C. for 24 hours to allow the cross-linking reaction in the adhesive layer to proceed. An adhesive layer with a release liner was prepared as described above.

[0128] <Preparation of Adhesive Sheet>

[0129] First, the second release liner is peeled off from the adhesive layer with the release liner. Next, the adhesive layer exposed by the peeling is attached to the substrate film side of the above-mentioned substrate. The adhesive sheet of Example 1 is prepared as described above. The adhesive sheet of Example 1 is a color-changing adhesive sheet having a substrate (color-changing layer, substrate film) and an adhesive layer on the substrate film, and the adhesive layer side surface is covered by the first release liner.

[0130] [Example 2]

[0131] In the preparation of the substrate, a second polyester resin P2 (trade name "Elitel UE-9200", a saturated copolymerized polyester resin, manufactured by UNITIKA Co., Ltd.) was used instead of the first polyester resin P1 as the polymer component of the color-changing layer. Except for this, the adhesive sheet of Example 2 (a color-changing adhesive sheet with a release liner) was prepared in the same manner as the adhesive sheet of Example 1.

[0132] [Example 3]

[0133] In the preparation of the substrate, a third polyester resin P3 (trade name "Elitel UE-9800", a saturated copolymerized polyester resin, manufactured by UNITIKA Co., Ltd.) was used as the polymer component of the color-changing layer instead of the first polyester resin P1. Except for this, the adhesive sheet of Example 3 (a color-changing adhesive sheet with a release liner) was prepared in the same manner as the adhesive sheet of Example 1.

[0134] [Example 4]

[0135] <Preparation of base material>

[0136] First, to a first acrylic resin solution containing a first acrylic resin P4 (trade name "ACRIT1403EA", manufactured by TAISEI FINE CHEMICAL Co., Ltd.), 2 parts by mass of a colorless pigment (trade name "S-205", manufactured by Yamada Chemical Industry Co., Ltd.) as a color-developing compound and 7 parts by mass of a photoacid generator (trade name "CPI-310B", manufactured by San-Apro Co., Ltd.) were added and mixed per 100 parts by mass of the first acrylic resin P4 to prepare a color-changeable resin composition.

[0137] Next, the color-changing resin composition was applied to a PET film (trade name "T912E75UE80", polyester film, thickness 75 μm, manufactured by Mitsubishi Chemical Corporation) as a substrate film to form a coating film. Next, the coating film was dried and cured by heating at 150° C. for 3 minutes. Thus, a color-changing layer with a thickness of 25 μm was formed on the substrate film. The substrate (substrate film / color-changing layer) in Example 4 was prepared as described above. The color-changing layer of the substrate in Example 4 contains the first acrylic resin P4 as a polymer component.

[0138] <Formation of Adhesive Layer>

[0139] A release liner-attached pressure-sensitive adhesive layer (first release liner / pressure-sensitive adhesive layer / second release liner) was prepared in the same manner as described above in Example 1.

[0140] <Preparation of Adhesive Sheet>

[0141] First, the second release liner is peeled off from the adhesive layer with the release liner. Next, the adhesive layer exposed by the peeling is attached to the substrate film side of the above-mentioned substrate. The adhesive sheet of Example 4 is prepared as described above. The adhesive sheet of Example 4 is a color-changing adhesive sheet having a substrate (color-changing layer, substrate film) and an adhesive layer on the substrate film, and the adhesive layer side surface is covered by the first release liner.

[0142] [Example 5]

[0143] In the preparation of the color-changing resin composition, a second acrylic resin solution containing a second acrylic resin P5 (trade name "ACRIT 1BR-305MK", manufactured by TAISEI FINE CHEMICAL Co., Ltd.) was used instead of the first acrylic resin solution. The adhesive sheet of Example 5 (a color-changing adhesive sheet with a release liner) was prepared in the same manner as the adhesive sheet of Example 4.

[0144] [Example 6]

[0145] In the preparation of the color-changing resin composition, a third acrylic resin solution containing the third acrylic resin P6 (trade name "ACRIT 1LO-9608", manufactured by TAISEI FINE CHEMICAL Co., Ltd.) was used instead of the first acrylic resin solution. An adhesive sheet of Example 6 (a color-changing adhesive sheet with a release liner) was prepared in the same manner as the adhesive sheet of Example 4.

[0146] [Example 7]

[0147] In the preparation of the color-changing resin composition, a pressure-sensitive adhesive sheet of Example 7 (a color-changing pressure-sensitive adhesive sheet with a release liner) was prepared in the same manner as the pressure-sensitive adhesive sheet of Example 4, except that a fourth acrylic resin solution containing a fourth acrylic resin P7 (trade name "ACRIT 0403KA", manufactured by TAISEI FINE CHEMICAL Co., Ltd.) was used instead of the first acrylic resin solution.

[0148] [Example 8]

[0149] First, a color-changing resin composition was prepared in the same manner as described above for Example 4 except that the fourth acrylic resin solution containing the fourth acrylic resin P7 (trade name "ACRIT0403KA", manufactured by TAISEI FINE CHEMICAL Co., Ltd.) was used instead of the first acrylic resin solution. Next, the color-changing resin composition was applied to the release-treated surface of the first release liner (trade name "Diafoil MRF#38", manufactured by Mitsubishi Chemical Corporation) with a thickness of 38 μm, which had been subjected to release treatment on one side, to form a coating film. Next, the coating film was dried by heating at 130° C. for 3 minutes. Thus, a color-changing layer with a thickness of 25 μm was formed on the first release liner. On the other hand, an adhesive layer with a release liner (first release liner / adhesive layer / second release liner) was prepared in the same manner as described above for Example 1. Then, the second release liner was peeled off from the adhesive layer with the release liner. Next, the adhesive layer exposed by the peeling was attached to the above-mentioned color-changing layer on the first release liner. As described above, a PSA sheet of Example 8 was prepared. The PSA sheet of Example 8 is a color-variable PSA sheet having a two-layer structure including a color-variable layer and a PSA layer, and the PSA layer-side surface is covered with a first release liner.

[0150] [Comparative Example 1]

[0151] In the preparation of the substrate, the fourth polyester resin P8 (trade name "Elitel UE-3220", a saturated copolymerized polyester resin, manufactured by UNITIKA Co., Ltd.) was used instead of the first polyester resin P1 as the polymer component of the color-changing layer. Otherwise, the adhesive sheet of Comparative Example 1 (a color-changing adhesive sheet with a release liner) was prepared in the same manner as the adhesive sheet of Example 1.

[0152] [Comparative Example 2]

[0153] In the preparation of the substrate, the fifth polyester resin P9 (trade name "Elitel UE-3500", a saturated copolymerized polyester resin, manufactured by UNITIKA Co., Ltd.) was used instead of the first polyester resin P1 as the polymer component of the color-changing layer. Otherwise, the adhesive sheet of Comparative Example 2 (a color-changing adhesive sheet with a release liner) was prepared in the same manner as the adhesive sheet of Example 1.

[0154] <Glass transition temperature>

[0155] The glass transition temperatures of the polyester resins P1 to P3, P8, and P9 and the acrylic resins P4 to P7 used as the polymer component of the color-variable layer were examined as follows.

[0156] First, a sample for measuring the glass transition temperature was prepared. In the preparation of each sample of polyester resins P1 to P3, P8, and P9, specifically, first, the polyester resin to be measured for the glass transition temperature was finely crushed. Next, about 5 mg of the crushed polyester resin was placed in an open aluminum tank (sample container). In this way, a sample for measurement (about 5 mg) was prepared. On the other hand, in the preparation of each sample of acrylic resins P4 to P7, specifically, first, about 130 g of an acrylic resin solution containing an acrylic resin to be measured for the glass transition temperature was placed in an open aluminum tank (sample container). Next, by heating at 130°C for 2 hours, the solvent was evaporated from the open tank, and the acrylic resin was dried. In this way, a sample for measurement (about 5 mg) was prepared.

[0157] Next, the sample for measurement was subjected to differential scanning calorimetry using a differential scanning calorimeter (trade name "DSCQ2000", manufactured by TA Instruments). In this measurement, the measurement temperature range was set to -30°C to 250°C, and the heating rate was set to 10°C / min. Through this measurement, a DSC curve was obtained. Then, in the obtained DSC curve, the midpoint glass transition temperature was obtained based on the "method for determining the glass transition temperature" of JIS K7121 (1987). Its value is shown in Table 1 as the glass transition temperature Tg (°C) of the polymer component.

[0158] <Transmittance before illumination>

[0159] For each of the pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 1 and 2, the average transmittance at a wavelength of 400 nm to 700 nm was examined as follows.

[0160] First, a sample for measurement was prepared. Specifically, after the first release liner was peeled off from the adhesive layer in the adhesive sheet (color-changing layer / base film / adhesive layer / first release liner), the adhesive layer exposed by the peeling was attached to Eagle glass (thickness 0.55 mm, made by Matsunami Glass Co., Ltd.), thereby obtaining a sample for measurement. Then, the transmittance of the sample for measurement at a wavelength of 400nm~700nm was measured using a transmittance measuring device (trade name "U4150 spectrophotometer", made by Hitachi High-Tech Co., Ltd.). In this measurement, the sample for measurement was set in the device in such a way that light was irradiated from the Eagle glass side to the sample for measurement. In addition, in this measurement, the measurement result (transmittance spectrum) obtained by measuring only Eagle glass under the same conditions was used as a baseline. The average transmittance (wavelength 400nm~700nm) measured was used as the average transmittance T1 (%) before UV irradiation and is shown in Table 1.

[0161] <Colorability>

[0162] The color-variable layer of each of the pressure-sensitive adhesive sheets of Examples 1 to 8 and Comparative Examples 1 and 2 was examined for colorability by ultraviolet irradiation as described below.

[0163] First, the adhesive sheet (variable color layer / base film / adhesive layer / first release liner) was irradiated with ultraviolet light (UV). Specifically, in an environment of 23°C and a relative humidity of 50%, the adhesive sheet was irradiated with UV from the variable color layer side (first UV irradiation). As a result, the colorless pigment in the variable color layer reacted with the photoacid generator to color the variable color layer. During UV irradiation, a UV-LED lamp with a wavelength of 365nm in a UV-LED irradiation device (model "QEL-350-RU6W-CW-MY") manufactured by Quark Technology Co., Ltd. was used as a light source, and the cumulative irradiation light amount in the range of wavelengths of 320 to 390nm was set to 8000mJ / cm 2 .

[0164] Next, a sample for measurement was prepared. Specifically, after the first release liner was peeled off from the adhesive layer in the above-mentioned adhesive sheet (color-changing layer / base film / adhesive layer / first release liner) after ultraviolet irradiation, the adhesive layer exposed by the peeling was bonded to Eagle glass (thickness 0.55mm, made by Matsunami Glass Co., Ltd.), thereby obtaining a sample for measurement. Then, the transmittance of the sample for measurement at a wavelength of 400nm~700nm was measured using a transmittance measuring device (trade name "U4150 spectrophotometer", made by Hitachi High-Tech Co., Ltd.). In this measurement, the sample for measurement was set in the device in such a way that light was irradiated from the Eagle glass side to the sample for measurement. In addition, in this measurement, the measurement result (transmittance spectrum) obtained by measuring only Eagle glass under the same conditions was used as a baseline. The measured average transmittance (wavelength 400nm~700nm) is used as the average transmittance T2 (%) after UV irradiation and is shown in Table 1.

[0165] <Durability test>

[0166] For each of the PSA sheets of Examples 1 to 8 and Comparative Examples 1 and 2, the degree of suppression of change in the discolored portion formed was examined as follows.

[0167] First, the adhesive sheet (variable color layer / base film / adhesive layer / first release liner) is irradiated with ultraviolet light through a photomask having linear openings, thereby forming linear color-changing portions in the variable color layer. The photomask is formed of a dry film photoresist disposed on the side surface of the variable color layer in the adhesive sheet, and the line width of the opening of the photomask is set to 100 μm. During the ultraviolet irradiation, a high-pressure mercury lamp in a lamp-type UV irradiation system (model "UL-750") manufactured by HOYA Corporation is used as a light source, and ultraviolet light is irradiated to the variable color layer through the photomask, and the accumulated irradiation light amount is set to 1000 mJ / cm 2 (Cumulative amount of irradiation light within the wavelength range of 320 to 390 nm).

[0168] Next, the line width of the linear discoloration portion formed in the variable color layer was measured (measurement of the initial line width). Specifically, first, the linear discoloration portion formed in the variable color layer was observed by a digital microscope (trade name "VHX-8000", manufactured by KEYENCE), and a portion of the discoloration portion and its vicinity were photographed at a magnification of 150 times. Next, the photographed image was binarized by image analysis software. Next, the line width of the linear discoloration portion (the first discoloration width W1) was measured in the binarized image.

[0169] Next, the PSA sheet having the linear color-changing portion formed in the color-changing layer (color-changing layer / base film / adhesive layer / first release liner) was subjected to a heat treatment at 85° C. for 168 hours (durability test).

[0170] Next, the line width (second discoloration width W2) of the linear discoloration portion in the discoloration layer of the adhesive sheet after the durability test was measured. The specific measurement method is the same as the measurement method described above for the measurement of the initial line width. The first discoloration width W1 of the linear discoloration portion before the durability test, the second discoloration width W2 of the linear discoloration portion after the durability test, and the rate of change (W2 / W1) of the second discoloration width W2 relative to the first discoloration width W1 are shown in Table 1.

[0171] The rate of change of the line width of the linear discoloration portion in the color-variable layer (W2 / W1) is smaller in each of the adhesive sheets of Examples 1 to 8 than in the adhesive sheets of Comparative Examples 1 and 2. In each of the adhesive sheets of Examples 1 to 8, W1 and W2 satisfy 0.5≤W2 / W1≤1.5. That is, in each of the adhesive sheets of Examples 1 to 8, the change (deterioration) of the discoloration portion of the color-variable layer is suppressed compared to the adhesive sheets of Comparative Examples 1 and 2.

[0172]

[0173] The above-mentioned embodiments are examples of the present invention, and the present invention is not to be construed in a limitative manner by the embodiments. It will be apparent to those skilled in the art that modifications of the present invention are included in the appended claims.

[0174] Industrial Applicability

[0175] The color-variable pressure-sensitive adhesive sheet of the present invention can be used as a pressure-sensitive adhesive sheet disposed on the image display side of a pixel panel in a display panel, for example.

Claims

1. A color-changing adhesive sheet, comprising: A substrate having a first surface and a second surface opposite to the first surface, and an adhesive layer disposed on the first surface, The substrate comprises a color-changeable layer capable of changing color by external stimulation, The first color change width W1 of the color change region formed in the color change layer by applying the external stimulus in a linear form to the color change layer, and the second color change width W2 of the color change region after the color change layer is further heated at 85°C for 168 hours satisfy 0.5≤W2 / W1≤1.

5.

2. The color-changeable adhesive sheet according to claim 1, wherein: The color-variable layer includes a polymer component having a glass transition temperature of 40° C. or higher and a colorant capable of developing color by the external stimulus.

3. The color-changeable adhesive sheet according to claim 2, wherein: The colorant is a color-developing compound that develops color by reacting with an acid, The color-changeable layer further contains a photoacid generator. 4 . The color-variable adhesive sheet according to claim 1 , which has an average transmittance of 70% or more at a wavelength of 400 nm to 700 nm before being given the external stimulus. The color-changeable adhesive sheet according to claim 1 , further comprising an adhesive layer disposed on the second surface.

6. The color-changeable adhesive sheet according to any one of claims 1 to 5, wherein The substrate further includes a substrate film, and has a multilayer structure including the substrate film and the color-variable layer.

7. The color-changeable adhesive sheet according to any one of claims 1 to 5, wherein The substrate is a color-changeable layer.

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