Adhesive composition, adhesive, and adhesive sheet

Abstract

To provide an adhesive appropriate even for an adhesion use of an optical member with a higher refractive index, an adhesive composition capable of forming the adhesive, and a pressure sensitive adhesive sheet containing the adhesive.SOLUTION: Provided is an adhesive composition for forming an adhesive containing an acrylic polymer. A monomer component composing the acrylic polymer contains: an aromatic ring-containing monomer (A1); and a monomer (A2) having at least one of a hydroxy group and a carboxy group. In the monomer component, a content of the aromatic ring-containing monomer (A1) is 75 to 99 wt.%, and a content of the monomer (A2) having at least one of the hydroxy group and the carboxy group is 1 to 25 wt.%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to adhesive compositions, adhesives, and adhesive sheets. [Background technology]

[0002] Adhesives (also known as pressure-sensitive adhesives; the same applies hereinafter) are widely used in various industrial fields, from home appliances to automobiles, various machinery, electrical equipment, and electronic devices, for purposes such as bonding and protection. One example of an application of adhesives is in display devices such as liquid crystal displays and organic EL displays, where transparent cover members such as polarizing films, phase difference films, and cover glass, and various other transparent optical members are bonded to other members. Patent documents 1 and 2 are cited as technical documents relating to adhesives for optical members. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2014-169382 [Patent Document 2] Japanese Patent Publication No. 2017-128732 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Here, the refractive index of acrylic adhesives is usually around 1.47, while the refractive index of optical components is generally high. It is known that when the above-mentioned acrylic adhesive is used to bond such optical components, reflection occurs at the interface due to the difference in refractive indices between the two. Patent documents 1 and 2 propose using monomers having multiple aromatic rings to raise the refractive index of the adhesive to 1.50 or higher, particularly preferably 1.51 or higher. However, some optical components have refractive indices of 1.56 or higher, and even 1.60 or higher, and the adhesives described in Patent documents 1 and 2 are not sufficiently suitable for bonding such high refractive index optical components.

[0005] Therefore, the present invention aims to provide an adhesive suitable for bonding optical components having a higher refractive index. Another related objective is to provide an adhesive composition capable of forming such an adhesive and an adhesive sheet containing the above adhesive. [Means for solving the problem]

[0006] This specification provides an adhesive composition for forming an adhesive containing an acrylic polymer. The monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1). Preferably, the monomer component further contains a monomer (A2) having at least one of a hydroxyl group and a carboxyl group. The content of the aromatic ring-containing monomer (A1) in the monomer component is preferably 75% by weight or more and 99% by weight or less. The content of the monomer (A2) having at least one of a hydroxyl group and a carboxyl group in the monomer component is preferably 1% by weight or more and 25% by weight or less. The adhesive composition having the above configuration is suitable for forming an adhesive with a high refractive index because the content of the aromatic ring-containing monomer (A1) in the monomer component constituting the acrylic polymer is within the above range. Such an adhesive can preferably be used, for example, for joining optical members with a refractive index of 1.56 or higher.

[0007] In the following, a monomer containing an aromatic ring (A1) may be referred to as "monomer (A1)," and a monomer (A2) having at least one of a hydroxyl group and a carboxyl group may be referred to as "monomer (A2)."

[0008] In some preferred embodiments of the technologies disclosed herein (including adhesive compositions, adhesives, and adhesive sheets; the same applies hereinafter), 50% by weight or more of the aromatic ring-containing monomer (A1) is a monomer having a homopolymer glass transition temperature (Tg) of 10°C or lower. This allows for a good balance between high refractive index and adhesion to the adherend, even with a high content of monomer (A1) in the monomer component. In the following, the Tg of the monomer homopolymer may be referred to as the Tg of the monomer.

[0009] In some preferred embodiments, the aromatic ring-containing monomer (A1) includes an aromatic ring-containing monomer having two or more aromatic rings in one molecule (hereinafter also referred to as "multiple aromatic ring-containing monomer"). By using a multiple aromatic ring-containing monomer, the refractive index of the adhesive can be effectively improved. The aromatic ring-containing monomer (A1) may contain only one type of multiple aromatic ring-containing monomer (for example, an aromatic ring-containing monomer whose homopolymer Tg is 10°C or less), or it may contain a combination of two or more multiple aromatic ring-containing monomers.

[0010] In some preferred embodiments, the monomer having two or more aromatic rings in a single molecule includes a monomer having a structural moiety in which two aromatic rings are linked via a linking group. Aromatic ring-containing monomers having such a structural moiety tend to have a lower Tg of homopolymer compared to aromatic ring-containing monomers having a structural moiety in which two aromatic rings are directly chemically bonded (e.g., a biphenyl structure) instead of the aforementioned structural moiety. Aromatic ring-containing monomers (A1) containing such a structure can achieve a better balance between high refractive index and adhesion to the adherend.

[0011] The adhesive compositions disclosed herein preferably further contain a crosslinking agent. The use of a crosslinking agent imparts appropriate cohesiveness to the adhesive, improving handling during the manufacturing, processing, storage, and application of adhesive sheets to substrates.

[0012] This specification provides an adhesive formed from any of the adhesive compositions disclosed herein. Such an adhesive may have a high refractive index due to a high content of aromatic ring-containing monomers (A1) in the monomer components constituting the acrylic polymer. According to the techniques disclosed herein, an adhesive having a refractive index greater than 1.570 (preferably 1.575 or higher, for example 1.580 or higher) can be realized.

[0013] In some embodiments of the adhesives disclosed herein, the adhesive is subject to the following conditions: (a) The storage modulus G'(25) at 25°C is less than 200 kPa; and (b) The storage modulus G'(50) at 50°C is less than 40 kPa; It is preferable that at least one of the following conditions is met. An adhesive exhibiting such viscoelastic properties may have a high refractive index and be easily adhered to the substrate.

[0014] This specification provides an adhesive sheet comprising an adhesive layer composed of any of the adhesives disclosed herein (which may be adhesives formed from any of the adhesive compositions disclosed herein). Such an adhesive sheet may preferably be used in a manner in which it is attached to a component (e.g., an optical component).

[0015] In some embodiments of the adhesive sheets disclosed herein, the haze value of the adhesive layer is preferably 1.0% or less. Adhesive sheets having such a highly transparent adhesive layer are suitable for bonding optical components.

[0016] Furthermore, combinations of the elements described herein may also be included within the scope of the invention for which patent protection is sought in this patent application. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic cross-sectional view showing the structure of an adhesive sheet according to one embodiment. [Figure 2] This is a schematic cross-sectional view showing the structure of an adhesive sheet according to another embodiment. [Figure 3] This is a schematic cross-sectional view showing the structure of an adhesive sheet according to another embodiment. [Modes for carrying out the invention]

[0018] Preferred embodiments of the present invention are described below. Matters other than those specifically mentioned herein that are necessary for carrying out the present invention can be understood by those skilled in the art based on the teachings on carrying out the invention described herein and the common technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed herein and the common technical knowledge in the art. In the following drawings, components and parts that perform the same function may be denoted by the same reference numeral and described accordingly, and redundant explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic representations for the purpose of clearly illustrating the present invention and do not necessarily accurately represent the size or scale of the actual product provided.

[0019] In this specification, the "base polymer" of an adhesive refers to the main component of the rubbery polymer contained in the adhesive. The rubbery polymer refers to a polymer that exhibits rubber elasticity in a temperature range near room temperature. In addition, in this specification, unless otherwise specified, the "main component" refers to a component contained in more than 50% by weight.

[0020] In this specification, "acrylic polymer" means a polymer that contains monomer units derived from monomers having at least one (meth)acryloyl group in one molecule as monomer units constituting the polymer. Hereinafter, monomers having at least one (meth)acryloyl group in one molecule will also be called "acrylic monomers." Therefore, in this specification, acrylic polymers are defined as polymers that contain monomer units derived from acrylic monomers. 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.

[0021] Furthermore, in this specification, "acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl group" comprehensively refers to both acryloyl and methacryloyl groups. Therefore, the concept of acrylic monomer as used herein may encompass both monomers having an acryloyl group (acrylic monomer) and monomers having a methacryloyl group (methacrylic monomer). Similarly, in this specification, "(meth)acrylic acid" comprehensively refers to acrylic acid and methacrylic acid, and "(meth)acrylate" comprehensively refers to acrylate and methacrylate. The same applies to other similar terms.

[0022] <Adhesive composition> The adhesive compositions disclosed herein are not limited in form, as long as they can form an adhesive containing an acrylic polymer (preferably an adhesive containing the acrylic polymer as a base polymer). The adhesive compositions may take various forms, such as a solvent-type adhesive composition containing an adhesive-forming component in an organic solvent, an active energy ray-curable adhesive composition prepared to form an adhesive by curing with active energy rays such as ultraviolet light or radiation, a water-dispersible adhesive composition in which the adhesive-forming component is dispersed in water, or a hot-melt adhesive composition that is applied in a heated and molten state and forms an adhesive when cooled to around room temperature.

[0023] The adhesive composition disclosed herein contains an aromatic ring-containing monomer (A1) as a monomer component constituting the acrylic polymer. Herein, "monomer component constituting the acrylic polymer" means a monomer that constitutes a repeating unit of the acrylic polymer in the adhesive formed from the adhesive composition, regardless of whether it is included in the adhesive composition in the form of a pre-formed polymer (which may be an oligomer) or in the form of an unpolymerized monomer. That is, the monomer component constituting the acrylic polymer may be included in the adhesive composition in the form of a polymer, an unpolymerized or partially polymerized substance. From the viewpoint of ease of preparation of the adhesive composition, etc., in some embodiments, an adhesive composition containing substantially all (for example, 95% by weight or more, preferably 99% by weight or more) of the monomer component in the form of a polymer is preferred.

[0024] (Monomer (A1)) As monomer (A1), a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule is used. Monomer (A1) can be one of these compounds alone or two or more compounds in combination.

[0025] Examples of the ethylenically unsaturated groups mentioned above include (meth)acryloyl groups, vinyl groups, and (meth)allyl groups. From the viewpoint of polymerization reactivity, (meth)acryloyl groups are preferred, and from the viewpoint of flexibility and tackiness, acryloyl groups are more preferred. From the viewpoint of suppressing a decrease in the flexibility of the adhesive, a compound having one ethylenically unsaturated group in one molecule (i.e., a monofunctional monomer) is preferably used as the monomer (A1).

[0026] The number of aromatic rings contained in one molecule of the compound used as monomer (A1) may be 1 or 2 or more. There is no particular upper limit to the number of aromatic rings, and it may be, for example, 16 or less. In some embodiments, from the viewpoint of ease of preparation of the adhesive composition and transparency of the adhesive, the number of aromatic rings may be, for example, 12 or less, preferably 8 or less, more preferably 6 or less, may be 5 or less, may be 4 or less, may be 3 or less, or may be 2 or less.

[0027] The aromatic ring of the compound used as monomer (A1) may be a carbon ring such as a benzene ring (which may be a benzene ring that constitutes part of a biphenyl or fluorene structure); a fused ring of a naphthalene ring, indene ring, azulene ring, anthracene ring, or phenanthrene ring; or a hetero ring such as a pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, pyrrole ring, pyrazole ring, imidazole ring, triazole ring, oxazole ring, isoxazole ring, thiazole ring, or thiophene ring. The heteroatoms included as ring constituent atoms in the above hetero ring may be one or more selected from the group consisting of, for example, nitrogen, sulfur, and oxygen. In some embodiments, the heteroatoms constituting the above hetero ring may be nitrogen and sulfur, or both. Monomer (A1) may have a structure in which one or more carbon rings and one or more hetero rings are fused, such as a dinaphthothiophene structure.

[0028] The above aromatic ring (preferably a carbocyclic ring) may have one or more substituents on its ring constituent atoms, or it may not have substituents. If substituents are present, examples of such substituents include, but are not limited to, alkyl groups, alkoxy groups, aryloxy groups, hydroxyl groups, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl groups, hydroxyalkyloxy groups, glycidyloxy groups, etc. In substituents containing carbon atoms, the number of carbon atoms included in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. In some embodiments, the above aromatic ring may have no substituents on its ring constituent atoms, or it may be an aromatic ring having one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, and halogen atoms (e.g., bromine atoms). Note that when an aromatic ring of monomer (A1) is said to have substituents on its ring constituent atoms, it means that the aromatic ring has substituents other than substituents having an ethylenically unsaturated group.

[0029] The aromatic ring and the ethylenically unsaturated group may be directly bonded or bonded via a linking group. The linking group may be a group comprising one or more structures selected from, for example, alkylene groups, oxyalkylene groups, poly(oxyalkylene) groups, phenyl groups, alkylphenyl groups, alkoxyphenyl groups, groups in which one or more hydrogen atoms are substituted with hydroxyl groups (e.g., hydroxyalkylene groups), oxy groups (-O- groups), thiooxy groups (-S- groups), etc. In some embodiments, aromatic ring-containing monomers may be preferred in which the aromatic ring and the ethylenically unsaturated group are directly bonded or bonded via a linking group selected from the group consisting of alkylene groups, oxyalkylene groups, and poly(oxyalkylene) groups. 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.

[0030] Examples of compounds that can be preferably used as monomer (A1) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. Aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds can each be used individually or in combination of two or more. One or more aromatic ring-containing (meth)acrylates may be used in combination with one or more aromatic ring-containing vinyl compounds.

[0031] In some embodiments, the monomer (A1) content in the monomer component constituting the acrylic polymer may be, for example, 70% by weight or more or more than 70% by weight, preferably 75% by weight or more, preferably 80% by weight or more from the viewpoint of easily obtaining a higher refractive index, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. The monomer (A1) content in the above monomer component is typically less than 100% by weight, and from the viewpoint of achieving a good balance between a high refractive index and adhesion to the adherend, it is advantageous to be approximately 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, 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 monomer (A1) content in the above monomer component may be less than 90% by weight, may be less than 85% by weight, or may be less than 80% by weight.

[0032] In some embodiments of the technology disclosed herein, monomers (A1) can preferably be monomers having two or more aromatic rings (preferably carbocyclic rings) in one molecule, as these are readily available to achieve a high refractive index effect. Examples of monomers having two or more aromatic rings in one molecule (multiple aromatic ring-containing monomers) include monomers having a structure in which two or more non-condensed aromatic rings are linked via linking groups, monomers having a structure in which two or more non-condensed aromatic rings are chemically bonded directly (i.e., without the involvement of other atoms), monomers having a condensed aromatic ring structure, monomers having a fluorene structure, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, and the like. Multiple aromatic ring-containing monomers can be used individually or in combination of two or more.

[0033] The above linking groups include, for example, oxy groups (-O-), thiooxy groups (-S-), and oxyalkylene groups (for example, -O-(CH2)). n - group, where n is 1 to 3, preferably 1), thiooxyalkylene group (e.g., -S-(CH2) n - group, where n is 1 to 3, preferably 1), linear alkylene group (i.e., -(CH2) n -Group (where n is 1 to 6, preferably 1 to 3), the above oxyalkylene group, the above thiooxyalkylene group, and the above linear alkylene group may be a group in which the alkylene group is partially halogenated or fully halogenated. From the viewpoint of the flexibility of the adhesive, preferred examples of the linking group include the oxy group, thiooxy group, oxyalkylene group, and linear alkylene group. Specific examples of monomers having a structure in which two or more non-condensed aromatic rings are linked via a linking group include phenoxybenzyl(meth)acrylate (e.g., m-phenoxybenzyl(meth)acrylate), thiophenoxybenzyl(meth)acrylate, benzylbenzyl(meth)acrylate, and the like.

[0034] Monomers having a structure in which two or more non-condensed aromatic rings are directly chemically bonded may include, for example, biphenyl structure-containing (meth)acrylate, triphenyl structure-containing (meth)acrylate, vinyl group-containing biphenyl, etc. Specific examples include o-phenylphenol (meth)acrylate and biphenylmethyl (meth)acrylate.

[0035] Examples of monomers having the above-mentioned 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, and 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate.

[0036] Specific examples of monomers having the above-mentioned fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene(meth)acrylate and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene(meth)acrylate. Note that monomers having a fluorene structure include a structural portion in which two benzene rings are directly chemically bonded, and therefore are included in the concept of monomers having a structure in which two or more non-condensed aromatic rings are directly chemically bonded.

[0037] Examples of monomers having the above-mentioned dinaphthothiophene structure include (meth)acryloyl group-containing dinaphthothiophene, vinyl group-containing dinaphthothiophene, (meth)allyl group-containing dinaphthothiophene, etc. A specific example is (meth)acryloyloxymethyl dinaphthothiophene (for example, CH2CH(R) at the 5th or 6th position of the dinaphthothiophene ring). 1 A compound with a structure in which C(O)OCH2- is bonded. Here, R 1 (These are a hydrogen atom or a methyl group.) (meth)acryloyloxyethyl dinaphthothiophene (for example, CH2CH(R) at the 5th or 6th position of the dinaphthothiophene ring)1 )C(O)OCH(CH3)- or CH2CH(R 1 A compound with a structure in which C(O)OCH2CH2- is bonded. Here, R 1 The group is a hydrogen atom or a methyl group. Examples include vinyl dinaphthothiophene (for example, a compound in which a vinyl group is bonded to the 5th or 6th position of the naphthothiophene ring), (meth)allyloxydinaphthothiophene, etc. Note that monomers having a dinaphthothiophene structure are also included in the concept of monomers having the above-mentioned condensed aromatic ring structure if they contain a naphthalene structure or if they have a structure in which a thiophene ring and two naphthalene structures are condensed.

[0038] Examples of monomers having the above-mentioned dibenzothiophene structure include (meth)acryloyl group-containing dibenzothiophene and vinyl group-containing dibenzothiophene. Since monomers having a dibenzothiophene structure have a structure in which a thiophene ring and two benzene rings are condensed, they are included in the concept of monomers having the above-mentioned condensed aromatic ring structure. Furthermore, neither the dinaphthothiophene structure nor the dibenzothiophene structure corresponds to a structure in which two or more non-condensed aromatic rings are directly chemically bonded.

[0039] In the techniques disclosed herein, monomers having one aromatic ring (preferably a carbocyclic ring) in one molecule may be used as monomer (A1). Monomers having one aromatic ring in one molecule can be useful, for example, for improving the flexibility of adhesives, adjusting adhesive properties, and improving transparency. In some embodiments, monomers having one aromatic ring in one molecule are preferably used in combination with monomers containing multiple aromatic rings from the viewpoint of improving the refractive index of the adhesive.

[0040] Examples of monomers having one aromatic ring in one molecule include carbon aromatic ring-containing (meth)acrylates such as benzyl (meth)acrylate, methoxybenzyl (meth)acrylate, phenyl (meth)acrylate, ethoxylated phenol (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxybutyl (meth)acrylate, cresyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, chlorobenzyl (meth)acrylate, etc.; 2-(4,6-dibromo-2-s-butylphenoxy)ethyl (meth)acrylate, 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate, 6- Examples 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 aromatic ring-containing vinyl compounds such as styrene, α-methylstyrene, vinyltoluene, and tert-butylstyrene; and compounds having vinyl substituents on heteroaromatic rings such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, and N-vinyloxazole.

[0041] As monomer (A1), monomers having a structure in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the aromatic ring in the various aromatic ring-containing monomers described above may be used. Monomers in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the aromatic ring in this manner can be understood as the ethoxylated product of the original monomer. The number of repeating oxyethylene units (-CH2CH2O-) in the above 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, phenoxydiethylene glycol di(meth)acrylate, and the like.

[0042] The content of multiple aromatic ring-containing monomers in monomer (A1) is not particularly limited and may be, for example, 5% or more by weight, 25% or more by weight, or 40% or more by weight. In some embodiments, the content of multiple aromatic ring-containing monomers in monomer (A1) may be, for example, 50% or more by weight, preferably 70% or more by weight from the viewpoint of easily obtaining a higher refractive index, and may be 85% or more by weight, 90% or more by weight, or 95% or more by weight. Substantially 100% by weight of monomer (A1) may be multiple aromatic ring-containing monomers. That is, only one or more multiple aromatic ring-containing monomers may be used as monomer (A1). Furthermore, in some embodiments, taking into consideration the balance between high refractive index and adhesion to the adherend, the content of the multiple aromatic ring-containing monomer in monomer (A1) 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.

[0043] The content of multiple aromatic ring-containing monomers in the monomer components constituting the acrylic polymer may be, for example, more than 35% by weight, and is advantageous to be more than 50% by weight, preferably more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, and may be 95% by weight or more. Considering the balance between high refractive index and adhesion to the adherend, the content of multiple aromatic ring-containing monomers in the above monomer components is advantageous to be approximately 99% by weight or less, is preferably 98% by weight or less, is more preferably 96% by weight or less, may be 93% by weight or less, may be 90% by weight or less, may be 85% by weight or less, may be 80% by weight or less, and may be 75% by weight or less. In some embodiments, from the viewpoint of facilitating the achievement of higher adhesive properties and / or optical properties (e.g., transparency), the content of the monomer containing multiple aromatic rings in the monomer component may be 70% by weight or less, 60% by weight or less, 50% by weight or less, or 40% by weight or less.

[0044] In some embodiments of the technology disclosed herein, high refractive index monomers may be preferably used as at least a portion of monomer (A1). Here, "high refractive index monomer" refers to a monomer whose refractive index is, for example, approximately 1.510 or higher, preferably approximately 1.530 or higher, and more preferably approximately 1.550 or higher. There is no particular upper limit to the refractive index of the high refractive index monomer, but from the viewpoint of ease of preparation of the adhesive composition and ease of compatibility with flexibility suitable for an 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. High refractive index monomers can be used alone or in combination of two or more. The refractive index of the monomer is measured using an Abbe refractometer under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. An ATAGO DR-M4 or equivalent Abbe refractometer can be used. If the manufacturer provides a nominal refractive index value at 25°C, that nominal value may be used.

[0045] As the above-mentioned high refractive index monomer, compounds with the appropriate refractive index can be appropriately selected from among the compounds included in the concept of aromatic ring-containing monomer (A1) disclosed herein (for example, the compounds and groups of compounds exemplified above). Specific examples include m-phenoxybenzyl acrylate (refractive index: 1.566, homopolymer Tg: -35°C), 1-naphthylmethyl acrylate (refractive index: 1.595, homopolymer Tg: 31°C), ethoxylated o-phenylphenol acrylate (number of oxyethylene unit repetitions: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, homopolymer Tg: 6°C), phenoxyethyl acrylate (refractive index (nD20): 1.517, homopolymer Tg: 2°C), and phenoxydiethylene glycol acrylate (refractive index: 1.510, homopolymer Examples 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 (abbreviation: 5VDNT, refractive index: 1.793).

[0046] The content of high refractive index monomers (i.e., aromatic ring-containing monomers having a refractive index of approximately 1.510 or higher, preferably approximately 1.530 or higher, and more preferably approximately 1.550 or higher) in monomer (A1) may be, for example, 50% by weight or more, preferably 70% by weight or more from the viewpoint of easily obtaining a higher refractive index, and may also be 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of monomer (A1) may be high refractive index monomers. Furthermore, in some embodiments, for example from the viewpoint of achieving a good balance between high refractive index and adhesion to the adherend, the content of high refractive index monomers in monomer (A1) 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.

[0047] The content of high refractive index monomers in the monomer components constituting the acrylic polymer may be, for example, more than 35% by weight, and 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, and may be 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. From the viewpoint of achieving a good balance between high refractive index and adhesion to the adherend, the content of high refractive index monomers in the above monomer components is advantageous to be 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, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less.

[0048] In some preferred embodiments of the technology disclosed herein, an aromatic ring-containing monomer (hereinafter sometimes referred to as "monomer L") is used as at least a portion of the monomer (A1), wherein the homopolymer Tg is 10°C or less (preferably 5°C or less or 0°C or less, more preferably -10°C or less, even more preferably -20°C or less, for example -25°C or less). Generally, increasing the content of aromatic ring-containing monomer (A1) in the monomer component (in particular, aromatic ring-containing monomer (A1) that corresponds to one or both of the multiple aromatic ring-containing monomers and high refractive index monomers described above) tends to increase the storage modulus G' of the adhesive. By using monomer L as part or all of the monomer (A1), the increase in the storage modulus G' can be suppressed. This makes it possible to improve the refractive index while better maintaining flexibility suitable for adhesion to the adherend. The lower limit of the Tg of monomer L is not particularly limited. Considering the balance with the refractive index improvement effect, in some embodiments, the Tg of monomer L may be, for example, -70°C or higher, -55°C or higher, or -45°C or higher. Monomer L can be used alone or in combination of two or more types.

[0049] As monomer L, any compound having the appropriate Tg can be appropriately selected from among the compounds included in the concept of aromatic ring-containing monomer (A1) disclosed herein (for example, the compounds and group of compounds exemplified above). One preferred example of an aromatic ring-containing monomer that can be used as monomer L is m-phenoxybenzyl acrylate (homopolymer Tg: -35°C). Another preferred example is phenoxydiethylene glycol acrylate (homopolymer Tg: -35°C).

[0050] The content of monomer L in monomer (A1) may be, for example, 50% by weight or more, preferably 60% by weight or more, more preferably 70% by weight or more, 75% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more from the viewpoint of enhancing flexibility. Substantially 100% by weight of monomer (A1) may be monomer L. Also, in some embodiments, for example, from the viewpoint of achieving a good balance between a high refractive index and adhesion to an adherend, the content of monomer L in monomer (A1) may be less than 100% by weight, 98% by weight or less, 90% by weight or less, 80% by weight or less, 65% by weight or less.

[0051] The content of monomer L in the monomer component constituting the acrylic polymer may be, for example, more than 35% by weight, advantageously more than 50% by weight, preferably more than 70% by weight, 75% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more from the viewpoint of improving the refractive index. From the viewpoint of achieving a good balance between a high refractive index and adhesion to an adherend, it is advantageous that the content of monomer L in the above monomer component is 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, 75% by weight or less.

[0052] In some embodiments, the glass transition temperature Tg A1 is appropriately approximately 20°C or lower, preferably 10°C or lower (for example, 5°C or lower), more preferably 0°C or lower, still more preferably -10°C or lower, -20°C or lower, -25°C or lower from the viewpoint of the flexibility of the adhesive. The lower limit of the glass transition temperature Tg A1 is not particularly limited. Considering the balance with the refractive index improvement effect, in some embodiments, the glass transition temperature Tg A1 may be, for example, -70°C or higher, -55°C or higher, -45°C or higher. The technology disclosed herein is the glass transition temperature TgA1 The method can also be suitably implemented in embodiments where the temperature is, for example, -40°C or higher, -35°C or higher, -33°C or higher, -30°C or higher, or -25°C or higher.

[0053] Here, the glass transition temperature Tg is determined based on the composition of monomer (A1). A1 This refers to the glass transition temperature (Tg) determined by Fox's formula, described later, based on the composition of only the monomer (A1) among the monomer components constituting the acrylic polymer. A1 This can be calculated by applying Fox's formula to only monomer (A1) among the monomer components constituting the acrylic polymer, and using the glass transition temperature of the homopolymer of each aromatic ring-containing monomer used as monomer (A1) and the weight fraction of each aromatic ring-containing monomer in relation to the total amount of monomer (A1). In the embodiment where only one type of monomer is used as monomer (A1), the Tg of the homopolymer of the monomer and the glass transition temperature Tg A1 This matches.

[0054] In some embodiments, the aromatic ring-containing monomer (A1) can be a combination of monomer L (i.e., an aromatic ring-containing monomer whose homopolymer Tg is 10°C or lower, preferably 5°C or lower or 0°C or lower, more preferably -10°C or lower, even more preferably -20°C or lower, for example -25°C or lower) and monomer H whose Tg is 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, in an adhesive with a high content of aromatic ring-containing monomer (A1) in the monomer component, it is possible to achieve a higher level of both high refractive index and flexibility suitable for adhesion to the adherend. The ratio of monomer L to monomer H used can be set so as to suitably exhibit these effects and is not particularly limited. For example, any of the above glass transition temperatures Tg A1 It is preferable to set the usage ratio of monomer L to monomer H so as to satisfy the following conditions.

[0055] In some embodiments, the aromatic ring-containing monomer (A1) can be preferably selected from compounds that do not contain a structure in which two or more non-condensed aromatic rings are directly chemically bonded (e.g., a biphenyl structure). For example, an acrylic polymer composed of monomer components with a composition in which the content of a compound containing a structure in which two or more non-condensed aromatic rings are directly chemically bonded is less than 5% by weight (more preferably less than 3% by weight, and may even be 0% by weight) is preferable. Limiting the amount of compound containing a structure in which two or more non-condensed aromatic rings are directly chemically bonded in this way can be advantageous from the viewpoint of realizing an adhesive that better balances high refractive index and adhesion to the adherend.

[0056] (Monomer (A2)) Monomer (A2) in the techniques disclosed herein is a monomer that 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 containing at least one carboxyl group and at least one ethylenically unsaturated group in one molecule. Monomer (A2) can be used to introduce crosslinking points into acrylic polymers or to impart appropriate cohesiveness to adhesives. Monomer (A2) can be used alone or in combination of two or more. Monomer (A2) is typically a monomer that does not contain an aromatic ring.

[0057] Examples of ethylenically unsaturated groups in monomer (A2) include (meth)acryloyl groups, vinyl groups, and (meth)allyl groups. From the viewpoint of polymerization reactivity, (meth)acryloyl groups are preferred, and from the viewpoint of flexibility and tackiness, acryloyl groups are more preferred. From the viewpoint of suppressing a decrease in the flexibility of the adhesive, monomer (A2) preferably consists of a compound in which the number of ethylenically unsaturated groups in one molecule is 1 (i.e., a monofunctional monomer).

[0058] 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. Examples of hydroxyl group-containing monomers that can be preferably used include 4-hydroxybutyl acrylate (Tg: -40°C) and 2-hydroxyethyl acrylate (Tg: -15°C). From the viewpoint of improving flexibility in the room temperature range, 4-hydroxybutyl acrylate with a lower Tg is more preferred. In one preferred embodiment, 50% or more by weight (e.g., more than 50% by weight, more than 70% by weight, or more than 85% by weight) of monomer (A2) may be 4-hydroxybutyl acrylate. Hydroxyl group-containing monomers can be used individually or in combination of two or more.

[0059] In some embodiments where a hydroxyl group-containing monomer is used as monomer (A2), the hydroxyl group-containing monomer may be one or more compounds selected from compounds that do not have a methacryloyl group. Preferred examples of hydroxyl group-containing monomers that do not have a methacryloyl group include the various hydroxyalkyl acrylates mentioned above. For example, it is preferable that more than 50% by weight, more than 70% by weight, or more than 85% by weight of the hydroxyl group-containing monomer used as monomer (A2) is hydroxyalkyl acrylate. The use of hydroxyalkyl acrylate allows for the introduction of hydroxyl groups into the acrylic polymer, which are useful for providing crosslinking points and imparting appropriate cohesiveness, and makes it easier to obtain an adhesive with good flexibility and tackiness at room temperature compared to using only the corresponding hydroxyalkyl methacrylate.

[0060] 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. Examples of carboxyl group-containing monomers that can be preferably used include acrylic acid and methacrylic acid. Carboxylate group-containing monomers can be used individually or in combination of two or more. Hydroxyl group-containing monomers and carboxyl group-containing monomers may also be used in combination.

[0061] The content of monomer (A2) in the monomer component constituting the acrylic polymer is not particularly limited and can be set according to the purpose. In some embodiments, the content of monomer (A2) may 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 monomer (A2) is preferably 1% by weight or more, may be 2% by weight or more, or may be 4% by weight or more. The upper limit of the content of monomer (A2) in the monomer component is set so that the total content with monomer (A1) does not exceed 100% by weight. In some embodiments, the content of monomer (A2) may be, for example, 30% by weight or less or 25% by weight or less, and from the viewpoint of making it easier to increase the refractive index by relatively increasing the content of monomer (A1), it is preferably 20% by weight or less, more preferably 15% by weight or less, may be less than 12% by weight, may be less than 10% by weight, or may be less than 7% by weight.

[0062] In embodiments where a hydroxyl group-containing monomer is used as monomer (A2), the content of the hydroxyl group-containing monomer in the monomer component is not particularly limited and may be, for example, 0.01% by weight or more (preferably 0.1% by weight or more, more preferably 0.5% by weight or more). In some embodiments, the content of the hydroxyl group-containing monomer is preferably 1% by weight or more of the monomer component, may be 2% by weight or more, or 4% by weight or more. The upper limit of the content of the hydroxyl group-containing monomer in the monomer component is set so that the total with the content of monomer (A1) does not exceed 100% by weight, for example, 30% by weight or less or 25% by weight or less is appropriate, and from the viewpoint of making it easier to increase the refractive index by relatively increasing the content of monomer (A1), it is preferably 20% by weight or less, more preferably 15% by weight or less, may be less than 12% by weight, may be less than 10% by weight, or may be less than 7% by weight.

[0063] In embodiments where a carboxyl group-containing monomer is used as monomer (A2), the content of the carboxyl group-containing monomer in the monomer component is not particularly limited and may be, for example, 0.01% by weight or more (preferably 0.1% by weight or more, more preferably 0.3% by weight or more). In some embodiments, the content of the carboxyl group-containing monomer may be 1% by weight or more, 2% by weight or more, or 4% by weight or more. The upper limit of the content of the carboxyl group-containing monomer in the monomer component is set so that the total amount with the amount of monomer (A1) used does not exceed 100% by weight, and for example, it is appropriate to set it to 30% by weight or less or 25% by weight or less. From the viewpoint of making it easier to increase the refractive index by relatively increasing the content of monomer (A1), it is preferable to set it to 20% by weight or less, more preferably to 15% by weight or less, and it may also be less than 12% by weight or less than 10% by weight. In some embodiments, from the viewpoint of improving the flexibility of the adhesive, it is advantageous to have a content of less than 7% by weight of the carboxyl group-containing monomer, preferably less than 5% by weight, and may also be less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. The technology disclosed herein can be preferably implemented, for example, in embodiments in which only a hydroxyl group-containing monomer is used as monomer (A2), that is, in embodiments in which no carboxyl group-containing monomer is used.

[0064] In some embodiments of the technology disclosed herein, the total content of monomer (A1) and monomer (A2) in the monomer component constituting the acrylic polymer may be, for example, 76% by weight or more, preferably 81% by weight or more, may be 86% by weight or more, may be 91% by weight or more, may be 96% by weight or more, may be 99% by weight or more, and may be substantially 100% by weight, from the viewpoint of facilitating the effective expression of these monomers.

[0065] (Monomer A3) The monomer components constituting the acrylic polymer may, if necessary, include monomers other than monomer (A1) and monomer (A2) described above. An example of such an optional component is alkyl (meth)acrylate (hereinafter also referred to as "monomer (A3)"). Monomer (A3) can be useful in adjusting the flexibility of the adhesive or improving its compatibility within the adhesive.

[0066] As monomers (A3), those with 1 to 20 carbon atoms (i.e., C 1-20 Alkyl (meth)acrylates having a linear or branched alkyl group at the ester terminus are preferably used. 1-20 Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isooctyl (meth)acrylate. Examples include, but are not limited to, 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, and eicosyl (meth)acrylate.

[0067] In some embodiments, alkyl (meth)acrylates 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 (A3). Such low-Tg alkyl (meth)acrylates can help improve the flexibility of the adhesive. 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)acrylates include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), and isononyl acrylate (iNA).

[0068] In some embodiments of using monomer (A3), it is preferable that at least a portion of monomer (A3) is an alkyl acrylate from the viewpoint of flexibility, tackiness, etc. For example, it is preferable that 50% by weight or more (more preferably 75% by weight or more, and even more preferably 90% by weight or more) of monomer (A3) is an alkyl acrylate. It is also possible to use only one or more alkyl acrylates as monomer (A3) and not use alkyl methacrylate.

[0069] In embodiments where the monomer component includes alkyl (meth)acrylate, the content of alkyl (meth)acrylate in the monomer component can be set so that its effect is appropriately exhibited. In some embodiments, 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. The upper limit of the content of monomer (A3) in the monomer component is set so that the sum of the content of monomers (A1) and (A2) does not exceed 100% by weight. In some embodiments, the content of monomer (A3) may be, for example, 24% by weight or less. Generally, alkyl (meth)acrylate has a relatively low refractive index, so in order to increase the refractive index, it is advantageous to limit the content of monomer (A3) in the monomer component and relatively increase the content of monomer (A1). From this viewpoint, the monomer (A3) content is appropriately less than 23% by weight of the monomer component, preferably less than 20% by weight, more preferably less than 17% by weight, 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 preferably be carried out in a manner that substantially does not use monomer (A3).

[0070] (Other monomers) The monomer components constituting the acrylic polymer may, if necessary, include monomers other than the above monomers (A1), (A2), and (A3) (hereinafter referred to as "other monomers"). These other monomers can be used, for example, for purposes such as adjusting the Tg of the acrylic polymer, adjusting the adhesive performance, and improving compatibility within the adhesive layer. These other monomers can be used individually or in combination of two or more.

[0071] Examples of the above-mentioned other monomers include monomers having functional groups other than hydroxyl and carboxyl groups (functional group-containing monomers). For example, other monomers that can improve the cohesive force and heat resistance of adhesives include sulfonic acid group-containing monomers, phosphate group-containing monomers, and cyano group-containing monomers. Furthermore, monomers that can introduce functional groups that can act as crosslinking sites into acrylic polymers, or that can contribute to improving adhesion to the adherend or improving compatibility within the adhesive layer, include amide group-containing monomers (e.g., (meth)acrylamide, N-methylol(meth)acrylamide, etc.), amino group-containing monomers (e.g., aminoethyl(meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, etc.), monomers having nitrogen atom-containing rings (e.g., N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), imide group-containing monomers, epoxy group-containing monomers, keto group-containing monomers, isocyanate group-containing monomers, and alkoxysilyl group-containing monomers. Furthermore, some monomers containing nitrogen atom rings, such as N-vinyl-2-pyrrolidone, also fall under the category of amide group-containing monomers. The same applies to the relationship between monomers containing nitrogen atom rings and monomers containing amino groups.

[0072] Other monomers that can be used besides the above-mentioned functional group-containing monomers include vinyl ester monomers such as vinyl acetate; non-aromatic ring-containing (meth)acrylates such as cyclohexyl (meth)acrylate and 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; and others. One preferred example of other monomers that can be used for purposes such as improving the flexibility of adhesives is ethoxyethoxyethyl acrylate (also known as ethyl carbitol acrylate, homopolymer Tg: -67℃).

[0073] When using the above-mentioned other monomers, the amount used is not particularly limited and can be appropriately set within a range where the total amount of monomer components does not exceed 100% by weight. From the viewpoint of making it easier to exhibit the refractive index improvement effect by using monomer (A1), it is appropriate for the content of the above-mentioned other monomers in the monomer component to be approximately 23% by weight or less (for example, 0 to 23% by weight), advantageously approximately 10% by weight or less (for example, 0 to 10% by weight), and preferably approximately 5% by weight or less, for example, approximately 1% by weight or less. The technology disclosed herein can preferably be implemented in a manner in which the monomer component substantially does not contain the above-mentioned other monomers.

[0074] In some embodiments, the monomer components constituting the acrylic polymer may have a composition in which the amount of methacryloyl group-containing monomer used is limited to a predetermined level. The amount of methacryloyl group-containing monomer used in the monomer component may be, for example, less than 5% by weight, less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. Limiting the amount of methacryloyl group-containing monomer used in this way may be advantageous from the viewpoint of realizing an adhesive that balances flexibility, tackiness, and high refractive index well. The monomer components constituting the acrylic polymer may also have a composition that does not contain methacryloyl group-containing monomer (for example, a composition consisting only of acryloyl group-containing monomer).

[0075] In some embodiments, the monomer components constituting the acrylic polymer preferably have a limited amount of carboxyl group-containing monomers used, from the viewpoint of suppressing coloration or discoloration (e.g., yellowing) of the adhesive. The amount of carboxyl group-containing monomers used in the monomer components may be, for example, less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, may be less than 0.1% by weight, or less than 0.05% by weight. Limiting the amount of carboxyl group-containing monomers used in this way is also advantageous from the viewpoint of suppressing corrosion of metal materials (e.g., metal wiring or metal films that may be present on the adherend) that may be in contact with or near the adhesive disclosed herein. The technology disclosed herein can preferably be implemented in embodiments in which the monomer components constituting the acrylic polymer do not contain carboxyl group-containing monomers. For similar reasons, in some embodiments, it is preferable that the monomer components constituting the acrylic polymer have a limited amount of monomers having acidic functional groups (including carboxyl groups, sulfonic acid groups, phosphate groups, etc.). In such embodiments, the preferred amount of carboxyl group-containing monomers described above can be applied as the amount of acidic functional group-containing monomers used in the monomer components. The technical sheets disclosed herein can preferably be implemented in embodiments in which the monomer components do not contain acidic group-containing monomers (i.e., embodiments in which the acrylic polymer is acid-free).

[0076] (glass transition temperature Tg T ) The monomer components that make up the acrylic polymer have a glass transition temperature (Tg) based on the composition of the monomer components. T It is preferable to have a composition such that the glass temperature Tg is approximately 15°C or lower. In some embodiments, the above glass temperature Tg T The glass transition temperature (Tg) is preferably 10°C or lower, more preferably 0°C or lower, even more preferably -10°C or lower, and may also be -20°C or lower, -25°C or lower, or -28°C or lower. T A low glass transition temperature (Tg) can be advantageous from the standpoint of improving the flexibility of the adhesive. TThe temperature may be, for example, -60°C or higher, and from the viewpoint of facilitating the raising of the refractive index of the adhesive, it is preferably -50°C or higher, more preferably above -45°C, and may also be above -40°C.

[0077] Here, the glass transition temperature Tg T Unless otherwise specified, this refers to the glass transition temperature determined by Fox's formula based on the composition of the above monomer components. Fox's formula is a relationship 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, as shown below. 1 / Tg = Σ(Wi / Tgi) In the Fox equation above, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (weight-based copolymerization ratio), and Tgi represents the glass transition temperature of the homopolymer of monomer i (unit: K). For calculating the glass transition temperature (Tg) of homopolymers, the values ​​listed in publicly available materials such as the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) shall be used. For monomers for which multiple values ​​are listed in the Polymer Handbook, the highest value shall be adopted. If the Tg of a homopolymer is not listed in publicly available materials, the value obtained by the measurement method described in Japanese Patent Publication No. 2007-51271 shall be used.

[0078] (Method for preparing acrylic polymers) In the technologies disclosed herein, the method for obtaining acrylic polymers composed of such monomer components is not particularly limited, and various polymerization methods known as synthesis methods for 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 when performing solution polymerization can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and can be, for example, around 20°C to 170°C (typically around 40°C to 140°C).

[0079] The solvent used for solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents. For example, one solvent or a mixture of two or more solvents can be used, selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); acetic acid esters such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; halogenated alkanes such as 1,2-dichloroethane; lower alcohols such as isopropyl alcohol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc.

[0080] The polymerization initiator can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, one or more azo polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; and so on. Another example of polymerization initiators is a redox initiator, which is a combination of a peroxide and a reducing agent. Polymerization initiators can be used individually or in combination of two or more. The amount of polymerization initiator used can be the usual amount, for example, it can be selected from a range of approximately 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) per 100 parts by weight of monomer component.

[0081] For the polymerization described above, 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, chain transfer agents that do not contain sulfur atoms (non-sulfur chain transfer agents) may 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. Chain transfer agents can be used individually or in combination of two or more. When using a chain transfer agent, the amount used can be approximately 0.01 to 1 part by weight per 100 parts by weight of monomer raw material.

[0082] The weight-average molecular weight (Mw) of the above acrylic polymer is not particularly limited, for example, approximately 10 × 10 4 ~500×10 4 It can be within this range. From the standpoint of adhesive performance, the Mw of the acrylic polymer is approximately 20 × 10 4 ~400×10 4 (more preferably approximately 30 x 10 4 ~150×10 4 For example, approximately 50 x 10 4 ~130×10 4 It is preferable that it be within the range of ).

[0083] Here, the Mw of the acrylic polymer can be determined by converting it to polystyrene equivalent using gel permeation chromatography (GPC). Specifically, it can be determined by measuring under the following conditions using a GPC measuring instrument, product name "HLC-8220GPC" (manufactured by Tosoh Corporation). [GPC measurement conditions] Sample concentration: 0.2% by weight (tetrahydrofuran solution) Sample injection volume: 10 μL Eluent: Tetrahydrofuran (THF) Flow rate (flow rate): 0.6mL / min Column temperature (measurement temperature): 40℃ column: Sample columns: 1 x "TSKguardcolumn SuperHZ-H" + 2 x "TSKgel SuperHZM-H" (manufactured by Tosoh Corporation) Reference column: Product name "TSKgel SuperH-RC" 1 piece (manufactured by Tosoh Corporation) Detector: Differential refractometer (RI) Standard sample: Polystyrene

[0084] (Plasticized material) In some embodiments of the adhesive compositions disclosed herein, the adhesive composition may optionally include, in addition to the acrylic polymer described above, a plasticizing material having a lower molecular weight than the acrylic polymer as an additive. The use of a plasticizing material can increase the flexibility of the adhesive, improving adhesion to the adherend and the flexibility and deformation-following ability of the adhesive sheet as a whole. From the viewpoint of compatibility and transparency within the adhesive, organic materials may be preferably used as the plasticizing material. The plasticizing material may be an additive (H) described later. RO It may also be a material that can be used as a substitute for other materials.

[0085] The molecular weight of the plasticizing material is not particularly limited, as long as it is lower than that of the acrylic polymer. In some embodiments, from the viewpoint of facilitating the expression of the plasticizing effect, the molecular weight of the plasticizing material is appropriately 30,000 or less, advantageously 25,000 or less, preferably less than 10,000 (e.g., less than 5,000), more preferably less than 3,000 (e.g., less than 1,000), may also be less than 800, less than 600, less than 500, or less than 400. Having a molecular weight of the plasticizing material that is not too large can be advantageous from the viewpoint of improving compatibility within the adhesive layer. Furthermore, from the viewpoint of facilitating the expression of a sufficient plasticizing effect, the molecular weight of the plasticizing material is appropriately 130 or more, preferably 150 or more, may also be 170 or more, may also be 200 or more, may also be 250 or more, or may also be 300 or more. Having a molecular weight of the plasticizing material that is not too low is also preferable from the viewpoint of improving the heat resistance of the adhesive sheet and suppressing contamination of the adherend. In some embodiments, the molecular weight of the plasticizing material may be 500 or more, 1000 or more, or 2000 or more.

[0086] Non-limiting examples of compounds that can be selected as plasticizing materials include: compounds that can be used as monomers (A1) (e.g., (meth)acrylates having aromatic rings such as benzyl, phenoxy, or naphthyl groups; monomers having a fluorene structure; monomers having a dinaphthothiophene structure; monomers having a dibenzothiophene structure, etc.); oligomers containing compounds that can be used as monomers (A1) as monomer units; and compounds with a structure obtained by removing the ethylenically unsaturated group portion from a compound that can be used as monomer (A1) and replacing it with a hydrogen atom or a group that does not have an ethylenically unsaturated group (e.g., 3-phenoxybenzyl alcohol). From the viewpoint of improving flexibility, oligomers containing compounds that can be used as monomers (A1) as monomer units may be copolymerized with low-Tg monomers such as n-butyl acrylate or 2-ethylhexyl acrylate. As a plasticizing material, one or more known plasticizers (for example, phthalate esters, terephthalate esters, adipic acid esters, adipic acid polyesters, glycol benzoate esters, etc.) may be used.

[0087] In some embodiments, organic materials with a refractive index of approximately 1.50 or higher (more preferably 1.53 or higher) can be preferably used as the plasticizing material. Specific examples of compounds that can be selected as plasticizing materials include: diethylene glycol dibenzoate (refractive index 1.55), dipropylene glycol dibenzoate (refractive index 1.54), 3-phenoxytoluene (refractive index 1.57), 3-ethyl biphenyl (refractive index 1.59), 3-methoxybiphenyl (refractive index 1.61), 4-methoxybiphenyl (refractive index 1.57), polyethylene glycol dibenzoate, 3-phenoxybenzyl alcohol (refractive index 1.59), triphenyl phosphate (refractive index 1.56), benzyl benzoate (refractive index 1.57), and 4-(tert-butyl) This includes, but is not limited to, phenyldiphenyl phosphate (refractive index 1.56), trimethylphenyl phosphate (refractive index 1.55), butylbenzyl phthalate (refractive index 1.54), rosin methyl ester (refractive index 1.53), alkylbenzyl phthalate (refractive index 1.53), butyl(phenylsulfonyl)amine (refractive index 1.53), trimethyltrimellitate (refractive index 1.52), benzyl phthalate (refractive index 1.52), 2-ethylhexyldiphenyl phosphate (refractive index 1.51), tris(2,4-di-tert-butylphenyl) phosphite, etc. From the viewpoint of refractive index and compatibility, for example, diethylene glycol dibenzoate can be preferably used. The upper limit of the refractive index of the plasticizing material is not particularly limited and may be, for example, 3.00 or less. In some embodiments, from the viewpoint of ease of preparation of the adhesive composition and compatibility within the adhesive, the refractive index of the plasticizing material is suitable to be 2.50 or less, advantageous to be 2.00 or less, may also be 1.90 or less, may also be 1.80 or less, or may also be 1.70 or less. The refractive index of the plasticizer is measured using an Abbe refractometer under the same conditions as the refractive index of the monomer, with a measurement wavelength of 589 nm and a measurement temperature of 25°C. If the manufacturer or other source provides a nominal refractive index value at 25°C, that nominal value may be used.

[0088] In the embodiment of using a plasticizing material, the amount of plasticizing material used per 100 parts by weight of acrylic polymer is not particularly limited and can be set according to the purpose. From the viewpoint of enhancing the plasticizing effect, the amount of plasticizing material used per 100 parts by weight of acrylic polymer may be, for example, 0.1 parts by weight or more, or 0.5 parts by weight or more, and from the viewpoint of obtaining a higher plasticizing effect, it is preferable to be 1 part by weight or more, more preferably 3 parts by weight or more, and may also be 5 parts by weight or more, 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or 20 parts by weight or more. Furthermore, from the viewpoint of achieving a good balance between increasing the refractive index of the adhesive and the plasticizing effect, it is appropriate to use approximately 100 parts by weight or less per 100 parts by weight of acrylic polymer, preferably 80 parts by weight or less, more preferably 60 parts by weight or less, and may also be 45 parts by weight or less, 35 parts by weight or less, or 25 parts by weight or less. In some embodiments where greater emphasis is placed on adhesive properties, the amount of plasticizer used per 100 parts by weight of acrylic polymer may be 15 parts by weight or less, 10 parts by weight or less, or 5 parts by weight or less.

[0089] (additives (H RO )) The adhesive composition disclosed herein may optionally contain an organic material having a higher refractive index than the acrylic polymer as an additive. Hereinafter, such an organic material will be referred to as "additive (H RO It is sometimes written as ")". Here, the above "H RO " indicates that it is an organic material with a high refractive index. Additives (H RO By using a combination of (H) and an acrylic polymer, an adhesive can be realized that more favorably balances refractive index and adhesive properties (peel strength, flexibility, etc.). RO The organic material used as an additive (H) may be a polymer or a nonpolymer. It may also have polymerizable functional groups or not. RO ) can be used individually or in combination of two or more types.

[0090] Additives (H RO The refractive index of the additive (H) can be set within an appropriate range in relation to the refractive index of the acrylic polymer, and is not limited to a specific range. RO The refractive index of the additive (H) can be selected from a range that is, for example, greater than 1.55, greater than 1.56, or greater than 1.57, and is higher than the refractive index of the acrylic polymer. From the viewpoint of increasing the refractive index of the adhesive, in some embodiments, the additive (H) RO The refractive index of (H) is advantageous to be 1.58 or higher, preferably 1.60 or higher, more preferably 1.63 or higher, may also be 1.65 or higher, may also be 1.70 or higher, and may also be 1.75 or higher. Additives with a higher refractive index (H) RO According to ), a smaller amount of additive (H RO The desired refractive index can also be achieved by using ). This is preferable from the viewpoint of suppressing a decrease in adhesive properties and optical properties. Additive (H RO There is no particular upper limit to the refractive index of the material, but from the viewpoint of compatibility within the adhesive and ease of achieving both a high refractive index and flexibility suitable for an adhesive, for example it may be 3.000 or less, 2.500 or less, 2.000 or less, 1.950 or less, 1.900 or less, or 1.850 or less. Note that additives (H RO The refractive index of ) is measured using an Abbe refractometer, similar to the refractive index of the monomer, under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. If the manufacturer or other source provides a nominal refractive index value at 25°C, that nominal value can be used.

[0091] Additives (H RO ) refractive index n b and the refractive index n of acrylic polymers a The difference between, i.e., n b -n a (Hereinafter, “Δn A It is also called ). ) is set to be greater than 0. In some embodiments, Δn AFor example, Δn can be 0.02 or greater, 0.05 or greater, 0.07 or greater, 0.10 or greater, 0.15 or greater, 0.20 or greater, or 0.25 or greater. A Acrylic polymers and additives (H RO By selecting ), additives (H RO The effect of improving the refractive index by using ) tends to be higher. Also, the additive (H) in the adhesive RO From the viewpoint of compatibility, in some embodiments, Δn A For example, it may be 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.35 or less.

[0092] In some embodiments, additive (H RO ) refractive index n b and the additive (H RO ) the refractive index n of the adhesive containing T The difference between, i.e., n b -n T (Hereinafter, “Δn B It is also called ). ) can be set to be greater than 0. In some embodiments, Δn B For example, Δn can be 0.02 or greater, 0.05 or greater, 0.07 or greater, 0.10 or greater, 0.15 or greater, 0.20 or greater, or 0.25 or greater. B The composition of the adhesive and additives (H RO By selecting ), additives (H RO The refractive index improvement effect tends to be higher with the use of ). Furthermore, from the viewpoint of compatibility within the adhesive and transparency of the adhesive, in some embodiments, Δn B For example, it may be 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.35 or less.

[0093] Additives (H ROThe molecular weight of the organic material used is not particularly limited and can be selected according to the purpose. From the viewpoint of achieving a good balance between the effect of increasing the refractive index and other properties (e.g., flexibility suitable for adhesives, optical properties such as haze), in some embodiments, the additive (H RO The molecular weight of the additive (H) is preferably less than 10,000, more preferably less than 5,000, more preferably less than 3,000 (e.g., less than 1,000), and may also be less than 800, less than 600, less than 500, or less than 400. RO The fact that the molecular weight of the additive (H) is not too large can be advantageous from the viewpoint 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. In some embodiments, the additive (H RO The molecular weight of the additive (H RO From the viewpoint of increasing the refractive index of ), it is preferably 170 or higher, more preferably 200 or higher, and may also be 230 or higher, 250 or higher, 270 or higher, 500 or higher, 1000 or higher, and 2000 or higher. In some embodiments, a polymer with a molecular weight of about 1000 to 10000 (for example, 1000 or more and less than 5000) is used as an additive (H RO It can be used as ). Additives (H RO For nonpolymers or polymers with a low degree of polymerization (e.g., 2-5 mers), the molecular weight can be calculated based on the chemical structure, or measured using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS). 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 molecular weight, that nominal value can be used.

[0094] Additives (H ROExamples of organic materials that could be options include, but are not limited to, organic compounds having aromatic rings, organic compounds having heterocycles (which may be aromatic rings or non-aromatic heterocycles), etc.

[0095] Additives (H RO The aromatic ring of the above-mentioned organic compound having an aromatic ring (hereinafter also referred to as the "aromatic ring-containing compound") used as monomer (A1) can be selected from the same aromatic rings as those of the compound used as monomer (A1).

[0096] The aromatic ring described above may have one or more substituents on its ring constituent atoms, or it may not have substituents. If substituents are present, examples of such substituents include, but are not limited to, alkyl groups, alkoxy groups, aryloxy groups, hydroxyl groups, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), hydroxyalkyl groups, hydroxyalkyloxy groups, glycidyloxy groups, etc. In substituents containing carbon atoms, the number of carbon atoms in the substituent is, for example, 1 to 10, advantageously 1 to 6, preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. In some embodiments, the aromatic ring described above may have no substituents on its ring constituent atoms, or it may be an aromatic ring having one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, and halogen atoms (e.g., bromine atoms).

[0097] Additives (H ROExamples of aromatic ring-containing compounds that can be used as additives include, for example: compounds that can be used as monomers (A1); oligomers containing compounds that can be used as monomers (A1) as monomer units; compounds obtained by replacing a compound that can be used as monomer (A1) with a group having an ethylenically unsaturated group (which may be a substituent bonded to a ring constituent atom) or a group that does not have a hydrogen atom or an ethylenically unsaturated group (e.g., 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.); etc., but are not limited to these. Additives (H RO Non-limiting specific examples of aromatic ring-containing compounds that can be used as ) include aromatic ring-containing monomers such as benzyl acrylate, m-phenoxybenzyl acrylate, 2-(o-phenylphenoxy)ethyl acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, phenoxypolyethylene glycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, monomers having the fluorene structure described above, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, etc.; aromatic ring-containing compounds that do not have an ethylenically unsaturated group, such as 3-phenoxybenzyl alcohol, dinaphthothiophene and its derivatives (for example, compounds in which one or more substituents selected from a hydroxyl group, methanol group, diethanol group, glycidyl group, etc. are attached to the dinaphthothiophene ring, one or more of which are hydroxyl groups, methanol groups, diethanol groups, glycidyl groups, etc.ethylenically unsaturated groups, one or more of which are aromatic ring-containing compounds; and the like. Furthermore, the aromatic ring-containing compound may be an oligomer containing such aromatic ring-containing monomers as monomer units (preferably an oligomer with a molecular weight of approximately 5000 or less, more preferably approximately 1000 or less; for example, a low polymer of about 2 to 5 units). The above oligomer may be, for example: a homopolymer of aromatic ring-containing monomers; a copolymer of one or more aromatic ring-containing monomers; a copolymer of one or more aromatic ring-containing monomers and other monomers; etc. As the other monomers, one or more monomers without aromatic rings may be used.

[0098] In some embodiments, additive (H RO As such, organic compounds having two or more aromatic rings in one molecule (hereinafter also referred to as "aromatic ring-containing compounds") can be preferably used because they easily provide a high refractive index effect. Aromatic ring-containing compounds may or may not have polymerizable functional groups such as ethylenically unsaturated groups. Furthermore, aromatic ring-containing compounds may be polymers or nonpolymers. The polymer may be an oligomer containing aromatic ring-containing monomers as monomer units (preferably an oligomer with a molecular weight of approximately 5000 or less, more preferably approximately 1000 or less; for example, a low polymer of about 2 to 5-mers). The oligomer may be, for example: a homopolymer of aromatic ring-containing monomers; a copolymer of one or more aromatic ring-containing monomers; a copolymer of one or more aromatic ring-containing monomers and other monomers; etc. The other monomers may be aromatic ring-containing monomers that do not fall under the category of aromatic ring-containing monomers, monomers that do not have aromatic rings, or combinations thereof.

[0099] Non-limiting examples of compounds containing multiple aromatic rings include compounds having a structure in which two or more non-condensed aromatic rings are linked via linking groups, compounds having a structure in which two or more non-condensed aromatic rings are chemically bonded directly (i.e., without the involvement of other atoms), compounds having a condensed aromatic ring structure, compounds having a fluorene structure, compounds having a dinaphthothiophene structure, compounds having a dibenzothiophene structure, and so on. Compounds containing multiple aromatic rings can be used individually or in combination of two or more.

[0100] Specific examples of compounds having the above-mentioned fluorene structure include monomers having the fluorene structure described above, as well as oligomers which are homopolymers or copolymers of such monomers, and 9,9-bisphenylfluorene and its derivatives, such as 9,9-bis(4-hydroxyphenyl)fluorene (refractive index: 1.68), 9,9-bis(4-aminophenyl)fluorene (refractive index: 1.73), 9,9-bis(4-hydroxy-3-methylphenyl)fluorene (refractive index: 1.68), and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (refractive index: 1.65).

[0101] Specific examples of compounds having the above-mentioned dinaphthothiophene structure include monomers having the aforementioned dinaphthothiophene structure, oligomers which are homopolymers or copolymers of such monomers, as well as hydroxyalkyl dinaphthothiophenes such as dinaphthothiophene (refractive index: 1.808); 6-hydroxymethyl dinaphthothiophene (refractive index: 1.766); dihydroxydinaphthothiophenes such as 2,12-dihydroxydinaphthothiophene (refractive index: 1.750); and 2,12- Examples of dinaphthothiophenes and their derivatives include dihydroxyalkyl oxydinaphthothiophenes such as dihydroxethyloxydinaphthothiophene (refractive index: 1.677); diglycidyloxydinaphthothiophenes such as 2,12-diglycidyloxydinaphthothiophene (refractive index: 1.723); and dinaphthothiophenes having two or more ethylenically unsaturated groups, such as 2,12-diallyloxydinaphthothiophene (abbreviation: 2,12-DAODNT, refractive index: 1.729).

[0102] Specific examples of compounds having the above-mentioned dibenzothiophene structure include monomers having the aforementioned dibenzothiophene structure, oligomers which are homopolymers or copolymers of such monomers, as well as dibenzothiophene (refractive index: 1.607), 4-dimethyldibenzothiophene (refractive index: 1.617), 4,6-dimethyldibenzothiophene (refractive index: 1.617), and the like.

[0103] Additives (H ROExamples of heterocyclic organic compounds (hereinafter also referred to as heterocyclic organic compounds) that can be options include thioepoxy compounds and compounds having triazine rings. An example of a thioepoxy compound is bis(2,3-epithiopropyl) disulfide and its polymer (refractive index 1.74) described in Japanese Patent Publication No. 3712653. An example of a compound having a triazine ring is a compound having at least one triazine ring (for example, 3 to 40, preferably 5 to 20) in one molecule. Since triazine rings are aromatic, compounds having triazine rings are also included in the above concept of aromatic ring-containing compounds, and compounds having multiple triazine rings are also included in the above concept of compounds containing multiple aromatic rings.

[0104] In some embodiments, additive (H RO As the additive (H), compounds that do not have ethylenically unsaturated groups can be preferably used. This suppresses deterioration of the adhesive composition due to heat and light (progression of gelation and decrease in leveling properties due to increased viscosity), and improves storage stability. Additives that do not have ethylenically unsaturated groups (H RO ) adopting the additive (H RO Adhesive sheets having an adhesive layer containing ) and laminates containing said adhesive sheets are preferable from the viewpoint of suppressing dimensional changes and deformations (warping, undulation, etc.) and the occurrence of optical distortion caused by the reaction of ethylenically unsaturated groups.

[0105] Additives (H RO In embodiments where an oligomer is used as a polymer, the oligomer can be obtained by polymerizing the corresponding monomer component by a known method. When the oligomer is produced by radical polymerization, polymerization initiators, chain transfer agents, emulsifiers, etc. used in radical polymerization can be added to the monomer component as appropriate, and polymerization can be carried out. The polymerization initiators, chain transfer agents, emulsifiers, etc. used in radical polymerization are not particularly limited and can be selected and used as appropriate. The weight-average molecular weight of the oligomer can be controlled by the amount of polymerization initiator and chain transfer agent used and the reaction conditions, and the amount used can be adjusted as appropriate depending on the type of these agents. Examples of the chain transfer agent include lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, α-thioglycerol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, and the like. The chain transfer agent may be used alone or in combination of two or more. The amount of the chain transfer agent used can be set according to the composition of the monomer components used for the synthesis of the oligomer, the type of the chain transfer agent, etc., so that an oligomer having a desired weight average molecular weight can be obtained. In some embodiments, the amount of the chain transfer agent used relative to 100 parts by weight of the total amount of the monomers used for the synthesis of the oligomer is preferably about 15 parts by weight or less, may be 10 parts by weight or less, or may be about 5 parts by weight or less. The lower limit of the amount of the chain transfer agent used relative to 100 parts by weight of the total amount of the monomers used for the synthesis of the oligomer is not particularly limited, and may be, for example, 0.01 part by weight or more, may be 0.1 part by weight or more, may be 0.5 part by weight or more, or may be 1 part by weight or more.

[0106] The amount of the additive (H RO ) used relative to 100 parts by weight of the acrylic polymer (when a plurality of compounds are used, the total amount thereof) is not particularly limited as long as it exceeds 0 parts by weight, and can be set according to the purpose. In some embodiments, the amount of the additive (H RO ) used relative to 100 parts by weight of the acrylic polymer can be, for example, 80 parts by weight or less. From the viewpoint of achieving a good balance between increasing the refractive index of the adhesive and suppressing the deterioration of the adhesive properties and optical properties, it is advantageous to set it to 60 parts by weight or less, and preferably 45 parts by weight or less. In some embodiments that place more importance on the adhesive properties and optical properties, the amount of the additive (H RO ) used relative to 100 parts by weight of the acrylic polymer can be, for example, 30 parts by weight or less, may be 20 parts by weight or less, may be 15 parts by weight or less, or may be 10 parts by weight or less. Also, from the viewpoint of increasing the refractive index of the adhesive, the amount of the additive (H ROThe amount used can be, for example, 1 part by weight or more, it is advantageous to use 3 parts by weight or more, it is preferable to use 5 parts by weight or more, it may also be 7 parts by weight or more, it may also be 10 parts by weight or more, it may also be 15 parts by weight or more, and it may also be 20 parts by weight or more.

[0107] (Crosslinking agent) The adhesive compositions disclosed herein may contain crosslinking agents as needed for purposes such as adjusting the cohesive force of the adhesive. As crosslinking agents, known crosslinking agents in the field of adhesives can be used, such as isocyanate crosslinking agents, epoxy crosslinking agents, aziridine crosslinking agents, oxazoline crosslinking agents, melamine resins, and metal chelate crosslinking agents. Among these, isocyanate crosslinking agents are preferably used. Other examples of crosslinking agents include monomers having two or more ethylenically unsaturated groups in one molecule, i.e., polyfunctional monomers. Crosslinking agents can be used individually or in combination of two or more.

[0108] As isocyanate crosslinking agents, isocyanate compounds with two or more functions can be used, for example: 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 polyisocyanate modified products obtained by modifying the above isocyanate compounds with allophanate bonds, biuret bonds, isocyanurate bonds, uretdione bonds, urea bonds, carbodiimide bonds, uretonimine bonds, oxadiazinetrione bonds, etc. Examples of commercially available products include the product names Takenate 300S, Takenate 500, Takenate 600, Takenate D165N, Takenate D178N (all manufactured by Takeda Pharmaceutical Company Limited), Sumijoule T80, Sumijoule L, Desmodule N3400 (all manufactured by Sumika Bayer Urethane Co., Ltd.), Myrionate MR, Myrionate MT, Coronate L, Coronate HL, Coronate HX (all manufactured by Tosoh Corporation). Isocyanate compounds can be used individually or in combination of two or more. A bifunctional isocyanate compound may be used in combination with a trifunctional or higher isocyanate compound.

[0109] 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 can be used individually or in combination of two or more.

[0110] Examples of polyfunctional monomers include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, and 1,6-hexa(meth)acrylate. Examples 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, and the like. Polyfunctional monomers can be used individually or in combination of two or more.

[0111] When using a crosslinking agent (which may be a polyfunctional monomer), the amount used is not particularly limited and can be in the range of approximately 0.001 to 5.0 parts by weight per 100 parts by weight of the monomer component. 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 component is preferably 3.0 parts by weight or less, more preferably 2.0 parts by weight or less, and may also be 1.0 part by weight or less, 0.5 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 component may be, for example, 0.005 parts by weight or more, 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.08 parts by weight or more.

[0112] A crosslinking catalyst may be used to more effectively advance the crosslinking reaction. Examples of crosslinking catalysts include metal-based crosslinking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, ferric narcem, butyltin oxide, and dioctyltin dilaurate. Among these, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. The amount of crosslinking catalyst used is not particularly limited. The amount of crosslinking catalyst used per 100 parts by weight of monomer component can be in the range of approximately 0.0001 parts by weight to 1 part by weight, and preferably in the range of 0.001 parts by weight to 0.5 parts by weight, taking into consideration the balance between the speed of the crosslinking reaction and the length of the pot life of the adhesive composition.

[0113] The adhesive composition may contain a compound that induces keto-enol tautomerism as a crosslinking retarder. This can extend the pot life of the adhesive composition. For example, a compound that induces keto-enol tautomerism can be preferably used in an adhesive composition containing an isocyanate-based crosslinking agent. Various β-dicarbonyl compounds can be used as the compound that induces keto-enol tautomerism. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) and acetoacetate esters (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably used. The compound that induces keto-enol tautomerism can be used alone or in combination of two or more. The amount of the compound that induces keto-enol tautomerism can be, for example, 0.1 parts by weight to 20 parts by weight, 0.5 parts by weight to 10 parts by weight, or 1 part by weight to 5 parts by weight, per 100 parts by weight of the monomer component.

[0114] (Adhesion agent) The adhesive compositions disclosed herein may contain a tackifier. Known tackifiers such as rosin-based tackifiers, terpene-based tackifiers, phenol-based tackifiers, hydrocarbon-based tackifiers, ketone-based tackifiers, polyamide-based tackifiers, epoxy-based tackifiers, and elastomer-based tackifiers can be used. These can be used individually or in combination of two or more. The amount of tackifier used is not particularly limited and can be set to achieve appropriate adhesive performance depending on the purpose and application. In some embodiments, from the viewpoint of refractive index and transparency, the amount of tackifier per 100 parts by weight of monomer component is appropriately 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 preferably be implemented in an embodiment that does not use a tackifier.

[0115] (Leveling agent) The adhesive compositions disclosed herein may optionally contain leveling agents for purposes such as improving the appearance of the adhesive layer formed from the composition (e.g., improving the uniformity of thickness) or improving the coatability of the adhesive composition. Non-limiting examples of leveling agents include acrylic leveling agents, fluorine leveling agents, and silicone leveling agents. The leveling agent can be selected appropriately from commercially available leveling agents and used by conventional methods.

[0116] In some embodiments, a polymer (hereinafter also referred to as "polymer (B)") which is a polymer of a monomer raw material (hereinafter also referred to as "monomer raw material B") containing a monomer having a polyorganosiloxane skeleton (hereinafter also referred to as "monomer S1") and an acrylic monomer can preferably be used as the leveling agent. Polymer (B) can be described as a copolymer of monomer S1 and an acrylic monomer. Polymer (B) can be used alone or in combination of two or more types.

[0117] Monomer S1 is not particularly limited, and any monomer containing a polyorganosiloxane skeleton can be used. Preferably, monomer S1 has a structure with a polymerizable reactive group at one end. In particular, monomer S1 has a structure with a polymerizable reactive group at one end and no functional group at the other end that crosslinks with an acrylic polymer. Examples of commercially available products include Shin-Etsu Chemical Co., Ltd.'s single-end reactive silicone oils (e.g., product numbers X-22-174ASX, X-22-2426, X-22-2475, KF-2012, etc.). Monomer S1 can be used alone or in combination of two or more.

[0118] The functional group equivalent of monomer S1 may be, for example, around 100 g / mol to 30,000 g / mol. In some preferred embodiments, the functional group equivalent may be, for example, 500 g / mol or more, 800 g / mol or more, 1,500 g / mol or more, or 2,000 g / mol or more. Alternatively, the functional group equivalent may be, for example, 20,000 g / mol or less, less than 10,000 g / mol, 7,000 g / mol or less, or 5,500 g / mol or less. When the functional group equivalent of monomer S1 is within the above range, a good leveling effect is easily achieved. Furthermore, when using two or more monomers with different functional group equivalents as monomer S1, the functional group equivalent of monomer S1 can be the sum of the products of the functional group equivalent of each monomer and the weight fraction of that monomer.

[0119] Here, "functional group equivalent" refers to the weight of the main skeleton (e.g., polydimethylsiloxane) attached to each functional group. The unit g / mol is calculated by converting 1 mol of functional group to g / mol. The functional group equivalent of monomer S1 is determined, for example, based on nuclear magnetic resonance (NMR). 1 It can be calculated from the spectral intensity of 1H-NMR (proton NMR). 1 The calculation of the functional group equivalent (g / mol) of monomer S1 based on the spectral intensity of H-NMR is as follows: 1 This can be done based on general structural analysis techniques related to H-NMR spectral analysis, and if necessary, by referring to the description in Japanese Patent Publication No. 5951153. In the functional group equivalent of monomer S1, the above-mentioned functional group refers to a polymerizable functional group (for example, an ethylenically unsaturated group such as a (meth)acryloyl group, vinyl group, or allyl group).

[0120] The content of monomer S1 in monomer raw material B can be an appropriate value within the range in which the desired effect is achieved using monomer S1, and is not limited to a specific range. In some embodiments, the content of monomer S1 in monomer raw material B may be, for example, 5 to 60% by weight, 10 to 50% by weight, or 15 to 40% by weight.

[0121] In addition to monomer S1, monomer raw material B contains an acrylic monomer copolymerizable with monomer S1. Thereby, the compatibility of polymer (B) in the adhesive layer can be improved. Examples of the acrylic monomer that can be used for monomer raw material B include alkyl acrylates. Here, "alkyl" refers to a chain-like (including linear and branched-chain) alkyl (group) and does not include the alicyclic hydrocarbon groups described below. In some embodiments, monomer raw material B is (meth)acrylic acid C 4-12 alkyl ester (preferably (meth)acrylic acid C 4-10 alkyl ester, for example (meth)acrylic acid C 6-10 alkyl ester) may contain at least one kind. In some other embodiments, monomer raw material B is methacrylic acid C 1-18 alkyl ester (preferably methacrylic acid C 1-14 alkyl ester, for example methacrylic acid C 1-10 alkyl ester) may contain at least one kind. As the acrylic monomer, monomer raw material B may contain, for example, one or more selected from methyl methacrylate (MMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA).

[0122] Other examples of the above acrylic monomers include (meth)acrylic acid esters having an alicyclic hydrocarbon group. For example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate, etc. can be used. It is not necessary to use (meth)acrylic acid esters having an alicyclic hydrocarbon group.

[0123] The content of the alkyl (meth)acrylate and the alicyclic hydrocarbon group-containing (meth)acrylate in monomer raw material B may be, for example, 10% by weight or more and 95% by weight or less, 20% by weight or more and 95% by weight or less, 30% by weight or more and 90% by weight or less, 40% by weight or more and 90% by weight or less, or 50% by weight or more and 85% by weight or less.

[0124] Other examples of monomers that may be included in monomer raw material B along with monomer S1 include the carboxyl group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, epoxy group-containing monomers, cyano group-containing monomers, isocyanate group-containing monomers, amide group-containing monomers, monomers having a nitrogen atom-containing ring, (meth)acrylate aminoalkyls, vinyl esters, vinyl ethers, olefins, (meth)acrylate esters having aromatic hydrocarbon groups, halogen atom-containing (meth)acrylates, etc., which can be used in acrylic polymers.

[0125] The Mw of polymer (B) may be, for example, 5,000 or more, preferably 10,000 or more, and may also be 15,000 or more. Alternatively, the Mw of polymer (B) may be, for example, 200,000 or less, preferably 100,000 or less, may also be 50,000 or less, and may also be 30,000 or less. By setting the Mw of polymer (B) within an appropriate range, suitable compatibility and leveling properties can be achieved.

[0126] Polymer (B) can be produced, for example, by polymerizing the above-mentioned monomers using known methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization. To adjust the molecular weight of polymer (B), a chain transfer agent may be used as needed. Examples of chain transfer agents that can be used include compounds having a mercapto group such as t-dodecyl mercaptan, mercaptoethanol, and α-thioglycerol; thioglycolic acid esters such as thioglycolic acid and methyl thioglycolate; and α-methylstyrene dimer. The amount of chain transfer agent used is not particularly limited and can be set as appropriate to obtain polymer (B) with the desired molecular weight. In some embodiments, the amount of chain transfer agent used per 100 parts by weight of monomer may be, for example, 0.1 to 5 parts by weight, 0.2 to 3 parts by weight, or 0.5 to 2 parts by weight.

[0127] The amount of polymer (B) used per 100 parts by weight of acrylic polymer can be, for example, 0.001 parts by weight or more, and from the viewpoint of obtaining a higher usage effect, it may be 0.01 parts by weight or more, or 0.03 parts by weight or more. Furthermore, the amount of polymer (B) used may be, for example, 3 parts by weight or less, and from the viewpoint of reducing the effect on the refractive index, it is appropriate to use 1 part by weight or less, and it may also be 0.5 parts by weight or less, or 0.1 parts by weight or less.

[0128] (Other additives) Furthermore, the adhesive compositions disclosed herein may optionally contain known additives that can be used in adhesive compositions, such as plasticizers, softeners, colorants (dyes, pigments, etc.), fillers, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, and preservatives, to the extent that the effects of the present invention are not significantly hindered. Such various additives can be used by conventional methods if they are conventionally known, and do not particularly characterize the present invention, so a detailed explanation is omitted.

[0129] <Adhesive> The adhesives disclosed herein can be formed, for example, using any of the adhesive compositions described above. Such adhesives may be adhesives obtained by curing adhesive compositions in the form of solvent-type, active energy ray-curable, water-dispersible, hot-melt type, etc., by drying, crosslinking, polymerization, cooling, etc., i.e., cured products of the above adhesive compositions. The curing means for the adhesive composition (e.g., drying, crosslinking, polymerization, cooling, etc.) may be applied individually, or two or more may be applied simultaneously or in multiple stages. In the case of solvent-type adhesive compositions, the adhesive can typically be formed by drying (preferably further crosslinking) the composition. In the case of active energy ray-curable adhesive compositions, the adhesive is typically formed by irradiating with active energy rays to carry out polymerization and / or crosslinking reactions. If drying is required for active energy ray-curable adhesive compositions, it is preferable to irradiate with active energy rays after drying.

[0130] (Refractive index) The adhesives disclosed herein may exhibit a refractive index above a predetermined level by containing an acrylic polymer with a high content of monomer (A1) in the monomer component. According to the technology disclosed herein, an adhesive having a refractive index of, for example, 1.560 or higher (preferably above 1.570), an adhesive composition capable of forming the adhesive, and an adhesive sheet containing the adhesive can be provided.

[0131] 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 the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. For example, an Abbe refractometer of model "DR-M4" manufactured by ATAGO or an equivalent product can be used. As a measurement sample, an adhesive layer consisting of the adhesive to be evaluated can be used. Specifically, the refractive index of an adhesive can be measured by the method described in the examples below. The refractive index of an adhesive can be adjusted, for example, by the composition of the adhesive (for example, the composition of the monomer components constituting the acrylic polymer).

[0132] In some embodiments, the refractive index of the adhesive may be preferably 1.575 or higher, more preferably 1.580 or higher, even more preferably 1.585 or higher, and particularly preferably 1.590 or higher (e.g., 1.595 or higher). An adhesive having such a refractive index can effectively suppress light reflection at the interface with the adherend when applied to a material with a high refractive index. According to the techniques disclosed herein, such a refractive index can be achieved even in adhesives that do not specifically use high refractive index particles as described later. 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, or 1.650 or less.

[0133] The adhesive disclosed herein may optionally contain high refractive index particles. Herein, high refractive index particles mean particles that, when included in the adhesive, can increase the refractive index of the adhesive. Hereinafter, high refractive index particles will be referred to as "particle P". HRI It is sometimes written as "HRI". HRI stands for high refractive index.

[0134] particle P HRI For example, one or more particles made of a material having a refractive index of 1.60 or higher, preferably 1.70 or higher (it may also be 1.80 or higher, 1.90 or higher, and even 2.00 or higher) may be used. HRI The upper limit of the refractive index of the material constituting it 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. Particle P HRI The refractive index of the material constituting the material is the refractive index measured for a single layer of the material (with a thickness that allows for refractive index measurement) using a commercially available spectroscopic ellipsometer under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. As a spectroscopic ellipsometer, for example, product name "EC-400" (manufactured by JA. Woolam) or an equivalent product can be used.

[0135] particle P HRIThe type is not particularly limited, and one or more materials capable of improving the refractive index of the adhesive sheet can be selected and used from among metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. HRI As such, inorganic oxides (e.g., metal oxides) that can improve the refractive index of the adhesive sheet are preferably used. HRI Suitable examples of materials constituting the particle 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 oxides (e.g., metal oxides) can be used individually 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, as metal particles, for example, iron-based, zinc-based, tungsten-based, and platinum-based materials can have high refractive indices. As organic particles, particles made of resins such as 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 above-mentioned inorganic materials and organic materials, and inorganic particles coated with organic materials such as resins. HRI From the viewpoint of compatibility with adhesive components, the above-mentioned organic and inorganic particles may be used in which the surface has been treated with a surface treatment agent.

[0136] particle P HRI The average particle size is not particularly limited, and particles of an appropriate size that can achieve the desired refractive index improvement when incorporated into the adhesive can be used. Particle P HRI The average particle size can be, for example, approximately 1 nm or more, and approximately 5 nm or more is appropriate. From the viewpoint of improving refractive index and handling, particle P HRIThe average particle size is preferably about 10 nm or more, but may also be about 20 nm or more, or about 30 nm or more. Furthermore, from the viewpoint of maintaining adhesive properties, the upper limit of the average particle size is suitable to be, 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 also be about 35 nm or less (for example, about 25 nm or less).

[0137] Furthermore, the above particle P HRI The average particle size refers to the volume-average particle diameter, and specifically, using a particle size distribution analyzer based on laser scattering and diffraction, the particle P HRI The particle size at 50% of the cumulative value in the particle size distribution measured for the dispersion (50% volume average particle diameter; hereafter referred to as D) 50 It is sometimes abbreviated as ). This refers to ). As a measuring device, for example, the "Microtrac MT3000II" product manufactured by Microtrac-Bell or an equivalent product can be used.

[0138] Particle P in adhesives HRI The content of the above particles P is not particularly limited. HRI The content may vary depending on the desired refractive index. For example, the above particle P HRI The content of this substance can be appropriately set to achieve a refractive index above a predetermined level, taking into consideration the required adhesive properties and other factors. Particle P in adhesives HRI The content can be, for example, approximately 75% by weight or less, and may be approximately 50% by weight or less, or approximately 30% by weight or less, from the viewpoint of adhesive properties and transparency. HRI The lower limit of the content is not particularly limited; for example, it may be more than 0% by weight, 1% or more by weight, or 5% or more by weight.

[0139] Particle P in adhesives HRI The content of particle P can also be determined by its relative relationship to the amount of the acrylic polymer contained in the adhesive. HRIThe content of P can be, for example, approximately 100 parts by weight or less per 100 parts by weight of the above acrylic polymer, and may be approximately 60 parts by weight or less, or approximately 40 parts by weight or less, from the viewpoint of adhesive properties and transparency. HRI The lower limit of the content is not particularly limited; for example, it may be more than 0% by weight, 1% or more by weight, or 5% or more by weight.

[0140] (Storage modulus G') The storage modulus G'(25) of the adhesive disclosed herein at 25°C is not particularly limited and may be, for example, 300 kPa or less, 270 kPa or less, or 250 kPa or less. From the viewpoint of increasing the flexibility of the adhesive in the room temperature range (e.g., 25°C) and making it easier to adhere to the adherend, the storage modulus G'(25) of the adhesive is appropriately less than 200 kPa, preferably less than 180 kPa, and more preferably less than 160 kPa (e.g., less than 140 kPa). In some embodiments, the storage modulus G'(25) of the adhesive may be less than 100 kPa or less than 90 kPa. The lower limit of the storage modulus G'(25) of the adhesive is not particularly limited, but from the viewpoint of processability and handling, it may be, for example, 30 kPa or more, 50 kPa or more, or 70 kPa or more.

[0141] The storage modulus G'(50) of the adhesive disclosed herein at 50°C is not particularly limited and may be, for example, less than 100 kPa. In some embodiments, the storage modulus G'(50) is appropriately less than 60 kPa, preferably less than 40 kPa, and more preferably less than 38 kPa (e.g., less than 36 kPa). Adhesives with such a limited storage modulus G'(50) can easily increase their adhesion to the adherend by heating, thereby improving adhesion to the adherend. There is no particular lower limit to the storage modulus G'(50) of the adhesive. In some embodiments, from the viewpoint of the heat resistance of the adhesive, the storage modulus G'(50) may be, for example, 10 kPa or more, 15 kPa or more, 20 kPa or more, or 23 kPa or more.

[0142] In some embodiments of the adhesives disclosed herein, the adhesive is subject to the following conditions: (a) The storage modulus G'(25) at 25°C is less than 200 kPa (e.g., 180 kPa or less); and (b) The storage modulus G'(50) at 50°C is less than 40 kPa (e.g., less than 38 kPa); It is preferable that the adhesive satisfies at least one of the above conditions. An adhesive that satisfies at least condition (a) above is preferred from the viewpoint of adhesion to the adherend in the room temperature range (e.g., 25°C). An adhesive that satisfies at least condition (b) above is preferred because its adhesion to the adherend can be easily improved by heating it to a temperature slightly above room temperature. An adhesive that does not satisfy condition (a) above but satisfies condition (b) above can be used as a heat-activated type adhesive that has good reworkability (repositionability) in the initial stages of application in the room temperature range and can effectively increase the peel strength from the adherend by heating it to a temperature slightly above room temperature.

[0143] (Storage modulus ratio (G'(50) / G'(25))) In some embodiments of the adhesives disclosed herein, the ratio of the storage modulus G'(50)[kPa] to the storage modulus G'(25)[kPa] of the adhesive, i.e., the storage modulus ratio G'(50) / G'(25), is, for example, 70% or less, and may be 40% or less, 30% or less, or 20% or less. Adhesives with a small G'(50) / G'(25) are suitable for use as the above-mentioned heat-activated type adhesives. The lower limit of G'(50) / G'(25) is not particularly limited. G'(50) / G'(25) is, for example, 5% or more, preferably 10% or more from the viewpoint of the heat resistance properties of the adhesive, and may be 12% or more, or 15% or more.

[0144] The storage moduli G'(25) and G'(50) can be measured by the method described in the examples below, and G'(50) / G'(25) can be calculated from the results. The storage moduli G'(25) and G'(50) and storage modulus ratio (G'(50) / G'(25)) of the adhesive are determined by the selection of the composition of the monomer components constituting the acrylic polymer (e.g., selection of the type and content of monomer (A1)), the presence or absence of crosslinking agent use, the selection of type and amount used, and additives (H RO ) and plasticizing materials can be adjusted by selecting the type and amount used, etc. For example, by using a relatively small amount of a second monomer, which has a different chemical structure from the first monomer, in addition to the first monomer, which is the main component of monomer (A1), in combination with the first monomer, G'(50) can be reduced and G'(50) / G'(25) can be lowered compared to when the first monomer is used alone as monomer (A1).

[0145] <Adhesive sheet> This specification provides an adhesive sheet having an adhesive layer. The adhesive constituting the adhesive layer may be an adhesive formed from any of the adhesive compositions disclosed herein (for example, a cured product of the adhesive composition). The above-mentioned adhesive sheet may be an adhesive sheet with a substrate having the adhesive layer on one or both sides of a non-peelable substrate (support substrate), or it may be an adhesive sheet without a substrate (i.e., an adhesive sheet without a non-peelable substrate; typically an adhesive sheet consisting of an adhesive layer) in which the adhesive layer is held by a release liner. The concept of adhesive sheet as used herein may include what is called adhesive tape, adhesive label, adhesive film, etc. The adhesive sheet disclosed herein may be in roll form or sheet form. Alternatively, it may be an adhesive sheet processed into various shapes.

[0146] Figures 1 and 2 show examples of the configuration of a double-sided adhesive substrate-less adhesive sheet (substrate-less double-sided adhesive sheet). The adhesive sheet 1 shown in Figure 1 has a configuration in which both sides 21A and 21B of the substrate-less adhesive layer 21 are protected by release liners 31 and 32, with at least the adhesive layer side being the release surface. The adhesive sheet 2 shown in Figure 2 has a configuration in which one surface (adhesive surface) 21A of the substrate-less adhesive layer 21 is protected by a release liner 31 with both sides being release surfaces. When this is wound, the other surface (adhesive surface) 21B of the adhesive layer 21 comes into contact with the back surface of the release liner 31, so that the other surface 21B is also protected by the release liner 31. The technology disclosed herein can be preferably implemented in such a substrate-less form from viewpoints such as reducing the thickness of the adhesive sheet or increasing the transparency of the adhesive sheet.

[0147] The adhesive sheet disclosed herein may, for example, have a cross-sectional structure schematically shown in Figure 3. The adhesive sheet 3 shown in Figure 3 comprises a support substrate 10 and a first adhesive layer 21 and a second adhesive layer 22 supported on the first surface 10A and the second surface 10B of the support substrate 10, respectively. Both the first surface 10A and the second surface 10B are non-peelable surfaces (non-peelable surfaces). The adhesive sheet 3 is used by attaching the surface of the first adhesive layer 21 (first adhesive surface) 21A and the surface of the second adhesive layer 22 (second adhesive surface) 22A to an adherend. That is, the adhesive sheet 1 is configured as a double-sided adhesive sheet (double-sided adhesive adhesive sheet). Before use, the 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, respectively, on which at least the adhesive surface side is a peelable surface (peelable surface). Alternatively, the release liner 32 may be omitted, and a release liner 31 with release surfaces on both sides may be used. By winding the adhesive sheet 3 around the release liner 3 and bringing the second adhesive surface 22A into contact with the back surface of the release liner 31, the second adhesive surface 22A may also be protected by the release liner 31.

[0148] The technology disclosed herein is preferably implemented in the form of a substrate-less or substrate-attached double-sided adhesive sheet for fixing or joining components (e.g., optical components). Alternatively, the adhesive sheet disclosed herein may be in the form of a substrate-attached single-sided adhesive sheet having an adhesive layer on only one side of a non-peelable substrate (support substrate), although not specifically shown. An example of a single-sided adhesive sheet is a configuration shown in Figure 3 in which either the first adhesive layer 21 or the second adhesive layer 22 is not present.

[0149] (Adhesive layer) The adhesive layer of the adhesive sheet disclosed herein can be formed by applying (e.g., coating) an adhesive composition to a suitable surface and then curing the composition. The application of the adhesive composition can be carried out using conventional coaters such as gravure roll coaters, reverse roll coaters, kiss roll coaters, dip roll coaters, bar coaters, knife coaters, and spray coaters.

[0150] The thickness of the adhesive layer is not particularly limited and can be, for example, 3 μm or more. In some embodiments, the thickness of the adhesive layer may be, for example, 5 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, 50 μm or more, 70 μm or more, or 85 μm or more. Adhesion tends to increase with increasing thickness of the adhesive layer. In some embodiments, the thickness of the adhesive layer may be, for example, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 120 μm or less. Having an adhesive layer that is not too thick can be advantageous from the viewpoint of making the adhesive sheet thinner. The technology disclosed herein can preferably be implemented, for example, in an embodiment in which the thickness of the adhesive layer is in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm). In the case of an adhesive sheet having a first adhesive layer and a second adhesive layer on the first and second surfaces of the substrate, the thickness of the adhesive layer described above can be applied to at least the thickness of the first adhesive layer. The thickness of the second adhesive layer can also be selected from a similar range. Furthermore, in the case of an adhesive sheet without a substrate, the thickness of the adhesive sheet is the same as the thickness of the adhesive layer.

[0151] (Haze value) In some embodiments, the haze value of the adhesive layer constituting the adhesive sheet may be, for example, 5.0% or less, preferably 2.0% or less, more preferably 1.0% or less, and may also be 0.9% or less, 0.8% or less, 0.5% or less, or 0.3% or less. Adhesive sheets having such a highly transparent adhesive layer can be preferably applied to applications requiring high light transmittance (e.g., optical applications) or applications where the adherend can be clearly seen through the adhesive sheet, with or without a substrate. The lower limit of the haze value of the adhesive layer is not particularly limited, and from the viewpoint of improving transparency, a smaller haze value is preferable. On the other hand, in some embodiments, considering the refractive index and adhesive properties, the haze value may be, for example, 0.05% or more, or 0.10% or more. These haze values ​​for the adhesive layer can also preferably be applied to the haze value of the adhesive sheet when the technology disclosed herein is implemented in the form of a substrate-less adhesive sheet (typically an adhesive sheet consisting of an adhesive layer).

[0152] Here, "haze value" refers to the ratio of diffusely transmitted light to total transmitted light when visible light is shone on the object being measured. 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 adhesive layer can be adjusted, for example, by selecting the composition and thickness of the adhesive layer.

[0153] In some embodiments, the total light transmittance of the adhesive layer is preferably 86.0% or higher (for example, 88.0% or higher, 90.0% or higher, or greater than 90.0%). The upper limit of the total light transmittance may practically be, for example, approximately 98% or less, approximately 96% or less, or approximately 95% or less. In some embodiments, considering the refractive index and adhesive properties, the total light transmittance of the adhesive layer may be approximately 94% or less, 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. As the transmittance meter, the "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory or an equivalent product is used.

[0154] (Peel strength) In some embodiments of the adhesive sheets disclosed herein, the peel strength of the adhesive sheet to the glass plate is preferably 2 N / 25 mm or more, more preferably 4 N / 25 mm or more, and may be 8 N / 25 mm or more, 10 N / 25 mm or more, or 12 N / 25 mm or more. The upper limit of the peel strength is not particularly limited and may be, for example, 30 N / 25 mm or less, 25 N / 25 mm or less, or 20 N / 25 mm or less.

[0155] Here, the peel strength is determined by pressing the adhesive sheet onto an alkali glass plate as the adherend, leaving it in an environment of 23°C and 50%RH for 30 minutes, and then measuring the adhesive strength when peeled off at a 180° angle and tensile speed of 300 mm / min. For measurement, if necessary, the adhesive sheet to be measured can be reinforced by attaching an appropriate backing material (for example, a polyethylene terephthalate (PET) film with a thickness of about 25 μm to 50 μm). More specifically, the peel strength can be measured according to the method described in the examples below.

[0156] <Supporting base material> Adhesive sheets according to some embodiments may take the form of an adhesive sheet with a substrate having an adhesive layer on one or both sides of the support substrate. The material of the support substrate is not particularly limited and can be appropriately selected according to the purpose and manner of use of the adhesive sheet. Non-limited examples of substrates that can be used include: polyolefin films mainly composed of polyolefins such as polypropylene (PP) and ethylene-propylene copolymer; polyester films mainly composed of polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); and polyvinyl chloride films mainly composed of polyvinyl chloride; foam sheets made of foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam; woven and nonwoven fabrics made by single-originating or blending various fibrous materials (which may be natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc.); papers such as Japanese paper, fine paper, kraft paper, and crepe paper; and metal foils such as aluminum foil and copper foil. Substrates with a composite composition of these may also be used. Examples of such composite substrates include, for instance, a substrate with a structure in which metal foil and the above-mentioned plastic film are laminated, and a plastic substrate reinforced with inorganic fibers such as glass cloth.

[0157] In some embodiments, various film substrates can be preferably used. The film substrate may be a porous substrate such as a foamed film or a nonwoven fabric sheet, a non-porous substrate, or a substrate with a structure in which a porous layer and a non-porous layer are laminated. In some embodiments, the film substrate may preferably include a resin film that is independently shape-retaining (self-supporting or independent) as a base film. Here, "resin film" means a resin film with a non-porous structure, which is typically substantially free of air bubbles (voidless). Therefore, the resin film is a concept distinct from foamed films and nonwoven fabrics. The resin film may preferably be one that is independently shape-retaining (self-supporting or independent). The resin film may have a single-layer structure or a multilayer structure of two or more layers (for example, a three-layer structure).

[0158] Examples of resin materials that can be used to constitute the resin film include polyamides (PA) such as polyester, polyolefin, nylon 6, nylon 66, and partially aromatic polyamides, polyimides (PI), polyamide-imides (PAI), polyetheretherketones (PEEK), polyethersulfones (PES), polyphenylene sulfide (PPS), polycarbonate (PC), polyurethane (PU), fluororesins such as ethylene-vinyl acetate copolymer (EVA) and polytetrafluoroethylene (PTFE), acrylic resins, polyacrylates, polystyrene, polyvinyl chloride, and polyvinylidene chloride.

[0159] The above-mentioned resin film may be formed using a resin material containing one of these resins alone, or it may be formed using a resin material blended with two or more of these resins. The above-mentioned resin film may be unoriented or oriented (e.g., uniaxially oriented or biaxially oriented). For example, PET film, PBT film, PEN film, unoriented polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, PP / PE blend film, etc., can be preferably used. Examples of resin films preferred from the viewpoint of strength and dimensional stability include PET film, PEN film, PPS film, and PEEK film. PET film and PPS film are particularly preferred from the viewpoint of availability, and PET film is preferred among them.

[0160] The resin film may contain known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, and antiblocking agents, as needed, within a range that does not significantly impair the effects of the present invention. The amount of additives to be added is not particularly limited and can be appropriately set depending on the application of the adhesive sheet, etc.

[0161] The method for manufacturing the resin film is not particularly limited. For example, conventionally known general resin film molding methods such as extrusion molding, inflation molding, T-die casting, and calender roll molding can be used as appropriate.

[0162] The above-mentioned substrate may be substantially composed of such a base film. Alternatively, the substrate may include auxiliary layers in addition to the base film. Examples of such auxiliary layers include optical property adjustment layers (e.g., coloring layers, anti-reflective layers), printing layers or lamination layers for imparting a desired appearance to the substrate, antistatic layers, undercoating layers, release layers, and other surface treatment layers.

[0163] In some embodiments, a light-transmitting substrate (hereinafter also referred to as a light-transmitting substrate) may be preferably used as the support substrate. This makes it possible to construct an adhesive sheet with a light-transmitting substrate. The total light transmittance of the light-transmitting substrate may be, for example, more than 50%, and may be 70% or more. In some preferred embodiments, the total light transmittance of the support substrate may be 80% or more, more preferably 90% or more, and may be 95% or more (for example, 95-100%). The above total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the product name "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory or an equivalent product may be used. A preferred example of the above light-transmitting substrate is a light-transmitting resin film. The above light-transmitting substrate may also be an optical film.

[0164] The thickness of the base material is not particularly limited and can be selected according to the purpose and manner of use of the adhesive sheet. The thickness of the base material may be, for example, 500 μm or less, preferably 300 μm or less from the viewpoint of handling and processability of the adhesive sheet, and may also be 150 μm or less, 100 μm or less, 50 μm or less, 25 μm or less, or 10 μm or less. As the thickness of the base material decreases, the ability to conform to the surface shape of the adherend tends to improve. Also, from the viewpoint of handling and processability, the thickness of the base material may be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

[0165] The surface of the substrate on which the adhesive layer is laminated may be subjected to conventionally known surface treatments as needed, such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or formation of an undercoat layer by applying an undercoat agent (primer). Such surface treatments may be performed to improve the anchoring ability of the 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 ones. The thickness of the undercoat layer is not particularly limited, but is usually appropriate at about 0.01 μm to 1 μm, and preferably at about 0.1 μm to 1 μm. Other treatments that may be applied to the substrate as needed include antistatic layer formation treatment, coloring layer formation treatment, and printing treatment. These treatments can be applied individually or in combination.

[0166] If the adhesive sheet disclosed herein is in the form of an adhesive sheet with a substrate, the thickness of the adhesive sheet may be, for example, 1000 μm or less, 350 μm or less, 200 μm or less, 120 μm or less, 75 μm or less, or 50 μm or less. Furthermore, from the viewpoint of handling and other factors, the thickness of the adhesive sheet may be, for example, 10 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more. Note that the thickness of the adhesive sheet refers to the thickness of the portion that is attached to the substrate. For example, in the adhesive sheet 3 with the configuration shown in Figure 3, it refers to the thickness from the first adhesive surface 21A to the second adhesive surface 22A, and does not include the thickness of the release liners 31 and 32.

[0167] <Adhesive sheet with release liner> The adhesive sheets disclosed herein may take the form of an adhesive product in which the surface (adhesive surface) of the adhesive layer is in contact with the release surface of a release liner. Accordingly, this specification provides an adhesive sheet with a release liner (adhesive product) comprising any of the adhesive sheets disclosed herein and a release liner having a release surface that contacts the adhesive surface of the adhesive sheet.

[0168] The release liner is not particularly limited, and for example, 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), or a release liner made of a resin film formed from a low-adhesion material such as a fluoropolymer (such as polytetrafluoroethylene) or a polyolefin resin (such as polyethylene or polypropylene) can be used. Due to their excellent surface smoothness, release liners having a release layer on the surface of a resin film as a liner substrate, or release liners made of a resin film formed from a low-adhesion material, can be preferably used. The resin film is not particularly limited as long as it is a film that can protect the adhesive layer, and examples include polyethylene (PE) film, polypropylene (PP) film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyester film (PET film, PBT film, etc.), polyurethane film, and ethylene-vinyl acetate copolymer film. For the formation of the above-mentioned peeling layer, known peeling agents such as silicone-based peeling agents, long-chain alkyl-based peeling agents, olefin-based peeling agents, fluorine-based peeling agents, fatty acid amide-based peeling agents, molybdenum sulfide, and silica powder can be used.

[0169] <Application> The materials to which the adhesive sheets disclosed herein are attached (adhered materials) are not particularly limited, but examples include metallic materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, zinc, etc., or alloys containing two or more of these; various resin materials such as 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, cellulosic polymers such as diacetylcellulose and triacetylcellulose, vinyl butyral polymers, liquid crystal polymers, etc. (typically plastic materials); and inorganic materials such as alumina, zirconia, alkali glass, alkali-free glass, quartz glass, and carbon. The adhesive sheets disclosed herein can be used by attaching them to members (e.g., optical members) made of the above materials.

[0170] The components or materials to which the adhesive sheets disclosed herein are to be attached (in the case of double-sided adhesive sheets, at least one of the adherends) may be made of materials with a higher refractive index than general acrylic adhesives. The refractive index of the adherend material is, for example, 1.50 or higher, and some adherend materials have a refractive index of 1.55 or higher or 1.58 or higher, and some even have a refractive index of 1.62 or higher (for example, around 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 adhesive sheets disclosed herein (suppression of light reflection due to refractive index difference) can be preferably exhibited on such materials. The upper limit of the refractive index of the above adherend material may be, for example, 1.80 or less, and possibly 1.70 or less. The adhesive sheets disclosed herein can preferably be used in a manner in which they are attached to adherends (e.g., components) with such high refractive index. 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 adhesive.

[0171] The component or material to which the adhesive sheet is to be attached (in the case of a double-sided adhesive sheet, at least one of the adherends) may be light-transmitting. With such adherends, the advantages of the technology disclosed herein (suppression of light reflection at the interface between the adherend and the adhesive sheet) are easily obtained. The total light transmittance of the adherend may be greater than, for example, 50%, preferably 70% or more. In some preferred embodiments, the total light transmittance of the adherend may be 80% or more, more preferably 90% or more, and 95% or more (e.g., 95-100%). The adhesive sheet disclosed herein may be preferably used in a manner in which it is attached to an adherend (e.g., an optical component) with a total light transmittance of a predetermined value or higher. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory or an equivalent product may be used.

[0172] In some preferred embodiments, the adherend (e.g., a component) to which the adhesive sheet is attached may have the above-mentioned refractive index and total light transmittance. Specifically, the adhesive sheet disclosed herein can be preferably used when attached to an adherend, such as a component, having a refractive index of 1.50 or higher (e.g., 1.55 or higher, 1.58 or higher, 1.62 or higher, around 1.66, etc.) and a total light transmittance greater than 50% (e.g., 70% or higher, preferably 80% or higher, more preferably 90% or higher, and even more preferably 95% or higher). The effects of the technology disclosed herein are particularly favorably exhibited when attached to such a component.

[0173] One example of a preferred application is an optical application. More specifically, the adhesive sheet disclosed herein can be preferably used as an optical adhesive sheet for applications such as bonding optical components together (for bonding optical components) or for manufacturing products using the optical components (optical products).

[0174] The above-mentioned optical components refer to components that have optical properties (for example, polarization, refractiveness, scattering, reflectivity, transmission, absorption, diffraction, optical rotation, visibility, etc.). The above-mentioned optical components are not particularly limited as long as they have optical properties, but examples include components that make up devices (optical devices) such as display devices (image display devices) and input devices, or components used in such devices. Examples include polarizers, waveplates, phase difference plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, anti-reflective films, hard coat (HC) films, shock-absorbing films, anti-fouling films, photochromic films, dimming films, transparent conductive films (ITO films), decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and even components in which these are laminated (these are sometimes collectively referred to as "functional films"). Furthermore, the terms "plate" and "film" above include forms such as plate-like, film-like, and sheet-like shapes, respectively. For example, "polarizing film" includes "polarizing plates" and "polarizing sheets," and "light guide plate" includes "light guide film" and "light guide sheet." In addition, the term "polarizing plate" above includes circular polarizing plates.

[0175] Examples of the above-mentioned display devices include liquid crystal displays, organic electroluminescent (EL) displays, micro-LEDs (μLEDs), mini-LEDs (miniLEDs), PDPs (plasma display panels), and electronic paper. Examples of the above-mentioned input devices include touch panels.

[0176] The optical components mentioned above are not particularly limited, but examples include components made of glass, acrylic resin, polycarbonate, polyethylene terephthalate, metal thin films, etc. (for example, sheet-like, film-like, or plate-like components). In this specification, "optical components" also include components that serve a decorative or protective role while maintaining the visibility of display devices and input devices (such as design films, decorative films, and surface protection films).

[0177] The technology disclosed herein can be preferably used, for example, to bond optical films such as films or fluorescent films having one or more functions such as light transmission, reflection, diffusion, guidance, focusing, and diffraction to other optical components (which may be other optical films). In particular, in bonding optical films having at least one function of light guidance, focusing, and diffraction, it is desirable that the entire bulk of the bonding layer has a high refractive index, and this may be a preferred application of the technology disclosed herein.

[0178] The adhesives disclosed herein can be preferably used for bonding optical films such as light guide films, diffusion films, fluorescent films, color-tuning films, prism sheets, lenticular films, and microlens array films. In these applications, there is a demand for thinner films and improved light extraction efficiency from the viewpoint of miniaturization and performance enhancement of optical components. The adhesives disclosed herein can be preferably used as adhesives that can meet these demands. More specifically, for example, in bonding light guide films and diffusion films, thinning can be contributed to by adjusting the refractive index of the adhesive layer as a bonding layer (e.g., increasing the refractive index). In bonding fluorescent films, the light extraction efficiency (which can also be understood as luminous efficiency) can be improved by appropriately adjusting the refractive index difference between the fluorescent emitter and the adhesive. In bonding color-tuning films, the scattering component can be reduced and light transmittance can be improved by appropriately adjusting the refractive index of the adhesive so that the refractive index difference with the color-tuning pigment is small. In bonding prism sheets, lenticular films, microlens array films, etc., the diffraction of light can be controlled and the viewing angle can be improved by appropriately adjusting the refractive index of the adhesive.

[0179] The adhesive sheet disclosed herein is preferably used in a manner in which it is attached to a high refractive index adherend (which may be a high refractive index layer or component, etc.) to suppress interfacial reflection with the adherend. In such a manner, the adhesive sheet is preferably used in a manner in which the refractive index difference with the adherend is small and the adhesion at the interface with the adherend is high, as described above. Furthermore, from the viewpoint of improving the uniformity of the appearance, it is preferable that the thickness of the adhesive layer is highly uniform, for example, that the surface smoothness of the adhesive surface is high. When the thickness of the high refractive index adherend is relatively small (for example, when it is 5 μm or less, 4 μm or less, or 2 μm or less), suppressing reflection at the interface is particularly significant from the viewpoint of suppressing discoloration and color unevenness due to interference of reflected light. An example of such a usage is the use in a polarizing plate with a phase difference layer, which has a polarizer, a first phase difference layer, and a second phase difference layer in that order, for bonding the polarizer and the first phase difference layer and / or the first phase difference layer and the second phase difference layer.

[0180] Furthermore, since the adhesive sheet disclosed herein is suitable for increasing the refractive index, it can preferably be used in a manner in which it is attached to an emissive layer such as an optical semiconductor (for example, a high-refractive-index emissive layer mainly composed of inorganic materials). By reducing the refractive index difference between the emissive layer and the adhesive layer, reflection at their interface can be suppressed and the light extraction efficiency can be improved. The adhesive sheet used in such a manner preferably comprises an adhesive layer with a high refractive index. Also, from the viewpoint of preventing deterioration of the self-luminous element due to moisture, it is preferable that the water absorption rate of the adhesive layer is low, for example, approximately 1.0% or less is appropriate, 0.7% or less is preferable, 0.5% or less (for example, less than 0.5%) is more preferable, 0.4% or less is also acceptable, 0.3% or less is also acceptable, 0.2% or less is also acceptable, and 0.1% or less is also acceptable. The lower limit of the water absorption rate of the adhesive layer is not particularly limited, but from a practical standpoint, such as maintaining compatibility with adhesive properties, it may be, for example, 0.01% or more, 0.05% or more, 0.1% or more, or 0.15% or more. 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.

[0181] In this specification, "self-luminous element" means a light-emitting element whose luminescence can be controlled by the value of the current flowing through it. A self-luminous element may consist of a single element or an assembly of elements. Specific examples of self-luminous elements include, but are not limited to, light-emitting diodes (LEDs) and organic ELs. In this specification, "light-emitting device" means a device that includes such self-luminous elements as components. Examples of the above-mentioned light-emitting device include, but are not limited to, light source module devices used for illumination (e.g., planar light-emitting module) and display devices with pixels.

[0182] Furthermore, the water absorption rate (also called moisture content) of the adhesive layer is measured by the following method. [Measurement of moisture content] The adhesive layer to be evaluated was placed on one side and the other side of the layer together with two release liners, measuring 4cm x 5cm (area: 20cm²). 2 Cut the material to the specified size, remove the release liner from one side, and bond it to the pre-weighed aluminum foil. Next, remove the release liner from the other side of the adhesive layer, place it in a constant temperature and humidity chamber at 60°C and 90% relative humidity, and remove it after 72 hours. After weighing the test piece with the adhesive layer and aluminum foil laminated, measure the moisture content using a moisture meter (Mitsubishi Chemical Analytec CA-200) equipped with a heating vaporizer (Mitsubishi Chemical Analytec VA-200) by Karl Fischer coulometric titration under the following conditions. Anode liquid: Aquamicron AKX (manufactured by Mitsubishi Chemical) Cathodelibrium: Aquamicron CXU (manufactured by Mitsubishi Chemical) Heating vaporization temperature: 150℃

[0183] The adhesive disclosed herein can be preferably used in microlenses and other lens components (for example, microlenses constituting a microlens array film, or lens components such as camera microlenses) used as components of cameras, light-emitting devices, etc., as a coating layer covering the lens surface, a bonding layer with a component facing the lens surface (for example, a component having a surface shape corresponding to the lens surface), or a filling layer filled between the lens surface and the component. Since the adhesive disclosed herein is suitable for increasing the refractive index, it can reduce the refractive index difference with high refractive index lenses (for example, lenses composed of high refractive index resin or lenses having a surface layer made of high refractive index resin). This is advantageous from the viewpoint of thinning the lenses and products equipped with the lenses, and can also contribute to suppressing aberrations and improving the Abbe number. The adhesive disclosed herein can also be used as a lens resin itself, for example, in the form of being filled into a recess or void of a suitable transparent component.

[0184] The manner in which optical members are bonded using the adhesive sheet disclosed herein is not particularly limited, but may include, for example, (1) bonding optical members to each other via the adhesive sheet disclosed herein, (2) bonding an optical member to a member other than an optical member via the adhesive sheet disclosed herein, or (3) a form in which the adhesive sheet disclosed herein includes an optical member and the adhesive sheet is bonded to an optical member or a member other than an optical member. In the embodiment of (3) above, the adhesive sheet that includes an optical member may be, for example, an adhesive sheet whose support is an optical member (e.g., an optical film). Such an adhesive sheet that includes an optical member as a support can also be understood as an adhesive-type optical member (e.g., an adhesive-type optical film). Furthermore, if the adhesive sheet disclosed herein is an adhesive sheet having a support, and the functional film is used as the support, the adhesive sheet disclosed herein can also be understood as an "adhesive-type functional film" having the adhesive layer disclosed herein on at least one side of the functional film.

[0185] Based on the above, the technology disclosed herein provides a laminate comprising an 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 between the refractive index of the adhesive sheet and the refractive index of the member (refractive index difference) may be the refractive index difference between the adherend and the adhesive sheet described above. The members constituting the laminate are as described above as members, materials, and adherends, so we will not repeat any redundant explanations.

[0186] As can be understood from the above description and the following examples, the matters disclosed in this specification include the following: [1] An adhesive composition for forming an adhesive containing an acrylic polymer, The monomer components constituting the above acrylic polymer include an aromatic ring-containing monomer (A1) and a monomer (A2) having at least one of a hydroxyl group and a carboxyl group. An adhesive composition in which, in the above monomer components, the content of the above aromatic ring-containing monomer (A1) is 75% by weight or more and 99% by weight or less, and the content of the above monomer (A2) having at least one of a hydroxyl group and a carboxyl group is 1% by weight or more and 25% by weight or less. [2] The adhesive composition according to [1] above, wherein 50% by weight or more of the aromatic ring-containing monomer (A1) is a monomer whose homopolymer glass transition temperature is 10°C or lower. [3] An adhesive composition for forming an adhesive containing an acrylic polymer, The monomer components constituting the above acrylic polymer include aromatic ring-containing monomer (A1), In the above monomer component, the content of the above aromatic ring-containing monomer (A1) is greater than 70% by weight and less than 100% by weight. An adhesive composition wherein 50% by weight or more of the above aromatic ring-containing monomer (A1) is an aromatic ring-containing monomer whose homopolymer glass transition temperature is 10°C or lower (preferably 5°C or lower). [4] The adhesive composition according to [3] above, wherein the monomer component further contains a monomer (A2) having at least one of a hydroxyl group and a carboxyl group. [5] The adhesive composition according to [4] above, wherein the monomer component contains at least one of the monomer (A2) having a hydroxyl group and a carboxyl group, and the content is 1% by weight or more and less than 30% by weight. [6] The adhesive composition according to any one of [1] to [5] above, wherein the aromatic ring-containing monomer (A1) comprises a monomer having two or more aromatic rings in one molecule. [7] The adhesive composition according to [6] above, wherein the monomer having two or more aromatic rings in one molecule includes a monomer having a structural portion in which two aromatic rings are linked via a linking group. [8] The adhesive composition according to any one of [1] to [7] above, further comprising a crosslinking agent. [9] The adhesive composition according to any one of [1] to [8] above, further comprising high refractive index particles.

[10] An adhesive formed from any of the adhesive compositions described in [1] to [9] above.

[0187]

[11] An adhesive containing an acrylic polymer, The monomer components constituting the above acrylic polymer include aromatic ring-containing monomer (A1), In the above monomer component, the content of the above aromatic ring-containing monomer (A1) is greater than 70% by weight and less than 100% by weight. The following conditions: (a) The storage modulus G'(25) at 25°C is less than 200 kPa; and (b) The storage modulus G'(50) at 50°C is less than 40 kPa; An adhesive that satisfies at least one of the following conditions.

[12] An adhesive containing an acrylic polymer, The monomer components constituting the above acrylic polymer include aromatic ring-containing monomer (A1), In the above monomer component, the content of the above aromatic ring-containing monomer (A1) is greater than 70% by weight and less than 100% by weight. An adhesive wherein 50% by weight or more of the above aromatic ring-containing monomer (A1) is an aromatic ring-containing monomer whose homopolymer glass transition temperature is 10°C or lower (preferably 5°C or lower).

[13] The adhesive according to

[11] or

[12] , wherein the monomer component further contains a monomer (A2) having at least one of a hydroxyl group and a carboxyl group.

[14] The adhesive according to

[13] , wherein the monomer component contains at least one of the monomer (A2) having a hydroxyl group and a carboxyl group, and the content is 1% by weight or more and less than 30% by weight.

[15] An adhesive containing an acrylic polymer, The monomer components constituting the above acrylic polymer include an aromatic ring-containing monomer (A1) and a monomer (A2) having at least one of a hydroxyl group and a carboxyl group. An adhesive comprising the above monomer components, wherein the content of the above aromatic ring-containing monomer (A1) is 75% by weight or more and 99% by weight or less, and the content of the above monomer (A2) having at least one of a hydroxyl group and a carboxyl group is 1% by weight or more and 25% by weight or less.

[16] The adhesive according to any one of

[11] and

[13] to

[15] above, wherein 50% by weight or more of the aromatic ring-containing monomer (A1) is a monomer whose homopolymer glass transition temperature is 10°C or lower.

[17] The adhesive according to any one of

[11] to

[16] above, wherein the aromatic ring-containing monomer (A1) comprises a monomer having two or more aromatic rings in one molecule.

[18] The adhesive according to

[17] , wherein the monomer having two or more aromatic rings in one molecule includes a monomer having a structural portion in which two aromatic rings are linked via a linking group.

[19] An adhesive described in any of

[11] to

[18] above, having a refractive index higher than 1.570.

[20] The following conditions: (a) The storage modulus G'(25) at 25°C is less than 200 kPa; and (b) The storage modulus G'(50) at 50°C is less than 40 kPa; An adhesive according to any one of the above

[12] to

[19] , which satisfies at least one of the conditions.

[21] The adhesive according to any of

[11] to

[20] above, further comprising high refractive index particles.

[22] An adhesive composition used in the preparation of any of the adhesives described in

[11] to

[21] above.

[0188]

[23] An adhesive sheet comprising an adhesive layer composed of any of the adhesives described in

[11] to

[21] above.

[24] The adhesive sheet described in

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

[25] An optical member with an adhesive sheet, comprising the adhesive sheet described in

[23] or

[24] above and an optical member bonded to one surface of the adhesive sheet. [Examples]

[0189] The following describes several embodiments relating to the present invention, but the present invention is not intended to be limited to those examples shown. In the following description, "parts" and "%" used to express the amount used or content refer to weight unless otherwise specified.

[0190] ≪Experimental Example 1≫ <Example 1> (Preparation of acrylic polymer solutions) A four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser was charged with 99.0 parts of m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A", refractive index: 1.566, homopolymer Tg: -35°C; hereinafter referred to as "A1-a"), 1.0 part of 4-hydroxybutyl acrylate (4HBA) as monomer components, 0.2 parts of 2,2'-azobisisobutyronitrile as polymerization initiator, and 150 parts of ethyl acetate as polymerization solvent. Nitrogen gas was introduced while gently stirring, and the polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at around 60°C to prepare a 40% solution of acrylic polymer P1. The above acrylic polymer P1 has a Tg (i.e., Tg) based on the composition of the above monomer components.T ) is -35℃, and Tg (i.e., Tg) is based on the composition of aromatic ring-containing monomers. A1 The temperature is -35°C.

[0191] (Preparation of adhesive composition) A 40% solution of the above acrylic polymer P1 was diluted to 20% with ethyl acetate. 500 parts of this solution (100 parts non-volatile content) were mixed with 10 parts (0.1 parts non-volatile content) of a 1% ethyl acetate solution of hexamethylene diisocyanate isocyanurate (manufactured by Tosoh Corporation, trade name "Coronate HX", trifunctional isocyanate compound) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking retarder, and 1 part (0.01 parts non-volatile content) of a 1% ethyl acetate solution of ferric narcem as a crosslinking catalyst. The mixture was stirred and mixed to prepare acrylic adhesive composition C1.

[0192] (Making adhesive sheets) The acrylic adhesive composition C1 prepared above was applied to the silicone-treated side of a polyethylene terephthalate (PET) film R1 (thickness 50 μm) with one side silicone-treated, and heated at 130°C for 2 minutes to form an adhesive layer with a thickness of 20 μm. Next, the silicone-treated side of a PET film R2 (thickness 25 μm) with one side silicone-treated was bonded to the surface of the adhesive layer. In this way, a substrate-less double-sided adhesive sheet S1 consisting of the above adhesive layer was obtained. Both sides of the adhesive sheet S1 are protected by PET films (release liners) R1 and R2.

[0193] <Examples 2-12> Solutions of acrylic polymers P2 to P12 according to Examples 2 to 12 were prepared in the same manner as the preparation of the acrylic polymer solution in Example 1, except that the composition of the monomer components was changed as shown in Table 1. The Mw of acrylic polymer P3 was 400,000. Acrylic adhesive compositions C2 to C12 according to Examples 2 to 12 were prepared in the same manner as the preparation of the adhesive composition in Example 1, except that solutions of acrylic polymers P2 to P12 were used instead of the solution of acrylic polymer P1. Adhesive sheets (substrate-less double-sided adhesive sheets consisting of an adhesive layer) S2 to S12 according to Examples 2 to 12 were prepared in the same manner as the adhesive sheet preparation in Example 1, except that acrylic adhesive compositions C2 to C12 were used instead of acrylic adhesive composition C1.

[0194] <Example 13> Except for changing the solvent from ethyl acetate to methyl ethyl ketone (MEK), a solution of acrylic polymer P13 (the monomer raw material composition was the same as in Example 3, A1-a / 4HBA = 95.0 / 5.0) and an acrylic adhesive composition C13 were prepared in the same manner as in Example 3, and an adhesive sheet (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) was fabricated. The Mw of acrylic polymer P13 was 480,000.

[0195] In the monomer component composition shown in Table 1, "A1-b" represents 1-naphthylmethyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate NMT-A", refractive index: 1.595, homopolymer Tg: 31℃), HEA represents 2-hydroxyethyl acrylate, BA represents n-butyl acrylate, and 2EHA represents 2-ethylhexyl acrylate.

[0196] <Measuring refractive index> For each example, the refractive index of the adhesive layer (substrate-less double-sided adhesive sheet) was measured using an Abbe refractometer (ATAGO, model "DR-M4") under the conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C.

[0197] <Haze value measurement> Test specimens were prepared by laminating the adhesive layer for each example onto alkali-free glass (thickness 0.8-1.0 mm, total light transmittance 92%, haze 0.4%), and the haze was measured using a haze meter (Murakami Color Technology Laboratory "HM-150"). The haze of the adhesive layer was determined by subtracting the haze of the alkali-free glass (0.4%) from the measured value.

[0198] <Measurement of Storage Modulus G'> For each example, a sample was prepared by laminating adhesive layers to a thickness of approximately 1.5 mm. Dynamic viscoelasticity measurements were performed using the Advanced Rheometric Expansion System (ARES) manufactured by Rheometric Scientific under the following conditions. From the measurement results, the storage modulus G' at 25°C and 50°C was read. [Measurement conditions] Transformation mode: Twist Measurement frequency: 1Hz Heating rate: 5°C / min Shape: Parallel plate 7.9mmφ

[0199] The results obtained are shown in Table 1.

[0200] [Table 1]

[0201] As shown in Table 1, the adhesive layers of Examples 1-9 and Examples 12 and 13, which have a high content of monomer (A1) in the monomer components constituting the acrylic polymer, showed a significantly higher refractive index compared to Examples 10 and 11. In a comparison between Example 3 and Example 13, which use different polymerization solvents, the optical properties were equivalent, but the storage modulus tended to be slightly lower in Example 13. In addition, the Tg measured by differential scanning calorimeter (DSC) was slightly lower in Example 13 than in Example 3.

[0202] <Measurement of peel strength> For some of the adhesive sheets prepared above, the peel strength against a glass plate was further measured. That is, in a measurement environment of 23°C and 50% RH, the release liner was peeled off from one side of the adhesive sheet, a PET film with a thickness of 50 μm was laminated and lined, and then cut into a size of 25 mm in width and 100 mm in length to be used as a test piece. The release liner on the other side was peeled off from the test piece, and a 2 kg roller was reciprocated once and pressure-bonded to the surface of an alkali glass plate (manufactured by Matsunami Glass Industry Co., Ltd., thickness 1.35 mm, blue plate edge polished product) as an adherend. After leaving this in the same environment for 30 minutes, using a universal tensile-compression testing machine, in accordance with JIS Z 0237:2000, the peel strength (adhesive force) [N / 25 mm] was measured under the conditions of a tensile speed of 300 mm / min and a peel angle of 180 degrees. As the universal tensile-compression testing machine, "Tensile-Compression Testing Machine, TG-1kN" manufactured by Minebea was used.

[0203]

Table 2

[0204] As can be seen from the comparison of Examples 3 to 5 shown in Table 2 (the content of monomer (A1) in the monomer component is 95% in all cases), by combining and using monomer A1-a with a relatively low Tg of the homopolymer and monomer A1-b with a relatively high Tg of the homopolymer, it was possible to realize a higher refractive index while suppressing an increase in the storage elastic modulus G'.

[0205] ≪Experimental Example 2≫ <Example 14> An adhesive composition C14 according to this example was prepared in the same manner as the preparation of the adhesive composition in Example 13, except that 0.5 part of diethylene glycol dibenzoate (additive) was further added to 100 parts of the acrylic polymer contained in the solution of the acrylic polymer. An adhesive sheet (a substrate-less double-sided adhesive sheet composed of an adhesive layer) S14 according to this example was prepared in the same manner as the preparation of the adhesive sheet in Example 13, except that the adhesive composition C14 was used instead of the adhesive composition C13.

[0206] <Examples 15-33> Adhesive compositions C15 to C33 for Examples 15 to 33 were prepared in the same manner as the preparation of the adhesive composition in Example 14, except that the type of additive and the amount used per 100 parts of acrylic polymer (phr; per hundred resin) were changed as shown in Table 3. Adhesive sheets (substrate-less double-sided adhesive sheets consisting of an adhesive layer) S15 to S33 for Examples 15 to 33 were prepared in the same manner as the preparation of the adhesive sheet in Example 14, except that adhesive compositions C15 to C33 were used instead of adhesive composition C14.

[0207] Here, the leveling agent used as an additive in Example 33 is polymer (B) synthesized as follows: 101.15 parts of ethyl acetate, 40 parts of methyl methacrylate (MMA), 20 parts of n-butyl methacrylate (BMA), 20 parts of 2-ethylhexyl methacrylate (2EHMA), 8.7 parts of polyorganosiloxane skeleton-containing methacrylate monomer with a functional group equivalent of 900 g / mol (trade name: X-22-174ASX, manufactured by Shin-Etsu Chemical Co., Ltd.), 11.3 parts of polyorganosiloxane skeleton-containing methacrylate monomer with a functional group equivalent of 4600 g / mol (trade name: KF-2012, manufactured by Shin-Etsu Chemical Co., Ltd.), and 0.8 parts of thioglycerol as a chain transfer agent were placed in a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, condenser, and dropping funnel. Then, after stirring at 70°C under a nitrogen atmosphere for 30 minutes, 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) was added as a thermal polymerization initiator, and the mixture was reacted at 70°C for 3 hours. Subsequently, after stirring at 80°C for 30 minutes, an additional 0.1 parts of AIBN was added, and the mixture was reacted at 80°C for 2 hours. After that, an additional 0.05 parts of AIBN was added, and the mixture was reacted at 80°C for 2 hours to obtain polymer (B). The Mw of the obtained polymer (B) was 20000.

[0208] For each example, the adhesive sheets obtained were measured for refractive index, peel strength, and storage modulus G' in the same manner as in Experimental Example 1. The results, along with the refractive index of each additive, are shown in Table 3.

[0209] [Table 3]

[0210] As shown in Table 3, the additives used in Examples 14 to 32 were all confirmed to function effectively as plasticizing materials that at least reduce the storage modulus G'(25). Diethylene glycol dibenzoate and triphenyl phosphate showed particularly high plasticizing effects. Furthermore, in visual observation when coating the adhesive composition onto the release liner R1, Example 33, which had a leveling agent added, tended to suppress the occurrence of repellency and unevenness compared to Example 13, indicating that the leveling agent had the effect of improving the homogeneity of the adhesive layer. When adhesive sheets were prepared in the same manner as in Examples 15 to 17, except that the solvent was changed from MEK to ethyl acetate, and evaluated in the same way, the adhesive sheets in Examples 15 to 17, which used MEK as the solvent, had equivalent optical properties and peel strength compared to the corresponding adhesive sheets using ethyl acetate as the solvent, but tended to have a slightly lower storage modulus.

[0211] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. [Explanation of symbols]

[0212] 1, 2, 3 Adhesive sheets 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. An adhesive composition for forming an adhesive containing an acrylic polymer, The monomer components constituting the acrylic polymer include an aromatic ring-containing monomer (A1), a hydroxyalkyl acrylate, and an alkyl acrylate having a linear or branched alkyl group with 1 to 20 carbon atoms at its ester terminus. The aromatic ring-containing monomer (A1) includes a plurality of aromatic ring-containing monomers having a structural portion in which two aromatic rings are linked via linking groups. An adhesive composition wherein, in the monomer component, the content of the aromatic ring-containing monomer (A1) is 75% by weight or more and 98% by weight or less, the content of the hydroxyalkyl acrylate is 1% by weight or more and 20% by weight or less, and the content of the alkyl acrylate is 1% by weight or more and 24% by weight or less.

2. The adhesive composition according to claim 1, wherein 50% by weight or more of the aromatic ring-containing monomer (A1) is a monomer whose homopolymer glass transition temperature is 10°C or lower.

3. The hydroxyalkyl acrylate is at least one selected from the group consisting of 4-hydroxybutyl acrylate and 2-hydroxyethyl acrylate, and the adhesive composition according to claim 1 or 2.

4. The adhesive composition according to any one of claims 1 to 3, further comprising a crosslinking agent.

5. An adhesive formed from the adhesive composition according to any one of claims 1 to 4.

6. The adhesive according to claim 5, wherein the refractive index is higher than 1.

570.

7. The adhesive layer formed from the aforementioned adhesive is subject to the following conditions: (a) The storage modulus G'(25) at 25°C is less than 200 kPa; and (b) The storage modulus G'(50) at 50°C is less than 40 kPa; The adhesive according to claim 5 or 6, which satisfies at least one of the conditions.

8. An adhesive sheet comprising an adhesive layer composed of the adhesive described in any one of claims 5 to 7.

9. The adhesive sheet according to claim 8, wherein the haze value of the adhesive layer is 1.0% or less.

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