KR20200112185A - Hard coating film and flexible display window including the same - Google Patents

Abstract

A hard coating film according to embodiments of the present invention comprises a base layer, and a hard coating layer formed on the base layer and satisfying a predetermined range of compressive modules of elasticity. The hard coating film can have stable bending properties while maintaining surface hardness. The hard coating film can be applied as a window film or a window substrate of a flexible display device to improve flexibility and optical properties of the flexible display device.

Description

Hard coating film and flexible display window including the same {HARD COATING FILM AND FLEXIBLE DISPLAY WINDOW INCLUDING THE SAME}

The present invention relates to a hard coating film and a flexible display window including the same. More specifically, it relates to a hard coating film having a multilayer structure and a flexible display window including the same.

In recent years, thinner and more flexible image display devices such as liquid crystal display (LCD) devices or organic light emitting display (OLED) devices have continued. Accordingly, the image display device is widely applied to various smart devices characterized by portability, including not only smart phones and tablet PCs, but also various wearable devices. have.

For example, a window film made of tempered glass may be formed on the display panel to protect the image display device from external environments such as scratches, drop impacts, external moisture, and oil. However, the window film is disadvantageous in weight reduction of a display panel or an image display device due to the characteristics of the tempered glass, and is easily broken by external impact. In addition, there is a limitation in implementing a flexible characteristic through a bendable or foldable function.

Accordingly, in recent years, research on a window film made of an optical plastic material, which can secure flexibility and impact resistance, and can replace the window film made of the tempered glass material, has been conducted.

In the case of a plastic window film, flexibility may be improved, but when folding and folding are repeated, stress may accumulate, resulting in film breakage and damage. In addition, surface strength such as scratch resistance may also be lower than that of glass.

Accordingly, there is a need to develop a hard coating film capable of implementing impact resistance corresponding to tempered glass while maintaining mechanical durability even in repeated folding and folding.

For example, Korean Patent Application Publication No. 2016-0100121 discloses a hard coating composition including a (meth)acrylate-based monomer mixture and a hard coating composition using the same, but there is a limitation in forming a hard coating film with improved flexibility and durability. There is.

Korean Patent Publication No. 10-2016-0100121

An object of the present invention is to provide a hard coating film having improved flexibility and durability.

An object of the present invention is to provide a flexible display window including the hard coating film.

An object of the present invention is to provide an image display device including the hard coating film.

1. Base layer; And a hard coating layer formed on the base layer and having a compressive elastic modulus according to Equation 1 below:

[Equation 1]

2 GPa ≤ A ≤ 0.9×B GPa

(In Equation 1, A is a compressive elastic modulus (GPa) under 1mN load of the hard coating layer, and B is a compressive elastic modulus (GPa) under 1mN load of the base layer).

2. In the above 1, the compressive modulus of the base layer under 1mN load is 5 GPa or more, the hard coating film.

3. In the above 2, the base layer comprises a polyimide resin film containing inorganic filler particles, a hard coating film.

4. In the above 1, wherein the hard coating layer comprises a (meth) acrylate-based resin, a hard coating film.

5. In the above 4, the hard coating layer further comprises inorganic nanoparticles dispersed in the (meth)acrylate-based resin, the hard coating film.

6. In the above 5, wherein the hard coating layer is formed from a hard coating composition containing a (meth) acrylate-based photopolymerizable compound, a photo initiator, the inorganic nanoparticles and a solvent, a hard coating film.

7. In the above 1, the neutral plane (Neutral Plane) is formed in the base layer, the hard coating film.

8. Flexible display window comprising the hard coating film of any one of the above 1 to 7.

9. Display panel; And

A flexible display device comprising the flexible display window according to claim 8 disposed on the display panel.

In the hard coating film according to exemplary embodiments of the present invention, by forming the elastic modulus of the hard coating layer to be less than a predetermined ratio range of the elastic modulus of the base layer, it is possible to relieve or reduce the stretching stress accumulated in the base layer. Therefore, it is possible to maintain the mechanical stability of the substrate layer even in repeated folding and bending.

In some embodiments, the elastic modulus of the base layer and the hard coating layer may be maintained above a predetermined value to ensure bending stability and scratch resistance on the surface.

The hard coating film may be applied as, for example, a window film or a window substrate of a flexible display device to improve flexibility and optical properties of the flexible display device.

1 is a schematic cross-sectional view illustrating a hard coating film according to exemplary embodiments.
2 is a schematic cross-sectional view illustrating a window stack according to exemplary embodiments.

Embodiments of the present invention provide a hard coating film comprising a base layer and a hard coating layer having a predetermined elastic modulus range, and having improved mechanical properties such as flexibility, bending resistance, and surface hardness. In addition, including the hard coating film Provides a flexible display window,

Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings. However, the following drawings attached to the present specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the contents of the present invention, so the present invention is described in such drawings. It is limited to matters and should not be interpreted.

1 is a schematic cross-sectional view illustrating a hard coating film according to exemplary embodiments.

Referring to FIG. 1, the hard coating film may include a base layer 100 and a hard coating layer 110 formed on one surface of the base layer 100.

The base layer 100 may use a transparent polymer film to be applied to a flexible display. For example, the base layer 100 is triacetyl cellulose, acetyl cellulose butyrate, ethylene-vinyl acetate copolymer, propionyl cellulose, butyryl cellulose, acetyl propionyl cellulose, polyester, polystyrene, polyamide, poly Etherimide, polyacrylic, polyimide, polyethersulfone, polysulfone, polyethylene, polypropylene, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl acetal, polyether ketone, polyether ether ketone , Polyether sulfone, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, may include a polymer film such as polycarbonate. The base layer 100 may include one or two or more of them.

In a preferred embodiment, the base layer 100 may include a polyimide-based resin to secure high elasticity applicable to a flexible display. In some embodiments, the compressive modulus of the base layer 100 may be about 5 GPa or more.

In one embodiment, the base layer 100 may further include inorganic filler particles therein. For example, inorganic filler particles such as silica or metal oxide particles may be included in the resin matrix included in the base layer 100. In this case, for example, the base layer 100 having a high elastic modulus of about 5 GPa or more can be easily obtained.

For example, the content of the inorganic filler particles may be appropriately adjusted within a range in which a compressive modulus of about 5 GPa or more is secured.

The hard coating layer 110 may be formed through a curing process such as an ultraviolet curing process after applying the hard coating composition on the base layer 100. For example, the hard coating composition may be, for example, a slit coating method, a knife coating method, a spin coating method, a casting method, a microgravure coating method, a gravure coating method, a bar coating method, a roll coating method, a wire bar coating method, Dip coating method, spray coating method, screen printing method, gravure printing method, flexo printing method, offset printing method, inkjet coating method, dispenser printing method, nozzle coating method, capillary coating method, etc. I can.

The hard coating composition includes a photopolymerizable compound, a photoinitiator and a solvent, and may further include other additives.

The photopolymerizable compound may be a component that is photocured to provide a matrix of the hard coating layer. According to exemplary embodiments, the photopolymerizable compound may include a (meth)acrylate-based oligomer or a (meth)acrylate-based monomer.

Examples of the (meth)acrylate-based oligomer include epoxy (meth)acrylate or urethane (meth)acrylate-based compounds. Preferably, a urethane (meth)acrylate-based compound may be used in consideration of the elasticity and flexural properties of the hard coating layer.

The urethane (meth)acrylate-based compound can be prepared by reacting a polyfunctional (meth)acrylate having a hydroxyl group in a molecule and a compound having an isocyanate group in the presence of a catalyst. Examples of the polyfunctional (meth)acrylate having a hydroxy group in the molecule include 2-hydroxyethyl (meth)acrylate, 2-hydroxyisopropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, Caprolactone ring-opening hydroxyacrylate, pentaerythritol tri/tetra(meth)acrylate mixture, dipentaerythritol penta/hexa(meth)acrylate mixture, etc. are mentioned.

As a non-limiting example of the compound having an isocyanate group, 1,4-diisocyanatobutane, 1,6-diisocyanatohexane, 1,8-diisocyanatooctane, 1,12-diisocyanatododecane, 1 ,5-diisocyanato-2-methylpentane, trimethyl-1,6-diisocyanatohexane, 1,3-bis(isocyanatomethyl)cyclohexane, trans-1,4-cyclohexenediisocyanate, 4, 4'-methylenebis(cyclohexylisocyanate), isophorone diisocyanate, toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, xylene-1,4-diisocyanate, tetramethylxylene-1 ,3-diisocyanate, 1-chloromethyl-2,4-diisocyanate, 4,4'-methylenebis (2,6-dimethylphenyl isocyanate), 4,4'-oxybis (phenyl isocyanate), hexamethylenedi Trifunctional isocyanate derived from isocyanate, and trimethane propanol adduct toluene diisocyanate, and the like.

The (meth)acrylate-based monomer may include, for example, a (meth)acryloyl group as a photocurable group. As a non-limiting example of the (meth)acrylate-based monomer, neopentyl glycol acrylate, 1,6-hexanediol (meth)acrylate, propylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, Polypropylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylol ethane tri (meth) acrylate, 1,2,4-cyclohexanetetra (meth) acrylate, pentaglycerol tri (meth) )Acrylate, pentaerythritol tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol tetra(meth)acrylic Rate, dipentaerythritol hexa(meth)acrylate, tripentaerythritol tri(meth)acrylate, tripentaerythritol hexatri(meth)acrylate, bis(2-hydroxyethyl)isocyanurate di(meth)acrylic Rate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, isooctyl (meth)acrylate, iso-decyl (meth)acrylate, stearyl (meth) ) Acrylate, tetrahydrofurfuryl (meth) acrylate, phenoxyethyl (meth) acrylate, isoborneol (meth) acrylate, and the like.

In some embodiments, the content of the photopolymerizable compound may be about 20 to 60 parts by weight based on 100 parts by weight of the hardening composition. When the content of the photopolymerizable compound is less than about 20 parts by weight, it may be difficult to secure sufficient hardness of the hard coating layer. When the content of the photopolymerizable compound exceeds about 60 parts by weight, a curling phenomenon may occur in the hard coating layer.

The photoinitiator is included to induce photocuring of the hard coating composition, and may include, for example, a photoradical initiator capable of forming a radical by irradiation with light.

According to exemplary embodiments, an acrylic resin structure may be formed through polymerization of a (meth)acrylate group included in the photopolymerizable compound by the photoinitiator.

Examples of the photoinitiators include Type 1 initiators that generate radicals by decomposition of molecules due to differences in chemical structure or molecular bond energy, and Type 2 initiators that coexist with tertiary amines to induce hydrogen deoxidation. .

For example, the Type 1 initiator is 4-phenoxydichloroacetphenone, 4-t-butyldichloroacetphenone, 4-t-butyltrichloroacetphenone, diethoxyacetphenone, 2-hydroxy-2-methyl -l-phenylpropan-1-one, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-l-one, 1-(4-dodecylphenyl)-2-hydroxy-2 -Acetphenones such as methylpropan-1-one, 4-(2-hydroxyethoxy)-phenyl(2-hydroxy-2-propyl)ketone, and 1-hydroxycyclohexylphenyl ketone; Benzoin, such as benzoin, benzoin methyl ether, benzoin ethyl ether, and benzyl dimethyl ketal; Phosphine oxides, titanocene compounds, etc. may be included.

For example, Type 2 initiators include benzophenone, benzoylbenzoic acid, benzoylbenzoic acid methyl ether, 4-phenylbenzophenone, hydroxybenzophenone, 4-benzol-4'-methyldiphenylsulfide, 3,3'- Benzophenones such as methyl-4-methoxybenzophenone, thioxanthone, 2-chlorothioxanthone, 2-methyl thioxanthone, 2,4-dimethyl thioxanthone, and thioxane such as isopropyl thioxanthone And tone-based compounds.

The above-described photoinitiator may be used alone or in combination of two or more. In addition, the Type 1 type and Type 2 type initiators may be used alone or in combination.

For example, the photoinitiator may be about 0.1 to 10 parts by weight, preferably about 0.1 to 5 parts by weight, based on 100 parts by weight of the total hard coating composition. When the content of the photoinitiator is less than about 0.1 part by weight, sufficient curing may not proceed, and thus mechanical properties and adhesion of the hard coating film or the hard coating layer may not be secured. When the content of the photoinitiator exceeds about 10 parts by weight, poor adhesion, cracking, and curling may occur due to cure shrinkage in the (meth)acrylate group.

In the hard coating composition according to the embodiments of the present invention, solvents commonly used in the art may be used without particular limitation.

For example, alcohol-based (methanol, ethanol, isopropanol, butanol, methylcellulose, ethylsolusob, etc.), ketone-based (methyl ethyl ketone, methyl butyl ketone, methyl isobutyl ketone, diethyl ketone, dipropyl ketone, Cyclohexanone, etc.), acetate (ethyl acetate, propyl acetate, normal butyl acetate, tertiary butyl acetate, methyl cellosolve acetate, ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, Propylene glycol monopropyl ether acetate, methoxybutyl acetate, methoxypentyl acetate, etc.), hydrocarbon-based (hexane, heptane, octane, etc.), benzene-based (benzene, toluene, xylene, etc.), ether-based (diethylene glycol dimethyl ether , Diethylene glycol diethyl ether, diethylene glycol dipropyl ether, diethylene glycol dibutyl ether, propylene glycol monomethyl ether, and the like). These may be used alone or in combination of two or more.

The content of the solvent is not particularly limited as long as it is an amount capable of dissolving the components of the above-described composition, and may be included in the remaining amount excluding the above-described components or additives described later. For example, the solvent may be included in about 20 to 70 parts by weight of the total 100 parts by weight of the hard coating composition. When the content of the solvent is less than about 20 parts by weight, the viscosity of the composition may be excessively increased, thereby deteriorating coating properties and workability. When the content of the solvent exceeds about 70 parts by weight, it is difficult to form a hard coating film or a hard coating layer having a uniform thickness, and may cause stains during drying, resulting in damage to optical properties.

In some embodiments, the hard coating composition may further include inorganic nanoparticles. As the inorganic nanoparticles are included, mechanical properties such as abrasion resistance, scratch resistance, and pencil hardness of the hard coating film or the hard coating layer may be additionally improved.

The kind of the inorganic nanoparticles is not particularly limited, for example, Al ₂ O ₃ , SiO ₂ , ZnO, ZrO ₂ , BaTiO ₃ , TiO ₂ , Ta ₂ O ₅ , Ti ₃ O ₅ , indium-tin-oxide It may be a metal oxide series including (ITO), indium-zinc-oxide (IZO), antimony-tin-oxide (ATO), ZnO-Al, Nb ₂ O ₃ , SnO, MgO, or a combination thereof. In one embodiment, Al ₂ O ₃ , SiO ₂ and/or ZrO ₂ may be used as the inorganic nanoparticles.

In one embodiment, the inorganic nanoparticles may be included in an amount of about 5 to 40 parts by weight of the total 100 parts by weight of the hard coating composition. When the content of the inorganic nanoparticles is less than about 5 parts by weight, mechanical properties such as sufficient wear resistance, scratch resistance, and pencil hardness may not be implemented. When the content of the inorganic nanoparticles exceeds about 40 parts by weight, it may rather interfere with polymerization or curing of the photocurable compound, thereby weakening mechanical properties.

The inorganic nanoparticles may be used in a form in which the inorganic particles are dispersed at a concentration of about 10 to 80% by weight in an organic solvent in the form of, for example, a silica sol.

The hard coating composition may further include an additive to improve physical properties such as film uniformity within a range that does not impair mechanical properties and transparency of the hard coating film or the hard coating layer. For example, the additive may include a leveling agent, an ultraviolet stabilizer, a heat stabilizer, and the like.

For example, the leveling agent may be added to improve smoothness and coatability of the hard coating film or the hard coating layer formed from the composition. The leveling agent may include a silicone-based, fluorine-based, or acrylic polymer-based agent. As an example of a commercially available leveling agent, BYK-307, BYK-323, BYK-331, BYK-333, BYK-337, BYK-373, BYK-375, BYK-377, BYK-378, BYK- of B.K Chem. UV3570; TEGO Glide 410, TEGO Glide 411, TEGO Glide 415, TEGO Glide 420, TEGO Glide 432, TEGO Glide 435, TEGO Glide 440, TEGO Glide 450, TEGO Glide 455, TEGO Rad 2100, TEGO Rad 2200N, TEGO Rad 2250, TEGO Rad 2300, TEGO Rad 2500; FC-4430 and FC-4432 of 3M are mentioned.

In some embodiments, the hard coating composition may further include an ultraviolet stabilizer and/or a heat stabilizer. The ultraviolet stabilizer may be added to prevent the surface of the coating film formed from the composition from being discolored or broken by exposure to ultraviolet rays by blocking or absorbing ultraviolet rays. UV stabilizers can be classified into absorbents, quenchers, and hindered amine light stabilizers (HALS), depending on their mechanism of action.For example, phenyl salicylates (absorbents), benzo Phenone (Benzophenone, absorbent), benzotriazole (absorbent), nickel derivative (quenching agent), radical scavenger (Radical Scavenger), and the like may be used. As the thermal stabilizer, polyphenol-based, phosphite-based and lactone-based thermal stabilizers may be used.

The additives may be suitably mixed and used at a level that does not impair the UV curing process and the hardness and optical properties of the hard coating layer. For example, the additive may be included in the range of about 0.1 to 1 part by weight of the total 100 parts by weight of the hard coating composition.

According to exemplary embodiments, the hard coating layer 110 may have a compressive elastic modulus according to Equation 1 below.

[Equation 1]

2 GPa ≤ A ≤ 0.9×B GPa

In Equation 1, A represents the compressive elastic modulus (GPa) of the hard coating layer 110 under a 1mN load. B represents the compressive elastic modulus (GPa) of the base layer 100 under a 1mN load.

As shown in Equation 1, the compressive elastic modulus of the hard coating layer 110 may be adjusted to about 2 GPa or more. Therefore, when the hard coating layer 110 is applied as a window of a flexible display, sufficient surface hardness and scratch resistance can be secured.

The compressive modulus of the hard coating layer 110 may be smaller than that of the base layer 100. Therefore, it is possible to move the neutral plane toward the base layer 100 in the hard coating film. Accordingly, a neutral surface in which the stress is substantially buffered or relieved in the hard coating film may be located in the base layer 100.

When folding and bending of the hard coating film are repeated, stretching stress is concentrated on the outer portion of the substrate layer 100, and accordingly, mechanical damage such as breakage, damage, and cracking occurs frequently in the outer portion of the substrate layer 100. I can.

However, as described above, the compressive modulus of the hard coating layer 110 may be reduced than that of the base layer 100 so that the neutral surface may be moved toward the outer portion of the base layer 100. Therefore, it is possible to improve the bending durability by solving the stretching stress in the base layer 100.

As shown in Equation 1, the compressive modulus of the hard coating layer 110 may be 90% or less of the compressive modulus of the base layer 100. If the compressive modulus of the hard coating layer 110 is not reduced to 90% or less of the compressive modulus of the base layer 100, the neutral surface does not move sufficiently, so that the effect of relieving the stretching stress of the base layer 100 may not be easily implemented. have.

The compressive modulus of the hard coating layer 110 is determined by the number of functions of the photopolymerizable compound contained in the above-described hard coating composition, the content of inorganic nanoparticles (for example, silica sol), and adjustment of the photocuring conditions (exposure amount, exposure time, Photoinitiator content, etc.).

In some embodiments, the compressive modulus of the base layer 100 may be about 5 GPa or more. In the above range, sufficient flexural stiffness through the base layer 100 can be secured, and the above-described neutral plane movement can be easily implemented. In one embodiment, the compressive modulus of the base layer 100 may be about 5 to 10 GPa. Within the above range, it is possible to easily maintain flexural rigidity while securing the overall flexibility of the hard coating film.

As shown in Equation 1, according to the embodiments of the present invention, a compressive modulus under a 1mN load may be used as a physical property or parameter for relieving the stretching stress through movement of the neutral plane.

It may be practically impossible to measure the inherent elongation modulus of the hard coating layer 110 itself, and accordingly, it may be difficult to substantially implement the reduction of elongation stress through controlling the elongation modulus.

However, according to embodiments of the present invention, by measuring the compressive modulus using a 1mN load, an elastic modulus substantially close to the inherent stretch modulus of the layer itself may be obtained. Accordingly, the position of the neutral plane and stress relief at the outer portion of the base layer 100 may be effectively implemented by adjusting the compressive elastic modulus.

In some embodiments, the thickness of the hard coating layer 110 may be smaller than the thickness of the base layer 100. Accordingly, the neutral surface can be more easily positioned within the base layer 100, and it is possible to efficiently and easily implement a stretch stress relief applied to the outer portion of the base layer 100.

For example, the thickness of the hard coating layer 110 may be in the range of about 10 to 30 μm, and the thickness of the base layer 100 may be in the range of about 40 to 100 μm.

In some embodiments, a protective film (not shown) (eg, a release film) may be additionally formed on the hard coating layer 110. For example, a protective film may be attached on the hard coating layer 110 through the adhesive layer.

According to exemplary embodiments of the present invention, a flexible display window or a window stack including the above-described hard coating film may be provided. 2 is a schematic cross-sectional view illustrating a window stack according to exemplary embodiments.

According to example embodiments, the window stack may further include a polarizing layer 60 and/or a touch sensor layer 50 under the base layer 100.

The polarizing layer 60 may include a polyvinyl alcohol-based polarizer or a polarizing plate including a protective film attached to at least one surface of the polarizer. Unlike this, the polarizing layer 60 includes a liquid crystal layer including a liquid crystal compound, and may include an alignment layer for imparting alignment to the liquid crystal layer. At least one retardation film may be formed on the polarizing layer.

The touch sensor layer 50 may include a base film and a plurality of electrode patterns formed on at least one surface of the base film and sensing a touch point through capacitive sensing. The touch sensor layer 50 may further include an insulating layer to insulate the electrode patterns.

In an embodiment, the polarizing layer 50 may be disposed directly on the touch sensor layer 60 or with the retardation film interposed therebetween.

As shown in FIG. 2, the window laminate may include a sequentially laminated structure of a touch sensor layer 50-a polarization layer 60-a hard coating film. Alternatively, the window laminate may have a sequentially stacked structure of a polarizing layer 60-a touch sensor layer 50-a hard coating film.

Embodiments of the present invention provide an image display device including the above-described hard coating film.

The image display device may include a display panel (eg, a thin film transistor (TFT) array panel) and the hard coating film or flexible display window disposed on the display panel.

In example embodiments, the hard coating film may be combined with the display panel in the form of a window stack described with reference to FIG. 2.

For example, the hard coating film or flexible display window has excellent hardness, abrasion resistance, and flexibility, and can be applied as a window film formed on the outermost surface of an image display device. In this case, the hard coating layer 110 may be disposed toward the user's viewer.

The image display device includes various image display devices such as a liquid crystal display device, an electroluminescent display device, a plasma display device, and a field emission display device, and may be a flexible display device having flexibility and bending characteristics. Preferably, the image display device may be a flexible organic light emitting diode (OLED) device.

Hereinafter, experimental examples including specific examples and comparative examples are presented to aid in understanding of the present invention, but these are merely illustrative of the present invention and do not limit the scope of the appended claims, and the scope and spirit of the present invention It is obvious to those skilled in the art that various changes and modifications can be made to the embodiments within the scope, and it is natural that such modifications and modifications fall within the appended claims.

Examples and Comparative Examples

Example 1

25 parts by weight pentaerythritol triacrylate, 25 parts by weight polyfunctional acrylate (DKS, New Frontier MF-101), 47 parts by weight methyl ethyl ketone, 2.7 parts by weight 1-hydroxycyclohexylphenyl ketone, 0.3 parts by weight silicone type An additive (BYK, BYK-UV3570) was blended using a stirrer and filtered through a filter made of polypropylene (PP) to prepare a hard coating composition.

After coating the hard coating composition on a polyimide-based film (50 μm) (manufactured by Sumitomo Chemical) containing 40% by weight of silica, the hard coating was applied by irradiating UV accumulated light amount of 1000J/cm ² under a solvent drying and nitrogen purging atmosphere. A hard coating film having a layer (10 μm) formed thereon was prepared.

Example 2

45 parts by weight of polyfunctional acrylate (DKS, New Frontier MF-101), 30 parts by weight of 12 nm nano silica sol (Catalyst, ELCOM V-8802), 22 parts by weight methyl ethyl ketone, 2.7 parts by weight 1-hydroxy Cyclohexylphenyl ketone, 0.3 parts by weight of a silicone additive (BYK, BYK-UV3570) were mixed using a stirrer and filtered through a filter made of PP to prepare a hard coating composition.

Thereafter, a hard coating film was prepared in the same manner as in Example 1.

Example 3

35 parts by weight of polyfunctional acrylate (DKS, New Frontier MF-101), 40 parts by weight of 12 nm nano silica sol (Catalyst, ELCOM V-8802), 22 parts by weight methyl ethyl ketone, 2.7 parts by weight 1-hydroxy Cyclohexylphenyl ketone, 0.3 parts by weight of a silicone additive (BYK, BYK-UV3570) were mixed using a stirrer and filtered through a filter made of PP to prepare a hard coating composition.

Thereafter, a hard coating film was prepared in the same manner as in Example 1.

Comparative Example 1

A hard coating film was prepared in the same manner as in Example 3, except that a polyimide base film containing no silica sol was used as the base layer.

Comparative Example 2

20 parts by weight pentaerythritol triacrylate, 55 parts by weight 12nm nanosilica sol (Catalyst, ELCOM V-8802), 22 parts by weight methyl ethyl ketone, 2.7 parts by weight 1-hydroxycyclohexylphenyl ketone, 0.3 parts by weight silicone type An additive (BYK, BYK-UV3570) was blended using a stirrer and filtered using a filter made of PP to prepare a hard coating composition.

Thereafter, a hard coating film was prepared in the same manner as in Example 1.

Comparative Example 3

50 parts by weight polyfunctional urethane acrylate (DKS, New Frontier MF-101), 47 parts by weight methyl ethyl ketone, 2.7 parts by weight 1-hydroxycyclohexylphenyl ketone, 0.3 parts by weight silicone additive (BYK, BYK-UV3570) ) Was blended with a stirrer and filtered using a filter made of PP to prepare a hard coating composition.

Comparative Example 4

30 parts by weight of polyfunctional acrylate (DKS, New Frontier MF-101), 45 parts by weight of 12nm nano silica sol (Catalyst, ELCOM V-8802), 22 parts by weight methyl ethyl ketone, 2.7 parts by weight 1-hydroxy Cyclohexylphenyl ketone, 0.3 parts by weight of a silicone additive (BYK, BYK-UV3570) were mixed using a stirrer and filtered through a filter made of PP to prepare a hard coating composition.

Thereafter, a hard coating film was prepared in the same manner as in Example 1.

Experimental example

The physical properties of the hard coating films of Examples and Comparative Examples were evaluated as follows.

1) Measurement of compressive modulus of hard coating layer and base layer (base film)

After fixing the film on the glass with a tape so that the layer to be measured faces upward, the compressive modulus was measured with a micro load of 1 mN using a nanoindenter (Fisher).

2) Scratch resistance evaluation

After bonding the base film to the glass with a transparent adhesive so that the hard-coated side goes to the top, reciprocate friction 10 times with a load of 500g/cm ² using steel wool #0000, and then check whether scratches have occurred on the film surface. I did.

<Evaluation criteria>

◎: less than 10 scratches

×: 10 or more scratches

7) Flexibility resistance

After the test of folding and unfolding 100,000 times under high temperature and high humidity (60 degrees, 90%) conditions with a radius of curvature of 1 mm so that both end surfaces of the hard coating layer are in contact with each other, whether or not the film is broken was observed.

<Evaluation criteria>

◎: less than 10 scratches

×: 10 or more scratches

The evaluation results measured as described above are shown in Table 1 below.

Hard coating layer
Compressive modulus Base layer
Compressive modulus Scratch resistance Flexibility resistance Example 1 3.8 GPa 7.1 GPa ◎ ◎ Example 2 5.4 GPa 7.1 GPa ◎ ◎ Example 3 6.1 GPa 7.1 GPa ◎ ◎ Comparative Example 1 6.1 GPa 4.2 GPa ◎ × Comparative Example 2 7.4 GPa 7.1 GPa ◎ × Comparative Example 3 1.1 GPa 7.1 GPa × ◎ Comparative Example 4 6.5 GPa 7.1 GPa ◎ ×

Referring to Table 1, in the case of the examples in which the 1mN load compressive modulus of the hard coating layer was adjusted according to Equation 1 above, the scratch resistance of the hard coating layer was improved and fracture was not included even in repeated folding.

In Comparative Examples 1, 2, and 4, which did not sufficiently reduce the compressive modulus of the hard coat layer, fracture of the base layer was caused. In the case of Comparative Example 3 in which the compressive modulus of the hard coating layer was excessively decreased, sufficient surface scratch resistance was not secured.

50: touch sensor layer 60: polarizing layer
100: base layer 110: hard coating layer

Claims (9)

Base layer; And
A hard coating film formed on the base layer and comprising a hard coating layer having a compressive elastic modulus according to Equation 1 below:
[Equation 1]
2 GPa ≤ A ≤ 0.9×B GPa
(In Equation 1, A is a compressive elastic modulus (GPa) under 1mN load of the hard coating layer, and B is a compressive elastic modulus (GPa) under 1mN load of the base layer). The hard coating film according to claim 1, wherein the base layer has a compressive modulus of 5 GPa or more under 1mN load. The hard coating film according to claim 2, wherein the base layer comprises a polyimide resin film containing inorganic filler particles. The hard coating film according to claim 1, wherein the hard coating layer includes a (meth)acrylate-based resin. The hard coating film of claim 4, wherein the hard coating layer further comprises inorganic nanoparticles dispersed in the (meth)acrylate-based resin. The hard coating film of claim 5, wherein the hard coating layer is formed from a hard coating composition comprising a (meth)acrylate-based photopolymerizable compound, a photoinitiator, the inorganic nanoparticles, and a solvent. The hard coating film according to claim 1, wherein a neutral plane is formed in the base layer. A flexible display window comprising the hard coating film of any one of claims 1 to 7. Display panel; And
A flexible display device comprising the flexible display window according to claim 8 disposed on the display panel.

Images