Light-emitting device

Abstract

To provide a light-emitting device having an adhesive layer that has a high refractive index and can withstand large deformations provided on a viewing side of a self-luminous element.SOLUTION: A light-emitting device is provided, comprising a self-luminous element, a low refractive index layer provided on a viewing side of the self-luminous element, and a high refractive index layer laminated directly on the low-refractive index layer. The high refraction index layer has a refractive index in excess of 1.560 and exhibits a deformation of 350% or more in a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a light-emitting device, and more particularly to a light-emitting device having an adhesive layer disposed on the visible side of a self-luminous element. [Background technology]

[0002] Generally, adhesives (also called pressure-sensitive adhesives; the same applies hereinafter) exhibit a soft solid (viscoelastic) state at temperatures around room temperature and have the property of easily adhering to a substrate under pressure. Taking advantage of this property, adhesives are widely used in various industrial fields, from home appliances to automobiles, various machinery, electrical equipment, and electronic equipment, for purposes such as joining, fixing, and protection. One example of an application of adhesives is in display devices such as liquid crystal displays and organic EL displays, where polarizing films, phase difference films, cover window members, and various other light-transmitting members are joined to other members. Patent documents 1 and 2 are technical documents relating to adhesives for optical components. Patent document 3 is a technical document relating to a light-emitting device having an adhesive layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-169382 [Patent Document 2] Japanese Patent Publication No. 2017-128732 [Patent Document 3] Japanese Patent Publication No. 2022-8015 [Overview of the project] [Problems that the invention aims to solve]

[0004] Patent documents 1 and 2 disclose an adhesive composition mainly composed of a (meth)acrylic acid ester polymer containing a monomer having multiple aromatic rings as a monomer unit, and an adhesive obtained by crosslinking the adhesive composition, proposing that the refractive index of the adhesive be set to 1.50 or higher, particularly preferably 1.51 or higher, by using a monomer having multiple aromatic rings. Furthermore, a technique for increasing the refractive index by blending particles made of high refractive index inorganic materials (for example, inorganic particles such as zirconium oxide particles or titanium oxide particles) into a resin is also known. However, adhesives containing inorganic particles have a trade-off relationship between refractive index and adhesive properties (e.g., peel strength, flexibility, etc.), making their application to the field of adhesives difficult. For example, when increasing the refractive index of the adhesive layer placed on the viewing side of a self-luminous element in a light-emitting device, it is necessary to consider the impact on optical properties (e.g., total light transmittance, haze, etc.) when blending inorganic particles. Against this background, the present inventors have proposed in Patent Document 3 a light-emitting device in which a high refractive index adhesive layer with high optical quality is placed on the viewing side of a self-luminous element.

[0005] In recent years, foldable displays and rollable displays have been put into practical use as displays for organic EL displays used in electronic devices such as smartphones. The adhesives used in these applications need to have the flexibility to follow the substrate that is repeatedly bent. Adhesives with excellent flexibility can easily follow and adhere to curved surfaces such as three-dimensional shapes, making them suitable for electronic devices with curved shapes. If the flexibility of adhesives with high refractive indices can be increased, they can be expected to be applied to applications that are repeatedly bent, such as the foldable displays mentioned above. However, adhesive polymers with high refractive indices tend to have high glass transition temperatures, such as having aromatic rings, and adhesives formed using high refractive index materials tend to have reduced flexibility. In adhesive design, there is a trade-off relationship between high refractive index and flexibility. If an adhesive can be realized that has a high refractive index while also having the flexibility to withstand use in applications involving large deformations, it would be useful in the foldable displays mentioned above, as it would allow for a higher refractive index in the adhesive layer placed on the viewing side of the self-luminous element.

[0006] This invention was created in view of the above circumstances, and aims to provide a light-emitting device in which an adhesive layer having a high refractive index and capable of withstanding large deformation is arranged on the visible side of the self-luminous element. [Means for solving the problem]

[0007] The light-emitting device provided in this specification includes a self-luminous element, a low refractive index layer positioned on the viewing side of the self-luminous element, and a high refractive index adhesive layer laminated in direct contact with the low refractive index layer. The high refractive index adhesive layer has a refractive index greater than 1.560 and exhibits a deformation of 350% or more in a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min. Because the high refractive index adhesive layer has a high refractive index and is capable of deformation of 350% or more in a low-temperature, high-speed deformation test, it can deform sufficiently at high speeds even in low-temperature environments and can withstand large deformations. A laminate constructed by combining a high refractive index adhesive layer satisfying the above characteristics with a low refractive index layer can be applied to applications involving large deformations, such as foldable displays, and a light-emitting device capable of improving front brightness by utilizing the high refractive index can be constructed.

[0008] In some embodiments, the high refractive index adhesive layer exhibits a stress of 5.0 N / mm² at 350% deformation in a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min. 2 The following is preferable: An adhesive satisfying the above characteristics has a high refractive index and can be sufficiently deformed at high speed while maintaining a certain level of flexibility even in low-temperature environments. Therefore, it is suitable as a high refractive index adhesive layer for applications involving large deformations.

[0009] In some embodiments, 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 preferably approximately 1.05 or higher. This makes it easier to obtain a front brightness improvement effect.

[0010] Furthermore, combinations of the elements described herein may also be included within the scope of the invention for which patent protection is sought in this patent application. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing the configuration of a light-emitting device according to one embodiment. [Figure 2] This is a schematic cross-sectional view showing the configuration of a laminated sheet used in a light-emitting device according to one embodiment. [Modes for carrying out the invention]

[0012] Preferred embodiments of the present invention are described below. Matters other than those specifically mentioned herein that are necessary for carrying out the present invention can be understood by those skilled in the art based on the teachings on carrying out the invention described herein and the common technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed herein and the common technical knowledge in the art. In the following drawings, components and parts that perform the same function may be denoted by the same reference numeral and described accordingly, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic representations for the purpose of clearly illustrating the present invention and do not necessarily accurately represent the size or scale of the actual product provided.

[0013] In this specification, "self-luminous element" means a light-emitting element whose luminescence can be controlled by the value of the current flowing through it. A self-luminous element may consist of a single element or an assembly of elements. Specific examples of self-luminous elements include, but are not limited to, light-emitting diodes (LEDs) and organic ELs. The light-emitting devices disclosed herein include such self-luminous elements as components. Examples of the above-mentioned light-emitting devices include, but are not limited to, light source module devices used for illumination (e.g., planar light-emitting module) and display devices with pixels formed therein.

[0014] The technical matters disclosed in this specification include light-emitting devices, high refractive index adhesive layers and adhesive compositions used for forming them, low refractive index layers and compositions used for forming them, laminated sheets (adhesive sheets) comprising a high refractive index adhesive layer and a low refractive index layer, laminated sheets with a release liner in which the adhesive surface of the laminated sheet is protected by a release liner, and the like.

[0015] <Example of a light-emitting device configuration> Figure 1 shows an example configuration of a light-emitting device provided by this specification. The light-emitting device 100 shown in Figure 1 includes a self-luminous element 70, a low refractive index layer 12 positioned on the viewing side of the self-luminous element 70, and a high refractive index adhesive layer 11 laminated in direct contact with the low refractive index layer 12. The light-emitting device 100 may further include a cover window member 80 positioned on the viewing side of the high refractive index adhesive layer 11. In the light-emitting device 100 shown in Figure 1, a laminated sheet 10 consisting of the high refractive index adhesive layer 11 and the low refractive index layer 12 is positioned between the self-luminous element 70 and the cover window member 80. One or more layers (not shown) may be interposed independently between the self-luminous element 70 and the low refractive index layer 12, between the high refractive index adhesive layer 11 and the cover window member 80, and further on the viewing side of the cover window member 80, or they may not be interposed. Alternatively, contrary to Figure 1, the high refractive index adhesive layer 11 may be positioned on the self-luminous element side and the low refractive index layer 12 on the cover window member side.

[0016] In the technologies disclosed herein, the low refractive index layer may be adhesive or non-adhesive. In some embodiments, the low refractive index layer is preferably an adhesive layer, i.e., a low refractive index adhesive layer. This makes the laminated sheet (adhesive sheet) of the low refractive index adhesive layer and the high refractive index adhesive layer double-sided adhesive, improving assembly in the manufacture of the light-emitting device. Such a laminated sheet may be in the form of a laminated sheet with a release liner, for example, as shown in Figure 2, before being incorporated into the light-emitting device, a laminated sheet 10 (substrate-less double-sided adhesive sheet 2) consisting of a high refractive index adhesive layer 11 and a low refractive index adhesive layer 12, where the surface (first surface) 10A on the high refractive index adhesive layer 11 side of the laminated sheet 10 is the first adhesive surface, and the surface (second surface) 10B on the low refractive index adhesive layer 12 side is 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 laminated in direct contact with a low-refractive-index layer contained in the light-emitting device. This high-refractive-index adhesive layer has a relatively higher refractive index than the low-refractive-index layer. Preferably, the high-refractive-index adhesive layer has a refractive index greater than 1.560 and exhibits a deformation of 350% or more in a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min. Thus, a high-refractive-index adhesive layer that has a high refractive index and can deform by 350% or more in a low-temperature, high-speed deformation test can deform sufficiently at high speeds even in low-temperature environments and can withstand large deformations. A laminate constructed by combining a high-refractive-index adhesive layer satisfying the above characteristics with a low-refractive-index layer can be applied to applications involving large deformations, such as foldable displays, and a light-emitting device capable of improving front brightness by utilizing the high refractive index of the high-refractive-index adhesive layer can be constructed.

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

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

[0020] The technical matters provided in this specification include an adhesive layer having a refractive index greater than 1.560 (high refractive index adhesive layer), an adhesive composition capable of forming the adhesive layer, and a laminated sheet containing the high refractive index adhesive layer. The laminated sheet may be, for example, a laminated adhesive layer consisting of the high refractive index adhesive layer and a low refractive index layer (typically a low refractive index adhesive layer), and may be configured in which the high refractive index adhesive layer and the low refractive index layer are laminated on one surface of a support substrate in this order or in the reverse order.

[0021] In some embodiments, the refractive index of the high refractive index adhesive layer is, for example, 1.563 or higher, preferably 1.565 or higher, and more preferably greater than 1.570. In some preferred embodiments, the refractive index of the 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. With a high refractive index adhesive layer having such a refractive index, the behavior of light transmitted through the high refractive index adhesive layer can be effectively controlled by utilizing the relationship of the relative refractive indices between the high refractive index adhesive layer and the directly adjacent low refractive index layer (typically a low refractive index adhesive layer). The preferred upper limit of the refractive index of the high refractive index adhesive layer is not limited to a specific range, as it may vary depending on the refractive index of the adjacent layer, etc. In some embodiments, considering the balance of flexibility, adhesive properties, transparency, etc., the refractive index of the high refractive index adhesive layer may be, for example, 1.700 or less, 1.670 or less, 1.650 or less, 1.620 or less, or 1.600 or less.

[0022] (Deformation characteristics) In some embodiments, the high refractive index adhesive layer preferably has a refractive index greater than 1.560, and also exhibits a deformation of 350% or more in a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min. Since the high refractive index adhesive layer satisfies the above characteristics while having a high refractive index, it can deform sufficiently at high speeds even in low-temperature environments and can withstand large deformations. A high refractive index adhesive layer satisfying the above characteristics preferably has a high refractive index and can withstand use in applications involving large deformations, such as foldable displays. The high refractive index adhesive layers disclosed herein encompass embodiments without the limitation of the above characteristics (deformation of 350% or more in a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min), and in such embodiments, the high refractive index adhesive layer is not limited to satisfying the above characteristics.

[0023] In some embodiments, the high refractive index adhesive layer preferably has a stress of 5.0 N / mm at a deformation amount of 350% in a deformation test performed at a temperature of -20°C and a speed of 300 mm / min. 2 The high refractive index adhesive layer satisfying the above characteristics can be highly deformed at high speed while maintaining a predetermined level of flexibility even in a low temperature environment while having a high refractive index. Therefore, it is suitable for use in applications involving large deformations. In some preferred embodiments, the stress at a deformation amount of 350% is 4.9 N / mm 2 or less, 4.8 N / mm 2 or less, 4.7 N / mm 2 or less, 4.6 N / mm 2 or less, or may be 4.5 N / mm 2 or less, 4.4 N / mm 2 or less, 4.3 N / mm 2 or less, 4.2 N / mm 2 or less, 4.1 N / mm 2 or less, 4.0 N / mm 2 or less, 3.9 N / mm 2 or less, 3.8 N / mm 2 or less, 3.7 N / mm 2 or less, 3.6 N / mm 2 or less, 3.5 N / mm 2 or less, 3.4 N / mm 2 or less, 3.3 N / mm 2 or less, 3.2 N / mm 2 or less, 3.1 N / mm 2 or less, 3.0 N / mm 2 or less, 2.9 N / mm 2 or less, 2.8 N / mm 2 or less, 2.7 N / mm 2 or less, 2.6 N / mm 2 or less, 2.5 N / mm 2 or less, 2.4 N / mm 2 or less, 2.3 N / mm 2 or less, or may be 2.2 N / mm 2 The lower limit of the stress at a deformation amount of 350% is theoretically 0.0 N / mm 2 or more, and in some preferred embodiments, 0.1 N / mm 2 or more, 0.2 N / mm 2Above, 0.3 N / mm 2 Above, 0.4N / mm 2 Above, 0.5N / mm 2 Above, 0.6 N / mm 2 Above, 0.7N / mm 2 Above, 0.8 N / mm 2 Above, 0.9 N / mm 2 Above, 1.0 N / mm 2 Above, 1.1 N / mm 2 Above, 1.2 N / mm 2 Above, 1.3 N / mm 2 Above, 1.4 N / mm 2 Above, 1.5N / mm 2 Above, 1.6 N / mm 2 Above, 1.7N / mm 2 Above, 1.8 N / mm 2 Above, 1.9 N / mm 2 Above, 2.0 N / mm 2 Above, 2.1 N / mm 2 Above is 2.2N / mm 2 The above is the same as the above, 2.3N / mm 2 Above, 2.4 N / mm 2 Above, 2.5N / mm 2 Above, 2.6 N / mm 2 Above, 2.7N / mm 2 Above, 2.8 N / mm 2 Above, 2.9 N / mm 2 Above, 3.0 N / mm 2 Above, 3.1 N / mm 2 Above, 3.2 N / mm 2 Above, 3.3 N / mm 2 Above, 3.4 N / mm 2 Above, 3.5N / mm 2 Above, 3.6 N / mm 2 Above, 3.7N / mm 2 Above, 3.8 N / mm 2 Above, 3.9 N / mm 2 Above, 4.0 N / mm 2 Above, 4.1 N / mm 2 Above, 4.2 N / mm 2 Above, 4.3 N / mm 2 Above, 4.4 N / mm 2 Above, 4.5 N / mm 2Above or above, or 4.6 N / mm² 2 The above is also acceptable. A high refractive index adhesive layer having stress at the above deformation amount of 350% can be flexible while possessing appropriate cohesive force.

[0024] In some embodiments, it is preferable that the high refractive index adhesive layer has a ratio (S(-20°C) / S(25°C)) of 50 or less between the stress S(-20°C) at 350% deformation in a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min, and the stress S(25°C) at 350% deformation in a deformation test conducted at a temperature of 25°C and a speed of 300 mm / min. A high refractive index adhesive layer satisfying the above characteristics can exhibit stable performance over a wide temperature range, including low temperatures. In some preferred embodiments, the above ratio (S(-20℃) / S(25℃)) may 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, and may also 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 0 or greater, and in some preferred embodiments it may be 1 or greater, 2 or greater, 3 or greater, 4 or greater, 5 or greater, 6 or greater, 7 or greater, 8 or greater, 9 or greater, 10 or greater, 11 or greater, 12 or greater, 13 or greater, 14 or greater, or 15 or greater, and may also be 16 or greater, 17 or greater, 18 or greater, 19 or greater, 20 or greater, 21 or greater, 22 or greater, 23 or greater, 24 or greater, 25 or greater, 26 or greater, 27 or greater, 28 or greater, 29 or greater, 30 or greater, or 31 or greater.

[0025] The deformation test conducted under the above conditions of -20°C and a speed of 300 mm / min is carried out more specifically by the method described in the test examples below. The deformation test conducted under the above conditions of 25°C and a speed of 300 mm / min is carried out in the same manner as the deformation test at -20°C, except that the temperature is changed to 25°C, and the stress at 350% deformation [N / mm 2By measuring [the stress], the ratio (S(-20°C) / S(25°C)) of the stress S(-20°C) at 350% deformation in a deformation test conducted under the conditions of temperature -20°C and speed 300 mm / min, and the stress S(25°C) at 350% deformation in a deformation test conducted under the conditions of temperature 25°C and speed 300 mm / min, can be determined.

[0026] The 350% deformability, stress at 350% deformation, and ratio (S(-20°C) / S(25°C)) of the high refractive index adhesive layer under conditions of -20°C and a speed of 300 mm / min 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 and amount of plasticizer used, whether or not to use crosslinking agents, and selecting the type and amount used, and whether or not to use additives, and selecting the type and amount used, etc.

[0027] (Storage modulus G') In some embodiments, the high refractive index adhesive layer has a storage modulus G'(0°C) of 1.0 × 10⁻¹⁰ 4 Pa~1.0×10 6 It is within the range of Pa. According to the above high refractive index adhesive layer, while having a high refractive index, the range of the storage modulus G'(0°C) is suppressed to a low range, thus achieving both high refractive index and flexibility. A high refractive index adhesive layer having a storage modulus G'(0°C) within the above range can achieve both high refractive index and flexibility, and may have the flexibility to withstand repeated bending operations. The above storage modulus G'(0°C) is preferably 5.0 × 10 5 It is less than or equal to Pa, and 2.0 × 10 5 It may be less than or equal to Pa, 1.0 × 10 5 It is also acceptable to have a value of less than Pa, 7.0 × 10 4 It is also acceptable to have a value of less than Pa, 5.0 × 10 4 It is also acceptable to have a value of less than Pa, 3.0 × 10 4 It may be less than Pa. Furthermore, the storage modulus G'(0℃) is preferably 2.0 × 10⁻⁶. 4 Pa or higher, more preferably 4.0 × 10 4 It is Pa or higher, 6.0 × 10 4 It can be Pa or higher, 1.0 × 105 It may also be above Pa.

[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 1.0×10 10 Pa, may be less than 1.0×10 9 Pa, may be less than 5.0×10 8 Pa, and it is appropriate that it is 1.0×10 8 Pa or less, may be 1.0×10 7 Pa or less, may be 1.0×10 7 Pa or less, may be 1.0×10 6 Pa or less, may be 1.0×10 6 Pa or less, may be 5.0×10 5 Pa or less. The high refractive index adhesive layer with the storage modulus G'(-20°C) restricted as above can have excellent flexibility. For example, it can have good flexibility in a lower temperature range and can withstand repeated bending operations in a wide temperature range including the low temperature range. The lower limit of the above storage modulus G'(-20°C) is not particularly limited. For example, it is 1.0×10 2 Pa or more, 1.0×10 3 Pa or more, and preferably it is 1.0×10 4 Pa or more, more preferably 1.0×10 5 Pa or more, and may be 5.0×10 5 Pa or more, may be 1.0×10 6 Pa or more. The high refractive index adhesive layer having the above storage modulus G'(-20°C) can have appropriate cohesive force while having flexibility. Also, according to the high refractive index adhesive layer having the above storage modulus G'(-20°C), there is a tendency that it is easy to achieve both high refractive index and flexibility even in a low temperature range.

[0029] The storage modulus G'(25°C) of the high refractive index adhesive layer disclosed herein is appropriately set according to the purpose of use, mode of use, etc., and is not limited to a specific range. From the viewpoint of ease of attachment to the adherend, etc., for example, 1.0×10 6It is appropriate for the pressure to be less than Pa, preferably 5.0 × 10⁻⁶. 5 Less than Pa, more preferably 3.0 × 10 5 It is less than Pa, and 1.0 × 10 5 It may be less than Pa, 5.0 × 10 4 It may be less than Pa. As described above, the high refractive index adhesive layer with a limited storage modulus G'(25°C) has good flexibility at normal operating temperatures such as room temperature. The lower limit of the storage modulus G'(25°C) is not particularly limited and can be set to, for example, 1.0 × 10 from the viewpoint of processability, handling, etc., and considering the high refractive index. 2 It is Pa or higher, 5.0 × 10 2 It is appropriate for the Pa level to be above, preferably 1.0 × 10⁻⁶. 3 Pa or higher, more preferably 3.0 × 10 3 It is Pa or higher, 5.0 × 10 3 Pa or higher is also acceptable. The high refractive index adhesive layer having the above storage modulus G' (25°C) tends to have appropriate cohesive force even in high-temperature ranges and has excellent heat resistance, making it preferable.

[0030] In some embodiments, the storage modulus G'(25°C) of the high refractive index adhesive layer at 25°C is preferably lower than the storage modulus G'(25°C) of the low refractive index layer, which will be described later. With this configuration, adhesion and flexibility are imparted to the laminate of the high refractive index adhesive layer and the low refractive index layer, improving the ability to follow steps and curved surfaces, and enabling the realization of a laminated sheet (adhesive sheet) that can be suitably applied to a variety of device designs.

[0031] (Storage modulus ratio) In some embodiments, the high refractive index adhesive layer is an adhesive in which the ratio of the storage modulus G'(0°C) at 0°C to the storage modulus G'(25°C) at 25°C (G'(0°C) / G'(25°C)) is in the range of 1 to 1000. A high refractive index adhesive layer satisfying the above characteristics suppresses changes in the modulus over a wide temperature range from 0°C to room temperature, making it easy to exhibit stable properties (flexibility, etc.) with respect to temperature changes. The above ratio (G'(0°C) / G'(25°C)) is suitable to be 300 or less, preferably 100 or less, more preferably 50 or less, and may also be 25 or less, 10 or less, or 5 or less. The lower limit of the above ratio (G'(0°C) / G'(25°C)) may be, for example, 2 or more, or 3 or more.

[0032] In some embodiments, the high refractive index adhesive layer is an adhesive in which the ratio of the storage modulus G'(-20°C) at -20°C to the storage modulus G'(25°C) at 25°C (G'(-20°C) / G'(25°C)) is in the range of 1 to 1000. A high refractive index adhesive layer satisfying the above characteristics suppresses changes in the modulus over a wide temperature range from lower temperatures to room temperature, thus exhibiting stable properties (flexibility, etc.) with respect to temperature changes. The above ratio (G'(-20°C) / G'(25°C)) may 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°C) / G'(25°C)) may 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 range and cohesive force (heat resistance, etc.) in the high temperature range. In some embodiments, the Tg of the high refractive index adhesive layer is, for example, 30°C or less, may be 15°C or less, or 5°C or less. In some preferred embodiments, the Tg of the high refractive index adhesive layer is 0°C or less from the viewpoint of flexibility, more preferably -5°C or less, even more preferably -10°C or less, and may be -15°C or less (e.g., -20°C or less). The lower the Tg of the high refractive index adhesive layer, the better the adhesive properties, such as adhesion to the adherend. Also, by setting the Tg of the high refractive index adhesive layer low, it is possible to suppress changes in the elastic modulus in the temperature range higher than Tg. The lower limit of the Tg of the high refractive index adhesive layer is, for example, -50°C or higher, -40°C or higher is appropriate, may be -30°C or higher, or -25°C or higher. A high refractive index adhesive layer having the above Tg tends to easily obtain appropriate cohesive force. Furthermore, it tends to easily form adhesives that combine a high refractive index with high deformability.

[0034] The storage modulus G' and glass transition temperature of the adhesive layer at each of the above temperatures can be measured by the dynamic viscoelasticity measurement method described in the test examples below, and each storage modulus ratio can be calculated from the results. The storage modulus G', each storage modulus ratio, and 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 and amount of plasticizer used, whether or not to use a crosslinking agent, and selecting the type and amount used, and whether or not to use an additive, and selecting the type and amount used.

[0035] (Change in elastic modulus after holding at 130°C for 1 hour) While not particularly limited, in some embodiments, it is preferable to use an adhesive as a high refractive index adhesive layer in which the ratio (G'1 / G'0) of the storage modulus G'1 at -20°C after holding the adhesive in a 130°C environment for 1 hour to the storage modulus G'0 at -20°C before holding it in a 130°C environment for 1 hour is 50 or less (specifically, 1 to 50). A high refractive index adhesive layer satisfying this characteristic can exhibit stable properties, as the change in elastic modulus is limited to 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, even more preferably 3 or less, and may be 2 or less, or less than 1.5.

[0036] The change in elastic modulus after holding at 130°C for 1 hour is measured by the following method. Specifically, the adhesive composition is applied to the silicone-treated side of PET film R1, which has a silicone treatment on one side, and heated at 130°C for 3 minutes to form an adhesive layer with a thickness of 20 μm. Next, the silicone-treated side of PET film R2, which has a silicone treatment on one side, is bonded to the surface of the adhesive layer. One of the release liners is peeled off from the resulting adhesive layer with release liner (release liner / adhesive layer / release liner), and it is held in an oven at 130°C for 1 hour. The oven used should have sufficient capacity for the measurement sample and be capable of heating while exhausting. For example, an oven manufactured by espec can be used. After the adhesive (layers) have been held at 130°C for 1 hour, they are stacked to a thickness of approximately 1.5 mm, and then autoclaved (0.5 MPa, 50°C, 15 minutes) to adhere each layer. For the sample obtained in this manner, the storage modulus G'(G'1)[Pa] at -20°C after being held in a 130°C environment for 1 hour is determined using the same method as for measuring the storage modulus G' described above. Then, the ratio (G'1 / G'0) of the obtained storage modulus G'1[Pa] to the storage modulus G'0[Pa] at -20°C before being held in a 130°C environment for 1 hour, which was measured beforehand, is determined.

[0037] (Total light transmittance) In some embodiments, the total light transmittance of the high refractive index adhesive layer is preferably 85.0% or higher (for example, 86.0% or higher, 88.0% or higher, 90.0% or higher, or greater than 90.0%). Theoretically, the upper limit of the total light transmittance is the value obtained by subtracting the light loss due to reflection at the air interface (Fresnel loss) from 100%, and in practice, it may be approximately 98% or less, approximately 96% or less, or approximately 95% or less. In some embodiments, considering the refractive index and adhesive properties, the total light transmittance of the high refractive index adhesive layer may be approximately 94% or less, approximately 93% or less, or approximately 92% or less. These total light transmittances for the high refractive index adhesive layer can also be preferably applied to the total light transmittance of a laminated sheet consisting of the high refractive index adhesive layer and the low refractive index layer (typically a low refractive index adhesive layer) described later.

[0038] The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. The transmittance meter used is the "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory, or an equivalent product. The 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 and thickness of the adhesive layer. Note that the above total light transmittance is sometimes referred to as the initial total light transmittance to distinguish it from the total light transmittance after the bending test described later.

[0039] Furthermore, in some embodiments, it is preferable that the high refractive index adhesive layer maintains a total light transmittance of the bent portion (total light transmittance after the bending test) at 85% or more of the total light transmittance before the bending test after 10 repetitions of a bending test, in which each side of the sheet-like adhesive is bent into a U-shape with a radius of 2 mm at 25°C. A high refractive index adhesive layer satisfying the above characteristics exhibits little change in optical properties (e.g., whitening) even with repeated bending, making it suitable for optical applications where bending is expected, such as foldable displays. The total light transmittance after the bending test is more preferably 90% or more, even more preferably 95% or more, and particularly preferably 98% or more (e.g., 99% or more) of the total light transmittance before the bending test. The total light transmittance after the above 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 and amount of plasticizer used, whether or not to use a crosslinking agent, and selecting the type and amount used, whether or not to use an additive, and selecting the type and amount used, etc.

[0040] The total light transmittance before and after the bending test described above is measured more specifically by the following method. Specifically, the adhesive layer is cut into a rectangle of 2 cm x 10 cm to obtain a test specimen. A cylindrical rod with a diameter of φ4 mm is fixed horizontally at a height sufficient for measurement, and the test specimen obtained above is placed on the rod, with one side bent into a U shape with a radius of 2 mm and held for 1 minute. Specifically, the test specimen is placed on the rod at its central part in the longitudinal direction to form an inverted U shape. The two ends located at the bottom of the test specimen are fixed with clips (13 g), and a 60 g weight is suspended from the clips via a 1 cm long thread, applying a load to the bent part of the test specimen. In this state, the test specimen is held in a predetermined temperature environment (25 °C) for 1 minute, and after 1 minute, the test specimen is removed from the rod. Next, under the same temperature conditions, the other side of the test specimen (the side opposite to the first side) is also bent into a U-shape with a radius of 2 mm on the opposite side of the bent portion of the first side, and held for 1 minute. This bending test, which constitutes one set, is repeated 10 times on the same bent portion of the test specimen. After that, the total light transmittance [%] after bending is measured on the bent portion using the same method as the initial total light transmittance measurement method.

[0041] (Haze value) In some embodiments, 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, and may also be 0.9% or less, 0.8% or less, 0.5% or less, or 0.3% or less. Such highly transparent adhesives are advantageous in applications requiring high light transmittance (e.g., optical applications) or applications where good visibility of the adherend through the adhesive is required. The lower limit of the haze value of the high refractive index adhesive layer is not particularly limited, and from the viewpoint of improving transparency, a smaller haze value is preferable. On the other hand, in some embodiments, considering the refractive index and adhesive properties, the haze value of the high refractive index adhesive layer may be, for example, 0.05% or more, or 0.10% or more. These haze values ​​for the high refractive index adhesive layer can also be suitably applied to the haze value of a laminated sheet consisting 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 diffusely transmitted light to total transmitted light when visible light is shone on the object being measured. It is also called the cloudiness 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 scattered 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, for example, by selecting the composition and thickness of the adhesive layer.

[0043] (Surface smoothness of the adhesive surface) In some embodiments, it is preferable that the surface (adhesive surface) of the high refractive index adhesive layer has high surface smoothness.

[0044] For example, it is preferable that the arithmetic mean roughness Ra of the adhesive surface is limited to a predetermined value or less. A configuration having an adhesive surface designed to have a low arithmetic mean roughness Ra is preferable from the viewpoint of optical homogeneity. By limiting the arithmetic mean roughness Ra, it is possible to suppress the occurrence of brightness unevenness caused by the surface state of the adhesive layer in usage modes in which light is extracted through the adhesive surface (such as an adhesive sheet placed on the viewpoint side of the self-luminous element in a light-emitting device). A low arithmetic mean roughness Ra of the adhesive surface is also advantageous in suppressing optical distortion, and suppression of optical distortion also contributes to the improvement of optical homogeneity. When the laminated sheet (adhesive sheet) disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface (for example, a laminated sheet consisting 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 a predetermined value or less, and it is more preferable that the arithmetic mean roughness Ra of both adhesive surfaces is limited to a predetermined value or less. Each adhesive surface of the double-sided adhesive sheet has high surface smoothness, which can preferably achieve adhesion with excellent optical homogeneity.

[0045] In some embodiments, the arithmetic mean roughness Ra of the adhesive surface is preferably about 70 nm or less, more preferably about 65 nm or less, even 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, etc., in some embodiments, the arithmetic mean roughness Ra of the adhesive surface may be, for example, about 10 nm or more, about 20 nm or more, or about 30 nm or more (for example, about 40 nm or more). In embodiments in which the laminated sheet has 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 of the same magnitude or may be different.

[0046] Furthermore, for example, it is preferable that the maximum height Rz of the adhesive surface is limited to a predetermined value or less. A configuration having an adhesive surface designed to have a low maximum height Rz is preferable from the viewpoint of optical homogeneity. By limiting the maximum height Rz, for example, in usage embodiments where light is extracted through the adhesive surface as described above, it is possible to suppress the occurrence of brightness unevenness caused by the surface condition of the adhesive layer. A low maximum height Rz of the adhesive surface is also advantageous in suppressing optical distortion. When the laminated sheet disclosed herein is in the form of 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 a predetermined value or less, and it is more preferable that the maximum height Rz of both adhesive surfaces is limited to a predetermined value or less. By having high surface smoothness on each adhesive surface of the double-sided adhesive sheet, adhesion with excellent optical homogeneity can be preferably achieved.

[0047] In some embodiments, the maximum height Rz of the adhesive surface is preferably about 600 nm or less, more preferably about 500 nm or less, even more preferably about 450 nm or less, particularly preferably about 400 nm or less, and may be less than 350 nm, less than 300 nm, or less than 250 nm. From the viewpoint of production efficiency, etc., in some embodiments, the maximum height Rz of the adhesive surface may be, for example, about 10 nm or more, about 50 nm or more, about 100 nm or more, or about 200 nm or more. In embodiments 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 about 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. As the non-contact surface roughness measuring device, an optical interference surface roughness measuring device is used, for example, a 3D optical profiler (product name "NewView7300", manufactured by ZYGO) or an equivalent can be used. Specifically, the arithmetic mean roughness Ra and maximum height Rz can be measured, for example, by the following measurement method, or by setting the measurement operation and measurement conditions to obtain results equivalent to or corresponding to those obtained by the said measurement method.

[0049] Specifically, the surface shape of the sample to be measured is measured under the following conditions using a 3D optical profiler (product name "NewView7300", manufactured by ZYGO) in an environment of 23°C and 50% RH. The arithmetic surface roughness Ra is calculated from the measured data in accordance with JIS B 0601-2001. The maximum height Rz is determined as the sum of the height Rp of the highest peak above the mean line of the roughness curve obtained from the above measurement and the depth Rv of the deepest valley below the mean line. The measurement is performed 5 times (i.e., N=5), and the average value is used. The above-mentioned measurement sample can be prepared, for example, by cutting the adhesive layer to be measured or an adhesive sheet containing the adhesive layer to a size of approximately 150 mm in length and 50 mm in width. If the adhesive surface is protected by a release liner, the release liner should be gently peeled off (for example, under conditions of a tensile speed of 300 mm / min and a peeling angle of 180°) to expose the adhesive surface. It is desirable to allow the sample to stand for about 30 minutes after the adhesive surface is exposed before performing the measurement. [Measurement conditions] Measurement area: 5.62mm x 4.22mm (Objective lens: 2.5x, Internal lens: 0.5x) Analysis 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 and properties (viscosity, leveling properties, etc.) of the adhesive composition used to form the adhesive layer, and the properties of the surface (release surface) of the release liner protecting the adhesive surface.

[0051] (Base polymer) In the technology disclosed herein, the type of adhesive constituting the high refractive index adhesive layer is not particularly limited. The adhesive may contain one or more types of rubber-like polymers that can be used in the field of adhesives, such as acrylic polymers, rubber polymers (natural rubber, synthetic rubber, mixtures thereof, etc.), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine polymers, as the adhesive polymer (meaning the structural polymer that forms the adhesive, hereinafter also referred to as the "base polymer"). From the viewpoint of adhesive performance and cost, an adhesive containing an acrylic polymer or a rubber polymer as the base polymer is preferably used. Among these, an adhesive using an acrylic polymer as the base polymer (acrylic adhesive) is preferred. The technology disclosed herein is preferably implemented in a manner that uses an acrylic adhesive.

[0052] The following description will primarily focus on high-refractive-index adhesive layers composed of acrylic adhesives, but the intention is not to limit the high-refractive-index adhesive layer in the disclosed technology to acrylic adhesive layers.

[0053] In this specification, the term "base polymer" of an adhesive refers to the main component of the rubbery polymer contained in the adhesive, and is not to be interpreted in any other way. The rubbery polymer refers to a polymer that exhibits rubber elasticity in the temperature range around room temperature. In addition, in this specification, unless otherwise specified, "main component" refers to a component that is present in an amount exceeding 50% by weight. Furthermore, in this specification, "acrylic polymer" refers to a polymer that contains monomer units derived from monomers having at least one (meth)acryloyl group in one molecule as monomer units constituting the polymer. Hereinafter, monomers having at least one (meth)acryloyl group in one molecule will also be referred to as "acrylic monomers." Therefore, in this specification, acrylic polymers are defined as polymers that contain monomer units derived from acrylic monomers. A typical example of an acrylic polymer is a polymer in which the proportion of acrylic monomers among the total monomers used in the synthesis of the acrylic polymer is more than 50% by weight (preferably more than 70% by weight, for example more than 90% by weight). Furthermore, in this specification, "(meth)acryloyl" comprehensively refers to acryloyl and methacryloyl. Similarly, "(meth)acrylate" comprehensively refers to acrylate and methacrylate, and "(meth)acrylic" comprehensively refers to acrylic and methacrylic. Therefore, the concept of acrylic monomers as used herein may encompass both monomers having an acryloyl group (acrylic monomers) and monomers having a methacryloyl group (methacrylic monomers).

[0054] (Acrylic polymer) As the high refractive index adhesive layer disclosed herein, an acrylic adhesive layer (high refractive index acrylic adhesive layer) may be preferably used. As the acrylic polymer that is the base polymer of the above acrylic adhesive, it is preferable that the acrylic polymer contains an aromatic ring-containing monomer (A1) as a monomer component constituting the acrylic polymer. That is, an acrylic polymer containing an aromatic ring-containing monomer (A1) as a monomer unit is preferred. Hereinafter, "monomer component constituting the acrylic polymer" means a monomer that constitutes a repeating unit of the acrylic polymer in the adhesive formed from the adhesive composition, regardless of whether it is included 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. That is, the monomer component constituting the acrylic polymer may be included in the adhesive composition in the form of a polymer, an unpolymerized or partially polymerized product. From the viewpoint of ease of preparation of the adhesive composition, etc., in some embodiments, an adhesive composition containing substantially all (for example, 95% by weight or more, preferably 99% by weight or more) of the monomer component in the form of a polymer is preferred.

[0055] (Monomer (A1)) As monomer (A1), a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule is used. Monomer (A1) can be one of these compounds alone or two or more compounds in combination.

[0056] Examples of the ethylenically unsaturated groups mentioned above include (meth)acryloyl groups, vinyl groups, and (meth)allyl groups. From the viewpoint of polymerization reactivity, (meth)acryloyl groups are preferred, and from the viewpoint of flexibility and tackiness, acryloyl groups are more preferred. From the viewpoint of suppressing the decrease in flexibility of the high refractive index adhesive layer, a compound having one ethylenically unsaturated group in one molecule (i.e., a monofunctional monomer) is preferably used as the monomer (A1).

[0057] The number of aromatic rings contained in one molecule of the compound used as monomer (A1) may be 1 or 2 or more. There is no particular upper limit to the number of aromatic rings, and it may be, for example, 16 or less. In some embodiments, from the viewpoint of ease of preparation of the acrylic polymer and transparency of the adhesive, the number of aromatic rings may be, for example, 12 or less, preferably 8 or less, more preferably 6 or less, may be 5 or less, may be 4 or less, may be 3 or less, or may be 2 or less.

[0058] The aromatic ring of the compound used as monomer (A1) may be a carbon ring such as a benzene ring (which may be a benzene ring that constitutes part of a biphenyl or fluorene structure); a fused ring of a naphthalene ring, indene ring, azulene ring, anthracene ring, or phenanthrene ring; or it may be a heterocycle such as a pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, pyrrole ring, pyrazole ring, imidazole ring, triazole ring, oxazole ring, isoxazole ring, thiazole ring, or thiophene ring. The heteroatoms included as ring constituent atoms in the above heterocycle may be one or more selected from the group consisting of, for example, nitrogen, sulfur, and oxygen. In some embodiments, the heteroatoms constituting the above heterocycle may be nitrogen and sulfur, or both. Monomer (A1) may have a structure in which one or more carbon rings and one or more heterocycles are fused, such as a dinaphthothiophene structure.

[0059] The above aromatic ring (preferably a carbocyclic ring) may have one or more substituents on its ring constituent atoms, or it may not have substituents. If substituents are present, examples of such substituents include, but are not limited to, alkyl groups, alkoxy groups, aryloxy groups, hydroxyl groups, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl groups, hydroxyalkyloxy groups, glycidyloxy groups, etc. In substituents containing carbon atoms, the number of carbon atoms included in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. In some embodiments, the above aromatic ring may have no substituents on its ring constituent atoms, or it may be an aromatic ring having one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, and halogen atoms (e.g., bromine atoms). Note that when an aromatic ring of monomer (A1) is said to have substituents on its ring constituent atoms, it means that the aromatic ring has substituents other than substituents having an ethylenically unsaturated group.

[0060] The aromatic ring and the ethylenically unsaturated group may be directly bonded or bonded via a linking group. The linking group may be a group comprising one or more structures selected from, for example, alkylene groups, oxyalkylene groups, poly(oxyalkylene) groups, phenyl groups, alkylphenyl groups, alkoxyphenyl groups, groups in which one or more hydrogen atoms are substituted with hydroxyl groups (e.g., hydroxyalkylene groups), oxy groups (-O- groups), thiooxy groups (-S- groups), etc. In some embodiments, aromatic ring-containing monomers may be preferred in which the aromatic ring and the ethylenically unsaturated group are directly bonded or bonded via a linking group selected from the group consisting of alkylene groups, oxyalkylene groups, and poly(oxyalkylene) groups. The number of carbon atoms in the alkylene group and the oxyalkylene group is preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. The number of repeating oxyalkylene units in the poly(oxyalkylene) group may be, for example, 2 to 3.

[0061] Examples of compounds that can be preferably used as monomer (A1) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. Aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds can each be used individually or in combination of two or more. One or more aromatic ring-containing (meth)acrylates may be used in combination with one or more aromatic ring-containing vinyl compounds.

[0062] In some preferred embodiments, monomers having two or more aromatic rings (preferably carbocyclic rings) in one molecule are used as monomer (A1) because a high refractive index effect is easily obtained. Examples of monomers having two or more aromatic rings in one molecule (multiple aromatic ring-containing monomers) include monomers having a structure in which two or more non-condensed aromatic rings are linked via linking groups, monomers having a structure in which two or more non-condensed aromatic rings are chemically bonded directly (i.e., without other atoms), monomers having a condensed aromatic ring structure, monomers having a fluorene structure, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, and so on. Among these, monomers having a structure in which two or more non-condensed aromatic rings are linked via linking groups (for example, phenoxybenzyl (meth)acrylate, described later) are preferably used. Multiple aromatic ring-containing monomers can be used individually or in combination of two or more.

[0063] The above linking groups include, for example, oxy groups (-O-), thiooxy groups (-S-), and oxyalkylene groups (for example, -O-(CH2)). n - group, where n is 1 to 3, preferably 1), thiooxyalkylene group (e.g., -S-(CH2) n - group, where n is 1 to 3, preferably 1), linear alkylene group (i.e., -(CH2) n- Group (where n is 1 to 6, preferably 1 to 3), the above oxyalkylene group, the above thiooxyalkylene group, and the above linear alkylene group may be a group in which the alkylene group is partially halogenated or fully halogenated. From the viewpoint of flexibility of the high refractive index adhesive layer, preferred examples of the linking group include the oxy group, thiooxy group, oxyalkylene group, and linear alkylene group. Specific examples of monomers having a structure in which two or more non-condensed aromatic rings are linked via a linking group include phenoxybenzyl(meth)acrylate (e.g., m-phenoxybenzyl(meth)acrylate), thiophenoxybenzyl(meth)acrylate, benzylbenzyl(meth)acrylate, and the like.

[0064] Monomers having a structure in which two or more non-condensed aromatic rings are directly chemically bonded may include, for example, biphenyl structure-containing (meth)acrylate, triphenyl structure-containing (meth)acrylate, vinyl group-containing biphenyl, etc. Specific examples include o-phenylphenol (meth)acrylate and biphenylmethyl (meth)acrylate.

[0065] Examples of monomers having the above-mentioned condensed aromatic ring structure include naphthalene ring-containing (meth)acrylate, anthracene ring-containing (meth)acrylate, vinyl group-containing naphthalene, vinyl group-containing anthracene, etc. Specific examples include 1-naphthylmethyl (meth)acrylate (also known as 1-naphthalenemethyl (meth)acrylate), hydroxyethylated β-naphthol acrylate, 2-naphthoethyl (meth)acrylate, 2-naphthoxyethyl acrylate, and 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate.

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

[0067] Examples of monomers having the above-mentioned dinaphthothiophene structure include (meth)acryloyl group-containing dinaphthothiophene, vinyl group-containing dinaphthothiophene, (meth)allyl group-containing dinaphthothiophene, etc. A specific example is (meth)acryloyloxymethyl dinaphthothiophene (for example, CH2CH(R) at the 5th or 6th position of the dinaphthothiophene ring). 1 A compound with a structure in which C(O)OCH2- is bonded. Here, R 1 (These are a hydrogen atom or a methyl group.) (meth)acryloyloxyethyl dinaphthothiophene (for example, CH2CH(R) at the 5th or 6th position of the dinaphthothiophene ring) 1 )C(O)OCH(CH3)- or CH2CH(R 1 A compound with a structure in which C(O)OCH2CH2- is bonded. Here, R 1 The group is a hydrogen atom or a methyl group. Examples include vinyl dinaphthothiophene (for example, a compound in which a vinyl group is bonded to the 5th or 6th position of the naphthothiophene ring), (meth)allyloxydinaphthothiophene, etc. Note that monomers having a dinaphthothiophene structure are also included in the concept of monomers having the above-mentioned condensed aromatic ring structure if they contain a naphthalene structure or if they have a structure in which a thiophene ring and two naphthalene structures are condensed.

[0068] Examples of monomers having the above-mentioned dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophene and vinyl group-containing dibenzothiophene. Since monomers having a dibenzothiophene structure have a structure in which a thiophene ring and two benzene rings are condensed, they are included in the concept of monomers having the above-mentioned condensed aromatic ring structure. Furthermore, neither the dinaphthothiophene structure nor the dibenzothiophene structure corresponds to a structure in which two or more non-condensed aromatic rings are directly chemically bonded.

[0069] In some preferred embodiments, monomer (A1) is used which has one aromatic ring (preferably a carbon ring) in one molecule. Monomers having one aromatic ring in one molecule (monomers containing one aromatic ring) can be useful, for example, for improving the flexibility of the high refractive index adhesive layer, adjusting its adhesive properties, and improving its transparency. Monomers containing one aromatic ring can be used alone or in combination of two or more. In some embodiments, monomers having one aromatic ring in one molecule may be used in combination with monomers containing multiple aromatic rings from the viewpoint of improving the refractive index of the high refractive index adhesive layer.

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

[0071] As monomer (A1), monomers having a structure in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the aromatic ring in the various aromatic ring-containing monomers described above may be used. Monomers in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the aromatic ring in this manner can be understood as the ethoxylated product of the original monomer. The number of repeating oxyethylene units (-CH2CH2O-) in the above oxyethylene chain is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, for example, 1. Specific examples of ethoxylated aromatic ring-containing monomers include ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol di(meth)acrylate, and the like.

[0072] The content of multiple aromatic ring-containing monomers in monomer (A1) is not particularly limited and may be, for example, 5% or more by weight, 25% or more by weight, or 40% or more by weight. In some embodiments, the content of multiple aromatic ring-containing monomers in monomer (A1) may be, for example, 50% or more by weight, preferably 70% or more by weight from the viewpoint of easily obtaining a higher refractive index, and may be 85% or more by weight, 90% or more by weight, or 95% or more by weight. Substantially 100% by weight of monomer (A1) may be multiple aromatic ring-containing monomers. That is, only one or more multiple aromatic ring-containing monomers may be used as monomer (A1). Furthermore, in several other embodiments, for example, taking into consideration the balance between high refractive index and large deformability, the content of the multiple aromatic ring-containing monomer in monomer (A1) may be less than 100% by weight, 98% or less by weight, 90% or less by weight, 80% or less by weight, 70% or less by weight, 65% or less by weight, 50% or less by weight, 25% or less by weight, or 10% or less by weight. The technology disclosed herein can also be carried out in embodiments in which the content of the multiple aromatic ring-containing monomer in monomer (A1) is less than 5% by weight. The multiple aromatic ring-containing monomer does not need to be used.

[0073] The content of multiple aromatic ring-containing monomers in the monomer components constituting the acrylic polymer is not particularly limited and can be set to realize a high refractive index adhesive layer that achieves both a desired refractive index and high deformability. The content of multiple aromatic ring-containing monomers in the above monomer components may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the viewpoint of making it easier to realize a high refractive index adhesive layer having a higher refractive index, the content of multiple aromatic ring-containing monomers in the above monomer components may be, for example, more than 35% by weight, more than 50% by weight is advantageous, more than 70% by weight is preferable, more than 75% by weight or more, more than 85% by weight or more, more than 90% by weight or more, more than 91% by weight or more, more than 92% by weight or more, more than 93% by weight or more, more than 94% by weight or more, more than 95% by weight or more, more than 96% by weight or more, more than 97% by weight or more, more than 98% by weight or more, or more than 99% by weight or more. The content of the multiple aromatic ring-containing monomer in the above monomer component is advantageous to be approximately 99% by weight or less, considering the balance between high refractive index and large deformability, and may 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 75% by weight or less. In some other embodiments, from the viewpoint of facilitating the realization of higher adhesive properties and / or optical properties (e.g., transparency), the content of the multiple aromatic ring-containing monomer in the above monomer component may 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 5% by weight or less. The technology disclosed herein can also be carried out in embodiments in which the content of the multiple aromatic ring-containing monomer in the above monomer component is less than 3% by weight.

[0074] The content of aromatic ring singular monomers in monomer (A1) is not particularly limited and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, the content of aromatic ring singular monomers in monomer (A1) may be, for example, 50% by weight or more, preferably 70% by weight or more from the viewpoint of easily obtaining a higher refractive index, and may be 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of monomer (A1) may be aromatic ring singular monomers. That is, only one or more aromatic ring singular monomers may be used as monomer (A1). Furthermore, in some embodiments, taking into consideration the balance between high refractive index and large deformability, for example, the content of the aromatic ring-containing monomer in monomer (A1) may be less than 100% by weight, 98% or less by weight, 90% or less by weight, 80% or less by weight, 70% or less by weight, 65% or less by weight, 50% or less by weight, 25% or less by weight, or 10% or less by weight. The technology disclosed herein can also be implemented in embodiments in which the content of the aromatic ring-containing monomer in monomer (A1) is less than 5% by weight. The aromatic ring-containing monomer does not need to be used.

[0075] The content of aromatic ring-containing monomers in the monomer components constituting the acrylic polymer is not particularly limited and can be set to realize a high refractive index adhesive layer that achieves both a desired refractive index and high deformability. The content of aromatic ring-containing monomers in the above monomer components may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the viewpoint of making it easier to realize a high refractive index adhesive layer having a higher refractive index, the content of aromatic ring-containing monomers in the above monomer components may be, for example, more than 35% by weight, more advantageously more than 50% by weight, preferably 60% by weight or more, more preferably more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, may be 95% by weight or more, or may be 98% by weight or more. The content of aromatic ring-containing monomers in the above monomer component may be approximately 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, may be 93% by weight or less, may be 90% by weight or less, may be 85% by weight or less, may be 80% by weight or less, or may be 75% by weight or less, taking into consideration the balance between high refractive index and large deformability. In some embodiments, from the viewpoint of facilitating the realization of higher adhesive properties and / or optical properties (e.g., transparency), the content of aromatic ring-containing monomers in the above monomer component may be 70% by weight or less, may be 60% by weight or less, may be 50% by weight or less, may be 40% by weight or less, may be 25% by weight or less, may be 15% by weight or less, or may be 5% by weight or less. The technology disclosed herein can also be implemented in embodiments in which the content of aromatic ring-containing monomers in the above monomer component is less than 3% by weight.

[0076] In some preferred embodiments, a high refractive index monomer may be preferably used as at least a portion of the monomer (A1). Here, "high refractive index monomer" refers to a monomer whose refractive index is, for example, approximately 1.510 or higher, preferably approximately 1.530 or higher, and more preferably approximately 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 the acrylic polymer and ease of compatibility with flexibility suitable as an adhesive, it may be, for example, 3.000 or less, 2.500 or less, 2.000 or less, 1.900 or less, 1.800 or less, or 1.700 or less. The high refractive index monomer can be used alone or in combination of two or more types. The refractive index of the monomer is measured using an Abbe refractometer under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. An ATAGO DR-M4 or equivalent Abbe refractometer can be used. If the manufacturer provides a nominal refractive index value at 25°C, that nominal value may be used.

[0077] As the above-mentioned high refractive index monomer, compounds with the appropriate refractive index can be appropriately selected from among the compounds included in the concept of aromatic ring-containing monomer (A1) disclosed herein (for example, the compounds and groups of compounds exemplified above). Specific examples include m-phenoxybenzyl acrylate (refractive index: 1.566, homopolymer Tg: -35°C), 1-naphthylmethyl acrylate (refractive index: 1.595, homopolymer Tg: 31°C), ethoxylated o-phenylphenol acrylate (number of oxyethylene unit repetitions: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, homopolymer Tg: 6°C), phenoxyethyl acrylate (refractive index (nD20): 1.517, homopolymer Tg: 2°C), and phenoxydiethylene glycol acrylate (refractive index: 1.510, homopolymer Examples include, but are not limited to, 6-acryloyloxymethyl dinaphthothiophene (6MDNTA, refractive index: 1.75), 6-methacryloyloxymethyl dinaphthothiophene (6MDNTMA, refractive index: 1.726), 5-acryloyloxyethyl dinaphthothiophene (5EDNTA, refractive index: 1.786), 6-acryloyloxyethyl dinaphthothiophene (6EDNTA, refractive index: 1.722), 6-vinyl dinaphthothiophene (6VDNT, refractive index: 1.802), and 5-vinyl dinaphthothiophene (abbreviation: 5VDNT, refractive index: 1.793).

[0078] The content of high refractive index monomers (i.e., aromatic ring-containing monomers having 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) is not particularly limited and may be, for example, 5% by weight or more, 25% by weight or more, 35% by weight or more, or 40% by weight or more. In some embodiments, from the viewpoint of easily obtaining a higher refractive index, the content of high refractive index monomers in monomer (A1) may be, for example, 50% by weight or more, preferably 70% 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. Substantially 100% by weight of monomer (A1) may be high refractive index monomers. Furthermore, in some embodiments, for example, from the viewpoint of achieving a good balance between high refractive index and large deformability, the content of the high refractive index monomer in monomer (A1) may be less than 100% by weight, 98% by weight or less, 90% by weight or less, 80% by weight or less, or 65% by weight or less. In some other embodiments, considering the adhesive properties and / or optical properties, the content of the high refractive index monomer in monomer (A1) may be 50% by weight or less, 25% by weight or less, 15% by weight or less, or 10% by weight or less. The technology disclosed herein can also be carried out in embodiments in which the content of the high refractive index monomer in monomer (A1) is less than 5% by weight. High refractive index monomers do not need to be used.

[0079] The content of high refractive index monomers in the monomer components constituting the acrylic polymer is not particularly limited and can be set to realize a high refractive index adhesive layer that achieves both a desired refractive index and high deformability. Furthermore, if necessary, it can be set considering compatibility with adhesive properties (e.g., adhesive strength) and / or optical properties (e.g., total light transmittance, haze value, etc.). The content of high refractive index monomers in the above monomer components may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, the content of high refractive index monomers in the monomer components constituting the acrylic polymer may be, for example, more than 35% by weight, more than 50% by weight is advantageous from the viewpoint of easily obtaining a higher refractive index, more than 70% by weight is preferable, may 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 achieving a good balance between high refractive index and large deformability, the content of high refractive index monomer in the above monomer component is advantageous to be 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, and may also be 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less. In some other embodiments, considering the adhesive properties and / or optical properties, the content of high refractive index monomer in the above monomer component may be 70% by weight or less, 50% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight or less. The technology disclosed herein can also be implemented in embodiments in which the content of high refractive index monomer in the above monomer component is less than 3% by weight.

[0080] In some preferred embodiments, an aromatic ring-containing monomer (hereinafter sometimes referred to as "monomer L") having a homopolymer Tg of 10°C or less is used as at least a portion of monomer (A1). Generally, increasing the content of aromatic ring-containing monomer (A1) in the monomer component (especially aromatic ring-containing monomer (A1) that falls under at least one of the above-mentioned multiple aromatic ring-containing monomers, single aromatic ring-containing monomers, and high refractive index monomers) tends to decrease the flexibility of the adhesive. By using monomer L as part or all of monomer (A1), the decrease in flexibility can be suppressed. This makes it possible to improve the refractive index while better maintaining large deformability. The Tg of monomer L may be, for example, 5°C or less, 0°C or less, -10°C or less, -20°C or less, or -25°C or less. The lower limit of the Tg of monomer L is not particularly limited. Considering the balance with the refractive index improvement effect, in some embodiments, the Tg of monomer L may be, for example, -70°C or higher, -55°C or higher, or -45°C or higher. In some other embodiments, the Tg of monomer L may be, for example, -30°C or higher, -10°C or higher, 0°C or higher, or 3°C or higher. Monomer L can be used alone or in combination of two or more types.

[0081] As monomer L, any compound having the appropriate Tg can be appropriately selected from among the compounds included in the concept of aromatic ring-containing monomer (A1) disclosed herein (for example, the compounds and groups of compounds exemplified above). Preferred examples of aromatic ring-containing monomers that can be used as monomer L include m-phenoxybenzyl acrylate (homopolymer Tg: -35°C), benzyl acrylate (homopolymer Tg: 6°C), phenoxyethyl acrylate (homopolymer Tg: 2°C), and phenoxydiethylene glycol acrylate (homopolymer Tg: -35°C).

[0082] The content of monomer L in monomer (A1) is not particularly limited and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, from the viewpoint of making it easier to obtain a high refractive index adhesive layer that achieves a higher level of both high refractive index and large deformability, the content of monomer L in monomer (A1) may be, for example, 50% by weight or more, preferably 60% by weight or more from the viewpoint of improving large deformability, may be 70% 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. It is also possible that substantially 100% by weight of monomer (A1) is monomer L. Furthermore, in some other embodiments, for example from the viewpoint of achieving a good balance between high refractive index and large deformability, the content of monomer L in monomer (A1) may be less than 100% by weight, 98% by weight or less, 90% by weight or less, 80% by weight or less, or 65% by weight or less.

[0083] The monomer L content in the monomer component constituting the acrylic polymer may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the viewpoint of making it easier to obtain a high refractive index adhesive layer that achieves a higher level of both high refractive index and large deformability, the monomer L content in the monomer component may be, for example, more than 35% by weight, and from the viewpoint of improving the refractive index, it is advantageous to be more than 50% by weight, preferably more than 70% by weight, and may 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 achieving a good balance between high refractive index and large deformability, the monomer L content in the above monomer component is advantageous to be approximately 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, and may be 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less.

[0084] In some embodiments, the aromatic ring-containing monomer (A1) may be a combination of monomer L (i.e., an aromatic ring-containing monomer whose homopolymer Tg is 10°C or less) and monomer H whose Tg is higher than 10°C. The Tg of monomer H may be, for example, greater than 10°C, greater than 15°C, or greater than 20°C. By using monomer L and monomer H in combination, a high refractive index adhesive layer with a high content of aromatic ring-containing monomer (A1) in the monomer component can achieve a higher level of both high refractive index and flexibility suitable for adhesion to the adherend. The ratio of monomer L to monomer H used can be set so as to suitably exhibit these effects and is not particularly limited.

[0085] In some embodiments, the aromatic ring-containing monomer (A1) can be preferably selected from compounds that do not contain a structure in which two or more non-condensed aromatic rings are directly chemically bonded (e.g., a biphenyl structure). For example, an acrylic polymer composed of monomer components with a composition in which the content of a compound containing a structure in which two or more non-condensed aromatic rings are directly chemically bonded is less than 5% by weight (more preferably less than 3% by weight, and may even be 0% by weight) is preferable. Limiting the amount of compound containing a structure in which two or more non-condensed aromatic rings are directly chemically bonded in this way can be advantageous from the viewpoint of realizing a high refractive index adhesive layer that achieves a better balance between high refractive index and large deformability.

[0086] The monomer (A1) content in the monomer component constituting the acrylic polymer is not particularly limited and can be set to realize a high refractive index adhesive layer that achieves a desired refractive index and large deformability, as well as adhesive properties (e.g., adhesive strength, etc.) and / or optical properties (e.g., total light transmittance, haze value, etc.). In some embodiments, the monomer (A1) content in the monomer component may be, for example, 30% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more, and may also be 70% by weight or more. In some preferred embodiments, the monomer (A1) content in the monomer component constituting the acrylic polymer may be, for example, more than 70% by weight, preferably 75% by weight or more, preferably 80% by weight or more from the viewpoint of easily obtaining a higher refractive index, may also be 85% by weight or more, may also be 90% by weight or more, and may also be 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 monomer (A1) content in the above monomer component is typically less than 100% by weight. From the viewpoint of achieving a good balance between high refractive index and large deformability, it is advantageous to have approximately 99% by weight or less, and may be 98% by weight or less, 96% by weight or less, 93% by weight or less, or 90% by weight or less. In some embodiments, from the viewpoint of facilitating the realization of higher adhesive properties and / or optical properties (e.g., transparency), the monomer (A1) content in the above monomer component may be less than 90% by weight, less than 85% by weight, or less than 80% by weight.

[0087] (Monomer (A2)) In some preferred embodiments, the monomer component constituting the acrylic polymer may further contain monomer (A2) in addition to monomer (A1). Monomer (A2) is a monomer that is at least one of a monomer having a hydroxyl group (hydroxyl group-containing monomer) and a monomer having a carboxyl group (carboxyl group-containing monomer). The hydroxyl group-containing monomer is a compound having at least one hydroxyl group and at least one ethylenically unsaturated group in one molecule. The carboxyl group-containing monomer is a compound containing at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. Monomer (A2) can be useful for introducing crosslinking points into the acrylic polymer or for imparting appropriate cohesiveness to the high refractive index adhesive layer. Monomer (A2) can be used alone or in combination of two or more. Monomer (A2) may or may not contain an aromatic ring. A monomer that does not contain an aromatic ring is preferably used as monomer (A2). Note that monomer (A2) is defined as a monomer different from monomer (A1) mentioned above. For example, monomer (A1) may be defined as a monomer that does not have a hydroxyl group or a carboxyl group.

[0088] Examples of ethylenically unsaturated groups in monomer (A2) include (meth)acryloyl groups, vinyl groups, and (meth)allyl groups. From the viewpoint of polymerization reactivity, (meth)acryloyl groups are preferred, and from the viewpoint of improving flexibility and tackiness, acryloyl groups are more preferred. From the viewpoint of improving the flexibility of the high refractive index adhesive layer, monomer (A2) preferably consists of a compound in which the number of ethylenically unsaturated groups in one molecule is 1 (i.e., a monofunctional monomer).

[0089] In some embodiments, monomers (A2) can be used in which the distance between the ethylenically unsaturated group (e.g., (meth)acryloyl group) and the hydroxyl group and / or carboxyl group is relatively long. This makes it easier to obtain a highly flexible crosslinked structure in embodiments in which the hydroxyl group and / or carboxyl group is used in the crosslinking reaction. For example, compounds can be used as monomers (A2) in which the number of atoms (typically carbon atoms and oxygen atoms) constituting the chain (linking chain) that connects the ethylenically unsaturated group and the hydroxyl group and / or carboxyl group 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) can be used. The upper limit of the number of constituent atoms in the above linking chain is, for example, 45 or less, and may be 20 or less (for example, 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). The number of constituent atoms in the linking chain that connects the ethylenically unsaturated group and the hydroxyl group and / or carboxyl group refers to the minimum number of atoms required to reach the hydroxyl group or carboxyl group from the ethylenically unsaturated group. For example, if the above linking chain is a straight alkylene group (i.e., -(CH2) n If the chain consists of oxyethylene groups (i.e., -(C2H4O)), then the number n is equal to the number of atoms constituting the linked chain. Also, for example, if the linked chain consists of oxyethylene groups (i.e., -(C2H4O) n -In the case of the oxyethylene group, the product of 3 (3n), which is the sum of the 2 carbon atoms and 1 oxygen atom constituting the oxyethylene group, and n is the number of atoms constituting the linked chain. Although not particularly limited, such monomers (A2) include, for example, -(CH2) between the ethylenically unsaturated group and the hydroxyl group and / or carboxyl group. n Alkylene units represented by -, or -(C m H 2mA material can be used that has at least one oxyalkylene unit represented by O)- (for example, an oxyethylene unit where m in the formula is 2, an oxypropylene unit where m in the formula is 3, or an oxybutylene unit where m in the formula is 4). The number of alkylene units and oxyalkylene units is not particularly limited and may be 1 or more (for example, 1 to 15 or 1 to 10 or 2 to 6 or 2 to 4). Also, n in the formula representing the alkylene unit is, for example, 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 oxyalkylene unit is an integer of 2 or more, for example, an integer from 2 to 4. The monomer (A2) may contain, in addition to the ethylenically unsaturated group, hydroxyl group and / or carboxyl group, alkylene unit and / or oxyalkylene unit, ester bond, ether bond, thioether bond, aromatic ring, aliphatic ring, or heterocycle (for example, a ring containing a nitrogen atom (N), an oxygen atom (O), or a sulfur atom (S)). Furthermore, the alkylene unit and oxyalkylene unit may have substituents.

[0090] Examples of hydroxyl group-containing monomers include, but are not limited to, hydroxyalkyl (meth)acrylates such as 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-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate; and polyalkylene glycol mono(meth)acrylates such as polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, and polybutylene glycol mono(meth)acrylate. Examples of hydroxyl group-containing monomers that can be preferably used include 4-hydroxybutyl acrylate (Tg: -40°C) and 2-hydroxyethyl acrylate (Tg: -15°C). From the viewpoint of improving flexibility in the room temperature range, 4-hydroxybutyl acrylate, which has a lower Tg, is more preferred. Furthermore, in embodiments in which hydroxyalkyl (meth)acrylate is used as the hydroxyl group-containing monomer and the hydroxyl group is utilized in the crosslinking reaction, from the viewpoint of obtaining a highly flexible crosslinked structure, it is preferable to use a monomer with a large number of carbon atoms in the hydroxyalkyl group in the hydroxyalkyl (meth)acrylate, for example, a hydroxyalkyl (meth)acrylate (e.g., 4-hydroxybutyl acrylate) in which the hydroxyalkyl group has 3 or more carbon atoms (e.g., 3 to 12, preferably 4 to 10). In some preferred embodiments, 50% or more by weight (e.g., more than 50%, more than 70%, or more than 85% by weight) of monomer (A2) may be 4-hydroxybutyl acrylate. The hydroxyl group-containing monomer can be used alone or in combination of two or more.

[0091] In some embodiments where a hydroxyl group-containing monomer is used as monomer (A2), the hydroxyl group-containing monomer may be one or more compounds selected from compounds that do not have a methacryloyl group. Preferred examples of hydroxyl group-containing monomers that do not have a methacryloyl 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 group-containing monomer used as monomer (A2) is hydroxyalkyl acrylate. The use of hydroxyalkyl acrylate allows for the introduction of hydroxyl groups into the acrylic polymer, which are useful for providing crosslinking points and imparting appropriate cohesiveness, and makes it easier to obtain an adhesive with good flexibility and tackiness at room temperature compared to using only the corresponding hydroxyalkyl methacrylate.

[0092] Examples of carboxyl group-containing monomers include, but are not limited to, acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate, as well as itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Examples of carboxyl group-containing monomers that can be preferably used include acrylic acid and methacrylic acid. Furthermore, in some embodiments, from the viewpoint of improving the flexibility of the high refractive index adhesive layer, it is preferable to use a compound represented by, for example, the following formula (1) as the carboxyl group-containing monomer. CH2=CR 1 -COO-R 2 -OCO-R 3 -COOH (1) Here, in equation (1) above, R 1 R is either a hydrogen or a methyl group. 2 and R 3 R is a divalent linking group (specifically, an organic group having 1 to 20 carbon atoms (for example, 2 to 10, preferably 2 to 5)), and may be the same or different from each other. 2 and R 3 This can be, for example, a divalent aliphatic hydrocarbon group, an aromatic hydrocarbon group, or an alicyclic hydrocarbon group. For example, the above R 2 and R3 This can be an alkylene having 2 to 5 carbon atoms. Specific examples of carboxyl group-containing monomers represented by formula (1) above include, for example, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxyethyl-phthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid, 2-(meth)acryloyloxyethyl-succinic acid, 2-(meth)acryloyloxypropylhexahydrohydrogen phthalate, 2-(meth)acryloyloxypropylhydrogen phthalate, and 2-(meth)acryloyloxypropyltetrahydrohydrogen phthalate. Carboxylate group-containing monomers can be used individually or in combination of two or more. Hydroxyl group-containing monomers and carboxyl group-containing monomers may also be used in combination.

[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 some embodiments, the content of monomer (A2) is, for example, 0.01% by weight or more, 0.1% by weight or more is appropriate, and preferably 0.5% by weight or more. From the viewpoint of obtaining a higher usage effect, in some embodiments, the content of monomer (A2) may be 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 monomer (A1) does not exceed 100% by weight. In some embodiments, the content of 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 increase the refractive index by relatively increasing the content of monomer (A1), it is preferably 20% by weight or less, more preferably 15% by weight or less, and may be less than 12% by weight, less than 10% by weight, or less than 7% by weight. In some preferred embodiments, from the viewpoint of improving the large deformability of the high refractive index adhesive layer, the content of the monomer (A2) may be less than 5% by weight, more preferably less than 3% by weight, and 1.5% by weight or less.

[0094] (Monomer A3) In some embodiments, the monomer component constituting the acrylic polymer may further contain alkyl (meth)acrylate (hereinafter also referred to as "monomer (A3)") in addition to the monomer (A1). Monomer (A3) may help improve the flexibility of the high refractive index adhesive layer. It may also help improve the compatibility of additives within the adhesive and adhesive properties such as adhesive strength. Monomer (A3) can be used alone or in combination of two or more types.

[0095] As monomers (A3), those with 1 to 20 carbon atoms (i.e., C 1-20 Alkyl (meth)acrylates having a linear or branched alkyl group at the ester terminus are preferably used. 1-20 Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isooctyl (meth)acrylate. Examples include, but are not limited to, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0096] In some embodiments, alkyl (meth)acrylates having a homopolymer Tg of -20°C or lower (more preferably -40°C or lower, for example -50°C or lower) can be preferably used as at least a portion of the monomer (A3). Such low-Tg alkyl (meth)acrylates can help improve the flexibility of the high-refractive-index adhesive layer. They can also help improve adhesive properties such as adhesive strength. The lower limit of the Tg of the alkyl (meth)acrylate is not particularly limited and may be, for example, -85°C or higher, -75°C or higher, -65°C or higher, or -60°C or higher. Specific examples of the low-Tg alkyl (meth)acrylate include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), heptyl acrylate, octyl acrylate, and isononyl acrylate (iNA). In some other embodiments, an alkyl (meth)acrylate having a homopolymer Tg greater than -20°C (e.g., -10°C or higher) may be used as at least part of the monomer (A3). The upper limit of the Tg of the alkyl (meth)acrylate is, for example, 10°C or lower, may be 5°C or lower, or 0°C or lower. Alkyl (meth)acrylates having a Tg in this range may be useful in adjusting the flexibility of the high refractive index adhesive layer. Although not particularly limited, it is preferable to use the alkyl (meth)acrylate having the above Tg in combination with the low Tg alkyl (meth)acrylate. A specific example of the alkyl (meth)acrylate having the above Tg is lauryl acrylate (LA).

[0097] In some embodiments of using monomer (A3), C is used as monomer (A3). 4-8 It is preferable to use alkyl (meth)acrylates. In particular, C 4-8 The use of alkyl acrylates is more preferable. 4-8 Alkyl (meth)acrylates can be used individually or in combination of two or more types. 4-8 The use of alkyl (meth)acrylates makes it easier to improve the flexibility of the high refractive index adhesive layer and tends to yield good adhesive properties (adhesion strength, etc.). C is used as monomer (A3). 4-8In an embodiment using alkyl (meth)acrylate, of the alkyl (meth)acrylates contained in the monomer component, C 4-8 The proportion of alkyl (meth)acrylate is appropriately 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, and may be substantially 100% by weight.

[0098] In some embodiments of using monomer (A3), C is used as monomer (A3). 1-6 Alkyl (meth)acrylates may be used. 1-6 The use of alkyl (meth)acrylates allows for adjustment of the storage modulus in each temperature range. For example, it is possible to set the storage modulus in the high-temperature range relatively high, or to suppress large differences in the storage modulus between the low-temperature and high-temperature ranges. 1-6 Alkyl (meth)acrylates tend to exhibit excellent copolymerization properties with monomers (A1). 1-6 Alkyl (meth)acrylates can be used individually or in combination of two or more types. 1-6 As for alkyl (meth)acrylates, C 1-6 Alkyl acrylates are preferred, C 2-6 Alkyl acrylates are more preferred, C 4-6 Alkyl acrylates are more preferred. In some other embodiments, C 1-6 The alkyl (meth)acrylate is preferably C 1-4 It is an alkyl (meth)acrylate, more preferably C 2-4 It is an alkyl (meth)acrylate, and more preferably C 2-4 It is an alkyl acrylate. 1-6 A suitable example of an alkyl (meth)acrylate is BA.

[0099] C in the monomer components that make up acrylic polymers 1-6The alkyl (meth)acrylate content 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 some embodiments, the above C 1-6 The alkyl (meth)acrylate content may be 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more (for example, 30% by weight or more) from the viewpoint of improving flexibility and adhesive strength. 1-6 The upper limit of the alkyl (meth)acrylate content is, for example, less than 50% by weight, and may be less than 35% by weight. In some embodiments, from the viewpoint of maintaining a high refractive index, the above C 1-6 The alkyl (meth)acrylate content is, for example, 24% by weight or less, preferably less than 20% by weight, more preferably less than 17% by weight, may be less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The technology disclosed herein is C 1-6 This can also be carried out in a manner that substantially does not use alkyl (meth)acrylates.

[0100] In some other embodiments using monomer (A3), C is used as monomer (A3). 7-12 Alkyl (meth)acrylates may be preferably used. 7-12 The use of alkyl (meth)acrylates can be used to favorably reduce the storage modulus. 7-12 Alkyl (meth)acrylates can be used individually or in combination of two or more types. 7-12 As for alkyl (meth)acrylates, C 7-10 Alkyl acrylates are preferred, C 7-9 Alkyl acrylates are more preferred, and C8 alkyl acrylates are even more preferred. 7-12 Examples of alkyl (meth)acrylates include 2EHA, iNA, and LA, with 2EHA being a preferred example.

[0101] C in the monomer components that make up acrylic polymers 7-12The alkyl (meth)acrylate content 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 some embodiments, the above C 7-12 The alkyl (meth)acrylate content may be 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more (for example, 30% by weight or more) from the viewpoint of improving flexibility and adhesive strength. 7-12 The upper limit of the alkyl (meth)acrylate content is, for example, less than 50% by weight, and may be less than 35% by weight. In some embodiments, from the viewpoint of maintaining a high refractive index, the above C 7-12 The alkyl (meth)acrylate content is, for example, 24% by weight or less, preferably less than 20% by weight, more preferably less than 17% by weight, may be less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The technology disclosed herein is C 7-12 This can also be carried out in a manner that substantially does not use alkyl (meth)acrylates.

[0102] In some embodiments of using monomer (A3), it is preferable that at least a portion of monomer (A3) is an alkyl acrylate from the viewpoint of improving flexibility. The use of alkyl acrylate is also advantageous in terms of adhesive properties such as adhesion strength. For example, it is preferable that 50% by weight or more of monomer (A3) is alkyl acrylate, more preferably 75% by weight or more, and even more preferably 90% by weight or more, and substantially 100% by weight of monomer (A3) may be alkyl acrylate. It is also possible to use only one or more alkyl acrylates as monomer (A3) and not use alkyl methacrylate.

[0103] In embodiments where the monomer component includes alkyl (meth)acrylate, the content of alkyl (meth)acrylate in the monomer component can be set so that its effect is appropriately exhibited. In some embodiments, the content of alkyl (meth)acrylate 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. The upper limit of the content of monomer (A3) in the monomer component is set so that the sum of the 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 some embodiments, the content of monomer (A3) may be, for example, 24% by weight or less. Generally, alkyl (meth)acrylate has a relatively low refractive index, so in order to increase the refractive index, it is advantageous to limit the content of monomer (A3) in the monomer component and relatively increase the content of monomer (A1). From this viewpoint, the monomer (A3) content is appropriately less than 23% by weight of the monomer component, preferably less than 20% by weight, more preferably less than 17% by weight, may be less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The technology disclosed herein can also be preferably implemented in a manner that does not substantially use monomer (A3).

[0104] (Other monomers) The monomer components constituting the acrylic polymer may, if necessary, include monomers other than the above monomers (A1), (A2), and (A3) (hereinafter referred to as "other monomers"). These other monomers can be used, for example, for purposes such as adjusting the Tg of the acrylic polymer, adjusting the adhesive performance, and improving compatibility within the adhesive layer. These other monomers can be used individually or in combination of two or more.

[0105] Examples of other monomers mentioned above include monomers having functional groups other than hydroxyl and carboxyl groups (functional group-containing monomers). For example, other monomers that can improve the cohesive force and heat resistance of adhesives include sulfonic acid group-containing monomers, phosphate group-containing monomers, and cyano group-containing monomers. Furthermore, monomers that can introduce functional groups that can act as crosslinking sites into acrylic polymers, or that can contribute to improving adhesion to the adherend or improving compatibility within the adhesive, include amide group-containing monomers (e.g., (meth)acrylamide, N-methylol(meth)acrylamide, etc.), amino group-containing monomers (e.g., aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, etc.), monomers having nitrogen atom-containing rings (e.g., N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), imide group-containing monomers, epoxy group-containing monomers, keto group-containing monomers, isocyanate group-containing monomers, and alkoxysilyl group-containing monomers. Furthermore, some monomers containing nitrogen atom rings, such as N-vinyl-2-pyrrolidone, also fall under the category of amide group-containing monomers. The same applies to the relationship between monomers containing nitrogen atom rings and monomers containing amino groups.

[0106] Other monomers that can be used besides the above-mentioned functional group-containing monomers include vinyl ester monomers such as vinyl acetate; non-aromatic ring-containing (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; olefin monomers such as ethylene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether; and others. One preferred 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, homopolymer Tg: -67℃).

[0107] When using the above-mentioned other monomers, the amount used is not particularly limited and can be appropriately set within a range where the total amount of monomer components does not exceed 100% by weight. From the viewpoint of making it easier to exhibit the refractive index improvement effect by using monomer (A1), the content of the above-mentioned other monomers in the monomer component can be, for example, approximately 35% by weight or less, it is appropriate to be approximately 25% by weight or less (e.g., 0 to 25% by weight), it may also be approximately 20% by weight or less (e.g., 0 to 20% by weight), it is advantageous to be approximately 10% by weight or less (e.g., 0 to 10% by weight), and preferably approximately 5% by weight or less, for example, approximately 1% by weight or less. The technology disclosed herein can preferably be implemented in a manner in which the monomer component substantially does not contain the above-mentioned other monomers.

[0108] In some embodiments, the monomer components constituting the acrylic polymer may have a composition in which the amount of methacryloyl group-containing monomer used is limited to a predetermined level. The amount of methacryloyl group-containing monomer used in the monomer component may be, for example, less than 5% by weight, less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. Limiting the amount of methacryloyl group-containing monomer used in this way may be advantageous from the viewpoint of realizing an adhesive that balances flexibility, tackiness, and high refractive index well. The monomer components constituting the acrylic polymer may also have a composition that does not contain methacryloyl group-containing monomer (for example, a composition consisting only of acryloyl group-containing monomer).

[0109] In some embodiments, the monomer component constituting the base polymer (e.g., acrylic polymer) of the high refractive index adhesive layer has a limited amount of carboxyl group-containing monomer used, from the viewpoint of suppressing coloration or discoloration (e.g., yellowing) of the high refractive index adhesive layer. The amount of carboxyl group-containing monomer used in the monomer component may be, for example, 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. Limiting the amount of carboxyl group-containing monomer used in this way is also advantageous from the viewpoint of suppressing corrosion of metallic materials (e.g., metal wiring or metal films that may be present on the adherend) that may be in contact with or near the high refractive index adhesive layer disclosed herein. The technology disclosed herein may be implemented in an embodiment in which the monomer component does not contain carboxyl group-containing monomer. For similar reasons, in some embodiments, the monomer component constituting the base polymer of the high refractive index adhesive layer may have a limited amount of monomers having acidic functional groups (including carboxyl groups, sulfonic acid groups, phosphate groups, etc.). In such embodiments, the preferred amount of carboxyl group-containing monomers described above can be applied as the amount of acidic functional group-containing monomers used in the monomer component. The techniques disclosed herein can be implemented in embodiments in which the monomer component does not contain acidic group-containing monomers (i.e., embodiments in which the base polymer of the high refractive index adhesive layer is acid-free).

[0110] (Glass transition temperature) The monomer components constituting the base polymer (e.g., acrylic polymer) of the high refractive index adhesive layer preferably have a composition such that the glass transition temperature (Tg) based on the composition of the monomer components is approximately 15°C or lower. In some embodiments, the Tg is preferably 10°C or lower, more preferably 5°C or lower, even more preferably 1°C or lower, and may be 0°C or lower. In some other embodiments, the Tg may be -10°C or lower, -20°C or lower, -25°C or lower, -30°C or lower, or -35°C or lower. A low Tg can be advantageous from the viewpoint of improving the flexibility of the high refractive index adhesive layer. Furthermore, the Tg may be, for example, -60°C or higher, and from the viewpoint of facilitating the high refractive index of the adhesive, it is preferably -50°C or higher, more preferably above -45°C, and may be above -40°C. In some embodiments, the Tg may be above -30°C, above -20°C, above -10°C, or -5°C or higher. A high refractive index adhesive layer that achieves both high refractive index and high deformability can preferably be formed by using a base polymer with a composition having a Tg within the above range.

[0111] Here, Tg, which is based on the composition of the monomer components constituting the base polymer (e.g., an acrylic polymer), refers, unless otherwise specified, to the glass transition temperature determined by Fox's formula based on the above monomer component composition. Fox's formula is a relationship between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below. 1 / Tg = Σ(Wi / Tgi) In the Fox equation above, 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). For calculating the glass transition temperature (Tg) of homopolymers, the values ​​listed in publicly available materials such as the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. For monomers for which multiple values ​​are listed in the Polymer Handbook, the highest value shall be adopted. If the Tg of a homopolymer is not listed in publicly available materials, the value obtained by the measurement method described in Japanese Patent Publication No. 2007-51271 shall be used.

[0112] (Method for preparing the base polymer) In the technologies disclosed herein, the method for obtaining a base polymer (e.g., an acrylic polymer) composed of such monomer components is not particularly limited, and known polymerization methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization can be appropriately employed. For example, solution polymerization can be preferably employed. The polymerization temperature when performing solution polymerization can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and can be, for example, around 20°C to 170°C (typically around 40°C to 140°C).

[0113] The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents. For example, one solvent or a mixture of two or more solvents can be used, selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); acetic acid esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc.

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

[0115] For the polymerization described above, various conventionally known chain transfer agents can be used as needed. For example, mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, thioglycolic acid, and α-thioglycerol can be used. Alternatively, a chain transfer agent that does not contain sulfur atoms (non-sulfur chain transfer agent) may 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 terpinolene; and styrenes such as α-methylstyrene and α-methylstyrene dimer. Chain transfer agents can be used individually or in combination of two or more. When using a chain transfer agent, the amount used can be approximately 0.01 to 1 part by weight per 100 parts by weight of the monomer component.

[0116] The weight-average molecular weight (Mw) of the base polymer (e.g., acrylic polymer) is not particularly limited, for example, approximately 30 × 10 4 That is all, approximately 50 x 10 4 The above is appropriate, approximately 70 x 10 4 It may be greater than or equal to approximately 80 x 10 4The above is also acceptable. By using a base polymer with Mw above a predetermined value, it is easier to obtain a moderate cohesive force that can exhibit the desired adhesive properties. In addition, it is possible to include more additives such as plasticizers, and it tends to be easier to achieve the desired flexibility. Furthermore, the upper limit of Mw of the base polymer is, for example, approximately 500 × 10 4 The following is the case, and from the perspective of adhesive performance, approximately 400 x 10 4 The following (more preferably approximately 150 x 10 4 For example, approximately 130 x 10 4 It is preferable that the above Mw is within the range of the following. In some embodiments, the above Mw is 100 × 10 4 It may be less than 80 x 10 4 The following is also acceptable: 60 x 10 4 The following may also be used. The effects of the techniques disclosed herein can preferably be realized in embodiments using acrylic polymers having Mw within the above range.

[0117] Here, the Mw of the polymer can be determined by converting it to polystyrene equivalent using gel permeation chromatography (GPC). Specifically, it can be determined by measuring under the following conditions using a GPC measuring instrument, product name "HLC-8220GPC" (manufactured by Tosoh Corporation). [GPC measurement conditions] Sample concentration: 0.2% by weight (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: Tetrahydrofuran (THF) Flow rate (flow rate): 0.6mL / min Column temperature (measurement temperature): 40℃ column: Sample columns: 1 x "TSKguardcolumn SuperHZ-H" + 2 x "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: Product name "TSKgel SuperH-RC" 1 piece (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: Polystyrene

[0118] (Plasticizer) In some embodiments, the high refractive index adhesive layer described above (e.g., a high refractive index acrylic adhesive layer) contains a plasticizer in addition to the base polymer. The use of a plasticizer can improve the flexibility of the high refractive index adhesive layer, thereby enabling large deformability. As the plasticizer, it is preferable to select and use one or more plasticizers from among those described below that have a refractive index of 1.55 or higher and can achieve the above-mentioned 350% deformation characteristics.

[0119] A preferred example of the plasticizer disclosed herein is a cyclic unsaturated organic compound having two or more double bond-containing rings. In other words, the plasticizer as a preferred example is a compound having two or more double bond-containing rings in one molecule. Therefore, the plasticizer has at least a first double bond-containing ring and a second double bond-containing ring. By having two or more double bond-containing rings, it is possible to improve the flexibility of the high-refractive-index adhesive layer and, consequently, achieve greater deformability without impairing the refractive index of the high-refractive-index adhesive layer, or while maintaining the refractive index. From the viewpoint of exhibiting a plasticizing effect, the number of double bond-containing rings in the plasticizer is preferably 6 or less, but may also be 4 or less, or 3 or less.

[0120] Furthermore, the plasticizer used in the technology disclosed herein is preferably a compound that is liquid at 30°C. In this specification, "liquid" means fluid, and in terms of the state of matter, it refers to a liquid. Such compounds include compounds with a melting point of 30°C or lower. By being liquid at 30°C, the plasticizing effect is suitably exhibited, and the flexibility of the high refractive index adhesive layer can be suitably improved, and consequently, large deformability can be suitably achieved. The 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 that is liquid at 30°C and has two or more double bond-containing rings as a plasticizer, a high refractive index adhesive layer that achieves both high refractive index and large deformability can be suitably formed.

[0121] The molecular weight of the plasticizer is not particularly limited, but usually a plasticizer with a molecular weight smaller than that of the base polymer (e.g., acrylic polymer) is used. From the viewpoint of facilitating the expression of the plasticizing effect, the molecular weight of the plasticizer is preferably 30,000 or less, more preferably 25,000 or less, and may be less than 10,000 (e.g., less than 5,000) or less than 3,000. In some embodiments, the molecular weight of the plasticizer is preferably 2,000 or less, more preferably 1,200 or less, even more preferably 900 or less, and may be 600 or less, 500 or less, 400 or less, 300 or less, or 250 or less (e.g., 220 or less). Having a plasticizer with a molecular weight that is not too large can be advantageous from the viewpoint of improving compatibility within the adhesive layer. Furthermore, from the viewpoint of easily exhibiting a sufficient plasticizing effect, the molecular weight of the plasticizer is appropriately 100 or more, preferably 130 or more, more preferably 150 or more, and may also be 170 or more, 200 or more, 220 or more, or 250 or more. It is also preferable that the molecular weight of the plasticizer is not too low from the viewpoint of the heat resistance performance of the adhesive and the suppression of contamination of the adherend. In some embodiments, the molecular weight of the plasticizer is, for example, 300 or more, appropriately 315 or more, and may also be 350 or more. Plasticizers with large molecular weights do not vaporize easily, so by using a plasticizer with a large molecular weight in the adhesive, it is easier to obtain an adhesive that can exhibit stable properties. In addition, plasticizers with large molecular weights do not easily move within the adhesive. Therefore, events that affect adhesive properties, such as the plasticizer moving to the surface of the adhesive, are less likely to occur. The molecular weight of the above plasticizer is more preferably 400 or more, even more preferably 450 or more, particularly preferably 500 or more, and may also be 530 or more. The molecular weight of the plasticizer is calculated based on its chemical structure. If the manufacturer provides a nominal molecular weight, that nominal value can be used.

[0122] While not particularly limited, in some embodiments, a plasticizer may be used in which the amount transferred to the gas phase at 130°C (vaporization rate at 130°C) is 10% or less by weight (specifically, 0 to 10% by weight). By using a plasticizer that satisfies this characteristic, the high refractive index adhesive layer containing the plasticizer will have its properties suppressed by changes in temperature and humidity. For example, it can be an adhesive that exhibits stable properties even when used in environments exposed to high temperatures and high humidity, or when used for long periods of time. The vaporization rate 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 determined from the weight change before and after holding the plasticizer at 130°C for one hour. More specifically, it can be measured by the following method. [Amount of plasticizer transferred to the gas phase] Approximately 1 g of plasticizer (measurement sample) is dropped into an aluminum cup and weighed to the nearest 0.01 mg using an electronic balance at 23°C and 45% RH (W0 g). Next, the cup containing the measurement sample is placed in a 130°C oven for 1 hour. The oven should have sufficient capacity for the measurement sample and be capable of heating while evacuating. For example, an oven manufactured by espec can be used. After holding at 130°C for 1 hour, the cup containing the measurement sample is removed from the oven, allowed to return to room temperature, and then weighed (W1 g). The weight of the measurement sample before heating in the oven W0 [g] and the weight of the measurement sample after heating in the oven W1 [g] are substituted into the formula: 1 - W1 / W0 to determine the amount of the measurement sample transferred to the gas phase at 130°C [%]. The measurement is performed on 3 samples (n=3), and the average value is adopted.

[0124] In some embodiments, although not particularly limited, the high refractive index adhesive layer exhibits a weight-based reduction of 5% or less (specifically, 0-5% by weight) of plasticizer in the high refractive index adhesive layer after being held at 130°C for 1 hour. A high refractive index adhesive layer satisfying this characteristic can maintain its effect (primarily the plasticizing effect) even after heating under predetermined conditions, as most of the plasticizer in the high refractive index adhesive layer remains within the layer. Therefore, the high refractive index adhesive layer is less susceptible to changes in properties caused by the plasticizer and can exhibit stable properties regardless of the usage environment and even when used for long periods. The weight reduction of plasticizer in the high refractive index adhesive layer after being held at 130°C for 1 hour is preferably less than 3% by weight, more preferably less than 1% by weight, and even more preferably less than 0.5% by weight, and may also be less than 0.3% by weight or 0.1% by weight or less. The reduction in the amount of plasticizer in the high refractive index adhesive layer after holding at 130°C for 1 hour can be determined from the weight change of the plasticizer in the high refractive index adhesive layer before and after holding 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, it can be measured by the following method. [Loss in weight of plasticizer in adhesive when heated] An adhesive composition is applied to the silicone-treated side of a PET film R1, which has a silicone treatment on one side, and heated at 130°C for 3 minutes to form an adhesive layer with a thickness of 20 μm. Next, the silicone-treated side of a PET film R2, which has a silicone treatment on one side, is bonded to the surface of the adhesive layer. One of the release liners is peeled off from the resulting adhesive layer with a release liner (release liner / adhesive layer / release liner), and the layer is held in a 130°C oven for 1 hour. The oven used should have sufficient capacity for the sample being measured and be capable of heating while evacuating. For example, an oven manufactured by espec can be used. Liquid chromatography (LC) measurements are performed on the adhesive before and after heating in the oven under the following conditions. From the LC results, the amount of plasticizer contained in the adhesive before and after heating is determined, and from the weight ratio, the reduction in plasticizer in the adhesive after being held in a 130°C environment for 1 hour [%] is determined. The measurement is performed on 3 samples (n=3), and the average value is adopted. Furthermore, prior to performing LC measurements on the adhesive, it is desirable to perform LC measurements on the plasticizer alone, create a calibration curve, and then quantify the plasticizer in the adhesive based on this calibration curve. [LC measurement conditions] Approximately 0.01 g of adhesive was taken, 2 mL of chloroform was added, and the mixture was shaken overnight. 8 mL of acetonitrile was added to this solution to reprecipitate the polymer components, and the supernatant was filtered through a 0.45 μm membrane filter. The resulting filtrate was diluted as appropriate and injected into an analyzer (HPLC Prominence, Shimadzu Corporation) for measurement. Column: GL Sciences, Inertsil ODS-3 (4.6mmφ × 250mm, 5μm) Column temperature: 40℃ Column flow rate: 1.0 mL / min Eluent: Ultrapure water / acetonitrile gradient conditions Injection volume: 1μL Detector: DAD (190nm~400nm, 272nm extraction)

[0126] In embodiments in which a plasticizer having a double bond-containing ring is used, the double bond-containing ring of the plasticizer may be a conjugated double bond-containing ring (typically an aromatic ring) or any unconjugated double bond-containing ring. The plasticizer may have at least one ring selected from aromatic rings and heterocycles as the double bond-containing ring. The heterocycle may have a structure that is contained within the aromatic ring, or it may have a double bond-containing heterocycle structure different from that of the aromatic ring. The double bond-containing rings (typically aromatic rings) that the above plasticizer may have may be carbon rings such as benzene rings (which may be benzene rings that constitute part of a biphenyl or fluorene structure); naphthalene rings, indene rings, azulene rings, anthracene rings, or phenanthrene rings; or hetero rings such as pyridine rings, pyrimidine rings, pyridazine rings, pyrazine rings, triazine rings, pyrrole rings, pyrazole rings, imidazole rings, triazole rings, oxazole rings, isoxazole rings, thiazole rings, or thiophene rings. The heteroatoms included as ring constituent atoms in the above hetero rings may be one or more selected from the group consisting of, for example, nitrogen, sulfur, and oxygen. In some embodiments, the heteroatoms constituting the above hetero ring may be nitrogen and sulfur, or both. The above plasticizer may have a structure in which one or more carbon rings and one or more hetero rings are fused, such as a dinaphthothiophene structure.

[0127] The double bond-containing ring described above (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. If substituents are present, examples of substituents include, but are not limited to, alkyl groups, alkoxy groups, aryloxy groups, hydroxyl groups, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl groups, hydroxyalkyloxy groups, and glycidyloxy groups. In substituents containing carbon atoms, the number of carbon atoms in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. In some embodiments, the double bond-containing ring may be an aromatic ring that has neither substituents on the ring constituent atoms nor substituents, or has one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, ethylenically unsaturated groups (e.g., (meth)acryloxy groups), hydroxyl groups, and hydroxyalkyl groups. Alkyl groups, alkoxy groups, and hydroxyalkyl groups are preferably used as substituents.

[0128] In some embodiments, compounds without ethylenically unsaturated groups can be preferably used as plasticizers. This suppresses deterioration of the adhesive composition due to heat and light (progression of gelation and decrease in leveling properties due to increased viscosity), thereby improving storage stability. Using plasticizers without ethylenically unsaturated groups is also preferable from the viewpoint of suppressing changes in elastic modulus, dimensional changes and deformation (warping, undulation, etc.), and the occurrence of optical distortion in the adhesive layer containing the plasticizer, which are caused by the reaction of ethylenically unsaturated groups.

[0129] As the plasticizer, a high refractive index plasticizer having a refractive index of approximately 1.50 or higher is preferably used. By using a high refractive index plasticizer, it is easier to achieve both a high refractive index and high deformability. From the viewpoint of maintaining and improving the refractive index of the high refractive index adhesive layer while obtaining flexibility, the refractive index of the plasticizer is preferably approximately 1.51 or higher, more preferably approximately 1.53 or higher, even more preferably approximately 1.55 or higher, and may also be approximately 1.56 or higher, approximately 1.58 or higher, approximately 1.60 or higher, or approximately 1.62 or higher. In some embodiments, from the viewpoint of ease of preparation of the adhesive composition and compatibility within the adhesive, the refractive index of the plasticizer is appropriate to be 2.50 or lower, advantageous to be 2.00 or lower, may also be 1.90 or lower, may also be 1.80 or lower, or may also be 1.70 or lower. The refractive index of the plasticizer is measured using an Abbe refractometer under the same conditions as the refractive index of the monomer, with a measurement wavelength of 589 nm and a measurement temperature of 25°C. If the manufacturer or other source provides a nominal refractive index value at 25°C, that nominal value may be used.

[0130] In some embodiments, one or more compounds selected from the following can be used as plasticizers: compounds having a structure in which two or more non-condensed double bond-containing rings (typically aromatic rings) are linked via linking groups; compounds having a structure in which two or more non-condensed double bond-containing rings (typically aromatic rings) are chemically bonded directly (i.e., without other atoms); compounds having a condensed double bond-containing ring (typically aromatic ring) structure; compounds having a fluorene structure; compounds having a dinaphthothiophene structure; compounds having a dibenzothiophene structure, etc.

[0131] In some preferred embodiments, compound A, having a structure in which two or more non-condensed double bond-containing rings are linked via linking groups, is used as the plasticizer. The linking groups are, for example, oxy groups (-O-), thiooxy groups (-S-), and oxyalkylene groups (e.g., -O-(CH2)). n - group, where n is 1 to 3, preferably 1), thiooxyalkylene group (e.g., -S-(CH2) n- group, where n is 1 to 3, preferably 1), linear alkylene group (i.e., -(CH2) n -Group (where n is 1 to 6, preferably 1 to 3), the above oxyalkylene group, the above thiooxyalkylene group, and the above linear alkylene group may be a group in which the alkylene group is partially halogenated or fully halogenated. The above linking group may also have an ester bond. In the plasticizer, the linking group that links the first double bond-containing ring (non-condensed ring) and the second double bond-containing ring (non-condensed ring) may also be selected from the same type as above. From the viewpoint of large deformability of the high refractive index adhesive layer, preferred examples of the above linking group include oxy group, thiooxy group, oxyalkylene group, and linear alkylene group. The number of atoms in the above linking group is not particularly limited, and in some embodiments, it may be, for example, 1 to 30, 1 to 25, 1 to 20, and preferably 1 to 18, preferably 1 to 12, more preferably 1 to 10, even more preferably 1 to 8, particularly preferably 1 to 5, and may be 1 to 3, 1 or 2. In some other preferred embodiments, the number of atoms in the linking group is, for example, 10 or more, preferably 15 or more, more preferably 20 or more, and even more preferably 22 or more (for example, 25 or more or 30 or more). The upper limit of the number of atoms in the linking group is, for example, 50 or less, preferably 40 or less, and may be 35 or less. In embodiments in which a plasticizer having an oxyalkylene group as the linking group is used, the number of atoms in the linking group is preferably applied. The number of atoms in the linking group refers to the minimum number of atoms required to reach from one non-condensed double bond-containing ring to the other non-condensed double bond-containing ring. For example, if the linking group is a linear alkylene group (i.e., -(CH2) n If the linking group consists of -(C2H4O) groups, then n is the number of atoms in the linking group. Also, for example, if the linking group is an oxyethylene group (i.e., -(C2H4O) nIn the case of a - group, the number of atoms in the linking group is the product of 3 (the sum of the 2 carbon atoms and 1 oxygen atom that make up the oxyethylene group) and n (3n). Preferred examples of the above compounds include compounds having a phenoxybenzyl group. Examples of the above compounds include phenoxybenzyl (meth)acrylate (e.g., m-phenoxybenzyl (meth)acrylate), phenoxybenzyl alcohol, oxybis[(alkoxyalkyl)benzene] (e.g., 4,4′-oxybis[(methoxymethyl)benzene]), polyethylene glycol benzoic acid ester, and the like.

[0132] In embodiments using compound A as a plasticizer, which has a structure in which two or more non-condensed double bond-containing rings are linked via linking groups, the amount of compound A used is not particularly limited and is set to achieve the adhesive properties and effects disclosed herein. From the viewpoint of large deformability, in several preferred embodiments, the amount of compound A used per 100 parts by weight of the base polymer is more than 30 parts by weight, more preferably 35 parts by weight or more, even more preferably 40 parts by weight or more, particularly preferably 45 parts by weight or more, and even more particularly preferably 50 parts by weight or more, and may be 55 parts by weight or more, or 60 parts by weight or more. Furthermore, from the viewpoint of achieving a good balance between high refractive index and large deformability of the high refractive index adhesive layer, the amount of compound A used per 100 parts by weight of the base polymer is appropriately approximately 200 parts by weight or less, preferably 150 parts by weight or less, more preferably 120 parts by weight or less, and may be 100 parts by weight or less, 80 parts by weight or less, or 70 parts by weight or less.

[0133] Furthermore, in an embodiment in which compound A having a structure in which two or more non-condensed double bond-containing rings are linked via linking groups is used as a plasticizer, the high refractive index adhesive layer may optionally contain one or more plasticizers other than compound A, or may not contain any. The plasticizers other than compound A can be used in appropriate amounts as long as they do not impair the effects of the technology disclosed herein. In such an embodiment, the amount of plasticizers other than compound A used is preferably less than 50% by weight of the total plasticizer used in the high refractive index adhesive layer, more preferably less than 30% by weight, more preferably less than 10% by weight, even more preferably less than 3% by weight, and particularly preferably less than 1% by weight. The technology disclosed herein can preferably be carried out using a high refractive index adhesive layer that is substantially free of plasticizers other than compound A.

[0134] In some preferred embodiments, an ethylene glycol compound having two or more double-bond-containing rings in one molecule can be used as a plasticizer. The number of oxyethylene units (i.e., -(C2H4O)- units) in the ethylene glycol compound is, for example, one or more, preferably two or more, more preferably three or more, and more preferably four or more (for example, five or more). The upper limit of the number of oxyethylene units is, for example, 10 or less, may be eight or less, or six or less. The ethylene glycol compound may be a compound having a structure in which two or more non-condensed double-bond-containing rings are linked via the oxyethylene units as linking groups. Such a compound may have one or two or more ester groups. Examples of the ethylene glycol compound include a compound having a structure in which two or more benzoic acid molecules are linked to triethylene glycol or polyethylene glycol by ester bonds.

[0135] In embodiments where an ethylene glycol-based compound having two or more double bond-containing rings in one molecule is used as a plasticizer, the amount of the ethylene glycol-based compound used is not particularly limited and is set to achieve the adhesive properties and effects disclosed herein. From the viewpoint of large deformability, in several preferred embodiments, the amount of the ethylene glycol-based compound used per 100 parts by weight of the base polymer is more than 30 parts by weight, more preferably 35 parts by weight or more, even more preferably 40 parts by weight or more, particularly preferably 45 parts by weight or more, and even more particularly preferably 50 parts by weight or more, and may be 55 parts by weight or more, or 60 parts by weight or more. Furthermore, from the viewpoint of achieving a good balance between high refractive index and large deformability of the high refractive index adhesive layer, the amount of the ethylene glycol-based compound used per 100 parts by weight of the base polymer is appropriately approximately 200 parts by weight or less, preferably 150 parts by weight or less, more preferably 120 parts by weight or less, and may be 100 parts by weight or less, 80 parts by weight or less, or 70 parts by weight or less.

[0136] Furthermore, in embodiments where an ethylene glycol-based compound having two or more double-bond-containing rings in one molecule is used as a plasticizer, the high refractive index adhesive layer may optionally contain one or more plasticizers other than the ethylene glycol-based compound, or it may not contain any. The plasticizers other than the ethylene glycol-based compound can be used in an appropriate amount as long as it does not impair the effects of the disclosed technology. In such embodiments, the amount of plasticizers other than the ethylene glycol-based compound used is preferably less than 50% by weight of the total plasticizer used in the high refractive index adhesive layer, more preferably less than 30% by weight, more preferably less than 10% by weight, even more preferably less than 3% by weight, and particularly preferably less than 1% by weight. The disclosed technology can preferably be implemented using a high refractive index adhesive layer that is substantially free of plasticizers other than the ethylene glycol-based compound.

[0137] In some other embodiments, liquid rosins such as liquid rosin esters and liquid camphenephenol can be used as plasticizers. The above liquid rosins (e.g., liquid rosin esters) may correspond to the compounds having the above-mentioned condensed double bond-containing ring structure.

[0138] Furthermore, one or more known plasticizers (for example, phthalate esters, terephthalate esters, adipic acid esters, adipic acid polyesters, glycol benzoate esters, etc.) may be used as the plasticizer.

[0139] The amount of plasticizer used is not particularly limited and can be set according to the purpose. From the viewpoint of large deformability, in some preferred embodiments, the amount of plasticizer used per 100 parts by weight of base polymer is more than 30 parts by weight, more preferably 35 parts by weight or more, even more preferably 40 parts by weight or more, particularly preferably 45 parts by weight or more, and even more preferably 50 parts by weight or more, and may be 55 parts by weight or more, or 60 parts by weight or more. Also, from the viewpoint of achieving a good balance between high refractive index and large deformability of the high refractive index adhesive layer, the amount of plasticizer used per 100 parts by weight of base polymer is appropriate 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 may be 100 parts by weight or less, 80 parts by weight or less, or 70 parts by weight or less. In some embodiments where adhesive properties are given more importance, the amount of plasticizer used per 100 parts by weight of base polymer may be 45 parts by weight or less, or 35 parts by weight or less.

[0140] (additives (H RO )) The high refractive index adhesive layer disclosed herein may optionally contain an organic material with a higher refractive index than the base polymer (e.g., an acrylic polymer) as an additive. Hereinafter, such an organic material will be referred to as an "additive (H RO It is sometimes written as ")". Here, the above "H RO" indicates that it is an organic material with a high refractive index. Additives (H RO By using ), a high refractive index adhesive layer can be realized that more favorably balances refractive index and adhesive properties (peel strength, flexibility, etc.). Additive (H RO The organic material used as an additive (H) may be a polymer or a nonpolymer. It may also have polymerizable functional groups or not. In this specification, the additive (H) RO ) is defined as a compound different from the plasticizers used as described above. For example, additives (H RO ) may not be liquid at 30°C (e.g., 25°C or 20°C). Additive (H RO ) can be used individually or in combination of two or more types.

[0141] Additives (H RO The refractive index of the additive (H) can be set within an appropriate range in relation to the refractive index of the base polymer (e.g., an acrylic polymer), and is not limited to a specific range. RO The refractive index of the additive (H) can be selected from a range that is, for example, greater than 1.55, greater than 1.56, or greater than 1.57, and is higher than the refractive index of the base polymer. From the viewpoint of increasing the refractive index of the high refractive index adhesive layer, in some embodiments, the additive (H) RO The refractive index of (H) is advantageous to be 1.58 or higher, preferably 1.60 or higher, more preferably 1.63 or higher, may also be 1.65 or higher, may also be 1.70 or higher, and may also be 1.75 or higher. Additives with a higher refractive index (H) RO According to this, a smaller amount of additive (H RO The desired refractive index can also be achieved by using ). This is preferable from the viewpoint of suppressing a decrease in adhesive properties and optical properties. Additive (H ROThere is no particular upper limit to the refractive index of the material, but from the viewpoint of compatibility within the adhesive and ease of achieving both a high refractive index and flexibility suitable for an adhesive, for example it may be 3.000 or less, 2.500 or less, 2.000 or less, 1.950 or less, 1.900 or less, or 1.850 or less. Note that additives (H RO The refractive index of ) is measured using an Abbe refractometer, similar to the refractive index of the monomer, under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. If the manufacturer or other source provides a nominal refractive index value at 25°C, that nominal value can be used.

[0142] Additives (H RO The molecular weight of the organic material used is not particularly limited and can be selected according to the purpose. From the viewpoint of achieving a good balance between the effect of increasing the refractive index and other properties (e.g., flexibility suitable for adhesives, optical properties such as haze), in some embodiments, the additive (H RO The molecular weight of the additive (H) is preferably less than 10,000, more preferably less than 5,000, more preferably less than 3,000 (e.g., less than 1,000), and may also be less than 800, less than 600, less than 500, or less than 400. RO The fact that the molecular weight of the additive (H) is not too large can be advantageous from the viewpoint of improving compatibility within the adhesive. RO The molecular weight of the additive (H) may be, for example, 130 or more, or 150 or more. In some embodiments, the additive (H RO The molecular weight of the additive (H RO From the viewpoint of increasing the refractive index of ), it is preferably 170 or higher, more preferably 200 or higher, and may also be 230 or higher, 250 or higher, 270 or higher, 300 or higher, 500 or higher, 1000 or higher, and 2000 or higher. In some embodiments, a polymer with a molecular weight of about 1000 to 10000 (for example, 1000 or more and less than 5000) is used as an additive (H RO It can be used as ). Additives (H ROFor nonpolymers or polymers with a low degree of polymerization (e.g., 2-5 mers), the molecular weight can be calculated based on the chemical structure, or measured using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS). RO If the polymer has a higher degree of polymerization, the weight-average molecular weight (Mw) based on GPC performed under appropriate conditions can be used. If the manufacturer provides a nominal molecular weight, that nominal value can be used.

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

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

[0145] The aromatic ring described above may have one or more substituents on its ring constituent atoms, or it may not have substituents. If substituents are present, examples of such substituents include, but are not limited to, alkyl groups, alkoxy groups, aryloxy groups, hydroxyl groups, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl groups, hydroxyalkyloxy groups, glycidyloxy groups, etc. In substituents containing carbon atoms, the number of carbon atoms in the substituent is, for example, 1 to 10, advantageously 1 to 6, preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. In some embodiments, the aromatic ring described above may have no substituents on its ring constituent atoms, or it may be an aromatic ring having one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, and halogen atoms (e.g., bromine atoms).

[0146] Additives (HRO Examples of aromatic ring-containing compounds that can be used as monomers include, for example: compounds that can be used as monomers (A1); oligomers containing a compound that can be used as monomer (A1) as a monomer unit; compounds having a structure obtained by replacing a compound that can be used as monomer (A1) with a group having an ethylenically unsaturated group (which may be a substituent bonded to a ring constituent atom) or a group that does not have a hydrogen atom or an ethylenically unsaturated group (for example, a hydroxyl group, an amino group, a halogen atom, an alkyl group, an alkoxy group, a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group, etc.), etc., which do not fall under the category of plasticizers disclosed herein, but are not limited to these.

[0147] In some embodiments, additive (H RO As such, organic compounds having two or more aromatic rings in one molecule (hereinafter also referred to as "multiple aromatic ring-containing compounds") can be preferably used because a high refractive index effect can be easily obtained. Multiple aromatic ring-containing compounds may or may not have polymerizable functional groups such as ethylenically unsaturated groups. Furthermore, multiple aromatic ring-containing compounds may be polymers or nonpolymers. Furthermore, the polymer may be an oligomer containing multiple aromatic ring-containing monomers 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 polymer of about 2 to 5-mers). The oligomer may be, for example: a homopolymer of multiple aromatic ring-containing monomers; a copolymer of two or more multiple aromatic ring-containing monomers; a copolymer of one or more multiple aromatic ring-containing monomers and other monomers; etc. The other monomers may be aromatic ring-containing monomers that do not fall under multiple aromatic ring-containing monomers, monomers that do not have aromatic rings, or combinations thereof. Additive (H RO In embodiments in which an oligomer is used as such, the oligomer can be obtained by polymerizing the corresponding monomer component in a known manner.

[0148] Non-limiting examples of compounds containing multiple aromatic rings include compounds having a structure in which two or more non-condensed aromatic rings are linked via linking groups, compounds having a structure in which two or more non-condensed aromatic rings are chemically bonded directly (i.e., without the involvement of other atoms), compounds having a condensed aromatic ring structure, compounds having a fluorene structure, compounds having a dinaphthothiophene structure, compounds having a dibenzothiophene structure, and so on. Compounds containing multiple aromatic rings can be used individually or in combination of two or more.

[0149] Additives (H RO Examples of heterocyclic organic compounds (hereinafter also referred to as heterocyclic organic compounds) that can be options include thioepoxy compounds and compounds having triazine rings. An example of a thioepoxy compound is bis(2,3-epithiopropyl) disulfide and its polymer (refractive index 1.74) described in Japanese Patent Publication No. 3712653. An example of a compound having a triazine ring is a compound having at least one triazine ring (for example, 3 to 40, preferably 5 to 20) in one molecule. Since triazine rings are aromatic, compounds having triazine rings are also included in the above concept of aromatic ring-containing compounds, and compounds having multiple triazine rings are also included in the above concept of compounds containing multiple aromatic rings.

[0150] In some embodiments, additive (H RO As the additive (H), compounds that do not have ethylenically unsaturated groups can be preferably used. This suppresses deterioration of the adhesive composition due to heat and light (progression of gelation and decrease in leveling properties due to increased viscosity), and improves storage stability. Additives that do not have ethylenically unsaturated groups (H RO ) adopting the additive (H RO In an adhesive layer containing ), it is preferable from the viewpoint of suppressing dimensional changes, deformation (warping, undulation, etc.), and the occurrence of optical distortion caused by the reaction of ethylenically unsaturated groups.

[0151] Additives (H RO) can be used in appropriate amounts, to the extent that the effects of the techniques disclosed herein are not significantly impaired. In some embodiments, the additive (H) can be used in proportion to 100 parts by weight of the base polymer (e.g., an acrylic polymer). RO The amount of additive (H) used (if multiple types of compounds are used, the total amount thereof) is not particularly limited as long as it is greater than 0 parts by weight, and can be set according to the purpose. In some embodiments, the amount of additive (H) per 100 parts by weight of the base polymer is RO The amount of additive (H) used can be, for example, 80 parts by weight or less, and from the viewpoint of achieving a good balance between increasing the refractive index of the high refractive index adhesive layer and suppressing the deterioration of adhesive properties and optical properties, it is advantageous to use 60 parts by weight or less, and preferably 45 parts by weight or less. In some embodiments where adhesive properties and optical properties are given more importance, the amount of additive (H) per 100 parts by weight of the base polymer can be reduced. RO The amount used 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 technology disclosed herein is an additive (H RO This can preferably be carried out in an embodiment that uses a high refractive index adhesive layer that does not contain ). Furthermore, from the viewpoint of increasing the refractive index of the high refractive index adhesive layer, the additive (H) is used in proportion to 100 parts by weight of the base polymer. RO The amount used can be, for example, 1 part by weight or more, it is advantageous to use 3 parts by weight or more, it is preferable to use 5 parts by weight or more, it may also be 7 parts by weight or more, it may also be 10 parts by weight or more, it may also be 15 parts by weight or more, and it may also be 20 parts by weight or more.

[0152] (Crosslinking agent) In the technology disclosed herein, the adhesive composition used for forming a high refractive index adhesive layer may contain a crosslinking agent as needed for purposes such as adjusting the cohesive force of the adhesive. As the crosslinking agent, known crosslinking agents in the field of adhesives can be used, such as isocyanate crosslinking agents, epoxy crosslinking agents, aziridine crosslinking agents, oxazoline crosslinking agents, melamine resins, and metal chelate crosslinking agents. Among these, isocyanate crosslinking agents and epoxy crosslinking agents are preferred. Other examples of crosslinking agents include monomers having two or more ethylenically unsaturated groups in one molecule, i.e., polyfunctional monomers. The crosslinking agent can be used alone or in combination of two or more.

[0153] As isocyanate crosslinking agents, isocyanate compounds with two or more functions can be used, for example, aliphatic polyisocyanates such as trimethylene diisocyanate, butylene diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), and dimer acid diisocyanate; and alicyclic polyisocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), and 1,3-bis(isocyanatomethyl)cyclohexane. Examples include socyanates; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate (XDI); and polyisosinate modified compounds obtained by modifying the above isocyanate compounds with allophanate bonds, biuret bonds, isocyanurate bonds, uretdione bonds, urea bonds, carbodiimide bonds, uretonimine bonds, oxadiazinetrione bonds, etc. (e.g., isocyanurate and allophanate forms of HDI). Examples of commercially available products include the product names Takenate 300S, Takenate 500, Takenate 600, Takenate D165N, Takenate D178N, Takenate D178NL (all manufactured by Mitsui Chemicals), Sumijoule T80, Sumijoule L, Desmodule N3400 (all manufactured by Sumika Bayer Urethane Co., Ltd.), Myrionate MR, Myrionate MT, Coronate L, Coronate HL, Coronate HX, Coronate 2770 (all manufactured by Tosoh Corporation), and the product name Duranate A201H (all manufactured by Asahi Kasei Corporation). Isocyanate compounds can be used individually or in combination of two or more. A bifunctional isocyanate compound and a trifunctional or higher isocyanate compound may be used in combination.

[0154] Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane. These can be used individually or in combination of two or more.

[0155] Examples of polyfunctional 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, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, and 1,6-hexa(meth)acrylate. Examples include sandiol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, bisphenol A di(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, butyldiol(meth)acrylate, hexyldiol di(meth)acrylate, and the like. Polyfunctional monomers can be used individually or in combination of two or more.

[0156] In some embodiments, at least a portion of the crosslinking agent is a difunctional crosslinking agent having two crosslinking reactive groups (e.g., isocyanate groups) per molecule. Using a difunctional crosslinking agent facilitates the formation of flexible crosslinked structures. Difunctional crosslinking agents can be used individually or in combination of two or more. Furthermore, difunctional crosslinking agents may be used in combination with trifunctional or higher crosslinking agents.

[0157] In some embodiments, acyclic crosslinking agents (also called chain-like crosslinking agents) that do not have ring structures such as aromatic rings or aliphatic rings are preferably used as crosslinking agents. For example, among the isocyanate-based crosslinking agents described above, the use of isocyanate compounds that do not have ring structures such as aromatic rings and isocyanurate rings is preferred. By using acyclic isocyanate compounds as crosslinking agents, it is easy to form crosslinking agents with high flexibility. Specific examples of the above acyclic isocyanates include aliphatic isocyanate compounds (e.g., PDI and HDI) and modified aliphatic isocyanate compounds (e.g., polyisocyanate modified products modified by allophanate bonds, biuret bonds, urea bonds, or carbodiimide bonds of PDI and HDI). Acyclic crosslinking agents can be used alone or in combination of two or more. In some preferred embodiments, acyclic bifunctional crosslinking agents can be used as the above crosslinking agents.

[0158] In some embodiments, a crosslinking agent can be used in which the distance between one crosslinking reactive group (e.g., an isocyanate group) and another crosslinking reactive group in one molecule is relatively long. This allows for the formation of a flexible crosslinked structure having a length greater than a predetermined length. For example, a compound can be used as a crosslinking agent in which the number of atoms constituting the linking chain that connects one crosslinking reactive group to another is 10 or more (e.g., 12 or more or 14 or more). The upper limit of the number of atoms constituting the linking chain is not particularly limited as it can be adjusted by polymerization or the like depending on the purpose, and may be, for example, 2000 or less, 1000 or less, 500 or less, 100 or less, 50 or less, 30 or less, or 20 or less. The number of atoms constituting the linking chain that connects the crosslinking reactive groups refers to the minimum number of atoms required to reach another crosslinking reactive group (or, if there are three or more crosslinking reactive groups, the crosslinking reactive group closest to the first crosslinking reactive group) from one crosslinking reactive group in one molecule of the crosslinking agent. The crosslinking agents having the above-mentioned linking chains can be used individually or in combination of two or more. In some preferred embodiments, acyclic bifunctional crosslinking agents can be used as the crosslinking agents. Examples of commercially available crosslinking agents include trade names such as Coronate 2770 (manufactured by Tosoh Corporation), Takenate D178NL (manufactured by Mitsui Chemicals), and Duranate A201H (manufactured by Asahi Kasei Corporation).

[0159] When using a crosslinking agent, the amount used is not particularly limited and can be in the range of approximately 0.001 to 5.0 parts by weight per 100 parts by weight of the base polymer. From the viewpoint of improving the flexibility of the high refractive index adhesive layer and adhesion to the adherend, in some embodiments, the amount of crosslinking agent used per 100 parts by weight of the base polymer is preferably 3.0 parts by weight or less, more preferably 2.0 parts by weight or less, and may also be 1.0 part by weight or less, or 0.5 parts by weight or less. In some preferred embodiments, the amount of crosslinking agent used per 100 parts by weight of the base polymer is less than 0.5 parts by weight, and may also 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 exhibiting the effects of using the crosslinking agent, in some embodiments, the amount of crosslinking agent used per 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, 0.08 parts by weight or more, or 0.1 parts by weight or more. In some preferred embodiments, the amount of crosslinking agent used per 100 parts by weight of base polymer is more than 0.1 parts by weight, may 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 techniques disclosed herein, by using an appropriate amount of crosslinking agent within the above range, a high refractive index adhesive layer capable of withstanding large deformations can be preferably formed.

[0160] A crosslinking catalyst may be used to more effectively advance the crosslinking reaction. Examples of crosslinking catalysts include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, zirconium tetraacetylacetonate, ferric narcem, butyltin oxide, and dioctyltin dilaurate. Among these, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. The amount of crosslinking catalyst used is not particularly limited. The amount of crosslinking catalyst used per 100 parts by weight of base polymer can be in the range of approximately 0.0001 parts by weight to 1 part by weight, and preferably in the range of 0.001 parts by weight to 0.5 parts by weight, taking into consideration the balance between the speed of the crosslinking reaction and the length of the pot life of the adhesive composition.

[0161] The adhesive composition may contain a compound that induces keto-enol tautomerism as a crosslinking retarder. This can extend the pot life of the adhesive composition. For example, a compound that induces keto-enol tautomerism can be preferably used in an adhesive composition containing an isocyanate-based crosslinking agent. Various β-dicarbonyl compounds can be used as the compound that induces keto-enol tautomerism. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) and acetoacetate esters (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably used. The compound that induces keto-enol tautomerism can be used alone or in combination of two or more. The amount of the compound that induces keto-enol tautomerism can be, for example, 0.1 parts by weight to 20 parts by weight, 0.5 parts by weight to 10 parts by weight, or 1 part by weight to 5 parts by weight, per 100 parts by weight of the base polymer.

[0162] (Adhesion agent) The high refractive index adhesive layer disclosed herein may contain a tackifier. Known tackifiers such as rosin-based tackifiers, terpene-based tackifiers, phenol-based tackifiers, hydrocarbon-based tackifiers, ketone-based tackifiers, polyamide-based tackifiers, epoxy-based tackifiers, and elastomer-based tackifiers can be used. These can be used individually or in combination of two or more. The amount of tackifier used is not particularly limited and can be set to achieve appropriate adhesive performance depending on the purpose and application. In some embodiments, from the viewpoint of refractive index and transparency, the amount of tackifier per 100 parts by weight of base polymer is appropriately 30 parts by weight or less, preferably 10 parts by weight or less, and more preferably 5 parts by weight or less. The technology disclosed herein can preferably be implemented in an embodiment that does not use a tackifier.

[0163] (High refractive index particles) The high refractive index adhesive layer disclosed herein may optionally contain high refractive index particles. Herein, high refractive index particles mean particles that, when included in the adhesive, can increase the refractive index of the adhesive. Hereinafter, high refractive index particles will be referred to as "particle P". HRI It is sometimes written as "HRI stands for high refractive index. Particle P HRI The type is not particularly limited, and one or more materials capable of improving the refractive index of the adhesive can be selected and used from among metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. HRI As such, inorganic oxides (e.g., metal oxides) that can improve the refractive index of the adhesive can preferably be used. Particle P HRI Suitable examples of materials constituting the particle include inorganic oxides (specifically metal oxides) such as titania (titanium oxide, TiO2), zirconia (zirconium oxide, ZrO2), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, and niobium oxide (Nb2O5, etc.). These inorganic oxides (e.g., metal oxides) can be used individually or in combination of two or more types. HRI The average particle size (referring to the 50% volume-average particle diameter based on laser scattering and diffraction) is not particularly limited and can be selected from a range of approximately 1 nm to 1000 nm.

[0164] Particle P in a high-refractive-index adhesive layer HRI The amount of [the substance] can be used in an appropriate amount, as long as it does not impair the effects of the technology disclosed herein. Furthermore, the above-mentioned particles P HRI The content may vary depending on the desired refractive index. For example, the above particle P HRI The content of can be appropriately set to achieve a refractive index above a predetermined level, taking into consideration the required adhesive properties, etc. In some embodiments, particles P in the high refractive index adhesive layer HRI The content of is, for example, less than 10% by weight in the high refractive index adhesive layer, may be less than 1% by weight, or less than 0.1% by weight. The technology disclosed herein is a high refractive index adhesive layer in which particles P HRI It may be implemented in a manner that substantially does not include it.

[0165] (Leveling agent) In some embodiments, the adhesive composition used to form a high refractive index adhesive layer may contain a leveling agent as needed for purposes such as improving the appearance of the high refractive index adhesive layer formed from the composition (e.g., improving the uniformity of thickness) or improving the coatability of the adhesive composition. Non-limiting examples of leveling agents include acrylic leveling agents, fluorine leveling agents, and silicone leveling agents. The leveling agent can be selected appropriately from commercially available leveling agents and used by conventional methods.

[0166] (Other additives) In the technology disclosed herein, the adhesive composition used to form the high refractive index adhesive layer may optionally contain known additives that can be used in adhesive compositions, such as softeners, colorants (dyes, pigments, etc.), fillers, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, and preservatives, to the extent that the effects of the present invention are not significantly hindered. Such various additives can be conventionally used by ordinary methods and do not particularly characterize the present invention, so a detailed explanation is omitted.

[0167] While not particularly limited, the effects of the technologies disclosed herein can preferably be achieved by using a high refractive index adhesive layer containing the above-described base polymer (typically an acrylic polymer) and a plasticizer. The technologies disclosed herein can preferably be implemented in a manner in which a high refractive index adhesive layer mainly composed of the above-described base polymer and plasticizer is used. Therefore, in some preferred embodiments, a composition can be adopted for the high refractive index adhesive layer in which the content of components other than the above-described base polymer and plasticizer (other components) is limited. For example, the total amount of the above-described base polymer and plasticizer in the high refractive index adhesive layer can be 75% by weight or more (e.g., 75% by weight or more and 100% by weight or less than 100% by weight), may be 85% by weight or more, may be 90% by weight or more, may be 95% by weight or more, may be 98% by weight or more, or may be 99% by weight or more (e.g., greater than 99% by weight). The restriction of the use of components other than the above-described base polymer and plasticizer can be advantageous in 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 the 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 laminated sheet 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 may be in the range of, for example, 1.35 to 1.55. In some embodiments, from the viewpoint of increasing the refractive index difference with the refractive index n1 of the high refractive index adhesive layer to facilitate the front brightness improvement effect described later, the refractive index n2 of the low refractive index layer is preferably, for example, 1.49 or less, more preferably 1.47 or less (for example, 1.46 or less, or 1.45 or less), and may also be 1.43 or less, 1.41 or less, or 1.40 or less. Furthermore, from the viewpoint of ease of material availability and ease of compatibility with adhesive properties, in some embodiments, the refractive index n2 of the low refractive index layer may be, for example, 1.36 or higher, 1.38 or higher, 1.40 or higher, 1.42 or higher, or 1.45 or higher. In embodiments where the low refractive index layer is a low refractive index adhesive layer, the relative relationship of the adhesive strength of each surface of the laminate (laminated sheet) of the high refractive index adhesive layer and the low refractive index adhesive layer can be adjusted.

[0169] In some embodiments, 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 may be, for example, greater than 1.00, approximately 1.01 or greater, approximately 1.02 or greater is appropriate, and approximately 1.03 or greater. In some embodiments, the ratio (n1 / n2) may be advantageous to be approximately 1.05 or greater, preferably approximately 1.06 or greater, more preferably approximately 1.07 or greater, and may be approximately 1.08 or greater. There is no particular upper limit to the ratio (n1 / n2). In some embodiments, from the viewpoint of adhesive properties and transparency, the ratio (n1 / n2) may be, for example, approximately 1.20 or less, approximately 1.18 or less, approximately 1.16 or less, approximately 1.14 or less, and approximately 1.12 or less.

[0170] In some embodiments, 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, that is, the refractive index difference (n1 - n2), may be greater than, for example, 0.00, may be 0.01 or more, preferably 0.02 or more, may be 0.03 or more, may be 0.05 or more, may be 0.07 or more, may be 0.09 or more, may be 0.10 or more, or may be 0.12 or more. The upper limit of the refractive index difference (n1 - n2) is not particularly limited. In some embodiments, from the viewpoints of adhesive properties, transparency, etc., the refractive index difference (n1 - n2) may be, for example, 0.30 or less, may be 0.26 or less, may be 0.21 or less, may be 0.18 or less, or may be 0.16 or less.

[0171] In some embodiments, it is preferable that the low refractive index layer has a deformation amount of 350% or more in a deformation test conducted under the conditions of a temperature of -20°C and a speed of 300 mm / min. By satisfying the above characteristics for both the high refractive index adhesive layer and the low refractive index layer, the laminated sheet (adhesive sheet) including the high refractive index adhesive layer and the low refractive index layer can be sufficiently deformed at high speed even in a low temperature environment and can withstand large deformations. The deformation test conducted under the conditions of a temperature of -20°C and a speed of 300 mm / min is more specifically conducted by the method described in the test examples below.

[0172] Also, in some embodiments, in the deformation test conducted on the low refractive index layer under the conditions of a temperature of -20°C and a speed of 300 mm / min, the stress at a deformation amount of 350% is 2 preferably 5.0 N / mm or less. The low refractive index layer that satisfies the above characteristics can have a high refractive index and can be sufficiently deformed at high speed while maintaining a predetermined degree of flexibility even in a low temperature environment. Therefore, it is suitable for use in applications involving large deformations. In some preferred embodiments, the stress at a deformation amount of 350% may be 4 N / mm 2 or less, may be 3 N / mm 2 or less, may be 2 N / mm 2 or less, may be 1 N / mm 2 or less, may be 0.5 N / mm 2 or less, or may be 0.3 N / mm 2The following may be used. The lower limit value of the stress at the above deformation amount of 350% is theoretically 0.0 N / mm 2 or more, and in some preferred embodiments, it may be 0.1 N / mm 2 or more.

[0173] The storage elastic modulus G'(25°C) of the low refractive index layer is not particularly limited, and can be, for example, in the range of 1.0 kPa to 500 kPa. From the viewpoint of enhancing the effect of imparting flexibility by the low refractive index layer and improving the followability to deformation, in some embodiments, it is appropriate that the storage elastic modulus G'(25°C) of the low refractive index layer is 400 kPa or less, preferably 300 kPa or less, more preferably 200 kPa or less (for example, 180 kPa or less, or 150 kPa or less), and may also be 120 kPa or less, 90 kPa or less, 70 kPa or less. Also, from the viewpoint of imparting appropriate cohesion to the low refractive index layer, in some embodiments, it is appropriate that the storage elastic modulus G'(25°C) of the low refractive index layer is 5.0 kPa or more, preferably 10 kPa or more, and may also be 15 kPa or more, 25 kPa or more, 35 kPa or more, 60 kPa or more, 80 kPa or more. From the viewpoint of making it easier to realize higher cohesive force and adhesive properties, in some embodiments, the storage elastic modulus G'(25°C) of the low refractive index layer may also be 95 kPa or more, 110 kPa or more, 140 kPa or more.

[0174] In embodiments where the low refractive index layer is an adhesive layer, the type of adhesive constituting the adhesive layer is not particularly limited. The adhesive constituting the low refractive index adhesive layer may contain one or more types of rubber-like polymers as a base polymer, such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, mixtures thereof), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine polymers, which can be used in the field of adhesives. From the viewpoint of adhesive performance and cost, an adhesive containing an acrylic polymer or a rubber polymer as a base polymer can be preferably adopted. Among these, an adhesive using an acrylic polymer as a base polymer (acrylic adhesive) is preferred. In embodiments where the high refractive index adhesive layer is an acrylic adhesive layer, from the viewpoint of adhesion between the high refractive index adhesive layer and the low refractive index adhesive layer, a configuration in which the low refractive index adhesive layer is an acrylic adhesive layer can be preferably adopted.

[0175] In some embodiments, the acrylic polymer is preferably a polymer of a monomer raw material that contains, for example, an alkyl (meth)acrylate and may further contain other monomers copolymerizable with the alkyl (meth)acrylate (copolymerizable monomers). The content of the alkyl (meth)acrylate in the monomer raw material 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 of a monomer component that contains alkyl (meth)acrylate as a main monomer and may further contain the copolymerizable monomer as a secondary monomer. Here, the main monomer refers to a component that accounts for more than 50% by weight of the monomer composition in the monomer raw material. More than 55% by weight or more than 60% by weight of the monomer composition may be alkyl (meth)acrylate. In some embodiments, the proportion of alkyl (meth)acrylate in the above monomer raw material of the acrylic polymer can be, 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. The upper limit of the proportion of alkyl (meth)acrylate is not particularly limited, but it is preferably 99.5% by weight or less (for example, 99% by weight or less), or from the viewpoint of preferably exhibiting properties based on the sub-monomers (for example, cohesive force), it may be 98% by weight or less (for example, less than 97% by weight).

[0176] As the alkyl (meth)acrylate, for example, a compound represented by the following formula (1) can be preferably used. CH2=C(R 1 )COOR 2 (1) Here, in equation (1) above, R 1 R is a hydrogen atom or a methyl group. 2 A chain-like alkyl group having 1 to 20 carbon atoms (hereinafter, this range of carbon atoms will be referred to as "C") 1-20 It is sometimes expressed as ". ) From the viewpoint of the storage modulus of the adhesive, R 2 C 1-12 (For example C 2-10 Typically C 4-8Alkyl (meth)acrylate, which is a chain-like alkyl group, is preferred. 2 C 1-20 Alkyl (meth)acrylates, which are chain-like alkyl groups, can be used individually or in combination of two or more. Preferred alkyl (meth)acrylates include n-butyl acrylate and 2-ethylhexyl acrylate.

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

[0178] In some embodiments, a fluorine-containing monomer can be used as the copolymerizable monomer to lower the refractive index n2 of the low refractive index layer. The content of the fluorine-containing monomer in the monomer raw material may be, for example, 10% by weight or more, 25% by weight or more, or 35% by weight or more. From the viewpoint of making it easier to realize a low refractive index layer with an even lower refractive index, the content of the fluorine-containing monomer is preferably 40% by weight or more, more preferably 45% by weight or more, even more preferably 55% by weight or more, and may 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 fluorine-containing monomer in the monomer raw material, and may be 100% by weight. In some embodiments, from the viewpoint of the cohesiveness of the low refractive index layer, etc., the content of the fluorine-containing monomer is appropriate to be 99.9% by weight or less, preferably 99.5% or less, may be 99% by weight or less, may be 97% by weight or less, or may be 92% by weight or less. Fluorine-containing monomers can be used individually or in combination of two or more.

[0179] As the fluorine-containing monomer, fluorine-containing acrylic monomers can be suitably used. The fluorine-containing acrylic monomer is not particularly limited as long as it is an acrylic monomer having at least one fluorine atom in its molecule. For example, fluorine-containing (meth)acrylic acid esters can be suitably used. A suitable example of a fluorine-containing (meth)acrylic acid ester is one having a fluorinated hydrocarbon group at its ester terminus. Examples of fluorinated hydrocarbon groups include fluorinated aliphatic hydrocarbon groups, fluorinated alicyclic hydrocarbon groups, and fluorinated aromatic hydrocarbon groups. Fluorinated aliphatic hydrocarbon groups are preferred as the fluorinated hydrocarbon group. Examples of fluorinated aliphatic hydrocarbon groups include fluorinated alkyl groups. In a fluorinated aliphatic hydrocarbon group, the aliphatic hydrocarbon moiety may be linear or branched. Furthermore, in a fluorinated aliphatic hydrocarbon group, the fluorine atom may be bonded to any carbon atom of the aliphatic hydrocarbon group moiety. The number of fluorine atoms bonded to a single carbon atom may be singular or multiple. The number of carbon atoms to which the fluorine atom is bonded is not particularly limited.

[0180] In fluorinated aliphatic hydrocarbon groups (especially fluorinated alkyl groups), the number of carbon atoms in the hydrocarbon group is not particularly limited. In some embodiments, considering compatibility with other copolymerizable monomers, fluorinated aliphatic hydrocarbon groups with, for example, 1 to 18 (preferably 1 to 12) carbon atoms are preferred. Specific examples of fluorinated aliphatic hydrocarbon groups include methyl fluorides such as trifluoromethyl, difluoromethyl, and monofluoromethyl groups; ethyl fluorides 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 groups; and the like. Examples of fluorinated alkyl groups with three or more carbon atoms include various fluorinated alkyl groups in which one or more fluorine atoms are bonded to one or more carbon atoms in the alkyl group, similar to the fluorinated methyl group and fluorinated ethyl group exemplified above.

[0181] Examples of fluorinated alicyclic hydrocarbon groups include fluorinated cycloalkyl groups. Similar to the fluorinated aliphatic hydrocarbon groups described above, in fluorinated alicyclic hydrocarbon groups, the fluorine atom may be bonded to any carbon atom of the alicyclic hydrocarbon group, and the number of fluorine atoms bonded to a single carbon atom may be singular or multiple. Furthermore, the number of carbon atoms to which the fluorine atom is bonded is not particularly limited. Examples of fluorinated alicyclic hydrocarbon groups include cyclohexyl groups having one fluorine atom, such as 2-fluorocyclohexyl, 3-fluorocyclohexyl, and 4-fluorocyclohexyl groups; cyclohexyl groups having two fluorine atoms, such as 2,4-difluorocyclohexyl and 2,6-difluorocyclohexyl groups; and cyclohexyl groups having three fluorine atoms, such as 2,4,6-trifluorocyclohexyl groups.

[0182] The fluorinated hydrocarbon group may or may not have substituents. Such substituents are not particularly limited and include, for example, hydrocarbon groups such as alkyl groups, alkoxy groups, hydroxyl groups, carboxyl groups, amino groups, nitro groups, cyano groups, halogen atoms, and the like. Substituents can be used individually or in combination of two or more.

[0183] Fluorine atom-containing (meth)acrylic acid esters [fluorinated (meth)acrylates] include, for example, fluorine atom-containing alkyl (meth)acrylic acid esters [fluorinated alkyl (meth)acrylates], fluorine atom-containing cycloalkyl (meth)acrylic acid esters [fluorinated cycloalkyl (meth)acrylates], and fluorine atom-containing aryl (meth)acrylic acid esters [fluorinated aryl (meth)acrylates].

[0184] As the fluorine atom-containing (meth)acrylic acid ester, fluorinated alkyl (meth)acrylates (especially fluorinated alkyl acrylates) are preferred. Examples of fluorinated alkyl (meth)acrylates include 2,2,2-trifluoroethyl acrylate (product name "Viscote 3F" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 2,2,3,3-tetrafluoropropyl acrylate (product name "Viscote 4F" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 1H,1H,5H-octafluoropentyl acrylate (product name "Viscote 8F" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 1H,1H,5H-octafluoropentyl methacrylate (product name "Viscote 8FM" manufactured by Osaka Organic Chemical Industry Co., Ltd.), 2-(heptadecafluorononyl)ethyl acrylate (product name "FA-108" manufactured by Kyoeisha Chemical Co., Ltd.), and 1H,1H,2H,2H-tridecafluorooctyl acrylate (product name "Viscote 13F" manufactured by Osaka Organic Chemical Industry Co., Ltd.).

[0185] In fluorinated alkyl (meth)acrylates, the number of carbon atoms in the fluorinated alkyl group is advantageous to be 3 or more, preferably 4 or more, more preferably 5 or more, even more preferably 6 or 7 or more, and particularly preferably 8 or more, from the viewpoint of low refractive index effect and flexibility. From the viewpoint of adhesive performance, the number of carbon atoms in the above fluorinated alkyl group is advantageous to be 18 or less, preferably 14 or less, more preferably 12 or less, and may also be 10 or less, or 9 or less. In some embodiments, the number of carbon atoms in the above fluorinated alkyl group may be 7 or less, or 5 or less. Furthermore, in some embodiments, as the fluorine atom-containing (meth)acrylic acid ester, a fluorinated alkyl (meth)acrylate in which fluorine is not bonded to the carbon at position 1 of the alkyl group is preferred, for example, a fluorinated alkyl (meth)acrylate in which fluorine is not bonded to either the carbon at position 1 or 2 of the alkyl group, such as 1H,1H,2H,2H-tridecafluorooctyl acrylate, can be preferably used.

[0186] In some embodiments, the low refractive index layer is an acrylic adhesive layer, and the acrylic polymer that is the base polymer of the adhesive may be a polymer of monomer raw materials that contains at least the above-mentioned fluorine-containing acrylic monomer (e.g., fluorinated alkyl (meth)acrylate) and may further contain other monomers copolymerizable with the fluorine-containing acrylic monomer (copolymerizable monomers). This monomer raw material may or may not contain alkyl (meth)acrylate. The content of the fluorine-containing acrylic monomer in the above monomer raw material may be, for example, 10% by weight or more, 25% by weight or more, or 35% by weight or more. From the viewpoint of making it easier to realize a low refractive index layer with an even lower refractive index, the content of the fluorine-containing acrylic monomer is preferably 40% by weight or more, more preferably 45% by weight or more, even 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. The upper limit of the content of fluorine-containing acrylic monomer in the monomer raw material is not particularly limited and may be 100% by weight. In some embodiments, from the viewpoint of the cohesiveness of the low refractive index layer, the content of the fluorine-containing acrylic monomer is suitable to be 99.9% by weight or less, preferably 99.5% or less, may be 99% by weight or less, may be 97% by weight or less, or may be 92% by weight or less. The fluorine-containing acrylic monomer can be used alone or in combination of two or more types.

[0187] The monomer raw material for preparing the base polymer of the low refractive index layer may be a composition that includes a copolymerizable monomer in addition to a fluorine-containing acrylic monomer (e.g., fluorinated alkyl (meth)acrylate). Examples of copolymerizable monomers include one or more functional group-containing monomers such as carboxyl group-containing monomers, hydroxyl group-containing monomers, acid anhydride group-containing monomers, amide group-containing monomers, amino group-containing monomers, monomers having a nitrogen atom-containing ring (e.g., N-vinyl cyclic amides such as N-vinyl-2-pyrrolidone), sulfonic acid group-containing monomers, and phosphate group-containing monomers. Other examples of copolymerizable monomers include vinyl ester monomers such as vinyl acetate, aromatic vinyl compounds such as styrene, non-aromatic ring-containing (meth)acrylates such as cycloalkyl (meth)acrylate and isobornyl (meth)acrylate, and alkoxy group-containing monomers. Specific examples include, but are not limited to, those mentioned above, which can be used as base polymers for high refractive index adhesive layers. For example, from the viewpoint of improving cohesive strength, acrylic polymers obtained by copolymerizing carboxyl group-containing monomers and / or hydroxyl group-containing monomers are preferred as the copolymerizable monomers.

[0188] In some preferred embodiments, the monomer raw material for preparing the base polymer of the low refractive index layer may have a composition containing a hydroxyl group-containing monomer. The hydroxyl group-containing monomer can be useful for improving cohesive force and introducing crosslinking points. Preferred examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate. From the viewpoint of improving flexibility at room temperature, 4-hydroxybutyl acrylate may be more preferably used. The content of the hydroxyl group-containing monomer in the monomer raw material is not particularly limited and may be, for example, 0.01% by weight or more (preferably 0.1% by weight or more, more preferably 0.5% by weight or more). In some embodiments, the content of the hydroxyl group-containing monomer may be 0.7% by weight or more, 0.9% by weight or more, or 1.5% by weight or more of the monomer raw material. The upper limit of the content of the hydroxyl group-containing monomer is not particularly limited and may be, for example, 15% by weight or less or 10% by weight or less. In some embodiments, from the viewpoint of lowering the refractive index, the content of the hydroxyl group-containing monomer in the above monomer raw material is suitable to be less than 10% by weight, preferably less than 5% by weight, may be less than 3% by weight, may be less than 2.5% by weight, or may be less than 1.5% by weight.

[0189] In some embodiments, the monomer raw material for preparing the base polymer of the low refractive index layer preferably has a limited content of carboxyl group-containing monomers from the viewpoint of suppressing coloration or discoloration (e.g., yellowing) of the low refractive index layer. The content of carboxyl group-containing monomers in the above monomer raw material may be, for example, 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). Limiting the content of carboxyl group-containing monomers in this way is also advantageous from the viewpoint of suppressing corrosion of metallic materials (e.g., metal wiring or metal films that may be present on the adherend) that may be in contact with or near the low refractive index layer. The technology disclosed herein can preferably be carried out in an embodiment in which the above monomer raw material does not contain carboxyl group-containing monomers. For similar reasons, in some embodiments, the monomer raw material for preparing the base polymer of the low refractive index layer preferably has a limited content of monomers having acidic functional groups (including carboxyl groups, sulfonic acid groups, phosphate groups, etc.). In such embodiments, the preferred content of carboxyl group-containing monomers described above can be applied as the content of acidic functional group-containing monomers in the monomer raw material. The techniques disclosed herein can preferably be carried out in embodiments in which the monomer raw material does not contain acidic group-containing monomers (i.e., embodiments in which the base polymer of the low refractive index layer is acid-free).

[0190] The base polymer for the low refractive index layer can be prepared by employing known polymerization methods as appropriate, similar to the base polymer for the high refractive index adhesive layer. The weight-average molecular weight (Mw) of the base polymer (e.g., acrylic polymer) is not particularly limited, for example, approximately 10 × 10 4 ~500×10 4 It may be within the range of approximately 20 × 10 4 ~200×10 4 It may also be within the range of . In some embodiments, from the viewpoint of adhesion with the high refractive index adhesive layer, the Mw of the base polymer of the low refractive index adhesive layer is 250 × 10 4 The following is appropriate: 200 × 10 4 The following are also acceptable: 150 x 10 4 The following is also acceptable: 120 x 10 4 (for example, 95 x 10) 4 The following is also acceptable: 75 x 10 4 The following is also acceptable: 68 × 10 4 The following is also acceptable: 60 x 10 4 The following is also acceptable. Furthermore, in some embodiments, from the viewpoint of the cohesiveness of the low refractive index adhesive layer, the Mw of the base polymer is, for example, 30 × 10 4 The above is sufficient, 40 x 10 4 The above is also acceptable: 50 x 10 4 The above is also acceptable. In some preferred embodiments, the base polymer Mw is approximately 70 × 10 4 It may be more than that, approximately 100 x 10 4 The above is also acceptable, 130 x 104 The above may also be 160×10 4 or more (for example, 180×10 4 or more). By using a base polymer having a Mw of a predetermined value or more, an appropriate cohesive force capable of exhibiting desired adhesive properties can be easily obtained. Further, by utilizing the cohesiveness based on the high molecular weight polymer as described above, flexibility excellent in flexibility and thus capable of withstanding large deformation can be easily obtained. To adjust Mw, a conventionally known chain transfer agent can be used as necessary.

[0191] Although not particularly limited, from the viewpoint of adhesion, the Tg of the base polymer (for example, an acrylic polymer) of the low refractive index layer is advantageously approximately 0°C or lower, preferably approximately -5°C or lower (for example, approximately -15°C or lower, or -25°C or lower). Further, from the viewpoint of the cohesive force of the adhesive layer, the Tg of the base polymer of the low refractive index layer is approximately -75°C or higher, preferably approximately -70°C or higher (for example, -50°C or higher, and further -30°C or higher). The Tg of an acrylic polymer can be adjusted by appropriately changing the monomer composition (that is, the types and usage ratio of monomers used for the synthesis of the polymer).

[0192] Known crosslinking agents can be used for the low refractive index layer. Further, the low refractive index layer can contain tackifiers and other additives. The crosslinking agent and the tackifier can be appropriately selected from the same ones that can be used for the high refractive index adhesive layer, and an appropriate amount can be used.

[0193] In embodiments where the adhesive composition used to form a low refractive index adhesive layer includes a crosslinking agent, an isocyanate-based crosslinking agent may be preferably used as the crosslinking agent. In some embodiments, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of the base polymer in 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, from the viewpoint of adhesion with the high refractive index adhesive layer. Furthermore, from the viewpoint of appropriately exhibiting the effects of the crosslinking agent, in some embodiments, the amount of isocyanate-based crosslinking agent used per 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 the adhesive layer> In the technologies disclosed herein, the adhesive constituting the adhesive layer (which may be a high refractive index adhesive layer and / or a low refractive index layer; the same applies hereinafter unless otherwise specified) can be formed using an adhesive composition. The form of the adhesive composition used is not particularly limited and may be various forms, such as a solvent-type adhesive composition containing an adhesive-forming component in an organic solvent, an active energy ray-curable adhesive composition prepared to form an adhesive by curing with active energy rays such as ultraviolet light or radiation, a water-dispersible adhesive composition in which the adhesive-forming component is dispersed in water, or a hot-melt adhesive composition that is applied in a heated and molten state and forms an adhesive when cooled to around room temperature. The adhesive may be an adhesive obtained by curing an adhesive composition of the form of solvent-type, active energy ray-curable, water-dispersible, or hot-melt type by drying, crosslinking, polymerization, cooling, etc., i.e., a cured product of the above adhesive composition. The curing means for the adhesive composition (e.g., drying, crosslinking, polymerization, cooling, etc.) may be applied by applying only one type, or two or more types may be applied simultaneously or in multiple stages. In solvent-based adhesive compositions, the adhesive can typically be formed by drying (preferably further crosslinking) the composition. In active energy ray-curable adhesive compositions, the adhesive is typically formed by irradiating with active energy rays to promote polymerization and / or crosslinking reactions. If drying is required for active energy ray-curable adhesive compositions, irradiation with active energy rays may be performed after drying. The adhesives disclosed herein can preferably be formed using solvent-based adhesive compositions, although this is not a limitation.

[0195] The adhesive layer in the technology disclosed herein can be formed by applying (e.g., coating) an adhesive composition to a suitable surface and then curing the composition. The application of the adhesive composition can be carried out using conventional coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, and spray coaters.

[0196] The adhesive layer in the technology disclosed herein may be a post-curing adhesive layer or an adhesive layer that does not exhibit post-curing properties. 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 having unreacted ethylenically unsaturated groups in the side chains of the base polymer, and adhesive layers containing unreacted polyfunctional monomers. In some embodiments, it is preferable that the adhesive layer does not exhibit post-curing properties. An adhesive layer that does not exhibit post-curing properties does not undergo dimensional changes associated with the post-curing reaction (i.e., has good dimensional stability), making it easier to suppress warping of the adhesive layer or the adherend to which the adhesive layer is attached. The absence of dimensional changes due to post-curing (e.g., curing shrinkage) can also be advantageous from the viewpoint of suppressing optical distortion of the adhesive layer.

[0197] The thickness of the adhesive layer in the technology disclosed herein is not particularly limited and can be, for example, 3 μm or more, and preferably 5 μm or more. An adhesive layer with a thickness of 5 μm or more makes it easier to obtain good adhesive properties. Furthermore, an adhesive layer of such thickness can absorb any irregularities that may exist on the surface of the adherend, making it easier to bond to the adherend with good adhesion. A thickness of 5 μm or more for the adhesive layer (for example, the thickness of a high refractive index adhesive layer) is also preferable from the viewpoint of preventing discoloration and color unevenness due to light interference. In some embodiments, the thickness of the adhesive layer may be 10 μm or more, 20 μm or more, 30 μm or more, 50 μm or more, 70 μm or more, or 85 μm or more. Also, in some embodiments, the thickness of the adhesive layer may be, for example, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 120 μm or less. In some preferred embodiments, the thickness of the adhesive layer is 100 μm or less, more preferably 75 μm or less, even more preferably 70 μm or less, and may be 50 μm or less, or even 30 μm or less. Having an adhesive layer that is not too thick can be advantageous from the viewpoint of thinning the laminated sheet or light-emitting device containing the adhesive layer. Also, a thin adhesive layer tends to have excellent conformability to the adherend. The technology disclosed herein can preferably be implemented, for example, in embodiments in which the thickness of the adhesive layer is in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm, even more preferably 5 μm to 75 μm).

[0198] In some embodiments, the thickness of the adhesive layer described above may apply to at least the thickness T1 of the high refractive index adhesive layer. The thickness T2 of the low refractive index adhesive layer may also be selected from a similar range. The thickness of the adhesive layer described above may also apply to the thickness T2 of the low refractive index layer, whether or not it is an adhesive layer. The thickness T1 of the high refractive index adhesive layer and the thickness T2 of the low refractive index layer may 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 may 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 (e.g., greater than 1.0). Also, the above ratio (T1 / T2) may be, for example, 20 or less, 10 or less, 5 or less, or 3 or less. In some embodiments, the above ratio (T1 / T2) may be less than 2, less than 1.5, or less than 1. In some other embodiments, the above ratio (T1 / T2) may be 0.8 or less, 0.6 or less, or 0.5 or less.

[0199] Methods for obtaining a laminated sheet consisting of a high refractive index adhesive layer and a low refractive index layer (typically a low refractive index adhesive layer) include, for example, forming the high refractive index adhesive layer and the low refractive index layer on a release surface (e.g., the release surface of a release liner) and bonding them together; applying a composition for forming the low refractive index layer onto the high refractive index adhesive layer and curing it; or conversely, applying an adhesive composition for forming the high refractive index adhesive layer onto the low refractive index layer and curing it; however, these methods are not limited to these. When bonding pre-formed high refractive index adhesive layers and low refractive index layers, treatments to promote adhesion between the layers may be performed as needed. For example, autoclaving and roll pressing can be performed, but these methods are not limited to these.

[0200] (Peel strength) The peel strength of the adhesive layer disclosed herein to the glass plate is not particularly limited. In some embodiments, the adhesive layer may have a peel strength to the glass plate of, for example, 0.1 N / 25 mm or more, or 0.5 N / 25 mm or more. In some preferred embodiments, the peel strength to the glass plate is 1.0 N / 25 mm or more, more preferably 1.5 N / 25 mm or more, even more preferably 2.0 N / 25 mm or more, and may also be 3.0 N / 25 mm or more, 5.0 N / 25 mm or more, or 10 N / 25 mm or more. An adhesive layer having a peel strength to the glass plate of such a predetermined value or more is suitable for joining and fixing, for example, glass members. The upper limit of the peel strength is not particularly limited and may be, for example, 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 pressing the adhesive onto an alkali glass plate as the adherend, leaving it in an environment of 23°C and 50% RH for 30 minutes, then placing it in a pressurized degassing device (autoclave) and autoclaving it at a temperature of 50°C and a pressure of 0.5 MPa for 30 minutes, and then leaving it in an atmosphere of 23°C and 50% RH for 24 hours, after which the peel strength is measured under conditions of a peel angle of 180 degrees and a tensile speed of 300 mm / min. For measurement, if necessary, the adhesive layer to be measured can be reinforced by attaching an appropriate backing material (for example, a polyethylene terephthalate (PET) film with a thickness of about 25 μm to 50 μm). More specifically, the peel strength can be measured by the following method. [Peel strength against glass plate] Under a measurement environment of 23°C and 50%RH, the release liner is peeled off from one side of the adhesive layer, a 50μm thick PET film is bonded to the backing, and the piece is cut to a size of 25mm wide and 100mm long to serve as the test specimen. The release liner is peeled off from the other side of the test specimen and pressed onto the surface of an alkali glass plate (manufactured by Matsunami Glass Industry Co., Ltd., 1.35mm thick, blue plate with polished edge) using a 2kg roller for one back-and-forth motion. After leaving this in the same environment for 30 minutes, it is then placed in a pressurized degassing device (autoclave) and autoclaved for 30 minutes at a temperature of 50°C and a pressure of 0.5MPa. After leaving it in an atmosphere of 23°C and 50%RH for 24 hours, the peel strength (adhesion strength) [N / 25mm] is measured using a universal tensile and compression tester in accordance with JIS Z 0237:2000, under conditions of a tensile speed of 300mm / min and a peel angle of 180 degrees. For example, the "Tensile Compression Tester, TG-1kN" manufactured by Minebea Corporation can be used as a universal tensile and compression testing machine. When the high refractive index adhesive layer disclosed herein is laminated with a low refractive index adhesive layer to form a laminated sheet in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, in some embodiments, the peel strength described above is preferably applied to at least 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 may be the same or different.

[0202] <Supporting base material> The high refractive index adhesive layer and the low refractive index layer may be laminated on one side of the support substrate in this order or in the reverse order. This configuration, in which the high refractive index adhesive layer and the low refractive index layer are laminated on the support substrate, can also be understood as an adhesive sheet with a substrate. Accordingly, this specification provides an adhesive sheet with a substrate (adhesive product) comprising a laminated sheet consisting of a high refractive index adhesive layer and a low refractive index layer (preferably the low refractive index adhesive layer), and a support substrate that supports the laminated sheet.

[0203] The material of the supporting substrate is not particularly limited and can be appropriately selected according to the purpose and manner of use. Non-limiting examples of usable substrates include: polyolefin films mainly composed of polyolefins such as polypropylene (PP) and ethylene-propylene copolymer; polyester films mainly composed of polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); and polyvinyl chloride films mainly composed of polyvinyl chloride; foam sheets made of foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam; woven and nonwoven fabrics made by single or blended fibrous materials (which may be natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc.); papers such as Japanese paper, fine paper, kraft paper, and crepe paper; and metal foils such as aluminum foil and copper foil. Substrates with a composite composition of these may also be used. Examples of such composite substrates include, for instance, a substrate with a structure in which metal foil and the above-mentioned plastic film are laminated, and a plastic substrate reinforced with inorganic fibers such as glass cloth.

[0204] In some embodiments, various film substrates can be preferably used. The film substrate may be a porous substrate such as a foamed film or a nonwoven fabric sheet, a non-porous substrate, or a substrate with a structure in which a porous layer and a non-porous layer are laminated. In some embodiments, the film substrate may preferably include a resin film that is independently shape-retaining (self-supporting or independent) as a base film. Here, "resin film" means a resin film with a non-porous structure, which is typically substantially free of air bubbles (voidless). Therefore, the resin film is a concept distinct from foamed films and nonwoven fabrics. The resin film may preferably be one that is independently shape-retaining (self-supporting or independent). The resin film may have a single-layer structure or a multilayer structure of two or more layers (for example, a three-layer structure).

[0205] Materials that make up resin films include, for example, polyester resins mainly composed of polyester such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyolefin resins mainly composed of polyolefins such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-butene copolymer; cellulose resins such as triacetylcellulose; acetate resins; polysulfone resins; polyethersulfone resins; polycarbonate resins; polyamide (PA) resins such as nylon 6, nylon 66, and partially aromatic polyamides; and polyimide (PI) resins. Examples include resins, transparent polyimide resins, polyamide-imide (PAI), polyetheretherketone (PEEK), polyethersulfone (PES), norbornene-based resins and other cyclic polyolefin resins, (meth)acrylic resins, polyvinyl chloride resins, polyvinylidene 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), and fluorinated polyimide resins, among others.

[0206] The above-mentioned resin film may be formed using a resin material containing one of these resins alone, or it may be formed using a resin material blended with two or more of these resins. The above-mentioned resin film may be unoriented or oriented (e.g., uniaxially oriented or biaxially oriented). For example, PET film, PBT film, PEN film, unoriented polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, PP / PE blend film, etc., can be preferably used. Examples of resin films preferred from the viewpoint of strength and dimensional stability include PET film, PEN film, PPS film, and PEEK film. PET film and PPS film are particularly preferred from the viewpoint of availability, and PET film is preferred among them.

[0207] The resin film may contain known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, and antiblocking agents, as needed, within a range that does not significantly impair the effects of the present invention. The amount of additives to be added is not particularly limited and can be appropriately set depending on the application of the adhesive sheet, etc.

[0208] The method for manufacturing the resin film is not particularly limited. For example, conventionally known general resin film molding methods such as extrusion molding, inflation molding, T-die casting, and calender roll molding can be used as appropriate.

[0209] The above-mentioned substrate may be substantially composed of such a base film. Alternatively, the substrate may 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 lamination layers for imparting a desired appearance to the substrate, antistatic layers, undercoating layers, release layers, and other surface treatment layers.

[0210] In some embodiments, a light-transmitting substrate (hereinafter also referred to as a light-transmitting substrate) may be preferably used as the support substrate. This makes it possible to construct an adhesive sheet with a light-transmitting substrate. The total light transmittance of the light-transmitting substrate may be, for example, more than 50%, and may be 70% or more. In some preferred embodiments, the total light transmittance of the support substrate may be 80% or more, more preferably 90% or more, and may be 95% or more (for example, 95-100%). The above total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the product name "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory or an equivalent product may be used. A preferred example of the above light-transmitting substrate is a light-transmitting resin film. The above light-transmitting substrate may also be an optical film.

[0211] The thickness of the substrate is not particularly limited and can be selected according to the purpose and manner of use. The thickness of the substrate may be, for example, 500 μm or less, preferably 300 μm or less from the viewpoint of handling and processability, but may also be 150 μm or less, 100 μm or less, 50 μm or less, 25 μm or less, or 10 μm or less. As the thickness of the substrate decreases, the ability to conform to the surface shape of the adherend tends to improve. Also, from the viewpoint of handling and processability, the thickness of the substrate may be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

[0212] The surface of the substrate on which the adhesive layer is laminated may be subjected to conventionally known surface treatments as needed, such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or formation of an undercoat layer by applying an undercoat agent (primer). Such surface treatments may be performed to improve the anchoring ability of the adhesive layer to the substrate. The composition of the primer used to form the undercoat layer is not particularly limited and can be appropriately selected from known ones. The thickness of the undercoat layer is not particularly limited, but is usually appropriate at about 0.01 μm to 1 μm, and preferably at about 0.1 μm to 1 μm. Other treatments that may be applied to the substrate as needed 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 with a substrate, the thickness of the adhesive sheet may be, for example, 1000 μm or less, 350 μm or less, 200 μm or less, 120 μm or less, 75 μm or less, or 50 μm or less. Furthermore, from the viewpoint of handling and other factors, the thickness of the adhesive sheet may be, for example, 10 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more. Note that the thickness of the adhesive sheet refers to the thickness of the portion that is attached to the substrate. For example, in the substrate-less double-sided adhesive sheet 2 with the configuration shown in Figure 2, it refers to the thickness from the first surface (first adhesive surface) 10A to the second surface (second adhesive surface) 10B of the adhesive layer, and does not include the thickness of the release liners 31 and 32.

[0214] <Laminated sheet> The laminated sheet (adhesive sheet) disclosed herein, which includes a high refractive index adhesive layer and a low refractive index layer, may be a laminated sheet consisting of a high refractive index adhesive layer and a low refractive index layer (preferably a low refractive index adhesive layer) as described above, or it may be a laminated sheet with a substrate further including a support substrate for supporting the laminated sheet.

[0215] In some embodiments, the haze value of the laminated sheet 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, and may also be 0.9% or less, 0.8% or less, 0.5% or less, or 0.3% or less. Such highly transparent laminated sheets are advantageous in applications where high light transmittance is required. There is no particular lower limit to the haze value of the laminated sheet, and from the viewpoint of improving transparency, a smaller haze value is preferable. On the other hand, in some embodiments, considering the refractive index and adhesive properties, the haze value may be, for example, 0.05% or more, or 0.10% or more. The haze value of the laminated sheet can be measured in the same way as the haze value of the adhesive layer described above. Specifically, it can be measured by the method described in the test examples below. The haze value of the laminated sheet can be obtained by the composition of the adhesive layer described above, and in configurations with a substrate, by selecting the type of substrate and the thickness of the substrate.

[0216] In some embodiments, the total light transmittance of the laminated sheet is preferably 85.0% or higher (for example, 88.0% or higher, 90.0% or higher, or greater than 90.0%). Such highly transparent laminated sheets are advantageous in applications where high light transmittance is required. The upper limit of the total light transmittance may practically be, for example, approximately 98% or less, approximately 96% or less, or approximately 95% or less. In some embodiments, considering the refractive index and adhesive properties, the total light transmittance of the laminated sheet may be approximately 94% or less, approximately 93% or less, or approximately 92% or less. The total light transmittance of the laminated sheet can be measured in the same way as the measurement of the total light transmittance of the adhesive layer described above. Specifically, it can be measured by the method described in the test examples below. The total light transmittance of the laminated sheet can be obtained by selecting the composition of the adhesive layer described above, or, in configurations with a substrate, by selecting the type and thickness of the substrate.

[0217] The thickness of the laminated sheet (substrate-less laminated sheet or substrate-attached laminated sheet) disclosed herein may be, for example, 1000 μm or less, 350 μm or less, 200 μm or less, 120 μm or less, 75 μm or less, or 50 μm or less. The thickness of the adhesive sheet may be, for example, 5 μm or more, 10 μm or more, 15 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more, from the viewpoint of handling and other factors. Note that the thickness of the adhesive sheet refers to the thickness of the portion that is attached to the substrate. For example, in the substrate-less double-sided adhesive sheet 2 with the configuration shown in Figure 2, it refers to the thickness from the first surface (first adhesive surface) 10A to the second surface (second adhesive surface) 10B of the adhesive layer, and does not include the thickness of the release liners 31 and 32.

[0218] <Laminated sheet with release liner> The high-refractive-index adhesive layer and the low-refractive-index layer disclosed herein may take the form of an adhesive product (laminated sheet with release liner) in which the adhesive surface of a laminated sheet containing the high-refractive-index adhesive layer and the low-refractive-index layer is in contact with the release surface of a release liner before being incorporated into a light-emitting device. Accordingly, this specification provides a laminated sheet with a release liner (adhesive product) comprising a laminated sheet of a high-refractive-index adhesive layer and a low-refractive-index layer, and a release liner having a release surface that contacts the adhesive surface of the laminated sheet.

[0219] The release liner is not particularly limited, and for example, a release liner having a release treatment layer on a release liner substrate such as a resin film or paper (which may be paper laminated with a resin such as polyethylene), or a release liner made of a resin film formed from a low-adhesion material such as a fluoropolymer (such as polytetrafluoroethylene) or a polyolefin resin (such as polyethylene or polypropylene) can be used. The release treatment layer may be formed by surface-treating the release liner substrate with a release treatment agent. The release treatment agent may be a known release treatment agent such as a silicone-based release treatment agent, a long-chain alkyl-based release treatment agent, a fluoro-based release treatment agent, or molybdenum(IV) sulfide. In some embodiments, a release liner having a release treatment layer made of a silicone-based release treatment agent can be preferably used. The thickness and formation method of the release treatment layer are not particularly limited and can be set so that appropriate release properties are exhibited on the adhesive side surface of the release liner.

[0220] In some embodiments, from the viewpoint of smoothness of the adhesive surface, a release liner (hereinafter also referred to as a release film) having a release treatment layer on a resin film (hereinafter also referred to as a release film substrate) as a release liner substrate can be preferably used. Various plastic films can be used as the release film substrate. In this specification, a plastic film is typically a non-porous sheet and is a concept distinct from, for example, nonwoven fabrics (i.e., does not include nonwoven fabrics).

[0221] Examples of materials for the above-mentioned plastic film include 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 triacetylcellulose; acetate resins; polysulfone resins; polyethersulfone resins; polycarbonate resins; polyamide resins; polyimide resins; norbornene resins; cyclic polyolefin resins; (meth)acrylic resins; polyvinyl chloride resins; polyvinylidene 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 one or more of these resins can be used. Among these, a polyester resin film (e.g., PET film) formed from a polyester resin is a preferred release film substrate.

[0222] The plastic film used as the release film substrate described above may be an unoriented film, a uniaxially oriented film, or a biaxially oriented film. Furthermore, the plastic film may have a single-layer structure or a multilayer structure including two or more sublayers. The plastic film may contain known additives that can be used in release film substrates for adhesive sheets, such as antioxidants, anti-aging agents, heat stabilizers, light stabilizers, UV absorbers, colorants such as pigments and dyes, lubricants, fillers, antistatic agents, and nucleating agents. In a multilayer plastic film, each additive may be incorporated into all sublayers or into only some of the sublayers.

[0223] In some preferred embodiments, the release film substrate (typically a plastic film) may preferably have a limited content of particles such as inorganic particles (which may be pigments, lubricants, fillers, etc.) in the layer on the release side, or may be substantially free of such particles. Here, substantially free means that the amount of particles (e.g., inorganic particles) in the layer is less than 1% by weight, preferably less than 0.1% by weight (e.g., 0 to 0.01% by weight). Release films with such a release film substrate tend to have a low arithmetic mean roughness Ra and maximum height Rz of the release surface. When the release film substrate (typically a plastic film) has a multilayer structure, the particle content in the layer on the release side may be 1 / 10 or less (e.g., 1 / 50 or less) of the particle content in the layers other than the release side layer.

[0224] In a laminated sheet with a release liner, having a release liner on a first adhesive surface and a second adhesive surface, the release liner placed on one adhesive surface (hereinafter also referred to as "the first release liner") and the release liner placed 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 the release film) is not particularly limited and may be, for example, about 10 μm to 500 μm. From the viewpoint of the strength and dimensional stability of the release liner, the thickness of the release liner is suitable to be 20 μm or more, preferably 30 μm or more, may be 35 μm or more, may be 40 μm or more, or may be 45 μm or more. Also, from the viewpoint of the handling of the release liner (e.g., ease of winding), the thickness of the release liner is suitable to be 300 μm or less, preferably 250 μm or less, may be 200 μm or less, may be 150 μm or less, or may be 130 μm or less. In some preferred embodiments, the thickness of the release liner is approximately 125 μm or less, may be approximately 115 μm or less, may be approximately 105 μm or less, may be approximately 90 μm or less, or may be approximately 70 μm or less. By setting the thickness of the release liner to below a predetermined value, winding marks are less likely to occur when the material is rolled up, removal from the adhesive sheet becomes smoother, and high surface smoothness can be easily obtained on the adhesive surface after the release liner has been removed.

[0226] In a laminated sheet with a release liner, comprising one release liner and the other release liner, the thicknesses of the release liners may be the same or different. In some embodiments, from the viewpoint of peelability and the like, it is preferable that one release liner and the other release liner have different thicknesses. For example, it is preferable that the thickness of the thicker release liner is approximately 1.1 times or more (for example, approximately 1.25 times or more; there is no particular upper limit, but for example, 5 times or less) the thickness of the thinner release liner.

[0227] (Arithmetic mean roughness Ra of the adhesive side surface) In some embodiments, it is preferable that the arithmetic mean roughness Ra of the adhesive surface side surface of the release liner (preferably a release film) is limited to a predetermined value or less (for example, approximately 100 nm or less, and even less than 50 nm) from the viewpoint of achieving an adhesive surface with high surface smoothness. In some embodiments, the arithmetic mean roughness Ra of the adhesive surface side surface of the release liner is preferably approximately 30 nm or less, more preferably approximately 25 nm or less, may also be approximately 20 nm or less, or may be approximately 18 nm or less. Furthermore, from the viewpoint of ease of manufacturing and handling of the release liner, in some embodiments, the above arithmetic mean roughness Ra may be, for example, approximately 5 nm or more, may also be approximately 10 nm or more, or may be approximately 15 nm or more. In a laminated sheet with a release liner in which release liners are arranged on a first adhesive surface and a second adhesive surface, it is preferable that the adhesive surface side surfaces of both release liners satisfy any of the above-mentioned arithmetic mean roughness Ra values. The arithmetic mean roughness Ra of the adhesive surface side surfaces of both release liners may be the same or different.

[0228] (Maximum height Rz on the adhesive side surface) In some embodiments, it is preferable that the maximum height Rz of the adhesive-side surface of the release liner (preferably a release film) is 700 nm or less, from the viewpoint of achieving an adhesive surface with high surface smoothness. In some embodiments, the maximum height Rz of the adhesive-side surface of the release liner is preferably about 600 nm or less, but may also be about 500 nm or less, about 400 nm or less, or about 300 nm or less. Furthermore, from the viewpoint of ease of manufacturing and handling of the release liner, in some embodiments, the above maximum height Rz may be, for example, about 50 nm or more, about 80 nm or more, about 100 nm or more, about 200 nm or more, or about 300 nm or more. In a laminated sheet with a release liner in which a release liner is arranged on a first adhesive surface and a second adhesive surface, it is preferable that the adhesive-side surfaces of both release liners satisfy any of the above-mentioned maximum heights Rz. The maximum heights Rz of the adhesive-side surfaces of both release liners may be the same or different.

[0229] (Surface properties of the back) The arithmetic mean roughness Ra and maximum height Rz of the back surface (opposite the adhesive layer side) of the release liner (preferably the release film) are not particularly limited. From the viewpoint of productivity, the arithmetic mean roughness Ra of the back surface of the release liner may be, for example, greater than 30 nm (e.g., greater than 35 nm, and even greater than approximately 50 nm). From the viewpoint of productivity, the maximum height Rz of the back surface of the release liner may be, for example, greater than 400 nm (e.g., greater than approximately 500 nm) or greater than 800 nm (e.g., greater than 1000 nm).

[0230] The arithmetic mean roughness Ra and maximum height Rz of the release film surface can be adjusted by selecting the film material, molding method, surface treatment such as release treatment, etc. For example, this can be done by adjusting the smoothness of the layers constituting the release surface (antiblocking layer, hard coat layer, oligomer prevention layer, etc.), reducing or eliminating (particle-free) filler particles in the surface layer or release film substrate, and 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. As the non-contact surface roughness measuring device, an optical interference type surface roughness measuring device is used, for example, a 3D optical profiler (product name "NewView7300", manufactured by ZYGO) or an equivalent can be used. For example, a glass plate (soda-lime glass plate manufactured by MATSUNAMI, 1.3 mm thick) can be attached to the surface of the release liner opposite to the measurement surface with adhesive and fixed, and the surface shape can be measured using a 3D optical profiler (product name "NewView7300", manufactured by ZYGO) in an environment of 23°C and 50% RH.

[0232] <Application> In the technology disclosed herein, a high refractive index adhesive layer can be used by bonding it to various adherends constituting a light-emitting device. The constituent materials of the adherends (adherend materials) are not particularly limited, but include, for example, metal materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, indium, zinc, etc., or alloys containing two or more of these, as well as, for example, polyimide resins, acrylic resins, polyethernitrile resins, polyethersulfone resins, polyester resins (PET resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyetheretherketone resins, polyamide resins (so-called aramid resins, etc.), polyarylate resins, and fluororesins. Examples of materials include various resin materials (typically plastics) such as polycarbonate resins, cellulosic polymers such as diacetylcellulose and triacetylcellulose, vinyl butyral polymers, liquid crystal polymers, and carbon materials such as graphene; metal oxides and mixtures thereof such as alumina, zirconia, titania, SiO2, ITO (indium tin oxide), and ATO (antimond-doped tin oxide); nitrides and composites thereof such as aluminum nitride, silicon nitride, titanium nitride, gallium nitride, and indium nitride; and inorganic materials such as alkali glass, alkali-free glass, quartz glass, borosilicate glass, and sapphire glass carbon. The high refractive index adhesive layer disclosed herein can be used by being attached to a component (e.g., an optical component) whose surface is at least made of the above materials. Furthermore, the low refractive index layer (preferably a low refractive index adhesive layer) in the technology disclosed herein can be used by being laminated (e.g., bonded) to the various adherends described above.

[0233] The high refractive index adhesive layer disclosed herein can be used in an application method that does not require heating to a temperature higher than room temperature (e.g., 20°C to 35°C) after bonding to the adherend. Furthermore, if permissible depending on the type of adherend, a heat treatment may be performed at at least one of the following timings: after bonding to the adherend, at the time of bonding, or before bonding. The heat treatment can be performed for purposes such as improving the adhesion of the adhesive to the adherend or promoting adhesion. The heat treatment temperature can be appropriately set within a range permissible depending on the constituent materials of the adhesive sheet and the type of adherend, taking into consideration the surface condition of the adherend, etc., in order to obtain the desired effect. For example, it may be around 100°C or lower, 80°C or lower, 60°C or lower, or 50°C or lower.

[0234] The member or material to which the adhesive layer is to be attached may be light-transmitting. In such a substrate, the advantage of the high transparency of the high refractive index adhesive layer disclosed herein is easily obtained. The total light transmittance of the substrate may be, for example, more than 50%, and may be 70% or more. In some preferred embodiments, the total light transmittance of the substrate is 80% or more, more preferably 90% or more, and even more preferably 95% or more (e.g., 95-100%). The high refractive index adhesive layer disclosed herein can preferably be used in a manner in which it is attached to a substrate (e.g., an optical member) with a total light transmittance of a predetermined value or higher. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory or an equivalent product is used.

[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) placed in contact with the adherend may be the same or different. For example, by making the refractive index of the adhesive layer relatively high compared to the refractive index of the adherend, light incident on the adhesive layer from the adherend side at an angle below the critical angle can be refracted toward the front, thereby increasing the front brightness. In this case, the refractive index of the adherend may be, for example, 1.55 or less, 1.50 or less, 1.48 or less, 1.45 or less, or less than 1.45, and may also be, for example, 1.10 or more, 1.20 or more, 1.30 or more, or 1.35 or more. Furthermore, using an adherend with a relatively high refractive index compared to the adhesive layer can refract light incident on the adherend from the adhesive layer side toward the front, thereby increasing the front brightness. In this case, the refractive index of the adherend may be, for example, 1.60 or higher, 1.65 or higher, or 1.70 or higher, and may also be, for example, 3.00 or lower, 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. In this case, the refractive index of the adherend may be around 1.55 to 1.80, around 1.55 to 1.75, or around 1.60 to 1.70. The refractive index of the adherend can be measured in the same way as the refractive index of the adhesive.

[0236] In some preferred embodiments, the adherend may have any of the above-described refractive indices and any of the above-described total light transmittances. The effects of the techniques disclosed herein are particularly favorably exhibited in a light-emitting device in which a high refractive index adhesive layer and / or a low refractive index layer are attached to or laminated to such an adherend.

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

[0238] The above-mentioned optical components refer to components that have optical properties (for example, polarization, refractiveness, scattering, reflectivity, transmission, absorption, diffraction, optical rotation, visibility, etc.). The above-mentioned optical components are not particularly limited as long as they have optical properties, but examples include components that make up devices (optical devices) such as display devices (image display devices) and input devices, or components used in such devices. Examples include polarizers, waveplates, phase difference plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflective films, hard coat (HC) films, shock-absorbing films, anti-fouling films, photochromic films, dimming films, transparent conductive films (ITO films), decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and even components in which these are laminated (these are sometimes collectively referred to as "functional films"). Furthermore, the terms "plate" and "film" above include forms such as plate-like, film-like, and sheet-like shapes, respectively. For example, "polarizing film" includes "polarizing plates" and "polarizing sheets," and "light guide plate" includes "light guide film" and "light guide sheet." In addition, the term "polarizing plate" above includes circular polarizing plates.

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

[0240] The optical components mentioned above are not particularly limited, but examples include components made of glass, acrylic resin, polycarbonate, polyethylene terephthalate, metal thin films, etc. (for example, sheet-like, film-like, or plate-like components). In this specification, "optical components" also include components that serve a decorative or protective role while maintaining the visibility of display devices and input devices (such as design films, decorative films, and surface protection films).

[0241] The high refractive index adhesive layer disclosed herein (which may take the form of a laminated sheet with a low refractive index layer) can be used, for example, by being placed between an optical film such as a film or fluorescent film having one or more functions such as light transmission, reflection, diffusion, guidance, focusing, or diffraction, and another optical component (which may be another optical film), and is preferably used to bond the optical film and the other optical component. In particular, in bonding an optical film having at least one function of light guidance, focusing, or diffraction, it is desirable that the entire bulk of the bonding layer has a high refractive index, and this may be a preferred application of the technology disclosed herein.

[0242] The high refractive index adhesive layer disclosed herein can be preferably used for bonding optical films such as light guide films, diffusion films, fluorescent films, color-tuning films, prism sheets, lenticular films, and microlens array films. In these applications, there is a demand for thinner films and improved light extraction efficiency from the viewpoint of miniaturization and performance enhancement of optical components. The high refractive index adhesive layer disclosed herein can be preferably used as an adhesive layer that can meet these demands. More specifically, for example, in bonding light guide films and diffusion films, thinning can be contributed to by adjusting the refractive index of the adhesive layer as a bonding layer (e.g., increasing the refractive index). In bonding fluorescent films, the light extraction efficiency (which can also be understood as luminous efficiency) can be improved by appropriately adjusting the refractive index difference between the fluorescent emitter and the adhesive. In bonding color-tuning films, the scattering component can be reduced and light transmittance can be improved by appropriately adjusting the refractive index of the adhesive so that the refractive index difference with the color-tuning pigment is small. In bonding prism sheets, lenticular films, microlens array films, etc., appropriately adjusting the refractive index of the adhesive can control the diffraction of light and contribute to improving brightness and / or viewing angle.

[0243] The high refractive index adhesive layer disclosed herein (which may be in the form of a laminated sheet with a low refractive index layer) is preferably used in a manner in which it is attached to a high refractive index adherend (which may be a high refractive index layer or component, etc.) to suppress interfacial reflection with the adherend. In such a manner, the high refractive index adhesive layer used preferably has a small refractive index difference with the high refractive index adherend and high adhesion at the interface with the adherend, as described above. Furthermore, from the viewpoint of improving the uniformity of the appearance, it is preferable that the thickness of the adhesive layer is highly uniform, for example, that the surface smoothness of the adhesive surface is high. When the thickness of the high refractive index adherend is relatively small (for example, 5 μm or less, 4 μm or less, or 2 μm or less), suppressing reflection at the interface is particularly significant from the viewpoint of suppressing discoloration and color unevenness due to interference of reflected light. One example of such usage is a polarizing plate with a phase difference layer, which comprises a polarizer, a first phase difference layer, and a second phase difference layer in that order, and which is used for bonding the polarizer to the first phase difference layer and / or the first phase difference layer to the second phase difference layer.

[0244] Furthermore, the high refractive index adhesive layer disclosed herein can preferably be used in a manner in which it is attached to an emissive layer such as an optical semiconductor (for example, a high-refractive-index emissive layer mainly composed of inorganic materials). By reducing the refractive index difference between the emissive layer and the high refractive index adhesive layer, reflection at their interface can be suppressed, and the light extraction efficiency can be improved. From the viewpoint of improving brightness, it is preferable that the high refractive index adhesive layer has low coloration. This is also advantageous from the viewpoint of suppressing unintentional coloration caused by the high refractive index adhesive layer.

[0245] The high refractive index adhesive layer disclosed herein can be preferably used in microlenses and other lens components used as components of cameras, light-emitting devices, etc. (for example, microlenses constituting a microlens array film, or lens components such as camera microlenses), as a coating layer covering the lens surface, a bonding layer with a component facing the lens surface (for example, a component having a surface shape corresponding to the lens surface), or a filling layer filled between the lens surface and the component. The high refractive index adhesive layer disclosed herein can reduce the refractive index difference with a high refractive index lens (for example, a lens made of a high refractive index resin, or a lens having a surface layer made of a high refractive index resin) even when placed in contact with the lens. This is advantageous from the viewpoint of thinning the lens and the product equipped with the lens, and can also contribute to suppressing aberrations and improving 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 itself, for example, in the form of being filled into a recess or void of a suitable transparent component.

[0246] The manner in which optical members are bonded using the adhesive layer disclosed herein (a high refractive index adhesive layer and / or a low refractive index adhesive layer, preferably a high refractive index adhesive layer which may be laminated on a low refractive index layer) is not particularly limited, but may include, for example, (1) bonding optical members to each other via the adhesive layer disclosed herein, (2) bonding an optical member to a member other than an optical member via the adhesive layer disclosed herein, or (3) bonding the adhesive layer disclosed herein in the form of an adhesive sheet containing an optical member, and the adhesive sheet being bonded to an optical member or a member other than an optical member. In the embodiment of (3) above, the adhesive sheet containing an optical member may be, for example, an adhesive sheet whose support is an optical member (e.g., an optical film). Such an adhesive sheet containing an optical member as a support can also be understood as an adhesive optical member (e.g., an adhesive optical film). Furthermore, if the adhesive layer disclosed herein constitutes an adhesive sheet having a support, and the functional film is used as the support, the adhesive sheet can also be understood as an "adhesive functional film" having the adhesive layer disclosed herein on at least one side of the functional film.

[0247] As described above, the technology disclosed herein provides an optical laminate comprising an adhesive layer disclosed herein and a member (for example, a resin film such as an optical film) to which the adhesive layer is laminated by bonding or the like. The member to which the adhesive layer is laminated by bonding or the like may have the refractive index of the adherend material described above. Furthermore, the difference between the refractive index of the adhesive layer and the refractive index of the member (refractive index difference) may be the refractive index difference between the adherend and the adhesive layer described above. The members constituting the laminate are as described above as members, materials, and adherends, so we will not repeat any redundant explanations.

[0248] The high refractive index adhesive layer and laminated sheet disclosed herein can withstand large deformations, and thus, taking advantage of this characteristic, are suitable for devices (optical devices) equipped with light-emitting devices such as liquid crystal displays, organic EL displays, and input devices such as touch panels in electronic devices such as portable electronic devices. They are particularly suitable as light-emitting devices in foldable displays and rollable displays. The high refractive index adhesive layer and laminated sheet disclosed herein can have the flexibility to withstand repeated bending operations, and therefore can follow well the shape of an object (foldable display, etc.) that is repeatedly bent when attached to a foldable display or rollable display. Examples of objects to which they can be attached in such usage are glass members such as window glass and cover glass used in foldable displays and rollable displays. Furthermore, the high refractive index adhesive layer and laminated sheet disclosed herein can easily follow and adhere to curved surfaces such as the three-dimensional shapes of portable electronic devices, and are therefore also suitable as light-emitting devices in electronic devices having such curved shapes. Furthermore, in some preferred embodiments, the high refractive index adhesive layer and laminated sheet may, in addition to being flexible, also have improved stability in properties such as elastic modulus. Since the above-mentioned portable electronic devices may be used in high-temperature environments, and their internal spaces may become hot due to the heat generated by the electronic components, there is a significant advantage to using an adhesive with good stability in these properties.

[0249] Examples of portable electronic devices that may be equipped with the light-emitting devices disclosed herein include, for example, mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (e.g., wristwear-type devices worn on the wrist like watches, modular-type devices attached to a part of the body with clips or straps, eyewear-type devices including glasses (monocular and binocular types, including head-mounted types), clothing-type devices attached to shirts, socks, hats, etc. as accessories, earwear-type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game consoles, electronic dictionaries, electronic organizers, e-books, in-car information equipment, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, "portable" means not merely being able to be carried, but having a level of portability that allows an individual (a typical adult) to carry it relatively easily.

[0250] As can be understood from the above description and the following test examples, the matters disclosed in this specification include the following: [1] Self-luminescent element and A low refractive index layer positioned on the viewing side of the aforementioned self-luminous element, A high refractive index adhesive layer laminated in direct contact with the low refractive index layer, Includes, The aforementioned high refractive index adhesive layer has a refractive index greater than 1.560, and the amount of deformation in a deformation test performed under the conditions of a temperature of -20°C and a speed of 300 mm / min is 350% or more, in a light-emitting device. [2] Self-luminescent elements and A low refractive index layer positioned on the viewing side of the aforementioned self-luminous element, A high refractive index adhesive layer laminated in direct contact with the low refractive index layer, Includes, The light-emitting device comprises a high refractive index adhesive layer having a refractive index greater than 1.560 and containing a plasticizer. [3] In a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min, the high refractive index adhesive layer exhibited a stress of 5.0 N / mm at a deformation of 350%. 2 The following is the light-emitting device described in [1] or [2] above. [4] The light-emitting device according to any one of [1] to [3] 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. [5] A laminated sheet comprising a low refractive index layer and a high refractive index adhesive layer laminated on the low refractive index layer, The aforementioned high refractive index adhesive layer has a refractive index greater than 1.560, and the amount of deformation in a deformation test performed under the conditions of a temperature of -20°C and a speed of 300 mm / min is 350% or more, in a laminated sheet. [6] A laminated sheet comprising a low refractive index layer and a high refractive index adhesive layer laminated on the low refractive index layer, The aforementioned high refractive index adhesive layer is a laminated sheet having a refractive index greater than 1.560 and containing a plasticizer. [7] In a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min, the high refractive index adhesive layer exhibited a stress of 5.0 N / mm at a deformation of 350%. 2 The laminated sheet described in [5] or [6] above, which is as follows: [8] The laminated sheet according to 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 laminated sheet with a release liner, comprising a laminated sheet as described in any of [5] to [8] above, and a release liner that protects the surface of the high refractive index adhesive layer.

[0251] The following describes several test examples relating to the present invention, but it is not intended to limit the present invention to these specific examples. In the following description, "parts" and "%" used to express the amount used or content refer to weight unless otherwise specified.

[0252] <Preparation of acrylic adhesive composition C1> In a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser, 95 parts of m-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), and 2 parts of 2-acryloyloxyethyl succinic acid (manufactured by Kyoeisha Chemical Co., Ltd., trade name "HOA-MS(N)", hereinafter referred to as "HOA-MS") were charged as monomer components, 0.2 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator, and ethyl acetate as the polymerization solvent. Nitrogen gas was introduced while gently stirring, and the polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at around 60°C to prepare a 40% solution of acrylic polymer P1. The Mw of acrylic polymer P1 was 500,000. The above acrylic polymer P1 solution was diluted with ethyl acetate to a polymer concentration of 30%. 334 parts of this solution (100 parts non-volatile content) were mixed with 60 parts polyethylene glycol benzoate (manufactured by Sanyo Chemical Industries, Ltd., trade name "Sunflex EB-300", molecular weight: 538, refractive index: 1.515, liquid at 20°C, hereinafter referred to as "EB-300") as plasticizer A1, 0.3 parts acyclic bifunctional isocyanate crosslinking agent (manufactured by Tosoh Corporation, trade name "Coronate 2770", hexamethylene diisocyanate (HDI) allophanate) as crosslinking agent, 2 parts acetylacetone as a crosslinking retarder, and 1 part 1% ethyl acetate solution of ferric narcem (0.01 parts non-volatile content) as a crosslinking catalyst. The mixture was stirred and mixed to prepare acrylic adhesive composition C1.

[0253] <Preparation of acrylic adhesive composition C2> A solution of acrylic polymer P2 was prepared in the same manner as the preparation of the solution of acrylic polymer P1, except that the monomer component composition was changed to 99 parts of POB-A and 1 part of HOA-MS. The Mw of acrylic polymer P2 was 500,000. The solution of acrylic polymer P2 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 an epoxy crosslinking agent (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name "Tetrad C", 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) were added to 334 parts of this solution (100 parts non-volatile content) and stirred to prepare acrylic adhesive composition C2.

[0254] <Preparation of acrylic adhesive composition C3> A solution of acrylic polymer P3 was prepared in the same manner as the preparation of the solution of acrylic polymer P1, except that the monomer component composition was changed to 95 parts POB-A, 2 parts lauryl acrylate (LA), 2 parts 2-ethylhexyl acrylate (2EHA), and 1 part 4HBA. The Mw of acrylic polymer P3 was 500,000. The above acrylic polymer P3 solution was diluted with ethyl acetate to a polymer concentration of 30%. 334 parts of this solution (100 parts non-volatile content) were mixed with 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") as plasticizer A2, 0.3 parts of the above isocyanate crosslinking agent (Coronate 2770), 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of ferric narcem (0.01 parts non-volatile content) as a crosslinking catalyst. The mixture was stirred to prepare acrylic adhesive composition C3.

[0255] <Preparation of acrylic adhesive composition C4> A solution of acrylic polymer P4 was prepared in the same manner as the preparation of the solution of acrylic polymer P1, except that the monomer component composition was changed to 90 parts POB-A, 9 parts 2EHA, and 1 part 4HBA. The Mw of acrylic polymer P4 was 500,000. The solution of acrylic polymer P4 was diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (100 parts non-volatile content) were mixed with 60 parts of the plasticizer A2 (POB-AL), 0.5 parts of the isocyanate crosslinking agent (Coronate 2770), 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of ferric Nasem (0.01 parts non-volatile content) as a crosslinking catalyst, and stirred to prepare acrylic adhesive composition C4.

[0256] <Preparation of acrylic adhesive composition C5> A solution of acrylic polymer P5 was prepared in the same manner as the preparation of the solution of acrylic polymer P1, except that the monomer component composition was changed to 98 parts POB-A, 1 part 4HBA, and 1 part HOA-MS. The Mw of acrylic polymer P5 was 500,000. The solution of acrylic polymer P5 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 acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of ferric narcem (0.01 parts non-volatile content) as a crosslinking catalyst were added to 334 parts of this solution (100 parts non-volatile content) and stirred to prepare acrylic adhesive composition C5.

[0257] <Preparation of acrylic adhesive composition C6> A solution of acrylic polymer P6 was prepared in the same manner as the preparation of the solution of acrylic polymer P1, except that the monomer component composition was changed to 99 parts n-butyl acrylate (BA) and 1 part 4HBA, and the concentration of the monomer component during polymerization was adjusted. The Mw of acrylic polymer P6 was 2 million. The solution of acrylic polymer P6 was diluted with ethyl acetate to a polymer concentration of 30%, and 10 parts (0.1 parts non-volatile content) of a 1% ethyl acetate solution of hexamethylene diisocyanate isocyanurate (manufactured by Tosoh Corporation, trade name "Coronate HX", trifunctional isocyanate compound) as a crosslinking agent was added to 334 parts (100 parts non-volatile content) of this solution and stirred to prepare acrylic adhesive composition C6.

[0258] <Making adhesive sheets> (Example 1) The acrylic adhesive composition C1 prepared above was applied to the silicone-treated side of a polyethylene terephthalate (PET) film R1 (thickness 50 μm) with one side silicone-treated, and heated at 130°C for 2 minutes to form an adhesive layer with a thickness of 20 μm. Next, the silicone-treated side of a PET film R2 (thickness 25 μm) with one side silicone-treated was bonded to the surface of the adhesive layer. In this way, an adhesive layer (high refractive index adhesive layer) was obtained in which both sides were protected by PET films (release liners) R1 and R2. The release liner R2 is relatively easier to peel than the release liner R1. Furthermore, the acrylic adhesive composition C6 prepared above was applied to the silicone-treated side of a PET film R1 (thickness 50 μm) with one side silicone-treated, and heated at 130°C for 2 minutes to form an adhesive layer with a thickness of 50 μm. The silicone-treated side of a PET film R2 (thickness 38 μm) with one side silicone-treated was then bonded to the surface of the adhesive layer. In this way, an adhesive layer (low refractive index adhesive layer) was obtained in which both sides were protected by PET films (release liners) R1 and R2. The release liner R2 was peeled off the high-refractive-index adhesive layer and the low-refractive-index adhesive layer, and the adhesive surfaces were bonded together and pressed with a hand roller. This laminate was autoclaved for 30 minutes at 50°C and 0.60 MPa, and then aged for 48 hours in a 50°C environment. In this way, a laminated sheet (substrate-less double-sided adhesive sheet) consisting of a two-layer structure of a high-refractive-index adhesive layer and a low-refractive-index adhesive layer was obtained. The surface of this adhesive sheet is protected by two release liners R1.

[0259] (Examples 2-5) Laminated sheets (substrate-less double-sided adhesive sheets) consisting of a two-layer structure of a high-refractive-index adhesive layer and a low-refractive-index adhesive layer were obtained in the same manner as in Example 1, except that the type of adhesive composition used to form each adhesive layer was changed as shown in Table 1.

[0260] <Measurement and Evaluation> (Refractive index) The refractive index of each adhesive layer was measured using an Abbe refractometer (ATAGO, model "DR-M4") under the conditions of 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 then punched out into a 7.9 mm diameter disc, which was used as the measurement sample. Dynamic viscoelasticity measurements were performed using the Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific under the following conditions. From the measurement results, the storage modulus G' at 25°C was read. The results are shown in Table 1. [Measurement conditions] Transformation mode: Twist Measurement frequency: 1Hz Temperature range: -50℃ to 150℃ Heating rate: 5°C / min Shape: Parallel plate 7.9mmφ

[0262] (Total light transmittance and haze value) Test specimens were prepared by laminating the adhesive sheet for each example onto alkali-free glass (thickness 0.8-1.0 mm, total light transmittance 92%, haze 0.4%). The total light transmittance and haze of these specimens were measured using a haze meter (manufactured by Murakami Color Technology Laboratory, product name "HAZEMETER HM-150") at a measurement environment of 23°C. The total light transmittance and haze values ​​of the adhesive sheet 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 has a length of 300 mm and a cross-sectional area of ​​1 mm². 2 The material was cut to the desired width, and the adhesive layer was rolled into a cylindrical shape under conditions of 23°C and 50%RH to obtain a test specimen. Using a tensile testing machine (Shimadzu Corporation, machine name "Precision Universal Testing Machine Autograph AG-X plus 5kN"), the above test specimen was subjected to a deformation test (tensile test) under the conditions of -20°C, a chuck distance of 100 mm, and a tensile speed of 300 mm / min, and the SS curve was determined to evaluate whether the test specimen deformed (stretched) by 350% or more. If the test specimen deformed by 350% or more, the stress at 350% deformation [N / mm²] was calculated. 2 The following was measured. The results are shown in Table 1. In the above deformation test, adhesives that can be deformed by 350% or more at -20°C are judged to be adhesives that can withstand large deformations.

[0264] Furthermore, if the thickness of the adhesive layer is relatively small, the deformation test may be performed using test specimens prepared to have a thickness of 5 μm or more (for example, about 5 μm to 200 μm) for purposes such as improving operability. The thickness of the test specimen can be adjusted, for example, by appropriately overlapping the adhesive layers. Alternatively, a test specimen of a thickness suitable for deformation testing may be prepared using the same adhesive composition used to form the adhesive layer to be measured, and the deformation test may be performed on that specimen. The deformation test can be performed, for example, using a test specimen with a thickness of about 10 μm to 50 μm. In addition, it is preferable to apply powder to the adhesive surface of the area to be chucked to eliminate the effect of stickiness of the adhesive during the test.

[0265] [Table 1]

[0266] As shown in Table 1, the adhesive sheets of Examples 1 to 4 included a high-refractive-index adhesive layer with a refractive index greater than 1.560 and a deformation of 350% or more in a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min, and a low-refractive-index layer. Furthermore, the high-refractive-index adhesive layer in these examples exhibited a stress of 5.0 N / mm² at a deformation of 350% in a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min. 2 The following was observed. Furthermore, 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 was 1.05 or higher. Such an adhesive sheet is recognized to have the front brightness improvement effect evaluated by the method described in the examples of Japanese Patent Application Publication No. 2022-8015. It can be seen that by using the above adhesive sheet, it is possible to construct a light-emitting device in which an adhesive layer having a high refractive index and being able to withstand large deformation is arranged on the visible side of the self-luminous element. On the other hand, although the refractive index of the high refractive index adhesive layer of the adhesive sheet according to Example 5 was greater than 1.560, in a deformation test at a temperature of -20°C and a speed of 300 mm, it broke at an early stage of deformation and could not withstand large deformation.

[0267] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. [Explanation of symbols]

[0268] 2. Substrate-less double-sided adhesive sheet 10 Laminated Sheets (Adhesive Sheets) 10A First surface (first adhesive surface) 10B Second surface (second adhesive surface) 11. High refractive index adhesive layer 12. Low refractive index adhesive layer (low refractive index layer) 70 Self-luminescent elements 80 Cover window member 100 Light-emitting devices

Claims

1. Self-luminescent elements, A low refractive index layer positioned on the viewing side of the aforementioned self-luminous element, A high refractive index adhesive layer laminated in direct contact with the low refractive index layer, Includes, The light-emitting device wherein the high refractive index adhesive layer has a refractive index greater than 1.560, and the amount of deformation in a deformation test performed under the conditions of a temperature of -20°C and a speed of 300 mm / min is 350% or more.

2. In a deformation test conducted at a temperature of -20°C and a speed of 300 mm / min, the aforementioned high refractive index adhesive layer exhibited a stress of 5.0 N / mm at a deformation of 350%. 2 The following is the light-emitting device according to claim 1.

3. The refractive index n of the high refractive index adhesive layer １ and the refractive index n of the low refractive index layer ２ The ratio (n １ / n ２ The light-emitting device according to claim 1 or 2, wherein the value of ) is 1.05 or greater.

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