Adhesive sheets, laminated sheets and displays

Abstract

The present invention provides adhesive sheets, laminated sheets, and displays that suppress peeling and bubbles from the adherend during repeated bending and prolonged maintenance of a bent state. [Solution] An adhesive sheet formed from an adhesive composition comprising (meth)acrylic resin (a) and at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2), satisfying (i), (ii), and (iiia). (i) Haze value is less than 1.5%. (ii) Adhesion to the glass plate at 25°C is 3N / 25mm or more. (iiia) Shear storage modulus at -20°C is less than 500 kPa.

Description

Technical Field

[0001] The present disclosure relates to an adhesive sheet, a laminated sheet using the same, and a display.

Background Art

[0002] An adhesive sheet having excellent transparency is used for attaching members of an image display device such as a liquid crystal display (LCD) or an organic electroluminescence display (OLED). For example, an adhesive sheet having excellent transparency is used for attaching a transparent conductive film used for a touch panel to a support glass. Further, such an adhesive sheet is used for attaching a liquid crystal module or an organic EL module to a polarizing plate.

[0003] In recent years, flexible displays such as foldable displays (Foldable display) or rollable displays (Rollable display) using a flexible substrate such as plastic have been developed. Such flexible displays are superior in light weight, thinness, flexibility, and further in designability as compared with conventional flat displays using a glass substrate.

[0004] As an adhesive sheet for a flexible device, Patent Document 1 discloses an assembly layer derived from a precursor containing about 0 to 50% by weight of C1 to C9 alkyl (meth)acrylate, about 40 to 99% by weight of C10 to C24 (meth)acrylate, about 0 to 30% by weight of hydroxyl (meth)acrylate, about 0 to 10% by weight of a non-hydroxyl functional polar monomer, and about 0 to 5% by weight of a crosslinking agent. Further, Patent Document 2 discloses an adhesive for a bending device in which the storage elastic modulus change degree, which is a value obtained by dividing the storage elastic modulus G'(-20) at -20°C by the storage elastic modulus G'(85) at 85°C, is more than 2.5, and the storage elastic modulus G'(-20) at -20°C is 0.070 MPa or more and 0.200 MPa or less.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] International Publication No. 2018 / 102179 [Patent Document 2] Japanese Patent Publication No. 2020-139034 [Overview of the project] [Problems that the invention aims to solve]

[0006] Flexible devices such as foldable displays are required to have properties (dynamic flexibility) that suppress peeling due to repeated deformation and also suppress air bubbles that cause wrinkles and sagging, at an even more stringent level than before. Furthermore, properties that prevent peeling and air bubbles from forming when the device is held in a bent state for a long period of time (static flexibility) are also required.

[0007] This disclosure is made in view of the above background and aims to provide reliable adhesive sheets, laminated sheets, and displays that are applicable to optical applications and suppress peeling from the adherend and the generation of bubbles during both repeated bending (dynamic bending) and prolonged holding of a bent state (static bending). [Means for solving the problem]

[0008] In order to achieve the above objectives, the inventors conducted extensive research and found that the problems of this disclosure can be solved in the following embodiments, and thus completed this disclosure. [1]: Formed from an adhesive composition comprising (meth)acrylic resin (a) and at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2), Silicone oligomer (s1) is, (α) Silicone oligomers having a functional group selected from the group consisting of a hydroxyl group, an epoxy group, and a (meth)acrylate group at one end of the molecular chain, and / or (β) A silicone oligomer having a functional group selected from the group consisting of a hydroxyl group, an epoxy group, and a (meth)acrylate group at both ends of the molecular chain, The silicone oligomer derivative (s2) is The reaction product is a reaction between a silicone oligomer (s1) and a compound (s3) having 1 to 18 carbon atoms and a reactive functional group that reacts with the functional group of the silicone oligomer (s1). An adhesive sheet that satisfies the following conditions (i), (ii), and (iiia). (i) The haze value is less than 1.5%. (ii) The adhesive strength to the glass plate at 25°C is 3N / 25mm or more. (iiia) The shear storage modulus at -20°C is less than 500 kPa. [2]: Formed from an adhesive composition comprising (meth)acrylic resin (a) and at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2), Silicone oligomer (s1) is, (α) Silicone oligomers having a functional group selected from the group consisting of a hydroxyl group, an epoxy group, and a (meth)acrylate group at one end of the molecular chain, and / or (β) A silicone oligomer having a functional group selected from the group consisting of a hydroxyl group, an epoxy group, and a (meth)acrylate group at both ends of the molecular chain, The silicone oligomer derivative (s2) is The reaction product is a reaction between a silicone oligomer (s1) and a compound (s3) having 1 to 18 carbon atoms and a reactive functional group that reacts with the functional group of the silicone oligomer (s1). An adhesive sheet that satisfies the following conditions (i), (ii), and (iiib). (i) The haze value is less than 1.5%. (ii) The adhesive strength to the glass plate at 25°C is 3N / 25mm or more. (iiib) The Tg in DSC is below -40°C. [3]: The adhesive sheet according to [1] or [2], wherein the number average molecular weight of the silicone oligomer (s1) is 5000 or less. [4]: The adhesive sheet according to any one of [1] to [3], comprising (meth)acrylic resin (a), which is obtained by polymerizing monomers comprising a (meth)acrylic monomer having a hydroxyl group, a (meth)acrylic monomer having a branched alkyl group having 4 to 12 carbon atoms, and a (meth)acrylic monomer having a linear alkyl group having 6 to 18 carbon atoms. [5]: The adhesive sheet is further an adhesive sheet according to any of [1] to [4] that satisfies (iv) below. (iv) When a stress of 10 kPa is applied at -20°C for 10 minutes, the strain α is 50-400%, and when the residual strain after 10 minutes from when the stress is reduced to 0 kPa is denoted as β, the recovery rate obtained by (α-β) / α×100 is 70% or more. [6]: A laminated sheet in which an adhesive sheet described in any of [1] to [5] is sandwiched between a first separator and a second separator. [7]: A display equipped with an adhesive sheet as described in any of [1] to [5]. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide highly reliable adhesive sheets, laminated sheets, and displays that are applicable to optical applications and suppress peeling from the adherend and the generation of bubbles during both repeated bending (dynamic bending) and prolonged bending (static bending). [Brief explanation of the drawing]

[0010] [Figure 1] A schematic cross-sectional view showing an example of the laminated sheet of this embodiment. [Figure 2] A partially enlarged view illustrating the teardrop shape of this embodiment. [Modes for carrying out the invention]

[0011] Hereinafter, the present disclosure will be described in detail. The embodiments described below illustrate an example of the present disclosure, and the present disclosure includes modifications implemented within the scope that does not change the gist of the present disclosure. In this specification, the lower and upper limits described before and after "~" are included in the range. Unless otherwise noted, each of the various compounding components can be used alone or in combination of two or more. When two or more are used in combination, the content uses the total value. Also, the numerical values specified in this specification are values obtained by the methods described in this specification. The adhesive sheet is synonymous with an adhesive film, an adhesive tape, an adhesive label, etc. (Meth)acrylic means at least one of acrylic and methacrylic, and (meth)acrylate means at least one of acrylate and methacrylate.

[0012] 1. Adhesive Sheet and Laminated Sheet <First Embodiment> The adhesive sheet according to the first embodiment is formed from an adhesive composition containing a (meth)acrylic resin (a) and at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2). The silicone oligomer (s1) is at least one of the following (α) and (β). (α) A silicone oligomer having a functional group selected from the group consisting of a hydroxyl group, an epoxy group, and a (meth)acrylate group at one end of the molecular chain. (β) A silicone oligomer having a functional group selected from the group consisting of a hydroxyl group, an epoxy group, and a (meth)acrylate group independently at both ends of the molecular chain. The silicone oligomer derivative (s2) is a reaction product of a silicone oligomer (s1) and a compound (s3) having 1 to 18 carbon atoms and having a reactive functional group that reacts with the functional group of the silicone oligomer (s1). The functional group is at least one of a hydroxyl group, an epoxy group, and a (meth) acrylate group. When the silicone oligomer (s1) used for the production of the silicone oligomer derivative (s2) is (β), it is only necessary that at least one of the functional groups at both ends of the molecular chain reacts with the compound (s3). When the functional groups at both ends react with the compound (s3), the compounds (s3) may be the same or different.

[0013] The adhesive sheet of the first embodiment satisfies the following (i), (ii), and (iiia). (i) The haze value is less than 1.5%. (ii) The adhesive force to a glass plate at 25 ° C is 3 N / 25 mm or more. (iiia) The shear storage modulus at -20 ° C is less than 500 kPa.

[0014] According to the adhesive sheet of the first embodiment, it is formed from an adhesive composition containing a (meth) acrylic resin (a) and at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2). By satisfying the above (i), (ii), and (iiia), it is possible to provide an adhesive sheet that has excellent flexibility while having transparency, adhesive force, cohesive force, and resilience of the adhesive sheet. Particularly, in a complex shape such as a teardrop, an excellent effect can be obtained at room temperature (23 ° C). Furthermore, in the temperature range from low temperature (-20 ° C) to high temperature (60 ° C), peeling and lifting of the adhesive sheet from the adherend can be suppressed. By combining at least one of the silicone oligomer (s1) and the silicone oligomer derivative (s2) with the (meth) acrylic resin (a), it is considered that flexibility that can withstand repeated bending can be imparted. In addition, by using an adhesive sheet in which the above (ii) and the above (iiia) are combined, it is considered that peeling and lifting from the adherend can be suppressed, and the occurrence of peeling and lifting from the adherend can also be suppressed in repeated bending.

[0015] The adherend of the adhesive sheet of the first embodiment is not limited. Examples of materials include acrylic resins such as polyethylene terephthalate and polymethyl methacrylate (PMMA), transparent plastic films such as polycarbonate, polycycloolefin, and polyimide, and optical glass. The adhesive sheet of the first embodiment can be used for a wide range of adhesive applications to adherends, but it is particularly suitable as an adhesive sheet for optical applications because it has excellent transparency and visibility, and it is particularly suitable as an adhesive sheet for flexible display applications because it does not easily whiten at the bent parts even after repeated bending and has excellent transparency and adhesive strength. The adhesive layer is preferably a single layer, but it may also be a multi-layer structure. In the case of a multi-layer structure, adhesive layers of the same composition may be laminated, or adhesive layers of different compositions may be laminated.

[0016] An example of a laminated sheet according to the first embodiment is shown in Figure 1. As shown in the figure, the laminated sheet 10 is made up of an adhesive sheet 1 sandwiched between a first separator 2 and a second separator 3. The first separator and the second separator (hereinafter collectively referred to simply as "separators") are release sheets that peel off from the adhesive sheet. The separator has a release layer formed by coating a release agent onto a substrate such as paper, plastic film, or synthetic paper. Examples of release agents include silicone, alkyd resin, melamine resin, fluororesin, and acrylic resin. The thickness of the separator is not particularly limited, and is, for example, about 10 to 200 μm.

[0017] The haze value of the adhesive sheet in the first embodiment is less than 1.5% (as stated in (i) above). This makes it possible to provide a laminate with high transparency, for example, when bonding transparent adherends together. From the viewpoint of achieving better transparency, the haze value in (i) above is preferably 1.2% or less, more preferably 0.8% or less, even more preferably 0.5% or less, and even more preferably 0.3% or less. The lower limit of the haze value is not limited, and the smaller the better. Considering the refractive index and adhesive strength, the lower limit can be, for example, 0.05%. In addition, the total light transmittance (380~780nm) of the adhesive sheet is preferably 85% or more, and more preferably 90% or more. Here, the haze value is expressed as the ratio of the diffuse transmittance to the total light transmittance of the adhesive sheet. Total light transmittance is the ratio of the amount of light transmitted through the adhesive sheet to the amount of light that enters the adhesive sheet. Diffuse transmittance is the ratio of the amount of light that passes through an object in directions other than the straight-line direction to the amount of light that enters the object, i.e., the amount of light that is diffused and transmitted. The haze value is the value obtained by the example described later.

[0018] The haze value can be reduced by homogeneously dispersing the components of the adhesive composition. Through extensive research, the inventors found that dispersibility can be improved by using at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2) in combination with (meth)acrylic resin (a). The haze value can be adjusted by the type, molecular weight, and functional groups of the silicone oligomer (s1) and silicone oligomer derivative (s2). Smaller molecular weights of the silicone oligomer (s1) and silicone oligomer derivative (s2) tend to result in higher compatibility.

[0019] The adhesive strength (at 25°C) of the adhesive sheet of the first embodiment is 3N / 25mm or more (see (ii) above). From the viewpoint of further improving resistance to peeling and lifting from the adherend during repeated bending, 4N / 25mm or more is more preferable, 5N / 25mm or more is even more preferable, 8N / 25mm or more is even more preferable, and 10N / 25mm or more is particularly preferable. The upper limit of the adhesive strength may vary depending on the application, but 60N / 25mm is preferred from the viewpoint of suppressing a decrease in other properties such as flexibility.

[0020] Adhesive sheets are required to maintain their adhesive strength even in high-temperature and high-humidity environments. From the viewpoint of providing highly reliable adhesive sheets even in high-temperature and high-humidity environments, the adhesive strength after an accelerated test of 2 hours of standing at 60°C and 90% humidity is preferably 0.5 N / 25 mm or higher, more preferably 1 N / 25 mm or higher, even more preferably 3 N / 25 mm or higher, and particularly preferably 5 N / 25 mm or higher, from the viewpoint of further improving resistance to peeling and bending from the adherend during repeated bending. The upper limit of the adhesive strength may vary depending on the application, but 60 N / 25 mm is preferred from the viewpoint of feasibility.

[0021] The adhesive strength of the adhesive sheet can be adjusted by the type of structural units derived from the monomers constituting the (meth)acrylic resin (a), the Tg, the type and content of functional groups. The adhesive strength can be increased by using (meth)acrylic resin (a) obtained using highly polar (meth)acrylic monomers derived from hydroxyl group-containing monomers, carboxyl group-containing monomers, etc. The lower the Tg of (meth)acrylic resin (a), the higher the adhesive strength tends to be. In addition, increasing the number of hydroxyl groups in (meth)acrylic resin (a) tends to increase the adhesive strength. Furthermore, the lower the amount of curing agent in the adhesive composition, the higher the adhesive strength tends to be. Increasing the content of at least one of the silicone oligomer (s1) and the silicone oligomer derivative (s2) tends to decrease the adhesive strength.

[0022] The adhesive sheet according to the first embodiment has a shear storage modulus (hereinafter also referred to as storage modulus) of less than 500 kPa at -20°C (see (iiia) above). The storage modulus corresponds to the portion of elastic energy stored when the material deforms, and is an index that represents the degree of hardness. The higher the value of the storage modulus, the harder the adhesive, and the lower the value of the storage modulus, the softer it is. By using the adhesive sheet with a storage modulus of less than 500 kPa, an adhesive sheet that combines cohesive strength and flexibility can be obtained. From the viewpoint of further improving long-term resistance to peeling and lifting during repeated bending, the storage modulus is more preferably 300 kPa or less, even more preferably 150 kPa or less, even more preferably 100 kPa or less, and particularly preferably 80 kPa or less. From the viewpoint of processability, the lower limit of the shear storage modulus is preferably 10 kPa or more.

[0023] Adhesive sheets are required to maintain their flexibility even in high-temperature and high-humidity environments. From the viewpoint of providing highly reliable adhesive sheets even in high-temperature and high-humidity environments, a shear storage modulus of less than 500 kPa after an accelerated test in which the sheet is left standing for 2 hours at 60°C and 90% humidity is preferable. By using an adhesive sheet with a storage modulus of less than 500 kPa, a more reliable adhesive sheet that can maintain its flexibility even in high-temperature and high-humidity environments can be provided. A storage modulus of 300 kPa or less is more preferable, 200 kPa or less is even more preferable, 100 kPa or less is even more preferable, and 80 kPa or less is particularly preferable. From the viewpoint of processability, the lower limit of the shear storage modulus is preferably 10 kPa.

[0024] The shear storage modulus of an adhesive sheet can be adjusted by the type, Tg, functional groups, and curing agent of the (meth)acrylic resin (a) that constitutes the adhesive composition described later. Increasing the degree of crosslinking tends to increase the shear storage modulus. In addition, increasing the amount of monomers that result in a high Tg in the polymer among the monomer raw materials of the (meth)acrylic resin also tends to increase the shear storage modulus. Furthermore, increasing the amount of silicone oligomer (s1) and silicone oligomer derivative (s2) tends to decrease the shear storage modulus. The shear storage modulus can also be adjusted by the type and amount of tackifying resin.

[0025] The adhesive sheet of the first embodiment is preferably further satisfied with (iv) below, from the viewpoint of suppressing peeling and lifting from the adherend and more effectively suppressing the occurrence of peeling and lifting from the adherend even with repeated bending. (iv) When a stress of 10 kPa is applied at -20°C for 10 minutes, the strain α is 50-400%, and when the residual strain after 10 minutes from when the stress is reduced to 0 kPa is denoted as β, the recovery rate obtained by (α-β) / α×100 is 70% or more. The lower limit of strain α when a stress of 10 kPa is applied at -20°C for 10 minutes as described in (iv) above is preferably 50%, more preferably 100%, even more preferably 200%, and even more preferably 300%. The upper limit of strain α as described in (iv) above is preferably 400%, more preferably 380%, and even more preferably 350%. By setting the strain α to 50% or more, the deformation-following ability of the adhesive layer can be improved. Furthermore, by setting the strain α to 400% or less, a balance between recovery rate and adhesive strength can be achieved, and peeling can be suppressed.

[0026] The lower limit of the recovery rate in (iv) above is preferably 70%, more preferably 80%, and even more preferably 85%. The upper limit of the recovery rate is 100%. A recovery rate of 100% means that the system returns to its initial state after the strain is released.

[0027] The recovery rate of the adhesive sheet can be adjusted by the type, Tg, and Mw of the (meth)acrylic resin (a) that constitutes the adhesive composition, as described later. It can also be adjusted by the type and amount of crosslinking agent. If the Mw of the (meth)acrylic resin (a) is too high, the recovery rate will decrease, so it is preferable to adjust Mw to the suitable range described later. The recovery rate tends to increase as the amount of curing agent increases.

[0028] The refractive index of the adhesive sheet in the first embodiment is not limited, but from the viewpoint of achieving excellent optical properties, 1.40 to 1.60 is preferred.

[0029] The glass transition temperature (hereinafter also referred to as Tg(DHR)) of the adhesive sheet of the first embodiment, as determined by viscoelasticity measurement (DHR), is not particularly limited, but from the viewpoint of obtaining good flexibility at low temperatures, -30 to -80°C is preferred, -35 to -70°C is more preferred, and -40 to -70°C is even more preferred. The Tg of the adhesive sheet can be adjusted by selecting the composition of the monomer component that polymerizes the (meth)acrylic resin (a), and by selecting the type and amount of silicone oligomer (s1) and silicone oligomer derivative (s2). The Tg measurement by viscoelasticity measurement (DHR) is the value obtained by the method described in the examples below.

[0030] The gel fraction of the adhesive sheet in the first embodiment is preferably 30-90% from the viewpoint of more effectively suppressing peeling and lifting due to repeated bending. The lower limit of the gel fraction is more preferably 40%, and even more preferably 50%. The gel fraction can be controlled by adjusting the crosslinking structure and the type and amount of additives. Specifically, it can be adjusted by the amount of functional groups such as hydroxyl groups and carboxyl groups of the (meth)acrylic resin (a), and the type and amount of curing agent. The gel fraction tends to increase with increasing the crosslinking structure, and decreases when the amount of silicone oligomer (s1), silicone oligomer derivative (s2), tackifying resin, etc., is increased.

[0031] The adhesive sheet of the first embodiment is a substrate-less double-sided adhesive sheet. Before use, it is stored in a laminated sheet state, for example, sandwiched between a first separator and a second separator. A preferred example of the laminated sheet of this disclosure (hereinafter also referred to as "this laminated sheet") is a laminate of a first separator / adhesive sheet / second separator.

[0032] In the first embodiment, the adhesive sheet is preferably a single-layer structure of the adhesive layer from the viewpoint of achieving both thinness and adhesive strength, but it may also be a laminate having multiple adhesive layers. Examples of laminates include a laminate having multiple adhesive layers formed from an adhesive composition, and a laminate in which a light-transmitting flexible substrate is provided as a core material between two adhesive layers. If the adhesive sheet of the first embodiment is a laminate, it is sufficient that the adhesive sheet satisfies the above (i), (ii), and (iiia). The adhesive composition may be an emulsion type, a solvent type, or a solvent-free type.

[0033] From the viewpoint of increasing productivity, the laminated sheet of the first embodiment is preferably produced in the form of a roll sheet in which a long double-sided adhesive sheet is wound around a core. For example, a roll sheet can be obtained by winding a long double-sided adhesive sheet around a cylindrical core with an outer diameter of about 100 to 1000 mm. The width of the laminated sheet is, for example, 100 to 3000 mm, and the length of the laminated sheet is, for example, 10 to 3000 m. In the case of a roll sheet, the laminated sheet is unwound, cut and / or punched when shipped or used. Then, after peeling off the first separator, the exposed adhesive sheet is attached to the adherend, and then the second separator is peeled off, and the exposed adhesive sheet is attached to another adherend. The adherends are joined together through these processes.

[0034] The thickness of the adhesive sheet in the first embodiment is arbitrary. From the viewpoint of maintaining good light transmittance, flexibility, and surface structure while exhibiting adhesive strength, a thickness of approximately 5 to 150 μm is preferable for the adhesive sheet. By making the thickness of the adhesive sheet 5 μm or more, stress relaxation during bending can be increased and fracture can be suppressed. The lower limit of the thickness of the adhesive sheet is more preferably 10 μm, and may be 13 μm, 15 μm, 17 μm, 20 μm, 25 μm, etc. By making the thickness of the adhesive sheet 5 μm or more, deterioration during repeated bending can be suppressed and peeling can be effectively prevented. The upper limit of the thickness of the adhesive sheet in the first embodiment is more preferably 140 μm, and may be 130, 125, 120 μm, etc.

[0035] <Second Embodiment> Next, the adhesive sheet according to the second embodiment will be described. The adhesive sheet of the second embodiment differs from the first embodiment in that it satisfies (iiib) below, instead of (iiia) specified in the first embodiment. The other configurations, physical properties, and manufacturing methods are the same as those described in the first embodiment. Note that (iiia) may also be satisfied in the second embodiment.

[0036] The adhesive sheet according to the second embodiment is formed from an adhesive composition comprising (meth)acrylic resin (a) and at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2). The silicone oligomer (s1) is at least one of (α) and (β) described above. The silicone oligomer derivative (s2) is the same as defined in the first embodiment, so its description is omitted.

[0037] The adhesive sheet of the second embodiment satisfies the following conditions (i), (ii), and (iiib). (i) The haze value is less than 1.5%. (ii) The adhesive strength to the glass plate at 25°C is 3N / 25mm or more. (iiib) The Tg in DSC is below -40°C.

[0038] The adhesive sheet according to the second embodiment has a glass transition temperature (Tg(DSC)) of -40°C or lower, as specified in (iiib) above, as determined by DSC measurement. Tg(DSC) is an index that indicates the temperature at which a polymer material begins to change from a hard, glassy state to a soft, rubbery state. The lower the Tg(DSC), the softer the material tends to be at room temperature. Tg(DSC) is an important index for evaluating the hardness and flexibility of adhesives. By using an adhesive sheet with a Tg(DSC) of -40°C or lower, an adhesive sheet that combines cohesive strength and flexibility can be obtained. From the viewpoint of further improving long-term resistance to peeling and lifting during repeated bending, a Tg(DSC) of -42°C or lower is more preferable, -43°C or lower is even more preferable, -47°C or lower is even more preferable, and -49°C or lower is particularly preferable. From the viewpoint of heat resistance, the lower limit of Tg(DSC) is preferably -100°C or higher, and more preferably -90°C, -85°C, and -80°C. Note that Tg(DSC) is a value determined by the examples described later.

[0039] The Tg(DSC) of the adhesive sheet in the second embodiment can be adjusted by the type of (meth)acrylic resin (a) constituting the adhesive composition described later, the shear storage modulus at -20°C as identified in the first embodiment, the functional groups, and the curing agent. Increasing the degree of crosslinking tends to increase the Tg(DSC). In addition, increasing the amount of monomers that result in a high Tg in the polymer among the monomers used as raw materials for the (meth)acrylic resin also tends to increase the Tg(DSC). Furthermore, increasing the amount of silicone oligomer (s1) and silicone oligomer derivative (s2) tends to decrease the Tg(DSC). The Tg(DSC) can also be adjusted by the type and amount of tackifying resin.

[0040] The adhesive sheet of the second embodiment is formed from an adhesive composition containing (meth)acrylic resin (a) and at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2). By satisfying (i), (ii), and (iiib) above, it is possible to provide an adhesive sheet that is highly flexible while possessing transparency, adhesive strength, cohesive strength, and resilience. In particular, excellent effects are obtained at room temperature (23°C) for complex shapes such as teardrops. Furthermore, peeling and lifting of the adhesive sheet from the adherend can be suppressed in the temperature range from low temperature (-20°C) to high temperature (60°C). It is believed that by combining (meth)acrylic resin (a) with at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2), flexibility that can withstand repeated bending can be provided. In addition, by combining (ii) above with (iiib) above in the adhesive sheet, it is believed that peeling and lifting from the adherend can be suppressed, and the occurrence of peeling and lifting from the adherend can be suppressed even with repeated bending.

[0041] To facilitate understanding, parts that overlap with the first embodiment are reproduced below as appropriate. The adhesive sheet of the second embodiment preferably satisfies (iv) described in the first embodiment above, from the viewpoint of suppressing peeling and lifting from the adherend and more effectively suppressing peeling and lifting from the adherend even with repeated bending. (iv) and its preferred range are the same as in the first embodiment, so that description applies mutatis mutandis. The refractive index of the adhesive sheet of the second embodiment is not limited, but from the viewpoint of having excellent optical properties, 1.40 to 1.60 is preferred. The lower limit of the gel fraction of the adhesive sheet of the second embodiment is preferably 30 to 90%, the same as in the first embodiment. Preferred forms, etc., apply mutatis mutandis to the description of the first embodiment.

[0042] The adhesive sheet of the second embodiment is a substrate-less double-sided adhesive sheet. Specific examples and preferred examples are as shown in the first embodiment. Similar to the first embodiment, the adhesive sheet of the second embodiment is preferably a single-layer adhesive structure from the viewpoint of achieving both thinness and adhesive strength, but it may also be a laminate having multiple adhesive layers. Examples of laminates include a laminate having multiple adhesive layers formed from an adhesive composition, and a laminate in which a light-transmitting flexible substrate is provided as a core material between two adhesive layers. If the adhesive sheet of the second embodiment is a laminate, it is sufficient that the adhesive sheet satisfies (i), (ii), and (iiib) above. The adhesive composition may be emulsion type, solvent type, or solvent-free type. The thickness of the adhesive sheet of the second embodiment is arbitrary, and its preferred range is the same as in the first embodiment.

[0043] 2. Adhesive composition The adhesive composition of this disclosure comprises (meth)acrylic resin (a) and at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2). The following describes each component of the adhesive composition that forms an adhesive sheet (hereinafter also referred to as "the adhesive sheet") which can be suitably applied to the first and second embodiments.

[0044] 2-1. (Meth)acrylic resin (a) (Meth)acrylic resin (a) is a resin that can be synthesized using (meth)acrylic monomer and is the main component of the adhesive composition. Here, the main component is the most abundant component among the nonvolatile components of the adhesive composition and is used alone or in combination of two or more. The lower limit of the blending ratio of (meth)acrylic resin (a) is preferably 60% by mass, more preferably 70% by mass, of 100% by mass of the nonvolatile components of the adhesive composition. The upper limit of the blending ratio of (meth)acrylic resin (a) is preferably 95% by mass, more preferably 90% by mass, and even more preferably 85% by mass, of 100% by mass of the nonvolatile components of the adhesive composition. Preferred examples of (meth)acrylic resin (a) include (meth)acrylic random copolymers and (meth)acrylic block copolymers. The preferred range of the blending ratio of (meth)acrylic resin (a) in 100% by mass of the adhesive sheet is the same as the preferred range of the blending ratio of (meth)acrylic resin (a) in 100% by mass of the nonvolatile components of the adhesive composition described above.

[0045] The weight-average molecular weight (Mw) of the (meth)acrylic resin is preferably between 500,000 and 2,000,000. Using (meth)acrylic resin (a) within the above range provides excellent durability and excellent die-cutting properties. The lower limit of Mw is more preferably 700,000, even more preferably 800,000, even more preferably 850,000, and particularly preferably 930,000. The upper limit of Mw is more preferably 1,800,000, even more preferably 1,700,000, and even more preferably 1,500,000.

[0046] The (meth)acrylic resin (a) is preferably a (meth)acrylic copolymer obtained by polymerizing monomers containing multiple types of (meth)acrylic monomers. Preferred examples of monomers for the (meth)acrylic resin (a) include monomers (m1) having alkyl groups (including cycloalkyl groups) (hereinafter also referred to as monomer (m1)) and (meth)acrylic monomers (m2) having functional groups (hereinafter also referred to as monomer (m2)). By including monomer (m2), a crosslinked structure is formed with the crosslinking agent described later, improving the cohesive strength of the adhesive layer and resulting in a tough adhesive sheet. If a material is found to be both monomer (m1) and monomer (m2), it is classified as monomer (m2).

[0047] The alkyl group of monomer (m1) may be either linear or branched. The alkyl group is preferably a C1-C20 alkyl group. Specific examples of monomer (m1) include: methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, and (meth)acrylate. Examples include nonyl acrylate, isononyl methacrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, nonadecyl methacrylate, eicosyl methacrylate, and lauryl methacrylate.

[0048] From the viewpoint of increasing flexibility while improving repeated bending, it is preferable that monomer (m1) be a combination of a (meth)acrylic monomer (m1-1) having a branched alkyl group (hereinafter also referred to as monomer (m1-1)) and a (meth)acrylic monomer (m1-2) having a linear alkyl group (hereinafter also referred to as monomer (m1-2)). By using monomer (m1-1) and monomer (m1-2) in combination, interaction with the adherend interface is more likely to occur, improving wettability and adhesion to the adherend interface.

[0049] The monomer (m1-1) is preferably a (meth)acrylic monomer having a branched alkyl group with 4 to 12 carbon atoms. By using a (meth)acrylic monomer having a branched alkyl group with 4 to 12 carbon atoms, stress relaxation and adhesion are improved, and dynamic flexibility is enhanced. From the viewpoint of increasing flexibility, the monomer (m1-2) is preferably a (meth)acrylic monomer (m1-2) having a linear alkyl group with 6 to 18 carbon atoms.

[0050] Preferred examples of monomer (m1-1) include isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate. Among these, 2-ethylhexyl (meth)acrylate is more preferred, and 2-ethylhexyl acrylate is even more preferred.

[0051] Preferred examples of monomers (m1-2) include hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and lauryl (meth)acrylate.

[0052] For 100% by mass of (meth)acrylic resin (a), the structural units derived from monomer (m1-1) are preferably 10 to 90% by mass, more preferably 20 to 80% by mass, and even more preferably 50 to 75% by mass. By having alkyl groups with branched structures in the side chains, the polymers intertwine appropriately, improving stress relaxation and increasing flexibility.

[0053] For 100% by mass of (meth)acrylic resin (a), the structural units derived from monomers (m1-2) are preferably 10 to 90% by mass, more preferably 20 to 80% by mass, and even more preferably 30 to 60% by mass. The presence of linear alkyl groups improves cohesive strength, increases toughness, and improves static flexibility.

[0054] As the monomer used in (meth)acrylic resin (a), an alkyl ester (m1-3) (hereinafter also referred to as monomer (m1-3)) with a cyclic alkyl group may be used. If a material falls under monomer (m1-1) or monomer (m1-2) and also falls under monomer (m1-3), it is classified as monomer (m1-3). By using monomer (m1-3), an adhesive sheet can be obtained that combines hardness and softness and has excellent flexibility. Examples of monomer (m1-3) include cyclohexyl (meth)acrylate, 4-n-butylcyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, and isobornyl (meth)acrylate. Among these, cyclohexyl (meth)acrylate and isobornyl (meth)acrylate are particularly preferred from the viewpoint of flexibility and adhesive strength. With respect to 100% by mass of (meth)acrylic resin (a), the structural units derived from monomers (m1-3) are preferably 0 to 20% by mass, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0055] The mass ratio of monomer (m1-2) to monomer (m1-1), (m1-1) / (m1-2), is preferably 0.10 to 9.0, and more preferably 0.20 to 4.0, from the viewpoint of more effectively exhibiting peeling and lifting during folding under low temperature, room temperature, and high temperature conditions.

[0056] From the viewpoint of the recovery rate of the adhesive sheet as described in (iv) above, the combination of monomer (m1-1) having 4 to 12 carbon atoms in the branched alkyl group and monomer (m1-2) having 6 to 18 carbon atoms in the linear alkyl group is preferable.

[0057] Examples of the functional groups of monomer (m2) include hydroxyl groups, epoxy groups, carboxyl groups, acid anhydrides, and nitrogen-containing groups (amino groups, amide groups, heterocyclic groups, etc.). Specifically, preferred examples of monomer (m2) include carboxyl group-containing (meth)acrylic monomers, hydroxyl group-containing (meth)acrylic monomers, epoxy group-containing (meth)acrylic monomers, amino group-containing (meth)acrylic monomers, and amide group-containing (meth)acrylic monomers. The inclusion of monomer (m2) improves the cohesive force of the adhesive, resulting in a tough adhesive sheet. From the viewpoint of improving flexibility and adhesion, monomer (m2) is preferably hydroxyl group-containing (meth)acrylic monomer (m2-1) (hereinafter also referred to as monomer (m2-1)). Furthermore, from the viewpoint of possessing a combination of cohesive force, adhesive force, and resilience, monomer (m2) is preferably carboxyl group-containing (meth)acrylic monomer (m2-2) (hereinafter also referred to as monomer (m2-2)).

[0058] Examples of monomers (m2-1) 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. Among these, 4-hydroxybutyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate are more preferred from the viewpoint of cohesiveness and adhesiveness.

[0059] Examples of monomers (m2-2) include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, p-carboxybenzyl (meth)acrylate, carboxypentyl (meth)acrylate, itaconic acid, maleic acid, fumaric acid, crotonic acid, citraconic acid, and isocrotonic acid. Among these, (meth)acrylic acid is preferred from the viewpoint of cohesiveness and adhesiveness.

[0060] Examples of epoxy group-containing (meth)acrylic monomers include glycidyl (meth)acrylate, methylglycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, and 6-methyl-3,4-epoxycyclohexylmethyl (meth)acrylate.

[0061] Examples of amino group-containing (meth)acrylic monomers include monomethylaminoethyl (meth)acrylate, monoethylaminoethyl (meth)acrylate, monomethylaminopropyl (meth)acrylate, and monoethylaminopropyl (meth)acrylate, which are monoalkylamino esters of (meth)acrylate.

[0062] (Meth)acrylic resin (a) may also use monomers other than monomer (m1) and monomer (m2) to the extent that it does not depart from the spirit of this disclosure. Examples include (meth)acrylamide; N,N-dialkyl(meth)acrylamide such as N,N-dimethyl(meth)acrylamide and N,N-diethyl(meth)acrylamide; N-monoalkyl(meth)acrylamide such as N-ethyl(meth)acrylamide and N-isopropyl(meth)acrylamide; N-vinyl carboxylic acid amides such as N-vinylformamide and N-vinylacetamide; (meth)acrylamides having a hydroxyl group such as N-(2-hydroxyethyl)acrylamide and N-methylolacrylamide; N-vinyl cyclic amides such as N-vinylpyrrolidone (NVP), N-vinylpiperidone, N-vinylcaprolactam and N-vinyl-3-morpholinone; and cyclic amides having an N-(meth)acrylate group such as 1-(meth)acryloyl-2-pyrrolidone and 1-(meth)acryloylpiperidine-2-one. Other examples include vinylpyridine, vinylpyrimidine, vinylpyrazine, vinylpyrrole, vinylimidazole, vinylisoxazole, (meth)acryloylmorpholine, (meth)acryloylpiperidine, and (meth)acryloylpyrrolidine.

[0063] The total amount of structural units derived from monomers (m2) is preferably 0.5 to 20% by mass relative to 100% by mass of (meth)acrylic resin (a). By setting it within this range, the cohesive force can be adjusted by the reaction with the curing agent, and both dynamic and static flexibility can be improved.

[0064] The constituent units derived from monomer (m2-1) are preferably 0.5 to 20% by mass relative to 100% by mass of (meth)acrylic resin (a). Being within this range allows for both adhesion strength and heat resistance of the adhesive layer.

[0065] The constituent units derived from monomer (m2-2) are preferably 10% by mass or less, more preferably 5% by mass or less, and preferably 3% by mass or less, based on 100% by mass of (meth)acrylic resin (a). By using monomer (m2-2) and monomer (m2-1) in combination, both cohesive force and relaxation properties of the adhesive layer can be achieved.

[0066] The constituent units derived from amino group-containing (meth)acrylic monomer are preferably 10% by mass or less relative to 100% by mass of (meth)acrylic resin (a). Being within this range allows for both adhesion and heat resistance of the adhesive layer.

[0067] As one embodiment of the (meth)acrylic resin (a) which is excellent in dynamic and static flexibility, there is a copolymer obtained by polymerizing monomers that include a (meth)acrylic monomer having a hydroxyl group as monomer (m2), a (meth)acrylic monomer having a branched alkyl group with 4 to 12 carbon atoms as monomer (m1-1), and a (meth)acrylic monomer having a linear alkyl group with 6 to 18 carbon atoms as monomer (m1-2). From the viewpoint of obtaining even better dynamic and static flexibility, the copolymer can be, for example, 30% or more, 50% or more, 70% or more, 80% or more, 90% or more, 95% or more, or 100% by mass of 100% by mass of the (meth)acrylic resin (a).

[0068] (Meth)acrylic resin (a) is obtained by polymerizing a monomer mixture. A polymerization initiator is used as needed during polymerization. The content of the polymerization initiator is, for example, 0.01 to 10 parts by mass per 100 parts by mass of the monomer mixture. A radical polymerization initiator is preferred. As radical polymerization initiators, generally known peroxides, azo compounds (such as 2,2'-azobisisobutyronitrile (AIBN)), etc. can be used. The polymerization method is not limited. For example, polymerization can be carried out by solution polymerization, bulk polymerization, emulsion polymerization, and suspension polymerization. Solution polymerization is preferred because it is easy to control the reaction and physical properties. Examples of solvents used in solution polymerization include acetone, methyl acetate, ethyl acetate, toluene, xylene, anisole, methyl ethyl ketone, and cyclohexanone. The polymerization temperature is, for example, 60 to 120°C, and the polymerization time is about 2 to 12 hours.

[0069] The acid value of (meth)acrylic resin (a) is preferably 15 mg KOH / g or less, more preferably 12 mg KOH / g or less, and even more preferably 10 mg KOH / g or less, from the viewpoint of increasing the adhesive strength of the adhesive sheet. The acid value may also be 0 mg KOH / g. The hydroxyl value of (meth)acrylic resin (a) is preferably 2 to 55 mg KOH / g, more preferably 4 to 50 mg KOH / g, and even more preferably 10 to 48 mg KOH / g, from the viewpoint of increasing the flexibility of the adhesive sheet and increasing its resistance to repeated bending.

[0070] 2-2. Silicone oligomer (s1) and silicone oligomer derivative (s2) Silicone oligomer (s1) is a polymer of silane compounds with a low degree of polymerization. (α) Silicone oligomers having a functional group selected from the group consisting of a hydroxyl group, an epoxy group, and a (meth)acrylate group at one end of the molecular chain, and / or (β) A silicone oligomer having a functional group selected from the group consisting of a hydroxyl group, an epoxy group, and a (meth)acrylate group at both ends of the molecular chain, independently. The degree of polymerization of the silicone oligomer (s1) is, for example, 2 to 100. The silicone oligomer (s1) is a silicone compound having a linear structure, a branched structure, or a three-dimensional network structure. Of the above structures, a linear structure and a branched structure are preferred from the viewpoint of improving compatibility with (meth)acrylic resin (a), and a linear structure is more preferred.

[0071] The silicone oligomer (s1) is preferably a silicone oligomer having repeating units represented by formula (1). [ka]

[0072] A commercially available silicone oligomer may be used as the silicone oligomer (s1). Examples of commercially available silicone oligomers include silicone oligomers having (meth)acrylate groups such as TM-0701T, FM-0711, FM-0721, FM-0725, FM-7711, and FM-7721; and silicone oligomers having hydroxyl groups such as FM-3325, FM-0411P, FM-0421, FM-0425, FM-DA21, FM-DA26, FM-4411, FM-4421, and FM-4425 (all manufactured by JNC Corporation, Cylaprene®). Furthermore, silicone oligomers having epoxy groups at both ends, such as X-22-163, KF-105, X-22-163A, X-22-163B, X-22-163C, X-22-163A, X-22-163A; methacrylic-modified silicone oligomers with epoxy groups at both ends, such as X-22-164, X-22-164AS, X-22-164A, X-22-164B, X-22-164C, X-22-164E; and acrylic-modified silicone oligomers with epoxy groups at both ends, such as X-22-2445. Examples include silicone oligomers having reaction-modified epoxy groups at one end, such as X-22-173BX and X-22-173DX; silicone oligomers having reaction-modified methacrylic groups at one end, such as X-22-174ASX, X-22-174BX, KF-2012, X-22-2426, and X-22-2404; and silicone oils having hydroxyl groups at both ends, such as KR-6000, KF-6002, KF-6002, and KF-6003 (all manufactured by Shin-Etsu Chemical Co., Ltd.).

[0073] From the viewpoint of improving resistance to peeling and lifting against repeated bending, and from the viewpoint of long-term stability, silicone oligomers having hydroxyl groups and (meth)acrylate groups are more preferred. From the viewpoint of mass production, silicone oligomer (α) is preferred, and from the viewpoint of improving reliability, silicone oligomer (β) is preferred.

[0074] The functional group equivalents of the silicone oligomer (s1) and the silicone oligomer derivative (s2) are preferably 100 to 5000. Here, the functional group equivalent is determined by molecular weight / number of functional groups. If there are functional groups at both ends, it is difunctional; if there is one end, it is monofunctional. The functional group equivalent is more preferably 300 to 4200, even more preferably 400 to 3000, and even more preferably 500 to 2500. The functional groups of the silicone oligomer (s1) are hydroxyl groups, epoxy groups, and (meth)acrylate groups, and if they are at both ends, the functional group equivalent is determined as difunctional regardless of whether they are the same or different types.

[0075] The silicone oligomer derivative (s2) is a reaction product of a silicone oligomer (s1) and a C1-C18 compound (s3) having a reactive functional group that reacts with the functional group of the silicone oligomer (s1). The reactive functional group of compound (s3) can be any functional group that reacts with the functional group of the silicone oligomer (s1). Preferred examples include carboxyl groups, isocyanate groups, amino groups, thiol groups, and epoxy groups. The preferred examples of the C1-C18 compound (s3) having a reactive functional group are not particularly limited. For example, alicyclic hydrocarbon groups, branched or unsaturated chain hydrocarbon groups, aromatic groups, and combinations thereof can be cited. Preferably, it is a branched or saturated or unsaturated chain hydrocarbon group.

[0076] A preferred example of a C1-C18 compound (s3) having a reactive functional group is a compound represented by general formula (2). XR 1 (2) Here, X is a reactive functional group. Preferred examples of X include a carboxyl group, an isocyanate group, an amino group, a thiol group, and an epoxy group. 1is a monovalent hydrocarbon group, which may be cyclic, linear, branched, or a combination thereof. Specific examples include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl groups; branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, isohexyl, isoheptyl, isooctyl, and tert-octyl groups; cyclic alkyl groups such as cyclopentyl and cyclohexyl groups; alkenyl groups such as vinyl, allyl, 1-propenyl, butenyl, and methallyl(2-methyl-2-propenyl) groups; allyl groups such as phenyl, tolyl, and xylyl groups; and aralkyl groups such as benzyl and phenethyl groups.

[0077] Preferred examples of compounds having a carboxyl group (s3) include myristoleic acid, pentadecenoic acid, palmitolesanic acid, heptadecenoic acid, oleic acid, linoleic acid, α-linolenic acid, γ-linolenic acid, and riciaaryl acid. Among these, oleic acid, palmitoleic acid, linoleic acid, and ricinoleic acid are preferred.

[0078] The number-average molecular weight (Mn) of the silicone oligomer (s1) and silicone oligomer derivative (s2) is preferably 5000 or less. By setting the Mn to 5000 or less, the compatibility of the silicone oligomer (s1) and silicone oligomer derivative (s2) with the (meth)acrylic resin (a) can be significantly improved. As a result, the adhesive sheet can exhibit superior flexibility while maintaining cohesive force and adhesive force. The Mn is more preferably 3000 or less, and even more preferably 2000 or less. The lower limit of the Mn is not limited to polymers, but is usually 100 or more.

[0079] While the molecular weight distribution (Mw / Mn) of silicone oligomers (s1) and silicone oligomer derivatives (s2) is often 1.8 or higher, from the viewpoint of effectively increasing the flexibility of the adhesive sheet, it is preferable that it be less than 1.8, more preferably 1.6 or lower, even more preferably 1.5 or lower, and even more preferably 1.4 or lower. The lower limit of the Mw / Mn is 1. That is, in order to increase the flexibility of the adhesive sheet, it is preferable that Mn be 5000 or less and Mw / Mn be less than 1.8. Furthermore, from the viewpoint of improving the compatibility of the resin composition of the adhesive sheet and effectively preventing peeling, it is preferable that the silicone oligomer (s1) does not contain cyclic siloxanes. Specifically, the cyclic siloxane content in the adhesive sheet is preferably less than 1000 ppm.

[0080] Furthermore, the total content of silicone oligomer (s1) and silicone oligomer derivative (s2) is preferably 5 to 50 parts by mass per 100 parts by mass of (meth)acrylic resin (a). By setting the total amount of silicone oligomer (s1) and silicone oligomer derivative (s2) within the above range, it is possible to provide high cohesive strength, maintain recovery rate, impart flexibility, and enhance durability. The content is more preferably 10 to 30 parts by mass.

[0081] By combining an acrylic copolymer (a) with at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2), compatibility is improved, and both a reduction in storage modulus and an improvement in recovery rate can be achieved. As a result, an adhesive sheet with excellent flexibility and resistance to repeated bending is obtained.

[0082] The adhesive sheet may contain silicone oligomers not classified as silicone oligomers (s1) or silicone oligomer derivatives (s2), and silicone oils not classified as silicone oligomers, to the extent that it does not depart from the spirit of this disclosure. stomach.

[0083] 2-3. Hardener The adhesive sheet may further contain a curing agent. The curing agent is preferably one that exhibits crosslinking properties with (meth)acrylic resin (a). A curing agent having two or more crosslinking groups is preferred. Preferred examples of curing agents include metal chelate compounds, epoxy curing agents, isocyanate curing agents, aziridine curing agents, amine curing agents, thiol curing agents, and acid anhydride curing agents. Each curing agent may be used alone, or two or more may be used in combination. Among the curing agents, metal chelate compounds, epoxy curing agents, and isocyanate curing agents are preferred. The number of functional groups is preferably 2 to 20, with 3 to 10 being a preferred number of functional groups. By using a hardening agent, the cohesive force of the adhesive layer is improved, and dynamic flexibility, static flexibility, and holding power can be adjusted.

[0084] Metal chelate compounds play a role in forming a three-dimensional crosslinked structure with (meth)acrylic resin (a), and refer to compounds having a metal atom M and a ligand L that coordinates to the metal atom M. By incorporating metal chelate compounds, the cohesive force and adhesive strength of the resulting adhesive sheet can be increased, and its durability can be improved. Ligands L include monodentate ligands, in which one part coordinates to the metal atom M, and / or polydentate ligands, in which two or more parts coordinate to the metal atom M. If there are two or more metal atoms M, they may be of the same type or different types. Similarly, if there are two or more ligands L, they may be of the same type or different types. In adhesive compositions, metal chelate compounds may be used alone or in combination of two or more types.

[0085] Examples of metal atoms M include aluminum, titanium, manganese, magnesium, zirconium, iron, cobalt, nickel, copper, zinc, germanium, indium, tin, hafnium, chromium, and vanadium. Among these, aluminum and zirconium are preferred from the viewpoint of cohesive force and adhesion.

[0086] Examples of polydentate ligands among ligand L include β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate; and β-diketones such as acetylacetone (also known as 2,4-pentanedione), 2,4-hexanedione, and benzoylacetone. These compounds are ketoenol tautomers, and in the case of polydentate ligand L, the enol may be deprotonated enolate (e.g., acetylacetonate). Examples of monodentate ligands among ligand L include halogen atoms such as chlorine and bromine; acyloxy groups such as pentanoyl, hexanoyl, 2-ethylhexanoyl, octanoyl, nonanoyl, decanoyl, dodecanoyl, and octadecanoyl; and alkoxy groups such as methoxy, ethoxy, n-propoxy, isopropoxy, and butoxy.

[0087] Preferred examples of metal chelating compounds include titanium chelating compounds such as tetrakis(acetylacetonate)titanium(IV), diisopropoxybis(ethylacetoacetate)titanium(IV), diisopropoxybis(acetylacetonate)titanium(IV), di-n-octyroxybis(octyleneglycolate)titanium(IV), diisopropoxybis(triethanolamine)titanium(IV), dihydroxybis(2-hydroxypropionate)titanium(IV) or dihydroxybis(2-hydroxypropionate)titanium(IV) ammonium salt, and tetrakis(acetylacetonate)zirconium(IV). , zirconium chelate compounds such as di-n-butoxybis(ethylacetate)zirconium(IV), tri-n-butoxymono(acetylacetonate)zirconium(IV), or tri-n-butoxymono(steart)zirconium(IV), tris(acetylacetonate)aluminum(III), tris(ethylacetate)aluminum(III), mono(acetylacetonate)bis(ethylacetate)aluminum(III), diisopropoxymono(ethylacetate)aluminum(III), or PrenAct® AL-M (manufactured by Kawaken Fine Chemicals Co., Ltd.);Examples include aluminum chelate compounds such as diisopropoxymono(9-octadecanylacetate)aluminum(III), magnesium chelate compounds such as bis(acetylacetonate)magnesium(II), bis(ethylacetate)magnesium(II), isopropoxymono(acetylacetonate)magnesium(II), or isopropoxymono(ethylacetate)magnesium(II), zinc chelate compounds such as bis(acetylacetonate)zinc(II) or bis(ethylacetate)zinc(II), indium chelate compounds such as bis(acetylacetonate)indium(III) or bis(ethylacetate)indium(III), tin chelate compounds such as bis(acetylacetonate)tin(II) or bis(ethylacetate)tin(II), or copper chelate compounds such as bis(acetylacetonate)copper(II) or bis(ethylacetate)copper(II).

[0088] The content of the metal chelating compound is preferably 0.01 to 10 parts by mass per 100 parts by mass of (meth)acrylic resin (a). By setting the amount of the metal chelating compound within the above range, high cohesive force can be achieved, and flexibility can be imparted while maintaining the recovery rate. The lower limit of the content is more preferably 0.03 parts by mass, and even more preferably 0.05 parts by mass. The upper limit of the content is more preferably 5 parts by mass, even more preferably 3 parts by mass, even more preferably 2 parts by mass, and particularly preferably 1.5 parts by mass.

[0089] Examples of epoxy curing agents include glycerin diglycidyl ether, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, and N,N,N',N'-tetraglycidylaminophenylmethane.

[0090] The isocyanate-based curing agent is preferably an isocyanate compound having two or more isocyanate groups. The isocyanate compounds are preferably, for example, isocyanate monomers of aromatic polyisocyanates, aliphatic polyisocyanates, aromatic aliphatic polyisocyanates, and alicyclic polyisocyanates, as well as their biuret, nurate, and adduct forms.

[0091] Examples of aromatic polyisocyanates include 1,3-phenylenediisocyanate, 4,4'-diphenyldiisocyanate, 1,4-phenylenediisocyanate, 4,4'-diphenylmethanediisocyanate, 2,4-tolylenediisocyanate, 2,6-tolylenediisocyanate, 4,4'-toluidinediisocyanate, 2,4,6-triisocyanatetoluene, 1,3,5-triisocyanatebenzene, dianisidinediisocyanate, 4,4'-diphenyletherdiisocyanate, and 4,4',4"-triphenylmethanetriisocyanate.

[0092] Examples of aliphatic polyisocyanates include trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate (also known as HMDI), pentamethylene diisocyanate, 1,2-propylene diisocyanate, 2,3-butylene diisocyanate, 1,3-butylene diisocyanate, dodecamethylene diisocyanate, and 2,4,4-trimethylhexamethylene diisocyanate.

[0093] Examples of aromatic aliphatic polyisocyanates include ω,ω'-diisocyanate-1,3-dimethylbenzene, ω,ω'-diisocyanate-1,4-dimethylbenzene, ω,ω'-diisocyanate-1,4-diethylbenzene, 1,4-tetramethylxylylenediisocyanate, and 1,3-tetramethylxylylenediisocyanate.

[0094] Alicyclic polyisocyanates include, for example, 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate (also known as IPDI, isophorone diisocyanate), 1,3-cyclopentane diisocyanate, 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, methyl-2,4-cyclohexane diisocyanate, methyl-2,6-cyclohexane diisocyanate, 4,4'-methylenebis(cyclohexyl isocyanate), and 1,4-bis(isocyanate methyl)cyclohexane.

[0095] The biuret compound is a self-condensate having a biuret bond formed by the self-condensation of isocyanate monomers. Examples of biuret compounds include the biuret compound of hexamethylene diisocyanate. The aforementioned nurate is a trimer of an isocyanate monomer. Examples include a trimer of hexamethylene diisocyanate, a trimer of isophorone diisocyanate, and a trimer of tolylene diisocyanate. The adduct is a bifunctional or greater isocyanate compound obtained by reacting an isocyanate monomer with a bifunctional or greater low molecular weight active hydrogen-containing compound. Examples of adducts include compounds obtained by reacting trimethylolpropane with hexamethylene diisocyanate, compounds obtained by reacting trimethylolpropane with tolylene diisocyanate, compounds obtained by reacting trimethylolpropane with xylylene diisocyanate, compounds obtained by reacting trimethylolpropane with isophorone diisocyanate, and compounds obtained by reacting 1,6-hexanediol with hexamethylene diisocyanate.

[0096] From the viewpoint of forming a sufficient cross-linked structure, trifunctional isocyanate compounds are preferred.

[0097] Examples of aziridine compounds include N,N'-diphenylmethane-4,4'-bis(1-aziridinylcarboxamide), tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, and 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane.

[0098] The carbodiimide compound is preferably a high molecular weight polycarbodiimide produced by decarboxylation condensation of a diisocyanate compound in the presence of a carbodiimide catalyst. Among the commercially available high molecular weight polycarbodiimides, the Carbodilite series from Nisshinbo Chemical and the Carbodista series from Teijin are preferred. Of these, Carbodilite V-03, 07, 09 and Carbodista TCC-FP10M are preferred due to their excellent compatibility with organic solvents.

[0099] Examples of amine-based curing agents include amines containing heteroaromatic rings, such as metaphenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, benzyldimethylamine, dimethylaminomethylbenzene, phenolic resins, and phenol novolac resins. Examples of thiol-based curing agents include tertiary amines such as N,N-dimethylaniline and mercaptobenzimidazole. Examples of acid anhydride-based curing agents include phthalic anhydride, trimellitic anhydride, and pyromellitic anhydride.

[0100] The hardening agent content is preferably 0.01 to 10% by mass relative to 100% by mass of the total amount of the adhesive sheet. By setting the amount of hardening agent within the above range, the cohesive force can be increased and the recovery rate of the adhesive sheet can be improved. The content is more preferably 0.05 to 5% by mass.

[0101] 2-4. Other ingredients The adhesive compositions of this disclosure may contain resins other than (meth)acrylic resin (a) without departing from the spirit of this disclosure. Examples of other resins include rubber resins (natural rubber, synthetic rubber, and mixtures thereof), silicone resins, urethane resins, polyamide resins, polyimide resins, polyester resins, fluororesins, and tackifying resins. These resins may be used individually or in combination of two or more. Examples of additives include silane coupling agents, antistatic agents, plasticizers, softeners, colorants, antioxidants, UV absorbers, antioxidants, light stabilizers, preservatives, flame retardants, and refractive index modifiers.

[0102] Petroleum resin or its copolymer can be used as the tackifying resin. Examples of petroleum resin or its copolymer include FTR-6100 (softening point 100°C, manufactured by Mitsui Chemicals), FTR-6110 (softening point 110°C, manufactured by Mitsui Chemicals), and FTR-6125 (softening point 125°C, manufactured by Mitsui Chemicals), Petrotac 70 (softening point 70°C, manufactured by Tosoh Corporation), Petrotac 90 (softening point 95°C, manufactured by Tosoh Corporation), Petrotac 120V (softening point 120°C, manufactured by Tosoh Corporation), Petocol 100T (softening point 100°C, manufactured by Tosoh Corporation), Petocol 120 (softening point 120°C, manufactured by Tosoh Corporation), and Petocol 130 (softening point 12 Examples include, but are not limited to, petroleum resins or copolymers thereof with a softening point of 80 to 150°C, and two or more of these may be used in combination.

[0103] Other tackifying resins besides those mentioned above can also be used as needed, provided they are liquid or solid at 25°C, and do not impair the required performance. Examples include rosin-based resins such as rosin esters, polymerized rosin, hydrogenated rosin, disproportionated rosin, maleic acid-modified rosin, fumaric acid-modified rosin, and rosinphenol resins; and terpene-based resins such as α-pinene resin, β-pinene resin, dipentene resin, aromatically modified terpene resin, hydrogenated terpene resin, terpenephenol resin, acid-modified terpene resin, and styrene-terpene resin. Furthermore, coumarone-indene resin, styrene-based resin, and alkylphenol resin are also examples. Two or more tackifying resins may be used in combination.

[0104] When a tackifying resin is incorporated, it is preferable to use 0 to 50 parts by mass per 100 parts by mass of (meth)acrylic resin (a). If the amount is 50 parts by mass or less, a decrease in adhesion or cohesive force due to the tackifying resin will not occur, and peeling and bubble formation can be suppressed even with repeated bending. From the above viewpoint, the upper limit is more preferably 40 parts by mass, and even more preferably 30 parts by mass. The lower limit is preferably 1 part by mass, and even more preferably 3 parts by mass, from the viewpoint of more effectively suppressing adhesion and peeling.

[0105] A silane coupling agent may be included as an optional component. Adding a silane coupling agent can increase the adhesion to the substrate. Examples of silane coupling agents include alkoxysilane compounds having a (meth)acryloxy group, such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropyltripropoxysilane, 3-(meth)acryloxypropyltributoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane; Alkoxysilane compounds having a vinyl group, such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinylmethyldimethoxysilane, and vinylmethyldiethoxysilane; Alkoxysilane compounds having an amino group, such as 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltripropoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldiethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane; Alkoxysilane compounds having a mercapto group, such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltripropoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylmethyldiethoxysilane; Alkoxysilane compounds having epoxy groups, such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropyltripropoxysilane, 3-glycidoxypropyltributoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; Tetraalkoxysilane compounds such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane; Examples include 3-chloropropyltrimethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, n-decyltrimethoxysilane, n-decyltriethoxysilane, styryltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate, 3-isocyanatetopropyltrimethoxysilane, 3-isocyanatetopropyltriethoxysilane, hexamethyldisilazane, and silicone resins having alkoxysilyl groups in the molecule. The amount of silane coupling agent added is preferably 0.01 to 2.0 parts by mass, and more preferably 0.05 to 1.0 parts by mass, per 100 parts by mass of (meth)acrylic resin (a).

[0106] 3. Manufacturing of adhesive sheets and laminated sheets The adhesive sheet is formed from the adhesive composition. One method for forming the adhesive sheet is to apply the adhesive composition to a first separator, dry and remove the solvent, etc., to form the adhesive sheet, and then laminate a second separator. Various methods can be used for the application. Examples include roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, and extrusion coating using a die coater. The drying temperature and drying time can be appropriately designed depending on the type of solvent. The drying temperatures are, for example, 40-200°C, 50-180°C, and 70-170°C. The drying times are, for example, 5 seconds to 20 minutes, 10 seconds to 10 minutes, and 15 seconds to 5 minutes. Alternatively, the adhesive sheet may be formed by directly applying the adhesive composition to the adherend.

[0107] 4. Display The display of this disclosure has a laminated structure in which a first adherend and a second adherend are joined together via an adhesive sheet of this disclosure. The first adherend and the second adherend are collectively referred to as the adherend. Either the first separator or the second separator of the laminated sheet is peeled off, and the first adherend is attached to the exposed adhesive sheet. Then, the other separator is peeled off, and the exposed adhesive sheet is attached to the second adherend. A fast-adhesion layer may be provided between the adhesive sheet and the adherend.

[0108] Examples of substrates include optical substrates, polarizing plates, transparent conductive films, light guide sheets, fluorescent sheets, dimming sheets, prism sheets, lenticular sheets, microlens array films, hard coat films, and light-transmitting flexible substrates. By bonding these together, a laminate constituting a flexible image display device is formed. A hard coat layer, an easy-adhesion coating layer, etc., may be laminated on the laminated surface between the adhesive sheet and the substrate.

[0109] This adhesive sheet offers excellent transparency and flexibility, making it suitable for foldable displays where repeated deformation, including bending characteristics, is required in the laminated structure and where it is applied to the viewing side. Suitable display panels include organic electroluminescence (EL) display panels, liquid crystal panels, plasma display panels, micro-LEDs, mini-LEDs, and electronic paper. [Examples]

[0110] The present disclosure will be described in more detail below based on the examples. However, the present disclosure is not limited thereto. Unless otherwise specified, "parts" in the examples refers to "parts by mass," and "%" refers to "mass%." Blank spaces in the table indicate that an ingredient is not included.

[0111] <(meth)acrylic resin (a) manufacturing example> [(Meth)acrylic resin (a-1)] Using a reaction vessel (hereinafter referred to as the reaction vessel) equipped with a stirrer, reflux condenser, nitrogen inlet tube, thermometer, and dropping tube, half the amount of monomer mixtures was charged into the reaction vessel: 20 parts of 2-ethylhexyl acrylate (2EHA) as monomer (m1-1), 18 parts of methyl acrylate (MA) as monomer (m1-2), 50 parts of butyl acrylate (BA) as monomer (m1-2), 10 parts of dodecyl acrylate (DOA) as monomer (m1-2), 1 part of hydroxyethyl acrylate (HEA) as monomer (m2-1), and 1 part of acrylic acid (AA) as monomer (m2-2), along with 0.2 parts of azobisisobutyronitrile as an initiator and 60 parts of ethyl acetate as a solvent. Then, the remaining half of the monomer mixture, 60 parts of ethyl acetate, and 0.2 parts of azobisisobutyronitrile were added and mixed, and the solution was added dropwise from the dropping tube over approximately 2 hours, and polymerization was carried out under a nitrogen atmosphere at approximately 80°C for 6 hours. After the reaction was complete, the solution was cooled and diluted with ethyl acetate to obtain a (meth)acrylic resin solution with a non-volatile content of 30%. The obtained (meth)acrylic resin was designated as (a-1). The (meth)acrylic resin (a-1) had a Mw of 1.2 million, a hydroxyl value of 4.8 mgKOH / g, and an acid value of 7.8 mgKOH / g.

[0112] [(Meth)acrylic resin (a-2)~(a-7)] Except for changes to the composition and blending amounts (parts by mass) listed in Table 1, (meth)acrylic resins (a-2) to (a-7) were synthesized in the same manner as in the production of (meth)acrylic resin (a-1). Blank spaces in the table indicate that a component was not included.

[0113] Details of the monomers listed in Table 1 are shown below. 2EHA: 2-ethylhexyl acrylate (8 carbon atoms, monomer m1-1) MA: Methyl acrylate (1 carbon atom, monomer m1-2) BA: Butyl acrylate (4 carbon atoms, monomer m1-2) DOA: Dodecyl acrylate (12 carbon atoms, monomer m1-2) IBXA: Isobornyl acrylate (alicyclic, monomer m1-3) DMAEA: 2-dimethylaminoethyl acrylate (monomer m2) HEA: Hydroxyethyl acrylate (monomer m2-1) AA: Acrylic acid (monomer m2-2) 4HBA: 4-hydroxybutyl acrylate (monomer m2-1) Am: Acrylamide (monomer m3) FM0721: Silicone oligomer (manufactured by JNC, silicone oligomer with one end of Mn5000 methacrylate)

[0114] <Measurement of weight-average molecular weight (Mw)> The weight-average molecular weight (Mw) was measured using the Shimadzu LC-GPC system. The weight-average molecular weight (Mw) was determined by conversion using polystyrene with a known molecular weight as the standard substance. Equipment name: Shimadzu Corporation LC-GPC system "Prominence" Column: Four Shodex LF804 columns manufactured by Resonaq Corporation were connected together. Mobile phase solvent: tetrahydrofuran Flow rate: 1.0mL / min Column temperature: 40℃

[0115] <Hydroxyl value> The hydroxyl value of (meth)acrylic resin (a) was measured according to JIS K 0070-1992 (acetylation method). Specifically, approximately 25 g of acetic anhydride was taken, pyridine was added, and the total volume was made 100 mL, which was thoroughly stirred to prepare the acetylation reagent. Approximately 2 g of the sample was accurately weighed into a flask, 5 mL of the acetylation reagent and 10 mL of pyridine were added, an air condenser was attached, and the mixture was heated at 100°C for 70 minutes, after which it was allowed to cool. Then, 35 mL of toluene was added as a solvent from the top of the condenser and stirred, and then 1 mL of water was added and stirred to decompose the acetic anhydride. To complete the decomposition, it was heated again for 10 minutes and allowed to cool, then the condenser was washed with 5 mL of ethanol, the washed ethanol was added to the sample solution, and then 50 mL of pyridine was added to the sample solution as a solvent and stirred. This sample solution was subjected to potentiometric titration with a 0.5 mol / L potassium hydroxide ethanol solution. The same procedure was repeated with the sample removed, and potentiometric titration was performed to calculate the hydroxyl value using the following formula. (Formula) Hydroxyl value (mgKOH / g) = ((α-γ) × Δ × 28.5) / ε + η α: Volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the blank test. γ: Volume (mL) of 0.5 mol / L potassium hydroxide ethanol solution used in the sample. Δ: Factor of 0.5 mol / L potassium hydroxide ethanol solution ε: Sample volume (g) η: Acid value

[0116] <Acid value> The acid value of (meth)acrylic resin (a) was measured in accordance with JIS K 0070-1992 (potentiometric titration method). A solvent prepared by mixing toluene and ethanol in a volume ratio of 4:1 was mixed with phenolphthalein solution as an indicator, and neutralized with 0.1 mol / L potassium hydroxide ethanol solution. Approximately 5 g of the sample was accurately weighed into a beaker, 50 mL of the solvent was added, and the mixture was stirred on a panel heater (80°C) for 6 hours. Potentiometric titration was then performed with 0.1 mol / L potassium hydroxide ethanol solution. The acid value was determined using the following formula. (Formula) Acid value (mgKOH / g)=(γ×Δ×56.11) / ε γ: Volume (mL) of 0.1 mol / L potassium hydroxide ethanol solution used in the sample. Δ: Factor of 0.1 mol / L potassium hydroxide ethanol solution ε: Sample (g)

[0117] [Table 1]

[0118] [Preparation of adhesive compositions, adhesive sheets, and laminated sheets] (Example 1) An adhesive composition was obtained by mixing 100 parts of a-1 (solids content), which is a (meth)acrylic resin (a), 30 parts of s1-1 as a silicone oligomer (s1), 0.1 parts of additive C-2 (silane coupling agent), and 1 part of curing agent D-1 (aluminum chelate A), and further adjusting the non-volatile content to 20% by adding ethyl acetate. The obtained adhesive composition was coated onto a first separator made of polyethylene terephthalate with a thickness of 38 μm using a comma coater so that the thickness after drying would be 10 μm, and an adhesive sheet was formed by hot air drying at 100°C for 2 minutes. Next, a second separator made of PET with a thickness of 75 μm was laminated to this adhesive sheet, and a laminated sheet consisting of the first separator / adhesive sheet / second separator was obtained by aging at a temperature of 40°C for 1 week.

[0119] (Examples 2-26, Comparative Examples 1-5) An adhesive composition, adhesive sheet, and laminated sheet were obtained in the same manner as in Example 1, except that the ingredients and their amounts (solid content) were changed as shown in Tables 2 and 3.

[0120] The symbols for each component listed in Table 2 are as follows: [Silicone oligomer (s1), silicone oligomer derivative (s2)] s1-1: FM-7711 (manufactured by JNC), both terminal (meth)acrylate groups, Mn 1000, functional group equivalent 500. s1-2: FM-0711 (manufactured by JNC), one-terminated (meth)acrylate group, Mn 1000, functional group equivalent 1000. s1-3: FM-0721 (manufactured by JNC Corporation), one-terminated (meth)acrylate group, Mn 5000, functional group equivalent 5000. s1-4: FM-0725 (manufactured by JNC), one-terminated (meth)acrylate group, Mn 10000, functional group equivalent 10000. s1-5: FM-4411 (manufactured by JNC), hydroxyl groups at both ends, Mn 1000, functional group equivalent 500. s1-6: FM-0411P (manufactured by JNC), one-terminated hydroxyl group, Mn 1000, functional group equivalent 1000. s1-7: X-22-163 (manufactured by Shin-Etsu Corporation), epoxy at both ends, Mn 400, functional group equivalent 200. s1'-8: KF-96-100cs (manufactured by Shin-Etsu Corporation), no denaturation. Mn6000 s1'-9: Cymac GS101 (manufactured by Toagosei Co., Ltd.), graft polymer (without hydroxyl, epoxy, or (meth)acrylate groups at the terminals), Mn 16000 s2-1: A silicone oligomer derivative obtained by adding 100 parts of FM-0411P and 30 parts of oleic acid, and performing a dehydration esterification reaction at 200°C while heating and stirring. [Additives] C-1: Tackifying resin FTR6100 (manufactured by Mitsui Chemicals, Inc.), styrene monomer / aliphatic monomer copolymer, softening point 95°C C-2:3-Glycidoxypropyltrimethoxysilane [Hardening agent] D-1: Aluminum ethyl acetacetate diisopropylate, Number of functional groups: 6 D-2: ZC700 (metal chelate compound), manufactured by Matsumoto Fine Chemical Co., Ltd., number of functional groups: 8 D-3: Isocyanate-based curing agent, manufactured by Mitsui Chemicals, D-110N, number of functional groups: 3

[0121] The solid content of each component was determined by the following method: The mass of the aluminum cup (W0) was weighed using a precision balance. Next, approximately 1 g of the sample solution was placed in the aluminum cup, and the mass of the sample in the aluminum cup (W1) was weighed using a precision balance. The sample in the aluminum cup was heated in a 150°C oven for 2 hours, then removed from the oven and allowed to return to room temperature. The residual mass (W2) of the heated sample in the aluminum cup was weighed using a precision balance. The solid content was then calculated using the formula (W2-W0) / (W1-W0)×100(%).

[0122] [Table 2]

[0123] [Table 3]

[0124] The properties of the adhesive sheet in this embodiment were determined by the following method. <Haze value of adhesive sheet> Test specimens were obtained by cutting the laminated sheets of each example and comparative example (first separator (38 μm, PET) / adhesive sheet (10 μm) / second separator (75 μm, PET)) to a width of 30 mm and a length of 200 mm. A glass plate (blue glass, manufactured by Kawamura Kyuzo Shoten Co., Ltd.) measuring 30 mm wide, 120 mm long, and 1.1 mm thick was attached to the surface of the adhesive sheet exposed by peeling off the first separator to create a laminate of "glass plate / adhesive sheet / second separator". This laminate was held in an autoclave at 50°C and 5 atm for 20 minutes to allow the adhesive sheet to adhere to the glass plate, thereby obtaining a measurement sample. The second separator of the measurement sample was peeled off, and the haze value (%) of the adhesive sheet was measured using an integrating sphere type light transmittance meter (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-8000) in accordance with JIS K7136 (2000 edition).

[0125] <Adhesive strength of adhesive sheets> Test specimens were obtained by cutting the laminated sheets of each example and comparative example (first separator (38 μm, PET) / adhesive sheet (10 μm) / second separator (75 μm, PET)) to a width of 30 mm and a length of 200 mm. The base material, a PET film (Toyobo Co., Ltd., Cosmo Shine A-4360, thickness 100 μm), was corona-treated at an output of 300 W, and the adhesive sheet from which the first separator had been peeled off was attached. Then, it was cut to a size of 25 mm in width and 100 mm in length to prepare a test adhesive sheet. The second separator of this test adhesive sheet was peeled off, and the adhesive sheet was attached to an alkali-free glass plate (EN-A1: Asahi Glass Co., Ltd.) that had been corona-treated at an output of 300 W in a 25°C - 50% relative humidity atmosphere, and further compressed with a roll in accordance with JIS Z-0237 (2000 edition) to obtain a sample. The same sample was compressed, and 24 hours later, the adhesive strength (unit: N / 25mm width) was measured using a tensile testing machine (Tensilon: manufactured by Orientec Co., Ltd.) at 25°C and 50% relative humidity, with a peel angle of 180° and a peel speed of 300 mm / min (Table 4). Samples prepared in the same manner were left to stand for 2 hours at 60°C and 90% relative humidity after 24 hours had elapsed since pressing. Adhesion was then measured under the same conditions as described above (Table 4).

[0126] <Shear storage modulus and Tg(DHR) of adhesive sheets> In each example and comparative example, laminated sheets were prepared in which the thickness of the adhesive sheet was changed from 10 μm to 50 μm. Specifically, two laminated sheets were prepared for each example and comparative example (first separator (38 μm, PET) / adhesive sheet (50 μm) / second separator (75 μm, PET)). The first separator was peeled off each laminated sheet, and the adhesive sheets were bonded together with a laminator to create a laminate of second separator / adhesive sheet / second separator. The second separator was peeled off from one side of this laminate, and the adhesive sheets were sequentially bonded to obtain a laminate with an adhesive sheet 1 mm thick (second separator / adhesive sheet (1 mm) / second separator). The second separator was peeled off from this laminate with the adhesive sheet and set in a viscoelasticity measuring device (TA Instruments "DHR2"). Using an 8mm diameter measuring probe, the storage modulus G' was measured under conditions of 0.1% strain, 1Hz frequency, and a heating rate of 10°C / min from -70°C to 200°C. The value of the storage modulus G' at -20°C was read from the obtained data (Table 4). In addition, the peak top of tanδ obtained during the measurement of the storage modulus G' was read as Tg(DHR) (Table 4).

[0127] <Shear storage modulus and Tg(DHR) of adhesive sheets after moist heat testing> A laminate was prepared using the same method as described above for the shear storage modulus. This laminate was then left to stand at 60°C and 90% humidity for 2 hours. Subsequently, the shear storage modulus and Tg were measured under the same conditions as described above.

[0128] <Tg(DSC) of adhesive sheet> For each example and comparative example, the first and second separators were peeled off from the laminated sheet (a laminated sheet consisting of a first separator (38 μm, PET) / adhesive sheet (50 μm) / second separator (75 μm, PET)), and 10 mg of the adhesive sheet was accurately weighed out and placed in an aluminum pan. The weighed sample was then set in a differential scanning calorimeter (TA Instruments, DSC2500). An identical aluminum pan without the sample was also set in the instrument as a reference. After holding at 100°C for 5 minutes, the samples were rapidly cooled to -120°C using liquid nitrogen. Subsequently, the temperature was increased at a rate of 5°C / min, and the Tg(DSC)(°C) of the adhesive sheet was determined from the obtained DSC chart. The nitrogen flow rate was 20 mL / min, and the measurement temperature range was -120 to 100°C. In the obtained DSC curve, the endothermic step in which the baseline changes was identified, and Tg was determined as the intersection point (onset temperature) when the low-temperature and high-temperature baselines were extended, respectively, during that endothermic step. This measurement was performed in accordance with JIS 7121 (1987 edition).

[0129] <Strain α and recovery rate of adhesive sheet> A laminate (second separator / adhesive sheet (1 mm) / second separator) with a 1 mm thick adhesive sheet was obtained using the same method as for the shear storage modulus. Two second separators were peeled off from this laminate and punched out in a circular shape with a diameter of 8 mm to be used as a sample. The obtained sample was placed on the measuring stage of a viscoelasticity measuring device (TA Instruments "DHR2"), and an 8 mm diameter measuring probe (plate) was brought into contact with it. After adjusting the normal load to 0.2 N, the gap was fixed. The strain when a stress of 10 kPa was applied at -20°C for 10 minutes was defined as α (%), and the residual strain 10 minutes after the stress was removed (i.e., 10 minutes after the stress was removed to 0 kPa) was read as β (%). The recovery rate obtained from (α-β) / α×100 was then calculated (Table 4). The strain α and residual strain β were calculated using the following formulas. Strain = (Plate radius (mm) × Probe rotation angle from initial position (rad)) / Gap (mm) Although strain is a dimensionless quantity, for the sake of explanation, we will multiply it by 100 and express it as a percentage. In this embodiment, the plate radius is 4 mm and the arc length of the plate is approximately 25 mm. A strain α of 100% refers to the state in which the sample has rotated by the amount of the gap (the state in which the displacement of the upper plate is equal to the fixed thickness). As mentioned above, the strain α and recovery rate in this disclosure are measured values ​​with an adhesive sheet thickness of 1 mm and a normal load of 0.2 N. However, changing the adhesive sheet thickness (e.g., 0.4 to 2.0 mm) or the normal load (e.g., 0.1 to 2.0 N) did not significantly affect the trend of the obtained values.

[0130] <Gel fraction of adhesive sheet> The gel fraction of the adhesive sheet was determined as the insoluble portion in ethyl acetate. Specifically, test specimens were obtained by cutting the laminated sheet of each example to 30 mm × 100 mm. Then, the insoluble component of the adhesive sheet (thickness: 10 μm) with the first and second separators removed was immersed in ethyl acetate at 50°C for 1 day, and the insoluble component was determined as the mass fraction (unit: mass%) of the adhesive sheet before immersion (Table 4). Specifically, it was calculated using the following formula (1). However, changing the thickness of the adhesive sheet (e.g., 10 to 50 μm) did not significantly affect the trend of the obtained values. (Formula 1) Gel fraction (mass%) = (Y / X) × 100 X = Mass of the adhesive sheet before immersion (g) Y = Mass of the adhesive sheet after immersion (g) The mass of the adhesive sheet after immersion was defined as the mass after removing it from ethyl acetate and drying it at 100°C for 30 minutes.

[0131] [Table 4]

[0132] The shear storage modulus and Tg of the adhesive sheet after the moist heat test (2 hours at 60°C and 90% humidity) were found to be almost the same as the measured values ​​shown in Table 4 above. For example, in the adhesive sheet of Example 4, as shown in Table 4, the shear storage modulus was 40 kPa and Tg (DHR) was -56°C, while the values ​​after the moist heat test (2 hours at 60°C and 90% humidity) were 44 kPa and -55°C, respectively.

[0133] [Evaluation Results] <Evaluation of static flexibility> At 25°C and 50% relative humidity, a colorless polyimide (manufactured by KOLON, 50 μm) was corona-treated at 300 W output. The adhesive sheet, exposed by peeling off the first separator from the laminated sheet (first separator (38 μm, PET) / adhesive sheet (10 μm) / second separator (75 μm, PET)) of each example and comparative example, was then laminated to it using a laminator. Next, the adhesive sheet, with the second separator peeled off, was laminated to a 188 μm thick PET film that had been corona-treated at 300 W output, using a laminator to obtain a test laminate consisting of PET film / adhesive sheet / colorless polyimide. The test laminate was cut to a size of 3 × 10 cm, and both ends of the PET film side of the test laminate were fixed to a teardrop bending test apparatus to form a teardrop shape with a teardrop width of 5 mm, a teardrop length of 30 mm, a neck width of 1 mm, and a total arc length of 70 mm in the center of the test laminate as shown in Figure 2. The inside of the teardrop is colorless polyimide, and the outside is PET film (the same applies hereafter). The test laminate was then folded so that both ends were close together, and the center of the test laminate was in the shape of a teardrop with a teardrop width of 5 mm and a teardrop length of 30 mm, and was held in an environment of -20°C for 24 hours. After that, the test piece was returned to a sheet shape, and the peeling of the adhesive sheet and the presence or absence of air bubbles were evaluated visually according to the following criteria (Table 5). 4. After 24 hours, no peeling of the adhesive sheet or / or air bubbles are observed. Excellent. 3: After 24 hours, the adhesive sheet had peeled off and / or bubbles had formed. Excellent. 2. After 5 hours, the adhesive sheet had peeled off and / or bubbles had formed. This is acceptable. 1: After 1 hour, the adhesive sheet had peeled off and / or bubbles had formed. Target not achieved. Furthermore, static flexibility was evaluated under the same conditions as described above, except that the measurement conditions were changed from -20°C to 60°C and 90% humidity (Table 5).

[0134] <Evaluation of dynamic flexibility> A test laminate was obtained using the same method as for the evaluation of static flexibility. Then, in order to form a teardrop shape with a teardrop width of 5 mm, a teardrop length of 30 mm, a neck width of 1 mm, and a total arc length of 70 mm as shown in Figure 2, the test laminate 11 was cut to a size of 3 × 10 cm, and both ends (not shown) of the PET film side of the test laminate 11 were fixed to the teardrop bending test device at the center of the test laminate 11. The total arc length is the length of the arc from the starting point of the teardrop length, passing through the outer circumference of the teardrop portion, to the ending point of the teardrop length. The state in which the test laminate is not bent and is in a 180° open state is defined as state b. As a normal test, using a bending test machine (manufactured by Yuasa System Equipment Co., Ltd.) at 25°C and 50% relative humidity, the test laminate was folded so that both ends were close to each other in order to form a teardrop shape with a teardrop width of 5 mm and a teardrop length of 30 mm, which is defined as state a, and then it was changed to state b. The process of changing state b → state a → state b was repeated as one cycle. After the test, the appearance was visually evaluated for peeling and lifting at the bent areas (teardrop-shaped areas) according to the following criteria (Table 5). 4: No peeling of the adhesive sheet and / or air bubbles are observed after 200,000 cycles. Excellent. 3: At the end of 200,000 cycles, the adhesive sheet peeled off and / or bubbles appeared. Excellent. 2: At the end of 50,000 cycles, the adhesive sheet had peeled off and / or bubbles had formed. This is acceptable. 1: At the end of 10,000 cycles, the adhesive sheet had peeled off and / or bubbles had formed. Target not met.

[0135] [Table 5]

[0136] The adhesive sheet of Comparative Example 1, which did not contain any silicone oligomers, had a shear storage modulus exceeding 500 kPa, and failed to meet the target in both static and dynamic bending tests. The adhesive sheet of Comparative Example 5, which did not contain any silicone oligomers, had an adhesive strength to a glass plate at 25°C of less than 3 N / 25 mm, and failed to meet the target in both static and dynamic bending tests. Comparative Examples 4 and 6, which contained silicone oligomers but did not contain either the silicone oligomer (s1) or the silicone oligomer derivative (s2) of this disclosure, had a haze value of 1.5% or more, resulting in appearance issues, and failed to meet the target in both static and dynamic bending tests. Furthermore, the adhesive sheet of Comparative Example 2, which contained silicone oligomer (s1) but did not satisfy (i), (ii), and (iiia), etc. of this disclosure, could not be measured for adhesive strength, shear storage modulus, or creep recovery of the adhesive sheet. Even though it contained a silicone oligomer (s1), the adhesive sheet of Comparative Example 3, which did not satisfy the adhesive strength requirements (i) and (ii) of this disclosure, failed to meet the target in both static and dynamic bending tests. On the other hand, adhesive sheets of the present disclosure that are formed from an adhesive composition comprising (meth)acrylic resin (a) and at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2), and that satisfy (i), (ii), and (iiia) or (i), (ii), and (iiib), have been confirmed to perform well in both static and dynamic bending tests, as shown in Examples 1 to 26. In other words, these examples have been confirmed to suppress peeling and bubble formation from the adherend even with repeated bending. Furthermore, it has been confirmed that peeling and bubble formation can be suppressed even when the bent state is maintained for a long period of time. [Explanation of Symbols]

[0137] 1: Adhesive sheet 2: First separator 3: Second separator 10: Laminated sheet 11: Test laminate

Claims

1. It is formed from an adhesive composition comprising (meth)acrylic resin (a) and at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2), Silicone oligomer (s1) is (α) Silicone oligomers having a functional group selected from the group consisting of hydroxyl groups, epoxy groups, and (meth)acrylate groups at one end of the molecular chain, and / or (β) A silicone oligomer having a functional group selected from the group consisting of a hydroxyl group, an epoxy group, and a (meth)acrylate group at both ends of the molecular chain, The silicone oligomer derivative (s2) is The reaction product is a reaction between a silicone oligomer (s1) and a compound (s3) having 1 to 18 carbon atoms that has a reactive functional group that reacts with the functional group of the silicone oligomer (s1). An adhesive sheet that satisfies the following conditions (i), (ii), and (iiia). (i) The haze value is less than 1.5%. (ii) The adhesive strength to the glass plate at 25°C is 3 N / 25 mm or more. (iiia) The shear storage modulus at -20°C is less than 500 kPa.

2. It is formed from an adhesive composition comprising (meth)acrylic resin (a) and at least one of a silicone oligomer (s1) and a silicone oligomer derivative (s2), Silicone oligomer (s1) is (α) Silicone oligomers having a functional group selected from the group consisting of hydroxyl groups, epoxy groups, and (meth)acrylate groups at one end of the molecular chain, and / or (β) A silicone oligomer having a functional group selected from the group consisting of a hydroxyl group, an epoxy group, and a (meth)acrylate group at both ends of the molecular chain, The silicone oligomer derivative (s2) is The reaction product is a reaction between a silicone oligomer (s1) and a compound (s3) having 1 to 18 carbon atoms that has a reactive functional group that reacts with the functional group of the silicone oligomer (s1). An adhesive sheet that satisfies the following conditions (i), (ii), and (iiib). (i) The haze value is less than 1.5%. (ii) The adhesive strength to the glass plate at 25°C is 3 N / 25 mm or more. (iiib) The Tg in DSC is below -40°C.

3. The adhesive sheet according to claim 1 or 2, wherein the number average molecular weight of the silicone oligomer (s1) is 5000 or less.

4. The adhesive sheet according to claim 1 or 2, wherein the (meth)acrylic resin (a) comprises a (meth)acrylic resin obtained by polymerizing monomers comprising a (meth)acrylic monomer having a hydroxyl group, a (meth)acrylic monomer having a branched alkyl group having 4 to 12 carbon atoms, and a (meth)acrylic monomer having a linear alkyl group having 6 to 18 carbon atoms.

5. The adhesive sheet further satisfies (iv) below. (iv) When a stress of 10 kPa is applied at -20°C for 10 minutes, the strain α is 50 to 400%, and when the residual strain after 10 minutes from when the stress is reduced to 0 kPa is denoted as β, the recovery rate obtained by (α - β) / α × 100 is 70% or more.

6. A laminated sheet comprising an adhesive sheet according to claim 1 or 2, sandwiched between a first separator and a second separator.

7. A display comprising the adhesive sheet according to claim 1 or 2.

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