Adhesive compositions, adhesives, and adhesive sheets for flexible displays

Abstract

To provide an adhesive composition capable of forming an adhesive material (adhesive layer) having adhesive force suitable for an adhesive material (adhesive layer), excellent flexibility, and excellent restorability.SOLUTION: An adhesive composition for a flexible display contains a plurality of (meth)acrylic copolymer components and a crosslinking agent. As the (meth)acrylic copolymer components, at least (A) a (meth)acrylic copolymer component and (B) a (meth)acrylic copolymer component are contained. The (meth)acrylic copolymer component (A) has a first reactive group and has a molecular weight distribution (Mw / Mn) of 3.0 or less. The (meth)acrylic copolymer component (B) does not have the first reactive group and has a molecular weight distribution (Mw / Mn) of more than 3.0. The crosslinking agent has a second reactive group which reacts with the first reactive group. The content of the (meth)acrylic copolymer component (A) in the plurality of (meth)acrylic copolymer components is 30-99 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an adhesive composition used in flexible displays, and more specifically to an adhesive composition that forms an adhesive used to bond one flexible member to another flexible member. [Background technology]

[0002] In various displays and touch panels for televisions, mobile phones, smartphones, etc., adhesives are generally used to join the components that make them up. The adhesive is provided, for example, in the form of an adhesive sheet with an adhesive layer on a support substrate, or an adhesive sheet without a support substrate, and the components are bonded together.

[0003] On the other hand, in recent years, flexible displays that are repeatedly bent and used in image display devices such as liquid crystal displays and organic electroluminescent (OLED) displays have been attracting attention. Flexible displays include foldable displays that can be folded and rollable displays that can be rolled into a cylindrical shape, and are expected to be used in mobile devices such as smartphones and tablet terminals, as well as storable stationary displays.

[0004] In such flexible displays, as an adhesive material for bonding flexible members that constitute members that are repeatedly bent and stretched to other flexible members, for example, Patent Document 1 discloses an adhesive material for repeatedly bending devices in which the ratio of the shear stress 60 seconds after a 1000% displacement to the maximum shear stress when one surface of the adhesive layer and the other surface are displaced by 1000% in opposite directions, and the gel fraction are controlled within a predetermined range (see Patent Document 1 (Claim 1)). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-108498 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In conventional flexible displays with an adhesive layer, the adhesive layer did not fully recover to its original state after repeated bending. As a result, repeated bending of the flexible display could lead to defects in appearance, such as lifting or peeling at the interface between the adhesive layer and the flexible material at the bending point, or the bending point appearing wavy.

[0007] The present invention has been made in view of the above circumstances, and aims to provide an adhesive composition that can form an adhesive (adhesive layer) that has suitable adhesive strength, excellent flexibility, and excellent resilience. [Means for solving the problem]

[0008] 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 to another flexible member constituting a flexible display, and is characterized in that it contains a plurality of (meth)acrylic copolymer components and a crosslinking agent, and the (meth)acrylic copolymer components contain at least (A)(meth)acrylic copolymer components and (B)(meth)acrylic copolymer components, 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 does not have a first reactive group and a molecular weight distribution (Mw / Mn) greater 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 plurality of (meth)acrylic copolymer components is 30% to 99% by mass. [Effects of the Invention]

[0009] By using the adhesive composition for flexible displays of the present invention, an adhesive material (adhesive layer) with suitable adhesive strength, 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 appearance defects such as cracks and warping, without lifting or peeling at the interface between the adhesive layer and the flexible member at the bending point, even when repeatedly bent. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view of an example of the adhesive sheet of the present invention. [Figure 2] This is a schematic cross-sectional view of an example of a flexible laminated member of the present invention. [Modes for carrying out the invention]

[0011] The following describes an example of a preferred embodiment of the present invention. However, the following embodiments are merely illustrative. The present invention is not limited in any way to the embodiments described below.

[0012] In this invention, "(meth)acrylic" means "at least one of acrylic and methacrylic." "(meth)acrylate" means "at least one of acrylate and methacrylate." "(meth)acryloyl" means "at least one of acryloyl and methacryloyl." "Vinyl monomer" means a monomer having a radically polymerizable carbon-carbon double bond in its molecule. "Structural unit derived from vinyl monomer" means a structural unit in which the radically polymerizable carbon-carbon double bond of vinyl monomer polymerizes to become a carbon-carbon single bond. "Structural unit derived from (meth)acrylate" means a structural unit in which the radically polymerizable carbon-carbon double bond of (meth)acrylate polymerizes to become a carbon-carbon single bond. "Structural unit derived from (meth)acrylic monomer" means a structural unit in which the radically polymerizable carbon-carbon double bond of (meth)acrylic monomer polymerizes to become a carbon-carbon single bond.

[0013] [Adhesive Composition for Flexible Display] The adhesive composition for flexible display of the present invention (hereinafter, may be simply referred to as "adhesive composition") is an adhesive composition for flexible display for bonding one flexible member and another flexible member constituting a flexible display. The adhesive composition contains a plurality of (meth)acrylic copolymer components and a crosslinking agent.

[0014] [(Meth)acrylic Copolymer Component] The adhesive composition contains, as the (meth)acrylic copolymer component, 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"). A mixture containing a plurality of the (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 a molecular weight distribution (Mw / Mn) of 3.0 or less. The (B) (meth)acrylic copolymer component does not have a first reactive group and has a molecular weight distribution (Mw / Mn) of more than 3.0. Further, the content of the (A) (meth)acrylic copolymer component in the plurality of (meth)acrylic copolymer components is 30% by mass to 99% by mass. By containing these (A) (meth)acrylic copolymer component and (B) (meth)acrylic copolymer component in a predetermined amount, an adhesive material having excellent resilience while being flexible can be formed, and further, it can have an adhesive force suitable as an adhesive material.

[0015] [(A) (Meth)acrylic Copolymer Component] The above-mentioned (A) (meth)acrylic copolymer component may be a copolymer having structural units derived from (meth)acrylic monomers as the main component (50% by mass or more). The (A) polymer component may be one type or two or more types. Further, the (A) polymer component may contain structural units derived from vinyl monomers other than (meth)acrylic monomers. The content of the structural units derived from (meth)acrylic monomers in the (A) polymer component is preferably 80% by mass or more, more preferably 90% by mass or more, based on 100% by mass of the polymer component. Note that the (A) polymer component may be composed only of structural units derived from (meth)acrylic monomers.

[0016] The (A) polymer component is preferably a (meth)acrylate copolymer. The (meth)acrylate copolymer may be a copolymer having structural units derived from (meth)acrylates as the main component (50% by mass or more), and may contain structural units derived from vinyl monomers other than (meth)acrylates. The (meth)acrylate is an ester compound in which a hydrogen atom of the carboxy group of (meth)acrylic acid is substituted with an organic group. The content of the structural units derived from (meth)acrylates in the (A) polymer component is preferably 80% by mass or more, more preferably 90% by mass or more, based on 100% by mass of the polymer component.

[0017] The (A) polymer component has a first reactive group. The first reactive group is a functional group having high reactivity with the second reactive group of a crosslinking agent described later. Examples of the functional group that can be the first reactive group include reactive functional groups. Examples of the first reactive group include a hydroxy group, a carboxy group, an epoxy group, etc., preferably a hydroxy group and / or a carboxy group, more preferably a hydroxy group or a carboxy group.

[0018] 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, 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 formed adhesive 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 formed adhesive is sufficiently long and exhibits excellent flexibility.

[0019] In the case where the polymer component (A) has a hydroxyl group as the primary reactive group, it is preferable that it also has a carboxyl group as a functional group other than the primary reactive group. In this case, the amount of carboxyl groups in the copolymer (A) is preferably 0.08 mmol / g or more, more preferably 0.16 mmol / g or more, even more preferably 0.32 mmol / g or more, 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.

[0020] Furthermore, if the hydroxyl group is the primary reactive group and the polymer component (A) has both a carboxyl group and a hydroxyl group, the molar ratio of carboxyl groups to hydroxyl groups per unit mass of the polymer component (A) (carboxyl group / hydroxyl group) is preferably 4 or more, more preferably 8 or more, even more preferably 16 or more, preferably 60 or less, more preferably 40 or less, and even more preferably 30 or less. If the molar ratio (carboxyl group / hydroxyl group) is within the above range, it results in an adhesive layer with high resilience and a suitable balance of tackiness and flexibility.

[0021] In the case where the polymer component (A) has a carboxyl group as the primary reactive group, it is preferable that it also has a hydroxyl group as a functional group other than the primary reactive group. In this case, the amount of hydroxyl groups in the polymer component (A) is preferably 0.01 mmol / g or more, more preferably 0.02 mmol / g or more, even more preferably 0.04 mmol / g or more, 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.

[0022] Furthermore, if the carboxyl group is the primary reactive group and the polymer component (A) has both a carboxyl group and a hydroxyl group, the molar ratio of carboxyl groups to hydroxyl groups per unit mass of the polymer component (A) (carboxyl group / hydroxyl group) is preferably 3.0 or more, more preferably 3.5 or more, even more preferably 4.0 or more, preferably 30 or less, more preferably 25 or less, and even more preferably 20 or less. If the molar ratio (carboxyl group / hydroxyl group) is within the above range, it results in an adhesive layer with high resilience and a good balance of tackiness and flexibility.

[0023] The polymer component (A) may be a random copolymer, a block copolymer, or a graft copolymer, and is preferably a random copolymer.

[0024] The weight-average molecular weight (Mw) of the polymer component (A) is preferably 100,000 or more, more preferably 200,000 or more, even more preferably more than 800,000, particularly preferably 1,000,000 or more, preferably 3,000,000 or less, more preferably 2,800,000 or less, and even more preferably 2,600,000 or less. If the Mw of the polymer component (A) is 100,000 or more, the cohesive force is increased and the heat resistance of the formed adhesive is improved, and if it is 3,000,000 or less, the coating workability of the adhesive composition is further improved. The method for measuring the weight-average molecular weight (Mw) will be described later.

[0025] The molecular weight distribution (Mw / Mn) of the polymer component (A) is 3.0 or less, preferably 2.5 or less, more preferably 2.2 or less, and even more preferably 2.0 or less. The smaller the Mw / Mn, the narrower the molecular weight distribution, resulting in a copolymer with uniform molecular weights, with the narrowest molecular weight distribution occurring when the value is 1.0. If the Mw / Mn is 3.0 or less, the content of molecules with lower molecular weights and molecules with higher molecular weights is lower compared to the molecular weight of the designed copolymer, resulting in an adhesive with excellent flexibility. In this invention, the molecular weight distribution (Mw / Mn) is a value calculated by (weight-average molecular weight (Mw)) / (number-average molecular weight (Mn)), and the methods for measuring Mw and Mn will be described later.

[0026] The glass transition temperature (Tg) of the polymer component (A) is preferably -70°C or higher, more preferably -60°C or higher, preferably 0°C or lower, more preferably -10°C or lower, and even more preferably -20°C or lower. If Tg is -70°C or higher, it provides sufficient cohesive force to the adhesive, improving the durability of the formed adhesive. If Tg is 0°C or lower, the adhesion of the formed adhesive to the adherend is increased, peeling at low temperatures is suppressed, and durability is improved.

[0027] The Tg of the polymer component is the value calculated by the following FOX equation (Equation (1)). In Equation (1), Tg represents the glass transition temperature (°C) of the copolymer. Tgi represents the glass transition temperature (°C) when vinyl monomer i forms a homopolymer. Wi represents the mass ratio of vinyl monomer i in the total vinyl monomers forming the copolymer, where ΣWi = 1. i is a natural number from 1 to n.

[0028]

number

[0029] ((B)(meth)acrylic copolymer component) The (B) (meth)acrylic copolymer component may be any copolymer having structural units derived from (meth)acrylic monomer as its main component (50% by mass or more). The (B) polymer component may be one type or two or more types. Furthermore, the (B) polymer component may contain structural units derived from vinyl monomers other than (meth)acrylic monomer. The content of structural units derived from (meth)acrylic monomer in the (B) polymer component is preferably 80% by mass or more, and more preferably 90% by mass or more, based on 100% by mass of the polymer component. The (B) polymer component may also consist only of structural units derived from (meth)acrylic monomer.

[0030] The polymer component (B) is preferably a (meth)acrylate copolymer. A (meth)acrylate copolymer is any copolymer having 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 polymer component (B) is preferably 80% by mass or more, and more preferably 90% by mass or more, based on 100% by mass of the polymer component.

[0031] The polymer component (B) described above does not have a first reactive group.

[0032] The polymer component (B) may be a random copolymer, a block copolymer, or a graft copolymer, and is preferably a random copolymer.

[0033] The weight-average molecular weight (Mw) of the polymer component (B) is preferably 100,000 or more, more preferably 200,000 or more, even more preferably 300,000 or more, particularly preferably 400,000 or more, preferably 3,000,000 or less, more preferably 800,000 or less, and even more preferably 600,000 or less. If the Mw of the polymer component (B) is 100,000 or more, the cohesive force is increased and the heat resistance of the formed adhesive 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.

[0034] The molecular weight distribution (Mw / Mn) of the polymer component (B) is greater than 3.0, preferably 3.5 or more, more preferably 4.0 or more, preferably 12.0 or less, more preferably 10.0 or less, and even more preferably 6.0 or less. If Mw / Mn is greater than 3.0, an adhesive with excellent tackiness and flexibility can be formed.

[0035] The glass transition temperature (Tg) of the polymer component (B) is preferably -70°C or higher, more preferably -60°C or higher, preferably 0°C or lower, more preferably -10°C or lower, and even more preferably -20°C or lower. If Tg is -70°C or higher, it provides sufficient cohesive force to the adhesive and improves the durability of the formed adhesive. If Tg is 0°C or lower, the adhesion of the formed adhesive to the adherend is increased, peeling at low temperatures is suppressed, and durability is improved.

[0036] The plurality of (meth)acrylic copolymer components include at least (A)(meth)acrylic copolymer component and (B)(meth)acrylic copolymer component.

[0037] The content of the (A)(meth)acrylic copolymer component in the plurality of (meth)acrylic copolymer components is 30% by mass or more, preferably 50% by mass or more, more preferably 55% by mass or more, and 99% by mass or less, preferably 95% by mass or less, more preferably 90% by mass or less. If the content of the (A)(meth)acrylic copolymer component is 30% by mass or more, an adhesive with excellent recovery rate can be formed, and if it is 99% by mass or less, an adhesive with excellent adhesive strength and flexibility can be formed.

[0038] The content of the (B)(meth)acrylic copolymer component in the plurality of (meth)acrylic copolymer components is 1% by mass or more, preferably 2% by mass or more, more preferably 5% by mass or more, and 40% by mass or less, preferably 35% by mass or less, more preferably 25% by mass or less. If the content of the (B)(meth)acrylic copolymer component is 1% by mass or more, an adhesive with excellent tackiness and flexibility can be formed, and if it is 40% by mass or less, an adhesive with excellent recovery rate can be formed.

[0039] 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 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and particularly preferably 85% by mass or more.

[0040] The mass ratio (A / B) of polymer component (A) to polymer component (B) in the plurality of (meth)acrylic copolymer components is preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, preferably 25 or less, more preferably 20 or less, and even more preferably 15 or less. If the mass ratio (A / B) is 1.0 or more, an adhesive with excellent recovery rate can be formed, and if it is 25 or less, an adhesive with excellent adhesive strength and flexibility can be formed.

[0041] The plurality of (meth)acrylic copolymer components may contain polymer components other than polymer component (A) and polymer component (B). Examples of the other polymer components include (meth)acrylic copolymer components that do not have a first reactive group and have a molecular weight distribution of 3.0 or less, and (meth)acrylic copolymer components that have a first reactive group and have a molecular weight distribution greater than 3.0.

[0042] The plurality of (meth)acrylic copolymer components may also preferably include a (C)(meth)acrylic copolymer component (hereinafter sometimes simply referred to as "(C) polymer component") which does not have a first reactive group and has a molecular weight distribution of 3.0 or less. By including the (C) polymer component, an adhesive can be formed that has excellent resilience while also possessing excellent tackiness and flexibility.

[0043] The (C)(meth)acrylic copolymer component may be a random copolymer, a block copolymer, or a graft copolymer, and is preferably a random copolymer.

[0044] The weight-average molecular weight (Mw) of the polymer component (C) is preferably 100,000 or more, more preferably 200,000 or more, even more preferably 400,000 or more, particularly preferably more than 600,000, preferably 3,000,000 or less, more preferably 2,500,000 or less, and even more preferably 2,000,000 or less. If the Mw of the polymer component (C) is 100,000 or more, the cohesive force is increased and the heat resistance of the formed adhesive 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.

[0045] The molecular weight distribution (Mw / Mn) of the (C)(meth)acrylic copolymer 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 molecular weight distribution (Mw / Mn) of the (C)(meth)acrylic copolymer component is 1.0 or more.

[0046] The content of the (C) polymer component in the plurality of (meth)acrylic copolymer components is 1% by mass or more, preferably 2% by mass or more, more preferably 4% by mass or more, and 30% by mass or less, preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. If the content of the (C) (meth)acrylic copolymer component is 1% by mass or more, an adhesive with excellent tackiness and flexibility can be formed, and if it is 30% by mass or less, an adhesive with excellent recovery rate can be formed.

[0047] The following describes the structural units that constitute the polymer component (A), polymer component (B), and other polymer components.

[0048] The polymer component (A) has a first reactive group. That is, the polymer component (A) contains a structural unit (a-1) having a first reactive group in its structure. The polymer component (B) does not contain a structural unit (a-1) having a first reactive group in its structure. The structural unit (a-1) having a first reactive group may be one type or may consist of two or more types. The first reactive group may be present in structural units derived from (meth)acrylic monomers (preferably (meth)acrylate monomers and / or (meth)acrylic acid) or in structural units derived from vinyl monomers other than (meth)acrylic monomers. That is, the structural unit (a-1) having a first reactive group may be a structural unit derived from a (meth)acrylic monomer (preferably (meth)acrylate monomers and / or (meth)acrylic acid) having a first reactive group, or a structural unit derived from a vinyl monomer other than (meth)acrylic monomers having a first reactive group.

[0049] The content of structural units (structural units (a-1)) derived from vinyl monomers having a first reactive group in the polymer component (A) is preferably 0.03% by mass or more, more preferably 0.09% by mass or more, even more preferably 0.15% by mass or more, preferably 6% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less, based on 100% by mass of the polymer component. If the content of structural units (a-1) in the polymer component (A) is within the above range, an adhesive with an excellent balance of adhesion to the adherend and durability can be formed. Note that vinyl monomers having a first reactive group include (meth)acrylic monomers having a first reactive group and vinyl monomers other than (meth)acrylic monomers having a first reactive group.

[0050] Examples of the (meth)acrylic monomer include (b1) a (meth)acrylic monomer that does not have a functional group that can act as a primary reactive group, and (b2) a (meth)acrylic monomer that has a functional group that can act as a primary reactive group. These monomers may be used individually 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 act as a primary reactive group is preferred. Examples of the (b2) (meth)acrylic monomer include (b2-1) a (meth)acrylate monomer that has a functional group that can act as a primary reactive group, and (meth)acrylic acid.

[0051] Examples of (meth)acrylic monomers that do not have a functional group that can be the first reactive group (b1) 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, and (meth)acrylamides. 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.

[0052] The (meth)acrylate having a linear alkyl group is preferably one in which the linear alkyl group has 1 to 20 carbon atoms, more preferably one in which the linear alkyl group has 1 to 15 carbon atoms, and even more preferably one in which the linear alkyl group has 8 to 15 carbon atoms. Examples of the (meth)acrylate having a linear alkyl group include linear alkyl esters of (meth)acrylic acid such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, n-decyl (meth)acrylate, n-lauryl (meth)acrylate, and n-stearyl (meth)acrylate.

[0053] The (meth)acrylate having a branched alkyl group is preferably a (meth)acrylate having a branched alkyl group having 3 to 20 carbon atoms, and preferably a (meth)acrylate having a branched alkyl group having 3 to 10 carbon atoms. Examples of the (meth)acrylate having a branched alkyl group include 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, which are branched alkyl esters of (meth)acrylic acid.

[0054] Examples of (meth)acrylates having an alkoxy group include alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate.

[0055] Examples of (meth)acrylates having polyalkylene glycol structural units include 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, polyethylene glycol (degree of polymerization = 2-10) phenyl ether (meth)acrylate, and other (meth)acrylates having polyethylene glycol structural units; 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, polypropylene glycol (degree of polymerization = 2-10) phenyl ether (meth)acrylate, and other (meth)acrylates having polypropylene glycol structural units.

[0056] Examples of (meth)acrylates having an alicyclic hydrocarbon group include (meth)acrylates having a cyclic alkyl group and (meth)acrylates having a polycyclic structure. Preferably, the (meth)acrylate having a cyclic alkyl group has 6 to 12 carbon atoms. Examples of cyclic alkyl groups include monocyclic alkyl groups (e.g., cycloalkyl groups), and may also have a chain-like portion. Specific examples of (meth)acrylates having a monocyclic cyclic alkyl group include cyclic alkyl esters of (meth)acrylic acid such as cyclohexyl (meth)acrylate, methylcyclohexyl (meth)acrylate, and cyclododecyl (meth)acrylate.

[0057] The (meth)acrylate having the 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 cross-linking ring structure (e.g., adamantyl group, norvonyl 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, and dicyclopentenyloxyethyl (meth)acrylate.

[0058] The (meth)acrylate having an aromatic group is preferably one having an aromatic group with 6 to 12 carbon atoms. Examples of aromatic groups include aryl groups, and may also have a chain portion, such as alkylaryl groups, araryl groups, and aryloxyalkyl groups. Examples of the (meth)acrylate having an aromatic group include compounds in which an aryl group is directly bonded to a (meth)acryloyloxy group, compounds in which an aralkyl group is directly bonded to a (meth)acryloyloxy group, and compounds in which an alkylaryl group is directly bonded to a (meth)acryloyloxy group. The number of carbon atoms in the aryl group is preferably 6 to 12. The number of carbon atoms in the aralkyl group is preferably 6 to 12. The number of carbon atoms in the alkylaryl group is preferably 6 to 12. Specific examples of (meth)acrylate having an aromatic group include benzyl (meth)acrylate, phenyl (meth)acrylate, and phenoxyethyl (meth)acrylate.

[0059] Examples of (meth)acrylates having a tertiary amino group include 2-(dimethylamino)ethyl (meth)acrylate and N,N-dimethylaminopropyl (meth)acrylate.

[0060] 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, 4-(meth)acryloylmorpholine, etc. The (meth)acrylamides are (meth)acrylic monomers but are not included in (meth)acrylate monomers.

[0061] Examples of (meth)acrylic monomers having a functional group that can become the first reactive group (b2) include (meth)acrylic monomers having a hydroxyl group (preferably (meth)acrylate monomers), (meth)acrylic monomers having a carboxyl group (preferably (meth)acrylic acid), and (meth)acrylic monomers having an epoxy group (preferably (meth)acrylate monomers). Among these, (meth)acrylic monomers having a hydroxyl group and / or (meth)acrylic monomers having a carboxyl group are preferred, and (meth)acrylic monomers having a hydroxyl group are more preferred.

[0062] Examples of (meth)acrylic monomers having a hydroxyl 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; hydroxyalkylcycloalkyl (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 with 1 to 5 carbon atoms are more preferred.

[0063] Examples of (meth)acrylic monomers having a carboxyl group include monomers obtained by reacting (meth)acrylates having a hydroxyl group, such as carboxyethyl (meth)acrylate, carboxypentyl (meth)acrylate, 2-(meth)acryloyloxyethyl succinate, 2-(meth)acryloyloxyethyl maleate, and 2-(meth)acryloyloxyethyl phthalate, with acid anhydrides such as maleic anhydride, succinic anhydride, and phthalic anhydride (for example, 2-acryloyloxyethyl hydrogen succinate, 2-methacryloyloxyethyl hydrogen succinate, 2-(acryloyloxy)ethyl hydrogen hexahydrophthalate, 2-(methacryloyloxyethyl hydrogen hexahydrophthalate, 1-(2-acryloyloxyethyl phthalate), 1-(2-methacryloyloxyethyl phthalate)), and (meth)acrylic acid. Among these, (meth)acrylic acid is preferred.

[0064] Examples of (meth)acrylic acid esters having the epoxy group include glycidyl (meth)acrylate and 3,4-epoxycyclohexylmethyl (meth)acrylate.

[0065] Examples of vinyl monomers other than the (meth)acrylic monomers mentioned above include (b3) vinyl monomers other than (meth)acrylic monomers that do not have a functional group that can act as a primary reactive group, and (b4) vinyl monomers other than (meth)acrylic monomers that have a functional group that can act as a primary reactive group. These monomers may be used individually or in combination of two or more.

[0066] Examples of vinyl monomers other than (meth)acrylic monomers that do not have a functional group that can be the first reactive group (b3) include aromatic vinyl monomers, vinyl monomers containing heterocycles, vinyl carboxylates, vinyl monomers containing tertiary amino groups, vinyl monomers containing quaternary ammonium bases, vinyl amides, α-olefins, dienes, halogenated vinyl monomers, and the like.

[0067] Examples of the aromatic vinyl monomers include styrene, α-methylstyrene, 4-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methoxystyrene, 2-hydroxymethylstyrene, and 1-vinylnaphthalene. Examples of vinyl monomers containing the heterocycle include 2-vinylthiophene, N-methyl-2-vinylpyrrole, 2-vinylpyridine, and 4-vinylpyridine. Examples of vinyl carboxylates include vinyl acetate, vinyl pivalate, and vinyl benzoate. Examples of vinyl monomers containing the aforementioned tertiary amino group include N,N-dimethylallylamine. Examples of vinyl monomers containing the aforementioned quaternary ammonium base include N-methacryloylaminoethyl-N,N,N-dimethylbenzylammonium chloride. Examples of the aforementioned vinylamides include N-vinylformamide, N-vinylacetamide, 1-vinyl-2-pyrrolidone, and N-vinyl-ε-captractam. Examples of the α-olefins mentioned above include 1-hexene, 1-octene, and 1-decene. Examples of the aforementioned dienes include butadiene, isoprene, 4-methyl-1,4-hexadiene, and 7-methyl-1,6-octadiene. Examples of the aforementioned vinyl halogenated monomers 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.

[0068] Examples of vinyl monomers other than (meth)acrylic monomers having a functional group that can be the first reactive group (b4) include vinyl monomers having a hydroxyl group, vinyl monomers having a carboxyl group, and vinyl monomers containing an epoxy group.

[0069] Examples of vinyl monomers having a hydroxyl group include p-hydroxystyrene and allyl alcohol. Examples of vinyl monomers having a carboxyl group include crotonic acid, maleic acid, itaconic acid, citraconic acid, and cinnamic acid. Examples of vinyl monomers containing the epoxy group include 2-allyloxirane, glycidyl vinyl ether, and 3,4-epoxycyclohexyl vinyl ether.

[0070] (Preparation of (meth)acrylic copolymer mixtures) The (meth)acrylic copolymer mixture can be prepared, for example, by mixing multiple (meth)acrylic copolymer components. The (meth)acrylic copolymer is obtained by polymerizing (meth)acrylic monomers. During polymerization, a polymerization composition containing multiple polymer components can be obtained by dividing or continuously adding the polymerization initiator, and such a polymerization composition may be used as multiple (meth)acrylic copolymer components. Furthermore, the polymer components contained in the polymerization composition or (meth)acrylic copolymer mixture can be identified by creating a differential molecular weight distribution curve by gel permeation chromatography and performing waveform separation on this curve.

[0071] When polymerizing the monomer composition, either free radical polymerization or living radical polymerization can be used as the polymerization method.

[0072] (Living radical polymerization method) Living radical polymerization retains the simplicity and versatility of conventional radical polymerization while being less prone to termination reactions and chain transfer. It also allows for growth without being hindered by side reactions that deactivate the growth ends, thus facilitating precise control of molecular weight distribution and the production of polymers with uniform composition. Therefore, copolymers produced by living radical polymerization have a uniform distribution of reactive functional groups across each molecular chain. In living radical polymerization, random copolymers can be produced by using mixtures of various monomers (vinyl monomers). Furthermore, block copolymers can be produced by sequentially reacting the vinyl monomers constituting the copolymer.

[0073] Living radical polymerization methods include those using compounds capable of generating nitroxide radicals (nitroxide method; NMP method), which differ in the method of stabilizing the polymerization growth ends; those using metal complexes such as copper and ruthenium, with halogenated compounds as polymerization initiators and polymerization carried out in a living manner from those initiators (ATRP method); those using sulfur-based reversible chain transfer agents (RAFT method); those using organotellurium compounds (TERP method); those using organioidone compounds (ITP method); and those using iodine compounds as polymerization initiators and organic compounds such as phosphorus compounds, nitrogen compounds, oxygen compounds, or hydrocarbons as catalysts (reversible transfer catalytic polymerization; RTCP method, reversible catalyst-mediated polymerization; RCMP method). 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 range, uniform composition, and coloration.

[0074] The TERP method is a method for polymerizing radical polymerizable compounds (vinyl monomers) using an organotellurium compound as a chain transfer agent, and is described, for example, in International Publication Nos. 2004 / 14848, 2004 / 14962, 2004 / 072126, and 2004 / 096870.

[0075] Specific polymerization methods for the TERP method include the following (a) to (d). (a) A method for polymerizing vinyl monomers using an organotellurium compound represented by formula (1). (b) A method for polymerizing vinyl monomers using a mixture of an organic tellurium compound represented by formula (1) and an azo polymerization initiator. (c) A method for polymerizing vinyl monomers using a mixture of an organic tellurium compound represented by formula (1) and an organic diterlide compound represented by formula (2). (d) A method for polymerizing vinyl monomers using a mixture of an organic tellurium compound represented by formula (1), an azo polymerization initiator, and an organic diterlide compound represented by formula (2).

[0076] [ka] [In equation (1), R 1 R is an alkyl group, aryl group, or aromatic heterocyclic group having 1 to 8 carbon atoms. 2 and R 3 Each of these is independently a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. 4 These are alkyl groups, aryl groups, substituted aryl groups, aromatic heterocyclic groups, alkoxy groups, acyl groups, amide groups, oxycarbonyl groups, cyano groups, allyl groups, or propargyl groups having 1 to 8 carbon atoms. In equation (2), R 1 This is an alkyl group, aryl group, or aromatic heterocyclic group having 1 to 8 carbon atoms.

[0077] Specific examples of organotellurium compounds represented by formula (1) include ethyl=2-methyl-2-n-butylteranyl-propionate, ethyl=2-n-butylteranyl-propionate, (2-hydroxyethyl)=2-methyl-methylteranyl-propionate, and other organotellurium compounds described in International Publication Nos. 2004 / 14848, 2004 / 14962, 2004 / 072126, and 2004 / 096870. Specific examples of organoditerlide compounds represented by formula (2) include dimethylditerlide and dibutylditerlide. Any azo polymerization initiator used in normal radical polymerization can be used without particular restrictions, such as 2,2'-azobis(isobutyronitrile) (AIBN), 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN), 1,1'-azobis(1-cyclohexanecarbonitride) (ACHN), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70).

[0078] The polymerization step involves mixing a vinyl monomer, an organic tellurium compound of formula (1), and, depending on the type of vinyl monomer, an azo polymerization initiator and / or an organic diterlide compound of formula (2) in a container purged with an inert gas, for purposes such as promoting the reaction, controlling the molecular weight and molecular weight distribution. Examples of inert gases used include nitrogen, argon, and helium. Argon and nitrogen are preferred. The amount of vinyl monomer used in (a), (b), (c), and (d) above may be adjusted as appropriate depending on the physical properties of the desired copolymer.

[0079] The polymerization reaction can be carried out without a solvent, but it may also be carried out using an aprotic or protic solvent commonly used in radical polymerization, while stirring the mixture. Examples of usable aprotic solvents 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. Solvents may be used alone or in combination of two or more. The amount of solvent used can be adjusted as appropriate; for example, 0.01 ml to 50 ml per 1 g of vinyl monomer is preferred. The reaction temperature and reaction time can be adjusted as appropriate depending on the molecular weight or molecular weight distribution of the resulting polymer components, but typically, the reaction is carried out at 0°C to 150°C for 1 minute to 100 hours with stirring. At this time, the reaction is usually carried out at atmospheric pressure, but it may also be carried out under increased or decreased pressure. After the polymerization reaction is complete, the target copolymer can be separated from the resulting reaction mixture by removing the solvent used, residual vinyl monomers, etc., using conventional separation and purification methods.

[0080] The growth ends of the copolymer obtained by the polymerization reaction are derived from the tellurium compound -TeR 1 (In the formula, R 1It has the same form as described above (), and it is deactivated by operations in air after the polymerization reaction, but tellurium atoms may remain. Since the copolymer with tellurium atoms remaining at the ends may be colored or have poor thermal stability, it is preferable to remove the tellurium atoms. Methods for removing tellurium atoms include radical reduction methods; methods of adsorbing with activated carbon or the like; methods of adsorbing metals with ion exchange resins or the like, and these methods can also be used in combination. In addition, the other end of the copolymer obtained by the polymerization reaction (the end opposite to the growing end) is -CR derived from a tellurium compound 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).).

[0081] (Free radical polymerization method) Free radical polymerization can be carried out using conventionally known methods. Polymerization initiators used in free radical polymerization include azo-based polymerization initiators and peroxide-based polymerization initiators. Examples of 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-cyclohexanecarbonitride) (ACHN), dimethyl-2,2'-azobisisobutyrate (MAIB), 4,4'-azobis(4-cyanovaleric acid) (ACVA), 1,1'-azobis(1-acetoxy-1-phenylethane), 2,2'-azobis(2-methylbutylamide), and 2,2'-azobis Examples include (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).

[0082] The polymerization reaction can be carried out without a solvent, but it may also be carried out using an aprotic or protic solvent commonly used in radical polymerization, while stirring the mixture. Examples of usable aprotic solvents 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, and trifluoromethylbenzene. Examples of protic solvents include water, methanol, ethanol, isopropanol, n-butanol, ethyl cellosolve, butyl cellosolve, 1-methoxy-2-propanol, hexafluoroisopropanol, and diacetone alcohol.

[0083] The amount of solvent used can be adjusted as appropriate. For example, per 1 g of vinyl monomer, 0.01 ml or more is preferred, more preferably 0.05 ml or more, even more preferably 0.1 ml or more, 50 ml or less is preferred, more preferably 10 ml or less, and even more preferably 1 ml or less.

[0084] The reaction temperature and reaction time can be adjusted as appropriate depending on the molecular weight or molecular weight distribution of the resulting polymer components, but typically, the reaction is carried out at 0°C to 150°C for 1 minute to 100 hours with stirring. At this time, the reaction is usually carried out at atmospheric pressure, but it may also be carried out under increased or decreased pressure. After the polymerization reaction is complete, the target polymerization composition can be separated from the resulting reaction mixture by removing the solvent used, residual vinyl monomers, etc., using conventional separation and purification methods.

[0085] (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 group of the polymer component (A) described above. The crosslinking agent is not particularly limited and examples include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, aziridine-based crosslinking agents, metal chelate-based crosslinking agents, melamine resin-based crosslinking agents, urea resin-based crosslinking agents, etc. One type of crosslinking agent may be used alone, or two or more types may be used in combination. 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 because they improve the recovery rate of the formed adhesive.

[0086] The average number of secondary reactive groups in one molecule of the crosslinking agent is 2 or more, preferably 8 or less, and more preferably 6 or less. The molecular weight of the crosslinking agent is preferably 200 or more, more preferably 300 or more, even more preferably 400 or more, preferably 1500 or less, even more preferably 1000 or less, and even more preferably 700 or less.

[0087] The content of the second reactive group in the crosslinking agent is preferably 1.5 mmol / g or more, more preferably 3 mmol / g or more, even more preferably 3.7 mmol / g or more, preferably 8 mmol / g or less, and more preferably 6 mmol / g or less. When the content of the second reactive group in the crosslinking agent is within this range, the valency of the crosslinking agent is low, the crosslinking points are evenly distributed within the adhesive, and the average distance between crosslinking points becomes longer. Therefore, the resulting adhesive has low initial stress and exhibits a high recovery rate.

[0088] Examples of combinations between the first reactive group of the polymer component (A) 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, a hydroxyl group can be cited as the first reactive group. When the second reactive group of the crosslinking agent is an epoxy group, a carboxyl group can be cited as the first reactive group.

[0089] The preferred combinations of the first reactive group of the polymer component (A) and the second reactive group of the crosslinking agent are: (1) a combination in which the first reactive group is a hydroxyl group and the second reactive group is an isocyanate group; and (2) a combination in which the first reactive group is a carboxyl group and the second reactive group is an epoxy group.

[0090] (Isocyanate-based crosslinking agent) An isocyanate-based 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 quantification, etc.) as a secondary reactive group in one molecule. The isocyanate-based crosslinking agent may be used alone or in combination of two or more types.

[0091] Examples of isocyanate-based crosslinking agents include aliphatic polyisocyanates, alicyclic polyisocyanates, aromatic polyisocyanates, and polyisocyanates that are polyfunctionalized by adducts of these with various polyols, isocyanurate bonds, biuret bonds, allophanate bonds, etc. Specifically, examples include compounds having two isocyanate groups (including isocyanate regenerating functional groups in which the isocyanate groups are temporarily protected by a blocking agent or quantification, 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 a blocking agent or quantification, etc.) in one molecule (trifunctional isocyanate-based crosslinking agents), and compounds having six isocyanate groups (including isocyanate regenerating functional groups in which the isocyanate groups are temporarily protected by a blocking agent or quantification, etc.) in one molecule (hexafunctional isocyanate-based crosslinking agents).

[0092] Examples of bifunctional isocyanate crosslinking agents include diisocyanate compounds such as aliphatic diisocyanate compounds, alicyclic diisocyanate compounds, and aromatic diisocyanate compounds. Additives of these diisocyanate compounds with diol compounds can also be used. Diisocyanate compounds are compounds represented by the general formula "O=C=NXN=C=O" (where 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" (where Y is a divalent aliphatic group, a divalent alicyclic group, a divalent aromatic group, etc.).

[0093] Examples of aliphatic diisocyanate compounds include ethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, 2-methyl-1,5-pentane diisocyanate, 3-methyl-1,5-pentane diisocyanate, and 2,2,4-trimethyl-1,6-hexamethylene diisocyanate. Among these, aliphatic diisocyanate compounds having 4 to 30 carbon atoms are preferred, and aliphatic diisocyanate compounds having 4 to 10 carbon atoms are more preferred.

[0094] Examples of alicyclic diisocyanate compounds include isophorone diisocyanate, cyclopentyl diisocyanate, cyclohexyl diisocyanate, hydrogenated xylylene diisocyanate, hydrogenated tolylene diisocyanate, hydrogenated diphenylmethane diisocyanate, and hydrogenated tetramethylxylene diisocyanate. Among these, alicyclic diisocyanate compounds with 7 to 30 carbon atoms are preferred.

[0095] Examples of aromatic diisocyanate compounds include phenylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate, diphenyl ether diisocyanate, diphenylmethane diisocyanate, and diphenylpropane diisocyanate, with aromatic diisocyanate compounds having 8 to 30 carbon atoms being preferred.

[0096] Examples of the aforementioned diol compounds 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, among which aliphatic diol compounds having 3 to 10 carbon atoms are preferred.

[0097] Examples of the aforementioned trifunctional isocyanate crosslinking agents include the adduct form of the diisocyanate compound, the biuret form of the diisocyanate compound, and the isocyanurate form of the diisocyanate compound (cyclic polymers of diisocyanate compounds).

[0098] Preferably, the isocyanate crosslinking agent does not have an aromatic ring. In particular, preferred isocyanate crosslinking agents include bifunctional isocyanate crosslinking agents selected from the group consisting of aliphatic diisocyanate compounds and adducts of aliphatic diol compounds; and trifunctional or hexafunctional isocyanate crosslinking agents selected from the group consisting of adducts of aliphatic diisocyanate compounds, biuret compounds of aliphatic diisocyanate compounds, and isocyanurate compounds of aliphatic diisocyanate compounds.

[0099] (Epoxy crosslinking agent) An epoxy crosslinking agent is a compound having two or more epoxy groups as secondary reactive groups in one molecule. The epoxy crosslinking agent may be used alone or in combination of two or more types.

[0100] Examples of epoxy crosslinking agents include aliphatic epoxy compounds, alicyclic epoxy compounds, aromatic epoxy compounds, and heterocyclic epoxy compounds.

[0101] Examples of the aliphatic epoxy compounds include ethylene glycidyl ether, ethylene glycol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylamine, diamine glycidylamine, 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, diglycidyl adipic acid ester, and 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane.

[0102] Examples of the alicyclic epoxy compound include 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane, 1,6-hexanediol diglycidyl ether, and N,N,N',N'-tetraglycidyl-m-xylylenediamine.

[0103] Examples of the aromatic epoxy compounds include bisphenol A epichlorohydrin type epoxy resins, diglycidylaniline, o-phthalate diglycidyl esters, resorcinol diglycidyl ethers, and bisphenol-S-diglycidyl ethers.

[0104] Examples of the aforementioned 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.

[0105] The epoxy crosslinking agent is preferably a compound having two epoxy groups in one molecule (a difunctional epoxy crosslinking agent), a compound having three epoxy groups in one molecule (a trifunctional epoxy crosslinking agent), or a compound having four epoxy groups in one molecule (a tetrafunctional epoxy crosslinking agent). If the crosslinking agent is a difunctional epoxy crosslinking agent, a trifunctional epoxy crosslinking agent, or a tetrafunctional epoxy crosslinking agent, the crosslinking points will be evenly distributed within the adhesive, and the average distance between crosslinking points will be long. Therefore, the resulting adhesive will have low initial stress and a high recovery rate.

[0106] The adhesive composition preferably contains only an isocyanate-based crosslinking agent or only an epoxy-based crosslinking agent. When containing only an isocyanate-based crosslinking agent, it is preferable to contain only a bifunctional isocyanate-based crosslinking agent having two isocyanate groups per molecule, a trifunctional isocyanate-based crosslinking agent having three isocyanate groups per molecule, or a hexafunctional isocyanate-based crosslinking agent having six isocyanate groups per molecule. Furthermore, when containing only an epoxy-based crosslinking agent, it is preferable to contain only a bifunctional epoxy-based crosslinking agent having two epoxy groups per molecule, a trifunctional epoxy-based crosslinking agent having three epoxy groups per molecule, or a tetrafunctional epoxy-based crosslinking agent having four epoxy groups per molecule.

[0107] The crosslinking agent content in the adhesive composition is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, preferably 0.2 parts by mass or less, and more preferably 0.17 parts by mass or less, per 100 parts by mass of the multiple (meth)acrylic copolymer components. When the crosslinking agent content is within the above range, the adhesive strength and recovery rate will be within a suitable range.

[0108] The molar ratio (moles of the first reactive group / molars of the second reactive group) of the crosslinking agent to the first reactive groups of the plurality of (meth)acrylic copolymer components is 1 or more, preferably 2 or more, more preferably 3 or more, 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, there is no excess of the second reactive group, and a high restoration rate is achieved. If the ratio is 70 or less, the reaction proceeds sufficiently and a high restoration rate is achieved.

[0109] The molar ratio of the first reactive groups of the plurality of (meth)acrylic copolymer components to the amount (moles) of the crosslinking agent (moles of the first reactive groups / molars of the crosslinking agent) is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, preferably 250 or less, more preferably less than 12, even more preferably 11 or less, and particularly preferably 8 or less. If the molar ratio is within the above range, the tackiness and recovery rate will be within a suitable range.

[0110] (Other additives) In addition to the copolymer component and crosslinking agent, other additives may be added to the adhesive composition. Examples of other additives include crosslinking accelerators, crosslinking retarders, tackifiers, polymerizable compounds, photopolymerization initiators, silane coupling agents, plasticizers, softeners, release aids, dyes, pigments, fluorescent whitening agents, antistatic agents, wetting agents, surfactants, thickeners, antifungal agents, preservatives, oxygen absorbers, ultraviolet absorbers, antioxidants, near-infrared absorbers, water-soluble quenchers, fragrances, metal deactivators, nucleating agents, alkylating agents, flame retardants, lubricants, and processing aids. These are selected and added as appropriate depending on the application and intended use of the adhesive.

[0111] (Crosslinking promoter) The adhesive composition may be used with a crosslinking accelerator added as needed. Examples of crosslinking accelerators include organotin compounds and metal chelate compounds. The crosslinking accelerator may be used alone or in combination of two or more types.

[0112] Examples of the organotin compounds include dibutyltin dilaurate, dioctyolustin dilaurylate, and dibutyltin dioctylate. The metal chelate compound is a complex in which ligands having two or more coordinating atoms form a ring and are bonded to a central metal.

[0113] 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, preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, and even more preferably 0.3 parts by mass or less, per 100 parts by mass of the plurality of (meth)acrylic copolymer components. By setting the content of the crosslinking accelerator within the above range, it is possible to obtain an excellent crosslinking promoting effect.

[0114] (Crosslinking retarder) The adhesive composition may be used with a crosslinking retarder if necessary. The crosslinking retarder is a compound that can suppress an excessive increase in the viscosity of the adhesive composition by blocking the functional groups of the crosslinking agent in the adhesive composition containing the crosslinking agent. The type of crosslinking retarder is not particularly limited, but for example, 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 can be used. The crosslinking retarder is preferably one that can act as a chelating agent, and β-diketones and β-ketoesters are preferred.

[0115] The amount of crosslinking retarder that can be incorporated into 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, preferably 4.0 parts by mass or less, more preferably 3.0 parts by mass or less, and even more preferably 1.5 parts by mass or less, per 100 parts by mass of the plurality of (meth)acrylic copolymer components. By adjusting the amount of the crosslinking retarder within the above range, it is possible to suppress excessive viscosity increase and gelation of the adhesive composition after incorporating the crosslinking agent into the adhesive composition, and to extend the storage stability (pot life) of the adhesive composition.

[0116] (Adhesive-forming resin) The adhesive composition may be used with a tackifying resin other than the copolymer component, as needed. The tackifying resin is not particularly limited, but examples include rosin-based tackifying resins, terpene-based tackifying resins, phenol-based tackifying resins, hydrocarbon-based tackifying resins, and the like.

[0117] Examples of rosin-based tackifying resins include unmodified rosin (raw rosin) such as gum rosin, wood rosin, and tall oil rosin, as well as modified rosin (polymerized rosin, stabilized rosin, disproportionated rosin, fully hydrogenated rosin, partially hydrogenated rosin, and other chemically modified rosin) obtained by polymerization, disproportionation, hydrogenation, etc., and various rosin derivatives.

[0118] Examples of the rosin derivatives include rosinphenol resins obtained by adding phenol to rosins (unmodified rosin, modified rosin) with an acid catalyst and then thermal polymerization; rosin ester resins such as ester compounds of rosin obtained by esterifying unmodified rosin with alcohols (unmodified rosin esters) and ester compounds of modified rosin obtained by esterifying modified rosin with alcohols (polymerized rosin esters, stabilized rosin esters, disproportionated rosin esters, fully hydrogenated rosin esters, partially hydrogenated rosin esters, etc.); unsaturated fatty acid modified rosin resins obtained by modifying unmodified rosin or modified rosin with unsaturated fatty acids; unsaturated fatty acid modified rosin ester resins obtained by modifying rosin ester resins with unsaturated fatty acids; rosin alcohol 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 resins; and metal salts of rosin resins (especially rosin ester resins) such as unmodified rosin and modified rosin.

[0119] Examples of terpene-based tackifying resins include terpene resins such as α-pinene polymers, β-pinene polymers, and dipentene polymers, as well as modified terpene resins obtained by modifying these terpene resins (phenol modification, aromatic modification, hydrogenation modification, hydrocarbon modification, etc.) (for example, terpene-phenol resins, styrene-modified terpene resins, aromatic-modified terpene resins, and hydrogenated terpene resins).

[0120] Examples of phenolic tackifying resins include condensates of various phenols (e.g., phenol, m-cresol, 3,5-xylenol, p-alkylphenol, resorcinol) and formaldehyde (e.g., alkylphenol resins, xyleneformaldehyde resins), resols obtained by addition reaction of the phenols and formaldehyde with an alkaline catalyst, and novolacs obtained by condensation reaction of the phenols and formaldehyde with an acid catalyst.

[0121] 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, pentene-1; dienes such as butadiene, 1,3-pentadiene, isoprene, etc.)], aliphatic cyclic hydrocarbon resins [alicyclic hydrocarbon resins obtained by cyclizing and then polymerizing so-called "C4 petroleum fractions" or "C5 petroleum fractions," cyclic diene compounds (cyclopentadiene, dicyclopentadiene, ethylidene norbornene, di Examples include polymers of pentene (such as pentene) or hydrogenated thereof, alicyclic hydrocarbon resins obtained by hydrogenating the aromatic rings of aromatic hydrocarbon resins and aliphatic-aromatic petroleum resins listed below, aromatic hydrocarbon resins [polymers of vinyl group-containing aromatic hydrocarbons with 8 to 10 carbon atoms (styrene, vinyltoluene, α-methylstyrene, indene, methylindene, etc.)], aliphatic-aromatic petroleum resins (styrene-olefin copolymers, etc.), aliphatic-alicyclic petroleum resins, hydrogenated hydrocarbon resins, coumarone resins, coumarone-indene resins, etc.

[0122] The content of the tackifying resin that can be incorporated into 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, preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 40 parts by mass or less, based on 100 parts by mass of the plurality of (meth)acrylic copolymer components. By adjusting the content of the tackifying resin within the above range, sufficient adhesion to the adherend can be ensured.

[0123] (polymerizable compound) The adhesive composition may also contain polymerizable compounds. By incorporating polymerizable compounds and polymerizing them within the adhesive, flexibility can be imparted to the adhesive.

[0124] Examples of polymerizable compounds include compounds having two or more polymerizable groups in one molecule. Examples of polymerizable groups include ethylenically unsaturated groups. The polymerizable compounds can be used alone or in combination of two or more. Examples of polymerizable compounds include compounds 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, preferably four or less, and more preferably three or less.

[0125] 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, isocyanurate ethylene oxide modified tri(meth)acrylate, allyl(meth)acrylate, vinyl(meth)acrylate, and urethane(meth)acrylate.

[0126] When a polymerizable compound is incorporated 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, preferably 100 parts by mass or less, and more preferably 50 parts by mass or less, per 100 parts by mass of the plurality of (meth)acrylic copolymer components.

[0127] (Photopolymerization initiator) When curing the polymerizable compound with active energy rays, it is preferable to incorporate a photopolymerization initiator into the adhesive composition. By incorporating 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 upon the action of light, and examples include photopolymerization initiators such as acetophenones, benzoins, thioxanthones, and acylphosphine oxides. These photopolymerization initiators can be used alone or in combination of two or more. Among these photopolymerization initiators, hydrogen abstraction type benzophenones and intramolecular cleavage type acetophenones are preferred because they can efficiently crosslink between molecules at an intermolecular or intramolecular level.

[0128] When a photopolymerization initiator is incorporated 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, 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, per 100 parts by mass of the plurality of (meth)acrylic copolymer components. If the content of the photopolymerization initiator is too low, the curing speed tends to decrease or curing to be insufficient, and if it is too high, the curing performance does not improve and the economic efficiency tends to decrease.

[0129] Furthermore, the adhesive composition may also contain an auxiliary agent for the photopolymerization initiator. Examples of the auxiliary agents that can be used in combination include triethanolamine, triisopropanolamine, 4,4'-dimethylaminobenzophenone (Michler ketone), 4,4'-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, ethyl 4-dimethylaminobenzoate, (n-butoxy)ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,4-diethylthioxanthone, and 2,4-diisopropylthioxanthone. These auxiliary agents may also be used alone or in combination of two or more.

[0130] (Silane coupling agent) The adhesive composition may be used with a silane coupling agent as needed. The silane coupling agent is not particularly limited, but examples 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-isocyanatetopropyltriethoxysilane.

[0131] The content of the silane coupling agent that can be incorporated into the adhesive composition is 0.01% by mass or more, more preferably 0.02% by mass or more, preferably 1 part by mass or less, and more preferably 0.6 parts by mass or less, based on 100 parts by mass of the plurality of (meth)acrylic copolymer components. By adjusting the content of the silane coupling agent within the above range, the water resistance at the interface when the adhesive is applied to a hydrophilic substrate such as glass can be improved.

[0132] (Plasticizer) The adhesive composition may optionally contain a plasticizer. The plasticizer is not particularly limited, but examples 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 their derivatives; dioctyl phthalate (DOP), dibutyl phthalate (DBP), dioctyl adipate, diisononyl adipate (DINA), isodecyl succinate, etc. The plasticizer may be used alone or in combination of two or more. Among these, liquid rubber is preferred.

[0133] The weight-average molecular weight (Mw) of the liquid rubber is preferably 5,000 or more, more preferably 10,000, preferably 600 million or less, and more preferably 500 million or less. By adjusting the Mw of the liquid rubber to the above range, an adhesive with excellent flexibility can be formed. The method for measuring the weight-average molecular weight (Mw) will be described later.

[0134] When a plasticizer is incorporated into the adhesive composition, the plasticizer content 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, preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less, per 100 parts by mass of the plurality of (meth)acrylic copolymer components. By adjusting the plasticizer content within the above range, an adhesive with excellent tackiness and resilience can be formed.

[0135] (Method for manufacturing adhesive composition) The adhesive composition can be produced by mixing the copolymer component, a crosslinking agent, and other additives as needed. The adhesive composition may contain a solvent derived from the production of the copolymer component, or it may be a solution diluted with an additional suitable solvent to achieve a viscosity suitable for forming an adhesive layer.

[0136] Examples of the aforementioned solvents 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 solvents such as ethyl cellosolve; and glycol ether solvents such as propylene glycol monomethyl ether. These solvents may be used individually or in mixtures of two or more.

[0137] The amount of solvent used can be adjusted as appropriate so that the adhesive composition has a viscosity suitable for coating, and there are no particular restrictions, but from the viewpoint of coating properties, for example, 1% to 90% by mass is preferred, more preferably 10% to 80% by mass, and even more preferably 20% to 70% by mass.

[0138] (Uses of adhesive compositions) The aforementioned adhesive composition is preferably used for flexible displays that can be repeatedly bent and stretched, and for forming adhesive layers (adhesives) used in flexible displays.

[0139] Examples of 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 stationary displays that can be stored away.

[0140] [Adhesive for flexible displays] The adhesive material for flexible displays of the present invention is a cured product of the adhesive composition. The adhesive material can be used as an adhesive material for flexible displays to bond one flexible member to another flexible member constituting a flexible display.

[0141] 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 100% by mass or less. By setting the gel fraction within the above range, an adhesive with excellent flexibility and resilience can be formed. The gel fraction can be controlled by the amount of crosslinking agent blended in the adhesive composition, the crosslinking treatment temperature, the crosslinking treatment time, etc.

[0142] [Adhesive sheet 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 constituting a flexible display to another flexible member, 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.

[0143] The configuration of the adhesive sheet includes an adhesive layer and a first flexible sheet member attached to one side of the adhesive layer; and an adhesive layer and 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.

[0144] Figure 1 shows an example of the adhesive sheet of the present invention. The adhesive sheet 10 in Figure 1 consists of an adhesive layer 12, a first flexible sheet member 14 that sandwiches the adhesive layer 12, and a second flexible sheet member 16. The adhesive layer 12 is in contact with the release surfaces of the first flexible sheet member 14 and the second flexible sheet member 16.

[0145] (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. Furthermore, 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 the overflow of the adhesive layer.

[0146] (Flexible sheet material) Examples of the flexible sheet member include a base sheet with flexibility, a release sheet, and the like. The base sheet is a sheet member that supports 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 phase difference film, an optical compensation film, a brightness-enhancing film, a diffusion film, an anti-reflective film, and the like. The release sheet protects the adhesive layer until it is attached to the substrate, and is peeled off from the adhesive layer before it is attached to the substrate.

[0147] Generally, a "sheet," according to the JIS definition, refers to a thin, flat product whose thickness is generally small relative to its length and width, while a "film," generally, refers to a thin, flat product whose thickness is extremely small relative to its length and width, with a maximum thickness arbitrarily limited, and which is usually supplied in roll form (Japanese Industrial Standard JIS K6900). For example, in terms of thickness, in a narrow sense, products with a thickness of 100 μm or more are sometimes called sheets, and those with a thickness of less than 100 μm are sometimes called films. However, the boundary between sheets and films is not clear, and there is no need to distinguish between the two in the wording of this invention, so in this invention, the term "sheet" includes "film," and the term "film" includes "sheet."

[0148] Examples of the flexible sheet member include polymer material sheets and glass sheets. The thickness of the flexible sheet member is not particularly limited, but from the viewpoint of ease of handling, it is preferably 2 μm to 500 μm, and more preferably 2 μm to 200 μm.

[0149] Examples of the aforementioned polymer 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; and polyvinyl alcohol resins.

[0150] The flexible sheet member may consist of a single layer comprising a layer containing one or more of the polymer materials, or it may consist of two or more layers, such as a layer containing one or more of the polymer materials and a layer containing one or more of a different polymer material.

[0151] The flexible sheet member is preferably a release sheet with a release treatment applied to the surface that comes into contact with 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.

[0152] The adhesive sheet comprises 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, wherein the first flexible sheet member is the first release sheet and the second flexible sheet member is the second release sheet, and it is preferable that the first and second release sheets are attached so that their respective release surfaces are in contact with the adhesive layer. When the adhesive layer is sandwiched between two release sheets, it is preferable that one release sheet be a heavy-peel type with a high peeling force and the other release sheet be a light-peel type with a low peeling force.

[0153] (Manufacturing of adhesive sheets) The adhesive sheet can be manufactured, for example, by coating the above-mentioned adhesive composition onto a flexible sheet member and curing it by drying and heat treatment as needed to form an adhesive layer.

[0154] 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, and kiss coating can be used for coating the adhesive composition; inkjet printing; and various printing methods such as offset printing, screen printing, and flexographic printing can be employed. Furthermore, before coating the adhesive composition, the surface of the release sheet may be subjected to surface treatments such as corona treatment, plasma treatment, hot air treatment, ozone treatment, and ultraviolet treatment.

[0155] The drying and heating process is not particularly limited as long as it removes the solvents used in the adhesive composition and allows it to harden, but it is preferable to carry it out 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.

[0156] When arranging a first flexible sheet member on one side of an adhesive layer and a second flexible sheet member on the other side, an adhesive composition is applied to the first flexible sheet member to form an adhesive layer 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 needed. Examples of curing conditions include 3 to 7 days at 60°C.

[0157] [Flexible laminated material] The flexible laminated member of the present invention comprises a first flexible member, a second flexible member, and an adhesive layer for bonding the first flexible member and the second flexible member to each other, wherein the adhesive layer is made of the adhesive material. Because the adhesive layer of the flexible laminated member is formed from the adhesive material, even when the flexible laminated member is repeatedly bent, appearance defects such as wavy appearance at the bent parts are suppressed.

[0158] Figure 2 shows an example of the flexible laminated member of the present invention. The flexible laminated member 20 in Figure 2 comprises a first flexible member 22, a second flexible member 24, and an adhesive layer 12 located between the first flexible member 22 and the second flexible member 24, which bond these flexible members together.

[0159] 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 bendable device; and a configuration in which the second flexible member is a bendable device and the first flexible member is a functional sheet member bonded to the bendable device. Examples of the bendable 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, barrier film, polarizing film, phase difference film, optical compensation film, brightness enhancement film, diffusion film, anti-reflective film, transparent conductive film, metal mesh film, cushion film, and the like.

[0160] The first flexible member and the second flexible member are members that can be repeatedly bent or curved. Examples of the first flexible member and the second flexible member include flexible substrate materials, functional sheet members, and 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 laminated member can be used in a flexible display.

[0161] (Method for manufacturing flexible laminated members) The method for manufacturing the flexible laminated member of the present invention is not particularly limited, and examples include the following methods (1) to (4).

[0162] (1) A method for obtaining a flexible laminated member by peeling off a release sheet attached to one side of an adhesive sheet, attaching the exposed adhesive layer to a first flexible member, peeling off a release sheet attached to the other side of the adhesive sheet, and attaching the exposed adhesive layer to a second flexible member. (2) A method for obtaining a flexible laminated member by applying an adhesive composition to one surface of the first flexible member, curing it by drying and heating as necessary to form an adhesive layer, and then attaching the release side of a release sheet to this adhesive layer, and then attaching the exposed adhesive layer to the second flexible member by peeling off the release sheet. (3) A method for obtaining a flexible laminated member by applying an adhesive composition to one surface of a first flexible member, curing it by drying and heating treatment as necessary to form an adhesive layer, and then attaching a second flexible member to this adhesive layer. (4) A method for obtaining a flexible laminated member by applying an adhesive composition to the release surface of a release sheet, curing it by drying and heating as needed to form an adhesive layer, and then attaching the first flexible member to this adhesive layer. Then, peeling off the release sheet and attaching the exposed adhesive layer to the second flexible member.

[0163] In addition, in any of the cases (1) to (4) above, the order in which the first flexible member and the second flexible member are used may be reversed. The adhesive layer can be formed using various coating and printing methods similar to those used in the manufacture of adhesive sheets, and the same applies to the drying and curing processes. Curing may also be performed as needed. Furthermore, the release sheet used in the manufacture of flexible laminated members can be the same as the release sheet used for adhesive sheets. [Examples]

[0164] The present invention will be described in more detail below based on specific examples. The present invention is not limited in any way to the following examples, and can be implemented with appropriate modifications without changing its essence. The polymerization rate of the polymerization composition, the weight-average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the polymer components, the thickness of the adhesive layer, and the evaluation of the adhesive were evaluated according to the methods described below.

[0165] The meanings of the abbreviations are as follows: EHA: 2-Ethylhexylacrylate LA: Lauryl acrylate AA: Acrylic acid HBA: 4-hydroxybutyl acrylate BTEE: Ethyl 2-methyl-2-n-butylteranyl propionate AIBN: Azobisisobutyronitrile AcOEt: Ethyl acetate

[0166] (Polymerization rate) Using a nuclear magnetic resonance (NMR) spectroscopy system (Bruker BioSpin, model: AVANCE500 (frequency 500MHz)), 1 1H-NMR was measured (solvent: CDCl3, internal standard: TMS). The integral ratio of the monomer-derived signal and the polymer-derived signal from the obtained NMR spectrum was determined to calculate the monomer polymerization rate.

[0167] (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 columns (Tosoh Corporation) were used, 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 volume of 10 μm, and a flow rate of 0.6 mL / min. Calibration curves were prepared using polystyrene (molecular weights 9,840,000, 5,480,000, 2,890,000, 1,090,000, 775,000, 427,000, 190,000, 96,400, 37,900, 10,200, 2,630, 440) as standard substances. Using GPC software (Ecosec Peak Separation (Version 1.04) from Tosoh Corporation), waveform separation was performed using Gaussian approximation for retention times of 6 to 11 minutes in the measured chromatograms. 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 to Threshold: 0.5, SmoothWidth: 8, start retention time: 6, and end retention time: 11.

[0168] (Adhesive layer thickness) The total thickness of the entire adhesive sheet was measured using a thickness measuring instrument (TH-104, manufactured by Tester Sangyo Co., Ltd.), and the thickness of the adhesive layer was determined by subtracting the thickness of the release liner from this total thickness.

[0169] (Gel fraction) The mass W2 of a wire mesh (400 mesh) cut to a width of 50 mm and a length of 120 mm was measured. 80 mg to 120 mg of adhesive layer (adhesive material) was taken from an adhesive sheet, and its mass W1 was measured. Test specimens were prepared by wrapping the adhesive material in wire mesh to prevent it from falling off. The test specimens were placed in a glass bottle, 40 g of ethyl acetate was poured in, and after shaking gently, they were left to stand at room temperature (25°C) for at least 72 hours. After standing, the test specimens were removed from the glass bottle and left at room temperature for at least 12 hours, and then dried in a vacuum oven at 100°C for 4 hours. After drying, the test specimens were cooled to room temperature, their mass W3 was measured, and the gel fraction was calculated using the following formula. Gel fraction (mass %) = (W3 - W2) / W1 × 100

[0170] (Stress relaxation time at 400% strain, recovery rate after 400% strain) The adhesive layers (adhesives) constituting the adhesive sheet were laminated together using a hand roller to create a laminate with a thickness of 600 μm, which was used as the test specimen. The measurement was performed using a viscoelasticity measuring device (Anton Paar, MCR302), with the sample sandwiched between 8 mm diameter parallel plates (whose adhesive surfaces were roughened with 240-grit sandpaper) and under a 25°C atmosphere. In the measurement, the specimen was compressed with an axial force of 1N and left to stand for 10 minutes. Then, the axial force was changed to 0.05N, and shear stress was immediately applied to strain it up to 400%. Subsequently, the specimen was held at 400% strain for 10 minutes, and the change in shear stress was measured to determine the stress relaxation time. Next, the shear stress was released (0kPa) and left for 10 minutes, and the final strain after 10 minutes was measured to determine the recovery rate. The stress relaxation time was defined as the time it took for the shear stress to reach 0.368 times the initial stress after the strain reached 400%. The initial stress was defined as the shear stress value 0.1 seconds after the start of shear stress application. The recovery rate was calculated based on the following formula. Recovery rate (%) = {(400 - final strain) / 400} × 100

[0171] (Strain at 20kPa stress, recovery rate after 20kPa stress application) The adhesive layers (adhesives) constituting the adhesive sheet were laminated together using a hand roller to create a laminate with a thickness of 600 μm, which was used as the test specimen. The measurement was performed using a viscoelasticity measuring device (Anton Paar, MCR302), with the sample sandwiched between 8 mm diameter parallel plates (whose adhesive surfaces were roughened with 240-grit sandpaper) and under a 25°C atmosphere. In the measurement, the test specimen was compressed with an axial force of 1N and left to stand for 10 minutes. Then, the axial force was changed to 0.05N, and a shear stress of 20kPa was applied for a creep test for 10 minutes, during which the strain (20kPa strain) was measured after 10 minutes. Next, the shear stress was released (0kPa) and left for 10 minutes, and the final strain after 10 minutes was measured to determine the recovery rate. Specimens that were too soft to measure were evaluated as "×". The recovery rate was calculated based on the following formula. Recovery rate (%) = {(20kPa strain - final strain) / 20kPa strain} × 100

[0172] (Measurement of adhesive strength) One release sheet of the adhesive sheet was peeled off from the adhesive layer, and the corona-treated surface of polyethylene terephthalate (PET) film (Toyobo Ester® Film E5100: manufactured by Toyobo, 50 μm thick) was bonded to the adhesive layer surface. The sheet was then cut to a size of 25 mm in width and 100 mm in length to create an adhesive sheet with a substrate. The adhesive strength of this adhesive sheet with a substrate to polyimide film or glass was measured according to the method of JIS Z 0237 (2009). Specifically, the release sheet was peeled from the adhesive layer, and the adhesive layer surface was pressed onto a polyimide film (Kapton® 100V: manufactured by Toray DuPont, 25 μm thick) or a white glass plate (S9112: manufactured by Matsunami Glass Industry Co., Ltd., 1.0-1.2 mm thick) by rolling a 2 kg roller back and forth twice. Next, the adhesive strength of the adhesive layer was measured using a Shimadzu Corporation precision universal testing machine "AUTOGRAPH® AGS-1kNX, 50N load cell" under conditions of a peeling speed of 300 mm / min and a peeling angle of 180°.

[0173] <Manufacturing of Polymerized Compositions> (Synthesis Example 1: Polymer composition Xa) In a flask equipped with an argon gas inlet tube and a stirrer, EHA (340.2g), LA (240.0g), AA (18.0g), HBA (1.8g), AIBN (26.1mg), and AcOEt (353.4g) were charged. After purging with argon, BTEE (105.0mg) was added, and the mixture was reacted at 60°C for 24 hours to polymerize. After the reaction was complete, AcOEt was added to the reaction solution to obtain a solution containing the polymerized composition Xa. The solid content of the solution was 26.2% by mass.

[0174] (Synthesis Examples 2-4: Polymerization Compositions Xb-Xd) Polymerization compositions Xb to Xd were prepared in the same manner as the preparation method for polymerization composition Xa. Table 1 shows the monomers, organotellurium compounds, azo polymerization initiators, solvents, reaction conditions, and polymerization rates used.

[0175] (Synthesis Example 5: Polymerization Composition Za) EHA (1,425.0 g), LA (1,000.0 g), AA (75.0 g), and AcOEt (1,666.7 g) were charged into a flask equipped with an argon gas inlet tube and a stirrer. After purging with argon, the temperature was raised to 82°C, and AIBN (1,094.7 mg) dissolved in AcOEt (50 g) was added dropwise over 2 hours. The reaction was then allowed to proceed for a further 4 hours to polymerize. After the reaction was complete, AcOEt was added to the reaction solution to obtain a solution containing the polymerized composition Za. The solid content of the solution was 36.2% by mass.

[0176] (Synthesis example 6: Polymer composition Zb) Polymerization composition Zb was prepared in the same manner as the preparation method for polymerization composition Zb. Table 1 shows the monomers, azo polymerization initiators, solvents, reaction conditions, and polymerization rates used.

[0177] Table 1 shows the polymerization conditions for each polymerization composition. The amounts of acidic groups and hydroxyl groups were calculated from the initial charge.

[0178] [Table 1]

[0179] (Polymer component in polymerization composition X) Gel permeation chromatography was performed on polymerization compositions Xa to Xd, and waveform separation was performed, revealing only polymer components Xa1, Xb1, Xc1, or Xd1, respectively. Table 2 shows the physical properties of polymer components Xa1 to Xd1.

[0180] [Table 2]

[0181] (Polymer component in polymerization composition Z) Gel permeation chromatography was performed on polymerization composition Za, and waveform separation was performed to identify polymer components Za1, Za2, and Za3. Gel permeation chromatography was performed on polymerization composition Zb, and waveform separation was performed to identify polymer components Zb1, Zb2, and Zb3. Tables 3 and 4 show the physical properties of each polymer component.

[0182] [Table 3]

[0183] [Table 4]

[0184] <Manufacturing of adhesive compositions> (Adhesive composition No. 1) To 381.7 parts by mass (100 parts by mass of polymer component) of a solution of polymerization composition Xa obtained in Synthesis Example 1, 0.148 parts by mass of a crosslinking agent (Duranate® D101) and butyl acetate were added and stirred to obtain adhesive composition No. 1 with a solid content of 20% by mass. In adhesive composition No. 1, the primary reactive group of polymer component Xa1 is a hydroxyl group, and the secondary reactive group of the crosslinking agent is an isocyanate group.

[0185] (Adhesive compositions No. 2-16) Adhesive compositions No. 2 to 16 were prepared in the same manner as adhesive composition No. 1, except that the formulation was changed as shown in Tables 5 and 6. The amounts of crosslinking agents shown in Tables 5 and 6 are calculated on a solid content basis. Solid content refers to components other than the solvent. In adhesive compositions No. 2 to 16, the primary reactive group of polymer components Xa1 to Xd1 is a hydroxyl group, and the secondary reactive group of the crosslinking agent is an isocyanate group.

[0186] <Making adhesive sheets> An adhesive composition was applied to the release surface of a first release sheet (PET film with a release treatment applied to its surface, Clean Sepa® HY-US20: manufactured by Higashiyama Film, 75 μm thick) using a Baker-type applicator so that the film thickness after drying would be 50 μm. Then, it was dried in a constant-temperature dryer at 60°C for 3 minutes, followed by drying at 150°C for 3 minutes. Next, the release surface of a second release sheet (PET film with a release treatment applied to its surface, Clean Sepa® HY-S10: manufactured by Higashiyama Film, 38 μm thick) was bonded to the adhesive layer formed on the first release sheet, and then aged at 60°C for 3 days to create an adhesive layer sandwiched between the two release sheets. The evaluation results of the adhesive layers (adhesives) formed from each adhesive composition are shown in Table 4.

[0187] [Table 5]

[0188] [Table 6] Crosslinking agent A: Duranate D101 (manufactured by Asahi Kasei Corporation, isocyanate-based crosslinking agent (hexamethylene diisocyanate-1,6-hexanediol adduct, 2 functional groups, solid content concentration 100% by mass, NCO content 19.7% by mass)) Crosslinking agent B: Duranate TPA-100 (manufactured by Asahi Kasei Corporation, isocyanate-based crosslinking agent (isocyanurate derivative of hexamethylene diisocyanate, 3 functional groups, solid content concentration 100% by mass, NCO content 23.1% by mass)) Crosslinking agent C: Duranate MHG-80B (manufactured by Asahi Kasei Corporation, isocyanate-based crosslinking agent (isocyanurate derivative of hexamethylene diisocyanate, 6 functional groups, solid content concentration 80% by mass, NCO content 15.1% by mass))

[0189] Adhesive compositions No. 1 and 2 are cases in which the adhesive composition contains (A) a (meth)acrylic copolymer component but does not contain (B) a (meth)acrylic copolymer component. The adhesives formed from these adhesive compositions No. 1 and 2 exhibited low strain when a shear stress of 20 kPa was applied and poor flexibility. They also had low adhesive strength to glass.

[0190] Adhesive compositions No. 3-11 and 13-16 contain an (A)(meth)acrylic copolymer component and a (B)(meth)acrylic copolymer component, with the (A)(meth)acrylic copolymer component content in the total polymer components ranging from 30% to 99% by mass. Adhesives formed from these compositions No. 3-11 and 13-16 exhibited good recovery rates after being strained to 400% and good strain when a shear stress of 20 kPa was applied. Furthermore, they showed good adhesion to both glass and PI film.

[0191] Adhesive composition No. 12 contains an adhesive composition containing (A)(meth)acrylic copolymer component and (B)(meth)acrylic copolymer component, but the content of (A)(meth)acrylic copolymer component in the total polymer components is less than 30% by mass. The adhesive formed from this adhesive composition No. 12 had poor recovery rate after being deformed to a strain of 400%. [Explanation of Symbols]

[0192] 10: Adhesive sheet 12: Adhesive layer 14: First flexible sheet member 16: Second flexible sheet member 20: Flexible laminated member 22: First flexible member 24: Second flexible member

Claims

1. An adhesive composition for a flexible display, for bonding one flexible member to another flexible member that constitutes a flexible display, It contains multiple (meth)acrylic copolymer components and a crosslinking agent. The (meth)acrylic copolymer component includes at least (A) a (meth)acrylic copolymer component and (B) a (meth)acrylic copolymer component, The (A) (meth)acrylic copolymer component has a hydroxyl group and a molecular weight distribution (Mw / Mn) of 3.0 or less. The (B) (meth)acrylic copolymer component does not have a hydroxyl group and has a molecular weight distribution (Mw / Mn) greater than 3.

0. The aforementioned crosslinking agent is an isocyanate-based crosslinking agent. An adhesive composition for flexible displays, characterized in that the content of the (A)(meth)acrylic copolymer component in the plurality of (meth)acrylic copolymer components is 30% by mass to 99% by mass.

2. The adhesive composition for flexible displays according to 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.

3. 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 greater than 800,000.

4. The adhesive composition for flexible displays according to 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.

5. The adhesive composition for flexible displays according to any one of claims 1 to 4, wherein the amount of isocyanate groups in the isocyanate crosslinking agent is 1.5 mmol / g to 8 mmol / g.

6. The adhesive composition for flexible displays according to any one of claims 1 to 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.

7. The adhesive composition for flexible displays according to any one of claims 1 to 6, wherein the amount of hydroxyl groups in the (A) (meth)acrylic copolymer component is 0.002 mmol / g to 0.8 mmol / g.

8. An adhesive material for a flexible display, for bonding one flexible component to another flexible component that constitutes a flexible display, An adhesive for flexible displays, characterized in that the adhesive material is a cured product of the adhesive composition described in any one of claims 1 to 7.

9. The adhesive for flexible displays according to claim 8, wherein the gel fraction of the cured product is 50% by mass or more.

10. An adhesive sheet for a flexible display, comprising an adhesive layer used to bond one flexible member to another flexible member constituting a flexible display, and a flexible sheet member attached to at least one surface of the adhesive layer, The adhesive sheet for flexible displays is characterized in that the adhesive layer is formed from the adhesive material described in claim 8 or 9.

11. The adhesive sheet comprises 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 the first release sheet, and the second flexible sheet member is the second release sheet. The adhesive sheet for a flexible display according to claim 10, wherein the first release sheet and the second release sheet are attached so that their respective release surfaces are in contact with the adhesive layer.

12. A flexible laminated member comprising a first flexible member, a second flexible member, and an adhesive layer for bonding the first flexible member and the second flexible member together, A flexible laminated member characterized in that the adhesive layer is made of the adhesive material described in claim 8 or 9.

13. The flexible laminated member according to claim 12, wherein at least one of the first flexible member and the second flexible member is a display element.

14. A flexible display characterized by comprising the flexible laminated member described in claim 12 or 13.

15. A (meth)acrylic copolymer mixture used in adhesive compositions for flexible displays, It contains at least (A) a (meth)acrylic copolymer component and (B) a (meth)acrylic copolymer component, The (A) (meth)acrylic copolymer component has a hydroxyl group and a molecular weight distribution (Mw / Mn) of 3.0 or less. The (B) (meth)acrylic copolymer component does not have a hydroxyl group and has a molecular weight distribution (Mw / Mn) greater than 3.

0. A (meth)acrylic copolymer mixture characterized in that the content of the (A) (meth)acrylic copolymer component in the (meth)acrylic copolymer mixture is 30% by mass to 99% by mass.

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