WO2024010041A1

WO2024010041A1 - Adhesive and adhesive sheet

Info

Publication number: WO2024010041A1
Application number: PCT/JP2023/024972
Authority: WO
Inventors: 慎太郎野依; 美希西改; 真也山本; 拓也永田
Original assignee: 日東電工株式会社
Priority date: 2022-07-08
Filing date: 2023-07-05
Publication date: 2024-01-11
Also published as: JP2024008704A

Abstract

To provide an adhesive capable of achieving both a high refractive index and a low elastic modulus. Provided is an adhesive containing a base polymer and a high-refractive-index additive (A). The high-refractive-index additive (A) is a compound having an asymmetrical structure. The content value for the high-refractive-index additive (A) is 30 parts by weight or greater per 100 parts by weight of the base polymer. The refractive index of the adhesive is 1.50 or greater.

Description

Adhesives and adhesive sheets

The present invention relates to adhesives and adhesive sheets. This application claims priority based on Japanese Patent Application No. 2022-110774 filed on July 8, 2022, and the entire contents of that application are incorporated herein by reference.

In general, adhesives (also referred to as pressure-sensitive adhesives, hereinafter the same) exhibit a soft solid state (viscoelastic body) in a temperature range around room temperature, and have the property of easily adhering to an adherend under pressure. Taking advantage of these properties, adhesives are widely used for purposes such as bonding, fixing, and protection in various industrial fields such as home appliances, automobiles, various machines, electrical equipment, and electronic equipment. An example of the use of the adhesive is for joining various light-transmitting members to each other or to other members in display devices such as liquid crystal display devices and organic EL (OLED) display devices. Technical documents regarding adhesives for optical members include

Patent Documents

1 and 2.

Japanese Patent Application Publication No. 2014-169382 Japanese Patent Application Publication No. 2017-128732

Patent Documents

1 and 2 disclose a pressure-sensitive adhesive composition whose main component is a (meth)acrylic acid ester polymer containing a monomer having a plurality of aromatic rings as a monomer unit, and a pressure-sensitive adhesive obtained by crosslinking the pressure-sensitive adhesive composition. discloses the use of a monomer having multiple aromatic rings to increase the refractive index of the adhesive to 1.50 or more, particularly preferably 1.51 or more. For example, some materials to which adhesives are attached, such as optical components, have a high refractive index, and if a common acrylic adhesive is used to bond such high refractive index materials, the difference in refractive index between the two will be reduced. It is known that reflection occurs at the interface due to By using an adhesive with a high refractive index as the adhesive used for bonding the high refractive materials, the interface reflection can be prevented or suppressed. Note that the refractive index of the acrylic adhesive is usually about 1.47.

By the way, an adhesive having good flexibility can be preferably used depending on the application site and usage mode. For example, in recent years, foldable displays and rollable displays have been put into practical use as displays such as organic EL display devices used in electronic devices such as smartphones. It is necessary to have the flexibility to follow the An adhesive having excellent flexibility easily follows and adheres to curved surfaces such as three-dimensional shapes, and is also suitable for use in electronic devices having curved shapes. If the flexibility of an adhesive having a high refractive index can be increased, it is useful because it can be applied to the above-mentioned applications where flexibility is required. However, high refractive index materials used as monomer components of adhesive polymers tend to have a high glass transition temperature, such as those with aromatic rings, and adhesives formed using high refractive index materials have a high elastic modulus. Tend. In designing an adhesive, there is a trade-off between a high refractive index and a low elastic modulus, and it would be practically beneficial if an adhesive capable of achieving both of these was realized.

The present invention was created in view of the above circumstances, and an object of the present invention is to provide an adhesive that can have both a high refractive index and a low elastic modulus. Another object of the present invention is to provide a pressure-sensitive adhesive sheet including a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive described above.

According to this specification, an adhesive containing a base polymer and a high refractive index additive (A) is provided. The high refractive index additive (A) is a compound with an asymmetric structure. The content of the high refractive index additive (A) is 30 parts by weight or more based on 100 parts by weight of the base polymer. The refractive index of the adhesive is 1.50 or more. Employing a compound with an asymmetric structure as the high refractive index additive (A) is advantageous from the viewpoint of suppressing an increase in the elastic modulus of the adhesive due to an increase in the amount of the high refractive index additive (A) added. By containing the high refractive index additive (A) having such a structure in a relatively large amount with respect to the base polymer, an adhesive having a high refractive index and a low elastic modulus can be realized.

In some embodiments, a compound having a double bond-containing ring is preferably used as the high refractive index additive (A). By containing such a compound, the refractive index of the adhesive can be efficiently increased.

In some embodiments, a compound having a heterocycle (also referred to as a heterocycle) may be preferably used as the high refractive index additive (A). By containing such a compound, the refractive index of the adhesive can be efficiently increased. As the above-mentioned compound having a heterocycle, compounds corresponding to compounds having a double bond-containing ring can be preferably employed.

In some embodiments, a compound containing a fused ring having a substituent (hereinafter also referred to as a "substituted fused ring-containing compound") may be preferably used as the high refractive index additive (A). By containing such a compound, the refractive index of the adhesive can be efficiently increased. The fused ring preferably has a structure containing at least one of a heterocycle and a double bond-containing ring.

In some preferred embodiments, the compound having a substituted condensed ring may be a dinaphthothiophene compound (hereinafter also referred to as "substituted DNT") having at least one substituent. According to the pressure-sensitive adhesive containing substituted DNT having an asymmetric structure as the high refractive index additive (A), a high refractive index and a low elastic modulus can be preferably achieved at the same time.

In some embodiments, a compound having a refractive index of 1.65 or more is preferably used as the high refractive index additive (A). By containing such a compound, the refractive index of the adhesive can be efficiently increased.

In some embodiments, the high refractive index additive (A) is preferably a compound with a molecular weight of 100 or more and 1000 or less. The high refractive index additive (A) having a molecular weight within the above range is easily compatible with the adhesive and is suitable for achieving both a high refractive index and a low elastic modulus.

In some preferred embodiments, the content of the aromatic ring-containing monomer in the monomer components constituting the base polymer is 0% by weight or more and less than 75% by weight. In a configuration in which a base polymer composed of monomer components having such a composition and the above-mentioned high refractive index additive (A) are used in combination, the technology disclosed herein (adhesive, adhesive for forming the adhesive) is used. (the same applies hereinafter) can be preferably exhibited.

Further, according to this specification, an adhesive comprising an adhesive layer consisting of any adhesive disclosed herein (which may be an adhesive formed from any adhesive composition disclosed herein) A sheet is provided. Since the adhesive disclosed herein can have both a high refractive index and a low elastic modulus, it is desirable that the adhesive sheet containing the above-mentioned adhesive has a high refractive index, for example, for use in foldable displays, and It can be preferably used for joining, fixing, protection, etc. in applications that require flexibility to withstand bending operations.

Note that appropriate combinations of the elements described in this specification may also be included within the scope of the invention for which protection by patent is sought by this patent application.

FIG. 1 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to an embodiment. FIG. 3 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to another embodiment. FIG. 3 is a cross-sectional view schematically showing the configuration of a pressure-sensitive adhesive sheet according to another embodiment.

Hereinafter, preferred embodiments of the present invention will be described. Matters other than those specifically mentioned in this specification that are necessary for carrying out the present invention are based on the teachings for carrying out the invention described in this specification and the common general knowledge at the time of filing. Can be understood by vendors. The present invention can be implemented based on the content disclosed in this specification and the common general knowledge in the field.
In addition, in the following drawings, the same reference numerals may be attached and explained to members and parts that have the same function, and overlapping explanations may be omitted or simplified. Further, the embodiments shown in the drawings are schematic for clearly explaining the present invention, and do not necessarily accurately represent the size or scale of the actually provided products.

<Adhesive>
The adhesive disclosed herein can be formed using an adhesive composition containing components (adhesive-forming components) corresponding to the configuration of the adhesive. Such adhesives are adhesives obtained by curing adhesive compositions in the form of solvent-based, active energy ray-curable, water-dispersed, hot-melt, etc. by drying, crosslinking, polymerization, cooling, etc., that is, the above-mentioned adhesives. It may be a cured product of the agent composition. Only one type of curing means (for example, drying, crosslinking, polymerization, cooling, etc.) for the adhesive composition may be applied, or two or more types may be applied simultaneously or in multiple stages. For solvent-based adhesive compositions, the composition can typically be dried (and preferably further crosslinked) to form the adhesive. In active energy ray-curable adhesive compositions, the adhesive is typically formed by irradiating active energy rays to advance a polymerization reaction and/or a crosslinking reaction. When it is necessary to dry the active energy ray-curable pressure-sensitive adhesive composition, it is preferable to irradiate it with active energy rays after drying. The adhesive disclosed herein can be preferably formed using a solvent-based adhesive composition from the viewpoint of ease of blending the high refractive index additive (A).

The adhesive disclosed herein includes at least a base polymer and a high refractive index additive (A) (hereinafter sometimes referred to as "additive (A)"). The type of adhesive is not particularly limited, and examples include acrylic adhesives, rubber adhesives (natural rubber, synthetic rubber, mixtures thereof, etc.), silicone adhesives, polyester adhesives, and urethane adhesives. It may be an adhesive, a polyether adhesive, a polyamide adhesive, a fluorine adhesive, or the like. The above-mentioned acrylic adhesive refers to an adhesive whose base polymer is an acrylic polymer. The same applies to rubber-based and other adhesives. In some embodiments, acrylic pressure-sensitive adhesives are preferred from the viewpoint of ease of adjusting adhesive properties, optical properties, and the like.

In this specification, the "base polymer" of the adhesive refers to the main component of the rubbery polymer contained in the adhesive. The above-mentioned rubbery polymer refers to a polymer that exhibits rubber elasticity in a temperature range around room temperature. Furthermore, in this specification, the term "main component" refers to a component contained in an amount exceeding 50% by weight, unless otherwise specified.

In this specification, the term "acrylic polymer" refers to a polymer containing 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." Accordingly, an acrylic polymer in this specification is defined as a polymer containing 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 components constituting the polymer are acrylic monomers.

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

In addition, in this specification, the term "monomer component constituting a polymer" refers to a component that is included in the adhesive composition in the form of a pre-formed polymer (which may be an oligomer), or is contained in the adhesive composition in the form of an unpolymerized monomer. It means a monomer that constitutes a repeating unit (monomer unit) of the polymer in the adhesive formed from the adhesive composition, regardless of whether it is included in the adhesive composition. That is, the monomer component constituting a predetermined polymer (for example, a base polymer, preferably an acrylic polymer) contained in the adhesive may be included in the adhesive composition in the form of a polymerized product, an unpolymerized product, or a partially polymerized product. It may be From the viewpoint of ease of preparation of the adhesive composition, in some embodiments, the adhesive composition contains substantially all of the monomer components (for example, 95% by weight or more, preferably 99% by weight or more) in the form of a polymer. Preferably.

Hereinafter, an adhesive containing an acrylic polymer as a base polymer (acrylic adhesive) will be mainly explained, but it is not intended that the adhesive in the technology disclosed herein be limited to an acrylic adhesive.

(Monomer (m1))
In some embodiments, the acrylic polymer includes an alkyl (meth)acrylate (hereinafter also referred to as "monomer (m1)") having a chain alkyl group at the ester end as a monomer component constituting the acrylic polymer. It is preferable to include. The chain alkyl group in the monomer (m1) may be linear or branched. The monomers (m1) can be used alone or in combination of two or more.

As the monomer (m1), for example, a compound represented by the following formula (1) can be suitably used.
CH ₂ =C(R ¹ )COOR ² (1)
Here, R ¹ in the above formula (1) is a hydrogen atom or a methyl group, and R ² is a chain alkyl group. The number of carbon atoms in the chain alkyl group is, for example, 1 to 20, preferably 1 to 18. Specific examples of the alkyl (meth)acrylates in which the chain alkyl group has 1 to 20 carbon atoms, that is, C _1-20 alkyl (meth)acrylates, include methyl (meth)acrylate, ethyl (meth)acrylate , propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, ( Pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, Nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, isodecyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, ( Tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, ( Examples include, but are not limited to, eicosyl meth)acrylate.

In an embodiment in which the monomer component constituting the acrylic polymer includes the monomer (m1), the content of alkyl (meth)acrylate in the monomer component can be set so that the effect of its use is appropriately exhibited. The content of alkyl (meth)acrylate in the monomer component may be, for example, 1% by weight or more, 5% by weight or more, 10% by weight or more, 20% by weight or more, or 25% by weight or more. , 30% by weight or more, or 35% by weight or more. In some embodiments, the content of alkyl (meth)acrylate in the monomer component is 40% from the viewpoint of making it easier to achieve both a high refractive index and a low elastic modulus in a well-balanced manner in a composition containing a relatively large amount of additive (A). Suitably at least 45% by weight, preferably at least 50% by weight (e.g. more than 50% by weight), and may be at least 55% by weight. , 60% by weight or more, 65% by weight or more, 70% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight or more, or 90% by weight or more, and may be 95% by weight or more. , 100% by weight. Further, from the viewpoint of making it easier to obtain a pressure-sensitive adhesive having appropriate cohesiveness, in some embodiments, it is appropriate that the content of alkyl (meth)acrylate in the monomer component is 99.9% by weight or less, It is preferably 99.8% by weight or less, more preferably 99.6% by weight or less, may be 99.5% by weight or less, may be 99.0% by weight or less, and may be 95% by weight or less. It may be less than 90% by weight, it may be less than 85% by weight, it may be less than 80% by weight, it may be less than 75% by weight, less than 70% by weight, less than 65% by weight, It may be 60% by weight or less or 55% by weight or less.

In some embodiments, as at least a portion of the monomer (m1), an alkyl (meth)acrylate whose homopolymer has a Tg of -20°C or lower (more preferably -40°C or lower, for example -50°C or lower) is preferably employed. It is possible. Such a low Tg alkyl (meth)acrylate can be useful in lowering the elastic modulus of the adhesive. It can also help improve adhesive properties such as adhesive strength. The lower limit of Tg of the alkyl (meth)acrylate is not particularly limited, and may be, for example, -85°C or higher, -75°C or higher, -65°C or higher, or -60°C or higher. Specific examples of the low Tg alkyl (meth)acrylates include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), heptyl acrylate, octyl acrylate, isononyl acrylate (iNA), and the like.

In some other embodiments, an alkyl (meth)acrylate whose homopolymer Tg is higher than -20°C (for example, higher than -10°C) may be employed as at least a part of the monomer (m1). The upper limit of Tg of the alkyl (meth)acrylate is, for example, 10°C or less, may be 5°C or less, or may be 0°C or less. Alkyl (meth)acrylates having a Tg in this range (hereinafter also referred to as "medium Tg") can be useful for adjusting the elastic modulus of the adhesive. Although not particularly limited, the alkyl (meth)acrylate having the above-mentioned Tg (medium Tg) is preferably used in combination with the above-mentioned low-Tg alkyl (meth)acrylate. A specific example of the medium Tg alkyl (meth)acrylate is lauryl acrylate (LA). Alternatively, the technology disclosed herein can also be practiced in an embodiment in which medium Tg alkyl (meth)acrylate is not substantially used.

In some embodiments using monomer (m1), it is preferred to use C _4-8 alkyl (meth)acrylate as monomer (m1). Among them, it is more preferable to use C _4-8 alkyl acrylate. The C _4-8 alkyl (meth)acrylates can be used alone or in combination of two or more. By using C _4-8 alkyl (meth)acrylate, it is easy to reduce the elastic modulus of the adhesive, and there is a tendency that good adhesive properties (adhesive strength, etc.) can be easily obtained. In the embodiment in which C _4-8 alkyl (meth)acrylate is used as the monomer (m1), the proportion of C _4-8 alkyl (meth)acrylate in the monomer (m1) is suitably 30% by weight or more. The content is preferably 50% by weight or more, more preferably 70% by weight or more, even more preferably 90% by weight or more, and may be substantially 100% by weight.

In some embodiments using monomer (m1), the content of C _4-8 alkyl (meth)acrylate in the monomer component is, for example, 1% by weight or more, 5% by weight or more, 10% by weight or more, 20% by weight or more. , 25% by weight or more, 30% by weight or more, or 35% by weight or more, 40% by weight or more, 45% by weight or more, 50% by weight or more, more than 50% by weight, 55% by weight or more, 60% by weight or more, It may be 65% by weight or more, 70% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more, or 100% by weight. Further, in some embodiments, the content of C _4-8 alkyl (meth)acrylate in the monomer component is, for example, 99.9% by weight or less, 99.8% by weight or less, 99.6% by weight or less, 99.5% by weight or less. % by weight or less, 99.0% by weight or less, 95% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less, 70% by weight or less, 65% by weight or less, It may be 60% by weight or less or 55% by weight or less.

In some embodiments using monomer (m1), C _1-6 alkyl (meth)acrylate may be preferably used as monomer (m1). By using C _1-6 alkyl (meth)acrylate, the storage modulus in each temperature range can be adjusted. For example, the storage modulus in the high temperature range can be set relatively high. C _1-6 alkyl (meth)acrylates can also help improve transparency (eg, reduce haze). Furthermore, C _1-6 alkyl (meth)acrylate tends to have excellent copolymerizability with the monomer (m3) described below. One type of C _1-6 alkyl (meth)acrylate can be used alone or two or more types can be used in combination. The C _1-6 alkyl (meth)acrylate is preferably C _1-6 alkyl acrylate, more preferably C _2-6 alkyl acrylate, and even more preferably C _4-6 alkyl acrylate. In some other embodiments, the C _1-6 alkyl (meth)acrylate is preferably a C _1-4 alkyl (meth)acrylate, more preferably a C _2-4 alkyl (meth)acrylate, even more preferably is C _2-4 alkyl acrylate. A preferred example of C _1-6 alkyl (meth)acrylate is BA.

The content of C _1-6 alkyl (meth)acrylate in the monomer components constituting the acrylic polymer may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, and 8% by weight. The above is fine. In some embodiments, from the viewpoint of lowering the elastic modulus and transparency, the content of the C _1-6 alkyl (meth)acrylate is, for example, 10% by weight or more, 20% by weight or more, 25% by weight or more, 30% by weight or more. It may be at least 40 wt%, at least 45 wt%, at least 50 wt%, at least 50 wt%, at least 55 wt%, at least 60 wt%, at least 65 wt%, and at least 70 wt%. % or more, 75 weight % or more, 80 weight % or more, 85 weight % or more, 90 weight % or more, or 95 weight % or more, and may be 100 weight %. Further, in some embodiments, the content of C _1-6 alkyl (meth)acrylate in the monomer component is, for example, 99.9% by weight or less, 99.8% by weight or less, 99.6% by weight or less, 99.5% by weight or less. % by weight or less, 99.0% by weight or less, 95% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less, 70% by weight or less, 65% by weight or less, It may be 60% by weight or less or 55% by weight or less, and from the viewpoint of better exhibiting the effects of other monomers, 50% by weight or less, 40% by weight or less, 30% by weight or less, 20% by weight or less, 10% by weight % or less, or 5% by weight or less, less than 3% by weight, or less than 1% by weight. The technology disclosed herein can also be practiced in an embodiment in which C _1-6 alkyl (meth)acrylate is not substantially used.

In some other embodiments using monomer (m1), C _7-12 alkyl (meth)acrylate may be preferably used as monomer (m1). By using C _7-12 alkyl (meth)acrylates, the storage modulus can be advantageously reduced. C _7-12 alkyl (meth)acrylates can also help improve adhesion (peel strength). One type of C _7-12 alkyl (meth)acrylate can be used alone or two or more types can be used in combination. As the C _7-12 alkyl (meth)acrylate, C _7-10 alkyl acrylate is preferred, C _7-9 alkyl acrylate is more preferred, and C ₈ alkyl acrylate is even more preferred. Examples of C _7-12 alkyl (meth)acrylates include 2EHA, iNA, and LA, and a preferred example includes 2EHA.

The content of C _7-12 alkyl (meth)acrylate in the monomer components constituting the acrylic polymer may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, and 8% by weight. The above is fine. In some embodiments, the content of the C _7-12 alkyl (meth)acrylate is, for example, 10% by weight or more, 20% by weight or more, 25% by weight from the viewpoint of lowering the elastic modulus, transparency, adhesiveness, etc. 30% by weight or more, or 35% by weight or more, 40% by weight or more, 45% by weight or more, 50% by weight or more, more than 50% by weight, 55% by weight or more, 60% by weight or more, 65% by weight or more , 70% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more, or 100% by weight. Further, in some embodiments, the content of C _7-12 alkyl (meth)acrylate in the monomer component is, for example, 99.9% by weight or less, 99.8% by weight or less, 99.6% by weight or less, 99.5% by weight or less. % by weight or less, 99.0% by weight or less, 95% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight or less, 70% by weight or less, 65% by weight or less, It may be 60% by weight or less or 55% by weight or less, and from the viewpoint of better exhibiting the effects of other monomers, 50% by weight or less, 40% by weight or less, 30% by weight or less, 20% by weight or less, 10% by weight % or less, or 5% by weight or less, less than 3% by weight, or less than 1% by weight. The technology disclosed herein can also be practiced in an embodiment that does not substantially use C _7-12 alkyl (meth)acrylate.

In some embodiments in which the monomer component includes a monomer (m1), from the viewpoint of lowering the elastic modulus, it is preferable that at least a part of the monomer (m1) is an alkyl acrylate. The use of alkyl acrylates is also advantageous in terms of adhesive properties such as adhesive strength. For example, it is preferable that 50% by weight or more of the monomer (m1) is alkyl acrylate, and the proportion of alkyl acrylate in the monomer (m1) is more preferably 75% by weight or more, still more preferably 90% by weight or more, Substantially 100% by weight of the monomer (m1) may be alkyl acrylate. An embodiment may be adopted in which only one or more alkyl acrylates are used as the monomer (m1) and no alkyl methacrylate is used.

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

Examples of the ethylenically unsaturated group possessed by the monomer (m2) include a (meth)acryloyl group, a vinyl group, and a (meth)allyl group. A (meth)acryloyl group is preferred from the viewpoint of polymerization reactivity, and an acryloyl group is more preferred from the viewpoint of lowering the elastic modulus and adhesiveness. From the viewpoint of lowering the elastic modulus of the adhesive, a compound having one ethylenically unsaturated group in one molecule (ie, a monofunctional monomer) is preferably used as the monomer (m2).

In some embodiments, a monomer in which the distance between an ethylenically unsaturated group (for example, a (meth)acryloyl group) and a hydroxyl group and/or a carboxy group is relatively long can be used as the monomer (m2). Thereby, in embodiments in which the hydroxyl group and/or carboxy group are used in the crosslinking reaction, a crosslinked structure with high flexibility can be easily obtained. For example, the number of atoms (typically carbon atoms or oxygen atoms) constituting the chain (linking chain) connecting the ethylenically unsaturated group and the hydroxyl group and/or carboxyl group is 3 or more (for example, 4 or more, 5 or more). or more, 6 or more, 7 or more, 8 or more, 9 or more, 10 or more, 11 or more, 12 or more, 13 or more, 14 or more, 15 or more, 16 or more, 17 or more, 18 or more or 19 or more). m2). The upper limit of the number of atoms constituting the connecting chain is, for example, 45 or less, 20 or less (for example, 19 or less, 18 or less, 17 or less, 16 or less, 15 or less, 14 or less, 13 or less, 12 or less, 11 or less, 10 or less, 9 or less or 8 or less). In addition, the number of atoms forming a linking chain connecting the ethylenically unsaturated group and the hydroxyl group and/or carboxy group refers to the minimum number of atoms required to reach the hydroxyl group or carboxy group from the ethylenically unsaturated group. . For example, when the above-mentioned connecting chain is composed of a linear alkylene group (ie, -(CH ₂ ) _n - group), the number of n is the number of atoms constituting the above-mentioned connecting chain. For example, when the connecting chain is an oxyethylene group (that is, a -(C ₂ H ₄ O) _n - group), 3 and n, which is the sum of 2 carbon atoms and 1 oxygen atom, constituting the oxyethylene group. The product (3n) is the number of atoms constituting the connecting chain. Although not particularly limited, such monomers (m2) include, for example, alkylene represented by -(CH ₂ ) _n - between the ethylenically unsaturated group and the hydroxyl group and/or carboxyl group. units, oxyalkylene units represented by -(C _m H _2m O)- (for example, oxyethylene units where m in the above formula is 2, oxypropylene units where m in the above formulas is 3, oxypropylene units in the above formulas) A compound having at least one oxybutylene unit in which m is 4) can be used. The number of alkylene units and oxyalkylene units is not particularly limited, and may be 1 or more (for example, 1 to 15, 1 to 10, 2 to 6, or 2 to 4). Further, n in the formula representing the above alkylene unit is, for example, an integer from 1 to 10, and may be 2 or more, 3 or more, 4 or more, or 6 or less, or 5 or less. good. In the formula representing the oxyalkylene unit, m is an integer of 2 or more, for example, an integer of 2 to 4. In addition to the above-mentioned ethylenically unsaturated groups, hydroxyl groups and/or carboxy groups, alkylene units and/or oxyalkylene units, the monomer (m2) also contains ester bonds, ether bonds, thioether bonds, aromatic rings, aliphatic rings, and heterocycles. (For example, a ring containing a nitrogen atom (N), an oxygen atom (O), or a sulfur atom (S)). Moreover, the above alkylene unit and oxyalkylene unit may have a substituent.

Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, and ) Hydroxy (meth)acrylates such as 8-hydroxyoctyl acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, and (4-hydroxymethylcyclohexyl)methyl (meth)acrylate. These include, but are not limited to, alkyl. Examples of hydroxyl group-containing monomers that can be preferably used include 4-hydroxybutyl acrylate (Tg: -40°C) and 2-hydroxyethyl acrylate (Tg: -15°C). From the viewpoint of improving flexibility in the room temperature range, 4-hydroxybutyl acrylate, which has a lower Tg, is more preferred. In addition, in an embodiment in which hydroxyalkyl (meth)acrylate is used as the hydroxyl group-containing monomer and the hydroxyl group is utilized in the crosslinking reaction, from the viewpoint of obtaining a highly flexible crosslinked structure, the hydroxyalkyl (meth)acrylate is Monomers with a large number of carbon atoms in the hydroxyalkyl group, such as hydroxyalkyl (meth)acrylates (for example, 4-hydroxy acrylate) in which the hydroxyalkyl group has 3 or more carbon atoms (for example, 3 to 12, preferably 4 to 10). butyl) is preferred. In one preferred embodiment, 50% or more (eg, greater than 50%, greater than 70% or greater than 85%) by weight of the monomer (m2) may be 4-hydroxybutyl acrylate. The hydroxyl group-containing monomers can be used alone or in combination of two or more.

In some embodiments in which a hydroxyl group-containing monomer is used as the monomer (m2), the hydroxyl group-containing monomer may be one or more selected from compounds that do not have a methacryloyl group. Preferred examples of the hydroxyl group-containing monomer that does not have a methacryloyl group include the above-mentioned various hydroxyalkyl acrylates. For example, it is preferable that more than 50% by weight, more than 70% by weight, or more than 85% by weight of the hydroxyl group-containing monomer used as the monomer (m2) is hydroxyalkyl acrylate. The use of hydroxyalkyl acrylates allows for the introduction of hydroxy groups into acrylic polymers that help provide cross-linking points and appropriate cohesive properties, and allows for the introduction of hydroxyl groups into acrylic polymers that help provide cross-linking points and provide adequate cohesive properties, and at room temperature compared to the corresponding hydroxyalkyl methacrylates alone. It is easy to obtain an adhesive with good flexibility and adhesiveness in this area.

Examples of carboxy group-containing monomers include acrylic monomers such as (meth)acrylic acid, carboxyethyl (meth)acrylate, and carboxypentyl (meth)acrylate, as well as itaconic acid, maleic acid, fumaric acid, crotonic acid, Examples include, but are not limited to, isocrotonic acid and the like. Examples of carboxy group-containing monomers that can be preferably used include acrylic acid and methacrylic acid. Further, in some embodiments, from the viewpoint of reducing the elastic modulus of the adhesive, a compound represented by the following formula (2), for example, can be preferably used as the carboxy group-containing monomer.
CH ₂ =CR ¹ -COO-R ² -OCO-R ³ -COOH (2)
Here, R ¹ in the above formula (2) is hydrogen or a methyl group. R ² and R ³ are divalent linking groups (specifically, organic groups having 1 to 20 carbon atoms (for example, 2 to 10, preferably 2 to 5)), and may be the same as each other. May be different. R ² and R ³ in the above formula (2) may be, for example, a divalent aliphatic hydrocarbon group, an aromatic hydrocarbon group, or an alicyclic hydrocarbon group. For example, R ² and R ³ above can be alkylene having 2 to 5 carbon atoms. Specific examples of the carboxy group-containing monomer represented by the above formula (2) include 2-(meth)acryloyloxyethyl hexahydrophthalic acid, 2-(meth)acryloyloxyethyl-phthalic acid, 2-( meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid, 2-(meth)acryloyloxyethyl-succinic acid, 2-(meth)acryloyloxypropyl hexahydrohydrogen phthalate, 2-(meth)acryloyloxypropylhydrogen phthalate, 2-(meth)acryloyloxypropyltetrahydrohydrogen phthalate, and the like. Carboxy group-containing monomers can be used singly or in combination of two or more. A hydroxyl group-containing monomer and a carboxyl group-containing monomer may be used in combination.

The content of the monomer (m2) in the monomer components constituting the acrylic polymer is not particularly limited and can be set depending on the purpose. In some embodiments, the content of the monomer (m2) may be, for example, 0.01% by weight or more, 0.1% by weight or more, or 0.5% by weight or more. From the viewpoint of obtaining higher usage effects, in some embodiments, the content of the monomer (m2) is preferably 0.8% by weight or more, may be 1.0% by weight or more, and 3.0% by weight or more. It may be at least 4.0% by weight or at least 4.0% by weight. The upper limit of the content of the monomer (m2) in the monomer component is set so that the total content of the monomer (m2) together with the content of other monomers does not exceed 100% by weight. In some embodiments, it is appropriate for the content of the monomer (m2) to be, for example, 30% by weight or less or 25% by weight or less, and from the viewpoint of better exhibiting the effects of other monomers, 20% by weight or less. It is preferably at most 15% by weight or less, more preferably at most 15% by weight, may be less than 12% by weight, may be less than 10% by weight, and may be less than 7% by weight. In some preferred embodiments, from the viewpoint of lowering the elastic modulus of the adhesive, the content of the monomer (m2) is 5.0% by weight or less (for example, less than 5.0% by weight), more preferably 3% by weight or less. It may be less than .0% by weight, may be less than 2.0% by weight, and may be less than 1.5% by weight.

In some embodiments, the total content of monomer (m1) and monomer (m2) in the monomer components constituting the acrylic polymer may be, for example, 21% by weight or more or 31% by weight or more, and the From the viewpoint of easily exhibiting the effect, the content is preferably 41% by weight or more, may be 51% by weight or more, may be 61% by weight or more, may be 71% by weight or more, may be 76% by weight or more, and may be 81% by weight or more. % 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. In some embodiments, the total content of monomer (m1) and monomer (m2) in the monomer component is, for example, 99% by weight or less, from the viewpoint of facilitating the advantageous effects of monomers other than these. may be 95% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, 75% by weight or less, 70% by weight or less, 65% by weight or less, 60% by weight It may be less than or equal to 55% by weight.

(Monomer (m3))
In some embodiments, the monomer component constituting the acrylic polymer may contain monomer (m3). As the monomer (m3), a compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule is used. The monomers (m3) can be used alone or in combination of two or more.

Examples of the ethylenically unsaturated group that the monomer (m3) has include a (meth)acryloyl group, a vinyl group, and a (meth)allyl group. A (meth)acryloyl group is preferred from the viewpoint of polymerization reactivity, and an acryloyl group is more preferred from the viewpoint of lowering the elastic modulus and adhesiveness. From the viewpoint of lowering the elastic modulus of the adhesive, a compound having one ethylenically unsaturated group in one molecule (ie, a monofunctional monomer) is preferably used as the monomer (m3).

The number of aromatic rings contained in one molecule of the compound used as the monomer (m3) may be 1 or 2 or more. The upper limit of the number of aromatic rings is not particularly limited, and may be, for example, 16 or less. In some embodiments, from the viewpoint of ease of preparation of the adhesive composition and transparency of the adhesive, the number of aromatic rings may be, for example, 12 or less, preferably 8 or less, and 6 or less. It is more preferable that the number is 5 or less, 4 or less, 3 or less, or 2 or less.

The aromatic ring possessed by the compound used as the monomer (m3) is a benzene ring (it can be a benzene ring that forms part of a biphenyl structure or a fluorene structure); a naphthalene ring, an indene ring, an azulene ring, an anthracene ring, and a phenanthrene ring. A condensed ring of , a thiophene ring; and the like may be used. The heteroatoms included as ring constituent atoms in the above-mentioned heterocycle may be, for example, one or more heteroatoms selected from the group consisting of nitrogen, sulfur, and oxygen. In some embodiments, the heteroatoms making up the heterocycle can be one or both of nitrogen and sulfur. The monomer (m3) may have a structure in which one or more carbon rings and one or more heterocycles are condensed, such as a dinaphthothiophene structure.

The aromatic ring (preferably a carbon ring) may have one or more substituents on the ring-constituting atoms, or may have no substituents. When having a substituent, the substituent includes an alkyl group, an alkoxy group, an aryloxy group, a hydroxyl group, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group. Examples include, but are not limited to. In a substituent containing carbon atoms, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be 1 or 2, for example. In some embodiments, the aromatic ring has no substituent on the ring constituent atoms, or one or more substituents selected from the group consisting of an alkyl group, an alkoxy group, and a halogen atom (e.g., a bromine atom). It can be an aromatic ring having Note that the aromatic ring of the monomer (m3) having a substituent on its ring-constituting atoms means that the aromatic ring has a substituent other than the substituent having an ethylenically unsaturated group.

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

Examples of compounds that can be preferably employed as the monomer (m3) include aromatic ring-containing (meth)acrylates and aromatic ring-containing vinyl compounds. The aromatic ring-containing (meth)acrylate and the aromatic ring-containing vinyl compound can each be used singly or in combination of two or more. One or more aromatic ring-containing (meth)acrylates and one or more aromatic ring-containing vinyl compounds may be used in combination.

In some embodiments, a monomer having two or more aromatic rings (preferably carbon rings) in one molecule may be used as the monomer (m3) because it is easy to obtain a high refractive index effect. Examples of monomers having two or more aromatic rings in one molecule (monomers containing multiple aromatic rings) include monomers having a structure in which two or more non-fused aromatic rings are bonded via a linking group, and two or more non-fused aromatic rings. Monomers with a structure in which rings are chemically bonded directly (that is, without intervening other atoms), monomers with a fused aromatic ring structure, monomers with a fluorene structure, monomers with a dinaphthothiophene structure, monomers with a dibenzothiophene structure , etc. The monomer containing multiple aromatic rings can be used alone or in combination of two or more.

The above-mentioned linking group is, for example, an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (for example, a -O-(CH ₂ ) _n - group, where n is 1 to 3, preferably 1). , thiooxyalkylene groups (e.g. -S-(CH ₂ ) _n - group, where n is 1 to 3, preferably 1), linear alkylene groups (i.e. -(CH ₂ ) _n - group, where n is 1 to 6, preferably 1 to 3), the alkylene group in the above oxyalkylene group, the above thiooxyalkylene group, and the above linear alkylene group may be partially halogenated or completely halogenated. From the viewpoint of the flexibility of the adhesive, preferred examples of the linking group include an oxy group, a thiooxy group, an oxyalkylene group, and a straight-chain alkylene group. Specific examples of monomers having a structure in which two or more non-fused aromatic rings are bonded via a linking group include phenoxybenzyl (meth)acrylate (for example, m-phenoxybenzyl (meth)acrylate), thiophenoxybenzyl (meth) Examples include acrylate, benzylbenzyl (meth)acrylate, and the like.

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

Examples of the monomer having the above-mentioned fused aromatic ring structure include naphthalene ring-containing (meth)acrylate, anthracene ring-containing (meth)acrylate, vinyl group-containing naphthalene, vinyl group-containing anthracene, and the like. Specific examples include 1-naphthylmethyl (meth)acrylate (also known as 1-naphthalenemethyl (meth)acrylate), hydroxyethylated β-naphthol acrylate, 2-naphthoethyl (meth)acrylate, 2-naphthoxyethyl acrylate, -(4-methoxy-1-naphthoxy)ethyl (meth)acrylate and the like.

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

Examples of the monomer having the dinaphthothiophene structure include (meth)acryloyl group-containing dinaphthothiophene, vinyl group-containing dinaphthothiophene, (meth)allyl group-containing dinaphthothiophene, and the like. Specific examples include (meth)acryloyloxymethyl dinaphthothiophene (for example, a compound having a structure in which CH ₂ CH (R ¹ ) C (O) OCH ₂ - is bonded to the 5th or 6th position of the dinaphthothiophene ring. , R ¹ is a hydrogen atom or a methyl group), (meth)acryloyloxyethyldinaphthothiophene (for example, CH ₂ CH(R ¹ )C(O) at the 5th or 6th position of the dinaphthothiophene ring) A compound with a structure in which OCH(CH ₃ )- or CH ₂ CH(R ¹ )C(O)OCH ₂ CH ₂ - is bonded. Here, R ¹ is a hydrogen atom or a methyl group), vinyldinaphthothiophene (For example, a compound having a structure in which a vinyl group is bonded to the 5th or 6th position of a naphthothiophene ring), (meth)allyloxydinaphthothiophene, and the like. In addition, monomers having a dinaphthothiophene structure are included in the above concept of monomers having a fused aromatic ring structure because they include a naphthalene structure or because they have a structure in which a thiophene ring and two naphthalene structures are condensed. Ru.

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

In some preferred embodiments, a monomer having one aromatic ring (preferably a carbon ring) in one molecule is used as the monomer (m3). A monomer having one aromatic ring in one molecule (monomer containing a single aromatic ring) can be useful, for example, in improving the flexibility of the adhesive, adjusting the adhesive properties, and improving the transparency. The monomer containing a single aromatic ring can be used alone or in combination of two or more. In some embodiments, a monomer having one aromatic ring in one molecule may be used in combination with a monomer containing multiple aromatic rings from the viewpoint of improving the refractive index of the adhesive.

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

As the monomer (m3), monomers having a structure in which an oxyethylene chain is interposed between the ethylenically unsaturated group and the aromatic ring in various aromatic ring-containing monomers as described above may be used. A monomer in which an oxyethylene chain is interposed between an ethylenically unsaturated group and an aromatic ring in this way can be understood as an ethoxylated product of the original monomer. The number of repeating oxyethylene units (-CH ₂ CH ₂ O-) in the oxyethylene chain is typically 1 to 4, preferably 1 to 3, more preferably 1 to 2, for example 1. Specific examples of ethoxylated aromatic ring-containing monomers include ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol. Examples include di(meth)acrylate.

The content of the monomer containing multiple aromatic rings in the monomer (m3) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, 40% by weight or more, or 50% by weight or more, and may have a higher refractive index. From the viewpoint of making it easier to obtain, the content may be 70% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomer (m3) may be a monomer containing multiple aromatic rings. That is, as the monomer (m3), only one type or two or more types of monomers containing a plurality of aromatic rings may be used. Further, in some embodiments, the content of the monomer containing multiple aromatic rings in the monomer (m3) is 100% by weight, for example, considering the balance between high refractive index, low elastic modulus, and if necessary, adhesive strength. It may be less than 98% by weight, it may be less than 90% by weight, it may be less than 80% by weight, it may be less than 70% by weight, it may be less than 65% by weight, it may be less than 50% by weight, and it may be less than 25% by weight. It may be less than 10% by weight, or less than 10% by weight. The technology disclosed herein can also be implemented in an embodiment in which the content of the monomer containing multiple aromatic rings in the monomer (m3) is less than 5% by weight. A monomer containing multiple aromatic rings may not be used.

The content of the monomer containing multiple aromatic rings in the monomer component constituting the acrylic polymer is not particularly limited, and can be set so as to realize an adhesive that has both desired refractive index and elastic modulus. The content of the monomer containing multiple aromatic rings in the monomer component may be, for example, 3% by weight or more, 10% by weight or more, or 20% by weight or more. The content of the monomer containing multiple aromatic rings in the monomer component is suitably about 60% by weight or less, taking into consideration the balance between high refractive index, low elastic modulus, and if necessary, adhesive strength. It may be 50% by weight or less (for example, less than 50% by weight), 40% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight or less. The technology disclosed herein can also be practiced in an embodiment in which the content of the monomer containing multiple aromatic rings in the monomer component is less than 3% by weight. A monomer containing multiple aromatic rings may not be used.

The content of the monomer containing a single aromatic ring in the monomer (m3) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, 40% by weight or more, or 50% by weight or more. From the viewpoint of making it easier to obtain, the content may be 70% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomer (m3) may be a monomer containing a single aromatic ring. That is, only one or more monomers containing a single aromatic ring may be used as the monomer (m3). Further, in some embodiments, the content of the monomer containing a single aromatic ring in the monomer (m3) is 100% by weight, for example, taking into account the balance between high refractive index, low elastic modulus, and if necessary, adhesive strength. It may be less than 98% by weight, it may be less than 90% by weight, it may be less than 80% by weight, it may be less than 70% by weight, it may be less than 65% by weight, it may be less than 50% by weight, and it may be less than 25% by weight. It may be less than 10% by weight, or less than 10% by weight. The technology disclosed herein can also be practiced in an embodiment in which the content of the monomer containing a single aromatic ring in the monomer (m3) is less than 5% by weight. A monomer containing a single aromatic ring may not be used.

The content of the monomer containing a single aromatic ring in the monomer component constituting the acrylic polymer is not particularly limited, and can be set so as to realize an adhesive that has both desired refractive index and elastic modulus. The content of the monomer containing a single aromatic ring in the monomer component may be, for example, 3% by weight or more, 10% by weight or more, or 20% by weight or more. The content of the monomer containing a single aromatic ring in the monomer component is suitably about 60% by weight or less, taking into account the balance between high refractive index, low elastic modulus, and if necessary, adhesive strength. It may be 50% by weight or less (for example, less than 50% by weight), 40% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight or less. The technology disclosed herein can also be practiced in an embodiment in which the content of the monomer containing a single aromatic ring in the monomer component is less than 3% by weight. A monomer containing a single aromatic ring may not be used.

In some embodiments of the technology disclosed herein, a high refractive index monomer can be preferably employed as at least a part of the monomer (m3). Here, the term "high refractive index monomer" refers to a monomer whose refractive index is, for example, about 1.510 or more, preferably about 1.530 or more, more preferably about 1.550 or more. In some embodiments, the refractive index of the high refractive index monomer may be 1.570 or more, 1.600 or more, 1.620 or more, 1.650 or more, It may be 1.675 or more or 1.700 or more. The upper limit of the refractive index of the high refractive index monomer is not particularly limited, but from the viewpoint of ease of preparation of the adhesive composition and compatibility with flexibility suitable as an adhesive, it is, for example, 3.000 or less, and 2. It may be .500 or less, 2.000 or less, 1.900 or less, 1.850 or less, 1.800 or less, 1.750 or less, or 1.700 or less. The high refractive index monomers can be used alone or in combination of two or more.

Note that the refractive index of the monomer is measured using an Abbe refractometer at a measurement wavelength of 589 nm and a measurement temperature of 25°C. As the Abbe refractometer, model "DR-M4" manufactured by ATAGO or its equivalent can be used. If a manufacturer or the like provides a nominal value of the refractive index at 25° C., that nominal value can be used.

The above-mentioned high refractive index monomer is one having a corresponding refractive index from among the compounds included in the concept of the aromatic ring-containing monomer (m3) disclosed herein (for example, the compounds and compound groups exemplified above). may be adopted as appropriate. Specific examples include m-phenoxybenzyl acrylate (refractive index: 1.566, homopolymer Tg: -35°C), 1-naphthylmethyl acrylate (refractive index: 1.595, homopolymer Tg: 31°C), Ethoxylated o-phenylphenol acrylate (number of repeating oxyethylene units: 1, refractive index: 1.578), benzyl acrylate (refractive index (nD20): 1.519, homopolymer Tg: 6°C), phenoxyethyl acrylate (Refractive index (nD20): 1.517, homopolymer Tg: 2°C), phenoxydiethylene glycol acrylate (refractive index: 1.510, homopolymer Tg: -35°C), 6-acryloyloxymethyl dinaphthothiophene ( 6MDNTA, refractive index: 1.737), 6-methacryloyloxymethyldinaphthothiophene (6MDNTMA, refractive index: 1.726), 5-acryloyloxyethyldinaphthothiophene (5EDNTA, refractive index: 1.786), 6 -Acryloyloxyethyldinaphthothiophene (6EDNTA, refractive index: 1.722), 6-vinyldinaphthothiophene (6VDNT, refractive index: 1.802), 5-vinyldinaphthothiophene (abbreviation: 5VDNT, refractive index: 1) .793), but is not limited to these.

The content of the high refractive index monomer (that is, the aromatic ring-containing monomer having a refractive index of about 1.510 or more, preferably about 1.530 or more, more preferably about 1.550 or more) in the monomer (m3) is particularly The content is not limited, and may be, for example, 5% by weight or more, 25% by weight or more, 35% by weight or more, or 40% by weight or more. In some embodiments, from the viewpoint of making it easier to obtain a higher refractive index, the content of the high refractive index monomer in the monomer (m3) may be, for example, 50% by weight or more, and preferably 70% by weight or more. , 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomers (m3) may be high refractive index monomers. In some embodiments, the content of the high refractive index monomer in the monomer (m3) is 100% by weight, for example, from the viewpoint of achieving a good balance between high refractive index, low elastic modulus, and if necessary, adhesive strength. It may be less than 98% by weight, less than 90% by weight, less than 80% by weight, or less than 65% by weight.

The content of the high refractive index monomer in the monomer component constituting the acrylic polymer is not particularly limited, and can be set so as to realize an adhesive that has both desired refractive index and elastic modulus. In addition, if necessary, it may be set in consideration of compatibility with adhesive properties (for example, adhesive strength, etc.) and/or optical properties (for example, total light transmittance, haze value, etc.). The content of the high refractive index monomer in the monomer component may be, for example, 3% by weight or more, 10% by weight or more, or 20% by weight or more. The content of the high refractive index monomer in the monomer component is suitably about 60% by weight or less from the viewpoint of achieving a good balance between high refractive index, low elastic modulus, and if necessary, adhesive strength. It may be 50% by weight or less (for example, less than 50% by weight), 40% by weight or less, 25% by weight or less, 15% by weight or less, 5% by weight or less, or less than 3% by weight. High refractive index monomers may not be used.

In some preferred embodiments, an aromatic ring-containing monomer (hereinafter sometimes referred to as "monomer L") whose homopolymer Tg is 10° C. or less is employed as at least a portion of the monomer (m3). The content of the aromatic ring-containing monomer (m3) in the monomer component (in particular, the aromatic ring-containing monomer (m3) that corresponds to at least one of the above-mentioned monomer containing multiple aromatic rings, monomer containing a single aromatic ring, and high refractive index monomer) When the amount is increased, the storage modulus G' of the adhesive generally tends to increase, but by employing monomer L as part or all of the monomer (m3), it is possible to suppress the increase in the storage modulus G'. can. This makes it possible to improve the refractive index while better maintaining a low elastic modulus. The Tg of the monomer L may be, for example, 5°C or less, 0°C or less, -10°C or less, -20°C or less, or -25°C or less. The lower limit of Tg of the monomer L is not particularly limited. Considering the balance with the refractive index improvement effect, in some embodiments, the Tg of the monomer L may be, for example, -70°C or higher, -55°C or higher, or -45°C or higher. In some other embodiments, the Tg of the monomer L may be, for example, -30°C or higher, -10°C or higher, 0°C or higher, or 3°C or higher. Monomer L can be used alone or in combination of two or more.

As the monomer L, one having a corresponding Tg is appropriately adopted from among the compounds included in the concept of the aromatic ring-containing monomer (m3) disclosed herein (for example, the compounds and compound groups exemplified above). be able to. Suitable examples of aromatic ring-containing monomers that can be used as monomer L include m-phenoxybenzyl acrylate (homopolymer Tg: -35°C), benzyl acrylate (homopolymer Tg: 6°C), phenoxyethyl acrylate (homopolymer Tg: 6°C), Tg: 2°C), and phenoxydiethylene glycol acrylate (homopolymer Tg: -35°C).

The content of monomer L in the monomer (m3) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, the content of monomer L in the monomer (m3) is, for example, 50% by weight or more, from the viewpoint of making it easier to obtain an adhesive that has both a high refractive index and a low elastic modulus at a higher level. Often, from the viewpoint of lowering the elastic modulus, it is 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, 95% by weight. The above is fine. Substantially 100% by weight of the monomers (m3) may be monomer L. In some embodiments, the content of monomer L in the monomer (m3) is less than 100% by weight, for example, from the viewpoint of achieving a good balance between high refractive index, low elastic modulus, and, if necessary, adhesive strength. The content may be 98% by weight or less, 90% by weight or less, 80% by weight or less, or 65% by weight or less.

The content of monomer L in the monomer components constituting the acrylic polymer may be, for example, 3% by weight or more, 10% by weight or more, or 20% by weight or more. The content of monomer L in the above monomer component is suitably about 60% by weight or less, from the viewpoint of achieving a good balance between high refractive index, low elastic modulus, and, if necessary, adhesive strength. % (for example, less than 50% by weight), 40% by weight or less, 25% by weight or less, 15% by weight or less, 5% by weight or less, or less than 3% by weight. Monomer L may not be used.

In some embodiments, the aromatic ring-containing monomer (m3) may be preferably selected from compounds that do not include a structure in which two or more non-fused aromatic rings are directly chemically bonded (for example, a biphenyl structure). For example, the monomer component has a composition in which the content of a compound containing a structure in which two or more non-fused aromatic rings are directly chemically bonded is less than 5% by weight (more preferably less than 3% by weight, and may be 0% by weight) An acrylic polymer constituted by is preferred. Limiting the amount of compounds that contain a structure in which two or more non-fused aromatic rings are directly chemically bonded in this way allows for a better balance between high refractive index, low elastic modulus, and, if necessary, adhesive strength. This can be advantageous from the viewpoint of realizing a pressure-sensitive adhesive.

The content of the monomer (m3) in the monomer components constituting the acrylic polymer is not particularly limited, and the content of the monomer (m3) in the monomer component constituting the acrylic polymer is not particularly limited, and the content of the monomer (m3) is not limited to a desired refractive index and elastic modulus, as well as adhesive properties (e.g., adhesive strength, etc.) and/or optical properties (e.g., total light rays). The pressure-sensitive adhesive can be set so as to achieve both transparency, haze value, etc.). The content of the monomer (m3) in the monomer component may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, 10% by weight or more, or 15% by weight. It may be more than 20% by weight. From the viewpoint of obtaining higher effects, in some embodiments, the content of the monomer (m3) in the monomer component may be 25% by weight or more, 30% by weight or more, 40% by weight or more, 45% by weight. or more or 50% by weight or more. The content of the monomer (m3) in the above monomer component is typically less than 100% by weight, suitably less than about 75% by weight (for example, 0% by weight or more and less than 75% by weight), and approximately It is preferably 60% by weight or less, 50% by weight or less (for example, less than 50% by weight), 40% by weight or less, 25% by weight or less, 15% by weight or less, 5% by weight or less It may be less than 3% by weight. The adhesive disclosed herein can also be preferably implemented in an embodiment in which the monomer component constituting the acrylic polymer does not contain the monomer (m3).

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

Examples of the above-mentioned other monomers include monomers having functional groups other than hydroxyl groups and carboxyl groups (functional group-containing monomers). For example, other monomers that can improve the cohesive force and heat resistance of the adhesive include sulfonic acid group-containing monomers, phosphoric acid group-containing monomers, cyano group-containing monomers, and the like. In addition, amide group-containing monomers ( For example, (meth)acrylamide, N-methylol (meth)acrylamide, etc.), amino group-containing monomers (such as aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, etc.), and nitrogen atom-containing rings. (for example, N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), imide group-containing monomers, epoxy group-containing monomers, keto group-containing monomers, isocyanate group-containing monomers, alkoxysilyl group-containing monomers, etc. Can be mentioned. Note that among the monomers having a nitrogen atom-containing ring, some such as N-vinyl-2-pyrrolidone also fall under the category of amide group-containing monomers. The same applies to the relationship between the monomer having a nitrogen atom-containing ring and the amino group-containing monomer.

Other monomers that can be used other than the above functional group-containing monomers include vinyl ester monomers such as vinyl acetate; non-aromatic ring-containing (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; ethylene, Olefinic monomers such as butadiene and isobutylene; Chlorine-containing monomers such as vinyl chloride; Alkoxy group-containing monomers such as methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, and ethoxyethoxyethyl (meth)acrylate; vinyl ethers such as methyl vinyl ether system monomer; etc.

In some embodiments, for the purpose of lowering the elastic modulus of the adhesive (especially lowering the elastic modulus in a low temperature range) or improving elongation deformability (for example, improving elongation at break), an alkoxy group is added as the other monomer. Containing monomers may be preferably used. Alkoxy group-containing monomers can also help reduce haze and improve adhesion. Suitable examples of alkoxy group-containing monomers include methoxyethyl acrylate (MEA) (homopolymer Tg: -50°C), ethoxyethoxyethyl acrylate (also known as ethyl carbitol acrylate, homopolymer Tg: -67°C), Examples include alkoxy group-containing acrylates. The content of the alkoxy group-containing monomer in the monomer components constituting the acrylic polymer may be, for example, 1% by weight or more, 3% by weight or more, and from the viewpoint of obtaining higher effects, 5% by weight or more. The content may be 10% by weight or more, or may be 15% by weight or more. Further, the content of the alkoxy group-containing monomer in the monomer component may be, for example, 40% by weight or less (for example, 0 to 40% by weight), which facilitates achieving both a high refractive index and a balance of properties as an adhesive. From this point of view, it is advantageous that it is 35% by weight or less, preferably 30% by weight or less, it may be 25% by weight or less, and it may be 22% by weight or less.

When using the above-mentioned other monomers, the amount used is not particularly limited, and can be appropriately set within a range where the total amount of the monomer components does not exceed 100% by weight. In some embodiments, the content of the above-mentioned other monomers in the monomer component is, for example, approximately 45% by weight or less (for example, 0 to 45% by weight) from the viewpoint of achieving both a high refractive index and a balance of properties as an adhesive. %), and it is appropriate to make it about 40% by weight or less, about 35% by weight or less, about 30% by weight or less, about 25% by weight or less, about 20% by weight or less It may be about 10% by weight or less, about 5% by weight or less, or about 1% by weight or less. The technology disclosed herein can also be preferably implemented in an embodiment in which the monomer component does not substantially contain the other monomers mentioned above.

In some embodiments, the monomer components constituting the acrylic polymer may have a composition in which the amount of the methacryloyl group-containing monomer used is suppressed to a predetermined amount or less. The amount of the methacryloyl group-containing monomer used in the monomer component may be, for example, less than 5% by weight, less than 3% by weight, less than 1% by weight, or less than 0.5% by weight. Limiting the amount of the methacryloyl group-containing monomer used in this way can be advantageous from the viewpoint of realizing a pressure-sensitive adhesive that has a good balance of flexibility, adhesiveness, and high refractive index. The monomer component constituting the acrylic polymer may have a composition that does not contain a methacryloyl group-containing monomer (for example, a composition that consists only of an acryloyl group-containing monomer).

In some embodiments, the amount of the carboxyl group-containing monomer used in the monomer component constituting the acrylic polymer is limited from the viewpoint of suppressing coloring or discoloration (for example, yellowing) of the adhesive. The amount of the carboxy group-containing monomer used in the monomer component may be, for example, less than 1% by weight, less than 0.5% by weight, less than 0.3% by weight, less than 0.1% by weight, 0. It may be less than .05% by weight. This limitation on the amount of carboxy group-containing monomers is due to the fact that metal materials that may be placed in contact with or in close proximity to the adhesive disclosed herein (e.g., metal wiring that may be present on an adherend) This is also advantageous from the viewpoint of suppressing corrosion of metal films, etc.). The technique disclosed herein can be carried out in an embodiment in which the monomer components constituting the acrylic polymer do not contain a carboxy group-containing monomer.
For the same reason, in some embodiments, the monomer components constituting the acrylic polymer include monomers having acidic functional groups (including carboxy groups, sulfonic acid groups, phosphoric acid groups, etc.). Preferably limited. As the amount of the acidic functional group-containing monomer used in the monomer component of this embodiment, the above-mentioned preferred amount of the carboxy group-containing monomer can be applied. The technology disclosed herein can be preferably implemented in an embodiment in which the monomer component does not contain an acidic group-containing monomer (that is, an embodiment in which the acrylic polymer is acid-free).

(Method for preparing acrylic polymer)
In the technology disclosed herein, the method for obtaining the acrylic polymer composed of such monomer components is not particularly limited, and may include solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, photopolymerization, etc. Various polymerization methods known as methods for synthesizing acrylic polymers can be appropriately employed. For example, a solution polymerization method can be preferably employed. The polymerization temperature when performing solution polymerization can be appropriately selected depending on the type of monomer and solvent used, the type of polymerization initiator, etc., and is, for example, about 20°C to 170°C (typically 40°C to 140°C). ℃).

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

The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators depending on the type of polymerization method. For example, one or more azo polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; aromatic carbonyl compounds ; etc. Still another example of the polymerization initiator is a redox initiator using a combination of a peroxide and a reducing agent. One type of polymerization initiator can be used alone or two or more types can be used in combination. The amount of the polymerization initiator used may be any normal amount, for example, about 0.005 to 1 part by weight (typically about 0.01 to 1 part by weight) per 100 parts by weight of the monomer component. ) can be selected from the range.

In the above polymerization, various conventionally known chain transfer agents can be used as necessary. For example, mercaptans such as n-dodecylmercaptan, t-dodecylmercaptan, thioglycolic acid, and α-thioglycerol can be used. Alternatively, a chain transfer agent that does not contain sulfur atoms (non-sulfur chain transfer agent) may be used. Examples of non-sulfur chain transfer agents include anilines such as N,N-dimethylaniline and N,N-diethylaniline; terpenoids such as α-pinene and terpinolene; α-methylstyrene, α-methylstyrene dimer, etc. styrenes; and the like. One type of chain transfer agent can be used alone or two or more types can be used in combination. When using a chain transfer agent, the amount used can be, for example, approximately 0.01 to 1 part by weight per 100 parts by weight of the monomer component.

(Glass transition temperature Tg _P of base polymer)
In the technology disclosed herein, the monomer component constituting the base polymer (e.g., acrylic polymer) of the adhesive has a composition such that the glass transition temperature _TgP based on the composition of the monomer component is approximately 10 ° C. or less. is preferred. In some embodiments, the glass transition temperature Tg _P is preferably 0° C. or lower (for example, lower than 0° C.), more preferably -10° C. or lower, and even more preferably -20° C. or lower. , -25°C or lower, -30°C or lower, -35°C or lower, -40°C or lower, -45°C or lower, -50°C or lower, -55°C or lower, The temperature may be -57°C or lower. A low glass transition temperature _TgP can be advantageous from the viewpoint of lowering the elastic modulus of the adhesive. The lower limit of the glass transition temperature _TgP is not particularly limited. In some embodiments, the glass transition temperature Tg _P may be, for example, -70°C or higher, and is advantageously -65°C or higher from the viewpoint of facilitating the realization of a pressure-sensitive adhesive having appropriate cohesiveness. The temperature may be -60°C or higher, or -55°C or higher. By combining a base polymer having a composition having a glass transition temperature _TgP in the above range and a high refractive additive (A), an adhesive having both a high refractive index and a low elastic modulus can be preferably realized.

Here, unless otherwise specified, the glass transition temperature _TgP refers to the glass transition temperature determined by the Fox equation based on the composition of the monomer components. The Fox equation, as shown below, is a relation between Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer.
1/Tg=Σ(Wi/Tgi)
In the above Fox equation, Tg is the glass transition temperature of the copolymer (unit: K), Wi is the weight fraction of monomer i in the copolymer (copolymerization ratio on a weight basis), and Tgi is the homopolymer of monomer i. represents the glass transition temperature (unit: K) of
As the glass transition temperature of the homopolymer used to calculate Tg, the value described in publicly known materials such as "Polymer Handbook" (3rd edition, John Wiley & Sons, Inc., 1989) is used. For monomers for which multiple values are listed in the Polymer Handbook, the highest value is used. If the Tg of the homopolymer is not described in known materials, the value obtained by the measurement method described in Japanese Patent Application Publication No. 2007-51271 shall be used.

(Weight average molecular weight of base polymer)
The weight average molecular weight (Mw) of the base polymer (for example, acrylic polymer) is not particularly limited, and may be, for example, approximately 30×10 ⁴ or more, approximately 40×10 ⁴ or more, or approximately 50× It may be 10 ⁴ or more. In a structure containing 30 parts by weight or more of the additive (A) based on 100 parts by weight of the base polymer, by using a base polymer with Mw of a predetermined value or more, a suitable adhesive property and elongation deformability can be achieved. It is easy to obtain cohesive force. In some embodiments, the Mw of the base polymer is suitably 55×10 ⁴ or more, advantageously 60×10 ⁴ or more, preferably 70×10 ⁴ or more, 80 It is more preferable to be at least ×10 ⁴ , and may be at least 90×10 ⁴ , at least 100×10 ⁴ , or at least 120×10 ⁴ . The fact that the Mw of the base polymer is not too low makes it easier to stably retain the additive (A) in the adhesive in a configuration containing 30 parts by weight or more of the additive (A) based on 100 parts by weight of the base polymer. It can also be advantageous from the viewpoint of improving the transparency of the adhesive. The upper limit of Mw of the base polymer is, for example, about 500×10 ⁴ or less, and from the viewpoint of adhesive performance, about 400×10 ⁴ or less (more preferably about 300×10 ⁴ or less, for example, about 200×10 ⁴ or less). It is preferably within a range of about 170×10 ⁴ or less, about 150×10 ⁴ or less, or about 130×10 ⁴ or less.

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

(High refractive index additive (A))
The high refractive index additive (A) in the technology disclosed herein is a compound with an asymmetric structure, and is typically an organic compound with an asymmetric structure. Here, the compound with an asymmetric structure refers to a compound having a molecular structure that is neither linearly symmetrical nor rotationally symmetrical. By using the additive (A) in combination with a base polymer (for example, an acrylic polymer), it is possible to realize an adhesive that suitably has both a high refractive index and a low elastic modulus. The fact that the compound used as the additive (A) has an asymmetric structure means that even if the amount used is relatively large based on 100 parts by weight of the base polymer (for example, acrylic polymer), the degree of increase in the elastic modulus of the adhesive will be moderate. It is advantageous from the viewpoint of The additive (A) can be used alone or in combination of two or more.

As the additive (A), a compound that corresponds to at least one of a compound having a double bond-containing ring and a compound having a heterocycle (which may be a double bond-containing ring), that is, a heterocycle and a double bond-containing ring. Compounds containing a ring corresponding to at least one of these can be preferably employed. By containing such a compound, the refractive index of the adhesive can be efficiently increased. The above compound may be advantageous from the viewpoint of ease of preparation of the adhesive composition (for example, solubility in a solvent used in a solvent-based adhesive composition) and compatibility within the adhesive.

The double bond-containing ring that the additive (A) has may be a conjugated double bond-containing ring (typically an aromatic ring) or a non-conjugated double bond-containing ring. From the viewpoint of increasing the refractive index, it is advantageous for the additive (A) to have at least one ring selected from an aromatic ring and a heterocycle (heterocycle) as the double bond-containing ring. . The above-mentioned heterocycle may have a structure included in an aromatic ring, or may have a double bond-containing heterocyclic structure different from an aromatic ring. Examples of the double bond-containing ring (typically an aromatic ring) that the additive (A) may have include a benzene ring (which may be a benzene ring forming part of a biphenyl structure or a fluorene structure); a naphthalene ring; It may be a carbocyclic ring such as an indene ring, an azulene ring, an anthracene ring, or a fused ring of a phenanthrene ring; a pyridine ring, a pyrimidine ring, a pyridazine ring, a pyrazine ring, a triazine ring, a pyrrole ring, a pyrazole ring, an imidazole ring, or a triazole ring. It may be a heterocyclic ring such as a ring, an oxazole ring, an isoxazole ring, a thiazole ring, or a thiophene ring. The heteroatoms included as ring constituent atoms in the above-mentioned heterocycle may be, for example, one or more heteroatoms selected from the group consisting of nitrogen, sulfur, and oxygen. In some embodiments, the heteroatoms making up the heterocycle can be one or both of nitrogen and sulfur. The additive (A) may have a structure in which one or more carbon rings and one or more heterocycles are condensed, such as a dinaphthothiophene structure.

In some embodiments, the additive (A) is an organic compound having two or more aromatic rings in one molecule (hereinafter referred to as a "compound containing multiple aromatic rings") because it is easy to obtain a high refractive index effect. ) can be preferably adopted. The compound containing multiple aromatic rings may or may not have a polymerizable functional group such as an ethylenically unsaturated group. Further, the compound containing multiple aromatic rings may be a polymer or a non-polymer. Further, the above polymer is an oligomer (preferably an oligomer having a molecular weight of about 5,000 or less, more preferably about 1,000 or less; for example, a low polymer of about 2 to 5 molecules) containing a monomer containing multiple aromatic rings as a monomer unit. obtain. The above oligomers are, for example: homopolymers of monomers containing a plurality of aromatic rings; copolymers of two or more monomers containing a plurality of aromatic rings; copolymers of one or more monomers containing a plurality of aromatic rings with other monomers. It can be a combination; etc. The above-mentioned other monomers may be aromatic ring-containing monomers that do not correspond to monomers containing multiple aromatic rings, may be monomers having no aromatic rings, or may be a combination thereof.

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 via a linking group; Examples include a compound having a chemically bonded structure (without intervening), a compound having a fused aromatic ring structure, a compound having a fluorene structure, a compound having a dinaphthothiophene structure, a compound having a dibenzothiophene structure, and the like. The compound containing multiple aromatic rings can be used alone or in combination of two or more.

Examples of compounds that can be used as the additive (A) include compounds that can be used as monomers (m3); oligomers containing as monomer units compounds that can be used as monomers (m3); compounds that can be used as monomers (m3) From, a group having an ethylenically unsaturated group (which may be a substituent bonded to a ring-constituting atom) or a group having no ethylenically unsaturated group, excluding the part of the group that constitutes an ethylenically unsaturated group. (For example, hydroxyl group, amino group, halogen atom, alkyl group, alkoxy group, alkoxyalkyl group, aryloxy group, ester group (acetoxyalkyl group, etc.), hydroxyalkyl group, hydroxyalkyloxy group, glycidyloxy group, etc.) or hydrogen Examples include, but are not limited to, compounds having an asymmetric structure, such as a compound having a structure in which an atom is replaced.

The double bond-containing ring (typically an aromatic ring, preferably a carbocyclic ring) may have one or more substituents on the ring-constituting atoms, or may have no substituents. good. In some embodiments, for example, a compound having a double bond-containing ring and having an asymmetric structure due to the above-mentioned substituents can be preferably used as the additive (A).

In some embodiments, a compound containing a fused ring having a substituent (substituted fused ring-containing compound) may be preferably used as the additive (A). By containing such a compound, the refractive index of the adhesive can be efficiently increased. The above compound may be advantageous from the viewpoint of ease of preparation of the adhesive composition (for example, solubility in a solvent used in a solvent-based adhesive composition) and compatibility within the adhesive. Here, the fused ring having a substituent refers to a fused ring having one or more substituents on the ring constituent atoms of at least one ring included in the fused ring. The fused ring preferably includes a ring that corresponds to at least one of a heterocycle and a double bond-containing ring. For example, a substituted condensed ring-containing compound having an asymmetric structure due to the above substituents can be preferably used as the additive (A).

In the additive (A) having a substituent on a ring-constituting atom, the substituent includes an alkyl group, an alkoxy group, an alkoxyalkyl group, an aryloxy group, an ester group (acetoxyalkyl group, etc.), an aryloxy group, a hydroxyl group. , halogen atoms (fluorine atom, chlorine atom, bromine atom, etc.), ethylenically unsaturated groups, hydroxyalkyl groups, hydroxyalkyloxy groups, glycidyloxy groups, etc., but are not limited to these. In a substituent containing carbon atoms, the number of carbon atoms contained in the substituent is preferably 1 to 4, more preferably 1 to 3, and may be 1 or 2, for example. In some embodiments, the double bond-containing ring has no substituents on the ring atoms, or has an alkyl group, an alkoxy group, an alkoxyalkyl group, an ester group, an ethylenically unsaturated group (e.g. (meth)acryloxy It may be an aromatic ring having one or more substituents selected from the group consisting of a hydroxyl group), a hydroxyl group, and a hydroxyalkyl group. Among these, preferred substituents include alkyl groups, alkoxy groups, and alkoxyalkyl groups, and the number of carbon atoms contained in these substituents is preferably 1 to 4, more preferably 1 to 3, For example, it can be 1 or 2.

A preferred example of a substituted fused ring-containing compound that can be used as the additive (A) is a dinaphthothiophene compound (substituted DNT) having at least one substituent. A pressure-sensitive adhesive containing substituted DNT with an asymmetric structure as the additive (A) can preferably achieve both a high refractive index and a low elastic modulus. The substituent that the substituted DNT has may be, for example, one or more selected from the group consisting of an alkyl group, an alkoxy group, an alkoxyalkyl group, a (meth)acryloxy group, and a vinyl group. From the viewpoint of lowering the elastic modulus, substituted DNT having one substituent is preferred. Specific examples of such substituted DNTs include saturated substituted DNTs such as 6-methoxymethyldinaphthothiophene (6MDNTM, refractive index: 1.759) and 6-ethyldinaphthothiophene (6EDNT, refractive index: 1.764). Substituted DNT having groups; 6-acryloyloxymethyldinaphthothiophene (6MDNTA, refractive index: 1.737), 6-methacryloyloxymethyldinaphthothiophene (6MDNTMA, refractive index: 1.726), 5-acryloyloxyethyl Dinaphthothiophene (5EDNTA, refractive index: 1.786), 6-acryloyloxyethyldinaphthothiophene (6EDNTA, refractive index: 1.722), 6-vinyldinaphthothiophene (6VDNT, refractive index: 1.802), Examples include substituted DNT having an ethylenically unsaturated substituent, such as 5-vinyldinaphthothiophene (abbreviation: 5VDNT, refractive index: 1.793).

In some embodiments, a compound having no ethylenically unsaturated group can be preferably employed as the additive (A). This may cause changes in the properties of the adhesive composition due to heat or light (e.g., decrease in coatability due to progress of gelation or increase in viscosity) or changes in adhesive performance (e.g., elasticity due to reaction of ethylenically unsaturated groups). (increase in elasticity and decrease in elongation deformability) and improve storage stability. Adopting an additive (A) that does not have an ethylenically unsaturated group means that in an adhesive sheet having an adhesive layer containing the additive (A), dimensional changes and deformation due to reactions of ethylenically unsaturated groups are avoided. It is also preferable from the viewpoint of suppressing the occurrence of optical distortion (warping, waving, etc.) and optical distortion.

The refractive index _na of the additive (A) can be selected so that a desired refractive index can be obtained in the adhesive containing the additive (A), and is not limited to a specific range. The refractive index _na of the additive (A) may be, for example, 1.510 or more, 1.530 or more, 1.550 or more, or 1.570 or more. Good too. In some embodiments, the refractive index _na of the additive (A) is suitably 1.600 or more, advantageously 1.620 or more, and 1.650 or more. It is preferably 1.675 or more, more preferably 1.700 or more. By using the additive (A) with a higher refractive index, the degree of freedom in selecting the base polymer that can constitute the adhesive having the desired refractive index increases, and for example, it is also possible to select a base polymer with a lower refractive index. It becomes possible. This can be advantageous from the viewpoint of realizing a pressure-sensitive adhesive that has both a high refractive index and a low elastic modulus in a well-balanced manner. The upper limit of the refractive index _na of the additive (A) is not particularly limited, but from the viewpoint of the low-temperature properties and transparency of the adhesive, it is suitable to be, for example, 3.000 or less, and 2.500 or less. It may be 2.000 or less, 1.900 or less, 1.850 or less, 1.825 or less, or 1.800 or less.

Note that the refractive index n _a of the high refractive index additive (A) is measured using a prism coupler under conditions of a measurement temperature of 25° C. and a measurement wavelength of 594 nm. As the prism coupler, a commercially available measuring device can be used, and for example, model "2010M" manufactured by Metricon or its equivalent can be used. If a manufacturer or the like provides a nominal value of the refractive index at 25° C., that nominal value can be used.

The refractive index n _a of the additive (A) is preferably higher than the refractive index n _T of the adhesive containing the additive (A). That is, a pressure-sensitive adhesive containing as an additive (A) a compound having a refractive index difference Δn _A larger than 0 defined by the following formula: Δn _A =n _a −n _T ; is preferable. In some embodiments, Δn _A may be, for example, 0.010 or more, and from the viewpoint of efficiently exhibiting the refractive index improvement effect by the additive (A), it is advantageous that it is 0.050 or more, It is preferably 0.100 or more, more preferably 0.125 or more, even more preferably 0.150 or more, may be 0.160 or more, or even 0.170 or more. It may be 0.180 or more or 0.190 or more. Further, from the viewpoint of the compatibility of the high refractive index additive (A) in the adhesive, the transparency of the adhesive, etc., in some embodiments, Δn _A may be, for example, 0.500 or less, It may be .400 or less, or it may be .300 or less.

The molecular weight of the additive (A) is not particularly limited, and may be, for example, 100 or more, 130 or more, or 150 or more. In some embodiments, the molecular weight of the additive (A) is preferably 170 or more, more preferably 200 or more, and even 230 or more, from the viewpoint of increasing the refractive index of the additive (A). Generally, it may be 250 or more, 270 or more, or 300 or more. Further, the molecular weight of the additive (A) may be approximately less than 10,000 or less than 5,000, and has the effect of increasing the refractive index and other properties (for example, flexibility suitable for adhesives, optical properties such as haze) From the viewpoint of achieving a good balance between It may be less than It can be advantageous that the molecular weight of the additive (A) is not too large from the viewpoint of ease of preparation of the adhesive composition and improvement of compatibility within the adhesive. In some embodiments, a compound having a molecular weight of about 200 to 600 (for example, 300 or more and less than 500) can be preferably used as the additive (A).

As for the molecular weight of the additive (A), for non-polymers or polymers with a low degree of polymerization (e.g. dimer to pentamer), the molecular weight calculated based on the chemical structure, or the molecular weight calculated based on the matrix-assisted laser desorption ionization flight. Measured values using time-based mass spectrometry (MALDI-TOF-MS) can be used. When the additive (A) 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 molecular weight is provided by a manufacturer, etc., that nominal value can be used.

In some embodiments of the technology disclosed herein, the additive (A) is a compound that is typically not gaseous at 25°C and is not liquid (liquid) or gaseous at 25°C. It is preferable. Note that in this specification, "liquid" means exhibiting fluidity, and refers to a liquid state as a substance state. Such compounds include those having a melting point above 25°C. Thereby, it is easy to obtain a pressure-sensitive adhesive having an appropriate cohesive force capable of exhibiting desired adhesive properties and elongation deformability. The melting point of the additive (A) is, for example, preferably 30°C or higher, more preferably 40°C or higher, even more preferably 50°C or higher, 60°C or higher, or 70°C or higher. , 80°C or higher. The upper limit of the melting point of the additive (A) is not particularly limited. In some embodiments, from the viewpoint of ease of preparation of the adhesive composition, transparency of the adhesive, etc., the melting point of the additive (A) may be, for example, 350°C or lower, or even 300°C or lower. Generally, the temperature may be 250°C or lower, or 200°C or lower.

In some embodiments, the compound used as the additive (A) is preferably soluble in a solvent (typically an organic solvent) from the viewpoint of ease of blending into the adhesive. Here, soluble means that the compound is at least 1.0% by weight (more preferably 2.0% by weight or more, still more preferably 5.0% by weight or more) at 25°C in at least one general-purpose solvent. The solubility is such that a solution can be prepared at a concentration of 0% by weight or more, 10% by weight or more, 15% by weight or more, or 20% by weight or more. Here, examples of the above-mentioned general-purpose solvents include acetate esters such as ethyl acetate and butyl acetate; lower ketones such as acetone and methyl ethyl ketone (MEK); aromatic hydrocarbon solvents such as benzene and toluene; mixed solvents thereof; etc. included. Among these, compounds that exhibit the above-mentioned solubility in one or both of ethyl acetate and MEK are preferred.

The content of the additive (A) in the adhesive disclosed herein (if multiple types of compounds are used, their total content) is within a range such that the content is 30 parts by weight or more based on 100 parts by weight of the base polymer. Therefore, it is possible to appropriately set the pressure-sensitive adhesive to obtain a pressure-sensitive adhesive having desired properties. In some embodiments, the content of the additive (A) relative to 100 parts by weight of the base polymer may be, for example, more than 30 parts by weight to better exhibit the effect of lowering the elastic modulus and/or increasing the refractive index. From this point of view, the amount is preferably 35 parts by weight or more, more preferably 40 parts by weight or more, 45 parts by weight or more, 50 parts by weight or more, 60 parts by weight or more, and 65 parts by weight or more. good. Further, the content of the additive (A) relative to 100 parts by weight of the base polymer may be, for example, 150 parts by weight or less to obtain an adhesive having an appropriate cohesive force capable of exhibiting desired adhesive properties and elongation deformability. In some embodiments, the amount is suitably 120 parts by weight or less, preferably 100 parts by weight or less, may be 90 parts by weight or less, may be 80 parts by weight or less, and may be 75 parts by weight. The following may be used. From the viewpoint of transparency and low-temperature properties of the adhesive, in some embodiments, the content of the additive (A) relative to 100 parts by weight of the base polymer may be 70 parts by weight or less, and may be 65 parts by weight or less. The amount may be 60 parts by weight or less, 55 parts by weight or less, 50 parts by weight or less, or 45 parts by weight or less.

In addition to the high refractive index additive (A) as described above, the adhesive disclosed herein contains an organic compound with a high refractive index that does not fall under the above additive (A) as an optional component. It's okay to stay. Examples of high refractive index organic compounds that do not fall under additive (A) include compounds that can be used as monomers (m3) and have a symmetrical structure; two or more non-fused aromatic rings bonded via a linking group; Compounds having a structure in which two or more non-fused aromatic rings are chemically bonded directly (i.e., without intervening other atoms), compounds having a fused aromatic ring structure, compounds having a fluorene structure, dinaphthothiophene Examples include compounds having a structure or a compound having a dibenzothiophene structure, which have a symmetrical structure. From the perspective of properly demonstrating the effects of additive (A), the amount of high refractive index organic compounds that do not fall under additive (A) should be less than 1/3 of the amount of additive (A) used on a weight basis. It is appropriate to set it as 1/4, and it is preferable to set it as less than 1/4, it may be less than 1/6, it may be less than 1/10, it may be less than 1/15, or it may be less than 1/30. In addition, the amount of the high refractive index organic compound that does not fall under the additive (A) is suitably less than 10 parts by weight based on 100 parts by weight of the base polymer, less than 5 parts by weight, less than 3 parts by weight, It is preferably less than 2 parts by weight or less than 1 part by weight. The technique disclosed herein can be preferably carried out in an embodiment in which a high refractive index organic compound that does not correspond to the additive (A) is not substantially used.

(Crosslinking agent)
The adhesive composition used to form the adhesive disclosed herein may contain a crosslinking agent, if necessary, for purposes such as adjusting the cohesive force of the adhesive. As the crosslinking agent, use a crosslinking agent known in the adhesive field, such as an isocyanate crosslinking agent, an epoxy crosslinking agent, an aziridine crosslinking agent, an oxazoline crosslinking agent, a melamine resin, a metal chelate crosslinking agent, etc. Can be done. Among these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents can be preferably employed. Other examples of crosslinking agents include monomers having two or more ethylenically unsaturated groups in one molecule, ie, polyfunctional monomers. One type of crosslinking agent can be used alone or two or more types can be used in combination.

As the isocyanate crosslinking agent, a bifunctional or more functional isocyanate compound can be used, such as aliphatic polystyrene such as trimethylene diisocyanate, butylene diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), dimer acid diisocyanate, etc. Isocyanates; Alicyclic isocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), 1,3-bis(isocyanatomethyl)cyclohexane; 2,4-tolylene diisocyanate, 4,4'- Aromatic isocyanates such as diphenylmethane diisocyanate and xylylene diisocyanate (XDI); the above isocyanate compounds are modified with allophanate bonds, biuret bonds, isocyanurate bonds, uretdione bonds, urea bonds, carbodiimide bonds, uretonimine bonds, oxadiazinetrione bonds, etc. modified polyisocyanates (for example, isocyanurate of HDI, allophanate of HDI, etc.); polyhydric alcohol adducts of the above-mentioned isocyanate compounds (for example, trimethylolpropane adduct of XDI, etc.); and the like. Examples of commercially available products include the trade names Takenate 300S, Takenate 500, Takenate 600, Takenate D110N, Takenate D120N, Takenate D140N, Takenate D160N, Takenate D165N, Takenate D178N, Takenate D178NL (all manufactured by Mitsui Chemicals), Sumidur T80. , Sumidur L, Desmodur N3400 (manufactured by Sumika Bayer Urethane), Millionate MR, Millionate MT, Coronate L, Coronate HL, Coronate HX, Coronate 2770 (manufactured by Tosoh Corporation), Product name Duranate A201H, Duranate Examples include TPA-100 (manufactured by Asahi Kasei Corporation). The isocyanate compounds can be used alone or in combination of two or more. A bifunctional isocyanate compound and a trifunctional or more functional isocyanate compound may be used together.

Examples of the epoxy crosslinking agent include bisphenol A, epichlorohydrin type epoxy resin, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, and trimethylol. Propane triglycidyl ether, diglycidylaniline, diamine glycidylamine, N,N,N',N'-tetraglycidyl-m-xylylenediamine and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, etc. can be mentioned. These can be used alone or in combination of two or more.

Examples of polyfunctional monomers include ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, Pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,12-dodecane Diol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, divinylbenzene, bisphenol A di(meth)acrylate, epoxy acrylate , polyester acrylate, urethane acrylate, butyldiol (meth)acrylate, hexyldiol di(meth)acrylate, and the like. One type of polyfunctional monomer can be used alone or two or more types can be used in combination.

In some embodiments, at least a portion of the crosslinking agent is a bifunctional crosslinking agent having two crosslinking reactive groups (eg, isocyanate groups) per molecule. By using a bifunctional crosslinking agent, a flexible crosslinked structure can be easily formed. One kind of bifunctional crosslinking agent can be used alone or two or more kinds can be used in combination. Moreover, a bifunctional crosslinking agent may be used in combination with a trifunctional or more functional crosslinking agent.

In some embodiments, an acyclic crosslinking agent (also referred to as a chain crosslinking agent) that does not have a ring structure such as an aromatic ring or an aliphatic ring is preferably used as the crosslinking agent. For example, among the above-mentioned isocyanate-based crosslinking agents, it is preferable to use isocyanate-based compounds that do not have a ring structure such as an aromatic ring or an isocyanurate ring. By using an acyclic isocyanate compound as a crosslinking agent, a highly flexible crosslinking agent can be easily formed. Specific examples of the acyclic isocyanates include aliphatic isocyanate compounds (e.g., PDI and HDI) and modified aliphatic isocyanate compounds (e.g., allophanate bonds, biuret bonds, urea bonds, and carbodiimide bonds of PDI and HDI). modified polyisocyanates). One type of acyclic crosslinking agent can be used alone or two or more types can be used in combination. In some preferred embodiments, an acyclic bifunctional crosslinking agent may be used as the crosslinking agent.

In some embodiments, a crosslinking agent in which the distance between one crosslinking reactive group (for example, an isocyanate group) and another crosslinking reactive group in one molecule may be used is relatively long. As a result, a flexible crosslinked structure having a length longer than a predetermined length is formed. For example, a compound in which the number of atoms constituting a linking chain connecting one crosslinking reactive group and another crosslinking reactive group in one molecule of the crosslinking agent is 10 or more (for example, 12 or more or 14 or more) is used as a crosslinking agent. It can be used as The upper limit of the number of atoms constituting the connecting chain is not particularly limited as it can be prepared by polymerization etc. depending on the purpose, and is, for example, 2000 or less, may be 1000 or less, may be 500 or less, may be 100 or less, It may be 50 or less, 30 or less, or 20 or less. Note that the number of atoms constituting a linking chain connecting the above-mentioned cross-linking-reactive groups refers to the number of atoms constituting a linking chain that connects the above-mentioned cross-linking-reactive groups. The minimum number of atoms required to reach the crosslinking-reactive group (the closest cross-linking-reactive group). The above-mentioned crosslinking agents having a connecting chain can be used alone or in combination of two or more. In some preferred embodiments, an acyclic bifunctional crosslinking agent may be used as the crosslinking agent. Examples of commercially available crosslinking agents include Coronate 2770 (manufactured by Tosoh Corporation), Takenate D178NL (manufactured by Mitsui Chemicals), Duranate A201H (manufactured by Asahi Kasei Corporation), and the like.

When using a crosslinking agent (which may be a polyfunctional monomer), the amount used is not particularly limited, and is, for example, in the range of about 0.001 parts by weight to 5.0 parts by weight based on 100 parts by weight of the above monomer components. can do. From the viewpoint of improving the adhesion to the adherend, in some embodiments, the amount of the crosslinking agent used per 100 parts by weight of the monomer component is preferably 3.0 parts by weight or less, more preferably 2.0 parts by weight or less. , 1.0 part by weight or less, 0.5 part by weight or less, or 0.2 part by weight or less. Further, from the viewpoint of appropriately exhibiting the effect of using the crosslinking agent, in some embodiments, the amount of the crosslinking agent used per 100 parts by weight of the monomer component may be, for example, 0.005 parts by weight or more, and 0.01 parts by weight. parts by weight or more, 0.05 parts by weight or more, 0.08 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, 0.4 parts by weight or more. But that's fine.

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

The adhesive composition may contain a compound that causes keto-enol tautomerism as a crosslinking retarder. Thereby, the effect of extending the pot life of the adhesive composition can be realized. For example, in a pressure-sensitive adhesive composition containing an isocyanate-based crosslinking agent, a compound that causes keto-enol tautomerism can be preferably used. Various β-dicarbonyl compounds can be used as the compound that causes keto-enol tautomerism. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) and acetoacetate esters (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably employed. Compounds that cause keto-enol tautomerism can be used singly or in combination of two or more. The amount of the compound that causes keto-enol tautomerism can be, for example, 0.1 parts by weight or more and 20 parts by weight or less, and 0.5 parts by weight or more and 10 parts by weight or less, based on 100 parts by weight of the monomer component. Alternatively, the amount may be 1 part by weight or more and 5 parts by weight or less.

(tackifier)
The adhesive disclosed herein may contain a tackifier. Examples of tackifiers include rosin-based tackifying resins, terpene-based tackifying resins, phenol-based tackifying resins, hydrocarbon-based tackifying resins, ketone-based tackifying resins, polyamide-based tackifying resins, epoxy-based tackifying resins, and elastomers. Known tackifier resins such as tackifier resins can be used. These can be used alone or in combination of two or more. The amount of the tackifying resin used is not particularly limited, and can be set so that appropriate adhesive performance is exhibited depending on the purpose and use. In some embodiments, from the viewpoint of refractive index and transparency, the amount of tackifier used per 100 parts by weight of the monomer component is appropriately 30 parts by weight or less, preferably 10 parts by weight or less. , more preferably 5 parts by weight or less. The technology disclosed herein can be preferably practiced without using a tackifier.

(High refractive index particles)
The adhesive disclosed herein can contain high refractive index particles as an optional component. Here, high refractive index particles mean particles that can increase the refractive index of the adhesive by being included in the adhesive. Hereinafter, the high refractive index particles may be referred to as "particles P _HRI ". HRI means high refractive index.

The particle P _HRI is made of a material having a refractive index of, for example, 1.60 or more, preferably 1.70 or more (may be 1.80 or more, 1.90 or more, or even 2.00 or more). One or more of the configured particles may be used. The upper limit of the refractive index of the material constituting the particles P _HRI is not particularly limited, and may be, for example, 3.00 or less, 2.80 or less, 2.50 or less, 2.20 or less, It may be 2.00 or less. The refractive index of the material constituting the particle P _HRI was measured using a commercially available spectroscopic ellipsometer at a measurement wavelength of 589 nm and a measurement temperature of 25°C for a single layer film (thickness that allows refractive index measurement) of the material. This is the refractive index measured under the following conditions. As the spectroscopic ellipsometer, for example, the product name "EC-400" (manufactured by JA. Woolam) or its equivalent product is used.

The type of particle P _HRI is not particularly limited, and one or more materials that can improve the refractive index of the adhesive are selected from metal particles, metal compound particles, organic particles, and organic-inorganic composite particles. can be selected and used. As the particles P _HRI , those that can improve the refractive index of the pressure-sensitive adhesive sheet can be preferably used from among inorganic oxides (for example, metal oxides). Suitable examples of materials constituting the particles P _HRI include titania (titanium oxide, TiO ₂ ), zirconia (zirconium oxide, ZrO ₂ ), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, niobium oxide ( Examples include inorganic oxides (specifically metal oxides) such as Nb ₂ O ₅ etc.). Particles made of these inorganic oxides (for example, metal oxides) can be used singly or in combination of two or more. Among these, particles made of titania or zirconia are preferable, and particles made of zirconia are particularly preferable. Further, as metal particles, for example, iron-based, zinc-based, tungsten-based, or platinum-based materials can have a high refractive index. As organic particles, particles made of resin such as styrene resin, phenol resin, polyester resin, and polycarbonate resin have a relatively high refractive index. Examples of the organic-inorganic composite particles include composites of the above-mentioned inorganic materials and organic materials, and inorganic particles coated with organic materials such as resins. As the particles P _HRI , from the viewpoint of compatibility with the adhesive component, the above-mentioned organic or inorganic particles surface-treated with a surface treatment agent may be used.

The average particle diameter of the particles P _HRI is not particularly limited, and particles of an appropriate size that can realize a desired refractive index improvement by being included in the adhesive may be used. The average particle diameter of the particles P _HRI can be, for example, about 1 nm or more, and suitably about 5 nm or more. From the viewpoint of improving the refractive index and handling properties, the average particle diameter of the particles P _HRI is preferably about 10 nm or more, may be about 20 nm or more, or may be about 30 nm or more. In addition, from the viewpoint of maintaining adhesive properties, the upper limit of the average particle diameter is, for example, approximately 300 nm or less, and from the viewpoint of improving the refractive index, it is preferably approximately 100 nm or less, more preferably approximately 70 nm or less, and even more preferably It is approximately 50 nm or less, and may be approximately 35 nm or less (for example, approximately 25 nm or less).

In addition, the average particle diameter of the particle P _HRI mentioned above refers to the volume average particle diameter, and specifically, the particle size distribution measured for the particle P _HRI dispersion using a particle size distribution measuring device based on a laser scattering/diffraction method. It refers to the particle diameter at an integrated value of 50% (50% volume average particle diameter; hereinafter sometimes abbreviated as _D50 ). As the measuring device, for example, the product name "Microtrac MT3000II" manufactured by Microtrac Bell Co., Ltd. or its equivalent can be used.

The content of particle P _HRI in the adhesive is not particularly limited. The content of the particles P _HRI may vary depending on the desired refractive index. For example, the content of the particles P _HRI can be appropriately set in consideration of required adhesive properties and the like so as to provide a refractive index of a predetermined value or higher. In some embodiments, the content of particle P _HRI in the adhesive can be, for example, about 75% by weight or less, and may be about 50% by weight or less from the viewpoint of adhesive properties and transparency, and may be about 30% by weight. The following may be used. The lower limit of the content of particle P _HRI is not particularly limited, and may be, for example, more than 0% by weight, 1% by weight or more, or 5% by weight or more. In some other embodiments, the content of particulate P _HRI in the adhesive is, for example, less than 10% by weight, may be less than 1% by weight, and may be less than 0.1% by weight. The techniques disclosed herein can be practiced in such a manner that the adhesive composition is substantially free of particle P _HRI .

The content of particulate P _HRI in an adhesive can also be specified in relation to the amount of base polymer included in the adhesive. The content of the particle P _HRI can be, for example, about 100 parts by weight or less with respect to 100 parts by weight of the base polymer, and may be about 60 parts by weight or less from the viewpoint of adhesive properties and transparency, and may be about 40 parts by weight. The following may be used. The lower limit of the content of particle P _HRI is not particularly limited, and may be, for example, more than 0 parts by weight, 1 part by weight or more, or 5 parts by weight or more with respect to 100 parts by weight of the base polymer. In some other embodiments, the content of particle P _HRI is, for example, less than 30 parts by weight, may be less than 10 parts by weight, may be less than 1 part by weight, based on 100 parts by weight of the base polymer, It may be less than 0.1 part by weight.

(Other additives)
In addition, the adhesive disclosed herein or the adhesive composition used to form the adhesive may contain plasticizers, softeners, colorants (dyes, pigments, etc.) to the extent that the effects of the present invention are not significantly impaired. , fillers, antistatic agents, antiaging agents, ultraviolet absorbers, antioxidants, light stabilizers, preservatives, and other known additives that can be used in adhesives may be included as necessary. . Regarding such various additives, conventionally known ones can be used in a conventional manner, and since they do not particularly characterize the present invention, detailed explanations will be omitted.

The adhesive according to some embodiments has a limited content of liquid compounds at 25°C. As a result, the effect of containing a predetermined amount or more of the additive (A) with respect to 100 parts by weight of the base polymer (for example, increasing the refractive index of the adhesive while maintaining the desired cohesiveness and elongation deformability) effect) is likely to be suitably demonstrated. The content of the compound that is liquid at 25°C is, for example, suitably less than 10 parts by weight, preferably less than 5 parts by weight, and less than 3 parts by weight or 1 part by weight, based on 100 parts by weight of the base polymer. More preferably, the amount is less than 1 part. The adhesive may be substantially free of compounds that are liquid at 25°C.

<Characteristics of adhesive>
(Refractive index)
The refractive index of the adhesive disclosed herein is not particularly limited as long as it is 1.50 or more, and can be set depending on the purpose (for example, in consideration of the refractive index of the adherend). According to the technology disclosed herein, a pressure-sensitive adhesive having such a refractive index, a pressure-sensitive adhesive composition capable of forming the pressure-sensitive adhesive, and a pressure-sensitive adhesive sheet containing the pressure-sensitive adhesive can be provided. In some embodiments, the refractive index of the adhesive may be, for example, 1.510 or more, 1.520 or more, 1.530 or more, 1.540 or more, 1. It may be .550 or more or 1.560 or more (for example, more than 1.570). In some preferred embodiments, the refractive index of the adhesive may be 1.575 or more, 1.580 or more, 1.585 or more, 1.590 or more, 1.595 or more. But that's fine. According to the pressure-sensitive adhesive having such a refractive index, light reflection at the interface with the adherend can be suitably suppressed in a usage mode in which the pressure-sensitive adhesive is attached to a material having a high refractive index. The preferable upper limit of the refractive index of the adhesive is not limited to a specific range because it may vary depending on the refractive index of the adherend, etc., and may be, for example, 1.700 or less, 1.670 or less, and 1. It may be 650 or less, 1.620 or less, or 1.600 or less. In some embodiments where flexibility and low-temperature properties are more important, the refractive index of the adhesive may be less than 1.595, less than 1.590, less than 1.580, or 1.570. less than 1.560, less than 1.550 or less than 1.540. The refractive index of the adhesive can be adjusted, for example, by the composition of the adhesive (eg, type of base polymer, composition ratio of monomer components, type and amount of additive (A) used).

Note that in this specification, the refractive index of an adhesive refers to the refractive index of the surface (adhesive surface) of the adhesive. The refractive index of the adhesive can be measured using a prism coupler under conditions of a measurement temperature of 25° C. and a measurement wavelength of 594 nm. As the prism coupler, a commercially available measuring device can be used, such as model "2010M" manufactured by Metricon or its equivalent. As the measurement sample, an adhesive layer made of the adhesive to be evaluated can be used. Specifically, the refractive index of the adhesive can be measured by the method described in Examples below.

(Storage modulus G')
According to the technology disclosed herein, it is possible to achieve a low elastic modulus of the adhesive while enjoying the effect of increasing the refractive index by the additive (A). Although not limited to a specific range, the storage modulus G' (25°C) of the adhesive at 25°C may be, for example, 1.0 x 10 ⁶ Pa or less, and 5.0 x 10 ⁵ Pa. It may be the following. The adhesive having the storage modulus G' (25° C.) has appropriate flexibility in the temperature range from around room temperature to higher, and can adhere well to an adherend, for example. The lower limit of the storage elastic modulus G' (25° C.) is not particularly limited, and may be, for example, 1.0×10 ³ Pa or more, or 5.0×10 ³ Pa or more. When the storage modulus G' (25° C.) is at least a predetermined value, the adhesive tends to have appropriate cohesive strength, for example, in a high temperature range from around room temperature. In some preferred embodiments, the storage modulus G' (25° C.) of the adhesive is advantageously less than 2.0×10 ⁵ Pa, preferably less than 1.5×10 ⁵ Pa. , more preferably less than 1.2×10 ⁵ Pa, may be less than 1.0×10 ⁵ Pa, may be less than 9.0×10 ⁴ Pa, and may be less than 8.0×10 ⁴ It may be less than Pa, it may be less than 7.0×10 ⁴ Pa, it may be less than 6.5×10 ⁴ Pa, it may be less than 6.0×10 ⁴ Pa. Further, the storage elastic modulus G' (25° C.) is preferably 6.0×10 ³ Pa or more, may be 8.0×10 ³ Pa or more, and may be 1.0×10 ⁴ Pa or more. 1.2×10 ⁴ Pa or more, 1.5×10 ⁴ Pa or more, 2.0×10 ⁴ Pa or more, 2.5×10 ⁴ Pa or more, 3 The pressure may be .5×10 ⁴ Pa or higher, or 4.0×10 ⁴ Pa or higher. An adhesive having a storage modulus G' (25° C.) in the above range can have both a high refractive index and flexibility, and can have flexibility that can withstand repeated bending operations.

The storage modulus G' (60°C) of the adhesive disclosed herein is not particularly limited, and is suitably less than 1.0×10 ⁶ Pa, preferably less than 5.0× less than 10 ⁵ Pa, more preferably less than 2.0 x 10 ⁵ Pa, may be less than 1.5 x 10 ⁵ Pa, may be less than 1.0 x 10 ⁵ Pa, 0.8 It may be less than ×10 ⁴ Pa. The adhesive whose storage modulus G' (60° C.) is limited as described above has good flexibility in a high temperature range. The lower limit of the storage elastic modulus G' (60° C.) is not particularly limited, and is, for example, 5.0×10 ² Pa or more, suitably 1.0×10 ³ Pa or more, preferably 2.0×10 3 Pa or more. It is 0×10 ³ Pa or more, more preferably 3.0×10 ³ Pa or more, and may be 5.0×10 ³ Pa or more. An adhesive having the above storage modulus G' (60° C.) is preferable because it has a suitable cohesive force even in a high temperature range and tends to have excellent heat resistance.

The storage modulus G' at -20°C (-20°C) of the adhesive disclosed herein is not particularly limited, and may be, for example, less than 1.0 x 10 ⁹ Pa, and may be less than 2.0 x 10 ⁸ Pa. It is suitable that the pressure is less than 1.5×10 ⁸ Pa, may be less than 1.0×10 ⁸ Pa, may be less than 5.0×10 ^{7 Pa, and may be less than 1.5×10 8} Pa. It may be 0x10 ⁷ Pa or less, 5.0x10 ⁶ Pa or less, 4.0x10 ⁶ Pa or less, or 3.0x10 ⁶ Pa or less. An adhesive whose storage modulus G' (-20° C.) is limited as described above can have particularly excellent flexibility. For example, it may have good flexibility in a lower temperature range, and may have flexibility that can withstand repeated bending operations in a wide temperature range including a low temperature range. The lower limit of the storage modulus G' (-20°C) is not particularly limited, and is suitably 5.0 x 10 ³ Pa or more, preferably 1.0 x 10 4 Pa or more, more preferably 1.0 x 10 ⁴ Pa or more. It is 5.0×10 ⁴ Pa or more, may be 1.0×10 ⁵ Pa or more, may be 5.0×10 ⁵ Pa or more, or may be 1.0×10 ⁶ Pa or more. An adhesive having the above storage modulus G' (-20° C.) can have flexibility and appropriate cohesive strength. Furthermore, the pressure-sensitive adhesive having the storage elastic modulus G' (-20° C.) tends to have both a high refractive index and flexibility even in a low temperature range.

(Glass-transition temperature)
The glass transition temperature (Tg) of the adhesive is not particularly limited, and can be set in consideration of flexibility in a low temperature range and cohesive strength (heat resistance, etc.) in a high temperature range. In some embodiments, the Tg of the adhesive may be, for example, 30°C or less, 20°C or less, 10°C or less, or 5°C or less. In some preferred embodiments, from the viewpoint of flexibility, the Tg of the adhesive is suitably 0°C or lower, more preferably -5°C or lower, even more preferably -10°C or lower, and -15°C or lower. ℃ or lower (for example, -20℃ or lower). The lower the Tg of the adhesive, the better the adhesive properties such as adhesion to adherends tend to be. Furthermore, by setting the Tg of the adhesive low, it is possible to suppress changes in the elastic modulus in a temperature range higher than Tg. The lower limit of the Tg of the adhesive is, for example, -50°C or higher, suitably -40°C or higher, and may be -30°C or higher. According to the pressure-sensitive adhesive having the above-mentioned Tg, there is a tendency that an appropriate cohesive force is easily obtained. In addition, there is a tendency to easily form a pressure-sensitive adhesive that has both a high refractive index and a low elastic modulus.

The storage modulus G' of the adhesive and the glass transition temperature Tg of the adhesive at each of the above temperatures can be measured by the method described in the Examples below, and each storage modulus ratio can be calculated from the results. can. Each storage elastic modulus G', each storage elastic modulus ratio, and glass transition temperature Tg of the adhesive are determined by, for example, the selection of the composition of the monomer components constituting the base polymer, the selection of the type and amount of additive (A), and crosslinking. It can be adjusted by selecting whether or not the agent is used, its type, and the amount used.

(Elongation at break _EB )
The elongation at break E _B of the adhesive is not particularly limited, and may be, for example, in the range of 200% or more and 10000% or less. From the viewpoint of flexibility and elongation deformability, in some embodiments, the elongation at break E _B may be, for example, 300% or more, advantageously 400% or more, and preferably 500% or more. It is preferably 750% or more, more preferably 1000% or more. In some embodiments where elongation deformability is more important, the elongation at break E _B of the adhesive is preferably 1250% or more, more preferably 1500% or more, and may be 1750% or more. , 2000% or more, 2250% or more, 2500% or more, 3000% or more, 4000% or more, or 5000% or more. Further, from the viewpoint of compatibility with other properties, processability and handling of the adhesive or the adhesive sheet containing the adhesive, in some embodiments, the elongation at break of the adhesive E _B is 9000. % or less, advantageously 8000% or less, preferably 7000% or less, more preferably 6000% or less, may be 5500% or less, 5000% or less % or less, 4500% or less, 4000% or less, or 3500% or less. The elongation at break E _B of the adhesive can be measured by the method described in Examples below. The elongation at break E _B of the adhesive can be adjusted by, for example, selecting the composition of the monomer components constituting the base polymer, selecting the type and amount of additives used, and selecting whether or not to use a crosslinking agent, and selecting the type and amount used. It is possible.

(Ratio (G'(25℃)/E _B ))
In some embodiments of the adhesive disclosed herein, the ratio of the storage modulus G'(25°C) to the elongation at break E _B , that is, the ratio (G'(25°C)/E _B ) is 450 Suitably, it is below 300, advantageously below 200, more preferably below 100, even more preferably below 50. The above ratio (G'(25℃)/E _B ) is the numerical value when the storage elastic modulus G'(25℃) of the adhesive at 25℃ is expressed in the unit of "Pa" and the rupture of the adhesive. It is a dimensionless number calculated from the numerical part when time elongation E _{and B} are expressed in units of "%". Higher (harder) storage modulus G'(25°C) and smaller elongation at break E _B both make the value of the above ratio (G'(25°C)/ _EB This is a factor that makes it larger. For example, a brittle material or a weak (low cohesive force) material tends to tear apart due to elongation deformation, and the value of elongation at break E _B tends to be small. On the other hand, lowering the storage modulus G'(25°C) and increasing the elongation at break E _B both result in lower storage modulus G'(25°C)/ _EB , gives an influence in the direction of making the value of the ratio smaller. An adhesive in which the above ratio (G'(25°C)/E _B ) is limited to a predetermined value or less exhibits good flexibility due to appropriate flexibility and appropriate elongation deformability (resistance to tearing). Therefore, an adhesive having a refractive index higher than a predetermined value and the above ratio (G'(25°C)/E _B ) within the above range is preferable from the viewpoint of achieving both a high refractive index and flexibility. The above-mentioned flexible pressure-sensitive adhesive may be suitable for applications where it is expected to be repeatedly bent, for example. In some embodiments, the ratio (G'(25°C)/E _B ) is preferably 40 or less (for example, 35 or less), and more preferably 30 or less, from the viewpoint of achieving better suppleness. , 25 or less, 20 or less, 15 or less, or 10 or less. The lower limit of the above ratio (G'(25°C)/E _B ) is not particularly limited. In some embodiments, the above ratio (G'(25°C)/E _B ) is, for example, 0.5 or more, considering the balance with other properties (e.g., optical properties, high temperature properties, low temperature properties, etc.). The number may be 1 or more, 2 or more, 3 or more, 5 or more, 10 or more, 15 or more, or 20 or more.

<Adhesive sheet>
This specification provides a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer. The adhesive constituting the adhesive layer may be an adhesive formed from any of the adhesive compositions disclosed herein (for example, a cured product of the adhesive composition).
The adhesive sheet may be a base-attached adhesive sheet having the adhesive layer on one or both sides of a non-peelable base material (supporting base material), and the adhesive layer is held by a release liner. A pressure-sensitive adhesive sheet without a base material (that is, a pressure-sensitive adhesive sheet without a non-peelable base material; typically a pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer) may be used. The concept of adhesive sheet here may include what is called an adhesive tape, an adhesive label, an adhesive film, and the like. The pressure-sensitive adhesive sheet disclosed herein may be in the form of a roll or a sheet. Alternatively, the adhesive sheet may be further processed into various shapes.

An example of the configuration of a double-sided adhesive type base material-less adhesive sheet (substrate-less double-sided adhesive sheet) is shown in FIGS. 1 and 2. The adhesive sheet 1 shown in FIG. 1 has a structure in which both

surfaces

21A and 21B of the adhesive layer 21 without a base material are protected by

release liners

31 and 32, respectively, with at least the adhesive layer side serving as a release surface. The adhesive sheet 2 shown in FIG. 2 has a structure in which one surface (adhesive surface) 21A of the adhesive layer 21 without a base material is protected by a release liner 31 whose both surfaces are release surfaces. When wound, the other surface (adhesive surface) 21B of the adhesive layer 21 comes into contact with the back surface of the release liner 31, so that the other surface 21B can also be protected by the release liner 31. The technique disclosed herein is preferably implemented in the form of a base material-less adhesive sheet consisting of an adhesive layer from the viewpoint of flexibility that follows an adherend that is repeatedly folded. The above-mentioned base material-less pressure-sensitive adhesive sheet is preferable also from the viewpoint of reducing the thickness of the pressure-sensitive adhesive sheet and increasing the transparency of the pressure-sensitive adhesive sheet.

The adhesive sheet disclosed herein may have a cross-sectional structure schematically shown in FIG. 3, for example. The adhesive sheet 3 shown in FIG. 3 includes a support base material 10 and a first adhesive layer 21 and a second adhesive layer 22 supported on the first surface 10A and second surface 10B of the support base material 10, respectively. Be prepared. The first surface 10A and the second surface 10B are both non-peeling surfaces (non-peeling surfaces). The adhesive sheet 3 is used by attaching the surface (first adhesive surface) 21A of the first adhesive layer 21 and the surface (second adhesive surface) 22A of the second adhesive layer 22 to an adherend. That is, the adhesive sheet 3 is configured as a double-sided adhesive sheet (adhesive sheet with adhesive properties on both sides). In the adhesive sheet 3 before use, the first adhesive surface 21A and the second adhesive surface 22A are each protected by

release liners

31 and 32, in which at least the adhesive surface side is a surface having releasability (release surface). It has a structure. Alternatively, the release liner 32 may be omitted, and a release liner 31 having release surfaces on both sides may be used, and the adhesive sheet 3 may be wound to bring the second adhesive surface 22A into contact with the back surface of the release liner 31. Accordingly, the second adhesive surface 22A may also be protected by the release liner 31.

The technology disclosed herein is preferably implemented in the form of the above-mentioned double-sided pressure-sensitive adhesive sheet without a base material or with a base material for fixing and joining members (for example, optical members). Alternatively, although not particularly shown, the adhesive sheet disclosed herein may be in the form of a single-sided adhesive sheet with a base material, which has an adhesive layer on only one side of a non-peelable base material (supporting base material). An example of the form of a single-sided adhesive sheet is a form in which the structure shown in FIG. 3 does not include either the first adhesive layer 21 or the second adhesive layer 22.

(Adhesive layer)
The adhesive layer of the adhesive sheet disclosed herein can be formed by applying (for example, coating) an adhesive composition to a suitable surface and then curing the composition. The adhesive composition can be applied using a conventional coater such as a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, and a spray coater.

The thickness of the adhesive layer is not particularly limited, and can be, for example, 3 μm or more. In some embodiments, the thickness of the adhesive layer is suitably 5 μm or more, for example, 10 μm or more, 15 μm or more, 20 μm or more, 30 μm or more, 50 μm or more. It may be 70 μm or more or 85 μm or more. Adhesive strength tends to increase as the thickness of the adhesive layer increases. Further, in some embodiments, the thickness of the adhesive layer may be, for example, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, or 120 μm or less. In some preferred embodiments, the thickness of the adhesive layer is 100 μm or less, more preferably 75 μm or less, even more preferably 70 μm or less, may be 50 μm or less, or may be 30 μm or less. It may be advantageous that the thickness of the adhesive layer is not too large from the viewpoint of making the adhesive sheet thinner. Moreover, a thin adhesive layer tends to have excellent followability to an adherend. The technology disclosed herein can be preferably carried out, for example, in an embodiment in which the thickness of the adhesive layer is in the range of 3 μm to 200 μm (more preferably 5 μm to 100 μm, still more preferably 5 μm to 75 μm). In addition, in the case of a pressure-sensitive adhesive sheet having a first pressure-sensitive adhesive layer and a second pressure-sensitive adhesive layer on the first and second surfaces of the base material, the thickness of the pressure-sensitive adhesive layer described above is at least the thickness of the first pressure-sensitive adhesive layer. can be applied to The thickness of the second adhesive layer may also be selected from a similar range. Further, in the case of a base material-less adhesive sheet, the thickness of the adhesive sheet matches the thickness of the adhesive layer.

(Haze value)
In some embodiments, the haze value (sometimes simply referred to as "haze") of the adhesive layer constituting the adhesive sheet may be, for example, 5.0% or less, and may be 3.0% or less. Preferably, it is 2.0% or less, more preferably 1.0% or less, 0.9% or less, 0.8% or less, 0.5% or less, It may be 0.3% or less. A pressure-sensitive adhesive sheet having a highly transparent pressure-sensitive adhesive layer is used for applications that require high light transmittance (for example, optical applications), with or without a base material, and for attaching an adherend through the pressure-sensitive adhesive sheet. It can be preferably applied to applications that require good visual recognition performance. The lower limit of the haze value of the adhesive layer is not particularly limited, and from the viewpoint of improving transparency, the smaller the haze value, the more preferable. On the other hand, in some embodiments, the haze value may be, for example, 0.05% or more, or 0.10% or more, taking into consideration the refractive index and adhesive properties. These haze values regarding the adhesive layer correspond to the haze value of the adhesive sheet when the technology disclosed herein is implemented in the form of a substrate-less adhesive sheet (typically, an adhesive sheet consisting of an adhesive layer). may also be preferably applied.

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

In some embodiments, the haze value of the adhesive sheet may be, for example, 10.0% or less, preferably 5.0% or less, more preferably 3.0% or less, and 2.0% or less. % or less, and may be 1.7% or less, 1.5% or less, 1.2% or less, 1.0% or less, or 0.8% or less. Adhesive sheets with such high transparency can be preferably applied to applications that require high light transmittance (for example, optical applications) and applications that require good visibility of adherends through the adhesive sheet. The lower limit of the haze value of the pressure-sensitive adhesive sheet is not particularly limited, and from the viewpoint of improving transparency, the smaller the haze value is, the more preferable it is. On the other hand, in some embodiments, the haze value may be, for example, 0.05% or more, 0.1% or more, or 0.2% or more, taking into account the refractive index and adhesive properties. Often, it may be 0.3% or more. The haze value of the pressure-sensitive adhesive sheet can be measured in the same manner as the measurement of the haze value of the pressure-sensitive adhesive layer. The haze value of the pressure-sensitive adhesive sheet can be obtained by selecting the composition of the pressure-sensitive adhesive layer described above, and the type and thickness of the base material in the case of a structure including a base material.

(Total light transmittance)
In some embodiments, the total light transmittance of the adhesive layer is preferably 85.0% or more (for example, 88.0% or more, 90.0% or more, or more than 90.0%). A pressure-sensitive adhesive sheet having a highly transparent pressure-sensitive adhesive layer is used for applications that require high light transmittance (for example, optical applications), with or without a base material, and for attaching an adherend through the pressure-sensitive adhesive sheet. It can be preferably applied to applications that require good visual recognition performance. In practical terms, the upper limit of the total light transmittance may be, for example, about 98% or less, about 96% or less, or about 95% or less. In some embodiments, the total light transmittance of the adhesive layer may be approximately 94% or less, approximately 93% or less, or approximately 92% or less, taking into account the refractive index and adhesive properties. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the product name "HAZEMETER HM-150" manufactured by Murakami Color Research Institute or its equivalent product is used. The total light transmittance can be measured according to the method described in Examples below. The total light transmittance of the adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the adhesive layer.

In some embodiments, the total light transmittance of the adhesive sheet is preferably 85.0% or more (for example, 88.0% or more, 90.0% or more, or more than 90.0%). Adhesive sheets with such high transparency can be preferably applied to applications that require high light transmittance (for example, optical applications) and applications that require good visibility of adherends through the adhesive sheet. In practical terms, the upper limit of the total light transmittance may be, for example, about 98% or less, about 96% or less, or about 95% or less. In some embodiments, the total light transmittance of the adhesive sheet may be about 94% or less, about 93% or less, or about 92% or less, taking into account the refractive index and adhesive properties. The total light transmittance of the pressure-sensitive adhesive sheet can be measured in the same manner as the measurement of the total light transmittance of the pressure-sensitive adhesive layer. The total light transmittance of the pressure-sensitive adhesive sheet can be obtained by selecting the composition of the pressure-sensitive adhesive layer described above, and the type and thickness of the base material in the case of a structure including a base material.

(Peel strength)
The peel strength of the adhesive sheet to the glass plate is not particularly limited. In some embodiments, the adhesive sheet has a peel strength against a glass plate (peel strength against a glass plate) of, for example, 0.1 N/25 mm or more, and may be 0.5 N/25 mm or more. In some preferred embodiments, the peel strength against the glass plate is 1.0 N/25 mm or more, more preferably 1.5 N/25 mm or more, even more preferably 2.0 N/25 mm or more, and 3.0 N/25 mm or more. It may be 25 mm or more, 5.0 N/25 mm or more, 6.0 N/25 mm or more, 7.0 N/25 mm or more, 8.0 N/25 mm or more, 9.0 N/25 mm or more, or 10 N/25 mm or more. It may be 25 mm or more. A pressure-sensitive adhesive sheet having a peel strength against a glass plate of a predetermined value or more is suitable for joining or fixing, for example, glass members. The upper limit of the peel strength is not particularly limited, and may be, for example, 30 N/25 mm or less, 25 N/25 mm or less, or 20 N/25 mm or less.

Here, the above peel strength is measured after being pressure-bonded to an alkali glass plate as an adherend and left for 30 minutes in an environment of 23°C and 50% RH, and then at a peel angle of 180 degrees and a tensile speed of 300 mm/min. It can be understood by measuring. In the measurement, if necessary, the adhesive sheet to be measured can be reinforced by attaching an appropriate backing material (for example, a polyethylene terephthalate (PET) film with a thickness of about 25 μm to about 50 μm). More specifically, the peel strength can be measured according to the method described in the Examples below.

(thickness of adhesive sheet)
The thickness of the adhesive sheet disclosed herein (substrate-less adhesive sheet or adhesive sheet with base material) may be, for example, 1000 μm or less, 350 μm or less, 200 μm or less, 120 μm or less, or 75 μm or less. The thickness may be 50 μm or less. In addition, from the viewpoint of handleability, the thickness of the adhesive sheet may be, for example, 5 μm or more, 10 μm or more, 25 μm or more, 30 μm or more, 40 μm or more, 80 μm or more, It may be 130 μm or more.
Note that the thickness of the adhesive sheet refers to the thickness of the portion to be attached to the adherend. For example, in the adhesive sheet 3 having the configuration shown in FIG. 3, the thickness refers to the thickness from the first adhesive surface 21A to the second adhesive surface 22A, and does not include the thickness of the

release liners

31 and 32.

<Support base material>
The pressure-sensitive adhesive sheet according to some embodiments may be in the form of a pressure-sensitive adhesive sheet with a base material, which includes a pressure-sensitive adhesive layer on one or both sides of a supporting base material. The material of the support base material is not particularly limited, and can be appropriately selected depending on the purpose and manner of use of the pressure-sensitive adhesive sheet. Non-limiting examples of substrates that can be used include polyolefin films based on polyolefins such as polypropylene (PP) and ethylene-propylene copolymers, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene terephthalate (PET). Plastic films such as polyester films whose main component is polyester such as phthalate (PEN), and polyvinyl chloride films whose main component is polyvinyl chloride; consisting of foams such as polyurethane foam, polyethylene (PE) foam, and polychloroprene foam. Foam sheets; Woven and non-woven fabrics made of various fibrous materials (can be natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc.) alone or in combination; Examples include papers such as Japanese paper, high-quality paper, kraft paper, and crepe paper; metal foils such as aluminum foil and copper foil; and the like. A base material having a composite structure of these materials may also be used. Examples of such composite base materials include base materials having a structure in which metal foil and the above-mentioned plastic film are laminated, and plastic base materials reinforced with inorganic fibers such as glass cloth.

In some embodiments, various film base materials can be preferably used. The film base material may be a porous base material such as a foam film or a non-woven fabric sheet, or a non-porous base material, and may have a porous layer and a non-porous layer. The base material may have a laminated structure. In some embodiments, the film base material may preferably include a base film that includes a (self-supporting or independent) resin film that can maintain its shape independently. Here, the term "resin film" refers to a resin film that has a non-porous structure and typically is substantially void-free. Therefore, the resin film is a concept that is distinguished from foam films and nonwoven fabrics. As the resin film, one that can maintain its shape independently (self-supporting or independent) can be preferably used. The resin film may have a single layer structure or a multilayer structure of two or more layers (for example, a three layer structure).

Examples of the resin material constituting the resin film include polyester; polyolefin; polycycloolefin derived from a monomer having an aliphatic ring structure such as norbornene structure; polyamide (PA) such as nylon 6, nylon 66, and partially aromatic polyamide. Polyimide (PI) such as transparent polyimide (CPI); Polyamideimide (PAI); Polyetheretherketone (PEEK); Polyethersulfone (PES); Polyphenylene sulfide (PPS); Polycarbonate (PC); Polyurethane (PU); Ethylene-vinyl acetate copolymer (EVA); Fluororesin such as polytetrafluoroethylene (PTFE); Acrylic resin; Cellulose polymer such as triacetyl cellulose (TAC); Polyarylate; Polystyrene; Polyvinyl chloride; Polyvinylidene chloride Resins such as; can be used.

The resin film may be formed using a resin material containing only one type of such resin, or may be formed using a resin material that is a blend of two or more types of resin. Good too. The resin film may be unstretched or may be stretched (for example, uniaxially or biaxially stretched). For example, PET film, PBT film, PEN film, unoriented polypropylene (CPP) film, biaxially oriented polypropylene (OPP) film, low density polyethylene (LDPE) film, linear low density polyethylene (LLDPE) film, PP/PE Blend films, cycloolefin polymer (COP) films, CPI films, TAC films, etc. can be preferably used. Examples of resin films preferable from the viewpoint of strength and dimensional stability include PET film, PEN film, PPS film, and PEEK film. PET film and PPS film are particularly preferred from the viewpoint of availability, and PET film is particularly preferred.

The resin film may contain known substances such as light stabilizers, antioxidants, antistatic agents, colorants (dyes, pigments, etc.), fillers, slip agents, anti-blocking agents, etc., to the extent that the effects of the present invention are not significantly impaired. Additives may be added as necessary. The blending amount of the additive is not particularly limited, and can be appropriately set depending on the use of the pressure-sensitive adhesive sheet.

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

The base material may be substantially composed of such a base film. Alternatively, the base material may include an auxiliary layer in addition to the base film. Examples of the above-mentioned auxiliary layers include optical property adjustment layers (e.g., colored layers, antireflection layers), printing layers and laminate layers for imparting a desired appearance to the substrate, antistatic layers, undercoat layers, and release layers. Examples include surface treatment layers such as.

In some embodiments, a light-transmitting base material (hereinafter also referred to as a light-transmitting base material) can be preferably employed as the supporting base material. Thereby, it becomes possible to construct a pressure-sensitive adhesive sheet with a base material having light transmittance. The total light transmittance of the light-transmissive base material may be, for example, more than 50%, and may be 70% or more. In some preferred embodiments, the total light transmittance of the support substrate is 80% or more, more preferably 90% or more, and may be 95% or more (eg, 95-100%). The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the product name "HAZEMETER HM-150" manufactured by Murakami Color Research Institute or its equivalent product is used. A preferred example of the above-mentioned light-transmitting base material is a light-transmitting resin film. The light-transmitting substrate may be an optical film.

The thickness of the base material is not particularly limited, and can be selected depending on the purpose and manner of use of the pressure-sensitive adhesive sheet. The thickness of the base material may be, for example, 500 μm or less, preferably 300 μm or less from the viewpoint of handling and processability of the adhesive sheet, 150 μm or less, 100 μm or less, 50 μm or less, and 25 μm or less. It may be less than 10 μm, and may be less than 10 μm. As the thickness of the base material decreases, the ability to follow the surface shape of the adherend tends to improve. Further, from the viewpoint of handleability, processability, etc., the thickness of the base material may be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

The side of the base material on which the adhesive layer will be laminated may be treated with corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or application of an undercoat (primer) to form an undercoat layer, as necessary. Conventionally known surface treatments such as forming may be applied. Such surface treatment may be a treatment for improving the anchoring ability of the adhesive layer to the base material. The composition of the primer used to form the undercoat layer is not particularly limited, and can be appropriately selected from known primers. The thickness of the undercoat layer is not particularly limited, but it is usually about 0.01 μm to 1 μm, preferably about 0.1 μm to 1 μm. Other treatments that may be applied to the base material as needed include antistatic layer formation treatment, colored layer formation treatment, printing treatment, and the like. These treatments can be applied alone or in combination.

<Adhesive sheet with release liner>
The adhesive sheet disclosed herein can take the form of an adhesive product in which the surface (adhesive surface) of an adhesive layer is brought into contact with the release surface of a release liner. Therefore, this specification provides a pressure-sensitive adhesive sheet with a release liner (adhesive product) that includes any pressure-sensitive adhesive sheet disclosed herein and a release liner having a release surface that comes into contact with the pressure-sensitive adhesive surface of the pressure-sensitive adhesive sheet. Ru.

The release liner is not particularly limited, and includes, for example, a release liner having a release layer on the surface of a liner base material such as a resin film or paper (paper laminated with a resin such as polyethylene), or a fluorine-based polymer. A release liner made of a resin film made of a low adhesive material such as (polytetrafluoroethylene, etc.) or polyolefin resin (polyethylene, polypropylene, etc.) can be used. Since they have excellent surface smoothness, a release liner having a release layer on the surface of a resin film as a liner base material or a release liner made of a resin film made of a low adhesive material can be preferably employed. The resin film is not particularly limited as long as it can protect the adhesive layer, and examples thereof include polyethylene (PE) film, polypropylene (PP) film, polybutene film, polybutadiene film, polymethylpentene film, and polyvinyl chloride film. , vinyl chloride copolymer film, polyester film (PET film, PBT film, etc.), polyurethane film, ethylene-vinyl acetate copolymer film, and the like. For forming the above-mentioned release layer, for example, silicone-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, silica powder, etc. , a known release agent can be used.

<Application>
The use of the adhesive sheet disclosed herein is not limited, and it can be used for various purposes. The adhesive sheet disclosed herein is equipped with an adhesive that has both a high refractive index and a low elastic modulus, so it can be used in various applications that require a high refractive index and flexibility by taking advantage of its characteristics. obtain. For example, in electronic devices such as portable electronic devices, display devices (image display devices) such as liquid crystal display devices, organic EL (electroluminescent) display devices, PDP (plasma display panels), electronic paper, input devices such as touch panels, etc. It is suitable as an adhesive sheet for equipment (optical equipment), especially foldable displays and rollable displays. For example, in foldable displays and rollable displays, it is preferably used as a means for joining, fixing, and protecting members having a high refractive index. The adhesive sheet disclosed herein has a high refractive index and is flexible enough to withstand repeated bending operations, so it can be repeatedly folded while attached to a foldable display or rollable display. It is possible to follow the adherends (foldable displays, etc.) that are Examples of objects to be pasted in such usage patterns include glass members such as window glasses and cover glasses used in foldable displays and rollable displays. Further, the adhesive sheet disclosed herein easily follows and adheres to curved surfaces such as three-dimensional shapes of portable electronic devices, so it is also suitable for use in electronic devices having such curved shapes. Further, in some preferred embodiments, the adhesive may have excellent heat resistance in addition to having a high refractive index and a low elastic modulus. The above-mentioned portable electronic device may be used in a high-temperature environment, and its internal space may become heated due to heat generated by electronic components, so the advantage of using the above-mentioned heat-resistant adhesive sheet is great.

Examples of the above-mentioned portable electronic devices include mobile phones, smartphones, tablet computers, notebook computers, and various wearable devices (e.g., wrist-wear devices that are worn on the wrist like watches, and devices that are attached to the body using clips, straps, etc.). Eyewear types include modular types that are attached to the body, eyewear types (monocular and binocular types, including head-mounted types), clothing types that are attached to shirts, socks, hats, etc. in the form of accessories, and earphones. digital cameras, digital video cameras, audio equipment (portable music players, IC recorders, etc.), calculators (calculators, etc.), portable game devices, electronic dictionaries, electronic notebooks, electronic books, in-vehicle information. This includes devices such as portable radios, portable televisions, portable printers, portable scanners, and portable modems. Note that in this specification, "portable" does not mean that it is simply portable; it also means that it has a level of portability that allows an individual (standard adult) to carry it relatively easily. shall mean.

The material to which the adhesive sheet disclosed herein is attached (adherend material) is not particularly limited, but includes, for example, copper, silver, gold, iron, tin, palladium, aluminum, nickel, titanium, Metal materials such as chromium, zinc, etc., or alloys containing two or more of these, such as polyimide resin, acrylic resin, polyether nitrile resin, polyether sulfone resin, polyester resin (PET resin, polyethylene naphthalate resins, etc.), polyvinyl chloride resins, polyphenylene sulfide resins, polyetheretherketone resins, polyamide resins (so-called aramid resins, etc.), polyarylate resins, polycarbonate resins, diacetyl cellulose and triacetyl cellulose. Examples include various resin materials (typically plastic materials) such as cellulose polymers, vinyl butyral polymers, and liquid crystal polymers, and inorganic materials such as alumina, zirconia, alkali glass, alkali-free glass, quartz glass, and carbon. . The adhesive sheet disclosed herein can be used by being attached to a member (for example, an optical member) made of the above-mentioned material.

The member or material to which the adhesive sheet disclosed herein is attached (at least one adherend in a double-sided adhesive sheet) is made of a material with a higher refractive index than a general acrylic adhesive. could be. The refractive index of the adherend material is, for example, 1.50 or more, and some adherend materials have a refractive index of 1.55 or more or 1.58 or more, and even have a refractive index of 1.62 or more (for example, 1. .66) exists. Such high refractive index adherend materials are typically resin materials. More specifically, it may be a polyester resin such as PET, a polyimide resin, an aramid resin, a polyphenylene sulfide resin, a polycarbonate resin, or the like. For such materials, the effect of using the adhesive sheet disclosed herein (suppression of reflection of light rays due to the difference in refractive index) can be preferably exhibited. The upper limit of the refractive index of the adherend material is, for example, 1.80 or less, and may be 1.70 or less. The pressure-sensitive adhesive sheet disclosed herein can be preferably used in an embodiment in which it is attached to an adherend (for example, a member) having a high refractive index as described above. A suitable example of such an adherend is a resin film having a refractive index of 1.50 to 1.80 (preferably 1.55 to 1.75, for example 1.60 to 1.70). The refractive index can be measured in the same manner as the refractive index of the adhesive.

The member or material to which the adhesive sheet is attached (at least one adherend in a double-sided adhesive sheet) may have light transmittance. With such an adherend, the advantage of the technique disclosed herein (suppression of light reflection at the interface between the adherend and the adhesive sheet) can easily be obtained. The total light transmittance of the adherend may be, for example, greater than 50%, preferably 70% or more. In some preferred embodiments, the total light transmittance of the adherend is 80% or more, more preferably 90% or more, and may be 95% or more (for example, 95 to 100%). The pressure-sensitive adhesive sheet disclosed herein can be preferably used in an embodiment in which it is attached to an adherend (for example, an optical member) having a total light transmittance of a predetermined value or more. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the product name "HAZEMETER HM-150" manufactured by Murakami Color Research Institute or its equivalent product is used.

In some preferred embodiments, the adherend (for example, member) to which the pressure-sensitive adhesive sheet is attached may have the above-mentioned refractive index and the above-mentioned total light transmittance. Specifically, the refractive index is 1.50 or more (for example, 1.55 or more, 1.58 or more, 1.62 or more, about 1.66, etc.), and the total light transmittance is greater than 50% ( The pressure-sensitive adhesive sheet disclosed herein is preferably used in an embodiment in which it is attached to an adherend, such as a member (for example, 70% or more, preferably 80% or more, more preferably 90% or more, and even 95% or more). obtain. The effects of the technique disclosed herein are particularly preferably exhibited in the embodiment in which the adhesive is attached to such a member.

An example of a preferred use is optical use. More specifically, the adhesive sheet disclosed herein is used, for example, as an optical pressure-sensitive adhesive sheet used for bonding optical members (for bonding optical members) or for manufacturing products (optical products) using the above-mentioned optical members. A pressure-sensitive adhesive sheet can be preferably used. The above-mentioned optical product may have a so-called polarizing plate-less configuration. For example, in an optical product that includes a light source, the optical product may be configured only of layers with a polarization degree of 80% or less on the viewing side from the light source (such as an organic EL panel).

The above-mentioned optical member refers to a member having optical properties (for example, polarization, light refraction, light scattering, light reflection, light transmission, light absorption, light diffraction, optical rotation, visibility, etc.). say. The above-mentioned optical member is not particularly limited as long as it has optical properties, but for example, it may be a member constituting a device (optical device) such as a display device (image display device) or an input device, or a member used in these devices. Members include, for example, polarizing plates, wavelength plates, retardation plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, antireflection films, hard coat (HC) films, shock absorption films, antifouling films, Photochromic films, light control films, transparent conductive films (ITO films), design films, decorative films, surface protection plates, prisms, lenses, color filters, transparent substrates, and members on which these are laminated (collectively referred to as (sometimes referred to as "functional film"). In addition, the above-mentioned "plate" and "film" each include shapes such as plate, film, and sheet. For example, "polarizing film" includes "polarizing plate" and "polarizing sheet", etc. The "light guide plate" includes "light guide film", "light guide sheet", etc. Furthermore, the above-mentioned "polarizing plate" includes a circularly polarizing plate.

Examples of the display device include a liquid crystal display device, an organic EL display device, a micro LED (μLED), a mini LED (miniLED), a PDP, and an electronic paper. Moreover, a touch panel etc. are mentioned as said input device.

The above-mentioned optical member is not particularly limited, but includes, for example, a member (for example, a sheet-like, film-like, or plate-like member) made of glass, acrylic resin, polycarbonate, PET, metal thin film, etc. Note that the term "optical member" in this specification includes members (design films, decorative films, surface protection films, etc.) that play a role of decoration and protection while maintaining the visibility of display devices and input devices.

The technology disclosed herein uses, for example, an optical film such as a film having one or more functions such as light transmission, reflection, diffusion, waveguide, condensing, and diffraction, or a fluorescent film, etc., with other optical members ( It can be preferably used for bonding to other optical films. In particular, when bonding optical films that have at least one of the functions of light waveguide, condensation, and diffraction, it is desirable that the entire bulk of the bonding layer has a high refractive index, and the technology disclosed herein is preferably applied. Can be targeted.

The adhesive disclosed herein can be preferably used for bonding optical films such as light guide films, diffusion films, fluorescent films, toning films, prism sheets, lenticular films, and microlens array films. In these applications, from the viewpoint of the trend toward miniaturization of optical members and higher performance, there is a demand for thinner optical members and improved light extraction efficiency. The adhesive disclosed herein can be preferably used as an adhesive that can meet such demands. More specifically, for example, when bonding a light guide film or a diffusion film, adjusting the refractive index (for example, increasing the refractive index) of the adhesive layer as a bonding layer can contribute to thinning. In bonding fluorescent films, light extraction efficiency (which can also be understood as luminous efficiency) can be improved by appropriately adjusting the refractive index difference between the fluorescent emitter and the adhesive. When bonding color toning films, by appropriately adjusting the refractive index of the adhesive so that the difference in refractive index with the color toning pigment is reduced, scattering components can be reduced, contributing to improved light transmittance. When bonding prism sheets, lenticular films, microlens array films, etc., appropriately adjusting the refractive index of the adhesive can control light diffraction and contribute to improving brightness and/or viewing angle.

The pressure-sensitive adhesive sheet disclosed herein is preferably used in an embodiment in which it is attached to a high refractive index adherend (which may be a high refractive index layer or member, etc.), and reduces interface reflection with the adherend. Can be suppressed. The pressure-sensitive adhesive sheet used in this embodiment preferably has a small refractive index difference with the adherend and high adhesion at the interface with the adherend, as described above. Further, from the viewpoint of improving the homogeneity of the appearance, it is preferable that the thickness of the adhesive layer is highly uniform, for example, it is preferable that the surface smoothness of the adhesive surface is high. When the thickness of the adherend with a high refractive index is relatively small (for example, 5 μm or less, 4 μm or less, or 2 μm or less), it is necessary to It is particularly useful to suppress reflexes. As an example of such a usage mode, in a polarizing plate with a retardation layer that includes a polarizer, a first retardation layer, and a second retardation layer in this order, bonding of the polarizer and the first retardation layer and/or Another example is an embodiment used for bonding the first retardation layer and the second retardation layer.

Furthermore, since the adhesive sheet disclosed herein is suitable for increasing the refractive index, it is preferably attached to a light emitting layer of an optical semiconductor or the like (for example, a high refractive light emitting layer mainly composed of an inorganic material). can be used. By reducing the difference in refractive index between the light emitting layer and the adhesive layer, reflection at the interface between them can be suppressed and light extraction efficiency can be improved. The pressure-sensitive adhesive sheet used in this embodiment preferably includes a pressure-sensitive adhesive layer with a high refractive index. Further, from the viewpoint of improving brightness, it is preferable that the pressure-sensitive adhesive sheet is lightly colored. This can also be advantageous from the viewpoint of suppressing unintentional coloring caused by the pressure-sensitive adhesive sheet.

Note that in this specification, a self-luminous element means a light-emitting element whose luminance can be controlled by the value of a flowing current. The self-luminous element may be composed of a single unit or an aggregate. Specific examples of self-luminous elements include, but are not limited to, light emitting diodes (LEDs) and organic EL. Furthermore, in this specification, a light-emitting device means a device including such a self-luminous element as a component. Examples of the light emitting device include, but are not limited to, a light source module device used for illumination (for example, a planar light emitting module) and a display device in which pixels are formed.

The adhesive disclosed herein can be used in microlenses and other lens members used as constituent members of cameras, light emitting devices, etc. (for example, microlenses constituting microlens array films, lens members such as microlenses for cameras). , a coating layer covering the lens surface, a bonding layer with a member facing the lens surface (for example, a member having a surface shape corresponding to the lens surface), a filling layer filled between the lens surface and the member, It can be preferably used as such. Since the adhesive disclosed herein is suitable for increasing the refractive index, it can be used with high refractive index lenses (for example, lenses made of high refractive index resin or lenses having a surface layer made of high refractive index resin). Even if there is, the difference in refractive index with the lens can be reduced. This is advantageous from the standpoint of making the lens and products equipped with the lens thinner, and can also contribute to suppressing aberrations and improving the Abbe number. The adhesive disclosed herein can also be used as a lens resin by itself, for example in the form of being filled in the recesses or voids of a suitable transparent member.

The mode of bonding optical members together using the adhesive sheet disclosed herein is not particularly limited, but includes, for example, (1) a mode of bonding optical members together via the pressure-sensitive adhesive sheet disclosed herein; ) The optical member may be attached to a member other than the optical member via the adhesive sheet disclosed herein, or (3) the adhesive sheet disclosed herein may include an optical member and the optical member may be attached to a member other than the optical member. The adhesive sheet may be attached to an optical member or a member other than an optical member. In the above embodiment (3), the pressure-sensitive adhesive sheet containing an optical member may be, for example, a pressure-sensitive adhesive sheet whose support is an optical member (for example, an optical film). A pressure-sensitive adhesive sheet that includes an optical member as a support in this manner can also be understood as a pressure-sensitive adhesive optical member (for example, a pressure-sensitive adhesive optical film). In addition, when the adhesive sheet disclosed herein is a type of adhesive sheet having a support and the functional film is used as the support, the adhesive sheet disclosed herein is a type of adhesive sheet having a support, and when the functional film is used as the support, the adhesive sheet disclosed herein is a type of adhesive sheet having a support. It can also be understood as an "adhesive functional film" having the adhesive layer disclosed herein on at least one side.

As described above, according to the technology disclosed herein, a laminate including the adhesive sheet disclosed herein and a member to which the adhesive sheet is attached is provided. The member to which the adhesive sheet is attached may have the refractive index of the adherend material described above. Further, the difference between the refractive index of the adhesive sheet and the refractive index of the member (refractive index difference) may be the refractive index difference between the adherend and the adhesive sheet described above. The members constituting the laminate are the same as those described above as the members, materials, and adherends, so duplicate explanations will not be repeated.

As understood from the above description and the following examples, the matters disclosed by this specification include the following.

[1] An adhesive comprising a base polymer and a high refractive index additive (A),
The high refractive index additive (A) is a compound with an asymmetric structure,
The content of the high refractive index additive (A) is 30 parts by weight or more based on 100 parts by weight of the base polymer,
The adhesive has a refractive index of 1.50 or more.
[2] The adhesive according to [1] above, wherein the high refractive index additive (A) is a compound having a double bond-containing ring.
[3] The adhesive according to [1] or [2] above, wherein the high refractive index additive (A) is a compound having a heterocycle.
[4] The adhesive according to any one of [1] to [3] above, wherein the high refractive index additive (A) is a compound containing a fused ring having a substituent.
[5] The adhesive according to [4] above, which contains a dinaphthothiophene compound having a substituent as the high refractive index additive (A).
[6] The adhesive according to any one of [1] to [5] above, which contains a compound having a refractive index of 1.65 or more as the high refractive index additive (A).
[7] The adhesive according to any one of [1] to [6] above, wherein the high refractive index additive (A) is a compound having a molecular weight of 100 or more and 1000 or less.
[8] The adhesive according to any one of [1] to [7] above, wherein the content of the aromatic ring-containing monomer in the monomer components constituting the base polymer is 0% by weight or more and less than 75% by weight. .
[9] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to any one of [1] to [8] above.

[10] The ratio of storage modulus G'(25°C) [Pa] to elongation at break E _B [%] at 25°C (G'(25°C)/E _B ) is 450 or less (for example, 1 or more and 50 The adhesive according to any one of [1] to [8] above, which is (below).
[11] The adhesive according to any one of [1] to [8] and [10] above, which has an elongation at break E _B of 500% or more.
[12] Any of the above [1] to [8], [10], [11], whose storage modulus G' (25°C) is within the range of 1.0 × 10 ⁴ to 1.0 × 10 ⁶ or the adhesive described in item 1.
[13] The adhesive according to any one of [1] to [8] and [10] to [12] above, which has a glass transition temperature of 0° C. or lower.

[14] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to any one of [1] to [8] and [10] to [13] above.
[15] The pressure-sensitive adhesive sheet according to [14] above, wherein the pressure-sensitive adhesive layer has a thickness of 5 μm or more and 100 μm or less.
[16] The pressure-sensitive adhesive sheet according to [14] or [15] above, which has a haze of 3% or less.
[17] The adhesive sheet according to any one of [14] to [16] above, which has a total light transmittance of 85% or more.
[18] The adhesive sheet according to any one of [14] to [17] above, which has a peel strength against a glass plate of 0.1 N/25 mm or more.

Hereinafter, some examples relating to the present invention will be described, but the present invention is not intended to be limited to what is shown in these specific examples. In the following description, "parts" and "%" expressing usage amounts and contents are based on weight unless otherwise specified.

<Example 1>
(Preparation of polymer solution)
In a four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube, and a condenser, 74 parts of n-butyl acrylate (BA) and m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light") were added as monomer components. acrylate POB-A", refractive index: 1.566. Hereinafter referred to as "POB-A".) 25 parts and 1 part of 4-hydroxybutyl acrylate (4HBA), 2,2'-azobis as a polymerization initiator. Charge 0.2 parts of isobutyronitrile (AIBN) and 150 parts of ethyl acetate as a polymerization solvent, introduce nitrogen gas with gentle stirring, and maintain the liquid temperature in the flask at around 60°C to conduct a polymerization reaction for 6 hours. A solution of polymer P1 (polymer concentration 40%) was prepared. The Mw of polymer P1 was 1.5 million.

(Preparation of adhesive composition)
The above solution of polymer P1 (polymer concentration 40%) was diluted with ethyl acetate to a polymer concentration of 20%. To 500 parts of this solution (containing 100 parts of polymer P1), 42 parts of 6-methoxymethyldinaphthothiophene (6MDNTM, refractive index: 1.759. 25% ethyl acetate solution can be prepared), crosslinking agent 0.1 part based on solid content of trimethylolpropane/xylylene diisocyanate adduct (manufactured by Mitsui Chemicals, trade name "Takenate D-110N", solid content concentration 75%) as a crosslinking retarder, 2 parts of acetylacetone as a crosslinking retarder, One part (non-volatile content: 0.01 part) of 1% ethyl acetate solution of Nasem ferric iron was added as a crosslinking catalyst and mixed with stirring to prepare a pressure-sensitive adhesive composition according to this example.

(Preparation of adhesive sheet)
The adhesive composition prepared above was applied to the silicone-treated surface of polyethylene terephthalate (PET) film R1 (thickness: 50 μm), which had been silicone-treated on one side, and heated at 130° C. for 2 minutes to form a film with a thickness of 50 μm. An adhesive layer was formed. Next, the silicone-treated side of PET film R2 (thickness: 25 μm), which had been silicone-treated on one side, was bonded to the surface of the pressure-sensitive adhesive layer. In this way, a substrate-less double-sided pressure-sensitive adhesive sheet consisting of the pressure-sensitive adhesive layer was obtained. Both sides of this adhesive sheet are protected by PET films (release liners) R1 and R2.

<Example 2>
A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 1, except that the amount of 6MDNTM used was changed to 70 parts with respect to 100 parts of polymer P1. A pressure-sensitive adhesive sheet according to this example (base material-less double-sided pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer having a thickness of 50 μm) was produced in the same manner as in Example 1 except that this pressure-sensitive adhesive composition was used.

<Example 3>
A solution of polymer P2 (polymer concentration 40%) was prepared in the same manner as in the preparation of the polymer solution in Example 1, except that the composition of the monomer components was changed to 74 parts of 2-ethylhexyl acrylate (2EHA), 25 parts of POB-A, and 1 part of 4HBA. was prepared. The Mw of polymer P2 was 1 million.
A pressure-sensitive adhesive composition according to this example was prepared in the same manner as the pressure-sensitive adhesive composition in Example 1 except that a solution of polymer P2 was used instead of a solution of polymer P1. A pressure-sensitive adhesive sheet according to this example (base material-less double-sided pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer having a thickness of 50 μm) was produced in the same manner as in Example 1 except that this pressure-sensitive adhesive composition was used.

<Example 4>
A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 3, except that the amount of 6MDNTM used was changed to 70 parts with respect to 100 parts of polymer P2. A pressure-sensitive adhesive sheet according to this example (base material-less double-sided pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer having a thickness of 50 μm) was produced in the same manner as in Example 1 except that this pressure-sensitive adhesive composition was used.

<Example 5>
A solution of polymer P3 (polymer concentration 40 %) was prepared. The Mw of polymer P3 was 1 million.
A pressure-sensitive adhesive composition according to this example was prepared in the same manner as the pressure-sensitive adhesive composition in Example 1 except that a solution of polymer P3 was used instead of a solution of polymer P1. A pressure-sensitive adhesive sheet according to this example (base material-less double-sided pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer having a thickness of 50 μm) was produced in the same manner as in Example 1 except that this pressure-sensitive adhesive composition was used.

<Example 6>
A solution of polymer P4 (polymer concentration 40%) was prepared in the same manner as in the preparation of the polymer solution in Example 1, except that the composition of the monomer components was changed to 99 parts BA and 1 part 4HBA. The Mw of polymer P4 was 1.5 million.
A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in the preparation of the pressure-sensitive adhesive composition in Example 2, except that a solution of polymer P4 was used instead of a solution of polymer P1. Using this adhesive composition, the adhesive sheet according to this example (based on the adhesive layer) was prepared in the same manner as in Example 1, except that the amount of application was adjusted so that an adhesive layer with a thickness of 20 μm was formed. A material-less double-sided adhesive sheet) was produced.

<Example 7>
A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 6, except that the amount of 6MDNTM used was changed to 60 parts with respect to 100 parts of polymer P4. A pressure-sensitive adhesive sheet according to this example (base material-less double-sided pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer having a thickness of 20 μm) was produced in the same manner as in Example 6 except that this pressure-sensitive adhesive composition was used.

<Example 8 to Example 10>
In preparing the adhesive composition in Example 6, 6MDNTM was replaced with 6-acryloyloxymethyldinaphthothiophene (6MDNTA, refractive index: 1.737) in Example 8, and 6-acryloyloxyethyldinaphthothiophene (6MDNTA, refractive index: 1.737) in Example 9. 6EDNTA, refractive index: 1.722), and in Example 10 42 parts of 6-ethyldinaphthothiophene (6EDNT, refractive index: 1.764) were used per 100 parts of polymer P4. The adhesive compositions according to each example were prepared in the same manner as in the preparation of the adhesive composition in Example 6 except for the above. A pressure-sensitive adhesive sheet (substrate-less double-sided pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer having a thickness of 50 μm) according to each example was produced in the same manner as in Example 1 except that the obtained pressure-sensitive adhesive composition was used.

<Example 11>
A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in Example 8 except that 6MDNTA was not used. A pressure-sensitive adhesive sheet according to this example (base material-less double-sided pressure-sensitive adhesive sheet consisting of a pressure-sensitive adhesive layer having a thickness of 50 μm) was produced in the same manner as in Example 1 except that this pressure-sensitive adhesive composition was used.

<Example 12>
In preparing the adhesive composition in Example 8, 42 parts of 2,12-diallyloxydinaphthothiophene (2,12-DAODNT, refractive index: 1.729) was added to 100 parts of polymer P4 in place of 6MDNTA. used. A pressure-sensitive adhesive composition according to this example was prepared in the same manner as in the preparation of the pressure-sensitive adhesive composition in Example 8 except for the above. A pressure-sensitive adhesive sheet (substrate-less double-sided pressure-sensitive adhesive sheet consisting of a 50 μm thick pressure-sensitive adhesive layer) according to this example was produced in the same manner as in Example 1 except that the obtained pressure-sensitive adhesive composition was used.

The structures of each substituted DNT used in Examples 1 to 10 and 12 are shown in Table 1. Among these, 2,12-DAODNT is a compound with a line symmetric structure, and the others are compounds with an asymmetric structure. The refractive index of these compounds was measured by the following method. That is, a 5% ethyl acetate solution or a 5% MEK solution of the compound to be measured was applied onto a glass plate so that the dry film thickness was 10 μm, and was dried by heating at 130° C. for 5 minutes. The refractive index of the target compound thus formed on the glass plate was measured using a prism coupler (manufactured by Metricon, model "2010M") under conditions of a measurement temperature of 25° C. and a measurement wavelength of 594 nm.

<Evaluation method>
(Refractive index of adhesive)
The refractive index of the adhesive layer (substrate-less double-sided adhesive sheet) according to each example was measured using a prism coupler (manufactured by Metricon, model "2010M") under conditions of a measurement temperature of 25° C. and a measurement wavelength of 594 nm.

(Storage modulus G' and glass transition temperature)
The adhesive layers according to each example were laminated to have a thickness of about 1.5 mm, and a disk shape with a diameter of 7.9 mm was punched out as a measurement sample. Dynamic viscoelasticity measurements were performed using the "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific under the following conditions. From the measurement results, the storage elastic modulus G' [Pa] of the adhesive at each temperature (-20°C, 25°C and 60°C) was determined. Further, the temperature corresponding to the peak top temperature of the loss tangent tan δ (loss modulus G"/storage modulus G') in the dynamic viscoelasticity measurement was determined as the glass transition temperature (Tg) [° C.] of the adhesive.
[Measurement condition]
Deformation mode: Torsion Measurement frequency: 1Hz
Temperature range: -50℃~150℃
Heating rate: 5℃/min Shape: Parallel plate 7.9mmφ

(Elongation at break _EB )
The adhesive layer (substrate-less double-sided adhesive sheet) according to each example was cut into a size of 30 mm in length and X mm in width while being sandwiched between PET films (release liners) R1 and R2. The width Xmm was set according to the thickness of the adhesive layer so that the cross-sectional area of the adhesive layer in the cross section along the width direction was approximately 2 mm ² . Next, one release liner is removed to expose one surface of the adhesive layer, and the adhesive layer is wound up on the other release liner with its length direction as an axis to form a cylindrical column with a length of 30 mm. A sample was prepared. The upper and lower parts of the above sample, each 10 mm in length, were fixed with the chuck jig of a tensile testing machine (manufactured by SHIMAZU, EZ-S 500N), and pulled under conditions of a chuck distance of 10 mm and a tensile speed of 300 mm/min in an environment of 25°C. By this, the elongation at break E _B [%] of the above sample was measured.

(Total light transmittance and haze)
Using a test piece in which the adhesive layer according to each example was attached to alkali-free glass (thickness 0.8 to 1.0 mm, total light transmittance 92%, haze 0.4%), under a measurement environment of 23 ° C. The total light transmittance and haze of the test piece were measured using a haze meter ("HM-150" manufactured by Murakami Color Research Institute). The values obtained by subtracting the total light transmittance and haze of the alkali-free glass from the measured values were defined as the total light transmittance [%] and haze [%] of the adhesive (layer). Regarding the base material-less pressure-sensitive adhesive sheet consisting of the pressure-sensitive adhesive layer, the total light transmittance [%] and haze [%] of the pressure-sensitive adhesive layer are the total light transmittance [%] and haze [%] of the pressure-sensitive adhesive sheet.

(Peel strength against glass plate)
Under a measurement environment of 23°C and 50% RH, the release liner was peeled off from one side of the adhesive sheet, and a 50 μm thick PET film was pasted and lined, and then cut into a size of 25 mm in width and 100 mm in length. was used as the test piece. The release liner on the other side of the test piece was peeled off, and a 2 kg roller was moved back and forth on the surface of an alkali glass plate (manufactured by Matsunami Glass Industries Co., Ltd., thickness 1.35 mm, blue plate edge polished) as an adherend. I crimped it. After leaving this in the same environment for 30 minutes, the peel strength (adhesive strength ) [N/25mm] was measured. As a universal tensile compression tester, "Tensile Compression Tester, TG-1kN" manufactured by Minebea was used. In addition, in the case of a single-sided adhesive sheet with a base material, backing with PET film is not essential.

Table 2 shows an overview and evaluation results of the adhesives for each example.

As shown in Table 2, the adhesives of Examples 1 to 10 containing 30 parts or more of a high refractive index additive with an asymmetric structure based on 100 parts of the base polymer suitably achieve both a high refractive index and a low elastic modulus. We were able to. The adhesive layers (substrate-less adhesive sheets) according to these examples had high transparency and exhibited good adhesion to glass when pressure bonded at room temperature. On the other hand, the adhesive of Example 11, which did not contain a high refractive index additive, had a low refractive index. In addition, in Example 12 in which the high refractive index additive was changed to a dinaphthothiophene compound with a symmetrical structure, the storage modulus G' at 25° C. increased significantly and the refractive index could not be measured due to cloudiness. The solubility of each substituted DNT used as an additive in Examples 1 to 10 in ethyl acetate was 6EDNTA>6MDNTM>6MDNTA>6EDNT. The solubility of 2,12-DAODNT in ethyl acetate was comparable to that of 6MDNTA.

Although specific examples of the present invention have been described above in detail, these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes to the specific examples illustrated above.

1, 2, 3 Adhesive sheet 10 Supporting base material

10A First surface

10B Second surface 21 Adhesive layer, first adhesive layer 21A Adhesive surface, first adhesive surface 21B Adhesive surface 22 Second adhesive layer 22A

Second adhesive Surface

31, 32 Release liner

Claims

An adhesive comprising a base polymer and a high refractive index additive (A),
The high refractive index additive (A) is a compound with an asymmetric structure,
The content of the high refractive index additive (A) is 30 parts by weight or more based on 100 parts by weight of the base polymer,
The adhesive has a refractive index of 1.50 or more.
The adhesive according to claim 1, wherein the high refractive index additive (A) is a compound having a double bond-containing ring.
The adhesive according to claim 1 or 2, wherein the high refractive index additive (A) is a compound having a heterocycle.
The adhesive according to claim 1 or 2, wherein the high refractive index additive (A) is a compound containing a fused ring having a substituent.
The adhesive according to claim 4, wherein the high refractive index additive (A) includes a dinaphthothiophene compound having a substituent.
The adhesive according to claim 1 or 2, wherein the high refractive index additive (A) contains a compound having a refractive index of 1.65 or more.
The adhesive according to claim 1 or 2, wherein the high refractive index additive (A) is a compound with a molecular weight of 100 or more and 1000 or less.
The adhesive according to claim 1 or 2, wherein the content of the aromatic ring-containing monomer in the monomer components constituting the base polymer is 0% by weight or more and less than 75% by weight.
A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to claim 1 or 2.