JP2023022805A - Adhesive composition and adhesive sheet - Google Patents

Abstract

To provide an adhesive composition capable of forming an adhesive having both a high refractive index and low elastic modulus.SOLUTION: Provided is an adhesive composition including an acrylic polymer and a plasticizer. A monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1). The plasticizer is a liquid compound at 30°C and has two or more double bond-containing rings.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to an adhesive composition and an adhesive sheet.

In general, pressure-sensitive adhesives (also referred to as pressure-sensitive adhesives; hereinafter the same) exhibit a soft solid (viscoelastic) state in a temperature range around room temperature, and have the property of easily adhering to adherends under pressure. Taking advantage of such properties, pressure-sensitive adhesives are widely used for the purposes of bonding, fixing, protection, etc. in various industrial fields such as home electric appliances, automobiles, various machines, electrical equipment, and electronic equipment. As an example of the application of adhesives, in display devices such as liquid crystal display devices and organic EL display devices, polarizing films, retardation films, cover window members, and other various light-transmitting members and other members are joined. The use to do is mentioned. Patent Documents 1 and 2 are cited as technical documents relating to pressure-sensitive adhesives for optical members.

JP 2014-169382 A JP 2017-128732 A

Patent Documents 1 and 2 disclose a pressure-sensitive adhesive composition mainly composed of 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 cross-linking the pressure-sensitive adhesive composition. and proposes that the refractive index of the pressure-sensitive adhesive is made 1.50 or more, particularly preferably 1.51 or more, by using a monomer having a plurality of aromatic rings. For example, among the materials to which adhesives are attached, such as optical members, there are materials with high refractive indexes. 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. Incidentally, the refractive index of the acrylic adhesive is usually about 1.47.

By the way, it is preferable to use a pressure-sensitive adhesive that has good flexibility depending on the application site and the mode of use. For example, in recent years, foldable displays and rollable displays have been put to practical use as displays such as organic EL displays used in electronic devices such as smartphones, and adhesives used for the above applications are adherends that can be repeatedly folded. It is necessary to have the flexibility to follow Adhesives with excellent flexibility easily follow and adhere to curved surfaces such as three-dimensional shapes, and are suitable for use in electronic devices having curved surfaces. If the flexibility of the pressure-sensitive adhesive having a high refractive index can be enhanced, it can be applied to the applications requiring the above-described flexibility and is useful. However, high refractive index materials used as monomer components of adhesive polymers and additives for adhesives tend to have a high glass transition temperature, such as having aromatic rings. , the elastic modulus tends to be higher. In the design of adhesives, there is a trade-off relationship between high refractive index and low elastic modulus, and it would be practically useful if an adhesive that can achieve both of them is realized.

The present invention was created in view of the above circumstances, and an object of the present invention is to provide a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive having both a high refractive index and a low elastic modulus. Another object of the present invention is to provide a pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition.

This specification provides a pressure-sensitive adhesive composition containing an acrylic polymer and a plasticizer. The monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1). In addition, the plasticizer is a compound that is liquid at 30° C. and has two or more double bond-containing rings. The pressure-sensitive adhesive composition having the above structure is suitable for forming a pressure-sensitive adhesive having a high refractive index, because the monomer component constituting the acrylic polymer contains the aromatic ring-containing monomer (A1). In addition, since the pressure-sensitive adhesive composition contains, as a plasticizer, a compound that has two or more double bond-containing rings and is liquid at 30°C, it is possible to form a pressure-sensitive adhesive that has a high refractive index and a low elastic modulus. is.

In some preferred embodiments, the compound is a liquid compound at 20°C. By using a compound that is liquid at 20° C. as the plasticizer, it is easy to form a pressure-sensitive adhesive with a low elastic modulus.

In some preferred embodiments, the plasticizer comprises more than 15 parts by weight per 100 parts by weight of the acrylic polymer. In some embodiments, the plasticizer comprises greater than 30 parts by weight per 100 parts by weight of the acrylic polymer. According to the pressure-sensitive adhesive composition having the composition described above, a pressure-sensitive adhesive having both a high refractive index and a low elastic modulus can be preferably formed.

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

In some preferred embodiments, the plasticizer has a first double bond-containing ring and a second double bond-containing ring. The first double bond-containing ring and the second double bond-containing ring are linked via a linking group having 1 to 5 atoms. Such a plasticizer has a linking group between two or more double bond-containing rings, and thus tends to lower the elastic modulus of the pressure-sensitive adhesive while maintaining a high refractive index. By using a plasticizer having such a structure, it is possible to achieve both a high refractive index and a low elastic modulus in a better balance.

In some embodiments, the plasticizer has a molecular weight in the range of 100-2000. A plasticizer having a molecular weight within the above range is easily compatible with the pressure-sensitive adhesive and easily exhibits a plasticizing effect.

In some embodiments, the monomer component constituting the acrylic polymer contains a monomer (A2) having at least one of a hydroxyl group and a carboxy group in addition to the aromatic ring-containing monomer (A1). By using an acrylic polymer having such a monomer composition, a high-refractive-index pressure-sensitive adhesive having both flexibility and good cohesive strength can be preferably obtained.

In some aspects, the content of the aromatic ring-containing monomer (A1) in the monomer component is 60% by weight or more. By using an acrylic polymer in which the polymerization ratio of the aromatic ring-containing monomer (A1) is 60% by weight or more, it is easy to obtain a pressure-sensitive adhesive having a high refractive index.

In some embodiments, 50% by weight or more of the aromatic ring-containing monomer (A1) is a monomer having a homopolymer glass transition temperature of 10° C. or lower. Thereby, even if the polymerization ratio of the aromatic ring-containing monomer (A1) is increased, it is possible to achieve both a high refractive index and a low elastic modulus in a well-balanced manner.

The adhesive composition disclosed herein preferably further contains a cross-linking agent. The use of a cross-linking agent imparts appropriate cohesiveness to the pressure-sensitive adhesive, making it possible to enhance the handleability of the pressure-sensitive adhesive sheet during production, processing, storage, attachment to an adherend, and the like.

Further, according to this specification, an adhesive comprising an adhesive layer made 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 achieve both a high refractive index and a low elastic modulus, the adhesive sheet containing the adhesive desirably has a high refractive index for use in foldable displays and the like, and can be used repeatedly. It is preferably used for bonding, fixing, protection, etc. in applications that require flexibility to withstand bending operations.

Any appropriate combination of the elements described in this specification may also be included in the scope of the invention for which patent protection is sought by this patent application.

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

Preferred embodiments of the present invention are described below. Matters other than those specifically referred to in this specification that are necessary for the implementation of the present invention are applicable based on the teaching of the implementation of the invention described in this specification and the common general knowledge at the time of filing. understandable to traders. The present invention can be implemented based on the contents disclosed in this specification and common general technical knowledge in the field.
In the drawings below, members and portions having the same function may be denoted by the same reference numerals, and redundant description may be omitted or simplified. In addition, the embodiments described in the drawings are schematics for the purpose of clearly explaining the present invention and do not necessarily represent the size or scale of the products actually provided.

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

As used herein, 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 is also referred to as "acrylic monomer". Accordingly, an acrylic polymer in this specification is defined as a polymer containing monomeric units derived from an acrylic monomer. 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 monomer components constituting the polymer are acrylic monomers.

In this specification, the term "acrylic monomer" refers to a monomer having at least one (meth)acryloyl group in one molecule. Here, "(meth)acryloyl group" is meant to comprehensively refer to acryloyl groups and methacryloyl groups. Therefore, the concept of an acrylic monomer as used herein can include both a monomer having an acryloyl group (acrylic monomer) and a monomer having a methacryloyl group (methacrylic monomer). Similarly, in this specification, "(meth)acrylic acid" means acrylic acid and methacrylic acid, and "(meth)acrylate" means acrylate and methacrylate, respectively. The same applies to other similar terms.

<Adhesive composition>
The pressure-sensitive adhesive composition disclosed herein is not particularly limited as long as it can form a pressure-sensitive adhesive containing an acrylic polymer (preferably a pressure-sensitive adhesive containing the acrylic polymer as a base polymer). . The pressure-sensitive adhesive composition is, for example, a solvent-based pressure-sensitive adhesive composition containing a pressure-sensitive adhesive-forming component in an organic solvent, or prepared to form a pressure-sensitive adhesive by curing with active energy rays such as ultraviolet rays and radiation. Active energy ray-curable pressure-sensitive adhesive composition, water-dispersed pressure-sensitive adhesive composition in which pressure-sensitive adhesive-forming components are dispersed in water, hot-melt type that is coated in a heat-melted state and forms pressure-sensitive adhesive when cooled to around room temperature It can be in various forms such as an adhesive composition. Although not particularly limited, the technique disclosed herein can be preferably implemented using a solvent-based pressure-sensitive adhesive composition. In an aspect having a solvent-based pressure-sensitive adhesive layer formed from a solvent-based pressure-sensitive adhesive composition, it is possible to preferably achieve both a high refractive index and a low elastic modulus.

The pressure-sensitive adhesive composition disclosed herein contains an aromatic ring-containing monomer (A1) as a monomer component constituting the acrylic polymer. Here, in the present specification, the "monomer component constituting the acrylic polymer" is contained in the pressure-sensitive adhesive composition in the form of a preformed polymer (which may be an oligomer), or is an unpolymerized monomer. It means a monomer that constitutes a repeating unit of an acrylic polymer in a pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition, regardless of whether it is contained in the pressure-sensitive adhesive composition in the form. That is, the monomer component constituting the acrylic polymer may be contained in the pressure-sensitive adhesive composition in any form of a polymer, an unpolymerized product, or a partially polymerized product. From the viewpoint of ease of preparation of the PSA composition, in some embodiments, the PSA 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. things are preferred.

(Monomer (A1))
A compound containing at least one aromatic ring and at least one ethylenically unsaturated group in one molecule is used as the monomer (A1). As the monomer (A1), such compounds can be used singly or in combination of two or more.

Examples of the ethylenically unsaturated groups include (meth)acryloyl groups, vinyl groups, and (meth)allyl groups. A (meth)acryloyl group is preferred from the viewpoint of polymerization reactivity, and an acryloyl group is more preferred from the viewpoint of flexibility and adhesiveness. From the viewpoint of suppressing a decrease in flexibility of the adhesive, as the monomer (A1), a compound having one ethylenically unsaturated group contained in one molecule (that is, a monofunctional monomer) is preferably used.

The number of aromatic rings contained in one molecule of the compound used as the monomer (A1) may be one, or two 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, the number of aromatic rings may be, for example, 12 or less, preferably 8 or less, and 6 or less, from the viewpoint of ease of preparation of the pressure-sensitive adhesive composition, transparency of the pressure-sensitive adhesive, and the like. is more preferable, and may be 5 or less, 4 or less, 3 or less, or 2 or less.

The aromatic ring possessed by the compound used as the monomer (A1) includes a benzene ring (which may be a benzene ring constituting part of a biphenyl structure or a fluorene structure); a naphthalene ring, an indene ring, an azulene ring, anthracene ring, and a phenanthrene ring. condensed ring; may be a carbocyclic ring such as pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, pyrrole ring, pyrazole ring, imidazole ring, triazole ring, oxazole ring, isoxazole ring, thiazole ring , a thiophene ring; and the like. The heteroatoms contained as ring-constituting atoms in the above heterocycle may be one or more selected from the group consisting of nitrogen, sulfur and oxygen, for example. In some embodiments, the heteroatoms that make up the heterocycle can be one or both of nitrogen and sulfur. The monomer (A1) 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 carbocyclic ring) may or may not have one or more substituents on the ring-constituting atoms. 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, and a glycidyloxy group. etc. are exemplified, but not limited to these. In substituents containing carbon atoms, the number of carbon atoms contained in the substituent is preferably 1-4, more preferably 1-3, and can be, for example, 1 or 2. In some embodiments, the aromatic ring has no substituents on the ring-constituting atoms, or has one or more substituents selected from the group consisting of alkyl groups, alkoxy groups and halogen atoms (e.g., bromine atoms). can be an aromatic ring having In addition, the fact that the aromatic ring of the monomer (A1) has a substituent on its ring-constituting atom means that the aromatic ring has a substituent other than a substituent having an ethylenically unsaturated group.

The aromatic ring and the ethylenically unsaturated group may be directly bonded or may be bonded via a linking group. The 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 hydroxyl groups. (eg, hydroxyalkylene group), oxy group (--O-- group), thiooxy group (--S-- group), and the like. In some embodiments, the aromatic ring and the ethylenically unsaturated group are directly attached or attached via a linking group selected from the group consisting of alkylene, oxyalkylene and poly(oxyalkylene) groups. Aromatic ring-containing monomers having a structure in which The number of carbon atoms in the alkylene group and the oxyalkylene group is preferably 1-4, more preferably 1-3, and can be, for example, 1 or 2. The number of repeating oxyalkylene units in the poly(oxyalkylene) group may be, for example, 2-3.

Examples of compounds that can be preferably employed as the monomer (A1) 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 be used singly or in combination of two or more. One or two or more aromatic ring-containing (meth)acrylates and one or two or more aromatic ring-containing vinyl compounds may be used in combination.

In some aspects, as the monomer (A1), a monomer having two or more aromatic rings (preferably carbocyclic rings) in one molecule can be used because a high refractive index-increasing effect is likely to be obtained. 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-condensed aromatic rings are bonded via a linking group, and two or more non-condensed aromatic rings. Monomers having a structure in which rings are directly (that is, not via other atoms) chemically bonded, monomers having a condensed aromatic ring structure, monomers having a fluorene structure, monomers having a dinaphthothiophene structure, monomers having a dibenzothiophene structure , etc. The monomers containing multiple aromatic rings may be used singly or in combination of two or more.

The linking group is, for example, an oxy group (-O-), a thiooxy group (-S-), an oxyalkylene group (eg, -O-(CH ₂ ) _n - group, where n is 1 to 3, preferably 1). , a thiooxyalkylene group (such as a —S—(CH ₂ ) _n — group, where n is 1 to 3, preferably 1), a linear alkylene group (ie, a —(CH ₂ ) _n — group, where n is 1 to 6, preferably 1 to 3), the above oxyalkylene group, the above thiooxyalkylene group and the above linear alkylene group in which the alkylene group is partially or completely halogenated, and the like. 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 linear 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 (e.g., m-phenoxybenzyl (meth)acrylate), thiophenoxybenzyl (meth) 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, a biphenyl structure-containing (meth)acrylate, a triphenyl structure-containing (meth)acrylate, a vinyl group-containing biphenyl, or the like. Specific examples include o-phenylphenol (meth)acrylate and biphenylmethyl (meth)acrylate.

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

Specific examples of the monomer having a fluorene structure include 9,9-bis(4-hydroxyphenyl)fluorene (meth)acrylate and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene (meth)acrylate. etc. Since the monomer having a fluorene structure includes a structural portion 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 a dinaphthothiophene structure include (meth)acryloyl group-containing dinaphthothiophene, vinyl group-containing dinaphthothiophene, (meth)allyl group-containing dinaphthothiophene, and the like. Specific examples include (meth)acryloyloxymethyldinaphthothiophene (for example, a compound having a structure in which CH ₂ CH(R ¹ )C(O)OCH ₂ — is bonded to the 5- or 6-position of the dinaphthothiophene ring. and R ¹ is a hydrogen atom or a methyl group.), (meth)acryloyloxyethyldinaphthothiophene (for example, at the 5- or 6-position of the dinaphthothiophene ring, CH ₂ CH(R ¹ )C(O) OCH(CH ₃ )— or a compound having a structure in which CH ₂ CH(R ¹ )C(O)OCH ₂ CH ₂ — is bonded, where R ¹ is a hydrogen atom or a methyl group), vinyldinaphthothiophene (For example, compounds having a structure in which a vinyl group is bonded to the 5th or 6th position of the naphthothiophene ring), (meth)allyloxydinaphthothiophene, and the like. Note that the monomer having a dinaphthothiophene structure is included in the concept of the monomer having a condensed aromatic ring structure by including a naphthalene structure and by having a structure in which a thiophene ring and two naphthalene structures are condensed. be.

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

In some preferred embodiments, a monomer having one aromatic ring (preferably carbocyclic ring) in one molecule is used as the monomer (A1). A monomer having one aromatic ring in one molecule (single aromatic ring-containing monomer) can be useful, for example, in improving the flexibility of the pressure-sensitive adhesive, adjusting the pressure-sensitive adhesive properties, and improving the transparency. A single aromatic ring-containing monomer may be used alone or in combination of two or more. In some aspects, 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 pressure-sensitive 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, phenoxypropyl (meth)acrylate 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, and 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;

As the monomer (A1), a monomer 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 having an oxyethylene chain interposed between an ethylenically unsaturated group and an aromatic ring in this manner can be understood as an ethoxylated product of the original monomer. The number of repeating oxyethylene units ( _{--CH.sub.2CH.sub.2O--} ) in _the oxyethylene chain is typically 1-4, preferably 1-3, more preferably 1-2, for example 1. Specific examples of ethoxylated aromatic ring-containing monomers include ethoxylated o-phenylphenol (meth)acrylate, ethoxylated nonylphenol (meth)acrylate, ethoxylated cresol (meth)acrylate, phenoxyethyl (meth)acrylate, and phenoxydiethylene glycol. di(meth)acrylate and the like.

The content of the monomer containing multiple aromatic rings in the monomer (A1) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some aspects, the content of the monomer containing multiple aromatic rings in the monomer (A1) may be, for example, 50% by weight or more, and is preferably 70% by weight or more from the viewpoint of facilitating obtaining a higher refractive index. , 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomer (A1) may be the multiple aromatic ring-containing monomer. That is, only one or two or more aromatic ring-containing monomers may be used as the monomer (A1). Further, in some aspects, for example, considering the balance between high refractive index and low elastic modulus, and if necessary, adhesive strength, the content of the monomer containing multiple aromatic rings in the monomer (A1) is 100% by weight. It may be less than 98% by weight, 90% by weight or less, 80% by weight or less, 70% by weight or less, 65% by weight or less, 50% by weight or less, and 25% by weight or less. % by weight or less, or 10% by weight or less. The technology disclosed herein can also be practiced in a mode in which the content of the monomer containing multiple aromatic rings in the monomer (A1) 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 a pressure-sensitive adhesive having 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 25% by weight or more. In some aspects, from the viewpoint of facilitating the realization of a pressure-sensitive adhesive having a higher refractive index, the content of the monomer containing multiple aromatic rings in the monomer component may be, for example, more than 35% by weight, or 50% by weight. Advantageously, more than 70% by weight, preferably 75% by weight or more, 85% by weight or more, 90% by weight or more, 91% by weight or more, 92% by weight or more, It may be 93% by weight or more, 94% by weight or more, 95% by weight or more, 96% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more. Advantageously, the content of the monomer containing multiple aromatic rings in the monomer component is about 99% by weight or less in consideration of the balance between high refractive index, low elastic modulus, and, if necessary, adhesive strength. 98 wt% or less, more preferably 96 wt% or less, 93 wt% or less, 90 wt% or less, 85 wt% or less, 80 wt% or less, 75 % by weight or less. In some embodiments, from the viewpoint of easily achieving higher adhesive properties and/or optical properties (e.g., transparency), the content of the monomer containing multiple aromatic rings in the monomer component may be 70% by weight or less, or 60% by weight. % by weight or less, 50% by weight or less, 40% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight or less. The technology disclosed herein can also be practiced in a mode in which the content of the monomer containing multiple aromatic rings in the monomer component is less than 3% by weight.

The content of the single aromatic ring-containing monomer in the monomer (A1) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some aspects, the content of the single aromatic ring-containing monomer in the monomer (A1) may be, for example, 50% by weight or more, and is preferably 70% by weight or more from the viewpoint of facilitating obtaining a higher refractive index. , 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomer (A1) may be a single aromatic ring-containing monomer. That is, as the monomer (A1), only one or more monomers containing a single aromatic ring may be used. In some aspects, for example, considering the balance between high refractive index and low elastic modulus, and if necessary, adhesive strength, the content of the monomer containing a single aromatic ring in the monomer (A1) is 100% by weight. It may be less than 98% by weight, 90% by weight or less, 80% by weight or less, 70% by weight or less, 65% by weight or less, 50% by weight or less, and 25% by weight or less. % by weight or less, or 10% by weight or less. The technology disclosed herein can also be practiced in a mode in which the content of the single aromatic ring-containing monomer in the monomer (A1) is less than 5% by weight. A single aromatic ring-containing monomer may not be used.

The content of the single aromatic ring-containing monomer in the monomer component constituting the acrylic polymer is not particularly limited, and can be set so as to realize a pressure-sensitive adhesive having both a desired refractive index and elastic modulus. The content of the single aromatic ring-containing monomer in the monomer component may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some aspects, from the viewpoint of facilitating the realization of a pressure-sensitive adhesive having a higher refractive index, the content of the single aromatic ring-containing monomer in the monomer component may be, for example, more than 35% by weight, or more than 50% by weight. is preferably 60% by weight or more, more preferably more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, may be 95% by weight or more , or 98% by weight or more. The content of the monomer containing a single aromatic ring in the monomer component may be approximately 99% by weight or less, or 98% by weight, in consideration of the balance between high refractive index, low elastic modulus, and, if necessary, adhesive strength. % or less, more preferably 96 wt% or less, 93 wt% or less, 90 wt% or less, 85 wt% or less, 80 wt% or less, 75 wt% It can be below. In some embodiments, from the viewpoint of easily achieving higher adhesive properties and/or optical properties (e.g., transparency), the content of the monomer containing a single aromatic ring in the monomer component may be 70% by weight or less, or 60% by weight. % by weight or less, 50% by weight or less, 40% by weight or less, 25% by weight or less, 15% by weight or less, or 5% by weight or less. The technology disclosed herein can also be practiced in a mode in which the content of the single aromatic ring-containing monomer in the monomer component is less than 3% by weight.

In some aspects of the technology disclosed here, a high refractive index monomer can be preferably employed as at least part of the monomer (A1). Here, "high refractive index monomer" refers to a monomer having a refractive index of, for example, approximately 1.510 or higher, preferably approximately 1.530 or higher, and more preferably approximately 1.550 or higher. Although the upper limit of the refractive index of the high refractive index monomer is not particularly limited, it is, for example, 3.000 or less from the viewpoint of ease of preparation of the pressure-sensitive adhesive composition and compatibility with flexibility suitable as a pressure-sensitive adhesive. It may be 0.500 or less, 2.000 or less, 1.900 or less, 1.800 or less, or 1.700 or less. The high refractive index monomers can be used singly or in combination of two or more.
The refractive index of the monomer is measured using an Abbe refractometer under conditions of 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 the manufacturer or the like provides the nominal value of the refractive index at 25° C., the nominal value can be adopted.

As the above-mentioned high refractive index monomer, those having a corresponding refractive index among the compounds included in the concept of the aromatic ring-containing monomer (A1) disclosed herein (e.g., the compounds and compound groups exemplified above) can 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 (repeating number of oxyethylene unit: 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-acryloyloxymethyldinaphthothiophene ( 6MDNTA, refractive index: 1.75), 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), etc., but are 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 higher, preferably about 1.530 or higher, more preferably about 1.550 or higher) in the monomer (A1) is particularly For example, it may be 5% by weight or more, 25% by weight or more, 35% by weight or more, or 40% by weight or more. In some embodiments, the content of the high refractive index monomer in the monomer (A1) may be, for example, 50% by weight or more, preferably 70% by weight or more, from the viewpoint of easily obtaining a higher refractive index. , 85% by weight or more, 90% by weight or more, or 95% by weight or more. Substantially 100% by weight of the monomers (A1) may be high refractive index monomers. Further, in some aspects, for example, from the viewpoint of achieving both a high refractive index and a low elastic modulus, and if necessary, adhesive strength in a well-balanced manner, the content of the high refractive index monomer in the monomer (A1) is 100% by weight. It may be less than 98% by weight, 90% by weight or less, 80% by weight or less, or 65% by weight or less.

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 a pressure-sensitive adhesive having both desired refractive index and elastic modulus. In addition, if necessary, it can be set in consideration of compatibility with adhesive properties (eg, adhesive strength, etc.) and/or optical properties (eg, 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 25% by weight or more. In some embodiments, the content of the high refractive index monomer in the monomer component constituting the acrylic polymer may be, for example, more than 35% by weight, and more than 50% by weight from the viewpoint of facilitating obtaining a higher refractive index. Advantageously, it is more than 70 wt%, it may be 75 wt% or more, it may be 85 wt% or more, it may be 90 wt% or more, it may be 95 wt% or more. The content of the high refractive index monomer in the monomer component is advantageously 99% by weight or less from the viewpoint of achieving a good balance between a high refractive index, a low elastic modulus, and, if necessary, adhesive strength. It is preferably 96% by weight or less, preferably 96% by weight or less, 93% by weight or less, 90% by weight or less, 85% by weight or less, 80% by weight or less, or 75% by weight. % or less.

In some preferred embodiments, an aromatic ring-containing monomer having a homopolymer Tg of 10° C. or less (hereinafter sometimes referred to as “monomer L”) is employed as at least part of the monomer (A1). The content of the aromatic ring-containing monomer (A1) in the monomer component (in particular, the aromatic ring-containing monomer (A1) corresponding to at least one of the above-described multiple aromatic ring-containing monomer, single aromatic ring-containing monomer and high refractive index monomer) Although the storage elastic modulus G' of the pressure-sensitive adhesive generally tends to increase when increased, the increase in the storage elastic modulus G' can be suppressed by adopting the monomer L as part or all of the monomer (A1). 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 lower, 0° C. or lower, −10° C. or lower, −20° C. or lower, or −25° C. or lower. The lower limit of Tg of monomer L is not particularly limited. Considering the balance with the effect of improving the refractive index, in some embodiments, the Tg of the monomer L may be -70°C or higher, -55°C or higher, or -45°C or higher. In some other embodiments, the Tg of monomer L may be, for example, −30° C. or higher, −10° C. or higher, 0° C. or higher, or 3° C. or higher. Monomer L can be used individually by 1 type or in combination of 2 or more types.

As the monomer L, those having a corresponding Tg are appropriately selected from among the compounds included in the concept of the aromatic ring-containing monomer (A1) disclosed herein (e.g., the compounds and compound groups exemplified above). be able to. Preferred examples of aromatic ring-containing monomers that can be used as monomer L include m-phenoxybenzyl acrylate (Tg of homopolymer: −35° C.), benzyl acrylate (Tg of homopolymer: 6° C.), phenoxyethyl acrylate (Tg of homopolymer: Tg: 2°C) and phenoxydiethylene glycol acrylate (Tg of homopolymer: -35°C).

The content of the monomer L in the monomer (A1) is not particularly limited, and may be, for example, 5% by weight or more, 25% by weight or more, or 40% by weight or more. In some embodiments, the content of the monomer L in the monomer (A1) is, for example, 50% by weight or more, from the viewpoint of facilitating the production of a pressure-sensitive adhesive that achieves both a high refractive index and a low elastic modulus at a higher level. Well, from the viewpoint of lowering the elastic modulus, it is preferably 60% by weight or more, may be 70% by weight or more, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, or may be 95% by weight. It can be more than that. Substantially 100% by weight of monomer (A1) may be monomer L. Further, in some aspects, for example, from the viewpoint of balancing a high refractive index, a low elastic modulus, and, if necessary, adhesive strength, the content of the monomer L in the monomer (A1) is less than 100% by weight. It 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 the monomer L in the monomer component constituting the acrylic polymer may be, for example, 3% by weight or more, 10% by weight or more, or 25% by weight or more. In some aspects, the content of the monomer L in the monomer component may be, for example, more than 35% by weight, from the viewpoint of making it easier to obtain a pressure-sensitive adhesive that achieves both a high refractive index and a low elastic modulus at a higher level, From the viewpoint of improving the refractive index, it is advantageous to be more than 50% by weight, preferably more than 70% by weight, may be 75% by weight or more, may be 85% by weight or more, may be 90% by weight or more, and may be 95% by weight or more. % by weight or more. The content of the monomer L in the monomer component is advantageously about 99% by weight or less from the viewpoint of balancing a high refractive index, a low elastic modulus, and, if necessary, adhesive strength, and 98% by weight. % or less, more preferably 96 wt% or less, 93 wt% or less, 90 wt% or less, 85 wt% or less, 80 wt% or less, 75 wt% It can be below.

In some embodiments, the glass transition temperature Tg _A1 based on the composition of the monomer (A1) is suitably about 20° C. or lower, preferably 10° C. or lower, from the viewpoint of lowering the elastic modulus. It may be 5° C. or lower, 0° C. or lower, −10° C. or lower, −20° C. or lower, or −25° C. or lower. The lower limit of the glass transition temperature Tg _A1 is not particularly limited. In some aspects, the glass transition temperature Tg _A1 may be -70° C. or higher, -55° C. or higher, or -45° C. or higher in consideration of the balance with the refractive index improvement effect. The technology disclosed herein can also be suitably practiced in embodiments where the glass transition temperature Tg _A1 is, for example, -40°C or higher, -35°C or higher, -33°C or higher, -30°C or higher, or -25°C or higher. In some other embodiments, the glass transition temperature Tg _A1 may be, for example, −10° C. or higher, 0° C. or higher, or 3° C. or higher.

Here, the glass transition temperature Tg _A1 based on the composition of the monomer (A1) is the Tg determined by the Fox formula described later based on the composition of only the monomer (A1) among the monomer components constituting the acrylic polymer. say. The glass transition temperature Tg _A1 is obtained by applying the Fox formula to only the monomer (A1) among the monomer components constituting the acrylic polymer, and the glass of the homopolymer of each aromatic ring-containing monomer used as the monomer (A1). It can be calculated from the transition temperature and the weight fraction of each aromatic ring-containing monomer in the total amount of the monomers (A1). In the embodiment using only one type of monomer as the monomer (A1), the Tg of the homopolymer of the monomer and the glass transition temperature Tg _A1 match.

In some embodiments, the aromatic ring-containing monomer (A1) is a combination of monomer L (that is, an aromatic ring-containing monomer whose homopolymer Tg is 10°C or lower) and monomer H whose Tg is higher than 10°C. can be used for The Tg of monomer H may be, for example, greater than 10°C, greater than 15°C, or greater than 20°C. By using the monomer L and the monomer H in combination, the adhesive having a high content of the aromatic ring-containing monomer (A1) in the monomer component has a high refractive index and is suitable for adhesion to the adherend. It is possible to achieve both flexibility and flexibility at a higher level. The amount ratio of the monomer L and the monomer H used can be set so as to suitably exhibit such effects, and is not particularly limited. For example, it is preferable to set the usage amount ratio of the monomer L and the monomer H so as to satisfy one of the glass transition temperatures Tg _A1 described above.

In some aspects, the aromatic ring-containing monomer (A1) can be preferably selected from compounds that do not contain a structure in which two or more non-fused aromatic rings are directly chemically bonded (for example, a biphenyl structure). For example, 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 composed of is preferred. By limiting the amount of the compound containing a structure in which two or more non-fused aromatic rings are directly chemically bonded in this way, it is possible to achieve both a high refractive index, a low elastic modulus, and, if necessary, adhesive strength in a well-balanced manner. It can be advantageous from the viewpoint of realizing a pressure-sensitive adhesive.

The content of the monomer (A1) in the monomer component constituting the acrylic polymer is not particularly limited, and the desired refractive index and elastic modulus, adhesive properties (e.g., adhesive strength, etc.) and / or optical properties (e.g., total ray transparency, haze value, etc.). In some embodiments, the content of the monomer (A1) in the monomer component may be, for example, 30% by weight or more, preferably 50% by weight or more, more preferably 60% by weight or more, and 70% by weight. % or more. In some preferred embodiments, the content of the monomer (A1) in the monomer component constituting the acrylic polymer may be, for example, more than 70% by weight, suitably 75% by weight or more, and a higher refractive index It is preferably 80% by weight or more from the viewpoint of making it easy to obtain a ratio, may be 85% by weight or more, may be 90% by weight or more, 91% by weight or more, 92% by weight or more, 93% by weight or more, 94% by weight or more , 95% by weight or more, 96% by weight or more, 97% by weight or more, 98% by weight or more, or 99% by weight or more. The content of the monomer (A1) in the monomer component is typically less than 100% by weight, and is about 99% from the viewpoint of balancing a high refractive index, a low elastic modulus, and, if necessary, adhesive strength. It is advantageously not more than 98% by weight, more preferably not more than 96% by weight, may be not more than 93% by weight, and may be not more than 90% by weight. In some embodiments, the content of the monomer (A1) in the monomer component may be less than 90% by weight, and may be less than 85% by weight, from the viewpoint of facilitating the realization of higher adhesive properties and/or optical properties (e.g., transparency). % or less than 80% by weight.

(Monomer (A2))
In some preferred embodiments, the monomer component constituting the acrylic polymer may further contain a monomer (A2) in addition to the monomer (A1). The monomer (A2) is a monomer corresponding to at least one of a monomer having a hydroxyl group (hydroxyl group-containing monomer) and a monomer having a carboxy 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 carboxy group-containing monomer is a compound containing at least one carboxy group and at least one ethylenically unsaturated group in one molecule. The monomer (A2) can be useful for introducing cross-linking points into the acrylic polymer and imparting appropriate cohesiveness to the pressure-sensitive adhesive. Monomer (A2) can be used individually by 1 type or in combination of 2 or more types. Monomer (A2) is typically a monomer containing no aromatic ring.

Examples of the ethylenically unsaturated groups possessed by the monomer (A2) include (meth)acryloyl groups, vinyl groups, and (meth)allyl groups. A (meth)acryloyl group is preferable from the viewpoint of polymerization reactivity, and an acryloyl group is more preferable from the viewpoint of low elastic modulus and adhesiveness. From the viewpoint of lowering the elastic modulus of the pressure-sensitive adhesive, as the monomer (A2), a compound containing one ethylenically unsaturated group in one molecule (that is, a monofunctional monomer) is preferably used.

In some embodiments, a monomer having a relatively long distance between an ethylenically unsaturated group (eg, (meth)acryloyl group) and a hydroxyl group and/or a carboxy group can be used as the monomer (A2). This makes it easier to obtain a highly flexible crosslinked structure in a mode in which the hydroxyl group and/or the carboxyl group are used for the crosslinking reaction. For example, the number of atoms (typically carbon atoms and oxygen atoms) constituting the chain (connecting chain) connecting the ethylenically unsaturated group and the hydroxyl group and / or carboxy group is 3 or more (e.g. 4 or more, 5 , 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) is a monomer ( A2) can be used. 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 connecting chain atoms connecting the ethylenically unsaturated group and the hydroxyl group and/or the carboxyl group refers to the minimum number of atoms required to reach the hydroxyl group or the carboxyl group from the ethylenically unsaturated group. . For example, when the linking chain consists of a linear alkylene group (that is, -(CH ₂ ) _n - group), the number of n is the number of atoms constituting the linking chain. Further, for example, when the linking chain is an oxyethylene group (that is, —(C ₂ H ₄ O) _n — group), the sum of 2 carbon atoms and 1 oxygen atom constituting the oxyethylene group is 3 and n The product (3n) with is the number of atoms constituting the above-mentioned connecting chain. Although not particularly limited, the monomer (A2) may be an alkylene represented by —(CH ₂ ) _n — between the ethylenically unsaturated group and the hydroxyl group and/or carboxy group. units and oxyalkylene units represented by -(C _m H _2m O)- (for example, oxyethylene units in which m is 2 in the above formula, oxypropylene units in which m is 3 in the above formula, 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 (eg, 1 to 15, 1 to 10, 2 to 6, or 2 to 4). Further, n in the formula representing the alkylene unit is, for example, an integer of 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 above oxyalkylene unit, m is an integer of 2 or more, for example an integer of 2-4. Monomer (A2), in addition to the ethylenically unsaturated group, hydroxyl group and / or carboxy group, alkylene unit and / or oxyalkylene unit, an ester bond, an ether bond, a thioether bond, an aromatic ring, an aliphatic ring, a hetero ring (For example, a ring containing a nitrogen atom (N), an oxygen atom (O), or a sulfur atom (S)). In addition, 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, (meth) ) Hydroxy (meth)acrylates such as 8-hydroxyoctyl acrylate, 10-hydroxydecyl (meth)acrylate, 12-hydroxylauryl (meth)acrylate, (4-hydroxymethylcyclohexyl)methyl (meth)acrylate, etc. Examples 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 having a lower Tg is more preferable. In addition, in the embodiment in which hydroxyalkyl (meth)acrylate is used as the hydroxyl group-containing monomer and the hydroxyl group is used for the crosslinking reaction, from the viewpoint of obtaining a highly flexible crosslinked structure, the above hydroxyalkyl (meth)acrylate A monomer having a large number of carbon atoms in the hydroxyalkyl group of, for example, a hydroxyalkyl (meth)acrylate having 3 or more (eg 3 to 12, preferably 4 to 10) carbon atoms in the hydroxyalkyl group (eg 4-hydroxy acrylate butyl) is preferred. In one preferred embodiment, 50 wt% or more (eg, greater than 50 wt%, greater than 70 wt%, or greater than 85 wt%) of monomer (A2) can be 4-hydroxybutyl acrylate. A hydroxyl-containing monomer can be used individually by 1 type or in combination of 2 or more types.

In some embodiments using a hydroxyl-containing monomer as the monomer (A2), the hydroxyl-containing monomer may be one or more selected from compounds having no methacryloyl group. Preferred examples of hydroxyl group-containing monomers having no methacryloyl group include the various hydroxyalkyl acrylates described above. For example, 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 (A2) is preferably hydroxyalkyl acrylate. By using hydroxyalkyl acrylates, it is possible to introduce hydroxy groups into the acrylic polymer that help provide cross-linking points and impart adequate cohesiveness, and at room temperature compared to using only the corresponding hydroxyalkyl methacrylates. It is easy to obtain an adhesive with good flexibility and adhesiveness in the 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. Moreover, in some aspects, from the viewpoint of reducing the elastic modulus of the adhesive, it is preferable to use, for example, a compound represented by the following formula (1) as the carboxy group-containing monomer.
_CH2 = ^CR1 -COO- ^R2 -OCO- ^R3 -COOH (1)
Here, R ¹ in the above formula (1) is hydrogen or a methyl group. R ² and R ³ are divalent linking groups (specifically, organic groups having 1 to 20 carbon atoms (eg, 2 to 10, preferably 2 to 5)) and may be the same. can be different. R ² and R ³ in formula (1) above 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 of 2 to 5 carbon atoms. Specific examples of the carboxy group-containing monomer represented by the above formula (1) include, for example, 2-(meth)acryloyloxyethylhexahydrophthalic acid, 2-(meth)acryloyloxyethyl-phthalic acid, 2-( meth)acryloyloxyethyl-2-hydroxyethyl-phthalic acid, 2-(meth)acryloyloxyethyl-succinic acid, 2-(meth)acryloyloxypropyl hexahydrohydrogen phthalate, 2-(meth)acryloyloxypropylhydrogen phthalate, 2-(meth)acryloyloxypropyl tetrahydrohydrogen phthalate, and the like. A carboxy group-containing monomer can be used individually by 1 type or in combination of 2 or more types. A hydroxyl group-containing monomer and a carboxy group-containing monomer may be used in combination.

The content of the monomer (A2) in the monomer component constituting the acrylic polymer is not particularly limited, and can be set according to the purpose. In some embodiments, the content of the monomer (A2) can be, for example, 0.01% by weight or more, 0.1% by weight or more, or 0.5% by weight or more. From the viewpoint of obtaining a higher use effect, in some embodiments, the content of the monomer (A2) is preferably 1% by weight or more, may be 2% by weight or more, or may be 4% by weight or more. . The upper limit of the content of the monomer (A2) in the monomer component is set so that the sum with the content of the monomer (A1) does not exceed 100% by weight. In some embodiments, the content of the monomer (A2) is, for example, 30% by weight or less or 25% by weight or less. From the viewpoint of facilitating conversion, it is preferably 20% by weight or less, more preferably 15% by weight or less, may be less than 12% by weight, may be less than 10% by weight, or may be less than 7% by weight. . In some preferred embodiments, the content of the monomer (A2) is less than 5% by weight, more preferably less than 3% by weight, and 1.5% by weight from the viewpoint of lowering the elastic modulus of the pressure-sensitive adhesive. It may be below.

The total content of the monomer (A1) and the monomer (A2) in the monomer component constituting the acrylic polymer may be, for example, 31% by weight or more, preferably 51% by weight or more, and may be 61% by weight or more. , 71% by weight or more. In some aspects, the total content of the monomer (A1) and the monomer (A2) in the monomer components constituting the acrylic polymer is, for example, 76% by weight from the viewpoint of favorably exhibiting the effects of these monomers. or more, preferably 81 wt% or more, 86 wt% or more, 91 wt% or more, 96 wt% or more, 99 wt% or more, substantially 100 wt% It's okay.

(Monomer A3)
In some preferred embodiments, the monomer component constituting the acrylic polymer may further contain an alkyl (meth)acrylate (hereinafter also referred to as "monomer (A3)") in addition to the monomer (A1). Monomer (A3) can help reduce the modulus of the adhesive. It can also help improve the compatibility of additives in the adhesive and adhesive properties such as adhesive strength. Monomer (A3) can be used individually by 1 type or in combination of 2 or more types.

As the monomer (A3), an alkyl (meth)acrylate having a straight or branched chain alkyl group having 1 to 20 carbon atoms (ie, C _1-20 ) at the ester end can be preferably used. Specific examples of C _1-20 alkyl (meth)acrylates include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-(meth)acrylate, Butyl, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, (meth)acrylate ) heptyl acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, ( meth) isodecyl acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, (meth) ) heptadecyl acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, nonadecyl (meth)acrylate, eicosyl (meth)acrylate and the like, but are not limited thereto.

In some embodiments, an alkyl (meth)acrylate having a homopolymer Tg of -20°C or lower (more preferably -40°C or lower, for example -50°C or lower) is preferably employed as at least part of the monomer (A3). can. Such low Tg alkyl (meth)acrylates can help reduce the elastic modulus of the pressure-sensitive adhesive. It can also help improve adhesive properties such as adhesive strength. The lower limit of the Tg of the alkyl (meth)acrylate is not particularly limited, and may be -85°C or higher, -75°C or higher, -65°C or higher, or -60°C or higher. Specific examples of the low Tg alkyl (meth)acrylate include n-butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), heptyl acrylate, octyl acrylate, isononyl acrylate (iNA), and the like. In some other embodiments, at least a portion of the monomers (A3) may employ an alkyl (meth)acrylate having a homopolymer Tg greater than −20° C. (eg, −10° C. or higher). The upper limit of the Tg of the alkyl (meth)acrylate is, for example, 10° C. or lower, may be 5° C. or lower, or may be 0° C. or lower. Alkyl (meth)acrylates with a Tg in this range can help adjust the elastic modulus of the adhesive. Although not particularly limited, it is preferable to use the alkyl (meth)acrylate having a Tg in combination with the low Tg alkyl (meth)acrylate. A specific example of the alkyl (meth)acrylate having the above Tg is lauryl acrylate (LA).

In some embodiments using monomer (A3), it is preferred to use C _4-8 alkyl (meth)acrylates as monomer (A3). Among them, the use of C _4-8 alkyl acrylate is more preferable. The C _4-8 alkyl (meth)acrylates can be used singly or in combination of two or more. The use of C _4-8 alkyl (meth)acrylate tends to reduce the elastic modulus of the pressure-sensitive adhesive and to provide good pressure-sensitive adhesive properties (adhesive strength, etc.). In an embodiment using a C _4-8 alkyl (meth)acrylate as the monomer (A3), the proportion of the C _4-8 alkyl (meth)acrylate among the alkyl (meth)acrylates contained in the monomer component is 30% by weight or more. is preferably 50% by weight or more, more preferably 70% by weight or more, still more preferably 90% by weight or more, and may be substantially 100% by weight.

In some embodiments using monomer (A3), C _1-6 alkyl (meth)acrylates can be preferably used as monomer (A3). The use of C _1-6 alkyl (meth)acrylates allows the storage modulus in each temperature range to be adjusted. For example, it is possible to set the storage elastic modulus in the high temperature range to be relatively high, or to suppress an increase in the difference in storage elastic modulus between the low temperature range and the high temperature range. In addition, the C _1-6 alkyl (meth)acrylate tends to be excellent in copolymerizability with the monomer (A1). The C _1-6 alkyl (meth)acrylates may be used singly or in combination of two or more. The C _1-6 alkyl (meth)acrylate is preferably a C _1-6 alkyl acrylate, more preferably a C _2-6 alkyl acrylate, and even more preferably a C _4-6 alkyl acrylate. In some other aspects, 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 a C _2-4 alkyl acrylate. Preferred examples of C _1-6 alkyl (meth)acrylates include BA.

The content of C _1-6 alkyl (meth)acrylate in the monomer component constituting the acrylic polymer may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight. It can be more than that. In some embodiments, the content of the C _1-6 alkyl (meth)acrylate may be 10% by weight or more, or 15% by weight or more, from the viewpoint of lowering the elastic modulus, adhesive strength, etc. It may be 20% by weight or more, or 25% by weight or more (for example, 30% by weight or more). The upper limit of the C _1-6 alkyl (meth)acrylate content in the monomer component is, for example, less than 50% by weight, and may be less than 35% by weight. In some embodiments, from the viewpoint of maintaining a high refractive index, the content of the C _1-6 alkyl (meth)acrylate is, for example, 24% by weight or less, preferably less than 20% by weight, and 17% by weight. It is more preferably less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The technology disclosed herein can also be practiced in an embodiment that does not substantially use C _1-6 alkyl (meth)acrylates.

In some other embodiments using monomer (A3), C _7-12 alkyl (meth)acrylates can preferably be used as monomer (A3). Storage modulus can be favorably reduced by the use of C _7-12 alkyl (meth)acrylates. The C _7-12 alkyl (meth)acrylates may be used singly or in combination of two or more. The C _7-12 alkyl (meth)acrylates are preferably C _7-10 alkyl acrylates, more preferably C _7-9 alkyl acrylates, and even more preferably C ₈ alkyl acrylates. Examples of C _7-12 alkyl (meth)acrylates include 2EHA, iNA, LA, and preferred examples include 2EHA.

The content of C _7-12 alkyl (meth)acrylate in the monomer component constituting the acrylic polymer may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight. It can be more than that. In some aspects, the content of the C _7-12 alkyl (meth)acrylate may be 10% by weight or more, or 15% by weight or more, from the viewpoint of lowering the elastic modulus, adhesive strength, etc. It may be 20% by weight or more, or 25% by weight or more (for example, 30% by weight or more). The upper limit of the C _7-12 alkyl (meth)acrylate content in the monomer component is, for example, less than 50% by weight, and may be less than 35% by weight. In some embodiments, from the viewpoint of maintaining a high refractive index, the content of the C _7-12 alkyl (meth)acrylate is, for example, 24% by weight or less, preferably less than 20% by weight, and 17% by weight. It is more preferably less than 12% by weight, less than 7% by weight, less than 3% by weight, or less than 1% by weight. The technology disclosed herein can also be practiced in a manner substantially free of C _7-12 alkyl (meth)acrylates.

In some embodiments using the monomer (A3), at least part of the monomer (A3) is preferably an alkyl acrylate from the viewpoint of lowering the elastic modulus. The use of alkyl acrylate is also advantageous in terms of adhesive properties such as adhesive strength. For example, it is preferable that 50% by weight or more of the monomer (A3) is an alkyl acrylate, and the proportion of the alkyl acrylate in the monomer (A3) is more preferably 75% by weight or more, still more preferably 90% by weight or more, Substantially 100% by weight of monomer (A3) may be alkyl acrylate. An aspect may be employed in which only one or two or more alkyl acrylates are used as the monomer (A3) and no alkyl methacrylate is used.

In the aspect in which the monomer component contains an alkyl (meth)acrylate, the content of the alkyl (meth)acrylate in the monomer component can be set so that the effect of use is appropriately exhibited. In some aspects, the content of the alkyl (meth)acrylate may be, for example, 1% by weight or more, 3% by weight or more, 5% by weight or more, or 8% by weight or more. The upper limit of the content of the monomer (A3) in the monomer component is set so that the total content of the monomers (A1) and (A2) does not exceed 100% by weight, for example, less than 50% by weight, and 35% by weight. % may be less. In some embodiments, the content of the monomer (A3) can be, for example, 24% by weight or less. Since the refractive index of alkyl (meth)acrylates is generally relatively low, in order to increase the refractive index, the content of the monomer (A3) in the monomer component is limited, and the content of the monomer (A1) is relatively increased. It is advantageous to From this point of view, the content of the monomer (A3) is suitably less than 23% by weight of the monomer component, preferably less than 20% by weight, more preferably less than 17% by weight. It may be less than wt%, it may be less than 7 wt%, it may be less than 3 wt%, it may be less than 1 wt%. The technology disclosed herein can also be preferably carried out in a mode in which the monomer (A3) is not substantially used.

(other monomers)
The monomer component constituting the acrylic polymer may optionally contain monomers other than the monomers (A1), (A2) and (A3) (hereinafter referred to as "other monomers"). The above-mentioned other monomers can be used, for example, for the purposes of adjusting the Tg of the acrylic polymer, adjusting the adhesive performance, improving the compatibility in the adhesive layer, and the like. These other monomers may be used singly or in combination of two or more.

Examples of the other monomers include monomers having functional groups other than hydroxyl groups and carboxy groups (functional group-containing monomers). For example, other monomers capable of improving the cohesive strength 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 (e.g., aminoethyl (meth)acrylate, N,N-dimethylaminoethyl (meth)acrylate, etc.), nitrogen atom-containing rings Monomers having (e.g., N-vinyl-2-pyrrolidone, N-(meth)acryloylmorpholine, etc.), imide group-containing monomers, epoxy group-containing monomers, keto group-containing monomers, isocyanate group-containing monomers, alkoxysilyl group-containing monomers, etc. mentioned. Incidentally, among the monomers having a nitrogen atom-containing ring, some, such as N-vinyl-2-pyrrolidone, also correspond to 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 in addition to the functional group-containing monomers include vinyl ester monomers such as vinyl acetate; non-aromatic ring-containing (meth)acrylates such as cyclohexyl (meth)acrylate and isobornyl (meth)acrylate; 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; and the like. A preferred example of other monomers that can be used for the purpose of improving the flexibility of the pressure-sensitive adhesive is ethoxyethoxyethyl acrylate (also known as ethyl carbitol acrylate, Tg of homopolymer: -67°C).

When the above-mentioned other monomers are used, the amount thereof is not particularly limited, and can be appropriately set within a range in which the total amount of the monomer components does not exceed 100% by weight. From the viewpoint of making it easier to exhibit the effect of improving the refractive index by using the monomer (A1), the content of the other monomer in the monomer component can be, for example, approximately 35% by weight or less, and approximately 25% by weight or less (for example, 0 ~25% by weight), approximately 20% by weight or less (for example, 0 to 20% by weight), and approximately 10% by weight or less (for example, 0 to 10% by weight). Preferably it is about 5% by weight or less, for example about 1% by weight or less. The technology disclosed herein can be preferably practiced in a mode in which the monomer component does not substantially contain the above-mentioned other monomers.

In some aspects, the monomer component 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. Restricting the amount of the methacryloyl group-containing monomer to be used in this way can be advantageous from the viewpoint of achieving a pressure-sensitive adhesive that achieves a good balance between flexibility and adhesiveness and a high refractive index. The monomer component that constitutes 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 aspects, the amount of the carboxy group-containing monomer used in the monomer component constituting the acrylic polymer is limited from the viewpoint of suppressing the coloring or discoloration (eg, yellowing) of the pressure-sensitive 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, and 0 less than 0.05% by weight. The fact that the amount of the carboxy group-containing monomer used is limited in this way is due to the fact that metal materials that can be placed in contact with or in close proximity to the adhesive disclosed herein (for example, metal wiring that can be present on the adherend, It is also advantageous from the viewpoint of suppressing corrosion of metal films, etc.). The technology disclosed herein can be carried out in a mode in which the monomer component constituting the acrylic polymer does not contain a carboxy group-containing monomer.
For the same reason, in some embodiments, the monomer component constituting the acrylic polymer has an acidic functional group (including a carboxy group, a sulfonic acid group, a phosphoric acid group, etc.). preferably restricted. 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 practiced in an aspect in which the monomer component does not contain an acidic group-containing monomer (that is, an aspect in which the acrylic polymer is acid-free).

(Glass transition temperature Tg _T )
The monomer component constituting the acrylic polymer preferably has a composition such that the glass transition temperature Tg _T based on the composition of the monomer component is about 15° C. or lower. In some aspects, the glass transition temperature Tg _T is preferably 10° C. or lower, more preferably 5° C. or lower, even more preferably 1° C. or lower, and may be 0° C. or lower. In some other embodiments, the glass transition temperature Tg _T may be −10° C. or lower, −20° C. or lower, −25° C. or lower, −30° C. or lower, or −35° C. It can be below. A low glass transition temperature Tg _T can be advantageous from the viewpoint of lowering the elastic modulus of the pressure-sensitive adhesive. Further, the glass transition temperature Tg _T may be, for example, −60° C. or higher, and is preferably −50° C. or higher, more preferably more than −45° C., from the viewpoint of facilitating the increase in the refractive index of the pressure-sensitive adhesive. It may be above -40°C. In some preferred embodiments, the glass transition temperature Tg _T may be greater than -30°C, greater than -20°C, greater than -10°C, or greater than -5°C. A pressure-sensitive adhesive having both a high refractive index and a low elastic modulus can be preferably formed by using an acrylic polymer having a composition having a glass transition temperature Tg _T within the above range.

Here, the glass transition temperature Tg _T means the glass transition temperature determined by the Fox formula based on the composition of the above monomer components, unless otherwise specified. The Fox equation is a relational expression between the Tg of a copolymer and the glass transition temperature Tgi of a homopolymer obtained by homopolymerizing each of the monomers constituting the copolymer, as shown below.
1/Tg=Σ(Wi/Tgi)
In the above Fox formula, Tg is the glass transition temperature of the copolymer (unit: K), Wi is the weight fraction of the monomer i in the copolymer (weight-based copolymerization ratio), and Tgi is the homopolymer of the monomer i. represents the glass transition temperature (unit: K).
As the glass transition temperature of the homopolymer used for calculating the Tg, the value described in 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 above Polymer Handbook, the highest value is adopted. If the Tg of the homopolymer is not described in known documents, the value obtained by the measurement method described in JP-A-2007-51271 shall be used.

(Method for preparing acrylic polymer)
In the technique disclosed herein, the method for obtaining an acrylic polymer composed of such monomer components is not particularly limited, and 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 at the time of solution polymerization can be appropriately selected according to the type of monomer and solvent used, the type of polymerization initiator, etc. ° C.).

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

The initiator used for polymerization can be appropriately selected from conventionally known polymerization initiators according to the type of polymerization method. For example, one or more azo polymerization initiators such as 2,2'-azobisisobutyronitrile (AIBN) can be preferably used. Other examples of polymerization initiators include persulfates such as potassium persulfate; peroxide initiators such as benzoyl peroxide and hydrogen peroxide; substituted ethane initiators such as phenyl-substituted ethane; aromatic carbonyl compounds. ; and the like. Still another example of the polymerization initiator is a redox initiator obtained by combining a peroxide and a reducing agent. A polymerization initiator can be used individually by 1 type or in combination of 2 or more types. The amount of the polymerization initiator used may be a 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. ).

For the above polymerization, conventionally known various 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 containing no sulfur atom (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. A chain transfer agent can be used individually by 1 type or in combination of 2 or more types. When using a chain transfer agent, the amount used can be, for example, about 0.01 to 1 part by weight per 100 parts by weight of the monomer component.

The weight average molecular weight (Mw) of the acrylic polymer is not particularly limited, and is, for example, about 30×10 ⁴ or more, suitably about 50×10 ⁴ or more, and about 70×10 ⁴ or more. may be about 80×10 ⁴ or more. By using an acrylic polymer having a Mw of a predetermined value or more, it is easy to obtain an appropriate cohesive force capable of exhibiting desired adhesive properties. In addition, more additives such as plasticizers can be contained, and there is a tendency to easily achieve a desired elastic modulus. The upper limit of the Mw of the acrylic polymer is, for example, about 500×10 ⁴ or less, and from the viewpoint of adhesion performance, about 400×10 ⁴ or less (more preferably about 150×10 ⁴ or less, for example about 130×10 ^{4 or less} ). below).

Here, the Mw of the acrylic polymer can be determined by gel permeation chromatography (GPC) in terms of polystyrene. Specifically, it can be obtained by measuring under the following conditions using a GPC measurement device with the trade name "HLC-8220GPC" (manufactured by Tosoh Corporation).
[Measurement conditions of GPC]
Sample concentration: 0.2% by weight (tetrahydrofuran solution)
Sample injection volume: 10 μL
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: Product name "TSKgel SuperH-RC" 1 column (manufactured by Tosoh Corporation)
Detector: differential refractometer (RI)
Standard sample: Polystyrene

(Plasticizer)
The adhesive composition disclosed herein is characterized by containing a plasticizer in addition to the acrylic polymer. The use of a plasticizer can reduce the elastic modulus of the adhesive. In addition, in the form molded into a pressure-sensitive adhesive sheet, flexibility and conformability to deformation can be improved. A cyclic unsaturated organic compound having two or more double bond-containing rings is used as the plasticizer disclosed herein. The plasticizer is, in other words, a compound having two or more double bond-containing rings in one molecule. Therefore, the plasticizer has at least a first double bond-containing ring and a second double bond-containing ring. Having two or more double bond-containing rings can contribute to lowering the elastic modulus of the pressure-sensitive adhesive without impairing or maintaining the refractive index of the pressure-sensitive adhesive. The number of double bond-containing rings contained in the plasticizer is preferably 6 or less, may be 4 or less, or may be 3 or less, from the viewpoint of exhibiting a plasticizing effect. A plasticizer can be used individually by 1 type or in combination of 2 or more types.

Also, the plasticizer used in the technology disclosed herein is a compound that is liquid at 30°C. In this specification, the term “liquid” means exhibiting fluidity, and refers to a liquid as a substance state. Such compounds include compounds having a melting point of 30° C. or lower. Since the plasticizer is liquid at 30° C., the plasticizing effect is preferably exhibited, and the elastic modulus of the pressure-sensitive adhesive can be effectively reduced. The plasticizer is preferably a compound that is liquid at 25°C, more preferably a compound that is liquid at 20°C. By using a compound that has two or more double bond-containing rings and is liquid at 30° C. as the plasticizer, a pressure-sensitive adhesive that has both a high refractive index and a low elastic modulus can be formed.

The double bond-containing ring possessed by the plasticizer disclosed herein may be either a conjugated double bond-containing ring (typically an aromatic ring) or a non-conjugated double bond-containing ring. . The plasticizer may have at least one ring selected from an aromatic ring and a heterocyclic ring (heterocyclic ring) as the double bond-containing ring. The heterocyclic ring may have a structure included in an aromatic ring, or may have a double bond-containing heterocyclic structure different from the aromatic ring. The double bond-containing ring (typically aromatic ring) that the plasticizer may have includes a benzene ring (which may be a benzene ring constituting part of a biphenyl structure or a fluorene structure); a naphthalene ring, an indene ring, Condensed ring of azulene ring, anthracene ring, phenanthrene ring; may be a carbocyclic ring such as pyridine ring, pyrimidine ring, pyridazine ring, pyrazine ring, triazine ring, pyrrole ring, pyrazole ring, imidazole ring, triazole ring, oxazole ring, isoxazole ring, thiazole ring, thiophene ring; and other heterocyclic rings. The heteroatoms contained as ring-constituting atoms in the above heterocycle may be one or more selected from the group consisting of nitrogen, sulfur and oxygen, for example. In some embodiments, the heteroatoms that make up the heterocycle can be one or both of nitrogen and sulfur. The plasticizer may have a structure in which one or more carbon rings and one or more heterocycles are condensed, such as a dinaphthothiophene structure.

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. 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, and a glycidyloxy group. etc. are exemplified, but not limited to these. In substituents containing carbon atoms, the number of carbon atoms contained in the substituent is preferably 1-4, more preferably 1-3, and can be, for example, 1 or 2. In some embodiments, the double bond-containing ring has no substituents on the ring atoms, alkyl groups, alkoxy groups, ethylenically unsaturated groups (e.g., (meth)acryloxy groups), hydroxy groups and hydroxy It may be an aromatic ring having one or more substituents selected from the group consisting of alkyl groups. Alkyl groups, alkoxy groups, and hydroxyalkyl groups are preferably used as substituents.

In some embodiments, compounds having no ethylenically unsaturated groups can be preferably employed as plasticizers. As a result, deterioration of the pressure-sensitive adhesive composition due to heat or light (decrease in leveling properties due to progression of gelation or increase in viscosity) can be suppressed, and storage stability can be enhanced. Employing a plasticizer that does not have an ethylenically unsaturated group means that, in a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing the plasticizer, changes in elastic modulus, dimensional changes, and deformation ( It is also preferable from the viewpoint of suppressing the occurrence of warpage, waviness, etc.), optical distortion, and the like.

As the plasticizer, a high refractive index plasticizer having a refractive index of about 1.50 or more can be preferably used. By using a high refractive index plasticizer, it is possible to achieve both a high refractive index and a low elastic modulus at a higher level. The refractive index of the plasticizer is preferably about 1.51 or more, more preferably about 1.53 or more, and even more preferably about 1.55, from the viewpoint of maintaining and improving the refractive index of the pressure-sensitive adhesive while reducing the elastic modulus. It may be about 1.56 or more, about 1.58 or more, about 1.60 or more, or about 1.62 or more. In some aspects, the refractive index of the plasticizer is suitably 2.50 or less, and 2.00 or less, from the viewpoint of ease of preparation of the pressure-sensitive adhesive composition, compatibility in the pressure-sensitive adhesive, and the like. and may be 1.90 or less, 1.80 or less, or 1.70 or less.
The refractive index of the plasticizer is measured using an Abbe refractometer under conditions of a measurement wavelength of 589 nm and a measurement temperature of 25° C. in the same manner as the refractive index of the monomer. If the manufacturer or the like provides the nominal value of the refractive index at 25° C., the nominal value can be adopted.

The molecular weight of the plasticizer is not particularly limited, but usually one having a molecular weight smaller than that of the acrylic polymer is used. The molecular weight of the plasticizer is suitably 30,000 or less, advantageously 25,000 or less, and may be less than 10,000 (e.g., less than 5,000), from the viewpoint of facilitating the expression of the plasticizing effect. It may be less than 3000. In some embodiments, the molecular weight of the plasticizer is preferably 2000 or less, more preferably 1200 or less, even more preferably 900 or less, may be 600 or less, may be 500 or less, may be 400 or less, may be 300 It may be less than or equal to 250 or less (for example, 220 or less). It may be advantageous from the viewpoint of improving the compatibility in the pressure-sensitive adhesive layer that the molecular weight of the plasticizer is not too large. Further, the molecular weight of the plasticizer is suitably 100 or more, preferably 130 or more, more preferably 150 or more, more preferably 170 or more, from the viewpoint of easily exhibiting a sufficient plasticizing effect. , 200 or more, 220 or more, or 250 or more. It is preferable that the molecular weight of the plasticizer is not too low from the viewpoint of the heat resistance of the pressure-sensitive adhesive sheet and the suppression of contamination of the adherend. In some embodiments, the molecular weight of the plasticizer is, for example, 300 or greater, suitably 315 or greater, and may be 350 or greater. Since a plasticizer with a large molecular weight is difficult to vaporize, the use of a plasticizer with a large molecular weight in an adhesive makes it easier to obtain an adhesive that can exhibit stable properties. Also, a plasticizer with a large molecular weight is less likely to move within the adhesive. Therefore, for example, the plasticizer is less likely to migrate to the surface of the pressure-sensitive adhesive to affect the pressure-sensitive adhesive properties. The molecular weight of the plasticizer is more preferably 400 or more, still more preferably 450 or more, particularly preferably 500 or more, and may be 530 or more.
As the molecular weight of the plasticizer, a molecular weight calculated based on the chemical structure is used. When the nominal value of the molecular weight is provided by the manufacturer or the like, the nominal value can be adopted.

In some embodiments, as a plasticizer, a compound having a structure in which two or more non-condensed double bond-containing rings (typically aromatic rings) are linked via a linking group, two or more non-condensed double bond-containing Compounds having a structure in which rings (typically aromatic rings) are directly (that is, not through other atoms) chemically bonded, compounds having a condensed double bond-containing ring (typically aromatic ring) structure, fluorene a compound having a structure, a compound having a dinaphthothiophene structure, a compound having a dibenzothiophene structure, etc., and being liquid at 30°C (e.g., 25°C or 20°C). Any of the above may be used.

In embodiments using a compound having a structure in which two or more non-fused double bond-containing rings are bonded via a linking group as the plasticizer, the linking group is, for example, an oxy group (—O—), a thiooxy group (—S —), an oxyalkylene group (eg —O—(CH ₂ ) _n — group, where n is 1 to 3, preferably 1), a thiooxyalkylene group (eg —S—(CH ₂ ) _n — group, where where n is 1 to 3, preferably 1), a linear alkylene group (that is, —(CH ₂ ) _n — group, where n is 1 to 6, preferably 1 to 3), the above oxyalkylene group, the above thiooxy The alkylene group and the alkylene group in the linear alkylene group may be a partially halogenated group or a fully halogenated group. The linking group may have a siloxane bond (--SiOR--) or an ester bond. In the plasticizer, the linking group that connects the first double bond-containing ring (non-fused ring) and the second double bond-containing ring (non-fused ring) may also be selected from the same types as above. From the viewpoint of lowering the elastic modulus of the pressure-sensitive adhesive, preferred examples of the linking group include an oxy group, a thiooxy group, an oxyalkylene group and a linear alkylene group. The number of atoms of the linking group is not particularly limited, and is, for example, 1 to 30, may be 1 to 25, may be 1 to 20, is suitably 1 to 18, preferably 1 to 12, more preferably 1 to 10, more preferably 1 to 8, particularly preferably 1 to 5, may be 1 to 3, or may be 1 or 2. The number of atoms in the linking group refers to the minimum number of atoms required to reach from one non-condensed double bond-containing ring to the other non-condensed double bond-containing ring. For example, when the linking group consists of a linear alkylene group (ie, -(CH ₂ ) _n - group), the number n is the number of atoms in the linking group. Further, for example, when the linking group is an oxyethylene group (that is, —(C ₂ H ₄ O) _n — group), the sum of 2 carbon atoms and 1 oxygen atom constituting the oxyethylene group is 3 and n The product (3n) of is the number of atoms of the linking group. Preferable examples of the above compounds include compounds having a phenoxybenzyl group. Examples of such compounds include phenoxybenzyl (meth)acrylate (e.g. m-phenoxybenzyl (meth)acrylate), phenoxybenzyl alcohol, oxybis[(alkoxyalkyl)benzene] (e.g. 4,4′-oxybis[(methoxy methyl)benzene]) and the like. Other examples of the above compounds include silicone plasticizers (specifically, siloxane compounds) described later.

The compound having a structure in which two or more double bond-containing rings (non-condensed rings) are directly chemically bonded may be, for example, a biphenyl structure-containing compound, a triphenyl structure-containing compound, and the like. Examples of compounds having a condensed double bond-containing ring structure include naphthalene ring-containing compounds and anthracene ring-containing compounds. Specific examples include 1-acetonaphthone and the like. In addition, since the compound having the fluorene structure includes a structural portion in which two benzene rings are directly chemically bonded, the concept of a compound having a structure in which the two or more double bond-containing rings (non-condensed rings) are directly chemically bonded. subsumed in The compound having the dinaphthothiophene structure is based on the concept of the compound having the condensed double bond-containing ring structure by including a naphthalene structure and by having a structure in which a thiophene ring and two naphthalene structures are condensed. subsumed. Since the compound having the dibenzothiophene structure has a structure in which a thiophene ring and two benzene rings are condensed, it is included in the concept of the compound having the condensed double bond-containing ring structure.

In some embodiments, a silicone plasticizer is used as the plasticizer. By using a silicone-based plasticizer, a stable plasticizing effect can be easily obtained, and a high adhesive strength can be easily obtained, so that the refractive index, flexibility and adhesive strength of the pressure-sensitive adhesive can be improved in a well-balanced manner. As the silicone-based plasticizer, a compound having two or more double bond-containing rings and being liquid at 30° C. can be used without particular limitation. Specifically, the silicone-based plasticizer is a siloxane compound, the number of Si atoms in the compound is 1 or more (typically 2 or more), and the upper limit is not particularly limited, for example about 10 or less. can be In one molecule of the silicone plasticizer, the Si atom and the double bond-containing ring may or may not be directly bonded. At least one of the Si atoms is preferably directly bonded to at least one double bond-containing ring. Silicone plasticizers can be used singly or in combination of two or more.

In some embodiments, the silicone-based plasticizer is composed of a siloxane compound having 2 to 5 Si atoms, and at least one of the Si atoms has two or more double bond-containing rings on the Si atom. Conjugates can be used. A silicone plasticizer composed of a siloxane compound having such a structure can exert a plasticizing effect based on the flexibility of the siloxane structure, and also has a double-layer structure having two or more Si atoms and two or more Si atoms. By having at least one Si atom to which the bond-containing ring is bonded, the ease of blending with the material to be plasticized, the compatibility, and the stability of the plasticizing effect (for example, the elastic modulus for storage under moist heat low rate of increase) can be achieved in a balanced manner. From the viewpoint of chemical stability, the siloxane compound preferably has no hydrogen atoms bonded to Si atoms. That is, a siloxane compound having no Si—H bond is preferred.

When the number of Si atoms in the siloxane compound is 3 or more, the siloxane compound may be chain-like or cyclic, but is preferably a chain-like siloxane compound from the viewpoint of volatilization suppression. The chain siloxane compound having 3 or more Si atoms may be linear or branched, but is preferably linear from the viewpoint of obtaining a higher plasticizing effect. Hereinafter, unless otherwise specified, a siloxane compound having 3 or more Si atoms means a chain (typically linear) siloxane compound having 3 or more Si atoms.

Each double bond-containing ring of the silicone plasticizer may independently be a conjugated double bond-containing ring (typically an aromatic ring) or a non-conjugated double bond-containing ring. good. The plasticizer may have at least one ring selected from an aromatic ring and a heterocyclic ring (heterocyclic ring) as the double bond-containing ring. The heterocyclic ring may have a structure included in an aromatic ring, or may have a double bond-containing heterocyclic ring structure different from the aromatic ring. The double bond-containing ring (typically aromatic ring) that the plasticizer may have may be a carbocyclic ring such as a benzene ring or a naphthalene ring, a pyridine ring, an imidazole ring, a triazole ring, an oxazole ring, and a thiazole ring. It may be a heterocyclic ring such as a ring or a thiophene ring. The heteroatoms included as ring-constituting atoms in the above heterocycle may be one or more selected from the group consisting of nitrogen, sulfur and oxygen, for example. In some embodiments, the heteroatoms that make up the heterocycle can be one or both of nitrogen and sulfur.

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. When having a substituent, examples of the substituent include an alkyl group, an alkoxy group, a hydroxyl group, a halogen atom (fluorine atom, chlorine atom, bromine atom, etc.), a hydroxyalkyl group, a hydroxyalkyloxy group, a glycidyloxy group, and the like. but not limited to: In substituents containing carbon atoms, the number of carbon atoms contained in the substituent is preferably 1-4, more preferably 1-3, and can be, for example, 1 or 2. In some aspects, each double bond-containing ring of the silicone plasticizer is independently an aromatic ring having no substituents on the ring-constituting atoms, an alkyl group, an alkoxy group, a hydroxy group and a hydroxyalkyl is selected from the group consisting of aromatic rings having one or more substituents selected from the group consisting of groups (preferably the group consisting of alkyl groups and alkoxy groups). For example, each double bond-containing ring of the silicone plasticizer is independently selected from aromatic rings (preferably carbocyclic rings) having no substituents on the ring-constituting atoms. In some preferred embodiments, each double bond-containing ring of the silicone plasticizer is a benzene ring.

The number of Si atoms in the siloxane compound is selected from the viewpoint of ease of exhibiting the plasticizing effect and its stability (for example, suppression of increase in elastic modulus due to volatilization and dissipation of the plasticizer from the material containing the plasticizer). , is preferably 3 or more. The number of Si atoms in the siloxane compound is preferably 4 or less, more preferably 3 or less, from the viewpoint of compatibility in the pressure-sensitive adhesive. Among them, a silicone plasticizer containing 3 Si atoms in the siloxane compound, that is, a silicone plasticizer composed of a trisiloxane compound is preferable.

The number of double bond-containing rings (e.g., benzene rings with or without substituents) possessed by the siloxane compound is at least 2, and the heat resistance of the plasticizing effect (e.g., elasticity against storage under moist heat) from the viewpoint of a low rate of increase in rate), it is preferably 3 or more, more preferably 4 or more, and may be 5 or more. In addition, the number of double bond-containing rings of the siloxane compound is typically 2n+2 or less, where n is the number of Si atoms in the siloxane compound, and from the viewpoint of enhancing the plasticizing effect, it is suitable to be 2n+1 or less. and is preferably 2n or less, may be 2n−1 or less, or may be 2n−2 or less. For example, in the embodiment in which the siloxane compound is a trisiloxane compound, the number of double bond-containing rings possessed by the trisiloxane compound is typically 8 or less, and may be, for example, 2 or more and 7 or less, or 3 or more. It may be 7 or less, or 4 or more and 7 or less. Among them, trisiloxane compounds having 4 or more and 6 or less (eg, 4 or 5) double bond-containing rings (eg, unsubstituted benzene rings) are preferred.

In some embodiments, at least one of the Si atoms contained in the siloxane compound (typically, the Si atoms constituting the siloxane chain) is Si having two or more double bond-containing rings bonded thereto. is an atom. From the viewpoint of improving the stability of the plasticizing effect, the number of Si atoms to which two or more double bond-containing rings are bonded in the siloxane compound may be two or more. In the siloxane compound having 3 or more Si atoms, the number of Si atoms to which two or more double bond-containing rings are bonded may be 2 or more, or 3 or more. Where n is the number of Si atoms in the compound, it may be n or less, n-1 or less, or n-2 or less. In some aspects, from the viewpoint of enhancing the plasticizing effect, at least one of the Si atoms contained in the siloxane compound (preferably a siloxane compound having 3 or more Si atoms) is bonded to the Si atom. The number of double bond-containing rings is 1 or 0. For example, a linear siloxane compound having 3 or more Si atoms and 5 or less Si atoms at both ends independently has two or three (preferably two) double bond-containing rings, and both A siloxane compound having a structure in which each non-terminal Si atom independently has one double bond-containing ring or no double bond-containing ring is preferred.

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

In some aspects, the siloxane compound preferably does not have an ethylenically unsaturated group (including those in which the double bond in the double bond-containing ring is an ethylenic double bond). A silicone plasticizer composed of a siloxane compound having no ethylenically unsaturated group is advantageous from the viewpoint of the stability of the plasticizing effect of the plasticizer. It is also preferable from the viewpoint of the storage stability of the sheet, and from the viewpoint of suppressing changes in elastic modulus, dimensional changes and deformations (warping, waviness, etc.), optical distortion, etc. caused by reactions of ethylenically unsaturated groups.

In some embodiments of the silicone-based plasticizer disclosed herein, at least one of the Si atoms contained in the siloxane compound (at least two Si atoms in the siloxane compound having 3 or more Si atoms) has a plasticizing effect. From the viewpoint of enhancement, it is preferred to have at least one methyl group on the Si atom. For example, it is preferred that the Si atoms located at both ends of the siloxane chain each independently have one or two (more preferably one) methyl groups. In some preferred embodiments, each Si atom contained in the siloxane compound independently has one or two methyl groups. According to the silicone plasticizer composed of a siloxane compound having such a structure, the plasticizing effect due to the flexibility of the siloxane structure and the structure in which at least one Si atom is bonded to two or more double bond-containing rings It is possible to achieve both the stability of the plasticizing effect and the stability of the plasticizing effect in a well-balanced manner.

In some aspects, the sum of the number of substituents bonded to the Si atoms, where n is the number of Si atoms contained in the siloxane compound (hereinafter also referred to as the total number of substituents) is typically is 2n+2, at least two of which are double bond-containing rings. In some embodiments, the ratio SR of the number of double bond-containing rings (preferably aromatic carbocyclic rings, such as benzene rings) to the total number of substituents in the silicone plasticizer is at least 16% and not less than 20%. or 25% or more. As the ratio SR increases, the heat resistance of the silicone plasticizer and the stability of the plasticizing effect of the silicone plasticizer generally tend to improve. In some embodiments, the ratio SR is advantageously 33% or more, preferably 40% or more, more preferably 50% or more (for example, 60% or more), and 65% or more. , or 75% or more. The ratio SR may be 100%, but from the viewpoint of ease of blending and compatibility, it is advantageous to be 85% or less, preferably 80% or less, and may be 75% or less. It may be 65% or less, or 60% or less (for example, 50% or less).

In some aspects, the molecular weight of the silicone plasticizer (specifically, a siloxane compound) is suitably 400 or more, and advantageously 430 or more, from the viewpoint of stability of the plasticizing effect. and is preferably 460 or more, may be 490 or more, or may be 520 or more. Further, the molecular weight of the siloxane compound is suitably 900 or less, advantageously 850 or less, and preferably 700 or less, from the viewpoint of plasticizing effect, ease of blending, compatibility, etc. It is preferably 650 or less, and may be 600 or less, 560 or less, 540 or less, or 500 or less.

As the molecular weight of the siloxane compound, a molecular weight calculated based on the chemical structure, or a value measured using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) can be used. When the nominal value of the molecular weight is provided by the manufacturer or the like, the nominal value can be adopted.

The refractive index of the silicone plasticizer disclosed herein is not particularly limited, and may be, for example, within the range of about 1.30 to 1.80. From the viewpoint of suppressing a decrease in the refractive index of a material (for example, a pressure-sensitive adhesive) in which the plasticizer is blended and achieving a low elastic modulus, the silicone-based plasticizer according to some embodiments has a refractive index of 1.45 or more. preferably 1.50 or more, more preferably 1.52 or more (eg, 1.53 or more or 1.54 or more), and 1.55 or more (eg, 1.54 or more). 56 or more or 1.57 or more). Moreover, the refractive index of the silicone plasticizer may be, for example, 1.70 or less, 1.65 or less, or 1.60 or less from the viewpoint of ease of blending, compatibility, and the like.

In some embodiments, an ethylene glycol-based compound having two or more double bond-containing rings in one molecule can be used as a plasticizer. The number of oxyethylene units (that is, —(C ₂ H ₄ O)—units) possessed by the ethylene glycol-based compound is, for example, 1 to 10, may be 1 to 6, or may be 2 to 4. The ethylene glycol-based compound has two or more non-condensed double bond-containing rings containing oxyethylene units (for example, 1 to 10, preferably 1 to 6, typically 2 to 4 oxyethylene units) as linking groups. ) can be a compound having a structure linked via Such compounds may have one or more ester groups. Examples of the ethylene glycol-based compound include compounds having a structure in which two or more benzoic acids are linked to ethylene glycol, diethylene glycol, triethylene glycol or polyethylene glycol via an ester bond.

Moreover, the technology disclosed herein can be carried out in a mode in which the ethylene glycol-based compound is not used as a plasticizer, or the amount used is limited. For example, the content of the ethylene glycol-based compound in the plasticizer contained in the pressure-sensitive adhesive composition can be less than 90% by weight. The content of the ethylene glycol-based compound in the plasticizer may be less than 50% by weight, may be less than 10% by weight, may be less than 3% by weight, or may be less than 1% by weight. , it may not substantially contain the above ethylene glycol-based compound as a plasticizer. Similarly, in the adhesive composition, the amount of the ethylene glycol-based compound used relative to 100 parts by weight of the acrylic polymer can be less than 0.5 parts by weight, and may be less than 0.1 parts by weight.

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

The amount of the plasticizer to be used is not particularly limited, and can be set according to the purpose. From the viewpoint of reducing the elastic modulus of the pressure-sensitive adhesive, the amount of the plasticizer used relative to 100 parts by weight of the acrylic polymer may be, for example, 1 part by weight or more, or may be 10 parts by weight or more. In some preferred embodiments, the amount of the plasticizer used relative to 100 parts by weight of the acrylic polymer is more than 15 parts by weight, may be 20 parts by weight or more, or may be 30 parts by weight or more (for example, more than 30 parts by weight). More preferably 40 parts by weight or more, more preferably 50 parts by weight or more, particularly preferably 60 parts by weight or more, may be 75 parts by weight or more, or may be 90 parts by weight or more. For example, when using the above-mentioned ethylene glycol-based compound as a plasticizer, it is preferable to use more than 30 parts by weight (for example, 40 parts by weight or more, further 50 parts by weight or more) with respect to 100 parts by weight of the acrylic polymer. . In addition, from the viewpoint of achieving both a high refractive index and a low elastic modulus of the pressure-sensitive adhesive in a well-balanced manner, the amount of the plasticizer used relative to 100 parts by weight of the acrylic polymer is preferably about 200 parts by weight or less. It is preferably 150 parts by weight or less, more preferably 120 parts by weight or less, may be 100 parts by weight or less, may be 80 parts by weight or less, or may be 70 parts by weight or less. In some aspects in which adhesive properties are emphasized more, the amount of the plasticizer used with respect to 100 parts by weight of the acrylic polymer may be 45 parts by weight or less, or may be 35 parts by weight or less.

(Additive (H _RO ))
The pressure-sensitive adhesive composition disclosed herein may optionally contain an organic material having a higher refractive index than the acrylic polymer as an additive. Hereinafter, such an organic material may be referred to as an "additive (H _RO )". Here, the above "H _RO " represents an organic material with a high refractive index (High Refractive index). By using the additive (H _RO ) and the acrylic polymer in combination, it is possible to realize a pressure-sensitive adhesive that satisfactorily achieves both refractive index and pressure-sensitive adhesive properties (peel strength, flexibility, etc.). The organic materials used as additives (H _RO ) may be polymeric or non-polymeric. Moreover, it may or may not have a polymerizable functional group. In this specification, the additive (H _RO ) is defined as different from the compound used as the plasticizer described above. Therefore, the additive (H _RO ) is specifically not liquid at 30° C. (eg 25° C. or 20° C.). Additives (H _RO ) can be used singly or in combination of two or more.

The refractive index of the additive (H _RO ) is not limited to a specific range because it can be set within an appropriate range in relation to the refractive index of the acrylic polymer. The refractive index of the additive (H _RO ) can be selected, for example, from a range greater than 1.55, greater than 1.56 or greater than 1.57 and higher than the refractive index of the acrylic polymer. From the viewpoint of increasing the refractive index of the adhesive, in some aspects, the refractive index of the additive (H _RO ) is advantageously 1.58 or more, preferably 1.60 or more, It is more preferably 1.63 or more, may be 1.65 or more, may be 1.70 or more, or may be 1.75 or more. With a higher refractive index additive (H _RO ), the desired refractive index can be achieved even with a smaller amount of additive (H _RO ). This is preferable from the viewpoint of suppressing deterioration of adhesive properties and optical properties. The upper limit of the refractive index of the additive (H _RO ) is not particularly limited. 000 or less, 2.500 or less, 2.000 or less, 1.950 or less, 1.900 or less, or 1.850 or less.
The refractive index of the additive (H _RO ) is measured using an Abbe refractometer under conditions of a measurement wavelength of 589 nm and a measurement temperature of 25° C. in the same manner as the refractive index of the monomer. If the manufacturer or the like provides the nominal value of the refractive index at 25° C., the nominal value can be adopted.

The difference between the refractive index n _b of the additive (H _RO ) and the refractive index _na of the acrylic polymer, that is, n _{b −na} (hereinafter also referred to as “Δn _A ”) is set to be greater than 0. be done. In some embodiments, Δn _A is, for example, 0.02 or greater, 0.05 or greater, 0.07 or greater, 0.10 or greater, 0.15 or greater, 0.20 or greater. Alternatively, it may be 0.25 or more. By selecting the acrylic polymer and the additive (H _RO ) so that Δn _A becomes larger, the effect of improving the refractive index by using the additive (H _RO ) tends to increase. Further, from the viewpoint of compatibility of the additive (H _RO ) in the adhesive, in some embodiments, Δn _A may be, for example, 0.70 or less, 0.60 or less, or 0.50 or less. 0.40 or less, or 0.35 or less.

In some embodiments, the difference between the refractive index n _b of the additive (H _RO ) and the refractive index n _T of the adhesive containing the additive (H _RO ), i.e., n _b −n _T (hereinafter “Δn _B ”) may be set to be greater than zero. In some embodiments, Δn _B is, for example, 0.02 or greater, 0.05 or greater, 0.07 or greater, 0.10 or greater, 0.15 or greater, 0.20 or greater. Alternatively, it may be 0.25 or more. By selecting the composition of the pressure-sensitive adhesive and the additive (H _RO ) so that Δn _B becomes larger, the effect of improving the refractive index by using the additive (H _RO ) tends to increase. In addition, in some embodiments, Δn _B may be, for example, 0.70 or less, 0.60 or less, or 0.50 It may be less than or equal to 0.40 or less or 0.35 or less.

The molecular weight of the organic material used as the additive (H _RO ) is not particularly limited and can be selected depending on the purpose. From the viewpoint of achieving a good balance between the effect of increasing the refractive index and other properties (e.g., flexibility suitable for adhesives, optical properties such as haze), in some embodiments, the molecular weight of the additive (H _RO ) is suitably less than about 10000, preferably less than 5000, more preferably less than 3000 (e.g. less than 1000), may be less than 800, may be less than 600, may be less than 500, It may be less than 400. It may be advantageous from the viewpoint of improving the compatibility in the adhesive that the molecular weight of the additive (H _RO ) is not too large. Moreover, the molecular weight of the additive (H _RO ) may be, for example, 130 or more, or 150 or more. In some aspects, the molecular weight of the additive (H _RO ) is preferably 170 or more, more preferably 200 or more, more preferably 230, from the viewpoint of increasing the refractive index of the additive (H _RO ). 250 or more, 270 or more, 500 or more, 1000 or more, or 2000 or more. In some embodiments, a polymer with a molecular weight of about 1000 to 10000 (eg, 1000 or more and less than 5000) can be used as the additive (H _RO ).
As the molecular weight of the additive (H _RO ), for a non-polymer or a polymer with a low degree of polymerization (for example, about 2- to 5-mers), the molecular weight calculated based on the chemical structure, or the matrix-assisted laser desorption/ionization Measurements using time-of-flight mass spectrometry (MALDI-TOF-MS) can be used. If the additive (H _RO ) 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. When the nominal value of the molecular weight is provided by the manufacturer or the like, the nominal value can be adopted.

Examples of organic materials that can be selected as the additive (H _RO ) include organic compounds having an aromatic ring, organic compounds having a heterocyclic ring (which may be an aromatic ring or a non-aromatic heterocyclic ring), and the like. including but not limited to:

The aromatic ring of the organic compound having an aromatic ring (hereinafter also referred to as "aromatic ring-containing compound") used as the additive (H _RO ) is the same as the aromatic ring of the compound used as the monomer (A1). can be selected from

The aromatic ring may or may not have one or more substituents on the ring-constituting atoms. 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, and a glycidyloxy group. etc. are exemplified, but not limited to these. In the substituent containing carbon atoms, the number of carbon atoms contained in the substituent is, for example, 1 to 10, preferably 1 to 6, preferably 1 to 4, more preferably 1 to 3. and can be, for example, 1 or 2. In some embodiments, the aromatic ring has no substituents on the ring-constituting atoms, or has one or more substituents selected from the group consisting of alkyl groups, alkoxy groups and halogen atoms (e.g., bromine atoms). can be an aromatic ring having

Examples of aromatic ring-containing compounds that can be used as additives (H _RO ) include: compounds that can be used as monomers (A1); oligomers that contain compounds that can be used as monomers (A1) as monomer units; monomers (A1 ), except for a group having an ethylenically unsaturated group (which may be a substituent bonded to a ring-constituting atom) or a portion constituting an ethylenically unsaturated group among the groups, a hydrogen atom or A compound having a structure substituted with a group having no ethylenically unsaturated group (e.g., hydroxyl group, amino group, halogen atom, alkyl group, alkoxy group, hydroxyalkyl group, hydroxyalkyloxy group, glycidyloxy group, etc.); include, but are not limited to, those not falling under the plasticizers disclosed herein.

In some embodiments, as the additive (H _RO ), an organic compound having two or more aromatic rings in one molecule (hereinafter referred to as "multiple aromatic ring-containing compound ”) 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. Also, the compound containing multiple aromatic rings may be a polymer or a non-polymer. Further, the 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-mers) containing multiple aromatic ring-containing monomers as monomer units. obtain. The above oligomers are, for example: homopolymers of monomers containing multiple aromatic rings; copolymers of two or more monomers containing multiple aromatic rings; copolymerization of one or more monomers containing multiple aromatic rings with other monomers. coalescence; and the like. The above-mentioned other monomer may be an aromatic ring-containing monomer that does not correspond to a monomer containing multiple aromatic rings, a monomer having no aromatic ring, or 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 linked via a linking group, two or more non-fused aromatic rings directly (i.e., other atoms compounds having a chemically bonded structure, compounds having a condensed aromatic ring structure, compounds having a fluorene structure, compounds having a dinaphthothiophene structure, compounds having a dibenzothiophene structure, and the like. The compounds containing multiple aromatic rings may be used singly or in combination of two or more.

Examples of organic compounds having a heterocyclic ring (hereinafter also referred to as heterocyclic ring-containing organic compounds) that can be options for the additive (H _RO ) include thioepoxy compounds, compounds having a triazine ring, and the like. Examples of thioepoxy compounds include bis(2,3-epithiopropyl)disulfide and its polymer (refractive index: 1.74) described in Japanese Patent No. 3712653. Examples of compounds having a triazine ring include compounds having at least one (eg, 3 to 40, preferably 5 to 20) triazine rings in one molecule. In addition, since the triazine ring has aromaticity, the compound having a triazine ring is also included in the concept of the compound containing the aromatic ring, and the compound having multiple triazine rings is also included in the concept of the compound containing multiple aromatic rings. be done.

In some embodiments, a compound having no ethylenically unsaturated groups can be preferably employed as the additive (H _RO ). As a result, deterioration of the pressure-sensitive adhesive composition due to heat or light (decrease in leveling properties due to progression of gelation or increase in viscosity) can be suppressed, and storage stability can be enhanced. Employing an additive (H _RO ) that does not have an ethylenically unsaturated group prevents a dimensional change due to reaction of the ethylenically unsaturated group in a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing the additive (H _RO ). It is also preferable from the viewpoint of suppressing deformation (warpage, waviness, etc.), generation of optical distortion, and the like.

In embodiments using oligomers as additives (H _RO ), the oligomers can be obtained by polymerizing the corresponding monomer components by known methods. When the oligomer is produced by radical polymerization, the polymerization can be carried out by appropriately adding a polymerization initiator, a chain transfer agent, an emulsifier, etc. used for radical polymerization to the monomer component. The polymerization initiator, chain transfer agent, emulsifier and the like used in the radical polymerization are not particularly limited and can be appropriately selected and used. The weight-average molecular weight of the oligomer can be controlled by adjusting the amount of the polymerization initiator and the chain transfer agent used and the reaction conditions, and the amount used is appropriately adjusted according to these types.
Examples of the chain transfer agent include lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, α-thioglycerol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimercapto-1-propanol, and the like. be done. A chain transfer agent may be used individually by 1 type, and may be used in mixture of 2 or more types. The amount of the chain transfer agent used can be set according to the composition of the monomer components used in the synthesis of the oligomer, the type of the chain transfer agent, etc., so as to obtain an oligomer having a desired weight-average molecular weight. In some embodiments, the amount of the chain transfer agent used for 100 parts by weight of the total amount of monomers used in the synthesis of the oligomer is suitably about 15 parts by weight or less, may be 10 parts by weight or less, or may be 5 parts by weight. It may be less than a degree. The lower limit of the amount of the chain transfer agent to be used with respect to 100 parts by weight of the total amount of monomers used for the synthesis of the oligomer is not particularly limited. It may be 5 parts by weight or more, or 1 part by weight or more.

The amount of the additive (H _RO ) used relative to 100 parts by weight of the acrylic polymer (the total amount thereof when using multiple types of compounds) is not particularly limited as long as it exceeds 0 parts by weight, and is set according to the purpose. can do. In some aspects, the amount of the additive (H _RO ) used relative to 100 parts by weight of the acrylic polymer can be, for example, 80 parts by weight or less, which increases the refractive index of the adhesive and reduces the adhesive properties and optical properties. From the viewpoint of achieving both suppression and suppression in a well-balanced manner, it is advantageous to set the content to 60 parts by weight or less, preferably 45 parts by weight or less. In some embodiments where adhesive properties and optical properties are more important, the amount of the additive (H _RO ) used relative to 100 parts by weight of the acrylic polymer may be, for example, 30 parts by weight or less, or may be 20 parts by weight or less. It may be 15 parts by weight or less, or may be 10 parts by weight or less. In addition, from the viewpoint of increasing the refractive index of the adhesive, the amount of the additive (H _RO ) used relative to 100 parts by weight of the acrylic polymer may be, for example, 1 part by weight or more, and may be 3 parts by weight or more. Advantageously, it is preferably at least 5 parts by weight, may be at least 7 parts by weight, may be at least 10 parts by weight, may be at least 15 parts by weight, may be at least 20 parts by weight.

(crosslinking agent)
The pressure-sensitive adhesive composition disclosed herein may contain a cross-linking agent, if necessary, for the purpose of adjusting the cohesive strength of the pressure-sensitive adhesive. As the cross-linking agent, a cross-linking agent known in the field of adhesives such as an isocyanate-based cross-linking agent, an epoxy-based cross-linking agent, an aziridine-based cross-linking agent, an oxazoline-based cross-linking agent, a melamine-based resin, a metal chelate-based cross-linking agent, etc. can be used. can be done. Among them, isocyanate-based cross-linking agents and epoxy-based cross-linking agents can be preferably employed. Other examples of cross-linking agents include monomers having two or more ethylenically unsaturated groups in one molecule, ie, polyfunctional monomers. A crosslinking agent can be used individually by 1 type or in combination of 2 or more types.

As the isocyanate-based cross-linking agent, an isocyanate compound having a functionality of 2 or more can be used. Isocyanates; cyclopentylene diisocyanate, cyclohexylene diisocyanate, isophorone diisocyanate (IPDI), 1,3-bis(isocyanatomethyl)cyclohexane and other cycloaliphatic isocyanates; 2,4-tolylene diisocyanate, 4,4'- Aromatic isocyanates such as diphenylmethane diisocyanate and xylylene diisocyanate (XDI); modification of the above isocyanate compounds with allophanate bond, biuret bond, isocyanurate bond, uretdione bond, urea bond, carbodiimide bond, uretonimine bond, oxadiazinetrione bond, etc. modified polyisocyanate (for example, isocyanurate of HDI, allophanate of HDI, etc.); and the like. Commercially available products include Takenate 300S, Takenate 500, Takenate 600, Takenate D165N, Takenate D178N, Takenate D178NL (manufactured by Mitsui Chemicals, Inc.), Sumidule T80, Sumidule L, and Desmodur N3400 (manufactured by Mitsui Chemicals, Inc.). Bayer Urethane Co., Ltd.), Millionate MR, Millionate MT, Coronate L, Coronate HL, Coronate HX, Coronate 2770 (manufactured by Tosoh Corporation), trade name Duranate A201H (manufactured by Asahi Kasei Corporation), and the like. An isocyanate compound can be used individually by 1 type or in combination of 2 or more types. A bifunctional isocyanate compound and a trifunctional or higher isocyanate compound may be used in combination.

Epoxy cross-linking agents include, for example, bisphenol A, epichlorohydrin type epoxy resin, ethylene glycidyl ether, polyethylene glycol diglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, 1,6-hexanediol glycidyl ether, 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 individually by 1 type or in combination of 2 or more types.

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. A polyfunctional monomer can be used individually by 1 type or in combination of 2 or more types.

In some embodiments, at least a portion of the crosslinkers are bifunctional crosslinkers having two crosslinkable reactive groups (eg, isocyanate groups) per molecule. By using a bifunctional cross-linking agent, it is easy to form a flexible cross-linked structure. A bifunctional cross-linking agent can be used individually by 1 type or in combination of 2 or more types. Also, the bifunctional cross-linking agent may be used in combination with a tri- or higher functional cross-linking agent.

In some embodiments, an acyclic cross-linking agent (also referred to as a chain cross-linking agent) having no ring structure such as an aromatic ring or an aliphatic ring is preferably used as the cross-linking agent. For example, among the isocyanate-based cross-linking agents described above, it is preferable to use an isocyanate-based compound that does not have a ring structure such as an aromatic ring or an isocyanurate ring. By using an acyclic isocyanate compound as the cross-linking agent, a highly flexible cross-linking agent can be easily formed. Specific examples of the acyclic isocyanate include aliphatic isocyanate-based compounds (e.g., PDI and HDI), modified products of aliphatic isocyanate-based compounds (e.g., PDI and HDI with allophanate bond, biuret bond, urea bond, and carbodiimide bond. modified polyisocyanate). Acyclic cross-linking agents may be used singly or in combination of two or more. In some preferred embodiments, an acyclic bifunctional crosslinker can be used as the crosslinker.

In some embodiments, a cross-linking agent having a relatively long distance between one cross-linking reactive group (eg, isocyanate group) and another cross-linking reactive group in one molecule can be used as the cross-linking agent. As a result, a flexible crosslinked structure having a predetermined length or more is formed. For example, a compound having 10 or more atoms (for example, 12 or more or 14 or more) constituting a linking chain connecting one crosslinkable reactive group and another crosslinkable reactive group in one molecule of a crosslinker is used as a crosslinker. can be used as The upper limit of the number of atoms constituting the connecting chain is not particularly limited because it can be prepared by polymerization or the like according to the purpose, and is, for example, 2000 or less, may be 1000 or less, may be 500 or less, or may be 100 or less. It may be 50 or less, 30 or less, or 20 or less. In addition, the number of atoms constituting the linking chain linking the above-mentioned cross-linking reactive groups means that in one molecule of the cross-linking agent, from one cross-linking reactive group to another cross-linking reactive group (when there are 3 or more cross-linking reactive groups, The minimum number of atoms required to reach the cross-linking reactive group closest to the cross-linking reactive group of The cross-linking agents having the linking chain may be used singly or in combination of two or more. In some preferred embodiments, an acyclic bifunctional cross-linking agent can be used as the cross-linking agent. Examples of commercially available cross-linking agents include Coronate 2770 (manufactured by Tosoh Corporation), Takenate D178NL (manufactured by Mitsui Chemicals), and Duranate A201H (manufactured by Asahi Kasei).

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

A cross-linking catalyst may be used to promote the cross-linking reaction more effectively. Examples of cross-linking catalysts include metallic cross-linking catalysts such as tetra-n-butyl titanate, tetraisopropyl titanate, zirconium tetraacetylacetonate, Nasem ferric, butyltin oxide, and dioctyltin dilaurate. Of these, tin-based cross-linking catalysts such as dioctyltin dilaurate are preferred. The amount of cross-linking catalyst used is not particularly limited. The amount of the cross-linking catalyst used relative to 100 parts by weight of the monomer component is, for example, about 0.0001 part by weight or more and 1 part by weight or less in consideration of the balance between the speed of the crosslinking reaction rate and the length of the pot life of the pressure-sensitive adhesive composition. and it is preferably in the range of 0.001 part by weight or more and 0.5 part by weight or less.

The pressure-sensitive adhesive composition can contain a compound that causes keto-enol tautomerism as a cross-linking retarder. This can achieve the effect of extending the pot life of the pressure-sensitive adhesive composition. For example, a compound that exhibits keto-enol tautomerism can be preferably used in a pressure-sensitive adhesive composition containing an isocyanate-based cross-linking agent. Various β-dicarbonyl compounds can be used as compounds that cause keto-enol tautomerism. For example, β-diketones (acetylacetone, 2,4-hexanedione, etc.) and acetoacetic esters (methyl acetoacetate, ethyl acetoacetate, etc.) can be preferably employed. The 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, or 0.5 parts by weight or more and 10 parts by weight or less, relative to 100 parts by weight of the monomer component. 1 part by weight or more and 5 parts by weight or less.

(Tackifier)
The adhesive composition disclosed herein may contain a tackifier. Tackifiers include rosin-based tackifier resins, terpene-based tackifier resins, phenol-based tackifier resins, hydrocarbon-based tackifier resins, ketone-based tackifier resins, polyamide-based tackifier resins, epoxy-based tackifier resins, and elastomers. Known tackifying resins can be used, such as system tackifying resins. These can be used individually by 1 type or in combination of 2 or more types. The amount of the tackifying resin to be used is not particularly limited, and can be set so as to exhibit appropriate adhesive performance depending on the purpose and application. In some embodiments, from the viewpoint of refractive index and transparency, the amount of the tackifier to be used with respect to 100 parts by weight of the monomer component is suitably 30 parts by weight or less, preferably 10 parts by weight or less. , 5 parts by weight or less. The technology disclosed herein can be preferably practiced in a mode that does not use a tackifier.

(leveling agent)
In some embodiments, the pressure-sensitive adhesive composition contains a , a leveling agent can be contained as necessary. Non-limiting examples of leveling agents include acrylic leveling agents, fluorine-based leveling agents, silicone-based leveling agents, and the like. An appropriate leveling agent can be selected from, for example, commercially available leveling agents and used in a conventional manner.

In some embodiments, the leveling agent is a monomer raw material containing a monomer having a polyorganosiloxane skeleton (hereinafter also referred to as "monomer S1") and an acrylic monomer (hereinafter also referred to as "monomer raw material B"). (hereinafter also referred to as "polymer (B)") can be preferably used. The polymer (B) can be said to be a copolymer of the monomer S1 and an acrylic monomer. A polymer (B) can be used individually by 1 type or in combination of 2 or more types.

The monomer S1 is not particularly limited, and any monomer containing a polyorganosiloxane skeleton can be used. As the monomer S1, one having a structure having a polymerizable reactive group at one end can be preferably used. Among them, a monomer S1 having a structure that has a polymerizable reactive group at one end and does not have a functional group that causes a cross-linking reaction with an acrylic polymer at the other end can be preferably employed. Commercially available products include, for example, Shin-Etsu Chemical Co., Ltd.'s one-end reactive silicone oil (e.g., product numbers such as X-22-174ASX, X-22-2426, X-22-2475, KF-2012, etc.). . Monomer S1 can be used individually by 1 type or in combination of 2 or more types.

The functional group equivalent weight of the monomer S1 can be, for example, about 100 g/mol to 30000 g/mol. In some preferred embodiments, the functional group equivalent weight is, for example, 500 g/mol or more, may be 800 g/mol or more, may be 1500 g/mol or more, or may be 2000 g/mol or more. Further, the functional group equivalent may be, for example, 20000 g/mol or less, less than 10000 g/mol, 7000 g/mol or less, or 5500 g/mol or less. When the functional group equivalent of the monomer S1 is within the above range, a good leveling effect is likely to be exhibited.
When two or more types of monomers having different functional group equivalents are used as the monomer S1, the functional group equivalent of the monomer S1 is the sum of the product of the functional group equivalent of each type of monomer and the weight fraction of the monomer. be able to.

Here, "functional group equivalent" means the weight of the main skeleton (for example, polydimethylsiloxane) bonded to one functional group. The label unit g/mol is converted to 1 mol of the functional group. The functional group equivalent of the monomer S1 can be calculated, for example, from the spectral intensity of ¹ H-NMR (proton NMR) based on nuclear magnetic resonance (NMR). Calculation of the functional group equivalent (g/mol) of the monomer S1 based on the spectral intensity of ¹ H-NMR is based on a general structural analysis method related to ¹ H-NMR spectral analysis, if necessary, according to Japanese Patent No. 5951153. This can be done with reference to the description in the publication. In the functional group equivalent of the monomer S1, the functional group means a polymerizable functional group (for example, an ethylenically unsaturated group such as (meth)acryloyl group, vinyl group, allyl group, etc.).

The content of the monomer S1 in the monomer raw material B is not limited to a specific range, and an appropriate value can be adopted as long as the desired effect is exhibited using the monomer S1. In some embodiments, the content of monomer S1 in monomer raw material B may be, for example, 5 to 60 wt%, 10 to 50 wt%, or 15 to 40 wt%.

The monomer raw material B contains, in addition to the monomer S1, an acrylic monomer copolymerizable with the monomer S1. This can improve the compatibility of the polymer (B) in the pressure-sensitive adhesive layer. Examples of acrylic monomers that can be used as the monomer raw material B include acrylic acid alkyl esters. The term "alkyl" as used herein refers to a chain (including linear and branched) alkyl (group), and does not include an alicyclic hydrocarbon group described later. In some embodiments, monomer feed B is a (meth)acrylic acid C _4-12 alkyl ester (preferably a (meth)acrylic acid C _4-10 alkyl ester, such as a (meth)acrylic acid C _6-10 alkyl ester) can contain at least one of In some other embodiments, monomer feedstock B may contain at least one methacrylic acid C _1-18 alkyl ester (preferably methacrylic acid C _1-14 alkyl ester, such as methacrylic acid C _1-10 alkyl ester). . Monomer raw material B may contain one or more selected from, for example, methyl methacrylate (MMA), n-butyl methacrylate (BMA) and 2-ethylhexyl methacrylate (2EHMA) as acrylic monomers.

Other examples of the acrylic monomers include (meth)acrylic acid esters having an alicyclic hydrocarbon group. For example, cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 1-adamantyl (meth)acrylate and the like can be used. A (meth)acrylic acid ester having an alicyclic hydrocarbon group may not be used.

The content of the (meth)acrylic acid alkyl ester and the (meth)acrylic acid ester having the alicyclic hydrocarbon group in the monomer raw material B may be, for example, 10% by weight or more and 95% by weight or less, and may be 20% by weight. 95% by weight or less, 30% by weight or more and 90% by weight or less, 40% by weight or more and 90% by weight or less, or 50% by weight or more and 85% by weight or less good too.

Other examples of monomers that can be contained in monomer raw material B together with monomer S1 include the carboxy group-containing monomers, acid anhydride group-containing monomers, hydroxyl group-containing monomers, and epoxy group-containing monomers exemplified above as monomers that can be used in acrylic polymers. , cyano group-containing monomers, isocyanate group-containing monomers, amide group-containing monomers, monomers having a nitrogen atom-containing ring, aminoalkyl (meth)acrylates, vinyl esters, vinyl ethers, olefins, aromatic hydrocarbon groups (Meth)acrylic acid esters, halogen atom-containing (meth)acrylates, and the like.

Mw of the polymer (B) may be, for example, 5,000 or more, preferably 10,000 or more, and may be 15,000 or more. The Mw of the polymer (B) may be, for example, 200,000 or less, preferably 100,000 or less, 50,000 or less, or 30,000 or less. Suitable compatibility and leveling properties can be exhibited by setting the Mw of the polymer (B) to an appropriate range.

The polymer (B) can be prepared, for example, by polymerizing the above-described monomers by known techniques such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization, and photopolymerization.
A chain transfer agent can be used as necessary to adjust the molecular weight of the polymer (B). Examples of chain transfer agents used include compounds having a mercapto group such as t-dodecylmercaptan, mercaptoethanol and α-thioglycerol; thioglycolic acid esters such as thioglycolic acid and methyl thioglycolate; α-methylstyrene. dimer; and the like. The amount of the chain transfer agent used is not particularly limited, and can be appropriately set so as to obtain the polymer (B) having the desired molecular weight. In some embodiments, the amount of chain transfer agent used relative to 100 parts by weight of monomer may be, for example, 0.1 to 5 parts by weight, 0.2 to 3 parts by weight, or even 0.5 to 2 parts by weight. good.

The amount of the polymer (B) used relative to 100 parts by weight of the acrylic polymer can be, for example, 0.001 parts by weight or more. It is good also as more than a weight part. The amount of the polymer (B) used may be, for example, 3 parts by weight or less. , or 0.1 parts by weight or less. The technology disclosed herein can be practiced in an aspect in which the PSA composition does not substantially contain the polymer (B).

(High refractive index particles)
The adhesive composition disclosed herein can contain high refractive index particles as an optional component. Here, the high refractive index particles mean particles capable of increasing the refractive index of the pressure-sensitive adhesive by being contained in the pressure-sensitive adhesive. Hereinafter, the high refractive index particles may be referred to as "particles P _HRI ". HRI stands for high refractive index.

The particle P _HRI is, for example, a material having a refractive index of 1.60 or more, preferably 1.70 or more (1.80 or more, 1.90 or more, or even 2.00 or more). One or more structured 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, or 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 for a single layer film of the material (a film thickness that allows refractive index measurement) at a measurement wavelength of 589 nm and a measurement temperature of 25 ° C. is the refractive index measured under the conditions of As the spectroscopic ellipsometer, for example, the product name "EC-400" (manufactured by JA. Woolam) or its equivalent is used.

The type of particles 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 _PHRI , inorganic oxides (eg, metal oxides) that can improve the refractive index of the pressure-sensitive adhesive sheet can be preferably used. Preferable examples of materials constituting the particles _PHRI include titania (titanium oxide, TiO ₂ ), zirconia (zirconium oxide, ZrO ₂ ), aluminum oxide, zinc oxide, tin oxide, copper oxide, barium titanate, niobium oxide ( Nb ₂ O ₅ , etc.) and other inorganic oxides (specifically, metal oxides). Particles composed of these inorganic oxides (for example, metal oxides) can be used singly or in combination of two or more. Among them, particles made of titania or zirconia are preferable, and particles made of zirconia are particularly preferable. As the metal particles, for example, iron-based, zinc-based, tungsten-based, and platinum-based materials can have a high refractive index. As the organic particles, particles made of resins such as styrene resins, phenol resins, polyester resins, and polycarbonate resins have a relatively high refractive index. Examples of the organic-inorganic composite particles include composites of the aforementioned inorganic material and organic material, inorganic particles coated with an organic material such as a resin, and the like. From the viewpoint of compatibility with the pressure-sensitive adhesive component, the particles _PHRI may be the above-mentioned organic or inorganic particles surface-treated with a surface-treating agent.

The average particle size of the particles _PHRI is not particularly limited, and particles having an appropriate size that can achieve the desired refractive index improvement by being contained in the pressure-sensitive adhesive can be used. The average particle size of the particles _PHRI can be, for example, about 1 nm or more, suitably about 5 nm or more. From the viewpoint of improving the refractive index and handling properties, the average particle size of the particles _PHRI is preferably approximately 10 nm or more, may be approximately 20 nm or more, or may be approximately 30 nm or more. Also, from the viewpoint of maintaining adhesive properties, etc., the upper limit of the average particle diameter is, for example, about 300 nm or less. It is about 50 nm or less, and may be about 35 nm or less (for example, about 25 nm or less).

The average particle diameter of the particles _PHRI refers to the volume average particle diameter _. 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 or its equivalent can be used.

The content of the particle _PHRI in the adhesive composition is not particularly limited. The content of the particles _PHRI can vary depending on the desired refractive index. For example, the content of the particles _PHRI can be appropriately set in consideration of the required adhesion properties and the like so that the refractive index is equal to or greater than a predetermined value. In some embodiments, the content of the particulate P _HRI in the adhesive composition can be, for example, about 75% by weight or less in the adhesive formed from the adhesive composition, and can improve adhesive properties and transparency. From a viewpoint, it may be about 50% by weight or less, or about 30% by weight or less. The lower limit of the particle _PHRI content 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 composition is, for example, less than 10% by weight, even less than 1% by weight, in the adhesive formed from the adhesive composition. well, even 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 particulate _PHRI .

The particle _PHRI content in the adhesive can also be specified by a relative relationship with the amount of acrylic polymer contained in the adhesive. The content of the particles P _HRI can be, for example, about 100 parts by weight or less with respect to 100 parts by weight of the acrylic polymer, and from the viewpoint of adhesive properties and transparency, it may be about 60 parts by weight or less, or about 40 parts by weight. It may be less than part. The lower limit of the particle _PHRI content 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 embodiments, the content of particulate 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, or may be less than 0 parts by weight, relative to 100 parts by weight of the acrylic polymer. It may be less than .1 part by weight.

(Other additives)
In addition, the pressure-sensitive adhesive composition disclosed herein contains softening agents, coloring agents (dyes, pigments, etc.), fillers, antistatic agents, anti-aging agents, ultraviolet absorbing agents, as long as the effects of the present invention are not significantly hindered. Known additives that can be used in pressure-sensitive adhesive compositions, such as agents, antioxidants, light stabilizers, preservatives, etc., may be included as necessary. In addition to the plasticizers disclosed herein, known plasticizers (e.g., phthalate ester, terephthalate ester, adipate ester, adipate polyester, benzoic acid glycol ester, etc.) and liquid camphenphenol It may contain one or more plasticizing materials such as As for such various additives, conventionally known ones can be used in a conventional manner, and since they do not particularly characterize the present invention, detailed description thereof will be omitted.

<Adhesive>
The adhesive disclosed herein can be formed using, for example, any of the adhesive compositions described above. Such an adhesive is an adhesive obtained by curing an adhesive composition in the form of solvent type, active energy ray-curable type, water dispersion type, hot-melt type, etc. by drying, crosslinking, polymerization, cooling, etc., that is, the above-mentioned adhesive It may be a cured product of the agent composition. As for the curing means (for example, drying, crosslinking, polymerization, cooling, etc.) of the pressure-sensitive adhesive composition, only one type may be applied, or two or more types may be applied simultaneously or in multiple stages. For solvent-borne adhesive compositions, typically the composition can be dried (preferably further crosslinked) to form the adhesive. In the active energy ray-curable pressure-sensitive adhesive composition, the pressure-sensitive adhesive is typically formed by irradiating an active energy ray to promote a polymerization reaction and/or a cross-linking reaction. When it is necessary to dry the active energy ray-curable pressure-sensitive adhesive composition, it is preferable to irradiate the active energy ray after drying.

(refractive index)
The refractive index of the pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition disclosed herein is higher than that of conventional general acrylic pressure-sensitive adhesives. According to the technology disclosed herein, a pressure-sensitive adhesive having a refractive index of, for example, 1.55 or more, 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. The refractive index of the pressure-sensitive adhesive is suitably 1.560 or more, preferably more than 1.570. In some embodiments, the adhesive may have a refractive index of 1.575 or higher, 1.580 or higher, or 1.585 or higher. A pressure-sensitive adhesive having such a refractive index can suitably suppress light reflection at the interface with an adherend in a mode of use in which it is attached to a material with a high refractive index. The preferred upper limit of the refractive index of the adhesive is not limited to a specific range because it may vary depending on the refractive index of the adherend and the like. It may be 650 or less, 1.620 or less, or 1.600 or less.

The refractive index of the pressure-sensitive adhesive can be adjusted, for example, by the composition of the pressure-sensitive adhesive (for example, the composition of monomer components constituting the acrylic polymer). Specifically, a pressure-sensitive adhesive exhibiting a predetermined or higher refractive index can be prepared by including an acrylic polymer having a large content of the monomer (A1) in the monomer component and an additive (H _RO ).

In this specification, the refractive index of the adhesive refers to the refractive index of the surface (adhesive surface) of the adhesive. The refractive index of the pressure-sensitive adhesive can be measured using a commercially available refractive index measuring device (Abbe refractometer) under conditions of a measurement wavelength of 589 nm and a measurement temperature of 25°C. As the Abbe refractometer, for example, model "DR-M4" manufactured by ATAGO or its equivalent is used. As a measurement sample, a pressure-sensitive adhesive layer made of the pressure-sensitive 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 pressure-sensitive adhesive while maintaining a high refractive index. Although not limited to a specific range, the storage modulus G' (0° C.) of the adhesive at 0° C. may be, for example, less than 1.0×10 ⁸ Pa and 5.0×10 ⁷ It may be less than Pa, less than 1.0×10 ⁷ Pa, or less than 5.0×10 ⁶ Pa. The pressure-sensitive adhesive having the storage elastic modulus G′ (0° C.) has appropriate flexibility in a temperature range from around 0° C. to above, and can adhere well to an adherend, for example. The lower limit of the storage elastic modulus G′ (0° C.) is not particularly limited, and is, for example, 1.0×10 ² Pa or higher, and may be 1.0×10 ³ Pa or higher. When the storage elastic modulus G′ (0° C.) is equal to or higher than a predetermined value, the pressure-sensitive adhesive tends to have an appropriate cohesive force, for example, in the normal temperature to high temperature range. In some preferred embodiments, the storage modulus G′ (0° C.) of the adhesive is 1.0×10 ⁶ Pa or less, more preferably 5.0×10 ⁵ Pa or less, and 2.0×10 5 Pa or less. It may be 10 ⁵ Pa or less, 1.0×10 ⁵ Pa or less, 7.0×10 ⁴ Pa or less, 5.0×10 ⁴ Pa or less, or 3.0×10 ⁴ Pa It can be below. In addition, the storage modulus G' (0°C) is preferably 1.0 x 10 ⁴ Pa or more, more preferably 2.0 x 10 ⁴ Pa or more, and still more preferably 4.0 x 10 ⁴ Pa or more. , 6.0×10 ⁴ Pa or more, or 1.0×10 ⁵ Pa or more. A pressure-sensitive adhesive having a storage elastic modulus G′ (0° C.) within the above range can achieve both a high refractive index and flexibility, and can have flexibility that can withstand repeated bending operations.

The storage modulus G′ (80° C.) at 80° C. of the pressure-sensitive adhesive disclosed herein is not particularly limited, and is, for example, suitably less than 1.0×10 ⁵ Pa, preferably 5.0× It is less than 10 ⁴ Pa, more preferably less than 3.0×10 ⁴ Pa, may be less than 1.0×10 ⁴ Pa, and may be 5.0×10 ³ Pa or less. The PSA having a limited storage elastic modulus G' (80°C) as described above has good flexibility in a high temperature range. The lower limit of the storage modulus G′ (80° C.) is not particularly limited, and is, for example, 1.0×10 ² Pa or more, preferably 5.0×10 ² Pa or more, preferably 1.0×10 2 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. A pressure-sensitive adhesive having the storage elastic modulus G′ (80° C.) has an appropriate cohesive force even in a high temperature range and tends to be excellent in heat resistance, which is preferable.

The storage modulus G′ (−10° C.) at −10° C. of the pressure-sensitive adhesive disclosed herein is not particularly limited, and may be, for example, less than 1.0×10 ⁹ Pa, or 1.0×10 ⁸ 5. It may be less than Pa, suitably less than 1.0×10 ⁷ Pa, preferably 5.0×10 ⁶ Pa or less, and may be 1.0×10 ⁶ Pa or less. It may be 0×10 ⁵ Pa or less, or 1.0×10 ⁵ Pa or less. A pressure-sensitive adhesive having a limited storage modulus G' (-10°C) as described above can have superior flexibility. For example, it can have good flexibility in a low temperature range and have flexibility to withstand repeated bending operations in a wide temperature range including a low temperature range. The lower limit of the storage modulus G′ (−10° C.) is not particularly limited, and is, for example, 1.0×10 ² Pa or more, preferably 1.0×10 ³ Pa or more, preferably 5 0×10 ³ Pa or more, more preferably 1.0×10 ⁴ Pa or more, may be 5.0×10 ⁴ Pa or more, may be 1.0×10 ⁵ Pa or more, and may be 5.0 ×10 ⁵ Pa or more may be used. A pressure-sensitive adhesive having the storage elastic modulus G′ (−10° C.) can be flexible and have appropriate cohesive strength. Moreover, the adhesive having the storage elastic modulus G′ (−10° C.) tends to easily achieve both a high refractive index and flexibility even in a low temperature range.

The storage modulus G′ (−20° C.) at −20° C. of the adhesive disclosed herein is not particularly limited, and may be, for example, less than 1.0×10 ¹⁰ Pa, or 1.0×10 ⁹ It may be less than Pa, is suitably 5.0×10 ⁸ Pa or less, may be 1.0×10 ⁸ Pa or less, may be 5.0×10 ⁷ Pa or less, or may be 1.0×10 8 Pa or less. It may be 10 ⁷ Pa or less, 5.0×10 ⁶ Pa or less, 1.0×10 ⁶ Pa or less, or 5.0×10 ⁵ Pa or less. A pressure-sensitive adhesive having a limited storage modulus G' (-20°C) as described above can have particularly excellent flexibility. For example, it can have good flexibility in a lower temperature range and have flexibility to 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, for example, 1.0×10 ² Pa or more, suitably 1.0×10 ³ Pa or more, preferably 1 0×10 ⁴ Pa or more, more preferably 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. A pressure-sensitive adhesive having the storage modulus G′ (−20° C.) can be flexible and have appropriate cohesive strength. Moreover, the adhesive having the storage elastic modulus G′ (−20° C.) tends to easily achieve both a high refractive index and flexibility even in a low temperature range.

(Storage modulus ratio)
In some embodiments, the adhesive has a ratio of storage modulus G' (0° C.) at 0° C. to storage modulus G' (80° C.) at 80° C. (G'(0° C.)/G'(80° C. )) is in the range of 1-1000. A pressure-sensitive adhesive that satisfies the above properties suppresses changes in elastic modulus in a wide temperature range from 0° C. to high temperatures, and thus tends to exhibit stable properties (flexibility, etc.) against temperature changes. The ratio (G'(0°C)/G'(80°C)) is suitably 300 or less, preferably 100 or less, more preferably 50 or less, and may be 25 or less, or even 10 or less. Well, it can be 5 or less. The lower limit of the ratio (G'(0° C.)/G'(80° C.)) may be, for example, 2 or more, or 3 or more.

In some embodiments, the adhesive has a ratio of storage modulus G' (-10°C) at -10°C to storage modulus G' (80°C) at 80°C (G'(-10°C)/G' (80° C.)) is in the range of 1 to 1,000. An adhesive that satisfies the above characteristics suppresses changes in elastic modulus over a wide temperature range from low to high temperatures, so it is easy to exhibit stable characteristics (flexibility, etc.) against temperature changes. preferable. The ratio (G'(-10°C)/G'(80°C)) is suitably 300 or less, preferably 150 or less, more preferably 100 or less, and may be 50 or less, or 30 or less. , 20 or less, or 10 or less. The lower limit of the ratio (G'(-10°C)/G'(80°C)) may be, for example, 2 or more, or 3 or more.

In some embodiments, the adhesive has a ratio of storage modulus G' (-20°C) at -20°C to storage modulus G' (80°C) at 80°C (G'(-20°C)/G' (80° C.)) is in the range of 1 to 1,000. Adhesives that satisfy the above properties exhibit stable properties (flexibility, etc.) against temperature changes because changes in elastic modulus are suppressed in a wide temperature range from lower temperature ranges to higher temperature ranges. be able to. The ratio (G'(-20°C)/G'(80°C)) may be 500 or less, 300 or less, 150 or less, 100 or less, 50 or less, or 30 or less. It's okay. The lower limit of the ratio (G'(-20°C)/G'(80°C)) may be, for example, 5 or more, 10 or more, 50 or more, or 100 or more.

The glass transition temperature (Tg) of the pressure-sensitive adhesive is not particularly limited, and can be set in consideration of flexibility in a low temperature range and cohesion (heat resistance, etc.) in a high temperature range. In some embodiments, the Tg of the adhesive is, for example, 30° C. or less, may be 15° C. or less, or may be 5° C. or less. In some preferred embodiments, the Tg of the adhesive is 0° C. or lower, more preferably -5° C. or lower, still more preferably -10° C. or lower, and -15° C. or lower (e.g., -20° C. or lower) from the viewpoint of flexibility. °C or less). The lower the Tg of the pressure-sensitive adhesive, the more excellent the pressure-sensitive adhesive properties such as adhesion to the adherend tend to be. Also, by setting the Tg of the pressure-sensitive adhesive low, it is possible to suppress changes in the elastic modulus in a temperature range higher than the Tg. The lower limit of the Tg of the adhesive is, for example, -50°C or higher, preferably -40°C or higher, and may be -30°C or higher. A pressure-sensitive adhesive having the above Tg tends to provide an appropriate cohesive force. Moreover, there is a tendency to easily form a pressure-sensitive adhesive having both a high refractive index and a low elastic modulus.

The storage elastic modulus G′ and the glass transition temperature Tg of the adhesive at each temperature can be measured by the method described in Examples below, and each storage elastic modulus ratio can be calculated from the results. can. Each storage modulus G′, each storage modulus ratio and glass transition temperature Tg of the pressure-sensitive adhesive are determined, for example, by selection of the composition of the monomer components constituting the acrylic polymer (for example, selection of the type and content of the monomer (A1) ), selection of the type and amount of plasticizer used, presence/absence of use of cross-linking agent, selection of type and amount used, presence/absence of use of additive, selection of type and amount used, and the like.

<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 pressure-sensitive adhesive sheet may be a pressure-sensitive adhesive sheet with a substrate having the pressure-sensitive adhesive layer on one or both sides of a non-releasable substrate (supporting substrate), and the pressure-sensitive adhesive layer is held by a release liner. It may be a substrate-less pressure-sensitive adhesive sheet (that is, a pressure-sensitive adhesive sheet having no non-releasable substrate, typically a pressure-sensitive adhesive layer). The concept of the adhesive sheet as used herein can 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 roll-shaped or sheet-shaped. Alternatively, it may be a pressure-sensitive adhesive sheet processed into various shapes.

1 and 2 show configuration examples of a double-sided pressure-sensitive adhesive sheet without a base material (double-sided pressure-sensitive adhesive sheet without a base material). The pressure-sensitive adhesive sheet 1 shown in FIG. 1 has a configuration in which both surfaces 21A and 21B of a substrate-less pressure-sensitive adhesive layer 21 are protected by release liners 31 and 32 whose release surfaces are at least on the pressure-sensitive adhesive layer side. The adhesive sheet 2 shown in FIG. 2 has a configuration in which one surface (adhesive surface) 21A of a substrate-less adhesive layer 21 is protected by a release liner 31 having release surfaces on both sides. When wound, the other surface (adhesive surface) 21B of the adhesive layer 21 contacts the back surface of the release liner 31, so that the other surface 21B is also protected by the release liner 31. The technology disclosed herein is preferably implemented in the form of a substrate-less pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer, from the viewpoint of flexibility to follow an adherend that is repeatedly bent. The substrate-less pressure-sensitive adhesive sheet is preferable, for example, from the viewpoint of reducing the thickness of the pressure-sensitive adhesive sheet and from the viewpoint of increasing the transparency of the pressure-sensitive adhesive sheet.

The adhesive sheet disclosed herein can have, for example, a cross-sectional structure schematically shown in FIG. The pressure-sensitive adhesive sheet 3 shown in FIG. Prepare. Both the first surface 10A and the second surface 10B are 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 (double-sided adhesive adhesive sheet). The pressure-sensitive adhesive sheet 3 before use has a first pressure-sensitive adhesive surface 21A and a second pressure-sensitive adhesive surface 22A protected by release liners 31 and 32, each of which has a peelable surface (release surface) on at least the pressure-sensitive adhesive surface side. have a configuration. Alternatively, the release liner 32 may be omitted and a release liner 31 having release surfaces on both sides may be used. Therefore, the second adhesive surface 22A may also be protected by the release liner 31 .

The technology disclosed herein is preferably practiced in the form of the above-described substrate-less or substrate-attached double-sided PSA sheet for fixing or bonding members (for example, optical members). Alternatively, the PSA sheet disclosed herein may be in the form of a substrate-attached single-sided PSA sheet having an adhesive layer only on one side of a non-releasable substrate (supporting substrate), although not shown. As an example of the form of the single-sided pressure-sensitive adhesive sheet, there is a form that does not have either the first pressure-sensitive adhesive layer 21 or the second pressure-sensitive adhesive layer 22 in the configuration shown in FIG.

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

The thickness of the pressure-sensitive adhesive layer is not particularly limited, and can be, for example, 3 μm or more. In some embodiments, the thickness of the pressure-sensitive adhesive layer is suitably, for example, 5 μm or more, and may be 10 μm or more, 15 μm or more, 20 μm or more, 30 μm or more, or 50 μm or more. or 70 μm or more or 85 μm or more. The adhesive strength tends to increase as the thickness of the adhesive layer increases. In some aspects, 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, and may be 50 μm or less, or 30 μm or less. It may be advantageous from the viewpoint of thinning of the adhesive sheet that the thickness of the adhesive layer is not too large. In addition, a thin pressure-sensitive adhesive layer tends to have excellent conformability to an adherend. The technique disclosed herein can be preferably carried out in a mode in which the thickness of the pressure-sensitive adhesive layer is, for example, 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 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 surface and the second surface of the substrate, the thickness of the pressure-sensitive adhesive layer is at least the thickness of the first pressure-sensitive adhesive layer. can be applied to The thickness of the second adhesive layer can also be selected from the same range. Moreover, in the case of a substrate-less pressure-sensitive adhesive sheet, the thickness of the pressure-sensitive adhesive sheet matches the thickness of the pressure-sensitive adhesive layer.

In some embodiments, the product of the storage modulus G'(0°C) [Pa] of the adhesive at 0°C and the thickness T [μm] of the adhesive layer (G'(0°C) x T) is For example, it is suitably in the range of 5.0×10 ⁴ to 7.5×10 ⁷ , preferably in the range of 5.0×10 ⁴ to 5.0×10 ⁷ . A thin pressure-sensitive adhesive layer, even if it has a relatively high elastic modulus, tends to have good flexibility by having the product (G′(0° C.)×T) within the above range. In addition, since the product (G'(0°C) x T) is limited to a predetermined value or less, the upper limit of the thickness of the adhesive layer and the storage elastic modulus G'(0°C) are limited. , it is easy to obtain excellent flexibility. In some preferred embodiments, the product (G′(0° C.)×T) may be 1.0×10 ⁵ or more, 2.0×10 ⁵ or more, or 8.0×10 ⁵ It can be more than that. The product (G'(0°C) x T) may be 2.0 x 10 ⁷ or less, 1.0 x 10 ⁷ or less, or 6.0 x 10 ⁶ or less. good.

(Haze value)
In some aspects, the haze value of the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet may be, for example, 5.0% or less, preferably 3.0% or less, and 2.0% or less. It is more preferably 1.0% or less, and may be 0.9% or less, 0.8% or less, 0.5% or less, or 0.3% or less. Such a pressure-sensitive adhesive sheet having a highly transparent pressure-sensitive adhesive layer can be used for applications that require high light transmittance (for example, optical applications) in a structure with or without a substrate, and for applications where an adherend is passed through the pressure-sensitive adhesive sheet. It can be preferably applied to applications that require good visibility performance. The lower limit of the haze value of the pressure-sensitive adhesive layer is not particularly limited, and from the viewpoint of improving transparency, the smaller the haze value, the better. On the other hand, in some aspects, the haze value may be, for example, 0.05% or more, or 0.10% or more, in consideration of the refractive index and adhesion properties. These haze values for the pressure-sensitive adhesive layer are the haze values of the pressure-sensitive adhesive sheet when the technology disclosed herein is implemented in the form of a substrate-less pressure-sensitive adhesive sheet (typically, a pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer). can also be preferably applied.

Here, the term "haze value" refers to the ratio of diffuse transmitted light to total transmitted light when an object to be measured is irradiated with visible light. Also called cloudiness value. A haze value can be represented by the following formula.
Th (%) = Td/Tt x 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 pressure-sensitive adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the pressure-sensitive adhesive layer.

In some embodiments, the haze value of the pressure-sensitive adhesive sheet may be, for example, 5.0% or less, preferably 3.0% or less, more preferably 2.0% or less, and 1.0%. % or less, and may be 0.9% or less, 0.8% or less, 0.5% or less, or 0.3% or less. Such highly transparent pressure-sensitive adhesive sheets 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 pressure-sensitive adhesive sheet. The lower limit of the haze value of the pressure-sensitive adhesive sheet is not particularly limited, and from the viewpoint of improving transparency, the smaller the haze value, the better. On the other hand, in some aspects, the haze value may be, for example, 0.05% or more, or 0.10% or more, in consideration of the refractive index and adhesion properties. The haze value of the pressure-sensitive adhesive sheet can be measured by the same method as for measuring the haze value of the pressure-sensitive adhesive layer. The haze value of the pressure-sensitive adhesive sheet can be obtained by selecting the composition of the pressure-sensitive adhesive layer described above, or by selecting the type of substrate and the thickness of the substrate in a configuration having a substrate.

In some aspects, the total light transmittance of the pressure-sensitive adhesive layer is preferably 85.0% or more (eg, 88.0% or more, 90.0% or more, or more than 90.0%). Such a pressure-sensitive adhesive sheet having a highly transparent pressure-sensitive adhesive layer can be used for applications that require high light transmittance (for example, optical applications) in a structure with or without a substrate, and for applications where an adherend is passed through the pressure-sensitive adhesive sheet. It can be preferably applied to applications where good visibility performance is required. Practically, the upper limit of the total light transmittance may be, for example, approximately 98% or less, approximately 96% or less, or approximately 95% or less. In some aspects, 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. Total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the trade name "Hazemeter HM-150" manufactured by Murakami Color Research Laboratory or its equivalent is used. The total light transmittance can be measured according to the method described in Examples below. The total light transmittance of the pressure-sensitive adhesive layer can be adjusted, for example, by selecting the composition, thickness, etc. of the pressure-sensitive adhesive layer.

In some aspects, the total light transmittance of the pressure-sensitive adhesive sheet is preferably 85.0% or more (eg, 88.0% or more, 90.0% or more, or more than 90.0%). Such highly transparent pressure-sensitive adhesive sheets 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 pressure-sensitive adhesive sheet. Practically, the upper limit of the total light transmittance may be, for example, approximately 98% or less, approximately 96% or less, or approximately 95% or less. In some aspects, the total light transmittance of the adhesive sheet may be approximately 94% or less, approximately 93% or less, or approximately 92% or less, in consideration of refractive index and adhesive properties. The total light transmittance of the adhesive sheet can be measured by the same method as the measurement of the total light transmittance of the 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, or by selecting the type and thickness of the base material in a structure having a base material.

(Peel strength)
The peel strength of the adhesive sheet to the glass plate is not particularly limited. In some aspects, the adhesive sheet has a peel strength to 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 to the glass plate is 1.0 N/25 mm or more, more preferably 1.5 N/25 mm or more, still 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, or 10 N/25 mm or more. Such a pressure-sensitive adhesive sheet having a peel strength against a glass plate of a predetermined value or higher is suitable for joining or fixing glass members, for example. 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-mentioned peel strength was measured by pressure bonding to an alkali glass plate as an adherend and leaving it for 30 minutes in an environment of 23° C. and 50% RH, and then peel strength under the conditions of a peel angle of 180 degrees and a tensile speed of 300 mm/min. is grasped 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 having a thickness of about 25 μm to 50 μm). More specifically, the peel strength can be measured according to the method described in Examples below.

(Thickness of adhesive sheet)
The thickness of the pressure-sensitive adhesive sheet disclosed herein (substrate-less pressure-sensitive adhesive sheet or substrate-attached pressure-sensitive adhesive sheet) 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. or less than 50 μm. The thickness of the pressure-sensitive adhesive sheet may be, for example, 5 µm or more, 10 µm or more, 25 µm or more, 80 µm or more, or 130 µm or more, from the viewpoint of handleability.
The thickness of the pressure-sensitive adhesive sheet refers to the thickness of the portion to be adhered to the adherend. For example, in the pressure-sensitive adhesive sheet 3 having the configuration shown in FIG.

<Support base material>
The pressure-sensitive adhesive sheet according to some embodiments may be in the form of a substrate-attached pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on one or both sides of a supporting substrate. The material of the supporting substrate is not particularly limited, and can be appropriately selected according to the intended use, mode of use, etc. 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), polyethylene Plastic films such as polyester films mainly composed of polyester such as phthalate (PEN), polyvinyl chloride films mainly composed of polyvinyl chloride; foams such as polyurethane foam, polyethylene (PE) foam, polychloroprene foam, etc. Foam sheet; woven fabric and non-woven fabric made of various fibrous materials (natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, semi-synthetic fibers such as acetate, etc.) alone or blended; paper such as Japanese paper, fine paper, kraft paper, and crepe paper; metal foil such as aluminum foil and copper foil; A base material having a structure in which these are combined may be used. Examples of such composite substrates include substrates having a structure in which a metal foil and the plastic film are laminated, plastic substrates reinforced with inorganic fibers such as glass cloth, and the like.

Various film substrates can be preferably used in some embodiments. The film substrate may be a porous substrate such as a foam film or a nonwoven fabric sheet, or may be a non-porous substrate. It may be a substrate having a structure in which is laminated. In some embodiments, as the film substrate, one containing a resin film that can independently maintain its shape (self-supporting or independent) as a base film can be preferably used. As used herein, "resin film" means a non-porous structure, typically a substantially voidless resin film. Therefore, the resin film is a concept distinguished from foam films and non-woven fabrics. As the resin film, a film 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 alicyclic 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); fluorine resin such as polytetrafluoroethylene (PTFE); acrylic resin; cellulose-based polymer such as triacetyl cellulose (TAC); polyarylate; ; and other resins can be used.

The resin film may be formed using a resin material containing only one of such resins, or may be formed using a resin material in which two or more of these resins are blended. good too. The resin film may be unstretched or may be stretched (for example, uniaxially stretched or biaxially stretched). For example, PET film, PBT film, PEN film, unstretched polypropylene (CPP) film, biaxially stretched polypropylene (OPP) film, low density polyethylene (LDPE) film, linear low density polyethylene (LLDPE) film, PP/PE A blend film, a cycloolefin polymer (COP) film, a CPI film, a TAC film, etc. can be preferably used. PET films, PEN films, PPS films and PEEK films are examples of preferred resin films from the viewpoint of strength and dimensional stability. PET films and PPS films are particularly preferred from the standpoint of availability, etc., and PET films are particularly preferred.

In the resin film, known additives such as light stabilizers, antioxidants, antistatic agents, coloring agents (dyes, pigments, etc.), fillers, slip agents, anti-blocking agents, etc. are added to the extent that the effects of the present invention are not significantly hindered. can be blended as needed. The blending amount of the additive is not particularly limited, and can be appropriately set according to 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, and calendar roll molding can be appropriately employed.

The substrate may be substantially composed of such a base film. Alternatively, the substrate may contain an auxiliary layer in addition to the base film. Examples of the auxiliary layers include optical property adjusting layers (e.g., colored layers, antireflection layers), printed layers and laminate layers for imparting a desired appearance to the substrate, antistatic layers, undercoat layers, and release layers. and other surface treatment layers.

In some embodiments, a light-transmissive base (hereinafter also referred to as a light-transmissive base) can be preferably employed as the supporting base. This makes it possible to construct a pressure-sensitive adhesive sheet with a substrate having optical transparency. The total light transmittance of the light transmissive substrate may be, for example, greater than 50% and may be 70% or more. In some preferred embodiments, the total light transmittance of the supporting substrate is 80% or higher, more preferably 90% or higher, and may be 95% or higher (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 trade name "Hazemeter HM-150" manufactured by Murakami Color Research Laboratory or its equivalent is used. A suitable example of the light-transmitting substrate is a resin film having light-transmitting properties. The light transmissive substrate may be an optical film.

The thickness of the base material is not particularly limited, and can be selected according to the intended use and mode 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 workability of the adhesive sheet, may be 150 μm or less, may be 100 μm or less, may be 50 μm or less, or may be 25 μm. It may be less than or equal to 10 μm or less. As the thickness of the substrate becomes smaller, the conformability to the surface shape of the adherend tends to improve. Moreover, from the viewpoint of handleability, workability, etc., the thickness of the substrate may be, for example, 2 μm or more, 10 μm or more, or 25 μm or more.

The surface of the substrate on which the pressure-sensitive adhesive layer is to be laminated may be subjected to corona discharge treatment, plasma treatment, ultraviolet irradiation treatment, acid treatment, alkali treatment, or application of a primer to form an undercoat layer, if necessary. Conventionally known surface treatments such as forming may be applied. Such a surface treatment may be a treatment for improving the anchoring property of the pressure-sensitive adhesive layer to the substrate. The composition of the primer used for forming the undercoat layer is not particularly limited, and can be appropriately selected from known ones. Although the thickness of the undercoat layer is not particularly limited, it is usually suitably about 0.01 μm to 1 μm, preferably about 0.1 μm to 1 μm. Other treatments that can be applied to the substrate as necessary include antistatic layer forming treatment, colored layer forming treatment, printing treatment, and the like. These treatments can be applied singly 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 the adhesive layer is brought into contact with the release surface of the release liner. Accordingly, this specification provides a PSA sheet with a release liner (adhesive product) comprising any of the PSA sheets disclosed herein and a release liner having a release surface in contact with the adhesive surface of the PSA sheet. be.

The release liner is not particularly limited. For example, a release liner having a release layer on the surface of a liner substrate such as a resin film or paper (which may be paper laminated with a resin such as polyethylene), or a fluoropolymer (Polytetrafluoroethylene, etc.) and polyolefin resins (Polyethylene, polypropylene, etc.) can be used. A release liner having a release layer on the surface of a resin film as a liner substrate or a release liner made of a resin film formed of a low-adhesive material can be preferably used because of its excellent surface smoothness. The resin film is not particularly limited as long as it can protect the pressure-sensitive 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 the formation of the release layer, for example, a silicone-based release agent, a long-chain alkyl-based release agent, an olefin-based release agent, a fluorine-based release agent, a fatty acid amide-based release agent, molybdenum sulfide, silica powder, etc. , a known release treatment agent can be used.

<Application>
The use of the pressure-sensitive adhesive sheet disclosed here is not limited, and it can be used for various purposes. The pressure-sensitive adhesive sheet disclosed herein includes a pressure-sensitive adhesive that has both a high refractive index and a low elastic modulus, and thus can be used for various applications that require a high refractive index and flexibility by taking advantage of these characteristics. obtain. For example, in electronic devices such as portable electronic devices, liquid crystal display devices, organic EL (electroluminescence) display devices, PDP (plasma display panels), display devices (image display devices) such as electronic paper, input devices such as touch panels, etc. devices (optical devices), particularly as a pressure-sensitive adhesive sheet for foldable displays and rollable displays. For example, in foldable displays and rollable displays, it is preferably used as means for bonding, fixing, protecting members having a high refractive index, and the like. The pressure-sensitive adhesive sheet disclosed herein has a high refractive index and is flexible enough to withstand repeated bending operations. It can follow the adherend (foldable display etc.) well. Examples of objects to be attached in such usage patterns include glass members such as window glass and cover glass used in foldable displays and rollable displays. In addition, since the adhesive sheet disclosed herein easily follows and adheres to a curved surface such as a three-dimensional shape of a mobile electronic device, it is also suitable for use in electronic devices having such a curved shape. Moreover, in some preferred embodiments, the pressure-sensitive adhesive may have excellent heat resistance in addition to having a high refractive index and a low elastic modulus. The portable electronic device is sometimes used in a high-temperature environment, and the internal space of the device may become hot due to the heat generated by the electronic components. Therefore, the heat-resistant adhesive sheet is highly advantageous.

Examples of the above portable electronic devices include, for example, mobile phones, smartphones, tablet computers, notebook computers, various wearable devices (for example, wrist wear types worn on the wrist like wristwatches, Modular type to be worn on the body, eyewear type including glasses type (monocular type and binocular type, including head-mounted type), clothing type to be attached to shirts, socks, hats, etc. in the form of accessories, earphones earwear type, etc.), 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, vehicle information Equipment, portable radios, portable televisions, portable printers, portable scanners, portable modems, etc. In this specification, the term “portable” means not only being able to be carried around, but also having a level of portability that allows an individual (a typical adult) to carry it relatively easily. shall mean.

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

The member or material (at least one adherend in the double-sided pressure-sensitive adhesive sheet) to which the pressure-sensitive adhesive sheet disclosed herein is attached is made of a material having a higher refractive index than a general acrylic pressure-sensitive adhesive. could be. The refractive index of the adherend material is, for example, 1.50 or more. .66) is also present. Such a high refractive index adherend material is typically a resin material. 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. The effect of using the pressure-sensitive adhesive sheet disclosed herein (suppression of reflection of light rays caused by a difference in refractive index) can be favorably exerted on such materials. 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 a mode of being attached to an adherend (for example, member) having a high refractive index as described above. Suitable examples of such adherends include resin films having a refractive index of 1.50 to 1.80 (preferably 1.55 to 1.75, eg 1.60 to 1.70). The refractive index can be measured by the same method as the refractive index of the adhesive.

A member or material to which the pressure-sensitive adhesive sheet is attached (at least one adherend in the double-sided pressure-sensitive adhesive sheet) may have optical transparency. With such an adherend, the advantage of the technique disclosed herein (suppression of light reflection at the interface between the adherend and the pressure-sensitive adhesive sheet) is likely to 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 adherend has a total light transmittance of 80% or higher, more preferably 90% or higher, and may be 95% or higher (eg, 95-100%). The pressure-sensitive adhesive sheet disclosed herein can be preferably used in a mode of being attached to an adherend (for example, an optical member) having a total light transmittance of a predetermined value or higher. The total light transmittance is measured using a commercially available transmittance meter in accordance with JIS K 7136:2000. As the transmittance meter, the trade name "Hazemeter HM-150" manufactured by Murakami Color Research Laboratory or its equivalent is used.

In some preferred embodiments, the adherend (for example, member) to which the pressure-sensitive adhesive sheet is attached may have the above-described refractive index and the above-described 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% ( For example, 70% or more, preferably 80% or more, more preferably 90% or more, and further 95% or more). obtain. The effect of the technique disclosed herein is particularly preferably exhibited in the aspect of being attached to such a member.

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

The optical member is a member having optical properties (e.g., polarization, light refraction, light scattering, light reflection, light transmission, light absorption, light diffraction, optical rotation, visibility, etc.). say. The optical member is not particularly limited as long as it is a member having optical properties. For example, a member constituting a device (optical device) such as a display device (image display device) or an input device, or used for these devices. Members include, for example, polarizing plates, wave plates, retardation plates, optical compensation films, brightness enhancement films, light guide plates, reflective films, antireflection films, hard coat (HC) films, impact 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 in which these are laminated (these are collectively referred to as may be referred to as a "functional film".) and the like. In addition, the above-mentioned "plate" and "film" include forms such as plate-like, film-like, sheet-like, etc. For example, "polarizing film" includes "polarizing plate" and "polarizing sheet", A "light guide plate" includes a "light guide film", a "light guide sheet", and the like. Moreover, the above-mentioned "polarizing plate" shall include 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 electronic paper. Moreover, a touch panel etc. are mentioned as said input device.

Examples of the optical member include, but are not limited to, members made of glass, acrylic resin, polycarbonate, PET, metal thin films, etc. (for example, sheet-like, film-like, or plate-like members). The term "optical member" in this specification also includes members (design films, decorative films, surface protective 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, waveguiding, light collection, diffraction, etc., or a fluorescent film, to be used as another optical member ( It may be another optical film.). In particular, in the bonding of optical films having at least one function of guiding, condensing, and diffracting light, 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, there is a demand for a reduction in thickness and an improvement in light extraction efficiency from the viewpoint of the trend toward miniaturization and higher performance of optical members. The adhesive disclosed herein can be preferably used as an adhesive that can meet such demands. More specifically, for example, in bonding a light guide film or a diffusion film, adjusting the refractive index (for example, increasing the refractive index) of an adhesive layer as a bonding layer can contribute to thinning. In bonding the fluorescent film, the light extraction efficiency (which can also be grasped as luminous efficiency) can be improved by appropriately adjusting the refractive index difference between the fluorescent light emitter and the adhesive. In bonding the toning film, by appropriately adjusting the refractive index of the pressure-sensitive adhesive so that the refractive index difference between the toning pigment and the toning pigment is small, the scattering component can be reduced, which can contribute to the improvement of the light transmittance. In bonding prism sheets, lenticular films, microlens array films, etc., by appropriately adjusting the refractive index of the pressure-sensitive adhesive, light diffraction can be controlled, contributing to improvement in brightness and/or viewing angle.

The pressure-sensitive adhesive sheet disclosed herein is preferably used in a mode in which it is attached to a high refractive index adherend (which may be a high refractive index layer or member, etc.), and the interface reflection with the adherend is can be suppressed. The pressure-sensitive adhesive sheet used in such an embodiment preferably has a small refractive index difference with the adherend and high adhesion at the interface with the adherend as described above. In addition, from the viewpoint of improving the homogeneity of the appearance, it is preferable that the thickness uniformity of the pressure-sensitive adhesive layer is high. For example, it is preferable that the surface smoothness of the pressure-sensitive adhesive layer is high. When the thickness of the high refractive index adherend is relatively small (for example, when it is 5 μm or less, 4 μm or less, or 2 μm or less), from the viewpoint of suppressing coloring and color unevenness due to interference of reflected light, It is particularly significant to suppress reflections. As an example of such a usage mode, in a polarizing plate with a retardation layer comprising a polarizer, a first retardation layer and a second retardation layer in this order, the bonding and / of the polarizer and the first retardation layer Alternatively, a mode in which it is used for joining the first retardation layer and the second retardation layer is exemplified.

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

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

The adhesive disclosed herein is used in microlenses and other lens members used as constituent members of cameras, light-emitting devices, etc. (for example, microlenses constituting microlens array films and 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, etc. can be preferably used. 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 a high refractive index resin or lenses having a surface layer made of a high refractive index resin). Even if there is, the refractive index difference with the lens can be reduced. This is advantageous from the viewpoint of thinning the lens and the product equipped with the lens, and can contribute to suppressing aberration and improving the Abbe number. The pressure-sensitive adhesive disclosed herein can also be used as a lens resin itself, for example, in the form of being filled in the recesses or voids of a suitable transparent member.

Modes for bonding optical members using the pressure-sensitive adhesive sheet disclosed herein are not particularly limited. ) The optical member may be attached to a member other than the optical member via the pressure-sensitive adhesive sheet disclosed herein, or (3) the pressure-sensitive adhesive sheet disclosed herein may contain the optical member. A mode in which the pressure-sensitive adhesive sheet is attached to an optical member or a member other than an optical member may be employed. In the aspect (3) above, 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). Such a pressure-sensitive adhesive sheet containing an optical member as a support can also be understood as a pressure-sensitive adhesive optical member (for example, pressure-sensitive adhesive optical film). Further, when the pressure-sensitive adhesive sheet disclosed herein is a type pressure-sensitive adhesive sheet having a support and the functional film is used as the support, the pressure-sensitive adhesive sheet disclosed herein is a functional film. 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 pressure-sensitive adhesive sheet is attached may have the refractive index of the adherend material described above. Moreover, the difference (refractive index difference) between the refractive index of the pressure-sensitive adhesive sheet and the refractive index of the member may be the refractive index difference between the adherend and the pressure-sensitive adhesive sheet described above. The members constituting the laminate are the same as the above-described members, materials, and adherends, so redundant description will not be repeated.

As understood from the above description and the following examples, the subject matter disclosed by this specification includes the following.
[1] containing an acrylic polymer and a plasticizer,
The monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1),
The pressure-sensitive adhesive composition, wherein the plasticizer is a compound having two or more double bond-containing rings and is liquid at 30°C.
[2] The pressure-sensitive adhesive composition according to [1] above, wherein the compound is liquid at 20°C.
[3] The pressure-sensitive adhesive composition according to [1] or [2] above, wherein the plasticizer is contained in an amount exceeding 15 parts by weight with respect to 100 parts by weight of the acrylic polymer.
[4] The pressure-sensitive adhesive composition according to any one of [1] to [3] above, wherein the plasticizer is contained in an amount exceeding 30 parts by weight with respect to 100 parts by weight of the acrylic polymer.
[5] The pressure-sensitive adhesive composition according to any one of [1] to [4] above, wherein the plasticizer has at least one ring selected from an aromatic ring and a heterocyclic ring as the double bond-containing ring. thing.
[6] The plasticizer has a first double bond-containing ring and a second double bond-containing ring, and the first double bond-containing ring and the second double bond-containing ring The pressure-sensitive adhesive composition according to any one of [1] to [5] above, wherein the ring is linked via a linking group having 1 to 5 atoms.
[7] The pressure-sensitive adhesive composition according to any one of [1] to [6] above, wherein the plasticizer has a molecular weight in the range of 100 to 2,000.
[8] The above [1] to [7], wherein the monomer component constituting the acrylic polymer contains a monomer (A2) having at least one of a hydroxyl group and a carboxy group in addition to the aromatic ring-containing monomer (A1). ], The pressure-sensitive adhesive composition according to any one of
[9] The pressure-sensitive adhesive composition according to any one of [1] to [8] above, wherein the content of the aromatic ring-containing monomer (A1) in the monomer component is 60% by weight or more.
[10] The pressure-sensitive adhesive according to any one of [1] to [9] above, wherein 50% by weight or more of the aromatic ring-containing monomer (A1) is a monomer having a homopolymer glass transition temperature of 10°C or lower. Composition.

[11] A pressure-sensitive adhesive formed from the pressure-sensitive adhesive composition according to any one of [1] to [9] above.
[12] The above, having a refractive index of 1.55 or more and a storage modulus G' (0°C) at 0°C of 1.0 x 10 ⁴ Pa to 1.0 x 10 ⁶ Pa. [11] The adhesive according to [11].
[13] The pressure-sensitive adhesive according to [11] or [12] above, which has a glass transition temperature in the range of -50°C to 0°C.
[14] The ratio of the storage modulus G' (0°C) to the storage modulus G' (80°C) at 80°C (G'(0°C)/G'(80°C)) is in the range of 1 to 1000. The pressure-sensitive adhesive according to any one of [11] to [13] above.
[15] The ratio of the storage modulus G' (-10°C) at -10°C to the storage modulus G' (80°C) at 80°C (G'(-10°C)/G' (80°C)) is 1 The pressure-sensitive adhesive according to any one of [11] to [14] above, wherein the range is from 1000 to 1000.

[16] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of [1] to [9] above.
[17] A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer comprising the pressure-sensitive adhesive according to any one of [11] to [15] above.
[18] The pressure-sensitive adhesive sheet according to [16] or [17] above, wherein the thickness of the pressure-sensitive adhesive layer is in the range of 5 to 75 μm.
[19] The product of the storage elastic modulus G'(0°C) [Pa] at 0°C and the thickness T [μm] of the pressure-sensitive adhesive layer (G'(0°C) × T) is 5.0 × 10 ⁴ to The pressure-sensitive adhesive sheet according to any one of [16] to [18] above, which is within the range of 5.0×10 ⁷ .
[20] The pressure-sensitive adhesive sheet according to any one of [16] to [19] above, which has a total light transmittance of 85% or more.
[21] The pressure-sensitive adhesive sheet according to any one of [16] to [20] above, which has a haze value of 3% or less.
[22] The pressure-sensitive adhesive sheet according to any one of [16] to [21] above, which has a peel strength to a glass plate of 0.1 N/25 mm or more.

Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in such specific examples. In the following description, "parts" and "%" representing amounts used and contents are based on weight unless otherwise specified.

<Example 1>
(Preparation of acrylic polymer solution)
A four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube and a cooler was charged with m-phenoxybenzyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light acrylate POB-A", refractive index: 1) as a monomer component. .566, Tg of homopolymer: −35° C., hereinafter referred to as “POB-A”) 95 parts and 5 parts of 4-hydroxybutyl acrylate (4HBA), 2,2′-azobisiso as a polymerization initiator 0.2 parts of butyronitrile and 150 parts of ethyl acetate as a polymerization solvent are charged, nitrogen gas is introduced while gently stirring, and the liquid temperature in the flask is maintained at around 60° C. to conduct a polymerization reaction for 6 hours. A solution (40%) of system polymer P1 was prepared. Mw of acrylic polymer P1 was 500,000.

(Preparation of adhesive composition)
The solution (40%) of the acrylic polymer P1 was diluted to 20% with ethyl acetate, and 500 parts of this solution (100 parts of nonvolatile matter) was added to an isocyanurate of hexamethylene diisocyanate as a cross-linking agent (manufactured by Tosoh Corporation, trade name "Coronate HX", trifunctional isocyanate compound) 10 parts of 1% ethyl acetate solution (0.1 parts of non-volatile content), 2 parts of acetylacetone as a crosslinking retarder, 1% ethyl acetate solution of Nasem ferric iron as a crosslinking catalyst (non-volatile content 0.01 part) was added and mixed with stirring to prepare an acrylic pressure-sensitive adhesive composition according to this example.

(Preparation of adhesive sheet)
The acrylic pressure-sensitive adhesive composition prepared above was applied to the silicone-treated surface of a polyethylene terephthalate (PET) film R1 (thickness: 50 μm) that had been silicone-treated on one side, and heated at 130° C. for 2 minutes to increase the thickness. An adhesive layer having a thickness of 20 μm was formed. Next, the silicone-treated surface of PET film R2 (thickness: 25 μm) having one surface silicone-treated was attached to the surface of the pressure-sensitive adhesive layer. In this way, a substrate-less double-sided pressure-sensitive adhesive sheet comprising 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>
(Preparation of acrylic polymer solution)
A four-necked flask equipped with a stirring blade, a thermometer, a nitrogen gas inlet tube and a cooler was charged with benzyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat #160", refractive index: 1.519, as a monomer component). Tg of homopolymer: 6° C. (hereinafter referred to as “BZA”) 99 parts and 1 part of 4HBA, 0.2 parts of 2,2′-azobisisobutyronitrile as a polymerization initiator, and ethyl acetate as a polymerization solvent 100 parts was charged, nitrogen gas was introduced while gently stirring, the liquid temperature in the flask was maintained at around 60°C, and the polymerization reaction was carried out for 6 hours to prepare a solution of acrylic polymer P2 (polymer concentration: 50%). . The Mw of the acrylic polymer P2 was 1,000,000.

(Preparation of adhesive composition)
The acrylic polymer P2 solution (polymer concentration 50%) was diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (100 parts of non-volatile matter) was added to an isocyanurate of hexamethylene diisocyanate (Tosoh Corporation) as a cross-linking agent. 10 parts of 1% ethyl acetate solution (non-volatile content 0.1 part), 2 parts of acetylacetone as a cross-linking retarder, and 1 part of Nasem ferric iron as a cross-linking catalyst. % ethyl acetate solution (0.01 part of non-volatile content) was added and mixed with stirring to prepare an acrylic pressure-sensitive adhesive composition according to this example.

(Preparation of adhesive sheet)
Using the obtained acrylic pressure-sensitive adhesive composition, in the same manner as in Example 1, a pressure-sensitive adhesive sheet according to this example (a substrate-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) was produced.

<Examples 3 to 5>
In the preparation of the acrylic pressure-sensitive adhesive composition in Example 2, POB-A (manufactured by Kyoeisha Chemical Co., Ltd., trade name "Light Acrylate POB- A", m-phenoxybenzyl acrylate, refractive index: 1.566, liquid at 20° C.) was additionally added with 30 parts (Example 3), 45 parts (Example 4) or 60 parts (Example 5). An acrylic pressure-sensitive adhesive composition according to each example was prepared in the same manner as in the preparation of the acrylic pressure-sensitive adhesive composition in 2. A pressure-sensitive adhesive sheet (base-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) according to each example was prepared in the same manner as the pressure-sensitive adhesive sheet in Example 1, except that each of the obtained acrylic pressure-sensitive adhesive compositions was used. .

<Example 6>
The composition of the monomer component is phenoxyethyl acrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name “Viscoat #192”, refractive index: 1.517, Tg of homopolymer: 2° C., hereinafter referred to as “PEA”) 99. A solution of acrylic polymer P3 was prepared in the same manner as in the preparation of the acrylic polymer solution in Example 2, except that the amount was changed to 1 part and 1 part of 4HBA. Mw of the acrylic polymer P3 was 1,000,000.
An acrylic pressure-sensitive adhesive composition according to this example was prepared in the same manner as the acrylic pressure-sensitive adhesive composition in Example 2 except that the solution of acrylic polymer P3 was used instead of the solution of acrylic polymer P2, Using the obtained acrylic pressure-sensitive adhesive composition, in the same manner as in Example 1, a pressure-sensitive adhesive sheet according to this example (a substrate-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) was produced.

<Example 7>
In the preparation of the acrylic pressure-sensitive adhesive composition in Example 3, the solution of acrylic polymer P3 was used in place of the solution of acrylic polymer P2. Otherwise, in the same manner as in the preparation of the acrylic pressure-sensitive adhesive composition in Example 3, an acrylic pressure-sensitive adhesive composition according to this example was prepared, and the obtained acrylic pressure-sensitive adhesive composition was used in the same manner as in Example 1. Then, a pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet without a base material comprising a pressure-sensitive adhesive layer) according to this example was produced.

<Example 8>
A solution of acrylic polymer P4 was prepared in the same manner as the acrylic polymer solution in Example 2 except that the composition of the monomer component was changed to 99 parts of BZA and 1 part of acrylic acid (AA). Mw of acrylic polymer P4 was 1,000,000.
The acrylic polymer P4 solution (polymer concentration 50%) was diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (nonvolatile content 100 parts) was added as a crosslinking agent to an epoxy crosslinking agent (manufactured by Mitsubishi Gas Chemical Co., Ltd. , trade name “Tetrad C”, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane) 0.1 part was added and mixed with stirring to prepare an acrylic pressure-sensitive adhesive composition according to this example. bottom.
A pressure-sensitive adhesive sheet according to this example (base-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) was prepared in the same manner as the pressure-sensitive adhesive sheet in Example 1, except that the obtained acrylic pressure-sensitive adhesive composition was used.

<Examples 9 to 12>
In the preparation of the acrylic pressure-sensitive adhesive composition in Example 8, 60 parts of POB-A as the plasticizer A1 (Example 9) and 4 parts as the plasticizer A2 are added to 100 parts of the non-volatile matter contained in the solution of the acrylic polymer P4. , 4'-oxybis[(methoxymethyl)benzene] (manufactured by Tokyo Chemical Industry Co., Ltd., refractive index: 1.56, liquid at 20 ° C.) 60 parts (Example 10), 3-phenoxybenzyl alcohol (Tokyo Kasei Kogyo Co., Ltd., refractive index: 1.591, liquid at 20 ° C.) 60 parts (Example 11), or 1-acetonaphthone as plasticizer A4 (Tokyo Chemical Industry Co., Ltd., refractive index: 1.63, 20 ° C. The acrylic pressure-sensitive adhesive composition according to each example was prepared in the same manner as the acrylic pressure-sensitive adhesive composition in Example 8, except that 60 parts of (Example 12) was further added. A pressure-sensitive adhesive sheet (base-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) according to each example was prepared in the same manner as the pressure-sensitive adhesive sheet in Example 1, except that each of the obtained acrylic pressure-sensitive adhesive compositions was used. .

<Example 13>
A solution of acrylic polymer P5 was prepared in the same manner as the acrylic polymer solution in Example 2 except that the composition of the monomer component was changed to 90 parts of BZA, 9 parts of n-butyl acrylate (BA) and 1 part of AA. Mw of acrylic polymer P5 was 1,000,000.
A solution of the acrylic polymer P5 (polymer concentration 50%) is diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (100 parts of nonvolatile matter) is added to 60 parts of the plasticizer A3 (POB-AL), and , 0.1 part of the above epoxy-based cross-linking agent was added and mixed with stirring to prepare an acrylic pressure-sensitive adhesive composition according to this example.
A pressure-sensitive adhesive sheet according to this example (base-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) was prepared in the same manner as the pressure-sensitive adhesive sheet in Example 1, except that the obtained acrylic pressure-sensitive adhesive composition was used.

<Example 14>
In the preparation of the acrylic pressure-sensitive adhesive composition in Example 13, biscresol fluorene (manufactured by Osaka Gas Chemicals Co., Ltd., 9,9-bis( 4-Hydroxy-3-methylphenyl)fluorene, refractive index: 1.68. Hereinafter, it may be referred to as "BCF." An acrylic pressure-sensitive adhesive composition according to this example was prepared in the same manner as in the preparation of the composition. The above additives were added as 10% ethyl acetate solutions.
A pressure-sensitive adhesive sheet according to this example (base-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) was prepared in the same manner as the pressure-sensitive adhesive sheet in Example 1, except that the obtained acrylic pressure-sensitive adhesive composition was used.

<Example 15 to Example 16>
A solution of acrylic polymer P6 was prepared in the same manner as the acrylic polymer solution in Example 2 except that the composition of the monomer components was changed to 90 parts of BZA, 9 parts of 2-ethylhexyl acrylate (2EHA) and 1 part of AA. Mw of the acrylic polymer P6 was 1,000,000.
In the preparation of the acrylic pressure-sensitive adhesive composition in Examples 13 and 14, the solution of acrylic polymer P6 was used in place of the solution of acrylic polymer P5. The other acrylic pressure-sensitive adhesive compositions of Examples 15 and 16 were prepared in the same manner as the acrylic pressure-sensitive adhesive compositions of Examples 13 and 14, and the obtained acrylic pressure-sensitive adhesive compositions were In the same manner as in Example 1, a pressure-sensitive adhesive sheet (base-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) according to each example was produced.

<Example 17 to Example 18>
A solution of acrylic polymer P7 was prepared in the same manner as the acrylic polymer solution in Example 2 except that the composition of the monomer components was changed to 80 parts of BZA, 19 parts of BA and 1 part of AA. A solution of acrylic polymer P8 was prepared in the same manner as the acrylic polymer solution in Example 2 except that the composition of the monomer components was changed to 66 parts of BZA, 33 parts of BA and 1 part of AA. Mw of the acrylic polymers P7 and P8 was 1,000,000.
In the preparation of the acrylic pressure-sensitive adhesive composition in Example 13, the solution of acrylic polymer P7 (Example 17) or P8 (Example 18) was used in place of the solution of acrylic polymer P5. Otherwise, in the same manner as the preparation of the acrylic pressure-sensitive adhesive composition in Example 13, the acrylic pressure-sensitive adhesive compositions according to Examples 17 and 18 were prepared, and the obtained acrylic pressure-sensitive adhesive compositions were used. , in the same manner as in Example 1, a pressure-sensitive adhesive sheet (a substrate-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) according to each example was produced.

<Example 19>
A solution of acrylic polymer P9 was prepared in the same manner as the acrylic polymer solution in Example 2 except that the composition of the monomer components was changed to 85 parts of POB-A, 14 parts of BA and 1 part of AA. Mw of acrylic polymer P9 was 1,000,000.
In the preparation of the acrylic pressure-sensitive adhesive composition in Example 13, the solution of acrylic polymer P9 was used in place of the solution of acrylic polymer P5. Otherwise, in the same manner as in the preparation of the acrylic pressure-sensitive adhesive composition in Example 13, an acrylic pressure-sensitive adhesive composition according to this example was prepared, and the obtained acrylic pressure-sensitive adhesive composition was used in the same manner as in Example 1. Then, a pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet without a base material comprising a pressure-sensitive adhesive layer) according to this example was produced.

<Example 20>
In the preparation of the acrylic pressure-sensitive adhesive composition in Example 19, 6-acryloyloxymethyldinaphthothiophene (a product manufactured by Sugai Chemical Industry Co., Ltd.) was further added as an additive to 100 parts of the non-volatile matter contained in the solution of the acrylic polymer P9. name "6MDNTA", dinaphthothiophene-6-methyl acrylate, refractive index 1.75, hereinafter sometimes referred to as "6MDNTA") was added. Otherwise, an acrylic pressure-sensitive adhesive composition according to this example was prepared in the same manner as the acrylic pressure-sensitive adhesive composition in Example 19, and the obtained acrylic pressure-sensitive adhesive composition was used in the same manner as in Example 1. Then, a pressure-sensitive adhesive sheet (double-sided pressure-sensitive adhesive sheet without a base material comprising a pressure-sensitive adhesive layer) according to this example was produced. The above additives were added as 10% ethyl acetate solutions.

<Example 21 to Example 22>
A solution of acrylic polymer P10 was prepared in the same manner as the acrylic polymer solution in Example 2 except that the composition of the monomer components was changed to 80 parts of POB-A, 19 parts of BA and 1 part of AA. Mw of the acrylic polymer P10 was 1,000,000.
In the preparation of the acrylic pressure-sensitive adhesive composition in Example 13, the solution of acrylic polymer P10 was used in place of the solution of acrylic polymer P5. Otherwise, in the same manner as the acrylic pressure-sensitive adhesive composition in Example 13, an acrylic pressure-sensitive adhesive composition according to Example 21 was prepared. Further, in the preparation of the acrylic pressure-sensitive adhesive composition according to Example 21, the amount of the epoxy cross-linking agent used was changed to 0.5 parts with respect to 100 parts of the non-volatile matter contained in the solution of the acrylic polymer P10. An acrylic pressure-sensitive adhesive composition according to was prepared.
Using each obtained acrylic pressure-sensitive adhesive composition, in the same manner as in Example 1, a pressure-sensitive adhesive sheet (a substrate-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) according to each example was produced.

<Example 23>
99 parts of POB-A and 2-acryloyloxyethyl-succinic acid (manufactured by Kyoeisha Chemical Co., Ltd., trade name "HOA-MS (N)", hereinafter referred to as "HOA-MS") to 1 part of the monomer component A solution of acrylic polymer P11 was prepared in the same manner as the acrylic polymer solution in Example 1, except for the changes. Mw of acrylic polymer P11 was 500,000.
The solution of the acrylic polymer P11 was diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (100 parts of nonvolatile matter) was added to 40 parts of the plasticizer A3 (POB-AL), and trimethylpentaphenyl as the plasticizer A5. Trisiloxane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "HIVAC F-5", molecular weight: 546, refractive index: 1.575, liquid at 20 ° C.) 20 parts, and the epoxy-based cross-linking agent (hereinafter referred to as cross-linking agent C1 Also called.) was added and mixed with stirring to prepare an acrylic pressure-sensitive adhesive composition according to this example.
A pressure-sensitive adhesive sheet according to this example (base-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) was prepared in the same manner as the pressure-sensitive adhesive sheet in Example 1, except that the obtained acrylic pressure-sensitive adhesive composition was used.

<Example 24>
A solution of acrylic polymer P12 was prepared in the same manner as the acrylic polymer solution in Example 23, except that the composition of the monomer components was changed to 95 parts of POB-A, 2 parts of lauryl acrylate (LA), 2 parts of 2EHA and 1 part of 4HBA. bottom. Mw of acrylic polymer P12 was 500,000.
The solution of the acrylic polymer P12 is diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (100 parts of nonvolatile matter) are added with 40 parts of the plasticizer A3 (POB-AL) and the plasticizer A5 (HIVAC F -5) 20 parts, an acyclic bifunctional isocyanate cross-linking agent (manufactured by Tosoh Corporation, trade name "Coronate 2770", hexamethylene diisocyanate (HDI) allophanate) as a cross-linking agent C2 0.3 parts, as a cross-linking retarder 2 parts of acetylacetone and 1 part of a 1% ethyl acetate solution of Nasem ferric iron as a cross-linking catalyst (0.01 part of non-volatile matter) were added and mixed with stirring to prepare an acrylic pressure-sensitive adhesive composition according to this example.
A pressure-sensitive adhesive sheet according to this example (base-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) was prepared in the same manner as the pressure-sensitive adhesive sheet in Example 1, except that the obtained acrylic pressure-sensitive adhesive composition was used.

<Example 25>
A solution of acrylic polymer P13 was prepared in the same manner as the acrylic polymer solution in Example 23, except that the composition of the monomer components was changed to 90 parts of POB-A, 9 parts of 2EHA and 1 part of 4HBA. Mw of acrylic polymer P13 was 500,000.
The solution of the acrylic polymer P13 is diluted with ethyl acetate to a polymer concentration of 30%, and 334 parts of this solution (100 parts of nonvolatile matter) is added with 80 parts of the plasticizer A5 (HIVAC F-5) and the crosslinker C2 (Coronate 2770) 0.5 part, 2 parts of acetylacetone as a cross-linking retarder, and 1 part of a 1% ethyl acetate solution of Nasem ferric iron (0.01 part of non-volatile matter) as a cross-linking catalyst were added and stirred to mix. A system adhesive composition was prepared.
A pressure-sensitive adhesive sheet according to this example (base-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) was prepared in the same manner as the pressure-sensitive adhesive sheet in Example 1, except that the obtained acrylic pressure-sensitive adhesive composition was used.

<Examples 26-28>
Solutions of acrylic polymers P14 and P15 were prepared in the same manner as the acrylic polymer solution in Example 23, except that the composition of the monomer components was changed as shown in Table 3. Mw of acrylic polymers P14 and P15 was 500,000 each.
A solution of the acrylic polymer P11, P14 or P15 is diluted with ethyl acetate to a polymer concentration of 30%, and the plasticizer A3 and the cross-linking agent C1 or C2 are added to 334 parts of this solution (100 parts of nonvolatile matter). For Examples 26 and 28, 2 parts of acetylacetone as a cross-linking retarder and 1 part of a 1% ethyl acetate solution of Nasem ferric iron (0.01 part of non-volatile matter) as a cross-linking catalyst were added. They were stirred and mixed to prepare an acrylic pressure-sensitive adhesive composition according to each example.
A pressure-sensitive adhesive sheet (a substrate-less double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer) according to each example was prepared in the same manner as the pressure-sensitive adhesive sheet in Example 1, except that the obtained acrylic pressure-sensitive adhesive composition was used.

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

(Storage modulus G' and glass transition temperature)
A sample for measurement was obtained by laminating the pressure-sensitive adhesive layers according to each example to a thickness of about 1.5 mm. Using "Advanced Rheometric Expansion System (ARES)" manufactured by Rheometric Scientific, dynamic viscoelasticity was measured under the following conditions. From the measurement results, the storage elastic modulus G′ [Pa] of the adhesive at each temperature (−20° C., −10° C., 0° C. and 80° C.) was determined. Also, the temperature corresponding to the peak top temperature of the loss tangent tan δ (loss elastic modulus G″/storage elastic modulus G′) in the dynamic viscoelasticity measurement was obtained as the glass transition temperature (Tg) [° C.] of the adhesive.
[Measurement condition]
Deformation mode: Torsion Measurement frequency: 1Hz
Temperature range: -50°C to 150°C
Heating rate: 5°C/min Shape: Parallel plate 7.9mmφ

(total light transmittance and haze)
Using a test piece in which the adhesive layer according to each example is attached to non-alkali glass (thickness 0.8 to 1.0 mm, total light transmittance 92%, haze 0.4%), under a measurement environment of 23 ° C. , a haze meter (“HM-150” manufactured by Murakami Color Research Laboratory) was used to measure the total light transmittance and haze of the test piece. The values obtained by subtracting the total light transmittance and haze of the alkali-free glass from the measured values were taken as the total light transmittance [%] and haze [%] of the adhesive (layer). For the substrate-less pressure-sensitive adhesive sheet comprising 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 the measurement environment of 23° C. and 50% RH, the release liner was peeled off from one side of the adhesive sheet, and a PET film having a thickness of 50 μm was laminated and backed, and then cut into a size of 25 mm in width and 100 mm in length. was used as a test piece. The release liner on the other side of the test piece is peeled off, and a 2 kg roller is reciprocated once on the surface of an alkali glass plate (manufactured by Matsunami Glass Industry Co., Ltd., thickness 1.35 mm, polished soda plate edge) as an adherend. and crimped. After leaving it under the same environment for 30 minutes, using a universal tensile compression tester, peel strength (adhesive strength ) [N/25 mm] was measured. As a universal tension/compression tester, “Tensile/compression tester, TG-1kN” manufactured by Minebea Co., Ltd. was used. In addition, in the case of a single-sided pressure-sensitive adhesive sheet with a substrate, backing with a PET film is not essential.

(Bending test)
A pressure-sensitive adhesive sheet with a release liner according to each example was cut into a rectangle of 2 cm×10 cm to obtain a test piece for measurement. A cylindrical bar of φ4 mm was horizontally fixed at a height sufficient for measurement, and the test piece obtained above was hung on the bar and bent. Specifically, the above-mentioned test piece was formed into an inverted U shape by hooking the central portion in the longitudinal direction on a bar. Then, both ends located below the test piece were fixed with a clip (13 g), a 60 g weight was suspended and fixed to the clip through a thread of 1 cm in length, and a load was applied to the bent portion of the test piece. . In this state, the test piece was held in a predetermined temperature environment (-20°C, -10°C or 0°C) for 1 minute, and after 1 minute, the test piece was removed from the bar. Then, in the same temperature environment, the test piece was left still on a horizontal surface so that the crest side of the bent portion faced downward, and left still for 10 minutes. After standing still for 10 minutes, the time required for the end (short side end) of the test piece to come into contact with the horizontal surface was measured. This test was conducted under the conditions of -20°C, -10°C and 0°C, respectively, and the flexibility was evaluated according to the following criteria.
E (Excellent): In the bending test under all temperature conditions (-20°C, -10°C and 0°C), the edge of the test piece touched the horizontal surface within 10 minutes.
G (Good): In the bending test under temperature conditions of -10°C and 0°C, the edge of the test piece touched the horizontal surface within 10 minutes.
A (Acceptable): In the bending test at a temperature of 0°C, the edge of the test piece touched the horizontal surface within 10 minutes.
P (Poor): In the bending test under all temperature conditions, the edge of the test piece did not touch the horizontal surface or the adhesive layer was peeled off from the release liner within 10 minutes.

Tables 1 to 3 show the outline and evaluation results of the pressure-sensitive adhesives according to each example.

As shown in Tables 1 to 3, an acrylic polymer polymerized using an aromatic ring-containing monomer (A1) and, as a plasticizer, a compound that is liquid at 30°C and has two or more double bond-containing rings is included. In Examples 3 to 5, Example 7, and Examples 9 to 28 using the adhesive composition, the adhesive had a refractive index of 1.55 or more and a storage elastic modulus G' (0°C) of 1.0 × 10 ⁶ Pa or less. A pressure-sensitive adhesive having a high refractive index and a low elastic modulus could be formed. The pressure-sensitive adhesive sheets according to these examples all passed the bending test (A or higher). On the other hand, in Examples 1 and 2, Example 6, and Example 8, an acrylic polymer containing an aromatic ring-containing monomer (A1) as a monomer unit could be used to form a high refractive index pressure-sensitive adhesive, but the storage elastic modulus G'( 0° C.) exceeded 1.0×10 ⁶ Pa and did not have a low elastic modulus. The pressure-sensitive adhesive sheets according to these examples failed the bending test (P).

More specifically, from the results of Examples 3 to 5, by increasing the amount of the plasticizer, the storage elastic modulus G' at each temperature is reduced while maintaining a high refractive index, resulting in a pressure-sensitive adhesive with a lower elastic modulus. can be produced. Further, Examples 9 to 12 are examples in which the plasticizer species were changed. From these results, it was found that by using a compound that has two or more double bond-containing rings and is liquid at 30°C as a plasticizer, a high refractive index and a It can be seen that both a low elastic modulus and a low elastic modulus can be achieved. Examples 13 to 16 and 20 are results of examination of additives, and it can be seen that a higher refractive index can be achieved by using various additives. Further, from the comparison between Examples 13 and 15, by selecting an alkyl (meth)acrylate species as a monomer component, the elastic modulus of the pressure-sensitive adhesive can be lowered while adjusting, for example, increasing the storage elastic modulus G′ in the high temperature range. It can be seen that Examples 17 and 18 are examples in which the usage ratio of the aromatic ring-containing monomer (A1) was changed, and it can be seen that a high refractive index can be maintained even if the usage amount of the aromatic ring-containing monomer (A1) is limited. In addition, in Examples 17 and 18, the difference in storage elastic modulus G' between the low temperature range and the high temperature range was better suppressed. This is believed to be due to the increased amount of alkyl (meth)acrylate (specifically, BA) accompanying the decrease in aromatic ring-containing monomer (A1). Examples 21 and 22 are examples in which the amount of the cross-linking agent is changed, and it can be seen that the storage elastic modulus G' can be improved by increasing the amount of the cross-linking agent. Examples 23 to 28 are examples in which the monomer composition of the polymer, the plasticizer species, the crosslinker species and/or the usage ratio of each component are changed. It can be seen that the storage modulus of the adhesive can be adjusted within a desired range while maintaining a high refractive index by designing the composition of the adhesive, such as adjusting the amount used.

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

1, 2, 3 adhesive sheet 10 support substrate 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 Faces 31, 32 release liner

Claims (10)

including an acrylic polymer and a plasticizer,
The monomer component constituting the acrylic polymer contains an aromatic ring-containing monomer (A1),
The pressure-sensitive adhesive composition, wherein the plasticizer is a compound having two or more double bond-containing rings and is liquid at 30°C. The pressure-sensitive adhesive composition according to claim 1, wherein the compound is a liquid compound at 20°C. The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the plasticizer is contained in an amount exceeding 15 parts by weight with respect to 100 parts by weight of the acrylic polymer. The pressure-sensitive adhesive composition according to any one of claims 1 to 3, wherein the plasticizer is contained in an amount exceeding 30 parts by weight with respect to 100 parts by weight of the acrylic polymer. The pressure-sensitive adhesive composition according to any one of claims 1 to 4, wherein the plasticizer has at least one ring selected from aromatic rings and heterocycles as the double bond-containing ring. The plasticizer has a first double bond-containing ring and a second double bond-containing ring, and the first double bond-containing ring and the second double bond-containing ring are , linked via a linking group having 1 to 5 atoms, the adhesive composition according to any one of claims 1 to 5. The adhesive composition according to any one of claims 1 to 6, wherein the plasticizer has a molecular weight in the range of 100-2000. Any one of claims 1 to 7, wherein the monomer component constituting the acrylic polymer contains, in addition to the aromatic ring-containing monomer (A1), a monomer (A2) having at least one of a hydroxyl group and a carboxy group. The pressure-sensitive adhesive composition according to . The pressure-sensitive adhesive composition according to any one of claims 1 to 8, wherein the content of the aromatic ring-containing monomer (A1) in the monomer component is 60% by weight or more. A pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of claims 1 to 9.

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