Light-emitting device

Abstract

The present invention provides a light-emitting device in which an adhesive layer having a high refractive index and capable of withstanding large deformation is disposed on the visual side of a self-emitting element. The solution is as follows: the light-emitting device includes: a self-emissive element; a low-refractive-index layer disposed on the viewing side closer to the self-emissive element; and a high-refractive-index adhesive layer deposited in direct contact with the low-refractive-index layer. The high-refractive-index adhesive layer has a refractive index greater than 1.560, and its deformation in a deformation test at a temperature of -20°C and a speed of 300 mm / min is greater than 350%.

Description

[Technical Field]

[0001] The present invention relates to a light-emitting device, and more specifically to a light-emitting device having an adhesive layer disposed on the visual side of a self-emitting element. [Previous Technology]

[0002] Generally speaking, adhesives (also known as pressure-sensitive adhesives, hereinafter the same) are in a soft solid (viscoelastic) state in the temperature range near room temperature, and have the property of being easily bonded to the substrate by pressure. Taking advantage of this property, adhesives are widely used in various industries, from household appliances to automobiles, various machinery, electrical machines, and electronic machines, for purposes such as bonding, fixing, and protection. One example of the use of adhesives is their application in display devices such as liquid crystal displays or organic EL displays, for bonding polarizing films, phase difference films, cover window components, and various other light-transmitting components and other components. Technical documents concerning adhesives for optical components include Patent Documents 1 and 2. Patent Document 3 relates to a light-emitting device having an adhesive layer. Previous Artificial Literature Patent Documents

[0003] Patent Document 1: Japanese Patent Application Publication No. 2014-169382; Patent Document 2: Japanese Patent Application Publication No. 2017-128732; Patent Document 3: Japanese Patent Application Publication No. 2022-8015 [Summary of the Invention]

[0004] The problem to be solved by the invention: Patent documents 1 and 2 disclose an adhesive composition with (meth)acrylate polymer as the main component, and an adhesive formed by crosslinking the adhesive composition. The (meth)acrylate polymer contains monomers having a plurality of aromatic rings as monomer units. Furthermore, it is proposed that the refractive index of the adhesive be 1.50 or higher, preferably 1.51 or higher, by using monomers having a plurality of aromatic rings. Also, a technique is known to increase the refractive index by incorporating particles composed of high-refractive-index inorganic materials (such as zirconia particles or titanium oxide particles) into a resin. However, adhesives incorporating inorganic particles are difficult to apply in the field of adhesives because the refractive index and adhesive properties (such as peel strength, flexibility, etc.) are inversely related. For example, in the case of increasing the refractive index of the adhesive layer disposed on the viewing side of a self-emitting element in a light-emitting device, the influence on optical properties (such as total light transmittance, haze, etc.) must also be considered when incorporating inorganic particles. In the aforementioned context, the inventors have proposed a light-emitting device in Patent Document 3 that has an adhesive layer with high refractive index and optical quality disposed on the visual side of the self-emitting element.

[0005] However, in recent years, foldable or rollable displays have become practical for displays used in electronic devices such as smartphones and OLED displays. Therefore, adhesives used for these applications must possess flexibility to accommodate repeatedly bent substrates. Adhesives with excellent flexibility also readily conform to and adhere to surfaces with curved shapes, such as 3D shapes, making them suitable for applications in electronic devices with curved surfaces. Regarding adhesives with high refractive indices, if flexibility can be improved, they can also be expected to be used in applications involving repeated bending, such as foldable displays. However, adhesive polymers with high refractive indices tend to have high glass transition temperatures, such as aromatic rings, which can lead to a decrease in flexibility in adhesives formed using high refractive index materials. In adhesive design, high refractive index and flexibility are mutually exclusive. If an adhesive with a high refractive index and the flexibility to withstand use with large deformations can be realized, then even in the aforementioned foldable displays, the adhesive layer disposed on the viewing side of the self-emissive element can still be made to have a high refractive index, which would be useful.

[0006] The present invention was created in view of the above circumstances, and its object is to provide a light-emitting device having an adhesive layer with a high refractive index and capable of withstanding large deformation disposed on the visual side of the self-emitting element.

[0007] Means for Solving the Problem The light-emitting device provided in this specification includes: a self-emissive element; a low-refractive-index layer disposed on the viewing side closer to the self-emissive element; and a high-refractive-index adhesive layer deposited in direct contact with the low-refractive-index layer. The high-refractive-index adhesive layer has a refractive index greater than 1.560, and its deformation in a deformation test at a temperature of -20°C and a speed of 300 mm / min is more than 350%. Because the high-refractive-index adhesive layer has a high refractive index and can undergo deformation of more than 350% in a low-temperature, high-speed deformation test, it can withstand large deformations even in low-temperature environments, allowing for high-speed and sufficient deformation. Combining the high-refractive-index adhesive layer and the low-refractive-index layer that satisfy the above characteristics constitutes a laminate, which can be applied to applications such as foldable displays that involve large deformations, thus constructing a light-emitting device that utilizes a high refractive index to enhance frontal brightness.

[0008] In several samples, when the high-refractive-index adhesive layer is subjected to a deformation test at a temperature of -20°C and a speed of 300 mm / min, the stress at a deformation of 350% should preferably be less than 5.0 N / mm². An adhesive that meets the above characteristics has a high refractive index and can maintain a predetermined level of flexibility even at low temperatures, and can be deformed at high speeds and with sufficient force. Therefore, it is suitable as a high-refractive-index adhesive layer for applications involving large deformations.

[0009] In several samples, the ratio (n1 / n2) of the refractive index n1 of the high-refractive-index adhesive layer to the refractive index n2 of the low-refractive-index layer should preferably be approximately 1.05 or higher. This allows for easy attainment of an improved front brightness effect.

[0010] Furthermore, any combination of the elements described in this specification may also be included in the scope of the invention for which patent protection is sought through this patent application.

Implementation Method

[0012] The following describes the ideal embodiments of the present invention. Matters not specifically mentioned in this specification that are necessary for the implementation of the invention can be understood by those skilled in the art based on the teachings regarding the implementation of the invention as described in this specification and common technical knowledge at the time of application. The present invention can be implemented based on the contents disclosed in this specification and common technical knowledge in the field. Furthermore, in the following drawings, components and parts that perform the same function are sometimes given the same symbols, and sometimes repeated descriptions are omitted or simplified. Also, the embodiments shown in the drawings are schematic for the purpose of clearly illustrating the present invention and do not necessarily represent the exact dimensions or scale of the actual product provided.

[0013] Furthermore, in this specification, a self-emissive element means a light-emitting element whose brightness can be controlled by the value of the current flowing through it. A self-emissive element can be a single unit or an assembly. Specific examples of self-emissive elements include light-emitting diodes (LEDs) and organic ELs, but are not limited thereto. The light-emitting device disclosed herein includes the aforementioned self-emissive element as a constituent element. Examples of the above-mentioned light-emitting device also include light source module devices (e.g., planar light-emitting modules) used for illumination or display devices forming pixels, but are not limited thereto.

[0014] The technical matters disclosed in this specification include: light-emitting device, high refractive index adhesive layer and adhesive composition for forming therethere, low refractive index layer and composition for forming therethere, laminate (adhesive sheet) including high refractive index adhesive layer and low refractive index layer, laminate with release liner protecting the adhesive surface of the laminate, etc.

[0015] <Example of the configuration of the light-emitting device> An example of the configuration of the light-emitting device provided in this specification is shown in FIG1. ​​The light-emitting device 100 shown in FIG1 includes: a self-emitting element 70; a low refractive index layer 12 disposed on the viewing side of the self-emitting element 70; and a high refractive index adhesive layer 11, which is laminated in direct contact with the low refractive index layer 12. The light-emitting device 100 may also include a cover window member 80 disposed on the viewing side of the high refractive index adhesive layer 11. In the light-emitting device 100 shown in FIG1, a laminated sheet 10 composed of a high refractive index adhesive layer 11 and a low refractive index layer 12 is disposed between the self-emitting element 70 and the cover window member 80. Between the self-emitting element 70 and the low refractive index layer 12, between the high refractive index adhesive layer 11 and the cover window member 80, and on the viewing side of the cover window member 80, one or two or more layers (not shown) may be independently interposed, or they may not be interposed. Alternatively, opposite to Figure 1, a high-refractive-index adhesive layer 11 may be disposed on the self-luminous element side, and a low-refractive-index layer 12 may be disposed on the cover window member side.

[0016] In the technology disclosed herein, the low-refractive-index layer may be adhesive or non-adhesive. Among several options, the low-refractive-index layer is preferably an adhesive layer, i.e., a low-refractive-index adhesive layer. This allows the laminate (adhesive sheet) of the low-refractive-index adhesive layer and the high-refractive-index adhesive layer to achieve double-sided adhesion, thereby improving assemblability in the manufacture of the light-emitting device. Before being assembled into the light-emitting device, the laminated sheet can, for example, be in the form of a laminated sheet with a release liner attached, as shown in FIG2: it is a laminated sheet 10 (a substrate-free double-sided adhesive sheet 2) composed of a high refractive index adhesive layer 11 and a low refractive index adhesive layer 12. The surface (first surface) 10A on the side of the high refractive index adhesive layer 11 of the laminated sheet 10 becomes the first adhesive surface, and the surface (second surface) 10B on the side of the low refractive index adhesive layer 12 becomes the second adhesive surface, and each of these adhesive surfaces is protected by release liners 31 and 32.

[0017] <High Refractive Index Adhesive Layer> The light-emitting device disclosed herein includes a high refractive index adhesive layer, which is deposited in direct contact with a low refractive index layer contained in the light-emitting device. The high refractive index adhesive layer has a relatively higher refractive index than the aforementioned low refractive index layer. The high refractive index adhesive layer preferably has a refractive index greater than 1.560 and a deformation amount of 350% or more in a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min. As described above, the high refractive index adhesive layer has a high refractive index and can undergo deformation of 350% or more in a low-temperature, high-speed deformation test. Even in a low-temperature environment, it can still deform at high speed and sufficiently, and can withstand large deformations. Combining the high refractive index adhesive layer that meets the above characteristics with a low refractive index layer constitutes a laminate. This laminate can be applied to applications such as foldable displays that involve large deformations, and can construct a light-emitting device that utilizes the high refractive index of the high refractive index adhesive layer to improve frontal brightness.

[0018] (Refractive Index) The light-emitting device disclosed herein has a high refractive index adhesive layer with a refractive index n1 greater than 1.560. The high refractive index adhesive layer can be achieved by using an adhesive (viscoelastic material) with a refractive index greater than 1.560 to form at least one surface (adhesive surface) of the high refractive index adhesive layer.

[0019] Furthermore, in this specification, the refractive index of the adhesive refers to the refractive index of the adhesive surface (adhesive surface). The refractive index of the adhesive can be measured using a commercially available refractive index measuring device (Abbe refractometer) at a measurement wavelength of 589 nm and a measurement temperature of 25°C. For example, the Abbe refractometer can be the ATAGO "DR-M4" or an equivalent. The test sample can be an adhesive layer composed of the adhesive of the evaluation object. Specifically, the refractive index of the adhesive can be measured using the method described in the test examples below. The refractive index of the adhesive can be adjusted by, for example, the composition of the adhesive (e.g., the composition of the monomer components constituting the base polymer, additives used as needed, etc.).

[0020] The technical matters provided in this specification include: an adhesive layer with a refractive index greater than 1.560 (a high refractive index adhesive layer), an adhesive composition capable of forming the adhesive layer, and a laminate containing the high refractive index adhesive layer. The laminate may, for example, be a laminated adhesive layer composed of the high refractive index adhesive layer and a low refractive index layer (typically a low refractive index adhesive layer), or it may be a structure in which a high refractive index adhesive layer and a low refractive index layer are sequentially or in reverse order laminated on one side of a supporting substrate.

[0021] Among several samples, it is appropriate for the refractive index of the high-refractive-index adhesive layer to be, for example, 1.563 or higher, 1.565 or higher, and preferably greater than 1.570. Among several ideal samples, the refractive index of the aforementioned high-refractive-index adhesive layer may be 1.575 or higher, 1.580 or higher, 1.585 or higher, 1.590 or higher, or 1.595 or higher. Based on the high-refractive-index adhesive layer having the aforementioned refractive index, the behavior of light transmitted through the high-refractive-index adhesive layer can be effectively controlled by utilizing the relationship between the relative refractive indices of the high-refractive-index adhesive layer and the directly adjacent low-refractive-index layer (typically a low-refractive-index adhesive layer). The ideal upper limit of the refractive index of the high-refractive-index adhesive layer may vary depending on the refractive index of the adjacent layer, and is therefore not limited to a specific range. Among several options, considering the balance between flexibility or adhesive properties, transparency, etc., the refractive index of the high refractive index adhesive layer can be, for example, below 1.700, below 1.670, below 1.650, below 1.620, or below 1.600.

[0022] (Deformation Characteristics) Among several samples, the high-refractive-index adhesive layer, in addition to having a refractive index greater than 1.560, preferably exhibits a deformation amount of 350% or more during a deformation test at a temperature of -20°C and a speed of 300 mm / min. The aforementioned high-refractive-index adhesive layer possesses a high refractive index and satisfies the above characteristics, thus allowing for high-speed and sufficient deformation even at low temperatures, and can withstand large deformations. A high-refractive-index adhesive layer satisfying the above characteristics ideally possesses a high refractive index and can withstand applications involving large deformations, such as foldable displays. Furthermore, the high-refractive-index adhesive layer disclosed in this specification includes samples without limiting the above characteristics (deformation amount of 350% or more during a deformation test at a temperature of -20°C and a speed of 300 mm / min), and in said samples, the high-refractive-index adhesive layer is not limited to those satisfying the above characteristics.

[0023] Furthermore, in several samples, when the high-refractive-index adhesive layer is subjected to a deformation test at a temperature of -20°C and a speed of 300 mm / min, the stress at a deformation of 350% should preferably be less than 5.0 N / mm². The high-refractive-index adhesive layer that meets the above characteristics has a high refractive index and can maintain a predetermined level of flexibility even at low temperatures, and can be deformed at high speeds and with sufficient force. Therefore, it is suitable for use in applications involving large deformations. In several ideal conditions, the stress at 350% of the aforementioned deformation can be below 4.9 N / mm², 4.8 N / mm², 4.7 N / mm², or 4.6 N / mm², or it can be below 4.5 N / mm², 4.4 N / mm², 4.3 N / mm², 4.2 N / mm², 4.1 N / mm², 4.0 N / mm², 3.9 N / mm², 3.8 N / mm², 3.7 N / mm², 3.6 N / mm², 3.5 N / mm², 3.4 N / mm², 3.3 N / mm², 3.2 N / mm², 3.1 N / mm², 3.0 N / mm², 2.9 N / mm², or 2.8 N / mm². Below 2, below 2.7 N / mm², below 2.6 N / mm², below 2.5 N / mm², below 2.4 N / mm², below 2.3 N / mm², or below 2.2 N / mm².Theoretically, the lower limit of stress at 350% of the aforementioned deformation can be above 0.0 N / mm², and in several ideal conditions, it can be above 0.1 N / mm², 0.2 N / mm², 0.3 N / mm², 0.4 N / mm², 0.5 N / mm², 0.6 N / mm², 0.7 N / mm², 0.8 N / mm², 0.9 N / mm², 1.0 N / mm², 1.1 N / mm², 1.2 N / mm², 1.3 N / mm², 1.4 N / mm², 1.5 N / mm², 1.6 N / mm², 1.7 N / mm², 1.8 N / mm², 1.9 N / mm², 2.0 N / mm², and 2.1 N / mm². 2 or more, or 2.2 N / mm² or more, or 2.3 N / mm² or more, 2.4 N / mm² or more, 2.5 N / mm² or more, 2.6 N / mm² or more, 2.7 N / mm² or more, 2.8 N / mm² or more, 2.9 N / mm² or more, 3.0 N / mm² or more, 3.1 N / mm² or more, 3.2 N / mm² or more, 3.3 N / mm² or more, 3.4 N / mm² or more, 3.5 N / mm² or more, 3.6 N / mm² or more, 3.7 N / mm² or more, 3.8 N / mm² or more, 3.9 N / mm² or more, 4.0 N / mm² or more, 4.1 N / mm² or more, 4.2 N / mm² or more, 4.3 N / mm² or more, 4.4 N / mm² or more, 4.5 N / mm² or more. 2 or more or 4.6 N / mm² or more. A high refractive index adhesive layer with stress at 350% of the above deformation can be made to be flexible and at the same time have moderate cohesive force.

[0024] Among several samples, the ratio of the stress S(-20℃) at 350% deformation in a deformation test of the high-refractive-index adhesive layer at a temperature of -20℃ and a speed of 300 mm / min to the stress S(25℃) at 350% deformation in a deformation test at a temperature of 25℃ and a speed of 300 mm / min (S(-20℃) / S(25℃)) should preferably be 50 or less. Based on the high-refractive-index adhesive layer that satisfies the above characteristics, stable performance can be achieved in a wide temperature range, including the low-temperature region. In several ideal samples, the above ratio (S(-20℃) / S(25℃)) can be 49 or less, 48 ​​or less, 47 or less, 46 or less, 45 or less, 44 or less, 43 or less, 42 or less, 41 or less, 40 or less, 39 or less, 38 or less, 37 or less, 36 or less, 35 or less, 34 or less, 33 or less, 32 or less, or 31 or less, or it can be 30 or less, 29 or less, 28 or less, 27 or less, 26 or less, 25 or less, 24 or less, 23 or less, 22 or less, 21 or less, 20 or less, 19 or less, 18 or less, 17 or less, 16 or less, or 15 or less. The lower limit of the above ratio (S(-20℃) / S(25℃)) is usually above 0. In several ideal samples, it can be above 1, above 2, above 3, above 4, above 5, above 6, above 7, above 8, above 9, above 10, above 11, above 12, above 13, above 14 or above 15, or it can be above 16, above 17, above 18, above 19, above 20, above 21, above 22, above 23, above 24, above 25, above 26, above 27, above 28, above 29, above 30 or above 31.

[0025] The deformation test was carried out under the above-mentioned conditions of -20°C and speed of 300 mm / min. More specifically, it can be carried out by the method described in the test example below. The deformation test carried out under the above-mentioned conditions of 25°C and speed of 300 mm / min was carried out in the same manner as the deformation test at -20°C, except that the temperature was changed to 25°C. The stress [N / mm 2] at 350% deformation was measured, and the ratio of the stress S(-20°C) at 350% deformation in the deformation test carried out under the conditions of -20°C and speed of 300 mm / min to the stress S(25°C) at 350% deformation in the deformation test carried out under the conditions of 25°C and speed of 300 mm / min (S(-20°C) / S(25°C)) was calculated from the results.

[0026] The 350% deformability of the high refractive index adhesive layer under the conditions of temperature -20℃ and speed 300mm / min, the stress and ratio (S(-20℃) / S(25℃)) at 350% can be adjusted by selecting the composition of the monomer components constituting the base polymer, setting the weight average molecular weight (Mw) of the base polymer, selecting the type or amount of plasticizer, whether or not a crosslinking agent is used and selecting its type and amount, whether or not an additive is used and selecting its type and amount.

[0027] (Storage modulus G') While not particularly limited, in several samples, the storage modulus G' (0°C) of the high-refractive-index adhesive layer is in the range of 1.0 × 10⁴ Pa to 1.0 × 10⁶ Pa. Based on the above-mentioned high-refractive-index adhesive layer, since it has a high refractive index and the range of storage modulus G' (0°C) is suppressed to a low range, it can be a product that balances high refractive index and flexibility. A high-refractive-index adhesive layer with a storage modulus G' (0°C) within the above range can be a product that balances high refractive index and flexibility and has the flexibility to withstand repeated bending operations. The aforementioned storage elastic modulus G' (0℃) is preferably 5.0 × 10⁵ Pa or less, and may be 2.0 × 10⁵ Pa or less, 1.0 × 10⁵ Pa or less, 7.0 × 10⁴ Pa or less, 5.0 × 10⁴ Pa or less, or 3.0 × 10⁴ Pa or less. Furthermore, the aforementioned storage elastic modulus G' (0℃) is preferably 2.0 × 10⁴ Pa or more, more preferably 4.0 × 10⁴ Pa or more, may be 6.0 × 10⁴ Pa or more, or may be 1.0 × 10⁵ Pa or more.

[0028] The storage modulus G' (-20°C) of the high refractive index adhesive layer disclosed herein is not particularly limited. For example, it may be less than 1.0 × 10¹⁰ Pa, less than 1.0 × 10⁹ Pa, and preferably less than 5.0 × 10⁸ Pa, less than 1.0 × 10⁸ Pa, less than 5.0 × 10⁷ Pa, less than 1.0 × 10⁷ Pa, less than 5.0 × 10⁶ Pa, less than 1.0 × 10⁶ Pa, or less than 5.0 × 10⁵ Pa. A high refractive index adhesive layer with the above-mentioned limited storage modulus G' (-20°C) can possess excellent flexibility. For example, it can possess good flexibility in a lower temperature region and flexibility capable of withstanding repeated bending operations in a wide temperature range, including the low temperature region. The lower limit of the aforementioned storage elastic modulus G' (-20°C) is not particularly limited. For example, it is appropriate to be 1.0 × 10² Pa or more, 1.0 × 10³ Pa or more, preferably 1.0 × 10⁴ Pa or more, more preferably 1.0 × 10⁵ Pa or more, and possibly 5.0 × 10⁵ Pa or more, or even 1.0 × 10⁶ Pa or more. A high-refractive-index adhesive layer having the aforementioned storage elastic modulus G' (-20°C) can be both flexible and possess moderate cohesive strength. Furthermore, according to the high-refractive-index adhesive layer having the aforementioned storage elastic modulus G' (-20°C), there is a tendency to easily maintain both high refractive index and flexibility even in low-temperature regions.

[0029] The storage modulus G' (25°C) of the high refractive index adhesive layer disclosed herein can be appropriately set according to the intended use or usage pattern, and is not limited to a specific range. From the viewpoint of ease of adhesion to the adhered object, for example, less than 1.0 × 10⁶ Pa is appropriate, less than 5.0 × 10⁵ Pa is preferable, less than 3.0 × 10⁵ Pa is more preferable, less than 1.0 × 10⁵ Pa is acceptable, and it can also be less than 5.0 × 10⁴ Pa. The high refractive index adhesive layer with the storage modulus G' (25°C) limited as described above has good flexibility at normal operating temperatures such as room temperature. There is no particular limitation on the lower limit of the aforementioned storage elastic modulus G' (25°C). From the viewpoint of processability and handling, and considering the need for higher refractive index, for example, 1.0 × 10² Pa or higher, or 5.0 × 10² Pa or higher, is appropriate, preferably 1.0 × 10³ Pa or higher, more preferably 3.0 × 10³ Pa or higher, and also acceptable is 5.0 × 10³ Pa or higher. A high-refractive-index adhesive layer with the aforementioned storage elastic modulus G' (25°C) still exhibits moderate cohesiveness even in high-temperature regions and tends to have excellent heat resistance, thus it is ideal.

[0030] Among several samples, the storage elastic modulus G'(25°C) of the high-refractive-index adhesive layer at 25°C is preferably lower than the storage elastic modulus G'(25°C) of the low-refractive-index layer described later. Based on this configuration, by imparting adhesion or flexibility to the laminate of the high-refractive-index adhesive layer and the low-refractive-index layer, compliance with height differences or with curved surfaces is improved, thereby enabling the realization of a laminate (adhesive sheet) suitable for various device design applications.

[0031] (Storage Modulus Ratio) In several samples, an adhesive with a storage modulus G'(0℃) at 0℃ to a storage modulus G'(25℃) at 25℃ (G'(0℃) / G'(25℃)) in the range of 1 to 1000 can be used as a high refractive index adhesive layer. Based on the high refractive index adhesive layer that satisfies the above characteristics, since the change in modulus of elasticity is suppressed over a wide temperature range from 0℃ to room temperature, it easily exhibits characteristics of stability against temperature changes (softness, etc.). It is appropriate for the ratio (G'(0℃) / G'(25℃)) to be 300 or less, preferably 100 or less, more preferably 50 or less, possibly 25 or less, possibly 10 or less, or possibly 5 or less. For example, the lower limit of the ratio (G'(0℃) / G'(25℃)) can be 2 or more, or possibly 3 or more.

[0032] Among several samples, an adhesive with a storage elastic modulus G'(-20°C) at -20°C to a storage elastic modulus G'(25°C) at 25°C (G'(-20°C) / G'(25°C)) in the range of 1 to 1000 can be used as a high refractive index adhesive layer. Based on the high refractive index adhesive layer that satisfies the above characteristics, since the change in elastic modulus over a wide temperature range from lower temperatures to room temperature is suppressed, it can exhibit stable properties (such as flexibility) to temperature changes. The above ratio (G'(-20°C) / G'(25°C)) can be 500 or less, 300 or less, 150 or less, 100 or less, 50 or less, or 30 or less. The lower limit of the above ratio (G'(-20℃) / G'(25℃)) can be, for example, 5 or more, 50 or more, 100 or more, or 200 or more.

[0033] (Glass Transition Temperature) The glass transition temperature (Tg) of the high refractive index adhesive layer is not particularly limited, and can be set considering flexibility in the low-temperature region or cohesion (heat resistance, etc.) in the high-temperature region. In several samples, the Tg of the high refractive index adhesive layer is, for example, below 30°C, below 15°C, or below 5°C. In several ideal samples, from the point of view of flexibility, the Tg of the high refractive index adhesive layer is below 0°C, preferably below -5°C, more preferably below -10°C, or below -15°C (e.g., below -20°C). The lower the Tg of the high refractive index adhesive layer, the better the adhesion properties, such as the adhesion to the adhered body. Furthermore, by setting the Tg of the high refractive index adhesive layer to a lower value, the change in the elastic modulus in the temperature region above Tg can be suppressed. The lower limit of the Tg of the high refractive index adhesive layer is, for example, above -50°C, or above -40°C, or even above -30°C or -25°C. Based on the high refractive index adhesive layer having the above-mentioned Tg, there is a tendency to easily obtain suitable cohesive strength. Furthermore, there is a tendency to easily form an adhesive that balances high refractive index and large deformability.

[0034] The storage modulus G' of the adhesive layer at the above temperatures and the glass transition temperature of the adhesive layer can be determined by the dynamic viscoelasticity test method described in the test examples below, and the ratio of each storage modulus can be calculated from the results. The storage modulus G', the ratio of each storage modulus, and the glass transition temperature of the adhesive layer (e.g., a high refractive index adhesive layer) can be adjusted, for example, by selecting the composition of the monomer components constituting the base polymer, setting the Mw of the base polymer, selecting the type or amount of plasticizer, whether or not a crosslinking agent is used and selecting its type and amount, whether or not an additive is used and selecting its type and amount, etc.

[0035] (Change in elastic modulus after being kept at 130°C for 1 hour) Although not particularly limited, in several samples, it is advisable to use the following adhesive as a high-refractive-index adhesive layer: the ratio (G'1 / G'0) of the stored elastic modulus G'1 at -20°C after being kept at 130°C for 1 hour to the stored elastic modulus G'0 at -20°C before being kept at 130°C for 1 hour is 50 or less (specifically 1 to 50). A high-refractive-index adhesive layer that meets this characteristic will exhibit stable properties, as the change in elastic modulus is limited within a predetermined range even when exposed to high temperatures. The above ratio (G'1 / G'0) is preferably 30 or less, more preferably 10 or less, more preferably 3 or less, may be 2 or less, or may be less than 1.5.

[0036] The change in elastic modulus after holding at 130°C for 1 hour was determined by the following method. Specifically, an adhesive composition was applied to the polysiloxane-treated surface of a PET film R1, which was treated with polysiloxane on one side. The film was heated at 130°C for 3 minutes to form an adhesive layer with a thickness of 20 µm. Then, the polysiloxane-treated surface of a PET film R2, which was treated with polysiloxane on one side, was adhered to the surface of the adhesive layer. One release liner was peeled off from the resulting adhesive layer with a release liner (release liner / adhesive layer / release liner), and the film was held in an oven at 130°C for 1 hour. The oven used was one with sufficient capacity for the test sample and capable of heating while venting exhaust. For example, an oven manufactured by Espec could be used. After laminating the adhesive (layer) that had been held at 130°C for 1 hour to a thickness of approximately 1.5 mm, the layers were subjected to autoclaving (0.5 MPa, 50°C, 15 minutes) to ensure adhesion between the layers. For the test sample obtained in the above manner, the storage elastic modulus G' (G'1) [Pa] at -20°C after being held at 130°C for 1 hour was determined using the same method as for determining the storage elastic modulus G'. Then, the ratio (G'1 / G'0) of the obtained storage elastic modulus G'1 [Pa] to the previously determined storage elastic modulus G'0 [Pa] at -20°C before being held at 130°C for 1 hour was calculated.

[0037] (Total Light Transmittance) In several samples, the total light transmittance of the high-refractive-index adhesive layer should preferably be 85.0% or higher (e.g., 86.0% or higher, 88.0% or higher, 90.0% or higher, or greater than 90.0%). The upper limit of the total light transmittance is theoretically derived from the value obtained by excluding 100% of the light loss caused by reflection at the air interface (Fresnel loss). In practice, it can be, for example, about 98% or lower, about 96% or lower, or about 95% or lower. In several samples, considering the refractive index or adhesive properties, the total light transmittance of the high-refractive-index adhesive layer can be about 94% or lower, about 93% or lower, or about 92% or lower. The total light transmittance of such high-refractive-index adhesive layers can also be applied to the total light transmittance of laminates composed of such high-refractive-index adhesive layers and low-refractive-index layers (typically low-refractive-index adhesive layers) described later.

[0038] Total light transmittance was measured using a commercially available transmittance meter according to JIS K 7136:2000. The transmittance meter may be the "HAZEMETER HM-150" manufactured by Murakami Color Technology Research Institute or an equivalent. Total light transmittance can be measured according to the method described in the test examples below. The total light transmittance of the high-refractive-index adhesive layer can be adjusted, for example, by selecting the composition or thickness of the adhesive layer. Furthermore, to distinguish it from the total light transmittance after the bending test described below, the above total light transmittance is sometimes referred to as the initial total light transmittance.

[0039] Furthermore, in several samples, the total light transmittance of the bent portion of the high-refractive-index adhesive layer after 10 repeated bending tests (total light transmittance after the bending test) should preferably remain at least 85% of the total light transmittance before the bending test. The aforementioned bending test is conducted by bending each side of the sheet adhesive into a U-shape with a radius of 2 mm at 25°C, and this operation constitutes one set of tests. The high-refractive-index adhesive layer that meets the above characteristics shows little change in its optical properties (e.g., whitening) even with repeated bending, and is therefore suitable for optical applications where bending is anticipated, such as foldable displays. The total light transmittance after the bending test should preferably be at least 90% of the total light transmittance before the bending test, more preferably at least 95%, and especially preferably at least 98% (e.g., at least 99%). The total light transmittance after the bending test can be adjusted by selecting the composition of the monomer components constituting the base polymer, setting the weight average molecular weight (Mw) of the base polymer, selecting the type or amount of plasticizer, whether or not a crosslinking agent is used and its type and amount, and whether or not an additive is used and its type and amount.

[0040] More specifically, the total light transmittance before and after the bending test was determined by the following method. Specifically, the adhesive layer was cut into a rectangle of 2cm × 10cm to obtain a test piece. A cylindrical rod of φ4mm was horizontally fixed at a sufficient height for the measurement, and the obtained test piece was placed on the rod, bending one side into a U-shape with a radius of 2mm and holding it for 1 minute. Specifically, the central portion of the test piece along its length was placed on the rod, forming an inverted U-shape. Next, a clamp (13g) was fixed at both ends below the test piece, and a 60g weight was suspended and fixed through a 1cm thread on the clamp, applying a load to the bent portion of the test piece. In this state, the test piece was held at a predetermined temperature (or 25°C) for 1 minute, and after 1 minute, the test piece was removed from the rod. Next, under the same temperature conditions, the other side of the test piece (the opposite side of one of the aforementioned sides) was bent into a U-shape with a radius of 2 mm using the opposite side of the bending portion of one of the aforementioned sides, and held for 1 minute. After repeating the bending test 10 times on the bending portion of the same test piece as a group, the total light transmittance [%] of the bending portion was measured using the same method as the initial total light transmittance measurement method described above.

[0041] (Haze Value) In several samples, the haze value of the high refractive index adhesive layer may be, for example, 5.0% or less, preferably 3.0% or less, more preferably 2.0% or less, even more preferably 1.0% or less, possibly 0.9% or less, possibly 0.8% or less, possibly 0.5% or less, or possibly 0.3% or less. As described, an adhesive with high transparency is advantageous for applications requiring high light transmittance (e.g., optical applications) or applications requiring good visibility of the adhered material's properties through the adhesive. There is no particular limitation on the lower limit of the haze value of the high refractive index adhesive layer; from the viewpoint of improving transparency, the lower the haze value, the better. On the other hand, in several samples, considering refractive index or adhesive properties, the haze value of the high refractive index adhesive layer may be, for example, 0.05% or more, or possibly 0.10% or more. The haze values ​​of the high refractive index adhesive layer can also be applied to the haze values ​​of laminates composed of the high refractive index adhesive layer and the low refractive index layer (typically a low refractive index adhesive layer) described later.

[0042] Here, "haze value" refers to the ratio of diffuse transmitted light to total transmitted light when visible light is irradiated onto the test object. It is also called Haze Value. The haze value can be expressed by the following formula: Th(%) = Td / Tt × 100 In the above formula, Th is the haze value (%), Td is the diffuse light transmittance, and Tt is the total light transmittance. The haze value can be measured according to the method described in the test examples below. The haze value of the adhesive layer can be adjusted by, for example, by selecting the composition or thickness of the adhesive layer.

[0043] (Surface smoothness of the adhesive surface) Among several samples, the surface (adhesive surface) of the high refractive index adhesive layer should have high surface smoothness.

[0044] For example, the arithmetic mean roughness Ra of the aforementioned adhesive surface should preferably be limited to a predetermined value or below. From the viewpoint of optical homogeneity, it is preferable to have an adhesive surface designed to have a lower arithmetic mean roughness Ra. By limiting the arithmetic mean roughness Ra, for example in applications where light is captured through the aforementioned adhesive surface (such as an adhesive sheet disposed in a light-emitting device on the viewpoint side closer to the self-emitting element), the effect of suppressing brightness unevenness caused by the surface condition of the adhesive layer can be achieved. The lower arithmetic mean roughness Ra of the adhesive surface also helps to suppress optical strain, and the suppression of optical strain also helps to improve optical homogeneity. When the laminate (adhesive sheet) disclosed herein is a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface (e.g., a laminate composed of a high-refractive-index adhesive layer and a low-refractive-index adhesive layer), it is preferable that at least the arithmetic mean roughness Ra of the first adhesive surface is limited to below a predetermined value, and more preferably that the arithmetic mean roughness Ra of both adhesive surfaces is limited to below a predetermined value. By ensuring high surface smoothness on each adhesive surface of the double-sided adhesive sheet, excellent optical homogeneity of bonding can be readily achieved.

[0045] In several samples, the arithmetic mean roughness Ra of the adhesive surface is preferably about 70 nm or less, more preferably about 65 nm or less, more preferably about 55 nm or less, and may be less than 50 nm, less than 45 nm, or less than 40 nm. From the viewpoint of production efficiency, in several samples, the arithmetic mean roughness Ra of the adhesive surface may, for example, be about 10 nm or more, about 20 nm or more, or about 30 nm or more (for example, about 40 nm or more). In a laminated sheet having a first adhesive surface and a second adhesive surface, the arithmetic mean roughness Ra of the first adhesive surface and the arithmetic mean roughness Ra of the second adhesive surface may be the same or different.

[0046] Furthermore, for example, the maximum height Rz of the aforementioned adhesive surface should preferably be limited to below a predetermined value. From the viewpoint of optical homogeneity, it is preferable to have an adhesive surface designed with a lower maximum height Rz. By limiting the maximum height Rz, for example in the usage scenario where light is captured through the aforementioned adhesive surface as described above, the effect of suppressing brightness unevenness caused by the surface state of the adhesive layer can be achieved. A lower maximum height Rz of the adhesive surface also helps to suppress optical strain. When the laminate disclosed here is a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, it is preferable that at least the maximum height Rz of the first adhesive surface is limited to below a predetermined value, and more preferably that the maximum height Rz of both adhesive surfaces is limited to below a predetermined value. By having high surface smoothness on each adhesive surface of the double-sided adhesive sheet, it is suitable to achieve bonding with excellent optical homogeneity.

[0047] In several samples, the maximum height Rz of the adhesive surface is preferably less than approximately 600 nm, more preferably less than approximately 500 nm, more preferably less than approximately 450 nm, especially preferably less than approximately 400 nm, and may be less than 350 nm, less than 300 nm, or less than 250 nm. From the viewpoint of production efficiency, in several samples, the maximum height Rz of the adhesive surface may, for example, be more than approximately 10 nm, more than approximately 50 nm, more than approximately 100 nm, or more than approximately 200 nm. In a sample having a first adhesive surface and a second adhesive surface, the maximum height Rz of the first adhesive surface and the maximum height Rz of the second adhesive surface may be the same or different.

[0048] The arithmetic mean roughness Ra and maximum height Rz of the adhesive surface are measured using a non-contact surface roughness measuring device. The non-contact surface roughness measuring device can be an optical interferometric surface roughness measuring device, such as a 3D optical profilometer (trade name "NewView7300", manufactured by ZYGO) or an equivalent. Specifically, the arithmetic mean roughness Ra and maximum height Rz can be measured, for example, by setting the measurement operation or measurement conditions in a manner that yields results equivalent to or corresponding to those obtained using the measurement method.

[0049] That is, the surface shape of the test specimen is measured using a 3D optical profilometer (trade name "NewView7300", manufactured by ZYGO) at 23°C and 50%RH under the following conditions. The arithmetic surface roughness Ra is calculated from the measured data according to JIS B 0601-2001. The maximum height Rz is the sum of the height Rp from the average line of the roughness curve to the highest point on the upper side and the depth Rv from the average line to the deepest valley on the lower side, calculated based on the data obtained from the above measurements (roughness curve). Five measurements are performed (i.e., N=5), and the average value is used. The test specimen can be prepared by cutting the adhesive layer of the test object or the adhesive sheet containing the adhesive layer into a size of about 150 mm in length and 50 mm in width. When the adhesive surface is protected by a release liner, gently peel off the release liner (e.g., at a stretching speed of 300 mm / min and a peel angle of 180°) to expose the adhesive surface. It is advisable to allow the surface to stand for approximately 30 minutes after exposure before performing the measurement. [Measurement Conditions] Measurement area: 5.62 mm × 4.22 mm (Objective lens: 2.5x, Internal lens: 0.5x) Resolution mode: Remove: Cylinder Data Fill: ON (Max: 25) Remove Spikes: ON (xRMS: 1) Filter: OFF

[0050] The arithmetic mean roughness Ra and maximum height Rz of the adhesive surface can be adjusted by the composition or properties (viscosity, leveling properties, etc.) of the adhesive composition used to form the adhesive layer, and the properties of the surface (peel surface) of the release liner protecting the adhesive surface.

[0051] (Base Polymer) In the technology disclosed herein, there is no particular limitation on the type of adhesive constituting the high refractive index adhesive layer. The adhesive may be one or more of various rubber-like polymers that can be used in the field of adhesives, including acrylic polymers, rubber polymers (natural rubber, synthetic rubber, mixtures thereof), polyester polymers, carbamate polymers, polyether polymers, polysiloxane polymers, polyamide polymers, fluoropolymers, etc., as the adhesive polymer (meaning a structural polymer that can shape the adhesive, hereinafter also referred to as "base polymer"). From the viewpoint of adhesive performance or cost, adhesives containing acrylic polymers or rubber polymers as the base polymer are suitable. Among these, adhesives using acrylic polymers as the base polymer (acrylic adhesives) are preferred. The technology disclosed herein is suitable for implementation in the case of using acrylic adhesives.

[0052] The following mainly describes a high refractive index adhesive layer made of acrylic adhesive, but it is not intended to limit the high refractive index adhesive layer in the art disclosed herein to acrylic adhesive layers.

[0053] Furthermore, in this specification, the term "base polymer" for an adhesive refers to the main component of the rubbery polymer contained in the adhesive, and is not interpreted in any other way. The aforementioned rubbery polymer refers to a polymer that exhibits rubber elasticity in a temperature range near room temperature. Also, in this specification, "main component" unless otherwise specified means a component containing more than 50% by weight. Furthermore, in this specification, "acrylic polymer" means a polymer containing monomer units as constituent monomer units: these monomer units are derived from monomers having at least one (meth)acrylic group per molecule. Hereinafter, monomers having at least one (meth)acrylic group per molecule are also referred to as "acrylic monomers." Therefore, acrylic polymers in this specification are defined as polymers containing monomer units derived from acrylic monomers. A typical example of an acrylic polymer is a polymer in which the proportion of acrylic monomers in the total monomers used in the synthesis of the acrylic polymer is greater than 50% by weight (preferably greater than 70% by weight, for example, greater than 90% by weight). Furthermore, in this specification, "(meth)acrylic" refers to both acrylonitrile and methacrylic. Similarly, "(meth)acrylate" refers to both acrylate and methacrylate, while "(meth)acrylic" refers to both acrylic and methacrylic acid. Therefore, the concept of acrylic monomers as used herein can include both monomers containing an acrylonitrile (acrylic monomers) and monomers containing a methacrylic group (methacrylic monomers).

[0054] (Acrylic Polymer) The high refractive index adhesive layer disclosed herein is suitable for use as an acrylic adhesive layer (high refractive index acrylic adhesive layer). The acrylic polymer used as the base polymer of the aforementioned acrylic adhesive is preferably one that contains an aromatic ring monomer (A1) as a monomeric component constituting the acrylic polymer. That is, it is preferably an acrylic polymer containing an aromatic ring monomer (A1) as a monomeric unit. Here, the term "monomeric component constituting the acrylic polymer" in this specification means a monomer that, whether contained in the adhesive composition in the form of a pre-formed polymer (which may be an oligomer) or in the form of an unpolymerized monomer, constitutes a repeating unit of the acrylic polymer in the adhesive formed from the adhesive composition. That is, the monomeric component constituting the acrylic polymer can be contained in the aforementioned adhesive composition in any form, including polymer, unpolymerized, and partially polymerized forms. From the perspective of ease of preparation of adhesive composition, among several types of adhesive compositions, it is preferable to include substantially all (e.g., 95% by weight or more, preferably 99% by weight or more) of the monomer components in the form of polymer.

[0055] (Monomer (A1)) The monomer (A1) may be a compound comprising at least one aromatic ring and at least one vinyl unsaturated group in one molecule. The monomer (A1) may be used alone or in combination of two or more of the compounds.

[0056] Examples of the aforementioned vinyl unsaturated groups include (meth)acryl, vinyl, and (meth)allyl. From the viewpoint of polymerization reactivity, (meth)acryl is preferable, while from the viewpoint of flexibility or adhesiveness, acrylonitrile is better. From the viewpoint of suppressing the reduction of flexibility in high-refractive-index adhesive layers, it is suitable to use a compound (i.e., a monofunctional monomer) in which the number of vinyl unsaturated groups in one molecule is 1.

[0057] The number of aromatic rings contained in the molecule of compound 1, which can be used as a monomer (A1), can be 1 or more. There is no particular upper limit to the number of aromatic rings, for example, it can be 16 or less. In several cases, from the viewpoint of ease of preparation of acrylic polymers or transparency of adhesives, the number of aromatic rings can be, for example, 12 or less, preferably 8 or less, more preferably 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less.

[0058] The aromatic ring of the compound used as a monomer (A1) may also be: a benzene ring (which may be a benzene ring constituting part of a biphenyl structure or a benzo[a]pyr] structure); a carbon ring such as a condensed ring of a naphthalene ring, an indene ring, an azurite ring, anthracene ring, or a phenanthrene ring; or a heterocycle such as a pyridine ring, a pyrimidine ring, a diazonium ring, a pyridine ring, a triazolium ring, a pyrrole ring, a pyrazole ring, an imidazole ring, a triazole ring, a succinazole ring, an isosuccinazole ring, a thiazole ring, or a thiophene ring. The heteroatoms contained in the above-mentioned heterocycles as ring-forming atoms may, for example, be one or more selected from the group consisting of nitrogen, sulfur, and oxygen. In several states, the heteroatoms constituting the heterocycles may be one or both of nitrogen and sulfur. The monomer (A1) may also have a structure, for example, a condensation structure of one or more carbon rings and one or more heterocycles, such as a dinaphthothiophene structure.

[0059] The aromatic ring (preferably a carbocyclic ring) may have one or more substituents on the ring constituent atoms, or it may not have substituents. When substituents are present, examples of substituents include alkyl, alkoxy, aryloxy, hydroxy, halogen atoms (fluorine, chlorine, bromine, etc.), hydroxyalkyl, hydroxyalkyloxy, epoxypropoxy, etc., but are not limited thereto. Among the substituents containing carbon atoms, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and for example, 1 or 2. In several cases, the aromatic ring may be an aromatic ring without substituents on the ring constituent atoms, or an aromatic ring having one or more substituents selected from the group consisting of alkyl, alkoxy, and halogen atoms (e.g., bromine atoms) on the ring constituent atoms. Furthermore, when the aromatic ring of the monomer (A1) has substituents on its ring constituent atoms, it means that the aromatic ring has substituents other than substituents with vinyl unsaturated groups.

[0060] The aromatic ring and the vinyl unsaturated group can be directly bonded or bonded through a linking group. The linking group may be, for example, a group containing one or more structures selected from alkyl, oxoalkyl, poly(oxoalkyl), phenyl, alkylphenyl, alkoxyphenyl, or groups in which one or more hydrogen atoms are replaced by hydroxyl groups (e.g., hydroxyalkyl), oxy(-O-), thiooxy(-S-), etc. Among several options, it is suitable to use aromatic ring monomers with structures in which the aromatic ring is directly bonded to the vinyl unsaturated group, or aromatic ring monomers with structures in which they are bonded through a linking group selected from the group consisting of alkyl, oxoalkyl, and poly(oxoalkyl). The number of carbon atoms in the alkyl and oxoalkyl groups is preferably 1 to 4, more preferably 1 to 3, for example, 1 or 2. The number of repetitions of the oxoalkyl unit in the poly(oxoalkyl) group may be, for example, 2 to 3.

[0061] Examples of suitable compounds that can be used as monomers (A1) include aromatic ring (meth)acrylates and aromatic ring vinyl compounds. Aromatic ring (meth)acrylates and aromatic ring vinyl compounds can be used alone or in combination of two or more. Alternatively, one or more aromatic ring (meth)acrylates and one or more aromatic ring vinyl compounds can be used in combination.

[0062] Among several ideal samples, considering the ease with which a high degree of high refractive index can be obtained, a monomer having two or more aromatic rings (preferably carbon rings) in one molecule can be used as the monomer (A1). Examples of monomers having two or more aromatic rings in one molecule (including monomers with multiple aromatic rings) include: monomers having two or more non-condensed aromatic rings bonded by a linker group, monomers having two or more non-condensed aromatic rings directly (i.e., without being separated by other atoms) chemically bonded, monomers having condensed aromatic ring structures, monomers having a cyclopentadienyl structure, monomers having a dibenzothiophene structure, and monomers having a dibenzothiophene structure. Among these, monomers having two or more non-condensed aromatic rings bonded by a linker group (e.g., m-phenoxybenzyl (meth)acrylate described later) are suitable for use. Monomers containing multiple aromatic rings can be used alone or in combination of two or more.

[0063] The linking group described above may be, for example: oxy (-O-), thiooxy (-S-), oxyalkyl (e.g., -O-(CH2)n-yl, where n is 1 to 3, preferably 1), thiooxyalkyl (e.g., -S-(CH2)n-yl, where n is 1 to 3, preferably 1), linear alkyl (i.e., -(CH2)n-yl, where n is 1 to 6, preferably 1 to 3), or groups in which the alkyl groups of the above-mentioned oxyalkyl, thiooxyalkyl, and linear alkyl have been partially or completely halogenated. From the viewpoint of the flexibility of the high-refractive-index adhesive layer, suitable examples of the above-mentioned linking group include oxy, thiooxy, oxyalkyl, and linear alkyl. Specific examples of monomers having a structure in which two or more non-condensed aromatic rings are linked by a linker group include phenoxybenzyl (meth)acrylates (e.g., m-phenoxybenzyl (meth)acrylate), thiophenoxybenzyl (meth)acrylates, and benzyl (meth)acrylate.

[0064] The monomers with structures consisting of two or more non-condensed aromatic rings directly chemically bonded can be, for example, (meth)acrylates containing a biphenyl structure, (meth)acrylates containing a triphenyl structure, or biphenyls containing a vinyl group. Specific examples include o-phenylphenol (meth)acrylate and biphenylmethyl (meth)acrylate.

[0065] Examples of monomers having a condensed aromatic ring structure include naphthyl ring (meth)acrylates, anthracene ring (meth)acrylates, vinylnaphthalene, and vinylanthracene. Specific examples include: 1-naphthylmethyl (meth)acrylate (also known as: 1-naphthylmethyl (meth)acrylate), hydroxyethylated β-naphthol acrylate, 2-naphthylethyl (meth)acrylate, 2-naphthoxyethyl acrylate, 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate, etc.

[0066] Specific examples of the monomers having the above-mentioned genus structure include 9,9-bis(4-hydroxyphenyl)genus(meth)acrylate and 9,9-bis[4-(2-hydroxyethoxy)phenyl]genus(meth)acrylate. Furthermore, monomers having the genus structure, because they contain a structural portion with two benzene rings directly chemically bonded, are included in the concept of monomers having the above-mentioned structure with two or more non-condensed aromatic rings directly chemically bonded.

[0067] The monomers having the dinaphthothiophene structure mentioned above include dinaphthothiophene containing (meth)propenyl, dinaphthothiophene containing vinyl, and dinaphthothiophene containing (meth)allyl. Specific examples include: (meth)propenyloxymethyl dinaphthothiophene (e.g., compounds with a structure of CH 2CH(R 1)C(O)OCH 2- bonded at the 5 or 6 position of the dinaphthothiophene ring; where R 1 is a hydrogen atom or a methyl group), (meth)propenyloxyethyl dinaphthothiophene (e.g., compounds with a structure of CH 2CH(R 1)C(O)OCH(CH 3)- or CH 2CH(R 1)C(O)OCH 2CH 2- bonded at the 5 or 6 position of the dinaphthothiophene ring; where R 1 is a hydrogen atom or a methyl group), vinyl dinaphthothiophene (e.g., compounds with a structure of vinyl bonded at the 5 or 6 position of the dinaphthothiophene ring), (meth)allyloxy dinaphthothiophene, etc. Furthermore, the monosystem having a dinaphthothiophene structure is also included in the concept of the monomer having a condensed aromatic ring structure by including a naphthalene structure and a structure having a thiophene ring and two naphthalene structures that have undergone condensation.

[0068] Examples of monomers having the dibenzothiophene structure include dibenzothiophene containing (meth)acrylyl and dibenzothiophene containing vinyl groups. Furthermore, monomers having the dibenzothiophene structure are included in the concept of monomers having condensed aromatic ring structures because they have a structure in which the thiophene ring and two benzene rings have undergone condensation. Moreover, neither the dinaphthothiophene nor the dibenzothiophene structure belongs to a structure in which two or more non-condensed aromatic rings are directly chemically bonded.

[0069] In several ideal samples, the monomer (A1) can be a monomer having one aromatic ring (preferably a carbon ring) per molecule. A monomer having one aromatic ring per molecule (including monomers with an odd number of aromatic rings) can, for example, help improve the flexibility of the high-refractive-index adhesive layer or adjust the adhesive properties, improve transparency, etc. Monomers with an odd number of aromatic rings can be used alone or in combination of two or more. In several samples, from the viewpoint of improving the refractive index of the high-refractive-index adhesive layer, a monomer having one aromatic ring per molecule can also be used in combination with monomers with multiple aromatic rings.

[0070] Examples of monomers having one aromatic ring in one molecule include: benzyl (meth)acrylate, methoxybenzyl (meth)acrylate, phenyl (meth)acrylate, ethoxylated phenol (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxybutyl (meth)acrylate, toluene (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, chlorobenzyl (meth)acrylate, and other carbon-containing aromatic ring (meth)acrylates; 2-(4,6-dibromo-2-di-butylphenoxy)ethyl (meth)acrylate, 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate, 6-(4,6-dibromo-2-dibutylphenoxy)hexyl (meth)acrylate, 6-(4,6-dibromo-2-isopropylphenoxy)hexyl (meth)acrylate, 2,6-dibromo-4-nonylphenyl acrylate, 2,6-dibromo-4-dodecylphenyl acrylate, and other bromine-substituted aromatic ring (meth)acrylates; vinyl compounds containing carbon aromatic rings, such as styrene, α-methylstyrene, vinyltoluene, and tert-butylstyrene; compounds with vinyl substituents on heteroaromatic rings, such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyridine, N-vinylpyrrole, N-vinylimidazolium, and N-vinylpyrazole.

[0071] The monomer (A1) may also be a monomer with a structure in which an oxyethyl chain is sandwiched between the vinyl unsaturated group and the aromatic ring of various aromatic ring monomers as described above. As described, the monomer in which an oxyethyl chain is sandwiched between the vinyl unsaturated group and the aromatic ring can be regarded as an ethoxylated version of the original monomer. The repeating number of the oxyethyl unit (-CH 2CH 2O-) in the oxyethyl chain is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, for example 1. Specific examples of ethoxylated aromatic ring monomers include: ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol di(meth)acrylate, etc.

[0072] There is no particular limitation on the content of monomers containing multiple aromatic rings in monomer (A1), for example, it can be 5% by weight or more, 25% by weight or more, or 40% by weight or more. In several states, the content of monomers containing multiple aromatic rings in monomer (A1) can be, for example, 50% by weight or more, and from the viewpoint of easily obtaining a higher refractive index, it is preferable to be 70% by weight or more, it can be 85% by weight or more, it can be 90% by weight or more, or it can be 95% by weight or more. Monomer (A1) can also be substantially 100% by weight of monomers containing multiple aromatic rings. That is, monomer (A1) can also use only one or two or more monomers containing multiple aromatic rings. Furthermore, in several other states, for example considering the balance between high refractive index and large deformability, the content of monomers containing multiple aromatic rings in the monomer (A1) can be less than 100% by weight, less than 98% by weight, less than 90% by weight, less than 80% by weight, less than 70% by weight, less than 65% by weight, less than 50% by weight, less than 25% by weight, or less than 10% by weight. The technique disclosed herein can still be implemented even in states where the content of monomers containing multiple aromatic rings in the monomer (A1) is less than 5% by weight. It is also possible to omit the use of monomers containing multiple aromatic rings.

[0073] There is no particular limitation on the content of monomers containing multiple aromatic rings in the monomer components constituting the acrylic polymer, and it can be set to achieve a high refractive index adhesive layer that balances the desired refractive index and large deformability. The content of monomers containing multiple aromatic rings in the aforementioned monomer components can be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. Among several options, from the viewpoint of easily achieving a high refractive index adhesive layer with a higher refractive index, it is advantageous for the content of monomers containing multiple aromatic rings in the aforementioned monomer components to be greater than 35% by weight, greater than 50% by weight, preferably greater than 70% by weight, and can be 75% by weight or more, 85% by weight or more, 90% by weight or more, or 91% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more, 95% by weight or more, 96% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more. Taking into account the balance between high refractive index and large deformability, it is advantageous to set the content of monomers containing multiple aromatic rings in the above-mentioned monomer composition to be approximately 99% by weight or less, and it can be 98% by weight or less, 96% by weight or less, 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or even 75% by weight or less. In several other states, from the viewpoint of easily achieving higher adhesive properties and / or optical properties (e.g., transparency), the content of monomers containing multiple aromatic rings in the above-mentioned monomer composition can be 70% by weight or less, 60% by weight or less, 50% by weight or less, 40% by weight or less, 25% by weight or less, 15% by weight or less, or even 5% by weight or less. The technology disclosed herein can still be implemented even in states where the content of monomers containing multiple aromatic rings in the above-mentioned monomer composition is less than 3% by weight.

[0074] There is no particular limitation on the content of monomers containing an odd number of aromatic rings in monomer (A1), for example, it can be 5% by weight or more, 25% by weight or more, or 40% by weight or more. In several states, the content of monomers containing an odd number of aromatic rings in monomer (A1) can be, for example, 50% by weight or more, and from the viewpoint of easily obtaining a higher refractive index, it is preferable to be 70% by weight or more, and it can be 85% by weight or more, 90% by weight or more, or 95% by weight or more. Monomer (A1) can also be substantially 100% by weight of monomers containing an odd number of aromatic rings. That is, monomer (A1) can also use only one or two or more monomers containing an odd number of aromatic rings. Furthermore, in several states, considering the balance between high refractive index and large deformability, the content of monomers containing an odd number of aromatic rings in the monomer (A1) can be less than 100% by weight, less than 98% by weight, less than 90% by weight, less than 80% by weight, less than 70% by weight, less than 65% by weight, less than 50% by weight, less than 25% by weight, or less than 10% by weight. The technique disclosed herein can still be implemented even in states where the content of monomers containing an odd number of aromatic rings in the monomer (A1) is less than 5% by weight. It is also possible to omit the use of monomers containing an odd number of aromatic rings.

[0075] There is no particular limitation on the content of monomers containing an odd number of aromatic rings in the monomer components constituting the acrylic polymer, and it can be set to achieve a high refractive index adhesive layer that balances the desired refractive index and large deformability. The content of monomers containing an odd number of aromatic rings in the aforementioned monomer components can be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. Among several options, from the viewpoint of easily achieving a high refractive index adhesive layer with a higher refractive index, the content of monomers containing an odd number of aromatic rings in the aforementioned monomer components can be, for example, greater than 35% by weight, greater than 50% by weight, preferably 60% by weight or more, more preferably greater than 70% by weight, 75% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more, or 98% by weight or more. The content of monomers containing an odd number of aromatic rings in the aforementioned monomeric components, taking into account the balance between high refractive index and large deformability, can be set to approximately 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, possibly 93% by weight or less, possibly 90% by weight or less, possibly 85% by weight or less, possibly 80% by weight or less, or possibly 75% by weight or less. Among several states, from the viewpoint of easily achieving higher adhesive properties and / or optical properties (e.g., transparency), the content of monomers containing an odd number of aromatic rings in the aforementioned monomeric components can be 70% by weight or less, possibly 60% by weight or less, possibly 50% by weight or less, possibly 40% by weight or less, possibly 25% by weight or less, possibly 15% by weight or less, or possibly 5% by weight or less. The technology disclosed herein can still be implemented even in states where the content of monomers containing an odd number of aromatic rings in the aforementioned monomeric components is less than 3% by weight.

[0076] In several ideal samples, at least a portion of the monomer (A1) may be a high-refractive-index monomer. Here, "high-refractive-index monomer" means a monomer with a refractive index of, for example, about 1.510 or higher, preferably about 1.530 or higher, or more preferably about 1.550 or higher. There is no particular upper limit to the refractive index of the high-refractive-index monomer, but from the viewpoint of ease of preparation of acrylic polymers or ease of combining suitability as an adhesive with flexibility, it may be, for example, 3.000 or lower, 2.500 or lower, 2.000 or lower, 1.900 or lower, 1.800 or lower, or 1.700 or lower. One high-refractive-index monomer may be used alone or in combination of two or more. Furthermore, the refractive index of the monomer is measured using an Abbe refractometer at a measurement wavelength of 589 nm and a measurement temperature of 25 °C. The Abbe refractometer can use the ATAGO "DR-M4" model or its equivalent. When a nominal value for the refractive index at 25°C is provided by the manufacturer, that nominal value can be used.

[0077] The aforementioned high refractive index monomer may be appropriately selected from compounds containing the concept of aromatic ring monomers (A1) disclosed herein (e.g., the compounds and groups of compounds exemplified above). Specific examples include: m-phenoxybenzyl acrylate (refractive index: 1.566, Tg of homopolymer: -35°C), 1-naphthylmethyl acrylate (refractive index: 1.595, Tg of homopolymer: 31°C), ethoxylated o-phenylphenol acrylate (repetition number of oxyethyl units: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, Tg of homopolymer: 6°C), phenoxyethyl acrylate (refractive index (nD20): 1.517, Tg of homopolymer: 2°C), phenoxydiethylene glycol acrylate (refractive index: 1.510, Tg of homopolymer: 1.510, Tg of homopolymer: 1.510, Tg of homopolymer: 1.510, Tg of homopolymer: 1.510, Tg of homopolymer: 1.510, Tg of homopolymer: 1.519 ... -35℃), 6-propenylidenemethyl dinaphthothiophene (6MDNTA, refractive index: 1.75), 6-methpropenylidenemethyl dinaphthothiophene (6MDNTMA, refractive index: 1.726), 5-propenylideneethyl dinaphthothiophene (5EDNTA, refractive index: 1.786), 6-propenylideneethyl dinaphthothiophene (6EDNTA, refractive index: 1.722), 6-vinyl dinaphthothiophene (6VDNT, refractive index: 1.802), 5-vinyl dinaphthothiophene (abbreviation: 5VDNT, refractive index: 1.793), etc., but not limited to these.

[0078] There is no particular limitation on the content of high-refractive-index monomers (i.e., aromatic ring-containing monomers with a refractive index of approximately 1.510 or higher, preferably approximately 1.530 or higher, and more preferably approximately 1.550 or higher) in monomer (A1). For example, it can be 5% by weight or more, 25% by weight or more, 35% by weight or more, or 40% by weight or more. In several states, from the viewpoint of easily obtaining higher refractive indices, the content of high-refractive-index monomers in monomer (A1) can be, for example, 50% by weight or more, preferably 70% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. Monomer (A1) can also be substantially 100% by weight high-refractive-index monomers. Furthermore, in several samples, for example from the perspective of balancing high refractive index and large deformability, the content of high refractive index monomer in monomer (A1) can be less than 100% by weight, less than 98% by weight, less than 90% by weight, less than 80% by weight, or less than 65% by weight. In other samples, considering adhesion and / or optical properties, the content of high refractive index monomer in monomer (A1) can be less than 50% by weight, less than 25% by weight, less than 15% by weight, or less than 10% by weight. The technique disclosed herein can still be implemented even in samples where the content of high refractive index monomer in monomer (A1) is less than 5% by weight. Alternatively, high refractive index monomer may not be used.

[0079] There is no particular limitation on the content of high-refractive-index monomers in the monomer components constituting the acrylic polymer. It can be set to achieve a high-refractive-index adhesive layer that balances the desired refractive index and large deformability. Furthermore, where necessary, it can be further set to balance adhesive properties (e.g., adhesion strength) and / or optical properties (e.g., total light transmittance, haze value, etc.). The content of high-refractive-index monomers in the aforementioned monomer components can, for example, be 3% by weight or more, 10% by weight or more, or 25% by weight or more. In several cases, the content of high-refractive-index monomers in the monomer components constituting the acrylic polymer can, for example, be greater than 35% by weight. From the viewpoint of easily obtaining higher refractive indices, greater than 50% by weight is advantageous, preferably greater than 70% by weight, and can be 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. From the perspective of balancing high refractive index and large deformability, it is advantageous for the content of high refractive index monomers in the above-mentioned monomer composition to be 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, and could be 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or even 75% by weight or less. In several other states, considering adhesion and / or optical properties, the content of high refractive index monomers in the above-mentioned monomer composition can be 70% by weight or less, 50% by weight or less, 25% by weight or less, 15% by weight or less, or even 5% by weight or less. The technology disclosed herein can still be implemented even in states where the content of high refractive index monomers in the above-mentioned monomer composition is less than 3% by weight.

[0080] In several ideal samples, at least a portion of the monomer (A1) is an aromatic ring monomer (hereinafter sometimes referred to as "monomer L") with a Tg of less than 10°C in the homopolymer. When the content of the aromatic ring monomer (A1) in the monomer composition (especially the aromatic ring monomer (A1) equivalent to at least one of the above-mentioned monomers containing multiple aromatic rings, monomers containing a single aromatic ring, and high refractive index monomers) tends to decrease, the flexibility of the adhesive tends to decrease, but by using monomer L as part or all of the monomer (A1), the decrease in flexibility can be suppressed. In this way, large deformability can be maintained better, and the refractive index can be improved. The Tg of monomer L can be, for example, less than 5°C, less than 0°C, less than -10°C, less than -20°C, or less than -25°C. There is no particular limitation on the lower limit of the Tg of monomer L. Considering the balance with the refractive index enhancement effect, in several states, the Tg of monomer L can be, for example, above -70℃, above -55℃, or above -45℃. In other states, the Tg of monomer L can be, for example, above -30℃, above -10℃, above 0℃, or above 3℃. Monomer L can be used alone or in combination of two or more types.

[0081] Monomer L may be suitably selected from compounds containing the concept of aromatic ring monomers (A1) disclosed herein (e.g., the compounds and groups of compounds exemplified above) that have the Tg. Suitable examples of aromatic ring monomers that may be used as monomer L include: m-phenoxybenzyl acrylate (Tg of homopolymer: -35°C), benzyl acrylate (Tg of homopolymer: 6°C), phenoxyethyl acrylate (Tg of homopolymer: 2°C), and phenoxydiethylene glycol acrylate (Tg of homopolymer: -35°C).

[0082] There is no particular limitation on the content of monomer L in monomer (A1), for example, it can be 5% by weight or more, 25% by weight or more, or 40% by weight or more. Among several states, from the viewpoint of easily obtaining a high-refractive-index adhesive layer that balances high refractive index and large deformability at a higher level, the content of monomer L in monomer (A1) can be, for example, 50% by weight or more, while from the viewpoint of improving large deformability, it is preferable to be 60% by weight or more, or 70% by weight or more, or 75% by weight or more, or 85% by weight or more, or 90% by weight or more, or 95% by weight or more. Monomer (A1) can also be substantially 100% by weight of monomer L. Furthermore, in several other states, for example from the perspective of balancing high refractive index and large deformability, the content of monomer L in monomer (A1) can be less than 100% by weight, less than 98% by weight, less than 90% by weight, less than 80% by weight, or less than 65% by weight.

[0083] The content of monomer L in the monomer component constituting the acrylic polymer can be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. Among several samples, from the viewpoint of easily obtaining a high-refractive-index adhesive layer that balances high refractive index and large deformability at a higher level, the content of monomer L in the monomer component can be, for example, greater than 35% by weight, and from the viewpoint of increasing refractive index, greater than 50% by weight is advantageous, preferably greater than 70% by weight, and can be 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. From the viewpoint of balancing high refractive index and large deformability, the content of monomer L in the above monomer component is advantageously set to approximately 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, can be 93% by weight or less, can be 90% by weight or less, can be 85% by weight or less, can be 80% by weight or less, or can be 75% by weight or less.

[0084] In several samples, the aromatic ring monomer (Al) can also be used in combination with monomer L (i.e., the aromatic ring monomer with a Tg of less than 10°C in the homopolymer) and monomer H with a Tg higher than 10°C. The Tg of monomer H can be, for example, higher than 10°C, higher than 15°C, or higher than 20°C. By using monomer L and monomer H in combination, in a high-refractive-index adhesive layer with a high content of aromatic ring monomer (Al) in the monomer composition, the high refractive index of the high-refractive-index adhesive layer and its flexibility suitable for adhesion to the substrate can be balanced to a higher level. The ratio of monomer L to monomer H used can be set to appropriately exhibit the aforementioned effect, and there is no particular limitation.

[0085] Among several samples, the aromatic ring monomer (A1) can be suitably selected from compounds that do not contain a structure with two or more non-condensed aromatic rings directly chemically bonded (e.g., a biphenyl structure). For example, it is preferable to use an acrylic polymer composed of a monomer component with a content of less than 5% by weight (preferably less than 3% by weight, or even 0% by weight). This limitation on the amount of compounds containing two or more non-condensed aromatic rings directly chemically bonded is advantageous from the viewpoint of achieving a more balanced high-refractive-index adhesive layer that takes into account both high refractive index and large deformability.

[0086] The content of monomer (Al) in the monomer component constituting the acrylic polymer is not particularly limited, and can be set to achieve a high refractive index adhesive layer that takes into account both the desired refractive index and large deformability, and thus adhesive properties (e.g., adhesion strength) and / or optical properties (e.g., total light transmittance, haze value, etc.). In several samples, the content of monomer (Al) in the above-mentioned monomer component may be, for example, 30% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more, or even 70% by weight or more. In several ideal samples, the content of monomer (Al) in the monomer components constituting acrylic polymers can be, for example, greater than 70% by weight, with 75% by weight or more being appropriate; and from the viewpoint of easily obtaining higher refractive indices, it is preferable to be 80% by weight or more, and it can be 85% by weight or more, 90% by weight or more, or 91% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more, 95% by weight or more, 96% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more. The content of monomer (Al) in the above monomer components is typically less than 100% by weight, and from the viewpoint of balancing high refractive index and large deformability, approximately 99% by weight or less is advantageous, and it can be 98% by weight or less, 96% by weight or less, 93% by weight or less, or 90% by weight or less. In several samples, from the viewpoint of easily achieving higher adhesive properties and / or optical properties (e.g., transparency), the content of monomer (Al) in the above monomer components can be less than 90% by weight, less than 85% by weight, or less than 80% by weight.

[0087] (Monomer (A2)) In several ideal samples, the monomer component constituting the acrylic polymer may contain monomer (A2) in addition to the monomer (A1) described above. The monomer (A2) is a monomer equivalent to at least one of a monomer having a hydroxyl group (hydroxyl-containing monomer) and a monomer having a carboxyl group (carboxyl-containing monomer). The hydroxyl-containing monomer is a compound having at least one hydroxyl group and at least one vinyl unsaturated group per molecule. The carboxyl-containing monomer is a compound containing at least one carboxyl group and at least one vinyl unsaturated group per molecule. Monomer (A2) may be used to introduce crosslinking points into the acrylic polymer or to impart appropriate aggregation properties to high-refractive-index adhesive layers. Monomer (A2) may be used alone or in combination of two or more. Monomer (A2) may contain an aromatic ring or may not contain an aromatic ring. Monomer (A2) may preferably be a monomer without an aromatic ring. Furthermore, monomer (A2) is defined as a monomer that is different from the aforementioned monomer (A1). For example, the aforementioned monomer (A1) can be defined as a monomer that does not have hydroxyl and carboxyl groups.

[0088] Examples of vinyl unsaturated groups in monomer (A2) include (meth)acryl, vinyl, and (meth)allyl. From the viewpoint of polymerization reactivity, (meth)acryl is preferable, while from the viewpoint of improving flexibility or adhesion, acrylonitrile is better. From the viewpoint of improving the flexibility of high-refractive-index adhesive layers, monomer (A2) can be a compound containing one vinyl unsaturated group per molecule (i.e., a monofunctional monomer).

[0089] Among several states, the monomer (A2) may be a monomer with a relatively long distance between the vinyl unsaturated group (e.g., (meth)acryl) and the hydroxyl and / or carboxyl groups. This allows for the easy acquisition of a highly flexible cross-linked structure in the states where the hydroxyl and / or carboxyl groups are used for the cross-linking reaction. For example, a compound constituting the chain (linking chain) connecting the vinyl unsaturated group and the hydroxyl and / or carboxyl groups (linking chain) may be used as the monomer (A2) if the number of atoms (typically carbon or oxygen atoms) is 3 or more (e.g., 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, 15 or more, 16 or more, 17 or more, 18 or more, or 19 or more). The upper limit for the number of atoms constituting the aforementioned linking chain is, for example, 45 or less, or 20 or less (e.g., 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, 10 or less, 9 or less, or 8 or less). Furthermore, the number of atoms constituting the linking chain connecting the aforementioned vinyl unsaturated group to the hydroxyl and / or carboxyl groups refers to the minimum number of atoms required to reach the hydroxyl or carboxyl group from the vinyl unsaturated group. For example, when the aforementioned linking chain is composed of a straight-chain extended alkyl group (i.e., -(CH₂)ₙ-yl), the number of 'n' becomes the number of atoms constituting the aforementioned linking chain. As another example, when the aforementioned linking chain is an oxy-extended ethyl group (i.e., -(C₂H₄O)ₙ-yl), the product of the sum of the number of carbon atoms 2 and the number of oxygen atoms 1 constituting the oxy-extended ethyl group (3) and 'n' (3n) becomes the number of atoms constituting the aforementioned linking chain. As the monomer (A2), at least one alkyl unit (e.g., -(CH2)n-) or an oxyalkyl unit (e.g., an oxyalkylene unit where m is 2, an oxypropylene unit where m is 3, or an oxybutylene unit where m is 4) can be used between the ethylene unsaturated group and the hydroxyl and / or carboxyl group, but there is no particular limitation. The number of the alkyl or oxyalkyl units is not particularly limited, and may be 1 or more (e.g., 1 to 15, 1 to 10, 2 to 6, or 2 to 4). Furthermore, n in the formula representing the alkyl unit may be an integer from 1 to 10, and may be 2 or more, 3 or more, 4 or more, 6 or less, or 5 or less. m in the formula representing the oxyalkyl unit may be an integer from 2 or more, for example, an integer from 2 to 4. The monomer (A2) may contain, in addition to the aforementioned vinyl unsaturated groups, hydroxyl and / or carboxyl groups, alkyl units and / or oxyalkyl units, ester or ether bonds, thioether bonds, aromatic rings, aliphatic rings, or heterocycles (e.g., rings containing nitrogen (N) or oxygen (O) and sulfur (S) atoms). Furthermore, the aforementioned alkyl or oxyalkyl units may also have substituents.

[0090] Examples of hydroxyl-containing monomers include: 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylaurate (meth)acrylate, (4-hydroxymethylcyclohexyl)meth(meth)acrylate, and other hydroxyalkyl (meth)acrylates; polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polybutylene glycol mono(meth)acrylate, and other polyalkylene glycol mono(meth)acrylates, but are not limited to these. Suitable examples of hydroxyl-containing monomers include 4-hydroxybutyl acrylate (Tg: -40℃) and 2-hydroxyethyl acrylate (Tg: -15℃). From the viewpoint of improving flexibility in the room temperature range, 4-hydroxybutyl acrylate with a lower Tg is preferable. Furthermore, in the case where hydroxyalkyl (meth)acrylate is used as a hydroxyl-containing monomer and the hydroxyl group is utilized in the crosslinking reaction, from the viewpoint of obtaining a crosslinked structure with high flexibility, it is preferable to use a monomer with a higher number of carbon atoms in the hydroxyalkyl group of the aforementioned hydroxyalkyl (meth)acrylate, and preferably a hydroxyalkyl (meth)acrylate with 3 or more carbon atoms in the aforementioned hydroxyalkyl group (e.g., 3 to 12, preferably 4 to 10) (e.g., 4-hydroxybutyl acrylate). In several ideal cases, 50% by weight or more (e.g., greater than 50% by weight, greater than 70% by weight, or greater than 85% by weight) of the monomer (A2) can be 4-hydroxybutyl acrylate. The hydroxyl-containing monomer can be used alone or in combination of two or more.

[0091] Among the several forms in which a hydroxyl-containing monomer is used as a monomer (A2), the aforementioned hydroxyl-containing monomer may be one or more compounds selected from those without a methacrylic group. Suitable examples of hydroxyl-containing monomers without a methacrylic group include the various hydroxyalkyl acrylates mentioned above. For example, it is preferable that more than 50% by weight, more than 70% by weight, or more than 85% by weight of the hydroxyl-containing monomer used as a monomer (A2) is a hydroxyalkyl acrylate. By using hydroxyalkyl acrylates, it is possible to introduce hydroxyl groups into acrylic polymers, which can help provide crosslinking points or impart moderate aggregation properties, and adhesives with good flexibility or adhesion in the room temperature range can be obtained more easily than when only the corresponding methacrylic hydroxyalkyl group is used.

[0092] Examples of carboxyl-containing monomers include acrylic acid, carboxyethyl methacrylate, carboxypentyl methacrylate, etc., as well as isocoric acid, maleic acid, fumaric acid, crotonic acid and isocortonic acid, but are not limited to these. Examples of suitable carboxyl-containing monomers include acrylic acid and methacrylic acid. Furthermore, from the viewpoint of improving the flexibility of the high refractive index adhesive layer, among several types of samples, the carboxyl-containing monomers are preferably compounds shown in the following formula (1). CH 2=CR 1-COO-R 2-OCO-R 3-COOH (1) Here, R 1 in the above formula (1) is hydrogen or methyl. R 2 and R 3 are divalent linkages (specifically, organic groups with 1 to 20 carbon atoms (e.g. 2 to 10, preferably 2 to 5), which may be the same or different from each other. In formula (1) above, R2 and R3 can be, for example, divalent aliphatic hydrocarbon groups, aromatic hydrocarbon groups, or alicyclic hydrocarbon groups. For example, R2 and R3 can be alkyl groups with 2 to 5 carbon atoms. Specific examples of carboxyl-containing monomers shown in formula (1) above include: 2-(meth)propenyloxyethyl hexahydrophthalic acid, 2-(meth)propenyloxyethyl-phthalic acid, 2-(meth)propenyloxyethyl-2-hydroxyethyl-phthalic acid, 2-(meth)propenyloxyethyl-succinic acid, 2-(meth)propenyloxypropyl hexahydrophthalic acid hydrogen ester, 2-(meth)propenyloxypropyl phthalic acid hydrogen ester, 2-(meth)propenyloxypropyl tetrahydrophthalic acid hydrogen ester, etc. Carboxyl-containing monomers can be used alone or in combination of two or more. Hydroxyl-containing monomers and carboxyl-containing monomers can also be used together.

[0093] The content of monomer (A2) in the monomer component constituting the acrylic polymer is not particularly limited and can be set according to the purpose. In several samples, the content of the aforementioned monomer (A2) is, for example, 0.01% by weight or more, 0.1% by weight or more, and preferably 0.5% by weight or more. From the viewpoint of obtaining a higher performance effect, in several samples, the content of the aforementioned monomer (A2) can be set to 1% by weight or more, 2% by weight or more, or 4% by weight or more. The upper limit of the content of monomer (A2) in the monomer component is set so that the total content with the monomer (A1) does not exceed 100% by weight. In several samples, the content of the aforementioned monomer (A2) is, for example, 30% by weight or less or 25% by weight or less, and from the viewpoint of making it easier to achieve a high refractive index by having a relatively high content of monomer (A1), it is preferable to set it to 20% by weight or less, more preferably 15% by weight or less, less than 12% by weight, less than 10% by weight, or less than 7% by weight. In several ideal samples, from the viewpoint of improving the large deformability of the high refractive index adhesive layer, the content of the above monomer (A2) is less than 5% by weight, preferably less than 3% by weight, and can also be less than 1.5% by weight.

[0094] (Monomer A3) In several samples, in addition to the monomer (A1) mentioned above, the monomer components constituting the acrylic polymer may also contain alkyl (meth)acrylate (hereinafter also referred to as "monomer (A3)"). Monomer (A3) can help improve the flexibility of the high refractive index adhesive layer. Furthermore, it can also help improve the adhesive properties such as the compatibility or adhesion of additives in the adhesive. Monomer (A3) can be used alone or in combination of two or more.

[0095] Monomer (A3) is suitable for use in alkyl (meth)acrylates with a straight-chain or branched alkyl group having 1 to 20 carbon atoms at the ester terminus (i.e., C1-20). (Meth)acrylate C Specific examples of 1-20 alkyl esters include: methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, isoamyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, nonyl methacrylate, isononyl methacrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptyl methacrylate, octadecyl methacrylate, isooctadecyl methacrylate, nonadecanyl methacrylate, ecicoacrylate, etc., but are not limited to these.

[0096] In several samples, at least a portion of the monomer (A3) may be suitable as a homopolymer of alkyl (meth)acrylate with a Tg of -20°C or lower (preferably -40°C or lower, for example -50°C or lower). The low Tg alkyl (meth)acrylate can help improve the flexibility of the high refractive index adhesive layer. Furthermore, it can also help improve adhesive properties such as adhesion strength. There is no particular limitation on the lower limit of the Tg of the aforementioned alkyl (meth)acrylate; for example, it may be above -85°C, above -75°C, above -65°C, or above -60°C. Specific examples of the aforementioned low Tg alkyl (meth)acrylate include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), heptaacrylate, octyl acrylate, and isononyl acrylate (iNA). In several other samples, at least a portion of the monomer (A3) may be a homopolymer of alkyl (meth)acrylate with a Tg higher than -20°C (e.g., above -10°C). The upper limit of the Tg of the aforementioned alkyl (meth)acrylate is, for example, below 10°C, below 5°C, or below 0°C. Alkyl (meth)acrylates with a Tg within this range can help adjust the flexibility of the high-refractive-index adhesive layer. Alkyl (meth)acrylates with the aforementioned Tg are preferably used in combination with the aforementioned low-Tg alkyl (meth)acrylates, but there are no particular limitations. A specific example of an alkyl (meth)acrylate with the aforementioned Tg is lauryl acrylate (LA).

[0097] Among the various forms of monomer (A3) used, C4-8 alkyl methacrylate is preferably used as monomer (A3). C4-8 alkyl acrylate is particularly preferred. One type of C4-8 alkyl methacrylate can be used alone or in combination of two or more. Using C4-8 alkyl methacrylate tends to easily improve the flexibility of the high-refractive-index adhesive layer and readily achieve good adhesive properties (adhesion, etc.). In forms using C4-8 alkyl methacrylate as monomer (A3), the ratio of C4-8 alkyl methacrylate to C4-8 alkyl methacrylate in the monomer composition should be at least 30% by weight, preferably at least 50% by weight, more preferably at least 70% by weight, more preferably at least 90% by weight, and substantially at least 100% by weight.

[0098] Among the several states of monomer (A3) used, C1-6 alkyl methacrylate can be used as monomer (A3). By using C1-6 alkyl methacrylate, the storage modulus of elasticity in each temperature range can be adjusted. For example, by setting the storage modulus of elasticity in the high-temperature range to be relatively high, the difference in storage modulus of elasticity between the low-temperature and high-temperature ranges can be suppressed. Furthermore, C1-6 alkyl methacrylate tends to have excellent copolymerization properties with monomer (A1). C1-6 alkyl methacrylate can be used alone or in combination of two or more. C1-6 alkyl methacrylate is preferably C1-6 alkyl acrylate, more preferably C2-6 alkyl acrylate, and even more preferably C4-6 alkyl acrylate. Among the other several states, (meth)acrylate C1-6 alkyl esters are preferably (meth)acrylate C1-4 alkyl esters, more preferably (meth)acrylate C2-4 alkyl esters, and even more preferably (meth)acrylate C2-4 alkyl esters. A suitable example of (meth)acrylate C1-6 alkyl ester is BA.

[0099] In the monomer components constituting acrylic polymers, the content of (meth)acrylate C1-6 alkyl esters may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. In several samples, from the viewpoint of improving flexibility and adhesion, the content of the aforementioned (meth)acrylate C1-6 alkyl esters may be 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more (e.g., 30% by weight or more). The upper limit of the content of (meth)acrylate C1-6 alkyl esters in the monomer components is, for example, less than 50% by weight, or less than 35% by weight. In several samples, from the viewpoint of maintaining a high refractive index, the content of the aforementioned (meth)acrylate C1-6 alkyl esters may be, for example, less than 24% by weight, preferably less than 20% by weight, more preferably less than 17% by weight, less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The techniques disclosed herein can still be implemented even without the substantial use of (meth)acrylate C1-6 alkyl esters.

[0100] Among the other states of monomer (A3) used, C7-12 alkyl methacrylate may be suitable as monomer (A3). By using C7-12 alkyl methacrylate, the storage modulus of elasticity can be appropriately reduced. C7-12 alkyl methacrylate may be used alone or in combination of two or more. C7-12 alkyl methacrylate is preferably C7-10 alkyl acrylate, more preferably C7-9 alkyl acrylate, and even more preferably C8 alkyl acrylate. Examples of C7-12 alkyl methacrylate include 2EHA, iNA, and LA, with 2EHA being a suitable example.

[0101] In the monomer components constituting acrylic polymers, the content of (meth)acrylate C7-12 alkyl esters may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. In several samples, from the viewpoint of improving flexibility and adhesion, the content of the aforementioned (meth)acrylate C7-12 alkyl esters may be 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more (e.g., 30% by weight or more). The upper limit of the content of (meth)acrylate C7-12 alkyl esters in the monomer components is, for example, less than 50% by weight, or less than 35% by weight. In several samples, from the viewpoint of maintaining a high refractive index, the content of the aforementioned (meth)acrylate C7-12 alkyl esters may be, for example, less than 24% by weight, preferably less than 20% by weight, more preferably less than 17% by weight, less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The techniques disclosed herein can still be implemented even without substantially using (meth)acrylate C7-12 alkyl esters.

[0102] Among the various forms of monomer (A3) used, from the viewpoint of improving flexibility, at least a portion of the monomer (A3) should preferably be alkyl acrylate. The use of alkyl acrylate is also advantageous in terms of adhesive properties such as adhesion. For example, alkyl acrylate should preferably be 50% by weight or more of the monomer (A3), and the ratio of alkyl acrylate in the monomer (A3) should preferably be 75% by weight or more, more preferably 90% by weight or more. The monomer (A3) can also be substantially 100% by weight of alkyl acrylate. It is also possible to use only one or two or more alkyl acrylates as monomer (A3) and not use alkyl methacrylate.

[0103] In samples containing alkyl (meth)acrylate as a monomer component, the content of alkyl (meth)acrylate in the monomer component can be set to appropriately exert its effect. In several samples, the content of the aforementioned alkyl (meth)acrylate can be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. The upper limit of the content of monomer (A3) in the monomer component is set so that the total content of monomers (A1) and (A2) does not exceed 100% by weight, for example, less than 50% by weight, or less than 35% by weight. In several samples, the content of the aforementioned monomer (A3) can be, for example, 24% by weight or less. Generally speaking, alkyl (meth)acrylate has a low refractive index, therefore, in order to increase the refractive index, it is advantageous to limit the content of monomer (A3) in the monomer component and make the content of monomer (A1) relatively higher. From the aforementioned viewpoint, it is appropriate for the content of monomer (A3) to be less than 23% by weight of the monomer component, preferably less than 20% by weight, more preferably less than 17% by weight, less than 12% by weight, less than 7% by weight, less than 3% by weight, or even less than 1% by weight. The technology disclosed herein can still be appropriately implemented even in a configuration where monomer (A3) is not substantially used.

[0104] (Other Monomers) The monomer components constituting acrylic polymers may also include monomers other than those mentioned above (A1), (A2), and (A3) (hereinafter referred to as "other monomers"), as needed. These other monomers may be used, for example, to adjust the Tg of the acrylic polymer, adjust adhesive properties, or improve compatibility within the adhesive layer. One of these other monomers may be used alone or in combination of two or more.

[0105] Examples of other monomers mentioned above include monomers with functional groups other than hydroxyl and carboxyl groups (including functionalized monomers). For example, other monomers that can improve the cohesiveness or heat resistance of adhesives include monomers containing sulfonic acid groups, monomers containing phosphate groups, and monomers containing cyano groups. Furthermore, monomers that can introduce functional groups into acrylic polymers to serve as crosslinking sites, or that can help improve adhesion to the adherend or enhance compatibility within the adhesive, include: amine-containing monomers (e.g., (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, etc.), amine-containing monomers (e.g., aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, etc.), monomers with a nitrogen-containing ring (e.g., N-vinyl-2-pyrrolidone, N-(meth)acrylamide morphofolin, etc.), amine-containing monomers, epoxy-containing monomers, ketone-containing monomers, isocyanate-containing monomers, and alkoxysilyl-containing monomers. In addition, monomers with a nitrogen-containing ring, such as N-vinyl-2-pyrrolidone, are also equivalent to amine-containing monomers. The relationship between the aforementioned monomers with nitrogen-containing rings and amine-containing monomers is similar.

[0106] Other monomers that can be used besides the functionalized monomers mentioned above include: vinyl acetate and other vinyl ester monomers; non-aromatic cyclic (meth)acrylates such as cyclohexyl methacrylate and isoborneol (meth)acrylate; olefin monomers such as ethylene, butadiene, and isobutene; chlorinated monomers such as vinyl chloride; alkoxy-containing monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether. A suitable example of other monomers that can be used for purposes such as improving the flexibility of adhesives is ethoxyethoxyethyl acrylate (also known as ethyl carbitol acrylate, Tg of homopolymer: -67°C).

[0107] When using the other monomers mentioned above, there are no particular restrictions on their usage, and they can be appropriately set within a range where the total amount of monomer components does not exceed 100% by weight. From the viewpoint of easily achieving the refractive index enhancement effect obtained by using monomer (Al), the content of the other monomers mentioned above in the monomer component can be set to, for example, about 35% by weight or less, about 25% by weight or less (for example, 0 to 25% by weight), is appropriate, about 20% by weight or less (for example, 0 to 20% by weight), about 10% by weight or less (for example, 0 to 10% by weight), preferably about 5% by weight or less, for example, about 1% by weight or less. The technique disclosed herein can be suitably implemented in a monomer component that substantially does not contain the other monomers mentioned above.

[0108] In several samples, the monomer component constituting the acrylic polymer may be a composition in which the amount of methacrylamide monomer used is suppressed to a predetermined level. For example, the amount of methacrylamide monomer used in the monomer component may be less than 5% by weight, less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. Such limitation on the amount of methacrylamide monomer used is advantageous from the viewpoint of achieving a balance between flexibility or adhesiveness and a high refractive index adhesive. The monomer component constituting the acrylic polymer may also be a composition that does not contain methacrylamide monomers (e.g., a composition consisting only of acrylamide monomers).

[0109] In several samples, from the viewpoint of suppressing discoloration or color change (e.g., yellowing) of the high-refractive-index adhesive layer, the amount of carboxyl-containing monomers used in the monomer component of the base polymer (e.g., acrylic polymer) constituting the high-refractive-index adhesive layer has been limited. The amount of carboxyl-containing monomers used in the monomer component may, for example, be less than 1% by weight, less than 0.5% by weight, less than 0.3% by weight, less than 0.1% by weight, or less than 0.05% by weight. This limitation on the amount of carboxyl-containing monomers is also advantageous from the viewpoint of suppressing corrosion of metallic materials, which are metallic materials that can contact the high-refractive-index adhesive layer disclosed herein, or metallic materials that can be disposed adjacent to the high-refractive-index adhesive layer disclosed herein (e.g., metallic wiring or metallic films present on the adherend). The technique disclosed herein can be implemented in samples where the monomer component does not contain carboxyl-containing monomers. For the same reason, in several samples, the amount of monomers containing acidic functional groups (including sulfonic acid groups, phosphoric acid groups, etc., in addition to carboxyl groups) in the monomer component of the base polymer constituting the high refractive index adhesive layer can also be limited. The amount of acidic functional group monomers in the monomer component of the sample can be the ideal amount of carboxyl group monomers mentioned above. The technology disclosed herein can be implemented in samples where the monomer component does not contain acidic functional group monomers (i.e., the base polymer of the high refractive index adhesive layer is acid-free).

[0110] (Glass Transition Temperature) The monomer composition of the base polymer (e.g., an acrylic polymer) constituting the high refractive index adhesive layer should preferably have a glass transition temperature (Tg) of approximately 15°C or lower, depending on the composition of the monomer composition. In several cases, the Tg is preferably below 10°C, more preferably below 5°C, more preferably below 1°C, and may also be below 0°C. In other cases, the Tg may be below -10°C, below -20°C, below -25°C, below -30°C, or below -35°C. From the viewpoint of improving the flexibility of the high refractive index adhesive layer, a low Tg is advantageous. Furthermore, the Tg may, for example, be above -60°C, and from the viewpoint of facilitating the high refractive index of the adhesive, it is preferably above -50°C, more preferably above -45°C, and may also be above -40°C. In several samples, the aforementioned Tg can be higher than -30°C, higher than -20°C, higher than -10°C, or even higher than -5°C. A high-refractive-index adhesive layer that combines high refractive index and large deformability can be suitably formed by using a base polymer with a Tg composition having the above-mentioned range.

[0111] Here, unless otherwise specified, Tg, based on the composition of the monomer components constituting the base polymer (e.g., an acrylic polymer), refers to the glass transition temperature obtained by the Fox formula based on the composition of the aforementioned monomer components. The Fox formula, as shown below, is a relationship between the Tg of the copolymer and the glass transition temperature Tgi of the homopolymer of each monomer constituting the copolymer. 1 / Tg=Σ(Wi / Tgi) In the above Fox formula, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (weight-based copolymerization ratio), and Tgi represents the glass transition temperature of the homopolymer of monomer i (unit: K). The glass transition temperature of the homopolymer used in the calculation of Tg is the value recorded in known sources such as the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989). For monomers with multiple values ​​recorded in the above Polymer Handbook, the highest value is used. When the Tg of homopolymers is not recorded in publicly available information, the value is obtained using the measurement method described in Japanese Patent Application Publication No. 2007-51271.

[0112] (Method for Preparing the Base Polymer) In the art disclosed herein, there are no particular limitations on the method for obtaining a base polymer (e.g., an acrylic polymer) composed of the monomer components described above. Known polymerization methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization can be appropriately employed. For example, solution polymerization is suitable. The polymerization temperature during solution polymerization can be appropriately selected according to the type of monomer and solvent used, the type of polymerization initiator, etc., and can be set to approximately 20°C to 170°C (typically approximately 40°C to 140°C).

[0113] The solvent used in solution polymerization (polymerization solvent) may be appropriately selected from conventionally known organic solvents. For example, one or more solvents selected from the following may be used: aromatic compounds such as toluene (typically aromatic hydrocarbons); acetates such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane or cyclohexane; haloalkanes such as 1,2-dichloroethane; lower alcohols such as isopropanol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tributyl methyl ether; ketones such as methyl ethyl ketone, etc.

[0114] The initiator used for polymerization can be appropriately selected from known polymerization initiators depending on the type of polymerization method. For example, one or more azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be used. Other examples of polymerization initiators include: persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; and aromatic carbonyl compounds. Other examples of polymerization initiators include redox initiators composed of peroxides and reducing agents. One polymerization initiator can be used alone or in combination of two or more. The amount of polymerization initiator used is the usual amount, for example, it can be selected in the range of about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) relative to 100 parts by weight of monomer component.

[0115] Various chain transfer agents known in the prior art can be used in the above polymerization as needed. For example, thiols such as n-dodecylthiol, tridecylthiol, hydrothioacetic acid, and α-thioglycerol can be used. Alternatively, chain transfer agents that do not contain sulfur atoms (non-sulfur chain transfer agents) can also be used. Examples of non-sulfur chain transfer agents include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenoids such as α-pinene and terpinene; and styrene-based agents such as α-methylstyrene and α-methylstyrene dimers. One chain transfer agent can be used alone or in combination of two or more. The amount of chain transfer agent used relative to 100 parts by weight of the monomer component can be set to approximately 0.01 to 1 part by weight.

[0116] The weight average molecular weight (Mw) of the base polymer (e.g., acrylic polymer) is not particularly limited, but is suitable for example, being approximately 30 × 10⁴ or higher, approximately 50 × 10⁴ or higher, approximately 70 × 10⁴ or higher, or approximately 80 × 10⁴ or higher. By using a base polymer with a predetermined Mw value or higher, it is easy to obtain a moderate cohesive force that can achieve the desired adhesive properties. Furthermore, it is possible to contain more additives such as plasticizers, which tends to easily achieve the desired flexibility. In addition, the upper limit of the Mw of the base polymer is, for example, approximately 500 × 10⁴ or lower, and from the point of view of adhesive properties, it is preferable to be in the range of approximately 400 × 10⁴ or lower (more preferably approximately 150 × 10⁴ or lower, for example, approximately 130 × 10⁴ or lower). In several samples, the aforementioned Mw can be less than 100 × 10⁴, less than 80 × 10⁴, or less than 60 × 10⁴. The effects of the technique disclosed herein are suitable for use in samples of acrylic polymers with Mw within the aforementioned range.

[0117] Here, the Mw of the polymer can be obtained by converting it to polystyrene using gel permeation chromatography (GPC). Specifically, the product name "HLC-8220GPC" (manufactured by Tosoh Corporation) can be used as the GPC measuring device, and the result can be obtained under the following conditions. [GPC Measurement Conditions] Sample concentration: 0.2% by weight (tetrahydrofuran solution) Sample injection volume: 10µL Solution: tetrahydrofuran (THF) Flow rate: 0.6mL / min Column temperature (measurement temperature): 40℃ Column: Sample column: 1 piece of product name "TSKguardcolumn SuperHZ-H" + 2 pieces of product name "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: 1 piece of product name "TSKgel SuperH-RC" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: polystyrene

[0118] (Plasticizer) In several samples, the high-refractive-index adhesive layer (e.g., a high-refractive-index acrylic adhesive layer) contains a plasticizer in addition to the base polymer. By using a plasticizer, the flexibility of the high-refractive-index adhesive layer can be improved, thereby achieving large deformability. It is preferable to use one or more plasticizers selected from the plasticizers described below, and the plasticizer should be able to achieve both a refractive index of 1.55 or higher and the aforementioned 350% deformability characteristics.

[0119] Suitable examples of plasticizers disclosed herein include cyclic unsaturated organic compounds having two or more rings containing double bonds. In other words, the plasticizer of the above-mentioned suitable examples is a compound having two or more rings containing double bonds in one molecule. Therefore, the above-mentioned plasticizer has at least a first ring containing double bonds and a second ring containing double bonds. By having two or more rings containing double bonds, the refractive index of the high refractive index adhesive layer can be maintained without damage, or the refractive index can be maintained while improving the flexibility of the high refractive index adhesive layer, thereby achieving large deformability. From the viewpoint of exerting a plasticizing effect, the number of rings containing double bonds in the above-mentioned plasticizer is preferably 6 or less, and may be 4 or less, or may be 3 or less.

[0120] Furthermore, the plasticizer used in the technology disclosed herein is preferably a compound that is liquid at 30°C. In addition, in this specification, "liquid" means fluidity, and in terms of the state of matter, it refers to a liquid. The compound includes compounds with melting points below 30°C. The aforementioned plasticizer is liquid at 30°C, thereby appropriately exerting a plasticizing effect, appropriately achieving improved flexibility of the high-refractive-index adhesive layer, and thus appropriately achieving large deformability. The aforementioned plasticizer is preferably a compound that is liquid at 25°C, and more preferably a compound that is liquid at 20°C. For example, by using a compound having two or more rings containing double bonds and being liquid at 30°C as a plasticizer, a high-refractive-index adhesive layer that balances high refractive index and large deformability can be appropriately formed.

[0121] There is no particular limitation on the molecular weight of the plasticizer, but generally a smaller molecular weight than the base polymer (e.g., acrylic polymer) is used. From the viewpoint of easily exhibiting plasticizing effect, a molecular weight of 30,000 or less is appropriate, 25,000 or less is advantageous, less than 10,000 (e.g., less than 5,000), or less than 3,000 is acceptable. Among several options, a molecular weight of 2,000 or less is preferable, 1,200 or less is more preferable, 900 or less is acceptable, 600 or less is acceptable, 500 or less is acceptable, 400 or less is acceptable, 300 or less is acceptable, or 250 or less (e.g., 220 or less) is acceptable. From the viewpoint of improving compatibility within the adhesive layer, a relatively low molecular weight of the plasticizer is advantageous. Furthermore, from the perspective of easily achieving a sufficient plasticizing effect, a molecular weight of 100 or higher for the plasticizer is appropriate, preferably 130 or higher, more preferably 150 or higher, and can be 170 or higher, 200 or higher, 220 or higher, or even 250 or higher. A molecular weight that is not too low is also desirable from the perspective of the adhesive's heat resistance or its ability to inhibit contamination of the adhered body. Among several options, a molecular weight of 300 or higher, 315 or higher for the plasticizer is appropriate, and can also be 350 or higher. Plasticizers with large molecular weights are less prone to vaporization; therefore, by using plasticizers with large molecular weights in adhesives, it is easy to obtain adhesives that exhibit stable properties. Furthermore, plasticizers with large molecular weights do not easily migrate within the adhesive. Therefore, phenomena such as plasticizer migration to the adhesive surface that affects adhesive properties are less likely to occur. The molecular weight of the aforementioned plasticizers is preferably 400 or higher, more preferably 450 or higher, especially 500 or higher, and can also be 530 or higher. Furthermore, the molecular weight of the plasticizer can be calculated based on its chemical structure. When a nominal molecular weight value is provided by the manufacturer, that nominal value can be used.

[0122] Although not specifically limited, in several samples, the plasticizer may be a plasticizer whose amount of transfer to the gas phase at 130°C (vaporization amount at 130°C) is 10% or less by weight (specifically 0 to 10% by weight). By using a plasticizer that meets this characteristic, the changes in the properties of the high-refractive-index adhesive layer containing the plasticizer due to temperature or humidity changes can be suppressed. For example, it can remain a stable adhesive even when used in environments exposed to high temperature or high humidity or during long-term use. The vaporization amount of the plasticizer at 130°C may be less than 10% by weight, less than 5% by weight, less than 3% by weight, or less than 1% by weight.

[0123] The amount of plasticizer transferred to the gas phase at 130°C can be obtained from the weight change of the plasticizer before and after maintaining it at 130°C for 1 hour. Peel strength can be more specifically determined by the following method: [Amount of plasticizer transferred to the gas phase] Approximately 1g of plasticizer (test sample) is dropped into an aluminum cup and weighed to 0.01mg (W0g) using an electronic balance at 23°C and 45%RH. Next, the cup containing the test sample is placed in an oven at 130°C for 1 hour. The oven should have sufficient capacity for the test sample and be able to heat while venting. For example, an oven manufactured by Espec can be used. After maintaining it at 130°C for 1 hour, the cup containing the test sample is removed from the oven, allowed to return to room temperature, and then weighed (W1g). Substituting the weight W0 [g] of the sample before oven heating and the weight W1 [g] of the sample after oven heating into the formula: 1 - W1 / W0, the amount of sample transferred to the gas phase at 130℃ [%] was calculated. The determination was performed on 3 samples (n=3), and the average value was used.

[0124] Although not specifically limited, in several samples, after the high-refractive-index adhesive layer is kept at 130°C for 1 hour, the reduction in plasticizer in the high-refractive-index adhesive layer is less than 5% by weight (specifically 0-5% by weight). Regarding the high-refractive-index adhesive layer that meets this characteristic, even under predetermined heating conditions, almost all the plasticizer in the high-refractive-index adhesive layer remains within the high-refractive-index adhesive layer, thus maintaining its effect (mainly plasticizing effect). Therefore, the characteristic changes of the aforementioned high-refractive-index adhesive layer caused by the plasticizer can be suppressed, thereby maintaining stable characteristics even under the operating environment or long-term use. The reduction in plasticizer in the high-refractive-index adhesive layer after being kept at 130°C for 1 hour should preferably be less than 3% by weight, more preferably less than 1% by weight, more preferably less than 0.5% by weight, less than 0.3% by weight, and less than 0.1% by weight. The reduction in plasticizer in the high-refractive-index adhesive layer after maintaining it at 130°C for 1 hour can be calculated from the weight change of the plasticizer in the high-refractive-index adhesive layer before and after maintaining it at 130°C for 1 hour.

[0125] The amount of plasticizer in the high-refractive-index adhesive layer can be quantified, for example, by liquid chromatography. More specifically, peel strength can be determined by the following method. [Heating loss of plasticizer in the adhesive] The adhesive composition is coated onto the polysiloxane-treated surface of a PET film R1, which is treated with polysiloxane on one side. The film is heated at 130°C for 3 minutes to form an adhesive layer with a thickness of 20 µm. Then, the polysiloxane-treated surface of a PET film R2, which is treated with polysiloxane on one side, is bonded to the surface of the adhesive layer. One release liner is peeled off from the resulting adhesive layer with a release liner (release liner / adhesive layer / release liner), and the film is kept in an oven at 130°C for 1 hour. The oven used is one with sufficient capacity for the test sample and capable of heating while venting. For example, an oven manufactured by Espec can be used. Liquid chromatography (LC) determination is performed on the adhesive before and after heating in the oven under the following conditions. The amount of plasticizer contained in the adhesive before and after heating was determined from the above LC results, and the reduction in plasticizer in the adhesive after being kept at 130°C for 1 hour was calculated from its weight ratio [%]. The determination was performed on 3 samples (n=3), and the average value was used. In addition, before performing LC determination on the above adhesive, it is advisable to perform LC determination on the plasticizer monomer, and then quantify the plasticizer in the adhesive according to the calibration curve. [LC determination conditions] Approximately 0.01 g of adhesive was taken and 2 mL of chloroform was added, and the mixture was shaken overnight. 8 mL of acetonitrile was added to the solution to allow the polymer components to precipitate again. The supernatant was filtered through a 0.45 µm membrane filter. The obtained filtrate was appropriately diluted and injected into the analytical apparatus (Shimadzu Corporation, HPLC Prominence) for determination. Column: GL Sciences, Inertsil ODS-3 (4.6mmφ×250mm, 5µm) Column temperature: 40℃ Column flow rate: 1.0mL / min Solution: Gradient conditions of ultrapure water / acetonitrile Injection volume: 1µL Detector: DAD (selected 190nm~400nm, 272nm)

[0126] In the use of plasticizers having double-bonded rings, the double-bonded rings in the plasticizer may be either conjugated double-bonded rings (typically aromatic rings) or rings containing non-conjugated double bonds. The plasticizer may have at least one type of ring selected from aromatic rings and heterocycles as the double-bonded ring. Furthermore, the heterocycle may have a structure contained within an aromatic ring, or it may have a heterocycle structure containing double bonds different from that of an aromatic ring. The aforementioned plasticizer may have a double-bonded ring (typically an aromatic ring) that is a benzene ring (which may be a benzene ring constituting part of a biphenyl or phenanthrene structure); a carbon ring such as a condensed ring of naphthalene, indene, azurite, anthracene, or phenanthrene; or a heterocyclic ring such as a pyridine ring, pyrimidine ring, pyridine ring, triazine ring, pyrrole ring, pyrazole ring, imidazole ring, triazole ring, acetazole ring, isoacetazole ring, thiazole ring, or thiophene ring. The heteroatoms constituting the rings in the aforementioned heterocyclic rings may, for example, be selected from one or more types of the group consisting of nitrogen, sulfur, and oxygen. In several cases, the heteroatoms constituting the heterocyclic rings may be one or both of nitrogen and sulfur. The aforementioned plasticizer may also have a structure, for example, a condensed structure of one or more carbon rings and one or more heterocyclic rings, such as a dinaphthothiophene structure.

[0127] The aforementioned ring containing a double bond (typically an aromatic ring, preferably a carbocyclic ring) may have one or more substituents on the ring constituent atoms, or it may not have substituents. When substituents are present, examples of substituents include alkyl, alkoxy, aryloxy, hydroxyl, halogen atoms (fluorine, chlorine, bromine, etc.), hydroxyalkyl, hydroxyalkyloxy, epoxypropoxy, etc., but are not limited thereto. Among substituents containing carbon atoms, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and for example, 1 or 2. In several cases, the aforementioned ring containing a double bond may be an aromatic ring without substituents on the ring constituent atoms, or it may be an aromatic ring with one or more substituents selected from the group consisting of alkyl, alkoxy, vinyl unsaturated groups (e.g., (meth)acryloxy), hydroxyl, and hydroxyalkyl. Substituents may suitably be alkyl, alkoxy, or hydroxyalkyl.

[0128] Among several samples, compounds without vinyl unsaturated groups can be appropriately used as plasticizers. This can suppress the deterioration of the adhesive composition due to heat or light (due to gelation or increased viscosity leading to decreased leveling properties), thus improving storage stability. The use of plasticizers without vinyl unsaturated groups is also advantageous from the viewpoint that it suppresses changes in elastic modulus, dimensional changes, or deformations (warping, undulations, etc.) and optical strain caused by the reaction of vinyl unsaturated groups in the adhesive layer containing such plasticizers.

[0129] A high refractive index plasticizer with a refractive index of approximately 1.50 or higher is suitable. By using a high refractive index plasticizer, it is easy to balance high refractive index and large deformability. From the viewpoint of obtaining flexibility while maintaining and improving the refractive index of the high refractive index adhesive layer, the refractive index of the plasticizer should preferably be approximately 1.51 or higher, preferably approximately 1.53 or higher, more preferably approximately 1.55 or higher, and can be approximately 1.56 or higher, approximately 1.58 or higher, approximately 1.60 or higher, or approximately 1.62 or higher. Among these several options, from the viewpoint of ease of preparation of the adhesive composition or compatibility within the adhesive, a refractive index of 2.50 or lower is appropriate, 2.00 or lower is advantageous, and can be 1.90 or lower, 1.80 or lower, or 1.70 or lower. Furthermore, the refractive index of the plasticizer is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C, similar to that of the monomer. If a nominal value for the refractive index at 25°C is provided by the manufacturer, that nominal value may be used.

[0130] Among several states, the plasticizer may be selected from one or more of the following compounds: compounds having a structure in which two or more non-condensed double-bonded rings (typically aromatic rings) are bonded by a linker group; compounds having a structure in which two or more non-condensed double-bonded rings (typically aromatic rings) are directly (i.e., chemically bonded without being separated by other atoms); compounds having a condensed double-bonded ring (typically aromatic ring) structure; compounds having a cyclopentadienyl structure; compounds having a dibenzothiophene structure; and compounds having a dibenzothiophene structure.

[0131] In several ideal samples, the plasticizer may be a compound A having a structure of two or more non-condensed double-bonded rings separated by a linker group. The linker group may be, for example: an oxy group (-O-), a thiooxy group (-S-), an oxyalkyl group (e.g., -O-(CH₂)ₙ-yl, where n is 1 to 3, preferably 1), a thiooxyalkyl group (e.g., -S-(CH₂)ₙ-yl, where n is 1 to 3, preferably 1), a straight-chain alkyl group (i.e., -(CH₂)ₙ-yl, where n is 1 to 6, preferably 1 to 3), or a partially or fully halogenated alkyl group among the above-mentioned oxyalkyl groups, thiooxyalkyl groups, and straight-chain alkyl groups. The linker group may also be one having an ester bond. In plasticizers, the linking group connecting the first double-bonded ring (non-condensed ring) and the second double-bonded ring (non-condensed ring) can also be selected from the same type as described above. From the viewpoint of the large deformability of the high-refractive-index adhesive layer, suitable examples of the above-mentioned linking group include oxy-, thiooxy-, oxy-extended alkyl, and straight-chain extended alkyl groups. The number of atoms of the above-mentioned linking group is not particularly limited. In several states, for example, it can be 1 to 30, 1 to 25, 1 to 20, 1 to 18 is appropriate, 1 to 12 is preferable, 1 to 10 is more preferable, 1 to 8 is more preferable, 1 to 5 is particularly preferable, 1 to 3 is acceptable, and 1 or 2 is also acceptable. Furthermore, in several other ideal states, the number of atoms of the above-mentioned linking group is, for example, 10 or more, preferably 15 or more, more preferably 20 or more, and even more preferably 22 or more (e.g., 25 or more or 30 or more). Furthermore, the upper limit for the number of atoms of the aforementioned linker is, for example, 50 or less, ideally 40 or less is appropriate, and 35 or less is also acceptable. In the case of using plasticizers with oxyalkyl groups as the aforementioned linker, the aforementioned number of atoms of the linker is suitable. Moreover, the number of atoms of the linker refers to the minimum number of atoms required to move from one non-condensed double-bonded ring to another. For example, when the linker is composed of a straight-chain alkyl group (i.e., -(CH₂)ₙ-yl), the number of atoms n becomes the number of atoms of the linker. As another example, when the linker is an oxyethyl group (i.e., -(C₂H₄O)ₙ-yl), the product of the sum of the number of carbon atoms 2 and the number of oxygen atoms 1 constituting the oxyethyl group (3n) and n becomes the number of atoms of the linker. Suitable examples of the aforementioned compounds include compounds containing phenoxybenzyl groups. Examples of the aforementioned compounds include phenoxybenzyl (meth)acrylates (e.g., m-phenoxybenzyl (meth)acrylate), phenoxybenzyl alcohol, oxybis[(alkoxyalkyl)benzene] (e.g., 4,4'-oxybis[(methoxymethyl)benzene]), polyethylene glycol benzoate, etc.

[0132] In the sample using compound A, which has a structure of two or more non-condensed double-bonded rings separated by linker groups, as a plasticizer, the amount of compound A used is not particularly limited, but is set to achieve the adhesive properties and effects disclosed herein. From the viewpoint of large deformability, in several ideal samples, the amount of compound A used relative to 100 parts by weight of the base polymer is greater than 30 parts by weight, preferably 35 parts by weight or more, more preferably 40 parts by weight or more, especially 45 parts by weight or more, even more preferably 50 parts by weight or more, and may be 55 parts by weight or more, or may be 60 parts by weight or more. Furthermore, from the perspective of balancing the high refractive index of the high refractive index adhesive layer with its large deformability, it is appropriate to set the amount of the above-mentioned compound A relative to 100 parts by weight of the base polymer to be about 200 parts by weight or less, preferably 150 parts by weight or less, more preferably 120 parts by weight or less, possibly 100 parts by weight or less, possibly 80 parts by weight or less, or possibly 70 parts by weight or less.

[0133] Furthermore, in the sample using compound A, which has a structure of two or more non-condensed double-bonded rings separated by linker bonds, as a plasticizer, the high-refractive-index adhesive layer may arbitrarily contain one or more plasticizers other than compound A, or may not contain any. The plasticizers other than compound A may be used in appropriate amounts without impairing the effects of the technology disclosed herein. In the sample, it is appropriate for the amount of plasticizers other than compound A used to be less than 50% by weight of the total plasticizer used in the high-refractive-index adhesive layer, preferably less than 30% by weight, more preferably less than 10% by weight, more preferably less than 3% by weight, and especially preferably less than 1% by weight. The technology disclosed herein can be suitably implemented using a high-refractive-index adhesive layer that substantially does not contain plasticizers other than compound A.

[0134] In several ideal samples, the plasticizer may be an ethylene glycol compound having two or more rings containing double bonds in one molecule. The number of oxyethyl units (i.e., -(C₂H₄O)- units in the aforementioned ethylene glycol compound is preferably 1 or more, 2 or more, more preferably 3 or more, and more preferably 4 or more (e.g., 5 or more). Furthermore, the upper limit for the number of the aforementioned oxyethyl units is, for example, 10 or less, possibly 8 or less, or possibly 6 or less. The aforementioned ethylene glycol compound may be a compound having the following structure: two or more non-condensed rings containing double bonds are linked by the aforementioned oxyethyl units as linking groups. The compound may have one or two or more ester groups. Examples of the aforementioned ethylene glycol compounds include compounds having two or more benzoic acids linked to triethylene glycol or polyethylene glycol via ester bonds.

[0135] In the case of using an ethylene glycol compound having two or more double-bonded rings in one molecule as a plasticizer, the amount of the ethylene glycol compound used is not particularly limited, but is set to achieve the adhesive properties and effects disclosed herein. From the viewpoint of large deformability, in several ideal cases, the amount of the ethylene glycol compound used relative to 100 parts by weight of the base polymer is greater than 30 parts by weight, preferably 35 parts by weight or more, more preferably 40 parts by weight or more, especially 45 parts by weight or more, even more preferably 50 parts by weight or more, and may be 55 parts by weight or more, or may be 60 parts by weight or more. Furthermore, from the perspective of balancing the high refractive index of the high refractive index adhesive layer with its large deformability, it is appropriate to set the amount of the above-mentioned ethylene glycol compound relative to 100 parts by weight of the base polymer to be about 200 parts by weight or less, preferably 150 parts by weight or less, more preferably 120 parts by weight or less, possibly 100 parts by weight or less, possibly 80 parts by weight or less, or possibly 70 parts by weight or less.

[0136] Furthermore, in the sample using an ethylene glycol-based compound having two or more double-bonded rings in one molecule as a plasticizer, the high-refractive-index adhesive layer may or may not contain one or more plasticizers other than the aforementioned ethylene glycol-based compound. The aforementioned plasticizers other than the ethylene glycol-based compound may be used in appropriate amounts without impairing the effects of the technology disclosed herein. In the sample, it is appropriate for the amount of the aforementioned plasticizers other than the ethylene glycol-based compound used to be less than 50% by weight of the total plasticizer used in the high-refractive-index adhesive layer, preferably less than 30% by weight, more preferably less than 10% by weight, more preferably less than 3% by weight, and especially preferably less than 1% by weight. The technology disclosed herein can be suitably implemented using a high-refractive-index adhesive layer that substantially does not contain plasticizers other than the aforementioned ethylene glycol-based compound.

[0137] In several other samples, liquid rosin esters and other liquid rosin derivatives, as well as liquid camphene phenols, may be used as plasticizers. The aforementioned liquid rosin derivatives (e.g., liquid rosin esters) may be equivalent to the aforementioned compounds having a condensed ring structure containing double bonds.

[0138] Furthermore, the plasticizer may be one or more of the known plasticizers (such as phthalate series, terephthalate series, adipate series, adipate polyester, ethylene glycol benzoate, etc.).

[0139] There is no particular limitation on the amount of plasticizer used; it can be set according to the purpose. From the viewpoint of large deformability, in several ideal samples, the amount of plasticizer used relative to 100 parts by weight of the base polymer is greater than 30 parts by weight, preferably 35 parts by weight or more, more preferably 40 parts by weight or more, especially 45 parts by weight or more, even more preferably 50 parts by weight or more, and can be 55 parts by weight or more, or can also be 60 parts by weight or more. Furthermore, from the viewpoint of balancing the high refractive index of the high refractive index adhesive layer with large deformability, it is appropriate to set the amount of plasticizer relative to 100 parts by weight of the base polymer to be approximately 200 parts by weight or less, preferably 150 parts by weight or less, more preferably 120 parts by weight or less, and can be 100 parts by weight or less, 80 parts by weight or less, or can also be 70 parts by weight or less. In several samples where adhesive properties are given greater emphasis, the amount of plasticizer used relative to 100 parts by weight of the base polymer can be 45 parts by weight or less, or 35 parts by weight or less.

[0140] (Additive (H RO)) The high refractive index adhesive layer disclosed herein may contain an organic material with a higher refractive index than the base polymer (e.g., an acrylic polymer) as an additive as desired. Hereinafter, the organic material is sometimes referred to as "additive (H RO)". Here, "H RO" refers to a high refractive index organic material. By using additive (H RO), a high refractive index adhesive layer that can more appropriately balance refractive index and adhesive properties (peel strength, flexibility, etc.) can be achieved. The organic material that can be used as an additive (H RO) can be a polymer or a non-polymer. Furthermore, it may have polymerizable functional groups or it may not have polymerizable functional groups. In addition, in this specification, additive (H RO) is defined as something different from the compound that can be used as the plasticizer mentioned above. For example, additive (H RO) may be something that is not liquid at 30°C (e.g., 25°C or 20°C). Additives (H RO) can be used alone or in combination of two or more.

[0141] The refractive index of the additive (H RO) can be set within an appropriate range relative to the refractive index of the base polymer (e.g., an acrylic polymer), and is therefore not limited to a specific range. The refractive index of the additive (H RO) can be, for example, greater than 1.55, greater than 1.56, or greater than 1.57, and can be selected from a range higher than the refractive index of the base polymer. From the viewpoint of increasing the refractive index of the high-refractive-index adhesive layer, among several options, a refractive index of the additive (H RO) of 1.58 or higher is advantageous, preferably 1.60 or higher, more preferably 1.63 or higher, and can be 1.65 or higher, 1.70 or higher, or 1.75 or higher. By using an additive (H RO) with a higher refractive index, the target refractive index can be achieved even with a smaller amount of additive (H RO). This is preferable from the viewpoint of suppressing the reduction of adhesive properties or optical properties. There is no particular upper limit to the refractive index of the additive (H RO). However, from the perspective of balancing compatibility with adhesives, high refractive index, and ease of use as an adhesive, it can be, for example, below 3.000, below 2.500, below 2.000, below 1.950, below 1.900, or below 1.850. Furthermore, the refractive index of the additive (H RO) is measured using an Abbe refractometer at a measurement wavelength of 589 nm and a measurement temperature of 25°C, in the same manner as the refractive index of the monomer. When a nominal value of the refractive index at 25°C is provided by the manufacturer, that nominal value can be used.

[0142] The molecular weight of the organic material used as an additive (H RO) is not particularly limited and can be selected according to the purpose. From the viewpoint of balancing the effect of high refractive index with other properties (such as the flexibility and optical properties of the adhesive, haze, etc.), among several options, a molecular weight of the additive (H RO) of approximately less than 10,000 is appropriate, preferably less than 5,000, more preferably less than 3,000 (e.g., less than 1,000), less than 800, less than 600, less than 500, or less than 400. From the viewpoint of improving compatibility in the adhesive, it is advantageous that the molecular weight of the additive (H RO) is not too large. Furthermore, the molecular weight of the additive (H RO) can be, for example, 130 or more, or even 150 or more. From the perspective of increasing the refractive index of the additive (H RO), the molecular weight of the additive (H RO) should preferably be above 170, more preferably above 200, and could be above 230, above 250, above 270, above 300, above 500, above 1000, or even above 2000. In several samples, polymers with a molecular weight of approximately 1000 to 10000 (e.g., above 1000 and below 5000) can be used as the additive (H RO). The molecular weight of the additive (H RO) can be calculated based on the chemical structure of non-polymer or low-polymerization-degree (e.g., around 2-5 polymers) polymers, or determined using matrix-assisted laser desorption / ionization time-of-flight mass analysis (MALDI-TOF-MS). When the additive (H RO) is a polymer with a higher degree of polymerization, the weight-average molecular weight (Mw) based on GPC performed under appropriate conditions can be used. When a nominal value of molecular weight is provided by the manufacturer or other relevant party, that nominal value may be used.

[0143] Examples of organic materials that can be used as additives (H RO) include organic compounds having aromatic rings, organic compounds having heterocycles (which may be aromatic rings or non-aromatic heterocycles), etc., but are not limited to these.

[0144] The aromatic ring of the above-mentioned organic compound with an aromatic ring that can be used as an additive (H RO) (hereinafter also referred to as "aromatic ring compound") can be selected from those with the same aromatic ring as those of the compound that can be used as a monomer (A1).

[0145] The aromatic ring may have one or more substituents on the ring constituent atoms, or it may not have substituents. When substituents are present, examples of substituents include alkyl, alkoxy, aryloxy, hydroxy, halogen atoms (fluorine, chlorine, bromine, etc.), hydroxyalkyl, hydroxyalkyloxy, epoxypropoxy, etc., but are not limited thereto. Among the substituents containing carbon atoms, the number of carbon atoms contained in the substituent is, for example, 1 to 10, 1 to 6 is advantageous, preferably 1 to 4, more preferably 1 to 3, for example, 1 or 2. In several cases, the aromatic ring may be an aromatic ring without substituents on the ring constituent atoms, or an aromatic ring with one or more substituents selected from the group consisting of alkyl, alkoxy, and halogen atoms (e.g., bromine atoms) on the ring constituent atoms.

[0146] Examples of aromatic ring compounds that can be used as additives (H RO) include, for example, compounds that can be used as monomers (A1); oligomers containing compounds that can be used as monomers (A1) as monomer units; compounds from which a group having an ethylene unsaturated group (which may be a substituent bonded to a ring-forming atom) or a portion of that group constituting an ethylene unsaturated group is removed and replaced with a hydrogen atom or a group without an ethylene unsaturated group (e.g., hydroxyl, amino, halogen atom, alkyl, alkoxy, hydroxyalkyl, hydroxyalkyloxy, epoxypropoxy, etc.) structure is given, and examples that do not conform to the plasticizers disclosed herein may be given, but are not limited thereto.

[0147] Among several samples, considering the ease with which a high refractive index effect can be obtained, an organic compound having two or more aromatic rings per molecule (hereinafter also referred to as "compound containing multiple aromatic rings") is suitable as an additive (HRO). The compound containing multiple aromatic rings may or may not have polymerizable functional groups such as vinyl unsaturated groups. Furthermore, the compound containing multiple aromatic rings may be a polymer or a non-polymer. Moreover, the aforementioned polymer may be an oligomer containing monomers containing multiple aromatic rings as monomer units (preferably an oligomer with a molecular weight of approximately 5000 or less, more preferably approximately 1000 or less; for example, a low-molecular-weight polymer of about 2 to 5 polymers). The aforementioned oligomers may be, for example, homopolymers of monomers containing multiple aromatic rings; copolymers of two or more monomers containing multiple aromatic rings; copolymers of one or more monomers containing multiple aromatic rings with other monomers, etc. The other monomers mentioned above may be aromatic ring monomers that do not conform to the category of monomers containing multiple aromatic rings, monomers without aromatic rings, or combinations thereof. In the case of using oligomers as additives (HRO), the oligomers can be obtained by polymerizing the corresponding monomer components using known methods.

[0148] Non-limiting examples of compounds containing a plurality of aromatic rings may include: compounds having a structure in which two or more non-condensed aromatic rings are bonded by a linker group; compounds having a structure in which two or more non-condensed aromatic rings are directly (i.e., not separated by other atoms) chemically bonded; compounds having a condensed aromatic ring structure; compounds having a cyclopentadienyl structure; compounds having a dibenzothiophene structure; and compounds having a dibenzothiophene structure. Compounds containing a plurality of aromatic rings may be used alone or in combination of two or more.

[0149] Examples of heterocyclic organic compounds (hereinafter also referred to as heterocyclic organic compounds) that can be used as additives (H RO) include thioepoxide compounds and compounds having trihalomethane rings. Examples of thioepoxide compounds include the bis(2,3-cyclothiopropyl) disulfide and its polymer (refractive index 1.74) disclosed in Japanese Patent No. 3712653. Examples of compounds having trihalomethane rings include compounds having at least one (e.g., 3 to 40, preferably 5 to 20) trihalomethane ring within one molecule. Furthermore, since trihalomethane rings are aromatic, compounds having trihalomethane rings are also included in the above concept of aromatic ring-containing compounds, and compounds having multiple trihalomethane rings are also included in the above concept of compounds containing multiple aromatic rings.

[0150] Among several samples, compounds without vinyl unsaturated groups can be appropriately used as additives (H RO). This can suppress the deterioration of the adhesive composition due to heat or light (due to gelation or increased viscosity leading to decreased leveling properties), thereby improving storage stability. The use of additives without vinyl unsaturated groups (H RO) is also advantageous from the viewpoint that it suppresses dimensional changes or deformations (warping, undulations, etc.) and optical strain caused by the reaction of vinyl unsaturated groups in the adhesive layer containing such additives (H RO).

[0151] The additive (H RO) may be used in an appropriate amount without significantly impairing the effects of the technology disclosed herein. In several samples, the amount of additive (H RO) relative to 100 parts by weight of the base polymer (e.g., an acrylic polymer) is not particularly limited (the total amount of each compound when multiple compounds are used) and may be set according to the purpose. In several samples, the amount of additive (H RO) relative to 100 parts by weight of the base polymer may be set to, for example, 80 parts by weight or less, and from the viewpoint of balancing the high refractive index of the high refractive index adhesive layer with the suppression of the reduction of adhesive or optical properties, it is advantageous to set it to 60 parts by weight or less, and preferably to 45 parts by weight or less. In several samples where adhesive or optical properties are of greater importance, the amount of additive (H RO) relative to 100 parts by weight of the base polymer may be, for example, 30 parts by weight or less, 10 parts by weight or less, 3 parts by weight or less, or 1 part by weight or less. The technique disclosed herein is suitable for implementation in the case of using a high-refractive-index adhesive layer without additives (HRO). Furthermore, from the viewpoint of increasing the refractive index of the high-refractive-index adhesive layer, the amount of additive (HRO) relative to 100 parts by weight of the base polymer can be, for example, 1 part by weight or more, 3 parts by weight or more, preferably 5 parts by weight or more, 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or 20 parts by weight or more.

[0152] (Crosslinking Agent) In the technology disclosed herein, the adhesive composition used to form a high-refractive-index adhesive layer may contain a crosslinking agent as needed to adjust the cohesive force of the adhesive. The crosslinking agent may be an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an azazoline-based crosslinking agent, a melamine-based resin, a metal chelate-based crosslinking agent, or other crosslinking agents known in the adhesive field. Isocyanate-based crosslinking agents and epoxy-based crosslinking agents are particularly suitable. Other examples of crosslinking agents include monomers having two or more vinyl unsaturated groups within one molecule, i.e., multifunctional monomers. One type of crosslinking agent may be used alone, or in combination of two or more types.

[0153] Isocyanate-based crosslinking agents can use isocyanate compounds with two or more functions, such as: trimethylene diisocyanate, butyl diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), diisocyanate, and other aliphatic polyisocyanates; cyclopentyl diisocyanate, cyclohexyl diisocyanate, isoflavone diisocyanate (IPDI), 1,3-bis(isocyanomethyl)cyclohexane Alicyclic isocyanates; aromatic isocyanates such as 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylene diisocyanate (XDI); polyisocyanate modifiers (e.g., HDI's trimerocyanate and HDI's urea-formate) formed by modifying isocyanate compounds with urea-formate bonds, biuret bonds, trimerocyanate bonds, urea-diketone bonds, urea bonds, carbodiimide bonds, urea-diketone bonds, and acetyltriketone bonds. Examples of commercially available products include: TAKENATE 300S, TAKENATE 500, TAKENATE 600, TAKENATE D165N, TAKENATE D178N, TAKENATE D178NL (all manufactured by Mitsui Chemicals), Sumidur T80, Sumidur L, Desmodur N3400 (all manufactured by Sumika Bayer Urethane), Millionate MR, Millionate MT, Coronate L, Coronate HL, Coronate HX, Coronate 2770 (all manufactured by Tosoh), and Durnate A201H (all manufactured by Asahi Kasei Corporation). Isocyanate compounds can be used alone or in combination of two or more. They can also be used in combination with difunctional isocyanate compounds and trifunctional or higher isocyanate compounds.

[0154] Examples of epoxy crosslinking agents include: bisphenol A, epichlorohydrin type epoxy resins, ethyl glycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diaminopropylamine, N,N,N',N'-tetraglycidyl-meta-diamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, etc. These can be used alone or in combination of two or more.

[0155] Examples of multifunctional monomers include: ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, neopentyl tetraethylene glycol di(meth)acrylate, neopentyl tetraethylene tri(meth)acrylate, dinepentyl tetraethylene hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl methacrylate, ethylene methacrylate, divinylbenzene, bisphenol A di(meth)acrylate, epoxy acrylate, polyester acrylate, carbamate acrylate, butyl glycol di(meth)acrylate, hexyl glycol di(meth)acrylate, etc. Multifunctional monomers can be used alone or in combination of two or more.

[0156] In several samples, at least a portion of the crosslinking agent may be a difunctional crosslinking agent having two crosslinking reactive groups (e.g., isocyanate groups) per molecule. By using a difunctional crosslinking agent, a soft crosslinked structure can be easily formed. A single difunctional crosslinking agent may be used alone or in combination of two or more. Furthermore, a difunctional crosslinking agent may also be used in combination with a trifunctional or higher crosslinking agent.

[0157] Among several states, acyclic crosslinking agents (also known as chain crosslinking agents) that do not have aromatic rings, aliphatic rings, or other cyclic structures are suitable as crosslinking agents. For example, among the above-mentioned isocyanate-based crosslinking agents, isocyanate compounds that do not have aromatic rings or triisocyanate rings are preferable. By using acyclic isocyanate compounds as crosslinking agents, it is easy to form crosslinking agents with high flexibility. Specific examples of the above-mentioned acyclic isocyanates include: aliphatic isocyanate compounds (e.g., PDI or HDI), or modified aliphatic isocyanate compounds (e.g., polyisocyanate modified PDI or HDI modified by urethane bonds, biuret bonds, urea bonds, and carbodiimide bonds). Acyclic crosslinking agents can be used alone or in combination of two or more. Among several ideal states, acyclic difunctional crosslinking agents can be used as the above-mentioned crosslinking agents.

[0158] Among several samples, a crosslinking agent in which one of the crosslinking reactive groups (e.g., isocyanate groups) in one molecule has a relatively long distance from other crosslinking reactive groups can be used as a crosslinking agent. This allows the formation of a flexible crosslinked structure with a predetermined length. For example, a compound in one molecule of the crosslinking agent whose number of atoms constituting the linking chain connecting the crosslinking reactive group and other crosslinking reactive groups is 10 or more (e.g., 12 or more or 14 or more) can be used as a crosslinking agent. The upper limit of the number of atoms constituting the linking chain can be adjusted according to the purpose through polymerization or the like, and is therefore not particularly limited; for example, it can be 2000 or less, 1000 or less, 500 or less, 100 or less, 50 or less, 30 or less, or 20 or less. Furthermore, the number of atoms constituting the linking chain of the aforementioned crosslinking reactive groups refers to the minimum number of atoms required in one molecule of the crosslinking agent to reach other crosslinking reactive groups (when there are three or more crosslinking reactive groups, it is the crosslinking reactive group closest to the aforementioned crosslinking reactive group). Crosslinking agents with the aforementioned linking chains can be used alone or in combination of two or more. In several ideal samples, non-cyclic difunctional crosslinking agents can be used as the aforementioned crosslinking agents. Commercially available examples of the aforementioned crosslinking agents include Coronate 2770 (manufactured by Tosoh Corporation), TAKENATE D178NL (manufactured by Mitsui Chemicals Corporation), and Durnate A201H (manufactured by Asahi Kasei Corporation).

[0159] There is no particular limitation on the amount of crosslinking agent used, and it can be set in the range of about 0.001 parts by weight to 5.0 parts by weight relative to 100 parts by weight of the base polymer. From the viewpoint of improving the flexibility of the high refractive index adhesive layer and the adhesion to the substrate, in several samples, the amount of crosslinking agent used relative to 100 parts by weight of the base polymer should preferably be 3.0 parts by weight or less, more preferably 2.0 parts by weight or less, and can be 1.0 parts by weight or less, or can be 0.5 parts by weight or less. In several ideal samples, the amount of crosslinking agent used relative to 100 parts by weight of the base polymer is less than 0.5 parts by weight, and can be 0.4 parts by weight or less, 0.3 parts by weight or less, or 0.2 parts by weight or less. Furthermore, from the viewpoint of appropriately utilizing the crosslinking agent, in several samples, the amount of crosslinking agent used relative to 100 parts by weight of the base polymer can be, for example, 0.005 parts by weight or more, 0.01 parts by weight or more, 0.05 parts by weight or more, 0.08 parts by weight or more, or 0.1 parts by weight or more. In several ideal samples, the amount of crosslinking agent used relative to 100 parts by weight of the base polymer is greater than 0.1 parts by weight, and can be 0.2 parts by weight or more, 0.3 parts by weight or more, or 0.4 parts by weight or more. According to the technology disclosed herein, by using an appropriate amount of crosslinking agent within the above-mentioned range, a high-refractive-index adhesive layer capable of withstanding large deformations can be suitably formed.

[0160] To make the crosslinking reaction more effective, a crosslinking catalyst may also be used. Examples of crosslinking catalysts include: tetrabutyl titanate, tetraisopropyl titanate, tetraacetyl acetone zirconium, acetyl acetone iron(III), butyltin oxide, dioctyltin dilaurate, and other metal-based crosslinking catalysts. Among these, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. There is no particular limitation on the amount of crosslinking catalyst used. Considering the balance between the speed of the crosslinking reaction and the shelf life of the adhesive composition, the amount of crosslinking catalyst used relative to 100 parts by weight of the base polymer can be set to, for example, approximately 0.0001 parts by weight or more and 1 part by weight or less, preferably 0.001 parts by weight or more and 0.5 parts by weight or less.

[0161] The adhesive composition may contain a compound capable of generating keto-enol tautomerism as a crosslinking delay agent. This extends the shelf life of the adhesive composition. For example, a compound capable of generating keto-enol tautomerism may be appropriately used in an adhesive composition containing an isocyanate-based crosslinking agent. Various β-dicarbonyl compounds may be used as compounds capable of generating keto-enol tautomerism. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) or acetyl acetates (methyl acetate, ethyl acetate, etc.) may be suitable. One or more compounds capable of generating keto-enol tautomerism may be used alone. The amount of the compound that can produce keto-enol tautomerism relative to 100 parts by weight of the base polymer can be, for example, 0.1 parts by weight or more and 20 parts by weight, 0.5 parts by weight or more and 10 parts by weight, or 1 part by weight or more and 5 parts by weight.

[0162] (Tackifier) ​​The high refractive index adhesive layer disclosed herein may also contain a tackifier. The tackifier may be a known tackifying resin such as rosin-based tackifying resin, terpene-based tackifying resin, phenol-based tackifying resin, hydrocarbon-based tackifying resin, ketone-based tackifying resin, polyamide-based tackifying resin, epoxy-based tackifying resin, or elastic system tackifying resin. One or more of these may be used alone or in combination. There is no particular limitation on the amount of tackifying resin used; it can be set according to the purpose and application to achieve appropriate adhesive properties. In several samples, from the viewpoint of refractive index or transparency, it is appropriate to use 30 parts by weight or less of the tackifier relative to 100 parts by weight of the base polymer, preferably 10 parts by weight or less, and more preferably 5 parts by weight or less. The technique disclosed herein can be suitably implemented in samples without the use of a tackifier.

[0163] (High Refractive Index Particles) The high refractive index adhesive layer disclosed herein may contain high refractive index particles as an arbitrary component. Here, high refractive index particles refer to particles that can increase the refractive index of the adhesive by including them in the adhesive. Hereinafter, high refractive index particles are sometimes referred to as "particle P HRI". HRI stands for high refractive index. There is no particular limitation on the type of particle P HRI, and one or more materials that can increase the refractive index of the adhesive can be selected from metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. Particle P HRI can be suitable from inorganic oxides (e.g., metal oxides) that can increase the refractive index of the adhesive. Suitable examples of materials constituting Particle PHRI include inorganic oxides (specifically metal oxides) such as titanium oxide (TiO₂), zirconium oxide (ZrO₂), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, and niobium oxide (Nb₂O₅). Particles composed of these inorganic oxides (e.g., metal oxides) can be used alone or in combination of two or more. The average particle size of the Particle PHRI (referring to the 50% volume average particle size obtained by laser scattering diffraction) is not particularly limited, and can be selected from, for example, in the range of approximately 1 nm to 1000 nm.

[0164] The content of Particle PHRI in the high refractive index adhesive layer can be used in an appropriate amount without compromising the effects of the technology disclosed herein. Furthermore, the content of the aforementioned Particle PHRI can vary depending on the target refractive index. For example, the content of the aforementioned Particle PHRI can be appropriately set to a predetermined or higher refractive index, taking into account the required adhesive properties. In several cases, the content of Particle PHRI in the high refractive index adhesive layer is, for example, less than 10% by weight, less than 1% by weight, or less than 0.1% by weight. The technology disclosed herein can be implemented in a case where the high refractive index adhesive layer substantially does not contain Particle PHRI.

[0165] (Leveling Agent) In several samples, the adhesive composition used to form a high-refractive-index adhesive layer may contain a leveling agent as needed to improve the appearance of the high-refractive-index adhesive layer formed by the composition (e.g., improving the uniformity of thickness) or to improve the coatability of the adhesive composition. Non-limiting examples of leveling agents include acrylic leveling agents, fluorinated leveling agents, and polysiloxane leveling agents. For example, a suitable leveling agent can be selected from commercially available leveling agents and used using conventional methods.

[0166] (Other Additives) In the art disclosed herein, the adhesive composition used to form the high refractive index adhesive layer may, as needed, include softeners, colorants (dyes, pigments, etc.), fillers, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, preservatives, and other known additives that can be used in adhesive compositions, to a extent that does not significantly impair the effects of the present invention. For the various additives mentioned, conventionally known additives can be used in accordance with conventional methods, without specifically imparting any features to the present invention; therefore, detailed descriptions are omitted.

[0167] Although not particularly limited, the effects of the technology disclosed herein can be suitably achieved by using a high-refractive-index adhesive layer comprising the aforementioned base polymer (typically an acrylic polymer) and a plasticizer. The technology disclosed herein is suitable for implementation in a sample using a high-refractive-index adhesive layer primarily composed of the aforementioned base polymer and the aforementioned plasticizer. Therefore, in several ideal samples, the high-refractive-index adhesive layer can be composed of components other than the aforementioned base polymer and the aforementioned plasticizer, with limited content. For example, in the high-refractive-index adhesive layer, the total amount of the aforementioned base polymer and the aforementioned plasticizer can be set to 75% by weight or more (e.g., 75% by weight or more and 100% by weight or less than 100% by weight), 85% by weight or more, 90% by weight or more, 95% by weight or more, 98% by weight or more, or 99% by weight or more (e.g., greater than 99% by weight). The restriction on the use of components other than the aforementioned base polymer and plasticizer is advantageous in terms of achieving high deformability of the high refractive index adhesive layer.

[0168] <Low Refractive Index Layer> In the technology disclosed herein, the refractive index n2 of the low refractive index layer (preferably a low refractive index adhesive layer) is preferably lower than the refractive index n1 of the high refractive index adhesive layer. This allows the behavior of light transmitted through the laminate containing these layers to be controlled by utilizing the refractive index difference between the high refractive index adhesive layer and the low refractive index layer. The refractive index n2 of the low refractive index layer can, for example, be in the range of approximately 1.35 to 1.55. From the viewpoint that increasing the refractive index difference with the high refractive index n1 of the adhesive layer easily improves the front brightness enhancement effect described later, the refractive index n2 of the low refractive index layer is preferably 1.49 or less, more preferably 1.47 or less (e.g., 1.46 or less or 1.45 or less), and can be 1.43 or less, 1.41 or less, or 1.40 or less. Furthermore, from the perspective of material availability and ease of balancing adhesive properties, in several samples, the refractive index n2 of the low-refractive-index layer can be, for example, 1.36 or higher, 1.38 or higher, 1.40 or higher, 1.42 or higher, or 1.45 or higher. Also, in samples where the low-refractive-index layer is a low-refractive-index adhesive layer, the relative relationship of the adhesion forces on each face of the laminate (laminated sheet) of the high-refractive-index adhesive layer and the low-refractive-index adhesive layer can be adjusted.

[0169] Among several samples, the ratio (n1 / n2) of the refractive index n1 of the high-refractive-index adhesive layer to the refractive index n2 of the low-refractive-index layer is, for example, greater than 1.00, approximately 1.01 or more, approximately 1.02 or more, or approximately 1.03 or more. Among several samples, a ratio (n1 / n2) of approximately 1.05 or more is advantageous, preferably approximately 1.06 or more, more preferably approximately 1.07 or more, or approximately 1.08 or more. There is no particular upper limit to the ratio (n1 / n2). Among several samples, from the viewpoint of adhesive properties or transparency, a ratio (n1 / n2) is, for example, approximately 1.20 or less, approximately 1.18 or less, approximately 1.16 or less, approximately 1.14 or less, or approximately 1.12 or less.

[0170] In several samples, the difference between the refractive index n1 of the high-refractive-index adhesive layer and the refractive index n2 of the low-refractive-index layer, i.e., the refractive index difference (n1-n2), can be, for example, greater than 0.00, greater than 0.01, greater than 0.02, greater than 0.03, greater than 0.05, greater than 0.07, greater than 0.09, greater than 0.10, or greater than 0.12. There is no particular upper limit to the refractive index difference (n1-n2). In several samples, from the viewpoint of adhesion characteristics or transparency, the refractive index (n1-n2) can be, for example, less than 0.30, less than 0.26, less than 0.21, less than 0.18, or less than 0.16.

[0171] Among several samples, the deformation amount of the low-refractive-index layer in the deformation test at a temperature of -20°C and a speed of 300 mm / min should be 350% or more. In addition to the high-refractive-index adhesive layer, the low-refractive-index layer also meets the above characteristics, thereby enabling the laminate (adhesive sheet) containing both the high-refractive-index adhesive layer and the low-refractive-index layer to deform at high speed and sufficiently even in low-temperature environments, and thus withstand large deformations. The deformation test at the aforementioned temperature of -20°C and speed of 300 mm / min can be more specifically carried out using the method described in the test examples below.

[0172] Furthermore, in several samples, when the low-refractive-index layer is subjected to a deformation test at a temperature of -20°C and a speed of 300 mm / min, the stress at 350% deformation should preferably be 5.0 N / mm² or less. The low-refractive-index layer that meets the above characteristics has a high refractive index and can maintain a predetermined level of flexibility even at low temperatures, and can deform at high speeds and fully. Therefore, it is suitable for applications involving large deformations. In several ideal samples, the stress at 350% deformation can be 4 N / mm² or less, 3 N / mm² or less, 2 N / mm² or less, 1 N / mm² or less, 0.5 N / mm² or less, or 0.3 N / mm² or less. Theoretically, the lower limit of the stress at 350% deformation is 0.0 N / mm² or more, and in several ideal samples, it can also be 0.1 N / mm² or more.

[0173] There is no particular limitation on the storage elastic modulus G' (25°C) of the low refractive index layer, for example, it can be in the range of 1.0 kPa to 500 kPa. From the viewpoint of improving the softness or enhancing the adaptability to deformation imparted by the low refractive index layer, among several conditions, it is appropriate for the storage elastic modulus G' (25°C) of the low refractive index layer to be below 400 kPa, preferably below 300 kPa, more preferably below 200 kPa (e.g., below 180 kPa or 150 kPa), and it can be below 120 kPa, below 90 kPa, or below 70 kPa. Furthermore, from the perspective of imparting appropriate cohesiveness to the low-refractive-index layer, among several samples, a storage elastic modulus G' (25°C) of 5.0 kPa or higher is appropriate, preferably 10 kPa or higher, possibly 15 kPa or higher, possibly 25 kPa or higher, possibly 35 kPa or higher, possibly 60 kPa or higher, or possibly 80 kPa or higher. From the perspective of easily achieving higher cohesiveness or adhesive properties, among several samples, a storage elastic modulus G' (25°C) of 95 kPa or higher, possibly 110 kPa or higher, or possibly 140 kPa or higher.

[0174] In the case where the low-refractive-index layer is the adhesive layer, there is no particular limitation on the type of adhesive constituting the adhesive layer. The adhesive constituting the low-refractive-index adhesive layer may be one or more of various rubber-like polymers that can be used in the field of adhesives, such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, mixtures thereof), polyester polymers, urethane polymers, polyether polymers, polysiloxane polymers, polyamide polymers, and fluoropolymers, as the base polymer. From the viewpoint of adhesive performance or cost, it is suitable to use an adhesive that contains an acrylic polymer or a rubber polymer as the base polymer. Among these, an adhesive that uses an acrylic polymer as the base polymer (acrylic adhesive) is preferred. In the case where the high refractive index adhesive layer is an acrylic adhesive layer, from the perspective of the adhesion between the high refractive index adhesive layer and the low refractive index adhesive layer, it is appropriate to use the low refractive index adhesive layer as the acrylic adhesive layer.

[0175] In several samples, the acrylic polymer is preferably a polymer containing, for example, the following monomer raw materials: alkyl methacrylate, and may further contain other monomers (copolymeric monomers) that are copolymerizable with the alkyl methacrylate. In the monomer raw material, the content of the alkyl methacrylate may be, for example, 10% by weight or more, 25% by weight or more, 35% by weight or more, or 45% by weight or more. The acrylic polymer may also be a polymer containing alkyl methacrylate as a main monomer and may further contain the aforementioned copolymeric monomer as a secondary monomer. Here, the main monomer means a component in the monomer raw material whose monomer composition accounts for more than 50% by weight. More than 55% by weight or more than 60% by weight of the aforementioned monomer composition may also be alkyl methacrylate. In several samples, the proportion of alkyl (meth)acrylate in the monomer raw materials of the acrylic polymer can be set to, for example, 70% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more, or 98% by weight or more. There is no particular upper limit to the above-mentioned alkyl (meth)acrylate ratio, but it is preferable to set it to 99.5% by weight or less (e.g., 99% by weight or less), or, from the viewpoint of appropriately utilizing the characteristics (e.g., cohesiveness) brought about by the by-monomers, it can also be set to 98% by weight or less (e.g., less than 97% by weight).

[0176] (Meth)acrylates may be suitable for use with compounds such as those shown in formula (1) below. CH 2=C(R 1)COOR 2 (1) Here, R 1 in the above formula (1) is a hydrogen atom or a methyl group. Also, R 2 is a chain alkyl group with 1 to 20 carbon atoms (hereinafter, the range of the number of carbon atoms is sometimes expressed as "C 1-20"). From the viewpoint of the storage elastic modulus of the adhesive, (meth)acrylates with a chain alkyl group of C 1-12 (e.g., C 2-10, typically C 4-8) are preferred. The above-mentioned (meth)acrylates with a chain alkyl group of C 1-20 can be used alone or in combination of two or more. Ideal (meth)acrylates include n-butyl acrylate and 2-ethylhexyl acrylate.

[0177] The aforementioned comonomers are useful for introducing crosslinking points into acrylic polymers or for improving the cohesive strength of acrylic polymers. The aforementioned comonomers may be one or more functional monomers, such as carboxyl-containing monomers, hydroxyl-containing monomers, anhydride-containing monomers, amide-containing monomers, monomers with nitrogen-containing rings, sulfonic acid-containing monomers, and phosphate-containing monomers. Other examples of comonomers include vinyl ester monomers such as vinyl acetate, aromatic vinyl compounds such as styrene, (meth)acrylates containing non-aromatic rings, and alkoxy-containing monomers. Specific examples may include monomers described above that can be used as base polymers for high-refractive-index adhesive layers, but are not limited thereto. For example, from the viewpoint of improving cohesive strength, the aforementioned comonomers are preferably acrylic polymers copolymerized from carboxyl-containing monomers and / or hydroxyl-containing monomers. Suitable examples of carboxyl-containing monomers include acrylic acid and methacrylic acid. Suitable examples of hydroxyl-containing monomers include 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate.

[0178] In several samples, to reduce the refractive index n2 of the low-refractive-index layer, a fluorinated monomer can be used as the aforementioned copolymerizable monomer. The content of the fluorinated monomer in the monomer raw material can be, for example, 10% by weight or more, 25% by weight or more, or 35% by weight or more. From the viewpoint of easily achieving a low-refractive-index layer with a lower refractive index, the content of the aforementioned fluorinated monomer is preferably 40% by weight or more, more preferably 45% by weight or more, more preferably 55% by weight or more, and can be 60% by weight or more, 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. There is no particular upper limit to the content of the fluorinated monomer in the monomer raw material, and it can also be 100% by weight. Among several samples, considering the aggregation properties of the low-refractive-index layer, a content of fluorinated monomers of 99.9% by weight or less is appropriate, preferably 99.5% or less, possibly 99% by weight or less, possibly 97% by weight or less, or possibly 92% by weight or less. One type of fluorinated monomer may be used alone or in combination of two or more.

[0179] Fluoropolymer monomers may be suitable for use with fluorinated acrylic monomers. There are no particular restrictions on fluorinated acrylic monomers if they are acrylic monomers having at least one fluorine atom within the molecule. For example, fluorinated (meth)acrylates may be suitable. Suitable examples of fluorinated (meth)acrylates include those with a fluorinated hydrocarbon group at the ester terminus. Examples of fluorinated hydrocarbon groups include fluorinated aliphatic hydrocarbon groups, fluorinated alicyclic hydrocarbon groups, and fluorinated aromatic hydrocarbon groups. Fluorinated hydrocarbon groups are preferably fluorinated aliphatic hydrocarbon groups. Examples of fluorinated aliphatic hydrocarbon groups include fluorinated alkyl groups. In fluorinated aliphatic hydrocarbon groups, the aliphatic hydrocarbon site may be linear or branched. Furthermore, in fluorinated aliphatic hydrocarbon groups, the fluorine atom may be bonded to any carbon atom of the aliphatic hydrocarbon group site. The number of fluorine atoms bonded to one carbon atom may be singular or plural. There are no particular restrictions on the number of carbon atoms bonded with fluorine atoms.

[0180] In fluorinated aliphatic hydrocarbon groups (which are fluorinated alkyl groups), there is no particular limitation on the number of carbon atoms in the hydrocarbon group. Among several samples, considering compatibility with other comonomers, fluorinated aliphatic hydrocarbon groups with a carbon number of approximately 1 to 18 (preferably 1 to 12) are preferred. Specific examples of fluorinated aliphatic hydrocarbon groups include fluorinated methyl groups such as trifluoromethyl, difluoromethyl, and monofluoromethyl; and fluorinated ethyl groups such as pentafluoroethyl, 1,1,2,2-tetrafluoroethyl, 1,2,2,2-tetrafluoroethyl, 1,1,2-trifluoroethyl, 1,2,2-trifluoroethyl, 2,2,2-trifluoroethyl, 1,1-difluoroethyl, 1,2-difluoroethyl, 2,2-difluoroethyl, 1-monofluoroethyl, and 2-monofluoroethyl. Fluorinated alkyl groups having 3 or more carbon atoms can be exemplified similarly to the fluorinated methyl or fluorinated ethyl groups shown above, as well as various fluorinated alkyl groups in which one or more carbon atoms in the alkyl group are bonded with a single or multiple fluorine atoms.

[0181] Examples of fluorinated alicyclic hydrocarbon groups include fluorinated cycloalkyl groups. Similar to the aforementioned fluorinated alicyclic hydrocarbon groups, in fluorinated alicyclic hydrocarbon groups, a fluorine atom can be bonded to any carbon atom of the alicyclic hydrocarbon group, and the number of fluorine atoms bonded to one carbon atom can be either singular or plural. Furthermore, there is no particular limitation on the number of carbon atoms bonded with fluorine atoms. Fluorinated alicyclic hydrocarbon groups include, for example: cyclohexyl groups with one fluorine atom, such as 2-fluorocyclohexyl, 3-fluorocyclohexyl, and 4-fluorocyclohexyl; cyclohexyl groups with two fluorine atoms, such as 2,4-difluorocyclohexyl and 2,6-difluorocyclohexyl; and cyclohexyl groups with three fluorine atoms, such as 2,4,6-trifluorocyclohexyl.

[0182] The fluorinated hydrocarbon group may or may not have substituents. The substituents are not particularly limited, and examples include: alkyl groups, alkoxy groups, hydroxyl groups, carboxyl groups, amino groups, nitro groups, cyano groups, halogen atoms, etc. One substituent may be used alone or in combination of two or more.

[0183] Fluorine-containing (meth)acrylates [fluorinated (meth)acrylates] include, for example: fluorine-containing (meth)acrylate alkyl esters [fluorinated alkyl (meth)acrylates], fluorine-containing (meth)acrylate cycloalkyl esters [fluorinated cycloalkyl (meth)acrylates], fluorine-containing (meth)acrylate aryl esters [fluorinated aryl (meth)acrylates], etc.

[0184] The fluorine-containing (meth)acrylate is preferably a fluorinated alkyl (meth)acrylate (especially a fluorinated alkyl acrylate). Examples of fluorinated alkyl (meth)acrylates include: 2,2,2-trifluoroethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat 3F", etc.), 2,2,3,3-tetrafluoropropyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat 4F", etc.), 1H,1H,5H-octafluoropentyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat 8F", etc.), 1H,1H,5H-octafluoropentyl methacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat 8FM", etc.), 2-(heptadecylfluorononyl)ethyl acrylate (manufactured by Kyoesha Chemical Co., Ltd., trade name "FA-108", etc.), 1H,1H,2H,2H-tridecylfluorooctyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat 13F", etc.), etc.

[0185] From the viewpoint of low refractive index effect or flexibility, it is advantageous for the fluorinated alkyl group in the fluorinated alkyl (meth)acrylate to have 3 or more carbon atoms, preferably 4 or more, more preferably 5 or more, more preferably 6 or 7 or more, and especially preferably 8 or more. From the viewpoint of adhesive properties, it is advantageous for the fluorinated alkyl group to have 18 or less carbon atoms, preferably 14 or less, more preferably 12 or less, possibly 10 or less, or possibly 9 or less. In several states, the fluorinated alkyl group may have 7 or less carbon atoms, or possibly 5 or less. Furthermore, in several states, the fluorine-containing (meth)acrylate is preferably a fluorinated alkyl (meth)acrylate in which the carbon at the 1-position of the alkyl group is not bonded with fluorine. For example, a fluorinated alkyl (meth)acrylate in which either the carbon at the 1-position or the carbon at the 2-position of the alkyl group is not bonded with fluorine, such as 1H,1H,2H,2H-tridecylfluorooctyl acrylate, is suitable.

[0186] In several samples, the low refractive index layer is an acrylic adhesive layer, and the acrylic polymer of the base polymer of the adhesive can be a polymer of monomer raw materials that at least contains the fluorinated acrylic monomers (e.g., fluorinated alkyl (meth)acrylates) as described above, and may further contain other monomers (copolymeric monomers) that have copolymerization properties with the fluorinated acrylic monomers. The monomer raw materials may contain alkyl (meth)acrylates, or may not contain them. In the above monomer raw materials, the content of the fluorinated acrylic monomers may, for example, be 10% by weight or more, 25% by weight or more, or 35% by weight or more. From the viewpoint of easily achieving a low refractive index layer with a lower refractive index, the content of the above fluorinated acrylic monomers is preferably 40% by weight or more, more preferably 45% by weight or more, more preferably 55% by weight or more, may be 60% by weight or more, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. There is no particular upper limit to the content of fluorinated acrylic monomers in the monomer raw materials, and it can be 100% by weight. Considering factors such as the aggregation properties of the low-refractive-index layer, a content of fluorinated acrylic monomers of 99.9% by weight or less is appropriate for several samples, preferably 99.5% or less, possibly 99% or less, possibly 97% or less, or possibly 92% or less. Fluorinated acrylic monomers can be used alone or in combination of two or more.

[0187] The monomer raw material used to formulate the substrate polymer of the low refractive index layer may be composed of a copolymer monomer in addition to fluorinated acrylic monomers (e.g., fluorinated alkyl (meth)acrylates). The copolymer monomers mentioned above may be one or more of the following functional monomers: carboxyl-containing monomers, hydroxyl-containing monomers, anhydride-containing monomers, amide-containing monomers, amine-containing monomers, monomers having a nitrogen-containing ring (e.g., N-vinyl-2-pyrrolidone and other N-vinylcyclic amides), sulfonic acid-containing monomers, phosphate-containing monomers, etc. Other examples of copolymer monomers include vinyl ester monomers such as vinyl acetate, aromatic vinyl compounds such as styrene, (meth)acrylates containing non-aromatic rings such as (meth)acrylate cycloalkyl esters or (meth)acrylate isoborneol esters, alkoxy-containing monomers, etc. Specific examples may include the monomers described above that can be used as substrate polymers for high refractive index adhesive layers, but are not limited thereto. For example, from the perspective of enhancing cohesiveness, the aforementioned copolymeric monomers should preferably be acrylic polymers copolymerized from carboxyl-containing monomers and / or hydroxyl-containing monomers.

[0188] In several ideal samples, the monomer raw material used to modulate the substrate polymer of the low refractive index layer may be a composition containing hydroxyl-containing monomers. Hydroxyl-containing monomers help to improve cohesiveness or introduce crosslinking points, etc. Suitable examples of hydroxyl-containing monomers include hydroxyalkyl methacrylates such as 2-hydroxyethyl acrylate or 4-hydroxybutyl acrylate. From the viewpoint of improving flexibility in the room temperature range, 4-hydroxybutyl acrylate is more suitable. There is no particular limitation on the content of hydroxyl-containing monomers in the monomer raw material, for example, it may be 0.01% by weight or more (preferably 0.1% by weight or more, more preferably 0.5% by weight or more). In several samples, the content of the above-mentioned hydroxyl-containing monomers may be 0.7% by weight or more, 0.9% by weight or more, or 1.5% by weight or more of the above-mentioned monomer raw material. There is no particular upper limit on the content of hydroxyl-containing monomers, for example, it may be 15% by weight or less or 10% by weight or less. From the perspective of reducing refractive index, it is appropriate for the content of hydroxyl monomers in the above monomer raw materials to be less than 10% by weight, preferably less than 5% by weight, less than 3% by weight, less than 2.5% by weight, or less than 1.5% by weight.

[0189] In several samples, from the viewpoint of suppressing the coloring or discoloration (e.g., yellowing) of the low-refractive-index layer, the content of carboxyl-containing monomers in the monomer raw material used to modulate the substrate polymer of the low-refractive-index layer should be limited. The content of carboxyl-containing monomers in the aforementioned monomer raw material may be less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, and even more preferably less than 0.1% by weight (e.g., less than 0.05% by weight). Such limitation of the content of carboxyl-containing monomers is also advantageous from the viewpoint of suppressing the use of metallic materials that are in contact with the low-refractive-index layer or that can be disposed adjacent to the low-refractive-index layer (e.g., metal wiring or metal films present on the adherend). The technique disclosed herein is suitable for implementation in samples where the aforementioned monomer raw material does not contain carboxyl-containing monomers. For the same reason, in several samples, the content of monomers with acidic functional groups (including sulfonic acid groups, phosphate groups, etc., in addition to carboxyl groups) in the monomer raw materials used to modulate the low-refractive-index layer should be limited. The content of acidic functional group monomers in the monomer raw materials of the aforementioned samples can be achieved using the ideal content of carboxyl group monomers mentioned above. The technique disclosed herein is suitable for implementation in samples where the aforementioned monomer raw materials do not contain acidic functional group monomers (i.e., the low-refractive-index layer substrate polymer is an acid-free sample).

[0190] The base polymer of the low-refractive-index layer can be appropriately formulated using known polymerization methods, just like the base polymer of the high-refractive-index adhesive layer. The weight-average molecular weight (Mw) of the base polymer (e.g., an acrylic polymer) is not particularly limited, and can be, for example, in the range of approximately 10 × 10⁴ to 500 × 10⁴, or in the range of approximately 20 × 10⁴ to 200 × 10⁴. In several cases, from the viewpoint of adhesion to the high-refractive-index adhesive layer, it is appropriate for the Mw of the base polymer of the low-refractive-index adhesive layer to be 250 × 10⁴ or less, and it can be 200 × 10⁴ or less, 150 × 10⁴ or less, 120 × 10⁴ or less (e.g., 95 × 10⁴ or less), 75 × 10⁴ or less, 68 × 10⁴ or less, or 60 × 10⁴ or less. Furthermore, from the viewpoint of the cohesiveness of the low-refractive-index adhesive layer, the Mw of the base polymer in several samples can be, for example, 30 × 10⁴ or more, 40 × 10⁴ or more, or 50 × 10⁴ or more. In several ideal samples, the Mw of the base polymer can be approximately 70 × 10⁴ or more, approximately 100 × 10⁴ or more, 130 × 10⁴ or more, or 160 × 10⁴ or more (e.g., 180 × 10⁴ or more). By using a base polymer with a predetermined Mw value or higher, it is easy to obtain a moderate cohesive force that can exert the desired adhesive properties. Moreover, by utilizing the cohesiveness brought about by the high molecular weight polymer as described above, it is easy to obtain excellent flexibility and thus flexibility that can withstand large deformations. To adjust the Mw, conventionally known chain transfer agents can be used as needed.

[0191] While not specifically limited, from the viewpoint of adhesion, it is advantageous for the base polymer (e.g., acrylic polymer) of the low refractive index layer to have a Tg of approximately 0°C or less, preferably approximately -5°C or less (e.g., approximately -15°C or less, or -25°C or less). Furthermore, from the viewpoint of the cohesive strength of the adhesive layer, the base polymer of the low refractive index layer should have a Tg of approximately -75°C or more, preferably approximately -70°C or more (e.g., -50°C or more, further preferably -30°C or more). The Tg of the acrylic polymer can be adjusted by appropriately changing the monomer composition (i.e., the types or proportions of monomers used in the synthesis of the polymer).

[0192] Known crosslinking agents may be used in the low refractive index layer. Furthermore, the low refractive index layer may contain tackifiers or other additives. The crosslinking agent or tackifier may be appropriately selected from those used in high refractive index adhesive layers and used in appropriate amounts.

[0193] In the adhesive composition containing a crosslinking agent used to form a low-refractive-index adhesive layer, the crosslinking agent may be, for example, an isocyanate-based crosslinking agent. In several samples, from the viewpoint of adhesion to the high-refractive-index adhesive layer, the amount of the isocyanate-based crosslinking agent relative to 100 parts by weight of the base polymer of the adhesive composition may be, for example, less than 0.5 parts by weight, less than 0.3 parts by weight, less than 0.2 parts by weight, or less than 0.15 parts by weight. Furthermore, from the viewpoint of appropriately utilizing the crosslinking agent's effect, in several samples, the amount of the isocyanate-based crosslinking agent relative to 100 parts by weight of the base polymer may be, for example, 0.005 parts by weight or more, 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.08 parts by weight or more.

[0194] <Preparation of Adhesive Layer> In the technology disclosed herein, the adhesive constituting the adhesive layer (which may be a high-refractive-index adhesive layer and / or a low-refractive-index layer; unless otherwise specified, the same applies hereinafter) can be formed using an adhesive composition. The form of the adhesive composition that can be used is not particularly limited, and may include, for example, various forms such as: solvent-based adhesive compositions containing adhesive-forming components in an organic solvent; active energy line-curing adhesive compositions that can be hardened by active energy lines such as ultraviolet light or radiation to form an adhesive; water-dispersible adhesive compositions in which adhesive-forming components are dispersed in water; and hot-melt adhesive compositions that can be applied in a molten state and cooled to near room temperature to form an adhesive. The adhesive can be an adhesive formed by hardening solvent-based, active energy line-curing, water-dispersible, or hot-melt adhesive compositions through drying, crosslinking, polymerization, cooling, etc., or it can be a hardened product of the aforementioned adhesive compositions. The curing methods (e.g., drying, crosslinking, polymerization, cooling, etc.) of adhesive compositions can be applied in one way or in two or more ways simultaneously or in multiple stages. For solvent-based adhesive compositions, typically the composition can be dried (preferably for further crosslinking) to form the adhesive. For active energy line curing adhesive compositions, typically the adhesive is formed by irradiating an active energy line to induce polymerization and / or crosslinking reactions. When drying of an active energy line curing adhesive composition is necessary, it can be followed by irradiation with an active energy line. The adhesives disclosed herein can be suitably formed using solvent-based adhesive compositions, but are not particularly limited thereto.

[0195] The adhesive layer of the adhesive sheet in the art disclosed herein can be formed by hardening the adhesive composition after applying (e.g., coating) it to a suitable surface. The coating of the adhesive composition can be carried out using conventional coating machines such as gravure roller coaters, reverse roller coaters, contact roller coaters, dip roller coaters, bar coaters, doctor blade coaters, and spray coaters.

[0196] The adhesive layer in the disclosed technology can be either a post-curing adhesive layer or a non-post-curing adhesive layer. Here, a post-curing adhesive layer refers to an adhesive layer that can be further cured by irradiation with heat or active energy rays (e.g., ultraviolet light). Examples of post-curing adhesive layers include adhesive layers with unreacted vinyl unsaturated groups on the side chains of the base polymer, or adhesive layers containing unreacted polyfunctional monomers. In several cases, the adhesive layer preferably does not have post-curing properties. Adhesive layers without post-curing properties do not undergo the dimensional changes associated with post-curing reactions (i.e., good dimensional stability), thus easily suppressing warping of the adhesive layer or the adhered object to which the adhesive layer is attached. The absence of dimensional changes (e.g., curing shrinkage) caused by post-curing is also advantageous from the viewpoint of suppressing the optical strain of the adhesive layer.

[0197] The thickness of the adhesive layer in the disclosed technology is not particularly limited, and can be, for example, 3µm or more, preferably 5µm or more. With an adhesive layer of 5µm or more thickness, good adhesive properties can be easily obtained. Furthermore, an adhesive layer of such thickness absorbs any unevenness that may exist on the surface of the adherend, thus easily and effectively bonding to the adherend. From the viewpoint of preventing coloring or uneven coloring caused by light interference, an adhesive layer thickness (e.g., the thickness of a high-refractive-index adhesive layer) of 5µm or more is also preferable. In several cases, the adhesive layer thickness can be 10µm or more, 20µm or more, 30µm or more, 50µm or more, 70µm or more, or 85µm or more. Furthermore, in several embodiments, the thickness of the adhesive layer can be, for example, 300µm or less, 250µm or less, 200µm or less, 150µm or less, or 120µm or less. In several ideal embodiments, the thickness of the adhesive layer is 100µm or less, preferably 75µm or less, more preferably 70µm or less, can be 50µm or less, or can be 30µm or less. From the viewpoint of thinning the laminate or light-emitting device containing this adhesive layer, it is advantageous that the thickness of the adhesive layer is not too large. Moreover, a thin adhesive layer tends to have excellent conformability to the adhered object. The technology disclosed herein can be appropriately implemented, for example, in embodiments where the thickness of the adhesive layer is in the range of 3µm to 200µm (preferably 5µm to 100µm, more preferably 5µm to 75µm).

[0198] Among several samples, the thickness of the adhesive layer can be at least applied to the thickness T1 of the high refractive index adhesive layer. The thickness T2 of the low refractive index adhesive layer can also be selected from the same range. Regardless of whether it is an adhesive layer, the thickness of the adhesive layer can also be applied to the thickness T2 of the low refractive index layer. The thickness T1 of the high refractive index adhesive layer and the thickness T2 of the low refractive index layer can be the same or different. The ratio (T1 / T2) of the thickness T1 of the high refractive index adhesive layer to the thickness T2 of the low refractive index layer can be, for example, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, or 1.0 or more (for example, greater than 1.0). Furthermore, the ratio (T1 / T2) can be, for example, 20 or less, 10 or less, 5 or less, or 3 or less. In several samples, the ratio (T1 / T2) may be less than 2, less than 1.5, or less than 1. In other samples, the ratio (T1 / T2) may be less than 0.8, less than 0.6, or less than 0.5.

[0199] A method for obtaining a laminated structure (laminated sheet) consisting of a high-refractive-index adhesive layer and a low-refractive-index layer (typically a low-refractive-index adhesive layer) may employ, for example, a method of forming a high-refractive-index adhesive layer and a low-refractive-index layer respectively on a release surface (e.g., the release surface of a release liner) and then bonding them together; a method of applying a composition used to form the low-refractive-index layer onto the high-refractive-index adhesive layer and then curing it; or conversely, a method of applying an adhesive composition used to form the high-refractive-index adhesive layer onto the low-refractive-index layer and then curing it, etc., but not limited to these methods. When bonding the pre-formed high-refractive-index adhesive layer and the low-refractive-index layer, treatments to promote adhesion between the layers may be performed as needed. For example, autoclaving or rolling processes may be performed, but not limited to these methods.

[0200] (Peel Strength) The peel strength of the adhesive layer disclosed herein to the glass plate is not particularly limited. In several examples, the peel strength of the adhesive layer to the glass plate is, for example, 0.1 N / 25 mm or more, or 0.5 N / 25 mm or more. In several ideal examples, the peel strength to the glass plate is 1.0 N / 25 mm or more, preferably 1.5 N / 25 mm or more, more preferably 2.0 N / 25 mm or more, and may be 3.0 N / 25 mm or more, 5.0 N / 25 mm or more, or 10 N / 25 mm or more. As described, an adhesive layer with a peel strength to the glass plate of a predetermined value or more is suitable for joining or fixing, for example, glass components. There is no particular limitation on the upper limit of the above peel strength, for example, it may be 30 N / 25 mm or less, 25 N / 25 mm or less, or 20 N / 25 mm or less.

[0201] Here, the peel strength is determined by the following method: after pressing onto an alkaline glass plate as the adherend and placing it at 23°C and 50%RH for 30 minutes, it is then subjected to autoclaving at 50°C and 0.5MPa for 30 minutes, followed by placement in a gas environment at 23°C and 50%RH for 24 hours. The peel strength is then measured at a peel angle of 180 degrees and a tensile speed of 300 mm / min. During the measurement, a suitable substrate (e.g., a polyethylene terephthalate (PET) film with a thickness of approximately 25µm to 50µm) can be attached to the adhesive layer of the test object for reinforcement, as needed. More specifically, the peel strength can be measured by the following method. [Peel Strength to Glass Plate] Under a test environment of 23°C and 50%RH, the release liner was peeled off from one side of the adhesive layer, and a 50µm thick PET film was laminated as a substrate. The film was then cut into test pieces with a width of 25mm and a length of 100mm. The release liner on the other side of the test piece was peeled off, and a 2kg roller was pressed back and forth once on the surface of the alkaline glass plate (Matsunami Glass Industry Co., Ltd., 1.35mm thick, frosted blue glass) used as the adhesive. After being placed in the same environment for 30 minutes, it was then placed in a pressure degassing device (autoclave) and subjected to autoclaving at 50°C and 0.5MPa for 30 minutes. After being placed in a gas environment of 23°C and 50%RH for 24 hours, the peel strength (adhesion force) [N / 25mm] was measured using a universal tensile and compression testing machine according to JIS Z 0237:2000 at a tensile speed of 300mm / min and a peel angle of 180 degrees. For example, a universal tensile and compression testing machine such as the "Tensile and Compression Testing Machine TG-1kN" manufactured by Minebea Corporation can be used. When a laminated sheet is formed by stacking a high-refractive-index adhesive layer and a low-refractive-index adhesive layer to create a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, in several samples, the aforementioned peel strength should preferably apply at least to the first adhesive surface (the adhesive surface composed of the high-refractive-index adhesive layer), and more preferably to both the first and second adhesive surfaces. The peel strength of the first adhesive surface to the glass plate and the peel strength of the second adhesive surface to the glass can be the same or different.

[0202] <Supporting Substrate> The high-refractive-index adhesive layer and the low-refractive-index layer may also be deposited sequentially or in reverse order on one side of the supporting substrate. The configuration of the high-refractive-index adhesive layer and the low-refractive-index layer deposited on the supporting substrate as described above can also be regarded as an adhesive sheet attached to the substrate. Therefore, according to this specification, an adhesive sheet (adhesive article) attached to a substrate is provided, comprising: a laminated sheet composed of a high-refractive-index adhesive layer and a low-refractive-index layer (preferably a low-refractive-index adhesive layer), and a supporting substrate supporting the laminated sheet.

[0203] The material of the supporting substrate is not particularly limited and can be appropriately selected according to the purpose or mode of use. Examples of non-limiting substrates that can be used include: polyolefin films with polyolefins such as polypropylene (PP) or ethylene-propylene copolymer as the main component; polyester films with polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN) as the main component; polyvinyl chloride films with polyvinyl chloride as the main component; foamed sheets composed of foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam; woven and non-woven fabrics made of various fibrous materials (such as natural fibers like hemp and cotton, synthetic fibers like polyester and vinylon, and semi-synthetic fibers like acetate) alone or in blends; paper such as Japanese paper, woodfree paper, kraft paper, and crepe paper; and metal foils such as aluminum foil and copper foil. Substrates composed of these composites are also acceptable. Examples of the composite substrate include substrates with structures formed by laminating metal foil and the aforementioned plastic film, and plastic substrates reinforced with inorganic fibers such as glass cloth.

[0204] Various film substrates can be used in several embodiments. These film substrates can be porous substrates such as foamed films or nonwoven sheets, non-porous substrates, or substrates with a structure consisting of porous layers and non-porous layers. Among the various embodiments, the film substrates can preferably include a resin film as the base film that is independent and can maintain its shape (either self-supporting or non-dependent). Here, "resin film" refers to a non-porous structure, typically a resin film that is substantially free of air bubbles (pores). Therefore, the resin film is a concept that can be distinguished from foamed films or nonwovens. The resin film can preferably be independent and can maintain its shape (either self-supporting or non-dependent). The resin film can be a single-layer structure or a multi-layer structure with two or more layers (e.g., a three-layer structure).

[0205] Materials constituting the resin film may include, for example: polyester resins with polyester as the main component, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyolefin resins with polyolefin as the main component, such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-butene copolymer; cellulose resins such as cellulose triacetate; acetate resins; polyurethane resins; polyether resins; polycarbonate resins; nylon 6; nylon 66; polyamide (PA) resins such as some aromatic polyamides; and polyimide (P... I) Cyclic polyolefin resins such as polyimide resins, transparent polyimide resins, polyamide-imide (PAI), polyether ether ketone (PEEK), polyether ether (PES), norethene resins, (meth)acrylic resins, polyvinyl chloride resins, polyvinyl chloride resins, polystyrene resins, polyvinyl alcohol resins, ethylene-vinyl acetate copolymer resins, ethylene-vinyl alcohol copolymer resins, polyarylate resins, polyphenylene sulfide (PPS) resins, polyurethane (PU), ethylene-vinyl acetate copolymer (EVA), polytetrafluoroethylene (PTFE), or fluorinated polyimide resins, etc.

[0206] The aforementioned resin film may be formed using a resin material comprising only one type of resin, or it may be formed using a mixture of two or more resin materials. The aforementioned resin film may be unstretched or stretched (e.g., uniaxially or biaxially stretched). For example, PET film, PBT film, PEN film, unstretched polypropylene (CPP) film, biaxially stretched polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, PP / PE blend film, etc., are suitable. From the viewpoint of strength or dimensional stability, ideal examples of resin films include PET film, PEN film, PPS film, and PEEK film. From the viewpoint of ease of acquisition, PET film and PPS film are particularly suitable, with PET film being preferred.

[0207] In the resin film, known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slipping agents, and anti-adhesion agents may be added as needed, within a range that does not significantly impair the effects of the present invention. The amount of additives added is not particularly limited and can be appropriately set according to the intended use of the adhesive sheet.

[0208] There are no particular limitations on the manufacturing method of the resin film. For example, commonly known resin film forming methods such as extrusion molding, gas molding, T-die casting, and calendering roll forming can be appropriately used.

[0209] The substrate described above may be substantially composed of the base film. Alternatively, the substrate may also include auxiliary layers in addition to the base film. Examples of such auxiliary layers include optical property adjustment layers (e.g., coloring layers, anti-reflective layers), printing layers or laminates for imparting a desired appearance to the substrate, antistatic layers, primer layers, release layers, and other surface treatment layers.

[0210] Among several samples, a light-transmitting substrate (hereinafter also referred to as a light-transmitting substrate) can be suitably used as the support substrate. This allows for the construction of an adhesive sheet with the light-transmitting substrate. The total light transmittance of the light-transmitting substrate can be, for example, greater than 50%, or more than 70%. In several ideal samples, the total light transmittance of the support substrate is 80% or more, preferably 90% or more, or more than 95% (e.g., 95-100%). The aforementioned total light transmittance is measured using a commercially available transmittance meter according to JIS K 7136:2000. The transmittance meter can be the Murakami Color Technology Research Institute's product under the trade name "HAZEMETER HM-150" or an equivalent. A suitable example of the aforementioned light-transmitting substrate is a light-transmitting resin film. The aforementioned light-transmitting substrate can also be an optical film.

[0211] The thickness of the substrate is not particularly limited and can be selected according to the intended use or application. For example, the substrate thickness can be 500µm or less, but from a processability or handling perspective, it is preferable to be 300µm or less, or 150µm or less, or 100µm or less, or 50µm or less, or 25µm or less, or even 10µm or less. A smaller substrate thickness tends to improve adaptability to the surface shape of the adherend. Furthermore, from a processability or handling perspective, the substrate thickness can be, for example, 2µm or more, 10µm or more, or 25µm or more.

[0212] The side of the substrate to which the adhesive layer is to be deposited may also undergo conventional surface treatments as required, such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or forming a base layer by applying a primer. These surface treatments can be used to improve the anchoring properties of the adhesive layer to the substrate. The composition of the primer used to form the base layer is not particularly limited and can be appropriately selected from known materials. The thickness of the base layer is not particularly limited, but is generally suitable at around 0.01µm to 1µm, preferably around 0.1µm to 1µm. Other treatments that can be performed on the substrate as required include antistatic layer formation treatment, coloring layer formation treatment, and printing treatment. These treatments can be applied individually or in combination.

[0213] In the technology disclosed herein, when a high-refractive-index adhesive layer and a low-refractive-index layer constitute an adhesive sheet for attaching a substrate, the thickness of the adhesive sheet may be, for example, 1000µm or less, 350µm or less, 200µm or less, 120µm or less, 75µm or less, or 50µm or less. Furthermore, from the viewpoint of processability, the thickness of the aforementioned adhesive sheet may be, for example, 10µm or more, 25µm or more, 80µm or more, or 130µm or more. In addition, the thickness of the adhesive sheet refers to the thickness of the portion adhered to the adhered object. For example, in the substrate-free double-sided adhesive sheet 2 constructed as shown in FIG. 2, the thickness refers to the thickness from the first surface (first adhesive surface) 10A of the adhesive layer to the second surface (second adhesive surface) 10B, excluding the thickness of the release liner 31, 32.

[0214] <Laminated Sheet> A laminate (adhesive sheet) comprising the high refractive index adhesive layer and the low refractive index layer disclosed herein may be a laminate composed of a high refractive index adhesive layer and a low refractive index layer (preferably a low refractive index adhesive layer), or it may be a laminate further comprising a substrate supporting the laminate.

[0215] Among several samples, the haze value of the laminate may be, for example, 5.0% or less, preferably 3.0% or less, more preferably 2.0% or less, even more preferably 1.0% or less, possibly 0.9% or less, possibly 0.8% or less, possibly 0.5% or less, or possibly 0.3% or less. As described above, laminates with high transparency are advantageous for applications requiring high light transmittance. There is no particular limitation on the lower limit of the haze value of the laminate; from the viewpoint of improving transparency, the lower the haze value, the better. On the other hand, among several samples, considering the refractive index or adhesive properties, the haze value may be, for example, 0.05% or more, or possibly 0.10% or more. The haze value of the laminate can be measured using the same method as the method used to measure the haze value of the adhesive layer described above. Specifically, it can be measured using the method described in the experimental examples below. The haze value of the laminated sheet can be obtained by selecting the composition of the adhesive layer or by selecting the type or thickness of the substrate in the composition having a substrate.

[0216] In several samples, the total light transmittance of the laminate is preferably 85.0% or higher (e.g., 88.0% or higher, 90.0% or higher, or greater than 90.0%). As described above, laminates with high transparency are advantageous for applications requiring high light transmittance. The upper limit of the total light transmittance can, in practical terms, be, for example, about 98% or less, about 96% or less, or about 95% or less. In several samples, considering refractive index or adhesive properties, the total light transmittance of the laminate can be about 94% or less, about 93% or less, or about 92% or less. The total light transmittance of the laminate can be measured using the same method as the method used to measure the total light transmittance of the adhesive layer described above. Specifically, it can be measured using the method described in the test examples below. The total light transmittance of the laminate can be obtained by selecting the composition of the adhesive layer described above or by selecting the type or thickness of the substrate in the composition having a substrate.

[0217] The thickness of the laminate (substrate-free laminate or substrate-attached laminate) disclosed herein may be, for example, 1000µm or less, 350µm or less, 200µm or less, 120µm or less, 75µm or less, or 50µm or less. Furthermore, from the viewpoint of processability, the thickness of the adhesive sheet may be, for example, 5µm or more, 10µm or more, 15µm or more, 25µm or more, 80µm or more, or 130µm or more. In addition, the thickness of the adhesive sheet refers to the thickness of the portion adhered to the substrate. For example, in the substrate-free double-sided adhesive sheet 2 configured as shown in FIG. 2, the thickness refers to the thickness from the first surface (first adhesive surface) 10A of the adhesive layer to the second surface (second adhesive surface) 10B, excluding the thickness of the release liner 31, 32.

[0218] <Laminated Sheet with Release Pad> Before the high-refractive-index adhesive layer and low-refractive-index layer disclosed herein are incorporated into a light-emitting device, the adhesive surface of the laminate containing the high-refractive-index adhesive layer and the low-refractive-index layer may be in the form of an adhesive article (laminated sheet with release pad) in which the release surface of the release pad abuts against the adhesive surface of the release pad. Therefore, according to this specification, a laminated sheet (adhesive article) with a release pad is provided, which includes a laminated sheet containing a high-refractive-index adhesive layer and a low-refractive-index layer, and a release pad having a release surface abutting against the adhesive surface of the laminated sheet.

[0219] The release liner is not particularly limited. For example, a release liner with a release treatment layer on a release liner substrate such as a resin film or paper (which may be paper laminated with resins such as polyethylene) can be used, or a release liner made of a resin film formed from a low-adhesion material such as a fluoropolymer (polytetrafluoroethylene, etc.) or a polyolefin resin (polyethylene, polypropylene, etc.) can be used. The release treatment layer can be formed by surface treatment of the release liner substrate with a release treatment agent. The release treatment agent can be a known release treatment agent such as a polysiloxane-based release treatment agent, a long-chain alkyl-based release treatment agent, a fluorine-based release treatment agent, or molybdenum sulfide (IV). Among several options, a release liner having a release treatment layer obtained using a polysiloxane-based release treatment agent can be used. The thickness or formation method of the release treatment layer is not particularly limited, and can be set to provide appropriate release properties on the adhesive side surface of the release liner.

[0220] Among several types, from the viewpoint of smoothness of the adhesive surface, a release liner (hereinafter also called a release film) having a release treatment layer on a resin film (hereinafter also called a release film substrate) as the release liner substrate is suitable. Various plastic films can be used as the release film substrate. In this specification, the term "plastic film" typically refers to a non-porous sheet material, for example, a concept that can be distinguished from non-woven fabric (i.e., does not include non-woven fabric).

[0221] Examples of materials for the aforementioned plastic film include, for instance, polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyolefin resins such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-butene copolymer; cellulose resins such as cellulose triacetate; acetate resins; polyurethane resins; polyether resins; polycarbonate resins; polyamide resins; polyimide resins; norethene resins; cyclic polyolefin resins such as (meth)acrylic acid resins; polyvinyl chloride resins; polyvinyl chloride resins; polystyrene resins; polyvinyl alcohol resins; ethylene-vinyl acetate copolymer resins; ethylene-vinyl alcohol copolymer resins; polyarylate resins; and polyphenylene sulfide resins. A release film substrate formed from any one or a mixture of two or more of these resins may also be used. Among the preferred release film substrates are polyester resin films (e.g., PET films) formed from polyester resins.

[0222] The plastic film that can be used as the release film substrate described above can be any one of a non-stretched film, a uniaxially stretched film, or a biaxially stretched film. Furthermore, the plastic film can be a single-layer structure or a multi-layer structure containing two or more sublayers. The plastic film may also contain known additives suitable for release film substrates of adhesive sheets, such as antioxidants, anti-aging agents, heat stabilizers, light stabilizers, ultraviolet absorbers, colorants (pigments or dyes), lubricants, fillers, antistatic agents, and nucleating agents. In multi-layer plastic films, each additive may be incorporated into all sublayers or only into a portion of the sublayers.

[0223] In several ideal configurations, the aforementioned release film substrate (typically a plastic film) is suitable for use where the content of inorganic particles (e.g., pigments, lubricants, fillers, etc.) in the layer on its release surface side is limited, or substantially free of such particles. Here, "substantially free" means that the amount of particles (e.g., inorganic particles) in that layer is less than 1% by weight, preferably less than 0.1% by weight (e.g., 0 to 0.01% by weight). Release films having the aforementioned release film substrate tend to have low arithmetic mean roughness Ra or maximum height Rz of the release surface. When the aforementioned release film substrate (typically a plastic film) has a multilayer structure, the particle content in the layer on the release surface side can be less than 1 / 10 (e.g., less than 1 / 50) of the particle content in layers other than that layer on the release surface side.

[0224] In a laminated sheet with a release liner having a release liner on the first adhesive surface and the second adhesive surface respectively, the release liner disposed on one adhesive surface (hereinafter also referred to as one release liner) and the release liner disposed on the other adhesive surface (hereinafter also referred to as the other release liner) may be made of the same material and have the same structure, or they may be made of different materials and have different structures.

[0225] The thickness of the release liner (preferably a release film) is not particularly limited, and can be, for example, around 10µm to 500µm. From the viewpoint of the strength or dimensional stability of the release liner, a thickness of 20µm or more is appropriate, preferably 30µm or more, and can be 35µm or more, 40µm or more, or 45µm or more. Furthermore, from the viewpoint of the release liner's treatment properties (e.g., ease of winding), a thickness of 300µm or less is appropriate, preferably 250µm or less, and can be 200µm or less, 150µm or less, or 130µm or less. In several ideal cases, the thickness of the release liner is approximately 125µm or less, can be approximately 115µm or less, can be approximately 105µm or less, can be approximately 90µm or less, or can be approximately 70µm or less. By setting the thickness of the release liner to below a predetermined value, it is less likely to form winding marks when rolled up, and it can be easily removed from the adhesive sheet, thereby easily obtaining a high surface smoothness on the adhesive surface after the release liner is removed.

[0226] In a laminated sheet with release liner, having one release liner and another release liner, the thicknesses of the release liners may be the same or different. In several versions, from the viewpoint of peeling workability, one release liner and another release liner should preferably have different thicknesses, for example, the thickness of the thicker release liner should preferably be about 1.1 times or more (e.g., about 1.25 times or more; there is no particular upper limit, for example, less than 5 times) the thickness of the thinner release liner.

[0227] (Arithmetic mean roughness Ra of the adhesive side surface) In several embodiments, from the viewpoint of achieving an adhesive surface with high surface smoothness, the arithmetic mean roughness Ra of the adhesive side surface of the release liner (preferably a release film) should preferably be limited to a predetermined value (e.g., about 100 nm or less, and further less than 50 nm). In several embodiments, the arithmetic mean roughness Ra of the adhesive side surface of the release liner should preferably be about 30 nm or less, more preferably about 25 nm or less, possibly about 20 nm or less, or possibly about 18 nm or less. Furthermore, from the viewpoint of ease of manufacture or processability of the release liner, in several embodiments, the aforementioned arithmetic mean roughness Ra may be about 5 nm or more, about 10 nm or more, or about 15 nm or more. In a laminated sheet with release liner attached, where release liners are respectively disposed on the first and second adhesive surfaces, the adhesive side surfaces of both release liners should preferably satisfy either of the aforementioned arithmetic mean roughness Ra. The arithmetic mean roughness Ra of the adhesive side surfaces of the two release liners may be the same or different.

[0228] (Maximum height Rz of the adhesive side surface) In several embodiments, from the viewpoint of achieving an adhesive surface with high surface smoothness, the maximum height Rz of the release liner (preferably a release film) should preferably be 700 nm or less. In several embodiments, the maximum height Rz of the adhesive side surface of the release liner should preferably be approximately 600 nm or less, but may be approximately 500 nm or less, approximately 400 nm or less, or approximately 300 nm or less. Furthermore, from the viewpoint of ease of manufacture or processability of the release liner, in several embodiments, the aforementioned maximum height Rz may, for example, be approximately 50 nm or more, approximately 80 nm or more, approximately 100 nm or more, approximately 200 nm or more, or approximately 300 nm or more. In a laminated sheet with release liner attached, where release liners are respectively disposed on the first and second adhesive surfaces, the adhesive side surfaces of both release liners should preferably satisfy either of the aforementioned maximum heights Rz. The maximum heights Rz of the adhesive side surfaces of the two release liners may be the same or different.

[0229] (Surface Properties of the Back Side) The arithmetic mean roughness Ra or maximum height Rz of the back side (opposite to the adhesive layer side) of the release liner (preferably a release film) is not particularly limited. From a production point of view, the arithmetic mean roughness Ra of the back side of the release liner may, for example, be greater than 30 nm (e.g., greater than 35 nm, further approximately 50 nm or more). From a production point of view, the maximum height Rz of the back side of the release liner may, for example, be greater than 400 nm (e.g., approximately 500 nm or more), or greater than 800 nm (e.g., 1000 nm or more).

[0230] The arithmetic mean roughness Ra and maximum height Rz of the release film surface can be adjusted by selecting the film material or by surface treatments such as forming method and release treatment. For example, the smoothness of the layers constituting the release surface (anti-adhesion layer, hard coating, oligomer prevention layer, etc.) can be adjusted, and the filler particles in the surface layer or release film substrate can be reduced or eliminated (particle-free). Other adjustments include adjusting the stretching conditions.

[0231] The arithmetic mean roughness Ra and maximum height Rz of the surface of the release liner (preferably a release film) are measured using a non-contact surface roughness measuring device. The non-contact surface roughness measuring device can be an optical interference surface roughness measuring device, such as a 3D optical profilometer (trade name "NewView7300", manufactured by ZYGO) or an equivalent. For example, a glass plate (1.3mm thick soda-lime glass plate manufactured by MATSUNAMI) can be adhered to the surface of the release liner opposite to the measurement surface and fixed with an adhesive. The surface shape is then measured using a 3D optical profilometer (trade name "NewView7300", manufactured by ZYGO) at 23°C and 50%RH.

[0232] <Application> In the technology disclosed herein, the high refractive index adhesive layer can be bonded to various adhered bodies constituting a light-emitting device. The constituent materials of the aforementioned adherend (adhesive material) are not particularly limited, and examples include: metallic materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, indium, zinc, or alloys containing two or more of these; or resins such as polyimide resins, acrylic resins, polyether nitrile resins, polyether pyrrolidone resins, polyester resins (PET resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyether ether ketone resins, polyamide resins (so-called arylamide resins, etc.), polyarylate resins, fluorine resins, polycarbonate resins, cellulose polymers such as cellulose diacetate or cellulose triacetate, vinyl butyral polymers, liquid crystal polymers, carbon materials such as graphene, etc. (typically plastic materials), alumina, zirconium oxide, titanium oxide, SiO2, etc. 2. Metal oxides and mixtures thereof such as ITO (indium tin oxide) and ATO (antimony-doped tin oxide), nitrides and their complexes such as aluminum nitride, silicon nitride, titanium nitride, gallium nitride, and indium nitride, alkali glass, alkali-free glass, quartz glass, borosilicate glass, sapphire glass, and carbon glass, etc. The high-refractive-index adhesive layer disclosed herein can be adhered to components (e.g., optical components) whose surfaces are at least made of the above-mentioned materials. Furthermore, the low-refractive-index layer (preferably a low-refractive-index adhesive layer) disclosed herein can be laminated (e.g., bonded) to the various substrates mentioned above.

[0233] The high refractive index adhesive layer disclosed herein can be used in the following attached state: an attached state in which, after being bonded to the substrate, it is not necessary to perform a heating process to a temperature higher than room temperature (e.g., 20°C to 35°C). Furthermore, depending on the type of substrate, heating treatment can be performed at least at any point after bonding the substrate, at the time of bonding, and before bonding. The heating treatment can be performed to improve the adhesion of the adhesive to the substrate or to promote bonding. The heating treatment temperature can be appropriately set within the range permissible by the constituent materials of the adhesive sheet or the type of substrate, taking into account the surface condition of the substrate, to obtain the desired effect; for example, it can be around 100°C or below, below 80°C, below 60°C, or below 50°C.

[0234] The component or material to which the adhesive layer is attached can be light-transmitting. With respect to the adherend, the high-refractive-index adhesive layer disclosed herein readily offers the advantage of high transparency. The total light transmittance of the adherend can, for example, be greater than 50%, or even greater than 70%. In several ideal cases, the total light transmittance of the adherend is 80% or greater, preferably 90% or greater, and more preferably 95% or greater (e.g., 95-100%). The high-refractive-index adhesive layer disclosed herein is suitable for use on adherends (e.g., optical components) with a total light transmittance greater than a predetermined value. The total light transmittance is measured using a commercially available transmittance meter according to JIS K 7136:2000. The transmittance meter can be the Murakami Color Technology Research Institute's product name "HAZEMETER HM-150" or an equivalent thereof.

[0235] The refractive index of the adherend and the refractive index of the adhesive layer (high-refractive-index adhesive layer or low-refractive-index layer) disposed against the adherend can be the same or different. For example, by making the refractive index of the adhesive layer relatively higher than that of the adherend, light incident on the adhesive layer at an angle below the critical angle from the adherend side can be refracted on the front side, increasing the front brightness. In this case, the refractive index of the adherend can be, for example, 1.55 or less, 1.50 or less, 1.48 or less, 1.45 or less, or less than 1.45, or, for example, 1.10 or more, 1.20 or more, 1.30 or more, or 1.35 or more. Furthermore, by having an adherend with a relatively high refractive index relative to the adhesive layer, light incident on the adherend from the adhesive layer side can be refracted on the front side, increasing the front brightness. At this point, the refractive index of the adherend can be, for example, 1.60 or higher, 1.65 or higher, or 1.70 or higher, and for example, 3.00 or lower, or 2.50 or lower, or 2.00 or lower. On the other hand, by reducing the refractive index difference between the adhesive layer and the adherend, light reflection at the interface can be suppressed. At this point, the refractive index of the adherend can be approximately 1.55 to 1.80, approximately 1.55 to 1.75, or approximately 1.60 to 1.70. The refractive index of the adherend can be measured using the same method as the refractive index of the adhesive.

[0236] Among several ideal samples, the aforementioned adherend can have any of the aforementioned refractive indices and any of the aforementioned total light transmittances. The effects of the technology disclosed herein are particularly suitable for use in light-emitting devices in which the adherend is attached or laminated with a high-refractive-index adhesive layer and / or a low-refractive-index layer.

[0237] The high-refractive-index adhesive layer and low-refractive-index layer disclosed herein can be attached to various substrates as described above in the form of laminated sheets. One example of a preferred application is optical applications. More specifically, for example, the laminated sheets disclosed herein can be used as optical adhesive sheets for applications such as bonding optical components (optical component bonding) or manufacturing articles using the aforementioned optical components (optical articles). Laminated sheets used in this manner can also be considered as interlayer sheets disposed between the layers of an optical laminate.

[0238] The aforementioned optical components refer to components that have optical properties (e.g., polarization, refraction, scattering, reflection, transmission, absorption, diffraction, rotation, and visibility). There is no particular limitation on the optical components that possess optical properties; examples include components constituting display devices (image display devices), input devices, and other machines (optical machines), or components used in such machines. Examples include polarizing plates, wavelength plates, phase difference plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflective films, hard coating (HC) films, impact absorption films, anti-fouling films, photochromic films, dimming films, transparent conductive films (ITO films), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, or components further formed by lamination of these (these are sometimes collectively referred to as "functional films"). Furthermore, the terms "plate" and "film" are respectively defined to include plate-like, film-like, and sheet-like forms. For example, "polarizing film" is defined to include "polarizing plate" or "polarizing sheet," while "light guide plate" is defined to include "light guide film" or "light guide sheet." Also, the term "polarizing plate" is defined to include a circular polarizing plate.

[0239] Examples of the aforementioned display devices include liquid crystal displays, organic EL (electroluminescent) displays, micro LEDs (µLEDs), mini LEDs (miniLEDs), PDPs (plasma display panels), and electronic paper. Furthermore, examples of the aforementioned input devices include touch panels.

[0240] The optical components described above are not particularly limited, and may include components made of glass, acrylic resin, polycarbonate, polyethylene terephthalate, metal films, etc. (e.g., sheet-like, film-like, or plate-like components). In addition, the term "optical component" in this specification also includes components that maintain the visibility of the display device or input device while serving a decorative or protective function (design films, decorative films, or surface protective films, etc.).

[0241] The high-refractive-index adhesive layer disclosed herein (which may be in the form of a laminate with a low-refractive-index layer) can be used, for example, in a configuration where an optical thin film or fluorescent thin film having one or more functions of light transmission, reflection, diffusion, waveguide, focusing, diffraction, etc., is placed between other optical components (which may be other optical thin films), and is suitable for bonding the aforementioned optical thin film to the aforementioned other optical components. In the bonding of optical thin films having at least one function of light waveguide, focusing, or diffraction, the entire bonding layer should preferably be of high refractive index, making it an ideal application of the technology disclosed herein.

[0242] The high refractive index adhesive layer disclosed herein is suitable for bonding optical films such as light guide films, diffusion films, fluorescent films, color-matching films, prisms, cylindrical lenses, and microlens array films. In these applications, from the perspective of miniaturization or high performance of optical components, there is a demand for thinner designs or improved light extraction efficiency. The high refractive index adhesive layer disclosed herein is suitable as an adhesive layer that meets these requirements. More specifically, for example, in bonding light guide films or diffusion films, adjusting the refractive index of the adhesive layer as the bonding layer (e.g., increasing the refractive index) can help achieve thinner designs. In bonding fluorescent films, the light extraction efficiency (which can also be considered as luminous efficiency) can be improved by appropriately adjusting the refractive index difference between the fluorescent emitter and the adhesive. In bonding color-matching films, by appropriately adjusting the refractive index of the adhesive to reduce the refractive index difference with the color-matching pigment, the scattering component can be reduced, thus helping to improve light transmittance. When bonding prisms, cylindrical films, microlens array films, etc., adjusting the refractive index of the adhesive appropriately can control the diffraction of light, which can help improve brightness and / or viewing angle.

[0243] The high-refractive-index adhesive layer disclosed herein (which may be in the form of a laminate with a low-refractive-index layer) is suitable for use in a configuration where it is attached to a high-refractive-index substrate (which may be a high-refractive-index layer or component, etc.) to suppress interfacial reflection with the substrate. The high-refractive-index adhesive layer that can be used in this configuration should preferably have a small refractive index difference with the high-refractive-index substrate and high adhesion at the interface with the substrate. Furthermore, from the viewpoint of improving the uniformity of appearance, the uniformity of the adhesive layer thickness should be high, for example, the surface smoothness of the adhesive surface should be high. When the thickness of the high-refractive-index substrate is small (e.g., 5µm or less, 4µm or less, or 2µm or less), suppressing interfacial reflection is particularly significant from the viewpoint of suppressing color or color unevenness caused by interference of reflected light. As one example of the usage, the following configuration can be used: in a polarizing plate having a polarizing element, a first phase difference layer and a second phase difference layer in sequence, the polarizing element can be bonded to the first phase difference layer and / or the first phase difference layer can be bonded to the second phase difference layer.

[0244] Furthermore, the high refractive index adhesive layer disclosed herein is suitable for use in the form of an emissive layer (e.g., an emissive layer mainly composed of inorganic materials) attached to a light-emitting layer such as a photonic semiconductor. By reducing the refractive index difference between the emissive layer and the high refractive index adhesive layer, reflection at these interfaces can be suppressed, thereby improving light extraction efficiency. From the viewpoint of improving brightness, the high refractive index adhesive layer should preferably be lightly tinted. This is also advantageous from the viewpoint of suppressing unintentional tinting caused by the high refractive index adhesive layer.

[0245] The high refractive index adhesive layer disclosed herein can be used in microlenses and other lens components (e.g., microlenses constituting microlens array films or camera microlenses) used as components of cameras or light-emitting devices, as a coating layer covering the lens surface, a bonding layer for a component facing the lens surface (e.g., a component having a surface shape corresponding to the lens surface), and a filling layer filling between the lens surface and the component. Even when the high refractive index adhesive layer disclosed herein is disposed against a high refractive index lens (e.g., a lens made of high refractive index resin, or a lens having a surface layer made of high refractive index resin), it can still reduce the refractive index difference with that lens. This is advantageous from the viewpoint of thinning the lens and the product having the lens, and can also help suppress aberrations or increase the Abbe number. In the technology disclosed herein, the adhesive (viscoelastic material) constituting the high refractive index adhesive layer can also be used as a lens resin, for example, in the form of filling the recesses or cavities of a suitable transparent component.

[0246] There is no particular limitation on the manner in which the adhesive layer disclosed herein (which is a high-refractive-index adhesive layer and / or a low-refractive-index adhesive layer, preferably a high-refractive-index adhesive layer that may also be deposited on a low-refractive-index layer) is used to bond optical components. For example, it may be the following manner: (1) bonding optical components to each other through the adhesive layer disclosed herein; or (2) bonding optical components to components other than optical components through the adhesive layer disclosed herein; or (3) the adhesive layer disclosed herein is in the form of an adhesive sheet containing optical components and the adhesive sheet is bonded to an optical component or a component other than optical components. Furthermore, in the above-mentioned (3) manner, the adhesive sheet containing optical components may be, for example, an adhesive sheet whose support is an optical component (e.g., an optical thin film). As described above, an adhesive sheet containing optical components as a support may also be regarded as an adhesive type optical component (e.g., an adhesive type optical thin film). Furthermore, when the adhesive layer disclosed herein constitutes an adhesive sheet of the type having a support and the aforementioned functional film is used as the support, the adhesive sheet can also be regarded as an "adhesive-type functional film" having the adhesive layer disclosed herein on at least one side of the functional film.

[0247] Based on the above, and according to the technology disclosed herein, an optical laminate is provided comprising the adhesive layer disclosed herein and a component (e.g., a resin film such as an optical film) having the adhesive layer deposited thereon by means of adhesion. The component having the adhesive layer deposited thereon by means of adhesion may have the refractive index of the aforementioned adherend material. Furthermore, the difference between the refractive index of the adhesive layer and the refractive index of the component (refractive index difference) may be the difference between the refractive index of the adherend and the adhesive layer. As the components constituting the laminate have been described above regarding the components, materials, and adherends, they will not be described again.

[0248] The high refractive index adhesive layer and laminate disclosed herein can withstand large deformations. Therefore, by utilizing their characteristics, they are suitable, for example, for machines (optical machines) with light-emitting devices, such as liquid crystal display devices, organic EL display devices, and touch panel input devices in portable electronic devices. In particular, they are suitable as light-emitting devices for foldable or rollable displays. The high refractive index adhesive layer and laminate disclosed herein have the flexibility to withstand repeated bending operations, so they can conform well to the repeatedly bent adhered object (foldable display, etc.) when attached to a foldable or rollable display. The attachment object in the above usage form can be glass components such as window glass or cover glass of foldable or rollable displays. Moreover, the high refractive index adhesive layer and laminate disclosed herein can also easily conform to and adhere to surfaces with curved shapes such as 3D shapes in portable electronic devices, so they are also suitable for light-emitting devices of electronic devices with such curved shapes. Furthermore, among several ideal samples, high-refractive-index adhesive layers and laminates can be those that, in addition to being flexible, also possess improved stability in properties such as elastic modulus. These portable electronic devices are sometimes used in high-temperature environments, and their internal spaces may become hot due to the heat generated by electronic components; therefore, using adhesives with the aforementioned stable properties offers significant advantages.

[0249] Examples of portable electronic devices that may have light-emitting devices disclosed herein include: portable telephones, smartphones, tablet computers, laptop computers, various wearable devices (such as wristbands worn on the wrist, modular devices attached to a part of the body in the form of clips or dangling, including eyeglasses (monocular or binocular; including headbands), clothing attached to shirts, socks, hats, etc., as accessories, and earphones attached to the ears), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), computers (electronic computers, etc.), portable game consoles, electronic dictionaries, electronic notebooks, electronic books, in-vehicle information machines, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. Furthermore, in this instruction manual, the term "portable" is not merely about being able to carry; it also refers to a degree of portability that makes it relatively easy for a person (a standard adult) to move.

[0250] As can be understood from the above description and the following test examples, the matters disclosed in this specification include the following. [1] A light-emitting device, comprising: a self-emitting element; a low refractive index layer disposed on the viewing side of the self-emitting element; and a high refractive index adhesive layer deposited in direct contact with the low refractive index layer; wherein the refractive index of the high refractive index adhesive layer is greater than 1.560, and the deformation amount in a deformation test performed at a temperature of -20°C and a speed of 300 mm / min is 350% or more. [2] A light-emitting device, comprising: a self-emitting element; a low refractive index layer disposed on the viewing side of the self-emitting element; and a high refractive index adhesive layer deposited in direct contact with the low refractive index layer; wherein the refractive index of the high refractive index adhesive layer is greater than 1.560 and contains a plasticizer. [3] In the light-emitting device of [1] or [2] above, the stress of the aforementioned high refractive index adhesive layer under a deformation test at a temperature of -20°C and a speed of 300 mm / min is less than 5.0 N / mm² when the deformation amount is 350%. [4] In the light-emitting device of any one of [1] to [3] above, the ratio (n1 / n2) of the refractive index n1 of the aforementioned high refractive index adhesive layer to the refractive index n2 of the aforementioned low refractive index layer is 1.05 or more. [5] A laminate comprising a low refractive index layer and a high refractive index adhesive layer laminated on the low refractive index layer; the refractive index of the aforementioned high refractive index adhesive layer is greater than 1.560, and the deformation amount under a deformation test at a temperature of -20°C and a speed of 300 mm / min is more than 350%. [6] A laminate comprising a low refractive index layer and a high refractive index adhesive layer laminated on the low refractive index layer; wherein the refractive index of the high refractive index adhesive layer is greater than 1.560 and contains a plasticizer. [7] A laminate as described in [5] or [6] above, wherein the stress of the high refractive index adhesive layer at a deformation test at a temperature of -20°C and a speed of 300 mm / min is less than 5.0 N / mm² at a deformation of 350%. [8] A laminate as described in any one of [5] to [7] above, wherein the ratio (n1 / n2) of the refractive index n1 of the high refractive index adhesive layer to the refractive index n2 of the low refractive index layer is 1.05 or more. [9] A laminate with a release liner, comprising: a laminate as described in any one of [5] to [8] above, and a release liner protecting the surface of the high refractive index adhesive layer.

[0251] Several test examples relating to the present invention will be described below, but the specific examples described are not intended to limit the present invention. In addition, in the following description, "parts" and "%" indicating the amount or content used are by weight unless otherwise specified.

[0252] <Preparation of Acrylic Adhesive Composition C1> In a four-necked flask equipped with a stirring blade, thermometer, nitrogen inlet tube, and cooler, 95 parts of phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "LIGHT ACRYLATE POB-A", refractive index: 1.566, hereinafter referred to as "POB-A"), 3 parts of 4-hydroxybutyl acrylate (4HBA), 2 parts of 2-acryloyloxyethyl succinate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "HOA-MS(N)", hereinafter referred to as "HOA-MS"), 0.2 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator, and ethyl acetate as a polymerization solvent were introduced while stirring slowly. The liquid temperature in the flask was maintained at around 60°C for 6 hours to prepare a 40% solution of acrylic polymer P1. The Mw of acrylic polymer P1 is 500,000. The above-mentioned acrylic polymer P1 solution was diluted with ethyl acetate to a polymer concentration of 30%. Then, 60 parts of polyethylene glycol benzoate (manufactured by Sanyo Chemical Industries, trade name "Sumflex EB-300", molecular weight: 538, refractive index: 1.515, liquid at 20°C, hereinafter referred to as "EB-300"), 0.3 parts of a non-cyclic difunctional isocyanate crosslinking agent (manufactured by Tosoh Corporation, trade name "Coronate 2770", hexamethylene diisocyanate (HDI) urea ester), 2 parts of acetoacetone as a crosslinking delay agent, and 1 part of a 1% ethyl acetate solution of acetoacetone iron (III) as a crosslinking catalyst (0.01 parts of non-volatile component) were added to 334 parts of this solution (100 parts of non-volatile component). The mixture was stirred and mixed to prepare acrylic adhesive composition C1.

[0253] <Preparation of Acrylic Adhesive Composition C2> Except for changing the monomer composition to 99 parts POB-A and 1 part HOA-MS, an acrylic polymer P2 solution was prepared in the same manner as the acrylic polymer P1 solution. The Mw of acrylic polymer P2 is 500,000. The acrylic polymer P2 solution was diluted with ethyl acetate to a polymer concentration of 30%, and 60 parts of the plasticizer A1 (EB-300) and 0.5 parts of epoxy crosslinking agent (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name "TETRAD C", 1,3-bis(N,N-diepoxypropylaminomethyl)cyclohexane) as crosslinking agent were added to 334 parts of this solution (100 parts of non-volatile components) and stirred to prepare acrylic adhesive composition C2.

[0254] <Preparation of Acrylic Adhesive Composition C3> Except for changing the composition of the monomer components to 95 parts POB-A, 2 parts lauryl acrylate (LA), 2 parts 2-ethylhexyl acrylate (2EHA), and 1 part 4HBA, an acrylic polymer P3 solution was prepared in the same manner as the acrylic polymer P1 solution described above. The Mw of acrylic polymer P3 is 500,000. The above-mentioned acrylic polymer P3 solution was diluted with ethyl acetate to a polymer concentration of 30%. Then, 60 parts of 3-phenoxybenzyl alcohol (manufactured by Tokyo Chemical Industry Co., Ltd., refractive index: 1.591, liquid at 20°C, hereinafter referred to as "POB-AL"), 0.3 parts of the above-mentioned isocyanate-based crosslinking agent (Coronate 2770), 2 parts of acetoacetone as a crosslinking delay agent, and 1 part of a 1% ethyl acetate solution of acetoacetone iron (III) as a crosslinking catalyst (0.01 parts of non-volatile components) were added to 334 parts of this solution (100 parts of non-volatile components). The mixture was stirred and stirred to prepare acrylic adhesive composition C3.

[0255] <Preparation of Acrylic Adhesive Composition C4> Except for changing the composition of the monomer components to 90 parts of POB-A, 9 parts of 2EHA, and 1 part of 4HBA, an acrylic polymer P4 solution was prepared in the same manner as the preparation of the acrylic polymer P1 solution. The Mw of acrylic polymer P4 is 500,000. The acrylic polymer P4 solution was diluted with ethyl acetate to a polymer concentration of 30%, and 60 parts of the plasticizer A2 (POB-AL), 0.5 parts of the isocyanate crosslinking agent (Coronate 2770), 2 parts of acetoacetone as a crosslinking delay agent, and 1 part of a 1% ethyl acetate solution of acetoacetone iron (III) as a crosslinking catalyst (0.01 parts of non-volatile component) were added to 334 parts of this solution (100 parts of non-volatile component). The mixture was stirred and mixed to prepare acrylic adhesive composition C4.

[0256] <Preparation of Acrylic Adhesive Composition C5> Except for changing the composition of the monomer components to 98 parts of POB-A, 1 part of 4HBA, and 1 part of HOA-MS, an acrylic polymer P5 solution was prepared in the same manner as the acrylic polymer P1 solution. The Mw of acrylic polymer P5 is 500,000. The acrylic polymer P5 solution was diluted with ethyl acetate to a polymer concentration of 30%, and 20 parts of the plasticizer A1 (EB-300), 0.1 parts of the isocyanate crosslinking agent (Coronate 2770), 2 parts of acetoacetone as a crosslinking delay agent, and 1 part of a 1% ethyl acetate solution of acetoacetone iron (III) as a crosslinking catalyst (0.01 parts of non-volatile component) were added to 334 parts of the solution (100 parts of non-volatile component). The mixture was stirred and mixed to prepare acrylic adhesive composition C5.

[0257] <Preparation of Acrylic Adhesive Composition C6> Except for changing the composition of the monomer components to 99 parts of n-butyl acrylate (BA) and 1 part of 4HBA, and adjusting the concentration of the monomer components during polymerization, an acrylic polymer P6 solution was prepared in the same manner as the preparation of the acrylic polymer P1 solution. The Mw of acrylic polymer P6 is 2 million. The above acrylic polymer P6 solution was diluted with ethyl acetate to a polymer concentration of 30%, and 10 parts of a 1% ethyl acetate solution of hexamethylene diisocyanate trimiocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a 3-functional isocyanate compound) as a crosslinking agent (0.1 parts of non-volatile component) was added to 334 parts of this solution (100 parts of non-volatile component) and stirred to prepare acrylic adhesive composition C6.

[0258] <Preparation of Adhesive Sheet> (Example 1) The acrylic adhesive composition C1 prepared above is coated onto the polysiloxane-treated surface of a polyethylene terephthalate (PET) film R1 (50µm thick) that has undergone polysiloxane treatment on one side. The film is heated at 130°C for 2 minutes to form an adhesive layer with a thickness of 20µm. Next, a polysiloxane-treated PET film R2 (25µm thick) that has undergone polysiloxane treatment on one side is bonded to the surface of the adhesive layer. In this manner, an adhesive layer (high refractive index adhesive layer) is obtained in a form where both sides are protected by PET films (release liner) R1 and R2. Furthermore, compared to release liner R1, release liner R2 is relatively easier to peel off. Furthermore, the aforementioned acrylic adhesive composition C6 was coated onto the polysiloxane-treated surface of a PET film R1 (50µm thick) that had undergone polysiloxane treatment on one side, and heated at 130°C for 2 minutes to form an adhesive layer with a thickness of 50µm. A PET film R2 (38µm thick) that had undergone polysiloxane treatment on one side was then bonded to the surface of the adhesive layer. In this manner, an adhesive layer (low refractive index adhesive layer) was obtained, with both sides protected by PET films (release liner) R1 and R2. The release liner R2 was peeled off from the high refractive index adhesive layer and the low refractive index adhesive layer, and the adhesive surfaces were bonded together using a hand roller. The laminate was then subjected to autoclaving at 50°C and 0.60MPa for 30 minutes, followed by curing at 50°C for 48 hours. A laminate (a substrate-free double-sided adhesive sheet) consisting of a two-layer structure of a high-refractive-index adhesive layer and a low-refractive-index adhesive layer is obtained in accordance with the above method. The surface of the adhesive sheet is protected by two release liner pads R1.

[0259] (Examples 2~5) Except for changing the type of adhesive composition used to form each adhesive layer as shown in Table 1, a laminate (substrate-free double-sided adhesive sheet) consisting of a two-layer structure of a high refractive index adhesive layer / low refractive index adhesive layer is obtained in the same manner as in Example 1.

[0260] <Measurement and Evaluation> (Refractive Index) The refractive index of each adhesive layer was measured using an Abbe refractometer (ATAGO CO., LTD., model "DR-M4") at a measurement wavelength of 589 nm and a measurement temperature of 25 °C. The results are shown in Table 1.

[0261] (Storage Modulus G') Each adhesive layer was laminated to a thickness of approximately 1.5 mm and punched into a disc shape with a diameter of 7.9 mm, which was used as the test specimen. Dynamic viscoelasticity was measured using the "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific under the following conditions. The storage modulus G' at 25°C was read from the measurement results. The results are listed in Table 1. [Measurement Conditions] Deformation mode: Torsion Measurement frequency: 1 Hz Temperature range: -50°C to 150°C Heating rate: 5°C / min Shape: Parallel plate 7.9 mm φ

[0262] (Total Light Transmittance and Haze Values) Using test pieces on which the adhesive sheets of each example were bonded to alkali-free glass (thickness 0.8~1.0 mm, total light transmittance 92%, haze 0.4%), the total light transmittance and haze of the test pieces were measured using a haze meter (Murakami Color Technology Research Institute, trade name "HAZEMETER HM-150") at a measurement environment of 23°C. The total light transmittance and haze values ​​of the adhesive sheets were obtained by subtracting the total light transmittance and haze of the alkali-free glass from the measured values. The results are shown in Table 1.

[0263] (Deformation Test) Each adhesive layer was cut into a length of 300 mm and a width of 1 mm², and rolled into a cylindrical shape at 23°C and 50% RH to obtain a test piece. A tensile testing machine (Shimadzu Corporation, device name "Autograph AG-X plus 5kN Precision Universal Testing Machine") was used to perform a deformation test (tensile test) on the test piece at -20°C, a clamping distance of 100 mm, and a tensile speed of 300 mm / min. The SS curve was obtained to evaluate whether the test piece deformed (elongated) by more than 350%. When the test piece deformed by more than 350%, the stress at 350% deformation [N / mm²] was measured. The results are listed in Table 1. In the above deformation test, adhesives that could deform by more than 350% at -20°C were judged to be adhesives capable of withstanding large deformations.

[0264] Furthermore, when the adhesive layer thickness is small, in order to improve operability, a test piece with a thickness of 5µm or more (e.g., about 5µm to 200µm) can be used to perform the above deformation test. The thickness of the test piece can be adjusted, for example, by appropriately stacking adhesive layers. Alternatively, a test piece with a thickness that is easy to deform can be made using the same adhesive composition as the adhesive layer used to form the test object, and the above deformation test can be performed on the test piece. For example, a test piece with a thickness of about 10µm to 50µm can be used to perform the above deformation test. Also, during the test, it is advisable to apply powder to the adhesive surface at the clamping point to remove the influence caused by adhesive adhesion beforehand.

[0265] [Table 1]

[0266] As shown in Table 1, the adhesive sheets in Examples 1-4 comprise: a high-refractive-index adhesive layer with a refractive index greater than 1.560 and a deformation amount of 350% or more in a deformation test performed at a temperature of -20°C and a speed of 300 mm / min, and a low-refractive-index layer. Furthermore, in the deformation test performed at a temperature of -20°C and a speed of 300 mm / min, the stress of the high-refractive-index adhesive layer at a deformation amount of 350% is 5.0 N / mm² or less. Also, the ratio (n₁ / n₂) of the refractive index n₁ of the high-refractive-index adhesive layer to the refractive index n₂ of the low-refractive-index layer is 1.05 or more. This adhesive sheet has been confirmed to have a front brightness enhancement effect evaluated by the method described in the embodiments of Japanese Patent Application Publication No. 2022-8015. It can be seen that by using the above-mentioned adhesive sheet, a light-emitting device can be constructed, which has an adhesive layer with a high refractive index and capable of withstanding large deformation on the visual side of the self-emitting element. On the other hand, although the adhesive sheet of Example 5 has a high refractive index adhesive layer with a refractive index greater than 1.560, it broke at an early stage of deformation in a deformation test at a temperature of -20°C and a speed of 300 mm, and could not withstand large deformation.

[0267] Specific examples of the present invention have been described in detail above, but these are merely illustrative and do not limit the scope of the patent application. The technology described in the patent application includes various modifications and alterations to the specific examples exemplified above. [Simplified Explanation of the Diagram]

[0011] FIG1 is a cross-sectional view schematically showing the configuration of a light-emitting device in one embodiment. FIG2 is a cross-sectional view schematically showing the configuration of a laminated sheet for a light-emitting device in one embodiment.

Claims

1. A light-emitting device, comprising: a self-emissive element; a low-refractive-index layer disposed on the viewing side of the self-emissive element; and a high-refractive-index adhesive layer deposited in direct contact with the low-refractive-index layer; wherein the high-refractive-index adhesive layer has a refractive index greater than 1.560, and undergoes a deformation test at a temperature of -20°C and a speed of 300 mm / min with a deformation amount of 350% or more.

2. The light-emitting device of claim 1, wherein the stress of the aforementioned high refractive index adhesive layer under a deformation test at a temperature of -20°C and a speed of 300 mm / min is less than 5.0 N / mm² when the deformation amount is 350%.

3. The light-emitting device as claimed in claim 1 or 2, wherein the ratio (n1 / n2) of the refractive index n1 of the aforementioned high refractive index adhesive layer to the refractive index n2 of the aforementioned low refractive index layer is 1.05 or more.

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