An adhesive composition for a flexible image display device, an adhesive layer for a flexible image display device, a laminate for a flexible image display device, and a flexible image display device.

Abstract

To provide an adhesive layer for flexible image display devices, a laminate for flexible image display devices and a flexible image display device, which do not cause the whitening of a bent part even after repeated bending, and also do not cause the displacement of an adhesive.SOLUTION: An adhesive composition for flexible image display devices contains a methacrylic copolymer (R) and a polyfunctional compound (T). The polyfunctional compound (T) has a molecular weight of 50-1000 and includes two or more functional groups, including any tertiary amino or amide group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a pressure-sensitive adhesive composition for a flexible image display device, a pressure-sensitive adhesive layer for a flexible image display device, a laminate for a flexible image display device, and a flexible image display device. [Background technology]

[0002] In recent years, input devices that combine image display devices such as liquid crystal displays (LCDs) and organic electroluminescence (organic EL) displays (OLEDs) with touch panels have become widespread. Transparent conductive films used in touch panels are laminated to members such as support glass via an adhesive layer. Polarizing plate films used in image devices are attached to liquid crystal modules or organic EL modules via an adhesive layer.

[0003] Flat displays using glass substrates have been mainstream as the image display devices, but in recent years, flexible displays such as foldable displays and rollable displays using flexible substrates such as plastic have been developed. Compared to conventional flat displays using glass substrates, such flexible displays have various advantages such as being lighter, thinner, more flexible, and having better designability.

[0004] The pressure-sensitive adhesive layer has traditionally been required to have the property of not foaming or peeling in high-temperature environments or high-temperature, high-humidity environments, but in recent years, flexibility has also become necessary. For example, in the case of a foldable display, flexibility refers to the suitability (flexibility) of the display to accommodate bending so that it can be used in the foldable display. Generally, flexibility requires a property (dynamic flexibility) that does not cause foaming, lifting, or peeling when repeatedly bent.

[0005] To solve these problems, Patent Document 1 discloses a pressure-sensitive adhesive composition that aims to prevent the pressure-sensitive adhesive layer from lifting or peeling even when repeatedly bent. Patent Document 2 discloses a pressure-sensitive adhesive layer for a bendable device, which has a storage modulus G' at -20°C and 85°C within a specific range. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2020-513451 [Patent Document 2] Japanese Patent Publication No. 2020-139034 Summary of the Invention [Problem to be solved by the invention]

[0007] Foldable displays use colorless polyimide for its strength and transparency, but when a laminate made of an adhesive layer and colorless polyimide is bent, the adhesive can peel off, especially at the bent part, or bubbles can form in the adhesive layer, causing whitening.Furthermore, repeated bending can cause the adhesive layer to shift at the edges, causing the adhesive layer to come into contact with surrounding components and worsening the bendability.

[0008] The present invention aims to provide a pressure-sensitive adhesive layer for a flexible image display device, a laminate for a flexible image display device, and a flexible image display device, which do not whiten at bent portions even when repeatedly bent and do not cause misalignment of the pressure-sensitive adhesive layer. [Means for solving the problem]

[0009] As a result of extensive research, the present inventors have found that the problems of the present invention can be solved in the following aspect, and have thus completed the present invention: That is, the present invention relates to a pressure-sensitive adhesive composition for flexible image displays, which comprises a (meth)acrylic copolymer (R) and a polyfunctional compound (T), wherein the polyfunctional compound (T) has a molecular weight of 50 to 1000 and has two or more functional groups, including either a tertiary amino group or an amide group. [Effects of the Invention]

[0010] According to the present invention having the above-mentioned configuration, a high-precision pressure-sensitive adhesive layer for a flexible image display device can be provided that is free from whitening at the bent portion and misalignment at the edge, thereby providing a flexible image display device that has good visibility and contrast even when bent and also has good bendability. DETAILED DESCRIPTION OF THE INVENTION

[0011] An example of an embodiment to which the present invention is applied will be described below. Numerical values ​​specified in this specification are values ​​determined by the methods disclosed in the embodiments or examples. Other embodiments are also included within the scope of the present invention as long as they are consistent with the spirit of the present invention. The adhesive layer for a flexible image display device of the present invention is synonymous with the adhesive layer. Unless otherwise specified, the various components in the adhesive layer can be used independently, either alone or in combination of two or more types. Furthermore, (meth)acrylic means acrylic or methacrylic, and (meth)acrylate means acrylate or methacrylate, respectively.

[0012] <Adhesive composition for flexible image display devices> The pressure-sensitive adhesive composition of the present invention contains a (meth)acrylic copolymer (R) and a polyfunctional compound (T). The pressure-sensitive adhesive composition may contain a curing agent, a tackifier, and a solvent, if necessary.

[0013] <(Meth)acrylic copolymer(R)> The (meth)acrylic copolymer (R) is a main component forming the pressure-sensitive adhesive layer and is a copolymer of acrylic monomers. The acrylic monomers preferably contain a carboxyl group-containing monomer and a (meth)acrylic acid alkyl ester monomer having 12 to 20 carbon atoms.

[0014] The carboxy group-containing monomer refers to a monomer having a (meth)acryloyl group or a vinyl group and a carboxy group. Specific examples include (meth)acrylic acid, β-carboxyethyl (meth)acrylate, itaconic acid, crotonic acid, maleic acid, fumaric acid, p-carboxybenzyl acrylate, ethylene oxide-modified (ethylene oxide addition mole number: 2 to 18) phthalic acrylate, and monohydroxyethyl succinate acrylate. Among these, acrylic acid and methacrylic acid are preferred.

[0015] The carboxyl group-containing monomer is preferably contained in an amount of 0.2 to 2.5 mass %, more preferably 0.2 to 1.5 mass %, based on 100 mass % of the monomer mixture. By containing 0.2 to 2.5 mass %, the cohesive strength due to hydrogen bonding between carboxyl groups is likely to be improved, thereby suppressing whitening at bent portions and reducing the amount of deformation after repeated bending.

[0016] The (meth)acrylic acid alkyl ester monomer having 12 to 20 carbon atoms refers to a (meth)acrylic acid alkyl ester monomer in which the alkyl group bonded to the ester group (also referred to as an oxocarbonyl group) has 1 to 20 carbon atoms, and examples thereof include dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, octadecyl (meth)acrylate, nonadecyl (meth)acrylate, and eicosyl (meth)acrylate.

[0017] The (meth)acrylic acid alkyl ester monomer having 12 to 20 carbon atoms is preferably contained in an amount of 10 to 50 mass %, more preferably 10 to 40 mass %, based on 100 mass % of the monomer mixture. By containing 10 to 50 mass %, the cohesive force due to entanglement of the acrylic side chains is improved, whitening of bent portions is suppressed, and the amount of deformation after repeated bending is reduced.

[0018] Alicyclic Monomers The (meth)acrylic copolymer (R) preferably further contains an alicyclic monomer, which improves adhesive strength and recovery rate. The alicyclic monomer contributes to improving cohesive strength as a hard segment, thereby improving adhesive peel strength and recovery rate.

[0019] The alicyclic monomer has a polymerizable functional group having an unsaturated double bond, such as a (meth)acryloyl group or a vinyl group, and also has an alicyclic structure-containing group. Here, the "alicyclic structure-containing group" refers to a moiety containing at least one alicyclic structure, and may be referred to as an alicyclic group hereinafter. Examples of the alicyclic group include a hydrocarbon group or a hydrocarbonoxy group having an alicyclic structure. Examples of the alicyclic monomer include isobornyl (meth)acrylate and cyclohexyl (meth)acrylate.

[0020] The alicyclic monomer is preferably contained in an amount of 1 to 20% by mass, more preferably 5 to 15% by mass, based on 100% by mass of the monomer mixture. When the content is 1% by mass or more, both hardness and softness can be achieved at a higher level. When the content is 20% by mass or less, flexibility is further improved.

[0021] The weight-average molecular weight (Mw) of the (meth)acrylic copolymer (A) is preferably 500,000 to 1,500,000, and more preferably 1,000,000 to 1,400,000. By setting it within this range, the flexibility and cohesive strength of the film are improved, and the number of bending tests that can be performed without causing poor appearance is increased.

[0022] ≪Polyfunctional compound (T)≫ The multifunctional compound (T) has two or more functional groups, at least one of which is a tertiary amino group or an amide group. The other functional group may be any one selected from the group consisting of a halogen group, a hydroxy group, a thiol group, an ester group, an amide group, a carbonyl group, a tertiary amino group, an ether group, and a thioether group. By containing two or more of these functional groups, one functional group bonds with a functional group in the (meth)acrylic copolymer (A), and the other functional group bonds with a functional group on the surface of the adherend, such as a colorless polyimide, thereby acting as a linker and improving adhesion to the adherend. The functional groups in the acrylic copolymer (A) and the adherend are, for example, carboxy groups or hydroxy groups, and are linked to the multifunctional compound (T) by hydrogen bonds or covalent bonds. Furthermore, the multifunctional compound (T) effectively links the functional groups of multiple (meth)acrylic copolymers (A), thereby improving the cohesive strength of the pressure-sensitive adhesive layer. This can prevent whitening due to the generation of bubbles in the pressure-sensitive adhesive layer and misalignment of the edges of the pressure-sensitive adhesive layer. The functional group of the tertiary amino group or amide group may be located at the terminal or inside the molecule, but is preferably located at the terminal.

[0023] As the functional group present together with the tertiary amino group or amide group in the molecule, a carbonyl group, an ether group, or a hydroxy group is more preferred. The polyfunctional compound (T) does not have an isocyanate group or a silyl group, and preferably does not contain a secondary amino group or a primary amino group because these groups deteriorate the stability of the pressure-sensitive adhesive composition over time. The number of functional groups containing a tertiary amino group or an amide group in the polyfunctional compound (T) is preferably 2 or more, more preferably 3 or more, from the viewpoint of enhancing the linking action, and is more preferably liquid at 25°C.

[0024] The molecular weight of the polyfunctional compound (T) is 50 to 1000, preferably 100 to 300. By setting the molecular weight within the above range, an optimal distance can be secured for linking functional groups such as carboxyl groups and hydroxyl groups of the (meth)acrylic copolymer (A) with functional groups present on the surface of the adherend, and the effects of improving the cohesive strength and adhesion to the adherend can be obtained.

[0025] Examples of polyfunctional compounds (T) containing two functional groups include: Examples include tetramethylethylenediamine, tetramethyl-1,3-propanediamine, tetramethyl-1,6-hexanediamine, tetramethyl-1,1-undecanediamine hexamethyltripropylenetetramine, triethylenediamine, 1,2-dimethylimidazole, dimethylaminoethanol, methylmorpholine, ethylmorpholine, 4-fluorodimethylaniline, and 2-chlorodimethylacetamide. Examples of polyfunctional compounds (T) containing three functional groups include: Examples include pentamethyldiethylenetriamine, pentamethyldipropylenetriamine, hexamethyltriethylenetetramine, 1,3-bis(dimethylamino)-2-propanol, dimethylaminoethoxyethanol, (2-hydroxyethyl)morpholine, bis(2-dimethylaminoethyl)ether, and trimethoxy(2-methoxyethyl)ethylenediamine. Examples of the polyfunctional compound (T) containing four or more functional groups include: Examples include ethylene glycol bis(3-dimethylaminopropyl)ether, dimethyl-4-(trifluoromethyl)aniline, bis(3-dimethylaminopropyl)amino-2-propanol, 1-benzyl-3,3-difluoropiperidine-4,4-diol, bis(2-morpholinoethyl)ether, N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine, 2,2,2-trifluorodimethylacetamide, diethyl-2,2,2-trifluoroacetamide, dimethyl-3-(trifluoromethyl)aniline, and dimethyl-2-(trifluoromethyl)aniline.

[0026] Among these, methylmorpholine, ethylmorpholine, (dimethylaminoethyl)morpholine, bis(dimethylamino)-2-propanol, tetramethyl(2-hydroxyl)ethyltriethylenediamine, tetramethyl(2-hydroxyl)propyltriethylenediamine, bis(3-dimethylaminopropyl)aminoethanol, bis(3-dimethylaminopropyl)amino-2-propanol, (2-hydroxyethyl)morpholine, dimethylaminoethanol, dimethylaminoethoxyethanol, trimethylaminoethylethanolamine, bis(2-dimethylaminoethyl)ether, ethylene glycol bis(3-dimethylaminopropyl)ether, and trimethoxy(2-methoxyethyl)ethylenediamine are particularly preferred. The above-mentioned polyfunctional compounds (T) may be used alone or in combination.

[0027] The polyfunctional compound (T) is preferably contained in an amount of 0.01 to 10 mass %, more preferably 0.01 to 5 mass %, relative to 100 parts by mass of the (meth)acrylic copolymer (A). By containing 0.01 to 10 mass %, whitening at bent portions and misalignment at edges can be suppressed.

[0028] [Hardening agent] The pressure-sensitive adhesive composition preferably contains a curing agent. By promoting crosslinking between the reactive functional groups of the (meth)acrylic copolymer (R) and the curing agent, the pressure-sensitive adhesive composition is cured and a crosslinked structure is formed. The curing agent is a compound other than the polyfunctional compound (T) and refers to an isocyanate-based curing agent. Examples of isocyanate-based curing agents include tolylene diisocyanate, methylene diphenyl diisocyanate, xylylene diisocyanate, tetramethyl xylylene diisocyanate, and their allophanate, biuret, isocyanurate, prepolymer, and adduct forms. The curing agent is preferably contained in an amount of 0.1 to 80% by mass relative to 100% by mass of the (meth)acrylic copolymer (R). By setting the amount within this range, it is possible to achieve high cohesive strength and an improved recovery rate. A more preferred range is 0.1 to 30% by mass, and even more preferably 0.1 to 10% by mass.

[0029] Tackifire The PSA composition preferably contains a tackifier. Examples of tackifiers include rosin and rosin derivatives, as well as terpene resins and modified terpene resins. Particularly preferred rosin and rosin derivatives include gum rosin, rosin ester (Pencel), maleic acid-modified rosin resin, and rosin-modified phenolic resin (Tamanol), all manufactured by Arakawa Chemical Industries, Ltd. Preferred terpene resins and modified terpene resins include terpene monomer homopolymer resins (YS Resin PX and YS Resin PXN), aromatic modified terpene resins (YS Resin TO), and terpene phenolic resins (YS Polystar series), all manufactured by Yasuhara Chemical Co., Ltd.

[0030] <Adhesive layer for flexible image display devices> The pressure-sensitive adhesive layer for a flexible image display device is formed from a pressure-sensitive adhesive composition. For example, a method for forming the pressure-sensitive adhesive layer includes applying the pressure-sensitive adhesive composition to a separator and then drying and removing the solvent, etc. to form the pressure-sensitive adhesive layer. Alternatively, the pressure-sensitive adhesive composition may be directly applied to a colorless polyimide, and then the solvent, etc. may be dried to form the pressure-sensitive adhesive layer.

[0031] The separator has a release layer formed by applying a release agent to a substrate such as paper, plastic film, synthetic paper, etc. Examples of the release agent include silicone, alkyd resin, melamine resin, fluororesin, and acrylic resin. The thickness of the separator is not particularly limited, but is generally about 10 to 200 μm.

[0032] The drying temperature for the above-mentioned solvent is preferably 40 to 200° C., more preferably 50 to 180° C., and particularly preferably 70 to 170° C. By setting the drying temperature within the above range, it is possible to obtain a pressure-sensitive adhesive layer having excellent adhesive properties.

[0033] The drying time can be appropriately selected and is preferably 5 seconds to 20 minutes, more preferably 5 seconds to 10 minutes, and particularly preferably 10 seconds to 5 minutes.

[0034] The pressure-sensitive adhesive composition can be applied by various methods, specifically, for example, roll coating, kiss roll coating, gravure coating, reverse coating, roll brushing, spray coating, dip roll coating, bar coating, knife coating, air knife coating, curtain coating, lip coating, extrusion coating using a die coater, etc.

[0035] To adjust the gel fraction of the adhesive layer, the adhesive sheet is cured after drying as needed by leaving it to stand in an environment of 23 to 60°C for 3 to 14 days.

[0036] The thickness of the pressure-sensitive adhesive layer of the present invention is preferably 5 to 150 μm, more preferably 15 to 100 μm. The pressure-sensitive adhesive layer may be a single layer, or may be a laminate of pressure-sensitive adhesives with different compositions. A thickness within this range is preferable in terms of not hindering bending and also in terms of adhesion. If the thickness exceeds 150 μm, polymer chains in the pressure-sensitive adhesive layer become more mobile during repeated bending, causing severe deterioration and the risk of peeling. If the thickness is less than 5 μm, the stress during bending cannot be alleviated, causing the risk of breakage.

[0037] The pressure-sensitive adhesive layer for flexible image display devices of the present invention is preferably in a form in which a separator is laminated on one side, or in a form in which the pressure-sensitive adhesive layer is sandwiched between separators on both sides, but in particular, a form in which the pressure-sensitive adhesive layer is sandwiched on both sides is preferred from the viewpoint of handling. The pressure-sensitive adhesive layer is preferably a single layer, but it is also preferable to provide a core material therebetween, which may be polyethylene terephthalate or polyimide.

[0038] By satisfying the gel fraction, glass transition temperature, and storage modulus at various temperatures described below, the pressure-sensitive adhesive layer can suppress whitening of the bent portion and misalignment of the edges when it is bonded to a light-transmitting substrate such as colorless polyimide and used as a flexible image display device while being bent.

[0039] [Gel fraction] The gel fraction of the pressure-sensitive adhesive layer is preferably 50% to 70%, more preferably 55 to 65%. By setting the gel fraction within the above range, whitening at bent portions is improved. The gel fraction can be adjusted by the curing time and curing temperature of the pressure-sensitive adhesive layer. It can also be controlled within the above range by adjusting the proportions of carboxyl group-containing monomers and hydroxyl group-containing monomers in the (meth)acrylic copolymer (R) and the amount of curing agent added.

[0040] [Glass transition temperature] The glass transition temperature of the pressure-sensitive adhesive layer is preferably -50°C or higher and -30°C or lower, more preferably -50 to -37°C. By setting the glass transition temperature within the above range, whitening at bending points and misalignment at edges are improved. The glass transition temperature can be adjusted by using a (meth)acrylic acid alkyl ester monomer having an alkyl group with 6 to 12 carbon atoms in the molecule in the (meth)acrylic copolymer (R). It can also be controlled within the above range by adjusting the content of tackifier, etc. The glass transition temperature is a value measured by DSC, and the detailed measurement method is described in the Examples.

[0041] [Storage modulus at -20℃] The storage modulus of the adhesive layer at -20°C is 5×10 4 Pa~5×10 5 Pa is preferred, 6 x 10 4 ~3×10 5 It is more preferable that the storage modulus at -20°C is in the above range.By setting the storage modulus at -20°C in the above range, flexibility and recovery at low temperatures are improved, and whitening of bent portions and displacement of edges can be suppressed. The storage modulus at -20°C can be adjusted by adding a tackifier. It can also be adjusted by using a (meth)acrylic copolymer (R) containing a (meth)acrylic acid alkyl ester monomer having an alkyl group with 6 to 12 carbon atoms in the molecule and a monomer having an alkyl group with 12 to 20 carbon atoms in the molecule.

[0042] [Storage modulus at 25°C] The storage modulus of the adhesive layer at 25°C is 1×10 4 Pa~5×104 Pa is preferred, 2×10 4 ~4×10 4 By setting the storage modulus at 25°C within the above range, the stress relaxation property of the resin is improved, and flexibility is improved. In addition, whitening of bent portions and displacement of edges at room temperature can be suppressed. The storage modulus at 25° C. can be adjusted by using a (meth)acrylic acid alkyl ester monomer having an alkyl group with 6 to 12 carbon atoms in the molecule in the (meth)acrylic copolymer (R).

[0043] [Storage modulus at 80℃] The storage modulus of the adhesive layer at 80°C is 5×10 3 Pa~3×10 4 Pa is preferred, 6 x 10 3 Pa~2×10 4 By setting the storage modulus at 80°C within the above range, the cohesive strength of the pressure-sensitive adhesive layer is improved, and flexibility is improved. Also, whitening of bent portions and displacement of edges at high temperatures can be suppressed. The storage modulus at 80° C. can be adjusted by using a monomer having an alkyl group with 1 to 4 carbon atoms in the molecule or an alicyclic monomer in the (meth)acrylic copolymer (R).

[0044] The storage modulus at the above various temperatures is a value measured by measuring the pressure-sensitive adhesive layer with a rheometer, and the detailed measurement conditions will be described in the Examples.

[0045] <Laminate for flexible image display devices> The laminate for a flexible image display device comprises a pressure-sensitive adhesive layer for a flexible image display device and a light-transmitting substrate. The light-transmitting substrate is a colorless polyimide, polyethylene terephthalate, or thin-film glass, and is a substrate having a transmittance of 80% or more at 400 nm to 700 nm. From the viewpoint of improving flexibility, the thickness is preferably 10 to 200 μm, and more preferably 20 to 100 μm.

[0046] <Adhesion to light-transmitting substrate> The adhesive strength of the pressure-sensitive adhesive layer to the light-transmitting substrate is preferably 15 to 35 N / 25 mm, more preferably 20 to 35 N / 25 mm, even more preferably 25 to 35 N / 25 mm, and most preferably 30 to 35 N / 25 mm. By keeping it within the above range, slippage of the edges of the pressure-sensitive adhesive layer is suppressed. The adhesive strength can be adjusted to the above range by subjecting the surface of the light-transmitting substrate containing the polyfunctional compound (T) to a corona treatment or plasma treatment.

[0047] The laminate for flexible image display devices is also preferably a laminate in which a polarizing plate, a touch sensor, a transparent conductive film, or a metal reinforcing plate such as stainless steel is laminated on the other surface of the pressure-sensitive adhesive layer on which the light-transmitting substrate is laminated. In one example of manufacturing a laminate for a flexible image display device, a separator is peeled off from one side of a pressure-sensitive adhesive layer sandwiched between separators on both sides, and a light-transmitting substrate is bonded to the exposed pressure-sensitive adhesive layer. The other opposing separator is then peeled off, and the exposed pressure-sensitive adhesive layer is bonded to a polarizing plate, a transparent conductive film, or a metal reinforcing plate such as stainless steel, thereby forming a laminate for a flexible image display device. A hard coat layer or an easy-adhesion coating layer may be laminated at the lamination interface between the pressure-sensitive adhesive layer and the light-transmitting substrate.

[0048] <Flexible image display device> A flexible image display device, one of its major features being its flexibility, comprises the above-mentioned laminate for a flexible image display device and an optical element. The optical element is a foldable organic EL (electroluminescence) display panel, liquid crystal panel, micro LED, etc., and can be suitably used as an image display device such as a flexible liquid crystal display device, organic EL display device, micro LED display device, PDP (plasma display panel), electronic paper, etc. Furthermore, it can be used regardless of the type of touch panel, such as a resistive film type or a capacitive type. [Example]

[0049] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. Note that the "parts" and "%" below are values ​​based on "parts by weight" and "% by weight", respectively.

[0050] <Measurement of weight average molecular weight (Mw) and number average molecular weight (Mn)> The weight average molecular weight (Mw) was measured using a GPC "LC-GPC system" manufactured by Shimadzu Corporation. The weight average molecular weight (Mw) was determined by conversion using polystyrene of known molecular weight as the standard substance. Device name: Shimadzu Corporation, LC-GPC system "Prominence" Columns: Four GMHXL columns manufactured by Tosoh Corporation and one HXL-H column manufactured by Tosoh Corporation were connected together. Mobile phase solvent: tetrahydrofuran Flow rate: 1.0ml / min Column temperature: -30℃

[0051] <Synthesis of (meth)acrylic copolymer (R)> Details of the acrylic monomers used in the synthesis of the (meth)acrylic copolymer (R) are shown below. <Acrylic Monomer> EHA: 2-ethylhexyl acrylate BA: butyl acrylate DOA: Dodecyl acrylate IBXA: Isobornyl acrylate CHA: Cyclohexyl acrylate AA: acrylic acid HBA: 4-hydroxybutyl acrylate

[0052] <Synthesis of (meth)acrylic copolymer R1> A reaction vessel (hereafter simply referred to as the "reaction vessel") equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube was charged with 58 parts of 2-ethylhexyl acrylate (EHA), 25 parts of dodecyl acrylate (DOA), 1.8 parts of 4-hydroxybutyl acrylate (HBA), 0.2 parts of acrylic acid (AA), 5 parts of cyclohexyl acrylate (CHA), 10 parts of n-butyl acrylate (BA), and 0.2 parts of 2,2'-azobisisobutyronitrile (hereafter simply referred to as "AIBN"), and the atmosphere inside the reaction vessel was replaced with nitrogen gas. The mixture was then heated to 50°C while stirring under a nitrogen atmosphere to initiate the reaction. The reaction solution was then reacted at 50°C for 4 hours. After completion of the reaction, the mixture was cooled and diluted with ethyl acetate to obtain (meth)acrylic copolymer (R1), an acrylic copolymer with a nonvolatile content of 30% and a viscosity of 3000 mPa·s. The weight average molecular weight (Mw) of the resulting (meth)acrylic copolymer (R1) was 1,400,000.

[0053] (Synthesis of (meth)acrylic copolymers R2 to R7) R2 to R7 were synthesized in the same manner as for the production of the (meth)acrylic copolymer (R1), except that the compositions and blending amounts (parts by mass) were changed to those shown in Table 1. The weight-average molecular weights (Mw) of the resulting pressure-sensitive adhesives are shown in Table 1. Note that blank spaces in the table indicate that no compound was blended.

[0054] [Table 1]

[0055] <Preparation of Pressure-Sensitive Adhesive Sheet According to Example 1> A pressure-sensitive adhesive composition was obtained by blending 100 parts of a (meth)acrylic copolymer (R1), 0.01 parts of a polyfunctional low molecular weight compound (T1), and 0.5 parts of a curing agent (C1), and then adding ethyl acetate to adjust the nonvolatile content to 20%.

[0056] The pressure-sensitive adhesive composition was applied to a 75 μm thick polyethylene terephthalate separator so that the thickness after drying would be 50 μm, and a pressure-sensitive adhesive layer was formed by drying with hot air at 100° C. Next, a 50 μm thick polyethylene terephthalate separator was attached to this pressure-sensitive adhesive layer to obtain the pressure-sensitive adhesive sheet of Example 1.

[0057] <Gel fraction measurement> The adhesive sheet was cut into a size of 30 mm x 100 mm, the separator on one side was peeled off, and the exposed adhesive layer was attached to a weighed 300-mesh stainless steel wire mesh (weight W0). The other separator was peeled off, and the mesh was folded to confine the adhesive layer within the mesh, to prepare a sample. The weight of the sample was weighed and designated W1. The sample was then left to stand in ethyl acetate for 24 hours, dried at 100°C for 1 hour, and weighed again, and the weight was designated W2. The weight was calculated using the following formula: Gel fraction (%) = {(W2 - W0) / (W1 - W0)} x 100

[0058] <Method for measuring glass transition temperature> The adhesive layer was removed from the adhesive sheet, and approximately 5 mg of sample was weighed into an aluminum standard container using a Mettler-Toledo "DSC-1." Measurements were then taken from -80 to 300°C under conditions of a temperature modulation amplitude of ±1°C, a temperature modulation period of 60 seconds, and a temperature rise rate of 2°C / min, and the glass transition temperature was determined from the differential thermal curve of the reversible component.

[0059] <Storage modulus measurements at -20℃, 25℃, and 80℃> Two pairs of sheets were prepared by removing the separator from one side of the pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive layers were bonded together using a laminator to create a separator / pressure-sensitive adhesive layer / separator laminate. The separator on one side of the laminate was repeatedly peeled off and bonded together to form a 1 mm thick pressure-sensitive adhesive layer laminate. This laminate was measured using a rheometer (TA Instruments, DHR-2) with a φ8 mm measurement probe under conditions of 0.1% strain, 1 Hz frequency, and a heating rate of 10°C / min from -70°C to 200°C. The storage moduli at -20°C, 25°C, and 80°C were read from the resulting measurement graph.

[0060] <Adhesion strength of adhesive layer to colorless polyimide> The separator on one side of the adhesive sheet was peeled off and the sheet was attached to a 50 μm PET film using a laminator. The other separator was then peeled off and the sheet was attached to the corona-treated surface of a 50 μm thick colorless polyimide (manufactured by KOLON Co., Ltd.) that had been corona-treated at 300 W power on one side using a laminator. The sheet was then placed in an autoclave at 50°C and 5 atmospheres for 20 minutes to allow the components to adhere together, yielding a measurement sample. The measurement sample was then left at 23°C for one day, after which the adhesive strength was measured at a peel speed of 300 mm / min and a peel angle of 180° using a tensile tester (Orientec Co., Ltd. "Tensilon") at 23°C and 50% relative humidity.

[0061] <Evaluation of whitening at bent points and edge misalignment in bending tests> The separator was peeled off from the prepared pressure-sensitive adhesive sheet, and the exposed pressure-sensitive adhesive layer was attached to a colorless polyimide (KOLON, 50 μm) using a laminator at 25°C and 50% relative humidity. The other separator was peeled off and attached to a 188 μm-thick PET film using a laminator to obtain a test laminate consisting of PET film / pressure-sensitive adhesive layer / colorless polyimide. The test laminate was then subjected to a normal-condition test at 25°C and 50% relative humidity using a bending tester (Yuasa System Co., Ltd.) with the inner diameter (diameter) set to 6 mm when bent, and 300,000 cycles of bending and 180° release were repeated. A separate test was also conducted with the inner diameter changed to 3 mm. The appearance after the test was evaluated for whitening at the bent area and edge misalignment according to the following criteria. Appearance: The test laminate was visually inspected for the presence of bubbles and the presence or absence of lifting or peeling of the adhesive layer under the following conditions. [Whitening of bent parts] 5: No air bubbles are visible within 5mm on either side of the folded point. 4: There are 10 or fewer air bubbles within 5 mm on each side of the folded point. 3: There are 11 to 50 air bubbles within 5 mm on each side of the folded point. 2: There are 51 to 100 bubbles within 5 mm on each side of the folded part. 1: There are 100 or more bubbles within 5 mm on each side of the folded part. [Edge misalignment] 5: The misalignment between the PET film and the polarizing plate is less than 1 mm. 4: The misalignment between the PET film and the polarizing plate is 1 mm or more and less than 2 mm. 3: The misalignment between the PET film and the polarizing plate is 2 mm or more and less than 3 mm. 3: The misalignment between the PET film and the polarizing plate is 3 mm or more and less than 4 mm. 1: The misalignment between the PET film and the polarizing plate is 4 mm or more.

[0062] (Examples 2 to 10, Comparative Examples 1 to 3) Pressure-sensitive adhesive sheets of Examples 2 to 10 and Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the blending amounts (parts by mass) were changed to those shown in Tables 2 and 3, and the pressure-sensitive adhesive layers were evaluated. Details of the polyfunctional low molecular weight compound (T1), curing agent (C), and additive (A) used in the preparation of the adhesive layer are shown below. ≪Polyfunctional low molecular compound (T1)≫ T1: Dimethylaminopyridine (molecular weight 122.17) T2: 3-Methoxydimethylpropanamide (molecular weight 131.18) T3: 2-[2-(dimethylamino)ethoxy]ethanol (molecular weight 133.19) T4: A mixture of bis(2-dimethylaminoethyl) ether (molecular weight 160.26) and dipropylene glycol (molecular weight 134.17) (trade name: TOYOCAT-ET, manufactured by Tosoh Corporation) T5: 1-morpholino-1-cyclopentene (molecular weight 153.23) T6: Tetramethylhexamethylenediamine (molecular weight 172.32) T7: Dimethylglycine ethyl ester (molecular weight 131.18) T8: Trifluorodimethylacetamide (molecular weight 141.09) T9: Polyoxypropylenediamine (molecular weight 2000) (trade name: JEFFAMINE D-2000, manufactured by HUNTSUMAN) T10: N-butylamine (molecular weight 73) <Hardening agent (C)> C1: Polyisocyanate compound: adduct of xylylene diisocyanate with trimethylolpropane C2: Polyisocyanate compound: Adduct of hexamethylene diisocyanate with trimethylolpropane Additive (A) A1: FTR6100: Styrene monomer / aliphatic monomer copolymer (Mitsui Chemicals, product name "FTR6100") A2: 3-glycidoxypropyltriethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KBM-403")

[0063] [Table 2]

[0064] [Table 3]

Claims

1. A pressure-sensitive adhesive composition for a flexible image display device, comprising a (meth)acrylic copolymer (R) and a polyfunctional compound (T), The (meth)acrylic copolymer (R) is a copolymer of (meth)acrylic monomers and has a carboxy group or a hydroxy group, the content of the polyfunctional compound (T) is 0.01 to 10 mass% relative to 100 parts by mass of the (meth)acrylic copolymer (R); A pressure-sensitive adhesive composition for a flexible image display device, wherein the polyfunctional compound (T) is dimethylaminopyridine, 3-methoxydimethylpropanamide, 2-[2-(dimethylamino)ethoxy]ethanol, (bis(2-dimethylaminoethyl)ether, 1-morpholino-1-cyclopentene, tetramethylhexamethylenediamine, dimethylglycine ethyl ester, or trifluorodimethylacetamide.

2. 2. The pressure-sensitive adhesive composition for flexible image displays according to claim 1, wherein the (meth)acrylic monomer comprises a (meth)acrylic acid alkyl ester monomer having an alkyl group having 12 to 20 carbon atoms.

3. The pressure-sensitive adhesive composition for flexible image displays according to claim 1 or 2, wherein the (meth)acrylic monomer contains a carboxy group-containing monomer.

4. An adhesive composition for a flexible image display device according to any one of claims 1 to 3, wherein the (meth)acrylic monomer contains an alicyclic monomer.

5. A pressure-sensitive adhesive layer for a flexible image display device, which is formed from the pressure-sensitive adhesive according to any one of claims 1 to 4.

6. The gel fraction is 50% to 70%; The glass transition temperature is -50°C or higher and -30°C or lower, The storage modulus measured at a frequency of 1 Hz is Storage modulus at -20°C is 5 x 10 4 Pa ~ 5 x 10 5 Pa, Storage modulus at 25°C is 1 x 10 4 Pa ~ 5 x 10 4 Pa, Storage modulus at 80°C is 5 x 10 3 Pa ~ 3 x 10 4 The pressure-sensitive adhesive layer for a flexible image display device according to claim 5, wherein the thickness of the pressure-sensitive adhesive layer is 100 μm or more.

7. 7. A laminate for a flexible image display device, comprising the pressure-sensitive adhesive layer for a flexible image display device according to claim 5 or 6, and a light-transmitting substrate, wherein the light-transmitting substrate is any one of colorless polyimide, polyethylene terephthalate, and thin film glass.

8. A flexible image display device comprising the laminate for a flexible image display device according to claim 7 and an optical element.

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