KR102442733B1 - Flexible window film and display apparatus comprising the same - Google Patents

Abstract

A flexible window film comprising a base layer, a hard coating layer formed on one surface of the base layer, and a first layer, a second layer and an adhesive layer sequentially formed from the base layer on the other surface of the base layer, the first layer comprising: A gradation layer, the second layer has a thickness of 0.5 μm to 30 μm, and the flexible window film has a refractive index relationship of Equation 1, and a flexible window film and a display device including the same are provided.

Description

Flexible window film and display device including same

The present invention relates to a flexible window film and a display device including the same.

Recently, interest in flexible display devices is increasing. In response to this interest, a window film mounted on a flexible display device is also required to have flexibility and/or flexibility. In one example, the flexible window film may include a base layer and a hard coating layer formed of a siloxane-based resin on one surface of the base layer.

The window film should additionally include an adhesive layer as well as the base layer and the hard coating layer formed on one surface of the base layer. If the base layer is not adhesive, the adhesive layer is essentially required in order to adhere the window film to the adherend. As described above, since the window film is laminated with several layers of an adhesive layer, a base layer, and a hard coating layer, interference mura or rainbow mura is inevitably generated due to a difference in refractive index between each layer. In particular, the window film is disposed at the outermost portion of the display device. Accordingly, the image formed through the display device is ultimately viewed through the window film. If the occurrence of interference mura or rainbow mura cannot be controlled in the window film, the final image may have poor screen quality. By controlling optical elements other than the window film, generation of interference mura or rainbow mura can be suppressed. However, since it only indirectly affects interference mura or rainbow mura generated in the window film, there is a limit to improvement of interference mura or rainbow mura.

Background art of the present invention is disclosed in Japanese Patent Application Laid-Open No. 2007-176542.

An object of the present invention is to provide a flexible window film capable of suppressing interference mura and/or rainbow mura.

Another object of the present invention is to provide a flexible window film having excellent adhesion between layers, particularly between a substrate layer, a first layer, and a second layer.

Another object of the present invention is to provide a flexible window film having excellent flexibility, flexibility, hardness and scratch resistance.

Another object of the present invention is to provide a flexible window film having excellent optical transparency.

The flexible window film of the present invention includes a base layer, a hard coat layer formed on one surface of the base layer, and a first layer, a second layer and an adhesive layer sequentially formed from the base layer on the other surface of the base layer, The first layer is a gradation layer, the second layer has a thickness of 0.5 μm to 30 μm, and the flexible window film may have a refractive index relationship of Equation 1:

<Equation 1>

The refractive index of the adhesive layer ≤ the refractive index of the second layer < the refractive index of the base layer.

The display device of the present invention may include the flexible window film of the present invention.

The present invention provides a flexible window film capable of suppressing interference mura and/or rainbow mura.

The present invention provides a flexible window film having excellent adhesion between layers, in particular, adhesion between a base layer, a first layer, and a second layer.

The present invention provides a flexible window film having excellent flexibility, flexibility, hardness and scratch resistance.

The present invention provides a flexible window film having excellent optical transparency.

1 is a cross-sectional view of a flexible window film according to an embodiment of the present invention.
2 is a cross-sectional view of a flexible window film according to another embodiment of the present invention.
3 is a cross-sectional view of a flexible display device according to an embodiment of the present invention.
4 is a cross-sectional view of a flexible display device according to another embodiment of the present invention.
5 is a cross-sectional view of a flexible display device according to another embodiment of the present invention.

With reference to the accompanying drawings, the embodiments will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar components throughout the specification. In the drawings, the length, thickness, etc. of each component are shown for explaining the present invention, and the present invention is not limited to the length, thickness, etc. described in the drawings.

In this specification, "upper" and "lower" are defined based on the drawings, and depending on the perspective of the city, "upper" may be changed to "lower" and "lower" to "upper", and "on" or What is referred to as “on” may include cases in which other structures are interposed in the middle as well as immediately above. On the other hand, "directly on" or "directly on" means that no other structure is interposed therebetween.

As used herein, “(meth)acryl” may mean acryl and/or methacrylic.

The inventor of the present invention relates to a flexible window film (hereinafter also referred to as a 'window film') in which a hard coating layer, a base layer, and an adhesive layer are sequentially stacked, a first layer and a second layer between the base layer and the adhesive layer is formed, the first layer is a gradation layer, and the second layer has a thickness of 0.5 μm to 30 μm and satisfies the refractive index relationship of Equation 1 below, thereby preventing interference of the window film due to the difference in refractive index between the base layer and the adhesive layer. Alternatively, it was confirmed that the occurrence of rainbow mura could be significantly reduced and flexibility and hardness could be excellent.

In the window film of the present invention, the first layer, the second layer, and the adhesive layer are sequentially formed from the base layer.

The "gradient layer" means that the refractive index of the first layer is not the same depending on the thickness and is a layer in which the refractive index gradually increases or adhesively decreases according to the thickness. In one embodiment, the "gradient layer" means that the first layer is a layer in which the refractive index adhesively decreases from the interface with the base layer toward the interface with the second layer.

Since the window film is optically transparent, it can be used in a transparent display device. The window film may have a light transmittance of 80% or more, specifically 85% to 100% in a visible light region, specifically, a wavelength of 400 nm to 800 nm. It can be used as a window film in the above range.

Since the window film is optically transparent, it can be used in a transparent display device. The window film may have a haze of 1% or less, specifically 0% to 1%, in a visible light region, specifically, a wavelength of 400 nm to 800 nm. It can be used as a window film in the above range.

The window film may have a pencil hardness of 3H or more, and a radius of curvature of 5 mm or less in both the compression direction and the tensile direction. In the above range, it can be used as a window film having good hardness and flexibility. The window film may have a pencil hardness of 3H to 9H, and a radius of curvature of 0mm to 2mm, for example, 0.1mm to 2mm. In the above range, it may be used as a flexible window film.

The window film may have a thickness of 30 μm to 200 μm, for example, 30 μm to 100 μm. It can be used as a flexible window film in the above range.

Hereinafter, a window film according to an embodiment of the present invention will be described with reference to FIG. 1 .

Referring to FIG. 1 , the window film is a base layer 110 , a hard coating layer 120 formed on one surface of the base layer 110 , and a first sequentially formed from the base layer 110 on the other surface of the base layer 110 . It may include a layer 130 , a second layer 140 , and an adhesive layer 150 .

base layer

The base layer 110 may support the window film to increase mechanical strength of the window film.

The base layer 110 may be formed of an optically transparent and flexible resin. For example, the resin is a polyester resin including polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, polycarbonate resin, polyimide resin, polyimide amide resin, polystyrene resin, polymethyl meta It may include at least one of poly(meth)acrylate resins including acrylates and the like, and cycloolefin polymer resins. The resin may be included in the base layer 110 alone or in a mixture of two or more. Preferably, the base layer 110 may include a film formed of a polyimide resin.

The base layer 110 may have a refractive index of 1.4 to 1.9, for example, 1.5 to 1.8.

The base layer 110 may have a thickness of 10 μm to 200 μm, specifically 20 μm to 150 μm, and more specifically 30 μm to 100 μm. It can be used for the window film in the above range.

As shown in FIG. 1 , the base layer 110 may be a single-layer film. However, a case in which the base layer is a laminate in which two or more resin films of the same or different types are laminated on each other by an adhesive layer, an adhesive layer, or an adhesive layer may also be included in the scope of the present invention.

Although not shown in FIG. 1 , on one or both surfaces of the base layer 110 , a hard coating layer or a primer layer facilitating the formation of the first layer or a functional coating layer for providing an additional function may be additionally formed.

Preferably, the base layer 110 may be a single-layer film formed of the above-described resin without a primer layer or an easily adhesive layer on one or both sides. Even without a primer layer or an easily adhesive layer, the adhesion between the base layer, the first layer, and the second layer can be increased by the first layer to be described in detail below. The "primer layer" and "easy-adhesive layer" may refer to a layer for easy adhesion between a film and an adhesive or a film and a film.

hard coating layer

The hard coating layer 120 is formed on one surface of the base layer 110 .

The hard coating layer 120 is formed directly on one surface of the base layer 110, so that the thickness of the window film can be reduced, and even in repeated folding, peeling between the hard coating layer 120 and the base layer 110 can be prevented. . The "directly formed" means that the hard coating layer 120 is directly laminated on the base layer 110 without an adhesive layer, an adhesive layer, or an adhesive layer. As will be described in detail below, the hard coating layer 120 may be prepared by directly coating and curing the composition for the hard coating layer on one surface of the base layer 110 .

The hard coating layer 120 may have a thickness of 1 μm to 100 μm, specifically 1 μm to 80 μm, and 1 μm to 10 μm. Within the above range, it may be used for a flexible window film.

The hard coating layer 120 may have a refractive index of 1.4 to 1.8, for example, 1.45 to 1.6.

The hard coating layer 120 may be formed of a composition for a hard coating layer including at least one of a (meth)acrylic resin and a siloxane resin. The composition for the hard coating layer may further include at least one of a crosslinking agent and an initiator. Preferably, the composition for the hard coating layer may include a (meth)acrylic resin and an initiator without a crosslinking agent.

In one embodiment, the hard coating layer may include a (meth)acrylic resin and an initiator without a crosslinking agent.

The (meth)acrylic resin is a (meth)acrylic monomer alone; Alternatively, it may include a (meth)acrylic resin formed by polymerization between a (meth)acrylic monomer and a (meth)acrylic monomer and a copolymerizable comonomer. The (meth)acrylic monomer may include a conventional monomer known to those skilled in the art. The comonomer may include a common monomer copolymerizable with a (meth)acrylic monomer, known to those skilled in the art.

In one embodiment, the (meth)acrylic resin may include a resin having a (meth)acrylate group at the terminal. Preferably, the (meth)acrylic resin may include a dendritic aliphatic compound having a (meth)acrylate group at the terminal. By including the resin, it can have many (meth)acrylate groups at the molecular terminal, and thus the reactivity can be increased.

(meth)acrylic resin may be used individually by 1 type, and may be used in combination of 2 or more type. Among (meth)acrylic resins, more than one of a dendrimer-type resin and a hyper-branched-type resin can be included. The dendrimer-type resin is a highly branched resin with a high regularity, and the hyper-branched resin is a branched resin with a relatively low regularity than the dendrimer-type resin. The hyper-branched resin may have excellent solubility in solvents due to its low viscosity compared to linear resins.

As the dendrimer-type resin, a multi-branched (dendrimer-type) polyester (meth)acrylate having a (meth)acrylate group at the terminal may be used, but is not limited thereto. As the hyper-branched resin, a multi-branched (dendrimer-type) poly(meth)acrylate having a (meth)acrylate group at the terminal may be used, but is not limited thereto. In one embodiment, a multi-branched (dipentaerythritol hexaacrylate-linked) poly(meth)acrylate having dipentaerythritol as a core and a (meth)acrylate group at the terminal may be used, but is not limited thereto. .

The (meth)acrylic resin may have a weight average molecular weight of 5,000 to 30,000, for example, 10,000 to 25,000. Within the above range, the hardness and scratch resistance of the window film may be excellent. The initiator may comprise conventional photoinitiators known to those skilled in the art as photo-radical initiators. For example, a hydroxyketone-based, phosphine oxide-based, benzoin-based or aminoketone-based photoradical initiator may be used. The initiator may be included in an amount of 1 to 10 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of the (meth)acrylic resin. In the above range, there may be an effect of not reducing optical properties or physical properties while curing is performed properly.

In another embodiment, the hard coating layer may include a (meth)acrylic resin, a crosslinking agent, and an initiator.

The crosslinking agent cross-links with the (meth)acrylic resin, and may include a (meth)acrylate compound having one or more (meth)acrylate groups, preferably two or more, more preferably 2 to 20. have.

In one embodiment, the crosslinking agent may include a polyfunctional (meth)acrylate. The polyfunctional (meth)acrylate may be included in the composition for the hard coat layer to further improve the hardness and flexibility of the hard coat layer.

The crosslinking agent may be included in an amount of 5 to 150 parts by weight, preferably 5 to 100 parts by weight, based on 100 parts by weight of the (meth)acrylic resin. Within the above range, there may be an effect of improving high hardness and bending flexibility.

The composition for the hard coating layer may further include an additive. Additives may provide additional functionality to the window film. The additive may include an additive that is conventionally added to the window film. Specifically, the additive may include at least one of a leveling agent, a UV absorber, a reaction inhibitor, an adhesion enhancer, a thixotropic agent, a conductivity imparting agent, a color adjuster, a stabilizer, an antistatic agent, and an antioxidant, but is limited thereto doesn't happen The additive may be included in an amount of 0.01 parts by weight to 5 parts by weight, specifically 0.1 parts by weight to 3 parts by weight, based on 100 parts by weight of the (meth)acrylic resin. In the above range, it is possible to improve the hardness and flexibility of the window film and implement the additive effect.

The composition for the hard coating layer may further include a solvent to facilitate coatability, coatability, or processability. The solvent may include at least one of methyl ethyl ketone, methyl isobutyl ketone, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate, but is not limited thereto. The solvent may be included as the balance in the composition for the hard coating layer.

The hard coating layer 120 may be formed by coating and curing the composition for the hard coating layer on one surface of the base layer 110 . A method of coating the composition for the hard coating layer on the base layer 110 is not particularly limited. For example, it may be bar coating, spin coating, dip coating, roll coating, flow coating, die coating, and the like. Curing may include at least one of photocuring and thermal curing. Photocuring may include irradiating with a light quantity of 10mJ/cm ² to 1,000mJ/cm ² at a wavelength of 400 nm or less.

adhesive layer

The adhesive layer 150 may be formed on the lowermost surface of the window film to adhere the window film to an adherend, for example, an optical element such as a polarizing plate, a display panel, or a touch screen panel.

The adhesive layer 150 may have a refractive index of 1.3 to 1.6, for example, 1.45 to 1.55.

The adhesive layer 150 may have a thickness of 5 μm to 100 μm. In the above range, it is possible to sufficiently adhere an optical element such as a window film and a polarizing plate.

The adhesive layer 150 may be formed of a composition for an adhesive layer. Specifically, the pressure-sensitive adhesive layer 150 is a (meth) acrylic resin, a urethane resin, a silicone resin, and at least one adhesive resin of an epoxy resin, and a curing agent, a photoinitiator, a composition for an adhesive layer further comprising at least one of a silane coupling agent can be formed with

The (meth)acrylic resin is a (meth)acrylic copolymer having an alkyl group, a hydroxyl group, an aromatic group, a carboxylic acid group, an alicyclic group, a heteroalicyclic group, and the like, and may include a conventional (meth)acrylic copolymer. Specifically, a (meth)acrylic monomer having a C1 to C10 unsubstituted alkyl group, a (meth)acrylic monomer having a C1 to C10 alkyl group having one or more hydroxyl groups, and a C6 to C20 aromatic group (meth)acrylic monomer , a (meth)acrylic monomer having a carboxylic acid group, a (meth)acrylic monomer having an alicyclic group of C3 to C20, nitrogen (N), oxygen (O), sulfur (S) having at least one of C3 to C10 heteroalicyclic It may be formed of a monomer mixture comprising at least one of (meth)acrylic monomers having a group.

The curing agent is a polyfunctional (meth)acrylate, and may be a bifunctional (meth)acrylate such as hexanediol diacrylate; trifunctional (meth)acrylate of trimethylolpropane tri(meth)acrylate; tetrafunctional (meth)acrylates such as pentaerythritol tetra(meth)acrylate; 5-functional (meth)acrylates, such as dipentaerythritol penta (meth)acrylate; It may include, but is not limited to, a hexa-functional (meth)acrylate such as dipentaerythritol hexa(meth)acrylate.

The photoinitiator may include the above-mentioned photoradical initiator as a conventional photoinitiator.

The silane coupling agent may include a silane coupling agent having an epoxy group, such as 3-glycidoxypropyltrimethoxysilane.

The composition for an adhesive layer may include 100 parts by weight of a (meth)acrylic resin, 0.1 parts by weight to 30 parts by weight of a curing agent, 0.1 parts by weight to 10 parts by weight of a photoinitiator, and 0.1 parts by weight to 20 parts by weight of a silane coupling agent. Within the above range, the flexible window film may be well attached to the display unit, the touch screen panel or the polarizing plate.

2nd floor

The second layer 140 is formed between the base layer 110 and the adhesive layer 150 . Since the window film has the refractive index relationship of Equation 1 below, generation of interference mura and/or rainbow mura due to a difference in refractive index between the base layer 110 and the adhesive layer 150 may be suppressed to some extent.

<Equation 1>

Refractive index of adhesive layer ≤ Refractive index of second layer < Refractive index of base layer

In one embodiment, the second layer 140 may have a refractive index of 1.4 to 1.6, for example, 1.45 to 1.6. In the above range, it may be easy to control the refractive index compared to the refractive index between the base layer and the adhesive layer, so that it may be easy to suppress the occurrence of interference mura and/or rainbow mura.

The second layer 140 may have a thickness of 0.5 μm to 30 μm. In the above range, it is possible to suppress the occurrence of interference mura and/or rainbow mura when forming a laminate of the base layer, the first layer, the second layer, and the adhesive layer, and the base layer, the first layer, the second layer, and the adhesion. By increasing the adhesion between the layers, there may be no gap between the layers even when the window film is repeatedly folded. Preferably, the second layer 140 may have a thickness of 0.5 μm to 10 μm, more preferably 0.5 μm to 5 μm.

The second layer 140 may be formed of a composition for the second layer that can secure the refractive index relationship of Equation 1 or the refractive index range described above.

For example, the second layer may be formed of a (meth)acrylate-based, urethane-based, imide-based, amide-based, imide-amide-based, imide-urethane-based or ester-based composition. The composition may include at least one of a resin, an oligomer, and a monomer.

In one embodiment, the composition for the second layer may include urethane (meth)acrylate including aliphatic urethane (meth)acrylate, aromatic urethane (meth)acrylate, and alicyclic urethane (meth)acrylate; bisphenol epoxy (meth)acrylates including bisphenol A epoxy (meth)acrylate, bisphenol S epoxy (meth)acrylate, bisphenol F epoxy (meth)acrylate, and the like; 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, neopentylglycol adipate di (meth)acrylate, dicyclopentanyl di(meth)acrylate, caprolactone-modified dicyclopentenyl di(meth)acrylate, ethylene oxide-modified di(meth)acrylate, di(meth)acryloxyethyl isocy Anurate, allylated cyclohexyl di(meth)acrylate, tricyclodecanedimethanol (meth)acrylate, dimethylol dicyclopentanedi(meth)acrylate, ethylene oxide-modified hexahydrophthalic acid di(meth)acrylate , tricyclodecane dimethanol (meth) acrylate, neopentyl glycol modified trimethylpropane di (meth) acrylate, adamantane di (meth) acrylate or 9,9-bis [4- (2-acryl) bifunctional (meth)acrylates such as royloxyethoxy)phenyl]fluorene; Trimethylolpropane tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, propionic acid modified dipentaerythritol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, propylene oxide trifunctional (meth)acrylates such as modified trimethylolpropane tri(meth)acrylate, trifunctional urethane (meth)acrylate, or tris(meth)acryloxyethyl isocyanurate; tetrafunctional (meth)acrylates such as diglycerin tetra(meth)acrylate or pentaerythritol tetra(meth)acrylate; 5-functional (meth)acrylates, such as dipentaerythritol penta (meth)acrylate; and dipentaerythritol hexa(meth)acrylate, caprolactone-modified dipentaerythritol hexa(meth)acrylate or urethane (meth)acrylate (ex. isocyanate monomer and trimethylolpropane tri(meth)acrylate) It may include one or more types of hexafunctional (meth)acrylates such as reactants.

For example, the composition for the second layer may include at least one of monofunctional to hexafunctional (meth)acrylate, aliphatic urethane acrylate, and epoxy acrylate.

The resin, oligomer, and monomer for the composition for the second layer may be synthesized by methods commonly known to those skilled in the art, or commercially available products may be used. For example, one or more of PETIA, CN8885, CN104, and EBECRYL 5902 may be used, but is not limited thereto.

The composition for the second layer may further include the above-described crosslinking agent, initiator, additive, and the like as long as it does not affect the refractive index relationship or refractive index range of Equation 1 above.

The composition for the second layer may further include a solvent in addition to at least one of a (meth)acrylate-based resin, a (meth)acrylate-based oligomer, and a monofunctional to hexafunctional (meth)acrylate-based monomer.

The solvent may facilitate the application of the composition for the second layer so that the surface of the second layer is formed smoothly. In addition, as described in detail below, the first layer 130 is formed by slowly eroding the base layer 110 by the solvent included in the composition for the second layer when the composition for the second layer is applied to the base layer 110 . Therefore, the solvent contained in the composition for the second layer can erode the base layer 110 to form the first layer, thereby forming a gradation layer capable of securing the refractive index of the following Equation 2 described in detail below, and at the same time It should be selected so as to be able to form a second layer having the above thickness range.

In one embodiment, when the base layer is a polyimide resin film, the solvent may include at least one of methyl ethyl ketone (MEK), dimethyl acetamide (DMAC), methyl pyrrolidone (NMP), and gamma butyrolactone. can A composition containing a solvent other than the above-mentioned solvent is difficult to erode the polyimide resin film, or even if it erodes, the refractive index of the following formula 2 cannot be secured or a gradation layer cannot be formed.

In one embodiment, the second layer may be a non-adhesive layer having no tackiness.

1st floor

The first layer 130 is formed between the base layer 110 and the second layer 140 . The first layer 130 is directly formed on the base layer 110 and the second layer 140 , respectively. The "directly formed" means that no other adhesive layer, adhesive layer or adhesive layer is formed between the first layer 130 and the base layer 110 and between the first layer 130 and the second layer 140 . means

The first layer 130 is a gradation layer. The first layer 130 is formed as a gradation layer between the base layer 110 and the second layer 140, so that the interference mura or rainbow mura improvement effect by only adjusting the refractive index of the base layer and the second layer is compared to the interference mura or rainbow The effect of improving mura can be significantly increased.

The refractive index of the first layer 130 is not the same depending on the thickness from the interface with the base layer 110 to the interface with the second layer 140, and the refractive index may gradually increase or decrease depending on the thickness. .

In one embodiment, when the base layer 110 has a higher refractive index than the second layer 140 , the first layer 130 increases from the interface with the base layer 110 to the interface with the second layer 140 . The refractive index may decrease with thickness.

In another embodiment, when the base layer 110 has a lower refractive index compared to the second layer 140 , the first layer 130 goes from the interface with the base layer 110 to the interface with the second layer 140 . The refractive index may increase with thickness.

The first layer 130 may have a refractive index of 1.4 to 1.8, for example, 1.45 to 1.7. In the above range, it is easy to control the refractive index between the base layer, the second layer, and the adhesive layer, thereby suppressing the occurrence of interference mura or rainbow mura.

The first layer 130 may include at least a gradation region having a refractive index relationship of the following Equation 2 between the base layer 110 and the second layer 140 in the thickness direction: a window by securing the refractive index relationship of the following Equation 2 The film can improve interference mura or rainbow mura.

<Equation 2>

The refractive index of the second layer < the refractive index of the gradation region of the first layer < the refractive index of the base layer.

In one embodiment, the gradation area may be a part of the first layer or may be the same as the first layer.

The first layer 130 may have a thickness of 0.01 μm to 1 μm. In the above range, it is possible to suppress the occurrence of interference mura and/or rainbow mura when forming a laminate of the base layer, the first layer, the second layer, and the adhesive layer, and the base layer, the first layer, the second layer, and the adhesion. By increasing the adhesion between the layers, there may be no gap between the layers even when the window film is repeatedly folded. Preferably, the first layer 130 may have a thickness of 0.1 μm to 0.5 μm.

The first layer 130 may be formed from the composition for the second layer forming the second layer 140 and the base layer. The first layer 130 may be formed by dissolving and/or eroding one surface of the base layer with a specific solvent included in the composition for the second layer when the composition for the second layer is applied to the base layer 110 . Accordingly, the first layer 130 may contain the same resin as that of the base layer 110 , and the first layer 130 and the base layer 110 may be integrally formed. The “integrally formed” means that the first layer 130 and the base layer 110 are formed as a single layer without a distinction between the layers and contain the same resin. Therefore, even if a primer layer or an easily adhesive layer is not formed between the base layer 110 and the second layer 140 , the interlayer adhesion may be excellent by the first layer 130 . The first layer 130 may simultaneously provide the effect of suppressing the generation of interference mura or rainbow mura due to the interlayer adhesion and gradation.

For example, when the base layer 110 is a polyimide resin film, the first layer 130 may be a polyimide resin-based layer. In one embodiment, the first layer 130 may contain a resin for the second layer 140 . For example, when the second layer 140 is formed of a (meth)acrylate-based resin, the first resin layer 130 may include a (meth)acrylate-based resin.

Hereinafter, the manufacturing method of the window film of this invention is demonstrated.

The window film forms a hard coating layer by coating and curing the composition for the hard coating layer on one surface of the base layer. The composition for the second layer is coated on the other side of the base layer and cured to form the first layer and the second layer at the same time. A window film may be prepared by coating and aging the composition for an adhesive layer on one surface of the second layer.

The coating method follows conventional methods known to those skilled in the art. For example, the coating method may be, but is not limited to, spray coating, die coating, or spin coating. Curing may include at least one of photocuring and thermal curing. During photocuring and thermal curing, curing conditions may be adjusted according to the thickness of each layer, the material of each layer, and the like. Curing may be performed together with drying, thereby lowering the surface roughness of each layer or shortening the curing time.

Hereinafter, a window film of another embodiment of the present invention will be described with reference to FIG. 2 .

Referring to FIG. 2 , the window film includes a base layer 110 ; The hard coating layer 120 and the third layer 160 sequentially formed from the base layer 110 on one surface of the base layer 110; and a first layer 130 , a second layer 140 , and an adhesive layer 150 sequentially formed from the base layer 110 on the other surface of the base layer 110 . It is substantially the same as the window film of one embodiment of the present invention except that the third layer 160 is further formed between the base layer 110 and the hard coating layer 120 .

The third layer 160 is formed between the base layer 110 and the hard coating layer 120 . The third layer 160 is directly formed on the base layer 110 and the hard coating layer 120 , respectively. The "directly formed" means that any other adhesive layer, adhesive layer or adhesive layer is not formed between the third layer 160 and the base layer 110, and between the third layer 160 and the hard coating layer 120. it means.

The third layer 160 is a gradation layer. The third layer 160 is formed as a gradation layer between the base layer 110 and the hard coating layer 120, so that the interference mura or rainbow mura is improved compared to the interference mura or rainbow mura improvement effect only by adjusting the refractive index of the base layer and the hard coating layer The effect can be significantly increased.

The third layer 160 does not have the same refractive index depending on the thickness as it goes from the base layer 110 to the hard coat layer 120 , and the refractive index may gradually increase or decrease depending on the thickness.

In one embodiment, when the base layer 110 has a higher refractive index compared to the hard coating layer 120 , the third layer 160 increases in thickness from the interface with the base layer 110 to the interface with the hard coating layer 120 . Accordingly, the refractive index may decrease.

In another embodiment, when the base layer 110 has a smaller refractive index compared to the hard coating layer 120 , the third layer 160 has a thickness from the interface with the base layer 110 to the interface with the hard coating layer 120 . As a result, the refractive index may increase.

The third layer 160 may have a refractive index of 1.4 to 1.8, for example, 1.45 to 1.7. In the above range, it is possible to easily control the refractive index between the base layer, the third layer, and the hard coating layer, thereby suppressing the occurrence of interference mura or rainbow mura.

The third layer 160 may be formed from the composition for the hard coating layer forming the hard coating layer 120 and the base layer. The third layer 160 may be formed by dissolving and/or eroding one surface of the base layer in a specific solvent included in the composition for the hard coat layer when the composition for the hard coat layer is applied to the base layer 110 . Accordingly, the third layer 160 may contain the same resin as that of the base layer 110 . For example, when the base layer 110 is a polyimide resin film, the third layer 160 may be a polyimide resin-based layer. In one embodiment, the third layer 130 may contain a resin for the hard coating layer (120). For example, when the hard coating layer 140 is formed of a (meth)acrylate-based resin, the third resin layer 160 may include a (meth)acrylate-based resin. The base layer 110 and the third layer 160 may be integrally formed.

Hereinafter, a flexible display device according to an embodiment of the present invention will be described with reference to FIG. 3 .

Referring to FIG. 3 , the flexible display device includes a display unit 350a, an adhesive layer 360 , a polarizing plate 370 , a touch screen panel 380 , and a flexible window film 390 , and a flexible window film 390 . may include the flexible window film according to embodiments of the present invention.

The display unit 350a is for driving the flexible display device 300 and may include a substrate and an optical element including an OLED, LED, or LCD element formed on the substrate. The display unit 350a may include a conventional structure known to those skilled in the art, and may include a lower substrate, a thin film transistor, an organic light emitting diode, a planarization layer, a protective film, and an insulating film.

The adhesive layer 360 adheres the display unit 350a and the polarizing plate 370 , and may be formed of a pressure-sensitive adhesive composition including a (meth)acrylate-based resin, a curing agent, an initiator, and a silane coupling agent.

The polarizer 370 may include a polarizer alone or the polarizer may include a polarizer and a protective film formed on one or both surfaces of the polarizer. Alternatively, the polarizing plate may include a polarizer and a protective coating layer formed on one or both surfaces of the polarizer. As the polarizer, the protective film, and the protective coating layer, conventional ones known to those skilled in the art may be used.

The touch screen panel 380 detects a change in capacitance generated when a human body or a conductor such as a stylus touches the touch screen panel 380 to generate an electrical signal, and the display unit 350a may be driven by this signal. The touch screen panel 380 is formed by patterning a flexible and conductive conductor, and may include a first sensor electrode and a second sensor electrode formed between the first sensor electrode and intersecting the first sensor electrode. have. The conductor for the touch screen panel 380 may include, but is not limited to, metal nanowires, conductive polymers, carbon nanotubes, and the like.

The flexible window film 390 may be formed at the outermost portion of the flexible display device 300 to protect the display device.

Although not shown in FIG. 3 , an adhesive layer is further formed between the polarizing plate 370 and the touch screen panel 380 and/or between the touch screen panel 380 and the flexible window film 390 , such that the polarizing plate, the touch screen panel, and the flexible The bond between the window films can be strengthened. The pressure-sensitive adhesive layer may be formed of a pressure-sensitive adhesive composition including a (meth)acrylate-based resin, a curing agent, an initiator, and a silane coupling agent. In addition, the adhesive layer may be an adhesive layer including the organic nanoparticles. In addition, although not shown in FIG. 3 , a polarizing plate is further formed under the display unit 350a to realize polarization of internal light.

Hereinafter, a flexible display device according to another embodiment of the present invention will be described with reference to FIG. 4 .

4 , the flexible display device includes a display unit 350a, a touch screen panel 380, a polarizer 370, and a flexible window film 390, and the flexible window film 390 is an embodiment of the present invention. It may include a flexible window film according to the above. The flexible display according to an embodiment of the present invention, except that the touch screen panel 380 is not directly formed on the flexible window film 390 and the touch screen panel 380 is formed under the polarizing plate 370 . substantially identical to the device. Also, at this time, the touch screen panel 380 may be formed together with the display unit 350a. In this case, since the touch screen panel 380 is formed on the display unit 350a together with the display unit 350a, it is thinner and brighter than the flexible display device according to an embodiment of the present invention, so that visibility may be good. Also, in this case, the touch screen panel 380 may be formed by deposition, but is not limited thereto. Although not shown in FIG. 4 , an adhesive layer is further formed between the display unit 350a and the touch screen panel 380 and/or between the touch screen panel 380 and the polarizing plate 370 to increase the mechanical strength of the display device. have. The pressure-sensitive adhesive layer may be formed of a pressure-sensitive adhesive composition including a (meth)acrylate-based resin, a curing agent, an initiator, and a silane coupling agent. In addition, the adhesive layer may be an adhesive layer including the organic nanoparticles. In addition, although not shown in FIG. 4 , a polarizing plate is further formed under the display unit 350a to induce polarization of internal light to improve the display image.

Hereinafter, a flexible display device according to another embodiment of the present invention will be described with reference to FIG. 5 .

Referring to FIG. 5 , the flexible display device includes a display unit 350b and a flexible window film 390 , and the flexible window film 390 may include a flexible window film according to embodiments of the present invention. It is substantially the same as the flexible display device according to an embodiment of the present invention, except that the device can be driven only by the display unit 350b and the polarizing plate and the touch screen panel are excluded.

The display unit 350b may include a substrate and an optical element including an LCD, OLED, or LED element formed on the substrate, and the display unit 350b may have a touch screen panel formed therein.

Hereinafter, the present invention will be described in more detail through examples, but these examples are for illustrative purposes only and should not be construed as limiting the present invention.

production example : for hard coating layer Composition preparation

67 parts by weight of a dendrimer type acrylic resin (Sirius 501, Osaka Organic Chemical Company), 1 part by weight of a photoinitiator (Irgacure-184, BASF), 31.5 parts by weight of methyl ethyl ketone, 0.5 parts by weight of a leveling agent (RS-75) A composition for a hard coating layer was prepared.

Example One

A composition for a second layer was prepared by mixing 19 parts by weight of PETIA (pentaerythritol triacrylate, refractive index: 1.48, ENTIS), 80 parts by weight of methyl ethyl ketone, and 1 part by weight of a photoinitiator (Irgacure-184).

A polyimide film (thickness: 50 μm, Samsung SDI, refractive index: 1.72) was used as the base layer. On one side of the polyimide film, the composition for a hard coating layer of Preparation Example was applied to a coating thickness of 10 μm, dried at 80° C. for 2 minutes, and then cured by irradiating an amount of UV 500 mJ/cm ² to cure the hard coating layer (thickness: 10 μm, refractive index). : 1.55) was formed. On the other side of the polyimide film, the prepared composition for the second layer was applied to a coating thickness of 1 μm, dried at 80° C. for 2 minutes, and cured by irradiating an amount of UV 500 mJ/cm ² to cure the other side of the polyimide resin film. A first layer and a second layer were sequentially formed on one surface. A flexible window film was manufactured by forming an adhesive layer (refractive index: 1.47, including an acrylic resin) on the other surface of the second layer.

The first layer was formed by eroding one surface of the polyimide resin film, and as a result of checking the refractive index, it was confirmed that it was a gradation layer. The thickness of the second layer is 1 μm.

Example 2 to Example 6

A flexible window film was prepared in the same manner as in Example 1, except that the composition of the composition for the second layer was changed as shown in Table 1 below and the coating thickness of the composition for the second layer was changed.

comparative example One

A window film was manufactured in the same manner as in Example 1, except that in Example 1, only the adhesive layer was formed without forming the first layer and the second layer on the other surface of the polyimide resin film.

comparative example 2 to comparative example 3

A window film was prepared in the same manner as in Example 1, except that in Example 1, the coating thickness of the composition for the second layer was changed and the thickness of the second layer was changed as shown in Table 2 below.

comparative example 4 to comparative example 5

A window film was prepared in the same manner as in Example 1, except that the composition for the second layer in Example 1 was changed as shown in Table 2 below.

comparative example 6

A hard coating layer was formed on one side of the base layer in Example 1, and a composition comprising 19 parts by weight of PETIA, 80 parts by weight of PGME and 1 part by weight of an initiator was coated on the other side of the base layer and cured to form a first layer. A window film was prepared by coating and curing the composition for the second layer of Table 2 below on one surface of the first layer to form a second layer.

The following physical properties were evaluated for the flexible window films prepared in Examples and Comparative Examples, and the results are shown in Tables 1 and 2 below.

How to evaluate physical properties

(1) Haze and light transmittance (unit: %): For the window film, haze and light transmittance were measured using a Hazemeter (NDH2000, Nippon Denshoku) and light transmittance CM-3600A (Konica Minolta).

(2) Scratch resistance (Scuff): Using a scuff tester, place a tip (diameter: 11mm) equipped with steel wool (ribenon #0000) on the top layer of the window film, load 1.5kg, speed 50mm/sec , and move it on the uppermost layer surface under the condition of a moving distance of 4 cm. Record the number of scratches that occurred after repeating this 10 times. The lower the number, the better the scratch resistance. When the number was 5 or less, it was evaluated as "good", and when the number was 6 or more, it was evaluated as "poor". The number of scratches was evaluated visually.

(3) Mura: After sequentially laminating an adhesive and a window film on a black sheet, the interference mura and rainbow mura were visually evaluated at an angle of 45 degrees under three wavelengths of light. When no interference mura was seen, it was evaluated as level 1, and when the interference mura was severe, it was evaluated as level 5.

(4) Radius of curvature (unit: mm): For the window film, foldability was evaluated at a radius of curvature of 1 mm by the mandrel test method. A specimen was prepared by cutting the window film into a rectangle of length x width (15 cm x 3 cm). The prepared specimen was wound around a jig for a radius of curvature test. At this time, the uppermost layer (fingerprint resistant layer or hard coating layer) of the window film was wound to contact the jig. After maintaining the wound state for 5 seconds, it was unwound from the jig for the radius of curvature test. The radius of curvature was measured by gradually decreasing the radius of the jig starting from the maximum radius of the jig.

(5) Pencil hardness: The coating layer of the window film was measured by the JIS K5400 method using a pencil hardness meter (Heidon). When measuring the pencil hardness, pencils of Mitsubishi's 6B to 9H were used. The load of the pencil with respect to the coating layer was 1 kg, the angle of drawing a pencil was 45 degrees, and the speed of drawing a pencil was 60 mm/min. If it is evaluated 5 times and scratches occur more than once, the pencil hardness is measured using a pencil of the lower level, and when evaluated 5 times, it is the maximum pencil hardness value when there are no scratches in all 5 times.

Example One 2 3 4 5 6 composition for the second layer Suzy PETIA
(19) CN8885
(19) CN104
(19) EBECRYL5902
(19) PETIA
(19) PETIA
(19) menstruum MEK
(80) MEK
(80) MEK
(80) MEK
(80) MEK
(65) MEK
(65) - - - - DMAC
(15) NMP
(15) photoinitiator One One One One One One 1st floor formation formation formation formation formation formation gradient area formation formation formation formation formation formation first layer refractive index 1.48~1.7 1.5~1.7 1.55-1.7 1.59~1.7 1.48~1.7 1.48~1.7 2nd layer refractive index 1.48 1.5 1.55 1.59 1.48 1.48 adhesive layer refractive index 1.47 1.47 1.47 1.47 1.47 1.47 Second layer thickness (㎛) One One One One One One haze 0.5 0.43 0.48 0.56 0.65 0.7 light transmittance 89.88 89.81 89.90 89.85 89.91 89.88 scratch resistance Good Good Good Good Good Good mura 3 3 One One One One radius of curvature One One One One One One pencil hardness 4H 4H 4H 4H 4H 4H

comparative example One 2 3 4 5 6 for the second floor
composition Suzy - PETIA
(19) PETIA
(19) PETIA
(19) PETIA
(19) PETIA
(19) menstruum - MEK
(80) MEK
(80) PGMEA
(80) PGME
(80) MEK
(80) photoinitiator - One One One One One 1st floor - formation formation unformed unformed formation gradient area - formation formation unformed unformed unformed first layer refractive index - 1.48~1.7 1.48~1.7 - - 1.48 2nd layer refractive index - 1.48 1.48 1.48 1.48 1.48 adhesive layer refractive index 1.47 1.47 1.47 1.47 1.47 1.47 Second layer thickness (㎛) - 0.1 40 One One One haze 0.5 0.43 0.5 0.6 0.5 0.4 light transmittance 89.9 89.81 89.8 89.8 89.8 89.9 scratch resistance Good Good Good Good Good Good mura 5 5 5 5 5 5 radius of curvature One One 20 One One 10 pencil hardness 4H 4H 4H 4H 4H 4H

*In Table 1 and Table 2 above

PETIA: refractive index 1.48

CN8885: refractive index 1.5

CN104: refractive index 1.55

EBECRYL 5902: refractive index 1.59

MEK: methyl ethyl ketone

DMAC: dimethylacetamide

PGMEA: Propylene glycol methyl ether acetate

PGME: propylene glycol methyl ether

* In Tables 1 and 2, numbers in parentheses ( ) mean content (unit: parts by weight).

As shown in Table 1 above, the flexible window film of the present invention suppresses interference mura and/or rainbow mura, and has excellent adhesion between layers, particularly between the substrate layer, the first layer and the second layer, flexibility, flexibility, and hardness. and excellent scratch resistance, and excellent optical transparency.

On the other hand, as shown in Table 2, Comparative Examples 2 and 3, in which the thickness of the second layer was outside the range of the present invention, caused severe mura, and Comparative Example 3 had poor flexibility. Comparative Examples 4 and 5 in which the first layer was not formed, and Comparative Example 6 in which the first layer was not formed even though the first layer was not formed was a gradation layer.

Simple modifications or changes of the present invention can be easily carried out by those of ordinary skill in the art, and all such modifications or changes can be considered to be included in the scope of the present invention.

Claims (19)

A flexible window film comprising a base layer, a hard coating layer formed on one surface of the base layer, and a first layer, a second layer and an adhesive layer sequentially formed from the base layer on the other surface of the base layer,
The first layer is a gradation layer,
The second layer has a thickness of 0.5 μm to 30 μm,
The flexible window film has a refractive index relationship of Equation 1 below:
<Equation 1>
The refractive index of the adhesive layer ≤ the refractive index of the second layer < the refractive index of the base layer;
The gradation layer has a refractive index relationship of the following formula 2 in the thickness direction, a flexible window film:
<Equation 2>
The refractive index of the second layer < the refractive index of the gradation layer < the refractive index of the base layer.
The flexible window film of claim 1 , wherein the refractive index of the first layer decreases according to a thickness of the first layer from the interface with the base layer toward the interface with the second layer.
delete The flexible window film of claim 1 , wherein the first layer is derived from the base layer.
The flexible window film of claim 1 , wherein the first layer contains the same resin as the base layer.
The flexible window film of claim 5 , wherein the base layer is a polyimide resin film, and the first layer is a polyimide resin-based layer.
The flexible window film of claim 6 , wherein the first layer further comprises a (meth)acrylate-based resin.
The flexible window film of claim 1 , wherein the base layer and the first layer are integrally formed.
The flexible window film of claim 1 , wherein the first layer has a refractive index of 1.4 to 1.8.
The flexible window film of claim 1, wherein the second layer is formed of a (meth)acrylate-based, urethane-based, imide-based, amide-based, imide-amide-based, imide-urethane-based or ester-based composition.
The flexible window film of claim 1, wherein the base layer is a polyimide resin film.
The flexible window film of claim 1 , wherein a primer layer or an easily adhesive layer is not formed on one or both surfaces of the base layer.
The flexible window film of claim 1 , wherein the base layer and the second layer are in close contact with each other by the first layer.
The flexible window film of claim 1, wherein the hard coating layer is formed of a composition comprising at least one of a dendrimer-type (meth)acrylic resin and a hyper-branched (meth)acrylic resin.
The flexible window film of claim 1, wherein a third layer is further formed between the hard coating layer and the base layer.
The flexible window film of claim 15 , wherein the third layer is a gradation layer.
The flexible window film of claim 15 , wherein the refractive index of the third layer increases or decreases according to a thickness of the third layer from the interface with the base layer to the interface with the hard coating layer.
The flexible window film of claim 15 , wherein the base layer and the third layer are integrally formed.
A display device comprising the flexible window film of any one of claims 1, 2, and 4 to 18.

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