Refractive index modifiers and their uses

Abstract

To provide a refractive index adjustment agent for adjusting the refractive index of adhesives.SOLUTION: The present invention provides a refractive index adjustment agent for adhesives. The refractive index adjustment agent is an organic compound comprising a structure having at least two substituents on a hub ring. The hub ring is a double bond-containing ring, and at least one of the at least two substituents is a substituent that has a double bond-containing ring.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a refractive index adjuster, and a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet that utilize the refractive index adjuster. [Background technology]

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

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

[0004] Patent Documents 1 and 2 relate to pressure-sensitive adhesive compositions primarily composed of a (meth)acrylic acid ester polymer. They propose that the (meth)acrylic acid ester polymer contain a predetermined amount of a monomer having multiple aromatic rings as a monomer unit, thereby providing a high refractive index for the resulting pressure-sensitive adhesive (see, for example, paragraph

[0011] ). For example, some materials, such as optical components, to which pressure-sensitive adhesives are applied have high refractive indexes. It is known that using a typical acrylic pressure-sensitive adhesive to bond such high-refractive-index materials can result in reflection at the interface due to the difference in refractive index between the materials. By using a pressure-sensitive adhesive with a refractive index close to that of the high-refractive-index material to bond the high-refractive-index material, the interfacial reflection can be prevented or suppressed. The refractive index of typical acrylic pressure-sensitive adhesives is typically around 1.47.

[0005] On the other hand, the refractive indexes of materials that can be used as adhesive substrates vary, and it is not necessarily efficient to individually design the composition (type and content ratio) of the monomer units that make up the adhesive's base polymer to match the refractive index of each adherend. For example, it would be beneficial if the refractive index of the adhesive could be adjusted using an additive component separate from the base polymer. Patent Documents 1 and 2 cite a refractive index adjuster as an example of an optional component that can be added to the adhesive composition if desired (paragraph

[0054] ), but do not describe the structure of the refractive index adjuster, and it is unclear whether it is organic or inorganic.

[0006] The present invention was created in view of the above circumstances, and aims to provide a refractive index adjuster for adjusting the refractive index of a pressure-sensitive adhesive. Another object of the present invention is to provide a pressure-sensitive adhesive containing the refractive index adjuster. Another related object is to provide a compound useful as the refractive index adjuster. [Means for solving the problem]

[0007] According to this specification, a refractive index modifier for pressure-sensitive adhesives is provided. The refractive index modifier is an organic compound having a structure with two or more substituents on a hub ring. Here, the hub ring is a double-bond-containing ring, and at least one of the two or more substituents is a substituent having a double-bond-containing ring. A compound that satisfies these structural requirements is used as a constituent component of a pressure-sensitive adhesive and is useful as a refractive index modifier that appropriately adjusts the refractive index of the pressure-sensitive adhesive.

[0008] In some embodiments of the technology disclosed herein (including refractive index adjusters, adhesive compositions containing the refractive index adjusters, adhesives containing the refractive index adjusters, adhesive sheets having the adhesives, etc.; the same applies hereinafter), the molecular weight of the refractive index adjuster is less than 3000. A refractive index adjuster having a molecular weight of less than 3000 is preferred from the standpoint of ease of incorporation into adhesives, etc.

[0009] In some embodiments, the refractive index adjuster has two or more substituents on the hub ring that have a double bond-containing ring. A refractive index adjuster having such a structure can be used as a component of a pressure-sensitive adhesive to efficiently adjust (e.g., increase) the refractive index of the pressure-sensitive adhesive.

[0010] In some embodiments, the refractive index adjuster has at least one substituent on the hub ring that has two or more double bond-containing rings. A refractive index adjuster having such a structure can be used as a component of a pressure-sensitive adhesive to efficiently adjust (e.g., increase) the refractive index of the pressure-sensitive adhesive.

[0011] A preferred example of the refractive index control agent disclosed herein is one in which the hub ring is a triazine ring. For example, the refractive index control agent is represented by the following formula (I): [ka] (In formula (I), X 1 ,X 2 and X 3 are each independently -O-, -S- and -NR 4-, where R 4 is a hydrogen atom or an alkyl group, R 1 ,R 2 and R 3 one or more of the groups are each independently an aromatic ring-containing group selected from the group consisting of an optionally substituted phenyl group and an optionally substituted biphenyl group, wherein the substituent is an alkyl group, an alkoxy group, or a cyano group; R 1 ,R 2 and R 3 When there are two or less aromatic ring-containing groups, the remainder are aliphatic hydrocarbon groups or hydrogen atoms; The refractive index adjuster having such a structure can be used as a constituent component of a pressure-sensitive adhesive to suitably adjust the refractive index of the pressure-sensitive adhesive (for example, to increase the refractive index).

[0012] According to this specification, there is provided a pressure-sensitive adhesive containing any of the refractive index adjusters disclosed herein. The pressure-sensitive adhesive having such a composition can exhibit a desired refractive index adjusted by the refractive index adjuster.

[0013] The adhesive disclosed herein preferably contains the refractive index adjuster and an acrylic polymer containing an aromatic ring-containing monomer (m1) as a monomer unit. The adhesive having such a composition can easily achieve a desired high refractive index (e.g., a refractive index of 1.550 or more).

[0014] According to this specification, the compound of formula (I): [ka] (In formula (I), X 1 ,X 2 and X 3 are each independently -O-, -S- and -NR 4 -, where R 4 is a hydrogen atom or an alkyl group, R 1 ,R 2,R 3 one or more of the groups are each independently an aromatic ring-containing group selected from the group consisting of an optionally substituted phenyl group and an optionally substituted biphenyl group, wherein the substituent is an alkyl group, an alkoxy group, or a cyano group; R 1 ,R 2 and R 3 When there are two or less aromatic ring-containing groups, the remainder are aliphatic hydrocarbon groups or hydrogen atoms; The compound is useful, for example, as a refractive index adjuster (particularly, a refractive index adjuster for adhesives).

[0015] Appropriate combinations of the elements described in this specification may also be included within the scope of the invention for which patent protection is sought by this patent application. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet according to one embodiment. [Figure 2] FIG. 10 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet according to another embodiment. [Figure 3] FIG. 10 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet according to another embodiment. [Figure 4] FIG. 1 is a diagram showing the 1H-NMR spectrum of Compound A1 according to Synthesis Example 1. [Figure 5] FIG. 1 is a diagram showing the 13C-NMR spectrum of Compound A1 according to Synthesis Example 1. [Figure 6] FIG. 1 is a diagram showing the 1H-NMR spectrum of Compound A2 according to Synthesis Example 2. [Figure 7] FIG. 1 is a diagram showing the 13C-NMR spectrum of Compound A2 according to Synthesis Example 2. [Figure 8] FIG. 1 is a diagram showing the 1H-NMR spectrum of Compound A3 according to Synthesis Example 3. [Figure 9] FIG. 1 is a diagram showing the 13C-NMR spectrum of Compound A3 according to Synthesis Example 3. [Figure 10] FIG. 1 is an enlarged view of a main portion of the 1H-NMR spectrum of Compound A4 according to Synthesis Example 4. [Figure 11] FIG. 1 is an enlarged view of a main portion of the 13C-NMR spectrum of Compound A4 according to Synthesis Example 4. [Figure 12] FIG. 1 is a diagram showing the 1H-NMR spectrum of Compound A5 according to Synthesis Example 5. [Figure 13] FIG. 1 is a diagram showing the 13C-NMR spectrum of Compound A5 according to Synthesis Example 5. [Figure 14] FIG. 1 is a diagram showing the 1H-NMR spectrum of Compound A6 according to Synthesis Example 6. [Figure 15] FIG. 1 is a diagram showing the 13C-NMR spectrum of Compound A6 according to Synthesis Example 6. [Figure 16] FIG. 1 is a diagram showing the 1H-NMR spectrum of Compound A7 according to Synthesis Example 7. [Figure 17] FIG. 1 is a diagram showing the 13C-NMR spectrum of Compound A7 according to Synthesis Example 7. [Figure 18] FIG. 1 is a diagram showing the 1H-NMR spectrum of Compound A8 according to Synthesis Example 8. [Figure 19] FIG. 1 shows the 13C-NMR spectrum of Compound A8 according to Synthesis Example 8. DETAILED DESCRIPTION OF THE INVENTION

[0017] Preferred embodiments of the present invention will be described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings on carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. In the following drawings, components and parts having the same function may be denoted by the same reference numerals, and redundant explanations may be omitted or simplified. The embodiments shown in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the actual product.

[0018] In this specification, the term "double bond-containing ring" encompasses both conjugated double bond-containing rings and non-conjugated double bond-containing rings, and is preferably a ring that corresponds to at least one of an aromatic ring and a heterocyclic ring (heterocycle). The heterocycle may have a structure encompassed by an aromatic ring (heteroaromatic ring), or may have a double bond-containing heterocyclic structure different from an aromatic ring. The heteroatoms contained as ring-constituting atoms in the heterocycle may be, for example, one or more selected from the group consisting of nitrogen (N), sulfur (S), and oxygen (O). Non-limiting examples of the double bond-containing ring include carbocyclic rings such as a benzene ring; a fused ring of a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, or a phenanthrene ring; and heterocyclic rings such as a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a pyrrole ring, a pyrazole ring, an imidazole ring, a triazole ring, an oxazole ring, an isoxazole ring, a thiazole ring, or a thiophene ring. The double bond-containing ring may be a non-fused ring (such as a benzene ring or a triazine ring) or a fused ring. The fused ring may have a structure in which one or more carbon rings are fused with one or more heterocyclic rings, such as a dinaphthothiophene structure or a benzotriazole structure.

[0019] Unless otherwise specified, the double bond-containing ring in this specification may have one or more substituents on the ring-constituting atoms, or may have no substituents. In this specification, examples of the "substituent" include an alkyl group (e.g., an alkyl group having 1 to 12 carbon atoms), an aryl group (including a phenyl group, a naphthyl group, a biphenyl group, etc., which may have one or more acyclic substituents on the ring-constituting atoms, such as an alkyl group, a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom), a hydroxyl group, an amino group, a monoalkylamino group, a dialkylamino group, and a cyano group), a cycloalkyl group, a hydroxyalkyl group, a monoalkylamino group, a dialkylamino group, a glycidyl group, an aralkyl group (e.g., a group having a structure in which one or more hydrogen atoms of an alkyl group having 1 to 12 carbon atoms, preferably 1 to 8 carbon atoms, are substituted with the above-mentioned aryl group), an alkenyl group (e.g., a vinyl group, an allyl group), a (meth)acryloyl group, and other ethylenically unsaturated groups, and groups having an ether bond, a thioether bond, or the like in the middle of the chain structure of these groups. Examples of such groups include, but are not limited to, groups containing one or more bonds selected from the group consisting of ether bonds and ester bonds (e.g., ethoxyethyl, ethoxyethoxyethyl, and phenoxyethyl groups); groups in which some or all of the hydrogen atoms bonded to carbon in these groups have been replaced with halogen atoms (e.g., fluorine, chlorine, and bromine atoms); groups having a heteroatom such as O, S, or N at the end of the double bond-containing ring side of these groups (e.g., alkoxy, aryloxy, cycloalkyloxy, hydroxyalkyloxy, glycidyloxy, alkylthio, and (meth)acryloyloxy groups; when the heteroatom is N, the remaining valence of the N is bonded to a hydrogen atom or another substituent); hydroxyl, amino, cyano, and halogen atoms (e.g., fluorine, chlorine, and bromine atoms). Examples of the above substituents include both those having a double bond-containing ring (e.g., aryl groups, aralkyl groups, and groups having a heteroatom such as O, S, or N at the end of these groups on the ring-constituting atom side) and those not having a double bond-containing ring (e.g., alkyl groups, alkoxy groups, alkylthio groups, etc.).

[0020] In this specification, the "base polymer" of a PSA refers to the main rubbery polymer component contained in the PSA. The rubbery polymer is a polymer that exhibits rubber elasticity in a temperature range around room temperature. In this specification, unless otherwise specified, the "main component" refers to a component that accounts for more than 50% by weight.

[0021] In this specification, the term "acrylic polymer" refers to a polymer containing, as a monomer unit constituting the polymer, a monomer unit derived from a monomer having at least one (meth)acryloyl group in one molecule. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule is also referred to as an "acrylic monomer." Therefore, in this specification, an acrylic polymer is defined as a polymer containing a monomer unit derived from an acrylic monomer. A typical example of an acrylic polymer is an acrylic polymer in which more than 50% by weight (preferably more than 70% by weight, for example more than 90% by weight) of the monomer components constituting the polymer are acrylic monomers.

[0022] Furthermore, in this specification, "acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl group" refers to an acryloyl group and a methacryloyl group in a comprehensive sense. Therefore, the concept of acrylic monomer here can include both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer). Similarly, in this specification, "(meth)acrylic acid" refers to acrylic acid and methacrylic acid in a comprehensive sense, and "(meth)acrylate" refers to acrylate and methacrylate in a comprehensive sense. The same applies to other similar terms.

[0023] <Refractive index adjuster> The refractive index modifier disclosed in this specification is an organic compound having a structure including a hub ring and two or more substituents bonded to constituent atoms of the hub ring. Here, the hub ring is a double-bond-containing ring, and at least one of the two or more substituents is a substituent having a double-bond-containing ring. Compounds that satisfy these structural requirements are useful as refractive index modifiers used as components of pressure-sensitive adhesives to adjust the refractive index of the pressure-sensitive adhesive.

[0024] The refractive index control agent disclosed herein may be a non-polymer, or may be a polymer having two or more repeating units of the above structure (i.e., a structure having a hub ring and two or more substituents bonded to constituent atoms of the hub ring). When the refractive index control agent is a polymer, the number of repeating units in the polymer is, for example, 2 to 30 or 2 to 10, preferably 2 to 6, and more preferably 2 to 4 (e.g., 2 to 3).

[0025] The molecular weight of the refractive index adjuster is not particularly limited and can be appropriately selected within a range that can exhibit the intended function. The molecular weight of the refractive index adjuster may be, for example, less than approximately 10,000, less than 7,000, less than 5,000, less than 3,500, or less than 3,000. In some embodiments, from the viewpoint of ease of incorporation into the adhesive, the molecular weight of the refractive index adjuster is advantageously less than 3,000, preferably less than 2,000, more preferably less than 1,500, less than 1,000, less than 800, less than 700, or less than 650. The molecular weight of the refractive index adjuster may also be, for example, 150 or more, 200 or more, or 250 or more. In some embodiments, from the viewpoint of easily performing the function of adjusting the refractive index (e.g., increasing the refractive index), the molecular weight of the refractive index adjuster is suitably 300 or more, preferably 350 or more, more preferably 400 or more, or may be 430 or more, 470 or more, 500 or more, or may be 550 or more. It is also preferable that the molecular weight of the refractive index adjuster is not too low from the viewpoint of the heat resistance of the pressure-sensitive adhesive and suppression of contamination of the adherend.

[0026] When the refractive index modifier is a non-polymer or a polymer with a low degree of polymerization (e.g., about dimer to pentamer), the molecular weight of the refractive index modifier can be calculated based on the chemical structure or measured using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS). For polymers with a higher degree of polymerization, the weight-average molecular weight (Mw) determined by GPC performed under appropriate conditions can be used. If the manufacturer provides a nominal value for the molecular weight, that nominal value can be used.

[0027] The hub ring in the refractive index adjuster disclosed herein is typically a double-bond-containing ring that corresponds to at least one of an aromatic ring and a heterocyclic ring (preferably a heteroaromatic ring). The hub ring may be a non-fused ring (monocyclic ring) or a fused ring, but is preferably a non-fused ring (e.g., a 3- to 8-membered ring, preferably a 5- to 7-membered ring). In some preferred embodiments, the hub ring is a non-fused heteroaromatic ring. The number of heteroatoms contained as ring-constituting atoms in the heteroaromatic ring may be one or more, for example, 1 to 3. In some embodiments, a heteroaromatic ring in which at least one of the heteroatoms contained as ring-constituting atoms is N is preferred, and a heteroaromatic ring in which all of the heteroatoms are N is more preferred. A triazine ring is a particularly preferred example of a heteroaromatic ring.

[0028] The number of substituents bonded to ring-constituting atoms of the hub ring is typically 2 or more and not more than the number of ring-constituting atoms, for example, 3 or more and not more than the number of ring-constituting atoms. The number of substituents having a double bond-containing ring among the substituents may be 1 or more, 2 or more, or 3 or more. The number of substituents not having a double bond-containing ring among the substituents may be 0, 1 or more and not more than the total number of the substituents minus 1, or 1 or more and not more than the total number of the substituents minus 2. The total number of substituents refers to the total number of substituents bonded to ring-constituting atoms of the hub ring, regardless of whether the substituent has a double bond-containing ring or not.

[0029] Among the substituents bonded to the ring-constituting atoms of the hub ring, those having a double bond-containing ring can contribute to improving the refractive index. A refractive index improver according to some embodiments has two or more substituents having a double bond-containing ring on the hub ring. A refractive index adjuster having such a structure can be used as a constituent component of a pressure-sensitive adhesive to efficiently adjust the refractive index of the pressure-sensitive adhesive (e.g., to increase the refractive index).

[0030] In the substituent having a double bond-containing ring, the number of double bond-containing rings possessed by the substituent may be one or two or more. Here, "having two or more double bond-containing rings" means having two or more double bond-containing rings that are not fused to each other. Each double bond-containing ring may independently be a non-fused ring or a fused ring. Having a substituent having two or more double bond-containing rings on a hub ring can be advantageous from the viewpoint of improving the refractive index. A refractive index improver according to some embodiments has one or more (preferably two or more, for example, three) substituents having two or more double bond-containing rings on the hub ring. A refractive index adjuster having such a structure can be used as a constituent component of a pressure-sensitive adhesive to efficiently adjust the refractive index of the pressure-sensitive adhesive (for example, to increase the refractive index).

[0031] In the substituent having two or more double bond-containing rings, the two or more double bond-containing rings may be chemically bonded directly (i.e., not via any other atom) as in a biphenyl structure, or may be bonded via a linking group. Examples of the linking group include an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (e.g., -O-(CH2)), and the like. n - group, where n is 1 to 3, preferably 1), thiooxyalkylene groups (e.g., -S-(CH2) n - group, where n is 1 to 3, preferably 1), straight chain alkylene groups (i.e., -(CH2) n - group, where n is 1 to 6, preferably 1 to 3), -NR 4 -group(R 4 represents a hydrogen atom or an alkyl group (for example, an alkyl group having 1 to 3 carbon atoms, preferably 1), -NR 4 -(CH2) n - group (n is 1 to 3, preferably 1), R 4 is a hydrogen atom or an alkyl group (for example, an alkyl group having 1 to 3 carbon atoms, preferably 1 carbon atom), the oxyalkylene group, the thiooxyalkylene group, the straight-chain alkylene group, and the —NR 4 -(CH2) nThe alkylene group in the - group may be a group in which it is partially halogenated or completely halogenated, etc. The linking group may have an ester bond. The number of atoms in the linking group is, for example, 1 to 6, preferably 1 to 4, and may be 1 to 2, 2, or 1. The number of atoms in the linking group refers to the minimum number of atoms required to reach from one double bond-containing ring to the other double bond-containing ring. For example, when the linking group is a straight-chain alkylene group (i.e., -(CH2) n -group), the number n is the number of atoms in the linking group. Preferred examples of the substituent from the viewpoint of increasing the refractive index include substituents containing a structure in which the two or more double bond-containing rings are chemically bonded directly or via an oxy group or a thiooxy group.

[0032] In some preferred embodiments, the substituent having the double bond-containing ring is bonded to a ring-constituting atom (e.g., a carbon atom) of the hub ring via a heteroatom (e.g., O, S, or N, preferably O or S) contained in the substituent. Compounds having such a structure are preferred because they can be suitable for increasing the refractive index of the compound itself or a composition containing the compound. The heteroatom bonded to the ring-constituting atom of the hub ring may be a ring-constituting atom of the double bond-containing ring (heterocycle) in the substituent having the double bond-containing ring, or may be an atom constituting a linking group connecting the double bond-containing ring and the hub ring. Examples of the linking group include a thiooxy group, an oxyalkylene group (e.g., -O-(CH2) n - group, where n is 1 to 3, preferably 1), thiooxyalkylene groups (e.g., -S-(CH2) n - group, where n is 1 to 3, preferably 1), -NR 4 -group, -NR 4 -(CH2) n - group (n is 1 to 3, preferably 1), R 4is a hydrogen atom or an alkyl group (for example, an alkyl group having 1 to 3 carbon atoms, preferably 1). The number of atoms in the linking group connecting the double bond-containing ring and the hub ring is, for example, 1 to 6, preferably 1 to 4, and may be 1 to 2, 2, or 1. The number of atoms in the linking group refers to the minimum number of atoms required to reach the double bond-containing ring of the substituent from the hub ring.

[0033] The double-bond-containing ring having a substituent bonded to a ring-constituting atom of the hub ring is typically an aromatic ring or a heterocyclic ring, and is preferably a non-fused ring. The double-bond-containing ring may have, on its ring-constituting atom, one or more substituents other than the substituent bonded to the hub ring or the substituent bonded to another double-bond-containing ring. Examples of such substituents include acyclic substituents such as alkyl groups, alkoxy groups, alkylthio groups, alkenyl groups, (meth)acryloyl groups, (meth)acryloyloxy groups, halogen atoms, hydroxyl groups, amino groups, monoalkylamino groups, dialkylamino groups, and cyano groups; and substituents having a non-double-bond-containing ring, such as cycloalkyl groups, cycloalkyloxy groups, and norbornyl groups. The alkyl groups contained in the alkyl groups, alkoxy groups, alkylthio groups, alkenyl groups, monoalkylamino groups, and dialkylamino groups each have, for example, 1 to 6 carbon atoms, preferably 1 to 4, and may be 1 to 2, 2, or 1.

[0034] In some preferred embodiments, the double bond-containing ring having a substituent bonded to a ring-constituting atom of the hub ring is an aromatic ring (preferably a carbon aromatic ring, particularly preferably a benzene ring) having or having no substituent. For example, at least one (e.g., one, two, or three) of the ring-constituting atoms of the hub ring has a group represented by the following formula (II): -X(CH2) n -Ar(Y) m (II) (In the above formula (II), X is —O—, —S—, or —NR 4 -(where R 4is selected from the group consisting of a hydrogen atom or an alkyl group, and is preferably -O- or -S-. n is 0 to 3, preferably 0 or 1, and more preferably 0. Ar is an aromatic ring, preferably a carbocyclic aromatic ring, and particularly preferably a benzene ring. Y is a substituent on a ring-constituting atom of Ar, and each Y is independently selected from the group consisting of an alkyl group (for example, an alkyl group having 1 to 3 carbon atoms, preferably 1), a cyano group, a hydroxyl group, a phenyl group, a tolyl group, a xylyl group, and a phenoxy group. m is 0 to 3, preferably 0 or 1, and more preferably 1. A compound having a structure in which a substituent represented by the following formula is bonded is preferred.

[0035] The refractive index modifier disclosed herein may have only the above-mentioned double bond-containing ring-containing substituent as the substituent bonded to the ring-constituting atoms of the hub ring. Such a structure allows more substituents having double bond-containing rings to be bonded to the hub ring, making it suitable for achieving a high refractive index. Meanwhile, the refractive index modifier disclosed herein may have both a double bond-containing ring-containing substituent and a double bond-free ring-free substituent as the substituents bonded to the ring-constituting atoms of the hub ring. In some embodiments, having the above-mentioned double bond-free ring-free substituent on the hub ring can contribute to improving solubility in solvents and compatibility in pressure-sensitive adhesives.

[0036] In an embodiment in which at least one of the substituents bonded to the ring-constituting atoms of the hub ring is a substituent not having a double bond-containing ring, the substituent not having a double bond-containing ring is each independently, for example, an alkyl group, a cycloalkyl group, a hydroxyalkyl group, an alkoxy group (e.g., a methoxy group, an ethoxy group), a hydroxyalkyloxy group, a glycidyloxy group, an alkylthio group (-SC n H 2n+1group), a monoalkylamino group, a dialkylamino group, an alkenyl group, a (meth)acryloyl group, a (meth)acryloyloxy group, a group in which one or more bonds selected from the group consisting of an ether bond, a thioether bond, and an ester bond are inserted in the chain structure of these groups, a group in which some or all of the hydrogen atoms bonded to carbon atoms in these groups have been replaced with halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), a hydroxyl group, an amino group, a cyano group, or a halogen atom.

[0037] Among the above-mentioned examples of substituents not having a double bond-containing ring, those containing an alkyl group in the substituent (such as an alkyl group, an alkoxy group, an alkylthio group, or an ethoxyethyl group) have, for example, 1 to 12 carbon atoms, preferably 2 to 12, 4 to 12, or 6 to 10 carbon atoms in some embodiments, and preferably 1 to 6, 1 to 4, or 1 to 2 carbon atoms in other embodiments. When the alkyl group has 3 or more atoms, the alkyl group may be linear or branched. Specific examples of branched alkyl groups include a 2-ethylhexyl group, an isooctyl group, and an isononyl group. Suitable examples of the substituent not having a double bond-containing ring include alkoxy groups (for example, alkoxy groups having 1 to 12, 1 to 8, 1 to 6, 1 to 4, or 1 to 2 carbon atoms) and alkylthio groups (for example, alkylthio groups having 2 to 12, 4 to 12, or 6 to 10 carbon atoms).

[0038] A preferred example of the refractive index adjuster disclosed herein is a triazine compound represented by the following formula (I). [ka]

[0039] In the above formula (I), X 1 ,X 2 and X 3 are each independently -O-, -S- and -NR 4 where R 4is a hydrogen atom or an alkyl group (for example, an alkyl group having 1 to 3 carbon atoms). 1 ,R 2 and R 3 At least one of R is independently an aromatic ring-containing group selected from the group consisting of an optionally substituted phenyl group and an optionally substituted biphenyl group. 1 ,R 2 and R 3 When there are two or less aromatic ring-containing groups among the above, the remainder are aliphatic hydrocarbon groups or hydrogen atoms.

[0040] In the formula (I), when the phenyl group or the biphenyl group has a substituent, the substituent is preferably each independently selected from the group consisting of an alkyl group (e.g., an alkyl group having 1 to 3 carbon atoms), an alkoxy group (e.g., an alkoxy group having 1 to 3 carbon atoms), and a cyano group. The aliphatic hydrocarbon group is preferably an alkyl group having 1 to 12, 1 to 8, 1 to 6, 1 to 4, or 1 to 2 carbon atoms, or an alkyl group having 2 to 12, 4 to 12, or 6 to 10 carbon atoms.

[0041] In the above formula (I), X 1 ,X 2 and X 3 From the viewpoint of increasing the refractive index, X 1 ,X 2 and X 3 Advantageously, two or more of X are selected from -O- and -S-. 1 ,X 2 and X 3 Compounds where each of X is -O- 1 ,X 2 and X 3 Compounds in which two or more of the groups are -S-, X 1 ,X 2 and X 3 In particular, compounds in which X 1 ,X 2 and X 3 are preferably —S—.

[0042] In the above formula (I), R 1 ,R 2 and R 3 From the viewpoint of increasing the refractive index, R 1 ,R 2 and R 3 are preferably aromatic ring-containing groups, and from the viewpoint of ease of synthesis, R 1 ,R 2 and R 3 are preferably the same aromatic ring-containing group. 1 ,R 2 and R 3 are both optionally substituted biphenyl groups (e.g., compounds in which R 1 ,R 2 and R 3 In terms of achieving a high refractive index, compounds in which R 1 ,R 2 and R 3 When one, two or three of the groups are optionally substituted biphenyl groups, the biphenyl group is preferably 2-biphenyl or 4-biphenyl from the viewpoint of ease of synthesis. 1 ,X 2 ,X 3 is bonded to the carbon atom at the 2nd position (ortho position) of the biphenyl group, and 4-biphenyl means that the corresponding X 1 ,X 2 ,X 3 is bonded to the carbon atom at the 4-position (para-position) of the biphenyl group. 1 ,R 2 and R 3 A compound in which each of the groups is a 2-biphenyl group is particularly preferred from the viewpoint of achieving a high refractive index and solubility in a solvent.

[0043] The compound represented by the above formula (I) can be synthesized, for example, by a method including reacting a commercially available halogenated triazine compound (cyanuric chloride, 2-(4-cyanophenyl)amino-4,6-dichloro-1,3,5-triazine, etc.) with an alcohol compound or a thiol compound depending on the structure of the target compound.

[0044] The refractive index of the refractive index adjuster disclosed herein is not particularly limited as long as it can be blended with an adhesive to adjust the refractive index of the adhesive to a desired range. The refractive index of the refractive index adjuster can be, for example, within the range of 1.500 to 2.000. The refractive index of the refractive index adjuster refers to the refractive index measured at a temperature of 25°C and a wavelength of 594 nm. The refractive index of the refractive index adjuster can be measured using a commercially available measuring device (for example, a prism coupler, model "2010M" manufactured by Metricon).

[0045] In some embodiments, the refractive index of the refractive index modifier may be, for example, 1.530 or higher, suitably 1.550 or higher, advantageously 1.560 or higher, preferably 1.580 or higher, and more preferably 1.590 or higher. In some preferred embodiments, the refractive index of the refractive index modifier may be, for example, 1.600 or higher, 1.610 or higher, 1.630 or higher, 1.650 or higher, 1.660 or higher, 1.670 or higher, 1.680 or higher, 1.690 or higher, or 1.700 or higher. A refractive index modifier with a higher refractive index can more efficiently achieve the effect of increasing the refractive index when incorporated into an adhesive. Furthermore, from the perspective of ease of synthesis and cost of the refractive index modifier, in some embodiments, the refractive index of the refractive index modifier may be 1.900 or lower, 1.800 or lower, 1.780 or lower, 1.750 or lower, or 1.730 or lower. In some embodiments of the refractive index control agent disclosed herein, the refractive index of the refractive index control agent is, for example, 1.590 or more and 1.750 or less, preferably 1.610 or more and 1.750 or less, more preferably 1.640 or more and 1.750 or less, and may be 1.660 or more and 1.730 or less, or 1.680 or more and 1.730 or less.

[0046] The refractive index control agent disclosed herein is preferably soluble in a solvent (typically an organic solvent) from the viewpoint of ease of incorporation into a pressure-sensitive adhesive. Here, "soluble" means that a solution containing the refractive index control agent at a concentration of at least 2 wt % or more (preferably 5 wt % or more, more preferably 10 wt % or more, even more preferably 20 wt % or more, and particularly preferably 40 wt % or more) can be prepared. For example, the refractive index control agent is preferably soluble in at least one of the following solvents: acetate esters such as ethyl acetate and butyl acetate; lower ketones such as acetone and methyl ethyl ketone (MEK); and aromatic hydrocarbon solvents such as benzene and toluene; and is particularly preferably soluble in one or both of ethyl acetate and MEK.

[0047] In the refractive index adjusters disclosed herein (e.g., triazine compounds represented by formula (I) above), advantageous structural features from the viewpoint of solubility in a solvent include (i) a non-planar shape and (ii) rotational non-symmetry with respect to the hub ring. Compounds that meet either (i) or (ii) above, or both, are preferred. Suitable examples of compounds that meet (i) above include compounds (A1) and (A4) described in the Examples below. These compounds have a ball-like (non-planar) shape overall due to their molecular structure. Furthermore, for example, compound (A5) described in the Examples below is rotationally symmetric (has a three-fold rotation axis), whereas compound (A6) is rotationally non-symmetric and falls under (ii) above. Compounds that satisfy (i) above and are rotationally symmetric with respect to the hub ring are preferred because they can have a high refractive index and good solubility.

[0048] <Adhesive> The pressure-sensitive adhesive disclosed herein is characterized by containing a refractive index adjuster as described above. The type of pressure-sensitive adhesive is not particularly limited, and may be, for example, an acrylic pressure-sensitive adhesive, a rubber pressure-sensitive adhesive (natural rubber-based, synthetic rubber-based, a mixture thereof, etc.), a silicone pressure-sensitive adhesive, a polyester pressure-sensitive adhesive, a urethane pressure-sensitive adhesive, a polyether pressure-sensitive adhesive, a polyamide pressure-sensitive adhesive, a fluorine-based pressure-sensitive adhesive, etc. The acrylic pressure-sensitive adhesive refers to a pressure-sensitive adhesive having an acrylic polymer as the base polymer. The same applies to other rubber-based pressure-sensitive adhesives. In some embodiments, acrylic pressure-sensitive adhesives are preferred from the viewpoints of ease of adjusting adhesive properties, optical properties, etc.

[0049] The adhesive disclosed herein can be formed using an adhesive composition containing a refractive index modifier (typically, an adhesive composition containing at least a base polymer and a refractive index modifier). The form of the adhesive composition is not particularly limited, and can be in various forms, such as a solvent-based adhesive composition containing adhesive-forming components in an organic solvent; an active energy ray-curable adhesive composition prepared to form an adhesive by curing (converting into a viscoelastic body) with active energy rays such as ultraviolet light or radiation; a water-dispersed adhesive composition in which adhesive-forming components are dispersed in water; or a hot-melt adhesive composition that is applied in a heated, molten state and forms an adhesive upon cooling to near room temperature. While not particularly limited, the adhesive disclosed herein can be preferably formed using a solvent-based adhesive composition from the viewpoint of ease of blending the refractive index modifier. Solvent-based adhesive compositions can typically be formed by drying (preferably further crosslinking) the composition to form the adhesive. Active energy ray-curable adhesive compositions are typically formed by irradiating them with active energy rays to promote polymerization and / or crosslinking reactions. When the active energy ray-curable pressure-sensitive adhesive composition needs to be dried, it is preferable to irradiate the active energy ray after drying.

[0050] The content of the refractive index adjuster in the adhesive is not particularly limited and can be set so as to obtain an adhesive having the desired refractive index. In some embodiments, the amount of the refractive index adjuster used relative to 100 parts by weight of the base polymer (e.g., acrylic polymer) of the adhesive can be, for example, 0.1 parts by weight or more. From the viewpoint of obtaining a higher effect of use, it is preferably 0.5 parts by weight or more, more preferably 1 part by weight or more, and may be 3 parts by weight or more, 5 parts by weight or more, 7 parts by weight or more, or even 9 parts by weight or more. Furthermore, the amount of the refractive index adjuster used relative to 100 parts by weight of the base polymer can be, for example, 80 parts by weight or less. From the viewpoint of easily obtaining good adhesive properties, it is advantageous to use it relative to 60 parts by weight or less, preferably 45 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, 20 parts by weight or less, or 15 parts by weight or less.

[0051] Refractive index n of the refractive index adjuster a and the refractive index n of the adhesive containing the refractive index adjuster T The absolute value of the difference between |n a -n T |(Hereinafter, |Δn A ) can be set to be greater than 0. In some embodiments, |Δn A is, for example, 0.010 or more, preferably 0.020 or more, more preferably 0.030 or more, may be 0.040 or more, 0.060 or more, 0.080 or more, 0.100 or more, 0.150 or more, 0.200 or more, or 0.250 or more. A It can be said that a pressure-sensitive adhesive having a large value of | has a refractive index adjuster that contributes more to the refractive index of the pressure-sensitive adhesive. In addition, in some embodiments, from the viewpoint of compatibility within the pressure-sensitive adhesive, transparency of the pressure-sensitive adhesive, etc., |Δn A The refractive index n of the refractive index adjuster may be, for example, 0.500 or less, 0.400 or less, 0.300 or less, 0.250 or less, less than 0.200, or less than 0.100. a and the refractive index of the adhesive, n T The relationship between a >n T But often, n a <n T That is, 0<Δn A Or, 0>Δn A The refractive index control agent disclosed herein can exhibit a higher refractive index than general adhesives (for example, acrylic adhesives), and therefore, for example, 0<Δn A In this embodiment, it can be preferably used as a refractive index increasing agent for pressure sensitive adhesives.

[0052] Refractive index n of the refractive index adjuster a and the refractive index of the base polymer, n b The absolute value of the difference between |n b -n a |(Hereinafter, |Δn B ) is set to be greater than 0. In some embodiments, |Δn Bis, for example, 0.010 or more, preferably 0.020 or more, more preferably 0.035 or more, may be 0.045 or more, 0.065 or more, 0.075 or more, 0.090 or more, 0.100 or more, 0.150 or more, 0.200 or more, or 0.250 or more. B By selecting a base polymer and a refractive index modifier so that the value of | is large, the refractive index modifier's effect of adjusting the refractive index tends to be enhanced. In addition, from the viewpoint of compatibility within the adhesive, transparency of the adhesive, etc., in some embodiments, |Δn B may be, for example, 0.550 or less, 0.450 or less, 0.350 or less, 0.300 or less, less than 0.250, less than 0.150, or less than 0.130. The refractive index n of the refractive index adjuster a and the refractive index of the base polymer, n b The relationship between a >n b But often, n a <n b That is, 0<Δn B Or, 0>Δn B The refractive index control agent disclosed herein can exhibit a higher refractive index than the base polymer of a general pressure-sensitive adhesive (for example, an acrylic polymer), and therefore, for example, 0<Δn B In this embodiment, it can be preferably used as a refractive index increasing agent for pressure sensitive adhesives.

[0053] The PSA disclosed herein will be further described below mainly using an acrylic PSA as an example, but it is not intended to limit the PSA disclosed herein to acrylic PSA.

[0054] Some preferred embodiments of the PSA are acrylic PSAs that use an acrylic polymer as a base polymer and contain an aromatic ring-containing monomer (m1) as a monomer component constituting the acrylic polymer. The refractive index adjuster disclosed herein can be used in PSAs containing such base polymers to effectively adjust (e.g., increase) the refractive index of the PSA. Herein, the term "monomer component constituting the acrylic polymer" refers to a monomer that constitutes a repeating unit of the acrylic polymer in the PSA formed from the PSA composition, regardless of whether the monomer component is contained in the PSA composition in the form of a preformed polymer (which may be an oligomer) or an unpolymerized monomer. That is, the monomer component constituting the acrylic polymer may be contained in the PSA composition in the form of a polymer, an unpolymer, or a partially polymerized monomer. From the viewpoint of ease of preparation of the PSA composition, etc., in some embodiments, PSA compositions in which substantially all (e.g., 95 wt. % or more, preferably 99 wt. % or more) of the monomer component constituting the acrylic polymer is in the form of a polymer are preferred.

[0055] (Monomer (m1)) As the monomer (m1), a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule can be used. As the monomer (m1), one of such compounds can be used alone or two or more of them can be used in combination.

[0056] Examples of the ethylenically unsaturated group include a (meth)acryloyl group, a vinyl group, and a (meth)allyl group. From the viewpoint of polymerization reactivity, a (meth)acryloyl group is preferred, and from the viewpoints of flexibility and adhesiveness, an acryloyl group is more preferred. From the viewpoint of the flexibility of the adhesive, a compound containing one ethylenically unsaturated group per molecule (i.e., a monofunctional monomer) is preferably used as the monomer (m1).

[0057] The number of aromatic rings contained in one molecule of the compound used as monomer (m1) may be 1 or 2 or more. The upper limit of the number of aromatic rings is not particularly limited and may be, for example, 16 or less. In some embodiments, from the viewpoint of ease of preparation of the PSA composition, transparency of the PSA, etc., the number of aromatic rings may be, for example, 12 or less, preferably 8 or less, more preferably 6 or less, or may be 5 or less, 4 or less, 3 or less, or 2 or less.

[0058] The aromatic ring of the compound used as monomer (m1) may be a carbocyclic ring such as a benzene ring (which may be a benzene ring constituting a part of a biphenyl structure or a fluorene structure); a fused ring of a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, or a phenanthrene ring; or a heterocyclic ring such as a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, a pyrrole ring, a pyrazole ring, an imidazole ring, a triazole ring, an oxazole ring, an isoxazole ring, a thiazole ring, or a thiophene ring. The heteroatoms contained as ring-constituting atoms in the heterocyclic ring may be, for example, one or more selected from the group consisting of nitrogen, sulfur, and oxygen. In some embodiments, the heteroatoms constituting the heterocyclic ring may be either or both nitrogen and sulfur. Monomer (m1) may have a structure in which one or more carbocyclic rings are fused with one or more heterocyclic rings, such as a dinaphthothiophene structure.

[0059] The aromatic ring (preferably a carbocyclic ring) may have one or more substituents on the ring-constituting atoms, or may have no substituents. When the aromatic ring has a substituent, examples of the substituent include, but are not limited to, an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom (such as a fluorine atom, a chlorine atom, or a bromine atom), a hydroxyalkyl group, a hydroxyalkyloxy group, and a glycidyloxy group. In a carbon atom-containing substituent, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. In some embodiments, the aromatic ring may have no substituents on the ring-constituting atoms, or may have one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen atom (such as a bromine atom). The term "the aromatic ring of the monomer (m1) has a substituent on its ring-constituting atom" refers to the aromatic ring having a substituent other than a substituent having an ethylenically unsaturated group.

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

[0061] Examples of compounds that can be preferably used as the monomer (m1) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. The aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds can be used alone or in combination of two or more. One or more aromatic ring-containing (meth)acrylates and one or more aromatic ring-containing vinyl compounds can be used in combination.

[0062] In some embodiments, a monomer having two or more aromatic rings (preferably carbon rings) in one molecule can be used as the monomer (m1) because it is easy to obtain a high refractive index effect. Examples of a monomer having two or more aromatic rings in one molecule (aromatic ring-containing monomer) include a monomer having a structure in which two or more non-condensed aromatic rings are bonded via a linking group, a monomer having a structure in which two or more non-condensed aromatic rings are chemically bonded directly (i.e., without the intervention of other atoms), a monomer having a condensed aromatic ring structure, a monomer having a fluorene structure, a monomer having a dinaphthothiophene structure, a monomer having a dibenzothiophene structure, etc. The aromatic ring-containing monomer can be used alone or in combination of two or more.

[0063] The linking group may be, for example, an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (e.g., -O-(CH2) n - group, where n is 1 to 3, preferably 1), thiooxyalkylene groups (e.g., -S-(CH2) n - group, where n is 1 to 3, preferably 1), straight chain alkylene groups (i.e., -(CH2) n- group (where n is 1 to 6, preferably 1 to 3), the oxyalkylene group, the thiooxyalkylene group, and the linear alkylene group in which the alkylene group is partially or completely halogenated. From the viewpoint of the flexibility of the adhesive, suitable examples of the linking group include an oxy group, a thiooxy group, an oxyalkylene group, and a linear alkylene group. Specific examples of monomers having a structure in which two or more non-condensed aromatic rings are bonded via a linking group include phenoxybenzyl (meth)acrylate (e.g., m-phenoxybenzyl (meth)acrylate), thiophenoxybenzyl (meth)acrylate, benzyl benzyl (meth)acrylate, etc.

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

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

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

[0067] Examples of the monomer having the dinaphthothiophene structure include (meth)acryloyl group-containing dinaphthothiophene, vinyl group-containing dinaphthothiophene, and (meth)allyl group-containing dinaphthothiophene. Specific examples include (meth)acryloyloxymethyl dinaphthothiophene (for example, dinaphthothiophene having CHCH(R) at the 5th or 6th position of the dinaphthothiophene ring). 1 )C(O)OCH2- bonded compound. 1 is a hydrogen atom or a methyl group), (meth)acryloyloxyethyl dinaphthothiophene (for example, CHCH(R 1 )C(O)OCH(CH3)- or CH2CH(R 1 )C(O)OCH2CH2- bonded compound. 1 is a hydrogen atom or a methyl group.), vinyl dinaphthothiophene (for example, a compound having a structure in which a vinyl group is bonded to the 5th or 6th position of a naphthothiophene ring), (meth)allyloxydinaphthothiophene, etc. Note that a monomer having a dinaphthothiophene structure is also included in the concept of a monomer having the above-mentioned fused aromatic ring structure because it contains a naphthalene structure or has a structure in which a thiophene ring and two naphthalene structures are fused together.

[0068] Examples of the monomer having the dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophene, vinyl group-containing dibenzothiophene, etc. Note that the monomer having the dibenzothiophene structure has a structure in which a thiophene ring and two benzene rings are fused, and therefore is included in the concept of the monomer having the fused aromatic ring structure. Note that neither the dinaphthothiophene structure nor the dibenzothiophene structure corresponds to a structure in which two or more non-fused aromatic rings are directly chemically bonded.

[0069] In some preferred embodiments, a monomer having one aromatic ring (preferably a carbon ring) per molecule is used as the monomer (m1). A monomer having one aromatic ring per molecule (aromatic ring single-containing monomer) can be useful, for example, for improving the flexibility of the adhesive, adjusting the adhesive properties, and improving the transparency. The aromatic ring single-containing monomer can be used alone or in combination of two or more. In some embodiments, a monomer having one aromatic ring per molecule may be used in combination with a monomer having multiple aromatic rings, from the viewpoint of improving the refractive index of the adhesive.

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

[0071] Monomer (m1) may be a monomer having an oxyethylene chain interposed between the ethylenically unsaturated group and the aromatic ring in the various aromatic ring-containing monomers described above. Such a monomer having an oxyethylene chain interposed between the ethylenically unsaturated group and the aromatic ring can be understood as an ethoxylated product of the original monomer. The number of repeating oxyethylene units (-CHCHO-) in the oxyethylene chain is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, for example, 1. Specific examples of ethoxylated aromatic ring-containing monomers include ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol di(meth)acrylate.

[0072] The content of the aromatic ring-containing monomer in the monomer (m1) is not particularly limited and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, the content of the aromatic ring-containing monomer in the monomer (m1) may be, for example, 50% by weight or more. From the viewpoint of easily obtaining a higher refractive index, it is preferably 70% by weight or more, or may be 85% by weight or more, 90% by weight or more, or may be 95% by weight or more. Substantially 100% by weight of the aromatic ring-containing monomer in the monomer (m1) may be. That is, only one or two or more aromatic ring-containing monomers may be used as the monomer (m1). In some embodiments, for example, taking into consideration the balance between a high refractive index and flexibility (e.g., viscoelastic properties such as storage modulus), the content of the aromatic ring-containing monomer in the monomer (m1) may be less than 100% by weight, 98% by weight or less, 90% by weight or less, 80% by weight or less, 70% by weight or less, 65% by weight or less, 50% by weight or less, 25% by weight or less, or 10% by weight or less. The technology disclosed herein can also be implemented in an embodiment in which the aromatic ring-containing monomer content in the monomer (m1) is less than 5% by weight. The aromatic ring-containing monomer need not be used.

[0073] The content of the aromatic ring-containing monomer in the monomer components constituting the acrylic polymer is not particularly limited and can be set according to the purpose. The content of the aromatic ring-containing monomer in the monomer components may be, for example, 3 wt% or more, 10 wt% or more, or 25 wt% or more. In some embodiments, from the viewpoint of easily realizing a pressure-sensitive adhesive having a higher refractive index, the content of the aromatic ring-containing monomer in the monomer components may be, for example, more than 35 wt%, advantageously more than 50 wt%, preferably more than 70 wt%, or may be 75 wt% or more, 85 wt% or more, 90 wt% or more, or even 95 wt% or more. In consideration of the balance between a high refractive index and flexibility, the content of the aromatic ring-containing monomer in the monomer components is advantageously approximately 99 wt% or less, preferably 98 wt% or less, more preferably 96 wt% or less, or may be 93 wt% or less, 90 wt% or less, 85 wt% or less, 80 wt% or less, or 75 wt% or less. In some embodiments, from the viewpoint of easily realizing higher adhesive properties and / or optical properties (e.g., transparency), the content of the multiple aromatic ring-containing monomer in the monomer component may be 70% by weight or less, 60% by weight or less, 50% by weight or less, 40% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight or less. The technology disclosed herein may also be implemented in an embodiment in which the content of the multiple aromatic ring-containing monomer in the monomer component is less than 3% by weight.

[0074] The content of the aromatic ring unit-containing monomer in the monomer (m1) is not particularly limited and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, the content of the aromatic ring unit-containing monomer in the monomer (m1) may be, for example, 50% by weight or more, and from the viewpoint of easily obtaining a higher refractive index, it is preferably 70% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. Substantially 100% by weight of the monomer (m1) may be the aromatic ring unit-containing monomer. That is, only one or two or more aromatic ring unit-containing monomers may be used as the monomer (m1). In some embodiments, for example, taking into consideration the balance between high refractive index and flexibility, the content of the aromatic ring unit-containing monomer in the monomer (m1) may be less than 100% by weight, 98% by weight or less, 90% by weight or less, 80% by weight or less, 70% by weight or less, 65% by weight or less, 50% by weight or less, 25% by weight or less, or 10% by weight or less. The technology disclosed herein can also be implemented in an embodiment in which the content of the aromatic ring unit-containing monomer in the monomer (m1) is less than 5% by weight. The aromatic ring unit-containing monomer need not be used.

[0075] The content of the aromatic ring unit-containing monomer in the monomer components constituting the acrylic polymer is not particularly limited and can be set according to the purpose. The content of the aromatic ring unit-containing monomer in the monomer components may be, for example, 3 wt% or more, 10 wt% or more, or 25 wt% or more. In some embodiments, from the viewpoint of easily realizing a pressure-sensitive adhesive having a higher refractive index, the content of the aromatic ring unit-containing monomer in the monomer components may be, for example, more than 35 wt%, advantageously more than 50 wt%, preferably more than 60 wt%, more preferably more than 70 wt%, even 75 wt% or more, 85 wt% or more, 90 wt% or more, 95 wt% or more, or even 98 wt% or more. The content of the aromatic ring unit-containing monomer in the monomer component may be approximately 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less, taking into consideration the balance between a high refractive index and flexibility. In some embodiments, from the viewpoint of easily achieving higher adhesive properties and / or optical properties (e.g., transparency), the content of the aromatic ring unit-containing monomer in the monomer component may be 70% by weight or less, 60% by weight or less, 50% by weight or less, 40% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight or less. The technology disclosed herein may also be implemented in an embodiment in which the content of the aromatic ring unit-containing monomer in the monomer component is less than 3% by weight.

[0076] In some embodiments of the technology disclosed herein, a high refractive index monomer may be preferably used as at least a portion of the monomer (m1). Here, "high refractive index monomer" refers to a monomer having a refractive index of, for example, about 1.510 or more, preferably about 1.530 or more, and more preferably about 1.550 or more. The upper limit of the refractive index of the high refractive index monomer is not particularly limited, but from the viewpoint of ease of preparation of the pressure-sensitive adhesive composition and ease of achieving compatibility with flexibility suitable for a pressure-sensitive adhesive, it may be, for example, 3.000 or less, 2.500 or less, 2.000 or less, 1.900 or less, 1.800 or less, or 1.700 or less. The high refractive index monomer may be used alone or in combination of two or more. The refractive index of the monomer is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C. The Abbe refractometer may be an ATAGO DR-M4 model or an equivalent. If the manufacturer provides a nominal value for the refractive index at 25°C, that nominal value may be used.

[0077] As the high refractive index monomer, a compound having the corresponding refractive index can be appropriately selected from compounds included in the concept of the aromatic ring-containing monomer (m1) disclosed herein (for example, the compounds and compound groups exemplified above). Specific examples include m-phenoxybenzyl acrylate (refractive index: 1.566, Tg of homopolymer: -35°C), 1-naphthylmethyl acrylate (refractive index: 1.595, Tg of homopolymer: 31°C), ethoxylated o-phenylphenol acrylate (number of repeating oxyethylene units: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, Tg of homopolymer: 6°C), phenoxyethyl acrylate (refractive index (nD20): 1.517, Tg of homopolymer: 2°C), and phenoxydiethylene glycol acrylate (refractive index: 1.510, Tg of homopolymer: 1.520). Examples of suitable dinaphthothiophene include, but are not limited to, 6-acryloyloxymethyl dinaphthothiophene (6MDNTA, refractive index: 1.75), 6-methacryloyloxymethyl dinaphthothiophene (6MDNTMA, refractive index: 1.726), 5-acryloyloxyethyl dinaphthothiophene (5EDNTA, refractive index: 1.786), 6-acryloyloxyethyl dinaphthothiophene (6EDNTA, refractive index: 1.722), 6-vinyl dinaphthothiophene (6VDNT, refractive index: 1.802), and 5-vinyl dinaphthothiophene (abbreviated as 5VDNT, refractive index: 1.793).

[0078] The content of the high refractive index monomer in the monomer (m1) (i.e., an aromatic ring-containing monomer having a refractive index of about 1.510 or more, preferably about 1.530 or more, more preferably about 1.550 or more) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, 35% by weight or more, or 40% by weight or more. In some embodiments, from the viewpoint of easily obtaining a higher refractive index, the content of the high refractive index monomer in the monomer (m1) may be, for example, 50% by weight or more, preferably 70% by weight or more, or 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomer (m1) may be the high refractive index monomer. In some embodiments, for example, from the viewpoint of achieving a good balance between a high refractive index and flexibility, the content of the high refractive index monomer in the monomer (m1) may be less than 100% by weight, 98% by weight or less, 90% by weight or less, 80% by weight or less, or 65% by weight or less.

[0079] The content of the high refractive index monomer in the monomer components constituting the acrylic polymer is not particularly limited and can be set according to the purpose. Furthermore, if necessary, it can be set taking into consideration compatibility with adhesive properties (e.g., adhesive strength) and / or optical properties (e.g., total light transmittance, haze value, etc.). The content of the high refractive index monomer in the monomer components may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, the content of the high refractive index monomer in the monomer components constituting the acrylic polymer may be, for example, more than 35% by weight. From the viewpoint of easily obtaining a higher refractive index, it is advantageous to be more than 50% by weight, preferably more than 70% by weight, more preferably 75% by weight or more, 85% by weight or more, 90% by weight or more, or even 95% by weight or more. From the viewpoint of achieving a good balance between a high refractive index and flexibility, the content of the high refractive index monomer in the above-mentioned monomer component is advantageously 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, or may be 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less.

[0080] In some preferred embodiments, an aromatic ring-containing monomer (hereinafter, sometimes referred to as "monomer L") having a homopolymer Tg of 10°C or less is used as at least a portion of the monomer (m1). Increasing the content of the aromatic ring-containing monomer (m1) (particularly the aromatic ring-containing monomer (m1) corresponding to at least one of the above-mentioned multiple aromatic ring-containing monomer, single aromatic ring-containing monomer, and high refractive index monomer) in the monomer components generally tends to increase the storage modulus G' of the PSA. However, by using monomer L as part or all of the monomer (m1), the increase in storage modulus G' can be suppressed. This allows the refractive index to be improved while better maintaining flexibility suitable for a PSA. The Tg of monomer L may be, for example, 5°C or less, 0°C or less, -10°C or less, -20°C or less, or -25°C or less. There is no particular lower limit for the Tg of monomer L. In consideration of the balance with the refractive index improving effect, in some embodiments, the Tg of the monomer L may be, for example, −70° C. or higher, −55° C. or higher, or −45° C. or higher. In other embodiments, the Tg of the monomer L may be, for example, −30° C. or higher, −10° C. or higher, 0° C. or higher, or 3° C. or higher. The monomer L may be used singly or in combination of two or more.

[0081] As the monomer L, a compound having the corresponding Tg can be appropriately selected from among the compounds encompassed by the concept of the aromatic ring-containing monomer (m1) disclosed herein (for example, the compounds and compound groups exemplified above). Suitable examples of aromatic ring-containing monomers that can be used as the monomer L include m-phenoxybenzyl acrylate (homopolymer Tg: -35°C), benzyl acrylate (homopolymer Tg: 6°C), phenoxyethyl acrylate (homopolymer Tg: 2°C), and phenoxydiethylene glycol acrylate (homopolymer Tg: -35°C).

[0082] The content of monomer L in monomer (m1) is not particularly limited and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, from the viewpoint of easily obtaining a PSA that simultaneously achieves a high refractive index and a high level of flexibility, the content of monomer L in monomer (m1) may be, for example, 50% by weight or more. From the viewpoint of reducing the modulus of elasticity, the content is preferably 60% by weight or more, and may be 70% by weight or more, 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. Monomer (m1) may account for substantially 100% by weight of monomer L. Furthermore, in some embodiments, from the viewpoint of simultaneously achieving a good balance between a high refractive index and flexibility, the content of monomer L in monomer (m1) may be less than 100% by weight, 98% by weight or less, 90% by weight or less, 80% by weight or less, or 65% by weight or less.

[0083] The content of monomer L in the monomer components constituting the acrylic polymer may be, for example, 3 wt% or more, 10 wt% or more, or 25 wt% or more. In some embodiments, from the viewpoint of easily obtaining a PSA that simultaneously achieves a high refractive index and a high level of flexibility, the content of monomer L in the monomer components may be, for example, more than 35 wt%, and from the viewpoint of improving the refractive index, it is advantageous to be more than 50 wt%, preferably more than 70 wt%, or it may be 75 wt% or more, 85 wt% or more, 90 wt% or more, or it may be 95 wt% or more. From the viewpoint of simultaneously achieving a good balance between a high refractive index and flexibility, the content of monomer L in the above-mentioned monomer components is advantageously about 99 wt% or less, preferably 98 wt% or less, more preferably 96 wt% or less, or it may be 93 wt% or less, 90 wt% or less, 85 wt% or less, 80 wt% or less, or it may be 75 wt% or less.

[0084] In some embodiments, the glass transition temperature Tg based on the composition of the monomer (m1) m1From the viewpoint of flexibility of the adhesive, the glass transition temperature Tg is suitably about 20°C or less, preferably 10°C or less, and may be, for example, 5°C or less, 0°C or less, -10°C or less, -20°C or less, or -25°C or less. m1 The lower limit of the glass transition temperature Tg is not particularly limited. m1 The glass transition temperature Tg may be, for example, −70° C. or higher, −55° C. or higher, or −45° C. or higher. m1 In some other embodiments, the glass transition temperature Tg m1 may be, for example, -10°C or higher, 0°C or higher, or 3°C or higher.

[0085] Here, the glass transition temperature Tg based on the composition of the monomer (m1) m1 The glass transition temperature (Tg) is calculated by the Fox formula (described later) based on the composition of only the monomer (m1) among the monomer components constituting the acrylic polymer. m1 The Tg and glass transition temperature Tg of the homopolymer of each aromatic ring-containing monomer used as the monomer (m1) can be calculated by applying Fox's formula to only the monomer (m1) among the monomer components constituting the acrylic polymer, and from the weight fraction of each aromatic ring-containing monomer in the total amount of the monomer (m1). In an embodiment in which only one type of monomer is used as the monomer (m1), the Tg and glass transition temperature Tg of the homopolymer of that monomer can be calculated. m1 is consistent with

[0086] In some embodiments, the aromatic ring-containing monomer (m1) can be a combination of monomer L (i.e., an aromatic ring-containing monomer having a homopolymer Tg of 10°C or less) and monomer H having a Tg higher than 10°C. The Tg of monomer H may be, for example, above 10°C, above 15°C, or above 20°C. By using monomer L and monomer H in combination, a PSA having a high content of aromatic ring-containing monomer (m1) in the monomer component can achieve both a high refractive index and flexibility suitable for adhesion to an adherend at a higher level. The ratio of the amounts of monomer L and monomer H used can be set so as to suitably exhibit this effect, and is not particularly limited. For example, when the Tg of any of the above-mentioned monomers is higher than 10°C, the PSA can be a high refractive index PSA having a high flexibility suitable for adhesion to an adherend. m1 It is preferable to set the ratio of the amounts of the monomers L and H used so as to satisfy the following.

[0087] In some embodiments, the aromatic ring-containing monomer (m1) can be preferably selected from compounds that do not contain a structure in which two or more non-fused aromatic rings are directly chemically bonded (e.g., a biphenyl structure). For example, an acrylic polymer composed of monomer components having a composition in which the content of a compound containing a structure in which two or more non-fused aromatic rings are directly chemically bonded is less than 5 wt% (more preferably less than 3 wt%, and may even be 0 wt%) is preferred. Limiting the amount of the compound containing a structure in which two or more non-fused aromatic rings are directly chemically bonded in this way can be advantageous from the perspective of realizing a pressure-sensitive adhesive that has a better balance between a high refractive index and flexibility.

[0088] The content of monomer (m1) in the monomer components constituting the acrylic polymer is not particularly limited and can be set depending on the purpose, for example, to realize a pressure-sensitive adhesive having one or more of the desired refractive index, elastic modulus, adhesive properties (e.g., adhesive strength), and optical properties (e.g., total light transmittance, haze value, etc.). In some embodiments, the content of monomer (m1) in the monomer components may be, for example, 30% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more, or even 70% by weight or more. In some preferred embodiments, the content of monomer (m1) in the monomer components constituting the acrylic polymer may be, for example, more than 70% by weight, suitably 75% by weight or more. From the viewpoint of easily obtaining a higher refractive index, it is preferably 80% by weight or more, and may be 85% by weight or more, 90% by weight or more, or even 95% by weight or more. The content of the monomer (m1) in the monomer component is typically less than 100% by weight, and from the viewpoint of achieving a good balance between a high refractive index and flexibility, it is advantageous to be approximately 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, and may be 93% by weight or less, or may be 90% by weight or less. In some embodiments, from the viewpoint of easily achieving higher adhesive properties and / or optical properties (e.g., transparency), the content of the monomer (m1) in the monomer component may be less than 90% by weight, less than 85% by weight, or even less than 80% by weight.

[0089] (Monomer (m2)) In some preferred embodiments, the monomer components constituting the acrylic polymer may further contain a monomer (m2) in addition to the monomer (m1). The monomer (m2) is at least one of a monomer having a hydroxyl group (hydroxyl group-containing monomer) and a monomer having a carboxyl group (carboxyl group-containing monomer). The hydroxyl group-containing monomer is a compound having at least one hydroxyl group and at least one ethylenically unsaturated group in one molecule. The carboxyl group-containing monomer is a compound having at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. The monomer (m2) can be useful for introducing crosslinking points into the acrylic polymer or imparting appropriate cohesiveness to the PSA. The monomer (m2) can be used alone or in combination of two or more. The monomer (m2) is typically a monomer that does not contain an aromatic ring.

[0090] Examples of the ethylenically unsaturated group contained in the monomer (m2) include a (meth)acryloyl group, a vinyl group, and a (meth)allyl group. From the viewpoint of polymerization reactivity, a (meth)acryloyl group is preferred, and from the viewpoints of flexibility and adhesiveness, an acryloyl group is more preferred. From the viewpoint of the flexibility of the adhesive, a compound containing one ethylenically unsaturated group per molecule (i.e., a monofunctional monomer) is preferably used as the monomer (m2).

[0091] Examples of hydroxyl group-containing monomers include, but are not limited to, hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. Preferred examples of hydroxyl group-containing monomers include 4-hydroxybutyl acrylate (Tg: −40° C.) and 2-hydroxyethyl acrylate (Tg: −15° C.). From the viewpoint of improving flexibility in the room temperature range, 4-hydroxybutyl acrylate, which has a lower Tg, is more preferred. In a preferred embodiment, 50% by weight or more (e.g., more than 50% by weight, more than 70% by weight, or more than 85% by weight) of the monomer (m2) may be 4-hydroxybutyl acrylate. The hydroxyl group-containing monomers can be used alone or in combination of two or more.

[0092] In some embodiments in which a hydroxyl group-containing monomer is used as the monomer (m2), the hydroxyl group-containing monomer may be one or more selected from compounds not containing a methacryloyl group. Suitable examples of hydroxyl group-containing monomers not containing a methacryloyl group include the various hydroxyalkyl acrylates described above. For example, it is preferred that more than 50 wt%, more than 70 wt%, or more than 85 wt% of the hydroxyl group-containing monomers used as the monomer (m2) are hydroxyalkyl acrylates. The use of hydroxyalkyl acrylates allows the introduction of hydroxy groups into the acrylic polymer, which are useful for providing crosslinking points and imparting appropriate cohesion, and also makes it easier to obtain a PSA with good flexibility and adhesion at room temperature compared to using only the corresponding hydroxyalkyl methacrylate.

[0093] Examples of carboxyl group-containing monomers include, but are not limited to, acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate, as well as itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. Preferred examples of carboxyl group-containing monomers include acrylic acid and methacrylic acid. The carboxyl group-containing monomers may be used alone or in combination of two or more. Hydroxyl group-containing monomers and carboxyl group-containing monomers may be used in combination.

[0094] The content of monomer (m2) in the monomer components constituting the acrylic polymer is not particularly limited and can be set according to the purpose. In some embodiments, the content of the monomer (m2) can be, for example, 0.01% by weight or more, 0.1% by weight or more, or 0.5% by weight or more. From the viewpoint of obtaining a higher usage effect, in some embodiments, the content of the monomer (m2) is preferably 1% by weight or more, or may be 2% by weight or more, or may be 4% by weight or more. The upper limit of the content of the monomer (m2) in the monomer components is set so that the total content of the monomer (m2) and the content of the monomer (m1) does not exceed 100% by weight. In some embodiments, the content of the monomer (m2) is suitably, for example, 30% by weight or less or 25% by weight or less. From the viewpoint of relatively increasing the content of the monomer (m1) to facilitate a high refractive index, the content is preferably 20% by weight or less, more preferably 15% by weight or less, and may be less than 12% by weight, 10% by weight, or 7% by weight. In some embodiments, the content of the monomer (m2) may be less than 5% by weight, less than 3% by weight, or 1.5% by weight or less.

[0095] The total content of monomer (m1) and monomer (m2) in the monomer components constituting the acrylic polymer may be, for example, 31% by weight or more, preferably 51% by weight or more, or 61% by weight or more, or 71% by weight or more. In some embodiments, the total content of monomer (m1) and monomer (m2) in the monomer components constituting the acrylic polymer may be, for example, 76% by weight or more, preferably 81% by weight or more, or 86% by weight or more, or 91% by weight or more, or 96% by weight or more, or 99% by weight or more, or even substantially 100% by weight, in order to facilitate the effects of these monomers to be favorably exhibited.

[0096] (monomer m3) In some preferred embodiments, the monomer components constituting the acrylic polymer may further contain, in addition to the above-mentioned monomer (m1), an alkyl(meth)acrylate (hereinafter also referred to as "monomer (m3)"). The monomer (m3) may be useful for improving the flexibility of the PSA. It may also be useful for improving the compatibility of additives in the PSA and adhesive properties such as adhesive strength. The monomer (m3) may be used alone or in combination of two or more.

[0097] The monomer (m3) may be a monomer having 1 to 20 carbon atoms (i.e., C 1-20 Alkyl (meth)acrylates having a linear or branched alkyl group at the ester terminal are preferably used. 1-20Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isooctyl (meth)acrylate. , nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate, and the like, but are not limited to these.

[0098] In some embodiments, an alkyl(meth)acrylate having a homopolymer Tg of −20° C. or lower (more preferably −40° C. or lower, e.g., −50° C. or lower) can be preferably used as at least a portion of the monomer (m3). Such an alkyl(meth)acrylate having a low Tg can be useful for reducing the elastic modulus of the PSA. It can also be useful for improving adhesive properties such as adhesive strength. The lower limit of the Tg of the alkyl(meth)acrylate is not particularly limited, and may be, for example, −85° C. or higher, −75° C. or higher, −65° C. or higher, or −60° C. or higher. Specific examples of the low Tg alkyl(meth)acrylate include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), isononyl acrylate (iNA), and the like.

[0099] In some embodiments using monomer (m3), monomer (m3) is selected from C 4-8 It is preferable to use alkyl (meth)acrylate. 4-8The use of alkyl acrylates is more preferred. 4-8 The alkyl (meth)acrylates may be used alone or in combination of two or more. 4-8 The use of alkyl (meth)acrylate tends to improve the flexibility of the adhesive and also tends to provide good adhesive properties (adhesion strength, etc.). 4-8 In the embodiment in which alkyl (meth)acrylate is used, among the alkyl (meth)acrylates contained in the monomer component, C 4-8 The proportion of alkyl (meth)acrylate is suitably 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 90% by weight or more, and may be substantially 100% by weight.

[0100] In some embodiments using monomer (m3), monomer (m3) is selected from C 1-6 Alkyl (meth)acrylates are preferably used. 1-6 By using alkyl (meth)acrylate, it is possible to adjust the storage modulus in each temperature range. For example, it is possible to set the storage modulus in the high temperature range relatively high, and to prevent the difference in storage modulus between the low temperature range and the high temperature range from increasing. 1-6 Alkyl (meth)acrylates also tend to have excellent copolymerizability with the monomer (m1). 1-6 The alkyl (meth)acrylates may be used alone or in combination of two or more. 1-6 As alkyl (meth)acrylate, C 1-6 Alkyl acrylates are preferred, C 2-6 Alkyl acrylates are more preferred, C 4-6 Alkyl acrylates are more preferred. 1-6 The alkyl (meth)acrylate is preferably C 1-4 alkyl (meth)acrylate, more preferably C 2-4 alkyl (meth)acrylate, more preferably C 2-4 It is an alkyl acrylate. 1-6A suitable example of the alkyl(meth)acrylate is BA.

[0101] C in the monomer components that make up acrylic polymers 1-6 The content of alkyl (meth)acrylate may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. 1-6 The content of alkyl (meth)acrylate may be 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more (for example, 30% by weight or more) from the viewpoint of reducing the modulus of elasticity, adhesive strength, etc. 1-6 The upper limit of the content of alkyl (meth)acrylate is, for example, less than 50% by weight, and may be less than 35% by weight. 1-6 The content of alkyl (meth)acrylate is, for example, 24% by weight or less, preferably less than 20% by weight, more preferably less than 17% by weight, may be less than 12% by weight, may be less than 7% by weight, may be less than 3% by weight, or may be less than 1% by weight. 1-6 It may also be possible to carry out an embodiment in which substantially no alkyl (meth)acrylate is used.

[0102] In some other embodiments using monomer (m3), monomer (m3) is selected from C 7-12 Alkyl (meth)acrylates are preferably used. 7-12 The use of alkyl (meth)acrylate can preferably reduce the storage modulus. 7-12 The alkyl (meth)acrylates may be used alone or in combination of two or more. 7-12 As alkyl (meth)acrylate, C 7-10 Alkyl acrylates are preferred, C 7-9 Alkyl acrylates are more preferred, and C8 alkyl acrylates are even more preferred. 7-12 A suitable example of the alkyl (meth)acrylate is 2EHA.

[0103] C in the monomer components that make up acrylic polymers 7-12 The content of alkyl (meth)acrylate may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. 7-12 The content of alkyl (meth)acrylate may be 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more (for example, 30% by weight or more) from the viewpoint of reducing the modulus of elasticity, adhesive strength, etc. 7-12 The upper limit of the content of alkyl (meth)acrylate is, for example, less than 50% by weight, and may be less than 35% by weight. 7-12 The content of alkyl (meth)acrylate is, for example, 24% by weight or less, preferably less than 20% by weight, more preferably less than 17% by weight, may be less than 12% by weight, may be less than 7% by weight, may be less than 3% by weight, or may be less than 1% by weight. 7-12 It may also be possible to carry out an embodiment in which substantially no alkyl (meth)acrylate is used.

[0104] In some embodiments using monomer (m3), from the viewpoint of achieving a low modulus of elasticity, it is preferable that at least a portion of the monomer (m3) is an alkyl acrylate. The use of an alkyl acrylate is also advantageous in terms of adhesive properties such as adhesive strength. For example, it is preferable that 50% by weight or more of the monomer (m3) is an alkyl acrylate, and the proportion of alkyl acrylate in the monomer (m3) is more preferably 75% by weight or more, and even more preferably 90% by weight or more. In some embodiments, substantially 100% by weight of the monomer (m3) may be an alkyl acrylate. In some embodiments, only one or more alkyl acrylates are used as the monomer (m3), and no alkyl methacrylate is used.

[0105] In embodiments in which the monomer component includes an alkyl (meth)acrylate, the content of the alkyl (meth)acrylate in the monomer component can be set so as to appropriately achieve the intended effect. In some embodiments, the content of the alkyl (meth)acrylate may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. The upper limit of the content of the monomer (m3) in the monomer component is set so that the total content of the monomers (m1) and (m2) does not exceed 100% by weight, and may be, for example, less than 50% by weight or less than 35% by weight. In some embodiments, the content of the monomer (m3) may be, for example, 24% by weight or less. Since the refractive index of alkyl (meth)acrylates is generally relatively low, in order to increase the refractive index, it is advantageous to limit the content of the monomer (m3) in the monomer component and relatively increase the content of the monomer (m1). From this viewpoint, the content of the monomer (m3) is suitably less than 23% by weight of the monomer components, preferably less than 20% by weight, more preferably less than 17% by weight, and may be less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The technology disclosed herein can also be preferably implemented in an embodiment in which the monomer (m3) is not substantially used.

[0106] (Other monomers) The monomer components constituting the acrylic polymer may contain, as necessary, monomers other than the above-mentioned monomers (m1), (m2), and (m3) (hereinafter referred to as "other monomers"). The above-mentioned other monomers can be used for purposes such as adjusting the Tg of the acrylic polymer, adjusting the adhesive performance, and improving compatibility within the adhesive layer. The above-mentioned other monomers can be used alone or in combination of two or more.

[0107] Examples of the other monomers include monomers having functional groups other than hydroxyl groups and carboxyl groups (functional group-containing monomers). For example, other monomers that can improve the cohesive strength and heat resistance of the adhesive include sulfonic acid group-containing monomers, phosphate group-containing monomers, and cyano group-containing monomers. Furthermore, examples of monomers that can introduce functional groups that can serve as crosslinking base points into acrylic polymers or that can contribute to improving adhesion to adherends or compatibility within the adhesive include amide group-containing monomers (e.g., (meth)acrylamide, N-methylol(meth)acrylamide, etc.), amino group-containing monomers (e.g., aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, etc.), monomers having nitrogen atom-containing rings (e.g., N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), imide group-containing monomers, epoxy group-containing monomers, keto group-containing monomers, isocyanate group-containing monomers, and alkoxysilyl group-containing monomers. Incidentally, some of the monomers having a nitrogen atom-containing ring, such as N-vinyl-2-pyrrolidone, also fall under the category of amide group-containing monomers. The same applies to the relationship between the above-mentioned monomers having a nitrogen atom-containing ring and amino group-containing monomers.

[0108] Examples of other monomers that can be used in addition to the functional group-containing monomers include vinyl ester monomers such as vinyl acetate; non-aromatic ring-containing (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; olefin monomers such as ethylene, butadiene, and isobutylene; chlorine-containing monomers such as vinyl chloride; alkoxy group-containing monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate; vinyl ether monomers such as methyl vinyl ether; etc. One suitable example of other monomers that can be used for purposes such as improving the flexibility of the adhesive is ethoxyethoxyethyl acrylate (also known as ethyl carbitol acrylate, Tg of homopolymer: -67°C).

[0109] When the other monomers are used, their amount is not particularly limited and can be appropriately set within a range in which the total amount of the monomer components does not exceed 100% by weight. From the viewpoint of easily achieving the refractive index-enhancing effect of the use of the monomer (m1), the content of the other monomers in the monomer components can be, for example, about 35% by weight or less, suitably about 25% by weight or less (e.g., 0 to 25% by weight), may be about 20% by weight or less (e.g., 0 to 20% by weight), advantageously about 10% by weight or less (e.g., 0 to 10% by weight), and preferably about 5% by weight or less, for example, about 1% by weight or less. The technology disclosed herein can be preferably implemented in an embodiment in which the monomer components are substantially free of the other monomers.

[0110] In some embodiments, the monomer components constituting the acrylic polymer may be a composition in which the amount of methacryloyl group-containing monomer used is suppressed to a predetermined level or less. The amount of methacryloyl group-containing monomer used in the monomer components may be, for example, less than 5 wt %, less than 3 wt %, less than 1 wt %, or less than 0.5 wt %. Limiting the amount of methacryloyl group-containing monomer used in this manner may be advantageous from the perspective of realizing a pressure-sensitive adhesive that has a good balance between flexibility, adhesiveness, and a high refractive index. The monomer components constituting the acrylic polymer may be a composition that does not contain a methacryloyl group-containing monomer (for example, a composition consisting only of an acryloyl group-containing monomer).

[0111] In some embodiments, the amount of carboxyl group-containing monomer used in the monomer component constituting the acrylic polymer is limited in order to suppress coloration or discoloration (e.g., yellowing) of the PSA. The amount of carboxyl group-containing monomer used in the monomer component may be, for example, less than 1 wt %, less than 0.5 wt %, less than 0.3 wt %, less than 0.1 wt %, or less than 0.05 wt %. Such a limited amount of carboxyl group-containing monomer is advantageous in terms of suppressing corrosion of metal materials that may be in contact with or adjacent to the PSA disclosed herein (e.g., metal wiring, metal films, etc. that may be present on an adherend). The technology disclosed herein can be implemented in an embodiment in which the monomer component constituting the acrylic polymer does not contain a carboxyl group-containing monomer. For the same reason, in some embodiments, the amount of monomers containing acidic functional groups (including carboxy groups, sulfonic acid groups, phosphate groups, etc.) used in the monomer components constituting the acrylic polymer is preferably limited. The amount of the acidic functional group-containing monomer used in the monomer components of such embodiments can be the same as the preferred amount of the carboxy group-containing monomer used above. The technology disclosed herein can be preferably implemented in an embodiment in which the monomer components do not contain acidic group-containing monomers (i.e., an embodiment in which the acrylic polymer is acid-free).

[0112] The refractive index of the acrylic polymer is, for example, 1.460 or more, preferably 1.500 or more, more preferably 1.530 or more, even more preferably 1.550 or more, and may be 1.560 or more, 1.570 or more, or 1.580 or more. The refractive index adjuster disclosed herein is preferably incorporated into a pressure-sensitive adhesive having an acrylic polymer having a refractive index of a predetermined level or higher as the base polymer, and used to further increase the refractive index of the pressure-sensitive adhesive. The upper limit of the refractive index of the acrylic polymer is not particularly limited. In some embodiments, from the viewpoint of adhesive properties and optical properties, the refractive index of the acrylic polymer is, for example, 1.700 or less, preferably 1.650 or less, and may be 1.630 or less, 1.610 or less, or 1.600 or less.

[0113] The refractive index of the base polymer is measured as the refractive index of an adhesive comprising the base polymer. In this specification, the refractive index of an adhesive refers to the refractive index of the surface (adhesive surface) of the adhesive. The refractive index of an adhesive can be measured using a commercially available refractive index measuring device (Abbe refractometer) under conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. As the Abbe refractometer, for example, the model "DR-M4" manufactured by ATAGO or an equivalent can be used. The measurement sample can be an adhesive layer comprising the adhesive to be evaluated. Specifically, the refractive index of an adhesive can be measured by the method described in the Examples below.

[0114] Furthermore, the adhesive containing the refractive index adjuster disclosed herein is not limited to an acrylic adhesive having an acrylic polymer as a base polymer composed of a monomer component containing a certain amount of the monomer (m1) (for example, 30% by weight or more of the monomer component) as described above, but may be, for example, an acrylic adhesive having an acrylic polymer as a base polymer composed of a monomer component that does not contain the above-mentioned monomer (m1) or has a relatively low content of the above-mentioned monomer (m1). The adhesive containing the refractive index adjuster disclosed herein may be, for example: the lower limit of the content of the monomer (m3) is 50% by weight, 60% by weight, 70% by weight, or 80% by weight, and the upper limit is 99.9% by weight, 99.5% by weight, 98% by weight, 95% by weight, or 90% by weight; the lower limit of the content of the monomer (m2) is 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, or 3 wt%, and the upper limit is 30 wt%, 20 wt%, 15 wt%, 10 wt%, 8 wt%, or 5 wt%; as an optional component, the monomer (m1) is contained in an amount of less than 30% by weight, 20% by weight or less, 10% by weight or less, or 5% by weight or less, and more than 0% by weight, 1% by weight or more, 3% by weight or more, 8% by weight or more, 12% by weight or more, or 18% by weight or more, or the monomer (m1) is not contained; Optionally, the composition contains less than 30% by weight, 20% by weight or less, 10% by weight or less, or 5% by weight or less of the above-mentioned other monomers, and more than 0% by weight, 0.1% by weight or more, 0.5% by weight or more, 1% by weight or more, 3% by weight or more, 8% by weight or more, 12% by weight or more, or 18% by weight or more, or no other monomers; The refractive index adjuster disclosed herein is preferably used in an embodiment in which it is incorporated into a pressure-sensitive adhesive having an acrylic polymer having such a refractive index as a base polymer, thereby effectively adjusting (typically increasing) the refractive index of the pressure-sensitive adhesive. The lower limit of the refractive index of the acrylic polymer is not particularly limited. The refractive index of the acrylic polymer may be, for example, 1.400 or more, 1.440 or more, 1.460 or more, or 1.470 or more.

[0115] (Method for preparing acrylic polymer) In the technology disclosed herein, the method for obtaining an acrylic polymer composed of such monomer components is not particularly limited, and various polymerization methods known as methods for synthesizing acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization can be preferably employed. The polymerization temperature during solution polymerization can be appropriately selected depending on the types of monomers and solvents used, the type of polymerization initiator, and the like, and can be, for example, about 20°C to 170°C (typically about 40°C to 140°C).

[0116] The solvent (polymerization solvent) used in solution polymerization can be appropriately selected from conventionally known organic solvents. For example, any one solvent or a mixture of two or more solvents selected from aromatic compounds (typically aromatic hydrocarbons) such as toluene, acetate esters such as ethyl acetate, aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane, halogenated alkanes such as 1,2-dichloroethane, lower alcohols (for example, monohydric alcohols having 1 to 4 carbon atoms) such as isopropyl alcohol, ethers such as tert-butyl methyl ether, and ketones such as methyl ethyl ketone can be used.

[0117] The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, one or more azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; and aromatic carbonyl compounds. Still other examples of polymerization initiators include redox-based initiators formed by combining a peroxide with a reducing agent. One polymerization initiator can be used alone, or two or more polymerization initiators can be used in combination. The amount of polymerization initiator used may be a typical amount, and can be selected, for example, from the range of approximately 0.005 to 1 part by weight (typically approximately 0.01 to 1 part by weight) per 100 parts by weight of the monomer components.

[0118] In the polymerization, various conventionally known chain transfer agents can be used as needed. For example, mercaptans such as n-dodecyl mercaptan, t-dodecyl mercaptan, thioglycolic acid, and α-thioglycerol can be used. Alternatively, a chain transfer agent that does not contain a sulfur atom (non-sulfur chain transfer agent) can be used. Examples of non-sulfur chain transfer agents include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenoids such as α-pinene and terpinolene; and styrenes such as α-methylstyrene and α-methylstyrene dimer. The chain transfer agents can be used alone or in combination of two or more. When a chain transfer agent is used, the amount used can be, for example, about 0.01 to 1 part by weight per 100 parts by weight of the monomer components.

[0119] (Base polymer glass transition temperature Tg T ) The monomer components constituting the base polymer (e.g., acrylic polymer) of the adhesive disclosed herein have a glass transition temperature Tg T In some embodiments, the glass transition temperature Tg T is preferably 10° C. or less, more preferably 5° C. or less, even more preferably 1° C. or less, and may be 0° C. or less. T The glass transition temperature Tg may be -10°C or lower, -20°C or lower, -25°C or lower, -30°C or lower, or -35°C or lower. T A low glass transition temperature (Tg) can be advantageous in terms of reducing the elastic modulus of the adhesive. T For example, the glass transition temperature Tg may be −80° C. or lower, −70° C. or higher, or −60° C. or higher. From the viewpoint of facilitating the high refractive index of the pressure-sensitive adhesive, in some embodiments, Tis preferably −50° C. or higher, more preferably greater than −45° C., and may be greater than −40° C. In some preferred embodiments, the glass temperature Tg T may be above -30°C, above -20°C, above -10°C, or above -5°C.

[0120] Here, the glass transition temperature Tg T Unless otherwise specified, the glass transition temperature (Tg) refers to the glass transition temperature calculated by the Fox equation based on the composition of the above-mentioned monomer components. The Fox equation, as shown below, is a relational expression between the Tg of a copolymer and the glass transition temperature (Tgi) of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer. 1 / Tg=Σ(Wi / Tgi) In the above Fox formula, Tg represents the glass transition temperature (unit: K) of the copolymer, Wi represents the weight fraction of monomer i in the copolymer (copolymerization ratio by weight), and Tgi represents the glass transition temperature (unit: K) of the homopolymer of monomer i. The glass transition temperature of a homopolymer used to calculate Tg is the value described in publicly available sources such as "Polymer Handbook" (3rd Edition, John Wiley & Sons, Inc., 1989). For monomers for which multiple values ​​are described in the Polymer Handbook, the highest value is used. If the Tg of a homopolymer is not described in publicly available sources, the value obtained by the measurement method described in JP 2007-51271 A is used.

[0121] (Mw of base polymer) The weight average molecular weight (Mw) of the base polymer (e.g., acrylic polymer) of the PSA disclosed herein is not particularly limited, and may be, for example, about 50×10 4 It is appropriate that the value is more than 70×10 4 It can be more than 80×10 4 By using a base polymer having a Mw of a predetermined value or more, it is easy to obtain an appropriate cohesive force that can exhibit the desired adhesive properties. The upper limit of the Mw of the base polymer is, for example, about 500 × 104 From the viewpoint of adhesive performance, it is approximately 400 × 10 4 or less (more preferably about 150×10 4 For example, approximately 130 x 10 4 It is preferable that the temperature is in the range of (or less).

[0122] Here, the Mw of the base polymer (e.g., acrylic polymer) can be determined in terms of polystyrene by gel permeation chromatography (GPC). Specifically, it can be determined by measuring under the following conditions using a GPC measuring device (trade name: "HLC-8220GPC" manufactured by Tosoh Corporation). [GPC measurement conditions] Sample concentration: 0.2 wt% (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: tetrahydrofuran (THF) Flow rate (flow rate): 0.6mL / min Column temperature (measurement temperature): 40°C column: Sample column: 1 "TSKguardcolumn SuperHZ-H" + 2 "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: 1 tube of "TSKgel SuperH-RC" (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: polystyrene

[0123] (Crosslinking agent) In the technology disclosed herein, the pressure-sensitive adhesive composition used to form the pressure-sensitive adhesive may contain a crosslinking agent as needed for purposes such as adjusting the cohesive strength of the pressure-sensitive adhesive. Examples of crosslinking agents that can be used include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, oxazoline-based crosslinking agents, melamine-based resins, and metal chelate-based crosslinking agents. Of these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred. Other examples of crosslinking agents include monomers having two or more ethylenically unsaturated groups in one molecule, i.e., polyfunctional monomers. The crosslinking agents can be used alone or in combination of two or more.

[0124] As the isocyanate-based crosslinking agent, a bifunctional or higher isocyanate compound can be used, and examples thereof include aliphatic polyisocyanates such as trimethylene diisocyanate, butylene diisocyanate, hexamethylene diisocyanate (HDI), and dimer acid diisocyanate; alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), and 1,3-bis(isocyanatomethyl)cyclohexane; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate (XDI); and modified polyisocyanates obtained by modifying the above-mentioned isocyanate compounds with an allophanate bond, a biuret bond, an isocyanurate bond, a uretdione bond, a urea bond, a carbodiimide bond, a uretonimine bond, an oxadiazinetrione bond, or the like. Examples of commercially available products include Takenate 300S, Takenate 500, Takenate 600, Takenate D165N, and Takenate D178N (all manufactured by Takeda Pharmaceutical Co., Ltd.), Sumidur T80, Sumidur L, and Desmodur N3400 (all manufactured by Sumika Bayer Urethane Co., Ltd.), Millionate MR, Millionate MT, Coronate L, Coronate HL, and Coronate HX (all manufactured by Tosoh Corporation). The isocyanate compounds can be used alone or in combination of two or more. A bifunctional isocyanate compound and a trifunctional or higher isocyanate compound may also be used in combination.

[0125] Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane. These may be used alone or in combination of two or more.

[0126] Examples of polyfunctional monomers include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexa(meth)acrylate, and 1,6-hexa(meth)acrylate. Examples of the polyfunctional monomer include sandiol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, divinylbenzene, bisphenol A di(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, butyldiol (meth)acrylate, hexyldiol di(meth)acrylate, etc. The polyfunctional monomer can be used alone or in combination of two or more.

[0127] When a crosslinking agent (which may be a polyfunctional monomer) is used, its amount is not particularly limited and can be, for example, in the range of about 0.001 to 5.0 parts by weight per 100 parts by weight of the monomer components. From the viewpoint of improving adhesion to the adherend, in some embodiments, the amount of crosslinking agent used per 100 parts by weight of the monomer components is preferably 3.0 parts by weight or less, more preferably 2.0 parts by weight or less, and may be 1.0 part by weight or less, 0.5 parts by weight or less, or 0.2 parts by weight or less. Furthermore, from the viewpoint of appropriately exhibiting the effects of using the crosslinking agent, in some embodiments, the amount of crosslinking agent used per 100 parts by weight of the monomer components may be, for example, 0.005 parts by weight or more, 0.01 parts by weight or more, 0.05 parts by weight or more, 0.08 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, or 0.4 parts by weight or more.

[0128] A crosslinking catalyst may be used to promote the crosslinking reaction more effectively. Examples of the crosslinking catalyst include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, nursem ferric, butyltin oxide, and dioctyltin dilaurate. Among these, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. The amount of the crosslinking catalyst used is not particularly limited. The amount of the crosslinking catalyst used per 100 parts by weight of the monomer component can be, for example, in the range of approximately 0.0001 to 1 part by weight, preferably 0.001 to 0.5 parts by weight, taking into account the balance between the crosslinking reaction rate and the pot life of the pressure-sensitive adhesive composition.

[0129] The PSA composition may contain a compound that undergoes keto-enol tautomerization as a crosslinking retarder. This can extend the pot life of the PSA composition. For example, a compound that undergoes keto-enol tautomerization can be preferably used in a PSA composition containing an isocyanate-based crosslinking agent. Various β-dicarbonyl compounds can be used as the compound that undergoes keto-enol tautomerization. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) and acetoacetic esters (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably used. The compound that undergoes keto-enol tautomerization can be used alone or in combination of two or more. The amount of the compound that undergoes keto-enol tautomerization can be, for example, 0.1 to 20 parts by weight, alternatively 0.5 to 10 parts by weight, or alternatively 1 to 5 parts by weight, per 100 parts by weight of the monomer components.

[0130] (high refractive index particles) The adhesive disclosed herein may contain high refractive index particles as an optional component. Herein, the high refractive index particles refer to particles that can increase the refractive index of an adhesive when contained in the adhesive. Hereinafter, the high refractive index particles will be referred to as "particles P HRI " HRI stands for high refractive index.

[0131] particle P HRI As the particle P, one or more types of particles made of a material having a refractive index of, for example, 1.60 or more, preferably 1.65 or more, more preferably 1.70 or more (it may be 1.80 or more, 1.90 or more, or even 2.00 or more) may be used. HRI The upper limit of the refractive index of the material constituting the particles P is not particularly limited, and may be, for example, 3.00 or less, 2.80 or less, 2.50 or less, 2.20 or less, or 2.00 or less. HRI The refractive index of the material constituting the material is the refractive index measured for a single layer film of the material (with a film thickness that allows refractive index measurement) using a commercially available spectroscopic ellipsometer at a measurement wavelength of 589 nm and a measurement temperature of 25°C. As the spectroscopic ellipsometer, for example, the product name "EC-400" (manufactured by J.A. Woolam) or an equivalent product can be used.

[0132] particle P HRI The type of particles P is not particularly limited, and one or more materials that can improve the refractive index of the adhesive can be selected and used from among metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. HRI As the particles P, inorganic oxides (for example, metal oxides) that can improve the refractive index of the pressure-sensitive adhesive sheet can be preferably used. HRISuitable examples of materials for constituting the particle P include inorganic oxides (specifically, metal oxides) such as titania (titanium oxide, TiO2), zirconia (zirconium oxide, ZrO2), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, and niobium oxide (Nb2O5, etc.). These inorganic oxide (e.g., metal oxide) particles can be used singly or in combination of two or more. Among these, particles made of titania or zirconia are preferred, and particles made of zirconia are particularly preferred. Furthermore, metal particles, such as iron-based, zinc-based, tungsten-based, and platinum-based materials, can have high refractive indices. Organic particles, such as particles made of resins like styrene-based resins, phenolic resins, polyester-based resins, and polycarbonate-based resins, have relatively high refractive indices. Examples of organic-inorganic composite particles include composites of the aforementioned inorganic and organic materials, and inorganic particles coated with organic materials like resins. Particle P HRI From the viewpoint of compatibility with the adhesive component, the above organic or inorganic particles may be surface-treated with a surface treatment agent.

[0133] particle P HRI The average particle size of the particles P is not particularly limited, and particles of an appropriate size that can achieve the desired improvement in refractive index when contained in the adhesive can be used. HRI The average particle size of the particles P can be, for example, about 1 nm or more, and is suitably about 5 nm or more. HRI The average particle size is preferably about 10 nm or more, may be about 20 nm or more, or may be about 30 nm or more. From the viewpoint of maintaining adhesive properties, the upper limit of the average particle size is, for example, about 300 nm or less, and from the viewpoint of improving the refractive index, it is preferably about 100 nm or less, more preferably about 70 nm or less, even more preferably about 50 nm or less, and may be about 35 nm or less (for example, about 25 nm or less).

[0134] In addition, the above particles P HRI The average particle size of the particle P refers to the volume average particle size. Specifically, the particle size distribution measurement device based on the laser scattering and diffraction method is used to measure the particle P HRIThe particle size at 50% of the cumulative value in the particle size distribution measured for the dispersion (50% volume average particle size; hereinafter, D 50 As a measuring device, for example, the product name "Microtrac MT3000II" manufactured by Microtrac Bell or an equivalent product can be used.

[0135] Particles in adhesives HRI The content of the particles P is not particularly limited. HRI The content of the particles P may vary depending on the desired refractive index. HRI The content of the particles P in the adhesive can be appropriately set so as to have a predetermined refractive index or higher, taking into consideration the required adhesive properties, etc. HRI The content of particles P can be, for example, about 75% by weight or less, and may be about 50% by weight or less, or about 30% by weight or less, from the viewpoint of adhesive properties and transparency. HRI The lower limit of the content of particles P in the pressure-sensitive adhesive is not particularly limited, and may be, for example, more than 0% by weight, 1% by weight or more, or 5% by weight or more. HRI The content of is, for example, less than 10% by weight, may be less than 1% by weight, or may be less than 0.1% by weight. HRI It can be implemented in a manner that is substantially free of

[0136] Particles in adhesives HRI The content of particles P can also be specified in terms of the relative relationship with the amount of base polymer contained in the PSA. HRI The content of particles P can be, for example, about 100 parts by weight or less relative to 100 parts by weight of the base polymer, and may be about 60 parts by weight or less, or about 40 parts by weight or less, from the viewpoint of adhesive properties and transparency. HRI The lower limit of the content of the particles P is not particularly limited, and may be, for example, more than 0 parts by weight, 1 part by weight or more, or 5 parts by weight or more. HRIThe content is, for example, less than 30 parts by weight, may be less than 10 parts by weight, may be less than 1 part by weight, or may be less than 0.1 part by weight, relative to 100 parts by weight of the base polymer.

[0137] (plasticizer) The adhesives disclosed herein may contain a plasticizer as an optional component. The use of a plasticizer can reduce the elastic modulus of the adhesive. Furthermore, when molded into an adhesive sheet, the flexibility and ability to follow deformation can be improved. As the plasticizer, any suitable material that can contribute to reducing the elastic modulus of the adhesive can be used. One type of plasticizer can be used alone, or two or more types can be used in combination.

[0138] In some embodiments, the plasticizer is preferably a compound that is liquid at 30°C. In this specification, "liquid" means that the material is fluid and is in a liquid state. Such compounds include compounds with a melting point of 30°C or lower. When the plasticizer is liquid at 30°C, the plasticizing effect is suitably exerted, and the elastic modulus of the adhesive can be effectively reduced. The plasticizer is preferably a compound that is liquid at 25°C, and more preferably a compound that is liquid at 20°C.

[0139] In order to prevent the refractive index of the adhesive from decreasing due to the incorporation of a plasticizer, in some embodiments, a compound having two or more double bond-containing rings in one molecule (excluding compounds having a structure corresponding to the refractive index adjuster) can be preferably used as the plasticizer. The number of double bond-containing rings possessed by the plasticizer is preferably 6 or less, and may be 4 or less, or 3 or less, in order to exert a plasticizing effect.

[0140] The double bond-containing ring of the plasticizer may be a conjugated double bond-containing ring (typically an aromatic ring) or a non-conjugated double bond-containing ring. The plasticizer may have at least one ring selected from an aromatic ring and a heterocyclic ring (heterocyclic ring) as the double bond-containing ring. The double bond-containing ring (typically an aromatic ring, preferably a carbocyclic ring) may have one or more substituents on the ring-constituting atoms, or may have no substituents. In the carbon atom-containing substituent, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, for example, 1 or 2. In some embodiments, the double bond-containing ring may be an aromatic ring having no substituents on the ring-constituting atoms, or having one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, ethylenically unsaturated groups (e.g., (meth)acryloxy groups), hydroxy groups, and hydroxyalkyl groups (preferably alkyl groups, alkoxy groups, and hydroxyalkyl groups).

[0141] In some embodiments, a compound having no ethylenically unsaturated group can be preferably used as the plasticizer. This can suppress deterioration of the pressure-sensitive adhesive composition due to heat or light (progression of gelation or decrease in leveling ability due to increased viscosity) and improve storage stability. The use of a plasticizer having no ethylenically unsaturated group is also preferable from the viewpoint of suppressing changes in elastic modulus, dimensional changes and deformation (warping, waviness, etc.), optical distortion, etc., caused by reactions of ethylenically unsaturated groups in a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing the plasticizer.

[0142] From the viewpoint of achieving a low elastic modulus while suppressing a decrease in the refractive index of the PSA, in some embodiments, a plasticizer having a refractive index of about 1.50 or more (preferably about 1.51 or more, more preferably about 1.53 or more, and even more preferably about 1.55 or more) can be preferably used. Plasticizers having a refractive index of about 1.56 or more, about 1.58 or more, about 1.60 or more, or about 1.62 or more may also be used. In some embodiments, from the viewpoint of ease of preparation of the PSA composition, compatibility within the PSA, etc., the refractive index of the plasticizer is suitably 2.50 or less, advantageously 2.00 or less, or may be 1.90 or less, 1.80 or less, or 1.70 or less. The refractive index of the plasticizer, like that of the monomer, is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C. If the manufacturer provides a nominal value for the refractive index at 25°C, that nominal value can be used.

[0143] The molecular weight of the plasticizer is not particularly limited, but typically a plasticizer having a molecular weight smaller than that of the base polymer is used. From the viewpoint of easily exerting the plasticizing effect, the molecular weight of the plasticizer is suitably 30,000 or less, advantageously 25,000 or less, and may be less than 10,000 (e.g., less than 5,000), or may be less than 3,000. In some embodiments, the molecular weight of the plasticizer is preferably 2,000 or less, more preferably 1,200 or less, even more preferably 900 or less, and may be 600 or less, 500 or less, 400 or less, 300 or less, or 250 or less (e.g., 220 or less). A plasticizer with a molecular weight that is not too large can be advantageous from the viewpoint of improving compatibility within the pressure-sensitive adhesive layer, etc. Furthermore, from the viewpoint of easily exerting a sufficient plasticizing effect, the molecular weight of the plasticizer is suitably 100 or more, preferably 130 or more, more preferably 150 or more, and may be 170 or more, 200 or more, 220 or more, or 250 or more. It is also preferable that the molecular weight of the plasticizer is not too low from the viewpoint of the heat resistance of the PSA sheet and suppression of contamination of the adherend. The molecular weight of the plasticizer is calculated based on its chemical structure. If the manufacturer provides a nominal molecular weight value, that nominal value can be used.

[0144] In some embodiments, an ethylene glycol-based compound having two or more double bond-containing rings per molecule can be used as the plasticizer. The number of oxyethylene units (i.e., -(C2H4O)- units) contained in the ethylene glycol-based compound is, for example, 1 to 10, or may be 1 to 6 or 2 to 4. The ethylene glycol-based compound can be a compound having a structure in which two or more non-condensed double bond-containing rings are linked via oxyethylene units (e.g., 1 to 10, preferably 1 to 6, typically 2 to 4 oxyethylene units) as linking groups. Such compounds can have one or more ester groups. Examples of the ethylene glycol-based compound include compounds having a structure in which two or more benzoic acids are linked to ethylene glycol, diethylene glycol, triethylene glycol, or polyethylene glycol via ester bonds.

[0145] In some other embodiments, liquid rosins such as liquid rosin esters can be used as plasticizers. The liquid rosins (e.g., liquid rosin esters) can correspond to the compounds having a condensed double bond-containing ring structure.

[0146] Other examples of plasticizers that can be used in the adhesives disclosed herein include known plasticizers other than those mentioned above (e.g., phthalate esters, terephthalate esters, adipic acid esters, adipic acid polyesters, benzoic acid glycol esters, etc.) and plasticizing materials such as liquid camphenephenol.

[0147] The amount of plasticizer used is not particularly limited and can be set according to the purpose. From the viewpoint of reducing the elastic modulus of the PSA, the amount of plasticizer used relative to 100 parts by weight of base polymer may be, for example, 1 part by weight or more, 10 parts by weight or more, 15 parts by weight or more (e.g., more than 15 parts by weight), 20 parts by weight or more, 30 parts by weight or more (e.g., more than 30 parts by weight), 40 parts by weight or more, 50 parts by weight or more, 60 parts by weight or more, 75 parts by weight or more, or 90 parts by weight or more. Furthermore, from the viewpoint of achieving a good balance between increasing the refractive index and decreasing the elastic modulus of the PSA, the amount of plasticizer used relative to 100 parts by weight of base polymer is suitably approximately 200 parts by weight or less, preferably 150 parts by weight or less, more preferably 120 parts by weight or less, and may be 100 parts by weight or less, 80 parts by weight or less, 70 parts by weight or less, 45 parts by weight or less, or 35 parts by weight or less.

[0148] (Additives (H RO )) The adhesive disclosed herein may contain, as an optional additive, an organic material having a higher refractive index than the base polymer (excluding compounds having a structure corresponding to the refractive index adjuster described above). Hereinafter, such an organic material will be referred to as an "additive (H RO )" where the above "H RO " indicates that it is an organic material with a high refractive index. RO By using a combination of the additive (H) and a refractive index adjuster, it is possible to realize a pressure-sensitive adhesive that more suitably balances the refractive index and adhesive properties (peel strength, flexibility, etc.). RO The organic material used as the additive (H) may be a polymer or a non-polymer. In addition, it may or may not have a polymerizable functional group. RO ) is defined as being different from the compounds used as plasticizers mentioned above. Therefore, the additive (H RO ) is specifically not liquid (liquid) at 30°C (e.g., 25°C or 20°C).RO ) can be used alone or in combination of two or more.

[0149] Additives (H RO The refractive index of the additive (H) can be set within an appropriate range depending on the relative relationship with the refractive index of the base polymer, and is not limited to a specific range. RO The refractive index of the additive (H ) may be selected from a range of, for example, more than 1.55, more than 1.56, or more than 1.57, and higher than the refractive index of the base polymer. RO The refractive index of the additive (H) is advantageously 1.58 or more, preferably 1.60 or more, more preferably 1.63 or more, and may be 1.65 or more, 1.70 or more, or 1.75 or more. RO The upper limit of the refractive index of ) is not particularly limited, but from the viewpoint of compatibility within the adhesive and ease of achieving both a high refractive index and flexibility suitable for the adhesive, it is, for example, 3.000 or less, or alternatively 2.500 or less, 2.000 or less, 1.950 or less, 1.900 or less, or 1.850 or less. In addition, additives (H RO The refractive index of the polymer is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C, just like the refractive index of the monomer. If the manufacturer provides a nominal value for the refractive index at 25°C, that nominal value can be used.

[0150] Additives (H RO The molecular weight of the organic material used as the additive (H) is not particularly limited and can be selected depending on the purpose. From the viewpoint of achieving a good balance between the effect of increasing the refractive index and other properties (for example, optical properties such as flexibility and haze suitable for adhesives), in some embodiments, the additive (H RO The molecular weight of the additive (H) is suitably less than about 10,000, preferably less than 5,000, more preferably less than 3,000 (for example, less than 1,000), and may be less than 800, less than 600, less than 500, or less than 400. ROIt is advantageous for the molecular weight of the additive (H) not to be too large in terms of improving compatibility within the adhesive. RO The molecular weight of the additive (H) may be, for example, 130 or more, or 150 or more. RO ) is the molecular weight of the additive (H RO From the viewpoint of increasing the refractive index of the polymer, the molecular weight is preferably 170 or more, more preferably 200 or more, and may be 230 or more, 250 or more, 270 or more, 500 or more, 1000 or more, or 2000 or more. In some embodiments, a polymer having a molecular weight of about 1000 to 10000 (for example, 1000 or more but less than 5000) is mixed with an additive (H RO ) can be used as Additives (H RO As for the molecular weight of the additive (H), in the case of a non-polymer or a polymer with a low degree of polymerization (for example, about dimer to pentamer), the molecular weight can be calculated based on the chemical structure or measured using MALDI-TOF-MS, as in the case of the refractive index adjuster. RO If the polymer has a higher degree of polymerization, the weight average molecular weight (Mw) based on GPC performed under appropriate conditions can be used. If the manufacturer provides a nominal value for the molecular weight, that nominal value can be used.

[0151] Additives (H RO Examples of organic materials that can be selected for the organic compound include, but are not limited to, organic compounds having aromatic rings, organic compounds having heterocycles (which may be aromatic or non-aromatic heterocycles), and the like. Additives (H RO The aromatic ring contained in the organic compound having an aromatic ring (hereinafter also referred to as "aromatic ring-containing compound") used as the monomer (m1) can be selected from the same aromatic rings contained in the compound used as the monomer (m2). Additives (H ROExamples of aromatic ring-containing compounds that can be used as the monomer (m1) include, but are not limited to, compounds that can be used as the monomer (m1); oligomers that contain, as a monomer unit, a compound that can be used as the monomer (m1); compounds 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 a compound that can be used as the monomer (m1) and replaced with a hydrogen atom or a group that does not have an ethylenically unsaturated group (for example, a hydroxyl group, an amino group, a halogen atom, an alkyl group, an alkoxy group, a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group, etc.); and the like, which do not fall under the category of refractive index adjusters disclosed herein or the above-mentioned plasticizers.

[0152] In some embodiments, the additive (H RO As the compound (a), an organic compound having two or more aromatic rings in one molecule (hereinafter also referred to as a "multiple aromatic ring-containing compound") can be preferably used because it is easy to obtain a high refractive index effect. The multiple aromatic ring-containing compound may or may not have a polymerizable functional group such as an ethylenically unsaturated group. The multiple aromatic ring-containing compound may be a polymer or a non-polymer. The polymer may be an oligomer containing a multiple aromatic ring-containing monomer as a monomer unit (preferably an oligomer having a molecular weight of approximately 5,000 or less, more preferably approximately 1,000 or less, for example, a low polymer of about 2 to 5). The oligomer may be, for example: a homopolymer of a multiple aromatic ring-containing monomer; a copolymer of one or more multiple aromatic ring-containing monomers; a copolymer of one or more multiple aromatic ring-containing monomers with another monomer; or the like. The other monomer may be an aromatic ring-containing monomer that does not fall under the category of multiple aromatic ring-containing monomer, a monomer not having an aromatic ring, or a combination thereof.

[0153] In some embodiments, the additive (H ROAs the additive (H) having no ethylenically unsaturated group, a compound having no ethylenically unsaturated group can be preferably used. This can suppress deterioration of the pressure-sensitive adhesive composition due to heat or light (progression of gelation or decrease in leveling ability due to increase in viscosity) and improve storage stability. RO ) is used to RO In a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing the ethylenically unsaturated group, this is also preferred from the viewpoint of suppressing dimensional changes and deformation (warping, waviness, etc.), optical distortion, etc. caused by the reaction of the ethylenically unsaturated group.

[0154] Additives (H) per 100 parts by weight of base polymer RO The amount of additive (H) used (when multiple types of compounds are used, the total amount thereof) is not particularly limited as long as it is more than 0 parts by weight, and can be set according to the purpose. In some embodiments, the amount of additive (H) used relative to 100 parts by weight of the base polymer RO The amount of additive (H) used can be, for example, 80 parts by weight or less, and from the viewpoint of achieving a good balance between increasing the refractive index of the adhesive and suppressing the deterioration of adhesive properties, it is advantageous to set it to 60 parts by weight or less, and preferably to set it to 45 parts by weight or less. In some embodiments where adhesive properties and optical properties are more important, the amount of additive (H) used relative to 100 parts by weight of the base polymer is RO The amount of the additive (H ) used may be, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less. From the viewpoint of increasing the refractive index of the adhesive, the amount of the additive (H ) used may be, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less. RO The amount of ) used can be, for example, 1 part by weight or more, advantageously 3 parts by weight or more, preferably 5 parts by weight or more, may be 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.

[0155] (tackifier) The PSA disclosed herein may contain a tackifier. Examples of tackifiers that can be used include known tackifier resins such as rosin-based tackifier resins, terpene-based tackifier resins, phenol-based tackifier resins, hydrocarbon-based tackifier resins, ketone-based tackifier resins, polyamide-based tackifier resins, epoxy-based tackifier resins, and elastomer-based tackifier resins. These can be used alone or in combination of two or more. The amount of tackifier resin used is not particularly limited and can be set so as to achieve appropriate adhesive performance depending on the purpose and application. In some embodiments, from the viewpoints of refractive index and transparency, the amount of tackifier used per 100 parts by weight of base polymer is suitably 30 parts by weight or less, preferably 10 parts by weight or less, and more preferably 5 parts by weight or less. The technology disclosed herein can be preferably implemented in an embodiment in which a tackifier is not used.

[0156] (Other additives) In addition, the adhesives disclosed herein may contain, as needed, known additives that can be used in adhesives, such as leveling agents, softeners, colorants (dyes, pigments, etc.), fillers, antistatic agents, antioxidants, UV absorbers, antioxidants, light stabilizers, preservatives, etc. As these various additives are conventionally known and can be used in the usual way, they do not particularly characterize the present invention, and therefore detailed description thereof will be omitted.

[0157] (refractive index) The refractive index of the adhesive disclosed herein is not particularly limited and can be set according to the purpose (e.g., taking into consideration the refractive index of the adherend). The refractive index of the adhesive disclosed herein can be, for example, approximately 1.300 to 1.900 (preferably approximately 1.450 to 1.800). In some embodiments, the refractive index of the adhesive is higher than that of conventional acrylic adhesives. The technology disclosed herein can provide an adhesive having a refractive index of, for example, 1.550 or higher, an adhesive composition capable of forming the adhesive, and an adhesive sheet containing the adhesive. The refractive index of the adhesive is suitably 1.560 or higher, preferably greater than 1.570. In some embodiments, the refractive index of the adhesive can be 1.575 or higher, 1.580 or higher, or 1.585 or higher. An adhesive having such a refractive index can suitably suppress light reflection at the interface with the adherend when used to attach to a material with a high refractive index. The preferred upper limit of the refractive index of the adhesive is not limited to a specific range, as it may vary depending on the refractive index of the adherend, etc., and may be, for example, 1.700 or less, 1.670 or less, 1.650 or less, 1.620 or less, or 1.600 or less. The refractive index of the adhesive can be adjusted, for example, by the composition of the adhesive (e.g., the type of base polymer, the type and amount of refractive index adjuster used, and whether or not other optional components are used).

[0158] In this specification, the refractive index of a pressure-sensitive adhesive refers to the refractive index of the surface (adhesive surface) of the pressure-sensitive adhesive. The refractive index of a pressure-sensitive adhesive can be measured using a commercially available refractive index measuring device (Abbe refractometer) under conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. As the Abbe refractometer, for example, the model "DR-M4" manufactured by ATAGO or an equivalent can be used. The measurement sample can be an adhesive layer made of the pressure-sensitive adhesive to be evaluated. Specifically, the refractive index of a pressure-sensitive adhesive can be measured by the method described in the Examples below.

[0159] (storage modulus G') The storage modulus G' at 25°C of the PSA disclosed herein (hereinafter also referred to as "storage modulus G'(25)") is appropriately set depending on the intended use and manner of use, and is not limited to a specific range. The storage modulus G'(25) of the PSA may be, for example, approximately 2000 kPa or less. In some embodiments, from the viewpoint of ease of application to an adherend, the storage modulus G'(25) of the PSA is advantageously approximately 1500 kPa or less, preferably 1000 kPa or less, and may be 800 kPa or less. In some embodiments, from the viewpoint of increasing the flexibility of the PSA at room temperature (e.g., 25°C) to facilitate adhesion to an adherend, the storage modulus G'(25) of the PSA is preferably approximately 650 kPa or less, and may be 550 kPa or less, 450 kPa or less, 350 kPa or less, or 300 kPa or less. In some embodiments where application and flexibility at room temperature are more important, the storage modulus G'(25) of the PSA may be, for example, less than 270 kPa or less than 250 kPa, less than 200 kPa, less than 180 kPa, or less than 160 kPa (e.g., less than 140 kPa). In some embodiments, the storage modulus G'(25) of the PSA may be less than 100 kPa or less than 90 kPa. There is no particular lower limit for the storage modulus G'(25) of the PSA, but from the viewpoint of processability, handleability, etc., it may be, for example, 30 kPa or more, 50 kPa or more, or 70 kPa or more. In some embodiments, the storage modulus G'(25) may be 100 kPa or more, 150 kPa or more, 200 kPa or more, 250 kPa or more, 300 kPa or more, 500 kPa or more, 600 kPa or more, or 700 kPa or more, taking into account the need for a high refractive index.

[0160] The storage modulus G' at 50°C (hereinafter also referred to as "storage modulus G'(50)") of the PSA disclosed herein is not particularly limited and can be, for example, less than 600 kPa. In some embodiments, the storage modulus G'(50) is suitably less than 400 kPa, preferably less than 250 kPa, and may be less than 200 kPa, less than 150 kPa, less than 100 kPa, less than 70 kPa, less than 50 kPa, less than 38 kPa, or less than 36 kPa. PSA having such a limited storage modulus G'(50) can easily increase its adhesion to an adherend by applying moderate heating as necessary, thereby improving its adhesion to an adherend. There is no particular lower limit for the storage modulus G'(50) of the PSA. In some embodiments, from the viewpoint of the heat resistance of the PSA, the storage modulus G'(50) may be, for example, 10 kPa or more, 15 kPa or more, 20 kPa or more, or 23 kPa or more. In some embodiments, in consideration of increasing the refractive index, the storage modulus G'(50) of the PSA may be 40 kPa or more, 70 kPa or more, 120 kPa or more, or 170 kPa or more.

[0161] In some embodiments of the adhesives disclosed herein, the adhesives meet the following conditions: (a) a storage modulus G'(25) at 25°C of 1500 kPa or less (preferably 1000 kPa or less, e.g., 550 kPa or less, 350 kPa or less, or 180 kPa or less); and (b) a storage modulus at 50°C, G'(50), of less than 400 kPa (preferably less than 200 kPa, more preferably less than 150 kPa, e.g., less than 100 kPa or less than 50 kPa); It is preferable that at least one of the following conditions is satisfied. A PSA that satisfies at least the above condition (a) is preferred from the viewpoint of adhesion to an adherend at room temperature (e.g., 25°C). A PSA that satisfies at least the above condition (b) is preferred because its adhesion (adhesion) to an adherend can be easily improved by heating to a temperature slightly higher than room temperature. A PSA that does not satisfy the above condition (a) but satisfies the above condition (b) can be used as a heat-activatable PSA that has good reworkability (repositionability) at the initial stage of application at room temperature and can effectively increase the peel strength from an adherend by heating to a temperature slightly higher than room temperature. The heat activation may be performed by heating the PSA to a temperature slightly higher than room temperature when applying it to an adherend. The temperature slightly higher than room temperature is, for example, about 60°C or lower, preferably about 55°C or lower (e.g., about 50°C or lower).

[0162] (glass transition temperature) The glass transition temperature (Tg) of the pressure-sensitive adhesive is not particularly limited and can be set taking into consideration flexibility in low-temperature ranges and cohesive strength (heat resistance, etc.) in high-temperature ranges. In some embodiments, the Tg of the pressure-sensitive adhesive is, for example, 50°C or lower, and may be 40°C or lower, 30°C or lower, 15°C or lower, or even 5°C or lower. In some preferred embodiments, the Tg of the pressure-sensitive adhesive is 0°C or lower, more preferably -5°C or lower, even more preferably -10°C or lower, and may be -15°C or lower (e.g., -20°C or lower), from the viewpoint of flexibility. The lower the Tg of the pressure-sensitive adhesive, the more excellent its adhesive properties, such as adhesion to the adherend. The lower limit of the Tg of the pressure-sensitive adhesive is, for example, -50°C or higher, suitably -40°C or higher, and may be -30°C or higher. Pressure-sensitive adhesives having the above Tg tend to easily obtain moderate cohesive strength.

[0163] The storage modulus G' and glass transition temperature Tg of the adhesive at each of the above temperatures are determined by dynamic viscoelasticity measurement. Specifically, a sheet of adhesive with a thickness of approximately 1.5 mm (which can be prepared, for example, by appropriately laminating adhesive layers) is punched into a 7.9 mm diameter disk and used as a measurement sample, and dynamic viscoelasticity measurement is performed under the following conditions. From the measurement results, the storage modulus G' [Pa] of the adhesive at each temperature can be determined. Furthermore, the glass transition temperature (Tg) [°C] of the adhesive is determined as the temperature corresponding to the peak-top temperature of the loss tangent tanδ (loss modulus G" / storage modulus G') in the dynamic viscoelasticity measurement. The measurement device that can be used is the Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific, Inc., or an equivalent. The storage modulus G' and glass transition temperature Tg of the adhesive can be adjusted, for example, by selecting the type and amount of refractive index adjuster, selecting the composition of the base polymer (e.g., selecting the type and content of monomer (m1)), whether or not to use a crosslinking agent, and selecting the type and amount used, etc. [Measurement conditions] Deformation mode: Torsion Measurement frequency: 1Hz Temperature range: -50℃~150℃ Heating rate: 5°C / min

[0164] <Adhesive sheet> This specification provides a pressure-sensitive adhesive sheet having any of the pressure-sensitive adhesives disclosed herein (which may be a pressure-sensitive adhesive formed from any of the pressure-sensitive adhesive compositions disclosed herein, for example, a cured product of the pressure-sensitive adhesive composition), preferably in the form of a pressure-sensitive adhesive layer. The PSA sheet may be a substrate-attached PSA sheet having the PSA layer on one or both sides of a non-releasable substrate (support substrate), or may be a substrate-less PSA sheet (i.e., a PSA sheet without a non-releasable substrate; typically, a PSA sheet consisting of a PSA layer) in which the PSA layer is supported on a release liner. The concept of PSA sheet here may include what are called PSA tapes, PSA labels, PSA films, etc. The PSA sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, it may be a PSA sheet processed into various shapes.

[0165] Examples of the configuration of a double-sided adhesive substrateless PSA sheet (substrateless double-sided PSA sheet) are shown in Figures 1 and 2. PSA sheet 1 shown in Figure 1 has a configuration in which both surfaces 21A and 21B of substrateless PSA layer 21 are protected by release liners 31 and 32, respectively, with at least the PSA layer side serving as a release surface. PSA sheet 2 shown in Figure 2 has a configuration in which one surface (adhesive surface) 21A of substrateless PSA layer 21 is protected by release liner 31, with both surfaces serving as release surfaces. When rolled up, other surface (adhesive surface) 21B of PSA layer 21 abuts against the back surface of release liner 31, so that other surface 21B is also protected by release liner 31. The technology disclosed herein is preferably implemented in the form of a substrateless PSA sheet made of a PSA layer, from the viewpoint of flexibility that allows it to conform to an adherend even when repeatedly folded. The substrateless PSA sheet is also preferable from the viewpoint of, for example, reducing the thickness of the PSA sheet and increasing the transparency of the PSA sheet.

[0166] The pressure-sensitive adhesive sheet disclosed herein may have, for example, a cross-sectional structure schematically shown in FIG. 3. The pressure-sensitive adhesive sheet 3 shown in FIG. 3 comprises a support substrate 10 and a first pressure-sensitive adhesive layer 21 and a second pressure-sensitive adhesive layer 22 supported on a first surface 10A and a second surface 10B, respectively, of the support substrate 10. Both the first surface 10A and the second surface 10B are non-releasable surfaces (non-releasable surfaces). The pressure-sensitive adhesive sheet 3 is used by attaching the surface (first adhesive surface) 21A of the first pressure-sensitive adhesive layer 21 and the surface (second adhesive surface) 22A of the second pressure-sensitive adhesive layer 22 to an adherend, respectively. That is, the pressure-sensitive adhesive sheet 3 is configured as a double-sided pressure-sensitive adhesive sheet (double-sided adhesive sheet). Before use, the pressure-sensitive adhesive sheet 3 has a configuration in which the first adhesive surface 21A and the second adhesive surface 22A are protected by release liners 31 and 32, at least the adhesive surface side of which is a releasable surface (releasable surface). Alternatively, the release liner 32 may be omitted, and a release liner 31 having release surfaces on both sides may be used, and the adhesive sheet 3 may be rolled up so that the second adhesive surface 22A is abutted against the back surface of the release liner 31, thereby configuring the second adhesive surface 22A to also be protected by the release liner 31.

[0167] The technology disclosed herein is preferably implemented in the form of the above-mentioned substrate-less or substrate-attached double-sided PSA sheet for fixing or joining components (e.g., optical components). Alternatively, although not specifically shown, the PSA sheet disclosed herein may be in the form of a substrate-attached single-sided PSA sheet having a PSA layer on only one side of a non-releasable substrate (support substrate). An example of a single-sided PSA sheet is one having the structure shown in FIG. 3 without either the first PSA layer 21 or the second PSA layer 22.

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

[0169] The thickness of the pressure-sensitive adhesive layer is not particularly limited and can be, for example, 3 μm or more. In some embodiments, the thickness of the pressure-sensitive adhesive layer is suitably, for example, 5 μm or more, and may be 10 μm or more, 15 μm or more, 20 μm or more, 30 μm or more, 50 μm or more, 70 μm or more, or 85 μm or more. Increasing the thickness of the pressure-sensitive adhesive layer tends to increase adhesive strength. Furthermore, in some embodiments, the thickness of the pressure-sensitive adhesive layer may be, for example, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 120 μm or less. In some preferred embodiments, the thickness of the pressure-sensitive adhesive layer is 100 μm or less, more preferably 75 μm or less, even more preferably 70 μm or less, and may be 50 μm or less, or 30 μm or less. A pressure-sensitive adhesive layer that is not too thick can be advantageous from the perspective of, for example, reducing the thickness of the pressure-sensitive adhesive sheet. Furthermore, a thin pressure-sensitive adhesive layer tends to have excellent conformability to an adherend. The technology disclosed herein can be preferably implemented, for example, in an embodiment in which the thickness of the pressure-sensitive adhesive layer is in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm, and even more preferably 5 μm to 75 μm). In the case of a pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on a first surface and a second surface of a substrate, the thickness of the pressure-sensitive adhesive layer described above can be applied to at least the thickness of the first pressure-sensitive adhesive layer. The thickness of the second pressure-sensitive adhesive layer can also be selected from a similar range. In the case of a substrate-less pressure-sensitive adhesive sheet, the thickness of the pressure-sensitive adhesive sheet is the same as the thickness of the pressure-sensitive adhesive layer.

[0170] (Optical properties) In some embodiments, the haze value of the pressure-sensitive adhesive layer may be, for example, 5.0% or less, preferably 3.0% or less, more preferably 2.0% or less, even more preferably 1.0% or less, and particularly preferably less than 1.0% (e.g., 0.9% or less). Pressure-sensitive adhesive sheets having such highly transparent pressure-sensitive adhesive layers, with or without a substrate, are preferably used in applications requiring high light transmittance (e.g., optical applications) or applications requiring good visibility of the adherend through the pressure-sensitive adhesive sheet. The lower limit of the haze value of the pressure-sensitive adhesive layer is not particularly limited, and a smaller haze value is preferable from the viewpoint of improving transparency. Meanwhile, in some embodiments, taking into consideration the refractive index and adhesive properties, the haze value may be, for example, 0.05% or more, or even 0.10% or more. These haze values ​​for the pressure-sensitive adhesive layer may also be preferably applied to the haze value of a pressure-sensitive adhesive sheet when the technology disclosed herein is implemented in the form of a substrateless pressure-sensitive adhesive sheet (typically, a pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer).

[0171] Here, the "haze value" refers to the ratio of diffuse transmitted light to total transmitted light when visible light is irradiated onto a measurement object. It is also called the cloudiness value. The haze value can be expressed by the following formula: Th(%)=Td / Tt×100 In the above formula, Th is the haze value (%), Td is the scattered light transmittance, and Tt is the total light transmittance. The haze value can be measured according to the method described in the Examples below. The haze value of the pressure-sensitive adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the pressure-sensitive adhesive layer.

[0172] In some embodiments, the haze value of the pressure-sensitive adhesive sheet may be, for example, 5.0% or less, preferably 3.0% or less, more preferably 2.0% or less, even more preferably 1.0% or less, and particularly preferably less than 1.0% (e.g., 0.9% or less). Such highly transparent pressure-sensitive adhesive sheets are preferably used in applications requiring high light transmittance (e.g., optical applications) or applications requiring good visibility of the adherend through the pressure-sensitive adhesive sheet. There is no particular lower limit for the haze value of the pressure-sensitive adhesive sheet, and from the viewpoint of improving transparency, a smaller haze value is preferable. Meanwhile, in some embodiments, taking into consideration the refractive index and adhesive properties, the haze value may be, for example, 0.05% or more, or even 0.10% or more. The haze value of the pressure-sensitive adhesive sheet can be measured in the same manner as in measuring the haze value of the pressure-sensitive adhesive layer. The haze value of the pressure-sensitive adhesive sheet can be obtained by selecting the composition of the pressure-sensitive adhesive layer described above, or, in configurations having a substrate, the type and thickness of the substrate.

[0173] In some embodiments, the total light transmittance of the pressure-sensitive adhesive layer is preferably 85.0% or more (e.g., 88.0% or more, 90.0% or more, or more than 90.0%). Pressure-sensitive adhesive sheets having such highly transparent pressure-sensitive adhesive layers, with or without a substrate, can be preferably used in applications requiring high light transmittance (e.g., optical applications) or applications requiring good visibility of the adherend through the pressure-sensitive adhesive sheet. The upper limit of the total light transmittance may be, for example, approximately 98% or less, approximately 96% or less, or approximately 95% or less in practice. In some embodiments, taking into account the refractive index and adhesive properties, the total light transmittance of the pressure-sensitive adhesive layer may be approximately 94% or less, approximately 93% or less, or approximately 92% or less. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. The transmittance meter used may be a product manufactured by Murakami Color Research Laboratory under the trade name "HAZEMETER HM-150" or an equivalent product. The total light transmittance can be measured according to the method described in the Examples below. The total light transmittance of the pressure-sensitive adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the pressure-sensitive adhesive layer.

[0174] In some embodiments, the total light transmittance of the pressure-sensitive adhesive sheet is preferably 85.0% or more (e.g., 88.0% or more, 89.0% or more, or 90.0% or more). Such highly transparent pressure-sensitive adhesive sheets can be preferably used in applications requiring high light transmittance (e.g., optical applications) or applications requiring good visibility of the adherend through the pressure-sensitive adhesive sheet. The upper limit of the total light transmittance may be, for example, approximately 98% or less, approximately 96% or less, or approximately 95% or less in practice. In some embodiments, taking into account the refractive index and adhesive properties, the total light transmittance of the pressure-sensitive adhesive sheet may be approximately 94% or less, approximately 93% or less, or approximately 92% or less. The total light transmittance of the pressure-sensitive adhesive sheet can be measured in the same manner as in measuring the total light transmittance of the pressure-sensitive adhesive layer described above. The total light transmittance of the pressure-sensitive adhesive sheet can be obtained by selecting the composition of the pressure-sensitive adhesive layer described above, or, in configurations having a substrate, the type and thickness of the substrate.

[0175] L of adhesive layer * a * b * Chromaticity b specified in the color system * is not particularly limited, but in some embodiments (for example, embodiments expected to be applied to optical applications), it is appropriate to set it in the range of ±15, preferably in the range of ±10, and more preferably in the range of ±5.0 (for example, in the range of ±1.0). In this specification, the term "range of ±X" is used to mean the range from -X to +X. Here, L in this specification * a * b * The color system shall comply with the standards recommended by the International Commission on Illumination in 1976 or the standards of JIS Z 8729. * a * b * The value may be measured at multiple locations (for example, five or more locations) on the surface of the pressure-sensitive adhesive layer using a color difference meter (product name "CR-400" manufactured by Minolta Co., Ltd.), and the average value may be used. The same applies to the examples described later.

[0176] (peel strength) The peel strength of the pressure-sensitive adhesive sheet to a glass plate is not particularly limited.In some embodiments, the peel strength of the pressure-sensitive adhesive sheet to a glass plate is, for example, 0.1N / 25mm or more, preferably 0.5N / 25mm or more, and may be 1.0N / 25mm or more, 1.5N / 25mm or more, 2.0N / 25mm or more, or 3.0N / 25mm or more.The upper limit of the peel strength is not particularly limited, and may be, for example, 30N / 25mm or less, 25N / 25mm or less, or 20N / 25mm or less. Here, the peel strength is determined by pressing the sheet against an alkaline glass plate as an adherend, leaving it in an environment of 23°C and 50% RH for 30 minutes, and then measuring the peel strength under conditions of a peel angle of 180° and a pulling speed of 300 mm / min. If necessary, the pressure-sensitive adhesive sheet to be measured can be reinforced by attaching an appropriate backing material (for example, a polyethylene terephthalate (PET) film with a thickness of about 25 μm to 50 μm) to the sheet.

[0177] (Adhesive sheet thickness) The thickness of the adhesive sheet (substrate-less adhesive sheet or substrate-attached adhesive sheet) disclosed herein may be, for example, 1000 μm or less, 350 μm or less, 200 μm or less, 120 μm or less, 75 μm or less, or 50 μm or less. From the standpoint of handleability, etc., the thickness of the adhesive sheet may be, for example, 5 μm or more, 10 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more. The thickness of the adhesive sheet refers to the thickness of the portion that is attached to the adherend. For example, in the case of adhesive sheet 3 having the configuration shown in Figure 3, the thickness refers to the thickness from first adhesive surface 21A to second adhesive surface 22A, and does not include the thickness of release liners 31 and 32.

[0178] <Supporting base material> PSA sheets according to some embodiments may be in the form of a substrate-attached PSA sheet comprising a PSA layer on one or both sides of a support substrate. The material of the support substrate is not particularly limited and can be appropriately selected depending on the intended use and manner of use of the PSA sheet. Non-limiting examples of usable substrates include plastic films such as polyolefin films primarily composed of polyolefins such as polypropylene (PP) or ethylene-propylene copolymers; polyester films primarily composed of polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); and polyvinyl chloride films primarily composed of polyvinyl chloride; foam sheets composed of foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam; woven and nonwoven fabrics made by spinning various fibrous materials (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc.) alone or in combination; papers such as Japanese paper, fine paper, kraft paper, and crepe paper; and metal foils such as aluminum foil and copper foil. Substrates having a composite structure of these materials are also possible. Examples of such composite substrates include substrates having a structure in which a metal foil and the above-mentioned plastic film are laminated together, and plastic substrates reinforced with inorganic fibers such as glass cloth.

[0179] In some embodiments, various film substrates can be preferably used. The film substrate may be a porous substrate such as a foam film or a nonwoven fabric sheet, or a nonporous substrate, or a substrate having a structure in which a porous layer and a nonporous layer are laminated. In some embodiments, the film substrate preferably includes a base film that is an independently shape-retaining (self-supporting or independent) resin film. Here, the term "resin film" refers to a resin film that has a nonporous structure and typically contains substantially no air bubbles (void-free). Therefore, the resin film is a concept that is distinct from foam films and nonwoven fabrics. The resin film preferably includes an independently shape-retaining (self-supporting or independent) resin film. The resin film may have a single-layer structure or a multilayer structure of two or more layers (e.g., a three-layer structure).

[0180] Examples of resin materials that can be used to form the resin film include polyesters; polyolefins; polycycloolefins derived from monomers having an aliphatic ring structure such as a norbornene structure; polyamides (PA) such as nylon 6, nylon 66, and partially aromatic polyamides; polyimides (PI) such as transparent polyimide (CPI); polyamideimide (PAI); polyether ether ketone (PEEK); polyethersulfone (PES); polyphenylene sulfide (PPS); polycarbonate (PC); polyurethane (PU); ethylene-vinyl acetate copolymer (EVA); fluororesins such as polytetrafluoroethylene (PTFE); acrylic resins; cellulose-based polymers such as triacetyl cellulose (TAC); polyarylates; polystyrene; polyvinyl chloride; and polyvinylidene chloride.

[0181] The resin film may be formed using a resin material containing one of these resins alone, or may be formed using a resin material containing a blend of two or more of these resins. The resin film may be unstretched or stretched (for example, uniaxially or biaxially stretched). For example, PET film, PBT film, PEN film, unstretched polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, PP / PE blend film, cycloolefin polymer (COP) film, CPI film, TAC film, etc. are preferably used. Examples of resin films that are preferred from the standpoint of strength and dimensional stability include PET film, PEN film, PPS film, and PEEK film. PET film and PPS film are particularly preferred from the standpoint of availability, and PET film is particularly preferred.

[0182] The resin film may contain known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, antiblocking agents, etc., as needed, provided that the effects of the present invention are not significantly impaired. The amount of additives added is not particularly limited and can be set appropriately depending on the application of the PSA sheet, etc.

[0183] The method for producing the resin film is not particularly limited, and any conventionally known resin film forming method such as extrusion molding, inflation molding, T-die casting, or calendar roll molding can be appropriately used.

[0184] The substrate may be substantially composed of such a base film. Alternatively, the substrate may include an auxiliary layer in addition to the base film. Examples of the auxiliary layer include an optical property adjusting layer (e.g., a coloring layer, an anti-reflection layer), a printed layer or a laminate layer for imparting a desired appearance to the substrate, an antistatic layer, an undercoat layer, a release layer, or other surface treatment layer.

[0185] In some embodiments, a substrate having optical transparency (hereinafter also referred to as an optically transparent substrate) can be preferably used as the support substrate. This makes it possible to construct a substrate-attached pressure-sensitive adhesive sheet having optical transparency. The total light transmittance of the optically transparent substrate may be, for example, more than 50%, or may be 70% or more. In some preferred embodiments, the total light transmittance of the support substrate is 80% or more, more preferably 90% or more, and may even be 95% or more (e.g., 95 to 100%). The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. The transmittance meter used may be a product name "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory or an equivalent. A suitable example of the optically transparent substrate is a resin film having optical transparency. The optically transparent substrate may also be an optical film.

[0186] The thickness of the substrate is not particularly limited and can be selected depending on the purpose and mode of use of the pressure-sensitive adhesive sheet. The thickness of the substrate may be, for example, 500 μm or less, and from the viewpoint of the handleability and processability of the pressure-sensitive adhesive sheet, it is preferably 300 μm or less, and may be 150 μm or less, 100 μm or less, 50 μm or less, 25 μm or less, or 10 μm or less. As the thickness of the substrate decreases, the ability to conform to the surface shape of the adherend tends to improve. Furthermore, from the viewpoint of handleability and processability, the thickness of the substrate may be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

[0187] The surface of the substrate on which the pressure-sensitive adhesive layer is to be laminated may be subjected to conventional surface treatments, such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or the formation of an undercoat layer by applying a primer. Such surface treatments may be intended to improve the anchoring of the pressure-sensitive adhesive layer to the substrate. The composition of the primer used to form the undercoat layer is not particularly limited and can be appropriately selected from known primers. The thickness of the undercoat layer is not particularly limited, but is typically approximately 0.01 μm to 1 μm, preferably approximately 0.1 μm to 1 μm. Other treatments that may be applied to the substrate as needed include antistatic layer formation treatment, colored layer formation treatment, printing treatment, etc. These treatments may be applied alone or in combination.

[0188] <Adhesive sheet with release liner> The PSA sheet disclosed herein can take the form of a PSA product in which the surface (adhesive surface) of the PSA layer is in contact with the release surface of a release liner. Accordingly, this specification provides a PSA sheet with a release liner (adhesive product) comprising any of the PSA sheets disclosed herein and a release liner having a release surface in contact with the adhesive surface of the PSA sheet.

[0189] The release liner is not particularly limited, and examples thereof include a release liner having a release layer on the surface of a liner substrate such as a resin film or paper (which may be paper laminated with a resin such as polyethylene), and a release liner made of a resin film formed from a low-adhesion material such as a fluorine-based polymer (such as polytetrafluoroethylene) or a polyolefin resin (such as polyethylene or polypropylene). Because of their excellent surface smoothness, release liners having a release layer on the surface of a resin film as a liner substrate and release liners made of a resin film formed from a low-adhesion material are preferably used. The resin film is not particularly limited as long as it is a film that can protect the pressure-sensitive adhesive layer, and examples thereof include polyethylene (PE) film, polypropylene (PP) film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyester film (such as PET film or PBT film), polyurethane film, and ethylene-vinyl acetate copolymer film. To form the release layer, known release treatment agents can be used, such as silicone-based release treatment agents, long-chain alkyl-based release treatment agents, olefin-based release treatment agents, fluorine-based release treatment agents, fatty acid amide-based release treatment agents, molybdenum sulfide, and silica powder.

[0190] <Application> The material (adherend material) to which the pressure-sensitive adhesive sheet disclosed herein can be attached is not particularly limited, and examples thereof include metal materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, zinc, etc., or alloys containing two or more of these metals; polyimide resins, acrylic resins, polyethernitrile resins, polyethersulfone resins, polyester resins (PET resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyetheretherketone resins, polyamide resins (so-called aramid resins, etc.); polyarylate resins, polycarbonate resins, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, vinyl butyral polymers, liquid crystal polymers, and other resin materials (typically plastic materials); and inorganic materials such as alumina, zirconia, alkali glass, alkali-free glass, quartz glass, and carbon. The pressure-sensitive adhesive sheet disclosed herein can be attached to a member (e.g., an optical member) made of the above materials.

[0191] The component or material to which the PSA sheet disclosed herein is attached (in the case of a double-sided PSA sheet, at least one of the adherends) may be made of a material with a higher refractive index than that of a typical acrylic PSA. The refractive index of the adherend material is, for example, 1.50 or higher, with some having a refractive index of 1.55 or higher, 1.58 or higher, and even 1.62 or higher (e.g., approximately 1.66). Such high-refractive-index adherend materials are typically resin materials. More specifically, they may be polyester resins such as PET, polyimide resins, aramid resins, polyphenylene sulfide resins, polycarbonate resins, etc. The effect of using the PSA sheet disclosed herein with such materials (suppression of light reflection due to the difference in refractive index) can be preferably exerted. The upper limit of the refractive index of the adherend material is, for example, 1.80 or lower, and may be 1.70 or lower. The PSA sheet disclosed herein can be preferably used in a mode in which it is attached to an adherend (e.g., a component) having a high refractive index as described above. A suitable example of such an adherend is a resin film having a refractive index of 1.50 to 1.80 (preferably 1.55 to 1.75, for example 1.60 to 1.70). The refractive index can be measured in the same manner as the refractive index of the pressure-sensitive adhesive.

[0192] The member or material to which the PSA sheet is attached (in the case of a double-sided PSA sheet, at least one of the adherends) may be optically transparent. With such an adherend, the benefits of the technology disclosed herein (suppression of light reflection at the interface between the adherend and the PSA sheet) are readily obtained. The total light transmittance of the adherend may be, for example, greater than 50%, preferably 70% or greater. In some preferred embodiments, the total light transmittance of the adherend is 80% or greater, more preferably 90% or greater, and may be 95% or greater (e.g., 95 to 100%). The PSA sheet disclosed herein is preferably used in an embodiment where it is attached to an adherend (e.g., an optical component) having a total light transmittance of a predetermined value or greater. The total light transmittance is measured in accordance with JIS K 7136:2000 using a commercially available transmittance meter. The transmittance meter used may be a product called "HAZEMETER HM-150" manufactured by Murakami Color Research Laboratory, or an equivalent.

[0193] In some preferred embodiments, the adherend (e.g., member) to which the PSA sheet is attached may have the above-mentioned refractive index and total light transmittance. Specifically, the PSA sheet disclosed herein can be preferably used in an embodiment where it is attached to an adherend, e.g., member, having a refractive index of 1.50 or higher (e.g., 1.55 or higher, 1.58 or higher, 1.62 or higher, or approximately 1.66, etc.) and a total light transmittance of more than 50% (e.g., 70% or higher, preferably 80% or higher, more preferably 90% or higher, or even 95% or higher). In an embodiment where it is attached to such a member, the effects of the technology disclosed herein are particularly preferably exhibited.

[0194] An example of a preferred application is an optical application. More specifically, the pressure-sensitive adhesive sheet disclosed herein can be preferably used as an optical pressure-sensitive adhesive sheet used for bonding optical members (for bonding optical members) or for manufacturing products (optical products) using the optical members.

[0195] The optical member refers to a member having optical properties (e.g., polarization, light refraction, light scattering, light reflectivity, light transmittance, light absorption, light diffraction, optical rotation, visibility, etc.). The optical member is not particularly limited as long as it has optical properties, and examples thereof include components constituting devices (optical devices) such as display devices (image display devices) and input devices, or components used in these devices, such as polarizing plates, wavelength plates, retardation plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflection films, hard coat (HC) films, impact absorbing films, antifouling films, photochromic films, light control films, transparent conductive films (ITO films), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and further components in which these are laminated (these may be collectively referred to as "functional films"). The above-mentioned "plate" and "film" respectively include forms such as a plate, a film, and a sheet, and for example, "polarizing film" includes "polarizing plate" and "polarizing sheet", and "light guide plate" includes "light guide film" and "light guide sheet", etc. Furthermore, the above-mentioned "polarizing plate" includes a circular polarizing plate.

[0196] Examples of the display device include a liquid crystal display device, an organic EL display device, a micro LED (μLED), a mini LED (miniLED), a PDP, electronic paper, etc. Examples of the input device include a touch panel, etc.

[0197] The optical member is not particularly limited, but examples thereof include members (e.g., sheet-shaped, film-shaped, or plate-shaped members) made of glass, acrylic resin, polycarbonate, PET, metal thin film, etc. In this specification, the term "optical member" also includes members (such as decorative films, ornamental films, and surface protection films) that serve to decorate or protect a display device or input device while maintaining its visibility.

[0198] The technology disclosed herein can be preferably used, for example, to bond an optical film, such as a film having one or more functions of light transmission, reflection, diffusion, waveguiding, light focusing, and diffraction, or a fluorescent film, to another optical member (which may be another optical film). In particular, in bonding an optical film having at least one function of light guide, light focusing, and diffraction, it is desirable that the entire bulk of the bonding layer has a high refractive index, and this can be a preferred application of the technology disclosed herein.

[0199] The pressure-sensitive adhesives disclosed herein can be preferably used for bonding optical films such as light-guiding films, diffusion films, fluorescent films, color-tuning films, prism sheets, lenticular films, and microlens array films. In these applications, due to the trend toward miniaturization and high performance of optical components, thinner films and improved light extraction efficiency are required. The pressure-sensitive adhesives disclosed herein can be preferably used as pressure-sensitive adhesives that can meet such requirements. More specifically, for example, in bonding light-guiding films or diffusion films, adjusting the refractive index of the pressure-sensitive adhesive layer as a bonding layer (e.g., increasing the refractive index) can contribute to thinner films. In bonding fluorescent films, appropriately adjusting the refractive index difference between the fluorescent emitter and the pressure-sensitive adhesive can improve light extraction efficiency (which can also be understood as luminous efficiency). In bonding color-tuning films, appropriately adjusting the refractive index of the pressure-sensitive adhesive to reduce the refractive index difference with the color-tuning pigment can reduce scattered components and contribute to improved light transmittance. In bonding prism sheets, lenticular films, microlens array films, and the like, appropriately adjusting the refractive index of the pressure-sensitive adhesive can control light diffraction, contributing to improved brightness and / or viewing angle.

[0200] The pressure-sensitive adhesive sheet disclosed herein is preferably used in an embodiment in which it is attached to an adherend having a high refractive index (which may be a high-refractive index layer, member, or the like), thereby suppressing interfacial reflection with the adherend. The pressure-sensitive adhesive sheet used in such an embodiment preferably has a small refractive index difference from the adherend and high adhesion at the interface with the adherend, as described above. Furthermore, from the viewpoint of enhancing the uniformity of the appearance, it is preferable that the pressure-sensitive adhesive layer has a highly uniform thickness, and for example, it is preferable that the adhesive surface has high surface smoothness. When the thickness of the high-refractive-index adherend is relatively small (for example, 5 μm or less, 4 μm or less, or 2 μm or less), suppressing interfacial reflection is particularly meaningful from the viewpoint of suppressing coloring and color unevenness due to interference of reflected light. One example of such a usage embodiment is an embodiment in which the pressure-sensitive adhesive sheet is used to bond the polarizer to the first retardation layer and / or the first retardation layer to the second retardation layer in a polarizing plate with a retardation layer, which includes a polarizer, a first retardation layer, and a second retardation layer in this order.

[0201] Furthermore, since the adhesive sheet disclosed herein is suitable for achieving a high refractive index, it can be preferably used in an embodiment in which it is attached to an emitting layer of an optical semiconductor or the like (for example, a highly refractive emitting layer composed mainly of inorganic materials). By reducing the difference in refractive index between the emitting layer and the adhesive layer, reflection at the interface therebetween can be suppressed, and light extraction efficiency can be improved. The adhesive sheet used in such an embodiment preferably has an adhesive layer with a high refractive index. Furthermore, from the viewpoint of improving brightness, it is preferable that the adhesive sheet has low coloration. This can also be advantageous from the viewpoint of suppressing unintentional coloration caused by the adhesive sheet.

[0202] The adhesive sheet disclosed herein can be preferably used in a light-emitting device including a self-luminous element as a component, in a configuration in which the adhesive sheet is arranged on the viewing side of the self-luminous element. Here, the self-luminous element refers to a light-emitting element whose luminance can be controlled by the value of the current flowing through it. The self-luminous element may be composed of a single element or an aggregate. Specific examples of the self-luminous element include, but are not limited to, light-emitting diodes (LEDs) and organic electroluminescent devices. Examples of light-emitting devices including the self-luminous element as a component include, but are not limited to, light source module devices (e.g., surface light-emitting module) used for lighting and display devices having pixels formed thereon.

[0203] The pressure-sensitive adhesives disclosed herein can be preferably used in microlenses and other lens components (e.g., microlenses constituting microlens array films and lens components such as camera microlenses) used as components of cameras, light-emitting devices, etc., as coating layers covering the lens surfaces, bonding layers for components facing the lens surfaces (e.g., components having a surface shape corresponding to the lens surfaces), filling layers filled between the lens surfaces and the components, etc. The pressure-sensitive adhesives disclosed herein are suitable for increasing the refractive index, and can therefore reduce the refractive index difference with high-refractive-index lenses (e.g., lenses made of high-refractive-index resins or lenses having a surface layer made of high-refractive-index resins). This is advantageous from the perspective of thinning the lenses and products incorporating the lenses, and can also contribute to suppressing aberrations and improving the Abbe number. The pressure-sensitive adhesives disclosed herein can also be used as lens resins themselves, for example, by filling recesses or voids in an appropriate transparent member.

[0204] The embodiment of bonding optical members using the pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and may be, for example, (1) a mode in which optical members are bonded to each other via the pressure-sensitive adhesive sheet disclosed herein, (2) a mode in which an optical member is bonded to a member other than an optical member via the pressure-sensitive adhesive sheet disclosed herein, or (3) a mode in which the pressure-sensitive adhesive sheet disclosed herein includes an optical member and the pressure-sensitive adhesive sheet is bonded to an optical member or a member other than an optical member. In the above-mentioned embodiment (3), the pressure-sensitive adhesive sheet including an optical member may be, for example, a pressure-sensitive adhesive sheet whose support is an optical member (e.g., an optical film). Such a pressure-sensitive adhesive sheet including an optical member as a support may also be understood as a pressure-sensitive adhesive optical member (e.g., a pressure-sensitive adhesive optical film). Furthermore, when the pressure-sensitive adhesive sheet disclosed herein is a pressure-sensitive adhesive sheet having a support and the above-mentioned functional film is used as the support, the pressure-sensitive adhesive sheet disclosed herein may also be understood as a "pressure-sensitive adhesive functional film" having the pressure-sensitive adhesive layer disclosed herein on at least one side of the functional film.

[0205] As described above, the technology disclosed herein provides a laminate comprising the adhesive sheet disclosed herein and a member to which the adhesive sheet is attached. The member to which the adhesive sheet is attached may have the refractive index of the adherend material described above. Furthermore, the difference (refractive index difference) between the refractive index of the adhesive sheet and the refractive index of the member may be the refractive index difference between the adherend and the adhesive sheet described above. The members constituting the laminate are as described above for the member, material, and adherend, and therefore redundant description will not be repeated.

[0206] As will be understood from the above description and the following examples, the matters disclosed by this specification include the following. [1] A refractive index adjuster for a pressure-sensitive adhesive, The refractive index adjuster is an organic compound having a structure with two or more substituents on a hub ring, wherein the hub ring is a double bond-containing ring, and at least one of the two or more substituents is a substituent having a double bond-containing ring. [2] The refractive index adjuster according to [1] above, having a molecular weight of less than 3,000. [3] The refractive index adjuster according to [1] or [2] above, wherein two or more of the substituents on the hub ring are substituents having a double bond-containing ring. [4] The refractive index control agent according to any one of the above [1] to [3], wherein at least one of the substituents on the hub ring is a substituent having two or more double bond-containing rings. [5] The refractive index control agent according to any one of the above [1] to [4], wherein the hub ring is a triazine ring.

[0207] [6] The following formula (I): [ka] (In formula (I), X 1 ,X 2 and X 3 are each independently -O-, -S- and -NR 4 -, where R 4 is a hydrogen atom or an alkyl group, R 1 ,R 2 and R 3 one or more of the groups are each independently an aromatic ring-containing group selected from the group consisting of an optionally substituted phenyl group and an optionally substituted biphenyl group, wherein the substituent is an alkyl group, an alkoxy group, or a cyano group; R 1 ,R 2 and R 3 When there are two or less aromatic ring-containing groups, the remainder are aliphatic hydrocarbon groups or hydrogen atoms; A compound represented by the formula: [7] X above 1 ,X 2 and X 3 wherein two or more of are independently selected from -O- and -S-. [8] X above 1 ,X 2 and X 3 The compound according to [6] above, wherein each of [9] X above 1 ,X 2 and X 3 The compound according to [6] above, wherein each of

[10] R above 1 ,R 2 and R 3 are each independently a substituted or unsubstituted 2-biphenyl.

[11] A refractive index adjuster comprising the compound according to any one of [6] to

[10] above.

[0208]

[12] A pressure-sensitive adhesive comprising the refractive index adjuster according to any one of [1] to [5] and

[11] above.

[13] The pressure-sensitive adhesive according to the above

[12] , further comprising an acrylic polymer containing an aromatic ring-containing monomer (m1) as a monomer unit.

[14] The pressure-sensitive adhesive according to

[12] or

[13] , wherein the monomer components constituting the acrylic polymer contain, in addition to the aromatic ring-containing monomer (m1), a monomer (m2) having at least one of a hydroxyl group and a carboxyl group.

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

[12] to

[14] , wherein the content of the aromatic ring-containing monomer (m1) in the monomer components is 60% by weight or more.

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

[12] to

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

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

[12] to

[16] above, wherein the content of the refractive index control agent relative to 100 parts by weight of the acrylic polymer is 0.1 parts by weight or more and 80 parts by weight or less.

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

[12] to

[17] , which has a refractive index of 1.550 or more.

[0209]

[19] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to any one of

[12] to

[18] above.

[20] The pressure-sensitive adhesive sheet according to

[19] above, wherein the pressure-sensitive adhesive layer has a thickness in the range of 5 to 75 μm.

[21] The pressure-sensitive adhesive sheet according to

[19] or

[20] above, which has a total light transmittance of 85% or more.

[22] The pressure-sensitive adhesive sheet according to any one of the above

[19] to

[21] , which has a haze value of 3% or less.

[23] L * a * b * Chromaticity b specified in the color system * The pressure-sensitive adhesive sheet according to any one of the above

[19] to

[22] , wherein the difference is in the range of ±5. [Example]

[0210] Several examples of the present invention will be described below, but it is not intended that the present invention be limited to these specific examples. In the following description, "parts" and "%" representing amounts used and contents are by weight unless otherwise specified.

[0211] In the following synthesis examples, the refractive index of each compound was measured as follows. That is, a 5% ethyl acetate solution or a 5% MEK solution of the compound to be measured was prepared. This solution was applied to a glass plate so that the dry film thickness was 10 μm, and the plate was dried by heating at 130° C. for 5 minutes. The refractive index of the compound to be measured thus formed as a film on the glass plate was measured using a prism coupler (Metricon, model "2010M") at a measurement temperature of 25° C. and a measurement wavelength of 594 nm.

[0212] <Synthesis Example 1: Synthesis of Compound A1> [ka]

[0213] Under a nitrogen atmosphere, biphenyl-2-ol (5.28 g, 31 mmol), acetone (50 mL), and potassium hydroxide (1.74 g, 31 mmol) were charged into a reaction vessel and stirred at room temperature for 30 minutes. A solution of cyanuric chloride (1.84 g, 10 mmol) in acetone (20 mL) was added dropwise over 15 minutes, and the mixture was stirred at room temperature for 2 hours, followed by stirring at 55 °C for 8 hours. The reaction mixture was poured into 800 mL of distilled water, resulting in the formation of an oily precipitate. The supernatant was removed by decantation and the mixture was dried under reduced pressure at 100 °C for 4 hours to obtain a glassy solid (2.7 g). This solid was dissolved in acetone (20 mL) and poured into hexane (100 mL). After standing at room temperature for 24 hours, the supernatant was removed, and the oily precipitate was collected and dried under reduced pressure at 80 °C for 4 hours to obtain 2.25 g (3.84 mmol) of compound A1. The yield was 38.4%. Compound A1 exhibited solubility such that a 50% solution could be prepared in each of methyl ethyl ketone (MEK) and ethyl acetate. The refractive index was 1.645. 1 H-NMR (400 MHz, CDCl3) spectrum and 13 The C-NMR (400 MHz, CDCl3) spectra are shown in Figures 4 and 5, respectively.

[0214] <Synthesis Example 2: Synthesis of Compound A2> [ka]

[0215] Under a nitrogen atmosphere, biphenyl-4-ol (5.28 g, 31 mmol), acetone (50 mL), potassium hydroxide (1.74 g, 31 mmol), and water (20 mL) were charged into a reaction vessel and stirred at room temperature for 30 minutes. A solution of cyanuric chloride (1.84 g, 10 mmol) in acetone (20 mL) was added dropwise over 15 minutes, and the mixture was stirred at room temperature for 24 hours, resulting in the precipitation of a white solid. The reaction solution was poured into 800 mL of distilled water, and the white powdery precipitate was collected by filtration and dried under reduced pressure at 80°C for 6 hours to obtain a white solid (5 g). This was recrystallized from acetone to obtain 4.85 g (7.94 mmol) of Compound A2. The yield was 79.4%. 1H-NMR (400 MHz, CDCl3) spectrum and 13 The C-NMR (400 MHz, CDCl3) spectra are shown in Figures 6 and 7, respectively.

[0216] <Synthesis Example 3: Synthesis of Compound A3> [ka]

[0217] Under a nitrogen atmosphere, biphenyl-4-ol (5.28 g, 31 mmol), acetone (50 mL), potassium hydroxide (1.74 g, 31 mmol), and water (20 mL) were charged into a reaction vessel and stirred at room temperature for 30 minutes. A solution of 2,4-dichloro-6-methoxytriazine (1.80 g, 10 mmol) in acetone (30 mL) was added to the reaction vessel and stirred at room temperature for 24 hours. The reaction mixture was poured into 800 mL of distilled water, and the resulting white powdery precipitate was collected by filtration, dried under reduced pressure at 80°C for 5 hours, and recrystallized from acetone to obtain 1.81 g (2.96 mmol) of compound A3. The yield was 30.2%. Compound A3 exhibited solubility such that a 7% solution could be prepared in MEK. The amount of compound A3 was 1.81 g (2.96 mmol). 1 H-NMR (400 MHz, CDCl3) spectrum and 13 The C-NMR (400 MHz, CDCl3) spectra are shown in Figures 8 and 9, respectively.

[0218] <Synthesis Example 4: Synthesis of Compound A4> [ka]

[0219] Under a nitrogen atmosphere, biphenyl-2-thiol (19.8 g, 106.3 mmol) and acetone (100 mL) were charged into a reaction vessel, and an 85% aqueous solution of potassium hydroxide (7.1 g, 67.3 mmol) was added. The mixture was stirred at room temperature for 1 hour. The system was cooled to 10 °C, and a solution of cyanuric chloride (6 g, 34.3 mmol) in acetone (60 mL) was added dropwise over 15 minutes. The mixture was then stirred at room temperature for 6 hours. Water was then added, the mixture was neutralized with 0.1 M hydrochloric acid, extracted with ethyl acetate, dried over sodium sulfate, filtered, and concentrated. The mixture was purified by silica gel column chromatography using a 10:1 (volume ratio) mixture of ethyl acetate and heptane to obtain 13 g (20.5 mmol) of compound A4. The yield was 59.8%. Compound A4 exhibited solubility sufficient to prepare 50% solutions in both methyl ethyl ketone (MEK) and ethyl acetate. The refractive index was 1.702. Compound A4 1 H-NMR (400 MHz, CDCl3) spectrum and 13 The C-NMR (400 MHz, CDCl3) spectra are shown in Figures 10 and 11, respectively.

[0220] <Synthesis Example 5: Synthesis of Compound A5> [ka]

[0221] Under a nitrogen atmosphere, cyanuric chloride (9.28 g, 50 mmol), N-methylpyrrolidone (100 mL), p-toluenethiol (20.65 g, 166 mmol), and triethylamine (17.8 g, 176 mmol) were charged into a reaction vessel and stirred at 80°C for 24 hours. Water (1500 mL) was then added, the mixture was neutralized with 0.1 M hydrochloric acid, extracted with ethyl acetate (1 L), dried over sodium sulfate (200 g), filtered, and the solvent was evaporated to obtain a paste-like mixture. This mixture was washed with acetone (100 mL) to obtain 7.35 g of crude product, which was recrystallized by heating in acetone to obtain 6.5 g (14.5 mmol) of compound A5. The yield was 29%. Compound A5 was soluble in MEK, allowing the preparation of a 5% solution. The refractive index was 1.672. 1H-NMR (400 MHz, DMSO-d6) spectrum and 13 The C-NMR (400 MHz, DMSO-d) spectra are shown in Figures 12 and 13, respectively.

[0222] <Synthesis Example 6: Synthesis of Compound A6> [ka]

[0223] Under a nitrogen atmosphere, 2-ethylhexanethiol (20 mmol), tetrahydrofuran (20 mL), and potassium hydroxide (1.24 g, 22 mmol) were charged to a reaction vessel and stirred at room temperature for 2 hours, then at 60 °C for 1 hour, and allowed to cool to room temperature. A solution of cyanuric chloride (4.06 g, 20 mmol) in tetrahydrofuran (20 mL) was added dropwise over 30 minutes. After stirring at room temperature for 24 hours, the sodium chloride was removed by filtration, and the solvent was distilled off to obtain an oily compound (2,4-dichloro-6-(2-ethylhexylthio)triazine). N-methylpyrrolidone (50 mL), p-toluenethiol (5.47 g, 44 mmol), and triethylamine (5.06 g, 50 mmol) were added to the mixture and stirred at 80 °C for 24 hours. Water (1500 mL) was then added, and the precipitated oil was collected and purified by silica gel column chromatography using hexane:dichloromethane = 3:1 (volume ratio) as a developing solvent to obtain 0.57 g (1.2 mmol) of compound A6. The yield was 6%. Compound A6 showed solubility in MEK and ethyl acetate, allowing the preparation of 50% solutions. The refractive index was 1.620. 1 H-NMR (400 MHz, CDCl3) spectrum and 13 The C-NMR (400 MHz, CDCl3) spectra are shown in Figures 14 and 15, respectively.

[0224] <Synthesis Example 7: Synthesis of Compound A7> [ka]

[0225] Under a nitrogen atmosphere, 2-ethylhexanethiol (20 mmol), tetrahydrofuran (20 mL), and potassium hydroxide (1.24 g, 22 mmol) were charged to a reaction vessel and stirred at room temperature for 2 hours, then at 60 °C for 1 hour, and then allowed to cool to room temperature. A solution of 2-(4-cyanophenyl)amino-4,6-dichloro-1,3,5-triazine (2.66 g, 10 mmol) in tetrahydrofuran (10 mL) was added dropwise over 30 minutes and stirred at room temperature for 24 hours. The sodium chloride was removed by filtration, and the solvent was evaporated to give a viscous oil. The resulting oil was purified by silica gel column chromatography using a 1:1 (volume ratio) mixture of hexane and dichloromethane as a developing solvent to give 2.62 g (5.4 mmol) of compound A7 as a white viscous oil. The yield was 54%. Compound A7 exhibited solubility sufficient to prepare 50% solutions in both MEK and ethyl acetate. The refractive index of compound A7 was 1.594. 1 H-NMR (400 MHz, CDCl3) spectrum and 13 The C-NMR (400 MHz, CDCl3) spectra are shown in Figures 16 and 17, respectively. The refractive index of compound A7 was 1.645.

[0226] <Synthesis Example 8: Synthesis of Compound A8> [ka]

[0227] Methanol (110 mL), water (14 mL), and sodium bicarbonate (18.2 g, 217 mmol) were charged into a reaction vessel, and cyanuric chloride (20.0 g, 108 mmol) was added in 10 approximately 2 g portions over approximately 30 minutes. After stirring at 30°C for 1 hour, water (50 mL) was added, and the resulting white precipitate was collected by filtration, washed with water (50 mL), then with methanol (30 mL), and dried under reduced pressure at room temperature for 12 hours to obtain 14.6 g (80 mmol) of 2,4-dichloro-6-methoxytriazine. The yield was 74.6%. Under a nitrogen atmosphere, biphenyl-4-thiol (2.00 g, 10.7 mmol), acetone (40 mL), potassium hydroxide (0.60 g, 10.7 mmol), and water (15 mL) were charged into a reaction vessel and stirred at room temperature for 30 min. A solution of 2,4-dichloro-6-methoxytriazine (0.90 g, 5.0 mmol) in acetone (30 mL) was added and stirred at room temperature for 24 h. The reaction solution was then poured into 800 mL of distilled water. The resulting white precipitate was collected by filtration and dried under reduced pressure at 80 °C for 5 h. It was then reprecipitated from a 5:1 (volume) hexane:acetone mixture and purified by silica gel column chromatography using a 3:1 to 1:1 (volume) hexane:methylene chloride mixture as the electrolyte, yielding 1.42 g of compound A8. The yield was 59.2%. Compound A8 exhibited solubility such that a 2.5% solution could be prepared in MEK. 1 H-NMR (400 MHz, CDCl3) spectrum and 13 The C-NMR (400 MHz, CDCl3) spectra are shown in Figures 18 and 19, respectively.

[0228] <Example 1> (Preparation of acrylic polymer solution) A four-neck flask equipped with a stirring blade, thermometer, nitrogen gas inlet, and condenser was charged with 95 parts of m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A," refractive index: 1.566, homopolymer Tg: -35°C; hereafter referred to as "POB-A") as monomer components, 5 parts of 4-hydroxybutyl acrylate (4HBA), 0.2 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 150 parts of ethyl acetate as a polymerization solvent. Nitrogen gas was introduced while gently stirring, and the liquid temperature in the flask was maintained at around 60°C. The polymerization reaction was carried out for 6 hours to prepare a 40% solution of acrylic polymer P1. The Mw of the acrylic polymer P1 was 500,000.

[0229] (Preparation of Pressure-Sensitive Adhesive Composition) The above-mentioned solution of acrylic polymer P1 (40%) was diluted to 20% with ethyl acetate, and 500 parts of this solution (100 parts non-volatiles) were mixed with 20 parts (10 parts non-volatiles) of a 50% ethyl acetate solution of compound A1, 10 parts (0.1 parts non-volatiles) of a 1% ethyl acetate solution of an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation, trade name "Coronate HX", a trifunctional isocyanate compound) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (0.01 parts non-volatiles) of a 1% ethyl acetate solution of nursem ferric as a crosslinking catalyst, followed by stirring and mixing to prepare a pressure-sensitive adhesive composition according to this example.

[0230] (Preparation of adhesive sheet) The acrylic pressure-sensitive adhesive composition prepared above was applied to the silicone-treated surface of a polyethylene terephthalate (PET) film R1 (50 μm thick) that had been silicone-treated on one side, and heated at 130°C for 2 minutes to form a 20 μm thick pressure-sensitive adhesive layer. Next, the silicone-treated surface of a PET film R2 (25 μm thick) that had been silicone-treated on one side was attached to the surface of the pressure-sensitive adhesive layer. In this way, a substrateless double-sided pressure-sensitive adhesive sheet consisting of the pressure-sensitive adhesive layer was obtained. Both sides of this pressure-sensitive adhesive sheet were protected by PET films (release liners) R1 and R2.

[0231] <Examples 2-4> Except for using compound A4 (Example 2), compound A5 (Example 4), or compound A6 (Example 4) instead of compound A1, the pressure-sensitive adhesive compositions of each example were prepared in the same manner as the preparation of the pressure-sensitive adhesive composition in Example 1. Except for using each of the resulting pressure-sensitive adhesive compositions, pressure-sensitive adhesive sheets of Examples 2 to 4 (substrate-less double-sided pressure-sensitive adhesive sheets consisting of a pressure-sensitive adhesive layer) were produced in the same manner as the production of the pressure-sensitive adhesive sheet in Example 1.

[0232] <Example 5> Except for using compound B1 (diethylene glycol dibenzoate, refractive index 1.535) instead of compound A1, pressure-sensitive adhesive compositions according to this example were prepared in the same manner as the preparation of the pressure-sensitive adhesive composition in Example 1. Except for using each of the resulting pressure-sensitive adhesive compositions, pressure-sensitive adhesive sheets according to this example (substrate-less double-sided pressure-sensitive adhesive sheets comprising a pressure-sensitive adhesive layer) were produced in the same manner as the production of the pressure-sensitive adhesive sheet in Example 1.

[0233] <Example 6> Except for not using compound A1, the PSA compositions of this example were prepared in the same manner as the PSA composition of Example 1. Except for using each of the obtained PSA compositions, the PSA sheets of this example (substrate-less double-sided PSA sheets comprising a PSA layer) were produced in the same manner as the PSA sheet of Example 1.

[0234] <Evaluation> (Refractive index of adhesive) The refractive index of the adhesive layer (substrate-less double-sided adhesive sheet) according to each example was measured using an Abbe refractometer (manufactured by ATAGO, model "DR-M4") under conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C.

[0235] (Total light transmittance and haze) The adhesive layer according to each example was attached to alkali-free glass (thickness 0.8 to 1.0 mm, total light transmittance 92%, haze 0.4%) to form a test piece, and the total light transmittance and haze of the test piece were measured using a haze meter ("HM-150" manufactured by Murakami Color Research Laboratory). The total light transmittance and haze of the alkali-free glass were subtracted from the measured value to obtain the total light transmittance [%] and haze [%] of the adhesive (layer). For a substrateless adhesive sheet comprising the adhesive layer, the total light transmittance [%] and haze [%] of the adhesive layer are the total light transmittance [%] and haze [%] of the adhesive sheet.

[0236] (chromaticity b * (measurement of The adhesive layer of each example was measured for chromaticity b * The measurement was carried out at five points on the surface of the pressure-sensitive adhesive layer, and the average value was calculated.

[0237] Table 1 shows the outline of the adhesive for each example and the evaluation results.

[0238] [Table 1]

[0239] As shown in Table 1, the pressure-sensitive adhesive compositions of Examples 1 to 4, which were prepared by blending the pressure-sensitive adhesive composition of Example 6 with Compounds A1 and A4 to A6, each of which has a higher refractive index than Compound B1 used in Example 5, all exhibited a higher refractive index than the pressure-sensitive adhesive compositions of Examples 5 and 6. The pressure-sensitive adhesives of Examples 1 to 4 exhibited good light transmittance, haze, and chromaticity b at levels suitable for optical applications. * It had the following characteristics.

[0240] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0241] 1,2,3 Adhesive sheet 10 Supporting base material 10A 1st side 10B 2nd side 21 adhesive layer, first adhesive layer 21A Adhesive surface, 1st adhesive surface 21B Adhesive side 22 Second adhesive layer 22A 2nd adhesive side 31,32 Release liner

Claims

1. A refractive index adjuster for an adhesive, comprising: The following formula (I): 【Chemical 1】 (In formula (I), X １ , X ２ and X ３ are both —O— or both —S—, R １ , R ２ and R3 is Both are aromatic ring-containing groups, or two are aromatic ring-containing groups and the remaining one is an alkyl group having 1 to 12 carbon atoms; The aromatic ring-containing groups are the same groups and are selected from the group consisting of optionally substituted phenyl groups and optionally substituted biphenyl groups, and when the phenyl group or the biphenyl group has a substituent, the substituent is selected from an alkyl group having 1 to 3 carbon atoms; is a triazine compound represented by the formula: The pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive having an acrylic polymer as a base polymer, and a monomer component constituting the acrylic polymer containing an aromatic ring-containing monomer (m1), and the content of the aromatic ring-containing monomer (m1) in the monomer component is 75% by weight or more.

2. A pressure-sensitive adhesive comprising the refractive index adjuster according to claim 1, the pressure-sensitive adhesive is an acrylic pressure-sensitive adhesive having an acrylic polymer as a base polymer, and a monomer component constituting the acrylic polymer including an aromatic ring-containing monomer (m1), A pressure-sensitive adhesive, wherein the content of the aromatic ring-containing monomer (m1) in the monomer components is 75% by weight or more.

3. The pressure-sensitive adhesive according to claim 2, having a refractive index of 1.550 or more.

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