JP7664697B2 - Adhesive composition for flexible displays, adhesive material, and adhesive sheet - Google Patents

Description

The present invention relates to an adhesive composition used in flexible displays, and more specifically to an adhesive composition that forms an adhesive used to bond one flexible member to another flexible member.

In various displays and touch panels for televisions, mobile phones, smartphones, etc., adhesives are generally used to bond the components that make up these displays and touch panels. The adhesives are provided, for example, in the form of a substrate-attached adhesive sheet having an adhesive layer on a supporting substrate, or a substrate-less adhesive sheet without a supporting substrate, and are used to bond the components together.

On the other hand, in recent years, flexible displays that are repeatedly bent and used in image display devices such as liquid crystal display devices and organic electroluminescence (organic EL) display devices have been attracting attention. Flexible displays include foldable displays that can be folded and rollable displays that can be rolled up into a cylindrical shape, and are expected to be used in mobile devices such as smartphones and tablet devices, and storable stationary displays.

For example, Patent Document 1 discloses an adhesive for bonding a flexible member constituting a component that is repeatedly bent and stretched in such a flexible display to another flexible member, in which the ratio of the shear stress 60 seconds after 1000% displacement to the maximum shear stress when one side of the adhesive layer and the other side are displaced 1000% in opposite directions, and the gel fraction are controlled within a predetermined range (see Patent Document 1 (Claim 1)).

JP 2019-108498 A

In conventional flexible displays with an adhesive layer, when the display was repeatedly bent, the adhesive layer did not fully recover from the bent state to its original state. As a result, repeated bending of the flexible display could result in poor appearance, such as lifting or peeling at the interface between the adhesive layer and the flexible member at the bent area, or the bent area appearing wavy.

The present invention has been made in consideration of the above circumstances, and aims to provide an adhesive composition capable of forming an adhesive material (adhesive layer) with excellent resilience.

The adhesive composition for flexible displays of the present invention, which has been able to solve the above problems, is an adhesive composition for flexible displays for bonding one flexible member constituting a flexible display to another flexible member, and is characterized in that the adhesive composition contains a (meth)acrylic copolymer having a first reactive group and a crosslinking agent having a second reactive group that reacts with the first reactive group, the amount of the first reactive group in the (meth)acrylic copolymer is 0.002 mmol/g to 0.4 mmol/g, the molar ratio of the second reactive group in the crosslinking agent to the first reactive group in the copolymer (molar amount of first reactive group/molar amount of second reactive group) is 1 or more, and the molar ratio of the first reactive group in the copolymer to the amount of the crosslinking agent (molar amount of first reactive group/molar amount of crosslinking agent) is less than 12.0.

By using the adhesive composition for flexible displays of the present invention, an adhesive material (adhesive layer) with excellent resilience can be formed. Therefore, by using the adhesive composition for flexible displays of the present invention, a flexible display can be manufactured that can suppress the occurrence of defects in appearance such as cracks and waviness, without the occurrence of lifting or peeling at the interface between the adhesive layer and the flexible member at the bending points, even when repeatedly bent.

1 is a schematic cross-sectional view of an example of a pressure-sensitive adhesive sheet of the present invention. FIG. 2 is a schematic cross-sectional view of an example of a flexible laminated member of the present invention.

The following describes an example of a preferred embodiment of the present invention. However, the following embodiment is merely an example. The present invention is not limited to the following embodiment.

In the present invention, "(meth)acrylic" refers to "at least one of acrylic and methacrylic". "(meth)acrylate" refers to "at least one of acrylate and methacrylate". "(meth)acryloyl" refers to "at least one of acryloyl and methacryloyl". "Vinyl monomer" refers to a monomer having a radically polymerizable carbon-carbon double bond in the molecule. "Structural unit derived from vinyl monomer" refers to a structural unit in which the radically polymerizable carbon-carbon double bond of a vinyl monomer is polymerized to a carbon-carbon single bond. "Structural unit derived from (meth)acrylate" refers to a structural unit in which the radically polymerizable carbon-carbon double bond of a (meth)acrylate is polymerized to a carbon-carbon single bond. "Structural unit derived from (meth)acrylic monomer" refers to a structural unit in which the radically polymerizable carbon-carbon double bond of a (meth)acrylic monomer is polymerized to a carbon-carbon single bond.

[Adhesive composition for flexible displays]
The adhesive composition for flexible displays of the present invention (hereinafter, may be simply referred to as "adhesive composition") is an adhesive composition for flexible displays for bonding one flexible member constituting a flexible display to another flexible member. The adhesive composition contains (A) a (meth)acrylic copolymer having a first reactive group, and (B) a crosslinking agent having a second reactive group that reacts with the first reactive group.

((A) (Meth)acrylic copolymer)
The (meth)acrylic copolymer may be a copolymer that contains a structural unit derived from a (meth)acrylic monomer as the main component (50% by mass or more), and may contain a structural unit derived from a vinyl monomer other than a (meth)acrylic monomer. The content of the structural unit derived from a (meth)acrylic monomer in the (A) copolymer is preferably 80% by mass or more, more preferably 90% by mass or more, based on 100% by mass of the entire copolymer. The copolymer (A) may be composed only of structural units derived from a (meth)acrylic monomer.

The (A) copolymer is preferably a (meth)acrylate-based copolymer. The (meth)acrylate-based copolymer may be any copolymer that contains structural units derived from (meth)acrylate as the main component (50% by mass or more), and may contain structural units derived from vinyl monomers other than (meth)acrylate. The (meth)acrylate is an ester compound formed from (meth)acrylic acid and a compound having a hydroxyl group. The content of structural units derived from (meth)acrylate in the (A) copolymer is preferably 80% by mass or more, more preferably 90% by mass or more, based on 100% by mass of the entire copolymer.

The copolymer (A) has a first reactive group. The first reactive group is a functional group that has high reactivity with a second reactive group of the crosslinking agent (B) described below. Examples of functional groups that can become the first reactive group include functional groups that have reactivity. The first reactive group is preferably a hydroxy group and/or a carboxy group.

Examples of the combination of the first reactive group of the copolymer (A) and the second reactive group of the crosslinking agent (B) include the following combinations.
When the second reactive group of the crosslinking agent (B) is an isocyanate group, the first reactive group can be a hydroxy group.
When the second reactive group of the crosslinking agent (B) is an epoxy group, the first reactive group can be a carboxy group.

Preferred combinations of the first reactive group of the copolymer (A) and the second reactive group of the crosslinking agent (B) are (1) a combination in which the first reactive group is a hydroxy group and the second reactive group is an isocyanate group; and (2) a combination in which the first reactive group is a carboxy group and the second reactive group is an epoxy group.

The amount of the first reactive group in the copolymer (A) is preferably 0.002 mmol/g or more, more preferably 0.006 mmol/g or more, and even more preferably 0.01 mmol/g or more, and is preferably 0.4 mmol/g or less, more preferably 0.2 mmol/g or less, and even more preferably 0.1 mmol/g or less. If the amount of the first reactive group is 0.002 mmol/g or more, the adhesive formed is appropriately crosslinked and exhibits a suitable recovery rate, and if it is 0.4 mmol/g or less, the distance between crosslinking points in the adhesive formed is sufficiently long and the adhesive is excellent in flexibility.

When the first reactive group of the copolymer (A) is a hydroxy group, it is preferable that the copolymer (A) further has a carboxy group as a functional group other than the first reactive group. In this case, the amount of carboxy groups in the copolymer (A) is preferably 0.08 mmol/g or more, more preferably 0.16 mmol/g or more, and even more preferably 0.32 mmol/g or more, and is preferably 1.3 mmol/g or less, more preferably 0.8 mmol/g or less, and even more preferably 0.6 mmol/g or less.

When the (A) copolymer is a carboxy group, it is preferable that the (A) copolymer further has a group as a functional group other than the first reactive group. In this case, the amount of carboxy groups in the (A) copolymer is preferably 0.08 mmol/g or more and 1.3 mmol/g or less.

When the (A) copolymer has both carboxy groups and hydroxy groups, the molar ratio of carboxy groups to hydroxy groups per unit mass of the (A) copolymer (carboxy groups/hydroxy groups) is preferably 4 or more, more preferably 8 or more, even more preferably 16 or more, and is preferably 60 or less, more preferably 40 or less, even more preferably 30 or less. If the molar ratio (carboxy groups/hydroxy groups) is within the above range, the adhesive layer will have high resilience and a good balance between adhesive strength and flexibility.

The copolymer (A) has a first reactive group. That is, the copolymer (A) contains a structural unit (a-1) having a first reactive group in its structure. The structural unit (a-1) having the first reactive group may be only one type, or may have two or more types. The first reactive group may be in a structural unit derived from a (meth)acrylic monomer (preferably a (meth)acrylate monomer and/or (meth)acrylic acid) or a structural unit derived from a vinyl monomer other than a (meth)acrylic monomer. That is, the structural unit (a-1) having the first reactive group may be a structural unit derived from a (meth)acrylic monomer (preferably a (meth)acrylate monomer and/or (meth)acrylic acid) having a first reactive group, or a structural unit derived from a vinyl monomer other than a (meth)acrylic monomer having a first reactive group.

The content of the structural unit (structural unit (a-1) having a first reactive group) derived from a vinyl monomer having a first reactive group in the copolymer (A) is preferably 0.03% by mass or more, more preferably 0.09% by mass or more, even more preferably 0.15% by mass or more, and is preferably 6% by mass or less, more preferably 3% by mass or less, even more preferably 1.5% by mass or less, based on 100% by mass of the entire copolymer. If the content of the structural unit (a-1) is within the above range, an adhesive having an excellent balance between adhesion to an adherend and durability can be formed. The vinyl monomer having a first reactive group includes a (meth)acrylic monomer having a first reactive group and a vinyl monomer other than a (meth)acrylic monomer having a first reactive group.

The (meth)acrylic monomer includes (b1) a (meth)acrylic monomer that does not have a functional group that can become a first reactive group, and (b2) a (meth)acrylic monomer that has a functional group that can become a first reactive group. These monomers may be used alone or in combination of two or more. The (b1) (meth)acrylic monomer is preferably (b1-1) a (meth)acrylate monomer that does not have a functional group that can become a first reactive group. The (b2) (meth)acrylic monomer includes (b2-1) a (meth)acrylate monomer that has a functional group that can become a first reactive group, and (meth)acrylic acid.

The (meth)acrylic monomer that does not have a functional group that can become the (b1) first reactive group includes (meth)acrylates having a linear alkyl group, (meth)acrylates having a branched alkyl group, (meth)acrylates having an alkoxy group, (meth)acrylates having a polyalkylene glycol structural unit, (meth)acrylates having an alicyclic hydrocarbon group, (meth)acrylates having an aromatic group, (meth)acrylates having a tertiary amino group, (meth)acrylamides, etc. Among these, at least one selected from the group consisting of (meth)acrylates having a linear alkyl group, (meth)acrylates having a branched alkyl group, (meth)acrylates having an alicyclic hydrocarbon group, (meth)acrylates having an aromatic group, and (meth)acrylamides is preferred.

As the (meth)acrylate having a linear alkyl group, a (meth)acrylate having a linear alkyl group with a carbon number of 1 to 20 is preferred, and a (meth)acrylate having a linear alkyl group with a carbon number of 1 to 10 is more preferred. Examples of the (meth)acrylate having a linear alkyl group include linear alkyl esters of (meth)acrylic acid such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-lauryl (meth)acrylate, and n-stearyl (meth)acrylate.

As the (meth)acrylate having a branched alkyl group, a (meth)acrylate having a branched alkyl group with a carbon number of 3 to 20 is preferred, and a (meth)acrylate having a branched alkyl group with a carbon number of 3 to 10 is preferred. Examples of the (meth)acrylate having a branched alkyl group include (meth)acrylic acid branched alkyl esters such as isopropyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate, and isodecyl (meth)acrylate.

Examples of the (meth)acrylate having an alkoxy group include (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate.

Examples of the (meth)acrylate having a polyalkylene glycol structural unit include (meth)acrylates having a polyethylene glycol structural unit such as polyethylene glycol (degree of polymerization = 2-10) methyl ether (meth)acrylate, polyethylene glycol (degree of polymerization = 2-10) ethyl ether (meth)acrylate, polyethylene glycol (degree of polymerization = 2-10) propyl ether (meth)acrylate, and polyethylene glycol (degree of polymerization = 2-10) phenyl ether (meth)acrylate; and (meth)acrylates having a polypropylene glycol structural unit such as polypropylene glycol (degree of polymerization = 2-10) methyl ether (meth)acrylate, polypropylene glycol (degree of polymerization = 2-10) ethyl ether (meth)acrylate, polypropylene glycol (degree of polymerization = 2-10) propyl ether (meth)acrylate, and polypropylene glycol (degree of polymerization = 2-10) phenyl ether (meth)acrylate.

The (meth)acrylate having an alicyclic hydrocarbon group includes a (meth)acrylate having a cyclic alkyl group and a (meth)acrylate having a polycyclic structure. The (meth)acrylate having a cyclic alkyl group is preferably a (meth)acrylate having a cyclic alkyl group with 6 to 12 carbon atoms. The cyclic alkyl group may include a cyclic alkyl group having a monocyclic structure (e.g., a cycloalkyl group), which may also have a chain portion. Specific examples of (meth)acrylates having a cyclic alkyl group with a monocyclic structure include (meth)acrylic acid cyclic alkyl esters such as cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, and cyclododecyl (meth)acrylate.

The (meth)acrylate having a polycyclic structure is preferably a (meth)acrylate having a polycyclic structure with 6 to 12 carbon atoms. Examples of the polycyclic structure include cyclic alkyl groups having a bridged ring structure (e.g., adamantyl group, norbornyl group, isobornyl group), and may also have a chain portion. Specific examples of (meth)acrylates having a polycyclic structure include bornyl (meth)acrylate, isobornyl (meth)acrylate, 1-adamantyl (meth)acrylate, 2-adamantyl (meth)acrylate, 2-methyl-2-adamantyl (meth)acrylate, 2-ethyl-2-adamantyl (meth)acrylate, norbornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentanyloxyethyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and the like.

The (meth)acrylate having an aromatic group is preferably a (meth)acrylate having an aromatic group with 6 to 12 carbon atoms. Examples of the aromatic group include an aryl group, and may also have a chain portion such as an alkylaryl group, an aryl group, or an aryloxyalkyl group. Examples of the (meth)acrylate having an aromatic group include a compound in which an aryl group is directly bonded to a (meth)acryloyloxy group, a compound in which an aralkyl group is directly bonded to a (meth)acryloyloxy group, and a compound in which an alkylaryl group is directly bonded to a (meth)acryloyloxy group. The number of carbon atoms of the aryl group is preferably 6 to 12. The number of carbon atoms of the aralkyl group is preferably 6 to 12. The number of carbon atoms of the alkylaryl group is preferably 6 to 12. Examples of the (meth)acrylate having an aromatic group include benzyl (meth)acrylate, phenyl (meth)acrylate, and phenoxyethyl (meth)acrylate.

Examples of the (meth)acrylate having a tertiary amino group include 2-(dimethylamino)ethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylate, etc.

Examples of the (meth)acrylamides include N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, (meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropyl(meth)acrylamide, N-tert-butyl(meth)acrylamide, N-octyl(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-ethoxymethyl(meth)acrylamide, N-propoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, diacetone acrylamide, and 4-(meth)acryloylmorpholine. The (meth)acrylamides are (meth)acrylic monomers, but are not included in (meth)acrylate monomers.

Examples of the (b2) (meth)acrylic monomer having a functional group that can become the first reactive group include (meth)acrylic monomers having a hydroxy group (preferably (meth)acrylate monomers), (meth)acrylic monomers having a carboxy group (preferably (meth)acrylic acid), and (meth)acrylic monomers having an epoxy group (preferably (meth)acrylate monomers). Among these, (meth)acrylic monomers having a hydroxy group and/or (meth)acrylic monomers having a carboxy group are preferred.

Examples of the (meth)acrylic monomer having a hydroxy group include hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, 6-hydroxyhexyl (meth)acrylate, 8-hydroxyoctyl (meth)acrylate, 10-hydroxydecyl (meth)acrylate, and 12-hydroxylauryl (meth)acrylate; hydroxyalkyl cycloalkane (meth)acrylates such as (4-hydroxymethylcyclohexyl)methyl (meth)acrylate; and caprolactone adducts of hydroxyalkyl (meth)acrylates. Among these, hydroxyalkyl (meth)acrylates are preferred, and (meth)acrylates having a hydroxyalkyl group having 1 to 5 carbon atoms are more preferred.

Examples of the (meth)acrylic monomer having a carboxy group include monomers obtained by reacting (meth)acrylates having a hydroxy group, such as carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl maleate, and 2-(meth)acryloyloxyethyl phthalate, with acid anhydrides, such as maleic anhydride, succinic anhydride, and phthalic anhydride, and (meth)acrylic acid. Among these, (meth)acrylic acid is preferred.

Examples of the (meth)acrylic acid ester having an epoxy group include glycidyl (meth)acrylate and 3,4-epoxycyclohexylmethyl (meth)acrylate.

Examples of the vinyl monomer other than the (meth)acrylic monomer include (b3) a vinyl monomer other than the (meth)acrylic monomer that does not have a functional group that can become a first reactive group, and (b4) a vinyl monomer other than the (meth)acrylic monomer that has a functional group that can become a first reactive group. These monomers may be used alone or in combination of two or more.

Examples of the vinyl monomer other than the (meth)acrylic monomer that does not have a functional group that can become the first reactive group (b3) include aromatic vinyl monomers, vinyl monomers containing a heterocycle, vinyl carboxylates, vinyl monomers containing a tertiary amino group, vinyl monomers containing a quaternary ammonium base, vinyl amides, α-olefins, dienes, halogenated vinyl monomers, etc.

Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, 4-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methoxystyrene, 2-hydroxymethylstyrene, and 1-vinylnaphthalene.
Examples of the vinyl monomer containing a heterocycle include 2-vinylthiophene, N-methyl-2-vinylpyrrole, 2-vinylpyridine, and 4-vinylpyridine.
Examples of the vinyl carboxylate include vinyl acetate, vinyl pivalate, and vinyl benzoate.
The vinyl monomer containing a tertiary amino group includes N,N-dimethylallylamine.
Examples of the vinyl monomer containing a quaternary ammonium base include N-methacryloylaminoethyl-N,N,N-dimethylbenzyl ammonium chloride.
Examples of the vinyl amides include N-vinylformamide, N-vinylacetamide, 1-vinyl-2-pyrrolidone, and N-vinyl-ε-caprolactam.
Examples of the α-olefin include 1-hexene, 1-octene, and 1-decene.
Examples of the dienes include butadiene, isoprene, 4-methyl-1,4-hexadiene, and 7-methyl-1,6-octadiene.
Examples of the halogenated vinyl monomer include vinyl fluoride, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, tetrafluoroethylene, hexafluoropropylene, tetrafluoropropylene, vinylidene chloride, vinyl chloride, 1-chloro-1-fluoroethylene, and 1,2-dichloro-1,2-difluoroethylene.

Examples of the vinyl monomer other than the (meth)acrylic monomer having a functional group that can become the first reactive group (b4) include a vinyl monomer having a hydroxyl group, a vinyl monomer having a carboxyl group, and a vinyl monomer containing an epoxy group.

Examples of the vinyl monomer having a hydroxy group include p-hydroxystyrene and allyl alcohol.
Examples of the vinyl monomer having a carboxy group include crotonic acid, maleic acid, itaconic acid, citraconic acid, and cinnamic acid.
Examples of the vinyl monomer containing an epoxy group include 2-allyloxirane, glycidyl vinyl ether, and 3,4-epoxycyclohexyl vinyl ether.

The copolymer (A) may be a random copolymer, a block copolymer, or a graft copolymer, and is preferably a random copolymer.

The weight average molecular weight (Mw) of the copolymer (A) is preferably 300,000 or more, more preferably 600,000 or more, even more preferably 900,000 or more, and is preferably 2.5 million or less, more preferably 2 million or less, and even more preferably 1.8 million or less. If the Mw of the copolymer (A) is 300,000 or more, the cohesive force is increased and the heat resistance of the formed adhesive material is improved, and if it is 2.5 million or less, the coating workability of the adhesive composition is improved. The method for measuring the weight average molecular weight (Mw) will be described later.

The molecular weight distribution (PDI) of the copolymer (A) is less than 3.0, preferably less than 2.5, more preferably less than 2.2, and even more preferably less than 1.8. The smaller the PDI, the narrower the molecular weight distribution width, resulting in a copolymer with a uniform molecular weight, and when the PDI value is 1.0, the molecular weight distribution width is the narrowest. If the PDI is less than 3.0, the content of small and large molecular weights is low compared to the molecular weight of the designed copolymer, and an adhesive material with excellent flex resistance is obtained. In the present invention, the molecular weight distribution (PDI) is a value calculated by (weight average molecular weight (Mw))/(number average molecular weight (Mn)), and the measurement method of Mw and Mn will be described later.

The glass transition temperature (Tg) of the copolymer (A) is preferably -70°C or higher, more preferably -60°C or higher, and is preferably 0°C or lower, more preferably -10°C or lower, and even more preferably -20°C or lower. If the Tg is -70°C or higher, sufficient cohesive strength is imparted to the adhesive, and the durability of the adhesive formed is improved, while if the Tg is 0°C or lower, the adhesive formed has high adhesion to the adherend, peeling at low temperatures is suppressed, and durability is improved.

The Tg of the copolymer (A) is a value calculated by the following FOX formula (Formula (1)). In Formula (1), Tg indicates the glass transition temperature (°C) of the copolymer. Tgi indicates the glass transition temperature (°C) when vinyl monomer i forms a homopolymer. Wi indicates the mass ratio of vinyl monomer i to all vinyl monomers that form the copolymer, and ΣWi = 1. i is a natural number from 1 to n.

The glass transition temperatures of representative homopolymers are shown in Table 1.

The copolymer (A) is produced by radically polymerizing a vinyl monomer using a living radical polymerization method. While maintaining the simplicity and versatility of conventional radical polymerization methods, the living radical polymerization method is less prone to termination reactions and chain transfer, and growth is not hindered by side reactions that deactivate the growing end, making it easy to precisely control the molecular weight distribution and produce polymers with uniform composition. Therefore, in copolymers produced by the living radical polymerization method, reactive functional groups are uniformly distributed in each molecular chain. Therefore, if a copolymer produced by the living radical polymerization method is used, the crosslinking point density in the adhesive will be uniform overall.

In the living radical polymerization method, a random copolymer can be obtained by using a mixture of the monomers (vinyl monomers) that make up the copolymer (A). Also, a block copolymer can be obtained by reacting the vinyl monomers that make up the copolymer in sequence.

Living radical polymerization methods include those using transition metal catalysts (ATRP method), those using sulfur-based reversible chain transfer agents (RAFT method), and those using organic tellurium compounds (TERP method), depending on the method used to stabilize the polymer growth terminal. Among these methods, the TERP method is preferred from the viewpoints of the variety of monomers that can be used, molecular weight control in the polymer region, uniform composition, and coloring.

The TERP method is a method in which an organic tellurium compound is used as a chain transfer agent to polymerize a radically polymerizable compound (vinyl monomer), and is described, for example, in WO 2004/14848, WO 2004/14962, WO 2004/072126, and WO 2004/096870.

Specific polymerization methods of the TERP method include the following (a) to (d).
(a) A method of polymerizing a vinyl monomer using an organotellurium compound represented by formula (1):
(b) A method of polymerizing a vinyl monomer using a mixture of an organotellurium compound represented by formula (1) and an azo-based polymerization initiator.
(c) A method of polymerizing a vinyl monomer using a mixture of an organotellurium compound represented by formula (1) and an organic ditelluride compound represented by formula (2).
(d) A method of polymerizing a vinyl monomer using a mixture of an organotellurium compound represented by formula (1), an azo-based polymerization initiator, and an organoditelluride compound represented by formula (2).

［式（１）において、Ｒ¹は、炭素数１～８のアルキル基、アリール基または芳香族ヘテロ環基である。Ｒ²およびＲ³は、それぞれ独立に、水素原子または炭素数１～８のアルキル基である。Ｒ⁴は、炭素数１～８のアルキル基、アリール基、置換アリール基、芳香族ヘテロ環基、アルコキシ基、アシル基、アミド基、オキシカルボニル基、シアノ基、アリル基またはプロパルギル基である。
式（２）において、Ｒ¹は、炭素数１～８のアルキル基、アリール基または芳香族ヘテロ環基である。］

In formula (1), R ¹ is an alkyl group having 1 to 8 carbon atoms, an aryl group, or an aromatic heterocyclic group. ^{R 2} and R ³ are each independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. R ⁴ is an alkyl group having 1 to 8 carbon atoms, an aryl group, a substituted aryl group, an aromatic heterocyclic group, an alkoxy group, an acyl group, an amido group, an oxycarbonyl group, a cyano group, an allyl group, or a propargyl group.
In formula (2), R ¹ is an alkyl group having 1 to 8 carbon atoms, an aryl group, or an aromatic heterocyclic group.

Specific examples of the organic tellurium compound represented by formula (1) include ethyl-2-methyl-2-n-butyltellanyl-propionate, ethyl-2-n-butyltellanyl-propionate, (2-hydroxyethyl)-2-methyl-methyltellanyl-propionate, and the organic tellurium compounds described in WO 2004/14848, WO 2004/14962, WO 2004/072126, and WO 2004/096870. Specific examples of the organic ditelluride compound represented by formula (2) include dimethyl ditelluride and dibutyl ditelluride. The azo polymerization initiator can be any azo polymerization initiator used in normal radical polymerization without any particular restrictions, such as 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN), 1,1'-azobis(1-cyclohexanecarbonitrile) (ACHN), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70), etc.

In the polymerization process, a vinyl monomer and an organic tellurium compound of formula (1) are mixed in a vessel purged with an inert gas, and an azo-based polymerization initiator and/or an organic ditelluride compound of formula (2) are further mixed for the purpose of promoting the reaction and controlling the molecular weight and molecular weight distribution depending on the type of vinyl monomer. Examples of the inert gas include nitrogen, argon, and helium. Argon and nitrogen are preferable. The amount of the vinyl monomer used in (a), (b), (c), and (d) may be appropriately adjusted depending on the physical properties of the desired copolymer.

The polymerization reaction can be carried out without a solvent, but may be carried out by stirring the mixture using an aprotic or protic solvent generally used in radical polymerization. Examples of aprotic solvents that can be used include anisole, benzene, toluene, propylene glycol monomethyl ether acetate, ethyl acetate, and tetrahydrofuran (THF). Examples of protic solvents include water, methanol, and 1-methoxy-2-propanol. Solvents may be used alone or in combination of two or more. The amount of solvent used may be adjusted appropriately, and is preferably 0.01 ml to 50 ml per 1 g of vinyl monomer. The reaction temperature and reaction time may be adjusted appropriately depending on the molecular weight or molecular weight distribution of the resulting copolymer, but the mixture is usually stirred at 0°C to 150°C for 1 minute to 100 hours. After the polymerization reaction is completed, the solvent used and the remaining vinyl monomer are removed from the resulting reaction mixture by a conventional separation and purification means, and the desired copolymer can be separated.

The growing end of the copolymer obtained by the polymerization reaction is in the form of -TeR ¹ (wherein R ¹ is the same as above) derived from the tellurium compound, and is deactivated by operation in air after the polymerization reaction is completed, but tellurium atoms may remain. Since a copolymer with tellurium atoms remaining at the end is colored or has poor thermal stability, it is preferable to remove the tellurium atoms. Methods for removing tellurium atoms include a radical reduction method; a method of adsorbing with activated carbon or the like; a method of adsorbing metal with an ion exchange resin or the like, and these methods can also be used in combination. The other end of the copolymer obtained by the polymerization reaction (the end opposite to the growing end) is in the form of -CR ² R ³ R ⁴ (wherein R ² , R ³ and R ⁴ are the same as R ² , R ³ and R ⁴ in formula (1)) derived from the tellurium compound.

((B) Crosslinking Agent)
The adhesive composition contains a crosslinking agent (B). The crosslinking agent (B) is a compound having two or more second reactive groups in one molecule that react with the first reactive group of the copolymer (A). The crosslinking agent (B) is not particularly limited, and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, metal chelate-type crosslinking agents, melamine resin-based crosslinking agents, and urea resin-based crosslinking agents. Among these, isocyanate-based crosslinking agents and epoxy-based crosslinking agents are preferred. In particular, isocyanate-based crosslinking agents are more preferred because they improve the recovery rate of the adhesive material formed.

The number of second reactive groups in one molecule of the (B) crosslinking agent is 2 or more, preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less. In other words, the (B) crosslinking agent is more preferably a bifunctional crosslinking agent having two second reactive groups in one molecule, or a trifunctional crosslinking agent having three second reactive groups in one molecule. If the (B) crosslinking agent is bifunctional or trifunctional, the crosslinking points are evenly distributed in the adhesive, and the average distance between crosslinking points is long. Therefore, the obtained adhesive has a low initial stress and a high recovery rate. The molecular weight of the (B) crosslinking agent is preferably 200 or more, more preferably 300 or more, and even more preferably 400 or more, and is preferably 1500 or less, more preferably 1000 or less, and even more preferably 700 or less.

The content of the second reactive group in the crosslinking agent (B) is preferably 1.5 mmol/g or more, more preferably 3 mmol/g or more, and even more preferably 3.7 mmol/g or more, and is preferably 8 mmol/g or less, more preferably 6 mmol/g or less. If the content of the second reactive group in the crosslinking agent (B) is within this range, the valence of the crosslinking agent (B) is low, the crosslinking points are evenly distributed in the adhesive, and the average distance between crosslinking points is long. Therefore, the resulting adhesive has low initial stress and shows a high recovery rate.

(Isocyanate-based crosslinking agent)
The isocyanate crosslinking agent is a compound having two or more isocyanate groups (including isocyanate regenerating functional groups in which the isocyanate groups are temporarily protected by a blocking agent or oligomerization) in one molecule as second reactive groups. The isocyanate crosslinking agent may be used alone or in combination of two or more kinds.

Examples of isocyanate-based crosslinking agents include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, and adducts of these with various polyols, polyisocyanates multifunctionalized with isocyanurate bonds, biuret bonds, allophanate bonds, etc. Among these, compounds having two isocyanate groups (including isocyanate regenerating functional groups in which isocyanate groups are temporarily protected by blocking agents or oligomerization, etc.) in one molecule (bifunctional isocyanate-based crosslinking agents) or compounds having three isocyanate groups (including isocyanate regenerating functional groups in which isocyanate groups are temporarily protected by blocking agents or oligomerization, etc.) in one molecule (trifunctional isocyanate-based crosslinking agents) are preferred. (B) If the crosslinking agent is a bifunctional isocyanate-based crosslinking agent or a trifunctional isocyanate-based crosslinking agent, the crosslinking points are distributed evenly within the adhesive material, and the average distance between crosslinking points is increased. As a result, the resulting adhesive has low initial stress and a high recovery rate.

Examples of bifunctional isocyanate crosslinking agents include aliphatic diisocyanate compounds, alicyclic diisocyanate compounds, aromatic diisocyanate compounds, and other diisocyanate compounds, and adducts of these diisocyanate compounds with diol compounds can also be used. A diisocyanate compound is a compound represented by the general formula "O=C=N-X-N=C=O" (X is a divalent aliphatic group, a divalent alicyclic group, a divalent aromatic group, etc.). A diol compound is a compound represented by the general formula "HO-Y-OH" (Y is a divalent aliphatic group, a divalent alicyclic group, a divalent aromatic group, etc.).

Examples of aliphatic diisocyanate compounds include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and 2,2,4-trimethyl-1,6-hexamethylene diisocyanate. Among these, aliphatic diisocyanate compounds having 4 to 30 carbon atoms are preferred, and aliphatic diisocyanate compounds having 4 to 10 carbon atoms are more preferred.

Examples of alicyclic diisocyanate compounds include isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated tetramethylxylene diisocyanate, etc., and among these, alicyclic diisocyanate compounds having 7 to 30 carbon atoms are preferred.

Examples of aromatic diisocyanate compounds include phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, diphenylpropane diisocyanate, etc., and aromatic diisocyanate compounds having 8 to 30 carbon atoms are preferred.

The diol compound includes aliphatic diol compounds such as 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, polyethylene glycol, and polypropylene glycol, and among these, aliphatic diol compounds having 3 to 10 carbon atoms are preferred.

The trifunctional isocyanate crosslinking agent includes an adduct of the diisocyanate compound, a biuret of the diisocyanate compound, and an isocyanurate of the diisocyanate compound (a cyclic trimer of diisocyanate compounds).

The isocyanate-based crosslinking agent preferably does not have an aromatic ring. In particular, the isocyanate-based crosslinking agent is preferably a bifunctional isocyanate-based crosslinking agent selected from the group consisting of an aliphatic diisocyanate compound and an adduct of an aliphatic diisocyanate compound and an aliphatic diol compound, or a trifunctional isocyanate-based crosslinking agent selected from the group consisting of an adduct of an aliphatic diisocyanate compound, a biuret of an aliphatic diisocyanate compound, and an isocyanurate of an aliphatic diisocyanate compound.

(Epoxy-based crosslinking agent)
The epoxy-based crosslinking agent refers to a compound having two or more epoxy groups as second reactive groups in one molecule. The epoxy-based crosslinking agent may be used alone or in combination of two or more kinds.

Examples of epoxy crosslinking agents include bisphenol A, epichlorohydrin-type epoxy resins, ethylene glycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, diglycidylaniline, diamine glycidylamine, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl glycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, polyglycerol polyglycidyl ether, sorbitan polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, o-phthalic acid diglycidyl ester, triglycidyl-tris(2-hydroxyethyl)isocyanurate, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, etc.

As the epoxy-based crosslinking agent, a compound having two epoxy groups in one molecule (bifunctional epoxy-based crosslinking agent) or a compound having three epoxy groups in one molecule (trifunctional epoxy-based crosslinking agent) is preferred. If the (B) crosslinking agent is a bifunctional epoxy-based crosslinking agent or a trifunctional epoxy-based crosslinking agent, crosslinking points are evenly distributed in the adhesive, and the average distance between crosslinking points is long. Therefore, the resulting adhesive has low initial stress and shows a high recovery rate.

The adhesive composition preferably contains only an isocyanate-based crosslinking agent as the crosslinking agent (B), and in particular, preferably contains only a bifunctional isocyanate-based crosslinking agent having two isocyanate groups in one molecule, or a trifunctional isocyanate-based crosslinking agent having three isocyanate groups in one molecule, as the crosslinking agent (B).

The content of the crosslinking agent (B) in the adhesive composition is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 0.2 parts by mass or less, more preferably 0.15 parts by mass or less, per 100 parts by mass of the copolymer (A). If the content of the crosslinking agent (B) is within the above range, the adhesive strength and recovery rate will be in the preferred range.

The molar ratio of the second reactive group of the (B) crosslinking agent to the first reactive group of the (A) copolymer (molar amount of the first reactive group/molar amount of the second reactive group) is 1 or more, preferably 2 or more, more preferably 3 or more, and is preferably 15 or less, more preferably 10 or less, and even more preferably 5 or less. If the molar ratio is 1 or more, the crosslinking agent reacts without excess or deficiency, no excess of the second reactive group is produced, and a high restoration rate is achieved, and if it is 15 or less, the reaction proceeds sufficiently and a high restoration rate is achieved.

The molar ratio of the first reactive group possessed by the (A) copolymer to the blending amount (molar amount) of the (B) crosslinking agent (molar amount) (molar amount of the first reactive group/molar amount of the crosslinking agent) is less than 12.0, more preferably 11.0 or less, and even more preferably 8.0 or less. If the molar ratio is less than 12.0, the restoration rate decreases. In addition, the molar ratio (molar amount of the first reactive group/molar amount of the crosslinking agent) is preferably 2 or more, more preferably 4 or more.

(Other additives)
In addition to the (A) copolymer and (B) crosslinking agent, other additives can be added to the adhesive composition.Other additives include crosslinking accelerators, crosslinking retarders, tackifier resins, plasticizers, softeners, peeling aids, silane coupling agents, dyes, pigments, dyestuffs, fluorescent whitening agents, antistatic agents, wetting agents, surfactants, thickeners, antifungal agents, preservatives, oxygen absorbers, ultraviolet absorbers, antioxidants, near infrared absorbers, water-soluble quenching agents, fragrances, metal deactivators, nucleating agents, alkylating agents, flame retardants, lubricants, processing aids, etc.These can be appropriately selected and mixed according to the application and purpose of the adhesive.

(Crosslinking Accelerator)
The adhesive composition may be used by blending a crosslinking accelerator as necessary. Examples of the crosslinking accelerator include an organic tin compound and a metal chelate compound. The crosslinking accelerator may be used alone or in combination of two or more kinds.

The organotin compounds include dibutyltin dilaurate, dioctylotin dilaurate, dibutyltin dioctylate, etc. The metal chelate compounds are complexes in which a ligand having two or more coordinating atoms forms a ring and is bonded to a central metal.

The content of the crosslinking accelerator in the adhesive composition is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, and even more preferably 0.04 parts by mass or more, relative to 100 parts by mass of the copolymer (A), and is preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, and even more preferably 0.3 parts by mass or less. By setting the content of the crosslinking accelerator within the above range, it is possible to obtain an excellent crosslinking promotion effect.

(Crosslinking Retarder)
The adhesive composition may be used by blending a crosslinking retarder as necessary. The crosslinking retarder is a compound capable of suppressing an excessive increase in viscosity of an adhesive composition containing a crosslinking agent by blocking a functional group of the crosslinking agent. The type of crosslinking retarder is not particularly limited, and examples thereof include β-diketones such as acetylacetone, hexane-2,4-dione, heptane-2,4-dione, and octane-2,4-dione; β-ketoesters such as methyl acetoacetate, ethyl acetoacetate, propyl acetoacetate, butyl acetoacetate, octyl acetoacetate, oleyl acetoacetate, lauryl acetoacetate, and stearyl acetoacetate; and benzoylacetone. The crosslinking retarder is preferably one that can act as a chelating agent, and is preferably a β-diketone or a β-ketoester.

The content of the crosslinking retarder that can be blended in the adhesive composition is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.5 parts by mass or more, and is preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less, even more preferably 1.5 parts by mass or less, relative to 100 parts by mass of the (A) copolymer. By adjusting the content of the crosslinking retarder within the above range, it is possible to suppress excessive viscosity increase and gelation of the adhesive composition after blending the (B) crosslinking agent into the adhesive composition, and to extend the storage stability (pot life) of the adhesive composition.

(Tackifier resin)
The pressure-sensitive adhesive composition may be used by blending a tackifier resin other than the copolymer (A) as necessary. The tackifier resin is not particularly limited, but examples thereof include rosin-based tackifier resins, terpene-based tackifier resins, phenol-based tackifier resins, and hydrocarbon-based tackifier resins.

Examples of rosin-based tackifying resins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin, modified rosins obtained by modifying these unmodified rosins through polymerization, disproportionation, hydrogenation, etc. (polymerized rosin, stabilized rosin, disproportionated rosin, fully hydrogenated rosin, partially hydrogenated rosin, other chemically modified rosins, etc.), and various rosin derivatives.

Examples of the rosin derivatives include rosin phenol-based resins obtained by adding phenol to rosins (unmodified rosin, modified rosin) using an acid catalyst and thermally polymerizing the phenol; rosin ester-based resins such as rosin ester compounds (unmodified rosin esters) obtained by esterifying unmodified rosin with alcohols, and modified rosin ester compounds (polymerized rosin ester, stabilized rosin ester, disproportionated rosin ester, fully hydrogenated rosin ester, partially hydrogenated rosin ester, etc.) obtained by esterifying modified rosin with alcohols; unsaturated fatty acid modified rosin-based resins obtained by modifying unmodified rosin or modified rosin with unsaturated fatty acid; unsaturated fatty acid modified rosin ester-based resins obtained by modifying rosin ester-based resins with unsaturated fatty acid; rosin alcohol-based resins obtained by reducing the carboxyl groups in unmodified rosin, modified rosin, unsaturated fatty acid modified rosin-based resins, and unsaturated fatty acid modified rosin ester-based resins; and metal salts of rosin-based resins (particularly rosin ester-based resins) such as unmodified rosin and modified rosin.

Terpene-based tackifying resins include, for example, terpene-based resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers, and modified terpene-based resins obtained by modifying these terpene-based resins (phenol-modified, aromatic-modified, hydrogen-modified, hydrocarbon-modified, etc.) (for example, terpene-phenolic resins, styrene-modified terpene resins, aromatic-modified terpene resins, and hydrogenated terpene resins).

Examples of phenolic tackifier resins include condensates of various phenols (e.g., phenol, m-cresol, 3,5-xylenol, p-alkylphenol, resorcin) with formaldehyde (e.g., alkylphenol resins, xylene formaldehyde resins), resols obtained by addition reaction of the phenols with formaldehyde using an alkaline catalyst, and novolacs obtained by condensation reaction of the phenols with formaldehyde using an acid catalyst.

Examples of hydrocarbon-based tackifying resins (petroleum-based tackifying resins) include aliphatic hydrocarbon resins [polymers of aliphatic hydrocarbons such as olefins and dienes with 4 to 5 carbon atoms (olefins such as butene-1, isobutylene, and pentene-1; dienes such as butadiene, 1,3-pentadiene, and isoprene)], aliphatic cyclic hydrocarbon resins [alicyclic hydrocarbon resins obtained by cyclizing and dimerizing so-called "C4 petroleum fractions" and "C5 petroleum fractions" and then polymerizing them, cyclic diene compounds (cyclopentadiene, dicyclopentadiene, ethylidene norbornene, dicyclopentadiene ... pentene, etc.) or their hydrogenated products, alicyclic hydrocarbon resins obtained by hydrogenating the aromatic rings of the aromatic hydrocarbon resins and aliphatic/aromatic petroleum resins listed below], aromatic hydrocarbon resins [polymers of vinyl group-containing aromatic hydrocarbons having 8 to 10 carbon atoms (styrene, vinyltoluene, α-methylstyrene, indene, methylindene, etc.)], aliphatic/aromatic petroleum resins (styrene-olefin copolymers, etc.), aliphatic/alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, coumarone-indene resins, etc.

The content of the tackifier resin that can be blended in the adhesive composition is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 20 parts by mass or more, relative to 100 parts by mass of the copolymer (A), and is preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less. By adjusting the content of the tackifier resin within the above range, sufficient adhesion to the adherend can be ensured.

(Silane coupling agent)
The adhesive composition may be used by blending a silane coupling agent as necessary. The silane coupling agent is not particularly limited, but examples thereof include epoxy group-containing silane coupling agents such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; amino group-containing silane coupling agents such as 3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, and N-phenyl-γ-aminopropyltrimethoxysilane; (meth)acrylic group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane and 3-methacryloxypropyltriethoxysilane; and isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane.

The content of the silane coupling agent that can be blended in the adhesive composition is preferably 1 part by mass or less, more preferably 0.01 to 1 part by mass, and even more preferably 0.02 to 0.6 parts by mass, per 100 parts by mass of the copolymer (A). By adjusting the content of the silane coupling agent within the above range, it is possible to increase the water resistance at the interface when the adhesive is applied to a hydrophilic adherend such as glass.

(Method for producing adhesive composition)
The adhesive composition can be produced by mixing the copolymer (A), the crosslinking agent (B), and other additives used as necessary. The adhesive composition may contain a solvent derived from the production of the copolymer (A), or may be a solution diluted with an appropriate solvent to have a viscosity suitable for forming an adhesive layer.

Examples of the solvent include aliphatic hydrocarbons such as hexane and heptane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methylene chloride and ethylene chloride; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; cellosolve-based solvents such as ethyl cellosolve; and glycol ether-based solvents such as propylene glycol monomethyl ether. These solvents may be used alone or in combination of two or more.

The amount of solvent used may be adjusted appropriately so that the adhesive composition has a viscosity suitable for coating, and is not particularly limited. From the viewpoint of coatability, however, for example, 1% by mass to 90% by mass is preferable, more preferably 10% by mass to 80% by mass, and even more preferably 20% by mass to 70% by mass.

(Uses of the adhesive composition)
The adhesive composition is preferably used for forming a flexible display that can be repeatedly bent and stretched for use, and an adhesive layer (adhesive material) for use in a flexible display.

Examples of the flexible displays that can be repeatedly bent and stretched include foldable displays that can be folded and rollable displays that can be rolled into a cylindrical shape. Flexible displays are expected to be used in mobile devices such as smartphones and tablet devices, as well as in storable stationary displays.

[Adhesive for flexible displays]
The adhesive for flexible displays of the present invention is a cured product of the adhesive composition. The adhesive can be used as an adhesive for flexible displays for bonding one flexible member and another flexible member constituting a flexible display.

[Adhesive sheets for flexible displays]
The adhesive sheet for flexible displays of the present invention is an adhesive sheet for flexible displays having an adhesive layer used to bond one flexible member and another flexible member that constitute a flexible display, and a flexible sheet member attached to at least one side of the adhesive layer, characterized in that the adhesive layer is formed from the adhesive material.

The adhesive sheet may be configured in a manner having an adhesive layer and a first flexible sheet member attached to one side of the adhesive layer; or in a manner having an adhesive layer, a first flexible sheet member attached to one side of the adhesive layer, and a second flexible sheet member attached to the other side of the adhesive layer.

Figure 1 shows an example of an adhesive sheet of the present invention. The adhesive sheet 10 in Figure 1 is composed of an adhesive layer 12, a first flexible sheet member 14 that sandwiches the adhesive layer 12, and a second flexible sheet member 16. The adhesive layer 12 is in contact with the releasable surfaces of the first flexible sheet member 14 and the second flexible sheet member 16.

(Adhesive layer)
The adhesive layer is formed from the adhesive material. The thickness of the adhesive layer is preferably 2 μm or more, more preferably 5 μm or more, and even more preferably 10 μm or more, from the viewpoint of ensuring sufficient adhesion to the adherend. The thickness of the adhesive layer is preferably 100 μm or less, more preferably 70 μm or less, and even more preferably 50 μm or less, from the viewpoint of suppressing protrusion of the adhesive layer.

(Flexible sheet member)
Examples of the flexible sheet member include a base sheet having flexibility, a release sheet, etc. The base sheet is a sheet member supporting the adhesive layer, and this sheet member may be a functional sheet member. Examples of the functional sheet member include a cover film, a barrier film, a polarizing film, a retardation film, an optical compensation film, a brightness improvement film, a diffusion film, an anti-reflection film, etc. The release sheet protects the adhesive layer until the adhesive layer is attached to the adherend, and is peeled off from the adhesive layer before the adhesive layer is attached to the adherend.

Generally, a "sheet" is defined in the JIS as a thin, flat product whose thickness is generally small relative to its length and width, and a "film" is generally a thin, flat product whose thickness is extremely small compared to its length and width, and whose maximum thickness is arbitrarily limited, and which is usually supplied in the form of a roll (Japanese Industrial Standard JIS K6900). For example, in terms of thickness, in the narrow sense, a product with a thickness of 100 μm or more is called a sheet, and a product with a thickness of less than 100 μm is sometimes called a film. However, the boundary between a sheet and a film is unclear, and since there is no need to distinguish between the two in the present invention, in the present invention, when a product is called a "sheet," it is also considered to include a "film," and when a product is called a "film," it is also considered to include a "sheet."

The flexible sheet member may be a sheet of a polymeric material, a glass sheet, or the like. The thickness of the flexible sheet member is not particularly limited, but from the viewpoint of ease of handling, etc., it is preferably 2 μm to 500 μm, and more preferably 2 μm to 200 μm.

The polymeric materials include polyimide resins; polyester resins such as polyethylene terephthalate resins and polyethylene naphthalate resins; polycarbonate resins; poly(meth)acrylate resins; polystyrene resins; polyamide resins; polyacrylonitrile resins; polyolefin resins such as polypropylene resins, polyethylene resins, and polycycloolefin resins; polyphenylene sulfide resins; polyvinyl chloride resins; polyvinylidene chloride resins; and polyvinyl alcohol resins.

The flexible sheet member may be composed of a single layer containing one or more of the polymeric materials, or may be composed of two or more layers, such as a layer containing one or more of the polymeric materials and a layer containing one or more of a different polymeric material.

The flexible sheet member is preferably a release sheet that has been subjected to a release treatment on the surface that contacts the adhesive layer. Examples of release agents used in the release treatment include silicone-based, fluorine-based, alkyd-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents.

The adhesive sheet has a first flexible sheet member attached to one side of the adhesive layer and a second flexible sheet member attached to the other side of the adhesive layer, the first flexible sheet member being a first release sheet and the second flexible sheet member being a second release sheet, and it is preferable that the first release sheet and the second release sheet are attached so that their respective release surfaces are in contact with the adhesive layer. When the adhesive layer is sandwiched between two release sheets, it is preferable that one release sheet is a heavy release type release sheet with a large release force and the other release sheet is a light release type release sheet with a small release force.

(Manufacturing of adhesive sheets)
The pressure-sensitive adhesive sheet can be produced, for example, by applying the above-mentioned pressure-sensitive adhesive composition onto a flexible sheet member and, if necessary, curing the composition by a dry heat treatment to form a pressure-sensitive adhesive layer.

For coating the adhesive composition, various coating methods such as reverse gravure coating, direct gravure coating, die coating, bar coating, wire bar coating, roll coating, spin coating, dip coating, spray coating, knife coating, kiss coating, etc., and various printing methods such as inkjet printing, offset printing, screen printing, flexographic printing, etc., can be used. In addition, before coating the adhesive composition, the surface of the release sheet may be subjected to a surface treatment such as corona treatment, plasma treatment, hot air treatment, ozone treatment, ultraviolet treatment, etc.

The drying and curing process is not particularly limited as long as it can remove the solvent used in the adhesive composition and can cure it, but it is preferable to carry out the process at a temperature of 60°C to 150°C for about 20 to 300 seconds. In particular, the drying temperature is preferably 100°C to 130°C.

When a first flexible sheet member is placed on one side of the adhesive layer and a second flexible sheet member is placed on the other side, the adhesive composition is applied to the first flexible sheet member, an adhesive layer is formed on the first flexible sheet member, and then the second flexible sheet member is attached to this adhesive layer. Furthermore, the adhesive layer may be cured as necessary. The curing conditions include, for example, 60°C for about 3 to 7 days.

[Flexible laminated material]
The flexible laminated member of the present invention is a flexible laminated member including a first flexible member, a second flexible member, and an adhesive layer that bonds the first flexible member and the second flexible member to each other, and is characterized in that the adhesive layer is made of the adhesive material. Since the adhesive layer of the flexible laminated member is made of the adhesive material, even if the flexible laminated member is repeatedly bent, defects in appearance such as wavy appearance at the bent parts are suppressed.

Figure 2 shows an example of a flexible laminated member of the present invention. The flexible laminated member 20 in Figure 2 comprises a first flexible member 22, a second flexible member 24, and an adhesive layer 12 between the first flexible member 22 and the second flexible member 24, which bonds these flexible members together.

The flexible laminated member may be configured, for example, in a configuration in which both the first flexible member and the second flexible member are components of a flexible device; or in a configuration in which the second flexible member is a flexible device and the first flexible member is a functional sheet member bonded to the flexible device. Examples of the flexible device include a foldable display that can be folded, and a rollable display that can be rolled into a cylindrical shape. Examples of the functional sheet member include a cover film, a barrier film, a polarizing film, a retardation film, an optical compensation film, a brightness enhancement film, a diffusion film, an anti-reflection film, a transparent conductive film, a metal mesh film, a cushion film, and the like.

The first flexible member and the second flexible member are members that can be repeatedly bent or curved when used. Examples of the first flexible member and the second flexible member include flexible substrate materials, functional sheet members, display elements (organic EL modules, electronic paper modules, etc.). It is preferable that at least one of the first flexible member and the second flexible member is a display element. The flexible laminate member can be used in a flexible display.

(Method for manufacturing flexible laminated member)
The method for producing the flexible laminated member of the present invention is not particularly limited, and examples thereof include the following methods (1) to (4).

(1) A method of obtaining a flexible laminated member by peeling off a release sheet attached to one side of an adhesive sheet, adhering the exposed adhesive layer to a first flexible member, and then peeling off a release sheet attached to the other side of the adhesive sheet, and adhering the exposed adhesive layer to a second flexible member.
(2) A method in which an adhesive composition is applied onto one surface of a first flexible member, and if necessary, cured by a dry heat treatment to form an adhesive layer, and then a releasable surface of a release sheet is attached to the adhesive layer, and the release sheet is peeled off to expose the adhesive layer and attach it to a second flexible member, thereby obtaining a flexible laminated member.
(3) A method in which an adhesive composition is applied to one side of a first flexible member, and if necessary hardened by drying and heating treatment to form an adhesive layer, and then a second flexible member is attached to this adhesive layer to obtain a flexible laminated member.
(4) A method in which an adhesive composition is applied onto a releasable surface of a release sheet, and if necessary, the adhesive composition is cured by a dry heat treatment to form an adhesive layer, and then a first flexible member is attached to the adhesive layer, and the release sheet is peeled off to expose the adhesive layer and a second flexible member are attached to the adhesive layer, thereby obtaining a flexible laminated member.

In any of the above cases (1) to (4), the order in which the first flexible member and the second flexible member are used may be reversed.
The adhesive layer can be formed by using various coating methods or printing methods similar to those used in the manufacture of adhesive sheets, and the same applies to the drying and curing processes. In addition, curing may be performed as necessary. In addition, the release sheet used in the manufacture of the flexible laminated member may be the same as the release sheet used for the adhesive sheet.

The present invention will be described in more detail below based on specific examples. The present invention is not limited to the following examples, and can be modified as appropriate within the scope of the present invention. The polymerization rate of the block copolymer, weight average molecular weight (Mw), molecular weight distribution (PDI), adhesive layer thickness, gel fraction of the adhesive, initial stress and recovery rate when strained 400%, and adhesive strength were evaluated according to the following methods.

The meanings of the abbreviations are as follows:
EHA: 2-Ethylhexyl acrylate LA: Lauryl acrylate AA: Acrylic acid HBA: 4-Hydroxybutyl acrylate BTEE: Ethyl-2-methyl-2-n-butyltellanyl-propionate AIBN: Azobisisobutyronitrile AcOEt: Ethyl acetate

(Polymerization rate)
^1H -NMR was measured (solvent: _CDCl3 , internal standard: TMS) using a nuclear magnetic resonance (NMR) measurement device (Bruker Biospin, model: AVANCE500 (frequency 500 MHz)). From the obtained NMR spectrum, the integral ratio of the proton signal (3H) of the vinyl group derived from the monomer and the proton signal (1H) bonded to the α-carbon of the carbonyl group derived from the polymer was determined, and the polymerization rate of the monomer was calculated.

(Weight average molecular weight (Mw) and molecular weight distribution (PDI))
The content was determined by gel permeation chromatography (GPC) using a high performance liquid chromatograph (Tosoh Corporation, model HLC-8320GPC). Two TSKgel Super Multipore HZ-H (Tosoh Corporation) columns were used, a tetrahydrofuran solution was used as the mobile phase, and a differential refractometer was used as the detector. The measurement conditions were a column temperature of 40°C, a sample concentration of 0.5 mg/mL, a sample injection amount of 10 μm, and a flow rate of 0.6 mL/min. A calibration curve was prepared using polystyrene (molecular weights: 9,840,000, 5,480,000, 2,890,000, 1,090,000, 775,000, 427,000, 190,000, 96,400, 37,900, 10,200, 2,630, 440) as a standard substance, and the weight average molecular weight (Mw) and number average molecular weight (Mn) were measured. The molecular weight distribution (PDI=Mw/Mn) was calculated from the measured values.

(Adhesive layer thickness)
The total thickness of the entire adhesive sheet was measured using a thickness measuring device (manufactured by Tester Sangyo Co., Ltd., "TH-104"), and the thickness of the adhesive layer was determined by subtracting the thickness of the release sheet from this total thickness.

(Gel Fraction)
The mass W2 of a wire mesh (400 mesh) cut out to a width of 50 mm and a length of 120 mm was measured. 80 mg to 120 mg of the adhesive layer (adhesive) was collected from the adhesive sheet, and the mass W1 was measured. The adhesive was wrapped in wire mesh to prevent it from falling off, and a test piece was prepared. The test piece was placed in a glass bottle, 40 g of ethyl acetate was poured into it, and the test piece was shaken lightly, and then left to stand at room temperature (25°C) for 72 hours or more. After standing, the test piece was removed from the glass bottle and left at room temperature for 12 hours or more, and further dried in a vacuum oven at 100°C for 4 hours. The dried test piece was cooled to room temperature, the mass W3 was measured, and the gel fraction was calculated from the following formula.
Gel fraction (mass%)=(W3−W2)/W1×100

(Initial stress and recovery rate when strained 400%)
The adhesive layers (adhesive materials) constituting the adhesive sheet were laminated together using a hand roller to prepare a laminate with a thickness of 600 μmm. Using this laminate as a sample, a stress relaxation test with a strain of 400% for 10 minutes and a creep test with a stress of 0 kPa for 10 minutes were performed continuously using a viscoelasticity measuring device (TA instruments, ARES G2) with a diameter of 8 mm under an atmosphere of 25° C. The initial stress was the value 0.1 seconds after the start of the shear stress application in the stress relaxation test. In addition, the recovery rate (%) was calculated from the strain after the 10-minute creep test based on the following formula. The recovery rate was evaluated as "◯" when it was 75% or more, and "×" when it was less than 75%.
Recovery rate (%) = {(400 - strain after 10 minutes creep test) / 400} x 100

(Adhesive strength)
One release sheet of the adhesive sheet was peeled off from the adhesive layer, and the corona-treated surface of a polyethylene terephthalate (PET) film (Toyobo Ester (registered trademark) film E5100: manufactured by Toyobo, thickness 50 μm) was attached to the adhesive layer surface, and the film was cut into a size of 25 mm wide and 100 mm long to prepare an adhesive sheet with a substrate. The adhesive strength of this adhesive sheet with a substrate to a polyimide film or glass as an adherend was measured in accordance with the method of JIS Z 0237 (2009).
Specifically, the release sheet was peeled off from the adhesive layer, and the adhesive layer surface was pressed against a polyimide film (Kapton (registered trademark) 100V: manufactured by Toray DuPont, thickness 25 μm) or white plate glass (S9112, manufactured by Matsunami Glass Industry Co., Ltd., thickness 1.0 to 1.2 mm) by two reciprocating strokes of a 2 kg roller. Next, the adhesive strength of the adhesive layer was measured using a precision universal testing machine manufactured by Shimadzu Corporation, "AUTOGRAPH (registered trademark) AGS-1kNX, 50 N load cell," under conditions of a peel speed of 300 mm/min and a peel angle of 180°.

<Production of Copolymer>
(Synthesis Example 1: Copolymer No.A)
A flask equipped with an argon gas inlet tube and a stirrer was charged with EHA (340.2 g), LA (240 g), AA (18 g), HBA (1.8 g), AIBN (26.1 mg), and AcOEt (353.4 g). After replacing with argon, BTEE (105 mg) was added and the reaction was carried out at 60° C. for 24 hours to polymerize.

After the reaction was completed, AcOEt was added to the reaction solution to obtain a copolymer solution containing Copolymer No. A. The Mw of the obtained Copolymer No. A was 1,624,000, the PDI was 1.77, and the solid content of the solution was 26.2 mass%. Table 2 shows the raw material monomers, organotellurium compound, azo-based polymerization initiator, solvent, reaction conditions, and polymerization rate used.

<Production of Adhesive Composition>
(Adhesive composition No. 1)
381 parts by mass (based on 100 parts by mass of the copolymer component) of the solution of copolymer No. A obtained in Synthesis Example 1, 0.148 parts by mass of crosslinker A (Duranate (registered trademark) D101), and 94.9 parts by mass of butyl acetate were added and stirred to obtain adhesive composition No. 1 having a solid content of 21.0% by mass. In adhesive composition No. 1, the first reactive group of the copolymer is a hydroxyl group, and the second reactive group of the crosslinker is an isocyanate group.

(Adhesive Compositions Nos. 2 to 8)
Except for changing the composition as shown in Table 3, adhesive compositions No. 2 to 8 were prepared in the same manner as adhesive composition No. 1. The amount of crosslinking agent shown in Table 3 is the amount converted into solid content. The solid content is the components other than the solvent. In adhesive compositions No. 2 to 8, the first reactive group of the copolymer is a hydroxyl group, and the second reactive group of the crosslinking agent is an isocyanate group.

<Preparation of adhesive sheet>
The adhesive composition was applied to the release surface of the first release sheet (PET film with a release treatment on the surface, Clean Sepa (registered trademark) HY-US20: manufactured by Higashiyama Film, thickness 75 μm) using a Baker-type applicator so that the film thickness after drying was 50 μm, and then dried at 60 ° C. for 3 minutes and then at 150 ° C. for 3 minutes using a thermostatic dryer. Next, the release surface of the second release sheet (PET film with a release treatment on the surface, Clean Sepa (registered trademark) HY-S10: manufactured by Higashiyama Film, thickness 38 μm) was attached to the adhesive layer formed on the first release sheet, and then aged at 60 for 3 days to prepare an adhesive layer sandwiched between two release sheets. The evaluation results of the adhesive layer (adhesive material) formed from each adhesive composition are shown in Table 3.

Crosslinking agent A: Duranate D101 (manufactured by Asahi Kasei Corporation, isocyanate-based crosslinking agent (hexamethylene diisocyanate-1,6-hexanediol adduct, number of functional groups: 2, solid content concentration: 100% by mass, NCO amount: 19.7% by mass)
Crosslinking agent B: Duranate TPA-100 (manufactured by Asahi Kasei Corporation, isocyanate-based crosslinking agent (isocyanurate of hexamethylene diisocyanate, number of functional groups: 3, solid content concentration: 100% by mass, NCO amount: 23.1% by mass)
Crosslinking agent C: Duranate MHG-80B (manufactured by Asahi Kasei Corporation, isocyanate-based crosslinking agent (isocyanurate of hexamethylene diisocyanate, number of functional groups: 6, solid content concentration: 80% by mass, NCO amount: 15.1% by mass)

Adhesive compositions No. 1 to 3 are those in which the copolymer has a predetermined amount of first reactive groups, and the molar ratio (molar amount of first reactive groups of the copolymer/molar amount of second reactive groups of the crosslinking agent) and the molar ratio (molar amount of first reactive groups of the copolymer/molar amount of the crosslinking agent) are within a predetermined range. The adhesive materials formed from these adhesive compositions No. 1 to 3 have practically acceptable adhesive strength to polyimide films and glass, and have excellent recovery after being distorted by 400%.

Adhesive compositions No. 4 to 8 are those in which the copolymer has a predetermined amount of first reactive groups, and the molar ratio (molar amount of first reactive groups of the copolymer/molar amount of second reactive groups of the crosslinking agent) is within a predetermined range, but the molar ratio (molar amount of first reactive groups of the copolymer/molar amount of the crosslinking agent) is 11.5 or more. The adhesive materials formed from these adhesive compositions No. 4 to 8 have adhesive strength to polyimide films and glass that is practically acceptable, but have poor recovery after being distorted by 400%.

10: Adhesive sheet 12: Adhesive layer 14: First flexible sheet member 16: Second flexible sheet member 20: Flexible laminate member 22: First flexible member 24: Second flexible member

Claims (11)

An adhesive composition for a flexible display for bonding one flexible member and another flexible member that constitute a flexible display,
the pressure-sensitive adhesive composition contains a (meth)acrylic copolymer having a hydroxy group and a carboxy group, and an isocyanate-based crosslinking agent having an isocyanate group;
the (meth)acrylic copolymer has a hydroxyl group amount of 0.01 mmol/g to 0.1 mmol/g ,
The (meth)acrylic copolymer has a carboxyl group amount of 0.08 mmol/g to 1.3 mmol/g,
the molar ratio of the isocyanate groups of the isocyanate crosslinking agent to the hydroxyl groups of the copolymer (molar amount of hydroxyl groups/molar amount of isocyanate groups) is 1 to 5 ;
A pressure-sensitive adhesive composition for flexible displays, characterized in that the molar ratio of the hydroxyl groups in the copolymer to the amount of the isocyanate-based crosslinking agent (molar amount of hydroxyl groups/molar amount of isocyanate-based crosslinking agent) is 2 to 11.0 . The adhesive composition for flexible displays according to claim 1, wherein the isocyanate-based crosslinking agent contains a bifunctional crosslinking agent having two isocyanate groups in one molecule, or a trifunctional crosslinking agent having three isocyanate groups in one molecule. The adhesive composition for flexible displays according to claim 1 or 2, wherein the isocyanate-based crosslinking agent is at least one selected from the group consisting of an aliphatic diisocyanate compound, an adduct of an aliphatic diisocyanate compound and an aliphatic diol compound, an adduct of an aliphatic diisocyanate compound, a biuret of an aliphatic diisocyanate compound, and an isocyanurate of an aliphatic diisocyanate compound. The adhesive composition for flexible displays according to any one of claims 1 to 3, wherein the weight average molecular weight of the copolymer is 300,000 to 2,500,000. The adhesive composition for flexible displays according to any one of claims 1 to 4, wherein the copolymer is obtained by living radical polymerization and has a molecular weight distribution (Mw/Mn) of less than 3.0. An adhesive for a flexible display for bonding one flexible member and another flexible member that constitute a flexible display,
An adhesive for flexible displays, comprising a cured product of the adhesive composition according to any one of claims 1 to 5. An adhesive sheet for a flexible display, comprising an adhesive layer used for bonding one flexible member and another flexible member constituting a flexible display, and a flexible sheet member attached to at least one surface of the adhesive layer,
An adhesive sheet for a flexible display, wherein the adhesive layer is formed from the adhesive material according to claim 6. the adhesive sheet has a first flexible sheet member attached to one side of the adhesive layer and a second flexible sheet member attached to the other side of the adhesive layer,
the first flexible sheet member is a first release sheet, the second flexible sheet member is a second release sheet,
The adhesive sheet for a flexible display according to claim 7 , wherein the first release sheet and the second release sheet are attached such that their respective release surfaces are in contact with the adhesive layer. A flexible laminate member including a first flexible member, a second flexible member, and an adhesive layer that bonds the first flexible member and the second flexible member to each other,
A flexible laminate member, wherein the adhesive layer is made of the adhesive material according to claim 6. The flexible laminate member according to claim 9, wherein at least one of the first flexible member and the second flexible member is a display element. A flexible display comprising the flexible laminate member according to claim 9 or 10.

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