Adhesive and Its Use

Abstract

To provide an adhesive with a low refractive index as well as being flexible.SOLUTION: An adhesive includes an acrylic polymer (F) containing a fluorine-containing acrylic monomer (M1) as a monomer unit. In the adhesive, a refractive index is 1.46 or less, and a storage elastic modulus G' at 25°C is 400 kPa or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an adhesive, and more particularly, to an adhesive containing an acrylic polymer containing a fluorine-containing acrylic monomer as a monomer unit and its use.

Background Art

[0002] Generally, an adhesive (also referred to as a pressure-sensitive adhesive. The same applies hereinafter) exhibits a state of a soft solid (viscoelastic body) in a temperature range near room temperature and has a property of easily adhering to an adherend by pressure. Taking advantage of such properties, adhesives are widely used for purposes such as joining, fixing, and protecting in various industrial fields such as home appliances, automobiles, various machines, electrical equipment, and electronic equipment. As technical documents related to adhesives, Patent Documents 1 to 4 can be cited.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Documents 1 to 4, adhesives containing (meth)acrylate copolymers containing structural units derived from fluorine-containing acrylic monomers have been proposed. These are all adhesives focusing on sebum resistance and / or chemical resistance, and the refractive index has not been considered.

[0005] An object of the present invention is to provide an adhesive having a low refractive index and being flexible. Another related object is to provide a laminated sheet including an adhesive layer composed of such an adhesive and a light-emitting device including the laminated sheet.

Means for Solving the Problems

[0006] According to this specification, there is provided an adhesive containing an acrylic polymer (F) including a fluorine-containing acrylic monomer (M1) as a monomer unit. The refractive index of the adhesive is 1.46 or less. The adhesive preferably has a storage elastic modulus G' (hereinafter sometimes referred to as "storage elastic modulus G' V2 (25)") of 400 kPa or less (for example, 1.0 kPa or more and 400 kPa or less). Such an adhesive can be preferably used, for example, in a form laminated on a layer having a higher refractive index (which may be an adhesive layer), for purposes such as controlling the behavior of light. Since the storage elastic modulus G' V2 (25) of the adhesive is limited to a predetermined value or less, it is advantageous from viewpoints such as ease of attachment to an adherend, adhesion, followability to the surface shape of the adherend, and followability to deformation of the adherend.

[0007] In the monomer component constituting the acrylic polymer (F), the content of the fluorine-containing acrylic monomer (M1) is preferably 25% by weight or more. By including an acrylic polymer (F) composed of a monomer component having such a composition, an adhesive having a refractive index of 1.46 or less can be preferably realized. The fluorine-containing acrylic monomer (M1) preferably includes an alkyl (meth)acrylate containing a fluorine atom, from viewpoints of ease of polymerization and the effect of reducing the refractive index.

[0008] In some embodiments, the acrylic polymer (F) includes a hydroxyl group-containing monomer as a monomer unit. The monomer unit derived from the hydroxyl group-containing monomer can contribute to realizing an adhesive that achieves both desired flexibility and appropriate cohesiveness.

[0009] According to this specification, a laminated sheet is provided that includes a low refractive index adhesive layer formed from any of the adhesives disclosed herein and a high refractive index adhesive layer laminated on the low refractive index adhesive layer. According to the laminated sheet including the adhesive layers with different refractive indices in such a laminated form, the behavior of light transmitted through the laminated sheet can be controlled by utilizing the refractive index difference between the high refractive index adhesive layer and the low refractive index adhesive layer. The ratio (n1 / n2) of the refractive index n1 of the high refractive index adhesive layer to the refractive index n2 of the low refractive index adhesive layer can be, for example, 1.02 or more.

[0010] In some embodiments, the refractive index n1 of the high refractive index adhesive layer can be greater than 1.570. A laminated sheet including such a high refractive index adhesive layer can better control the behavior of light transmitted through the laminated sheet due to the large refractive index difference from the low refractive index adhesive layer.

[0011] In some embodiments, the high refractive index adhesive layer has a storage elastic modulus G' (hereinafter sometimes referred to as "storage elastic modulus G' V1 (25)") at 25°C that is 700 kPa or less. A laminated sheet including a high refractive index adhesive layer with the storage elastic modulus G' V1 (25) limited to a predetermined value or less is preferable from the viewpoints of ease of attachment and flexibility.

[0012] In some embodiments, the laminated sheet has a total light transmittance of 86% or more and a haze value of 3.0% or less. Such a highly transparent laminated sheet can be preferably used for applications such as bonding of optical members and control of the behavior of light transmitted through the laminated sheet.

[0013] The laminated sheet disclosed herein is suitable, for example, as a component of a light emitting device. Therefore, according to this specification, a light emitting device is provided that includes any of the laminated sheets disclosed herein and a self-luminous element.

[0014] It should be noted that combinations of the respective elements described in this specification as appropriate can also be included in the scope of the invention claimed for patent protection in this patent application.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in this specification and necessary for the implementation of the present invention can be understood by those skilled in the art based on the teachings regarding the implementation of the invention described in this specification and the common general knowledge in the art at the time of filing. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the art. In the following drawings, members and parts having the same function may be denoted by the same reference numerals for explanation, and duplicate explanations may be omitted or simplified. Also, the embodiments shown in the drawings are schematized for clearly explaining the present invention, and do not necessarily accurately represent the size and scale of the actually provided product.

[0017] In this specification, the self-luminous element means a light-emitting element capable of controlling the emission luminance according to the value of the flowing current. The self-luminous element may be composed of a single body or an aggregate. Specific examples of the self-luminous element include, but are not limited to, a light-emitting diode (LED) and an organic EL. The light-emitting device disclosed herein includes such a self-luminous element as a component. Examples of the above light-emitting device include, but are not limited to, a light source module device (for example, a surface light-emitting body module) used as illumination and a display device in which pixels are formed.

[0018] The technologies disclosed by this specification may include low refractive index adhesives and adhesive compositions used for forming the same, high refractive index adhesive layers and adhesive compositions used for forming the same, laminated sheets (adhesive sheets) including high refractive index adhesive layers and low refractive index adhesive layers, laminated sheets with release liners in which the adhesive surfaces of the laminated sheets are protected by release liners, light-emitting devices including high refractive index adhesive layers and low refractive index adhesive layers, and the like. The technologies disclosed by this specification may further include interlayer sheets including high refractive index adhesive layers and low refractive index adhesive layers and disposed between layers of an optical laminate.

[0019] <Configuration example of an adhesive sheet> The adhesives disclosed herein can be used, for example, as adhesive sheets including layers (adhesive layers) formed from the adhesives, and are preferably used in the form of adhesive sheets having adhesive surfaces constituted by the adhesive layers. The above-mentioned adhesive sheets may be adhesive sheets with substrates in the form of having adhesive layers on one or both sides of a non-peeling substrate (support substrate), or may be substrate-free adhesive sheets such as those in the form in which the adhesive layers are held by release liners (that is, adhesive sheets having no non-peeling substrates. Typically, adhesive sheets composed of adhesive layers). The concept of the adhesive sheets referred to herein may include those referred to as adhesive tapes, adhesive labels, adhesive films, and the like. The adhesive sheets disclosed herein may be in the form of rolls or single sheets. Alternatively, they may be adhesive sheets processed into various shapes.

[0020] A configuration example of an adhesive sheet including an adhesive layer formed from the adhesive disclosed herein is shown in FIG. 1. This adhesive sheet 1 is configured as a single-sided adhesive sheet (one-sided adhesive sheet) including an adhesive layer 10 having a first surface 10A serving as an attachment surface (adhesive surface) to an adherend, and a support substrate 20 laminated on a second surface 10B of the adhesive layer 10. The second surface 10B of the adhesive layer 10 is joined to a first surface (non-peelable surface) 20A of the support substrate 20. As the support substrate 20, for example, a plastic film such as a polyester film can be used. The support substrate 20 may be an optical film such as a polarizing plate. Before use (before attachment to an adherend), the adhesive sheet 1 may be in the form of an adhesive sheet 50 with a release liner, in which the adhesive surface 10A is protected by a release liner 30 having at least the adhesive layer side as a peelable surface (peel surface), as shown in FIG. 1, for example. Alternatively, the second surface 20B of the support substrate 20 (the surface on the opposite side to the first surface 20A, also referred to as the back surface) is a peel surface, and the adhesive surface 10A may be protected by winding or laminating such that the adhesive surface 10A abuts against the second surface 20B.

[0021] The adhesive layer 10 may have a single-layer structure, or may have a laminated structure in which two or more sub-adhesive layers having different compositions are directly in contact (i.e., not separated by a layer of non-adhesive material). The refractive indices of the sub-adhesive layers constituting the laminated structure may be the same or different. In an adhesive layer having a laminated structure including two or more sub-adhesive layers with different refractive indices, at least one sub-adhesive layer is preferably a low refractive index adhesive layer satisfying a refractive index of 1.46 or less (preferably, further satisfying a storage elastic modulus G'(25) of 400 kPa or less). The refractive index and the storage elastic modulus G'(25) of the other sub-adhesive layers are not particularly limited, and for example, the refractive index may be 1.46 or less, may be more than 1.46, and for the storage elastic modulus G'(25), it may be 400 kPa or less, or may be more than 400 kPa.

[0022] The pressure-sensitive adhesive sheet disclosed herein may be in the form of a substrate-free double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer. The pressure-sensitive adhesive layer constituting the substrate-free double-sided pressure-sensitive adhesive sheet may have a single-layer structure, similar to the pressure-sensitive adhesive layer 10 in the pressure-sensitive adhesive sheet 1 shown in FIG. 1, or may have a laminated structure in which two or more sub-pressure-sensitive adhesive layers with different compositions are directly laminated in contact with each other. FIG. 2 shows a configuration example of a substrate-free double-sided pressure-sensitive adhesive sheet 2 composed of a pressure-sensitive adhesive layer 10 having a laminated structure including a first pressure-sensitive adhesive layer 11 and a second pressure-sensitive adhesive layer 12 with different compositions. The second pressure-sensitive adhesive layer 12 is a low refractive index pressure-sensitive adhesive layer satisfying a refractive index of 1.46 or less, and may further be a layer satisfying a storage elastic modulus G’(25) of 400 kPa or less. The first pressure-sensitive adhesive layer 11 may be a relatively higher refractive index pressure-sensitive adhesive layer (high refractive index pressure-sensitive adhesive layer) in relation to the second pressure-sensitive adhesive layer 12. The pressure-sensitive adhesive sheet 2 having such a configuration can be regarded as a laminated sheet having a laminated structure of a high refractive index pressure-sensitive adhesive layer / low refractive index pressure-sensitive adhesive layer.

[0023] Before use, the substrate-free double-sided pressure-sensitive adhesive sheet 2 may be in a form protected by release liners 31 and 32 in which the first surface (first adhesive surface) 10A and the second surface (second adhesive surface) 10B of the pressure-sensitive adhesive layer 10 are at least the pressure-sensitive adhesive layer side is a release surface (release surface). Alternatively, the back surface (the surface opposite to the pressure-sensitive adhesive side) of the release liner 31 is a release surface, and the adhesive surfaces 10A and 10B may be protected by winding or laminating so that the adhesive surface 10B abuts on the back surface of the release liner 31. Such a substrate-free double-sided pressure-sensitive adhesive sheet can be used, for example, by bonding a substrate (preferably a light-transmissive substrate, which can be an optical member such as an optical film) to at least one of the first adhesive surface and the second adhesive surface.

[0024] The low refractive index adhesive disclosed herein (an adhesive having a refractive index of 1.46 or less) can be used, for example, in a form incorporated into a light-emitting device. A configuration example of such a light-emitting device is shown in FIG. 3. The light-emitting device 100 shown in FIG. 3 includes a self-luminous element 70, a low refractive index adhesive layer 12 disposed on the viewing side of the self-luminous element 70, and a high refractive index adhesive layer 11 laminated in direct contact with the low refractive index adhesive layer 12. The light-emitting device 100 may further include a cover window member 80 disposed on the viewing side of the high refractive index adhesive layer 11. In the light-emitting device 100 shown in FIG. 3, a laminated sheet 10 composed of a high refractive index adhesive layer 11 and a low refractive index adhesive layer 12 is disposed between the self-luminous element 70 and the cover window member 80. Between the self-luminous element 70 and the low refractive index adhesive layer 12, between the high refractive index adhesive layer 12 and the cover window member 80, and further on the viewing side of the cover window member 80, one or more layers (not shown) may or may not be interposed independently. Also, contrary to FIG. 3, the high refractive index adhesive layer 11 may be disposed on the self-luminous element side and the low refractive index adhesive layer 12 may be disposed on the cover window member side. Alternatively, the low refractive index adhesive disclosed herein may be used in a light-emitting device having a configuration in which the high refractive index adhesive layer 11 in FIG. 3 is omitted or replaced with a non-adhesive high refractive index layer (such as a hard resin layer).

[0025] The adhesive sheet disclosed herein can be a component of an optical member with an adhesive sheet in which an optical member is joined to at least one surface of the adhesive layer. For example, the adhesive sheet 1 shown in FIG. 1 can be a component of an optical member with an adhesive sheet in which an optical member is joined to the first surface 10A of the adhesive layer 10. The optical member can be, for example, a glass plate, a resin film, a metal plate, or the like. Also, in the adhesive sheet 1 shown in FIG. 1, when the support substrate 20 is an optical member such as an optical film, the adhesive sheet 1 can be regarded as an optical member with an adhesive sheet in which an optical member is joined to the second surface 10B of the adhesive layer 10.

[0026] In addition, although not particularly illustrated, the adhesive sheet disclosed herein may be in the form of a double-sided adhesive sheet with a substrate (double-sided adhesive sheet with a substrate) including a support substrate having non-peelable first and second surfaces, with a first adhesive layer fixedly laminated on the first surface and a second adhesive layer fixedly laminated on the second surface. As a configuration example of such a double-sided adhesive sheet with a substrate, in the single-sided adhesive sheet 1 shown in FIG. 1, the second surface 20B of the support substrate 20 is a non-peelable surface, and a second adhesive layer is provided on the second surface 20B. The second surface of the second adhesive layer is joined to the second surface 20B of the support substrate 20, and the first surface of the second adhesive layer (the surface opposite to the second surface) serves as the second adhesive surface of the double-sided adhesive sheet with a substrate. The composition of the adhesive constituting the second adhesive layer may be the same as or different from the composition of the adhesive constituting the first adhesive layer. Before use, the double-sided adhesive sheet with a substrate can be in a form in which the first adhesive surface and the second adhesive surface are protected by a release liner, similar to the above-described substrate-free double-sided adhesive sheet.

[0027] In the following, for the sake of convenience of explanation, the adhesive having a refractive index of 1.46 or less (low refractive index adhesive) may be described in comparison with a layer having a higher refractive index, but it is not intended to limit the usage mode of the low refractive index adhesive disclosed herein.

[0028] <Low refractive index adhesive> This specification provides an adhesive having a refractive index of 1.46 or less. An adhesive having such a refractive index can be preferably used, for example, in a form laminated on a layer with a higher refractive index (which may be an adhesive layer), for purposes such as controlling the behavior of light. In some embodiments, from the perspective of increasing the refractive index difference from the refractive index n1 of the high refractive index layer to facilitate enhancing the front luminance improvement effect described later, the refractive index n2 of the low refractive index adhesive layer is preferably 1.45 or less, more preferably 1.44 or less, may be 1.43 or less, may be 1.41 or less, may be 1.40 or less, and may be less than 1.40 (for example, less than 1.39, and further less than 1.38). Also, from the perspective of ease of obtaining materials and compatibility with adhesive properties, in some embodiments, the refractive index n2 of the low refractive index adhesive may be, for example, 1.35 or more, preferably 1.36 or more, may be 1.38 or more, may be 1.40 or more, and may be 1.42 or more. The technology disclosed herein can be preferably implemented, for example, in an embodiment where the refractive index n2 of the low refractive index adhesive is 1.35 or more and 1.46 or less (more preferably, 1.36 or more and 1.45 or less).

[0029] In this specification, the refractive index of the adhesive refers to the refractive index of the surface (adhesive surface) of the adhesive. The refractive index of the adhesive can be measured using a commercially available refractive index measuring device (Abbe refractometer) under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. As the Abbe refractometer, for example, the model "DR-M4" manufactured by ATAGO Co., Ltd. or its equivalent can be used. As the measurement sample, an adhesive layer composed of the adhesive to be evaluated can be used. Specifically, the refractive index of the adhesive can be measured by the method described in the examples below. The refractive index of the adhesive can be adjusted, for example, by the composition of the adhesive (for example, the composition of the monomer components constituting the base polymer, additives that can be used as necessary, etc.).

[0030] The storage elastic modulus G' of the low refractive index adhesive disclosed herein V2 (25) is suitably 400 kPa or less from the perspectives of ease of attachment to the adherend, adhesion, surface shape followability, deformation followability, etc. In some embodiments, the storage elastic modulus G'V2 (25) is preferably 300 kPa or less, more preferably 200 kPa or less (for example, 180 kPa or less, or 150 kPa or less), may be 120 kPa or less, may be 90 kPa or less, and may be 70 kPa or less. Storage elastic modulus G’ V2 (25) being low can also be advantageous from the viewpoint of enhancing effects such as imparting flexibility by the low refractive index adhesive layer and improving followability to deformation, for example, in the usage mode laminated on the high refractive index layer. Storage elastic modulus G’ V2 (25) has no particular lower limit and can be, for example, 1.0 kPa or more. In some embodiments, from the viewpoint of easily imparting appropriate cohesiveness to the low refractive index adhesive layer, storage elastic modulus G’ V2 (25) is suitably, for example, 5.0 kPa or more, preferably 10 kPa or more, may be 15 kPa or more, may be 25 kPa or more, may be 35 kPa or more, may be 60 kPa or more, and may be 80 kPa or more. In some embodiments, from the viewpoint of easily realizing higher cohesive force and adhesive properties, storage elastic modulus G’ V2 (25) may be 95 kPa or more, may be 110 kPa or more, and may be 140 kPa or more.

[0031] In some preferred embodiments, the storage elastic modulus G’ at 25 °C of the low refractive index adhesive layer (that is, the storage elastic modulus G’ V2 (25)) is preferably lower than the storage elastic modulus G’ at 25 °C of the high refractive index layer that can be disposed adjacent to the low refractive index adhesive layer (hereinafter, may be referred to as “storage elastic modulus G’ V1 (25)”). That is, G’ V2 (25) < G’ V1 (25) is preferable. According to such a configuration, by laminating a low refractive index adhesive layer having a relatively low storage elastic modulus on a high refractive index layer (for example, a high refractive index adhesive layer) in which the storage elastic modulus G’ tends to increase as a compensation for increasing the refractive index, adhesiveness and flexibility are imparted, so that step followability and followability to a curved surface or the like are improved, and a laminated sheet (adhesive sheet) that can be preferably applied to various device design uses can be realized.

[0032] The low refractive index pressure-sensitive adhesive disclosed herein contains an acrylic polymer (F) having a fluorine-containing acrylic monomer (M1) as a monomer unit. The low refractive index pressure-sensitive adhesive is preferably an acrylic pressure-sensitive adhesive containing such an acrylic polymer (F) as a base polymer.

[0033] In this specification, the "base polymer" of the pressure-sensitive adhesive refers to the main component of the rubbery polymer contained in the pressure-sensitive adhesive, and is not construed in any other limited way. The above-mentioned rubbery polymer refers to a polymer that exhibits rubber elasticity in a temperature range near room temperature. Also, in this specification, the "main component" refers to a component contained in an amount exceeding 50% by weight, unless otherwise specified. Also, in this specification, the "acrylic polymer" refers to a polymer containing a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule as a monomer unit constituting the polymer. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as an "acrylic monomer". Therefore, the acrylic polymer in this specification is defined as a polymer containing a monomer unit derived from an acrylic monomer. Typical examples of the acrylic polymer include polymers in which the proportion of the acrylic monomer among all the monomers used in the synthesis of the acrylic polymer exceeds 50% by weight (preferably exceeds 70% by weight, for example, exceeds 90% by weight). Also, in this specification, "(meth)acryloyl" means comprehensively referring to acryloyl and methacryloyl. Similarly, "(meth)acrylate" means comprehensively referring to acrylate and methacrylate, and "(meth)acrylic" means comprehensively referring to acrylic and methacrylic, respectively. Therefore, the concept of the acrylic monomer referred to herein can include both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer).

[0034] (Acrylic polymer (F)) The acrylic polymer (F) in the technology disclosed herein contains a fluorine-containing acrylic monomer (M1) as a monomer component constituting the polymer. That is, the acrylic polymer (F) contains the fluorine-containing acrylic monomer (M1) as a monomer unit. By appropriately using the fluorine-containing acrylic monomer (M1), the refractive index of the acrylic polymer (F) can be lowered.

[0035] Here, in this specification, the "monomer component constituting the acrylic polymer" means a monomer that constitutes the repeating unit of the acrylic polymer in the adhesive formed from the adhesive composition, regardless of whether it is contained in the adhesive composition in the form of a pre-formed polymer (which may be an oligomer) or in the form of an unpolymerized monomer. That is, the monomer component constituting the acrylic polymer may be contained in the above adhesive composition in any form of polymer, unpolymerized substance, or partially polymerized substance. From the viewpoint of ease of preparation of the adhesive composition, etc., in some embodiments, an adhesive composition containing substantially all (for example, 95% by weight or more, preferably 99% by weight or more) of the monomer component in the form of a polymer is preferred. An adhesive composition containing substantially all of the monomer component in the form of a polymer is also preferred from the viewpoint of easily forming an adhesive sheet with less distortion and warping.

[0036] The acrylic polymer (F) can be a polymer of a monomer raw material that contains at least a fluorine-containing acrylic monomer (M1) (hereinafter, may be abbreviated as "monomer (M1)") and may further contain other monomers (copolymerizable monomers) having copolymerizability with the monomer (M1). The monomer (M1) is not particularly limited as long as it is an acrylic monomer having at least one fluorine atom in the molecule. For example, a fluorine-containing (meth)acrylate can be preferably used. Preferable examples of the fluorine-containing (meth)acrylate include those having a fluorinated hydrocarbon group at the ester terminal. Examples of the fluorinated hydrocarbon group include a fluorinated aliphatic hydrocarbon group, a fluorinated alicyclic hydrocarbon group, and a fluorinated aromatic hydrocarbon group. As the fluorinated hydrocarbon group, a fluorinated aliphatic hydrocarbon group is preferable. Examples of the fluorinated aliphatic hydrocarbon group include a fluorinated alkyl group. In the fluorinated aliphatic hydrocarbon group, the aliphatic hydrocarbon moiety may be linear or branched. Also, in the fluorinated aliphatic hydrocarbon group, the fluorine atom may be bonded to any carbon atom of the aliphatic hydrocarbon group moiety. The number of fluorine atoms bonded to one carbon atom may be single or plural. The number of carbon atoms to which the fluorine atom is bonded is not particularly limited.

[0037] In a fluorinated aliphatic hydrocarbon group (especially a fluorinated alkyl group), the number of carbon atoms in the hydrocarbon group moiety is not particularly limited. In some embodiments, considering the compatibility with other copolymerizable monomers, a fluorinated aliphatic hydrocarbon group having about 1 to 18 (preferably 1 to 12) carbon atoms is preferred. Specific examples of the fluorinated aliphatic hydrocarbon group include fluorinated methyl groups such as trifluoromethyl group, difluoromethyl group, monofluoromethyl group; fluorinated ethyl groups such as pentafluoroethyl group, 1,1,2,2-tetrafluoroethyl group, 1,2,2,2-tetrafluoroethyl group, 1,1,2-trifluoroethyl group, 1,2,2-trifluoroethyl group, 2,2,2-trifluoroethyl group, 1,1-difluoroethyl group, 1,2-difluoroethyl group, 2,2-difluoroethyl group, 1-monofluoroethyl group, 2-monofluoroethyl group; and the like. As the fluorinated alkyl group having 3 or more carbon atoms, various fluorinated alkyl groups in which one or more of the carbon atoms in the alkyl group moiety are bonded with one or more fluorine atoms can be exemplified in the same manner as the above-exemplified fluorinated methyl group and fluorinated ethyl group.

[0038] Examples of the fluorinated alicyclic hydrocarbon group include fluorinated cycloalkyl groups. Similar to the above fluorinated aliphatic hydrocarbon group, in the fluorinated alicyclic hydrocarbon group, the fluorine atom may be bonded to any carbon atom of the alicyclic hydrocarbon group, and the number of fluorine atoms bonded to one carbon atom may be either single or plural. Furthermore, the number of carbon atoms to which the fluorine atom is bonded is not particularly limited. The fluorinated alicyclic hydrocarbon group includes, for example, cyclohexyl groups having one fluorine atom such as 2-fluorocyclohexyl group, 3-fluorocyclohexyl group, 4-fluorocyclohexyl group; cyclohexyl groups having two fluorine atoms such as 2,4-difluorocyclohexyl group, 2,6-difluorocyclohexyl group; cyclohexyl groups having three fluorine atoms such as 2,4,6-trifluorocyclohexyl group, etc.

[0039] The fluorinated hydrocarbon group may or may not have a substituent. Such substituents are not particularly limited, and examples include hydrocarbon groups such as alkyl groups, alkoxy groups, hydroxy groups, carboxy groups, amino groups, nitro groups, cyano groups, and halogen atoms. The substituents can be used alone or in combination of two or more.

[0040] The fluorine atom-containing (meth)acrylate [fluorinated (meth)acrylate] includes, for example, fluorine atom-containing alkyl (meth)acrylate [fluorinated alkyl (meth)acrylate], fluorine atom-containing cycloalkyl (meth)acrylate [fluorinated cycloalkyl (meth)acrylate], fluorine atom-containing aryl (meth)acrylate [fluorinated aryl (meth)acrylate], and the like.

[0041] As the fluorine atom-containing (meth)acrylate, fluorinated alkyl (meth)acrylate (particularly, fluorinated alkyl acrylate) is preferable. Examples of the fluorinated alkyl (meth)acrylate include 2,2,2-trifluoroethyl acrylate (trade name "Biscoat 3F" manufactured by Osaka Organic Chemical Industry Co., Ltd., etc.), 2,2,3,3-tetrafluoropropyl acrylate (trade name "Biscoat 4F" manufactured by Osaka Organic Chemical Industry Co., Ltd., etc.), 1H,1H,5H-octafluoropentyl acrylate (trade name "Biscoat 8F" manufactured by Osaka Organic Chemical Industry Co., Ltd., etc.), 1H,1H,5H-octafluoropentyl methacrylate (trade name "Biscoat 8FM" manufactured by Osaka Organic Chemical Industry Co., Ltd., etc.), 2-(heptadecafluorononyl)ethyl acrylate (trade name "FA-108" manufactured by Kyoeisha Chemical Co., Ltd., etc.), 1H,1H,2H,2H-tridecafluorooctyl acrylate (trade name "Biscoat 13F" manufactured by Osaka Organic Chemical Industry Co., Ltd., etc.), and the like.

[0042] From the viewpoints of the low refractive index effect, flexibility, etc., the number of carbon atoms in the fluorinated alkyl group in the fluorinated alkyl (meth)acrylate is advantageously 3 or more, preferably 4 or more, more preferably 5 or more, still more preferably 6 or more or 7 or more, and particularly preferably 8 or more. From the viewpoints of the adhesion performance, etc., the number of carbon atoms in the fluorinated alkyl group is advantageously 18 or less, preferably 14 or less, more preferably 12 or less, and may be 10 or less or 9 or less. In some embodiments, the number of carbon atoms in the fluorinated alkyl group may be 7 or less or 5 or less. Further, in some embodiments, as the fluorine atom-containing (meth)acrylic acid ester, a fluorinated alkyl (meth)acrylate in which fluorine is not bonded to the carbon at the 1-position of the alkyl group is preferred, and for example, a fluorinated alkyl (meth)acrylate in which fluorine is not bonded to either the carbon at the 1-position or the carbon at the 2-position of the alkyl group, such as 1H,1H,2H,2H-tridecafluorooctyl acrylate, may be preferably employed.

[0043] The content of the monomer (M1) in the monomer raw material for preparing the acrylic polymer (F) may be, for example, 10% by weight or more, suitably 25% by weight or more, and may be 35% by weight or more. From the viewpoint of facilitating the realization of a pressure-sensitive adhesive with a lower refractive index, the content of the monomer (M1) is preferably 40% by weight or more, more preferably 45% by weight or more, still more preferably 55% by weight or more, and may be 60% by weight or more, 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The upper limit of the content of the monomer (M1) in the monomer raw material is not particularly limited and may be 100% by weight. In some embodiments, from the viewpoints of the cohesiveness of the pressure-sensitive adhesive, etc., the content of the monomer (M1) is suitably 99.9% by weight or less, preferably 99.5% or less, and may be 99% by weight or less, 97% by weight or less, or 92% by weight or less. The monomer (M1) can be used alone or in combination of two or more.

[0044] The monomer raw materials for preparing the acrylic polymer (F) can be a composition containing a copolymerizable monomer in addition to the monomer (M1). The copolymerizable monomer can be useful for introducing crosslinking points into the acrylic polymer or enhancing the cohesive force of the acrylic polymer. Examples of the copolymerizable monomer include one or more functional group-containing monomers such as carboxy group-containing monomers, hydroxy group-containing monomers, acid anhydride group-containing monomers, amide group-containing monomers, amino group-containing monomers, monomers having a nitrogen atom-containing ring (e.g., N-vinyl cyclic amides such as N-vinyl-2-pyrrolidone), sulfonic acid group-containing monomers, and phosphoric acid group-containing monomers. Other examples of the copolymerizable monomer include non-aromatic ring-containing (meth)acrylates such as alkyl (meth)acrylates, cycloalkyl (meth)acrylates, and isobornyl (meth)acrylate, vinyl ester monomers such as vinyl acetate, aromatic vinyl compounds such as styrene, alkoxy group-containing monomers, and the like. Specific examples of the copolymerizable monomer include, but are not limited to, the same monomers as those that can be used for preparing the acrylic polymer (A) described later.

[0045] In some embodiments, from the perspective of improving cohesive force and the like, the acrylic polymer (F) using one or more monomers selected from the group consisting of a hydroxy group-containing monomer and a carboxy group-containing monomer (hereinafter, also referred to as "monomer (M2)") as the copolymerizable monomer is preferred. Examples of the hydroxy group-containing monomer include the same ones as the hydroxy group-containing monomers exemplified for the monomer (m2) described later. Preferable examples of the hydroxy group-containing monomer include 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate. From the perspective of flexibility, 4-hydroxybutyl acrylate is more preferable. Examples of the carboxy group-containing monomer include the same ones as the carboxy group-containing monomers exemplified for the monomer (m2) described later. Preferable examples of the carboxy group-containing monomer include acrylic acid and methacrylic acid.

[0046] The content of monomer (M2) in the monomer raw material for preparing the acrylic polymer (F) is not particularly limited and can be appropriately set so that the desired use effect is exhibited. The content of monomer (M2) 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 above monomer (M2) may be 0.7% by weight or more, 0.9% by weight or more, or 1.5% by weight or more of the monomer raw material. The upper limit of the content of monomer (M2) is not particularly limited and can be appropriately set so that the total with the content of other monomers does not exceed 100% by weight. From the viewpoint of relatively increasing the content of monomer (M1) to facilitate lowering the refractive index, it is appropriate that the content of monomer (M2) is, for example, 15% by weight or less or 10% by weight or less, preferably less than 10% by weight, more preferably less than 5% by weight, may be less than 3% by weight, may be less than 2.5% by weight, or may be less than 1.5% by weight. It is not necessary to use monomer (M2).

[0047] In some preferred embodiments, the monomer raw material for preparing the acrylic polymer (F) can be a composition containing a hydroxyl group-containing monomer as monomer (M2). The hydroxyl group-containing monomer can be useful for improving the cohesive force and introducing crosslinking points. Preferred examples of the hydroxyl group-containing monomer include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate. From the viewpoint of improving flexibility in the room temperature range, 4-hydroxybutyl acrylate can be more preferably used. The content of the hydroxyl group-containing monomer in the monomer raw material 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 group-containing monomer may be 0.7% by weight or more, 0.9% by weight or more, or 1.5% by weight or more of the monomer raw material. The upper limit of the content of the hydroxyl group-containing monomer is not particularly limited and can be, for example, 15% by weight or less or 10% by weight or less. In some embodiments, from the viewpoint of reducing the refractive index, it is appropriate that the content of the hydroxyl group-containing monomer in the monomer raw material is less than 10% by weight, preferably less than 5% by weight, may be less than 3% by weight, may be less than 2.5% by weight, or may be less than 1.5% by weight.

[0048] In some embodiments, the monomer raw material for preparing the acrylic polymer (F) can include a copolymerizable monomer other than monomer (M2) (i.e., a copolymerizable monomer having no hydroxyl group- and carboxyl group-containing monomer). Hereinafter, such a copolymerizable monomer may be referred to as "monomer (M3)". As monomer (M3), among the various copolymerizable monomers described above, those not corresponding to monomer (M2) can be used.

[0049] The content of monomer (M3) in the monomer raw materials for preparing the acrylic polymer (F) is not particularly limited and can be appropriately set so as to exhibit the desired usage effect. The content of monomer (M3) can be, for example, 0.1% by weight or more (preferably 1% by weight or more, more preferably 5% by weight or more). In some embodiments, the content of the above monomer (M2) may be 7% by weight or more of the monomer raw materials, may be 10% by weight or more, or may be 15% by weight or more. From the perspective of improving flexibility and the like, in some embodiments, the content of the above monomer (M2) may be 10% by weight or more, may be 25% by weight or more, may be 35% by weight or more, may be 45% by weight or more, may exceed 55% by weight, or may exceed 60% by weight. The upper limit of the content of monomer (M3) is not particularly limited and can be appropriately set so that the total with the content of other monomers does not exceed 100% by weight. The content of monomer (M3) can be, for example, 90% by weight or less, or may be 85% by weight or less. From the perspective of relatively increasing the content of monomer (M1) to facilitate reduction of the refractive index, the content of monomer (M3) is preferably 80% by weight or less, and more preferably 70% by weight or less. In some embodiments, from the perspective of reducing the refractive index, the content of monomer (M3) in the monomer raw materials is suitably less than 60% by weight, preferably less than 50% by weight, may be less than 45% by weight, may be less than 35% by weight, may be less than 20% by weight, may be less than 10% by weight, or may be less than 5% by weight. It is not necessary to use monomer (M3).

[0050] Preferable examples of the monomer that can be used as the monomer (M3) include alkyl (meth)acrylate, a monomer having a nitrogen atom-containing ring (for example, N-vinyl cyclic amide such as N-vinyl-2-pyrrolidone), non-aromatic ring-containing (meth)acrylate such as cycloalkyl (meth)acrylate and isobornyl (meth)acrylate, and the like. The monomer (M3) may be used alone or in combination of two or more. For example, a mode of using one kind of alkyl (meth)acrylate alone, a mode of using two or more kinds of alkyl (meth)acrylates in combination, a mode of using a combination of an alkyl (meth)acrylate and an N-vinyl cyclic amide, a mode of using a combination of an alkyl (meth)acrylate and a non-aromatic ring-containing (meth)acrylate, and the like can be preferably adopted.

[0051] As the alkyl (meth)acrylate, for example, a compound represented by the following formula (1) can be preferably used. CH2=C(R 1 )COOR 2 (1) Here, R 1 in the above formula (1) is a hydrogen atom or a methyl group. Further, R 2 is a linear alkyl group having 1 to 20 carbon atoms (hereinafter, such a carbon atom number range may be represented as "C 1-20 "). From the viewpoint of the storage elastic modulus of the adhesive and the like, an alkyl (meth)acrylate in which R 2 is a linear alkyl group of C 1-12 (for example, C 2-10 , typically C 4-8 ) is preferable. The alkyl (meth)acrylate in which the above R 2 is a linear alkyl group of C 1-20 can be used alone or in combination of two or more. Preferable alkyl (meth)acrylates include n-butyl acrylate and 2-ethylhexyl acrylate.

[0052] In some embodiments, the monomer raw materials for preparing the acrylic polymer (F) preferably have a limited content of carboxy group-containing monomers from the viewpoint of suppressing coloring or discoloration (e.g., yellowing) of the adhesive. The content of the carboxy group-containing monomer in the monomer raw materials may be, for example, less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, and even more preferably less than 0.1% by weight (e.g., less than 0.05% by weight). Limiting the content of the carboxy group-containing monomer in this way is also advantageous from the viewpoint of suppressing corrosion of metal materials (e.g., metal wirings, metal films, etc. that may be present on the adherend) that can be placed in contact with or in proximity to the adhesives disclosed herein. The technology disclosed herein can be preferably implemented in embodiments where the monomer raw materials do not contain carboxy group-containing monomers. For the same reason, in some embodiments, the monomer raw materials for preparing the acrylic polymer (F) preferably have a limited content of monomers having acidic functional groups (including sulfonic acid groups, phosphoric acid groups, etc. in addition to carboxy groups). As the content of the acidic functional group-containing monomer in the monomer raw materials of such embodiments, the preferred content of the carboxy group-containing monomer described above can be applied. The technology disclosed herein can be preferably implemented in embodiments where the monomer raw materials do not contain acidic group-containing monomers (i.e., embodiments where the acrylic polymer (F) is acid-free).

[0053] The acrylic polymer (F) can be prepared by appropriately adopting a known polymerization method, similar to the acrylic polymer (A) described below. The weight average molecular weight (Mw) of the acrylic polymer (F) is not particularly limited and may be, for example, approximately 10×10 4 ~500×10 4 and may be in the range of approximately 20×10 4 ~200×10 4 In some embodiments, from the viewpoint of adhesion to the adherend or an adjacent layer (which may be a high refractive index layer such as a high refractive index adhesive layer), etc., the Mw of the acrylic polymer (F) is 150×10 4It is appropriate that it is as follows, 120×10 4 It is preferably as follows (for example, 95×10 4 or less), more preferably 75×10 4 or less, may be 68×10 4 or less, may be 60×10 4 or less. Also, in some embodiments, from the perspective of the cohesiveness of the adhesive, etc., the Mw of the acrylic polymer (F) may be, for example, 30×10 4 or more, may be 40×10 4 or more, may be 50×10 4 or more. To prepare the Mw, a conventionally known chain transfer agent can be used as necessary.

[0054] Although not particularly limited, from the perspective of adhesiveness, the Tg of the acrylic polymer (F) is advantageously approximately 0°C or lower, preferably approximately -5°C or lower (for example, approximately -15°C or lower, or -25°C or lower). Also, from the perspective of the cohesive force of the adhesive layer, the Tg of the acrylic polymer (F) is approximately -75°C or higher, preferably approximately -70°C or higher (for example, -50°C or higher, and further -30°C or higher). The Tg of the acrylic polymer (F) can be adjusted by appropriately changing the monomer composition (that is, the types and usage ratio of monomers used in the synthesis of the polymer).

[0055] When using an alkyl (meth)acrylate as the monomer (M3), from the perspective of easily lowering the Tg of the acrylic polymer (F), in some embodiments, the Tg calculated by Fox's equation based on the usage amount of only the above alkyl (meth)acrylate is advantageously less than -50°C, preferably less than -55°C, may be less than -60°C, or may be less than -65°C.

[0056] (Method for preparing acrylic polymer (F)) In the technology disclosed herein, the method for obtaining the acrylic polymer (F) composed of the monomer components as described above is not particularly limited, and known polymerization methods such as solution polymerization method, emulsion polymerization method, bulk polymerization method, suspension polymerization method, photopolymerization method, etc. can be appropriately employed. In some embodiments, the solution polymerization method can be preferably employed. The polymerization temperature when performing solution polymerization can be appropriately selected according to the types of monomers and solvents used, the types of polymerization initiators, etc., and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0057] The solvent (polymerization solvent) used for solution polymerization can be appropriately selected from conventionally known organic solvents. For example, aromatic compounds such as toluene (typically aromatic hydrocarbons); acetate esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (for example, monohydric alcohols having 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc. Any one solvent selected therefrom, or a mixed solvent of two or more kinds can be used.

[0058] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators according to the type of polymerization method. For example, one or more kinds of 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; aromatic carbonyl compounds; etc. Still other examples of polymerization initiators include redox initiators by a combination of a peroxide and a reducing agent. The polymerization initiator can be used alone or in combination of two or more kinds. The amount of the polymerization initiator used can be a normal amount used, 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) with respect to 100 parts by weight of the monomer component.

[0059] For the above polymerization, various conventionally known chain transfer agents can be used as necessary. For example, mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, thioglycolic acid, α-thioglycerol, etc. can be used. Alternatively, a chain transfer agent that does not contain a sulfur atom (non-sulfur-based chain transfer agent) may be used. Examples of non-sulfur-based chain transfer agents include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenoids such as α-pinene and terpinolene; styrenes such as α-methylstyrene and α-methylstyrene dimer; and the like. The chain transfer agent can be used alone or in combination of two or more. When using a chain transfer agent, the amount used can be, for example, approximately 0.01 to 1 part by weight relative to 100 parts by weight of the monomer raw material.

[0060] The weight average molecular weight (Mw) of the base polymer is not particularly limited and can be, for example, approximately 10×10 4 ~500×10 4 In the range. From the viewpoint of adhesion performance, the Mw of the base polymer is 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 ) is preferably in the range.

[0061] Here, the Mw of the polymer can be determined by converting to polystyrene by gel permeation chromatography (GPC). Specifically, it can be determined by measuring under the following conditions using a GPC measuring device with the trade name "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 velocity): 0.6 mL / min Column temperature (measurement temperature): 40 °C Column: Sample column: One column of product name "TSKguardcolumn SuperHZ-H" + two columns of product name "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: One column of product name "TSKgel SuperH-RC" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: Polystyrene

[0062] (Crosslinking agent) In the technology disclosed herein, the pressure-sensitive adhesive composition used for forming the low refractive index pressure-sensitive adhesive layer may contain a crosslinking agent as necessary for the purpose of adjusting the cohesive force of the pressure-sensitive adhesive or the like. As the crosslinking agent, known crosslinking agents in the field of pressure-sensitive adhesives such as 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 can be used. Among them, isocyanate-based crosslinking agents can be preferably employed. As another example of the crosslinking agent, a monomer having two or more ethylenically unsaturated groups in one molecule, that is, a polyfunctional monomer can be mentioned. The crosslinking agent can be used alone or in combination of two or more. Regarding the specific examples and the amount of use of the crosslinking agent, the description of the crosslinking agent that can be used for the pressure-sensitive adhesive composition for forming the high refractive index pressure-sensitive adhesive layer, which will be described later, can also be applied to the pressure-sensitive adhesive composition for forming the low refractive index pressure-sensitive adhesive layer.

[0063] In an embodiment where the pressure-sensitive adhesive composition used for forming the low refractive index pressure-sensitive adhesive layer contains a crosslinking agent, an isocyanate-based crosslinking agent can be preferably employed as the above crosslinking agent. In some embodiments, the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the acrylic polymer (F) may be, for example, less than 0.5 part by weight, may be less than 0.3 part by weight, may be less than 0.2 part by weight, or may be less than 0.15 part by weight, from the viewpoint of adhesion to the adherend and adjacent layers. Further, from the viewpoint of appropriately exerting the effect of the crosslinking agent, in some embodiments, the amount of the isocyanate-based crosslinking agent used per 100 parts by weight of the acrylic polymer (F) may be, for example, 0.005 part by weight or more, may be 0.01 part by weight or more, may be 0.05 part by weight or more, or may be 0.08 part by weight or more.

[0064] (Other additives) The low refractive index pressure-sensitive adhesive can contain, as optional components, a plasticizing material, a leveling agent, a tackifier, inorganic particles, other additives, and the like. These optional components can be appropriately selected from the same ones that can be used for the high refractive index pressure-sensitive adhesive layer, and an appropriate amount can be used.

[0065] <High refractive index pressure-sensitive adhesive> The pressure-sensitive adhesive (low refractive index pressure-sensitive adhesive) disclosed herein can be used in a form laminated with a pressure-sensitive adhesive having a relatively higher refractive index (high refractive index pressure-sensitive adhesive) in relation to the pressure-sensitive adhesive. In such a usage form, the ratio (n1 / n2) of the refractive index n1 of the high refractive index pressure-sensitive adhesive to the refractive index n2 of the low refractive index pressure-sensitive adhesive layer may be, for example, greater than 1.00, may be approximately 1.01 or more, is suitably approximately 1.02 or more, and may be approximately 1.03 or more. In some embodiments, the ratio (n1 / n2) is advantageously approximately 1.05 or more, preferably approximately 1.07 or more, more preferably approximately 1.10 or more, and may be approximately 1.11 or more. The upper limit of the ratio (n1 / n2) is not particularly limited. In some embodiments, from the perspective of the adhesive properties of the adhesive surface formed by the high refractive index pressure-sensitive adhesive and / or the adhesive surface formed by the low refractive index pressure-sensitive adhesive, the transparency of each adhesive layer, and thus the transparency of the laminated sheet including the high refractive index pressure-sensitive adhesive and the low refractive index pressure-sensitive adhesive, etc., the ratio (n1 / n2) may be, for example, approximately 1.20 or less, may be approximately 1.18 or less, may be approximately 1.16 or less, may be approximately 1.14 or less, may be approximately 1.12 or less.

[0066] In some embodiments, the difference between the refractive index n1 of the high refractive index pressure-sensitive adhesive and the refractive index n2 of the low refractive index pressure-sensitive adhesive, that is, the refractive index difference (n1 - n2), may be, for example, greater than 0.00, may be 0.01 or more, is preferably 0.02 or more, may be 0.03 or more, may be 0.05 or more, may be 0.10 or more, may be 0.15 or more, may be 0.20 or more, may be 0.25 or more. The upper limit of the refractive index difference (n1 - n2) is not particularly limited. In some embodiments, from the perspective of the adhesive properties of the adhesive surface formed by the high refractive index pressure-sensitive adhesive and / or the adhesive surface formed by the low refractive index pressure-sensitive adhesive, the transparency of each adhesive layer, and thus the transparency of the laminated sheet including the high refractive index pressure-sensitive adhesive and the low refractive index pressure-sensitive adhesive, etc., the refractive index difference (n1 - n2) may be, for example, 0.30 or less, may be 0.26 or less, may be 0.21 or less, may be 0.18 or less, may be 0.16 or less.

[0067] The preferable lower limit of the refractive index of the high refractive index adhesive may vary depending on the refractive index of the low refractive index adhesive and is not limited to a specific range. For example, the refractive index of the high refractive index adhesive may be 1.45 or more, 1.47 or more, 1.50 or more, 1.53 or more, 1.55 or more, or 1.56 or more. Using a high refractive index adhesive with a higher refractive index is preferable from the viewpoint of increasing the refractive index difference from the low refractive index adhesive and is also advantageous from the viewpoint of increasing the design freedom of the low refractive index adhesive.

[0068] In some embodiments, the refractive index of the high refractive index adhesive may be, for example, 1.570 or more, preferably more than 1.570, preferably 1.580 or more, more preferably 1.585 or more, and even more preferably 1.590 or more (for example, 1.595 or more). According to the high refractive index adhesive layer having such a refractive index, by utilizing the relative refractive index relationship between the high refractive index adhesive layer and the low refractive index adhesive layer as described above, the behavior of light transmitted through the low refractive index adhesive layer and / or the high refractive index adhesive layer can be effectively controlled. In some embodiments of the technology disclosed herein, the refractive index of the high refractive index adhesive may be, for example, 1.600 or more or more than 1.600, 1.605 or more or more than 1.605, or 1.610 or more or more than 1.610. The preferable upper limit of the refractive index of the high refractive index adhesive may vary depending on the refractive index of the adjacent layer etc. and is not limited to a specific range. In some embodiments, considering the balance with adhesive properties and transparency, the refractive index of the high refractive index adhesive may be, for example, 1.700 or less, 1.670 or less, or 1.650 or less.

[0069] (Storage elastic modulus G') In the technology disclosed herein, the storage elastic modulus G' (hereinafter also referred to as "storage elastic modulus G' V1 (25)") of the high refractive index adhesive at 25°C is appropriately set according to the purpose of use, usage mode, etc. and is not limited to a specific range. The storage elastic modulus G' V1(25) can be, for example, approximately 700 kPa or less. In some embodiments, from the viewpoint of ease of attachment to the adherend, etc., the storage elastic modulus G’ V1 (25) 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 enhancing the flexibility of the high refractive index adhesive in the room temperature range (e.g., 25 °C) and facilitating adhesion to the adherend, the storage elastic modulus G’ V1 (25) is advantageously approximately 330 kPa or less, preferably 300 kPa or less. In some embodiments where adhesion and flexibility at room temperature are more emphasized, the storage elastic modulus G’ V1 (25) 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 elastic modulus G’ V1 (25) may be less than 100 kPa or less than 90 kPa. The storage elastic modulus G’ V1 The lower limit of (25) is not particularly limited, but from the viewpoints of processability and handleability, etc., it may be, for example, 30 kPa or more, may be 50 kPa or more, or may be 70 kPa or more. In some embodiments, considering high refractive index, the storage elastic modulus G’ V1 (25) may be 100 kPa or more, may be 150 kPa or more, may be 200 kPa or more, may be 250 kPa or more, or may be 300 kPa or more.

[0070] In the technology disclosed herein, the storage elastic modulus G’ of the high refractive index adhesive at 50 °C (hereinafter, also referred to as “storage elastic modulus G’ V1 (50)”).) is not particularly limited and can be, for example, less than 100 kPa. In some embodiments, the storage elastic modulus G’ V1 (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). Thus, the storage elastic modulus G’ V1The high refractive index adhesive with limited (50) can easily enhance the adhesion to the adherend by appropriately heating as needed, thereby improving the adhesiveness to the adherend. Storage modulus G’ V1 The lower limit of (50) is not particularly limited. In some embodiments, from the perspective of heat resistance characteristics, etc., the storage modulus G’ V1 (50) may be, for example, 10 kPa or more, 15 kPa or more, 20 kPa or more, or 23 kPa or more.

[0071] In some embodiments of the technology disclosed herein, the high refractive index adhesive layer has the following conditions: (a) The storage modulus G’ V1 (25) is 350 kPa or less (preferably less than 200 kPa, for example, 180 kPa or less); and (b) The storage modulus G’ V1 (50) is less than 60 kPa (preferably less than 50 kPa, more preferably less than 40 kPa, for example, 38 kPa or less); It is preferable to satisfy at least one of them. The high refractive index adhesive layer that satisfies at least the above condition (a) is preferable from the perspective of adhesion and flexibility to the adherend at room temperature (for example, 25 °C). The high refractive index adhesive layer that satisfies at least the above condition (b) is preferable because the adhesion (adhesiveness) to the adherend can be easily improved by heating to a temperature slightly higher than room temperature. An adhesive sheet having a high refractive index adhesive layer that does not satisfy the above condition (a) and satisfies (b) has good reworkability (re-stickability) at the initial stage of pasting at room temperature, and can effectively increase the peel strength from the adherend by heating to a temperature slightly higher than room temperature, and can be used as a heat-activated type adhesive sheet. The above heat activation may be performed by heating the adhesive sheet to a temperature slightly higher than room temperature when pasting to the adherend. The temperature slightly higher than the above room temperature is, for example, about 60 °C or lower, preferably about 55 °C or lower (for example, about 50 °C or lower).

[0072] In some embodiments of the technology disclosed herein, the storage modulus G’ V1Storage elastic modulus G’ with respect to (25) [kPa] V1 Ratio of (50) [kPa], i.e., storage elastic modulus ratio G’ V1 (50) / G’ V1 (25) is, for example, 70% or less, may be 40% or less, may be 30% or less, or may be 20% or less. G’ V1 (50) / G’ V1 An adhesive sheet having a high refractive index adhesive layer with a small (25) is suitable for use as the above heat - activated type adhesive sheet. G’ V1 (50) / G’ V1 The lower limit of (25) is not particularly limited. G’ V1 (50) / G’ V1 (25) is, for example, 5% or more, preferably 10% or more from the viewpoint of heat - resistant characteristics, may be 12% or more, or may be 15% or more.

[0073] Storage elastic modulus G’ V1 (25) and G’ V1 (50) can be determined by dynamic viscoelasticity measurement, and from the results, G’ V1 (50) / G’ V1 (25) can be calculated. The dynamic viscoelasticity measurement can be carried out by a conventional method using a commercially available dynamic viscoelasticity measuring device. For example, it can be carried out under the following measurement conditions using ARES manufactured by TA Instruments or its equivalent. As a sample for measurement, a sample prepared to a thickness of about 1.5 mm by laminating the adhesive layer to be evaluated as necessary is used. [Measurement conditions] Deformation mode: Torsion Measurement frequency: 1 Hz Temperature rising rate: 5 °C / min Shape: Parallel plate 7.9 mm φ

[0074] Storage elastic modulus G’ V1 (25), G’ V1 (50) and storage elastic modulus ratio (G’ V1 (50) / G’ V1(25) can be adjusted by the selection of the composition of the monomer components constituting the base polymer of the adhesive (for example, the selection of the type and content of the monomer (m1) described later), the presence or absence, type, and amount of use of the crosslinking agent, the presence or absence, type, and amount of use of the refractive index improver and plasticizing material described later, etc. For example, as the monomer (m1), in addition to the first monomer which is the main component of the monomer (m1), a relatively small amount of a second monomer having a chemical structure different from that of the first monomer is used in combination with the first monomer. In addition to the case where the first monomer is used alone as the monomer (m1), G’ V1 (50) can be reduced, and G’ V1 (50) / G’ V1 (25) can be decreased.

[0075] The type of the adhesive constituting the high refractive index adhesive layer is not particularly limited. The above adhesive can contain one or more of various rubber-like polymers such as acrylic polymers, rubber-based polymers (natural rubber, synthetic rubber, mixtures thereof, etc.), polyester-based polymers, urethane-based polymers, polyether-based polymers, silicone-based polymers, polyamide-based polymers, and fluorine-based polymers as an adhesive polymer (also referred to as a "base polymer" hereinafter in the sense of a structural polymer forming an adhesive). From the viewpoints of adhesive performance and cost, etc., an adhesive containing an acrylic polymer or a rubber-based polymer as a base polymer can be preferably employed. Among them, an adhesive having an acrylic polymer as a base polymer (acrylic adhesive) is preferable. The technology disclosed herein is preferably implemented in a mode using an acrylic adhesive.

[0076] Hereinafter, the high refractive index adhesive layer composed of an acrylic adhesive will be mainly described, but it is not intended to limit the high refractive index adhesive layer in the technology disclosed herein to an acrylic adhesive layer.

[0077] (Acrylic polymer (A)) The high refractive index adhesive layer disclosed herein can be an acrylic adhesive layer. As the acrylic polymer which is the base polymer of the acrylic adhesive layer, those containing an aromatic ring-containing monomer (m1) as a monomer component constituting the acrylic polymer are preferable. That is, an acrylic polymer containing an aromatic ring-containing monomer (m1) as a monomer unit is preferable. Hereinafter, such an acrylic polymer is also referred to as "acrylic polymer (A)".

[0078] (Monomer (m1)) As the monomer (m1), a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule is used. As the monomer (m1), one kind of such a compound can be used alone or two or more kinds can be combined and used.

[0079] Examples of the above ethylenically unsaturated group include (meth)acryloyl group, vinyl group, (meth)allyl group, etc. From the viewpoint of polymerization reactivity, the (meth)acryloyl group is preferable, and from the viewpoints of flexibility and adhesiveness, the acryloyl group is more preferable. From the viewpoint of suppressing the decrease in flexibility of the adhesive, as the monomer (m1), a compound in which the number of ethylenically unsaturated groups contained in one molecule is 1 (that is, a monofunctional monomer) is preferably used.

[0080] The number of aromatic rings contained in one molecule of the compound used as the monomer (m1) may be 1 or 2 or more. The upper limit of the number of aromatic rings contained in the monomer (m1) is not particularly limited and can be, for example, 16 or less. In some embodiments, from the viewpoints of ease of preparation of the acrylic polymer (A) and transparency of the adhesive, the number of the above aromatic rings may be, for example, 12 or less, preferably 8 or less, more preferably 6 or less, and may also be 5 or less, 4 or less, 3 or less, or 2 or less.

[0081] The aromatic ring of the compound used as monomer (m1) may be, for example, a benzene ring (which may be a benzene ring constituting part of a biphenyl structure or a fluorene structure); a condensed ring such as a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, or a phenanthrene ring; etc., and may be a carbocyclic ring, or may be 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 above heterocyclic ring may be one or more selected from the group consisting of, for example, nitrogen, sulfur, and oxygen. In some embodiments, the heteroatom constituting the above heterocyclic ring may be one or both of nitrogen and sulfur. Monomer (m1) may have a structure in which one or more carbocyclic rings and one or more heterocyclic rings are condensed, such as a dinaphthothiophene structure, for example.

[0082] The above aromatic ring (preferably a carbocyclic ring) may or may not have one or more substituents on the ring-constituting atoms. When having substituents, examples of the substituents 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, a glycidyloxy group, etc. In a substituent containing a carbon atom, 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 above aromatic ring may be an aromatic ring having no substituents on the ring-constituting atoms or having 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). Note that for the aromatic ring of monomer (m1) to have a substituent on its ring-constituting atoms means that the aromatic ring has a substituent other than a substituent having an ethylenically unsaturated group.

[0083] The aromatic ring and the ethylenically unsaturated group may be directly bonded or may be bonded via a linking group. The above 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 having a structure in which one or more hydrogen atoms in these groups are substituted with a hydroxyl group (for example, a hydroxyalkylene group), an oxy group (-O- group), a thiooxy group (-S- group), etc., and may be a group containing one or more structures selected from these. In some embodiments, an aromatic ring-containing monomer having a structure in which the aromatic ring and the ethylenically unsaturated group are directly bonded or are bonded via a linking group selected from the group consisting of an alkylene group, an oxyalkylene group, and a poly(oxyalkylene) group may be preferably employed. The number of carbon atoms in the above alkylene group and the above oxyalkylene group is preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. The number of repeating units of the oxyalkylene unit in the above poly(oxyalkylene) group may be, for example, 2 to 3.

[0084] Examples of compounds that may be preferably employed as the monomer (m1) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. The aromatic ring-containing (meth)acrylates and the aromatic ring-containing vinyl compounds can each 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 may be used in combination.

[0085] The content of monomer (m1) in the monomer components constituting the acrylic polymer (A) is not particularly limited and can be set so as to realize an adhesive layer that can achieve both a desired refractive index and adhesive properties (such as peel strength, flexibility, etc.) and / or optical properties (such as total light transmittance, haze value, etc.). In some embodiments, the content of monomer (m1) in the monomer components may be, for example, 30% by weight or more, preferably 50% by weight or more, may be 60% by weight or more, and may be 70% by weight or more. From the perspective of facilitating the obtaining of a higher refractive index, in some preferred embodiments, the content of the monomer (m1) may be, for example, more than 70% by weight, may be 75% by weight or more, may be 80% by weight or more, may be 85% by weight or more, may be 90% by weight or more, and may be 95% by weight or more. The upper limit of the content of monomer (m1) in the monomer components is 100% by weight. From the perspective of achieving a good balance between a high refractive index and adhesive properties and / or optical properties, it is advantageous that the content of the monomer (m1) is less than 100% by weight. For example, it is preferably approximately 99% by weight or less, more preferably 98% by weight or less, may be 97% by weight or less, and may be 96% by weight or less. In some embodiments, the content of the monomer (m1) may be 93% by weight or less, may be 90% by weight or less, may be 80% by weight or less, and may be 75% by weight or less. In some embodiments that place more emphasis on adhesive properties and / or optical properties, the content of the monomer (m1) in the monomer components may be 70% by weight or less, may be 60% by weight or less, and may be 45% by weight or less.

[0086] In some aspects of the technology disclosed herein, as the monomer (m1), a monomer having two or more aromatic rings (preferably carbocyclic rings) in one molecule can be preferably employed because a high refractive index increasing effect can be easily obtained. Examples of the monomer having two or more aromatic rings in one molecule (hereinafter, also referred to as "aromatic ring multi-containing monomer") include 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 (i.e., without intervening other atoms) chemically bonded, a monomer having a condensed aromatic ring structure, a monomer having a fluorene structure, a monomer having a dinaphthothiophene structure, a monomer having a dibenzothiophene structure, and the like. The aromatic ring multi-containing monomers can be used alone or in combination of two or more kinds.

[0087] The above linking group is, 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), a thiooxyalkylene group (e.g., -S-(CH2) n - group, where n is 1 to 3, preferably 1), a linear alkylene group (i.e., -(CH2) n - group, where n is 1 to 6, preferably 1 to 3), a group in which the alkylene group in the above oxyalkylene group, the above thiooxyalkylene group, and the above linear alkylene group is partially halogenated or completely halogenated, and the like. From the viewpoint of the flexibility of the adhesive and the like, preferred examples of the above linking group include an oxy group, a thiooxy group, an oxyalkylene group, and a linear alkylene group. Specific examples of the monomer 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, benzylbenzyl (meth)acrylate, and the like.

[0088] Monomers having a structure in which two or more non-condensed aromatic rings are directly chemically bonded can be, for example, biphenyl structure-containing (meth)acrylates, triphenyl structure-containing (meth)acrylates, vinyl group-containing biphenyls, and the like. Specific examples include o-phenylphenol (meth)acrylate, biphenylmethyl (meth)acrylate, and the like.

[0089] Examples of the monomers having the condensed aromatic ring structure include naphthalene ring-containing (meth)acrylates, anthracene ring-containing (meth)acrylates, vinyl group-containing naphthalenes, vinyl group-containing anthracenes, and the like. Specific examples include 1-naphthylmethyl (meth)acrylate (alias: 1-naphthalenemethyl (meth)acrylate), hydroxyethylated β-naphthol acrylate, 2-naphthoethyl (meth)acrylate, 2-naphthoxyethyl acrylate, 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate, and the like.

[0090] Specific examples of the monomers having the fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene (meth)acrylate, 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (meth)acrylate, and the like. Since monomers having a fluorene structure contain a structural part in which two benzene rings are directly chemically bonded, they are included in the concept of monomers having a structure in which two or more non-condensed aromatic rings are directly chemically bonded.

[0091] Examples of the monomers having the dinaphthothiophene structure include (meth)acryloyl group-containing dinaphthothiophenes, vinyl group-containing dinaphthothiophenes, (meth)allyl group-containing dinaphthothiophenes, and the like. Specific examples include (meth)acryloyloxymethyldinaphthothiophene (for example, a compound having a structure in which CH2CH(R 1 )C(O)OCH2- is bonded to the 5th or 6th position of the dinaphthothiophene ring. Here, R 1 is a hydrogen atom or a methyl group.), (meth)acryloyloxyethyldinaphthothiophene (for example, at the 5th or 6th position of the dinaphthothiophene ring, CH2CH(R1 ) C(O)OCH(CH3)- or CH2CH(R 1 ) C(O)OCH2CH2- bonded compounds. Here, R 1 is a hydrogen atom or a methyl group.), vinyldinaphthothiophene (for example, a compound having a structure in which a vinyl group is bonded to the 5-position or 6-position of the naphthothiophene ring), (meth)allyloxydinaphthothiophene, and the like. In addition, the monomer having a dinaphthothiophene structure is included in the concept of the monomer having the condensed aromatic ring structure by including a naphthalene structure and by having a structure in which a thiophene ring and two naphthalene structures are condensed.

[0092] Examples of the monomer having the dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophene, vinyl group-containing dibenzothiophene, and the like. In addition, since the monomer having a dibenzothiophene structure has a structure in which a thiophene ring and two benzene rings are condensed, it is included in the concept of the monomer having the condensed aromatic ring structure. Note that neither the dinaphthothiophene structure nor the dibenzothiophene structure corresponds to a structure in which two or more non-condensed aromatic rings are directly chemically bonded.

[0093] As the monomer (m1) in the technology disclosed herein, a monomer having one aromatic ring (preferably a carbocyclic ring) in one molecule may be used. The monomer having one aromatic ring in one molecule can be useful, for example, for improving the flexibility of the adhesive, adjusting the adhesive properties, and improving the transparency. In some embodiments, the monomer having one aromatic ring in one molecule is preferably used in combination with a monomer containing a plurality of aromatic rings from the viewpoint of improving the refractive index of the adhesive.

[0094] Examples of monomers having one aromatic ring in the molecule include carbon aromatic ring-containing (meth)acrylates such as benzyl (meth)acrylate, methoxybenzyl (meth)acrylate, phenyl (meth)acrylate, ethoxylated phenol (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxybutyl (meth)acrylate, cresyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, chlorobenzyl (meth)acrylate; bromine-substituted aromatic ring-containing (meth)acrylates such as 2-(4,6-dibromo-2-s-butylphenoxy)ethyl (meth)acrylate, 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate, 6-(4,6-dibromo-2-s-butylphenoxy)hexyl (meth)acrylate, 6-(4,6-dibromo-2-isopropylphenoxy)hexyl (meth)acrylate, 2,6-dibromo-4-nonylphenyl acrylate, 2,6-dibromo-4-dodecylphenyl acrylate; carbon aromatic ring-containing vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, tert-butylstyrene; compounds having a vinyl substituent on a heteroaromatic ring such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyl oxazole; and the like.

[0095] As the monomer (m1), a monomer having a structure in which an oxyethylene chain is interposed between an ethylenically unsaturated group and an aromatic ring in various aromatic ring-containing monomers as described above may be used. The monomer having an oxyethylene chain interposed between the ethylenically unsaturated group and the aromatic ring can be regarded as an ethoxylate of the original monomer. The repeating number of oxyethylene units (-CH2CH2O-) in the oxyethylene chain is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, and is, for example, 1. Specific examples of the ethoxylated aromatic ring-containing monomers include ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol di(meth)acrylate, and the like.

[0096] The content of the monomer containing a plurality of aromatic rings in the monomer (m1) is not particularly limited, and may be, for example, 5% by weight or more, may be 25% by weight or more, or may be 40% by weight or more. In some embodiments, from the viewpoint of facilitating the realization of an adhesive having a higher refractive index, the content of the monomer containing a plurality of aromatic rings in the monomer (m1) may be, for example, 50% by weight or more, preferably 70% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. Substantially 100% by weight of the monomer (m1) may be a monomer containing a plurality of aromatic rings. That is, only one or more monomers containing a plurality of aromatic rings may be used as the monomer (m1). Further, in some embodiments, for example, considering the balance between the high refractive index and the adhesive properties and / or optical properties, the content of the monomer containing a plurality of aromatic rings in the monomer (m1) may be less than 100% by weight, may be 98% by weight or less, may be 90% by weight or less, may be 80% by weight or less, or may be 65% by weight or less. In some embodiments, considering the adhesive properties and / or optical properties, the content of the monomer containing a plurality of aromatic rings in the monomer (m1) may be 70% by weight or less, may be 50% by weight or less, may be 25% by weight or less, or may be 10% by weight or less. The technology disclosed herein can also be implemented in embodiments where the content of the monomer containing a plurality of aromatic rings in the monomer (m1) is less than 5% by weight. It is not necessary to use a monomer containing a plurality of aromatic rings.

[0097] The content of the monomer containing a plurality of aromatic rings in the monomer component constituting the acrylic polymer is not particularly limited, and can be set so as to realize an adhesive layer that can achieve a desired refractive index and adhesive properties (such as peel strength, flexibility, etc.) and / or optical properties (such as total light transmittance, haze value, etc.). The content of the monomer containing a plurality of aromatic rings in the monomer component may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the perspective of facilitating the realization of an adhesive having a higher refractive index, the content of the monomer containing a plurality of aromatic rings in the monomer component may be, for example, more than 35% by weight, preferably more than 50% by weight, may be more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. The content of the monomer containing a plurality of aromatic rings in the monomer component may be 100% by weight, but from the perspective of achieving a good balance between a high refractive index and adhesive properties and / or optical properties, it is advantageous to be less than 100% by weight, preferably approximately 99% by weight or less, more preferably 98% by weight or less, may be 96% by weight or less, may be 93% by weight or less, may be 90% by weight or less, may be 85% by weight or less, may be 80% by weight or less, or may be 75% by weight or less. In some embodiments, considering the adhesive properties and / or optical properties, the content of the monomer containing a plurality of aromatic rings in the monomer component may be 70% by weight or less, may be 50% by weight or less, may be 25% by weight or less, may be 15% by weight or less, or may be 5% by weight or less. The technology disclosed herein can also be implemented in embodiments where the content of the monomer containing a plurality of aromatic rings in the monomer component is less than 3% by weight.

[0098] In some aspects of the technology disclosed herein, a high refractive index monomer may preferably be employed as at least a part of the monomer (m1). Here, the "high refractive index monomer" refers to a monomer having a refractive index of, for example, approximately 1.510 or more, preferably approximately 1.530 or more, more preferably approximately 1.550 or more. The upper limit of the refractive index of the high refractive index monomer is not particularly limited, but from the viewpoints of ease of preparation of the adhesive composition and ease of compatibility with flexibility suitable for an adhesive, it is, for example, 3.000 or less, may be 2.500 or less, may be 2.000 or less, may be 1.900 or less, may be 1.800 or less, may be 1.700 or less. The high refractive index monomer can be used alone or in combination of two or more kinds. The refractive index of the monomer is measured using an Abbe refractometer under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. As the Abbe refractometer, the model "DR-M4" manufactured by ATAGO Co., Ltd. or its equivalent can be used. When the nominal value of the refractive index at 25°C is provided by the manufacturer or the like, that nominal value can be adopted.

[0099] As the high refractive index monomer, a compound having a corresponding refractive index can be appropriately adopted from among the compounds (for example, the compounds and compound groups exemplified above) included in the concept of the aromatic ring-containing monomer (m1) disclosed herein. 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 units of oxyethylene unit: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, Tg of homopolymer: 6°C), phenoxyethyl acrylate (refractive index (nD20): 1.517, Tg of homopolymer: 2°C), phenoxydiethylene glycol acrylate (refractive index: 1.510, Tg of homopolymer: -35°C), 6-acryloyloxymethyldinaphthothiophene (6MDNTA, refractive index: 1.75), 6-methacryloyloxymethyldinaphthothiophene (6MDNTMA, refractive index: 1.726), 5-acryloyloxyethyldinaphthothiophene (5EDNTA, refractive index: 1.786), 6-acryloyloxyethyldinaphthothiophene (6EDNTA, refractive index: 1.722), 6-vinyldinaphthothiophene (6VDNT, refractive index: 1.802), 5-vinyldinaphthothiophene (abbreviation: 5VDNT, refractive index: 1.793), etc., but are not limited thereto.

[0100] The content of the high refractive index monomer in the monomer (m1) (i.e., an aromatic ring-containing monomer having a refractive index of approximately 1.510 or more, preferably approximately 1.530 or more, more preferably approximately 1.550 or more) is not particularly limited and may be, for example, 5% by weight or more, may be 25% by weight or more, may be 35% by weight or more, or may be 40% by weight or more. In some embodiments, from the perspective of facilitating the obtaining of 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, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. Substantially 100% by weight of the monomer (m1) may be the high refractive index monomer. Also, in some embodiments, for example, from the perspective of achieving a good balance between the high refractive index and the 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, may be 98% by weight or less, may be 90% by weight or less, may be 80% by weight or less, or may be 65% by weight or less. In some embodiments, considering the 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, may be 50% by weight or less, may be 25% by weight or less, may be 15% by weight or less, or may be 10% by weight or less. The technology disclosed herein can also be implemented in embodiments where the content of the high refractive index monomer in the monomer component (m1) is less than 5% by weight. It is not necessary to use the high refractive index monomer.

[0101] The content of the high refractive index monomer in the monomer component constituting the acrylic polymer is not particularly limited and can be set so as to realize an adhesive layer that can achieve a desired refractive index and adhesive properties (such as peel strength, flexibility, etc.) and / or optical properties (such as total light transmittance, haze value, etc.). The content of the high refractive index monomer in the monomer component may be, for example, 3% by weight or more, may be 10% by weight or more, and may be 25% by weight or more. In some embodiments, from the perspective of facilitating the realization of an adhesive having a higher refractive index, the content of the high refractive index monomer in the monomer component may be, for example, more than 35% by weight, preferably more than 50% by weight, may be more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, and may be 95% by weight or more. The content of the high refractive index monomer in the monomer component may be 100% by weight, but from the perspective of achieving a good balance between the high refractive index and the adhesive properties and / or optical properties, it is advantageous to be less than 100% by weight, preferably 99% by weight or less, more preferably 98% by weight or less, may be 96% by weight or less, may be 93% by weight or less, may be 90% by weight or less, may be 85% by weight or less, may be 80% by weight or less, and may be 75% by weight or less. In some embodiments, considering the 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, may be 50% by weight or less, may be 25% by weight or less, may be 15% by weight or less, and may be 5% by weight or less. The technology disclosed herein can also be implemented in embodiments where the content of the high refractive index monomer in the monomer component is less than 3% by weight.

[0102] In some preferred embodiments of the technology disclosed herein, as at least a part of the monomer (m1), an aromatic ring-containing monomer (hereinafter, may be referred to as "monomer L") having a Tg of the homopolymer of 10 °C or lower (preferably 5 °C or lower, or 0 °C or lower, more preferably -10 °C or lower, still more preferably -20 °C or lower, for example -25 °C or lower) is employed. When the content of the aromatic ring-containing monomer (m1) in the monomer component (particularly, the aromatic ring-containing monomer (m1) corresponding to one or both of the above-described aromatic ring-containing monomers and high refractive index monomers) is increased, the storage elastic modulus G' of the pressure-sensitive adhesive generally tends to increase. However, by employing monomer L as a part or all of the monomer (m1), an increase in the storage elastic modulus G' can be suppressed. Thereby, while better maintaining the flexibility suitable for a pressure-sensitive adhesive, the refractive index can be improved. The lower limit of the Tg of monomer L is not particularly limited. In consideration of the balance with the refractive index improvement effect, in some embodiments, the Tg of monomer L may be, for example, -70 °C or higher, -55 °C or higher, or -45 °C or higher. Monomer L can be used alone or in combination of two or more kinds.

[0103] As monomer L, a compound having a corresponding Tg can be appropriately selected from among the compounds (for example, the compounds and compound groups exemplified above) included in the concept of the aromatic ring-containing monomer (m1) disclosed herein. One preferred example of the aromatic ring-containing monomer that can be used as monomer L is m-phenoxybenzyl acrylate (Tg of the homopolymer: -35 °C). Another preferred example is phenoxydiethylene glycol acrylate (Tg of the homopolymer: -35 °C).

[0104] The content of monomer L in monomer (m1) is not particularly limited and may be, for example, 5% by weight or more, may be 25% by weight or more, or may be 40% by weight or more. In some embodiments, from the perspective of facilitating the obtaining of an adhesive that achieves a higher level of compatibility between a high refractive index and flexibility, the content of monomer L in monomer (m1) may be, for example, 50% by weight or more, may be 60% by weight or more, may be 70% by weight or more, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. Substantially 100% by weight of monomer (A1) may be monomer L. Also, in some embodiments, from the perspective of achieving a good balance between flexibility and a high refractive index suitable for an adhesive, for example, the content of monomer L in monomer (m1) may be less than 100% by weight, may be 98% by weight or less, may be 90% by weight or less, may be 80% by weight or less, may be 70% by weight or less, may be 50% by weight or less, may be 25% by weight or less, or may be 10% by weight or less. The technology disclosed herein can also be implemented in embodiments where the content of monomer L in monomer (m1) is less than 5% by weight. It is not necessary to use monomer L.

[0105] The content of monomer L in the monomer components constituting the acrylic polymer may be, for example, 3% by weight or more, may be 10% by weight or more, and may be 25% by weight or more. In some embodiments, from the perspective of facilitating the obtaining of an adhesive that achieves a higher level of compatibility between high refractive index and flexibility, the content of monomer L in the monomer components may be, for example, more than 35% by weight, preferably more than 50% by weight, may be more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, and may be 95% by weight or more. The content of monomer L in the above monomer components may be 100% by weight, but in consideration of the balance between high refractive index and adhesive properties and / or optical properties, it is advantageous to be less than 100% by weight, preferably approximately 99% by weight or less, more preferably 98% by weight or less, may be 96% by weight or less, may be 95% by weight or less, may be 93% by weight or less, may be 90% by weight or less, may be 85% by weight or less, may be 80% by weight or less, may be 75% by weight or less. In some embodiments, the content of monomer L in the above monomer components may be 70% by weight or less, may be 50% by weight or less, may be 25% by weight or less, may be 15% by weight or less, and may be 5% by weight or less. The technology disclosed herein can also be implemented in embodiments where the content of monomer L in the above monomer components is less than 3% by weight.

[0106] In some embodiments, the glass transition temperature Tg based on the composition of monomer (m1) m1 is advantageously approximately 20°C or lower, preferably 10°C or lower (for example, 5°C or lower), more preferably 0°C or lower, and even more preferably -10°C or lower, may be -20°C or lower, and may be -25°C or lower, from the perspective of the flexibility of the adhesive. The glass transition temperature Tg m1 has no particular lower limit. Considering the balance with the refractive index improvement effect, in some embodiments, the glass transition temperature Tg m1 may be, for example, -70°C or higher, may be -55°C or higher, and may be -45°C or higher. The technology disclosed herein relates to the glass transition temperature Tg m1It can also be preferably implemented in an embodiment where it is, for example, -40°C or higher, -35°C or higher, -33°C or higher, -30°C or higher, or -25°C or higher.

[0107] Here, the glass transition temperature Tg based on the composition of monomer (m1) m1 refers to the Tg obtained by the Fox's equation described later based on the composition of only monomer (m1) among the monomer components constituting the acrylic polymer. The glass transition temperature Tg m1 is obtained by applying the Fox's equation described later only to monomer (m1) among the monomer components constituting the acrylic polymer, and can be calculated from the glass transition temperature of the homopolymer of each aromatic ring-containing monomer used as monomer (m1) and the weight fraction of each aromatic ring-containing monomer in the total amount of monomer (m1). In an embodiment where only one type of monomer is used as monomer (m1), the Tg of the homopolymer of the monomer and the glass transition temperature Tg m1 are the same.

[0108] In some embodiments, as the aromatic ring-containing monomer (m1), monomer L (i.e., an aromatic ring-containing monomer having a Tg of the homopolymer of 10°C or lower, preferably 5°C or lower, more preferably -10°C or lower, still more preferably -20°C or lower, for example -25°C or lower) and monomer H having a Tg higher than 10°C can be used in combination. 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 where the content of the aromatic ring-containing monomer (m1) in the monomer component is relatively large, the high refractive index and flexibility of the adhesive can be made compatible at a higher level. The usage ratio of monomer L to monomer H can be set so that such an effect is preferably exhibited and is not particularly limited. For example, it is preferable to set the usage ratio of monomer L to monomer H so as to satisfy any of the above-described glass transition temperatures Tg. m1

[0109] 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-condensed aromatic rings are directly chemically bonded (for example, a biphenyl structure). For example, an acrylic polymer composed of a monomer component having a composition in which the content of a compound containing a structure in which two or more non-condensed aromatic rings are directly chemically bonded is less than 5% by weight (more preferably less than 3% by weight, and may be 0% by weight) is preferred. Limiting the amount of the compound containing a structure in which two or more non-condensed aromatic rings are directly chemically bonded in this way can be advantageous from the viewpoint of realizing an adhesive that balances flexibility, adhesiveness, and a high refractive index.

[0110] (Monomer (m2)) In some embodiments of the technology disclosed herein, the monomer component constituting the acrylic polymer may further contain a monomer (m2) in addition to the above monomer (m1). The above monomer (m2) is a monomer corresponding to 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 above hydroxyl group-containing monomer is a compound having at least one hydroxyl group and at least one ethylenically unsaturated group in one molecule. The above carboxyl group-containing monomer is a compound containing at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. Monomer (m2) can be useful for introducing crosslinking points into the acrylic polymer or imparting appropriate cohesiveness to the adhesive. Monomer (m2) can be used alone or in combination of two or more. Monomer (m2) is typically a monomer that does not contain an aromatic ring.

[0111] Examples of the ethylenically unsaturated group of monomer (m2) include a (meth)acryloyl group, a vinyl group, a (meth)allyl group, and the like. 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, as monomer (m2), a compound in which the number of ethylenically unsaturated groups contained in one molecule is 1 (that is, a monofunctional monomer) is preferably used.

[0112] Examples of the hydroxyl group-containing monomer 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. Examples of the hydroxyl group-containing monomer that can be preferably used include 4-hydroxybutyl acrylate (Tg: -40°C) and 2-hydroxyethyl acrylate (Tg: -15°C). From the viewpoint of improving flexibility in the room temperature range, 4-hydroxybutyl acrylate having a lower Tg is more preferable. In a preferred embodiment, 50% by weight or more (for example, more than 50% by weight, more than 70% by weight, or more than 85% by weight) of the monomer (m2) can be 4-hydroxybutyl acrylate. The hydroxyl group-containing monomer can be used alone or in combination of two or more.

[0113] In some embodiments where a hydroxyl group-containing monomer is used as the monomer (m2), the hydroxyl group-containing monomer can be one or more selected from compounds having no methacryloyl group. Preferable examples of the hydroxyl group-containing monomer having no methacryloyl group include the various hydroxyalkyl acrylates described above. For example, it is preferable that more than 50% by weight, more than 70% by weight, or more than 85% by weight of the hydroxyl group-containing monomer used as the monomer (m2) is hydroxyalkyl acrylate. By using hydroxyalkyl acrylate, a hydroxyl group that helps provide crosslinking points and impart appropriate cohesiveness can be introduced into the acrylic polymer, and an adhesive having good flexibility and adhesiveness in the room temperature range is more easily obtained compared to the case where only the corresponding hydroxyalkyl methacrylate is used.

[0114] Examples of the carboxy group-containing monomer include, but are not limited to, acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, and itaconic acid, maleic acid, fumaric acid, crotonic acid, isocrotonic acid and the like. Examples of the carboxy group-containing monomer that can be preferably used include acrylic acid and methacrylic acid. The carboxy group-containing monomer can be used alone or in combination of two or more. The hydroxy group-containing monomer and the carboxy group-containing monomer may be used in combination.

[0115] The content of the monomer (m2) in the monomer component constituting the acrylic polymer is not particularly limited and can be set according to the purpose. In some embodiments, the content of 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 use effect, in some embodiments, the content of the monomer (A2) is preferably 1% by weight or more, may be 2% by weight or more, and may be 4% by weight or more. The upper limit of the content of the monomer (m2) in the monomer component is set so that the total with the content of 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, and from the viewpoint of relatively increasing the content of the monomer (m1) to facilitate an increase in refractive index, it is preferably 20% by weight or less, more preferably 15% by weight or less, may be less than 12% by weight, may be less than 10% by weight, and may be less than 7% by weight.

[0116] In an embodiment where a hydroxyl group-containing monomer is used as the monomer (m2), the content of the hydroxyl group-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 group-containing monomer is preferably 1% by weight or more of the monomer component, may be 2% by weight or more, or may be 4% by weight or more. The upper limit of the content of the hydroxyl group-containing monomer in the monomer component is set so that the total with the content of other monomers does not exceed 100% by weight. For example, it is appropriate to set it to 30% by weight or less or 25% by weight or less. From the viewpoint of relatively increasing the content of the monomer (m1) to facilitate an increase in refractive index, it is preferably 20% by weight or less, more preferably 15% by weight or less, may be less than 12% by weight, may be less than 10% by weight, or may be less than 7% by weight.

[0117] In an embodiment where a carboxyl group-containing monomer is used as the 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% by weight or more (preferably 0.1% by weight or more, more preferably 0.3% by weight or more). In some embodiments, the content of the carboxyl group-containing monomer may be 1% by weight or more, may be 2% by weight or more, or may be 4% by weight or more. The upper limit of the content of the carboxyl group-containing monomer in the monomer component is set so that the total with the usage amount of other monomers does not exceed 100% by weight. For example, it is appropriate to set it to 30% by weight or less or 25% by weight or less. From the viewpoint of relatively increasing the content of the monomer (m1) to facilitate an increase in refractive index, it is preferably 20% by weight or less, more preferably 15% by weight or less, may be less than 12% by weight, or may be less than 10% by weight. In some embodiments, from the viewpoint of improving the flexibility of the pressure-sensitive adhesive, it is advantageous that the content of the carboxyl group-containing monomer is less than 7% by weight, preferably less than 5% by weight, may be less than 3% by weight, may be less than 1% by weight, or may be less than 0.5% by weight. The technology disclosed herein can be preferably implemented, for example, in an embodiment where only a hydroxyl group-containing monomer is used as the monomer (m2), that is, in an embodiment where a carboxyl group-containing monomer is not used.

[0118] The total content of the monomer (m1) and the monomer (m2) in the monomer component constituting the acrylic polymer may be, for example, 31% by weight or more, preferably 51% by weight or more, may be 61% by weight or more, or may be 71% by weight or more. In some embodiments, the total content of the monomer (m1) and the monomer (m2) in the monomer component constituting the acrylic polymer may be, for example, 76% by weight or more, preferably 81% by weight or more, may be 86% by weight or more, may be 91% by weight or more, may be 96% by weight or more, may be 99% by weight or more, or may be substantially 100% by weight, from the viewpoint of preferably facilitating the exhibition of the effects of these monomers.

[0119] (Monomer m3) The monomer components constituting the acrylic polymer may, if necessary, contain monomers other than the above-mentioned monomer (m1) and the above-mentioned monomer (m2). As an example of such an optional component, an alkyl (meth)acrylate (hereinafter also referred to as "monomer (m3)") can be mentioned. Monomer (m3) can be useful for adjusting the flexibility of the adhesive and improving the compatibility within the adhesive.

[0120] As monomer (m3), an alkyl (meth)acrylate having a linear or branched alkyl group with 1 to 20 carbon atoms (that is, C 1-20 of) at the ester terminal can be preferably used. C 1-20 Specific examples of the alkyl (meth)acrylate 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, 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, etc., but are not limited thereto.

[0121] In some embodiments, at least a part of the monomer (m3) may preferably be an alkyl (meth)acrylate whose homopolymer has a Tg of -20°C or lower (more preferably -40°C or lower, for example -50°C or lower). Such an alkyl (meth)acrylate with a low Tg can help improve the flexibility of the adhesive. The lower limit of the Tg of the above 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 above low-Tg alkyl (meth)acrylate include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), isononyl acrylate (iNA), and the like.

[0122] In some embodiments where the monomer (m3) is used, from the viewpoints of flexibility, adhesiveness, etc., it is preferable that at least a part 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, still more preferably 90% by weight or more) of the monomer (m3) is an alkyl acrylate. An embodiment where only one or more alkyl acrylates are used as the monomer (m3) and no alkyl methacrylate is used may also be possible.

[0123] In an embodiment where the monomer component contains an alkyl (meth)acrylate, the content of the alkyl (meth)acrylate in the monomer component can be set so that its use effect is appropriately exerted. In some embodiments, the content of the above 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 above alkyl (meth)acrylate may be 15% by weight or more, 30% by weight or more, or 45% by weight or more. The upper limit of the content of monomer (m3) in the monomer component is set so that the total with the content of other monomers does not exceed 100% by weight, and can be, for example, less than 50% by weight. In some embodiments, the content of the above monomer (m3) can be, for example, less than 35% by weight. Generally, since the refractive index of alkyl (meth)acrylate is relatively low, in order to increase the refractive index, it is advantageous to limit the content of monomer (m3) in the monomer component and relatively increase the content of monomer (m1). From this perspective, the content of monomer (m3) is advantageously 24% by weight or less of the monomer component, 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. It is not necessary to substantially use monomer (m3).

[0124] (Other monomers) The monomer component constituting the acrylic polymer may optionally contain monomers other than the above monomers (m1), (m2), and (m3) (hereinafter referred to as "other monomers"). The above other monomers can be used, for example, for the purpose of adjusting the Tg of the acrylic polymer, adjusting the adhesive performance, improving the compatibility in the adhesive layer, etc. The above other monomers can be used alone or in combination of two or more.

[0125] Examples of the above-mentioned other monomers include monomers having functional groups other than hydroxyl groups and carboxyl groups (functional group-containing monomers). For example, as other monomers that can improve the cohesive strength and heat resistance of the adhesive, sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, cyano group-containing monomers, etc. can be mentioned. Further, a functional group that can serve as a cross-linking point can be introduced into the acrylic polymer, or as a monomer that can contribute to the improvement of the peel strength and the improvement of the compatibility in the adhesive layer, amide group-containing monomers (for example, (meth)acrylamide, N-methylol (meth)acrylamide, etc.), amino group-containing monomers (for example, aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, etc.), monomers having a nitrogen atom-containing ring (for example, N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), imide group-containing monomers, epoxy group-containing monomers, keto group-containing monomers, isocyanate group-containing monomers, alkoxysilyl group-containing monomers, etc. can be mentioned. Among the monomers having a nitrogen atom-containing ring, there are those that also fall under the category of amide group-containing monomers, such as N-vinyl-2-pyrrolidone. The same applies to the relationship between the above-mentioned monomers having a nitrogen atom-containing ring and amino group-containing monomers.

[0126] Other monomers that can be used in addition to the above-mentioned functional group-containing monomers include vinyl ester-based monomers such as vinyl acetate; non-aromatic ring-containing (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; olefin-based 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-based monomers such as methyl vinyl ether; etc. A preferred example of other monomers that can be used for the purpose of improving the flexibility of the adhesive is ethoxyethoxyethyl acrylate (alias: ethyl carbitol acrylate, Tg of homopolymer: -67°C).

[0127] When using the above-mentioned other monomers, the amount used is not particularly limited and can be appropriately set within the range where the total amount of the monomer components does not exceed 100% by weight. In some embodiments, from the perspective of facilitating the refractive index improvement effect by using monomer (m1), the content of the above-mentioned other monomers in the monomer components can be, for example, approximately 35% by weight or less, and it is appropriate to be approximately 25% by weight or less (e.g., 0 to 25% by weight), and may be approximately 20% by weight or less (e.g., 0 to 20% by weight), may be approximately 10% by weight or less, may be approximately 5% by weight or less, and may be, for example, approximately 1% by weight or less. The technology disclosed herein can be preferably implemented in an embodiment where the monomer components substantially do not contain the above-mentioned other monomers.

[0128] In some embodiments, the monomer components constituting the acrylic polymer can have a composition in which the amount of the methacryloyl group-containing monomer used is suppressed to a predetermined amount or less. The amount of the methacryloyl group-containing monomer used in the monomer components can be, for example, less than 5% by weight, may be less than 3% by weight, may be less than 1% by weight, and may be less than 0.5% by weight. Limiting the amount of the methacryloyl group-containing monomer used in this way can be advantageous from the perspective of realizing an adhesive that well balances flexibility, adhesiveness, and a high refractive index. The monomer components constituting the acrylic polymer may have a composition that does not contain a methacryloyl group-containing monomer (for example, a composition consisting only of acryloyl group-containing monomers).

[0129] In some embodiments, the monomer components constituting the base polymer (e.g., acrylic polymer) of the high refractive index adhesive layer preferably have the amount of carboxy group-containing monomer restricted from the viewpoint of suppressing coloring or discoloration (e.g., yellowing) of the adhesive layer. The amount of carboxy group-containing monomer in the monomer components may be, for example, less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, may be less than 0.1% by weight, or may be less than 0.05% by weight. The fact that the amount of carboxy group-containing monomer is restricted in this way is also advantageous from the viewpoint of suppressing corrosion of metal materials (e.g., metal wirings, metal films, etc. that may exist on the adherend) that can be disposed in contact with or in proximity to the high refractive index adhesive layer. The technology disclosed herein can be preferably implemented in an embodiment where the monomer components do not contain carboxy group-containing monomers. For the same reason, in some embodiments, the monomer components constituting the base polymer of the high refractive index adhesive layer preferably have the amount of monomers having acidic functional groups (including sulfonic acid groups, phosphoric acid groups, etc. in addition to carboxy groups) restricted. As the amount of acidic functional group-containing monomers in the monomer components of such embodiments, the preferred amounts of carboxy group-containing monomers described above can be applied. The technology disclosed herein can be preferably implemented in an embodiment where the monomer components do not contain acidic group-containing monomers (i.e., an embodiment where the base polymer of the high refractive index adhesive layer is acid-free).

[0130] (The glass transition temperature Tg of the base polymer T ) In some embodiments, the base polymer (e.g., acrylic polymer) of the adhesive layer has a glass transition temperature Tg T based on the composition of the monomer components constituting the polymer, which is suitably about 20°C or lower, preferably about 10°C or lower, more preferably 0°C or lower, may be -10°C or lower, may be -20°C or lower, may be -25°C or lower, may be -28°C or lower, or may be -30°C or lower. The glass transition temperature Tg TA low value can be advantageous from the viewpoint of improving the flexibility of the pressure-sensitive adhesive. Further, the glass transition temperature Tg T may be, for example, -60°C or higher, preferably -50°C or higher, more preferably above -45°C, may be above -40°C, may be above -35°C, may be above -25°C, may be above -15°C, or may be above -5°C, from the viewpoint of facilitating an increase in the refractive index of the pressure-sensitive adhesive.

[0131] Here, the glass transition temperature Tg of the polymer T refers to the glass transition temperature determined by Fox's equation based on the composition of the monomer components constituting the polymer, unless otherwise specified. Fox's equation is a relational equation between the Tg of a copolymer and the glass transition temperatures Tgi of the homopolymers obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below. 1 / Tg = Σ(Wi / Tgi) In the above Fox's equation, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio based on weight), and Tgi represents the glass transition temperature of the homopolymer of monomer i (unit: K). As the glass transition temperature of the homopolymer used for calculating Tg, the values described in known materials such as "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. For monomers for which multiple types of values are described in the above Polymer Handbook, the highest value shall be adopted. When the Tg of the homopolymer is not described in known materials, the value obtained by the measurement method described in JP-A-2007-51271 shall be used.

[0132] (Method for preparing the base polymer) In the technology disclosed herein, the method for obtaining the base polymer of the high refractive index pressure-sensitive adhesive layer (for example, the acrylic polymer (A) composed of the monomer components as described above) is not particularly limited. For example, the above description of the method for preparing the acrylic polymer (F) can also be applied to the method for preparing the base polymer of the high refractive index pressure-sensitive adhesive layer.

[0133] (Refractive index increasing agent) In some aspects of the technology disclosed herein, the high refractive index adhesive layer (e.g., an acrylic adhesive layer) may contain, in addition to the base polymer, a refractive index increasing agent as needed. Here, the refractive index increasing agent as used herein refers to a material that can increase the refractive index of the adhesive layer by its use. As the refractive index increasing agent, a material having a higher refractive index than the refractive index of the adhesive layer containing the refractive index increasing agent can be preferably used. Also, as the refractive index increasing agent, a material having a higher refractive index than the base polymer (e.g., acrylic polymer (A)) of the adhesive layer containing the refractive index increasing agent can be preferably used. By the appropriate use of the refractive index increasing agent, a higher refractive index and practical adhesive performance can be preferably achieved simultaneously. In some aspects, the refractive index increasing agent is preferably an organic material. The organic material used as the refractive index increasing agent may be a polymer or a non-polymer. Also, it may or may not have a polymerizable functional group. The refractive index increasing agent can be used alone or in combination of two or more kinds.

[0134] Refractive index increasing agent (e.g., additive (H) described later ROThe refractive index of (( )) can be set within an appropriate range in relation to the refractive index of the base polymer, and thus is not limited to a specific range. The refractive index of the refractive index improver can be selected, for example, from a range 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 improver is advantageously 1.58 or more, preferably 1.60 or more, more preferably 1.63 or more, may be 1.65 or more, may be 1.70 or more, or may be 1.75 or more. According to a refractive index improver with a higher refractive index, the target refractive index can be achieved even with the use of a smaller amount of the refractive index improver. This is preferable from the viewpoint of suppressing the deterioration of the adhesive properties and optical properties. The upper limit of the refractive index of the refractive index improver is not particularly limited, but from the viewpoints of compatibility in the adhesive and ease of achieving both high refractive index and flexibility suitable for an adhesive, for example, it is 3.000 or less, may be 2.500 or less, may be 2.000 or less, may be 1.950 or less, may be 1.900 or less, or may be 1.850 or less.

[0135] In some embodiments, the refractive index improver (for example, the additive (H described later) RO ) has a refractive index n b and the refractive index n a of the base polymer, that is, n b -n a (hereinafter also referred to as "Δn A ").) is set to be greater than 0. In some embodiments, Δn A is, for example, 0.02 or more, may be 0.05 or more, may be 0.07 or more, may be 0.10 or more, may be 0.15 or more, may be 0.20 or more, or may be 0.25 or more. By selecting the base polymer and the refractive index improver so that Δn A becomes larger, the refractive index improving effect by the use of the refractive index improver tends to be higher. Also, from the viewpoints of compatibility in the adhesive layer and transparency of the adhesive layer, in some embodiments, Δn A may be, for example, 0.70 or less, may be 0.60 or less, may be 0.50 or less, may be 0.40 or less, or may be 0.35 or less.

[0136] In some embodiments, the refractive index n of the refractive index improver (e.g., the additive (H described below RO )) b and the refractive index n of the pressure-sensitive adhesive layer containing the refractive index improver T The difference between them, that is, n b -n T (hereinafter also referred to as "Δn B ").) is set to be greater than 0. In some embodiments, Δn B is, for example, 0.02 or more, may be 0.05 or more, may be 0.07 or more, may be 0.10 or more, may be 0.15 or more, or may be 0.20 or more or 0.25 or more. By selecting the composition of the pressure-sensitive adhesive layer and the refractive index improver so that Δn B becomes larger, the refractive index improvement effect due to the use of the refractive index improver tends to be higher. Also, from the viewpoints of compatibility within the pressure-sensitive adhesive layer and transparency of the pressure-sensitive adhesive layer, etc., in some embodiments, Δn B may be, for example, 0.70 or less, may be 0.60 or less, may be 0.50 or less, may be 0.40 or less, or may be 0.35 or less.

[0137] The amount of the refractive index improver used with respect to 100 parts by weight of the base polymer (when a plurality of types of refractive index improvers 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 the refractive index improver used with respect to 100 parts by weight of the 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, may be 7 parts by weight or more, may be 10 parts by weight or more, may be 15 parts by weight or more, or may be 20 parts by weight or more. Further, in some embodiments, the amount of the refractive index improver used with respect to 100 parts by weight of the 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 the deterioration of the adhesive properties and optical properties, it is advantageously 60 parts by weight or less, and preferably 45 parts by weight or less. In some embodiments that place more emphasis on the adhesive properties and optical properties, the amount of the refractive index improver used with respect to 100 parts by weight of the base polymer may be, for example, 30 parts by weight or less, may be 20 parts by weight or less, may be 15 parts by weight or less, may be 10 parts by weight or less, may be 5 parts by weight or less, or may be 3 parts by weight or less. The technology disclosed herein can also be preferably implemented in embodiments where the amount of the refractive index improver used with respect to 100 parts by weight of the base polymer in the adhesive layer is less than 1 part by weight or where the refractive index improver is not substantially used. Here, not substantially used means not used at least intentionally.

[0138] (Additive (H RO )) In some embodiments, as the refractive index improver, an organic material having a higher refractive index than the base polymer can be preferably employed. Hereinafter, such an organic material may be referred to as "additive (H RO )". Here, the above "H RO " represents an organic material (Organic material) having a high refractive index (High Refractive index). The base polymer (for example, an acrylic polymer, preferably acrylic polymer (A)) and the additive (H ROBy using in combination with [( RO ), an adhesive that more suitably balances the refractive index and the adhesive properties (such as peel strength and flexibility) and / or the optical properties (such as total light transmittance and haze value) can be realized. The organic material used as the additive (H RO ) may be a polymer or a non-polymer. Further, it may or may not have a polymerizable functional group. The additive (H

[0139] ) can be used alone or in combination of two or more. RO The refractive index of the additive (H

[0140] ) is measured under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25 °C using an Abbe refractometer, similar to the refractive index of the monomer. When the manufacturer or the like provides a nominal value of the refractive index at 25 °C, that nominal value can be adopted. RO The molecular weight of the organic material used as the additive (H RO ) is not particularly limited and can be selected according to the purpose. The molecular weight of the additive (H RO ) can be selected, for example, from the range of 30,000 or less. Further, the additive (H RO ) is preferably a polymer or a non-polymer having a lower molecular weight than the base polymer. From the viewpoint of well-balancing the effect of increasing the refractive index and other properties (for example, flexibility suitable for an adhesive, optical properties such as haze), in some embodiments, the molecular weight of the additive (H RO ) 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. The fact that the molecular weight of the additive (H RO ) is not too large can be advantageous from the viewpoint of improving the compatibility in the adhesive layer. Further, the molecular weight of the additive (H RO ) may be, for example, 130 or more, and may also be 150 or more. In some embodiments, the molecular weight of the additive (H ROFrom the perspective of increasing the refractive index, it 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 and less than 5000) is used as the additive (H RO ) can be used. As the molecular weight of the additive (H RO ), for a non-polymer or a polymer with a low degree of polymerization (for example, about a dimer to pentamer), the molecular weight calculated based on the chemical structure can be used. When the additive (H RO ) is a polymer with a higher degree of polymerization, the weight-average molecular weight (Mw) based on GPC performed under appropriate conditions can be used. When the nominal value of the molecular weight is provided by the manufacturer or the like, that nominal value can be adopted.

[0141] Examples of organic materials that can be alternatives for the additive (H RO ) include, but are not limited to, organic compounds having an aromatic ring, organic compounds having a heterocyclic ring (which may be an aromatic ring or a non-aromatic heterocyclic ring).

[0142] The aromatic ring of the above-mentioned organic compound having an aromatic ring (hereinafter also referred to as "aromatic ring-containing compound") used as the additive (H RO ) can be selected from the same ones as the aromatic ring of the compound used as the monomer (m1).

[0143] The above aromatic ring may or may not have one or more substituents on the ring-constituting atoms. When having substituents, examples of the substituents 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, a bromine atom, etc.), a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group, etc. In the substituents containing carbon atoms, the number of carbon atoms contained in the substituent is, for example, 1 to 10, preferably 1 to 6, more preferably 1 to 4, still more preferably 1 to 3, and may be, for example, 1 or 2. In some embodiments, the above aromatic ring may be an aromatic ring having no substituent on the ring-constituting atoms or having 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).

[0144] Additive (H RO ) Examples of the aromatic ring-containing compound that can be used as include, for example: a compound that can be used as monomer (m1); an oligomer containing a compound that can be used as monomer (m1) as a monomer unit; a compound having a structure in which a group having an ethylenically unsaturated group (which may be a substituent bonded to the ring-constituting atom) or a part constituting the ethylenically unsaturated group in the group is replaced with a hydrogen atom or a group having no ethylenically unsaturated group (such as 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.) from the compound that can be used as monomer (m1); etc., but are not limited thereto. Additive (H RO)Non-limiting specific examples of the aromatic ring-containing compound that can be used as include 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 monomer having the fluorene structure described above, the monomer having a dinaphthothiophene structure, the monomer having a dibenzothiophene structure, etc.; aromatic ring-containing compounds having no ethylenically unsaturated group such as 3-phenoxybenzyl alcohol, dinaphthothiophene and its derivatives (for example, a compound having a structure in which one or more substituents selected from a hydroxy group, a methanol group, a diethanol group, a glycidyl group, etc. are bonded to 1 or 2 or more of the dinaphthothiophene rings), etc. can be included. Further, the aromatic ring-containing compound can be an oligomer (preferably an oligomer having a molecular weight of about 5000 or less, more preferably about 1000 or less. For example, a low polymer of about 2 to 5 monomers) containing such an aromatic ring-containing monomer as a monomer unit. The above oligomer can 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 and other monomers; etc. As the above other monomers, one or more monomers having no aromatic ring can be used.

[0145] In some embodiments, the additive (H ROAs for [the compound], since a high refractive index increasing effect can be easily obtained, an organic compound having two or more aromatic rings in one molecule (hereinafter, also referred to as "compound containing a plurality of aromatic rings") can be preferably employed. The compound containing a plurality of aromatic rings may or may not have a polymerizable functional group such as an ethylenically unsaturated group. Further, the compound containing a plurality of aromatic rings may be a polymer or a non-polymer. Further, the above polymer may be an oligomer (preferably an oligomer having a molecular weight of approximately 5000 or less, more preferably approximately 1000 or less. For example, a low polymer of about a dimer to pentamer) containing a compound containing a plurality of aromatic rings as a monomer unit. The above oligomer may be, for example: a homopolymer of a compound containing a plurality of aromatic rings; a copolymer of one or more compounds containing a plurality of aromatic rings; a copolymer of one or more compounds containing a plurality of aromatic rings and another monomer; and the like. The above another monomer may be an aromatic ring-containing monomer that does not correspond to the compound containing a plurality of aromatic rings, a monomer having no aromatic ring, or a combination thereof.

[0146] Non-limiting examples of the compound containing a plurality of aromatic rings include a compound having a structure in which two or more non-condensed aromatic rings are bonded via a linking group, a compound having a structure in which two or more non-condensed aromatic rings are directly (i.e., without intervening other atoms) chemically bonded, a compound having a condensed aromatic ring structure, a compound having a fluorene structure, a compound having a dinaphthothiophene structure, a compound having a dibenzothiophene structure, and the like. The compound containing a plurality of aromatic rings can be used alone or in combination of two or more.

[0147] Specific examples of the compound having the above fluorene structure include monomers having the above-described fluorene structure, oligomers which are homopolymers or copolymers of such monomers, and 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), 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (refractive index: 1.65), etc., and 9,9-bis(phenyl)fluorene and its derivatives.

[0148] Specific examples of the compound having the above dinaphthothiophene structure include monomers having the above-described dinaphthothiophene structure, oligomers which are homopolymers or copolymers of such monomers, and dinaphthothiophene (refractive index: 1.808); hydroxyalkyldinaphthothiophenes such as 6-hydroxymethyldinaphthothiophene (refractive index: 1.766); dihydroxydinaphthothiophenes such as 2,12-dihydroxydinaphthothiophene (refractive index: 1.750); dihydroxyalkyloxydinaphthothiophenes such as 2,12-dihydroxyethyloxydinaphthothiophene (refractive index: 1.677); diglycidyloxydinaphthothiophenes such as 2,12-diglycidyloxydinaphthothiophene (refractive index 1.723); dinaphthothiophenes having two or more ethylenically unsaturated groups such as 2,12-diallyloxydinaphthothiophene (abbreviation: 2,12-DAODNT, refractive index 1.729); etc., and dinaphthothiophene and its derivatives.

[0149] Specific examples of the compound having the above dibenzothiophene structure include monomers having the above-described dibenzothiophene structure, oligomers which are homopolymers or copolymers of such monomers, and dibenzothiophene (refractive index: 1.607), 4-dimethyldibenzothiophene (refractive index: 1.617), 4,6-dimethyldibenzothiophene (refractive index: 1.617), etc.

[0150] Additive (H RO) Examples of organic compounds having a heterocyclic ring (hereinafter also referred to as heterocyclic ring-containing organic compounds) that can be an option include thioepoxy compounds, compounds having a triazine ring, and the like. 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 (for example, 3 to 40, preferably 5 to 20) in one molecule. Since the triazine ring has aromaticity, compounds having a triazine ring are also included in the concept of the above aromatic ring-containing compounds, and compounds having a plurality of triazine rings are also included in the concept of the above compounds containing a plurality of aromatic rings.

[0151] In some embodiments, a compound having no ethylenically unsaturated group may be preferably employed as the additive (H RO ). Thereby, alteration of the pressure-sensitive adhesive composition due to heat or light (such as progress of gelation and decrease in leveling property due to increase in viscosity) can be suppressed, and storage stability can be enhanced. Employing an additive (H RO ) having no ethylenically unsaturated group is also preferable from the viewpoint of suppressing dimensional changes, deformation (such as warping and undulation), generation of optical distortion, etc. caused by the reaction of ethylenically unsaturated groups in the pressure-sensitive adhesive layer containing the additive (H RO ), a laminate (such as a laminated sheet) containing the pressure-sensitive adhesive layer, and the like.

[0152] In an embodiment where an oligomer is used as the additive (H RO ), the oligomer can be obtained by polymerizing the corresponding monomer component by a known method. When the above oligomer is produced by radical polymerization, a polymerization initiator, a chain transfer agent, an emulsifier, etc. used for radical polymerization can be appropriately added to the above monomer component to carry out the polymerization. The polymerization initiator, chain transfer agent, emulsifier, etc. used for the above 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 the polymerization initiator and chain transfer agent used and the reaction conditions, and the amount used is appropriately adjusted according to these types. Examples of the chain transfer agent include lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, α-thioglycerol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, and the like. The chain transfer agent may be used alone or in combination of two or more. The amount of the chain transfer agent used can be set so as to obtain an oligomer having a desired weight average molecular weight according to the composition of the monomer components used in the synthesis of the oligomer, the type of the chain transfer agent, and the like. In some embodiments, the amount of the chain transfer agent used relative to 100 parts by weight of the total amount of the monomers used in the synthesis of the oligomer is preferably about 15 parts by weight or less, may be 10 parts by weight or less, or may be about 5 parts by weight or less. The lower limit of the amount of the chain transfer agent used relative to 100 parts by weight of the total amount of the monomers used in the synthesis of the oligomer is not particularly limited, and may be, for example, 0.01 part by weight or more, may be 0.1 part by weight or more, may be 0.5 part by weight or more, or may be 1 part by weight or more.

[0153] In the embodiment of using the additive (H RO ) as the refractive index improver, the amount of the additive (H RO ) used relative to 100 parts by weight of the base polymer (when a plurality of types 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 pressure-sensitive adhesive, the amount of the additive (H RO ) used relative to 100 parts by weight of the base polymer can be, for example, 1 part by weight or more, advantageously 3 part by weight or more, preferably 5 part by weight or more, may be 7 part by weight or more, may be 10 part by weight or more, may be 15 part by weight or more, or may be 20 part by weight or more. In some embodiments, the amount of the additive (H RO ) used relative to 100 parts by weight of the base polymer can be, for example, 80 part by weight or less, and from the viewpoint of achieving a good balance between increasing the refractive index of the pressure-sensitive adhesive and suppressing the deterioration of the adhesive properties and optical properties, it is advantageously 60 part by weight or less, and preferably 45 part by weight or less. In some embodiments that place more emphasis on the adhesive properties and optical properties, the additive (HRO ) may be used in an amount of, 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.

[0154] (Plasticizing material) In some embodiments, the high refractive index adhesive layer may contain a plasticizing material having a lower molecular weight than the base polymer of the adhesive layer. By using the plasticizing material, the flexibility of the high refractive index adhesive layer can be increased, and the adhesion to the adherend, the overall flexibility, the followability to deformation, etc. can be improved. From the viewpoints of compatibility and transparency in the adhesive layer, an organic material may preferably be employed as the plasticizing material. The plasticizing material may be a material that can also be used as the refractive index improver described above (for example, the above additive (H RO )) may also be a material that can be used.

[0155] The molecular weight of the plasticizing material only needs to be lower than that of the base polymer and is not particularly limited. In some embodiments, from the viewpoint of facilitating the manifestation of the plasticizing effect, 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 (for example, less than 1,000), may be less than 800, may be less than 600, may be less than 500, or may be less than 400. The fact that the molecular weight of the plasticizing material is not too large can be advantageous from the viewpoint of improving compatibility in the adhesive layer and the like. Also, in some embodiments, from the viewpoint of facilitating the exertion of a sufficient plasticizing effect, the molecular weight of the plasticizing material is suitably 130 or more, preferably 150 or more, may be 170 or more, may be 200 or more, may be 250 or more, or may be 300 or more. In some embodiments, the molecular weight of the plasticizing material may be 500 or more, 1,000 or more, or 2,000 or more. The fact that the molecular weight of the plasticizing material is not too low is also preferable from the viewpoints of the heat resistance performance of the adhesive layer and the suppression of contamination of the adherend.

[0156] Non-limiting examples of compounds that can be alternatives to the plasticizable material include compounds that can be used as monomer (m1) (for example, (meth)acrylates having an aromatic ring such as a benzyl group, a phenoxy group, a naphthyl group, etc., monomers having a fluorene structure, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, etc.); oligomers containing a compound that can be used as monomer (m1) as a monomer unit; compounds having a structure in which a part having an ethylenically unsaturated group in a compound that can be used as monomer (m1) is replaced with a hydrogen atom or a group having no ethylenically unsaturated group (for example, 3-phenoxybenzyl alcohol); etc. In the oligomers containing a compound that can be used as monomer (m1) as a monomer unit, low Tg monomers such as n-butyl acrylate and 2-ethylhexyl acrylate may be copolymerized from the viewpoint of improving flexibility. As the plasticizable material, one or more known plasticizers (for example, phthalate esters, terephthalate esters, adipate esters, adipic acid-based polyesters, benzoic acid glycol esters, etc.) may be used.

[0157] In some embodiments, as the plasticizing material, an organic material having a refractive index of about 1.50 or more (more preferably 1.53 or more) can be preferably used. Specific examples of compounds that can be alternatives for 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)phenyl diphenyl phosphate (refractive index 1.56), trimethylphenyl 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), tris(2,4-di-tert-butylphenyl) phosphite, etc., but are not limited thereto. From the viewpoints of refractive index and compatibility, for example, diethylene glycol dibenzoate can be preferably adopted. The upper limit of the refractive index of the plasticizing material is not particularly limited and can be, for example, 3.00 or less. In some embodiments, from the viewpoints of ease of preparation of the pressure-sensitive adhesive composition and compatibility in the pressure-sensitive adhesive, etc., the refractive index of the plasticizing material is suitably 2.50 or less, advantageously 2.00 or less, may be 1.90 or less, may be 1.80 or less, or may be 1.70 or less. Note that the refractive index of the plasticizing material is measured under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C using an Abbe refractometer, in the same manner as the refractive index of the monomer. When the nominal value of the refractive index at 25°C is provided by the manufacturer or the like, that nominal value can be adopted.

[0158] In an embodiment using a plasticizing material, the amount of the plasticizing material used relative to 100 parts by weight of the 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 the plasticizing material used relative to 100 parts by weight of the base polymer may be, for example, 0.1 part by weight or more, may be 0.5 part by weight or more, and preferably 1 part by weight or more from the viewpoint of obtaining a higher plasticizing effect, more preferably 3 parts by weight or more, may be 5 parts by weight or more, may be 7 parts by weight or more, may be 10 parts by weight or more, may be 15 parts by weight or more, may be 20 parts by weight or more. Further, from the viewpoint of achieving a good balance between increasing the refractive index, transparency and plasticizing effect of the adhesive, it is appropriate that the amount of the plasticizing material used relative to 100 parts by weight of the base polymer is approximately 100 parts by weight or less, preferably 80 parts by weight or less, more preferably 60 parts by weight or less, may be 45 parts by weight or less, may be 35 parts by weight or less, may be 25 parts by weight or less. In some embodiments that place more emphasis on the adhesive properties and optical properties, the amount of the plasticizing material used relative to 100 parts by weight of the base polymer may be 15 parts by weight or less, may be 10 parts by weight or less, may be 5 parts by weight or less.

[0159] (Leveling agent) In some embodiments, the pressure-sensitive adhesive composition used for forming the pressure-sensitive adhesive layer may contain a leveling agent as needed for the purpose of improving the appearance of the pressure-sensitive adhesive layer formed from the composition (for example, improving the uniformity of the thickness) and improving the coatability of the pressure-sensitive adhesive composition. Non-limiting examples of the leveling agent include acrylic leveling agents, fluorine-based leveling agents, silicone-based leveling agents, and the like. The leveling agent can be appropriately selected from commercially available leveling agents and used by a conventional method.

[0160] In some embodiments, as the leveling agent, a polymer (hereinafter also referred to as "polymer (B)") which is a polymer 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 can be preferably used. 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.

[0161] Monomer S1 is not particularly limited, and any monomer containing a polyorganosiloxane skeleton can be used. As monomer S1, those having a structure with a polymerizable reactive group at one end can be preferably used. Among them, a monomer S1 having a polymerizable reactive group at one end and no functional group that causes a cross-linking reaction with the base polymer (for example, an acrylic polymer) of the pressure-sensitive adhesive composition in which the leveling agent is blended at the other end can be preferably adopted. Commercially available products include, for example, one-end reactive silicone oils manufactured by Shin-Etsu Chemical Co., Ltd. (for example, product numbers such as X-22-174ASX, X-22-2426, X-22-2475, KF-2012). Monomer S1 can be used alone or in combination of two or more.

[0162] The functional group equivalent of monomer S1 can be, for example, about 100 g / mol to 30,000 g / mol. In some preferred embodiments, the above functional group equivalent is, for example, 500 g / mol or more, and may be 800 g / mol or more, 1500 g / mol or more, or 2000 g / mol or more. Also, the above functional group equivalent may be, for example, 20,000 g / mol or less, less than 10,000 g / mol, 7000 g / mol or less, or 5500 g / mol or less. When the functional group equivalent of monomer S1 is within the above range, a good leveling effect is likely to be exhibited. In addition, when using two or more types of monomers with different functional group equivalents as monomer S1, the functional group equivalent of monomer S1 can be the sum of the products of the functional group equivalents of the respective types of monomers and their weight fractions.

[0163] Here, the "functional group equivalent" means the weight of the main skeleton (e.g., polydimethylsiloxane) bonded per one functional group. Regarding the unit g / mol, it is converted to 1 mol of functional groups. The functional group equivalent of monomer S1 can be calculated, for example, based on 1 the spectral intensity of 1H-NMR (proton NMR) from nuclear magnetic resonance (NMR). 1 The calculation of the functional group equivalent (g / mol) of monomer S1 based on the spectral intensity of 1H-NMR is 1 performed based on general structural analysis methods related to 1H-NMR spectral analysis, and referring to the description in Japanese Patent No. 5951153 if necessary. In the functional group equivalent of monomer S1, the above functional group means a polymerizable functional group (e.g., ethylenically unsaturated groups such as (meth)acryloyl group, vinyl group, allyl group, etc.).

[0164] The content of monomer S1 in monomer raw material B can be an appropriate value within the range where the desired effect is exhibited using the monomer S1, and is not limited to a specific range. In some embodiments, the content of monomer S1 in monomer raw material B may be, for example, 5 to 60% by weight, may be 10 to 50% by weight, or may be 15 to 40% by weight.

[0165] In addition to monomer S1, monomer raw material B contains an acrylic monomer copolymerizable with monomer S1. Thereby, the compatibility of polymer (B) in the adhesive layer can be improved. Examples of the acrylic monomer that can be used in monomer raw material B include alkyl acrylates. Here, the "alkyl" refers to a chain-like (including linear and branched) alkyl (group) and does not include the alicyclic hydrocarbon groups described later. In some embodiments, monomer raw material B is a C 4-12 alkyl (meth)acrylate (preferably a C4-10 alkyl esters, such as C 6-10 alkyl esters) may be contained. In some other embodiments, monomer raw material B is C 1-18 alkyl ester (preferably C 1-14 alkyl esters, such as C 1-10 alkyl esters) may be contained. Monomer raw material B, as an acrylic monomer, may include, for example, one or more selected from methyl methacrylate (MMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA).

[0166] Other examples of the above acrylic monomers 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 (meth)acrylic acid esters having an alicyclic hydrocarbon group.

[0167] The content of the above (meth)acrylic acid alkyl ester and the (meth)acrylic acid ester having an alicyclic hydrocarbon group in monomer raw material B may be, for example, 10% by weight or more and 95% by weight or less, may be 20% by weight or more and 95% by weight or less, may be 30% by weight or more and 90% by weight or less, may be 40% by weight or more and 90% by weight or less, or may be 50% by weight or more and 85% by weight or less.

[0168] As other examples of monomers that may be included in the monomer raw material B together with the monomer S1, carboxyl 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, (meth)acrylic acid aminoalkyls, vinyl esters, vinyl ethers, olefins, (meth)acrylic acid esters having an aromatic hydrocarbon group, halogen atom-containing (meth)acrylates, etc., which were exemplified above as monomers that can be used for acrylic polymers, can be mentioned.

[0169] The Mw of the polymer (B) may be, for example, 5,000 or more, preferably 10,000 or more, and may also be 15,000 or more. Further, the Mw of the polymer (B) may be, for example, 200,000 or less, preferably 100,000 or less, may also be 50,000 or less, and may also be 30,000 or less. By setting the Mw of the polymer (B) within an appropriate range, suitable compatibility and leveling properties can be exhibited.

[0170] The polymer (B) can be produced, for example, by polymerizing the above-mentioned monomers by a known method such as a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a suspension polymerization method, a photopolymerization method, etc. In order to adjust the molecular weight of the polymer (B), a chain transfer agent can be used as necessary. Examples of the chain transfer agent to be used include compounds having a mercapto group such as t-dodecyl mercaptan, mercaptoethanol, α-thioglycerol; thioglycolic acid esters such as thioglycolic acid and methyl thioglycolate; α-methylstyrene dimer; etc. The amount of the chain transfer agent used is not particularly limited and can be appropriately set so as to obtain a polymer (B) having a 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, may also be 0.2 to 3 parts by weight, and may also be 0.5 to 2 parts by weight.

[0171] The amount of polymer (B) used relative to 100 parts by weight of the base polymer (for example, an acrylic polymer) can be, for example, 0.001 parts by weight or more, may be 0.01 parts by weight or more, and may be 0.03 parts by weight or more from the viewpoint of obtaining a higher usage effect. Also, the amount of the polymer (B) used may be, for example, 3 parts by weight or less, and it is appropriate to be 1 part by weight or less, may be 0.5 parts by weight or less, and may be 0.1 parts by weight or less from the viewpoint of reducing the influence on the refractive index.

[0172] (Inorganic particles) The technology disclosed herein can be preferably implemented in a mode that does not substantially use inorganic particles as a refractive index improver. However, in some modes, it may be acceptable to use inorganic particles as a refractive index improver to the extent that the application effect of the technology disclosed herein is not significantly impaired. Examples of inorganic particles that can be used as a refractive index improver include inorganic particles composed of inorganic oxides (specifically, metal oxides) such as titania (titanium oxide, TiO2), zirconia (zirconium oxide, ZrO2), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, niobium oxide (such as Nb2O5, etc.). The average particle size of the above inorganic particles (referring to the 50% volume average particle size based on the laser scattering / diffraction method) can be selected, for example, from the range of about 10 nm to 100 nm. The refractive index of the inorganic particles is measured using a commercially available spectroscopic ellipsometer under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 23 °C for a single-layer film (with a film thickness capable of measuring the refractive index) of the material constituting the inorganic particles. As the spectroscopic ellipsometer, for example, the product name "EC-400" (manufactured by JA.Woolam) or its equivalent is used. When using inorganic particles as a refractive index improver, the amount used is preferably less than 5 parts by weight, and more preferably less than 1 part by weight, relative to 100 parts by weight of the base polymer. Additive (H RO ) In the mode of use, the amount of the above inorganic particles used is preferably 2 times or less, and more preferably 1 time or less or 0.5 times or less, based on weight, of the amount of the above additive (H RO ).

[0173] (Crosslinking agent) In the technology disclosed herein, the pressure-sensitive adhesive composition used for forming the pressure-sensitive adhesive layer can contain a crosslinking agent as needed for purposes such as adjusting the cohesive force of the pressure-sensitive adhesive. As the crosslinking agent, known crosslinking agents in the field of pressure-sensitive adhesives such as 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 can be used. Among them, an isocyanate-based crosslinking agent can be preferably employed. As another example of the crosslinking agent, a monomer having two or more ethylenically unsaturated groups in one molecule, that is, a polyfunctional monomer can be mentioned. The crosslinking agent can be used singly or in combination of two or more kinds.

[0174] As the isocyanate-based crosslinking agent, polyisocyanate compounds having two or more functional groups can be used. For example, aliphatic polyisocyanates such as trimethylene diisocyanate, butylene diisocyanate, hexamethylene diisocyanate (HDI), dimer acid diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), 1,3-bis(isocyanatomethyl)cyclohexane; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate (XDI); polyisocyanate modified products obtained by modifying the above isocyanate compounds with allophanate bonds, biuret bonds, isocyanurate bonds, uretdione bonds, urea bonds, carbodiimide bonds, uretonimine bonds, oxadiazinetrione bonds, etc.; and the like. Examples of commercially available products include Takeneate 300S, Takeneate 500, Takeneate 600, Takeneate D165N, Takeneate D178N (all manufactured by Takeda Pharmaceutical Company Limited), Sumidule T80, Sumidule L, Desmodule N3400 (all manufactured by Sumitomo Bayer Urethane Co., Ltd.), Millionate MR, Millionate MT, Coronate L, Coronate HL, Coronate HX (all manufactured by Tosoh Corporation), and the like. The isocyanate compound can be used alone or in combination of two or more. A bifunctional isocyanate compound and a polyfunctional isocyanate compound having three or more functional groups may be used in combination.

[0175] Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol diglycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diaminoglycidylamine, N,N,N’,N’-tetraglycidyl-m-xylenediamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, and the like. These can be used alone or in combination of two or more kinds.

[0176] 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, 1,6-hexanediol di(meth)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, butyl diol (meth)acrylate, hexyl diol di(meth)acrylate, and the like. The polyfunctional monomers can be used alone or in combination of two or more kinds.

[0177] When using a crosslinking agent (which can be a polyfunctional monomer), the amount used is not particularly limited. For example, it can be in the range of about 0.001 to 5.0 parts by weight per 100 parts by weight of the base polymer. From the perspective of improving the flexibility of the adhesive, in some embodiments, the amount of the crosslinking agent used per 100 parts by weight of the base polymer is preferably 3.0 parts by weight or less, more preferably 2.0 parts by weight or less, and may also be 1.0 part by weight or less, 0.5 part by weight or less, or 0.2 part by weight or less. Also, from the perspective of appropriately exerting the effect of the crosslinking agent, in some embodiments, the amount of the crosslinking agent used per 100 parts by weight of the base polymer may be, for example, 0.005 part by weight or more, may be 0.01 part by weight or more, may be 0.05 part by weight or more, or may be 0.08 part by weight or more.

[0178] In order to make the crosslinking reaction proceed more effectively, a crosslinking catalyst may be used. Examples of the crosslinking catalyst include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, ferric naphthenate, butyltin oxide, dioctyltin dilaurate, etc. Among them, 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 about 0.0001 part by weight or more and 1 part by weight or less, preferably in the range of 0.001 part by weight or more and 0.5 part by weight or less, considering the balance between the speed of the crosslinking reaction and the pot life of the adhesive composition.

[0179] In the adhesive composition, a compound that causes keto-enol tautomerism can be contained as a crosslinking retarder. Thereby, the effect of extending the pot life of the adhesive composition can be achieved. For example, in an adhesive composition containing an isocyanate-based crosslinking agent, a compound that causes keto-enol tautomerism can be preferably used. As the compound that causes keto-enol tautomerism, various β-dicarbonyl compounds can be used. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) and acetoacetic acid esters (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably employed. The compound that causes keto-enol tautomerism can be used alone or in combination of two or more. The amount of the compound that causes keto-enol tautomerism used can be, for example, 0.1 part by weight or more and 20 parts by weight or less, preferably 0.5 part by weight or more and 10 parts by weight or less, and more preferably 1 part by weight or more and 5 parts by weight or less based on 100 parts by weight of the base polymer.

[0180] (Adhesion promoter) In the adhesive layer in the technology disclosed herein, an adhesion promoter may be contained. As the adhesion promoter, known adhesion-promoting resins such as rosin-based adhesion-promoting resins, terpene-based adhesion-promoting resins, phenol-based adhesion-promoting resins, hydrocarbon-based adhesion-promoting resins, ketone-based adhesion-promoting resins, polyamide-based adhesion-promoting resins, epoxy-based adhesion-promoting resins, and elastomer-based adhesion-promoting resins can be used. These can be used alone or in combination of two or more. The amount of the adhesion-promoting resin used is not particularly limited and can be set so as to exhibit appropriate adhesive performance according to the purpose and application. In some embodiments, from the viewpoints of refractive index and transparency, the amount of the adhesion promoter 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 based on 100 parts by weight of the base polymer of the adhesive layer. The technology disclosed herein can be preferably implemented in an embodiment without using an adhesion promoter.

[0181] (Other additives) In the technology disclosed herein, the pressure-sensitive adhesive composition used for forming 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, ultraviolet absorbers, antioxidants, light stabilizers, preservatives, etc., as long as the effects of the present invention are not significantly hindered. Since such various additives are conventionally known and can be used by conventional methods and are not particularly characteristic of the present invention, detailed descriptions thereof are omitted.

[0182] <Fabrication of the pressure-sensitive adhesive layer> In the technology disclosed herein, the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer (which may be a high refractive index pressure-sensitive adhesive layer and / or a low refractive index pressure-sensitive adhesive layer; the same applies hereinafter) can be a pressure-sensitive adhesive obtained by curing a pressure-sensitive adhesive composition in the form of a solvent type, active energy ray curable type, water dispersion type, hot melt type, etc. by drying, crosslinking, polymerization, cooling, etc., that is, a cured product of the above pressure-sensitive adhesive composition. As the curing means of the pressure-sensitive adhesive composition (for example, drying, crosslinking, polymerization, cooling, etc.), only one type may be applied, or two or more types may be applied simultaneously or stepwise. In the case of a solvent type pressure-sensitive adhesive composition, typically, the composition can be dried (preferably, further crosslinked) to form a pressure-sensitive adhesive. In the case of an active energy ray curable type pressure-sensitive adhesive composition, typically, a pressure-sensitive adhesive is formed by irradiating active energy rays to cause a polymerization reaction and / or a crosslinking reaction to proceed. When it is necessary to dry the active energy ray curable type pressure-sensitive adhesive composition, it is advisable to irradiate active energy rays after drying.

[0183] In the technology disclosed herein, the pressure-sensitive adhesive layer can be formed by applying (for example, coating) the pressure-sensitive adhesive composition onto an appropriate surface and then curing the composition. The application of the pressure-sensitive adhesive composition can be carried out using conventional coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, spray coaters, etc.

[0184] The adhesive layer in the technology disclosed herein may be an adhesive layer having post-curing properties or an adhesive layer not having post-curing properties. Here, the adhesive layer having post-curing properties refers to an adhesive layer that can be further cured by irradiation with heat or active energy rays (e.g., ultraviolet rays). Examples of the adhesive layer having post-curing properties include an adhesive layer having unreacted ethylenically unsaturated groups in the side chains of the base polymer and an adhesive layer containing unreacted polyfunctional monomers. In some embodiments, it is preferable that the adhesive layer does not have post-curing properties. Since the adhesive layer not having post-curing properties does not cause dimensional changes associated with the post-curing reaction (i.e., has good dimensional stability), it is easy to suppress warping of the adhesive layer or the adherend to which the adhesive layer is attached. The absence of dimensional changes due to post-curing (e.g., curing shrinkage) can also be advantageous from the viewpoint of suppressing optical distortion of the adhesive layer.

[0185] The thickness of the adhesive layer is not particularly limited and can be, for example, 3 μm or more, preferably 5 μm or more. With an adhesive layer having a thickness of 5 μm or more, good adhesive properties are easily obtained. Further, an adhesive layer having such a thickness can absorb irregularities that may exist on the surface of the adherend and is easily joined to the adherend with good adhesion. The fact that the thickness of the adhesive layer (e.g., the thickness of the high refractive index adhesive layer) is 5 μm or more is also preferable from the viewpoint of preventing coloration and color unevenness due to light interference. In some embodiments, the thickness of the adhesive layer may be 10 μm or more, 20 μm or more, 30 μm or more, 50 μm or more, 70 μm or more, or 85 μm or more. Also, in some embodiments, the thickness of the adhesive layer may be, for example, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 120 μm or less. The fact that the thickness of the adhesive layer is not too large can be advantageous from the viewpoint of thinning the laminated sheet or the light-emitting device including the adhesive layer. The technology disclosed herein can be preferably implemented, for example, in an embodiment where the thickness of the adhesive layer is in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm). In some embodiments, the thickness of the adhesive layer described above can be applied at least to the thickness T1 of the high refractive index adhesive layer. The thickness T2 of the low refractive index adhesive layer can also be selected from a similar range. The thickness T1 of the high refractive index adhesive layer and the thickness T2 of the low refractive index adhesive layer may be the same or different. The ratio (T1 / T2) of the thickness T1 of the high refractive index adhesive layer to the thickness T2 of the low refractive index adhesive layer can be, for example, 0.1 or more, 0.3 or more, 0.5 or more, 0.8 or more, 1.2 or more, 1.5 or more. Also, the above ratio (T1 / T2) can be, for example, 20 or less, 10 or less, 5 or less, 3 or less. In some embodiments, the above ratio (T1 / T2) can be less than 2, less than 1.5, or less than 1.

[0186] As a method of obtaining a structure (laminated sheet) in which a low refractive index adhesive layer and a high refractive index layer (typically, a high refractive index adhesive layer) are laminated, for example, a method of forming a high refractive index adhesive layer and a low refractive index adhesive layer on a releasable surface (e.g., the release surface of a release liner) and laminating them, a method of laminating the low refractive index adhesive layer formed on the releasable surface to a non-adhesive high refractive index layer, a method of applying and curing an adhesive composition for forming the low refractive index adhesive layer on the high refractive index layer, conversely, a method of applying and curing a composition for forming the high refractive index layer on the low refractive index adhesive layer, etc. can be adopted, but it is not limited thereto. When laminating the high refractive index layer and the low refractive index adhesive layer, if necessary, a treatment for promoting the adhesion of these layers may be performed. For example, autoclave treatment, roll press treatment, etc. can be performed, but it is not limited thereto.

[0187] (Peel strength) In some embodiments, the peel strength of the adhesive layer disclosed herein with respect to the glass plate is suitably about 1.0 N / 25 mm or more (for example, 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, 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.

[0188] Here, the above-mentioned peel strength is obtained by pressing it against an alkali glass plate as an adherend, leaving it in an environment of 23 °C and 50% RH for 30 minutes, then putting it into a pressure defoaming device (autoclave), performing an autoclave treatment at a temperature of 50 °C and a pressure of 0.5 MPa for 30 minutes, and further leaving it in an atmosphere of 23 °C and 50% RH for 24 hours, and then measuring the 180° peel adhesion at a peel angle of 180 degrees and a tensile speed of 300 mm / min. In the measurement, if necessary, an appropriate backing material (for example, a polyethylene terephthalate (PET) film with a thickness of about 25 μm to about 50 μm) can be attached to the measurement object for reinforcement. More specifically, the peel strength can be measured according to the method described in the examples below. When the low refractive index adhesive layer disclosed herein is laminated with a high refractive index adhesive layer to form a laminated sheet in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, in some embodiments, the above-mentioned peel strength is preferably applied to at least the second adhesive surface (the adhesive surface formed by the low refractive index adhesive layer), and more preferably applied to both the first adhesive surface and the second adhesive surface. The peel strength of the first adhesive surface with respect to the glass plate and the peel strength of the second adhesive surface with respect to the glass may be the same or different.

[0189] <Support substrate> The low refractive index adhesive disclosed herein can be used in the form of an adhesive sheet with a substrate including an adhesive layer formed from the adhesive and a support substrate.

[0190] The material of the support substrate is not particularly limited and can be appropriately selected according to the purpose of use, usage mode, etc. Non-limiting examples of the support substrate that can be used include polyolefin films mainly composed of polyolefins such as polypropylene (PP) and ethylene-propylene copolymers, polyester films mainly composed of polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), plastic films such as polyvinyl chloride films mainly composed of polyvinyl chloride; foam sheets made of foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam; various fibrous substances (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc. can be used.) woven fabrics and non-woven fabrics by single or blended spinning, etc.; papers such as Japanese paper, high-quality paper, kraft paper, and crepe paper; metal foils such as aluminum foil and copper foil; etc. A substrate having a composite structure of these may also be used. Examples of such a composite substrate include, for example, a substrate having a structure in which a metal foil and the above plastic film are laminated, and a plastic substrate reinforced with inorganic fibers such as glass cloth.

[0191] In some embodiments, various film substrates can be preferably used. The above film substrate may be a porous substrate such as a foam film or a non-woven fabric sheet, a non-porous substrate, or a substrate having a structure in which a porous layer and a non-porous layer are laminated. In some embodiments, as the above film substrate, those containing an independently shape-maintainable (self-supporting or non-dependent) resin film as a base film can be preferably used. Here, the "resin film" means a resin film having a non-porous structure and typically substantially free of air bubbles (voidless). Therefore, the above resin film is a concept distinct from foam films and non-woven fabrics. As the above resin film, an independently shape-maintainable (self-supporting or non-dependent) one can be preferably used. The above resin film may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure).

[0192] Examples of the material constituting the resin film include polyester resins mainly composed of polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); polyolefin resins mainly composed of polyolefins such as polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, and ethylene-butene copolymer; cellulose resins such as triacetyl cellulose; acetate resins; polysulfone resins; polyethersulfone resins; polycarbonate resins; polyamide (PA) resins such as nylon 6, nylon 66, and partially aromatic polyamide; polyimide (PI) resins; transparent polyimide resins; polyamideimide (PAI); polyetheretherketone (PEEK); polyethersulfone (PES); 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; polyphenylene sulfide (PPS) resins; polyurethane (PU); ethylene-vinyl acetate copolymer (EVA); fluorine-based resins such as polytetrafluoroethylene (PTFE) and fluorinated polyimide, and the like.

[0193] The above resin film may be formed using a resin material containing only one such resin, or may be formed using a resin material in which two or more kinds are blended. The above resin film may be unstretched, or may be stretched (for example, uniaxially stretched or biaxially stretched). For example, PET film, PBT film, PEN film, unstretched polypropylene (CPP) film, biaxially stretched polypropylene (OPP) film, low density polyethylene (LDPE) film, linear low density polyethylene (LLDPE) film, PP / PE blend film, etc. can be preferably used. Examples of resin films preferred from the viewpoints of strength and dimensional stability include PET film, PEN film, PPS film, and PEEK film. PET film and PPS film are particularly preferred from the viewpoint of easy availability, and among them, PET film is preferred.

[0194] In the resin film, known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, antiblocking agents, etc. can be blended as necessary within a range where the effects of the present invention are not significantly hindered. The blending amount of the additive is not particularly limited and can be appropriately set according to the use of the adhesive sheet, etc.

[0195] The method for manufacturing the resin film is not particularly limited. For example, conventionally known general resin film forming methods such as extrusion molding, inflation molding, T-die casting molding, calender roll molding, etc. can be appropriately adopted.

[0196] The above base material may be substantially composed of such a base film. Alternatively, the above base material may include an auxiliary layer in addition to the above base film. Examples of the above auxiliary layer include an optical property adjustment layer (for example, a coloring layer, an antireflection layer), a printing layer or a laminate layer for imparting a desired appearance to the base material, an antistatic layer, an undercoat layer, a release layer, etc., which are surface treatment layers.

[0197] In some embodiments, as the support substrate, a substrate having light transmissivity (hereinafter also referred to as a light-transmissive substrate) may preferably be employed. Thereby, it becomes possible to form an adhesive sheet with a light-transmissive substrate. The total light transmittance of the light-transmissive 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 be 95% or more (for example, 95 to 100%). The above total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, a product named "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory or its equivalent is used. Preferred examples of the above light-transmissive substrate include resin films having light transmissivity. The above light-transmissive substrate may be an optical film.

[0198] The thickness of the substrate is not particularly limited and can be selected according to the purpose of use, usage mode, etc. The thickness of the substrate may be, for example, 500 μm or less, preferably 300 μm or less from the viewpoints of handleability and processability, and may be 150 μm or less, 100 μm or less, 50 μm or less, 25 μm or less, or 10 μm or less. When the thickness of the substrate decreases, the followability to the surface shape of the adherend tends to improve. Also, from the viewpoints of handleability, processability, etc., the thickness of the substrate may be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

[0199] On the surface of the base material on the side where the adhesive layer is laminated, if necessary, conventionally known surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and formation of an undercoat layer by applying an undercoat agent (primer) may be performed. Such surface treatment can be a treatment for improving the anchoring property of the adhesive layer to the base material. The composition of the primer used for forming the undercoat layer is not particularly limited and can be appropriately selected from known ones. The thickness of the undercoat layer is not particularly limited, but usually, about 0.01 μm to 1 μm is appropriate, and about 0.1 μm to 1 μm is preferable. Other treatments that can be applied to the base material as necessary include antistatic layer formation treatment, coloring layer formation treatment, printing treatment, etc. These treatments can be applied alone or in combination.

[0200] In the technology disclosed herein, when the low refractive index adhesive layer constitutes the pressure-sensitive adhesive sheet with a base material, the thickness of the pressure-sensitive adhesive sheet may be, for example, 1000 μm or less, 350 μm or less, 200 μm or less, 120 μm or less, 75 μm or less, or 50 μm or less. Also, from the viewpoint of handleability and the like, the thickness of the above pressure-sensitive adhesive sheet may be, for example, 10 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more. Note that the thickness of the pressure-sensitive adhesive sheet refers to the thickness of the portion attached to the adherend. For example, in the base material-less double-sided pressure-sensitive adhesive sheet 2 having the configuration shown in FIG. 2, it refers to the thickness from the first surface (first adhesive surface) 10A to the second surface (second adhesive surface) 10B of the adhesive layer, and does not include the thickness of the release liners 31 and 32.

[0201] <Pressure-sensitive adhesive sheet> The low refractive index adhesive disclosed herein can be used in the form of a pressure-sensitive adhesive sheet that includes an adhesive layer (low refractive index adhesive layer) formed from the adhesive and may further include other layers (high refractive index adhesive layer, support base material, etc.).

[0202] (Total light transmittance) In the technology disclosed herein, the total light transmittance of the low refractive index adhesive layer is desirably 86% or more, preferably 88% or more, more preferably 90% or more (for example, exceeding 90.0%), may be 90.5% or more, may be 93% or more, or may be 95% or more. The upper limit of the total light transmittance is theoretically the value obtained by subtracting the light loss (Fresnel loss) due to reflection occurring at the air interface from 100%, and in practical use, it may be approximately 98% or less, may be approximately 96% or less, or may be approximately 95% or less. In some embodiments, considering the refractive index and adhesive properties, the total light transmittance of the low refractive index adhesive layer may be approximately 94% or less, may be approximately 93% or less, or may be approximately 92% or less. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, a product named "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory or its equivalent is used. More specifically, for example, the total light transmittance of the low refractive index adhesive layer can be measured according to the examples described later. The total light transmittance of the low refractive index adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the low and high refractive index adhesive layers. The above description regarding the total light transmittance of the low refractive index adhesive layer can also be applied to the total light transmittance of the adhesive sheet including the low refractive index adhesive layer and the support substrate, the total light transmittance of the high refractive index layer, the total light transmittance of the laminated sheet (adhesive sheet) including the low refractive index adhesive layer and the high refractive index layer (typically the high refractive index adhesive layer), and the like.

[0203] (Haze value) The haze value of the low refractive index adhesive layer is preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less, and even more preferably 0.9% or less. A low haze value of the low refractive index adhesive layer is advantageous in applications where high light transmittance is required (for example, optical applications) or in applications where the ability to clearly visually recognize the adherend through the low refractive index adhesive layer is required. In some embodiments, the haze value of the low refractive index adhesive layer may be 0.8% or less, 0.5% or less, or 0.3% or less. The lower limit of the haze value of the low refractive index adhesive layer is not particularly limited, and from the perspective of improving transparency, the lower the haze value, the more preferable. On the other hand, in some embodiments, considering the refractive index and adhesive properties, the haze value of the low refractive index adhesive layer 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. The above description regarding the haze value of the low refractive index adhesive layer can also be applied to the haze value of the adhesive sheet including the low refractive index adhesive layer and the support substrate, the haze value of the high refractive index layer, the haze value of the laminated sheet (adhesive sheet) including the low refractive index adhesive layer and the high refractive index layer (typically a high refractive index adhesive layer), and the like.

[0204] Here, the "haze value" refers to the ratio of the diffused transmitted light to the total transmitted light when the measurement object is irradiated with visible light. 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 measurement of the haze value can be performed according to the method described in the examples below. The haze value of the adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the adhesive layer.

[0205] (Surface smoothness of the adhesive surface) In some embodiments, the surface (adhesive surface) of the adhesive layer preferably has high surface smoothness.

[0206] For example, it is preferable that the arithmetic mean roughness Ra of the adhesive surface is limited to a predetermined value or less. A configuration including an adhesive surface designed to have a low arithmetic mean roughness Ra is preferable from the viewpoint of optical homogeneity. By restricting the arithmetic mean roughness Ra, for example, in a usage mode in which light is extracted through the adhesive surface (such as an adhesive sheet disposed on the viewing side of a self-luminous element in a light-emitting device), it is possible to exhibit the effect of suppressing the occurrence of luminance unevenness due to the surface state of the adhesive layer. A low arithmetic mean roughness Ra of the adhesive surface is also advantageous for suppressing optical distortion, and suppressing optical distortion 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 (for example, in the form of a laminated sheet including a high refractive index adhesive layer and a low refractive index adhesive layer), it is preferable that at least the arithmetic mean roughness Ra of the first adhesive surface is limited to a predetermined value or less, and it is more preferable that the arithmetic mean roughness Ra of both adhesive surfaces is limited to a predetermined value or less. By each adhesive surface of the double-sided adhesive sheet having high surface smoothness, it is possible to preferably realize adhesion excellent in optical homogeneity.

[0207] In some embodiments, the arithmetic mean roughness Ra of the adhesive surface is preferably approximately 70 nm or less, more preferably approximately 65 nm or less, still more preferably approximately 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 and the like, in some embodiments, the arithmetic mean roughness Ra of the adhesive surface may be, for example, approximately 10 nm or more, approximately 20 nm or more, or approximately 30 nm or more (for example, approximately 40 nm or more). In an embodiment 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 the same or different.

[0208] Further, 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 lower maximum height Rz is preferable from the viewpoint of optical homogeneity. By limiting the maximum height Rz, for example, in a usage mode in which light is extracted through the adhesive surface as described above, it is possible to exhibit the effect of suppressing the occurrence of luminance unevenness due to the surface state of the adhesive layer. A low maximum height Rz of the adhesive surface is also advantageous for 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 at least the maximum height Rz of the first adhesive surface is limited to a predetermined value or less, and it is more preferable that the maximum height Rz of both adhesive surfaces is limited to a predetermined value or less. By each adhesive surface of the double-sided adhesive sheet having high surface smoothness, adhesion excellent in optical homogeneity can be preferably realized.

[0209] 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, still more preferably approximately 450 nm or less, 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 viewpoint of production efficiency and the like, in some embodiments, the maximum height Rz of the adhesive surface 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 an embodiment having a first adhesive surface and a second adhesive surface, the maximum height Rz of the first adhesive surface and the maximum height Rz of the second adhesive surface may be the same or different.

[0210] The arithmetic mean roughness Ra and the maximum height Rz of the adhesive surface are measured using a non-contact surface roughness measuring device. As the non-contact surface roughness measuring device, an optical interference type surface roughness measuring device is used. For example, a three-dimensional optical profiler (trade name "NewView7300", manufactured by ZYGO Corporation) or its equivalent can be used. Specifically, for example, the arithmetic mean roughness Ra and the maximum height Rz can be measured by the following measuring method, or by setting the measuring operation and measuring conditions so that results equivalent to or corresponding to those obtained by the measuring method can be obtained.

[0211] That is, in an environment of 23°C and 50% RH, using a three-dimensional optical profiler (trade name "NewView7300", manufactured by ZYGO Corporation), the surface shape of the measurement sample is measured under the following conditions. The arithmetic surface roughness Ra is calculated from the measured data in accordance with JIS B 0601-2001. The maximum height Rz is obtained as the sum of the height Rp of the highest peak above the average line and the depth Rv of the deepest valley below the average line for the data (roughness curve) obtained by the above measurement. The measurement is performed 5 times (that is, N = 5), and their average value is used. The above measurement sample can be prepared, for example, by cutting an adhesive layer to be measured or an adhesive sheet including the adhesive layer into a size of about 150 mm in length and 50 mm in width. When the adhesive surface is protected by a release liner, the release liner is gently peeled off (for example, under the conditions of a peeling speed of 300 mm / min and a peeling angle of 180°) to expose the adhesive surface. It is desirable to perform the measurement after allowing the adhesive surface to stand for about 30 minutes after exposure. [Measurement Conditions] Measurement area: 5.62 mm × 4.22 mm (Objective lens: 2.5 times, internal lens: 0.5 times) Analysis mode: Remove: Cylinder Data Fill: ON (Max: 25) Remove Spikes: ON (xRMS: 1) Filter: OFF

[0212] The arithmetic mean roughness Ra and the maximum height Rz of the adhesive surface can be adjusted by the composition and properties (such as viscosity, leveling property, etc.) of the adhesive composition used for forming the adhesive layer, the properties of the surface (release surface) of the release liner that protects the adhesive surface, and the like.

[0213] (Water absorption rate) In some embodiments where the low refractive index adhesive disclosed herein is used together with a high refractive index adhesive layer, it is preferable that the water absorption rate of the high refractive index adhesive layer is limited to a predetermined value or less. By limiting the water absorption rate of the high refractive index adhesive layer, dimensional changes of the high refractive index adhesive layer due to fluctuations in the amount of water in the high refractive index adhesive layer (for example, absorption and release of moisture such as moisture in the environment) tend to be suppressed. Thereby, warping of the high refractive index adhesive layer or the optical laminate including the high refractive index adhesive layer due to a mismatch in dimensional changes between the high refractive index adhesive layer and an adjacent layer (which can be a low refractive index adhesive layer, a support substrate, a release liner, an adherend, etc.) can be suppressed. The ability to suppress fluctuations in the amount of water in the high refractive index adhesive layer is also preferable from the viewpoint of maintaining the flatness, transparency, refractive index, etc. of the high refractive index adhesive layer constant. Further, a high refractive index adhesive layer with a low water absorption rate is suitable as a component of a member or product that contains elements that dislike moisture, such as an organic EL element, because it is difficult to occlude moisture.

[0214] In some embodiments, the water absorption rate of the high refractive index adhesive layer is suitably about 1.0% or less, preferably 0.7% or less, more preferably 0.5% or less (for example, less than 0.5%), and may be 0.4% or less, 0.3% or less, or 0.2% or less. The lower limit of the water absorption rate of the high refractive index adhesive layer is not particularly limited, but from a practical viewpoint such as 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. The water absorption rate of the low refractive index adhesive layer may be the same as or different from that of the high refractive index adhesive layer. From the viewpoint of obtaining a higher effect, it is more preferable that the water absorption rates of both the high refractive index adhesive layer and the low refractive index adhesive layer are limited to a predetermined value or less.

[0215] The water absorption rate (also referred to as the moisture content) of the high refractive index adhesive layer is measured by the following method. The water absorption rate of the low refractive index adhesive layer is also measured by the same method. [Measurement of Moisture Content] The adhesive layer to be evaluated is cut out to a size of 4 cm × 5 cm (area: 20 cm 2 ) together with two release liners disposed on one surface and the other surface thereof, and the release liner on one surface is removed and bonded to an aluminum foil that has been weighed in advance. Next, the release liner on the other surface of the adhesive layer is removed, and the sample is placed in a thermo-hygrostat at a temperature of 60°C and a relative humidity of 90%, and taken out after 72 hours. After weighing the test piece in which the adhesive layer and the aluminum foil are laminated, a moisture meter (Mitsubishi Chemical Analytech CA-200 type) equipped with a heating vaporization device (Mitsubishi Chemical Analytech VA-200 type) is used, and the moisture content is measured by the Karl Fischer coulometric titration method under the following conditions. Anolyte: Aquamicron AKX (manufactured by Mitsubishi Chemical) Catholyte: Aquamicron CXU (manufactured by Mitsubishi Chemical) Heating vaporization temperature: 150°C

[0216] (Gel Fraction) The gel fraction of the adhesive layer disclosed herein is appropriately set according to the purpose of use, usage mode, etc., and is not limited to a specific range. The above gel fraction is, for example, approximately 99% or less, and preferably approximately 97% or less. From the viewpoint of preferably achieving both a low refractive index and adhesive properties, in some preferred embodiments, the above gel fraction is approximately 95% or less, more preferably approximately 92% or less (for example, approximately 90% or less). That the gel fraction is not too high is also preferable from the viewpoint of appropriately following the unevenness that may exist on the surface of the adherend (for example, the uneven structure provided for the purpose of improving the light extraction efficiency in a light-emitting device) and achieving good adhesion. In some embodiments, the gel fraction may be approximately 88% or less, approximately 75% or less, or approximately 65% or less. Further, from the viewpoint of imparting appropriate cohesiveness to the adhesive and appropriately expressing the adhesive properties, the above gel fraction is, for example, approximately 10% or more, preferably approximately 20% or more, and may be approximately 30% or more. From the viewpoint of the deformation resistance of the adhesive layer (prevention of bubbles due to extrusion by pressure or entrapment of foreign matter), the above gel fraction is preferably approximately 30% or more, more preferably approximately 40% or more, and may be approximately 45% or more, approximately 50% or more, approximately 65% or more, or approximately 75% or more. The gel fraction of the adhesive sheet including a high refractive index adhesive layer and a low refractive index adhesive layer (for example, a laminated sheet in the form of a substrate-free double-sided adhesive sheet composed of a high refractive index adhesive layer and a low refractive index adhesive layer) is also preferably within the range exemplified above. The gel fraction can be adjusted by the molecular weight, molecular structure, concentration, crosslinking degree, etc. of the base polymer. The gel fraction is measured by the following method.

[0217] [Measurement of Gel Fraction] A predetermined amount of the adhesive sample (weight Wg1) is wrapped in a porous polytetrafluoroethylene membrane with an average pore diameter of 0.2 μm (weight Wg2) in a sachet shape, and the mouth is tied with string (weight Wg3). As the above porous polytetrafluoroethylene (PTFE) membrane, a product named "Nitron (registered trademark) NTF1122" (average pore diameter 0.2 μm, porosity 75%, thickness 85 μm) available from Nitto Denko Corporation or its equivalent product is used. Immerse this package in a sufficient amount of ethyl acetate and keep it at room temperature (typically 23 °C) for 7 days to elute only the sol fraction in the adhesive outside the above-mentioned film. Then, take out the package, wipe off the ethyl acetate adhering to the outer surface, dry the package at 130 °C for 2 hours, and measure the weight (Wg4) of the package. The gel fraction of the adhesive layer is determined by substituting each value into the following formula. Gel fraction (%) = [(Wg4 - Wg2 - Wg3) / Wg1] × 100

[0218] The gel fraction of the high refractive index adhesive layer and the gel fraction of the low refractive index adhesive layer may be the same or different. In some embodiments, the gel fraction of the low refractive index adhesive layer can be made lower than the gel fraction of the high refractive index adhesive layer. According to such a configuration, due to the contribution of the low refractive index adhesive layer having a relatively low gel fraction, it is easy to enhance the overall flexibility. As a result, it is possible to achieve a good balance between high refractive index and flexibility.

[0219] In some embodiments of the technology disclosed herein, the peak temperature of tanδ of the adhesive constituting the high refractive index adhesive layer is preferably approximately -50 °C or higher and preferably approximately 50 °C or lower. Here, tanδ (loss tangent) of the adhesive refers to the ratio of the loss modulus G” to the storage modulus G’ of the adhesive. That is, tanδ = G” / G’. The tanδ of the adhesive is measured by sandwiching a disk-shaped adhesive sample with a thickness of about 2 mm and a diameter of 7.9 mm between parallel plates, applying a shear strain at a frequency of 1 Hz using a viscoelasticity testing apparatus, and performing a temperature dispersion test of the adhesive in shear mode under the conditions of a measurement temperature range of -60 °C to 60 °C and a heating rate of 5 °C / min. The peak temperature of tanδ of the adhesive (hereinafter, sometimes denoted as Tpeak) is determined from the transition of tanδ in the above temperature range. As the viscoelasticity testing apparatus, ARES manufactured by TA Instruments or its equivalent can be used.

[0220] In some embodiments, the Tpeak of the high refractive index adhesive layer is advantageously 45°C or lower, or 35°C or lower, preferably 30°C or lower (e.g., 25°C or lower), may be 20°C or lower, and may be 15°C or lower. An adhesive with a lower Tpeak tends to more easily provide good initial adhesiveness and adhesion in the room temperature range. On the other hand, it is preferable that the Tpeak of the adhesive is not too low from the viewpoint of imparting appropriate cohesiveness to the adhesive and also tends to be suitable for compatibility with increasing the refractive index. From such a viewpoint, in some embodiments, the Tpeak of the adhesive may be, for example, -40°C or higher, may be -30°C or higher, may be -20°C or higher, may be -5°C or higher, may be 5°C or higher, may be 15°C or higher, and may even be 25°C or higher. An adhesive with a relatively high Tpeak can be preferably used in a mode where, when attaching to an adherend, one or both of the adhesive and the adherend are heated to a temperature slightly higher than room temperature as necessary. The Tpeak of the adhesive can be adjusted by, for example, the selection of the composition of the adhesive (e.g., the composition of the monomer components constituting the base polymer, the presence or absence, type, and amount of use of refractive index improvers and plasticizing materials). The Tpeak of the above-described adhesive is preferably applied at least to the high refractive index adhesive layer, more preferably applied to both the high refractive index adhesive layer and the low adhesive refractive index layer. The Tpeak of the high refractive index adhesive layer and the Tpeak of the low adhesive refractive index layer may be the same or different.

[0221] <Laminated sheet with release liner> Before being incorporated into a light-emitting device, the high refractive index adhesive layer and the low refractive index adhesive layer disclosed herein can be in the form of a pressure-sensitive adhesive product (laminated sheet with release liner) in which the pressure-sensitive adhesive surface of a laminated sheet including the high refractive index adhesive layer and the low refractive index adhesive layer is in contact with the release surface of a release liner. Therefore, according to this specification, a laminated sheet with a release liner (pressure-sensitive adhesive product) including a laminated sheet of a high refractive index adhesive layer and a low refractive index adhesive layer and a release liner having a release surface in contact with the pressure-sensitive adhesive surface of the laminated sheet is provided.

[0222] The release liner is not particularly limited. For example, a release liner having a release treatment layer on a release liner substrate such as a resin film or paper (which may be paper laminated with a resin such as polyethylene), or a release liner made of a resin film formed of a low-adhesion material such as a fluoropolymer (such as polytetrafluoroethylene) or a polyolefin resin (such as polyethylene, polypropylene) can be used. The release treatment layer can be formed by surface-treating the release liner substrate with a release treatment agent. The release treatment agent can 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 by a silicone-based release treatment agent can be preferably employed. The thickness and formation method of the release treatment layer are not particularly limited and can be set so that appropriate releasability is exhibited on the surface on the adhesive side of the release liner.

[0223] In some embodiments, from the viewpoint of the smoothness of the adhesive surface and the like, a release liner (hereinafter also referred to as a release film) having a configuration with a release treatment layer on a resin film as the release liner substrate (hereinafter also referred to as a release film substrate) can be preferably employed. As the release film substrate, various plastic films can be used. In this specification, a plastic film is typically a non-porous sheet and is, for example, a concept that is distinguished from a non-woven fabric (that is, does not include a non-woven fabric).

[0224] Examples of the material of 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 copolymer, and ethylene-butene copolymer; cellulose resins such as triacetyl cellulose; acetate resins; polysulfone resins; polyethersulfone resins; polycarbonate resins; polyamide resins; polyimide resins; 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; polyphenylene sulfide resins, etc. A release film substrate formed from any one or a mixture of two or more of these resins can be used. Among them, a polyester resin film (e.g., PET film) formed from a polyester resin is preferably used as the release film substrate.

[0225] The plastic film used as the above-described release film substrate may be an unstretched film, a uniaxially stretched film, or a biaxially stretched film. Further, the plastic film may have a single-layer structure or a multilayer structure including two or more sub-layers. The plastic film may be blended with known additives that can be used for the release film substrate of the adhesive sheet, such as antioxidants, anti-aging agents, heat stabilizers, light stabilizers, ultraviolet absorbers, colorants such as pigments and dyes, lubricants, fillers, antistatic agents, and nucleating agents. In a plastic film having a multilayer structure, each additive may be blended in all sub-layers or only in some sub-layers.

[0226] In some preferred embodiments, as the release film substrate (typically a plastic film), the content of particles such as inorganic particles (which can be, for example, pigments, lubricants, fillers, etc.) in the layer on the release surface side is restricted, or a substrate substantially free of such particles can be preferably used. Here, being substantially free means that the amount of particles (for example, inorganic particles) in the layer is less than 1% by weight, preferably less than 0.1% by weight (for example, 0 to 0.01% by weight). A release film provided with such a release film substrate is likely to have a low arithmetic mean roughness Ra and maximum height Rz of the release surface. When the release film substrate (typically a plastic film) has a multilayer structure, the particle content in the layer on the release surface side can be 1 / 10 or less (for example, 1 / 50 or less) of the particle content in the layer other than the layer on the release surface side.

[0227] In a laminated sheet with a release liner having a form in which release liners are respectively provided on the first adhesive surface and the second adhesive surface, the release liner disposed on one adhesive surface (hereinafter also referred to as one release liner) and the release liner disposed on the other adhesive surface (hereinafter also referred to as the other release liner) may have the same kind of material and configuration, or may have different materials and configurations.

[0228] 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 viewpoints 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, may be 35 μm or more, may be 40 μm or more, or may be 45 μm or more. Also, from the viewpoints of the handleability (e.g., ease of winding) of the release liner, etc., the thickness of the release liner is suitably 300 μm or less, preferably 250 μm or less, may be 200 μm or less, may be 150 μm or less, or may be 130 μm or less. In some preferred embodiments, the thickness of the release liner is approximately 125 μm or less, may be approximately 115 μm or less, may be approximately 105 μm or less, may be approximately 90 μm or less, or may be approximately 70 μm or less. By setting the thickness of the release liner to a predetermined value or less, it becomes difficult to form winding marks when made into a roll, the removal from the adhesive sheet becomes smooth, and high surface smoothness is easily obtained on the adhesive surface after the release liner is removed.

[0229] In the laminated sheet with a release liner in an embodiment including one release liner and the other release liner, the thicknesses of those release liners may be the same or different. In some embodiments, from the viewpoints of release workability, etc., it is preferable that one release liner and the other release liner have different thicknesses. For example, it is preferable that the thickness of the thicker release liner is approximately 1.1 times or more (e.g., approximately 1.25 times or more. The upper limit is not particularly limited, but is, for example, 5 times or less) the thickness of the thinner release liner.

[0230] (Arithmetic mean roughness Ra of the surface on the adhesive side) In some embodiments, it is preferable from the viewpoint of realizing an adhesive surface having high surface smoothness that the arithmetic mean roughness Ra of the surface on the adhesive side of the release liner (preferably a release film) is limited to a predetermined value or less (for example, approximately 100 nm or less, and more preferably less than 50 nm). In some embodiments, the arithmetic mean roughness Ra of the surface on the adhesive side of the release liner is preferably, for example, approximately 30 nm or less, more preferably approximately 25 nm or less, may be approximately 20 nm or less, or may be approximately 18 nm or less. Also, from the viewpoints of ease of manufacturing and handleability of the release liner, etc., in some embodiments, the arithmetic mean roughness Ra may be, for example, approximately 5 nm or more, may be approximately 10 nm or more, or may be approximately 15 nm or more. In a laminated sheet with a release liner in which release liners are disposed on the first adhesive surface and the second adhesive surface, respectively, it is preferable that the surfaces on the adhesive side of both release liners satisfy any of the above-described arithmetic mean roughnesses Ra. The arithmetic mean roughnesses Ra of the surfaces on the adhesive side of both release liners may be the same or different.

[0231] (Maximum height Rz of the surface on the adhesive side) In some embodiments, it is preferable from the viewpoint of realizing an adhesive surface having high surface smoothness that the maximum height Rz of the surface on the adhesive side of the release liner (preferably a release film) is 700 nm or less. In some embodiments, the maximum height Rz of the surface on the adhesive side of the release liner is preferably approximately 600 nm or less, may be approximately 500 nm or less, may be approximately 400 nm or less, or may be approximately 300 nm or less. Also, from the viewpoints of ease of manufacturing and handleability of the release liner, etc., in some embodiments, the maximum height Rz may be, for example, approximately 50 nm or more, may be approximately 80 nm or more, may be approximately 100 nm or more, may be approximately 200 nm or more, or may be approximately 300 nm or more. In a laminated sheet with a release liner in which release liners are disposed on the first adhesive surface and the second adhesive surface, respectively, it is preferable that the surfaces on the adhesive side of both release liners satisfy any of the above-described maximum heights Rz. The maximum heights Rz of the surfaces on the adhesive side of both release liners may be the same or different.

[0232] (Surface properties of the back side) The arithmetic mean roughness Ra and the maximum height Rz of the back side (the side opposite to the adhesive layer side) of the release liner (preferably a release film) are not particularly limited. From the viewpoint of productivity and the like, the arithmetic mean roughness Ra of the back side of the release liner may be, for example, more than 30 nm (for example, more than 35 nm, and further, approximately 50 nm or more). The maximum height Rz of the back side of the release liner may be, from the viewpoint of productivity and the like, for example, more than 400 nm (for example, approximately 500 nm or more), and may also be more than 800 nm (for example, 1000 nm or more).

[0233] The arithmetic mean roughness Ra and the maximum height Rz of the surface of the release film can be adjusted by surface treatments such as the selection of the film material, the molding method, and the release treatment. For example, adjustment of the smoothness of the layer constituting the release surface (anti-blocking layer, hard coat layer, oligomer prevention layer, etc.), reduction or non-use (particle-free) of filler particles in the surface layer or the release film substrate, and other adjustments of stretching conditions can be mentioned.

[0234] The arithmetic mean roughness Ra and the maximum height Rz of the surface of the release liner (preferably a release film) are measured using a non-contact surface roughness measuring device. As the non-contact surface roughness measuring device, a surface roughness measuring device using an optical interference method is used. For example, a three-dimensional optical profiler (trade name "NewView7300", manufactured by ZYGO Corporation) or its equivalent can be used. For example, a glass plate (soda lime glass plate manufactured by MATSUNAMI, thickness 1.3 mm) is bonded and fixed to the surface opposite to the measurement surface of the release liner with an adhesive, and the surface shape can be measured using a three-dimensional optical profiler (trade name "NewView7300", manufactured by ZYGO Corporation) in an environment of 23 °C and 50% RH.

[0235] [Application] The adhesives (e.g., low refractive index adhesives) disclosed herein can be used by being adhered to various adherends. The constituent material (adherend material) of the above adherend is not particularly limited. For example, metal materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, indium, zinc, etc., or alloys containing two or more of these, and various resin materials (typically plastic materials) such as polyimide-based resins, acrylic-based resins, polyether nitrile-based resins, polyether sulfone-based resins, polyester-based resins (PET-based resins, polyethylene naphthalate-based resins, etc.), polyvinyl chloride-based resins, polyphenylene sulfide-based resins, polyether ether ketone-based resins, polyamide-based resins (so-called aramid resins, etc.), polyarylate-based resins, fluorine-based resins, polycarbonate-based resins, cellulose-based polymers such as diacetyl cellulose and triacetyl cellulose, vinyl butyral-based polymers, liquid crystal polymers, carbon materials such as graphene, metal oxides such as alumina, zirconia, titania, SiO2, ITO (indium tin oxide), ATO (antimony-doped tin oxide) and their mixtures, nitrides such as aluminum nitride, silicon nitride, titanium nitride, gallium nitride, indium nitride and their composites, inorganic materials such as alkali glass, alkali-free glass, quartz glass, borosilicate glass, sapphire glass carbon, etc. can be mentioned. The adhesives disclosed herein can be used by being adhered to at least a member (e.g., an optical member) whose surface is made of the above materials.

[0236] The adhesive disclosed herein can be used in an application mode that does not require a heating treatment to a temperature higher than a temperature range around room temperature (for example, 20°C to 35°C) after being adhered to an adherend. Also, when permitted according to the type of the adherend, etc., a heat treatment may be performed at least at any timing of after the adhesion to the adherend, at the time of adhesion, and before the adhesion. The heat treatment can be performed for the purpose of improving the adhesion of the adhesive to the adherend, promoting adhesion, etc. The heat treatment temperature can be appropriately set within a range permitted according to the constituent materials of the adhesive sheet and the type of the adherend, considering the surface state of the adherend, etc., so as to obtain a desired effect. For example, it may be about 100°C or lower, 80°C or lower, 60°C or lower, or 50°C or lower.

[0237] The members and materials to which the adhesive is applied can be light-transmissive. In such an adherend, the advantage that the adhesive disclosed herein can be highly transparent is easily obtained. The total light transmittance of the above adherend may be, for example, more than 50%, or 70% or more. In some preferred embodiments, the total light transmittance of the above adherend is 80% or more, more preferably 90% or more, and even more preferably 95% or more (for example, 95 to 100%). The adhesive disclosed herein can be preferably used in an application mode of adhering to an adherend (for example, an optical member) having a total light transmittance of a predetermined value or more. The above total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the product name "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory or its equivalent is used.

[0238] The refractive index of the adherend and the refractive index of the adhesive layer (typically a low refractive index adhesive layer, and may be a high refractive index adhesive layer in a form having a high refractive index adhesive layer) disposed in contact with the adherend may be the same or different. For example, by making the refractive index of the adhesive layer relatively higher than that of the adherend, light incident on the adhesive layer from the adherend side at an angle below the critical angle can be refracted to the front side, and the front luminance can be increased. In this case, the refractive index of the adherend may be, for example, 1.55 or less, 1.50 or less, 1.48 or less, 1.45 or less, and may be less than 1.45. Also, for example, it can be 1.10 or more, 1.20 or more, 1.30 or more, or 1.35 or more. Further, according to an adherend having a relatively high refractive index with respect to the adhesive layer, light incident on the adherend from the adhesive layer side can be refracted to the front side, and the front luminance can be increased. 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, and for example, may be 3.00 or less, 2.50 or less, or 2.00 or less. On the other hand, by reducing the refractive index difference between the adhesive layer and the adherend, light reflection at the interface can be suppressed. In this case, the refractive index of the adherend may be about 1.55 to 1.80, may also be about 1.55 to 1.75, or may be 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 adhesive.

[0239] In some preferred embodiments, the above adherend may have any of the refractive indices described above and any of the total light transmittances described above. In an optical product (for example, a light emitting device) in a form in which a high refractive index adhesive layer and / or a low refractive index adhesive layer is attached or laminated to such an adherend, the effects of the technology disclosed herein are particularly preferably exhibited.

[0240] The low refractive index adhesive layer and the high refractive index adhesive layer disclosed herein can be used by being attached to various adherends as described above in the form of a laminated sheet containing them. As an example of a preferred use, optical applications can be mentioned. More specifically, for example, as an optical adhesive sheet used for applications such as bonding optical members (for bonding optical members) or for manufacturing products (optical products) using the above optical members, the laminated sheet disclosed herein can be preferably used. The laminated sheet used in such a manner can also be understood as an interlayer sheet disposed between the layers of an optical laminate.

[0241] The above optical member refers to a member having optical properties (for example, polarization property, light refraction property, light scattering property, light reflection property, light transmission property, light absorption property, light diffraction property, optical rotation property, visibility, etc.). The above optical member is not particularly limited as long as it is a member having optical properties, and examples thereof include members constituting devices (optical devices) such as display devices (image display devices) and input devices, or members used in these devices. For example, polarizing plates, wavelength plates, retardation plates, optical compensation films, brightness enhancement films, light guide plates, reflection films, antireflection films, hard coat (HC) films, shock absorption films, antifouling films, photochromic films, dimming films, transparent conductive films (ITO films), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and furthermore, members in which these are laminated (these may be collectively referred to as "functional films"). Note that the above "plates" and "films" include plate-like, film-like, sheet-like forms, etc. For example, "polarizing film" includes "polarizing plate" and "polarizing sheet", etc., and "light guide plate" includes "light guide film" and "light guide sheet", etc. Also, the above "polarizing plate" includes a circular polarizing plate.

[0242] Examples of the above 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), and an electronic paper. Examples of the above input device include a touch panel.

[0243] The optical member is not particularly limited, and examples thereof include members made of glass, acrylic resin, polycarbonate, polyethylene terephthalate, metal thin films, etc. (for example, sheet-like, film-like, or plate-like members). In addition, the "optical member" in this specification shall also include members that play a role in decoration and protection while maintaining the visibility of a display device or an input device (such as a design film, a decorative film, or a surface protection film).

[0244] The low refractive index adhesive layer disclosed herein (which may be in the form of a laminated sheet with a high refractive index layer) can be used, for example, in a manner disposed between an optical film such as a film or a fluorescent film having one or more functions such as light transmission, reflection, diffusion, waveguide, light collection, and diffraction, and another optical member (which may be another optical film). Preferably, it can be used to bond the optical film and the other optical member. Among them, in the bonding of an optical film having at least one function of light waveguide, light collection, and diffraction, it is desirable that the entire bulk of the bonding layer has a high refractive index, and it can be a preferred application target when implementing the technology disclosed herein in an embodiment including a high refractive index layer (typically a high refractive index adhesive layer).

[0245] The adhesive layer disclosed herein can be preferably used for joining optical films such as a light guide film, a diffusion film, a fluorescent film, a color - adjusting film, a prism sheet, a lenticular film, a microlens array film, etc. In these applications, from the viewpoints of the trend of miniaturization and high - performance improvement of optical members, thinning and improvement of light extraction efficiency are required. As an adhesive layer capable of meeting such requirements, the adhesive layer disclosed herein can be preferably utilized. More specifically, for example, in the joining of a light guide film or a diffusion film, adjusting the refractive index of the adhesive layer as a joining layer (for example, increasing the refractive index) can contribute to thinning. In the joining of a fluorescent film, by appropriately adjusting the refractive index difference between the fluorescent emitter and the adhesive, the light extraction efficiency (which can also be grasped as the emission efficiency) can be improved. In the joining of a color - adjusting film, by appropriately adjusting the refractive index of the adhesive so that the refractive index difference from the color - adjusting pigment becomes small, the scattering component can be reduced, contributing to the improvement of light transmittance. In the joining of a prism sheet, a lenticular film, a microlens array film, etc., by appropriately adjusting the refractive index of the adhesive, the diffraction of light can be controlled, contributing to the improvement of brightness and / or viewing angle.

[0246] The high refractive index adhesive layer disclosed herein is preferably used, for example, in the form of a laminated sheet with a low refractive index adhesive layer, in a manner of being attached to a high refractive index adherend (which can be a high refractive index layer, member, etc.). It can suppress the interfacial reflection with the above adherend. The high refractive index adhesive layer used in such a manner preferably has a small refractive index difference from the high refractive index adherend as described above and high adhesion at the interface with the adherend. Further, from the viewpoint of enhancing the homogeneity of the appearance, it is preferable that the thickness uniformity of the adhesive layer is high. For example, it is preferable that the surface smoothness of the adhesive surface is high. When the thickness of the high refractive index adherend is relatively small (for example, 5 μm or less, 4 μm or less, or 2 μm or less), it is particularly meaningful to suppress the reflection at the interface from the viewpoint of suppressing coloration and color unevenness due to the interference of reflected light. As an example of such a usage mode, in a polarizing plate with a retardation layer including a polarizer, a first retardation layer, and a second retardation layer in this order, a mode of being used for bonding the polarizer and the first retardation layer and / or bonding the first retardation layer and the second retardation layer can be mentioned.

[0247] Further, the high refractive index adhesive layer disclosed herein can be preferably used in a manner of being attached to a light emitting layer such as an optical semiconductor (for example, a high refractive index light emitting layer mainly composed of an inorganic material). By reducing the refractive index difference between the light emitting layer and the high refractive index adhesive layer, the reflection at their interface can be suppressed, and the light extraction efficiency can be improved. Further, from the viewpoint of preventing the deterioration of the light emitting element due to moisture, it is preferable that the water absorption rate of the high refractive index adhesive layer is low. From the viewpoint of improving the luminance, it is preferable that the high refractive index adhesive layer has low coloration. This can also be advantageous from the viewpoint of suppressing unintentional coloration caused by the high refractive index adhesive layer.

[0248] The high refractive index adhesive layer disclosed herein can be preferably used as a coating layer covering a lens surface, a bonding layer with a member facing the lens surface (e.g., a member having a surface shape corresponding to the lens surface), a filling layer filled between the lens surface and the member, etc. in a microlens or other lens members (e.g., microlenses constituting a microlens array film, lens members such as microlenses for cameras) used as constituent members of cameras, light emitting devices, etc. The high refractive index adhesive layer disclosed herein can reduce the refractive index difference from a lens (e.g., a lens made of a high refractive index resin or a lens having a surface layer made of a high refractive index resin) even when arranged in contact with the lens. This is advantageous from the viewpoint of thinning the lens and products equipped with the lens, and can also contribute to suppressing aberration and improving the Abbe number. In the technology disclosed herein, the adhesive (viscoelastic material) constituting the high refractive index adhesive layer can itself be used as a lens resin, for example, in a form filled in a recess or void of a suitable transparent member.

[0249] As a mode of bonding optical members using the adhesive layer disclosed herein (which is a high refractive index adhesive layer and / or a low refractive index adhesive layer, and preferably a low refractive index adhesive layer that may be laminated on the high refractive index layer), it is not particularly limited. For example, (1) a mode of bonding optical members via the adhesive layer disclosed herein, (2) a mode of bonding an optical member to a member other than an optical member via the adhesive layer disclosed herein, or (3) a mode in which the adhesive layer disclosed herein is in the form of an adhesive sheet containing an optical member and the adhesive sheet is bonded to an optical member or a member other than an optical member may be used. In the mode of (3) above, the adhesive sheet in the form containing an optical member may be, for example, an adhesive sheet whose support is an optical member (e.g., an optical film). Thus, an adhesive sheet in the form containing an optical member as a support can also be regarded as an adhesive type optical member (e.g., an adhesive type optical film). Further, when the adhesive layer disclosed herein constitutes an adhesive sheet having a support and the above functional film is used as the support, the adhesive sheet can also be regarded as an "adhesive type functional film" having the adhesive layer disclosed herein on at least one side of the functional film.

[0250] From the above, according to the technology disclosed herein, an optical laminate including the adhesive layer disclosed herein and a member (e.g., a resin film such as an optical film) to which the adhesive sheet is attached is provided. The member to which the adhesive layer is attached can have the refractive index of the adherend material described above. Also, the difference in refractive index (refractive index difference) between the refractive index of the adhesive layer and the refractive index of the member can be the refractive index difference between the adherend and the adhesive layer described above. Regarding the members constituting the laminate, since they are as described above for the members, materials, and adherends, repeated explanations will not be repeated.

[0251] As can be understood from the above description and the following examples, the matters disclosed in this specification include the following.

[0252] 〔101〕 An adhesive containing an acrylic polymer (F) containing a fluorine-containing acrylic monomer (M1) as a monomer unit, having a refractive index of 1.46 or less and an adhesive having a storage elastic modulus G' at 25 °C of 1.0 kPa or more and 400 kPa or less. 〔102〕 The adhesive according to 〔101〕 above, wherein in the monomer component constituting the acrylic polymer (F), the content of the fluorine-containing acrylic monomer (M1) is 25% by weight or more. 〔103〕 The adhesive according to 〔101〕 or 〔102〕 above, wherein the fluorine-containing acrylic monomer (M1) contains a fluorine atom-containing alkyl (meth)acrylate. 〔104〕 The adhesive according to any one of 〔101〕 to 〔103〕 above, wherein the acrylic polymer (F) contains a hydroxyl group-containing monomer as a monomer unit. 〔105〕 A low refractive index adhesive layer formed from the adhesive according to any one of 〔101〕 to 〔104〕 above, a high refractive index adhesive layer laminated on the low refractive index adhesive layer, and a laminated sheet comprising the same. 〔106〕 The laminated sheet according to 〔105〕 above, wherein the ratio (n1 / n2) of the refractive index n1 of the high refractive index adhesive layer to the refractive index n2 of the low refractive index adhesive layer is 1.02 or more. 〔107〕 The laminated sheet according to 〔105〕 or 〔106〕 above, wherein the refractive index n1 of the high refractive index adhesive layer exceeds 1.570. 〔108〕 The laminated sheet according to any one of 〔105〕 to 〔107〕 above, wherein the high refractive index adhesive layer has a storage elastic modulus G' at 25 °C of 700 kPa or less. 〔109〕 The laminated sheet according to any one of 〔105〕 to 〔108〕 above, having a total light transmittance of 86% or more and a haze value of 3.0% or less. 〔110〕 A light-emitting device comprising a self-luminous element and the laminated sheet according to any one of 〔105〕 to 〔109〕 above, wherein the laminated sheet is disposed on the viewing side of the self-luminous element.

[0253] 〔1〕 An adhesive sheet including an adhesive layer, It has an adhesive surface composed of the above adhesive layer, The adhesive layer is an adhesive sheet having a refractive index exceeding 1.570, a total light transmittance of 86% or more, and a haze value of 3.0% or less. 〔2〕 The adhesive sheet according to the above 〔1〕, wherein the adhesive layer has a thickness of 5 μm or more. 〔3〕 The adhesive sheet according to the above 〔1〕 or 〔2〕, having a peel strength (adhesive force) with respect to a glass plate of 3 N / 25 mm or more. 〔4〕 The adhesive sheet according to any one of the above 〔1〕 to 〔3〕, wherein the arithmetic mean roughness Ra of the adhesive surface is 100 nm or less. 〔5〕 The adhesive sheet according to any one of the above 〔1〕 to 〔4〕, wherein the water absorption rate of the adhesive layer is 1.0% or less. 〔6〕 The adhesive sheet according to any one of the above 〔1〕 to 〔5〕, which is configured as a laminate including the adhesive layer and a light-transmissive substrate. 〔7〕 The adhesive sheet according to the above 〔6〕, wherein the light-transmissive substrate is a resin film. 〔8〕 The adhesive sheet according to any one of the above 〔1〕 to 〔5〕, which is a double-sided adhesive adhesive sheet composed of the adhesive layer. 〔9〕 The adhesive sheet according to any one of the above 〔1〕 to 〔8〕, A release liner disposed on the adhesive surface of the adhesive sheet, And an adhesive sheet with a release liner. 〔10〕 An adhesive composition used for forming the adhesive layer of the adhesive sheet according to any one of the above 〔1〕 to 〔8〕.

[0254] 〔11〕 An acrylic polymer (A) containing an aromatic ring-containing monomer (m1) as a monomer unit, An additive (H RO ) which is an organic material having a higher refractive index than the above acrylic polymer (A), And an adhesive composition. 〔12〕 The adhesive composition according to the above 〔11〕, wherein the refractive index of the additive (H RO ) is 1.60 or more.

[13] The content of the above additive (H RO ) with respect to 100 parts by weight of the above acrylic polymer (A) is more than 0 part by weight and 60 parts by weight or less, and the pressure-sensitive adhesive composition according to the above

[11] or

[12] .

[14] The above additive (H RO ) contains at least one compound selected from the group consisting of an aromatic ring-containing compound and a heterocyclic ring-containing compound, and the pressure-sensitive adhesive composition according to any one of the above

[11] to

[13] .

[15] The above additive (H RO ) contains a compound having two or more aromatic rings in one molecule, and the pressure-sensitive adhesive composition according to any one of the above

[11] to

[14] .

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

[15] containing a compound satisfying at least one of them.

[17] In the monomer component constituting the above acrylic polymer (A), the content of the above aromatic ring-containing monomer (m1) is 50% by weight or more, and the pressure-sensitive adhesive composition according to any one of the above

[11] to

[16] .

[18] In the monomer component constituting the above acrylic polymer (A), the content of the above aromatic ring-containing monomer (m1) is more than 70% by weight and less than 100% by weight, and 50% by weight or more of the above aromatic ring-containing monomer (m1) is a monomer having a glass transition temperature of the homopolymer of 10°C or lower, and the pressure-sensitive adhesive composition according to any one of the above

[11] to

[17] .

[19] The monomer component constituting the above acrylic polymer (A) further contains a monomer (m2) having at least one of a hydroxyl group and a carboxyl group, and the pressure-sensitive adhesive composition according to any one of the above

[11] to

[18] .

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

[11] to

[18] , which is used for forming the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to any one of the above [1] to [8]. An adhesive formed from the adhesive composition according to any one of

[11] to

[20] above, having a refractive index higher than 1.570. 〔22〕 An adhesive sheet comprising an adhesive layer composed of an adhesive formed from the adhesive composition according to any one of

[11] to

[20] above. 〔23〕 The adhesive sheet according to

[22] above, wherein the haze value of the adhesive layer is 1.0% or less.

[0255] 〔24〕 An interlayer sheet used by being disposed between layers of a laminate in an optical application, comprising a viscoelastic layer V1 having a refractive index n1 of 1.570 or more, and having a total light transmittance of 86% or more; having a haze value of 1.0% or less; and, having a storage elastic modulus G' at 25°C of 30 kPa to 700 kPa; An interlayer sheet satisfying the above conditions. 〔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] above, 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〕 Further comprising a viscoelastic layer V2 laminated on the viscoelastic layer V1, wherein the storage elastic modulus G' of the viscoelastic layer V2 at 25°C V2 is lower than the storage elastic modulus G' of the viscoelastic layer V1 at 25°C V1 The interlayer sheet according to any one of

[24] to

[27] above. 〔29〕 The interlayer sheet according to

[28] above, 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 adhesive composition according to any one of

[11] to

[18] above.

[31] The viscoelastic layer V1 is an interlayer sheet as described in any one of the above

[24] to

[29] , which is an adhesive layer in the pressure-sensitive adhesive sheet as described in any one of the above [1] to [5].

[32] An interlayer sheet according to any one of the above

[24] to

[31] , and a resin film laminated on the interlayer sheet, An optical laminate comprising.

[33] An interlayer sheet according to any one of the above

[24] to

[31] , and a release liner covering at least one surface of the interlayer sheet, An interlayer sheet with a release liner comprising.

[0256]

[34] A self-luminous element, a low refractive index layer disposed on the viewing side of the self-luminous element, a high refractive index pressure-sensitive adhesive layer laminated in direct contact with the low refractive index layer, comprising, The high refractive index pressure-sensitive adhesive layer has a refractive index n1 of more than 1.570, a total light transmittance of 86% or more, and a haze value of 3.0% or less. A light-emitting device.

[35] The light-emitting device according to the above

[34] , wherein the ratio (n1 / n2) of the refractive index n1 of the high refractive index pressure-sensitive adhesive layer to the refractive index n2 of the low refractive index layer is 1.05 or more.

[36] The light-emitting device according to the above

[35] or

[36] , wherein the arithmetic mean roughness Ra of the surface of the high refractive index pressure-sensitive adhesive layer is 100 nm or less.

[37] The light-emitting device according to any one of the above

[34] to

[36] , wherein the ratio (T1 / T2) of the thickness T1 of the high refractive index pressure-sensitive adhesive layer to the thickness T2 of the low refractive index layer is 0.5 to 5.

[38] The light-emitting device according to any one of the above

[34] to

[37] , wherein the thickness T1 of the high refractive index pressure-sensitive adhesive layer is 5 μm or more.

[39] The laminated sheet composed of the high refractive index pressure-sensitive adhesive layer and the low refractive index layer has a total light transmittance of 86% or more and a haze value of 3.0% or less. The light-emitting device according to any one of the above

[34] to

[38] . 〔40〕The light-emitting device according to any one of 〔34〕to 〔39〕, wherein the high refractive index adhesive layer is a layer formed from the adhesive composition according to any one of 〔11〕to 〔18〕. 〔41〕The light-emitting device according to any one of 〔34〕to 〔40〕, wherein the high refractive index adhesive layer is an adhesive layer in the adhesive sheet according to any one of 〔1〕to 〔5〕. 〔42〕The light-emitting device according to any one of 〔34〕to 〔41〕, wherein the low refractive index layer is a layer composed of the adhesive according to any one of 〔101〕to 〔104〕. 〔43〕The interlayer sheet according to any one of 〔24〕to 〔31〕, wherein the viscoelastic layer V2 is a layer composed of the adhesive according to any one of 〔101〕to 〔104〕.

Examples

[0257] Hereinafter, some experimental aspects related to the present invention will be described. In the following description, "parts" and "%" representing usage amounts and contents are based on weight unless otherwise specified.

[0258] <Preparation of Adhesive Composition C1> Into a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a cooler, 99.0 parts of 1H,1H,2H,2H-tridecafluorooctyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Biscoat 13F") as a monomer component, 1.0 part of 4-hydroxybutyl acrylate (4HBA), 0.2 part of 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator, and 200 parts of ethyl acetate as a polymerization solvent were charged. While gently stirring, nitrogen gas was introduced, and the polymerization reaction was carried out for 9 hours while maintaining the liquid temperature in the flask at around 60°C to prepare a solution (33%) of acrylic polymer P1. The polymerization average molecular weight (Mw) of this acrylic polymer P1 was 800,000. The solution (33%) of the above acrylic polymer P1 was diluted to 30% with ethyl acetate. To 100 parts of the non-volatile content (solid content), 10 parts (non-volatile content 0.1 part) of a 1% ethyl acetate solution of the isocyanurate form of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) as a cross-linking agent was added and stirred and mixed to prepare an adhesive composition C1.

[0259] <Preparation of Adhesive Compositions C2 - C10> Solutions of acrylic polymers P2 - P10 were prepared in the same manner as the preparation of the solution of acrylic polymer P1, except that the composition of the monomer components was changed as shown in Table 1. Adhesive compositions C2 - C10 were prepared in the same manner as the preparation of adhesive composition C1, except that solutions of acrylic polymers P2 - P10 were used instead of the solution of acrylic polymer P1.

[0260] In the composition of the monomer components shown in Table 1, "V13F" represents 1H,1H,2H,2H-tridecafluorooctyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Biscoat 13F"), "V8F" represents 1H,1H,5H-octafluoropentyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Biscoat 8F"), and "V3F" represents 2,2,2-trifluoroethyl acrylate (trade name "Biscoat 3F" manufactured by Osaka Organic Chemical Industry Co., Ltd.). Also, 2EHA represents 2-ethylhexyl acrylate, NVP represents N-vinyl-2-pyrrolidone, IBXA represents isobornyl acrylate, and CHA represents cyclohexyl acrylate, respectively.

[0261] <Production of Adhesive Sheet (1)> (Example 1) The pressure-sensitive adhesive composition C1 prepared above was applied to the silicone-treated surface of a polyethylene terephthalate (PET) film R1 (thickness: 50 μm) having silicone treatment on one side, and heated at 130°C for 2 minutes to form a pressure-sensitive adhesive layer with a thickness of 25 μm. The silicone-treated surface of a PET film R2 (thickness: 38 μm) having silicone treatment on one side was bonded to the surface of the pressure-sensitive adhesive layer. In this way, a pressure-sensitive adhesive layer (substrate-free double-sided pressure-sensitive adhesive sheet) in a form protected by PET films (release liners) R1 and R2 on both sides was obtained. Note that the release liner R2 has relatively easy peelability compared to the release liner R1.

[0262] (Examples 2 to 10) Adhesive layers (substrate-free double-sided pressure-sensitive adhesive sheets) according to Examples 2 to 10 were prepared in the same manner as in Example 1, except that adhesive compositions C2 to C10 were used instead of the adhesive composition C1.

[0263] After allowing the obtained pressure-sensitive adhesive sheets to sufficiently adapt to an environment of 23°C and 50% RH, they were used for the following measurements and evaluations.

[0264] (Measurement and Evaluation (1)) (Refractive Index) For each pressure-sensitive adhesive layer, the refractive index was measured using an Abbe refractometer (manufactured by ATAGO Co., Ltd., model "DR-M4") under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. The results are shown in Table 1.

[0265] (Storage Elastic Modulus G') Samples for measurement were prepared by laminating each pressure-sensitive adhesive layer to a thickness of about 1.5 mm. Dynamic viscoelasticity measurement was performed using ARES manufactured by TA Instruments under the following conditions. From the measurement results, the storage elastic modulus G' at 25°C was read. The results are shown in Table 1. [Measurement Conditions] Deformation Mode: Torsion Measurement Frequency: 1 Hz Temperature Rise Rate: 5°C / min Shape: Parallel Plate 7.9 mmφ

[0266] (Total light transmittance and haze value) Using a test piece obtained by laminating the pressure-sensitive adhesive sheet according to each example onto a non-alkali glass (thickness: 0.8 to 1.0 mm, total light transmittance: 92%, haze: 0.4%), in a measurement environment at 23°C, the total light transmittance and haze of the above test piece were measured using a haze meter (manufactured by Murakami Color Research Laboratory, trade name "HAZEMETER HM-150"). The values obtained by subtracting the total light transmittance and haze of the above non-alkali glass from the measured values were taken as the total light transmittance and haze value of the pressure-sensitive adhesive sheet. The results are shown in Table 1.

[0267] (Peeling strength against glass plate) In a measurement environment at 23°C and 50% RH, the release liner was peeled from one surface of the pressure-sensitive adhesive sheet according to each example, a PET film with a thickness of 50 μm was laminated and used as a backing, and then it was cut into a size of 25 mm in width and 100 mm in length to obtain a test piece. The release liner on the other surface was peeled from the test piece, and a 2 kg roller was reciprocated once on the surface of an alkali glass plate (manufactured by Matsunami Glass Industry Co., Ltd., thickness: 1.35 mm, blue plate edge ground product) as an adherend to perform pressure bonding. This was left in the same environment for 30 minutes, then put into a pressure-defoaming device (autoclave), and autoclave treatment was performed at a temperature of 50°C and a pressure of 0.5 MPa for 30 minutes. After further leaving it in an atmosphere of 23°C and 50% RH for 24 hours, using a universal tensile-compression testing machine, in accordance with JIS Z 0237:2000, under the conditions of a tensile speed of 300 mm / min and a peeling angle of 180 degrees, the peeling strength (adhesive force) [N / 25 mm] was measured. As the universal tensile-compression testing machine, "Tensile-Compression Testing Machine, TG-1kN" manufactured by Minebea Co., Ltd. was used.

[0268]

Table 1

[0269] As shown in Table 1, the pressure-sensitive adhesive sheets of Examples 1 to 9 all had a refractive index of 1.46 or less and a storage elastic modulus G'(25) of 400 kPa. These pressure-sensitive adhesive sheets showed high transparency and practical peeling strength suitable for bonding optical members.

[0270] <Preparation of Adhesive Composition C11> Into a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a cooler, 65 parts of 2EHA, 30 parts of 1H,1H,5H-octafluoropentyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name: Biscoat 8F), 3 parts of N-vinyl-2-pyrrolidone (NVP, manufactured by Nippon Shokubai), 2 parts of 4HBA, 0.2 part of AIBN as a polymerization initiator, and 200 parts of ethyl acetate as a polymerization solvent were charged. While gently stirring, nitrogen gas was introduced, and the polymerization reaction was carried out for 9 hours while maintaining the liquid temperature in the flask at around 60 °C to prepare a solution (33%) of acrylic polymer P11. The polymerization average molecular weight (Mw) of the above acrylic polymer P11 was 550,000. The solution (33%) of the above acrylic polymer P11 was diluted to 30% with ethyl acetate, and 10 parts (non-volatile content: 0.1 part) of a 1% ethyl acetate solution of isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) was added as a crosslinking agent to 100 parts of the non-volatile content (solid content) and stirred and mixed to prepare an adhesive composition C11.

[0271] <Preparation of Adhesive Composition C12> Into a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a cooler, 95 parts of m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A", refractive index: 1.566, Tg of homopolymer: -35 °C. Hereinafter abbreviated as "POB-A") and 5 parts of 4HBA, 0.2 part of AIBN as a polymerization initiator, and 100 parts of toluene as a polymerization solvent were charged. While gently stirring, nitrogen gas was introduced, and the polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at around 60 °C to prepare a solution (50%) of acrylic polymer P12. The polymerization average molecular weight (Mw) of this acrylic polymer P12 was 500,000. The above acrylic polymer P12 has a Tg (i.e., Tg T ) of -35 °C based on the composition of the above monomer components, and a Tg (i.e., Tg m1 ) of -35 °C based on the composition of the aromatic ring-containing monomer. The solution (50%) of the above acrylic polymer P12 was diluted to 30% with ethyl acetate. To 334 parts of this solution (100 parts of non-volatile matter), 10 parts 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 (0.1 part of non-volatile matter), 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of ferric naphthenate as a crosslinking catalyst (0.01 part of non-volatile matter) were added and stirred and mixed to prepare an adhesive composition C12.

[0272] <Preparation of Adhesive Composition C13> Into a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a cooler, 72 parts of POB-A as a monomer component, 23 parts of 1-naphthylmethyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate NMT-A", refractive index: 1.595, Tg of homopolymer: 31 °C. Hereinafter abbreviated as "NMT-A"), 5 parts of 4HBA, 0.2 part of AIBN as a polymerization initiator, and 100 parts of toluene as a polymerization solvent were charged. While gently stirring, nitrogen gas was introduced, and the polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at around 60 °C to prepare a solution (50%) of an acrylic polymer P13. The polymerization average molecular weight (Mw) of this acrylic polymer P13 was 500,000. Into a separable flask equipped with a thermometer, a stirrer, a reflux condenser, and a nitrogen gas inlet tube, 20 parts of POB-A as a monomer component, 80 parts of NMT-A, 0.2 part of AIBN as a polymerization initiator, 3.5 parts of α-thioglycerol as a chain transfer agent, and 67 parts of methyl ethyl ketone were charged. Then, nitrogen gas was passed through, and nitrogen substitution was carried out for about 1 hour while stirring. Thereafter, the flask was heated to 70 °C and reacted for 12 hours to obtain an acrylic oligomer (oligomer B) having a weight average molecular weight (Mw) of 4000 and a refractive index of 1.63. The solution (50%) of the above acrylic polymer C13 was diluted to 30% with ethyl acetate. To 334 parts of this solution (100 parts of non-volatile matter), 20 parts of the oligomer B prepared above, 10 parts of a 1% ethyl acetate solution of an isocyanurate form of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) (0.1 part of non-volatile matter) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of ferric naphthenate (0.01 part of non-volatile matter) as a crosslinking catalyst were added and stirred and mixed to prepare an adhesive composition C13.

[0273] <Production of Adhesive Sheet (2)> (Example 11) The adhesive composition C11 prepared above was applied to the silicone-treated surface of a release liner R1 (thickness 50 μm) and heated at 130°C for 2 minutes to form an adhesive layer with a thickness of 10 μm. The silicone-treated surface of a release liner R2 (thickness 38 μm) was laminated on the surface of the above adhesive layer. In this way, an adhesive layer (substrate-free double-sided adhesive sheet) formed from the adhesive composition C11 in a form where both sides were protected by PET films (release liners) R1 and R2 was obtained.

[0274] (Example 12) The adhesive composition C12 prepared above was applied to the silicone-treated surface of a release liner R1 and heated at 130°C for 2 minutes to form an adhesive layer with a thickness of 25 μm. The silicone-treated surface of a release liner R2 was laminated on the surface of the above adhesive layer. In this way, an adhesive layer (substrate-free double-sided adhesive sheet) formed from the adhesive composition C12 in a form where both sides were protected by PET films (release liners) R1 and R2 was obtained. The release liner R2 was peeled off from each of the obtained adhesive layers and the adhesive layer prepared in Example 11, and the adhesive surfaces were bonded together and crimped with a hand roller. The laminate was subjected to autoclave treatment at 50°C and 0.60 MPa for 30 minutes, and then aged in an environment at 50°C for 48 hours. In this way, a laminated sheet (substrate-free double-sided adhesive sheet) having a two-layer structure of an adhesive layer (high refractive index adhesive layer) formed from the adhesive composition C12 / an adhesive layer (low refractive index adhesive layer) formed from the adhesive composition C11 was obtained. The surface of this adhesive sheet is protected by two release liners R1.

[0275] (Example 13) A laminated sheet (substrate-free double-sided adhesive sheet) having a two-layer structure of a high refractive index adhesive layer / a low refractive index adhesive layer was obtained in the same manner as in Example 12, except that the type of the adhesive composition used for forming each adhesive layer and the thickness of each adhesive layer were changed as shown in Table 2.

[0276] (Examples 14, 15) In the same manner as in Example 13, an adhesive layer having a single-layer structure composed of each of the adhesive compositions C12 and C13 and having the thickness shown in Table 2 was produced, and an adhesive sheet according to Examples 14 and 15 was obtained.

[0277] <Measurement and Evaluation (2)> After sufficiently conditioning the adhesive sheets obtained in Examples 11 to 15 in an environment at 23°C and 50% RH, the measurement and evaluation of each item were carried out in the same manner as in the above-mentioned "Measurement and Evaluation (1)". For the substrate-free double-sided adhesive sheet having a two-layer structure of a high refractive index adhesive layer / a low refractive index adhesive layer, the peel strength on the high refractive index adhesive layer side was measured. The results are shown in Table 2.

[0278]

Table 2

[0279] As shown in Table 2, the pressure-sensitive adhesive sheets of Examples 11 to 13 included a pressure-sensitive adhesive layer having a refractive index of 1.46 or less and exhibited high transparency in the pressure-sensitive adhesive sheets. These pressure-sensitive adhesive sheets exhibited a practical peel strength suitable for bonding optical members.

[0280] <Evaluation of the front luminance improvement effect> On a white LED light-emitting light source, the pressure-sensitive adhesive sheets according to each of Examples 11 to 15 were attached, and after the light source was lit for 30 minutes or more in a dark room environment to stabilize it, a spectro-radiometer SR-UL1R (manufactured by Topcon Techno House Co., Ltd.) was used to measure the front luminance at the portion where the pressure-sensitive adhesive sheet was attached. Using the average value of the luminance measured three times, those having a luminance improvement effect of 10% or more with respect to the luminance of the light source without the pressure-sensitive adhesive sheet attached were evaluated as G (Good), and those having a luminance improvement of less than 10% were evaluated as P (Poor). The results are shown in Table 3.

[0281]

Table 3

[0282] As shown in Table 3, according to the pressure-sensitive adhesive sheets (laminated sheets) of Examples 12 and 13 having a laminated structure pressure-sensitive adhesive layer in which a low refractive index pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition C11 and a high refractive index pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition C12 or C13 were combined, a front luminance improvement effect of 10% or more was recognized as compared with the case where the pressure-sensitive adhesive sheet was not used. In the pressure-sensitive adhesive sheets of Examples 11, 14, and 15 in which the pressure-sensitive adhesive layer had a single-layer structure, no front luminance improvement effect was recognized by the pressure-sensitive adhesive sheet alone.

[0283] <Preparation of the pressure-sensitive adhesive composition C14> Into a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a cooler, 79 parts of POB-A, 20 parts of n-butyl acrylate, 1 part of 4HBA as monomer components, 0.2 part of AIBN as a polymerization initiator, and 100 parts of toluene as a polymerization solvent were charged. While gently stirring, nitrogen gas was introduced, and the polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at around 60 °C to prepare a solution (50%) of an acrylic polymer P14. The Mw of this acrylic polymer P14 was 520,000. The solution (50%) of the above acrylic polymer P14 was diluted to 30% with ethyl acetate. To 334 parts of this solution (100 parts of non-volatile matter), 10 parts (0.1 part of non-volatile matter) of a 1% ethyl acetate solution of coronate HX as a cross-linking agent, 2 parts of acetylacetone as a cross-linking retarder, and 1 part (0.01 part of non-volatile matter) of a 1% ethyl acetate solution of ferric naphthenate as a cross-linking catalyst were added and stirred and mixed to prepare an adhesive composition C14.

[0284] <Preparation of Adhesive Composition C15> A solution (50%) of an acrylic polymer P15 was prepared in the same manner as the preparation of the solution of acrylic polymer P14, except that the composition (weight ratio) of the monomer components was changed to POB-A / ethyl carbitol acrylate (CBA) / 4HBA = 79 / 20 / 1. The Mw of this acrylic polymer P15 was 460,000. An adhesive composition C15 was prepared in the same manner as the preparation of the adhesive composition C14, except that the solution of acrylic polymer P15 was used instead of the solution of acrylic polymer P14.

[0285] <Preparation of Adhesive Composition C16> A solution (50%) of an acrylic polymer P16 was prepared in the same manner as the preparation of the solution of acrylic polymer P14, except that the composition (weight ratio) of the monomer components was changed to P2H-A / 4HBA = 99 / 1. In the composition of the above monomer components, "P2H-A" represents phenoxydiethylene glycol acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate P2H-A", refractive index: 1.510, Tg of homopolymer: -35 °C). The Mw of this acrylic polymer P16 was 1,000,000. A solution (50%) of acrylic polymer P16 was diluted to 30% with ethyl acetate. To 334 parts of this solution (100 parts of non-volatile content), 20 parts of 6-ethyl acrylate-dinaphtho[2,1-b:1’,2’-d]thiophene (6-acryloyloxyethyl dinaphthothiophene manufactured by Sugai Chemical Industry Co., Ltd., abbreviation: 6EDNTA, refractive index: 1.722) as an additive (H RO ), 10 parts of a 1% ethyl acetate solution of Coronate HX (0.1 part of non-volatile content) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of ferric naphthenate (0.01 part of non-volatile content) as a crosslinking catalyst were added and stirred and mixed to prepare an adhesive composition C16.

[0286] <Production of Adhesive Sheet> (Examples 16 to 18) A laminated sheet (substrate-free double-sided adhesive sheet) having a two-layer structure of a high refractive index adhesive layer / low refractive index adhesive layer was obtained in the same manner as in Example 12, except that the type of the adhesive composition used for forming each adhesive layer and the thickness of each adhesive layer were as shown in Table 4. The Mw of the acrylic polymer P4, which is the base polymer of the adhesive composition C4, is 5.5 million.

[0287] <Measurement and Evaluation (3)> After allowing the adhesive sheets obtained in Examples 16 to 18 to sufficiently adapt to an environment of 23°C and 50% RH, the measurement and evaluation of each item were carried out in the same manner as in the above-mentioned "Measurement and Evaluation (2)". The results are shown in Table 4.

[0288]

Table 4

[0289] As shown in Table 4, the laminated sheets of Examples 16 to 18 having a structure in which a low refractive index adhesive layer formed from the adhesive composition C4 and an adhesive layer having a refractive index 0.01 or more (more specifically, 0.10 or more) higher than that of the low refractive index adhesive layer are laminated all showed high transparency. These adhesive sheets showed a practical peel strength suitable for bonding optical members.

[0290] The specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples exemplified above.

Explanation of Reference Numerals

[0291] 1 Adhesive sheet 2 Adhesive sheet (laminated sheet) 10 Adhesive layer 10A First surface (first adhesive surface) 10B Second surface (second adhesive surface) 11 First adhesive layer (high refractive index adhesive layer) 12 Second adhesive layer (low refractive index adhesive layer) 70 Self-luminous element 80 Cover window member 100 Light-emitting device

Claims

1. A low refractive index adhesive layer formed from an adhesive containing an acrylic polymer (F) containing a fluorine-containing acrylic monomer (M1) and a hydroxyl group-containing monomer as monomer units, and a high refractive index adhesive layer laminated on the low refractive index adhesive layer, wherein the content of the hydroxyl group-containing monomer in the monomer components constituting the acrylic polymer (F) is 0.5% by weight or more and 15% by weight or less, the refractive index of the adhesive is 1.46 or less, and the storage elastic modulus G' of the adhesive at 25°C is 1.0 kPa or more and 400 kPa or less, a laminated sheet.

2. The laminated sheet according to claim 1, wherein in the monomer components constituting the acrylic polymer (F), the content of the fluorine-containing acrylic monomer (M1) is 25% by weight or more.

3. The laminated sheet according to claim 1 or 2, wherein the fluorine-containing acrylic monomer (M1) contains an alkyl (meth)acrylate containing a fluorine atom.

4. The refractive index n of the high refractive index adhesive layer １ and the ratio (n １ / n ２ ) with the refractive index n2 of the low refractive index adhesive layer is 1.02 or more. The laminated sheet according to any one of claims 1 to 3

5. The refractive index n of the high refractive index adhesive layer １ is more than 1.570, and the laminated sheet according to any one of claims 1 to 4.

6. The laminated sheet according to any one of claims 1 to 5, wherein the adhesive constituting the high refractive index adhesive layer has a storage elastic modulus G' at 25°C of 700 kPa or less.

7. The laminated sheet according to any one of claims 1 to 6, having a total light transmittance of 86% or more and a haze value of 3.0% or less.

8. A self-luminous element, and the laminated sheet according to any one of claims 1 to 7, comprising a light-emitting device, wherein the laminated sheet is disposed on the viewing side of the self-luminous element.

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