JP7698704B2 - Adhesive composition for flexible displays, adhesive material, and adhesive sheet - Google Patents

Description

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

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

On the other hand, in recent years, flexible displays that are repeatedly bent and used have been attracting attention in image display devices such as liquid crystal display devices and organic electroluminescence (organic EL) display devices. 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.

In such flexible displays, for example, Patent Document 1 discloses an adhesive material for bonding a flexible member constituting a component that is repeatedly bent and stretched to another flexible member, which is used for repeatedly bending devices, 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, the adhesive layer does not fully recover from the bent state to its original state when repeatedly bent. As a result, repeated bending of a flexible display can result in poor appearance, such as lifting or peeling at the interface between the adhesive layer and the flexible member at the bent points, or the bent points 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 (adhesive layer) having suitable adhesive strength, excellent flexibility, and 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 and another flexible member constituting a flexible display, and is characterized in that it contains multiple (meth)acrylic copolymer components and a crosslinking agent, and the (meth)acrylic copolymer components contain at least (A) (meth)acrylic copolymer component and (B) (meth)acrylic copolymer component, the (A) (meth)acrylic copolymer component has a first reactive group and has a molecular weight distribution (Mw/Mn) of 3.0 or less, the (B) (meth)acrylic copolymer component has a first reactive group and has a molecular weight distribution (Mw/Mn) of more than 3.0, the crosslinking agent has a second reactive group that reacts with the first reactive group, and the content of the (A) (meth)acrylic copolymer component in the multiple (meth)acrylic copolymer components is 75% by mass to 99% by mass.

By using the adhesive composition for flexible displays of the present invention, an adhesive (adhesive layer) having suitable adhesive strength and excellent flexibility and 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.

Hereinafter, an example of a preferred embodiment of the present invention will be described. 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 a flexible display of the present invention (hereinafter, may be simply referred to as "adhesive composition") is an adhesive composition for a flexible display for bonding one flexible member constituting a flexible display to another flexible member. The adhesive composition contains a plurality of (meth)acrylic copolymer components and a crosslinking agent.

((Meth)acrylic copolymer component)
The adhesive composition contains at least (A) (meth)acrylic copolymer component (hereinafter, may be simply referred to as "(A) polymer component") and (B) (meth)acrylic copolymer component (hereinafter, may be simply referred to as "(B) polymer component") as (meth)acrylic copolymer components. A mixture containing a plurality of (meth)acrylic copolymer components may be referred to as a (meth)acrylic copolymer mixture. The (A) (meth)acrylic copolymer component has a first reactive group and has a molecular weight distribution (Mw/Mn) of 3.0 or less. The (B) (meth)acrylic copolymer component has a first reactive group and has a molecular weight distribution (Mw/Mn) of more than 3.0. The content of the (A) (meth)acrylic copolymer component in the plurality of (meth)acrylic copolymer components is 75% by mass to 99% by mass. By containing the (A) (meth)acrylic copolymer component and the (B) (meth)acrylic copolymer component in predetermined amounts, an adhesive material can be formed that is flexible yet has excellent recovery properties, and further has adhesive strength suitable for use as an adhesive material.

((A) (Meth)acrylic copolymer component)
The (A) (meth)acrylic copolymer component may be a copolymer containing a structural unit derived from a (meth)acrylic monomer as the main component (50% by mass or more). The (A) polymer component may be one type or two or more types. The (A) polymer component may contain a structural unit derived from a vinyl monomer other than the (meth)acrylic monomer. The content of the structural unit derived from the (meth)acrylic monomer in the (A) polymer component is preferably 80% by mass or more, more preferably 90% by mass or more, in 100% by mass of the polymer component. The (A) polymer component may be composed only of a structural unit derived from a (meth)acrylic monomer.

The (A) polymer component is preferably a (meth)acrylate copolymer. The (meth)acrylate copolymer may be any copolymer that has a structural unit derived from (meth)acrylate as the main component (50% by mass or more), and may contain a structural unit derived from a vinyl monomer other than (meth)acrylate. The (meth)acrylate is an ester compound in which the hydrogen atom of the carboxyl group of (meth)acrylic acid is substituted with an organic group. The content of the structural unit derived from (meth)acrylate in the (A) polymer component is preferably 80% by mass or more, more preferably 90% by mass or more, in 100% by mass of the polymer component.

The polymer component (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 described below. Examples of functional groups that can become the first reactive group include functional groups that have reactivity. Examples of the first reactive group include a hydroxy group, a carboxy group, an epoxy group, etc., and are preferably a hydroxy group and/or a carboxy group, and more preferably a hydroxy group or a carboxy group.

The amount of the first reactive group in the polymer component (A) is preferably 0.002 mmol/g or more, more preferably 0.006 mmol/g or more, even more preferably 0.01 mmol/g or more, and is preferably 0.8 mmol/g or less, more preferably 0.6 mmol/g or less, even more preferably 0.5 mmol/g or less, particularly preferably 0.2 mmol/g or less, and most 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 0.8 mmol/g or less, the distance between crosslinking points of the adhesive formed is sufficiently long and has excellent flexibility.

When the (A) polymer component is a hydroxy group, it is preferable that the (A) polymer component 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 (A) copolymer 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.

In addition, when a hydroxy group is the first reactive group and the (A) polymer component has both a carboxy group and a hydroxy group, the molar ratio of the carboxy group to the hydroxy group per unit mass of the (A) polymer component (carboxy group/hydroxy group) 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 group/hydroxy group) is within the above range, the adhesive layer has high resilience and a good balance between adhesive strength and flexibility.

When the (A) polymer component is a carboxy group, it is preferable that the (A) polymer component further has a hydroxy group as a functional group other than the first reactive group. In this case, the amount of hydroxy groups in the (A) polymer component is preferably 0.01 mmol/g or more, more preferably 0.02 mmol/g or more, and even more preferably 0.04 mmol/g or more, and is preferably 0.25 mmol/g or less, more preferably 0.20 mmol/g or less, and even more preferably 0.15 mmol/g or less.

In addition, when a carboxy group is the first reactive group and the (A) polymer component has both a carboxy group and a hydroxy group, the molar ratio of the carboxy group to the hydroxy group per unit mass of the (A) polymer component (carboxy group/hydroxy group) is preferably 3.0 or more, more preferably 3.5 or more, even more preferably 4.0 or more, and is preferably 30 or less, more preferably 25 or less, even more preferably 20 or less. If the molar ratio (carboxy group/hydroxy group) is within the above range, the adhesive layer has high resilience and a good balance between adhesion and flexibility.

The (A) polymer component may be a random copolymer, a block copolymer, or a graft copolymer, preferably a random copolymer.

The weight average molecular weight (Mw) of the (A) polymer component is preferably 100,000 or more, more preferably 200,000 or more, even more preferably 600,000 or more, particularly preferably more than 800,000, and is preferably 3,000,000 or less, more preferably 2,500,000 or less, and even more preferably 2,300,000 or less. If the (A) polymer component has an Mw of 100,000 or more, the cohesive force is increased and the heat resistance of the formed adhesive material is improved, and if it is 3,000,000 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 (Mw/Mn) of the (A) polymer component is 3.0 or less, preferably 2.5 or less, more preferably 2.2 or less, and even more preferably 1.8 or less. The smaller the Mw/Mn, the narrower the molecular weight distribution width, resulting in a copolymer with a uniform molecular weight, and when the value is 1.0, the molecular weight distribution width is the narrowest. If Mw/Mn is 3.0 or less, 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 bending resistance is obtained. In the present invention, the molecular weight distribution (Mw/Mn) 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 (A) polymer component 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, improving the durability of the adhesive formed, and if it is 0°C or lower, the adhesive formed will have high adhesion to the adherend, preventing peeling at low temperatures, and improving durability.

The Tg of the polymer component 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 in all vinyl monomers that form the copolymer, and ΣWi = 1. i is a natural number from 1 to n.

The (A) polymer component preferably contains a polymer component ((A1) polymer component) having a weight-average molecular weight of 1 million or more and a polymer component ((A2) polymer component) having a weight-average molecular weight of less than 1 million. By containing the polymer component (A1) and the polymer component (A2), a more flexible adhesive material can be formed.

The weight average molecular weight (Mw) of the (A1) polymer component is preferably 1 million or more, more preferably 1.3 million or more, and even more preferably 1.5 million or more, and is preferably 3 million or less, more preferably 2.5 million or less, and even more preferably 2.3 million or less. The molecular weight distribution (Mw/Mn) of the (A1) polymer component is 3.0 or less, preferably 2.5 or less, more preferably 2.2 or less, and even more preferably 1.8 or less.

The weight average molecular weight (Mw) of the (A2) polymer component is preferably 100,000 or more, more preferably 200,000 or more, even more preferably 600,000 or more, particularly preferably more than 800,000, and is preferably less than 1,000,000, more preferably 950,000 or less, and even more preferably 900,000 or less. The molecular weight distribution (Mw/Mn) of the (A2) polymer component is 3.0 or less, preferably 2.5 or less, more preferably 2.2 or less, and even more preferably 1.8 or less.

The ratio (Mw1/Mw2) of the weight average molecular weight (Mw1) of the (A1) polymer component to the weight average molecular weight (Mw2) of the (A2) polymer component is preferably 1.5 or more, more preferably 2.0 or more, and is preferably 4.0 or less, more preferably 3.0 or less. If the ratio (Mw1/Mw2) is within the above range, a more flexible adhesive material can be formed while having excellent resilience. In addition, when a plurality of (A1) polymer components and/or (A2) polymer components are contained, the ratio (Mw1/Mw2) is the ratio of the largest weight average molecular weight of each component.

The mass ratio (A1/A2) of the (A1) polymer component to the (A2) polymer component in the (A) polymer component is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.3 or more, and is preferably 1.0 or less, more preferably 0.8 or less, even more preferably 0.6 or less. If the mass ratio (A1/A2) is within the above range, a more flexible adhesive material can be formed while having excellent resilience. In addition, when a plurality of (A1) polymer components and (A2) polymer components are contained, the mass ratio of the polymer component with the largest weight average molecular weight in each component is taken as the ratio (A1/A2).

((B) (Meth)acrylic copolymer component)
The (B) (meth)acrylic copolymer component may be a copolymer containing a structural unit derived from a (meth)acrylic monomer as a main component (50% by mass or more). The (B) polymer component may be one type or two or more types. The (B) polymer component may contain a structural unit derived from a vinyl monomer other than the (meth)acrylic monomer. The content of the structural unit derived from the (meth)acrylic monomer in the (B) polymer component is preferably 80% by mass or more, more preferably 90% by mass or more, in 100% by mass of the polymer component. The (B) polymer component may be composed only of a structural unit derived from a (meth)acrylic monomer.

The (B) polymer component is preferably a (meth)acrylate copolymer. A (meth)acrylate copolymer is 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 content of structural units derived from (meth)acrylate in the (B) polymer component is preferably 80% by mass or more, and more preferably 90% by mass or more, in 100% by mass of the polymer component.

The (B) polymer component 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 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, and more preferably a hydroxy group or a carboxy group.

The amount of the first reactive group in the (B) polymer component is preferably 0.002 mmol/g or more, more preferably 0.006 mmol/g or more, even more preferably 0.01 mmol/g or more, and is preferably 0.8 mmol/g or less, more preferably 0.6 mmol/g or less, even more preferably 0.5 mmol/g or less, particularly preferably 0.2 mmol/g or less, and most 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 0.8 mmol/g or less, the distance between crosslinking points of the adhesive formed is sufficiently long and has excellent flexibility.

When the (B) polymer component is a hydroxy group, it is preferable that the (B) polymer component 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 (B) copolymer 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.

In addition, when a hydroxy group is the first reactive group and the (B) polymer component has both a carboxy group and a hydroxy group, the molar ratio of the carboxy group to the hydroxy group per unit mass of the (B) polymer component (carboxy group/hydroxy group) 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 group/hydroxy group) is within the above range, the adhesive layer has high resilience and a good balance between adhesive strength and flexibility.

When the (B) polymer component is a carboxy group, it is preferable that the (B) polymer component further has a hydroxy group as a functional group other than the first reactive group. In this case, the amount of hydroxy groups in the (B) polymer component is preferably 0.01 mmol/g or more, more preferably 0.02 mmol/g or more, and even more preferably 0.04 mmol/g or more, and is preferably 0.25 mmol/g or less, more preferably 0.20 mmol/g or less, and even more preferably 0.15 mmol/g or less.

In addition, when a carboxy group is the first reactive group and the (B) polymer component has both a carboxy group and a hydroxy group, the molar ratio of the carboxy group to the hydroxy group per unit mass of the (A) polymer component (carboxy group/hydroxy group) is preferably 3.0 or more, more preferably 3.5 or more, even more preferably 4.0 or more, and is preferably 30 or less, more preferably 25 or less, even more preferably 20 or less. If the molar ratio (carboxy group/hydroxy group) is within the above range, the adhesive layer has high resilience and a good balance between adhesion and flexibility.

The (B) polymer component may be a random copolymer, a block copolymer, or a graft copolymer, preferably a random copolymer.

The weight average molecular weight (Mw) of the (B) polymer component is preferably 100,000 or more, more preferably 200,000 or more, even more preferably 300,000 or more, and particularly preferably 400,000 or more, and is preferably 3 million or less, more preferably 1 million or less, and even more preferably 800,000 or less. If the (B) polymer component has an Mw of 100,000 or more, the cohesive force is increased and the heat resistance of the formed adhesive material is improved, and if it is 3 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 (Mw/Mn) of the (B) polymer component is greater than 3.0, preferably greater than 5.0, more preferably greater than 7.0, and is preferably less than 12.0, more preferably less than 11.0, and even more preferably less than 10.0. If Mw/Mn is greater than 3.0, an adhesive having excellent adhesive strength and flexibility can be formed.

The glass transition temperature (Tg) of the (B) polymer component 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, improving the durability of the adhesive formed, and if it is 0°C or lower, the adhesive formed will have high adhesion to the adherend, preventing peeling at low temperatures, and improving durability.

The multiple (meth)acrylic copolymer components contain at least (A) a (meth)acrylic copolymer component and (B) a (meth)acrylic copolymer component.

The content of the (A) (meth)acrylic copolymer component in the plurality of (meth)acrylic copolymer components is 75% by mass or more, preferably 77% by mass or more, more preferably 80% by mass or more, and 99% by mass or less, preferably 97% by mass or less, more preferably 95% by mass or less. If the content of the (A) (meth)acrylic copolymer component is 75% by mass or more, an adhesive having an excellent recovery rate can be formed, and if it is 99% by mass or less, an adhesive having excellent adhesive strength and flexibility can be formed.

The content of the (B) (meth)acrylic copolymer component in the plurality of (meth)acrylic copolymer components is 1% by mass or more, preferably 3% by mass or more, more preferably 5% by mass or more, and 25% by mass or less, preferably 23% by mass or less, more preferably 20% by mass or less. If the content of the (B) (meth)acrylic copolymer component is 1% by mass or more, an adhesive having excellent adhesive strength and flexibility can be formed, and if it is 25% by mass or less, an adhesive having excellent recovery rate can be formed.

The total content of the (A) (meth)acrylic copolymer component and the (B) (meth)acrylic copolymer component in the plurality of (meth)acrylic copolymer components is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. It is also preferable that the (meth)acrylic copolymer component contains only the (A) (meth)acrylic copolymer component and the (B) (meth)acrylic copolymer component.

The mass ratio (A/B) of the (A) polymer component to the (B) polymer component in the multiple (meth)acrylic copolymer components is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more, and is preferably 25 or less, more preferably 20 or less, and even more preferably 15 or less. If the mass ratio (A/B) is 3 or more, an adhesive with an excellent recovery rate can be formed, and if it is 25 or less, an adhesive with excellent adhesion and flexibility can be formed.

The plurality of (meth)acrylic copolymer components may contain a polymer component other than the polymer component (A) and the polymer component (B).
An example of the other polymer component is a (meth)acrylic copolymer component that does not have a first reactive group.

The structural units constituting the (A) polymer component, (B) polymer component and other polymer components are described below.

The (A) polymer component and the (B) polymer component have a first reactive group. That is, the (A) polymer component and the (B) polymer component contain a structural unit (a-1) having a first reactive group in their structures. 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 (A) polymer component 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, and even more preferably 1% by mass or less, in 100% by mass of the polymer component. If the content of the structural unit (a-1) in the (A) polymer component is within the above range, an adhesive having an excellent balance of 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 content of the structural unit (structural unit (a-1) having a first reactive group) derived from the vinyl monomer having a first reactive group in the (B) polymer component 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, and even more preferably 1% by mass or less, in 100% by mass of the polymer component. If the content of the structural unit (a-1) in the (B) polymer component is within the above range, an adhesive having an excellent balance of 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.

Examples of the (meth)acrylic monomer include (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. As the (b1) (meth)acrylic monomer, (b1-1) a (meth)acrylate monomer that does not have a functional group that can become a first reactive group is preferred. As the (b2) (meth)acrylic monomer, (b2-1) a (meth)acrylate monomer that has a functional group that can become a first reactive group, and (meth)acrylic acid are included.

Examples of the (meth)acrylic monomer that does not have a functional group that can become the (b1) first reactive group include (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, a (meth)acrylate having a linear alkyl group with a carbon number of 1 to 15 is more preferred, and a (meth)acrylate having a linear alkyl group with a carbon number of 8 to 15 is even more preferred. Examples of the (meth)acrylate having a linear alkyl group include (meth)acrylic acid linear alkyl esters 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 in which the number of carbon atoms in the branched alkyl group is 3 to 20 is preferred, and a (meth)acrylate having a branched alkyl group in which the number of carbon atoms in the branched alkyl group is 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.

Examples of the (meth)acrylate having an alicyclic hydrocarbon group include (meth)acrylates having a cyclic alkyl group and (meth)acrylates having a polycyclic structure.
The (meth)acrylate having a cyclic alkyl group is preferably a (meth)acrylate having a cyclic alkyl group with a carbon number of 6 to 12. Examples of the cyclic alkyl group include a cyclic alkyl group having a monocyclic structure (e.g., a cycloalkyl group), which may also have a chain portion. Specific examples of the (meth)acrylate 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 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. Specific examples of the (meth)acrylate having an aromatic group include benzyl (meth)acrylate, phenyl (meth)acrylate, and phenoxyethyl (meth)acrylate.

Examples of (meth)acrylates 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.

(b2) Examples of the (meth)acrylic monomer having a functional group that can become the first reactive group include a (meth)acrylic monomer having a hydroxy group (preferably a (meth)acrylate monomer), a (meth)acrylic monomer having a carboxy group (preferably (meth)acrylic acid), a (meth)acrylic monomer having an epoxy group (preferably a (meth)acrylate monomer), etc. Among these, a (meth)acrylic monomer having a hydroxy group and/or a (meth)acrylic monomer having a carboxy group is preferred, and a (meth)acrylic monomer having a hydroxy group is more 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 cycloalkyl (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 a (meth)acrylate having a hydroxy group, such as carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl maleate, or 2-(meth)acryloyloxyethyl phthalate, with an acid anhydride, such as maleic anhydride, succinic anhydride, or phthalic anhydride (for example, 2-acryloyloxyethyl hydrogen succinate, 2-methacryloyloxyethyl hydrogen succinate, 2-(acryloyloxy)ethyl hydrogen hexahydrophthalate, 2-(methacryloyloxyethyl hydrogen hexahydrophthalate, 1-(2-acryloyloxyethyl) phthalate, and 1-(2-methacryloyloxyethyl) phthalate), 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, 3,4-epoxycyclohexylmethyl (meth)acrylate, etc.

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 vinyl monomers 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 vinyl monomers other than the (meth)acrylic monomer having a functional group that can become the first reactive group (b4) include vinyl monomers having a hydroxy group, vinyl monomers having a carboxy group, and vinyl monomers 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.

(Preparation of (meth)acrylic copolymer mixture)
The (meth)acrylic copolymer mixture can be prepared, for example, by mixing a plurality of (meth)acrylic copolymer components. The (meth)acrylic copolymer can be obtained by polymerizing a (meth)acrylic monomer. In addition, a polymerization composition containing a plurality of polymer components can be obtained by adding a polymerization initiator in portions or continuously during polymerization, and such a polymerization composition can be used as a plurality of (meth)acrylic copolymer components. In addition, the polymer components contained in the polymerization composition or the (meth)acrylic copolymer mixture can be confirmed by preparing a differential molecular weight distribution curve by gel permeation chromatography and performing waveform separation on the curve.

The polymerization method for polymerizing the monomer composition can be either free radical polymerization or living radical polymerization.

(Living radical polymerization method)
Living radical polymerization maintains the simplicity and versatility of conventional radical polymerization, while being less susceptible to termination reactions and chain transfer, and grows without being 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, the copolymer produced by living radical polymerization has reactive functional groups uniformly distributed in each molecular chain. In living radical polymerization, a random copolymer can be produced by using a mixture of each monomer (vinyl monomer). In addition, a block copolymer can be produced by sequentially reacting the vinyl monomers that make up the copolymer.

Living radical polymerization methods include a method using a compound capable of generating nitroxide radicals (nitroxide method; NMP method) depending on the method of stabilizing the polymerization growth end; a method using a metal complex such as copper or ruthenium to polymerize a halogenated compound as a polymerization initiator compound in a living manner from the polymerization initiator compound (ATRP method); a method using a sulfur-based reversible chain transfer agent (RAFT method); a method using an organic tellurium compound (TERP method); a method using an organic iodine compound (ITP method); a method using an iodine compound as a polymerization initiator compound and an organic compound such as a phosphorus compound, a nitrogen compound, an oxygen compound, or a hydrocarbon as a catalyst (reversible transfer catalyst polymerization; RTCP method, reversible catalyst-mediated polymerization; RCMP method), etc. Among these methods, the TERP method is preferred from the viewpoint of the diversity of monomers that can be used, molecular weight control in the polymer region, uniform composition, or coloring.

The TERP method is a method of polymerizing a radically polymerizable compound (vinyl monomer) using an organic tellurium compound as a chain transfer agent, and is a method 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 limitation. Examples of the azo polymerization initiator include 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), and the like.

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 it may be carried out by stirring the mixture using an aprotic or protic solvent commonly used in radical polymerization. Examples of aprotic solvents that can be used include acetonitrile, methyl ethyl ketone, anisole, benzene, toluene, propylene glycol monomethyl ether acetate, ethyl acetate, tetrahydrofuran (THF), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), acetone, dioxane, chloroform, and carbon tetrachloride. Examples of protic solvents include water, methanol, ethanol, isopropanol, n-butanol, ethyl cellosolve, butyl cellosolve, 1-methoxy-2-propanol, hexafluoroisopropanol, and diacetone alcohol. The solvent may be used alone or in combination of two or more kinds. The amount of the solvent used may be adjusted appropriately, and for example, 0.01 ml to 50 ml per 1 g of vinyl monomer is preferable. The reaction temperature and reaction time may be appropriately adjusted depending on the molecular weight or molecular weight distribution of the resulting polymer component, but typically, the reaction is carried out at 0°C to 150°C for 1 minute to 100 hours. The reaction is typically carried out at normal pressure, but may be increased or decreased. After the polymerization reaction is completed, the solvent used and the remaining vinyl monomer are removed from the resulting reaction mixture by a typical separation and purification means, and the target 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.

(Free Radical Polymerization Method)
The free radical polymerization method may be a conventionally known method. Examples of the polymerization initiator used in the free radical polymerization include azo-based polymerization initiators and peroxide-based polymerization initiators. Examples of the azo-based polymerization initiators include 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(2-methylbutyronitrile) (AMBN), 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN), 1,1'-azobis(1-cyclohexanecarbonitrile) (ACHN), dimethyl-2,2'-azobisisobutyrate (MAIB), 4,4'-azobis(4-cyanovaleric acid) (ACVA), 1,1'-azobis(1-acetoxy-1-phenylethane), 2,2'-azobis(2-methylbutyramide), 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) (V-70), 2,2'-azobis(2-methylamidinopropane) dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2'-azobis(2,4,4-trimethylpentane), 2-cyano-2-propylazoformamide, 2,2'-azobis(N-butyl-2-methylpropionamide), or 2,2'-azobis(N-cyclohexyl-2-methylpropionamide) can be exemplified.

The polymerization reaction can be carried out without a solvent, but it can also be carried out by stirring the mixture using an aprotic or protic solvent commonly used in radical polymerization. Examples of aprotic solvents that can be used include acetonitrile, anisole, benzene, toluene, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), acetone, 2-butanone (methyl ethyl ketone), dioxane, propylene glycol monomethyl ether acetate, chloroform, carbon tetrachloride, tetrahydrofuran (THF), ethyl acetate, trifluoromethylbenzene, etc. Examples of protic solvents include water, methanol, ethanol, isopropanol, n-butanol, ethyl cellosolve, butyl cellosolve, 1-methoxy-2-propanol, hexafluoroisopropanol, diacetone alcohol, etc.

The amount of solvent used may be adjusted as appropriate; for example, it is preferably 0.01 ml or more, more preferably 0.05 ml or more, and even more preferably 0.1 ml or more per 1 g of vinyl monomer; it is preferably 50 ml or less, more preferably 10 ml or less, and even more preferably 1 ml or less.

The reaction temperature and reaction time may be adjusted as appropriate depending on the molecular weight or molecular weight distribution of the resulting polymer component, but typically the reaction is carried out at 0°C to 150°C and for 1 minute to 100 hours with stirring. The reaction is usually carried out at normal pressure, but pressure may be increased or decreased. After the polymerization reaction is complete, the solvent used and residual vinyl monomers are removed from the resulting reaction mixture by conventional separation and purification means, and the desired polymer composition can be isolated.

(Crosslinking Agent)
The adhesive composition contains a crosslinking agent. The crosslinking agent is a compound having two or more second reactive groups in one molecule that react with the first reactive groups of the above-mentioned (A) polymer component and (B) polymer component. The crosslinking agent is not particularly limited, and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, metal chelate-based crosslinking agents, melamine resin-based crosslinking agents, and urea resin-based crosslinking agents. The crosslinking agents may be used alone or in combination of two or more. Among these, isocyanate-based crosslinking agents and/or epoxy-based crosslinking agents are preferred. In particular, isocyanate-based crosslinking agents or epoxy-based crosslinking agents are more preferred, and epoxy-based crosslinking agents are even more preferred, since they improve the recovery rate of the adhesive material formed.

The average number of second reactive groups in one molecule of the crosslinking agent is 2 or more, more preferably 3 or more, even more preferably 4 or more, particularly preferably 5 or more, and preferably 8 or less. In other words, the crosslinking agent is more preferably a multifunctional crosslinking agent having 4 or more second reactive groups in one molecule. If the crosslinking agent is tetrafunctional or more, the average distance between crosslinking points in the polymer in the adhesive becomes longer. Therefore, the resulting adhesive has a low initial stress and a high recovery rate. The molecular weight of the crosslinking agent is preferably 200 or more, more preferably 300 or more, even more preferably 400 or more, and is preferably 1500 or less, more preferably 1000 or less, even more preferably 700 or less.

The content of the second reactive group of the crosslinking agent is preferably 1.5 mmol/g or more, more preferably 3.0 mmol/g or more, and even more preferably 3.7 mmol/g or more, and is preferably 10 mmol/g or less, more preferably 8 mmol/g or less, and even more preferably 6 mmol/g or less. If the content of the second reactive group of the crosslinking agent is within this range, the valence of the crosslinking agent is low, the crosslinking points are evenly distributed within 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.

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

As a combination of the first reactive group possessed by the (A) polymer component and the (B) polymer component and the second reactive group possessed by the crosslinking agent, the following combinations are preferred: (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.

(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. Specifically, compounds having two isocyanate groups (including isocyanate regenerating functional groups in which the isocyanate groups are temporarily protected by blocking agents or oligomerization, etc.) in one molecule (bifunctional isocyanate-based crosslinking agents), compounds having three isocyanate groups (including isocyanate regenerating functional groups in which the isocyanate groups are temporarily protected by blocking agents or oligomerization, etc.) in one molecule (trifunctional isocyanate-based crosslinking agents), compounds having six isocyanate groups (including isocyanate regenerating functional groups in which the isocyanate groups are temporarily protected by blocking agents or oligomerization, etc.) in one molecule (hexafunctional isocyanate-based crosslinking agents), etc.

Examples of bifunctional isocyanate crosslinking agents include diisocyanate compounds such as aliphatic diisocyanate compounds, alicyclic diisocyanate compounds, and aromatic diisocyanate compounds, and adducts of these diisocyanate compounds with diol compounds can also be used. Diisocyanate compounds are compounds 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.). Diol compounds are compounds 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, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, etc., of which 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.

Examples of the diol compound include 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.

Examples of the trifunctional isocyanate-based crosslinking agents and hexafunctional isocyanate-based crosslinking agents include adducts of the diisocyanate compounds, biuret forms of diisocyanate compounds, and isocyanurates of diisocyanate compounds (cyclic polymers of diisocyanate compounds).

It is preferable that the isocyanate-based crosslinking agent 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 or hexafunctional 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.

Epoxy-based crosslinking agents include aliphatic epoxy compounds, alicyclic epoxy compounds, aromatic epoxy compounds, heterocyclic epoxy compounds, etc.

Examples of the aliphatic epoxy compounds include ethylene glycidyl ether, ethylene glycol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidyl amine, diamine glycidyl amine, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, sorbitol polyglycidyl ether, glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, glycerin diglycidyl ether, glycerin triglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, adipic acid diglycidyl ester, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, and the like.

Examples of the alicyclic epoxy compounds include 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, N,N,N',N'-tetraglycidyl-m-xylylenediamine, etc.

Examples of the aromatic epoxy compounds include bisphenol A epichlorohydrin type epoxy resins, diglycidyl aniline, o-phthalic acid diglycidyl ester, resorcinol diglycidyl ether, bisphenol-S-diglycidyl ether, etc.

Examples of the heterocyclic epoxy compounds include triglycidyl-tris(2-hydroxyethyl)isocyanurate, 1,3,5-tris-(2,3-epoxybutyl)isocyanurate, 1,3,5-tris-(3,4-epoxybutyl)isocyanurate, 1,3,5-tris-(4,5-epoxypentyl)isocyanurate, and sorbitan polyglycidyl ether.

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

It is preferable that the adhesive composition contains only an isocyanate-based crosslinking agent or only an epoxy-based crosslinking agent as a crosslinking agent. When the adhesive composition contains only an isocyanate-based crosslinking agent as a crosslinking agent, it is preferable that the adhesive composition contains only a bifunctional isocyanate-based crosslinking agent having two isocyanate groups in one molecule, a trifunctional isocyanate-based crosslinking agent having three isocyanate groups in one molecule, or a hexafunctional isocyanate-based crosslinking agent having six isocyanate groups in one molecule. When the adhesive composition contains only an epoxy-based crosslinking agent as a crosslinking agent, it is preferable that the adhesive composition contains only a bifunctional epoxy-based crosslinking agent having two epoxy groups in one molecule, a trifunctional epoxy-based crosslinking agent having three epoxy groups in one molecule, or a tetrafunctional epoxy-based crosslinking agent having four epoxy groups in one molecule.

The content of the crosslinking agent in the adhesive composition is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of the multiple (meth)acrylic copolymer components, and is preferably 0.2 parts by mass or less, and more preferably 0.17 parts by mass or less. If the content of the crosslinking agent is within the above range, the adhesive strength and recovery rate will be in a suitable range.

The molar ratio of the second reactive groups of the crosslinking agent to the first reactive groups of the multiple (meth)acrylic copolymer components (molar amount of first reactive groups/molar amount of second reactive groups) is 1 or more, preferably 2 or more, more preferably 3 or more, and is preferably 70 or less, more preferably 15 or less, even more preferably 10 or less, and particularly 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 groups is produced, and a high restoration rate is achieved, and if it is 70 or less, the reaction proceeds sufficiently and a high restoration rate is achieved.

The molar ratio of the first reactive groups possessed by the plurality of (meth)acrylic copolymer components to the blending amount (molar amount) of the crosslinking agent (molar amount) (molar amount of first reactive groups/molar amount of crosslinking agent) is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, and is preferably 250 or less, more preferably 18 or less, even more preferably less than 12, particularly preferably 11 or less, and most preferably 8 or less. If the molar ratio is within the above range, the adhesive strength and recovery rate will be in a suitable range.

(Other additives)
In addition to the copolymer component and the crosslinking agent, other additives can be added to the adhesive composition.Other additives include crosslinking accelerators, crosslinking retarders, tackifier resins, polymerizable compounds, photopolymerization initiators, silane coupling agents, plasticizers, softeners, peeling aids, dyes, pigments, dyestuffs, fluorescent brighteners, 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 are 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.

Examples of 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 coordination 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, even more preferably 0.04 parts by mass or more, and is preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, even more preferably 0.3 parts by mass or less, per 100 parts by mass of the multiple (meth)acrylic copolymer components. 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, per 100 parts by mass of the multiple (meth)acrylic copolymer components. 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 crosslinking agent in 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 component, if 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, and other chemically modified rosins, etc.), as well as 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 then 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 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.

Examples of terpene-based tackifying resins include terpene-based resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers, as well as modified terpene-based resins obtained by modifying these terpene-based resins (phenol-modified, aromatic-modified, hydrogen-modified, hydrocarbon-modified, etc.) (e.g., terpene-phenolic resins, styrene-modified terpene resins, aromatic-modified terpene resins, and hydrogenated terpene resins).

Examples of phenolic tackifying resins include condensates of various phenols (e.g., phenol, m-cresol, 3,5-xylenol, p-alkylphenol, resorcinol) with formaldehyde (e.g., alkylphenol resins, xylene formaldehyde resins), resols obtained by addition reaction of the phenols with formaldehyde using an alkaline catalyst, and novolaks 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 ... Examples of suitable polymers include polymers of vinyl groups having 8 to 10 carbon atoms (styrene, vinyltoluene, α-methylstyrene, indene, methylindene, etc.) or hydrogenated products thereof, alicyclic hydrocarbon resins obtained by hydrogenating the aromatic rings of the aromatic hydrocarbon resins or aliphatic/aromatic petroleum resins described 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, and coumarone-indene resins.

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, even more preferably 20 parts by mass or more, and preferably 60 parts by mass or less, more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, per 100 parts by mass of the plurality of (meth)acrylic copolymer components. By adjusting the content of the tackifier resin within the above range, sufficient adhesion to the adherend can be ensured.

(Polymerizable compound)
The adhesive composition may contain a polymerizable compound. By adding a polymerizable compound and polymerizing the polymerizable compound in the adhesive, flexibility can be imparted to the adhesive.

The polymerizable compound may be a compound having two or more polymerizable groups in one molecule. Examples of the polymerizable group include an ethylenically unsaturated group. The polymerizable compound may be used alone or in combination of two or more. The polymerizable compound may be a compound having two or more (meth)acryloyl groups, and polyfunctional monomers and polyfunctional oligomers are preferred. The number of ethylenically unsaturated groups in one molecule of the polymerizable compound is preferably two or more, more preferably four or less, and more preferably three or less.

Examples of compounds having two or more (meth)acryloyl groups include hexanediol di(meth)acrylate, butanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, isocyanuric acid ethylene oxide modified tri(meth)acrylate, allyl (meth)acrylate, vinyl (meth)acrylate, and urethane (meth)acrylate.

When a polymerizable compound is blended into the adhesive composition, the content of the polymerizable compound is preferably 0.1 parts by mass or more, more preferably 2.5 parts by mass or more, and is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, per 100 parts by mass of the multiple (meth)acrylic copolymer components.

(Photopolymerization initiator)
When the polymerizable compound is cured by active energy rays, it is preferable to add a photopolymerization initiator to the adhesive composition. By adding a photopolymerization initiator, the reaction during irradiation with active energy rays can be stabilized. The photopolymerization initiator is not particularly limited as long as it generates radicals by the action of light, and examples thereof include photopolymerization initiators such as acetophenones, benzoins, benzophenones, thioxanthones, and acylphosphine oxides. These photopolymerization initiators can be used alone or in combination of two or more kinds. Among these photopolymerization initiators, hydrogen abstraction type benzophenones and intramolecular cleavage type acetophenones are preferable because they can efficiently crosslink between molecules or within molecules.

When a photopolymerization initiator is blended into the adhesive composition, the content of the photopolymerization initiator is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.5 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 2 parts by mass or less, relative to 100 parts by mass of the multiple (meth)acrylic copolymer components. If the content of the photopolymerization initiator is too low, the curing speed tends to decrease or the curing tends to be insufficient, and if the content is too high, the curability does not improve and the economic efficiency tends to decrease.

The adhesive composition may also contain an auxiliary agent for the photopolymerization initiator. Examples of the auxiliary agent include triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, 4-dimethylaminobenzoic acid ethyl, 4-dimethylaminobenzoic acid (n-butoxy)ethyl, 4-dimethylaminobenzoic acid isoamyl, 4-dimethylaminobenzoic acid 2-ethylhexyl, 2,4-diethylthioxanthone, and 2,4-diisopropylthioxanthone. These auxiliary agents may be used alone or in combination of two or more.

(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 0.01% by mass or more, more preferably 0.02% by mass or more, and preferably 1 part by mass or less, more preferably 0.6 parts by mass or less, per 100 parts by mass of the multiple (meth)acrylic copolymer components. 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.

(Plasticizer)
The adhesive composition may contain a plasticizer as necessary. The plasticizer is not particularly limited, but examples thereof include oils such as paraffin oil and process oil; liquid rubbers such as liquid polyisoprene, liquid polybutadiene, and liquid ethylene-propylene rubber; tetrahydrophthalic acid, azelaic acid, benzoic acid, phthalic acid, trimellitic acid, pyromellitic acid, adipic acid, sebacic acid, fumaric acid, maleic acid, itaconic acid, citric acid, and derivatives thereof; dioctyl phthalate (DOP), dibutyl phthalate (DBP), dioctyl adipate, diisononyl adipate (DINA), and isodecyl succinate. The plasticizer may be used alone or in combination of two or more. Among these, liquid rubber is preferred.

The weight average molecular weight (Mw) of the liquid rubber is preferably 5,000 or more, more preferably 10,000, and is preferably 600 million or less, more preferably 500 million or less. By adjusting the Mw of the liquid rubber within the above range, an adhesive material with excellent flexibility can be formed. The method for measuring the weight average molecular weight (Mw) will be described later.

When a plasticizer is blended with the adhesive composition, the content of the plasticizer is preferably 1 part by mass or more, more preferably 5 parts by mass or more, even more preferably 10 parts by mass or more, and preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, per 100 parts by mass of the multiple (meth)acrylic copolymer components. By adjusting the content of the plasticizer within the above range, an adhesive having excellent adhesive strength and recovery properties can be formed.

(Method for producing adhesive composition)
The adhesive composition can be produced by mixing the copolymer components, the crosslinking agent, and other additives used as necessary. The adhesive composition may contain a solvent derived from the production of the copolymer components, 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 preferred, 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.

The gel fraction of the cured product is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably more than 70% by mass, and particularly preferably 75% by mass or more and 100% by mass or less. By setting the gel fraction within the above range, an adhesive material with excellent flexibility and resilience can be formed. The gel fraction can be controlled by the amount of crosslinking agent in the adhesive composition, the crosslinking temperature, the crosslinking time, etc.

[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.

An example of an adhesive sheet of the present invention is shown in Figure 1. The adhesive sheet 10 in Figure 1 is composed of an adhesive layer 12, and a first flexible sheet member 14 and a second flexible sheet member 16 that sandwich the adhesive layer 12. 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."

Examples of the flexible sheet member include a sheet of a polymer material, a glass sheet, etc. The thickness of the flexible sheet member is not particularly limited, but from the viewpoint of excellent handleability, etc., it is preferably 2 μm to 500 μm, and more preferably 2 μm to 200 μm.

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

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 polymeric material different from the layer containing one or more of the polymeric materials.

The flexible sheet member is preferably a release sheet having a release treatment applied to 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 preferably 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, the second flexible sheet member being a second release sheet, and the first release sheet and the second release sheet being 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.

The adhesive composition can be applied by 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.; inkjet method; and various printing methods such as offset printing, screen printing, flexographic printing, etc. In addition, before applying 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 heating process is not particularly limited as long as it can remove the solvent used in the adhesive composition and harden 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 heating 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.

An example of a flexible laminated member of the present invention is shown in Figure 2. 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, bonding these flexible members together.

Examples of the configuration of the flexible laminated member include a configuration in which both the first flexible member and the second flexible member are components of a flexible device; 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 polymer composition, the weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the polymer component, the thickness of the adhesive layer, and the adhesive material 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 signal derived from the monomer to the signal derived from the polymer was obtained, and the polymerization rate of the monomer was calculated.

(Weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn))
Gel permeation chromatography (GPC) was performed using a high performance liquid chromatograph (Tosoh Corporation, model HLC-8320GPC). Two TSKgel Super HZM-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 created 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, and 440) as a standard substance.
Using GPC software (Ecosec Peak Separation (Version 1.04) manufactured by Tosoh Corporation), waveform separation was performed by Gaussian approximation for the retention time of 6 to 11 minutes of the measured chromatogram, and the weight average molecular weight (Mw), molecular weight distribution (Mw/Mn), and content of each polymer component were determined. The waveform separation parameters were set as follows: Threshold: 0.5, SmoothWidth: 8, start retention time: 6, end retention time: 11.

(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

(Stress relaxation time at 400% strain, recovery rate after 400% strain)
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 μm, which was used as a test piece. Measurements were performed using a viscoelasticity measuring device (Anton Paar, MCR302) with the sample sandwiched between 8 mm diameter parallel plates (the adhesive surfaces of which were roughened using sandpaper no. 240) in an atmosphere of 25°C.
In the measurement, the test piece was compressed with an axial force of 1 N and left for 10 minutes, then the axial force was changed to 0.05 N, and a shear stress was immediately applied to distort the specimen to 400% strain. The specimen was then held at 400% strain for 10 minutes, and the change in shear stress was measured to measure the stress relaxation time. Next, the shear stress was released (0 kPa) and the specimen was left for 10 minutes, and the final strain after 10 minutes was measured to determine the recovery rate.
The stress relaxation time was the time required for the shear stress to become 0.368 times the initial stress after the strain reached 400%. The shear stress value 0.1 seconds after the start of application of the shear stress was defined as the initial stress.
The recovery rate was calculated based on the following formula.
Recovery rate (%) = {(400 - final strain) / 400} x 100

(Strain at 20 kPa stress, recovery rate after application of 20 kPa stress)
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 μm, which was used as a test piece. Measurements were performed using a viscoelasticity measuring device (Anton Paar, MCR302) with the sample sandwiched between 8 mm diameter parallel plates (the adhesive surfaces of which were roughened using sandpaper no. 240) in an atmosphere of 25°C.
In the measurement, the test piece was compressed with an axial force of 1 N and left to stand for 10 minutes, then the axial force was changed to 0.05 N, a shear stress of 20 kPa was applied, and a creep test was performed for 10 minutes, and the strain after 10 minutes (20 kPa strain) was measured. Next, the shear stress was released (0 kPa) and the piece was left for 10 minutes, and the final strain after 10 minutes was measured to determine the recovery rate. Note that pieces that were too soft to measure were evaluated as "X".
The recovery rate was calculated based on the following formula.
Recovery rate (%) = {(20 kPa strain - final strain) / 20 kPa strain} x 100

(Repeated elongation test)
The adhesive layers (adhesive materials) constituting the adhesive sheet were laminated together using a hand roller to prepare a laminate having a thickness of 600 μmm. The laminate was cut into a size of 10 mm in width and 70 mm in length to prepare a test piece.
The test was performed using a precision universal testing machine (AUTOGRAPH (registered trademark) AGX, manufactured by Shimadzu Corporation) in an environment of 23°C and 50% humidity, with a gripping distance of 30 mm and a tensile speed of 30 mm/min.
In the test, the specimen was stretched from a tensile stress of 0 kPa to a tensile stress of 50 kPa, and then contracted until the tensile stress reached 0 kPa. This stretching and contraction was repeated 12 times, and the presence or absence of breakage was confirmed. Those without breakage were evaluated as "good", and those with breakage were evaluated as "bad".

(Measurement of 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 Polymer Composition>
(Synthesis Example 1: Polymer composition X _a )
EHA (340.2 g), LA (240.0 g), AA (18.0 g), HBA (1.8 g), AIBN (26.1 mg), and AcOEt (353.4 g) were charged into a flask equipped with an argon gas inlet tube and a stirrer, and after argon replacement, BTEE (105.0 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 solution containing the polymerization composition _Xa . The solid content of the solution was 26.2% by mass.

(Synthesis Example 2: Polymer composition X _b )
A solution containing the polymer composition _Xb was obtained in the same manner as in Synthesis Example 1. Table 1 shows the monomers, organotellurium compounds, azo-based polymerization initiators, solvents, reaction conditions, and polymerization rates used.

(Synthesis Example 3: Polymer composition Y _a )
EHA (1,334.0 g), LA (600.0 g), AA (60.0 g), HBA (6.0 g), and AcOEt (1,333.3 g) were charged into a flask equipped with an argon gas inlet tube and a stirrer, and the mixture was replaced with argon, and then the temperature was raised to 82° C., and AIBN (875.8 mg) dissolved in AcOEt (45 g) was added dropwise over 2 hours, and the mixture was allowed to react for another 4 hours to polymerize. After the reaction was completed, AcOEt was added to the reaction solution to obtain a solution containing the polymerization composition Y _a . The solid content of the solution was 39.5% by mass.

(Synthesis Example 4: Polymer composition Y _b )
A solution containing the polymer composition _Yb was obtained in the same manner as in Synthesis Example 3. Table 1 shows the monomers, azo-based polymerization initiators, solvents, reaction conditions, and polymerization rates used.

The polymerization conditions for each polymerization composition are shown in Table 1. The content of each structural unit in the polymerization composition, the amount of functional groups in 1 g of the polymerization composition, and the glass transition temperature were calculated from the charge ratio and polymerization rate of the monomers used in the polymerization reaction.

(Polymer components in polymer compositions _Xa and _Xb )
Polymer composition _Xa was subjected to gel permeation chromatography and waveform separation, and only polymer component _Xa 1 was confirmed. Polymer composition _Xb was also subjected to gel permeation chromatography _and waveform separation, and only polymer component Xb 1 was confirmed. Table 2 shows the physical properties of polymer components _Xa1 and _Xb1 .

(Polymer components in polymer compositions Y _a and Y _b )
Polymer composition Y _a was subjected to gel permeation chromatography and waveform separation, whereby polymer components Y _a 1, Y _a 2, and Y _a 3 were identified. Polymer composition Y _b was subjected to gel permeation chromatography and waveform separation, whereby polymer components Y _b 1, Y _b 2, and Y _b 3 were identified. Table 3 shows the physical properties of polymer components Y _a 1 to Y _a 3 and Y _b 1 to Y _b 3.

<Production of Adhesive Composition>
(Adhesive composition No. 1)
To 381.7 parts by mass (100 parts by mass of polymer component) of the solution of polymer composition _Xa obtained in Synthesis Example 1, 0.154 parts by mass of crosslinking agent A (Duranate (registered trademark) MHG-80B) and butyl acetate were added and stirred to obtain adhesive composition No. 1 having a solid content of 20% by mass. In adhesive composition No. 1, the first reactive groups of polymer components _Xa1 , _Ya1 , _Ya2 and _Ya3 are hydroxy groups, and the second reactive group of crosslinking agent A is an isocyanate group.

(Adhesive Compositions Nos. 2 to 11)
Except for changing the composition as shown in Tables 4 and 5, adhesive compositions No. 2 to 11 were prepared in the same manner as adhesive composition No. 1. The amount of crosslinking agent A shown in Tables 4 and 5 is the amount converted to solid content. The solid content is the component other than the solvent. In adhesive compositions No. 2 to 8, the first reactive group of polymer components X _a 1, Y _a 1, Y _a 2, and Y _a 3 is a hydroxy group, and the second reactive group of crosslinking agent A is an isocyanate group. In adhesive compositions No. 9 to 11, the first reactive group of polymer components X _b 1, Y _b 1, Y _b 2, and Y _b 3 is a carboxy group, and the second reactive group of crosslinking agent B is an epoxy 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 bonded to the adhesive layer formed on the first release sheet, and then aged at 60 ° C. for 3 days to prepare an adhesive layer sandwiched between two release sheets. The evaluation results of the adhesive layers (adhesives) formed from each adhesive composition are shown in Table 4.

架橋剤Ａ：デュラネート（登録商標）ＭＨＧ－８０Ｂ（旭化成製、イソシアネート系架橋剤（ヘキサメチレンジイソシアネート－のイソシアヌレート体、官能基数６、固形分濃度８０質量％、ＮＣＯ量１５．１質量％））
架橋剤Ｂ：ＴＥＴＲＡＤ（登録商標）－Ｃ（三菱ガス化学製、１，３－ビス（Ｎ，Ｎ－ジグリシジルアミノメチル）シクロヘキサン、官能基数４、固形分濃度１００質量％、エポキシ基量；９．８ｍｍｏｌ／ｇ）
可塑剤：クラプレン（登録商標）ＬＩＲ－４１０（液状イソプレン系ゴム、重量平均分子量３００００）

Crosslinking agent A: Duranate (registered trademark) MHG-80B (manufactured by Asahi Kasei, isocyanate-based crosslinking agent (isocyanurate of hexamethylene diisocyanate, functional group number 6, solid content concentration 80% by mass, NCO amount 15.1% by mass)
Crosslinking agent B: TETRAD (registered trademark)-C (manufactured by Mitsubishi Gas Chemical Company, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, number of functional groups: 4, solid content concentration: 100% by mass, epoxy group amount: 9.8 mmol/g)
Plasticizer: Kuraray (registered trademark) LIR-410 (liquid isoprene rubber, weight average molecular weight 30,000)

Adhesive composition No. 1 is a case where the adhesive composition contains the (A) (meth)acrylic copolymer component but does not contain the (B) (meth)acrylic copolymer component. The adhesive material formed from this adhesive composition No. 1 had a small amount of strain when a shear stress of 20 kPa was applied, and had poor flexibility. In addition, the adhesive strength to glass was also low.

Adhesive compositions No. 2 and 3 are adhesive compositions containing (A) a (meth)acrylic copolymer component and (B) a (meth)acrylic copolymer component, and the content of the (A) (meth)acrylic copolymer component in the total polymer components is 75% by mass to 99% by mass. The adhesives formed from these adhesive compositions No. 2 and 3 were good in terms of recovery rate after straining to 400%, strain amount when a shear stress of 20 kPa was applied, and repeated elongation test. In addition, the adhesive strength was good to both glass and PI film.

Adhesive compositions No. 4 to 8 are adhesive compositions containing (A) a (meth)acrylic copolymer component and (B) a (meth)acrylic copolymer component, but the content of the (A) (meth)acrylic copolymer component in the total polymer components is less than 75 mass%. Among these, the adhesives formed from adhesive compositions No. 4 to 6 had poor recovery rates after straining to 400%. Also, the adhesives formed from adhesive compositions No. 7 and 8 broke in repeated elongation tests.

Adhesive compositions No. 9 to 11 are adhesive compositions containing (A) a (meth)acrylic copolymer component and (B) a (meth)acrylic copolymer component, and the content of the (A) (meth)acrylic copolymer component in the total polymer components is 75% by mass to 99% by mass. The adhesive materials formed from these adhesive compositions No. 9 to 11 were good in terms of recovery rate after straining to 400%, strain amount when a shear stress of 20 kPa was applied, and repeated elongation test. In addition, the adhesive strength was good to both glass and PI film.

The present invention includes the following aspects:

(Aspect 1)
The adhesive composition for a flexible display is used for bonding one flexible member and another flexible member constituting a flexible display, the adhesive composition for a flexible display comprising a plurality of (meth)acrylic copolymer components and a crosslinking agent, the (meth)acrylic copolymer components comprising at least an (A) (meth)acrylic copolymer component and a (B) (meth)acrylic copolymer component, the (A) (meth)acrylic copolymer component having a first reactive group and a molecular weight distribution (Mw/Mn) of 3.0 or less, the (B) (meth)acrylic copolymer component having a first reactive group and a molecular weight distribution (Mw/Mn) of more than 3.0, the crosslinking agent having a second reactive group that reacts with the first reactive group, and a content of the (A) (meth)acrylic copolymer component in the plurality of (meth)acrylic copolymer components is 75% by mass to 99% by mass.

(Aspect 2)
The pressure-sensitive adhesive composition for flexible displays according to embodiment 1, wherein the weight average molecular weight of the (A) (meth)acrylic copolymer component and the (B) (meth)acrylic copolymer component is 100,000 to 3,000,000.

(Aspect 3)
The pressure-sensitive adhesive composition for flexible displays according to aspect 1 or 2, wherein the (meth)acrylic copolymer component (A) has a weight average molecular weight of 100,000 or more.

(Aspect 4)
The pressure-sensitive adhesive composition for flexible displays according to any one of Aspects 1 to 3, wherein the weight average molecular weight of the (meth)acrylic copolymer component (B) is 800,000 or less.

(Aspect 5)
The pressure-sensitive adhesive composition for flexible displays according to any one of Aspects 1 to 4, wherein the crosslinking agent is an isocyanate-based crosslinking agent and/or an epoxy-based crosslinking agent.

(Aspect 6)
The pressure-sensitive adhesive composition for flexible displays according to aspect 5, 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.

(Aspect 7)
The pressure-sensitive adhesive composition for flexible displays according to embodiment 5, wherein the epoxy-based crosslinking agent is at least one selected from the group consisting of an aliphatic epoxy compound, an alicyclic epoxy compound, an aromatic epoxy compound, and a heterocyclic epoxy compound.

(Aspect 8)
The pressure-sensitive adhesive composition for flexible displays according to any one of Aspects 1 to 7, wherein the first reactive group is a hydroxy group and/or a carboxy group.

(Aspect 9)
An adhesive for a flexible display for bonding one flexible member and another flexible member constituting a flexible display, the adhesive being a cured product of the adhesive composition according to any one of Aspects 1 to 8.

(Aspect 10)
A pressure-sensitive adhesive for flexible displays according to claim 9, wherein the cured product has a gel fraction of 50% by mass or more.

(Aspect 11)
An adhesive sheet for a flexible display, comprising an adhesive layer used for bonding one flexible member and another flexible member that constitute a flexible display, and a flexible sheet member attached to at least one surface of the adhesive layer, wherein the adhesive layer is formed from the adhesive material described in aspect 9 or 10.

(Aspect 12)
An adhesive sheet for a flexible display as described in aspect 11, wherein 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 the first release sheet and the second release sheet being attached so that their respective release surfaces are in contact with the adhesive layer.

(Aspect 13)
A flexible laminate member comprising 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, characterized in that the adhesive layer is made of the adhesive material described in aspect 9 or 10.

(Aspect 14)
14. The flexible laminate member of claim 13, wherein at least one of the first flexible member and the second flexible member is a display element.

(Aspect 15)
A flexible display comprising the flexible laminate member according to aspect 13 or 14.

(Aspect 16)
A (meth)acrylic copolymer mixture used in an adhesive composition for a flexible display, comprising at least a (meth)acrylic copolymer component (A) and a (meth)acrylic copolymer component (B), the (A) (meth)acrylic copolymer component having a first reactive group and a molecular weight distribution (Mw/Mn) of 3.0 or less, the (B) (meth)acrylic copolymer component having a first reactive group and a molecular weight distribution (Mw/Mn) of more than 3.0, the first reactive group being a hydroxy group and/or a carboxy group, and a content of the (A) (meth)acrylic copolymer component in the (meth)acrylic copolymer mixture being 75% by mass to 99% by mass.

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 (16)

An adhesive composition for a flexible display for bonding one flexible member and another flexible member that constitute a flexible display,
Contains a plurality of (meth)acrylic copolymer components and a crosslinking agent,
The (meth)acrylic copolymer component contains at least (A) a (meth)acrylic copolymer component and (B) a (meth)acrylic copolymer component,
the (A) (meth)acrylic copolymer component has a first reactive group and a molecular weight distribution (Mw/Mn) of 3.0 or less,
the (B) (meth)acrylic copolymer component has a first reactive group and a molecular weight distribution (Mw/Mn) of more than 3.0;
the crosslinker has a second reactive group that reacts with the first reactive group;
A pressure-sensitive adhesive composition for flexible displays, characterized in that a content of the (A) (meth)acrylic copolymer component in the plurality of (meth)acrylic copolymer components is 75% by mass to 99% by mass. The adhesive composition for flexible displays described in claim 1, wherein the weight average molecular weight of the (A) (meth)acrylic copolymer component and the (B) (meth)acrylic copolymer component is 100,000 to 3,000,000. The adhesive composition for flexible displays according to claim 1 or 2, wherein the weight average molecular weight of the (A) (meth)acrylic copolymer component is 100,000 or more. An adhesive composition for flexible displays described in any one of claims 1 to 3, wherein the weight average molecular weight of the (B) (meth)acrylic copolymer component is 800,000 or less. The adhesive composition for flexible displays according to any one of claims 1 to 4, wherein the crosslinking agent is an isocyanate-based crosslinking agent and/or an epoxy-based crosslinking agent. The adhesive composition for flexible displays according to claim 5, 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 claim 5, wherein the epoxy-based crosslinking agent is at least one selected from the group consisting of an aliphatic epoxy compound, an alicyclic epoxy compound, an aromatic epoxy compound, and a heterocyclic epoxy compound. An adhesive composition for flexible displays according to any one of claims 1 to 7, wherein the first reactive group is a hydroxy group and/or a carboxy group. 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 8. The adhesive for flexible displays according to claim 9, wherein the gel fraction of the cured product is 50% by mass or more. 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,
11. An adhesive sheet for a flexible display, wherein the adhesive layer is formed from the adhesive material according to claim 9. 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 11 , 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, characterized in that the adhesive layer is made of the adhesive material according to claim 9 or 10. The flexible laminate member of claim 13, 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 13 or 14. A (meth)acrylic copolymer mixture used in an adhesive composition for a flexible display, comprising:
Contains at least (A) a (meth)acrylic copolymer component and (B) a (meth)acrylic copolymer component,
the (A) (meth)acrylic copolymer component has a first reactive group and a molecular weight distribution (Mw/Mn) of 3.0 or less,
the (B) (meth)acrylic copolymer component has a first reactive group and a molecular weight distribution (Mw/Mn) of more than 3.0;
the first reactive groups are hydroxy groups and/or carboxy groups;
The (meth)acrylic copolymer mixture is characterized in that a content of the (A) (meth)acrylic copolymer component in the (meth)acrylic copolymer mixture is 75% by mass to 99% by mass.

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