TWI885102B - Adhesive composition, adhesive and adhesive sheet - Google Patents

Abstract

The present invention provides an adhesive composition, comprising: an acrylic polymer (A) comprising 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 acrylic polymer (A). Also provided is an adhesive sheet having an adhesive formed from the adhesive composition.

Description

Adhesive composition, adhesive and adhesive sheet

The present invention relates to an adhesive composition, an adhesive, and an adhesive sheet. This application claims priority based on Japanese Patent Application No. 2020-052408 filed on March 24, 2020, Japanese Patent Application No. 2020-166426 filed on September 30, 2020, and Japanese Patent Application No. 2021-049059 filed on March 23, 2021, and all the contents of these applications are incorporated into this specification by reference.

Generally speaking, adhesives (also called pressure-sensitive adhesives, the same below) are in the state of soft solids (viscoelastic bodies) in the temperature range near room temperature, and have the property of being able to be simply bonded to the adherend by pressure. By utilizing this property, adhesives are widely used in various industrial fields, from home appliances to automobiles, various machinery, electrical machinery, electronic machinery, etc., for the purpose of bonding, fixing, and protection. As an example of the use of adhesives, it can be cited that in display devices such as liquid crystal display devices or organic EL display devices, polarizing films, phase difference films, cover window components, other various light-transmitting components, and other components are bonded. Technical documents related to adhesives for optical components include patent documents 1 and 2. Prior art literature Patent literature

Patent document 1: Japanese patent application publication No. 2014-169382 Patent document 2: Japanese patent application publication No. 2017-128732

Problem to be solved by the invention Patent documents 1 and 2 propose an adhesive composition with a (meth)acrylate polymer as a main component and an adhesive formed by crosslinking the adhesive composition, and the (meth)acrylate polymer contains a monomer having a plurality of aromatic rings as a monomer unit. However, it is difficult to obtain an adhesive having a higher refractive index than the above-mentioned (meth)acrylate polymer using the technology described in patent documents 1 and 2. On the other hand, there is also a known technique of mixing particles made of inorganic materials with high refractive index (such as inorganic particles such as zirconium oxide particles or titanium oxide particles) into resin to increase the refractive index. However, adhesives mixed with inorganic particles are difficult to apply in the adhesive field because the refractive index and adhesive properties (such as peeling strength, softness, etc.) are in a trade-off relationship. For adhesives used for optical purposes, there is also a concern that mixing with inorganic particles will reduce the optical properties.

Therefore, the object of the present invention is to provide an adhesive whose refractive index has been increased by a method that is also suitable for optical applications. Another related object is to provide an adhesive composition that can form the adhesive and an adhesive sheet containing the adhesive.

Means for solving the problem According to the adhesive composition provided in this specification, it 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 become one with a high refractive index. The adhesive composition disclosed herein, in addition to the acrylic polymer (A), further includes an additive (H _RO ) of an organic material having a higher refractive index than the acrylic polymer (A), thereby forming an adhesive that balances the improvement of the refractive index by the above additive (H _RO ) and the suppression of the reduction of adhesive properties. Furthermore, by using the above-mentioned additive (H _RO ), the reduction of optical properties (such as transmittance, haze, etc.) can be suppressed, and the refractive index of the adhesive can be effectively increased.

In several ideal aspects of the technology disclosed herein (including adhesive compositions, adhesives, adhesive sheets, and technologies implemented in other forms; the same applies hereinafter), the refractive index of the additive (H _RO ) can be, for example, about 1.60 or more. The refractive index of the adhesive can be effectively increased by using an additive (H _RO ) of an organic material having a higher refractive index than the acrylic polymer (A) and a refractive index of about 1.60 or more.

In several aspects, the content of the additive (H _RO ) is, for example, greater than 0 parts by weight and less than 60 parts by weight relative to 100 parts by weight of the acrylic polymer (A). The adhesive composition containing the additive (H _RO ) in such a content is preferred because it is easy to form an adhesive that balances the improvement of the refractive index by using the additive (H _RO ) and the suppression of the decrease of the adhesive properties and/or optical properties.

In some embodiments, the additive (H _RO ) comprises at least one compound selected from the group consisting of aromatic ring-containing compounds and heterocyclic ring-containing compounds. The technology disclosed herein can be suitably implemented in the embodiment using the compound as the additive (H _RO ).

In several aspects, the additive (H _RO ) includes a compound having two or more aromatic rings in one molecule. The technology disclosed herein can be suitably implemented in the aspect of using the compound as the additive (H _RO ). The compound having two or more aromatic rings in one molecule can be, for example, a compound that satisfies at least one of the following: (i) a structure including two non-condensed aromatic rings directly chemically bonded; and (ii) a structure including two condensed aromatic rings. The technology disclosed herein can be suitably implemented in the aspect of using the compound as the additive (H _RO ).

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

In some embodiments, the content of the aromatic ring-containing monomer (m1) in the monomer components constituting the acrylic polymer (A) is greater than 70 wt % and less than 100 wt %. Such acrylic polymer (A) is preferred because it is easy to increase the refractive index and to form an adhesive with good adhesive properties.

In several aspects, 50% by weight or more of the aromatic ring-containing monomer (m1) contained in the monomer component constituting the acrylic polymer (A) may be a monomer having a homopolymer glass transition temperature of 10° C. or less. Thus, even if the content of the aromatic ring-containing monomer (m1) in the monomer component is increased, it is still easy to form an adhesive that balances high refractive index and adhesive properties. In addition, the Tg of the homopolymer of a monomer is sometimes expressed as the Tg of the monomer.

In several ideal aspects, 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 "a monomer containing multiple aromatic rings"). The use of a monomer containing multiple aromatic rings can effectively increase the refractive index of the adhesive. The aromatic ring-containing monomer (m1) may include only one type of monomer containing multiple aromatic rings (for example, a monomer containing multiple aromatic rings whose homopolymer Tg is below 10°C), or may include a combination of two or more monomers containing multiple aromatic rings.

In several ideal aspects, 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 linker. For example, a monomer having multiple aromatic rings having the structural portion, for example, a monomer having multiple aromatic rings having a structural portion in which two aromatic rings are directly chemically bonded (e.g., a biphenyl structure), tends to have a lower Tg of the homopolymer. By including the aromatic ring-containing monomer (m1) having the above-mentioned structure, the softness and high refractive index suitable for use as an adhesive can be better balanced.

In some embodiments, the monomer components constituting the acrylic polymer (A) may contain, in addition to the above-mentioned aromatic ring-containing monomer (m1), a monomer (m2) having at least one of a hydroxyl group and a carboxyl group. The acrylic polymer (A) composed of the above-mentioned monomer components can easily form an adhesive having good adhesive properties.

In addition, in the following, the monomer (m1) containing an aromatic ring 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)".

The adhesive composition disclosed herein may further include a crosslinking agent. By using a crosslinking agent, the adhesive can be given a moderate cohesiveness, thereby improving the handling properties of the adhesive sheet during manufacturing, processing, storage, and attachment to an adherend.

According to the present specification, an adhesive formed by any of the adhesive compositions disclosed herein can be provided. The adhesive contains the above-mentioned additive (H _RO ) in addition to the above-mentioned acrylic polymer (A), thereby suppressing the decrease of adhesive properties and/or optical properties while improving the refractive index. In an ideal embodiment, the refractive index of the above-mentioned adhesive can be, for example, greater than 1.570 (preferably 1.575 or more, more preferably 1.580 or more).

According to the present specification, an adhesive sheet can be provided, which includes an adhesive layer formed by an adhesive, and the adhesive is an adhesive formed by any adhesive composition disclosed herein (for example, an adhesive having a refractive index greater than 1.570, preferably greater than 1.575, and more preferably greater than 1.580). The adhesive sheet is suitable for use in a state of being attached to a component (for example, an optical component).

In some aspects of the adhesive sheet disclosed herein, the haze value of the adhesive layer is less than 1.0%. The adhesive sheet having the adhesive layer with high transparency as described above can be suitably used in, for example, the optical field.

In addition, an appropriate combination of the elements described in this specification may also be included in the scope of the invention for which patent protection is sought through this patent application.

The following describes the ideal implementation form of the present invention. Matters other than those specifically mentioned in this specification and necessary for the implementation of the present invention can be understood by those familiar with this art based on the teachings on the implementation of the invention contained in this specification and the technical common sense at the time of application. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in this field. In addition, in the following figures, components and parts that play the same role are given the same symbols for description, and repeated descriptions are omitted or simplified. In addition, the implementation forms recorded in the figures are schematic for the purpose of clearly explaining the present invention, and do not completely correctly represent the size or scale of the actual product provided.

In this specification, a self-luminous element means a light-emitting element whose luminance can be controlled by the value of the current flowing therethrough. A self-luminous element can be constituted as a single body or as an aggregate. Specific examples of self-luminous elements include light-emitting diodes (LEDs) and organic ELs, but are not limited thereto. When a light-emitting device is mentioned in this specification, the light-emitting device may include the self-luminous element as a constituent element. The examples of the above-mentioned light-emitting devices also include light source module devices (such as planar light-emitting body modules) used for lighting or display devices formed with pixels, but are not limited thereto.

In this specification, the "base polymer" of the adhesive means the main component of the rubber polymer contained in the adhesive, and no other limitation is given. The above-mentioned rubber polymer refers to a polymer that exhibits rubber elasticity in a temperature range near room temperature. In addition, in this specification, "main component" means a component containing more than 50% by weight unless otherwise specified.

In this specification, "acrylic polymer" means a polymer containing the following monomer units as monomer units constituting the polymer: the monomer unit is derived from a monomer having at least one (meth)acryl group in one molecule. Hereinafter, a monomer having at least one (meth)acryl 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 monomer units derived from acrylic monomers. Typical examples of acrylic polymers include polymers in which the ratio of acrylic monomers in the total monomers that can be used to synthesize the polymer is greater than 50% by weight (preferably greater than 70% by weight, for example greater than 90% by weight).

In addition, in this specification, "(meth)acryl" refers to acryl and methacryl. Similarly, "(meth)acrylate" refers to acrylate and methacrylate, and "(meth)acrylic acid" refers to acrylic acid and methacrylic acid. Therefore, the concept of acrylic monomers mentioned here can include both monomers having an acryl group (acrylic monomers) and monomers having a methacryl group (methacrylic acid monomers).

<Adhesive composition> The adhesive composition disclosed herein can be any adhesive that contains an acrylic polymer (A) (preferably an adhesive that contains an acrylic polymer (A) as a base polymer), and its form is not particularly limited. The above-mentioned adhesive composition can be, for example, in the following various forms: a solvent-type adhesive composition in which adhesive-forming components are contained in an organic solvent, an active energy ray-curing adhesive composition that is prepared to form an adhesive by curing with active energy rays such as ultraviolet rays or radiation, a water-dispersible adhesive composition in which adhesive-forming components are dispersed in water, a hot-melt adhesive composition that can form an adhesive when applied in a heated and molten state and cooled to near room temperature, etc.

(Acrylic polymer (A)) The adhesive composition disclosed herein contains an acrylic polymer (A), and the acrylic polymer (A) contains 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, the "monomer component constituting the acrylic polymer" in this specification means a monomer that constitutes a repeating unit of the acrylic polymer in the adhesive formed by the adhesive composition, whether it is contained in the adhesive composition in the form of a pre-formed polymer (which may be an oligomer) or in the form of an unpolymerized monomer. That is, the monomer component constituting the acrylic polymer may be contained in the above-mentioned adhesive composition in any form of a polymer, an unpolymerized monomer, or a partially polymerized monomer. From the viewpoint of ease of preparation of the adhesive composition, in several aspects, it is preferable that substantially all (e.g., 95% by weight or more, preferably 99% by weight or more) of the monomer components are contained in the form of a polymer. An adhesive composition containing substantially all of the monomer components in the form of a polymer is also preferable from the viewpoint of being easy to form an adhesive sheet with little strain or warping.

(Monomer (m1)) Monomer (m1) can be a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule. Monomer (m1) can be used alone or in combination of two or more.

Examples of the above-mentioned ethylenically unsaturated group include (meth)acrylic group, vinyl group, (meth)allyl group, etc. From the viewpoint of polymerization reactivity, (meth)acrylic group is preferred, and from the viewpoint of flexibility or adhesiveness, acryl group is more preferred. From the viewpoint of suppressing the decrease in the flexibility of the adhesive, the monomer (m1) can be suitably a compound having 1 ethylenically unsaturated group contained in one molecule (i.e., a monofunctional monomer).

The number of aromatic rings contained in the molecule of the compound 1 that can be 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 several aspects, from the viewpoint of ease of preparation of the acrylic polymer (A) or 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, 5 or less, 4 or less, 3 or less, or 2 or less.

The aromatic ring possessed by the compound that can be 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 carbon ring such as a condensed ring of a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, and a phenanthrene ring; or a heterocyclic ring such as a pyridine ring, a pyrimidine ring, an indole ring, a pyrrolidine ring, a pyrazole ring, an imidazole ring, a triazole ring, an oxadiazole ring, an isoxadiazole ring, a thiazole ring, and a thiophene ring. The heteroatom contained in the heterocyclic ring as a ring-constituting atom may be, for example, one or more selected from the group consisting of nitrogen, sulfur and oxygen. In several embodiments, the heteroatom constituting the heterocyclic ring may be one or both of nitrogen and sulfur. The monomer (m1) may also have a structure in which one or more carbon rings and one or more heterocyclic rings are condensed, such as a dinaphthothiophene structure.

The above aromatic ring (preferably a carbocyclic ring) may have 1 or 2 or more substituents on the ring-constituting atoms, or may have no substituents. When having a substituent, the substituent may be exemplified by an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), a hydroxyalkyl group, a hydroxyalkoxy group, a glycidoxy group, etc., but is not limited thereto. In a substituent containing a carbon atom, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. In several aspects, the above aromatic ring may be an aromatic ring having no substituents on the ring-constituting atoms, or may be an aromatic ring having 1 or 2 or more substituents selected from the group consisting of an alkyl group, an alkoxy group and a halogen atom (e.g., a bromine atom) on the ring-constituting atoms. Furthermore, the fact that the aromatic ring of the monomer (m1) has a substituent on an atom constituting the ring means that the aromatic ring has a substituent other than a substituent having an ethylenically unsaturated group.

The aromatic ring and the ethylenically unsaturated group may be bonded directly or via a linking group. The linking group may be, for example, a group including 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 replaced by a hydroxyl group (e.g., a hydroxyalkylene group), an oxy group (-O-group), a thiooxy group (-S-group), etc. In several aspects, an aromatic ring-containing monomer having a structure in which the aromatic ring and the ethylenically unsaturated group are bonded directly or via a linking group selected from the group consisting of an alkylene group, an oxyalkylene group, and a poly(oxyalkylene) group may be suitably used. The carbon number of the alkylene group and the oxyalkylene group is preferably 1-4, more preferably 1-3, for example 1 or 2. The number of repetitions of the oxyalkylene unit in the poly(oxyalkylene) group may be, for example, 2-3.

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

The content of the monomer (m1) in the monomer component constituting the acrylic polymer (A) is not particularly limited, and can be set to achieve an adhesive layer that takes into account the 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 several aspects, the content of the monomer (m1) in the above-mentioned monomer component can be, for example, 30% by weight or more, and preferably 50% by weight or more, can be 60% by weight or more, and can also be 70% by weight or more. From the perspective of easily obtaining a higher refractive index, in several ideal aspects, the content of the above-mentioned monomer (m1) can be, for example, greater than 70% by weight, can be 75% by weight or more, can be 80% by weight or more, can be 85% by weight or more, can be 90% by weight or more, and can also be 95% by weight or more. The upper limit of the content of the monomer (m1) in the above-mentioned monomer component is 100 weight %. From the perspective of balancing the high refractive index with the adhesion properties and/or optical properties, it is advantageous to set the content of the above-mentioned monomer (m1) to be less than 100 weight %, for example, it is preferably about 99 weight % or less, more preferably 98 weight % or less, it can be 97 weight % or less, and it can also be 96 weight % or less. In several aspects, the content of the above-mentioned monomer (m1) can be 93 weight % or less, 90 weight % or less, 80 weight % or less, or 75 weight % or less. In several aspects that attach more importance to the adhesion properties and/or optical properties, the content of the above-mentioned monomer (m1) in the above-mentioned monomer component can be 70 weight % or less, 60 weight % or less, or 45 weight % or less.

In several aspects of the technology disclosed herein, a monomer having two or more aromatic rings (preferably a carbon ring) in one molecule can be suitably used as the monomer (m1) in order to easily obtain a higher refractive index effect. Examples of monomers having two or more aromatic rings in one molecule (hereinafter also referred to as "monomers containing multiple aromatic rings") include: monomers having a structure in which two or more non-condensed aromatic rings are bonded via a linking group, monomers having a structure in which two or more non-condensed aromatic rings are directly (i.e., not separated by other atoms) chemically bonded, monomers having a condensed aromatic ring structure, monomers having a fluorene structure, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, etc. The monomer containing plural aromatic rings may be used alone or in combination of two or more.

The linking group may be, for example, an oxy group (—O—), a thiooxy group (—S—), an oxyalkylene group (for example, an —O—(CH ₂ ) _n -group, where n is 1 to 3 and preferably 1), a thiooxyalkylene group (for example, an —S—(CH ₂ ) _n -group, where n is 1 to 3 and preferably 1), a linear alkylene group (i.e., a —(CH ₂ ) _n -group, where n is 1 to 6 and preferably 1 to 3), the above oxyalkylene groups, the above thiooxyalkylene groups, and the above linear alkylene groups in which the alkylene groups are partially or completely halogenated. From the viewpoint of the softness of the adhesive, suitable examples of the linking group include an oxy group, a thiooxy group, an oxyalkylene group, and a linear alkylene group. Specific examples of 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, and benzylbenzyl (meth)acrylate.

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

Examples of the monomer having a condensed aromatic ring structure include naphthalene ring-containing (meth)acrylate, anthracene ring-containing (meth)acrylate, vinyl naphthalene-containing, vinyl anthracene-containing, etc. Specific examples include 1-naphthylmethyl (meth)acrylate (also known as 1-naphthylmethyl (meth)acrylate), hydroxyethylated β-naphthol acrylate, 2-naphthylethyl (meth)acrylate, 2-naphthyloxyethyl acrylate, 2-(4-methoxy-1-naphthyloxy)ethyl (meth)acrylate, etc.

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

Examples of the monomer having a dinaphthothiophene structure include dinaphthothiophene containing a (meth)acryl group, dinaphthothiophene containing a vinyl group, and dinaphthothiophene containing a (meth)allyl group. Specific examples include: (meth)acryloyloxymethyl dinaphthothiophene (for example, a compound having a structure of _CH2CH ( ^R1 )C(O) _OCH2- bonded to the 5-position or 6-position of the dinaphthothiophene ring; here, ^R1 is a hydrogen atom or a methyl group), (meth)acryloyloxyethyl dinaphthothiophene (for example, a compound having a structure of _CH2CH ( ^R1 )C(O)OCH(CH3)- or _CH2CH ( _R1 )C(O) _OCH2CH2- bonded to the 5-position or 6-position of the _{dinaphthothiophene} ring; here, ^R1 is a hydrogen atom or ^a methyl group), vinyl dinaphthothiophene (for example, a compound having a structure of vinyl bonded to the 5-position or 6-position of the naphthothiophene ring), (meth)allyloxy dinaphthothiophene, and the like. In addition, the monomer having a dinaphthothiophene structure is also included in the concept of the monomer having a condensed aromatic ring structure by including a naphthalene structure and a structure in which a thiophene ring and two naphthalene structures are condensed.

Examples of the above-mentioned monomers having a dibenzothiophene structure include dibenzothiophene containing a (meth)acryloyl group and dibenzothiophene containing a vinyl group. In addition, since the monomers having a dibenzothiophene structure have a structure in which a thiophene ring and two benzene rings are condensed, they are included in the concept of the above-mentioned monomers having a condensed aromatic ring structure. In addition, the dinaphthothiophene structure and the dibenzothiophene structure are not structures in which two or more non-condensed aromatic rings are directly chemically bonded.

As the monomer (m1) of the technology disclosed herein, a monomer having one aromatic ring (preferably a carbon ring) in one molecule may also be used. A monomer having one aromatic ring in one molecule, for example, helps to improve the flexibility of the adhesive or adjust the adhesive properties, improve the transparency, etc. In several aspects, from the perspective of improving the refractive index of the adhesive, a monomer having one aromatic ring in one molecule is preferably used in combination with a monomer containing multiple aromatic rings.

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

The monomer (m1) may also be a monomer having a structure in which an oxyethylene chain is sandwiched between an ethylenically unsaturated group and an aromatic ring, as in the above-mentioned various aromatic ring-containing monomers. The monomer having an oxyethylene chain sandwiched between an ethylenically unsaturated group and an aromatic ring as described above may be regarded as an ethoxylate of the original monomer. The number of repetitions of the oxyethylene unit (-CH ₂ CH ₂ O-) in the above-mentioned oxyethylene chain 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 nonoxyphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxydiethylene glycol di(meth)acrylate, and the like.

The content of the monomer containing multiple aromatic rings in the monomer (m1) is not particularly limited, and can be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In several aspects, from the perspective of easily achieving an adhesive with a higher refractive index, the content of the monomer containing multiple aromatic rings in the monomer (m1) can be, for example, 50% by weight or more, and preferably 70% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The monomer (m1) can also be substantially 100% by weight of a monomer containing multiple aromatic rings. That is, the monomer (m1) can also use only one or more monomers containing multiple aromatic rings. Furthermore, in several aspects, for example, considering the balance between high refractive index and adhesion and/or optical properties, the content of monomers containing multiple aromatic rings in monomer (m1) may be less than 100% by weight, may be less than 98% by weight, may be less than 90% by weight, may be less than 80% by weight, or may be less than 65% by weight. In several aspects, considering adhesion and/or optical properties, the content of monomers containing multiple aromatic rings in monomer (m1) may be less than 70% by weight, may be less than 50% by weight, may be less than 25% by weight, or may be less than 10% by weight. The technology disclosed herein can be implemented even in the aspect that the content of monomers containing multiple aromatic rings in monomer (m1) is less than 5% by weight. Monomers containing multiple aromatic rings may also not be used.

The content of the monomer containing multiple aromatic rings in the monomer component constituting the acrylic polymer (A) is not particularly limited, and can be set to achieve an adhesive layer that takes into account the desired refractive index and adhesive properties (e.g., peel strength, flexibility, etc.) and/or optical properties (e.g., total light transmittance, haze value, etc.). The content of the monomer containing multiple aromatic rings in the above monomer component can be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In several aspects, from the perspective of easily achieving an adhesive with a higher refractive index, the content of the monomer containing multiple aromatic rings in the above-mentioned monomer component can be, for example, greater than 35% by weight, preferably greater than 50% by weight, greater than 70% by weight, greater than 75% by weight, greater than 85% by weight, greater than 90% by weight, or greater than 95% by weight. The content of the monomer containing multiple aromatic rings in the above-mentioned monomer component can be 100% by weight, but from the perspective of balancing the high refractive index with the adhesive property and/or the optical property, it is advantageous to set it to less than 100% by weight, preferably to be about 99% by weight or less, more preferably to be 98% by weight or less, to be 96% by weight or less, to be 93% by weight or less, to be 90% by weight or less, to be 85% by weight or less, to be 80% by weight or less, or to be 75% by weight or less. In several aspects, considering the adhesion and/or optical properties, the content of the monomer containing multiple aromatic rings in the above monomer component can be 70 wt% or less, 50 wt% or less, 25 wt% or less, 15 wt% or less, or 5 wt% or less. The technology disclosed herein can be implemented even in the aspect that the content of the monomer containing multiple aromatic rings in the above monomer component is less than 3 wt%.

In several aspects of the technology disclosed herein, a high refractive index monomer may be preferably used as at least a part of the monomer (m1). Here, "high refractive index monomer" means a monomer whose refractive index is, for example, about 1.510 or more, preferably about 1.530 or more, and more preferably about 1.550 or more. There is no particular upper limit on the refractive index of the high refractive index monomer, but from the perspective of ease of preparation of the adhesive composition or ease of balance between flexibility and suitability as an adhesive, for example, it may be 3.000 or less, 2.500 or less, 2.000 or less, 1.900 or less, 1.800 or less, or 1.700 or less. The high refractive index monomer may be used alone or in combination of two or more. The refractive index of the monomer is measured using an Abbe refractometer at a measurement wavelength of 589 nm and a measurement temperature of 25°C. The Abbe refractometer may be a "DR-M4" model manufactured by ATAGO or an equivalent. When a nominal value of the refractive index at 25°C is provided by a manufacturer, the nominal value may be used.

The high refractive index monomer can be appropriately selected from the compounds included in the concept of the aromatic ring-containing monomer (m1) disclosed herein (e.g., the compounds and compound groups exemplified above) and have the refractive index. 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 repetitions of oxyethylidene units: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, Tg of homopolymer: 6°C), phenoxyethyl acrylate (refractive index (nD20): 1.517, Tg of homopolymer: 2°C), phenoxydiethylene glycol acrylate (refractive index: 1.510, Tg of homopolymer: -35°C), 6-acryloxymethyl dinaphthothiophene (6MDNTA, refractive index: 1.75), 6-methacryloxymethyl dinaphthothiophene (6MDNTMA, refractive index: 1.726), 5-acryloxyethyl dinaphthothiophene (5EDNTA, refractive index: 1.786), 6-acryloxyethyl dinaphthothiophene (6EDNTA, refractive index: 1.722), 6-vinyl dinaphthothiophene (6VDNT, refractive index: 1.802), 5-vinyl dinaphthothiophene (abbreviation: 5VDNT, refractive index: 1.793), etc., but are not limited thereto.

The content of the high refractive index monomer (i.e., an aromatic ring-containing monomer having a refractive index of about 1.510 or more, preferably about 1.530 or more, and more preferably about 1.550 or more) in the monomer (m1) 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 several aspects, from the perspective of easily obtaining a higher refractive index, the content of the high refractive index monomer in the monomer (m1) may be, for example, 50% by weight or more, preferably 70% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. The monomer (m1) may also be substantially 100% by weight of a high refractive index monomer. Furthermore, in several aspects, for example, from the perspective of balancing the high refractive index with the adhesion and/or optical properties, the content of the high refractive index monomer in the monomer (m1) may be less than 100 wt%, may be less than 98 wt%, may be less than 90 wt%, may be less than 80 wt%, or may be less than 65 wt%. In several aspects, considering the adhesion and/or optical properties, the content of the high refractive index monomer in the monomer (m1) may be less than 70 wt%, may be less than 50 wt%, may be less than 25 wt%, may be less than 15 wt%, or may be less than 10 wt%. The technology disclosed herein can be implemented even in the aspect that the content of the high refractive index monomer in the monomer component (m1) is less than 5 wt%. It is also possible not to use a high refractive index monomer.

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 to achieve an adhesive layer that takes into account the 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-mentioned monomer component can be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In several aspects, from the perspective of easily achieving an adhesive with a higher refractive index, the content of the high refractive index monomer in the above-mentioned monomer component can be, for example, greater than 35% by weight, preferably greater than 50% by weight, greater than 70% by weight, greater than 75% by weight, greater than 85% by weight, greater than 90% by weight, or greater than 95% by weight. The content of the high refractive index monomer in the above-mentioned monomer component can be 100 weight %, but from the perspective of balancing the high refractive index with the adhesion characteristics and/or optical characteristics, it is advantageous to set it to less than 100 weight %, preferably 99 weight % or less, more preferably 98 weight % or less, 96 weight % or less, 93 weight % or less, 90 weight % or less, 85 weight % or less, 80 weight % or less, or 75 weight % or less. In several aspects, considering the adhesion characteristics and/or optical characteristics, the content of the high refractive index monomer in the above-mentioned monomer component can be 70 weight % or less, 50 weight % or less, 25 weight % or less, 15 weight % or less, or 5 weight % or less. The technology disclosed herein can be implemented even in the aspect that the content of the high refractive index monomer in the above-mentioned monomer component is less than 3 weight %.

In several ideal aspects of the technology disclosed herein, at least a portion of the monomer (m1) is an aromatic ring-containing monomer (hereinafter referred to as "monomer L") having a homopolymer Tg of 10°C or less (preferably 5°C or less or 0°C or less, more preferably -10°C or less, and even more preferably -20°C or less, for example -25°C or less). When the content of the aromatic ring-containing monomer (m1) in the monomer component is increased (especially an aromatic ring-containing monomer (m1) equivalent to one or both of the above-mentioned monomer containing multiple aromatic rings and the high refractive index monomer), the storage modulus G' of the adhesive tends to increase. However, by using the monomer L as part or all of the monomer (m1), the increase in the storage modulus G' can be suppressed. Thereby, the softness suitable for use as an adhesive can be better maintained, and the refractive index can be increased. The lower limit of the Tg of the monomer L is not particularly limited. Considering the balance with the refractive index increase effect, in several aspects, the Tg of the monomer L can be, for example, above -70°C, above -55°C, or above -45°C. The monomer L can be used alone or in combination of two or more.

The monomer L can be appropriately selected from the compounds included in the concept of the aromatic ring-containing monomer (m1) disclosed herein (e.g., the compounds and compound groups exemplified above) and having the Tg. One appropriate example of the aromatic ring-containing monomer that can be used as the monomer L is m-phenoxybenzyl acrylate (homopolymer Tg: -35°C). Another appropriate example is phenoxydiethylene glycol acrylate (homopolymer Tg: -35°C).

The content of monomer L in monomer (m1) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In several aspects, from the perspective of easily obtaining an adhesive having both high refractive index and softness at a higher level, the content of monomer L in monomer (m1) may be, for example, 50% by weight or more, 60% by weight or more, 70% by weight or more, 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. Monomer (A1) may also be substantially 100% by weight of monomer L. In some aspects, for example, from the perspective of balancing the softness and high refractive index suitable for use as an adhesive, the content of monomer L in monomer (m1) may be less than 100 wt%, 98 wt% or less, 90 wt% or less, 80 wt% or less, 70 wt% or less, 50 wt% or less, 25 wt% or less, or 10 wt% or less. The technology disclosed herein can be implemented even when the content of monomer L in monomer (m1) is less than 5 wt%. Monomer L may not be used.

The content of the monomer L in the monomer component constituting the acrylic polymer (A) may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In several aspects, from the viewpoint of easily obtaining an adhesive having both a high refractive index and flexibility at a higher level, the content of the monomer L in the monomer component may be, for example, greater than 35% by weight, greater than 50% by weight, greater than 70% by weight, greater than 75% by weight, greater than 85% by weight, greater than 90% by weight, or greater than 95% by weight. The content of monomer L in the above-mentioned monomer component can be 100 weight %, but considering the balance between high refractive index and adhesion characteristics and/or optical characteristics, it is advantageous to set it to less than 100 weight %, and preferably it is about 99 weight % or less, preferably 98 weight % or less, can be 96 weight % or less, can be 95 weight % or less, can be 93 weight % or less, can be 90 weight % or less, can be 85 weight % or less, can be 80 weight % or less, and can also be 75 weight % or less. In several aspects, the content of monomer L in the above-mentioned monomer component can be 70 weight % or less, can be 50 weight % or less, can be 25 weight % or less, can be 15 weight % or less, and can also be 5 weight % or less. The technology disclosed herein can still be implemented even in the aspect that the content of monomer L in the above-mentioned monomer component is less than 3 weight %.

In several aspects, from the viewpoint of the softness of the adhesive, it is advantageous for the glass transition temperature Tg _m1 of the composition of the monomer (m1) to be about 20°C or less, preferably 10°C or less (e.g., 5°C or less), more preferably 0°C or less, more preferably -10°C or less, -20°C or less, or -25°C or less. There is no particular restriction on the lower limit of the glass transition temperature Tg _m1 . Considering the balance with the refractive index enhancement effect, in several aspects, the glass transition temperature Tg _m1 may be, for example, above -70°C, above -55°C, or above -45°C. The technology disclosed herein can be suitably implemented even in aspects where the glass transition temperature Tg _m1 is, for example, above -40°C, above -35°C, above -33°C, above -30°C, or above -25°C.

Here, the glass transition temperature Tg _m1 based on the composition of the monomer (m1) means Tg obtained by the Fox equation described below based on the composition of only the monomer (m1) among the monomer components constituting the acrylic polymer (A). The glass transition temperature Tg _m1 can be calculated from the glass transition temperature of the homopolymer of each aromatic ring-containing monomer used as the monomer (m1) and the weight fraction of each aromatic ring-containing monomer in the total amount of the monomer (m1) by applying the Fox equation described below to only the monomer (m1) among the monomer components constituting the acrylic polymer (A). In the case where only one monomer is used as the monomer (m1), the Tg of the homopolymer of the monomer is consistent with the glass transition temperature Tg _m1 .

In several aspects, the aromatic ring-containing monomer (m1) can be used in combination with a monomer L (i.e., an aromatic ring-containing monomer whose homopolymer Tg is below 10°C, preferably below 5°C or below 0°C, more preferably below -10°C, more preferably below -20°C, for example, below -25°C) and a monomer H having a Tg higher than 10°C. The Tg of monomer H can be, for example, higher than 10°C, higher than 15°C, or higher than 20°C. By using a combination of monomer L and monomer H, for example, in a configuration in which the content of the aromatic ring-containing monomer (m1) in the monomer component is relatively high, a high refractive index and softness of the adhesive can be taken into account at a higher level. The usage ratio of monomer L and monomer H can be set to appropriately exhibit the above-mentioned effects, and there is no particular limitation. For example, the usage ratio of monomer L to monomer H is preferably set to satisfy any of the above-mentioned glass transition temperatures Tg _m1 .

In several aspects, the aromatic ring-containing monomer (m1) can be suitably 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, it is preferably an acrylic polymer composed of the following monomer components: the content of the compound containing a structure in which two or more non-condensed aromatic rings are directly chemically bonded is less than 5% by weight (preferably less than 3% by weight, and may also be 0% by weight). As described above, limiting the amount of the compound containing a structure in which two or more non-condensed aromatic rings are directly chemically bonded is advantageous from the perspective of achieving an adhesive that balances softness or adhesion with a high refractive index.

(Monomer (m2)) In several aspects of the technology disclosed herein, the monomer component constituting the acrylic polymer (A) may contain a monomer (m2) in addition to the above-mentioned monomer (m1). The above-mentioned monomer (m2) is a monomer equivalent to at least one of a monomer having a hydroxyl group (hydroxyl-containing monomer) and a monomer having a carboxyl group (carboxyl-containing monomer). The above-mentioned hydroxyl-containing monomer is a compound having at least one hydroxyl group and at least one ethylenically unsaturated group in one molecule. The above-mentioned carboxyl-containing monomer is a compound having at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. Monomer (m2) helps to introduce crosslinking points into the acrylic polymer (A) or to give the adhesive a moderate cohesiveness. Monomer (m2) can be used alone or in combination of two or more. The monomer (m2) is typically a monomer not containing an aromatic ring.

Examples of the ethylenically unsaturated group possessed by the monomer (m2) include (meth)acrylic group, vinyl group, (meth)allyl group, etc. From the viewpoint of polymerization reactivity, a (meth)acrylic group is preferred, and from the viewpoint of flexibility or adhesiveness, an acryl group is more preferred. From the viewpoint of suppressing the decrease in the flexibility of the adhesive, the monomer (m2) can be suitably a compound having 1 ethylenically unsaturated group contained in one molecule (i.e., a monofunctional monomer).

Examples of hydroxyl-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl)methyl (meth)acrylate and other hydroxyalkyl (meth)acrylates, but are not limited thereto. Examples of hydroxyl-containing monomers that can be suitably used include 4-hydroxybutyl acrylate (Tg: -40°C) and 2-hydroxyethyl acrylate (Tg: -15°C). From the viewpoint of improving the flexibility at room temperature, 4-hydroxybutyl acrylate having a lower Tg is preferred. In an ideal embodiment, 50% by weight or more (e.g., greater than 50% by weight, greater than 70% by weight, or greater than 85% by weight) of the monomer (m2) may be 4-hydroxybutyl acrylate. The hydroxyl group-containing monomer may be used alone or in combination of two or more.

In several aspects of using a hydroxyl-containing monomer as the monomer (m2), the hydroxyl-containing monomer may be one or more selected from compounds without a methacryloyl group. Suitable examples of hydroxyl-containing monomers without a methacryloyl group include the above-mentioned various hydroxyalkyl acrylates. For example, it is preferred that more than 50% by weight, more than 70% by weight, or more than 85% by weight of the hydroxyl-containing monomer used as the monomer (m2) is a hydroxyalkyl acrylate. By using a hydroxyalkyl acrylate, a hydroxyl group that helps to provide a crosslinking point or impart a moderate cohesiveness can be introduced into the acrylic polymer (A), and it is easier to obtain an adhesive with good flexibility or adhesion at room temperature than when only the corresponding methacrylic acid hydroxyalkyl is used.

Examples of carboxyl group-containing monomers include acrylic acid monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate, but are not limited to these. Examples of carboxyl group-containing monomers that can be suitably used include acrylic acid and methacrylic acid. Carboxyl group-containing monomers can be used alone or in combination of two or more. Hydroxyl group-containing monomers and carboxyl group-containing monomers can also be used in combination.

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 several aspects, the content of the above-mentioned 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 perspective of obtaining a higher use effect, in several aspects, the content of the above-mentioned monomer (A2) is preferably set to 1% by weight or more, can be set to 2% by weight or more, and can also be set to 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 of the content of the monomer (m1) does not exceed 100% by weight. In several aspects, it is appropriate to set the content of the above-mentioned monomer (m2) to, for example, less than 30 weight % or less than 25 weight %. From the perspective of making the content of the monomer (m1) relatively large and easily increasing the refractive index, it is preferably set to less than 20 weight %, more preferably less than 15 weight %, and can be less than 12 weight %, less than 10 weight %, or less than 7 weight %.

In the embodiment of using a hydroxyl-containing monomer as the monomer (m2), the content of the hydroxyl-containing monomer in the monomer component is not particularly limited, and can be, for example, 0.01 wt % or more (preferably 0.1 wt % or more, more preferably 0.5 wt % or more). In several embodiments, the content of the hydroxyl-containing monomer is preferably 1 wt % or more of the monomer component, can be 2 wt % or more, and can also be 4 wt % or more. The upper limit of the content of the hydroxyl-containing monomer in the monomer component is set so that the total of the content of the monomer (m1) does not exceed 100 weight %, for example, it is appropriate to set it to 30 weight % or less or 25 weight % or less. From the perspective of making the content of the monomer (m1) relatively large and facilitating a high refractive index, it is preferably set to 20 weight % or less, more preferably to 15 weight % or less, and can be less than 12 weight %, less than 10 weight %, or less than 7 weight %.

In the aspect of using a carboxyl-containing monomer as the monomer (m2), the content of the carboxyl-containing monomer in the monomer component is not particularly limited, for example, it can be 0.01% by weight or more (preferably 0.1% by weight or more, more preferably 0.3% by weight or more). In several aspects, the content of the above-mentioned carboxyl-containing monomer can be set to 1% by weight or more, can be set to 2% by weight or more, and can also be set to 4% by weight or more. The upper limit of the content of the carboxyl-containing monomer in the monomer component is set to a total of no more than 100% by weight with the amount of monomer (m1) used, for example, it is appropriate to set it to 30% by weight or less or 25% by weight or less, and from the viewpoint of making the content of the monomer (m1) relatively large and easy to high refractive index, it is preferably set to 20% by weight or less, preferably set to 15% by weight or less, can be less than 12% by weight, and can also be less than 10% by weight. In several aspects, from the perspective of improving the softness of the adhesive, it is advantageous to set the content of the carboxyl-containing monomer to less than 7 wt %, preferably less than 5 wt %, less than 3 wt %, less than 1 wt %, or less than 0.5 wt %. The technology disclosed herein can be suitably implemented in an aspect in which only hydroxyl-containing monomers are used as monomers (m2), that is, in an aspect in which no carboxyl-containing monomers are used.

The total content of the monomer (m1) and the monomer (m2) in the monomer components constituting the acrylic polymer (A) may be, for example, 31% by weight or more, preferably 51% by weight or more, 61% by weight or more, or 71% by weight or more. In several aspects, the total content of the monomer (m1) and the monomer (m2) in the monomer components constituting the acrylic polymer (A) may be, for example, 76% by weight or more, preferably 81% by weight or more, 86% by weight or more, 91% by weight or more, 96% by weight or more, 99% by weight or more, or substantially 100% by weight, from the viewpoint of facilitating and appropriately exerting the effects of the monomers.

(Monomer m3) The monomer components constituting the acrylic polymer (A) may also include monomers other than the above-mentioned monomer (m1) and the above-mentioned monomer (m2) as required. An example of the above-mentioned arbitrary component is alkyl (meth)acrylate (hereinafter also referred to as "monomer (m3)"). Monomer (m3) helps to adjust the softness of the adhesive or improve the compatibility in the adhesive.

The monomer (m3) can be suitably used in an alkyl (meth)acrylate having a linear or branched alkyl group with 1 to 20 carbon atoms (i.e., _C1-20 ) at the end of the ester. Specific examples of the _C1-20 alkyl (meth)acrylate include: methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, dibutyl (meth)acrylate, tertiary butyl (meth)acrylate, amyl (meth)acrylate, isoamyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecanyl (meth)acrylate, octadecyl (meth)acrylate, isooctadecyl (meth)acrylate, nonadecanyl (meth)acrylate, eicosyl (meth)acrylate, etc., but are not limited thereto.

In several aspects, at least a portion of the monomer (m3) may be suitably an alkyl (meth)acrylate having a homopolymer Tg of below -20°C (preferably below -40°C, for example below -50°C). The low Tg alkyl (meth)acrylate helps to improve the softness of the adhesive. There is no particular restriction on the lower limit of the Tg of the above-mentioned alkyl (meth)acrylate, for example, it may be above -85°C, above -75°C, above -65°C, or above -60°C. Specific examples of the above-mentioned low Tg alkyl (meth)acrylate include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), isononyl acrylate (iNA), etc.

In several aspects of using the monomer (m3), from the viewpoint of flexibility or adhesion, at least a part of the monomer (m3) is preferably an alkyl acrylate. For example, it is preferred that 50% by weight or more (preferably 75% by weight or more, and more preferably 90% by weight or more) of the monomer (m3) is an alkyl acrylate. It is also possible to use only one or two or more alkyl acrylates as the monomer (m3) and no alkyl methacrylate.

In the aspect that the monomer component includes (meth) alkyl acrylate, the content of the (meth) alkyl acrylate in the monomer component can be set to properly exert its use effect. In several aspects, the content of the above-mentioned alkyl (meth) acrylate can be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. In several aspects, the content of the above-mentioned alkyl (meth) acrylate can be 15% by weight or more, 30% by weight or more, or 45% by weight or more. The upper limit of the content of the monomer (m3) in the monomer component is set so that the total content of the monomer (m3) and the content of other monomers does not exceed 100% by weight, for example, it can be less than 50% by weight. In several aspects, the content of the above-mentioned monomer (m3) can be, for example, less than 35% by weight. Generally speaking, the refractive index of alkyl (meth)acrylate is relatively low, so in order to increase the refractive index, it is advantageous to limit the content of the monomer (m3) in the monomer component and to make the content of the monomer (m1) relatively high. From the above point of view, it is advantageous for the content of the monomer (m3) to be 24 wt % or less of the monomer component, preferably less than 23 wt %, more preferably less than 20 wt %, less than 17 wt %, less than 12 wt %, less than 7 wt %, less than 3 wt %, or less than 1 wt %. It is also possible not to use the monomer (m3) substantially.

(Other monomers) The monomer components constituting the acrylic polymer (A) may also include monomers other than the above-mentioned monomers (m1), (m2), and (m3) (hereinafter referred to as "other monomers") as required. The above-mentioned other monomers may be used, for example, to adjust the Tg of the acrylic polymer (A), adjust the adhesive performance, improve the compatibility in the adhesive layer, etc. The above-mentioned other monomers may be used alone or in combination of two or more.

Examples of the other monomers include monomers having functional groups other than hydroxyl and carboxyl groups (functional group-containing monomers). For example, other monomers that can improve the cohesive force or heat resistance of the adhesive include sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, cyano group-containing monomers, and the like. In addition, examples of monomers that can introduce functional groups that can serve as crosslinking points into the acrylic polymer (A) or that can contribute to improving peel strength or compatibility in the adhesive layer include amide group-containing monomers (e.g., (meth)acrylamide, N-hydroxymethyl (meth)acrylamide, etc.), amine group-containing monomers (e.g., aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, etc.), monomers having a nitrogen atom-containing ring (e.g., N-vinyl-2-pyrrolidone, N-(meth)acryloylmethacrylate, etc.), imide group-containing monomers, epoxy group-containing monomers, ketone group-containing monomers, isocyanate group-containing monomers, alkoxysilyl group-containing monomers, and the like. In addition, some monomers having a nitrogen atom ring, such as N-vinyl-2-pyrrolidone, are also equivalent to amide group-containing monomers. The relationship between the above-mentioned monomers having a nitrogen atom ring and amine group-containing monomers is also the same.

Other monomers that can be used in addition to the above-mentioned functional group-containing monomers include: vinyl ester monomers such as vinyl acetate; non-aromatic ring-containing (meth)acrylates such as cyclohexyl (meth)acrylate and isoborneol (meth)acrylate; olefin monomers such as ethylene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride; alkoxy-containing monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether, etc. An appropriate example of other monomers used for the purpose of improving the softness of the adhesive is ethoxyethoxyethyl acrylate (also known as ethyl carbitol acrylate, Tg of the homopolymer: -67°C).

When the above-mentioned other monomers are used, their usage amount is not particularly limited and can be appropriately set within the range where the total amount of the monomer components does not exceed 100 weight %. In several aspects, from the perspective of easily exerting the refractive index enhancement effect obtained by using the monomer (m1), the content of the above-mentioned other monomers in the monomer components can be set to, for example, about 35 weight % or less, about 25 weight % or less (for example, 0-25 weight %) is appropriate, about 20 weight % or less (for example, 0-20 weight %), about 10 weight % or less, about 5 weight % or less, and about 1 weight % or less. The technology disclosed herein can be appropriately implemented in an aspect where the monomer components do not substantially contain the above-mentioned other monomers.

In several aspects, the monomer components constituting the acrylic polymer (A) may be a composition in which the amount of methacryl-containing monomers is suppressed to a predetermined amount or less. The amount of methacryl-containing monomers in the monomer components may be, for example, less than 5% by weight, less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. Limiting the amount of methacryl-containing monomers as described above is advantageous from the perspective of achieving an adhesive that balances flexibility or adhesion with a high refractive index. The monomer components constituting the acrylic polymer (A) may also be a composition that does not contain methacryl-containing monomers (e.g., a composition consisting only of acryl-containing monomers).

In several aspects, from the perspective of inhibiting the coloring or discoloration (e.g., yellowing) of the adhesive, the amount of carboxyl-containing monomers used in the monomer components constituting the acrylic polymer (A) is preferably limited. The amount of carboxyl-containing monomers used in the monomer components may be, for example, less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, less than 0.1% by weight, or less than 0.05% by weight. The fact that the amount of carboxyl-containing monomers used is limited is also beneficial from the perspective of inhibiting corrosion of metal materials (e.g., metal wiring or metal films that may exist on the adherend) that may contact or be arranged adjacent to the adhesive disclosed herein. The technology disclosed herein may be appropriately implemented in the aspect that the above-mentioned monomer components do not contain carboxyl-containing monomers. For the same reason, in several aspects, the amount of monomers having acidic functional groups (including sulfonic acid groups, phosphoric acid groups, etc. in addition to carboxyl groups) in the monomer components constituting the acrylic polymer (A) is preferably limited. The amount of monomers containing acidic functional groups in the monomer components of the above aspects can be applied to the ideal amount of carboxyl group-containing monomers. The technology disclosed herein can be appropriately implemented in the aspect that the above monomer components do not contain acidic functional monomers (i.e., the acrylic polymer (A) is acid-free).

(Glass transition temperature Tg _T ) In several aspects, the glass transition temperature Tg _T of the monomer components constituting the acrylic polymer (A) is preferably about 20°C or less, preferably about 10°C or less, more preferably 0°C or less, and may be -10°C or less, -20°C or less, -25°C or less, -28°C or less, or -30°C or less. From the viewpoint of improving the flexibility of the adhesive, a low glass transition temperature Tg _T is advantageous. The glass transition temperature _TgT may be, for example, above -60°C, but from the viewpoint of facilitating the high refractive index of the adhesive, it is preferably above -50°C, more preferably above -45°C, may be above -40°C, may be above -35°C, may be above -25°C, may be above -15°C, and may also be above -5°C.

Here, the glass transition temperature _TgT means the glass transition temperature obtained by the Fox equation based on the composition of the above-mentioned monomer components unless otherwise specified. The Fox equation is shown below, and is a relationship equation between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer after each monomer constituting the copolymer is polymerized. 1/Tg=Σ(Wi/Tgi) In the above-mentioned Fox 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). Regarding the glass transition temperature of the homopolymer used for the calculation of Tg, the value described in the known materials such as "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) is used. For monomers with multiple values listed in the above-mentioned Polymer Handbook, the highest value is used. When the Tg of the homopolymer is not listed in the public data, the value obtained by the measurement method described in Japanese Patent Application Publication No. 2007-51271 is used.

(Preparation method of acrylic polymer (A)) In the technology disclosed herein, the method for obtaining the acrylic polymer (A) composed of the monomer components as described above is not particularly limited, and various polymerization methods known as synthetic methods of acrylic polymers such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization can be appropriately adopted. For example, solution polymerization can be appropriately adopted. The polymerization temperature during solution polymerization can be appropriately selected according to the types of monomers and solvents used, the type of polymerization initiator, etc., and can be set to, for example, about 20°C to 170°C (typically about 40°C to 140°C).

The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents. For example, any one solvent or a mixed solvent of two or more solvents selected from the following can be used: aromatic compounds such as toluene (typically aromatic hydrocarbons); acetates such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane or cyclohexane; halides such as 1,2-dichloroethane; lower alcohols such as isopropanol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tertiary butyl methyl ether; ketones such as methyl ethyl ketone, etc.

The initiator used for the polymerization can be appropriately selected from 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 appropriately 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. Another example of the polymerization initiator is a redox-based initiator composed 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 may be a normal amount, for example, it may be selected from the range of about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) relative to 100 parts by weight of the monomer component.

In the above-mentioned polymerization, various conventionally known chain transfer agents may be used as needed. For example, thiols such as n-dodecyl mercaptan, tert-dodecyl mercaptan, thioglycolic acid, and α-thioglycerol may be used. Alternatively, a chain transfer agent that does not contain a sulfur atom (non-sulfur chain transfer agent) may also be used. Examples of non-sulfur chain transfer agents include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenes such as α-pinene and terpinolene; styrenes such as α-methylstyrene and α-methylstyrene dimer, and the like. Chain transfer agents may be used alone or in combination of two or more. When a chain transfer agent is used, the amount used may be, for example, about 0.01 to 1 part by weight relative to 100 parts by weight of the monomer raw material.

The weight average molecular weight (Mw) of the acrylic polymer (A) is not particularly limited, and may be, for example, in the range of about 10×10 ⁴ to 500×10 ^4. From the viewpoint of adhesive performance, the Mw of the acrylic polymer (A) is preferably in the range of about 20×10 ⁴ to 400×10 ⁴ (preferably about 30×10 ⁴ to 150×10 ⁴ , for example, about 50×10 ⁴ to 130×10 ⁴ ).

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

(Additive (H _RO )) As the additive (H _RO ) in the technology disclosed herein, an organic material with a higher refractive index can be used in relative relationship with the above-mentioned acrylic polymer (A). Here, the above-mentioned "H _RO " represents an organic material (Organic material) with a high refractive index (High Refractive index). By combining the above-mentioned additive (H _RO ) and the acrylic polymer (A), an adhesive that can appropriately take into account the refractive index and adhesive properties (peel strength, flexibility, etc.) and/or optical properties (total light transmittance, haze value, etc.) can be achieved. The organic material that can be used as the additive (H _RO ) may be a polymer or a non-polymer. In addition, it may have a polymerizable functional group or may not have a polymerizable functional group. The additive (H _RO ) may be used alone or in combination of two or more.

The refractive index of the additive (H _RO ) can be set to an appropriate range in relation to the refractive index of the acrylic polymer (A), and is therefore not limited to a specific range. The refractive index of the additive (H _RO ) is, for example, greater than 1.55, greater than 1.56, or greater than 1.57, and can be selected from a range higher than the refractive index of the acrylic polymer (A). From the perspective of increasing the refractive index of the adhesive, in several aspects, it is advantageous for the refractive index of the additive (H _RO ) to be greater than 1.58, preferably greater than 1.60, more preferably greater than 1.63, and may be greater than 1.65, may be greater than 1.70, and may be greater than 1.75. By using an additive (H _RO ) with a higher refractive index, the target refractive index can be achieved even by using a relatively small amount of the additive (H _RO ). This is ideal from the perspective of suppressing the reduction of adhesive properties or optical properties. There is no particular upper limit on the refractive index of the additive (H _RO ), but from the perspective of compatibility in the adhesive, ease of achieving a high refractive index, and suitability as an adhesive for flexibility, it can be, for example, 3.000 or less, 2.500 or less, 2.000 or less, 1.950 or less, 1.900 or less, or 1.850 or less. In addition, the refractive index of the additive (H _RO ) is measured using an Abbe refractometer at a measurement wavelength of 589 nm and a measurement temperature of 25° C., similarly to the refractive index of the monomer. If a nominal value of the refractive index at 25° C. is provided by a manufacturer, the nominal value may be adopted.

The difference between the refractive index _nb of the additive ( _HRO ) and the refractive index _na of the acrylic polymer (A), that is, _nb - _na (hereinafter also referred to as "ΔnA _" ), is set to be greater than 0. In several aspects, _ΔnA is, for example, greater than 0.02, greater than 0.05, greater than 0.07, greater than 0.10, greater than 0.15, greater than 0.20, or greater than 0.25. By selecting the acrylic polymer (A) and the additive ( _HRO ) so as to increase _ΔnA , the effect of increasing the refractive index by using the additive ( _HRO ) tends to be higher. Furthermore, from the perspective of compatibility of the additive (H _RO ) in the adhesive layer, in several aspects, Δn _A may be, for example, less than 0.70, less than 0.60, less than 0.50, less than 0.40, or less than 0.35.

In some embodiments, the difference between the refractive index _nb of the additive ( _HRO ) and the refractive index _nT of the adhesive layer containing the additive ( _HRO ), that is, _nb - _nT (hereinafter also referred to as " _ΔnB "), is set to be greater than 0. In some embodiments, _{ΔnB is} , for example, greater than 0.02, greater than 0.05, greater than 0.07, greater than 0.10, greater than 0.15, greater than 0.20, or greater than 0.25. By selecting the composition of the adhesive layer and the additive ( _HRO ) so as to increase _ΔnB , the effect of using the additive ( _HRO ) to increase the refractive index tends to be higher. Furthermore, from the viewpoint of compatibility in the adhesive layer or transparency of the adhesive layer, in several aspects, Δn _B may be, for example, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.35 or less.

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 perspective of balancing the effect of high refractive index and other properties (such as optical properties such as flexibility and haze suitable for adhesives), in several aspects, the molecular weight of the additive (H _RO ) is preferably less than about 10,000, preferably less than 5,000, more preferably less than 3,000 (for example, less than 1,000), less than 800, less than 600, less than 500, or less than 400. It is beneficial to not have an additive (H _RO ) with a molecular weight that is too large in order to improve the compatibility in the adhesive layer. In addition, the molecular weight of the additive (H _RO ) can be, for example, 130 or more, or 150 or more. In several aspects, from the viewpoint of increasing the refractive index of the additive (H _RO ), the molecular weight of the additive (H _RO ) is preferably 170 or more, preferably 200 or more, 230 or more, 250 or more, 270 or more, 500 or more, 1000 or more, or 2000 or more. In several aspects, a polymer having a molecular weight of about 1000 to 10000 (e.g., 1000 or more and less than 5000) can be used as the additive (H _RO ). The molecular weight of the additive (H _RO ) can be a molecular weight calculated based on the chemical structure of a non-polymer or a polymer with a low degree of polymerization (e.g., about 2 to 5 polymers), or a measured value obtained using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). When the additive (H _RO ) is a polymer with a higher degree of polymerization, the weight average molecular weight (Mw) obtained by GPC under appropriate conditions can be used. When a nominal value of the molecular weight is provided by the manufacturer, the nominal value can be used.

Examples of organic materials that can be selected as the additive (H _RO ) include organic compounds having an aromatic ring, organic compounds having a heterocyclic ring (which may be an aromatic ring or a non-aromatic heterocyclic ring), etc., but are not limited thereto.

The aromatic ring of the organic compound having an aromatic ring (hereinafter also referred to as "aromatic ring-containing compound") which can be used as the additive (H _RO ) can be selected from the same aromatic rings as those of the compound which can be used as the monomer (m1).

The aromatic ring may have 1 or 2 or more substituents on the ring-constituting atoms, or may have no substituents. When having substituents, the substituents may be alkyl, alkoxy, aryloxy, hydroxyl, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl, hydroxyalkoxy, glycidoxy, etc., but are not limited thereto. In the substituent containing carbon atoms, the number of carbon atoms contained in the substituent is, for example, 1 to 10, 1 to 6 is advantageous, 1 to 4 is preferably, 1 to 3 is more preferably, and may be, for example, 1 or 2. In several aspects, the aromatic ring may be an aromatic ring having no substituents on the ring-constituting atoms, or may be an aromatic ring having 1 or 2 or more substituents selected from the group consisting of alkyl, alkoxy and halogen atoms (e.g., bromine atoms) on the ring-constituting atoms.

Examples of aromatic ring-containing compounds that can be used as additives (H _RO ) include compounds that can be used as monomers (m1); oligomers containing compounds that can be used as monomers (m1) as monomer units; compounds having a structure in which a group having an ethylenically unsaturated group (which may be a substituent bonded to a ring-constituting atom) or a portion of the group that constitutes an ethylenically unsaturated group is removed from the compound that can be used as a monomer (m1) and replaced with a hydrogen atom or a group that does not have an ethylenically unsaturated group (e.g., a hydroxyl group, an amine group, a halogen atom, an alkyl group, an alkoxy group, a hydroxyalkyl group, a hydroxyalkoxy group, a glycidoxy group, etc.), etc., but are not limited thereto. Non-limiting specific examples of aromatic ring-containing compounds that can be used as additives (H _RO ) include: benzyl acrylate, m-phenoxybenzyl acrylate, 2-(o-phenylphenoxy)ethyl acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, phenoxypolyethylene glycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, the above-mentioned monomers having a fluorene structure, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure and other aromatic ring-containing monomers; 3-phenoxybenzyl alcohol, dinaphthothiophene and its derivatives (for example, compounds having a structure in which one or two or more substituents selected from hydroxyl, methanol, diethanol and glycidyl groups are bonded to the dinaphthothiophene ring) and other aromatic ring-containing compounds without ethylenically unsaturated groups. Furthermore, the aromatic ring-containing compound may be an oligomer (preferably an oligomer having a molecular weight of about 5000 or less, more preferably about 1000 or less; for example, a dimer to pentamer) containing the aromatic ring-containing monomer as a monomer unit. The oligomer may be, for example: a homopolymer of the 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. The other monomers may be one or more monomers without an aromatic ring.

In several aspects, from the perspective of easily obtaining a higher refractive index-enhancing effect, an organic compound having two or more aromatic rings in one molecule (hereinafter also referred to as a "compound containing multiple aromatic rings") can be suitably used as an additive (H _RO ). The compound containing multiple aromatic rings may or may not have polymerizable functional groups such as ethylenic unsaturated groups. Furthermore, the compound containing multiple aromatic rings may be a polymer or a non-polymer. Furthermore, the above-mentioned polymer may be an oligomer containing a monomer containing multiple aromatic rings as a monomer unit (preferably an oligomer having a molecular weight of about 5000 or less, more preferably about 1000 or less; for example, a low polymer of about 2 to 5 polymers). The oligomers may be, for example, homopolymers of monomers containing multiple aromatic rings; copolymers of one or more monomers containing multiple aromatic rings; copolymers of one or more monomers containing multiple aromatic rings and other monomers, etc. The other monomers may be aromatic ring-containing monomers that are not monomers containing multiple aromatic rings, monomers without aromatic rings, or combinations thereof.

Non-limiting examples of compounds containing multiple 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., not separated by 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, etc. Compounds containing multiple aromatic rings may be used alone or in combination of two or more.

Specific examples of the above-mentioned compound having a fluorene structure include, in addition to the above-mentioned monomer having a fluorene structure, or an oligomer of a homopolymer or copolymer of the above-mentioned monomer, 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 other 9,9-bisphenylfluorene and its derivatives.

Specific examples of the compound having a dinaphthothiophene structure include, in addition to the monomer having a dinaphthothiophene structure, or a homopolymer or copolymer of the monomer, dinaphthothiophene (refractive index: 1.808); hydroxyalkyl dinaphthothiophene such as 6-hydroxymethyl dinaphthothiophene (refractive index: 1.766); dihydroxy dinaphthothiophene such as 2,12-dihydroxy dinaphthothiophene (refractive index: 1.750); 2,12-dihydroxy dinaphthothiophene (refractive index: 1.766); Dihydroxyalkyloxy dinaphthothiophene such as hydroxyethyloxy dinaphthothiophene (refractive index: 1.677); diglycidyloxy dinaphthothiophene such as 2,12-diglycidyloxy dinaphthothiophene (refractive index 1.723); dinaphthothiophene having two or more ethylenically unsaturated groups such as 2,12-diallyloxy dinaphthothiophene (abbreviation: 2,12-DAODNT, refractive index 1.729) and their derivatives.

Specific examples of the above-mentioned compound having a dibenzothiophene structure include, in addition to the above-mentioned monomer having a dibenzothiophene structure, or a homopolymer or copolymer oligomer of the above-mentioned monomer, dibenzothiophene (refractive index: 1.607), 4-dimethyldibenzothiophene (refractive index: 1.617), 4,6-dimethyldibenzothiophene (refractive index: 1.617), etc.

Examples of heterocyclic organic compounds (hereinafter also referred to as heterocyclic organic compounds) that can be selected as additives (H _RO ) include thioepoxy compounds and compounds having tricyclic rings. Examples of thioepoxy compounds include bis(2,3-cyclothiopropyl) disulfide and its polymer (refractive index 1.74) described in Japanese Patent No. 3712653. Examples of compounds having tricyclic rings include compounds having at least one (e.g., 3 to 40, preferably 5 to 20) tricyclic rings in one molecule. In addition, the tricyclic ring has aromatic properties, and thus a compound having a tricyclic ring is also included in the concept of the above-mentioned compound containing an aromatic ring, and a compound having a plurality of tricyclic rings is also included in the concept of the above-mentioned compound containing a plurality of aromatic rings.

In several aspects, a compound without ethylenically unsaturated groups can be suitably used as an additive (H _RO ). This can inhibit the adhesive composition from being deteriorated by heat or light (gelation progresses or viscosity increases, resulting in reduced leveling properties), thereby improving storage stability. The use of an additive without ethylenically unsaturated groups (H _RO ) is also preferred from the viewpoint of inhibiting dimensional changes or deformations (warping, undulation, etc.) caused by the reaction of ethylenically unsaturated groups, the generation of optical strain, etc. in an adhesive sheet having an adhesive layer containing the additive (H _RO ) or a laminate containing the adhesive sheet.

In the case where an oligomer is used as an additive (H _RO ), the oligomer can be obtained by polymerizing the corresponding monomer component by a known method. When the above-mentioned oligomer is produced by free radical polymerization, a polymerization initiator, a chain transfer agent, an emulsifier, etc. that can be used for free radical polymerization can be appropriately added to the above-mentioned monomer component to carry out polymerization. The above-mentioned polymerization initiator, chain transfer agent, emulsifier, etc. that can be used for free radical polymerization are not particularly limited and can be appropriately selected and used. In addition, the weight average molecular weight of the oligomer can be controlled by the amount of polymerization initiator and chain transfer agent used and the reaction conditions, and the amount used can be appropriately adjusted according to the type of the polymerization initiator and chain transfer agent. The chain transfer agent may be, for example, lauryl mercaptan, glycidyl mercaptan, isethanoic acid, 2-isobutyl ethanol, α-thioglycerol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-diisobutyl-1-propanol, etc. The chain transfer agent may be used alone or in combination of two or more. The amount of the chain transfer agent used may be set so as to obtain an oligomer having a desired weight average molecular weight, depending on the composition of the monomer components that can be used for the synthesis of the oligomer or the type of the chain transfer agent. In several embodiments, the amount of the chain transfer agent used is appropriately set to about 15 parts by weight or less, and may be 10 parts by weight or less, or may be about 5 parts by weight or less, relative to 100 parts by weight of the total amount of monomers that can be used for the synthesis of the oligomer. The lower limit of the amount of the chain transfer agent used relative to 100 parts by weight of the total amount of monomers that can be used to synthesize the oligomer is not particularly limited, and can be, for example, 0.01 parts by weight or more, 0.1 parts by weight or more, 0.5 parts by weight or more, or 1 part by weight or more.

The amount of the additive (H _RO ) used relative to 100 parts by weight of the acrylic polymer (A) (the total amount of the same when multiple compounds are used) is not particularly limited as long as it is greater than 0 parts by weight, and can be set according to the purpose. In several aspects, the amount of the additive (H _RO ) used relative to 100 parts by weight of the acrylic polymer (A) can be set to, for example, 80 parts by weight or less, and from the perspective of balancing the high refractive index of the adhesive and suppressing the decrease in adhesion characteristics or optical characteristics, it is advantageous to set it to 60 parts by weight or less, and preferably to set it to 45 parts by weight or less. In several aspects in which adhesion characteristics or optical characteristics are more important, the amount of the additive (H _RO ) used relative to 100 parts by weight of the acrylic polymer (A) can be, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less. Furthermore, from the viewpoint of increasing the refractive index of the adhesive, the amount of the additive (H _RO ) used can be, for example, 1 part by weight or more, 3 parts by weight or more is advantageous, 5 parts by weight or more is preferred, 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or 20 parts by weight or more, based on 100 parts by weight of the acrylic polymer (A).

(Crosslinking agent) The adhesive composition disclosed herein may contain a crosslinking agent as required in order to adjust the cohesive force of the adhesive. The crosslinking agent may be an isocyanate crosslinking agent, an epoxy crosslinking agent, an aziridine crosslinking agent, an oxazoline crosslinking agent, a melamine resin, a metal chelate crosslinking agent, or the like, which are known crosslinking agents in the adhesive field. Among them, an isocyanate crosslinking agent may be suitably used. As another example of a crosslinking agent, a monomer having two or more ethylenically unsaturated groups in one molecule, i.e., a multifunctional monomer, may be cited. The crosslinking agent may be used alone or in combination of two or more.

Isocyanate crosslinking agents may be difunctional or higher-functional isocyanate compounds, for example, trimethylene diisocyanate, butyl diisocyanate, hexamethylene diisocyanate (HDI), diisocyanate and other aliphatic polyisocyanates; cyclopentyl diisocyanate, cyclohexyl diisocyanate, isophorone diisocyanate (IPDI), 1,3-bis(isocyanatomethyl)cycloisocyanate; Alicyclic isocyanates such as hexane; aromatic isocyanates such as 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and isocyanate (XDI); polyisocyanate modified by modifying isocyanate compounds with allocarboxylate bonds, diurea bonds, isocyanurate bonds, uretdione bonds, urea bonds, carbodiimide bonds, uretonimine bonds, and diisocyanate-trione bonds, etc. Examples of commercial products include: trade names TAKENATE 300S, TAKENATE 500, TAKENATE 600, TAKENATE D165N, TAKENATE D178N (all manufactured by Takeda Pharmaceutical Co., Ltd.), Sumidur T80, Sumidur L, Desmodur N3400 (all manufactured by Sumika Bayer Urethane Co., Ltd.), Millionate MR, Millionate MT, Coronate L, Coronate HL, Coronate HX (all manufactured by Tosoh Corporation), etc. The isocyanate compound may be used alone or in combination of two or more. A bifunctional isocyanate compound and a trifunctional or higher isocyanate compound may also be used in combination.

Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin type epoxy resins, ethyl glycidyl ether, polyethylene glycol diglycidyl ether, glyceryl diglycidyl ether, glyceryl triglycidyl ether, 1,6-hexanediol glycidyl ether, trihydroxymethylpropane triglycidyl ether, diglycidyl aniline, diaminoglycidylamine, N,N,N',N'-tetraglycidyl-intermediate diamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, etc. These can be used alone or in combination of two or more.

Examples of the multifunctional 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, 1,1 2-Dodecanediol di(meth)acrylate, trihydroxymethylpropane tri(meth)acrylate, tetrahydroxymethylmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, bisphenoxyethanolfluorene di(meth)acrylate, bisphenol A di(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, butyl glycol di(meth)acrylate, hexyl glycol di(meth)acrylate, etc. The polyfunctional monomer may be used alone or in combination of two or more.

The amount of the crosslinking agent (which may be a multifunctional monomer) used is not particularly limited, and may be set in a range of about 0.001 to 5.0 parts by weight relative to 100 parts by weight of the above-mentioned monomer component. From the perspective of improving the softness of the adhesive, in several aspects, the amount of the crosslinking agent used relative 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 parts by weight or less, 0.5 parts by weight or less, or 0.2 parts by weight or less. Furthermore, from the perspective of properly exerting the effect of the crosslinking agent, in several aspects, the amount of the crosslinking agent used relative to 100 parts by weight of the monomer component can be, for example, 0.005 parts by weight or more, 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.08 parts by weight or more.

In order to make the crosslinking reaction more effective, a crosslinking catalyst can also be used. Examples of crosslinking catalysts include: tetrabutyl titanium, tetraisopropyl titanium, iron (III) acetylacetonate, butyltin oxide, dioctyltin dilaurate and other metal-based crosslinking catalysts. Among them, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. There is no particular restriction on the amount of the crosslinking catalyst used. Considering the balance between the speed of the crosslinking reaction and the service life of the adhesive composition, the amount of the crosslinking catalyst used relative to 100 parts by weight of the monomer component can be set to, for example, a range of about 0.0001 parts by weight or more and 1 part by weight or less, and preferably a range of 0.001 parts by weight or more and 0.5 parts by weight or less.

The adhesive composition may contain a compound that can produce keto-enol tautomerism as a crosslinking delayer. In this way, the effect of extending the service life of the adhesive composition can be achieved. For example, a compound that can produce keto-enol tautomerism can be appropriately used in an adhesive composition containing an isocyanate crosslinker. Various β-dicarbonyl compounds can be used as compounds that can produce keto-enol tautomerism. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) or acetoacetates (methyl acetoacetate, ethyl acetoacetate, etc.) can be appropriately used. Compounds that can produce keto-enol tautomerism can be used alone or in combination of two or more. The amount of the compound capable of producing keto-enol tautomerism used can be, for example, 0.1 parts by weight to 20 parts by weight, 0.5 parts by weight to 10 parts by weight, or 1 part by weight to 5 parts by weight, relative to 100 parts by weight of the monomer component.

(Tackifier) The adhesive composition disclosed herein may also contain a tackifier. The tackifier may be a rosin-based tackifier resin, a terpene-based tackifier resin, a phenol-based tackifier resin, a hydrocarbon-based tackifier resin, a ketone-based tackifier resin, a polyamide-based tackifier resin, an epoxy-based tackifier resin, an elastic system-based tackifier resin, or other known tackifier resins. These may be used alone or in combination of two or more. The amount of the tackifier resin used is not particularly limited and may be set to exhibit appropriate adhesive properties according to the purpose and use. In some embodiments, from the perspective of refractive index or transparency, the amount of the binder used is preferably 30 parts by weight or less, preferably 10 parts by weight or less, and more preferably 5 parts by weight or less, relative to 100 parts by weight of the monomer component. The technology disclosed herein can be appropriately implemented in an embodiment without using a binder.

(Plasticizer) In the several aspects of the adhesive composition disclosed herein, the adhesive composition may further include a plasticizer having a molecular weight lower than that of the acrylic polymer (A) as an additive that can be used as desired. By using a plasticizer, the softness of the adhesive layer can be improved, thereby improving the adhesion to the adherend, or the softness of the adhesive sheet as a whole or the ability to follow deformation. From the perspective of compatibility or transparency in the adhesive layer, the plasticizer can be an organic material. The plasticizer can also be a material that can be used as the above-mentioned additive (H _RO ).

The molecular weight of the plasticizing material is not particularly limited as long as it is lower than that of the acrylic polymer (A). In several aspects, from the perspective of easily exhibiting 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 (e.g., less than 1,000), less than 800, less than 600, less than 500, or less than 400. It is advantageous that the molecular weight of the plasticizing material is not too large from the perspective of improving the compatibility in the adhesive layer. In some aspects, from the perspective of being able to exert a sufficient plasticizing effect, the molecular weight of the plasticizing material is preferably 130 or more, preferably 150 or more, more preferably 170 or more, 200 or more, 250 or more, or 300 or more. In some aspects, the molecular weight of the plasticizing material may be 500 or more, 1000 or more, or 2000 or more. It is also preferred that the molecular weight of the plasticizing material is not too low from the perspective of heat resistance of the adhesive sheet or suppression of contamination of the adherend.

Non-limiting examples of compounds that can be selected as plasticizers include: compounds that can be used as monomers (m1) (e.g., aromatic ring (meth)acrylates having benzyl, phenoxy, naphthyl, etc., monomers having a fluorene structure, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, etc.); oligomers containing compounds that can be used as monomers (m1) as monomer units; compounds having structures in which a portion having an ethylenically unsaturated group is removed from a compound that can be used as a monomer (m1) and replaced with a hydrogen atom or a group without an ethylenically unsaturated group (e.g., 3-phenoxybenzyl alcohol), etc. From the viewpoint of improving softness, low Tg monomers such as n-butyl acrylate or 2-ethylhexyl acrylate may also be copolymerized in oligomers containing compounds that can be used as monomers (m1) as monomer units. As the plasticizing material, one or more of known plasticizers (such as phthalate-based plasticizers, terephthalate-based plasticizers, adipate-based plasticizers, adipic acid-based polyesters, and ethylene glycol benzoate) may be used.

In several aspects, the plasticizer may be an organic material having a refractive index of about 1.50 or more (preferably 1.53 or more). Specific examples of compounds that can be selected as plasticizers 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), methyl rosin (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 viewpoint of refractive index and compatibility, for example, diethylene glycol dibenzoate can be suitably used. The upper limit of the refractive index of the plasticizing material is not particularly limited, and for example, it can be 3.00 or less. In several aspects, from the viewpoint of ease of preparation of the adhesive composition or compatibility in the adhesive, the refractive index of the plasticizer is suitable to be 2.50 or less, 2.00 or less is advantageous, 1.90 or less, 1.80 or less, or 1.70 or less. In addition, the refractive index of the plasticizer is measured using an Abbe refractometer at a measurement wavelength of 589 nm and a measurement temperature of 25°C, similar to the refractive index of the monomer. When a nominal value of the refractive index at 25°C is provided by a manufacturer, the nominal value may be adopted.

In the case of using a plasticizer, the amount of the plasticizer used relative to 100 parts by weight of the acrylic polymer (A) is not particularly limited and can be set according to the purpose. From the perspective of improving the plasticizing effect, the amount of the plasticizer used relative to 100 parts by weight of the acrylic polymer (A) can be, for example, 0.1 parts by weight or more, or 0.5 parts by weight or more, and from the perspective of obtaining a higher plasticizing effect, it is preferably set to 1 part by weight or more, preferably 3 parts by weight or more, and can be 5 parts by weight or more, 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or 20 parts by weight or more. Furthermore, from the perspective of balancing the high refractive index of the adhesive with the transparency and the plasticizing effect, the amount of the plasticizer used relative to 100 parts by weight of the acrylic polymer (A) is appropriate to be set at about 100 parts by weight or less, preferably 80 parts by weight or less, preferably 60 parts by weight or less, and can be 45 parts by weight or less, 35 parts by weight or less, or 25 parts by weight or less. In several aspects where the adhesive properties or optical properties are more important, the amount of the plasticizer used relative to 100 parts by weight of the acrylic polymer (A) can be, for example, 15 parts by weight or less, 10 parts by weight or less, or 5 parts by weight or less.

(Leveling agent) The adhesive composition disclosed herein may contain a leveling agent as required in order to improve the appearance of the adhesive layer formed by the composition (for example, to improve the uniformity of thickness) or to improve the coating properties of the adhesive composition. Non-limiting examples of leveling agents include acrylic leveling agents, fluorine leveling agents, silicone leveling agents, etc. The leveling agent can be selected from commercially available leveling agents and used in a conventional manner.

In several aspects, the leveling agent may suitably use the following polymer (hereinafter also referred to as "polymer (B)"), which is a polymer comprising a monomer having a polyorganosiloxane skeleton (hereinafter also referred to as "monomer S1") and a monomer raw material of an acrylic monomer (hereinafter also referred to as "monomer raw material B"). Polymer (B) may be referred to as a copolymer of monomer S1 and an acrylic monomer. Polymer (B) may be used alone or in combination of two or more.

Monomer S1 is not particularly limited, and any monomer containing a polyorganosiloxane skeleton can be used. Monomer S1 can be suitably used in a structure having a polymerizable reactive group at one end. Among them, monomer S1 having a structure having a polymerizable reactive group at one end and not having a functional group at the other end that produces a cross-linking reaction with an acrylic polymer (A) can be suitably used. Commercially available materials include, for example, one-terminal reactive polysilicone oils manufactured by Shin-Etsu Chemical Co., Ltd. (e.g., models such as X-22-174ASX, X-22-2426, X-22-2475, and KF-2012). Monomer S1 can be used alone or in combination of two or more.

The functional group equivalent of monomer S1 can be, for example, about 100 g/mol to 30,000 g/mol. In several ideal embodiments, the functional group equivalent is, for example, 500 g/mol or more, 800 g/mol or more, 1,500 g/mol or more, or 2,000 g/mol or more. In addition, the functional group equivalent can be, for example, less than 20,000 g/mol, less than 10,000 g/mol, less than 7,000 g/mol, or less than 5,500 g/mol. If the functional group equivalent of monomer S1 is within the above range, it is easy to exert a good leveling effect. In addition, when two or more monomers with different functional group equivalents are used as monomer S1, the functional group equivalent of monomer S1 can be the sum of the products of the functional group equivalents of each type of monomer and the weight fraction of the monomer.

Here, "functional group equivalent" means the weight of the main skeleton (e.g., polydimethylsiloxane) bonded to each functional group. The relevant marked unit g/mol is converted into 1 mol of functional groups. The functional group equivalent of monomer S1 can be calculated, for example, from the spectral intensity of ¹ H-NMR (proton NMR) based on nuclear magnetic resonance (NMR). The calculation of the functional group equivalent (g/mol) of monomer S1 based on the spectral intensity of ¹ H-NMR can be based on the general structural analysis method of ¹ H-NMR spectrum analysis, and if necessary, refer to the description of Japanese Patent Gazette No. 5951153. In the functional group equivalent of monomer S1, the above-mentioned functional group means a polymerizable functional group (e.g., ethylenically unsaturated groups such as (meth)acryl, vinyl, and allyl).

The content of monomer S1 in monomer raw material B can be an appropriate value within the range in which the desired effect can be exerted by using the monomer S1, and is not limited to a specific range. In several aspects, the content of monomer S1 in monomer raw material B can be, for example, 5-60% by weight, 10-50% by weight, or 15-40% by weight.

In addition to monomer S1, monomer raw material B also includes an acrylic monomer that can be copolymerized with monomer S1. Thereby, the compatibility of polymer (B) in the adhesive layer can be improved. Examples of acrylic monomers that can be used for monomer raw material B include alkyl acrylates. The "alkyl" mentioned here refers to a chain (including straight chain and branched chain) alkyl (group), and does not include the alicyclic hydrocarbon group described later. In several aspects, monomer raw material B may contain at _least one C _4-12 alkyl (meth)acrylate (preferably C _4-10 alkyl (meth)acrylate, such as C _6-10 alkyl (meth)acrylate). In several other aspects, monomer raw material B may contain at least one C 1-18 alkyl methacrylate (preferably C _1-14 alkyl methacrylate, such as C _1-10 alkyl (meth)acrylate). The monomer raw material B may contain, as the acrylic monomer, one or more selected from methyl methacrylate (MMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA).

Other examples of the acrylic monomers include (meth)acrylates having alicyclic alkyl groups. For example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isoborneol (meth)acrylate, dicyclopentyl (meth)acrylate, 1-adamantyl (meth)acrylate, etc. can be used. (Meth)acrylates having alicyclic alkyl groups do not need to be used.

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

Other examples of monomers that can be included in the monomer raw material B together with the monomer S1 include: carboxyl group-containing monomers, 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 aminoalkyl esters, vinyl esters, vinyl ethers, olefins, (meth)acrylates having aromatic hydrocarbon groups, and (meth)acrylates containing halogen atoms, etc., which can be used in acrylic polymers.

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

The polymer (B) can be prepared by polymerizing the above-mentioned monomers by known methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, photopolymerization, etc. In order to adjust the molecular weight of the polymer (B), a chain transfer agent can be used as required. Examples of the chain transfer agent used include: tertiary dodecyl mercaptan, hydroxyethyl alcohol, α-thioglycerol and other compounds having hydroxyl groups; thioglycolic acid, methyl thioglycolate and other thioglycolic acid esters; α-methylstyrene dimer, etc. The amount of the chain transfer agent used is not particularly limited and can be appropriately set to obtain a polymer (B) with a desired molecular weight. In several embodiments, the amount of the chain transfer agent used relative to 100 parts by weight of the monomer can be, for example, 0.1 to 5 parts by weight, 0.2 to 3 parts by weight, or 0.5 to 2 parts by weight.

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

(Inorganic particles) The technology disclosed herein can be suitably implemented without substantially using inorganic particles for increasing the refractive index, but high refractive index inorganic particles can be used as an auxiliary in addition to the additive (H _RO ) without hindrance as long as the application effect of the technology disclosed herein is not significantly impaired. Examples of the above-mentioned inorganic particles include inorganic particles composed of inorganic oxides (specifically metal oxides) such as titanium oxide (titania, TiO ₂ ), zirconium oxide (zirconia, ZrO ₂ ), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, niobium oxide (Nb ₂ O ₅ , etc.). The average particle size of the inorganic particles (referring to the 50% volume average particle size obtained by laser scattering diffraction method) can be selected from a range of about 10 nm to 100 nm. The amount of the inorganic particles used is preferably less than 5 parts by weight, and more preferably less than 1 part by weight, relative to 100 parts by weight of the acrylic polymer (A). In the case of using an additive (H _RO ), the amount of the inorganic particles used is preferably less than 2 times the amount of the additive (H _RO ) used on a weight basis, and preferably less than 1 time or less than 0.5 times.

(Other additives) The adhesive composition disclosed herein may also include plasticizers, softeners, colorants, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, preservatives, and other known additives that can be used in adhesive compositions as needed within the scope that does not significantly hinder the effect of the present invention. For the various additives mentioned above, the previously known ones can be used according to the usual method, and no special features are given to the present invention, so detailed description is omitted.

<Adhesive> The adhesive disclosed herein can be formed, for example, using any of the above-mentioned adhesive compositions. The adhesive can be an adhesive formed by curing a solvent-type, active energy ray-curing, water-dispersible, hot-melt-type adhesive composition by drying, crosslinking, polymerization, cooling, etc., and can be a cured product of the above-mentioned adhesive composition. The curing means (such as drying, crosslinking, polymerization, cooling, etc.) of the adhesive composition can be applied only one, or two or more can be applied simultaneously or in multiple stages. For a solvent-type adhesive composition, the composition can typically be dried (preferably further crosslinked) to form an adhesive. In the case of an active energy ray-curable adhesive composition, the adhesive is typically formed by irradiating the active energy ray to cause a polymerization reaction and/or a crosslinking reaction to proceed. When the active energy ray-curable adhesive composition must be dried, the active energy ray may be irradiated after drying.

(Refractive index) The adhesive disclosed herein may be one that exhibits a predetermined refractive index or higher. According to the technology disclosed herein, it is possible to provide: an adhesive having a refractive index of, for example, 1.560 or higher (preferably 1.570 or higher, more preferably greater than 1.570), an adhesive composition that can form the adhesive, and an adhesive sheet containing the adhesive.

In addition, in this specification, the refractive index of the adhesive means the refractive index of the surface (adhesive surface) of the adhesive. The refractive index of the adhesive can be measured using a commercially available refractive index measuring device (Abbe refractometer) under the conditions of a measuring wavelength of 589nm and a measuring temperature of 25°C. The Abbe refractometer can use, for example, the model "DR-M4" manufactured by ATAGO or its equivalent. The measuring sample can use an adhesive layer composed of the adhesive of the evaluation object. The refractive index of the adhesive can be specifically measured by the method described in the embodiments described later. The refractive index of the adhesive can be adjusted, for example, by the composition of the adhesive.

In several aspects, the refractive index of the above-mentioned adhesive is preferably greater than 1.575 (for example, greater than 1.575), more preferably greater than 1.580, more preferably greater than 1.585, and particularly preferably greater than 1.590 (for example, greater than 1.595). By using an adhesive having the above-mentioned refractive index, the refractive index difference between the adhesive and the adherend can be used to effectively control the behavior of light. In several aspects of the adhesive disclosed herein, the refractive index of the adhesive can be, for example, greater than or equal to 1.600, greater than or equal to 1.605, or greater than or equal to 1.610. The ideal upper limit of the refractive index of the adhesive may vary depending on the refractive index of the adherend, etc., and is therefore not limited to a specific range. In some aspects, in consideration of the balance with adhesive properties or transparency, the refractive index of the adhesive may be, for example, 1.700 or less, 1.670 or less, or 1.650 or less.

<Adhesive sheet> According to the present specification, an adhesive sheet having an adhesive layer is provided. The adhesive constituting the adhesive layer may be an adhesive formed by any adhesive composition disclosed herein (e.g., a cured product of the adhesive composition). The adhesive sheet may be a substrate-attached adhesive sheet in the form of an adhesive layer on one or both sides of a non-peelable substrate (support substrate), or may be a substrate-free adhesive sheet in the form of the adhesive layer being retained on a peel pad (i.e., an adhesive sheet without a non-peelable substrate, typically an adhesive sheet consisting of an adhesive layer). The concept of the adhesive sheet mentioned here may include 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, or may be an adhesive sheet further processed into various shapes.

An example of the structure of the adhesive sheet disclosed herein is shown in FIG1. The adhesive sheet 1 is a single-sided adhesive sheet (single-sided adhesive sheet), which includes: an adhesive layer 10, whose first surface 10A serves as an attachment surface (adhesive surface) attached to an adherend; and a supporting substrate 20, which is laminated on the second surface 10B of the adhesive layer 10. The second surface 10B of the adhesive layer 10 is bonded to the first surface (non-releasable surface) 20A of the supporting substrate 20. As the supporting substrate 20, a plastic film such as a polyester film can be used. The supporting substrate 20 can also be an optical film such as a polarizing plate. The adhesive sheet 1 before use (before being attached to the adherend) can be, for example, in the form of an adhesive sheet 50 with a peeling liner, in which the adhesive surface 10A is protected by a peeling liner 30, and the peeling liner 30 is a peeling surface (peeling surface) at least on the adhesive layer side. Alternatively, it can be in the following form: the second surface 20B (the surface on the side opposite to the first surface 20A, also called the back surface) of the supporting substrate 20 becomes the peeling surface, and is rolled or laminated in a manner that the adhesive surface 10A abuts against the second surface 20B to protect the adhesive surface 10A. The adhesive layer 10 may be a single-layer structure or a laminated structure in which two or more sub-adhesive layers of different compositions are directly in contact with each other (ie, not separated by a layer made of a non-adhesive material).

The peeling pad is not particularly limited. For example, a peeling pad having a peeling treatment on the surface of a liner substrate such as a resin film or paper, or a peeling pad made of a low-adhesion material such as a fluorine-based polymer (polytetrafluoroethylene, etc.) or a polyolefin-based resin (polyethylene, polypropylene, etc.) can be used. For the above-mentioned peeling treatment, a peeling treatment agent such as a polysilicone-based or long-chain alkyl-based peeling agent can be used. In several aspects, a resin film that has been subjected to a peeling treatment can be appropriately used as a peeling pad.

The adhesive sheet disclosed herein may also be a double-sided adhesive sheet without a substrate composed of an adhesive layer. As shown in FIG2 , the double-sided adhesive sheet without a substrate may be in the following form before use: the first surface (first adhesive surface) 10A and the second surface (second adhesive surface) 10B of the adhesive layer 10 are protected by release pads 31 and 32, at least one side of the adhesive layer being a release surface (release surface). Alternatively, the following configuration may be adopted: the back side (the surface opposite to the adhesive side) of the peeling pad 31 becomes the peeling surface, and the adhesive surface 10B is wound or laminated in such a manner that it abuts against the back side of the peeling pad 31, thereby protecting the adhesive surfaces 10A and 10B. The double-sided adhesive sheet without a substrate may be used by bonding a substrate (which may be an optical component such as an optical film) to at least one of the first adhesive surface and the second adhesive surface. The adhesive layer constituting the double-sided adhesive sheet without substrate may be a single-layer structure similar to the adhesive layer 10 in the adhesive sheet 1 shown in FIG. 1 , or may be a laminated structure formed by two or more sub-adhesive layers of different compositions directly contacting each other.

The adhesive sheet disclosed herein may be a constituent element of an optical component of an adhesive sheet with an optical component bonded to one surface of an adhesive layer. For example, the adhesive sheet 1 shown in FIG. 1 may be a constituent element of an optical component 100 of an adhesive sheet with an optical component bonded to one surface 10A of an adhesive layer 10, as shown in FIG. 3. The optical component may be, for example, a glass plate, a resin film, a metal plate, etc. Furthermore, in the adhesive sheet 1 shown in FIG. 1, when the supporting substrate 20 is an optical component such as an optical film, the adhesive sheet 1 may be regarded as an optical component of an adhesive sheet with an optical component bonded to the second surface 10B of the adhesive layer 10.

Furthermore, although not specifically illustrated, the adhesive sheet disclosed herein may also be in the form of a double-sided adhesive sheet with a substrate (double-sided adhesive sheet with a substrate): a supporting substrate having a first surface and a second surface with non-releasable properties, and a first adhesive layer is fixedly layered on the first surface, and a second adhesive layer is fixedly layered on the second surface. As an example of the configuration of the double-sided adhesive sheet with substrate, the following configuration can be cited: in the single-sided adhesive sheet 1 shown in FIG. 1 , the second surface 20B of the supporting substrate 20 is a non-releasable surface and a second adhesive layer is provided on the second surface 20B, the second surface of the second adhesive layer is bonded to the second surface 20B of the supporting substrate 20, and the first surface (the surface on the side opposite to the second surface) of the second adhesive layer becomes the second adhesive surface of the double-sided adhesive sheet with substrate. The composition of the adhesive constituting the second adhesive layer may be the same as the composition of the adhesive constituting the first adhesive layer, or may be different from each other. The double-sided adhesive sheet with a substrate before use can be in a form where the first adhesive surface and the second adhesive surface are protected by a peelable liner, similar to the double-sided adhesive sheet without a substrate.

When the adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet with both sides being adhesive surfaces (including double-sided adhesive sheets without a substrate and double-sided adhesive sheets with a substrate; the same shall apply hereinafter unless otherwise specified), the refractive indexes of the first adhesive surface and the second adhesive surface are not particularly limited. In several aspects, it is preferred that at least the first adhesive surface satisfies any of the above refractive indices, and the double-sided adhesive sheet may also satisfy any of the above refractive indices. In several aspects, the refractive index _n2 of the second adhesive surface may be substantially the same as the refractive index _n1 of the first adhesive surface. More specifically, the absolute value of the difference in the refractive index of the two adhesive surfaces, i.e., | _n1 - _n2 |, may be, for example, less than 0.05, or less than 0.03, or less than 0.01. The lower limit of |n ₁ -n ₂ | may be 0.00 or greater than 0.00. The relative relationship of the refractive indexes of the two adhesive surfaces may be n ₁ >n ₂ , n ₁ <n ₂ , or n ₁ =n ₂ . In several other aspects, the difference between the refractive index n ₁ of the first adhesive surface and the refractive index n ₂ of the second adhesive surface of the adhesive sheet, i.e., n ₁ -n ₂ , may be, for example, greater than 0.00, may be 0.01 or greater, may be 0.03 or greater, may be 0.05 or greater, may be 0.10 or greater, may be 0.15 or greater, may be 0.20 or greater, or may be 0.25 or greater. The magnitude relationship between _{n 1} and n ₂ may also be opposite. 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 the following method: in a double-sided adhesive sheet with a substrate, the first and second adhesive layers having different refractive indices are laminated on a non-releasable supporting substrate; or, the adhesive layer constituting the double-sided adhesive sheet without a substrate is made into a laminated structure of two or more sub-adhesive layers having different refractive indices.

The adhesive layer of the adhesive sheet disclosed herein can be formed by applying (e.g., coating) an adhesive composition to a suitable surface and then hardening the composition. The adhesive composition can be coated using a conventional coating machine such as a gravure roll coater, a reverse roll coater, a contact roll coater, a dip roll coater, a rod coater, a scraper coater, or a spray coater.

The adhesive layer of the adhesive sheet disclosed herein may be an adhesive layer with post-curing properties or an adhesive layer without post-curing properties. Here, the adhesive layer with post-curing properties refers to an adhesive layer that can be further cured by irradiation with heat or active energy rays (such as ultraviolet rays). Examples of adhesive layers with post-curing properties include: an adhesive layer having unreacted ethylenically unsaturated groups in the side chains of a base polymer (such as an acrylic polymer (A)), or an adhesive layer containing unreacted multifunctional monomers. In several aspects, the adhesive layer is preferably not post-curing. An adhesive layer without post-curing properties will not undergo dimensional changes associated with a subsequent curing reaction (i.e., it has good dimensional stability), and thus it is easy to suppress the warping of the adhesive sheet or the adherend to which the adhesive sheet is attached. The absence of dimensional changes caused by post-curing (such as curing shrinkage) is also beneficial from the perspective of suppressing the optical strain of the adhesive layer.

The thickness of the adhesive layer is not particularly limited, and can be set to 3µm or more, for example. In several embodiments, the thickness of the adhesive layer can be, for example, 5µm or more, 10µm or more, 20µm or more, 30µm or more, 50µm or more, 70µm or more, or 85µm or more. In several embodiments, the thickness of the adhesive layer can be, for example, 300µm or less, 250µm or less, 200µm or less, 150µm or less, or 120µm or less. The fact that the thickness of the adhesive layer is not too large is advantageous from the perspective of thinning the adhesive sheet. The technology disclosed herein is suitable for implementation in a state where the thickness of the adhesive layer is in the range of 3µm to 200µm (preferably 5µm to 100µm). In addition, when the first and second surfaces of the substrate have an adhesive sheet having a first adhesive layer and a second adhesive layer, the thickness of the adhesive layer can at least be applied to the thickness of the first adhesive layer. The thickness of the second adhesive layer can also be selected from the same range. In addition, in a double-sided adhesive sheet without a substrate composed of an adhesive layer, the thickness of the adhesive layer is the thickness of the adhesive sheet.

(Total light transmittance) In the technology disclosed herein, the total light transmittance of the adhesive layer is, for example, more than 50% is appropriate, and more than 70% is preferred. In several ideal embodiments, the total light transmittance of the adherend is more than 85%, preferably more than 86%, more preferably more than 88%, more preferably more than 90% (for example, more than 90.0%), and may be more than 90.5%. The adhesive sheet having an adhesive layer with high transparency as described above may have a substrate structure or may not have a substrate structure and is suitable for applications requiring high light transmittance (for example, optical applications) or applications requiring good visual identification of the properties of the adherend through the adhesive sheet. In several embodiments, the total light transmittance of the adhesive layer may be more than 93%, and may be more than 95%. The upper limit of the total light transmittance is theoretically a value obtained by 100% exclusion of light loss (Fresnel loss) caused by reflection at the air interface, and in practice it can be less than about 98%, less than about 96%, or less than about 95%. In several aspects, the total light transmittance of the adhesive layer can be less than about 94%, less than about 93%, or less than about 92%, taking into account the refractive index or adhesive properties. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. The transmittance meter can use the trade name "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory or its equivalent. More specifically, the total light transmittance of the adhesive layer can be measured, for example, according to the embodiments described below. The total light transmittance of the adhesive layer can be adjusted by, for example, selecting the composition or thickness of the adhesive layer.

When the adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet attached to a substrate in which the first adhesive layer and the second adhesive layer are fixedly laminated on a supporting substrate, it is preferred that at least the first adhesive layer satisfy any of the above-mentioned total light transmittances. In a usage mode in which light penetrates in the thickness direction of the adhesive sheet, it is preferred that both the first adhesive layer and the second adhesive layer satisfy any of the above-mentioned total light transmittances. The relative relationship of the total light transmittances of the two adhesive layers may be the first adhesive layer > the second adhesive layer, the first adhesive layer < the second adhesive layer, or the first adhesive layer = the second adhesive layer.

(Haze value) In several embodiments, the haze value of the adhesive layer constituting the adhesive sheet may be, for example, 5.0% or less, preferably 3.0% or less (e.g., 2.0% or less), preferably 1.0% or less, and even more preferably 0.9% or less. The adhesive sheet having the adhesive layer with high transparency as described above may have a substrate structure or may not have a substrate structure and is suitable for applications requiring high light transmittance (e.g., optical applications) or applications requiring good visual identification of the properties of the adherend through the adhesive sheet. In several embodiments, the haze value of the adhesive layer may be 0.8% or less, 0.5% or less, or 0.3% or less. There is no particular restriction on the lower limit of the haze value of the adhesive layer. From the perspective of improving transparency, the smaller the haze value, the better. On the other hand, in several aspects, considering the refractive index or 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. Such haze values of the adhesive layer may also be appropriately applied to the haze values of the adhesive sheet when the technology disclosed herein is implemented in the form of an adhesive sheet without a substrate (typically an adhesive sheet composed of an adhesive layer).

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

When the adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet attached to a substrate in which the first adhesive layer and the second adhesive layer are fixedly laminated on a supporting substrate, it is sufficient that at least the first adhesive layer satisfies any of the above-mentioned haze values, and the haze value of the second adhesive layer is not particularly limited. In the use mode in which light penetrates in the thickness direction of the adhesive sheet, the haze value of the second adhesive layer preferably satisfies any of the above-mentioned haze values of the first adhesive layer. The relative relationship of the mist values of the two adhesive layers may be the first adhesive layer > the second adhesive layer, the first adhesive layer < the second adhesive layer, or the first adhesive layer = the second adhesive layer.

(Surface smoothness of adhesive surface) In several aspects of the adhesive sheet disclosed herein, the adhesive surface of the adhesive sheet preferably has high surface smoothness.

For example, the arithmetic mean roughness Ra of the adhesive surface is preferably limited to below a predetermined value. From the perspective of optical homogeneity, it is preferable to have an adhesive surface designed to have a lower arithmetic mean roughness Ra. By limiting the arithmetic mean roughness Ra, for example, in a usage mode where light is captured through the adhesive surface (such as an adhesive sheet arranged on the viewpoint side of the light-emitting element in a light-emitting device), it is possible to suppress uneven brightness caused by the surface state of the adhesive layer. The low arithmetic mean roughness Ra of the adhesive surface is also beneficial for suppressing optical strain, and suppressing optical strain also helps to improve optical homogeneity. When the adhesive sheet disclosed herein is in the form of a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface, it is preferred that at least the arithmetic average roughness Ra of the first adhesive surface is limited to below a predetermined value, and it is preferred that the arithmetic average roughness Ra of both adhesive surfaces is limited to below a predetermined value. By having each adhesive surface of the double-sided adhesive sheet have high surface smoothness, it is possible to achieve a bonding with excellent optical homogeneity.

In several embodiments, the arithmetic mean roughness Ra of the adhesive surface is preferably less than about 70 nm, more preferably less than about 65 nm, more preferably less than about 55 nm, less than 50 nm, less than 45 nm, or less than 40 nm. From the perspective of production efficiency, in several embodiments, the arithmetic mean roughness Ra of the adhesive surface of the adhesive sheet can be, for example, more than about 10 nm, more than about 20 nm, or more than about 30 nm (for example, more than about 40 nm). In the embodiment in which the adhesive sheet has a first adhesive surface and a second adhesive surface, the arithmetic mean roughness Ra of the first adhesive surface and the arithmetic mean roughness Ra of the second adhesive surface can be the same or different.

Furthermore, for example, the maximum height Rz of the above-mentioned adhesive surface is preferably limited to below a predetermined value. From the viewpoint of optical homogeneity, it is preferable to have an adhesive surface designed to have a lower maximum height Rz. By limiting the maximum height Rz, for example, in the above-mentioned usage mode of capturing light through the above-mentioned adhesive surface, the effect of suppressing uneven brightness due to the surface state of the adhesive layer can be exerted. The low maximum height Rz of the adhesive surface is also beneficial to suppressing optical strain. 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 below a predetermined value, and it is preferable that the maximum height Rz of both adhesive surfaces is limited to below a predetermined value. Since each adhesive surface of the double-sided adhesive sheet has a high surface smoothness, it is possible to achieve a bonding with excellent optical homogeneity.

In several aspects, the maximum height Rz of the adhesive surface is preferably less than about 600nm, more preferably less than about 500nm, more preferably less than about 450nm, and particularly preferably less than about 400nm. It can be less than 350nm, less than 300nm, or less than 250nm. From the perspective of production efficiency, in several aspects, the maximum height Rz of the adhesive surface of the adhesive sheet can be, for example, more than about 10nm, more than about 50nm, more than about 100nm, or more than about 200nm. In the aspect in which the adhesive sheet has a first adhesive surface and a second adhesive surface, the maximum height Rz of the first adhesive surface and the maximum height Rz of the second adhesive surface can be the same or different.

The arithmetic mean roughness Ra and the maximum height Rz of the adhesive surface are measured using a non-contact surface roughness measuring device. The non-contact surface roughness measuring device can use an optical interference surface roughness measuring device, for example, a 3D optical profiler (trade name "NewView7300", manufactured by ZYGO) or its equivalent. Specifically, for example, the arithmetic mean roughness Ra and the maximum height Rz can be measured by setting the measurement operation or measurement conditions in a manner that can obtain results equivalent to or corresponding to the case using the measurement method. That is, the surface shape of the measurement sample is measured under the following conditions in an environment of 23°C and 50%RH using a 3D optical profiler (trade name "NewView7300", manufactured by ZYGO). The arithmetic surface roughness Ra is calculated from the measured data in accordance with JIS B 0601-2001. The maximum height Rz is the sum of the height Rp from the average line of the roughness curve to the highest top on the upper side and the depth Rv from the average line to the deepest valley on the lower side for the data obtained by the above measurement (roughness curve). Ra and Rz are measured 5 times (i.e. N=5), and the average value is used. The above measurement sample can be prepared by cutting the adhesive layer of the measurement object or the adhesive sheet containing the adhesive layer into a size of about 150mm in length and 50mm in width. When the adhesive surface is protected by a peelable liner, remove the peelable liner steadily (e.g. at a pulling speed of 300 mm/min and a peeling angle of 180°) to expose the adhesive surface. It is advisable to let the adhesive surface stand for about 30 minutes before measuring. [Measurement conditions] Measurement area: 5.62 mm × 4.22 mm (Objective lens: 2.5x, internal lens: 0.5x) Analysis mode: Remove: Cylinder Data Fill: ON (Max: 25) Remove Spikes: ON (xRMS: 1) Filter: OFF

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

(Storage modulus G') In the adhesive sheet disclosed herein, the storage modulus G' of the adhesive constituting the adhesive layer at 25°C (hereinafter also referred to as "storage modulus G'(25)") can be appropriately set according to the purpose of use or usage mode, and is not limited to a specific range. The storage modulus G'(25) of the adhesive can be, for example, about 700 kPa or less. In several embodiments, from the perspective of ease of attachment to the adherend, it is advantageous for the storage modulus G'(25) of the adhesive to be about 600 kPa or less, preferably 500 kPa or less, and more preferably 400 kPa or less (for example, 350 kPa or less). In several aspects, from the perspective of improving the flexibility of the adhesive at room temperature (e.g., 25° C.) and making it easier to adhere to the adherend, the storage elastic modulus G'(25) of the adhesive is advantageously about 330 kPa or less, and preferably 300 kPa or less. In several aspects where more emphasis is placed on adhesion or flexibility at room temperature, the storage elastic modulus G'(25) of the adhesive may be, for example, less than 270 kPa or less than 250 kPa, and is advantageously less than 200 kPa, and is preferably less than 180 kPa, and more preferably less than 160 kPa (e.g., less than 140 kPa). In several aspects, the storage elastic modulus G'(25) of the adhesive may be less than 100 kPa or less than 90 kPa. The lower limit of the storage elastic modulus G'(25) of the adhesive is not particularly limited, but from the perspective of processability or handling, it may be, for example, 30 kPa or more, 50 kPa or more, or 70 kPa or more. In several aspects, considering the high 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.

In the adhesive sheet disclosed herein, the storage modulus G' (hereinafter also referred to as "storage modulus G'(50)") of the adhesive constituting the adhesive layer at 50°C is not particularly limited, and may be, for example, less than 100 kPa. In several aspects, it is appropriate for the storage modulus G'(50) to be less than 60 kPa, and preferably less than 40 kPa, and more preferably less than 38 kPa (for example, less than 36 kPa). The adhesive having the limited storage modulus G'(50) as described above can easily improve its adhesion to the adherend by appropriately heating as required, thereby improving its adhesion to the adherend. There is no particular limitation on the lower limit of the storage modulus G'(50) of the adhesive. In several aspects, from the perspective of the heat resistance of the adhesive, the storage elastic modulus G'(50) may be, for example, greater than 10 kPa, greater than 15 kPa, greater than 20 kPa, or greater than 23 kPa.

In the several aspects of the adhesive disclosed herein, the adhesive preferably meets at least one of the following conditions: (a) the storage elastic modulus G'(25) at 25°C is less than 350 kPa (preferably less than 200 kPa, for example, less than 180 kPa); 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). An adhesive that at least meets the above condition (a) is ideal from the perspective of adhesion to the adherend at room temperature (e.g., 25°C). Adhesives that at least meet the above condition (b) are preferred because they can easily improve the adhesion to the adherend by heating to a temperature slightly higher than room temperature. Adhesives that do not meet the above condition (a) but meet the above condition (b) can be used as heat-activated adhesives, which have good initial reworkability (re-adhesion) when attached at room temperature, and can effectively improve the peeling strength of the adherend by heating to a temperature slightly higher than room temperature. The above heat activation can also be performed by heating the adhesive to a temperature slightly higher than room temperature when attached to the adherend. The temperature slightly higher than room temperature is, for example, about 60°C or lower, and preferably about 55°C or lower (for example, about 50°C or lower).

In several aspects of the adhesive sheet disclosed herein, the ratio of the storage modulus G'(50) [kPa] of the adhesive constituting the adhesive layer to the storage modulus G'(25) [kPa], i.e., the storage modulus ratio G'(50)/G'(25), is, for example, 70% or less, 40% or less, 30% or less, or 20% or less. An adhesive with a small G'(50)/G'(25) is suitable for use as the above-mentioned heat-activated adhesive. There is no particular restriction on the lower limit of G'(50)/G'(25). G'(50)/G'(25) is, for example, 5% or more. From the viewpoint of the heat resistance of the adhesive, it is preferably 10% or more, and may be 12% or more, or may be 15% or more.

The storage elastic modulus G'(25) and G'(50) can be obtained by dynamic viscoelasticity measurement, and G'(50)/G'(25) can be calculated from the result. Dynamic viscoelasticity measurement can be performed in a conventional manner using a commercially available dynamic viscoelasticity measurement device, such as the "Advanced Rheometric Expansion System (ARES)" manufactured by TA Instruments or its equivalent, under the following measurement conditions. The test specimen is a test specimen in which the adhesive layer of the evaluation object is adjusted to a thickness of about 1.5 mm by lamination as required. [Measurement conditions] Deformation mode: Torsion Measurement frequency: 1 Hz Heat rise rate: 5°C/min Shape: Parallel plate 7.9 mm φ

The storage elastic modulus G'(25), G'(50) and storage elastic modulus ratio of the adhesive layer can be adjusted by selecting the composition of the monomer components constituting the acrylic polymer (A) (for example, selecting the type and content of the monomer (m1)), whether or not a crosslinking agent is used, and selecting the type and amount of use, whether or not the above-mentioned additive (H _RO ) or plasticizer is used, and selecting the type and amount of use, etc. For example, as the monomer (m1), in addition to the first monomer that is the main component of the monomer (m1), a second monomer having a chemical structure different from that of the first monomer can be used in a relatively small amount and combined with the first monomer, thereby reducing G'(50) when the first monomer is used alone as the monomer (m1) and reducing G'(50)/G'(25).

When the adhesive sheet disclosed herein is a double-sided adhesive sheet having a first adhesive surface and a second adhesive surface (for example, a double-sided adhesive sheet with a substrate having a first adhesive layer and a second adhesive layer, a double-sided adhesive sheet without a substrate in which a sub-adhesive layer constituting the first adhesive surface and a sub-adhesive layer constituting the second adhesive surface are laminated without a non-adhesive substrate in between, etc.; the same applies to other identical descriptions), the above-mentioned storage elastic modulus G'(25), G'(50) and storage elastic modulus ratio are applied to at least the adhesive layer constituting the first adhesive surface, and are preferably applied to both the adhesive layer constituting the first adhesive surface and the adhesive layer constituting the second adhesive surface. The storage elastic modulus G' of the adhesive layer constituting the first adhesive surface and the storage elastic modulus G' of the adhesive layer constituting the second adhesive surface may be of the same degree or may be different.

In several aspects of the technology disclosed herein, the peak temperature of tanδ of the adhesive constituting the adhesive layer is preferably above about -50°C and preferably below about 50°C. Here, tanδ (loss tangent) of the adhesive means the ratio of the loss elastic modulus G" to the storage elastic modulus G' of the adhesive. That is, tanδ=G"/G'. The tanδ of the adhesive can be determined by sandwiching a disc-shaped adhesive sample with a thickness of about 2mm and a diameter of 7.9mm with parallel plates, applying a shear strain of 1Hz using a viscoelastic tester, and performing a temperature dispersion test of the adhesive in a shear mode at a temperature range of -60℃~60℃ and a heating rate of 5℃/min. The storage elastic modulus G'(Pa) and loss elastic modulus G"(Pa) at this time can be obtained by the following formula: tanδ=G"/G'. The peak temperature of the tanδ of the adhesive (hereinafter referred to as Tpeak) can be obtained from the transition of tanδ in the above temperature range. The viscoelastic tester can use ARES manufactured by TA Instruments or its equivalent.

In several aspects, it is advantageous for the Tpeak of the adhesive to be below 45°C or below 35°C, and preferably below 30°C (for example, below 25°C), below 20°C, or below 15°C. With an adhesive having a lower Tpeak, it tends to be easy to obtain good initial adhesion or tightness at room temperature. On the other hand, it is ideal for the Tpeak of the adhesive to be not too low from the perspective of giving the adhesive a moderate degree of cohesion, and it tends to be suitable for taking into account a high refractive index. From the above viewpoint, in several aspects, the Tpeak of the adhesive can be, for example, above -40°C, above -30°C, above -20°C, above -5°C, above 5°C, above 15°C, or even above 25°C. When an adhesive with a high Tpeak is attached to an adherend, it is appropriate to heat one or both of the adhesive and the adherend to a temperature slightly higher than room temperature. The Tpeak of the adhesive can be adjusted by selecting the composition of the adhesive (e.g., the composition of the monomer components constituting the acrylic polymer (A), whether an additive (H _RO ) or a plasticizer is used, and the type and amount of the plasticizer). 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, the Tpeak of the adhesive is preferably applied to at least the adhesive layer constituting the first adhesive surface, and is preferably applied to both the adhesive layer constituting the first adhesive surface and the adhesive layer constituting the second adhesive surface. The Tpeak of the adhesive layer constituting the first adhesive surface and the Tpeak of the adhesive layer constituting the second adhesive surface may be of the same degree or may be different.

(Water absorption rate) In several aspects of the adhesive sheet disclosed herein, the water absorption rate of the adhesive layer constituting the adhesive sheet is preferably limited to below a predetermined value. By limiting the water absorption rate of the adhesive layer, there is a tendency to suppress the change in the size of the adhesive layer caused by the change in the amount of water in the adhesive layer (for example, the absorption and release of moisture such as humidity in the environment). In this way, the warping of the adhesive sheet or the adherend to which the adhesive sheet is attached caused by the inconsistency of the size change between the adhesive layer and the adjacent layer (which may be a supporting substrate, a peeling pad, an adherend, etc.) can be suppressed. The fact that the amount of water in the adhesive layer can be suppressed is also advantageous from the viewpoint that the flatness, transparency, refractive index, etc. of the adhesive layer can be kept constant. Also, an adhesive layer with a low water absorption rate is not easy to absorb water, so it is suitable as an adhesive sheet for components or products such as organic EL elements that contain elements that do not like water.

In several aspects, the water absorption rate of the adhesive layer is preferably about 1.0% or less, preferably 0.7% or less, more preferably 0.5% or less (e.g., less than 0.5%), can be 0.4% or less, can be 0.3% or less, can be 0.2% or less, and can also be 0.1% or less. There is no particular restriction on the lower limit of the water absorption rate of the adhesive layer. From the practical point of view of taking into account the adhesive properties, for example, it can be 0.01% or more, 0.05% or more, 0.1% or more, and can also be 0.15% or more. 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 preferred that the water absorption rate of at least the adhesive layer constituting the first adhesive surface is limited to below a predetermined value. From the viewpoint of obtaining a higher effect, it is preferred that the water absorption rate of the adhesive layer constituting the first adhesive surface and the adhesive layer constituting the second adhesive surface are both limited to below a predetermined value.

In addition, the water absorption rate (also called moisture content) of the adhesive layer was measured using the following method. [Measurement of moisture content] The adhesive layer to be evaluated was cut into a size of 4cm×5cm (area: ^20cm2 ) with two peeling pads placed on one side and the other side. After removing the peeling pad on one side, it was attached to the pre-weighed aluminum foil. Then, the peeling pad on the other side of the adhesive layer was removed, and it was placed in a constant temperature and humidity tank at a temperature of 60℃ and a relative humidity of 90%, and taken out after 72 hours. After weighing the test piece with the adhesive layer and the aluminum foil, the moisture content was measured by Karl Fischer electrometric titration under the following conditions using a moisture meter (Mitsubishi Chemical Analytech CA-200) equipped with a heating vaporization device (Mitsubishi Chemical Analytech VA-200). Anode liquid: AQUAMICRON AKX (Mitsubishi Chemical) Cathode liquid: AQUAMICRON CXU (Mitsubishi Chemical) Heating vaporization temperature: 150℃

(Gel fraction) The gel fraction of the adhesive layer can be appropriately set according to the purpose of use or the usage mode, and is not limited to a specific range. The gel fraction is, for example, about 99% or less, and about 97% or less is appropriate. From the perspective of easily and appropriately taking into account both high refractive index and adhesive properties, in several ideal modes, the gel fraction is about 95% or less, and preferably about 92% or less (for example, about 90% or less). The gel fraction is not too high because it can appropriately follow the unevenness that may exist on the surface of the adherend (for example, the uneven structure provided in the light-emitting device to improve the light extraction efficiency, etc.), thereby achieving good adhesion. In several aspects, the gel fraction may be less than about 88%, less than about 75%, or less than about 65%. In addition, from the perspective of giving the adhesive a proper cohesiveness and appropriately exhibiting adhesive properties, the gel fraction of the adhesive layer is, for example, more than about 10%, and it is appropriate to set it to more than about 20%, and it may also be more than about 30%. From the perspective of the deformation resistance of the adhesive layer (preventing overflow caused by pressure or bubbles caused by the inclusion of foreign objects, etc.), the above-mentioned gel fraction is preferably more than about 30%, more preferably more than about 40%, can be more than about 45%, can be more than about 50%, can be more than about 65%, and can also be more than about 75%. The gel fraction of the adhesive sheet (typically an adhesive sheet without a substrate) is also preferably set within the above-mentioned range. The gel fraction can be adjusted by the molecular weight or molecular structure, concentration, crosslinking degree, etc. of the acrylic polymer (A). The gel fraction is measured by the following method.

[Determination of gel fraction] A predetermined amount of adhesive sample (weight Wg ₁ ) is wrapped in a small bag with a porous polytetrafluoroethylene film (weight Wg ₂ ) with an average pore size of 0.2µm, and the opening is tied with a kite line (weight Wg ₃ ). The porous polytetrafluoroethylene (PTFE) film is a product name "Nitoflon (registered trademark) NTF1122" (average pore size 0.2µm, porosity 75%, thickness 85µm) available from Nitto Denko Corporation or its equivalent. The bundle is immersed in a sufficient amount of ethyl acetate and kept at room temperature (typically 23°C) for 7 days until only the sol in the adhesive is dissolved out of the above film. Then the bundle is taken out and the ethyl acetate attached to the outer surface is wiped off. The bundle is dried at 130°C for 2 hours and the weight of the bundle is measured (Wg ₄ ). The gel fraction of the adhesive layer can be obtained by substituting each value into the following formula. Gel fraction (%) = [(Wg ₄ -Wg ₂ -Wg ₃ )/Wg ₁ ] × 100

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, the above-mentioned gel fraction is applied to at least the adhesive layer constituting the first adhesive surface, and is preferably applied to both the adhesive layer constituting the first adhesive surface and the adhesive layer constituting the second adhesive surface. The gel fraction of the adhesive layer constituting the first adhesive surface and the gel fraction of the adhesive layer constituting the second adhesive surface may be the same or different.

(Peeling strength) In several aspects of the adhesive sheet disclosed herein, the peeling strength of the adhesive sheet for the glass plate is suitable to be about 1.0N/25mm or more (e.g., 1.5N/25mm or more), preferably 2N/25mm or more, more preferably 3N/25mm or more, 4N/25mm or more, 6N/25mm or more, 8N/25mm or more, 10N/25mm or more, or 12N/25mm or more. There is no particular limit to the upper limit of the peeling strength, for example, it can be less than 30N/25mm, less than 25N/25mm, or less than 20N/25mm.

Here, the peel strength is determined by the following method: press it onto an alkaline glass plate as the adherend and place it in an environment of 23°C and 50%RH for 30 minutes, then place it in a pressurized degassing device (autoclave) at a temperature of 50°C and a pressure of 0.5MPa for 30 minutes, and then place it in a gas environment of 23°C and 50%RH for 24 hours, then perform 180° peeling at a peeling angle of 180 degrees and a tensile speed of 300mm/minute to measure the adhesion. During the measurement, a suitable backing material (e.g., a polyethylene terephthalate (PET) film with a thickness of about 25µm to 50µm) can be attached to the adhesive sheet of the measurement object as required for reinforcement. More specifically, the peel strength can be measured according to the method described in the embodiments described 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 several embodiments, the above peel strength is preferably applied to at least the first adhesive surface, and is preferably applied to both the first adhesive surface and the second adhesive surface. The peel strength of the first adhesive surface against the glass plate and the peel strength of the second adhesive surface against the glass may be the same or different.

(Supporting substrate) The adhesive sheet of several aspects may be in the form of an adhesive sheet with a substrate having an adhesive layer on one or both sides of the supporting substrate. The material of the supporting substrate is not particularly limited and can be appropriately selected according to the purpose of use or the use aspect of the adhesive sheet. Non-limiting examples of the substrate that can be used include: plastic films such as polyolefin films with polyolefins such as polypropylene (PP) or ethylene-propylene copolymer as the main component, polyester films with polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) as the main component, polyvinyl chloride films with polyvinyl chloride as the main component; Foam sheets made of foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam; woven and non-woven fabrics made of various fibrous materials (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinyl, and semi-synthetic fibers such as acetate) alone or in a blend; Japanese paper, woodfree paper, kraft paper, and wrinkled paper; metal foils such as aluminum foil and copper foil. It can also be a composite substrate. Examples of the composite substrate include a substrate with a structure formed by laminating metal foil and the above-mentioned plastic film, and a plastic substrate reinforced with inorganic fibers such as glass cloth.

In several aspects, various film substrates can be suitably used. The film substrate can be a porous substrate such as a foam film or a non-woven sheet, a non-porous substrate, or a substrate having a structure formed by laminating porous layers and non-porous layers. In several aspects, the film substrate can suitably use a resin film that is independent and can maintain its shape (self-supporting or non-dependent) as a base film. Here, "resin film" refers to a non-porous structure and is typically a resin film that does not substantially contain bubbles (no holes). Therefore, the resin film is a concept that can be distinguished from a foam film or a non-woven sheet. The resin film that is independent and can maintain its shape (self-supporting or non-dependent) can suitably be used. The resin film may be a single-layer structure or a multi-layer structure of two or more layers (e.g., a three-layer structure).

Materials constituting the resin film include, for example, 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-butylene copolymer, cellulose resins such as cellulose triacetate, acetate resins, polysulfone resins, polyethersulfone resins, polycarbonate resins, polyamide (PA) resins such as nylon 6, nylon 66, and partially aromatic polyamides, and polyimide (PI) resins. Cyclic polyolefin resins such as polyol, transparent polyimide resin, polyamide imide (PAI), polyetheretherketone (PEEK), polyether sulphate (PES), 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), polytetrafluoroethylene (PTFE) or fluorinated polyimide and other fluorinated resins, etc.

The above-mentioned resin film may be formed using a resin material containing only one of the above-mentioned resins, or may be formed using a resin material blended with two or more kinds of resins. The above-mentioned 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. may be suitably used. From the viewpoint of strength or dimensional stability, examples of ideal resin films include PET film, PEN film, PPS film, and PEEK film. From the viewpoint of ease of acquisition, PET film and PPS film are particularly suitable, among which PET film is preferred.

In the resin film, known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slipping agents, and anti-adhesive agents may be mixed as needed within the range that does not significantly hinder the effect of the present invention. The mixing amount of the additives is not particularly limited and can be appropriately set according to the purpose of the adhesive sheet.

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

The substrate may be substantially composed of the base film. Alternatively, the substrate may include an auxiliary layer in addition to the base film. Examples of the auxiliary layer include an optical property adjustment layer (e.g., a coloring layer, an anti-reflection layer), a printing layer or a laminating layer for giving the substrate a desired appearance, an antistatic layer, a primer layer, a peeling layer, and other surface treatment layers.

In several aspects, a light-transmitting substrate (hereinafter also referred to as a light-transmitting substrate) can be suitably used as a supporting substrate. In this way, an adhesive sheet with a light-transmitting substrate can be formed. The total light transmittance of the light-transmitting substrate can be, for example, greater than 50%, and can also be greater than 70%. In several ideal aspects, the total light transmittance of the supporting substrate is greater than 80%, preferably greater than 90%, and can also be greater than 95% (for example, 95~100%). The above-mentioned total light transmittance is measured according to JIS K 7136:2000 using a commercially available transmittance meter. The transmittance meter can use the product name "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory or its equivalent. A suitable example of the above-mentioned light-transmitting substrate is a light-transmitting resin film. The above-mentioned light-transmitting substrate can also be an optical film.

The thickness of the substrate is not particularly limited and can be selected according to the purpose or use of the adhesive sheet. The thickness of the substrate can be, for example, 500µm or less, and from the perspective of the handling or processing of the adhesive sheet, it is preferably 300µm or less, and can be 150µm or less, 100µm or less, 50µm or less, 25µm or less, or 10µm or less. If the thickness of the substrate is reduced, there is a tendency to improve the tracking of the surface shape of the adherend. In addition, from the perspective of handling or processing, the thickness of the substrate can be, for example, 2µm or more, 10µm or more, or 25µm or more.

The side of the substrate on which the adhesive layer is to be deposited may also be subjected to conventional surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkaline treatment, and forming a primer layer by applying a primer (primer) as required. The surface treatment may be a treatment for improving the anchoring property of the adhesive layer to the substrate. The composition of the primer used to form the primer layer is not particularly limited and can be appropriately selected from known materials. The thickness of the primer layer is not particularly limited, and is generally about 0.01µm to 1µm, and preferably about 0.1µm to 1µm. Other treatments that may be applied to the substrate as required include antistatic layer formation, coloring layer formation, printing, etc. These treatments may be applied individually or in combination.

When the adhesive sheet disclosed herein is in the form of an adhesive sheet attached to a substrate, the thickness of the adhesive sheet may be, for example, less than 1000µm, less than 350µm, less than 200µm, less than 120µm, less than 75µm, or less than 50µm. Moreover, from the perspective of handling, the thickness of the adhesive sheet may be, for example, more than 10µm, more than 25µm, more than 80µm, or more than 130µm. In addition, the thickness of the adhesive sheet refers to the thickness of the portion attached to the adherend. For example, in the adhesive sheet 1 of the structure 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 supporting substrate, and does not include the thickness of the peeling pad 30.

<Adhesive sheet with peel-off liner> The adhesive sheet disclosed herein can be in the form of an adhesive product in which the surface (adhesive surface) of the adhesive layer abuts against the peel-off surface of the peel-off liner. Therefore, according to this specification, an adhesive sheet with peel-off liner (adhesive product) can be provided, which includes any adhesive sheet disclosed herein and a peel-off liner having a peel-off surface abutting against the adhesive surface of the adhesive sheet.

The peeling liner is not particularly limited, and can be used, for example, as a peeling liner having a peeling layer on the surface of a liner substrate such as a resin film or paper (which can be a paper laminated with a resin such as polyethylene), or as a peeling liner composed of a resin film formed of a low-adhesion material such as a fluorine-based polymer (polytetrafluoroethylene, etc.) or a polyolefin-based resin (polyethylene, polypropylene, etc.). In view of excellent surface smoothness, it can be suitably used as a peeling liner having a peeling layer on the surface of a resin film as a liner substrate, or as a peeling liner composed of a resin film formed of a low-adhesion material. The resin film is not particularly limited as long as it can protect the adhesive layer, and examples thereof include polyethylene (PE) film, polypropylene (PP) film, polybutylene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyester film (PET film, PBT film, etc.), polyurethane film, ethylene-ethyl acetate copolymer film, etc. The above-mentioned release layer can be formed using known release agents such as polysilicone-based release agents, long-chain alkyl-based release agents, olefin-based release agents, fluorine-based release agents, fatty amide-based release agents, molybdenum sulfide, and silica powder.

<Application> The adhesive sheet disclosed herein can be used by being attached to various adherends. The constituent material of the adherend (adherend material) is not particularly limited, and examples thereof include: metal materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, indium, zinc, etc., or alloys containing two or more of these, or materials such as polyimide resins, acrylic resins, polyether nitrile resins, polyether sulfone resins, polyester resins (PET resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, etc. Olefin resins, polyphenylene sulfide resins, polyetheretherketone resins, polyamide resins (so-called aromatic amide resins, etc.), polyarylate resins, fluorine resins, polycarbonate resins, cellulose polymers such as cellulose diacetate or cellulose triacetate, vinyl butyral polymers, liquid crystal polymers, various resin materials such as graphene and other carbon materials (typically plastic materials), aluminum oxide, zirconium oxide, titanium oxide, SiO _2. Metal oxides such as ITO (indium tin oxide), ATO (antimony doped tin oxide) and mixtures thereof, nitrides such as aluminum nitride, silicon nitride, titanium nitride, gallium nitride, indium nitride and their complexes, inorganic materials such as alkaline glass, alkali-free glass, quartz glass, borosilicate glass, sapphire glass, etc. The adhesive sheet disclosed herein can be used by attaching at least the surface to a component (e.g., an optical component) made of the above materials.

The adhesive sheet disclosed herein can be used in the following attachment state: after being attached to the adherend, it is not necessary to heat it to a temperature higher than room temperature (e.g., 20°C to 35°C). In addition, if the material of the adhesive sheet (e.g., the material of the substrate) or the type of the adherend permits, it can also be heated at at least any time point after, at, or before the adherend is attached. The heat treatment can be performed for the purpose of improving the adhesion of the adhesive to the adherend or promoting adhesion. The heat treatment temperature can be appropriately set to obtain the desired effect within the range allowed by the constituent material of the adhesive sheet or the type of adherend, taking into account the surface condition of the adherend, etc., for example, it can be around 100°C or below, below 80°C, below 60°C, or below 50°C.

The component or material to which the adhesive sheet is attached (at least one adherend in a double-sided adhesive sheet) may be light-transmissive. As for the adherend, the technology disclosed herein can be applied to easily obtain the advantages of suppressing the reduction of optical properties (transparency, etc.) and improving the refractive index at the same time. The total light transmittance of the adherend may be greater than 50%, or may be greater than 70%, for example. In several ideal embodiments, the total light transmittance of the adherend is greater than 80%, preferably greater than 90%, and more preferably greater than 95% (for example, 95~100%). The adhesive sheet disclosed herein is suitable for use in a state of being attached to an adherend (for example, an optical component) having a total light transmittance greater than a predetermined value. The total light transmittance is measured according to JIS K 7136:2000 using a commercially available transmittance meter. As the transmittance meter, a product name "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory or an equivalent product can be used.

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 high relative to the refractive index of the adherend, light incident on the adhesive layer from the side of the adherend at an angle below the critical angle can be refracted on the front side, thereby increasing the front brightness. At this time, the refractive index of the adherend can be, for example, less than 1.55, less than 1.50, less than 1.48, less than 1.45, or less than 1.45, or more than 1.10, more than 1.20, more than 1.30, or more than 1.35. Furthermore, by making the adherend have a relatively high refractive index relative to the adhesive layer, light incident on the adherend from the adhesive layer side can be refracted on the front side, thereby increasing the front brightness. At this time, 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 may be suppressed. At this time, the refractive index of the adherend may be about 1.55 to 1.80, about 1.55 to 1.75, or about 1.60 to 1.70. The refractive index of the adherend may be measured by the same method as the refractive index of the adhesive.

In several ideal embodiments, the adherend may have any of the above refractive indices and any of the above total light transmittances. In the embodiment of being attached to the adherend, the effect brought by the technology disclosed herein can be particularly well exerted.

One example of a preferred application is optical application. More specifically, for example, the adhesive sheet disclosed herein can be suitably used as an optical adhesive sheet for bonding optical components (optical component bonding) or for manufacturing products using the above optical components (optical products).

The above-mentioned optical components refer to components having optical properties (such as polarization, light refraction, light scattering, light reflection, light transmission, light absorption, light diffraction, optical rotation, visibility, etc.). The above-mentioned optical components are not particularly limited as long as they are components with optical properties. Examples include components constituting display devices (image display devices), input devices and other machines (optical machines) or components used in such machines, such as polarizing plates, wavelength plates, phase difference plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflective films, hard coating (HC) films, impact absorption films, anti-fouling films, photochromic films, dimming films, transparent conductive films (ITO films), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, or further components formed by layering such components (these are sometimes collectively referred to as "functional films"), etc. In addition, the above-mentioned "plate" and "film" are respectively set to include plate-shaped, film-shaped, sheet-shaped, etc. For example, "polarizing film" is set to include "polarizing plate" or "polarizing sheet", etc., and "light guide plate" is set to include "light guide film" or "light guide sheet", etc. Moreover, the above-mentioned "polarizing plate" is set to include a circular polarizing plate.

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

The optical component is not particularly limited, and examples thereof include components made of glass, acrylic resin, polycarbonate, polyethylene terephthalate, metal film, etc. (e.g., sheet-shaped, film-shaped, or plate-shaped components). In addition, the "optical component" in this specification is also intended to include components that maintain the visibility of the display device or input device while serving as a decorative or protective function (design film, decorative film, or surface protection film, etc.).

The technology disclosed herein can be used to bond optical films such as films with one or more functions of light transmission, reflection, diffusion, waveguide, light focusing, diffraction, etc. or fluorescent films to other optical components (which may be other optical films). Among them, in bonding optical films with at least one function of light waveguide, light focusing, diffraction, the entire bonding layer should have a high refractive index, which can become an ideal application object of the technology disclosed herein.

The adhesive disclosed herein can be suitably used for the bonding of optical films such as light-guiding films, diffusion films, fluorescent films, color-adjusting films, prism films, columnar mirror films, and microlens array films. In such applications, from the perspective of miniaturization or high performance of optical components, thinning or improvement of light extraction efficiency is required. The adhesive disclosed herein can be suitably used as an adhesive that can meet the above requirements. In more detail, for example, when bonding a light-guiding film or a diffusion film, adjusting the refractive index of the adhesive layer serving as the bonding layer (e.g., increasing the refractive index) can help achieve thinning. The bonding of fluorescent films can improve the light extraction efficiency (which can also be regarded as luminescence efficiency) by appropriately adjusting the refractive index difference between the fluorescent light-emitting body and the adhesive. When bonding color films, by properly adjusting the refractive index of the adhesive to minimize the difference in refractive index with the coloring pigment, the scattering component can be reduced, which helps to improve light transmittance. When bonding prisms, lenticular films, microlens array films, etc., by properly adjusting the refractive index of the adhesive to control light diffraction, it can help to improve brightness and/or viewing angle.

The adhesive sheet disclosed herein can be suitably used in a state of being attached to an adherend with a high refractive index (which can be a layer or component with a high refractive index, etc.), and can suppress the interface reflection with the above-mentioned adherend. The adhesive sheet that can be used in the above-mentioned state preferably has a small refractive index difference with the adherend as described above and high adhesion at the interface with the adherend. In addition, from the perspective of improving the uniformity of the appearance, the thickness homogeneity of the adhesive layer should be high, for example, the surface smoothness of the adhesive surface should be high. When the thickness of the high refractive index adherend is small (for example, less than 5µm, less than 4µm or less than 2µm), from the perspective of suppressing coloring or color unevenness caused by interference of reflected light, suppressing reflection at the interface is particularly meaningful. As an example of the usage, the following can be cited: in a polarizing plate with a phase difference layer having a polarizer, a first phase difference layer and a second phase difference layer in sequence, it can be used for bonding the polarizer and the first phase difference layer and/or bonding the first phase difference layer and the second phase difference layer.

Furthermore, the adhesive sheet disclosed herein is suitable for high refractive index, and therefore can be suitably used in a state of being attached to a luminescent layer of an optical semiconductor or the like (for example, a high refractive luminescent layer mainly composed of inorganic materials). By reducing the refractive index difference between the luminescent layer and the adhesive layer, reflection at the interface can be suppressed, thereby improving light extraction efficiency. The adhesive sheet that can be used in the above state preferably has an adhesive layer with a high refractive index. Furthermore, from the perspective of being able to prevent the self-luminescent element from deteriorating due to moisture in advance, the water absorption rate of the adhesive layer should be low. From the perspective of improving brightness, the adhesive sheet should be low in coloration. It is also advantageous from the perspective of suppressing unintentional coloration caused by the adhesive sheet.

The adhesive disclosed herein can be suitably used as a coating layer covering the lens surface, a bonding layer for a component opposite to the lens surface (e.g., a component having a surface shape corresponding to the lens surface), a filling layer filled between the lens surface and the component, etc., in microlenses and other lens components (e.g., microlenses constituting a microlens array film or lens components such as a microlens for a camera) used as components of a camera or a light-emitting device. The adhesive disclosed herein is suitable for increasing the refractive index, so even if it is a lens with a high refractive index (for example, a lens made of a high refractive index resin, or a lens having a surface layer made of a high refractive index resin), the refractive index difference with the lens can be reduced. This is advantageous from the perspective of thinning the above-mentioned lens and the product having the lens, and can also help to suppress aberration or increase the Abbe number. The adhesive disclosed herein can also be used as a lens resin in the form of filling a concave portion or gap of an appropriate transparent component.

The use of the adhesive sheet disclosed herein to bond optical components is not particularly limited, and may be, for example, the following: (1) bonding optical components to each other through the adhesive sheet disclosed herein; or (2) bonding optical components to components other than optical components through the adhesive sheet disclosed herein; or (3) bonding the adhesive sheet disclosed herein to an optical component or components other than optical components. In addition, in the above-mentioned aspect (3), the adhesive sheet containing the optical component may be, for example, an adhesive sheet whose support is an optical component (e.g., an optical film). As described above, the adhesive sheet containing the optical component as a support may also be regarded as an adhesive optical component (e.g., an adhesive optical film). Furthermore, when the adhesive sheet disclosed herein is a type of adhesive sheet having a support and the above-mentioned functional film is used as the above-mentioned support, the adhesive sheet disclosed herein can also be regarded as an "adhesive functional film" having the adhesive layer disclosed herein on at least one side of the functional film.

From the above, according to the technology disclosed herein, a laminate having an adhesive sheet disclosed herein and a component to which the adhesive sheet is attached can be provided. The component to which the adhesive sheet can be attached can be a component having the refractive index of the material of the adherend described above. Furthermore, the difference between the refractive index of the adhesive sheet and the refractive index of the component (refractive index difference) can be the refractive index difference between the adherend and the adhesive sheet described above. The components constituting the laminate are as described above with respect to the components, materials, and adherend, and therefore will not be described repeatedly.

As can be understood from the above description and the following embodiments, the matters disclosed in this specification include the following matters. [1] An adhesive sheet comprising an adhesive layer; and It has an adhesive surface formed by the above adhesive layer; The refractive index of the above adhesive layer is greater than 1.570, the total light transmittance is greater than 86%, and the haze value is less than 3.0%. [2] An adhesive sheet as described in [1] above, wherein the thickness of the above adhesive layer is greater than 5µm. [3] An adhesive sheet as described in [1] or [2] above, wherein the peeling strength (adhesion) of the adhesive sheet to the glass plate is greater than 3N/25mm. [4] An adhesive sheet as described in any one of [1] to [3] above, wherein the arithmetic average roughness Ra of the above adhesive surface is less than 100nm. [5] An adhesive sheet as described in any one of [1] to [4] above, wherein the water absorption rate of the adhesive layer is 1.0% or less. [6] An adhesive sheet as described in any one of [1] to [5] above, which is in the form of a laminate comprising the adhesive layer and a light-transmitting substrate. [7] An adhesive sheet as described in [6] above, wherein the light-transmitting substrate is a resin film. [8] An adhesive sheet as described in any one of [1] to [5] above, which is a double-sided adhesive sheet composed of the adhesive layer. [9] An adhesive sheet with a peel-off pad, comprising: The adhesive sheet as described in any one of [1] to [8] above; and A peel-off pad disposed on the adhesive surface of the adhesive sheet. [10] An adhesive composition for forming an adhesive layer of an adhesive sheet as described in any one of [1] to [8] above.

[11] An adhesive composition comprising: an acrylic polymer (A) comprising 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 acrylic polymer (A). [12] The adhesive composition of [11] above, wherein the refractive index of the additive (H _RO ) is greater than 1.60. [13] The adhesive composition of [11] or [12] above, wherein the content of the additive (H _RO ) relative to 100 parts by weight of the acrylic polymer (A) is greater than 0 parts by weight and less than 60 parts by weight. [14] The adhesive composition of any one of [11] to [13] above, wherein the additive (H _RO ) comprises at least one compound selected from the group consisting of aromatic ring-containing compounds and heterocyclic ring-containing compounds. [15] The adhesive composition of any one of [11] to [14] above, wherein the additive (H _RO ) comprises a compound having two or more aromatic rings in one molecule. [16] The adhesive composition of [15] above, wherein the additive (H _RO ) comprises a compound satisfying at least one of the following as the compound having two or more aromatic rings in one molecule: (i) a structure comprising two non-condensed aromatic rings directly chemically bonded; and (ii) a structure comprising two condensed aromatic rings. [17] The adhesive composition as described in any one of the above [11] to [16], wherein the content of the above aromatic ring-containing monomer (m1) in the monomer components constituting the above acrylic polymer (A) is 50% by weight or more. [18] The adhesive composition as described in any one of the above [11] to [17], wherein the content of the above aromatic ring-containing monomer (m1) in the monomer components constituting the above acrylic polymer (A) is greater than 70% by weight and less than 100% by weight, and more than 50% by weight of the above aromatic ring-containing monomer (m1) is a monomer having a glass transition temperature of 10°C or less in the homopolymer. [19] An adhesive composition as described in any one of [11] to [18] above, wherein the monomer component constituting the acrylic polymer (A) further comprises a monomer (m2), wherein the monomer (m2) has at least one of a hydroxyl group and a carboxyl group. [20] An adhesive composition as described in any one of [11] to [18] above, which is used to form an adhesive layer of an adhesive sheet as described in any one of [1] to [8] above. [21] An adhesive formed from an adhesive composition as described in any one of [11] to [20] above, and having a refractive index higher than 1.570. [22] An adhesive sheet comprising an adhesive layer formed from an adhesive, wherein the adhesive is formed from an adhesive composition as described in any one of [11] to [20] above. [23] The adhesive sheet as described in [22] above, wherein the haze value of the adhesive layer is less than 1.0%.

[24] A spacer for use between layers of a laminate for optical purposes; and comprising a viscoelastic layer _V1 having a refractive index _n1 of 1.570 or more, and satisfying: a total light transmittance of 86% or more; a haze value of 1.0% or less; and a storage elastic modulus G' of 30 kPa to 700 kPa at 25°C. [25] The spacer of [24], wherein the thickness is 5 µm or more. [26] The spacer of [24] or [25], wherein the viscoelastic layer _V1 comprises a main polymer and a plasticizer having a molecular weight lower than that of the main polymer. [27] The spacer of [26], wherein the weight average molecular weight of the plasticizer is 30,000 or less. [28] The interlayer spacer as described in any one of [24] to [27], further comprising a viscoelastic layer _V2 laminated on the viscoelastic layer _V1 , wherein the storage elastic modulus _G'V2 of the viscoelastic layer _V2 at 25°C is lower than the storage elastic modulus G'V1 of the viscoelastic layer _V1 at 25°C. [ ₂₉ ] The interlayer spacer as described in [28], wherein the refractive index _n2 of the viscoelastic layer _V2 is lower than the refractive index _n1 of the viscoelastic layer _V1 . [30] A layer spacer as described in any one of [24] to [29] above, wherein the viscoelastic layer _V1 is a layer formed by the adhesive composition as described in any one of [11] to [18] above. [31] A layer spacer as described in any one of [24] to [29] above, wherein the viscoelastic layer _V1 is an adhesive layer in the adhesive sheet as described in any one of [1] to [5] above. [32] An optical laminate comprising: a layer spacer as described in any one of [24] to [31] above, and a resin film laminated on the layer spacer. [33] A layer spacer with a peel-off liner, comprising: a layer spacer as described in any one of [24] to [31] above, and a peel-off liner covering at least one surface of the layer spacer.

Examples The following will describe various examples of the present invention, but the specific examples are not intended to limit the present invention. In addition, in the following description, "parts" and "%" indicating the amount or content are based on weight unless otherwise specified.

<Example 1> (Preparation of acrylic polymer solution) m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "LIGHT ACRYLATE POB-A (refractive index: 1.566, homopolymer Tg: -35°C; hereinafter referred to as "POB-A") 95 parts and 4-hydroxybutyl acrylate (4HBA) 5 parts, 2,2'-azobisisobutyronitrile (AIBN) as a polymerization initiator 0.2 parts, and toluene 100 parts as a polymerization solvent were added, and nitrogen was introduced while slowly stirring, and the liquid temperature in the flask was maintained at about 60°C for 6 hours to carry out polymerization reaction, thereby preparing a solution (50%) of acrylic polymer A1. The polymerization average molecular weight (Mw) of the acrylic polymer A1 was 500,000. In the acrylic polymer A1, the Tg (i.e., Tg _T ) according to the composition of the monomer components is -35°C, and the Tg (i.e., Tg _m1 ) according to the composition of the aromatic ring-containing monomer is -35°C.

(Preparation of adhesive composition) The solution of the acrylic polymer A1 (50%) was diluted to 30% with ethyl acetate, and 5 parts of 6-acryloyloxymethyl dinaphthothiophene (6-naphthothiophene-6-methylacrylate manufactured by SUGAI Chemical Industry Co., Ltd., trade name "6MDNTA", refractive index 1.75) as an additive (H _RO ) and 334 parts of the solution (100 parts of non-volatile components) were added to the solution. HX", 10 parts of a 1% ethyl acetate solution (0.1 parts of non-volatile components) of a trifunctional isocyanate compound), 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution (0.01 parts of non-volatile components) of acetylacetonate iron (III) as a crosslinking catalyst were stirred and mixed to prepare an acrylic adhesive composition C1.

(Adhesive sheet preparation) The acrylic adhesive composition C1 prepared above is applied to the silicone-treated surface of a single-sided silicone-treated polyethylene terephthalate (PET) film R1 (thickness 50µm), and heated at 130°C for 2 minutes to form an adhesive layer with a thickness of 25µm. Then, the silicone-treated surface of a single-sided silicone-treated PET film R2 (thickness 25µm) is attached to the surface of the adhesive layer. A substrate-free double-sided adhesive sheet S1 composed of the adhesive layer is obtained in the above manner. Both sides of the adhesive sheet S1 are protected by PET films (peel-off pads) R1 and R2.

<Examples 2 to 5> Except that the type of additive (H _RO ) and the amount used relative to 100 parts of acrylic polymer (phr; per hundred resin) were changed as shown in Table 1, acrylic adhesive compositions C2 to C5 of Examples 2 to 5 were prepared in the same manner as the preparation of acrylic adhesive composition C1 in Example 1. Here, "BPFL" in Table 1 represents 9,9-bis(4-hydroxyphenyl)fluorene (manufactured by Osaka Gas Chemicals Co., Ltd., with a refractive index of 1.68), and "BAFL" represents 9,9-bis(4-aminophenyl)fluorene (manufactured by Osaka Gas Chemicals Co., Ltd., with a refractive index of 1.73). Adhesive sheets S2 to S5 of Examples 2 to 5 (double-sided adhesive sheets without a substrate composed of an adhesive layer) were prepared in the same manner as the adhesive sheet in Example 1, except that acrylic adhesive compositions C2 to C5 were used to replace acrylic adhesive composition C1.

<Example 6> Into a separable flask equipped with a thermometer, a stirrer, a reflux cooling tube and a nitrogen inlet tube were placed 20 parts of POB-A, 80 parts of 1-naphthylmethylacrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "LIGHT ACRYLATE NMT-A", refractive index: 1.595, homopolymer Tg: 31°C; hereinafter referred to as "NMT-A"), 0.2 parts of AIBN as a polymerization initiator, 3.5 parts of α-thioglycerol as a chain transfer agent and 67 parts of methyl ethyl ketone, and then nitrogen was introduced and nitrogen substitution was performed for about 1 hour while stirring. Then, 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. . The type of additive (H _RO ) was changed to the above oligomer B, and its usage was set to 30 parts (30 phr) relative to 100 parts of the acrylic polymer. The acrylic adhesive composition C6 of this example was prepared in the same manner as the preparation of the acrylic adhesive composition C1 in Example 1. The adhesive sheet (a double-sided adhesive sheet without a substrate composed of an adhesive layer) S6 of this example was prepared in the same manner as the preparation of the adhesive sheet in Example 1, except that the acrylic adhesive composition C6 was used instead of the acrylic adhesive composition C1.

<Example 7> An acrylic adhesive composition C7 was prepared in the same manner as the acrylic adhesive composition C1 in Example 1 except that the additive (H _RO ) was not used. An adhesive sheet (a double-sided adhesive sheet without a substrate composed of an adhesive layer) S7 of this example was prepared in the same manner as the adhesive sheet in Example 1 except that the acrylic adhesive composition C7 was used instead of the acrylic adhesive composition C1 and the thickness of the adhesive layer was set to 20 μm.

<Example 8> Except that the composition of the monomer components is changed, POB-A is changed to 72 parts, NMT-A is changed to 23 parts, and 4HBA is changed to 5 parts, a solution of acrylic polymer A2 is prepared in the same manner as the preparation of the acrylic polymer solution in Example 1. The polymerization average molecular weight (Mw) of the acrylic polymer A2 is 450,000. Except that the solution of acrylic polymer A2 is used instead of the solution of acrylic polymer A1, an acrylic adhesive composition C8 of this example is prepared in the same manner as the preparation of the adhesive composition in Example 1. Except that the acrylic adhesive composition C8 is used instead of the acrylic adhesive composition C1, an adhesive sheet (a double-sided adhesive sheet without a substrate composed of an adhesive layer) S8 of this example is prepared in the same manner as the preparation of the adhesive sheet in Example 1.

<Examples 9 to 13> Except that the type and amount of the additive ((H _RO )) were changed as shown in Table 1, acrylic adhesive compositions C9 to C13 of Examples 9 to 13 were prepared in the same manner as the preparation of acrylic adhesive composition C8 in Example 8. Adhesive sheets (double-sided adhesive sheets without a substrate composed of an adhesive layer) S9 to S13 of Examples 9 to 13 were prepared in the same manner as the preparation of the adhesive sheet in Example A1, except that acrylic adhesive compositions C9 to C13 were used to replace acrylic adhesive composition C1.

<Example 14> The acrylic adhesive composition C14 of Example 14 was prepared in the same manner as the preparation of the acrylic adhesive composition C8 in Example 8, except that the additive ((H _RO )) was not used. The adhesive sheet (a double-sided adhesive sheet without a substrate composed of an adhesive layer) S14 of this example was prepared in the same manner as the preparation of the adhesive sheet in Example 8, except that the acrylic adhesive composition C14 was used instead of the acrylic adhesive composition C8.

<Example 15> Except that the composition of the monomer components was changed, 2-ethylhexyl acrylate (2EHA) was changed to 90 parts, and 4HBA was changed to 10 parts, the acrylic polymer A3 solution (40%) was prepared in the same manner as the acrylic polymer solution in Example 1. The solution (40%) of the acrylic polymer A3 was diluted to 20% with ethyl acetate, and 10 parts of a zirconia particle dispersion based on solid content, 10 parts of a 1% ethyl acetate solution of a triisocyanate of hexamethylene diisocyanate (manufactured by Tosoh, trade name "Coronate HX", a trifunctional isocyanate compound) as a crosslinking agent (0.1 parts of non-volatile components), 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of iron (III) acetylacetonate as a crosslinking catalyst (0.01 parts of non-volatile components) were added to 500 parts of the solution (100 parts of non-volatile components) and stirred to prepare an acrylic adhesive composition C15. The above-mentioned zirconia particle dispersion is a surface-treated zirconia particle dispersion in which surface-treated zirconia particles (average particle size 20 nm, solid component refractive index: 1.64, surface treatment: carboxylic acid/phosphoric acid hydrophobic treatment, manufactured by Kyoeisha Chemical Co., Ltd.) are dispersed in propylene glycol monomethyl ether (PGME). The acrylic adhesive composition C15 is used to replace the acrylic adhesive composition C1, and the thickness of the adhesive layer is set to 20 µm. In addition, the adhesive sheet of Example 15 (a double-sided adhesive sheet without a substrate composed of an adhesive layer) S15 is prepared in the same manner as the adhesive sheet in Example 1.

<Example 16> Except changing the monomer composition to POB-A/n-butyl acrylate (BA)/4HBA=79/20/1, a solution of acrylic polymer A4 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 1. The polymerization average molecular weight (Mw) of acrylic polymer A4 is 520,000. Except using the solution of acrylic polymer A4 to replace the solution of acrylic polymer A1, the acrylic adhesive composition C16 of this example was prepared in the same manner as Example 2 to produce an adhesive sheet (a double-sided adhesive sheet without a substrate composed of an adhesive layer) S16.

<Example 17> Except changing the monomer composition to POB-A/ethyl carbitol acrylate (CBA)/4HBA=79/20/1, a solution of acrylic polymer A5 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 1. The polymerization average molecular weight (Mw) of acrylic polymer A5 is 460,000. Except using a solution of acrylic polymer A4 instead of a solution of acrylic polymer A1, an acrylic adhesive composition C17 of this example was prepared in the same manner as Example 2 to produce an adhesive sheet (a double-sided adhesive sheet without a substrate composed of an adhesive layer) S17.

<Example 18> Except that the composition of the monomer components is changed to POB-A/phenoxy diethylene glycol acrylate/4HBA=79/20/1, a solution of acrylic polymer A6 is prepared in the same manner as the preparation of the acrylic polymer solution in Example 1. Phenoxy diethylene glycol acrylate is a product name "LIGHT ACRYLATE P2H-A" manufactured by Kyoei Chemical Co., Ltd. The polymerization average molecular weight (Mw) of acrylic polymer A6 is 480,000. Except that the solution of acrylic polymer A6 is used instead of the solution of acrylic polymer A1, the acrylic adhesive composition C18 of this example is prepared in the same manner as Example 2 to prepare an adhesive sheet (a double-sided adhesive sheet without a substrate composed of an adhesive layer) S18.

<Example 19> Except that the additive (H _RO ) was changed to 2,12-diallyloxydinaphthothiophene (manufactured by SUGAI Chemical Industries, Ltd., abbreviation: 2,12-DAODNT, refractive index: 1.729), the acrylic adhesive composition C19 of this example was prepared in the same manner as in Example 2 to produce an adhesive sheet (a double-sided adhesive sheet without a substrate composed of an adhesive layer) S19.

<Examples 20-22> Except that no additive (H _RO ) was used, acrylic adhesive compositions C20-22 were prepared in the same manner as Examples 16-18, respectively, to produce adhesive sheets (double-sided adhesive sheets without a substrate and composed of an adhesive layer) S20-22.

<Measurement and Evaluation> (Refractive Index) For each adhesive layer (double-sided adhesive sheet without substrate), the refractive index was measured using an Abbe refractometer (manufactured by ATAGO CO., LTD., model "DR-M4") at a measurement wavelength of 589 nm and a measurement temperature of 25°C. The results are listed in Tables 1 and 2.

(Total light transmittance and haze value) The total light transmittance and haze of the test piece with the adhesive layer of each example bonded to the alkali-free glass (thickness 0.8~1.0mm, total light transmittance 92%, haze 0.4%) were measured using a haze meter (manufactured by Murakami Color Technology Laboratory, trade name "HAZEMETER HM-150") at 23°C. The total light transmittance and haze of the adhesive layer were obtained by subtracting the total light transmittance and haze of the alkali-free glass from the measured values. The results are listed in Tables 1 and 2.

(Storage modulus G') The adhesive layer of each example was laminated to a thickness of about 1.5 mm as a test sample. ARES manufactured by TA Instruments was used to perform dynamic viscoelasticity measurement under the following conditions. The storage modulus G' at 25°C was read from the measurement results. The results are listed in Tables 1 and 2. [Measurement conditions] Deformation mode: Torsion Measurement frequency: 1 Hz Heating rate: 5°C/min Shape: Parallel plate 7.9 mm φ

(Peel strength) The peel strength of each adhesive sheet against a glass plate was measured. That is, in a measuring environment of 23°C and 50% RH, the peel pad was peeled off from one side of the adhesive sheet, and a 50µm thick PET film was attached as a backing, and then the sheet was cut into a test piece with a width of 25mm and a length of 100mm. The peel pad on the other side of the test piece was peeled off, and a 2kg roller was pressed against the surface of an alkaline glass plate (manufactured by Matsunami Glass Industry Co., Ltd., thickness 1.35mm, blue plate frosted product) as the adherend in one reciprocating motion. It was placed in this environment for 30 minutes, then placed in a pressurized degassing device (autoclave) and autoclaved for 30 minutes at a temperature of 50°C and a pressure of 0.5MPa. After being placed in a gas environment of 23°C and 50%RH for 24 hours, the peel strength (adhesion) [N/25mm] was measured using a universal tensile compression tester in accordance with JIS Z 0237:2000 at a tensile speed of 300mm/min and a peeling angle of 180 degrees. The universal tensile compression tester used was a "tensile compression tester, TG-1kN" manufactured by Minebea Corporation. The results are listed in Tables 1 and 2.

[Table 1]

[Table 2]

As shown in Table 1, the adhesives of Examples 1 to 6, in which the additive (H _RO ) is added to the adhesive of Example 7 not containing the additive (H _RO ), show a higher refractive index than Example 7. The adhesives have high transparency and good peeling strength. The same tendency is also seen in the comparison between Example 14 and Examples 8 to 13. On the other hand, compared with Examples 1 to 14, Example 15, in which the refractive index is increased by mixing high refractive index inorganic particles, has significantly poorer transparency (especially significantly higher haze) and does not show practical adhesive performance (peeling strength) suitable for use as an adhesive.

In Examples 16 to 19 shown in Table 2, it is also confirmed that the use of the additive (H _RO ) can achieve the effect of increasing the refractive index. The adhesives of Examples 16 to 19 have high transparency and good peeling strength. From the above, it can be seen that the adhesives of Examples 1 to 6, Examples 8 to 13, and Examples 16 to 19 have suppressed the reduction of optical properties and have a high refractive index, so they are suitable for the bonding of optical components (such as optical films having at least one function of light waveguide, light focusing, and diffraction).

The specific examples of the present invention have been described in detail above, but these are only examples and do not limit the scope of the patent application. The technology described in the scope of the patent application includes various modifications and changes of the specific examples described above.

1,2: Adhesive sheet 10: Adhesive layer 10A: 1st surface (adhesive surface) 10B: 2nd surface 20: Support substrate 20A: 1st surface (non-peelable surface) 20B: 2nd surface (back surface) 30,31,32: Peel-off pad 50: Adhesive sheet with peel-off pad 70: Optical component 100: Component with adhesive sheet

FIG. 1 is a cross-sectional view schematically showing the structure of an adhesive sheet in one embodiment. FIG. 2 is a cross-sectional view schematically showing the structure of an adhesive sheet in another embodiment. FIG. 3 is a cross-sectional view schematically showing an optical component in which an adhesive sheet in one embodiment is attached to an optical component.

1: Adhesive sheet

10: Adhesive layer

10A: Surface 1 (adhesive surface)

10B: Surface 2

20: Support substrate

20A: Surface 1 (non-peelable surface)

20B: Side 2 (back)

30: Peel off the liner

50: Adhesive sheet with peel-off liner

Claims (10)

An adhesive composition comprises: an acrylic polymer (A) comprising 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 acrylic polymer (A); wherein the additive (H _RO ) comprises a compound having two or more aromatic rings in one molecule, and the additive (H _RO ) comprises a compound satisfying at least one of the following as the compound having two or more aromatic rings in one molecule: (i) a structure comprising two non-condensed aromatic rings directly chemically bonded; and (ii) a structure comprising two condensed aromatic rings. The adhesive composition of claim 1, wherein the refractive index of the additive (H _RO ) is greater than 1.60. The adhesive composition of claim 1 or 2, wherein the content of the additive (H _RO ) is greater than 0 parts by weight and less than 60 parts by weight relative to 100 parts by weight of the acrylic polymer (A). The adhesive composition of claim 1 or 2, wherein the additive (H _RO ) comprises a heterocyclic compound. In the adhesive composition of claim 1 or 2, the content of the aromatic ring-containing monomer (m1) in the monomer components constituting the acrylic polymer (A) is 50% by weight or more. The adhesive composition of claim 1 or 2, wherein the content of the aforementioned aromatic ring-containing monomer (m1) in the monomer components constituting the aforementioned acrylic polymer (A) is greater than 70% by weight and less than 100% by weight, and more than 50% by weight of the aforementioned aromatic ring-containing monomer (m1) is a monomer having a homopolymer glass transition temperature below 10°C. In the adhesive composition of claim 1 or 2, the monomer components constituting the acrylic polymer (A) further contain a monomer (m2), wherein the monomer (m2) has at least one of a hydroxyl group and a carboxyl group. An adhesive is formed from the adhesive composition of any one of claims 1 to 7 and has a refractive index higher than 1.570. An adhesive sheet comprises an adhesive layer composed of an adhesive, wherein the adhesive is formed from the adhesive composition of any one of claims 1 to 7. The adhesive sheet of claim 9, wherein the haze value of the adhesive layer is less than 1.0%.

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