Adhesive sheets and adhesive sheets with release liner

Abstract

To provide an adhesive sheet that includes an adhesive layer having both of a high refractive index and excellent optical properties, and an adhesive sheet with a release liner.SOLUTION: Provided is an adhesive sheet including an adhesive layer. The adhesive sheet has an adhesive surface constituted by the adhesive layer. The adhesive layer has a refractive index of more than 1.570, a total light transmittance of 86% or more, and a haze value of 3.0% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive sheet and a pressure-sensitive adhesive sheet with a release liner. [Background technology]

[0002] Generally, adhesives (also referred to as pressure-sensitive adhesives; the same applies hereinafter) are in a soft solid (viscoelastic) state at temperatures around room temperature and have the property of easily adhering to an adherend when pressure is applied. Utilizing these properties, adhesives are widely used for purposes such as joining, fixing, and protection in a variety of industrial fields, from home appliances to automobiles, various machines, electrical appliances, and electronic devices. One example of the use of adhesives is bonding polarizing films, retardation films, cover window components, and various other light-transmitting components to other components in displays such as liquid crystal displays and organic EL displays. Patent Documents 1 and 2 are examples of technical documents related to adhesives for optical components. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-169382 [Patent Document 2] Japanese Patent Application Publication No. 2017-128732 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Documents 1 and 2 propose a pressure-sensitive adhesive composition containing, as its main component, a (meth)acrylic acid ester polymer containing a monomer unit having multiple aromatic rings, and a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition, but do not disclose specific pressure-sensitive adhesives with a refractive index exceeding 1.570. While a technique for increasing the refractive index by blending inorganic particles with a resin (e.g., inorganic particles such as zirconium oxide particles or titanium oxide particles) is known, pressure-sensitive adhesives containing inorganic particles have a trade-off between refractive index and adhesive properties (e.g., peel strength, flexibility, etc.), making their application to the pressure-sensitive adhesive field difficult. In particular, for pressure-sensitive adhesives intended for optical applications, the blending of inorganic particles must also take into consideration the impact on optical properties (e.g., total light transmittance, haze, etc.). Therefore, there are currently no known pressure-sensitive adhesive sheets that have a pressure-sensitive adhesive layer that combines a refractive index exceeding 1.570 with good optical properties (e.g., transparency) suitable for optical applications and that exhibit practical adhesive performance.

[0005] The present invention has been made in view of the above circumstances, and aims to provide a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer that combines a high refractive index and good optical properties. Another aim of the present invention is to provide a pressure-sensitive adhesive sheet with a release liner that includes the above pressure-sensitive adhesive sheet. [Means for solving the problem]

[0006] According to this specification, a pressure-sensitive adhesive sheet is provided that includes a pressure-sensitive adhesive layer and has a pressure-sensitive adhesive surface formed by the pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer has a refractive index of more than 1.570, a total light transmittance of 86% or more, and a haze value of 3.0% or less. The pressure-sensitive adhesive sheet is useful as a high-refractive-index pressure-sensitive adhesive sheet that is also suitable for optical applications because it has a highly transparent pressure-sensitive adhesive layer. Furthermore, by attaching the pressure-sensitive adhesive surface of the pressure-sensitive adhesive sheet to an adherend, the high-refractive-index pressure-sensitive adhesive layer can be easily disposed on the adherend.

[0007] In some embodiments, the thickness of the pressure-sensitive adhesive layer is 5 μm or more. A pressure-sensitive adhesive layer having such a thickness is likely to provide good adhesive properties. Furthermore, a pressure-sensitive adhesive layer having such a thickness is likely to absorb irregularities that may exist on the surface of an adherend and be bonded to the adherend with good adhesion, so that a pressure-sensitive adhesive layer with a high refractive index can be appropriately provided on the adherend.

[0008] The pressure-sensitive adhesive sheet according to some embodiments has a peel strength (adhesive strength) to a glass plate of 3 N / 25 mm or more. Such an adhesive strength is preferable from the viewpoint of bonding reliability with an adherend.

[0009] In some embodiments, the adhesive surface has an arithmetic mean roughness Ra of 100 nm or less. Having such a highly smooth adhesive surface is preferable from the viewpoint of optical homogeneity. For example, in a use mode in which light is extracted through the adhesive surface (such as an adhesive sheet arranged closer to the viewpoint than the light-emitting element in a light-emitting device), the occurrence of brightness unevenness due to the surface condition of the adhesive layer can be suppressed.

[0010] In some embodiments, the water absorption rate of the pressure-sensitive adhesive layer is 1.0% or less. A pressure-sensitive adhesive layer with low water absorption rate can suppress dimensional changes of the pressure-sensitive adhesive layer due to fluctuations in the moisture content in the pressure-sensitive adhesive layer. This can suppress warping of the pressure-sensitive adhesive sheet or the adherend to which the pressure-sensitive adhesive sheet is attached.

[0011] In some embodiments, the pressure-sensitive adhesive sheet is configured as a laminate including the pressure-sensitive adhesive layer and a light-transmitting substrate (e.g., a resin film). By attaching a pressure-sensitive adhesive sheet having such a configuration to an adherend, a structure in which the adherend and the light-transmitting substrate are laminated via a high-refractive-index pressure-sensitive adhesive layer can be easily formed.

[0012] In some embodiments, the PSA sheet is a double-sided PSA sheet comprising the PSA layer. A double-sided PSA sheet comprising a PSA layer has excellent flexibility because it does not have a non-releasable substrate (support substrate). With such a double-sided PSA sheet without a non-releasable substrate (hereinafter also referred to as a substrate-less double-sided PSA sheet), a PSA layer with a high refractive index can be easily placed on an adherend, and a highly flexible bond can be formed between the adherend and another member via the PSA sheet.

[0013] Furthermore, according to this specification, there is provided a PSA sheet with a release liner, comprising any of the PSA sheets disclosed herein and a release liner disposed on the adhesive surface of the PSA sheet. The PSA sheet disclosed herein is preferably manufactured, stored, distributed, processed, etc. in the form of a PSA sheet with a release liner, in which a release liner is disposed on the adhesive surface, and can be used in an embodiment in which the release liner is peeled off from the adhesive surface before application to an adherend.

[0014] Appropriate combinations of the elements described in this specification may also be included within the scope of the invention for which patent protection is sought by this patent application. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet according to one embodiment. [Figure 2] FIG. 10 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet according to another embodiment. [Figure 3] 1 is a cross-sectional view schematically showing an optical member with a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive sheet according to one embodiment is attached to an optical member. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present invention will be described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings on carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. In the following drawings, components and parts having the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. The embodiments shown in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the actual product.

[0017] In this specification, the term "self-luminous element" refers to a light-emitting element whose luminance can be controlled by the value of the current flowing through it. The self-luminous element may be composed of a single element or an aggregate. Specific examples of the self-luminous element include, but are not limited to, a light-emitting diode (LED) and an organic electroluminescent (EL). When a light-emitting device is mentioned in this specification, the light-emitting device may include such a self-luminous element as a component. Examples of the light-emitting device include, but are not limited to, a light source module device (e.g., a surface light-emitting module) used for lighting and a display device formed with pixels.

[0018] <Adhesive sheet configuration example> This specification provides a pressure-sensitive adhesive sheet having an adhesive surface constituted by a pressure-sensitive adhesive layer. The pressure-sensitive adhesive sheet may be a substrate-attached pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on one or both sides of a non-releasable substrate (support substrate), or may be a substrate-less pressure-sensitive adhesive sheet (i.e., a pressure-sensitive adhesive sheet without a non-releasable substrate; typically, a pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer) in which the pressure-sensitive adhesive layer is held by a release liner. The concept of pressure-sensitive adhesive sheet here may include what are called pressure-sensitive adhesive tapes, pressure-sensitive adhesive labels, pressure-sensitive adhesive films, etc. The pressure-sensitive adhesive sheets disclosed herein may be in the form of rolls or sheets. Alternatively, they may be pressure-sensitive adhesive sheets processed into various shapes.

[0019] One structural example of the pressure-sensitive adhesive sheet disclosed herein is shown in FIG. 1. This pressure-sensitive adhesive sheet 1 is configured as a single-sided pressure-sensitive adhesive sheet (single-sided pressure-sensitive adhesive sheet) including a pressure-sensitive adhesive layer 10 having a first surface 10A that serves as the surface (adhesive surface) to be attached to an adherend, and a support substrate 20 laminated to a second surface 10B of the pressure-sensitive adhesive layer 10. The second surface 10B of the pressure-sensitive adhesive layer 10 is bonded to a first surface (non-releasable surface) 20A of the support substrate 20. A plastic film such as a polyester film can be used as the support substrate 20. The support substrate 20 may also be an optical film such as a polarizing plate. Before use (before attachment to an adherend), the pressure-sensitive adhesive sheet 1 can be in the form of a release-liner-attached pressure-sensitive adhesive sheet 50, in which the adhesive surface 10A is protected by a release liner 30, at least the pressure-sensitive adhesive layer side of which serves as a releasable surface (release surface), as shown in FIG. 1, for example. Alternatively, the second surface 20B of the support substrate 20 (the surface opposite to the first surface 20A, also referred to as the back surface) may be the release surface, and the adhesive surface 10A may be protected by being wound or laminated so that the adhesive surface 10A abuts against this second surface 20B. The adhesive layer 10 may have a single layer structure, or a laminate structure in which two or more sub-adhesive layers with different compositions are laminated in direct contact (i.e., not separated by a layer of non-adhesive material).

[0020] The PSA sheet disclosed herein may be in the form of a substrateless double-sided PSA sheet comprising a PSA layer. As shown in FIG. 2 , before use, the substrateless double-sided PSA sheet 2 may be in a form in which the first surface (first adhesive surface) 10A and the second surface (second adhesive surface) 10B of the PSA layer 10 are protected by release liners 31, 32, at least the PSA layer side of which is a releasable surface (release surface). Alternatively, the back surface of the release liner 31 (the surface opposite the PSA side) may be a release surface, and the PSA surface 10B may be wound or laminated against the back surface of the release liner 31, thereby protecting the PSA surfaces 10A, 10B. Such a substrateless double-sided PSA sheet may be used, for example, by bonding a substrate (preferably a light-transmitting substrate, which may be an optical member such as an optical film) to at least one of the first and second adhesive surfaces. The adhesive layer constituting the substrateless double-sided adhesive sheet may have a single layer structure, similar to adhesive layer 10 in adhesive sheet 1 shown in Figure 1, or may have a laminate structure in which two or more sub-adhesive layers with different compositions are laminated in direct contact with each other.

[0021] The pressure-sensitive adhesive sheet disclosed herein may be a component of a pressure-sensitive adhesive sheet-attached optical member in which an optical member is bonded to at least one surface of the pressure-sensitive adhesive layer. For example, the pressure-sensitive adhesive sheet 1 shown in FIG. 1 may be a component of a pressure-sensitive adhesive sheet-attached optical member 100 in which an optical member 70 is bonded to a first surface 10A of the pressure-sensitive adhesive layer 10, as shown in FIG. 3. The optical member may be, for example, a glass plate, a resin film, a metal plate, or the like. Furthermore, in the pressure-sensitive adhesive sheet 1 shown in FIG. 1, when the support substrate 20 is an optical member such as an optical film, the pressure-sensitive adhesive sheet 1 may be understood as a pressure-sensitive adhesive sheet-attached optical member in which an optical member is bonded to a second surface 10B of the pressure-sensitive adhesive layer 10.

[0022] Furthermore, although not specifically shown, the PSA sheet disclosed herein may be in the form of a substrate-attached double-sided PSA sheet (substrate-attached double-sided PSA sheet) that includes a support substrate having a non-releasable first and second surfaces, with a first PSA layer fixedly laminated to the first surface and a second PSA layer fixedly laminated to the second surface. An example of the configuration of such a substrate-attached double-sided PSA sheet is the single-sided PSA sheet 1 shown in FIG. 1 , in which the second surface 20B of the support substrate 20 is a non-releasable surface and a second PSA layer is provided on the second surface 20B, the second surface of the second PSA layer is bonded to the second surface 20B of the support substrate 20, and the first surface of the second PSA layer (the surface opposite the second surface) forms the second PSA surface of the substrate-attached double-sided PSA sheet. The composition of the PSA constituting the second PSA layer may be the same as or different from the composition of the PSA constituting the first PSA layer. Before use, the substrate-attached double-sided PSA sheet may be in a form in which the first and second adhesive surfaces are protected by release liners, similar to the substrate-less double-sided PSA sheet described above.

[0023] <Characteristics of the adhesive layer> (refractive index) The pressure-sensitive adhesive sheet disclosed herein has a pressure-sensitive adhesive layer with a refractive index of greater than 1.570. Such a pressure-sensitive adhesive layer can be realized by configuring at least one surface (adhesive surface) of the pressure-sensitive adhesive layer with a pressure-sensitive adhesive with a refractive index of greater than 1.570. The technology disclosed herein can provide a pressure-sensitive adhesive with a refractive index greater than 1.570, a pressure-sensitive adhesive composition capable of forming the pressure-sensitive adhesive, and a pressure-sensitive adhesive sheet including the pressure-sensitive adhesive.

[0024] In this specification, the refractive index of a pressure-sensitive adhesive refers to the refractive index of the surface (adhesive surface) of the pressure-sensitive adhesive. The refractive index of a pressure-sensitive adhesive can be measured using a commercially available refractive index measuring device (Abbe refractometer) at a measurement wavelength of 589 nm and a measurement temperature of 25°C. As an Abbe refractometer, for example, the model "DR-M4" manufactured by ATAGO or an equivalent can be used. The measurement sample can be an adhesive layer made of the pressure-sensitive adhesive to be evaluated. Specifically, the refractive index of a pressure-sensitive adhesive can be measured by the method described in the Examples below. The refractive index of a pressure-sensitive adhesive can be adjusted, for example, by the composition of the pressure-sensitive adhesive (e.g., the composition of the monomer components constituting the base polymer, additives that may be used as needed, etc.).

[0025] In some embodiments, the refractive index of the pressure-sensitive adhesive is preferably 1.580 or greater, more preferably 1.585 or greater, and even more preferably 1.590 or greater (e.g., 1.595 or greater). A pressure-sensitive adhesive having such a refractive index can effectively control the behavior of light passing through the pressure-sensitive adhesive by utilizing the relative refractive index relationship between the pressure-sensitive adhesive and the adherend. In some embodiments of the pressure-sensitive adhesive disclosed herein, the refractive index of the pressure-sensitive adhesive can be, for example, 1.600 or greater or greater than 1.600, 1.605 or greater or greater than 1.605, or 1.610 or greater or greater than 1.610. The preferred upper limit of the refractive index of the pressure-sensitive adhesive is not limited to a specific range, as it may vary depending on the refractive index of the adherend, etc. In some embodiments, the refractive index of the pressure-sensitive adhesive can be, for example, 1.700 or less, 1.670 or less, or 1.650 or less, taking into account the balance between adhesive properties and transparency.

[0026] When the adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet (including both substrate-less double-sided adhesive sheets and substrate-attached double-sided adhesive sheets; the same applies hereinafter unless otherwise specified) in which one side is a first adhesive surface and the other side is a second adhesive surface, it is sufficient that at least the first adhesive surface satisfies one of the refractive indices described above, and the refractive index of the second adhesive surface is not particularly limited. In some embodiments, the refractive index n2 of the second adhesive surface may be approximately the same as the refractive index n1 of the first adhesive surface. More specifically, the absolute value of the difference in refractive index between the two adhesive surfaces, i.e., |n1-n2|, may be, for example, less than 0.05, or less than 0.03, or less than 0.01. The lower limit of |n1-n2| may be 0.00 or may be greater than 0.00. The relative relationship between the refractive indexes of the two adhesive surfaces may be n1>n2, and n1 <n2でもよく、n1=n2でもよい。 In some other embodiments, the difference between the refractive index n1 of the first adhesive surface and the refractive index n2 of the second adhesive surface of the PSA sheet, i.e., n1 - n2, may be, for example, greater than 0.00, 0.01 or greater, 0.03 or greater, 0.05 or greater, 0.10 or greater, 0.15 or greater, 0.20 or greater, or 0.25 or greater. The magnitude relationship between n1 and n2 may be reversed. A double-sided PSA sheet having different refractive indices on the first and second adhesive surfaces can be achieved, for example, by laminating first and second PSA layers having different refractive indices to a non-peelable support substrate in a substrate-attached double-sided PSA sheet, or by forming a substrate-less double-sided PSA sheet into a laminate structure of two or more sub-adhesive layers, and in this laminate structure, making the refractive index of the PSA constituting the first adhesive surface different from the refractive index of the PSA constituting the second adhesive surface.

[0027] (Total light transmittance) The pressure-sensitive adhesive sheet disclosed herein comprises a pressure-sensitive adhesive layer having the above-described high refractive index and a total light transmittance of 86% or more. Pressure-sensitive adhesive sheets having such a highly transparent pressure-sensitive adhesive layer, with or without a substrate, are preferably used in applications requiring high light transmittance (e.g., optical applications) or applications requiring good visibility of the adherend through the pressure-sensitive adhesive sheet. In some embodiments, the total light transmittance of the pressure-sensitive adhesive layer is preferably 88% or more, more preferably 90% or more (e.g., greater than 90.0%), and may be 90.5% or more, 93% or more, or 95% or more. Theoretically, the upper limit of the total light transmittance is the value obtained by subtracting light loss due to reflection at the air interface (Fresnel loss) from 100%. In practice, it may be approximately 98% or less, approximately 96% or less, or approximately 95% or less. In some embodiments, taking into consideration the refractive index and adhesive properties, the total light transmittance of the pressure-sensitive adhesive layer may be approximately 94% or less, approximately 93% or less, or approximately 92% or less. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. The transmittance meter used may be a product manufactured by Murakami Color Research Laboratory under the trade name "HAZEMETER HM-150" or an equivalent. More specifically, the total light transmittance of the pressure-sensitive adhesive layer can be measured, for example, according to the examples described below. The total light transmittance of the pressure-sensitive adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the pressure-sensitive adhesive layer.

[0028] When the pressure-sensitive adhesive sheet disclosed herein is in the form of a substrate-attached double-sided pressure-sensitive adhesive sheet in which a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer are fixedly laminated to a support substrate, it is sufficient that at least the first pressure-sensitive adhesive layer satisfies one of the total light transmittances described above, and the total light transmittance of the second pressure-sensitive adhesive layer is not particularly limited. In a use mode in which light passes through the pressure-sensitive adhesive sheet in the thickness direction, it is preferable that the total light transmittance of the second pressure-sensitive adhesive layer satisfies one of the total light transmittances of the first pressure-sensitive adhesive layer described above. The relative relationship between the total light transmittances of the two pressure-sensitive adhesive layers may be first pressure-sensitive adhesive layer > second pressure-sensitive adhesive layer, first pressure-sensitive adhesive layer < second pressure-sensitive adhesive layer, or first pressure-sensitive adhesive layer = second pressure-sensitive adhesive layer.

[0029] (Haze value) The pressure-sensitive adhesive sheet disclosed herein includes a pressure-sensitive adhesive layer having the above-described high refractive index and a haze value of 3.0% or less. In some embodiments, the haze value of the pressure-sensitive adhesive layer is preferably 2.0% or less, more preferably 1.0% or less, and even more preferably 0.9% or less. Pressure-sensitive adhesive sheets having such highly transparent pressure-sensitive adhesive layers, with or without a substrate, are preferably used in applications requiring high light transmittance (e.g., optical applications) or applications requiring good visibility of the adherend through the pressure-sensitive adhesive sheet. In some embodiments, the haze value of the pressure-sensitive adhesive layer may be 0.8% or less, 0.5% or less, or 0.3% or less. There is no particular lower limit for the haze value of the pressure-sensitive adhesive layer, and a smaller haze value is preferable from the viewpoint of improving transparency. Meanwhile, in some embodiments, taking into consideration the refractive index and adhesive properties, the haze value may be, for example, 0.05% or more, 0.1% or more, 0.2% or more, 0.3% or more, or 0.4% or more. These haze values ​​for the pressure-sensitive adhesive layer can also be preferably applied to the haze values ​​of a substrateless pressure-sensitive adhesive sheet (typically a pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer) when the technology disclosed herein is implemented in the form of the sheet.

[0030] Here, the "haze value" refers to the ratio of diffuse transmitted light to total transmitted light when visible light is irradiated onto a measurement object. 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 Examples below. The haze value of the pressure-sensitive adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the pressure-sensitive adhesive layer.

[0031] When the pressure-sensitive adhesive sheet disclosed herein is in the form of a substrate-attached double-sided pressure-sensitive adhesive sheet in which a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer are fixedly laminated to a support substrate, it is sufficient that at least the first pressure-sensitive adhesive layer satisfies one of the haze values ​​described above, and the haze value of the second pressure-sensitive adhesive layer is not particularly limited. In a use mode in which light passes through the pressure-sensitive adhesive sheet in the thickness direction, it is preferable that the haze value of the second pressure-sensitive adhesive layer satisfies one of the haze values ​​of the first pressure-sensitive adhesive layer described above. The relative relationship of the haze values ​​of the two pressure-sensitive adhesive layers may be first pressure-sensitive adhesive layer > second pressure-sensitive adhesive layer, first pressure-sensitive adhesive layer < second pressure-sensitive adhesive layer, or first pressure-sensitive adhesive layer = second pressure-sensitive adhesive layer.

[0032] (Surface smoothness of adhesive surface) In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the pressure-sensitive adhesive surface of the pressure-sensitive adhesive sheet preferably has high surface smoothness.

[0033] For example, the adhesive surface preferably has an arithmetic mean roughness Ra limited to a predetermined value or less. A configuration including 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 effectively suppress the occurrence of brightness unevenness due to the surface condition of the adhesive layer, for example, in a usage mode in which light is extracted through the adhesive surface (such as an adhesive sheet arranged closer to the viewpoint than the light-emitting elements in a light-emitting device). A low arithmetic mean roughness Ra of the adhesive surface is also advantageous in suppressing optical distortion, which also contributes to improving optical homogeneity. When the adhesive 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 the arithmetic mean roughness Ra of at least the first adhesive surface be limited to a predetermined value or less, and it is more preferable that the arithmetic mean roughness Ra of both adhesive surfaces be limited to a predetermined value or less. High surface smoothness on each adhesive surface of the double-sided adhesive sheet can favorably achieve adhesion with excellent optical homogeneity.

[0034] 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, and 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 of the adhesive sheet may be, for example, about 10 nm or more, about 20 nm or more, or about 30 nm or more (e.g., about 40 nm or more). In embodiments in which the adhesive 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 similar or different.

[0035] 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 including 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 a use mode in which light is extracted through the adhesive surface as described above, it is possible to effectively suppress the occurrence of brightness unevenness due to 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 adhesive 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 the maximum height Rz of at least the first adhesive surface is limited to a predetermined value or less, and it is more preferable that the maximum heights Rz of both adhesive surfaces are limited to a predetermined value or less. When each adhesive surface of the double-sided adhesive sheet has high surface smoothness, adhesion with excellent optical homogeneity can be preferably achieved.

[0036] In some embodiments, the maximum height Rz of the adhesive surface is preferably approximately 600 nm or less, more preferably approximately 500 nm or less, even more preferably approximately 450 nm or less, and particularly preferably approximately 400 nm or less, and may be less than 350 nm, less than 300 nm, or less than 250 nm. From the standpoint of production efficiency, etc., in some embodiments, the maximum height Rz of the adhesive surface of the adhesive sheet may be, for example, approximately 10 nm or more, approximately 50 nm or more, approximately 100 nm or more, or approximately 200 nm or more. In embodiments in which the adhesive sheet has 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 similar or different.

[0037] The arithmetic mean roughness Ra and maximum height Rz of the adhesive surface are measured using a non-contact surface roughness measuring device. A non-contact surface roughness measuring device using an optical interference method, such as a 3D optical profiler (trade name "NewView7300" manufactured by ZYGO) or an equivalent, can be used. Specific measurement procedures and conditions can be set according to the measurement conditions described in the Examples below, or to obtain results equivalent to or corresponding to those obtained when the measurement conditions are followed.

[0038] The arithmetic mean roughness Ra and maximum height Rz of the adhesive surface can be adjusted by the composition and properties (viscosity, leveling ability, etc.) of the adhesive composition used to form the adhesive layer, and the properties of the surface (release surface) of the release liner that protects the adhesive surface.

[0039] (Water absorption rate) In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet preferably has a water absorption rate limited to a predetermined value or less. For example, it is preferable that the above-mentioned refractive index, total light transmittance, and haze value are satisfied, and that the water absorption rate is limited to a predetermined value or less. By limiting the water absorption rate of the pressure-sensitive adhesive layer, dimensional changes in the pressure-sensitive adhesive layer due to fluctuations in the moisture content (e.g., absorption and release of moisture such as environmental humidity) tend to be suppressed. This can suppress warping of the pressure-sensitive adhesive sheet or the adherend to which the pressure-sensitive adhesive sheet is attached, which is caused by discrepancies in dimensional changes between the pressure-sensitive adhesive layer and its adjacent layer (which may be a supporting substrate, release liner, adherend, etc.). Suppressing fluctuations in the moisture content of the pressure-sensitive adhesive layer is also preferable from the viewpoint of maintaining constant flatness, transparency, refractive index, etc. of the pressure-sensitive adhesive layer. Furthermore, a pressure-sensitive adhesive layer with low water absorption rate is less likely to occlude moisture, making it suitable as a pressure-sensitive adhesive sheet for use in components or products containing elements that are sensitive to moisture, such as organic electroluminescence (EL) elements.

[0040] In some embodiments, the water absorption rate of the pressure-sensitive adhesive layer is suitably approximately 1.0% or less, preferably 0.7% or less, more preferably 0.5% or less (e.g., less than 0.5%), and may be 0.4% or less, 0.3% or less, or 0.2% or less. There is no particular lower limit for the water absorption rate of the pressure-sensitive adhesive layer, but from a practical standpoint, such as achieving compatibility with adhesive properties, it may be, for example, 0.01% or more, 0.05% or more, 0.1% or more, 0.15% or more, or 0.25% or more. When the pressure-sensitive adhesive sheet disclosed herein is in the form of a substrate-attached double-sided pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer, it is preferable that the water absorption rate of at least the first pressure-sensitive adhesive layer be limited to a predetermined value or less. From the standpoint of achieving greater effectiveness, it is more preferable that the water absorption rates of both the first and second pressure-sensitive adhesive layers be limited to a predetermined value or less.

[0041] The water absorption rate (also referred to as moisture content) of the pressure-sensitive adhesive layer is measured by the following method, which is also employed in the examples described below. [Moisture content measurement] The adhesive layer to be evaluated was placed on a 4 cm x 5 cm (area: 20 cm) sheet with two release liners placed on one side and the other side. 2 ) and the release liner on one side is removed and the specimen is attached to pre-weighed aluminum foil. Next, the release liner on the other side of the adhesive layer is removed, and the specimen is placed in a thermo-hygrostat chamber at a temperature of 60°C and a relative humidity of 90%, and then removed after 72 hours. After weighing the test specimen with the adhesive layer and aluminum foil laminated together, the moisture content is measured by Karl Fischer coulometric titration under the following conditions using a moisture meter (Mitsubishi Chemical Analytech Model CA-200) equipped with a thermal vaporizer (Mitsubishi Chemical Analytech Model VA-200). Anolyte: Aquamicron AKX (Mitsubishi Chemical) Catholyte: Aquamicron CXU (Mitsubishi Chemical) Heat evaporation temperature: 150℃

[0042] (gel fraction) The gel fraction of the pressure-sensitive adhesive layer is appropriately set depending on the intended use and mode of use, and is not limited to a specific range. The gel fraction is, for example, approximately 99% or less, and suitably approximately 97% or less. From the viewpoint of easily achieving both a high refractive index and adhesive properties, in some preferred embodiments, the gel fraction may be approximately 95% or less, more preferably approximately 92% or less (e.g., approximately 90% or less). A gel fraction that is not too high is also preferred from the viewpoint of adequate conformity to irregularities that may exist on the adherend surface (e.g., irregularities provided for the purpose of improving light extraction efficiency in a light-emitting device) and good adhesion. In some embodiments, the gel fraction may be approximately 88% or less, approximately 75% or less, or approximately 65% ​​or less. Furthermore, from the viewpoint of imparting appropriate cohesiveness to the pressure-sensitive adhesive and appropriately exhibiting adhesive properties, the gel fraction of the pressure-sensitive adhesive layer is, for example, approximately 10% or more, suitably approximately 20% or more, and may be approximately 30% or more. From the viewpoint of deformation resistance of the pressure-sensitive adhesive layer (prevention of bubbles due to protrusion caused by pressure or entrapment of foreign matter, etc.), the gel fraction is preferably about 30% or more, more preferably about 40% or more, and may be about 45% or more, about 50% or more, about 65% or more, or about 75% or more. The gel fraction of the pressure-sensitive adhesive sheet (typically a substrate-less pressure-sensitive adhesive sheet) is also preferably within the range exemplified above. The gel fraction can be adjusted by the molecular weight, molecular structure, concentration, degree of crosslinking, etc. of the base polymer. The gel fraction is measured by the following method.

[0043] [Gel fraction measurement] A predetermined amount of adhesive sample (weight Wg1) is wrapped in a porous polytetrafluoroethylene membrane (weight Wg2) with an average pore size of 0.2 μm, and the opening is tied with string (weight Wg3). The porous polytetrafluoroethylene (PTFE) membrane is available from Nitto Denko Corporation under the trade name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2 μm, porosity 75%, thickness 85 μm) or an equivalent. The package is immersed in a sufficient amount of ethyl acetate and kept at room temperature (typically 23°C) for 7 days to allow only the sol component of the adhesive to elute out of the film, after which the package is removed and the ethyl acetate adhering to the outer surface is wiped off, the package is dried at 130°C for 2 hours, and the weight (Wg4) of the package is measured. The gel fraction of the adhesive layer can be calculated by substituting each value into the following formula: Gel fraction (%) = [(Wg4 - Wg2 - Wg3) / Wg1] x 100

[0044] When the PSA sheet disclosed herein is in the form of a double-sided PSA sheet having a first adhesive surface and a second adhesive surface, the above-mentioned gel fraction can be applied to at least the PSA layer constituting the first adhesive surface, and is preferably applied to both the PSA layer constituting the first adhesive surface and the PSA layer constituting the second adhesive surface. The gel fraction of the PSA layer constituting the first adhesive surface and the gel fraction of the PSA layer constituting the second adhesive surface may be similar to or different from each other.

[0045] (storage modulus G') In the pressure-sensitive adhesive sheet disclosed herein, the storage modulus G' at 25°C of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer (hereinafter also referred to as "storage modulus G'(25)") is appropriately set depending on the intended use and mode of use, and is not limited to a specific range. The storage modulus G'(25) of the pressure-sensitive adhesive can be, for example, approximately 700 kPa or less. In some embodiments, from the viewpoint of ease of application to an adherend, the storage modulus G'(25) of the pressure-sensitive adhesive is advantageously approximately 600 kPa or less, preferably 500 kPa or less, and more preferably 400 kPa or less (e.g., 350 kPa or less). In some embodiments, from the viewpoint of increasing the flexibility of the pressure-sensitive adhesive at room temperature (e.g., 25°C) to facilitate adhesion to an adherend, the storage modulus G'(25) of the pressure-sensitive adhesive is advantageously approximately 330 kPa or less, and preferably 300 kPa or less. In some embodiments where application and flexibility at room temperature are more important, the storage modulus G'(25) of the PSA may be, for example, less than 270 kPa or less than 250 kPa, advantageously less than 200 kPa, preferably less than 180 kPa, and more preferably less than 160 kPa (e.g., less than 140 kPa). In some embodiments, the storage modulus G'(25) of the PSA may be less than 100 kPa or may be less than 90 kPa. There is no particular lower limit for the storage modulus G'(25) of the PSA, but from the viewpoints of processability, handleability, and the like, it may be, for example, 30 kPa or more, 50 kPa or more, or 70 kPa or more. In some embodiments, taking into consideration the need for a high refractive index, the storage modulus G'(25) may be 100 kPa or more, 150 kPa or more, 200 kPa or more, 250 kPa or more, or 300 kPa or more.

[0046] In the pressure-sensitive adhesive sheet disclosed herein, the storage modulus G' at 50°C of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer (hereinafter also referred to as "storage modulus G'(50)") is not particularly limited and may be, for example, less than 100 kPa. In some embodiments, the storage modulus G'(50) is suitably less than 60 kPa, preferably less than 40 kPa, and more preferably less than 38 kPa (e.g., less than 36 kPa). A pressure-sensitive adhesive having such a limited storage modulus G'(50) can easily increase its adhesion to an adherend by applying appropriate heating as necessary, thereby improving its adhesion to an adherend. There is no particular limit to the lower limit of the storage modulus G'(50) of the pressure-sensitive adhesive. In some embodiments, from the viewpoint of the heat resistance of the pressure-sensitive adhesive, the storage modulus G'(50) may be, for example, 10 kPa or more, 15 kPa or more, 20 kPa or more, or 23 kPa or more.

[0047] In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer satisfies the following conditions: (a) a storage modulus G'(25) at 25°C of 350 kPa or less (preferably less than 200 kPa, e.g., 180 kPa or less); and (b) a storage modulus G'(50) at 50°C of less than 60 kPa (preferably less than 50 kPa, more preferably less than 40 kPa, e.g., less than 38 kPa); It is preferable that at least one of the following conditions is satisfied. A PSA that satisfies at least the above condition (a) is preferred from the viewpoint of adhesion to an adherend at room temperature (e.g., 25°C). A PSA that satisfies at least the above condition (b) is preferred because its adhesion (adhesion) to an adherend can be easily improved by heating to a temperature slightly higher than room temperature. A PSA that does not satisfy the above condition (a) but satisfies the above condition (b) can be used as a heat-activatable PSA that has good reworkability (repositionability) at the initial stage of application at room temperature and can effectively increase the peel strength from an adherend by heating to a temperature slightly higher than room temperature. The heat activation may be performed by heating the PSA to a temperature slightly higher than room temperature when applying it to an adherend. The temperature slightly higher than room temperature is, for example, about 60°C or lower, preferably about 55°C or lower (e.g., about 50°C or lower).

[0048] In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the ratio of the storage modulus G'(50) [kPa] to the storage modulus G'(25) [kPa] of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer, i.e., the storage modulus ratio G'(50) / G'(25), is, for example, 70% or less, or alternatively, 40% or less, 30% or less, or even 20% or less. Pressure-sensitive adhesives with a small G'(50) / G'(25) ratio are suitable for use as the above-mentioned heat-activatable pressure-sensitive adhesive. There is no particular lower limit for G'(50) / G'(25). G'(50) / G'(25) is, for example, 5% or more, and from the viewpoint of the heat resistance of the pressure-sensitive adhesive, preferably 10% or more, or alternatively, 12% or more, or even 15% or more.

[0049] The storage moduli G'(25) and G'(50) can be determined by dynamic viscoelasticity measurement, and G'(50) / G'(25) can be calculated from the results. Dynamic viscoelasticity measurement can be performed using a commercially available dynamic viscoelasticity measuring device in a standard manner, for example, TA Instruments' "Advanced Rheometric Expansion System (ARES)" or an equivalent, under the following measurement conditions. The sample used for measurement is the pressure-sensitive adhesive layer to be evaluated, which has been laminated as necessary to a thickness of approximately 1.5 mm. [Measurement conditions] Deformation mode: Torsion Measurement frequency: 1Hz Heating rate: 5°C / min Shape: Parallel plate 7.9mmφ

[0050] The storage moduli G'(25), G'(50) and storage modulus ratio of the PSA layer can be adjusted by selecting the composition of the monomer components constituting the base polymer of the PSA (e.g., selecting the type and content of monomer (m1)), whether or not a crosslinking agent is used, selecting the type and amount used, whether or not a refractive index enhancer or plasticizing material (described below) is used, selecting the type and amount used, etc. For example, by using, as monomer (m1), in addition to a first monomer that is the main component of monomer (m1), a relatively small amount of a second monomer having a chemical structure different from that of the first monomer in combination with the first monomer, G'(50) can be reduced and G'(50) / G'(25) can be lowered in addition to when the first monomer is used alone as monomer (m1).

[0051] When the PSA sheet disclosed herein is in the form of a double-sided PSA sheet having a first adhesive surface and a second adhesive surface (for example, a substrate-attached double-sided PSA sheet having a first PSA layer and a second PSA layer, or a substrate-less double-sided PSA sheet in which a sub-adhesive layer constituting the first adhesive surface and a sub-adhesive layer constituting the second adhesive surface are laminated together without a non-adhesive substrate between them; the same applies to other similar descriptions), the above-mentioned storage moduli G'(25), G'(50) and storage modulus ratio apply to at least the PSA layer constituting the first adhesive surface, and preferably to both the PSA layer constituting the first adhesive surface and the PSA layer constituting the second adhesive surface. The storage moduli G' of the PSA layer constituting the first adhesive surface and the PSA layer constituting the second adhesive surface may be similar or different.

[0052] In some embodiments of the technology disclosed herein, the peak temperature of tan δ of the adhesive constituting the adhesive layer is preferably about -50°C or higher, and preferably about 50°C or lower. Here, tan δ (loss tangent) of the adhesive refers to the ratio of the loss modulus G" to the storage modulus G' of the adhesive. In other words, tan δ = G" / G'. Tan δ of the adhesive is determined by sandwiching a disk-shaped adhesive sample with a thickness of about 2 mm and a diameter of 7.9 mm between parallel plates, and using a viscoelasticity testing device to apply a shear strain at a frequency of 1 Hz while conducting a temperature dispersion test of the adhesive in a shear mode under conditions of a measurement temperature range of -60°C to 60°C and a heating rate of 5°C / min, and from the storage modulus G' (Pa) and loss modulus G" (Pa) measured at that time, using the following formula: tan δ = G" / G';. The peak temperature of tan δ of the adhesive (hereinafter sometimes referred to as Tpeak) can be determined from the change in tan δ over the above temperature range. As the viscoelasticity testing device, an ARES manufactured by TA Instruments or an equivalent product can be used.

[0053] In some embodiments, the Tpeak of the PSA is advantageously 45°C or less or 35°C or less, preferably 30°C or less (e.g., 25°C or less), and may be 20°C or less, or 15°C or less. PSA with a lower Tpeak tends to be more likely to provide good initial adhesion and adhesion in the room temperature range. On the other hand, a PSA with a Tpeak that is not too low is preferred from the viewpoint of imparting appropriate cohesiveness to the PSA and tends to be suitable for achieving a high refractive index at the same time. From this viewpoint, in some embodiments, the Tpeak of the PSA may be, for example, -40°C or more, -30°C or more, -20°C or more, -5°C or more, 5°C or more, 15°C or more, or even 25°C or more. PSA with a relatively high Tpeak can be preferably used in an embodiment in which, when attaching to an adherend, one or both of the PSA and the adherend are heated to a temperature slightly higher than room temperature, as necessary. The Tpeak of a pressure-sensitive adhesive can be adjusted by selecting the composition of the pressure-sensitive adhesive (for example, the composition of the monomer components that make up the base polymer, whether or not a refractive index enhancer or plasticizing material is used, and selecting the type and amount used). When the PSA sheet disclosed herein is in the form of a double-sided PSA sheet having a first adhesive surface and a second adhesive surface, the Tpeak of the PSA described above is preferably applied to at least the PSA layer constituting the first adhesive surface, and more preferably to both the PSA layer constituting the first adhesive surface and the PSA layer constituting the second adhesive surface. The Tpeak of the PSA layer constituting the first adhesive surface and the Tpeak of the PSA layer constituting the second adhesive surface may be similar to or different from each other.

[0054] <Adhesive layer> (base polymer) In the technology disclosed herein, the type of adhesive constituting the adhesive layer is not particularly limited. The adhesive may contain, as an adhesive polymer (hereinafter also referred to as a "base polymer," meaning a structural polymer that forms the adhesive), one or more of various rubber-like polymers that can be used in the field of adhesives, such as acrylic polymers, rubber polymers (e.g., natural rubber, synthetic rubber, and mixtures thereof), polyester polymers, urethane polymers, polyether polymers, silicone polymers, polyamide polymers, and fluorine-based polymers. From the viewpoints of adhesive performance, cost, and the like, adhesives containing acrylic polymers or rubber polymers as base polymers are preferably used. Among these, adhesives using acrylic polymers as the base polymer (acrylic adhesives) are preferred. The technology disclosed herein is preferably implemented in an embodiment using an acrylic adhesive.

[0055] The following description will mainly focus on adhesive layers made of acrylic adhesives, i.e., adhesive sheets having acrylic adhesive layers, but it is not intended to limit the adhesive layers of the adhesive sheets disclosed herein to those made of acrylic adhesives.

[0056] In this specification, the "base polymer" of a PSA refers to the main component of the rubbery polymer contained in the PSA, and is not to be construed in any other limiting sense. The rubbery polymer refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature. In this specification, the "main component" refers to a component that accounts for more than 50% by weight, unless otherwise specified. In this specification, the term "acrylic polymer" refers to a polymer containing, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as an "acrylic monomer." Therefore, in this specification, an acrylic polymer is defined as a polymer containing a monomer unit derived from an acrylic monomer. A typical example of an acrylic polymer is a polymer in which the proportion of acrylic monomers in all 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). In this specification, "(meth)acryloyl" refers collectively to acryloyl and methacryloyl. Similarly, "(meth)acrylate" refers collectively to acrylate and methacrylate, and "(meth)acrylic" refers collectively to acrylic and methacrylic. Therefore, the concept of an acrylic monomer as used herein can include both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer).

[0057] (Acrylic polymer (A)) The pressure-sensitive adhesive sheet disclosed herein can be preferably implemented in an embodiment including an acrylic pressure-sensitive adhesive layer having a refractive index greater than 1.570, a total light transmittance of 86% or greater, and a haze value of 3.0% or less (preferably 2.0% or less, more preferably 1.0% or less). The acrylic polymer serving as the base polymer of the acrylic pressure-sensitive adhesive layer preferably contains an aromatic ring-containing monomer (m1) as a monomer component constituting the acrylic polymer. That is, an acrylic polymer containing an aromatic ring-containing monomer (m1) as a monomer unit is preferred. Hereinafter, such an acrylic polymer may also be referred to as "acrylic polymer (A)." Herein, the term "monomer component constituting the acrylic polymer" refers to a monomer that constitutes a repeating unit of the acrylic polymer in the pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition, regardless of whether the monomer component is contained in the pressure-sensitive adhesive composition in the form of a preformed polymer (which may be an oligomer) or an unpolymerized monomer. That is, the monomer component constituting the acrylic polymer may be contained in the pressure-sensitive adhesive composition in the form of a polymer, an unpolymerized monomer, or a partially polymerized monomer. In some embodiments, from the viewpoint of ease of preparation of the PSA composition, a PSA composition containing substantially all (e.g., 95 wt % or more, preferably 99 wt % or more) of the monomer components in the form of a polymer is preferred. A PSA composition containing substantially all of the monomer components in the form of a polymer is also preferred from the viewpoint of ease of forming a PSA sheet with less distortion and warpage.

[0058] (Monomer (m1)) As the monomer (m1), a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule can be used. As the monomer (m1), one of such compounds can be used alone or two or more of them can be used in combination.

[0059] Examples of the ethylenically unsaturated group include a (meth)acryloyl group, a vinyl group, and a (meth)allyl group. From the viewpoint of polymerization reactivity, a (meth)acryloyl group is preferred, and from the viewpoints of flexibility and adhesiveness, an acryloyl group is more preferred. From the viewpoint of suppressing a decrease in the flexibility of the adhesive, a compound containing one ethylenically unsaturated group per molecule (i.e., a monofunctional monomer) is preferably used as the monomer (m1).

[0060] The number of aromatic rings contained in one molecule of the compound used as monomer (m1) may be 1 or 2 or more. The upper limit of the number of aromatic rings contained in monomer (m1) is not particularly limited, and may be, for example, 16 or less. In some embodiments, from the viewpoint of ease of preparation of the acrylic polymer (A) and transparency of the PSA, the number of aromatic rings may be, for example, 12 or less, preferably 8 or less, more preferably 6 or less, or may be 5 or less, 4 or less, 3 or less, or 2 or less.

[0061] The aromatic ring of the compound used as monomer (m1) may be, for example, a carbocyclic ring such as a benzene ring (which may be a benzene ring constituting a part of a biphenyl structure or a fluorene structure); a fused ring of a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, or a phenanthrene ring; or a heterocyclic ring such as a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, a pyrrole ring, a pyrazole ring, an imidazole ring, a triazole ring, an oxazole ring, an isoxazole ring, a thiazole ring, or a thiophene ring. The heteroatom contained as a ring-constituting atom in the heterocyclic ring may be, for example, one or more selected from the group consisting of nitrogen, sulfur, and oxygen. In some embodiments, the heteroatom constituting the heterocyclic ring may be one or both of nitrogen and sulfur. Monomer (m1) may have a structure in which one or more carbocyclic rings are fused with one or more heterocyclic rings, such as a dinaphthothiophene structure.

[0062] The aromatic ring (preferably a carbocyclic ring) may have one or more substituents on the ring-constituting atoms, or may have no substituents. When the aromatic ring has a substituent, examples of the substituent include, but are not limited to, an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom (such as a fluorine atom, a chlorine atom, or a bromine atom), a hydroxyalkyl group, a hydroxyalkyloxy group, and a glycidyloxy group. In a carbon atom-containing substituent, the number of carbon atoms contained 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 aromatic ring may have no substituents on the ring-constituting atoms, or may have one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen atom (such as a bromine atom). The term "the aromatic ring of the monomer (m1) has a substituent on its ring-constituting atom" refers to the aromatic ring having a substituent other than a substituent having an ethylenically unsaturated group.

[0063] The aromatic ring and the ethylenically unsaturated group may be bonded directly or via a linking group. The linking group may be, for example, an alkylene group, an oxyalkylene group, a poly(oxyalkylene) group, a phenyl group, an alkylphenyl group, an alkoxyphenyl group, a group in which one or more hydrogen atoms in these groups are substituted with hydroxyl groups (e.g., a hydroxyalkylene group), an oxy group (-O- group), a thiooxy group (-S- group), or the like. In some embodiments, aromatic ring-containing monomers having a structure in which the aromatic ring and the ethylenically unsaturated group are bonded directly or via a linking group selected from the group consisting of an alkylene group, an oxyalkylene group, and a poly(oxyalkylene) group are preferably used. 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.

[0064] Examples of compounds that can be preferably used as the monomer (m1) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. The aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds can be used alone or in combination of two or more. One or more aromatic ring-containing (meth)acrylates and one or more aromatic ring-containing vinyl compounds can be used in combination.

[0065] The content of the monomer (m1) in the monomer components constituting the acrylic polymer (A) is not particularly limited and can be set so as to realize a pressure-sensitive adhesive layer that achieves both the desired refractive index and adhesive properties (e.g., peel strength, flexibility, etc.) and / or optical properties (e.g., total light transmittance, haze value, etc.). In some embodiments, the content of the monomer (m1) in the monomer components may be, for example, 30% by weight or more, preferably 50% by weight or more, 60% by weight or more, or even 70% by weight or more. From the viewpoint of easily obtaining a higher refractive index, in some preferred embodiments, the content of the monomer (m1) may be, for example, more than 70% by weight, 75% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or even 95% by weight or more. The upper limit of the content of the monomer (m1) in the monomer components is 100% by weight. From the viewpoint of achieving a good balance between a high refractive index and adhesive properties and / or optical properties, it is advantageous for the content of the monomer (m1) to be less than 100% by weight, and for example, it is preferably approximately 99% by weight or less, more preferably 98% by weight or less, and may be 97% by weight or less, or may be 96% by weight or less. In some embodiments, the content of the monomer (m1) may be 93% by weight or less, 90% by weight or less, 80% by weight or less, or 75% by weight or less. In some embodiments in which adhesive properties and / or optical properties are more important, the content of the monomer (m1) in the monomer component may be 70% by weight or less, 60% by weight or less, or 45% by weight or less.

[0066] In some embodiments of the technology disclosed herein, a monomer having two or more aromatic rings (preferably carbon rings) in one molecule can be preferably used as the monomer (m1) because it is easy to achieve a high refractive index. Examples of a monomer having two or more aromatic rings in one molecule (hereinafter also referred to as a "monomer containing multiple aromatic rings") include a monomer having a structure in which two or more non-fused aromatic rings are bonded via a linking group, a monomer having a structure in which two or more non-fused aromatic rings are chemically bonded directly (i.e., without the intervention of other atoms), a monomer having a fused aromatic ring structure, a monomer having a fluorene structure, a monomer having a dinaphthothiophene structure, and a monomer having a dibenzothiophene structure. The monomer containing multiple aromatic rings can be used alone or in combination of two or more.

[0067] The linking group may be, for example, an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (e.g., -O-(CH2) n - group, where n is 1 to 3, preferably 1), thiooxyalkylene groups (e.g., -S-(CH2) n - group, where n is 1 to 3, preferably 1), straight chain alkylene groups (i.e., -(CH2) n - group (where n is 1 to 6, preferably 1 to 3), the oxyalkylene group, the thiooxyalkylene group, and the linear alkylene group in which the alkylene group is partially or completely halogenated. From the viewpoint of the flexibility of the adhesive, suitable examples of the linking group include an oxy group, a thiooxy group, an oxyalkylene group, and a linear alkylene group. Specific examples of monomers having a structure in which two or more non-condensed aromatic rings are bonded via a linking group include phenoxybenzyl (meth)acrylate (e.g., m-phenoxybenzyl (meth)acrylate), thiophenoxybenzyl (meth)acrylate, benzyl benzyl (meth)acrylate, and the like.

[0068] The monomer having a structure in which two or more non-fused aromatic rings are directly chemically bonded can be, for example, a biphenyl structure-containing (meth)acrylate, a triphenyl structure-containing (meth)acrylate, a vinyl group-containing biphenyl, etc. Specific examples include o-phenylphenol (meth)acrylate, biphenylmethyl (meth)acrylate, etc.

[0069] Examples of the monomer having the 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, 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate, etc.

[0070] Specific examples of the monomer having the fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene(meth)acrylate, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene(meth)acrylate, etc. Note that the monomer having the fluorene structure includes a structural portion in which two benzene rings are directly chemically bonded, and therefore is included in the concept of the monomer having a structure in which two or more non-fused aromatic rings are directly chemically bonded.

[0071] Examples of the monomer having the dinaphthothiophene structure include (meth)acryloyl group-containing dinaphthothiophene, vinyl group-containing dinaphthothiophene, and (meth)allyl group-containing dinaphthothiophene. Specific examples include (meth)acryloyloxymethyl dinaphthothiophene (for example, dinaphthothiophene having CHCH(R) at the 5th or 6th position of the dinaphthothiophene ring). 1 )C(O)OCH2- bonded compound. 1 is a hydrogen atom or a methyl group), (meth)acryloyloxyethyl dinaphthothiophene (for example, CHCH(R1 )C(O)OCH(CH3)- or CH2CH(R 1 )C(O)OCH2CH2- bonded compound. 1 is a hydrogen atom or a methyl group.), vinyl dinaphthothiophene (for example, a compound having a structure in which a vinyl group is bonded to the 5th or 6th position of a naphthothiophene ring), (meth)allyloxydinaphthothiophene, etc. Note that a monomer having a dinaphthothiophene structure is also included in the concept of a monomer having the above-mentioned fused aromatic ring structure because it contains a naphthalene structure or has a structure in which a thiophene ring and two naphthalene structures are fused together.

[0072] Examples of the monomer having the dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophene, vinyl group-containing dibenzothiophene, etc. Note that the monomer having the dibenzothiophene structure has a structure in which a thiophene ring and two benzene rings are fused, and therefore is included in the concept of the monomer having the fused aromatic ring structure. Note that neither the dinaphthothiophene structure nor the dibenzothiophene structure corresponds to a structure in which two or more non-fused aromatic rings are directly chemically bonded.

[0073] As the monomer (m1) in the technology disclosed herein, a monomer having one aromatic ring (preferably a carbon ring) per molecule may be used. A monomer having one aromatic ring per molecule can be useful, for example, for improving the flexibility of the pressure-sensitive adhesive, adjusting the adhesive properties, improving the transparency, etc. In some embodiments, a monomer having one aromatic ring per molecule is preferably used in combination with a monomer containing multiple aromatic rings, from the viewpoint of improving the refractive index of the pressure-sensitive adhesive.

[0074] Examples of monomers having one aromatic ring in one molecule include carbon-containing aromatic ring (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, and chlorobenzyl (meth)acrylate; 2-(4,6-dibromo-2-s-butylphenoxy)ethyl (meth)acrylate, 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate, and 6- Examples of the aromatic ring-containing (meth)acrylate 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-containing aromatic ring-containing vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and tert-butylstyrene; and compounds having a vinyl substituent on a heteroaromatic ring such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, and N-vinyloxazole.

[0075] Monomer (m1) may be a monomer having an oxyethylene chain interposed between the ethylenically unsaturated group and the aromatic ring in the various aromatic ring-containing monomers described above. Such a monomer having an oxyethylene chain interposed between the ethylenically unsaturated group and the aromatic ring can be understood as an ethoxylated product of the original monomer. The number of repeating oxyethylene units (-CHCHO-) in the 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, and phenoxydiethylene glycol di(meth)acrylate.

[0076] The content of the aromatic ring-containing monomer in the monomer (m1) 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 easily realizing a pressure-sensitive adhesive having a higher refractive index, the content of the aromatic ring-containing monomer in the monomer (m1) may be, for example, 50% by weight or more, preferably 70% by weight or more, or 85% by weight or more, 90% by weight or more, or even 95% by weight or more. Substantially 100% by weight of the aromatic ring-containing monomer in the monomer (m1) may be. That is, only one or two or more aromatic ring-containing monomers may be used as the monomer (m1). Furthermore, in some embodiments, for example, taking into consideration the balance between a high refractive index and adhesive properties and / or optical properties, the content of the aromatic ring-containing monomer in the monomer (m1) may be less than 100% by weight, or may be 98% by weight or less, 90% by weight or less, 80% by weight or less, or 65% by weight or less. In some embodiments, taking into consideration adhesive properties and / or optical properties, the content of the aromatic ring-containing monomer in the monomer (m1) may be 70% by weight or less, 50% by weight or less, 25% by weight or less, or 10% by weight or less. The technology disclosed herein may also be implemented in an embodiment in which the aromatic ring-containing monomer content in the monomer (m1) is less than 5% by weight. The aromatic ring-containing monomer may not be used.

[0077] The content of the aromatic ring-containing monomer in the monomer components constituting the acrylic polymer is not particularly limited and can be set so as to realize a pressure-sensitive adhesive layer that satisfies both the desired refractive index and adhesive properties (e.g., peel strength, flexibility, etc.) and / or optical properties (e.g., total light transmittance, haze value, etc.). The content of the aromatic ring-containing monomer in the monomer components may be, for example, 3 wt% or more, 10 wt% or more, or 25 wt% or more. In some embodiments, to facilitate the realization of a pressure-sensitive adhesive having a higher refractive index, the content of the aromatic ring-containing monomer in the monomer components may be, for example, more than 35 wt%, preferably more than 50 wt%, more than 70 wt%, 75 wt% or more, 85 wt% or more, 90 wt% or more, or even 95 wt% or more. The content of the multiple aromatic ring monomer in the monomer component can be 100% by weight. However, from the viewpoint of achieving a good balance between a high refractive index and adhesive properties and / or optical properties, it is advantageous to set it to less than 100% by weight, preferably approximately 99% by weight or less, more preferably 98% by weight or less, and may be 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 embodiments, taking into consideration adhesive properties and / or optical properties, the content of the multiple aromatic ring monomer in the 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 an embodiment in which the content of the multiple aromatic ring monomer in the monomer component is less than 3% by weight.

[0078] In some embodiments of the technology disclosed herein, a high refractive index monomer may be preferably used as at least a portion of the monomer (m1). Here, "high refractive index monomer" refers to a monomer having a refractive index of, for example, about 1.510 or more, preferably about 1.530 or more, and more preferably about 1.550 or more. The upper limit of the refractive index of the high refractive index monomer is not particularly limited, but from the viewpoint of ease of preparation of the pressure-sensitive adhesive composition and ease of achieving compatibility with flexibility suitable for a pressure-sensitive 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 may be used alone or in combination of two or more. The refractive index of the monomer is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C. The Abbe refractometer may be an ATAGO DR-M4 model or an equivalent. If the manufacturer provides a nominal value for the refractive index at 25°C, that nominal value may be used.

[0079] As the high refractive index monomer, a compound having the corresponding refractive index can be appropriately selected from compounds included in the concept of the aromatic ring-containing monomer (m1) disclosed herein (for example, the compounds and compound groups exemplified above). Specific examples include m-phenoxybenzyl acrylate (refractive index: 1.566, Tg of homopolymer: -35°C), 1-naphthylmethyl acrylate (refractive index: 1.595, Tg of homopolymer: 31°C), ethoxylated o-phenylphenol acrylate (number of repeating oxyethylene units: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, Tg of homopolymer: 6°C), phenoxyethyl acrylate (refractive index (nD20): 1.517, Tg of homopolymer: 2°C), and phenoxydiethylene glycol acrylate (refractive index: 1.510, Tg of homopolymer: 1.520). Examples of suitable dinaphthothiophene 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 (abbreviated as 5VDNT, refractive index: 1.793).

[0080] The content of the high refractive index monomer in the monomer (m1) (i.e., an aromatic ring-containing monomer having a refractive index of about 1.510 or more, preferably about 1.530 or more, more preferably about 1.550 or more) 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 the high refractive index monomer in the monomer (m1) may be, for example, 50% by weight or more, preferably 70% by weight or more, or 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomer (m1) may be the high refractive index monomer. In some embodiments, for example, from the viewpoint of achieving a good balance between a high refractive index and adhesive properties and / or optical properties, the content of the high refractive index monomer in the monomer (m1) 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 embodiments, taking into account adhesive properties and / or optical properties, the content of the high refractive index monomer in the monomer (m1) may be 70% by weight or less, 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 may also be implemented in an embodiment in which the content of the high refractive index monomer in the monomer component (m1) is less than 5% by weight. The high refractive index monomer need not be used.

[0081] The content of the high refractive index monomer in the monomer components constituting the acrylic polymer is not particularly limited and can be set so as to realize a pressure-sensitive adhesive layer that achieves both the desired refractive index and adhesive properties (e.g., peel strength, flexibility, etc.) and / or optical properties (e.g., total light transmittance, haze value, etc.). The content of the high refractive index monomer in the monomer components may be, for example, 3 wt% or more, 10 wt% or more, or 25 wt% or more. In some embodiments, from the viewpoint of easily realizing a pressure-sensitive adhesive having a higher refractive index, the content of the high refractive index monomer in the monomer components may be, for example, more than 35 wt%, preferably more than 50 wt%, more than 70 wt%, 75 wt% or more, 85 wt% or more, 90 wt% or more, or even 95 wt% or more. The content of the high refractive index monomer in the monomer component can be 100% by weight. However, from the viewpoint of achieving a good balance between a high refractive index and adhesive properties and / or optical properties, it is advantageous to set it to less than 100% by weight, preferably 99% by weight or less, more preferably 98% by weight or less, and may be 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 embodiments, taking into consideration adhesive properties and / or optical properties, the content of the high refractive index monomer in the 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 an embodiment in which the content of the high refractive index monomer in the monomer component is less than 3% by weight.

[0082] In some preferred embodiments of the technology disclosed herein, an aromatic ring-containing monomer (hereinafter, sometimes referred to as "monomer L") having a homopolymer Tg of 10°C or lower (preferably 5°C or lower or 0°C or lower, more preferably -10°C or lower, even more preferably -20°C or lower, for example -25°C or lower) is used as at least a portion of the monomer (m1). Increasing the content of the aromatic ring-containing monomer (m1) (particularly the aromatic ring-containing monomer (m1) corresponding to one or both of the above-mentioned multiple aromatic ring-containing monomer and high refractive index monomer) in the monomer components generally tends to increase the storage modulus G' of the PSA. However, by employing monomer L as part or all of the monomer (m1), the increase in storage modulus G' can be suppressed. This allows the refractive index to be improved while better maintaining flexibility suitable for a PSA. The lower limit of the Tg of monomer L is not particularly limited. In consideration of the balance with the refractive index-enhancing 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. The monomer L can be used alone or in combination of two or more.

[0083] As the monomer L, a compound having the corresponding Tg can be appropriately selected from among the compounds encompassed by the concept of the aromatic ring-containing monomer (m1) disclosed herein (for example, the compounds and compound groups exemplified above). One suitable example of an aromatic ring-containing monomer that can be used as the monomer L is m-phenoxybenzyl acrylate (Tg of the homopolymer: -35°C). Another suitable example is phenoxydiethylene glycol acrylate (Tg of the homopolymer: -35°C).

[0084] The content of monomer L in monomer (m1) 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 easily obtaining a PSA that achieves both a high refractive index and flexibility at a higher level, the content of monomer L in monomer (m1) may be, for example, 50% by weight or more, 60% by weight or more, 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. Monomer (A1) may account for substantially 100% by weight of monomer L. In some embodiments, for example, from the viewpoint of achieving a good balance between flexibility suitable for a pressure-sensitive adhesive and a high refractive index, the content of monomer L in monomer (m1) may be less than 100% by weight, 98% by weight or less, 90% by weight or less, 80% by weight or less, 70% by weight or less, 50% by weight or less, 25% by weight or less, or 10% by weight or less. The technology disclosed herein can also be implemented in an embodiment in which the content of monomer L in monomer (m1) is less than 5% by weight. Monomer L need not be used.

[0085] The content of monomer L in the monomer components constituting the acrylic polymer may be, for example, 3 wt% or more, 10 wt% or more, or 25 wt% or more. In some embodiments, from the viewpoint of easily obtaining a PSA that combines a high refractive index and flexibility at a higher level, the content of monomer L in the monomer components may be, for example, more than 35 wt%, preferably more than 50 wt%, more than 70 wt%, 75 wt% or more, 85 wt% or more, 90 wt% or more, or even 95 wt% or more. The content of monomer L in the monomer components may be 100 wt%, but in consideration of the balance between a high refractive index and adhesive properties and / or optical properties, it is advantageous to set it to less than 100 wt%, preferably approximately 99 wt% or less, more preferably 98 wt% or less, or 96 wt% or less, 95 wt% or less, 93 wt% or less, 90 wt% or less, 85 wt% or less, 80 wt% or less, or 75 wt% or less. In some embodiments, the content of monomer L in the monomer mixture 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 may also be practiced in embodiments in which the content of monomer L in the monomer mixture is less than 3% by weight.

[0086] In some embodiments, the glass transition temperature Tg based on the composition of the monomer (m1) m1 From the viewpoint of flexibility of the adhesive, it is advantageous that the glass transition temperature Tg is about 20°C or less, preferably 10°C or less (for example, 5°C or less), more preferably 0°C or less, and even more preferably -10°C or less, and may be -20°C or less, or -25°C or less. m1 The lower limit of the glass transition temperature Tg is not particularly limited. m1 The glass transition temperature Tg may be, for example, −70° C. or higher, −55° C. or higher, or −45° C. or higher. m1is preferably -40°C or higher, -35°C or higher, -33°C or higher, -30°C or higher, or -25°C or higher, for example.

[0087] Here, the glass transition temperature Tg based on the composition of the monomer (m1) m1 The glass transition temperature (Tg) is calculated by the Fox formula (described later) based on the composition of only the monomer (m1) among the monomer components constituting the acrylic polymer. m1 The Tg and glass transition temperature Tg of the homopolymer of each aromatic ring-containing monomer used as the monomer (m1) can be calculated by applying the Fox formula described below to only the monomer (m1) among the monomer components constituting the acrylic polymer, and from the weight fraction of each aromatic ring-containing monomer in the total amount of the monomer (m1). In an embodiment in which only one type of monomer is used as the monomer (m1), the Tg and glass transition temperature Tg of the homopolymer of that monomer can be calculated. m1 is consistent with

[0088] In some embodiments, the aromatic ring-containing monomer (m1) can be a combination of monomer L (i.e., an aromatic ring-containing monomer having a homopolymer Tg of 10°C or less, preferably 5°C or less or 0°C or less, more preferably -10°C or less, even more preferably -20°C or less, for example -25°C or less) and monomer H having a Tg higher than 10°C. The Tg of monomer H may be, for example, above 10°C, above 15°C, or above 20°C. By using monomer L and monomer H in combination, for example, in a configuration in which the content of aromatic ring-containing monomer (m1) in the monomer components is relatively high, it is possible to achieve a high refractive index and flexibility of the adhesive at a higher level. The ratio of the amounts of monomer L and monomer H used can be set so as to suitably exhibit such effects and is not particularly limited. For example, the Tg of any of the above-mentioned monomers having a glass transition temperature Tg m1 It is preferable to set the ratio of the amounts of the monomers L and H used so as to satisfy the following.

[0089] In some embodiments, the aromatic ring-containing monomer (m1) can be preferably selected from compounds that do not contain a structure in which two or more non-fused aromatic rings are directly chemically bonded (e.g., a biphenyl structure). For example, an acrylic polymer composed of monomer components having a composition in which the content of a compound containing a structure in which two or more non-fused aromatic rings are directly chemically bonded is less than 5 wt % (more preferably less than 3 wt %, and may even be 0 wt %) is preferred. Limiting the amount of the compound containing a structure in which two or more non-fused aromatic rings are directly chemically bonded in this way can be advantageous from the perspective of realizing a pressure-sensitive adhesive that balances flexibility, adhesiveness, and a high refractive index.

[0090] (Monomer (m2)) In some embodiments of the technology disclosed herein, the monomer components constituting the acrylic polymer may further contain a monomer (m2) in addition to the monomer (m1). The monomer (m2) 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 having at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. The monomer (m2) can be useful for introducing crosslinking points into the acrylic polymer or imparting appropriate cohesiveness to the PSA. The monomer (m2) can be used alone or in combination of two or more types. The monomer (m2) is typically a monomer that does not contain an aromatic ring.

[0091] Examples of the ethylenically unsaturated group contained in the monomer (m2) include a (meth)acryloyl group, a vinyl group, and a (meth)allyl group. From the viewpoint of polymerization reactivity, a (meth)acryloyl group is preferred, and from the viewpoints of flexibility and adhesiveness, an acryloyl group is more preferred. From the viewpoint of suppressing a decrease in the flexibility of the adhesive, a compound containing one ethylenically unsaturated group per molecule (i.e., a monofunctional monomer) is preferably used as the monomer (m2).

[0092] 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. Preferred examples of hydroxyl group-containing monomers 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. In a preferred embodiment, 50% by weight or more (e.g., more than 50% by weight, more than 70% by weight, or more than 85% by weight) of the monomer (m2) may be 4-hydroxybutyl acrylate. The hydroxyl group-containing monomers can be used alone or in combination of two or more.

[0093] In some embodiments in which a hydroxyl group-containing monomer is used as the monomer (m2), the hydroxyl group-containing monomer may be one or more selected from compounds not containing a methacryloyl group. Suitable examples of hydroxyl group-containing monomers not containing a methacryloyl group include the various hydroxyalkyl acrylates described above. For example, it is preferred that more than 50 wt%, more than 70 wt%, or more than 85 wt% of the hydroxyl group-containing monomers used as the monomer (m2) are hydroxyalkyl acrylates. The use of hydroxyalkyl acrylates allows the introduction of hydroxy groups into the acrylic polymer, which are useful for providing crosslinking points and imparting appropriate cohesion, and also makes it easier to obtain a PSA with good flexibility and adhesion at room temperature compared to using only the corresponding hydroxyalkyl methacrylate.

[0094] 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. Preferred examples of carboxyl group-containing monomers include acrylic acid and methacrylic acid. The carboxyl group-containing monomers may be used alone or in combination of two or more. Hydroxyl group-containing monomers and carboxyl group-containing monomers may be used in combination.

[0095] The content of monomer (m2) in the monomer components constituting the acrylic polymer is not particularly limited and can be set according to the purpose. In some embodiments, the content of the monomer (m2) can be, for example, 0.01% by weight or more, 0.1% by weight or more, or 0.5% by weight or more. From the viewpoint of obtaining a higher usage effect, in some embodiments, the content of the monomer (A2) is preferably 1% by weight or more, or may be 2% by weight or more, or may be 4% by weight or more. The upper limit of the content of monomer (m2) in the monomer components is set so that the total content of the monomer (m2) and other monomers does not exceed 100% by weight. In some embodiments, the content of the monomer (m2) is suitably, for example, 30% by weight or less or 25% by weight or less. From the viewpoint of relatively increasing the content of monomer (m1) to facilitate a high refractive index, the content is preferably 20% by weight or less, more preferably 15% by weight or less, and may be less than 12% by weight, 10% by weight, or 7% by weight.

[0096] In embodiments in which a hydroxyl-containing monomer is used as monomer (m2), the content of the hydroxyl-containing monomer in the monomer component is not particularly limited and can 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-containing monomer is preferably 1% by weight or more of the monomer component, and may be 2% by weight or more, or even 4% by weight or more. The upper limit of the content of the hydroxyl-containing monomer in the monomer component is set so that the total content of other monomers does not exceed 100% by weight, and is suitably, for example, 30% by weight or less or 25% by weight or less. From the viewpoint of relatively increasing the content of monomer (m1) to facilitate a high refractive index, the upper limit is preferably 20% by weight or less, more preferably 15% by weight or less, and may be less than 12% by weight, 10% by weight or less, or even less than 7% by weight.

[0097] In embodiments using a carboxyl group-containing monomer as monomer (m2), the content of the carboxyl group-containing monomer in the monomer component is not particularly limited and can be, for example, 0.01 wt% or more (preferably 0.1 wt% or more, more preferably 0.3 wt% or more). In some embodiments, the content of the carboxyl group-containing monomer may be 1 wt% or more, 2 wt% or more, or even 4 wt% or more. The upper limit of the content of the carboxyl group-containing monomer in the monomer component is set so that the total amount of the carboxyl group-containing monomer and the amount of other monomers used does not exceed 100 wt%, and is suitably, for example, 30 wt% or less or 25 wt% or less. From the viewpoint of facilitating a high refractive index by relatively increasing the content of monomer (m1), the upper limit is preferably 20 wt% or less, more preferably 15 wt% or less, and may be less than 12 wt% or less than 10 wt%. In some embodiments, from the viewpoint of improving the flexibility of the PSA, the content of the carboxyl group-containing monomer is advantageously less than 7 wt%, preferably less than 5 wt%, or may be less than 3 wt%, less than 1 wt%, or may be less than 0.5 wt%. The technology disclosed herein can be preferably practiced, for example, in an embodiment in which only a hydroxyl group-containing monomer is used as the monomer (m2), i.e., an embodiment in which no carboxyl group-containing monomer is used.

[0098] The total content of monomer (m1) and monomer (m2) in the monomer components constituting the acrylic polymer may be, for example, 31% by weight or more, preferably 51% by weight or more, or 61% by weight or more, or 71% by weight or more. In some embodiments, the total content of monomer (m1) and monomer (m2) in the monomer components constituting the acrylic polymer may be, for example, 76% by weight or more, preferably 81% by weight or more, or 86% by weight or more, or 91% by weight or more, or 96% by weight or more, or 99% by weight or more, or even substantially 100% by weight, in order to facilitate the effects of these monomers to be favorably exhibited.

[0099] (monomer m3) The monomer components constituting the acrylic polymer may contain, as necessary, monomers other than the above-mentioned monomers (m1) and (m2). An example of such an optional component is alkyl(meth)acrylate (hereinafter also referred to as "monomer (m3)"). Monomer (m3) can be useful for adjusting the flexibility of the PSA and improving compatibility within the PSA.

[0100] The monomer (m3) may be a monomer having 1 to 20 carbon atoms (i.e., C 1-20 Alkyl (meth)acrylates having a linear or branched alkyl group at the ester terminal 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. , 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, eicosyl (meth)acrylate, and the like, but are not limited to these.

[0101] In some embodiments, an alkyl(meth)acrylate having a homopolymer Tg of −20° C. or lower (more preferably −40° C. or lower, e.g., −50° C. or lower) can be preferably used as at least a portion of the monomer (m3). Such an alkyl(meth)acrylate with a low Tg can be useful for improving the flexibility of the PSA. 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), isononyl acrylate (iNA), and the like.

[0102] In some embodiments using the monomer (m3), from the viewpoint of flexibility, adhesiveness, etc., it is preferable that at least a portion of the monomer (m3) is an alkyl acrylate. For example, it is preferable that 50% by weight or more (more preferably 75% by weight or more, and even more preferably 90% by weight or more) of the monomer (m3) is an alkyl acrylate. It is also possible to use only one or more alkyl acrylates as the monomer (m3), without using any alkyl methacrylates.

[0103] In embodiments in which the monomer component includes an alkyl (meth)acrylate, the content of the alkyl (meth)acrylate in the monomer component can be set so as to appropriately achieve the intended effect. In some embodiments, the content of the 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. In some embodiments, the content of the alkyl (meth)acrylate may be, for example, 15% by weight or more, 30% by weight or more, or 45% by weight or more. The upper limit of the content of the monomer (m3) in the monomer component is set so that the total content together with the content of other monomers does not exceed 100% by weight, and may be, for example, less than 50% by weight. In some embodiments, the content of the monomer (m3) may be, for example, less than 35% by weight. Since alkyl (meth)acrylates generally have a relatively low refractive index, in order to increase the refractive index, it is advantageous to limit the content of the monomer (m3) in the monomer component and relatively increase the content of the monomer (m1). From this viewpoint, the content of the monomer (m3) is advantageously 24% by weight or less of the monomer components, preferably less than 23% by weight, more preferably less than 20% by weight, and may be less than 17% by weight, less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The monomer (m3) may not be used substantially.

[0104] (Other monomers) The monomer components constituting the acrylic polymer may contain, as necessary, monomers other than the above-mentioned monomers (m1), (m2), and (m3) (hereinafter referred to as "other monomers"). The above-mentioned other monomers can be used for purposes such as adjusting the Tg of the acrylic polymer, adjusting the adhesive performance, and improving compatibility within the adhesive layer. The above-mentioned other monomers can be used alone or in combination of two or more.

[0105] Examples of the other monomers include monomers having functional groups other than hydroxyl groups and carboxyl groups (functional group-containing monomers). For example, examples of other monomers that can improve the cohesive strength and heat resistance of the adhesive include sulfonic acid group-containing monomers, phosphate group-containing monomers, and cyano group-containing monomers. Furthermore, examples of monomers that can introduce functional groups that can serve as crosslinking base points into acrylic polymers or that can contribute to improving peel strength and compatibility within the adhesive layer 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. Incidentally, some of the monomers having a nitrogen atom-containing ring, such as N-vinyl-2-pyrrolidone, also fall under the category of amide group-containing monomers. The same applies to the relationship between the above-mentioned monomers having a nitrogen atom-containing ring and amino group-containing monomers.

[0106] Examples of other monomers that can be used in addition to the 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; etc. One suitable example of other monomers that can be used for purposes such as improving the flexibility of the adhesive is ethoxyethoxyethyl acrylate (also known as ethyl carbitol acrylate, Tg of homopolymer: -67°C).

[0107] When the other monomers are used, their amount is not particularly limited and can be appropriately set within a range in which the total amount of the monomer components does not exceed 100% by weight. In some embodiments, from the viewpoint of easily achieving the refractive index-enhancing effect of the use of the monomer (m1), the content of the other monomers in the monomer components can be, for example, about 35% by weight or less, suitably about 25% by weight or less (e.g., 0 to 25% by weight), or may be about 20% by weight or less (e.g., 0 to 20% by weight), about 10% by weight or less, about 5% by weight or less, or, for example, about 1% by weight or less. The technology disclosed herein can be preferably implemented in an embodiment in which the monomer components are substantially free of the other monomers.

[0108] In some embodiments, the monomer components constituting the acrylic polymer may be a composition in which the amount of methacryloyl group-containing monomer used is suppressed to a predetermined level or less. The amount of methacryloyl group-containing monomer used in the monomer components may be, for example, less than 5 wt %, less than 3 wt %, less than 1 wt %, or less than 0.5 wt %. Limiting the amount of methacryloyl group-containing monomer used in this manner may be advantageous from the perspective of realizing a pressure-sensitive adhesive that has a good balance between flexibility, adhesiveness, and a high refractive index. The monomer components constituting the acrylic polymer may be a composition that does not contain a methacryloyl group-containing monomer (for example, a composition consisting only of an acryloyl group-containing monomer).

[0109] In some embodiments, the monomer component constituting the base polymer (e.g., acrylic polymer) of the pressure-sensitive adhesive layer preferably contains a limited amount of carboxyl group-containing monomer in order to prevent coloration or discoloration (e.g., yellowing) of the pressure-sensitive adhesive. The amount of carboxyl group-containing monomer in the monomer component may be, for example, less than 1 wt %, preferably less than 0.5 wt %, more preferably less than 0.3 wt %, or may be less than 0.1 wt %, or may be less than 0.05 wt %. Such a limited amount of carboxyl group-containing monomer is advantageous in terms of preventing corrosion of metal materials (e.g., metal wiring or metal films that may be present on an adherend) that may be in contact with or adjacent to the pressure-sensitive adhesive disclosed herein. The technology disclosed herein can be preferably implemented in an embodiment in which the monomer component does not contain a carboxyl group-containing monomer. For the same reason, in some embodiments, the monomer component constituting the base polymer of the pressure-sensitive adhesive layer preferably contains a limited amount of monomers having acidic functional groups (including carboxy groups, sulfonic acid groups, phosphate groups, etc.). The amount of the acidic functional group-containing monomer in the monomer component of such embodiments can be the same as the preferred amount of the carboxy group-containing monomer described above. The technology disclosed herein can be preferably implemented in an embodiment in which the monomer component does not contain an acidic group-containing monomer (i.e., an embodiment in which the base polymer of the pressure-sensitive adhesive layer is acid-free).

[0110] (Base polymer glass transition temperature Tg T ) In some embodiments, the base polymer of the pressure-sensitive adhesive layer (e.g., an acrylic polymer) has a glass transition temperature Tg T The glass transition temperature Tg is suitably about 20°C or less, preferably about 10°C or less, more preferably 0°C or less, and may be -10°C or less, -20°C or less, -25°C or less, -28°C or less, or -30°C or less. T A low glass transition temperature TgT may be, for example, -60°C or higher, and from the viewpoint of facilitating the high refractive index of the pressure-sensitive adhesive, is preferably -50°C or higher, more preferably higher than -45°C, may be higher than -40°C, may be higher than -35°C, may be higher than -25°C, may be -15°C or higher, or may be -5°C or higher.

[0111] Here, the glass transition temperature Tg of the polymer T Unless otherwise specified, the glass transition temperature (Tg) refers to the glass transition temperature calculated by the Fox equation based on the composition of the monomer components constituting the polymer. The Fox equation, as shown below, is a relational expression 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. 1 / Tg=Σ(Wi / Tgi) In the above Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio by weight), and Tgi represents the glass transition temperature (unit: K) of the homopolymer of monomer i. The glass transition temperature of a homopolymer used to calculate Tg is the value described in publicly available sources such as "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989). For monomers for which multiple values ​​are described in the Polymer Handbook, the highest value is used. If the Tg of a homopolymer is not described in publicly available sources, the value obtained by the measurement method described in JP 2007-51271 A is used.

[0112] (Method for preparing base polymer) In the technology disclosed herein, the method for obtaining the base polymer of the pressure-sensitive adhesive layer (for example, the acrylic polymer (A) composed of the above-mentioned 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 used. In some embodiments, solution polymerization can be preferably used. The polymerization temperature during solution polymerization can be appropriately selected depending on the types of monomers and solvents used, the type of polymerization initiator, etc., and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

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

[0114] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, one or more azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; and aromatic carbonyl compounds. Still other examples of polymerization initiators include redox-based initiators formed by combining a peroxide with a reducing agent. One polymerization initiator can be used alone, or two or more polymerization initiators can be used in combination. The amount of polymerization initiator used may be a typical amount, and can be selected, for example, from the range of approximately 0.005 to 1 part by weight (typically approximately 0.01 to 1 part by weight) per 100 parts by weight of the monomer components.

[0115] In the polymerization, 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 a sulfur atom (non-sulfur chain transfer agent) can 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. The chain transfer agents can be used alone or in combination of two or more. When a chain transfer agent is used, the amount used can be, for example, about 0.01 to 1 part by weight per 100 parts by weight of the monomer raw material.

[0116] The weight average molecular weight (Mw) of the base polymer is not particularly limited, and is, for example, about 10 × 10 4 ~500×10 4 From the viewpoint of adhesive performance, the Mw of the base polymer can be in the range of approximately 20×10 4 ~400×10 4 (More preferably, approximately 30×10 4 ~150×10 4 , for example, approximately 50×10 4 ~130×10 4 ) range is preferred.

[0117] Here, the Mw of the polymer can be determined in terms of polystyrene by gel permeation chromatography (GPC). Specifically, it can be determined by measuring under the following conditions using a GPC measuring device "HLC-8220GPC" (manufactured by Tosoh Corporation). [GPC measurement conditions] Sample concentration: 0.2 wt% (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: tetrahydrofuran (THF) Flow rate (flow rate): 0.6mL / min Column temperature (measurement temperature): 40°C column: Sample column: 1 "TSKguardcolumn SuperHZ-H" + 2 "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: 1 tube of "TSKgel SuperH-RC" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: polystyrene

[0118] (Refractive index enhancer) In some embodiments of the technology disclosed herein, the pressure-sensitive adhesive layer (e.g., an acrylic pressure-sensitive adhesive layer) may contain a refractive index enhancer, if necessary, in addition to the base polymer. Herein, the term "refractive index enhancer" refers to a material that can increase the refractive index of the pressure-sensitive adhesive layer when used. A material having a higher refractive index than the pressure-sensitive adhesive layer containing the refractive index enhancer is preferably used as the refractive index enhancer. Furthermore, a material having a higher refractive index than the base polymer (e.g., the acrylic polymer (A)) of the pressure-sensitive adhesive layer containing the refractive index enhancer is preferably used as the refractive index enhancer. Appropriate use of the refractive index enhancer can favorably achieve both a higher refractive index and practical adhesive performance. In some embodiments, the refractive index enhancer is preferably an organic material. The organic material used as the refractive index enhancer may be a polymer or a non-polymer. It may or may not have a polymerizable functional group. The refractive index enhancers may be used alone or in combination of two or more.

[0119] Refractive index improver (e.g., additive (H ROThe refractive index of the refractive index enhancer is not limited to a specific range and can be set within an appropriate range relative to the refractive index of the base polymer. The refractive index of the refractive index enhancer can be selected from a range of, for example, greater than 1.55, greater than 1.56, or greater than 1.57, and higher than the refractive index of the base polymer. From the viewpoint of increasing the refractive index of the adhesive, in some embodiments, the refractive index of the refractive index enhancer is advantageously 1.58 or higher, preferably 1.60 or higher, more preferably 1.63 or higher, and may be 1.65 or higher, 1.70 or higher, or 1.75 or higher. A refractive index enhancer with a higher refractive index can achieve the desired refractive index even with the use of a smaller amount of the refractive index enhancer. This is preferable from the viewpoint of suppressing deterioration of adhesive properties and optical properties. The upper limit of the refractive index of the refractive index enhancer is not particularly limited, but from the viewpoint of compatibility within the adhesive and ease of achieving both a high refractive index and flexibility suitable for the adhesive, it is, for example, 3.000 or less, or alternatively 2.500 or less, 2.000 or less, 1.950 or less, 1.900 or less, or 1.850 or less.

[0120] In some embodiments, a refractive index enhancer (e.g., an additive (H RO )) refractive index n b and the refractive index of the base polymer, n a The difference between b -n a (Hereinafter, “Δn A "). ) is set to be greater than 0. In some embodiments, Δn A is, for example, 0.02 or more, and may be 0.05 or more, 0.07 or more, 0.10 or more, 0.15 or more, 0.20 or more, or 0.25 or more. A By selecting a base polymer and a refractive index enhancer so that Δn is larger, the refractive index enhancing effect by using the refractive index enhancer tends to be higher. Also, from the viewpoint of compatibility in the pressure-sensitive adhesive layer, transparency of the pressure-sensitive adhesive layer, etc., in some embodiments, A may be, for example, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.35 or less.

[0121] In some embodiments, a refractive index enhancer (e.g., an additive (H RO )) refractive index n b and the refractive index n of the pressure-sensitive adhesive layer containing the refractive index enhancer T The difference between b -n T (Hereinafter, “Δn B "). ) is set to be greater than 0. In some embodiments, Δn B is, for example, 0.02 or more, and may be 0.05 or more, 0.07 or more, 0.10 or more, 0.15 or more, 0.20 or more, or 0.25 or more. B By selecting the composition of the pressure-sensitive adhesive layer and the refractive index enhancer so that Δn is larger, the refractive index enhancing effect by using the refractive index enhancer tends to be higher. Also, from the viewpoint of compatibility within the pressure-sensitive adhesive layer, transparency of the pressure-sensitive adhesive layer, etc., in some embodiments, B may be, for example, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.35 or less.

[0122] The amount of refractive index enhancer used per 100 parts by weight of base polymer (when multiple types of refractive index enhancers are used, the total amount) is not particularly limited and can be set according to the purpose. From the viewpoint of increasing the refractive index of the adhesive, the amount of refractive index enhancer used per 100 parts by weight of base polymer can be, for example, 1 part by weight or more, advantageously 3 parts by weight or more, preferably 5 parts by weight or more, or may be 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or may be 20 parts by weight or more. In some embodiments, the amount of refractive index enhancer used per 100 parts by weight of base polymer 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 adhesive and suppressing deterioration of adhesive properties and optical properties, it is advantageous to set it to 60 parts by weight or less, and preferably 45 parts by weight or less. In some embodiments where adhesive properties and optical properties are more important, the amount of refractive index enhancer used per 100 parts by weight of base polymer may be, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, 10 parts by weight or less, 5 parts by weight or less, or 3 parts by weight or less. The technology disclosed herein can also be preferably implemented in an embodiment where the amount of refractive index enhancer used per 100 parts by weight of base polymer in the adhesive layer is less than 1 part by weight, or where substantially no refractive index enhancer is used. Here, "substantially not used" means that the refractive index enhancer is not used, at least intentionally.

[0123] (Additives (H RO )) In some embodiments, an organic material having a higher refractive index than the base polymer may be preferably used as the refractive index improver. Hereinafter, such an organic material will be referred to as an "additive (H RO )" where the above "H RO " indicates that the material is an organic material with a high refractive index. The base polymer (e.g., an acrylic polymer, preferably an acrylic polymer (A)) and the additive (H ROBy using the additive (H) in combination, it is possible to realize a pressure-sensitive adhesive that more suitably balances the refractive index with adhesive properties (peel strength, flexibility, etc.) and / or optical properties (total light transmittance, haze value, etc.). RO The organic material used as the additive (H) may be a polymer or a non-polymer. It may or may not have a polymerizable functional group. RO ) can be used alone or in combination of two or more.

[0124] Additives (H RO The refractive index of the polymer is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C, just like the refractive index of the monomer. If the manufacturer provides a nominal value for the refractive index at 25°C, that nominal value can be used.

[0125] Additives (H RO The molecular weight of the organic material used as the additive (H) is not particularly limited and can be selected depending on the purpose. From the viewpoint of achieving a good balance between the effect of increasing the refractive index and other properties (for example, optical properties such as flexibility and haze suitable for adhesives), in some embodiments, the additive (H RO The molecular weight of the additive (H) is suitably less than about 10,000, preferably less than 5,000, more preferably less than 3,000 (for example, less than 1,000), and may be less than 800, less than 600, less than 500, or less than 400. RO It is advantageous from the viewpoint of improving compatibility in the adhesive layer that the molecular weight of the additive (H) is not too large. RO The molecular weight of the additive (H) may be, for example, 130 or more, or 150 or more. RO ) is the molecular weight of the additive (H ROFrom the viewpoint of increasing the refractive index of the polymer, the molecular weight is preferably 170 or more, more preferably 200 or more, and may be 230 or more, 250 or more, 270 or more, 500 or more, 1000 or more, or 2000 or more. In some embodiments, a polymer having a molecular weight of about 1000 to 10000 (for example, 1000 or more but less than 5000) is mixed with an additive (H RO ) can be used as Additives (H RO Regarding the molecular weight of the additive (H), for non-polymers or polymers with a low degree of polymerization (e.g., dimers to pentamers), the molecular weight calculated based on the chemical structure or the measured value using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS) can be used. 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 value for the molecular weight, that nominal value can be used.

[0126] Additives (H RO Examples of organic materials that can be selected for the organic compound include, but are not limited to, organic compounds having aromatic rings, organic compounds having heterocycles (which may be aromatic or non-aromatic heterocycles), and the like.

[0127] Additives (H RO The aromatic ring contained in the organic compound having an aromatic ring (hereinafter also referred to as "aromatic ring-containing compound") used as the monomer (m1) can be selected from the same aromatic rings contained in the compound used as the monomer (m2).

[0128] The aromatic ring may have one or more substituents on the ring-constituting atoms, or may have no substituents. When the aromatic ring has a substituent, examples of the substituent include, but are not limited to, an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom (such as a fluorine atom, a chlorine atom, or a bromine atom), a hydroxyalkyl group, a hydroxyalkyloxy group, and a glycidyloxy group. In the case of a carbon atom-containing substituent, the number of carbon atoms contained in the substituent is, for example, 1 to 10, advantageously 1 to 6, preferably 1 to 4, and more preferably 1 to 3, and may be, for example, 1 or 2. In some embodiments, the aromatic ring may have no substituents on the ring-constituting atoms, or may have one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen atom (such as a bromine atom).

[0129] Additives (H RO Examples of aromatic ring-containing compounds that can be used as the additive (H) include, but are not limited to, compounds that can be used as the monomer (m1); oligomers that contain, as a monomer unit, compounds that can be used as the monomer (m1); compounds in which, from a compound that can be used as the monomer (m1), a group having an ethylenically unsaturated group (which may be a substituent bonded to a ring-constituting atom) or a portion of the group that constitutes an ethylenically unsaturated group is replaced with a hydrogen atom or a group that does not have 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.). RO), aromatic ring-containing monomers such as benzyl acrylate, m-phenoxybenzyl acrylate, 2-(o-phenylphenoxy)ethyl acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, phenoxypolyethylene glycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, the above-mentioned monomers having a fluorene structure, monomers having a dinaphthothiophene structure, and monomers having a dibenzothiophene structure; aromatic ring-containing compounds not having an ethylenically unsaturated group, such as 3-phenoxybenzyl alcohol, dinaphthothiophene and derivatives thereof (for example, compounds having a structure in which one or more substituents selected from hydroxyl groups, methanol groups, diethanol groups, glycidyl groups, etc. are bonded to a dinaphthothiophene ring); and the like. The aromatic ring-containing compound may also be an oligomer (preferably an oligomer having a molecular weight of about 5,000 or less, more preferably about 1,000 or less, for example, a low polymer of about 2 to 5) containing such an aromatic ring-containing monomer as a monomer unit. The oligomer may be, for example, a homopolymer of an aromatic ring-containing monomer; a copolymer of one or more aromatic ring-containing monomers; a copolymer of one or more aromatic ring-containing monomers with another monomer; or the like. As the other monomer, one or more monomers not having an aromatic ring may be used.

[0130] In some embodiments, the additive (H ROAs the compound (a), an organic compound having two or more aromatic rings in one molecule (hereinafter also referred to as a "multiple aromatic ring-containing compound") can be preferably used because it is easy to obtain a high refractive index effect. The multiple aromatic ring-containing compound may or may not have a polymerizable functional group such as an ethylenically unsaturated group. The multiple aromatic ring-containing compound may be a polymer or a non-polymer. The polymer may be an oligomer containing a multiple aromatic ring-containing monomer as a monomer unit (preferably an oligomer having a molecular weight of approximately 5,000 or less, more preferably approximately 1,000 or less, for example, a low polymer of about 2 to 5). The oligomer may be, for example: a homopolymer of a multiple aromatic ring-containing monomer; a copolymer of one or more multiple aromatic ring-containing monomers; a copolymer of one or more multiple aromatic ring-containing monomers with another monomer; or the like. The other monomer may be an aromatic ring-containing monomer that does not fall under the category of multiple aromatic ring-containing monomer, a monomer not having an aromatic ring, or a combination thereof.

[0131] Non-limiting examples of compounds containing multiple aromatic rings include compounds having a structure in which two or more non-fused aromatic rings are bonded via a linking group, compounds having a structure in which two or more non-fused aromatic rings are chemically bonded directly (i.e., not via other atoms), compounds having a fused aromatic ring structure, compounds having a fluorene structure, compounds having a dinaphthothiophene structure, compounds having a dibenzothiophene structure, etc. The compounds containing multiple aromatic rings can be used alone or in combination of two or more.

[0132] Specific examples of the compound having the fluorene structure include the above-mentioned monomers having the fluorene structure, oligomers which are homopolymers or copolymers of such monomers, as well as 9,9-bisphenylfluorene and derivatives thereof, such as 9,9-bis(4-hydroxyphenyl)fluorene (refractive index: 1.68), 9,9-bis(4-aminophenyl)fluorene (refractive index: 1.73), 9,9-bis(4-hydroxy-3-methylphenyl)fluorene (refractive index: 1.68), and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (refractive index: 1.65).

[0133] Specific examples of the compound having the dinaphthothiophene structure include the above-mentioned monomers having the dinaphthothiophene structure, oligomers which are homopolymers or copolymers of such monomers, as well as hydroxyalkyldinaphthothiophenes such as dinaphthothiophene (refractive index: 1.808); 6-hydroxymethyldinaphthothiophene (refractive index: 1.766); dihydroxydinaphthothiophenes such as 2,12-dihydroxydinaphthothiophene (refractive index: 1.750); 2,12- Examples of such dinaphthothiophenes include dihydroxyalkyloxydinaphthothiophenes such as dihydroxyethyloxydinaphthothiophene (refractive index: 1.677); diglycidyloxydinaphthothiophenes such as 2,12-diglycidyloxydinaphthothiophene (refractive index: 1.723); and dinaphthothiophenes having two or more ethylenically unsaturated groups such as 2,12-diallyloxydinaphthothiophene (abbreviation: 2,12-DAODNT, refractive index: 1.729), and derivatives thereof.

[0134] Specific examples of the compound having the dibenzothiophene structure include the above-mentioned monomers having the dibenzothiophene structure, oligomers which are homopolymers or copolymers of such monomers, as well as dibenzothiophene (refractive index: 1.607), 4-dimethyldibenzothiophene (refractive index: 1.617), 4,6-dimethyldibenzothiophene (refractive index: 1.617), and the like.

[0135] Additives (H ROExamples of organic compounds having a heterocycle (hereinafter also referred to as heterocycle-containing organic compounds) that can be selected as the heterocycle-containing organic compound include thioepoxy compounds and compounds having a triazine ring. Examples of thioepoxy compounds include bis(2,3-epithiopropyl) disulfide and its polymer (refractive index: 1.74) described in Japanese Patent No. 3712653. Examples of compounds having a triazine ring include compounds having at least one triazine ring (e.g., 3 to 40, preferably 5 to 20) in one molecule. Note that, since the triazine ring is aromatic, compounds having a triazine ring are also included in the concept of the aromatic ring-containing compound, and compounds having multiple triazine rings are also included in the concept of the multiple aromatic ring-containing compound.

[0136] In some embodiments, the additive (H RO As the additive (H) having no ethylenically unsaturated group, a compound having no ethylenically unsaturated group can be preferably used. This can suppress deterioration of the pressure-sensitive adhesive composition due to heat or light (progression of gelation or decrease in leveling ability due to increase in viscosity) and improve storage stability. RO ) is used to RO In a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing the ethylenically unsaturated group, or in a laminate including the pressure-sensitive adhesive sheet, it is also preferable from the viewpoint of suppressing dimensional changes and deformations (warping, waviness, etc.), optical distortion, etc., which are caused by the reaction of the ethylenically unsaturated group.

[0137] Additives (H RO In an embodiment in which an oligomer is used as the copolymerization initiator, the oligomer can be obtained by polymerizing the corresponding monomer components by a known method. When the oligomer is produced by radical polymerization, a polymerization initiator, a chain transfer agent, an emulsifier, etc. used in radical polymerization can be appropriately added to the monomer components, and polymerization can be carried out. The polymerization initiator, chain transfer agent, emulsifier, etc. used in the radical polymerization are not particularly limited and can be appropriately selected and used. The weight-average molecular weight of the oligomer can be controlled by the amount of polymerization initiator and chain transfer agent used and the reaction conditions, and the amount used is appropriately adjusted depending on the type of these. Examples of the chain transfer agent include lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, α-thioglycerol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. The chain transfer agent may be used alone or in combination of two or more. The amount of chain transfer agent used can be determined depending on the composition of the monomer components used in the synthesis of the oligomer, the type of chain transfer agent, and the like, so as to obtain an oligomer having a desired weight-average molecular weight. In some embodiments, the amount of chain transfer agent used per 100 parts by weight of the total amount of monomers used in the synthesis of the oligomer is suitably approximately 15 parts by weight or less, and may be 10 parts by weight or less, or even about 5 parts by weight or less. The lower limit of the amount of chain transfer agent used relative to 100 parts by weight of the total amount of monomers used in synthesizing the oligomer is not particularly limited, but may be, for example, 0.01 parts by weight or more, 0.1 parts by weight or more, 0.5 parts by weight or more, or 1 part by weight or more.

[0138] Additives (H RO In the embodiment using the additive (H RO The amount of additive (H) used (when a plurality of compounds are used, the total amount thereof) is not particularly limited and can be set according to the purpose. From the viewpoint of increasing the refractive index of the adhesive, the amount of additive (H) used relative to 100 parts by weight of the base polymer is RO The amount of additive (H) used can be, for example, 1 part by weight or more, advantageously 3 parts by weight or more, preferably 5 parts by weight or more, even 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or even 20 parts by weight or more. In some embodiments, the amount of additive (H) used per 100 parts by weight of the base polymer is 1 part by weight or more. 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 adhesive and suppressing deterioration of adhesive properties and optical properties, it is advantageous to set it to 60 parts by weight or less, and preferably to set it to 45 parts by weight or less. In some embodiments where adhesive properties and optical properties are more important, the amount of additive (H) used relative to 100 parts by weight of the base polymer isRO The amount of ) used may be, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less.

[0139] (Plasticized material) In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the pressure-sensitive adhesive layer may contain, in addition to the base polymer (e.g., acrylic polymer (A)) as described above, a plasticizing material having a lower molecular weight than the base polymer. The use of a plasticizing material can increase the flexibility of the pressure-sensitive adhesive layer, improving adhesion to the adherend, and improving the flexibility and conformability to deformation of the pressure-sensitive adhesive sheet as a whole. From the viewpoint of compatibility and transparency within the pressure-sensitive adhesive layer, organic materials can be preferably used as the plasticizing material. The plasticizing material may be a refractive index improver as described above (e.g., the above-mentioned additive (H RO )) may also be a material that can be used as a

[0140] The molecular weight of the plasticizing material is not particularly limited as long as it is lower than that of the base polymer. In some embodiments, the molecular weight of the plasticizing material may be 30,000 or less, 25,000 or less, less than 10,000, preferably less than 5,000, more preferably less than 3,000 (e.g., less than 1,000), less than 800, less than 600, less than 500, or less than 400, from the viewpoint of easily exerting the plasticizing effect. A molecular weight of the plasticizing material that is not too large can be advantageous from the viewpoint of improving compatibility within the adhesive layer. In some embodiments, the molecular weight of the plasticizing material is suitably 130 or more, preferably 150 or more, 170 or more, 200 or more, 250 or more, or 300 or more, from the viewpoint of easily exerting a sufficient plasticizing effect. In some embodiments, the molecular weight of the plasticizing material may be 500 or more, 1,000 or more, or 2,000 or more. It is preferable that the molecular weight of the plasticizing material is not too low from the viewpoint of the heat resistance of the pressure-sensitive adhesive sheet and the prevention of contamination of the adherend.

[0141] Non-limiting examples of compounds that can be selected as plasticizing materials include compounds that can be used as monomer (m1) (e.g., (meth)acrylates having an aromatic ring such as a benzyl group, a phenoxy group, or a naphthyl group, a monomer having a fluorene structure, a monomer having a dinaphthothiophene structure, a monomer having a dibenzothiophene structure, etc.); oligomers containing a compound that can be used as monomer (m1) as a monomer unit; and compounds in which the portion having an ethylenically unsaturated group in a compound that can be used as monomer (m1) has been removed and replaced with a hydrogen atom or a group not having an ethylenically unsaturated group (e.g., 3-phenoxybenzyl alcohol). To improve flexibility, oligomers containing a compound that can be used as monomer (m1) as a monomer unit may be copolymerized with a low Tg monomer such as n-butyl acrylate or 2-ethylhexyl acrylate. As the plasticizing material, one or more of known plasticizers (for example, phthalate esters, terephthalate esters, adipate esters, adipic acid polyesters, benzoic acid glycol esters, etc.) may be used.

[0142] In some embodiments, the plasticizing material may preferably be an organic material having a refractive index of about 1.50 or more (more preferably 1.53 or more). Specific examples of compounds that may be selected as the plasticizing material include diethylene glycol dibenzoate (refractive index 1.55), dipropylene glycol dibenzoate (refractive index 1.54), 3-phenoxytoluene (refractive index 1.57), 3-ethylbiphenyl (refractive index 1.59), 3-methoxybiphenyl (refractive index 1.61), 4-methoxybiphenyl (refractive index 1.57), polyethylene glycol dibenzoate, 3-phenoxybenzyl alcohol (refractive index 1.59), triphenyl phosphate (refractive index 1.56), benzyl benzoate (refractive index 1.57), 4-(tert-butyl) Examples of suitable plasticizers include, but are not limited to, phenyl diphenyl phosphate (refractive index 1.56), trimethyl phenyl phosphate (refractive index 1.55), butyl benzyl phthalate (refractive index 1.54), rosin methyl ester (refractive index 1.53), alkyl benzyl phthalate (refractive index 1.53), butyl(phenylsulfonyl)amine (refractive index 1.53), trimethyl trimellitate (refractive index 1.52), benzyl phthalate (refractive index 1.52), 2-ethylhexyl diphenyl phosphate (refractive index 1.51), and tris(2,4-di-tert-butylphenyl) phosphite. From the standpoint of refractive index and compatibility, diethylene glycol dibenzoate is preferred. The upper limit of the refractive index of the plasticizer is not particularly limited and can be, for example, 3.00 or less. In some embodiments, from the viewpoint of ease of preparation of the pressure-sensitive adhesive composition, compatibility within the pressure-sensitive adhesive, etc., the refractive index of the plasticizing material is suitably 2.50 or less, advantageously 2.00 or less, or may be 1.90 or less, 1.80 or less, or 1.70 or less. The refractive index of the plasticized material is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C, just like the refractive index of the monomer. If the manufacturer provides a nominal value for the refractive index at 25°C, that nominal value can be used.

[0143] In embodiments using a plasticizing material, the amount of plasticizing material used per 100 parts by weight of base polymer is not particularly limited and can be set according to the purpose. From the viewpoint of enhancing the plasticizing effect, the amount of plasticizing material used per 100 parts by weight of base polymer may be, for example, 0.1 parts by weight or more, or even 0.5 parts by weight or more. From the viewpoint of obtaining a higher plasticizing effect, it is preferably 1 part by weight or more, more preferably 3 parts by weight or more, or may be 5 parts by weight or more, 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or even 20 parts by weight or more. Furthermore, from the viewpoint of achieving a good balance between increasing the refractive index of the adhesive and transparency and plasticizing effect, the amount of plasticizing material used per 100 parts by weight of base polymer is suitably approximately 100 parts by weight or less, preferably 80 parts by weight or less, more preferably 60 parts by weight or less, or may be 45 parts by weight or less, 35 parts by weight or less, or 25 parts by weight or less. In some embodiments where adhesive properties and optical properties are more important, the amount of plasticizing material used per 100 parts by weight of base polymer may be 15 parts by weight or less, 10 parts by weight or less, or 5 parts by weight or less.

[0144] (Leveling agent) In some embodiments, the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer may contain a leveling agent as needed for the purposes of improving the appearance of the pressure-sensitive adhesive layer formed from the composition (for example, improving the uniformity of the thickness) or improving the coatability of the pressure-sensitive adhesive composition. Non-limiting examples of leveling agents include acrylic leveling agents, fluorine-based leveling agents, and silicone-based leveling agents. The leveling agent may be selected from commercially available leveling agents and used in the usual manner.

[0145] In some embodiments, the leveling agent can preferably be a polymer (hereinafter also referred to as "polymer (B)") that is a polymerization product of a monomer raw material (hereinafter also referred to as "monomer raw material B") containing a monomer having a polyorganosiloxane skeleton (hereinafter also referred to as "monomer S1") and an acrylic monomer. Polymer (B) can be said to be a copolymer of monomer S1 and an acrylic monomer. Polymer (B) can be used alone or in combination of two or more types.

[0146] Monomer S1 is not particularly limited, and any monomer containing a polyorganosiloxane skeleton can be used. Monomers having a structure with a polymerizable reactive group at one end can be preferably used as monomer S1. Among them, monomers S1 having a structure with a polymerizable reactive group at one end and no functional group at the other end that undergoes a crosslinking reaction with a base polymer (referring to the base polymer of the pressure-sensitive adhesive composition to which the leveling agent is blended, such as an acrylic polymer) can be preferably used. Commercially available products include, for example, single-end reactive silicone oils manufactured by Shin-Etsu Chemical Co., Ltd. (e.g., product numbers X-22-174ASX, X-22-2426, X-22-2475, KF-2012, etc.). Monomer S1 can be used alone or in combination of two or more types.

[0147] The functional group equivalent of the monomer S1 may be, for example, about 100 g / mol to 30,000 g / mol. In some preferred embodiments, the functional group equivalent is, for example, 500 g / mol or more, or may be 800 g / mol or more, 1,500 g / mol or more, or 2,000 g / mol or more. The functional group equivalent may be, for example, 20,000 g / mol or less, less than 10,000 g / mol, 7,000 g / mol or less, or 5,500 g / mol or less. When the functional group equivalent of the monomer S1 is within the above range, a good leveling effect is likely to be exhibited. When two or more types of monomers having different functional group equivalents are used as the monomer S1, the functional group equivalent of the monomer S1 can be the sum of the products of the functional group equivalents of each type of monomer and the weight fraction of the monomer.

[0148] Here, "functional group equivalent" means the weight of the main skeleton (e.g., polydimethylsiloxane) bonded to one functional group. The unit g / mol is calculated as 1 mol of functional group. The functional group equivalent of the monomer S1 can be calculated, for example, by nuclear magnetic resonance (NMR) analysis. 1 It can be calculated from the spectral intensity of H-NMR (proton NMR). 1 The functional group equivalent weight (g / mol) of monomer S1 was calculated based on the H-NMR spectrum intensity: 1 This can be done based on a general structural analysis method involving H-NMR spectrum analysis, and if necessary, by referring to the description in Japanese Patent No. 5951153. In the functional group equivalent of the monomer S1, the functional group refers to a polymerizable functional group (for example, an ethylenically unsaturated group such as a (meth)acryloyl group, a vinyl group, or an allyl group).

[0149] The content of monomer S1 in monomer raw material B is not limited to a specific range and can be any appropriate value within the range in which the desired effect is achieved using monomer S1. In some embodiments, the content of monomer S1 in monomer raw material B may be, for example, 5 to 60% by weight, 10 to 50% by weight, or 15 to 40% by weight.

[0150] In addition to the monomer S1, the monomer raw material B contains an acrylic monomer copolymerizable with the monomer S1. This can improve the compatibility of the polymer (B) in the pressure-sensitive adhesive layer. Examples of acrylic monomers that can be used for the monomer raw material B include alkyl acrylates. The term "alkyl" used here refers to a chain (including linear and branched) alkyl (group) and does not include the alicyclic hydrocarbon group described below. In some embodiments, the monomer raw material B contains (meth)acrylic acid C 4-12 Alkyl ester (preferably (meth)acrylic acid C4-10 Alkyl esters, such as (meth)acrylic acid C 6-10 In some other embodiments, the monomer feedstock B may contain at least one of methacrylic acid C 1-18 Alkyl ester (preferably methacrylic acid C 1-14 Alkyl esters, such as methacrylic acid C 1-10 Monomer raw material B may contain, as an acrylic monomer, one or more selected from the group consisting of methyl methacrylate (MMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA).

[0151] Other examples of the acrylic monomer include (meth)acrylic acid esters having an alicyclic hydrocarbon group. For example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, etc. can be used. It is not necessary to use a (meth)acrylic acid ester having an alicyclic hydrocarbon group.

[0152] The content of the (meth)acrylic acid alkyl ester and the (meth)acrylic acid ester having an alicyclic hydrocarbon group in the monomer raw material B may be, for example, 10% by weight or more and 95% by weight or less, 20% by weight or more and 95% by weight or less, 30% by weight or more and 90% by weight or less, 40% by weight or more and 90% by weight or less, or 50% by weight or more and 85% by weight or less.

[0153] Other examples of monomers that can be contained in the monomer raw material B together with the monomer S1 include the carboxy group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, amide group-containing monomers, monomers having a nitrogen atom-containing ring, aminoalkyl (meth)acrylates, vinyl esters, vinyl ethers, olefins, (meth)acrylic acid esters having an aromatic hydrocarbon group, and halogen atom-containing (meth)acrylates, all of which are exemplified above as monomers that can be used in acrylic polymers.

[0154] The Mw of polymer (B) may be, for example, 5,000 or more, preferably 10,000 or more, or 15,000 or more. The Mw of polymer (B) may be, for example, 200,000 or less, preferably 100,000 or less, or 50,000 or less, or 30,000 or less. By setting the Mw of polymer (B) within an appropriate range, favorable compatibility and leveling properties can be exhibited.

[0155] The polymer (B) can be prepared, for example, by polymerizing the above-mentioned monomers by a known method such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, or photopolymerization. A chain transfer agent can be used as needed to adjust the molecular weight of polymer (B). Examples of the chain transfer agent include compounds having a mercapto group, such as t-dodecyl mercaptan, mercaptoethanol, and α-thioglycerol; thioglycolic acid esters, such as thioglycolic acid and methyl thioglycolate; and α-methylstyrene dimer. The amount of the chain transfer agent used is not particularly limited and can be appropriately determined so as to obtain polymer (B) having the desired molecular weight. In some embodiments, the amount of the chain transfer agent used relative to 100 parts by weight of the monomer may be, for example, 0.1 to 5 parts by weight, 0.2 to 3 parts by weight, or 0.5 to 2 parts by weight.

[0156] The amount of polymer (B) used relative to 100 parts by weight of base polymer (e.g., acrylic polymer) can be, for example, 0.001 parts by weight or more, and from the viewpoint of obtaining a higher effect of use, it may be 0.01 parts by weight or more, or may be 0.03 parts by weight or more. The amount of polymer (B) used may be, for example, 3 parts by weight or less, and from the viewpoint of reducing the influence on the refractive index, it is appropriate to set it to 1 part by weight or less, and it may be 0.5 parts by weight or less, or may be 0.1 parts by weight or less.

[0157] (Inorganic particles) The technology disclosed herein can be preferably implemented in an embodiment in which inorganic particles are substantially not used as a refractive index enhancer. However, in some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the use of inorganic particles as a refractive index enhancer is acceptable to the extent that the desired optical properties (total light transmittance, haze value) are satisfied and the properties as a pressure-sensitive adhesive are not significantly impaired. Examples of inorganic particles that can be used as a refractive index enhancer include inorganic particles composed of inorganic oxides (specifically, metal oxides) such as titania (titanium oxide, TiO), zirconia (zirconium oxide, ZrO), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, and niobium oxide (NbO, etc.). The average particle size (meaning the 50% volume average particle size determined by laser scattering and diffraction) of the inorganic particles can be selected, for example, from a range of approximately 10 nm to 100 nm. The refractive index of inorganic particles is measured using a commercially available spectroscopic ellipsometer at a measurement wavelength of 589 nm and a measurement temperature of 23°C for a single layer film (thickness that allows refractive index measurement) of the material that constitutes the inorganic particles. As the spectroscopic ellipsometer, for example, a product name "EC-400" (manufactured by J.A. Woolam Co.) or an equivalent product is used. When inorganic particles are used as a refractive index improver, the amount used is preferably less than 5 parts by weight, more preferably less than 1 part by weight, per 100 parts by weight of the base polymer. The additive (H RO In the embodiment in which the inorganic particles are used, the amount of the inorganic particles used is, by weight, RO ) is preferably used in an amount of not more than 2 times, more preferably not more than 1 time or not more than 0.5 times.

[0158] (Crosslinking agent) In the technology disclosed herein, the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer may contain a crosslinking agent as needed for purposes such as adjusting the cohesive strength of the pressure-sensitive adhesive. Examples of crosslinking agents that can be used include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, oxazoline-based crosslinking agents, melamine-based resins, and metal chelate-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferably used. Other examples of crosslinking agents include monomers having two or more ethylenically unsaturated groups in one molecule, i.e., polyfunctional monomers. The crosslinking agents can be used alone or in combination of two or more.

[0159] As the isocyanate-based crosslinking agent, a bifunctional or higher isocyanate compound can be used, and examples thereof include aliphatic polyisocyanates such as trimethylene diisocyanate, butylene diisocyanate, hexamethylene diisocyanate (HDI), and dimer acid diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), and 1,3-bis(isocyanatomethyl)cyclohexane; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate (XDI); and modified polyisocyanates obtained by modifying the above isocyanate compounds with an allophanate bond, biuret bond, isocyanurate bond, uretdione bond, urea bond, carbodiimide bond, uretonimine bond, oxadiazinetrione bond, or the like. Examples of commercially available products include Takenate 300S, Takenate 500, Takenate 600, Takenate D165N, and Takenate D178N (all manufactured by Takeda Pharmaceutical Co., Ltd.), Sumidur T80, Sumidur L, and Desmodur N3400 (all manufactured by Sumika Bayer Urethane Co., Ltd.), Millionate MR, Millionate MT, Coronate L, Coronate HL, and Coronate HX (all manufactured by Tosoh Corporation). The isocyanate compounds can be used alone or in combination of two or more. A bifunctional isocyanate compound and a trifunctional or higher isocyanate compound may also be used in combination.

[0160] 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 may be used alone or in combination of two or more.

[0161] 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-hexanediol di(meth)acrylate. acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, divinylbenzene, bisphenoxyethanol fluorene di(meth)acrylate, bisphenol A di(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, butyldiol (meth)acrylate, hexyldiol di(meth)acrylate, etc. The polyfunctional monomers can be used alone or in combination of two or more.

[0162] When a crosslinking agent (which may be a polyfunctional monomer) is used, the amount used is not particularly limited and can be, for example, in the range of about 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 PSA, 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 be 1.0 part by weight or less, 0.5 parts by weight or less, or 0.2 parts by weight or less. Furthermore, from the viewpoint of appropriately exerting 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, or 0.08 parts by weight or more.

[0163] A crosslinking catalyst may be used to promote the crosslinking reaction more effectively. Examples of the crosslinking catalyst include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, nursem ferric, butyltin oxide, and dioctyltin dilaurate. Among these, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. The amount of the crosslinking catalyst used is not particularly limited. The amount of the crosslinking catalyst used per 100 parts by weight of the base polymer can be, for example, in the range of approximately 0.0001 to 1 part by weight, preferably 0.001 to 0.5 parts by weight, taking into consideration the balance between the crosslinking reaction rate and the pot life of the pressure-sensitive adhesive composition.

[0164] The PSA composition may contain a compound that undergoes keto-enol tautomerization as a crosslinking retarder. This can extend the pot life of the PSA composition. For example, a compound that undergoes keto-enol tautomerization can be preferably used in a PSA composition containing an isocyanate-based crosslinking agent. Various β-dicarbonyl compounds can be used as the compound that undergoes keto-enol tautomerization. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) and acetoacetic esters (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably used. The compound that undergoes keto-enol tautomerization can be used alone or in combination of two or more. The amount of the compound that undergoes keto-enol tautomerization can be, for example, 0.1 to 20 parts by weight, alternatively 0.5 to 10 parts by weight, or alternatively 1 to 5 parts by weight, per 100 parts by weight of the base polymer.

[0165] (tackifier) The pressure-sensitive adhesive layer in the technology disclosed herein may contain a tackifier. Examples of tackifiers that can be used include known tackifier resins such as rosin-based tackifier resins, terpene-based tackifier resins, phenol-based tackifier resins, hydrocarbon-based tackifier resins, ketone-based tackifier resins, polyamide-based tackifier resins, epoxy-based tackifier resins, and elastomer-based tackifier resins. These can be used alone or in combination of two or more. The amount of tackifier resin used is not particularly limited and can be set so as to achieve appropriate adhesive performance depending on the purpose and application. In some embodiments, from the standpoint of refractive index and transparency, the amount of tackifier used is suitably 30 parts by weight or less, preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, per 100 parts by weight of the base polymer of the pressure-sensitive adhesive layer. The technology disclosed herein can be preferably implemented in an embodiment in which a tackifier is not used.

[0166] (Other additives) In the technology disclosed herein, the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive layer may contain, as necessary, known additives that can be used in pressure-sensitive adhesive compositions, such as plasticizers, softeners, colorants, antistatic agents, antioxidants, UV absorbers, antioxidants, light stabilizers, preservatives, etc. These various additives can be conventionally known and can be used in the usual way, and do not particularly characterize the present invention, so detailed description thereof will be omitted.

[0167] (Preparation of adhesive layer) In the technology disclosed herein, the adhesive constituting the adhesive layer may be an adhesive obtained by curing a solvent-based, active energy ray-curable, water-dispersible, hot-melt, or other adhesive composition by drying, crosslinking, polymerization, cooling, or the like, i.e., a cured product of the adhesive composition. The adhesive composition may be cured using a single method (e.g., drying, crosslinking, polymerization, cooling, or the like), or two or more methods may be applied simultaneously or in multiple stages. For solvent-based adhesive compositions, the adhesive can typically be formed by drying (preferably further crosslinking) the composition. For active energy ray-curable adhesive compositions, the adhesive is typically formed by irradiating the composition with active energy rays to promote a polymerization reaction and / or a crosslinking reaction. When an active energy ray-curable adhesive composition requires drying, it is preferable to irradiate the composition with active energy rays after drying.

[0168] The PSA layer of the PSA sheet disclosed herein can be formed by applying (e.g., coating) a PSA composition to a suitable surface and then curing the composition. The PSA composition can be applied using a conventional coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, or a spray coater.

[0169] The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet disclosed herein may be a pressure-sensitive adhesive layer having post-curing properties, or may be a pressure-sensitive adhesive layer having no post-curing properties. Here, a pressure-sensitive adhesive layer having post-curing properties refers to a pressure-sensitive adhesive layer that can be further cured by irradiation with heat or active energy rays (e.g., ultraviolet rays). Examples of a pressure-sensitive adhesive layer having post-curing properties include a pressure-sensitive adhesive layer having unreacted ethylenically unsaturated groups in the side chains of the base polymer, and a pressure-sensitive adhesive layer containing unreacted polyfunctional monomers. In some embodiments, it is preferable that the pressure-sensitive adhesive layer does not have post-curing properties. A pressure-sensitive adhesive layer having no post-curing properties does not undergo dimensional changes associated with the post-curing reaction (i.e., has good dimensional stability), and therefore is likely to suppress warping of the pressure-sensitive adhesive sheet or the adherend to which the pressure-sensitive adhesive sheet is attached. The absence of dimensional changes (e.g., cure shrinkage) due to post-curing can also be advantageous from the perspective of suppressing optical distortion of the pressure-sensitive adhesive layer.

[0170] The thickness of the pressure-sensitive adhesive layer is not particularly limited and can be, for example, 3 μm or more, preferably 5 μm or more. A pressure-sensitive adhesive layer having a thickness of 5 μm or more is likely to provide good adhesive properties. Furthermore, a pressure-sensitive adhesive layer of such a thickness easily absorbs irregularities that may exist on the surface of an adherend, allowing it to be adhered to the adherend with good adhesion. A pressure-sensitive adhesive layer thickness of 5 μm or more is also preferred from the viewpoint of preventing coloring or color unevenness due to light interference. In some embodiments, the thickness of the pressure-sensitive 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. In some embodiments, the thickness of the pressure-sensitive 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. A pressure-sensitive adhesive layer that is not too thick can be advantageous from the viewpoint of, for example, reducing the thickness of the pressure-sensitive adhesive sheet. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which the thickness of the pressure-sensitive adhesive layer is in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm). In the case of a pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on a first surface and a second surface of a substrate, the thickness of the pressure-sensitive adhesive layer described above can be applied to at least the thickness of the first pressure-sensitive adhesive layer. The thickness of the second pressure-sensitive adhesive layer can also be selected from a similar range. Furthermore, in a substrate-less double-sided pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer, the thickness of the pressure-sensitive adhesive layer is the thickness of the pressure-sensitive adhesive sheet.

[0171] (peel strength) In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the peel strength of the pressure-sensitive adhesive sheet to a glass plate is suitably approximately 1.0 N / 25 mm or more (e.g., 1.5 N / 25 mm or more), preferably 2 N / 25 mm or more, more preferably 3 N / 25 mm or more, and may be 4 N / 25 mm or more, 6 N / 25 mm or more, 8 N / 25 mm or more, 10 N / 25 mm or more, or 12 N / 25 mm or more. 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.

[0172] Here, the peel strength is determined by pressing the sheet onto an alkaline glass plate as an adherend, leaving it in an environment of 23°C and 50% RH for 30 minutes, then placing it in a pressure degassing apparatus (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, and then measuring the 180° peel adhesive strength under conditions of a peel angle of 180° and a pulling speed of 300 mm / min. When measuring, if necessary, the pressure-sensitive adhesive sheet 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 according to the method described in the Examples below. When the PSA sheet disclosed herein is in the form of a double-sided PSA sheet having a first adhesive surface and a second adhesive surface, in some embodiments, the above-mentioned peel strength is preferably applied to at least the first adhesive surface, and more preferably to both the first adhesive surface and the second adhesive surface. The peel strength of the first adhesive surface to a glass plate and the peel strength of the second adhesive surface to glass may be similar or different.

[0173] <Support base material> PSA sheets according to some embodiments may be in the form of a substrate-attached PSA sheet comprising a PSA layer on one or both sides of a support substrate. The material of the support substrate is not particularly limited and can be appropriately selected depending on the intended use and manner of use of the PSA sheet. Non-limiting examples of usable substrates include plastic films such as polyolefin films primarily composed of polyolefins such as polypropylene (PP) or ethylene-propylene copolymers; polyester films primarily composed of polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); and polyvinyl chloride films primarily composed of polyvinyl chloride; foam sheets composed of foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam; woven and nonwoven fabrics made by spinning various fibrous materials (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc.) alone or in combination; papers such as Japanese paper, fine paper, kraft paper, and crepe paper; and metal foils such as aluminum foil and copper foil. Substrates having a composite structure of these materials are also possible. Examples of such composite substrates include substrates having a structure in which a metal foil and the above-mentioned plastic film are laminated together, and plastic substrates reinforced with inorganic fibers such as glass cloth.

[0174] In some embodiments, various film substrates can be preferably used. The film substrate may be a porous substrate such as a foam film or a nonwoven fabric sheet, or a nonporous substrate, or a substrate having a structure in which a porous layer and a nonporous layer are laminated. In some embodiments, the film substrate preferably includes a base film that is an independently shape-retaining (self-supporting or independent) resin film. Here, the term "resin film" refers to a resin film that has a nonporous structure and typically contains substantially no air bubbles (void-free). Therefore, the resin film is a concept that is distinct from foam films and nonwoven fabrics. The resin film preferably includes an independently shape-retaining (self-supporting or independent) resin film. The resin film may have a single-layer structure or a multi-layer structure of two or more layers (e.g., a three-layer structure).

[0175] Examples of materials constituting the resin film include polyester-based resins mainly composed of polyester, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyolefin-based resins mainly composed of polyolefin, such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-butene copolymer; cellulose resins such as triacetyl cellulose; acetate-based resins; polysulfone-based resins; polyethersulfone-based resins; polycarbonate-based resins; polyamide (PA)-based resins such as nylon 6, nylon 66, and partially aromatic polyamide; and polyimide (PI)-based resins. Examples of suitable resins include transparent polyimide resins, polyamideimide (PAI), polyether ether ketone (PEEK), polyethersulfone (PES), cyclic polyolefin resins such as norbornene-based 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), fluorine-based resins such as polytetrafluoroethylene (PTFE) and fluorinated polyimides, and the like.

[0176] The resin film may be formed using a resin material containing one of these resins alone, or may be formed using a resin material containing a blend of two or more of these resins. The resin film may be unstretched or stretched (for example, uniaxially or biaxially stretched). For example, PET film, PBT film, PEN film, unstretched polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, PP / PE blend film, etc. are preferably used. Examples of resin films that are preferred from the standpoint 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 standpoint of availability, etc., and PET film is particularly preferred.

[0177] The resin film may contain known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, antiblocking agents, etc., as needed, provided that the effects of the present invention are not significantly impaired. The amount of additives added is not particularly limited and can be set appropriately depending on the application of the PSA sheet, etc.

[0178] The method for producing the resin film is not particularly limited, and any conventionally known resin film forming method such as extrusion molding, inflation molding, T-die casting, or calendar roll molding can be appropriately used.

[0179] The substrate may be substantially composed of such a base film. Alternatively, the substrate may include an auxiliary layer in addition to the base film. Examples of the auxiliary layer include an optical property adjusting layer (e.g., a coloring layer, an anti-reflection layer), a printed layer or a laminate layer for imparting a desired appearance to the substrate, an antistatic layer, an undercoat layer, a release layer, or other surface treatment layer.

[0180] In some embodiments, a substrate having optical transparency (hereinafter also referred to as an optically transparent substrate) can be preferably used as the support substrate. This makes it possible to construct a substrate-attached pressure-sensitive adhesive sheet having optical transparency. The total light transmittance of the optically transparent substrate may be, for example, more than 50%, or may be 70% or more. In some preferred embodiments, the total light transmittance of the support substrate is 80% or more, more preferably 90% or more, and may even be 95% or more (e.g., 95 to 100%). The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. The transmittance meter used may be a product name "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory or an equivalent. A suitable example of the optically transparent substrate is a resin film having optical transparency. The optically transparent substrate may also be an optical film.

[0181] The thickness of the substrate is not particularly limited and can be selected depending on the purpose and mode of use of the pressure-sensitive adhesive sheet. The thickness of the substrate may be, for example, 500 μm or less, and from the viewpoint of the handleability and processability of the pressure-sensitive adhesive sheet, it is preferably 300 μm or less, and may 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. Furthermore, from the viewpoint of handleability and processability, the thickness of the substrate may be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

[0182] The surface of the substrate on which the pressure-sensitive adhesive layer is to be laminated may be subjected to conventional surface treatments, such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or the formation of an undercoat layer by applying a primer. Such surface treatments may be intended to improve the anchoring of the pressure-sensitive 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 primers. The thickness of the undercoat layer is not particularly limited, but is typically approximately 0.01 μm to 1 μm, preferably approximately 0.1 μm to 1 μm. Other treatments that may be applied to the substrate as needed include antistatic layer formation treatment, colored layer formation treatment, printing treatment, etc. These treatments may be applied alone or in combination.

[0183] When the PSA sheet disclosed herein is in the form of a substrate-attached PSA sheet, the thickness of the PSA 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. From the viewpoint of handleability, the thickness of the PSA sheet may be, for example, 10 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more. The thickness of the adhesive sheet refers to the thickness of the portion that is attached to the adherend. For example, in the case of adhesive sheet 1 having the configuration shown in Fig. 1, the thickness refers to the thickness from first surface (adhesive surface) 10A of the adhesive layer to second surface 20B of the support substrate, and does not include the thickness of release liner 30.

[0184] <Adhesive sheet with release liner> The PSA sheet disclosed herein can take the form of a PSA product in which the surface (adhesive surface) of the PSA layer is in contact with the release surface of a release liner. Accordingly, this specification provides a PSA sheet with a release liner (adhesive product) comprising any of the PSA sheets disclosed herein and a release liner having a release surface in contact with the adhesive surface of the PSA sheet.

[0185] The release liner is not particularly limited, and examples thereof include 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), and a release liner made of a resin film formed from a low-adhesion material such as a fluorine-based polymer (e.g., polytetrafluoroethylene) or a polyolefin-based resin (e.g., polyethylene, polypropylene). 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 fluorine-based release treatment agent, or molybdenum (IV) sulfide. In some embodiments, a release liner having a release treatment layer formed with a silicone-based release treatment agent may be preferably used. The thickness and method of forming the release treatment layer are not particularly limited, and can be set so as to exhibit appropriate releasability on the adhesive surface of the release liner.

[0186] 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 that is distinguished from, for example, nonwoven fabrics (i.e., does not include nonwoven fabrics).

[0187] Examples of materials for the 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 copolymers, and ethylene-butene copolymers; cellulose resins such as triacetyl cellulose; acetate resins; polysulfone resins; polyethersulfone resins; polycarbonate resins; polyamide resins; polyimide resins; and cyclic polyolefin resins such as norbornene 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. Release film substrates formed from one or a mixture of two or more of these resins can be used. Among these, a preferred release film substrate is a polyester resin film (e.g., a PET film) formed from a polyester resin.

[0188] The plastic film used as the release film substrate may be any of an unstretched film, a uniaxially stretched film, and a biaxially stretched film. 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 pressure-sensitive adhesive sheets, such as antioxidants, antiaging 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 contained in all sublayers or only in some of the sublayers.

[0189] In some preferred embodiments, the release film substrate (typically a plastic film) preferably has a limited content of particles such as inorganic particles (e.g., pigments, lubricants, fillers, etc.) in the layer on the release surface side, or is 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 wt %, preferably less than 0.1 wt % (e.g., 0 to 0.01 wt %). Release films equipped with such a release film substrate tend to have 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 surface side can be 1 / 10 or less (e.g., 1 / 50 or less) of the particle content in layers other than the release surface side layer.

[0190] In a pressure-sensitive adhesive sheet with release liners that has release liners on both the first adhesive surface and the second adhesive surface, the release liner placed on one adhesive surface (hereinafter also referred to as the one 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 configuration, or may be made of different materials and have different configurations.

[0191] The thickness of the release liner (preferably a release film) is not particularly limited and can 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 suitably 20 μm or more, preferably 30 μm or more, and may be 35 μm or more, 40 μm or more, or 45 μm or more. Furthermore, from the viewpoint of the handleability of the release liner (e.g., ease of rolling), the thickness of the release liner is suitably 300 μm or less, preferably 250 μm or less, and may be 200 μm or less, 150 μm or less, or 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 a specified value or less, it is less likely to leave marks when rolled up, it can be removed more smoothly from the adhesive sheet, and it is more likely to achieve high surface smoothness on the adhesive surface after the release liner is removed.

[0192] In embodiments having one release liner and another release liner, the thicknesses of the release liners may be the same or different. In some embodiments, from the viewpoint of ease of release, 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 about 1.1 times or more (e.g., about 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.

[0193] (Arithmetic mean roughness Ra of adhesive surface) In some embodiments, the release liner (preferably a release film) preferably has an arithmetic mean roughness Ra of the adhesive surface limited to a predetermined value or less (e.g., approximately 100 nm or less, or even less than 50 nm) from the viewpoint of realizing an adhesive surface with high surface smoothness. In some embodiments, the arithmetic mean roughness Ra of the adhesive surface of the release liner is, for example, preferably approximately 30 nm or less, more preferably approximately 25 nm or less, and may be approximately 20 nm or less, or may be approximately 18 nm or less. Furthermore, from the viewpoint of ease of production and handleability of the release liner, in some embodiments, the arithmetic mean roughness Ra may be, for example, approximately 5 nm or more, approximately 10 nm or more, or approximately 15 nm or more. In a pressure-sensitive adhesive sheet with release liners in a form in which a release liner is disposed on each of the first and second adhesive surfaces, it is preferable that the adhesive surfaces of both release liners satisfy one of the above-mentioned arithmetic mean roughnesses Ra. The arithmetic mean roughnesses Ra of the adhesive surfaces of both release liners may be similar or different.

[0194] (Maximum height Rz of adhesive surface) In some embodiments, the release liner (preferably a release film) preferably has a maximum height Rz of the adhesive surface of 700 nm or less, from the viewpoint of realizing an adhesive surface with high surface smoothness. In some embodiments, the maximum height Rz of the adhesive surface of the release liner is preferably approximately 600 nm or less, and may be approximately 500 nm or less, approximately 400 nm or less, or approximately 300 nm or less. Furthermore, from the viewpoint of ease of production and handleability of the release liner, in some embodiments, the maximum height Rz may be, for example, approximately 50 nm or more, approximately 80 nm or more, approximately 100 nm or more, approximately 150 nm or more, or approximately 200 nm or more. In a pressure-sensitive adhesive sheet with release liners in a form in which a release liner is disposed on each of the first and second adhesive surfaces, it is preferable that the adhesive surfaces of both release liners satisfy one of the maximum heights Rz described above. The maximum heights Rz of the adhesive surfaces of both release liners may be similar or different.

[0195] (Surface texture on the back) The arithmetic mean roughness Ra and maximum height Rz of the back surface (opposite the pressure-sensitive adhesive layer) of the release liner (preferably a release film) are not particularly limited. From the viewpoint of productivity, etc., 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, or even approximately 50 nm or greater). From the viewpoint of productivity, etc., the maximum height Rz of the back surface of the release liner may be, for example, greater than 400 nm (e.g., approximately 500 nm or greater) or greater than 800 nm (e.g., 1000 nm or greater).

[0196] The arithmetic mean roughness Ra and maximum height Rz of the release film surface can be adjusted by the selection of film material, molding method, surface treatment such as release treatment, etc. Examples include adjusting the smoothness of the layers that make up the release surface (anti-blocking layer, hard coat layer, oligomer prevention layer, etc.), reducing or eliminating the use of filler particles (particle-free) in the surface layer or release film substrate, and adjusting the stretching conditions.

[0197] The arithmetic mean roughness Ra and maximum height Rz of the surface of a release liner (preferably a release film) are measured using a non-contact surface roughness measuring device. A non-contact surface roughness measuring device employing an optical interference method, such as a 3D optical profiler (trade name "NewView7300" manufactured by ZYGO) or an equivalent, can be used. For example, a glass plate (a soda-lime glass plate manufactured by MATSUNAMI, 1.3 mm thick) can be attached to the surface of the release liner opposite the measurement surface with an adhesive, and the surface shape can be measured using a 3D optical profiler (trade name "NewView7300" manufactured by ZYGO) in an environment of 23°C and 50% RH.

[0198] <Application> The pressure-sensitive adhesive sheet disclosed herein can be attached to various adherends for use. The constituent material of the adherend (adherend material) is not particularly limited, but examples thereof include 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, and examples thereof include 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, fluorine-based resins, etc. Examples of suitable materials include resins (typically plastic materials) such as polycarbonate resins, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, 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 (antimony-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. The pressure-sensitive adhesive sheet disclosed herein can be used by being attached to a member (e.g., an optical member) whose surface is at least made of the above material.

[0199] The pressure-sensitive adhesive sheet disclosed herein can be used in an application mode that does not require heating to a temperature higher than room temperature (e.g., 20°C to 35°C) after being attached to an adherend. Furthermore, if acceptable depending on the constituent materials of the pressure-sensitive adhesive sheet (e.g., the material of the substrate) and the type of adherend, heat treatment may be performed at least at any one of the following times: after attachment to the adherend, at the time of attachment, and before attachment. Heat treatment can be performed for purposes such as improving the adhesiveness of the pressure-sensitive adhesive to the adherend or promoting adhesion. The heat treatment temperature can be set appropriately to obtain the desired effect, within the range acceptable depending on the constituent materials of the pressure-sensitive adhesive sheet and the type of adherend, taking into account the surface condition of the adherend, and may be, for example, about 100°C or lower, 80°C or lower, 60°C or lower, or 50°C or lower.

[0200] The member or material to which the PSA sheet is attached (in the case of a double-sided PSA sheet, at least one of the adherends) may be optically transparent. For such adherends, the technology disclosed herein can be applied to easily obtain the benefits of increasing the refractive index while suppressing deterioration of optical properties (such as transparency). The total light transmittance of the adherend may be, for example, greater than 50%, or may be 70% or more. In some preferred embodiments, the total light transmittance of the adherend is 80% or more, more preferably 90% or more, and even more preferably 95% or more (e.g., 95 to 100%). The PSA sheet disclosed herein is preferably used in an embodiment in which it is attached to an adherend (e.g., an optical component) having a total light transmittance of a predetermined value or more. The total light transmittance is measured in accordance with JIS K 7136:2000 using a commercially available transmittance meter. The transmittance meter used may be a product called "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory, or an equivalent.

[0201] The refractive index of the pressure-sensitive adhesive layer and the refractive index of the adherend may be similar or different. For example, by increasing the refractive index of the pressure-sensitive adhesive layer relative to the refractive index of the adherend, light incident on the pressure-sensitive adhesive layer from the adherend side at an angle equal to or smaller than the critical angle can be refracted toward the front side, 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, or 1.45 or less, or may be less than 1.45, or may be, for example, 1.10 or more, 1.20 or more, 1.30 or more, or 1.35 or more. Furthermore, an adherend having a refractive index relatively higher than that of the pressure-sensitive adhesive layer can refract light incident on the adherend from the pressure-sensitive adhesive layer side toward the front side, thereby increasing the front brightness. In this case, the refractive index of the adherend may be, for example, 1.60 or more, 1.65 or more, or 1.70 or more, or may be, for example, 3.00 or less, 2.50 or less, or 2.00 or less. On the other hand, by reducing the difference in refractive index between the pressure-sensitive adhesive layer and the adherend, light reflection at the interface can be suppressed. In this case, the refractive index of the adherend may be about 1.55 to 1.80, about 1.55 to 1.75, or about 1.60 to 1.70. The refractive index of the adherend can be measured in the same manner as the refractive index of the pressure-sensitive adhesive.

[0202] In some preferred embodiments, the adherend may have any of the refractive indices described above and any of the total light transmittances described above. In embodiments where the film is attached to such an adherend, the effects of the technology disclosed herein are particularly favorably exhibited.

[0203] An example of a preferred application is an optical application. More specifically, the pressure-sensitive adhesive sheet disclosed herein can be preferably used as an optical pressure-sensitive adhesive sheet used for bonding optical members (for bonding optical members) or for manufacturing products (optical products) using the optical members.

[0204] The optical member refers to a member having optical properties (e.g., polarization, light refraction, light scattering, light reflectivity, light transmittance, light absorption, light diffraction, optical rotation, visibility, etc.). The optical member is not particularly limited as long as it has optical properties, and examples thereof include components constituting devices (optical devices) such as display devices (image display devices) and input devices, or components used in these devices, such as polarizing plates, wavelength plates, retardation plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflection films, hard coat (HC) films, impact absorbing films, antifouling films, photochromic films, light control films, transparent conductive films (ITO films), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and further components in which these are laminated (these may be collectively referred to as "functional films"). The above-mentioned "plate" and "film" respectively include forms such as a plate, a film, and a sheet, and for example, "polarizing film" includes "polarizing plate" and "polarizing sheet", and "light guide plate" includes "light guide film" and "light guide sheet", etc. Furthermore, the above-mentioned "polarizing plate" includes a circular polarizing plate.

[0205] Examples of the display device include a liquid crystal display device, an organic EL (electroluminescence) display device, a micro LED (μLED), a mini LED (miniLED), a PDP (plasma display panel), electronic paper, etc. Examples of the input device include a touch panel, etc.

[0206] The optical member is not particularly limited, but examples thereof include members (e.g., sheet-, film-, or plate-shaped members) made of glass, acrylic resin, polycarbonate, polyethylene terephthalate, metal thin film, etc. In this specification, the term "optical member" also includes members (such as design films, decorative films, and surface protection films) that serve to decorate or protect a display device or input device while maintaining its visibility.

[0207] The technology disclosed herein can be preferably used, for example, to bond an optical film, such as a film having one or more functions of light transmission, reflection, diffusion, waveguiding, light focusing, and diffraction, or a fluorescent film, to another optical member (which may be another optical film). In particular, in bonding an optical film having at least one function of light guide, light focusing, and diffraction, it is desirable that the entire bulk of the bonding layer has a high refractive index, and this can be a preferred application of the technology disclosed herein.

[0208] The pressure-sensitive adhesives disclosed herein can be preferably used for bonding optical films such as light-guiding films, diffusion films, fluorescent films, color-tuning films, prism sheets, lenticular films, and microlens array films. In these applications, due to the trend toward miniaturization and high performance of optical components, thinner films and improved light extraction efficiency are required. The pressure-sensitive adhesives disclosed herein can be preferably used as pressure-sensitive adhesives that can meet such requirements. More specifically, for example, in bonding light-guiding films or diffusion films, adjusting the refractive index of the pressure-sensitive adhesive layer as a bonding layer (e.g., increasing the refractive index) can contribute to thinner films. In bonding fluorescent films, appropriately adjusting the refractive index difference between the fluorescent emitter and the pressure-sensitive adhesive can improve light extraction efficiency (which can also be understood as luminous efficiency). In bonding color-tuning films, appropriately adjusting the refractive index of the pressure-sensitive adhesive to reduce the refractive index difference with the color-tuning pigment can reduce scattered components and contribute to improved light transmittance. In bonding prism sheets, lenticular films, microlens array films, and the like, appropriately adjusting the refractive index of the pressure-sensitive adhesive can control light diffraction, contributing to improved brightness and / or viewing angle.

[0209] The pressure-sensitive adhesive sheet disclosed herein is preferably used in an embodiment in which it is attached to an adherend having a high refractive index (which may be a high-refractive index layer, member, or the like), thereby suppressing interfacial reflection with the adherend. The pressure-sensitive adhesive sheet used in such an embodiment preferably has a small refractive index difference from the adherend and high adhesion at the interface with the adherend, as described above. Furthermore, from the viewpoint of enhancing the uniformity of the appearance, it is preferable that the pressure-sensitive adhesive layer has a highly uniform thickness, and for example, it is preferable that the adhesive surface has high surface smoothness. 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 interfacial reflection is particularly meaningful from the viewpoint of suppressing coloring and color unevenness due to interference of reflected light. One example of such a usage embodiment is an embodiment in which the pressure-sensitive adhesive sheet is used to bond the polarizer to the first retardation layer and / or the first retardation layer to the second retardation layer in a polarizing plate with a retardation layer, which includes a polarizer, a first retardation layer, and a second retardation layer in this order.

[0210] Furthermore, since the adhesive sheet disclosed herein is suitable for achieving a high refractive index, it can be preferably used in an embodiment in which it is attached to a light-emitting layer of an optical semiconductor or the like (for example, a highly refractive light-emitting layer composed mainly of inorganic materials). By reducing the difference in refractive index between the light-emitting layer and the adhesive layer, reflection at the interface between them can be suppressed, and light extraction efficiency can be improved. The adhesive sheet used in such an embodiment preferably has an adhesive layer with a high refractive index. Furthermore, from the viewpoint of preventing deterioration of the self-luminous element due to moisture, it is preferable that the adhesive layer has a low water absorption rate. From the viewpoint of improving brightness, it is preferable that the adhesive sheet has low coloration. This can also be advantageous from the viewpoint of suppressing unintentional coloration caused by the adhesive sheet.

[0211] The pressure-sensitive adhesives disclosed herein can be preferably used in microlenses and other lens components (e.g., microlenses constituting microlens array films and lens components such as camera microlenses) used as components of cameras, light-emitting devices, etc., as coating layers covering the lens surfaces, bonding layers for components facing the lens surfaces (e.g., components having a surface shape corresponding to the lens surfaces), filling layers filled between the lens surfaces and the components, etc. The pressure-sensitive adhesives disclosed herein are suitable for increasing the refractive index, and can therefore reduce the refractive index difference with high-refractive-index lenses (e.g., lenses made of high-refractive-index resins or lenses having a surface layer made of high-refractive-index resins). This is advantageous from the perspective of thinning the lenses and products incorporating the lenses, and can also contribute to suppressing aberrations and improving the Abbe number. The pressure-sensitive adhesives disclosed herein can also be used as lens resins themselves, for example, by filling recesses or voids in an appropriate transparent member.

[0212] The embodiment of bonding optical members using the pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and may be, for example, (1) a mode in which optical members are bonded to each other via the pressure-sensitive adhesive sheet disclosed herein, (2) a mode in which an optical member is bonded to a member other than an optical member via the pressure-sensitive adhesive sheet disclosed herein, or (3) a mode in which the pressure-sensitive adhesive sheet disclosed herein includes an optical member and the pressure-sensitive adhesive sheet is bonded to an optical member or a member other than an optical member. In the above-mentioned embodiment (3), the pressure-sensitive adhesive sheet including an optical member may be, for example, a pressure-sensitive adhesive sheet whose support is an optical member (e.g., an optical film). Such a pressure-sensitive adhesive sheet including an optical member as a support may also be understood as a pressure-sensitive adhesive optical member (e.g., a pressure-sensitive adhesive optical film). Furthermore, when the pressure-sensitive adhesive sheet disclosed herein is a pressure-sensitive adhesive sheet having a support and the above-mentioned functional film is used as the support, the pressure-sensitive adhesive sheet disclosed herein may also be understood as a "pressure-sensitive adhesive functional film" having the pressure-sensitive adhesive layer disclosed herein on at least one side of the functional film.

[0213] As described above, the technology disclosed herein provides a laminate comprising the adhesive sheet disclosed herein and a member to which the adhesive sheet is attached. The member to which the adhesive sheet is attached may have the refractive index of the adherend material described above. Furthermore, the difference (refractive index difference) between the refractive index of the adhesive sheet and the refractive index of the member may be the refractive index difference between the adherend and the adhesive sheet described above. The members constituting the laminate are as described above for the member, material, and adherend, and therefore redundant description will not be repeated.

[0214] As will be understood from the above description and the following examples, the matters disclosed by this specification include the following. [1] A pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer, an adhesive surface formed by the adhesive layer; The pressure-sensitive adhesive layer has a refractive index of more than 1.570, a total light transmittance of 86% or more, and a haze value of 3.0% or less. [2] The pressure-sensitive adhesive sheet according to [1] above, wherein the pressure-sensitive adhesive layer has a thickness of 5 μm or more. [3] The pressure-sensitive adhesive sheet according to [1] or [2] above, which has a peel strength (adhesive strength) to a glass plate of 3 N / 25 mm or more. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the pressure-sensitive adhesive surface has an arithmetic mean roughness Ra of 100 nm or less. [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4] above, wherein the pressure-sensitive adhesive layer has a water absorption rate of 1.0% or less. [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, which is configured as a laminate including the pressure-sensitive adhesive layer and a light-transmitting substrate. [7] The pressure-sensitive adhesive sheet according to [6] above, wherein the light-transmitting substrate is a resin film. [8] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, which is a double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer. [9] The pressure-sensitive adhesive sheet according to any one of [1] to [8] above, a release liner disposed on the adhesive surface of the pressure-sensitive adhesive sheet; and A pressure-sensitive adhesive sheet with a release liner, comprising:

[10] A pressure-sensitive adhesive composition used to form a pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to any one of [1] to [8] above.

[0215]

[11] An acrylic polymer (A) containing an aromatic ring-containing monomer (m1) as a monomer unit; The additive (H) is an organic material having a higher refractive index than the acrylic polymer (A). RO )and, A pressure-sensitive adhesive composition comprising:

[12] The above additives (H RO ) has a refractive index of 1.60 or more.

[13] The amount of the additive (H) relative to 100 parts by weight of the acrylic polymer (A). RO The pressure-sensitive adhesive composition according to the above

[11] or

[12] , wherein the content of the hydroxybenzoate is more than 0 parts by weight and not more than 60 parts by weight.

[14] The above additives (H RO The pressure-sensitive adhesive composition according to any one of the above

[11] to

[13] , wherein the compound (I) contains at least one compound selected from the group consisting of aromatic ring-containing compounds and heterocycle-containing compounds.

[15] The above additives (H RO The pressure-sensitive adhesive composition according to any one of the above

[11] to

[14] , which contains a compound having two or more aromatic rings in one molecule.

[16] The above additives (H RO ) is a compound having two or more aromatic rings in one molecule, (i) contains a structure in which two non-fused aromatic rings are directly chemically bonded; and (ii) containing a structure in which two aromatic rings are fused together; The pressure-sensitive adhesive composition according to

[15] above, comprising a compound that satisfies at least one of the following:

[17] The pressure-sensitive adhesive composition according to any one of

[11] to

[16] , wherein the content of the aromatic ring-containing monomer (m1) in the monomer components constituting the acrylic polymer (A) is 50% by weight or more.

[18] In the monomer components constituting the acrylic polymer (A), the content of the aromatic ring-containing monomer (m1) is more than 70% by weight and less than 100% by weight, The pressure-sensitive adhesive composition according to any one of the above

[11] to

[17] , wherein 50 wt % or more of the aromatic ring-containing monomers (m1) are monomers whose homopolymer has a glass transition temperature of 10°C or lower.

[19] The pressure-sensitive adhesive composition according to any one of

[11] to

[18] , wherein the monomer components constituting the acrylic polymer (A) further contain a monomer (m2) having at least one of a hydroxyl group and a carboxy group.

[20] The pressure-sensitive adhesive composition according to any one of

[11] to

[18] above, which is used to form a pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to any one of [1] to [8] above.

[21] A pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition according to any one of

[11] to

[20] above, which has a refractive index higher than 1.570.

[22] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer constituted by a pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition according to any one of

[11] to

[20] above.

[23] The pressure-sensitive adhesive sheet according to

[22] above, wherein the pressure-sensitive adhesive layer has a haze value of 1.0% or less.

[0216]

[24] An interlayer sheet used by being placed between layers of a laminate in optical applications, A viscoelastic layer V1 having a refractive index n1 of 1.570 or more; Total light transmittance is 86% or more; A haze value of 1.0% or less; and The storage modulus G' at 25°C is 30 kPa to 700 kPa; Meet the interlayer sheet.

[25] The interlayer sheet according to

[24] above, having a thickness of 5 μm or more.

[26] The interlayer sheet according to

[24] or

[25] , wherein the viscoelastic layer V1 contains a main polymer and a plasticizing material having a lower molecular weight than the main polymer.

[27] The interlayer sheet according to

[26] above, wherein the weight average molecular weight of the plasticizing material is 30,000 or less.

[28] The viscoelastic layer V2 is further laminated on the viscoelastic layer V1, Storage modulus G' of the viscoelastic layer V2 at 25°C V2 is the storage modulus G' of the viscoelastic layer V1 at 25°C V1 The interlayer sheet according to any one of the above

[24] to

[27] , wherein the thickness is lower than the thickness of the interlayer sheet.

[29] The interlayer sheet according to

[28] , wherein the refractive index n2 of the viscoelastic layer V2 is lower than the refractive index n1 of the viscoelastic layer V1.

[30] The interlayer sheet according to any one of

[24] to

[29] above, wherein the viscoelastic layer V1 is a layer formed from the pressure-sensitive adhesive composition according to any one of

[11] to

[18] above.

[31] The interlayer sheet according to any one of

[24] to

[29] above, wherein the viscoelastic layer V1 is the adhesive layer in the adhesive sheet according to any one of [1] to [5] above.

[32] The interlayer sheet according to any one of

[24] to

[31] above, a resin film laminated on the interlayer sheet; An optical laminate comprising:

[33] The interlayer sheet according to any one of

[24] to

[31] above, a release liner covering at least one surface of the interlayer sheet; an interlayer sheet with a release liner, comprising: [Example]

[0217] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to these specific examples. In the following description, "parts" and "%" representing amounts used and contents are by weight unless otherwise specified.

[0218] <Example 1> (Preparation of acrylic polymer solution) A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser was charged with 99 parts of m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A," refractive index: 1.566, homopolymer Tg: -35°C; hereinafter abbreviated as "POB-A") as a monomer component, 1 part of 4-hydroxybutyl acrylate (4HBA), 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 100 parts of toluene as a polymerization solvent. Nitrogen gas was introduced while gently stirring, and the liquid temperature in the flask was maintained at around 60°C. The polymerization reaction was carried out for 6 hours to prepare a solution (50%) of acrylic polymer A1. The acrylic polymer A1 had a Tg (i.e., Tg) based on the composition of the monomer components. T ) is −35° C., and the Tg based on the composition of the aromatic ring-containing monomer (i.e., Tg m1 ) is -35℃.

[0219] (Preparation of Pressure-Sensitive Adhesive Composition) The above acrylic polymer A1 solution (50%) was diluted to 30% with ethyl acetate, and 334 parts of this solution (100 parts non-volatiles) was mixed with 10 parts (0.1 parts non-volatiles) of a 1% ethyl acetate solution of hexamethylene diisocyanate isocyanurate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (0.01 parts non-volatiles) of a 1% ethyl acetate solution of nursem ferric iron as a crosslinking catalyst, followed by stirring and mixing to prepare acrylic pressure-sensitive adhesive composition C1.

[0220] (Preparation of adhesive sheet) The acrylic pressure-sensitive adhesive composition C1 prepared above was applied to the silicone-treated surface of a polyethylene terephthalate (PET) film R1 (thickness: 50 μm, arithmetic mean roughness of the silicone-treated surface: Ra: 21 nm, maximum height: Rz: 233 nm) that had been silicone-treated on one side, and heated at 130°C for 2 minutes to form a 20 μm-thick pressure-sensitive adhesive layer. Next, the silicone-treated surface of a PET film R2 (thickness: 25 μm, arithmetic mean roughness of the silicone-treated surface: Ra: 15 nm, maximum height: Rz: 180 nm) that had been silicone-treated on one side was bonded to the surface (first adhesive surface) of the pressure-sensitive adhesive layer. In this way, a substrateless double-sided pressure-sensitive adhesive sheet S1 consisting of the pressure-sensitive adhesive layer was obtained. Both sides of the pressure-sensitive adhesive sheet S1 were protected by PET films (release liners) R1 and R2. The release liner R2 bonded to the first adhesive surface had a relatively light release property compared to the release liner R1 (the release liner to which the pressure-sensitive adhesive composition was applied) that protected the second adhesive surface.

[0221] <Examples 2-3, 7-8, 10-14> Solutions of acrylic polymers A2 to A3, 7 to A8, and 10 to A14 according to the respective examples were prepared in the same manner as in the preparation of the acrylic polymer solution in Example 1, except that the composition of the monomer components was changed as shown in Table 1. Acrylic pressure-sensitive adhesive compositions C2 to C3, 7 to C8, and 10 to C14 according to each example were prepared in the same manner as in the preparation of the pressure-sensitive adhesive composition in Example 1, except that the solution of the acrylic polymer according to each example above was used instead of the solution of the acrylic polymer A1. Adhesive sheets S2 to 3, 7 to 8, and 10 to 14 according to each example (substrate-less double-sided adhesive sheets consisting of an adhesive layer) were prepared in the same manner as in Example 1, except that the acrylic adhesive composition according to each example above was used instead of acrylic adhesive composition C1 and the thickness of the adhesive layer was as shown in Table 1. In the composition of the monomer components shown in Table 1, "NMT-A" represents 1-naphthylmethyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name "Light Acrylate NMT-A", refractive index: 1.595, Tg of homopolymer: 31°C), HEA represents 2-hydroxyethyl acrylate, BA represents n-butyl acrylate, and 2EHA represents 2-ethylhexyl acrylate.

[0222] <Example 4> The solution (50%) of the acrylic polymer A3 prepared in Example 3 was diluted to 30% with ethyl acetate, and 334 parts of this solution (100 parts of nonvolatile matter) was mixed with an additive (H RO Acrylic pressure-sensitive adhesive composition C4 was prepared by adding 5 parts of 6-acryloyloxymethyldinaphthothiophene (dinaphthothiophene-6-methylacrylate manufactured by Sugai Chemical Industry Co., Ltd., trade name "6MDNTA", refractive index 1.75) as a crosslinking agent, 10 parts (non-volatile content 0.1 part) of a 1% ethyl acetate solution of an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (non-volatile content 0.01 part) of a 1% ethyl acetate solution of nursem ferric as a crosslinking catalyst, and stirring and mixing them. An adhesive sheet S4 (a substrateless double-sided adhesive sheet consisting of an adhesive layer) according to this example was prepared in the same manner as in Example 1, except that acrylic adhesive composition C4 was used instead of acrylic adhesive composition C1 and the thickness of the adhesive layer was set to 25 μm.

[0223] <Examples 5-6> Additives (H ROAcrylic PSA compositions C5 and C6 according to Examples 5 and 6 were prepared in the same manner as for the preparation of acrylic PSA composition C4 in Example 4, except that the type of resin and the amount used per 100 parts of the acrylic polymer (phr; per hundred resin) were changed as shown in Table 1. Here, in Table 1, "BPFL" represents 9,9-bis(4-hydroxyphenyl)fluorene (manufactured by Osaka Gas Chemicals Co., Ltd., refractive index 1.68), and "BAFL" represents 9,9-bis(4-aminophenyl)fluorene (manufactured by Osaka Gas Chemicals Co., Ltd., refractive index 1.73). Adhesive sheets of Examples 5 and 6 (substrate-less double-sided adhesive sheets consisting of an adhesive layer) were prepared in the same manner as in the preparation of the adhesive sheet of Example 4, except that acrylic adhesive compositions C5 and C6 were used instead of acrylic adhesive composition C4.

[0224] <Example 9> The solution (50%) of the acrylic polymer A8 prepared in Example 8 was diluted to 30% with ethyl acetate, and 334 parts of this solution (100 parts of nonvolatile matter) was mixed with an additive (H RO Acrylic pressure-sensitive adhesive composition C9 was prepared by adding 10 parts of BPFL as a crosslinking agent, 10 parts (0.1 part non-volatile content) of a 1% ethyl acetate solution of an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (0.01 part non-volatile content) of a 1% ethyl acetate solution of nursem ferric as a crosslinking catalyst, and mixing them with stirring. An adhesive sheet S9 (a substrateless double-sided adhesive sheet consisting of an adhesive layer) according to this example was prepared in the same manner as in Example 8, except that acrylic adhesive composition C9 was used instead of acrylic adhesive composition C8.

[0225] <Example 15> A solution (40%) of acrylic polymer A14 was prepared in the same manner as in the preparation of the acrylic polymer solution in Example 1, except that the composition of the monomer components was changed to 90 parts of 2-ethylhexyl acrylate (2EHA) and 10 parts of 4HBA. The above-mentioned solution (40%) of acrylic polymer A14 was diluted to 20% with ethyl acetate, and 500 parts of this solution (100 parts nonvolatiles) were mixed with 10 parts (solids basis) of a zirconia particle dispersion, 10 parts (0.1 parts nonvolatiles) of a 1% ethyl acetate solution of an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (0.01 parts nonvolatiles) of a 1% ethyl acetate solution of nursem ferric iron as a crosslinking catalyst, followed by stirring and mixing to prepare acrylic pressure-sensitive adhesive composition C15. The zirconia particle dispersion liquid used was a surface-treated zirconia particle dispersion liquid prepared by dispersing surface-treated zirconia particles (average particle size 20 nm, solid content refractive index: 1.64, surface treatment: carboxylic acid-based / phosphoric acid-based hydrophobic treatment, manufactured by Kyoeisha Chemical Co., Ltd.) in propylene glycol monomethyl ether (PGME). An adhesive sheet S15 (a substrateless double-sided adhesive sheet consisting of an adhesive layer) of Example 15 was prepared in the same manner as in the preparation of the adhesive sheet in Example 14, except that acrylic adhesive composition C15 was used instead of acrylic adhesive composition C14.

[0226] The obtained pressure-sensitive adhesive sheet was allowed to fully acclimate to an environment of 23°C and 50% RH, and then used for the following measurements and evaluations.

[0227] <Measurement and Evaluation (1)> (refractive index) The refractive index of the pressure-sensitive adhesive layer (substrate-less double-sided pressure-sensitive adhesive sheet) according to each example was measured using an Abbe refractometer (manufactured by ATAGO, model "DR-M4") at a measurement wavelength of 589 nm and a measurement temperature of 25° C. The results are shown in Table 1.

[0228] (Total light transmittance and haze value) The adhesive layer according to each example was attached to alkali-free glass (thickness 0.8-1.0 mm, total light transmittance 92%, haze 0.4%) to form a test piece, which was then measured for total light transmittance and haze using a haze meter (manufactured by Murakami Color Research Laboratory, trade name "HAZEMETER HM-150") at a measurement temperature of 23°C. The total light transmittance and haze of the adhesive layer were determined by subtracting the total light transmittance and haze of the alkali-free glass from the measured values. The results are shown in Table 1.

[0229] (Water absorption rate) The water absorption rate of the pressure-sensitive adhesive of each example was measured by the method described above, and the results are shown in Table 1. The water absorption rate of Example 13 was not measured.

[0230] The storage modulus G'(25) of the pressure-sensitive adhesive layer in each example was measured using the method described above, and it was confirmed to be 350 kPa or less in all of Examples 1 to 14. On the other hand, the pressure-sensitive adhesive layer in Example 15, in which the refractive index was improved by blending inorganic particles with a high refractive index, had a storage modulus G'(25) as high as 750 kPa, and was lacking in flexibility and adhesiveness.

[0231] [Table 1]

[0232] <Example 16> A substrateless double-sided adhesive sheet S16 according to this example was obtained in the same manner as in the preparation of the substrateless double-sided adhesive sheet S3 according to Example 3, except that the amount of acrylic adhesive composition C3 applied was adjusted so that an adhesive layer with a thickness of 5 μm was formed.

[0233] <Measurement and Evaluation (2)> The following measurements and evaluations were further carried out on some of the pressure-sensitive adhesive sheets prepared above. The results are shown in Table 2.

[0234] (Arithmetic mean roughness (Ra) and maximum height (Rz) of the adhesive surface) A measurement sample was prepared by cutting the substrate-less double-sided PSA sheet according to each example, together with the release liners R1 and R2 protecting the first and second adhesive surfaces, into a size of 150 mm in length and 50 mm in width. The release liner R1 side of the measurement sample was fixed to a test plate, and the release liner R2 was peeled off from the first adhesive surface of the measurement sample using a tensile tester (model name "Autograph AG-IS" manufactured by Shimadzu Corporation) at 23°C, 50% RH, a tensile speed of 300 mm / min, and a peel angle of 180° to expose the first adhesive surface. After leaving the sample for 30 minutes, the surface profile of the first adhesive surface was measured using a three-dimensional optical profiler (product name "NewView7300" manufactured by ZYGO Corporation) at 23°C and 50% RH. The arithmetic surface roughness Ra was calculated from the measured data in accordance with JIS B 0601-2001. The maximum height (Rz) was calculated as the sum of the height Rp of the highest peak above the mean line of the roughness curve and the depth Rv of the deepest valley below the mean line of the data (roughness curve) obtained by the above measurement. The measurement conditions were as follows: The measurements of Ra and Rz were carried out five times (i.e., N=5), and the average values ​​thereof were used. [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

[0235] (optical distortion) A commercially available mirror (2 mm thick) made from plain glass using a silver coating process was prepared. The mirror itself was confirmed to be free of distortion by visual inspection and by projecting a reflected image onto a screen using the same method described below. In a clean room, the surface of the mirror was wiped with a clean cloth to remove any foreign matter. Then, the release film R2 was peeled off from the substrateless double-sided PSA sheet of each example to expose the first adhesive surface. The mirror was then attached to the surface with appropriate tension to prevent the introduction of foreign matter, air bubbles, or deformation streaks. To remove any microbubbles, a degassing treatment was performed using a pressure-reducing degassing device (autoclave) (treatment conditions: 50°C, 0.5 MPa, 30 minutes). After cooling at room temperature for at least 30 minutes, the release film R1 was peeled off to expose the second adhesive surface, producing an optical distortion evaluation sample (a laminate consisting of a PSA sheet and a mirror). The evaluation sample was positioned with the adhesive sheet facing the point light source, at an angle of approximately 45 degrees relative to the light from the point light source. A white screen was placed at the end of the light beam, and the reflected image was projected onto it. The point light source can be a Hamamatsu Photonics Xenon Lamp C2577 or an equivalent product, and in this experiment the Xenon Lamp C2577 was used. The point light source, evaluation sample, and screen were positioned so that the distance between the evaluation sample and the point light source, and the distance between the evaluation sample and the screen were each approximately 50 cm. The point light source was turned on, and the image reflected by the sample and projected onto the screen was visually observed to evaluate the presence and degree of optical distortion according to the following three levels. E: No optical distortion is observed. A: Some optical distortion is observed, but it is within the range that is practically acceptable. P: Obvious optical distortion is observed.

[0236] (peel strength against glass plate) Under a measurement environment of 23°C and 50% RH, the release liner was peeled from one side of the pressure-sensitive adhesive sheet, and a 50 μm-thick PET film was attached as a backing. The resulting specimen was then cut to a size of 25 mm wide and 100 mm long to serve as a test piece. The release liner was peeled from the other side of the test piece, and the specimen was pressed against the surface of an alkali glass plate (manufactured by Matsunami Glass Industry Co., Ltd., 1.35 mm thick, polished blue plate edge) using a 2 kg roller, with one stroke of a roller. The specimen was left in the same environment for 30 minutes, then placed in a pressure-degassing apparatus (autoclave) and autoclaved for 30 minutes at a temperature of 50°C and a pressure of 0.5 MPa. After further leaving the specimen in an atmosphere of 23°C and 50% RH for 24 hours, the peel strength (adhesive strength) [N / 25 mm] was measured using a universal tension-compression tester in accordance with JIS Z 0237:2000, at a tensile speed of 300 mm / min and a peel angle of 180°. The universal tension and compression tester used was the Minebea "Tension and Compression Tester, TG-1kN."

[0237] [Table 2]

[0238] The pressure-sensitive adhesive sheets of Examples 1 to 13 shown in Table 1 exhibited a high refractive index exceeding 1.570 and also exhibited high transparency. Furthermore, as shown in Table 2, they exhibited practical peel strength for pressure-sensitive adhesives and also had excellent surface smoothness. In comparison with Example 3 and Example 16, which used the same pressure-sensitive adhesive composition, Example 16 obtained better results in the evaluation of optical distortion. Although not shown in Table 2, the water absorption of Example 16 was 0.2%. On the other hand, Example 15, in which the refractive index was improved by incorporating inorganic particles with a high refractive index, was clearly inferior in transparency compared to Examples 1 to 13 (in particular, the haze was significantly higher), and as shown in Table 2, the surface smoothness was low, obvious optical distortion was observed, and the adhesive performance (peel strength) was not suitable for practical use as an adhesive.

[0239] <Examples 17, 18, 23> Solutions of acrylic polymers according to Examples 17, 18, and 23 were prepared, and acrylic pressure-sensitive adhesive compositions were prepared in the same manner as in Example 1, except that the compositions of the monomer components were as shown in Table 3. Pressure-sensitive adhesive sheets according to each Example were produced in the same manner as in the production of the pressure-sensitive adhesive sheet in Example 1, except that the acrylic pressure-sensitive adhesive composition according to each Example was used instead of acrylic pressure-sensitive adhesive composition C1, and the thickness of the pressure-sensitive adhesive layer was set to 25 μm.

[0240] In the composition of the monomer components shown in Table 3, "BZA" represents benzyl acrylate (manufactured by Osaka Organic Chemical Industry Ltd., trade name "Viscoat #160", refractive index (nD20): 1.519, homopolymer Tg: 6°C), "PEA" represents phenoxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Ltd., trade name "Viscoat #192", refractive index (nD20): 1.517, homopolymer Tg: 2°C), "P2H-A" represents phenoxydiethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate P2H-A", refractive index: 1.510, homopolymer Tg: -35°C), HEMA represents 2-hydroxyethyl methacrylate, and CBA represents ethyl carbitol acrylate.

[0241] <Example 19> A solution of acrylic polymer A19 according to this example was prepared in the same manner as in Example 1, except that the composition of the monomer components was as shown in Table 3. The solution of acrylic polymer A19 was used instead of the solution of acrylic polymer A3, and the additive (H RO An acrylic pressure-sensitive adhesive composition of this example was prepared and a pressure-sensitive adhesive sheet was produced in the same manner as in Example 4, except that 10 phr of 2,12-diallyloxydinaphthothiophene (manufactured by Sugai Chemical Industry Co., Ltd., abbreviation: 2,12-DAODNT, refractive index: 1.729) was used as the diluent.

[0242] <Examples 20-22> Solutions of acrylic polymers according to Examples 20 to 22 were prepared in the same manner as in Example 1, except that the compositions of the monomer components were as shown in Table 3. The solutions of the acrylic polymers according to the respective examples were used instead of the solution of acrylic polymer A3, and the additive (HRO The acrylic pressure-sensitive adhesive compositions of each example were prepared and pressure-sensitive adhesive sheets were produced in the same manner as in Example 4, except that 20 phr of 6-ethylacrylate-dinaphtho[2,1-b:1',2'-d]thiophene (6-acryloyloxyethyldinaphthothiophene, manufactured by Sugai Chemical Industry Co., Ltd., abbreviation: 6EDNTA, refractive index: 1.722) was used as the acrylic pressure-sensitive adhesive.

[0243] The pressure-sensitive adhesive sheets obtained in Examples 17 to 23 were thoroughly acclimatized to an environment of 23°C and 50% RH, and then the various items were measured and evaluated in the same manner as in "Measurement and Evaluation (1)" above. The results are shown in Table 3.

[0244] [Table 3]

[0245] The pressure-sensitive adhesive sheets of Examples 17 to 23 shown in Table 3 all exhibited a high refractive index exceeding 1.570 and high transparency. Of these, the pressure-sensitive adhesive sheet of Example 23 felt harder to the touch and also had a higher water absorption rate than the pressure-sensitive adhesive sheets of Examples 17 to 22. From the above, the adhesive sheets of Examples 1 to 13, 16, and 17 to 23 (substrate-less double-sided adhesive sheets consisting of an adhesive layer) have a high refractive index while suppressing a decrease in optical properties, and are therefore suitable for applications such as joining optical components (e.g., optical films having at least one function of light guiding, focusing, or diffraction).

[0246] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0247] 1,2 Adhesive sheet 10 adhesive layer 10A First surface (adhesive surface) 10B Second Surface 20 Supporting base material 20A Page 1 20B 2nd side (back) 30, 31, 32 Release liner 50 adhesive sheets with release liner 70 Optical Components 100 Adhesive sheet attached material

Claims

1. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer, an adhesive surface formed by the adhesive layer, the pressure-sensitive adhesive layer has a refractive index of more than 1.570, a total light transmittance of 86% or more, and a haze value of 3.0% or less; the pressure-sensitive adhesive layer contains an acrylic polymer as a base polymer and does not contain a plasticizing material; the monomer components constituting the acrylic polymer contain 50% by weight or more of an aromatic ring-containing monomer and further contain a hydroxyl group-containing monomer; wherein the monomer component satisfies the following conditions: (A) more than 50% by weight of the hydroxyl group-containing monomer is a hydroxyalkyl acrylate, the content of the hydroxyalkyl acrylate in the monomer component is 1% by weight or more but less than 7% by weight, and the content of an aromatic ring-containing monomer having a Tg of 0°C or less in the monomer component is 3% by weight or more; and (B) the hydroxyl group-containing monomer includes 4-hydroxybutyl acrylate, and the content of 4-hydroxybutyl acrylate in the monomer component is 1% by weight or more and less than 7% by weight; An adhesive sheet that satisfies at least one of the above.

2. The pressure-sensitive adhesive sheet according to claim 1 , wherein the pressure-sensitive adhesive layer has a thickness of 5 μm or more.

3. The pressure-sensitive adhesive sheet according to claim 1 or 2, which has a peel strength from a glass plate of 3 N / 25 mm or more.

4. The pressure-sensitive adhesive sheet according to any one of claims 1 to 3, wherein the pressure-sensitive adhesive surface has an arithmetic mean roughness Ra of 100 nm or less.

5. The pressure-sensitive adhesive sheet according to any one of claims 1 to 4, wherein the pressure-sensitive adhesive layer has a water absorption rate of 1.0% or less.

6. The aromatic ring-containing monomer includes a monomer having two or more aromatic rings in one molecule, The pressure-sensitive adhesive sheet according to any one of claims 1 to 5, wherein the monomer having two or more aromatic rings in one molecule is at least one of a monomer having a structure in which two or more non-condensed aromatic rings are bonded via a linking group, a monomer having a structure in which two or more non-condensed aromatic rings are directly chemically bonded, a monomer having a condensed aromatic ring structure, a monomer having a fluorene structure, a monomer having a dinaphthothiophene structure, and a monomer having a dibenzothiophene structure.

7. The pressure-sensitive adhesive sheet according to any one of claims 1 to 6, wherein the content of the hydroxyl group-containing monomer in the monomer components is 1% by weight or more and 30% by weight or less.

8. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, which is configured as a laminate including the pressure-sensitive adhesive layer and a light-transmitting substrate.

9. The pressure-sensitive adhesive sheet according to claim 8 , wherein the light-transmitting substrate is a resin film.

10. The pressure-sensitive adhesive sheet according to any one of claims 1 to 7, which is a double-sided pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive layer.

11. The pressure-sensitive adhesive sheet according to any one of claims 1 to 10, a release liner disposed on the adhesive surface of the pressure-sensitive adhesive sheet; A pressure-sensitive adhesive sheet with a release liner, comprising:

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