Adhesive sheet

Abstract

Provided is an adhesive sheet that has hard regions and soft regions in the same plane of an adhesive layer, it being difficult to visually recognize boundaries between the hard regions and soft regions in the sheet.　The adhesive sheet 10 is provided with an adhesive layer 1. In the adhesive layer 1, a hard region 11a, a soft region 12, and a hard region 11b are adjacent in this order along one direction D in the same plane. The hard regions 11a and 11b are harder than the soft region 12. The absolute value of the difference between the refractive index (Soft) of the soft region 12 at a wavelength of 594 nm and the refractive index (Hard) of the hard regions 11a, 11b adjacent to the soft region 12 at a wavelength of 594 nm satisfies formula (1). The elastic modulus G (Hard) of the hard region 12 at room temperature and the elastic modulus G (Soft) of the soft regions 11a, 11b adjacent to the soft region 12 at room temperature satisfy formula (2).　Formula (1): │Refractive index (Soft) - Refractive index (Hard)│ ≤ 0.1 Formula (2): 2 ≤ G (Hard) / G (Soft) ≤ 5 × 103

Description

Adhesive Sheet

[0001] The present invention relates to an adhesive sheet.

[0002] A display panel has a laminated structure including, for example, a pixel panel, a touch panel, a polarizing plate, a cover film, and the like. In the manufacturing process of such a display panel, for example, a transparent adhesive sheet (optically adhesive sheet) is used to bond the elements included in the laminated structure. On the other hand, development of repeatedly bendable (foldable) display panels is progressing for applications such as smartphones and tablet terminals, for example. In a foldable display panel, each element in the laminated structure is fabricated to be repeatedly bendable, and an optically adhesive sheet is used for bonding between such elements. Optically adhesive sheets for foldable devices such as foldable display panels are described in, for example, the following Patent Document 1.

[0003] Japanese Unexamined Patent Publication No. 2018-111754

[0004] Optically adhesive sheets for foldable devices such as foldable display panels are required to be less prone to crease marks (crazes) at the bent portion when the device is opened. Examples of such an adhesive sheet include those provided with a pressure-sensitive adhesive layer having regions with relatively different hardnesses within the same plane. However, regions with relatively different hardnesses usually have different optical properties, resulting in different appearances in each region, and the boundary between the regions tends to be visible. Therefore, adhesive sheets used for optical members are required to make the boundary between regions with relatively different hardnesses less visible.

[0005] The present invention is made to solve such a problem, and an object thereof is to provide an adhesive sheet that includes a hard region and a soft region within the same plane of the pressure-sensitive adhesive layer, and makes the boundary between the hard region and the soft region less visible.

[0006] As a result of diligent efforts to solve the above problem, the present inventors have found that a specific adhesive sheet includes a hard region and a soft region within the same plane of the pressure-sensitive adhesive layer, and makes the boundary between the hard region and the soft region less visible. The present invention has been completed based on these findings.

[0007] In other words, the present invention provides an adhesive sheet comprising an adhesive layer having a hard region, a soft region, and a hard region adjacent to each other in this order along one direction within the same plane, wherein the hard region is harder than the soft region, the absolute value of the difference between the refractive index (Soft) of the soft region at a wavelength of 594 nm and the refractive index (Hard) of the hard region adjacent to the soft region at a wavelength of 594 nm satisfies the following formula (1), and the elastic modulus G (Hard) of the hard region at room temperature and the elastic modulus G (Soft) of the soft region adjacent to the soft region at room temperature satisfy the following formula (2). |Refractive index (Soft) - Refractive index (Hard)| ≤ 0.1 (1) 2 ≤ G (Hard) / G (Soft) ≤ 5 × 10 ３ (2)

[0008] Furthermore, the present invention provides an adhesive sheet comprising an adhesive layer having a hard region, a soft region, and a hard region adjacent to each other in this order along one direction within the same plane, wherein the hard region is harder than the soft region, and the absolute difference between the transmittance of the soft region (Soft) and the transmittance of the hard region adjacent to the soft region (Hard) satisfies the following formula (3): |Transmittance (Soft) - Transmittance (Hard)| ≤ 5 (3)

[0009] Furthermore, the present invention provides an adhesive sheet comprising an adhesive layer having a hard region, a soft region, and a hard region adjacent to each other in this order along one direction within the same plane, wherein the hard region is harder than the soft region, and the absolute difference between the haze (Soft) of the soft region and the haze (Hard) of the hard region adjacent to the soft region satisfies the following formula (4): |Haze (Soft) - Haze (Hard)| ≤ 0.5 (4)

[0010] The adhesive sheet of the present invention has a hard region and a soft region within the same surface of the adhesive layer, making the boundary between the hard region and the soft region difficult to see. Therefore, even when the adhesive sheet of the present invention is applied to a foldable device such as a foldable display panel, the boundary between regions with relatively different hardnesses is difficult to see, resulting in excellent visibility.

[0011] This shows a cross-sectional view of an adhesive sheet according to one embodiment of the present invention. This shows a cross-sectional view according to one embodiment of a state in which the adhesive sheet shown in Figure 1 is laminated so as to span two adherends. This shows a simplified plan view of the laminate shown in Figure 2. This is a simplified cross-sectional view showing the laminate shown in Figure 2 in a folded state. This shows a plan view of the state in which the adhesive composition is arranged in the embodiment.

[0012] [Adhesive Sheet] In this specification, "adhesion" refers to the property of two surfaces adhering tightly to each other based on cohesive forces derived from the chemical structure of the composition in response to external pressure (e.g., minute pressure), and being able to be peeled off if necessary. In contrast, "bonding" refers to the property of two surfaces being firmly joined together by a chemical reaction (hardening) of the composition, which produces a hardened product and is not intended to be peeled off.

[0013] Furthermore, in this specification, the form of the "adhesive" is not particularly limited and may be liquid at room temperature (for example, a fluid solid (paste), an adhesive composition, etc.), or a solid at room temperature. Also, the form of the "adhesive" is not particularly limited and may be in the form of a sheet. In this specification, the "adhesive layer" is a non-fluid sheet-like (layered) adhesive layer.

[0014] The adhesive sheet of the present invention comprises at least an adhesive layer on the same surface comprising a hard region, a soft region, and a hard region adjacent to each other in this order along one direction. The hard region is a region that is harder than the soft region. That is, the soft region is a region that is softer than the hard region. The hardness of the two hard regions may be the same or different. In this specification, the adhesive layer may be referred to as "the adhesive layer of the present invention."

[0015] The adhesive sheet of the present invention may be a so-called "substrate-less type" adhesive sheet that does not have a base material (substrate layer), or it may be an adhesive sheet that has a base material. In this specification, a "substrate-less type" adhesive sheet may be referred to as a "substrate-less adhesive sheet," and an adhesive sheet that has a base material may be referred to as a "substrate-attached adhesive sheet." Examples of the above-mentioned substrate-less adhesive sheet include a double-sided adhesive sheet consisting only of the adhesive layer of the present invention, and a double-sided adhesive sheet consisting of the adhesive layer of the present invention and other adhesive layers (adhesive layers other than the adhesive layer of the present invention). Examples of the above-mentioned substrate-attached adhesive sheet include a single-sided adhesive sheet having the adhesive layer of the present invention on one side of the base material, a double-sided adhesive sheet having the adhesive layer of the present invention on both sides of the base material, and a double-sided adhesive sheet having the adhesive layer of the present invention on one side of the base material and other adhesive layers on the other side. The above-mentioned "substrate (substrate layer)" refers to the support, and is the part that is attached to the adherend together with the adhesive layer when the adhesive sheet of the present invention is used (attached) to an adherend. The release liner that is peeled off when the adhesive sheet is used (applied) is not included in the above-mentioned substrate.

[0016] The adhesive sheet of the present invention will be described below with reference to the drawings. However, the adhesive sheet of the present invention is not limited to the embodiments shown in each drawing.

[0017] Figure 1 is a cross-sectional view showing an adhesive sheet according to one embodiment of the present invention. The adhesive sheet 10 shown in Figure 1 is a substrate-less adhesive sheet consisting of an adhesive layer 1. The adhesive layer 1 is sandwiched between the release surfaces of the release liners 21 and 22. Within the same plane of the adhesive layer 1, a hard region 11a, a soft region 12, and a hard region 11b are adjacent in this order along one direction D. That is, two rectangular hard regions 11a and 11b are located on both sides of the same plane of the rectangular soft region 12. In the adhesive layer 1, the soft region 12 and the hard regions 11a and 11b are formed from one end to the other in a direction perpendicular to one direction D. The center of the adhesive layer 1 in one direction D is the soft region 12, and the two hard regions 11a and 11b are adjacent on both sides of the central soft region 12. The hard regions 11a and 11b are harder than the soft region 12. The boundaries between the soft region 12 and the hard region 11a, and between the soft region 12 and the hard region 11b, are parallel to the opposing sides of the adhesive layer 1. In Figure 1, the boundaries between the soft region 12 and the hard region 11a, and between the soft region 12 and the hard region 11b are drawn with solid lines, but these boundaries do not actually need to be observed visually.

[0018] Preferably, the absolute value of the difference between the refractive index (Soft) of the soft region at a wavelength of 594 nm and the refractive index (Hard) of the hard region adjacent to the soft region at a wavelength of 594 nm satisfies the following formula (1). When the following formula (1) is satisfied, the boundary between the hard region and the soft region becomes difficult to see, resulting in a good appearance when the adhesive sheet of the present invention is used by being bonded to an optical component. |Refractive index (Soft) - Refractive index (Hard)| ≤ 0.1 (1)

[0019] In the above formula (1), |refractive index (Soft) - refractive index (Hard)| is preferably 0.07 or less, more preferably 0.05 or less, and even more preferably 0.03 or less.

[0020] The refractive index (Soft) and refractive index (Hard) are not particularly limited, but can be selected from, for example, the range of 1.1 to 1.9.

[0021] In this specification, the refractive index of an adhesive sheet refers to the refractive index of the surface of the adhesive sheet. The refractive index of an adhesive sheet can be measured using a prism coupler under the conditions of a measurement temperature of 25°C and a measurement wavelength of 594 nm. For adhesive sheets with a thickness of less than 20 μm, measurement using the light propagation mode is generally suitable. For adhesive sheets with a thickness of 20 μm or more, measurement using the critical angle mode is generally suitable. A commercially available measuring device can be used as the prism coupler; for example, the "Model 2010 / M prism coupler" or an equivalent from Metricon can be used.

[0022] The modulus of elasticity G (Hard) at room temperature (23±2°C) in the hard region and the modulus of elasticity G (Soft) at room temperature (23±2°C) in the soft region preferably satisfy the following formula (2). When the following formula (2) is satisfied, the difference between the hard region and the soft region is sufficiently large and appropriate, and peeling around the bent portion is less likely to occur. Examples of the above modulus of elasticity include the storage modulus and the loss modulus. 2 ≤ G (Hard) / G (Soft) ≤ 5 × 10 ３ (2)

[0023] In formula (2) above, [G (Hard) / G (Soft)] is preferably 5 or more, and more preferably 10 or more. Also, in formula (2) above, [G (Hard) / G (Soft)] is preferably 1 × 10 ３ The following is preferred, and more preferably 1 × 10 ２ The following are possible values: 90 or less, 80 or less, 70 or less, 60 or less, 50 or less, 40 or less, 30 or less, 20 or less, or 10 or less.

[0024] The above G (Hard) is preferably 80 kPa or more, more preferably 90 kPa or more, and even more preferably 140 kPa or more. The above G (Hard) is preferably 1000 kPa or less, more preferably 500 kPa or less, and even more preferably 300 kPa or less.

[0025] The above G (Soft) is preferably 70 kPa or less, more preferably 60 kPa or less, even more preferably 50 kPa or less, and particularly preferably 30 kPa or less. The above G (Soft) is preferably 1 kPa or more, more preferably 5 kPa or more, and even more preferably 10 kPa or more.

[0026] The storage modulus of each region in the adhesive layer is a value measured by dynamic viscoelasticity. The above storage modulus can be controlled by the type of base polymer, monomer composition, weight-average molecular weight, amount of crosslinking agent used (amount added), and type and content of other additives of the adhesive that constitute each region in the adhesive layer. Specifically, the above modulus (storage modulus) can be measured by the following measurement method.

[0027] <Method for Measuring Elastic Modulus> Multiple adhesive layer pieces cut from the area to be measured are bonded together to create an adhesive sheet with a thickness of approximately 2 mm. This sheet is then punched out to obtain a cylindrical pellet (9 mm in diameter) which serves as the measurement sample. The measurement sample is then fixed to a parallel plate jig with a diameter of 8 mm, and dynamic viscoelasticity measurement is performed. In this measurement, the deformation mode is set to torsion, the measurement temperature range to -70°C to 150°C, the heating rate to 5°C / min, and the frequency to 1 Hz. From the measurement results, the storage modulus of elasticity in the range of -20 to 100°C, including room temperature, is read. Dynamic viscoelasticity measurement can be performed by conventional methods using commercially available dynamic viscoelasticity measuring devices, for example, using the "Advanced Rheometric Expansion System (ARES)" manufactured by TA Instruments Inc. or an equivalent product.

[0028] Preferably, the absolute difference between the transmittance (Soft) (total light transmittance) [%] of the soft region and the transmittance (Hard) (total light transmittance) [%] of the hard region adjacent to the soft region satisfies the following formula (3). When the following formula (3) is satisfied, the boundary between the hard region and the soft region becomes difficult to see, resulting in a good appearance when the adhesive sheet of the present invention is used by laminating it to an optical component. |Transmittance (Soft) - Transmittance (Hard)| ≤ 5 (3)

[0029] In the above formula (3), |transmittance (Soft) - transmittance (Hard)| is preferably 3 or less, more preferably 1 or less, and even more preferably 0.5 or less.

[0030] The transmittance (Soft) and transmittance (Hard) are not particularly limited, but can be selected from the range of 1 to 100, respectively. The total light transmittance mentioned above is a value measured in accordance with JIS K7361-1.

[0031] Preferably, the absolute value of the difference between the haze (Soft) [%] of the soft region and the haze (Hard) [%] of the hard region adjacent to the soft region satisfies the following formula (4). When the following formula (4) is satisfied, the boundary between the hard region and the soft region becomes difficult to see, resulting in a good appearance when the adhesive sheet of the present invention is used by laminating it to an optical component. |Haze (Soft) - Haze (Hard)| ≤ 0.5 (4)

[0032] In the above formula (4), |Hayes (Soft) - Hayes (Hard)| is preferably 0.3 or less, more preferably 0.2 or less, and even more preferably 0.1 or less.

[0033] Haze (Soft) and Haze (Hard) are not particularly limited, but can be selected from a range of, for example, 99% or less (e.g., 0-99%). The above "haze" refers to the ratio of diffusely transmitted light to total transmitted light when visible light is irradiated onto the object to be measured, and is also called the haze value. Haze can be expressed by the following formula: Th (%) = Td / Tt × 100 In the above formula, Th is haze (%), Td is the scattered light transmittance, and Tt is the total light transmittance. The above haze value can be adjusted, for example, by selecting the composition and thickness of the adhesive layer.

[0034] In addition, if it is difficult to cut out an adhesive layer of a predetermined size from the area to be measured when measuring the various physical properties described herein, an adhesive layer with the same composition as the area to be measured may be prepared, and an adhesive layer of the predetermined size may be cut out from that adhesive layer to prepare a measurement sample.

[0035] Soft and hard regions, which have different elastic moduli and similar characteristics in one or more of the group consisting of refractive index, transmittance, and haze, can be prepared by making the types of base polymers and constituent monomers and their amounts similar for each region, and by creating differences in the degree of polymer crosslinking within each region, for example, by making differences in the type and amount of crosslinking agent used.

[0036] The adhesive sheet of the present invention is preferably used by laminating it on the same side so as to span two adherends with a separation region. Figure 2 shows a cross-sectional view of one embodiment in which the adhesive sheet shown in Figure 1 is laminated on the same side so as to span the two adherends. The adhesive sheet 10 is arranged so as to be laminated in the following order: cover member 2, adhesive sheet 10, glass plate 3, adhesive sheet 4, and optical member 5. The adhesive sheet 10 is interposed between the cover member 2 and the glass plate 3, bonding them together. The adhesive sheet 4 is interposed between the optical member 5 and the glass plate 3, bonding them together. The adhesive sheet 10 is the adhesive sheet of the present invention, and the adhesive sheet 4 may be the adhesive sheet of the present invention, or an adhesive sheet other than the adhesive sheet of the present invention (other adhesive sheets). Alternatively, the adhesive sheet 10 may be the other adhesive sheet and the adhesive sheet 4 may be the adhesive sheet of the present invention.

[0037] The optical laminate 13, formed by directly stacking a cover member 2, an adhesive sheet 10, a glass plate 3, an adhesive sheet 4, and an optical member 5 in this order, is used by adhering it to two adherends 6 and 7, which are arranged with a separation region R on the same side (i.e., the same side of the adhesive sheet 10), via adhesive sheets 8 and 9. At this time, the adhesive sheet 10 is positioned such that the soft region 12 overlaps with the separation distance R and a portion of the adherends 6 and 7 in the thickness direction (a direction perpendicular to one direction D in Figure 2), and the hard regions 11a and 11b overlap with the remaining portion of the adherends 6 and 7 in the thickness direction. The hard regions 11a and 11b are not positioned to overlap with the separation region R in the thickness direction. The two adherends 6 and 7 are used by bending them, for example, at or near the bending portion V within the separation region R.

[0038] Figure 3 shows a simplified plan view of the laminate shown in Figure 2. In Figure 3, the cover member 2 in the optical laminate 13 and the adhesive sheets 8 and 9 provided on the adherends 6 and 7 are omitted in order to make it easier to recognize the positional relationship between the soft region 12 and the hard regions 11a and 11b of the adhesive sheet 10 and the separated region R. The cross-sectional view of Figure 2 corresponds to the II-II' cross-sectional view of Figure 3, except that it has the cover member 2 and the adhesive sheets 8 and 9.

[0039] When the width of the soft region 12 is X and the width of the separated region R is Y, the adhesive sheet 10 satisfies the following equation (5). The width Y is the shortest distance between the side surface of the adherend 6 and the side surface of the adherend 7 opposite to that side surface. X / Y ≥ 3 (5)

[0040] FIG. 4 is a simplified cross-sectional view showing a state where the laminate shown in FIG. 2 is folded at the folding portion V. In FIG. 4, configurations other than the pressure-sensitive adhesive sheet 10 in the optical laminate 13 and the pressure-sensitive adhesive sheets 8, 9 are omitted to facilitate recognition of the positional relationship between the soft region 12 and the hard regions 11a, 11b in the pressure-sensitive adhesive sheet 10 and the adherends 6, 7. As shown in FIG. 2 and FIG. 3, the adherends 6, 7 are bonded to the optical laminate 13 with a separation region R provided therebetween, so when the optical laminate 13 is folded, the adherends 6, 7 do not bend, and only the optical laminate 13 bends. The folding portion V and its periphery are the soft region 12, which assumes a teardrop shape as shown in FIG. 4 when folded. When the pressure-sensitive adhesive sheet 10 is folded, the hard regions 11a and 11b are less likely to deform, so the soft region 12 is forced to deform. Here, the configuration where X / Y is 3 or more means that in the soft region 12, the width corresponding to the width Y is equal to or larger than the width that overlaps with the adherend 6 or 7 in the thickness direction. When X / Y is 3 or more, the strain applied to the soft region 12 when the pressure-sensitive adhesive sheet 10 is folded is small, so that creases (crazes) are less likely to occur at the folded portion even after the pressure-sensitive adhesive sheet 10 is stored in the folded state for a long period of time, and peeling is less likely to occur around the folding portion V (such as near the boundary between the soft region 12 and the hard regions 11a, 11b, and near the edges of the adherends 6, 7). In addition, since the pressure-sensitive adhesive layer 1 has the hard regions 11a, 11b and the soft region 12, adhesive squeeze-out during punching is less likely to occur than in the case where the pressure-sensitive adhesive layer is composed only of a soft region, resulting in excellent punching processability.

[0041] As described above, the width X is preferably 3 times or more the width Y, more preferably 3.1 times or more, and even more preferably 3.2 times or more. Further, the width X is preferably 10 times or less the width Y, more preferably 8 times or less, still more preferably 6 times or less, and particularly preferably 5 times or less. When the width X is 10 times or less, the excess soft region that extends outside the adherend when the adherend is folded can be reduced.

[0042] The length of the width X of the soft region 12 is appropriately selected depending on the width Y of the separation region R and the size of the adherend, and is, for example, 10 mm or more, preferably 20 mm or more, more preferably 30 mm or more, and still more preferably 40 mm or more. When the length of the width X is 10 mm or more, the width Y can be sufficiently secured, and the adherend can be easily folded. The length of the width X is, for example, 100 mm or less, preferably 70 mm or less, more preferably 60 mm or less, and still more preferably 50 mm or less. When the width X is 100 mm or less, the excess soft region that extends outside the adherend when the adherend is folded can be reduced.

[0043] The length of the width Y of the separation region R is appropriately selected depending on the width X of the soft region 12 and the size of the adherend, and is, for example, 1 to 40 mm, preferably 5 to 30 mm, and more preferably 10 to 20 mm. When the length of the width Y is 1 mm or more, the width Y can be sufficiently secured, and the adherend can be easily folded. When the length of the width Y is 40 mm or less, the excess soft region that extends outside the adherend when the adherend is folded can be reduced.

[0044] In Figures 1 to 3, the hard regions 11a, 11b and the soft region 12 extend in one direction D and are formed in parallel to each other, and have a rectangular shape. However, in the pressure-sensitive adhesive layer of the present invention, the shapes of the hard regions 11a, 11b and the soft region 12 are not particularly limited as long as the pressure-sensitive adhesive sheet can be folded for use.

[0045] The hard regions 11a, 11b and the soft region 12 may have the same or different width lengths (lengths in one direction D). Also, in Figures 1 to 3, the two hard regions 11a, 11b have the same width length, but they may be different.

[0046] On the side of the hard region 11a opposite to the soft region 12, there may be a region with a different hardness from the hard region 11a (for example, a soft region 12). Similarly, on the side of the hard region 11b opposite to the soft region 12, there may be a region with a different hardness from the hard region 11b (for example, a soft region 12). Furthermore, the adhesive layer of the present invention may have two or more soft regions, or three or more hard regions. In this case, the hardness of the multiple soft regions may be the same or different. Similarly, the hardness of the multiple hard regions may be the same or different. Also, in Figure 2, the width lengths of the two hard regions 11a and 11b located at both ends are the same, but one may be longer and the other shorter. Note that the width lengths of all soft regions and all hard regions in the adhesive layer may be the same or different, respectively. When there are multiple hard regions and / or multiple soft regions, all hard regions may be harder than all soft regions, or they may be harder than adjacent regions. Furthermore, all soft regions may be softer than all hard regions, or they may be softer than adjacent regions.

[0047] The soft region 12 and the hard regions 11a and 11b may or may not have clearly defined boundaries. The area near the boundary between the soft region 12 and the hard regions 11a and 11b may be a boundary region where the hardness changes gradually. In the boundary region, there is a hardness gradient, and along one direction D, the hardness gradually changes from the hard region 11a to the soft region 12, from the center of the hard region 11a to the center of the soft region 12. Therefore, the boundary region is the area from the point where the hardness gradient begins to the point where the gradient ends. When the boundary region is present, the hardness of the soft region 12 and the hard region 11a are the physical properties of the parts outside the boundary region, respectively. The same applies to the boundary between the soft region 12 and the hard region 11b. When the boundary region is present, the width X has its end point at the center in one direction D of the boundary region.

[0048] The shape of the boundary between the soft region 12 and the hard regions 11a and 11b is linear in Figures 1 to 3, but it is not particularly limited as long as the soft region 12 is bendable, and it may be a wavy line or the like. The adhesive layer 1 is symmetrical in one direction D. For example, in Figures 1 to 3, the hard regions 11a and 11b and the soft region 12 are positioned in the adhesive layer 1 so as to be symmetrical with respect to the bendable portion V.

[0049] The maximum value A of the elastic modulus of the soft region in the range of -20 to 100°C is preferably 60 kPa or less, more preferably 55 kPa or less, and even more preferably 50 kPa or less. When the maximum value A is 60 kPa or less, the soft region has appropriate flexibility in a wide range of temperature environments, and the adherend can be easily folded. The lower the maximum value A, the more flexible it is, but from the viewpoint of excellent handling, it is preferably 10 kPa or more, more preferably 20 kPa or more, and even more preferably 30 kPa or more. Examples of the elastic modulus include the storage modulus and the loss modulus.

[0050] The minimum value B of the elastic modulus of the soft region in the range of -20 to 100°C is preferably 30 kPa or less, more preferably 20 kPa or less, and even more preferably 15 kPa or less. When the minimum value B is 30 kPa or less, the soft region has appropriate flexibility under a wide temperature range. A lower minimum value B indicates greater flexibility, but from the viewpoint of excellent handling, it is preferably 1 kPa or more, more preferably 3 kPa or more, and even more preferably 5 kPa or more. Examples of the elastic modulus include the storage modulus and the loss modulus.

[0051] Preferably, the above maximum value A and minimum value B satisfy the following formula (6). When the following formula (6) is satisfied, the difference between the maximum value A and minimum value B is small, and the soft region has appropriate flexibility under a wide temperature environment. 0.1 ≤ B / A < 1 (6)

[0052] In formula (6) above, [B / A] is preferably 0.1 to 0.8, more preferably 0.15 to 0.5.

[0053] The peel adhesive strength F (Hard) in the hard region at room temperature (23±2℃) is preferably greater than 3N / 10mm, more preferably 3.5N / 10mm or more, even more preferably 4N / 10mm or more, and particularly preferably 4.5N / 10mm or more. When the peel adhesive strength F (Hard) is greater than 3N / 10mm, the adhesion in the hard region is excellent and peeling is less likely to occur. A higher peel adhesive strength F (Hard) is preferable as it provides better adhesion, but for example, it is 20N / 10mm or less.

[0054] The peel adhesive strength F (Soft) in the above-mentioned soft region at room temperature (23±2℃) is preferably greater than 3N / 10mm, more preferably 3.5N / 10mm or more, even more preferably 4N / 10mm or more, and particularly preferably 4.5N / 10mm or more. When the peel adhesive strength F (Soft) is greater than 3N / 10mm, the adhesion in the soft region is excellent and peeling is less likely to occur. A higher peel adhesive strength F (Soft) is preferable as it provides better adhesion, but for example, it is 20N / 10mm or less.

[0055] The above peel adhesion strengths F(Hard) and F(Soft) preferably satisfy the following formula (7). Typically, the hard region has a lower peel adhesion strength than the soft region. When the following formula (7) is satisfied, the difference between the hard and soft regions is small, and peeling is less likely to occur near the boundary between the soft and hard regions. 0.9 ≤ F(Hard) / F(Soft) ≤ 1.1 (7)

[0056] In the above formula (7), [F (Hard) / F (Soft)] is preferably 0.95 to 1.05.

[0057] It is preferable that the hard regions 11a, 11b and the soft region 12 have similar optical properties other than total light transmittance, haze value, and refractive index. When the optical properties are similar, the boundary between the hard region and the soft region is difficult to see, resulting in a good appearance when the adhesive sheet of the present invention is used by laminating it to an optical member. The optical properties of the two hard regions may be the same or different. Examples of such optical properties include transparency and visible light transmittance.

[0058] (Method for manufacturing the adhesive layer) The adhesive layer having the soft region and the hard region can be manufactured by known or conventional methods. Examples of methods for manufacturing the adhesive layer include the first to fourth methods. The first to fourth methods may be used individually or in combination of two or more.

[0059] The first method involves using adhesive compositions with different compositions for forming the soft region and the hard region. Examples of differing adhesive compositions include those that differ in the type of base polymer of the adhesive constituting the adhesive layer, the monomer composition of the base polymer, the weight-average molecular weight of the base polymer, the type of crosslinking agent, the amount of crosslinking agent used (amount added), and the type and content of other additives. For example, if the amount of crosslinking agent used is different, the region using a larger amount of crosslinking agent will be a relatively hard region, and the region using a smaller amount of crosslinking agent will be a relatively soft region.

[0060] Examples of base polymers constituting the soft and hard regions include known and conventional polymers, such as acrylic polymers, urethane acrylate resins, urethane resins, rubber resins, epoxy resins, epoxy acrylate resins, oxetane resins, silicone resins, silicone acrylic resins, polyester resins, polyether resins (such as polyvinyl ether), polyamide resins, fluororesins, vinyl acetate / vinyl chloride copolymers, and polyolefins.

[0061] Examples of the above-mentioned crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, amine-based crosslinking agents, silicone-based crosslinking agents, silane-based crosslinking agents, and polyfunctional monomers such as polyfunctional (meth)acrylates. In this specification, the above-mentioned "crosslinking agent" refers to a compound that can form crosslinks in a resin, and may be referred to as a "curing agent."

[0062] Examples of the above-mentioned other additives include crosslinking accelerators, tackifying resins (rosin derivatives, polyterpene resins, petroleum resins, oil-soluble phenols, etc.), oligomers, antioxidants, fillers (metal powders, organic fillers, inorganic fillers, etc.), antioxidants, plasticizers, softeners, surfactants, antistatic agents, surface lubricants, leveling agents, light stabilizers, UV absorbers, polymerization inhibitors, granular materials, foil-like materials, and release modifiers.

[0063] In the first method, for example, an adhesive composition that forms a soft region and an adhesive composition that forms a hard region are first applied to the release surface or substrate of the same release liner, respectively. The application of the adhesive composition that forms the soft region and the adhesive composition that forms the hard region may be done simultaneously or sequentially. After applying the adhesive composition to the release surface or substrate of the release liner to form an adhesive composition layer, the adhesive composition layer is solidified by volatilization and removal of the solvent by heating or polymerization by irradiation with active energy rays to form an adhesive layer, thereby creating an adhesive layer having a soft region and a hard region. In addition, heating, drying, etc. may be performed in addition to the irradiation with active energy rays as needed.

[0064] The second method involves using the same adhesive composition for both the soft region and the hard region, adding a modifier in such a way that the proportions differ between the soft and hard regions, and then forming an adhesive layer. In this case, an active energy ray polymerizable adhesive composition can be used as the adhesive composition.

[0065] In the second method, for example, first, an adhesive composition for forming an adhesive layer is applied to the release surface of the release liner or the substrate. After applying the adhesive composition to the release surface of the release liner or the substrate to form an adhesive composition layer, a modifier is added to the areas to be designated as soft regions and / or hard regions. The addition can be done by application. The modifier may be added to only one of the areas to be designated as soft regions and / or hard regions, or it may be added to both. If it is added to both, the amounts added should be different. The modifier to be added may be the modifier itself, or it may be a solution or dispersion in which it is dissolved and dispersed in a solvent.

[0066] The above-mentioned modifiers can be used without particular limitations, and those added in the field of adhesives can be used. Examples include polymerization initiators, crosslinking agents, ultraviolet absorbers, rust inhibitors, antistatic agents, crosslinking accelerators, silane coupling agents, tackifying resins, anti-aging agents, colorants such as dyes, antioxidants, chain transfer agents, plasticizers, softeners, surfactants, and fillers. Regions with a large amount of crosslinking agent will have a high crosslinking density of the base polymer when the adhesive layer is formed, resulting in a relatively hard region. Regions with a large amount of plasticizer will result in a relatively soft region. After adding the modifiers, the adhesive composition layer can be solidified by volatilization and removal of the solvent by heating or polymerization by irradiation with active energy rays to form an adhesive layer, thereby creating an adhesive layer having both soft and hard regions.

[0067] A third method involves using the same adhesive composition for both the soft region and the hard region, but with different degrees of polymerization. In this case, an active energy ray polymerizable adhesive composition can be used as the adhesive composition.

[0068] In the third method, for example, first, an adhesive composition for forming the adhesive layer is applied to the release surface of the release liner or the substrate. After applying the adhesive composition to the release surface of the release liner or the substrate to form the adhesive composition layer, a photomask is placed over a portion of the area, and the adhesive composition layer is irradiated with active energy rays. In addition, heating, drying, etc. may be performed as needed in addition to the irradiation with active energy rays. In this way, the adhesive layer is formed by solidifying the adhesive composition layer through polymerization by irradiation with active energy rays. In the area covered with the photomask, the active energy rays are not irradiated, or the amount of active energy rays irradiated is small, and the degree of polymerization in that area is relatively small. On the other hand, in the area not covered with the photomask, the amount of active energy rays irradiated is large, and the degree of polymerization in that area is relatively large. The two areas formed in this way have different physical properties such as hardness, and can be a soft area and a hard area.

[0069] In the third method, a photomask having regions with different transmittances of active energy rays may be placed over the entire surface of the adhesive composition layer and irradiated with active energy rays. In this way, an adhesive layer having soft and hard regions with different amounts of active energy irradiated can be produced.

[0070] The fourth method involves forming an adhesive layer using the same adhesive composition for both the soft region and the hard region, and then impregnating the adhesive layer with the modifier such that the amounts of the modifier differ in the soft region and the hard region. In this case, an active energy ray polymerizable adhesive composition can be used as the adhesive composition.

[0071] In the fourth method, for example, first, an adhesive composition for forming the adhesive layer is applied to the release surface of the release liner or the substrate. After applying the adhesive composition to the release surface of the release liner or the substrate to form the adhesive composition layer, the adhesive layer is solidified by volatilization and removal of the solvent by heating or polymerization by irradiation with active energy rays. Subsequently, a modifier is impregnated into the areas to be designated as soft regions and / or hard regions. In this way, an adhesive layer having soft regions and hard regions can be produced.

[0072] Impregnation can be carried out by coating. The modifier may be impregnated into only one of the areas to be treated as a soft region and the area to be treated as a hard region, or it may be impregnated into both. If both are impregnated, the amount of modifier added should be different. The modifier to be impregnated may be the modifier itself, or it may be a solution or dispersion obtained by dissolving and dispersing it in a solvent.

[0073] (Substrate) When the adhesive sheet of the present invention is an adhesive sheet with a substrate, the substrate is not particularly limited, but examples include plastic films, anti-reflective (AR) films, anti-glare (AG) films, polarizing plates, and various optical films such as phase difference plates. Other examples of substrates include porous materials such as paper, cloth, and nonwoven fabrics, nets, foamed sheets, and metal foils. Examples of materials such as plastic films include polyester resins such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetylcellulose (TAC), polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymer, and cyclic olefin polymers such as the trade name "Arton" (cyclic olefin polymer, manufactured by JSR Corporation) and the trade name "Zeonor" (cyclic olefin polymer, manufactured by Nippon Zeon Co., Ltd.). Note that one or more of these plastic materials may be used.

[0074] The surface of the substrate on the side with the adhesive layer may be subjected to surface treatments such as physical treatments like corona discharge treatment, plasma treatment, sandblasting, ozone exposure treatment, flame exposure treatment, high-voltage electric shock exposure treatment, or ionization radiation treatment; chemical treatments like chromic acid treatment; or surface treatments such as easy adhesion treatment with a coating agent (primer) in order to improve adhesion and retention with the adhesive layer. It is preferable that the surface treatment to improve adhesion is applied to the entire surface of the substrate on the side with the adhesive layer.

[0075] The above-mentioned substrate may be a noise-reducing film. The noise-reducing film is not particularly limited as long as it has noise-reducing performance, but examples include a film substrate on which a noise-reducing layer is formed on at least one side. The noise-reducing layer may be a single layer or a multi-layer, and is not particularly limited as long as it has the function of reducing electromagnetic noise, but from the viewpoint of transparency, a transparent conductive layer is preferred. As the transparent conductive layer, a thin film layer formed of a conductive organic or inorganic material, or a conductive layer formed by partial contact of conductive organic or inorganic materials can be used.

[0076] The thickness of the above-mentioned substrate is not particularly limited, but is preferably 10 to 150 μm, more preferably 15 to 125 μm, and even more preferably 25 to 100 μm. The above-mentioned substrate may be in the form of a single layer or multiple layers.

[0077] The above-mentioned adhesive sheet may have a release liner on the surface (adhesive surface or bonding surface) of the adhesive layer, etc., until use. If the above-mentioned adhesive sheet is a double-sided adhesive sheet, each adhesive surface may be protected by two release liners, or it may be protected in a roll-like form (winding body) by a single release liner with both sides being release surfaces. The release liner is used as a protective material for the adhesive layer and is peeled off when it is attached to the object. Furthermore, if the above-mentioned adhesive sheet is a substrate-less adhesive sheet, the release liner also plays the role of a support for the adhesive layer. Note that the release liner is not necessarily required.

[0078] Examples of the configuration of the adhesive sheet described above include the configuration of the adhesive sheet 10 shown in Figure 1 [release liner / adhesive layer / release liner], [adhesive layer / release liner], [base material / adhesive layer / release liner], [release liner / adhesive layer / base material / adhesive layer / release liner], and [base material / adhesive layer / base material / adhesive layer / release liner]. In the configuration comprising two adhesive layers, at least one adhesive layer is the adhesive layer of the present invention, but from the viewpoint of the adhesive sheet being bendable, it is preferable that both are the adhesive layers of the present invention. Furthermore, the arrangement shapes of the soft region and the hard region in the two adhesive layers of the present invention may be the same or different.

[0079] The adhesive sheet of the present invention is not particularly limited in its use and can be used for any purpose. The adhesive sheet of the present invention can be used, for example, in optical applications, i.e., for bonding to optical components. The adhesive sheet of the present invention is used, for example, in optical components of electrical and electronic equipment when attaching (mounting) various components or parts to a predetermined part (e.g., a housing). Note that "electrical and electronic equipment" refers to equipment that falls under at least one of electrical equipment or electronic equipment. Examples of the above electrical and electronic equipment include image display devices such as liquid crystal displays, electroluminescent displays, and plasma displays, and portable electronic devices. Examples of the above image display devices include image display devices in portable electronic devices, and displays (roll displays) inside and outside vehicles such as trains and buses.

[0080] Examples of the above-mentioned portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (e.g., wristwear-type devices worn on the wrist like watches, modular-type devices attached to a part of the body with clips or straps, eyewear-type devices including glasses (monocular and binocular types, including head-mounted types), clothing-type devices attached to shirts, socks, hats, etc. as accessories, earwear-type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game consoles, electronic dictionaries, electronic organizers, e-books, in-car information systems, portable radios, portable televisions, portable printers, portable scanners, and portable modems. In this specification, "portable" means not merely being able to carry something, but having a level of portability that allows an individual (a typical adult) to carry it relatively easily.

[0081] The above-mentioned adhesive sheet is preferably used, for example, for bonding components and modules that make up portable electronic devices to each other, or for fixing components and modules that make up portable electronic devices to the casing. More specifically, examples include bonding cover glass or lenses (especially glass lenses) to touch panels or touch sensor films (especially touch sensor films having metal wiring such as metal mesh films or silver nanowire films), bonding polarizing films to touch panels or touch sensors, bonding display panels to touch panels or touch sensor films, fixing cover glass or lenses (especially glass lenses) to the casing, fixing display panels to the casing, fixing input devices such as sheet keyboards and touch panels to the casing, bonding protective panels of information display sections to the casing, bonding casings to each other, bonding casings to decorative sheets, and fixing or bonding various components and modules that make up portable electronic devices. In this specification, a display panel refers to a structure that is at least composed of a lens (especially a glass lens) and a touch panel. Furthermore, in this specification, a lens is a concept that includes both transparent materials that exhibit light refraction and transparent materials that do not exhibit light refraction. In other words, the term "lens" in this specification also includes simple window panels that do not have a refractive effect.

[0082] Furthermore, the adhesive sheet can be suitably used with transparent conductive films (metal mesh films, silver nanowire films) in which the metal wiring is metal mesh wiring or silver nanowires, and in particular with optical components (touch sensor films) having a metal mesh film. When optical components having metal wiring such as metal mesh films or silver nanowire films are bonded together via the adhesive sheet, the low dielectric constant suppresses noise generation while providing sufficient adhesive strength and excellent resistance to drop impacts.

[0083] The adhesive sheet of the present invention has a hard region and a soft region within the same plane of the adhesive layer, and the boundary between the hard region and the soft region is difficult to see. Therefore, the adhesive sheet of the present invention is preferably used for bonding components (especially between components) in electrical and electronic equipment that is used in a bendable manner, such as a bendable adherend, such as a bendable image display device (flexible display) (especially a foldable image display device (foldable display)).

[0084] [Optical Laminate] A laminate comprising the adhesive sheet and optical member of the present invention, such as optical laminate 13, may be referred to as "the optical laminate of the present invention." The optical laminate of the present invention preferably comprises a cover member, an adhesive sheet (A), a glass plate, an adhesive sheet (B), and an optical member in this order. In the optical laminate of the present invention, the cover member side is preferably the viewing side when laminated on, for example, an image display device. In the optical laminate of the present invention, at least one of the adhesive sheets is the adhesive sheet of the present invention, and both may be the adhesive sheets of the present invention. From the viewpoint of superior scratch resistance of the optical member, it is preferable that adhesive sheet (A) is the adhesive sheet of the present invention.

[0085] The optical laminate 13 shown in Figure 2 is one embodiment of the optical laminate of the present invention. In the optical laminate 13, the cover member 2 functions as an element for protecting other optical components (for example, touch sensors and image display devices) in the optical laminate 13.

[0086] Examples of the cover member include a cover glass and a plastic cover. The cover member may be bonded to the glass plate 3 via an adhesive sheet 10 or other adhesive sheets, as shown in Figure 2. Examples of plastics that make up the plastic cover include polyester resins such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, triacetylcellulose (TAC), polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, and ethylene-propylene copolymer. Only one type of plastic material may be used, or two or more types may be used.

[0087] From the viewpoint of being thin yet strong and being able to be bent, the glass plate 3 is preferably made of a type of glass other than alkali glass, such as alkali-free glass. The thickness of the glass plate 3 is preferably 30 to 70 μm, and more preferably 30 to 50 μm, from the viewpoint of being able to be bent.

[0088] The thickness of the adhesive sheet (A) and the adhesive sheet (B) described above is preferably 25 to 100 μm, and more preferably 70 to 100 μm, from the viewpoint of providing excellent stress relief when subjected to impact, minimizing the likelihood of indentations remaining on the optical laminate, and minimizing the likelihood of cracks occurring in the glass plate.

[0089] In the optical laminate 13, the optical member 5 has a film on the surface facing the adhesive sheet 4. Examples of the film include various optical films such as plastic films, anti-reflective (AR) films, anti-glare (AG) films, polarizing plates, and phase difference plates. Examples of materials such as the plastic film include those described and illustrated as plastics that can constitute the cover member 2. In addition to the above-mentioned film, the optical member 5 may include one or more selected from the group consisting of a touch sensor, a noise reduction layer, and an image display device.

[0090] Examples of the above-mentioned image display devices include liquid crystal displays, organic / inorganic electroluminescent displays, and plasma displays. Examples of the above-mentioned image display devices include image display devices in portable electronic devices, in-vehicle displays, and digital signage (electronic billboards and electronic display boards). The above-mentioned image display devices may be in a form (structure) such as a so-called "flexible type," or they may be in a form (structure) that can be bent or folded, such as a so-called "foldable type" or "rollable type."

[0091] The above-mentioned touch sensor is a capacitive touch sensor, and is, for example, a transparent conductive film in which a transparent conductive layer is provided on a glass plate or a transparent plastic film (particularly PET film, polycarbonate film, or cyclic olefin polymer film). It is preferable that the adhesive layer of the present invention is bonded so as to be in contact with the above-mentioned transparent conductive layer.

[0092] Examples of the transparent conductive layer include thin films of ITO (indium tin oxide), ZnO, SnO, and CTO (cadmium tin oxide). Other materials such as silver, copper, and CNT (carbon nanotube) can also be used to form the transparent conductive layer. Furthermore, metal mesh sensors such as Ag nanowires and Ag / Cu can be used in the transparent conductive layer. The touch sensor may also have wiring formed from thin films of copper or silver paste at its ends.

[0093] The optical laminate of the present invention preferably comprises an image display device and a touch sensor. The optical laminate of the present invention can be used in known or conventional optical products that include an image display device and a touch sensor. Examples of such optical products include the electrical and electronic devices described above, and can be used in, for example, image display devices, portable electronic devices, roll displays, etc.

[0094] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit it.

[0095] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0096] Example 1 (Preparation of Acrylic Prepolymer Solution 1) In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, 57.5 parts by mass of 2-ethylhexyl acrylate (2EHA), 39 parts by mass of lauryl acrylate (LA), 0.5 parts by mass of N-vinyl-2-pyrrolidone (NVP), 2 parts by mass of 4-hydroxybutyl acrylate (4HBA), 1 part by mass of hydroxyethyl acrylate (HEA), 0.05 parts by mass of a photopolymerization initiator (trade name "Omnirad 184", manufactured by IGM Resins Italia Srl), and 0.05 parts by mass of another photopolymerization initiator (trade name "Omnirad 651", manufactured by IGM Resins Italia Srl) were added, and nitrogen gas was introduced, followed by nitrogen purging for approximately 20 minutes while stirring. Subsequently, 5 mW / cm ２ Polymerization was carried out by irradiating with ultraviolet light, and the reaction rate was adjusted to 5-15% to obtain acrylic prepolymer solution 1.

[0097] (Preparation of adhesive composition 1) To the above acrylic prepolymer solution 1, 0.06 parts by mass of dipentaerythritol hexaacrylate (DPHA) as a crosslinking agent and 0.3 parts by mass of (product name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) as a silane coupling agent were added and stirred to prepare adhesive composition 1.

[0098] (Preparation of Acrylic Prepolymer Solution 2) In a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, 78 parts by mass of 2-ethylhexyl acrylate (2EHA), 18 parts by mass of N-vinyl-2-pyrrolidone (NVP), 4 parts by mass of hydroxyethyl acrylate (HEA), 0.03 parts by mass of photopolymerization initiator (trade name "Omnirad 184", manufactured by IGM Resins Italia Srl), and 0.03 parts by mass of photopolymerization initiator (trade name "Omnirad 651", manufactured by IGM Resins Italia Srl) were added, and nitrogen gas was introduced and the mixture was purged with nitrogen for about 20 minutes while stirring. After that, the mixture was purged with nitrogen at 5 mW / cm². ２Polymerization was carried out by irradiating with ultraviolet light, and the reaction rate was adjusted to 5-15% to obtain acrylic prepolymer solution 2.

[0099] (Preparation of Adhesive Composition 2) To the above acrylic prepolymer solution 2, 0.09 parts by mass of 1,6-hexanediol diacrylate (HDDA) (trade name "A-HD-N", manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) as a crosslinking agent and 0.4 parts by mass of (trade name "KBM-403", manufactured by Shin-Etsu Chemical Co., Ltd.) as a silane coupling agent were added and stirred to prepare adhesive composition 2.

[0100] (Preparation of Adhesive Sheet) As shown in Figure 5, the adhesive composition 1 (14) and the adhesive composition 2 (15) were placed near one edge E on the release surface of the release liner 21 (product name "MRE38", manufactured by Mitsubishi Chemical Corporation, polyethylene terephthalate film with release treatment on one side, thickness 38 μm) in the order of adhesive composition 2 (15), adhesive composition 1 (14), adhesive composition 2 (15). Then, by moving the applicator 16 from one edge to the other edge, the adhesive composition 1 and adhesive composition 2 were spread in one direction to form an adhesive composition layer (thickness 50 μm). After that, the release surface of the release liner 22 (product name "MRF38", manufactured by Mitsubishi Chemical Corporation) was attached to the adhesive composition layer. Next, a black light was used to measure 2.5 mW / cm². ２ The ultraviolet light at an illuminance of 2400 mJ / cm² is measured by the cumulative light intensity of 2400 mJ / cm². ２ Polymerization was carried out by irradiation until the desired result was reached. In this way, an adhesive sheet 10 (thickness 50 μm) was manufactured, consisting of an adhesive layer 1 having relatively hard regions 11a and 11b and a relatively soft region 12.

[0101] In Example 2 and Comparative Examples 1-2, adhesive sheets were manufactured in the same manner as in Example 1, except that the monomer composition of the acrylic prepolymer solution used and the type and amount of crosslinking agent in the curing agent were changed as shown in Table 1. In Table 1, "POB-A" refers to the trade name "Light Acrylate POB-A" (3-phenoxyphenyl) methyl acrylate, and "DCPDMA" refers to dicyclopentanyl methacrylate. In Table 1, "oligomer" refers to the acrylic oligomer obtained by the preparation of the oligomer described below.

[0102] (Preparation of Oligomers) First, in a reaction vessel equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, a mixture containing 60 parts by mass of dicyclopentanyl methacrylate (DCPMA), 40 parts by mass of methyl methacrylate (MMA), 3.5 parts by mass of α-thioglycerol as a chain transfer agent, and 100 parts by mass of toluene as a solvent was stirred at 70°C for 1 hour under a nitrogen atmosphere. Next, 0.2 parts by mass of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was added to the mixture to prepare a reaction solution, which was reacted under a nitrogen atmosphere at 70°C for 1 hour, and then at 80°C for 2 hours (polymerization reaction). Next, the reaction solution was heated to 130°C to volatilize and remove toluene, chain transfer agent, and unreacted monomers. This yielded an acrylic oligomer (solid form) as a hydrophobic oligomer without polar groups. The weight-average molecular weight of this acrylic oligomer was 5100.

[0103] <Evaluation> The adhesive sheets obtained in the examples and comparative examples were evaluated as follows. The results are shown in Table 1.

[0104] (1) Elastic Modulus For the soft and hard regions of the adhesive layers obtained in the examples and comparative examples, measurement samples with a thickness of 2 mm were prepared by laminating them, and the elastic modulus was measured by dynamic viscoelasticity measurement using the "Advanced Rheometric Expansion System (ARES)" manufactured by TA Instruments. The measurement conditions were as follows. The elastic modulus G (Soft) of the soft region, the elastic modulus G (Hard) of the hard region, and [G (Hard) / G (Soft)] were calculated at 25°C. [Measurement Conditions] Deformation mode: Torsion Measurement frequency: 1 Hz Heating rate: 5°C / min Shape: Parallel plate 8 mmφ

[0105] (2) The refractive index of the soft and hard regions of the adhesive layers obtained in the refractive index examples and comparative examples was measured using a prism coupler.

[0106] (3) Transmittance (Total Light Transmittance) The total light transmittance was measured for the soft and hard regions of the adhesive layers obtained in the examples and comparative examples. Specifically, the release liners on both sides of the adhesive sheet were peeled off, attached to a measuring jig, and the total light transmittance was measured using a spectrophotometer (product name "U4150", manufactured by Hitachi High-Tech Corporation).

[0107] (4) The haze of the soft and hard regions of the adhesive layers obtained in the haze examples and comparative examples was measured using a haze meter. Specifically, the release liners on both sides of the adhesive sheet were peeled off, and one side was bonded to alkali-free glass (thickness 0.8 to 1.0 mm, total light transmittance 92%, haze 0.4%) to test specimens. The haze of the test specimens was measured using a haze meter (product name "HAZEMETER HM-150", manufactured by Murakami Color Technology Laboratory Co., Ltd.) under a measurement environment of 23°C. The value obtained by subtracting the haze of the alkali-free glass from the measured value was taken as the haze value of the adhesive layer.

[0108] (5) Visibility of the boundary The release liners on both sides were peeled off from the adhesive sheets obtained in the examples and comparative examples, and PET films were bonded to them to create a laminate of [PET film / adhesive layer / PET film]. The laminate was held up to the direction of the fluorescent lamp so that the laminate was positioned between the fluorescent lamp and the evaluator's eye position, and the light from the fluorescent lamp was transmitted in the thickness direction of the laminate, and the laminate was observed visually. The distance between the fluorescent lamp and the laminate was set to 1 m, and the distance between the laminate and the evaluator's eye position was set to 0.3 m. The boundary between the soft area and the hard area was evaluated as "○" if it could not be seen, and as "×" if it could be seen.

[0109]

[0110] As shown in Table 1, the adhesive sheet of the example had no visible boundary between the soft and hard regions, and was judged to have good visibility. On the other hand, Comparative Example 1 had a small G(Hard) / G(Soft) ratio, and was judged not to have hard and soft regions within the same plane of the adhesive layer. Furthermore, when the |refractive index (Soft) - refractive index (Hard)| ratio was large (Comparative Example 2), it was difficult to visually distinguish the boundary between the hard and soft regions.

[0111] 1 Adhesive layer 2 Cover member 3 Glass plate 4 Adhesive sheet 5 Optical member 6, 7 Adhesive body 8, 9 Adhesive sheet 10 Adhesive sheet 11a, 11b Hard region 12 Soft region 13 Optical laminate 14 Adhesive composition 1 15 Adhesive composition 2 16 Applicator 21, 22 Peel-off liner D One direction E Edge R Separation region V Folded portion X Width of soft region Y Width of separation region

Claims

1. An adhesive sheet comprising an adhesive layer having a hard region, a soft region, and a hard region adjacent to each other in this order along one direction on the same plane, wherein the hard region is harder than the soft region, the absolute difference between the refractive index (Soft) of the soft region at a wavelength of 594 nm and the refractive index (Hard) of the hard region adjacent to the soft region at a wavelength of 594 nm satisfies the following equation (1), and the elastic modulus G (Hard) of the hard region at room temperature and the elastic modulus G (Soft) of the soft region adjacent to the soft region at room temperature satisfy the following equation (2). |Refractive index (Soft) - Refractive index (Hard)| ≤ 0.1 (1) 2 ≤ G (Hard) / G (Soft) ≤ 5 × 10 ３ (2) 2. An adhesive sheet comprising an adhesive layer having a hard region, a soft region, and a hard region adjacent to each other in this order along one direction within the same plane, wherein the hard region is harder than the soft region, and the absolute difference between the transmittance (Soft) of the soft region and the transmittance (Hard) of the hard region adjacent to the soft region satisfies the following equation (3): |Transmittance (Soft) - Transmittance (Hard)| ≤ 5 (3) 3. An adhesive sheet comprising an adhesive layer having a hard region, a soft region, and a hard region adjacent to each other in this order along one direction within the same plane, wherein the hard region is harder than the soft region, and the absolute difference between the haze (Soft) of the soft region and the haze (Hard) of the hard region adjacent to the soft region satisfies the following equation (4): |Haze (Soft) - Haze (Hard)| ≤ 0.5 (4)

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