Adhesive composition, adhesive, and adhesive sheet

Abstract

Provided is an adhesive composition for forming an adhesive containing an acrylic polymer. A monomer component constituting the above-described acrylic polymer contains: a monomer containing an aromatic ring (A1), and a monomer having at least one of a hydroxyl group and a carboxyl group (A2). In the above-described monomer component, the content of the monomer containing an aromatic ring (A1) is 75% by weight or more and 99% by weight or less, and the content of the monomer having at least one of a hydroxyl group and a carboxyl group (A2) is 1% by weight or more and 25% by weight or less.

Description

Technical Field

[0001] This invention relates to adhesive compositions, adhesives, and adhesive sheets.

[0002] This application claims priority based on Japanese Patent Application No. 2020-052408 filed on March 24, 2020, Japanese Patent Application No. 2020-166426 filed on September 30, 2020, and Japanese Patent Application No. 2021-049064 filed on March 23, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0003] Adhesives (also known as pressure-sensitive adhesives, hereinafter the same) are widely used in various industries, from household appliances to automobiles, various machinery, electrical equipment, and electronic devices, for purposes such as bonding, fixing, and protection. As an example of the use of adhesives, their application in display devices such as liquid crystal displays and organic EL displays, bonding transparent covering components such as polarizing films, phase refraction films, and cover glass, as well as various other transparent optical components, to other components, can be cited. Patent documents 1 and 2 are cited as examples of technical documents relating to adhesives for optical components.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2014-169382

[0007] Patent Document 2: Japanese Patent Application Publication No. 2017-128732 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] Here, the refractive index of acrylic adhesives is typically around 1.47. In contrast, the refractive index of optical components is typically high. When the aforementioned acrylic adhesive is used in the bonding of such optical components, it is known that reflection will occur at the interface due to the difference in refractive index between the two. Patent documents 1 and 2 propose that the refractive index of the adhesive be 1.50 or higher, particularly preferably 1.51 or higher, by using monomers having multiple aromatic rings. However, there are also optical components with refractive indices of 1.56 or higher, and even 1.60 or higher. The adhesives described in Patent Documents 1 and 2 are not sufficiently suitable for bonding such high-refractive-index optical components.

[0010] Therefore, an object of the present invention is to provide an adhesive also suitable for bonding optical components with higher refractive indices. Another related object is to provide an adhesive composition capable of forming the adhesive and an adhesive sheet comprising the aforementioned adhesive.

[0011] Solution for solving the problem

[0012] According to this specification, an adhesive composition is provided for forming an adhesive comprising an acrylic polymer. The monomer component constituting the acrylic polymer contains a monomer (A1) having an aromatic ring. Preferably, the monomer component also contains a monomer (A2) having at least one of a hydroxyl group and a carboxyl group. The content of the monomer (A1) having an aromatic ring in the monomer component is preferably 75% by weight or more and 99% by weight or less. The content of the monomer (A2) having at least one of a hydroxyl group and a carboxyl group in the monomer component is preferably 1% by weight or more and 25% by weight or less. The adhesive composition configured above, by setting the content of the monomer (A1) having an aromatic ring in the monomer component constituting the acrylic polymer within the above range, is suitable for forming an adhesive with a high refractive index. This adhesive is also preferably used for, for example, bonding optical components with a refractive index of 1.56 or higher.

[0013] It should be noted that monomers containing aromatic rings (A1) are sometimes referred to as "monomers (A1)" and monomers having at least one of hydroxyl and carboxyl groups (A2) are sometimes referred to as "monomers (A2)".

[0014] In some preferred embodiments of the techniques disclosed herein (including adhesive compositions, adhesives, and adhesive sheets, hereinafter the same), at least 50% by weight of the aromatic ring-containing monomer (Al) is a monomer with a glass transition temperature (Tg) of 10°C or lower than that of the homopolymer. Therefore, even with an increased content of monomer (Al) in the monomer composition, a good balance can be achieved between high refractive index and good adhesion to the adhered material. It should be noted that the Tg of the homopolymer of the monomer is sometimes referred to below as the Tg of the monomer itself.

[0015] In some preferred embodiments, the aromatic ring-containing monomer (A1) described above comprises aromatic ring-containing monomers having two or more aromatic rings within one molecule (hereinafter also referred to as "monomers containing multiple aromatic rings"). By using monomers containing multiple aromatic rings, the refractive index of the adhesive can be effectively increased. The aromatic ring-containing monomer (A1) may contain only one type of monomer containing multiple aromatic rings (e.g., a monomer containing multiple aromatic rings with a Tg below 10°C for the homopolymer), or it may combine two or more types of monomers containing multiple aromatic rings.

[0016] In some preferred embodiments, the monomers having two or more aromatic rings within one molecule include monomers having a structural portion in which two aromatic rings are bonded together by a linking group. Monomers containing multiple aromatic rings with this structural portion tend to have a lower Tg in homopolymers compared to monomers containing multiple aromatic rings with a structural portion having two directly chemically bonded aromatic rings (e.g., a biphenyl structure). According to the aromatic ring monomer (A1) containing this structure, a better balance can be achieved between high refractive index and adhesion to the adherend.

[0017] The adhesive compositions disclosed herein preferably further comprise a crosslinking agent. By using a crosslinking agent to impart appropriate cohesiveness to the adhesive, the processability of the adhesive sheet during manufacturing, processing, storage, and adhesion to substrates can be improved.

[0018] According to this specification, an adhesive is provided that is formed from any of the adhesive compositions disclosed herein. This adhesive is able to become a high-refractive-index adhesive by increasing the content of aromatic-ring-containing monomers (Al) in the monomer components constituting the acrylic polymer. According to the technology disclosed herein, adhesives with refractive indices higher than 1.570 (preferably 1.575 or higher, for example 1.580 or higher) can be achieved.

[0019] In some of the adhesives disclosed herein, the adhesive preferably satisfies at least one of the following conditions:

[0020] (a) The energy storage modulus G'(25) at 25°C is less than 200 kPa; and

[0021] (b) The energy storage modulus G'(50) at 50°C is less than 40 kPa.

[0022] Adhesives exhibiting this viscoelastic property can be high-refractive-index adhesives that readily bond with their substrates.

[0023] According to this specification, an adhesive sheet is provided comprising an adhesive layer made of any of the adhesives disclosed herein (which may be adhesives formed from any of the adhesive compositions disclosed herein). The adhesive sheet may preferably be used in a manner that adheres to a component (e.g., an optical component).

[0024] In some embodiments of the adhesive sheet disclosed herein, the haze value of the adhesive layer is preferably 1.0% or less. Such an adhesive sheet with a highly transparent adhesive layer is suitable for bonding applications of optical components.

[0025] It should be noted that a technical solution formed by appropriately combining the various elements described in this specification may also be included within the scope of protection claimed in this patent application. Attached Figure Description

[0026] Figure 1 A cross-sectional view illustrating the structure of an adhesive sheet according to one embodiment is shown for illustrative purposes.

[0027] Figure 2 A cross-sectional view illustrating the structure of an adhesive sheet according to another embodiment is shown for illustrative purposes.

[0028] Figure 3 A cross-sectional view illustrating the structure of an adhesive sheet according to another embodiment is shown for illustrative purposes. Detailed Implementation

[0029] The following describes suitable embodiments of the present invention. For matters necessary for carrying out the present invention, other than those specifically mentioned in this specification, those skilled in the art can understand them based on the teachings on carrying out the invention described in this specification and common general knowledge at the time of application. The present invention can be implemented based on the disclosures in this specification and common general knowledge in the art.

[0030] It should be noted that in the following figures, components / parts that perform the same function are sometimes given the same reference numerals for description, and repeated descriptions are sometimes omitted or simplified. Furthermore, the embodiments described in the figures are schematic for the purpose of clearly illustrating the invention and do not necessarily accurately represent the dimensions or scale of the actual product provided.

[0031] In this specification, the "base polymer" of the adhesive refers to the main component of the rubbery polymer contained in the adhesive. The aforementioned rubbery polymer refers to a polymer that exhibits rubber-like elasticity in a temperature range near room temperature. Furthermore, in this specification, unless otherwise specified, "main component" refers to a component contained in greater than 50% by weight.

[0032] In this specification, "acrylic polymer" refers to a polymer comprising monomer units derived from a monomer having at least one (meth)acryloyl group in one molecule as monomer units constituting the polymer. Hereinafter, a monomer having at least one (meth)acryloyl group in one molecule will also be referred to as an "acrylic monomer". Therefore, acrylic polymers in this specification are defined as polymers comprising monomer units derived from acrylic monomers. Typical examples of acrylic polymers include acrylic polymers in which more than 50% by weight (preferably more than 70% by weight, for example more than 90% by weight) of the monomer composition constituting the polymer is an acrylic monomer.

[0033] In addition, in this specification, "acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl" is a general term for both acryloyl and methacryloyl groups. Therefore, the concept of acrylic monomers as used herein can include both monomers having an acryloyl group (acrylic monomers) and monomers having a methacryloyl group (methacrylic monomers). Similarly, in this specification, "(meth)acrylic acid" is a general term for both acrylic acid and methacrylic acid, and "(meth)acrylate" is a general term for both acrylates and methacrylates. Other similar terms are used in the same way.

[0034] <Adhesive Composition>

[0035] The adhesive composition disclosed herein is any composition capable of forming an adhesive comprising an acrylic polymer (preferably an adhesive comprising the acrylic polymer as a base polymer), and its form is not particularly limited. The aforementioned adhesive composition may, for example, take various forms such as: a solvent-based adhesive composition comprising an adhesive-forming component in an organic solvent; an active energy ray-cured adhesive composition prepared by curing with active energy rays such as ultraviolet light or radiation to form an adhesive; a water-dispersible adhesive composition in which an adhesive-forming component is dispersed in water; and a hot-melt adhesive composition, etc., formed by coating in a molten state upon heating and cooling to near room temperature.

[0036] The adhesive composition disclosed herein contains aromatic ring-containing monomers (A1) as monomeric components constituting the aforementioned acrylic polymer. Here, in this specification, "monomeric components constituting the acrylic polymer" refers to monomers that form repeating units of the acrylic polymer in the adhesive formed from this adhesive composition, whether contained in the adhesive composition in the form of a pre-formed polymer (which may be an oligomer) or in the form of unpolymerized monomers. That is, the monomeric components constituting the acrylic polymer can be contained in the aforementioned adhesive composition in any of the following forms: polymer, unpolymerized, or partially polymerized. From the viewpoint of ease of preparation of the adhesive composition, in some embodiments, it is preferred to include an adhesive composition containing substantially all (e.g., 95% by weight or more, preferably 99% by weight or more) of the monomeric components in polymer form.

[0037] (Single (A1))

[0038] As a monomer (A1), a compound containing at least one aromatic ring and at least one olefinic unsaturated group is used in one molecule. As a monomer (A1), one of the compounds may be used alone or in combination of two or more.

[0039] Examples of the aforementioned olefin unsaturated groups include (meth)acryloyl, vinyl, and (meth)allyl. From the viewpoint of polymerization reactivity, (meth)acryloyl is preferred, and from the viewpoint of flexibility and adhesiveness, acryloyl is more preferred. From the viewpoint of suppressing the reduction of the adhesive's flexibility, as a monomer (A1), it is preferable to use a compound containing one olefin unsaturated group per molecule (i.e., a monofunctional monomer).

[0040] The number of aromatic rings contained in one molecule of the compound used as a monomer (A1) can be one or more. There is no particular upper limit to the number of aromatic rings, for example, it can be 16 or less. In some embodiments, from the viewpoint of ease of preparation of the adhesive composition, transparency of the adhesive, etc., the number of aromatic rings can be, for example, 12 or less, preferably 8 or less, more preferably 6 or less, 5 or less, 4 or less, 3 or less, or 2 or less.

[0041] The aromatic ring of the compound used as a monomer (A1) may be a benzene ring (which may be a benzene ring that forms part of a biphenyl or fluorene structure); a fused ring of a naphthalene ring, indene ring, azulene ring, anthracene ring, or phenanthrene ring; or a heterocyclic ring, such as a pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, pyrrole ring, pyrazole ring, imidazole ring, triazole ring, oxazole ring, isoxazole ring, thiazole ring, or thiophene ring. The heteroatoms included as cyclizing atoms in the aforementioned heterocyclic rings may, for example, be one or more selected from the group consisting of nitrogen, sulfur, and oxygen. In some embodiments, the heteroatoms constituting the aforementioned heterocyclic rings may be one or both of nitrogen and sulfur. The monomer (A1) may also have a structure, for example, such as a dinaphthothiophene structure, formed by the fusion of one or more carbon rings with one or more heterocyclic rings.

[0042] The aromatic ring (preferably a carbocyclic ring) may have one or more substituents on the cyclizing atom, or it may not have any substituents. When substituents are present, examples of such substituents include alkyl, alkoxy, aryloxy, hydroxy, halogen atoms (fluorine, chlorine, bromine, etc.), hydroxyalkyl, hydroxyalkyloxy, epoxypropoxy, etc., but are not limited to these. Among the substituents containing carbon atoms, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, for example, 1 or 2. In some embodiments, the aromatic ring may be an aromatic ring that does not have substituents on the cyclizing atom, or has one or more substituents selected from the group consisting of alkyl, alkoxy, and halogen atoms (e.g., bromine atoms). It should be noted that the aromatic ring of the monomer (A1) having substituents on its cyclizing atom means that the aromatic ring has substituents other than those containing olefinic unsaturated groups.

[0043] The aromatic ring and the olefinic unsaturated group can be directly bonded or bonded via a linking group. The linking group can be, for example, a group containing one or more structures selected from alkylene, oxoalkylene, poly(oxoalkylene), phenyl, alkylphenyl, alkoxyphenyl, or groups in which one or more hydrogen atoms are replaced by hydroxyl groups (e.g., hydroxyalkylene), oxy (-O-), thiooxy (-S-), etc. In some embodiments, it is preferable to use a monomer containing an aromatic ring, either directly bonded to the olefinic unsaturated group or bonded via a linking group selected from the group consisting of alkylene, oxoalkylene, and poly(oxoalkylene). The number of carbon atoms in the alkylene and oxoalkylene groups is preferably 1 to 4, more preferably 1 to 3, for example, 1 or 2. The number of repetitions of the oxoalkylene unit in the poly(oxoalkylene) group can be, for example, 2 to 3.

[0044] Examples of compounds that can be preferably used as monomers (A1) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. One aromatic ring-containing (meth)acrylate and one aromatic ring-containing vinyl compound can each be used alone or in combination of two or more. Alternatively, one or more aromatic ring-containing (meth)acrylates can be used in combination with one or more aromatic ring-containing vinyl compounds.

[0045] In some embodiments, the content of monomer (Al) in the monomer component constituting the acrylic polymer can be, for example, 70% by weight or more, or more than 70% by weight, with 75% by weight or more being suitable. From the viewpoint of easily obtaining a higher refractive index, it is preferably 80% by weight or more, and can be 85% by weight or more, 90% by weight or more, or 95% by weight or more. The content of monomer (Al) in the above-mentioned monomer component is typically less than 100% by weight, and from the viewpoint of achieving a good balance between high refractive index and adhesion of the adhered material, about 99% by weight or less is advantageous, preferably 98% by weight or less, more preferably 96% by weight or less, and can be 93% by weight or less, or 90% by weight or less. In some embodiments, from the viewpoint of easily achieving higher adhesive properties and / or optical properties (e.g., transparency), the content of monomer (Al) in the above-mentioned monomer component can be less than 90% by weight, less than 85% by weight, or less than 80% by weight.

[0046] In some embodiments of the technology disclosed herein, monomers (A1) that readily achieve high refractive index are preferably selected from the perspective of easily obtaining high refractive index effects. Examples of monomers having two or more aromatic rings per molecule (monomers containing multiple aromatic rings) include: monomers having a structure in which two or more non-fused aromatic rings are bonded together by a linking group; monomers having a structure in which two or more non-fused aromatic rings are directly (i.e., without the aid of other atoms) chemically bonded together; monomers having a fused aromatic ring structure; monomers having a fluorene structure; monomers having a dinaphthothiophene structure; and monomers having a dibenzothiophene structure. Monomers containing multiple aromatic rings can be used alone or in combination of two or more.

[0047] The linking group mentioned above can be, for example, an oxygen group (-O-), a thiooxy group (-S-), or an oxoalkylene group (e.g., -O-(CH2)). n - group, where n is 1 to 3, preferably 1), thiooxyalkylene (e.g., -S-(CH2) n - group, where n is 1 to 3, preferably 1), straight-chain alkylene (i.e., -(CH2)). n - group (where n is 1 to 6, preferably 1 to 3), or groups formed by partially or completely halogenating the alkylene oxides, thioalkylene oxides, and straight-chain alkylene oxides mentioned above. From the viewpoint of adhesive flexibility, suitable examples of the above-mentioned linking groups include oxy groups, thiooxy groups, alkylene oxides, and straight-chain alkylene oxides. Specific examples of monomers having a structure in which two or more non-fused aromatic rings are bonded together by a linking group include (meth)acrylate phenoxybenzyl ester (e.g., (meth)acrylate m-phenoxybenzyl ester), (meth)acrylate thiophenoxybenzyl ester, (meth)acrylate benzyl benzyl ester, etc.

[0048] The monomers described above, which have structures formed by the direct chemical bonding of two or more non-fused aromatic rings, can be, for example, (meth)acrylates containing a biphenyl structure, (meth)acrylates containing a triphenyl structure, or vinyl-containing biphenyls. Specific examples include o-phenylphenol (meth)acrylate and biphenyl methyl methacrylate.

[0049] Examples of monomers with fused aromatic ring structures include (meth)acrylates containing a naphthyl ring, (meth)acrylates containing anthracene ring, vinyl-containing naphthalene, and vinyl-containing anthracene. Specific examples include 1-naphthyl methyl (meth)acrylate (also known as 1-naphthyl methyl (meth)acrylate), hydroxyethylated β-naphthol acrylate, 2-naphthyl ethyl (meth)acrylate, 2-naphthoxyethyl acrylate, and 2-(4-methoxy-1-naphthoxy)ethyl (meth)acrylate.

[0050] Specific examples of monomers with the aforementioned fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene(meth)acrylate and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene(meth)acrylate. It should be noted that monomers with the fluorene structure comprise a structural portion formed by the direct chemical bonding of two benzene rings, and are therefore included in the concept of monomers with structures formed by the direct chemical bonding of two or more non-fused aromatic rings.

[0051] Examples of monomers having the dinaphthothiophene structure include dinaphthothiophenes containing (meth)acryloyl groups, dinaphthothiophenes containing vinyl groups, and dinaphthothiophenes containing (meth)allyl groups. Specific examples include (meth)acryloyloxymethyl dinaphthothiophene (e.g., with CH2CH(R) bonded at the 5 or 6 position of the dinaphthothiophene ring). 1 Compounds with the structure )C(O)OCH2-. Here, R 1 It consists of a hydrogen atom or a methyl group. ), (meth)acryloyloxyethyl dinaphthothiophene (for example, CH2CH(R) bonded at the 5 or 6 position of the dinaphthothiophene ring). 1 )C(O)OCH(CH3)- or CH2CH(R 1 Compounds with the structure )C(O)OCH2CH2-. Here, R 1 These include monomers with hydrogen atoms or methyl groups, vinyl dinaphthothiophene (e.g., compounds with a vinyl group bonded to the 5th or 6th position of the dinaphthothiophene ring), (methyl)allyloxy dinaphthothiophene, etc. It should be noted that monomers with a dinaphthothiophene structure are included in the concept of monomers with fused aromatic ring structures because they contain a naphthalene structure and also because they have a structure formed by the fusion of a thiophene ring and two naphthalene structures.

[0052] Examples of monomers having the above-mentioned dibenzothiophene structure include dibenzothiophene containing (meth)acryloyl groups and dibenzothiophene containing vinyl groups. It should be noted that monomers having the dibenzothiophene structure are included in the concept of monomers having fused aromatic ring structures because they have a structure formed by the fusion of a thiophene ring and two benzene rings.

[0053] It should be noted that neither dinaphthothiophene nor dibenzothiophene structures belong to structures formed by the direct chemical bonding of two or more non-fused aromatic rings.

[0054] As the monomer (A1) disclosed herein, a monomer having one aromatic ring (preferably a carbocyclic ring) per molecule can also be used. A monomer having one aromatic ring per molecule can, for example, contribute to improving the flexibility of the adhesive, adjusting its adhesive properties, and improving its transparency. In some embodiments, from the viewpoint of increasing the refractive index of the adhesive, a monomer having one aromatic ring per molecule is preferably used in combination with a monomer containing multiple aromatic rings.

[0055] Examples of monomers having one aromatic ring in one molecule include benzyl (meth)acrylate, methoxybenzyl (meth)acrylate, phenyl (meth)acrylate, ethoxylated phenol (meth)acrylate, phenoxypropyl (meth)acrylate, phenoxybutyl (meth)acrylate, cresol (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and benzyl chloro (meth)acrylate, all containing a carbon-containing aromatic ring; 2-(4,6-dibromo-2-sec-butylphenoxy)ethyl (meth)acrylate, 2-(4,6-dibromo-2-isopropylphenoxy)ethyl (meth)acrylate, and so on. (Meth)acrylates containing bromine-substituted aromatic rings, such as 6-(4,6-dibromo-2-sec-butylphenoxy)hexyl acrylate, 6-(4,6-dibromo-2-isopropylphenoxy)hexyl acrylate, 2,6-dibromo-4-nonylphenyl acrylate, and 2,6-dibromo-4-dodecylphenyl acrylate; vinyl compounds containing carbon aromatic rings, such as styrene, α-methylstyrene, vinyltoluene, and tert-butylstyrene; compounds with vinyl substituents on heteroaromatic rings, such as N-vinylpyridine, N-vinylpyrimidine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazolium, and N-vinyloxazole; etc.

[0056] As a monomer (A1), monomers with an oxyethylidene chain sandwiched between the olefinic unsaturated group and the aromatic ring in the various aromatic ring-containing monomers described above can also be used. Such monomers with an oxyethylidene chain sandwiched between the olefinic unsaturated group and the aromatic ring can be considered as ethoxylated derivatives of the original monomer. The repeating number of the oxyethylidene unit (-CH2CH2O-) in the aforementioned oxyethylidene chain is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, and for example, 1. Specific examples of ethoxylated aromatic ring-containing monomers include ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol di(meth)acrylate.

[0057] The content of monomers containing multiple aromatic rings in monomer (A1) is not particularly limited, and can 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 monomers containing multiple aromatic rings in monomer (A1) can be, for example, 50% or more by weight, and preferably 70% or more by weight, 85% or more by weight, 90% or more by weight, or 95% or more by weight, from the viewpoint of easily obtaining a higher refractive index. It is also possible for monomer (A1) to be substantially 100% by weight of monomers containing multiple aromatic rings. That is, as monomer (A1), only one or two or more monomers containing multiple aromatic rings can be used. In some other ways, for example, taking into account the balance between high refractive index and adhesion to the adhered material, the content of monomers containing multiple aromatic rings in the monomer (A1) can be less than 100% by weight, less than 98% by weight, less than 90% by weight, less than 80% by weight, less than 70% by weight, less than 65% by weight, less than 50% by weight, less than 25% by weight, or less than 10% by weight.

[0058] The content of monomers containing multiple aromatic rings in the monomer components constituting acrylic polymers can, for example, be higher than 35% by weight, and from the viewpoint of easily obtaining higher refractive indices, it is advantageous to be higher than 50% by weight, preferably higher than 70% by weight, and can be 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. Considering the balance between high refractive index and adhesion to the adhered material, it is advantageous to set the content of monomers containing multiple aromatic rings in the above-mentioned monomer components to about 99% by weight or less, preferably to 98% by weight or less, more preferably to 96% by weight or less, and can be 93% by weight or less, 90% by weight or less, 85% by weight or less, or 75% by weight or less. In some embodiments, from the viewpoint of easily achieving higher adhesive properties and / or optical properties (e.g., transparency), the content of monomers containing multiple aromatic rings in the above-mentioned monomer components can be 70% by weight or less, 60% by weight or less, 50% by weight or less, or 40% by weight or less.

[0059] In some embodiments of the technology disclosed herein, a high-refractive-index monomer may preferably be used as at least a portion of the monomer (A1). Here, "high-refractive-index monomer" refers to a monomer whose refractive index is, for example, about 1.510 or higher, preferably about 1.530 or higher, and more preferably about 1.550 or higher. There is no particular upper limit to the refractive index of the high-refractive-index monomer; from the viewpoint of balancing ease of preparation of the adhesive composition with ease of achieving suitable flexibility as an adhesive, it may be, for example, 3.000 or lower, 2.500 or lower, 2.000 or lower, 1.900 or lower, 1.800 or lower, or 1.700 or lower. One high-refractive-index monomer may be used alone or in combination of two or more.

[0060] It should be noted that the refractive index of the monomer was measured using an Abbe refractometer at a measurement wavelength of 589 nm and a measurement temperature of 25°C. The Abbe refractometer can be the ATAGO "DR-M4" model or its equivalent. If the manufacturer provides a nominal value for the refractive index at 25°C, that value can be used.

[0061] As the aforementioned high refractive index monomer, a substance with a suitable refractive index can be appropriately selected from the compounds included in the concept of aromatic ring-containing monomers (A1) disclosed herein (e.g., the compounds and groups of compounds exemplified above). Specific examples include m-phenoxybenzyl acrylate (refractive index: 1.566, Tg of homopolymer: -35°C), 1-naphthyl methyl acrylate (refractive index: 1.595, Tg of homopolymer: 31°C), ethoxylated o-phenylphenol acrylate (repetition number of oxyethylidene unit: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, Tg of homopolymer: 6°C), phenoxyethyl acrylate (refractive index (nD20): 1.517, Tg of homopolymer: 2°C), and phenoxydiethylene glycol acrylate (refractive index: 1.510, Tg of homopolymer: -35°C). g: -35℃), 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), 5-vinyl dinaphthothiophene (abbreviated as: 5VDNT, refractive index: 1.793), etc., but not limited to these.

[0062] The content of high-refractive-index monomers (i.e., aromatic ring-containing monomers with a refractive index of about 1.510 or more, preferably about 1.530 or more, more preferably about 1.550 or more) in monomer (A1) can be, for example, 50% by weight or more. From the viewpoint of easily obtaining higher refractive indices, it is preferably 70% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. It is also possible for monomer (A1) to be substantially 100% by weight of high-refractive-index monomers. In addition, in some embodiments, for example, from the viewpoint of achieving a good balance between high refractive index and adhesion to the adherend, the content of high-refractive-index monomers in monomer (A1) can be less than 100% by weight, such as 98% by weight or less, 90% by weight or less, 80% by weight or less, or 65% by weight or less.

[0063] The content of high-refractive-index monomers in the monomer components constituting acrylic polymers can, for example, be higher than 35% by weight. From the viewpoint of easily obtaining higher refractive indices, it is advantageous to be higher than 50% by weight, preferably higher than 70% by weight, and can be 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. From the viewpoint of achieving a good balance between high refractive index and adhesion to the adherend, it is advantageous for the content of high-refractive-index monomers in the aforementioned monomer components to be 99% by weight or less, preferably 98% by weight or less, more preferably 96% by weight or less, and can be 93% by weight or less, 90% by weight or less, 85% by weight or less, or 75% by weight or less.

[0064] In some preferred embodiments of the technology disclosed herein, a monomer containing aromatic rings (hereinafter sometimes referred to as "monomer L") with a Tg of 10°C or less (preferably 5°C or less or 0°C, more preferably -10°C or less, even more preferably -20°C or less, for example -25°C or less) is used as at least a portion of the monomer (A1). If the content of the aromatic ring-containing monomer (A1) in the monomer composition is increased (especially the aromatic ring-containing monomer (A1) equivalent to one or both of the aforementioned monomers containing multiple aromatic rings and high refractive index monomers), the storage modulus G' of the adhesive generally tends to increase. By using monomer L as part or all of the monomer (A1), the increase in storage modulus G' can be suppressed. Therefore, it is possible to maintain better flexibility suitable for bonding to the adhered material and to increase the refractive index. There is no particular limitation on the lower limit of the Tg of monomer L. Considering the balance with the effect of increasing the refractive index, in some embodiments, the Tg of monomer L can be, for example, above -70°C, above -55°C, or above -45°C. Monomer L can be used alone or in combination of two or more types.

[0065] As monomer L, a substance having a suitable Tg can be appropriately selected from the compounds included in the concept of aromatic ring-containing monomers (A1) disclosed herein (e.g., the compounds and groups of compounds exemplified above). As a suitable example of an aromatic ring-containing monomer that can be used as monomer L, m-phenoxybenzyl acrylate (Tg of homopolymer: -35°C) is listed. As another suitable example, phenoxydiethylene glycol acrylate (Tg of homopolymer: -35°C) is listed.

[0066] The content of monomer L in monomer (A1) can be, for example, 50% by weight or more, and from the viewpoint of further improving flexibility, preferably 60% by weight or more, 70% by weight or more, 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. It is also possible for monomer (A1) to be substantially 100% by weight of monomer L. Furthermore, in some embodiments, for example, from the viewpoint of achieving a good balance between high refractive index and adhesion to the adhered material, the content of monomer L in monomer (A1) can be less than 100% by weight, such as 98% by weight or less, 90% by weight or less, 80% by weight or less, or 65% by weight or less.

[0067] The content of monomer L in the monomer component constituting the acrylic polymer can, for example, be higher than 35% by weight. From the viewpoint of increasing the refractive index, it is advantageous to be higher than 50% by weight, preferably higher than 70% by weight, and can be 75% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. From the viewpoint of achieving a good balance between high refractive index and adhesion to the adherend, it is advantageous to set the content of monomer L in the above-mentioned monomer component to about 99% by weight or less, preferably to 98% by weight or less, more preferably to 96% by weight or less, and can be 93% by weight or less, 90% by weight or less, 85% by weight or less, or 75% by weight or less.

[0068] In some approaches, from the viewpoint of adhesive flexibility, the glass transition temperature Tg of the monomer (Al) composition is considered. A1 A temperature below approximately 20°C is suitable, preferably below 10°C (e.g., below 5°C), more preferably below 0°C, and even more preferably below -10°C. It can be below -20°C or below -25°C. Glass transition temperature Tg A1 There is no particular lower limit. Considering the balance with the effect of increasing the refractive index, in some approaches, the glass transition temperature Tg... A1 For example, it can be above -70°C, above -55°C, or above -45°C. The technology disclosed herein can also be based on the glass transition temperature Tg. A1It shall be implemented in a manner suitable for temperatures above -40°C, -35°C, -33°C, -30°C, or -25°C.

[0069] Here, the glass transition temperature Tg is based on the composition of the monomer (Al). A1 This refers to the glass transition temperature (Tg) calculated using the Fox equation (described later), based solely on the composition of the monomers (Al) that constitute acrylic polymers. A1 The glass transition temperature (Tg) of the homopolymer of an acrylic polymer can be calculated using the Fox formula, focusing solely on the monomer (A1) constituting the monomer composition. This is based on the glass transition temperature (Tg) of the homopolymer of each aromatic ring-containing monomer used as monomer (A1) and the weight fraction of each aromatic ring-containing monomer in the total monomer (A1). In the case where only one monomer is used as monomer (A1), the Tg of the homopolymer of that monomer is related to its glass transition temperature (Tg). A1 Consistent.

[0070] In some methods, monomer L (i.e., a monomer containing an aromatic ring with a Tg of 10°C or less, preferably 5°C or less or 0°C, more preferably -10°C or less, further preferably -20°C or less, for example -25°C or less) and monomer H with a Tg higher than 10°C can be used as the aromatic ring-containing monomer (A1). The Tg of monomer H can be, for example, higher than 10°C, higher than 15°C, or higher than 20°C. By using monomer L and monomer H in combination, in adhesives with a high content of aromatic ring-containing monomer (A1) in the monomer composition, a higher level of balance between the high refractive index of the adhesive and the flexibility suitable for bonding the adhered objects can be achieved. The ratio of monomer L to monomer H can be set in a way that suitably manifests this effect and is not particularly limited. For example, it is preferable to satisfy any of the above-mentioned glass transition temperatures Tg. A1 The ratio of monomer L to monomer H is set in a certain way.

[0071] In some embodiments, the aromatic monomer (A1) is preferably selected from compounds that do not contain a structure formed by direct chemical bonding of two or more non-fused aromatic rings (e.g., a biphenyl structure). For example, acrylic polymers composed of monomer components having a content of less than 5% by weight (more preferably less than 3% by weight, or even 0% by weight) of compounds containing a structure formed by direct chemical bonding of two or more non-fused aromatic rings are preferred. From the viewpoint of achieving an adhesive that achieves a better balance between high refractive index and adhesion to the adhered surfaces, thus limiting the amount of compounds containing a structure formed by direct chemical bonding of two or more non-fused aromatic rings can be advantageous.

[0072] (Single (A2))

[0073] The monomer (A2) disclosed herein is a monomer belonging to at least one of a hydroxyl-containing monomer (hydroxyl-containing monomer) and a carboxyl-containing monomer (carboxyl-containing monomer). The hydroxyl-containing monomer is a compound having at least one hydroxyl group and at least one olefinically unsaturated group per molecule. The carboxyl-containing monomer is a compound containing at least one carboxyl group and at least one olefinically unsaturated group per molecule. Monomer (A2) can facilitate the introduction of crosslinking points into acrylic polymers or impart appropriate cohesiveness to adhesives. Monomer (A2) can be used alone or in combination of two or more. Monomer (A2) is typically a monomer that does not contain an aromatic ring.

[0074] Examples of olefinic unsaturated groups present in monomer (A2) include (meth)acryloyl, vinyl, and (meth)allyl groups. From the viewpoint of polymerization reactivity, (meth)acryloyl is preferred, and from the viewpoint of flexibility and adhesiveness, acryloyl is more preferred. From the viewpoint of suppressing the reduction of the adhesive's flexibility, it is preferable to use a compound (i.e., a monofunctional monomer) containing one olefinic unsaturated group per molecule as monomer (A2).

[0075] Examples of hydroxyl-containing monomers include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl methacrylate, 8-hydroxyoctyl methacrylate, 10-hydroxydecyl methacrylate, 12-hydroxylaurate methacrylate, and methyl methacrylate (4-hydroxymethylcyclohexyl)methacrylate, but are not limited to these. Examples of preferred hydroxyl-containing monomers include 4-hydroxybutyl acrylate (Tg: -40°C) and 2-hydroxyethyl methacrylate (Tg: -15°C). From the viewpoint of improved softness in the room temperature range, 4-hydroxybutyl acrylate with a lower Tg is more preferred. In a preferred embodiment, 4-hydroxybutyl acrylate may be present in 50% by weight or more (e.g., more than 50% by weight, more than 70% by weight, or more than 85% by weight) of the monomer (A2). One hydroxyl-containing monomer may be used alone or in combination of two or more.

[0076] In some methods of using a hydroxyl-containing monomer as monomer (A2), the hydroxyl-containing monomer may be one or more compounds selected from those without a methacryloyl group. Suitable examples of hydroxyl-containing monomers without a methacryloyl group include the various hydroxyalkyl acrylates mentioned above. For example, it is preferable that more than 50%, more than 70%, or more than 85% by weight of the hydroxyl-containing monomer used as monomer (A2) is a hydroxyalkyl acrylate. By using hydroxyalkyl acrylates, hydroxyl groups that help provide crosslinking points and impart moderate cohesiveness can be introduced into acrylic polymers, and adhesives with good flexibility and adhesion in the room temperature range are readily obtained compared to the case where only the corresponding hydroxyalkyl methacrylate is used.

[0077] Examples of carboxyl-containing monomers include acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylic acid, and carboxypentyl (meth)acrylic acid, as well as itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid, but are not limited to these. Examples of preferred carboxyl-containing monomers include acrylic acid and methacrylic acid. One type of carboxyl-containing monomer can be used alone, or two or more can be used in combination. Hydroxyl-containing monomers and carboxyl-containing monomers can also be used in combination.

[0078] 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) can be, for example, 0.01% by weight or more, 0.1% by weight or more, or 0.5% by weight or more. From the viewpoint of obtaining a higher performance effect, in some embodiments, the content of monomer (A2) is preferably set to 1% by weight or more, can be set to 2% by weight or more, or can be set to 4% by weight or more. The upper limit of the content of monomer (A2) in the monomer component is set such that the total content of monomer (A1) does not exceed 100% by weight. In some embodiments, it is appropriate to set the content of monomer (A2) to 30% by weight or less or 25% by weight or less, for example. From the viewpoint of making it easier to increase the refractive index by relatively increasing the content of monomer (A1), it is preferably set to 20% by weight or less, more preferably to 15% by weight or less, and can be less than 12% by weight, less than 10% by weight, or less than 7% by weight.

[0079] In methods using hydroxyl-containing monomers as monomers (A2), the content of hydroxyl-containing monomers in the monomer composition is not particularly limited, and can be, for example, 0.01% by weight or more (preferably 0.1% by weight or more, more preferably 0.5% by weight or more). In some methods, the content of the hydroxyl-containing monomers is preferably set to 1% by weight or more of the monomer composition, and can be set to 2% by weight or more, or 4% by weight or more. The upper limit of the content of hydroxyl-containing monomers in the monomer composition is set such that the total content with the monomer (A1) does not exceed 100% by weight, for example, setting it to 30% by weight or less or 25% by weight or less is appropriate. From the viewpoint of making it easier to increase the refractive index by relatively increasing the content of monomer (A1), it is preferably set to 20% by weight or less, more preferably 15% by weight or less, and can be less than 12% by weight, less than 10% by weight, or less than 7% by weight.

[0080] In methods using carboxyl-containing monomers as monomers (A2), the content of carboxyl-containing monomers in the monomer composition is not particularly limited, and can be, for example, 0.01% by weight or more (preferably 0.1% by weight or more, more preferably 0.3% by weight or more). In some methods, the content of the carboxyl-containing monomers can be set to 1% by weight or more, 2% by weight or more, or 4% by weight or more. The upper limit of the content of carboxyl-containing monomers in the monomer composition is set such that the total amount used with the monomer (A1) does not exceed 100% by weight. For example, it is appropriate to set it to 30% by weight or less or 25% by weight or less. From the viewpoint of making it easier to increase the refractive index by relatively increasing the content of monomer (A1), it is preferable to set it to 20% by weight or less, more preferably 15% by weight or less, and can be less than 12% by weight or less than 10% by weight. In some methods, from the viewpoint of improving the flexibility of the adhesive, it is advantageous to set the content of the carboxyl-containing monomers to less than 7% by weight, preferably less than 5% by weight, less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. The techniques disclosed herein can be preferably implemented, for example, by using only hydroxyl-containing monomers as monomers (A2), i.e., without using carboxyl-containing monomers.

[0081] In some aspects of the technology disclosed herein, the total content of monomers (A1) and (A2) in the monomeric components constituting the acrylic polymer can be, for example, 76% by weight or more, preferably 81% by weight or more, 86% by weight or more, 91% by weight or more, 96% by weight or more, 99% by weight or more, or substantially 100% by weight, from the viewpoint of easily and appropriately exerting the effects of these monomers.

[0082] (Single A3)

[0083] The monomer components constituting acrylic polymers may, as needed, include monomers other than those described above (A1) and (A2). As an example of such an arbitrary component, alkyl (meth)acrylate (hereinafter also referred to as "monomer (A3)") can be listed. Monomer (A3) can help adjust the flexibility of the adhesive and improve its compatibility within the adhesive.

[0084] As a monomer (A3), it is preferable to use one having 1 to 20 carbon atoms at the ester terminus (i.e., C3). 1-20 Alkyl (meth)acrylates with straight or branched alkyl groups. As (meth)acrylate C 1-20 Specific examples of alkyl esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, isooctyl methacrylate, and nonyl methacrylate. Isononyl methacrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecanyl methacrylate, stearyl methacrylate, isostearyl methacrylate, nonadecanyl methacrylate, eicosyl methacrylate, etc., but not limited to these.

[0085] In some methods, it is preferable to use alkyl (meth)acrylates with a Tg of -20°C or lower (more preferably -40°C or lower, for example -50°C or lower) as at least a portion of the monomer (A3). Such low-Tg alkyl (meth)acrylates can help improve the flexibility of the adhesive. There is no particular limitation on the lower limit of the Tg of the aforementioned alkyl (meth)acrylates; for example, it can be above -85°C, above -75°C, above -65°C, or above -60°C. Specific examples of the aforementioned low-Tg alkyl (meth)acrylates include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), and isononyl acrylate (iNA).

[0086] In some methods of using monomer (A3), from the viewpoint of flexibility, adhesion, etc., it is preferable that at least a portion of the monomer (A3) is an alkyl acrylate. For example, it is preferable that 50% by weight or more (more preferably 75% by weight or more, and even more preferably 90% by weight or more) of the monomer (A3) is an alkyl acrylate. It is also possible to use only one or two or more alkyl acrylates as monomer (A3) without using alkyl methacrylates.

[0087] In monomer components comprising alkyl (meth)acrylates, the content of alkyl (meth)acrylates in the monomer component can be set in a manner that appropriately exerts its effect. In some embodiments, the content of the aforementioned alkyl (meth)acrylates can be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. The upper limit of the content of monomer (A3) in the monomer component is set such that the total content of monomers (A1) and (A2) does not exceed 100% by weight. In some embodiments, the content of the aforementioned monomer (A3) can be, for example, 24% by weight or less. Alkyl (meth)acrylates generally have a low refractive index; therefore, in order to achieve a high 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 point of view, it is appropriate for the content of monomer (A3) to be less than 23% by weight of the monomer component, preferably less than 20% by weight, more preferably less than 17% by weight, less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The techniques disclosed herein can preferably be implemented in a manner that substantially does not use a monomer (A3).

[0088] (Other monomers)

[0089] The monomer components constituting acrylic polymers may, as needed, include monomers other than those mentioned above (A1), (A2), and (A3) (hereinafter referred to as "other monomers"). These other monomers may be used for purposes such as adjusting the Tg of the acrylic polymer, adjusting adhesive properties, and improving compatibility within the adhesive layer. One of these other monomers may be used alone, or two or more may be used in combination.

[0090] Examples of other monomers mentioned above include monomers having functional groups other than hydroxyl and carboxyl groups (monomers containing functional groups). For example, monomers containing sulfonic acid groups, phosphate groups, and cyano groups can be listed as other monomers that can improve the cohesiveness and heat resistance of adhesives. In addition, monomers that can introduce functional groups that can serve as crosslinking sites into acrylic polymers, or that help improve the adhesion to the adherend and the compatibility within the adhesive layer, can be listed as amide-containing monomers (e.g., (meth)acrylamide, N-hydroxymethyl(meth)acrylamide, etc.), amino-containing monomers (e.g., (meth)acrylate aminoethyl ester, (meth)acrylate N,N-dimethylaminoethyl ester, etc.), monomers with a nitrogen-containing ring (e.g., N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), imide-containing monomers, epoxy-containing monomers, ketone-containing monomers, isocyanate-containing monomers, and alkoxysilyl-containing monomers, etc. It should be noted that monomers with nitrogen-containing rings, such as N-vinyl-2-pyrrolidone, also belong to the category of amide-containing monomers. The same applies to the relationship between the aforementioned monomers with nitrogen-containing rings and amino-containing monomers.

[0091] Other monomers that can be used besides the functionalized monomers mentioned above include vinyl acetate and other vinyl ester monomers; (meth)acrylates containing non-aromatic rings, such as cyclohexyl methacrylate and isobornyl methacrylate; olefin monomers such as ethylene, butadiene, and isobutene; chlorinated monomers such as vinyl chloride; alkoxy-containing monomers such as methoxyethyl methacrylate, ethoxyethyl methacrylate, and ethoxyethoxyethyl methacrylate; vinyl ether monomers such as methyl vinyl ether; etc. As a suitable example of other monomers that can be used for purposes such as improving the flexibility of adhesives, ethoxyethoxyethyl acrylate (also known as ethyl carbitol acrylate, Tg of homopolymer: -67°C) can be listed.

[0092] When using the other monomers mentioned above, there are no particular restrictions on their usage, and they can be appropriately set within a range where the total amount of monomer components does not exceed 100% by weight. From the viewpoint of easily maximizing the refractive index increase effect brought about by the use of monomer (Al), it is appropriate to set the content of the other monomers mentioned above in the monomer component to about 23% by weight or less (e.g., 0 to 23% by weight), it is advantageous to set it to about 10% by weight or less (e.g., 0 to 10% by weight), and preferably about 5% by weight or less, for example, about 1% by weight or less. The technology disclosed herein can preferably be implemented in a manner in which the monomer component substantially does not contain the other monomers mentioned above.

[0093] In some embodiments, the monomeric components constituting acrylic polymers may be compositions in which the amount of methacrylamide monomers used is suppressed to a specified level. For example, the amount of methacrylamide monomers used in the monomeric components may be less than 5% by weight, less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. From the viewpoint of achieving a well-balanced adhesive that combines flexibility, adhesion, and high refractive index, limiting the amount of methacrylamide monomers used in this way can be advantageous. The monomeric components constituting acrylic polymers may also be compositions that do not contain methacrylamide monomers (e.g., compositions containing only acryloyl monomers).

[0094] In some embodiments, for the monomer components constituting the acrylic polymer, from the viewpoint of suppressing coloring or discoloration (e.g., yellowing) of the adhesive, it is preferable to limit the amount of carboxyl-containing monomers used. The amount of carboxyl-containing monomers used in the monomer components may, for example, be less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.3% by weight, less than 0.1% by weight, or less than 0.05% by weight. Limiting the amount of carboxyl-containing monomers in this way is also advantageous from the viewpoint of suppressing corrosion of metallic materials (e.g., metal wiring, metal films, etc. that may be present on the adhered objects) that may come into contact with or approach the adhesives disclosed herein. The techniques disclosed herein can preferably be implemented in a manner where the monomer components constituting the acrylic polymer do not contain carboxyl-containing monomers.

[0095] For the same reason, in some embodiments, the amount of monomers constituting the acrylic polymer is preferably limited to those having acidic functional groups (including sulfonic acid groups, phosphoric acid groups, etc., in addition to carboxyl groups). The amount of acidic functional group-containing monomers used in the monomer components of this embodiment can be determined by the preferred amount of carboxyl-containing monomers described above. The disclosed technology can preferably be implemented in a manner where the monomer components do not contain acidic groups (i.e., the acrylic polymer is acid-free).

[0096] (glass transition temperature Tg) T )

[0097] The monomer components constituting acrylic polymers preferably have a glass transition temperature (Tg) based on the composition of the monomer components. T The composition is below approximately 15°C. In some embodiments, the aforementioned glass transition temperature Tg... T Preferably below 10°C, more preferably below 0°C, even more preferably below -10°C, but can be below -20°C, below -25°C, or below -28°C. Glass transition temperature Tg T A lower glass transition temperature (Tg) can be advantageous from the perspective of improved adhesive flexibility. Additionally, the glass transition temperature (Tg) is also important. TFor example, the temperature can be -60°C or higher. From the viewpoint of making it easier to increase the refractive index of the adhesive, it is preferable to be -50°C or higher, more preferably higher than -45°C, and may also be higher than -40°C.

[0098] Here, the glass transition temperature Tg T Unless otherwise specified, this refers to the glass transition temperature calculated using the Fox formula based on the composition of the aforementioned monomer components. The Fox formula, as shown below, is the relationship between the glass transition temperature (Tg) of the copolymer and the glass transition temperature (Tgi) of the homopolymer formed by the homopolymerization of each of the monomers constituting the copolymer.

[0099] 1 / Tg=Σ(Wi / Tgi)

[0100] In the above Fox formula, Tg represents the glass transition temperature of the copolymer (unit: K), Wi represents the weight fraction of monomer i in the copolymer (weight-based copolymerization ratio), and Tgi represents the glass transition temperature of the homopolymer of monomer i (unit: K).

[0101] The glass transition temperature (Tg) of homopolymers used for calculating Tg is the value recorded in known sources such as the "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989). For monomers for which multiple values ​​are recorded in the aforementioned Polymer Handbook, the highest value is used. Where the Tg of homopolymers is not recorded in known sources, the value obtained by the determination method described in Japanese Patent Application Publication No. 2007-51271 is used.

[0102] (Preparation methods of acrylic polymers)

[0103] In the technology disclosed herein, there are no particular limitations on the method for obtaining acrylic polymers composed of such monomer components. Various polymerization methods known as synthetic techniques for acrylic polymers, such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization, can be appropriately employed. For example, solution polymerization is preferred. The polymerization temperature during solution polymerization can be appropriately selected based on the type of monomer and solvent used, the type of polymerization initiator, etc., and can be set to approximately 20°C to 170°C (typically approximately 40°C to 140°C).

[0104] The solvent used in solution polymerization (polymerization solvent) can be appropriately selected from conventionally known organic solvents. For example, one or a mixture of two or more solvents can be used, selected from aromatic compounds such as toluene (typically aromatic hydrocarbons); acetates such as ethyl acetate; aliphatic or alicyclic hydrocarbons such as hexane and cyclohexane; haloalkanes such as 1,2-dichloroethane; lower alcohols such as isopropanol (e.g., monohydric alcohols with 1 to 4 carbon atoms); ethers such as tert-butyl methyl ether; ketones such as methyl ethyl ketone; etc.

[0105] The initiator used in the polymerization can be appropriately selected from conventionally known polymerization initiators, depending on the type of polymerization method. For example, one or more azo-based polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) are preferred. Other examples of polymerization initiators include: persulfates such as potassium persulfate; peroxide-based initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane-based initiators such as phenyl-substituted ethane; aromatic carbonyl compounds; etc. Further examples of polymerization initiators include redox initiators based on combinations of peroxides and reducing agents. One polymerization initiator can be used alone or in combination of two or more. The amount of polymerization initiator used is the usual amount, for example, it can be selected from a range of about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) relative to 100 parts by weight of monomer content.

[0106] In the above polymerization, various conventionally known chain transfer agents can be used as needed. For example, thiols such as n-dodecyl mercaptan, tert-dodecyl mercaptan, mercaptoacetic acid, and α-thioglycerol can be used. Alternatively, chain transfer agents without sulfur atoms (non-sulfur chain transfer agents) can also be used. Examples of non-sulfur chain transfer agents include: anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenes such as α-pinene and terpinene; styrene such as α-methylstyrene and α-methylstyrene dimer; etc. One chain transfer agent can be used alone or in combination of two or more. The amount of chain transfer agent used relative to 100 parts by weight of the monomer raw material can be set to, for example, approximately 0.01 to 1 part by weight.

[0107] The weight-average molecular weight (Mw) of the aforementioned acrylic polymers is not particularly limited, and can be, for example, about 10 × 10⁻⁶. 4 ~500×10 4 From the viewpoint of adhesive properties, the Mw of acrylic polymers is preferably in the range of approximately 20 × 10⁻⁶. 4 ~400×10 4 (More preferably about 30×10) 4 ~150×10 4 For example, approximately 50×10 4 ~130×104 ) range.

[0108] Here, the Mw of the acrylic polymer can be obtained by converting polystyrene using gel permeation chromatography (GPC). Specifically, the GPC measuring device, "HLC-8220GPC" (manufactured by Tosoh Corporation), can be used, and the Mw can be determined under the following conditions.

[0109] [GPC Measurement Conditions]

[0110] Sample concentration: 0.2% by weight (tetrahydrofuran solution)

[0111] Sample injection volume: 10 μL

[0112] Eluent: Tetrahydrofuran (THF)

[0113] Flow rate: 0.6 mL / min

[0114] Column temperature (measurement temperature): 40℃

[0115] column:

[0116] Sample column: 1 brand name "TSKguardcolumn SuperHZ-H" + 2 pieces "TSKgel SuperHZM-H" brand name (manufactured by Tosoh Corporation)

[0117] Reference column: 1 brand name "TSKgel SuperH-RC" (manufactured by Tosoh Corporation)

[0118] Detector: Differential refractometer (RI)

[0119] Standard sample: polystyrene

[0120] (Plasticized materials)

[0121] In some embodiments of the adhesive compositions disclosed herein, the adhesive composition may include, in addition to the acrylic polymer as described above, a plasticizing material with a molecular weight lower than that of the acrylic polymer as an additive used as desired. The use of the plasticizing material can improve the flexibility of the adhesive layer, enhance adhesion to the adhered objects, improve the overall flexibility of the adhesive sheet, and improve its adaptability to deformation. From the viewpoint of compatibility and transparency within the adhesive layer, organic materials are preferred as the plasticizing material. The plasticizing material can be, or can be used as, the additive described later (H...). RO (materials).

[0122] The molecular weight of the plasticizing material is not particularly limited as long as it is lower than that of the aforementioned acrylic polymers. In some embodiments, from the viewpoint of easily exhibiting a plasticizing effect, a molecular weight of 30,000 or less is suitable, 25,000 or less is advantageous, and preferably less than 10,000 (e.g., less than 5,000). More preferably, it is less than 3,000 (e.g., less than 1,000), and can be less than 800, less than 600, less than 500, or less than 400. When the molecular weight of the plasticizing material is not too high, it can be advantageous from the viewpoint of improved compatibility within the adhesive layer. Furthermore, from the viewpoint of easily achieving a sufficient plasticizing effect, a molecular weight of 130 or more is suitable, preferably 150 or more, and can be 170 or more, 200 or more, 250 or more, or 300 or more. When the molecular weight of the plasticizing material is not too low, it is also preferred from the viewpoint of the heat resistance of the adhesive sheet and the suppression of contamination of the adhered material. In some methods, the molecular weight of the plasticizing material can be above 500, above 1000, or above 2000.

[0123] Non-limiting examples of compounds that can be used as plasticizing materials include: compounds that can be used as monomers (A1) (e.g., (meth)acrylates having aromatic rings such as benzyl, phenoxy, and naphthyl; monomers having a fluorene structure; monomers having a dinaphthothiophene structure; monomers having a dibenzothiophene structure, etc.); oligomers containing compounds that can be used as monomers (A1) as monomer units; compounds with structures formed by removing and replacing the portion having an olefinically unsaturated group from compounds that can be used as monomers (A1) with a hydrogen atom or a group that does not have an olefinically unsaturated group (e.g., 3-phenoxybenzyl alcohol); etc. For oligomers containing compounds that can be used as monomers (A1) as monomer units, from the viewpoint of improving flexibility, low Tg monomers such as n-butyl acrylate and 2-ethylhexyl acrylate can also be copolymerized, for example. As a plasticizing material, one or more of the known plasticizers (such as phthalate esters, terephthalate esters, adipate esters, adipate polyesters, dibenzoic acid esters, etc.) can be used.

[0124] In some methods, organic materials with a refractive index of about 1.50 or higher (more preferably 1.53 or higher) are preferably used as plasticizers. Specific examples of compounds that can be used as plasticizers include: diethylene glycol dibenzoate (refractive index 1.55), dipropylene glycol dibenzoate (refractive index 1.54), 3-phenoxytoluene (refractive index 1.57), 3-ethylbiphenyl (refractive index 1.59), 3-methoxybiphenyl (refractive index 1.61), 4-methoxybiphenyl (refractive index 1.57), polyethylene glycol dibenzoate, 3-phenoxybenzyl alcohol (refractive index 1.59), triphenyl phosphate (refractive index 1.56), benzyl benzoate (refractive index 1.57), 4-(tert-butyl) Phenyl diphenyl phosphate (refractive index 1.56), trimethylphenyl phosphate (refractive index 1.55), butyl benzyl phthalate (refractive index 1.54), rosin methyl ester (refractive index 1.53), alkyl benzyl phthalate (refractive index 1.53), butyl(benzenesulfonyl)amine (refractive index 1.53), trimethyl trimellitate (refractive index 1.52), benzyl phthalate (refractive index 1.52), 2-ethylhexyl diphenyl phosphate (refractive index 1.51), tris(2,4-di-tert-butylphenyl) phosphite, etc., but not limited to these. From the viewpoint of refractive index and compatibility, diethylene glycol dibenzoate, for example, may be preferred. There is no particular upper limit to the refractive index of the plasticizing material, for example, it can be below 3.00. In some approaches, from the viewpoints of ease of preparation of the adhesive composition and compatibility within the adhesive, it is appropriate for the refractive index of the plasticizing material to be below 2.50, advantageous to be below 2.00, below 1.90, below 1.80, or below 1.70.

[0125] It should be noted that the refractive index of the plasticized material is measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25°C, just like the refractive index of the monomer. If the manufacturer provides a nominal value for the refractive index at 25°C, that value can be used.

[0126] In using plasticizing materials, the amount of plasticizing material relative to 100 parts by weight of the acrylic polymer is not particularly limited and can be set according to the purpose. From the viewpoint of improving the plasticizing effect, the amount of plasticizing material relative to 100 parts by weight of the acrylic polymer can be, for example, 0.1 parts by weight or more, or 0.5 parts by weight or more. From the viewpoint of obtaining a higher plasticizing effect, it is preferable to set it to 1 part by weight or more, more preferably 3 parts by weight or more, 5 parts by weight or more, 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or 20 parts by weight or more. In addition, from the viewpoint of achieving a good balance between the high refractive index of the adhesive and the plasticizing effect, it is appropriate to set the amount of plasticizing material relative to 100 parts by weight of the acrylic polymer to be about 100 parts by weight or less, preferably 80 parts by weight or less, more preferably 60 parts by weight or less, 45 parts by weight or less, 35 parts by weight or less, or 25 parts by weight or less. In some approaches that place greater emphasis on adhesive properties, the amount of plasticizer used relative to 100 parts by weight of acrylic polymer can be less than 15 parts by weight, less than 10 parts by weight, or less than 5 parts by weight.

[0127] (additives (H) RO ))

[0128] The adhesive compositions disclosed herein may contain an organic material with a refractive index higher than that of the acrylic polymer as an additive, used as desired. Hereinafter, such an organic material is sometimes referred to as "additive (H)". RO )". Here, the above "H" RO "High refractive index" indicates an organic material. This is achieved through the combined use of additives (H... RO ( ) and acrylic polymers can achieve adhesives that more appropriately balance refractive index and adhesive properties (peel strength, flexibility, etc.). Used as an additive (H RO The organic material can be a polymer or a non-polymer. Furthermore, it may or may not have polymerizable functional groups. Additives (H) RO One type can be used alone or two or more types can be used in combination.

[0129] Additives (H) RO The refractive index of the additive (H) can be set to an appropriate range based on its relative relationship with the refractive index of the acrylic polymer, and is therefore not limited to a specific range. ROThe refractive index of the adhesive can be selected, for example, from a range higher than 1.55, higher than 1.56, or higher than 1.57, and higher than the refractive index of acrylic polymers. From the viewpoint of increasing the refractive index of the adhesive, in some ways, the additive (H... RO It is advantageous for the refractive index of the additive to be 1.58 or higher, preferably 1.60 or higher, more preferably 1.63 or higher, and can be 1.65 or higher, 1.70 or higher, or 1.75 or higher. Using an additive with a higher refractive index (H...) RO Even when using a smaller amount of additive (H) RO This can also achieve the target refractive index. This is preferable from the viewpoint of suppressing the reduction of adhesive properties and optical properties. Additive (H) RO There is no particular upper limit to the refractive index of the adhesive. From the perspective of compatibility within the adhesive, ease of achieving high refractive index and flexibility suitable for use as an adhesive, it can be, for example, below 3.000, below 2.500, below 2.000, below 1.950, below 1.900, or below 1.850.

[0130] It should be noted that the additive (H) RO The refractive index of the sample was measured using an Abbe refractometer at a wavelength of 589 nm and a temperature of 25 °C, in the same manner as the refractive index of the monomer. If the manufacturer provides a nominal value for the refractive index at 25 °C, that value can be used.

[0131] Additives (H) RO The refractive index n b Refractive index n of acrylic polymers a The difference, i.e., n b -n a (hereinafter also referred to as "Δn") A The value is set to greater than 0. In some methods, Δn A For example, it can be 0.02 or higher, 0.05 or higher, 0.07 or higher, 0.10 or higher, 0.15 or higher, or 0.20 or higher, or 0.25 or higher. This can be achieved by selecting acrylic polymers and additives (H... RO And thus Δn A It becomes larger, with additives (H) RO The use of [a specific ingredient] tends to increase the refractive index effect. Additionally, additives (H [a specific ingredient]) within the adhesive [can also contribute to this effect]. RO From the perspective of compatibility, in some ways, Δn A For example, it can be below 0.70, below 0.60, below 0.50, below 0.40, or below 0.35.

[0132] In some methods, additives (H) RO The refractive index n b With the addition of this additive (H) RO The refractive index n of the adhesive T The difference, i.e., n b -n T (hereinafter also referred to as "Δn") B ") can be set to greater than 0. In some methods, Δn B For example, it can be 0.02 or higher, 0.05 or higher, 0.07 or higher, 0.10 or higher, 0.15 or higher, or 0.20 or higher, or 0.25 or higher. This can be achieved by selecting the composition of the adhesive and the additives (H... RO And thus Δn B It becomes larger, with additives (H) RO The use of [a specific ingredient] tends to increase the refractive index effect. Furthermore, from the perspectives of adhesive compatibility and adhesive transparency, in some methods, Δn [is considered to increase the refractive index]. B For example, it can be below 0.70, below 0.60, below 0.50, below 0.40, or below 0.35.

[0133] As an additive (H) RO The molecular weight of the organic materials 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 high refractive index and other properties (such as suitability for adhesive flexibility, haze, and other optical properties), in some methods, additives (H... RO The molecular weight of the additive (H) is preferably below about 10,000, more preferably below 5,000, and even more preferably below 3,000 (e.g., below 1,000). It can be below 800, below 600, below 500, or below 400. RO When the molecular weight of the additive (H) is not too large, it can be advantageous from the viewpoint of improving compatibility within the adhesive. Additionally, the additive (H) RO The molecular weight of the additive (H) can be, for example, 130 or more, or 150 or more. In some methods, the molecular weight of the additive (H) is... RO From the perspective of increasing the refractive index of ), additives (H) RO The molecular weight of the additive is preferably 170 or higher, more preferably 200 or higher, and can be 230 or higher, 250 or higher, 270 or higher, 500 or higher, 1000 or higher, or 2000 or higher. In some embodiments, polymers with a molecular weight of around 1000 to 10000 (e.g., 1000 or higher but lower than 5000) can be used as additives (H). RO ).

[0134] As an additive (H) RO The molecular weight of the additive (H) can be calculated based on its chemical structure for non-polymers or polymers with low polymerization degree (e.g., around 2-5 polymers), or determined using matrix-assisted laser desorption / ionization time-of-flight mass spectrometry (MALDI-TOF-MS). RO When the polymer is a polymer with a higher degree of polymerization, the weight-average molecular weight (Mw) based on GPC performed under appropriate conditions can be used. If a nominal value of the molecular weight is provided by the manufacturer, etc., that nominal value can be used.

[0135] It can be used as an additive (H) RO Examples of organic materials for the option include, but are not limited to, organic compounds having aromatic rings, organic compounds having heterocycles (which may be aromatic or non-aromatic heterocycles).

[0136] As an additive (H) RO The aromatic ring of the above-mentioned organic compound with an aromatic ring (hereinafter also referred to as "aromatic ring-containing compound") may be selected from the same aromatic ring as that of the compound used as a monomer (A1).

[0137] The aromatic ring described above may have one or more substituents on the cyclizing atom, or it may not have any substituents. When substituents are present, examples of such substituents include alkyl, alkoxy, aryloxy, hydroxy, halogen atoms (fluorine, chlorine, bromine, etc.), hydroxyalkyl, hydroxyalkyloxy, epoxypropoxy, etc., but are not limited to these. Among the substituents containing carbon atoms, the number of carbon atoms contained in the substituent is, for example, 1 to 10, advantageously 1 to 6, preferably 1 to 4, more preferably 1 to 3, for example, 1 or 2. In some embodiments, the aromatic ring described above may be an aromatic ring that does not have substituents on the cyclizing atom, or has one or more substituents selected from the group consisting of alkyl, alkoxy, and halogen atoms (e.g., bromine atoms).

[0138] As an additive (H) RO Examples of aromatic ring-containing compounds include, for example, compounds that can be used as monomers (A1); oligomers containing compounds that can be used as monomers (A1) as monomer units; compounds formed by removing and replacing a group having an olefinically unsaturated group (which may be a substituent bonded to a cyclic atom) or a portion of that group constituting the olefinically unsaturated group with a hydrogen atom or a group not having an olefinically unsaturated group (e.g., hydroxyl, amino, halogen atom, alkyl, alkoxy, hydroxyalkyl, hydroxyalkyloxy, epoxypropoxy, etc.) from a compound that can be used as an additive (H RONon-limiting examples of aromatic ring-containing compounds may include: benzyl acrylate, m-phenoxybenzyl acrylate, 2-(o-phenylphenoxy)ethyl acrylate, phenoxyethyl acrylate, phenoxydiethylene glycol acrylate, phenoxy polyethylene glycol acrylate, 2-hydroxy-3-phenoxypropyl acrylate, monomers having a fluorene structure, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure, etc., aromatic ring-containing monomers; 3-phenoxybenzyl alcohol, dinaphthothiophene and its derivatives (e.g., compounds with a structure in which one or more substituents selected from hydroxyl, methanol, diethanol, glycidyl, etc., are bonded to the dinaphthothiophene ring), etc., aromatic ring-containing compounds without olefinic unsaturated groups; etc. Furthermore, aromatic ring-containing compounds may be oligomers containing such aromatic ring-containing monomers as monomer units (preferably oligomers with a molecular weight of about 5000 or less, more preferably about 1000 or less; for example, oligomers of about 2 to 5 polymers). The aforementioned oligomers may be, for example, homopolymers of monomers containing aromatic rings; copolymers of one or more monomers containing aromatic rings; copolymers of one or more monomers containing aromatic rings with other monomers; etc. As the aforementioned other monomers, one or more monomers without aromatic rings may be used.

[0139] In some methods, as an additive (H) RO From the perspective of easily obtaining a high refractive index effect, organic compounds having two or more aromatic rings per molecule (hereinafter also referred to as "compounds containing multiple aromatic rings") are preferred. Compounds containing multiple aromatic rings may or may not have polymerizable functional groups such as olefinic unsaturated groups. Furthermore, compounds containing multiple aromatic rings can be polymers or non-polymers. Additionally, the aforementioned polymers can be oligomers containing monomers containing multiple aromatic rings as monomer units (preferably oligomers with a molecular weight of about 5000 or less, more preferably about 1000 or less; for example, oligomers of about 2 to 5 polymers). The aforementioned oligomers can be, for example, homopolymers of monomers containing multiple aromatic rings; copolymers of one or more monomers containing multiple aromatic rings; copolymers of one or more monomers containing multiple aromatic rings with other monomers; etc. The aforementioned other monomers can be monomers containing aromatic rings that are not monomers containing multiple aromatic rings, monomers without aromatic rings, or combinations thereof.

[0140] Non-limiting examples of compounds containing multiple aromatic rings include: compounds having a structure in which two or more non-fused aromatic rings are bonded together by a linking group; compounds having a structure in which two or more non-fused aromatic rings are directly (i.e., without the aid of other atoms) chemically bonded together; compounds having a fused aromatic ring structure; compounds having a fluorene structure; compounds having a dinaphthothiophene structure; and compounds having a dibenzothiophene structure. Compounds containing multiple aromatic rings may be used alone or in combination of two or more.

[0141] As specific examples of the compounds having the fluorene structure, in addition to the monomers having the fluorene structure and the oligomers of the homopolymers or copolymers thereof, examples include 9,9-bis(4-hydroxyphenyl)fluorene (refractive index: 1.68), 9,9-bis(4-aminophenyl)fluorene (refractive index: 1.73), 9,9-bis(4-hydroxy-3-methylphenyl)fluorene (refractive index: 1.68), 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (refractive index: 1.65), and other 9,9-bisphenylfluorene and their derivatives.

[0142] As specific examples of compounds having the dinaphthothiophene structure, in addition to the monomers having the dinaphthothiophene structure and oligomers of homopolymers or copolymers thereof, examples include dinaphthothiophene (refractive index: 1.808); 6-hydroxymethyl dinaphthothiophene (refractive index: 1.766) and other hydroxyalkyl dinaphthothiophenes; 2,12-dihydroxydinaphthothiophene (refractive index: 1.750) and other dihydroxydinaphthothiophenes; 2,12-di... Dihydroxyalkyloxydinaphthothiophene (refractive index: 1.677) and other dihydroxyalkyloxydinaphthothiophenes; 2,12-diglycidyloxydinaphthothiophene (refractive index: 1.723) and other diglycidyloxydinaphthothiophenes; 2,12-diallyloxydinaphthothiophene (abbreviation: 2,12-DAODNT, refractive index: 1.729) and other dinaphthothiophenes having two or more olefinic unsaturated groups; and other dinaphthothiophenes and their derivatives.

[0143] As specific examples of compounds having the dibenzothiophene structure, in addition to the monomers having the dibenzothiophene structure and the oligomers that are homopolymers or copolymers of the monomers, examples include dibenzothiophene (refractive index: 1.607), 4-dimethyldibenzothiophene (refractive index: 1.617), and 4,6-dimethyldibenzothiophene (refractive index: 1.617).

[0144] As a potential additive (H) ROExamples of heterocyclic organic compounds (hereinafter also referred to as heterocyclic organic compounds) that are options for the following can be listed: thioepoxides, compounds having triazine rings, etc. As an example of a thioepoxide, the bis(2,3-cyclothiopropyl) disulfide and its polymer (refractive index 1.74) disclosed in Japanese Patent No. 3712653 can be listed. As an example of a compound having a triazine ring, compounds having at least one triazine ring (e.g., 3 to 40, preferably 5 to 20) per molecule can be listed. It should be noted that triazine rings are aromatic; therefore, compounds having triazine rings are also included in the above concept of compounds containing aromatic rings. Furthermore, compounds having multiple triazine rings are also included in the above concept of compounds containing multiple aromatic rings.

[0145] In some methods, as an additive (H) RO The preferred choice is a compound without olefinic unsaturated groups. This suppresses the deterioration of the adhesive composition caused by heat and light (due to gelation and increased viscosity leading to decreased leveling properties) and improves storage stability. From the presence of this additive (H... RO From the viewpoint of suppressing dimensional changes, deformations (warping, undulations, etc.), and optical distortions caused by the reaction of olefinic unsaturated groups in adhesive sheets containing adhesive layers and laminates containing such adhesive sheets, it is also preferable to use additives (H) that do not have olefinic unsaturated groups. RO ).

[0146] Using oligomers as additives (H) RO In this process, the oligomer can be obtained by polymerizing the corresponding monomer components using known methods. When manufacturing the above-mentioned oligomer via free radical polymerization, polymerization initiators, chain transfer agents, emulsifiers, etc., used for free radical polymerization can be appropriately added to the monomer components to carry out polymerization. There are no particular limitations on the polymerization initiators, chain transfer agents, emulsifiers, etc., used for free radical polymerization, and they can be selected and used appropriately. It should be noted that 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; their amounts should be adjusted appropriately according to their types.

[0147] Examples of chain transfer agents include lauryl thiol, glycidyl thiol, thioethanol, 2-mercaptoethanol, α-thioglycerol, mercaptoacetic acid, 2-ethylhexyl mercaptoacetic acid, and 2,3-dimercapto-1-propanol. One chain transfer agent can be used alone, or two or more can be used in combination. The amount of chain transfer agent used can be set according to the composition of the monomer components used in the synthesis of the oligomer, the type of chain transfer agent, etc., to obtain an oligomer with the desired weight-average molecular weight. In some cases, it is appropriate to set the amount of chain transfer agent to about 15 parts by weight or less relative to 100 parts by weight of the total amount of monomers used in the synthesis of the oligomer; it can be 10 parts by weight or less, or about 5 parts by weight or less. There is no particular limitation on the lower limit of the amount of chain transfer agent used relative to 100 parts by weight of the total amount of monomers used in the synthesis of the oligomer; for example, it can be 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.

[0148] Additives (H) RO The amount of additive (H) relative to 100 parts by weight of acrylic polymer (or their total amount when using multiple compounds) 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 methods, additives (H) RO The amount of the acrylic polymer used, for example, can be set to 80 parts by weight or less, relative to 100 parts by weight. From the viewpoint of achieving a good balance between increasing the refractive index of the adhesive and suppressing the reduction of adhesive and optical properties, setting it to 60 parts by weight or less is advantageous, and preferably 45 parts by weight or less. In some approaches where adhesive and optical properties are given greater emphasis, the additive (H... RO The amount of additive (H) used relative to 100 parts by weight of acrylic polymer can be, for example, 30 parts by weight or less, 20 parts by weight or less, 15 parts by weight or less, or 10 parts by weight or less. Furthermore, from the viewpoint of increasing the refractive index of the adhesive, the additive (H) RO The amount used relative to 100 parts by weight of acrylic polymer can be, for example, 1 part by weight or more, 3 parts by weight or more, preferably 5 parts by weight or more, 7 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or 20 parts by weight or more.

[0149] (Cross-linking agent)

[0150] For purposes such as adjusting the cohesive strength of the adhesive, a crosslinking agent may be included as needed. As a crosslinking agent, crosslinking agents known in the field of adhesives can be used, such as isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, oxazoline-based crosslinking agents, melamine-based resins, and metal chelate-based crosslinking agents. Among these, isocyanate-based crosslinking agents are preferred. Other examples of crosslinking agents include monomers having two or more olefinic unsaturated groups per molecule, i.e., polyfunctional monomers. One type of crosslinking agent may be used alone, or two or more may be used in combination.

[0151] As isocyanate-based crosslinking agents, isocyanate compounds with two or more functionalities can be used, such as aliphatic polyisocyanates like trimethylene diisocyanate, butylene diisocyanate, hexamethylene diisocyanate (HDI), and dimer diisocyanate; alicyclic isocyanates like cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), and 1,3-bis(isocyanate-methyl)cyclohexane; aromatic isocyanates like 2,4-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, and phenylenediamine diisocyanate (XDI); and polyisocyanate modifiers that have been modified using urea-formate bonds, biuret bonds, isocyanurate bonds, urea-dione bonds, urea bonds, carbodiimide bonds, urea-ketimide bonds, and oxadiazine-trione bonds; etc. Examples of commercially available products include Takenate 300S, Takenate 500, Takenate 600, Takenate D165N, Takenate D178N (and above, manufactured by Takeda Pharmaceutical Company Limited), Sumidur T80, Sumidur L, Desmodur N3400 (and above, manufactured by Sumika Bayer Urethane Co., Ltd.), Millionate MR, Millionate MT, Coronate L, Coronate HL, Coronate HX (and above, manufactured by Tosoh Corporation), etc. Isocyanate compounds can be used alone or in combination of two or more. They can also be used in combination of difunctional isocyanate compounds and trifunctional or higher isocyanate compounds.

[0152] Examples of epoxy-based crosslinking agents include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerol diglycidyl ether, glycerol triglycidyl ether, 1,6-hexanediol glycidyl ether, trimethylolpropane triglycidyl ether, diglycidyl aniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylenediamine, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane. These can be used alone or in combination of two or more.

[0153] Examples of multifunctional monomers include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl methacrylate, ethylene methacrylate, divinylbenzene, bisphenol A di(meth)acrylate, epoxy acrylate, polyester acrylate, urethane acrylate, butyl glycol (meth)acrylate, and hexyl glycol di(meth)acrylate. Multifunctional monomers can be used alone or in combination of two or more.

[0154] When using a crosslinking agent (which can be a multifunctional monomer), the amount used is not particularly limited; for example, it can be set to a range of about 0.001 parts by weight to 5.0 parts by weight relative to 100 parts by weight of the monomer component. From the viewpoint of improving the adhesion of the adhered objects, in some embodiments, the amount of crosslinking agent used relative to 100 parts by weight of the monomer component is preferably 3.0 parts by weight or less, more preferably 2.0 parts by weight or less, and can be 1.0 parts by weight or less, 0.5 parts by weight or less, or 0.2 parts by weight or less. In addition, from the viewpoint of appropriately maximizing the effect of the crosslinking agent, in some embodiments, the amount of crosslinking agent used relative to 100 parts by weight of the monomer component can be, for example, 0.005 parts by weight or more, 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.08 parts by weight or more.

[0155] To facilitate a more efficient crosslinking reaction, a crosslinking catalyst can be used. Examples of crosslinking catalysts include metal-based crosslinking catalysts such as tetrabutyl titanate, tetraisopropyl titanate, iron acetylacetone, butyl tin oxide, and dioctyltin dilaurate. Among these, tin-based crosslinking catalysts such as dioctyltin dilaurate are preferred. There is no particular limitation on the amount of crosslinking catalyst used. Considering the balance between the rate of the crosslinking reaction and the pot life of the adhesive composition, the amount of crosslinking catalyst used relative to 100 parts by weight of the monomer component can be set, for example, in the range of about 0.0001 parts by weight and less than 1 part by weight, preferably in the range of 0.001 parts by weight and less than 0.5 parts by weight.

[0156] The adhesive composition may contain a keto-enol tautomer as a crosslinking delay agent. This extends the pot life of the adhesive composition. For example, in adhesive compositions containing isocyanate-based crosslinking agents, a keto-enol tautomer is preferably used. Various β-dicarbonyl compounds can be used as keto-enol tautomers. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) and acetoacetates (methyl acetoacetate, ethyl acetoacetate, etc.) are preferred. One keto-enol tautomer can be used alone or in combination of two or more. The amount of the keto-enol tautomer relative to 100 parts by weight of the monomer component can be, for example, 0.1 parts by weight or more and 20 parts by weight or less, 0.5 parts by weight or more and 10 parts by weight or less, or 1 part by weight or more and 5 parts by weight or less.

[0157] (Thickening agent)

[0158] The adhesive compositions disclosed herein may contain tackifiers. Known tackifiers such as rosin-based, terpene-based, phenolic, hydrocarbon-based, ketone-based, polyamide-based, epoxy-based, and elastic-system tackifiers can be used as tackifiers. One or more of these can be used alone or in combination. The amount of tackifier used is not particularly limited and can be set according to the purpose and application to achieve appropriate adhesive properties. In some embodiments, from the viewpoint of refractive index and transparency, it is appropriate to use 30 parts by weight or less of the tackifier relative to 100 parts by weight of the monomer component, preferably 10 parts by weight or less, and more preferably 5 parts by weight or less. The technology disclosed herein can preferably be implemented without the use of tackifiers.

[0159] (Leveling agent)

[0160] The adhesive compositions disclosed herein may contain leveling agents as needed to improve the appearance of the adhesive layer formed from the composition (e.g., to improve the uniformity of thickness) and to improve the coatability of the adhesive composition. Non-limiting examples of leveling agents include acrylic leveling agents, fluorinated leveling agents, and silicone leveling agents. For example, suitable substances can be selected from commercially available leveling agents and used by conventional methods.

[0161] In some embodiments, as the leveling agent described above, a polymer (hereinafter referred to as "polymer (B)") comprising a monomer raw material (hereinafter referred to as "monomer S1") having a polyorganosiloxane backbone and an acrylic monomer (hereinafter referred to as "monomer raw material B") may preferably be used. Polymer (B) may refer to a copolymer of monomer S1 and an acrylic monomer. Polymer (B) may be used alone or in combination of two or more.

[0162] There are no particular limitations on monomer S1, and any monomer containing a polyorganosiloxane backbone can be used. Monomer S1 is preferably a monomer with a polymerizable reactive group at one end. Specifically, monomer S1 with a polymerizable reactive group at one end and no functional group at the other end that would crosslink with acrylic polymers is preferred. Commercially available examples include single-terminal reactive silicone oils manufactured by Shin-Etsu Chemical Co., Ltd. (e.g., trade names 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.

[0163] The functional group equivalent of monomer S1 can be, for example, around 100 g / mol to 30,000 g / mol. In some preferred embodiments, the functional group equivalent is, for example, 500 g / mol or more, 800 g / mol or more, 1500 g / mol or more, or 2000 g / mol or more. Alternatively, the functional group equivalent can be, for example, below 20,000 g / mol, below 10,000 g / mol, below 7,000 g / mol, or below 5,500 g / mol. When the functional group equivalent of monomer S1 is within the above range, it is easy to achieve good leveling effect.

[0164] It should be noted that 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 equivalents of each monomer and the weight fraction of that monomer.

[0165] Here, "functional group equivalent" refers to the weight of the backbone (e.g., polydimethylsiloxane) bonded by each functional group. The unit g / mol is used to convert to 1 mol of functional groups. The functional group equivalent of monomer S1 can be determined, for example, based on nuclear magnetic resonance (NMR)... 1 It is calculated from the spectral intensity of H-NMR (proton NMR). 1 The calculation of the functional group equivalent (g / mol) of monomer S1 from the spectral intensity of H-NMR can be based on 1 The usual structural analysis methods in H-NMR spectroscopy should be followed as described in Japanese Patent No. 5951153, as needed. In the functional group equivalent of monomer S1, the aforementioned functional groups refer to polymerizable functional groups (e.g., olefinic unsaturated groups such as (meth)acryloyl, vinyl, allyl, etc.).

[0166] The content of monomer S1 in monomer raw material B can be an appropriate value within the range that allows the desired effect to be 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 can be, for example, 5-60% by weight, 10-50% by weight, or 15-40% by weight.

[0167] In addition to monomer S1, monomer raw material B also contains acrylic monomers capable of copolymerizing with monomer S1. This improves the compatibility of the 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 chain-like (including linear and branched) alkyl groups, excluding alicyclic hydrocarbon groups described later. In some embodiments, monomer raw material B may contain (meth)acrylic acid C. 4-12 Alkyl ester (preferably (meth)acrylic acid C) 4-10 Alkyl esters, such as (meth)acrylic acid C 6-10 At least one of alkyl esters. In some other embodiments, monomer raw material B may contain methacrylic acid C. 1-18 Alkyl ester (preferably C methacrylate) 1-14 Alkyl esters, such as C methacrylate 1-10 At least one of alkyl esters. Monomer raw material B may, for example, contain one or more of methyl methacrylate (MMA), n-butyl methacrylate (BMA), and 2-ethylhexyl methacrylate (2EHMA) as acrylic monomers.

[0168] Other examples of the aforementioned acrylic monomers include (meth)acrylates having alicyclic hydrocarbon groups. Examples include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentyl (meth)acrylate, and 1-adamantyl (meth)acrylate. Alternatively, (meth)acrylates without alicyclic hydrocarbon groups may also be used.

[0169] The content of the above-mentioned alkyl methacrylate and the above-mentioned methacrylate having alicyclic hydrocarbon group in monomer raw material B can be, for example, 10% or more and 95% or less by weight, 20% or more and 95% or less by weight, 30% or more and 90% or less by weight, 40% or more and 90% or less by weight, or 50% or more and 85% or less by weight.

[0170] Other examples of monomers that can be included together with monomer S1 in monomer raw material B include: carboxyl-containing monomers, anhydride-containing monomers, hydroxyl-containing monomers, epoxy-containing monomers, cyano-containing monomers, isocyanate-containing monomers, amide-containing monomers, monomers having a ring containing a nitrogen atom, aminoalkyl esters of (meth)acrylate, vinyl esters, vinyl ethers, olefins, (meth)acrylates having an aromatic hydrocarbon group, (meth)acrylates containing a halogen atom, etc.

[0171] The Mw of polymer (B) can be, for example, 5000 or more, preferably 10000 or more, or 15000 or more. Alternatively, the Mw of polymer (B) can be, for example, 200000 or less, preferably 100000 or less, 50000 or less, or 30000 or less. By setting the Mw of polymer (B) within an appropriate range, suitable compatibility and leveling properties can be achieved.

[0172] Polymer (B) can be produced, for example, by polymerizing the aforementioned monomers using known methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization.

[0173] To adjust the molecular weight of polymer (B), chain transfer agents can be used as needed. Examples of chain transfer agents include: compounds containing thiol groups such as n-dodecyl mercaptan, mercaptoethanol, and α-thioglycerol; thioglycolic acid esters such as thioglycolic acid and methyl thioglycolate; α-methylstyrene dimers; etc. There are no particular limitations on the amount of chain transfer agent used; it can be appropriately set to obtain polymer (B) with the desired molecular weight. In some methods, the amount of chain transfer agent used relative to 100 parts by weight of the monomer can be, for example, 0.1 to 5 parts by weight, 0.2 to 3 parts by weight, or 0.5 to 2 parts by weight.

[0174] The amount of polymer (B) used relative to 100 parts by weight of acrylic polymer can be set to, for example, 0.001 parts by weight or more. From the viewpoint of obtaining a better performance, it can be set to 0.01 parts by weight or more, or 0.03 parts by weight or more. Alternatively, the amount of polymer (B) used can be, for example, 3 parts by weight or less. From the viewpoint of reducing the influence on the refractive index, it is appropriate to set it to 1 part by weight or less, or 0.5 parts by weight or less, or 0.1 parts by weight or less.

[0175] (Other additives)

[0176] Furthermore, the adhesive compositions disclosed herein may, as needed, include plasticizers, softeners, colorants (dyes, pigments, etc.), fillers, antistatic agents, anti-aging agents, ultraviolet absorbers, antioxidants, light stabilizers, preservatives, and other known additives that can be used in adhesive compositions, without significantly impairing the effects of the invention. Regarding these various additives, conventionally known substances can be used by conventional methods, and since they do not particularly characterize the invention, detailed descriptions are omitted.

[0177] <Adhesive>

[0178] The adhesives disclosed herein can be formed using any of the adhesive compositions described above. This adhesive can be a cured product of the aforementioned adhesive compositions, obtained by curing solvent-based, active energy ray-cured, water-dispersible, or hot-melt adhesive compositions through drying, crosslinking, polymerization, cooling, etc. The curing method of the adhesive composition (e.g., drying, crosslinking, polymerization, cooling, etc.) can be applied in only one manner, or in two or more manner simultaneously or in multiple stages. For solvent-based adhesive compositions, typically the composition can be dried (preferably further crosslinked) to form an adhesive. For active energy ray-cured adhesive compositions, typically, polymerization and / or crosslinking reactions are carried out by irradiation with active energy rays to form the adhesive. When drying is required for active energy ray-cured adhesive compositions, irradiation with active energy rays after drying is preferable.

[0179] (Refractive index)

[0180] The adhesive disclosed herein is an acrylic polymer containing a high content of monomer (Al) in its monomeric components, thereby exhibiting a refractive index of a specified value or higher. According to the technology disclosed herein, adhesives with a refractive index of, for example, 1.560 or higher (preferably higher than 1.570), adhesive compositions capable of forming such adhesives, and adhesive sheets containing the aforementioned adhesives can be provided.

[0181] It should be noted that, in this specification, the refractive index of the adhesive refers to the refractive index of the adhesive surface (adhesive surface). The refractive index of the adhesive can be measured using a commercially available refractive index measuring device (Abbe refractometer) at a measurement wavelength of 589 nm and a measurement temperature of 25°C. For example, the Abbe refractometer can be the ATAGO "DR-M4" or an equivalent model. As the test sample, an adhesive layer formed from the adhesive of the object being evaluated can be used. Specifically, the refractive index of the adhesive can be measured using the method described in the examples below. The refractive index of the adhesive can be adjusted, for example, by the composition of the adhesive (e.g., the composition of the monomer components constituting the acrylic polymer).

[0182] In some embodiments, the refractive index of the adhesive is preferably 1.575 or higher, more preferably 1.580 or higher, even more preferably 1.585 or higher, and particularly preferably 1.590 or higher (e.g., 1.595 or higher). With an adhesive having this refractive index, when used to adhere to a material with a high refractive index, light reflection at the interface with the adhered object can be appropriately suppressed. According to the technology disclosed herein, such a refractive index can be achieved even for adhesives that do not specifically use the high refractive index particles described below. The preferred upper limit of the refractive index of the adhesive can vary depending on the refractive index of the adhered object, and is therefore not limited to a specific range; for example, it can be 1.700 or lower, 1.670 or lower, or 1.650 or lower.

[0183] The adhesives disclosed herein may contain high-refractive-index particles as any component. Here, high-refractive-index particles refer to particles that, by being included in the adhesive, can increase the refractive index of the adhesive. Hereafter, high-refractive-index particles are sometimes referred to as "particle P". HRI HRI stands for High Refractive Index.

[0184] As particulate P HRI For example, one or more types of materials comprising particles having a refractive index of 1.60 or higher, preferably 1.70 or higher (but may be 1.80 or higher, 1.90 or higher, and even 2.00 or higher) may be used. The constituent particles P HRI There is no specific upper limit to the refractive index of the material; for example, it can be below 3.00, below 2.80, below 2.50, below 2.20, or below 2.00. The constituent particles P HRIThe refractive index of the material is the refractive index measured for a single layer of that material (set as the film thickness for which the refractive index can be measured) using a commercially available spectroellipsometer at a measurement wavelength of 589 nm and a measurement temperature of 25 °C. As the spectroellipsometer, for example, the product name "EC-400" (manufactured by JA.Woolam) or its equivalent can be used.

[0185] Particle P HRI There are no particular limitations on the type of material; one or more materials that can improve the refractive index of the adhesive sheet can be selected from metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. As particle P... HRI Particles that can improve the refractive index of the adhesive sheet can be preferably used from inorganic oxides (e.g., metal oxides). As a constituent particle P HRI Suitable examples of materials include inorganic oxides (specifically, metal oxides) such as titanium oxide (titanium oxide, TiO2), zirconium oxide (zirconia, ZrO2), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, and niobium oxide (Nb2O5, etc.). Particles formed from these inorganic oxides (e.g., metal oxides) can be used alone or in combination of two or more. Particles formed from titanium oxide and zirconium oxide are preferred, and particles formed from zirconium oxide are particularly preferred. Furthermore, as metal particles, materials such as iron-based, zinc-based, tungsten-based, and platinum-based materials can have high refractive indices. As organic particles, particles formed from resins such as styrene-based resins, phenolic resins, polyester resins, and polycarbonate resins have relatively high refractive indices. As organic-inorganic composite particles, examples include composites of the above-mentioned inorganic and organic materials, and particles obtained by coating inorganic particles with organic materials such as resins. As particle P... HRI From the viewpoint of compatibility with adhesive components, particles that have undergone surface treatment of the aforementioned organic and inorganic particles with a surface treatment agent can be used.

[0186] Particle P HRI The average particle size is not particularly limited, and particles of an appropriate size that can achieve the desired increase in refractive index by being included in the binder can be used. Particle P HRI The average particle size can be set to approximately 1 nm or more, and approximately 5 nm or more is appropriate. From the perspectives of improved refractive index and processability, particle P... HRI The average particle size is preferably about 10 nm or more, and can be about 20 nm or more, or about 30 nm or more. In addition, from the viewpoint of maintaining adhesive properties, the upper limit of the above-mentioned average particle size is, for example, about 300 nm or less. From the viewpoint of improving the refractive index, it is preferably about 100 nm or less, more preferably about 70 nm or less, and even more preferably about 50 nm or less. It can also be about 35 nm or less (for example, about 25 nm or less).

[0187] It should be noted that the above-mentioned particle P HRI The average particle size refers to the volume average particle size, specifically, the particle size distribution measured using a particle size distribution measuring device based on laser scattering / diffraction, targeting particle P. HRI The particle size at the 50% cumulative value of the particle size distribution measured in the dispersion (50% volume average particle size; sometimes abbreviated as D below). 50 As a measuring device, for example, the product name "Microtrac MT3000II" or its equivalent, manufactured by Microtrac BEL, can be used.

[0188] Particles in adhesives HRI The content of the above-mentioned particles P is not specifically limited. HRI The content of P can vary depending on the target refractive index. For example, considering the required adhesive properties, the content of the aforementioned particles P... HRI The content of [amount] can be appropriately set to achieve a refractive index above the specified value.

[0189] Particles in adhesives HRI The content can be set to, for example, about 75% by weight or less; from the viewpoint of adhesive properties and transparency, it can be set to about 50% by weight or less, or even about 30% by weight or less. Particle P HRI There is no particular limit to the lower limit of its content; for example, it can be higher than 0% by weight, higher than 1% by weight, or higher than 5% by weight.

[0190] Particles in adhesives HRI The content can also be determined based on its relative relationship with the amount of the aforementioned acrylic polymer contained in the adhesive. Particle P HRI The content relative to 100 parts by weight of the aforementioned acrylic polymer can be, for example, set to about 100 parts by weight or less. From the viewpoint of adhesive properties and transparency, it can be set to about 60 parts by weight or less, or even about 40 parts by weight or less. Particle P HRI There is no particular limit to the lower limit of its content; for example, it can be higher than 0% by weight, higher than 1% by weight, or higher than 5% by weight.

[0191] (Storage modulus G')

[0192] The storage modulus G'(25) of the adhesive disclosed herein at 25°C is not particularly limited, and may be, for example, below 300 kPa, below 270 kPa, or below 250 kPa. From the viewpoint of improving the flexibility of the adhesive in the room temperature range (e.g., 25°C) and making it easier to bond with the adherend, it is appropriate for the storage modulus G'(25) of the adhesive to be below 200 kPa, preferably below 180 kPa, and more preferably below 160 kPa (e.g., below 140 kPa). In some embodiments, the storage modulus G'(25) of the adhesive may be below 100 kPa or below 90 kPa. There is no particular limitation on the lower limit of the storage modulus G'(25) of the adhesive, and from the viewpoint of processability, handleability, etc., it may be above 30 kPa, above 50 kPa, or above 70 kPa.

[0193] The storage modulus G'(50) of the adhesive disclosed herein at 50°C is not particularly limited, and may be, for example, below 100 kPa. In some embodiments, a storage modulus G'(50) below 60 kPa is appropriate, preferably below 40 kPa, and more preferably below 38 kPa (e.g., below 36 kPa). Adhesives with such a limited storage modulus G'(50) can readily improve their adhesion to the adherends by heating, thereby improving the bonding strength of the adherends. There is no particular limitation on the lower limit of the storage modulus G'(50) of the adhesive. In some embodiments, from the viewpoint of the heat resistance properties of the adhesive, the storage modulus G'(50) may be, for example, above 10 kPa, above 15 kPa, above 20 kPa, or above 23 kPa.

[0194] In some of the adhesives disclosed herein, the adhesive preferably satisfies at least one of the following conditions:

[0195] (a) The energy storage modulus G'(25) at 25°C is less than 200 kPa (e.g., less than 180 kPa); and

[0196] (b) The energy storage modulus G'(50) at 50°C is less than 40 kPa (e.g., less than 38 kPa).

[0197] From the viewpoint of adhesion to the adherend at room temperature (e.g., 25°C), an adhesive that at least satisfies condition (a) above is preferred. An adhesive that at least satisfies condition (b) above is preferred because its adhesion to the adherend can be easily improved by heating it to a temperature slightly higher than room temperature. For an adhesive that does not satisfy condition (a) above but satisfies condition (b) above, it has good reprocessability (re-adhesion) at the initial bonding stage at room temperature and can be used as a heat-activated adhesive that can effectively improve the peel strength from the adherend by heating it to a temperature slightly higher than room temperature.

[0198] (Storage modulus ratio (G'(50) / G'(25)))

[0199] In some embodiments of the adhesive disclosed herein, the ratio of the storage modulus G'(50) [kPa] to the storage modulus G'(25) [kPa], i.e., the storage modulus ratio G'(50) / G'(25), is, for example, 70% or less, or 40% or less, or 30% or less, or 20% or less. Adhesives with a small G'(50) / G'(25) ratio are suitable for use as the aforementioned heat-activated adhesives. There is no particular limitation on the lower limit of G'(50) / G'(25). For example, G'(50) / G'(25) is 5% or more, and from the viewpoint of the heat resistance properties of the adhesive, it is preferably 10% or more, or 12% or more, or 15% or more.

[0200] Storage moduli G'(25) and G'(50) can be determined by the method described in the examples below, and G'(50) / G'(25) can be calculated from the results. The storage moduli G'(25) and G'(50) and the storage modulus ratio (G'(50) / G'(25)) of the adhesive can be determined by the selection of the composition of the monomer components constituting the acrylic polymer (e.g., the selection of the type and content of monomer (Al), the use of crosslinking agent, the selection of type and amount of crosslinking agent, and the selection of additives (H). RO The selection of whether to use plasticizing materials, the type and amount of plasticizing materials used, etc., can be adjusted. For example, as a monomer (A1), by using a first monomer as the main component of the first monomer (A1) and combining it with a second monomer with a different chemical structure than the first monomer in a smaller amount, compared with the case of using the first monomer as the monomer (A1) alone, G'(50) and G'(25) can be reduced.

[0201] <Adhesive Sheet>

[0202] According to this specification, an adhesive sheet is provided having an adhesive layer. The adhesive constituting the adhesive layer may be an adhesive formed from any of the adhesive compositions disclosed herein (e.g., a cured product of the adhesive composition).

[0203] The aforementioned adhesive sheet can be a substrate-supported adhesive sheet having the adhesive layer on one or both sides of a non-peelable substrate (supporting substrate), or a substrate-free adhesive sheet (i.e., an adhesive sheet without a non-peelable substrate; typically, an adhesive sheet formed of an adhesive layer). The concept of adhesive sheet as used herein can include objects referred to as adhesive tape, adhesive labels, adhesive films, etc. The adhesive sheets disclosed herein can be in roll form or in single sheet form. Alternatively, they can be adhesive sheets further processed into various shapes.

[0204] The structure of a double-sided adhesive substrate-free adhesive sheet (substrate-free double-sided adhesive sheet) is illustrated in the figure. Figure 1 , 2 . Figure 1 The adhesive sheet 1 shown has a structure in which both sides 21A and 21B of the substrate-free adhesive layer 21 are protected by release liner 31 and 32, which at least the adhesive layer side serves as the release surface. Figure 2 The adhesive sheet 2 shown has a structure in which one surface (adhesive surface) 21A of the substrate-free adhesive layer 21 is protected by a release liner 31, which serves as a release surface on both sides. When it is wound, the other surface (adhesive surface) 21B of the adhesive layer 21 abuts against the back of the release liner 31, thereby forming a structure in which the other surface 21B is also protected by the release liner 31. For example, from the viewpoint of reducing the thickness of the adhesive sheet and improving the transparency of the adhesive sheet, the technology disclosed herein can preferably be implemented in this substrate-free form.

[0205] The adhesive sheet disclosed herein may, for example, have Figure 3 The cross-sectional structure is schematically shown in the diagram. Figure 3 The adhesive sheet 3 shown includes a support substrate 10, and a first adhesive layer 21 and a second adhesive layer 22 supported by a first surface 10A and a second surface 10B of the support substrate 10, respectively. Both the first surface 10A and the second surface 10B are non-peelable surfaces. The adhesive sheet 3 is used to adhere 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 the substrate. That is, the adhesive sheet 1 is constructed as a double-sided adhesive sheet. Before use, the adhesive sheet 3 has the following configuration: the first adhesive surface 21A and the second adhesive surface 22A are protected by release liner pads 31 and 32, which are at least peelable surfaces (peelable surfaces) on the adhesive side. Alternatively, the following configuration can be adopted: the release liner 32 is omitted, and a release liner with both sides serving as the release surface is used as the release liner 31. The second adhesive surface 22A is brought into contact with the back of the release liner 31 by winding the adhesive sheet 3, so that the second adhesive surface 22A is also protected by the release liner 31.

[0206] The technology disclosed herein can preferably be implemented in the form of a substrate-free or substrate-supported double-sided adhesive sheet for fixing or joining components (e.g., optical components). Alternatively, although not specifically illustrated, the adhesive sheet disclosed herein can also be in the form of a substrate-supported single-sided adhesive sheet with an adhesive layer on only one side of a non-peelable substrate (supporting substrate). Examples of single-sided adhesive sheets include those in... Figure 3 The configuration shown does not have either the first adhesive layer 21 or the second adhesive layer 22.

[0207] (Adhesive layer)

[0208] 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 coating machines such as gravure roller coaters, reverse roller coaters, licking roller coaters, dip roller coaters, bar coaters, doctor blade coaters, and spray coaters.

[0209] 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 can be, for example, 5 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, 50 μm or more, 70 μm or more, or 85 μm or more. Increasing the thickness of the adhesive layer tends to increase the adhesive strength. In other embodiments, the thickness of the adhesive layer can be, for example, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 120 μm or less. When the thickness of the adhesive layer is not too large, it can be advantageous from the viewpoint of making the adhesive sheet thinner. The technology disclosed herein can preferably be implemented with the thickness of the adhesive layer in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm). It should be noted that 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 thickness of the adhesive layer can be at least the thickness of the first adhesive layer. The thickness of the second adhesive layer can also be selected from the same range. Alternatively, 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.

[0210] (Haze value)

[0211] In some embodiments, the haze value of the adhesive layer constituting the adhesive sheet can be, for example, 5.0% or less, preferably 2.0% or less, more preferably 1.0% or less, 0.9% or less, 0.8% or less, 0.5% or less, or 0.3% or less. Adhesive sheets with such highly transparent adhesive layers, whether in a substrate-containing or substrate-free configuration, are preferably used for applications requiring high light transmittance (e.g., optical applications) or applications requiring good visual identification of the adhered objects through the adhesive sheet. There is no particular limitation on the lower limit of the haze value of the adhesive layer; from the viewpoint of improved transparency, a lower haze value is preferred. On the other hand, in some embodiments, considering refractive index and adhesive properties, the haze value can be, for example, 0.05% or more, or 0.1% or more. These haze values ​​related to the adhesive layer can also preferably be applied to the haze value of the adhesive sheet when the technology disclosed herein is implemented in the form of a substrate-free adhesive sheet (typically an adhesive sheet formed by an adhesive layer).

[0212] Here, "haze value" refers to the ratio of diffuse transmitted light to total transmitted light when visible light is irradiated onto the object being measured. It is also called turbidity. The haze value can be expressed by the following formula.

[0213] Th(%)=Td / Tt×100

[0214] In the above formula, Th is the haze value (%), Td is the scattered light transmittance, and Tt is the total transmittance. The haze value can be measured according to the method described in the examples below. The haze value of the adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the adhesive layer.

[0215] In some embodiments, the total light transmittance of the adhesive layer is preferably 86.0% or higher (e.g., 88.0% or higher, 90.0% or higher, or higher than 90.0%). Practically, the upper limit of the total light transmittance can be, for example, about 98% or lower, about 96% or lower, or about 95% or lower. In some embodiments, considering refractive index and adhesive properties, the total light transmittance of the adhesive layer can be about 94% or lower, about 93% or lower, or about 92% or lower. The total light transmittance is measured using a commercially available transmittance meter according to JIS K 7136:2000. As a transmittance meter, the trade name "HAZEMETER HM-150" manufactured by Murakami Color Technology Research Institute or its equivalent can be used.

[0216] (Peel strength)

[0217] In some embodiments of the adhesive sheet disclosed herein, the peel strength of the adhesive sheet to the glass plate is preferably 2 N / 25 mm or more, more preferably 4 N / 25 mm or more, and can be 8 N / 25 mm or more, 10 N / 25 mm or more, or 12 N / 25 mm or more. There is no particular limitation on the upper limit of the peel strength; for example, it can be 30 N / 25 mm or less, 25 N / 25 mm or less, or 20 N / 25 mm or less.

[0218] Here, the peel strength can be determined as follows: after pressing the adhesive onto an alkaline glass plate (the substrate) and placing it at 23°C and 50% RH for 30 minutes, the 180° peel adhesion force is measured at a peel angle of 180 degrees and a tensile speed of 300 mm / min. During the measurement, if necessary, a suitable lining material (e.g., a polyethylene terephthalate (PET) film with a thickness of approximately 25 μm to 50 μm) can be applied to the adhesive sheet to reinforce it. Specifically, the peel strength can be measured according to the method described in the examples below.

[0219] <Supporting substrate>

[0220] Some adhesive sheets can be in the form of a substrate-supported adhesive sheet with an adhesive layer on one or both sides of the supporting substrate. The material of the supporting substrate is not particularly limited and can be appropriately selected according to the purpose and method of use of the adhesive sheet. Non-limiting examples of usable substrates include polyolefin films with polyolefins as the main component, such as polypropylene (PP) and ethylene-propylene copolymer; polyester films with polyesters as the main component, such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN); and polyvinyl chloride films with polyvinyl chloride as the main component; foamed sheets formed from foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam; woven and nonwoven fabrics based on various fibrous materials (such as natural fibers like hemp and cotton, synthetic fibers like polyester and vinylon, and semi-synthetic fibers like cellulose acetate); paper types such as Japanese paper, premium paper, kraft paper, and crepe paper; and metal foils such as aluminum foil and copper foil; etc. It can be a substrate composed of these composite materials. Examples of such composite substrates include substrates with structures formed by laminating metal foil and the aforementioned plastic film, and plastic substrates reinforced with inorganic fibers such as glass cloth.

[0221] In some embodiments, various film substrates can be preferably used. These film substrates can be porous substrates such as foamed films or nonwoven sheets, or non-porous substrates, or substrates with a structure consisting of laminated porous and non-porous layers. In some embodiments, a substrate comprising a self-supporting or independent resin film capable of independently maintaining its shape can be preferably used as the base film. Here, "resin film" refers to a non-porous structure, typically a substantially bubble-free (non-porous) resin film. Therefore, the resin film is a concept distinct from foamed films and nonwoven fabrics. As the resin film, a self-supporting or independent film capable of independently maintaining its shape can be preferably used. The resin film can be a single-layer structure or a multi-layer structure with two or more layers (e.g., a three-layer structure).

[0222] Resin materials used to form resin films include, for example, polyester, polyolefin, nylon 6, nylon 66, some aromatic polyamides such as polyamide (PA), polyimide (PI), polyamide-imide (PAI), polyether ether ketone (PEEK), polyether sulfone (PES), polyphenylene sulfide (PPS), polycarbonate (PC), polyurethane (PU), ethylene-vinyl acetate copolymer (EVA), polytetrafluoroethylene (PTFE) and other fluoropolymers, acrylic resins, polyacrylates, polystyrene, polyvinyl chloride, polyvinylidene chloride and other resins.

[0223] The aforementioned resin film can be a film formed using a resin material containing only one such resin, or a film formed using a blend of two or more resin materials. The resin film can be unstretched or stretched (e.g., uniaxially or biaxially stretched). For example, PET film, PBT film, PEN film, unstretched polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low-density polyethylene (LDPE) film, linear low-density polyethylene (LLDPE) film, PP / PE blend film, etc., are preferred. Examples of resin films preferred from the viewpoint of strength and dimensional stability include PET film, PEN film, PPS film, and PEEK film. From the viewpoint of ease of acquisition, PET film and PPS film are particularly preferred, with PET film being the most preferred.

[0224] In the resin film, known additives such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, lubricants, and antiblocking agents may be added as needed, without significantly impairing the effects of the present invention. The amount of additives added is not particularly limited and can be appropriately set according to the intended use of the adhesive sheet.

[0225] There are no particular limitations on the manufacturing method of resin films. For example, commonly known resin film forming methods such as extrusion molding, blow molding, T-die casting, and calendering can be appropriately used.

[0226] The aforementioned substrate may be substantially composed of such a base film. Alternatively, the aforementioned substrate may also include auxiliary layers in addition to the aforementioned base film. Examples of such auxiliary layers include optical property adjustment layers (e.g., coloring layers, anti-reflective layers), printing layers for imparting a desired appearance to the substrate, laminated layers, antistatic layers, primer layers, release layers, and other surface treatment layers.

[0227] In some embodiments, a light-transmitting substrate (hereinafter also referred to as a light-transmitting substrate) is preferably used as the supporting substrate. This allows for the formation of a light-transmitting adhesive sheet with a substrate. The total light transmittance of the light-transmitting substrate can be, for example, higher than 50%, or higher than 70%. In some preferred embodiments, the total light transmittance of the supporting substrate is 80% or higher, more preferably 90% or higher, and may also be 95% or higher (e.g., 95-100%). The aforementioned total light transmittance is measured using a commercially available transmittance meter according to JIS K 7136:2000. The transmittance meter used is the Murakami Color Technology Research Institute's trade name "HAZEMETER HM-150" or its equivalent. A suitable example of the aforementioned light-transmitting substrate is a light-transmitting resin film. The aforementioned light-transmitting substrate can be an optical film.

[0228] The thickness of the substrate is not particularly limited and can be selected according to the intended use and application method of the adhesive sheet. For example, the substrate thickness can be 500 μm or less, but from the viewpoint of the adhesive sheet's processability and workability, it is preferably 300 μm or less, 150 μm or less, 100 μm or less, 50 μm or less, 25 μm or less, or even 10 μm or less. A smaller substrate thickness tends to improve the ability to follow the surface shape of the adhered object. Furthermore, from the viewpoint of processability and workability, the substrate thickness can be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

[0229] For one side of the laminated adhesive layer in the substrate, conventional surface treatments such as corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, and the formation of a primer-based coating can be performed as needed. Such surface treatments can be used to improve the anchoring of the adhesive layer to the substrate. The composition of the primer used in the formation of the primer coating is not particularly limited and can be appropriately selected from known compositions. The thickness of the primer coating is not particularly limited, but is typically suitable at around 0.01 μm to 1 μm, preferably around 0.1 μm to 1 μm. Other treatments that can be performed on 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.

[0230] When the adhesive sheet disclosed herein is in the form of an adhesive sheet with a substrate, the thickness of the adhesive sheet can 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 processability, the thickness of the adhesive sheet can be, for example, 10 μm or more, 25 μm or more, 80 μm or more, or 130 μm or more.

[0231] It should be noted that the thickness of the adhesive sheet refers to the thickness of the portion that is adhered to the object being bonded. For example, for Figure 3 The adhesive sheet 3 shown refers to the thickness from the first adhesive surface 21A to the second adhesive surface 22A, excluding the thickness of the release liner 31 and 32.

[0232] <Adhesive sheet with release liner>

[0233] The adhesive sheet disclosed herein can take the form of an adhesive article obtained by abutting the surface (adhesive surface) of an adhesive layer against the release surface of a release liner. Therefore, according to this specification, an adhesive sheet (adhesive article) with a release liner is provided, comprising: any of the adhesive sheets disclosed herein, and a release liner having a release surface abutting against the adhesive surface of the adhesive sheet.

[0234] There are no particular limitations on the release liner. For example, release liners with a release layer on the surface of the liner substrate, such as resin film or paper (which may be paper laminated with resins such as polyethylene), or release liners containing resin films made of low-adhesion materials such as fluoropolymers (polytetrafluoroethylene, etc.) or polyolefin resins (polyethylene, polypropylene, etc.) can be used. From the perspective of excellent surface smoothness, release liners with a release layer on the surface of the resin film used as the liner substrate, or release liners containing resin films made of low-adhesion materials, are preferred. As for the resin film, there are no particular limitations as long as it is a film that can protect the adhesive layer. Examples include polyethylene (PE) film, polypropylene (PP) film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyester film (PET film, PBT film, etc.), polyurethane film, and ethylene-vinyl acetate copolymer film. In forming the aforementioned release layer, known release agents such as organosilicon-based release agents, long-chain alkyl-based release agents, olefin-based release agents, fluorine-based release agents, fatty acid amide-based release agents, molybdenum sulfide, and silica powder can be used.

[0235] <Applications>

[0236] The materials (adhesive materials) to which the adhesive sheet disclosed herein is adhered are not particularly limited, but may include: metallic materials such as copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, chromium, zinc, or alloys containing two or more of these materials; polyimide resins, acrylic resins, polyether nitrile resins, polyethersulfone resins, polyester resins (PET resins, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyether ether ketone resins, polyamide resins (such as aramid resins), polyarylate resins, polycarbonate resins, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, vinyl butyral polymers, liquid crystal polymers, and various other resin materials (typically plastic materials); alumina, zirconium oxide, alkaline glass, alkali-free glass, quartz glass, carbon, and other inorganic materials. The adhesive sheet disclosed herein can be used to adhere to components (such as optical components) made of the above-mentioned materials.

[0237] The components and materials to which the adhesive sheet disclosed herein is applied (for double-sided adhesive sheets, at least one of the adherends) can be formed of materials with a refractive index higher than that of typical acrylic adhesives. The refractive index of the adherend material is, for example, 1.50 or higher, including materials with a refractive index of 1.55 or higher or 1.58 or higher, and even materials with a refractive index of 1.62 or higher (e.g., around 1.66). Such high-refractive-index adherend materials are typically resin materials. More specifically, they can be polyester resins such as PET, polyimide resins, aramid resins, polyphenylene sulfide resins, polycarbonate resins, etc. With such materials, the effect of using the adhesive sheet disclosed herein (suppression of light reflection due to the refractive index difference) is preferably achieved. The upper limit of the refractive index of the aforementioned adherend material is, for example, 1.80 or lower, and can be 1.70 or lower. The adhesive sheet disclosed herein can preferably be used by bonding to high-refractive-index adherends (e.g., components) as described above. Suitable examples of such adherends include resin films with 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 determined using the same method as for the refractive index of adhesives.

[0238] The component or material to which the adhesive sheet is bonded (for double-sided adhesive sheets, at least one of the adhered materials) can be translucent. With such adhered materials, the advantage of the technique disclosed herein (suppression of light reflection at the interface between the adhered material and the adhesive sheet) is readily obtained. The total light transmittance of the aforementioned adhered material is, for example, higher than 50%, preferably 70% or more. In some preferred embodiments, the total light transmittance of the aforementioned adhered material is 80% or more, more preferably 90% or more, and can be 95% or more (e.g., 95-100%). The adhesive sheet disclosed herein can preferably be used to bond to an adhered material (e.g., an optical component) with a total light transmittance of a specified value or higher. The aforementioned total light transmittance is measured using a commercially available transmittance meter according to JIS K 7136:2000. The transmittance meter used is the Murakami Color Technology Research Institute's trade name "HAZEMETERHM-150" or an equivalent thereof.

[0239] In some preferred embodiments, the adhered object (e.g., a component) to which the adhesive sheet is bonded may have the aforementioned refractive index and total light transmittance. Specifically, the adhesive sheet disclosed herein is preferably used to bond objects, such as components, with 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 of more than 50% (e.g., 70% or higher, preferably 80% or higher, more preferably 90% or higher, and further preferably 95% or higher). In such bonding to components, the effects of the technology disclosed herein are particularly preferably achieved.

[0240] As an example of preferred applications, optical applications can be cited. More specifically, for example, the adhesive sheet disclosed herein can be preferably used for optical applications such as bonding optical components (for bonding optical components) and manufacturing articles using the aforementioned optical components (optical articles).

[0241] The aforementioned optical components refer to components possessing optical properties (such as polarization, refraction, scattering, reflection, transmission, absorption, diffraction, rotation, and visual recognition). There is no particular limitation on the term "optical component" as long as it possesses optical properties. Examples include components constituting display devices (image display devices), input devices, and other equipment (optical devices), or components used in these devices. Examples include polarizing plates, wavelength plates, phase retardation plates, optical compensation films, brightness-enhancing films, light guide plates, reflective films, anti-reflective films, hard-coated (HC) films, impact-absorbing films, anti-fouling films, photochromic films, dimming films, transparent conductive films (ITO films), exterior films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and components further laminated with these (sometimes collectively referred to as "functional films"). It should be noted that the terms "plate" and "film" mentioned above each include plate-like, film-like, and sheet-like forms. For example, "polarizing film" includes "polarizing plate" and "polarizing sheet," and "light guide plate" includes "light guide film" and "light guide sheet." In addition, the term "polarizing plate" mentioned above includes circular polarizing plate.

[0242] Examples of display devices include liquid crystal displays, organic EL (electroluminescent) displays, micro LEDs (μLEDs), mini LEDs, PDPs (plasma display panels), and electronic paper. Additionally, examples of input devices include touch panels.

[0243] The term "optical component" is not particularly limited, and examples include components formed from glass, acrylic resins, polycarbonate, polyethylene terephthalate, metal films, etc. (e.g., sheet-like, film-like, plate-like components). It should be noted that "optical component" in this specification also includes components that maintain the visual legibility of the display device and input device and serve decorative and protective functions (such as outer films, decorative films, surface protective films, etc.).

[0244] The techniques disclosed herein are preferably used, for example, to bond optical thin films, such as thin films and fluorescent thin films, which have one or more functions of light transmission, reflection, diffusion, waveguide, light collection, and diffraction to other optical components (which may be other optical thin films). In the bonding of optical thin films with at least one function of light waveguide, light collection, and diffraction, it is ideal for the bonding layer to have an overall high refractive index, which is a preferred application of the techniques disclosed herein.

[0245] The adhesives disclosed herein are preferably used for bonding optical films such as light guide films, diffusion films, fluorescent films, color-matching films, prism sheets, lens-shaped films, and microlens array films. In these applications, from the perspective of miniaturization and high performance of optical components, there is a demand for thinner designs and improved light extraction efficiency. The adhesives disclosed herein are preferred as adhesives capable of meeting these requirements. More specifically, for example, in the bonding of light guide films and diffusion films, adjusting the refractive index of the adhesive layer as the bonding layer (e.g., increasing the refractive index) can contribute to thinning. In the bonding of fluorescent films, appropriately adjusting the refractive index difference between the phosphor and the adhesive can improve light extraction efficiency (which can also be considered as luminous efficiency). In the bonding of color-matching films, appropriately adjusting the refractive index of the adhesive to have a small refractive index difference with the color-matching pigment can reduce scattering components and contribute to improved light transmittance. In the bonding of prism sheets, lens-shaped films, and microlens array films, appropriately adjusting the refractive index of the adhesive can control light diffraction and contribute to improved brightness and / or viewing angle.

[0246] The adhesive sheet disclosed herein is preferably used by adhering it to a high-refractive-index substrate (which may be a high-refractive-index layer, component, etc.) to suppress interfacial reflection with the substrate. As described above, the adhesive sheet used in this manner preferably has a small refractive index difference with the substrate and high adhesion at the interface with the substrate. Furthermore, from the viewpoint of improving the uniformity of appearance, it is preferable that the thickness uniformity of the adhesive layer is high, for example, it is preferable that the surface smoothness of the adhesive surface is high. When the thickness of the high-refractive-index substrate is small (e.g., 5 μm or less, 4 μm or less, or 2 μm or less), suppressing reflection at the interface is particularly meaningful from the viewpoint of suppressing coloring and color unevenness caused by interference of reflected light. As an example of this usage, a method for bonding the polarizing element to the first retardation layer and / or the first retardation layer to the second retardation layer can be cited in a polarizing plate with a retardation layer comprising a polarizing element, a first retardation layer, and a second retardation layer in sequence.

[0247] Furthermore, the adhesive sheet disclosed herein is suitable for high refractive index applications, and therefore can preferably be used by bonding it to a light-emitting layer (e.g., a high-refractive-index light-emitting layer mainly composed of inorganic materials) of a photonic semiconductor. By reducing the refractive index difference between the light-emitting layer and the adhesive layer, reflection at their interface can be suppressed, and light extraction efficiency can be improved. The adhesive sheet used in this manner preferably has an adhesive layer with a high refractive index. In addition, from the viewpoint of preventing the self-emissive element from deteriorating due to moisture in advance, it is preferable that the water absorption rate of the adhesive layer is low, for example, about 1.0% or less is appropriate, preferably 0.7% or less, more preferably 0.5% or less (e.g., less than 0.5%), and can be 0.4% or less, 0.3% or less, 0.2% or less, or 0.1% or less. There is no particular limitation on the lower limit of the water absorption rate of the adhesive layer, and from a practical viewpoint such as considering adhesion properties, it can be, for example, 0.01% or more, 0.05% or more, 0.1% or more, or 0.15% or more. From the viewpoint of improving brightness, the adhesive sheet is preferably low-coloring. This can also be advantageous from the perspective of suppressing unintentional staining caused by adhesive sheets.

[0248] It should be noted that, in this specification, a self-emissive element refers to a light-emitting element whose brightness can be controlled by the value of the current flowing through it. A self-emissive element can be composed of a single unit or an assembly. Specific examples of self-emissive elements include, but are not limited to, light-emitting diodes (LEDs) and organic ELs. Furthermore, in this specification, a light-emitting device refers to a device that includes such a self-emissive element as a constituent element; such a light-emitting device may include such a self-emissive element as a constituent element. Examples of the aforementioned light-emitting devices include light source module devices used for illumination (e.g., planar light-emitting modules) and display devices that form pixels, but are not limited to them.

[0249] In addition, the water absorption rate (also known as moisture content) of the above-mentioned adhesive layer was determined by the following method.

[0250] [Moisture content determination]

[0251] Cut a 4cm x 5cm (area: 20cm²) section from the adhesive layer of the object being evaluated, along with two release liner sheets placed on one and the other sides. 2 The release liner on one side of the adhesive layer was removed and adhered to a pre-weighed aluminum foil. Next, the release liner on the other side of the adhesive layer was placed in a constant temperature and humidity bath at 60°C and 90% relative humidity for 72 hours. The resulting test piece, consisting of the adhesive layer and aluminum foil, was weighed and then the moisture content was determined using a moisture meter (Mitsubishi Chemical Analytech CA-200) equipped with a heating vaporization device (Mitsubishi Chemical Analytech VA-200) under the following conditions via Karl Fischer electrostatic titration.

[0252] Anode solution: AQUAMICRON AKX (manufactured by Mitsubishi Chemical)

[0253] Cathodic solution: AQUAMICRON CXU (manufactured by Mitsubishi Chemical)

[0254] Heating and vaporization temperature: 150℃

[0255] The adhesive disclosed herein can be used preferably as a coating layer covering the lens surface, a bonding layer to a component (e.g., a microlens constituting a microlens array film, a camera microlens, etc.) in microlenses and other lens components used as constituent parts of cameras, light-emitting devices, etc., as well as a filler layer filling the space between the lens surface and the component. The adhesive disclosed herein is suitable for high refractive index applications, thus reducing the refractive index difference even with high refractive index lenses (e.g., lenses made of high refractive index resin, lenses with a surface layer made of high refractive index resin). This is advantageous from the viewpoint of thinning the lens and the article containing the lens, and also contributes to the suppression of aberrations and the improvement of the Abbe number. The adhesive disclosed herein can also be used itself as a lens resin, for example, by filling recesses or gaps in suitable transparent components.

[0256] There are no particular limitations on the method of bonding optical components using the adhesive sheet disclosed herein. For example, it can be (1) bonding optical components to each other using the adhesive sheet disclosed herein, (2) bonding optical components to components other than optical components using the adhesive sheet disclosed herein, or (3) bonding the adhesive sheet disclosed herein to an optical component or a component other than an optical component. It should be noted that in the above-mentioned (3) method, the adhesive sheet in the form of containing an optical component can be, for example, an adhesive sheet in the form of an optical component (e.g., an optical film) as a support. Such an adhesive sheet in the form of containing an optical component as a support can also be regarded as an adhesive optical component (e.g., an adhesive optical film). In addition, when the adhesive sheet disclosed herein is an adhesive sheet of the type having a support and the above-mentioned functional film is used as the support, the adhesive sheet disclosed herein can also be regarded as an "adhesive functional film" having an adhesive layer disclosed herein on at least one side of the functional film.

[0257] As described above, according to the technology disclosed herein, a laminate is provided, comprising the adhesive sheet disclosed herein and a component to which the adhesive sheet is adhered. The component to which the adhesive sheet is adhered may have the refractive index of the aforementioned adhered material. Furthermore, the difference between the refractive index of the adhesive sheet and the refractive index of the component (refractive index difference) may be the difference between the refractive index of the adhered material and the adhesive sheet. Regarding the components constituting the laminate, as described above as components, materials, and adhered materials, further description is not required.

[0258] As can be understood from the above description and the following embodiments, the matters disclosed in this specification include the following.

[0259] [1] An adhesive composition for forming an adhesive comprising an acrylic polymer,

[0260] The monomer components constituting the above-mentioned acrylic polymers include: a monomer containing an aromatic ring (A1), and a monomer having at least one of a hydroxyl group and a carboxyl group (A2).

[0261] In the above-mentioned monomer components, the content of the monomer containing an aromatic ring (A1) is 75% by weight or more and 99% by weight or less, and the content of the monomer having at least one of a hydroxyl group and a carboxyl group (A2) is 1% by weight or more and 25% by weight or less.

[0262] [2] According to the adhesive composition described in [1] above, 50% by weight or more of the aromatic ring-containing monomer (A1) is a monomer with a glass transition temperature of 10°C or less of a homopolymer.

[0263] [3] An adhesive composition for forming an adhesive comprising an acrylic polymer,

[0264] The monomer components constituting the above-mentioned acrylic polymers contain monomers with aromatic rings (A1).

[0265] Of the aforementioned monomeric components, the content of the aromatic ring-containing monomer (A1) is higher than 70% by weight and lower than 100% by weight.

[0266] More than 50% by weight of the aromatic ring-containing monomer (A1) mentioned above are aromatic ring-containing monomers with a glass transition temperature of 10°C or less (preferably 5°C or less) of the homopolymer.

[0267] [4] The adhesive composition according to [3] above, wherein the monomer component further contains a monomer (A2) having at least one of hydroxyl and carboxyl groups.

[0268] [5] According to the adhesive composition described in [4] above, wherein the content of the monomer (A2) having at least one of hydroxyl and carboxyl groups in the monomer component is 1% by weight or more and less than 30% by weight.

[0269] [6] The adhesive composition according to any one of [1] to [5] above, wherein the aromatic ring-containing monomer (A1) comprises a monomer having two or more aromatic rings in one molecule.

[0270] [7] The adhesive composition according to [6] above, wherein the monomer having two or more aromatic rings in one molecule comprises a monomer having a structural portion having two aromatic rings bonded by means of a linking group.

[0271] [8] The adhesive composition according to any one of [1] to [7] above further comprises a crosslinking agent.

[0272] [9] The adhesive composition according to any one of [1] to [8] above further comprises high refractive index particles.

[0273]

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

[0274]

[11] An adhesive comprising an acrylic polymer,

[0275] The monomer components constituting the above-mentioned acrylic polymers contain monomers with aromatic rings (A1).

[0276] Of the aforementioned monomeric components, the content of the aromatic ring-containing monomer (A1) is higher than 70% by weight and lower than 100% by weight.

[0277] The adhesive satisfies at least one of the following conditions:

[0278] (a) The energy storage modulus G'(25) at 25°C is less than 200 kPa; and

[0279] (b) The energy storage modulus G'(50) at 50°C is less than 40 kPa.

[0280]

[12] An adhesive comprising an acrylic polymer,

[0281] The monomer components constituting the above-mentioned acrylic polymers contain monomers with aromatic rings (A1).

[0282] Of the aforementioned monomeric components, the content of the aromatic ring-containing monomer (A1) is higher than 70% by weight and lower than 100% by weight.

[0283] More than 50% by weight of the aromatic ring-containing monomer (A1) mentioned above are aromatic ring-containing monomers with a glass transition temperature of 10°C or less (preferably 5°C or less) of the homopolymer.

[0284]

[13] The adhesive according to

[11] or

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

[0285]

[14] According to the adhesive described in

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

[0286]

[15] An adhesive comprising an acrylic polymer,

[0287] The monomer components constituting the above-mentioned acrylic polymers include: a monomer containing an aromatic ring (A1), and a monomer having at least one of a hydroxyl group and a carboxyl group (A2).

[0288] In the above-mentioned monomer components, the content of the monomer containing an aromatic ring (A1) is 75% by weight or more and 99% by weight or less, and the content of the monomer having at least one of a hydroxyl group and a carboxyl group (A2) is 1% by weight or more and 25% by weight or less.

[0289]

[16] The adhesive according to any one of

[11] and

[13] to

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

[0290]

[17] The adhesive according to any one of

[11] to

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

[0291]

[18] According to the adhesive described in

[17] above, wherein the monomer having two or more aromatic rings in one molecule comprises a monomer having a structural portion having two aromatic rings bonded together by means of a linking group.

[0292]

[19] The adhesive according to any one of

[11] to

[18] above has a refractive index higher than 1.570.

[0293]

[20] The adhesive according to any one of

[12] to

[19] above satisfies at least one of the following conditions:

[0294] (a) The energy storage modulus G'(25) at 25°C is less than 200 kPa; and

[0295] (b) The energy storage modulus G'(50) at 50°C is less than 40 kPa.

[0296]

[21] The adhesive according to any one of

[11] to

[20] above further comprises high refractive index particles.

[0297]

[22] An adhesive composition for use in the preparation of any one of the adhesives described in

[11] to

[21] above.

[0298]

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

[11] to

[21] above.

[0299]

[24] According to the adhesive described in

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

[0300]

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

[23] or

[24] above, and an optical component bonded to a surface of the adhesive sheet.

[0301] Example

[0302] The following describes some embodiments related to the present invention, but it is not intended to limit the invention to the scope shown in these specific examples. It should be noted that in the following description, "parts" and "%" indicating the amount used or the content are based on weight unless otherwise specified.

[0303] Experiment Example 1

[0304] <Example 1>

[0305] (Preparation of acrylic polymer solutions)

[0306] In a four-necked flask equipped with a stirring blade, thermometer, nitrogen inlet tube, and condenser, 99.0 parts of m-phenoxybenzyl acrylate (manufactured by Kyoei Chemical Co., Ltd., trade name "LIGHT ACRYLATE POB-A", refractive index: 1.566, Tg of homopolymer: -35℃, hereinafter referred to as "A1-a"), 1.0 part of 4-hydroxybutyl acrylate (4HBA), 0.2 parts of 2,2'-azobisisobutyronitrile (2,2'-azobisisobutyronitrile) as polymerization initiator, and 150 parts of ethyl acetate as polymerization solvent were added. Nitrogen gas was introduced while stirring slowly, and the liquid temperature in the flask was maintained at 60℃ for 6 hours to prepare a 40% solution of acrylic polymer P1. The Tg of the above acrylic polymer P1 based on the above monomer components (i.e., Tg) was measured. T The temperature is -35℃, based on the Tg (i.e., Tg) of the monomer containing the aromatic ring. A1 The temperature is -35℃.

[0307] (Preparation of the adhesive composition)

[0308] The above-mentioned acrylic polymer P1 solution (40%) was diluted to 20% with ethyl acetate. 10 parts of a 1% ethyl acetate solution (0.1 parts non-volatile component) of hexamethylene diisocyanate isocyanurate (manufactured by Tosoh Corporation, trade name "Coronate HX", a 3-functional isocyanate compound) as a crosslinking agent, 2 parts of acetylacetone as a crosslinking delay agent, and 1 part of a 1% ethyl acetate solution (0.01 parts non-volatile component) of iron acetylacetone as a crosslinking catalyst were added to this solution (100 parts non-volatile component). The mixture was stirred and mixed to prepare the acrylic adhesive composition C1.

[0309] (Making the adhesive sheet)

[0310] The acrylic adhesive composition C1 prepared above was coated onto the silicone-treated surface of a polyethylene terephthalate (PET) film R1 (50 μm thick) with one side treated with silicone. The film was then heated at 130°C for 2 minutes to form an adhesive layer with a thickness of 20 μm. Next, a silicone-treated PET film R2 (25 μm thick) with one side treated with silicone was laminated onto the surface of the adhesive layer. This process yields a substrate-free double-sided adhesive sheet S1 formed from the adhesive layer. Both sides of the adhesive sheet S1 are protected by PET films (release liner) R1 and R2.

[0311] <Example 2 to Example 12>

[0312] The composition of the monomer components was changed as shown in Table 1. Otherwise, solutions of acrylic polymers P2 to P12 in Examples 2 to 12 were prepared in the same manner as the preparation of the acrylic polymer solution in Example 1. The Mw of acrylic polymer P3 was 400,000.

[0313] The acrylic adhesive compositions C2 to C12 of Examples 2 to 12 were prepared in the same manner as the preparation of the adhesive composition in Example 1, except that solutions of acrylic polymers P2 to P12 were used instead of acrylic polymer P1.

[0314] Acrylic adhesive compositions C2 to C12 were used instead of acrylic adhesive composition C1. Otherwise, adhesive sheets (substrate-free double-sided adhesive sheets formed of adhesive layers) S2 to S12 of Examples 2 to 12 were made in the same manner as the adhesive sheet in Example 1.

[0315] <Example 13>

[0316] The solvent was changed from ethyl acetate to methyl ethyl ketone (MEK). Otherwise, a solution of acrylic polymer P13 (with the same monomer composition as in Example 3: Al-a / 4HBA = 95.0 / 5.0) and acrylic adhesive composition C13 were prepared in the same manner as in Example 3 to produce an adhesive sheet (a substrate-free double-sided adhesive sheet formed by the adhesive layer). The Mw of acrylic polymer P13 was 480,000.

[0317] It should be noted that in the composition of the monomer components shown in Table 1, "A1-b" represents 1-naphthyl methyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "LIGHT ACRYLATE NMT-A", refractive index: 1.595, Tg of homopolymer: 31℃), HEA represents 2-hydroxyethyl acrylate, BA represents n-butyl acrylate, and 2EHA represents 2-ethylhexyl acrylate.

[0318] <Determination of Refractive Index>

[0319] For each example of adhesive layer (substrate-free double-sided adhesive sheet), the refractive index 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.

[0320] <Determination of Haze Value>

[0321] Test pieces were prepared by bonding the adhesive layer of each example to alkali-free glass (thickness 0.8–1.0 mm, total light transmittance 92%, haze 0.4%), and the haze was measured using a haze meter (Murakami Color Technology Research Institute “HM-150”). The value obtained by subtracting the haze (0.4%) of the alkali-free glass from the measured value was taken as the haze of the adhesive layer.

[0322] <Determination of Storage Modulus G'>

[0323] Each example of adhesive layer was laminated to a thickness of approximately 1.5 mm, and this was used as the sample for measurement. Dynamic viscoelasticity was measured using the "Advanced Rheometric Expansion System (ARES)" manufactured by RheometricScientific under the following conditions. The storage modulus G' at 25°C and 50°C was read from the measurement results.

[0324] [Measurement Conditions]

[0325] Deformation mode: Torsion

[0326] Measurement frequency: 1Hz

[0327] Heating rate: 5℃ / minute

[0328] Shape: Parallel plate

[0329] The results are shown in Table 1.

[0330] [Table 1]

[0331] Table 1

[0332]

[0333] As shown in Table 1, the binder layers of Examples 1-9 and Examples 12 and 13, which contain a higher content of monomer (Al) in the monomer components constituting the acrylic polymer, exhibited significantly higher refractive indices compared to Examples 10 and 11. In a comparison between Examples 3 and 13, which used different polymerization solvents, the optical properties were identical; however, Example 13 showed a slight tendency towards a slightly lower storage modulus. Furthermore, the Tg measured using differential scanning calorimetry (DSC) was slightly lower in Example 13 compared to Example 3.

[0334] <Determination of peel strength>

[0335] For some of the adhesive sheets prepared above, the peel strength to glass plates was further measured. Specifically, under a testing environment of 23°C and 50% RH, the release liner was peeled off from one side of the adhesive sheet, and a 50μm thick PET film was laminated as a lining. The sheet was then cut into pieces 25mm wide and 100mm long to serve as test pieces. The release liner was peeled off from the other side of the test piece, and a 2kg roller was used to press it against the surface of an alkaline glass plate (Matsunami Glass Industry Co., Ltd., 1.35mm thick, with ground edges) as the adherend, performing one round trip. After being placed in this environment for 30 minutes, the peel strength (adhesive force) [N / 25mm] was measured using a universal tensile and compression testing machine according to JIS Z 0237:2000, at a tensile speed of 300mm / min and a peel angle of 180 degrees. A Minebea TG-1kN universal tensile and compression testing machine was used.

[0336] [Table 2]

[0337] Table 2

[0338]

[0339] According to the comparison of Examples 3 to 5 shown in Table 2 (the content of monomer (A1) in the monomer composition is 95%), it can be seen that by combining the monomer A1-a with the relatively low Tg of the homopolymer with the monomer A1-b with the relatively high Tg of the homopolymer, the increase of the storage modulus G' can be suppressed and a high refractive index can be further achieved.

[0340] Experiment Example 2

[0341] <Example 14>

[0342] Compared to 100 parts of acrylic polymer contained in the acrylic polymer solution, 0.5 parts of diethylene glycol dibenzoate (additive) are further added. Otherwise, the adhesive composition C14 of this example is prepared in the same manner as the adhesive composition in Example 13. Adhesive composition C14 is used instead of adhesive composition C13. Otherwise, the adhesive sheet (substrate-free double-sided adhesive sheet formed of adhesive layer) S14 of this example is prepared in the same manner as the adhesive sheet in Example 13.

[0343] <Example 15~Example 33>

[0344] The types of additives and the amount used relative to 100 parts per hundred resin of acrylic polymer were changed as shown in Table 3. Otherwise, adhesive compositions C15 to C33 of Examples 15 to 33 were prepared in the same manner as the adhesive composition in Example 14. Adhesive compositions C14 were replaced with adhesive compositions C15 to C33 respectively. Otherwise, adhesive sheets (substrate-free double-sided adhesive sheets formed of adhesive layers) S15 to S33 of Examples 15 to 33 were prepared in the same manner as the adhesive sheet in Example 14.

[0345] Here, in Example 33, the leveling agent used as an additive is a polymer (B) synthesized as described below. That is, 101.15 parts of ethyl acetate, 40 parts of methyl methacrylate (MMA), 20 parts of n-butyl methacrylate (BMA), 20 parts of 2-ethylhexyl methacrylate (2EHMA), 8.7 parts of a methacrylate monomer with a functional group equivalent of 900 g / mol containing a polyorganosiloxane backbone (trade name: X-22-174ASX, manufactured by Shin-Etsu Chemical Industry Co., Ltd.), 11.3 parts of a methacrylate monomer with a functional group equivalent of 4600 g / mol containing a polyorganosiloxane backbone (trade name: KF-2012, manufactured by Shin-Etsu Chemical Industry Co., Ltd.), and 0.8 parts of thioglycerol as a chain transfer agent are added to a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen inlet tube, a condenser, and a dropping funnel. Then, after stirring at 70°C under a nitrogen atmosphere for 30 minutes, 0.2 parts of 2,2'-azobisisobutyronitrile (AIBN) as a thermal polymerization initiator were added, and the reaction was carried out at 70°C for 3 hours. Next, after stirring at 80°C for 30 minutes, 0.1 parts of AIBN were added, and the reaction was carried out at 80°C for 2 hours. Then, 0.05 parts of AIBN were added, and the reaction was carried out at 80°C for 2 hours to obtain polymer (B). The Mw of the obtained polymer (B) was 20000.

[0346] For the adhesive sheets obtained from each example, the refractive index, peel strength, and storage modulus G' were measured in the same manner as in Experimental Example 1. The results are presented together with the refractive indices of each additive in Table 3.

[0347] [Table 3]

[0348] Table 3

[0349]

[0350] As shown in Table 3, it was confirmed that the additives used in Examples 14 to 32 all functioned effectively as plasticizers that at least reduced the storage modulus G'(25). Diethylene glycol dibenzoate and triphenyl phosphate (triphenyl phosphate) showed particularly high plasticizing effects. In addition, during visual observation when the adhesive composition was coated onto the release liner R1, for Example 33 with the addition of a leveling agent, the formation of pinholes and unevenness tended to be suppressed compared to Example 13, confirming the effect of the leveling agent in improving the homogeneity of the adhesive layer. It should be noted that, except that the solvent was changed from MEK to ethyl acetate, the adhesive sheets were prepared and evaluated in the same manner as in Examples 15 to 17. The results showed that the adhesive sheets of Examples 15 to 17 using MEK as the solvent had the same optical properties and peel strength as the corresponding adhesive sheets using ethyl acetate as the solvent, but the storage modulus tended to be slightly reduced.

[0351] The specific examples of the present invention have been described in detail above, but these are merely illustrative and do not limit the scope of protection of the claims. The solutions described in the scope of protection of the claims include those derived from various modifications and alterations of the specific examples illustrated above.

[0352] Explanation of reference numerals in the attached figures

[0353] 1, 2, 3 Adhesive sheets

[0354] 10 Support substrate

[0355] 10A Page 1

[0356] 10B Page 2

[0357] 21 Adhesive layer, first adhesive layer

[0358] 21A Adhesive surface, first adhesive surface

[0359] 21B Adhesive Surface

[0360] 22 Second adhesive layer

[0361] 22A Second Adhesive Surface

[0362] 31, 32 Peeling off the gasket

Claims

1. An adhesive composition for forming an adhesive comprising an acrylic polymer, wherein, The monomeric components constituting the acrylic polymer include: a monomer containing an aromatic ring (A1), 4-hydroxybutyl acrylate, and alkyl acrylates having a straight-chain or branched alkyl group having 1 to 20 carbon atoms at the ester terminus. The aromatic-ring-containing monomer (A1) includes monomers containing multiple aromatic rings having two or more aromatic rings per molecule. These monomers do not include monomers with fused aromatic ring structures. The monomeric components constituting the acrylic polymer do not include methacryloyl monomers. In the monomer components, the content of the aromatic ring-containing monomer (A1) is 75% by weight or more and 99% by weight or less, the content of 4-hydroxybutyl acrylate is 1% by weight or more and 15% by weight or less, and the content of alkyl acrylate is 1% by weight or more and 24% by weight or less. The adhesive composition also includes a crosslinking agent.

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

3. The adhesive composition according to claim 2, wherein, The monomer containing multiple aromatic rings includes a monomer having a structural portion having two aromatic rings bonded together by means of a linking group.

4. An adhesive formed from the adhesive composition according to any one of claims 1 to 3.

5. The adhesive according to claim 4, wherein the refractive index is higher than 1.

570.

6. The adhesive according to claim 4 or 5, wherein it satisfies at least one of the following conditions: (a) The energy storage modulus G'(25) at 25°C is less than 200 kPa; and (b) The energy storage modulus G'(50) at 50°C is less than 40 kPa.

7. An adhesive sheet comprising an adhesive layer made of the adhesive according to any one of claims 4 to 6.

8. The adhesive sheet according to claim 7, wherein, The haze value of the adhesive layer is below 1.0%.

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