Adhesive composition, adhesive, and adhesive sheet

Abstract

To provide an adhesive with a refractive index improved by a method appropriate even for an optical use, an adhesive composition capable of forming the adhesive, and a pressure sensitive adhesive sheet containing the adhesive.SOLUTION: An adhesive composition includes: an acrylic polymer (A) containing an aromatic ring-containing monomer (m1) as a monomer unit; and an additive (HRO) being an organic material with a refractive index higher than that of the acrylic polymer (A). Further, a pressure sensitive adhesive sheet has an adhesive formed by the adhesive composition.SELECTED DRAWING: Figure 1

Description

Technical Field

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

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 from household appliances to automobiles, various machines, electrical equipment, electronic equipment, etc. As an example of the use of adhesives, in display devices such as liquid crystal display devices and organic EL display devices, there is an application of joining a polarizing film, a retardation film, a cover window member, and various other light-transmissive members to other members. Patent Documents 1 and 2 can be cited as technical documents regarding adhesives for optical members.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Patent Documents 1 and 2 propose an adhesive composition mainly composed of a (meth)acrylic acid ester polymer containing a monomer having a plurality of aromatic rings as monomer units, and an adhesive obtained by crosslinking the adhesive composition. However, with the techniques described in Patent Documents 1 and 2, it is difficult to obtain an adhesive having a refractive index higher than that of the above (meth)acrylic acid ester polymer. On the other hand, a technique of blending particles made of an inorganic material having a high refractive index (for example, inorganic particles such as zirconium oxide particles and titanium oxide particles) into a resin to increase the refractive index is also known. However, since there is a trade-off relationship between the refractive index and the adhesive properties (for example, peel strength, flexibility, etc.) of the adhesive containing the inorganic particles, it is difficult to apply it to the field of adhesives. In the case of adhesives for optical applications, there is also concern about a decrease in optical properties due to the blending of inorganic particles.

[0005] Therefore, an object of the present invention is to provide an adhesive having an improved refractive index by a method suitable for optical applications. Another related object is to provide an adhesive composition capable of forming such an adhesive and an adhesive sheet containing the adhesive.

Means for Solving the Problems

[0006] The adhesive composition provided by this specification includes an acrylic polymer (A) containing an aromatic ring-containing monomer (m1) as a monomer unit, and an additive (H RO ) which is an organic material having a higher refractive index than the above acrylic polymer (A). The acrylic polymer (A) containing an aromatic ring-containing monomer (m1) as a monomer unit can have a high refractive index. The adhesive composition disclosed herein, in addition to such an acrylic polymer (A), further includes an additive (H RO ) which is an organic material having a higher refractive index than the above acrylic polymer (A). By doing so, an adhesive can be formed in which the improvement of the refractive index by the above additive (H RO ) and the suppression of the decrease in adhesive properties are well balanced. Further, according to the above additive (H RO ), it is possible to effectively improve the refractive index of the adhesive while suppressing a decrease in optical properties (for example, transmittance, haze, etc.).

[0007] In some preferred embodiments of the technology disclosed herein (including the technology implemented in the form of an adhesive composition, an adhesive, an adhesive sheet, and others. The same applies hereinafter.), the refractive index of the above additive (H RO ) can be, for example, approximately 1.60 or more. According to the additive (H RO ) which is an organic material having a higher refractive index than the acrylic polymer (A) and a refractive index satisfying approximately 1.60 or more, the refractive index of the adhesive can be effectively improved.

[0008] In some embodiments, the content of the above additive (H RO ) with respect to 100 parts by weight of the acrylic polymer (A) can be, for example, more than 0 parts by weight and 60 parts by weight or less. An adhesive composition containing the additive (H RO ) at such a content is preferable because it is easy to form an adhesive in which the improvement in refractive index due to the use of the additive (H RO ) and the suppression of the deterioration of the adhesive properties and / or optical properties are well balanced.

[0009] In some embodiments, 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. The technology disclosed herein can be preferably implemented in an embodiment where such a compound is used as the additive (H RO ).

[0010] In some embodiments, the above additive (H RO ) contains a compound having two or more aromatic rings in one molecule. The technology disclosed herein can be preferably implemented in an embodiment where such a compound is used as the additive (H RO ). The compound having two or more aromatic rings in one molecule can be, for example, (i) a compound containing a structure in which two non-condensed aromatic rings are directly chemically bonded, and (ii) a compound containing a structure in which two aromatic rings are condensed, and can be a compound satisfying at least one of them. The technology disclosed herein can be preferably implemented in an embodiment where such a compound is used as the additive (H RO ).

[0011] In some embodiments, the content of the aromatic ring-containing monomer (m1) in the monomer component constituting the acrylic polymer (A) is 50% by weight or more. The acrylic polymer (A) composed of the monomer component having such a composition can have a high refractive index, and thus is suitable as the acrylic polymer (A) in the technology disclosed herein.

[0012] In some embodiments, the content of the aromatic ring-containing monomer (m1) in the monomer component constituting the acrylic polymer (A) exceeds 70% by weight and is less than 100% by weight. Such an acrylic polymer (A) is preferable because it is easy to increase the refractive index and easy to form an adhesive having good adhesive properties.

[0013] In some embodiments, 50% by weight or more of the aromatic ring-containing monomer (m1) contained in the monomer component constituting the acrylic polymer (A) can be a monomer having a glass transition temperature of the homopolymer of 10°C or lower. Thereby, even if the content of the aromatic ring-containing monomer (m1) in the monomer component is increased, it is easy to form an adhesive that well balances a high refractive index and adhesive properties. In the following, the Tg of the homopolymer of a monomer may be referred to as the Tg of the monomer.

[0014] In some preferred embodiments, the aromatic ring-containing monomer (m1) includes an aromatic ring-containing monomer having two or more aromatic rings in one molecule (hereinafter, also referred to as "aromatic ring multi-containing monomer"). By using the aromatic ring multi-containing monomer, the refractive index of the adhesive can be effectively improved. The aromatic ring-containing monomer (m1) may contain only one type of aromatic ring multi-containing monomer (for example, an aromatic ring multi-containing monomer having a Tg of the homopolymer of 10°C or lower), or may contain a combination of two or more types of aromatic ring multi-containing monomers.

[0015] In some preferred embodiments, the monomer having two or more aromatic rings in one molecule includes a monomer having a structural portion in which two aromatic rings are bonded via a linking group. The monomer containing a plurality of aromatic rings having such a structural portion has a tendency that the Tg of the homopolymer is lower than that of, for example, a monomer containing a plurality of aromatic rings having a structural portion in which two aromatic rings are directly chemically bonded (e.g., a biphenyl structure). According to the aromatic ring-containing monomer (m1) containing a monomer having such a structure, flexibility suitable for an adhesive and a high refractive index can be more balanced.

[0016] In some embodiments, the monomer component constituting the acrylic polymer (A) may further contain a monomer (m2) having at least one of a hydroxyl group and a carboxyl group in addition to the aromatic ring-containing monomer (m1). According to the acrylic polymer (A) composed of the monomer component having such a composition, it is easy to form an adhesive having good adhesive properties.

[0017] Hereinafter, the aromatic ring-containing monomer (m1) may be referred to as "monomer (m1)", and the monomer (m2) having at least one of a hydroxyl group and a carboxyl group may be referred to as "monomer (m2)".

[0018] The adhesive composition disclosed herein may further contain a crosslinking agent. By using a crosslinking agent, appropriate cohesiveness can be imparted to the adhesive, and the handleability during the production, processing, storage, and attachment to an adherend of the adhesive sheet can be improved.

[0019] According to this specification, an adhesive formed from any of the adhesive compositions disclosed herein is provided. Such an adhesive can have an improved refractive index while suppressing a decrease in adhesive properties and / or optical properties by including the above additive (H RO ). In a preferred embodiment, the refractive index of the adhesive can be, for example, more than 1.570 (preferably 1.575 or more, more preferably 1.580 or more).

[0020] According to this specification, there is provided an adhesive sheet including an adhesive layer composed of an adhesive formed from any of the adhesive compositions disclosed herein (for example, an adhesive having a refractive index exceeding 1.570, preferably 1.575 or more, more preferably 1.580 or more). Such an adhesive sheet can be preferably used in a manner of being adhered to a member (for example, an optical member).

[0021] In some embodiments of the adhesive sheet disclosed herein, the haze value of the adhesive layer is 1.0% or less. Such an adhesive sheet having a highly transparent adhesive layer can be preferably used, for example, in the optical field.

[0022] In addition, combinations of the respective elements described in this specification as appropriate may also be included in the scope of the invention for which patent protection is sought by this patent application.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0024] 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 relevant field. In the following drawings, members and parts that perform the same function may be described with the same reference numerals, and duplicate descriptions may be omitted or simplified. Also, the embodiments described in the drawings are schematic for clearly explaining the present invention, and do not necessarily accurately represent the size and scale of the actually provided product.

[0025] 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. When referring to a light-emitting device in this specification, the light-emitting device may include 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 used as illumination (for example, a planar light emitter module) and a display device in which pixels are formed.

[0026] In this specification, the "base polymer" of the adhesive refers to the main component of the rubber-like polymer contained in the adhesive, and is not interpreted in any other limited way. The above rubber-like 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.

[0027] 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 a polymer in which the proportion of the acrylic monomer among all the monomers used for synthesizing the polymer exceeds 50% by weight (preferably exceeds 70% by weight, for example, exceeds 90% by weight).

[0028] In this specification, “(meth)acryloyl” comprehensively refers to acryloyl and methacryloyl. Similarly, “(meth)acrylate” comprehensively refers to acrylate and methacrylate, and “(meth)acrylic” comprehensively refers to acrylic and methacrylic. Therefore, the concept of the acrylic monomer herein may include both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer).

[0029] <Adhesive composition> The adhesive composition disclosed herein may be any that can form an adhesive containing an acrylic polymer (A) (preferably, an adhesive containing the acrylic polymer (A) as a base polymer), and its form is not particularly limited. The above adhesive composition may be, for example, a solvent-type adhesive composition in which an adhesive-forming component is contained in an organic solvent, an active energy ray-curable adhesive composition prepared to be cured by active energy rays such as ultraviolet rays and radiation to form an adhesive, a water-dispersion-type adhesive composition in which an adhesive-forming component is dispersed in water, a hot-melt-type adhesive composition that is applied in a heat-melted state and forms an adhesive when cooled to near room temperature, and the like in various forms.

[0030] (Acrylic polymer (A)) The pressure-sensitive adhesive composition disclosed herein contains an acrylic polymer (A) containing an aromatic ring-containing monomer (m1) as a monomer unit. The acrylic polymer (A) is a polymer containing an aromatic ring-containing monomer (m1) as a monomer component constituting the acrylic polymer. 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 pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition, regardless of whether it is contained in the pressure-sensitive 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 pressure-sensitive adhesive composition in any form of polymer, unpolymerized substance, or partially polymerized substance. From the viewpoint of ease of preparation of the pressure-sensitive adhesive composition and the like, in some embodiments, a pressure-sensitive adhesive composition containing substantially all of the monomer components (for example, 95% by weight or more, preferably 99% by weight or more) in the form of a polymer is preferred. A pressure-sensitive adhesive composition containing substantially all of the monomer components in the form of a polymer is also preferred from the viewpoint of easily forming a pressure-sensitive adhesive sheet with less distortion and warping.

[0031] (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 in combination of two or more kinds.

[0032] Examples of the above ethylenically unsaturated group include a (meth)acryloyl group, a vinyl group, a (meth)allyl group, etc. From the viewpoint of polymerization reactivity, the (meth)acryloyl group is preferred, and from the viewpoints of flexibility and adhesiveness, the acryloyl group is more preferred. From the viewpoint of suppressing a decrease in the flexibility of the pressure-sensitive 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.

[0033] The number of aromatic rings contained in one molecule of the compound used as the monomer (m1) may be 1 or may be 2 or more. The upper limit of the number of aromatic rings contained in the monomer (m1) is not particularly limited and may 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 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.

[0034] The aromatic ring of the compound used as the monomer (m1) may be, for example, a benzene ring (which may be a benzene ring constituting a 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; or other carbocyclic rings. It may also 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, for example, one or more selected from the group consisting of nitrogen, sulfur, and oxygen. In some embodiments, the heteroatom constituting the above heterocyclic ring may be one or both of nitrogen and sulfur. The 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.

[0035] 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, a bromine atom, etc.), a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group, etc. In the 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 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). Note that the aromatic ring of the monomer (m1) having a substituent on the ring-constituting atoms means that the aromatic ring has a substituent other than the substituent having an ethylenically unsaturated group.

[0036] 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, a group containing one or more structures selected from 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 (such as a hydroxyalkylene group), an oxy group (-O- group), a thiooxy group (-S- group), etc. 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 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.

[0037] Examples of compounds that can be preferably employed as monomer (m1) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. The aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds can 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.

[0038] The content of monomer (m1) in the monomer component 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 component 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 viewpoint of facilitating the obtaining of a higher refractive index, in some preferred embodiments, the content of the above 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 component is 100% by weight. From the viewpoint of achieving a good balance between a high refractive index and adhesive properties and / or optical properties, it is advantageous that the content of the above monomer (m1) is less than 100% by weight, for example, 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 above 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 above monomer (m1) in the monomer component may be 70% by weight or less, may be 60% by weight or less, and may be 45% by weight or less.

[0039] 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 adopted because a high refractive index increasing effect is 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 chemically bonded (i.e., without intervening other atoms), 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 monomer can be used alone or in combination of two or more kinds.

[0040] The above linking group is, for example, an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (e.g., -O-(CH 2 ) n - group, where n is 1 to 3, preferably 1), a thiooxyalkylene group (e.g., -S-(CH 2 ) n - group, where n is 1 to 3, preferably 1), a linear alkylene group (i.e., -(CH 2 ) 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.

[0041] 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.

[0042] 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.

[0043] 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 the monomers having the fluorene structure contain a structural part in which two benzene rings are directly chemically bonded, they are included in the concept of the monomers having a structure in which two or more non-condensed aromatic rings are directly chemically bonded.

[0044] 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 CH 2 CH(R 1 )C(O)OCH 2 - is bonded. Here, R 1is a hydrogen atom or a methyl group.), (meth)acryloyloxyethyl dinaphthothiophene (for example, at the 5- or 6-position of the dinaphthothiophene ring, CH 2 CH(R 1 )C(O)OCH(CH 3 )- or CH 2 CH(R 1 )C(O)OCH 2 CH 2 -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- or 6-position of the naphthothiophene ring), (meth)allyloxydinaphthothiophene, etc. are mentioned. In addition, monomers having a dinaphthothiophene structure are included in the concept of monomers having the above 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.

[0045] Examples of the monomers having the above dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophene, vinyl group-containing dibenzothiophene, etc. In addition, monomers having a dibenzothiophene structure are included in the concept of monomers having the above condensed aromatic ring structure because they have a structure in which a thiophene ring and two benzene rings are condensed. 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.

[0046] 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. Monomers having one aromatic ring in one molecule can be useful, for example, for improving the flexibility of the adhesive, adjusting the adhesive properties, improving transparency, etc. In some embodiments, monomers having one aromatic ring in one molecule are preferably used in combination with monomers containing a plurality of aromatic rings from the viewpoint of improving the refractive index of the adhesive.

[0047] 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, etc.; 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, etc.; carbon aromatic ring-containing vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, tert-butylstyrene, etc.; compounds having a vinyl substituent on a heteroaromatic ring such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyl oxazole, etc.; and the like.

[0048] As the monomer (m1), a monomer having a structure in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the aromatic ring in various aromatic ring-containing monomers as described above may be used. Such a monomer in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the aromatic ring can be regarded as an ethoxylate of the original monomer. The oxyethylene unit (-CH 2 CH 2The number of repetitions of O-) is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, and for example, 1. Specific examples of the ethoxylated aromatic ring-containing monomer 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.

[0049] 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, 25% by weight or more, or 40% 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 (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 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). Also, 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 the monomer containing a plurality of aromatic rings.

[0050] The content of the monomer containing a plurality of aromatic rings in the monomer component constituting the acrylic polymer (A) 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, may be 10% by weight or more, or 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 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 can be 100% by weight, but from the perspective of achieving a good 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 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.

[0051] 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, or may be 1.700 or less. The high refractive index monomer can be used alone or in combination of two or more. Note that 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.

[0052] As the above 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), and the like, but not limited thereto.

[0053] 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, 25% by weight or more, 35% by weight or more, or 40% by weight or more. In some embodiments, from the perspective of making it easier to obtain 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 also be 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomer (m1) may be the high refractive index monomer. 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 also be 98% by weight or less, 90% by weight or less, 80% by weight or less, or 65% by weight or less. In some embodiments, 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, 50% by weight or less, 25% by weight or less, 15% by weight or less, or 10% by weight or less. The technology disclosed herein can also be 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.

[0054] The content of the high refractive index monomer in the monomer component 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.). The content of the high refractive index monomer in the above 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 above 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 above monomer component can 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 above 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 above monomer component is less than 3% by weight.

[0055] In some preferred embodiments of the technology disclosed herein, as at least a part of the monomer (m1), an aromatic ring-containing monomer (hereinafter sometimes 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.

[0056] 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).

[0057] 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 well-balanced compatibility 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.

[0058] The content of monomer L in the monomer component constituting the acrylic polymer (A) may be, for example, 3% by weight or more, may be 10% by weight or more, or may be 25% by weight or more. In some embodiments, from the perspective of easily obtaining an adhesive that achieves a higher level of both high refractive index and flexibility, the content of monomer L 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 monomer L in the monomer component may be 100% by weight, but considering 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 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 monomer L in the monomer component is less than 3% by weight.

[0059] 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, still more preferably -10°C or lower, may be -20°C or lower, or 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, or may be -45°C or higher. The technology disclosed herein is applicable to cases where 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.

[0060] 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 (A). 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 (A), 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.

[0061] In some embodiments, as the aromatic ring-containing monomer (m1), monomer L (that is, 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 can 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

[0062] ​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 (e.g., 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 well balances flexibility, adhesiveness, and a high refractive index.

[0063] (Monomer (m2)) In some embodiments of the technology disclosed herein, the monomer component constituting the acrylic polymer (A) 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 help introduce crosslinking points into the acrylic polymer (A) or impart 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.

[0064] Examples of the ethylenically unsaturated group of monomer (m2) include a (meth)acryloyl group, a vinyl group, a (meth)allyl group, etc. 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 (i.e., a monofunctional monomer) is preferably used.

[0065] Examples of the hydroxyl group-containing monomer include, but are not limited to, 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.

[0066] 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. Suitable examples of the hydroxyl group-containing monomer having no methacryloyl group include the various above-mentioned hydroxyalkyl acrylates. 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 (A), and an adhesive having good flexibility and adhesiveness in the room temperature range can be easily obtained as compared with the case where only the corresponding hydroxyalkyl methacrylate is used.

[0067] 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.

[0068] The content of the monomer (m2) in the monomer component constituting the acrylic polymer (A) 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, or 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 the monomer (m1) 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 the 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.

[0069] 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 the monomer (m1) 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.

[0070] 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, 2% by weight or more, or 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 amount of the monomer (m1) 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 the 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 adhesive, the content of the carboxyl group-containing monomer is advantageously 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.

[0071] The total content of the monomer (m1) and the monomer (m2) in the monomer component constituting the acrylic polymer (A) 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 (A) is, from the viewpoint of preferably facilitating the exhibition of the effects of these monomers, 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.

[0072] (Monomer m3) The monomer component constituting the acrylic polymer (A) may, if necessary, contain monomers other than the above monomers (m1) and (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 pressure-sensitive adhesive and improving the compatibility within the pressure-sensitive adhesive.

[0073] As monomer (m3), an alkyl (meth)acrylate having a linear or branched alkyl group with 1 to 20 carbon atoms (i.e., 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.

[0074] In some embodiments, at least a part of the monomer (m3) may preferably be an alkyl (meth)acrylate having a Tg of the homopolymer 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.

[0075] In some embodiments of using the monomer (m3), from the viewpoints of flexibility, adhesiveness, etc., at least a part of the monomer (m3) is preferably 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.

[0076] 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 such a 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, may be less than 17% by weight, may be less than 12% by weight, may be less than 7% by weight, may be less than 3% by weight, or may be less than 1% by weight. It is not necessary to substantially use monomer (m3).

[0077] (Other monomers) The monomer component constituting the acrylic polymer (A) 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 (A), 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.

[0078] 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 (A), 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.

[0079] 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 (also known as ethyl carbitol acrylate, Tg of homopolymer: -67°C).

[0080] When using the above-mentioned other monomers, the amount used is not particularly limited and can be appropriately set as long as 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 the monomer (m1), the content of the above-mentioned other monomers in the monomer component can be, for example, approximately 35% by weight or less, and it is appropriate to be approximately 25% by weight or less (for example, 0 to 25% by weight), and may be approximately 20% by weight or less (for example, 0 to 20% by weight), may be approximately 10% by weight or less, may be approximately 5% by weight or less, or may be approximately 1% by weight or less. The technology disclosed herein can be preferably implemented in an embodiment where the monomer component substantially does not contain the above-mentioned other monomers.

[0081] In some embodiments, the monomer component constituting the acrylic polymer (A) can have a composition in which the amount of the methacryloyl group-containing monomer used is suppressed to a predetermined level or less. The amount of the methacryloyl group-containing monomer used in the monomer component can be, for example, 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. Limiting the amount of the methacryloyl group-containing monomer used in this way can be advantageous from the perspective of realizing an adhesive that achieves a good balance between flexibility, adhesiveness, and a high refractive index. The monomer component constituting the acrylic polymer (A) may have a composition that does not contain a methacryloyl group-containing monomer (for example, a composition consisting only of acryloyl group-containing monomers).

[0082] In some embodiments, the monomer component constituting the acrylic polymer (A) preferably has a limited amount of carboxy group-containing monomer from the viewpoint of suppressing coloring or discoloration (e.g., yellowing) of the adhesive. The amount of the carboxy group-containing monomer in the monomer component 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 limitation of the amount 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 adhesive disclosed herein. The technology disclosed herein can be preferably implemented in an embodiment where the monomer component does not contain a carboxy group-containing monomer. For the same reason, in some embodiments, the monomer component constituting the acrylic polymer (A) preferably has a limited amount of monomer having an acidic functional group (including sulfonic acid group, phosphoric acid group, etc. in addition to the carboxy group). As the amount of the acidic functional group-containing monomer in the monomer component of such an embodiment, the preferred amounts of the carboxy group-containing monomer described above can be applied. The technology disclosed herein can be preferably implemented in an embodiment where the monomer component does not contain an acidic group-containing monomer (i.e., an embodiment where the acrylic polymer (A) is acid-free).

[0083] (Glass transition temperature Tg T ) In some embodiments, the monomer component constituting the acrylic polymer (A) has a glass transition temperature Tg T based on the composition of the monomer component, 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 low glass transition temperature Tg T can be advantageous from the viewpoint of improving the flexibility of the adhesive. Also, the glass transition temperature Tg TIt may be, for example, -60°C or higher, preferably -50°C or higher, more preferably above -45°C, and may be above -40°C, may be above -35°C, may be above -25°C, may be -15°C or higher, or may be -5°C or higher, from the viewpoint of facilitating an increase in the refractive index of the adhesive.

[0084] Here, the glass transition temperature Tg T refers to the glass transition temperature determined by Fox's equation based on the composition of the above monomer components, unless otherwise specified. Fox's equation is a relational expression 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 with multiple types of values 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 No. 2007-51271 shall be used.

[0085] (Method for preparing acrylic polymer (A)) In the technology disclosed herein, the method for obtaining the acrylic polymer (A) composed of such monomer components is not particularly limited, and various polymerization methods known as synthesis methods for acrylic polymers, such as solution polymerization method, emulsion polymerization method, bulk polymerization method, suspension polymerization method, photopolymerization method, etc., can be appropriately adopted. For example, the solution polymerization method can be preferably adopted. The polymerization temperature during 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).

[0086] 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 solvents can be used.

[0087] 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 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. 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.

[0088] 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, and α-thioglycerol 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 with respect to 100 parts by weight of the monomer raw material.

[0089] The weight average molecular weight (Mw) of the above acrylic polymer (A) is not particularly limited and can be, for example, approximately 10×10 4 ~500×10 4 In view of the adhesion performance, the Mw of the acrylic polymer (A) 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 ) and is preferably in this range.

[0090] Here, the Mw of the acrylic polymer (A) 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 "TSKguardcolumn SuperHZ-H" + two "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: One "TSKgel SuperH-RC" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: Polystyrene

[0091] (Additive (H RO )) In the technology disclosed herein, as the additive (H RO ), an organic material having a higher refractive index is used in relation to the above-described acrylic polymer (A). Here, the above "H RO " represents an organic material (Organic material) having a high refractive index (High Refractive index). By combining such an additive (H RO ) with the acrylic polymer (A), it is possible to realize an adhesive that preferably balances the refractive index and the adhesive properties (peel strength, flexibility, etc.) and / or the optical properties (total light transmittance, haze value, etc.). 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 RO ) can be used alone or in combination of two or more kinds.

[0092] Additive (H RO ) can be set within an appropriate range in relation to the refractive index of the acrylic polymer (A), and thus is not limited to a specific range. The refractive index of the additive (H RO ) can be selected, for example, from a range exceeding 1.55, exceeding 1.56, or exceeding 1.57 and higher than the refractive index of the acrylic polymer (A). From the viewpoint of increasing the refractive index of the adhesive, in some aspects, the additive (H RO) has a refractive index of 1.58 or more, preferably 1.60 or more, more preferably 1.63 or more, and may be 1.65 or more, 1.70 or more, or 1.75 or more. For additives (H RO ) with a higher refractive index, the target refractive index can be achieved even with the use of a smaller amount of additive (H RO ). This is preferable from the viewpoint of suppressing deterioration of the adhesive properties and optical properties. The upper limit of the refractive index of the additive (H RO ) 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. Note that the refractive index of the additive (H RO ) 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 nominal value of the refractive index at 25 °C is provided by the manufacturer or the like, that nominal value can be adopted.

[0093] The difference between the refractive index n RO of the additive (H b ) and the refractive index n a of the acrylic polymer (A), 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, or may be 0.20 or more or 0.25 or more. By selecting the acrylic polymer (A) and the additive (H A ) so that Δn RO becomes larger, the refractive index improvement effect by the use of the additive (H RO ) tends to be higher. Also, from the viewpoint of the compatibility of the additive (H RO ) in the adhesive layer, in some embodiments, Δn Amay 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.

[0094] In some embodiments, the refractive index n RO of the additive (H b ) and the refractive index n RO of the pressure-sensitive adhesive layer containing the additive (H T ), that is, n b -n T (hereinafter also referred to as "Δn B ") can be 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, may be 0.20 or more, or may be 0.25 or more. By selecting the composition of the pressure-sensitive adhesive layer and the additive (H B ) so that Δn RO becomes larger, the refractive index improvement effect due to the use of the additive (H RO ) 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.

[0095] 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. From the viewpoint of achieving a good balance between the effect of increasing the refractive index and other properties (for example, flexibility suitable for the pressure-sensitive 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), 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 additive (H RO ) is not too large can be advantageous from the viewpoint of improving compatibility within the pressure-sensitive adhesive layer. Also, the additive (H RO) may have a molecular weight of, for example, 130 or more, or 150 or more. In some embodiments, the additive (H RO ) has a molecular weight preferably of 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, from the viewpoint of increasing the refractive index of the additive (H RO ). In some embodiments, a polymer having a molecular weight of about 1000 to 10000 (for example, 1000 or more and less than 5000) can be used as the additive (H RO ). 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 or the measured value using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) 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 a manufacturer or the like, that nominal value can be adopted.

[0096] 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).

[0097] The aromatic ring of the 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).

[0098] 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).

[0099] Additive (H RO ) Examples of the aromatic ring-containing compound that can be used as an additive 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 atoms) 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 compounds that can be used as include benzyl acrylate, m-phenoxybenzyl acrylate, 2-(o-phenylphenoxy)ethyl acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, phenoxypolyethylene glycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, monomers having the fluorene structure described above, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, and other aromatic ring-containing monomers; aromatic ring-containing compounds having no ethylenically unsaturated group, such as 3-phenoxybenzyl alcohol, dinaphthothiophene, and its derivatives (for example, compounds 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 the dinaphthothiophene ring); and the like may be included. Further, the aromatic ring-containing compound 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 2 to 5 monomers) containing such an aromatic ring-containing monomer as a monomer unit. The oligomer may be, for example: a homopolymer of an aromatic ring-containing monomer; a copolymer of one or more aromatic ring-containing monomers; a copolymer of one or more aromatic ring-containing monomers and other monomers; and the like. As the other monomers, one or more monomers having no aromatic ring may be used.

[0100] 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 2 to 5 monomers) 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 other monomers; etc. The above other monomers may be aromatic ring-containing monomers that do not correspond to the compound containing a plurality of aromatic rings, monomers having no aromatic ring, or combinations thereof.

[0101] Non-limiting examples of the compound containing a plurality of aromatic rings include compounds having a structure in which two or more non-condensed aromatic rings are bonded via a linking group, compounds having a structure in which two or more non-condensed aromatic rings are directly (i.e., without intervening other atoms) chemically bonded, compounds having a condensed aromatic ring structure, compounds having a fluorene structure, compounds having a dinaphthothiophene structure, compounds 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.

[0102] 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), and the like, including 9,9-bis(phenyl)fluorene and its derivatives.

[0103] Specific examples of the compound having the above dithienothiophene structure include monomers having the above-described dithienothiophene structure, oligomers which are homopolymers or copolymers of such monomers, and dithienothiophene (refractive index: 1.808); hydroxyalkyldithienothiophenes such as 6-hydroxymethyldithienothiophene (refractive index: 1.766); dihydroxydithienothiophenes such as 2,12-dihydroxydithienothiophene (refractive index: 1.750); dihydroxyalkyloxydithienothiophenes such as 2,12-dihydroxyethyloxydithienothiophene (refractive index: 1.677); diglycidyloxydithienothiophenes such as 2,12-diglycidyloxydithienothiophene (refractive index 1.723); dithienothiophenes having two or more ethylenically unsaturated groups such as 2,12-diallyloxydithienothiophene (abbreviation: 2,12-DAODNT, refractive index 1.729); and the like, including dithienothiophene and its derivatives.

[0104] 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), and the like.

[0105] Additive (H ROExamples of the organic compound having a heterocyclic ring (hereinafter also referred to as a heterocyclic ring-containing organic compound) that can be an option of [[ID=]] are a thioepoxy compound, a compound having a triazine ring, and the like. Examples of the thioepoxy compound include bis(2,3-epithiopropyl) disulfide and its polymer (refractive index 1.74) described in Japanese Patent No. 3712653. Examples of the compound having a triazine ring include a compound having at least one triazine ring (for example, 3 to 40, preferably 5 to 20) in one molecule. Since the triazine ring has aromaticity, the compound having a triazine ring is also included in the concept of the above aromatic ring-containing compound, and the compound having a plurality of triazine rings is also included in the concept of the above aromatic ring plurality-containing compound.

[0106] In some embodiments, a compound having no ethylenically unsaturated group can be preferably employed as the additive (H RO ). Thereby, alteration of the pressure-sensitive adhesive composition due to heat or light (decrease in leveling property due to progress of gelation or increase in viscosity) can be suppressed, and the 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 the ethylenically unsaturated group in a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing the additive (H RO ), a laminate containing the pressure-sensitive adhesive sheet, and the like.

[0107] 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 that an oligomer having a desired weight average molecular weight can be obtained according to the composition of the monomer components used for 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 for 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 for the synthesis of the oligomer is not particularly limited, and may be, for example, 0.01 part by weight or more, 0.1 part by weight or more, 0.5 part by weight or more, or 1 part by weight or more.

[0108] The amount of the additive (H RO ) used relative to 100 parts by weight of the acrylic polymer (A) (when a plurality of compounds are used, the total amount thereof) is not particularly limited as long as it exceeds 0 parts by weight, and can be set according to the purpose. In some embodiments, the amount of the additive (H RO ) used relative to 100 parts by weight of the acrylic polymer (A) 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 pressure-sensitive adhesive and suppressing the deterioration of the adhesive properties and optical properties, it is advantageous to be 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 additive (H RO ) used relative to 100 parts by weight of the acrylic polymer (A) 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, or may be 10 parts by weight or less. Further, from the viewpoint of increasing the refractive index of the pressure-sensitive adhesive, the amount of the additive (H ROThe usage amount of 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.

[0109] (Crosslinking agent) In the pressure-sensitive adhesive composition disclosed herein, a crosslinking agent can be contained 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 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.

[0110] As the isocyanate-based crosslinking agent, polyisocyanate compounds with 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 (manufactured by Takeda Pharmaceutical Company Limited), Sumidule T80, Sumidule L, Desmodule N3400 (manufactured by Sumitomo Bayer Urethane Co., Ltd.), Millionate MR, Millionate MT, Coronate L, Coronate HL, Coronate HX (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 with three or more functional groups may be used in combination.

[0111] Examples of the epoxy crosslinking agent include bisphenol A, an epoxy resin of the epichlorohydrin type, 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 - xylylenediamine, and 1,3 - bis(N,N - diglycidylaminomethyl)cyclohexane. These can be used alone or in combination of two or more.

[0112] Examples of the polyfunctional monomer 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, etc. The polyfunctional monomer can be used alone or in combination of two or more.

[0113] When using a crosslinking agent (which may be a polyfunctional monomer), the amount used is not particularly limited, and can be, for example, in the range of about 0.001 parts by weight to 5.0 parts by weight with respect to 100 parts by weight of the above monomer component. From the viewpoint of improving the flexibility of the adhesive, in some embodiments, the amount of the crosslinking agent used with respect to 100 parts by weight of the monomer component is preferably 3.0 parts by weight or less, more preferably 2.0 parts by weight or less, and may be 1.0 part by weight or less, 0.5 part by weight or less, or 0.2 part by weight or less. Also, from the viewpoint of appropriately exerting the effect of the crosslinking agent, in some embodiments, the amount of the crosslinking agent used with respect to 100 parts by weight of the monomer component may be, for example, 0.005 parts by weight or more, may be 0.01 parts by weight or more, may be 0.05 parts by weight or more, or may be 0.08 parts by weight or more.

[0114] 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 with respect to 100 parts by weight of the monomer component can be, for example, in the range of about 0.0001 parts by weight or more and 1 part by weight or less, and preferably in the range of 0.001 parts 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.

[0115] 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 with respect to 100 parts by weight of the monomer component.

[0116] (Adhesion promoter) The adhesive composition disclosed herein may contain an adhesion promoter. 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 with respect to 100 parts by weight of the monomer component is suitably 30 parts by weight or less, preferably 10 parts by weight or less, and more preferably 5 parts by weight or less. The technology disclosed herein can be preferably implemented in an embodiment without using an adhesion promoter.

[0117] (Plasticizing material) In some embodiments of the pressure-sensitive adhesive composition disclosed herein, the pressure-sensitive adhesive composition may further contain a plasticizing material having a lower molecular weight than the acrylic polymer (A) as an additive used as desired. By using the plasticizing material, the flexibility of the pressure-sensitive adhesive layer can be enhanced, and the adhesion to the adherend, the flexibility of the entire pressure-sensitive adhesive sheet, and the followability to deformation can be improved. From the viewpoints of compatibility and transparency in the pressure-sensitive 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 additive (H RO ).

[0118] The molecular weight of the plasticizing material only needs to be lower than that of the acrylic polymer (A) 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 pressure-sensitive adhesive layer and the like. Further, 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 pressure-sensitive adhesive sheet and the suppression of contamination of the adherend.

[0119] 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 portion 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); and the like. 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.

[0120] In some embodiments, as the plasticizing material, an organic material having a refractive index of approximately 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 employed. 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.

[0121] In the embodiment of using a plasticizing material, the amount of the plasticizing material used per 100 parts by weight of the acrylic polymer (A) 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 per 100 parts by weight of the acrylic polymer (A) 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, the amount of the plasticizer used per 100 parts by weight of the acrylic polymer (A) is suitably about 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 per 100 parts by weight of the acrylic polymer (A) may be 15 parts by weight or less, may be 10 parts by weight or less, may be 5 parts by weight or less.

[0122] (Leveling agent) The adhesive composition disclosed herein may contain a leveling agent as needed for the purpose of improving the appearance of the adhesive layer formed from the composition (for example, improving the thickness uniformity) and improving the coatability of the 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 selected from commercially available leveling agents, for example, and used by a conventional method.

[0123] 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 referred to as a copolymer of monomer S1 and an acrylic monomer. Polymer (B) can be used alone or in combination of two or more.

[0124] 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, monomer S1 having a structure with a polymerizable reactive group at one end and no functional group capable of undergoing a crosslinking reaction with acrylic polymer (A) 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. (product numbers such as X-22-174ASX, X-22-2426, X-22-2475, KF-2012, etc.). Monomer S1 can be used alone or in combination of two or more.

[0125] 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, may be 800 g / mol or more, may be 1500 g / mol or more, or may be 2000 g / mol or more. Also, the above functional group equivalent may be, for example, 20,000 g / mol or less, may be less than 10,000 g / mol, may be 7000 g / mol or less, or may be 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 various monomers and the weight fractions of the monomers.

[0126] Here, the "functional group equivalent weight" means the weight of the main skeleton (e.g., polydimethylsiloxane) bonded to each functional group. In terms of the unit g / mol, it is converted to 1 mol of the functional group. The functional group equivalent weight of monomer S1 can be calculated, for example, from the spectral intensity of 1 1H-NMR (proton NMR) based on nuclear magnetic resonance (NMR). 1 The calculation of the functional group equivalent weight (g / mol) of monomer S1 based on the spectral intensity of 1H-NMR 1 can be performed based on the general structural analysis method related to 1H-NMR spectral analysis, and referring to the description in Japanese Patent No. 5951153 if necessary. In the functional group equivalent weight of monomer S1, the above functional group means a polymerizable functional group (e.g., an ethylenically unsaturated group such as a (meth)acryloyl group, vinyl group, allyl group, etc.).

[0127] The content of monomer S1 in monomer raw material B can adopt 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 also be 10 to 50% by weight, or may also be 15 to 40% by weight.

[0128] 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 group described later. In some embodiments, monomer raw material B is (meth)acrylic acid C 4-12 alkyl ester (preferably (meth)acrylic acid C 4-10 alkyl ester, for example, (meth)acrylic acid C 6-10 alkyl ester) may contain at least one kind. In some other embodiments, monomer raw material B is methacrylic acid C 1-18An alkyl ester (preferably a C 1-14 alkyl ester, such as a C 1-10 alkyl ester) may be contained. The monomer raw material B may contain, as an acrylic monomer, for example, one or more selected from methyl methacrylate (MMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA).

[0129] 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 a (meth)acrylic acid ester having an alicyclic hydrocarbon group.

[0130] The content of the above (meth)acrylic acid alkyl ester and the (meth)acrylic acid ester having an alicyclic hydrocarbon group in the monomer raw material B may be, for example, 10% by weight or more and 95% by weight or less, 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.

[0131] Other examples of the monomers that may be contained in the monomer raw material B together with the monomer S1 include the carboxy group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, amide group-containing monomers, monomers having a nitrogen atom-containing ring, (meth)acrylic acid aminoalkyls, vinyl esters, vinyl ethers, olefins, (meth)acrylic acid esters having an aromatic hydrocarbon group, halogen atom-containing (meth)acrylates, etc. exemplified above as monomers that can be used in acrylic polymers.

[0132] The Mw of 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 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 polymer (B) within an appropriate range, suitable compatibility and leveling properties can be exhibited.

[0133] Polymer (B) can be produced, for example, by polymerizing the above-described monomers by known methods such as solution polymerization method, emulsion polymerization method, bulk polymerization method, suspension polymerization method, photopolymerization method, etc. In order to adjust the molecular weight of 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, methyl thioglycolate; α-methylstyrene dimer; and the like. The amount of the chain transfer agent used is not particularly limited and can be appropriately set so as to obtain 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.

[0134] The amount of polymer (B) used relative to 100 parts by weight of acrylic polymer (A) can be, for example, 0.001 part by weight or more, may be 0.01 part by weight or more, and may be 0.03 part by weight or more from the viewpoint of obtaining a higher use effect. Further, the amount of the above polymer (B) used may be, for example, 3 parts by weight or less, is suitably 1 part by weight or less from the viewpoint of reducing the influence on the refractive index, may be 0.5 part by weight or less, and may be 0.1 part by weight or less.

[0135] (Inorganic particles) The technology disclosed herein can be preferably implemented in a manner that substantially does not use inorganic particles for increasing the refractive index. However, within the limit that does not significantly impair the application effect of the technology disclosed herein, the auxiliary use of inorganic particles with a high refractive index in addition to the additive (H RO ) is not prohibited. Examples of the inorganic particles include inorganic particles composed of inorganic oxides (specifically metal oxides) such as titania (titanium oxide, TiO 2 ), zirconia (zirconium oxide, ZrO 2 ), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, niobium oxide (Nb 2 O 5 , etc.). The average particle diameter of the inorganic particles (referring to the 50% volume average particle diameter based on the laser scattering / diffraction method) can be selected, for example, from the range of about 10 nm to 100 nm. The amount of the inorganic particles used is preferably less than 5 parts by weight, more preferably less than 1 part by weight, based on 100 parts by weight of the acrylic polymer (A). In the mode of using the additive (H RO ), the amount of the inorganic particles used is preferably 2 times or less, more preferably 1 time or less or 0.5 times or less, based on the weight, of the amount of the additive (H RO ).

[0136] (Other additives) The pressure-sensitive adhesive composition disclosed herein may contain, as necessary, known additives that can be used in pressure-sensitive adhesive compositions, such as plasticizers, softening agents, colorants, antistatic agents, antioxidants, ultraviolet absorbers, antioxidants, light stabilizers, preservatives, etc., within the range where the effects of the present invention are not significantly hindered. Regarding such various additives, those known in the art can be used by conventional methods and are not particularly characteristic of the present invention, so detailed descriptions are omitted.

[0137] <Pressure-sensitive adhesive> The pressure-sensitive adhesives disclosed herein can be formed, for example, using any of the pressure-sensitive adhesive compositions described above. Such pressure-sensitive adhesives can be adhesives formed by curing a pressure-sensitive adhesive composition in the form of a solvent-based, active energy ray-curable, water-dispersible, hot melt type, etc. by drying, crosslinking, polymerization, cooling, etc., that is, cured products of the above pressure-sensitive adhesive compositions. As the curing means (e.g., drying, crosslinking, polymerization, cooling, etc.) of the pressure-sensitive adhesive composition, only one type may be applied, or two or more types may be applied simultaneously or in multiple steps. In the case of a solvent-based 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 pressure-sensitive adhesive composition, typically, a pressure-sensitive adhesive is formed by irradiating active energy rays to proceed with a polymerization reaction and / or a crosslinking reaction. When it is necessary to dry the active energy ray-curable pressure-sensitive adhesive composition, it is advisable to irradiate active energy rays after drying.

[0138] (Refractive index) The pressure-sensitive adhesives disclosed herein can exhibit a refractive index of a predetermined value or more. According to the technology disclosed herein, there can be provided a pressure-sensitive adhesive having a refractive index of, for example, 1.560 or more (preferably 1.570 or more, more preferably exceeding 1.570), a pressure-sensitive adhesive composition capable of forming the pressure-sensitive adhesive, and a pressure-sensitive adhesive sheet including the above pressure-sensitive adhesive.

[0139] In addition, in this specification, the refractive index of the pressure-sensitive adhesive refers to the refractive index of the surface (adhesive surface) of the pressure-sensitive adhesive. The refractive index of the pressure-sensitive 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 is used. As the measurement sample, an adhesive layer made of the pressure-sensitive adhesive to be evaluated can be used. Specifically, the refractive index of the pressure-sensitive adhesive can be measured by the method described in the examples below. The refractive index of the pressure-sensitive adhesive can be adjusted, for example, by the composition of the pressure-sensitive adhesive.

[0140] In some embodiments, the refractive index of the adhesive is preferably 1.575 or more (e.g., more than 1.575), more preferably 1.580 or more, still more preferably 1.585 or more, and particularly preferably 1.590 or more (e.g., 1.595 or more). According to the adhesive having such a refractive index, the behavior of light can be effectively controlled by utilizing the refractive index difference between the adhesive and the adherend. In some embodiments of the adhesives disclosed herein, the refractive index of the adhesive can 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 adhesive may vary depending on the refractive index of the adherend and the like, and thus is not limited to a specific range. In some embodiments, considering the balance with adhesive properties and transparency, the refractive index of the adhesive may be, for example, 1.700 or less, 1.670 or less, or 1.650 or less.

[0141] <Adhesive sheet> This specification provides an adhesive sheet having an adhesive layer. The adhesive constituting the adhesive layer can be an adhesive formed from any of the adhesive compositions disclosed herein (e.g., a cured product of the adhesive composition). The adhesive sheet may be an adhesive sheet with a substrate having an adhesive layer on one or both sides of a non-peeling substrate (support substrate), or a substrate-free adhesive sheet such as a form in which the adhesive layer is held by a release liner (i.e., an adhesive sheet having no non-peeling substrate. Typically, an adhesive sheet consisting of an adhesive layer). The concept of the adhesive sheet referred to herein may include those referred to as adhesive tapes, adhesive labels, adhesive films, and the like. The adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, it may be an adhesive sheet processed into various shapes.

[0142] A configuration example of the adhesive sheet 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 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-peeling 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 the adherend), the adhesive sheet 1 may be in the form of an adhesive sheet 50 with a release liner, for example, as shown in FIG. 1, where the adhesive surface 10A is protected by a release liner 30 having a release surface (peeling surface) on at least the adhesive layer side. Alternatively, the second surface 20B of the support substrate 20 (the surface opposite to the first surface 20A, also referred to as the back surface) is a peeling 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. The adhesive layer 10 may have a single-layer structure or a laminated structure in which two or more sub-adhesive layers having different compositions are directly laminated (i.e., not separated by a layer composed of a non-adhesive material).

[0143] The release liner is not particularly limited. For example, a release liner in which the surface of a liner substrate such as a resin film or paper is release-treated, or a release liner made of a low-adhesion material such as a fluoropolymer (e.g., polytetrafluoroethylene) or a polyolefin resin (e.g., polyethylene, polypropylene) can be used. For the above release treatment, for example, a release treatment agent such as a silicone-based or long-chain alkyl-based agent can be used. In some embodiments, a release-treated resin film can be preferably employed as the release liner.

[0144] 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. As shown in FIG. 2, before use, the substrate-free double-sided pressure-sensitive adhesive sheet 2 may be in a form in which the first surface (first pressure-sensitive adhesive surface) 10A and the second surface (second pressure-sensitive adhesive surface) 10B of the pressure-sensitive adhesive layer 10 are protected by release liners 31 and 32 having at least the pressure-sensitive adhesive layer side as a releasable surface (release surface). Alternatively, the back surface (the surface opposite to the pressure-sensitive adhesive side) of the release liner 31 may be the release surface, and the pressure-sensitive adhesive surfaces 10A and 10B may be protected by winding or laminating the pressure-sensitive adhesive surface 10B in contact with 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 (which can be an optical member such as an optical film) to at least one of the first pressure-sensitive adhesive surface and the second pressure-sensitive adhesive surface. The pressure-sensitive adhesive layer constituting the substrate-free double-sided pressure-sensitive adhesive sheet may be 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 be a laminated structure in which two or more sub-pressure-sensitive adhesive layers having different compositions are directly in contact and laminated.

[0145] The pressure-sensitive adhesive sheet disclosed herein can be a component of a pressure-sensitive adhesive sheet-attached optical member in which an optical member is bonded to one surface of the pressure-sensitive adhesive layer. For example, as shown in FIG. 3, the pressure-sensitive adhesive sheet 1 shown in FIG. 1 can be a component of a pressure-sensitive adhesive sheet-attached optical member 100 in which an optical member 70 is bonded to one surface 10A of the pressure-sensitive adhesive layer 10. The optical member can be, for example, a glass plate, a resin film, a metal plate, or the like. Further, in the pressure-sensitive adhesive sheet 1 shown in FIG. 1, when the support substrate 20 is an optical member such as an optical film, the pressure-sensitive adhesive sheet 1 can be regarded as a pressure-sensitive adhesive sheet-attached optical member in which an optical member is bonded to the second surface 10B of the pressure-sensitive adhesive layer 10.

[0146] In addition, although not particularly illustrated, the adhesive sheet disclosed herein includes a support substrate having non-peeling first and second surfaces, a first adhesive layer is fixedly laminated on the first surface, and a second adhesive layer is fixedly laminated on the second surface, and may be in the form of a double-sided adhesive sheet with a substrate (double-sided adhesive sheet with a substrate). 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-peeling surface, and a second adhesive layer is provided on the second surface 20B, and 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) is 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 may 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.

[0147] When the adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet in which both sides are adhesive surfaces (including both the substrate-free double-sided adhesive sheet and the double-sided adhesive sheet with a substrate. The same applies hereinafter unless otherwise specified.), the refractive indices of the first adhesive surface and the second adhesive surface are not particularly limited. In some embodiments, it is preferable that at least the first adhesive surface satisfies any of the above-described refractive indices, and the double-sided adhesive sheet in which both the first adhesive surface and the second adhesive surface satisfy any of the above-described refractive indices may also be used. In some embodiments, the refractive index n of the second adhesive surface 2 may be approximately the same as the refractive index n of the first adhesive surface 1 . More specifically, the absolute value of the difference in refractive indices between the two adhesive surfaces, that is, |n 1 -n 2 | may be, for example, less than 0.05, or less than 0.03, or less than 0.01. The lower limit of |n 1 -n 2 | may be 0.00 or greater than 0.00. The relative relationship between the refractive indices of the two adhesive surfaces may be n 1 >n 2 , or n 1<n 2 may also be, n 1 =n 2 is also possible. In some other embodiments, the refractive index n of the first adhesive surface of the adhesive sheet 1 and the refractive index n of the second adhesive surface 2 The difference between them, that is, n 1 -n 2 may be greater than 0.00, for example, may be 0.01 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 magnitude relationship between n 1 and n 2 may be reversed. A double-sided adhesive sheet having different refractive indices on the first adhesive surface and the second adhesive surface can be realized, for example, by laminating first and second adhesive layers having different refractive indices on a non-peeling support substrate in a double-sided adhesive sheet with a substrate, or by making the adhesive layer constituting the substrate-free double-sided adhesive sheet into a laminated structure of two or more sub-adhesive layers having different refractive indices.

[0148] The adhesive layer of the adhesive sheet disclosed herein can be formed by applying (for example, coating) an adhesive composition to a suitable surface and then curing the composition. The application of the adhesive composition can be carried out using conventional coaters such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, a spray coater, etc.

[0149] The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet disclosed herein may be a pressure-sensitive adhesive layer having post-curing properties or a pressure-sensitive adhesive layer not having post-curing properties. Here, the pressure-sensitive adhesive layer having post-curing properties refers to a pressure-sensitive adhesive layer that can be further cured by irradiation with heat or active energy rays (e.g., ultraviolet rays). Examples of the pressure-sensitive adhesive layer having post-curing properties include a pressure-sensitive adhesive layer having unreacted ethylenically unsaturated groups in the side chains of a base polymer (e.g., acrylic polymer (A)), and a pressure-sensitive adhesive layer containing unreacted polyfunctional monomers. In some embodiments, it is preferable that the pressure-sensitive adhesive layer does not have post-curing properties. Since the pressure-sensitive 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 pressure-sensitive adhesive sheet or the adherend to which the pressure-sensitive adhesive sheet is attached. The fact that dimensional changes (e.g., curing shrinkage) due to post-curing do not occur can also be advantageous from the viewpoint of suppressing optical distortion of the pressure-sensitive adhesive layer.

[0150] The thickness of the pressure-sensitive adhesive layer is not particularly limited, and can be, for example, 3 μm or more. In some embodiments, the thickness of the pressure-sensitive adhesive layer can be, for example, 5 μm or more, 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 pressure-sensitive adhesive layer can 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 pressure-sensitive adhesive layer is not too large can be advantageous from the viewpoint of thinning the pressure-sensitive adhesive sheet and the like. The technology disclosed herein can be preferably implemented, for example, in an embodiment where the thickness of the pressure-sensitive adhesive layer is in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm). In the case of a pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on the first surface and the second surface of the base material, the above-described thickness of the pressure-sensitive adhesive layer can be applied at least to the thickness of the first pressure-sensitive adhesive layer. The thickness of the second pressure-sensitive adhesive layer can also be selected from the same range. Also, in a substrate-less double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer, the thickness of the pressure-sensitive adhesive layer becomes the thickness of the pressure-sensitive adhesive sheet.

[0151] (Total light transmittance) In the technology disclosed herein, it is appropriate that the total light transmittance of the adhesive layer is, for example, greater than 50%, and preferably 70% or more. In some preferred embodiments, the total light transmittance of the adherend is 85% or more, preferably 86% or more, more preferably 88% or more, even more preferably 90% or more (for example, exceeding 90.0%), and may be 90.5% or more. Such an adhesive sheet having a highly transparent adhesive layer can be preferably applied to applications where high light transmittance is required (for example, optical applications) in a configuration with or without a substrate, and applications where the performance of being able to clearly visually recognize the adherend through the adhesive sheet is required. In some embodiments, the total light transmittance of the adhesive layer may be 93% or more, or 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%. Practically, 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 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 in accordance with JIS K 7136:2000 using a commercially available transmittance meter. 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 adhesive layer can be measured according to the examples described later. The total light transmittance of the adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the adhesive layer.

[0152] When the adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet with a substrate in which the first adhesive layer and the second adhesive layer are fixedly laminated on the support substrate, it is preferable that at least the first adhesive layer satisfies any of the above-described total light transmittances. In a usage mode where light passes through in the thickness direction of the adhesive sheet, it is preferable that both the first adhesive layer and the second adhesive layer satisfy any of the above-described total light transmittances. The relative relationship between the total light transmittances of the two adhesive layers may be the first adhesive layer > the second adhesive layer, may be the first adhesive layer < the second adhesive layer, or may be the first adhesive layer = the second adhesive layer.

[0153] (Haze value) In some embodiments, the haze value of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet may be, for example, 5.0% or less, preferably 3.0% or less (e.g., 2.0% or less), more preferably 1.0% or less, and even more preferably 0.9% or less. The pressure-sensitive adhesive sheet having such a highly transparent pressure-sensitive adhesive layer can be preferably applied to applications where high light transmittance is required (e.g., optical applications) in configurations with or without a substrate, and to applications where the performance of clearly visualizing an adherend through the pressure-sensitive adhesive sheet is required. In some embodiments, the haze value of the pressure-sensitive adhesive layer may be 0.8% or less, 0.5% or less, or 0.3% or less. The lower limit of the haze value of the pressure-sensitive adhesive layer is not particularly limited, and from the perspective of improving transparency, the smaller the haze value, the more preferable. On the other hand, in some embodiments, considering the refractive index and adhesive properties, the haze value may be, for example, 0.05% or more, 0.1% or more, 0.2% or more, 0.3% or more, or 0.4% or more. These haze values regarding the pressure-sensitive adhesive layer can also be preferably applied to the haze value of the pressure-sensitive adhesive sheet when implementing the technologies disclosed herein in the form of a substrate-free pressure-sensitive adhesive sheet (typically, a pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer).

[0154] 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 pressure-sensitive adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the pressure-sensitive adhesive layer.

[0155] When the pressure-sensitive adhesive sheet disclosed herein is in the form of a double-sided pressure-sensitive adhesive sheet with a substrate, in which a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer are fixedly laminated on the support substrate, at least the first pressure-sensitive adhesive layer only needs to satisfy any of the haze values described above, and the haze value of the second pressure-sensitive adhesive layer is not particularly limited. In a usage mode where light passes through in the thickness direction of the pressure-sensitive adhesive sheet, it is preferable that the haze value of the second pressure-sensitive adhesive layer satisfies any of the haze values of the first pressure-sensitive adhesive layer described above. The relative relationship between the haze values of the two pressure-sensitive adhesive layers may be the first pressure-sensitive adhesive layer > the second pressure-sensitive adhesive layer, the first pressure-sensitive adhesive layer < the second pressure-sensitive adhesive layer, or the first pressure-sensitive adhesive layer = the second pressure-sensitive adhesive layer.

[0156] (Surface smoothness of the adhesive surface) In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the adhesive surface of the pressure-sensitive adhesive sheet preferably has high surface smoothness.

[0157] 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 limiting the arithmetic mean roughness Ra, for example, in a usage mode where light is extracted through the adhesive surface (such as a pressure-sensitive adhesive sheet disposed on the viewing angle side of a self-luminous element in a light-emitting device), it is possible to exert an effect of suppressing the occurrence of luminance unevenness caused by the surface state of the pressure-sensitive 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 pressure-sensitive adhesive sheet disclosed herein is in the form of a double-sided pressure-sensitive adhesive sheet having a first adhesive surface and a second adhesive surface, 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 pressure-sensitive adhesive sheet having high surface smoothness, adhesion excellent in optical homogeneity can be preferably realized.

[0158] In some embodiments, the arithmetic mean roughness Ra of the adhesive surface is preferably about 70 nm or less, more preferably about 65 nm or less, still more preferably about 55 nm or less, and may be less than 50 nm, less than 45 nm, or less than 40 nm. From the perspective of production efficiency and the like, in some embodiments, the arithmetic mean roughness Ra of the adhesive surface of the adhesive sheet may be, for example, about 10 nm or more, about 20 nm or more, or about 30 nm or more (for example, about 40 nm or more). In an embodiment where 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.

[0159] Also, 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 perspective of optical homogeneity. By limiting the maximum height Rz, for example, in a usage mode where light is extracted through the adhesive surface as described above, it is possible to exert an 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.

[0160] 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 perspective of production efficiency and the like, in some embodiments, the maximum height Rz of the adhesive surface of the adhesive sheet may be, for example, approximately 10 nm or more, approximately 50 nm or more, approximately 100 nm or more, or approximately 200 nm or more. In an embodiment where the adhesive sheet has a first adhesive surface and a second adhesive surface, the maximum height Rz of the first adhesive surface and the maximum height Rz of the second adhesive surface may be the same or different.

[0161] 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, a surface roughness measuring device using an optical interference method is used, and 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 measurement method or by setting the measurement operation and measurement conditions so that results equivalent or corresponding to those obtained by the measurement method are obtained. 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 according to JIS B 0601-2001 from the measured data. The maximum height Rz is determined 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 measurements of Ra and Rz are performed 5 times (i.e., N = 5), and their average values are used. The above-mentioned sample for measurement 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 leaving it standing for about 30 minutes after exposing the adhesive surface. [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

[0162] The arithmetic mean roughness Ra and the maximum height Rz of the adhesive surface can be adjusted according to the composition and properties (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.

[0163] (Storage modulus G’) In the pressure-sensitive adhesive sheet disclosed herein, the storage elastic modulus G' of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer at 25°C (hereinafter also referred to as "storage elastic modulus G'(25)") 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'(25) of the pressure-sensitive adhesive can be, for example, approximately 700 kPa or less. In some embodiments, from the viewpoint of ease of attachment to the adherend, etc., it is advantageous for the storage elastic modulus G'(25) of the pressure-sensitive adhesive to be approximately 600 kPa or less, preferably 500 kPa or less, and more preferably 400 kPa or less (for example, 350 kPa or less). In some embodiments, from the viewpoint of enhancing the flexibility of the pressure-sensitive adhesive in the room temperature range (for example, 25°C) and making it easier to adhere to the adherend, it is advantageous for the storage elastic modulus G'(25) of the pressure-sensitive adhesive to be approximately 330 kPa or less, and preferably 300 kPa or less. In some embodiments where adhesion and flexibility at room temperature are more emphasized, the storage elastic modulus G'(25) of the pressure-sensitive adhesive 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 (for example, less than 140 kPa). In some embodiments, the storage elastic modulus G'(25) of the pressure-sensitive adhesive may be less than 100 kPa or less than 90 kPa. The lower limit of the storage elastic modulus G'(25) of the pressure-sensitive adhesive is not particularly limited, but from the viewpoints of processability, handleability, etc., it may be, for example, 30 kPa or more, 50 kPa or more, or 70 kPa or more. In some embodiments, considering an increase in refractive index, the storage elastic modulus G'(25) may be 100 kPa or more, 150 kPa or more, 200 kPa or more, 250 kPa or more, or 300 kPa or more.

[0164] In the pressure-sensitive adhesive sheet disclosed herein, the storage elastic modulus G' at 50°C of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer (hereinafter, also referred to as "storage elastic modulus G'(50)") is not particularly limited and can be, for example, less than 100 kPa. In some embodiments, it is appropriate for the storage elastic modulus G'(50) to be less than 60 kPa, preferably less than 40 kPa, and more preferably less than 38 kPa (for example, less than 36 kPa). The pressure-sensitive adhesive with the storage elastic modulus G'(50) thus limited can easily enhance the adhesion to the adherend by performing appropriate heating as necessary, thereby improving the adhesiveness to the adherend. The lower limit of the storage elastic modulus G'(50) of the pressure-sensitive adhesive is not particularly limited. In some embodiments, from the perspective of the heat resistance characteristics of the pressure-sensitive adhesive, the storage elastic modulus G'(50) can be, for example, 10 kPa or more, 15 kPa or more, 20 kPa or more, or 23 kPa or more.

[0165] In some embodiments of the pressure-sensitive adhesive disclosed herein, the pressure-sensitive adhesive satisfies the following conditions: (a) The storage elastic modulus G'(25) at 25°C is 350 kPa or less (preferably less than 200 kPa, for example, 180 kPa or less); and (b) The storage elastic modulus G'(50) at 50°C is less than 60 kPa (preferably less than 50 kPa, more preferably less than 40 kPa, for example, less than 38 kPa); It is preferable to satisfy at least one of them. An adhesive that satisfies at least the above condition (a) is preferable from the viewpoint of adhesion to an adherend at room temperature (e.g., 25°C). An adhesive that satisfies at least the above condition (b) is preferable because the adhesion (adhesiveness) to an adherend can be easily improved by heating to a temperature slightly higher than room temperature. An adhesive that does not satisfy the above condition (a) and satisfies the above (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. The above heat activation may be performed by heating the adhesive to a temperature slightly higher than room temperature when pasting to an adherend. The temperature slightly higher than room temperature is, for example, about 60°C or lower, preferably about 55°C or lower (e.g., about 50°C or lower).

[0166] In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the ratio of the storage elastic modulus G'(50) [kPa] to the storage elastic modulus G'(25) [kPa] of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer, that is, the storage elastic modulus ratio G'(50) / G'(25) is, for example, 70% or less, may be 40% or less, may be 30% or less, or may be 20% or less. An adhesive with a small G'(50) / G'(25) is suitable for use as the above heat-activated type adhesive. The lower limit of G'(50) / G'(25) is not particularly limited. G'(50) / G'(25) is, for example, 5% or more, preferably 10% or more from the viewpoint of the heat resistance characteristics of the adhesive, may be 12% or more, or may be 15% or more.

[0167] The storage elastic moduli G’(25) and G’(50) can be determined by dynamic viscoelasticity measurement, and G’(50) / G’(25) can be calculated from the results. 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 the "Advanced Rheometric Expansion System (ARES)" manufactured by TA Instruments or its equivalent. As the sample for measurement, a sample prepared to a thickness of about 1.5 mm by laminating the pressure-sensitive 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

[0168] The storage elastic moduli G’(25), G’(50) and the storage elastic modulus ratio of the pressure-sensitive adhesive layer can be adjusted by the selection of the composition of the monomer components constituting the acrylic polymer (A) (for example, the selection of the type and content of the monomer (m1)), the presence or absence of use of a crosslinking agent, the selection of the type and amount of use, the above-mentioned additive (H RO ) and the presence or absence of use of a plasticizing material, the selection of the type and amount of use, 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, whereby in addition to the case where the first monomer is used alone as the monomer (m1), G’(50) can be reduced and G’(50) / G’(25) can be decreased.

[0169] When the pressure-sensitive adhesive sheet disclosed herein is in the form of a double-sided pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive surface and a second pressure-sensitive adhesive surface (for example, a double-sided pressure-sensitive adhesive sheet with a base material having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer, a base material-free double-sided pressure-sensitive adhesive sheet in which a sub-pressure-sensitive adhesive layer constituting the first pressure-sensitive adhesive surface and a sub-pressure-sensitive adhesive layer constituting the second pressure-sensitive adhesive surface are laminated without an intervening non-pressure-sensitive adhesive base material, etc. The same applies to other similar descriptions.), the above-described storage elastic modulus G'(25), G'(50), and storage elastic modulus ratio are applied to at least the pressure-sensitive adhesive layer constituting the first pressure-sensitive adhesive surface, and preferably to both the pressure-sensitive adhesive layer constituting the first pressure-sensitive adhesive surface and the pressure-sensitive adhesive layer constituting the second pressure-sensitive adhesive surface. The storage elastic modulus G' of the pressure-sensitive adhesive layer constituting the first pressure-sensitive adhesive surface and the storage elastic modulus G' of the pressure-sensitive adhesive layer constituting the second pressure-sensitive adhesive surface may be the same or different.

[0170] In some aspects of the technology disclosed herein, the peak temperature of tanδ of the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer is preferably approximately -50°C or higher and preferably approximately 50°C or lower. Here, tanδ (loss tangent) of the pressure-sensitive adhesive refers to the ratio of the loss elastic modulus G'' to the storage elastic modulus G' of the pressure-sensitive adhesive. That is, tanδ = G'' / G'. The tanδ of the pressure-sensitive adhesive is obtained by sandwiching a disk-shaped pressure-sensitive adhesive sample with a thickness of approximately 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 pressure-sensitive adhesive in a 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 pressure-sensitive adhesive (hereinafter sometimes referred to 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.

[0171] In some embodiments, it is advantageous for the Tpeak of the adhesive to be 45°C or lower, or 35°C or lower, preferably 30°C or lower (for example, 25°C or lower), and it may be 20°C or lower, or 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 it 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, -30°C or higher, -20°C or higher, -5°C or higher, 5°C or higher, 15°C or higher, or even 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 (for example, the composition of the monomer components constituting the acrylic polymer (A), the selection of the presence or absence, type, and amount of use of the additive (H RO ), and the use of a plasticizing material). When the pressure-sensitive adhesive sheet disclosed herein is in the form of a double-sided pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive surface and a second pressure-sensitive adhesive surface, the above-described Tpeak of the adhesive is preferably applied to at least the pressure-sensitive adhesive layer constituting the first pressure-sensitive adhesive surface, and more preferably applied to both the pressure-sensitive adhesive layer constituting the first pressure-sensitive adhesive surface and the pressure-sensitive adhesive layer constituting the second pressure-sensitive adhesive surface. The Tpeak of the pressure-sensitive adhesive layer constituting the first pressure-sensitive adhesive surface and the Tpeak of the pressure-sensitive adhesive layer constituting the second pressure-sensitive adhesive surface may be the same or different.

[0172] (Water absorption rate) In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, it is preferable that the water absorption rate of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet is limited to a predetermined value or less. By limiting the water absorption rate of the pressure-sensitive adhesive layer, dimensional changes of the pressure-sensitive adhesive layer due to fluctuations in the amount of moisture in the pressure-sensitive adhesive layer (for example, absorption and release of moisture such as humidity in the environment) tend to be suppressed. Thereby, it is possible to suppress warping of the pressure-sensitive adhesive sheet or the adherend to which the pressure-sensitive adhesive sheet is attached, which is caused by a mismatch in dimensional changes between the pressure-sensitive adhesive layer and an adjacent layer (which can be a support substrate, a release liner, an adherend, etc.). The ability to suppress fluctuations in the amount of moisture in the pressure-sensitive adhesive layer is also preferable from the viewpoint of maintaining the flatness, transparency, refractive index, etc. of the pressure-sensitive adhesive layer constant. In addition, a pressure-sensitive adhesive layer with a low water absorption rate is suitable as a pressure-sensitive adhesive sheet used for a member or product containing an element that dislikes moisture, such as an organic EL element, because it is difficult to occlude moisture.

[0173] In some embodiments, the water absorption rate of the pressure-sensitive 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, 0.2% or less, or 0.1% or less. The lower limit of the water absorption rate of the pressure-sensitive 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, or 0.15% or more. When the pressure-sensitive adhesive sheet disclosed herein is in the form of a double-sided pressure-sensitive adhesive sheet having a first adhesive surface and a second adhesive surface, it is preferable that the water absorption rate of at least the pressure-sensitive adhesive layer constituting the first adhesive surface is limited to a predetermined value or less. From the viewpoint of obtaining a higher effect, it is more preferable that the water absorption rates of both the pressure-sensitive adhesive layer constituting the first adhesive surface and the pressure-sensitive adhesive layer constituting the second adhesive surface are limited to a predetermined value or less.

[0174] Note that the water absorption rate (also referred to as the moisture content) of the pressure-sensitive adhesive layer is measured by the following method. [Measurement of moisture content] The pressure-sensitive adhesive layer to be evaluated is 4 cm × 5 cm (area: 20 cm together with two release liners arranged on one surface and the other surface thereof. 2Cut it out to the size of ), remove the release liner on one surface, and laminate it onto the pre-weighed aluminum foil. Next, remove the release liner on the other surface of the adhesive layer, put it into a thermo-hygrostat chamber at a temperature of 60 °C and a relative humidity of 90%, and take it out after 72 hours. After weighing the test piece in which the adhesive layer and the aluminum foil are laminated, use a moisture meter (Mitsubishi Chemical Analytech CA-200 type) equipped with a heating vaporization device (Mitsubishi Chemical Analytech VA-200 type), and measure the moisture content under the following conditions by the Karl Fischer coulometric titration method. Anolyte: Aquamicron AKX (manufactured by Mitsubishi Chemical) Catholyte: Aquamicron CXU (manufactured by Mitsubishi Chemical) Heating vaporization temperature: 150 °C

[0175] (Gel fraction) The gel fraction of the adhesive layer 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 facilitating the favorable coexistence of a high refractive index and adhesive properties, in some preferred embodiments, the above gel fraction can be approximately 95% or less, more preferably approximately 92% or less (for example, approximately 90% or less). The fact 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. Also, from the viewpoint of imparting appropriate cohesiveness to the adhesive and appropriately expressing the adhesive properties, the gel fraction of the adhesive layer is, for example, approximately 10% or more, and 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 (typically a substrate-free adhesive sheet) 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 acrylic polymer (A). The gel fraction is measured by the following method.

[0176] [Measurement of Gel Fraction] A predetermined amount of the adhesive sample (weight Wg 1 ) is wrapped in a porous polytetrafluoroethylene membrane with an average pore diameter of 0.2 μm (weight Wg 2 ) in a sachet shape, and the mouth is tied with a string (weight Wg 3 ). As the above porous polytetrafluoroethylene (PTFE) membrane, the product name "Nitoflon (registered trademark) NTF1122" (average pore diameter 0.2 μm, porosity 75%, thickness 85 μm) available from Nitto Denko Corporation or its equivalent 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 (Wg 4 ) of the package. The gel fraction of the adhesive layer is determined by substituting each value into the following formula. Gel fraction (%) = [(Wg 4 - Wg 2 - Wg 3 ) / Wg 1 × 100

[0177] When the pressure-sensitive adhesive sheet disclosed herein is in the form of a double-sided pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive surface and a second pressure-sensitive adhesive surface, the above-mentioned gel fraction is applied to at least the adhesive layer constituting the first pressure-sensitive adhesive surface, preferably to both the adhesive layer constituting the first pressure-sensitive adhesive surface and the adhesive layer constituting the second pressure-sensitive adhesive surface. The gel fraction of the adhesive layer constituting the first pressure-sensitive adhesive surface and the gel fraction of the adhesive layer constituting the second pressure-sensitive adhesive surface may be the same or different.

[0178] (Peel strength) In some embodiments of the pressure-sensitive adhesive sheet disclosed herein, the peel strength of the pressure-sensitive adhesive sheet with respect to a 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.

[0179] Here, the peel strength is determined by pressing it onto an alkali glass plate as the adherend, leaving it for 30 minutes in an environment of 23°C and 50% RH, then putting it into a pressure degassing device (autoclave), performing an autoclave treatment for 30 minutes under the conditions of a temperature of 50°C and a pressure of 0.5 MPa, and further leaving it for 24 hours in an atmosphere of 23°C and 50% RH, and then measuring the 180° peel adhesion force under the conditions of 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 adhesive sheet to be measured for reinforcement. More specifically, the peel strength can be measured according to the method described in the examples below. 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, in some embodiments, the above-described peel strength is preferably applied to at least the first adhesive surface, 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.

[0180] (Support substrate) The pressure-sensitive adhesive sheet according to some embodiments can be in the form of a pressure-sensitive adhesive sheet with a substrate having a pressure-sensitive adhesive layer on one or both sides of a support substrate. The material of the support substrate is not particularly limited and can be appropriately selected according to the purpose of use and the usage mode of the pressure-sensitive adhesive sheet, etc. Non-limiting examples of substrates 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 foams, polyethylene (PE) foams, and polychloroprene foams; 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, fine paper, kraft paper, crepe paper, etc.; 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 composite substrates 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.

[0181] In some embodiments, various film substrates can be preferably used. The film substrate may be a porous substrate such as a foam film or a non-woven fabric sheet, or 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 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 voids (voidless). Therefore, the resin film is a concept distinct from a foam film or a non-woven fabric. As the resin film, an independently shape-maintainable (self-supporting or non-dependent) one can be preferably used. The resin film may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure).

[0182] Examples of the materials 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); cyclic polyolefin resins such as polyetheretherketone (PEEK), polyethersulfone (PES), and 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.

[0183] The above resin film may be formed using a resin material containing one such resin alone, 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, etc., and among them, PET film is preferred.

[0184] In the resin film, known additives such as a light stabilizer, an antioxidant, an antistatic agent, a colorant (dye, pigment, etc.), a filler, a slip agent, and an antiblocking agent can be blended as necessary within a range not significantly interfering with the effects of the present invention. The blending amount of the additive is not particularly limited and can be appropriately set according to the use of the adhesive sheet, etc.

[0185] 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, and calendar roll molding can be appropriately employed.

[0186] The above base material can 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 surface treatment layer such as a release layer.

[0187] In some embodiments, as the support substrate, a substrate having light transmissivity (hereinafter also referred to as a light-transmissive substrate) may be preferably employed. Thereby, it becomes possible to form a pressure-sensitive adhesive sheet with a substrate having light transmissivity. The total light transmittance of the light-transmissive substrate may be, for example, more than 50%, and may also 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 Institute or its equivalent is used. Suitable examples of the above light-transmissive substrate include resin films having light transmissivity. The above light-transmissive substrate may be an optical film.

[0188] The thickness of the substrate is not particularly limited and can be selected according to the purpose of use and usage mode of the pressure-sensitive adhesive sheet, etc. The thickness of the substrate may be, for example, 500 μm or less, preferably 300 μm or less from the viewpoint of the handleability and processability of the pressure-sensitive adhesive sheet, and may also 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 and processability, etc., the thickness of the substrate may be, for example, 2 μm or more, and may also be 10 μm or more or 25 μm or more.

[0189] 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.

[0190] When the pressure-sensitive adhesive sheet disclosed herein is in the form of a 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 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 pressure-sensitive adhesive sheet 1 having the configuration shown in FIG. 1, it refers to the thickness from the first surface (adhesive surface) 10A of the adhesive layer to the second surface 20B of the support base material, and does not include the thickness of the release liner 30.

[0191] <Pressure-sensitive adhesive sheet with release liner> The pressure-sensitive adhesive sheet disclosed herein can take the form of a pressure-sensitive adhesive product in which the surface (adhesive surface) of the adhesive layer is in contact with the release surface of the release liner. Therefore, according to this specification, a pressure-sensitive adhesive sheet with a release liner (pressure-sensitive adhesive product) including any of the pressure-sensitive adhesive sheets disclosed herein and a release liner having a release surface in contact with the adhesive surface of the pressure-sensitive adhesive sheet is provided.

[0192] The release liner is not particularly limited. For example, a release liner having a release layer on the surface of a liner substrate such as a resin film or paper (which can 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 or polypropylene) can be used. Due to excellent surface smoothness, a release liner having a release layer on the surface of a resin film as a liner substrate or a release liner made of a resin film formed of a low-adhesion material can be preferably adopted. The resin film is not particularly limited as long as it can protect the adhesive layer. For example, polyethylene (PE) film, polypropylene (PP) film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyester film (such as PET film, PBT film, etc.), polyurethane film, ethylene-vinyl acetate copolymer film, etc. can be mentioned. For the formation of the above release layer, known release treatment agents such as silicone-based release treatment agents, long-chain alkyl-based release treatment agents, olefin-based release treatment agents, fluorine-based release treatment agents, fatty acid amide-based release treatment agents, molybdenum sulfide, silica powder, etc. can be used.

[0193] <Use> The adhesive sheet disclosed herein can be used by being attached to various adherends. The constituent material (adherend material) of the 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, alumina, zirconia, titania, SiO 2 , metal oxides such as 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, etc. The adhesive sheet disclosed herein can be used by being attached to a member (for example, an optical member) at least the surface of which is made of the above materials.

[0194] The pressure-sensitive adhesive sheet disclosed herein can be used in an attachment mode that does not require heating to a temperature higher than a temperature range around room temperature (for example, 20°C to 35°C) after being attached to an adherend. Further, when permitted according to the constituent materials of the pressure-sensitive adhesive sheet (for example, the material of the base material) and the type of the adherend, heat treatment may be performed at least at any one of the timing after attachment to the adherend, the timing of attachment, and before attachment. The heat treatment can be performed for the purpose of improving the adhesion of the pressure-sensitive adhesive to the adherend and promoting adhesion. The heat treatment temperature can be appropriately set within a range permitted according to the constituent materials of the pressure-sensitive adhesive sheet and the type of the adherend, taking into account the surface state of the adherend and the like, so that a desired effect can be obtained. For example, it may be about 100°C or lower, 80°C or lower, 60°C or lower, or 50°C or lower.

[0195] The members and materials to which the pressure-sensitive adhesive sheet is to be attached (in the case of a double-sided pressure-sensitive adhesive sheet, at least one of the adherends) can have light transmissibility. In such an adherend, the advantage of increasing the refractive index while suppressing a decrease in optical properties (such as transparency) can be easily obtained by applying the technology disclosed herein. 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 still more preferably 95% or more (for example, 95 to 100%). The pressure-sensitive adhesive sheet disclosed herein can be preferably used in a mode of being attached 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, a product named "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory or its equivalent is used.

[0196] The refractive index of the adhesive layer and the refractive index of 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 may 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 may be, for example, 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 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.

[0197] 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 the mode of attaching to such an adherend, the effects of the technology disclosed herein are particularly preferably exhibited.

[0198] As an example of a preferred use, an optical use 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 manufacturing applications of products (optical products) using the above optical members, the adhesive sheet disclosed herein can be preferably used.

[0199] The above-mentioned optical member refers to a member having optical properties (e.g., polarization, photorefractivity, light scattering, light reflection, light transmittance, light absorption, light diffraction, optical rotation, visibility, etc.). The above-mentioned optical member is not particularly limited as long as it is a member having optical properties. For example, members constituting devices (optical devices) such as display devices (image display devices) and input devices, or members used in these devices can be mentioned. For example, polarizing plates, wave 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 further members in which these are laminated (these may be collectively referred to as "functional films") can be mentioned. Note that the above-mentioned "plates" and "films" include forms such as plate-like, film-like, and sheet-like. For example, "polarizing film" includes "polarizing plate" and "polarizing sheet", and "light guide plate" includes "light guide film" and "light guide sheet". Also, the above-mentioned "polarizing plate" includes circular polarizing plates.

[0200] Examples of the above-mentioned 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-mentioned input device include a touch panel.

[0201] The above-mentioned optical member is not particularly limited. For example, members made of glass, acrylic resin, polycarbonate, polyethylene terephthalate, metal thin films, etc. (e.g., sheet-like, film-like, or plate-like members) can be mentioned. Note that the "optical member" in this specification also includes members (such as design films, decorative films, and surface protection films) that play a role in decoration and protection while maintaining the visibility of display devices and input devices.

[0202] The technology disclosed herein can be preferably used, for example, for bonding an optical film such as a film having one or more functions such as light transmission, reflection, diffusion, waveguide, light collection, diffraction, or a fluorescent film to another optical member (which may be another optical film). Among them, in bonding an optical film having at least one function of light waveguide, light collection, or diffraction, it is desirable that the entire bulk of the bonding layer has a high refractive index, and thus it can be a preferred application target of the technology disclosed herein.

[0203] The adhesive disclosed herein can be preferably used, for example, for bonding optical films such as a light guide film, a diffusion film, a fluorescent film, a color - tuning 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 that can meet such requirements, the adhesive disclosed herein can be preferably utilized. More specifically, for example, in bonding a light guide film or a diffusion film, thinning can be contributed by adjusting the refractive index of the adhesive layer as the bonding layer (for example, increasing the refractive index). In bonding a fluorescent film, the light extraction efficiency (which can also be regarded as the luminescence efficiency) can be improved by appropriately adjusting the refractive index difference between the fluorescent emitter and the adhesive. In bonding a color - tuning film, the scattering component can be reduced and the light transmittance can be improved by appropriately adjusting the refractive index of the adhesive so that the refractive index difference from the color - tuning pigment becomes small. In bonding 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 and the luminance and / or the viewing angle can be improved.

[0204] The pressure-sensitive adhesive sheet disclosed herein is preferably used in a manner of being attached to a high refractive index adherend (which may be a high refractive index layer, member, etc.), and can suppress the interfacial reflection with the above adherend. The pressure-sensitive adhesive sheet used in such a manner preferably has a small refractive index difference from the adherend and high adhesion at the interface with the adherend as described above. Further, from the viewpoint of enhancing the homogeneity of the appearance, it is preferable that the thickness uniformity of the pressure-sensitive 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, there is a mode of being used for the bonding between the polarizer and the first retardation layer and / or the bonding between the first retardation layer and the second retardation layer in a polarizing plate with a retardation layer including a polarizer, a first retardation layer, and a second retardation layer in this order.

[0205] In addition, since the pressure-sensitive adhesive sheet disclosed herein is suitable for increasing the refractive index, it 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 pressure-sensitive adhesive layer, the reflection at their interface can be suppressed, and the light extraction efficiency can be improved. The pressure-sensitive adhesive sheet used in such a manner preferably includes a pressure-sensitive adhesive layer having a high refractive index. Further, from the viewpoint of preventing the deterioration of the self-luminous element due to moisture, it is preferable that the water absorption rate of the pressure-sensitive adhesive layer is low. From the viewpoint of improving the luminance, it is preferable that the pressure-sensitive adhesive sheet has low coloration. This can also be advantageous from the viewpoint of suppressing unintentional coloration caused by the pressure-sensitive adhesive sheet.

[0206] The adhesives 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 components such as cameras and light-emitting devices. Since the adhesives disclosed herein are suitable for increasing the refractive index, even for lenses with a high refractive index (e.g., lenses made of a high refractive index resin or lenses having a surface layer made of a high refractive index resin), the refractive index difference from the lens can be reduced. This is advantageous from the perspective of thinning the above lenses and products equipped with such lenses, and can also contribute to suppressing aberration and improving the Abbe number. The adhesives disclosed herein can also be used as a lens resin itself, for example, in a form filled in a recess or void of a suitable transparent member.

[0207] The mode of bonding optical members using the adhesive sheet disclosed herein is not particularly limited. For example, (1) a mode of bonding optical members to each other via the adhesive sheet disclosed herein, (2) a mode of bonding an optical member to a member other than an optical member via the adhesive sheet disclosed herein, or (3) a mode in which the adhesive sheet disclosed herein includes 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 (3) above, the adhesive sheet in a form including 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 a form including 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 sheet disclosed herein is an adhesive sheet having a support and the above functional film is used as the support, the adhesive sheet disclosed herein can also be regarded as an "adhesive type functional film" having an adhesive layer disclosed herein on at least one side of the functional film.

[0208] As described above, according to the technology disclosed herein, a laminate is provided that includes the pressure-sensitive adhesive sheet disclosed herein and a member to which the pressure-sensitive adhesive sheet is attached. The member to which the pressure-sensitive adhesive sheet 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 pressure-sensitive adhesive sheet and the refractive index of the member can be the refractive index difference between the adherend and the pressure-sensitive adhesive sheet described above. Since the members constituting the laminate are as described above for the members, materials, and adherends, overlapping explanations will not be repeated.

[0209] As can be understood from the above description and the following examples, the matters disclosed in this specification include the following. [1] A pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer, having a pressure-sensitive adhesive surface formed by the above pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer has a refractive index exceeding 1.570, a total light transmittance of 86% or more, and a haze value of 3.0% or less, the pressure-sensitive adhesive sheet. [2] The pressure-sensitive adhesive sheet according to [1] above, wherein the pressure-sensitive adhesive layer has a thickness of 5 μm or more. [3] The pressure-sensitive adhesive sheet according to [1] or [2] above, having a peel strength (adhesive force) with respect to a glass plate of 3 N / 25 mm or more. [4] The pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the pressure-sensitive adhesive surface has an arithmetic mean roughness Ra of 100 nm or less. [5] The pressure-sensitive adhesive sheet according to any one of [1] to [4] above, wherein the pressure-sensitive adhesive layer has a water absorption rate of 1.0% or less. [6] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, configured as a laminate including the pressure-sensitive adhesive layer and a light-transmissive substrate. [7] The pressure-sensitive adhesive sheet according to [6] above, wherein the light-transmissive substrate is a resin film. [8] The pressure-sensitive adhesive sheet according to any one of [1] to [5] above, which is a double-sided adhesive pressure-sensitive adhesive sheet composed of the pressure-sensitive adhesive layer. [9] The pressure-sensitive adhesive sheet according to any one of [1] to [8] above, and a release liner disposed on the pressure-sensitive adhesive surface of the pressure-sensitive adhesive sheet, An adhesive sheet with a release liner, which includes 〔10〕An adhesive composition used for forming the adhesive layer of the adhesive sheet according to any one of 〔1〕 to 〔8〕 above.

[0210] 〔11〕An acrylic polymer (A) containing an aromatic ring-containing monomer (m1) as a monomer unit, and an additive (H RO ) which is an organic material having a higher refractive index than the above acrylic polymer (A), and An adhesive composition containing the same. 〔12〕The refractive index of the above additive (H RO ) is 1.60 or more, and the adhesive composition according to 〔11〕 above. 〔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 adhesive composition according to 〔11〕 or 〔12〕 above. 〔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 adhesive composition according to any one of 〔11〕 to 〔13〕 above. 〔15〕The above additive (H RO ) contains a compound having two or more aromatic rings in one molecule, and the adhesive composition according to any one of 〔11〕 to 〔14〕 above. 〔16〕The above additive (H RO ) is, as the compound having two or more aromatic rings in one molecule, (i) includes a structure in which two non-condensed aromatic rings are directly chemically bonded, and (ii) includes a structure in which two aromatic rings are condensed, and the adhesive composition according to 〔15〕 above contains a compound satisfying at least one of the above. 〔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 adhesive composition according to any one of 〔11〕 to 〔16〕 above. 〔18〕In the monomer component constituting the acrylic polymer (A), the content of the aromatic ring-containing monomer (m1) exceeds 70% by weight and is less than 100% by weight. The pressure-sensitive adhesive composition according to any one of the above

[11] to

[17] , wherein 50% by weight or more of the aromatic ring-containing monomer (m1) is a monomer having a glass transition temperature of 10 ° C or lower for the homopolymer. 〔19〕The monomer component constituting the 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 to form the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to any one of the above [1] to [8]. 〔21〕A pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition according to any one of the above

[11] to

[20] , having a refractive index higher than 1.570. 〔22〕A pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer composed of a pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition according to any one of the above

[11] to

[20] . 〔23〕The pressure-sensitive adhesive sheet according to the above

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

[0211] 〔24〕An interlayer sheet used by being disposed between layers of a laminate in an optical application, with a refractive index n 1 being 1.570 or more for the viscoelastic layer V 1 including, 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; satisfying the requirements, an interlayer sheet. 〔25〕The interlayer sheet according to the above

[24] , having a thickness of 5 μm or more. 〔26〕The viscoelastic layer V 1 includes a main polymer and a plasticizing material having a lower molecular weight than the main polymer, and the interlayer sheet according to the above

[24] or

[25] . 〔27〕 The weight average molecular weight of the above plasticizing material is 30,000 or less, and the interlayer sheet described in the above

[26] . 〔28〕 The above viscoelastic layer V 1 The viscoelastic layer V laminated thereon 2 further comprises, the above viscoelastic layer V 2 The storage elastic modulus G' at 25°C of V2 is the storage elastic modulus G' at 25°C of the above viscoelastic layer V 1 The storage elastic modulus G' at 25°C of V1 is lower than that of the interlayer sheet described in any one of the above

[24] to

[27] . 〔29〕 The refractive index n of the above viscoelastic layer V 2 of 2 is the refractive index n of the above viscoelastic layer V 1 of 1 is lower than that of the interlayer sheet described in the above

[28] . 〔30〕 The above viscoelastic layer V 1 is a layer formed from the pressure-sensitive adhesive composition described in any one of the above

[11] to

[18] , and the interlayer sheet described in any one of the above

[24] to

[29] . 〔31〕 The above viscoelastic layer V 1 is the pressure-sensitive adhesive layer in the pressure-sensitive adhesive sheet described in any one of the above [1] to [5], and the interlayer sheet described in any one of the above

[24] to

[29] . 〔32〕 The interlayer sheet described in any one of the above

[24] to

[31] , and a resin film laminated on the above interlayer sheet, and An optical laminate comprising. 〔33〕 The interlayer sheet described in any one of the above

[24] to

[31] , and a release liner covering at least one surface of the above interlayer sheet, and A release liner-attached interlayer sheet comprising.

Examples

[0212] Hereinafter, several examples related to the present invention will be described, but the present invention is not intended to be limited to the specific examples shown. In the following description, "parts" and "%" representing the amount used and the content are based on weight unless otherwise specified.

[0213] <Example 1> (Preparation of Acrylic Polymer Solution) 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"), 5 parts of 4-hydroxybutyl acrylate (4HBA), 0.2 part of 2,2'-azobisisobutyronitrile (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 A1. The polymerization average molecular weight (Mw) of this acrylic polymer A1 was 500,000. The above acrylic polymer A1 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.

[0214] (Preparation of Adhesive Composition) The solution (50%) of the above acrylic polymer A1 was diluted to 30% with ethyl acetate. To 334 parts of this solution (100 parts of non-volatile matter), 5 parts of 6-acryloyloxymethyldinaphthothiophene (dinaphthothiophene-6-methyl acrylate form manufactured by Suga Chemical Industry Co., Ltd., trade name "6MDNTA", refractive index 1.75) as an additive (H RO ), 10 parts (0.1 part of non-volatile matter) of a 1% ethyl acetate solution of isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", trifunctional isocyanate compound) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (0.01 part of non-volatile matter) of a 1% ethyl acetate solution of ferric naphthenate as a crosslinking catalyst were added and stirred and mixed to prepare an acrylic adhesive composition C1.

[0215] (Production of Adhesive Sheet) The acrylic pressure-sensitive adhesive composition C1 prepared above was applied to the silicone-treated surface of a polyethylene terephthalate (PET) film R1 (thickness: 50 μm) with 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. Next, the silicone-treated surface of a PET film R2 (thickness: 25 μm) with silicone treatment on one side was bonded to the surface of the pressure-sensitive adhesive layer. In this way, a substrate-less double-sided pressure-sensitive adhesive sheet S1 composed of the above pressure-sensitive adhesive layer was obtained. Both sides of the pressure-sensitive adhesive sheet S1 are protected by PET films (release liners) R1 and R2.

[0216] <Examples 2 to 5> Additive (H RO ) were changed as shown in Table 1 for the type and the amount used (phr; per hundred resin) with respect to 100 parts of the acrylic polymer. Otherwise, in the same manner as the preparation of the acrylic pressure-sensitive adhesive composition C1 in Example 1, acrylic pressure-sensitive adhesive compositions C2 to C5 according to Examples 2 to 5 were prepared. Here, "BPFL" in Table 1 represents 9,9-bis(4-hydroxyphenyl)fluorene (manufactured by Osaka Gas Chemical Co., Ltd., refractive index 1.68), and "BAFL" represents 9,9-bis(4-aminophenyl)fluorene (manufactured by Osaka Gas Chemical Co., Ltd., refractive index 1.73). Except that acrylic pressure-sensitive adhesive compositions C2 to C5 were used instead of the acrylic pressure-sensitive adhesive composition C1, in the same manner as the preparation of the pressure-sensitive adhesive sheet in Example 1, pressure-sensitive adhesive sheets (substrate-less double-sided pressure-sensitive adhesive sheets composed of pressure-sensitive adhesive layers) S2 to S5 according to Examples 2 to 5 were prepared.

[0217] <Example 6> Into a separable flask equipped with a thermometer, a stirrer, a reflux condenser tube, and a nitrogen gas inlet tube, 20 parts of POB-A, 80 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"), 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 (hereinafter referred to as oligomer B) having a weight average molecular weight (Mw) of 4000 and a refractive index of 1.63. Additive (H RO ) The type of was changed to the above oligomer B, and its usage amount was 30 parts (30 phr) with respect to 100 parts of the acrylic polymer. Otherwise, in the same manner as the preparation of the acrylic pressure-sensitive adhesive composition C1 in Example 1, the acrylic pressure-sensitive adhesive composition C6 according to this example was prepared. The pressure-sensitive adhesive sheet (substrate-less double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) S6 according to this example was produced in the same manner as in the production of the pressure-sensitive adhesive sheet in Example 1, except that the acrylic pressure-sensitive adhesive composition C6 was used instead of the acrylic pressure-sensitive adhesive composition C1.

[0218] <Example 7> Additive (H RO ) The acrylic pressure-sensitive adhesive composition C7 was prepared in the same manner as the preparation of the acrylic pressure-sensitive adhesive composition C1 in Example 1, except that it was not used. The pressure-sensitive adhesive sheet (substrate-less double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) S7 according to this example was produced in the same manner as in the production of the pressure-sensitive adhesive sheet in Example 1, except that the acrylic pressure-sensitive adhesive composition C7 was used instead of the acrylic pressure-sensitive adhesive composition C1 and the thickness of the pressure-sensitive adhesive layer was 20 μm.

[0219] <Example 8> The solution of acrylic polymer A2 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 1, except that the composition of the monomer components was changed to 72 parts of POB-A, 23 parts of NMT-A, and 5 parts of 4HBA. The weight-average molecular weight (Mw) of this acrylic polymer A2 was 450,000. The acrylic pressure-sensitive adhesive composition C8 according to this example was prepared in the same manner as the preparation of the pressure-sensitive adhesive composition in Example 1, except that the solution of acrylic polymer A2 was used instead of the solution of acrylic polymer A1. The pressure-sensitive adhesive sheet (a substrate-free double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) S8 according to this example was produced in the same manner as the production of the pressure-sensitive adhesive sheet in Example 1, except that the acrylic pressure-sensitive adhesive composition C8 was used instead of the acrylic pressure-sensitive adhesive composition C1.

[0220] <Examples 9 to 13> Additive (H RO ) The acrylic pressure-sensitive adhesive compositions C9 to C13 according to Examples 9 to 13 were prepared in the same manner as the preparation of the acrylic pressure-sensitive adhesive composition C8 in Example 8, except that the type and amount of the additive were changed as shown in Table 1. The pressure-sensitive adhesive sheets (substrate-free double-sided pressure-sensitive adhesive sheets composed of a pressure-sensitive adhesive layer) S9 to S13 according to Examples 9 to 13 were produced in the same manner as the production of the pressure-sensitive adhesive sheet in Example A1, except that the acrylic pressure-sensitive adhesive compositions C9 to C13 were used instead of the acrylic pressure-sensitive adhesive composition C1, respectively.

[0221] <Example 14> Additive (H RO ) The acrylic pressure-sensitive adhesive composition C14 according to Example 14 was prepared in the same manner as the preparation of the acrylic pressure-sensitive adhesive composition C8 in Example 8, except that the additive was not used. The pressure-sensitive adhesive sheet (a substrate-free double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) S14 according to this example was produced in the same manner as the production of the pressure-sensitive adhesive sheet in Example 8, except that the acrylic pressure-sensitive adhesive composition C14 was used instead of the acrylic pressure-sensitive adhesive composition C8.

[0222] <Example 15> The solution (40%) of acrylic polymer A3 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 1, except that the composition of the monomer components was changed to 90 parts of 2-ethylhexyl acrylate (2EHA) and 10 parts of 4HBA. The solution (40%) of the above acrylic polymer A3 was diluted to 20% with ethyl acetate. To 500 parts of this solution (100 parts of non-volatile content), 10 parts of a zirconia particle dispersion based on solid content, 10 parts of a 1% ethyl acetate solution of isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound, 0.1 part of non-volatile content), 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 content) were added and stirred and mixed to prepare an acrylic pressure-sensitive adhesive composition C15. As the above zirconia particle dispersion, a surface-treated zirconia particle dispersion in which surface-treated zirconia particles (average particle size 20 nm, solid content refractive index: 1.64, surface treatment: carboxylic acid-based / phosphoric acid-based hydrophobization treatment, manufactured by Kyoeisha Chemical Co., Ltd.) were dispersed in propylene glycol monomethyl ether (PGME) was used. An adhesive sheet S15 according to Example 15 (a substrate-free double-sided adhesive sheet composed of an adhesive layer) was produced in the same manner as in the production of the adhesive sheet in Example 1, except that the acrylic pressure-sensitive adhesive composition C15 was used instead of the acrylic pressure-sensitive adhesive composition C1 and the thickness of the adhesive layer was 20 μm.

[0223] <Example 16> The solution of acrylic polymer A4 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 1, except that the composition of the monomer components was changed to POB-A / n-butyl acrylate (BA) / 4HBA = 79 / 20 / 1. The polymerization average molecular weight (Mw) of acrylic polymer A4 was 520,000. An acrylic pressure-sensitive adhesive composition C16 according to this example was prepared in the same manner as in Example 2, except that the solution of acrylic polymer A4 was used instead of the solution of acrylic polymer A1, and an adhesive sheet S16 (a substrate-free double-sided adhesive sheet composed of an adhesive layer) was produced.

[0224] <Example 17> A solution of acrylic polymer A5 was prepared in the same manner as in Example 1 for the preparation of the acrylic polymer solution, except that the composition of the monomer components was changed to POB-A / ethyl carbitol acrylate (CBA) / 4HBA = 79 / 20 / 1. The polymerization average molecular weight (Mw) of acrylic polymer A5 was 460,000. An acrylic pressure-sensitive adhesive composition C17 according to this example was prepared in the same manner as in Example 2, except that a solution of acrylic polymer A4 was used instead of the solution of acrylic polymer A1, and a pressure-sensitive adhesive sheet (a substrate-free double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) S17 was produced.

[0225] <Example 18> A solution of acrylic polymer A6 was prepared in the same manner as in Example 1 for the preparation of the acrylic polymer solution, except that the composition of the monomer components was changed to POB-A / phenoxydiethylene glycol acrylate / 4HBA = 79 / 20 / 1. As the phenoxydiethylene glycol acrylate, the product name "Light Acrylate P2H-A" manufactured by Kyoeisha Chemical Co., Ltd. was used. The polymerization average molecular weight (Mw) of acrylic polymer A6 was 480,000. An acrylic pressure-sensitive adhesive composition C18 according to this example was prepared in the same manner as in Example 2, except that a solution of acrylic polymer A6 was used instead of the solution of acrylic polymer A1, and a pressure-sensitive adhesive sheet (a substrate-free double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) S18 was produced.

[0226] <Example 19> Additive (H RO ) was changed to 2,12-diallyloxydinaphthothiophene (manufactured by Suga Chemical Industry Co., Ltd., abbreviation: 2,12-DAODNT, refractive index 1.729), and an acrylic pressure-sensitive adhesive composition C19 according to this example was prepared in the same manner as in Example 2, and a pressure-sensitive adhesive sheet (a substrate-free double-sided pressure-sensitive adhesive sheet composed of a pressure-sensitive adhesive layer) S19 was produced.

[0227] <Examples 20 to 22> Additive (H ROExcept for not using [[ID=]], acrylic pressure-sensitive adhesive compositions C20 to C22 were prepared in the same manner as in Examples 16 to 18, respectively, and pressure-sensitive adhesive sheets (substrate-free double-sided pressure-sensitive adhesive sheets composed of pressure-sensitive adhesive layers) S20 to S22 were produced.

[0228] <Measurement and Evaluation> (Refractive Index) For the pressure-sensitive adhesive layers (substrate-free double-sided pressure-sensitive adhesive sheets) according to each example, 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 Tables 1 and 2.

[0229] (Total Light Transmittance and Haze Value) Using a test piece in which the pressure-sensitive adhesive layer according to each example was bonded to non-alkali glass (thickness 0.8 to 1.0 mm, total light transmittance 92%, haze 0.4%), the total light transmittance and haze of the above test piece were measured using a haze meter (manufactured by Murakami Color Research Laboratory, product name "HAZEMETER HM-150") under a measurement environment of 23°C. 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 values of the pressure-sensitive adhesive layer. The results are shown in Tables 1 and 2.

[0230] (Storage Modulus G') A sample for measurement was prepared by laminating the pressure-sensitive adhesive layers according to each example 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 modulus G' at 25°C was read. The results are shown in Tables 1 and 2. [Measurement Conditions] Deformation Mode: Torsion Measurement Frequency: 1 Hz Temperature Rise Rate: 5°C / min Shape: Parallel Plate 7.9 mmφ

[0231] (Peel Strength) For each of the adhesive sheets, the peel strength with respect to a glass plate was measured. That is, in a measurement environment of 23°C and 50% RH, the release liner was peeled from one surface of the adhesive sheet, a PET film with a thickness of 50 μm was laminated and lined, and then a piece cut to a size of 25 mm in width and 100 mm in length was used as a test piece. The release liner on the other surface was peeled from the test piece, and a 2 kg roller was reciprocated once to press-bond it to 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. This was left in the same environment for 30 minutes, then put into a pressure defoaming device (autoclave) and subjected to an autoclave treatment 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 peel angle of 180 degrees, the peel 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. The results are shown in Tables 1 and 2.

[0232]

Table 1

[0233]

Table 2

[0234] As shown in Table 1, the adhesives of Examples 1 to 6 in which additive (H RO ) was added to the adhesive of Example 7 that does not contain additive (H RO ) showed a higher refractive index than Example 7. These adhesives had high transparency and good peel strength. The same tendency was also observed in the comparison between Example 14 and Examples 8 to 13. On the other hand, Example 15 in which the refractive index was improved by blending inorganic particles with a high refractive index was clearly inferior in transparency (especially, the haze was extremely high) compared to Examples 1 to 14, and did not show adhesive performance (peel strength) suitable for practical use as an adhesive.

[0235] Similarly, in Examples 16 to 19 shown in Table 2, it was confirmed that the use of the additive (H RO ) exerted the effect of improving the refractive index. The adhesives of Examples 16 to 19 were highly transparent and had good peel strength. From the above, since the adhesives of Examples 1 to 6, Examples 8 to 13, and Examples 16 to 19 have a high refractive index while suppressing a decrease in optical properties, they are suitable for applications such as bonding of optical members (for example, optical films having at least one function of light wave guiding, light collection, and diffraction).

[0236] 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 illustrated above.

Explanation of Reference Numerals

[0237] 1,2 Adhesive sheet 10 Adhesive layer 10A First surface (adhesive surface) 10B Second surface 20 Support substrate 20A First surface 20B Second surface (back surface) 30, 31, 32 Release liner 50 Adhesive sheet with release liner 70 Optical member 100 Member with adhesive sheet

Claims

1. An acrylic polymer (A) containing an aromatic ring-containing monomer (m1) as a monomer unit, and Additive (H), which is an organic material having a higher refractive index than the acrylic polymer (A) ＲＯ ), and containing the additive (HRO) includes a compound having two or more aromatic rings in one molecule, the additive (HRO), as the compound having two or more aromatic rings in the one molecule, (i) includes a structure in which two non-condensed aromatic rings are directly chemically bonded, and (ii) includes a structure in which two aromatic rings are condensed, An adhesive composition containing at least one of the compounds satisfying the above.

2. The refractive index of the additive (H ＲＯ ) is 1.60 or more, and the pressure-sensitive adhesive composition according to claim 1.

3. The content of the additive (H ＲＯ ) with respect to 100 parts by weight of the acrylic polymer (A) is more than 0 part by weight and 60 parts by weight or less. The pressure-sensitive adhesive composition according to claim 1 or 2.

4. The additive (H ＲＯ ) is the pressure-sensitive adhesive composition according to any one of claims 1 to 3, containing at least one compound selected from the group consisting of an aromatic ring-containing compound and a heterocyclic ring-containing compound.

5. In the monomer component constituting the acrylic polymer (A), the content of the aromatic ring-containing monomer (m1) is 50% by weight or more. The adhesive composition according to any one of Claims 1 to 4.

6. In the monomer component constituting the acrylic polymer (A), the content of the aromatic ring-containing monomer (m1) exceeds 70% by weight and is less than 100% by weight, Among the aromatic ring-containing monomers (m1), 50% by weight or more is a monomer having a glass transition temperature of 10°C or lower for the homopolymer. The adhesive composition according to any one of Claims 1 to 5.

7. The monomer component constituting the acrylic polymer (A) further contains a monomer (m2) having at least one of a hydroxyl group and a carboxyl group. The adhesive composition according to any one of Claims 1 to 6.

8. An adhesive formed from the adhesive composition according to any one of Claims 1 to 7, having a refractive index higher than 1.

570.

9. An adhesive sheet including an adhesive layer constituted by an adhesive formed from the adhesive composition according to any one of Claims 1 to 7.

10. The haze value of the adhesive layer is 1.0% or less. The adhesive sheet according to Claim 9.

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