Adhesive composition and adhesive sheet

Abstract

The present invention provides an adhesive composition capable of forming an adhesive that achieves both a high refractive index and a low modulus of elasticity. [Solution] An adhesive composition is provided comprising an acrylic polymer and a plasticizer. The monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1). The plasticizer is a compound that is liquid at 30°C and has two or more double-bond-containing rings.

Description

[Technical Field]

[0001] This invention relates to an adhesive composition and an adhesive sheet. [Background technology]

[0002] Generally, adhesives (also called pressure-sensitive adhesives; the same applies hereinafter) exhibit a soft solid (viscoelastic) state at temperatures around room temperature and have the property of easily adhering to a substrate under pressure. Taking advantage of this property, adhesives are widely used in various industrial fields, from home appliances to automobiles, various machinery, electrical equipment, and electronic devices, for purposes such as joining, fixing, and protection. One example of an application of adhesives is in display devices such as liquid crystal displays and organic EL displays, where polarizing films, phase difference films, cover window members, and various other light-transmitting members are joined to other members. Patent documents 1 and 2 are cited as technical documents relating to adhesives for optical components. [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 project] [Problems that the invention aims to solve]

[0004] Patent documents 1 and 2 disclose an adhesive composition mainly composed of a (meth)acrylic acid ester polymer containing a monomer having multiple aromatic rings as a monomer unit, and an adhesive obtained by crosslinking the adhesive composition. They propose that by using a monomer having multiple aromatic rings, the refractive index of the adhesive can be set to 1.50 or higher, particularly preferably 1.51 or higher. For example, among materials to which adhesives are attached, such as optical components, there are materials with high refractive indices, and it is known that when a general acrylic adhesive is used to bond such high refractive index materials, reflection occurs at the interface due to the difference in refractive indices between the two. By using an adhesive with a high refractive index for bonding the above-mentioned high refractive index materials, the above-mentioned interface reflection can be prevented or suppressed. The refractive index of acrylic adhesives is usually around 1.47.

[0005] Incidentally, adhesives with good flexibility are preferably used depending on the application site and mode of use. For example, in recent years, foldable displays and rollable displays have been put into practical use as displays such as organic EL displays used in electronic devices such as smartphones, and adhesives used in the above applications also need to have the flexibility to follow the substrate that is repeatedly bent. Adhesives with excellent flexibility can easily follow and adhere to curved surfaces such as three-dimensional shapes, and are suitable for electronic devices with curved shapes. Adhesives with high refractive index can also be applied to the above-mentioned applications requiring flexibility if their flexibility can be increased, and are useful. However, high refractive index materials used as monomer components of adhesive polymers or additives for adhesives tend to have high glass transition temperatures, such as having aromatic rings, and adhesives formed using high refractive index materials tend to have high elastic modulus. In adhesive design, there is a trade-off relationship between high refractive index and low elastic modulus, and it would be practically beneficial if an adhesive that can achieve both could be realized.

[0006] The present invention was created in view of the above circumstances, and aims to provide an adhesive composition capable of forming an adhesive that achieves both a high refractive index and a low modulus of elasticity. Another object of the present invention is to provide an adhesive sheet containing an adhesive layer formed from the above adhesive composition. [Means for solving the problem]

[0007] This specification provides an adhesive composition comprising an acrylic polymer and a plasticizer. The monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1). The plasticizer is a compound that is liquid at 30°C and has two or more double-bond-containing rings. Because the monomer component constituting the acrylic polymer of the adhesive composition has an aromatic ring-containing monomer (A1), it is suitable for forming an adhesive with a high refractive index. Furthermore, because the adhesive composition contains a compound that is liquid at 30°C and has two or more double-bond-containing rings as a plasticizer, it is possible to form an adhesive with a high refractive index while having a low modulus of elasticity.

[0008] In some preferred embodiments, the compound is a liquid compound at 20°C. Using a liquid compound at 20°C as a plasticizer facilitates the formation of adhesives with a low modulus of elasticity.

[0009] In some preferred embodiments, the plasticizer is present in amounts exceeding 15 parts by weight per 100 parts by weight of the acrylic polymer. In some embodiments, the plasticizer is present in amounts exceeding 30 parts by weight per 100 parts by weight of the acrylic polymer. With an adhesive composition having the above composition, an adhesive that achieves both a high refractive index and a low modulus of elasticity can be preferably formed.

[0010] In some preferred embodiments, the plasticizer has at least one ring selected from aromatic rings and heterocycles as the double bond-containing ring. By using a compound having the above chemical structure as a plasticizer, it is easy to obtain an adhesive that achieves both a high refractive index and a low modulus of elasticity.

[0011] In some preferred embodiments, the plasticizer has a first double bond-containing ring and a second double bond-containing ring. The first double bond-containing ring and the second double bond-containing ring are linked via a linking group having 1 to 5 atoms. Such a plasticizer, by having a linking group between two or more double bond-containing rings, tends to have a high refractive index while easily reducing the elastic modulus of the adhesive. By using a plasticizer with such a structure, a better balance between a high refractive index and a low elastic modulus can be achieved.

[0012] In some embodiments, the molecular weight of the plasticizer is in the range of 100 to 2000. Plasticizers having a molecular weight within this range are easily compatible with adhesives and readily exhibit a plasticizing effect.

[0013] In some embodiments, the monomer components constituting the acrylic polymer include, in addition to the aromatic ring-containing monomer (A1), a monomer (A2) having at least one of a hydroxyl group and a carboxyl group. By using an acrylic polymer having such a monomer composition, a high refractive index adhesive that achieves both flexibility and good cohesive strength can be preferably obtained.

[0014] In some embodiments, the content of the aromatic ring-containing monomer (A1) in the monomer component is 60% by weight or more. By using an acrylic polymer in which the polymerization ratio of the aromatic ring-containing monomer (A1) is 60% by weight or more, an adhesive with a high refractive index can be easily obtained.

[0015] In some embodiments, 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. This makes it possible to achieve a good balance between a high refractive index and a low modulus of elasticity even when the polymerization ratio of the aromatic ring-containing monomer (A1) is increased.

[0016] 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.

[0017] Furthermore, this specification provides an adhesive sheet comprising an adhesive layer made of any of the adhesives disclosed herein (which may be an adhesive formed from any of the adhesive compositions disclosed herein). Since the adhesives disclosed herein can achieve both a high refractive index and a low modulus of elasticity, the adhesive sheet comprising the adhesive is preferably used for bonding, fixing, and protection in applications where a high refractive index is desirable and flexibility to withstand repeated bending operations is required, such as in foldable display applications.

[0018] 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]

[0019] [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]

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] <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. The techniques disclosed herein can preferably be carried out using solvent-type adhesive compositions. In embodiments comprising a solvent-type adhesive layer formed from a solvent-type adhesive composition, a combination of a high refractive index and a low modulus of elasticity can preferably be achieved.

[0025] 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.

[0026] (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.

[0027] 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).

[0028] 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.

[0029] 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 it may be a heterocycle 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 heterocycle 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 heterocycle may be nitrogen and sulfur, or both. Monomer (A1) may have a structure in which one or more carbon rings and one or more heterocycles are fused, such as a dinaphthothiophene structure.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] In some embodiments, monomers having two or more aromatic rings (preferably carbocyclic rings) in one molecule can be used as monomer (A1) because they easily provide 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 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] In some preferred embodiments, monomer (A1) is used which has one aromatic ring (preferably a carbon ring) in one molecule. Monomers having one aromatic ring in one molecule (monomers containing one aromatic ring) can be useful, for example, for improving the flexibility of adhesives, adjusting adhesive properties, and improving transparency. Monomers containing one aromatic ring can be used alone or in combination of two or more. In some embodiments, monomers having one aromatic ring in one molecule may be used in combination with monomers containing multiple aromatic rings from the viewpoint of improving the refractive index of the adhesive.

[0041] 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.

[0042] 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.

[0043] 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 low modulus of elasticity, and if necessary, adhesive strength, 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. The technology disclosed herein can also be carried out in embodiments in which the content of the multiple aromatic ring-containing monomer in monomer (A1) is less than 5% by weight. The multiple aromatic ring-containing monomer may not be used.

[0044] The content of multiple aromatic ring-containing monomers in the monomer components constituting the acrylic polymer is not particularly limited and can be set to realize an adhesive that achieves both a desired refractive index and elastic modulus. The content of multiple aromatic ring-containing monomers in the above monomer components may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the viewpoint of making it easier to realize an adhesive with a higher refractive index, the content of multiple aromatic ring-containing monomers in the above monomer components may be, for example, more than 35% by weight, more than 50% by weight is advantageous, more than 70% by weight is preferable, more than 75% by weight or more, more than 85% by weight or more, more than 90% by weight or more, more than 91% by weight or more, more than 92% by weight or more, more than 93% by weight or more, more than 94% by weight or more, more than 95% by weight or more, more than 96% by weight or more, more than 97% by weight or more, more than 98% by weight or more, or more than 99% by weight or more. The content of the multiple aromatic ring-containing monomer in the above monomer component is advantageous to be approximately 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, and may also 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. In some embodiments, from the viewpoint of facilitating the realization of higher adhesive properties and / or optical properties (e.g., transparency), the content of the multiple aromatic ring-containing monomer in the above monomer component may be 70% by weight or less, 60% by weight or less, 50% by weight or less, 40% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight or less. The technology disclosed herein can also be implemented in embodiments in which the content of the multiple aromatic ring-containing monomer in the above monomer component is less than 3% by weight.

[0045] The content of aromatic ring singular monomers in monomer (A1) is not particularly limited and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, the content of aromatic ring singular monomers 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 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 aromatic ring singular monomers. That is, only one or more aromatic ring singular monomers may be used as monomer (A1). Furthermore, in some embodiments, taking into consideration the balance between high refractive index and low modulus of elasticity, and if necessary, adhesive strength, the content of the aromatic ring-containing monomer in monomer (A1) may be less than 100% by weight, 98% or less by weight, 90% or less by weight, 80% or less by weight, 70% or less by weight, 65% or less by weight, 50% or less by weight, 25% or less by weight, or 10% or less by weight. The technology disclosed herein can also be carried out in embodiments in which the content of the aromatic ring-containing monomer in monomer (A1) is less than 5% by weight. The aromatic ring-containing monomer may not be used at all.

[0046] The content of aromatic ring-containing monomers in the monomer components constituting the acrylic polymer is not particularly limited and can be set to realize an adhesive that achieves both a desired refractive index and elastic modulus. The content of aromatic ring-containing monomers in the above monomer components may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the viewpoint of making it easier to realize an adhesive with a higher refractive index, the content of aromatic ring-containing monomers in the above monomer components may be, for example, more than 35% by weight, more advantageously more than 50% by weight, preferably 60% by weight or more, more 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, may be 95% by weight or more, or may be 98% by weight or more. The content of aromatic ring-containing monomers in the above monomer component may 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, may be 90% by weight or less, may be 85% by weight or less, may be 80% by weight or less, or may be 75% by weight or less, taking into consideration the balance between high refractive index, low elastic modulus, and, if necessary, adhesive strength. In some embodiments, from the viewpoint of facilitating the realization of higher adhesive properties and / or optical properties (e.g., transparency), the content of aromatic ring-containing monomers in the above monomer component may be 70% by weight or less, may be 60% by weight or less, may be 50% by weight or less, may be 40% by weight or less, may be 25% by weight or less, may be 15% by weight or less, or may be 5% by weight or less. The technology disclosed herein can also be implemented in embodiments in which the content of aromatic ring-containing monomers in the above monomer component is less than 3% by weight.

[0047] 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.

[0048] 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).

[0049] 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) is not particularly limited and may be, for example, 5% by weight or more, 25% by weight or more, 35% by weight or more, or 40% by weight or more. In some embodiments, from the viewpoint of easily obtaining a higher refractive index, the content of high refractive index monomers in monomer (A1) may be, for example, 50% by weight or more, preferably 70% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight or more. Substantially 100% by weight of monomer (A1) may be high refractive index monomers. Furthermore, in some embodiments, from the viewpoint of achieving a good balance between high refractive index and low elastic modulus, and if necessary, adhesive strength, the content of the high refractive index 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, or 65% by weight or less.

[0050] The content of high-refractive-index monomers in the monomer components constituting the acrylic polymer is not particularly limited and can be set to realize an adhesive that achieves both the desired refractive index and elastic modulus. Furthermore, if necessary, it can be set considering compatibility with adhesive properties (e.g., adhesive strength) and / or optical properties (e.g., total light transmittance, haze value, etc.). The content of high-refractive-index monomers in the above monomer components may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, the content of high-refractive-index monomers in the monomer components constituting the acrylic polymer may be, for example, more than 35% by weight, more than 50% by weight is advantageous from the viewpoint of easily obtaining a higher refractive index, more than 70% by weight is preferable, may be 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. 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 also 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, from the viewpoint of achieving a good balance between high refractive index, low modulus of elasticity, and adhesive strength if necessary.

[0051] In some preferred embodiments, an aromatic ring-containing monomer (hereinafter sometimes referred to as "monomer L") having a homopolymer Tg of 10°C or less is used as at least a portion of monomer (A1). Generally, increasing the content of aromatic ring-containing monomer (A1) in the monomer component (especially aromatic ring-containing monomer (A1) that falls under at least one of the above-mentioned multiple aromatic ring-containing monomers, single aromatic ring-containing monomers, and high refractive index monomers) tends to increase the storage modulus G' of the adhesive. By using monomer L as part or all of monomer (A1), the increase in storage modulus G' can be suppressed. This makes it possible to improve the refractive index while better maintaining a low modulus. The Tg of monomer L may be, for example, 5°C or less, 0°C or less, -10°C or less, -20°C or less, or -25°C or less. 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. In some other embodiments, the Tg of monomer L may be, for example, -30°C or higher, -10°C or higher, 0°C or higher, or 3°C or higher. Monomer L can be used alone or in combination of two or more types.

[0052] 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 groups of compounds exemplified above). Preferred examples of aromatic ring-containing monomers that can be used as monomer L include m-phenoxybenzyl acrylate (homopolymer Tg: -35°C), benzyl acrylate (homopolymer Tg: 6°C), phenoxyethyl acrylate (homopolymer Tg: 2°C), and phenoxydiethylene glycol acrylate (homopolymer Tg: -35°C).

[0053] The content of monomer L in monomer (A1) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, from the viewpoint of facilitating obtaining a pressure-sensitive adhesive that achieves both a high refractive index and a low elastic modulus at a higher level, the content of monomer L in monomer (A1) may be, for example, 50% by weight or more; from the viewpoint of lowering the elastic modulus, it is preferably 60% by weight or more, and may be 70% by weight or more, 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of monomer (A1) may be monomer L. Also, in some embodiments, from the viewpoint of achieving a good balance among a high refractive index, a low elastic modulus, and further adhesive force if necessary, 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, or 65% by weight or less.

[0054] The content of monomer L in the monomer components constituting the acrylic polymer may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some embodiments, from the viewpoint of facilitating obtaining a pressure-sensitive adhesive that achieves both a high refractive index and a low elastic modulus at a higher level, the content of monomer L in the monomer components may be, for example, more than 35% by weight; from the viewpoint of improving the refractive index, it is advantageously 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 among a high refractive index, a low elastic modulus, and further adhesive force if necessary, the content of monomer L in the above monomer components is advantageously approximately 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, and may be 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less.

[0055] In some embodiments, the glass transition temperature Tg based on the composition of monomer (A1) A1From the viewpoint of reducing the elastic modulus, it is appropriate for the glass transition temperature (Tg) to be approximately 20°C or lower, preferably 10°C or lower, for example, 5°C or lower, 0°C or lower, -10°C or lower, -20°C or lower, or -25°C or lower. A1 The lower limit is not particularly limited. In some embodiments, considering the balance with the refractive index improvement effect, the glass transition temperature Tg A1 The glass transition temperature Tg may be, for example, -70°C or higher, -55°C or higher, or -45°C or higher. The technology disclosed herein relates to the glass transition temperature Tg A1 The process can also be suitably carried out in embodiments where the glass transition temperature Tg is, for example, -40°C or higher, -35°C or higher, -33°C or higher, -30°C or higher, or -25°C or higher. In some other embodiments, the process can also be suitably carried out in embodiments where the glass transition temperature Tg A1 For example, the temperature may be -10°C or higher, 0°C or higher, or 3°C or higher.

[0056] 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.

[0057] 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) 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 condition.

[0058] 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, low elastic modulus, and, if necessary, adhesive strength.

[0059] The monomer (A1) content in the monomer component constituting the acrylic polymer is not particularly limited and can be set to realize an adhesive that achieves a desired refractive index and elastic modulus, as well as adhesive properties (e.g., adhesive strength, etc.) and / or optical properties (e.g., total light transmittance, haze value, etc.). In some embodiments, the monomer (A1) content in the monomer component may be, for example, 30% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more, and may also be 70% by weight or more. In some preferred embodiments, the monomer (A1) content in the monomer component constituting the acrylic polymer may be, for example, 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 also be 85% by weight or more, may also be 90% by weight or more, and may also be 91% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more, 95% by weight or more, 96% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more. The monomer (A1) content in the above monomer component is typically less than 100% by weight. From the viewpoint of achieving a good balance between high refractive index, low elastic modulus, and adhesive strength if necessary, it is advantageous to have approximately 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, and may also be 93% by weight or less, or 90% by weight or less. In some embodiments, from the viewpoint of facilitating the realization of 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, less than 85% by weight, or less than 80% by weight.

[0060] (Monomer (A2)) In some preferred embodiments, the monomer components constituting the acrylic polymer may further contain monomer (A2) in addition to monomer (A1). Monomer (A2) 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 useful for introducing crosslinking points into the acrylic polymer or for imparting appropriate cohesiveness to the adhesive. 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.

[0061] 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 lowering the modulus of elasticity and tackiness, acryloyl groups are more preferred. From the viewpoint of lowering the modulus of elasticity 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).

[0062] In some embodiments, monomers (A2) can be used in which the distance between the ethylenically unsaturated group (e.g., (meth)acryloyl group) and the hydroxyl group and / or carboxyl group is relatively long. This makes it easier to obtain a highly flexible crosslinked structure in embodiments in which the hydroxyl group and / or carboxyl group is used in the crosslinking reaction. For example, compounds can be used as monomers (A2) in which the number of atoms (typically carbon atoms and oxygen atoms) constituting the chain (linking chain) that connects the ethylenically unsaturated group and the hydroxyl group and / or carboxyl group is 3 or more (e.g., 4 or more, 5 or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, 15 or more, 16 or more, 17 or more, 18 or more, or 19 or more) can be used. The upper limit of the number of constituent atoms in the above linking chain is, for example, 45 or less, and may be 20 or less (for example, 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, 10 or less, 9 or less, or 8 or less). The number of constituent atoms in the linking chain that connects the ethylenically unsaturated group and the hydroxyl group and / or carboxyl group refers to the minimum number of atoms required to reach the hydroxyl group or carboxyl group from the ethylenically unsaturated group. For example, if the above linking chain is a straight alkylene group (i.e., -(CH2) n If the chain consists of oxyethylene groups (i.e., -(C2H4O)), then the number n will be the number of atoms constituting the linked chain. Also, for example, if the linked chain consists of oxyethylene groups (i.e., -(C2H4O) n In the case of the - group, the product of 3 (3n), which is the sum of the 2 carbon atoms and 1 oxygen atom constituting the oxyethylene group, and n, is the number of atoms constituting the linked chain. Although not particularly limited, such monomers (A2) include, for example, -(CH2) between the ethylenically unsaturated group and the hydroxyl group and / or carboxyl group. n Alkylene units represented by -, or -(C m H 2mA material can be used that has at least one oxyalkylene unit represented by O)- (for example, an oxyethylene unit where m in the formula is 2, an oxypropylene unit where m in the formula is 3, or an oxybutylene unit where m in the formula is 4). The number of alkylene units and oxyalkylene units is not particularly limited and may be 1 or more (for example, 1 to 15 or 1 to 10 or 2 to 6 or 2 to 4). Also, n in the formula representing the alkylene unit is, for example, an integer from 1 to 10, and may be 2 or more, 3 or more, 4 or more, 6 or less, or 5 or less. m in the formula representing the oxyalkylene unit is an integer of 2 or more, for example, an integer from 2 to 4. The monomer (A2) may contain, in addition to the ethylenically unsaturated group, hydroxyl group and / or carboxyl group, alkylene unit and / or oxyalkylene unit, ester bond, ether bond, thioether bond, aromatic ring, aliphatic ring, or heterocycle (for example, a ring containing a nitrogen atom (N), an oxygen atom (O), or a sulfur atom (S)). Furthermore, the alkylene unit and oxyalkylene unit may have substituents.

[0063] 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, which has a lower Tg, is more preferred. Furthermore, in embodiments in which hydroxyalkyl (meth)acrylate is used as the hydroxyl group-containing monomer and the hydroxyl group is utilized in the crosslinking reaction, from the viewpoint of obtaining a highly flexible crosslinked structure, it is preferable to use a monomer with a large number of carbon atoms in the hydroxyalkyl group in the hydroxyalkyl (meth)acrylate, for example, a hydroxyalkyl (meth)acrylate (e.g., 4-hydroxybutyl acrylate) in which the hydroxyalkyl group has 3 or more carbon atoms (e.g., 3 to 12, preferably 4 to 10). In one preferred embodiment, 50% or more by weight (e.g., more than 50%, more than 70%, or more than 85% by weight) of monomer (A2) may be 4-hydroxybutyl acrylate. The hydroxyl group-containing monomer can be used alone or in combination of two or more.

[0064] 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.

[0065] 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. Furthermore, in some embodiments, from the viewpoint of reducing the elastic modulus of the adhesive, it is preferable to use a compound represented by, for example, the following formula (1) as the carboxyl group-containing monomer. CH2=CR 1 -COO-R 2 -OCO-R 3 -COOH (1) Here, in equation (1) above, R 1 R is either a hydrogen or a methyl group. 2 and R 3 R is a divalent linking group (specifically, an organic group having 1 to 20 carbon atoms (for example, 2 to 10, preferably 2 to 5)), and may be the same or different from each other. 2 and R 3 This can be, for example, a divalent aliphatic hydrocarbon group, an aromatic hydrocarbon group, or an alicyclic hydrocarbon group. For example, the above R 2 and R 3This can be an alkylene having 2 to 5 carbon atoms. Specific examples of carboxyl group-containing monomers represented by formula (1) above include, for example, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxyethyl-phthalic acid, 2-(meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid, 2-(meth)acryloyloxyethyl-succinic acid, 2-(meth)acryloyloxypropylhexahydrohydrogen phthalate, 2-(meth)acryloyloxypropylhydrogen phthalate, and 2-(meth)acryloyloxypropyltetrahydrohydrogen phthalate. 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.

[0066] 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. In some preferred embodiments, from the viewpoint of lowering the elastic modulus of the adhesive, the content of the monomer (A2) may be less than 5% by weight, more preferably less than 3% by weight, and 1.5% by weight or less.

[0067] The total content of monomer (A1) and monomer (A2) in the monomer component constituting the acrylic polymer may be, for example, 31% by weight or more, preferably 51% by weight or more, may be 61% by weight or more, or may be 71% by weight or more. In some embodiments, the total content of 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, or may be substantially 100% by weight.

[0068] (Monomer A3) In some preferred embodiments, the monomer component constituting the acrylic polymer may further contain alkyl (meth)acrylate (hereinafter also referred to as "monomer (A3)") in addition to monomer (A1). Monomer (A3) may help reduce the elastic modulus of the adhesive. It may also help improve the compatibility of additives within the adhesive and adhesive properties such as adhesive strength. Monomer (A3) can be used alone or in combination of two or more types.

[0069] 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. 1-20Specific examples of alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isooctyl (meth)acrylate. 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.

[0070] In some embodiments, alkyl (meth)acrylates having a homopolymer Tg of -20°C or lower (more preferably -40°C or lower, for example -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 to lower the elastic modulus of the adhesive. They can also help to improve adhesive properties such as adhesive strength. The lower limit of the Tg of the alkyl (meth)acrylate is not particularly limited and may be, for example, -85°C or higher, -75°C or higher, -65°C or higher, or -60°C or higher. Specific examples of the low-Tg alkyl (meth)acrylate include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), heptyl acrylate, octyl acrylate, and isononyl acrylate (iNA). In some other embodiments, an alkyl (meth)acrylate having a homopolymer Tg greater than -20°C (e.g., -10°C or higher) may be used as at least part of the monomer (A3). The upper limit of the Tg of the alkyl (meth)acrylate is, for example, 10°C or lower, may be 5°C or lower, or 0°C or lower. Alkyl (meth)acrylates having a Tg in this range may be useful in adjusting the elastic modulus of the adhesive. Although not particularly limited, it is preferable to use the alkyl (meth)acrylate having the above Tg in combination with the low Tg alkyl (meth)acrylate. A specific example of the alkyl (meth)acrylate having the above Tg is lauryl acrylate (LA).

[0071] In some embodiments of using monomer (A3), C is used as monomer (A3). 4-8 It is preferable to use alkyl (meth)acrylates. In particular, C 4-8 The use of alkyl acrylates is more preferable. 4-8 Alkyl (meth)acrylates can be used individually or in combination of two or more types. 4-8 The use of alkyl (meth)acrylates makes it easier to reduce the elastic modulus of the adhesive and tends to yield good adhesive properties (adhesion strength, etc.). C is used as monomer (A3). 4-8In an embodiment using alkyl (meth)acrylate, of the alkyl (meth)acrylates contained in the monomer component, C 4-8 The proportion of alkyl (meth)acrylate is appropriately 30% by weight or more, preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, and may be substantially 100% by weight.

[0072] In some embodiments of using monomer (A3), C is used as monomer (A3). 1-6 Alkyl (meth)acrylates may be preferably used. 1-6 The use of alkyl (meth)acrylates allows for adjustment of the storage modulus in each temperature range. For example, it is possible to set the storage modulus in the high-temperature range relatively high, or to suppress large differences in the storage modulus between the low-temperature and high-temperature ranges. 1-6 Alkyl (meth)acrylates tend to exhibit excellent copolymerization properties with monomers (A1). 1-6 Alkyl (meth)acrylates can be used individually or in combination of two or more types. 1-6 As for alkyl (meth)acrylates, C 1-6 Alkyl acrylates are preferred, C 2-6 Alkyl acrylates are more preferred, C 4-6 Alkyl acrylates are more preferred. In some other embodiments, C 1-6 The alkyl (meth)acrylate is preferably C 1-4 It is an alkyl (meth)acrylate, more preferably C 2-4 It is an alkyl (meth)acrylate, and more preferably C 2-4 It is an alkyl acrylate. 1-6 A suitable example of an alkyl (meth)acrylate is BA.

[0073] C in the monomer components that make up acrylic polymers 1-6The alkyl (meth)acrylate content may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. In some embodiments, the above C 1-6 The alkyl (meth)acrylate content may be 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more (for example, 30% by weight or more) from the viewpoint of lowering the elastic modulus and adhesive strength. 1-6 The upper limit of the alkyl (meth)acrylate content is, for example, less than 50% by weight, and may be less than 35% by weight. In some embodiments, from the viewpoint of maintaining a high refractive index, the above C 1-6 The alkyl (meth)acrylate content is, for example, 24% by weight or less, preferably less than 20% by weight, more preferably less than 17% by weight, may be less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The technology disclosed herein is C 1-6 This can also be carried out in a manner that substantially does not use alkyl (meth)acrylates.

[0074] In some other embodiments using monomer (A3), C is used as monomer (A3). 7-12 Alkyl (meth)acrylates may be preferably used. 7-12 The use of alkyl (meth)acrylates can be used to favorably reduce the storage modulus. 7-12 Alkyl (meth)acrylates can be used individually or in combination of two or more types. 7-12 As for alkyl (meth)acrylates, C 7-10 Alkyl acrylates are preferred, C 7-9 Alkyl acrylates are more preferred, and C8 alkyl acrylates are even more preferred. 7-12 Examples of alkyl (meth)acrylates include 2EHA, iNA, and LA, with 2EHA being a preferred example.

[0075] C in the monomer components that make up acrylic polymers 7-12The alkyl (meth)acrylate content may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. In some embodiments, the above C 7-12 The alkyl (meth)acrylate content may be 10% by weight or more, 15% by weight or more, 20% by weight or more, or 25% by weight or more (for example, 30% by weight or more) from the viewpoint of lowering the elastic modulus and adhesive strength. 7-12 The upper limit of the alkyl (meth)acrylate content is, for example, less than 50% by weight, and may be less than 35% by weight. In some embodiments, from the viewpoint of maintaining a high refractive index, the above C 7-12 The alkyl (meth)acrylate content is, for example, 24% by weight or less, preferably less than 20% by weight, more preferably less than 17% by weight, may be less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The technology disclosed herein is C 7-12 This can also be carried out in a manner that substantially does not use alkyl (meth)acrylates.

[0076] In some embodiments of using monomer (A3), it is preferable that at least a portion of monomer (A3) is alkyl acrylate from the viewpoint of lowering the elastic modulus. The use of alkyl acrylate is also advantageous in terms of adhesive properties such as adhesive strength. For example, it is preferable that 50% by weight or more of monomer (A3) is alkyl acrylate, more preferably 75% by weight or more, and even more preferably 90% by weight or more, and substantially 100% by weight of monomer (A3) may be alkyl acrylate. It is also possible to use only one or more alkyl acrylates as monomer (A3) and not use alkyl methacrylate.

[0077] 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, for example, less than 50% by weight or less than 35% 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 also be preferably implemented in a manner that does not substantially use monomer (A3).

[0078] (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.

[0079] Examples of other monomers mentioned above 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, 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.

[0080] 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℃).

[0081] 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), the content of the above-mentioned other monomers in the monomer component can be, for example, approximately 35% by weight or less, it is appropriate to be approximately 25% by weight or less (e.g., 0 to 25% by weight), it may also be approximately 20% by weight or less (e.g., 0 to 20% by weight), it is advantageous to be approximately 10% by weight or less (e.g., 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.

[0082] 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).

[0083] In some embodiments, the monomer components constituting the acrylic polymer 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, less than 0.5% by weight, less than 0.3% by weight, 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 metallic materials (e.g., metal wiring or metal films that may be present on the adherend) that may be in contact with or placed in close proximity to the adhesive disclosed herein. The technology disclosed herein can also be implemented in an embodiment 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 techniques 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).

[0084] (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 in which the glass transition temperature Tg is approximately 15°C or lower. In some embodiments, the above glass transition temperature Tg T The glass transition temperature Tg is preferably 10°C or lower, more preferably 5°C or lower, even more preferably 1°C or lower, and may be 0°C or lower. In some other embodiments, the above glass transition temperature Tg T The temperature may be below -10°C, below -20°C, below -25°C, below -30°C, or below -35°C. (Glass transition temperature Tg) TA low value can be advantageous from the standpoint of reducing the elastic modulus of the adhesive. Also, the glass transition temperature Tg T The glass transition temperature Tg may be, for example, -60°C or higher, preferably -50°C or higher, more preferably above -45°C, and may also be above -40°C, from the viewpoint of facilitating the raising of the refractive index of the adhesive. In some preferred embodiments, the above glass transition temperature Tg T The glass transition temperature Tg may be above -30°C, above -20°C, above -10°C, or above -5°C. The adhesive that achieves both a high refractive index and a low modulus of elasticity has a glass transition temperature Tg within the above range. T It can preferably be formed by using an acrylic polymer having a composition containing [specific properties].

[0085] 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 homopolymers 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 monomer i homopolymer (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.

[0086] (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).

[0087] 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.

[0088] 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.

[0089] 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, a chain transfer agent that does not contain sulfur atoms (non-sulfur chain transfer agent) 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 the monomer component.

[0090] The weight-average molecular weight (Mw) of the above acrylic polymer is not particularly limited, for example, approximately 30 × 10 4 That is all, approximately 50 x 10 4 The above is appropriate, approximately 70 x 10 4 It may be greater than or equal to approximately 80 x 10 4 The above is also acceptable. By using an acrylic polymer with Mw above a predetermined value, it is easier to obtain a moderate cohesive force that can exhibit the desired adhesive properties. In addition, it is possible to include more additives such as plasticizers, and it tends to be easier to achieve the desired modulus of elasticity. Furthermore, the upper limit of Mw for the acrylic polymer is, for example, approximately 500 × 10 4 The following is the case, and from the perspective of adhesive performance, approximately 400 x 10 4 The following (more preferably approximately 150 x 10 4 For example, approximately 130 x 10 4 It is preferable that it be within the following range.

[0091] 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

[0092] (Plasticizer) The adhesive composition disclosed herein is characterized by containing a plasticizer in addition to an acrylic polymer. The use of a plasticizer can reduce the elastic modulus of the adhesive. Furthermore, in the form molded into an adhesive sheet, flexibility and conformability to deformation can be improved. The plasticizer disclosed herein is a cyclic unsaturated organic compound having two or more double bond-containing rings. In other words, the plasticizer is a compound having two or more double bond-containing rings in one molecule. Therefore, the plasticizer has at least a first double bond-containing ring and a second double bond-containing ring. By having two or more double bond-containing rings, it is possible to contribute to lowering the elastic modulus of the adhesive without impairing the refractive index of the adhesive, or while maintaining the refractive index. From the viewpoint of exhibiting a plasticizing effect, the number of double bond-containing rings in the plasticizer is preferably 6 or less, but may be 4 or less, or 3 or less. The plasticizer can be used alone or in combination of two or more types.

[0093] Furthermore, the plasticizer used in the technology disclosed herein is a compound that is liquid at 30°C. In this specification, "liquid" means fluidity and refers to a liquid state of matter. Such compounds include compounds with a melting point of 30°C or lower. Because the plasticizer is liquid at 30°C, the plasticizing effect is suitably exhibited, and the low modulus of elasticity of the adhesive can be effectively achieved. The plasticizer is preferably a compound that is liquid at 25°C, and more preferably a compound that is liquid at 20°C. By using a compound that is liquid at 30°C and has two or more double bond-containing rings as the plasticizer, an adhesive that achieves both a high refractive index and a low modulus of elasticity can be formed.

[0094] The double bond-containing rings of the plasticizers disclosed herein may be conjugated double bond-containing rings (typically aromatic rings) or non-conjugated double bond-containing rings. The plasticizers may have at least one ring selected from aromatic rings and heterocycles as the double bond-containing rings. The heterocycle may have a structure that is included in the aromatic ring, or it may have a double bond-containing heterocycle structure different from the aromatic ring. The double bond-containing rings (typically aromatic rings) that the plasticizers may have may be carbon rings such as benzene rings (which may be benzene rings that constitute part of a biphenyl structure or a fluorene structure); naphthalene rings, indene rings, azulene rings, anthracene rings, phenanthrene rings; or heterocycles such as pyridine rings, pyrimidine rings, pyridazine rings, pyrazine rings, triazine rings, pyrrole rings, pyrazole rings, imidazole rings, triazole rings, oxazole rings, isoxazole rings, thiazole rings, thiophene rings. In the above heterocycle, the heteroatoms included as ring constituent atoms 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 heterocycle may be nitrogen and sulfur, or both. The plasticizer may have a structure in which one or more carbon rings and one or more heterocycles are fused, such as the dinaphthothiophene structure.

[0095] The double bond-containing ring described above (typically an aromatic ring, preferably a carbocyclic ring) may have one or more substituents on the ring constituent atoms, or it may not have substituents. If substituents are present, examples of 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, and glycidyloxy groups. In substituents containing carbon atoms, the number of carbon atoms 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 double bond-containing ring may be an aromatic ring that has neither substituents on the ring constituent atoms nor substituents, or has one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, ethylenically unsaturated groups (e.g., (meth)acryloxy groups), hydroxyl groups, and hydroxyalkyl groups. Alkyl groups, alkoxy groups, and hydroxyalkyl groups are preferably used as substituents.

[0096] In some embodiments, compounds without ethylenically unsaturated groups can be preferably used as plasticizers. This suppresses deterioration of the adhesive composition due to heat and light (progression of gelation and decrease in leveling properties due to increased viscosity), thereby improving storage stability. Using plasticizers without ethylenically unsaturated groups is also preferable from the viewpoint of suppressing changes in elastic modulus, dimensional changes and deformation (warping, undulation, etc.), and the occurrence of optical distortion in adhesive sheets having an adhesive layer containing the plasticizer, which are caused by the reaction of ethylenically unsaturated groups.

[0097] As the plasticizer, a high refractive index plasticizer having a refractive index of approximately 1.50 or higher is preferably used. By using a high refractive index plasticizer, a higher level of compatibility between high refractive index and low modulus of elasticity can be achieved. From the viewpoint of maintaining and improving the refractive index of the adhesive while lowering the modulus of elasticity, the refractive index of the plasticizer is preferably approximately 1.51 or higher, more preferably approximately 1.53 or higher, even more preferably approximately 1.55 or higher, and may also be approximately 1.56 or higher, approximately 1.58 or higher, approximately 1.60 or higher, or approximately 1.62 or higher. In some embodiments, from the viewpoint of ease of preparation of the adhesive composition and compatibility within the adhesive, the refractive index of the plasticizer is suitable to be 2.50 or lower, advantageous to be 2.00 or lower, may also be 1.90 or lower, may also be 1.80 or lower, or may also be 1.70 or lower. 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.

[0098] The molecular weight of the plasticizer is not particularly limited, but usually a plasticizer with a molecular weight smaller than that of the acrylic polymer is used. From the viewpoint of facilitating the expression of the plasticizing effect, the molecular weight of the plasticizer is preferably 30,000 or less, more preferably 25,000 or less, and may be less than 10,000 (e.g., less than 5,000) or less than 3,000. In some embodiments, the molecular weight of the plasticizer is preferably 2,000 or less, more preferably 1,200 or less, even more preferably 900 or less, and may be 600 or less, 500 or less, 400 or less, 300 or less, or 250 or less (e.g., 220 or less). Having a plasticizer with a molecular weight that is not too large can be advantageous from the viewpoint of improving compatibility within the adhesive layer. Furthermore, from the viewpoint of easily exhibiting a sufficient plasticizing effect, the molecular weight of the plasticizer is appropriately 100 or more, preferably 130 or more, more preferably 150 or more, and may also be 170 or more, 200 or more, 220 or more, or 250 or more. It is also preferable that the molecular weight of the plasticizer is not too low from the viewpoint of the heat resistance performance of the adhesive sheet and the suppression of contamination of the adherend. In some embodiments, the molecular weight of the plasticizer is, for example, 300 or more, appropriately 315 or more, and may also be 350 or more. Plasticizers with large molecular weights are less likely to vaporize, so by using a plasticizer with a large molecular weight in the adhesive, it is easier to obtain an adhesive that can exhibit stable properties. In addition, plasticizers with large molecular weights are less likely to move within the adhesive. Therefore, for example, events that affect adhesive properties, such as the plasticizer moving to the surface of the adhesive, are less likely to occur. The molecular weight of the above plasticizer is more preferably 400 or more, even more preferably 450 or more, particularly preferably 500 or more, and may also be 530 or more. The molecular weight of the plasticizer is calculated based on its chemical structure. If the manufacturer provides a nominal molecular weight, that nominal value can be used.

[0099] In some embodiments, the plasticizer may be one or more selected from the group consisting of: compounds having a structure in which two or more non-fused double bond-containing rings (typically aromatic rings) are bonded via a linking group; compounds having a structure in which two or more non-fused double bond-containing rings (typically aromatic rings) are chemically bonded directly (i.e., without interposition of another atom); compounds having a fused double bond-containing ring (typically aromatic ring) structure; compounds having a fluorene structure; compounds having a dinaphthothiophene structure; compounds having a dibenzothiophene structure; and the like, which are liquid at 30°C (e.g., 25°C or 20°C).

[0100] In an embodiment where a compound having a structure in which two or more non-fused double bond-containing rings are bonded via a linking group is used as the plasticizer, the linking group is, for example, an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (e.g., -O-(CH2) n n- group, wherein n is 1 to 3, preferably 1), a thiooxyalkylene group (e.g., -S-(CH2) n n- group, wherein n is 1 to 3, preferably 1), a linear alkylene group (i.e., -(CH2) nThe linking group may be a -group (where n is 1 to 6, preferably 1 to 3), an oxyalkylene group, a thiooxyalkylene group, or a linear alkylene group in which the alkylene group is partially halogenated or fully halogenated. The linking group may have a siloxane bond (-SiOR-) or an ester bond. In the plasticizer, the linking group that connects the first double bond-containing ring (non-condensed ring) and the second double bond-containing ring (non-condensed ring) may also be selected from the same types as above. From the viewpoint of reducing the elastic modulus of the adhesive, preferred examples of the linking group include an oxy group, a thiooxy group, an oxyalkylene group, and a linear alkylene group. The number of atoms in the linking group is not particularly limited, and may be, for example, 1 to 30, 1 to 25, 1 to 20, preferably 1 to 18, preferably 1 to 12, more preferably 1 to 10, even more preferably 1 to 8, particularly preferably 1 to 5, may be 1 to 3, or even 1 or 2. The number of atoms in the linking group refers to the minimum number of atoms required to reach from one non-condensed double bond-containing ring to the other non-condensed double bond-containing ring. For example, if the linking group is a linear alkylene group (i.e., -(CH2) n If the linking group consists of -(C2H4O) groups, then n is the number of atoms in the linking group. Also, for example, if the linking group is an oxyethylene group (i.e., -(C2H4O) n In the case of a - group, the number of atoms in the linking group is the product of 3 (the sum of the 2 carbon atoms and 1 oxygen atom that make up the oxyethylene group) and n (3n). Preferred examples of the above compounds include compounds having a phenoxybenzyl group. Examples of the above compounds include phenoxybenzyl (meth)acrylate (e.g., m-phenoxybenzyl (meth)acrylate), phenoxybenzyl alcohol, oxybis[(alkoxyalkyl)benzene] (e.g., 4,4′-oxybis[(methoxymethyl)benzene]), etc. Other examples of the above compounds include silicone-based plasticizers (specifically siloxane compounds) which will be discussed later.

[0101] Compounds having a structure in which two or more double-bond-containing rings (non-condensed rings) are directly chemically bonded may include, for example, biphenyl-containing compounds and triphenyl-containing compounds. Examples of compounds having a condensed double-bond-containing ring structure include naphthalene-containing compounds and anthracene-containing compounds. A specific example is 1-acetonaphthone. Compounds having the fluorene structure are included in the concept of compounds having a structure in which two or more double-bond-containing rings (non-condensed rings) are directly chemically bonded, because they contain a structural portion in which two benzene rings are directly chemically bonded. Compounds having the dinaphthothiophene structure are included in the concept of compounds having a condensed double-bond-containing ring structure because they contain a naphthalene structure and have a structure in which a thiophene ring is fused with two naphthalene structures. Compounds having the dibenzothiophene structure are included in the concept of compounds having a condensed double-bond-containing ring structure because they have a structure in which a thiophene ring is fused with two benzene rings.

[0102] In some embodiments, silicone-based plasticizers are used as plasticizers. By using silicone-based plasticizers, a stable plasticizing effect is easily obtained, and high adhesive strength is easily achieved, thus enabling a balanced improvement in the refractive index, flexibility, and adhesive strength of the adhesive. As silicone-based plasticizers, compounds having two or more double-bond-containing rings and being liquid at 30°C can be used without particular limitation. Specifically, the silicone-based plasticizer is a siloxane compound, and the number of Si atoms in the compound is one or more (typically two or more), and there is no particular upper limit, for example it may be around 10 or less. In one molecule of silicone-based plasticizer, the Si atoms and double-bond-containing rings may or may not be directly bonded. Preferably, at least one of the above Si atoms is directly bonded to at least one double-bond-containing ring. Silicone-based plasticizers can be used individually or in combination of two or more types.

[0103] In some embodiments, the silicone-based plasticizer may consist of a siloxane compound having 2 to 5 Si atoms, wherein at least one of the Si atoms is bonded to two or more double-bonded rings. A silicone-based plasticizer consisting of a siloxane compound having such a structure can exhibit a plasticizing effect based on the flexibility of the siloxane structure, and by having 2 to 5 Si atoms and at least one Si atom bonded to two or more double-bonded rings, it is possible to achieve a good balance between ease of compounding and compatibility with the material to be plasticized and the stability of the plasticizing effect (for example, a low rate of increase in elastic modulus when stored under humid heat). From the viewpoint of chemical stability, it is preferable that the siloxane compound does not have hydrogen atoms bonded to the Si atoms. That is, a siloxane compound without Si-H bonds is preferred.

[0104] When the number of Si atoms in the above siloxane compound is 3 or more, the siloxane compound may be linear or cyclic, but it is preferable to be a linear siloxane compound from the viewpoint of suppressing volatilization. The above linear siloxane compound with 3 or more Si atoms may be linear or branched, but it is preferable to be linear from the viewpoint of obtaining a higher plasticizing effect. Hereinafter, unless otherwise specified, a siloxane compound with 3 or more Si atoms means a linear (typically linear) siloxane compound with 3 or more Si atoms.

[0105] Each double-bond-containing ring in the above-mentioned silicone plasticizer may independently be a conjugated double-bond-containing ring (typically an aromatic ring) or a non-conjugated double-bond-containing ring. The plasticizer may have at least one ring selected from aromatic rings and heterocycles as the double-bond-containing ring. The heterocycle may have a structure that is included in the aromatic ring, or it may have a double-bond-containing heterocycle structure different from the aromatic ring. The double-bond-containing ring (typically an aromatic ring) that the plasticizer may have may be a carbon ring such as a benzene ring or a naphthalene ring, or a heterocycle such as a pyridine ring, imidazole ring, triazole ring, oxazole ring, thiazole ring, or thiophene ring. The heteroatoms included as ring constituent atoms in the above heterocycle 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 heterocycle may be nitrogen and sulfur, or both.

[0106] The above double bond-containing ring (typically an aromatic ring, preferably a carboelectric ring) may have one or more substituents on the ring constituent atoms, or it may not have substituents. If substituents are present, examples of substituents include, but are not limited to, alkyl groups, alkoxy 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, each double bond-containing ring in the silicone plasticizer is independently selected from aromatic rings without substituents on the ring constituent atoms, and aromatic rings having one or more substituents selected from the group consisting of alkyl groups, alkoxy groups, hydroxyl groups, and hydroxyalkyl groups (preferably the group consisting of alkyl groups and alkoxy groups). For example, each double bond-containing ring in the silicone plasticizer is independently selected from aromatic rings (preferably carboelectric rings) without substituents on the ring constituent atoms. In some preferred embodiments, each double-bond-containing ring in the silicone plasticizer is a benzene ring.

[0107] The number of Si atoms in the above siloxane compound is preferably 3 or more, from the viewpoint of ease of exhibiting the plasticizing effect and its stability (for example, suppression of the increase in elastic modulus due to the volatilization and dissipation of the plasticizer from the material into which the plasticizer is blended). Furthermore, the number of Si atoms in the above siloxane compound is preferably 4 or less, and more preferably 3 or less, from the viewpoint of compatibility within the adhesive. Among these, a silicone-based plasticizer having 3 Si atoms in the above siloxane compound, i.e., a silicone-based plasticizer consisting of a trisiloxane compound, is preferred.

[0108] The number of double-bond-containing rings (e.g., benzene rings with or without substituents) in the above siloxane compound is at least 2, preferably 3 or more, more preferably 4 or more, and may be 5 or more, from the viewpoint of heat resistance of the plasticizing effect (e.g., low rate of increase in elastic modulus when stored under humid heat). Furthermore, the number of double-bond-containing rings in the above siloxane compound is typically 2n+2 or less, where n is the number of Si atoms in the siloxane compound, and from the viewpoint of enhancing the plasticizing effect, it is appropriate to be 2n+1 or less, preferably 2n or less, may be 2n-1 or less, or 2n-2 or less. For example, in an embodiment in which the above siloxane compound is a trisiloxane compound, the number of double-bond-containing rings in the trisiloxane compound is typically 8 or less, and may be, for example, 2 to 7, 3 to 7, or 4 to 7. Among these, trisiloxane compounds in which the number of double-bond-containing rings (e.g., unsubstituted benzene rings) is 4 to 6 (e.g., 4 or 5) are preferred.

[0109] In some embodiments, at least one of the Si atoms in the siloxane compound (typically, Si atoms constituting the siloxane chain) is a Si atom to which two or more double bond-containing rings are bonded. From the viewpoint of improving the stability of the plasticization effect, the number of Si atoms to which two or more double bond-containing rings are bonded in the siloxane compound may be two or more. In a siloxane compound with three or more Si atoms, the number of Si atoms to which two or more double bond-containing rings are bonded may be two or more, three or more, and may be n or less, n-1 or less, or n-2 or less, depending on the number of Si atoms in the siloxane compound, n. In some embodiments, from the viewpoint of enhancing the plasticization effect, at least one of the Si atoms in the siloxane compound (preferably a siloxane compound with three or more Si atoms) has one or zero double bond-containing rings bonded to it. For example, a linear siloxane compound having 3 to 5 Si atoms is preferred, wherein each Si atom at both ends independently has 2 or 3 (preferably 2) double bond-containing rings, and each Si atom other than those at the ends independently has 1 double bond-containing ring or no double bond-containing rings.

[0110] The above siloxane compound may contain Si atoms to which groups other than the double bond-containing ring are bonded. Examples of groups other than the double bond-containing ring include, but are not limited to, alkyl groups, aralkyl groups, alkoxy groups, halogen atoms (fluorine atoms, chlorine atoms, bromine atoms, etc.), fluoroalkyl groups, hydroxyalkyl groups, hydroxyalkyloxy groups, epoxy groups, glycidyloxy groups, amino groups, monoalkylamino groups, dialkylamino groups, carboxyl groups, carboxyalkyl groups, mercapto groups, and the like. In substituents containing carbon atoms, the number of carbon atoms in the substituent is, for example, 1 to 8, preferably 1 to 4, more preferably 1 to 3, and may be, for example, 1 or 2. The groups other than the double bond-containing ring bonded to each Si atom in the siloxane compound can be independently selected from the group consisting of the groups exemplified above.

[0111] In some embodiments, it is preferable that the siloxane compound does not have an ethylenically unsaturated group (including those in which the double bond in a double bond-containing ring is an ethylenically unsaturated double bond). A silicone-based plasticizer consisting of a siloxane compound without an ethylenically unsaturated group is advantageous from the viewpoint of the stability of the plasticizing effect of the plasticizer, and is also preferable from the viewpoint of storage stability of the adhesive sheet having an adhesive layer containing the silicone-based plasticizer, and from the viewpoint of suppressing changes in elastic modulus, dimensional changes and deformation (warping, undulation, etc.), and the occurrence of optical distortion caused by the reaction of ethylenically unsaturated groups.

[0112] In some embodiments of the silicone-based plasticizers disclosed herein, it is preferable that at least one Si atom (at least two in the case of siloxane compounds with three or more Si atoms) in the siloxane compound has at least one methyl group on the Si atom, from the viewpoint of enhancing the plasticizing effect. For example, it is preferable that each Si atom located at both ends of the siloxane chain independently has one or two (more preferably one) methyl groups. In some preferred embodiments, each Si atom in the siloxane compound independently has one or two methyl groups. A silicone-based plasticizer comprising a siloxane compound with such a structure can achieve a good balance between the plasticizing effect due to the flexibility of the siloxane structure and the stability of the plasticizing effect due to the structure in which at least one Si atom is bonded to two or more double-bond-containing rings.

[0113] In some embodiments, the total number of substituents bonded to the Si atoms in the siloxane compound (hereinafter also referred to as the total number of substituents) is typically 2n+2, of which at least two are double bond-containing rings. In some embodiments, the proportion SR of double bond-containing rings (preferably aromatic carbon rings, e.g., benzene rings) among the total number of substituents in the silicone plasticizer is at least 16%, may be 20% or more, or 25% or more. Generally, as the above proportion SR increases, the heat resistance of the silicone plasticizer and the stability of the plasticizing effect by the silicone plasticizer tend to improve. In some embodiments, the above proportion SR is advantageous to be 33% or more, preferably 40% or more, more preferably 50% or more (e.g., 60% or more), may be 65% or more, or 75% or more. The above ratio SR can be 100%, but from the viewpoint of ease of formulation and compatibility, it is advantageous to have 85% or less, preferably 80% or less, and may also be 75% or less, 65% or less, or 60% or less (for example, 50% or less).

[0114] In some embodiments, the molecular weight of the silicone-based plasticizer (specifically, the siloxane compound) is suitable to be 400 or more, advantageous to be 430 or more, preferably 460 or more, may also be 490 or more, or may be 520 or more, from the viewpoint of stability of the plasticizing effect. Furthermore, the molecular weight of the siloxane compound is suitable to be 900 or less, advantageous to be 850 or less, preferably 700 or less, more preferably 650 or less, may also be 600 or less, may also be 560 or less, may also be 540 or less, or may be 500 or less, from the viewpoint of plasticizing effect, ease of formulation, compatibility, etc.

[0115] The molecular weight of the above siloxane compound can be calculated based on its chemical structure, or it can be measured using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS). If the manufacturer provides a nominal molecular weight, that nominal value can be used.

[0116] The refractive index of the silicone-based plasticizer disclosed herein is not particularly limited and may be in the range of approximately 1.30 to 1.80. From the viewpoint of suppressing a decrease in the refractive index of the material (e.g., adhesive) into which the plasticizer is blended while lowering the elastic modulus, the silicone-based plasticizer according to some embodiments is suitable to have a refractive index of 1.45 or higher, preferably 1.50 or higher, more preferably 1.52 or higher (e.g., 1.53 or higher or 1.54 or higher), and even more preferably 1.55 or higher (e.g., 1.56 or higher or 1.57 or higher). Furthermore, from the viewpoint of ease of blending and compatibility, the refractive index of the silicone-based plasticizer may be, for example, 1.70 or lower, 1.65 or lower, or 1.60 or lower.

[0117] In some embodiments, ethylene glycol compounds having two or more double-bond-containing rings in one molecule can be used as plasticizers. The number of oxyethylene units (i.e., -(C2H4O)- units) in the ethylene glycol compound is, for example, 1 to 10, may be 1 to 6, or 2 to 4. The ethylene glycol compound may be a compound having a structure in which two or more non-condensed double-bond-containing rings are linked via oxyethylene units (e.g., 1 to 10, preferably 1 to 6, typically 2 to 4 oxyethylene units) as linking groups. Such a compound may have one or more ester groups. Examples of the ethylene glycol compound include compounds having a structure in which two or more benzoic acid molecules are linked to ethylene glycol, diethylene glycol, triethylene glycol, or polyethylene glycol by ester bonds.

[0118] Furthermore, the technologies disclosed herein can be implemented in a manner in which the ethylene glycol compound is not used as a plasticizer, or its use is limited. For example, the content of the ethylene glycol compound in the plasticizer contained in the adhesive composition may be less than 90% by weight. The content of the ethylene glycol compound in the plasticizer may be less than 50% by weight, less than 10% by weight, less than 3% by weight, or less than 1% by weight, and the adhesive composition may not substantially contain the ethylene glycol compound as a plasticizer. Similarly, the amount of the ethylene glycol compound used in the adhesive composition per 100 parts by weight of acrylic polymer may be less than 0.5 parts by weight, or less than 0.1 parts by weight.

[0119] In some other embodiments, liquid rosins such as liquid rosin esters can be used as plasticizers. The above liquid rosins (e.g., liquid rosin esters) may correspond to compounds having the above-mentioned condensed double bond-containing ring structure.

[0120] The amount of the plasticizer used is not particularly limited and can be set according to the purpose. From the viewpoint of reducing the elastic modulus of the pressure-sensitive adhesive, the amount of the plasticizer used per 100 parts by weight of the acrylic polymer may be, for example, 1 part by weight or more, or may be 10 parts by weight or more. In some preferred embodiments, the amount of the plasticizer used per 100 parts by weight of the acrylic polymer is more than 15 parts by weight, may be 20 parts by weight or more, may be 30 parts by weight or more (for example, more than 30 parts by weight), more preferably 40 parts by weight or more, still more preferably 50 parts by weight or more, particularly preferably 60 parts by weight or more, may be 75 parts by weight or more, and may be 90 parts by weight or more. For example, when the above-mentioned ethylene glycol-based compound is used as the plasticizer, it is preferably used in an amount exceeding 30 parts by weight (for example, 40 parts by weight or more, further 50 parts by weight or more) based on 100 parts by weight of the acrylic polymer. In addition, from the viewpoint of achieving a good balance between increasing the refractive index and decreasing the elastic modulus of the pressure-sensitive adhesive, the amount of the plasticizer used per 100 parts by weight of the acrylic polymer is appropriately approximately 200 parts by weight or less, preferably 150 parts by weight or less, more preferably 120 parts by weight or less, may be 100 parts by weight or less, may be 80 parts by weight or less, and may be 70 parts by weight or less. In some embodiments that place more emphasis on pressure-sensitive adhesive properties, the amount of the plasticizer used per 100 parts by weight of the acrylic polymer may be 45 parts by weight or less, or may be 35 parts by weight or less.

[0121] (Additive (H RO ) The pressure-sensitive adhesive composition disclosed herein may contain, as an optionally used additive, an organic material having a higher refractive index than the above acrylic polymer. Hereinafter, such an organic material may be referred to as "additive (H RO )". Here, the above "H RO " indicates that the material is an organic material (Organic material) with a high refractive index (High Refractive index). Additive (H RO ) in combination with an acrylic polymer makes it possible to achieve a pressure-sensitive adhesive that more suitably achieves both refractive index and pressure-sensitive adhesive properties (peel strength, flexibility, etc.). Additive (H ROThe organic material used as an additive (H) may be a polymer or a nonpolymer. It may also have polymerizable functional groups or not. In this specification, the additive (H) RO ) is defined as something different from the compounds used as plasticizers mentioned above. Therefore, the additive (H RO Specifically, it is not liquid at 30°C (e.g., 25°C or 20°C). Additive (H RO ) can be used individually or in combination of two or more types.

[0122] 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 this, a smaller amount of additive (H RO The desired refractive index can also be achieved by using (H). 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.

[0123] 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 A 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. 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.

[0124] 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, ΔnB 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.

[0125] Additives (H RO The 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). ROIf 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.

[0126] Additives (H RO Examples 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.

[0127] 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 a monomer (A1) can be selected from the same aromatic rings as those of the compound used as monomer (A1).

[0128] The above aromatic ring may have one or more substituents on the ring constituent atoms, or it may not have substituents. If substituents are present, examples of 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 above aromatic ring may have no substituents on the 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).

[0129] Additives (H ROExamples of aromatic ring-containing compounds that can be used as monomers include, for example: compounds that can be used as monomers (A1); oligomers containing a compound that can be used as monomer (A1) as a monomer unit; compounds having a structure 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 (for example, a hydroxyl group, an amino group, a halogen atom, an alkyl group, an alkoxy group, a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group, etc.), etc., which do not fall under the category of plasticizers disclosed herein, but are not limited to these.

[0130] In some embodiments, additive (H RO As such, organic compounds having two or more aromatic rings in one molecule (hereinafter also referred to as "multiple aromatic ring-containing compounds") can be preferably used because they easily provide a high refractive index effect. Multiple aromatic ring-containing compounds may or may not have polymerizable functional groups such as ethylenically unsaturated groups. Furthermore, multiple aromatic ring-containing compounds may be polymers or nonpolymers. The polymer may be an oligomer containing multiple 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 multiple aromatic ring-containing monomers; a copolymer of two or more multiple aromatic ring-containing monomers; a copolymer of one or more multiple 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 multiple aromatic ring-containing monomers, monomers that do not have aromatic rings, or combinations thereof.

[0131] 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.

[0132] Additives (H RO Examples 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.

[0133] 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 In adhesive sheets having an adhesive layer containing ), it is preferable from the viewpoint of suppressing dimensional changes and deformation (warping, undulation, etc.) and the occurrence of optical distortion caused by the reaction of ethylenically unsaturated groups.

[0134] Additives (H ROIn 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 above-mentioned chain transfer agents include lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, α-thioglycerol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimercapto-1-propanol. The chain transfer agent may be used alone or in combination of two or more types. The amount of chain transfer agent used can be set to obtain an oligomer with a desired weight-average molecular weight, depending on the composition of the monomer components used in the synthesis of the oligomer and the type of chain transfer agent. In some embodiments, the amount of chain transfer agent used per 100 parts by weight of the total amount of monomer used in the synthesis of the oligomer is appropriately about 15 parts by weight or less, but may also be 10 parts by weight or less, or about 5 parts by weight or less. There is no particular lower limit to the amount of chain transfer agent used relative to 100 parts by weight of the total amount of monomer used in the synthesis of oligomers, but it may be, for example, 0.01 parts by weight or more, 0.1 parts by weight or more, 0.5 parts by weight or more, or 1 part by weight or more.

[0135] Additive (H) per 100 parts by weight of acrylic polymer RO The amount of additive (H) used (if multiple types of compounds are used, the total amount thereof) is not particularly limited as long as it is greater than 0 parts by weight, and can be set according to the purpose. In some embodiments, the amount of additive (H) per 100 parts by weight of acrylic polymer is ROThe amount of additive (H) used can be, for example, 80 parts by weight or less, and from the viewpoint of achieving a good balance between increasing the refractive index of the adhesive and suppressing the deterioration of adhesive properties and optical properties, it is advantageous to use 60 parts by weight or less, and preferably 45 parts by weight or less. In some embodiments where adhesive properties and optical properties are given more importance, the amount of additive (H) per 100 parts by weight of acrylic polymer is RO The amount used may be, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less. Also, from the viewpoint of increasing the refractive index of the adhesive, the amount of additive (H) per 100 parts by weight of acrylic polymer may be RO The 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.

[0136] (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 and epoxy crosslinking agents are preferred. Other examples of crosslinking agents include monomers having two or more ethylenically unsaturated groups in one molecule, i.e., polyfunctional monomers. Crosslinking agents can be used individually or in combination of two or more.

[0137] As isocyanate crosslinking agents, isocyanate compounds with two or more functions can be used, for example, aliphatic polyisocyanates such as trimethylene diisocyanate, butylene diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), and dimer acid diisocyanate; and alicyclic polyisocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), and 1,3-bis(isocyanatomethyl)cyclohexane. Examples include socyanates; aromatic isocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, and xylylene diisocyanate (XDI); and polyisosinate modified compounds 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. (e.g., isocyanurate and allophanate forms of HDI). Examples of commercially available products include the product names Takenate 300S, Takenate 500, Takenate 600, Takenate D165N, Takenate D178N, Takenate D178NL (all manufactured by Mitsui Chemicals), Sumijoule T80, Sumijoule L, Desmodule N3400 (all manufactured by Sumika Bayer Urethane Co., Ltd.), Myrionate MR, Myrionate MT, Coronate L, Coronate HL, Coronate HX, Coronate 2770 (all manufactured by Tosoh Corporation), and the product name Duranate A201H (all manufactured by Asahi Kasei Corporation). Isocyanate compounds can be used individually or in combination of two or more. A bifunctional isocyanate compound and a trifunctional or higher isocyanate compound may be used in combination.

[0138] 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.

[0139] 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.

[0140] In some embodiments, at least a portion of the crosslinking agent is a difunctional crosslinking agent having two crosslinking reactive groups (e.g., isocyanate groups) per molecule. Using a difunctional crosslinking agent facilitates the formation of flexible crosslinked structures. Difunctional crosslinking agents can be used individually or in combination of two or more. Furthermore, difunctional crosslinking agents may be used in combination with trifunctional or higher crosslinking agents.

[0141] In some embodiments, acyclic crosslinking agents (also called chain-like crosslinking agents) that do not have ring structures such as aromatic rings or aliphatic rings are preferably used as crosslinking agents. For example, among the isocyanate-based crosslinking agents described above, the use of isocyanate compounds that do not have ring structures such as aromatic rings and isocyanurate rings is preferred. By using acyclic isocyanate compounds as crosslinking agents, it is easy to form crosslinking agents with high flexibility. Specific examples of the above acyclic isocyanates include aliphatic isocyanate compounds (e.g., PDI and HDI) and modified aliphatic isocyanate compounds (e.g., polyisocyanate modified products modified by allophanate bonds, biuret bonds, urea bonds, or carbodiimide bonds of PDI and HDI). Acyclic crosslinking agents can be used alone or in combination of two or more. In some preferred embodiments, acyclic bifunctional crosslinking agents can be used as crosslinking agents.

[0142] In some embodiments, a crosslinking agent can be used in which the distance between one crosslinking reactive group (e.g., an isocyanate group) and another crosslinking reactive group in one molecule is relatively long. This allows for the formation of a flexible crosslinked structure having a length greater than a predetermined length. For example, a compound can be used as a crosslinking agent in which the number of atoms constituting the linking chain that connects one crosslinking reactive group to another is 10 or more (e.g., 12 or more or 14 or more). The upper limit of the number of atoms constituting the linking chain is not particularly limited as it can be adjusted by polymerization or the like depending on the purpose, and may be, for example, 2000 or less, 1000 or less, 500 or less, 100 or less, 50 or less, 30 or less, or 20 or less. The number of atoms constituting the linking chain that connects the crosslinking reactive groups refers to the minimum number of atoms required to reach another crosslinking reactive group (or, if there are three or more crosslinking reactive groups, the crosslinking reactive group closest to the first crosslinking reactive group) from one crosslinking reactive group in one molecule of the crosslinking agent. The crosslinking agents having the above-mentioned linking chains can be used individually or in combination of two or more. In some preferred embodiments, acyclic bifunctional crosslinking agents can be used as the crosslinking agents. Examples of commercially available crosslinking agents include trade names such as Coronate 2770 (manufactured by Tosoh Corporation), Takenate D178NL (manufactured by Mitsui Chemicals), and Duranate A201H (manufactured by Asahi Kasei Corporation).

[0143] 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, 0.08 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, or 0.4 parts by weight or more.

[0144] 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, zirconium tetraacetylacetonate, 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.

[0145] 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.

[0146] (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.

[0147] (Leveling agent) In some embodiments, the adhesive composition may optionally contain a leveling agent 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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 1H-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).

[0152] 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.

[0153] Monomer raw material B includes monomer S1, as well as an acrylic monomer copolymerizable with monomer S1. This can improve the compatibility of polymer (B) within the adhesive layer. Examples of acrylic monomers that can be used in monomer raw material B include alkyl acrylates. Here, "alkyl" refers to a linear (including linear and branched) alkyl (group) and does not include the alicyclic hydrocarbon group described later. In some embodiments, monomer raw material B is (meth)acrylic acid C 4-12 Alkyl ester (preferably (meth)acrylate C) 4-10 Alkyl esters, for example, (meth)acrylate C 6-10 It may contain at least one alkyl ester. In some other embodiments, monomer raw material B is methacrylate C 1-18 Alkyl ester (preferably C methacrylate) 1-14 Alkyl esters, for example, C methacrylate 1-10 It may contain at least one alkyl ester. Monomer raw material B may contain one or more acrylic monomers selected from, for example, methyl methacrylate (MMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA).

[0154] Other examples of the above-mentioned acrylic monomers include (meth)acrylic acid esters having alicyclic hydrocarbon groups. 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 alicyclic hydrocarbon groups.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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 be 1 part by weight or less, and it may be 0.5 parts by weight or less, or 0.1 parts by weight or less. The technology disclosed herein can be implemented in a manner in which the adhesive composition substantially does not contain polymer (B).

[0160] (High refractive index particles) The adhesive composition 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.

[0161] 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. HRIThe 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.

[0162] particle P HRI The type is not particularly limited, and one or more materials capable of improving the refractive index of the adhesive can be selected and used from among metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. HRI As 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.

[0163] particle PHRI 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 HRI The 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).

[0164] 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.

[0165] Particles P in an adhesive composition HRI The content of the above particles P is not particularly limited. HRI The content of the above particle P may vary depending on the desired refractive index. For example, the above particle P HRI The content of can be appropriately set to have a refractive index above a predetermined level, taking into consideration the required adhesive properties, etc. In some embodiments, particles P in the adhesive composition HRI The content of P in the adhesive formed from the adhesive composition 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. HRIThe lower limit of the content is not particularly limited and may be, for example, more than 0% by weight, 1% or more by weight, or 5% or more by weight. In some other embodiments, particles P in the adhesive composition HRI The content of is, for example, less than 10% by weight, may be less than 1% by weight, or less than 0.1% by weight, in the adhesive formed from the adhesive composition. The technology disclosed herein relates to an adhesive composition in which particles P HRI It may be implemented in a manner that substantially does not include it.

[0166] Particle P in adhesives HRI The content of particle P can also be determined by its relative relationship to the amount of acrylic polymer contained in the adhesive. HRI The content of P can be, for example, approximately 100 parts by weight or less per 100 parts by weight of 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 and may be, for example, more than 0% by weight, 1% or more by weight, or 5% or more by weight. In some embodiments, particle P HRI The content of is, for example, less than 30 parts by weight per 100 parts by weight of acrylic polymer, and may be less than 10 parts by weight, less than 1 part by weight, or less than 0.1 parts by weight.

[0167] (Other additives) Furthermore, the adhesive compositions disclosed herein may optionally contain known additives that can be used in adhesive compositions, such as 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. In addition, separate from the plasticizers disclosed herein, one or more known plasticizers (e.g., phthalate esters, terephthalate esters, adipic acid esters, adipic acid polyesters, glycol benzoate esters, etc.) or liquid camphenephenol or other plasticizing materials may be included. 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.

[0168] <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.

[0169] (Refractive index) The refractive index of the adhesive formed from the adhesive composition disclosed herein is higher than that of conventional acrylic adhesives. The technology disclosed herein provides an adhesive having a refractive index of, for example, 1.55 or higher, an adhesive composition capable of forming the adhesive, and an adhesive sheet containing the adhesive. The refractive index of the adhesive is preferably 1.560 or higher, and more preferably greater than 1.570. In some embodiments, the refractive index of the adhesive may be 1.575 or higher, 1.580 or higher, or 1.585 or higher. An adhesive having such a refractive index can suitably suppress light reflection at the interface with the adherend when applied to a material with a high refractive index. The preferred upper limit of the refractive index of the adhesive is not limited to a specific range, as it may vary depending on the refractive index of the adherend, etc., and may be, for example, 1.700 or less, 1.670 or less, 1.650 or less, 1.620 or less, or 1.600 or less.

[0170] The refractive index of an adhesive can be adjusted, for example, by the composition of the adhesive (e.g., the composition of the monomer components constituting the acrylic polymer). Specifically, this can be done by using an acrylic polymer with a high content of monomer (A1) in the monomer components, or by using an additive (H RO By including ), an adhesive exhibiting a refractive index above a predetermined level can be prepared.

[0171] 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. As an Abbe refractometer, for example, the ATAGO model "DR-M4" 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 the adhesive can be measured by the method described in the examples below.

[0172] (Storage modulus G') The technology disclosed herein makes it possible to achieve a low modulus of elasticity in an adhesive while maintaining a high refractive index. Although not limited to a specific range, the storage modulus of elasticity G'(0°C) of the adhesive at 0°C is, for example, 1.0 × 10⁻⁶. 8 It may be less than Pa, 5.0 × 10 7 It is also acceptable if it is less than Pa, 1.0 × 10 7 It is also acceptable if it is less than Pa, 5.0 × 10 6 It may be less than Pa. The adhesive having the above storage modulus G'(0°C) has moderate flexibility in the temperature range from around 0°C to above, and can adhere well to the adherend, for example. The lower limit of the above storage modulus G'(0°C) is not particularly limited, for example 1.0 × 10 2 It is greater than Pa, and 1.0 × 10 3 It may be Pa or higher. When the storage modulus G'(0°C) is above a predetermined value, the adhesive tends to have appropriate cohesive force, for example, in the range from room temperature to high temperatures. In some preferred embodiments, the storage modulus G'(0°C) of the adhesive is 1.0 × 10⁻⁶. 6 Pa or less, more preferably 5.0 × 10 5It is less than or equal to Pa, and 2.0 × 10 5 It may be less than or equal to Pa, 1.0 × 10 5 It is also acceptable to have a value of less than Pa, 7.0 × 10 4 It is also acceptable to have a value of less than Pa, 5.0 × 10 4 It is also acceptable to have a value of less than Pa, 3.0 × 10 4 It may be less than or equal to Pa. Furthermore, the storage modulus G'(0°C) is preferably 1.0 × 10⁻⁶. 4 Pa or higher, more preferably 2.0 × 10⁻⁶ 4 Pa or higher, more preferably 4.0 × 10 4 It is Pa or higher, 6.0 × 10 4 It can be Pa or higher, 1.0 × 10 5 It may be Pa or higher. An adhesive having a storage modulus G'(0℃) within the above range can achieve both a high refractive index and flexibility, and may have the flexibility to withstand repeated bending operations.

[0173] The storage modulus G'(80°C) of the adhesives disclosed herein is not particularly limited, for example, 1.0 × 10⁻⁶ 5 It is appropriate for the pressure to be less than Pa, preferably 5.0 × 10⁻⁶. 4 Less than Pa, more preferably 3.0 × 10 4 It is less than Pa, and 1.0 × 10 4 It may be less than Pa, 5.0 × 10 3 It may be less than Pa. Adhesives with a limited storage modulus G'(80°C) as described above have good flexibility in the high-temperature range. The lower limit of the storage modulus G'(80°C) is not particularly limited, for example, 1.0 × 10⁻⁶. 2 It is Pa or higher, 5.0 × 10 2 It is appropriate for the Pa level to be above, preferably 1.0 × 10⁻⁶. 3 Pa or higher, more preferably 3.0 × 10 3 It is Pa or higher, 5.0 × 10 3 The storage modulus G'(80°C) described above is preferable because it tends to have moderate cohesive force even in high-temperature ranges and has excellent heat resistance.

[0174] The storage modulus G'(-10°C) of the adhesives disclosed herein is not particularly limited, for example, 1.0 × 10⁻⁶ 9 It may be less than Pa, 1.0 × 10 8 It is also acceptable if it is less than Pa, 1.0 × 10 7 It is appropriate for the pressure to be less than Pa, preferably 5.0 × 10⁻⁶. 6 It is less than or equal to Pa, and 1.0 × 10 6 It may be less than or equal to Pa, 5.0 × 10 5 It is also acceptable to have a value of less than Pa, 1.0 × 10 5 It may be less than Pa. Adhesives with a limited storage modulus G'(-10°C) as described above may have better flexibility. For example, they may have good flexibility in the low temperature range and flexibility that can withstand repeated bending operations over a wide temperature range, including the low temperature range. The lower limit of the storage modulus G'(-10°C) is not particularly limited, for example, 1.0 × 10 2 It is greater than Pa, and 1.0 × 10 3 It is appropriate for the pressure to be Pa or higher, preferably 5.0 × 10⁻⁶. 3 Pa or higher, comfort level 1.0 × 10 4 It is Pa or higher, 5.0 × 10 4 It may be Pa or higher, 1.0 × 10 5 Pa or higher is also acceptable, 5.0 × 10 5 It may be Pa or higher. The adhesive having the above storage modulus G'(-10℃) can be flexible while possessing appropriate cohesive force. Furthermore, the adhesive having the above storage modulus G'(-10℃) tends to easily achieve both a high refractive index and flexibility even in the low-temperature range.

[0175] The storage modulus G'(-20°C) of the adhesives disclosed herein is not particularly limited, for example, 1.0 × 10 10 It may be less than Pa, 1.0 × 10 9 It is also acceptable if it is less than Pa, 5.0 × 10 8 It is appropriate that it be less than or equal to Pa, and 1.0 × 10 8 It may be less than or equal to Pa, 5.0 × 10 7 It is also acceptable to have a value of less than Pa, 1.0 × 10 7 It is also acceptable to have a value of less than Pa, 5.0 × 106 It is also acceptable to have a value of less than Pa, 1.0 × 10 6 It is also acceptable to have a value of less than Pa, 5.0 × 10 5 It may be less than Pa. Adhesives with a limited storage modulus G'(-20°C) as described above may have particularly excellent flexibility. For example, they may have good flexibility in a lower temperature range and flexibility that can withstand repeated bending operations over a wide temperature range, including low temperatures. The lower limit of the storage modulus G'(-20°C) is not particularly limited, for example, 1.0 × 10 2 It is greater than Pa, and 1.0 × 10 3 It is appropriate for the Pa level to be above, preferably 1.0 × 10⁻⁶. 4 Pa or higher, comfort level 1.0 × 10 5 It is Pa or higher, 5.0 × 10 5 It may be Pa or higher, 1.0 × 10 6 It may be Pa or higher. The adhesive having the above storage modulus G'(-20℃) can be flexible while possessing appropriate cohesive force. Furthermore, the adhesive having the above storage modulus G'(-20℃) tends to easily achieve both a high refractive index and flexibility even in the low-temperature range.

[0176] (Storage modulus ratio) In some embodiments, an adhesive is used in which the ratio of the storage modulus G'(0°C) at 0°C to the storage modulus G'(80°C) at 80°C (G'(0°C) / G'(80°C)) is in the range of 1 to 1000. With an adhesive that satisfies the above characteristics, the change in the modulus is suppressed over a wide temperature range from 0°C to high temperatures, so it is easy to exhibit stable properties (flexibility, etc.) with respect to temperature changes. The above ratio (G'(0°C) / G'(80°C)) is suitable to be 300 or less, preferably 100 or less, more preferably 50 or less, and may also be 25 or less, 10 or less, or 5 or less. The lower limit of the above ratio (G'(0°C) / G'(80°C)) may be, for example, 2 or more, or 3 or more.

[0177] In some embodiments, the adhesive used is one in which the ratio of the storage modulus G'(-10°C) at -10°C to the storage modulus G'(80°C) at 80°C (G'(-10°C) / G'(80°C)) is in the range of 1 to 1000. Adhesives satisfying the above characteristics are preferable because they suppress changes in the modulus over a wide temperature range from low to high temperatures, thus exhibiting stable properties (flexibility, etc.) with respect to temperature changes. The ratio (G'(-10°C) / G'(80°C)) is suitable to be 300 or less, preferably 150 or less, more preferably 100 or less, and may also be 50 or less, 30 or less, 20 or less, or 10 or less. The lower limit of the ratio (G'(-10°C) / G'(80°C)) may be, for example, 2 or more, or 3 or more.

[0178] In some embodiments, an adhesive is used in which the ratio of the storage modulus G'(-20°C) at -20°C to the storage modulus G'(80°C) at 80°C (G'(-20°C) / G'(80°C)) is in the range of 1 to 1000. With an adhesive that satisfies the above characteristics, the change in the modulus is suppressed over a wide temperature range from lower to higher temperatures, so that it can exhibit stable properties (flexibility, etc.) with respect to temperature changes. The above ratio (G'(-20°C) / G'(80°C)) may be 500 or less, 300 or less, 150 or less, 100 or less, 50 or less, or 30 or less. The lower limit of the above ratio (G'(-20°C) / G'(80°C)) may be, for example, 5 or more, 10 or more, 50 or more, or 100 or more.

[0179] The glass transition temperature (Tg) of the adhesive is not particularly limited and can be set considering flexibility in the low temperature range and cohesive force (heat resistance, etc.) in the high temperature range. In some embodiments, the Tg of the adhesive is, for example, 30°C or less, but may also be 15°C or less, or 5°C or less. In some preferred embodiments, the Tg of the adhesive is, from the viewpoint of flexibility, 0°C or less, more preferably -5°C or less, even more preferably -10°C or less, and may also be -15°C or less (e.g., -20°C or less). The lower the Tg of the adhesive, the better the adhesive properties, such as adhesion to the adherend. Also, by setting the Tg of the adhesive low, it is possible to suppress changes in the elastic modulus in the temperature range higher than the Tg. The lower limit of the Tg of the adhesive is, for example, -50°C or higher, -40°C or higher is appropriate, and may also be -30°C or higher. Adhesives having the above Tg tend to easily obtain appropriate cohesive force. Also, there is a tendency to form adhesives that achieve both a high refractive index and a low elastic modulus.

[0180] The storage modulus G' and glass transition temperature Tg of the adhesive at each of the above temperatures can be measured by the method described in the examples below, and each storage modulus ratio can be calculated from the results. Each storage modulus G', each storage modulus ratio, and glass transition temperature Tg of the adhesive can be adjusted, for example, by selecting the composition of the monomer components constituting the acrylic polymer (e.g., selection of the type and content of monomer (A1)), selecting the type and amount of plasticizer used, whether or not to use a crosslinking agent, and the selection of its type and amount, whether or not to use an additive, and the selection of its type and amount, etc.

[0181] <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.

[0182] 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 is preferably implemented in the form of a substrate-less adhesive sheet consisting of an adhesive layer, from the viewpoint of flexibility to follow an adherend that is repeatedly bent. The above-mentioned substrate-less adhesive sheet is also preferable from the viewpoint of reducing the thickness of the adhesive sheet and increasing the transparency of the adhesive sheet.

[0183] 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 3 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.

[0184] 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.

[0185] (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.

[0186] 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 is appropriately 5 μm or more, may be 10 μm or more, 15 μm or more, 20 μm or more, 30 μm or more, 50 μm or more, 70 μm or more, or 85 μm or more. 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. In some preferred embodiments, the thickness of the adhesive layer is 100 μm or less, more preferably 75 μm or less, even more preferably 70 μm or less, may be 50 μm or less, or 30 μm or less. Not having an excessively large thickness of the adhesive layer can be advantageous from the viewpoint of making the adhesive sheet thinner. Furthermore, thin adhesive layers tend to exhibit superior conformability to the adherend. The technology disclosed herein can preferably be implemented, for example, in a manner 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, and even more preferably 5 μm to 75 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 a substrate, the above-mentioned thickness of the adhesive layer can apply 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. 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.

[0187] In some embodiments, the product of the storage modulus of the adhesive at 0°C G'(0°C)[Pa] and the thickness of the adhesive layer T[μm] (G'(0°C)×T) is, for example, 5.0×10 4 ~7.5×10 7 It is appropriate that it be within the range of 5.0 × 10 4 ~5.0×10 7It is preferably within the range. In a thin pressure-sensitive adhesive layer, even if the elastic modulus is relatively high, the product G'(0°C)×T falling within the above range tends to allow the pressure-sensitive adhesive layer to readily exhibit good flexibility. In addition, since the product G'(0°C)×T is limited to a predetermined value or less, the upper limits of the thickness of the pressure-sensitive adhesive layer and the storage elastic modulus G'(0°C) are restricted, which makes it easy to obtain excellent flexibility. In some preferred embodiments, the product G'(0°C)×T is 1.0×10 5 or higher, or may be 2.0×10 5 or higher, or may be 8.0×10 5 or higher. In addition, the product G'(0°C)×T may be 2.0×10 7 or less, or may be 1.0×10 7 or less, or may be 6.0×10 6 or less.

[0188] (Haze Value) In some embodiments, the haze value of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet may be, for example, 5.0% or less, preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less, and may be 0.9% or less, 0.8% or less, 0.5% or less, or 0.3% or less. Such a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer with high transparency can be preferably applied to applications requiring high light transmittance (e.g., optical applications), regardless of whether it has a substrate or not, and to applications requiring performance that allows an adherend to be clearly viewed through the pressure-sensitive adhesive sheet. The lower limit of the haze value of the pressure-sensitive adhesive layer is not particularly limited, and from the viewpoint of improving transparency, a smaller haze value is more preferable. On the other hand, in some embodiments, in consideration of refractive index and pressure-sensitive adhesive properties, the haze value may be, for example, 0.05% or more, or 0.10% or more. These haze values for the pressure-sensitive adhesive layer can also be preferably applied to the haze value of a pressure-sensitive adhesive sheet when the technology disclosed herein is implemented in the form of a substrate-free pressure-sensitive adhesive sheet (typically, a pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer).

[0189] Here, the "haze value" refers to the ratio of diffuse transmitted light to total transmitted light when visible light is irradiated onto a measurement object. It is also referred to as cloudiness value. The haze value can be expressed by the following formula. Th(%)=Td / Tt×100 In the above formula, Th is the haze value (%), Td is the scattered light transmittance, and Tt is the total light transmittance. The measurement of the haze value can be performed according to the method described in the examples mentioned later. The haze value of the pressure-sensitive adhesive layer can be adjusted, for example, by selecting the composition, thickness and the like of the pressure-sensitive adhesive layer.

[0190] In some embodiments, the haze value of the pressure-sensitive adhesive sheet may be, for example, 5.0% or less, preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less, and may be 0.9% or less, 0.8% or less, 0.5% or less, or 0.3% or less. Such a highly transparent pressure-sensitive adhesive sheet can be suitably applied to uses requiring high light transmittance (for example, optical uses) and uses requiring the ability to favorably visually recognize an adherend through the pressure-sensitive adhesive sheet. The lower limit of the haze value of the pressure-sensitive adhesive sheet is not particularly limited, and from the viewpoint of improving transparency, the smaller the haze value is, the more preferable it is. On the other hand, in some embodiments, in consideration of refractive index and pressure-sensitive adhesive properties, the haze value may be, for example, 0.05% or more, or may be 0.10% or more. The haze value of the pressure-sensitive adhesive sheet can be measured by the same method as the measurement of the haze value of the pressure-sensitive adhesive layer described above. The above haze value of the pressure-sensitive adhesive sheet can be obtained by the composition of the pressure-sensitive adhesive layer described above, or by selecting the type and thickness of the substrate in a configuration including a substrate.

[0191] In some embodiments, the total light transmittance of the adhesive layer is preferably 85.0% or higher (for example, 88.0% or higher, 90.0% or higher, or greater than 90.0%). Adhesive sheets having such a highly transparent adhesive layer can be preferably applied to applications where high light transmittance is required (e.g., optical applications) or applications where the adherend can be clearly seen through the adhesive sheet, with or without a substrate. 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 light transmittance meter, the "HAZEMETER HM-150" manufactured by Murakami Color Technology Laboratory or an equivalent product is used. The total light transmittance can be measured according to the method described in the examples below. The total light transmittance of the adhesive layer can be adjusted, for example, by selecting the composition and thickness of the adhesive layer.

[0192] In some embodiments, the total light transmittance of the adhesive sheet is preferably 85.0% or higher (for example, 88.0% or higher, 90.0% or higher, or greater than 90.0%). Such highly transparent adhesive sheets can be preferably applied to applications requiring high light transmittance (e.g., optical applications) or applications requiring good visibility of the adherend through the adhesive sheet. The upper limit of the total light transmittance may practically be 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 sheet may be approximately 94% or less, approximately 93% or less, or approximately 92% or less. The total light transmittance of the adhesive sheet can be measured in the same way as the measurement of the total light transmittance of the adhesive layer described above. The total light transmittance of the adhesive sheet can be obtained by selecting the composition of the adhesive layer described above, or, in configurations with a substrate, by selecting the type and thickness of the substrate.

[0193] (Peel strength) The peel strength of the adhesive sheet to the glass plate is not particularly limited. In some embodiments, the adhesive sheet may have a peel strength to the glass plate of, for example, 0.1 N / 25 mm or more, or 0.5 N / 25 mm or more. In some preferred embodiments, the peel strength to the glass plate is 1.0 N / 25 mm or more, more preferably 1.5 N / 25 mm or more, even more preferably 2.0 N / 25 mm or more, and may also be 3.0 N / 25 mm or more, 5.0 N / 25 mm or more, or 10 N / 25 mm or more. An adhesive sheet having a peel strength to the glass plate of such a predetermined value or more is suitable for joining and fixing, for example, glass components. 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.

[0194] 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 peel strength under conditions of a peel angle of 180 degrees and a 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.

[0195] (Thickness of the adhesive sheet) The thickness of the adhesive sheet (substrate-less adhesive sheet or substrate-attached adhesive sheet) disclosed herein may be, for example, 1000 μm or less, 350 μm or less, 200 μm or less, 120 μm or less, 75 μm or less, or 50 μm or less. Furthermore, from the viewpoint of handling and other factors, the thickness of the adhesive sheet may be, for example, 5 μm or more, 10 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more. 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.

[0196] <Support 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 or blended 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.

[0197] 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).

[0198] Examples of resin materials that can be used to constitute the resin film include polyester; polyolefins; polycycloolefins derived from monomers having aliphatic ring structures such as norbornene structures; polyamides (PA) such as nylon 6, nylon 66, and partially aromatic polyamides; polyimides (PI) such as transparent polyimide (CPI); polyamide-imide (PAI); polyetheretherketone (PEEK); polyethersulfone (PES); polyphenylene sulfide (PPS); polycarbonate (PC); polyurethane (PU); ethylene-vinyl acetate copolymer (EVA); fluororesins such as polytetrafluoroethylene (PTFE); acrylic resins; cellulosic polymers such as triacetylcellulose (TAC); polyarylate; polystyrene; polyvinyl chloride; and polyvinylidene chloride.

[0199] 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, cycloolefin polymer (COP) film, CPI film, TAC 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.

[0200] 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.

[0201] 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.

[0202] 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.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] <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.

[0207] 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, ethylene-vinyl acetate copolymer film, etc. 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.

[0208] <Application> The application of the pressure-sensitive adhesive sheet disclosed herein is not limited, and it can be used for various purposes. Since the pressure-sensitive adhesive sheet disclosed herein comprises a pressure-sensitive adhesive that achieves both a high refractive index and a low elastic modulus, it can be utilized in various applications that require high refractive index and flexibility by taking advantage of this characteristic. For example, in electronic equipment such as portable electronic devices, it is suitable as a pressure-sensitive adhesive sheet for various devices (optical devices) including display devices (image display devices) such as liquid crystal display devices, organic EL (electroluminescence) display devices, PDP (plasma display panels), and electronic paper, input devices such as touch panels, and particularly for foldable displays and rollable displays. For example, in foldable displays and rollable displays, it is preferably used as a means for bonding, fixing, and protecting members having a high refractive index. Since the pressure-sensitive adhesive sheet disclosed herein can have flexibility that withstands repeated bending operations while having a high refractive index, it can favorably follow an adherend (such as a foldable display) that is repeatedly bent when attached to a foldable display or a rollable display. Examples of objects to be bonded in such usage include glass members such as window glass and cover glass used in foldable displays and rollable displays. Furthermore, the pressure-sensitive adhesive sheet disclosed herein can easily follow and adhere to curved surfaces such as the three-dimensional shape of portable electronic devices, and therefore is also suitable for use in electronic devices having such curved shapes. In some preferred embodiments, in addition to having a high refractive index and a low elastic modulus, the pressure-sensitive adhesive can also be excellent in heat resistance. The aforementioned portable electronic devices may be used in high-temperature environments, and their internal spaces may be heated by heat generated from electronic components, so there are significant advantages to using the heat-resistant pressure-sensitive adhesive sheet described above.

[0209] Examples of portable electronic devices include, for example, mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (e.g., wristwear-type devices worn on the wrist like watches, modular devices attached to a part of the body with clips or straps, eyewear-type devices including glasses (monocular and binocular, including head-mounted types), clothing-type devices attached to shirts, socks, hats, etc. as accessories, earwear-type devices attached to the ears like earphones, etc.), digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game consoles, electronic dictionaries, electronic organizers, e-books, in-car information equipment, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, "portable" means not merely being able to carry something, but having a level of portability that allows an individual (a typical adult) to carry it relatively easily.

[0210] 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.

[0211] 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.

[0212] 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.

[0213] 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.

[0214] 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).

[0215] 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.

[0216] Examples of the above-mentioned display devices include liquid crystal displays, organic EL displays, micro-LEDs (μLEDs), mini-LEDs (miniLEDs), PDPs, and electronic paper. Examples of the above-mentioned input devices include touch panels.

[0217] The optical components mentioned above are not particularly limited, but examples include components made of glass, acrylic resin, polycarbonate, PET, 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).

[0218] 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.

[0219] 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.

[0220] 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.

[0221] 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 improving brightness, it is preferable that the adhesive sheet has low coloration. This is also advantageous from the viewpoint of suppressing unintentional coloration caused by the adhesive sheet.

[0222] 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.

[0223] 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.

[0224] 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.

[0225] 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.

[0226] As can be understood from the above description and the following examples, the matters disclosed in this specification include the following: [1] comprising an acrylic polymer and a plasticizer, The monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1), The plasticizer is an adhesive composition having two or more double-bond-containing rings and being liquid at 30°C. [2] The adhesive composition according to [1] above, wherein the compound is a liquid compound at 20°C. [3] The adhesive composition according to [1] or [2] above, wherein the plasticizer is contained in an amount exceeding 15 parts by weight per 100 parts by weight of the acrylic polymer. [4] The adhesive composition according to any one of [1] to [3] above, wherein the plasticizer is contained in more than 30 parts by weight per 100 parts by weight of the acrylic polymer. [5] The adhesive composition according to any one of [1] to [4] above, wherein the plasticizer has at least one ring selected from aromatic rings and heterocycles as the double bond-containing ring. [6] The adhesive composition according to any one of [1] to [5] above, wherein the plasticizer has a first double bond-containing ring and a second double bond-containing ring, and the first double bond-containing ring and the second double bond-containing ring are linked via a linking group having 1 to 5 atoms. [7] The adhesive composition according to any one of [1] to [6] above, wherein the molecular weight of the plasticizer is in the range of 100 to 2000. [8] The adhesive composition according to any one of [1] to [7] above, wherein the monomer component constituting the acrylic polymer contains, in addition to the aromatic ring-containing monomer (A1), a monomer (A2) having at least one of a hydroxyl group and a carboxyl group. [9] The adhesive composition according to any one of [1] to [8] above, wherein the content of the aromatic ring-containing monomer (A1) in the monomer component is 60% by weight or more.

[10] The adhesive composition according to any one of [1] to [9] 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.

[0227]

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

[12] The refractive index is 1.55 or higher, and the storage modulus G'(0°C) at 0°C is 1.0 × 10⁻⁶ 4 Pa~1.0×10 6The adhesive described in

[11] above, which is within the range of Pa.

[13] The adhesive described in

[11] or

[12] above, wherein the glass transition temperature is in the range of -50°C to 0°C.

[14] An adhesive according to any one of

[11] to

[13] above, wherein the ratio of the storage modulus G'(0°C) to the storage modulus G'(80°C) at 80°C (G'(0°C) / G'(80°C)) is in the range of 1 to 1000.

[15] An adhesive according to any of

[11] to

[14] above, wherein the ratio of the storage modulus G'(-10°C) at -10°C to the storage modulus G'(80°C) at 80°C (G'(-10°C) / G'(80°C)) is in the range of 1 to 1000.

[0228]

[16] An adhesive sheet comprising an adhesive layer formed from any of the adhesive compositions described in [1] to [9] above.

[17] An adhesive sheet comprising an adhesive layer made of any of the adhesives described in

[11] to

[15] above.

[18] The adhesive sheet according to

[16] or

[17] above, wherein the thickness of the adhesive layer is in the range of 5 to 75 μm.

[19] The product of the storage modulus G'(0°C)[Pa] at 0°C and the thickness T[μm] of the adhesive layer (G'(0°C)×T) is 5.0×10 4 ~5.0×10 7 An adhesive sheet described in any of the above

[16] to

[18] , which is within the range.

[20] An adhesive sheet as described in any of

[16] to

[19] above, having a total light transmittance of 85% or more.

[21] An adhesive sheet as described in any of

[16] to

[20] above, having a haze value of 3% or less.

[22] An adhesive sheet according to any of

[16] to

[21] above, wherein the peel strength to a glass plate is 0.1 N / 25 mm or more. [Examples]

[0229] The following describes several embodiments relating to the present invention, but the present invention is not intended to be limited to these specific examples. In the following description, "parts" and "%" used to express the amount used or content refer to weight unless otherwise specified.

[0230] <Example 1> (Preparation of acrylic polymer solutions) In a four-necked flask equipped with a stirring blade, thermometer, nitrogen gas inlet tube, and condenser, 95 parts of m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A", refractive index: 1.566, homopolymer Tg: -35℃; hereinafter referred to as "POB-A") and 5 parts of 4-hydroxybutyl acrylate (4HBA) were charged as monomer components, 0.2 parts of 2,2'-azobisisobutyronitrile as a polymerization initiator, and 150 parts of ethyl acetate as a polymerization solvent. Nitrogen gas was introduced while gently stirring, and the polymerization reaction was carried out for 6 hours while maintaining the liquid temperature in the flask at around 60℃ to prepare a 40% solution of acrylic polymer P1. The Mw of acrylic polymer P1 was 500,000.

[0231] (Preparation of adhesive composition) A 40% solution of the above-mentioned 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 the acrylic adhesive composition according to this example.

[0232] (Making adhesive sheets) The acrylic adhesive composition 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 consisting of the above adhesive layer was obtained. Both sides of this adhesive sheet are protected by PET films (release liners) R1 and R2.

[0233] <Example 2> (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 parts of benzyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscote #160", refractive index: 1.519, homopolymer Tg: 6°C; hereinafter referred to as "BZA") and 1 part of 4HBA as monomer components, 0.2 parts of 2,2'-azobisisobutyronitrile as polymerization initiator, and 100 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 solution of acrylic polymer P2 (polymer concentration 50%). The Mw of acrylic polymer P2 was 1 million.

[0234] (Preparation of adhesive composition) A solution of the above-mentioned acrylic polymer P2 (polymer concentration 50%) was diluted with ethyl acetate to a polymer concentration of 30%. To 334 parts of this solution (100 parts non-volatile content), 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 was added, 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 was added and stirred to prepare the acrylic adhesive composition according to this example.

[0235] (Making adhesive sheets) Using the obtained acrylic adhesive composition, an adhesive sheet (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) according to this example was prepared in the same manner as in Example 1.

[0236] <Examples 3-5> In preparing the acrylic adhesive composition in Example 2, 30 parts (Example 3), 45 parts (Example 4), or 60 parts (Example 5) of POB-A (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB-A", m-phenoxybenzyl acrylate, refractive index: 1.566, liquid at 20°C) were added as plasticizer A1 to 100 parts of the non-volatile content contained in the solution of acrylic polymer P2. Otherwise, the acrylic adhesive composition for each example was prepared in the same manner as the preparation of the acrylic adhesive composition in Example 2. Using the obtained acrylic adhesive composition, adhesive sheets (substrate-less double-sided adhesive sheets consisting of an adhesive layer) for each example were prepared in the same manner as the preparation of the adhesive sheet in Example 1.

[0237] <Example 6> A solution of acrylic polymer P3 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 2, except that the monomer component composition was changed to 99 parts of phenoxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat #192", refractive index: 1.517, homopolymer Tg: 2℃; hereinafter referred to as "PEA") and 1 part of 4HBA. The Mw of acrylic polymer P3 was 1 million. The acrylic adhesive composition according to this example was prepared in the same manner as the preparation of the acrylic adhesive composition in Example 2, except that a solution of acrylic polymer P3 was used instead of a solution of acrylic polymer P2. Using the obtained acrylic adhesive composition, an adhesive sheet according to this example (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) was prepared in the same manner as in Example 1.

[0238] <Example 7> In the preparation of the acrylic adhesive composition in Example 3, a solution of acrylic polymer P3 was used instead of a solution of acrylic polymer P2. The acrylic adhesive composition according to this example was prepared in the same manner as in Example 3, and an adhesive sheet according to this example (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) was prepared using the obtained acrylic adhesive composition in the same manner as in Example 1.

[0239] <Example 8> A solution of acrylic polymer P4 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 2, except that the monomer component composition was changed to 99 parts of BZA and 1 part of acrylic acid (AA). The Mw of acrylic polymer P4 was 1 million. A solution of the above-mentioned acrylic polymer P4 (polymer concentration 50%) was diluted with ethyl acetate to a polymer concentration of 30%. 334 parts of this solution (100 parts non-volatile content) were mixed with 0.1 parts of an epoxy crosslinking agent (manufactured by Mitsubishi Gas Chemical Co., Ltd., trade name "Tetrad C", 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) as a crosslinking agent, and the mixture was stirred to prepare the acrylic adhesive composition according to this example. An adhesive sheet (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) according to this example was prepared in the same manner as the adhesive sheet preparation in Example 1, except that the obtained acrylic adhesive composition was used.

[0240] <Examples 9-12> In preparing the acrylic adhesive composition in Example 8, the acrylic adhesive composition for each example was prepared in the same manner as in Example 8, except that 60 parts of POB-A as plasticizer A1 (Example 9), 60 parts of 4,4′-oxybis[(methoxymethyl)benzene] (manufactured by Tokyo Chemical Industry Co., Ltd., refractive index: 1.56, liquid at 20°C) as plasticizer A2 (Example 10), 60 parts of 3-phenoxybenzyl alcohol (manufactured by Tokyo Chemical Industry Co., Ltd., refractive index: 1.591, liquid at 20°C) as plasticizer A3 (Example 11), or 60 parts of 1-acetonaphthone (manufactured by Tokyo Chemical Industry Co., Ltd., refractive index: 1.63, liquid at 20°C) as plasticizer A4 (Example 12) were added to 100 parts of the non-volatile content contained in the solution of acrylic polymer P4. Except for using the obtained acrylic adhesive compositions, adhesive sheets (substrate-less double-sided adhesive sheets consisting of an adhesive layer) were prepared in the same manner as in Example 1.

[0241] <Example 13> A solution of acrylic polymer P5 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 2, except that the monomer component composition was changed to 90 parts BZA, 9 parts n-butyl acrylate (BA), and 1 part AA. The Mw of acrylic polymer P5 was 1 million. A solution of the above-mentioned acrylic polymer P5 (polymer concentration 50%) was diluted with ethyl acetate to a polymer concentration of 30%. 334 parts of this solution (100 parts non-volatile content) were mixed with 60 parts of the above-mentioned plasticizer A3 (POB-AL) and 0.1 parts of the above-mentioned epoxy crosslinking agent, and the mixture was stirred to prepare the acrylic adhesive composition according to this example. An adhesive sheet (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) according to this example was prepared in the same manner as the adhesive sheet preparation in Example 1, except that the obtained acrylic adhesive composition was used.

[0242] <Example 14> In preparing the acrylic adhesive composition in Example 13, 15 parts of biscresol fluorene (manufactured by Osaka Gas Chemical Co., Ltd., 9,9-bis(4-hydroxy-3-methylphenyl)fluorene, refractive index: 1.68; hereinafter sometimes referred to as "BCF") were added as solids to 100 parts of the non-volatile content in the solution of acrylic polymer P5. Otherwise, the acrylic adhesive composition according to this example was prepared in the same manner as the acrylic adhesive composition in Example 13. The above additive was added as a 10% ethyl acetate solution. An adhesive sheet (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) according to this example was prepared in the same manner as the adhesive sheet preparation in Example 1, except that the obtained acrylic adhesive composition was used.

[0243] <Examples 15-16> A solution of acrylic polymer P6 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 2, except that the monomer component composition was changed to 90 parts BZA, 9 parts 2-ethylhexyl acrylate (2EHA), and 1 part AA. The Mw of acrylic polymer P6 was 1 million. In the preparation of the acrylic adhesive compositions in Examples 13 and 14, a solution of acrylic polymer P6 was used instead of a solution of acrylic polymer P5. The acrylic adhesive compositions for Examples 15 and 16 were prepared in the same manner as in Examples 13 and 14, and using the obtained acrylic adhesive compositions, adhesive sheets (substrate-less double-sided adhesive sheets consisting of an adhesive layer) for each example were prepared in the same manner as in Example 1.

[0244] <Examples 17-18> A solution of acrylic polymer P7 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 2, except that the monomer component composition was changed to 80 parts BZA, 19 parts BA, and 1 part AA. Similarly, a solution of acrylic polymer P8 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 2, except that the monomer component composition was changed to 66 parts BZA, 33 parts BA, and 1 part AA. The Mw of acrylic polymers P7 and P8 was 1 million. In preparing the acrylic adhesive composition in Example 13, a solution of acrylic polymer P7 (Example 17) or P8 (Example 18) was used instead of a solution of acrylic polymer P5. The acrylic adhesive compositions for Examples 17 and 18 were prepared in the same manner as in Example 13, and adhesive sheets (substrate-less double-sided adhesive sheets consisting of an adhesive layer) for each example were prepared using the obtained acrylic adhesive compositions in the same manner as in Example 1.

[0245] <Example 19> A solution of acrylic polymer P9 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 2, except that the monomer component composition was changed to 85 parts POB-A, 14 parts BA, and 1 part AA. The Mw of acrylic polymer P9 was 1 million. In the preparation of the acrylic adhesive composition in Example 13, a solution of acrylic polymer P9 was used instead of a solution of acrylic polymer P5. The acrylic adhesive composition according to this example was prepared in the same manner as in Example 13, and an adhesive sheet according to this example (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) was prepared using the obtained acrylic adhesive composition in the same manner as in Example 1.

[0246] <Example 20> In the preparation of the acrylic adhesive composition in Example 19, 23 parts of 6-acryloyloxymethyldinaphthothiophene (trade name "6MDNTA" manufactured by Sugai Chemical Industry Co., Ltd., dinaphthothiophene-6-methyl acrylate, refractive index 1.75; hereinafter sometimes referred to as "6MDNTA") were added as an additive to 100 parts of the non-volatile content contained in the solution of acrylic polymer P9. The acrylic adhesive composition according to this example was prepared in the same manner as in the preparation of the acrylic adhesive composition in Example 19, and an adhesive sheet according to this example (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) was prepared using the obtained acrylic adhesive composition in the same manner as in Example 1. The above additive was added as a 10% ethyl acetate solution.

[0247] <Examples 21-22> A solution of acrylic polymer P10 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 2, except that the monomer component composition was changed to 80 parts POB-A, 19 parts BA, and 1 part AA. The Mw of acrylic polymer P10 was 1 million. In the preparation of the acrylic adhesive composition in Example 13, a solution of acrylic polymer P10 was used instead of a solution of acrylic polymer P5. The acrylic adhesive composition according to Example 21 was prepared in the same manner as in Example 13. Furthermore, in the preparation of the acrylic adhesive composition according to Example 21, the amount of the epoxy crosslinking agent used per 100 parts of nonvolatile content in the solution of acrylic polymer P10 was changed to 0.5 parts to prepare the acrylic adhesive composition according to Example 22. Using each of the obtained acrylic adhesive compositions, adhesive sheets (substrate-less double-sided adhesive sheets consisting of an adhesive layer) corresponding to each example were prepared in the same manner as in Example 1.

[0248] <Example 23> A solution of acrylic polymer P11 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 1, except that the monomer component composition was changed to 99 parts of POB-A and 1 part of 2-acryloyloxyethyl succinic acid (manufactured by Kyoeisha Chemical Co., Ltd., trade name "HOA-MS(N)", hereinafter referred to as "HOA-MS"). The Mw of acrylic polymer P11 was 500,000. The above acrylic polymer P11 solution was diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (100 parts non-volatile content) were mixed with 40 parts of the above plasticizer A3 (POB-AL), 20 parts of trimethylpentaphenyltrisiloxane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "HIVAC F-5", molecular weight: 546, refractive index: 1.575, liquid at 20°C) as plasticizer A5, and 0.3 parts of the above epoxy crosslinking agent (hereinafter also referred to as crosslinking agent C1), and stirred to prepare the acrylic adhesive composition according to this example. An adhesive sheet (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) according to this example was prepared in the same manner as the adhesive sheet preparation in Example 1, except that the obtained acrylic adhesive composition was used.

[0249] <Example 24> A solution of acrylic polymer P12 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 23, except that the monomer component composition was changed to 95 parts POB-A, 2 parts lauryl acrylate (LA), 2 parts 2EHA, and 1 part 4HBA. The Mw of acrylic polymer P12 was 500,000. The above acrylic polymer P12 solution was diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (100 parts non-volatile content) were mixed with 40 parts of the above plasticizer A3 (POB-AL), 20 parts of the above plasticizer A5 (HIVAC F-5), 0.3 parts of an acyclic bifunctional isocyanate crosslinking agent C2 (manufactured by Tosoh Corporation, trade name "Coronate 2770", hexamethylene diisocyanate (HDI) allophanate), 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of ferric narcem (0.01 parts non-volatile content) as a crosslinking catalyst, and stirred to prepare the acrylic adhesive composition according to this example. An adhesive sheet (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) according to this example was prepared in the same manner as the adhesive sheet preparation in Example 1, except that the obtained acrylic adhesive composition was used.

[0250] <Example 25> A solution of acrylic polymer P13 was prepared in the same manner as the preparation of the acrylic polymer solution in Example 23, except that the monomer component composition was changed to 90 parts POB-A, 9 parts 2EHA, and 1 part 4HBA. The Mw of acrylic polymer P13 was 500,000. The above acrylic polymer P13 solution was diluted with ethyl acetate to a polymer concentration of 30%. 334 parts of this solution (100 parts non-volatile content) were mixed with 80 parts of the above plasticizer A5 (HIVAC F-5), 0.5 parts of the above crosslinking agent C2 (Coronate 2770), 2 parts of acetylacetone as a crosslinking retarder, and 1 part of a 1% ethyl acetate solution of ferric narcem (0.01 parts non-volatile content) as a crosslinking catalyst. The mixture was stirred to prepare the acrylic adhesive composition according to this example. An adhesive sheet (a substrate-less double-sided adhesive sheet consisting of an adhesive layer) according to this example was prepared in the same manner as the adhesive sheet preparation in Example 1, except that the obtained acrylic adhesive composition was used.

[0251] <Examples 26-28> Solutions of acrylic polymers P14 and P15 were prepared in the same manner as in Example 23, except that the monomer component composition was changed as shown in Table 3. The Mw values ​​of acrylic polymers P14 and P15 were 500,000 each. The solutions of the above acrylic polymers P11, P14, or P15 were diluted with ethyl acetate to a polymer concentration of 30%. To 334 parts of this solution (100 parts non-volatile content), the above plasticizer A3 and the above crosslinking agent C1 or C2 were added as shown in Table 3. For Examples 26 and 28, 2 parts of acetylacetone as a crosslinking retarder and 1 part of a 1% ethyl acetate solution of ferric narcem (0.01 parts non-volatile content) as a crosslinking catalyst were added and stirred to prepare the acrylic adhesive compositions for each example. Adhesive sheets (substrate-less double-sided adhesive sheets consisting of an adhesive layer) for each example were prepared in the same manner as in Example 1, except that the obtained acrylic adhesive composition was used.

[0252] <Evaluation Method> (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.

[0253] (Storage modulus G' and glass transition temperature) The adhesive layers for each example were stacked to a thickness of approximately 1.5 mm to create a sample for measurement. 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' [Pa] of the adhesive at each temperature (-20°C, -10°C, 0°C, and 80°C) was determined. In addition, the temperature corresponding to the peak top temperature of the loss tangent tanδ (loss modulus G'' / storage modulus G') in the above dynamic viscoelasticity measurement was determined as the glass transition temperature (Tg) [°C] of the adhesive. [Measurement conditions] Transformation mode: Twist Measurement frequency: 1Hz Temperature range: -50℃ to 150℃ Heating rate: 5°C / min Shape: Parallel plate 7.9mmφ

[0254] (Total light transmittance and haze) 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%). The total light transmittance and haze of these specimens were measured using a haze meter (HM-150, manufactured by Murakami Color Technology Laboratory) at a measurement environment of 23°C. The values ​​obtained by subtracting the total light transmittance and haze of the alkali-free glass from the measured values ​​were defined as the total light transmittance [%] and haze [%] of the adhesive (layer). For substrate-less adhesive sheets consisting of the above adhesive layer, the total light transmittance [%] and haze [%] of the adhesive layer become the total light transmittance [%] and haze [%] of the adhesive sheet.

[0255] (Peel strength against glass plate) Under a measurement environment of 23°C and 50% RH, the release liner was peeled off one side of the adhesive sheet, a 50 μm thick PET film was bonded to the backing, and the sheet was cut to a size of 25 mm wide and 100 mm long to serve as the test specimen. The release liner was peeled off the other side of the test specimen and pressed onto the surface of an alkali glass plate (Matsunami Glass Industry Co., Ltd., 1.35 mm thick, blue plate with polished edge) using a 2 kg roller for one back-and-forth motion. After leaving this in the same environment for 30 minutes, the peel strength (adhesion strength) [N / 25 mm] was measured using a universal tensile and compression tester in accordance with JIS Z 0237:2000, under conditions of a tensile speed of 300 mm / min and a peel angle of 180 degrees. The universal tensile and compression tester used was the "Tensile and Compression Tester, TG-1kN" manufactured by Minebea Co., Ltd. Note that PET film backing is not mandatory for single-sided adhesive sheets with a substrate.

[0256] (Bending test) A 2cm x 10cm rectangle was cut from the adhesive sheet with a release liner for each example to obtain a test specimen. A cylindrical rod with a diameter of φ4mm was fixed horizontally at a height sufficient for measurement, and the test specimen obtained above was placed on the rod and bent. Specifically, the test specimen was placed on the rod at its central part in the longitudinal direction, forming an inverted U-shape. The lower ends of the test specimen were fixed with clips (13g), and a 60g weight was suspended from the clips via a 1cm long thread, applying a load to the bent part of the test specimen. In this state, the test specimen was held in a predetermined temperature environment (-20℃, -10℃, or 0℃) for 1 minute, and after 1 minute, the test specimen was removed from the rod. Then, in the same temperature environment, the test specimen was placed on a horizontal surface with the peak of its bend facing downwards and left to stand for 10 minutes. The time until the end (short side end) of the test specimen touched the horizontal surface after 10 minutes was measured. This test was conducted under conditions of -20°C, -10°C, and 0°C, and flexibility was evaluated according to the following criteria. E (Excellent): In bending tests under all temperature conditions (-20°C, -10°C, and 0°C), the end of the specimen touched the horizontal surface within 10 minutes. G (Good): In bending tests at temperatures of -10°C and 0°C, the end of the test specimen made contact with the horizontal surface within 10 minutes. A (Acceptable): In a bending test at a temperature of 0°C, the end of the test specimen made contact with the horizontal surface within 10 minutes. P (Poor): In all temperature conditions of the bending test, the edge of the test specimen did not make contact with the horizontal surface within 10 minutes, or the adhesive layer peeled off from the release liner.

[0257] Tables 1-3 show an overview of the adhesives used in each example and the evaluation results.

[0258] [Table 1]

[0259] [Table 2]

[0260] [Table 3]

[0261] As shown in Tables 1-3, in Examples 3-5, 7, and 9-28, which used an adhesive composition comprising an acrylic polymer polymerized using an aromatic ring-containing monomer (A1) and a compound that is liquid at 30°C and has two or more double-bond-containing rings as a plasticizer, the refractive index was 1.55 or higher, and the storage modulus G'(0°C) was 1.0 × 10⁻⁶. 6 We were able to form adhesives with a refractive index of Pa or less, that is, adhesives with a high refractive index and a low modulus of elasticity. The adhesive sheets in these examples all passed the bending test (A or higher). On the other hand, in Examples 1-2, 6, and 8, we were able to form adhesives with a high refractive index using acrylic polymers containing aromatic ring-containing monomers (A1) as monomer units, but the storage modulus of elasticity G' (0℃) was 1.0 × 10⁻⁶. 6 The elastic modulus did not exceed Pa and was not low. The adhesive sheets in these examples failed the bending test (P).

[0262] More specifically, the results from Examples 3-5 show that by increasing the amount of the plasticizer, the storage modulus G' at each temperature can be reduced while maintaining a high refractive index, making it possible to produce an adhesive with a lower modulus of elasticity. Examples 9-12 show examples where the type of plasticizer was changed, and these results show that a high refractive index and a low modulus of elasticity can be achieved simultaneously by using a compound that is liquid at 30°C and has two or more double bond-containing rings as a plasticizer. Examples 13-16 and 20 show the results of additive studies, and it can be seen that a higher refractive index can be achieved by using various additives. Furthermore, a comparison between Example 13 and Example 15 shows that by selecting an alkyl (meth)acrylate species as the monomer component, it is possible to adjust the adhesive to have a lower modulus of elasticity while increasing the storage modulus G' at high temperatures, for example. Examples 17-18 show examples where the usage ratio of aromatic ring-containing monomer (A1) was changed, and it can be seen that a high refractive index can be maintained even when the amount of aromatic ring-containing monomer (A1) used is limited. Furthermore, in Examples 17-18, the difference in storage modulus G' between the low-temperature and high-temperature ranges was better suppressed. This is thought to be due to the increased amount of alkyl (meth)acrylate (specifically BA) accompanying the reduction in aromatic ring-containing monomer (A1). Examples 21-22 show examples where the amount of crosslinking agent was changed, demonstrating that the storage modulus G' can be improved by increasing the amount of crosslinking agent. Examples 23-28 show examples where the monomer composition of the polymer, the type of plasticizer, the type of crosslinking agent, and / or the usage ratio of each component were changed, demonstrating that the storage modulus of the adhesive can be adjusted to a desired range while maintaining a high refractive index by designing the adhesive composition, such as adjusting the monomer composition of the acrylic polymer, selecting the type of plasticizer, and adjusting the amount of plasticizer used.

[0263] 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]

[0264] 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. It contains an acrylic polymer and a plasticizer. The monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1), The aforementioned plasticizer is a compound that is liquid at 30°C and has two or more double bond-containing rings. The plasticizer has a first double bond-containing ring and a second double bond-containing ring, and the first double bond-containing ring and the second double bond-containing ring are linked via linking groups having 1 to 5 atoms. An adhesive composition wherein the molecular weight of the plasticizer is 600 or less.

2. The adhesive composition according to claim 1, wherein the compound is a liquid compound at 20°C.

3. The adhesive composition according to claim 1 or 2, wherein the plasticizer is contained in more than 15 parts by weight per 100 parts by weight of the acrylic polymer.

4. The adhesive composition according to any one of claims 1 to 3, wherein the plasticizer is contained in more than 30 parts by weight per 100 parts by weight of the acrylic polymer.

5. The adhesive composition according to any one of claims 1 to 4, wherein the plasticizer has at least one ring selected from aromatic rings and heterocycles as the double bond-containing ring.

6. The adhesive composition according to any one of claims 1 to 5, wherein the monomer component constituting the acrylic polymer contains, in addition to the aromatic ring-containing monomer (A1), a monomer (A2) having at least one of a hydroxyl group and a carboxyl group.

7. The adhesive composition according to any one of claims 1 to 6, wherein the content of the aromatic ring-containing monomer (A1) in the monomer component is 60% by weight or more.

8. An adhesive sheet comprising an adhesive layer formed from the adhesive composition according to any one of claims 1 to 7.

Images