KR101971832B1 - Flexible Display Device - Google Patents

Abstract

The present invention relates to a flexible display device comprising: a display panel; a functional structure disposed on the display panel; a window disposed on the functional structure; a first adhesive layer formed between the display panel and the functional structure; and a second adhesive layer formed between the functional structure and the window, wherein the first adhesive layer and the second adhesive layer have Tan δ of 0.8 to 1 at -20°C. According to the present invention, the flexible display device includes a plurality of layers and is excellent in flex resistance and durability.

Description

[0001] The present invention relates to a flexible display device,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a flexible display device, and more particularly, to a flexible display device including a plurality of layers and having excellent bendability and durability.

Recently, the display market is rapidly changing to flat display, which can be easily and light in weight. Such a flat panel display includes a liquid crystal display (LCD), a plasma display panel (PDP), and an organic electroluminescence display (OLED).

A window substrate for protecting the display panel from an external environment may be disposed on the display panel. The flexible substrate may be formed of a flexible plastic material, for example, while the flexible substrate is being developed. Further, additional members of a display device such as a polarizing plate and a touch screen panel may be disposed between the window substrate and the display panel.

For example, Korean Patent Publication No. 2012-0076026 discloses a touch screen panel including a transparent substrate and a polarizing plate.

However, since a plurality of layers such as a polarizing plate, a touch screen panel, and a window substrate are laminated on a display panel, sufficient flex resistance and durability required in a flexible display device may not be realized. Therefore, development of a flexible display device of a multi-layer structure having excellent durability while ensuring sufficient flexing resistance to prevent damage such as cracking or breakage to each layer during bending or folding operation is required.

Korean Patent Publication No. 2012-0076026

It is an object of the present invention to provide a flexible display device that includes a plurality of layers and is excellent in bending resistance and durability.

On the other hand, the present invention provides a display panel comprising: a display panel; A functional structure disposed on the display panel; A window disposed on the functional structure; A first pressure-sensitive adhesive layer formed between the display panel and the functional structure; And a second pressure-sensitive adhesive layer formed between the functional structure and the window, wherein the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer have a tan δ of 0.8 to 1 at -20 ° C.

In one embodiment of the present invention, the display panel may include an organic light emitting diode (OLED) panel or a liquid crystal display (LCD) panel.

In one embodiment of the present invention, the functional structure may include at least one of a touch sensor, a polarizing layer, and a retardation layer.

The flexible display device according to the present invention has a multi-layer structure, and the Tan δ at -20 ° C. of the pressure-sensitive adhesive layer between each layer is controlled to 0.8 to 1, so that the minimum bending deformation and stress are added to each layer, While excellent durability.

1 is a cross-sectional view schematically showing a flexible display device according to an embodiment of the present invention.
2 is a schematic cross-sectional view illustrating a display panel of a flexible display device according to an embodiment of the present invention.
3 is a schematic plan view showing a touch sensor of a flexible display device according to an embodiment of the present invention.
4 is a graph showing a strain profile of a flexible display device according to an embodiment of the present invention.
5 is a cross-sectional view schematically showing a flexible display device according to another embodiment of the present invention.
6 is a cross-sectional view schematically showing a flexible display device according to still another embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 is a cross-sectional view schematically showing a flexible display device according to an embodiment of the present invention.

Referring to FIG. 1, the flexible display device may include a display panel 100, a functional structure 200, and a window 300.

The display panel 100 may include, for example, an organic light emitting diode (OLED) panel or a liquid crystal display (LCD) panel. The detailed structure and structure of the display panel 100 will be described later with reference to FIG.

The functional structure 200 may include at least one of a touch sensor, a polarizing layer, and a retardation layer, for example. The detailed structure and structure of the touch sensor will be described later with reference to Fig.

The thickness of the functional structure 200 may be 50 to 150 mu m.

The polarizing layer may be provided, for example, as a polarizing plate including a stretched polarizer. In this case, the polarizing plate may include a polarizer and a protective film formed on at least one surface of the polarizer.

The elongated polarizer may include, for example, a stretched polyvinyl alcohol (PVA) based resin. The polyvinyl alcohol-based resin is preferably a polyvinyl alcohol-based resin obtained by saponifying a polyvinyl acetate-based resin. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith. Examples of the other monomer include an acrylamide monomer having an unsaturated carboxylic acid type, an unsaturated sulfonic acid type, an olefin type, a vinyl ether type, and an ammonium group. The polyvinyl alcohol-based resin may be modified or may be polyvinyl formal or polyvinyl acetal modified with, for example, aldehydes.

Examples of the protective film include polyester resins such as polyethylene terephthalate, polyethylene isophthalate, polyethylene naphthalate and polybutylene terephthalate; Cellulose-based resins such as diacetylcellulose and triacetylcellulose; Polycarbonate resin; Acrylic resins such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; A cyclic olefin-based polymer (COP), and the like.

The polarizing layer may comprise a coated polarizer. In this case, the polarizing layer may be directly coated on the touch sensor, and the functional structure 200 may include a laminated structure of the touch sensor and the polarizing layer. For example, the polarizing layer may include an alignment film and a liquid crystal layer formed on the alignment film.

For example, an alignment film coating composition containing an orienting polymer, a photopolymerization initiator and a solvent is applied and cured on the touch sensor to form the alignment film, and then a liquid crystal coating composition is applied and cured on the alignment film to form an alignment film and a liquid crystal A polarizing layer including a layer can be formed.

The oriented polymer may include, for example, a polyacrylate resin, a polyamic acid resin, a polyimide resin, a polymer including a cinnamate group, and the like. The liquid crystal coating composition may include a reactive liquid crystal compound and a dichroic dye.

The retardation layer may be a coating layer or a film. The retardation layer may be provided integrally with the polarizing layer.

The retardation layer may be a single layer or a multi-layer, and may be a 1/4 wavelength plate in the case of a single layer and a multi-layer in a 1/4 wavelength plate and a 1/2 wavelength plate in a multi-layer case. In the case of a multi-layer of a quarter-wave plate and a half-wave plate, the color difference and the image quality are excellent when applied to a display device by the phase difference correction.

For example, the window 300 may be exposed to the user's viewing side of the flexible display device and may be provided as a protective film for the external environment.

The window 300 may comprise a flexible plastic material or a substrate layer comprising a polymeric material. For example, the substrate layer may be formed of a material selected from the group consisting of polyimide (PI), polyethersulphone (PES), polyacrylate (PAR), polyetherimide (PEI), polyethylene naphthalate PEN), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyarylate, polycarbonate (PC), cellulose triacetate (TAC), cellulose Cellulose acetate propionate (CAP), and the like. Of these, polyimide is particularly preferable. These may be used alone or in combination of two or more.

The window 300 may further include a hard coating layer formed on at least one side of the substrate layer. The hard coating layer is formed using a hard coating composition including, for example, a photocurable compound, a photoinitiator and a solvent, thereby further securing excellent flexibility, abrasion resistance and surface hardness of the window 300.

The photocurable compound may include, for example, a siloxane-based compound, an acrylate-based compound, a vinyl group-containing compound, and the like. These may be used alone or in combination of two or more.

The photoinitiator is not particularly limited as long as it initiates polymerization of the photo-curable compound by generating an ion, a Lewis acid or a radical by irradiation of an active energy ray such as visible light, ultraviolet light, X-ray or electron beam. Examples of the photoinitiator include aromatic diazonium salts, onium salts such as aromatic iodonium salts and aromatic sulfonium salts, acetophenone compounds, benzoin compounds, benzophenone compounds and thioxanthone compounds.

The thickness of the window 300 may be 50 to 100 mu m.

According to an embodiment of the present invention, a first pressure sensitive adhesive layer 50 may be formed between the display panel 100 and the functional structure 200. In one embodiment, the first pressure sensitive adhesive layer 50 may be in direct contact with the surfaces of the display panel 100 and the functional structure 200. For example, after the first pressure sensitive adhesive layer 50 is formed on the bottom surface of the functional structure 200 (for example, a touch sensor, a polarizing layer or a retardation layer), the exposed surface of the first pressure sensitive adhesive layer 50 And can be attached to the upper surface of the display panel 100.

A second pressure sensitive adhesive layer (90) may be formed between the functional structure (200) and the window (300). In one embodiment, the second pressure sensitive adhesive layer 90 may be in direct contact with the surfaces of the functional structure 200 and the window 300. For example, after the second pressure sensitive adhesive layer 90 is formed on the bottom surface of the window 300, the exposed surface of the second pressure sensitive adhesive layer 90 may be adhered to the upper surface of the functional structure 200.

As used herein, the term "pressure-sensitive adhesive layer" is used to mean a layer formed by an adhesive, as well as a layer formed by an adhesive. The pressure-sensitive adhesive layer may be formed using a pressure sensitive adhesive (PSA) composition or an optically clear adhesive (OCA) composition.

The first and second pressure-sensitive adhesive layers 50 and 90 may have a viscoelastic characteristic applicable to a flexible display while having an appropriate adhesive force so as not to cause peeling or bubbling when the flexible display device is bent.

In the flexible display device according to the embodiment of the present invention, the first and second pressure-sensitive adhesive layers 50 and 90 have a tan δ of 0.8 to 1 at -20 ° C.

The value of the tangent delta (tan delta) means the ratio of the loss elastic modulus (G ") / storage elastic modulus (G ') of the pressure sensitive adhesive layer and is an index of ease of deformation of the pressure sensitive adhesive layer. The method for measuring the value is not particularly limited, and can be measured by, for example, the method described in Experimental Examples described later.

In one embodiment of the present invention, by controlling the tangent delta value of the first and second pressure-sensitive adhesive layers 50 and 90 to 0.8 to 1 at a low temperature of -20 占 폚, the first and second pressure-sensitive adhesive layers 50 and 90 The flexural strength and durability of the flexible display device can be improved.

The first and second pressure-sensitive adhesive layers 50 and 90 may have a storage elastic modulus (G ') of 0.05 to 0.15 MPa at -20 ° C.

If the storage elastic modulus of the first and second pressure-sensitive adhesive layers 50 and 90 at -20 캜 is less than 0.05 MPa, the durability may deteriorate. If the storage elastic modulus exceeds 0.15 MPa, the flexibility may be decreased.

The thickness of the first and second pressure-sensitive adhesive layers 50 and 90 may be 20 to 200 탆, and preferably 20 to 100 탆.

The storage modulus and thickness of the first and second pressure-sensitive adhesive layers 50 and 90 at -20 ° C may be the same or different from each other.

The tan δ and storage elastic modulus of the first and second pressure-sensitive adhesive layers (50, 90) at -20 ° C. can be adjusted by changing the composition of the pressure-sensitive adhesive composition for forming them.

The first and second pressure-sensitive adhesive layers 50 and 90 may be formed using an acrylic, silicone, or urethane pressure-sensitive adhesive composition.

In one embodiment of the present invention, the first and second pressure-sensitive adhesive layers 50 and 90 may be formed from a pressure-sensitive adhesive composition comprising a (meth) acrylate resin, a (meth) acrylate ester monomer and a photoinitiator.

In particular, the first and second pressure-sensitive adhesive layers 50 and 90 may be formed from a pressure-sensitive adhesive composition comprising an aliphatic (meth) acrylate polymer, a (meth) acrylate ester monomer and a photoinitiator.

The aliphatic (meth) acrylate polymer is a component that plays a role in controlling the viscosity-to-elasticity balance of the pressure-sensitive adhesive composition and includes, for example, polymers of alkyl (meth) acrylate monomers, especially C ₄ -C ₈ alkyl (meth) Lt; / RTI >

Specific examples of the alkyl (meth) acrylate monomers include n-butyl (meth) acrylate, 2-butyl (meth) acrylate, t-butyl (meth) acrylate, Ethyl (meth) acrylate, methyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, Octyl (meth) acrylate. Of these, C ₄ -C ₈ alkyl (meth) acrylate monomers such as n-butyl acrylate and 2-ethylhexyl acrylate are preferably used. These may be used alone or in combination of two or more.

The method for producing the aliphatic (meth) acrylate polymer is not particularly limited, and bulk polymerization, emulsion polymerization or suspension polymerization, which are conventionally used in the art, can be used, and bulk polymerization is preferred. A polymerization initiator usually used in polymerization, a chain transfer agent for controlling the molecular weight, and the like can be used.

The aliphatic (meth) acrylate polymer may be a partial polymer partially polymerized with the above-mentioned monomers.

These partial polymerizates exhibit a syrup shape (viscous liquid phase) in which the polymer formed from a part of the monomer and the unreacted monomer coexist. Accordingly, the polymeric syrup may be referred to as a partial polymer of such an aspect.

The method of partially polymerizing the monomer is not particularly limited, and various polymerization methods can be appropriately selected and used. For example, a photopolymerization or thermal polymerization method can be used.

The solids content of the partial polymer, i. E. The polymer syrup, may be from 20 to 60% by weight, preferably from 30 to 50% by weight. If the solid content of the polymer syrup is less than 20% by weight, the durability of the pressure-sensitive adhesive composition may deteriorate, and if it exceeds 60% by weight, the coating property of the pressure-sensitive adhesive composition may be deteriorated.

The solids content of the polymer syrup is equal to the amount of polymer formed. For example, if the solids content is 40% by weight, the amount of polymer formed is 40% by weight relative to 100% by weight of the total polymer syrup.

In one embodiment of the present invention, the aliphatic (meth) acrylate polymer may be contained in an amount of 30 to 50% by weight based on 100% by weight of the whole of the pressure-sensitive adhesive composition. If the aliphatic (meth) acrylate polymer is contained in an amount of less than 30% by weight, the durability of the pressure-sensitive adhesive composition may deteriorate. If the amount of the aliphatic (meth) acrylate polymer exceeds 50% by weight, the coating property of the pressure-

The (meth) acrylate ester monomer is a component that acts as a dispersion medium for the aliphatic (meth) acrylate polymer and can be polymerized under the action of a photoinitiator.

The (meth) acrylate ester monomer may include an alkyl (meth) acrylate used in the production of the aliphatic (meth) acrylate polymer.

The (meth) acrylate ester monomer may further include a C ₁₀ -C ₂₀ alkyl (meth) acrylate.

Specific examples of the C ₁₀ -C ₂₀ alkyl (meth) acrylate include decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, lauryl (Meth) acrylate. These may be used alone or in combination of two or more.

In one embodiment of the present invention, the (meth) acrylate ester monomer may be contained in an amount of 45 to 70% by weight based on 100% by weight of the whole of the pressure-sensitive adhesive composition. When the content of the (meth) acrylate ester monomer satisfies the above range, Tan δ and storage elastic modulus at -20 ° C. can be controlled within an appropriate range.

The photoinitiator can be used without limitation as long as it is used in the art. Type 1 type photoinitiator, in which radicals are generated by decomposition of molecules due to difference in chemical structure or molecular binding energy, and type 2 photoinitiator, which is a hydrogen reclamation type, coexisting with tertiary amines. Specific examples of the Type 1 type photoinitiator include 4-phenoxydichloroacetophenone, 4-t-butyldichloroacetophenone, 4-t-butyl trichloroacetophenone, diethoxyacetophenone, 2-hydroxy- 2-methylpropan-1-one, 1- (4-dodecylphenyl) -2-hydroxy-2-methyl (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl phenyl ketone and the like, benzoin, benzoin methyl Benzoin ethers such as benzoin ethyl ether and benzyldimethyl ketal, acylphosphine oxides, and titanocene compounds. Specific examples of the Type 2 type photoinitiator include benzophenone, benzoyl benzoic acid, benzoyl benzoic acid methyl ether, 4-phenylbenzophenone, hydroxybenzophenone, 4-benzoyl- Benzophenones such as methyl-4-methoxybenzophenone, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, and isopropylthioxanthone Oxantones and the like. These may be used alone or in combination of two or more. The Type 1 type photoinitiator and the Type 2 type photoinitiator may be used alone or in combination.

The photoinitiator may be contained in an amount of 0.01 to 5.0% by weight based on 100% by weight of the total adhesive composition. When the photoinitiator is contained in an amount less than 0.01% by weight, it may be difficult to effectively initiate the crosslinking reaction. When the photoinitiator is contained in an amount exceeding 5.0% by weight, discoloration or the like may occur due to the residual initiator.

In one embodiment of the present invention, the first and second pressure-sensitive adhesive layers 50 and 90 may be formed from a pressure-sensitive adhesive composition comprising a silicone urethane (meth) acrylate resin, a (meth) acrylate ester monomer and a photoinitiator .

The silicone urethane (meth) acrylate resin may be a resin having a silicon bond (-Si-O-) and a urethane group in the molecule and having a (meth) acryloyloxydane group.

The silicone urethane (meth) acrylate resin may be a reaction product of (meth) acrylate having a hydroxyl group at both ends with a polysilicon having a hydroxyl group, a polyisocyanate, and a hydroxyl group.

The polysilicon having a hydroxyl group at both terminals may be a compound represented by the following formula (1).

[Chemical Formula 1]

In this formula,

R ¹ and R ³ are each independently a C ₁ -C ₁₀ alkylene group or a C ₁ -C ₁₀ oxyalkylene group,

R ² is a C ₁ -C ₁₀ alkyl group, a C ₃ -C ₁₀ cycloalkyl group or an aryl group,

n is an integer of 1 to 30;

As used herein, a C ₁ -C ₁₀ alkylene group means a linear or branched divalent hydrocarbon having 1 to 10 carbon atoms and includes, for example, methylene, ethylene, propylene, butylene, pentylene and the like However, the present invention is not limited thereto.

As used herein, a C ₁ -C ₁₀ oxyalkylene group means a functional group in which at least one of the chain carbons in the linear or branched divalent hydrocarbon having 1 to 10 carbon atoms is substituted with oxygen, for example, ethyl Propyloxyethyl, and the like, but is not limited thereto.

As used herein, a C ₁ -C ₁₀ alkyl group means a linear or branched monovalent hydrocarbon group having 1 to 10 carbon atoms, and examples thereof include methyl, ethyl, n-propyl, i-propyl, n-butyl , i-butyl, t-butyl, n-pentyl, n-hexyl, and the like.

C ₃ -C ₁₀ cycloalkyl group as used herein means a simple or fused ring hydrocarbon having 3 to 10 carbon atoms and includes, for example, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and the like, It is not.

As used herein, an aryl group includes both an aromatic group and a heteroaromatic group and a partially reduced derivative thereof. The arromatic group is a simple or fused ring of 5 to 15 members, and the heteroaromatic group means an aromatic group containing at least one of oxygen, sulfur or nitrogen. Exemplary aryl groups include, but are not limited to, phenyl, naphthyl, pyridinyl, furanyl, thiophenyl, indolyl, quinolinyl, imidazolinyl, But are not limited to, oxazolyl, thiazolyl, tetrahydronaphthyl, and the like.

The weight average molecular weight of the polysilicon having a hydroxyl group at both terminals may be 800 to 2,000.

As the polyisocyanate, an aliphatic diisocyanate, an alicyclic diisocyanate, and / or an aromatic diisocyanate can be used.

Examples of the aliphatic diisocyanate include methyl diisocyanate, 1,2-ethanediyl diisocyanate, 1,3-propanediyl diisocyanate, 1,6-hexanediyl diisocyanate, 3-methyl-octane-1,8-diyl diisocyanate And the like.

Examples of the alicyclic diisocyanate include 4,4'-methylenedicyclohexyl diisocyanate, 1,2-cyclopropanediyl diisocyanate, 1,3-cyclobutanediyl diisocyanate, 1,4-cyclohexanediyl diisocyanate, , 3-cyclohexanediyl diisocyanate, isophorone diisocyanate, 4-methyl-cyclohexane-1,3-diyl diisocyanate, and the like.

Examples of the aromatic diisocyanate include 1,2-phenylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 3-chloro-1,2-benzene diisocyanate, , 2-benzene diisocyanate, 5-chloro-1,2-benzene diisocyanate, 2-chloro-1,3-benzene diisocyanate, 4-chloro-1,3-benzene diisocyanate, Benzene diisocyanate, 3-chloro-1,4-benzene diisocyanate, 3-methyl-1,2-benzene diisocyanate, 4-methyl- 1,2-benzene diisocyanate, 2-methyl-1,3-benzene diisocyanate, 4-methyl-1,3-benzene diisocyanate, 5-methyl-1,3-benzene diisocyanate Benzene diisocyanate, 3-methyl-1,4-benzene diisocyanate, 3-methoxy-1,2-benzene diisocyanate, 4-methoxy- Methoxy-1,2-benzene diisocyanate, 2-methoxy-1,3-benzene diisocyanate, 4-methoxy-1,3-benzene diisocyanate, 5-methoxy- Benzene diisocyanate, 3-methoxy-1,4-benzene diisocyanate, 3,4-dimethyl-1,2-benzene diisocyanate, 4,5-dimethyl Benzene diisocyanate, 2,3-dimethyl-1,4-benzene diisocyanate, 3-chloro-4-methyl-1,2-benzene diisocyanate, Benzene diisocyanate, 4-chloro-5-methoxy-1,3-benzene diisocyanate, 3-methyl- Benzene diisocyanate, 5-chloro-2-fluoro-1,3-benzene diisocyanate, 2-chloro-3- 4-benzene diisocyanate, 2,3-diisocyanate pyridine, Diisocyanate-3-methylpyridine, 2,5-diisocyanate-4-methylpyridine, 2, 2-diisocyanate, 5-diisocyanate-6-methylpyridine, and the like.

Examples of the (meth) acrylate having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 3-hydroxybutyl (Meth) acrylic acid alkyl ester having a hydroxy group such as methyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and 6-hydroxyhexyl (meth) acrylate; Polyfunctional (meth) acrylates having a hydroxyl group such as trimethylolpropane di (meth) acrylate, pentaerythritol tri (meth) acrylate and dipentaerythritol penta (meth) acrylate; Polyethylene glycol monoacrylate, polypropylene glycol monoacrylate, and the like.

The silicone urethane (meth) acrylate resin may be prepared by, for example, introducing the polyisocyanate into a reaction system with polysilicon having a hydroxyl group at both ends and a hydroxyl group-containing (meth) acrylate under a solventless condition, (Meth) acrylate having an isocyanate group is obtained by reacting the polyisocyanate with the polysilicon having a hydroxyl group at both ends of the end thereof under a solvent, and then the (meth) acrylate having the hydroxy group is supplied, And the like. The reaction may be carried out at 20 to 120 ° C for 30 minutes to 24 hours.

In the production of the silicone urethane (meth) acrylate resin, a polymerization inhibitor, a urethanization catalyst and the like may be used if necessary.

The polystyrene reduced weight average molecular weight (hereinafter referred to as "weight average molecular weight") of the silicone urethane (meth) acrylate resin measured by gel permeation chromatography (using GPC and tetrahydrofuran as an elution solvent) is not particularly limited , For example from 1,500 to 3,000.

In one embodiment of the present invention, the silicone urethane (meth) acrylate resin may be contained in an amount of 30 to 50% by weight based on 100% by weight of the entire adhesive composition. If the silicone urethane (meth) acrylate resin is contained in an amount less than 30% by weight, the durability of the pressure-sensitive adhesive composition may deteriorate, and if it is contained in an amount exceeding 50% by weight, the coating property of the pressure-

As the (meth) acrylate ester monomer, aliphatic (meth) acrylate, (meth) acrylate having an ether group, (meth) acrylate having a hydroxyl group, (meth) acrylamide having a nitrogen atom, Particularly, aliphatic (meth) acrylates can be used.

Examples of the aliphatic (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) (Meth) acrylate, isobutyl (meth) acrylate, 2-ethylbutyl (meth) acrylate, n-pentyl (Meth) acrylate, n-octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, isodecyl (Meth) acrylate, isooctyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, stearyl Acrylate, hexadecyl (meth) acrylate , Isoamyl (meth) acrylate, and the like can be exemplified, in particular, lauryl (meth) acrylate, isodecyl (meth) preferred to use a C ₁₀ -C ₂₀ alkyl (meth) acrylate such as acrylate Do.

Examples of the (meth) acrylate having an ether group include 3-methoxybutyl (meth) acrylate, 2-methoxyethyl (meth) acrylate, 3-methoxypropyl (meth) (Meth) acrylate, ethoxy-diethylene glycol (meth) acrylate, and ethyl carbitol (meth) acrylate, which have an addition molar number of oxyethylene in the range of 1 to 15 .

Examples of the (meth) acrylate having a hydroxy group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate.

Examples of the (meth) acrylamide having a nitrogen atom include (meth) acrylamide, dimethyl (meth) acrylamide, acryloylmorpholine, dimethylaminopropyl (meth) acrylamide, isopropyl (Meth) acrylamide, hydroxyethyl (meth) acrylamide, diacetone (meth) acrylamide and the like.

In one embodiment of the present invention, the (meth) acrylate ester monomer may be contained in an amount of 45 to 70% by weight based on 100% by weight of the whole of the pressure-sensitive adhesive composition. When the content of the (meth) acrylate ester monomer satisfies the above range, Tan δ and storage elastic modulus at -20 ° C. can be controlled within an appropriate range.

The photoinitiator means an initiator that absorbs an active energy ray to generate a radical. Specific examples of the photoinitiator include benzoin compounds, benzophenone compounds, thioxanthone compounds, and acetophenone compounds.

The photoinitiator may be contained in an amount of 0.01 to 5.0% by weight based on 100% by weight of the total adhesive composition. When the photoinitiator is contained in an amount less than 0.01% by weight, it may be difficult to effectively initiate the crosslinking reaction. When the photoinitiator is contained in an amount exceeding 5.0% by weight, discoloration or the like may occur due to the residual initiator.

According to one embodiment of the present invention, as the first and second pressure-sensitive adhesive layers (50, 90) are inserted between the respective layers or members included in the flexible display device, the flexible display device is subjected to tensile, When the same stress occurs, strain separation may occur.

Therefore, a Neutral Plane (NP) may be formed in each layer or each member included in the flexible display device.

1, a first neutral plane NP1 is formed in the display panel 100, a second neutral plane NP2 is formed in the functional structure 200, a third neutral plane NP2 is formed in the window 300, The surface NP3 may be formed.

The temperature of the first and second pressure-sensitive adhesive layers (50, 90) at -20 캜 so that the neutral plane is formed by the strain separation through the first and second pressure-sensitive adhesive layers (50, 90) Tan δ can be adjusted. As described above, the neutral plane is formed for each member of each layer of the flexible display device by the first and second pressure-sensitive adhesive layers (50, 90) at a low temperature of -20 캜, And stress damage in each layer of the display panel 100, the functional structure 200, and the window 300 can be suppressed.

The formation of the neutral plane through the first and second pressure-sensitive adhesive layers 50, 90 will be described in more detail below with reference to FIG.

2 is a schematic cross-sectional view illustrating a display panel of a flexible display device according to an embodiment of the present invention.

Referring to FIG. 2, the display panel 100 may include a thin film transistor (TFT), an insulating structure, a pixel electrode 145, and a display layer 160 disposed on a panel substrate 105.

The panel substrate 105 may be provided as a base substrate of the display panel 100. The panel substrate 105 may include a flexible resin material such as, for example, polyimide.

The thin film transistor may include an active layer 110, a gate electrode 120, a source electrode 132, and a drain electrode 134. The insulating structure may include a gate insulating film 115, an interlayer insulating film 125, and a via insulating film 140.

The active layer 110 is formed on the upper surface of the panel substrate 105 and may include polysilicon or an oxide semiconductor (for example, indium gallium zinc oxide (IGZO) or the like). The gate insulating layer 115 may be formed on the panel substrate 105 to cover the active layer 110.

The gate electrode 120 may be disposed on the gate insulating layer 115 and overlapped with the active layer 110. The gate electrode 120 may include a metal such as Al, Ti, Cu, W, Ta, or Ag.

An interlayer insulating film 125 covering the gate electrode 120 is formed on the gate insulating film 115 and then a source electrode 125 is formed through the interlayer insulating film 125 and the gate insulating film 115 to be in contact with the active layer 110 132 and the drain electrode 134 can be formed. The source electrode 132 and the drain electrode 134 may include a metal such as Al, Ti, Cu, W, Ta, or Ag.

A via insulating layer 140 covering the source electrode 132 and the drain electrode 134 may be formed on the interlayer insulating layer 125. The via insulating layer 140 may be formed using an organic insulating material such as an acrylic resin, a siloxane resin, or the like.

A pixel electrode 145 electrically connected to the drain electrode 134 may be formed on the via insulating layer 140. The pixel electrode 145 may include a via portion that contacts the drain electrode 134 through the via insulating layer 140. The pixel electrode 145 may include a metal such as Al, Ti, Cu, W, Ta, Ag, and / or a transparent conductive oxide (e.g., indium tin oxide (ITO)).

The pixel defining layer 150 may be formed on the via insulating layer 140 and the display layer 160 may be formed on the pixel electrode 145 exposed by the pixel defining layer 150. The display layer 160 may be formed of, for example, a liquid crystal layer included in an organic light emitting layer (EML) or an LCD device included in an OLED device.

The counter electrode 170 may be formed on the pixel defining layer 150 and the display layer 160. The counter electrode 170 may be provided as a common electrode, a reflective electrode, or a cathode of an image display apparatus.

The display panel 100 includes a plurality of pixels, and the thin film transistor and the pixel electrode 145 may be arranged for each pixel. The counter electrode 170 may be provided as a common electrode that continuously extends over a plurality of pixels.

An encapsulation layer 180 may be formed on the counter electrode 170. The encapsulation layer 180 may comprise an inorganic insulating material such as silicon oxide, silicon nitride, and / or an organic insulating material such as acrylic, siloxane, urethane, and the like.

The display panel 100 may further include a pixel circuit electrically connected to the thin film transistor. For example, the pixel circuit includes a data line, a scan line, a power supply line, and the like, and each pixel can be defined for each crossing region of the data line and the scan line.

As described above, the first neutral plane NP1 is formed inside the display panel 100 at a low temperature of -20 占 폚, so that when bending at a low temperature of -20 占 폚, cracks of the pixel circuit, , Damage such as breakage can be suppressed.

The thickness of the display panel 100 may be 80 to 400 탆.

3 is a schematic plan view showing a touch sensor of a flexible display device according to an embodiment of the present invention. For example, the touch sensor may be applied to the functional structure 200 in the form of a touch screen panel or a touch sensor film.

Referring to FIG. 3, the touch sensor may include a sensing electrode 210, a trace 220, and a pad 230 formed on a substrate 205.

The touch sensor may include a sensing area (A) and a peripheral area (B). The sensing electrode 210 is formed on the substrate 205 of the sensing area A and the trace 220 and the pad 230 may be formed on the substrate 205 of the peripheral area B.

The sensing electrode 210 may include a first sensing electrode 210a and a second sensing electrode 210b arranged in a first direction and a second direction which are parallel to the upper surface of the substrate 205 and cross each other at right angles, ).

The first sensing electrode 210a extends in the first direction, and a plurality of first sensing electrodes 210a may be formed along the second direction. The second sensing electrode 210b may extend in the second direction and may include a plurality of second sensing electrodes 210b along the first direction.

Each of the first and second sensing electrodes 210a and 210b may include a polygonal unit pattern and may include a connecting portion or a bridge electrode that connects neighboring unit patterns. The inside of the unit pattern may include a conductive pattern patterned in a mesh type.

The traces 220 may be branched from the sensing electrodes 210a and 210b and the ends of the traces 220 may be connected to the pads 230. [ The touch sensor may be connected to an external circuit such as a flexible printed circuit board (FPCB) through a pad 230.

As described above, the second neutral plane NP2 is formed inside the touch sensor at a low temperature of -20 占 폚. When the sensing electrode 210, the bridge electrode, and the trace 220 are bent at a low temperature of -20 占 폚, Cutting, cracking, and the like can be prevented.

4 is a graph showing a strain profile of a flexible display device according to an embodiment of the present invention.

Referring to FIG. 4, when the flexible display device is bent at a low temperature of -20 占 폚, the display panel 100, the functional structure 200, and the window 300, Can be formed.

As used herein, the term " neutral surface " means that when the flexible display device is bent, the compressive stress (denoted as "-" in FIG. 4) and the tensile stress (denoted as "+" Is defined. Accordingly, the strain can be converged to substantially zero on the neutral plane.

When the flexible display device is bent, a compressive force is exerted on the inner side bent and a tensile force is exerted on the outer side, thereby damaging the internal structure.

According to one embodiment of the present invention, when the flexible display device is bent at a low temperature of the order of -20 占 폚, since each of the optical member or the information transferring member included in the flexible display device includes a neutral surface, So that breakage, crack, and damage of the internal structure can be prevented. Therefore, the flexible or bendable range of the flexible display device can be extended at a low temperature of -20 占 폚, so that flexibility and mechanical reliability can be improved together.

4, strain separation is generated between the display panel 100 and the functional structure 200 by the first pressure-sensitive adhesive layer 50 so that the first neutral plane NP1 and the second neutral plane < RTI ID = 0.0 > NP2 may be formed in the display panel 100 and the functional structure 200, respectively.

Further, strain separation may be generated between the functional structure 200 and the window 300 by the second pressure-sensitive adhesive layer 90, and a third neutral plane NP3 may be formed in the window 300. [

In one embodiment of the present invention, the total thickness of the flexible display device may range from 200 to 1,000 mu m.

5 is a cross-sectional view schematically showing a flexible display device according to another embodiment of the present invention.

Referring to FIG. 5, the functional structure may include a touch sensor 200a and a polarizing layer 200b. Further, a third pressure sensitive adhesive layer 70 may be formed between the touch sensor 200a and the polarizing layer 200b.

The third pressure-sensitive adhesive layer 70 may have a tan δ of 0.8 to 1 at -20 ° C. Accordingly, flexural resistance and durability of the flexible display device including the third pressure-sensitive adhesive layer 70 can be improved.

The storage elastic modulus of the third pressure-sensitive adhesive layer 70 at -20 캜 may be 0.05 to 0.15 MPa. If the storage elastic modulus of the third pressure-sensitive adhesive layer 70 at -20 캜 is less than 0.05 MPa, durability may deteriorate, and if it exceeds 0.15 MPa, flexibility may be decreased.

The third pressure sensitive adhesive layer 70 may have a thickness of 5 to 30 탆.

The pressure-sensitive adhesive composition for forming the third pressure-sensitive adhesive layer (70) may be the same as the pressure-sensitive adhesive composition for forming the first and second pressure-sensitive adhesive layers (50, 90).

Strain separation between the touch sensor 200a and the polarizing layer 200b is promoted by the third pressure-sensitive adhesive layer 70 when the flexible display device is bent at a low temperature of -20 占 폚, A neutral plane may be formed in each of the layers 200b.

For example, a second neutral plane NP2 may be formed inside the touch sensor 200a, and a third neutral plane NP3 may be formed inside the polarizing layer 200b. The fourth neutral plane NP4 may be formed in the window 300 by strain separation through the second pressure-sensitive adhesive layer 90 as described above.

6 is a cross-sectional view schematically showing a flexible display device according to still another embodiment of the present invention.

Referring to FIG. 6, the flexible display device may further include a protective film 350 that is exposed to the viewer's side as an outermost layer, for example. For example, the protective film 350 may be laminated on the window 300.

In an embodiment of the present invention, the protective film 350 may be adhered on the upper surface of the window 300 through the fourth pressure-sensitive adhesive layer 80.

The fourth pressure-sensitive adhesive layer 80 may have a tan δ of 0.8 to 1 at -20 ° C, such as the first and second pressure-sensitive adhesive layers 50 and 90 described above. Accordingly, flexural resistance and durability of the flexible display device including the fourth pressure-sensitive adhesive layer (80) can be improved.

The storage elastic modulus of the fourth pressure-sensitive adhesive layer 80 at -20 캜 may be 0.05 to 0.15 MPa. If the storage elastic modulus of the fourth pressure-sensitive adhesive layer 80 at -20 캜 is less than 0.05 MPa, durability may deteriorate. If the fourth pressure-sensitive adhesive layer 80 exceeds 0.15 MPa, flex resistance may be decreased.

The thickness of the fourth pressure-sensitive adhesive layer 80 may be 5 to 30 탆.

The pressure-sensitive adhesive composition for forming the fourth pressure-sensitive adhesive layer (80) may be the same as the pressure-sensitive adhesive composition for forming the first and second pressure-sensitive adhesive layers (50, 90).

The protective film 350 includes a flexible resin film, and may include, for example, a polyimide film. The protective film 350 may have a thickness of 20 to 50 mu m.

A neutral plane (e.g., a fourth neutral plane NP4) may be formed inside the protective film 350 by the fourth pressure-sensitive adhesive layer 80 when the flexible display device is bent at a low temperature of -20 占 폚 have. Therefore, the durability and the crack resistance against the external impact of the protective film 350 are further improved, and the flexible display device can be protected.

Hereinafter, the present invention will be described more specifically with reference to Examples, Comparative Examples and Experimental Examples. It should be apparent to those skilled in the art that these examples, comparative examples and experimental examples are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

Manufacturing example  1: Silicone urethane ( Meta ) Acrylate  Manufacture of resin

Polyisocyanate, polysilicon having a hydroxyl group at both terminals and dibutyltin dilaurate as a catalyst were charged into a 2 L three-necked flask equipped with an electronic stirrer, a heating mantle, a cooling tube and a temperature controller under the following composition (unit: parts by weight) And the reaction temperature was raised to 70 DEG C while stirring and the reaction was maintained for 4 hours. Thereafter, (meth) acrylate having a hydroxy group and methoxyhydroquinone as a polymerization inhibitor were dropped and reacted in the composition shown in Table 1, and the reaction was maintained for 2 hours after completion of the addition. When the characteristic peak of NCO of 2260 cm < ^-1 > peak on FT-IR disappeared, the reaction was terminated to obtain a silicone urethane (meth) acrylate resin.

Production Example 1 Polyisocyanate ¹⁾ 524 Polysilicon having hydroxy groups at both ends ²⁾ 933 Dibutyl tin dilaurate 0.4 Methoxyhydroquinone 0.3 (Meth) acrylate having a hydroxy group ³⁾ 232

1) 4,4'-methylenedicyclohexyl diisocyanate (molecular weight 262)

2) X-22-160AS (Shin-Etsu, molecular weight 933)

3) 2-hydroxyethyl acrylate (molecular weight: 116)

Manufacturing example  2: ( Meta ) Acrylate  Manufacture of syrups

Ethylhexyl acrylate (2-EHA) monomer was added to a 1 L reactor equipped with a cooling device to regulate the temperature of the reflux of nitrogen gas, and nitrogen gas was purged for 1 hour to remove oxygen, 80 < 0 > C. 0.5 parts by weight of 1-hydroxycyclohexyl phenyl ketone as a photoinitiator was added to 100 parts by weight of the monomer. 40 parts by weight of a (meta) acrylate syrup, that is, a (meth) acrylate polymer having a solid content of 40 wt% and a 2-ethylhexyl acrylate (2-EHA) monomer 60 By weight was prepared. And then used in the preparation of the pressure-sensitive adhesive composition in the form of the (meth) acrylate syrup.

Manufacturing example  3: ( Meta ) Acrylate  Manufacture of syrups

N-butyl acrylate (BA) monomer was added to a 1 L reactor equipped with a cooling device to regulate the temperature of the reflux of nitrogen gas, and nitrogen gas was purged for 1 hour to remove oxygen, Respectively. 0.5 parts by weight of 1-hydroxycyclohexyl phenyl ketone as a photoinitiator was added to 100 parts by weight of the monomer. (Meth) acrylate polymer having a solid content of 40% by weight, that is, a mixture of 40 parts by weight of a (meth) acrylate polymer and 60 parts by weight of an n-butyl acrylate (BA) monomer by irradiation with a UV lamp . And then used in the preparation of the pressure-sensitive adhesive composition in the form of the (meth) acrylate syrup.

Manufacturing example  4: ( Meta ) Acrylate  Manufacture of syrups

The tetrahydrofurfuryl acrylate (THFA) monomer was added to a 1 L reactor equipped with a cooling device to regulate the temperature of the reflux of the nitrogen gas, and nitrogen gas was purged for 1 hour to remove oxygen, Respectively. 0.5 parts by weight of 1-hydroxycyclohexyl phenyl ketone as a photoinitiator was added to 100 parts by weight of the monomer. (Meth) acrylate polymer having a solid content of 40% by weight, that is, (meth) acrylate polymer and 60 parts by weight of tetrahydrofurfuryl acrylate (THFA) monomer were irradiated with a UV lamp (10 mW) A mixture was prepared. And then used in the preparation of the pressure-sensitive adhesive composition in the form of the (meth) acrylate syrup.

Example  1 to 5 and Comparative Example  1 to 4: Flexible  Manufacture of display devices

A pressure-sensitive adhesive composition was prepared by mixing the respective components in the composition shown in Table 2 (unit: wt%).

Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 The silicone urethane (meth) acrylate resin of Production Example 1 40 50 30 - - 70 75 5 - The (meth) acrylate polymer of Preparation Example 2 - - - 28 16 - - - - The (meth) acrylate polymer of Preparation Example 3 - - - 8 16 - - - The (meth) acrylate polymer of Preparation Example 4 - - - - - - - - 38.8 Photoinitiator ¹⁾ 3 3 3 3 3 3 3 3 3 Lauryl acrylate 30 25 50 7 - - 12 45 - Isodecyl acrylate 27 22 17 - 17 27 10 47 - 2-ethylhexyl acrylate 42 24 n-butyl acrylate 12 24 Tetrahydrofurfuryl acrylate 58.2

1) 1-Hydroxycyclohexyl phenyl ketone

Each of the pressure-sensitive adhesive compositions prepared above was coated on a release film coated with a silicone release agent to a thickness of 25 mu m, a release film was bonded thereon, and irradiated with light of 500 mJ / cm < ² > To prepare respective pressure-sensitive adhesive sheets.

A pixel electrode, an organic light emitting layer (display layer), an opposite electrode, and an encapsulation layer were formed in this order on a panel substrate (polyimide, thickness 30 탆) having a width of 10 cm and a length of 10 cm, A display panel was manufactured.

Each of the pressure sensitive adhesive sheets prepared above was laminated on the display panel to form a first pressure sensitive adhesive layer.

Next, a polarizing plate including a touch sensor (including an ITO electrode pattern layer formed on a TAC film) and a polarizing plate including a stretched polarizer (a PVA polarizer film obtained by bonding a TAC protective film to both surfaces thereof) Were laminated to form a functional structure. The total thickness of the functional structure was 100 탆.

Each of the pressure sensitive adhesive sheets prepared above was laminated on the functional structure to form a second pressure sensitive adhesive layer.

A window substrate (polyimide, thickness: 70 m) was further laminated on the second pressure-sensitive adhesive layer to prepare a flexible display device.

Experimental Example  One: Flexible  Evaluation of physical properties of display device

The physical properties of the flexible display devices manufactured in Examples and Comparative Examples were measured by the following methods, and the results are shown in Table 3 below.

(1) Tangent delta and storage modulus ( G ' )

Tangent delta and storage elastic modulus (G ') were measured at -20 ° C using a viscoelasticity measuring device (MCR-301, Anton Paar). Specifically, the sample of the pressure-sensitive adhesive sheet prepared in the above-mentioned Examples and Comparative Examples was 30 mm in length and 30 mm in width. After bonding the measurement sample to the glass plate, the pressure- %. ≪ / RTI > The tangent delta is a value calculated by calculating G "(loss elastic modulus) / G '(storage elastic modulus).

(2) Flexibility

Flexibility was evaluated using a folding tester (DLDMLH-FS, YUASA). The flexible display device manufactured in Examples and Comparative Examples was cut into a size of 100 mm x 10 mm to prepare samples. When the samples were mounted on the tester, the samples were reversely bonded to each other so that the curved tensile force was applied to the organic light- , And another sample was subjected to flexural compressive stress to the organic light emitting layer. After the sample was mounted, the evaluation was carried out at a speed of 3R and 30 times / minute for 200,000 times.

The flexure of the sample was then observed with an optical microscope (ECLIPSE LV100ND, manufactured by NIKON), and the flexural resistance was evaluated based on the following criteria.

<Evaluation Criteria>

◎: No crack

○: No cracks, no more than 5 cracks, and no full length in the width direction

?: No less than 5 cracks and no more than 10 cracks, and no growth in the entire length in the width direction

X: 11 or more cracks, cracks exist in the entire width direction

(3) Mandrell

In order to evaluate the bending characteristics, the flexible display device manufactured in the above-mentioned Examples and Comparative Examples was cut into a size of 1 cm x 10 cm to prepare a sample, and the sample was placed on a steel bar of each diameter (2? To 20?) The window substrate is placed downward and bent by hand to indicate the smallest diameter that does not cause cracks or streaks on the surface.

(4) Heat resistance durability

The heat resistance durability was evaluated by observing whether bubbles or peeling occurred after allowing the flexible display device manufactured in the above Examples and Comparative Examples to stand at a temperature of 100 ° C for 500 hours.

<Evaluation Criteria>

Ⓞ: No bubble or peeling

○: Bubbles or peeling <5

?: 5 pieces? Bubbles or peeling <10 pieces

X: 10 pieces &lt; bubble &

tan δ G '(MPa) Flexibility Mandrell Heat resistance durability Example 1 0.9 0.1 ◎ 3φ ◎ Example 2 0.8 0.14 ◎ 4φ ◎ Example 3 One 0.07 ◎ 2φ ◎ Example 4 0.9 0.09 ◎ 3φ ◎ Example 5 0.8 0.13 ◎ 3φ ◎ Comparative Example 1 0.6 0.7 × 11φ × Comparative Example 2 0.4 0.8 × 14φ × Comparative Example 3 2 0.01 × 10φ × Comparative Example 4 0.3 1.1 × 20φ ×

As shown in Table 3, the flexible display devices of Examples 1 to 5 including the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer having a tan δ of 0.8 to 1 at -20 ° C were confirmed to have excellent bending resistance and durability . On the other hand, the flexible display devices of Comparative Examples 1 to 4 including the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer in which the tan δ at -20 ° C is out of the range of 0.8 to 1 can be confirmed to have poor flexing resistance and durability.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Do. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Accordingly, the actual scope of the invention is defined by the appended claims and their equivalents.

50: first pressure-sensitive adhesive layer 70: third pressure-sensitive adhesive layer
80: fourth pressure sensitive adhesive layer 90: second pressure sensitive adhesive layer
100: display panel 105: panel substrate
110: active layer 115: gate insulating film
120: gate electrode 125: interlayer insulating film
132: source electrode 134: drain electrode
140: via insulating film 145: pixel electrode
150: pixel defining layer 160: display layer
170: counter electrode 180: encapsulation layer
200: Functional structure 200a: Touch sensor
200b: polarizing layer 205: substrate
210: sensing electrode 220: trace
230: Pad 300: Window
350: protective film

Claims (13)

A display panel;
A functional structure disposed on the display panel;
A window disposed on the functional structure;
A first pressure-sensitive adhesive layer formed between the display panel and the functional structure; And
And a second pressure-sensitive adhesive layer formed between the functional structure and the window,
Wherein the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer have a tan δ of 0.8 to 1 at -20 ° C. and a storage modulus of 0.05 to 0.15 MPa at -20 ° C. The flexible display device of claim 1, wherein the display panel comprises an organic light emitting diode (OLED) panel or a liquid crystal display (LCD) panel. The flexible display device according to claim 1, wherein the functional structure includes at least one of a touch sensor, a polarizing layer, and a retardation layer. The flexible display device according to claim 1, wherein the window comprises a base layer and a hard coating layer formed on at least one side of the base layer. delete The flexible display device according to claim 1, wherein the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer are formed from a pressure-sensitive adhesive composition comprising a (meth) acrylate resin, a (meth) acrylate ester monomer and a photoinitiator. The flexible display device according to claim 6, wherein the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer are formed from a pressure-sensitive adhesive composition comprising an aliphatic (meth) acrylate polymer, a (meth) acrylate ester monomer and a photoinitiator. The flexible display device according to claim 6, wherein the first pressure-sensitive adhesive layer and the second pressure-sensitive adhesive layer are formed from a pressure-sensitive adhesive composition comprising a silicone urethane (meth) acrylate resin, a (meth) acrylate ester monomer and a photoinitiator. The flexible display device according to claim 7 or 8, wherein the (meth) acrylate ester monomer comprises a C ₁₀ -C ₂₀ alkyl (meth) acrylate. The flexible display device according to claim 7 or 8, wherein the (meth) acrylate ester monomer is contained in an amount of 45 to 70% by weight based on 100% by weight of the total adhesive composition. The method of claim 1, wherein the functional structure comprises a touch sensor and a polarizing layer,
And a third pressure-sensitive adhesive layer formed between the touch sensor and the polarizing layer,
Wherein the third pressure-sensitive adhesive layer has Tan 隆 of 0.8 to 1 at -20 캜. The flexible display device according to claim 1, further comprising a protective film disposed on the window. The flexible display device according to claim 12, further comprising a fourth pressure-sensitive adhesive layer formed between the window and the protective film, wherein the fourth pressure-sensitive adhesive layer has a tan δ of 0.8 to 1 at -20 ° C.

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